3,885 research outputs found
Absence of Fragmentation in Two-Dimensional Bose-Einstein Condensation
We investigate the possibility that the BEC-like phenomena recently detected
on two-dimensional finite trapped systems consist of fragmented condensates. We
derive and diagonalize the one-body density matrix of a two-dimensional
isotropically trapped Bose gas at finite temperature. For the ideal gas, the
procedure reproduces the exact harmonic-oscillator eigenfunctions and the Bose
distribution. We use a new collocation-minimization method to study the
interacting gas in the Hartree-Fock approximation and obtain a ground-state
wavefunction and condensate fraction consistent with those obtained by other
methods. The populations of the next few eigenstates increase at the expense of
the ground state but continue to be negligible; this supports the conclusion
that two-dimensional BEC is into a single state.Comment: 6 pages, 1 figur
Processing and Transmission of Information
Contains reports on three research projects.Lincoln Laboratory (Purchase Order DDL-B187)United States Department of the ArmyUnited States Department of the NavyUnited States Department of the Air Force (Contract AF19(122)-458
Nonlocal appearance of a macroscopic angular momentum
We discuss a type of measurement in which a macroscopically large angular
momentum (spin) is "created" nonlocally by the measurement of just a few atoms
from a double Fock state. This procedure apparently leads to a blatant
nonconservation of a macroscopic variable - the local angular momentum. We
argue that while this gedankenexperiment provides a striking illustration of
several counter-intuitive features of quantum mechanics, it does not imply a
non-local violation of the conservation of angular momentum.Comment: 10 pages, 1 figur
Embedding the affine complement of three intersecting lines in a finite projective plane
An (r, 1)–design is a pair (V, F) where V is a ν–set and F is a family of non-null subsets of V (b in number) which satisfy the following. (1) Every pair of distinct members of V is contained in precisely one member of F. (2) Every member of V occurs in precisely r members of F. A pseudo parallel complement PPC(n, α) is an (n+1, 1)–design with ν=n2−αn and b≦n2+n−α in which there are at least n−α a blocks of size n. A pseudo intersecting complement PIC(n, α) is an (n+1, 1)–design with ν=n2−αn+α−1 and b≦n2+n−α in which there are at least n−α+1 blocks of size n−1. It has previously been shown that for α≦4, every PIC(n, α) can be embedded in a PPC(n, α−1) and that for n>(α4−2α3+2α2+α−2)/2, every PPC(n, α) can be embedded in a finite projective plane of order n. In this paper we investigate the case of α=3 and show that any PIC(n, 3) is embeddable in a PPC(n,2) provided n≧14
Anisotropic Spin Diffusion in Trapped Boltzmann Gases
Recent experiments in a mixture of two hyperfine states of trapped Bose gases
show behavior analogous to a spin-1/2 system, including transverse spin waves
and other familiar Leggett-Rice-type effects. We have derived the kinetic
equations applicable to these systems, including the spin dependence of
interparticle interactions in the collision integral, and have solved for
spin-wave frequencies and longitudinal and transverse diffusion constants in
the Boltzmann limit. We find that, while the transverse and longitudinal
collision times for trapped Fermi gases are identical, the Bose gas shows
diffusion anisotropy. Moreover, the lack of spin isotropy in the interactions
leads to the non-conservation of transverse spin, which in turn has novel
effects on the hydrodynamic modes.Comment: 10 pages, 4 figures; submitted to PR
Giant viscosity enhancement in a spin-polarized Fermi liquid
The viscosity is measured for a Fermi liquid, a dilute He-He mixture,
under extremely high magnetic field/temperature conditions ( T, mK). The spin splitting energy is substantially greater than
the Fermi energy ; as a consequence the polarization tends to unity
and s-wave quasiparticle scattering is suppressed for . Using a
novel composite vibrating-wire viscometer an enhancement of the viscosity is
observed by a factor of more than 500 over its low-field value. Good agreement
is found between the measured viscosity and theoretical predictions based upon
a -matrix formalism.Comment: 4 pages, 4 figure
Low-Temperature Spin Diffusion in a Spin-Polarized Fermi Gas
We present a finite temperature calculation of the transverse spin-diffusion
coefficient, , in a dilute degenerate Fermi gas in the presence of a
small external magnetic field, . While the longitudinal diffusion
coefficient displays the conventional low-temperature Fermi-liquid behavior,
, the corresponding results for show three
separate regimes: (a) for ; (b) , for and large spin-rotation
parameter , and (c) for and . Our results are qualitatively consistent with the available
experimental data in weakly spin-polarized and mixtures.Comment: 13 pages, REVTEX, 3 figures available upon request, RU-94-4
Classification of phase transitions of finite Bose-Einstein condensates in power law traps by Fisher zeros
We present a detailed description of a classification scheme for phase
transitions in finite systems based on the distribution of Fisher zeros of the
canonical partition function in the complex temperature plane. We apply this
scheme to finite Bose-systems in power law traps within a semi-analytic
approach with a continuous one-particle density of states for different values of and to a three dimensional harmonically
confined ideal Bose-gas with discrete energy levels. Our results indicate that
the order of the Bose-Einstein condensation phase transition sensitively
depends on the confining potential.Comment: 7 pages, 9 eps-figures, For recent information on physics of small
systems see "http://www.smallsystems.de
First Report of Columbia Root Knot Nematode (\u3ci\u3eMeloidogyne chitwoodi\u3c/i\u3e) in Potato in Texas
Columbia root-knot nematode, Meloidogyne chitwoodi Golden et al. (1) was identified from potatoes, Solanum tuberosum L., collected from Dallam County, Texas in October 2000. Seed potatoes are the most likely source for this introduction. This nematode is currently found infecting potatoes grown in California, Colorado, Idaho, New Mexico, Nevada, Oregon, Utah, and Washington. Some countries prohibit import of both seed and table stock potatoes originating in states known to harbor M. chitwoodi. Lesions on the potatoes had discrete brown coloration with white central spots in the outer 1 cm of the tuber flesh. Female nematode densities averaged 3 per square centimeter of a potato section beneath the lesions. Nematodes were morphologically identified as M. chitwoodi based on the perineal pattern of mature females and the tail shape of juveniles per Golden et al. (1)
Acute inhibition of MEK suppresses congenital melanocytic nevus syndrome in a murine model driven by activated NRAS and Wnt signaling
Congenital melanocytic nevus (CMN) syndrome is the association of pigmented melanocytic nevi with extra-cutaneous features, classically melanotic cells within the central nervous system, most frequently caused by a mutation of NRAS codon 61. This condition is currently untreatable and carries a significant risk of melanoma within the skin, brain, or leptomeninges. We have previously proposed a key role for Wnt signaling in the formation of melanocytic nevi, suggesting that activated Wnt signaling may be synergistic with activated NRAS in the pathogenesis of CMN syndrome. Some familial pre-disposition suggests a germ-line contribution to CMN syndrome, as does variability of neurological phenotypes in individuals with similar cutaneous phenotypes. Accordingly, we performed exome sequencing of germ-line DNA from patients with CMN to reveal rare or undescribed Wnt-signaling alterations. A murine model harboring activated NRASQ61K and Wnt signaling in melanocytes exhibited striking features of CMN syndrome, in particular neurological involvement. In the first model of treatment for this condition, these congenital, and previously assumed permanent, features were profoundly suppressed by acute post-natal treatment with a MEK inhibitor. These data suggest that activated NRAS and aberrant Wnt signaling conspire to drive CMN syndrome. Post-natal MEK inhibition is a potential candidate therapy for patients with this debilitating condition
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