Entropy and specific heat for open systems in steady states

The fundamental assumption of statistical mechanics is that the system is equally likely in any of the accessible microstates. Based on this assumption, the Boltzmann distribution is derived and the full theory of statistical thermodynamics can be built. In this paper, we show that the Boltzmann distribution in general can not describe the steady state of open system. Based on the effective Hamiltonian approach, we calculate the specific heat, the free energy and the entropy for an open system in steady states. Examples are illustrated and discussed.Comment: 4 pages, 7 figure

Multi-agent collaborative search : an agent-based memetic multi-objective optimization algorithm applied to space trajectory design

This article presents an algorithm for multi-objective optimization that blends together a number of heuristics. A population of agents combines heuristics that aim at exploring the search space both globally and in a neighbourhood of each agent. These heuristics are complemented with a combination of a local and global archive. The novel agent-based algorithm is tested at first on a set of standard problems and then on three specific problems in space trajectory design. Its performance is compared against a number of state-of-the-art multi-objective optimization algorithms that use the Pareto dominance as selection criterion: non-dominated sorting genetic algorithm (NSGA-II), Pareto archived evolution strategy (PAES), multiple objective particle swarm optimization (MOPSO), and multiple trajectory search (MTS). The results demonstrate that the agent-based search can identify parts of the Pareto set that the other algorithms were not able to capture. Furthermore, convergence is statistically better although the variance of the results is in some cases higher

Modulational instability criteria for two-component Bose-Einstein condensates

The stability of colliding Bose-Einstein condensates is investigated. A set of coupled Gross-Pitaevskii equations is thus considered, and analyzed via a perturbative approach. No assumption is made on the signs (or magnitudes) of the relevant parameters like the scattering lengths and the coupling coefficients. The formalism is therefore valid for asymmetric as well as symmetric coupled condensate wave states. A new set of explicit criteria is derived and analyzed. An extended instability region, in addition to an enhanced instability growth rate is predicted for unstable two component bosons, as compared to the individual (uncoupled) state.Comment: 4 pages, 1 figur

Analysis of some global optimization algorithms for space trajectory design

In this paper, we analyze the performance of some global search algorithms on a number of space trajectory design problems. A rigorous testing procedure is introduced to measure the ability of an algorithm to identify the set of ²-optimal solutions. From the analysis of the test results, a novel algorithm is derived. The development of the novel algorithm starts from the redefinition of some evolutionary heuristics in the form of a discrete dynamical system. The convergence properties of this discrete dynamical system are used to derive a hybrid evolutionary algorithm that displays very good performance on the particular class of problems presented in this paper

Assessment of the PROBIT approach for estimating the prevalence of global, moderate and severe acute malnutrition from population surveys

Abstract Objective Prevalence of acute malnutrition is classically estimated by the proportion of children meeting a case definition in a representative population sample. In 1995 the WHO proposed the PROBIT method, based on converting parameters of a normally distributed variable to cumulative probability, as an alternative method requiring a smaller sample size. The present study compares classical and PROBIT methods for estimating the prevalence of global, moderate and severe acute malnutrition (GAM, MAM and SAM) defined by weight-for-height Z-score (WHZ) or mid-upper arm circumference (MUAC). Design Bias and precision of classical and PROBIT methods were compared by simulating a total of 1·26 million surveys generated from 560 nutrition surveys. Setting Data used for simulation were derived from nutritional surveys of children aged 6-59 months carried out in thirty-one countries around the world. Subjects Data of 459 036 children aged 6-59 months from representative samples were used to generate simulated populations. Results The PROBIT method provided an estimate of GAM, MAM and SAM using WHZ or MUAC proportional to the true prevalence with a small systematic overestimation. The PROBIT method was more precise than the classical method for estimating the prevalence for GAM, MAM and SAM by WHZ or MUAC for small sample sizes (i.e. n<150 for SAM and GAM; n<300 for MAM), but lost this advantage when sample sizes increased. Conclusions The classical method is preferred for estimating acute malnutrition prevalence from large sample surveys. The PROBIT method may be useful in sentinel-site surveillance systems with small sample size

The undergraduate research apprenticeship - improving the relevance of science teaching through authentic research experience.

The undergraduate experience is arguably the most important in shaping the future career trajectories of students. It is here that early exposure to the widest possible range of disciplines and practical experiences will have the most impact. In the face of a reduction in the number of students entering both undergraduate science and research as a career option, we must urgently initiate strategies to engage and retain students in science. This can be achieved by a research experience in a ‘mentored apprenticeship model’ in the context of an authentic laboratory/field during their formative undergraduate years. It is widely acknowledged that an interactive, enquiry-based approach to learning provides the most meaningful and lasting learning experience for students. It is similarly accepted that, within science, undergraduate research experiences are pivotal in providing context to student learning and providing a true sense of what it means to be a 'scientist'. In this discussion forum we will summarise research-based experiences currently available for Bachelor of Science (BSc) students at The University of Queensland (UQ). We will then look in detail at a proposed new ‘mentored apprenticeship model’, being examined for introduction into the UQ BSc from 2008 following the recent major review. The proposed model builds on the existing UQ Advanced Study Program in Science combined with the University of Michigan’s Undergraduate Research Opportunity Program and aims to: • achieve an increased level of student engagement to complement other strategies for motivating students who are in large first year classes • show students the functional/practical relevance of the core content of their course material • provide students with a personal experience of doing science so that they can plan their future studies from a more informed perspective • minimize the attrition rate from the first year science cohort • provide a mentored cohort experience to engage and support under-represented groups such as indigenous and international students • actively build on the tremendous investment in institutes at UQ by increasing the direct involvement of these research academics in the undergraduate science program (for example, places for 25 students have already been committed by one of the UQ research institutes) • increase the number of students proceeding to postgraduate education as the next step to a worthwhile and personally rewarding career trajectory in science. The proposed ‘mentored apprenticeship model’ provides a step-wise approach to a student’s growth as an apprentice scientist. As undergraduates progress through their degree-program their learning experiences in science should also progress closer and closer to those of a ‘scientist’ until, on graduation, they are fully-prepared for their science-related career. The new model achieves this through establishing strong working partnerships between students and research groups, supplementing traditional practical components of undergraduate courses by ‘doing’ more science and providing students with an opportunity to talk more about science. Within this forum participants will be asked to explore: • How are the theoretical frameworks of enquiry-based learning being translated into practical applications? • What are the outcomes of an undergraduate research opportunity? • How do we assess this learning? • What are the experiences of other institutions – how have they met the challenge of an authentic research experience, in a research-intensive university, for large numbers of students? • Are there discipline-specific variations to these approaches

Dynamical decoherence in a cavity with a large number of two-level atoms

We consider a large number of two-level atoms interacting with the mode of a cavity in the rotating-wave approximation (Tavis-Cummings model). We apply the Holstein-Primakoff transformation to study the model in the limit of the number of two-level atoms, all in their ground state, becoming very large. The unitary evolution that we obtain in this approximation is applied to a macroscopic superposition state showing that, when the coherent states forming the superposition are enough distant, then the state collapses on a single coherent state describing a classical radiation mode. This appear as a true dynamical effect that could be observed in experiments with cavities.Comment: 9 pages, no figures. This submission substitutes paper quant-ph/0212148 that was withdrawn. Version accepted for publication in Journal of Physics B: Atomic, Molecular & Optical Physic

Static Properties of Trapped Bose-Fermi Mixed Condensate of Alkali Atoms

Static properties of a bose-fermi mixture of trapped potassium atoms are studied in terms of coupled Gross-Pitaevskii and Thomas-Fermi equations for both repulsive and attractive bose-fermi interatomic potentials. Qualitative estimates are given for solutions of the coupled equations, and the parameter regions are obtained analytically for the boson-density profile change and for the boson/fermion phase separation. Especially, the parameter ratio $R_{int}$ is found that discriminates the region of the large boson-profile change. These estimates are applied for numerical results for the potassium atoms and checked their consistency. It is suggested that a small fraction of fermions could be trapped without an external potential for the system with an attractive boson-fermion interaction.Comment: 8 pages,5 figure