Superconductivity in non-stoichiometric and tin-substituted La2CuO4: preparation, characterization, Mössbauer and microwave-absorption studies

Two samples of non-stoichiometric La₂CuO₄ were synthesized, one with La/Cu<2, and the other with 10% Sn substituting Cu. They were investigated by X-ray diffraction, Mössbauer spectroscopy, and microwave-absorption techniques. The microwave-absorption data indicated that they were both superconducting, with the transition temperatures T_c of 40.5 and 41.5 K, the one doped with Sn possessing the higher T_c. The Mössbauer spectra revealed that there exist two kinds of Sn(IV) atoms disordered with Cu. Their isomer shift, δ=−0.244(4) mm/s, is in agreement with Sn(IV) coordinated by oxygen. One site was characterized by a single Mössbauer line, being associated with a weakly distorted environment, wherein the Sn, coordinated more symmetrically, is surrounded by four Cu²⁺ ions. On the other hand, the other site, characterized by a Mössbauer doublet exhibited a quadrupole splitting Δ=1.07(2) mm/s, being associated with a highly distorted coordination, explained to be due to Sn occupying two adjacent cationic sites. To our knowledge, such a substitution for copper ions not resulting in a decrease of T_c has not been reported previously.     

Dynamics of an array formed by three neutrally buoyant cylindrical cantilevers subjected to tensile follower forces

The flexural-rotational coupled motion of three identical flexible cylindrical cantilevers joined symmetrically to a central head is investigated. Effects of the tensile follower forces and inertia parameters on the natural frequencies of the system are studied. The analysis suggests two types of inplane motion: one corresponding to the oscillation of the cantilevers without any rotation of the central body, while the other involves coupled motion of the array. The former corresponds to the repeated eigenvalues which are identical to those of a single cantilever having the same axial tension parameter, P. Three sets of eigenvalues govern the out-of-plane motion: (a) the central head remaining stationary with no rolling motion of the array; (b) vertical motion of the central body without any rolling motion of the array; and (c) rigid body rolling motion without any vertical motion of the central head. There is a possibility of dynamic instability for small inertia parameters and large axial tension.     

Untersuchung der OberflÄchenspannung der Systeme:

Zusammenfassung Die Oberfl?chenspannungen der Systeme: 1. Wasser/propionsaures Natrium mit verschiedenen Alkoholen; 2. Wasser/buttersaures Natrium mit verschiedenen Alkoholen; 3. Wasser/crotonsaures Natrium mit verschiedenen Alkoholen und 4. Wasser/caprylsaures Natrium mit verschiedenen Alkoholen wurden gemessen, und die Ergebnisse werden im Sinne der in früheren Arbeiten (3, 4) ver?ffentlichten Hypothese diskutiert.

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Summary The surface tension of the systems (1) water-sodium propionate and different alcohols, (2) water-sodium butyrate and different alcohols, (3) water-sodium crotonate and different alcohols and (4) water-sodium caprylate and different alcohols has been determined and the results have been discussed on the basis of the hypothesis suggested in previous papers (3, 4).

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übersetzt von Dr. K, Jaeckel (Marburg/L.)

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Wir danken Herrn Dr. A. Chatterji, Head of the Chemistry Department, für sein Entgegenkommen. Einer von uns (J. M.) dankt dem Scientific Research Grants Committee für ein Stipendium zur Durchführung der Arbeit.     

Adh?sive Bindung verschiedener Materialien an harten Zahnmaterialien. VIII. Nickel- und Kupfer-Ionen an Hydroxyapatit. Die Rolle des Ionenaustausches und der Oberfl?chenkernbildung

Ohne Zusammenfassung     

Phonon spectroscopy of photochemical reactions in organic solids: Photodimerization of 2,6-dimethyl-p-benzoquinone

The Raman phonon spectroscopic study shows that the photodimerization of 2,6-dimethyl-p-benzoquinone. In the solid state is initially a homogeneous reaction but later becomes heterogeneous as the product accumulates. The Ion-temperature electronic absorption spectrum reveals that the reaction is phonon assisted by a polaron formed due to a strong electron- phonon coupling in the cxcited ¹nπ^* state.     

A simple and rapid method for determination of boron in fast breeder reactor components

The present paper describes a new analytical method developed for direct determination of boron in steels using radio frequency glow discharge optical emission spectrometer. “Single parameter alternative method” technique has been used to optimize the various experimental conditions of glow discharge plasma such as forward power, gas pressure inside plasma chamber, pre-integration time, and integration time. Different emission lines for boron were studied and inter element interference effect is also discussed in the paper. A complete statistical analysis has been done to validate the developed method. A RSD of less than ±5% is achieved for boron in the range of 0.0010–0.020% in Steels using this method.     

Effect of adsorption of vapours on the electrical conductivity of some polyene semiconductors: adsorption and desorption kinetics

The change in semiconductive properties of β-apo-8′-carotenal, astacene and methyl bixin on adsorption of various vapours on the crystallite surfaces has been studied at a constant sample temperature. The adsorption of vapours enhances the semiconductivity of the polyenes appreciably. This enhancement depends on the chemical nature and also on the pressure of the adsorbed vapour. The adsorption and desorption kinetics follow the modified Roginsky-Zeldovich relation. A two stage desorption process, the first stage of which gives a Lennard-Jones potential energy curve and is followed by a rate-determining transition over a potential energy barrier to the second stage of adsorption forming weakly bound complexes between the vapour molecules and the polyene crystallites, can explain satisfactorily the experimentally observed kinetic data.     

Grafting onto wool. VIII. Graft copolymerization of methyl methacrylate (MMA) by use of Ce4+ -amine system as redox initiator

In an attempt to determine the role of a variety of amines in ceric-ion-initiated grafting, poly-(methyl methacrylate) was graft copolymerized onto Himachali wool in the presence of a variety of amines that included ammonia, diethylamine (DEA), dipropylamine (DPA), triethylamine (TEA), triethanol amine, and pyridine. All amines (with the exception of DEA) reduced the percent grafting. The reactivity of various amines toward graft copolymerization followed the order: DEA > DPA > NH₃ > TEA > triethanol amine > Py. An explanation based on the basicity, nucleophilicity, and steric requirement of amines is given to explain the observed reactivity order shown by the various amines toward graft copolymerization.