Field Theory Methods in Classical Dynamics

A Dirac picture perturbation theory is developed for the time evolution operator in classical dynamics in the spirit of the Schwinger–Feynman–Dyson perturbation expansion and detailed rules are derived for computations. Complexification formalisms are given for the time evolution operator suitable for phase space analyses, and then extended to a two-dimensional setting for a study of the geometrical Berry phase as an example. Finally a direct integration of Hamilton's equations is shown to lead naturally to a path integral expression, as a resolution of the identity, as applied to arbitrary functions of generalized coordinates and momenta.     

Collisional excitation of Na-Rydberg atoms

The scattering of heavy ion with a multilevel Rydberg atom in the presence of an electromagnetic field is studied. The interaction of Rydberg atom and the e.m field is explored using non-perturbative quasi-energy technique. Although the results are presented for selected excitations but in actual calculations we have included many levels of the atom. The effect of various parameters are shown on collisional excitation process. As an illustration detailed calculations are performed for the inelastic proton-Na Rydberg atom collision accompanied by the transfer of photons and the effects of dressing due to the field are considered. The emphasis of the present work is on collision induced transitions especially the case that involves change of orbital as well as principal quantum number. Received 26 December 2001 / Received in final form 8 April 2002 Published online 19 July 2002     

Lateral interactions in the thermal desorption of H2 from clean Cu/Ni(110) alloy surfaces

The adsorption of hydrogen on a clean Cu10%/Ni90% (110) alloy single crystal was studied using flash desorption spectroscopy (FDS), Auger electron spectroscopy (AES), and work function measurements. Surface compositions were varied from 100% Ni to 35% Ni. The hydrogen chemisorption on a-surface of 100% nickel revealed strong attractive interactions between the hydrogen atoms in accordance with previous work on Ni(100). Three desorption states (β₁, β₂ and α) appeared in the desorption spectra. The highest temperature (α) state was occupied only after the initial population of the β₂-state. As the amount of copper was increased in the nickel substrate, desorption from the higher energy binding α-state was reduced, indicating a decrease in the attractive interactions among hydrogen atoms. The hydrogen coverage at saturation was not affected by the addition of copper to the nickel substrate until the copper concentration was greater than 25% at which a sharp reduction in saturation coverage occurred. This phenomenon was apparently due to the adsorption of hydrogen on Ni atoms followed by occupation of NiNi and CuNi bridged adsorption sites, while occupation of CuCu sites was restricted due to an energy barrier to migration.     

Purification and some properties of squalene-2,3-epoxide: lanosterol cyclase from rat liver

Squalene-2,3-epoxide: lanosterol cyclase was purified from rat liver in five steps as a soluble and homogeneous protein. The purified enzyme showed a single band on SDS-polyacrylamide gel electrophoresis with a molecular weight of 75 kD. In its native state it behaved as a homo-dimer. The isoelectric point of 5.5 and the apparent Km value for (3S)-squalene-epoxide of 55 microM were estimated for the cyclase.     

The Implications of Cognitive-style Findings for Operational Research

Cognitive style refers to differences that can be perceived in individuals due to differing cognitive structures. There has been a large amount of research on how cognitive style affects managerial decision-making, particularly in the context of management information systems, but little or no attempt to relate these findings to operational research. This paper reviews the findings of cognitive-style research from the perspective of operational research, and draws a number of useful inferences concerning the matching of OR aids to managers, the presentation of information and recommendations, the use and acceptance of OR, and the structure of OR groups. Further, it is argued that cognitive-style findings help to give a justification to the move towards ‘soft’ approaches to analysis.     

Electron traps and positive DLTS signals in VPE GaAs MESFETs

Capacitance DLTS measurements have been performed in VPE GaAs MESFETs prepared on Bridgman Cr-doped and LEC undoped semi-insulating substrates. A band of electron traps not intrinsically related to the VPE growth process and accumulating near the metal (gate) — semiconductor interface was detected in all the samples. Deeper regions into the channel were free from any detectable trap. Near pinch-off conditions, a positive capacitance signal was found to dominate the DLTS spectra only in the case of samples prepared on Cr-doped substrates. The hypothesis of this positive transient being related to changes in the occupation of surface states in the ungated surface access regions has been checked by comparing experimental and calculated dependencies of the signal amplitude on reverse gate voltage. Unexplained discrepancies, together with the absence of positive signal in MESFETs prepared on LEC undoped substrates, suggest the possibility of hole emission from hole traps within the bulk of the device.