April 2001, Volume 1, Number 1
Summary: 
YMERI, H., NAUWELAERS, B., MAEX, K., VANDENBERGHE, S., DE
ROEST, D.,STUCCHI, M. FrequencyDependent Expression for Mutual Impedance per Unit Length of Interconnects on Lossy Semiconducting Substrate [full paper] Simple and accurate closedform expressions for the frequencydependent mutual inductance and resistance per unit length of coupled interconnects on lossy silicon substrate are presented. Based on the closedform evaluation of the integral equations for the magnetic vector potential (taking into account the induced current density distribution inside silicon substrate), the closedform expressions for the series impedance parameters are obtained. The validity of the proposed analytic solutions has been checked by a comparison with a quasiTEM spectral domain approach and an equivalentcircuit modeling procedure.

Jerzy BARGLIK  Ivo DOLEŽEL  Martin ŠKOPEK  Bohuš ULRYCH Surface Induction Hardening of AxiSymmetric Bodies [full paper] The paper deals with the mathematical and computer modelling of the surface induction hardening of axisymmetric ferromagnetic bodies. The mathematical description of this nonstationary process consists of two secondorder partial differential equations describing the heating of the body (time evolution of the electromagnetic and consequent temperature field) and a theoretically empirical algorithm for mapping the consequent cooling in various liquid media and hardening. The task is solved in the quasicoupled formulation, with partial respecting the temperature dependencies of all important material parameters. The theoretical analysis is supplemented with several illustrative examples, whose solution was performed in cooperation of professional code QuickField and singlepurpose user program package developed and written by the authors (as far as they know, no existing commercial program is able to map the complete process). The results showing the distribution of hardness as well as particular material components (martensite, ferrite, pearlite) within the hardened body are discussed.

Viktor ŠPÁNY  Pavol GALAJDA  Milan GUZAN The State Space Mystery in MultipleValued Logic Circuit with Load Plane – Part I [full paper] In the article presented we deal with new knowledge of the behaviour of dynamical systems both from theoretical and practical point of view. Switching sequential circuits are an indispensable part of many modern electronic devices, such as memory cells, flipflop sensors and many others. Since the invention of flipflop switching circuits, the study of their dynamic behaviour has played an everincreasing role. The dynamic properties of sequential circuits can be investigated by means of switching between the system's attractor. In this paper the boundary surfaces are discussed that play a crucial role in the process of switching. By "analysis of the multivalued logic (MVL) circuit" we understand graphical representation of boundary surfaces that divide the basins of attraction. Each region of attraction contains one stable equilibrium, i.e. a stable singularity or a stable limit cycle. At existence of stable limit cycle are boundary surfaces very complicated and the control of such MVL circuit would most probably be problematic. Therefore we expected that when the stable limit cycles are absent the shape of the boundary surfaces will be simple and therethrough investigated structure would be more simply controlled. The simulation of the MVL structure shown that no always is morphology of the boundary surfaces simple when the stable limit cycles are absent. The knowledge about of morphology of the boundary surfaces corresponding to stable attractors makes it possible to design reliable methods of control of MVL structures.

Štefan HUDÁK  Slavomír ŠIMOŇÁK Multi FDT Interfacing [full paper] A widely recognized and accepted assertion in computer science community states that there will not exist a single formal description technique (FDT) for all aspects of the systems to be expressible. The paper tackle upon the issue of interfacing different FDTs for design and analysis phases of the discrete systems. Direct vs. indirect interfacing is treated. There is a number of reasons why a formal specification is useful, and it grows more important, as the designated system becomes larger and more complex. Very often that requirements are rather intuitive and imprecise, and are expressed in terms of problem domain they came from. Formal specification (of a system) is a formal expression of requirements on the system designed and thus lays between the requirements and destination code of the system. The advantage of formal description techniques (FDTs) usage is also the ability of validation of requirements understanding and detection of errors at early stages of system development [5]. For large and complex systems, testing cannot prove the right functionality of the system, because it is incomplete and thus does not check the behavior of the system in all reachable states.

Ladislav VARGA  Peter LEŠČINSKÝ  Ľubomír BEŇA Mechanical Calculation of Overhead Power Line Conductor under Combined Load [full paper] This paper deals with mechanical solution of overhead transmission lines under combined (ice and concentrated mechanical load), functioning in vertical direction. Line conductor under nonequally distributed loads along the span is analysed as combined, i.e. inhomogeneous elastic thread, that is not continuous parabola along whole span. For the sake of the use of conductor state equation, inhomogeneous mechanical load must be replaced by equivalent homogenous load by means of the load factor. To solve of these problems allows socalled “ method of equivalent support”. The basic principle of this method is substitution of conductor under optional loading by equivalent elementary onedistance hinge jointed support loaded as conductor. By this method (by destination of support diffracted moments from equations of equilibrium) is possible common determination of expressions for the calculation of mechanical parameters of conductor under combined loading. Theoretical analysis, i.e. sequence of venting relations for determination of shape of suspended conductor, mechanical stress, loading factor, equivalent mechanical load, length of conductor and its sag in arbitrary point on level span for common combination loading is complemented by example for concrete, us defined combined loads. Concrete, ice coatingone concentrated load and ice coatingthree concentrated load. The example of concentrated load are interphase spacers used for increase of safety of overhead transmission lines by elimination of danger touching of conductors or by elimination of undesirable consequence s of dynamic effects at the line. Given method can be used for designing and installation of this spacers, as well as to determination of result static state and the result changes of mechanical parameters of line after their installing.

Pavol GALAJDA  Dušan KOCUR  Rudolf ZETÍK Spread Spectrum Communication via Chaotic Synchronizations and Modulations [full paper] During the past, there has been tremendous interest worldwide in the possibility of exploiting chaos in wideband communication systems. Several different chaotic modulation techniques have been proposed up to date. In this paper it is demonstrated how Chua’s circuits can be used to implement a secure communication systems. Finally chaotic system for use with standard spreadspectrum modulation is introduced.

Alena PIETRIKOVÁ  Stanislav SLOSARČÍK  Radoslav KOKUĽA  Ján ŠALIGA Bent Multilayer Modules based on LTCC [full paper] The top of a bend in flexural laminated modules has been found to cause warping and cracks in LTCC (Low Temperature Cofired Ceramics) substrates. Experiments have been conducted on the effects of various manufacturer's bending on the structural integrity of DuPont's 951 LTCC and on the delimitation of optimal (marginal) conditions for bending: the bent angle and the number of bent layers. Flexural strengths and stress concentration factors of substrates were measured, and then compared to the literature. This model was able to predict the cracks observed in bent samples and provides a design guideline for unconventional utilization of bent ceramic laminates based on LTCC which should be used for the bent shaped thick film modules. The presented results of investigations and simulations have been realized on the multilayer modulus made in 8 versions, 5 thickness and two types ceramics: as a plane module and ceramic modules warp under the angle up 90° based on Low Temperature 951Cofired Green Tape TM . Measurement of crosstalk signal and pulse response in multilayer bent system was described. The results of the investigations can be summarized in design rules for LTCC bent modules (maximum number of layers, maximum bent angle, arrangement and stocking conductor lines in bent laminated electronic modules).

Pavel ZÁSKALICKÝ Optimization of Excitation of the Switched Reluctance Motor [full paper] The present paper describes the methodology of the excitation current calculation of switched reluctance motors in the vicinity of the unaligned rotor position. Torque direction of the reluctance machine does not depend on the direction of the excitation current, but on the mutual position of the stator pole and rotor tooth. For this reason, the excitation can be unipolar, what considerably simplifies power supplies and controls circuits. The torque of the machine depends both on the excitation current value and the rate of the change in inductance with respect to rotor position. To reach the maximum torque it is necessary to excite supplying transistors in a suitable time in which the current would reach its maximum value in the instant of overlapping the stator pole and rotor tooth. The relation between the inductance of the phase and the rotor position in the region of the unaligned axis may be replaced by parabola. The stator resistance is neglected, to get an analytical solution of the differential equation of the machine electrical circuit. The current equation enables to calculate the optimal switching angle.

Rastislav LUKÁČ  Ján LIZÁK Optimised Permutation Filter [full paper] This paper focuses the use of permutation theory in image processing, namely we present new results related to optimised permutation filters. Thus, to form an estimate in the environment corrupted by impulse noise, an optimised set of rank rules provides the best tool for outliers rejection. Nonlinear filters based on permutation theory, called permutation filters, incorporate to a filter design both temporalorder and rankorder information included in a permutation group. Unlike a majority of rankorder based filters, where only rankorder information of an ordered input set is considered, by using the full potential of the permutation group transformation, an estimate accuracy given by optimised permutation filters is extremely high. In general, an optimisation algorithm does not exclude the use both mean absolute error and mean square error criteria. However, in the case of the mean absolute error criteria, the optimised permutation filter should provide the signaldetails preservation rather than the noise attenuation and contrariwise the achieving of the optimised permutation filter under minimisation the mean square error criteria is characterised by the noise suppression rather than the preservation of image features. Based on above discussion, the novelty of this paper lies at the analysis the optimisation parameters such as “forgetting factor” and optimisation criteria. We will show that in the case of small window sizes (e.g. a window size equal to five), there is necessary to achieve the best balance between the noise suppression and the signaldetails preservation. Thus, we provide an optimisation criteria compromise. Next, the influence of used optimisation criteria is decreased with an increased window size, since a permutation group size is larger considerably than an input sequence. For this “static” case, we provide the dependence of estimation accuracy on the “forgetting” parameter. All above conclusions are supported by a number of figures and tables.

Martin TOMÁŠEK Design of Distributed System Based on Technology of Mobile Agents [full paper] An information system operating in environment that is highly distributed, heterogeneous, extremely dynamic and comprising many autonomous nodes must handle several emerging problems. Concept of highlevel communication is the most important problem within the flexible distributed system. Our research on distributed systems in heterogeneous computational environment tries to combine technologies as software agents and mobile code. The paper presents principles and an architecture where mobile agents could move across distributed environments, integrate with local resources and other mobile agents, and communicate with the users. There are also two concepts of interagent communication defined: sessionoriented communication scheme and anonymous communication scheme.

Eva OCELÍKOVÁ Dimensionality Reduction of Feature Space [full paper] This paper deals with the problem of dimensionality reduction of feature space. Two major categories of dimensionality reduction methods, namely feature selection and feature extraction are described and their differences from the viewpoint of usability are discussed.Feature selection methods can be defined as choose the best subset of size d from the given set of D features. The best subset optimized a criterion function ) ( J over all possible subsets of d features. Unlike feature selection methods, feature extraction methods are based on a transformation of the original features. The term feature transformation also applies to these methods. Although from a purely mathematical point of view, feature selection is a special case of feature extraction (the transformation matrix has "1"s on the main diagonal and "0"s otherwise), the have significant practical differences. These differences will determine which approach better fits a task's requirements and goals. Feature preserves data interpretability; feature extraction causes a loss of interpretability. Feature selection has lower discriminative power then feature extraction does. These properties reveal that these methods are somewhat contradictory. Feature selection methods will be more suitable where the user wants to preserve the interpretability of the original data and prefers decision making on the basis of meaningful features. Furthermore, they will be suitable when the user wants to reduce the tediousness and costs of data acquisition by finding the data components that can be completely excluded from the remaining acquisition process. Feature extraction methods will be suitable when the data acquisition process does not represent any problem and there is no need to keep the original interpretability of data. This article focuses on the feature selection methods, namely "exhaustive search" method and "d best features" method, which are discussed in more detail.

Milan PEŤKO Solar Source Design with AC Output [full paper] The article discusses the design of low power solar source. The power solar source consists of battery, electronic part and a solar module that uses solar cells. The paper presents an electronic part and design of solar module with AC output. The solar module is used in a mobile low power source as a source of electrical energy. The presented paper deals with comparison between measured values and simulation data of combined solar cells circuit. Next, the paper presents electronic application by using PWM. There has been realized the solar cell simulation from load characteristic measurements and by using mathematical model. By the application of simulating program of PSpice various solar cells connections and its reversible checks the simulation model at certain measurement conditions can be verified. The main aim of the application is to obtain a high efficiency and reasonable pricing. In order to obtain high efficiency the different electronic applications are used. The electronic part is divided into: stabiliser, alternating inverter, switch transistors, filter, transformer. The paper deals mainly with alternating inverter. By connecting one of the various alternating inverters the efficiency of transforming of voltage is changed. The consequential equipment was suggested step by step. There are cheaper applications, but the efficiency is lower, or there are more expensive ones with a higher efficiency or combination of them. The measuring data are depicted only for application of higher efficiency.
