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Notes: The linear and quasilinear behavior of the drift-like perturbation with a parallel velocity shear is studied in a sheared slab geometry. Full analytic studies show that when the magnetic shear has the same sign as the second derivative of the parallel velocity with respect to the radial coordinate, the linear mode may become unstable and turbulent momentum transport increases. On the other hand, when the magnetic shear has opposite sign to the second derivative of the parallel velocity, the linear mode is completely stabilized and turbulent momentum transport reduces. © 2000 American Institute of Physics.

Notes: It is suggested that the ponderomotive force induced by radio frequency (rf) waves in the range of the Alfven frequency can create a transport barrier in a tokamak. The linear and nonlinear behavior of the driftlike perturbation with a parallel velocity shear is studied in the presence of rf waves. It is shown if the radial profile of the rf field energy is properly chosen the linear mode is stabilized and turbulent momentum transport reduces. The rf power required for this stabilization is found to be rather modest and hence should be easily obtained in actual experiments. © 2000 American Institute of Physics.

Notes: The structural aspects of clustering of Nd3+ ions in Nd2O3-doped SiO2 glasses and the effect of Al3+ codoping on these clusters have been investigated with pulsed electron paramagnetic resonance (EPR) techniques over a temperature range of 1.5–4 K. The Nd2O3 concentrations in these glasses range between 700 and 2400 ppm by weight. The Nd3+ echo-detected EPR (EDEPR) spectra of the Al-free glasses show indications of weak exchange coupling between Nd3+ ions due to clustering. The EDEPR spectra also suggest that the local coordination environment of Nd3+ ions is affected by codoping with Al. The electronic spin-lattice relaxation rates are found to be not sensitive to the spatial distribution of Nd3+ ions over the entire temperature range of measurements. On the other hand, the concentration dependence of phase relaxation rates show clear evidence of clustering of Nd3+ ions in Al-free glasses, even at the lowest Nd2O3 doping levels. These Nd3+ clusters are found to break up and homogenize with an increase in the average Nd–Nd distance on codoping with Al. Analyses of the hyperfine sublevel correlation spectrum of a Nd and Al codoped glass indicate that the homogenization of Nd3+ clusters is possibly a consequence of the formation of Nd–O–Al linkages. © 2001 American Institute of Physics.

Notes: The preparation of vanadate glasses containing barium oxide and their electrical properties in the temperature range of 80–500 K have been reported in this article. Analysis of the electrical properties has been made in the light of different hopping models. The multiphonon assisted hopping model of small polarons in the nonadiabatic regime, proposed by D. Emin [Phys. Rev. Lett. 32, 303 (1974)] have been observed to describe the temperature dependence of the conductivity data of these glasses over the entire temperature range of measurement. The parameters obtained from the fits of the experimental data to this model are reasonable and consistent with the glass composition. J. Schnakenberg's model [Phys. Status Solidi 28, 623 (1968)] is also consistent with the temperature dependence of the conductivity data. Mott's optical phonon assisted hopping model at high temperatures provides smaller values of the localization length. However, Mott's variable range hopping model is valid at low temperatures. © 2000 American Institute of Physics.

Notes: Observation of energy-dependent transmission of nonequilibrium minority electrons through a symmetric double-barrier (DB) quantum well heterostructure is reported. The DB is placed in the base of a GaInAs/AlInAs bipolar transistor. The electrons are launched into the DB with variable kinetic energies using a tunnel barrier in the emitter and varying the emitter-base voltage. The resulting peak in the collector current provides for the first time evidence of quasi-ballistic resonant tunneling of minority carriers into the eigenstates of a quantum well. The small peak-to-valley ratio and the broad peak also demonstrate the importance of scattering and of the anisotropy in momentum space of the incident distribution function in the region between the ballistic electron launcher and the DB.

Notes: The problem of maintaining the oxygen stoichiometry of the Y1Ba2Cu3Ox (the so-called 123) compound at the desired level of x=6.0±0.1 when fabricating superconducting wires using the powder-in-tube method is addressed. A solution to this problem appears to be incorporating an unstable oxide like Ag2O in the core material, such that it acts as an in situ oxygen donor during the final sintering or annealing stage. Moreover, the segregation of Ag at the grain boundaries of the 123 grains and at the porosities seems to be a possible reason for the considerable improvement of the critical current density Jc of these wires. The effect of processing parameters, like different sintering temperatures and addition of various percentages of either Ag or Ag2O, is presented. Finally, in order to test conservation of superconductive properties during handling, the wires were subjected to different degrees of bending, and the subsequent effect on superconducting transition temperature, Tc and Jc, is reported.

Notes: At North Carolina State University, we have recently employed photoassisted molecular beam epitaxy to successfully prepare p-type modulation-doped HgCdTe. The modulation-doped HgCdTe samples were grown on lattice-matched (100) CdZnTe substrates cut from boules grown at Santa Barbara Research Center. In this letter, we report details of the growth experiments and describe the structural, optical, and electrical properties that this new infrared quantum alloy of HgCdTe possesses.

Notes: A fabrication technique for producing bulk and irregular-shaped aluminum/high Tc superconductor composites by traditional powder metallurgy method is reported. During the course of fabrication, the oxygen stoichiometry can be maintained at the desired level in order to retain superconductivity by addition of certain metal oxides or metal carbonates with low oxidation tendency, e.g., Ag2O, Ag2CO3, and CdO. Moreover, replacement of oxygen with fluorine is also possible by addition of certain unstable fluorides like AgF. Superconductivity measurements of Al/YBa2Cu3Ox random composites with additions of different oxygen or fluorine donors show a similiar or improved Tc in comparison to the pure 123 compound. The concept of oxygen/fluorine donor can also be used in other fabrication techniques of metal/123 composites to stabilize the oxygen/fluorine stoichiometry.

Notes: A strong sexual incompatibility barrier that exists between the two cultivated jute species, Corchorus capsularis and Corchorus olitorius, limits the scope for improvement through genetic introgression. Protoplast fusion was carried out to generate interspecific hybrid cell lines. Cotyledonary cell protoplasts of C. capsularis and anthocyaninpigmented hypocotyl protoplasts of C. olitorius were used in the fusion experiments, which appeared to be visually useful in the early selection of the fused products. A chloroplast DNA (cpDNA) marker was developed in jute, which showed species-specific hybridization patterns with EcoRI-digested total genomic DNA of C. capsularis and C. olitorius. This cpDNA marker was used in the characterization of the somatic hybrid cell lines at their early stages of growth. Evidence for the presence of both types of cpDNA in the hybrid cell lines was obtained when the total genomic DNA of 4- to 7-month-old hybrid cell lines was challenged with the chloroplast DNA marker through Southern analysis. It was shown that the early segregation of the parental chloroplasts did not occur in jute, although this is common in other plant species. The hybrid nature of the fused cell lines could also be identified through peroxidase isozyme analysis. Isozyme banding patterns were complex and varied among the hybrid cell lines.

Notes: Nine isonitrogenous (35% crude protein approximately) and isocaloric (18.37 kJ g−1) experimental diets (RLL20–BCFL40) were formulated with either raw or treated (inoculated with fish intestinal bacteria) Leucaena leucocephala leaf meal at 20%, 30% and 40% levels replacing other ingredients partially from a fish meal based reference diet (RD). Two specific strains of fish intestinal bacteria, Bacillus subtilis (isolated from Cyprinus carpio) and B. circulans (isolated from Oreochromis mossambicus) having extracellular cellulolytic and amylolytic activities, were used to inoculate Leucaena leaf meal for 15 days at 37°C. The crude fibre, cellulose and hemicellulose contents and the antinutritional factors, tannin, phytic acid and mimosine in the leaf meal decreased due to inoculation. However, free amino acids and fatty acids increased in the treated leaf meal. The response of rohu, Labeo rohita, fingerlings fed the experimental diets for 80 days was compared with fish fed a RD. Both the inclusion level and type of Leucaena leaf meal in diets significantly affected the growth performance of rohu. Fish fed diets containing inoculated Leucaena leaf meal performed better in comparison with those with the RD. On the basis of growth response, feed conversion ratio, protein efficiency ratio and apparent net protein utilization, diet formulated with 30%Leucaena leaf meal inoculated with B. circulans resulted in the best performance of rohu fingerlings followed by diet with 40%B. subtilis inoculated Leucaena leaf meal. The apparent protein digestibility (APD) was better in fish fed diets containing B. circulans inoculated leaf meal. An increasing level of raw Leucaena leaf meal was associated with a decrease in the carcass protein content of rohu fingerlings. The activity of α-amylase increased with the increasing level of treated leaf meal in diets. Cellulase activity increased with increasing level of inclusion of raw leaf meal, and was comparatively lower in fish fed diets with treated leaf meal. Activities of protease and lipase were higher in fish fed the RD. The results showed that it is possible to incorporate Leucaena leaf meal inoculated with enzyme-producing fish intestinal bacteria in carp diets up to 40% level of inclusion.