Zirconium tungstate/cyanate ester nanocomposites with tailored thermal expansivity

The dimensional stability of polymer matrix composites can be enhanced by reducing the mismatch in the coefficient of thermal expansion (CTE) between the high CTE polymer matrix and low CTE fiber reinforcements, which leads to development of residual stresses and matrix microcracking. A potential strategy to diminish these residual stresses involves development of polymer nanocomposites with well dispersed nanoparticles that reduce the extent of mismatch in CTE. In this work, we explore the potential for development of bulk polymer nanocomposites with tailored thermal expansivity through incorporation of zirconium tungstate nanoparticles that are characterized by a negative CTE in a unique low viscosity bisphenol E cyanate ester (BECy) thermosetting polymer matrix. Incorporation of up to 10 vol.% whisker-like nanoparticles, synthesized by a hydrothermal method, results in a 20% reduction in the CTE of the polymer matrix. However, the nanoparticles exert a dramatic catalytic effect on the cure reaction of BECy resin and subsequently decrease the onset temperature of the glass transition for the cured polymer network, at high filler loadings.     

A methodology for fast scheduling of partitioned systolic algorithms

Various methods for mapping signal processing algorithms into systolic arrays have been developed in the past few years. In this paper, efficient scheduling techniques are developed for the partitioning problem, i.e. problems with size that do not match the array size. In particular, scheduling for the Locally Parallel-Globally Sequential (LPGS) technique and the Locally Sequential-Globally Parallel (LSGP) technique are developed. The scheduling procedure developed exploits the fact that after LPGS and LSGP partitioning, the locality constraints are less stringent allowing for more flexibility in the choice of algorithms and inter-processor communication. A flexible scheduling order is developed that is useful in evaluating the trade-off between execution time and size of storage buffers. The benefits of the scheduling techniques are illustrated with the help of matrix multiplication and least squares examples. This work was supported in part by the UCSD/NSF Integrated Circuits And Systems Research Center and by the ARMY Research Office under Grant No. DAAL-03-90-G-0095.     

Cobalt based nanostructured alloys: Versatile high performance robust hydrogen evolution reaction electro-catalysts for electrolytic and photo-electrochemical water splitting

Engineering reduced noble metal containing electro-catalysts exhibiting superior electrochemical performance is important for efficient and economic production of hydrogen from electrolytic and photoelectrochemical (PEC) water splitting reactions. In this study, nanostructured Co–Ir solid solution alloys, Co_1?x(Ir_x) (x = 0.2, 0.3, 0.4) have been studied as electro-catalysts for hydrogen evolution reaction (HER). Co_1?x(Ir_x) (x = 0.3, 0.4) exhibit similar onset over-potential to Pt/C and lower over-potential required for Co_1?x(Ir_x) (x = 0.3, 0.4) than Pt/C in acidic, neutral as well as basic media, suggesting excellent electrochemical activity of Co–Ir alloys, further studied using theoretical first principles density functional theory calculations. Co_1?x(Ir_x) exhibit excellent electrochemical stability in acidic media similar to that of Pt/C. The applied bias photon-to-current efficiency obtained using Co_1?x(Ir_x) (x = 0.3, 0.4) electro-catalysts and (Sn_0.95Nb_0.05)O₂:N-600 NTs as photoanode in H-type cell is ～5.74% and ～7.92%, respectively which is ～40% and ～93% higher than Pt/C (～4.1%) indicating considerable promise of the system.     

Pushing the frontiers of first-principles based computer simulations of chemical and biological systems

The Laboratory of Computational Chemistry and Biochemistry is active in the development and application of first-principles based simulations of complex chemical and biochemical phenomena. Here, we review some of our recent efforts in extending these methods to larger systems, longer time scales and increased accuracies. Their versatility is illustrated with a diverse range of applications, ranging from the determination of the gas phase structure of the cyclic decapeptide gramicidin S, to the study of G protein coupled receptors, the interaction of transition metal based anti-cancer agents with protein targets, the mechanism of action of DNA repair enzymes, the role of metal ions in neurodegenerative diseases and the computational design of dye-sensitized solar cells. Many of these projects are done in collaboration with experimental groups from the Institute of Chemical Sciences and Engineering (ISIC) at the EPFL.     

Cure characterization of soybean oil—Styrene—Divinylbenzene thermosetting copolymers

Bio‐based resins are an alternative to petroleum‐based resins in the production of fiber‐reinforced polymers (FRPs) by processes such as pultrusion. A detailed understanding of the cure behavior of the resin is essential to determine the process variables for production of FRPs. In this work, the cure kinetics of soybean oil‐styrene‐divinylbenzene thermosetting polymers is characterized by differential scanning calorimetry (DSC) measurements. By varying the concentration of the cationic initiator from 1 to 3 weight percent (wt %), the most viable resin composition for pultrusion is identified. The ability of phenomenological reaction models to describe the DSC measurements for the optimum resin composition is tested and kinetic equations, which can be used to determine the degree of cure at any temperature and time, are determined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009