Behaviour of Hastelloy C22 steel in sulphate solutions at pH 3 and low temperatures

The behaviour of Hastelloy C22 steel (N06022 UNS) in solutions at pH 3 and different temperatures, for radioactive water reprocessing plants was studied. The corrosion potential was found to increase with temperature. In the neighbourhood of the active-passive potentials, Hastelloy steel was corroded by means of a transient form. In addition, the potentials of the active and transpassive peaks shifted towards more negative values with increasing temperature. The transpassive peak increased with temperature and its potential shifted towards smaller values. The temperature increase led to a reduction of the passive region and a higher current in the passivity. As shown by current instabilities during the backward scan and a higher current than those in the forward transpassivity scan, all of the oxide layer could not be destroyed at the breakdown transpassive potentials. From electrochemical impedance spectroscopy (EIS), apparently the thickness of the passive oxide decreased with temperature in the prepassive region. In passivity, the EIS showed an enhancement of corrosion for higher potentials or temperatures. At the passivity-transpassivity limit potentials, an inductive loop may be the result of adsorption. It was found that the diameter of the capacitive semi-circle and the inductive loop decreased when the temperature increased, indicating an enhancement of corrosion and a decrease in adsorption. The number of active sites and oxidation rate were determined at different potentials.     

On the dissipation process in Bi2Sr2Ca2Cu3O10 tapes and bulk samples with preferential grain orientation in zero external magnetic field

Current-voltage characteristics of Bi₂Sr₂Ca₂Cu₃O₁₀ tapes and bulk samples with preferentially oriented crystallites have been measured in zero applied magnetic field and for temperatures close to the mean-field critical-temperature,T _c0. It was shown that the power-law dependence,V=AI ^a, valid for two-dimensional systems, does not correctly describe the data, which clearly indicate the existence of a finite critical-current density,J _c. The experimentalI-V curves are fitted quite well with the model which attributes the finite critical-current density to the coupling between the CuO₂ double layers. It was found thatJ _c vanishes at a temperature value belowT _c0. This behavior can result from the occurrence of vortex fluctuation-induced layer decoupling and/or from the contribution of entropy to the vortex unbinding process.     

Block versus trellis: an introduction to coded modulation

Coded modulation has had a very significant impact on the communications scene in the decade or so since its introduction, finding practical applications from voice-band modems for telephone lines to deep-space communications. The paper introduces the principles of coded modulation and describes the two main schemes: block coded modulation (BCM) and trellis coded modulation (TCM). In particular it considers the argument between the proponents of BCM and TCM, and points out some pitfalls in the use of performance measures such as asymptotic coding gain for these schemes. It concludes that in terms of performance versus decoder complexity the schemes seem to be quite close, and the choice of the system designer may be determined by other factors     

Analytic investigation of the process of formation of a spatially inhomogeneous structural state in a steel plate subjected to rapid cooling

We analyze the process of formation of a spatially inhomogeneous phase composition of several types of steel in cooling with convective heat exchange with the environment. The principles of the classical theory of heat conduction and the theory of interpolational models of structural state formation in rapidly cooled steels are used for numerical prediction. On this basis, we develop a technique for the analysis of phase composition. It is shown that the percentage of the martensitic constituent in steels increases as the external heat removal becomes more intense; at the same time, the tendency to complete hardening in steel is intensified. These observations are in a good agreement with experiment.Pidstrygach Institute of Applied Problems in Mechanics and Mathematics, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 6, pp. 101–104, November–December, 1993.     

Early and intensive physiotherapy accelerates recovery postarthroscopic meniscectomy: results of a randomized controlled study

The efficacy of an early, intensive, supervised rehabilitation program to accelerate knee strength recovery in the first 3 weeks postmeniscectomy by arthroscopy was evaluated using a randomized controlled trial design. The maximal voluntary isokinetic strength of 31 men, randomly allocated to either a treatment (EXP) or a control (CTL) group, was measured twice by a blind rater: preoperatively (pretest) and 3 weeks postsurgery (posttest), using a computer-controlled Kin-Com dynamometer (Chattecx Corporation, Chattanooga, TN). Strength deficits of the operated leg at the pretest and posttest were established in percent of the values obtained for the sound leg at the pretest. In the interval between the surgery and the posttest, the patients of the EXP group (n = 15) received nine supervised treatments combined to home exercises whereas patients of the control group (n = 16) had no specific physiotherapy treatment but were given instructions in postsurgical management and prescribed exercises by the orthopedic surgeons. Patients of the EXP group had better knee extensor strength recovery than patients of the CTL group (ANCOVA, p < 0.001). The size of the strength difference (3 weeks postsurgery) between EXP and CTL subgroups (n = 8) matched according to preoperative deficits was as large as 26% and the residual deficits of the untreated patients were two to three times larger than those of the treated patients. The results of this study highlight the importance of instituting an early intensive and supervised rehabilitation program, especially for workers returning to a strenuous job requiring good knee extensor muscle function.     

Inhibition of plasma membrane Ca(2+)-ATPase activity by volatile anesthetics

BACKGROUND: The precise sites and mechanisms of action of volatile anesthetics remain unknown. Recently, several integral membrane proteins have been suggested as potential targets to which anesthetics can bind at hydrophobic regions. Impairment of cell Ca2+ homeostasis has been postulated as one of the possible mechanisms of anesthetic action. To test these hypotheses, the authors selected the human erythrocyte Ca(2+)-ATPase as a model membrane protein. This enzyme is an integral membrane protein that is instrumental in maintaining Ca2+ homeostasis in the cell in which it is the sole Ca(2+)-transporting system. Thus, any functional alteration of the Ca(2+)-ATPase by anesthetics may lead to serious perturbations in Ca(2+)-regulated processes in the cell. METHODS: The Ca(2+)-ATPase activity was measured as a function of increased concentration of four volatile anesthetics: halothane, isoflurane, enflurane, and desflurane. RESULTS: All four anesthetics significantly inhibited the Ca(2+)-ATPase activity in a dose-dependent manner. The half-maximal inhibition occurred at anesthetic concentrations from 0.3 to 0.7 vol% at 37 degrees C, which, except for desflurane, is a clinically relevant concentration range. The greater the clinical potency of the volatile anesthetics studied, the less was the concentration required to inhibit the Ca(2+)-ATPase activity. The inhibition was less at 25 degrees C than at 37 degrees C, which is consistent with direct interactions of the nonpolar interfaces of the enzyme with the nonpolar of the portions of the anesthetics. CONCLUSIONS: The authors' findings indicate that the Ca(2+)-ATPase is a suitable model for investigating the mechanism of action of volatile anesthetics on the integral membrane protein, and that this inhibition may be specific.     

Chemical activation of the SHS process in the Nb−C system

The phenomenon of chemical activation is investigated using combustion of the Nb–C system in the presence of an activating additive, namely, polytetrafluoroethylene, as an example. Regions of the parameters of the process are found where the interaction occurs by two different mechanisms. The characteristic features of the process are established and the role of the activating additive in each region is determined.Institute of Chemical Physics, Academy of Sciences of Armenia, Yerevan. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No.5, pp.590–593, November, 1993.     

Optimization of parameters of recirculating apparatus for obtaining liquid nitrogen using mixtures

Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 12, pp. 20–23, December, 1993.     

A novel four-point bend test for strength measurement of opticalfibers and thin beams. II. Statistical analysis

In the first part of this work, a novel implementation of the well-known four-point bend test is described that determines the strength of thin beams and optical fibers by measuring the loading pin displacement, rather than the applied load. This paper extends the analysis of the nonlinear bending behavior to account for the stochastic nature of strength. A statistical analysis is presented that determines the effective tested length in bending and the tension to bending strength ratio. Results are given for both surface and volume flaws as well as for specimens of both circular and rectangular section. Strength measurements on a deliberately weakened silica optical fiber are consistent with the predictions of the analysis