Monte Carlo Simulations of Doped, Diluted Magnetic Semiconductors - a System with Two Length Scales

We describe a Monte Carlo simulation study of the magnetic phase diagram of diluted magnetic semiconductors doped with shallow impurities in the low concentration regime. We show that because of a wide distribution of interaction strengths, the system exhibits strong quantum effects in the magnetically ordered phase. A discrete spin model, found to closely approximate the quantum system, shows long relaxation times, and the need for specialized cluster algorithms for updating spin configurations. Results for a representative system are presented.Comment: 12 pages, latex, 7 figures; submitted to International Journal of Modern Physics C, Proceedings of the U.S.-Japan Bilateral Seminar: Understanding and Conquering Long Time Scales in Computer Simulation

Meta-heuristic algorithms in car engine design: a literature survey

Meta-heuristic algorithms are often inspired by natural phenomena, including the evolution of species in Darwinian natural selection theory, ant behaviors in biology, flock behaviors of some birds, and annealing in metallurgy. Due to their great potential in solving difficult optimization problems, meta-heuristic algorithms have found their way into automobile engine design. There are different optimization problems arising in different areas of car engine management including calibration, control system, fault diagnosis, and modeling. In this paper we review the state-of-the-art applications of different meta-heuristic algorithms in engine management systems. The review covers a wide range of research, including the application of meta-heuristic algorithms in engine calibration, optimizing engine control systems, engine fault diagnosis, and optimizing different parts of engines and modeling. The meta-heuristic algorithms reviewed in this paper include evolutionary algorithms, evolution strategy, evolutionary programming, genetic programming, differential evolution, estimation of distribution algorithm, ant colony optimization, particle swarm optimization, memetic algorithms, and artificial immune system

Energy Dependence of Jet Quenching and Life-time of the Dense Matter in High-energy Heavy-ion Collisions

Suppression of high $p_T$ hadron spectra in high-energy heavy-ion collisions at different energies is studied within a pQCD parton model incorporating medium induced parton energy loss. The $p_T$ dependence of the nuclear modification factor $R_{AA}(p_T)$ is found to depend on both the energy dependence of the parton energy loss and the power-law behavior of the initial jet spectra. The high $p_T$ hadron suppression at $\sqrt{s}=62.4$ GeV and its centrality dependence are studied in detail. The overall values of the modification factor are found to provide strong constraints on the lifetime of the dense matter.Comment: 6 pages in RevTex with 3 postscript figure

Food prices and obesity: long-run effect in US metropolitan areas

Once considered as a serious public health issue only in developed countries, now overweight and obesity have dramatically increased in low- and middle-income countries, especially in urban settings (WHO, 2008). The main purpose of this study is to explore the economic incentives for this rapid growth in obesity rates, by studying variations in obesity over time and across geographic regions in the United States. Although a number of researchers and policymakers have devoted significant resources to address the recent rapid rise in obesity in the United States, âthe prevalence of overweight and obesity has increased sharply since the mid 1970sâ (Centers for Disease Control, 2008) and most of this increase occurred in the 1980s and 1990s (Cutler, et al., 2003). More importantly, changes in food prices have also occurred over the past 30 years and have occurred simultaneously with the obesity epidemic (Finkelstein, et al., 2005). In this study, we investigate how the decline in food prices in the last three decades affects the long-run growth of obesity rates. We take the advantage of the large panel data that cover for the time periods with the fastest growth of obesity rates, by using metropolitan samples from the National Health Interview Survey (NHIS) and information on prices of food at home and food away from home from these major metropolitan areas for years 1976 to 2001. Specifically, instead of using absolute food prices, we explore the impacts from changes in relative prices of food at home and food away from home (i.e. food prices relative to prices for a market basket of consumer goods and services in these metropolitan areas), as well as changes in prices of food at home and food away from home on the growth in obesity rates during this time frame. We also control for the changes in contextual factors and changes in value of female in these metropolitan areas. Our findings reveal the important fact that changes in relative food prices can explain about 20 percent of the obesity growth during this time period and such effect is more pronounced for the low-educated. The results of the study provide an interpretation of the long-run growth of obesity rates in urban settings.Consumer/Household Economics, Food Consumption/Nutrition/Food Safety, Health Economics and Policy,

Disorder driven collapse of the mobility gap and transition to an insulator in fractional quantum Hall effect

We study the nu=1/3 quantum Hall state in presence of the random disorder. We calculate the topologically invariant Chern number, which is the only quantity known at present to unambiguously distinguish between insulating and current carrying states in an interacting system. The mobility gap can be determined numerically this way, which is found to agree with experimental value semiquantitatively. As the disorder strength increases towards a critical value, both the mobility gap and plateau width narrow continuously and ultimately collapse leading to an insulating phase.Comment: 4 pages with 4 figure