Entropic effects on the size dependence of cluster structure

We show that the vibrational entropy can play a crucial role in determining the equilibrium structure of clusters by constructing structural phase diagrams showing how the structure depends upon both size and temperature. These phase diagrams are obtained for example rare gas and metal clusters.     

Charge overlap effects dependence on the nature of the interaction

The He-He, He-H(1s), H(1s)-H(1s) and H(1s)-H(2s) interactions are considered as model systems for studying how charge overlap effects in second-order dispersion energies vary as a function of the nature of the interacting species. The non-expanded second-order energy and the corresponding multipole R ^-1 expansions, through all powers of R ^-1, are obtained for each interaction using Unsöld's average energy approximation. The results are used to discuss the limitations of the usefulness of the R ^-1 expansions.     

Absorption edge effects on the temperature dependence of threshold currents in GaAS laser diodes

The loss α, governing the threshold current in GaAs laser diodes is attributed to absorptive transitions involving tail states rather than free carriers.The determination of α from lasing photon energy and absorption edge data for compensated and uncompensated material yield a temperature dependence of α which can account for the temperature dependence of threshold currents observed experimentally.     

Pressure dependence of the lattice constant of diamond: Isotopic effects

The pressure dependence of lattice constants of ¹³C-enriched diamond and diamond of natural isotopic composition have been studied by using x-ray synchrotron radiation and the imaging plate technique. The compression curves reveal features which indicate an inversion of the isotope effect at high pressure. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 73–77 (25 January 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

On the almost periodic solution of generalized shunting inhibitory cellular neural networks with continuously distributed delays

Using fixed point theory, Lyapunov functional and some inequality techniques, with the shunting inhibitory cellular neural networks with continuously distributed delays and variable coefficients, this Letter establishes some sufficient conditions insuring the existence, uniqueness and stability of one almost periodic solution. Comparing with known results, the obtained ones have wider application range, and are applicable to the networks with variable constants. Even for some networks with constant coefficients, only our criteria can give explicit asseveration. Thus our results extend and ameliorate some known works. Finally, the excellence along with the validity of the obtained criteria is shown by one illustrative example.     

The effects of chemotherapeutics on cellular metabolism and consequent immune recognition

A widely held view is that oncolytic agents induce death of tumor cells directly. In this report we review and discuss the apoptosis-inducing effects of chemotherapeutics, the effects of chemotherapeutics on metabolic function, and the consequent effects of metabolic function on immune recognition. Finally, we propose that effective chemotherapeutic and/or apoptosis-inducing agents, at concentrations that can be achieved physiologically, do not kill tumor cells directly. Rather, we suggest that effective oncolytic agents sensitize immunologically altered tumor cells to immune recognition and immune-directed cell death.     

Relating the coverage dependence of oxygen adsorption on Au and Pt fcc(1 1 1) surfaces through adsorbate-induced surface electronic structure effects

Using density functional theory (DFT) we studied the adsorption of oxygen on gold and platinum fcc (1 1 1) surfaces as a function of coverage. We show how increasing coverages of oxygen atoms lead to a broadening of the surface atom d-bands and a consequent reduction in the average energy of the d-band center due to conservation of the d-band filling. The reduction in the energy of the d-band center leads to a correlated increase (weakening) in the adsorption energy. This underlying electronic structure relationship exists on both the gold and platinum surfaces, and we show that the coverage dependent adsorption energies of oxygen on these two surfaces are related by a simple near-linear correlation.     

Orientational effects in the energy dependence of the reaction cross-section from model calculations

Summary A dynamical model to calculate the kinetic-energy dependence of the reaction cross-section is presented. The most important aspects of the present treatment area) an orientational dependence of the reaction barrier,b) the onset of a recrossing mechanism andc) the operation of alignment forces during the reaction time. Application to several reactions of oriented or nonoriented reactants’ geometry gives a satisfactory fit of the excitation function data providing a clear insight into the diagnosis of the reaction dynamics that governs the reactive collision.

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Riassunto Si presenta un modello dinamico per calcolare la dipendenza dall’energia cinetica della sezione d’urto della reazione. Gli aspetti piú importanti di questo modello sono:a) una dipendenza orientazionale della barriera di reazione,b) l’insorgenza di un meccanismo di reincrocio ec) l’intervento di forze di allineamento durante il tempo di reazione. L’applicazione a parecchie reazioni con geometria dei reagenti orientata o non orientata dà un’approssimazione soddisfacente dei dati della funzione di eccitazione fornendo una chiara visione della diagnosi della dinamica di reazione che controlla la collisione reattiva.

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Резюме Предлагается динамическая модель для вычисления зависимости поперечного сечения реакции от кинетической знергии. Наиболее важные аспекты предлагаемого подхода: 1) ориентационная зависимость барьера реакции; 2) возникновение механизма пересечения; 3) действие сил ориентации во время реакции. Примение предложенного подхода к некоторым реакциям в случае ориентированной или неориентированной геометрии реагентов дает удовлетворительное соответствие с имеюцимися данными и обеспечивает правильное представление диагностики динамики реакции, которая определяет процесс соударения.

     

The dependence of metal-insulator-metal conductance curves on the chemisorbed ion concentration in the barrier1

The conductance curves of metal-insulator-metal junctions have been found to change in a systematic way with the number of chemisorbed ions in the barrier. Inelastic Electron Tunneling Spectroscopy peak intensity measurements were made on the A1-Pb junctions studied here to determine the number of formate ions chemisorbed on the alumina.     

A note on the depth dependence and current density effects upon the radiation damage in graphite

This note is in two parts. The first describes the surprisingly large depth at which the radiation damage can be observed after irradiating graphite with²MeV⁴He⁺ ions. The second part deals with the dependence of the induced damage with the deposited power density at sample temperatures up to 1250°C.     

Field dependence of the superconducting properties induced by proximity effects: Breakdown fields

It has been shown that the proximity-effect induced superconductivity in the normal partN of a superconductor-normal metal binary layer (such asIn Bi/Zn) can screen a magnetic field up to a critical fieldH _b. AtH _b, a sharp penetration of flux intoN occurs. However, the breakdown fieldH _b can only be observed for certain values of the thickness ofN and of temperature. We study here the domain of existence ofH _b as a function of these two parameters. We also show that studies onH _b yield some information on the properties of the pair potential inN. Thus measurements onH _b performed at the critical temperature ofN confirm the theoretical predictions concerning the remarkable behavior of the order parameter inN at this temperature.     

Mode-coupling effects in the density dependence of the shear viscosities of dense argon and methane

We argue that the density dependence of the shear viscosities of dense argon at 174, 223, and 301 K and of dense methane at 298 K can be understood on the basis of the mode coupling theory for hard spheres, in particular near the fluid-solid phase transition.