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排序方式: 共有598条查询结果,搜索用时 15 毫秒
551.
Roles have been widely used for modeling theauthority, responsibility, functions, and interactions,associated with manager positions within organizations.In this paper, we discuss the issues related tospecifying roles for both human and automated managersof distributed computer systems. The starting point isthat a role can be defined in terms of the authorizationand obligation policies, for a particular managerposition, which specify what actions the manager ispermitted or is obliged to do on a set of targetobjects. This permits individuals to be assigned orremoved from positions without respecifying the policiesfor the role. However these policies are insufficientfor fully specifying relationships between managers andthe targets they manage or between different managerroles. There is a need to specify the interactionprotocols and how managers coordinate and synchronizetheir activities. The role-based framework consists ofa set of tools enabling the creation of roles frompolicies, the specification of the concurrencyconstraints for role activities and the specification ofprotocols for role interaction. In addition, the issuesrelated to conflicts which can occur between policieswithin a role or between interacting roles are brieflydiscussed. 相似文献
552.
Dauerschwingversuche an Flachproben aus geschmiedeten und gewalzten Blechen zweier Titanlegierungen unter Planbiegung sowie an Rundproben aus geschmiedeten Stangen unter Zug-Druck-, Umlaufbiege- und Verdrehwechselbelastung. Einfluß von Probenform und -fertigung sowie Wärmebehandlung und Beanspruchungsart auf die Wechselfestigkeit. Ermittlung der Kerbwirkungszahlen. Metallographische Untersuchungen über die Ursachen der Lebensdauerstreuungen und Ausbreitung von Dauerbruchanrissen. Vergleich der Ergebnisse mit Angaben im Schrifttum. 相似文献
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555.
A CAD system based on combining structural optimization methods and graphical interaction is presented. The optimization methods implement the automated decisions and algorithms while the interaction provides the means to implement the designer's decisions. A new interactive optimization procedure for optimal truss design is proposed. The structural topology, geometry and member sizes are treated as design variables. Results show that the system provides a powerful tool to obtain a practical optimum design. 相似文献
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558.
The decomposition of small amounts (100 ppb) of tri- or perchloroethylene in drinking water has been investigated. The combined action of γ-radiation and ozone results in a considerable synergistic effect. Furthermore, the presence of ozone eliminates completely the formation of nitrite occurring under γ-irradiation alone. 相似文献
559.
Emil Simiu 《Engineering Structures》1981,3(4):242-248
This is the second in a series of review papers devoted to the state-of-the-art in wind engineering. The first paper, consisting of an introduction to the series and a discussion of engineering aspects of the wind environment, is published in this issue of Engineering Structures, pp233–241. 相似文献
560.
Keller Donald A.; Shibata Masayuki; Marcus Emil; Ornstein Rick L.; Rein Robert 《Protein engineering, design & selection : PEDS》1995,8(9):893-904
The fuzzy end elimination theorem (FEE) is a mathematicallyproven theorem that identifies rotameric states in proteinswhich are incompatible with the global minimum energy conformation.While implementing the FEE we noticed two different aspectsthat directly affected the final results at convergence. First,the identification of a single dead-ending rotameric state cantrigger a domino effect that initiates the identificationof additional rotameric states which become dead-ending. A recursivecheck for deadending rotameric states is therefore necessaryevery time a dead-ending rotameric state is identified. It isshown that, if the recursive check is omitted, it is possibleto miss the identification of some dead-ending rotameric statescausing a premature termination of the elimination process.Second, we examined the effects of removing dead-ending rotamericstates from further considerations at different moments of time.Two different methods of rotameric state removal were examinedfor an order dependence. In one case, each rotamer found tobe incompatible with the global minimum energy conformationwas removed immediately following its identification. In theother, dead-ending rotamers were marked for deletion but retainedduring the search, so that they influenced the evaluation ofother rotameric states. When the search was completed, all markedrotamers were removed simultaneously. In addition, to expandfurther the usefulness of the FEE, a novel method is presentedthat allows for further reduction in the remaining set of conformationsat the FEE convergence. In this method, called a tree-basedsearch, each dead-ending pair of rotamers which does not leadto the direct removal of either rotameric state is used to reducesignificantly the number of remaining conformations. In thefuture this method can also be expanded to triplet and quadrupletsets of rotameric states. We tested our implementation of theFEE by exhaustively searching ten protein segments and foundthat the FEE identified the global minimum every time. For eachsegment, the global minimum was exhaustively searched in twodifferent environments: (i) the segments were extracted fromthe protein and exhaustively searched in the absence of thesurrounding residues; (ii) the segments were exhaustively searchedin the presence of the remaining residues fixed at crystal structureconformations. We also evaluated the performance of the methodfor accurately predicting side chain conformations. We examinedthe influence of factors such as type and accuracy of backbonetemplate used, and the restrictions imposed by the choice ofpotential function, parameterization and rotamer database. Conclusionsare drawn on these results and future prospects are given 相似文献