Low-temperature oxidation of silicon in microwave oxygen plasma

The growth of silicon dioxide at low temperature in an oxygen plasma is investigated using a simplified electrodeless microwave discharge arrangement. The growth behaviour of the oxide is discussed in terms of plasma parameters. The compositional and electrical characterization of the grown oxide have been made to examine its performance for device applications. The results are compared with earlier observations by other authors.     

Kinetics of leaching chalcopyrite-bearing waste rock with thermophilic and mesophilic bacteria

The leaching characteristics and kinetics of a thermophilic, chemolithotrophic microorganism were studied and compared with those of mesophilic T. ferrooxidans. Chalcopyrite waste rock was used for laboratory scale shake flask leaching systems. The optimum (leaching) temperatures were determined to be between 30 and 40°C for Thiobacillus ferrooxidans and between 50 and 60°C for the thermophiles. The thermophilic microorganisms were observed to function as a kind of take-over organism with increasing temperature. Viable cell counts (most probable number measurements) for both microorganisms were observed to be highly correlated with total copper in solution after 6 weeks of leaching, and over a range of temperatures (20–70°C). Observations by scanning electron microscopy showed the bulk of precipitates formed during leaching were comprised of gypsum crystals, and that thermophilic organisms were attached in profusion to some mineral surfaces seen by X-ray energy dispersive analysis to be somewhat uniformly coated with a thin sulfur layer. The propensity for attachment of the thermophiles as compared with T. ferrooxidans was consistent with observations of other thermophilic microbes. The reaction order for T. ferrooxidans was 0.92, compared with 1.29 for the thermophilic microorganisms. Correspondingly, the activation energy for the thermophiles was 26.77 kcal mole^? compared with 22.22 kcal mole^?1 and 7.11 kcal mole^?1 for the T. ferrooxidans and sterile control reactions, respectively. The rate of reaction increased by 1.93 for each 10°C temperature increase for the thermophiles, compared with 1.83 for T. ferrooxidans.     

Pb-S-O vapor system re-evaluated using genetic algorithms

The efficacy of biologically inspired genetic algorithms for optimization is now well established. This article discusses the scope of using such an algorithm as an equation solver and presents detailed calculations on the Pb-S-O vapor system containing a total of 20 species as a paradigm case. This further increases the scope of applications of this evolutionary methodology in the domain of phase equilibria research, and this methodology is expected to be more advantageous than many other conventional techniques.     

Studies of blood pH and blood gases of humans under moderate and high altitude stress: effect of acetazolamide supplementation

Studies have been carried out on blood pH, Pco2, Po2, (HCO‐3), sodium and potassium levels of 30 human subjects at a moderate and at a high altitude in the north eastern Himalayan range. Blood pH was found to be increased, whereas Po2 and PCo2 levels decreased appreciably under high altitude stress. However, no significant change was observed in plasma bicarbonate level. Plasma sodium level was found to be lowered, while that of potassium level was raised at high altitude in comparison to the moderate altitude. Treatment with acetazolamide was found to be effective in lowering blood pH, Pco2 (HCO‐3) and plasma potassium level at high altitude, while PO2 level increased in comparison to the placebo group. On return of the subjects from high to moderate altitude, the studied parameters reverted to the initial moderate altitude base data.     

Plasma immunoglobulin levels of humans under high altitude stress

Studies have been carried out on plasma IgG, IgA, IgM and IgD levels of 20 male Indian sea level dwellers at sea level and at a high altitude (3658 m). An increase in plasma IgG, IgA and IgD levels with no change in IgM were observed under high altitude stress in comparison to the sea level base data. On return of the subjects from high to sea level, IgA and IgD levels, but not the IgG, reverted to the values observed at the initial sea level conditions.     

Arsenic and other elements in hair, nails, and skin-scales of arsenic victims in West Bengal, India

For the first time, biological tissues (hair, nails, and skin-scales) of arsenic victims from an arsenic affected area of West Bengal (WB), India were analyzed for trace elements. Analysis was carried out by inductively coupled plasma-mass spectrometry (ICP-MS) for 10 elements (As, Se, Hg, Zn, Pb, Ni, Cd, Mn, Cu, and Fe). A microwave digester was used for digestion of the tissue samples. To validate the method, certified reference materials--human hair (GBW 07601) and bovine muscle (CRM 8414)--were analyzed for all elements. The W test was used to study the normal/log normal distribution for each element in the tissue samples. For hair (n=44) and nails (n=33), all elements show log-normal distribution. For skin-scale samples (n=11), data are not sufficient to provide the information about the trend. Geometric mean, standard error, and range for each element were presented and compared with literature values for other populations. This study reveals the higher levels of toxic elements As, Mn, Pb, and Ni in the tissue samples compared with available values in the literature. The elevated levels of these toxic metals in the tissues may be due to exposure of these elements through drinking water and food. The correlations of Mn and Ni with other essential elements, e.g. Fe, Cu, Zn, suggest that Mn and Ni may substitute for those elements in hair, nails, and skin-scales. However, correlation represents the relation between two elements only and does not take into consideration of the presence of other elements. Principle component analysis was applied to explain the behavior among the elements present in hair and nails. This study reveals that in the arsenic-affected areas of WB, the concentrations of other toxic elements in drinking water and foodstuff should be monitored to evaluate the arsenic poisoning.     

In Vitro and In Vivo Characterization of Biodegradable Poly(organophosphazenes) for Biomedical Applications

The need and the growing interest in polymers as biomaterials have led to the synthesis of new polymers with a variety of physico-chemical properties. Biomedical application of such materials not only depends on their physical properties but also on biocompatibility and biodegradability. Polyphosphazenes are a family of ‘hybrid inorganic–organic polymers’ with inorganic elements in the backbone and organic side-groups. The polyphosphazenes constitute a family of greatly diverse performance materials with a broad spectrum of properties. The present review focuses on the biodegradable polyphosphazenes, their biocompatibility, and degradation behavior both in vitro and in vivo. This review also covers the use of biodegradable polyphosphazenes as controlled release devices.     

A DIMENSIONAL ANALYSIS OF DISSOLUTIONS OF A BITUMEN CONCENTRATE DERIVED FROM UTAH TAR SAND

ABSTRACT

Dissolution of bitumen concentrate derived from Utah tar sand by hot-water separation was studied in a stirred-tank reactor. The dissolution constitutes an important step in the bitumen concentrate clean-up process. A dimensional analysis was performed for the system which was utilized to construct a number of bitumen concentrate dissolution maps from the experimental data.     

Effect of strain rate on quasistatic tensile flow behaviour of solution annealed 304 austenitic stainless steel at room temperature

Room temperature tensile test results of solution annealed 304 stainless steel at strain rates ranging between 5 × 10⁻⁴ and 1 × 10⁻¹ s⁻¹ reveal that with increase in strain rate yield strength increases and tensile strength decreases, both maintaining power–law relationships with strain rate. The decrease in tensile strength with increasing strain rate is attributed to the lesser amount of deformation-induced martensite formation and greater role of thermal softening over work hardening at higher strain rates. Tensile deformation of the steel is found to occur in three stages. The deformation transition strains are found to depend on strain rate in such a manner that Stage-I deformation (planar slip) is favoured at lower strain rate. A continuously decreasing linear function of strain rate sensitivity with true strain has been observed. Reasonably good estimation for the stress exponent relating dislocation velocity and stress has been made. The linear plot of reciprocal of strain rate sensitivity with true strain suggests that after some critical amount of deformation the increased dislocation density in austenite due to the formation of some critical amount of deformation-induced martensite plays important role in carrying out the imposed strain rate.     

Ineffectiveness and poor reliability of arsenic removal plants in West Bengal, India

In the recent past, arsenic contamination in groundwater has emerged as an epidemic in different Asian countries, such as Bangladesh, India, and China. Arsenic removal plants (ARP) are one possible option to provide arsenic-safe drinking water. This paper evaluates the efficiency of ARP projects in removing arsenic and iron from raw groundwater, on the basis of our 2-year-long study covering 18 ARPs from 11 manufacturers, both from home and abroad, installed in an arsenic affected area of West Bengal, India, known as the Technology Park Project (TP project). Immediately after installation of ARPs on August 29, 2001, the villagers began using filtered water for drinking and cooking, even though our first analysis on September 13, 2001 found that 10 of 13 ARPs failed to remove arsenic below the WHO provisional guideline value (10 microg/L), while six plants could not achieve the Indian Standard value (50 microg/L). The highest concentration of arsenic in filtered water was observed to be 364 microg/L. Our 2-year study showed that none of the ARPs could maintain arsenic in filtered water below the WHO provisional guideline value and only two could meet the Indian standard value (50 microg/L) throughout. Standard statistical techniques showed that ARPs from the same manufacturers were not equally efficient. Efficiency of the ARPs was evaluated on the basis of point and interval estimates of the proportion of failure. During the study period almost all the ARPs have undergone minor or major modifications to improve their performance, and after our study, 15 (78%) out of 18 ARPs were no longer in use. In this study, we also analyzed urine samples from villagers in the TP project area and found that 82% of the samples contained arsenic above the normal limit.