Subtle temperature-induced changes in small molecule conformer dynamics-observed and quantified by NOE spectroscopy

NOE-distance relationships are shown to be sufficiently accurate to monitor very small changes in conformer populations in response to temperature (<0.5%/10 degrees C) - in good agreement with Boltzmann-predictions, illustrating the effectiveness of accurate NOE-distance measurements in obtaining high quality dynamics as well as structural information for small molecules

Limits to Sympathetic Evaporative Cooling of a Two-Component Fermi Gas

We find a limit cycle in a quasi-equilibrium model of evaporative cooling of a two-component fermion gas. The existence of such a limit cycle represents an obstruction to reaching the quantum ground state evaporatively. We show that evaporatively the \beta\mu ~ 1. We speculate that one may be able to cool an atomic fermi gas further by photoassociating dimers near the bottom of the fermi sea.Comment: Submitted to Phys. Rev

Multiple-membership multiple-classification models for social network and group dependences

The social network literature on network dependences has largely ignored other sources of dependence, such as the school that a student attends, or the area in which an individual lives. The multilevel modelling literature on school and area dependences has, in turn, largely ignored social networks. To bridge this divide, a multiple-membership multiple-classification modelling approach for jointly investigating social network and group dependences is presented. This allows social network and group dependences on individual responses to be investigated and compared. The approach is used to analyse a subsample of the Adolescent Health Study data set from the USA, where the response variable of interest is individual level educational attainment, and the three individual level covariates are sex, ethnic group and age. Individual, network, school and area dependences are accounted for in the analysis. The network dependences can be accounted for by including the network as a classification in the model, using various network configurations, such as ego-nets and cliques. The results suggest that ignoring the network affects the estimates of variation for the classifications that are included in the random part of the model (school, area and individual), as well as having some influence on the point estimates and standard errors of the estimates of regression coefficients for covariates in the fixed part of the model. From a substantive perspective, this approach provides a flexible and practical way of investigating variation in an individual level response due to social network dependences, and estimating the share of variation of an individual response for network, school and area classifications

Prospects for p-wave paired BCS states of fermionic atoms

We present theoretical prospects for creating p-wave paired BCS states of magnetic trapped fermionic atoms. Based on our earlier proposal of using dc electric fields to control both the strength and anisotropic characteristic of atom-atom interaction and our recently completed multi-channel atomic collision calculations we discover that p-wave pairing with $^{40}$K and $^{82,84,86}$Rb in the low field seeking maximum spin polarized state represent excellent choices for achieving superfluid BCS states; and may be realizable with current technology in laser cooling, magnetic trapping, and evaporative/sympathetic cooling, provided the required strong electric field can be applied. We also comment on the prospects of similar p-wave paired BCS states in $^{6}$Li, and more generally on creating other types exotic BCS states. Our study will open a new area in the vigorous pursuit to create a quantum degenerate fermionic atom vapor.Comment: to be publishe

Correlations in a Confined gas of Harmonically Interacting Spin-Polarized Fermions

For a fermion gas with equally spaced energy levels, the density and the pair correlation function are obtained. The derivation is based on the path integral approach for identical particles and the inversion of the generating functions for both static responses. The density and the pair correlation function are evaluated explicitly in the ground state of a confined fermion system with a number of particles ranging from 1 to 220 and filling the Fermi level completely.Comment: 11 REVTEX pages, 3 postscript figures. Accepted for publication in Phys. Rev. E, Vol. 58 (August 1, 1998

Optical linewidth of a low density Fermi-Dirac gas

We study propagation of light in a Fermi-Dirac gas at zero temperature. We analytically obtain the leading density correction to the optical linewidth. This correction is a direct consequence of the quantum statistical correlations of atomic positions that modify the optical interactions between the atoms at small interatomic separations. The gas exhibits a dramatic line narrowing already at very low densities.Comment: 4 pages, 2 figure

Two-species mixture of quantum degenerate Bose and Fermi gases

We have produced a macroscopic quantum system in which a Li-6 Fermi sea coexists with a large and stable Na-23 Bose-Einstein condensate. This was accomplished using inter-species sympathetic cooling of fermionic Li-6 in a thermal bath of bosonic Na-23

Rotating Bose gas with hard-core repulsion in a quasi-2D harmonic trap: vortices in BEC

We consider a gas of N(=6, 10, 15) Bose particles with hard-core repulsion, contained in a quasi-2D harmonic trap and subjected to an overall angular velocity $\Omega$ about the z-axis. Exact diagonalization of the $n\times n$ many-body Hamiltonian matrix in given subspaces of the total (quantized) angular momentum L$_{z}$, with $n\sim 10^{5}$(e.g. for L$_{z}$=N=15, n =240782) was carried out using Davidson's algorithm. The many-body variational ground state wavefunction, as also the corresponding energy and the reduced one-particle density-matrix were calculated. With the usual identification of $\Omega$ as the Lagrange multiplier associated with L$_{z}$ for a rotating system, the $L_{z}-\Omega$ phase diagram (or the stability line) was determined that gave a number of critical angular velocities $\Omega_{{\bf c}i}, i=1,2,3,... ,$ at which the ground state angular momentum and the associated condensate fraction undergo abrupt jumps. A number of (total) angular momentum states were found to be stable at successively higher critical angular velocities $\Omega_{{\bf c}i}, \ i=1,2,3,...$for a given N. For$L_{z}>N$, the condensate was strongly depleted. The critical$\Omega_{{\bf c}i}$values, however, decreased with increasing interaction strength as well as the particle number, and were systematically greater than the non-variational Yrast-state values for the single vortex state with L$_{z}$=N. We have also observed that the condensate fraction for the single vortex state (as also for the higher vortex states) did not change significantly even as the 2-body interaction strength was varied over several$(\sim 4)$ orders of magnitude in the moderately to the weakly interacting regime.Comment: Revtex, 11 pages, 1 table as ps file, 4 figures as ps file

Phase diagram of quantized vortices in a trapped Bose-Einstein condensed gas

We investigate the thermodynamic stability of quantized vortices in a dilute Bose gas confined by a rotating harmonic trap at finite temperature. Interatomic forces play a crucial role in characterizing the resulting phase diagram, especially in the large $N$ Thomas-Fermi regime. We show that the critical temperature for the creation of stable vortices exhibits a maximum as a function of the frequency of the rotating trap and that the corresponding transition is associated with a discontinuity in the number of atoms in the condensate. Possible strategies for approaching the vortical region are discussed.Comment: Revtex, 4 pages, 2 figure

Sympathetic cooling of an atomic Bose-Fermi gas mixture

Sympathetic cooling of an atomic Fermi gas by a Bose gas is studied by solution of the coupled quantum Boltzmann equations for the confined gas mixture. Results for equilibrium temperatures and relaxation dynamics are presented, and some simple models developed. Our study illustrate that a combination of sympathetic and forced evaporative cooling enables the Fermi gas to be cooled to the degenerate regime where quantum statistics, and mean field effects are important. The influence of mean field effects on the equilibrium spatial distributions is discussed qualitatively.Comment: 8 pages, 9 figures, accepted for publication in Phys.Rev.Let