Elemental and iron isotopic composition of aerosols collected in a parking structure

The trace metal contents and iron isotope composition of size-resolved aerosols were determined in a parking structure in Tempe, AZ, USA. Particulate matter (PM) < 2.5 µm in diameter (the fine fraction) and PM > 2.5 µm were collected. Several air toxics (e.g., arsenic, cadmium, and antimony) were enriched above the crustal average, implicating automobiles as an important source. Extremely high levels of fine copper (up to 1000 ng m^− 3) were also observed in the parking garage, likely from brake wear. The iron isotope composition of the aerosols were found to be + 0.15 ± 0.03‰ and + 0.18 ± 0.03‰ for the PM < 2.5 µm and PM > 2.5 µm fractions, respectively. The similarity of isotope composition indicates a common source for each size fraction. To better understand the source of iron in the parking garage, the elemental composition in four brake pads (two semi-metallic and two ceramic), two tire tread samples, and two waste oil samples were determined. Striking differences in the metallic and ceramic brake pads were observed. The ceramic brake pads contained 10-20% copper by mass, while the metallic brake pads contained about 70% iron, with very little copper. Both waste oil samples contained significant amounts of calcium, phosphorous, and zinc, consistent with the composition of some engine oil additives. Differences in iron isotope composition were observed between the source materials; most notably between the tire tread (average = + 0.02‰) and the ceramic brake linings (average = + 0.65‰). Differences in isotopic composition were also observed between the metallic (average = + 0.18‰) and ceramic brake pads, implying that iron isotope composition may be used to resolve these sources. The iron isotope composition of the metallic brake pads was found to be identical to the aerosols, implying that brake dust is the dominant source of iron in a parking garage.     

Valuing the attributes of renewable energy investments

Increasing the proportion of power derived from renewable energy sources is becoming an increasingly important part of many countries's strategies to achieve reductions in greenhouse gas emissions. However, renewable energy investments can often have external costs and benefits, which need to be taken into account if socially optimal investments are to be made. This paper attempts to estimate the magnitude of these external costs and benefits for the case of renewable technologies in Scotland, a country which has set particularly ambitious targets for expanding renewable energy. The external effects we consider are those on landscape quality, wildlife and air quality. We also consider the welfare implications of different investment strategies for employment and electricity prices. The methodology used to do this is the choice experiment technique. Renewable technologies considered include hydro, on-shore and off-shore wind power and biomass. Welfare changes for different combinations of impacts associated with different investment strategies are estimated. We also test for differences in preferences towards these impacts between urban and rural communities, and between high- and low-income households.     

On the flow of power law fluid over a stretching sheet-techniques and solutions

Summary The flow of an inelastic power law fluid over a stretching sheet has been investigated. In the absence of an exact analytical solution several solutions embodying techniques based on different methodologies have been presented. The usefulness of these solutions has been discussed based on the comparison with the exact numerical solution.     

On exact solutions of flow problems of a second grade fluid through two parallel porous walls

Exact analytical solutions of two problems of laminar flow of a second grade fluid through two parallel porous walls are obtained. For each problem the rate of injection at one wall is assumed equal to the rate of suction at the other wall. Two geometries are considered: rectangular - when the flow takes place between two parallel flat walls, and cylindrical - when the flow takes place through an annulus. For the exact solution no assumption is made on the size of K, the viscoelastic fluid parameter, or the cross-flow Reynolds number. However, it is assumed that a Taylor series expansion of the solution exists near K=0. Also assuming K small, perturbation solutions are developed for both the geometries. The exact solutions reveal that the viscoelasticity of the fluid tends to destroy the formation of the boundary layer at the wall where the suction takes place for large values of the cross-flow Reynolds number. It is further shown that the commonly used perturbation technique does not give satisfactory results even for moderate values of the cross-flow Reynolds number.     

On extra boundary condition in the stagnation point flow of a second grade fluid

The two dimensional stagnation point flow of a second grade fluid is considered. The flow is governed by a boundary value problem in which the order of differential equations is one more than the number of available boundary conditions. It is shown that without augmenting the boundary conditions at infinity it is possible to obtain a numerical solution of the problem for all values of K, where K is the dimensionless viscoelastic fluid parameter. The numerical results using the algorithm foreshadow an asymptotic behavior for large K. The asymptotic solution is derived up to terms of O(K⁻¹). Perturbation solutions are also obtained up to the terms of O(K²). Finally an approximate solution is developed, based on stretching of the independent variable and minimizing the residual of the differential equation in the least square sense. All these solutions are compared with the exact numerical solution and the appropriate conclusions are drawn.     

Graphene-wrapped sulfur particles as a rechargeable lithium-sulfur battery cathode material with high capacity and cycling stability

We report the synthesis of a graphene-sulfur composite material by wrapping poly(ethylene glycol) (PEG) coated submicrometer sulfur particles with mildly oxidized graphene oxide sheets decorated by carbon black nanoparticles. The PEG and graphene coating layers are important to accommodating volume expansion of the coated sulfur particles during discharge, trapping soluble polysulfide intermediates, and rendering the sulfur particles electrically conducting. The resulting graphene-sulfur composite showed high and stable specific capacities up to ～600 mAh/g over more than 100 cycles, representing a promising cathode material for rechargeable lithium batteries with high energy density.     

Three-dimensional profiling with binary fringes using phase-shifting interferometry algorithms

Three-dimensional shape measurements by sinusoidal fringe projection using phase-shifting interferometry algorithms are distorted by the nonlinear response in intensity of commercial video projectors and digital cameras. To solve the problem, we present a method that consists in projecting and acquiring a temporal sequence of strictly binary patterns, whose (adequately weighted) average leads to a sinusoidal fringe pattern with the required number of bits. Since binary patterns consist of "ones" and "zeros"--and no half-tones are involved--the nonlinear response of the projector and the camera will not play a role, and a nearly unit contrast gray-level sinusoidal fringe pattern is obtained. Validation experiments are presented.     

Monitoring challenges: A closer look at parental monitoring, maternal psychopathology, and adolescent sexual risk.

The present study sought to examine associations between maternal psychopathology, parental monitoring, and adolescent sexual activity among adolescents in mental health treatment. Seven hundred ninety mother-adolescent dyads recruited from adolescent mental health treatment settings completed audio computer-assisted structured interview assessments examining parent psychiatric symptoms, parental monitoring, and adolescent sexual risk behavior. Path analysis was used to examine the associations between variables of interest. Maternal caregivers who reported more mental health symptoms were more likely to have adolescents who reported recent sex and this relationship was mediated by less parental monitoring. These findings suggest that maternal caregivers with mental health symptoms may need specific interventions that provide assistance and support in monitoring their teens in order to reduce sexual risk taking among adolescents in mental health treatment. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Insulin-Dependent H2O2 Production Is Higher in Muscle Fibers of Mice Fed with a High-Fat Diet

Insulin resistance is defined as a reduced ability of insulin to stimulate glucose utilization. C57BL/6 mice fed with a high-fat diet (HFD) are a model of insulin resistance. In skeletal muscle, hydrogen peroxide (H₂O₂) produced by NADPH oxidase 2 (NOX2) is involved in signaling pathways triggered by insulin. We evaluated oxidative status in skeletal muscle fibers from insulin-resistant and control mice by determining H₂O₂ generation (HyPer probe), reduced-to-oxidized glutathione ratio and NOX2 expression. After eight weeks of HFD, insulin-dependent glucose uptake was impaired in skeletal muscle fibers when compared with control muscle fibers. Insulin-resistant mice showed increased insulin-stimulated H₂O₂ release and decreased reduced-to-oxidized glutathione ratio (GSH/GSSG). In addition, p47^phox and gp91^phox (NOX2 subunits) mRNA levels were also high (~3-fold in HFD mice compared to controls), while protein levels were 6.8- and 1.6-fold higher, respectively. Using apocynin (NOX2 inhibitor) during the HFD feeding period, the oxidative intracellular environment was diminished and skeletal muscle insulin-dependent glucose uptake restored. Our results indicate that insulin-resistant mice have increased H₂O₂ release upon insulin stimulation when compared with control animals, which appears to be mediated by an increase in NOX2 expression.