Silicon matrix disorder in amorphous hydrogenated silicon alloys

The authors report a detailed investigation of correlations between Urbach energies from photothermal deflection spectroscopy and Raman half-widths of transverse optic (TO)-like Si-Si modes as a measure of silicon matrix disorder in glow-discharge amorphous hydrogenated silicon (a-Si:H) and a-SiGe:H, as well as in glow-discharge and sputtered a-SiC:H and a-SiN:H. A corresponding decrease in TO full width at half-maximum (FWHM) and Urbach energy E₀ for soft deposition techniques yields bond angle distributions as narrow as 8.5° for the best a-Si:H films. Even at the lowest levels of nitrogen incorporation, simultaneous increases in E₀ and TO-like half-widths indicate that lattice distortions occur due to threefold coordination of nitrogen in the a-Si:H matrix. In contrast, no deviation of silicon TO-FWHM could be detected in a-SiC:H of up to 35 at.% of carbon content, whereas Urbach edges broaden in a well-known manner that is interpreted in terms of -CH₃ incorporation into the amorphous network. Diborane doping and sputter deposition, however, give rise to lattice distortions in a-SiC:H, which reflects changes in the carbon coordination     

The Synthesis of Vicinal Diacylamines via Bamberger Ring Cleavage of Substituted Imidazoles. 1,2,4-Triacylaminobutanes Bearing Different Acyl Groups

Bamberger ring cleavage acylation of N-p-toluenesulfonyl (tosyl) histamine followed by hydrogenation yields 3,4-diacylaminobutanetosylamine, a triamine containing groups with different chemical reactivities.     

Sliding-induced adhesion of stiff polymer microfibre arrays. I. Macroscale behaviour.

Gecko-inspired microfibre arrays with 42 million polypropylene fibres cm(-2) (each fibre with elastic modulus 1 GPa, length 20 microm and diameter 0.6 microm) were fabricated and tested under pure shear loading conditions, after removing a preload of less than 0.1 N cm(-2). After sliding to engage fibres, 2 cm2 patches developed up to 4N of shear force with an estimated contact region of 0.44 cm2. The control unfibrillated surface had no measurable shear force. For comparison, a natural setal patch tested under the same conditions on smooth glass showed approximately seven times greater shear per unit estimated contact region. Similar to gecko fibre arrays, the synthetic patch maintains contact and increases shear force with sliding. The high shear force observed (approx. 210 nN per fibre) suggests that fibres are in side contact, providing a larger true contact area than would be obtained by tip contact. Shear force increased over the course of repeated tests for synthetic patches, suggesting deformation of fibres into more favourable conformations.     

Sintering of Colloidal Ru/γ-Al2O3 Catalyst in Hydrogen

Colloidal 5.1 wt% Ru/γ-Al₂O₃ catalyst was prepared by a microwave assisted, solvothermal reduction of RuCl₃ in ethylene glycol in the presence of γ-Al₂O₃. The catalyst subjected to heat-treatment in hydrogen up to 700 °C, was characterized by BET, XRD, TEM and H₂ chemisorption. As-prepared catalyst contained Ru nanoparticles with mean size of 1.5 nm and narrow size distribution uniformly distributed over the support. The nanoparticles were stable on the alumina to 500 °C, but treatment at 600–700 °C caused some sintering of Ru due to migration and coalescence of a part of smallest ruthenium nanoparticles. However, even after H₂ treatment at 700 °C, large amount of Ru nanoparticles with sizes of 1–3 nm remained in the catalyst. H₂ chemisorption data revealed decrease of Ru dispersion from 0.28 to 0.19 by hydrogen treatment at 700 °C and were in good correspondence with TEM results. On the contrary, mean crystallite sizes obtained from XRD were strongly overestimated.     

A Superlinearly and Globally Convergent Algorithm for Power Control and Resource Allocation With General Interference Functions

In wireless networks, users are typically coupled by interference. Hence, resource allocation can strongly depend on receive strategies, such as beamforming, CDMA receivers, etc. We study the problem of minimizing the total transmission power while maintaining individual quality-of-service (QoS) values for all users. This problem can be solved by the fixed-point iteration proposed by Yates (1995) as well as by a recently proposed matrix-based iteration (Schubert and Boche, 2007). It was observed by numerical simulations that the matrix-based iteration has interesting numerical properties, and achieves the global optimum in only a few steps. However, an analytical investigation of the convergence behavior has been an open problem so far. In this paper, we show that the matrix-based iteration can be reformulated as a Newton-type iteration of a convex function, which is not guaranteed to be continuously differentiable. Such a behavior can be caused by ambiguous representations of the interference functions, depending on the choice of the receive strategy. Nevertheless, superlinear convergence can be shown by exploiting the special structure of the problem. Namely, the function is convex, locally Lipschitz continuous, and an invertible directional derivative exists for all points of interest.     

Response activation in overlapping tasks and the response-selection bottleneck.

The authors investigated the impact of response activation on dual-task performance by presenting a subliminal prime before the stimulus in Task 2 (S2) of a psychological refractory period (PRP) task. Congruence between prime and S2 modulated the reaction times in Task 2 at short stimulus onset asynchrony despite a PRP effect. This Task 2 congruence effect was paralleled by a Task 1 congruence effect and emerged exclusively under conditions of cross talk, whereas it did not occur under dual-task conditions preventing cross talk between tasks. This suggests that response activation operates during the PRP in dual tasks and affects the response times in Task 2 via cross talk between common processing elements at prebottleneck stages but not by directly affecting the postbottleneck stages. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrochemically formed transient ReS2/Re2O7 heterojunction with high energy conversion efficiency

During electrochemical oxidation of ReS₂ crystals the anodic photocurrent in aqueous electrolytes increases up to 140-fold. This phenomenon is accompanied by the formation of an unstable Re₂O₇ surface layer and a characteristic change of the photocurrent spectrum in the near UV. This is explained in terms of the formation of a heterojunction between ReS₂ and Re₂O₇. Upon addition of the I^–/I ₃ ^– redox couple a temporarily working electrochemical solar cell is obtained. Since the observed quantum efficiency exceeded the theoretical expectation, further studies of the interfacial quantum processes were made. It turned out that the enhancement effect is due to light collection by scattering processes in the highly refractive Re₂O₇ film and at the epoxy insulation.     

EFFECT OF HETEROCYCLIC AMINE ADDITIVES ON THE ABSORPTION RATES OF CARBONYL SULFIDE AND CARBON DIOXIDE IN AQUEOUS METHYLDIETHANOLAMINE SOLUTIONS

Absorption rates of carbonyl sulfide and carbon dioxide into aqueous methyldiethanolamine solutions with and without heterocyclic amine additives were measured in a stirred cell apparatus. All of the heterocyclic amine additives catalyzed COS absorption more strongly than that for CO₂. In instances in which absorption rates were improved by the additives, those with the lowest pK_b's were the most effective, although steric factors also apparently influence reaction kinetics.