Showing papers by "Wrocław University of Technology published in 1993"

Discrete-time Markovian jump linear systems

Abstract: The research is oriented to the control of discrete — time linear systems with randomly changing parameters which can be described by a finite — state Markov chain. The cost critrion is a quadratic form of the controls and states of the system. The criterion parameters also depend on the states of the Markov chain. Two models of observation of the Markov chain are adopted — delay for one step and undelay. It is shown that under appropriate mean square detectability and stability conditions the infinite horizon optimal control problem for the general case of Markovian jump linear quadratic systems has a unique solution when the control system is mean square stable. Necessary and sufficient conditions are given to determine if a system is mean square stable.

Interval and fuzzy extensions of classical transportation problems

Abstract: For a given Transportation Problem, several assumptions can be considered on the supply and demand levels. In accordance with the kind of information the decision maker has, s/he may express those values in many ways. Here three situations are considered: the decision maker can exactly define them as point values, s/he can give them as interval values or, if s/he has vague information, express them as fuzzy numbers. For each of these three cases, different models (classical, interval and fuzzy) of the Transportation Problem may be obtained, respectively. This paper deals with these three different models. The links among them are provided, focusing on the case of the Fuzzy Transportation Problem, for which methods of solution are proposed and discussed.

On the electro‐optic properties of single crystals of sodium, potassium and rubidium acid phthalates

Abstract: The linear electro-optic (Pockels) effect in a series of alkali metal acid phthalate crystals has been studied. Single electro-optic coefficients r and r for sodium (NaAP), potassium (KAP) and rubidium (RbAP) acid phthalates have been measured by employing the modified Mach–Zehnder interferometric technique. The best electro-optic crystal in this series is RbAP with r = 9.10 × 10−12 m V−1, r = 3.05 × 10−12 m V−1 and a sizable figure of merit for electro-optic phase retardation, comparable with that of KDP. The dispersion properties of the electro-optic coefficients for KAP are discussed in detail.

Artificial neural networks for real-time estimation of basic waveforms of voltages and currents

Abstract: New parallel algorithms for the estimation of the parameters of a power system sinewave contaminated by noise are proposed. The problem of estimation is formulated as an optimization problem and solved by using the gradient descent method. Algorithms based on the least absolute value, the least-squares and the minimax (Chebyshev) criteria are developed and compared. The implementation of the algorithms by an appropriate neural network is also given. Illustrative computer simulation results confirm validity and high performance of the proposed solution. >

Absolutely continuous cocycles over irrational rotations

Abstract: For homeomorphisms $$\left( {z,w} \right)\mathop \to \limits^{T\varphi } \left( {z . e^{2xi\alpha } ,\varphi \left( z \right)w} \right)$$ (z, w ∈S 1,α is irrational,ϕ:S 1→S 1) of the torusS 1×S 1 it is proved thatTϕ has countable Lebesgue spectrum in the orthocomplement of the eigenfunctions wheneverϕ is absolutely continuous with nonzero topological degree and the derivative ofϕ is of bounded variation. Some other cocycles with bounded variation are studied and generalizations of the above result to certain distal homeomorphisms on finite dimensional tori are presented.

A relationship between asymmetric Lévy-stable distributions and the dielectric susceptibility

Abstract: This paper, as a complement to the work of Montroll and Bendler, is concerned with the Levy-stable distributions and their connection to the dielectric response of dipolar materials in the frequency domain. The necessary and sufficient condition for this connection is found. The presented probabilistic analysis is based on the mathematically correct representation of the meaning of the relaxation function of a system of dipoles and shows why the same form of a distribution of relaxation rates, namely, the completely asymmetric Levy-stable distribution, should apply in all different relaxing systems. This is in contrast to the traditional definition of the relaxation function, expressed as a weighted average of exponential relaxation functions, which does not explain the universality of the dielectric relaxation law. It also follows from the present considerations that not only is the imaginary part χ″(ω) of the dielectric susceptibility directly related to the Levy-stable distribution (as was found by Montroll and Bendler), but so is the real partχ′(ω). As a consequence the relationχ″(ω)/χ′(ω)=cot(nπ/2) forω>ωp and 0

Parameters affecting economic selection of cable sizes

Abstract: The evaluation of power cable costs considers the present worth of funds required for a new cable installation. Two components make up this cost, first the initial investment cost, and second, the cost of losses ever the life of the cable. Generally, for a given voltage class, the capital investment component increases as the conductor size increases. Conversely the losses decrease as conductor size increases. Selection of cable size is currently based on ampacity considerations; that is, a cable with a minimum acceptable cross-sectional area is usually selected without consideration of the cost of the losses that will occur during the life of the cable. Since the cost of losses over the lifetime of the cable may require substantial selection of a larger conductor size than required, ampacity consideration will often result in smaller value of losses and, hence, may lead to a lower overall cost. A number of examples which demonstrate sensitivity of the conductor cross-section and overall cost to variations in key parameters of the model are presented in the paper. >

On inverting singular kinematics and geodesic trajectory generation for robot manipulators

Abstract: In this paper, a new method is proposed of solving the inverse kinematic problem for robot manipulators whose kinematics are allowed to possess singularities. The method is based upon the so-called generalized Newton algorithm, introduced by S. Smale, and can be adopted to both nonredundant and redundant kinematics. Moreover, given a pair of points in the external space of a manipulator, the method is capable of generating a minimum-length trajectory joining the points (a geodesic), in particular a straight-line trajectory. Results of representative computer experiments, including those with the PUMA 560 kinematics, are reported in order to illustrate the performance of the method.

Inhibition of aminopeptidases by phosphonic acid and phosphinic acid analogues of aspartic and glutamic acids.

Abstract: More than 30 phosphonic and phosphinic acid analogues of aspartic and glutamic acids were synthesized in order to probe how the structural differences of these molecules were reflected in their ability to inhibit cytosolic (LAP) and microsomal (APM) aminopeptidases. Although most of the compounds studied were found to exert only a modest inhibitory effect, the studies provide some information on the structural requirements of the binding subsites and catalytic centers of both enzymes.

THE PHENOMENON OF CONGLOMERATE CRYSTALLIZATION. XXVII. THE EFFECT OF CHARGE COMPENSATING ANION ON THE CRYSTALLIZATION BEHAVIOUR OF [Co(en)2ox]-Cl·4H2O, [Co(en)2ox]Br·H2O, [Co(en)2ox]PF6 AND [Co(en)2ox]I

Abstract: [Co(en)2ox]Cl·4H2O (I) and [Co(en)2ox]Br·H2O (II), crustallize from water at 21°C as conglomerates, space group P212121. Their structures and absolute configurations were determined by refinement of data using both enantiomeric configurations. [Co(en)2ox]PF6 (III) crystallizes as a racemate, space group P21/c. [Co(en)2ox]I (IV) crystallizes in both of the monoclinic space groups C2 and C2/c, in agreement with the phase diagram studies of Yamanari, et al. (see ref. 4). However, we have not been successful in crystallographic studies of this substance since in neither case was it possible to obtain ordered crystals. The conglomerate crystallization pathway selected by (I) and (II), and probably (IV), is shown to be the result of inter-cationic, three-point attachments reminiscent of that postulated as the origin of enzymatic chiral recognition. In this process, spiral strings are formed which resemble polypeptide helices, and which are stitched together by the counternions (and/or waters of crystal...

Optical properties of discontinuous copper films

Abstract: The optical properties of discontinuous copper films on quartz substrates at volume fractions ranging from 0.19 to 1.0 are investigated. The range of dielectric properties, the percolation threshold, and the range of metallic properties are determined. The transmittance spectra of copper films with low volume fractions are interpreted in terms of a modified Maxwell-Garnett theory.

Porous copolymers of trimethylolpropane triacrylate and acrylonitrile

Abstract: The homopolymer of trimethylolpropane triacrylate (TMPA) was synthesized by suspension polymerization using a thermodynamically good solvent (toluene) as a porogen (vol. ratio 1:1). This polymer possesses a high specific surface area (437 m2 · g−1) and porosity (50%). It was found by sorption of benzene and cyclohexane that the majority of the pores are in the range of 1–5 nm. Sorption of phenol, a standard sorbate, from a water solution is proportional to the specific surface area of the mesopores. This sorption is higher than that of nonspecific sorbents (like styrene/divinylbenzene copolymers) and smaller than the sorption of specific ones (like acrylonitrile/divinylbenzene copolymers). Two sets of reactive copolymers were obtained. In the first set, TMPA (20–40 vol.-%) was polymerized with acrylonitrile (AN) in the presence of a constant amount of toluene as an inert diluent (vol. ratio 1:1). In the second set of copolymers the cross-linking degree was kept constant (30 or 40 vol.-% of TMPA) but various solvent mixtures were used, namely: toluene/tetradecane or hexadecane, toluene/2-ethylhexanol, cyclohexanol/tetradecane or hexadecane, cyclohexanol/2-ethylhexanol (vol. ratio 9:1). It was found that all the copolymers are macroporous (volume of pores approx. 1,0 cm3 · g−1) but those obtained in the presence of good solvents display a higher specific surface area and hence better sorption properties towards phenol than those obtained in the presence of poor solvents. The swelling of AN/TMPA copolymers is smaller than that of the TMPA homopolymer due to the presence of additional physical crosslinks formed by the strongly polar nitrile groups.

Further examinations of carbon/polyesterimide thick-film resistors

Abstract: A carbon (carbon black and/or graphite)/polyesterimide resin system has been used as a material for polymer thick-film resistors. The physical and chemical properties of this system as a function of curing temperature were evaluated by means of resistance measurements during the curing process, thermogravimetric analysis, adhesion measurements and scanning electron microscopy examinations. The temperature range between 250 and 300 ‡C has been chosen as the most suitable. The basic electrical properties and the resistance stability to low and high temperature shocks and humidity exposure have been evaluated in relation to the conductive filler used in the ink.

Fuzzy sets in few classical operational research problems

Abstract: The fuzzy set theory offers fresh opportunities for operational research, too. The theory makes possible considerations on some new problems so it extends possibilities of the well known classical models and methods. The latter is shown in the paper by presenting some results in network flows, network planning and assignment problems.

Working parameters of domestic refrigerators filled with propane-butane mixture

Abstract: Some hydrocarbons like propane-butane mixture are prospective alternatives to CFC refrigerants Thermodynamic analysis has proved that propane-butane mixture is characterized by properties similar to those of the R12 refrigerant Domestic refrigerators charged with propane-butane mixture are investigated here The tests prove that R12 can be replaced by the proposed mixture

Laminar and turbulent flow of dilute polymer solutions in smooth and rough pipes

Abstract: In this paper an empirical formula to describe the flow resistance curves λ =f(Re*) of dilute polymer solutions in smooth and rough pipes has been calculated. The experimental curves obtained by the present author and other investigators were compared with the curves derived from the formula. Experiments observing the flow of dilute aqueous solutions of polyacrylamide Rokrysol WF-2 (molecular weight, 3 × 106) and DP9-3981S (molecular weight, 1.5 × 107) through smooth and rough pipes were carried out in laminar, transitional and turbulent flow regions. The concentration of the polymer solution was varied from 0.001% to 0.05%. The pipes used had diameters of 5.8, 11.0 and 21.0 mm with roughness of between 0 and 0.5 mm.