Ultralight amorphous silicon alloy photovoltaic modules for space applications

Ultralight and ultrathin, flexible, rollup monolithic PV modules have been developed consisting of multijunction, amorphous silicon alloys for either terrestrial or aerospace applications. The rate of progress in increasing conversion efficiency of stable multijunction and multigap PV cells indicates that arrays of these modules can be available for NASA's high power systems in the 1990's. Because of the extremely light module weight and the highly automated process of manufacture, the monolithic a-Si alloy arrays are expected to be strongly competitive with other systems for use in NASA's space station or in other large aerospace applications

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

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

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

Neuromantic : from semi-manual to semi-automatic reconstruction of neuron morphology

The ability to create accurate geometric models of neuronal morphology is important for understanding the role of shape in information processing. Despite a significant amount of research on automating neuron reconstructions from image stacks obtained via microscopy, in practice most data are still collected manually. This paper describes Neuromantic, an open source system for three dimensional digital tracing of neurites. Neuromantic reconstructions are comparable in quality to those of existing commercial and freeware systems while balancing speed and accuracy of manual reconstruction. The combination of semi-automatic tracing, intuitive editing, and ability of visualizing large image stacks on standard computing platforms provides a versatile tool that can help address the reconstructions availability bottleneck. Practical considerations for reducing the computational time and space requirements of the extended algorithm are also discussed

Promoting deep learning through design - discussion, student activity and assessment

There is widespread evidence that Australia is currently facing falling student participation rates in science and mathematics subjects at secondary school and university undergraduate levels. The future implications of this science-deficit are widely acknowledged. Unfortunately, science teaching itself is also widely seen as being dull, too content-heavy, delivered to mass-audiences and assessed in ways promoting surface approaches to learning. To address these issues, and issues relating to the apparent lack of challenge for very able students in their first year at university, The University of Queensland developed the Advanced Study Program in Science (ASPinS). This initiative offers an enhanced learning experience to a select group of high-achieving students in addition to their existing undergraduate study in a Science-related degree program. ASPinS offers these students the opportunity to interact with leading research scientists, broaden their understanding of important scientific issues, experience new interactive learning opportunities, undertake research projects and obtain an authentic insight into science as a career. This presentation, however, will only focus on the unique first year course offered within the 3 year ASPinS experience – BIOL1017 “Perspectives in Science”. In this course students are encouraged to think about important current scientific issues from different perspectives – both scientific and non-scientific. Panels of expert scientists use their knowledge and experience to present real scientific issues for students to examine and discuss. These panel discussions cover a spectrum of medical, environmental and social issues, covering different viewpoints and possible solutions. Combining this effective panel model with an array of student-led activities provides an ideal environment for learning. Students are made to apply their new knowledge, discuss issues and construct thoughts, opinions and products – depending on the specifically designed activities. Relevant assessment tasks include group-writing activities and oral presentations which enable students to demonstrate their learning through authentic contexts that are carefully designed to influence the way students learn. Authentic assessment tasks enable students to see a purpose for the product (assessment) they are producing while at the same time enabling them to synthesise the various scientific ‘facts’ and issues they have been discussing. This level of assessment activity, by its nature, encourages higher-order learning. Student evaluations have consistently confirmed that the key to the success of each Module within the course lies in the breadth of speakers selected to represent the different angles associated with the topic under discussion and the related activities and assessment tasks. The findings indicate that students value the opportunity to explore the multi-disciplinary nature of science-related issues and to actually discuss the issues. The “Perspectives in Science” course is a model for the success of combining teaching and learning theory and scholarship, to a particular set of objectives, to create a highly effective learning environment and a meaningful student experience

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

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

Exact solution of the Hu-Paz-Zhang master equation

The Hu-Paz-Zhang equation is a master equation for an oscillator coupled to a linear passive bath. It is exact within the assumption that the oscillator and bath are initially uncoupled . Here an exact general solution is obtained in the form of an expression for the Wigner function at time t in terms of the initial Wigner function. The result is applied to the motion of a Gaussian wave packet and to that of a pair of such wave packets. A serious divergence arising from the assumption of an initially uncoupled state is found to be due to the zero-point oscillations of the bath and not removed in a cutoff model. As a consequence, worthwhile results for the equation can only be obtained in the high temperature limit, where zero-point oscillations are neglected. In that limit closed form expressions for wave packet spreading and attenuation of coherence are obtained. These results agree within a numerical factor with those appearing in the literature, which apply for the case of a particle at zero temperature that is suddenly coupled to a bath at high temperature. On the other hand very different results are obtained for the physically consistent case in which the initial particle temperature is arranged to coincide with that of the bath

Emergence of a measurement basis in atom-photon scattering

The process of quantum measurement has been a long standing source of debate. A measurement is postulated to collapse a wavefunction onto one of the states of a predetermined set - the measurement basis. This basis origin is not specified within quantum mechanics. According to the theory of decohernce, a measurement basis is singled out by the nature of coupling of a quantum system to its environment. Here we show how a measurement basis emerges in the evolution of the electronic spin of a single trapped atomic ion due to spontaneous photon scattering. Using quantum process tomography we visualize the projection of all spin directions, onto this basis, as a photon is scattered. These basis spin states are found to be aligned with the scattered photon propagation direction. In accordance with decohernce theory, they are subjected to a minimal increase in entropy due to the photon scattering, while, orthogonal states become fully mixed and their entropy is maximally increased. Moreover, we show that detection of the scattered photon polarization measures the spin state of the ion, in the emerging basis, with high fidelity. Lastly, we show that while photon scattering entangles all superpositions of pointer states with the scattered photon polarization, the measurement-basis states themselves remain classically correlated with it. Our findings show that photon scattering by atomic spin superpositions fulfils all the requirements from a quantum measurement process