Theory and modeling of ion acceleration from the interaction of ultra-intense lasers with solid density targets

The interaction of a high intensity, short-pulse laser with a thin target can lead to the generation of a highly collimated beam of fast ions off the rear target surface. These ion beams have the potential to impact inertial confinement fusion applications, including their use in diagnostics and fast-ignition. Recent work by the authors in the modeling of ion acceleration, using both full particle-in-cell and hybrid (particle ions, reduced electron physics) models, is leading to improved understanding of the physics governing ion acceleration

Particle-in-cell studies of laser-driven hot spots and a statistical model for mesoscopic properties of Raman backscatter

The authors use explicit particle-in-cell simulations to model stimulated scattering processes in media with both solitary and multiple laser hot spots. These simulations indicate coupling among hot spots, whereby scattered light, plasma waves, and hot electrons generated in one laser hot spot may propagate to neighboring hot spots, which can be destabilized to enhanced backscatter. A nonlinear statistical model of a stochastic beam exhibiting this coupled behavior is described here. Calibration of the model using particle-in-cell simulations is performed, and a threshold is derived for “detonation” of the beam to high reflectivity

The effect of oestradiol implants on regional and total bone mass: a three-year longitudinal study

Objective: Although there is evidence from cross-sectional studies that percutaneous oestrogen administration protects against menopausal bone loss, few longitudinal data are available. We have examined the effect of 3 years' treatment with percutaneous oestradiol on total body calcium, spinal trabecular bone mineral density and radial bone mineral content in post-menopausal women. Design and patients: Twenty-nine post-menopausal women, aged 37–55 years, who had undergone hysterectomy and had experienced the onset of menopausal symptoms within the previous 2 years, were studied before and for 3 years during hormone replacement with oestradiol implants, given at approximately 6-monthly intervals. Measurements: Total body calcium was measured by prompt gamma neutron activation analysis, spinal trabecular bone mineral density by quantitative computed tomography and radial bone mineral content by single-photon absorptiometry. Results: There was a significant increase in the mean total body calcium, spinal trabecular bone mineral density and radial bone mineral content over the 3 years of the study. The mean (± SEM) percentage change per annum was +2 4% (±0.8) for total body calcium (P <0 01), + 3.3% (±0.6) for spinal trabecular bone mineral density (P < 0.001) and +12% (± 0.6) for radial bone mineral content (P < 0 05). Conclusions: Percutaneous oestradiol replacement therapy prevents menopausal bone loss and is associated with a sustained and significant increase in total body calcium, spinal trabecular bone mineral density and radial bone mineral content over a 3-year treatment period. Oestradiol implants thus have skeletal effects comparable to those of oral or transdermal oestrogens

Extra-classical receptive field effects measured in striate cortex with fMRI

The aim of this study was to measure the contextual influence of globally coherent motion on visual cortical responses using functional magnetic resonance imaging. Our motivation was to test a prediction from representational theories of perception (i.e. predictive coding) that primary visual responses should be suppressed by top-down influences during coherent motion. We used a sparse stimulus array such that each element could not fall within the same classical receptive field of primary visual cortex neurons (i.e. precluding lateral interactions within V1). This enabled us to attribute differences, in striate cortex responses, to extra-classical receptive field effects mediated by backward connections. In accord with theoretical predictions we were able to demonstrate suppression of striate cortex activations to coherent relative to incoherent motion. These results suggest that suppression of primary visual cortex responses to coherent motion reflect extra-classical effects mediated by backward connections