Field theory of mesoscopic fluctuations in superconductor/normal-metal systems

The thermodynamic and transport properties of normal disordered conductors are strongly influenced by the proximity of a superconductor. A cooperation between mesoscopic coherence and Andreev scattering of particles from the superconductor generates new types of interference phenomena. A field theoretic approach is introduced which is capable of exploring both the averaged properties and mesoscopic fluctuations of superconductor/normal-metal systems. As an example the method is applied to the study of the level statistics of a SNS junction. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 1, 21–26 (10 January 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Diluted generalized random energy model

A layered random spin model, equivalent to the generalized random energy model (GREM), is introduced. In analogy with diluted spin systems, a diluted GREM (DGREM) is constructed. It can be applied to calculate approximately the thermodynamic properties of spin glass models in low dimensions. For the Edwards-Anderson model it gives the correct critical dimension and 5% accuracy for the ground state energy in two dimensions. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 6, 415–419 (25 March 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

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Book reviews

     

Records in the Fα-scheme. II. Limit laws

Limit theorems for the number of records in a sequence of independent nonidentically distributed random variables are obtained. A generalization of the so-called F^α-scheme is given. Bibliography: 4 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 216, 1994, pp. 42–51. Translated by A. Sudakov.     

The dynamic response of an inhomogeneous plasma diode to an appliedpotential drop

Recent measurements of the response to an applied step voltage in collisionless plasmas have demonstrated the importance of the initial ion density distribution for the resulting time evolution and the formation of electric double layers. The dynamic response of a plasma diode to an applied step voltage is studied by particle-in-cell simulations and an analytical model. It is shown that an ion-density cavity (a local ion-density minimum with a width of many Debye lengths) can support large potential drops for several electron transit times. The potential drop extends over a distance related to the cavity width. When the applied potential drop exceeds a certain critical value, which depends on the cavity depth, the drop instead concentrates in a cathode sheath, which also is the response obtained for homogeneous initial plasma. The existence regions for the two different response in the appropriate parameter plane are found from the simulations and shown to agree with the regions predicted analytically. The analytical potential profiles agree with those simulated     

Large-scale computer simulation of fully developed turbulent channel flow with heat transfer

Recently, with the advent of supercomputers, there has been considerable interest in the use of direct numerical simulation to obtain information about turbulent shear flow at low Reynolds number. This paper presents a pseudospectral technique to solve the full three-dimensional time-dependent Navier-Stokes and advection-diffusion equations without the use of subgrid-scale modelling. The technique has not been previously used for fully developed turbulent channel flow simulation and is based on methods applied in other contexts. The emphasis of this paper is to provide a reasonably detailed account of how the simulation is done rather than to present new calculations of turbulence. The details of an algorithm for turbulent channel flow simulation and the grid and time step sizes needed to integrate through transient behaviour to steady state turbulence have not been published before and are presented here. Results from a Cray-2 simulation of fully developed turbulent flow in a channel with heat transfer are presented along with a critical comparison between experiment and computation. The first- and second-order moments agree well with experimental measurements; the agreement is poor for higher-order moments such as the skewness and flatness near the walls of the channel. Detailed information given about the effects of spatial grid resolution on a computed results is important for estimating the size of the computation required to study various aspects of a turbulent flow.     

Effect of antigen size on optimal ligand density of immobilized antibodies for a high-performance liquid chromatographic support

The antigen binding capacities for purified polyclonal antibodies immobilized onto a silica-based high-performance liquid chromatographic (HPLC) affinity support are described for three serum proteins over a range of antibody ligand densities. The rate of decline in the specific activity of the immobilized antibodies with respect to increasing ligand density was found to increase with the molecular weights of the antigens. The antibodies used were purified from whole antiserum using high-performance affinity chromatography and were examined using HPLC on an SCX stationary phase. Conditions are also described for efficient coupling of the ligand to the support.     

Production of slow muonic hydrogen isotopes in vacuum

Muonic hydrogen isotopes (μ⁻ p, μ⁻ d, and μ⁻t) are simple quantum mechanical systems ideally suited for studies of numerous fundamental phenomena in electroweak and strong interactions as well as in applied areas such as muon chemistry or muon catalyzed fusion. Emission of muonic hydrogen isotopes into vacuum helps to overcome the limitations which are normally imposed on conventional investigations with gaseous and liquid targets. A proof of principle experiment for this new technique was performed at TRIUMF last year. Negative muons with 30 MeV/c momentum were stopped in a thin film of solid hydrogen and produced very low energy μ⁻d in vacuum. The distribution center of the normal velocity components of emitted μ⁻d atoms was measured to be ∼1 cm/μs. The yield of μ⁻d in vacuum is an increasing function of H₂ film thickness δ up to a value of δ≥1 mm.