31,143 research outputs found
Ground-State Properties of a Rotating Bose-Einstein Condensate with Attractive Interaction
The ground state of a rotating Bose-Einstein condensate with attractive
interaction in a quasi-one-dimensional torus is studied in terms of the ratio
of the mean-field interaction energy per particle to the
single-particle energy-level spacing. The plateaus of quantized circulation are
found to appear if and only if with the lengths of the plateaus
reduced due to hybridization of the condensate over different angular-momentum
states.Comment: 4 pages, 2 figures, Accepted for publication in Physical Reveiw
Letter
The Quantum de Laval Nozzle: stability and quantum dynamics of sonic horizons in a toroidally trapped Bose gas containing a superflow
We study an experimentally realizable system containing stable black
hole-white hole acoustic horizons in toroidally trapped Bose-Einstein
condensates - the quantum de Laval nozzle. We numerically obtain stationary
flow configurations and assess their stability using Bogoliubov theory, finding
both in hydrodynamic and non-hydrodynamic regimes there exist dynamically
unstable regions associated with the creation of positive and negative energy
quasiparticle pairs in analogy with the gravitational Hawking effect. The
dynamical instability takes the form of a two mode squeezing interaction
between resonant pairs of Bogoliubov modes. We study the evolution of
dynamically unstable flows using the truncated Wigner method, which confirms
the two mode squeezed state picture of the analogue Hawking effect for low
winding number.Comment: 12 pages, 10 figure
Health and sustainable development
If sustainable development is to mean anything, people must be healthy enough to benefit from it and not have their lives cut off prematurely. Development without health is meaningless. But the processes which are likely to occur in a world undergoing globalisation, climate change, urbanisation, population increase and many other changes, will impact upon human health in complex ways. Some of them will benefit us, others will create new or augmented threats to survival and health, while many others will have a complex mixture of effects
Predictors of disease-free and overall survival in retroperitoneal sarcomas: A modern 16-year multi-institutional study from the United States Sarcoma Collaboration (USSC)
Spectral Densities of Response Functions for the O(3) Symmetric Anderson and Two Channel Kondo Models
The O(3) symmetric Anderson model is an example of a system which has a
stable low energy marginal Fermi liquid fixed point for a certain choice of
parameters. It is also exactly equivalent, in the large U limit, to a localized
model which describes the spin degrees of freedom of the linear dispersion two
channel Kondo model. We first use an argument based on conformal field theory
to establish this precise equivalence with the two channel model. We then use
the numerical renormalization group (NRG) approach to calculate both
one-electron and two-electron response functions for a range of values of the
interaction strength U. We compare the behaviours about the marginal Fermi
liquid and Fermi liquid fixed points and interpret the results in terms of a
renormalized Majorana fermion picture of the elementary excitations. In the
marginal Fermi liquid case the spectral densities of all the Majorana fermion
modes display a |omega| dependence on the lowest energy scale, and in addition
the zero Majorana mode has a delta function contribution. The weight of this
delta function is studied as a function of the interaction U and is found to
decrease exponentially with U for large U. Using the equivalence with the two
channel Kondo model in the large U limit, we deduce the dynamical spin
susceptibility of the two channel Kondo model over the full frequency range. We
use renormalized perturbation theory to interpret the results and to calculate
the coefficient of the ln omega divergence found in the low frequency behaviour
of the T=0 dynamic susceptibility.Comment: 26 pages, 18 figures, to be published in Eur. Phys. J.
Magnetic fields and differential rotation on the pre-main sequence
Maps of magnetic field topologies of rapidly rotating stars obtained over the last decade or so have provided unique insight into the operation of stellar dynamos. However, for solar-type stars many of the targets imaged to date have been lower-mass zero-age main sequence stars. We present magnetic maps and differential rotation measurements of two-higher mass pre-main sequence stars HD 106506 (~10 Myrs) and HD 141943 (~15 Myrs). These stars should evolve into mid/late F-stars with predicted high differential rotation and little magnetic activity. We investigate what effect the extended convection zones of these pre-main sequence stars has on their differential rotation and magnetic topologies. Ā©2009 American Institute of Physic
Properties of the stochastic Gross-Pitaevskii equation: Projected Ehrenfest relations and the optimal plane wave basis
We investigate the properties of the stochastic Gross-Pitaevskii equation
describing a condensate interacting with a stationary thermal cloud derived by
Gardiner and coworkers. We find the appropriate Ehrenfest relations for the
SGPE, including the effect of growth noise and projector terms arising from the
energy cutoff. This is carried out in the high temperature regime appropriate
for the SGPE, which simplifies the action of the projectors. The validity
condition for neglecting the projector terms in the Ehrenfest relations is
found to be more stringent than the usual condition of validity of the
truncated Wigner method or classical field method -- which is that all modes
are highly occupied. In addition it is required that the overlap of the
nonlinear term with the lowest energy eigenstate of the non-condensate band is
small. We show how to use the Ehrenfest relations along with the corrections
generated by the projector to monitor dynamical artifacts arising from the
cutoff. We also investigate the effect of using different bases to describe a
harmonically trapped BEC at finite temperature by comparing the condensate
fraction found using the plane wave and single particle bases. We show that the
equilibrium properties are strongly dependent on the choice of basis. There is
thus an optimal choice of plane wave basis for a given cut-off energy and we
show that this basis gives the best reproduction of the single particle
spectrum, the condensate fraction and the position and momentum densities.Comment: 23 pages, 5 figure
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