Nonlinear NMR in 3He-B with arbitrary orientation

The high -field nonlinear NMR absorption signal of the B phase of ³He with an arbitrary orientation of the rotation axis n with respect to the field is calculated to third order in the amplitude of the perpendicular magnetization. An instability like those in ferromagnetic resonances is predicted, which changes its asymmetry with respect to the sense of sweeping at an orientation angle of 35 .On leave of absence from the Technical University of Munich. Postdoctoral Research Fellow of the DFG (German Science Foundation).     

A Paradigm for Dynamic Coordination of Multiple Robots

In this paper, we present a paradigm for coordinating multiple robots in the execution of cooperative tasks. The basic idea in the paper is to assign to each robot in the team, a role that determines its actions during the cooperation. The robots dynamically assume and exchange roles in a synchronized manner in order to perform the task successfully, adapting to unexpected events in the environment. We model this mechanism using a hybrid systems framework and apply it in different cooperative tasks: cooperative manipulation and cooperative search and transportation. Simulations and real experiments demonstrating the effectiveness of the proposed paradigm are presented.     

Experiences with SLALOM on the distributed Pleiades/ESP system

The paper describes experiences gained during the process of Implementing a standard serial benchmark (SLALOM) on a distributed computing system (Pleiades running ESP/C⁺⁺). Based on a real problem In computer graphics, SLALOM Is a timed benchmark that Includes problem set-up and I/O costs. The purpose of our experiments has been to maximize the speedup of a distributed implementation of SLALOM when compared to Its serial implementation. As a result of these experiments, we have developed several guidelines for adapting algorithms for distributed systems.     

Oxidation reactions with in situ generated oxidants

The main achievements and future prospects of in situ oxidations are discussed, focusing on the advantages and limits of the technique. This is based on hydrogen peroxide, peracids, metal peroxo and metal oxo species, generated in situ by oxygen and a reducing agent: hydrogen, carbon monoxide, metallic iron or zinc, hydrides, aldehydes and other organic reductants. Hydrogen peroxide and hydrogen, respectively, are preferred reagents for the inherent cleanliness of their use, producing only water as the byproduct. Examples are the epoxidation of propylene by air and alkylated anthrahydroquinones, catalysed by titanium silicalite (TS-1), and the hydroxylation of alkanes and aromatics on TS-1 and on other heterogeneous catalysts loaded with noble metals. The halogenation of phenol with hydrogen/oxygen/halogenidric acid mixtures on Pd/TS-1, has also been reported. Carbon monoxide was used to replace hydrogen in in situ oxidations occurring at higher temperatures. Reducing agents other than hydrogen and carbon monoxide lead to the formation of more than stoichiometric amounts of coproducts, which add complexity to the overall process for their separation and recycle/disposal. In the in situ oxidations by Gif^III/IV systems and by aldehyde/oxygen mixtures, large amounts of metallic wastes and carboxylic acid are co-produced, respectively, hindering their application in bulk chemicals production. Future developments might arise from the design of superior catalysts both for the in situ generation of hydrogen peroxide or peroxidic species from oxygen/hydrogen mixtures and for its subsequent efficient use. Oxygen/carbon monoxide and nitrous oxide can replace hydrogen/oxygen in oxidations at progressively higher temperatures, albeit no in situ oxidation with N₂O as yet has been reported. The general features of hydrogen peroxide and nitrous oxide are briefly compared and discussed.     

Combined effect of lignosulfonate and carbonate on pure portland clinker compounds hydration. IV. Hydration of tricalcium aluminate-sodium oxide solid solution

The combined effect of lignosulfonate and sodium carbonate on the hydration of C₃A and C₃ANa₂O solid solution was examined by DTG and TG curves, by XRD analysis and by zeta potential measurements. It is confirmed that the simultaneous addition of lignosulfonate and carbonate completely blocks the C₃A hydration with an induction period whose length is proportional to the percentage of admixtures. On the other hand, no induction period was observed in the hydration of C₃ANa₂O solid solution in the presence of both lignosulfonate and carbonate. The effect of the admixtures on the zeta potential is substantially the same for C₃A and C₃ANa₂O solid solution. The liquefying effect of NC and lgs combined addition seems to be more pronounced on C₃A than on C₃ANa₂O solid solution.     

Particle Sizes of Fumed Silica

Fumed silica is a synthetic amorphous silicon dioxide produced by burning silicon tetrachloride in an oxygen-hydrogen flame. Surface areas range from 50–400 m²/g. Using particle sizing techniques, fumed silica shows micron sized particles leading to surface areas markedly lower than expected. Fumed silica appears as a fluffy solid with bulk densities down to 0.03 g/cm³, being invariant over the wide range of surface areas. Attempts to relate the variation of the surface area directly to the performance of fumed silica in technical applications, such as its thickening efficiency in fluids, mainly fail and remain ambiguous.     

Reactive blending methodologies for biopol

Multicomponent polymeric systems containing Biopol as one of the phases are described as obtained according to two different procedures: radical polymerization of an acrylic polymer in the presence of Biopol, and melt-mixing of Biopol with polycaprolactone in the presence of peroxide. The decomposition of peroxide causes, in both cases, the formation of intergrafted species responsible for interfacial activity and compatibilization. The results of chemical, chemical–physical, morphological and mechanical tests, confirming the occurrence of such interactions, are reported.     

Nanomodified NiFe- and NiFeP-carbon felt as anode electrocatalysts in yeast-biofuel cell

The improvement of the electron transfer from the microorganisms to the anode is considered to be one of the most important factors for increasing the biofuel cell efficiency. In our recent study, a significant improvement of the yeast-biofuel cell output was achieved by application of Ni-modified carbon felt anodes. In this study, the electrocatalytic properties of new nanomodified carbon materials were investigated. Nickel–iron and nickel–iron–phosphorous nanostructures were electrodeposited on carbon felt by means of pulse plating technique. The produced materials were analyzed for cytotoxicity and applied as anodes in a double-chamber mediatorless yeast-biofuel cell. The use of all modified electrodes resulted in increase of the biofuel cell outputs in comparison with those obtained with non-modified carbon felt; however, higher maximum power density values, exceeding up to 5-folds that of the control, have been achieved with NiFeP-carbon felt anodes. The observed electrocatalytic effects were connected with the particular elemental content, size distribution, and morphology of modified materials as well as with a hypothesis for switching on adaptive mechanisms as a response to Ni and Fe presence, resulting in facilitated electron transfer across the cell membrane.