超导临界温度理论(Ⅰ)

本文求出了Eliashberg方程在T=T_c时的解,得到了下面的临界温度级数表示式: 其中α₀(μ^*),α₁(μ^*)等系数是μ^*的函数.此式表明,T_c不仅依赖于λ,〈ω²〉和μ^*,而且依赖于有效声子谱α²F(ω)的各级矩〈ω²n〉.这是区别于前人的T_c公式最重要的一点。这说明像McMillan以及Allen和Dynes的T_c公式不仅是近似的,而主要是他们没有能正确地概括出α²F(ω)对T_c的影响.     

Emission of radiation by charged particles reflected from solid surfaces

It is predicted that charged particles reflected from solid surfaces could emit radiation due to the change in their direction of motion upon reflection. The theoretical spectrum of this radiation is obtained for specular reflection. The general concept of ‘transition radiation’ is reconsidered to include this new effect which is found to dominate for low-energy, non-penetrating electrons and for high-energy electrons at grazing incidence.     

Metabolism of xanthohumol and isoxanthohumol, prenylated flavonoids from hops (Humulus lupulus L.), by human liver microsomes

The female flowers of hops (Humulus lupulus L.) used to flavor beer contain the prenylated flavonoids xanthohumol (XN) and isoxanthohumol (IX). IX is moderately estrogenic in vitro and XN has pharmacological properties that might make it useful as a cancer chemopreventive agent. The metabolism of these dietary flavonoids was investigated in vitro using human liver microsomes. Hydroxylation of a prenyl methyl group was the primary route of oxidative metabolism forming either cis or trans hydroxylated metabolites of IX but only the trans isomer of XN. The double bond on the prenyl group of both compounds formed an epoxide which was opened by an intramolecular reaction with the neighboring hydroxyl group. The potent phytoestrogen 8-prenylnaringenin (8-PN) was detected as a demethylation product of IX. However, the analogous demethylation reaction was not observed for XN. Since XN can be converted to IX through acid-catalyzed cyclization in the stomach, XN might contribute to the in vivo levels of estrogenic 8-PN following consumption of hops extracts.     

Influence of hydrogen bonding on coordination polymer assembly

An extended dipyridyl ligand (L1) capable of hydrogen bonding with guest species via urea functionalities has been designed and synthesised. Assembly of a silver(I) coordination polymer of L1 is dependent on the nature of the hydrogen bond acceptor in a logical extension of the monopyridyl analogue.     

Les pyrochlores ferroelectriques derives de Cd2Nb2O6S: Mise en évidence des transitions de phase par des techniques d'optique non linéaire

The ferroelectric pyrochlore compound Cd₂Nb₂O₆S and solid solution Cd₂Nb₂O_7?xS_x have been studied by second optical harmonic generation. The excitation source was a YAG: Nd³⁺ laser emitting at λ = 1.06 μm. The intensity variation of second harmonic as a function of temperature was investigated. A strong signal appears in the two ferroelectric phases. The transition temperatures are easily observed; dielectric and calorimetric results are confirmed.     

Magnetic susceptibility of fluoride glasses with 3d and 4f elements

The low field ac magnetic susceptibility has been studied as a function of temperature and frequency in a series of fluoride glasses containing Mn²⁺, rare-earth ions, or an admixture of the two types. All glasses exhibit magnetic freezing in the ⁴He or ³He temperature ranges, but the nature of the freezing appears to depend on the local anisotropy. In the case of Mn²⁺ or Mn²⁺ -Gd³⁺ ions, a sharp freezing analogous to that in CuMn was observed. For Ln³⁺ or Mn²⁺ -Ln³⁺ ions (Ln=Dy, Ho), the observed progressive freezing could be of a dynamic nature.     

A new method for the preparation of diphenylmethyl ethers

Various diphenylmethyl ethers are prepared under mild conditions by using tri-diphenylmethyl phosphate as alkylating agent. O-Diphenylmethyl-L(?)-Lactic Acid is prepared by this method.