Effect of substitution of Ce on superconducting properties of Bi1.7Pb0.3Sr2Ca2−x Ce x Cu3O10+δ system

We have investigated the superconducting properties of the Bi_1.7 Pb_0.3Sr₂Ca_2−xCe _x Cu₃O_10+δ system with x=0.00, 0.02, 0.04, 0.08 and 0.1 by X-ray diffraction and magnetic susceptibility. The substitution of Ce for Ca has been found to drastically change the superconducting properties of the system. X-ray diffraction studies on these compounds indicate decrease in the c-parameter with increased substitution of Ce at Ca site and volume fraction of high T _c (2 : 2 : 2 : 3) phase decreases and low T _c phase increases. The magnetic susceptibility of this compound shows that the diamagnetic on set superconducting transition temperature (onset) varies from 109 K to 51 K for x=0.00, 0.02, 0.04, 0.08 and 0.1. These results suggest the possible existence of Ce in a tetravalent state rather than a trivalent state in this system; that is, Ca²⁺ → Ce⁴⁺ replacement changes the hole carrier concentration. Hole filling is the cause of lowering T _c of the system.     

Kinetics and mechanism of iodination of p-aminobenzoic acid and o-aminobenzoic acid. Novel catalytic behavior of added phosphate buffers

Kinetics of iodination ofp-aminobenzoic acid ando-aminobenzoic acid at different pH and solvent media has been studied. The order of the reaction with respect to the iodinating agent and substrates was established. Reactions were carried out with buffer mixtures of primary and secondary phosphates and catalytic constants were evaluated. Effect of temperature and dielectric constant of solvents used were studied. Suitable mechanism and composite rate law have been suggested.

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Optical nonlinearities in substituted conjugated polymers

Conjugated polymers with sidegroups such as methyl, trimethylsilyl, p-methoxy phenyl, o-methoxy phenyl, and hexyl groups on a polyphenylacetylene chain are studied in an attempt to understand the contribution of factors such as the backbone, conformation of the chain, sidegroups and polymerization catalyst on the optical nonlinearities. The results of degenerate four-wave mixing experiments at 532 nm with nanosecond pulses indicate that the substitution of an electron-donating group away from the backbone can enhance the third-order susceptibility. Some of the polymers show optical limiting action at this wavelength. The thermal contribution to the measured susceptibility is also determined.     

FCC → SC phase transition in alkali halides

The NaCl → CsCl structural pressure transformation is studied using a new interionic potential. The theoretical transition pressures are in good agreement with experiment.     

THE HADAMARD INEQUALITY FOR CONVEX FUNCTION VIA FRACTIONAL INTEGRALS

In this paper, we establish several inequalities for some differantiable mappings that are connected with the Riemann-Liouville fractional integrals. The analysis used in the proofs is fairly elementar...     

NQR investigations in crystalline 2,6-dichlorobenzamide

Two resonance lines were observed in 2,6-dichlorobenzamide, both in liquid nitrogen and at room temperatures, using a self quenched super-regenerative NQR spectrometer. Analysis of the Zeeman effect on the two lines using an uncut crystal grown from solution reveals: (1) the crystal belongs to the orthorhombic system; (2) there are two crystallographically equivalent but physically non-equivalent directions for the principal field gradient making an angle of 71° for the low frequency line, and four such directions for the high frequency line; (3) the directions of the crystalline axes a, b and c are tentatively fixed as (90°, 90°), (90°, 90°) and (0°,—); (4) from morphological studies a: b: c are estimated as 0.959 ± 0.005: 1:1,402 ± 0.005 and, from the estimated density (1.440 gms/cc) of the crystal, the absolute values a, b, c are calculated, on the basis of four molecules per unit cell, as a = 8.33 Å, b = 8.68 Å and c = 12.18 Å; (5) there are a mininium of four molecules per unit cell; the four molecules lie in four different planes which are, however, connected by symmetry operations. There is an inplane bending by 6.5° between the two C? Cl bonds away from one another and (6) the ionic, single bond and double bond characters for both chlorines are almost equal and are in the ratio 25:72:3.     

Extraction and spectrophotometric determination of cobalt(II) with thiobenzoylacetone and simultaneous determination of cobalt and nickel

Thiobenzoylacetone in benzene is used for the extraction and spectrophotometric determination of cobalt at pH 8.4-9.1. The orange-yellow complex is measured at 460 nm. The system conforms to Beer's law over the range 0.20-4.58 microg ml of extract. The colour of the complex is stable for at least 144 hr. Cobalt(II) is quantitatively extracted and determined in the presence of 200:1 (w w ratios) of various ions. The method is made selective by using common sequestering agents such as thiourea or fluoride or by selective extraction with mesityl oxide, tributylphosphate and acetylacetone. It is possible to determine cobalt in the presence of nickel by simultaneous spectrophotometry. The method is rapid, simple, selective and sensitive.     

Thermogravimetric study of the oxidation behaviour of uranium dicarbide

Systematic studies were carried out on the oxidation behaviour of uranium dicarbide in air in the temperature range 25 °C to 700 °C employing thermogravimetry, evolved gas detection X-ray diffraction and chemical analysis. The mechanistic aspects were investigated and the oxidation was found to proceed through reaction processes involving oxidation of uranium to-UO₃ with release of chemically bound carbon, reaction of released carbon leading to the formation of CO₂ which gets liberated stepwise, decomposition of-UO₃ to U₃O₈ and oxidation of free carbon to CO₂. Examination of the thermoanalytical behaviour of sintered graphite, UO₃, mixtures of graphite with UO₃ and with U₃O₈ supported the above findings.

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Zusammenfassung Das Oxydationsverhalten von Urandikarbid in Luft im Temperaturbereich zwischen 25 und 700 °C wurde mittels Thermogravimetrie, Gasprodukteanalyse, Röntgendiffraktion und chemischer Analyse systematisch untersucht. Studien des Mechanismus ergaben, daß die Oxydation über Teilschritte abläuft, die folgende Schritte beinhalten: Oxydation von Uran zu-UO₃ unter Freisetzung chemisch gebundenen Kohlenstoffes, Reaktion des freigesetzten Kohlenstoffes unter Bildung von CO₂, das schrittweise entweicht, Zerfall von-UO₃ zu U₃O₈ und Oxydation von freiem Kohlenstoff zu CO₂. Diese Feststellungen wurden durch Untersuchung des thermoanalytischen Verhaltens gesinterter Graphit- und UO₃-Proben sowie Mischproben von Graphit mit UO₃ bzw. U₃O₈ bekräftigt.

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, , 25–700°. , , -UO₃ , , , -UO₃ U₃O₈ . ë , UO₃, UO₃ U₃O₈ .

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The authors wish to thank Dr. M. K. Ahmed for his help in O/U measurements and Dr. P. R. Vasudeva Rao for useful advices during the course of the work.     

Kα X-ray satellite spectra of Ti, V, Cr and Mn induced by photons

K X-ray emission spectra of Ti, V, Cr and Mn generated by photon excitation have been studied with a crystal spectrometer. The measured energy shifts of K_α satellite relative to the diagram line are compared with values obtained by electron excitation and with different theoretical estimates. The present experimental values of K_αL¹/K_αL⁰ relative intensities are compared with values obtained by electron excitation.