Amorphous structure and electronic properties of the Ge1Sb2Te4 phase change material

Ge1Sb2Te4 is one of the most commonly used phase change materials, due to the large optical and electrical contrast between a metastable crystalline phase and the amorphous phase. We use ab initio molecular dynamics to generate an amorphous Ge1Sb2Te4 structure. By analysing the distance distributions, we show that the structure can be analysed in terms of 21% of tetrahedrally coordinated Ge atoms and 79% of 3-fold Ge atoms. These are involved in distorted octahedral shells with bond length correlations that are similar to the a-GeTe structure as a consequence of a Peierls-distortion. The electronic properties are shown to be in reasonable agreement with the experiment with an electronic gap of 0.45 eV with. The optical conductivity curve is also in agreement with the experiment, with a maximal conductivity at an energy of ～3 eV.     

Acetobacter cellulose pellicle as a temporary skin substitute

Applied Biochemistry and Biotechnology - A bacterial strain with morphological and biochemical properties close toAcetobacter xylinum has been cultured in nonagitated, inverted sucrose- and yeast...     

Measurement of enthalpic parameters using a differential calorimetric method: Application to in-Bi alloys

An attempt is made to develop a calorimetric method by taking full advantage of the differential possibilities offered by the Tian-Calvet calorimeter. This method is intended to measure the enthalpic parameter, defined as the limiting value (dilute solutions) of the derivative of the partial enthalpy of mixing with respect to the concentration, in liquid In-Bi alloys. The results, although rather scattered, exhibit a systematic discrepancy when compared with those obtained by the classical direct reaction calorimetry method with the same calorimeter. They are in better agreement with the values estimated from simple thermodynamic models.

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Zusammenfassung Es wurde der Versuch unternommen, ein kalorimetrisches Verfahren zu entwickeln, das die Vorteile der Differentiation beim Tian-Calvet-Kalorimeter voll ausnutzt. Mittels dieser Methode sollte unter Berücksichtigung der Konzentration an flüssigen In-Bi Legierungen ein Enthalpieparameter gemessen werden, der als Grenzwert (verdünnte Lösung) der Ableitung der partiellen Mischungsenthalpie definiert wurde. Die Ergebnisse zeigen trotz größerer Streuung eine systematische Abweichung von den Werten, die auf demselben Kalorimeter mit dem klassischen DRC-Verfahren erhalten wurden und befinden sich in besserer Übereinstimmung mit den Werten, die auf der Basis einfacher thermodynamischer Modelle geschätzt wurden.

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n2-sets in a projective plane which determine exactly n2+n lines

In this paper n²-sets, in a projective plane, determining exactly n²+n lines are completely characterized.Research partially supported by G.N.S.A.G.A. (C.N.R.).Paper written while the second author was at the University of Rome supported by a grant within the Italian Hungarian cultural exchange program.     

Temperature-induced density anomaly in Te-Rich liquid germanium tellurides: p versus sp3 bonding?

The density anomaly of liquid Ge(0.15)Te(0.85) measured between 633 and 733 K is investigated with ab initio molecular dynamics calculations at four temperatures and at the corresponding experimental densities. For box sizes ranging from 56 to 112 atoms, an 8 k-points sampling of the Brillouin zone is necessary to obtain reliable results. Contrary to other Ge chalcogenides, no sp(3) hybridization of the Ge bonding is observed. As a consequence, the negative thermal expansion of the liquid is not related to a tetrahedral bonding as in the case of water or silica. We show that it results from the symmetry recovery of the local environment of Ge atoms that is distorted at low temperature by a Peierls-like mechanism acting in the liquid state in the same way as in the parent solid phases.     

Adsorption of selenium wires in silicalite-1 zeolite: a first order transition in a microporous system

A tight binding grand canonical Monte Carlo simulation of the adsorption of selenium in silicalite-1 zeolite is presented. The calculated adsorption-desorption isotherms exhibit characteristic features of a first order transition, unexpected for adsorption in a microporous system with pore size of the order of 0.5 to 0.6 nm. We analyze this behavior as a result of the favored twofold coordinated chain structure of selenium that grows inside the complex three-dimensional microchannel network of silicalite. This analysis is confirmed by simpler calculations of a lattice gas-type model.     

On the order structure in the line geometry of a projective space

A definition is made of an ordered Grassmann space and every ordered Grassmann space is shown to be isomorphic to the Grassmann space related to an ordered projective space.Dedicated to Professor W. Benz on the occasion of his 60^th birthday     

Evidence of a reentrant peierls distortion in liquid GeTe

We report a detailed study of the ultrasonic damping near the nematic-smectic- A phase transition of terephtal-bis- p-p(')-butylaniline (TBBA). Two mechanisms contribute to the damping. One is isotropic; it is associated with the critical fluctuations, and leads to a scaling behavior of the 3D- XY type which is observed up to 15 degrees C from the transition, even though the transition is first order. The other is anisotropic; it appears only in the smectic- A phase, and is associated with the relaxation of the order-parameter modulus.