A novel design approach for the epitaxial layer for 4H-SiC and 6H-SiC power bipolar devices

The paper evaluates the optimal design of the low-doped base region inside power diodes and other bipolar devices. It is demonstrated theoretically that a low-doped base region of P⁺N⁻N⁺ diodes can provide a high breakdown voltage and an optimal on-resistance . A simple, accurate and CPU timesaving approach is presented to extract an optimal value for the base region width, W_B, and its doping concentration, N_D. The paper details an analytical relation between W_B and N_D, and gives a method for quantifying the trade-off between their values for a given breakdown voltage and for obtaining the minimal on-resistance. Analytical results are confronted with experimental results for 4H-SiC- and 6H-SiC-based diodes.     

Concentration landscape generators for shear free dynamic chemical stimulation

In this paper we first introduce a novel fabrication process, which allows for easy integration of thin track-etched nanoporous membranes, within 2D or 3D microchannel networks. In these networks, soluble chemical compounds can diffuse out of the channels through well-defined and spatially organized microfabricated porous openings. Interestingly, multiple micron-scale porous areas can be integrated in the same device and each of these areas can be connected to a different microfluidic channel and reservoir. We then present and characterize several membrane-based microdevices and their use for the generation of stable diffusible concentration gradients and complex dynamic chemical landscapes under shear free conditions. We also demonstrate how a simple flow-focusing geometry can be used to generate "on-demand" concentration profiles. In turn, these devices should provide an ideal experimental framework for high throughput cell-based assays: long term high-resolution video microscopy experiments can be performed, under multiple spatially and temporally controlled chemical conditions, with simple protocols and in a cell-friendly environment.     

Measurement of the 85Rb(γ, n)84mRb cross-section in the energy range 10-19 MeV with bremsstrahlung photons

We study the charmonium 2S states ??? and ??? _c , and the bottomonium 2S states ???? and ??? _b , using the light-front quark model and the 2S state wave function of harmonic oscillator as the approximation of the 2S quarkonium wave function. The decay constants, transition form factors and masses of these mesons are calculated and compared with experimental data. Predictions of quantities such as Br(???????? _c ) are made. The 2S wave function may help us learn more about the structure of these heavy quarkonia.     

Hydrophilic/hydrophobic features of TiO2 nanoparticles as a function of crystal phase, surface area and coating, in relation to their potential toxicity in peripheral nervous system

The hydrophilic/hydrophobic properties of a variety of commercial TiO(2) nanoparticles (NP), to be employed as inorganic filters in sunscreen lotions, were investigated both as such (dry powders) and dispersed in aqueous media. Water uptake and the related interaction energy have been determined by means of adsorption microcalorimetry of H(2)O vapor, whereas dispersion features in aqueous solutions were investigated by dynamic light scattering and electrokinetic measurements (zeta potential). The optimized dispersions in cell culture medium were employed to assess the possible in vitro neuro-toxicological effect on dorsal root ganglion (DRG) cells upon exposure to TiO(2)-NP, as a function of crystal phase, surface area and coating. All investigated materials, with the only exception of the uncoated rutile, were found to induce apoptosis on DRG cells; the inorganic/organic surface coating was found not to protect against the TiO(2)-induced apoptosis. The risk profile for DRG cells, which varies for the uncoated samples in the same sequence as the photo-catalytic activity of the different polymorphs: anatase-rutile>anatase>rutile, was found not to be correlated with the surface hydrophilicity of the uncoated/coated specimens. Aggregates/agglomerates hydrodynamic diameter was comprised in the ~200-400 nm range, compatible with the internalization within DRG cells.     

Baryon-Baryon correlations at small relative momentum in Neon- and Argon-nucleus collisions betweenE/A=200 and 1000 MeV

Two-proton correlation functions at small relative momentum have been systematically studied with the large solid angle detector DIOGENE at Saturne for interactions induced by Ne and Ar beams on various targets, and incident energies per nucleon ranging from 200 to 1000 MeV. From these distributions, informations on the space-time structure of the source have been derived as a function of the centrality of the collision, the target-projectile combinations and the incident energy, using the model of Koonin. Special attention has been devoted to take into account all experimental biases in order to get the distorted theoretical correlation curves before comparison to the experimental data. Other interesting conclusions have been obtained when comparing the extracted source radii to the dimensions of the overlapping volume of target by projectile in a pure geometrical model of the collision (clean cut geometry). Some results concerning fragment-fragment small angle correlations are also presented.     

Optical studies on the red luminescence of InGaN epilayers

Photoluminescence, photoluminescence excitation and time-resolved photoluminescence studies were performed in a partially relaxed InGaN epilayer, and exhibiting a 3D growth mode at the surface. Two emission bands, a red (centred at 1.88 eV) and a blue (centred at 2.58 eV) were observed. In order to investigate their origin and their relation with the strain relaxation along the growth direction, the sample was etched. After etching, only an asymmetrical broad emission band centred at 2.15 eV was observed.The decrease of decay time and the increase of the band edge absorption energy with increasing monitored photon energy, along the red emission, are assigned to the effect of localization of excitons at potential minima, originated in compositional and strain inhomogeneities of the sample. Therefore, the blue shift observed on this band with an increase in temperature, is caused by the population of higher energy states. The large difference between the luminescence intensities, decay times and the thermal quenching of the red and blue (centred at 2.58 eV) band is also accounted for by the localization model. It is demonstrated that the luminescence observed after etching is a superposition of two bands, one originated from the InGaN film, and the other from the GaN underlayer. The large difference between absorption and emission energies, compared with those measured in the as-grown sample, within the same spectral region, indicates that this emission has a different origin. It is suggested that deep levels might be responsible for the luminescence observed after etching.     

Crochelins: Siderophores with an Unprecedented Iron‐Chelating Moiety from the Nitrogen‐Fixing Bacterium Azotobacter chroococcum

Microbes use siderophores to access essential iron resources in the environment. Over 500 siderophores are known, but they utilize a small set of common moieties to bind iron. Azotobacter chroococcum expresses iron‐rich nitrogenases, with which it reduces N₂. Though an important agricultural inoculant, the structures of its iron‐binding molecules remain unknown. Here, the “chelome” of A. chroococcum is examined using small molecule discovery and bioinformatics. The bacterium produces vibrioferrin and amphibactins as well as a novel family of siderophores, the crochelins. Detailed characterization shows that the most abundant member, crochelin A, binds iron in a hexadentate fashion using a new iron‐chelating γ‐amino acid. Insights into the biosynthesis of crochelins and the mechanism by which iron may be removed upon import of the holo‐siderophore are presented. This work expands the repertoire of iron‐chelating moieties in microbial siderophores.