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

Geometric phase in dephasing systems

Beyond the quantum Markov approximation, we calculate the geometric phase of a two-level system driven by a quantized magnetic field subject to phase dephasing. The phase reduces to the standard geometric phase in the weak coupling limit and it involves the phase information of the environment in general. In contrast with the geometric phase in dissipative systems, the geometric phase acquired by the system can be observed on a long time scale. We also show that with the system decohering to its pointer states, the geometric phase factor tends to a sum over the phase factors pertaining to the pointer states.Comment: 4 page

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

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

Instabilities of wave function monopoles in Bose-Einstein condensates

We present analytic and numerical results for a class of monopole solutions to the two-component Gross-Pitaevski equation for a two-species Bose condensate in an effectively two-dimensional trap. We exhibit dynamical instabilities involving vortex production as one species pours through another, from which we conclude that the sub-optical sharpness of potentials exerted by matter waves makes condensates ideal tools for manipulating condensates. We also show that there are two equally valid but drastically different hydrodynamic descriptions of a two-component condensate, and illustrate how different phenomena may appear simpler in each.Comment: 4 pages, 9 figures (compressed figures become legible when zoomed or when paper is actually printed

Prevalence study of yaws in the Democratic Republic of Congo using the lot quality assurance sampling method.

BACKGROUND: Until the 1970s the prevalence of non-venereal trepanomatosis, including yaws, was greatly reduced after worldwide mass treatment. In 2005, cases were again reported in the Democratic Republic of the Congo. We carried out a survey to estimate the village-level prevalence of yaws in the region of Equator in the north of the country in order to define appropriate strategies to effectively treat the affected population. METHODOLOGY/PRINCIPAL FINDINGS: We designed a community-based survey using the Lot Quality Assurance Sampling method to classify the prevalence of active yaws in 14 groups of villages (lots). The classification into high, moderate, or low yaws prevalence corresponded to World Health Organization prevalence thresholds for identifying appropriate operational treatment strategies. Active yaws cases were defined by suggestive clinical signs and positive rapid plasma reagin and Treponema pallidum hemagglutination serological tests. The overall prevalence in the study area was 4.7% (95% confidence interval: 3.4-6.0). Two of 14 lots had high prevalence (>10%), three moderate prevalence (5-10%) and nine low prevalence (<5%.). CONCLUSIONS/SIGNIFICANCE: Although yaws is no longer a World Health Organization priority disease, the presence of yaws in a region where it was supposed to be eradicated demonstrates the importance of continued surveillance and control efforts. Yaws should remain a public health priority in countries where previously it was known to be endemic. The integration of sensitive surveillance systems together with free access to effective treatment is recommended. As a consequence of our study results, more than 16,000 people received free treatment against yaws

Effective non-linear dynamics of binary condensates and open problems

We report on a recent result concerning the effective dynamics for a mixture of Bose-Einstein condensates, a class of systems much studied in physics and receiving a large amount of attention in the recent literature in mathematical physics; for such models, the effective dynamics is described by a coupled system of non-linear Sch\"odinger equations. After reviewing and commenting our proof in the mean field regime from a previous paper, we collect the main details needed to obtain the rigorous derivation of the effective dynamics in the Gross-Pitaevskii scaling limit.Comment: Corrected typos, updated reference

Two-species magneto-optical trap with 40K and 87Rb

We trap and cool a gas composed of 40K and 87Rb, using a two-species magneto-optical trap (MOT). This trap represents the first step towards cooling the Bose-Fermi mixture to quantum degeneracy. Laser light for the MOT is derived from laser diodes and amplified with a single high power semiconductor amplifier chip. The four-color laser system is described, and the single-species and two-species MOTs are characterized. Atom numbers of 1x10^7 40K and 2x10^9 87Rb are trapped in the two-species MOT. Observation of trap loss due to collisions between species is presented and future prospects for the experiment are discussed.Comment: 4 pages, 4 figures; accepted for publication in Physical Review