Some inhomogeneous magnetized viscous-fluid cosmological models with varyingΛ

Some cylindrically symmetric inhomogeneous viscous-fluid cosmological models with electromagnetic field are obtained. To get a solution a supplementary condition between metric potentials is used. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density. Without assuming anyad hoc law, we obtain a cosmological constant as a decreasing function of time. The behaviour of the electromagnetic field tensor together with some physical aspects of the model are also discussed.     

On the effect of a longitudinal magnetic field on oscillatory characteristics of a subnormal region in discharge in argon

Oscillating nature of current pulses under d.c. excitation in subnormal region with longitudinal magnetic field at pressure range 0.20 torr to 0.85 torr have been studied. The frequency, bandwidth, peak-peak voltage, cut-off current and rise time of the current pulses have been observed with pressure, average tube current and magnetic field. A study of these oscillograms in magnetic field, average tube current and pressure are presented. The probable mechanism for the generation of oscillation based on space-charge field modification with magnetic field is discussed     

Morphologies of microporous polyethylene and polypropylene crystallized from solution in supercritical propane

The morphologies of solvent-free, microporous, mechanically self-supporting cylinders of linear polyethylene and isotactic polypropylene, crystallized from solution in supercritical propane, were examined by an SEM technique. The morphology of gels (or foams), obtained with little or no shrinkage from 2% to 35% solutions by weight of polyethylene (99% to 85% porosities), is shown in some detail. Lamellae with very little or considerable mutual organization occur, often in the form of stacks with straight or coiled axes (axialites). Further growth of these can lead to particles with a roughly spherical overall shape and a predominantly radial orientation of the lamellae at the particle surface. Subcooled isotactic polypropylene, on the other hand, crystallizes in the form of perfectly shaped birefringent microspheres of very uniform size. ©1995 John Wiley & Sons, Inc.     

A heteropolynuclear R2[S2WS2Re(O)(Cl)S2WS2] (R = PPh4 and Et4N) complex. The first example of a tetrathiometalate ligand co-ordinated to an oxo-metal core

A solution of [ReOCl3(PPh3)2] in benzene reacts with solid (NH4)2WS4, in the presence of traces of H2O, to give [ReOCl(WS4)2]2–, isolated as its PPh4 (1) and NEt4 (2) salts. Both (1) and (2) exhibit (Re=O) at ca. 930, (Re=Cl) at ca. 330 (W=S)t at ca. 495 and (W–S–Re) bridging vibration at ca. 460cm–1. The FAB mass spectrum of (1) shows a peak for [ReO(WS4)2]+(m/z=826 amu) in the positive mode and that for PPh4[ReOCl(WS4)]– (m/z=889amu) in the negative mode, confirming the suggested composition. This is the second example of a d2 metal ion forming a tetrathiometalate complex and also the first example of an oxometal ion (excepting those of W and Mo) forming a molecular complex with tetrathio- tungstate or -molybdate ligands.     

Removal of Cr(VI) from Aqueous Solution Using Activated Cow Dung Carbon

Removal of hexavalent chromium from aqueous medium by using activated cow dung carbon was studied. Cow dung was carbonized and activated by treating with concentrated H(2)SO(4) followed by heating for 24 h at 120 degrees C. The extent of adsorption was studied as a function of pH, contact time, amount of adsorbent, concentration of adsorbate, and temperature. At lower pH (<3.5), the prepared sorbent was capable of removing approximately 90% Cr(VI) at 5 ppm concentration from aqueous synthetic solution. The dynamics of migration of the sorbate ions from the bulk onto the sorbent surface was studied and the results obtained under various experimental conditions were found to follow standard adsorption isotherms. The reaction kinetics was found to be of first order. Copyright 2000 Academic Press.     

Infrared spectroscopy for the study of urinary calculi

The occurance of the urinary stones varies according to the geographical regions. The presence of stones in the urinary system causes pain and discomfort. These generate colics and hence are sometimes life threatening. In the present study, infrared measurements have been made on several stone samples. It has been found that calcium oxalate, calcium phosphate, magnesiunm ammonium phosphate, calcium carbonate, uric acid, -cystine and xanthin are present, as expected. Also, silicon dioxide is found to be present in some of the stones but in small quantity, in addition to the above constituents. This constituent is responsible to exhibit piezoelectricity in the urinary calculi.     

Base hydrolysis ofcis-(methyl/ethylamine)bis(ethylenediamine) (salicylato)cobalt(III) complexes

The kinetics of the base hydrolysis ofcis-[Co(en)₂(RNH₂)-(SalH)]²⁺ (R=Me or Et; SalH=HOC₆H₄CO ₂ ⁻ ) were investigated in aqueous ClO ₄ ⁻ in the 0.004–0.450 mol dm⁻³ [OH⁻] range, I=0.50 mol dm⁻³ at 30–40°C. The phenoxide species is hydrolysed via [OH⁻]-independent and [OH⁻]-dependent paths, the latter being first order in [OH⁻]. The high rate of alkali-independent hydrolysis of the phenoxide species is associated with high ΔH^≠ and ΔS^≠ values, in keeping with the SNICB mechanism involving an amido conjugate base generated by the phenoxide-assisted NH-deprotonation of the coordinated amine. The [OH⁻]-dependent path also involves the conventional SN₁ CB mechanism. The rate constant, k₁, for the SNICB path exhibits a steric acceleration with the increasing size of the non-labile alkylamine, whereas the rate constant, k₂, for the SN₁CB path shows a reverse trend. TMC 2578     

Bimetallic TiO2 Nanoparticles for Lignin-Based Model Compounds Valorization by Integrating an Optocatalytic Flow-Microreactor

The challenge of improving the activity of TiO₂ by modifying it with metals and using it for targeted applications in microreactor environments is an active area of research. Recently, microreactors have emerged as successful candidates for many photocatalytic reactions, especially for the selective oxidation process. The current work introduces ultrasound-assisted catalyst deposition on the inner walls of a perfluoro-alkoxy alkane (PFA) microtube under mild conditions. We report Cu-Au/TiO₂ and Fe-Au/TiO₂ nanoparticles synthesized using the sol–gel method. The obtained photocatalysts were thoroughly characterized by UV–Vis diffuse-reflectance spectroscopy (DRS), high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and N₂ physisorption. The photocatalytic activity under UV (375 nm) and visible light (515 nm) was estimated by the oxidation of lignin-based model aromatic alcohols in batch and fluoropolymer-based flow systems. The bimetallic catalyst exhibited improved photocatalytic selective oxidation. Herein, four aromatic alcohols were individually investigated and compared. In our experiments, the alcohols containing hydroxy and methoxy groups (coniferyl and vanillin alcohol) showed high conversion (93% and 52%, respectively) with 8% and 17% selectivity towards their respective aldehydes, with the formation of other side products. The results offer an insight into ligand-to-metal charge transfer (LMCT) complex formation, which was found to be the main reason for the activity of synthesized catalysts under visible light.