The hood of the truck blazed with dazzling corona discharges and St. Elmo's fire coruscated around the headlamps and other metal fixtures.
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For his Doctor of Philosophy (Dir. Phil.) under Warburg's supervision, Warburg suggested that he study corona discharges. Franck found this topic too complex, so he changed the focus of his thesis.
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The absence of oxygen in the atmosphere within significantly reduces the damage of the windings insulation by eventual corona discharges; these can be problematic as the generators typically operate at high voltage, often 20 kV.
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In many high voltage applications, the corona is an unwanted side effect. Corona discharge from high voltage electric power transmission lines constitutes an economically significant waste of energy. Corona discharges are suppressed by improved insulation, corona rings, and making high voltage electrodes in smooth rounded shapes.
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The generator is hermetically sealed to prevent escape of the hydrogen gas. The absence of oxygen in the atmosphere within significantly reduces the damage of the windings' insulation by eventual corona discharges. The hydrogen gas is circulated within the rotor enclosure, and cooled by a gas-to-water heat exchanger.
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These noises are produced by the discharge present in all these operations. ;Solar noise :Noise that originates from the Sun is called solar noise. Under normal conditions there is constant radiation from the Sun due to its high temperature. Electrical disturbances such as corona discharges, as well as sunspots can produce additional noise.
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Corona discharges appear at atmospheric pressures in strongly non-uniform electric fields. Sharp edges of high voltage electrodes produce such fields in their vicinity. When the field in the rest space is negligible – this happens at large distances to the electric grounds – the corona discharge can be ignited. Otherwise, the high voltage electrodes may spark to the ground.
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A flashtube generates a short pulse of intense light useful for photography by sending a heavy current through a gas arc discharge. Corona discharges are used in photocopiers. Electric discharges can convey substantial energy to the electrodes at the ends of the discharge. A spark gap is used in internal combustion engines to ignite the fuel/air mixture on every power stroke.
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The corona discharge between the object and the plate due to high-voltage is captured by the film. The developed film results in a Kirlian photograph of the object. Color photographic film is calibrated to produce faithful colors when exposed to normal light. Corona discharges can interact with minute variations in the different layers of dye used in the film, resulting in a wide variety of colors depending on the local intensity of the discharge.
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Experiments have shown that neither circuit offers any marked performance advantage over the other. However, in the typical circuit, the spark gap's short circuiting action prevents high-frequency oscillations from 'backing up' into the supply transformer. In the alternate circuit, high amplitude high frequency oscillations that appear across the capacitor also are applied to the supply transformer's winding. This can induce corona discharges between turns that weaken and eventually destroy the transformer's insulation.
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Lower operating voltages lead to longer rise times of pulses, without appreciably changing the dead times. Spurious pulses are caused mostly by secondary electrons emitted by the cathode due to positive ion bombardment. The resulting spurious pulses have the nature of a relaxation oscillator and show uniform spacing, dependent on the tube fill gas and overvoltage. At high enough overvoltages, but still below the onset of continuous corona discharges, sequences of thousands of pulses can be produced.
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The maximal achievable potential is roughly equal to the sphere radius R multiplied by the electric field Emax at which corona discharges begin to form within the surrounding gas. For air at standard temperature and pressure (STP) the breakdown field is about 30 kV/cm. Therefore, a polished spherical electrode 30 cm in diameter could be expected to develop a maximal voltage Vmax = R·Emax of about 450 kV. This explains why Van de Graaff generators are often made with the largest possible diameter.
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Although corona discharge is usually undesirable, until recently it was essential in the operation of photocopiers (xerography) and laser printers. Many modern copiers and laser printers now charge the photoconductor drum with an electrically conductive roller, reducing undesirable indoor ozone pollution. Lightning rods use corona discharge to create conductive paths in the air that point towards the rod, deflecting potentially-damaging lightning away from buildings and other structures. Corona discharges are also used to modify the surface properties of many polymers.
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One ionization method the utilizes CI is atmospheric-pressure chemical ionization (APCI). In APCI the ionization occurs at atmospheric pressure with ions produced by corona discharges on a solvent spray, and it is often coupled with high-performance liquid chromatography (HPLC) which provides quality determination of polar and ionic compounds in the collected atmospheric aerosols. The use of APCI allows for the sampling of the filters without the need of solvents for the extraction. The APCI is typically connected to a quadruple mass spectrometer.
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Corona discharges produce electric currents of the order of 1 – 100 μA at high voltages of the order of several kV. These currents and the corresponding discharge power are low comparing to the currents and the power of the arc and the dielectric barrier discharges. However, the advantage of the corona discharge is simplicity of the DC high voltage electronics. While electric sparks limit the high voltage, and thus the corona power, the latter can be further increased with a help of pulse-periodic high voltages.
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49, 614 (2009)M. Teschke and J. Engemann, US020090122941A1, U.S. Patent application Since the piezoelectric material of the transformer, such as lead zirconate titanate, is often a dielectric, the produced electric discharge resembles properties of the dielectric barrier discharge. In addition, when operated in far from the electric ground, it also produces corona discharges on the sharp edges of the piezo-transformer. Due to the unique construction principles, the piezoelectric barrier discharge is the economic and compact source of the dielectric barrier and corona plasmas.
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One of the earliest recipes consists of 45% carnauba wax, 45% white rosin, and 10% white beeswax, melted, mixed together, and left to cool in a static electric field of several kilovolts/cm. The thermo-dielectric effect, related to this process, was first described by Brazilian researcher Joaquim Costa Ribeiro. Electrets can also be manufactured by embedding excess negative charge within a dielectric using a particle accelerator, or by stranding charges on, or near, the surface using high voltage corona discharges, a process called corona charging. Excess charge within an electret decays exponentially.
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In earlier times it was often used to discourage reverse engineering of proprietary products built as printed circuit modules. It is also commonly used in high voltage products to allow live parts to be placed closer together (eliminating corona discharges due to the potting compound's high dielectric strength), so that the product can be smaller. This also excludes dirt and conductive contaminants (such as impure water) from sensitive areas. Another use is to protect deep-submergence items such as sonar transducers from collapsing under extreme pressure, by filling all voids.
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Streamers are transient (exist only for a short time) and filamentary, which makes them different from corona discharges. They are used in applications such as ozone production, air purification or plasma medicine. If a streamer reaches the opposite polarity conductor it creates an ionized conductive path through which a large current can flow, releasing a large amount of heat, resulting in an electric arc; this is the process through which lightning leaders create a path for lightning bolts. Streamers can also be observed as sprites in the upper atmosphere.
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Electron avalanches are essential to the dielectric breakdown process within gases. The process can culminate in corona discharges, streamers, leaders, or in a spark or continuous electric arc that completely bridges the gap. The process may extend huge sparks — streamers in lightning discharges propagate by formation of electron avalanches created in the high potential gradient ahead of the streamers' advancing tips. Once begun, avalanches are often intensified by the creation of photoelectrons as a result of ultraviolet radiation emitted by the excited medium's atoms in the aft-tip region.
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Electric discharges produced in the gas from the high voltage side of the piezoelectric transformer have properties found also in the corona discharges and in the dielectric barrier discharges. While the former mode occurs when the high voltage side of the piezoelectric transformer is operated far from the electric grounds, the latter mode occurs when it is operated close to the electric grounds separated by a dielectric. Near the open electric grounds, the piezoelectric transformer produces periodic sparks. Transition to the electric arc does not occur because of the limited power of the transformer.
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Corona discharges only occur when the electric field (potential gradient) at the surface of conductors exceeds a critical value, the dielectric strength or disruptive potential gradient of air. It is roughly 30 kilovolts per centimeter, but decreases with atmospheric pressure, so corona is more of a problem at high altitudes. The electric field at a conductor is greatest where the curvature is sharpest, and therefore corona discharge occurs first at sharp points, corners and edges. The terminals on very high voltage equipment are frequently designed with large diameter rounded shapes such as balls and toruses called corona caps, to suppress corona formation.
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Electron avalanches are essential to the dielectric breakdown process within gases. The process can culminate in corona discharges, streamers, leaders, or in a spark or continuous arc that completely bridges the gap between the electrical conductors that are applying the voltage. The process extends to huge sparks — streamers in lightning discharges propagate by formation of electron avalanches created in the high potential gradient ahead of the streamers' advancing tips. Once begun, avalanches are often intensified by the creation of photoelectrons as a result of ultraviolet radiation emitted by the excited medium's atoms in the aft-tip region.
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Polyester film (KT) capacitors of the "stacked" type are often used now instead of polystyrene capacitors (KS), which have become less available. Metallized film capacitors have self-healing properties, and small imperfections do not lead to the destruction of the component, which makes these capacitors suitable for RFI/EMI suppression capacitors with fault protection against electrical shock and flame propagation, although repeated corona discharges which self-heal can lead to significant loss of capacitance. PTFE film capacitors are used in applications that must withstand extremely high temperatures. such as in military equipment, in aerospace, in geological probes, or burn-in circuits.
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Davis's post-graduate work at the Cavendish Laboratory at Cambridge had prepared him to engage with the new physics which followed the work of scientists such as Albert Einstein, Max Planck, and Niels Bohr, concepts which he helped to introduce into the Columbia curriculum. Among his many important works was a study of ionization and radiation potentials and the theory behind corona discharges. Much of his later work was in studying X-rays, and he helped improve the double X-ray spectrometer. Davis served for many years as a consultant on X-rays to the staff of the Crocker Institute of Cancer Research at Columbia.
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The typical power of such transformers is of the order of 10 W. The efficiency of the plasma generation reaches 90%, while the remaining 10% of the power is lost due to mechanical heating of the piezoelectric transformer. Due to low electric currents, typical for the dielectric barrier and the corona discharges, the piezoelectric direct discharge produces a non-equilibrium plasma. This means that its constituent electrons, ions and the neutral gas particles have different kinetic energy distributions. Temperature of the neutral gas within the plasma volume remains lower than 50 C. At the same time, the electrons and the ions reach energies of 1 – 10 eV.
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A corona discharge is an electrical discharge brought on by the ionization of a fluid such as air surrounding a conductor that is electrically charged. Spontaneous corona discharges occur naturally in high-voltage systems unless care is taken to limit the electric field strength. A corona will occur when the strength of the electric field (potential gradient) around a conductor is high enough to form a conductive region, but not high enough to cause electrical breakdown or arcing to nearby objects. It is often seen as a bluish (or another colour) glow in the air adjacent to pointed metal conductors carrying high voltages and emits light by the same property as a gas discharge lamp.
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Long exposure photograph of a Tesla coil showing the repeated electric discharges The dielectric breakdown strength of dry air, at Standard Temperature and Pressure (STP), between spherical electrodes is approximately 33 kV/cm.A. H. Howatson, "An Introduction to Gas Discharges", Pergamom Press, Oxford, 1965, page 67 This is only as a rough guide, since the actual breakdown voltage is highly dependent upon the electrode shape and size. Strong electric fields (from high voltages applied to small or pointed conductors) often produce violet-colored corona discharges in air, as well as visible sparks. Voltages below about 500–700 volts cannot produce easily visible sparks or glows in air at atmospheric pressure, so by this rule these voltages are "low".
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Personnel at the Fourth Naval District have suggested that the alleged event was a misunderstanding of routine research during World War II at the Philadelphia Naval Shipyard. An earlier theory was that "the foundation for the apocryphal stories arose from degaussing experiments which have the effect of making a ship undetectable or 'invisible' to magnetic mines." Another possible origin of the stories about levitation, teleportation and effects on human crew might be attributed to experiments with the generating plant of the destroyer , whereby a higher-frequency generator produced corona discharges, although none of the crew reported suffering effects from the experiment. Observers have argued that it is inappropriate to grant credence to an unusual story promoted by one individual, in the absence of corroborating evidence.
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The electrostatic repulsion of ions, ionic recombination, and air convection currents due to heating tend to break up ionized regions, so streamers have a short lifetime. A streamer discharge, also known as filamentary discharge, is a type of transient electrical discharge which forms at the surface of a conductive electrode carrying a high voltage in an insulating medium such as air. Streamers are luminous writhing branching sparks, plasma channels composed of ionized air molecules, which repeatedly strike out from the electrode into the air. Like the related corona discharges and brush discharges, a streamer discharge represents a region around a high voltage conductor where the air has suffered electrical breakdown and become conductive (ionized), so electric charge is leaking off the electrode into the air.
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The mechanism of the phenomenon of sonoluminescence is unknown. Hypotheses include: hotspot, bremsstrahlung radiation, collision-induced radiation and corona discharges, nonclassical light, proton tunneling, electrodynamic jets and fractoluminescent jets (now largely discredited due to contrary experimental evidence). From left to right: apparition of bubble, slow expansion, quick and sudden contraction, emission of light In 2002, M. Brenner, S. Hilgenfeldt, and D. Lohse published a 60-page review that contains a detailed explanation of the mechanism. An important factor is that the bubble contains mainly inert noble gas such as argon or xenon (air contains about 1% argon, and the amount dissolved in water is too great; for sonoluminescence to occur, the concentration must be reduced to 20–40% of its equilibrium value) and varying amounts of water vapor.
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In the example, the upward-moving belt must be more positive than the downward-moving belt. As the belt continues to move, a constant "charging current" travels via the belt, and the sphere continues to accumulate positive charge until the rate that charge is being lost (through leakage and corona discharges) equals the charging current. The larger the sphere and the farther it is from ground, the higher will be its peak potential. In the example, the wand with metal sphere (8) is connected to ground, as is the lower comb (7); electrons are drawn up from ground due to the attraction by the positive sphere, and when the electric field is great enough (see below) the air breaks in the form of an electrical discharge spark (9).
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