Preface

ThisspecialissueoftheJournalofComputerScienceandTechnologycontainsthePro-ceedingsoftheinternationalSummerSchoolandWorkshoponFormalModelsofProgram-mingandtheirApplications,heldinBeijingonSeptember17-20,1997.ThiseventwaspartoftheKIT(KeepinTouch)ProjectSYMSEMoftheEuropeanUnion,andwasjointlyorganizedwithLaboratoryofComputerScience,InstituteofSoftware.'KeepinTouch'isaprogrammeaimedatmaintainingandenhancingthelinksbetweennon-EuropeanscientistsandEuropeaninstitutions.Thepartnersofthissp…     

Monadic second-order definable text languages

Atext is a word together with a (additional) linear ordering. Each text has a generic tree representation, called itsshape. Texts are considered in a logical and in an algebraic framework. It is proved that, for texts of bounded primitivity, the class of monadic second-order definable text languages coincides with both the class of recognizable text languages and the class of text languages generated by right-linear text grammars. In particular it is demonstrated that the construction of the shape of a text can be formalized in terms of our monadic second-order logic. This approach can be extended to the case of graphs. This research was supported by the EBRA Working Group ASMICS 2.     

A mixture-of-experts framework for adaptive Kalman filtering

This paper proposes a modular and flexible approach to adaptive Kalman filtering using the framework of a mixture-of-experts regulated by a gating network. Each expert is a Kalman filter modeled with a different realization of the unknown system parameters such as process and measurement noise. The gating network performs on-line adaptation of the weights given to individual filter estimates based on performance. This scheme compares very favorably with the classical Magill filter bank, which is based on a Bayesian technique, in terms of: estimation accuracy; quicker response to changing environments; and numerical stability and computational demands. The proposed filter bank is further enhanced by periodically using a search algorithm in a feedback loop. Two search algorithms are considered. The first algorithm uses a recursive quadratic programming approach which extremizes a modified maximum likelihood function to update the parameters of the best performing filter in the bank. This particular approach to parameter adaptation allows a real-time implementation. The second algorithm uses a genetic algorithm to search for the parameter vector and is suited for post-processed data type applications. The workings and power of the overall filter bank and the suggested adaptation schemes are illustrated by a number of examples.     

Adaptive combination of PCA and VQ networks

In this paper we consider the principal component analysis (PCA) and vector quantization (VQ) neural networks for image compression. We present a method where the PCA and VQ steps are adaptively combined. A learning algorithm for this combined network is derived. We demonstrate that this approach can improve the results of the successive application of the individually optimal methods.     

Converter configurations and switching frequency for a GTO reactivepower compensator

This paper compares two converter configurations for a multi-10 MVA gate-turn-off (GTO) reactive power compensator (STATCOM) from the viewpoints of converter connection and switching frequency. One is a single-bridge system consisting of a three-phase bridge converter unit and a transformer. Its pulsewidth modulation (PWM) frequency varies from 450 to 1800 Hz, and its line frequency is 50 Hz. The other is a multiconnected converter system consisting of plural, single-, or three-phase converter units and transformers. Its switching frequencies are chosen to be the lowest possible. The evaluated items are harmonic distortion, power loss, GTO utilization factor, and control response. Our simulation study shows that the multiconnected converter system with the lowest switching frequency is superior to the single-bridge system with the higher switching frequency in every case, even when there are severe line faults requiring very quick response. A new control strategy is adopted for obtaining quick response     

An electrostatic microactuator using LIGA process for a magnetic head tracking system of hard disk drives

 We demonstrate an electrostatic micro actuator which is fabricated by LIGA process. The actuator is designed for a magnetic head tracking system of hard disk drives (HDDs). The actuator is essential to achieve very high track density of HDDs. We realize the aspect ratio of 125 by the LIGA process using a Si-Au mask. We propose to use PMMA molds both as the mechanical structure and as the insulator between electrodes. We believe there are great opportunity for the LIGA process in making micro actuators of HDDs. Received: 25 August 1997 / Accepted: 24 October 1997     

Implementing the Double Bootstrap

The single bootstrap already is popular in economics, though the double bootstrap has better convergence properties. We discuss the theory and implementation of the double bootstrap, both with and without the pivotal transformation, and give detailed examples of each. One example is a nonlinear double bootstrap of a Cobb-Douglas production function, and explains the use of Gauss-Newton Regressions as a device to decrease computational time. Another example is double bootstrapping elasticities from a translog production function.     

A new method for mass fabrication of metallic microstructures

 This paper reports on a new method for the production of metallic microstructures with high aspect ratios that combines the advantages of injection moulding with the high precision replication of surfaces by galvanic and electroless metal deposition. LIGA made moulding tools are used to produce plastic “lost forms”, which are partially metallized by a silver cluster beam of high directionality to achieve electrical conductivity. For structures with an interconnected Ag layer at the bottom, galvanic metal deposition is used to form massive microstructures without voids. For isolated structures where contacting is not possible, chemical deposition was used for metal build-up starting from the metallized areas. However, massive electroless deposition beyond about 3 μm was not yet possible due to problems with internal stress in the deposited metal layer that cause delamination from the template. This stress must be reduced by appropriate modifications of the electrolyte. Received: 25 August 1997/Accepted: 22 September 1997