[en] A novel universal (material-independent) negative differential resistance is shown to exist in strictly one-dimensional systems (quantum wires) as a consequence of energy and momentum conservation in the interaction of one-dimensional confined carriers with one-dimensional confined acoustic phonons. The average (steady state) carrier energy should also exhibit a non-monotonic dependence on the driving electric field. Candidate systems to exhibit this negative differential resistance are suspended semiconductor nanobridges and semiconducting carbon nanotubes

[en] Transparent and conducting films of mixed oxides of zinc and zirconium have been prepared by sol-gel method. The amount of zirconium have been varied in between 0 to 3 at.%. XRD patterns showed that the nature of films are polycrystalline but the preferred orientation changes from (1 0 0) to (1 0 1) and finally (0 0 2) with increasing amount of Zr doping. The morphology and crystallite size of the films are strongly dependent on the doping concentration. The resistivity decreases with doping concentration up to 1.5 at.% but increases with concentration more than that. The maximum carrier concentration is (∼10¹⁹ cm^-3) and the mobility is minimized at this doping concentration. The optical bandgap was estimated from the reflectance and transmittance spectra. The obtained optical bandgap is about 3.3 eV, for unstrained ZnO but slight shrinkage in bandgap is noticed up to 2 at.% doping. There is corresponding rise in width of band tail which is a measure of the disorder in the system

[en] In an operating nuclear power plant when the load changes, either due to grid demand or due to the change in reactor output, the steam and feed water system undergoes an unsteady state of operation - till the new steady load condition is established. During this transient operation, various parameters of the system undergo changes. To understand the exact nature of the changes in some important parameters like steam flow, feed flow, steam pressure, deaerator storage tank levels etc, the various plant components are modelled for dynamic simulation. Because of the large thermal inertia of the steam generator system, to study the effect of load changes due to grid demand, modelling of the steam generator itself can be avoided, if it can be shown that the transient time - i.e. the interval between two steady state conditions are small. The present paper elaborates the modelling details of the various components, details of analysis by computer programme and the results obtained for some specific transient study applied to 235 MWe nuclear power plant. (author). 4 refs., 7 figs

[en] Calculations of the heat of formation of dilute solid solutions of AlCl₃, ScCl₃, GaCl₃, YCl₃, and InCl₃ in each of the three alkali chlorides NaCl, KCl, and RbCl are reported. The Born-Mayer repulsive parameters (B-M RPs) for nearest-neighbour interaction and the solution enthalpies of trivalent defects in alkali halides have been derived from the correlation between B-M RPs and the charge density overlap parameters of the interacting ions

[en] The solution enthalpies of some monovalent, divalent, and trivalent defects in some alkali halides are calculated following the standard procedure of minimising the total lattice energy change numerically, as a function of the relaxation of the nearest neighbours, when the defect cation occupies a substitutional position. The energies considered are electrostatic, dipole, dipole-dipole, and repulsive. It is found that inclusion of dipole-dipole energy helps to avoid the polarisation catastrophe problem for divalent and trivalent defects. The Born-Mayer repulsive parameters of the aliovalent defects are obtained from the charge density overlap method. Thus it is shown that a single method is capable of yielding positive values of solution enthalpies for all the aliovalent defects considered. (author)

[en] To observe a direct effect of 17beta-estradiol (E2) on thyroid activity, thyroid follicles were isolated from hypobranchial muscles of a freshwater murrel, Channa gachua. Thyroid follicles were incubated (5 X 10⁶ follicles/well) in vitro at 30 degree C for 2 hr without hormone and then 3 hr with E2 or bovine thyroid-stimulating hormone (bTSH). Addition of 10 and 100 ng of E2 to thyroid follicles resulted in 2- and 3-fold increases in thyroxine (T4) release. When 100 ng of bTSH was added to check the isolated follicular function, it stimulated T4 release to more than 3-fold. Increasing doses of E2 from 1 to 100 ng caused a dose-dependent stimulation of T4 release, while a 1000-ng dose reduced T4 release compared to 100 ng. When thyroid follicles of this experiment were lysed by sonication and T4 content was determined, it corroborated the profile of T4 release in response to varied E2 doses. E2 was ineffective in increasing ¹²⁵I uptake by the follicles, while bTSH elevated it by 45% over the control. Incubation of varied concentrations of [³H]estradiol with cytosol and nuclear fractions of thyroid follicles in the presence of a 100-fold excess of diethylstilbestrol showed saturable specific binding of E2

[en] Different SiAlON composites based on α'-SiAlON are investigated, with respect to the phase relationships, densification behavior, and mechanical properties. The compositions are located on a phase-diagram line parallel to the Si₃N₄-Y₂O₃·9AlN compound in the Si₃N₄-SiO₂-AlN-Al₂O₃-Y₂O₃-YN system. Analysis of the reaction sequences shows that the formation of the composites is associated with the transient appearance of Y₄Al₂O₉ (YAM), yttrium-aluminum-garnet (YAG), melilite, and a nitrogen-rich liquid phase. The small shift of compositions on the Si₃N₄-Y₂O₃·9AlN compound phase-diagram line toward the Al₂O₃-rich side offers the advantage of a higher sinterability and the removal of the melilite phase from a wide range of compositions containing α'-SiAlON and polytypes. The α'/β'-SiAlON composites show better mechanical properties in comparison to pure α'-SiAlON and composites of α'-SiAlON and polytypes. A post-heat-treatment causes the crystallization of YAG as a grain-boundary phase and leads to excellent strength retention up to temperatures of 1,350 C

[en] In cyclotron the magnetic field shaping is provided by the main magnet and along with that a set of auxiliary coils called the trim coil. The room temperature cyclotron (K=130) at VECC, Kolkata requires seventeen number of Trim Coil Power Supply to drive the magneto-optic system for proper beam dynamics of the cyclotron. Numbers of these are continuously variable high-current dc (750 A, 12 V) power supplies. For stable beam from the cyclotron a need is felt for the prototype design of such a power supply with higher long-term current stability along with high reliability to minimize the down time of the cyclotron. (author)

[en] This note describes how a commercial UV-VIS-NIR spectrophotometer may be adapted to function as a double beam photoacoustic spectrophotometer operating at visible wavelengths. Modification of a Varian Cary 17 spectrophotometer was carried out first by dismounting the photomultiplier tube detector module and the cell compartment of the spectrophotometer. The sample and the reference beams were focused through two externally mounted quartz lenses onto the sample and reference photoacoustic cells, respectively

[en] In the superconducting cyclotron the magnetic field shaping is provided by a set of coil called trim coil. Due to the relativistic increase of mass of charge particles given by m= m_o/√(1-v²/c²), the synchronization between the applied field and the time of revolution of the charge particles in a uniform magnetic field does not hold good. By using these set of auxiliary coils (trim coils) the magnetic field is made to increase towards the periphery of the circular pole face. (author)