Effect of HCl on the adsorption of oxygen on Cu(110) surface: An eels study

Oxygen is shown to adsorb molecularly on a clean Cu(110) surface at 80 K and dissociate around 150 K forming atomic oxygen. Adsorption of oxygen on an HCl covered surface at low temperatures results in the formation of adsorbed hydroxyl groups and water in addition to adsorbed molecular oxygen. The molecular oxygen species is stable up to 190 K on the HCl covered surface.

Differential transcription of multiple copies of a silk worm gene encoding tRNA

Ten different tRNAGly1 genes from the silk worm, Bombyx mori, have been cloned and characterized. These genes were transcribed in vitro in homologous nuclear extracts from the posterior silk gland (PSG) or nuclear extracts derived from the middle silk gland or ovarian tissues. Although the transcription levels were much higher in the PSG nuclear extracts, the transcriptional efficiency of the individual genes followed a similar pattern in all the extracts. Based on the levels of in vitro transcription, the ten tRNAGly1 genes could be divided into three groups, viz., those which were transcribed at very high levels (e.g., clone pR8), high to medium levels (e.g., pBmil, pBmpl, pBmhl, pBmtl) and low to barely detectable levels (e.g., pBmsl, pBmjl and pBmkl). The coding sequences of all these tRNA genes being identical, the differential transcription suggested that the flanking sequences modulate their transcriptional efficiency. The presence of positive and negative regulatory elements in the 5' flanking regions of these genes was confirmed by transcription competition experiments. A positive element was present in the immediate upstream A + T-rich sequences in all the genes, but no consensus sequences correlating to the transcriptional status could be generated. The presence of negative elements on the other hand was indicated only in some of the genes and therefore may have a role in the differential transcription of these tRNAGly genes in vivo.

Investigation of the (PEG)xLiCl system using conductivity, DSC and NMR techniques

Electrolytes based on polyethylene glycol (PEG, mol.wt.8000) and LiCl of compositions, (PEG)(x)LiCl, x=4, 6, 8, 10, 12, 40, 60, where x is the O/Li ratio, were prepared by solution casting from methanol solutions. FTIR studies indicate that the ether oxygens of the polymer chain participate in Li+ ion conduction. The presence of a salt-polymer complex that melts around 190 degrees C was evidenced by DSC measurements for the electrolytes with compositions x<12. The highest conductivity was obtained at the composition x=10 which was attributed to the presence of a mostly amorphous compound. NMR measurements indicated two regions of motional narrowing, one attributable to the glass transition and another to translational diffusion.

Correlated electronic states of C-60 fragments

We have studied electronic states of various fragments of C-60 within the Pariser-Parr-Pople (PPP) model and have obtained structural, magnetic and spectral properties of these molecules. The fragments studied include corannulene, fluoranthene and pyracylene. Pyracylene is studied using the exact valence bond (VB) approach while fluoranthene and corannulene are studied using a novel restricted CI technique which employs molecular orbitals for constructing the VB functions. The electronic excitations, bond order and ring currents are calculated for these systems. From these studies, the wide range of absorptions in C-60 can be viewed as those localized on pyracylene units or on the corannulene/fluoranthene units. The bond orders and ring currents show the hexagons to be similar to benzene rings. The pentagon-hexagon bonds are also found to be longer than the hexagon-hexagon bonds.

Design of some 2-D filters through the transformation technique

The transformation technique is a tool FIR designing 2-D filters, useful for the design of specially shaped filters with passband/stopband regions not centred around the origin. The authors extend this technique to design two types or filters. A notch filter has a stopband centred about a small region in the 2-D frequency plane. The authors propose an extension to the transformation technique with the windowing concept to achieve the design of notch filters. A directional filter has a passband extending fully along: a straight line pacing through the origin. The transformation technique is: further extended to yield such directional filters. Design and application examples for both these fillers are also presented.

Gibbs energies of formation of chromium carbides

The carbon potentials corresponding to the two-phase mixtures Cr + Cr23C6, Cr23C6 + Cr7C3, and Cr7C3 + Cr3C2 in the binary system Cr-C were measured in the temperature range 973 to 1173 K by using the methane-hydrogen gas equilibration technique. Special precautions were taken to prevent oxidation of the samples and to minimize thermal segregation in the gas phase. The standard Gibbs energies of formation of Cr23C6, Cr7C3, and Cr3C2 were derived from the measured carbon potentials. These values are compared with those reported in the literature. The Gibbs energies obtained in this study agree well with those obtained from solid-state cells incorporating CaF2 and ThO2(Y2O3) as solid electrolytes and sealed capsule isopiestic measurements reported in the literature.

The formation of ?-FeSiAl5 and Be---Fe phases in Al---7Si---0.3Mg alloy containing Be

Thermal analysis and interrupted quench experiments have been carried out to study the formation of beta-FeSiAl5 and (Be-Fe)-BeSiFe2Al8 phases in Al-7Si-0.3Mg alloy with and without Be addition. In the base alloy with 0.6% Fe (without Be addition), a needle- and plate-shaped beta-phase is present in the interdendritic regions and is formed by a ternary eutectic reaction. In the Be- added alloy with 0.6% Fe, a Be-Fe phase of Chinese script and polygon shapes grows along with the primary alpha-Al dendrites, leading to superior mechanical properties. It is proposed that this Be-Fe phase is formed by a peritectic reaction. Be addition has also resulted in some grain refinement.

Antioxidant and antihepatotoxic effect of Spirulina laxissima against carbon tetrachloride induced hepatotoxicity in rats

The vast biodiversity of nature provides bioactive compounds that may be useful in the fight against chronic diseases. This study was designed to investigate the protective effects of the ethanol extract of Spirulina laxissima West (Pseudanabaenaceae) (EESL) against carbon tetrachloride (CCl4) induced hepatotoxicities in rats. Male albino rats of Sprague-Dawley strain were treated orally with the ethanol extract of S. laxissima (50, 100 mg kg(-1) body wt.) 1 h before each CCl4 administration. The ethanol extract of S. laxissima showed the maximum antioxidant property in vitro. There were statistically significant losses in the activities of antioxidant enzymes and an increase in TBARS and liver function marker enzymes in the serum of the CCl4-treated group compared with the control group. However, all the tested groups were able to counteract these effects. The antioxidant activity of the extracts might be attributable to its proton-donating ability, as evidenced by DPPH. In the present study, the decline in the level of antioxidant observed in CCl4-treated rats is a clear manifestation of excessive formation of radicals and activation of the lipid peroxidation system resulting in tissue damage. The significant increases in the concentration of antioxidant enzymes in tissues of animals treated with CCl4 + EESL indicate the antioxidant effect of EESL. This study suggests that EESL can protect the liver against CCl4-induced oxidative damage in rats, and the hepatoprotective effect might be correlated with its antioxidant and radical-scavenging effects.

Multifunctional cryogenic sensors from n-BaTiO3 ceramics having strong negative temperature coefficient of resistance

Donor-doped n-BaTiO3 polycrystalline ceramics show a strong negative temperature coefficient of resistivity below the orthorhombic-rhombohedral phase transition point, from 10(2-3) Omega cm af 190 K to 10(10-13) Omega cm at less than or similar to 50 K, with thermal coefficient of resistance alpha = 20-23% K-1. Stable thermal sensors for low-temperature applications are realized therefrom. The negative temperature coefficient of resistivity region can be modified by substituting isovalent ions in the lattice. Highly nonlinear current-voltage (I-V) curves are observed at low temperatures, with a voltage maximum followed by the negative differential resistance. The I-V curves are sensitive to dissipation so that cryogenic sensors can be fabricated for liquid level control, flow rate monitoring, radiation detection or in-rush voltage limitation.

Non-viral ex vivo hepatic gene transfer by in situ lipofection of liver and intraperitoneal transplantation of hepatocytes

Perfusion of liver with plasmid DNA-lipofectin complexes via the portal vein results in efficient accumulation of the vector in hepatocytes. Such hepatocytes, when administered intraperitoneally into a hepatectomized rat, repopulate the liver and express the transgene efficiently. This procedure obviates the need for large-scale hepatocyte culture for ex vivo gene transfer. Further, intraperitoneal transplantation is a simple and cost-effective strategy of introducing genetically modified hepatocytes into liver. Thus, in situ lipofection of liver and intraperitoneal transfer of hepatocytes can be developed into a novel method of non-viral ex vivo gene transfer technique that has applications in the treatment of metabolic disorders of liver and hepatic gene therapy.

Stabilities of ternary carbides UWC1.75 and UWC2

The methane-hydrogen gas equilibration technique has been used to measure the chemical potential of carbon associated with two three-phase fields of the system U-W-C in the temperature range 973 to 1173 K. By combining the values of the chemical potential of carbon in the three-phase fields UC + W + UWC1.75 and UC + UWC1.75 + UWC2 Obtained in this study with the data on the Gibbs energy of formation of UC available in the literature, expressions for the Gibbs energies of formation of the two ternary carbides were derived: Delta(f)G degrees [UWC1.75] = -131, 600 - 300 T (+/-8000) J mol(-1) Delta(f)G degrees [UWC2] = -144, 800 - 32.0 T (+/- 10,000) J mol(-1) Although estimates of Gibbs energies of formation of the two ternary carbides TSWC1.75 and UWC2 have been reported, there have been no previous experimental determinations of thermodynamic properties of these compounds.

X-ray reflectivity study of semiconductor interfaces

The results of an X-ray reflectivity study of thick AlAs-AlGaAs and thin GeSi-Ge multilayers grown using metal-organic vapour-phase epitaxy and ion-beam sputtering deposition techniques, respectively, are presented. Asymmetry in interfaces is observed in both of these semiconductor multilayers. It is also observed that although the Si-on-Ge interface is sharp, an Si0.4Ge0.6 alloy is formed at the Ge-on-Si interface. In the case of the III-V semiconductor, the AlAs-on-AlGaAs interface shows much greater roughness than that observed in the AlGaAs-on-AlAs interface. For thin multilayers it is demonstrated that the compositional profile as a function of depth can be obtained directly from the X-ray reflectivity data.

Antiferroelectric lead zirconate thin films by pulsed laser ablation

Lead Zirconate (PbZrO3) thin films were deposited by pulsed laser ablation method. Pseudocubic (110) oriented in-situ films were grown at low pressure. The field enforced anti-ferroelectric (AFE) to ferroelectric (FE) phase transformation behaviour was investigated by means of a modified Sawyer Tower circuit as well as capacitance versus applied voltage measurements. The maximum polarisation obtained was 36 mu C cm(-2) and the critical field to induce ferroelectric state and to reverse the antiferroelectric slates were 65 and 90 kV cm(-1) respectively. The dielectric properties were investigated as a function of frequency and temperature. The dielectric constant of the AFE lead zirconate thin him was 190 at 100 kHz which is more than the bulk ceramic value (120) with a dissipation factor of less than 0.07. The polarisation switching kinetics of the antiferroelectric PbZrO3 thin films showed that the switching time to be around 275 ns between antipolar state to polar states. (C) 1999 Elsevier Science S.A. All rights reserved.

Thermodynamic modeling of quaternary Al-Ga-In-As system

The present research describes the modeling of the thermodynamic properties of the liquid Al-Ga-In-As alloys at 1073 and 1173 K, and investigates the solid-liquid equilibria in the systems. The isothermal molar excess free energy function for the liquid alloys is represented in terms of 37 parameters pertaining to six of the constituent binaries, four ternaries and the quaternary interactions in the system. The corresponding solid alloys which consist of AlAs, GaAs and InAs are assumed to be quasi-regular ternary solutions. The solidus and liquidus compositions are calculated at 1073 and 1173 K using the derived values of the partial components for the solid and liquid alloys at equilibrium. They are in good agreement with those of the experimentally determined values available in the literature. (C) 1999 Elsevier Science S.A. All rights reserved.