A study on one-dimensional dynamic damage in pure copper

Based on meso-damage mechanics, a model of dynamic ductile damage under tensile stress is developed, in which work-hardening behavior, rate-dependent contribution and inertial effects are taken into account. Plate-impact test on pure copper under one-dimensional plane strain condition is conducted. Some significant mechanical phenomena are observed by means of microscopic observations of the spalled specimen. The mathematical model presented in this paper is incorporated in a hydrodynamic one-dimensional finite-difference computer code, to simulate the process of spallation in pure copper sample. Comparison of numerical calculations and experimental results shows that the model can describe spall damage successfully.     

Infinite-horizon investment consumption model with a nonterminal bankruptcy

This paper solves a general continuous-time consumption and portfolio decision problem for a single agent for whom there exists, upon bankruptcy, a possibility of recovery from his bankruptcy. The main contribution of the paper is in the modeling of the recovery process. Moreover, it is shown that the model with recovery has a one-to-one correspondence with the model with terminal bankruptcy treated in the literature.This research was supported by Grants SSHRC-410-83-9888 and NSERC-A4619 to the first author and by Grants NSF-DMS-86-01510 and AFOSR-88-0183 to the second author. Comments from E. Presman are gratefully acknowledged.     

Estimation of frequency by random sampling

Summary We consider the estimation of frequency ω of a sinusoidal oscillation contaminated by a stationary noise under a random sampling scheme according to a stationary point processN. We prove the strong consistency and the asymptotic normality for a certain estimator of ω. Then we apply these results to the case whereN is a stationary delayed renewal process.     

Two clarifications on the likelihood surface in functional models

The paper consists of two parts. In the first part a previous result by Solari [(1969) J. Roy. Statist. Soc. Ser. B31] for a simplified two-variable model is generalized to the multivariate case. In the second part the behaviour of the likelihood surface is clarified when we have replications of observations.     

Carleman estimates for stochastic parabolic equations with Neumann boundary conditions and applications

By a dual method, two Carleman estimates for forward and backward stochastic parabolic equations with Neumann boundary conditions are established. Then they are used to study a null controllability problem and a state observation problem for some stochastic forward parabolic equations with Neumann boundary conditions.     

On the construction of nearly optimal strategies for a general problem of control of partially observed diffusions

In the paper a stochastic control problem consisting of continuously acting controls, impulse controls and stopping times of a partially observed diffusion with discounted cost functional is considered. The problem is successively approximated by time, observation, control and space discretizations to obtain finally a completely observed finite valued control problem. It is shown that the optimal strategy for the approximating problem, which can be numerically computed, is nearly optimal for the original problem     

Some generalized limit theorems concerning delayed sums of random sequence

For a sequence of arbitrarily dependent m-valued random variables (Xn) n∈N , the generalized strong limit theorem of the delayed average is investigated. In our proof, we improved the method proposed by Liu [6] . As an application, we also studied some limit properties of delayed average for inhomogeneous Markov chains.     

Phase relationships in the Gd–Co–Al ternary system at 500°C

The phase relationships in the Gd–Co–Al ternary system at 500°C have been investigated mainly by X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy. The existence of two ternary compounds GdCo_0.74Al_1.26 and Gd₂Co₂Al has been confirmed. Twenty-two single-phase regions (including solid solution regions of the binary compounds), 43 two-phase regions, and 22 three-phase regions were found to exist at this isothermal section. In this work, no new binary or ternary phase was found.     

西北地区普通高中化学听评课现状及有效实施对策研究

以甘肃省兰州市15所普通高中的179名化学教师为研究对象,从听评课的目的、态度、内容、方式、制度、组织实施、文化等7个维度深入分析当前高中化学听评课现状。研究发现,兰州市普通高中化学听评课现状具体表现为：教师在观念层面没有真正意识到听评课对于课堂教学研究的意义与价值,操作层面不会通过听评课开展课堂教学研究;学校在制度层面缺乏对教师通过听评课开展课堂教学研究的保障引领,组织实施层面忽视教师个人的主观能动性和个体差异性,另外个人主义和表面合作的文化不利于教师通过听评课开展课堂教学研究;不同类型的教师在听评课的7个维度方面表现出不同程度的差异性。基于此,学校层面应该重建专业的听评课制度,培育专业的教研文化,组建专业的研究共同体;教师层面应该转变传统的听评课观念,培养课堂教学研究的意识,提升课堂教学研究的能力。