Electrochemical preparation of epinephrine/Nafion chemically modified electrodes and their electrocatalytic oxidation of ascorbic acid and dopamine

Two types of epinephrine and cyclized epinephrine quinone films have been prepared using cyclic voltammetry from the epinephrine in the strong acidic solutions and neutral aqueous solutions over different scanning potential ranges. The cyclic voltammogram of the epinephrine film is characterized by one redox couple at about +0.5 V (versus Ag|AgCl) and cyclized epinephrine quinone film exhibits one redox couples at about −0.15 V (versus Ag|AgCl) .In addition to cyclic voltammetry and an electrochemical quartz crystal microbalance (EQCM) were used to study the growth mechanism of the epinephrine and cyclized epinephrine quinone molecules. The electrocatalytic oxidation of catecholamines (dopamine and norepinephrine) and also ascorbic acid were investigated in acidic aqueous solutions using epinephrine films. The rotating ring-disk electrode technique was used to investigate the mechanism of electrochemical oxidation of dopamine and ascorbic acid.     

Formation of Zinc–Antimony-Based Spinel Phases

Formation of spinel phases in ZnO–Sb₂O₃and ZnO–Sb₂O₃–Bi₂O₃systems is studied by the use of X-ray diffraction. The formation of nonstoichiometric Zn_2.33Sb_0.67O₄phase is observed in both the systems at ∼900°C. However, in these systems, at higher temperatures ( T ≥ 1100°C), formation of the inverse spinel phase Zn₇Sb₂O₁₂is observed. The study has been extended to understand the effect of CrO₃doping on the stability of the different spinel phases in the previously mentioned systems. Interestingly, in both the systems, samples doped with CrO₃, displayed the presence of Zn_2.33Sb_0.67O₄phase <1200°C, indicating the stabilization of the spinel phase by CrO₃.     

Crystallization Kinetics and Properties of Nonstoichiometric Cordierite-Based Thick-Film Dielectrics

Dielectric thick films based on a nonstoichiometric cordierite (2.4MgO·2Al₂O₃·5SiO₂, containing 3 wt% B₂O₃, 3 wt% P₂O₅, and 3 wt% PbO) were investigated, in regard to their microstructure, crystallization kinetics, and properties. A stable glass-ceramic thick-film microstructure that was formed on a 96% alumina substrate was observed after firing at a temperature of 915°C for 30 min in a nitrogen atmosphere. No µ-cordierite was observed in the X-ray diffraction (XRD) patterns of the thick film. The crystallization kinetics were studied via quantitative XRD analysis using the Avrami equation, and the rate constant increased as the temperature increased. The decreasing tendency of the Avrami parameter, relative to temperature, suggested a change in growth directionality during crystallization. The activation energy for crystallization of the thick film was determined to be ~83 kcal/mol (~350 kJ/mol). The coefficient of thermal expansion (CTE) and the dielectric constant of the glass phase were evaluated using the bulk-sample data. For the case of a 3-wt%-PbO sample fired at 950°C for 30 min in a nitrogen atmosphere, the remaining glass was estimated, using the parallel mixing rule, to have a dielectric constant of 15.3 at 1 MHz. The dielectric constant of the remaining glass was dependent on the PbO content and the heat-treatment temperature. The estimated CTE of the remaining glass for the 3-wt%-PbO sample was 19 × 10^-6/°C.     

Development of pitch-based carbon–copper composites

Carbon–copper composites with varying copper to carbon ratio of 0.66–1.5 (by weight) were developed from coal-tar-pitch-derived green coke (as such or modified with natural graphite) as carbon source and electrolytic grade copper powder at different heat treatment temperatures (HTTs) of 1000–1400 °C. The physical, mechanical, and electrical properties differ depending upon the HTT and also on copper to carbon ratio (Cu/C). The composites prepared at HTT of 1100 °C having Cu/C ratio of 0.66 and 0.9 exhibited a high bending strength of 150 and 140 MPa, bulk density of 2.63 and 2.81 gm/cm³, electrical resistivity of 1.6 and 0.96 m Ω cm and shore hardness of 88 and 84, respectively, in spite of well-known inadequate wettability between copper and carbon. Increasing the temperature from 1100 °C for processing of the composites deteriorated the properties mainly due to the loss of copper through melting above 1100 °C as revealed by X-ray, scanning electron microscopy, thermal analysis and EDAX studies.     

Forced convection along a longitudinal cylinder embedded in a saturated porous medium

The thermal boundary layer along an isothermal cylinder in a porous 3edium is studied numerically by a finite difference scheme and also using the method of extended perturbation series. The series in terms of the transverse curvature parameter ξ extended to seven terms and is subsequently improved by applying the Shanks transformation twice and thrice, respectively. Results for heat transfer characteristics are found in very good agreement.     

The processing electronics system for the pointed mode operation ofIXAE on the Indian satellite IRS-P3

Indian Remote Sensing Satellite-P3 (IRS-P3: 1996-017A) was launched into a near-Earth, polar, Sun-synchronous orbit by India's Polar Satellite Launch Vehicle (PSLV-D3) on March 21, 1996. The Indian X-ray Astronomy Experiment (IXAE) is one of the prime payloads onboard IRS-P3. IXAE has two sets of detectors: three pointed-mode proportional counters (PPCs) and one X-ray Sky Monitor (XSM). IRS-P3 is configured to operate in two modes, namely, Earth-pointing mode and stellar-pointing mode. In Earth-pointing mode the remote sensing payloads are in operation; in addition, XSM maps the sky for bright X-ray sources and X-ray transients. In stellar mode, the PPCs observe several Galactic, bright X-ray, and extragalactic sources. The microprocessor-based processing electronics system was designed and developed for PPC data-handling and telemetering the stored data to the ground station. The system has been working well from the day the IXAE was commissioned. The processing electronics system for the PPCs, its interfaces, and the in-orbit instrument performance are described. Some results of the pointed mode observations are also presented     

A nonlinear theory of wake development

Summary A simple new series, using an expansion of the velocity profile in parabolic cylinder functions, has been developed to describe the nonlinear evolution of a steady, laminar, incompressible wake from a given arbitrary initial profile. The first term in this series is itself found to provide a very satisfactory prediction of the decay of the maximum velocity defect in the wake behind a flat plate or aft of the recirculation zone behind a symmetric blunt body. A detailed analysis, including higher order terms, has been made of the flat plate wake with a Blasius profile at the trailing edge. The same method yields, as a special case, complete results for the development of linearized wakes with arbitrary initial profile under the influence of arbitrary pressure gradients. Finally, for purposes of comparison, a simple approximate solution is obtained using momentum integral methods, and found to predict satisfactorily the decay of the maximum velocity defect.     

Microstructural and High-Temperature Electrical Characterization of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>FeO<Subscript>3 − δ</Subscript>

Strontium-doped lanthanum ferrites (LSF) were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), 4-point D.C. electrical conductivity and bulk property measurements. The results were compared to those of previous studies as well as selected processing conditions. The investigation focused on effects of sintering temperature, time, atmosphere (air, O₂ and N₂) and composition of La_1–xSr_xFeO_3– (x = 0.2–0.9), on the sintering behavior, microstructural development and electrical conductivity. An oxalate precipitation method was used to prepare lanthanum ferrite powders. Simultaneous thermogravimetric and differential thermal analysis (TGA/DTA) studies found calcination temperatures of 800 and 850^C were necessary to form single-phase crystalline powders, as determined by XRD. Specimens were sintered from 1300 to 1400^C with dwell times from to 2 hrs. Results from SEM/EDS analysis showed the presence of a second phase in the samples fired in air or oxygen. The second phase was not detected by x-ray diffraction due to the small amount of material present. Samples fired in nitrogen had the lowest conductivity while those fired in oxygen had the highest. A composition of x = 0.5 resulted in the highest conductivity, 352 S/cm, at an operating temperature of 550C in air. High strontium additions (x = 0.9) lowered the linear shrinkage of LSF.