A search algorithm for linear codes: progressive dimension growth

This paper presents an algorithm, called progressive dimension growth (PDG), for the construction of linear codes with a pre-specified length and a minimum distance. A number of new linear codes over GF(5) that have been discovered via this algorithm are also presented.      

Temperature and magnetic field dependence of superconductivity in nanoscopic metallic grains

We study pairing correlations in ultrasmall superconductor in the nanoscopic limit by means of a toy model where electrons are confined in a single, multiply degenerate energy level. We solve the model exactly to investigate the temperature and magnetic field dependence of number parity effect (dependence of ground state energy on evenness or oddness of the number of electrons). We find a different parity effect parameter to critical temperature ratio (4 rather than 3.5) which turns out to be consistent with exact solution of the BCS gap equation for our model. This suggests the equivalence between the parity effect parameter and the superconducting gap. We also find that magnetic field is suppressed as temperature increases.     

From low to high-temperature superconductivity: A dimensional crossover phenomenon? A finite size effect?

We explore the Ginzburg-Landau version of a model for layered superconductors, in which superconducting material consisting ofM unit cells is separated by insulating layers that areN unit cells thick. Invoking the recently proposed interlayer coupling—which enhances pairing within the superconducting sheets—the order parameter coupling turns out to be of Heisenberg type, analogous to layered magnets. The mean field result forT _c (M, N) is found to be in remarkable agreement with experiment for ultrathin NbSe₂ crystals and Sn–SiO, Al–AlO₂, YBCO/PrBCO superlattices. The fact thatT _c (M, N) increases with increasingM is traced back to a finite size effect, corresponding to a crossover from nearly two to three-dimensional superconductivity. This change from low to high-temperature superconductivity is found to be independent of the sign of the interlayer interaction. An electrostatic model for the interaction on YBCO/PrBCO superlattices is in reasonable agreement with experiment. The orbital upper critical fieldH _c2 turns out to be unlimited ited whileH _c2 is proportional toT _c (M, N).     

Microfluidic based impedance biosensor for pathogens detection in food products

A MEMS‐based impedance biosensor was designed, fabricated, and tested to effectively detect the presence of bacterial cells including E. coli O157:H7 and Salmonella typhimurium in raw chicken products using detection region made of multiple interdigitated electrode arrays. A positive dielectrophoresis based focusing electrode was used in order to focus and concentrate the bacterial cells at the centerline of the fluidic microchannel and direct them toward the detection microchannel. The biosensor was fabricated using surface micromachining technology on a glass substrate. The results demonstrate that the device can detect Salmonella with concentrations as low as 10 cells/mL in less than 1 h. The device sensitivity was improved by the addition of the focusing electrodes, which increased the signal response by a factor between 6 and 18 times higher than without the use of the focusing electrodes. The biosensor is selective and can detect other types of pathogen by changing the type of the antibody immobilized on the detection electrodes. The device was able to differentiate live from dead bacteria.     

Photoinduced changes of reflectivity in single crystals of YBa2Cu3O6.5 (ortho II)

We report measurements of the photoinduced change in reflectivity of an untwinned single crystal of YBa2Cu3O6.5 in the ortho II structure. The decay rate of the transient change in reflectivity is found to decrease rapidly with decreasing temperature and, below T(c), with decreasing laser intensity. We interpret the decay as a process of thermalization of antinodal quasiparticles, with a rate determined by inelastic scattering of quasiparticle pairs.     

Abrupt transition in quasiparticle dynamics at optimal doping in a cuprate superconductor system

We report time-resolved measurements of the photoinduced change in reflectivity, DeltaR, in the Bi2Sr2Ca(1-y)Dy(y)Cu2O8+delta (BSCCO) system of cuprate superconductors as a function of hole concentration. We find that the kinetics of quasiparticle decay and the sign of DeltaR both change abruptly where the superconducting transition temperature T(c) is maximal. These coincident changes suggest that a sharp transition in quasiparticle dynamics takes place precisely at optimal doping in the BSCCO system.     

New quinary linear codes from quasi-twisted codes and their duals

One of the central problems in algebraic coding theory is construction of linear codes with best possible parameters. Quasi-twisted (QT) codes have been promising to solve this problem. Despite extensive search in this class and discovery of a large number of new codes, we have been able to find still more new codes that are QT over the alphabet ${\mathbb{F}}_5$ using a more comprehensive search strategy.