Showing papers by "University of Maribor published in 1997"
01 Jan 1997
220 citations
TL;DR: In this paper, phase equilibria for polyethyleneglycol and carbon dioxide mixtures were determined and the S-L transition of all binary systems were represented by one line.
Abstract: Phase equilibria (solid-liquid-gas) for polyethyleneglycol (with molar masses 1500, 4000, 8000 and 35 000 g mol−1) and carbon dioxide mixtures were determined. It was found that the S-L-V lines in P-T projection for all polyethyleneglycols studied show a temperature minimum and a temperature maximum. These phenomena have not been reported previously in the literature. If a reduced temperature (obtained by dividing the temperature of the solid-liquid transition under pressure by the melting point of PEG at 1 bar) is introduced, the S-L transition of all binary systems are represented by one line. The solubility of CO2 in liquid polyethyleneglycols is influenced by pressure and temperature, and is almost independent of the molecular mass of polyethyleneglycol. In a P-T projection, the vapour-liquid equilibrium is represented by a straight line if isopleths are plotted as a function of the reduced temperature. By combining the P-Tred projections of the S-L and L-V transitions, one master diagram can obtained which is valid for all binary mixtures of polyethyleneglycol and CO2 in the pressure and temperature range investigated.
158 citations
TL;DR: The Wiener number W(G) of a graph G is the sum of distances between all pairs of vertices of G, and this result is applied to prove that W(PH) = W(HS) + 36W(ID), where PH is a phenylene, HS a pertinently vertex-weighted hexagonal squeeze of PH, and ID the inner dual of thehexagonal squeeze.
137 citations
TL;DR: For any n ≥ 1 and any k ≥ 1, a graph S(n, k) is introduced in this article, and it is proved that there are at most two shortest paths between any two vertices of this graph.
Abstract: For any n ≥ 1 and any k ≥ 1, a graph S(n, k) is introduced. Vertices of S(n, k) are n-tuples over {1, 2,. . . k} and two n-tuples are adjacent if they are in a certain relation. These graphs are graphs of a particular variant of the Tower of Hanoi problem. Namely, the graphs S(n, 3) are isomorphic to the graphs of the Tower of Hanoi problem. It is proved that there are at most two shortest paths between any two vertices of S(n, k). Together with a formula for the distance, this result is used to compute the distance between two vertices in O(n) time. It is also shown that for k ≥ 3, the graphs S(n, k) are Hamiltonian.
137 citations
TL;DR: In this paper, an artificial neural network (ANN) was applied to inrush detection and reconstruction of distorted secondary CT currents due to saturation, which improved the reliability of the protection operation.
Abstract: This paper suggests the possibility of improving digital power transformer protection. The establishment of inrush in power transformers is becoming unreliable in existing numerical protection. An artificial neural network (ANN) was applied to inrush detection. The saturation of protective current transformers (CT) cannot be totally eliminated despite proper dimensioning. ANN was used for the reconstruction of distorted secondary CT currents due to saturation. In both cases, an ANN was included in the protection algorithm as an extension of the existing methods, which improved the reliability of the protection operation. The paper presents the digital protection algorithm completed in this way and the laboratory equipment by means of which experimental results were obtained. The results confirm faster and more reliable recognition of transformer inrush, as well as satisfactory reconstruction of the distorted secondary CT currents.
129 citations
01 Jan 1997
TL;DR: This paper presents an overview of mixed-integer nonlinear programming techniques by first providing a unified treatment of the Branch and Bound, Outer-Approximation, Generalized Benders and Extended Cutting Plane methods as applied to nonlinear discrete optimization problems that are expressed in algebraic form.
Abstract: This paper presents an overview of mixed-integer nonlinear programming techniques by first providing a unified treatment of the Branch and Bound, Outer-Approximation, Generalized Benders and Extended Cutting Plane methods as applied to nonlinear discrete optimization problems that are expressed in algebraic form. The extension of these methods is also considered for logic based representations. Finally, an overview of the applications in many areas in process engineering is presented.
101 citations
TL;DR: In this paper, the Particles from Gas Saturated Solutions (PGSS) was used to improve technological characteristics of the poorly water soluble calcium antagonist nifedipine and coprecipitates of PEG 4000 were prepared and evaluated.
93 citations
TL;DR: A novel microbend sensor structure composed of single-mode leads and multimode sensing fiber exhibited a level of sensitivity as much as six times higher than that of the classical microbEND sensor configuration when the same sensing fiber was used.
Abstract: We proposed and experimentally investigated a novel microbend sensor structure. The structure is composed of single-mode leads and multimode sensing fiber. The proposed structure exhibited a level of sensitivity as much as six times higher than that of the classical microbend sensor configuration when the same sensing fiber was used. Additionally, single-mode leads reduce lead noise and allow the use of more-coherent sources. The total loss of the proposed nondeformed structure is near 2 dB when the proper splicing method is used.
83 citations
TL;DR: A linear time algorithm is presented which, for a given benzenoid system G, computes the Wiener index of G, based on an isometric embedding of G into the Cartesian product of three trees, combined with the notion of the Wieners index of vertex-weighted graphs.
Abstract: A linear time algorithm is presented which, for a given benzenoid system G, computes the Wiener index of G. The algorithm is based on an isometric embedding of G into the Cartesian product of three trees, combined with the notion of the Wiener index of vertex-weighted graphs. An analogous approach yields also a linear algorithm for computing the Szeged index of benzenoid systems.
81 citations
TL;DR: In this article, a numerical model for determining the pitting resistance of gear teeth flanks is presented, which considers the material fatigue process leading to pitting, i.e. the conditions required for crack initiation and then simulation of fatigue crack propagation.
Abstract: — A numerical model for determining the pitting resistance of gear teeth flanks is presented in this paper. The model considers the material fatigue process leading to pitting, i.e. the conditions required for crack initiation and then simulation of fatigue crack propagation. The theory of dislocation motion on persistent slip bands is used to describe the process of crack initiation, where the microstructure of a material plays a crucial role. The simulation of crack growth takes into account both short crack growth, where the modified Bilby, Cottrell and Swinden model is used for simulation of dislocation motion, and long crack growth, where the theory of linear elastic fracture mechanics is applied. The stress field in the contact area of meshing spur gear teeth and the functional relationship between the stress intensity factor and crack length are determined by the finite element method. For numerical simulations of crack initiation and crack propagation in the contact area of spur gear teeth, an equivalent model of two cylinders is used. On the basis of numerical results, and with consideration of some particular material parameters, the service life of gear teeth flanks is estimated. The developed model is applied to a real spur gear pair, which is also experimentally tested. The comparison of numerical and experimental results shows good agreement and it can be concluded that the developed model is appropriate for determining the pitting resistance of gear teeth flanks.
73 citations
TL;DR: In this paper, the pitting resistance of gear teeth flanks is determined by using finite element methods using an equivalent model of two cylinders with the same radii as the curvature radii of gear flanks in the inner point of a single teeth pair engagement, which represents the worst loading case.
TL;DR: The article examines the sequential heuristic procedure for optimisation of roll cutting in the clothing industry through a combination of approximations and heuristics and found an item-oriented solution.
01 Dec 1997
TL;DR: A powerful automated scheduling method for highly constrained situations based on genetic algorithms and machine learning is developed and can be easily incorporated into an interactive user interface, which can be of major importance when scheduling patients, and human resources in general, is considered.
Abstract: In medicine and health care there are a lot of situations when patients have to be scheduled on different devices and/or with different physicians or therapists. It may concern preventive examinations, laboratory tests or convalescent therapies, therefore we are always looking for an optimal schedule that would result in finishing all the activities scheduled as soon as possible, with the least patient waiting time and maximum device utilization. Since patient scheduling is a highly complex problem, it is impossible to make a qualitative schedule by hand or even with exact heuristic methods. Therefore we developed a powerful automated scheduling method for highly constrained situations based on genetic algorithms and machine learning. In this paper we present the method, together with the whole process of schedule generation, the important parameters to direct the evolution and how the algorithm is guaranteed to produce only feasible solutions, not breaking any of the required constraints. We applied the described method to a problem of scheduling patients with different therapy needs to a limited number of therapeutic devices, but the algorithm can be easily modified for use in similar situations. The results are quite encouraging and since all the solutions are feasible, the method can be easily incorporated into an interactive user interface, which can be of major importance when scheduling patients, and human resources in general, is considered.
TL;DR: In this paper, two-dimensional analysis is used to calculate the service life of a gear with a crack in a tooth root, whereby the direction of maximum strain energy release rate G is sought.
TL;DR: This paper develops a method for neural network control design with sliding modes in which robustness is inherent and robustness in learning control can be improved.
Abstract: This paper develops a method for neural network control design with sliding modes in which robustness is inherent. Neural network control is formulated to become a class of variable structure (VSS) control. Sliding modes are used to determine best values for parameters in neural network learning rules, thereby robustness in learning control can be improved. A switching manifold is prescribed and the phase trajectory is demanded to satisfy both, the reaching condition and the sliding condition for sliding modes.
TL;DR: In this paper, the authors determined the diffusion coefficient of methanol in supercritical CO2 inside the silica aerogel from the dependence of the width of the non-transparent damage area on diffusion times.
Abstract: Drying of alcogel is the most critical step in production of transparent and monolithic silica aerogel. If alcohol extraction with liquid or supercritical carbon dioxide is used, diffusion of alcohol through the alcogel to the CO2 plays an important role. Dependent on the diffusion times, the quality and shape of aerogel samples vary from cracked (short diffusion times) to transparent crack-free aerogels (long diffusion times). At medium diffusion times, the non-transparent area was observed inside the aerogel samples. Diffusion coefficients of methanol in the liquid CO2 at two different temperatures and the diffusion coefficient of methanol in supercritical CO2 inside the silica aerogel were determined from the dependence of the width of the non-transparent damage area on diffusion times.
TL;DR: In this paper, a multilevel-hierarchical approach to the MINLP synthesis of process flowsheets is proposed, which enables one to address different process operations like reactions, connectivity and species allocation, separation, energy and heat integration and HEN through simultaneous superstructure optimization.
TL;DR: It turns out that calcium oscillations can arise without a permanent influx of calcium into the cell, when a calcium-buffering system such as calmodulin is included.
18 May 1997
TL;DR: Detailed determination of parameters values reveal an important influence of the interaction of the direct and quadrature axis excitation on the parameters variation.
Abstract: The paper describes the determination of the parameters of the two-axis model of a synchronous motor with permanent magnets using the results of the measurement of load conditions at different sine voltages and constant frequency. For the determination of parameters of the two-axis model the modified conventional method was used. The machine parameters are determined from measurement data by the results of the calculation of the induced voltage E/sub i/ and internal load angle /spl delta//sub i/. Computational difficulties at parameters determination owing to random inaccuracies in the measurements data are overcome with use of orthogonal polinoms approximation. Detailed determination of parameters values reveal an important influence of the interaction of the direct and quadrature axis excitation on the parameters variation.
TL;DR: In this article, complex design procedures for a continuous and for a single product batch plant were compared, and the final conclusion after applying economic analysis to all variants with single-purpose equipment is that a continuous plant with recycles after energy integration is more profitable than a batch one for all capacities, unless special reasons exist why reactors should be operated the batch way.
Abstract: Complex design procedures for a continuous and for a single product batch plant were compared. Production rate, process structure and energy integration which influence desision-making about continuous or batch operating mode, were considered. The final conclusion after applying economic analysis to all variants with single-purpose equipment is that a continuous plant with recycles after energy integration is more profitable than a batch one for all capacities, unless special reasons exist why reactors should be operated the batch way. An example calculation for a process which is planned to produce a specialty product with three reactions is used to compare the net present worth of continuous and discontinuous operation modes.
TL;DR: A condition on the factor graphs is presented which ensures that such components are isomorphic and it is demonstrated that several familiar and easily constructible graphs are amenable to that condition.
Abstract: Weichsel (Proc. Amer. Math. Soc. 13 (1962), 47-52) proved that the Kronecker product of two connected bipartite graphs consists of two connected components. A condition on the factor graphs is presented which ensures that such components are isomorphic. It is demonstrated that several familiar and easily constructible graphs are amenable to that condition. A partial converse is proved for the above condition and it is conjectured that the converse is true in general. Math. Subj. Class. (1991): 05C60 Key terms: Kronecker product, bipartite graphs, graph isomorphism ∗This work was supported in part by the Ministry of Science and Technology of Slovenia under the grants P1-0206-101 and J1-7036.
TL;DR: In this paper, the authors combine the thermodynamic and the algorithmic methods of process synthesis for complex and energy intensive processes, and the combined approach can be used for optimal design of energy and material parameters of continuous processes.
11 Jul 1997-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, a multianode photomultiplier tube, type H6568 manufactured by Hamamatsu company, has been tested in view of using it for measuring Cherenkov rings in the HERA-B experiment.
Abstract: A new multianode photomultiplier tube, type H6568 manufactured by Hamamatsu company, has been tested in view of using it for measuring Cherenkov rings in the HERA-B experiment. The results of measurements of single-photoelectron pulse-height distributions, uniformity of response, cross-talk, photon detection efficiency, rate dependence of the gain and ageing will be presented and discussed. In addition, the response of the PMT to scintillations of perfluorobutane (C 4 F 10 ), argon and air has been measured.
TL;DR: In this article, the authors investigated differences in EEG alpha activity between gifted and non-identified students, and found that gifted students exhibited higher overall hemispheric activation in a relaxed mental state and exploring the problem, and a lower activation when problem solving was involved.
Abstract: The study investigated differences in electroencephalography (EEG) alpha activity between gifted and non-identified students. Seventeen gifted and 17 non-identified students participated in the experiment. Their EEG was recorded while they solved four problems. Two measures were used: 1) an asymmetry index or differences in hemispheric activity and 2) the overall difference between a relaxed mental state and problem solving. The findings can be summarized as follows: First, gifted students in a relaxed mental condition showed greater left hemispheric activation than did non-identified students. In contrast, during problem solving, non-identified students showed greater left hemispheric activity than did gifted students. Second, gifted students exhibited a higher overall hemispheric activation in a relaxed mental state and exploring the problem, and a lower activation when problem solving was involved, than did non-identified students.
TL;DR: The whole optimization procedure is illustrated by the optimization of an existing large-scale chemical process at increasing levels of simultaneity ranging from the sequential to the simultaneous HEN optimization.
01 Dec 1997
TL;DR: A new algorithm for automated computer-assisted detection of follicles in the ultrasound images of the ovary is proposed, which has a typical object recognition scheme (preprocessing, segmentation, and classification).
Abstract: Monitoring follicles is especially important in human reproduction. Today, the monitoring of follicles is done non-automatic, with human interaction. This work can be very demanding and inaccurate, and in most cases means only an additional burden for the experts. In this paper, new algorithm for automated computer-assisted defection of follicles in ultrasound images of ovary is proposed. It has typical object recognition scheme (preprocessing, segmentation and classification). The algorithm is assembled on the following idea: first, the ovary is estimated (coarse) and then follicles are searched. The methods used are known from literature (despeckle filter, Kirsh's operator, optimal thresholding, thinning shape descriptions), the majority of the work was done experimenting with these methods and selecting the appropriate thresholds. The algorithms computational complexity is of order O(n/sup 2/), which means about 6 minutes of processing time per ultrasound image of dimensions of 768/spl times/576 pixels (on HP 715 machines). Algorithm is not perfect, but it can be easily modified and improved. Recognition rate of follicles with these procedure is around 70%.
TL;DR: It is proved that the fuzzy control system equipped with the discrete supervisory controller is globally stable in the Lyapunov sense.
Abstract: The task of the supervisory controller is to stabilize the systems states within a bounded region defined by designer. In this paper, a discrete approach to the solution of the stable fuzzy control system is presented. It is proved that the fuzzy control system equipped with the discrete supervisory controller is globally stable in the Lyapunov sense. Finally, a fuzzy controller with a discrete supervisory controller is applied to the balance control system, both in simulations and in the real-time implementation.
TL;DR: This paper extends an algorithm to recognize Cartesian graph bundles over a K 4 ⧹ e -free simple base, without induced K 3,3 and conjectures the existence of algorithm for recognition of Cartesiangraph bundle over aK 4⧹ i -freesimple base.
TL;DR: In this paper, the pore size distributions determined from permporometry and liquid-liquid displacement were found, and significant differences in pore sizes were found between the two methods.
TL;DR: In this article, a systematic WKB expansion to all orders for a one-dimensional system with potential was performed and the series was able to sum the series to the exact energy spectrum, and the error of the WKB approximation measured in the natural units of the mean energy level spacing does not go to zero when the quantum number goes to infinity.
Abstract: We perform a systematic WKB expansion to all orders for a one-dimensional system with potential . We are able to sum the series to the exact energy spectrum. Then we show that at any finite order the error of the WKB approximation measured in the natural units of the mean energy level spacing does not go to zero when the quantum number goes to infinity. Therefore we make the general conclusion that the semiclassical approximations fail to predict the individual energy levels within a vanishing fraction of the mean energy level spacing.