5,612 research outputs found
Universal scaling in BCS superconductivity in two dimensions in non-s waves
The solutions of a renormalized BCS model are studied in two space dimensions
in , and waves for finite-range separable potentials. The gap
parameter, the critical temperature , the coherence length and the
jump in specific heat at as a function of zero-temperature condensation
energy exhibit universal scalings. In the weak-coupling limit, the present
model yields a small and large appropriate to those for high-
cuprates. The specific heat, penetration depth and thermal conductivity as a
function of temperature show universal scaling in and waves.Comment: 11 pages, LATEX, 4 postscript figures embedded using eps
Convergent variational calculation of positronium-hydrogen-atom scattering lengths
We present a convergent variational basis-set calculational scheme for
elastic scattering of positronium atom by hydrogen atom in S wave. Highly
correlated trial functions with appropriate symmetry are needed for achieving
convergence. We report convergent results for scattering lengths in atomic
units for both singlet () and triplet () states.Comment: 11 pages, 1 postscript figure, Accepted in J. Phys. B (Letter
Free expansion of fermionic dark solitons in a boson-fermion mixture
We use a time-dependent dynamical mean-field-hydrodynamic model to study the
formation of fermionic dark solitons in a trapped degenerate fermi gas mixed
with a Bose-Einstein condensate in a harmonic as well as a periodic
optical-lattice potential. The dark soliton with a "notch" in the probability
density with a zero at the minimum is simulated numerically as a nonlinear
continuation of the first vibrational excitation of the linear
mean-field-hydrodynamic equations, as suggested recently for pure bosons. We
study the free expansion of these dark solitons as well as the consequent
increase in the size of their central notch and discuss the possibility of
experimental observation of the notch after free expansion.Comment: 14 pages, 6 figure
Two phase transitions in (s+id)-wave Bardeen-Cooper-Schrieffer superconductivity
We establish universal behavior in temperature dependencies of some
observables in -wave BCS superconductivity in the presence of a weak
wave. There also could appear a second second-order phase transition. As
temperature is lowered past the usual critical temperature , a less
ordered superconducting phase is created in wave, which changes to a more
ordered phase in wave at (). The presence of two phase
transitions manifest in two jumps in specific heat at and . The
temperature dependencies of susceptibility, penetration depth, and thermal
conductivity also confirm the new phase transition.Comment: 6 pages, 5 post-script figures
Performance of a prototype active veto system using liquid scintillator for a dark matter search experiment
We report the performance of an active veto system using a liquid
scintillator with NaI(Tl) crystals for use in a dark matter search experiment.
When a NaI(Tl) crystal is immersed in the prototype detector, the detector tags
48% of the internal K-40 background in the 0-10 keV energy region. We also
determined the tagging efficiency for events at 6-20 keV as 26.5 +/- 1.7% of
the total events, which corresponds to 0.76 +/- 0.04 events/keV/kg/day.
According to a simulation, approximately 60% of the background events from U,
Th, and K radioisotopes in photomultiplier tubes are tagged at energies of 0-10
keV. Full shielding with a 40-cm-thick liquid scintillator can increase the
tagging efficiency for both the internal K-40 and external background to
approximately 80%.Comment: Submitted to Nuclear Instruments and Methods in Physics Research
Section
Universal behavior of a trapped Fermi superfluid in the BCS-unitarity crossover
From an extensive calculation of static properties of a trapped Fermi
superfluid at zero temperature using a density-functional formulation, we
demonstrate a universal behavior of its observables, such as energy, chemical
potential, radius etc., over the crossover from the BCS limit to unitarity
leading to scaling over many orders of magnitude in fermion number. This
scaling allows to predict the static properties of the system, with a large
number () of fermions, over the crossover with an error of 1-2%,
from the knowledge of those for a small number () of fermions.Comment: 6 page
Influence of high-order mechanics on simulation of glacier response to climate change: insights from Haig Glacier, Canadian Rocky Mountains
Evolution of glaciers in response to climate change has mostly been simulated using simplified dynamical models. Because these models do not account for the influence of high-order physics, corresponding results may exhibit some biases. For Haig Glacier in the Canadian Rocky Mountains, we test this hypothesis by comparing simulation results obtained from 3-D numerical models that deal with different assumptions concerning physics, ranging from simple shear deformation to comprehensive Stokes flow. In glacier retreat scenarios, we find a minimal role of high-order mechanics in glacier evolution, as geometric effects at our site (the presence of an overdeepened bed) result in limited horizontal movement of ice (flow speed on the order of a few meters per year). Consequently, high-order and reduced models all predict that Haig Glacier ceases to exist by ca. 2080 under ongoing climate warming. The influence of high-order mechanics is evident, however, in glacier advance scenarios, where ice speeds are greater and ice dynamical effects become more important. Although similar studies on other glaciers are essential to generalize such findings, we advise that high-order mechanics are important and therefore should be considered while modeling the evolution of active glaciers. Reduced model predictions may be adequate for other glaciologic and topographic settings, particularly where flow speeds are low and where mass balance changes dominate over ice dynamics in determining glacier geometry
Localization of a dipolar Bose-Einstein condensate in a bichromatic optical lattice
By numerical simulation and variational analysis of the Gross-Pitaevskii
equation we study the localization, with an exponential tail, of a dipolar
Bose-Einstein condensate (DBEC) of Cr atoms in a three-dimensional
bichromatic optical-lattice (OL) generated by two monochromatic OL of
incommensurate wavelengths along three orthogonal directions. For a fixed
dipole-dipole interaction, a localized state of a small number of atoms () could be obtained when the short-range interaction is not too attractive
or not too repulsive. A phase diagram showing the region of stability of a DBEC
with short-range interaction and dipole-dipole interaction is given
Black soliton in a quasi-one-dimensional trapped fermion-fermion mixture
Employing a time-dependent mean-field-hydrodynamic model we study the
generation of black solitons in a degenerate fermion-fermion mixture in a
cigar-shaped geometry using variational and numerical solutions. The black
soliton is found to be the first stationary vibrational excitation of the
system and is considered to be a nonlinear continuation of the vibrational
excitation of the harmonic oscillator state. We illustrate the stationary
nature of the black soliton, by studying different perturbations on it after
its formation.Comment: 7 pages, 10 figure
Relativistic Effect on Low-Energy Nucleon-Deuteron Scattering
The relativistic effect on differential cross sections, nucleon-to-nucleon
and nucleon-to-deuteron polarization transfer coefficients, and the spin
correlation function, of nucleon-deuteron elastic scattering is investigated
employing several three-dimensional relativistic three-body equations and
several nucleon-nucleon potentials. The polarization transfer coefficients are
found to be sensitive to the details of the nucleon-nucleon potentials and the
relativistic dynamics employed, and prefer trinucleon models with the correct
triton binding energy. (To appear in Phys. Rev. C)Comment: pages: 21, LaTex text + 7 ps-figures at the en
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