Electronic structure of Chevrel Phases: Emphasis on the part played by the cluster twisting angle through a LCAO-EHT tight binding study

The electronic structure of PbMo₆S₈ has been investigated using the so-called EHT-tight-binding method. An idealized cubic and an experimental distorted geometry are used, with standard atomic orbital parameters and diagonal H-matrix elements. A full band structure is presented in the idealized case. In both cases, the density of state curves computed using an integration over the Brillouin zone are also presented. The results show the importance of the twisting angle on the electronic structure near the Fermi level.     

A new method for the determination of the compound nucleus coherence width at high excitation energy

The coherence width of the compound nucleus can be obtained from cross correlations of the energy spectra taken at different energies instead of the correlation function of the excitation function. In this way it is sufficient to cover an incident energy interval of the order of the compound nucleus width. We have applied this method to the reaction ¹²C + ²⁸Si. The coherence width of ⁴⁰Ca is found in reasonable agreement with previous determinations. Indication is obtained for the presence of a second (smaller) coherence width which could correspond to anomalous long-living compound nucleus states.     

Transfer processes in fractal media

An irreversible process in fractal media involves coupling relation between the space and the time. The present note displays how the fractional derivation has to be introduced to describe this effect. As a result the law of the chemical diffusion to a fractal is given.     

Le ligande isocyanure de benzoyle CNCOR: II. Spectres de vibrations du (η6-benzoate de methyle) chrome(0) dicarbonyle (isocyanure de benzoyle): (η6-C6H5CO2CH3)Cr(CO)2(CNCOC6H5)

Infrared and Raman spectra (4000-40 cm^?1 of (η⁶-C₆H₅CO₂CH₃)Cr(CO)₂(CNCOC₆H₅) are recorded and interpreted with the aid of isotopic derivatives. Vibration modes and modification of the aromatic ring bonds by coordination are discussed.     

Luminescence decay of distant donor-acceptor pairs in phosphorous-doped ZnTe

Luminescence decay of isolated donor-acceptor pairs has been measured over the range of pair distance R ～ 180 Å in phosphorous-doped ZnTe. Analysis of the recombination rate as a function of the pair distance suggests an asymptotic behaviour of the acceptor envelope function of the type exp(-r/a_A), with $\text{a}{}_{\mathrm{A}}\text{= 40 ± 10}\text{A}\text{?}$. This effective Bohr radius would correspond to an hydrogenic mass $\text{m}{}^1\text{= (0.13 ± 0.03)}\text{m}{}_{\mathrm{o}}$, which is close to the light hole mass as measured from cyclotron resonance experiments, $\text{m}{}^1\text{= (0.154 ± 0.005)}\text{m}{}_{\mathrm{o}}$. A discussion on the validity of the isolated donor-acceptor pair model is also given.     

A contraction of the Poincaré group suitable for high energy

A covariance group suitable for describing ultrarelativistic kinematics is constructed through an Inönü-Wigner contraction of the Poincaré group. Eikonalization, helicity conservation and impact parameter representation arise as a consequence of our scheme.     

Microbial asparaginase recovery by membrane processes

A feasibility study in the use of membranes for the recovery of L-asparaginase from the fermentation stage has been undertaken. In the cell harvesting stage 100 l of broth (0.55% dry weight approx) of Erwinia carotovora is concentrated to 3.2 l by a I m² prototype cross flow microfiltration unit in just over 4 hours. Cell disruption was carried out by raising the cell suspension to pH 11.5 to release the enzyme, which is stable in alkali, for a short period. After neutralisation by acetic acid addition, the enzyme is separated from the cell debris by filtration with 0.45 μm Asypor membranes. A preliminary economic analysis shows that the membrane process can compete favourably with the conventional process, which employs high speed centrifuges.