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881.
J. T. Chayes L. Chayes Daniel S. Fisher T. Spencer 《Communications in Mathematical Physics》1989,120(3):501-523
Thed-dimensional, nearest-neighbor disordered Ising ferromagnet: $$H = - \sum {J_{ij} \sigma _i \sigma _j }$$ is studied as a function of both temperature,T, and a disorder parameter,λ, which measures the size of fluctuations of couplingsJ ij ≧0. A finite-size scaling correlation length,ζ f (T, λ), is defined in terms of the magnetic response of finite samples. This correlation length is shown to be equivalent, in the scaling sense, to the quenched average correlation lengthζ(T, λ), defined as the asymptotic decay rate of the quenched average two-point function. Furthermore, the magnetic response criterion which definesζ f is shown to have a scale-invariant property at the critical point. The above results enable us to prove that the quenched correlation length satisfies: $$C\left| {\log \xi (T)} \right|\xi (T) \geqq \left| {T - T_c } \right|^{ - {2 \mathord{\left/ {\vphantom {2 d}} \right. \kern-\nulldelimiterspace} d}}$$ which implies the boundv≧2/d for the quenched correlation length exponent. 相似文献
882.
883.
The absorption of pulsed CO2-laser radiation by ethylene has been measured at total pressures from 25 to 3000 Torr, using the P(12) and P(14) lines in the 10.6 m band, with incident fluences from 0.1 to 0.7 J/cm2. Marked deviations from the Beer-Lambert absorption law were observed, with the effective absorption coefficient varying with pressure, fluence, absorption path-length and the addition of non-absorbing gas. Pressure broadening of the rotational lines of the ethylene absorption spectrum was shown to be the major cause of these deviations, together with lesser effects which can be attributed to the rise in temperature of the absorbing gas during the laser pulse. 相似文献
884.
L. Fournes B. Chevalier B. Lloret J. Etourneau 《Zeitschrift für Physik B Condensed Matter》1989,75(4):501-505
Eu(Ir1–x
Pd
x
)2Si2 solid solutions which exist only for 0x0.125 and 0.75x1 crystallize in the tetragonal ThCr2Si2-type structure. X-ray diffraction data, magnetic susceptibility and151Eu Mössbauer measurements suggest that these compounds can be characterized as homogeneous mixed valence systems. At room temperature and for 0x0.125, the europium valence decreases asx increases. For 0.75x1, a sharp continuous valence transition from Eu2+ to Eu3+ occurs near 48 K, 54 K and 78 K forx=0.75, 0.81 and 0.94 respectively. These valence changes are discussed in relation with the Eu–(Ir, Pd) interatomic distance. 相似文献
885.
Powders of YBa2Cu3O7–
were mixed with Ag, Cu, and CuO powders, pressed and sintered in air and oxygen. Grain-growth enhancement has been observed in the doped samples on sintering in oxygen at 980°C and its attributable to a partial melting and decomposition followed by crystallization during cooling. While the mechanisms of the partial melt may differ with dopant, grain growth enhancement appears to be a common feature of partial melt followed by slow cooling. The possibility of using suitable dopants in aiding an aligned grain structure is pointed out. 相似文献
886.
Effect of methanol dilution on H-ZSM-5 zeolite deactivation in the process of light olefin formation
A. .A. Cichowlas P. T. Wierzchowski L. W. Zatorski 《Reaction Kinetics and Catalysis Letters》1986,32(2):341-346
Conversion of methanol in the presence of H2O, O2, H2, CO, CO2 and He was studied at 733 K on H-ZSM-5 zeolite. The effect of diluent on the selectivity to light olefins and resistance to coking of H-ZSM-5 were observed. Among the diluents studied only water exerts a promoting effect on prolonged activity of the catalyst. Some explanations of the deactivation process are given.
H2O, O2, H2, CO, CO2 He H-ZSM-5 733K. H-ZSM-5. . .相似文献
887.
Yu. A. Yuzhelevskii E. G. Kagan V. N. Frolov A. L. Klebanskii 《Chemistry of Heterocyclic Compounds》1970,4(1):24-28
The influence of the number of 3, 3, 3-trifluoropropyl(methyl)siloxane links (/) in the cyclotetrasiloxanes mD4-m, where D represents the dimethylsiloxane link and m=0–4, on the rearrangement of these compounds in acetone solution under the action of sodium siloxanolate has been studied. The rearrangement takes place with the formation of a linear polysiloxane the degradation of which yields, in addition to the initial ring, cyclosiloxanes with a different structure. The rate of rearrangement of mD4-m and of the formation of a linear polysiloxane rises with an increase in m from 0 to 3. The equilibrium concentration of the linear polysiloxane formed from mD4-m is inversely proportional to m. Results have been obtained on the kinetics of the formation of the cyclosiloxanes mDn, where m=0–5, n=0–5, and m+n=3–6, in the rearrangement of the rings D3, 2D2, 3D, and 4. The reactivity of the siloxane links rises in the sequence (CH3)2Si-O-Si(CH3)2 < (CF3CH2CH2)-(CH3) Si-O-Si(CH3)2 <(CF3CH2CH2) (CH3)Si-O-Si(CH3) (CH2CH2CF3) . Because of the negative inductive effect transferred through the siloxane links, the 3, 3, 3-trifluoropropyl groups strongly activate the siloxane ring with respect to nucleophiiic reagents.For part I, see [3]. 相似文献
888.
Commercial grade 2-butyne-1,4-diol has been used in electroplating for several years. In laboratory experiments, its presence in the electrolyte increases the current efficiency of zinc electro-winning. Its chemical behaviour in solution is not well known. The present paper indicates that the brownish technical grade 2-butyne-1,4-diol contains the monomer, the dimer and some trimer. Pure monomeric 2-butyne-1,4-diol is a white solid obtained by evaporation of the technical grade product. The monomer is slowly transformed into dimer and possibly into a trimer when dissolved in water. Various analytical techniques were used in the study of this system. Factor analysis with column cross-validation was applied to chromatographic data to help in the resolution of the system. 相似文献
889.
Keggin heteropolyanions [XM(12)O(40)](n-) have various isomeric structures, alpha and beta being the most common. Conventionally, the alpha structure appears to be the most stable, but calculations carried out at the DFT level for X = P(V), Si(IV), Al(III), As(V), Ge(IV), and Ga(III) and M = W(VI) and Mo(VI) show that this stability depends on several factors, particularly on the nature of the heteroatom (X) and the total charge of the cluster. In this paper, we apply the clathrate model to the Keggin molecule to carry out a fragment-interaction study to elucidate when and why the traditional relative stability of various isomers can be inverted. The fully oxidized anions that have inverted the traditional stability trend in this series are [AlW(12)O(40)](5-) and [GaW(12)O(40)](5-), both of which contain a third-group heteroatom and an overall charge of -5. beta-isomers are always more easily reduced than alpha-isomers. This experimental observation suggests that reduction favors the stability of beta-isomers and one of the most important results of this study is that the alpha/beta inversion is achieved in most cases after the second reduction. The alpha- and beta-isomers may have different properties because the energy of the LUMO, a symmetry-adapted d(xy)-metal orbital, is different. 相似文献
890.