Variational calculations of positron characteristics in metals

Energies of the formation of monovacancies, as well as the binding energies and work functions of quasi-free and localized positrons and positroniums have been calculated in terms of the gradient version of the density-functional method using the stable-jellium model. The calculations show that for the metals possessing negative positron work function, the presence of vacancies in the subsurface region can lead to the change in the sign of the work function. The same effect of the change in the sign of the work function of a quasi-free positron can be caused by the presence of a dielectric coating on the metal surface. Comparison with the experiment is performed.     

Determination of Strength of Adhesion Contacts in Filled Elastomers from Elastic Modulus Change

The concentration of particles of the filler that have separated from the binder is determined by comparing the values of the modulus of elasticity of a filled polymer for the initial sample and after loading with a measured load. Analyzing the curve of the dependence of the concentration of the debonded filler on the stress that has caused the debonding makes it possible to estimate the adhesion strength of the binder-to-filler bond.     

On the prediction of shell stability from their vibrational behavior

Summary.  The theoretical possibility of vibrational nondestructive control of the shell stability conditioned by the correlation of natural vibrations and stability loss phenomena is substantiated when analyzing the solution of the problem of natural vibrations of preliminarily loaded shells. Received July 2, 2001; revised July 4, 2002     

The role of positron emission tomography in pharmacokinetic analysis

The physiological and biochemical measurements that can be performed noninvasively in humans with modern imaging techniques offer great promise for defining the precise state of a patient's disease and its response to therapy. In general, there are two critical points in drug development when PET measurements are likely to be particularly useful: (1) In preclinical studies, a new drug can be precisely compared to standard therapies or a series of analogs can be screened for further development on the basis of performance in appropriate animal models. (2) In phase I-II human studies, classic pharmacokinetic measurements can be coupled with imaging measurements (a) to define optimal dosing schedule; (b) to define the potential utility of interventions in particular clinical situations; and (c) to formulate the design of phase III studies that are crucial for drug licensure. In general, the types of measurements that are possible can be grouped into the following categories: 1. In those situations in which the drug can be radiolabeled, the time course of tissue delivery can be determined noninvasively in vivo in health and disease. Such information should be useful for determining dosing schedules, establishing efficacy, and predicting possible toxicity. 2. Ligand-receptor binding can be assessed in vivo in two ways. The ability of the drug to displace standard radiolabeled ligands from their receptors can be determined; alternatively, labeled drug can be used to more directly assess the distribution and time course of binding. These measurements are particularly useful for studying drugs that are active in the central nervous and cardiovascular systems. 3. Measurements of tissue metabolism will be useful in determining the effects of therapies aimed at particular metabolic abnormalities. In addition, these measurements may be useful in defining viability and function of tissues in such widely disparate clinical situations as cancer chemotherapy and cardiology. For example, effects of CNS or cardiovascular drugs can be monitored by observing 18FDG metabolism in brain and heart. We suggest that the joining of classic clinical pharmacology to exquisite imaging measurements will help form the basis for 21st-century clinical drug development.     

Performance of hybrid ARQ schemes for the fading channel

We define and adopt a theoretical method, based on the sphere-packing bound, for evaluating and comparing the achievable performance of different hybrid automatic repeat request schemes for the fading channel. The channel state evolution is assumed to be represented by a finite-state Markov chain. To assess the correctness and the accuracy of the analysis, some simulation results, based on the use of turbo codes, are also presented.     

High-capacity, self-assembled metal-oxide-semiconductor decoupling capacitors

We combine nanometer-scale polymer self assembly with advanced semiconductor microfabrication to produce metal-oxide-semiconductor (MOS) capacitors with accumulation capacitance more than 400% higher than planar devices of the same lateral area. The self assembly technique achieves this degree of enhancement using only standard processing techniques, thereby obviating additional process complexity. These devices are suitable for use as on-chip power supply decoupling capacitors, particularly in high-performance silicon-on-insulator technology.     

Some notes on rate-compatible punctured turbo codes (RCPTC) design

In this letter, we propose and compare some design criteria for the search of good rate-compatible systematic turbo codes (RCPTC) families. The considerations presented by Benedetto et al. to find "best" component encoders for turbo-code construction are extended to find good rate-compatible puncturing patterns leading to codes with promising performances.     

Influence of diffusive processes on the formation of the radial structure of an electric arc in metal vapor

The role of diffusive processes in the establishment of the radial structure of a free-burning electric arc was investigated experimentally and numerically. It is shown that the increased content of plasma-forming particles in the peripheral region of arcs observed in many experiments arises from the inadequacy of the assumption on the plasma equilibrium state. This effect can be attributed to the plasma nonequilibrium established as a result of resonant radiation from the hotter axial region undergoing absorption and reemission at the edge of the arc. Pis’ma Zh. Tekh. Fiz. 24, 40–45 (November 26, 1998)     

Electron work function and the surface tension of a metallic surface with an insulating coating

The electron work function, contact potential difference, and surface tension of elastically deformed faces of metal with an insulating coating have been calculated within the Kohn-Sham method. The calculations demonstrate the opposite deformation dependences of the electron work function and contact potential difference. An insulating coating leads to a negative change in the work function and a positive change in the contact potential difference. It is shown that the measurements of the contact potential difference of a deformed face by the Kelvin method give only the change in the value of the one-electron effective potential on the plane of a virtual image behind the surface rather than the value of the electron work function. The calculated values of the electron work function and surface tension for Al, Au, Cu, and Zn are in agreement with the results of experiments for polycrystals and first-principles calculations.