Stability of a spatial polling system with greedy myopic service

This paper studies a spatial queueing system on a circle, polled at random locations by a myopic server that can only observe customers in a bounded neighborhood. The server operates according to a greedy policy, always serving the nearest customer in its neighborhood, and leaving the system unchanged at polling instants where the neighborhood is empty. This system is modeled as a measure-valued random process, which is shown to be positive recurrent under a natural stability condition that does not depend on the server??s scan radius. When the interpolling times are light-tailed, the stable system is shown to be geometrically ergodic. The steady-state behavior of the system is briefly discussed using numerical simulations and a heuristic light-traffic approximation.     

Synthesis and characterisation of cyclopentadienyl complexes of barium: precursors for atomic layer deposition of BaTiO3

Cyclopentadienyl complexes Ba(C5Me5)2(THF)2 (1), Ba(C5Me5)2(A) (A = THF, dien, trien, diglyme, triglyme) (2-5), Ba(Pr(i)3C5H2)2(THF)2 (6), Ba(Bu(t)3C5H2)2(THF) (7), Ba(Me2NC2H4C5Me4)2 (8) and Ba(EtOC2H4C5Me4)2 (9) were prepared and characterised with TGA/SDTA, NMR and MS. Crystal structures of 2, 4, 5, 7, 8 and 9 are presented. All complexes prepared sublime under reduced pressure and complexes 1, 6 and 7 showed volatility also under atmospheric pressure. Complexes 1, 6 and 7 lose the coordinated THF when evaporated while complexes 2-5 are sublimable as complete molecules under reduced pressure. Complexes with bulky cyclopentadienyl ligands (6 and 7) are the most thermally stable and volatile among the prepared barocenes. X-ray structure determinations reveal that all the complexes studied are monomeric. Complexes 1, 7 and 8 were successfully tested in BaTiO3 thin film depositions by atomic layer deposition (ALD).     

Thermal decomposition of rare earth oxysulfides in air

The thermal decomposition of rare earth oxysulfides (excluding Sc, Ce and Pm) has been studied in air. The oxysulfides are oxidized to oxysulfates between 600 and 900 and the oxysulfate phase, which is unstable at higher temperatures, decomposes to oxide. The stability of the oxysulfate and its decomposition temperature decreases with decreasing radius of the rare earth ion. For the heavier rare earths the oxidation to oxysulfate takes place only partially before the decomposition to oxide begins.

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Zusammenfassung Die thermische Zersetzung der Oxysulfide der seltenen Erden (mit Ausnahme von Sc, Ce und Pm) wurde in Luft untersucht. Die Oxysulfide werden zwischen 600 und 900 zu Oxysulfaten oxidiert und die Oxysulfatphase, welche bei höheren Temperaturen instabil ist, wird zu Oxid zersetzt. Die Stabilität des Oxysulfats und seine Zersetzungstemperatur nehmen mit abnehmendem Radius des seltenen Erden-Ions ab. Bei den schwereren seltenen Erden erfolgt die Oxysulfatbildung nur teilweise vor den Einsetzen des Abbaus zu Oxid.

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- , Sc, m. 600 900° , , . - . - , .

     

Speciation of activators in electroluminescent thin films: an EXAFS study of cerium and terbium doped strontium sulfide

Extended X-ray absorption fine structure (EXAFS) was used to determine the local structure of the luminescent centers in Tb³⁺ and Ce³⁺ -doped strontium sulfide thin films deposited by Atomic Layer Epitaxy (ALE). The rare earths were observed to enter mainly the substitutional sites but at the same time a part of the atoms form RES clusters (RE = rare earth). The presence of both substitutional sites and RES clusters has been observed for the first time in this study for rare earths in II–VI compounds. Received: 9 February 1998 / Revised: 22 May 1998 / Accepted: 29 May 1998     

Thermogravimetric Study of Volatile Precursors For Chemical Thin Film Deposition. Estimation of vapor pressures and source temperatures

Normal pressure thermogravimetry (TG) measurements were used to study the sublimation behavior of several volatile metal compounds, used as metal precursors in thin film fabrication by chemical vapor phase methods, like atomic layer deposition (ALD) and chemical vapor deposition (CVD). The results indicated that dynamic TG measurements may be used to find correct source temperatures to be used in an ALD reactor: a good correlation between the source temperatures used in ALD and temperatures corresponding to mass losses of 10 and 50% in TG was verified. It was also found that isothermal TG measurements offer a simple way for the vapor pressure measurements which otherwise are not trivial for solids with only moderate volatility. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solvent free oxidation of primary alcohols and diols using thymine iron(III) catalyst

In this study, we developed an efficient and selective iron-based catalyst system for the synthesis of ketones from secondary alcohols and carboxylic acids from primary alcohol. In situ generated iron catalyst of thymine-1-acetate (THA) and FeCl(3) under solvent-free condition exhibits high activity. As an example, 1-octanol and 2-octanol were oxidized to 1-octanoic acid and 2-octanone with 89% and 98% yields respectively.     

Heterolytic dihydrogen activation by B(C6F5)3 and carbonyl compounds

Aromatic carbonyl compounds in combination with B(C(6)F(5))(3) are able to activate H(2) heterolytically. The reactivity of the carbonyl-B(C(6)F(5))(3) adduct is initiated by its thermal dissociation into components. After H(2) addition, aromatic carbonyl compounds convert into aryl-substituted methanes or alcohols.     

A Thermoanalytical Study of Copper(I) Thiocarbamide Compounds

Hydrated isostructural 1:3 complexes of copper(I) chloride and bromide with thiourea were synthesised and their thermal decomposition studied by simultaneous TG/DTA complemented by ex situ FTIR and XRD studies. The decomposition of Cu(tu)₃Cl·H₂O is initiated by dehydration around 100°C, followed by a total multi-step degradation of the structure in the temperature range of 200–600°C. The counter ion has some influence on the temperatures and composition of the solid residue. The results were compared with those obtained with the 1:1 complex Cu(tu)Cl·1/2H₂O. This revised version was published online in August 2006 with corrections to the Cover Date.     

Practical Method for 2‐Hydroxyphenylketimine Synthesis

A series of hydroxyphenylketimines, of which 15 are new, was synthesized in methanol at high temperature (200°C) using a sealed steel reactor. This reaction setup especially enhances the synthesis of 2‐hydroxyphenylketimines, with yields up to six times higher than those obtained with the conventional acid‐catalyzed method under refluxing conditions. In fact, some imines were achievable only by the autoclave method.     

Thin Film Deposition Methods for CuInSe 2 Solar Cells

CuInSe₂ and its alloys with Ga and/or S are among the most promising absorber materials for thin film solar cells. CuInSe₂-based solar cells have shown long-term stability and the highest conversion efficiencies of all thin film solar cells, above 19%. Solar cells based on these materials are also very stable, thus allowing long operational lifetimes. The preparation of a thin film solar cell is a multistage process where every step affects the resulting cell performance and the production cost. CuInSe₂ and other Cu chalcopyrites can be prepared by a variety of methods, ranging from physical vapor deposition methods such as evaporation and sputtering to low-temperature liquid phase methods such as electrodeposition. The present review discusses first the concept and operation principle of thin film solar cells, as well as the most important thin film solar cell materials. Next, the properties of CuInSe₂ and related compounds, as well as features of solar cells made thereof are reviewed. The last part of the text deals with deposition methods used for the preparation of CuInSe₂ and Cu(In,Ga)Se₂ thin film absorbers and solar cells. Although the emphasis here is on absorber preparation methods, buffer and conducting oxide preparation are discussed as well.