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

A conjugate gradient minimisation approach to generating holographic traps for ultracold atoms

Direct minimisation of a cost function can in principle provide a versatile and highly controllable route to computational hologram generation. However, to date iterative Fourier transform algorithms have been predominantly used. Here we show that the careful design of cost functions, combined with numerically efficient conjugate gradient minimisation, establishes a practical method for the generation of holograms for a wide range of target light distributions. This results in a guided optimisation process, with a crucial advantage illustrated by the ability to circumvent optical vortex formation during hologram calculation. We demonstrate the implementation of the conjugate gradient method for both discrete and continuous intensity distributions and discuss its applicability to optical trapping of ultracold atoms.Comment: 11 pages, 4 figure

THE 1996 FARM BILL: IMPLICATIONS FOR FARMERS

Agricultural and Food Policy,

What to Choose? The Value of Label Claims to Produce Consumers

This paper addresses three key empirical questions related to health, nutrient, and process claims on front-label packaging; namely, 1) How do consumers value alternative claims on product and process-based attributes for fresh produce; 2) Are these values additively separable; and 3) To what degree is there heterogeneity between consumers on these values? We use a hypothetical choice experiment on red leaf lettuce attribute bundles, and estimate several logit models (MNL and ML) that provide estimates of marginal utilities (and with the inclusion of varying prices, marginal values) of various attributes related to general health claims, specific nutrition and health claims, certification logos related to health and nutrition currently found in the marketplace, as well as certified organic claims (relative to the conventional reference group). The results showed that consumers do distinguish between competing claims and logos, though the impacts are not always as expected, likely due to the information set used at the time of the choice. We found some evidence of attribute bundling between the health claims and the familiar Five-a-day program logo, and between organic production and a claim regarding vitamin C content. Finally, we found that use of the unconditional distributions (relative to the conditional)in a ML model overstates the degree of preference heterogeneity across the sample and overstates the magnitude of the marginal effects of the random parameters. This may create misleading impressions regarding the existence and size of specialized niche markets, the response of consumers to varying health, nutrition, or process claims, and/or the response of consumers to the introduction of new products with these (or similar) claims.Consumer/Household Economics, Demand and Price Analysis,

Modelling the spread of American foulbrood in honeybees

We investigate the spread of American foulbrood (AFB), a disease caused by the bacterium Paenibacillus larvae, that affects bees and can be extremely damaging to beehives. Our dataset comes from an inspection period carried out during an AFB epidemic of honeybee colonies on the island of Jersey during the summer of 2010. The data include the number of hives of honeybees, location and owner of honeybee apiaries across the island. We use a spatial SIR model with an underlying owner network to simulate the epidemic and characterize the epidemic using a Markov chain Monte Carlo (MCMC) scheme to determine model parameters and infection times (including undetected ‘occult’ infections). Likely methods of infection spread can be inferred from the analysis, with both distance- and owner-based transmissions being found to contribute to the spread of AFB. The results of the MCMC are corroborated by simulating the epidemic using a stochastic SIR model, resulting in aggregate levels of infection that are comparable to the data. We use this stochastic SIR model to simulate the impact of different control strategies on controlling the epidemic. It is found that earlier inspections result in smaller epidemics and a higher likelihood of AFB extinction

Direct Marketing of Fresh Produce: Understanding Consumer Purchasing Decisions

Consumer/Household Economics, Crop Production/Industries, Marketing, Q13,

Spread of Infectious Diseases with a Latent Period

Infectious diseases spread through human networks. Susceptible-Infected-Removed (SIR) model is one of the epidemic models to describe infection dynamics on a complex network connecting individuals. In the metapopulation SIR model, each node represents a population (group) which has many individuals. In this paper, we propose a modified metapopulation SIR model in which a latent period is taken into account. We call it SIIR model. We divide the infection period into two stages: an infected stage, which is the same as the previous model, and a seriously ill stage, in which individuals are infected and cannot move to the other populations. The two infectious stages in our modified metapopulation SIR model produce a discontinuous final size distribution. Individuals in the infected stage spread the disease like individuals in the seriously ill stage and never recover directly, which makes an effective recovery rate smaller than the given recovery rate.Comment: 6 pages, 3 figure

Eat Your Fruits and Veggies: Who Informs Consumers about Produce Choices and Nutrition?

Food consumption trends in the U.S. may be affected by and/or contributing to the growth in food- and nutrition-related information channels. Information channels are increasing in number, as are the sources (McCluskey & Swinnnen 2004) that provide information. This paper examines consumer perceptions of the relative desirability of various food and nutrition information sources and education methods as well as the relative credibility of various food and nutrition sources. Using data from a 2006 nationwide consumer survey, comparative summary statistics show significant differences between information delivery methods and sources that consumers use and trust. By understanding how consumers receive and value information we can better target consumer groups.Food Consumption/Nutrition/Food Safety,