Rational Pythagorean-hodograph space curves

A method for constructing rational Pythagorean-hodograph (PH) curves in R³ is proposed, based on prescribing a field of rational unit tangent vectors. This tangent field, together with its first derivative, defines the orientation of the curve osculating planes. Augmenting this orientation information with a rational support function, that specifies the distance of each osculating plane from the origin, then completely defines a one-parameter family of osculating planes, whose envelope is a developable ruled surface. The rational PH space curve is identified as the edge of regression (or cuspidal edge) of this developable surface. Such curves have rational parametric speed, and also rational adapted frames that satisfy the same conditions as polynomial PH curves in order to be rotation-minimizing with respect to the tangent. The key properties of such rational PH space curves are derived and illustrated by examples, and simple algorithms for their practical construction by geometric Hermite interpolation are also proposed.     

Rational Beta-splines for representing curves and surfaces

The rational Beta-spline representation, which offers the features of the rational form as well as those of the Beta-spline, is discussed. The rational form provides a unified representation for conventional free-form curves and surfaces along with conic sections and quadratic surfaces, is invariant under projective transformation, and possesses weights, which can be used to control shape in a manner similar to shape parameters. Shape parameters are an inherent property of the Beta-spline and provide intuitive and natural control over shape. The Beta-spline is based on geometric continuity, which provides an appropriate measure of smoothness in computer-aided geometric design. The Beta-spline has local control with respect to vertex movement, is affine invariant, and satisfies the convex hull property. The rational Beta-spline enjoys the benefit of all these attributes. The result is a general, flexible representation, which is amenable to implementation in modern geometric modeling systems     

有理三次三角Hermite插值样条曲线及其应用

给出一种有理三次三角Hermite插值样条曲线,具有三次Hermite插值样条相似的性质。该样条含有三角函数和形状参数,利用形状参数的不同取值可以调控插值曲线的形状,甚至不用解方程组,就能使曲线达到C2连续。此外,选择合适的控制点和形状参数,这种样条可以精确表示星形线和四叶玫瑰线等超越曲线。     

Equilibria, prudent compromises, and the "waiting" game.

While evaluation of many e-negotiation agents are carried out through empirical studies, this work supplements and complements existing literature by analyzing the problem of designing market-driven agents (MDAs) in terms of equilibrium points and stable strategies. MDAs are negotiation agents designed to make prudent compromises taking into account factors such as time preference, outside option, and rivalry. This work shows that 1) in a given market situation, an MDA negotiates optimally because it makes minimally sufficient concession, and 2) by modeling negotiation of MDAs as a game gamma of incomplete information, it is shown that the strategies adopted by MDAs are stable. In a bilateral negotiation, it is proven that the strategy pair of two MDAs forms a sequential equilibrium for gamma. In a multilateral negotiation, it is shown that the strategy profile of MDAs forms a market equilibrium for gamma.     

Efficient and inefficient ant coverage methods

Ant robots are simple creatures with limited sensing and computational capabilities. They have the advantage that they are easy to program and cheap to build. This makes it feasible to deploy groups of ant robots and take advantage of the resulting fault tolerance and parallelism. We study, both theoretically and in simulation, the behavior of ant robots for one-time or repeated coverage of terrain, as required for lawn mowing, mine sweeping, and surveillance. Ant robots cannot use conventional planning methods due to their limited sensing and computational capabilities. To overcome these limitations, we study navigation methods that are based on real-time (heuristic) search and leave markings in the terrain, similar to what real ants do. These markings can be sensed by all ant robots and allow them to cover terrain even if they do not communicate with each other except via the markings, do not have any kind of memory, do not know the terrain, cannot maintain maps of the terrain, nor plan complete paths. The ant robots do not even need to be localized, which completely eliminates solving difficult and time-consuming localization problems. We study two simple real-time search methods that differ only in how the markings are updated. We show experimentally that both real-time search methods robustly cover terrain even if the ant robots are moved without realizing this (say, by people running into them), some ant robots fail, and some markings get destroyed. Both real-time search methods are algorithmically similar, and our experimental results indicate that their cover time is similar in some terrains. Our analysis is therefore surprising. We show that the cover time of ant robots that use one of the real-time search methods is guaranteed to be polynomial in the number of locations, whereas the cover time of ant robots that use the other real-time search method can be exponential in (the square root of) the number of locations even in simple terrains that correspond to (planar) undirected trees. This revised version was published online in August 2006 with corrections to the Cover Date.     

Composing web services enacted by autonomous agents through agent-centric contract net protocol

ContextAgents are considered as one of the fundamental technologies underlying open and dynamic systems that are largely enabled by the semantic web and web services. Recently, there is a trend to introduce the notion of autonomy empowered by agents into web services. However, it has been argued that the characteristics of autonomy will make agents become available intermittently and behave variedly over time, which therefore increase the complexity on devising mechanisms for composing services enacted by autonomous agents.ObjectiveIn this work, we propose an extension to Contract Net protocol, called Agent-centric Contract Net Protocol (ACNP), as a negotiation mechanism with three key features for composing web services enacted by autonomous agents.Method(1) A matchmaking mechanism embedded in a middle agent (as a service matchmaker) for discovering web services that are available intermittently is presented based on the concept of agent roles; (2) A selection algorithm based on risk-enabled reputation model (REAL) embedded in a manager agent (as a service composer) is introduced to serve a basis for selecting web services with variant performance; and (3) A negotiation mechanism between a manager agent and contractor agents (as atomic services) is devised and enables both a service composer and the atomic services to request, refuse or agree on adapting changes of services.ResultsThe problem of assembling a computer is discussed in this paper.ConclusionIt is increasingly recognised that web services would become more autonomous by introducing diverse agent technologies to better constitute more complex systems in open and dynamic environments. As web service technologies are best exploited by composite services, it is imperative to devise mechanisms for composing services of autonomy.     

A procedure for negotiating efficient and non-efficient compromises

An interactive procedure for group decision-making problems is presented in this paper. The procedure is based on the aspiration theory and utilizes both satisficing and optimizing approaches. The possiblity of decision-makers forming coalitions is taken into account. The outcome of the modelled decision process is a compromise decision which can fulfil fairness and equity criteria. The compromise may also be an efficient solution. The procedure can be the basis for a group decision suport systems and such a system for a microcomputer network is discussed. An example of negotiations between management and trade union is presented.     

法律合约与智能合约一致性综述

从计算机科学的角度对法律合约与智能合约的一致性研究现状进行了总结和分析。首先,分别对法律合约描述语言和智能合约开发语言进行了分类和分析,总结了每种语言的特点;其次,根据合同自动化执行的三个发展阶段对法律合约和智能合约的一致性内涵进行了分析和讨论;分别基于形式化模型和合约模板总结了由法律合约生成智能合约代码的方法和关键技术,并对其进行了讨论和评价;最后,对未来法律合约与智能合约的一致性研究进行了总结和展望。     

Harmonic rational Bézier curves, p-Bézier curves and trigonometric polynomials

In a recent article, Ge et al. (1997) identify a special class of rational curves (Harmonic Rational Bézier (HRB) curves) that can be reparameterized in sinusoidal form. Here we show how this family of curves strongly relates to the class of p-Bézier curves, curves easily expressible as single-valued in polar coordinates. Although both subsets do not coincide, the reparameterization needed in both cases is exactly the same, and the weights of a HRB curve are those corresponding to the representation of a circular arc as a p-Bézier curve. We also prove that a HRB curve can be written as a combination of its control points and certain Bernstein-like trigonometric basis functions. These functions form a normalized totally positive B-basis (that is, the basis with optimal shape preserving properties) of the space of trigonometric polynomials {1, sint, cost, …. sinmt, cosmt} defined on an interval of length < π.     

Quaternion rational surfaces: Rational surfaces generated from the quaternion product of two rational space curves

A quaternion rational surface is a surface generated from two rational space curves by quaternion multiplication. The goal of this paper is to demonstrate how to apply syzygies to analyze quaternion rational surfaces. We show that we can easily construct three special syzygies for a quaternion rational surface from a μ-basis for one of the generating rational space curves. The implicit equation of any quaternion rational surface can be computed from these three special syzygies and inversion formulas for the non-singular points on quaternion rational surfaces can be constructed. Quaternion rational ruled surfaces are generated from the quaternion product of a straight line and a rational space curve. We investigate special μ-bases for quaternion rational ruled surfaces and use these special μ-bases to provide implicitization and inversion formulas for quaternion rational ruled surfaces. Finally, we show how to determine if a real rational surface is also a quaternion rational surface.     

Paperfolding morphisms, planefilling curves, and fractal tiles

An interesting class of automatic sequences emerges from iterated paperfolding. The sequences generate curves in the plane with an almost periodic structure. We generalize the results obtained by Davis and Knuth on the self-avoiding and planefilling properties of these curves, giving simple geometric criteria for a complete classification. Finally, we show how the automatic structure of the sequences leads to self-similarity of the curves, which turns the planefilling curves in a scaling limit into fractal tiles. For some of these tiles we give a particularly simple formula for the Hausdorff dimension of their boundary.     

A Big Picture on Recent Vulnerabilities: Active AX,Web server compromises and insecure documents

You may not know it, but some of your employees are installing vulnerable software — and you are silently accepting it, you may even encourage them to do so…     

Context, situations, and design agents

The terms “context” and “situation” are often used interchangeably or to denote a variety of concepts. This paper aims to show that these are two different but related concepts and it reifies their difference within the framework of design agents. The external world of an agent is described as the aggregation of all entities that the agent could possibly sense or effect, where context is from its external world that an agent interacts with and is aware of. The interpreted world of an agent is described in terms of the experiences of that agent, where situations are processes that direct how interactive experiences proceed. Situations determine what part of the external world are in the current context, and situations influence interaction and so influence what and how common ground is acquired.     

A cross-dependence based ranking system for efficient and inefficient units in DEA

Decision making units (DMUs) can be ranked using data envelopment analysis (DEA) technologies. This paper develops a new ranking system under the condition of variable returns to scale (VRS) based on a measure of cross-dependence efficiency (MCDE), where the evaluation for an efficient DMU is dependent of the efficiency changes of all inefficient units due to its absence in the reference set, while the appraisal of inefficient DMUs depends on the influence of the exclusion of each efficient unit from the reference set. The infeasibility problem that arises from the conventional super-efficiency models is eliminated. A new approach to ranking inefficient units is embedded in the proposed ranking system. Through an example, advantages of our proposal are demonstrated. A real application illustrates the effectiveness of the cross-dependence based ranking system.     

正弦B样条类曲线及其在曲线参数化中的应用

从B样条基函数出发,导出了正弦B样条类SBSC（Sine Basic Spline Class）函数,定义了SBSC曲线,讨论了SBSC曲线和B样条曲线的关系,提供了B样条曲线重新参数化的一种有效方法。     

Mobile code, distributed computing, and agents

The author briefly describes some of the Jini networking system's features and attempts to show how this system's assumptions differ from those used to construct other distributed system frameworks. The author then characterizes mobile agent systems, showing such system's intrinsic differences from Jini and some of their basic problems. Finally, he discusses how agent systems could use the Jini system approach to solve some of these intrinsic problems.     

Rational expectations, optimal control and information technology adoption

The existing economics and IS literature on technology adoption often considers network externalities as one of the main factors that affect adoption decisions. It assumes that potential adopters achieve a certain level of expectations about network externalities when they have to decide whether to adopt a particular technology. However, there has been little discussion on how the potential adopters reach their expectations. This article attempts to fill a gap in the literature on adoption of information technology (IT), by offering an optimal control perspective motivated by the rational expectations hypothesis (REH) and exploring the process dynamics associated with the actions of decision makers who must adjust their expectations about the benefits of a new technology over time due to bounded rationality. Our model primarily addresses technologies that exhibit strong network externalities. It stresses adaptive learning to show why different firms that initially have heterogeneous expectations about the potential value of a technology eventually are able to arrive at contemporaneous decisions to adopt the same technology, creating the desired network externalities. This further allows the firms to become catalysts to facilitate processes that lead to market-wide adoption. We also discuss the conditions under which adoption inertia will take over in the marketplace, and the related managerial implications.Acknowledgement The authors wish to thank the participants in the Information and Decision Sciences Workshop at Carlson School of Management of University of Minnesota, and the anonymous reviewers of this article and a related paper for helpful suggestions. We also appreciate input offered by Norm Chervany, Eric Clemons, Gordon Davis, Rajiv Dewan, Fred Riggins, Paul Glewwe, Paul Johnson, Rajiv Sabherwal, Jan Stallaert and Chuck Wood. An earlier version of this research appeared in the Proceedings of the 2002 INFORMS Conference on Information Systems and Technology, and reflects the input of several helpful reviewers. A related paper is Au, Y. A., and Kauffman, R. J., What Do You Know? Rational Expectations and Information Technology Investment, Journal of Management Information Systems, 20, 2 (Fall 2003), 49–76.