Transport Mean Free Path for Magneto-Transverse Light Diffusion

We derive an expression for the transport mean free path $\ell^*_\perp$ associated with magneto-transverse light diffusion for a random collection of Faraday-active Mie scatterers. This expression relates the magneto-transverse diffusion in multiple scattering directly to the magneto-transverse scattering of a single scatterer.Comment: 5 pages, 1 figure, Latex, accepted for publication in Europhysics Letter

Gallavotti-Cohen-Type symmetry related to cycle decompositions for Markov chains and biochemical applications

We slightly extend the fluctuation theorem obtained in \cite{LS} for sums of generators, considering continuous-time Markov chains on a finite state space whose underlying graph has multiple edges and no loop. This extended frame is suited when analyzing chemical systems. As simple corollary we derive in a different method the fluctuation theorem of D. Andrieux and P. Gaspard for the fluxes along the chords associated to a fundamental set of oriented cycles \cite{AG2}. We associate to each random trajectory an oriented cycle on the graph and we decompose it in terms of a basis of oriented cycles. We prove a fluctuation theorem for the coefficients in this decomposition. The resulting fluctuation theorem involves the cycle affinities, which in many real systems correspond to the macroscopic forces. In addition, the above decomposition is useful when analyzing the large deviations of additive functionals of the Markov chain. As example of application, in a very general context we derive a fluctuation relation for the mechanical and chemical currents of a molecular motor moving along a periodic filament.Comment: 23 pages, 5 figures. Correction

Coherent Backscattering of light in a magnetic field

This paper describes how coherent backscattering is altered by an external magnetic field. In the theory presented, magneto-optical effects occur inside Mie scatterers embedded in a non-magnetic medium. Unlike previous theories based on point-like scatterers, the decrease of coherent backscattering is obtained in leading order of the magnetic field using rigorous Mie theory. This decrease is strongly enhanced in the proximity of resonances, which cause the path length of the wave inside a scatterer to be increased. Also presented is a novel analysis of the shape of the backscattering cone in a magnetic field.Comment: 27 pages, 5 figures, Revtex, to appear in Phys. Rev.

Modulating spin transfer torque switching dynamics with two orthogonal spin-polarizers by varying the cell aspect ratio

We study in-plane magnetic tunnel junctions with additional perpendicular polarizer for subnanosecond-current-induced switching memories. The spin-transfer-torque switching dynamics was studied as a function of the cell aspect ratio both experimentally and by numerical simulations using the macrospin model. We show that the anisotropy field plays a significant role in the dynamics, along with the relative amplitude of the two spin-torque contributions. This was confirmed by micromagnetic simulations. Real-time measurements of the reversal were performed with samples of low and high aspect ratio. For low aspect ratios, a precessional motion of the magnetization was observed and the effect of temperature on the precession coherence was studied. For high aspect ratios, we observed magnetization reversals in less than 1 ns for high enough current densities, the final state being controlled by the current direction in the magnetic tunnel junction cell.Comment: 6 pages, 7 figure

Phase transitions in a ferrofluid at magnetic field induced microphase separation

In the presence of a magnetic field applied perpendicular to a thin sample layer, a suspension of magnetic colloidal particles (ferrofluid) can form spatially modulated phases with a characteristic length determined by the competition between dipolar forces and short-range forces opposing density variations. We introduce models for thin-film ferrofluids in which magnetization and particle density are viewed as independent variables and in which the non-magnetic properties of the colloidal particles are described either by a lattice-gas entropy or by the Carnahan-Starling free energy. Our description is particularly well suited to the low-particle density regions studied in many experiments. Within mean-field theory, we find isotropic, hexagonal and stripe phases, separated in general by first-order phase boundaries.Comment: 12 pages, RevTex, to appear in PR

Modification of textured silicon wafer surface morphology for fabrication of heterojunction solar cell with open circuit voltage over 700mV

Crystalline silicon wafer (c-Si) can be extremely well passivated by plasma enhanced chemical vapor deposited (PECVD) amorphous silicon (a-Si:H) films. As a result, on flat substrates, solar cells with very high open circuit voltage are readily obtained. On textured substrates however the passivation is more cumbersome, likely due to the presence of localized recombinative paths situated at the pyramid valleys. Here, we show that this issue may be resolved by selecting a silicon substrate morphology featuring large pyramids. Chemical post-texturization treatments can further reduce the surface recombination velocity. This sequence has allowed us to fabricate solar cells with open circuit voltage over 700 mV, demonstrating also on device level the effect of pyramid density and surface micro-roughness on the surface passivation quality

Corpus Callosum Morphology in Capuchin Monkeys Is Influenced by Sex and Handedness

Sex differences have been reported in both overall corpus callosum area and its regional subdivisions in humans. Some have suggested this reflects a unique adaptation in humans, as similar sex differences in corpus callosum morphology have not been reported in any other species of primate examined to date. Furthermore, an association between various measurements of corpus callosum morphology and handedness has been found in humans and chimpanzees. In the current study, we report measurements of corpus callosum cross-sectional area from midsagittal MR images collected in vivo from 14 adult capuchin monkeys, 9 of which were also characterized for hand preference on a coordinated bimanual task. Adult females were found to have a significantly larger corpus callosum: brain volume ratio, rostral body, posterior midbody, isthmus, and splenium than adult males. Left-handed individuals had a larger relative overall corpus callosum area than did right-handed individuals. Additionally, a significant sex and handedness interaction was found for anterior midbody, with right-handed males having a significantly smaller area than right-handed females. These results suggest that sex and handedness influences on corpus callosum morphology are not restricted to Homo sapiens

Properties of interfaces in amorphous/crystalline silicon heterojunctions

To study recombination at the amorphous/crystalline Si (a- Si:H/c-Si) heterointerface, the amphoteric nature of silicon (Si) dangling bonds is taken into account. Modeling interface recombination measured on various test structures provides insight into the microscopic passivation mechanisms, yielding an excellent interface defect density reduction by intrinsic a-Si:H and tunable field-effect passivation by doped layers. The potential of this model's applicability to recombination at other Si heterointerfaces is demonstrated. Solar cell properties of a-Si:H/c-Si heterojunctions are in good accordance with the microscopic interface properties revealed by modeling, that are, e.g., slight asymmetries in the neutral capture cross-sections and band offsets. The importance of atomically abrupt interfaces and the difficulties to obtain them on pyramidally textured c-Si is studied in combination with transmission electron microscopy

Laminar degeneration of frontal and temporal cortex in Parkinson disease dementia

To investigate cortical laminar degeneration in Parkinson’s disease (PD) with dementia (PDD). Changes in density of α-synuclein-immunoreactive Lewy bodies (LB), Lewy neurites (LN), and Lewy grains (LG) together with surviving neurons, abnormally enlarged neurons (EN), vacuoles, and glial cell nuclei were measured across cortical laminae of frontal and temporal cortex in fifteen cases of PDD using quantitative methods and polynomial curve-fitting. Most frequently, LB and LN were distributed across all laminae, while LG were distributed in upper cortical laminae. Low densities of EN were present in most cases distributed across all cortical laminae. Densities of vacuoles and glia were greatest in upper and lower cortical laminae, respectively. In most gyri, there were no spatial correlations between the densities of LB, LN, and LG. Cortical degeneration of frontal and temporal lobes in PDD affects all cortical laminae. Laminar distributions may result from the spread of α-synuclein pathology from subcortical regions and subsequent spread via the cortico-cortical pathways. This spread may be a major factor in the development of dementia in PD