Gravity induced vortices and stepwise growth of these vortices in vertical counterflow of liquid helium

Detailed measurements of the second sound excess attenuation in vertical counterflow show the existence of a zero critical velocity and of steps which can be interpreted as a Josephson A.C. effect related to vortex motion.     

Effets de cryptands et activation de bases—II: Genese d'enolates et essais d'activation de LiH,NaH et KH dans l'ether,le THF et le benzene

The generation of the lithium, sodium and potassium enolates of cyclohexanone using LiH, NaH and KH has been investigated. The utilization of macrocyclic ligands (which selectively complex the metal cation) activated the alkaline hydride reagent. However, the most dramatic effect was the activation of the enolate, enabling proton abstraction from the solvent.     

Une nouvelle synthese de l'ellipticine et ses analogues structuraux

Two new syntheses of the 6H-pyrido [4,3-b] carbazole system are described. The first method involves the cyclization of a (2-alkyl-skatyl)-piperidone whereas the second leads to ellipticine by the participation of the indole nucleus in the rearrangement of tertiary acetylenic alcohols in acidic medium.     

Implications of the Glauber model for inelastic hadron-nucleus scattering

The Glauber model for elastic hadron-nucleus scattering is extended to inelastic processes by supplementing it with the Abramovskii, Gribov, Kancheli cutting rules. Inelastic screening due to low mass states is also included. The results can be interpreted in terms of the probabilistic multiple collision model. The mutual relationship of the two approaches is discussed.     

Losses of optical multimode strip-waveguides made by thick film technology

Loss measurements on straight and curved multimode strip-waveguides made from photosensitive sheets by a photolithographic process are reported. The cross section of the waveguides vary from 20 μm × 50 μm to 100 μm × 100 μm. The loss is detected by measuring the light scattered out of the waveguide. Waveguides fabricated by a modified technology are compared to conventional ones at wavelengths of 0.633 μm and 0.83 μm. Using the modified technology losses of 2 dB/cm at λ = 0.83 μm have been measured for both straight and curved (radius 30 mm) guides.     

Variable metric optimization of molecular geometry in electronically excited states

The variable metric (VM) method is used to optimize molecular geometry in electronically excited states. A general expression for the first derivative of energy in the particular excited state is derived, considering configuration interaction of all singly excited configurations. A special expression for the excited states energy derivative is given for calculations with semiempirical methods of CNDO type. The geometry optimizations of a set of molecules in various excited states have been carried out by the CNDO/2 method. The results of computations have been discussed and compared with the available experimental data. A good agreement of the calculated geometries with the experimental ones has been shown in the first excited states and a relatively good agreement in the higher states, with some exceptions. Some special features of the proposed method are discussed.     

Parameter variation in low-quartz between 94 and 298K

The structure of low quartz has been refined at 94, 115, 150, 190, 240 and 298K using Mo Kα intensities up to 2θ = 90° with residuals around 1.25%. The major structural change from 94 to 298K is an increase of the SiOSi angle from 142.69(4) to 143.65(5) corresponding to a rotation by ～0.8° of a rigid SiO₄ tetrahedron around the crystallographic 2-axis through its central Si. The orientations of the principal axes of vibration of Si and O do not change significantly with temperature. The temperature dependence of the mean-square displacement of O along its principal axes follows the Debye formula of thermal motion quite well, while for Si the experimental slopes are significantly less than their calculated values.