Electrochemical reduction of Bi2Sr2Ca1Cu2O8 superconductor single crystals

Single crystals and polycrystalline pellets of the high-temperature cuprate superconductor Bi₂Sr₂Ca₁Cu₂O₈ were doped at room temperature by electrochemical reduction at > 95% Coulombic efficiency using lithium dopant ions in propylene carbonate electrolyte. Cyclic voltammetry and potential step measurements on single crystals suggest an unusual reduction mechanism, with a diffusion coefficient for Li⁺ in the c-axis direction of bulk superconductor of ca. 3 × 10⁻¹¹ cm²s⁻¹. Sintered pellets of polycrystalline powder could be doped more rapidly, with an apparent diffusion coefficient of 7 × 10⁻⁸ cm²s⁻¹. X-ray susceptibility analysis show extensive disordering occurs on heavy Li doping, with a first-order transition from a crystalline/superconducting to an amorphous/non-superconducting phase. Single, crystals of Bi₂Sr₂Ca₁Cu₂O₈ exhibited a color change on reduction from metallic gray to golden bronze. The reduced material was highly air-sensitive, forming a hydroxide surface film on exposure to ambient atmosphere.     

A rate-dependent algebraic stress model for turbulence

Based on the stress transport model, a rate-dependent algebraic expression for the Reynolds stress tensor is developed. It is shown that the new model includes the normal stress effects and exhibits viscoelastic behavior. Furthermore, it is compatible with recently developed improved models of turbulence. The model is also consistent with the limiting behavior of turbulence in the inertial sublayer and is capable of predicting secondary flows in noncircular ducts. The TEACH code is modified according to the requirements of the rate-dependent model and is used to predict turbulent flow fields in a channel and behind a backward-facing step. The predicted results are compared with the available experimental data and those obtained from the standard k-ε and algebraic stress models. It is shown that the predictions of the new model are in better agreements with the experimental data.     

A note on the solution of a class of two-point boundary value problems involving a mixed boundary condition

In this note, we consider a class of two-point boundary value problems involving a pa- rameter in one of the boundary conditions. We shall show that if we know the solution corresponding to a particular value of the parameter, then the solution for any other value of the parameter can be obtained by a simple algebraic method.     

Simultaneous determination of ascorbic acid and dehydroascorbic acid by HPLC with postcolumn derivatisation and fluorometric detection

Summary A reproducible method is described for the separation and simultaneous and specific quantitation of ascorbic acid and dehydroascorbic acid by ion-pairing reversed-phase HPLC with fluorometric detection. Copper sulphate and copper acetate were compared as oxidizing reagents for ascorbic acid and 1,2-diaminobenzene dihydrochloride and 1,2-diamino-3,4-dimethylbenzene dihydrochloride as derivatising reagents. The HPLC-method was applied to human plasma. The detection limit reaches 16 ng for ascorbic acid and 3 ng for dehydroascorbic acid. Sample preparation is carried out by solid phase extraction with a recovery of 98%; it is compared with conventional precipitation of plasma proteins by metaphosphoric acid.     

Studies of the kinetics of the reduction of chromate by glutathione and related thiols

The reduction of chromate by glutathione, its mono- and diethyl esters, -cysteine, 2-mercapto-propionic acid and mercapto-succinic acid has been studied. The empirical rate law k_obs = ab[Thiol]²/(1 + b[Thiol]) is obeyed by all of these thiols, at neutral pH. No evidence could be obtained for a first-order pathway in glutathione under these conditions. These observations are used to comment on the stability of intermediates potentially important in explaining chromate toxicity.     

Efficacy of the accent method of voice therapy

The management of voice disorders may follow one of four approaches: surgical, pharmacological, technical aid, and/or voice therapy. The latter approach offers a wide variety of techniques, each based on certain theoretical beliefs. One of these techniques is the Smith Accent Method. The principles and goals of the Accent Method are presented. The results of its application are discussed. This technique proved effective for cases of functional voice disorders, vocal nodules, and some degrees of vocal fold paralysis.     

Dynamic behavior classification of a model for a continuous bio-reactor subject to product inhibition

The dynamic behavior of the continuous biological reactor subject to product inhibition is analysed and classified in terms of multiplicity and stability of steady states and existence and stability character of limit cycles. Various boundary conditions are derived which delineate the parameter space into regions of dynamically different behavior. The predicted types of behavior are then illustrated by numerical computation of cells and product concentration trajectories.     

A generalized Adadorov theory for anisotropic thin-walled beams

This paper presents a generalized Adadorov theory for anisotropic thin—walled beams. The theory takes account of the shear strain of the middle surface, which exerts a significant influence on the anisotropic thin-walled beams. A new approach is established to solve the governing equations, which have the same form for both open and closed section beams. The numerical examples show that the effects of the shear strain cannot be neglected for this class of beams.This work was part of research project supported by the National Natural Science Foundation of China