Electrochemical Properties of Si‐Ge Heterostructures as an Anode Material for Lithium Ion Batteries

Si‐Ge composites have recently been explored as an anode material for lithium‐ion batteries due to their stable cycle performance and excellent rate capability. Although previous reports show the benefits of Si‐Ge composites on electrochemical performance, the specific mechanism and structural effects have been overlooked. Here, the structural effect of Si‐Ge heterogeneous nanostructures on both mechanics and kinetics is systematically studied through theoretical analysis and detailed experimental results. Si‐Ge and Ge‐Si core–shell nanowires are employed for this study. The Si‐Ge core–shell nanowires show a much improved electrochemical performance, especially cycle performance and rate capability, when compared to those of the Ge‐Si core–shell nanowires electrode. On the basis of the detailed experimental results and associated theoretical analysis, its is demonstrated that the strain distribution and Li diffusivity and/or diffusion path are significantly affected by the Si‐Ge heterostructure, which induce different mechanics and kinetics associated with lithium.     

Residual stress measurements in melt infiltrated SiC/SiC ceramic matrix composites using Raman spectroscopy

Raman spectroscopy was utilized to characterize the chemical composition and residual stresses formed in melt infiltrated SiC/SiC CMCs during processing. Stresses in SiC fibers, in SiC chemical vapor (CVI) infiltrated matrix, in SiC melt infiltrated matrix, and in free silicon were measured for two different plates of CMCs. Stresses in the free silicon averaged around 2?GPa in compression, while stresses in the matrix SiC were 1.45?GPa in tension. The SiC CVI phase had stresses ranging between 0.9?GPa and 1.2?GPa in tension and the SiC fibers experienced stresses of .05–0.7?GPa in tension. These results were validated with the proposed model of the system. While the mismatch in the coefficients of thermal expansion between the constituents contributes to the overall residual stress state, the silicon expansion upon solidification was found to be the major contributor to residual stresses within the composite.     

Visual activity in Hollywood film: 1935 to 2005 and beyond.

The structure of Hollywood film has changed in many ways over the last 75 years, and much of that change has served to increase the engagement of viewers' perceptual and cognitive processes. We report a new physical measure for cinema—the visual activity index (VAI)—that reflects one of these changes. This index captures the amount of motion and movement in film. We define whole-film VAI as (1 – median r), reflecting the median correlation of pixels in pairs of near-adjacent frames measured along the entire length of a film or film sequence. Analyses of 150 films show an increase in VAI from 1935 to 2005, with action and adventure films leading the way and with dramas showing little increase. Using these data and those from three more recent high-intensity films, we explore a possible perceptual and cognitive constraint on popular film: VAI as a function of the log of sequence or film duration. We find that many “queasicam” sequences, those shot with an unsteady camera, often exceed our proposed constraint. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Shear‐Stress‐Mediated Refolding of Proteins from Aggregates and Inclusion Bodies

Recombinant protein overexpression of large proteins in bacteria often results in insoluble and misfolded proteins directed to inclusion bodies. We report the application of shear stress in micrometer‐wide, thin fluid films to refold boiled hen egg white lysozyme, recombinant hen egg white lysozyme, and recombinant caveolin‐1. Furthermore, the approach allowed refolding of a much larger protein, cAMP‐dependent protein kinase A (PKA). The reported methods require only minutes, which is more than 100 times faster than conventional overnight dialysis. This rapid refolding technique could significantly shorten times, lower costs, and reduce waste streams associated with protein expression for a wide range of industrial and research applications.     

Platinum nanoparticle shape effects on benzene hydrogenation selectivity

Benzene hydrogenation was investigated in the presence of a surface monolayer consisting of Pt nanoparticles of different shapes (cubic and cuboctahedral) and tetradecyltrimethylammonium bromide (TTAB). Infrared spectroscopy indicated that TTAB binds to the Pt surface through a weak C-H...Pt bond of the alkyl chain. The catalytic selectivity was found to be strongly affected by the nanoparticle shape. Both cyclohexane and cyclohexene product molecules were formed on cuboctahedral nanoparticles, whereas only cyclohexane was produced on cubic nanoparticles. These results are the same as the product selectivities obtained on Pt(111) and Pt(100) single crystals in earlier studies. The apparent activation energy for cyclohexane production on cubic nanoparticles is 10.9 +/- 0.4 kcal/mol, while for cuboctahedral nanoparticles, the apparent activation energies for cyclohexane and cyclohexene production are 8.3 +/- 0.2 and 12.2 +/- 0.4 kcal/mol, respectively. These activation energies are lower, and corresponding turnover rates are three times higher than those obtained with single-crystal Pt surfaces.     

Extending the Salinilactone Family

Five new members of the salinilactone family, salinilactones D–H, are reported. These bicyclic lactones are produced by Salinispora bacteria and display extended or shortened alkyl side chains relative to the recently reported salinilactones A–C. They were identified by GC/MS, gas chromatographic retention index, and comparison with synthetic samples. We further investigated the occurrence of salinilactones across six newly proposed Salinispora species to gain insight into how compound production varies among taxa. The growth-inhibiting effect of this compound family on multiple biological systems including non-Salinispora actinomycetes was analyzed. Additionally, we found strong evidence for significant cytotoxicity of the title compounds.