多溴苊烯化合物的分子结构和热力学性质

多溴苊烯是潜在的一类有机污染物,本文采用密度泛函理论在B3LYP/6-311G**水平上,优化这类化合物的分子几何结构135个,获得它们在理想气态的一些热力学性质的数值,研究这些性质与取代的溴原子数目和位置的关系,根据各异构体的标准生成Gibbs自由能的相对大小,求出它们热力学稳定性的顺序。结果表明:大部分多溴苊烯分子具有平面的几何构型。最稳定及最不稳定异构体的△_fH~θ及△_fG~θ,都随Br原子数目增加而逐渐增加。溴原子数目相同的△_fH~θ和△_fG~θ与溴原子的取代位置有很大的关系,其相对稳定性由分子内Br…Br核排斥作用的强弱而决定。     

BLISS/S: a new method for two-level structural optimization

The paper describes a two-level method for structural optimization for a minimum weight under the local strength and displacement constraints. The method divides the optimization task into separate optimizations of the individual substructures (in the extreme, the individual components) coordinated by the assembled structure optimization. The substructure optimizations use local cross-sections as design variables and satisfy the highly nonlinear local constraints of strength and buckling. The design variables in the assembled structure optimization govern the structure overall shape and handle the displacement constraints. The assembled structure objective function is the objective in each of the above optimizations. The substructure optimizations are linked to the assembled structure optimization by the sensitivity derivatives. The method was derived from a previously reported two-level optimization method for engineering systems, e.g. aerospace vehicles, that comprise interacting modules to be optimized independently, coordination provided by a system-level optimization. This scheme was adapted to structural optimization by treating each substructure as a module in a system, and using the standard finite element analysis as the system analysis. A numerical example, a hub structure framework, is provided to show the new method agreement with a standard, no-decomposition optimization. The new method advantage lies primarily in the autonomy of the individual substructure optimization that enables concurrency of execution to compress the overall task elapsed time. The advantage increases with the magnitude of that task. Received December 5, 1999?Revised mansucript received April 26, 2000     

Optimality-criteria-based probabilistic structural design

The possibility of extending absolute minimum weight designs for sandwich beam systems or fibre-reinforced beams and plates is considered when both the extreme loading applied to the system and the beam bending resistance properties are described in probabilistic rather than deterministic terms. It is shown that such an extension is possible provided certain plausible assumptions are made about the probabilistic modelling of the system. Examples considered include simple and continuous beams under loading of uncertain magnitude, direction or location. It is shown that the classical (deterministic) optimal solutions remain valid under reasonable assumptions. The extension of the probabilistic solutions to a wider class of examples is discussed. Received October 20, 2000     

Structural Synthesis of Modular Weakly Connected Neural Networks. II. Nuclear Neural Networks

The simplest modular neural network is investigated, in which each module is a single-layer perceptron (a neural kernel). Numerical indices of quality by the criteria of operating speed and plasticity are proposed to characterize structural properties of nuclear neural networks. Based on the indices introduced, optimum procedures of structural synthesis are constructed.     

Analytical benchmarks for topological optimization IV: square-shaped line support

Michell’s problem of optimizing truss topology for stress or compliance constraints under a single load condition is solved analytically for plane trusses having a square-shaped line support. Geometrical characteristics of the Hencky nets giving the truss layout are expressed in terms of Lommel functions. Analytically derived truss volumes for the above problem are compared with those of trusses supported along circles of equivalent area. Some general implications of the results are also discussed.     

Design of laminated composite structures for optimum fiber direction and layer thickness,using optimality criteria

In this study, two optimality criteria are presented for optimum design of composite laminates using finite element method. Thickness of the layers and fiber orientation angles in each finite element are considered as the design variables. It will be shown that the optimum design of composite laminates with varying fiber orientations and layers thicknesses may be found by using these optimality criteria in an efficient way, without performing the sensitivity analysis.     

From concepts to consistent object specifications: Translation of a domain-oriented feature framework into practice

A steady increase in consumer demands,and severe constraints from both a somewhat damaged environment and newly installed government policies,require today‘s product design and development to be faster and more efficient than ever before,yet utilizing even fewer resources.New holistic approaches,such at total product life cycle modeling which embraces all aspercts of a product‘s life cycle,are current attempts to solve these problems,Within the field of product design and modeling,feature technology has proved to be one very promising solution component.Owing to the tremendous increase in information technology,to transfer from low level data processing towards knowledge modeling and information processing is about to bring a change in almost every computerized application.From this viewpoint,current problems of both feature frameworks and feature systems are analyzed in respect to static and dynamic consistency breakdowns.The analysis ranges from early stager of designing(feature)concepts to final system implementation and application.For the first tie,an integrated view is given on approaches,solutions and practical experience,with feature concepts and structures,providing both a feature framework and its implementation with sufficient system architecture and computational power to master a fair number of known consistency breakdowns,while providing for robust contexts for feature semantics and integrated models.Within today;s heavy use of information technology these are pre-requisites if the full potential of feature technology is to be successfully translated into practice.     

Classical Modal Display Logic in the Calculus of Structures and Minimal Cut-free Deep Inference Calculi for S5

We begin by showing how to faithfully encode the Classical ModalDisplay Logic (CMDL) of Wansing into the Calculus of Structures(CoS) of Guglielmi. Since every CMDL calculus enjoys cut-elimination,we obtain a cut-elimination theorem for all corresponding CoScalculi. We then show how our result leads to a minimal cut-freeCoS calculus for modal logic S5. No other existing CoS calculifor S5 enjoy both these properties simultaneously.     

Multidisciplinary Simulation of the Maneuvering of an Aircraft

A computational methodology for the simulation of the transient aeroelastic response of an unrestrained and flexible aircraft during high-G maneuvers is presented. The key components of this methodology are: (a) a three-field formulation for coupled fluid/structure interaction problems; (b) a second-order time-accurate and geometrically conservative flow solver for CFD computations on unstructured dynamic meshes; (c) a corotational finite element method for the solution of geometrically nonlinear and unrestrained structural dynamics problems; (d) a robust method for updating an unrestrained and unstructured moving fluid mesh; and (e) a second-order time-accurate staggered algorithm for time-integrating the coupled fluid/structure semi-discrete equations of motion. This computational methodology is illustrated with the simulation on a parallel processor of several three-dimensional high-G pullup maneuvers of the Langley Fighter in the transonic regime, using a detailed finite element aeroelastic model.