Chromatographic and Spectrophotometric Studies in Selected Acacia Species

JPC – Journal of Planar Chromatography – Modern TLC - Phytochemical studies were carried out in different parts of three Acacia species viz. A. catechu, A. nilotica and A. leucophloea,...     

Metal template synthesis of chromium(III) complexes

Chromium(III) complexes of Schiff bases resulting from the condensation of one mole of diacetyl with two moles of ethylene-diamine or 1,3 diaminopropane has been isolated by metal template reaction. The isolated complexes have been assigned cis configurations.     

c-Axis orientation control of YBa2Cu3O7−x films grown on inclined-substrate-deposited MgO-buffered metallic substrates

Biaxially textured YBa₂Cu₃O_7−x (YBCO) films were grown on non-textured metal substrates with inclined-substrate-deposited (ISD) MgO as template. The biaxial texture feature of the films was examined by X-ray pole-figure analysis, φ-scan, and 2θ-scan. A tilt angle of 32° of the MgO[001] with respect to the substrate normal was observed. Epitaxial growth of YBCO films with c-axis tilt angle of 32° with respect to the substrate normal was obtained on these substrates with SrTiO₃(STO) as buffer layer. Whereas, by choosing yttria-stabilized ZrO₂ and CeO₂ instead of STO as buffer layer, a c-axis untilted YBCO film was obtained. Higher values of T_c=91 K and J_c=5.5×10⁵ A/cm² were obtained on the c-axis untilted YBCO films with 0.46 μm thickness at 77 K in zero field. Comparative studies revealed a unique role of CeO₂ in controlling the orientation of the YBCO films grown on ISD-MgO buffered metal substrates.     

Defect structure of lanthanum-doped calcium titanate

The defect structure of lanthanum-doped polycrystalline calcium titanate was investigated by measuring the oxygen partial pressure (10⁰–10^?18 atm.) dependence of the electrical conductivity at 1000° C and 1050°C. Two types of charge compensation were observed, namely electronic and ionic. For P₀₂ < 10^?15 atm. the carrier concentration was fixed by the amount of lanthanum (donor) added and the conductivity was found to be independent of oxygen partial pressure (electronic compensation). For higher oxygen partial pressure conditions (P₂₂ > 10^?13 atm.) the extra charge of the lanthanum was compensated by doubly ionized calcium vacancies (ionic compensation). In the ionic compensation region, a model involving a shear structure is discussed.     

Existence of solution for nonlinear Volterra integral equations

We prove an existence theorem for a class of nonlinear Volterra integral equations.     

Controllability of nonlinear systems via fixed-point theorems

This article presents a survey of papers published on controllability of nonlinear systems, including nonlinear delay systems, by means of fixed-point principles.     

Local null controllability of nonlinear functional differential systems in Banach space

Sufficient conditions for the local null controllability of non-linear functional differential systems with unbounded linear operators in Banach space are established. The results are obtained using the semigroup of linear operators, fractional powers of operators, and the Schauder fixed-point theorem. Applications to parabolic differential systems are given.The work of the first and second authors was supported by CSIR, New Delhi, India.     

Carbanion mechanisms : VIII. Metallation of arylmethanes by n-butyllithium. Spectrophotometric study of ion pairing

Results of a spectrophotometric study of the reaction of n-butyllithium are reported, in tetrahydrofuran (THF) medium, for triphenylmethane, diphenylmethane, di-p-tolylmethane, p-phenyltoluene and toluene. The temperature dependence of the absorption spectra for diphenylmethyllithium and di-p-tolylmethyllithium in THF gave evidence of an equilibrium between contact and solvent separated ion pair species, the latter predominating at low temperature. For di-p-tolylmethyllithium in THF this equilibrium is characterized by ΔH ?5.9 kcal/mol and ΔS ?18 e.u.     

Structural and electrical properties of nickel–iron thin film on copper substrate for dynamic random access memory applications

Using pulse electrodeposition technique, nano crystalline NiFe films were deposited on conductive copper substrates, under galvanostatic mode in an ultrasonic field at different conditions such as pulse current magnitude, deposition time and ultrasonic bath temperature. As-prepared NiFe/Cu thin films were characterized for phase analysis, surface morphology, surface roughness and resistivity measurements. The results show that the use of ultrasonic bath at room temperature has reduced the surface roughness, resistivity, average grain size and crystallite size of NiFe/Cu thin films. The resistivity is reduced with increasing deposition current from 44.2 µΩ cm at 40 mA to 33.0 µΩ cm at 100 mA. On the other hand, a significant drop of the resistivity from 35.7 to 9.4 µΩ cm is observed if the deposition time was reduced from 5 to 3 min.