2,888 research outputs found
Finite temperature analysis of a quasi2D dipolar gas
We present finite temperature analysis of a quasi2D dipolar gas. To do this,
we use the Hartree Fock Bogoliubov method within the Popov approximation. This
formalism is a set of non-local equations containing the dipole-dipole
interaction and the condensate and thermal correlation functions, which are
solved self-consistently. We detail the numerical method used to implement the
scheme. We present density profiles for a finite temperature dipolar gas in
quasi2D, and compare these results to a gas with zero-range interactions.
Additionally, we analyze the excitation spectrum and study the impact of the
thermal exchange
Excited states of a static dilute spherical Bose condensate in a trap
The Bogoliubov approximation is used to study the excited states of a dilute
gas of atomic bosons trapped in an isotropic harmonic potential
characterized by a frequency and an oscillator length . The self-consistent static Bose condensate has
macroscopic occupation number , with nonuniform spherical condensate
density ; by assumption, the depletion of the condensate is small (). The linearized density fluctuation operator and velocity potential operator satisfy coupled equations
that embody particle conservation and Bernoulli's theorem. For each angular
momentum , introduction of quasiparticle operators yields coupled eigenvalue
equations for the excited states; they can be expressed either in terms of
Bogoliubov coherence amplitudes and that determine the
appropriate linear combinations of particle operators, or in terms of
hydrodynamic amplitudes and . The hydrodynamic picture
suggests a simple variational approximation for that provides an upper
bound for the lowest eigenvalue and an estimate for the
corresponding zero-temperature occupation number ; both expressions
closely resemble those for a uniform bulk Bose condensate.Comment: 5 pages, RevTeX, contributed paper accepted for Low Temperature
Conference, LT21, August, 199
A simple mean field equation for condensates in the BEC-BCS crossover regime
We present a mean field approach based on pairs of fermionic atoms to
describe condensates in the BEC-BCS crossover regime. By introducing an
effective potential, the mean field equation allows us to calculate the
chemical potential, the equation of states and the atomic correlation function.
The results agree surprisingly well with recent quantum Monte Carlo
calculations. We show that the smooth crossover from the bosonic mean field
repulsion between molecules to the Fermi pressure among atoms is associated
with the evolution of the atomic correlation function
Variation in Organic Standards Prior to the National Organic Program
Interest in establishing nationally uniform certification, labeling, and management standards for organic products grew out of concern that the existence of multiple standards led to consumer and supply chain confusion about, and lack of confidence in, these products. The National Organic Program Final Rule, issued in December 2000, is the result of this interest. We analyze the certification system that was in place prior to the new national rule to evaluate the extent of differences between certification standards and how the national rule is likely to impact the market for organic products. Our analysis suggests that most differences among US certification standards were minor. Also, the most important impacts of the national standard may be in facilitating trade in ingredients and products certified by different certifiers, increasing buyer confidence, and facilitating exports. However, the national rule may decrease the ability of organic certifiers and consumers to place differing emphasis on the multiple goals of organic production and may decrease the flexibility of organic standards to respond to changing market conditions, including new technologies.organic agriculture, organic certification standards, organic labeling, organic market, Agribusiness, Marketing,
Hartree shift in unitary Fermi gases
The Hartree energy shift is calculated for a unitary Fermi gas. By including
the momentum dependence of the scattering amplitude explicitly, the Hartree
energy shift remains finite even at unitarity. Extending the theory also for
spin-imbalanced systems allows calculation of polaron properties. The results
are in good agreement with more involved theories and experiments.Comment: 31 pages, many figure
Thermodynamic properties of a dipolar Fermi gas
Based on the semi-classical theory, we investigate the thermodynamic
properties of a dipolar Fermi gas. Through a self-consistent procedure, we
numerically obtain the phase space distribution function at finite temperature.
We show that the deformations in both momentum and real space becomes smaller
and smaller as one increases the temperature. For homogeneous case, we also
calculate pressure, entropy, and heat capacity. In particular, at low
temperature limit and in weak interaction regime, we obtain an analytic
expression for the entropy, which agrees qualitatively with our numerical
result. The stability of a trapped gas at finite temperature is also explored
Multiscale quantum-defect theory for two interacting atoms in a symmetric harmonic trap
We present a multiscale quantum-defect theory (QDT) for two identical atoms
in a symmetric harmonic trap that combines the quantum-defect theory for the
van der Waals interaction [B. Gao, Phys. Rev. A \textbf{64}, 010701(R) (2001)]
at short distances with a quantum-defect theory for the harmonic trapping
potential at large distances. The theory provides a systematic understanding of
two atoms in a trap, from deeply bound molecular states and states of different
partial waves, to highly excited trap states. It shows, e.g., that a strong
wave pairing can lead to a lower energy state around the threshold than a
wave pairing.Comment: 10 pages, 6 figure
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