Showing papers by "University of Maribor published in 1994"

Decision trees based on automatic learning and their use in cardiology

Abstract: Computerized information systems, especially decision support systems, have become an increasingly important role in medical applications, particularly in those where important decision must be made effectively and reliably. But the possibility of using computers in medical decision making is limited by many difficulties, including the complexity of conventional computer languages, methodologies and tools. Thus a conceptual simple decision making model with the possibility of automating learning should be used. In this paper we introduce a cardiological knowledge-based system based on the decision tree approach supporting the mitral valve prolapse determination. Prolapse is defined as the displacement of a bodily part from its normal position. The term mitral valve prolaps (PMV), therefore, implies that the mitral leaflets are displaced relative to some structure, generally taken to be the mitral annulus. The implications of the PMV are the following: disturbed normal laminar blood flow, turbulence of the blood flow, injury of the chordae tendinae, the possibility of thrombus's composition, bacterial endocarditis, and finally hemodynamic changes defined as mitral insufficiency and mitral regurgitation. Uncertainty persists about how it should be diagnosed and about its clinical importance. It is our deep belief that the echocardiography enables properly trained experts armed with proper criteria to evaluate PMV almost 100%. But unfortunately, there are some problems concerned with the use of echocardiography. In that manner we have decided to start a research project aimed at finding new criteria and enabling the general practitioner to evaluate PMV using conventional methods and to select potential patients from the general population. To empower one to perform needed activities we have developed a computer tool called ROSE (computeRised prOlaps Syndrom dEtermination) based on algorithms of automatic learning. This tool supports the definition of new criteria and the selection of potential PMV-patients.

Observer-based sliding mode control of a robotic manipulator

Abstract: This paper presents a new approach for the design of variable structure control (VSC) of nonlinear systems. The approach is based on estimation of joint acceleration signals with introduction of load estimation with the asymptotic observer. The control system is insensitive to parameter variations for a chosen switching hypersurface in conditions when it is reached by the dynamic motion with the required dynamics. The parameter insensitive response provided by this control method is demonstrated on the model of the SCARA robot. Simulation results confirm the validity of accurate tracking capability and the robust performance.

Landau-de Gennes theory of the chevron structure in a smectic liquid crystal

Abstract: The covariant form of the Landau–de Gennes free energy is used to study the chevron structure formed by cooling from the Sm-A to the nonchiral Sm-C phase in a surface-stabilized cell with planar boundary conditions. We show that the chevron is the thermodynamic equilibrium structure. The chevron structure is studied depending on the liquid-crystal elastic properties, temperature, and the surface orientational anchoring strength. We show that the bistability of the chevron structure results from the continuity of the molecular director over the chevron tip of finite width, and is strongly dependent on the surface orientational anchoring. We estimate analytically the threshold temperature for the chevron formation and show that above this temperature the bookshelf geometry is stable. We show that the energy of the chevron interface follows a power-law dependence on reduced temperature with the exponent of 3/2.

Implantable stimulator for selective stimulation of the common peroneal nerve: a preliminary report.

Abstract: We present details of the modelling, design, and experimental testing of an implantable system with a monopolar half-cuff electrode for selective stimulation of fibres within certain superficial regions of the human common peroneal nerve which is capable of making a selective activation of muscles, thus contributing to strong dorsal flexion and moderate eversion of the hemiplegic foot. The development of the cuff electrode was based partly on data obtained from histological examination of human common peroneal nerves, and from previously described models of excitation of myelinated nerve fibres. The modelling objectives were to determine the electric field that would be generated within the deep peroneal branch of the nerve by a monopolar half-cuff electrode installed on the nerve behind the lateral head of the fibula. The extent of initial excitation of the nerve fibres within the superficial region of the deep peroneal branch elicited by a monopolar half-cuff electrode was predicted. In the past 6 month...

Lipase catalysed esterification at high pressure

Abstract: From the comparation of esterification between oleic acid and oleyl alcohol, catalyzed by the Mucor miehei immobilized lipase in a batch stirred tank reactor, in a solvent free system and system where the solvent was supercritical carbon dioxide it is obvious that reaction rates are higher at supercritical conditions than in the solvent free system. To obtain the data on the solubility of substrates and product (oleyl oleate) in supercritical carbon dioxide, fluid phase equilibria measurements in the static equilibrium cell have been done. The results showed that the temperature change between 30 d`C and 50 d`C doesn't affect the solubility of the substances in SC CO2 very much, but with higher pressure (between 100 and 300 bar) the solubilities of oleic acid, oleyl alcohol and oleyl oleate slightly increase. From the data it is obvious that oleic acid and oleyl alcohol have better solubility in supercritical CO2 than oleyl oleate and therefore the separation of both substrates from oleyl oleate with supe...

Structure of the subgenual organ in the green lacewing, Chrysoperla carnea.

Abstract: REM and TEM studies of the subgenual organ in Chrysoperla carnea (Neuroptera: Chrysopidae) show that it is composed of three scolopidia, each with one sensory, one scolopale and one cap cell. The distal part of the dendrite shows a cilium with a ‘9 + 0’ structure. The cross-handing pattern of the ciliary root has a periodicity of bands of about 61 nm. The scolopale material in a certain part of the scolopale cell is organized into five rods. The cell bodies of all three cap cells form a lens-like structure. the velum, which is fixed to the leg wall and the trachea with an extracellular material. The importance of the velum is discussed. Four types of intercellular junction are found; spot desmosomes. belt desmosomes, septate junctions and gap junctions.

Determination of partial molar volumes at infinite dilution using SFC technique

Abstract: The use of supercritical-fluid chromatography for determining partial molar volumes of some substances (linear, cyclic and aromatic hydrocarbons, benzaldehyde) at infinite dilution in supercritical C02 is presented and discussed. Partial molar volumes at infinite dilution are obtained from the variation of the retention properties with the density of mobile phase at 313.15 K and in the pressure range from 80 to 280 bar.

Boundary element method for steady 2D high-Reynolds-number flow

Abstract: We deal with the numerical simulation of fluid dynamics using the boundary-domain integral technique (BEM). The steady 2D diffusion-convection equations are discussed and applied to solve the plane Navier-Stokes equations. A vorticity-velocity formulation has beeen used. The numerical scheme was tested on the well-known'driven cavity'problem. Results for Re=1000 and 10,000 are compared with benchmark solutions. There are also results for Re=15,000 but they have only qualitative value. The purpose was to show the stability and robustness of the method even when the grid is relatively coarse

Measurement of 90Sr activity with Cherenkov radiation in a silica aerogel

Abstract: A method of determination of 90Y (E β max = 2.27 MeV , t 1 2 = 64 h) , the daughter of 90Sr (E β max = 0.546 MeV , t 1 2 = 28.5 yr) , on the basis of Cherenkov radiation of the β particles in a silica aerogel has been tested. The relatively high end-point energy of the 90Y β-spectrum, together with a suitably chosen aerogel refractive index and thus electron threshold energy, permits elimination or at least a considerable reduction of the interference of other β emitters with lower end-point energies. The interference of γ emitters is reduced by using a thin, transmission multiwire proportional chamber in coincidence with the aerogel Cherenkov detector. Any possible contribution of other radionuclides to the count rate may be monitored by the shape of the Cherenkov pulse height spectrum, which depends sensitively on the electron energy. With an aerogel refractive index of 1.055, which corresponds to an electron threshold energy of 1.09 MeV, we have obtained an efficiency of 5 × 10−3 for 90Y. The background counting rate of 15 × 10−3 s−1 is stable (σ = 1 × 10−3s−1) and allows the determination of 1 Bq of 90Y activity in a few hours of measurement of a thin sample. If the ratio of 90Y to 90Sr activity is known (e.g. in equilibrium), the activity of 90Sr may be obtained.

Three years of support for a theory: two-generation cycles in the transition from a preindustrial to a modern society

Abstract: Historical data show that the countries that made their transition from a preindustrial life and economy to modern ones first (ie, the West,) have experienced 70–year or two–generation cycles in the process The latecomers (eg, Yugoslavia and the Soviet Bloc countries) passed through the same stages later on In such a perspective the period from the 1920s to the 1990s can be viewed as a two–generation cycle with essentially the role of enlightened absolutism, under the name of communism, in Central and Eastern Europe The feudal style of living and ruling was replaced by it, and preconditions for the transition to a modern market economy were created One can conclude that the falling apart of communism and its empires was primarily an organic economic development process, not an incidental nationalistic issue Our predictions from 1987 and 1989 have been confirmed over the past few years by the real events in Yugoslavia and the Soviet Bloc

Dynamic programming and convex clustering

Abstract: In this paper the notion of convexity of clusterings for the given ordering of units is introduced. In the case when at least one (optimal) solution of the clustering problem is convex, dynamic programming leads to a polynomial algorithm with complexityO(kn3). We prove that, for several criterion functions, convex optimal clusterings exist when dissimilarity is pyramidal for a given ordering of units.

Influence of different heat treatments on corrosion resistance of martensitic stainless steels

Abstract: The changes in microstructure, caused by different heat treatments, have considerable influence on the corrosion resistance of stainless steels. The heat treatment causes an alteration of carbide contained in steels. Changes in the constant B for these steels, (B = Rp · iCOR) have been observed in quenched, tempered and annealed conditions. Pitting corrosion resistance of martensitic stainless steels in quenched and tempered conditions in 0.1M H2SO4 by adding Cl− ions has been investigated. Einflus der Warmebehandlung auf die Korrosionsbestandigkeit nichtrostender martensitischer Stahle Die Anderung des Gefuges, verursacht durch Warmebehandlung, macht sich nennenswert auf die Korrosionsbestandigkeit nichtrostender Stahle bemerkbar. Warmebehandlung verursacht eine Veranderung der im Stahl enthaltenen Karbide. Veranderungen in der Konstante B (B = Rp · iCOR) wurden fur diese Stahle im abgeschreckten, getemperten und gegluhten Zustand festgestellt. Die Lochkorrosionsbestandigkeit von nichtrostenden martensitischen Stahlen im abgeschreckten und getemperten Zustand wurde in chloridhaltiger 0,1M H2SO4 untersucht.

On the locally anisotropic uniaxial stochastic reorientations of molecular cores in some mesomorphic phases

Abstract: Based upon the model of random walk of a particle on an arc of the circular segment, it is argued that the measurements of aniline ring spectral densities of motion, J1(ω0) and J2(2ω0) of 50.7-d4 sample [Dong, R. Y., Phys. Rev. A42, 858 (1990)] represent the case of a strong biasing of the ring uniaxial reorientation about its para-axis in the nematic and for the first time also in the Sm A phase. The para-axes themselves seem to be subjected to the slower reorientational motion about the direction of the macroscopic uniaxial symmetry. Both motions are thermally activated and seem to be additionally slowed down in the smectic A phase, accompanied, however, by an increase of the segment apex angle at the nematic-Sm A transition temperature. It is suggested, that the two spectral densities of motion are likely to undergo a discontinuity at the nematic-Sm A phase transition, yet only J1(ω0) might be amenable to an experimental verification.

On the use of quartz crystal capacitive dependence for measurement of 0–1 ml volumes

Abstract: The use of a differential oscillator sensor structure in a capacitance sensor is presented. Investigations are focused on the design and operational analysis of an oscillator differential structure in which the oscillation frequencies of the two oscillators are very close, and on the application analysis of capacitive-dependent crystals. In addition, the excitation of the entire sensor with stochastic test signals has been analysed by the correlation deconvolution method, also known as the direct digital method (DDM). The compensation of temperature and voltage influences, as well as disturbing noise signals, is included. The area of operation and the uncertainty of the sensor with and without the test signal are given as well. When designing the capacitance sensor, the problems regarding the source of stable oscillation, temperature compensation, the influence of supply voltage, noise, and A/D and D/A conversion occur in the operation range under 1 pF. The pulse-width module, which forms pulse-width-modulated high-frequency current pulses, is the proposed solution. With these pulses the capacitor in the integration element is charged or discharged. In this way we benefit from the fact that the capacitor's voltage increases linearly if it is charged by a constant current. As the charging is affected only by the current pulses, which require an adequate current, the disturbing noise signals do not affect the capacitor charging. Likewise, the pulse-width module compensates the effects of temperature and voltage by means of modulation. The correlation determination of the measuring value is of prime importance for the determination of end values. Two computer-aided modes of operation are suggested: dynamic measurement control and the correlation determination of differences. Several experiments have been carried out to investigate the method's possible applications. The experimental results of 0–1 ml volume measurements are shown. The method is linear in the range of work and ensures an uncertainty below 0.01% in this range. The volume-measurement uncertainty (0–1 ml) is less than 0.05% ( T = 15–25 °C).