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971.
Mary J. Brown Andrea A. Mammoli Marc S. Ingber 《International journal for numerical methods in engineering》2003,58(11):1617-1635
The evaluation of a domain integral is the dominant bottleneck in the numerical solution of viscous flow problems by vorticity methods, which otherwise demonstrate distinct advantages over primitive variable methods. By applying a Barnes–Hut multipole acceleration technique, the operation count for the integration is reduced from O(N2) to O(NlogN), while the memory requirements are reduced from O(N2) to O(N). The algorithmic parameters that are necessary to achieve such scaling are described. The parallelization of the algorithm is crucial if the method is to be applied to realistic problems. A parallelization procedure which achieves almost perfect scaling is shown. Finally, numerical experiments on a driven cavity benchmark problem are performed. The actual increase in performance and reduction in storage requirements match theoretical predictions well, and the scalability of the procedure is very good. Copyright © 2003 John Wiley Sons, Ltd. 相似文献
972.
William Messner Marc Bodson 《International Journal of Adaptive Control and Signal Processing》1995,9(2):199-212
The paper investigates the design of adaptive feedforward cancellation (AFC) algorithms with sinusoidal regressors for repetitive control. Such adaptive algorithms are equivalent to linear controllers based on the internal model principle (IMP). Using this equivalence and root locus rules, the phase advance of the regressor of the adaptive algorithm can be chosen to maximize the phase margin at low gains. A surprising result is that selecting the optimal phase advance is equivalent to placing a zero in the open right half-plane in certain cases. A complete design and analysis for the compensation of a single-frequency periodic disturbance is done. A new variation of the AFC algorithm is also developed in which the adaptive portion acts in parallel with a feedthrough term. the IMP equivalent of this algorithm has two zeros instead of one. Analysis and simulation show this method to have superior convergence and robustness properties when compared with the method having no feedthrough term. Discrete time versions of the algorithms are briefly considered. 相似文献
973.
Koivula Anu; Reinikainen Tapani; Ruohonen Laura; Valkeajarvi Anne; Claeyssens Marc; Teleman Olle; Kleywegt Gerard J.; Szardenings Michael; Rouvinen Juha; Jones T.Alwyn; Teeri Tuula T. 《Protein engineering, design & selection : PEDS》1996,9(8):691-699
Trichoderma reesei cellobiohydrolase II (CBHII) is an exoglucanasecleaving primarily cellobiose units from the non-reducing endof cellulose chains. The ß-l,4 glycosidic bond iscleaved by acid catalysis with an aspartic acid, D221, as thelikely proton donor, and another aspartate, D175, probably ensuringits protonation and stabilizing charged reaction intermediates.The catalytic base has not yet been identified experimentally.The refined crystal structure of CBHII also shows a tyrosineresidue, Y169, located close enough to the scissile bond tobe involved in catalysis. The role of this residue has beenstudied by introducing a mutation Y169F, and analysing the kineticand binding behaviour of the mutated CBHII. The crystal structureof the mutated enzyme was determined to 2.0 Å resolutionshowing no changes when compared with the structure of nativeCBHII. However, the association constants of the mutant enzymefor cellobiose and cellotriose are increased threefold and for4-methylumbelliferyl cellobioside over 50-fold. The catalyticconstants towards cellotriose and cellotetraose are four timeslower for the mutant. These data suggest that Y169, on interactingwith a glucose ring entering the second subsite in a narrowtunnel, helps to distort the glucose ring into a more reactiveconformation. In addition, a change in the pH activity profilewas observed. This indicates that Y169 may have asecond rolein the catalysis, namely to affect the protonation state ofthe active site carboxylates, D175 and D221. 相似文献
974.
W. G. Keilin and L. J. Bloom (1986) explored 70 issues related to child custody evaluation practices. The current study replicates Keilin and Bloom's study and looks at an additional 42 items. Two hundred and one psychologists from 39 states were surveyed about 112 aspects of child custody evaluation practices. The analysis was divided into evaluation practices, sole-joint custody decision making, and recommendations. Comparisons between the findings of this study and those of Keilin and Bloom are made. The current practice of child custody evaluations is reported. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
975.
John R. Hobdell Marc S. Lavine Alan H. Windle 《Journal of Computer-Aided Materials Design》1996,3(1-3):359-368
Summary Liquid-crystalline polymers exhibit fascinating structure at many size scales. This paper describes how computer models at different size scales can be linked together by a hierarchical approach to give a better understanding of the properties and behaviour of these materials. The atomic scale is considered first, where semi-empirical molecular orbital techniques are used to calculate the torsional energy functions associated with rotating the backbone bonds of the polymer. Secondly, entire chains are simulated using a Monte Carlo technique based on the torsional energy functions to deduce the persistence length of the polymer of interest. A theoretical relationship enables the Frank elastic constants to be determined from the persistence length. The elastic constants may then be used as input parameters for models both to predict microstructure and to help understand the role of defects in the shear flow of these materials. The hierarchical approach provides a meaningful framework within which data obtained from small-scale models are used to parameterise models at a larger scale. 相似文献
976.
In the policy literature, crises are often presented as opportunities for reform initiation. Little is known, however, about the effects that crises may have on the implementation of such reform initiatives. This article explores how a crisis may affect the administrative relations between central authorities and field administrations. The crisis impact on central-field relations appears to be twofold. First, a crisis may facilitate, if not induce, the centralization of decision-making processes. Secondly, a crisis may affect the degree of consensus between central authorities and field administrations with regard to problem definitions and preferred solutions. This paper uses a case study of the Dutch prison system to explore the crisis impact on these two dimensions of central-field relations. In this particular case, crisis circumstances did not facilitate a successful implementation of a major policy overhaul. We suggest that crises may offer opportunities for reform implementation, but only under highly restricted conditions. When these conditions are not met, crises may have perverse effects on central-field relations which limit the prospects for the effective implementation of reform. 相似文献
977.
An automatic noise parameter measurement test set is described in two sections : (i) A novel noise parameter extraction procedure from a set of noise figure measurements is developped. The experimental minimum noise figure is no longer required and the sensitivity to measurement incertainties is found to be very low. (ii) An automatic input tuner with a large number of precalibrated and reproducible positions is designed and realized. The last part give examples of broadband (8 to 17 GHz) noise parameters characterization ofmmic GaAsmesfets when both the automatic tuner and the extraction procedure are used. 相似文献
978.
Thousands of man-made chemicals are annually released into the environment by agriculture, transport, industries, and other human activities. In general, chemical analysis of environmental samples used to assess the pollution status of a specific ecosystem is complicated by the complexity of the mixture, and in some cases by the very low toxicity thresholds of chemicals present. In that sense, a proteomics approach, capable of detecting subtle changes in the level and structure of individual proteins within the whole proteome in response to the altered surroundings, has obvious applications in the field of ecotoxicology. In addition to identifying new protein biomarkers, it can also help to provide an insight into underlying mechanisms of toxicity. Despite being a comparatively new field with a number of caveats, proteomics applications have spread from microorganisms and plants to invertebrates and vertebrates, gradually becoming an established technology used in environmental research. This review article highlights recent advances in the field of environmental proteomics, mainly focusing on experimental approaches with a potential to understand toxic modes of action and to identify novel ecotoxicological biomarkers. 相似文献
979.
980.
Véronique Verrez-Bagnis Marc Jér?me 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1995,201(3):230-235
Paramyosin is a muscle protein which is characteristic of all invertebrates but which is not present in vertebrate muscles. Given the functional importance of paramyosin, the purpose of this paper was to study the physico-chemical properties, including the amino acid composition and rheological behaviour, of purified paramyosin and to investigate its mode of interaction with myosin. Paramyosin was purified from the limpet (Patella caerula) by an ethanol precipitation step. It was soluble at ionic strengths below 0.05 m NaCl and its maximum solubility at neutral pH occurred at approximately 0.4 M NaCl. At this high ionic strength, the pH dependence of solubility was such that paramyosin passed quickly into solution when pH exceeded pH 5, the transitional pH value. By using an immunological method, it was shown that interactions between paramyosin and myosin occurred, even in the presence of actin. The molecular assembly of both proteins was probably specified by hydrophobic interactions, as well as by interactions enhanced by divalent cations. The changes in the dynamic shear storage modulus (G) started between 40°C and 50°C, and reached a maximum at about 75°C. 相似文献