Superconductivity with transition temperature up to 80 K for TbSr2Cu2.7Mo0.3O7+δ

A Tb-123 phase with the composition, TbSr₂Cu_2.7Mo_0.3O_7+δ, has been synthesized in single-phase form by the solid-state reaction route. Its phase purity has been confirmed from neutron powder diffraction studies. The as-synthesized Tb-123 sample does not show superconductivity down to 5 K. On the other hand, an unusually high antiferromagnetic ordering temperature (T_N) of around 7 K is seen for the Tb moments. After 120-atm-O₂ post-annealing, bulk superconductivity is achieved in this compound with a superconducting transition temperature (T_c) of about 30 K, without any significant effect on T_N. To achieve higher oxygen content and higher T_c, the as-synthesized sample was subjected to high-pressure oxygenation, carried out in a closed cell, at 5 GPa and 400 °C in the presence of AgO as an excess-oxygen source. This sample exhibited superconductivity onset at around 80 K with a Meissner fraction larger than 10% at 5 K. Our observation of superconductivity at 80 K is the highest T_c to-date for the Tb-123 type compounds.     

Capacitated Multiple Item Ordering with Incremental Quantity Discounts

This paper presents a heuristic algorithm for determining order quantities for multiple items given incremental quantity discounts and a single resourse constraint. The heuristic is based on Lagrangian relaxation. The performance of the heuristic is compared, for small problems, with a procedure that generates optimal solutions. Results from computational experiments are given that demonstrate the quality and computational efficiency of the heuristic algorithm.     

Thermoanalytical investigations of niobium(V) chloride aryloxides

Niobium(V) chloride aryloxides [NbCl₃(OAr)₂] and [NbCl₂(OAr)₃] (Oar = —OC₆H₄Bu ^t -4 and —OC₆H₄OMe-4) have been prepared by reacting NbCl₅ with two and three equivalents of the respective phenol in CCl₄. The complexes have been characterized by elemental analysis, molecular weight determination, i.r., ¹H-n.m.r., u.v.–vis. and MS techniques. Thermal behaviour (t.g.–d.t.) of the complexes has also been studied and decomposition schemes proposed. The kinetic and thermodynamic parameters namely, the activation energy 'E ^*', the frequency factor 'A', entropy of activation 'S' and specific rate constant 'kr' etc. have been calculated employing the Coats–Redfern equation. The non-isothermal t.g. data has also been utilized to determine the most probable mechanism and corresponding activation energy for the decomposition of niobium(V) complexes by testing seven different theoretically possible decomposition mechanisms.     

Interplay of chromatographic and electrophoretic processes in capillary electrochromatography

The separation mechanism in capillary electrochromatography (CEC) is a hybrid differential migration process, which entails the features of both high-performance liquid chromatography and capillary zone electrophoresis, i.e., chromatographic retention and electrophoretic migration. The adsorption of the different sample components on the stationary phase can be modified by the presence of the electric field across the column. Here, we use our previously published approach to decouple chromatographic retention from electrophoretic migration that allows us to investigate the "modification" of the retention process in CEC. This paper presents a methodology for characterization of changes in the retention of neutral and charged sample components, under identical conditions of stationary and mobile phase.     

Some analytical solutions of time-dependent,continuously operating heat sources

The amount of heat released in a volume whose extent can be ignored as compared with the dimensions of the surroundings of interest, may be classified as (i) the point-heat source, (ii) the line-heat source, and (iii) the plane-heat source. The temperature solutions of these transient conduction problems in an extended, homogeneous, and isotropic medium, are discussed in closed form. These analytical solutions are presented for the case of time-dependent, continuously operating heat source of the form , wherev is a positive real number. The dimensionless temperature solutions for all the problems are presented in terms of the Whittaker function. It is found that the present analysis covers well known (classical) solutions as well as some new solutions.

---

Einige analytische Lösungen für zeitabhängige, kontinuierlich wirkende Wärmequellen

Zusammenfassung Der Betrag an freigesetzter Wärme in einem Volumenbereich, dessen Ausdehnung vernachlässigbar ist gegenüber den Abmessungen des interessierenden Umgebungsbietes, läßt sich wie folgt klassifizieren: (i) punktförmige Wärmequelle, (ii) Linienquelle und (iii) ebene Wärmequelle. Die Temperaturfeld — Lösung für diese instationäre Wärmeleitungsproblem in einem ausgedehnten, homogenen und isotropen Medium lassen sich in geschlossener Form angeben, und zwar für den Fall zeitabhängiger, kontinuierlich wirkender Wärmequellen mit dem Zeitgesetz , wobeiv eine positive ganze Zahl ist. In jedem der o.g. Fälle wird das normierte Temperaturfeld durch die Whittaker — Funktion beschrieben. Die hier vorgelegte Untersuchung liefert sowohl die bekannten klassischen, wie auch einige neue Lösungen.

     

On the Diophantine Queueing System, <Emphasis Type="Italic">D/D</Emphasis><Superscript><Emphasis Type="Italic">a,b</Emphasis></Superscript><Emphasis Type="Italic">/</Emphasis>1

This paper considers the solution of a deterministic queueing system. In this system, the single server provides service in bulk with a threshold for the acceptance of customers into service. Analytic results are given for the steady-state probabilities of the number of customers in the system and in the queue for random and pre-arrival epochs. The solution of this system is a prerequisite to a four-point approximation to the model GI/G ^a,b /1. The paper demonstrates that the solution of such a system is not a trivial problem and can produce interesting results. The graphical solution discussed in the literature requires that the traffic intensity be a rational number. The results so generated may be misleading in practice when a control policy is imposed, even when the probability distributions for the interarrival and service times are both deterministic.     

REACTIONS OF THIOPHENES IN GLOW DISCHARGES

Abstract

Recent studies on the reaction of thiophenes in the lowtemperature plasma of glow discharges have disclosed the formation of thioketene and carbon monosulfide. Alkylthiophenes, on the other hand, undergo a complex series of reactions leading to benzene whereas phenylthiophenes mainly give naphtalene.     

Chaos and order in librating quantum planar elastic pendulum

Nonlinear Dynamics - We investigate, numerically and analytically, the quantum mechanics of planar elastic pendulum in libration. The classical phase space of the system consists of both regular...