Atomistic models of hydrogenated amorphous silicon nitride from first principles

We present a theoretical study of hydrogenated amorphous silicon nitride (a-SiNx:H), with equal concentrations of Si and N atoms (x=1), for two considerably different densities (2.0 and 3.0 g/cm3). Densities and hydrogen concentration were chosen according to experimental data. Using first-principles molecular-dynamics within density-functional theory the models were generated by cooling from the liquid. Where both models have a short-range order resembling that of crystalline Si3N4 because of their different densities and hydrogen concentrations they show marked differences at longer length scales. The low-density nitride forms a percolating network of voids with the internal surfaces passivated by hydrogen. Although some voids are still present for the high-density nitride, this material has a much denser and uniform space filling. The structure factors reveal some tendency for the nonstoichiometric high-density nitride to phase separate into nitrogen rich and poor areas. For our slowest cooling rate (0.023 K/fs) we obtain models with a modest number of defect states, where the low (high) density nitride favors undercoordinated (overcoordinated) defects. Analysis of the structural defects and electronic density of states shows that there is no direct one-to-one correspondence between the structural defects and states in the gap. There are several structural defects that do not contribute to in-gap states and there are in-gap states that do only have little to no contributions from (atoms in) structural defects. Finally an estimation of the size and cooling rate effects on the amorphous network is reported.

Environmental influence on the observed relaxation behaviour of two chromium systems

EPR recovery curves were measured for KCr alum and ruby with 2.7% chromium. A considerable influence of the heat transport properties of the bath is observed. Taking care of this influence a spin relaxation time τ = (0.7 ± 0.2) ms could be observed for ruby and a spin-lattice relaxation time T1 ∝ T-1. For KCr alum an anomalous behaviour of T1 was observed which may be due to a phonon bottleneck

Ovarian Abscess With Spontaneous Vaginal Drainage.

The occurrence of a rare ovarian abscess, spontaneously drained through the vagina after an abdominal hysterectomy is described. The treatment was an oophorectomy. The various forms of primary ovarian abscess are discussed in connection with these observations. This case illustrates the need for adequate manipulation of the gonad during pelvic surgery in order to avoid parenchymal contamination and the subsequent formation of such abscesses.11561596159

Ab initio study of magnesium alanate, Mg(AlH4)2

Magnesium alanate Mg(AlH4)2 has recently raised interest as a potential material for hydrogen storage. We apply ab initio calculations to characterize structural, electronic and energetic properties of Mg(AlH4)2. Density functional theory calculations within the generalized gradient approximation (GGA) are used to optimize the geometry and obtain the electronic structure. The latter is also studied by quasi-particle calculations at the GW level. Mg(AlH4)2 is a large band gap insulator with a fundamental band gap of 6.5 eV. The hydrogen atoms are bonded in AlH4 complexes, whose states dominate both the valence and the conduction bands. On the basis of total energies, the formation enthalpy of Mg(AlH4)2 with respect to bulk magnesium, bulk aluminum and hydrogen gas is 0.17 eV/H2 (at T = 0). Including corrections due to the zero point vibrations of the hydrogen atoms this number decreases to 0.10 eV/H2. The enthalpy of the dehydrogenation reaction Mg(AlH4)2 -> MgH2 +2Al+3H2(g) is close to zero, which impairs the potential usefulness of magnesium alanate as a hydrogen storage material.Comment: 5 pages, 3 figure

Some preliminary observations on the biology of Strongylocentrotus lividus (Lamarck)

The present study of Strongylocentrotus lividus is an attempt to add to the knowledge in this field with particular reference to a tropical species of whose biology little is known. The aim of the study was to examine the growth of the animals in relation to the development of their gonads, to elucidate the food preferences of the sea urchins and to study their associations with other animals

Bridging Faultlines by Valuing Diversity: Diversity Beliefs, Information Elaboration, and Performance in Diverse Work Groups

Although there are numerous potential benefits to diversity in work groups, converging dimensions of diversity often prevent groups from exploiting this potential. In a study of heterogeneous decision-making groups, we examined whether the disruptive effects of diversity faultlines can be overcome by convincing groups of the value in diversity. Groups were either persuaded of the value of diversity or of the value of similarity for group performance, and they were provided with either homogeneous or heterogeneous information. As expected, informationally diverse groups performed better when they held pro-diversity rather than pro-similarity beliefs, whereas the performance of informationally homogeneous groups was unaffected by diversity beliefs. This effect was mediated by group-level information elaboration. Implications for diversity management in organizations are discussed.Diversity;Diversity Beliefs;Faultlines;Information Elaboration;Team Performance

The electroclinic effect and modulated phases in smectic liquid crystals

We explore the possibility that the large electroclinic effect observed in ferroelectric liquid crystals arises from the presence of an ordered array of disclination lines and walls. If the spacing of these defects is in the subvisible range, this modulated phase would be similar macroscopically to a smectic A phase. The application of an electric field distorts the array, producing a large polarization, and hence a large electroclinic effect. We show that with suitable elastic parameters and sufficiently large chirality, the modulated phase is favored over the smectic A and helically twisted smectic C* phases. We propose various experimental tests of this scenario.Comment: 9 pages, 7 figures; new version includes dipolar interactions and bend-twist couplin

Interacting Dimensions of Diversity: Cross-Categorization and the Functioning of Diverse Work Groups

We conducted an experiment to show how the interplay between informational diversity and other dimensions of diversity can account for some of the inconsistent effects of informational diversity in previous research. 70 four-person groups involved in a decision-making task received homogeneous or heterogeneous information. By manipulating gender composition and bogus personality feedback we created groups that either had a potential faultline (a basis for subgroup categorization) or were homogeneous on these dimensions. In potential faultline groups, heterogeneity of information either converged with or cross-cut the other dimensions of diversity. Results showed that informational diversity enhanced group functioning when it was crossed rather than converged with the potential faultline.Diversity;Information Elaboration;Cross-Categorization;Group Processes