Estaban estudiando materiales que se cristalizan con un patrón helicoidal retorcido.
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Lists of spiral (helicoidal) tunnels and tunnels on a curved alignment on roads and railway lines worldwide.
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Helicoidal flow is the cork-screw-like flow of water in a meander. It is one example of a secondary flow. Helicoidal flow is a contributing factor to the formation of slip-off slopes and river cliffs in a meandering section of the river. The helicoidal motion of the flow aids the processes of hydraulic action and corrasion on the outside of the meander, and sweeps sediment across the floor of the meander towards the inside of the meander, forming point bar deposits.
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However, by 1836 a young engineer called Charles Fox had improved on Nicholson's helicoidal method and other writers were proposing alternative approaches to the problem.
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Helicoidal electrodes are placed cirumjacent to the nerve and are made of flexible platinum ribbon in a helical design. This design allows the electrode to conform to the size and shape of the nerve in attempts to minimize mechanical trauma. The structural design causes low selectivity. Helicoidal electrodes are currently used for FES stimulation of the vagus nerve to control intractable epilepsy, sleep apnea, and to treat depressive syndromes.
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The helicoidal method of laying down the stone or brick courses championed by Nicholson, Fox and Buck is only an approximation to the ideal. Since the courses are only square to the faces of the arch at the crown and deviate more from perpendicularity the closer they are to the springing line, thereby over- correcting the deficiencies of the false skew arch and weakening the obtuse angle, the mathematical purists recommend that helicoidal construction be restricted to segmental arches and not be used in full-centred (semicircular) designs. Despite this there were many full-centred skew bridges built to the helicoidal pattern and many still stand, Kielder Viaduct and Neidpath Viaduct being just two examples.
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Brown, 2006, op. cit., p. 26. The brickwork is considerably more complex than in a helicoidal design and, in order to ensure that the courses of bricks meet the faces of the arch at right angles, many had to be cut to produce tapers. The corne de vache approach tends to result in a structure that is almost as strong as one built to the logarithmic pattern and considerably stronger than one built to the helicoidal pattern but, again, the extra complexity has meant that the method has not seen widespread adoption, especially since the simpler helicoidal structure can be built much stronger if a segmental design is chosen, rather than a full-centred one.
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The Golden wentletrap has a bright yellow helicoidal shell which grows up to 1 cm in length. It's often found on corals from genus Tubastraea on which it feeds.
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The height of the shell attains 0.8 mm, its diameter 0.8 mm. The yellowish white shell has a helicoidal shape. Its umbilicus is narrow. The shell contains 2½ whorls, slightly flattened at the periphery and then rounded.
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As flow enters the bank of an alluvial river, the centrifugal force created by the bend instigates helicoidal flow, a corkscrew like pattern of flow, which drives the hydraulic action acting on the opposing bank. This is where the primary process in river channel migration of bank erosion occurs. Often the bank is undercut, another result of the helicoidal flow, which leads to the creation of cut banks. Factors that limit the rate of bank erosion include the rate of deposition of the point bar, stream power, and the critical shear stress of the stream bed.
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He contended that helicoidal striation is a general feature of muscles and that muscular conduction takes place along this helicoidal path, even though the evidence for this generality was against him, yet his cinematographic records supported his interpretation for arachnids and other arthropods. Between 1922 and 1934 Oscar Tiegs was almost entirely concerned with the physiology of nerve and muscle, apparently influenced by Brailsford Robertson. In 1925 he published the results of experiments regarding the importance of creatine. This line of research was inspired by the lactic acid hypotheses of muscular action at the time and before phosphagen was discovered.
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TBP's C-terminus composes of a helicoidal shape that (incompletely) complements the T-A-T-A region of DNA. This incompleteness allows DNA to be passively bent on binding. For information on the use of TBP in cells see: RNA polymerase I, RNA polymerase II, and RNA polymerase III.
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Springer, Amsterdam, Netherlands. 391 pp. As water in a meandering river travels around a bend, it moves in a secondary corkscrew-like flow as it travels downstream, in a pattern called helicoidal flow. This phenomenon causes increased water velocity in the outside bend of the meander, driving lateral bank erosion.
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In the Antalo Limestone: large Paracenoceratidae cephalopods (nautilus); Nerineidae indet.; sea urchins; Rhynchonellid brachiopod; crustaceans; coral colonies; crinoid stems. In the Tertiary silicified lacustrine deposits: Pila (gastropod); Lanistes sp.; Pirenella conica; and land snails (Achatinidae indet.). All snail shells, both fossil and recent, are called t’uyo in Tigrinya language, which means ‘helicoidal’.
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They mine the leaves of their host plant. They create a strongly arched composite leaf case of 7–8 mm. The case consists of a number of mined leaflets placed transversely on top of each other, resulting in a somewhat helicoidal case. The mouth opening is located more or less to the side.
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Zoophycos occurs in two forms, one planar, and one which resembles a corkscrew. In the latter helicoidal form, successive turns have larger or smaller radii. A marginal tube surrounds the perimeter of the corkscrew, linked to the vertical shaft that connects the burrow to the surface. Spreiten occur between the marginal tube and the corkscrew axis.
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The 36 m-tall bell tower has a simple brickwork appearance, but was originally also to be covered with marble plates. It was finished in the late 15th-early 16th centuries by the Florentine architect Donato Benti. In the interior is a curious helicoidal staircase. The baptistery (1786) was originally a 17th- century oratory dedicated to St. Hyacinth.
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A critical parameter in the development of the Bouligand-inspired tool path is the pitch angle. The pitch angle γ is the angle at which the helicoidal structure is formed. The relative size of the pitch angle is critical for the mechanical response of a Bouligand-inspired AM toolpiece. For γ < 45° (small angle), interfacial crack growth and interfacial microcracking is observed.
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In several parts of China & India, there are lighting pylons with combinations of solar panels and wind- turbines at their top. This allows space already used for lighting to be used more efficiently with two complementary energy productions units. Most common models use horizontal axis wind-turbines, but now models are appearing with vertical axis wind-turbines, using a helicoidal shaped, twisted-Savonius system.
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Karlodinium decipiens is a species of unarmored dinoflagellates from the genus Karlodinium. It was first isolated from the Australian region of the Southern Ocean, but has a widespread distribution, through the Southern Ocean to the Tasman Sea, to the coast of Spain. It is large-sized and is characterized by having a helicoidal chloroplast arrangement and a big central nucleus. It is considered potentially ichthyotoxic.
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Unlike the primary wall, the cellulose microfibrils are aligned parallel in layers, the orientation changing slightly with each additional layer so that the structure becomes helicoidal. Cells with secondary cell walls can be rigid, as in the gritty sclereid cells in pear and quince fruit. Cell to cell communication is possible through pits in the secondary cell wall that allow plasmodesmata to connect cells through the secondary cell walls.
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While a helix is produced by projecting a straight line onto the surface of a cylinder, Sang's method requires that a series of logarithmic curves be projected onto a cylindrical surface, hence its name. French; Ives, 1902, op. cit., p. 100. In terms of strength and stability, a skew bridge built to the logarithmic pattern has advantages over one built to the helicoidal pattern, especially so in the case of full-centred designs.
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For example, an isotropic chiral material can comprise a random dispersion of handed molecules or inclusions, such as a liquid consisting of chiral molecules. Handedness can also be present at the macroscopic level in structurally chiral materials. For example, the molecules of cholesteric liquid crystals are randomly positioned but macroscopically they exhibit a helicoidal orientational order. Other examples of structurally chiral materials can be fabricated either as stacks of uniaxial laminas or using sculptured thin films.
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The obelisk under construction (May 15th 2009). To mark the 300th anniversary of its foundation (1702-2002), Caja Madrid commissioned the architect and sculptor Santiago Calatrava to design a monument that would be donated to the Villa de Madrid. It was conceived as a monument able to describe a helicoidal movement, yet the hefty maintenance costs led to the Ayuntamiento de Madrid's preference for keeping it "static". According to the initial project, the work would measure 120 meters tall.
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Oscar Tiegs' doctoral thesis work was to be the basis for much of his later work, in embryological studies, and the study of fine structures in muscle. He found clear evidence that the apparent striation of muscle fibres did not arise from separate disks, but from a helicoidal organisation within the fibre. He also found a similar condition in vertebrate muscles. Later he discovered that former histologists had recorded the same thing, but their observations had received little attention.
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Boxmoor Skew Bridge in 2011, looking in a SSW direction from London Road Boxmoor Skew Bridge detail, showing the chamfered acute quoins and stepped extrados In 1839, George Watson Buck, having also worked on the London and Birmingham Railway under Stephenson before moving to the Manchester and Birmingham Railway, published a work entitled A Practical and Theoretical Essay on Oblique Bridges in which he also acknowledged Nicholson's contribution but, finding it lacking in detail, applied his own original trigonometrical approach and considerable practical experience to the problem. This book was acknowledged as the definitive work on the subject of the helicoidal skew arch and remained a standard text book for railway engineers until the end of the 19th century. Buck's trigonometrical approach allowed every dimension of a skew arch to be calculated without recourse to taking measurements from scale drawings and it allowed him to calculate the theoretical minimum angle of obliquity to which a practical semicircular helicoidal skew bridge could be designed and safely built. Buck, 1839, op. cit.
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He turned to the helicoidal or spiral method, introduced by British architect Peter Nicholson in 1828. This method was mathematically rigorous, but since Truesdell studied mathematics as a hobby, he decided to accept the challenge. The voussoir stones were cut with curved surfaces to form a series of parallel spiral courses. The initial calculation of the curves was difficult, but once the calculation was performed, all of the voussoirs (except for the ring stones) could be cut from the same pattern.
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William Froude (1810–1879) Skew arch at Cowley Bridge Junction showing the complex brickwork The corne de vache or "cow's horn" method is another way of laying courses such that they meet the face of the arch orthogonally at all elevations. Hyde, 1899, op. cit., pp. 74–101. Unlike the helicoidal and logarithmic methods, in which the intrados of the arch barrel is cylindrical, the corne de vache method results in a warped hyperbolic paraboloid surface that dips in the middle, rather like a saddle.
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He inclined the columns so they could better resist the perpendicular pressure on their section. He also gave them a double-turn helicoidal shape (right turn and left turn), as in the branches and trunks of trees. This created a structure that is now known as fractal. Together with a modulation of the space that divides it into small, independent and self- supporting modules, it creates a structure that perfectly supports the mechanical traction forces without need for buttresses, as required by the neo-Gothic style.
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The fundamental zero-order Bessel beam has an amplitude maximum at the origin, while a high-order Bessel beam (HOBB) has an axial phase singularity along the beam axis; the amplitude is zero there. HOBBs can be of vortex (helicoidal) or non-vortex types. X-waves are special superpositions of Bessel beams which travel at constant velocity, and can exceed the speed of light. Mathieu beams and parabolic (Weber) beams are other types of non-diffractive beams that have the same non-diffractive and self-healing properties of Bessel beams but different transverse structures.
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The helicoidal shape, on the other hand, splits up the force of the wind in resistance, leeway and lift. In that way, the lift does not have an influence on the stability and decreases the weight transmitted to the foundations. The project extrapolates two typologies from areas never associated with buildings of great height: the twisting shape of the ship sail that escapes the wind and minimises its pressure, and the structure of the cable bridge that results in a significant saving of materials by collaborating the horizontal scaffolding with the rods and the supports.
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The third floor is in the same style as the second, but with smaller windows and fake framed columns. The top of the facade is designed as a balustrade with six statues of divinities: Hercules, Jupiter, Venus, Mercury, Apollo and Minerva. The latter are cut from local marble, with the exception of the Hercules, which is believed to have come from an ancient temple once located on the Roman Capitoline Hill. The interior is home to a bizarre helicoidal stone staircase, that leads from the underground stores all the way up to the roof.
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A direct indicating dial thermometer really common in daily use devices (such as a patio thermometer or a meat thermometer) uses a bimetallic strip wrapped into a coil in its most used design. The coil changes the linear movement of the metal expansion into a circular movement thanks to the helicoidal shape it draws. One end of the coil is fixed to the housing of the device as a fix point and the other drives an indicating needle inside a circular indicator. A bimetallic strip is also used in a recording thermometer.
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A twist represents the velocity of a rigid body as an angular velocity around an axis and a linear velocity along this axis. All points in the body have the same component of the velocity along the axis, however the greater the distance from the axis the greater the velocity in the plane perpendicular to this axis. Thus, the helicoidal field formed by the velocity vectors in a moving rigid body flattens out the further the points are radially from the twist axis. The points in a body undergoing a constant screw motion trace helices in the fixed frame.
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Flanking the hall, two sets of stairs lead to the piano nobile, a large squared staircase by Bernini to the left and a smaller oval staircase by Borromini to the right. The famous helicoidal staircase by Borromini. As well as Borromini's false-perspective windows reveals, other influential aspects of Palazzo Barberini that were repeated throughout Europe include the unit of a central two-storey hall backed by an oval salone and the symmetrical wings that extended forward from the main block to create a cour d'honneur. The garden is known as a giardino segreto ("secret garden"), for its concealment from an outsider's view.
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Using this model it can be shown, for example, that the origin of the unusual ground insulating ferromagnetic state of a solid like K2CuF4 can be traced to its orbital ordering. Even when starting from a relatively high-symmetry structure the combined effect of exchange interactions, spin-orbit coupling, orbital- ordering and crystal deformations activated by the JTE can lead to very low symmetry magnetic patterns with specific properties. For example, in CsCuCl3 an incommensurable helicoidal pattern appears both for the orbitals and the distortions along the z-axis. Moreover, many of these compounds show complex phase diagrams when varying temperature or pressure.
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This contributed to a new dynamic of innovation in musical instrument and bow making far beyond the work of Rolland himself: in less than ten years, hundreds of manufactures of carbon bows were appearing around the world. In 2012 Rolland introduced a significant innovation in the design of the bow with the Galliane frog. Galliane frogs give a slight helicoidal shape to the bow hair, allowing the performer to play with a fuller hair ribbon from frog to tip. In 2016 Rolland evolved the orchestra conducting baton, creating a new shape that transformed the conventional bulb of the baton.
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The Helicoidal Skyscraper can be considered a sustainable building or an example of the green architecture concept due to several aspects of its design. As a tall building, for instance, it addresses the energy problem by minimising the quantities of materials needed for its construction. Also, its unique logarithmic spiral would have reacted to the wind with a vertical force that drives it upwards, taking with the air pollution - out from the streets below. It avoids the capability of most tall buildings to serve as obstructions that affect the atmospheric circulation and the dispersion of pollutants.
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In general, since particles also have a velocity component along the magnetic field line, the Lorentz force constrains them to bend and move along spirals around the field lines at the cyclotron frequency. If collisions between the particles are very frequent, they are scattered in every direction. This happens in the photosphere, where the plasma carries the magnetic field in its motion. In the corona, on the contrary, the mean free- path of the electrons is of the order of kilometres and even more, so each electron can do a helicoidal motion long before being scattered after a collision.
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The Seventh Street Improvement Arches are a double-arched masonry highway bridge that formerly spanned the St. Paul and Duluth Railroad tracks in Saint Paul, Minnesota, United States. The Seventh Street Improvement Arches are historically significant for its rarity and the technically demanding nature of its skewed, helicoidal spiral, stone-arch design. The bridge is one of the few of its type in the United States, and is the only known bridge of its type in Minnesota. It was built from 1883 to 1884 by Michael O'Brien and McArthur Brothers of Chicago and was designed by William A. Truesdell.
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LSAW are made by bending and welding wide steel plates and most commonly used in oil and gas industry applications. Due to their high cost, LSAW pipes are seldom used in lower value non-energy applications such as water pipelines. SSAW pipes are produced by spiral (helicoidal) welding of steel coil and have a cost advantage over LSAW pipes, as the process uses coils rather than steel plates. As such, in applications where spiral-weld is acceptable, SSAW pipes may be preferred over LSAW pipes. Both LSAW pipes and SSAW pipes compete against ERW pipes and seamless pipes in the diameter ranges of 16”-24”.
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The sediment taken from the bank during the process of bank erosion is deposited on the opposing side of the channel fueling the process called point bar deposition. The helicoidal flow also plays a role in this process by acting as a cross channel component that moves the sediment to the other side. The processes of point bar deposition and bank erosion are intertwined and in most cases the erosion rate of cut banks is equal to the deposition rate of point bars. In addition, point bars act as topographic obstructions once formed that further drive flow into the opposite bank, creating a positive feedback loop.
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The lower level, or crypt, quite low, has a central chamber and another two located on either side. The upper floor is accessed via a double exterior stairway adjoining the facade, leading into an identical layout as the lower floor; a central or noble hall with six blind semicircular arches along the walls, supported by columns built into the wall, and a mirador at each end. These are accessed via three arches, similar to those onto the wall, resting on columns with helicoidal rope moulding, typical of Pre-Romanesque. The barrel vault is made from tufa stone, and is held up by six transverse arches resting on consoles.
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Because each of these displacements has a screw axis, the movement has an associated ruled surface known as a screw surface. This surface is not the same as the axode, which is traced by the instantaneous screw axes of the movement of a body. The instantaneous screw axis, or 'instantaneous helical axis' (IHA), is the axis of the helicoidal field generated by the velocities of every point in a moving body. When a spatial displacement specializes to a planar displacement, the screw axis becomes the displacement pole, and the instantaneous screw axis becomes the velocity pole, or instantaneous center of rotation, also called an instant center.
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Jacob Willem "Wim" Cohen (27 August 1923 Leeuwarden - 12 November 2000) was a Dutch mathematician, well known for over hundred scientific publications and several books in queueing theory. Cohen was born in a Jewish family, as the son of Benjamin Cohen and Aaltje Klein. Having acquired an autodidact knowledge of mathematics while in hiding during World War II, Cohen got an Engineer's degree (1949) and Ph.D. degree (1955) in mechanical engineering at Delft University, on a dissertation entitled Stress Calculations in Helicoidal Shells and Propeller Blades. He worked as teletraffic engineer with the Telecommunications group at Philips (1950–57), at the applied mathematics department at Delft (1957–73) and University of Utrecht (1973-1998).
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The secondary flow is then upward toward the surface where it mixes with the primary flow or moves slowly across the surface, back toward the concave bank.Journal of Geophysical Research, Volume 107 (2002) This motion is called helicoidal flow. On the floor of the river bed the secondary flow sweeps sand, silt and gravel across the river and deposits the solids near the convex bank, in similar fashion to sugar or tea leaves being swept toward the center of a bowl or cup as described above. This process can lead to accentuation or creation of D-shaped islands, meanders through creation of cut banks and opposing point bars which in turn may result in an oxbow lake.
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Gaudí kept the rectangular shape of the old building's balconies—with iron railings in the shape of masks—giving the rest of the facade an ascending undulating form. He also faced the facade with ceramic fragments of various colours ("trencadís"), which Gaudí obtained from the waste material of the Pelegrí glass works. The interior courtyard is roofed by a skylight supported by an iron structure in the shape of a double T, which rests on a series of catenary aches. The helicoidal chimneys are a notable feature of the roof, topped with conical caps, covered in clear glass in the centre and ceramics at the top, and surmounted by clear glass balls filled with sand of different colours.
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Temple Expiatori de la Sagrada Família From 1915 Gaudí devoted himself almost exclusively to his magnum opus, the Sagrada Família, a synthesis of his architectural evolution. After completion of the crypt and the apse, still in Gothic style, the rest of the church is conceived in an organic style, imitating natural shapes with their abundance of ruled surfaces. He intended the interior to resemble a forest, with inclined columns like branching trees, helicoidal in form, creating a simple but sturdy structure. Gaudí applied all of his previous experimental findings in this project, from works such as the Park Güell and the crypt of the Colònia Güell, creating a church that is at once structurally perfect, harmonious and aesthetically satisfying.
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This solution, timidly advanced in the Holy Chamber, fully matured in Santa Maria del Naranco. The palace, on a rectangular ground plan, has two floors; the lower level, or crypt, quite low, has a central chamber and another two located on either side. The upper floor is accessed via a double exterior stairway adjoining the facade, leading into an identical layout as the lower floor; a central or noble hall with six blind semicircular arches along the walls, supported by columns built into the wall, and a mirador at each end. These are accessed via three arches, similar to those onto the wall, resting on columns with helicoidal rope moulding, typical of Pre-Romanesque.
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The expansion of a plasma in a magnetic nozzle is inherently more complex than the expansion of a gas in a solid nozzle, and is the result of several intertwined phenomena, which ultimately rely on the large mass difference between electrons and ions and the electric and magnetic interactions between them and the applied field. If the strength of the applied magnetic field is sufficient, it magnetizes the light electrons in the plasma, which therefore describe a helicoidal motion about the magnetic lines. In practice, this is achieved with magnetic fields in the range of a few hundred Gauss. The guiding center of each electron is forced to travel along one magnetic tube.
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The R shears are then linked by a second set, the R' shear that form at about 75° to the main fault trace. These two fault orientations can be understood as conjugate fault sets at 30° to the short axis of the instantaneous strain ellipse associated with the simple shear strain field caused by the displacements applied at the base of the cover sequence. With further displacement the Riedel fault segments will tend to become fully linked, often with the development of a further set of shears known as 'P shears', which are roughly symmetrical to the R shears with respect to the overall shear direction, until a throughgoing fault is formed. The somewhat oblique segments will link downwards into the fault at the base of the cover sequence with a helicoidal geometry.
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Also outstanding was its high performance and perfect balance at all speeds, thanks to the balance shaft with counterrotating masses under the crankshaft. The engine had two interchangeable cylinder heads, one for each group of three cylinders, and cylinder liners of a special cast iron. It was a 7.5 l 120° V6 machine, delivering initially 110 and later 120 horsepower, enough for the vehicle to reach a top speed of 90 km/h, with its maximum weight of 11,320 kg Another of the fundamental characteristics of the Z-207 was the independent front suspension with two superimposed trapezoids with helicoidal springs, each with a corresponding shock absorber offering a degree of comfort hitherto never attained in an industrial vehicle. A big spring joined both wheels, so guaranteeing great strength even in full load.
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Skew arch at Cowley Bridge Junction The hulls of Swan (above) and Raven (below) on display in the Science museum, London Froude was born at Dartington, Devon, England, the son of Robert Froude, Archdeacon of Totnes and was educated at Westminster School and Oriel College, Oxford, graduating with a first in mathematics in 1832. His first employment was as a surveyor on the South Eastern Railway which, in 1837, led to Brunel giving him responsibility for the construction of a section of the Bristol and Exeter Railway. It was here that he developed his empirical method of setting out track transition curves and introduced an alternative design to the helicoidal skew arch bridge at Rewe and Cowley Bridge Junction, near Exeter. During this period he lived in Cullompton and was Vicar's Warden at St Andrew's Church from 1842 to 1844.
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Havana's Coppelia is a Cuban Revolution modernist building from 1966. It features five white granite discs annexed to one great helicoidal staircase, with wood and tinted glass division panels, all under one big round roof supported by twelve reinforced concrete arachnid columns. The flying-saucer-shaped building represents a UFO that has landed in Havana and is one of the largest ice cream parlors in the world. Holding a maximum of 1000 guests, it is located on the part of Calle 23 known as La Rampa in the Vedado district, and occupies the entire city block between Calles 23 and 21, and Calles K and L. Coppelia has been a major city landmark for both locals and visitors since its opening in 1966, but acquired additional fame when it was featured in one of the most widely viewed Cuban films, Strawberry and Chocolate.
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Most screwpile lighthouses were made with iron piles, though a few were made with wooden piles covered with metal screw sleeves (these sleeves were probably adopted because they were less expensive and easier to insert into the bottom, plus the sleeve protected the wood from marine-boring invertebrates). The typical screwpile lighthouse was hexagonal or octagonal in plan consisting of a central pile which was set first and then the six or eight perimeter piles were screwed in place around it. Seven Foot Knoll Lighthouse, Inner Harbor, Baltimore, Maryland Metal screwpiles were used to form the foundation of many lighthouses built on sandy or muddy bottoms. The helicoidal or screw-like cast-iron flange at the end of the metal pile was augured into the bottom increasing the bearing capacity of the pile as well as its anchoring properties.
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Inaugurated in 1973 under the name of "Parque El Salitre", and located between the 68th Avenue and the 63rd Street, near the Parque Simon Bolivar in Bogotá. It was then considered as one of the most modern parks on Latin America. Some years later, the park was closed to the public in 1999, in order to be remodeled. Its reinauguration took place in December 2000, under a new name "Salitre Mágico" and under the Mexican firm CIE, with a total of 29 rides located all over the park, among these there was a roller coaster nicknamed "the Screw" due to its helicoidal form which was imported from the United States and reassembled in Bogotá; some other new attractions such as a giant Chicago Wheel called the "Rueda Millenium" (Millennium Wheel) with a total height of 40 m which offers a panoramic view of the city.
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Secondly, it enabled him to develop an arbitrary number of concentric intermediate surfaces so as to plan the courses in multi-ring skew arch barrels, allowing them for the first time to be constructed in brick, and therefore much more economically than was previously possible. In order to explain how he visualised the courses of voussoirs in a stone skew arch, Fox wrote, "The principle which I have adopted is, to work the stones in the form of a spiral quadrilateral solid, wrapped round a cylinder, or, in plainer language, the principle of a square threaded screw: hence it becomes quite evident, that the transverse sections of all these spiral stones are the same throughout the whole arch. It will be obvious, that the beds of the stones should be worked into true spiral [helicoidal] planes." So, a stone skew arch built to Fox's plan would have its voussoirs cut with a slight twist, in order to follow the shape of a square threaded screw.
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While claiming a superior method, Fox openly acknowledged Nicholson's contribution but in 1837 he felt the need to reply to a published letter written in support of Nicholson by fellow engineer Henry Welch, the County Bridge Surveyor for Northumberland. Unfortunately the three men became involved in a paper war that, following a number of earlier altercations in which the originality of his writings was questioned, left the 71-year-old Nicholson feeling bitter and unappreciated. The following year Fox, still aged only 28 and employed by Robert Stephenson as an engineer on the London and Birmingham Railway, presented his paper encapsulating these principles to the Royal Institution and from this was born the English or helicoidal method of constructing brick skew arches. Using this method many thousands of skew bridges were built either entirely of brick or of brick with stone quoins by railway companies in the United Kingdom, a substantial number of which survive and are still in use today.
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A masonry skew arch bridge photographed shortly after its completion in 1898, showing the helicoidal nature of its stonework A skew arch (also known as an oblique arch) is a method of construction that enables an arch bridge to span an obstacle at some angle other than a right angle. This results in the faces of the arch not being perpendicular to its abutments and its plan view being a parallelogram, rather than the rectangle that is the plan view of a regular, or "square" arch. In the case of a masonry skew arch, the construction requires precise stonecutting, as the cuts do not form right angles, but once the principles were fully understood in the early 19th century, it became considerably easier and cheaper to build a skew arch of brick. The problem of building skew arch masonry bridges was addressed by a number of early civil engineers and mathematicians, including Giovanni Barbara (1726), William Chapman (1787), Benjamin Outram (1798), Peter Nicholson (1828), George Stephenson (1830), Edward Sang (1835), Charles Fox (1836), George W. Buck (1839) and William Froude (c. 1844).
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The Delta HF 4WD was unveiled at the April 1986 Turin Motor Show, becoming the top of the Delta range. The HF 4WD's 1,995 cc, twin-cam, 8-valve engine with two counter-rotating balancing shafts was derived from the Lancia Thema i.e. turbo saloon. It was equipped with a Garrett turbocharger, a wastegate valve, an air-to-air intercooler and Weber IAW integrated electronic ignition and fuel injection; to support turbocharging it also adopted tri- metallic crankpin and main bearings, sodium-filled valves, bronze valve guides and an oil cooler. Engine output was at 5,250 rpm, and of torque at 2,750 rpm, that could rise to for short periods of time thanks to an overboost function. On the Delta HF 4WD the torque split ratio of the central epicyclic differential stood at 56/44 front to rear. The basic suspension layout of the Delta 4WD remained the same as in the rest of the two-wheel drive Delta range: MacPherson strut–type independent suspension on all four corners, dual-rate dampers and helicoidal springs, with the struts and springs set slightly off- centre. The suspension mounting provided more isolation by incorporating flexible rubber links.
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