6,639 research outputs found
Numerical Regularization of Electromagnetic Quantum Fluctuations in Inhomogeneous Dielectric Media
Electromagnetic Casimir stresses are of relevance to many technologies based
on mesoscopic devices such as MEMS embedded in dielectric media, Casimir
induced friction in nano-machinery, micro-fluidics and molecular electronics.
Computation of such stresses based on cavity QED generally require numerical
analysis based on a regularization process. A new scheme is described that has
the potential for wide applicability to systems involving realistic
inhomogeneous media. From a knowledge of the spectrum of the stationary modes
of the electromagnetic field the scheme is illustrated by estimating
numerically the Casimir stress on opposite faces of a pair of perfectly
conducting planes separated by a vacuum and the change in this result when the
region between the plates is filled with an incompressible inhomogeneous
non-dispersive dielectric.Comment: 5 pages, 2 figures, submitted to PR
Variation of the first Hilbert coefficients of parameters with a common integral closure
A problem posed by Wolmer V. Vasconcelos on the variation of the first
Hilbert coefficients of parameter ideals with a common integral closure in a
local ring is studied. Affirmative answers are given and counterexamples are
explored as well
Selection and photometric properties of K+A galaxies
Two different simple measurements of galaxy star formation rate with
different timescales are compared empirically on fiber spectra of
galaxies with mag taken from the Sloan Digital Sky Survey in the
redshift range : a ratio \Aamp / \Kamp found by fitting a linear
sum of an average old stellar poplulation spectrum (\Kamp) and average A-star
spectrum (\Aamp) to the galaxy spectrum, and the equivalent width (EW) of the
\Halpha emission line. The two measures are strongly correlated, but there is
a small clearly separated population of outliers from the median correlation
that display excess \Aamp /\Kamp relative to \Halpha EW. These ``K+A'' (or
``E+A'') galaxies must have dramatically decreased their star-formation rates
over the last Gyr. The K+A luminosity distribution is very similar to
that of the total galaxy population. The K+A population appears to be
bulge-dominated, but bluer and higher surface-brightness than normal
bulge-dominated galaxies; it appears that K+A galaxies will fade with time into
normal bulge-dominated galaxies. The inferred rate density for K+A galaxy
formation is at redshift .
These events are taking place in the field; K+A galaxies don't primarily lie in
the high-density environments or clusters typical of bulge-dominated
populations.Comment: submitted to Ap
Realization of Strong Coupling Fixed Point in Multilevel Kondo Models
Impurity four- and six-level Kondo model, in which an ion is tunneling among
four- and six-stable points and interacting with surrounding conduction
electrons, are investigated by using the perturbative and numerical
renormalization group methods. It is shown that purely orbital Kondo effects
occur at low temperatures in these systems which are direct generalizations of
the Kondo effect in the so-called two-level system. This result offers a good
explanation for the enhanced and magnetically robust Sommerfeld coefficient
observed in SmOs_4Sb_12 and some other filled-skutterudites.Comment: 3 pages, 3 figures, for proceedings of ASR-WYP-2005. To be published
in Journal of Physical Society Japan supplemen
Aspects of quantum energy and stress in inhomogeneous unbounded dielectric continua
This article explores a number of issues associated with the problem of calculating and detecting electromagnetic quantum induced energy and stress in a stationary dielectric material with a smooth inhomogeneous polarizability. By concentrating on a particular system composed of an ENZ-type (epsilon-near-zero) meta-material, chosen to have a particular anisotropic and smooth inhomogeneous permittivity, confined in an infinitely long perfectly conducting open rectangular waveguide, we are able to deduce analytically from the source-free Maxwell’s equations and their boundary conditions a complete set of bounded harmonic electromagnetic evanescent eigen-modes and their associated eigen-frequencies. Since these solutions prohibit the existence of asymptotic scattering states in the guide, the application of the conventional Lifshitz approach to the Casimir stress problem becomes uncertain. An alternative approach is adopted based upon the spectral properties of the system and a regularization scheme constructed with direct applicability to more general systems composed of dielectrics with smooth inhomogeneous permittivities and open systems that may only admit evanescent modes. This more general scheme enables one, for the first time, to prescribe precise criteria for the extraction of finite quantum expectation values from regularized mode sums together with error bounds on these values, and is used to derive analytic or numeric results for regularized electromagnetic ground state expectation values in the guide
Efficient LZ78 factorization of grammar compressed text
We present an efficient algorithm for computing the LZ78 factorization of a
text, where the text is represented as a straight line program (SLP), which is
a context free grammar in the Chomsky normal form that generates a single
string. Given an SLP of size representing a text of length , our
algorithm computes the LZ78 factorization of in time
and space, where is the number of resulting LZ78 factors.
We also show how to improve the algorithm so that the term in the
time and space complexities becomes either , where is the length of the
longest LZ78 factor, or where is a quantity
which depends on the amount of redundancy that the SLP captures with respect to
substrings of of a certain length. Since where
is the alphabet size, the latter is asymptotically at least as fast as
a linear time algorithm which runs on the uncompressed string when is
constant, and can be more efficient when the text is compressible, i.e. when
and are small.Comment: SPIRE 201
Disentangling the Dynamical Mechanisms for Cluster Galaxy Evolution
The determination of the dynamical causes of the morphological Butcher-Oemler
(BO) effect, or the rapid transformation of a large population of late-type
galaxies to earlier Hubble types in the rich cluster environment between
intermediate redshifts and the local universe, has been an important unsolved
problem which is central to our understanding of the general problems of galaxy
formation and evolution. In this article, we survey the existing proposed
mechanisms for cluster galaxy transformation, and discuss their relevance and
limitations to the explanation of the morphological BO effect. A new infrared
diagnostic approach is devised to disentangle the relative importance of
several major physical mechanisms to account for the BO effect, and an example
of the first application of this procedure to a single rich, intermediate
redshift galaxy cluster is given to demonstrate the viability of this approach.
The preliminary result of this analysis favors the interaction-enhanced secular
evolution process as the major cause of the cluster-galaxy morphological
transformation. This conclusion is also supported by a wide range of other
published results which are assembled here to highlight their implications on a
coherent physical origin for the morphological BO effect.Comment: Accepted for publication in the PAS
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