A Refinement Calculus for Shared-Variable Parallel and Distributed Programming

Parallel computers have not yet had the expected impact on mainstream computing. Parallelism adds a level of complexity to the programming task that makes it very error-prone. Moreover, a large variety of very different parallel architectures exists. Porting an implementation from one machine to another may require substantial changes. This paper addresses some of these problems by developing a formal basis for the design of parallel programs in the form of a refinement calculus. The calculus allows the stepwise formal derivation of an abstract, low-level implementation from a trusted, high-level specification. The calculus thus helps structuring and documenting the development process. Portability is increased, because the introduction of a machine-dependent feature can be located in the refinement tree. Development efforts above this point in the tree are independent of that feature and are thus reusable. Moreover, the discovery of new, possibly more efficient solutions is facilitated. Last but not least, programs are correct by construction, which obviates the need for difficult debugging. Our programming/specification notation supports fair parallelism, shared-variable and message-passing concurrency, local variables and channels. The calculus rests on a compositional trace semantics that treats shared-variable and message-passing concurrency uniformly. The refinement relation combines a context-sensitive notion of trace inclusion and assumption-commitment reasoning to achieve compositionality. The calculus straddles both concurrency paradigms, that is, a shared-variable program can be refined into a distributed, message-passing program and vice versa. Received July 2001 / Accepted in revised form May 2002     

长25-29井卡钻事故的处理

长２５－２９井在完井阶段通井过程中发生粘附卡钻事故，在处理卡钻过程中又发生卡套铣筒、井漏、溢流等事故及复杂情况。通过对井下情况的认真分析，采取先堵漏后循环再解卡的处理方案，顺利地解除了该次卡钻事故，大大地减少了经济损失。     

某微型起爆器引起的一起误爆事故分析

该文分析某微型起爆器引起的一起误爆事故，指出该起爆器设计上的缺陷及其对作业安全的威胁，提出防患建议。     

MKR──一种有效的增量式概念获取系统

本文对示例式学习的ＩＤ５Ｒ算法进行了深入的研究并作了进一步的改进，提高了其计算效率．并提出一种适合于增量式学习的抗干扰机制，拓广了算法的适用范围．     

Real-World Robotics: Learning to Plan for Robust Execution

In executing classical plans in the real world, small discrepancies between a planner's internal representations and the real world are unavoidable. These can conspire to cause real-world failures even though the planner is sound and, therefore, proves that a sequence of actions achieves the goal. Permissive planning, a machine learning extension to classical planning, is one response to this difficulty. This paper describes the permissive planning approach and presents GRASPER, a permissive planning robotic system that learns to robustly pick up novel objects.     

钻杆接头螺纹退刀尺寸对接头寿命的影响

钻杆接头螺纹退刀尺寸是指外螺纹接头的台肩面到螺纹消失前第一个完整螺纹之间的距离。GB9253．1－88规定退刀尺寸应小于或等于12．7mm内螺纹，钻杆接头内螺纹的锤孔尺寸为16±2mm，以保证内、外螺纹啮合良好。经检测发现，从日本NKK公司进口的所有φ127mm钻杆接头外螺纹退刀尺寸都大于12．7mm，镗孔尺寸为16～18mm。而APISpec7K规定钻杆接头内螺纹最小镗孔尺寸为15．9mm。鉴于此，建议对我国的有关标准作相应修改，与API标准保持一致。     

反向回转双激振器振动机控制同步的理论研究

本文对两激振器作反向回转的振动机控制同步进行了理论研究和计算机仿真。推导出了考虑质心偏移时两主轴的转矩差方程，在此基础上建立了控制系统的数学模型，设计了具有鲁棒性的非线性变结构滑模控制器．仿真结果表明，控制同步不仅可以消除由质心偏移、电机特性差等原因引起的稳态相位差，同时还能大大降低瞬态相位差，从而使机体的振动方向保持不变，减小起、制动过程中机体的摇摆振动．     

面向对象系统中的特性表机制与复合对象

本文主要讨论特性表机制与复合对象的概念、功能及实现．在基于知识的面向对象系统中引入特性表机制与复合对象概念的目的在于增强系统的知识表达能力．文中提出的特性表机制包括了三种类型的特性说明表：类说明特性表、继承关系特性表和变量特性说明表．复合对象在系统中是通过引入一个称为“影子类”的新概念来构造和实现的．     

A process oriented semantics of the PRAM-language FORK

The parallel language FORK [1], based on a scalable shared memory model, is a PASCAL-like language with some additional parallel constructs. A PRAM (Parallel Random Access Machine) algorithm can be expressed on a high level of abstraction as a FORK program which is translated into efficient PRAM code guaranteeing theoretically predicted runtimes.

In this paper, we concentrate on those features of the language FORK related to parallelism, such as the group concept, a shared memory access and synchronous or asynchronous execution. We present a trace-based denotational interleaving semantics where processes describe synchronous computations. Processes are created or deleted dynamically and run asynchronously. Interleaving rules reflect the underlying CRCW (concurrent-read-concurrent-write) PRAM model.