77,603 research outputs found
Efficient Computation of Power, Force, and Torque in BEM Scattering Calculations
We present concise, computationally efficient formulas for several quantities
of interest -- including absorbed and scattered power, optical force (radiation
pressure), and torque -- in scattering calculations performed using the
boundary-element method (BEM) [also known as the method of moments (MOM)]. Our
formulas compute the quantities of interest \textit{directly} from the BEM
surface currents with no need ever to compute the scattered electromagnetic
fields. We derive our new formulas and demonstrate their effectiveness by
computing power, force, and torque in a number of example geometries. Free,
open-source software implementations of our formulas are available for download
online
Numerical methods for computing Casimir interactions
We review several different approaches for computing Casimir forces and
related fluctuation-induced interactions between bodies of arbitrary shapes and
materials. The relationships between this problem and well known computational
techniques from classical electromagnetism are emphasized. We also review the
basic principles of standard computational methods, categorizing them according
to three criteria---choice of problem, basis, and solution technique---that can
be used to classify proposals for the Casimir problem as well. In this way,
mature classical methods can be exploited to model Casimir physics, with a few
important modifications.Comment: 46 pages, 142 references, 5 figures. To appear in upcoming Lecture
Notes in Physics book on Casimir Physic
(Perturbed) Conformal Field Theory Applied To 2D Disordered Systems: An Introduction
We describe applications of (perturbed) conformal field theories to
two-dimensional disordered systems. We present various methods of study~: (i)
{\it A direct method} in which we compute the explicit disorder dependence of
the correlation functions for any sample of the disorder. This method seems to
be specific to two dimensions. The examples we use are disordered versions of
the Abelian and non-Abelian WZW models. We show that the disordered WZW model
over the Lie group \CG at level is equivalent at large impurity density
to the product of the WZW model over the coset space \CG^C/\CG at level
times an arbitrary number of copies of the original WZW model. (ii)
{\it The supersymmetric method} is introduced using the random bond Ising model
and the random Dirac theory as examples. In particular, we show that the
relevent algebra is the affine Lie superalgebra, an algebra with
zero superdimension. (iii) {\it The replica method} is introduced using the
random phase sine-Gordon model as example. We describe particularities of its
renormalization group flow. (iv) {\it A variationnal approach} is also
presented using the random phase sine-Gordon model as example. Lectures
presented at the '95 Cargese Summer School on "Low dimensional application of
quantum field theory".Comment: 41 pages, latex, uuencoded file with 2 figues include
Persistent Currents and Magnetization in two-dimensional Magnetic Quantum Systems
Persistent currents and magnetization are considered for a two-dimensional
electron (or gas of electrons) coupled to various magnetic fields.
Thermodynamic formulae for the magnetization and the persistent current are
established and the ``classical'' relationship between current and
magnetization is shown to hold for systems invariant both by translation and
rotation. Applications are given, including the point vortex superposed to an
homogeneous magnetic field, the quantum Hall geometry (an electric field and an
homogeneous magnetic field) and the random magnetic impurity problem (a random
distribution of point vortices).Comment: 27 pages latex, 1 figur
Extracting partial decay rates of helium from complex rotation: autoionizing resonances of the one-dimensional configurations
Partial autoionization rates of doubly excited one-dimensional helium in the
collinear Zee and eZe configuration are obtained by means of the complex
rotation method. The approach presented here relies on a projection of
back-rotated resonance wave functions onto singly ionized
channel wave functions and the computation of the corresponding particle
fluxes. In spite of the long-range nature of the Coulomb potential between the
electrons and the nucleus, an asymptotic region where the fluxes are stationary
is clearly observed. Low-lying doubly excited states are found to decay
predomintantly into the nearest single-ionization continuum. This approach
paves the way for a systematic analysis of the decay rates observed in
higher-dimensional models, and of the role of electronic correlations and
atomic structure in recent photoionization experiments
Hawking Radiation, Covariant Boundary Conditions and Vacuum States
The basic characteristics of the covariant chiral current are obtained from a
chiral effective action. These results are used to justify the covariant
boundary condition used in recent approaches
\cite{Isowilczek,Isoumtwilczek,shailesh,shailesh2,Banerjee} of computing the
Hawking flux from chiral gauge and gravitational anomalies. We also discuss a
connection of our results with the conventional calculation of nonchiral
currents and stress tensors in different (Unruh, Hartle-Hawking and Boulware)
states.Comment: 18 pages, no figures, minor changes, to appear in Phys. Rev.
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