Assessing Concentration Dependence of FCC Metal Alloy Diffusion Coefficients Using Kinetic Monte Carlo

Intrinsic diffusion coefficients have been calculated for a solid solution binary fcc metal alloy with vacancies using grand canonical and kinetic Monte Carlo (MC) methods for a variety of model Hamiltonians. Model Hamiltonians include a kinetically and thermodynamically ideal case, solute-vacancy attraction and repulsion, and solute-solute attraction and repulsion. These model Hamiltonians are chosen to have constant average activation energies in order to focus on contributions from other thermodynamic and kinetic factors. The thermodynamic factor calculated using MC is compared to a mean-field regular solution model. It is shown that the mean-field model accurately predicts the thermodynamic factors for each model alloy Hamiltonian except for the alloys with a solute-solute interaction and concentration that are in the spinodal region (as predicted by the regular solution model). The MC determined concentration-dependent intrinsic diffusion coefficients are compared to values determined from the dilute five-frequency model and Darken and Manning analytical approximations. The results indicate that for a solid solution with known average barriers and vacancy concentration, Darken and Manning approximation-based analytic expressions and mean-field theory can be used to predict concentration-dependent diffusion coefficients within a factor of approximately three, provided the system is outside of the spinodal region. The good accuracy of this approximate approach follows from the fact that the thermodynamic factor is the main contribution to the concentration dependence of the diffusion constants, and that this thermodynamic factor is well described by mean-field theory.     

An Open Grid Services Architecture Primer

To expand the use of distributed computer infrastructures as well as facilitate grid interoperability, OGSA has developed standards and specifications that address a range of scenarios, including high-throughput computing, federated data management, and service mobility.     

The Transition to Solid-State Lighting

Lighting constitutes more than 20% of total U.S. electricity consumption, a similar fraction in the European Union, and an even higher fraction in many developing countries. Because many current lighting technologies are highly inefficient, improved technologies for lighting hold great potential for energy savings and for reducing associated greenhouse gas emissions. Solid-state lighting shows great promise as a source of efficient, affordable, color-balanced white light. Indeed, assuming market discount rates, engineering-economic analysis demonstrates that white solid-state lighting already has a lower levelized annual cost (LAC) than incandescent bulbs. The LAC for white solid-state lighting will be lower than that of the most efficient fluorescent bulbs by the end of this decade. However, a large literature indicates that households do not make their decisions in terms of simple expected economic value. After a review of the technology, we compare the electricity consumption, carbon emissions, and cost-effectiveness of current lighting technologies, accounting for expected performance evolution through 2015. We then simulate the lighting electricity consumption and implicit greenhouse gases emissions for the U.S. residential and commercial sectors through 2015 under different policy scenarios: voluntary solid-state lighting adoption, implementation of lighting standards in new construction, and rebate programs or equivalent subsidies. Finally, we provide a measure of cost-effectiveness for solid-state lighting in the context of other climate change abatement policies.     

Individual and situational factors that influence the efficacy of personalized feedback substance use interventions for mandated college students.

Little is known about individual and situational factors that moderate the efficacy of personalized feedback interventions (PFIs). Mandated college students (N = 348) were randomly assigned either to a PFI delivered in the context of a brief motivational interview (BMI; n = 180) or to a written PFI only (WF) condition and were followed up at 4 months and 15 months postintervention. The authors empirically identified heterogeneous subgroups utilizing mixture modeling analysis based on heavy episodic drinking and alcohol-related problems. The 4 identified groups were dichotomized into an improved group (53.4%) and a nonimproved group (46.6%). Logistic regression results indicated that the BMI was no more efficacious than the WF across all mandated students. However, mandated students who experienced a serious incident requiring medical or police attention and those with higher levels of alcohol-related problems at baseline benefited more from the BMI than from the WF. It may be an efficacious and cost-effective approach to provide a written PFI for low-risk mandated students and an enhanced PFI with a BMI for those students who experience a serious incident or have higher baseline alcohol-related problems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Variable toroidal ferrite phase shifter

Careful design of the magnetic bias circuit used in ferrite phase shifters can help to reduce space, weight and energy consumption. Low reluctance circuits must avoid air-gaps and this can be achieved using toroidal-shaped ferrite inserts positioned inside a rectangular waveguide. Here, these ferrite inserts are fabricated using a viscous plastic processing method that avoids machining and produces a continuous magnetic circuit. Finite-element methods are used to initially model the magnetostatic solution for the bias circuit before being used to analyse the microwave performance of a double toroid phase shifter. A closedform technique is introduced to model the dielectric slab waveguide impedance transformer. The final insertion loss was ,1 dB over the 9.5?10.3 GHz band and return loss of 20 dB was achievable. The phase shift calculation agrees to within 10% of the measured values.     

High density net shape components by direct laser re-melting of single-phase powders

Direct Metal Laser Re-Melting is a variant of the Selective Laser Sintering process, a Rapid Prototyping (RP) technology. This tool-less manufacturing technology has the potential of producing complex, high quality components from single-phase metal powders in short time scales. This is made possible by the production of consecutive two-dimensional layers. Unfortunately, finished components manufactured by this technique have their integrity and material properties dictated by the porosity within the laser re-melted structure. In order to maintain structural integrity comparable to conventionally produced components, metal components produced by the rapid prototyping method should exhibit a porosity of the order of maximum of 2% with corresponding bulk material properties. To achieve these objectives, process and laser parameters require optimisation for maximum densities to be attained. This paper reports on the development of a scanning strategy that produces stainless steel (316L) laser re-melted components which exhibit porosities of <1%, while maintaining the concept of rapid prototyping.     

Enhancement of the surface expression of tumor necrosis factor alpha (TNFalpha) but not the p55 TNFalpha receptor in the THP-1 monocytic cell line by matrix metalloprotease inhibitors

The monocytic cell line THP-1 can be induced to express and release tumor necrosis factor alpha (TNFalpha) and both TNFalpha receptors (p55 and p75) upon exposure to bacterial lipopolysaccharide (LPS). The broad-spectrum matrix metalloprotease (MMP) inhibitors [4-(N-hydroxyamino)-2R-isobutyl-3S-(phenylthiomethyl)succinyl]-L-p henylalanine-N-methylamide (GI-129471) and marimastat [2S-[N4(R*),2R*,3S*]]-N4[2,2-dimethyl-1-[(methylamino)carbonyl]propyl]-N 1,2-dihydroxy-3-(2-methylpropyl)butanediamide (BB-2516) were effective inhibitors of LPS-induced TNFalpha (soluble) release with IC50 values of 0.2 and 4.0 microM, respectively. Upon LPS stimulation, the expression of pro-TNFalpha (membrane associated) on the cell surface (FACS analysis) could not be observed. However, in the presence of GI-129471, a concentration-dependent increase in TNFalpha surface expression was observed. Peak expression (percentage of cells expressing pro-TNFalpha and mean fluorescence units) in the presence of GI-129471 was at 2 hr, and steadily declined to return to near control levels by 8 hr. This time course was similar to TNFalpha release, which also peaked at 2-4 hr after LPS exposure and then declined. Stimulation of THP-1 cells with LPS + phorbol myristate acetate increased the percentage of cells expressing pro-TNFalpha by 10-fold. In the presence of GI-129471, these increases were augmented further and peaked between 2 and 4 hr, but also returned to near control levels of expression by 24 hr. This was in contrast to the release of soluble TNFalpha, which continued to accumulate over a 24-hr time course. TNFalpha receptor I (p55, TNFRI) and II (p75, TNFRII) shedding was also inhibited by GI-129471 (IC50 = 1.5 and 3.1 microM, respectively) and BB-2516 (IC50 = 14 and 15 microM, respectively). Unlike pro-TNFalpha surface expression, surface expression of both TNFalpha receptors steadily increased over 72 hr. In contrast to pro-TNFalpha surface expression, TNFRI surface expression was not augmented by these MMP inhibitors in THP-1 cells after LPS stimulation. Surface expression of TNFRII was augmented by these MMP inhibitors. These results suggest that even in the continued presence of LPS stimulation and an inhibitor of TNFalpha processing, the augmented surface expression of TNFalpha is transient. The potential "deleterious" implications of high levels of surface pro-TNFalpha expression in the presence of these inhibitors may be lessened by its transient nature.     

Coexpression of leptin receptor and preproneuropeptide Y mRNA in arcuate nucleus of mouse hypothalamus

Leptin, the protein product of the adipose tissue-specific ob (obese) gene (1), reduces the body weight, adiposity and food intake of obese ob/ob mice on peripheral or central injection (2, 3, 4). [125I]leptin binding has been detected in mouse choroid plexus (5), from which a leptin receptor gene was expression cloned (5). The gene has at least 6 splice variants (6, 7). Leptin receptor mRNA was localized in the hypothalamus by in situ hybridization being particularly abundantly expressed in the arcuate nucleus (8). There is evidence linking the physiological effects of injected leptin with hypothalamic neuropeptide Y (9, 10) (NPY), which has potent central effects on food intake and energy balance (11), and is also expressed in the arcuate nucleus. Here we report dual in situ hybridization studies for leptin receptor and NPY gene expression in the mouse arcuate nucleus, where the majority of cells examined expressed both genes. This provides the first direct evidence that leptin acts on cells that express NPY mRNA.