The Experts below are selected from a list of 9843 Experts worldwide ranked by ideXlab platform
Alexander Seidel - One of the best experts on this subject based on the ideXlab platform.
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Thin torus perturbative analysis of elementary excitations in the gaffnian and haldane rezayi quantum hall states
Physical Review B, 2014Co-Authors: Amila Weerasinghe, Alexander SeidelAbstract:We present a systematic perturbative approach to study excitations in the Thin Cylinder/torus limit of the quantum Hall states. The approach is applied to the Haldane-Rezayi and Gaffnian quantum Hall states, which are both expected to have gapless excitations in the usual two-dimensional thermodynamic limit. For the Haldane-Rezayi state, we confirm that gapless excitations are present also in the "one-dimensional" thermodynamic limit of an infinite Thin Cylinder, in agreement with earlier considerations based on the wave functions alone. In contrast, we identify the lowest excitations of the Gaffnian state in the Thin Cylinder limit, and conclude that they are gapped, using a combination of perturbative and numerical means. We discuss possible scenarios for the cross-over between the two-dimensional and the one-dimensional thermodynamic limit in this case.
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Halperin (m,m',n) bilayer quantum Hall states on Thin Cylinders.
Physical review letters, 2008Co-Authors: Alexander Seidel, Kun YangAbstract:The Halperin (m, m', n) bilayer quantum Hall states are studied on Thin Cylinders. In this limit, charge-density-wave patterns emerge that are characteristic of the underlying quantum Hall state. The general patterns are worked out from a variant of the plasma analogy. Torus degeneracies are recovered, and for some important special cases a connection to well-known spin chain physics is made. By including interlayer tunneling, we also work out the critical behavior of a possible phase transition between the (331) state and the non-Abelian Moore-Read state in the Thin Cylinder limit.
O R Tutty - One of the best experts on this subject based on the ideXlab platform.
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flow along a long Thin Cylinder
Journal of Fluid Mechanics, 2008Co-Authors: O R TuttyAbstract:Two different approaches have been used to calculate turblent flow along a long Thin culinder where the flow is aligned with the Cylinder. A boundary-layer code is used to predict the mean flow for very long Cylinders (length to ratio of up to O(106)), with the effects of the turbulence estimated through a turbulence model. Detailed comparison with experimental results shows that the mean properties of the flow are predicted wiThin experimental accuracy. The boundary-layer model predicts that, sufficiently far downstream, the surface shear stress will be (almost) constant. This is consistent with experimental results from long Cylinders in the form of sonar arrays. A periodic Navier-Stokes problem is formulated, and solutions generated for the boundary-layer model and experiments. Strongly turbulent flow occurs only near the surface of the Cylinder, with relatively weak turbulence over most of the boundary layer. For a thick boundary layer with the boundary-layer thickness much larger than the Cylinder radius, the mean flow is effectively constant near the surface, in both temporal and spatial frameworks, while the outer flow continues to develop in time or space. Calculations of the circumferentially averaged surface pressure spectrum sho that, in physical terms, as the radius of the Cylinder decreases, the surface noise from the turbulence increases, with the maximum noise at a Reynolds number of O(103). An increase in noise with a decrease in radius (Reynolds number) is consistent with experimental results.
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boundary layer flow on a long Thin Cylinder
Physics of Fluids, 2002Co-Authors: O R Tutty, W G Price, A T ParsonsAbstract:The development of the boundary layer along a long Thin Cylinder aligned with the flow is considered. Numerical solutions are presented and compared with previous asymptotic results. Very near the leading edge the flow is given by the Blasius solution for a flat plate. However, there is soon a significant deviation from Blasius flow, with a Thinner boundary layer and higher wall shear stress. Linear normal mode stability of the flow is investigated. It is found that for Reynolds numbers less than a critical value of 1060 the flow is unconditionally stable. Also, axisymmetric modes are only the fourth least stable modes for this problem, with the first three three-dimensional modes all having a lower critical Reynolds number. Further, for Reynolds numbers above the critical value, the flow is unstable only for a finite distance, and returns to stability sufficiently far downstream.
P. Z. Bar-yoseph - One of the best experts on this subject based on the ideXlab platform.
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Spectral strip analysis for composite Cylinders subjected to lateral impact
Computational Mechanics, 1996Co-Authors: D. Ben-david, P. Z. Bar-yosephAbstract:An efficient computational method, combining the spectral element and the finite-strip method (spectral-strip) is developed in order to obtain numerical results to time dependent problems of cylindrical composite structures subjected to lateral impact, wiThin moderate CPU times. The finite strip method is applied to cylindrical structures uses global interpolation in the circumferential direction, and spectral emenents in the meridional cross section. A term superposition solution is obtained, where every iteration refines the solution and is independent of former iterations. In this manner, a full three-dimensional solution to the problem of the dynamic response of cross-ply cylindrical composite shells subjected to a lateral impact, is obtained. The stability and the accuracy of the method are examined. The main goal is to predict the damage caused by a high velocity non penetrating impact of microparticles. Two types of shells are studied—Thin and thick cross-ply laminates. The effect of curvature on a high velocity impact is studied. Also, the stress field obtained by the finite element code is investigated and damage evaluation is discussed. The present work focuses on moderate and high velocity impacts and therefore the force duration is of the order of the through-the-thickness propagation time, causing the imapct region to be in tension due to the reflected stress wave. The results demonstrate the dilatational compression wave traverses the shell thickness as a result of the impact and the dilatational tension wave reflected from the interior free surface as well as the propagation of shear waves in different directions. Using failure criteria, one can find that the compressive stress wave causes matrix cracking and the tensile stress wave causes both delamination and matrix cracking. It is shown that for a Thin Cylinder, the impact phenomenon is concentrated near the striking region while for a thick-walled Cylinder the results of the impact are visible in points far from the striking point as well. The interference of the stress waves that circumevent the Cylinder create other points of local maxima for the equivalent stresses. The code written for the finite element solution embloys the object oriented programming through the C++ language. A special matrix class is developed to perform various linear algebra operations.
Alexande Rohrbach - One of the best experts on this subject based on the ideXlab platform.
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5d tracking of a nanorod in a focused laser beam a theoretical concept
Optics Express, 2014Co-Authors: Markus Griesshamme, Alexande RohrbachAbstract:Back-focal plane (BFP) interferometry is a very fast and precise method to track the 3D position of a sphere wiThin a focused laser beam using a simple quadrant photo diode (QPD). Here we present a concept of how to track and recover the 5D state of a cylindrical nanorod (3D position and 2 tilt angles) in a laser focus by analyzing the interference of unscattered light and light scattered at the Cylinder. The analytical theoretical approach is based on Rayleigh-Gans scattering together with a local field approximation for an infinitely Thin Cylinder. The approximated BFP intensities compare well with those from a more rigorous numerical approach. It turns out that a displacement of the Cylinder results in a modulation of the BFP intensity pattern, whereas a tilt of the Cylinder results in a shift of this pattern. We therefore propose the concept of a local QPD in the BFP of a detection lens, where the QPD center is shifted by the angular coordinates of the Cylinder tilt.
D. Ben-david - One of the best experts on this subject based on the ideXlab platform.
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Spectral strip analysis for composite Cylinders subjected to lateral impact
Computational Mechanics, 1996Co-Authors: D. Ben-david, P. Z. Bar-yosephAbstract:An efficient computational method, combining the spectral element and the finite-strip method (spectral-strip) is developed in order to obtain numerical results to time dependent problems of cylindrical composite structures subjected to lateral impact, wiThin moderate CPU times. The finite strip method is applied to cylindrical structures uses global interpolation in the circumferential direction, and spectral emenents in the meridional cross section. A term superposition solution is obtained, where every iteration refines the solution and is independent of former iterations. In this manner, a full three-dimensional solution to the problem of the dynamic response of cross-ply cylindrical composite shells subjected to a lateral impact, is obtained. The stability and the accuracy of the method are examined. The main goal is to predict the damage caused by a high velocity non penetrating impact of microparticles. Two types of shells are studied—Thin and thick cross-ply laminates. The effect of curvature on a high velocity impact is studied. Also, the stress field obtained by the finite element code is investigated and damage evaluation is discussed. The present work focuses on moderate and high velocity impacts and therefore the force duration is of the order of the through-the-thickness propagation time, causing the imapct region to be in tension due to the reflected stress wave. The results demonstrate the dilatational compression wave traverses the shell thickness as a result of the impact and the dilatational tension wave reflected from the interior free surface as well as the propagation of shear waves in different directions. Using failure criteria, one can find that the compressive stress wave causes matrix cracking and the tensile stress wave causes both delamination and matrix cracking. It is shown that for a Thin Cylinder, the impact phenomenon is concentrated near the striking region while for a thick-walled Cylinder the results of the impact are visible in points far from the striking point as well. The interference of the stress waves that circumevent the Cylinder create other points of local maxima for the equivalent stresses. The code written for the finite element solution embloys the object oriented programming through the C++ language. A special matrix class is developed to perform various linear algebra operations.
