Fabrication of a composite powder and its application as an active brazing alloy

A copper-based active brazing alloy containing a high titanium content was produced by an electroless coating technique. Particles with a narrow density distribution were produced by deposition of nano-copper on a fine titanium powder. Both conventional titanium powder and sponge titanium were studied. The effects of pH and time on copper deposition were investiguated.Higher pH was found to increase the quantity of copper deposited. Using multiple depositions, a copper-titanium ratio of 75 wt% copper-25 wt% titanium could be achieved after several platings for pH varying between 12 and 12.8. The particle size distribution of the composite powder shows uniform growth of the copper shell and no agglomeration under pH 12. Major agglomeration of the final powder was observed for a bath pH of 12.8.Complete melting of the composite powder has been studied by DSC and the sessile drop technique. Melting began within the diffusion zone formed at the interface through the Cu₄Ti → Cu(s) + L peritectic reaction that occurs at 885^∘C. The melting process continued by successive peritectic reactions and dissolution of the remaining elements of the diffusion couple. The wetting behavior of this alloy was evaluated on different ceramic substrates (Al₂O₃, Si₃N₄) and found to be similar to literature observations.     

Quantifying construct validity: Two simple measures.

Construct validity is one of the most central concepts in psychology. Researchers generally establish the construct validity of a measure by correlating it with a number of other measures and arguing from the pattern of correlations that the measure is associated with these variables in theoretically predictable ways. This article presents 2 simple metrics for quantifying construct validity that provide effect size estimates indicating the extent to which the observed pattern of correlations in a convergent-discriminant validity matrix matches the theoretically predicted pattern of correlations. Both measures, based on contrast analysis, provide simple estimates of validity that can be compared across studies, constructs, and measures meta-analytically, and can be implemented without the use of complex statistical procedures that may limit their accessibility. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phase evolution of Mg–Al–Zr nanophase alloys prepared by mechanical alloying

Al–Mg and Al–Mg–Zr alloys were processed by mechanical alloying. The phase constitution of the powders was strongly dependent on the composition of the starting mixture. In as-milled powders, an Al(Mg) solid solution was formed with up to 40 at% Al, which after annealing transformed to the equilibrium β-Al₃Mg₂ phase. For high Mg concentrations (60–90 at%) the dominant phase was γ-Al₁₂Mg₁₇ in accordance with the equilibrium phase diagram. The addition of Zr led to the appearance of Zr–Al intermetallics causing Mg to precipitate out of the Al(Mg) solution. The effect of zirconium was also to refine the structure and to retard grain growth.     

Taylor vortex flow with suction

Perturbation methods are used to study the bifurcation of Couette flow to Taylor vortices in the presence of a small amount of suction flow through the inner cylinder. Taylor vortex flow is described as a small amplitude expansion of the velocity and pressure near the critical Gortler parameter. The suction flow modifies the critical G?rtler number, stabilizing the original Couette flow.     

Analysis of a natural resources management system in the Calakmul Biosphere Reserve

An analysis of the natural resource management system was carried out for the ejido X-kanha located in the northern part of the Calakmul Biosphere Reserve in Campeche, Mexico. Through field research using participatory rural appraisal (PRA), the activities carried out by different user groups were identified. Gender roles as well as age roles were analyzed. Results show that each family depends upon the diversification of productive activities in order to meet economic needs. Diversification of activities is carried out in both space and time, making use of different ecosystems during varied seasons throughout the year. Women's activities correspond to housekeeping and house administration; they take care of home gardens and are responsible for water collection and wood gathering. Men carry out the activities of working in the milpa, cattle raising, honey production, chicle collection, and wood felling.A series of PRA activities carried out with the people of X-Kanha led to the identification of limitations to more optimal uses of natural resources. The characterization of limitations and associated alternatives is used to provide a guideline to aid the efforts of NGOs and other organizations interested in the conservation of natural resources, and for the well-being of the local population.     

Development and Simulation of Sulfur‐doped Graphene Supported Platinum with Exemplary Stability and Activity Towards Oxygen Reduction

Sulfur‐doped graphene (SG) is prepared by a thermal shock/quench anneal process and investigated as a unique Pt nanoparticle support (Pt/SG) for the oxygen reduction reaction (ORR). Particularly, SG is found to induce highly favorable catalyst‐support interactions, resulting in excellent half‐cell based ORR activity of 139 mA mg_Pt ^?1 at 0.9 V vs RHE, significant improvements over commercial Pt/C (121 mA mg_Pt ^?1) and Pt‐graphene (Pt/G, 101 mA mg_Pt ^?1). Pt/SG also demonstrates unprecedented stability, maintaining 87% of its electrochemically active surface area following accelerated degradation testing. Furthermore, a majority of ORR activity is maintained, providing 108 mA mg_Pt ^?1, a remarkable 171% improvement over Pt/C (39.8 mA mg_Pt ^?1) and an 89% improvement over Pt/G (57.0 mA mg_Pt ^?1). Computational simulations highlight that the interactions between Pt and graphene are enhanced significantly by sulfur doping, leading to a tethering effect that can explain the outstanding electrochemical stability. Furthermore, sulfur dopants result in a downshift of the platinum d‐band center, explaining the excellent ORR activity and rendering SG as a new and highly promising class of catalyst supports for electrochemical energy technologies such as fuel cells.