HYPOTHETICAL REASONING ABOUT ACTIONS: FROM SITUATION CALCULUS TO EVENT CALCULUS

Hypothetical reasoning about actions is the activity of preevaluating the effect of performing actions in a changing domain; this reasoning underlies applications of knowledge representation, such as planning and explanation generation. Action effects are often specified in the language of situation calculus, introduced by McCarthy and Hayes in 1969. More recently, the event calculus has been defined to describe actual actions, i.e., those that have occurred in the past, and their effects on the domain. Altough the two formalisms share the basic ontology of atomic actions and fluents, situation calculus cannot represent actual actions while event calculus cannot represent hypotethical actions. In this article, the language and the axioms of event calculus are extended to allow representing and reasoning about hypothetical actions, performed either at the present time or in the past, altough counterfactuals are not supported. Both event calculus and its extension are defined as logic programs so that theories are readily adaptable for Prolog query interpretation. For a reasonably large class of theories and queries, Prolog interpretation is shown to be sound and complete w.r.t. the main semantics for logic programs.     

Van der Waals coefficients and cohesive energies of lead chalcogenides

The cohesive energies of PbS PbSe and PbTe, having NaCl type of crystal structure, are calculated using the generalized Huggins-Mayer form (GHM) for the Born repulsion energy. The van der Waals interactions (VDW) are estimated from the London and Mayer formulae and compared with those estimated from the Slater-Kirkwood variational method. The cohesive energies calculated adopting the VDW coefficients calculated from the later method are in good agreement with the experimental values. The difference between the experimental cohesive energies and the calculated, assuming variational method, are 2·26, 2·97 and 3·75 eV respectively for PbS, PbSe and PbTe which are in good agreement with the reported values for the covalent bonding correction using Heitler-London-Lowdin method (HLL) which are respectively 2·1, 2·9 and 3·3 eV (Tanaka and Morita 1979).     

Normal Differentiability and Extrema of Functionals in a Locally Convex Space

The problem of extension of the classical extremum conditions for strongly differentiable functionals in a Banach space to normally differentiable and compactly normally differentiable functionals in a locally convex space is investigated.     

一类弱非线性振动方程的变分迭代算法

本文提出了一种求解非线性方程的迭代算法,这种方法是先给方程一个带待定函数的试函数作为初始近似解,然后用拉氏乘子法构造一个迭代公式,而拉氏乘子可用变分的概念最佳确定。应用这种方法不会出现长期项,其结果比传统的摄动方法要好得多。     

Rapid stress analysis of geometrically complex domains using implicit meshing

In an economically competitive industrial setting, it is advantageous to generate accurate engineering analysis results as rapidly as possible in order to minimize the design cycle time. For many structural problems, the goal of the computational analysis is to obtain the stress field. The standard tool for obtaining the stress field is the finite-element method. The task of obtaining the stress field using finite-element analysis is complicated by the fact that many industrial problems are geometrically complex and thus require a significant number of man hours to generate a finite-element mesh appropriate for stress analysis. This mesh generation task can be greatly simplified by using the method of implicit meshing. In conventional finite-element analysis, the given domain is explicitly meshed. In the implicit meshing method, the geometrically complex domain is embedded into a geometrically simpler domain. The finite-element method is then applied to the embedding domain. The original domain inherits its discretization from that of the embedding domain. Herein, the implicit meshing method is applied to the stress analysis of linear elasto-static problems. It is shown that with the appropriate choice of finite element and integration technique, the implicit meshing method can provide accurate stress fields with only moderate mesh refinement.     

Analysis of delayed convergence in the three-noded Timoshenko beam element using the function space approach

Despite satisfying only completeness and continuity requirements, elements often perform erroneously in a certain class of problems, called the locking situations, where they display spurious stress oscillations and enhanced stiffness properties. The function space approach that effectively substantiates the postulates of the field consistency paradigm is an efficient tool to reveal the fundamental cause of locking phenomena, and propose methods to eliminate this pathological problem. In this paper, we review the delayed convergence behaviour of three-noded Timoshenko beam elements using the rigorous function space approach. Explicit, closed form algebraic results for the element strains, stresses and errors have been derived using this method. The performance of the field-inconsistent three-noded Timoshenko beam element is compared with that of the field-inconsistent two-noded beam element. It is demonstrated that while the field-inconsistent two-noded linear element is prone to shear locking, the field-inconsistent three-noded element is not very vulnerable to this pathological problem, despite the resulting shear oscillations.     

变分调整的海面风场数值模式

精确地给出协调的海面风场是正确模拟出海浪等海洋环境要素场的前提条件,特别在强海况的情况下尤其如此。本文给出了利用边界层动力学模式进行变分调整方法确定海面逐时风场的全过程。     

耦合相互作用对光纤中类明孤子传输特性的影响

本文采用变分法，导出了双全同耦合光纤中类明孤子参数的演化方程组，在此基础上讨论了类明孤子在耦合光纤中的传输特性，分析了耦合相互作用对类明孤子参数的影响。     

求解受钉传载荷正交各向异性板双边缺口边缘裂纹应力强度因子的复变－广义变分解法

本文以单边边缘裂纹二维应力场与位移场展开式为基础，采用广义变分方法研究受钉传载菏各向异性板双边缺口边缘裂纹应力强度因子。首先建立精确满足正文各向异性板基本微分方程、裂纹表面边界条件、钉载孔处位移单值条件与合力平衡条件的应力场和位移场的级数表达式。然后应用广义变分方法满足边界条件从而确定应力强度因子，在变分方程中只存在沿板边界的线积分、计算程序简单，输入数据很少，结果收敛迅速，并与已知结果相当吻合而且所需机时较少。