101,392 research outputs found
Computing the Casimir energy using the point-matching method
We use a point-matching approach to numerically compute the Casimir
interaction energy for a two perfect-conductor waveguide of arbitrary section.
We present the method and describe the procedure used to obtain the numerical
results. At first, our technique is tested for geometries with known solutions,
such as concentric and eccentric cylinders. Then, we apply the point-matching
technique to compute the Casimir interaction energy for new geometries such as
concentric corrugated cylinders and cylinders inside conductors with focal
lines.Comment: 11 pages, 18 figure
Superconductive proximity effect in interacting disordered conductors
We present a general theory of the superconductive proximity effect in
disordered normal--superconducting (N-S) structures, based on the recently
developed Keldysh action approach. In the case of the absence of interaction in
the normal conductor we reproduce known results for the Andreev conductance G_A
at arbitrary relation between the interface resistance R_T and the diffusive
resistance R_D. In two-dimensional N-S systems, electron-electron interaction
in the Cooper channel of normal conductor is shown to strongly affect the value
of G_A as well as its dependence on temperature, voltage and magnetic field. In
particular, an unusual maximum of G_A as a function of temperature and/or
magnetic field is predicted for some range of parameters R_D and R_T. The
Keldysh action approach makes it possible to calculate the full statistics of
charge transfer in such structures. As an application of this method, we
calculate the noise power of an N-S contact as a function of voltage,
temperature, magnetic field and frequency for arbitrary Cooper repulsion in the
normal metal and arbitrary values of the ratio R_D/R_T.Comment: RevTeX, 28 pages, 18 PostScript figures; added and updated reference
Accurate 2.5-D boundary element method for conductive media
The solution of the time-harmonic Maxwell equations using a boundary element method, for 2-D geometries illuminated by arbitrary 3-D excitations, gives rise to numerical difficulties if highly conductive media are present. In particular, the interaction integrals arising in the method of moments involve kernels that strongly oscillate in space and, at the same time, decay exponentially. We present an accurate method to tackle these issues over a very broad conductivity range (from lossy dielectric to conductor skin-effect regime), for both magnetic and nonmagnetic conductors. Important applications are the modal analysis of waveguides with nonperfect conductors, scattering problems, and shielding problems with enclosures with arbitrary permeability and conductivity and 3-D noise sources
Electron-electron interaction corrections to the thermal conductivity in disordered conductors
We evaluate the electron-electron interaction corrections to the electronic
thermal conductivity in a disordered conductor in the diffusive regime. We use
a diagrammatic many-body method analogous to that of Altshuler and Aronov for
the electrical conductivity. We derive results in one, two and three dimensions
for both the singlet and triplet channels, and in all cases find that the
Wiedemann-Franz law is violated.Comment: 8 pages, 2 figures Typos corrected in formulas (15) and (A.4) and
Table 1; discussion of previous work in introduction extended; reference
clarifying different definitions of parameter F adde
Spin polarization in a T-shape conductor induced by strong Rashba spin-orbit coupling
We investigate numerically the spin polarization of the current in the
presence of Rashba spin-orbit interaction in a T-shaped conductor proposed by
A.A. Kiselev and K.W. Kim (Appl. Phys. Lett. {\bf 78} 775 (2001)). The
recursive Green function method is used to calculate the three terminal spin
dependent transmission probabilities. We focus on single-channel transport and
show that the spin polarization becomes nearly 100 % with a conductance close
to for sufficiently strong spin-orbit coupling. This is interpreted
by the fact that electrons with opposite spin states are deflected into an
opposite terminal by the spin dependent Lorentz force. The influence of the
disorder on the predicted effect is also discussed. Cases for multi-channel
transport are studied in connection with experiments
Numerical Simulation of Vortex-Induced Vibrations of Riser-Conductor Systems Including Soil-Structure Interactions
A fully three-dimensional numerical approach for analyzing deepwater drilling riser-conductor system vortex-induced vibrations (VIV) including soil-structure interactions (SSI) is presented. The drilling riser-conductor system is modeled as a tensioned beam with linearly distributed tension and is solved by a fully implicit discretization scheme. The fluid field around the riser-conductor system is obtained by Finite-Analytic Navier-Stokes (FANS) code, which numerically solves the unsteady Navier-Stokes equations. The SSI is taken into account by modeling the lateral soil resistance force according to p-y curves. Overset grid method is adopted to mesh the fluid domain with approximately 0.86 million computational points in total. Meshes are much finer in regions close to the pipe outer boundary and coarser in the far-field regions. A partitioned Fluid-Structure Interaction (FSI) method is achieved by communication between the fluid solver and pipe motion solver.
A pipe VIV simulation without SSI is firstly presented and served as a benchmark case for following simulations. Two SSI models based on a popular p-y curve are then applied to the VIV simulations. Results from those simulations are compared and analyzed. The effects of two key soil properties on the VIV simulations of riser-conductor systems are then studied. Conclusions are made and suggestions are given for VIV analysis of riser-conductor systems and future researc
Superconducting proximity effects in metals with a repulsive pairing interaction
Studies of the superconducting proximity effect in normal
conductor/superconductor junctions almost universally assume no
effective electron-electron coupling in the region. While such an
approximation leads to a simple description of the proximity effect, it is
unclear how it could be rigorously justified. We reveal a much more complex
picture of the proximity effect in bilayers, where is a clean s-wave
BCS superconductor and is a simple metal with a repulsive effective
electron coupling. We elucidate the proximity effect behavior using a highly
accurate method to self-consistently solve the Bogoliubov-deGennes equations.
We present our results for a wide range of values of the interface scattering,
the Fermi wave vector mismatch, the temperature, and the ratio of the
effective interaction strengths in the and region. We find that the
repulsive interaction, represented by a negative , strongly alters the
signatures of the proximity effect as can be seen in the spatial dependence of
the Cooper pair amplitude and the pair potential, as well as in the local
density of states near the interface.Comment: 12 pages, including 10 figures. To appear in Phys. Rev.
Computer aided design of printed wiring boards
A method is described for the computer-aided layout of
printed wiring boards. The type of board considered is a single
sided board containing discrete components. The required input for
the layout algorithm is coded from the relevant circuit diagram,
together with a description of the component dimensions. This
information is then stored within the computer in a data structure.
The circuit components and their interconnections are represented
by a set of nodes and branches.
The principles of graph theory are used to construct an
abstract model of the layout. A number of the nodes and branches
of the circuit are first used in the construction of a planar graph.
A method is then described for inserting the remaining branches into
the graph to form a "pseudo planar graph". This represents a set of
components and conductor paths which can be laid out on a single
sided board without intersections. The number of conductor
crossings is thus minimised before the actual layout commences.
An algorithm is then described for automatically constructing
a board layout from the pseudo planar graph. The relative interconnections
are already known so the placement of components and
routing of conductor paths can proceed simultaneously. The layout
is therefore constructed in a series of logical steps working across
from one edge of the board to the other. This approach contrasts
with the more usual methods of layout in which components are
placed first, followed by a search for conductor routes.
The layout algorithm is also provided with facilities for
man-machine interaction by means of a graphical display and light
pen. Interaction allows the user to alter the positions of components during the construction of the layout. Thus the skill
and experience of the user can be combined with the speed and
accuracy of the automatic algorithm. Interaction also enables
special conditions to be incorporated into the layout which would
otherwise entail considerable programming effort.
Three different circuits are used to test the layout
algorithm. The results are shown for layouts constructed both
automatically and by the use of interaction. One layout is also
compared with a manually-produced layout of the same circuit. The
results show that a feasible method has been developed for the
layout of printed wiring boards by computer. Comparable results
are produced in considerably less time than normal layout methods
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