Derivation of Strictly Stable High Order Difference Approximations for Variable-Coefficient PDE

A new way of deriving strictly stable high order difference operators for partial differential equations (PDE) is demonstrated for the 1D convection diffusion equation with variable coefficients. The derivation is based on a diffusion term in conservative, i.e. self-adjoint, form. Fourth order accurate difference operators are constructed by mass lumping Galerkin finite element methods so that an explicit method is achieved. The analysis of the operators is confirmed by numerical tests. The operators can be extended to multi dimensions, as we demonstrate for a 2D example. The discretizations are also relevant for the Navier–Stokes equations and other initial boundary value problems that involve up to second derivatives with variable coefficients.     

Dijkstra, Floyd and Warshall meet Kleene

Around 1960, Dijkstra, Floyd and Warshall published papers on algorithms for solving single-source and all-sources shortest path problems, respectively. These algorithms, nowadays named after their inventors, are well known and well established. This paper sheds an algebraic light on these algorithms. We combine the shortest path problems with Kleene algebra, also known as Conway’s regular algebra. This view yields a purely algebraic version of Dijkstra’s shortest path algorithm and the one by Floyd/Warshall. Moreover, the algebraic abstraction yields applications of these algorithms to structures different from graphs and pinpoints the mathematical requirements on the underlying cost algebra that ensure their correctness.     

Physical attractiveness and health: Comment on Weeden and Sabini (2005).

Evolutionary behavioral biology suggests that certain characteristics of the human face and body are important for mate preferences and are therefore subject to sexual selection. J. Weeden and J. Sabini (see record 2005-11504-001) identify a number of weaknesses in the association between traits' attractiveness and health. In contrast, the authors argue that (a) studies on preferences for physical characteristics that rely on 1 trait permit only limited interpretation, (b) limitations placed on J. Weeden and J. Sabini's review exclude important associations, (c) there are misconceptions in their treatment of some traits, and (d) their selected literature provides an inaccurate picture regarding effect size. The authors suggest that future research in this field should seek conceptual and methodological constancy in trait selection and in the evaluation of attractiveness- and health-related traits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

XML strategies for legacy database search

Over the past few years, XML (Extensible Markup Language) has become the standard for data and document interchange between distributed systems. With the continuing proliferation of the Internet, XML has also become a key technology for transactional e-business. A large percentage of Internet interactions, however, involves searching through documents, Web pages, databases, and other information resources. This article explores some of the ways XML can improve these types of searches. It focuses particularly on searches through legacy databases and on the changes you can make to your legacy systems to effectively exploit XML.     

Extracting Interpretable Fuzzy Rules from RBF Networks

Radial basis function networks and fuzzy rule systems are functionally equivalent under some mild conditions. Therefore, the learning algorithms developed in the field of artificial neural networks can be used to adapt the parameters of fuzzy systems. Unfortunately, after the neural network learning, the structure of the original fuzzy system is changed and interpretability, which is considered to be one of the most important features of fuzzy systems, is usually impaired. This Letter discusses the differences between RBF networks and interpretable fuzzy systems. Based on these discussions, a method for extracting interpretable fuzzy rules from RBF networks is suggested. Simulation examples are given to embody the idea of this paper.     

Mutation Testing in the Refinement Calculus

This article discusses mutation testing strategies in the context of refinement. Here, a novel generalisation of mutation testing techniques is presented to be applied to contracts ranging from formal specifications to programs. It is demonstrated that refinement and its dual abstraction are the key notions leading to a precise and yet simple theory of mutation testing. The refinement calculus of Back and von Wright is used to express concepts like contracts, useful mutations, test cases and test coverage.     

Numerical integration of singular integrands using low-discrepancy sequences

We investigate quasi-Monte Carlo integration for functions on thes-dimensional unit cube having point singularities. Error bounds are proved and the theoretical results are verified by computations using Halton, Sobol’ and Niederreiter sequences. Supported by the Austrian Science Foundation (Project 10223-PHY).     

GPS-based Clock Synchronization in a Mobile,Distributed Real-Time System

In a vehicle tracking system computers aboard moving vehicles determine periodically their geographical position and transmit it to a control center. This paper presents a commercial vehicle tracking system as an example of a distributed real-time system with mobile components and focuses on the issue of clock synchronization. The mobile components of the system obtain highly accurate timing information from the Global Positioning System which is used to synchronize their local clocks to UTC world time. Thus a tight clock synchronization is achieved without imposing additional load on the communication channels of the system.     

Towards Pseudonymous e-Commerce

The lack of privacy is one of the main reasons that limits trust in e-commerce. Current e-commerce practice enforces a customer to disclose her identity to the e-shop and the use of credit cards makes it straightforward for an e-shop to know the real identity of its customers. Although there are some payment systems based on untraceable tokens, they are not as widely used as credit cards. Furthermore, even without buying anything, a customer is already disclosing some information about who or where she may be by just connecting to the e-shop's web server and leaving behind an IP-address. In this paper, we present novel components that enable secure pseudonymous e-commerce. On the one hand, these components allow a customer to browse through an e-shop, select goods, and pay the goods with her credit card such that neither the e-shop operator nor the credit card issuer nor an eavesdropper is able to get any information about the customer's identity. On the other hand, it is guaranteed that none of the involved parties is able to act dishonestly during the credit card payment. Such a system could greatly enhance trust in e-commerce since it overcomes the customers' privacy concerns.