This image combines the light of four wavelengths emitted by excitations from four different elements.
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Cable news demands a steady stream of excitations and "breaking" updates, a constant instability that keeps you tuning in.
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The difficulty with nuclear excitations, however, is that they require much higher energy levels than electron energy transitions because their protons and neutrons are more densely packed.
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Stars like our own Sun— Alpha Centauri A and B, for example—experience solar-like oscillations, which are excitations that result from turbulent convection occurring in their outer layers.
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A few years after his work with Dr. Bardeen, Dr. Pines collaborated with two other physicists, Aage Niels Bohr and Ben Roy Mottelson, on a paper describing excitations in nuclei.
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As part of the DAMA/LIBRA-phase 2 upgrade, the team at Gran Sasso switched out hardware to make their detectors sensitive to lower-energy excitations inside the sodium iodide crystals.
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"The quasiparticles they observed are essentially excitations in a material that behave like Majorana particles," Giorgio Gratta, a professor of physics at Stanford who was not involved in the experiment, said in a statement.
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Since fields tend to spill into each other quantum mechanically, when a pair of particles materialized in the inflaton field and got dragged apart by cosmic expansion, occasionally one of the pair should have spontaneously morphed into two graviton particles—excitations of the gravitational field.
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SPT states are short-range entangled while topologically ordered states are long-range entangled. Both intrinsic topological order, and also SPT order, can sometimes have protected gapless boundary excitations. The difference is subtle: the gapless boundary excitations in intrinsic topological order can be robust against any local perturbations, while the gapless boundary excitations in SPT order are robust only against local perturbations that do not break the symmetry. So the gapless boundary excitations in intrinsic topological order are topologically protected, while the gapless boundary excitations in SPT order are symmetry protected.
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Other excitations rearrange the valence bonds, leading to low-energy excitations even for short-range bonds. Very special about spin liquids is, that they support exotic excitations, meaning excitations with fractional quantum numbers. A prominent example is the excitation of spinons which are neutral in charge and carry spin S= 1/2. In spin liquids, a spinon is created if one spin is not paired in a valence bond.
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The classification of traditional coupled-cluster methods rests on the highest number of excitations allowed in the definition of T. The abbreviations for coupled-cluster methods usually begin with the letters "CC" (for "coupled cluster") followed by # S – for single excitations (shortened to singles in coupled-cluster terminology), # D – for double excitations (doubles), # T – for triple excitations (triples), # Q – for quadruple excitations (quadruples). Thus, the T operator in CCSDT has the form : T = T_1 + T_2 + T_3. Terms in round brackets indicate that these terms are calculated based on perturbation theory. For example, the CCSD(T) method means: # Coupled cluster with a full treatment singles and doubles.
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In principle RIXS can probe a very broad class of intrinsic excitations of the system under study—as long as the excitations are overall charge neutral. This constraint arises from the fact that in RIXS the scattered photons do not add or remove charge from the system under study. This implies that, in principle RIXS has a finite cross section for probing the energy, momentum and polarization dependence of any type of electron-hole excitation: for instance the electron-hole continuum and excitons in band metals and semiconductors, charge transfer and crystal field excitations in strongly correlated materials, lattice excitations (phonons), orbital excitations, and so on. In addition magnetic excitations are also symmetry-allowed in RIXS, because the angular momentum that the photons carry can in principle be transferred to the electron's spin moment.
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Those excitations turn out to be gauge bosons. The ends of strings are defects which correspond to another type of excitations. Those excitations are the gauge charges and can carry Fermi or fractional statistics. The condensations of other extended objects such as "membranes", "brane-nets", and fractals also lead to topologically ordered phases; Topological Orders and Chern–Simons Theory in strongly correlated quantum liquid.
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Furthermore, ICD was reported after core-electron excitations of hydroxide in dissolved water.
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These include states with topological order, with and without an energy gap to excitations, and critical states without quasiparticle excitations. Many of these contributions have been linked to experiments, especially to the rich phase diagrams of the high temperature superconductors.
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For example, a crystal at absolute zero is in the ground state, but if one phonon is added to the crystal (in other words, if the crystal is made to vibrate slightly at a particular frequency) then the crystal is now in a low-lying excited state. The single phonon is called an elementary excitation. More generally, low-lying excited states may contain any number of elementary excitations (for example, many phonons, along with other quasiparticles and collective excitations). When the material is characterized as having "several elementary excitations", this statement presupposes that the different excitations can be combined together.
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Excitations with momenta in the linear region are called phonons; those with momenta close to the minimum are called rotons. Excitations with momenta near the maximum are called maxons. The term "roton" is also used for the quantized eigenmode of a freely rotating molecule.
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Therefore, as a starting point, they are treated as free, independent entities, and then corrections are included via interactions between the elementary excitations, such as "phonon-phonon scattering". Therefore, using quasiparticles / collective excitations, instead of analyzing 1018 particles, one needs to deal with only a handful of somewhat-independent elementary excitations. It is, therefore, a very effective approach to simplify the many- body problem in quantum mechanics. This approach is not useful for all systems, however: In strongly correlated materials, the elementary excitations are so far from being independent that it is not even useful as a starting point to treat them as independent.
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It is pointed out that the GLR test with a carefully designed numerical algorithm is robust against unsufficient excitations.
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A more modern characterization of quantum spin liquids involves their topological order, long-range quantum entanglement properties, and anyon excitations.
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Semiconductor Quantum Optics. Cambridge University Press. . describe luminescence of semiconductors resulting from spontaneous recombination of electronic excitations, producing a flux of spontaneously emitted light. This description established the first step toward semiconductor quantum optics because the SLEs simultaneously includes the quantized light–matter interaction and the Coulomb-interaction coupling among electronic excitations within a semiconductor.
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Fractionalized excitations as point particles can be bosons, fermions or anyons in 2+1 spacetime dimensions. It is known that point particles can be only either bosons or fermions in 3+1 and higher spacetime dimensions. However, the loop (or string) or membrane like excitations are extended objects can have fractionalized statistics. Current research works show that the loop and string like excitations exist for topological orders in the 3+1 dimensional spacetime, and their multi-loop/string-braiding statistics are the key signatures for identifying 3+1 dimensional topological orders.
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The compound is also widely regarded as a prime candidate to realize Kitaev quantum spin liquid state with Majorana Fermion excitations.
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Discovered by Harry Dember (1882–1943) in 1925, this effect is due to the sum of the excitations of an electron by two means: photonic illumination and electron bombardment (i.e. the sum of the two excitations extracts the electron). In Dember’s initial study, he referred only to metals; however, more complex materials have been analyzed since then.
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Plasmonic lithography uses surface plasmon excitations to generate beyond-diffraction limit patterns, benefiting from subwavelength field confinement properties of surface plasmon polaritons.
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In quantum chemistry, the multireference configuration interaction (MRCI) method consists of a configuration interaction expansion of the eigenstates of the electronic molecular Hamiltonian in a set of Slater determinants which correspond to excitations of the ground state electronic configuration but also of some excited states. The Slater determinants from which the excitations are performed are called reference determinants. The higher excited determinants (also called configuration state functions (CSFs) or shortly configurations) are then chosen either by the program according to some perturbation theoretical ansatz according to a threshold provided by the user or simply by truncating excitations from these references to singly, doubly, ... excitations resulting in MRCIS, MRCISD, etc. For the ground state using more than one reference configuration means a better correlation and so a lower energy.
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Neutron diffraction (elastic scattering) techniques are used for analyzing structures; where inelastic neutron scattering is used in studying atomic vibrations and other excitations.
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Roger Arthur Cowley, FRS, FRSE, FInstP (24 February 1939 – 27 January 2015) was an English physicist who specialised in the excitations of solids.
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Some quantum theories of gravity posit a spin-2 quantum field that is quantized, giving rise to gravitons. In string theory one generally starts with quantized excitations on top of a classically fixed background. This theory is thus described as background dependent. Particles like photons as well as changes in the spacetime geometry (gravitons) are both described as excitations on the string worldsheet.
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In other words, it presupposes that the excitations can coexist simultaneously and independently. This is never exactly true. For example, a solid with two identical phonons does not have exactly twice the excitation energy of a solid with just one phonon, because the crystal vibration is slightly anharmonic. However, in many materials, the elementary excitations are very close to being independent.
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In condensed matter physics, low-energy excitations in graphene and topological insulators, among others, are fermionic quasiparticles described by a pseudo-relativistic Dirac equation.
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1209 (1968). and investigated nonradiative excitations of protons in hydrogen bonds in DNA. He predicted a new quasiparticle – protonic exciton – and investigated its properties.
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Woods, A. D B, and R. A. Cowley. "Structure and Excitations of Liquid Helium." Reports on Progress in Physics 36.9 (1973): 1135-231. Print.
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Nahar has published extensively on radiative and collisional atomic processes in astrophysical and laboratory plasmas, including Photoionization, electron-ion recombination,"Electron-Ion Recombination Rate Coefficients, Photoionization Cross Sections, and Ionization Fractions for Astrophysically Abundant Elements. I. Carbon and Nitrogen", S. N. Nahar and A. K. Pradhan, in The Astrophysical Journal, vol. 111, no. 339, 1997 photo- excitations and de-excitations, and electron-ion scattering.
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In condensed matter physics, a Bogoliubov quasiparticle or Bogoliubon is a quasiparticle that occurs in superconductors. Whereas superconductivity is characterized by the condensation of Cooper pairs into the same ground quantum state, Bogoliubov quasiparticles are elementary excitations above the ground state, which are superpositions (linear combinations) of the excitations of negatively charged electrons and positively charged electron holes, and are therefore neutral fermions (spin- particles).
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The induced motion of the shorter nanotube is explained as the reverse of the heat dissipation that occurs in friction wherein the sliding of two objects in contact results in the dissipation of some of the kinetic energy as phononic excitations caused by the interface corrugation. The presence of a thermal gradient in a nanotube causes a net current of phononic excitations traveling from the hotter region to the cooler region. The interaction of these phononic excitations with mobile elements (the carbon atoms in the shorter nanotube) causes the motion of the shorter nanotube. This explains why the shorter nanotube moves towards the cooler electrode.
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The tendency for all the Cooper pairs in a body to "condense" into the same ground quantum state is responsible for the peculiar properties of superconductivity. Cooper originally considered only the case of an isolated pair's formation in a metal. When one considers the more realistic state of many electronic pair formations, as is elucidated in the full BCS theory, one finds that the pairing opens a gap in the continuous spectrum of allowed energy states of the electrons, meaning that all excitations of the system must possess some minimum amount of energy. This gap to excitations leads to superconductivity, since small excitations such as scattering of electrons are forbidden.
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In string theory, the left-moving and the right-moving excitations are completely decoupled, and it is possible to construct a string theory whose left-moving (counter-clockwise) excitations are treated as a bosonic string propagating in D = 26 dimensions, while the right-moving (clockwise) excitations are treated as a superstring in D = 10 dimensions. The mismatched 16 dimensions must be compactified on an even, self-dual lattice (a discrete subgroup of a linear space). There are two possible even self-dual lattices in 16 dimensions, and it leads to two types of the heterotic string. They differ by the gauge group in 10 dimensions.
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Ca10Cr7O28 is a frustrated Kagome bilayer magnet, which does not develop long-range order even below 1 K, and has a diffuse spectrum of gapless excitations.
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Spin waves are propagating disturbances in the ordering of magnetic materials. These low-lying collective excitations occur in magnetic lattices with continuous symmetry. From the equivalent quasiparticle point of view, spin waves are known as magnons, which are bosonic modes of the spin lattice that correspond roughly to the phonon excitations of the nuclear lattice. As temperature is increased, the thermal excitation of spin waves reduces a ferromagnet's spontaneous magnetization.
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DMFT has been employed to study non-equilibrium transport and optical excitations. Here, the reliable calculation of the AIM's Green function out of equilibrium remains a big challenge.
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In modern physics, all fundamental particles are regarded as excitations of quantum fields. There are several distinct ways in which tachyonic particles could be embedded into a field theory.
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Topological excitations are certain features of classical solutions of gauge field theories. Namely, a gauge field theory on a manifold M with a gauge group G may possess classical solutions with a (quantized) topological invariant called topological charge. The term topological excitation especially refers to a situation when the topological charge is an integral of a localized quantity. Examples:F. A. Bais, Topological excitations in gauge theories; An introduction from the physical point of view.
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However, it was shown by Tomonaga in 1950 that this principle is only valid in one-dimensional systems. Bosonization is an effective field theory that focuses on low-energy excitations.
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Flower constancy, insect psychology, and plant evolution. Naturwissenschaften, 86: 361-377. · Chittka, L. (1992). The color hexagon: a chromaticity diagram based on photoreceptor excitations as a generalized representation of colour opponency.
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The chemistry of systems at room temperature is determined by the electronic properties, which is essentially fermionic, since room temperature thermal excitations have typical energies much higher than the hyperfine values.
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The phenomenon, similar to photodarkening in fibers, was recently observed in chunks of Yb-doped ceramics and crystals. At the high concentration of excitations, the absorption jumps up, causing the avalanche of the broadband luminescence. Increase of absorption can be caused by formation of color centers by electrons in the conduction band, created by several neighboring excited ions. (The energy of one or two excitations is not sufficient to pop an electron into the conduction band).
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Silvana Botti is a full professor for Physics at the University of Jena. She is an expert in the development of first-principles methods for electronic excitations and methods for theoretical spectroscopy.
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It shakes up the electronic system, creating excitations to which the X-ray photon loses energy and momentum. The number of electrons in the valence sub-system is constant throughout the process.
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In solid-state physics, Raman spectroscopy is used to characterize materials, measure temperature, and find the crystallographic orientation of a sample. As with single molecules, a solid material can be identified by characteristic phonon modes. Information on the population of a phonon mode is given by the ratio of the Stokes and anti-Stokes intensity of the spontaneous Raman signal. Raman spectroscopy can also be used to observe other low frequency excitations of a solid, such as plasmons, magnons, and superconducting gap excitations.
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"Non-abelian bosonization in two dimensions", Communications in Mathematical Physics 92 455-472. online cf. Wess–Zumino–Witten model. The basic physical idea behind bosonization is that particle-hole excitations are bosonic in character.
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Some predictions of the string theory include existence of extremely massive counterparts of ordinary particles due to vibrational excitations of the fundamental string and existence of a massless spin-2 particle behaving like the graviton.
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The origin of closely spaced C60+ bands was not understood until 2018, when the quantum chemistry studies revealed the Jahn-Teller distortion of C60+ excited state. This distortion leads to the two excited states (Bg and Ag) populated upon light illumination. Two states form two progressions of closely spaced absorption bands. The strong bands at 9632 Å and 9577 Å were assigned to the cold electronic excitations, while the weak bands at 9428 Å, 9365 Å, and 9348 Å to the hot vibronic excitations.
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In the paper that coined the term "tachyon", Gerald Feinberg studied Lorentz invariant quantum fields with imaginary mass. Because the group velocity for such a field is superluminal, naively it appears that its excitations propagate faster than light. However, it was quickly understood that the superluminal group velocity does not correspond to the speed of propagation of any localized excitation (like a particle). Instead, the negative mass represents an instability to tachyon condensation, and all excitations of the field propagate subluminally and are consistent with causality.
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The neutral excitations of various fractional quantum Hall states are excitons of composite fermions, that is, particle hole pairs of composite fermions. The energy dispersion of these excitons has been measured by light scattering and phonon scattering.
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Eugen Tarnow suggests that dreams are ever-present excitations of long-term memory, even during waking life. The strangeness of dreams is due to the format of long-term memory, reminiscent of Penfield & Rasmussen's findings that electrical excitations of the cortex give rise to experiences similar to dreams. During waking life an executive function interprets long-term memory consistent with reality checking. Tarnow's theory is a reworking of Freud's theory of dreams in which Freud's unconscious is replaced with the long-term memory system and Freud's "Dream Work" describes the structure of long-term memory.
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In theoretical physics, the term dressed particle refers to a bare particle together with some excitations of other quantum fields that are physically inseparable from the bare particle. For example, a dressed electron includes the chaotic dynamics of electron–positron pairs and photons surrounding the original electron. A further noteworthy example is represented by polaritons in solid-state physics, dressed quasiparticles of dipolar excitations in a medium with photons. In radiobiology, a dressed particle is a bare particle together with its Debye sphere that neutralizes its electric charge.
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Resonant inelastic X-ray scattering (RIXS) is an X-ray spectroscopy technique used to investigate the electronic structure of molecules and materials. Inelastic X-ray scattering is a fast developing experimental technique in which one scatters high energy, X-ray photons inelastically off matter. It is a photon-in/photon-out spectroscopy where one measures both the energy and momentum change of the scattered photon. The energy and momentum lost by the photon are transferred to intrinsic excitations of the material under study and thus RIXS provides information about those excitations.
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While the Abraham–Lorentz force is largely neglected for many experimental considerations, it gains importance for plasmonic excitations in larger nanoparticles due to large local field enhancements. Radiation damping acts as a limiting factor for the plasmonic excitations in surface-enhanced Raman scattering. The damping force was shown to broaden surface plasmon resonances in gold nanoparticles, nanorods and clusters. The effects of radiation damping on nuclear magnetic resonance were also observed by Nicolaas Bloembergen and Robert Pound, who reported its dominance over spin–spin and spin–lattice relaxation mechanisms for certain cases.
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If the material under investigation is only available in the form of nanocrystalline powders or suffers from poor crystallinity, the methods of electron crystallography can be applied for determining the atomic structure. For all above mentioned X-ray diffraction methods, the scattering is elastic; the scattered X-rays have the same wavelength as the incoming X-ray. By contrast, inelastic X-ray scattering methods are useful in studying excitations of the sample such as plasmons, crystal-field and orbital excitations, magnons, and phonons, rather than the distribution of its atoms.
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This is indeed the idea of quantum field theory, which considers each mode of the matter field as an oscillator subject to quantum fluctuations, and the bosons are treated as the excitations (or energy quanta) of the field.
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This section contains examples of quasiparticles and collective excitations. The first subsection below contains common ones that occur in a wide variety of materials under ordinary conditions; the second subsection contains examples that arise only in special contexts.
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12216–12225 (1991)V.M. Shalaev, M.I. Stockman, and R. Botet, Resonant excitations and nonlinear optics of fractals, Physica A, v. 185, pp. 181–186 (1992) a theory of random metal-dielectric films was worked out in collaboration with A. K. Sarychev.
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Inelastic interactions include phonon excitations, inter- and intra-band transitions, plasmon excitations, inner shell ionizations, and Cherenkov radiation. The inner-shell ionizations are particularly useful for detecting the elemental components of a material. For example, one might find that a larger-than-expected number of electrons comes through the material with 285 eV less energy than they had when they entered the material. This is approximately the amount of energy needed to remove an inner-shell electron from a carbon atom, which can be taken as evidence that there is a significant amount of carbon present in the sample.
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Electronic stopping refers to the slowing down of a projectile ion due to the inelastic collisions between bound electrons in the medium and the ion moving through it. The term inelastic is used to signify that energy is lost during the process (the collisions may result both in excitations of bound electrons of the medium, and in excitations of the electron cloud of the ion as well). Linear electronic stopping power is identical to unrestricted linear energy transfer. Instead of energy transfer, some models consider the electronic stopping power as momentum transfer between electron gas and energetic ion.
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In the superspace picture, aperiodic crystals are obtained from the section of a periodic crystal of higher dimension (up to 6D) cut at an irrational angle. While phonons change the position atoms relative to the crystal structure in space, phasons change the position of atoms relative to the quasi-crystal structure and the cut through superspace that defines it. Phonon modes are therefore excitations of the "in plane" real (also called parallel or external) space whereas phasons are excitations of the perpendicular (also called internal) space. The hydrodynamic theory of the quasicrystals predicts that the conventional (phonon) strain relaxes rapidly.
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72, pp. 4149–4152, (1994)S. Gresillon, L. Aigouy, A.C. Boccara, J.C. Rivoal, X. Quelin, C. Desmarest, P. Gadenne, V.A. Shubin, A.K. Sarychev, and V.M. Shalaev Experimental Observation of Localized Optical Excitations in Random Metal- Dielectric Films, Physical Review Letters, v. 82, pp.
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A successful mathematical classification method for physical lattice defects, which works not only with the theory of dislocations and other defects in crystals but also, e.g., for disclinations in liquid crystals and for excitations in superfluid 3He, is the topological homotopy theory.
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Here, a vacuum angle (or 'theta angle') distinguishes between topologically different sectors in the vacuum. These topological sectors correspond to the robustly quantized phases. The quantum Hall transitions can then be understood by looking at the topological excitations (instantons) that occur between those phases.
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Arguing that dreams in which one relives trauma serve a binding function in the mind, connected to repetition compulsion, Freud admits that such dreams are an exception to the rule that the dream is the fulfillment of a wish.Freud, Beyond. p. 304. Asserting that the first task of the mind is to bind excitations to prevent trauma (so that the pleasure principle does not begin to dominate mental activities until the excitations are bound), he reiterates the clinical fact that for "a person in analysis ... the compulsion to repeat the events of his childhood in the transference evidently disregards the pleasure principle in every way".Freud, Beyond. p. 308.
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The underlying physical mechanism that permits tunnelling electrons to excite atomic spin transitions has been studied by several authors. Whereas the most frequent mode of operation probes spin excitations from the ground state to excited states, the possibility to drive the system away from equilibrium and probe transition between excited states, as well as the possibility of controlling the spin orientation of single atoms with spin polarized currents were also reported. In the case of coupled spin structures, the technique provides information not only about the energies spin excitations, but also about their spread across the structure, making it possible to image the spin wave modes in nanoengineered spin chains.
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In another example, the aggregate motion of electrons in the valence band of a semiconductor or a hole band in a metal behave as though the material instead contained positively charged quasiparticles called electron holes. Other quasiparticles or collective excitations include the phonon (a particle derived from the vibrations of atoms in a solid), the plasmons (a particle derived from plasma oscillation), and many others. These particles are typically called quasiparticles if they are related to fermions, and called collective excitations if they are related to bosons, although the precise distinction is not universally agreed upon. A guide to Feynman diagrams in the many-body problem, by Richard D. Mattuck, p10.
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The nature of the neutrinos is not settled—they may be either Dirac or Majorana fermions. In condensed matter physics, bound Majorana fermions can appear as quasiparticle excitations—the collective movement of several individual particles, not a single one, and they are governed by non-abelian statistics.
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Wang, H.; Ferrio, K.; Steel, D.; Hu, Y.; Binder, R.; Koch, S. W. (1993). "Transient nonlinear optical response from excitation induced dephasing in GaAs". Physical Review Letters 71 (8): 1261–1264. doi:10.1103/PhysRevLett.71.1261 non-Markovian effects, and semiconductor excitations with terahertz (abbreviated as THz) fields.
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This experimental hall was built for the beginning of the 12 GeV beam- energy program starting in 2014. This hall houses the GlueX experiment, which is designed to map out the light unflavored meson spectrum in detail in the search for explicit gluonic excitations in mesons.
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Tokurakawa, M., et al., "Diode-pumped 188 fs mode-locked Yb3+:Y2O3 ceramic laser", Applied Physics Letters, Vol. 90, p. 71 (2007) At high concentration of excitations (of order of 1%) and poor cooling, the quenching of emission at laser frequency and avalanche broadband emission takes place.
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Comparing the energy of a neutron, electron or photon with a wavelength of the order of the relevant length scale in a solid— as given by the de Broglie equation considering the interatomic lattice spacing is in the order of Ångströms—it derives from the relativistic energy–momentum relation that an X-ray photon has more energy than a neutron or electron. The scattering phase space (the range of energies and momenta that can be transferred in a scattering event) of X-rays is therefore without equal. In particular, high- energy X-rays carry a momentum that is comparable to the inverse lattice spacing of typical condensed matter systems so that, unlike Raman scattering experiments with visible or infrared light, RIXS can probe the full dispersion of low energy excitations in solids. RIXS can utilize the polarization of the photon: the nature of the excitations created in the material can be disentangled by a polarization analysis of the incident and scattered photons, which allow one, through the use of various selection rules, to characterize the symmetry and nature of the excitations.
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When photon echo experiments are performed in semiconductors with exciton resonances,Noll, G.; Siegner, U.; Shevel, S.; Göbel, E. (1990). "Picosecond stimulated photon echo due to intrinsic excitations in semiconductor mixed crystals". Physical Review Letters 64 (7): 792–795. doi:10.1103/PhysRevLett.64.792Webb, M.; Cundiff, S.; Steel, D. (1991).
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This includes the activation synthesis theory—the theory that dreams result from brain stem activation during REM sleep; the continual activation theory—the theory that dreaming is a result of activation and synthesis but dreams and REM sleep are controlled by different structures in the brain; and dreams as excitations of long term memory—a theory which claims that long term memory excitations are prevalent during waking hours as well but are usually controlled and become apparent only during sleep. There are multiple theories about dream function as well. Some studies claim that dreams strengthen semantic memories. This is based on the role of hippocampal neocortical dialog and general connections between sleep and memory.
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One should also note the semantical subtleness of the name SPT: "symmetry protected" does not mean that the stability of the state is conserved "because of the symmetry", but it is just meant that the symmetry is kept by the interactions corresponding to the process. We also know that an intrinsic topological order has emergent fractional charge, emergent fractional statistics, and emergent gauge theory. In contrast, a SPT order has no emergent fractional charge/fractional statistics for finite- energy excitations, nor emergent gauge theory (due to its short-range entanglement). Note that the monodromy defects discussed above are not finite- energy excitations in the spectrum of the Hamiltonian, but defects created by modifying the Hamiltonian.
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Her research focuses on theoretical spectroscopy and the development of first- principles methods for electronic excitations based on (time-dependent) density functional theory and many-body perturbation theory. She edited the book "First Principles Approaches to Spectroscopic Properties of Complex Materials". She is an associate editor of Npj Computational Materials.
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The DeBeer group is actively involved in the development and application of RXES/RIXS based methods in both the hard and soft X-ray regime. These include 1s-Valence RIXS as a means to obtain ligand-selective XAS and 2p3d RIXS as a means to map out the d-d excitations.
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The response time and sensitivity of photonic detectors can be much higher, but usually these have to be cooled to cut thermal noise. The materials in these are semiconductors with narrow band gaps. Incident IR photons can cause electronic excitations. In photoconductive detectors, the resistivity of the detector element is monitored.
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Their quasi-particle excitations have no fractional charge and fractional statistics. Strictly speaking, topological insulator is an example of symmetry-protected topological (SPT) order, where the first example of SPT order is the Haldane phase of spin-1 chain. But the Haldane phase of spin-2 chain has no SPT order.
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By modifying the kinetic energy of the field, it is possible to produce Lorentz invariant field theories with excitations that propagate superluminally. However, such theories, in general, do not have a well-defined Cauchy problem (for reasons related to the issues of causality discussed above), and are probably inconsistent quantum mechanically.
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Indirect RIXS process. An electron is excited from a deep-lying core level into the valence shell. Excitations are created through the Coulomb interaction U_c between the core hole (and in some cases the excited electron) and the valence electrons. Resonant inelastic X-ray scattering processes are classified as either direct or indirect.
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Solitons in 1D, such as polyacetylene, lead to half charges. Spin-charge separation into spinons and holons was detected in electrons in 1D SrCuO2. Quantum wires with fractional phase behavior have been studied. Spin liquids with fractional spin excitations occur in frustrated magnetic crystals, like ZnCu3(OH)6Cl2 (herbertsmithite), and in α-RuCl3.
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Degenerate Higher-Order Scalar-Tensor theories (or DHOST theories) are theories of modified gravity. They have a Lagrangian containing second-order derivatives of a scalar field but do not generate ghosts (kinetic excitations with negative kinetic energy), because they only contain one propagating scalar mode (as well as the two usual tensor modes).
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In TiCl3, each Ti atom has one d electron, rendering its derivatives paramagnetic, i.e. the substance is attracted into a magnetic field. Solutions of titanium(III) chloride are violet, which arises from excitations of its d-electron. The colour is not very intense since the transition is forbidden by the Laporte selection rule.
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Tománek and his research group have worked in areas in nanoscience and nanotechnology. As a graduate student at FU Berlin, he studied structural end electronic properties of surfaces, including reconstruction and photoemission spectra. He was intrigued by the unusual structure and electronic properties of atomic clusters., including collective electronic excitations and superconductivity.
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Nobel Prize Nominations Fröhlich, who pursued theoretical research notably in the fields of superconductivity and bioelectrodynamics, proposed a theory of coherent excitations in biological systems known as Fröhlich coherence. A system that attains this coherent state is known as a Fröhlich condensate, similar to room-temperature non-equilibrium Bose–Einstein condensation of quasiparticles.
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The upper laser level is excited efficiently by electrons with more than 11 eV, best energy is 15 eV. The electron temperature in the streamers only reaches 0.7 eV. Helium due to its higher ionisation energy and lack of vibrational excitations increases the temperature to 2.2 eV. Higher voltages increase the temperature.
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In addition to having been termed an "interdisciplinary area for research, an area which demonstrates the concomitant relationship between physiology and social behavior" (Di Mascio et al. 1955: 4), sociophysiology may also be described as "social ethology" and "social energetics" (Waxweiler 1906: 62). That is, the "physiology of reactive phenomena caused by the mutual excitations of individuals of the same species" (Waxweiler 1906: 62)."Éthologie sociale; énergétique sociale — physiologie des phénomènes réactionnels dus aux excitations mutuelles des individus de même espèce" (Waxweiler 1906: 62). The interdisciplinary nature of sociophysiology largely entails a "synthesis of psychophysiology and social interaction" (Adler 2002: 884) such that a "socio-psycho-biological study" (Mauss 1936: 386) of "biologico-sociological phenomena" (Mauss 1936: 385) may ensue.
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In addition to Standard Model particles, the theory includes thirty colored X bosons, responsible for proton decay, and three W' and Z' bosons. The pattern of weak isospin, W, weaker isospin, W', strong g3 and g8, and baryon minus lepton, B, charges for particles in the SO(10) Grand Unified Theory, rotated to show the embedding in E6. The goal of E8 Theory is to describe all elementary particles and their interactions, including gravitation, as quantum excitations of a single Lie group geometry—specifically, excitations of the noncompact quaternionic real form of the largest simple exceptional Lie group, E8. A Lie group, such as a one-dimensional circle, may be understood as a smooth manifold with a fixed, highly symmetric geometry.
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's superlens, benefit from plasmonic excitations to focus Fourier components of incoming light beyond the diffraction limit. Chaturvedi et al. has demonstrated the imaging of a 30 nm chromium grating through silver superlens photolithography at 380 nm, while Shi et al. simulated a 20 nm lithography resolution at 193 nm wavelength with an aluminum superlens.
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Bose–Einstein condensation can occur in quasiparticles, particles that are effective descriptions of collective excitations in materials. Some have integer spins and can be expected to obey Bose–Einstein statistics like traditional particles. Conditions for condensation of various quasiparticles have been predicted and observed. The topic continues to be an active field of study.
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Thus, the electrons emitted from the sample as a consequence of the Mössbauer absorptions are: (a) primary (IC or Auger) electrons originated in the de- excitations of the nuclei excited by the incident beam, and (b) secondary electrons originated by conventional interactions of photons (or resonant absorption of gamma rays) emitted after resonant absorptions.
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2: The energies of the two types of excitations, from. See text. Figure 2 shows the two excitation energies \epsilon_1(p) and \epsilon_2 (p) for a small value of \gamma = 0.787. The two curves are similar to these for all values of \gamma >0, but the Bogoliubov approximation (dashed) becomes worse as \gamma increases.
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Plasmons are a quantity of collective electron oscillations. Excitons are excited electrons bound to the hole produced by their excitation. Molecular crystal excitons were combined with the collective excitations within metals to create plexcitons. This allowed EET to reach distances of around 20,000 nanometers, an enormous increase over the some 10 nanometers possible previously.
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Nicholls first studied Physics at Oxford before joining the Institute for Molecular Biophysics at Florida State University. There he studied quantum dispersion of excitations in biological systems with William Rhodes and football with Bobby Bowden. He earned his Ph.D. in biophysics in 1988 and began a post-doc with Barry Honig at Columbia University, New York.
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Liouville theory appears in the context of string theory when trying to formulate a non-critical version of the theory in the path integral formulation. Also in the string theory context, if coupled to a free bosonic field, Liouville field theory can be thought of as the theory describing string excitations in a two-dimensional space(time).
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Shalaev’s PhD work (supervised by Prof. A.K. Popov) and early research involved theoretical analysis of resonant interaction of laser radiation with gaseous media, in particular i) Doppler- free multi-photon processes in strong optical fields and their applications in nonlinear opticsA.K. Popov, V.M. Shalaev, Doppler-free transitions induced by strong double-frequency optical excitations, Optics Communications, v. 35, pp.
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Andrei Nickolay Slavin (born August 19, 1951; St. Petersburg, Russia) from the Oakland University, Rochester, MI is a fellow of the American Physical Society[2][2][2] (2009) and was also named Fellow of the Institute of Electrical and Electronics Engineers (IEEE) in 2012 for contributions to magnetic excitations and magnetization dynamics induced by spin transfer.
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In 1896, Freud also published his seduction theory, claiming to have uncovered repressed memories of incidents of sexual abuse for all his current patients, from which he proposed that the preconditions for hysterical symptoms are sexual excitations in infancy.Freud, Sigmund. 1953 [1896]. "The Aetiology of Hysteria." Pp. 191–221 in The Standard Edition 3, edited by J. Strachey.
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The Möbius function also arises in the primon gas or free Riemann gas model of supersymmetry. In this theory, the fundamental particles or "primons" have energies . Under second quantization, multiparticle excitations are considered; these are given by for any natural number . This follows from the fact that the factorization of the natural numbers into primes is unique.
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Law of Intensity: in order for a sensation to increase in strength, it must be stimulated by excitations that are also increasing in magnitude. 3\. Law of Tension: as the strength of a sensation increases, the level of tension also increases. Tension is associated with unpleasantness, pain, fatigue and even the destruction of the sensation itself.
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In the 1970s Di Vecchia was one of the pioneers of string theory. Among other things, he formulated with Lars Brink and others the locally supersymmetric Lagrangian for fermionic strings (i.e. those with fermionic excitations, half-integer spin). Previously, the Nambu-Goto action had been known for the bosonic string and different groups tried to construct a fermionic action.
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First introduced by M. Pollak, the Coulomb gap is a soft gap in the single- particle density of states (DOS) of a system of interacting localized electrons. Due to the long-range Coulomb interactions, the single-particle DOS vanishes at the chemical potential, at low enough temperatures, such that thermal excitations do not wash out the gap.
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In addition to QCD in four spacetime dimensions, the two- dimensional Schwinger model also exhibits confinement. Compact Abelian gauge theories also exhibit confinement in 2 and 3 spacetime dimensions. Confinement has recently been found in elementary excitations of magnetic systems called spinons. If the electroweak symmetry breaking scale were lowered, the unbroken SU(2) interaction would eventually become confining.
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Spinon moving in spin liquids. The valence bonds do not have to be formed by nearest neighbors only and their distributions may vary in different materials. Ground states with large contributions of long range valence bonds have more low-energy spin excitations, as those valence bonds are easier to break up. On breaking, they form two free spins.
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Results from her research have revealed a complex interplay between the electrons in a metallic substrate and the vibrations in molecules adsorbed on the surface. For example, Hirschmugl found that when certain vibrations of the adsorbate relax (decay), they create electronic excitations in the metal. Previously, it had been believed that these decaying vibrations would only create other vibrations.
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However, it is clear that in a general case the behaviour of Bose–Einstein condensate can be described by coupled evolution equations for condensate density, superfluid velocity and distribution function of elementary excitations. This problem was in 1977 by Peletminskii et al. in microscopical approach. The Peletminskii equations are valid for any finite temperatures below the critical point.
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The traditional Kondo effect involves a local quantum degree of freedom interacting with a Fermi liquid or Luttinger liquid in the bulk. Sachdev described cases where the bulk was a strongly-interacting critical state without quasiparticle excitations. The impurity was characterized by a Curie suspectibility of an irrational spin, and a boundary entropy of an irrational number of states.
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While lattice computations have suggested that Yang–Mills theory indeed has a mass gap and a tower of excitations, a theoretical proof is still missing. This is one of the Clay Institute Millennium problems and it remains an open problem. Such states for Yang–Mills theory should be physical states, named glueballs, and should be observable in the laboratory.
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Extreme examples of complex quantum entanglement arise in metallic states of matter without quasiparticle excitations, often called strange metals. Remarkably, there is an intimate connection between the quantum physics of strange metals found in modern materials (which can be studied in tabletop experiments), and quantum entanglement near black holes of astrophysics. This connection is most clearly seen by first thinking more carefully about the defining characteristic of a strange metal: the absence of quasiparticles. In practice, given a state of quantum matter, it is difficult to completely rule out the existence of quasiparticles: while one can confirm that certain perturbations do not create single quasiparticle excitations, it is almost impossible to rule out a non-local operator which could create an exotic quasiparticle in which the underlying electrons are non-locally entangled.
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Passive synthesis is exemplified by habit. Habit incarnates the past (and gestures to the future) in the present by transforming the weight of experience into an urgency. Habit creates a multitude of "larval selves," each of which functions like a small ego with desires and satisfactions. In Freudian discourse, this is the domain of bound excitations associated with the pleasure principle.
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Many physicists simply give up on a microscopic approach, and make informed guesses of the expected phases (perhaps based on NJL model results). For each phase, they then write down an effective theory for the low-energy excitations, in terms of a small number of parameters, and use it to make predictions that could allow those parameters to be fixed by experimental observations.
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The interaction of matter with light, i.e., electromagnetic fields, is able to generate a coherent superposition of excited quantum states in the material. Coherent denotes the fact that the material excitations have a well defined phase relation which originates from the phase of the incident electromagnetic wave. Macroscopically, the superposition state of the material results in an optical polarization, i.e.
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Calorimeters assume the sample is in thermal equilibrium or nearly so. In crystalline materials at very low temperature this is not necessarily the case. A good deal more information can be found by measuring the elementary excitations of the crystal lattice, or phonons, caused by the interacting particle. This can be done by several methods including superconducting transition edge sensors.
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I. Stockman, V.M. Shalaev, M. Moskovits, R. Botet, T.F. George, Enhanced Raman scattering by fractal clusters: Scale-invariant theory, Physical Review B, v. 46, pp. 2821–2830 (1992)D.P. Tsai, J. Kovacs, Zh. Wang, M. Moskovits, V.M. Shalaev, J.S. Suh, and R. Botet, Photon Scanning Tunneling Microscopy Images of Optical Excitations of Fractal Metal Colloid Clusters, Physical Review Letters, v.
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Davidson correction improves both size consistency and size extensivity of CISD energies. Therefore, Davidson correction is frequently referred to in literature as size-consistency correction or size-extensivity correction. However, neither Davidson correction itself nor the corrected energies are size-consistent or size- extensive. This is especially the case in larger molecules, where contribution from higher than quadruple excitations becomes more significant.
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With Albert Einstein's special relativity and the Michelson–Morley experiment, it became clear that electromagnetic waves did not travel as vibrations in a physical aether; and there was in Einstein's physics no difference between the effects of a field and action at a distance. In quantum field theory, fields become the fundamental objects of study, and particles are excitations of these fields.
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Plasmonic nanolithography (also known as plasmonic lithography or plasmonic photolithography) is a nanolithographic process that utilizes surface plasmon excitations such as surface plasmon polaritons (SPPs) to fabricate nanoscale structures. SPPs, which are surface waves that propagate in between planar dielectric-metal layers in the optical regime, can bypass the diffraction limit on the optical resolution that acts as a bottleneck for conventional photolithography.
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Selective excitations, pag. 114-115 In 1977 Bodenhausen and Freeman showed how it was possible by observing spectrum of a heteronucleus (an atomic nucleus other than a proton) to achieve indirect detection of the proton resonance frequencies, and the correlations of chemical shifts between protons and heteronuclei.G. Bodenhausen, R. Freeman: J. Magn. Reson. 28, 463 (1977)Slichter, Principles of Magnetic Resonance, p.
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More recently, results have been published in which superconducting qubits were used to resolve quanta of magnon number states,D. Lachance-Quiriom, Y. Tabuchi, S. Ishino, A. Noguchi, T. Ishikawa, R. Yamazaki, and Y. Nakamura, "Resolving quanta of collective spin excitations in a millimeter-sized ferromagnet", Science Advances 3, 7, e1603150 (2017), to create a quantitatively non-classical photon number distribution,S.
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In this case one of the blades of the scissors must be identified with the moving cloud of atoms and the other one with the trap. Also this excitation mode was experimentally confirmed. In close analogy similar collective excitations have predicted in a number of other systems, including metal clusters, quantum dots, Fermi condensates and crystals, but none of them has yet been experimentally investigated or found.
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Talat Shahnaz Rahman is a Pakistani condensed matter physicist whose research topics include surface phenomena and excited media, including catalysis, vibrational dynamics, and magnetic excitations. She has also helped develop molecules that can "walk" across a solid surface by moving one part of the molecule while keeping another part attached to the surface. She is UCF Pegasus Professor of Physics at the University of Central Florida.
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In general, these possess large moduli spaces of vacua which are not related by any symmetry, for example, the masses of the various excitations may differ at various points on the moduli space. The moduli spaces of supersymmetric gauge theories are in general easier to calculate than those of nonsupersymmetric theories because supersymmetry restricts the allowed geometries of the moduli space even when quantum corrections are included.
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In superfluid 4He the elementary collective excitations are phonons and rotons. A particle striking an electron or nucleus in this superfluid can produce rotons, which may be detected bolometrically or by the evaporation of helium atoms when they reach a free surface. 4He is intrinsically very pure so the rotons travel ballistically and are stable, so that large volumes of fluid can be used.
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Charge carriers can also be generated in the course of optical excitation. It is important to realize, however, that the primary optical excitations are neutral excitons with a Coulomb-binding energy of typically 0.5–1.0 eV. The reason is that in organic semiconductors their dielectric constants are as low as 3–4. This impedes efficient photogeneration of charge carriers in neat systems in the bulk.
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String theory is formulated on a background spacetime just as quantum field theory is. Such a background fixes spacetime curvature, which in general relativity is like saying that the gravitational field is fixed. However, analysis shows that the excitations of the string fields act as gravitons, which can perturb the gravitational field away from the fixed background. So, string theory actually includes dynamic quantised gravity.
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As with IR spectroscopy, only fundamental excitations (\Delta u=\pm1) are allowed according to the QHO. There are however many cases where overtones are observed. The rule of mutual exclusion, which states that vibrational modes cannot be both IR and Raman active, applies to certain molecules. The specific selection rules state that the allowed rotational transitions are \Delta J=\pm2, where J is the rotational state.
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Repeating the above calculation under the assumption that the DOS near E_f is proportional to (E-E_f)^\alpha shows that \alpha>=d-1 . This is an upper bound for the Coulomb gap. Efros considered single electron excitations, and obtained an integro-differential equation for the DOS, showing the Coulomb gap in fact follows the above equation (i.e., the upper bound is a tight bound).
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Since this is a question of non-perturbative quantum field theory, finding a reliable answer is difficult, pursued in the asymptotic safety program. Another possibility is that there are new, undiscovered symmetry principles that constrain the parameters and reduce them to a finite set. This is the route taken by string theory, where all of the excitations of the string essentially manifest themselves as new symmetries.
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Bayesian operational modal analysis (BAYOMA) adopts a Bayesian system identification approach for operational modal analysis (OMA). Operational modal analysis aims at identifying the modal properties (natural frequencies, damping ratios, mode shapes, etc.) of a constructed structure using only its (output) vibration response (e.g., velocity, acceleration) measured under operating conditions. The (input) excitations to the structure are not measured but are assumed to be 'ambient' ('broadband random').
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In contrast to 2DNMR, nonlinear two-dimensional infrared spectroscopy also involves the excitation to overtones. These excitations result in excited state absorption peaks located below the diagonal and cross peaks. In 2DNMR, two distinct techniques, COSY and NOESY, are frequently used. The cross peaks in the first are related to the scalar coupling, while in the latter they are related to the spin transfer between different nuclei.
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It is named for the Soviet and Ukrainian physicist Alexander Davydov. The Davydov model describes the interaction of the amide I vibrations with the hydrogen bonds that stabilize the α-helix of proteins. The elementary excitations within the α-helix are given by the phonons which correspond to the deformational oscillations of the lattice, and the excitons which describe the internal amide I excitations of the peptide groups. Referring to the atomic structure of an α-helix region of protein the mechanism that creates the Davydov soliton (polaron, exciton) can be described as follows: vibrational energy of the C=O stretching (or amide I) oscillators that is localized on the α-helix acts through a phonon coupling effect to distort the structure of the α-helix, while the helical distortion reacts again through phonon coupling to trap the amide I oscillation energy and prevent its dispersion.
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Different electronic excitations within semiconductors are already widely used in lasers, electronic components and computers. At the same time, they constitute an interesting many-body system whose quantum properties can be modified, e.g., via a nanostructure design. Consequently, THz spectroscopy on semiconductors is relevant in revealing both new technological potentials of nanostructures as well as in exploring the fundamental properties of many-body systems in a controlled fashion.
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The weak bonding between olefin molecules allows local thermal excitations to disrupt the crystalline order of a given chain piece-by-piece, giving it much poorer heat resistance than other high-strength fibers. Its melting point is around ,ultra high molecular weight polyethylene; UHMWPE. chemyq.com and, according to DSM, it is not advisable to use UHMWPE fibres at temperatures exceeding for long periods of time. It becomes brittle at temperatures below .
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The Delta states discussed here are only the lowest-mass quantum excitations of the proton and neutron. At higher masses, additional Delta states appear, all defined by having units of isospin, but with a spin quantum numbers including , , , ... . A complete listing of all properties of all these states can be found in Beringer et al. (2013). There also exist antiparticle Delta states with opposite charges, made up of the corresponding antiquarks.
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In the soft X-ray range, RIXS has been shown to reflect crystal field excitations, which are often hard to observe with any other technique. Application of RIXS to strongly correlated materials is of particular value for gaining knowledge about their electronic structure. For certain wide band materials such as graphite, RIXS has been shown to (nearly) conserve crystal momentum and thus has found use as a complementary bandmapping technique.
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NbSe3 and K0.3MoO3 are two examples in which charge density waves have been observed at relatively high temperatures of 145 K and 180 K respectively. Furthermore, the 1-D nature of the material causes a breakdown of the Fermi liquid theory for electron behavior. Therefore, a 1-D conductor should behave as a Luttinger liquid instead. A Luttinger liquid is a paramagnetic one-dimensional metal without Landau quasi-particle excitations.
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James Robert Beene, from the Oak Ridge National Laboratory, was made a Fellow in the American Physical Society after being nominated by the Division of Nuclear Physics at ORNL in 1991. Beene was recognized for his outstanding contributions and investigations in heavy ion nuclear physics, particularly studies of the nuclear giant resonance structures via Coulomb excitations, and their subsequent decay via photon and neutron emission with 4-TT detector systems.
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Dosimetry attempts to factor in this effect with radiation weighting factors. Linear energy transfer is closely related to stopping power, since both equal the retarding force. The unrestricted linear energy transfer is identical to linear electronic stopping power, as discussed below. But the stopping power and LET concepts are different in the respect that total stopping power has the nuclear stopping power component, and this component does not cause electronic excitations.
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Just like every other quantum field, excitations of the inflaton field are expected to be quantized. The field quanta of the inflaton field are known as inflatons. Depending on the modeled potential energy density, the inflaton field's ground state might, or might not, be zero. The term inflaton follows the typical style of other quantum particles’ names – such as photon, gluon, boson, and fermion – deriving from the word inflation.
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The transient regime can be important for the quasi-continuous lasers that needs to operate in the pulsed regime, for example, to avoid the overheating. The only numerical solutions were believed to exist for the strong pulsation, spiking. The strong spiking is possible, when U/V \ll 1, i.e., the lifetime of excitations in the active medium is large compared to the lifetime of photons inside the cavity.
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Goldstone's theorem examines a generic continuous symmetry which is spontaneously broken; i.e., its currents are conserved, but the ground state is not invariant under the action of the corresponding charges. Then, necessarily, new massless (or light, if the symmetry is not exact) scalar particles appear in the spectrum of possible excitations. There is one scalar particle—called a Nambu–Goldstone boson—for each generator of the symmetry that is broken, i.e.
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In essence steps leading up to this investigation and demonstration was the employment of an anisotropic metamaterial with a hyperbolic dispersion. The effect was such that ordinary evanescent waves propagate along the radial direction of the layered metamaterial. On a microscopic level the large spatial frequency waves propagate through coupled surface plasmon excitations between the metallic layers. In 2007, just such an anisotropic metamaterial was employed as a magnifying optical hyperlens.
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His later work on surface excitations and on optical amplification, attenuation and detection has also proved to be important. Loudon worked at the University of Essex as Professor, Chairman and Dean. He has also worked at British Telecom, Royal Radar Establishment, Bell Telephone Laboratories and Radio Corporation of America, and he has been a consultant to these organisations over several years, contributing to both applied and fundamental research.
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Anyons are quasiparticles in a two-dimensional space. Anyons are neither fermions nor bosons, but like fermions, they cannot occupy the same state. Thus, the world lines of two anyons cannot intersect or merge, which allows their paths to form stable braids in space-time. Anyons can form from excitations in a cold, two- dimensional electron gas in a very strong magnetic field, and carry fractional units of magnetic flux.
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Fig.1. Simplified scheme of levels a gain medium A universal model valid for all laser types does not exist. The simplest model includes two systems of sub-levels: upper and lower. Within each sub-level system, the fast transitions ensure that thermal equilibrium is reached quickly, leading to the Maxwell–Boltzmann statistics of excitations among sub- levels in each system (fig.1). The upper level is assumed to be metastable.
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Brian Greene, The Elegant Universe, Vintage Books (2000) Under no circumstances do any excitations ever propagate faster than light in such theories—the presence or absence of a tachyonic mass has no effect whatsoever on the maximum velocity of signals (there is no violation of causality). While the field may have imaginary mass, any physical particles do not; the "imaginary mass" shows that the system becomes unstable, and sheds the instability by undergoing a type of phase transition called tachyon condensation (closely related to second order phase transitions) that results in symmetry breaking in current models of particle physics. The term "tachyon" was coined by Gerald Feinberg in a 1967 paper, but it was soon realized that Feinberg's model in fact did not allow for superluminal speeds. Instead, the imaginary mass creates an instability in the configuration:- any configuration in which one or more field excitations are tachyonic will spontaneously decay, and the resulting configuration contains no physical tachyons.
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A source of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range is used, although X-rays can also be used. The laser light interacts with molecular vibrations, phonons or other excitations in the system, resulting in the energy of the laser photons being shifted up or down. The shift in energy gives information about the vibrational modes in the system. Infrared spectroscopy typically yields similar, complementary, information.
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UIC faculty Juan Carlos Campuzano, University of Illinois at Chicago Campuzano obtained his B.S. and Ph.D. in physics from University of Wisconsin–Milwaukee in 1972 and 1978, respectively. He has also worked as a Post-Doctoral Fellow and Research Associate at the University of Liverpool and the University of Cambridge.US Department of Energy His research interests include infrared spectroscopy on metal surfaces, electronic excitations in high temperature superconductors and other materials, etc.
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Coulomb excitation is a technique in experimental nuclear physics to probe the electromagnetic aspect of nuclear structure. In coulomb excitation, a nucleus is excited by an inelastic collision with another nucleus through the electromagnetic interaction. In order to ensure that the interaction is electromagnetic in nature — and not nuclear — a "safe" scattering angle is chosen. This method is particularly useful for investigating collectivity in nuclei, as collective excitations are often connected by electric quadrupole transitions.
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Models for the ear of a direct kind have been created, most notably by Nobel Laureate Georg von Békésy. He used glass slides, razor blades, and an elastic membrane to represent the helicotrema. He could measure vibrations along the basilar membrane in response to different excitations frequencies. He found that the pattern of displacements for given frequency sine wave along the basilar membrane rose somewhat gradually to a peak and thereafter fell.
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Spin-polarized electron energy loss spectroscopy or SPEELS is a technique that is mainly used to measure the dispersion relation of the collective excitations, over the whole Brillouin zone. Spin waves are collective perturbations in a magnetic solid. Their properties depend on their wavelength (or wave vector). For long wavelength (short wave vector) spin wave the resulting spin precession has a very low frequency and the spin waves can be treated classically.
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He contributed to neutron scattering techniques, especially inelastic scattering to investigate the dynamics of materials. Nagler also worked with high resolution and time resolved x-ray scattering methods, using both in-house and synchrotron based x-ray sources. Nagler contributed to the study of excitation (magnetic) and critical behavior (quantum) in materials science, as well as the study of non- equilibrium thermodynamics systems, quantum fluctuations, spin gap systems, and excitations in condensed matter.
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The (uud) and (udd) particles are higher-mass excitations of the proton (, uud) and neutron (, udd), respectively. However, the and have no direct nucleon analogues. The states were established experimentally at the University of Chicago cyclotron and the Carnegie Institute of Technology synchro-cyclotron in the mid-1950s using accelerated positive pions on hydrogen targets. The existence of the , with its unusual +2 charge, was a crucial clue in the development of the quark model.
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He found that states with topological order contain non-trivial boundary excitations and developed chiral Luttinger theory for the boundary states (1990). The boundary states can become ideal conduction channel which may lead to device application of topological phases. He proposed the simplest topological order — Z2 topological order (1990), which turns out to be the topological order in the toric code. He also proposed a special class of topological order: non-Abelian quantum Hall states.
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Elementary excitations in condensed matter systems that can be measured by RIXS. The indicated energy scales are the ones relevant for transition metal oxides. Compared to other scattering techniques, RIXS has a number of unique features: it covers a large scattering phase-space, is polarization dependent, element and orbital specific, bulk sensitive and requires only small sample volumes. In RIXS one measures both the energy and momentum change of the scattered photon.
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Very recently, ICD has been identified to be an additional source of low energy electrons in water. There, ICD is faster than the competing proton transfer that is usually the prominent pathway in the case of electronic excitation of water clusters. The response of condensed water to electronic excitations is of utmost importance for biological systems. For instance, it was shown in experiments that low energy electrons do affect constituents of DNA effectively.
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Mukherjee developed a general time – dependent perturbative theory which remains valid for arbitrarily large time range and is free from secular divergences Later, he generalized this in the many – body regime and formulated the first general time-dependent coupled cluster theory for wave functions of arbitrary complexity. First applications to photo- excitations and energy transfer were highly successful. The method should prove to be useful to study photo-fragmentation and dissociation processes.
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In quantum field theory, a vacuum state or vacuum is a state of quantum fields which is at locally minimal potential energy. Quantum particles are excitations which deviate from a minimal potential energy state, therefore a vacuum state has no particles in it. Depending on the specifics of a quantum field theory, it can have more than one vacuum state. Different vacua, despite all "being empty" (having no particles), will generally have different vacuum energy.
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VOTCA-XTP is an extension to VOTCA-CTP, allowing to simulate excitation transport and properties.Jens Wehner, Lothar Brombacher, Joshua Brown, Christoph Junghans, Onur Çaylak, Yuriy Khalak, Pranav Madhikar, Gianluca Tirimbò, and Björn Baumeier. "Electronic Excitations in Complex Molecular Environments: Many-Body Green's Functions Theory in VOTCA-XTP" Journal of Chemical Theory and Computation. doi:10.1021/acs.jctc.8b00617 Therefore, it provides its own implementation of GW-BSE and a basic DFT implementation, employing localized basissets.
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The background dependence of string theory can have important physical consequences, such as determining the number of quark generations. In contrast, loop quantum gravity, like general relativity, is manifestly background independent, eliminating the background required in string theory. Loop quantum gravity, like string theory, also aims to overcome the nonrenormalizable divergences of quantum field theories. LQG never introduces a background and excitations living on this background, so LQG does not use gravitons as building blocks.
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Polaritons, caused by light coupling to excitons, occur in optical cavities and condensation of exciton-polaritons in an optical microcavity was first published in Nature in 2006. Semiconductor cavity polariton gases transition to ground state occupation at 19K. Bogoliubov excitations were seen polariton BECs in 2008. The signatures of BEC were observed at room temperature for the first time in 2013, in a large exciton energy semiconductor device and in a polymer microcavity.
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The application of quantum mechanics to physical objects such as the electromagnetic field, which are extended in space and time, is known as quantum field theory.A standard text is Peskin and Schroeder 1995. In particle physics, quantum field theories form the basis for our understanding of elementary particles, which are modeled as excitations in the fundamental fields. Quantum field theories are also used throughout condensed matter physics to model particle-like objects called quasiparticles.
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An example of mass gap arising for massless theories, already at the classical level, can be seen in spontaneous breaking of symmetry or Higgs mechanism. In the former case, one has to cope with the appearance of massless excitations, Goldstone bosons, that are removed in the latter case due to gauge freedom. Quantization preserves this gauge freedom property. A quartic massless scalar field theory develops a mass gap already at classical level.
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Inertial confinement fusion has the potential to produce orders of magnitude more neutrons than spallation. Neutrons are capable of locating hydrogen atoms in molecules, resolving atomic thermal motion and studying collective excitations of photons more effectively than X-rays. Neutron scattering studies of molecular structures could resolve problems associated with protein folding, diffusion through membranes, proton transfer mechanisms, dynamics of molecular motors, etc. by modulating thermal neutrons into beams of slow neutrons.
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The Bose glass phase is characterized by a finite compressibility, the absence of a gap, and by an infinite superfluid susceptibility., It is insulating despite the absence of a gap, as low tunneling prevents the generation of excitations which, although close in energy, are spatially separated. The Bose glass has been shown to have a non-zero Edwards-Anderson order parameter and has been suggested to display replica symmetry breaking, however this has not been proven.
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Both superconductivity and superinsulation rest on the pairing of conduction electrons into Cooper pairs. In superconductors, all the pairs move coherently, allowing for the electric current without resistance. In superinsulators, both Cooper pairs and normal excitations are confined and the electric current cannot flow. A mechanism behind superinsulation is the proliferation of magnetic monopoles at low temperatures. In two dimensions (2D), magnetic monopoles are quantum tunneling events (instantons) that are often referred to as monopole “plasma”.
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In the Raman effect, photons are red- or blue-shifted by optical phonons with a frequency of about 15 THz. However, silicon waveguides also support acoustic phonon excitations. The interaction of these acoustic phonons with light is called Brillouin scattering. The frequencies and mode shapes of these acoustic phonons are dependent on the geometry and size of the silicon waveguides, making it possible to produce strong Brillouin scattering at frequencies ranging from a few MHz to tens of GHz.
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Some theories consider sleep to be an important factor in establishing well-organized long- term memories. (See also sleep and learning.) Sleep plays a key function in the consolidation of new memories. According to Tarnow's theory, long-term memories are stored in dream format (reminiscent of the Penfield & Rasmussen's findings that electrical excitations of the cortex give rise to experiences similar to dreams). During waking life an executive function interprets long- term memory consistent with reality checking .
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However, the experimentalists alluded to the fact, that calorimetric tests with 10-GeV electrons were executed already in 1969. There, copper was used as beam dump, and an accuracy of 1% was achieved. In modern calorimeters called electromagnetic or hadronic depending on the interaction, the energy of the particle showers is often measured by the ionization caused by them. Also excitations can arise in scintillators (see scintillation), whereby light is emitted and then measured by a scintillation counter.
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Dispersions for bosonic (left) and fermionic (right) Dirac materials. In contrast to the fermionic case where Pauli exclusion confines excitations close to the Fermi energy, the description of boson requires the entire Brillioun zone. While historic interest focussed on fermionic quasiparticles that have potential for technological applications, particularly in electronics, the mathematical structure of the Dirac equation is not restricted to the statistics of the particles. This has led to recent development of the concept of bosonic Dirac matter.
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Each of these relies on specific physical assumptions regarding, e.g., correlation functions of the environment. For example, in the weak coupling limit derivation, one typically assumes that (a) correlations of the system with the environment develop slowly, (b) excitations of the environment caused by system decay quickly, and (c) terms which are fast-oscillating when compared to the system timescale of interest can be neglected. These three approximations are called Born, Markov, and rotating wave, respectively.
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832 In 1969, he calculated one-loop diagrams in the early string theory, with Daniele Amati and Bouchiat. In the beginning of the 1970s, he also studied, with Sakita, string theories as conformal field theories in two dimensions and then soliton theories as field theories of collective excitations, e.g., in the context of WKB wave functions. In the 1980s he studied soliton (Skyrmion) models of quarks in the limit of many color degrees of freedom (large-N limit).
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The limit describes several loss mechanisms that are inherent to any solar cell design. The first are the losses due to blackbody radiation, a loss mechanism that affects any material object above absolute zero. In the case of solar cells at standard temperature and pressure, this loss accounts for about 7% of the power. The second is an effect known as "recombination", where the electrons created by the photoelectric effect meet the electron holes left behind by previous excitations.
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For solid materials, Raman scattering is used as a tool to detect high-frequency phonon and magnon excitations. Raman lidar is used in atmospheric physics to measure the atmospheric extinction coefficient and the water vapour vertical distribution. Stimulated Raman transitions are also widely used for manipulating a trapped ion's energy levels, and thus basis qubit states. Raman spectroscopy can be used to determine the force constant and bond length for molecules that do not have an infrared absorption spectrum.
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Furthermore, the field of Yang–Mills theories was included in the Clay Mathematics Institute's list of "Millennium Prize Problems". Here the prize-problem consists, especially, in a proof of the conjecture that the lowest excitations of a pure Yang–Mills theory (i.e. without matter fields) have a finite mass-gap with regard to the vacuum state. Another open problem, connected with this conjecture, is a proof of the confinement property in the presence of additional Fermion particles.
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Some phase transitions, such as superconducting and ferromagnetic, can have order parameters for more than one degree of freedom. In such phases, the order parameter may take the form of a complex number, a vector, or even a tensor, the magnitude of which goes to zero at the phase transition. There also exist dual descriptions of phase transitions in terms of disorder parameters. These indicate the presence of line-like excitations such as vortex- or defect lines.
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Usually, an elementary excitation is called a "quasiparticle" if it is a fermion and a "collective excitation" if it is a boson. However, the precise distinction is not universally agreed upon. There is a difference in the way that quasiparticles and collective excitations are intuitively envisioned. A quasiparticle is usually thought of as being like a dressed particle: it is built around a real particle at its "core", but the behavior of the particle is affected by the environment.
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Pressure influences the plasma etching process. For plasma etching to happen, the chamber has to be under low pressure, less than 100 Pa. In order to generate low-pressure plasma, the gas has to be ionized. The ionization happens by a glow charge. Those excitations happen by an external source, which can deliver up to 30 kW and frequencies from 50 Hz (dc) over 5–10 Hz (pulsed dc) to radio and microwave frequency (MHz-GHz).
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Horst Ludwig Störmer (born April 6, 1949) is a German physicist, Nobel laureate and emeritus professor at Columbia University.Home page at Columbia He was awarded the 1998 Nobel Prize in Physics jointly with Daniel Tsui and Robert Laughlin "for their discovery of a new form of quantum fluid with fractionally charged excitations" (the fractional quantum Hall effect). He and Tsui were working at Bell Labs at the time of the experiment cited by the Nobel committee.
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In 1977 they discovered that doping with iodine vapor could enhance the conductivity of polyacetylene. The three scientists were awarded the Nobel Prize in Chemistry in 2000 in recognition of the discovery. With regard to the mechanism of electric conduction, it is strongly believed that nonlinear excitations in the form of solitons play a role. In 1979, Shirakawa became an assistant professor in the University of Tsukuba; three years later, he advanced to a full professor.
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In the past decade, this observation led to the attraction of theoretical studies towards near-field effects of the earthquake rotational loading on the structural response.M. R. Falamarz-Sheikhabadi, M. Ghafory- Ashtiany, Rotational components in structural loading, Soil Dynamics and Earthquake Engineering, Vol. 75 (2015) 220-233. The results of these studies implied that the rotational components may result in significant damage of structures sensitive to high-frequency excitations, and, hence, their influence should be incorporated in seismic codes.
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Another example of Frenkel exciton includes on-site d-d excitations in transition metal compounds with partially-filled d-shells. While d-d transitions are in principle forbidden by symmetry, they become weakly-allowed in a crystal when the symmetry is broken by structural relaxations or other effects. Absorption of a photon resonant with a d-d transition leads to the creation of an electron-hole pair on a single atomic site, which can be treated as a Frenkel exciton.
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Effects on Schumann resonances have been reported following geomagnetic and ionospheric disturbances. More recently, discrete Schumann resonance excitations have been linked to transient luminous events – sprites, ELVES, jets, and other upper- atmospheric lightning. A new field of interest using Schumann resonances is related to short-term earthquake prediction. Interest in Schumann resonances was renewed in 1993 when E. R. Williams showed a correlation between the resonance frequency and tropical air temperatures, suggesting the resonance could be used to monitor global warming.
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Anyons are generally classified as abelian or non-abelian, according to whether the elementary excitations of the theory transform under an abelian representation of the braid group or a non-abelian one. Abelian anyons have been detected in connection to the fractional quantum Hall effect. The possible construction of anyonic Dirac matter relies on the symmetry protection of crossings of anyonic energy bands. In comparison to bosons and fermions the situation gets more complicated as translations in space do not necessarily commute.
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Heated to temperatures above , ferromagnetic materials become paramagnetic and their magnetic behavior is dominated by spin waves or magnons, which are boson collective excitations with energies in the meV range. The magnetization that occurs below is a famous example of the "spontaneous" breaking of a global symmetry, a phenomenon that is described by Goldstone's theorem. The term "symmetry breaking" refers to the choice of a magnetization direction by the spins, which have spherical symmetry above , but a preferred axis (the magnetization direction) below .
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Such degenerate states are often the case of atomic and molecular valence states. To counter the restrictions, there was an attempt to implement second-order perturbation theory in conjunction with complete active space self-consistent field (CASSCF) wave functions. At the time, it was rather difficult to compute three- and four-particle density matrices which are needed for matrix elements involving internal and semi- internal excitations. The results was rather disappointing with little or no improvement from usual CASSCF results.
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Stephen Douglas Kevan (born 1954) is an American condensed matter physicist who researches "surface and thin film physics; electronic structure and collective excitations at surfaces; nanoscale spatial and temporal fluctuations in magnetic and other complex materials". He is the current director of the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory in Berkeley, California. He is also a faculty member on leave from the University of Oregon and served as division deputy for science at the ALS prior to his directorship.
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The absorption peaks of NEXAFS spectra are determined by multiple scattering resonances of the photoelectron excited at the atomic absorption site and scattered by neighbor atoms. The local character of the final states is determined by the short photoelectron mean free path, that is strongly reduced (down to about 0.3 nm at 50 eV) in this energy range because of inelastic scattering of the photoelectron by electron- hole excitations (excitons) and collective electronic oscillations of the valence electrons called plasmons.
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A Weyl semimetal is a solid state crystal whose low energy excitations are Weyl fermions that carry electrical charge even at room temperatures. A Weyl semimetal enables realization of Weyl fermions in electronic systems. It is a topologically nontrivial phase of matter, together with Helium-3 A superfluid phase, that broadens the topological classification beyond topological insulators. The Weyl fermions at zero energy correspond to points of bulk band degeneracy, the Weyl nodes (or Fermi points), that are separated in momentum space.
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Particle physics (also known as high energy physics) is a branch of physics that studies the nature of the particles that constitute matter and radiation. Although the word particle can refer to various types of very small objects (e.g. protons, gas particles, or even household dust), usually investigates the irreducibly smallest detectable particles and the fundamental interactions necessary to explain their behaviour. By our current understanding, these elementary particles are excitations of the quantum fields that also govern their interactions.
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A lower energy pump pulse photoexcites an electron in a ground state or HOMO into a higher lying excited state. After a time delay, a second, higher energy pulse photoemits the excited electron into free electron states above the vacuum level.Time-resolved two-photon photoelectron (2PPE) spectroscopy is a time-resolved spectroscopy technique which is used to study electronic structure and electronic excitations at surfaces. The technique utilizes femtosecond to picosecond laser pulses in order to first photoexcite an electron.
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Direct experimental confirmation of the gap has been done via tunneling experiments, which probed the single-particle DOS in two and three dimensions. The experiments clearly showed a linear gap in two dimensions, and a parabolic gap in three dimensions. Another experimental consequence of the Coulomb gap is found in the conductivity of samples in the localized regime. The existence of a gap in the spectrum of excitations would result in a lowered conductivity than that predicted by Mott variable-range hopping.
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The PNLF method is unbiased by metallicity. This is because oxygen is a primary nebular coolant; any drop in its concentration raises the plasma's electron temperature and raises the amount of collisional excitations per ion. This compensates for having a smaller number of emitting ions in the PNe resulting in little change in the λ5007 emissions . Consequently, a reduction in oxygen density only lowers the emergent [O III] λ5007 emission line intensity by approximately the square root of the difference in abundance.
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The result is for each frame of each signal a head-internal representation which indicates roughly how loud each frequency component would be perceived. Now, a further idealization step of the reference signal takes place by filtering out excessive timbre and low level stationary noise. At the same time, linear frequency distortions and stationary noise are partially removed from the degraded signal. A subtraction of the idealized excitations finally leads to the Distortion Density, which is measure for the audibility of distortions.
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Working with Don DuBois, they derived a correction to Landau's relation for the damping excitations of unmagnetized plasma. For 1965-1966, Kivelson took a leave from RAND to join her husband's sabbatical leave in Boston. Through a fellowship from the Radcliffe Institute for Advanced Study, Kivelson was able to conduct scientific research in a university setting at Harvard and MIT. Motivated by her experiences in academia through the Radcliffe Institute, Kivelson joined UCLA in 1967 as an assistant research geophysicist.
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Scissors Modes are collective excitations in which two particle systems move with respect to each other conserving their shape. For the first time they were predicted to occur in deformed atomic nuclei by N. LoIudice and F. Palumbo, who used a semiclassical Two Rotor Model, whose solution required a realization of the O(4) algebra that was not known in mathematics. In this model protons and neutrons were assumed to form two interacting rotors to be identified with the blades of scissors. Their relative motion (Fig.
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1) generates a magnetic dipole moment whose coupling with the electromagnetic field provides the signature of the mode. Scissors Mode in atomic nuclei: the proton (p) and neutron (n) rotors precess around their bisector. Such states have been experimentally observed for the first time by A. Richter and collaborators in a rare earth nucleus, 156Gd, and then systematically investigated experimentally and theoretically in all deformed atomic nuclei. Inspired by this, D. Guéry-Odelin and S. Stringari predicted similar collective excitations in Bose-Einstein condensates in magnetic traps.
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Finally, ferrimagnetism as prototypically displayed by magnetite is in some sense an intermediate case: here the magnetization is globally uncompensated as in ferromagnetism, but the local magnetization points in different directions. The above discussion pertains to the ground state structure. Of course, finite temperatures lead to excitations of the spin configuration. Here two extreme points of view can be contrasted: in the Stoner picture of magnetism (also called itinerant magnetism), the electronic states are delocalized, and their mean-field interaction leads to the symmetry breaking.
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This was followed by a master's degree at Australia's first cyclotron, where he began his work as a high- energy physicist. His thesis from the University of Melbourne was on Coulomb excitations of the atom. In 1959 Rushbrooke won a scholarship that took him to King's College, Cambridge. Following work at the Cavendish Laboratory and completion of his PhD, Rushbrooke spent a year at CERN in Geneva before returning to Cambridge to take up a fellowship at Downing College as director of studies in physics.
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Laser plasma displays, developed in 2005 by the University of Texas, utilize a series of powerful lasers that focus light in desired positions in order to create plasma excitations with the oxygen and nitrogen molecules in the air. This type of holographic display is capable of producing images in thin air, without the need for any sort of screen or external refraction media. The laser plasma display is able to depict very bright and visible objects, but it lacks in terms of resolution and picture quality.
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While photons exist as excitations of a vector potential and so contain an oscillating dipole term, gravitons are a spin-2 field and so have an oscillating quadrupole term. For efficient lasing to occur, there are several conditions that must be met: # There must be particles in an excited state capable of emitting radiation at the desired frequency. In a normal laser, these would be valence electrons in an excited state. For a gaser, the more straightforward analog would be a binary system of massive bodies.
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They showed its ground state has a rich structure of broken symmetries including one exhibiting canted anti- ferromagnetism. Rajaraman and PhD student Sankalpa Ghosh studied topologically non trivial "meron" and bi-meron excitations in layer-spin for bilayer Hall systems taking into account differences in interlayer and intra-layer coulomb energy. They also analyzed CP_{3} solitons arising in a four-component description of electrons carrying both spin and layer-spin. These solitons carry nontrivial intertwined windings of real spin and layer degrees of freedom.
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Photodarkening is an optical effect observed in the interaction of laser radiation with amorphous media (glasses) in optical fibers. Until now, such creation of color centers was reported only in glass fibers . Photodarkening limits the density of excitations in fiber lasers and amplifiers. The experimental results suggest that operating at a saturated regime helps to reduce photodarkening.N. Li; S. Yoo; X. Yu; D. Jain; J. K. Sahu (2014)“Pump Power Depreciation by Photodarkening in Ytterbium-Doped Fibers and Amplifiers”, IEEE Photonics Technology Letters, Vol.
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In the preceding section the excitations of the FK model were derived by considering the model in a continuum-limit approximation. Since the properties of kinks are only modified slightly by the discreteness of the primary model, the SG equation can adequately describe most features and dynamics of the system. The discrete lattice does, however, influence the kink motion in a unique way with the existence of the Peierls–Nabarro (PN) potential V_{PN}(X). Here, X is the position of the kink's center.
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Ammonia was first detected in interstellar space in 1968, based on microwave emissions from the direction of the galactic core. This was the first polyatomic molecule to be so detected. The sensitivity of the molecule to a broad range of excitations and the ease with which it can be observed in a number of regions has made ammonia one of the most important molecules for studies of molecular clouds. The relative intensity of the ammonia lines can be used to measure the temperature of the emitting medium.
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A large class of 2+1D topological orders is realized through a mechanism called string-net condensation. This class of topological orders can have a gapped edge and are classified by unitary fusion category (or monoidal category) theory. One finds that string- net condensation can generate infinitely many different types of topological orders, which may indicate that there are many different new types of materials remaining to be discovered. The collective motions of condensed strings give rise to excitations above the string-net condensed states.
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In physics, quasiparticles and collective excitations (which are closely related) are emergent phenomena that occur when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in vacuum. For example, as an electron travels through a semiconductor, its motion is disturbed in a complex way by its interactions with other electrons and with atomic nuclei. The electron behaves as though it has a different effective mass travelling unperturbed in vacuum. Such an electron is called an electron quasiparticle.
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One simplifying factor is that the system as a whole, like any quantum system, has a ground state and various excited states with higher and higher energy above the ground state. In many contexts, only the "low-lying" excited states, with energy reasonably close to the ground state, are relevant. This occurs because of the Boltzmann distribution, which implies that very-high-energy thermal fluctuations are unlikely to occur at any given temperature. Quasiparticles and collective excitations are a type of low-lying excited state.
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The light absorbed in the infrared region does not correspond to electronic excitation of the substance studied, but rather to different kinds of vibrational excitation. The vibrational excitations are characteristic of different groups in a molecule, that can in this way be identified. The infrared spectrum typically has very narrow absorption lines, which makes them unsuited for quantitative analysis but gives very detailed information about the molecules. The frequencies of the different modes of vibration varies with isotope, and therefore different isotopes give different peaks.
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In 1889 Calzecchi assisted the famous physicist Galileo Ferraris, testing the installation of electric lighting in Fermo. Meanwhile, the great physics discoveries of Heinrich Hertz, Wilhelm Conrad Röntgen, Nicola Tesla and Augusto Righi were made, including the transmission of telegraph signals without wires. Since 1884 Calzecchi had been researching the properties of metal powders, finding high electrical conductivity due to various excitations such as extra current, lightning, electrostatic induction, etc. Calzecchi's experiments with tubes of metal filings led to the development of the first radio wave detector, the coherer, in 1890 by Edouard Branly.
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Experiment using two tuning forks oscillating at the same frequency. One of the forks is being hit with a rubberized mallet. Although the first tuning fork hasn't been hit, the other fork is visibly excited due to the oscillation caused by the periodic change in the pressure and density of the air by hitting the other fork, creating an acoustic resonance between the forks. However, if a piece of metal is placed on a prong, the effect dampens, and the excitations become less and less pronounced as resonance isn't achieved as effectively.
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In several of these studies, Johnson played a leading role. Together with Thomas DeGrand (University of Colorado), Joseph Kiskis (UC Davis), and Jaffe, Johnson showed that the spectra of light-quark baryons and mesons could be accommodated in QCD. With Thorn, Johnson demonstrated the emergence of string-like excitations of hadrons in QCD, and Johnson and Jaffe explored the spectra and interactions of exotic hadrons composed purely of gluons or made of more than three quarks. Studies of such unusual hadrons remains a topic of current experimental and theoretical interest.
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The idea that the photon could emerge as Nambu-Goldstone modes in a theory with spontaneous Lorentz violation first arose in the context of special relativity. In 1951, Paul Dirac considered a vector theory with a Lagrange-multiplier potential as an alternative model giving rise to the charge of the electron. It was later recognized that this was a theory with spontaneous Lorentz breaking. Twelve years later, in 1963, James Bjorken proposed a model in which collective excitations of a fermion field could lead to composite photons emerging as Nambu-Goldstone modes.
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Some states of matter exhibit symmetry breaking, where the relevant laws of physics possess some form of symmetry that is broken. A common example is crystalline solids, which break continuous translational symmetry. Other examples include magnetized ferromagnets, which break rotational symmetry, and more exotic states such as the ground state of a BCS superconductor, that breaks U(1) phase rotational symmetry. Goldstone's theorem in quantum field theory states that in a system with broken continuous symmetry, there may exist excitations with arbitrarily low energy, called the Goldstone bosons.
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It has been found that the amount of light radiated into the substrate decreases with distance from the substrate. This means that nano-particles on the surface are desirable for radiating light into the substrate, but if there is no distance between the particle and substrate, then the light is not trapped and more light escapes. The surface plasmons are the excitations of the conduction electrons at the interface of metal and the dielectric. Metallic nano-particles can be used to couple and trap freely propagating plane waves into the semiconductor thin film layer.
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Electron micrograph of 2D crystals of the LH1-Reaction center photosynthetic unit. A photosynthetic reaction center is a complex of several proteins, pigments and other co-factors that together execute the primary energy conversion reactions of photosynthesis. Molecular excitations, either originating directly from sunlight or transferred as excitation energy via light-harvesting antenna systems, give rise to electron transfer reactions along the path of a series of protein-bound co-factors. These co-factors are light-absorbing molecules (also named chromophores or pigments) such as chlorophyll and phaeophytin, as well as quinones.
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Roton dispersion relation, showing the quasiparticle energy E(p) as a function of momentum p. A quasiparticle with momentum generated in the local energy minimum is called a roton. In theoretical physics, a roton is an elementary excitation, or quasiparticle, seen in superfluid helium-4 and Bose-Einstein condensates with long-range dipolar interactions or spin-orbit coupling. The dispersion relation of elementary excitations in this superfluid shows a linear increase from the origin, but exhibits first a maximum and then a minimum in energy as the momentum increases.
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This component can interact with fermions via Yukawa coupling to give them mass as well. Mathematically, the Higgs field has imaginary mass and is therefore a tachyonic field. While tachyons (particles that move faster than light) are a purely hypothetical concept, fields with imaginary mass have come to play an important role in modern physics. Under no circumstances do any excitations ever propagate faster than light in such theories the presence or absence of a tachyonic mass has no effect whatsoever on the maximum velocity of signals (there is no violation of causality).
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Although the Higgs field exists everywhere, proving its existence was far from easy. In principle, it can be proved to exist by detecting its excitations, which manifest as Higgs particles (the Higgs boson), but these are extremely difficult to produce and detect, due to the energy required to produce them and their very rare production even if the energy is sufficient. It was therefore several decades before the first evidence of the Higgs boson was found. Particle colliders, detectors, and computers capable of looking for Higgs bosons took more than 30 years to develop.
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In 1991, Levitov proposed that lowest energy configurations of repulsive particles in cylindrical geometries reproduce the spirals of botanical phyllotaxis. More recently, Nisoli et al. (2009) showed that to be true by constructing a "magnetic cactus" made of magnetic dipoles mounted on bearings stacked along a "stem". They demonstrated that these interacting particles can access novel dynamical phenomena beyond what botany yields: a "Dynamical Phyllotaxis" family of non local topological solitons emerge in the nonlinear regime of these systems, as well as purely classical rotons and maxons in the spectrum of linear excitations.
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This is due to the low cross-section for non-resonant photo-ionization produced by the laser. A pulsed laser system facilitates the efficient coupling of a time-of-flight mass spectrometer (TOF- MS) to the resonance ionization set-up due to the instrument's abundance sensitivity. This is because TOF systems can produce an abundance sensitivity of up to 104 whereas magnetic mass spectrometers can only achieve up to 102. The total selectivity in a RIS process is a combination of the sensitivities in the various resonance transitions for multiple step-wise excitations.
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Orbitons can be thought of as energy stored in an orbital occupancy that can move throughout a material, in other words, an orbital-based excitation. An orbiton propagates through a material as a series of orbital excitations and relaxations of the electrons in a material without changes in either the spin of those electrons or the charge at any point in the material. Electrons, being of like charge, repel each other. As a result, in order to move past each other in an extremely crowded environment, they are forced to modify their behavior.
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Burkard Hillebrands' research field is mostly in spintronics. His special interests are in spin dynamics and magnonics, material properties of thin magnetic films, heterostructures as well as multilayers nanostructures. In the field of spin dynamics and magnonics he is particularly interested in the properties of spin waves and their quanta, magnons, and their application to future information technologies. He is also interested in research on dynamic magnetic excitations in confined magnetic structures, linear and nonlinear spin wave propagation phenomena, magnon gases and condensates, magnon supercurrents, magnonic crystals and magnetic storage.
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Thermal fluctuations generally affect all the degrees of freedom of a system: There can be random vibrations (phonons), random rotations (rotons), random electronic excitations, and so forth. Thermodynamic variables, such as pressure, temperature, or entropy, likewise undergo thermal fluctuations. For example, for a system that has an equilibrium pressure, the system pressure fluctuates to some extent about the equilibrium value. Only the 'control variables' of statistical ensembles (such as the number of particules N, the volume V and the internal energy E in the microcanonical ensemble) do not fluctuate.
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At the most basic level, the field at each point in space is a simple harmonic oscillator, and its quantization places a quantum harmonic oscillator at each point. Excitations of the field correspond to the elementary particles of particle physics. However, even the vacuum has a vastly complex structure, so all calculations of quantum field theory must be made in relation to this model of the vacuum. The vacuum has, implicitly, all of the properties that a particle may have: spin, or polarization in the case of light, energy, and so on.
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Canonically, if the field at each point in space is a simple harmonic oscillator, its quantization places a quantum harmonic oscillator at each point. Excitations of the field correspond to the elementary particles of particle physics. Thus, according to the theory, even the vacuum has a vastly complex structure and all calculations of quantum field theory must be made in relation to this model of the vacuum. The theory considers vacuum to implicitly have the same properties as a particle, such as spin or polarization in the case of light, energy, and so on.
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In quantum mechanics, the Schrieffer–Wolff transformation is a unitary transformation used to perturbatively diagonalize the system Hamiltonian to first order in the interaction. As such, the Schrieffer-Wolff transformation is an operator version of second-order perturbation theory. The Schrieffer- Wolff transformation is often used to project out the high energy excitations of a given quantum many-body Hamiltonian in order to obtain an effective low energy model. The Schrieffer–Wolff transformation thus provides a controlled perturbative way to study the strong coupling regime of quantum-many body Hamiltonians.
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Stoichiometric equation representing the metabolism of an aldehyde substrate by ALDH3A1 using NADP+ as a cofactor Electronic excitations of alkene and aromatic functional groups allow certain nucleic acids, proteins, fatty acids and organic molecules to absorb ultraviolet radiation (UVR). Moderate UVR exposure oxidizes specific proteins that eventually serve as signaling agents for an array of metabolic and inflammatory pathways. Overexposure to UVR, on the other hand, can be detrimental to the tissue. In the presence of molecular oxygen, UVR leads to the formation of reactive oxygen species (ROS) that are implicated in many degradation pathways.
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Piecuch has established himself as one the leaders of electronic structure theory. Of particular note are his contributions to coupled-cluster and many-body theories. His work on the renormalized and active-space coupled-cluster methods is especially important, since the resulting approximations, such as CR-CC(2,3), CCSDt, or CC(t;3), and their extensions utilizing the equation-of-motion coupled-cluster concepts, for example, CR-EOMCC, EOMCCSDt, etc., can accurately describe potential energy surfaces, biradicals, and electronic excitations in molecules without resorting to complex multi-reference wave functions.
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Shape waves are excitations propagating along Josephson vortices or fluxons. In the case of two-dimensional Josephson junctions (thick long Josephson junctions with an extra dimension) described by the 2D sine-Gordon equation, shape waves are distortions of a Josephson vortex line of an arbitrary profile. Shape waves have remarkable properties exhibiting Lorentz contraction and time dilation similar to that in special relativity. Position of the shape wave excitation on a Josephson vortex acts like a “minute-hand” showing the time in the rest-frame associated with the vortex.
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X-ray Raman scattering (XRS) is non-resonant inelastic scattering of x-rays from core electrons. It is analogous to vibrational Raman scattering, which is a widely used tool in optical spectroscopy, with the difference being that the wavelengths of the exciting photons fall in the x-ray regime and the corresponding excitations are from deep core electrons. XRS is an element- specific spectroscopic tool for studying the electronic structure of matter. In particular, it probes the excited-state density of states (DOS) of an atomic species in a sample.
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In condensed matter physics, a quantum spin liquid is an unusual phase of matter that can be formed by interacting quantum spins in certain magnetic materials. Quantum spin liquids (QSL) are generally characterized by their long-range quantum entanglement, fractionalized excitations, and absence of ordinary magnetic order. The quantum spin liquid state was first proposed by physicist Phil Anderson in 1973 as the ground state for a system of spins on a triangular lattice that interact antiferromagnetically with their nearest neighbors; i.e. neighboring spins seek to be aligned in opposite directions.
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Sachdev developed the theory of quantum transport at non-zero temperatures in the simplest model system without quasiparticle excitations: a conformal field theory in 2+1 dimensions, realized by the superfluid-insulator transitions of ultracold bosons in an optical lattice. A comprehensive picture emerged from quantum-Boltzmann equations, the operator product expansion, and holographic methods. The latter mapped the dynamics to that in the vicinity of the horizon of a black hole. These were the first proposed connections between condensed matter quantum critical systems, hydrodynamics, and quantum gravity.
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Sachdev developed the theory of magneto-thermoelectric transport in 'strange' metals: these are states of quantum matter with variable density without quasiparticle excitations. Such metals are found, most famously, near optimal doping in the hole-doped cuprates, but also appear in numerous other correlated electron compounds. For strange metals in which momentum is approximately conserved, a set of hydrodynamic equations were proposed in 2007, describing two-component transport with momentum drag component and a quantum-critical conductivity. This formulation was connected to the holography of charged black holes, memory functions, and new field-theoretic approaches.
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Direct laser writing is a very popular form of optical maskless lithography, which offers flexibility, ease of use, and cost effectiveness in R&D; processing. This equipment offers rapid patterning at sub-micrometre resolutions, and offers a compromise between performance and cost when working with feature sizes of approximately 200 nm or greater. Interference lithography or holographic exposures are not maskless processes and therefore do not count as "maskless", although they have no 1:1 imaging system in between. Plasmonic direct writing lithography uses localized surface plasmon excitations via scanning probes to directly expose the photoresist.
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A great deal of modern solid state physics as produced today stems from this original and early paper. His influence on the development of solid state physics extends to a deep understanding of many facets such as surface physics, of thermionic emission, of transport phenomena in semiconductors and of collective excitations in solids such as spin waves. He created the theoretical physics division at Bell Telephone Laboratory. Because of this, the total research effort at this institution and brought about much of the most original research in condensed matter physics during the latter half of the 20th century.
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The SLEs not only set the standard in describing quantum- light emission in semiconductors but they are also ideally suited for modeling quantum-light sources and filters based on semiconductor technology. The extensions of SLEs include resonance fluorescence and higher-order photon- correlation effects and are the basis to expand the quantum-optical spectroscopy. He and his coworkers are working on a systematic theory to describe excitation of solids with THz fields. Typical laser excitations are resonant with band-to-band transitions, not the energy difference of several relevant many-body states that actually match the THz-photon energy.
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Upon Lewis base coordination, the former vacant p orbital at boron becomes occupied and cyclic delocalization of the π electron system is no longer feasible, corresponding to the loss of antiaromaticity. However, strong bond length alternation in the BC4 backbone is still observed and remain almost unaffected by these fundamental electronic changes. In contrast, spectroscopic measurements are much more sensitive to adduct formation. Unlike the respective borole precursors which are intensely coloured, the adducts are pale yellow solids with characteristic UV-Vis excitations at λmax = 350–380 nm which agrees with an increase in the HOMO- LUMO gap.
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Neutron resonance spin echo is a quasielastic neutron scattering technique developed by Gähler and Goloub. In its classic form it is used analogously to conventional neutron spin echo (NSE) spectrometry for quasielastic scattering where tiny energy changes from the sample to the neutron have to be resolved. In contrast to NSE, the large magnetic solenoids are replaced by two resonant flippers respectively. This allows for variants in combination with triple axes spectrometers to resolve narrow linewidth of excitations or MIEZE (Modulation of IntEnsity with Zero Effort) for depolarizing conditions and incoherent scattering which are not possible with conventional NSE.
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In the case of bosons, there is no Pauli exclusion principle to confine excitations close to the chemical potential (Fermi energy for fermions) so the entire Brillouin zone must be included. At low temperatures, the bosons will collect at the lowest energy point, the \Gamma-point of the lower band. Energy must be added to excite the quasiparticles to the vicinity of the linear crossing point. Several examples of Dirac matter with fermionic quasi-particles occur in systems where there is a hexagonal crystal lattice; so bosonic quasiparticles on an hexagonal lattice are the natural candidates for bosonic Dirac matter.
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This makes solid oxygen particularly interesting, as it is considered a "spin-controlled" crystal that displays antiferromagnetic magnetic order in the low temperature phases. The magnetic properties of oxygen have been studied extensively.See also: For papers dealing with the magnetic properties of solid oxygen we refer to magnetisation of condensed oxygen under high pressures and in strong magnetic fields by R.J. Meier, C.J. Schinkel and A. de Visser, J. Phys. C15 (1982) 1015–1024, far infrared absorption dealing with the magnetic excitations or spinwaves in Meier R J, Colpa J H P and Sigg H 1984 J. Phys.
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The triple-axis spectrometry method was first developed by Bertram Brockhouse at the National Research Experimental NRX reactor at the Chalk River Laboratories in Canada. The first results from the prototype triple-axis spectrometer were published in January 1955 and the first true triple-axis spectrometer was built in 1956. Bertram Brockhouse shared the 1994 Nobel prize for Physics for this development, which allowed elementary excitations, such as phonons and magnons, to be observed directly. The Nobel citation was "for pioneering contributions to the development of neutron scattering techniques for studies of condensed matter" and "for the development of neutron spectroscopy".
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The Nilsson model is a nuclear shell model treating the atomic nucleus as a deformed sphere. In 1953, the first experimental examples were found of rotational bands in nuclei, with their energy levels following the same J(J+1) pattern of energies as in rotating molecules. Quantum mechanically, it is impossible to have a collective rotation of a sphere, so this implied that the shape of these nuclei was nonspherical. In principle, these rotational states could have been described as coherent superpositions of particle-hole excitations in the basis consisting of single-particle states of the spherical potential.
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For very light ions slowing down in heavy materials, the nuclear stopping is weaker than the electronic at all energies. Especially in the field of radiation damage in detectors, the term "non-ionizing energy loss" (NIEL) is used as a term opposite to the linear energy transfer (LET), see e.g. Refs. Since per definition nuclear stopping power does not involve electronic excitations, NIEL and nuclear stopping can be considered to be the same quantity in the absence of nuclear reactions. The total non-relativistic stopping power is therefore the sum of two terms: F(E) = F_e (E) + F_n (E).
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He is currently full professor at the Physics Department KTH Royal Institute of Technology. He received multiple awards in recognition of his research on superconductivity and superfluidity. His results, obtained with several collaborators and students, include a theory of new types of superconducting states in multicomponent systems Type-1.5 superconductivity, (reviewed in ) theory of metallic and superconducting superfluids and inter-component pairing induced by thermal fluctuation in multicomponent systems (reviewed in ), prediction, often referred as Babaev-Faddeev-Niemi hypothesis of unconventional excitations in superconducting state: knotted solitons also dubbed as Hopfions. He is actively engaged in science communication to general public .
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Mukherjee has been the earliest developer of a class of many- body methods for electronic structure which are now standard and highly acclaimed works in the field. These methods, collectively called multireference coupled cluster (MRCC) formalisms, are versatile and powerful methods for predicting with quantitative accuracy the energetics of a vast range of molecular excitations and ionization. The attractive aspects of the formalisms are size-extensivity, compactness and high accuracy. He also developed a linear response theory based on coupled cluster formalism (CCLRT), which is similar in scope to the SAC-CI and done independently of it.
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Figure 1: Polaritonics may resolve the incongruence between electronics, which suffers technological and physical barriers to increased speed, and photonics, which requires lossy integration of light source and guiding structures. Other quasiparticles/collective excitations such as magnon-polaritons and exciton- polaritons, their location identified above, may be exploitable in the same way that phonon-polaritons have been for polaritonics. Polaritonics is an intermediate regime between photonics and sub-microwave electronics (see Fig. 1). In this regime, signals are carried by an admixture of electromagnetic and lattice vibrational waves known as phonon-polaritons, rather than currents or photons.
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He also contributed in developing superconducting magnets at BARC and his work assisted in the development of Yafet-Kittel type of ferrimagnetism. His studies have been documented by way of a number of articles and the article repository of the Indian Academy of Sciences has listed 23 of them. Besides, he published a monograph, Magnetism, along with L. Madhav Rao and his work has been cited by other scientists. Murthy introduced such experimental techniques as Compton profile spectroscopy, Mossbauer spectroscopy and Raman spectroscopy at BARC and pioneered basic research on subjects like electron states, of cooperative effects and long wavelength excitations.
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They transform nonlinearly (shift) under the action of these generators, and can thus be excited out of the asymmetric vacuum by these generators. Thus, they can be thought of as the excitations of the field in the broken symmetry directions in group space—and are massless if the spontaneously broken symmetry is not also broken explicitly. If, instead, the symmetry is not exact, i.e. if it is explicitly broken as well as spontaneously broken, then the Nambu–Goldstone bosons are not massless, though they typically remain relatively light; they are then called pseudo-Goldstone bosons or pseudo-Nambu–Goldstone bosons (abbreviated PNGBs).
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Thus the extra dimensions need not be small and compact but may be large extra dimensions. D-branes are dynamical extended objects of various dimensionalities predicted by string theory that could play this role. They have the property that open string excitations, which are associated with gauge interactions, are confined to the brane by their endpoints, whereas the closed strings that mediate the gravitational interaction are free to propagate into the whole spacetime, or "the bulk". This could be related to why gravity is exponentially weaker than the other forces, as it effectively dilutes itself as it propagates into a higher-dimensional volume.
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Instead one expects that one may recover a kind of semiclassical limit or weak field limit where something like "gravitons" will show up again. In contrast, gravitons play a key role in string theory where they are among the first (massless) level of excitations of a superstring. LQG differs from string theory in that it is formulated in 3 and 4 dimensions and without supersymmetry or Kaluza-Klein extra dimensions, while the latter requires both to be true. There is no experimental evidence to date that confirms string theory's predictions of supersymmetry and Kaluza–Klein extra dimensions.
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The quark model, together with quantum mechanics predicts that there should be orbital excitations of particles. The lowest lying of these states are ones where the two light quarks (the up and down) combine into a spin-0 state, one unit of orbital angular momentum is added, and this combines with the intrinsic spin of the charm quark to make a , pair of particles. The higher of these (the (2625)) was discovered in 1993 by ARGUS. At first it was not clear what state had been discovered, but the subsequent discovery of the lower state (2593) by CLEO clarified the situation.
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In quantum chromodynamics (or in the more general case of quantum gauge theories), if a connection which is color confining occurs, it is possible for stringlike degrees of freedom called QCD strings or QCD flux tubes to form. These stringlike excitations are responsible for the confinement of color charges since they are always attached to at least one string which exhibits tension. Their existence can be predicted from the dual spin network/spin foam models (this duality is exact over a lattice). To a surprisingly good approximation, these strings are described phenomenologically by the Polyakov action, making them noncritical strings.
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Although commonly attributed to the paper in which Kondo model was obtained from the Anderson impurity model by J.R. Schrieffer and P.A. Wolff., Joaquin Mazdak Luttinger and Walter Kohn used this method in an earlier work about non-periodic k·p perturbation theory . Using the Schrieffer–Wolff transformation, the high energy charge excitations present in Anderson impurity model are projected out and a low energy effective Hamiltonian is obtained which has only virtual charge fluctuations. For the Anderson impurity model case, the Schrieffer–Wolff transformation showed that Kondo model lies in the strong coupling regime of the Anderson impurity model.
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After the applied voltage is removed, the CNTs remain in a 1 or low resistance state due to physical adhesion (Van der Waals force) with an activation energy (Ea) of approximately 5eV. If the NRAM cell is in the 1 state, applying a voltage greater than the read voltage will generate CNT phonon excitations with sufficient energy to separate the CNT junctions. This is the phonon driven RESET operation. The CNTs remain in the OFF or high resistance state due to the high mechanical stiffness (Young's Modulus 1 TPa) with an activation energy (Ea) much greater than 5 eV.
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Since 1999 he is also president of the Donostia International Physics Center (DIPC). Etxenike has co-authored over 400 scientific articles. His research has focused on explaining the behaviour of solid bodies and their interaction with beams of charged particles. His work has opened new lines of research and has stimulated innovative theoretical and experimental lines of work in very diverse fields of condensed matter physics such as electron and tunnel microscopy, physical chemistry on the femtosecond scale, electronic surface localization, reverse photo-emission, atomic collisions, the interaction of ions with plasma particles, ion implantation and surface excitations in superfluid helium.
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The physical basis of MRI is the spatial encoding of the nuclear magnetic resonance (NMR) signal obtainable from water protons (i.e. hydrogen nuclei) in biologic tissue. In terms of MRI, signals with different spatial encodings that are required for the reconstruction of a full image need to be acquired by generating multiple signals - usually in a repetitive way using multiple radio-frequency excitations. The generic FLASH technique emerges as a gradient echo sequence which combines a low-flip angle radio- frequency excitation of the NMR signal (recorded as a spatially encoded gradient echo) with a rapid repetition of the basic sequence.
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In the first period of his scientific career Sandro Stringari focused on the magnetic properties of atomic nuclei and on the isospin degree of freedom, developing the innovative sum rule approach to the collective excitations. Starting from the 80’s he oriented his interests in the direction of atomic clusters and quantum liquids. Major contributions of this period are the study of the evaporation mechanism of helium clusters and the T=0 extension of the Hohenberg-Mermin-Wagner theorem. His interests in the physics of Bose-Einstein condensates (BEC) started with the workshop on Bose-Einstein Condensation (BEC), known as the “Levico conference”, organized in 1993 at Levico.
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Thanks to CoRoT they were also detected in the solar-like star HD 49933 and also in the red giant star HD 181907. In both cases the location of the helium ionization zone could be accurately derived. # Amplitudes and line widths in solar-like oscillation spectra: One of the major successes of the CoRoT space mission has definitely been the detection of solar-like oscillations in stars slightly hotter than the Sun. As was previously done for the Sun, measurements of amplitudes and line widths in their frequency spectra resulted in new constraints in the modeling of stochastic excitations of acoustic modes by turbulent convection.
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Steven T. Bramwell (born 7 June 1961) is a British physicist and chemist who works at the London Centre for Nanotechnology and the Department of Physics and Astronomy, University College London. He is known for his experimental discovery of spin ice with M. J. Harris and his calculation of a critical exponent observed in two-dimensional magnets with P. C. W. Holdsworth. A probability distribution for global quantities in complex systems, the "Bramwell-Holdsworth-Pinton (BHP) distribution", (to be implemented in Mathematica) is named after him. In 2009 Bramwell's group was one of several to report experimental evidence of magnetic monopole excitations in spin ice.
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These are promising demonstrations of how the switching of electric and magnetic properties in multiferroics, mediated by the mixed character of the magnetoelectric dynamics, may lead to ultrafast data processing, communication and quantum computing devices. Current research into MF dynamics aims to address various open questions; the practical realisation and demonstration of ultra-high speed domain switching, the development of further new applications based on tunable dynamics, e.g. frequency dependence of dielectric properties, the fundamental understanding of the mixed character of the excitations (e.g. in the ME case, mixed phonon-magnon modes – 'electromagnons'), and the potential discovery of new physics associated with the MF coupling.
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The RF flipper coils utilized in NRSE are much smaller than the DC coils used in classical NSE, leading to a large reduction in stray fields around the coils. This makes it possible to tilt the RF flipper coils and perform NRSE in a triple axis spectrometer configuration. The tilting of the coils, makes spin-echo focusing possible, where the entire energy dispersion of an excitation can be measured with very high resolution (as low as 1 µeV) over the entire Brillouin zone. Therefore, this technique allows the investigation of linewidths of dispersing excitations, including both phonons and magnons, over the entire Brillouin zone.
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Theoretical understanding of condensed matter physics is closely related to the notion of emergence, wherein complex assemblies of particles behave in ways dramatically different from their individual constituents. For example, a range of phenomena related to high temperature superconductivity are understood poorly, although the microscopic physics of individual electrons and lattices is well known. Similarly, models of condensed matter systems have been studied where collective excitations behave like photons and electrons, thereby describing electromagnetism as an emergent phenomenon. Emergent properties can also occur at the interface between materials: one example is the lanthanum aluminate-strontium titanate interface, where two non-magnetic insulators are joined to create conductivity, superconductivity, and ferromagnetism.
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For superconductors he predicted in 1982 a tricritical point in the phase diagram between type-I and type-II superconductors where the order of the transition changes from second to first. The predictions were confirmed in 2002 by Monte Carlo computer simulations. The theory is based on a disorder field theory dual to the order field theory of L.D. Landau for phase transitions which Kleinert developed in the books on Gauge Fields in Condensed Matter. In this theory, the statistical properties of fluctuating vortex or defect lines are described as elementary excitations with the help of fields, whose Feynman diagrams are the pictures of the lines.
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Cooling to liquid nitrogen temperature (77 K) reduces thermal excitations of valence electrons so that only a gamma ray interaction can give an electron the energy necessary to cross the band gap and reach the conduction band. Cooling with liquid nitrogen is inconvenient, as the detector requires hours to cool down to operating temperature before it can be used, and cannot be allowed to warm up during use. Ge(Li) crystals could never be allowed to warm up, as the lithium would drift out of the crystal, ruining the detector. HPGe detectors can be allowed to warm up to room temperature when not in use.
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In 1948, he predicted the phenomenon that is known as Davydov splitting or factor-group splitting, "the splitting of bands in the electronic or vibrational spectra of crystals due to the presence of more than one (interacting) equivalent molecular entity in the unit cell." In the period 1958–1960 he developed the theory of collective excited states in spherical and non-spherical nuclei, known as Davydov-Filippov Model and Davydov-Chaban Model. In 1973, Davydov applied the concept of molecular solitons in order to explain the mechanism of muscle contraction in animals. He studied theoretically the interaction of intramolecular excitations or excess electrons with autolocal breaking of the translational symmetry.
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In quantum field theory, the definition of Wilson loop observables as bona fide operators on Fock spaces is a mathematically delicate problem and requires regularization, usually by equipping each loop with a framing. The action of Wilson loop operators has the interpretation of creating an elementary excitation of the quantum field which is localized on the loop. In this way, Faraday's "flux tubes" become elementary excitations of the quantum electromagnetic field. Wilson loops were introduced in 1974 in an attempt at a nonperturbative formulation of quantum chromodynamics (QCD), or at least as a convenient collection of variables for dealing with the strongly interacting regime of QCD.
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The problem of confinement, which Wilson loops were designed to solve, remains unsolved to this day. The fact that strongly coupled quantum gauge field theories have elementary nonperturbative excitations which are loops motivated Alexander Polyakov to formulate the first string theories, which described the propagation of an elementary quantum loop in spacetime. Wilson loops played an important role in the formulation of loop quantum gravity, but there they are superseded by spin networks (and, later, spinfoams), a certain generalization of Wilson loops. In particle physics and string theory, Wilson loops are often called Wilson lines, especially Wilson loops around non-contractible loops of a compact manifold.
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RIXS is element and orbital specific: chemical sensitivity arises by tuning to the absorption edges of the different types of atoms in a material. RIXS can even differentiate between the same chemical element at sites with inequivalent chemical bondings, with different valencies or at inequivalent crystallographic positions as long as the X-ray absorption edges in these cases are distinguishable. In addition, the type of information on the electronic excitations of a system being probed can be varied by tuning to different X-ray edges (e.g., K, L or M) of the same chemical element, where the photon excites core-electrons into different valence orbitals.
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In 2008, Jin and her team developed a technique analogous to Angle-resolved photoemission spectroscopy which allowed them to measure excitations of their degenerate gas with both energy- and momentum- resolution. They used this approach to study the nature of fermion pairing across the BCS-BEC crossover, the same system her group had first explored in 2003. These experiments provided the first experimental evidence of a pseudogap in the BCS-BEC crossover. Jin continued to advance the frontiers of ultracold science when she and her colleague, Jun Ye, managed to cool polar molecules that possess a large electric dipole moment to ultracold temperatures, also in 2008.
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Instead of faster-than-light particles, the imaginary mass creates an instability: Any configuration in which one or more field excitations are tachyonic must spontaneously decay, and the resulting configuration contains no physical tachyons. This process is known as tachyon condensation, and is now believed to be the explanation for how the Higgs mechanism itself arises in nature, and therefore the reason behind electroweak symmetry breaking. Although the notion of imaginary mass might seem troubling, it is only the field, and not the mass itself, that is quantised. Therefore, the field operators at spacelike separated points still commute (or anticommute), and information and particles still do not propagate faster than light.
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Electronic excitation spectroscopy, or ultraviolet-visible (UV-vis) spectroscopy, is performed in the visible and ultraviolet regions of the electromagnetic spectrum and is useful for probing the difference in energy between the highest energy occupied (HOMO) and lowest energy unoccupied (LUMO) molecular orbitals. This information is useful to physical organic chemists in the design of organic photochemical systems and dyes, as absorption of different wavelengths of visible light give organic molecules color. A detailed understanding of an electronic structure is therefore helpful in explaining electronic excitations, and through careful control of molecular structure it is possible to tune the HOMO-LUMO gap to give desired colors and excited state properties.
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Debashis Mukherjee is a theoretical chemist, well known for his research in the fields of molecular many body theory, theoretical spectroscopy, finite temperature non-perturbative many body theories. Mukherjee has been the first to develop and implement a class of many-body methods for electronic structure which are now standard works in the field. These methods, collectively called multireference coupled cluster formalisms, are versatile and powerful methods for predicting with quantitative accuracy the energetics and cross-sections of a vast range of molecular excitations and ionization. A long-standing problem of guaranteeing proper scaling of energy for many electron wave-functions of arbitrary complexity has also been first resolved by him.
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Quantum mechanics was successful at describing non-relativistic systems with fixed numbers of particles, but a new framework was needed to describe systems in which particles can be created or destroyed, for example, the electromagnetic field, considered as a collection of photons. It was eventually realized that special relativity was inconsistent with single-particle quantum mechanics, so that all particles are now described relativistically by quantum fields. When the canonical quantization procedure is applied to a field, such as the electromagnetic field, the classical field variables become quantum operators. Thus, the normal modes comprising the amplitude of the field become quantized, and the quanta are identified with individual particles or excitations.
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In the X-ray region there is sufficient energy to probe changes in the electronic state (transitions between orbitals; this is in contrast with the optical region, where the energy loss is often due to changes in the state of the rotational or vibrational degrees of freedom). For instance, in the ultra soft X-ray region (below about 1 keV), crystal field excitations give rise to the energy loss. The photon-in-photon-out process may be thought of as a scattering event. When the x-ray energy corresponds to the binding energy of a core-level electron, this scattering process is resonantly enhanced by many orders of magnitude.
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Lanthanide dopants are used as activator ions because they have multiple 4f excitation levels and completely filled 5s and 5p shells, which shield their characteristic 4f electrons, thus producing sharp f-f transition bands. These transitions provide substantially longer lasting excited states, since they are Laporte forbidden, thus allowing longer time necessary for the multiple excitations required for upconversion. The concentration of activator ions in UCNPs is also critically important, as this determines the average distance between the activator ions and therefore affects how easily energy is exchanged. If the concentration of activators is too high and energy transfer too facile, cross-relaxation may occur, reducing emission efficiency.
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Panayotis G. Kevrekidis is a professor in the Department of Mathematics and Statistics at the University of Massachusetts Amherst. Kevrekidis earned his B.Sc. in physics in 1996 from the University of Athens. He obtained his M.S. in 1998 and Ph.D. in 2000 from Rutgers University, the latter under the joint supervision of Joel Lebowitz and Panos G. Georgopoulos. His thesis was entitled “Lattice Dynamics of Solitary Wave Excitations”. He then assumed a post-doctoral position split between the Program in Applied and Computational Mathematics of Princeton University (10/2000–02/2001) and the Theoretical Division and the Center for Nonlinear Studies of Los Alamos National Laboratory (03/2001–08/2001).
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His last research concerned the search for the organizing principles responsible for emergent behavior in materials where unexpectedly new classes of behavior emerge in response to the strong and competing interactions among their elementary constituents. Some recent research results on correlated electron materials are the development of a consistent phenomenological description of protected magnetic behavior in the pseudogap state of underdoped cuprate superconductors and the discovery of the protected emergence of itinerancy in the Kondo lattice in heavy electron materials and its description using a two-fluid model. He remained interested in the superfluidity of neutron stars revealed by pulsar glitches and in elementary excitations in the helium liquids.
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Jung, Collected Works vol. 7 (1953), "The Structure of the Unconscious" (1916), ¶437–507 (pp. 263–292). In "The Significance of Constitution and Heredity in Psychology" (November 1929), Jung wrote: > And the essential thing, psychologically, is that in dreams, fantasies, and > other exceptional states of mind the most far-fetched mythological motifs > and symbols can appear autochthonously at any time, often, apparently, as > the result of particular influences, traditions, and excitations working on > the individual, but more often without any sign of them. These "primordial > images" or "archetypes," as I have called them, belong to the basic stock of > the unconscious psyche and cannot be explained as personal acquisitions.
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Microscopically the volume of a single pore in a porous media may be divided into two regions; surface area S and bulk volume V (Figure 1). Figure 1: Nuclear spin relaxation properties in a simplified pore are divided into bulk volume V and pore surface area S. The surface area is a thin layer with thickness \delta of a few molecules close to the pore wall surface. The bulk volume is the remaining part of the pore volume and usually dominates the overall pore volume. With respect to NMR excitations of nuclear states for hydrogen-containing molecules in these regions, different relaxation times for the induced excited energy states are expected.
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Hopfield dielectric – in quantum mechanics a model of dielectric consisting of quantum harmonic oscillators interacting with the modes of the quantum electromagnetic field. The collective interaction of the charge polarization modes with the vacuum excitations, photons leads to the perturbation of both the linear dispersion relation of photons and constant dispersion of charge waves by the avoided crossing between the two dispersion lines of polaritons. Similarly to the acoustic and the optical phonons and far from the resonance one branch is photon-like while the other charge wave-like. Mathematically the Hopfield dielectric for the one mode of excitation is equivalent to the Trojan wave packet in the harmonic approximation.
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In non-equilibrium physics, the Keldysh formalism is a general framework for describing the quantum mechanical evolution of a system in a non-equilibrium state or systems subject to time varying external fields (electrical field, magnetic field etc.). Historically, it was foreshadowed by the work of Schwinger and proposed almost simultaneously by Keldysh and, separately, Kadanoff and Baym. It was further developed by later contributors such as O. V. Konstantinov and V. I. Perel. Extension to driven-dissipative open quantum systems is given in The Keldysh formalism provides a systematic way to study non-equilibrium systems, usually based on the two-point functions corresponding to excitations in the system.
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The kinetic of excitations in ytterbium-doped materials is simple and can be described within the concept of effective cross-sections; for most ytterbium- doped laser materials (as for many other optically pumped gain media), the McCumber relation holds, although the application to the ytterbium-doped composite materials was under discussion. Usually, low concentrations of ytterbium are used. At high concentrations, the ytterbium-doped materials show photodarkening (glass fibers) or even a switch to broadband emission (crystals and ceramics) instead of efficient laser action. This effect may be related with not only overheating, but also with conditions of charge compensation at high concentrations of ytterbium ions.
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E. C. G. Sudarshan, V.K Deshpande and Baidyanath Misra were the first to propose the existence of particles faster than light and named them "meta-particles". After that the possibility of particles moving faster than light was also proposed by Robert Ehrlich and Arnold Sommerfeld, independently of each other. In the 1967 paper that coined the term, Gerald Feinberg proposed that tachyonic particles could be quanta of a quantum field with imaginary mass. However, it was soon realized that excitations of such imaginary mass fields do not under any circumstances propagate faster than light, and instead the imaginary mass gives rise to an instability known as tachyon condensation.
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Sometimes it is called one dimensional Bose gas with delta interaction. It also can be considered as quantum non-linear Schrödinger equation. The ground state as well as the low-lying excited states were computed and found to be in agreement with Bogoliubov's theory when the potential is small, except for the fact that there are actually two types of elementary excitations instead of one, as predicted by Bogoliubov's and other theories. The model seemed to be only of academic interest until, with the sophisticated experimental techniques developed in the first decade of the 21st century, it became possible to produce this kind of gas using real atoms as particles.
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Minkowski has pursued research along three main avenues: spontaneous phenomena in strong interactions and resonance structure, quark and gluon pairing;Properties of Hadron States Containing a Condensed Phase of Quark- Antiquark Excitations, Nucl. Phys, 57B (1973) 557On the Anomalous Divergence of the Dilatation Current in Gauge Theories, Bern University preprint, unpublished unification of gauge symmetries, extensions to include gravity, extensions to cosmology;On the Spontaneous Origin of Newton's Constant, Phys. Letters 71B (1978) 419On the Cosmological Equations in the Presence of a Spatially Homogeneous Torsion Field, Phys. Letters 173B (1986) 247 Letters, 85B (1979) 231 and electroweak interactions and their interplay with the strong interactions.
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The G2 uses seven calculations: # the molecular geometry is obtained by a MP2 optimization using the 6-31G(d) basis set and all electrons included in the perturbation. This geometry is used for all subsequent calculations. # The highest level of theory is a quadratic configuration interaction calculation with single and double excitations and a triples excitation contribution (QCISD(T)) with the 6-311G(d) basis set. Such a calculation in the Gaussian and Spartan programs also give the MP2 and MP4 energies which are also used. # The effect of polarization functions is assessed using an MP4 calculation with the 6-311G(2df,p) basis set.
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At zero temperature, the Bose- Hubbard model (in the absence of disorder) is in either a Mott insulating state at small t / U , or in a superfluid state at large t / U . The Mott insulating phases are characterized by integer boson densities, by the existence of an energy gap for particle-hole excitations, and by zero compressibility. The superfluid is characterized by long-range phase coherence, a spontaneous breaking of the Hamiltonian's continuous U(1) symmetry, a non-zero compressibility and superfluid susceptibility. At non- zero temperature, in certain parameter regimes there will also be a regular fluid phase which does not break the U(1) symmetry and does not display phase coherence.
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Static force fields are fields, such as a simple electric, magnetic or gravitational fields, that exist without excitations. The most common approximation method that physicists use for scattering calculations can be interpreted as static forces arising from the interactions between two bodies mediated by virtual particles, particles that exist for only a short time determined by the uncertainty principle. The virtual particles, also known as force carriers, are bosons, with different bosons associated with each force. pp. 16-37 The virtual-particle description of static forces is capable of identifying the spatial form of the forces, such as the inverse-square behavior in Newton's law of universal gravitation and in Coulomb's law.
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It was assumed that the distribution of lightning in the satellite maps was a good proxy for Schumann excitations sources, even though satellite observations predominantly measure in-cloud lightning rather than the cloud-to-ground lightning that are the primary exciters of the resonances. Both simulations—those neglecting the day-night asymmetry, and those taking this asymmetry into account—showed the same Asia-America chimney ranking. On the other hand, some optical satellite and climatological lightning data suggest the South American thunderstorm center is stronger than the Asian center. The reason for the disparity among rankings of Asian and American chimneys in Schumann resonance records remains unclear, and is the subject of further research.
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It therefore also includes essential elements of photochemistry. Key aspects of quantum photoelectrochemistry are calculations of optical excitations, photoinduced electron and energy transfer processes, excited state evolution, as well as interfacial charge separation and charge transport in nanoscale energy conversion systems.Multiscale Modelling of Interfacial Electron Transfer, Petter Persson, Chapter 3 in: Solar Energy Conversion – Dynamics of Electron and Excitation Transfer P. Piotrowiak (Ed.), RSC Energy and Environment Series (2013) Quantum photoelectrochemistry calculation of photoinduced interfacial electron transfer in a dye-sensitized solar cell. Quantum photoelectrochemistry in particular provides fundamental insight into basic light-harvesting and photoinduced electro-optical processes in several emerging solar energy conversion technologies for generation of both electricity (photovoltaics) and solar fuels.
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Change of field gradient spreads the responding FID signal in the frequency domain, but this can be recovered and measured by a refocusing gradient (to create a so-called "gradient echo"), or by a radio frequency pulse (to create a so-called "spin- echo"), or in digital postprocessing of the spread signal. The whole process can be repeated when some T1-relaxation has occurred and the thermal equilibrium of the spins has been more or less restored. The repetition time (TR) is the time between two successive excitations of the same slice.Page 26 in: Typically, in soft tissues T1 is around one second while T2 and T are a few tens of milliseconds.
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Nonlinear metamaterials can overcome this limitation, since the local fields of the resonant structures can be much larger than the average value of the field \- in this respect metamaterials are similar to other composite media, such e.g. as random metal-dielectric composites, including fractal clusters and semicoutinouos/percolation metal films, where the areas with enhanced local light fieldsD.P. Tsai, J. Kovacs, Zh. Wang, M. Moskovits, V.M. Shalaev, J.S. Suh, and R. Botet, Photon Scanning Tunneling Microscopy Images of Optical Excitations of Fractal Metal Colloid Clusters, Physical Review Letters, v. 72, pp. 4149–4152, (1994) \- “hot spots” - produce giant linear and non-linear optical responses V. M. Shalaev, Electromagnetic Properties of Small-Particle Composites, Physics Reports, v.
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Neveu studied in Paris at the École Normale Supérieure (ENS). In 1969 he received his diploma (Thèse de troisième cycle) at University of Paris XI in Orsay with Philippe Meyer and Claude Bouchiat and in 1971 he completed his doctorate (Doctorat d'État) there. In 1969 he and his classmate from ENS and Orsay, Joël Scherk, together with John H. Schwarz and David Gross at Princeton University, examined divergences in one-loop diagrams of the bosonic string theory (and discovered the cause of tachyon divergences). From 1971 to 1974 Neveu was at the Laboratory for High Energy Physics of the University of Paris XI where he and Scherk showed that spin-1 excitations of strings could describe Yang–Mills theories.
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In 1953, the first experimental examples were found of rotational bands in nuclei, with their energy levels following the same J(J+1) pattern of energies as in rotating molecules. Quantum mechanically, it is impossible to have a collective rotation of a sphere, so this implied that the shape of these nuclei was nonspherical. In principle, these rotational states could have been described as coherent superpositions of particle-hole excitations in the basis consisting of single-particle states of the spherical potential. But in reality, the description of these states in this manner is intractable, due to the large number of valence particles—and this intractability was even greater in the 1950s, when computing power was extremely rudimentary.
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Gavrilă completed in 1977 his previous work on the relativistic theory of the photoelectric effect in the inner atomic orbitals that he had begun in his Ph.D. thesis in 1958; thus, he applied radiative corrections to his previous calculationsJames McEnnan and M. Gavrilă: Radiative corrections to the atomic photoeffect, Physical Review A, 15 (4), 1537–1556 (1977). James McEnnan and M. Gavrilă: Radiative corrections to the high-frequency end of the bremsstrahlung spectrum, Physical Review A, 15 (4), 1557–1562 (1977). He also investigated two-photon excitations and the elastic photon scattering amplitude in the hydrogen ground state,.Mihai Gavrilă: Elastic Scattering of Photons by a Hydrogen Atom, Physical Review, 163 (1), 147–155 (1967)M.
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In recent years molecular transport junctions have been produced with one single molecule between two electrodes, sometimes with an additional gate electrode near the molecule. The advantage of this method in comparison with STM-IETS is that there is contact between both electrodes and the adsorbate, whereas in STM-IETS there is always a tunneling gap between the tip and the adsorbate. The disadvantage of this method is that it is experimentally very challenging to create and identify a junction with exactly one molecule between the electrodes. The STM-IETS technique was extended to the spin excitations of an individual atom by Andreas J. Heinrich, J. A. Gupta, C. Lutz and Don Eigler in 2004, at IBM Almaden.
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In a hot QCD medium, when the temperature is raised well beyond the Hagedorn temperature, the and its excitations are expected to melt. This is one of the predicted signals of the formation of the quark–gluon plasma. Heavy-ion experiments at CERN's Super Proton Synchrotron and at BNL's Relativistic Heavy Ion Collider have studied this phenomenon without a conclusive outcome as of 2009. This is due to the requirement that the disappearance of mesons is evaluated with respect to the baseline provided by the total production of all charm quark-containing subatomic particles, and because it is widely expected that some are produced and/or destroyed at time of QGP hadronization.
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In time-of-flight mass spectrometry, ions are accelerated by an electrical field to the same kinetic energy with the velocity of the ion depending on the mass-to-charge ratio. Thus the time-of-flight is used to measure velocity, from which the mass-to-charge ratio can be determined. The time-of-flight of electrons is used to measure their kinetic energy.Time-of-Flight Techniques For The Investigation Of Kinetic Energy Distributions Of Ions And Neutrals Desorbed By Core Excitations In near infrared spectroscopy, the ToF method is used to measure the media-dependent optical pathlength over a range of optical wavelengths, from which composition and properties of the media can be analyzed.
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Although quantum field theory arose from the study of interactions between elementary particles, it has been successfully applied to other physical systems, particularly to many-body systems in condensed matter physics. Historically, the Higgs mechanism of spontaneous symmetry breaking was a result of Yoichiro Nambu's application of superconductor theory to elementary particles, while the concept of renormalization came out of the study of second-order phase transitions in matter. Soon after the introduction of photons, Einstein performed the quantization procedure on vibrations in a crystal, leading to the first quasiparticle—phonons. Lev Landau claimed that low-energy excitations in many condensed matter systems could be described in terms of interactions between a set of quasiparticles.
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The objective of operational modal analysis is to extract resonant frequencies, damping, and/or operating shapes (unscaled mode shapes) of a structure. This method sometime called output-only modal analysis because only the response of the structure is measured. The structure might be excited using natural operating conditions or some other excitations might be applied to the structure;Improved Modal Characterization Using Hybrid Data however, as long as the operating shapes are not scaled based on the applied force, it is called operational modal analysis (e.g. operating shapes of a wind turbine blade excited by a shaker are measured using operating modal analysis Using Stereophotogrammetry to Measure Vibrations of a Wind Turbine Blade ).
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Since 1984, Sridhar's scientific and academic career has been closely associated with Northeastern University. Since 2011, Sridhar has been a visiting Lecturer at Harvard Medical School where he researches radiation oncology. He is the founding director of the Nanomedicine Innovation Center, an interdisciplinary center with research and education thrusts in nanomedicine. Sridhar is the author of over 450 publications, on his work in nanomedicine, neurotechnology,Medical Express: Professor works toward a better brainwave monitorNeuroGadget: $50.000 grant for developing better brainwave monitors with Electric Field EncephalographySeriousScience: Srinivas Sridhar MRI, nanophotonics, nanomaterials,PhysOrg:Physicists develop 3D metamaterial nanolens that achieves super-resolution imagingBioOptics: Nanotech: a revolution for resolution metamaterials, quantum chaos, superconductivity and collective excitations in materials.
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The fractional quantum Hall effect(FQHE) is a strongly correlated system of general interest in the field of condensed matter. Previous DFT applications maps the FQHE to a reference system of non- interacting electrons, but fail to capture many interesting features of FQHE. The progress has been recently made to map the FQHE instead to a reference system of non-interacting composite fermions, which are emergent particles in FQHE. When a non-local exchange-correlation is incorporated to take care of the long-range gauge interaction between composite fermions, this DFT method successfully captures not only configurations with nonuniform densities but also topological properties such as fractional charge and fractional braid statistics for the quasiparticles excitations.
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Inelastic scattering is useful for probing such excitations of matter, but not in determining the distribution of scatterers within the matter, which is the goal of X-ray crystallography. X-rays range in wavelength from 10 to 0.01 nanometers; a typical wavelength used for crystallography is 1 Å (0.1 nm), which is on the scale of covalent chemical bonds and the radius of a single atom. Longer-wavelength photons (such as ultraviolet radiation) would not have sufficient resolution to determine the atomic positions. At the other extreme, shorter-wavelength photons such as gamma rays are difficult to produce in large numbers, difficult to focus, and interact too strongly with matter, producing particle-antiparticle pairs.
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Although that some studies show that the all excitations caused by gliotransmission lead to epileptic discharges, but it could possibly increase the intensity of length of epileptiform activity. The 5 first mentioned transmitters are primarily excitatory and can thus lead to neural apoptosis through excitotoxicity when expressed at large amounts. From neurodegenerative diseases, there is evidence at least for Alzheimer's disease that point to increased glial activation and amount (both glia and astrocyte) which accompanies simultaneous decrease in the number of neurons. Excess quantities of the gliotransmitter TNF, documented in the cerebrospinal fluid in Alzheimer's disease, are hypothesized to play a role in the pathogenesis of this disorder, perhaps by dysregulating synaptic mechanisms which are modulated by TNF.
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Color superconductivity is a phenomenon predicted to occur in quark matter if the baryon density is sufficiently high (well above nuclear density) and the temperature is not too high (well below 1012 kelvins). Color superconducting phases are to be contrasted with the normal phase of quark matter, which is just a weakly interacting Fermi liquid of quarks. In theoretical terms, a color superconducting phase is a state in which the quarks near the Fermi surface become correlated in Cooper pairs, which condense. In phenomenological terms, a color superconducting phase breaks some of the symmetries of the underlying theory, and has a very different spectrum of excitations and very different transport properties from the normal phase.
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Petek has developed coherent photoelectron spectroscopy and microscopy as methods for studying the dephasing and spatial propagation of polarization fields in solid state materials and nanostructure. He is developing methods for multidimensional multiphoton-photoemission spectroscopy. Together with Jin Zhao, Ken Jordan and Ken Onda, Petek also discovered wet electron states, where electrons are partially solvated by water and other protic solvents at molecule vacuum interfaces. Together with Min Feng and Jin Zhao, Petek discovered atom-like superatom states of C60, and similar hollow molecules. Petek’s research with Shijing Tan has involved studies of metal plasmon excitations with semiconductor substrates, where the charge injection from highly optically active plasmonic modes into semiconductor substrates could be used for solar energy harvesting.
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It is sometimes noted that the time of the decay of the nucleus cannot be controlled, and that the finite half- life invalidates the result. This objection can be dispelled by sizing the hemispheres appropriately with regards to the half-life of the nucleus. The radii are chosen so that the more distant hemisphere is much farther away than the half-life of the decaying nucleus, times the flight-time of the alpha ray. To lend concreteness to the example, assume that the half-life of the decaying nucleus is 0.01 microsecond (most elementary particle decay half-lives are much shorter; most nuclear decay half-lives are much longer; some atomic electromagnetic excitations have a half-life about this long).
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This scheme is scalable and relies on the recent advances in ion trapping techniques (several dozens of ions can be successfully trapped, for example, in linear Paul traps by making use of anharmonic axial potentials). Another platform for implementing the boson sampling setup is a system of interacting spins: recent observation show that boson sampling with M particles in N modes is equivalent to the short-time evolution with M excitations in the XY model of 2N spins. One necessitates several additional assumptions here, including small boson bunching probability and efficient error postselection. This scalable scheme, however, is rather promising, in the light of considerable development in the construction and manipulation of coupled superconducting qubits and specifically the D-Wave machine.
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Using this technique, the spin excitation spectrum of an individual integer spin was obtained by Hirjibehedin et al. for a S=2 single Fe atom on a surface of Cu2N/Cu(100), that made it possible to measure a quantum spin tunneling splitting of 0.2 meV. Using the same technique other groups measured the spin excitations of S=1 Fe phthalocyanine molecule on a copper surface and a S=1 Fe atom on InSb, both of which had a quantum spin tunneling splitting of the S_z=\pm1 doublet larger than 1 meV. In the case of molecular magnets with large S and small E/D ratio, indirect measurement techniques are required to infer the value of the quantum spin tunneling splitting.
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Some correspond to massless particles like the photon; also in this group are a set of massless scalar particles. If a Dp-brane is embedded in a spacetime of d spatial dimensions, the brane carries (in addition to its Maxwell field) a set of d - p massless scalars (particles which do not have polarizations like the photons making up light). Intriguingly, there are just as many massless scalars as there are directions perpendicular to the brane; the geometry of the brane arrangement is closely related to the quantum field theory of the particles existing on it. In fact, these massless scalars are Goldstone excitations of the brane, corresponding to the different ways the symmetry of empty space can be broken.
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Attempts to explore the continuous loop representation was made by Gambini and Trias for canonical Yang–Mills theory, however there were difficulties as they represented singular objects. As we shall see the loop formalism goes far beyond a simple gauge invariant description, in fact it is the natural geometrical framework to treat gauge theories and quantum gravity in terms of their fundamental physical excitations. The introduction by Ashtekar of a new set of variables (Ashtekar variables) cast general relativity in the same language as gauge theories and allowed one to apply loop techniques as a natural nonperturbative description of Einstein's theory. In canonical quantum gravity the difficulties in using the continuous loop representation are cured by the spatial diffeomorphism invariance of general relativity.
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In the absorption edge region of metals, the photoelectron is excited to the first unoccupied level above the Fermi level. Therefore, its mean free path in a pure single crystal at zero temperature is as large as infinite, and it remains very large, increasing the energy of the final state up to about 5 eV above the Fermi level. Beyond the role of the unoccupied density of states and matrix elements in single electron excitations, many-body effects appear as an "infrared singularity" at the absorption threshold in metals. In the absorption edge region of insulators the photoelectron is excited to the first unoccupied level above the chemical potential but the unscreened core hole forms a localized bound state called core exciton.
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Based on the Schrieffer-Wolff transformation, it was shown that the Kondo model lies in the strong coupling regime of the Anderson impurity model. The Schrieffer-Wolff transformation projects out the high energy charge excitations in the Anderson impurity model, obtaining the Kondo model as an effective Hamiltonian. Schematic of the weakly coupled high temperature situation in which the magnetic moments of conduction electrons in the metal host pass by the impurity magnetic moment at speeds of vF, the Fermi velocity, experiencing only a mild antiferromagnetic correlation in the vicinity of the impurity. In contrast, as the temperature tends to zero the impurity magnetic moment and one conduction electron moment bind very strongly to form an overall non-magnetic state.
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In processes where heat is generated, quantum states of lower energy, present as possible excitations in fields between atoms, act as a reservoir for part of the energy, from which it cannot be recovered, in order to be converted with 100% efficiency into other forms of energy. In this case, the energy must partly stay as heat, and cannot be completely recovered as usable energy, except at the price of an increase in some other kind of heat-like increase in disorder in quantum states, in the universe (such as an expansion of matter, or a randomisation in a crystal). As the universe evolves in time, more and more of its energy becomes trapped in irreversible states (i.e., as heat or other kinds of increases in disorder).
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217 In a late, unfinished paper he examined how sometimes 'the instinct is allowed to retain its satisfaction and proper respect is shown to reality...at the price of a rift in the ego which never heals but increases as time goes on...a splitting of the ego'. Lacan would develop this line of thought, and maintain indeed that 'it is in the disintegration of the imaginary unity constituted by the ego that the subject finds the signifying material of his symptoms'.Jacques Lacan, Ecrits (London 1997) p. 137 From another standpoint, Object relations theory has explored 'the encounter with the "other" that threatens the ego's integrity', as when the object in question is lacking in 'its expected function as "container" of excitations'.
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To understand why particle statistics work the way that they do, note first that particles are point-localized excitations and that particles that are spacelike separated do not interact. In a flat d-dimensional space M, at any given time, the configuration of two identical particles can be specified as an element of M × M. If there is no overlap between the particles, so that they do not interact directly, then their locations must belong to the space the subspace with coincident points removed. The element describes the configuration with particle I at x and particle II at y, while describes the interchanged configuration. With identical particles, the state described by ought to be indistinguishable from the state described by .
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The scientific research at MAMI focusses on the investigation of the structure and dynamics of hadrons, particles consisting of quarks and gluons bound by the strong force. The most important hadrons are protons and neutrons, the basic constituents of atomic nuclei and, therefore, the building blocks of ordinary matter. Electrons and photons interact with the electric charges and the magnetization of quarks inside a hadron in a relatively weak and well understood way providing undistorted information about basic hadronic properties like (transverse) size, magnetic moments, distribution of charge and magnetism, flavor structure, polarizabilities and excitation spectrum. At MAMI the full potential of electroweak probes is explored in an energy region characteristic for the first hadronic excitations and with a spatial resolution in the order of the typical hadron size of about 1 fm.
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Bloch remained in European academia, working on superconductivity with Wolfgang Pauli in Zürich; with Hans Kramers and Adriaan Fokker in Holland; with Heisenberg on ferromagnetism, where he developed a description of boundaries between magnetic domains, now known as "Bloch walls", and theoretically proposed a concept of spin waves, excitations of magnetic structure; with Niels Bohr in Copenhagen, where he worked on a theoretical description of the stopping of charged particles traveling through matter; and with Enrico Fermi in Rome. In 1932, Bloch returned to Leipzig to assume a position as "Privatdozent" (lecturer). In 1933, immediately after Hitler came to power, he left Germany because he was Jewish, returning to Zürich, before traveling to Paris to lecture at the Institut Henri Poincaré."Bloch, Felix", Current Biography, H. W. Wilson Company, 1954.
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Since, DFT has become an important tool for methods of nuclear spectroscopy such as Mössbauer spectroscopy or perturbed angular correlation, in order to understand the reason of specific electric field gradients in crystals. Despite recent improvements, there are still difficulties in using density functional theory to properly describe: intermolecular interactions (of critical importance to understanding chemical reactions), especially van der Waals forces (dispersion); charge transfer excitations; transition states, global potential energy surfaces, dopant interactions and some strongly correlated systems; and in calculations of the band gap and ferromagnetism in semiconductors. The incomplete treatment of dispersion can adversely affect the accuracy of DFT (at least when used alone and uncorrected) in the treatment of systems which are dominated by dispersion (e.g. interacting noble gas atoms) or where dispersion competes significantly with other effects (e.g.
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After absorbing energy, an electron may jump from the ground state to a higher energy excited state. Excitations of copper 3d orbitals on the CuO2-plane of a high Tc superconductor; The ground state (blue) is x2-y2 orbitals; the excited orbitals are in green; the arrows illustrate inelastic x-ray spectroscopy In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being raised to an excited state.
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However, in stronger bias regimes a more sophisticated treatment is required, as there is no longer a variational principle. In the elastic tunneling case (where the passing electron does not exchange energy with the system), the formalism of Rolf Landauer can be used to calculate the transmission through the system as a function of bias voltage, and hence the current. In inelastic tunneling, an elegant formalism based on the non-equilibrium Green's functions of Leo Kadanoff and Gordon Baym, and independently by Leonid Keldysh was advanced by Ned Wingreen and Yigal Meir. This Meir-Wingreen formulation has been used to great success in the molecular electronics community to examine the more difficult and interesting cases where the transient electron exchanges energy with the molecular system (for example through electron-phonon coupling or electronic excitations).
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Quantum tunneling of the magnetization was reported in 1996 for a crystal of Mn12ac molecules with S=10. Quoting Thomas and coworkers, "in an applied magnetic field, the magnetization shows hysteresis loops with a distinct 'staircase' structure: the steps occur at values of the applied field where the energies of different collective spin states of the manganese clusters coincide. At these special values of the field, relaxation from one spin state to another is enhanced above the thermally activated rate by the action of resonant quantum-mechanical tunneling". Quantum tunneling of the magnetization was reported in ferritin present in horse spleen proteins A direct measurement of the quantum spin tunneling splitting energy can be achieved using single spin scanning tunneling inelastic spectroscopy, that permits to measure the spin excitations of individual atoms on surfaces.
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In "The Significance of Constitution and Heredity in Psychology" (November 1929), Jung wrote: > And the essential thing, psychologically, is that in dreams, fantasies, and > other exceptional states of mind the most far-fetched mythological motifs > and symbols can appear autochthonously at any time, often, apparently, as > the result of particular influences, traditions, and excitations working on > the individual, but more often without any sign of them. These "primordial > images" or "archetypes," as I have called them, belong to the basic stock of > the unconscious psyche and cannot be explained as personal acquisitions. > Together they make up that psychic stratum which has been called the > collective unconscious. The existence of the collective unconscious means > that individual consciousness is anything but a tabula rasa and is not > immune to predetermining influences.
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Rather, the photon seems to be a point-like particle since it is absorbed or emitted as a whole by arbitrarily small systems, including systems much smaller than its wavelength, such as an atomic nucleus (≈10−15 m across) or even the point-like electron. While many introductory texts treat photons using the mathematical techniques of non-relativistic quantum mechanics, this is in some ways an awkward oversimplification, as photons are by nature intrinsically relativistic. Because photons have zero rest mass, no wave function defined for a photon can have all the properties familiar from wave functions in non-relativistic quantum mechanics. In order to avoid these difficulties, physicists employ the second-quantized theory of photons described below, quantum electrodynamics, in which photons are quantized excitations of electromagnetic modes.
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Light that travels through transparent matter does so at a lower speed than c, the speed of light in a vacuum. The factor by which the speed is decreased is called the refractive index of the material. In a classical wave picture, the slowing can be explained by the light inducing electric polarization in the matter, the polarized matter radiating new light, and that new light interfering with the original light wave to form a delayed wave. In a particle picture, the slowing can instead be described as a blending of the photon with quantum excitations of the matter to produce quasi-particles known as polariton (see this list for some other quasi-particles); this polariton has a nonzero effective mass, which means that it cannot travel at c.
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They were published by Springer-Verlag in 2008 and 2009, respectively. He published his third book in November 2013, an edited volume together with a number of his collaborators on Localized Excitations in Nonlinear Complex Systems: Current State of the Art and Future Perspectives, again by Springer-Verlag and his fourth book in 2014 with two co-editors on The sine-Gordon Model and its Applications: From Pendula and Josephson Junctions to Gravity and High Energy Physics. As quantitative measures of his impact to the research community, one can mention the h-index of 42 (in Web of Science, 52 in Google Scholar) and that his work (excluding self-citations) has been cited over 5300 times. Kevrekidis has created a tradition on nonlinear waves within the University of Massachusetts Amherst.
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The atomic X-ray absorption spectrum (XAS) of a core-level in an absorbing atom is separated into states in the discrete part of the spectrum called "bounds final states" or "Rydberg states" below the ionization potential (IP) and "states in the continuum" part of the spectrum above the ionization potential due to excitations of the photoelectron in the vacuum. Above the IP the absorption cross section attenuates gradually with the X-ray energy. Following early experimental and theoretical works in the thirties, in the sixties using synchrotron radiation at the National Bureau of Standards it was established that the broad asymmetric absorption peaks are due to Fano resonances above the atomic ionization potential where the final states are many body quasi-bound states (i.e., a doubly excited atom) degenerate with the continuum.
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Many works, starting with his PhD thesis in Cambridge study the interaction of electrons, atoms, and ions with surfaces. An important concept introduced and developed by Etxenike are image-potential states at metal surfaces in which electrons can be trapped in the potential of their own image charge. Etxenike and co-workers computed and analyzed these states for many different materials and surfaces as well as their interaction with surface excitations such as surface plasmons, surface plasmon polaritons, and surface phonons. Etxenike is co-author of a highly cited review on the theory of surface plasmons They analyzed theoretically the technique of scanning tunneling microscopy (STM) in order to interpret STM images and, in particular, relate them to the topography of the studied surfaces and to the spectroscopy of surface states ("scanning tunneling spectroscopy").
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Thus, he wrote in 1891: > [I]f excitation and impulsive behaviour are due to the fact that from the > sensory surfaces excitations abnormal in quality, quantity and intensity do > arise, and do act on the motor surfaces, then an improvement could be > obtained by creating an obstacle between the two surfaces. The extirpation > of the motor or the sensory zone would expose us to the risk of grave > functional disturbances and to technical difficulties. It would be more > advantageous to practice the excision of a strip of cortex behind and on > both sides of the motor zone creating thus a kind of ditch in the temporal > lobe.Quoted in Burckhardt attended the Berlin Medical Conference of 1889, which was also attended by such heavyweight psychiatrists as Victor Horsley, Valentin Magnan and Emil Kraepelin, and presented a paper on his brain operations.
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The generally too-high excitation energies of CIS or CISD are lowered. But usually excited states have more than one dominant configuration and so the ground state is more correlated due to: a) now including some configurations with higher excitations (triply and quadruply in MRCISD); b) the neglect of other dominant configurations of the excited states which are still uncorrelated. Selecting the references can be done manually ( \Phi_1, \Phi_2, \Phi_5, ...), automatically (all possible configurations within an active space of some orbitals) or semiautomatically (taking all configurations as references that have been shown to be important in a previous CI or MRCI calculation) This method has been implemented first by Robert Buenker and Sigrid D. Peyerimhoff in the seventies under the name Multi-Reference Single and Double Configuration Interaction (MRSDCI). The MRCI method can also be implemented in semi-empirical methods.
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XRS is an inelastic x-ray scattering process, in which a high-energy x-ray photon gives energy to a core electron, exciting it to an unoccupied state. The process is in principle analogous to x-ray absorption (XAS), but the energy transfer plays the role of the x-ray photon energy absorbed in x-ray absorption, exactly as in Raman scattering in optics vibrational low-energy excitations can be observed by studying the spectrum of light scattered from a molecule. Because the energy (and therefore wavelength) of the probing x-ray can be chosen freely and is usually in the hard x-ray regime, certain constraints of soft x-rays in the studies of electronic structure of the material are overcome. For example, soft x-ray studies may be surface sensitive and they require a vacuum environment.
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During his time at Yale, Stuart Rice began to study the transport properties of liquids. He helped to determine the properties of liquid noble gases and methane, while also exploring the theoretical background of transport in liquids as well, comparing the results to simulations of Lennard-Jones fluids. Following this work he helped to develop the theory of electronic excitations (excitons) in molecular crystals and liquids, eventually moving into the area of radiationless molecular transitions, beginning his own experimental work after the development of the Bixon-Jortner model, while also working with collaborators on extending the theoretical model of these transitions. This research led him to investigate the effects of quantum chaos on excited molecules, and to couple the developing model of transitions with quantum chaos in order to attain control of the transition of excited molecules.
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In this range multi-electron excitations and many-body final states in strongly correlated systems are relevant; # In the high kinetic energy range of the photoelectron, the scattering cross-section with neighbor atoms is weak, and the absorption spectra are dominated by EXAFS (Extended X-ray Absorption Fine Structure), where the scattering of the ejected photoelectron of neighboring atoms can be approximated by single scattering events. In 1985, it was shown that multiple scattering theory can be used to interpret both XANES and EXAFS; therefore, the experimental analysis focusing on both regions is now called XAFS. XAS is a type of absorption spectroscopy from a core initial state with a well defined symmetry; therefore, the quantum mechanical selection rules select the symmetry of the final states in the continuum, which are usually a mixture of multiple components. The most intense features are due to electric-dipole allowed transitions (i.e.
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The presence of an intermediate band will allow the absorption of such photons resulting in the generation of electron-hole pairs, adding to those created by direct optical transitions. In two independent electron excitations, photons are absorbed with transitions from valence (VB) to intermediate band (IB) and from intermediate (IB) to conduction band (VB). In order to achieve optimal results, any devices and processes are assumed ideal as associated conditions include infinite carrier mobility, full absorption of desired photons, partial filling of the IB in order to both donate and receive electrons and no possibility of extracting current from the IB. Within this framework, the limiting efficiency of an intermediate-band solar cell (IBSC) has been calculated to be 63.1%. The presence of an intermediate band can be the result of several techniques, but most notably of the introduction of impurities in the crystal structure.
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Also, the experiments conducted essentially showed that the Abney effect does not hold for all changes in light purity, but is limited very much to certain means of purity degradation, namely the addition of white light. Since the experiments undertaken varied the bandwidth of the light, a similar albeit different means of altering the purity and therefore hue of the monochromatic light, the nonlinearity of the results displayed differently from what had traditionally been seen. Ultimately, the researchers came to the conclusion that variations in spectral bandwidth cause postreceptoral mechanisms to compensate for the filtering effects imposed by cone sensitivities and preretinal absorption and that the Abney effect occurs because the eye has, in a sense, been tricked into seeing a color that would not naturally occur and must therefore approximate the color. This approximation to compensate for the Abney effect is a direct function of the cone excitations experienced with a broadband spectrum.
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First, the belief that mental illness was organic in nature, and reflected an underlying brain pathology; next, that the nervous system was organized according to an associationist model comprising an input or afferent system (a sensory center), a connecting system where information processing took place (an association center), and an output or efferent system (a motor center); and, finally, a modular conception of the brain whereby discrete mental faculties were connected to specific regions of the brain. Burckhardt's hypothesis was that by deliberately creating lesions in regions of the brain identified as association centers a transformation in behavior might ensue. According to his model, those mentally ill might experience "excitations abnormal in quality, quantity and intensity" in the sensory regions of the brain and this abnormal stimulation would then be transmitted to the motor regions giving rise to mental pathology. He reasoned, however, that removing material from either of the sensory or motor zones could give rise to "grave functional disturbance".
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Seismic microzonation map of Greater Bangkok prepared based on predominant period of site obtained from microtremor observations Tuladhar, R., Yamazaki, F., Warnitchai, P & Saita, J., Seismic Microzonation of the Greater Bangkok area using Microtremor Observations, Earthquake Engineering and Structural Dynamics, v33, 2004: 211-225 Seismic microzonation is defined as the process of subdividing a potential seismic or earthquake prone area into zones with respect to some geological and geophysical characteristics of the sites such as ground shaking, liquefaction susceptibility, landslide and rock fall hazard, earthquake-related flooding, so that seismic hazards at different locations within the area can correctly be identified. Microzonation provides the basis for site-specific risk analysis, which can assist in the mitigation of earthquake damage. In most general terms, seismic microzonation is the process of estimating the response of soil layers under earthquake excitations and thus the variation of earthquake characteristics on the ground surface.Finn, W.D.L. (1991) Geotechnical Engineering Aspects of Microzonation, Proc.
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It is possible then for a single complex to undergo multiple intersystem crossings, which is the case in light- induced excited spin-state trapping (LIESST), where, at low temperatures, a low-spin complex can be irradiated and undergo two instances of intersystem crossing. For Fe(II) complexes, the first intersystem crossing occurs from the singlet to the triplet state, which is then followed by intersystem crossing between the triplet and the quintet state. At low temperatures, the low-spin state is favored, but the quintet state is unable to relax back to the low- spin ground state due to their differences in zero-point energy and metal- ligand bond length. The reverse process is also possible for cases such as [Fe(ptz)6](BF4)2, but the singlet state is not fully regenerated, as the energy needed to excite the quintet ground state to the necessary excited state to undergo intersystem crossing to the triplet state overlaps with multiple bands corresponding to excitations of the singlet state that lead back to the quintet state.
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Then, in 1972, he began the work on composite, disordered and amorphous materials that lasted until his retirement. On his 60th birthday, in 1982, Rosenberg was gloomily contemplating the need to find a new topic of research to last until his retirement, when a note from an old colleague, Ray Orbach in California, showed that his experimental results on the low temperature properties of amorphous solids found a natural explanation in terms of the newly discovered mathematical theory of fractals, by now of course familiar through the strange and beautiful pictures that they generate. This new approach to the interpretation of excitations in disordered solids was first expressed in the paper "Fractal interpretation of vibrational properties of cross-linked polymers, glasses and irradiated quartz," Alexander, Laermans, Orbach, and Rosenberg, Phys Rev (1993) B28 4615-4619 which, according to Orbach, was a very controversial piece of work, greeted with considerable skepticism. Rosenberg was regarded as a gifted lecturer, not only to undergraduates and to colleagues at conferences, but also to a much wider audience, both on the radio and on television.
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There is an entire literature concerning the "structure of matter", ranging from the "electrical structure" in the early 20th century, to the more recent "quark structure of matter", introduced today with the remark: Understanding the quark structure of matter has been one of the most important advances in contemporary physics. In this connection, physicists speak of matter fields, and speak of particles as "quantum excitations of a mode of the matter field". And here is a quote from de Sabbata and Gasperini: "With the word "matter" we denote, in this context, the sources of the interactions, that is spinor fields (like quarks and leptons), which are believed to be the fundamental components of matter, or scalar fields, like the Higgs particles, which are used to introduced mass in a gauge theory (and that, however, could be composed of more fundamental fermion fields)." In the late 19th century with the discovery of the electron, and in the early 20th century, with the discovery of the atomic nucleus, and the birth of particle physics, matter was seen as made up of electrons, protons and neutrons interacting to form atoms.
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The fundamental geometric idea of E8 Theory is that our universe and its contents exists as quantum excitations of the largest simple real quaternionic exceptional Lie group, E8(−24). This is described via an extension of Cartan geometry employing a superconnection. The relevant Cartan geometry is modeled on Klein geometry, beginning with a homogeneous space, G/H, in which the initial Lie group is G = E8(−24) and the subgroup is H = SL(2,C)xS(U(3)×U(2))xZ3, in which Z3 = {1,T,T2} is the cyclic group of order three corresponding to a triality automorphism, T, of E8(−24). Usually, in Cartan geometry, the deformation of a Lie group, G, preserving the structure of a subgroup, H, is described by allowing the Lie group's Maurer–Cartan form, θ, to vary, becoming the Cartan connection, :C = W + Ɛ The resulting geometry, G̃, is that of a principal bundle, with W the principal H-connection, a 1-form valued in Lie(H) over a base manifold, B, modeled on G/H, with the frame, Ɛ, a 1-form valued in Lie(G/H).
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Spontaneous symmetry breaking occurs in a theory when the state with lowest energy does not have as many symmetries as the theory itself, therefore one sees degenerate vacua connected by the quotient between the symmetry of the theory and the symmetry of the state, and the particle spectrum is classified by the symmetry group of the lowest energy state (vacuum). In the case that the quotient can be parametrized by continuous parameter(s), the local fluctuations of these parameters can be regarded as bosonic excitations (if the symmetry is bosonic), usually called Goldstone boson, which has profound implications. When coupled to gauge fields, these bosons mix into the longitudinal polarizations of the gauge fields and give masses to the fields, this is how Higgs mechanism works. Usually the way to realize spontaneous symmetry breaking is to introduce a scalar field that has a tachyonic mass parameter, classically, then the classical vacuum is the solution that stays at the bottom of the potential, with the leading quantum contribution from the uncertainty principle, the vacuum can be viewed as a Gaussian wave packet around the lowest point of the potential.
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