Phonons and spin excitations in the extended t-J model

We consider the effects of spin-phonon coupling within the slave-boson mean-field treatment of the extended t-J model. With no additional assumptions the theory is found to give a semi-quantitative account of the frequency and linewidth anomalies observed for certain phonon modes in Y Ba₂Cu₃O₇ at the superconducting transition. We report also investigations of the role of this coupling in affecting thermodynamic properties and spin dynamics.     

Combustion synthesis of advanced materials: Part I. Reaction parameters

An explanation of combustion (self propagating high temperature) synthesis (SHS) is given together with a historical perspective of the examination of such exothermic reactions. The application of thermochemical functions has been used to predict theoretically the maximum adiabatic temperature, T_ad. This, combined with a knowledge of the ignition temperature, T_ig, and the actual combustion temperature, T_c, has been used to determine the heat loss from the SHS reaction and the amount of heat needed to raise the adjacent, cold, reactant layer to the ignition temperature in order to maintain the self sustaining nature of the propagating mode of the reaction. The pertinent reaction parameters that control self propagating high temperature (combustion) synthesis reactions have been examined. These include: reactant particle size and shape; powder mixing and compaction; green density; reaction stoichiometry; impurities; volatiles and diluents; reaction environment; mode and technique of ignition; heating rate; and the effect of these parameters on the generation of heat, exothermicity and control of the SHS reaction.     

Crystallinity and lateral crystallite size of different UHMW PE materials

Nascent high-molecular-weight (UHMW) polyethylene (PE) samples of different origins show a rather high crystallinity of about 70–75% and contain both a major portion of orthorhombic extended chain crystallites and a minor portion of triclinic crystallites. The triclinic content is greater the higher the molecular weight of the sample and the higher the activity of the used catalyser. A melting / recooling treatment results in a reduction of crystallinity by about 15–25% and disappearance of the triclinic phase. Further, an irreversible conversion of nascent orthorhombic extended chain crystallites to orthorhombic folded chain crystallites of increased lateral dimensions and crystalline perfections takes place during the melting / recooling treatment. The results are compared to those obtained for lower-molecular-weight PE samples and for high-strength / modulus PE fibers of different origins.     

Modified Imidazoles: Degradation Inhibitors and Adhesion Promoters for Polyimide Films on Copper Substrates

Polyimide films on copper substrates that are exposed to elevated temperatures and an oxidizing environment will be subject to degradation. In order to halt this degradation without changing the properties of the system, a polymeric agent could be placed between the polyimide and the copper. This paper will investigate three such materials that will not only slow down the degradation of the polyimide and the oxidation of the copper, but will also improve adhesion within the system. Fourier transform infrared reflection-absorption spectroscopy (FTIR-RAS) will be used to investigate the polyimide/polymeric agent/copper system.     

A machine vision system for high speed object tracking using a moments algorithm

A system has been developed for tracking the motion of objects in two dimensions in real-time. The system consists of a conventional CCD camera linked to a transputer-based frame grabber and an array of nine transputers. A parallel moments algorithm is used to extract the co-ordinates of the object's centre of gravity and orientation at field rate, i.e. 60 Hz. Since the position data are made available in real-time—with a small time delay—the system has the potential for inclusion in a feedback loop. Results are presented for tracking the trajectory of a chocolate bar diverted by an air jet. The potential of the system for higher sampling rates—up to 200 Hz—is discussed.     

Fatty diet and multiple sclerosis]

INTRODUCTION AND DEVELOPMENT: Multiple sclerosis (ME) is an inflammatory disease of the myelin of the central nervous system, the origin of which is still unknown. Genetic, infectious, immunological and environmental factors have all been blamed, but none of these factors on their own can explain the whole spectrum of this disease. Of the environmental factors, fat in the diet has given rise to most discussion. At the present time, it is known that polyunsaturated essential fatty acids form a part of biological membranes. A relationship has been found between the dietary fat consumed and the plasma levels and cell membrane content. CONCLUSIONS: The possible immuno-modulation function of these fatty acids justify rigorous evaluation of this hypothesis.