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341.
Roger Salmon Jean-Pierre Bonnet Michel Graciet Marc Onillon Paul Hagenmuller 《Solid State Communications》1980,34(5):301-303
In order to decrease the resistivity of zinc oxide grains which is responsible for the intensity limitation observed at high current densities, the dependence of current-voltage characteristics of zinc oxide based varistors on oxygen partial pressure has been investigated. From these studies it appears that the conductivity increases with decreasing oxygen partial pressure, this phenomenon being more significant at low voltages than at higher ones. These results can be related to a slight increase of the donor density, while the superficial trap density decreases strongly, involving a collapse of the barrier height and of the non-linearity exponent. 相似文献
342.
E. Grech Z. Malarski M. Ilczyszyn O. Czupiński L. Sobczyk J. Rozière B. Bonnet J. Potier 《Journal of Molecular Structure》1985,128(4):249-258
Infrared and Raman studies have been performed on polycrystalline and monocrystalline samples of quinuclidin-3-one hemipercholate which at low temperature contain symmetric [NHN]+ hydrogen bonds. The most characteristic feature of the IR spectrum is a continuous broad absorption polarized parallel to the hydrogen bond direction.The Evans holes in the low-frequency range are most probably due to the coupling of protonic vibrations with internal modes of quinuclidine moieties leading to a modulation of the bridge geometry. Unusual isotopic and temperature effects could indicate a particular shape of the potential for the proton motion. 相似文献
343.
344.
An amperometric biosensor based on acetylcholinesterase was constructed by simple adsorption of the enzyme on screen-printed electrodes (SPEs). This sensor was used to detect the inhibitory effects of organophosphorus and carbamate insecticides on acetylcholinesterase, and more particularly of chlorpyrifos ethyl oxon (CP-o). We demonstrate that enzyme adsorption on SPEs allows to obtain stable sensors that present good characteristics and are as efficient as other screen-printed biosensors based on covalent binding or entrapment of acetylcholinesterase (AChE). 相似文献
345.
α-Ketocyclohexylcarbenium ions are formed by dehalogenation in HgSbF6Ch2Cl2 of the corresponding α-bromo carbonyl compounds 6,7, 8 and 9. In this medium they lead principally to bicyclic oxonium salts, the structure of which depends on the group adjacent to the carbonyl group, and positions of ring substituents. By a suitable choice of Y, it is possible to “functionalise” an α-keto cyclohexane system in either 3 or 4 positions. 相似文献
346.
The crystal structure of RbSbF2SO4 has been determined on a single crystal (R = 0.078 for 710 reflections). The structure shows sulfate anions distorted by the SOSb bonds. The antimony atom is from an SbF2 unit. This antimony dihalogen is from the family of the compounds which are in MX3SbX3 (M = Al, Ga, In) (X = Cl, Br) systems. 相似文献
347.
The capabilities of the DARC system are discussed and illustrated by the storage and retrieval functions of the 13C-n-m.r. data bank of the DARC PLURIDATA system. The data covered by the bank, as well as the input stream to the bank and validation of the spectra, are described. Particular stress is laid on the DARC structural retrieval system, which illustrates the interactive interrogation of a chemical data bank by means of the structural diagram of a molecule, i.e. the universal language in chemistry. The potential of the 13C-n.m.r. data bank in computer-aided structural elucidation is outlined. 相似文献
348.
Stevens JM Belghazi M Jaouen M Bonnet D Schmitter JM Mansuy D Sari MA Artaud I 《Journal of mass spectrometry : JMS》2003,38(9):955-961
Nitrile hydratases (NHases) are industrially significant iron- and cobalt-containing enzymes used in the large-scale synthesis of acrylamide. Previous reports have shown that the active site peptides of NHases are post-translationally modified by oxidation of cysteine residues, and that these modifications are essential for catalysis. We report mass spectrometric evidence of the oxidation states of the active site cysteines in the iron coordination spheres of two iron-containing nitrile hydratases, namely R312 NHase from Rhodococcus rhodochrous strain R312 and NI1 NHase from Comamonas testosteroni. At least one of these cysteines is oxidised to a sulfinic acid (SO(2)H) and there is also evidence suggesting an additional oxidation to a sulfenic acid (SOH). This is the first evidence for the presence of these oxidation states for full-length NHases and for Fe-NHases from different microorganisms. The presence of these covalent modifications was confirmed by performing mass spectrometry on the active site peptide of R312 NHase, under native, reduced and carboxymethylated conditions. We also show the nitrosylation of the iron by mass spectrometry, as well as the release of NO by photoirradiation. 相似文献
349.
A topological spaceX whose topology is the order topology of some linear ordering onX, is called aninterval space. A space in which every closed subspace is homeomorphic to a clopen subspace, is called aCO space and a space isscattered if every non-empty subspace has an isolated point. We regard linear orderings as topological spaces, by equipping them with their order topology. IfL andK are linear orderings, thenL
*, L+K, L · K denote respectively the reverse ordering ofL, the ordered sum ofL andK and the lexicographic order onL x K (so · 2=+). Ordinals are considered as linear orderings, and cardinals are initial ordinals. For cardinals , l 0, letL(K,)=K+1+*.Theorem: Let X be a compact interval scattered space. Then X is a CO space if and only if X is homeomorphic to a space of the form +1+1
L(K
i
i), where is any ordinal, n , for every ii ,i are regular cardinals and Kii, and if n>0, then max({Ki:i相似文献
350.