Electroded avalanche amorphous selenium (a-Se) photosensor

Although avalanche amorphous selenium (a-Se) is a very promising photoconductor for a variety of imaging applications, it is currently restricted to applications with electron beam readout in vacuum pick-up tube called a High-gain Avalanche Rushing Photoconductor (HARP). The electron beam readout is compatible with high definition television (HDTV) applications, but for use in solid-state medical imaging devices it should be replaced by an electronic readout with a two-dimensional array of metal pixel electrodes. However, due to the high electric field required for avalanche multiplication, it is a technological challenge to avoid possible dielectric breakdown at the edges, where electric field experiences local enhancement. It has been shown recently that this problem can be overcome by the use of a Resistive Interface Layer (RIL) deposited between a-Se and the metal electrode, however, at that time, at a sacrifice in transport properties.Here we show that optimization of RIL deposition technique allows for electroded avalanche a-Se with transport properties and time performance previously not achievable with any other a-Se structures. We have demonstrated this by detailed analysis of transport properties performed by Time-of-Flight (TOF) technique. Our results showed that a stable gain of 200 is reached at 104 V/μm for a 15-μm thick a-Se layer, which is the maximum theoretical gain for this thickness. We conclude that RIL is an enabling technology for practical implementation of solid-state avalanche a-Se image sensors.     

Synthesis of bridged 1,4-diazepane derivatives via Schmidt reactions

A series of bridged 1,4-diazepanes (i.e., diazabicyclo[n.3.2]alkanes, n = 3-5) selectively protected at one of the nitrogen atoms was prepared, for possible application in drug design, via Schmidt rearrangement of the corresponding ketones.     

Para-acylcalix[6]arenes: their synthesis, per-O-functionalisation, solid-state structures and interfacial assembly properties

The para-acylcalix[6]arenes bearing butanoyl, hexanoyl and octanoyl chains have been synthesized by Friedel–Crafts acylation of the parent calixarene. Persubstitution at the phenolic face was achieved to yield the methoxy-diethoxy, ethoxycarbonylmethoxy, methoxycarboxylic acid and butoxysulphonate derivatives. In the case of the derivatives, 5,11,17,23,29,35-hexa-octanoyl-37,38,39,40,41,42-hexa-methoxy-diethoxy-calix[6]arene, 5,11,17,23,29,35-hexa-butanoyl-37,38,39,40,41,42-hexaethoxycarbonyl methoxy-calix[6]arene and 5,11,17,23,29,35-hexa-octanoyl-37,38,39,40,41,42-hexaethoxycarbonyl methoxy-calix[6]arene the solid state structures were determined and show inclusion of two ester groups in the cavity. While for the para-acylcalix[6]arenes no stable monolayers can be formed at the air–water interface, stable monolayers are formed with the methoxy-diethoxy, ethoxycarbonylmethoxy, methoxycarboxylato compounds which show apparent molecular areas in the range 150–200 Å² depending on the length of the acyl chains.     

Additivity of the space of densities of simple-layer potentials with a finite dirichlet integral and integrability of normal derivatives of harmonic W 2 1 -functions on Lipschitz surfaces

We prove that the normal derivatives of piecewise harmonic functions and the densities of surface simple-layer potentials with a finite Dirichlet integral belong to the Lebesgue space on Lipschitz surfaces.     

Shape preserving approximation on the real line with exponential weights

The well-known “Bernstein’s weighted problem” deals with the possibility of weighted approximation on the whole real line. In this paper, we show the possibility of k-monotone approximation on the real line with Freud’s weight .     

Fractal structure and microporosity of nascent particles and sintered powders based on poly(tetrafluoroethylene)

Fractal characteristics of the surface of various powders based on the suspension poly(tetrafluoroethylene) F-4 are studied by the method of low-temperature adsorption of argon. Analysis of the degree of crystallinity, density of the solid phase, and free-volume characteristics (positron-annihilation lifetime spectroscopy) makes it possible to conclude that the granules contain nanopores. Owing to the separation of the contributions from nanoporous and fractal components of the specific surface of the particles, fractal dimension d = 2.60 is estimated in the scaling relationship σ ～ R ^{d ? 3}, where σ is the specific surface and R is the radius of the particle. For this set of powders, the linear dependence of specific air permeability q of the pressed pellets with a porosity of 70 vol % on the dimensions of granules is obtained. This case corresponds to fractal dimensions of the surface of d = 2.5 in the other scaling expression, q ～ R ^{6 ? 2d} . Similar fractal parameters estimated by the adsorption and aerodynamic methods confirm that the hydrodynamic resistance of a porous layer increases owing to an irregular surface of the powder granules. The correlation between the parameters of the heterophase dispersion polymerization and the specific features of the morphology and characteristics of the polymerizate is found for three types of PTFE.     

Micromechanical creep model for pure copper

A Unit Cell made of copper is simulated and investigated under creep conditions within the framework of micromechanics. Geometrical 3D model of the copper microstructure is represented as a Unit Cell with grains of random crystallographical orientation and geometry. Such simulation enables algorithm of Voronoi tessellation. The stress-strain behavior of grains in the general case is anisotropic due to the ordered crystalline structure. The anisotropic model for a material with a cubic symmetry is implemented in Abaqus and used to assign behavior of grain interior in elastic and creep regions. Material parameters for elastic model are taken from elastic tests of single crystal copper [1]. Power law material parameters for creep model are taken from creep test performed for single crystal copper [2]. The model parameter ξ is validated numerically. Creep results are presented for the case of proportional loading during the primary and secondary creep. Statistical analysis of creep curves received for 55 different realizations of Unit Cell geometry is carried out. As a result confident interval and mathematical expectation of creep data are calculated. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)