1,741 research outputs found
Dynamic vs Oblivious Routing in Network Design
Consider the robust network design problem of finding a minimum cost network
with enough capacity to route all traffic demand matrices in a given polytope.
We investigate the impact of different routing models in this robust setting:
in particular, we compare \emph{oblivious} routing, where the routing between
each terminal pair must be fixed in advance, to \emph{dynamic} routing, where
routings may depend arbitrarily on the current demand. Our main result is a
construction that shows that the optimal cost of such a network based on
oblivious routing (fractional or integral) may be a factor of
\BigOmega(\log{n}) more than the cost required when using dynamic routing.
This is true even in the important special case of the asymmetric hose model.
This answers a question in \cite{chekurisurvey07}, and is tight up to constant
factors. Our proof technique builds on a connection between expander graphs and
robust design for single-sink traffic patterns \cite{ChekuriHardness07}
Stokes phenomenon and matched asymptotic expansions
This paper describes the use of matched asymptotic expansions to illuminate the description of functions exhibiting Stokes phenomenon. In particular the approach highlights the way in which the local structure and the possibility of finding Stokes multipliers explicitly depend on the behaviour of the coefficients of the relevant asymptotic expansions
On the distribution of the nodal sets of random spherical harmonics
We study the length of the nodal set of eigenfunctions of the Laplacian on
the \spheredim-dimensional sphere. It is well known that the eigenspaces
corresponding to \eigval=n(n+\spheredim-1) are the spaces \eigspc of
spherical harmonics of degree , of dimension \eigspcdim. We use the
multiplicity of the eigenvalues to endow \eigspc with the Gaussian
probability measure and study the distribution of the \spheredim-dimensional
volume of the nodal sets of a randomly chosen function. The expected volume is
proportional to \sqrt{\eigval}. One of our main results is bounding the
variance of the volume to be O(\frac{\eigval}{\sqrt{\eigspcdim}}).
In addition to the volume of the nodal set, we study its Leray measure. For
every , the expected value of the Leray measure is .
We are able to determine that the asymptotic form of the variance is
\frac{const}{\eigspcdim}.Comment: 47 pages, accepted for publication in the Journal of Mathematical
Physics. Lemmas 2.5, 2.11 were proved for any dimension, some other,
suggested by the referee, modifications and corrections, were mad
Scale-Invariant Curvature Fluctuations from an Extended Semiclassical Gravity
We present an extension of the semiclassical Einstein equations which couples
n-point correlation functions of a stochastic Einstein tensor to the n-point
functions of the quantum stress-energy tensor. We apply this extension to
calculate the quantum fluctuations during an inflationary period, where we take
as a model a massive conformally coupled scalar field on a perturbed de Sitter
space and describe how a renormalization independent, almost-scale-invariant
power spectrum of the scalar metric perturbation is produced. Furthermore, we
discuss how this model yields a natural basis for the calculation of
non-Gaussianities of the considered metric fluctuations.Comment: 16 pages, 2 figures; final versio
Correlated exponential functions in high precision calculations for diatomic molecules
Various properties of the general two-center two-electron integral over the
explicitly correlated exponential function are analyzed for the potential use
in high precision calculations for diatomic molecules. A compact one
dimensional integral representation is found, which is suited for the numerical
evaluation. Together with recurrence relations, it makes possible the
calculation of the two-center two-electron integral with arbitrary powers of
electron distances. Alternative approach via the Taylor series in the
internuclear distance is also investigated. Although numerically slower, it can
be used in cases when recurrences lose stability. Separate analysis is devoted
to molecular integrals with integer powers of interelectronic distances
and the vanishing corresponding nonlinear parameter. Several methods
of their evaluation are proposed.Comment: 26 pages, includes two tables with exemplary calculation
Quasi-Normal Modes of a Schwarzschild White Hole
We investigate perturbations of the Schwarzschild geometry using a
linearization of the Einstein vacuum equations within a Bondi-Sachs, or null
cone, formalism. We develop a numerical method to calculate the quasi-normal
modes, and present results for the case . The values obtained are
different to those of a Schwarzschild black hole, and we interpret them as
quasi-normal modes of a Schwarzschild white hole.Comment: 5 pages, 4 Figure
Vector and tensor perturbations in Horava-Lifshitz cosmology
We study cosmological vector and tensor perturbations in Horava-Lifshitz
gravity, adopting the most general Sotiriou-Visser-Weinfurtner generalization
without the detailed balance but with projectability condition. After deriving
the general formulas in a flat FRW background, we find that the vector
perturbations are identical to those given in general relativity. This is true
also in the non-flat cases. For the tensor perturbations, high order
derivatives of the curvatures produce effectively an anisotropic stress, which
could have significant efforts on the high-frequency modes of gravitational
waves, while for the low-frenquency modes, the efforts are negligible. The
power spectrum is scale-invariant in the UV regime, because of the particular
dispersion relations. But, due to lower-order corrections, it will eventually
reduce to that given in GR in the IR limit. Applying the general formulas to
the de Sitter and power-law backgrounds, we calculate the power spectrum and
index, using the uniform approximations, and obtain their analytical
expressions in both cases.Comment: Correct some typos and add new references. Version to be published in
Physical Reviews
Nearsightedness of Electronic Matter in One Dimension
The concept of nearsightedeness of electronic matter (NEM) was introduced by
W. Kohn in 1996 as the physical principal underlining Yang's electronic
structure alghoritm of divide and conquer. It describes the fact that, for
fixed chemical potential, local electronic properties at a point , like the
density , depend significantly on the external potential only at
nearby points. Changes of that potential, {\it no matter how large},
beyond a distance , have {\it limited} effects on local electronic
properties, which tend to zero as function of . This remains true
even if the changes in the external potential completely surrounds the point
. NEM can be quantitatively characterized by the nearsightedness range,
, defined as the smallest distance from ,
beyond which {\it any} change of the external potential produces a density
change, at , smaller than a given . The present paper gives a
detailed analysis of NEM for periodic metals and insulators in 1D and includes
sharp, explicit estimates of the nearsightedness range. Since NEM involves
arbitrary changes of the external potential, strong, even qualitative changes
can occur in the system, such as the discretization of energy bands or the
complete filling of the insulating gap of an insulator with continuum spectrum.
In spite of such drastic changes, we show that has only a limited
effect on the density, which can be quantified in terms of simple parameters of
the unperturbed system.Comment: 10 pages, 9 figure
Statistical physics of power fluctuations in mode locked lasers
We present an analysis of the power fluctuations in the statistical steady
state of a passively mode locked laser. We use statistical light-mode theory to
map this problem to that of fluctuations in a reference equilibrium statistical
physics problem, and in this way study the fluctuations non-perturbatively. The
power fluctuations, being non-critical, are Gaussian and proportional in
amplitude to the inverse square root of the number of degrees of freedom. We
calculate explicit analytic expressions for the covariance matrix of the
overall, pulse and cw power variables, providing complete information on the
single-time power distribution in the laser, and derive a set of
fluctuation-dissipation relations between them and the susceptibilities of the
steady-state quantities.Comment: 7 pages, 1 figure, RevTe
Full-analytic frequency-domain 1pN-accurate gravitational wave forms from eccentric compact binaries
The article provides ready-to-use 1pN-accurate frequency-domain gravitational
wave forms for eccentric nonspinning compact binaries of arbitrary mass ratio
including the first post-Newtonian (1pN) point particle corrections to the
far-zone gravitational wave amplitude, given in terms of tensor spherical
harmonics. The averaged equations for the decay of the eccentricity and growth
of radial frequency due to radiation reaction are used to provide stationary
phase approximations to the frequency-domain wave forms.Comment: 28 pages, submitted to PR
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