Reductive activation of nitrate reductases

Protein film voltammetry of Paracoccus pantotrophus respiratory nitrate reductase (NarGH) and Synechococcus elongatus assimilatory nitrate reductase (NarB) shows that reductive activation of these enzymes may be required before steady state catalysis is observed. For NarGH complementary spectroscopic studies suggest a structural context for the activation. Catalytic protein film voltammetry at a range of temperatures has allowed quantitation of the activation energies for nitrate reduction. For NarGH with an operating potential of ca. 0.05 V the activation energy of ca. 35 kJ mol-1 is over twice that measured for NarB whose operating potential is ca. -0.35 V.     

The determination of quartz in clay materials

The quartz contents (maximum, 4 wt.%) of four clay materials and a tourmaline were determined by differential thermal analysis, by X-ray diffraction and by chemical analysis. The results are used to make a critical comparison of these three methods. DTA gives a better precision than X-ray diffraction analysis. The chemical method is judged unreliable in that feldspar and mica, present as minor components, are recorded in part as quartz.

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Zusammenfassung Der Quarzgehalt (max. 4%) von vier Tonmineralien und von Turmalin wurde durch Differentialthermoanalyse, Röntgendiffraktion und chemische Analyse bestimmt. Die Ergebnisse ermöglichten einen kritischen Vergleich der drei Methoden. Die DTA ist genauer als die Röntgendiffraktion. Die Chemische Analyse ist unzuverläßlich, da kleinere Mengen an Feldspat und Glimmer ebenfalls teilweise als Quarz erfaßt werden.

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Résumé On a déterminé la teneur en quartz (4% en poids au maximum) de quatre argiles et d'une tourmaline en se servant de l'analyse thermique différentielle, de la diffraction de rayons X et de l'analyse chimique. On a utilisé les résultats pour faire une étude critique des trois méthodes. L'ATD donne une meilleure précision que l'analyse par diffraction X. L'analyse chimique présente peu de sûreté car le feldspath et le mica, présents à l'état de constituants mineurs, interviennent en partie comme le quartz.

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The authors express their thanks to the Directors of English Clays Lovering Pochin & Co. Ltd. for permission to publish this paper.     

Some Isoperimetric Inequalities in Electrochemistry and Hele Shaw Flows

Isoperimetric inequalities are applied to a moving-boundaryproblem for doubly-connected domains. This problem occurs forexample in electrochemistry, in which case the domains in questionare the electrolyte of an electrolytic cell. The two electrodessurrounding the electrolyte are assumed to grow or dissolve,at different rates in general, by electrochemical reaction.We obtain optimal estimates showing, for example, that the leastchange in volume of each electrode always occurs in sphericalsymmetry.     

Bi2223带材临界电流沿长度方向的统计分布

本文采用四引线法测量了Bi2223带材临界电流沿长度方向的分布,采用正态分布、对数正态分布、威布尔分布和最小极值分布对临界电流分布进行了拟合检验,确定了临界电流的最优统计分布模型.