164,757 research outputs found

### Nonuniversal Effects in the Homogeneous Bose Gas

Effective field theory predicts that the leading nonuniversal effects in the
homogeneous Bose gas arise from the effective range for S-wave scattering and
from an effective three-body contact interaction. We calculate the leading
nonuniversal contributions to the energy density and condensate fraction and
compare the predictions with results from diffusion Monte Carlo calculations by
Giorgini, Boronat, and Casulleras. We give a crude determination of the
strength of the three-body contact interaction for various model potentials.
Accurate determinations could be obtained from diffusion Monte Carlo
calculations of the energy density with higher statistics.Comment: 24 pages, RevTex, 5 ps figures, included with epsf.te

### On the extension of 2- polynomials

Let $X$ be a three dimensional real Banach space. Ben\'itez and Otero \cite
{BeO} showed that if the unit ball of $X$ is is an intersection of two
ellipsoids, then every 2-polynomial defined in a linear subspace of $X$ can be
extended to $X$ preserving the norm. In this article, we extend this result to
any finite dimensional Banach space

### A remark on contraction semigroups on Banach spaces

Let $X$ be a complex Banach space and let $J:X \to X^*$ be a duality section
on $X$ (i.e. $\langle x,J(x)\rangle=\|J(x)\|\|x\|=\|J(x)\|^2=\|x\|^2$). For any
unit vector $x$ and any ($C_0$) contraction semigroup $T=\{e^{tA}:t \geq 0\}$,
Goldstein proved that if $X$ is a Hilbert space and if $|\langle T(t)
x,J(x)\rangle| \to 1$ as $t \to \infty$, then $x$ is an eigenvector of $A$
corresponding to a purely imaginary eigenvalue. In this article, we prove the
similar result holds if $X$ is a strictly convex complex Banach space

### Joint Vertex Degrees in an Inhomogeneous Random Graph Model

In a random graph, counts for the number of vertices with given degrees will
typically be dependent. We show via a multivariate normal and a Poisson process
approximation that, for graphs which have independent edges, with a possibly
inhomogeneous distribution, only when the degrees are large can we reasonably
approximate the joint counts as independent. The proofs are based on Stein's
method and the Stein-Chen method with a new size-biased coupling for such
inhomogeneous random graphs, and hence bounds on distributional distance are
obtained. Finally we illustrate that apparent (pseudo-) power-law type
behaviour can arise in such inhomogeneous networks despite not actually
following a power-law degree distribution.Comment: 30 pages, 9 figure

### Quantum Transport Calculations Using Periodic Boundary Conditions

An efficient new method is presented to calculate the quantum transports
using periodic boundary conditions. This method allows the use of conventional
ground state ab initio programs without big changes. The computational effort
is only a few times of a normal ground state calculation, thus it makes
accurate quantum transport calculations for large systems possible.Comment: 9 pages, 6 figure

### On the dispersion management of fluorite whispering-gallery mode resonators for Kerr optical frequency comb generation in the telecom and mid-infrared range

Optical whispering gallery mode (WGM) resonators have been very attracting
platforms for versatile Kerr frequency comb generations. We report a systematic
study on the material dispersion of various optical materials that are capable
of supporting quality factors above $10^9$. Using an analytical approximation
of WGM resonant frequencies in disk resonators, we investigate the effect of
the geometry and transverse mode order on the total group-velocity dispersion
($GVD$). We demonstrate that the major radii and the radial mode indices play
an important role in tailoring the $GVD$ of WGM resonators. In particular, our
study shows that in WGM disk-resonators, the polar families of modes have very
similar $GVD$, while the radial families of modes feature dispersion values
that can differ by up to several orders of magnitude. The effect of these giant
dispersion shifts are experimentally evidenced in Kerr comb generation with
magnesium fluoride. From a more general perspective, this critical feature
enables to push the zero-dispersion wavelength of fluorite crystals towards the
mid-infrared (mid-IR) range, thereby allowing for efficient Kerr comb
generation in that spectral range. We show that barium fluoride is the most
interesting crystal in this regard, due to its zero dispersion wavelength
($ZDW$) at $1.93 \rm{\mu m}$ and an optimal dispersion profile in the mid-IR
regime. We expect our results to facilitate the design of different platforms
for Kerr frequency comb generations in both telecommunication and mid-IR
spectral ranges

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