Festköperreaktionen in Chalkogenidsystemen. III. Bestimmung der Aktivierungsenergie von Pulvereaktionen aus Leitfähigkeitsglowkurven

In the case of the formation of thiospinels (MnCr₂S₄, ZnCr₂S₄ and CdCr₂S₄) a simple method for the determination of the activation energy of solid state reactions in polycrystalline samples by means of conductivity measurements is shown. The maxima and minima of conductivity (glow curve maxima and -minima) in the σ vs T-curves got by annealing with linearly increasing temperature are shifted towards higher temperatures with increasing rate of heating(q). By plotting ln (q/T) vs 1/T_σmax a straight line results. The activation energy of the reaction may be deduced from the slope of this straight line in analogy to the determination of the trap depth of electrons from glow curves observed in thermoluminescence.     

Beiträge zur Chemie des Schwefels. 108. Schmelzwärme und spezifische Wärme des flüssigen Schwefels. Einfluß von Verunreinigungen

Using an adiabatic calorimeter, the heat of transition S_α ? S_β, the heat of fusion of S_β and the specific heat of the liquid had been determined on sulfur samples refined by zone melting and samples doped with chlorine, bromine and iodine. The data obtained from pure sulfur (heat of fusion: 1608 ± 8 J/Tom, specific heat of the liquid at 120°C: 29,4 J/Tom.°C) are about 10% lower than comparable values of other authors. Apparently they represent heat of fusion and specific heat of the pure cyclooctasulfur. The measurements on doped samples (δH_S = 1736 ± 10 J/Tom) are in agreement with the data reported in literature and include a portion of enthalpy from the transition reaction of cycloocta-sulfur (S_λ) to catenaocta-sulfur (S_π), requiring extremly long equilibrium times in pure sulfur. The influence of impurity on the caloric properties of the liquid sulfur is also indicated by the increasing width and decreasing highness of the C_p-maximum at 159°C with increasing amount of halogens. For the heat of transition S_α → S_β, independent of the amount of impurity, the literature data could be confirmed. At the samples doped with iodine there was observed a previously unreported transition near 65,9°C.     

Exploiting C3-symmetry in the dynamic coordination of a chiral trisoxazoline to copper(II): improved enantioselectivity, and catalyst stability in asymmetric lewis acid catalysis

Chiral C3-symmetric trisoxazolines are highly efficient stereodirecting ligands in enantioselective Cu(II) Lewis acid catalysis which is based on the concept of a stereoelectronic hemilability of the divalent copper; in direct comparison with the analogous bisoxazoline systems they are more efficient in the enantioselective alpha-amination as well as the enantioselective Mannich reaction of prochiral beta-ketoesters.     

Current Interruption at Powers up to 1 GW with Crossed-Field Tubes

This paper describes the current interruption and voltage holdoff capabilities of a wide range of crossed-field tubes (XFTs). The XFTs investigated have active electrode areas ranging from 96 to 8000 cm2 with mean diameters from 2 to 56 cm. For the larger XFTs, currents up to 10 kA have been interrupted at voltages up to 100 kV, corresponding to a switched power of 1 GW. Experiments have shown the peak interruptible current to vary linearly with tube radius. The mechanism responsible for the limitation may be related to the self-generated magnetic field, but other factors are also shown to play a role.     

A generalized,one-way,stackless quicksort

This note generalizes the one-way, stackless quicksort of Huang and Knuth to work for any type of sort key. It thus proves that quicksort can run with minimal space inO(N logN) average time.On leave from FH Fulda, D-6400 Fulda (Germany).     

On bounded time-dependent perturbations of operator cosine functions

In this note it is shown that the Cauchy problem associated with the infinitesimal generatorA of a strongly continuous operator cosine function remains uniformly well-posed under bounded time-dependent perturbations ofA.     

Periodische operatorwertige Cosinusfunktionen

In dieser Note werden stark stetige periodische Cosinusfunktionen mit Werten im Bereich der stetigen linearen Operatoren auf einem Banachraum untersucht. Dabei ergänzen und präzisieren wir die Untersuchungen von E. Giusti. Insbesondere wird ein durchsichtiger und vollständiger Beweis eines Satzes von Giusti über die Charakterisierung periodischer Cosinusfunktionen mit Hilfe von Spektraleigenschaften ihres infinitesimalen Erzeugers angegeben.