The Monte-Carlo model of a light-emitting diode

The first complete Monte-Carlo model of a surface light-emitting diode is presented in this paper. In the model all important phenomena (including the two-dimensional diffusion of minority carriers before their recombination in the active region and the re-emission of radiation) are taken into account. The influence of various construction parameters on the external quantum efficiency of the homojunction GaAs diode is examined.     

On a two-velocity model of the Boltzmann-Enskog equation

Summary A simple two-velocity model (-model)of the Boltzmann-Enskog equation for a gas of hard spheres is proposed. Physical properties of such a model are analyzed and its differences with respect to the Carleman model are investigated. Global existence theorems and some qualitative properties of solutions of the -model are also proved.On leave from Dept. of Mathematics and Mechanics, University of Warsaw, Poland.     

Domain-wall energy in sintered Nd15Fe77B8 permanent magnet

From measurements of the magnetic domain widthsD versus grain thicknessL, we have determined the domain wall energy in the demagnetized state for a sintered Nd₁₅Fe₇₇B₈ magnet: = 56 erg/cm². Using this wall energy and the published magnetocry-stalline constantK ₁=4.9×10⁷ erg/cm³, we have calculated the exchange constantA=4.0×10^–6 erg/cm, domain wall thickness _B=89 Å, and the critical diameter for single domain particlesD _c=0.67 m.     

The polymorphic transformations of cobalt molybdate

Polymorphic transformations of CoMoO₄ were studied by means of high temperature X-ray measurements within the temperature range 25–1200°C. On heating phase a obtained from low temperature modification b a new modification a′ was discovered. Phase a obtained by thermal decomposition of solvated α-CoMoO₄ shows different behaviour. At 700–930°C depending on the conditions of preparation it transforms irreversibly into still another modification a″. On cooling, a mixture of phases a + a″ is obtained, the presence of a″ being responsible for the explosionwise transition into b, observed around the room temperature.     

Über eine neue automatische Apparatur zur Zentigramm-Bestimmung von Kohlenstoff und Wasserstoff in organischen Substanzen

Zusammenfassung Das vom Verfasser undE. Sucharda schon 1928 angewandte Prinzip, die durch das Verhalten der Substanz beim Erhitzen bewirkten Druckschwankungen im Verbrennungsrohre zum Zwecke der automatischen Regulierung der Vergasungsgeschwindigkeit der Substanz bei der Elementaranalyse auszunutzen, wurde bei der Konstruktion einer neuen, elektrisch betriebenen, automatischen Apparatur angewandt. Hierbei wird das mit der Substanz gefüllte Mikroschiffchen mittels eines elektrischen Hochfrequenzgenerators erhitzt. Der Stromzufluß zu dem Hochfrequenzgenerator wird durch die erwähnten Druckschwankungen einoder ausgeschaltet. Die Verbrennung verläuft dann bei praktisch konstantem Druck im Verbrennungsrohre, also auch bei konstantem Sauerstoffüberschuß. Die neue Apparatur wird an Hand beigefügter Abbildungen beschrieben. Als Absorptionsmittel für Stickstoffoxyde werden 1 bis 2 g Bleidioxyd in einem 12 cm langen Porzellanschiffchen bei 190° angewandt. Die Absorption des Wassers erfolgt durch wasserfreies Kobaltchlorid, die der Kohlensäure ausschließlich durch Ascarit. Die Sauerstoffgeschwindigkeit im Verbrennungsrohre beträgt 8 ml pro Minute. Bei Substanzen, die mehr als 10% N enthalten, wird zwischen den Kohlensäureabsorptionsapparat und den Wasserabsorptionsapparat ein mit Mangandioxyd gefüllter Apparat eingeschaltet.

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Summary The principle used by the author andE. Sucharda as early as 1928, which employs the variations in pressure in the combustion tube resulting from the behavior of the substance when heated, for automatically regulating the rate of gasifying the substance was applied in the construction of a new electrically operated automatic apparatus. The micro boat charged with the sample is heated by means of a high frequency generator. The flow of current to the high frequency generator is switched on and off by the variations in pressure mentioned above. The combustion then proceeds at practically constant pressure in the combustion tube, and even when there is a constant excess of oxygen. The new apparatus is described in the accompanying figures. The nitrogen oxides are absorbed in 1 to 2 grams of lead dioxide contained in a porcelain boat (12 cm long) at 190°. The absorption of the water is by means of anhydrous cobalt chloride, while the carbon dioxide is taken up in ascarite. The speed of the oxygen in the combustion tube is 8 ml per minute. In the case of samples that contain more than 10% nitrogen, an apparatus filled with manganese dioxide is placed between the carbon dioxide absorber and the apparatus for taking up the water.

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Résumé Le principe de l'utilisation des variations de pression qui se produisent dans un tube à combustion en analyse élémentaire, lors du chauffage de la substance, a été utilisé dès 1928 par l'auteur etE. Sucharda pour la régulation automatique de la gazéification de cette substance. Il a été appliqué à la construction d'un nouvel appareil automatique commandé électriquement. La micronacelle qui contient la substance est chauffée électriquement à l'aide d'un générateur de courant de haute fréquence. Les variations de pression pendant la combustion provoquent l'ouverture ou la fermeture du circuit d'alimentation de ce générateur. Il en résulte que la combustion est effectuée à pression pratiquement constante ainsi qu'à excès d'oxygène constant. Ce nouvel appareil est décrit sur les figures de la publication.On utilise 1 à 2 grammes de bioxyde de plomb disposés dans une nacelle de porcelaine de 12 cm de longueur, portée à 190° pour absorber les oxydes de l'azote. L'eau est absorbée par du chlorure de cobalt anhydre et l'anhydride carbonique exclusivement par de l'ascarite. Le débit du courant d'oxygène dans le tube de combustion est de 8 ml par minute. Pour les substances contenant plus de 10% d'azote, on intercale un absorbeur à bioxyde de manganèse entre l'absorbeur à anhydride carbonique et l'absorbeur à eau.

     

The kinetics of tritium-hydrogen exchange in xanthosine,theobromine and monomethylated derivatives of xanthine

Tritium exchange at C-8 of xanthosine, theobromine, 1-, 3- and 7-methylxanthine in water has been studied. The rates of detritiation of these compounds have been determined over a pH range at constant temperature. Several mechanisms of exchange involving various ionic forms of substrate operating at different pH have been suggested.     

Microchemical investigation of medicinal plants. XV

Summary A method is described for the determination of alkaloids in morning glory leaves by means of spectrophotofluorimetry. The total alkaloidal contents found in different batches of leaves ranged from 0.027 to 0.04%.

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Zusammenfassung Ein Verfahren zur Bestimmung der Gesamtalkaloide in den Blättern vonIpomoea violacea wurde angegeben. Spektralfluoreszenzmessungen ergaben für verschiedene Chargen solcher Blätter Gehalte von 0,027 bis 0,04%.

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For part XIV see Mikrochim. Acta [Wien]1976 I, 227.     

The cyclic fixation and reduction of molecular nitrogen with [WH4(Ph2PCH2CH2PPh2)2] in γ-irradiated solutions

Yields of NH₃ and N₂H₄ in radiation-catalytic reduction of N₂ by means of a hydride complex of W^IV with dppe in thf solution and in mixtures of thf with other solvents have been estimated. A mechanism proposed earlier of reduction of coordinated N₂ has been confirmed and the role of solvent in reduction of N₂ to NH₃ and amines has been explained.