1,021 research outputs found
Low-lying excitations of a trapped rotating Bose-Einstein condensate
We investigate the low-lying excitations of a weakly-interacting,
harmonically-trapped Bose-Einstein condensed gas under rotation, in the limit
where the angular mometum of the system is much less than the number of the
atoms in the trap. We show that in the asymptotic limit the
excitation energy, measured from the energy of the lowest state, is given by
, where is the number of octupole
excitations and is the unit of the interaction energy.Comment: 3 pages, RevTex, 2 ps figures, submitted to PR
Discovery of an optical bow-shock around pulsar B0740-28
We report the discovery of a faint H-alpha pulsar wind nebula (PWN) powered
by the radio pulsar B0740-28. The characteristic bow-shock morphology of the
PWN implies a direction of motion consistent with the previously measured
velocity vector for the pulsar. The PWN has a flux density more than an order
of magnitude lower than for the PWNe seen around other pulsars, but, for a
distance 2 kpc, it is consistent with propagation through a medium of atomic
density n_H ~ 0.25 cm^{-3}, and neutral fraction of 1%. The morphology of the
PWN in the area close to the pulsar is distinct from that in downstream
regions, as is also seen for the PWN powered by PSR B2224+65. In particular,
the PWN associated with PSR B0740-28 appears to close at its rear, suggesting
that the pulsar has recently passed through a transition from low density to
high density ambient gas. The faintness of this source underscores that deep
searches are needed to find further examples of optical pulsar nebulae.Comment: 5 pages, 1 figure, to appear in Astronomy & Astrophysics Letter
Scattering Wave Functions at Bound State Poles
The normalisation relation between the bound and scattering S-state wave
functions, extrapolated to the bound state pole, is derived from the
Schroedinger equation. It is shown that, unlike previous work, the result does
not depend on the details of the potential through the corresponding Jost
function but is given uniquely in terms of the binding energy. The
generalisations to higher partial waves and one-dimensional scattering are
given.Comment: 15 pages Latex. No graph
Condensation of `composite bosons' in a rotating BEC
We provide evidence for several novel phases in the dilute limit of rotating
BECs. By exact calculation of wavefunctions and energies for small numbers of
particles, we show that the states near integer angular momentum per particle
are best considered condensates of composite entities, involving vortices and
atoms. We are led to this result by explicit comparison with a description
purely in terms of vortices. Several parallels with the fractional quantum Hall
effect emerge, including the presence of the Pfaffian state.Comment: 4 pages, Latex, 3 figure
Weakly Interacting Bose-Einstein Condensates Under Rotation: Mean-field versus Exact Solutions
We consider a weakly-interacting, harmonically-trapped Bose-Einstein
condensed gas under rotation and investigate the connection between the
energies obtained from mean-field calculations and from exact diagonalizations
in a subspace of degenerate states. From the latter we derive an approximation
scheme valid in the thermodynamic limit of many particles. Mean-field results
are shown to emerge as the correct leading-order approximation to exact
calculations in the same subspace.Comment: 4 pages, RevTex, submitted to PR
The Yrast Spectra of Weakly Interacting Bose-Einstein Condensates
The low energy quantal spectrum is considered as a function of the total
angular momentum for a system of weakly interacting bosonic atoms held together
by an external isotropic harmonic potential. It is found that besides the usual
condensation into the lowest state of the oscillator, the system exhibits two
additional kinds of condensate and associated thermodynamic phase transitions.
These new phenomena are derived from the degrees of freedom of "partition
space" which describes the multitude of different ways in which the angular
momentum can be distributed among the atoms while remaining all the time in the
lowest state of the oscillator
Eta-Helium Quasi-Bound States
The cross section and tensor analysing power t_20 of the d\vec{d}->eta 4He
reaction have been measured at six c.m. momenta, 10 < p(eta) < 90 MeV/c. The
threshold value of t_20 is consistent with 1/\sqrt{2}, which follows from
parity conservation and Bose symmetry. The much slower momentum variation
observed for the reaction amplitude, as compared to that for the analogous
pd->eta 3He case, suggests strongly the existence of a quasi-bound state in the
eta-4He system and optical model fits indicate that this probably also the case
for eta-3He.Comment: LaTeX, uses elsart.sty, 10 pages, 3 Postscript figures, Submitted to
Physics Letters
Exact Eignstates for Trapped Weakly Interacting Bosons in Two Dimensions
A system of N two-dimensional weakly interacting bosons in a harmonic trap is
considered. When the two-particle potential is a delta function Smith and
Wilkin have analytically proved that the elementary symmetric polynomials of
particle coordinates measured from the center of mass are exact eigenstates. In
this study, we point out that their proof works equally well for an arbitrary
two-particle potential which possesses the translational and rotational
symmetries. We find that the interaction energy associated with the eigenstate
with angular momentum L is equal to aN(N-1)/2+(b-a)NL/2, where a and b are the
interaction energies of two bosons in the lowest-energy one-particle state with
zero and one unit of angular momentum, respectively. Additionally, we study
briefly the case of attractive quartic interactions. We prove rigorously that
the lowest-energy state is the one in which all angular momentum is carried by
the center of mass motion.Comment: 4 pages, minor changes made, to appear in PRA Brie
Satellite-Derived Distributions, Inventories and Fluxes of Dissolved and Particulate Organic Matter Along the Northeastern U.S. Continental Margin
Estuaries and the coastal ocean experience a high degree of variability in the composition and concentration of particulate and dissolved organic matter (DOM) as a consequence of riverine and estuarine fluxes of terrigenous DOM, sediments, detritus and nutrients into coastal waters and associated phytoplankton blooms. Our approach integrates biogeochemical measurements, optical properties and remote sensing to examine the distributions and inventories of organic carbon in the U.S. Middle Atlantic Bight and Gulf of Maine. Algorithms developed to retrieve colored DOM (CDOM), Dissolved (DOC) and Particulate Organic Carbon (POC) from NASA's MODIS-Aqua and SeaWiFS satellite sensors are applied to quantify the distributions and inventories of DOC and POC. Horizontal fluxes of DOC and POC from the continental margin to the open ocean are estimated from SeaWiFS and MODIS-Aqua distributions of DOC and POC and horizontal divergence fluxes obtained from the Northeastern North Atlantic ROMS model. SeaWiFS and MODIS imagery reveal the importance of estuarine outflow to the export of CDOM and DOC to the coastal ocean and a net community production of DOC on the shelf
Yrast line for weakly interacting trapped bosons
We compute numerically the yrast line for harmonically trapped boson systems
with a weak repulsive contact interaction, studying the transition to a vortex
state as the angular momentum L increases and approaches N, the number of
bosons. The L=N eigenstate is indeed dominated by particles with unit angular
momentum, but the state has other significant components beyond the pure vortex
configuration. There is a smooth crossover between low and high L with no
indication of a quantum phase transition. Most strikingly, the energy and wave
function appear to be analytical functions of L over the entire range 2 < L <
N. We confirm the structure of low-L states proposed by Mottelson, as mainly
single-particle excitations with two or three units of angular momentum.Comment: 9 pages, 3 EPS-figures, uses psfig.st
- …