Quantum and Classical Dynamics of a BEC in a Large-Period Optical Lattice

We experimentally investigate diffraction of a Rb-87 Bose-Einstein condensate from a 1D optical lattice. We use a range of lattice periods and timescales, including those beyond the Raman-Nath limit. We compare the results to quantum mechanical and classical simulations, with quantitative and qualitative agreement, respectively. The classical simulation predicts that the envelope of the time-evolving diffraction pattern is shaped by caustics: singularities in the phase space density of classical trajectories. This behavior becomes increasingly clear as the lattice period grows.Comment: 7 pages, 6 figure

Many-body Theory vs Simulations for the pseudogap in the Hubbard model

The opening of a critical-fluctuation induced pseudogap (or precursor pseudogap) in the one-particle spectral weight of the half-filled two-dimensional Hubbard model is discussed. This pseudogap, appearing in our Monte Carlo simulations, may be obtained from many-body techniques that use Green functions and vertex corrections that are at the same level of approximation. Self-consistent theories of the Eliashberg type (such as the Fluctuation Exchange Approximation) use renormalized Green functions and bare vertices in a context where there is no Migdal theorem. They do not find the pseudogap, in quantitative and qualitative disagreement with simulations, suggesting these methods are inadequate for this problem. Differences between precursor pseudogaps and strong-coupling pseudogaps are also discussed.Comment: Accepted, Phys. Rev. B15 15Mar00. Expanded version of original submission, Latex, 8 pages, epsfig, 5 eps figures (Last one new). Discussion on fluctuation and strong coupling induced pseudogaps expande

Learning in technology-enhanced medical simulation : locations and knowings

The use of simulators has become a common teaching strategy in medical education. It is seen as offering opportunities to address the needs for training interprofessional collaboration by focusing on communication, situation awareness, decision making and coping with stress. While there is a large body of quantitative effect studies supporting the use of technology-enhanced simulations in medical training [3], there is a lack of rigorous, theory-based, qualitative studies to clarify how and when to effectively use simulations to train health care professionals. This qualitative study aims to investigate simulation-based medical training situations, focusing on performance, material arrangements and production of forms of knowing/learning

COMBINING QUANTITATIVE AND QUALITATIVE APPROACHES TO RURAL DEVELOPMENT ANALYSIS: THE CASE OF AGRICULTURAL INTENSIFICATION IN LEBANON

While peripheral rural regions in Lebanon face typical problems of lagging development and economic marginalisation, they have not been regarded as a priority for policy-makers, and significant disparities between these and other regions have emerged as a result. Local extensionists have encouraged technological innovation as a means to improving farmers’ livelihoods, and this has led to increasing input use and an intensification of agricultural production. This paper applies contrasting quantitative and qualitative methodologies to analyse the effects of such changes at the level of the overall economy of Lebanon and also to explore the impacts on rural households. A Computable General Equilibrium (CGE) model explores several simulation scenarios in which agricultural output increases due to intensification in the use of intermediate inputs. The results are evaluated at local level through the use of qualitative case-study analysis carried out in the Hermel region of northeast Lebanon. Quantitative simulations indicate that, while intensification has a positive effect overall on the Lebanese economy, the effects on rural households and the income of farmers are negative; the case-study demonstrates that, at local level, agricultural trade liberalisation, increased agricultural output and greater volatility of commodity prices has resulted in farmers opting for lower input use and more secure market forms of production.Community/Rural/Urban Development,

Plasmon Resonance in Multilayer Graphene Nanoribbons

Plasmon resonance in nanopatterned single layer graphene nanoribbon (SL-GNR), double layer graphene nanoribbon (DL-GNR) and triple layer graphene nanoribbon (TL-GNR) structures is studied both experimentally and by numerical simulations. We use 'realistic' graphene samples in our experiments to identify the key bottle necks in both experiments and theoretical models. The existence of electrical tunable plasmons in such stacked multilayer GNRs was first experimentally verified by infrared microscopy. We find that the strength of the plasmonic resonance increases in DL-GNR when compared to SL-GNRs. However, we do not find a further such increase in TL-GNRs compared to DL-GNRs. We carried out systematic full wave simulations using finite element technique to validate and fit experimental results, and extract the carrier scattering rate as a fitting parameter. The numerical simulations show remarkable agreement with experiments for unpatterned SLG sheet, and a qualitative agreement for patterned graphene sheet. We believe that further improvements such as introducing a bandgap into the numerical model could lead to a better quantitative agreement of numerical simulations with experiments. We also note that such advanced modeling would first require better quality graphene samples and accurate measurements

Nonlinearity and stochasticity in the density--velocity relation

We present results of the investigations of the statistical properties of a joint density and velocity divergence probability distribution function (PDF) in the mildly non-linear regime. For that purpose we use both perturbation theory results, extended here for a top-hat filter, and numerical simulations. In particular we derive the quantitative (complete as possible up to third order terms) and qualitative predictions for constrained averages and constrained dispersions -- which describe the nonlinearities and the stochasticity properties beyond the linear regime -- and compare them against numerical simulations. We find overall a good agreement for constrained averages; however, the agreement for constrained dispersions is only qualitative. Scaling relations for the Omega-dependence of these quantities are satisfactory reproduced. Guided by our analytical and numerical results, we finally construct a robust phenomenological description of the joint PDF in a closed analytic form. The good agreement of our formula with results of N-body simulations for a number of cosmological parameters provides a sound validation of the presented approach. Our results provide a basis for a potentially powerful tool with which it is possible to analyze galaxy survey data in order to test the gravitational instability paradigm beyond the linear regime and put useful constraints on cosmological parameters. In particular we show how the nonlinearity in the density--velocity relation can be used to break the so-called Omega-bias degeneracy in cosmic density-velocity comparisons.Comment: 12 pages, 11 figures; revised version with minor changes in the presentation, accepted for publication in MNRA