Nonstandard Analysis in ACL2

ACL2 refers to a mathematical logic based on applicative Common Lisp, as well as to an automated theorem prover for this logic. The numeric system of ACL2 reflects that of Common Lisp, including the rational and complex-rational numbers and excluding the real and complex irrationals. In conjunction with the arithmetic completion axioms, this numeric type system makes it possible to prove the nonexistence of specific irrational numbers, such as 2. This paper describes ACL2(r), a version of ACL2 with support for the real and complex numbers. The modifications are based on nonstandard analysis, which interacts better with the discrete flavor of ACL2 than does traditional analysis.     

Some Remarks on the Semantics of FIPA's Agent Communication Language

The Foundation for Intelligent Physical Agents (FIPA) standardisation body has produced a set of specifications outlining a generic model for the architecture and operation of agent-based systems. The FIPA'97 Specification Part 2 is the normative specification of an Agent Communication Language (ACL) which agents use to talk to each other. The FIPA ACL is based on speech act theory. Its syntax is defined by performatives parameterised by attribute value pairs, while its semantics is given in terms of the mental states of the communicating agents (i.e. intentionality). However, it is not clear if the formal semantics is meant as a normative or informative specification. The primary purpose of this paper is then to give an expository analysis of the FIPA ACL semantics to clarify this situation. We also offer some guidelines motivated from our own analysis, experience and understanding of how the semantic definitions and logical axioms should be interpreted and applied. However, our conclusion is that while the FIPA ACL specification offers significant potential to a developer using it for guidance, there are limitations on using an agent's mental state to specify the meaning of a performative as part of a normative standard. We consider some possibilities for making improvements in this direction.     

A Framework for Verifying Bit-Level Pipelined Machines Based on Automated Deduction and Decision Procedures

We describe an approach to verifying bit-level pipelined machine models using a combination of deductive reasoning and decision procedures. While theorem-proving systems such as ACL2 have been used to verify bit-level designs, they typically require extensive expert user support. Decision procedures such as those implemented in UCLID can be used to automatically and efficiently verify term-level pipelined machine models, but these models use numerous abstractions, implement a subset of the instruction set, and are far from executable. We show that by integrating UCLID with the ACL2 theorem-proving system, we can use ACL2 to reduce the proof that an executable, bit-level machine refines its instruction set architecture to a proof that a term-level abstraction of the bit-level machine refines the instruction set architecture, which is then handled automatically by UCLID. We demonstrate the efficiency of our approach by applying it to verify a complex, seven-stage, bit-level interface pipelined machine model that implements 593 instructions and has features such as branch prediction, exceptions, and predicated instruction execution. Such a proof is not possible using UCLID and would require prohibitively more effort using just ACL2. This research was funded in part by NSF grants CCF-0429924, IIS-0417413, and CCF-0438871.     

Crash failure detection in asynchronous agent communication languages

Agent Communication Languages (ACLs) have been developed to provide a way for agents to communicate with each other supporting cooperation in Multi-Agent Systems (MAS). In the past few years many ACLs have been proposed for MAS and new standards are emerging such as the ACL developed by the Foundation for Intelligent Physical Agents (FIPA). Despite these efforts, an important issue in the research on ACLs is still open and concerns how these languages should deal with failures of agents in asynchronous MAS. The Fault Tolerant Agent Communication Language ( - ) presented in this paper addresses this issue dealing with crash failures of agents. - provides high-level communication primitives which support a fault-tolerant anonymous interaction protocol designed for open MAS. We present a formal semantics for - and a formal specification of the underlying agent architecture. This formal framework allows us to prove that the ACL satisfies a set of well defined knowledge-level programming requirements. To illustrate the language features we show how - can be effectively used to write high-level executable specifications of fault tolerant protocols, such as the Contract Net one.     

Dynamic control and conventional strength ratios of the quadriceps and hamstrings in subjects with anterior cruciate ligament deficiency

The hamstrings:quadriceps muscle strength ratio has been used as an indicator of normal balance between the knee flexors and extensors. A more functional approach to this strength ratio would be to compare opposite muscle actions of antagonistic muscle groups. The dynamic strength control ratio (DSCR) should give a more appropriate measure relating to knee function. There is a lack of normative data relating to DSCR for anterior cruciate ligament (ACL) deficient subjects. Effects of ACL deficiency on isokinetic peak torque for eccentric and concentric muscle actions of the quadriceps and hamstrings, in conjunction with isometric peak torque, were examined in 10 patients awaiting reconstructive surgery (male = 8, female = 2 ; age = 32.8 +/- 8.3 years; height = 1.77 +/- 0.08 m; mass = 72.1 +/- 12.5 kg). These variables were assessed using an isokinetic dynamometer. The results were considered in terms of the conventional ratio and DSCR. Anterior tibial drawer was measured using a knee ligament arthrometer to confirm clinical diagnosis of ACL rupture. The isokinetic peak torque data analysed were for angular velocities of 1.05 rad s(-1) (60 degrees s(-1)). Significant strength deficits were apparent between normal and injured sides for: concentric isokinetic quadriceps action (p < 0.05); isometric quadriceps action at 70 degrees of knee flexion (p < 0.05); isometric quadriceps action at 40 degrees of knee flexion (p<0.01); eccentric isokinetic hamstrings action (p < 0.05). With bilateral comparison, the conventional strength ratios showed no significant difference, as did the DSCR. The bilateral comparison of isometric strength ratios revealed significant losses in quadriceps strength for the injured side (p < 0.05) but no significant losses in hamstring strength (p > 0.05). Thus, differences can be seen in conventional ratios and DSCR for ACL-deficient subjects. This is an area of clinical interest with the increasing frequency of ACL reconstruction using hamstrings tendons.     

基于改进弹簧振子模型的实时肌腱模拟

在膝关节前交叉韧带重建仿真系统中,为了进行人体肌腱实时模拟,提出一种基于改进弹簧振子模型的实时肌腱模拟方法,通过定义非线性弹簧,降低线性弹簧振子模型“超弹性”现象的发生概率,从而增强肌腱应力的仿真效果,利用添加临时性约束弹簧的方法进行碰撞处理,同时用隐式欧拉方法求解模型,提高肌腱模拟的整体性和实时性。实验结果表明,该方法符合系统对实时性和真实感的要求。     

A Mechanically Checked Proof of Correctness of the AMD K5 Floating Point Square Root Microcode

We present a rigorous mathematical proof of the correctness of the floating point square root instruction of the AMD K5 microprocessor. The instruction is represented as a program in a formal language that was designed for this purpose, based on the K5 microcode and the architecture of its FPU. We prove a statement of its correctness that corresponds directly with the IEEE Standard. We also derive an equivalent formulation, expressed in terms of rational arithmetic, which has been encoded as a formula in the ACL2 logic and mechanically verified with the ACL2 prover. Finally, we describe a microcode modification that was implemented as a result of this analysis in order to ensure the correctness of the instruction.     

A Logical Model for Agent Communication Languages

The current ACL proposals show some shortcomings with respect to the definition of their semantics. Our paper aims at tackling those issues by defining an ACL semantics as a specification of the analytical effects of agent communicative acts. We analyze agent communication in terms of concepts taken from Speech Act Theory, as several researchers have already done, but move away from the mainstream view of artificial agent research, as we define communicative acts in terms of changes at the level of social relationship between agents. We take commitment to be a primitive concept underlying the social dimension of multiagent systems, and define a basic artificial institution whose aim is to provide agents with the means to affect the commitment network that binds them to each other.     

Agent communication and artificial institutions

In this paper we propose an application-independent model for the definition of artificial institutions that can be used to define open multi-agent systems. Such a model of institutional reality makes us able also to define an objective and external semantics of a commitment-based Agent Communication Language (ACL). In particular we propose to regard an ACL as a set of conventions to act on a fragment of institutional reality, defined in the context of an artificial institution. Another contribution of the work presented in this paper is an operational definition of norms, a crucial component of artificial institutions. In fact in open systems interacting agents might not conform to the specifications. We regard norms as event-driven rules that when are fired by events happening in the system create or cancel a set of commitments. An interesting aspect of our proposal is that both the definition of the ACL and the definition of norms are based on the same notion of commitment. Therefore an agent capable of reasoning on commitments can reason on the semantics of communicative acts and on the system of norms.     

Ordinal Arithmetic: Algorithms and Mechanization

Termination proofs are of critical importance for establishing the correct behavior of both transformational and reactive computing systems. A general setting for establishing termination proofs involves the use of the ordinal numbers, an extension of the natural numbers into the transfinite that were introduced by Cantor in the nineteenth century and are at the core of modern set theory. We present the first comprehensive treatment of ordinal arithmetic on compact ordinal notations and give efficient algorithms for various operations, including addition, subtraction, multiplication, and exponentiation. Using the ACL2 theorem proving system, we implemented our ordinal arithmetic algorithms, mechanically verified their correctness, and developed a library of theorems that can be used to significantly automate reasoning involving the ordinals. To enable users of the ACL2 system to fully utilize our work required that we modify ACL2, e.g., we replaced the underlying representation of the ordinals and added a large library of definitions and theorems. Our modifications are available starting with ACL2 version 2.8.     

An Observation Approach to the Semantics of Agent Communication Languages

We show how a formal framework for the observation issue in computer systems can be used for the specification of an agent behavior, abstracting away from agent inner details while focusing on its interactive behavior. This model can also be used as a specification of agent communication languages (ACLs), providing the proper abstraction level to represent the conditions causing an agent to send a message, as well as its effect on the receiving agent. In particular, this approach generalizes upon existing ACL semantics, such as FIPA ACL, that relate agent communicative acts to the agent mental state. Since the observation framework induces a more abstract architecture than other known approaches, our semantics are likely to be applicable to a wider set of agent architectures, thus better supporting standardization aims. Some application examples are shown, describing how various aspects of ACL semantics can be specified within our framework.     

Dynamic control and conventional strength ratios of the quadriceps and hamstrings in subjects with anterior cruciate ligament deficiency

The hamstrings:quadriceps muscle strength ratio has been used as an indicator of normal balance between the knee flexors and extensors. A more functional approach to this strength ratio would be to compare opposite muscle actions of antagonistic muscle groups. The dynamic strength control ratio (DSCR) should give a more appropriate measure relating to knee function. There is a lack of normative data relating to DSCR for anterior cruciate ligament (ACL) deficient subjects. EVects of ACL deficiency on isokinetic peak torque for eccentric and concentric muscle actions of the quadriceps and hamstrings, in conjunction with isometric peak torque, were examined in 10 patients awaiting reconstructive surgery (male= 8, female= 2; age= 32.8 ± 8.3 years; height= 1.77 ± 0.08 m; mass= 72.1 ± 12.5 kg). These variables were assessed using an isokinetic dynamometer. The results were considered in terms of the conventional ratio and DSCR. Anterior tibial drawer was measured using a knee ligament arthrometer to confirm clinical diagnosis of ACL rupture. The isokinetic peak torque data analysed were for angular velocities of 1.05 rad s^?1 (60° s^?1). Significant strength deficits were apparent between normal and injured sides for: concentric isokinetic quadriceps action (p < 0.05); isometric quadriceps action at 70° of knee flexion (p < 0.05); isometric quadriceps action at 40° of knee flexion (p < 0.01); eccentric isokinetic hamstrings action (p < 0.05). With bilateral comparison, the conventional strength ratios showed no significant difference, as did the DSCR. The bilateral comparison of isometric strength ratios revealed significant losses in quadriceps strength for the injured side (p < 0.05) but no significant losses in hamstring strength (p > 0.05). Thus, differences can be seen in conventional ratios and DSCR for ACL-deficient subjects. This is an area of clinical interest with the increasing frequency of ACL reconstruction using hamstrings tendons.     

Formal Proofs About Rewriting Using ACL2

We present an application of the ACL2 theorem prover to reason about rewrite systems theory. We describe the formalization and representation aspects of our work using the first-order, quantifier-free logic of ACL2 and we sketch some of the main points of the proof effort. First, we present a formalization of abstract reduction systems and then we show how this abstraction can be instantiated to establish results about term rewriting. The main theorems we mechanically proved are Newman's lemma (for abstract reductions) and Knuth–Bendix critical pair theorem (for term rewriting).     

ACL技术配置应用

本文介绍了ACL(AccessControlList)在QOS(QualityOfService)中的技术配置。ACL是一种服务级别协定(ServiceLevelA-greement),保证各种业务得到所承诺的服务质量。本文根据ACL应用环境,对ACL进行分类,详细介绍在路由器和操作系统上配置A-CL的具体步骤,达到提高网络服务质量管理的目的。     

基于数字有机体的访问控制链表(ACL)的设计与实现

当前随着大规模网络应用的不断出现,特别是大规模的存储需求,分布式系统和虚拟存储系统也随之诞生,以Linux为开发平台的分布式系统也成为当今主流。而如何保证大量存储资源的安全性成为当今研究的热点。细粒度的自主访问控制是操作系统安全增强方法中经常采用的技术,访问控制列表ACL是其中最主要且流行的技术。以ext2文件系统为例介绍了ACL的具体实现方法和主要数据结构,并以此为基础讨论了ACL在数字有机体系统上的设计与实现。     

基于数字有机体的访问控制链表（ACL）的设计与实现

当前随着大规模网络应用的不断出现,特别是大规模的存储需求,分布式系统和虚拟存储系统也随之诞生,以Linux为开发平台的分布式系统也成为当今主流。而如何保证大量存储资源的安全性成为当今研究的热点。细粒度的自主访问控制是操作系统安全增强方法中经常采用的技术,访问控制列表ACL是其中最主要且流行的技术。以ext2文件系统为例介绍了ACL的具体实现方法和主要数据结构．并以此为基础讨论了ACL在数字有机体系统上的设计与实现。     

Finite element analysis of 3-D beam-columns on a nonlinear foundation

A numerically integrated finite element for the analysis of three-dimensional, nonlinear Winkler foundations is developed. Together with a linear beam-column element they are used to solve problems of beams, columns and beam-columns on linear and nonlinear foundations in two and three dimensions. The Newton-Raphson method is used in the solution. Excellent results are illustrated by comparisons with available solutions.     

The State of the Art in Agent Communication Languages

Like societies of humans, there is a need for agents in a multi-agent system to rely on one another, enlist the support of peers in order to solve complex tasks. Agents will be able to cooperate only through a meaningful communication language that can bear correctly their mental states and convey precisely the content of their messages. In search for the ideal agent communication language (ACL), several initiatives like the pioneering work of the Knowledge Sharing Effort and the Foundation for Intelligent Physical Agents (FIPA) are paving the way for a platform where all agents would be able to interact regardless of their implementation environment. ACL is a new field of study that could gain from a survey in expanding its application areas. For this purpose, we examine in this paper the state of the art in ACL design and suggest some principles for building a generalized ACL framework. We then evaluate some existing ACL models, and present the current issues in ACL research, and new perspectives. Received 22 July 1999 / Revised 23 March 2000 / Accepted 2 May 2000     

面向前交叉韧带重建术后评估的测力机器人

针对膝关节前交叉韧带（ACL）重建手术后缺乏及时有效的效果评估、手术缺乏安全性等问题,研制了 一种基于零重力的膝关节ACL 测力机器人,测定其重建前后的张紧力．首先,对ACL 的手术环境进行了分析,提 出了对手术机器人结构和控制的要求．然后,建立了ACL 侧向受力的数学模型．接着,详细介绍了膝关节ACL 测 力机器人的机械结构设计和控制系统设计．最后,对该机器人进行顶杆位移和力的测试精度实验,并进行了羊骨的 测试和术后评估实验,证明该机器人可以用于ACL 重建手术的评估,ACL 侧向受力数学模型是正确的．