Thermodynamics and kinetics analyses of ZrB2 formation in molten aluminium alloys

Smelter grade aluminium can be used as a source for electrical conductor grade aluminium after the transition metal impurities such as zirconium (Zr), vanadium (V), titanium (Ti) and chromium (Cr) have been removed. Zirconium (Zr), in particular, has a significant effect on the electrical conductivity of aluminium. In practice, the transition metal impurities are removed by adding boron-containing substances into the melt in the casthouse. This step is called boron treatment. The work presented in this paper, which focuses on the thermodynamics and kinetics of Zr removal from molten Al–1?wt-%Zr–0.23?wt-%B alloy, is part of a broader systematic study on the removal of V, Ti, Cr and Zr from Al melt through boron treatment carried out by the authors. The thermodynamic analyses of Zr removal through the formation of ZrB₂ were carried out in the temperature range of 675–900°C using the thermochemical package FactSage. It was predicted that ZrB₂ is stable compared to Al–borides (AlB₁₂, AlB₂) hence would form during boron treatment of molten Al–Zr–B alloys. Al–Zr–B alloys were reacted at 750?±?10°C for 60 minutes, and the change in the chemistry and microstructure were tracked and analysed at particular reaction times. The results showed that the reaction between Zr and AlB₁₂/B was fast as revealed by the formation of boride ring at the early minutes of reaction. The presence of black phase (AlB₁₂), i.e. the original source of B, after holding the melt for 60 minutes advocated that the reaction between Zr and AlB₁₂/B was incomplete, hence still not reached the equilibrium state. The kinetics data suggested a higher reaction rate at the early minutes (2 minutes) of reaction compared to at a later stage (2–60 minutes). Nevertheless, a simple single-stage liquid mass transfer controlled kinetic model can be used to describe the overall process kinetic. The analysis of integrated rate law versus reaction time revealed that the mass transfer coefficient (k_m) of Zr in molten alloy is 9.5?×?10^?4?m?s^?1, which is within a typical range (10^?3 to 10^?4?m?s^?1) observed in other metallurgical solid–liquid reactions. This study suggests that the overall kinetics of reaction was predominantly controlled by the mass transfer of Zr through the liquid aluminium phase.     

Kafka in the academy: a note on ethics in IA education

In studying how to protect the United States' critical infrastructure, a presidential commission divided it into several sectors: information and communications, banking and finance, energy, physical distribution, and vital human services. Given that all sectors are strongly interconnected, the vulnerability of one represents dangers for the others. For example, a failure in the communications infrastructure would quickly have consequences in the finance and physical distribution sectors, which rely on it for coordination. Disruption of finance and transportation would quickly spill over into the energy and human services sectors. The communications and information infrastructures' self-evident long-term dependence on energy and finance completes the cycle.     

Instantiated features and the use of "rules."

Classification "rules" in expert and everyday discourse are usually deficient by formal standards, lacking explicit decision procedures and precise terms. The authors argue that a central function of such weak rules is to focus on perceptual learning rather than to provide definitions. In 5 experiments, transfer following learning of family resemblance categories was influenced more by familiar-appearing features than by novel-appearing features equally acceptable under the rule. This occurred both when rules were induced and when rules were given at the beginning of instruction. To model this and other phenomena in categorization, features must be represented on 2 levels: informational and instantiated. These 2 feature levels are crucial to provide broad generalization while reflecting the known peculiarities of a complex world. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The future of enzymes in cosmetics

The skin employs a host of protective mechanisms to defend itself against the ravages of the environment. One of the most widely studied protective mechanisms is the system of free radical scavengers. Free radical scavengers help to protect the skin by neutralizing dangerous substances that can be generated by sun exposure and pollution. Two such protective substances - superoxide dismutase and peroxidase - were examined for their ability to reduce UV-induced erythema. The ability to reduce erythema is a measure of anti-irritant capabilities, which can also be thought of as free radical scavenging ability. There has been some research that shows that superoxide dismutase (SOD) and peroxidase work synergistically. The action of SOD, which neutralizes the superoxide anion, can sometimes produce hydrogen peroxide, which can have a detrimental effect on the lipid barriers of the skin. When peroxidase is present, it can work to neutralize the hydrogen peroxide, thus giving a full spectrum of free radical protection. The present study employs a superoxide dismutase extracted from yeast. The peroxidase is found in an aqueous extract of fennel (Foeniculum vulgare). Minimal erythemal dose (MED) was determined on the panellists. Test compounds were then applied and then they were exposed to solar simulators in doses equivalent to their respective MEDs. Development of erythema was then measured via chromameter, and reduction in the development of redness was determined.     

Evaluation of culture enrichment procedures for use with Salmonella detection immunoassay

To design efficient culture strategies for use with immunoassays to detect Salmonella in food, the growth of these organisms was investigated according to the Bacteriological Analytical Manual (BAM) and enrichment-immunoassay (EI) culture procedures. The cultures were further evaluated using a commercial enzyme-linked immunosorbent assay (ELISA) kit. The BAM procedure includes pre-enrichment in nutrient broth (NB) for 16 h followed by selective enrichment in either Rappaport-Vassiliadis (RV) or tetrathionate brilliant green (TBG) broth for 16 h. The EI procedure includes pre-enrichment in NB for 4 h, selective enrichment in RV for 16 h and post-enrichment in NB for 4 h. The effects of different incubation times for pre- and post-enrichment, and different culture media for selective enrichment (TBG and RV) and post-enrichment in NB and Brain Heart Infusion broth (BHI) on the growth of the bacteria and ELISA titers in the EI procedure were also investigated. Salmonella enteritidis and S. typhimurium inoculated at different initial concentrations between 0.1 and 35 CFU/ml grew to similar concentrations of 10(7) to 10(8) colony forming unit (CFU)/ml in pure culture and generally 2 to 4 fold lower concentrations (P<0.05) in mixed culture using spiked chicken rinse. In the BAM procedure, the concentration of Salmonella cultured in RV was higher (P<0.01) than that in TBG. The cultures in TBG showed positive results for ELISA, but those in RV were generally negative. In the EI procedure, the ELISA titers from cultures post-enriched in NB or BHI were higher (P<0.01) when TBG, as compared to RV, was used for selective enrichment. Post-enrichment in BHI yielded higher numbers of Salmonella and higher ELISA titers than those in NB (P<0.05) for post-enrichment. This study demonstrated that in both culture procedures small numbers of Salmonella could be increased to at least 10(7) CFU/ml which is detectable by most ELISAs, and that the type of the culture media used may have a significant impact on ELISA results.     

The Effect of (Mis-Specified) GARCH Filters on the Finite Sample Distribution of the BDS Test

This paper considers the effect of using a GARCH filter on the properties of the BDS test statistic as well as a number of other issues relating to the application of the test. It is found that, for certain values of the user-adjustable parameters, the finite sample distribution of the test is far-removed from asymptotic normality. In particular, when data generated from some completely different model class are filtered through a GARCH model, the frequency of rejection of iid falls, often substantially. The implication of this result is that it might be inappropriate to use non-rejection of iid of the standardised residuals of a GARCH model as evidence that the GARCH model fits the data.     

Vibration-based terrain classification for planetary exploration rovers

Safe, autonomous mobility in rough terrain is an important requirement for planetary exploration rovers. Knowledge of local terrain properties is critical to ensure a rover's safety on slopes and uneven surfaces. Visual features are often used to classify terrain; however, vision can be sensitive to lighting variations and other effects. This paper presents a method to classify terrain based on vibrations induced in the rover structure by wheel-terrain interaction during driving. This sensing mode is robust to lighting variations. Vibrations are measured using an accelerometer mounted on the rover structure. The classifier is trained using labeled vibration data during an offline learning phase. Linear discriminant analysis is used for online identification of terrain classes, such as sand, gravel, or clay. This approach has been experimentally validated on a laboratory testbed and on a four-wheeled rover in outdoor conditions.     

Low Temperature Upper Critical Field Studies in Organic Superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3

Low temperature upper critical field studies have been carried out in a new organic superconductor -(BEDT-TTF) ₂ SF ₅ CH ₂ CF ₂ SO ₃. For field parallel to the superconducting layers, the upper critical field determined from transport measurements exceeds the BCS Pauli limit at low temperatures. The angular dependence of the resistive transition shows that the upper critical field can be best described by a quasi-two-dimensional model with a cusp near the field parallel to the plane direction.