Showing papers by "University of Maribor published in 1993"
TL;DR: In this article, it was shown that zero is the only additive mapping which is skew-commuting on a 2-torsion free semiprime ring, and that any nonzero additive mapping cannot have this property.
Abstract: A mapping f of a ring R into itself is called skew-commuting on a subset S of R if f(s)s + sf(s) = 0 for all s ∈ S. We prove two theorems which show that under rather mild assumptions a nonzero additive mapping cannot have this property. The first theorem asserts that if R is a prime ring of characteristic not 2, and f: R → R is an additive mapping which is skew-commuting on an ideal I of R, then f(I) = 0. The second theorem states that zero is the only additive mapping which is skew-commuting on a 2-torsion free semiprime ring.
46 citations
TL;DR: The modelling, design, and experimental testing of a nerve cuff multielectrode system for selective activation of fibres in superficial peripheral nerve trunk regions which is capable of activating fibre activation in physiological order is presented.
45 citations
TL;DR: In this paper, two color-formulation strategies, tristimulus colorimetric and least-squares curve fitting, are discussed: the trISTIMULUS matching strategy (ΔED65)2 + ( ΔEA)2+ ( ΔEWWF)2 → min, and the least squares curve fitting strategy ( Σjw2j[ΔR(λj)]2→ min).
Abstract: The article discusses two types of colour-formulation strategies: the tristimulus colorimetric strategy (ΔX,ΔY,ΔZ) → (0,0,0) and the least-squares curve fitting Σjw2j[ΔR(λj)]2 → min. Then a new matching strategy (ΔED65)2 + (ΔEA)2 + (ΔEWWF)2 → min is stated, which tries to combine the advantages of the first two strategies: more “balanced” colour differences for several different illuminants (the case of curve fitting) and small colour differences for the illuminant involved in the matching process (the case of tristimulus matching). An algorithm following this new general strategy is constructed using the case of single-constant Kubelka-Munk theory as an example. Results of a few numerical experiments are included for illustration.
31 citations
TL;DR: A model to simulate transverse lipid movement in the human erythrocyte membrane is presented, based on a system of differential equations describing the time-dependence of phospholipid redistribution and the steady state distribution between the inner and outer membrane monolayer, and is called the compensatory flux.
Abstract: A model is presented to simulate transverse lipid movement in the human erythrocyte membrane. The model is based on a system of differential equations describing the time-dependence of phospholipid redistribution and the steady state distribution between the inner and outer membrane monolayer. It takes into account several mechanisms of translocation: (i) ATP-dependent transport via the aminophospholipid translocase; (ii) protein-mediated facilitated and (iii) carrier independent transbilayer diffusion. A reasonable modelling of the known lipid asymmetry could only be achieved by introducing mechanism (iii). We have called this pathway the compensatory flux, which is proportional to the gradient of phospholipids between both membrane leaflets. Using realistic model parameters, the model allows the calculation of the transbilayer motion and distribution of endogenous phospholipids of the human erythrocyte membrane for several biologically relevant conditions. Moreover, the model can also be applied to experiments usually performed to assess phospholipid redistribution in biological membranes. Thus, it is possible to simulate transbilayer motion of exogenously added phospholipid analogues in erythrocyte membranes. Those experiments have been carried out here in parallel using spin labeled lipid analogues. The general application of this model to other membrane systems is outlined.
19 citations
TL;DR: In this paper, it was shown that U contains a nonzero left ideal of R as well as a non-zero right ideal in the subring of R generated by all [D(x), x], x ∞ R, under the assumption that the characteristic of R is not 2.
Abstract: Let D be a nonzero derivation of a noncommutative prime ring R , and let U be the subring of R generated by all [ D(x), x], x ∞ R . A classical theorem of Posner asserts that U is not contained in the center of R . Under the additional assumption that the characteristic of R is not 2, we prove a more general result stating that U contains a nonzero left ideal of R as well as a nonzero right ideal of R .
19 citations
TL;DR: In this paper, the stability of escaped radial structures and planar polar structures (with and without line defects) was analyzed in terms of the ratio of elastic constants K 24/K 11, K 33/k 11, anchoring strength and external magnetic field applied perpendicular to the symmetry axis of the cylinder.
Abstract: Different nematic structures confined to a long cylindrical cavity with homeotropic surface anchoring are studied using a numerical minimization of the free energy of the uniaxial nematic liquid crystal. The stability of escaped radial structures and planar polar structures (with and without line defects) is analysed in terms of the ratio of elastic constants K 24/K 11, K 33/K 11, anchoring strength and external magnetic field applied perpendicular to the symmetry axis of the cylinder. We draw the analogy between the stability diagram of the cylindrical structures and structures in a spherical droplet. In particular, a simple way extracting the value of the saddle-splay elastic constant K 24 from the stability studies is discussed.
16 citations
15 citations
TL;DR: In this paper, a numerical method for calculating the crack propagation in the tooth root of a case-hardened and hardened gear is described, based on the linear elastic fracture mechanics taking into account the total values of loadings and properties of the individual layers of the gear material.
Abstract: The paper describes the numerical method for calculating the crack propagation in the tooth root of a case-hardened and hardened gear. The method is based on the linear elastic fracture mechanics taking into account the total values of loadings and properties of the individual layers of the gear material. The main points are the determination of the stress intensity factor and the numerical calculations of the crack propagation, crack speed and path1.
15 citations
TL;DR: In this paper, an approach to optimal design of statically loaded structures with non-linear response is proposed to replace the original problem with a sequence of similar problems from which corresponding approximate problems can easily be obtained.
Abstract: A commonly adopted procedure to solve a structural optimum design problem is to improve the design iteratively by solving a sequence of simpler problems, where each of these is obtained as an approximation of the original problem. Considering structures with linear response, this procedure works very well and can be implemented quite straightforwardly. However, considering structures with non-linear response, the situation is more sophisticated since structural stability properties have to be taken into account.
The paper presents an approach to optimal design of statically loaded structures with non-linear response. It is proposed to replace the original problem with a sequence of similar problems from which corresponding approximate problems can easily be obtained. These similar problems additionally contain an estimation of the critical load constraint while other constraints are imposed at some properly chosen load level, which is lower or at most equal to the critical load level. By this approach, the structural stability requirements are taken into account in an effective manner. The efficiency is illustrated with several examples involving kinematic as well as material non-linear effects.
14 citations
TL;DR: Computed test examples show that preconditioned CG methods can offer some major advantages over direct methods in the case of memory demands and computer time consumption.
Abstract: The paper deals with the iterative solution of systems of linear equations arising in viscous flow computation by the boundary-domain integral method (BDIM) with the subdomain technique. Three versions of conjugate gradient method — the bi-conjugate gradient method (bi-CG), conjugate gradients squared (CGS) and its variant bi-CGSTAB - are compared with the Gauss elimination direct method. Different types of preconditioning of matrices are tested including Jacobi and incomplete factorisation (ILU) preconditioners. A comparison of iterative and direct methods is done on a few test examples including Poiseuille's flow in a narrow channel and flow in a channel with circular obstacles. Special attention is given to behaviour of iterative methods in cases of fluid flows with higher Re numbers, where systems of linear equations become ill-conditioned. Whereas for low Re numbers all types of preconditioning used behave very well, this is not the case with higher Re numbers, where only ILU preconditioning preserves the stability and convergence of conjugate gradient methods. Among CG methods CGS and bi-CGSTAB are to be preferred since they reduce the error in the fastest and smoothest way. Computed test examples show that preconditioned CG methods can offer some major advantages over direct methods in the case of memory demands and computer time consumption.
10 citations
TL;DR: In this paper, Slovenia marks one year of independence and the first day of Slovenia's independence from Slovenia in 1993. Europe-Asia Studies: Vol. 45, No. 5, pp. 887-905.
Abstract: (1993). Slovenia—one year of independence. Europe-Asia Studies: Vol. 45, No. 5, pp. 887-905.
06 Sep 1993
TL;DR: A meta data model is introduced as a tool to apply re-use concepts also to database design to provide a structured repository of data models such that a database designer can use models or submodels of previous projects in his actual design and thus accelerating the design process.
Abstract: Software re-use has become a major issue in software engineering research to overcome the so called application backlog in software production. In this paper we introduce a meta data model as a tool to apply re-use concepts also to database design. The main idea is to provide a structured repository of data models such that a database designer can use models or submodels of previous projects in his actual design and thus accelerating the design process. In this meta data model objects are thus organized according to their similarity. In particular, the structure supports the search for similar objects.
TL;DR: The energy level dynamics in the Dyson-Pechukas-Yukawa picture aiming at the understanding of the statistical properties of energy spectra of generic Hamiltonian systems between integrability and chaos was studied in this article.
Abstract: We study the energy level dynamics in the Dyson-Pechukas-Yukawa picture aiming at the understanding of the statistical properties of energy spectra of generic Hamiltonian systems between integrability and chaos. We discuss the role of the major integrals of motion, namely the "energy" and the square of the "angular momentum", which are the only two constants of motion quadratic in perturbation matrix elements. This fact implies the maximum-entropy property of the underlying canonical distribution, which thus makes the Yukawa joint distribution the most probable one. The resulting reduced statistics (a one-parameter family) is expected to provide significant global theoretical description in the quasi-universal non-semi-classical regime of finite typically observed in case of soft chaos (in the transition region between integrability and chaos). However, the power law level repulsion at small spacings cannot be adequately described, since one observes the linear level repulsion instead (or quadratic if there is no antiunitary symmetry), except possibly in the limit of infinitely many levels.
TL;DR: In this paper, thermodynamic properties of immobilized Mucor miehei lipase activity, which catalyses the synthesis of n-butyl oleate are presented.
Abstract: Enzymes lower the activation energy for reaction. Activation energy can be properly determined from Arrhenius plot, however the temperature range is quite limited. At temperatures, higher than the usual biological range, thermal deactivation occurs. In this paper some thermodynamic properties of immobilized Mucor miehei lipase activity, which catalyses the synthesis of n-butyl oleate are presented. Esterification was performed batch-wise in a stirred tank reactor with equimolar substrate ratio. Very low activation energy was determined (9.561 kJ/mol). At temperatures higher than 80 °C rapid thermal deactivation occurred. The constant of this process was found to be 0.898 and enthalpy was 25.877 kJ/mol.
Wirkung der Reaktionsparameter auf die mit immobilisierter Lipase aus Mucor miehei katalysierte Synthese von Olsaure-n-butylester
Enzyme bauen die fur die Reaktionen benotigte Aktivierungsenergie ab. Die Aktivierungsenergie kann dem Arrhenius-Diagramm genau entnommen werden, der Temperaturbereich ist jedoch ziemlich begrenzt. Bei Temperaturen oberhalb des normalen biologischen Bereiches kommt es zu einer thermischen Desaktivierung. In diesem Beitrag werden einige thermodynamische Eigenschaften der immobilisierten Lipase aus Mucor miehei, die die Synthese von Olsaure-n-butylester katalysiert, dargestellt. Die Estersynthese wurde in einem Mischreaktor im Batch-Verfahren mit aquimolaren Substratmengen durchgefuhrt. Eine sehr niedrige Aktivierungsenergie (9.561 kJ/mol) wurde festgestellt. Bei Temperaturen oberhalb 80 °C kam es zu einer schnellen thermischen Desaktivierung. Die Konstante fur diesen Prozes betrug 0.898, die Enthalpie 25.877 kJ/mol.
TL;DR: In this article, the authors show that if an additive mappingf of a prime ring satisfiesd(x)f(x = 0 for allx ∈ R, thenf vanishes on some nonzero left ideal of R and on some notzero right ideal ofR.
Abstract: LetR be a prime ring andd be a nonzero derivation ofR. If an additive mappingf ofR satisfiesd(x)f(x) = 0 for allx ∈ R, thenf vanishes on some nonzero left ideal ofR and on some nonzero right ideal ofR.
05 Sep 1993
01 Sep 1993
TL;DR: Studies on the unsteadiness of requirements specification with special attention to identification and assessment of the requirements risk are presented and results of assessment can be used for management, control and avoidance of requirements risk detected during the system analysis phase.
Abstract: In the computer aided software engineering environments a wide range of data about the development process can be collected. Basing on these easy - collected data our aim is to upgrade a CASE tool to bid such an information on the basis of past activities to the subjects of the software development team which can be interpreted as an estimation of the development process. This information must be evaluated upon the dynamics of the system specification in progress. The dynamic of this process is influenced by the needs of the user. The needs are mostly based on his/her assumptions about the planned system. In this paper studies on the unsteadiness of requirements specification with special attention to identification and assessment of the requirements risk are presented. Results of assessment can be used for management, control and avoidance of requirements risk detected during the system analysis phase.
01 Jan 1993
TL;DR: In this article, the authors defined small business as a company employing 4 to 100 employees and used the total number of employees as a criterion for research analysis, sometimes this is combined with such financial indicators as total annual sales, operating capital or total assets.
Abstract: Small businesses, an essential part of the economy for United States, West European and newly industrialised Pacific countries, constitute majority of business organisations and contribute an ever increasing proportion of economic growth. For example, in the United States they account for about 97% of all businesses, contribute 45% of the Gross National Product and represent 57% of the employment (Ibrahim and Goodwin, 1986; Park, 1990). in Singapore they represent 90% of all registered companies and employ 44% of the workforce (Grant and Raman, 1992). in Slovenia, and in other East European countries, the proportion of small businesses is considerable smaller but is growing fast, because of corporate restructuring or founding of new firms. Small business research often defines small firms differently. Criteria depending on the nature of the business and industry, also vary. Most authors use the total number of employees as a criterion for research analysis. Sometimes this is combined with such financial indicators as total annual sales, operating capital or total assets. Employee criteria range from 15 (Ibrahim and Goodwin, 1986) to 50 (Schleich et al., 1990) for a service sector, to as much as 500 for manufacturing companies (Park, 1990; Yeh et al., 1990). in this study, small business is defined as a company employing 4 to 100 employees.
01 Mar 1993
27 Oct 1993
TL;DR: Reflections about handling of exceptions in hard real-time environments is given, which is among the less elaborated topics in this domain.
Abstract: The objective of this paper is to give some reflections about handling of exceptions in hard real-time environments, which is among the less elaborated topics in this domain.
TL;DR: In this article, the first author was partially supported by the Ministry of Science and Technology of Slovenia, and the second author was supported by NSERC of Canada and the third author was funded by the European Research Council of Slovenia.
Abstract: The first author was partially supported by the Ministry of Science and Technology of Slovenia. The third author was partially supported by NSERC of Canada.
TL;DR: In this article, a REDUCE program to calculate the Birkhoff-Gustavson normal form of a Hamiltonian system with N degrees of freedom is presented, which enables the calculation of the approximate integrals of motion up to a given order in powers of coordinates and momenta.
TL;DR: In this paper, the differential quartz-oscillator method, which is based on the small frequency shift of two oscillators, is analyzed and the experimental results of the measurement of 0-1 ml volumes are given.
Abstract: This paper analyses the differential quartz-oscillator method, which is based on the small frequency shift of two oscillators. This frequency shift is achieved by changing the probe capacitance in the range below 1 pF, which is the area of application of this method. It comprises drift compensation due to the temperature and voltage changes. By the aid of the direct digital method, which reduces the influence of disturbances, the uncertainty of the measurement results is improved. Several experiments have been carried out to investigate its possible applications. The experimental results of the measurement of 0–1 ml volumes are given. The method is linear in this range. It ensures an error below 0.01% and the volume measurement inaccuracy (0–1 ml) is less than 0.05% ( T =15–25 °C).
01 Jan 1993
TL;DR: End-user computing (EUC) is direct hands-on use and development of Information Systems (is) by principal users of the system’s outputs or by their immediate support staff by their immediately support staff.
Abstract: End-user computing (EUC) is direct hands-on use and development of Information Systems (is) by principal users of the system’s outputs or by their immediate support staff (Werherbe, 1988). the rapid growth of EUC has dramatically affected the nature of information systems in many countries. Traditional is development methods have been overwhelmed resulting in long lead times and application backlog. User needs far exceed what is departments can deliver. Recent advances both in hardware and in software alter the economics of computing. Networks of powerful PCs gradually replace mainframes. Decentralisation of organisation business units causes a decentralisation of computing power. the Mis departments have less involvement and less control over purchasing decisions for individual departments. Many organisations implement a strategy that shifts more of the responsibility of system development away from the is Department toward the end-user. On the other hand, the is staff often must support an increasing range of hardware and software and offer appropriate, training for end-users (Rogers, 1992).
TL;DR: In this article, the authors characterized automorphisms and of R satisfying 6D,6D 1, and C 1 DC 1 for a prime ring of characteristic not 2, and showed that automorphism is an algebraic analogue of operator algebras.
Abstract: Let R be a prime ring of characteristic not 2. Automorphisms and of R satisfying 6D,6D 1 , andC 1 DC 1 are characterized. This result is an algebraic analogue of some results for operator algebras.
Proceedings Article•
01 Jan 1993TL;DR: The findings indicate profound differences in IS management issues between Slovenia and the USA and these differences are believed to be largely applicable to other new Central and Eastern European democracies.
Abstract: Formerly one of the Yugoslav republics, Slovenia declared its independence in June 1991 Together with Hungary, the Czech Republic and Poland, Slovenia belongs to the group of leading IS technology markets among the new democracies in Central and Eastern Europe The Delphi technique was used by the authors to compile a list of the key issues in information systems (IS) management in Slovenia, to quantify them, and, through iterations, to strengthen consensus about their importance The results are presented and compared with those obtained in similar studies in the USA The findings indicate profound differences in IS management issues between Slovenia and the USA and these differences are believed to be largely applicable to other new Central and Eastern European democracies
TL;DR: In this article, the authors developed a special piston rough vacuum pump for medical application, the realization of sealing between piston and cylinder wall was an essential problem, and efforts were made in searching for the most adequate gasket shape and material.
TL;DR: It is shown how the true concurrency model for concurrent systems, so-called directed, acyclic, arc-labelled graphs, and propositional Concurrent Temporal Logic can be adapted to give atrue concurrency semantics to shared variables programs, and to write first-order specifications of the programs, so that also concurrency can be specified.
TL;DR: In this paper, the authors obtained trajectories resembling space twisted cycloids for a current ring, after solving the toroidal magnetic field numerically, neglecting the space charge effect, and showed the confining characteristics of such an arrangement which could be used for a straight and curved charged particles guideline.