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91.
In the early nineties of the previous century, leaf languages were introduced as a means for the uniform characterization of many complexity classes, mainly in the range between P (polynomial time) and PSPACE (polynomial space). It was shown that the separability of two complexity classes can be reduced to a combinatorial property of the corresponding defining leaf languages. In the present paper, it is shown that every separation obtained in this way holds for every generic oracle in the sense of Blum and Impagliazzo. We obtain several consequences of this result, regarding, e. g., universal oracles, simultaneous separations and type‐2 complexity. 相似文献
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Pure sand and gravel qualities are becoming to be rare resources and technical goods of increasing strategic importance for various industrial branches worldwide. Quartz sand as a crystalline raw material is chemically transformed into intermediates for the final production of synthetic amorphous silicon dioxides (SAS). Precipitated SAS are produced by chemical reaction of sodium silicates. Chlorosilanes are produced by reaction of silicon and ferrosilicon with HCl. They are used to produce pyrogenic SAS. High‐resolution transmission electron microscopy is needed to reveal the fine structure of these amorphous materials. Pyrogenic and precipitated SAS show a similar nanostructure as silica‐gels and ‐aerogels. Differences in amorphicity and short range order in finely divided, alkaline‐free, amorphous SAS on the one hand and in alkaline‐containing amorphous SiO2‐networks such as solid sodium silicates on the other still are not completely clarified. 相似文献
95.
Avramopoulos A Serrano-Andrés L Li J Reis H Papadopoulos MG 《The Journal of chemical physics》2007,127(21):214102
We employ a series of state-of-the-art computational techniques to study the effect of inserting one or more Xe atoms in HC2H and HC4H, on the linear and nonlinear optical (L&NLO) properties of the resulting compounds. It has been found that the inserted Xe has a great effect on the L&NLO properties of the organoxenon derivatives. We analyze the bonding in HXeC2H, and the change of the electronic structure, which is induced by inserting Xe, in order to rationalize the observed extraordinary L&NLO properties. The derivatives, which are of interest in this work, have been synthesized in a Xe matrix. Thus the effect of the local field (LF), due to the Xe environment, on the properties of HXeC2H, has also been computed. It has been found that the LF effect on some properties is significant. The calculations have been performed by employing a hierarchy of basis sets and the techniques MP2 and CCSD(T) for taking into account correlation. For the interpretation of the results we have employed the complete active space valence bond and CASSCF/CASPT2 methods. 相似文献
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The temperature‐composition phase equilibria of the Hg0.8Cd0.2Te‐HgI2 system were investigated between about 100 and 800 °C using Debye‐Scherrer powder X‐ray diffraction techniques, differential thermal analysis, differential scanning calorimetry, and thermochemical and structural calculations. This system is a pseudobinary temperature‐ composition plane in the HgTe‐CdTe‐HgI2 pseudoternary phase diagram. Measurable solid solutions of HgI2 in Hg0.8Cd0.2Te with the cubic zinc blende‐type structure exist between about 290 and 700 °C, with a maximum solubility of 4.9 ± 0.3 mole‐% HgI2 at 363 ± 3 °C. Further addition of HgI2 to HgI2‐saturated Hg0.8Cd0.2Te yields the formation of CdI2, which reduces the mole fraction (x) of CdTe in the Hg1—xCdxTe host lattice. After sufficient HgI2 is added, the host lattice is depleted in CdTe and forms Hg3Te2I2 in addition to CdI2. Phase fields containing the ternary compound Hg3TeI4, which we first observed in the HgTe‐HgI2 system, also exist in the present system. Quaternary analogs of the known ternary compounds Hg3Te2I2 and Hg3TeI4, i.e., Hg3—yCdyTe2I2 and Hg3—yCdyTeI4, were not observed under present experimental conditions. 相似文献
99.
A large number of preparatively interesting compounds have become readily available by the simultaneous action of sulfur and ammonia or amines on ketones. Direct syntheses of Δ3-thiazolines, Δ3-imidazoline-5-thiones, 5,6-dihydro-4H-1,4-thiazines, and the 1,2,3,4,5,6-hexathiocane system from ketones, sulfur, and ammonia or amines, and further possibilities for the synthesis of these heterocyclic systems have been proposed. Other heterocycles containing N or N and S (thiazoles, thiophenes, thiazolidines, tetrahydrothiazolo[2,3-c]-1,4-thiazines, thiomorpholines, 4-amino-2H-imidazoles, etc.) are readily obtainable by further reactions of these compounds. Hydrolysis of the Δ3-thiazolines yields α-mercapto ketones, which are the starting materials for other syntheses. Most of the syntheses described proceed at room temperature and at normal pressure. 相似文献
100.