2,026 research outputs found
A Typology for Quantum Hall Liquids
There is a close analogy between the response of a quantum Hall liquid (QHL)
to a small change in the electron density and the response of a superconductor
to an externally applied magnetic flux - an analogy which is made concrete in
the Chern-Simons Landau-Ginzburg (CSLG) formulation of the problem. As the
Types of superconductor are distinguished by this response, so too for QHLs: a
typology can be introduced which is, however, richer than that in
superconductors owing to the lack of any time-reversal symmetry relating
positive and negative fluxes. At the boundary between Type I and Type II
behavior, the CSLG action has a "Bogomol'nyi point," where the quasi-holes
(vortices) are non-interacting - at the microscopic level, this corresponds to
the behavior of systems governed by a set of model Hamiltonians which have been
constructed to render exact a large class of QHL wavefunctions. All Types of
QHLs are capable of giving rise to quantized Hall plateaux.Comment: 4 +epsilon pages, 1 figure; v2 has added references and minor
changes, version published in Phys. Rev. B. (Rapid Communications
Drag resistance of 2D electronic microemulsions
Motivated by recent experiments of Pillarisetty {\it et al}, \prl {\bf 90},
226801 (2003), we present a theory of drag in electronic double layers at low
electron concentration. We show that the drag effect in such systems is
anomolously large, it has unusual temperature and magnetic field dependences
accociated with the Pomeranchuk effect, and does not vanish at zero
temperature
Controlling the Sign of Magnetoconductance in Andreev Quantum Dots
We construct a theory of coherent transport through a ballistic quantum dot
coupled to a superconductor. We show that the leading-order quantum correction
to the two-terminal conductance of these Andreev quantum dots may change sign
depending on (i) the number of channels carried by the normal leads or (ii) the
magnetic flux threading the dot. In contrast, spin-orbit interaction may affect
the magnitude of the correction, but not always its sign. Experimental
signatures of the effect include a non-monotonic magnetoconductance curve and a
transition from an insulator-like to a metal-like temperature dependence of the
conductance. Our results are applicable to ballistic or disordered dots.Comment: Final version (4pages 3figs)- improved presentation and fig 3, and
updated reference
Hamiltonian Frenet-Serret dynamics
The Hamiltonian formulation of the dynamics of a relativistic particle
described by a higher-derivative action that depends both on the first and the
second Frenet-Serret curvatures is considered from a geometrical perspective.
We demonstrate how reparametrization covariant dynamical variables and their
projections onto the Frenet-Serret frame can be exploited to provide not only a
significant simplification of but also novel insights into the canonical
analysis. The constraint algebra and the Hamiltonian equations of motion are
written down and a geometrical interpretation is provided for the canonical
variables.Comment: Latex file, 14 pages, no figures. Revised version to appear in Class.
Quant. Gra
Mesoscopic mechanism of adiabatic charge transport
We consider adiabatic charge transport through mesoscopic metallic samples
caused by a periodically changing external potential. We find that both the
amplitude and the sign of the charge transferred through a sample per period
are random sample specific quantities. The characteristic magnitude of the
charge is determined by the quantum interference.Comment: 4 pages, 2 figure
Mesoscopic mechanism of exchange interaction in magnetic multilayers
We discuss a mesoscopic mechanism of exchange interaction in
ferromagnet-normal metal-ferromagnet multilayers. We show that in the case when
the metal's thickness is larger than the electron mean free path, the relative
orientation of magnetizations in the ferromagnets is perpendicular. The
exchange energy between ferromagnets decays with the metal thickness as a power
law
Defects and boundary layers in non-Euclidean plates
We investigate the behavior of non-Euclidean plates with constant negative
Gaussian curvature using the F\"oppl-von K\'arm\'an reduced theory of
elasticity. Motivated by recent experimental results, we focus on annuli with a
periodic profile. We prove rigorous upper and lower bounds for the elastic
energy that scales like the thickness squared. In particular we show that are
only two types of global minimizers -- deformations that remain flat and saddle
shaped deformations with isolated regions of stretching near the edge of the
annulus. We also show that there exist local minimizers with a periodic profile
that have additional boundary layers near their lines of inflection. These
additional boundary layers are a new phenomenon in thin elastic sheets and are
necessary to regularize jump discontinuities in the azimuthal curvature across
lines of inflection. We rigorously derive scaling laws for the width of these
boundary layers as a function of the thickness of the sheet
Spacetime Embedding Diagrams for Black Holes
We show that the 1+1 dimensional reduction (i.e., the radial plane) of the
Kruskal black hole can be embedded in 2+1 Minkowski spacetime and discuss how
features of this spacetime can be seen from the embedding diagram. The purpose
of this work is educational: The associated embedding diagrams may be useful
for explaining aspects of black holes to students who are familiar with special
relativity, but not general relativity.Comment: 22 pages, 21 figures, RevTex. To be submitted to the American Journal
of Physics. Experts will wish only to skim appendix A and to look at the
pictures. Suggested Maple code is now compatible with MapleV4r
Evaluation of adaptive reserve of the vascular system of the abdominal cavity in healthy children and children with cystic fibrosis
Objective: to develop the methodology to assess the adaptive reserve of the vascular system of the abdominal cavity in children based on the determination of hemodynamic parameters in abdominal arteries and veins in the dynamics of the functional tests. Materials and methods: the study included 48 healthy children and 33 children with a mixed form of cystic fibrosis from 4 to 17 years old. Doppler method determined the parameters of blood circulation in the abdominal vessels (abdominal segment of the aorta, celiac trunk, superior mesenteric, common hepatic, the splenic artery, the lower hollow, portal, and splenic vein). Adaptive reserve of the vascular system was assessed using postprandial and respiratory testes. Results: eating and breath holding in healthy children caused a dilatation of the abdominal vessels and a significant increase in volumetric blood flow velocity. In the presence of liver damage, a decrease of adaptive reserve of regional hemodynamics of the abdominal cavity was registered. The main changing was a decrease in the degree of physiological dilation of the abdominal vessels and the lack of adequate growth of the values of volumetric blood flow velocity after performing the functional tests. Conclusions: reduction of adaptive reserve of the vascular system of the abdomen is an early sign of liver injury in cystic fibrosis and precedes the appearance of structural defects of the body
A theory of \pi/2 superconducting Josephson junctions
We consider theoretically a Josephson junction with a superconducting
critical current density which has a random sign along the junction's surface.
We show that the ground state of the junction corresponds to the phase
difference equal to \pi/2. Such a situation can take place in superconductor-
ferromagnet junction
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