Nucleation and growth of nickel by electrodeposition under galvanostatic conditions

The first stages of nickel electrodeposition on amorphous carbon and polycrystalline silver substrates have been studied under galvanostatic conditions. An island growth mode is observed on the two types of substrate. For equivalent conditions the cluster density is higher on silver substrates than on carbon substrates. Dissolution of some nickel clusters is observed a short time after the onset of electrolysis on carbon substrates. This is confirmed by the evolution of the current efficiency and the evolution of the metal surface cluster density as a function of the quantity of electricity.     

A hyperheuristic approach to examination timetabling problems: benchmarks and a new problem from practice

Many researchers studying examination timetabling problems focus on either benchmark problems or problems from practice encountered in their institutions. Hyperheuristics are proposed as generic optimisation methods which explore the search space of heuristics rather than direct solutions. In the present study, the performance of tournament-based hyperheuristics for the exam timetabling problem are investigated. The target instances include both the Toronto and ITC 2007 benchmarks and the examination timetabling problem at KAHO Sint-Lieven (Ghent, Belgium). The Toronto and ITC 2007 benchmarks are post-enrolment-based examination timetabling problems, whereas the KAHO Sint-Lieven case is a curriculum-based examination timetabling problem. We drastically improve the previous (manually created) solution for the KAHO Sint-Lieven problem by generating a timetable that satisfies all the hard and soft constraints. We also make improvements on the best known results in the examination timetabling literature for seven out of thirteen instances for the To ronto benchmarks. The results are competitive with those of the finalists of the examination timetabling track of the International Timetabling Competition.     

Application of single-level,pointwise algebraic,and smoothed aggregation multigrid methods to direct numerical simulations of incompressible turbulent flows

Single- and multi-level iterative methods for sparse linear systems are applied to unsteady flow simulations via implementation into a direct numerical simulation solver for incompressible turbulent flows on unstructured meshes. The performance of these solution methods, implemented in the well-established SAMG and ML packages, are quantified in terms of computational speed and memory consumption, with a direct sparse LU solver (SuperLU) used as a reference. The classical test case of unsteady flow over a circular cylinder at low Reynolds numbers is considered, employing a series of increasingly fine anisotropic meshes. As expected, the memory consumption increases dramatically with the considered problem size for the direct solver. Surprisingly, however, the computation times remain reasonable. The speed and memory usage of pointwise algebraic and smoothed aggregation multigrid solvers are found to exhibit near-linear scaling. As an alternative to multi-level solvers, a single-level ILUT-preconditioned GMRES solver with low drop tolerance is also considered. This solver is found to perform sufficiently well only on small meshes. Even then, it is outperformed by pointwise algebraic multigrid on all counts. Finally, the effectiveness of pointwise algebraic multigrid is illustrated by considering a large three-dimensional direct numerical simulation case using a novel parallelization approach on a large distributed memory computing cluster.     

Effects of molecular oxygen on multiphoton-excited photochemical analysis of hydroxyindoles

We have examined the effects of dissolved molecular oxygen on multiphoton-excited (MPE) photochemical derivatization of serotonin (5HT) and related cellular metabolites in various buffer systems and find that oxygen has a profound effect on the formation efficiency of visible-emitting photoproducts. Previously, end-column MPE photoderivatization provided low mass detection limits for capillary electrophoretic analysis of hydroxyindoles, but relied on the use of Good's buffers to generate high-sensitivity visible signal. In the present studies, visible emission from 5HT photoderivatized in different buffers varied by 20-fold under ambient oxygen levels but less than 2-fold in the absence of oxygen; oxygen did not significantly alter the photoproduct excited-state lifetime (approximately 0.8 ns). These results support a model in which oxygen interferes with formation of visible-emitting photoproducts by quenching a reaction intermediate, an effect that can be suppressed by buffer molecules. Deoxygenation of capillary electrophoresis separation buffers improves mass detection limits for 5-hydroxyindoles fractionated in 600-nm channels by approximately 2-fold to < or =30000 molecules and provides new flexibility in identifying separation conditions for resolving 5HT from molecules with similar electrophoretic mobilities, such as the catecholamine neurotransmitters.     

Identification of potent human anti-IL-1RI antagonist antibodies

Interleukin-1 (IL-1) blockade by IL-1 receptor antagonist benefits some arthritis patients by reducing joint damage. This fact inspired us to develop antagonist human therapeutic antibodies against IL-1R(I) using phage libraries that display single-chain variable fragment (scFv) antibody fragments. Panning libraries against human IL-1R(I) generated 39 unique scFv-phage whose binding to IL-1R(I) was competed by IL-1 ligands. Fifteen of these scFv-phage, identified using IL-1R(I)-binding assays and dissociation rate ranking, were reformatted as scFv-Fc and IgG(4) molecules. The ease of producing antibodies in the scFv-Fc format permitted rapid identification of four lead clones (C10, C13, C14, C15) that inhibit NF-kappaB nuclear translocation induced by IL-1. Reformatting these clones as IgG(4) molecules increased their inhibition potency by 相似文献   

An in situ study of metal complexation by an immobilized synthetic biopolymer using tapping mode liquid cell atomic force microscopy

Near-field scanning optical microscopy and tapping mode, liquid cell atomic force microscopy were used to study the conformational changes in simple short-chain silica-immobilized biopolymer, poly(L-cysteine) (PLCys), as the polymer was exposed to reducing, metal-rich, and acidic environments, respectively, to simulate on-line metal preconcentration. In a reducing environment (0.01 M dithiothreitol in pH 7.0 ammonium acetate buffer), the PLCys features resembled islands on the surface of the glass, 36 +/- 7 nm in height and 251 +/- 60 nm in diameter. Upon exposure to metal (Cd2+ buffered at pH 7.0), the PLCys islands broke up into smaller metal binding clusters whose features were lower in height, 22 +/- 5 nm, and diameter, 213 +/- 53 nm. Exposure to 0.01 M HCl used for metal stripping resulted in protonation of the polymer chains and further reduction in the polymer height to 12 +/- 5 nm. These changes in molecular structure have given new insight into the mechanisms involved to achieve strong binding as well as rapid, quantitative release of bound metals to flexible short-chain synthetic biopolymers.