Reaction chemistry and subsolidus phase equilibria in lead-based relaxor systems: Part I Formation and stability of the perovskite and pyrochlore compounds in the system PbO-MgO-Nb2O5

The reaction chemistry involved in the synthesis of perovskite Pb(Mg_1/3Nb_2/3)O₃ [Pb₃MgNb₂O₉] was studied by the solid state reaction technique using precursor oxides as reactants. At the initial stage of the reaction process, a large fraction of PbO present in the mixtures combined with Nb₂O₅ and a small amount of MgO to form an oxygen-deficient pyrochlore phase with a composition Pb_1.714(Mg_0.286Nb_1.714)O_6.286 [Pb₆MgNb₆O₂₂]. The pyrochlore phase thus formed further reacted with the remaining PbO and MgO to yield the perovskite Pb(Mg_1/3Nb_2/3)O₃. The pyrochlore Pb_1.714(Mg_0.286Nb_1.714)O_6.286 accomodates a small amount of PbO into its lattice and forms a narrow homogeneity range which extends from the composition Pb_1.714(Mg_0.286Nb_1.714)O_6.286 [Pb₆MgNb₆O₂₂] to a composition Pb₂(Mg_0.286Nb_1.714)O_6.571 [Pb₇MgNb₆O₂₃] with a corresponding increase in the lattice constant value from a = 10.586 to 10.601 Å. The pyrochlore phase melts incongruently at a temperature near 1230°C to yield Mg₄Nb₂O₉ and a liquid. Below this temperature, the perovskite Pb(Mg_1/3Nb_2/3)O₃ coexists with the pyrochlore solid solutions. However, the compound Pb(Mg_1/3Nb_2/3)O₃ is not compatible with Nb₂O₅ and these two phases react with one another to form the pyrochlore Pb_1.714(Mg_0.286Nb_1.714)O_6.286 and MgO.     

Analysis and computation of non-equilibrium two-phase flows

Non-equilibrium fluid mechanics and thermodynamics of two-phase vapour-droplet and gas-particle flow are considered. Formation of the droplets as well as their subsequent interaction with the vapour are discussed. A new theory of nucleation in steam turbines is developed that reproduces many aspects of measured droplet size spectra which cannot be explained by any available steady-flow theories. (Steam turbines are responsible for 80% of global electricity production and the presence of moisture significantly reduces turbine efficiency costing 50 million pounds per annum in UK alone.) Fluid dynamic interactions discussed include flow instabilities induced by condensation, condensation wave theory, relaxation gas dynamics for vapour-droplet flow, thermal choking due to non-equilibrium condensation, the structure of shock waves and their development through unsteady processes, and jump conditions and the interpretation of total pressure in two-phase flows.     

Performance comparison of triple and tandem multijunction a-Si:Hsolar cells: a numerical study

The numerically simulated performances of two subcell tandem and three subcell triple amorphous silicon-based, multijunction solar cells are compared. The current-voltage characteristics are calculated using a simulation program which allows for accurate determination of single-junction or multijunction cell response under monochromatic or global AM1.5 spectrum. The validity of the solar cell model is confirmed by the excellent agreement between the simulated and measured characteristics of in-house fabricated 13.0% tandem and 13.7% triple cells with a minimum optical bandgap of 1.4 eV. It is shown that if an even narrower bandgap material of 1.3 eV were used, the triple junction device would exceed the tandem by over 1% under global AM1.5 (14.2% versus 13.2%). Assuming that both cells absorb the same amount of light, this difference is mainly due to the weaker electric fields in the double-junction cell in which the individual cell thicknesses are larger     

Numerical modeling of an amorphous-silicon-based p-i-n solar cell

A simulation program for amorphous-silicon-based p-i-n solar cells which allows for accurate calculation of single-junction or multijunction cell response under monochromatic or global AM1.5 illumination is discussed. The device model is based on a complete set of Poisson and current continuity equations describing the amorphous intrinsic and microcrystalline or amorphous n⁺ and p⁺ contacts. It predicts solar cell behavior with uniform and nonuniform optical (mobility) bandgaps, spatially dependent doping densities, and various layer thicknesses, as demonstrated by the very good agreement between the experimental and simulated current-voltage characteristics of single cells, with the bandgaps in the range of 1.75 to 1.47 eV. The material parameters used in the simulation have been obtained from experimental results reported in the literature. The possibility of obtaining higher efficiencies using novel cell designs has also been investigated. Calculations have been carried out on cell structures in which the bandgap of the intrinsic layer is profiled to help hole transport. The most efficient structure, also confirmed by recent experimental data, incorporates normal profiling throughout the bulk of the intrinsic layer with a thin graded buffer at the p⁺ -intrinsic junction     

Models for minimum ignition temperature of organic dust clouds

The minimum ignition temperature of dust clouds is one of the important factors required for the design of preventive measures against dust explosion. The mathematical models available to predict this parameter have been analyzed for thier application to organic dust clouds. A solution of the most general model proposed by Mitsui and Tanaka is presented, together with its comparision with experimental data. It has been found to be quite successful in predicting the minimum ignition temperature for metal dusts but not for organic dusts. Recommendations for the development of a new model to predict the minimum ignition temperature of an organic dust, such as polyethylene, have been given.     

Autonomous thyroid adenoma, papillary thyroid carcinoma, and ectopic parathyroid adenoma in a patient with primary hyperparathyroidism and a nontoxic multinodular goiter

OBJECTIVE: To discuss the method for nipple-areola preserved mastectomy with one-stage breast reconstruction in cancer surgery. METHODS: Because of the merits of sufficient blood supply and plasticity of rectus abdominis musculocutaneous flap, we used one-stage breast reconstruction after modified radical mastectomy. The incision line was covered and the nipple-areola was preserved. The reconstructed breast was naturally in contour. RESULTS: 21 cases were treated from 1990 to 1995, and 18 of them received horizontal-rhombus shaped rectus abdominis musculocutaneous flaps and 3 longitudinal-rhombus flaps for breast reconstruction. Nipple-areola was preserved in 16 cases. Objective evaluation after operation showed that the excellent and satisfied rate reached to 90.5%; and subjective evaluation showed that the excellent and satisfied rate reached to 95.2%. Thirteen cases have been followed up for 3 years, and 9 for 5 years. Three-year survival rate was 100% (13/13), and 5-year 88.9% (8/9). CONCLUSION: The method is recommendable for the treatment of stage I-II breast cancer.     

Possible involvement of plasmids in degradation of malathion and chlorpyriphos by Micrococcus sp

Culture is the basic method in bacteriology. It allowed the discovery of Helicobacter pylori. Problems in the culture of this fragile, slow-growing bacterium concern transport and processing in the laboratory, but they can be solved. Culture has a 100% specificity. When performed properly, it has a sensitivity in the range of the other best diagnostic methods for Helicobacter pylori. It allows strain typing and, most importantly, susceptibility testing to antibiotics, because an increased rate of acquired resistance of Helicobacter pylori is currently observed. Culture must be performed in clinical trials, at least when antibiotics, to which Helicobacter pylori may be resistant, are used. In clinical practice, culture and susceptibility testing can generally be restricted to treatment failures. However, it is important to monitor Helicobacter pylori susceptibility to antibiotics at a national or regional level in order to give recommendations for primary treatment.     

Microwave Preparation of SiO2-B2O3-Na2O-K2O-CaO-Fe2O3-TiO2 Glass System

This study reports preparation of glass composition （54.50 wt.%） SiO2, （10.80 wt.%） B2O3, （14.20 wt.%） Na2O, （1.20 wt.%） K2O, （6.00 wt.%） CaO, （4.00 wt.%） Fe2O3 and （9.30 wt.%） TiO2 by melt quenching method using direct microwave heating and conventional resistive heating. Study of dielectric loss factor of the glass as function of temperature illustrated increasing loss factor above 370 ℃, 550 ℃, 650 ℃ and 900 ℃, indicating enhanced microwave absorption by the glass at above these temperatures. Chemical analysis results of both the glasses depicted more volatilization loss of volatile ingredients in conventional heating. The study of chemical durability was performed from leachate analysis describing less leaching of Na2O, K2O and other constituents from glass melted in microwave furnace. Glass transition temperatures （Tg） were found to be 576.3 ℃ and 569.5 ℃ for glass melted in conventional and microwave heating route, respectively. Laboratory experiment of glass melting utilizing microwave energy as an alternate heating source demonstrated 70%-75% electrical power saving.     

Analysis of steady-state characteristics of misaligned hydrodynamic journal bearings with isotropic roughness effect

The present work deals with the concept of a stochastic process to solve the problem of isotropic steady-state characteristics of hydrodynamic journal bearings of finite width, considering two types of misalignment, axial (vertical displacement) and twisting (horizontal displacement). Using a finite-difference method, the steady-state film pressures are obtained by solving a Reynolds type equation based on the principle of isotropic roughness pattern. With the help of the steady-state film pressures, the steady-state performance characteristics, in terms of load-carrying capacity, attitude angle, leakage flow-rate, friction coefficient and misalignment moment of a journal bearing with the slenderness ratio of unity, are obtained for various values of isotropic roughness parameter, eccentricity ratio and degree of misalignment.     

A study on the adsorption mechanism of mercury on Aspergillus versicolor biomass

The adsorption behavior of mercury on Aspergillus versicolor biomass (AVB) has been investigated in aqueous solution to understand the physicochemical process involved and to explore the potentiality of AVB in pollution control management. This biomass has been successfully used for reducing the mercury concentration level in the effluent of chloralkali and battery industries to a permissible limit. The results establish that 75.6 mg of mercury is adsorbed per gram of biomass. The adsorption process is found to be a function of pH of the solution, with the optimum range being pH 5.0-6.0. The process obeys the Langmuir-Freundlich isotherm model. Scanning electron microscopic analysis demonstrates a conspicuous surface morphology change of the mercury-adsorbed biomass. A nearly uniform distribution of metal ions on the mycelial surface excepting a few aggregation points is revealed by X-ray elemental mapping profiles. The results of zeta potential measurement, Fourier transform infrared (FTIR) spectroscopy, and blocking of the functional groups by chemical modification reflect the binding of mercury on the biomass occurs through electrostatic and complexation reactions. The accumulation of mercury on the cell wall associated with negligible diffusion and or transportation into cytoplasm finds support from the results of adsorption kinetics and transmission electron micrographs. Mercury adsorption on biomass also leads to elongation of cells and cytoplasmic aggregation of spheroplast/protoplasts, indicating that the cell wall acts as a permeation barrier against this toxic metal.