Binary baseband polar signals in combination with continuous and impulsive noise with i.s.i.

This letter presents the performance of a binary baseband polar system in the presence of a mixture of continuous and impulsive noise and intersymbol interference (i.s.i.). The results obtained are very general and the system performance in special cases like purely continuous noise or purely impulsive noise with or without i.s.i. can be easily derived from the general results.     

Critical magnetic fields of Cu-Pb-Cu proximity-effect sandwiches studied by acoustic surface waves

The temperature dependence of the surface-wave attenuation in Cu-Pb-Cu sandwiches, in the absence of a magnetic field, agrees well with the BCS expression. We compare the temperature dependence of the parallel and perpendicular critical fields with expressions derived from the Ginzburg-Landau theory. We get satisfactory agreement, provided that for the thinner specimens we take the mean free paths in the proximity-effect sandwich to be somewhat smaller than the values found for monitor strips. This implies that some interdiffusion between the Pb and the Cu is taking place.     

Validity studies in clustering methodologies

Clustering algorithms tend to generate clusters even when applied to random data. This paper provides a semi-tutorial review of the state-of-the-art in cluster validity, or the verification of results from clustering algorithms. The paper covers ways of measuring clustering tendency, the fit of hierarchical and partitional structures and indices of compactness and isolation for individual clusters. Included are structural criteria for validating clusters and the factors involved in choosing criteria, according to which the literature of cluster validity is classified. An application to speaker identification demonstrates several indices. The development of new clustering techniques and the wide availability of clustering programs necessitates vigorous research in cluster validity.     

Carbothermal reduction synthesis of nanocrystalline zirconium carbide and hafnium carbide powders using solution-derived precursors

Zirconium carbide (ZrC) and hafnium carbide (HfC) powders were produced by the carbothermal reduction reaction of carbon and the corresponding metal oxide (ZrO₂ and HfO₂, respectively). Solution-based processing was used to achieve a fine-scale (i.e., nanometer-level) mixing of the reactants. The reactions were substantially completed at relatively low temperatures (<1500°C) and the resulting products had small average crystallite sizes (50–130 nm). However, these products contained some dissolved oxygen in the metal carbide lattice and higher temperatures were required to complete the carbothermal reduction reactions. Dry-pressed compacts prepared using ZrC-based powders with 100 nm crystallite size could be pressurelessly sintered to 99% relative density at 1950°C.     

Bio-Inorganic Studies on the Fe(II) Sparfloxacin Complex

The qualitative and quantitative analysis of an antibiotic drug, 5-amino-1 cyclopropyl-7 (cis-3, 5 dimethyl-1-piperazyl)-6,8- dihydro-1, 4 dihydro-4-oxo-3-quinoline carboxylic acid (Sparfloxacin, SFX) and its pharmaceutical formulation i.e.sparx-100 tablet, has been done using polarographic and amperometric methods. Complexation behavior of SFX with Fe(II), both in solid and liquid phases has been studied by elemental analysis, IR.-spectra and polarographic and amperometric methods. SFX produces a single cathodic reduction wave in 0.1 M ammonium tartrate (supporting electrolyte) at pH 6.0 +/-0.1. The wave is diffusion controlled and wave height is proportional to the concentration of SFX. The complex is also reversibly reduced at the electrode surface with diffusion-controlled kinetics. The stoichiometry of the Fe(II)- SFX complex is 1:1. Antibacterial studies on the drug and its metal complex have been performed against different bacteria. The observed results revealed the complex to be more potent in its antibacterial activity as compared to the parent drug. On the basis of observed results it could be concluded that the prepared Fe(II)- SFX complex may be recommended to the therapeutic experts for its possible use as a more potent antibiotic drug.     

Layer-by-layer growth of CdSe-based nanocrystal light-emitting diodes

The partial exchange of surface-passivating trioctylphosphine oxide (TOPO) on CdSe and ZnS-clad CdSe (CdSe/ZnS) nanocrystals with primary amines was utilized to grow ultra-thin films of these nanocrystals under nonaqueous conditions. This growth was achieved using 1,12-diaminododecane in a layer-by-layer assembly format, where one of the amino groups binds with the nanocrystal surface and the other regenerates the interface for further binding of nanocrystals. The nature of the growth is dependent on the relative surface affinity between the TOPO and the primary amine toward the zinc or cadmium sites on the nanocrystals. Using this technique, high-quality luminescent films of these nanocrystals can be built with well-defined thicknesses. Electroluminescent devices have been fabricated using this methodology.     

Structural, electrical and thermodynamical aspects of hydrogenated La-Ni-Si alloy

The structural, electrical and thermodynamic properties of a La-Ni-Si [La = 28.9%, Ni = 67.5%, Si = 3.6%] alloy have been investigated. Powder XRD results show that the lattice constants and unit cell volume of the alloy increase after hydrogen storage. It was also found that the resistance of the alloy increased with dissolved hydrogen concentration. Hydrogen absorption pressure composition isotherms have also been investigated which show the presence of two single a and β regions and one mixed (α + β) phase. The thermo-dynamic parameters viz. the relative partial molar enthalpy (ΔH) and relative partial molar entropy (ΔS) of dissolved hydrogen, are found to be in the range 8–18 kJ (mol H)^-1 and 25–63 JK^-1 (mol H)^-1. From the dependence of ΔH on the hydrogen concentration,X, the different phases [α, α + β, β] and phase boundaries of the alloy-H system are identified. Thermal conductivity and diffusivity of La-Ni-Si and its hydride have been measured at room temperature by using TPS technique. Thermal conductivity was found to decrease due to absorbed hydrogen in the alloy.     

Processing, microstructure, and mechanical properties of cast In-Situ Al(Mg, Ti)-Al2O3(TiO2) composite

In-situ particle-reinforced aluminum alloy-based cast composites have been synthesized by solidification of the slurry obtained by dispersion of externally added titanium dioxide (TiO₂) particles in molten aluminum at different processing temperatures. Alumina particles (Al₂O₃) form in situ through chemical reaction of TiO₂ particles with molten aluminum. Simultaneously, the chemical reaction also releases titanium, which dissolves into molten aluminum and results in the formation of intermetallic phase Ti(Al_1−x ,Fe _x )₃ during solidification. Increasing the processing temperature increases (1) the amount of elongated as well as blocky intermetallic phase Ti(Al_1−x ,Fe _x )₃, (2) the proportion of alumina particles in the reinforcing oxides, and (3) the porosity content in the resulting cast in-situ composite. The difference in particle content and porosity between the top and the bottom of the cast ingot increases with increasing processing temperature. The hardness of the cast in-situ composite is significantly more than that of the matrix alloy due to the presence of reinforcing particles, but the hardness is greatly impaired by the presence of porosity at the top of the cast ingot. The percent elongation of the cast in-situ composite decreases with increasing processing temperature possibly due to increasing porosity as well as an increasing amount of elongated intermetallic phase, which affects the percent elongation of the matrix alloy. The tensile and yield stresses of the cast in-situ composite decreases with increasing processing temperature again due to increasing porosity, which affects the ultimate tensile stress more than the yield stress. In the cast in-situ composite containing 3.31 ± 0.77 vol pct of porosity, the Brinell hardness is about 6 times its yield stress. The estimated yield stress of the cast in-situ composite at zero porosity as given by the linear least-squares fit appears to increase with particle content at a significantly higher rate than that predicted by the shear-lag model.     

A novel converter topology for multiple individually regulated outputs

Power supply voltages in digital systems have reduced considerably in recent years, and often digital components requiring different voltages are present on the same board. This has increased the demand for multiple output power distribution systems with tight individual load voltage regulation. This paper presents a power distribution system having a central power supply that acts as a controlled current source whose output is connected to individual loads on a time shared basis. All the magnetics are concentrated in the converter acting as the current source. The current source can be realized by a current controlled buck, buck-boost, or single-ended primary inductance converter (SEPIC). First, a comparative analysis of buck, buck-boost, and SEPIC based implementation of the current source is carried out. Next, a buck-based current source implementation with constant frequency pulse-width modulation control for the output voltages is described. Detailed component and control design, simulations, and experimental results for a 100-W prototype are presented.     

Self-sustained phase-shift modulated resonant converters: modeling, design, and performance

This paper presents an improved control technique for the full bridge series, parallel, and series-parallel resonant converters. This control technique combines a self-sustained oscillation mode with a phase shift modulation technique that can significantly reduce the range of frequency variation necessary for obtaining zero voltage switching in the resonant converters. This frequency reduction provides optimized component ratings and operating frequency. A simple and accurate low order mathematical model based on the sampled data technique that fully describes the steady-state, and dynamic performance of the resonant converters, has been developed. A refinement algorithm is developed to enhance the accuracy of the modeling technique and the converter design. The improved converter performance and the feasibility of the developed dynamic model have been investigated using the series-parallel resonant converter topology with a capacitive output filter. Finally, MATLAB numerical solutions, PSIM simulation results, and experimental results are given to highlight the merits of the proposed work.