165,572 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 be a three dimensional real Banach space. Ben\'itez and Otero \cite
{BeO} showed that if the unit ball of is is an intersection of two
ellipsoids, then every 2-polynomial defined in a linear subspace of can be
extended to 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 be a complex Banach space and let be a duality section
on (i.e. ). For any
unit vector and any () contraction semigroup ,
Goldstein proved that if is a Hilbert space and if as , then is an eigenvector of
corresponding to a purely imaginary eigenvalue. In this article, we prove the
similar result holds if 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
An experimental study of a self-confined flow with ring-vorticity distribution
A new form of self-confined flow was investigated in which a recirculation zone forms away from any solid boundary. An inviscid flow analysis indicated that in a purely meridional axisymmetric flow a stationary, spherical, self-confined region should occur in the center of a streamlined divergent-convergent enlargement zone. The spherical confinement region would be at rest and at constant pressure. Experimental investigations were carried out in a specially built test apparatus to establish the desired confined flow. The streamlined divergent-convergent interior shape of the test section was fabricated according to the theoretical calculation for a particular streamline. The required inlet vorticity distribution was generated by producing a velocity profile with a shaped gauze screen in the straight pipe upstream of the test section. Fluid speed and turbulence intensity were measured with a constant-temperature hot-wire anemometer system. The measured results indicated a very orderly and stable flow field
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
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