Renormalization Group Theory of the Three-Dimensional Dilute Bose Gas

We study the three-dimensional atomic Bose gas using renormalization group techniques. Using our knowledge of the microscopic details of the interatomic interaction, we determine the correct initial values of our renormalization group equations and thus obtain also information on nonuniversal properties. As a result, we can predict for instance the critical temperature of the gas and the superfluid and condensate density of the Bose-Einstein condensed phase in the regime $na\Lambda_{th}^2\ll 1$.Comment: 48 pages of ReVTeX and 13 postscript figures. Submitted for publication in Physical Review

Theory of Interacting Quantum Gases

We present a unified picture of the interaction effects in dilute atomic quantum gases. We consider fermionic as well as bosonic gases and, in particular, discuss for both forms of statistics the fundamental differences between a gas with effectively repulsive and a gas with effectively attractive interatomic interactions, i.e.\ between a gas with either a positive or a negative scattering length.Comment: Invited paper for the NIST Journal of Researc

Dynamics of Fluctuating Bose-Einstein Condensates

We present a generalized Gross-Pitaevskii equation that describes also the dissipative dynamics of a trapped partially Bose condensed gas. It takes the form of a complex nonlinear Schr\"odinger equation with noise. We consider an approximation to this Langevin field equation that preserves the correct equilibrium for both the condensed and the noncondensed parts of the gas. We then use this formalism to describe the reversible formation of a one-dimensional Bose condensate, and compare with recent experiments. In addition, we determine the frequencies and the damping of collective modes in this case.Comment: 4 pages of REVTeX, including 4 figure

Competition Leverage: How the Demand Side Affects Optimal Risk Adjustment

We study optimal risk adjustment in imperfectly competitive health insurance markets when high-risk consumers are less likely to switch insurer than low-risk consumers. First, we find that insurers still have an incentive to select even if risk adjustment perfectly corrects for cost differences among consumers. Consequently, the outcome is not efficient even if cost differences are fully compensated. To achieve first best, risk adjustment should overcompensate for serving high-risk agents to take into account the difference in mark- ups among the two types. Second, the difference in switching behavior creates a trade off between efficiency and consumer welfare. Reducing the difference in risk adjustment subsidies to high and low types increases consumer welfare by leveraging competition from the elastic low-risk market to the less elastic high-risk market. Finally, mandatory pooling can increase consumer surplus even further, at the cost of efficiency.health insurance;risk adjustment;imperfect competition;leverage

Competition for Traders and Risk

Abstract: The financial crisis has been attributed partly to perverse incentives for traders at banks and has led policy makers to propose regulation of banks’ remuneration packages. We explain why poor incentives for traders cannot be fully resolved by only regulating the bank’s top executives, and why direct intervention in trader compensation is called for. We present a model with both trader moral hazard and adverse selection on trader abilities. We demonstrate that as competition on the labour market for traders intensifies, banks optimally offer top traders contracts inducing them to take more risk, even if banks fully internalize the costs of negative outcomes. In this way, banks can reduce the surplus they have to offer to lower ability traders. In addition, we find that increasing banks’ capital requirements does not unambiguously lead to reduced risk-taking by their top traders.optimal contracts;remuneration policy;imperfect competition;financial institutions;risk

Selective Contracting and Foreclosure in Health Care Markets

We analyze exclusive contracts between health care providers and insurers in a model where some consumers choose to stay uninsured. In case of a monopoly insurer, exclusion of a provider changes the distribution of consumers who choose not to insure. Although the foreclosed care provider remains active in the market for the non-insured, we show that exclusion leads to anti-competitive effects on this non-insured market. As a consequence exclusion can raise industry profits, and then occurs in equilibrium. Under competitive insurance markets, the anticompetitive exclusive equilibrium survives. Uninsured consumers, however, are now not better off without exclusion. Competition among insurers raises prices in equilibria without exclusion, as a result of a horizontal analogue to the double marginalization effect. Instead, under competitive insurance markets exclusion is desirable as long as no provider is excluded by all insurers.health insurance;uninsured;selective contracting;exclusion;foreclosure;anti-competitive effects

“The hidden hunger”: Understanding the burden of anaemia and its determinants among pregnant and non-pregnant women in Ethiopia

Anaemia is a global public health problem associated with increased mortality and morbidity. The highest prevalence of anaemia exists in the developing world where its causes are multi-factorial. The objective of the study was to assess the burden of anaemia and its determinants among pregnant and non-pregnant women in Ethiopia. The 2005 Demographic and Health Survey data of Ethiopia were used. Permission to download and analyze the data was granted from ORC Macro, in Calverton, USA. SPSS v10.0 was used to analyze the data. Both univariate and multivariate analysis were carried out. Trend analysis was done using the stat-calc programme on Epi-info 2002. For all statistical tests, significance level was set at p-value of 0.05. A total of 5960 women of child bearing age were included in the analysis. The mean haemoglobin was 12.72g/dl (95%CI: 12.66, 12.78g/dl). The general prevalence of anaemia among women was 27.7% (95%CI: 26.6, 28.9%). The prevalence of anaemia was 33.0% (95%CI: 28.7, 37.2%) and 27.3% (95%CI: 26.1, 28.4%) among pregnant and non-pregnant women respectively. The chi2 for linear trend test revealed a significant negative association between prevalence of anaemia and women’s educational status, grouped altitude of residential places and household wealth index categories (p<0.05, for all three variables). The prevalence of anaemia was positively associated with past five years fertility level (chi2 for linear trend=35.2, df =2, p<0.0001). Not possessing any toilet facilities (OR 1.85 95%CI: 1.66, 2.1), being resident of rural area (OR 2.02 95%CI: 1.75, 2.32) and not using contraceptive methods (OR 1.63 95%CI: 1.34, 1.98) were also associated with prevalence of anaemia among women. Logistic regression showed toilet possession to be the only independent predictor of prevalence of anaemia among pregnant women (Adj OR 2.17 95%CI: 1.28, 3.85). However, regression analysis among non-pregnant women revealed not having any toilet facilities (Adj OR 1.20 95%CI: 1.02, 1.42), lowering altitude categories of residential areas and not using contraception methods (Adj OR 1.39 95%CI: 1.13, 1.72) to be independent predictors of prevalence of anaemia. In conclusion, anaemia is a moderate public health problem among women in Ethiopia but there exist significant differences in magnitude by socio-economic status of women and their families and where they live. Interventions designed to address maternal anaemia should pay attention to both nutritional and non-nutritional intervention strategies that may include environmental sanitation, de-worming, and provision and promotion of family planning methods

Prunus serotina unleashed: invader dominance after 70 years of forest development

Propagule pressure and disturbance have both been found to facilitate invasion. Therefore, knowledge on the history of introduction and disturbance is vital for understanding an invasion process, and research should focus on areas in which the invasive species has not been deliberately introduced or managed to study unconfounded colonization patterns. Comparing the outcome of such spontaneous colonization processes for different ecosystems might provide a useful framework for setting management priorities for invasive species that enter new, uninvaded areas. We focused on the 70-year spontaneous spread of the invasive tree species Prunus serotina in a pine forest in the Netherlands. To reconstruct the invasion pattern, we combined historical maps, tree ring analysis, spatially explicit tree inventory data, seed density data, and regeneration data for both native and non-native species. Prunus serotina was the only species that showed successful regeneration: the species was present throughout the forest in the tree, shrub, and herb layer. Native species were not able to outgrow the seedling stage. Our data demonstrate that P. serotina is a gap-dependent species with high seed production that builds up a seedling bank. We also compared the results of this study with a similar study on P. serotina colonization in a deciduous forest in Belgium, where P. serotina invasion was not successful. The sharp contrast between the outcomes of the two invasion processes shows the importance of studying an invasive species and the recipient ecosystem jointly and made us raise the hypothesis that herbivore pressure may facilitate P. serotina invasio