3,161 research outputs found
Collective Dynamics of Bose--Einstein Condensates in Optical Cavities
Recent experiments on Bose--Einstein condensates in optical cavities have
reported a quantum phase transition to a coherent state of the matter-light
system -- superradiance. The time dependent nature of these experiments demands
consideration of collective dynamics. Here we establish a rich phase diagram,
accessible by quench experiments, with distinct regimes of dynamics separated
by non-equilibrium phase transitions. We include the key effects of cavity
leakage and the back-reaction of the cavity field on the condensate. Proximity
to some of these phase boundaries results in critical slowing down of the decay
of many-body oscillations. Notably, this slow decay can be assisted by large
cavity losses. Predictions include the frequency of collective oscillations, a
variety of multi-phase co-existence regions, and persistent optomechanical
oscillations described by a damped driven pendulum. These findings open new
directions to study collective dynamics and non-equilibrium phase transitions
in matter-light systems.Comment: 5 pages, 5 figure
Coherent Particle Transfer in an On-Demand Single-Electron Source
Coherent electron transfer from a localized state trapped in a quantum dot
into a ballistic conductor, taking place in on-demand electron sources, in
general may result in excitation of particle-hole pairs. We consider a simple
model for these effects, involving a resonance level with time-dependent
energy, and derive Floquet scattering matrix describing inelastic transitions
of particles in the Fermi sea. We find that, as the resonance level is driven
through the Fermi level, particle transfer may take place completely without
particle-hole excitations for certain driving protocols. In particular, such
noiseless transfer occurs when the level moves with constant rapidity, its
energy changing linearly with time. A detection scheme for studying the
coherence of particle transfer is proposed.Comment: 5 pages, 3 figures. Updated introduction, Fig. 1, and reference
Experimental pig-to-pig transmission dynamics for African swine fever virus, Georgia 2007/1 strain
African swine fever virus (ASFV) continues to cause outbreaks in domestic pigs and wild boar in Eastern European countries. To gain insights into its transmission dynamics, we estimated the pig-to-pig basic reproduction number (R 0) for the Georgia 2007/1 ASFV strain using a stochastic susceptible-exposed-infectious-recovered (SEIR) model with parameters estimated from transmission experiments. Models showed that R 0 is 2·8 [95% confidence interval (CI) 1·3–4·8] within a pen and 1·4 (95% CI 0·6–2·4) between pens. The results furthermore suggest that ASFV genome detection in oronasal samples is an effective diagnostic tool for early detection of infection. This study provides quantitative information on transmission parameters for ASFV in domestic pigs, which are required to more effectively assess the potential impact of strategies for the control of between-farm epidemic spread in European countries.ISSN:0950-2688ISSN:1469-440
Angular distribution of photoluminescence as a probe of Bose Condensation of trapped excitons
Recent experiments on two-dimensional exciton systems have shown the excitons
collect in shallow in-plane traps. We find that Bose condensation in a trap
results in a dramatic change of the exciton photoluminescence (PL) angular
distribution. The long-range coherence of the condensed state gives rise to a
sharply focussed peak of radiation in the direction normal to the plane. By
comparing the PL profile with and without Bose Condensation we provide a simple
diagnostic for the existence of a Bose condensate. The PL peak has strong
temperature dependence due to the thermal order parameter phase fluctuations
across the system. The angular PL distribution can also be used for imaging
vortices in the trapped condensate. Vortex phase spatial variation leads to
destructive interference of PL radiation in certain directions, creating nodes
in the PL distribution that imprint the vortex configuration.Comment: 4 pages, 3 figure
Performance of an environmental test to detect Mycobacterium bovis infection in badger social groups
A study by Courtenay and others (2006) demonstrated that
the probability of detecting Mycobacterium bovis by PCR in
soil samples from the spoil heaps of main badger setts correlated
with the prevalence of excretion (infectiousness) of
captured badgers belonging to the social group. It has been
proposed that such a test could be used to target badger culling
to setts containing infectious animals (Anon 2007). This
short communication discusses the issues surrounding this
concept, with the intention of dispelling any misconceptions
among relevant stakeholders (farmers, policy makers and
conservationists)
Phase lag in epidemics on a network of cities
We study the synchronisation and phase-lag of fluctuations in the number of
infected individuals in a network of cities between which individuals commute.
The frequency and amplitude of these oscillations is known to be very well
captured by the van Kampen system-size expansion, and we use this approximation
to compute the complex coherence function that describes their correlation. We
find that, if the infection rate differs from city to city and the coupling
between them is not too strong, these oscillations are synchronised with a well
defined phase lag between cities. The analytic description of the effect is
shown to be in good agreement with the results of stochastic simulations for
realistic population sizes.Comment: 10 pages, 6 figure
Fractal measures of spatial pattern as a heuristic for return rate in vegetative systems
Measurement of population persistence is a long-standing problem in ecology; in particular, whether it is possible to gain insights into persistence without long time-series. Fractal measurements of spatial patterns, such as the Korcak exponent or boundary dimension, have been proposed as indicators of the persistence of underlying dynamics. Here we explore under what conditions a predictive relationship between fractal measures and persistence exists. We combine theoretical arguments with an aerial snapshot and time series from a long-term study of seagrass. For this form of vegetative growth, we find that the expected relationship between the Korcak exponent and persistence is evident at survey sites where the population return rate can be measured. This highlights a limitation of the use of power-law patch-size distributions and other indicators based on spatial snapshots. Moreover, our numeric simulations show that for a single species and a range of environmental conditions that the Korcak–persistence relationship provides a link between temporal dynamics and spatial pattern; however, this relationship is specific to demographic factors, so we cannot use this methodology to compare between species
- …