General diagram of the phase remtions of actinide metals under pressure

Abstract

The proposed diagram is based on the results of high-pressure X-ray diffraction work and visualizes the general trends in phase relations of actinide metals under pressure. The transition from dhcp to ccp, which occurs under the action of pressure in heavy actinides and light lanthanides, also occurs with decreasing atomic number at ambient pressure. The same structural sequence is found in the lanthanide and the actinide metals, but its first two members, hcp and Sm-type, are missing in the actinide metals, and the phase transitions are shifted to lower pressures and higher atomic numbers in the actinides.     

Bulk moduli and high-pressure phases of the uranium rocksalt structure compounds: II. The monopnictides

Abstract

The high-pressure crystal structures of the compounds UX, where X = N, P, As and Sb, have been studied using X-ray diffraction in the pressure range up to about 60 GPa Rhornbohedral distortions are observed for UN and Up above 29 GPa and lO GPa, respectively. In Up a further transformation to an orthorhombic phase occurs at 28 GPa. UAs and USb transform to the CsCl structure at 20 GPa and 9 GPa, respectively. The latter transformations show a considerable hysteresis when the pressure is released. The scaling behaviour of the bulk modulus has been studied. It is confirmed that a log-log plot of bulk modulus versus specific volume for the cubic phases gives a straight line with a slope near ? 5/3.     

Four contact electrical measurements on the anisotropic high-Tc superconductors: voltage reversals

We describe three mechanisms for the anomalous voltage reversals which are occasionally observed during four contact current-voltage measurements on the high temperature superconductors. Voltage reversals have been frequently observed for whiskers of the bismuth strontium calcium copper oxide (BSSCO) compounds, and we describe measurements made on high quality whiskers of the 2:2:1:2 and 2:2:2:3 phases. A simple model based on extreme anisotropy plus offset contacts can explain the gross features of four contact measurements in the ohmic flux-flow regime, but not the wealth of reversal phenomena found for the IVVI configuration in the lower temperature irreversibility region.     

Reduction of acid chlorides with sodium borohydride in N,N-dimethylformamide: Nature of the reaction intermediate and a method for its conversion to the corresponding aldehyde with minimal alcohol formation

By use of sodium borohydride under the proper reaction conditions, direct conversion of both aliphatic and aromatic acid chlorides to the corresponding aldehyde can be achieved in 80–95% yield.     

Design and application of a femtosecond optical parametric oscillator for time-resolved spectroscopy of semiconductor heterostructures

Femtosecond pulses of a collinearly pumped Optical Parametric Oscillator (OPO) are applied for investigations of the carrier dynamics in ternary and quaternary semiconductor quantum wells. The design and the specifications of the OPO are given in detail. We show that no measurable jitter exists between the pump pulses and the output pulses of the OPO. Therefore, it is possible to use the OPO and its pump laser for two-color experiments with a time resolution limited by the pulse lengths. We present and discuss results of transient four-wave mixing experiments on (InGa) As/InP quantum wells, and find a new kind of polarization-dependent quantum beat phenomenon. In addition, non-degenerate experiments on quantum wells from the quaternary (InGaAl) As material system, using two pulses at different wavelengths (one from the OPO and one from the pump laser), are discussed as a novel experimental technique to study carrier trapping into quantum wells.     

A novel reducing agent derived from formic acid and two equivalents of a grignard reagent: Chemoselective reduction of aldehydes

Aldehydes are reduced at a moderate rate by use of a novel reagent obtained by the addition of two molar equivalents of ethylmagnesium bromide to formic acid in tetrahydrofuran solution. Under similar conditions the reduction of ketones proceeds quite slowly.