Showing papers by "University of Ljubljana published in 1996"

The n2 method for the seismic damage analysis of rc buildings

Abstract: A comprehensive, though relatively simple, non-linear method for the seismic damage analysis of reinforced concrete buildings (the N2 method) has been elaborated. The basic features of the method are: the use of two separate mathematical models, application of the response spectrum approach and of the non-linear static analysis, and the choice of a damage model which includes cumulative damage. The method yields results of reasonable accuracy provided that the structure oscillates predominantly in the first mode. Three variants of a seven-storey building have been used as illustrative examples for the application of the method. Four different types of the analysis, with different degrees of sophistication, have been performed in order to estimate the influence of several assumptions and approximations used in the N2 method.

The quasi-wiener and the kirchhoff indices coincide

Abstract: In 1993 two novel distance-based topological indices were put forward. In the case of acyclic molecular graphs both are equal to the Wiener index, but both differ from it if the graphs contain cycles. One index is defined (Mohar, B.; Babic, D.; Trinajstic, N. J. Chem. Inf. Comput. Sci. 1993, 33, 153−154) in terms of eigenvalues of the Laplacian matrix, whereas the other is conceived (Klein, D. J.; Randic, M. J. Math. Chem. 1993, 12, 81−95) as the sum of resistances between all pairs of vertices, assuming that the molecule corresponds to an electrical network, in which the resistance between adjacent vertices is unity. Eventually, the former quantity was named quasi-Wiener index and the latter Kirchhoff index. We now demonstrate that the quasi-Wiener and Kirchhoff indices of all graphs coincide.

The evaluation of waste, surface and ground water quality using the Allium test procedure.

Abstract: The bulbs of Allium cepa were grown in test liquids of various pollution levels as follows: undiluted industrial and municipal waste water; biological treatment plant output water; water from the Drava river upstream and downstream of the city of Maribor; and non-chlorinated drinking water as a negative control test. The paper presents the response of the Allium cepa genetic material to the presence of potential cytotoxic and genotoxic substances in test liquids and the suitability of the Allium cepa testing procedure as a method for short-term determination of water pollution level. The suitability of the Allium test procedure as a system for environmental monitoring is presented. The influence of water pollution on macroscopic and cytologic parameters of the common onion by application of the biological testing method was examined. The macroscopic parameter was inhibition of root growth. The cytological parameters were: aberrant cells in metaphase and anaphase, index of micronuclei appearance and inhibition of cell division. The possibility of categorization the different polluted test liquids into quality classes is presented according to the influence of the test liquids on macroscopic and cytologic parameters. Test liquids are divided into 8 quality classes: the first class is the least polluted surface waters, the second and the third classes are more polluted surface water, the fourth and the fifth classes are biological treatment plant output waters, the sixth till the eighth quality classes are untreated waste waters. The most polluted test liquids (untreated industrial and municipal waste waters) caused sublethal and even lethal effects. The most polluted tested liquids cause the inhibition of root growth over 50% (even up to 74%), decrease of mitotic index over 36% (even up to 66%), increase of presence of interphase cells with micronuclei over 3% and increase of presence of aberrant cells for more than 10 times in comparison to control test.

Performance of the DELPHI detector

Abstract: DELPHI (DEtector with Lepton, Photon and Hadron Identification) is a detector for e^+e^- physics, designed to provide high granularity over a 4\pi solid angle, allowing an effective particle identification. It has been operating at the LEP (Large Electron-Positron) collider at CERN since 1989. This article reviews its performance.

Tuning and test of fragmentation models based on identified particles and precision event shape data

Abstract: Event shape and charged particle inclusive distributions are measured using 750000 decays of the Z to hadrons from the DELPHI detector at LEP. These precise data allow a decisive confrontation with models of the hadronization process. Improved tunings of the JETSET, ARIADNE and HERWIG parton shower models and the JETSET matrix element model are obtained by fitting the models to these DELPHI data as well as to identified particle distributions from all LEP experiments. The description of the data distributions by the models is critically reviewed with special importance attributed to identified particles.

Kinetics of the catalytic liquid-phase hydrogenation of aqueous nitrate solutions

Abstract: Liquid-phase reduction using a solid Pd/Cu bimetallic catalyst provides a potential technique for the removal of nitrates from waters. Kinetic measurements were performed for a wide range of reactant concentrations and reaction conditions in an isothermal semi-batch slurry reactor operating at atmospheric pressure. The effects of catalyst loading and initial nitrate concentration on the reaction rate were also investigated. The proposed intrinsic rate expression for nitrate disappearance is based on the conventional Langmuir-Hinshelwood kinetic approach, considering both equilibrium nitrate as well as dissociative hydrogen adsorption processes to different types of active sites, and assuming an irreversible bimolecular surface reaction between adsorbed reactant species to be the rate-controlling step. The apparent activation energy for catalytic liquid-phase nitrate reduction and the heat of nitrate adsorption, in the temperature range 280.5–293 K, were found to be 47 and 22 kJ/mol, respectively. It is confirmed that the process of catalytic liquid-phase hydrogenation of aqueous nitrate solutions undergoes a redox mechanism.

Explained variation in survival analysis

Abstract: Several measures of explained variation have been suggested for the Cox proportional hazards regression model. We have categorized these measures into three classes which correspond to three different definitions of multiple R2 of the general linear model. In an empirical study we compared the performance of these measures and classified them by their adherence to a set of criteria which we think should be met by a measure of explained variation for survival data. We suggest that currently there is no uniformly superior measure, particularly as the concepts of either uncensored or censored populations may lead to different choices. For uncensored populations, a measure by Kent and O'Quigley and the squared rank correlation between survival time and the predictor from a Cox regression model appear recommendable choices. For the latter, censored survival times are terminated using a very recent data augmentation algorithm for multiple imputation under proportional hazards. With censored populations, Schemper's measure, V2, could be considered. We give an introductory example, discuss aspects of application and stress the desirability of routinely evaluating explained variation in studies of survival.

Improvement of transient stability using unified power flow controller

Abstract: The aim of the paper is to analyze the effect of a unified power flow controller (UPFC) on transient stability margin enhancement of a longitudinal power system. To utilize the UPFC possibilities fully, the three controllable UPFC parameters were determined during the digital simulation process performed by the NETOMAC simulation program. The basis for determination of the suitable damping strategy and for determination of the optimal UPFC parameters is a mathematical model, which describes the interdependence between longitudinal transmission system parameters, operating conditions and UPFC parameters in the form of analytical equations. On the basis of the mathematical model, the theoretical UPFC limits were also detected, and their appearance explained.

The effect of insulin-like growth factor-1 on adult rat cardiac contractility

Abstract: There is increasing evidence that insulin-like growth factor-1 (IGF-1) may play a role in both physiological and pathophysiological events in the mammalian myocardium. The present study investigated the acute effects of IGF-1 on isometric force development in isolated rat cardiac muscle and on intracellular calcium (Ca2+) handling in isolated cardiac myocytes. IGF-1 had a positive inotropic effect on rat ventricular papillary muscles increasing force development by 17.8 ± 4.6%, 18.5 ± 5.8% and 11.9 ± 4.9% (n = 12−20) at concentrations of 1, 10 and 100 ng/ml respectively. Isoprenaline increased tension in these papillary muscles by 56.7 ± 7.7% at a concentration of 100 nM (n = 22). In comparison, insulin increased papillary muscle force development by 11.6 ±3.2%, 17.7±4.1%and 19.7 ± 5.6% at concentrations of 1, 10 and 100 nM respectively (n = 16−20). In the single cardiac myocyte IGF-1 increased, the peak cytosolic free Ca2+ concentration, the amplitude of the Ca2+ transient and the time to peak Ca2+ as measured with the fluorescent bioprobe Indo-1 AM. The positive inotropic response to IGF-1 by rat ventricular muscle is therefore associated with a rise in free, peak cytosolic Ca2+ in isolated cardiac myocytes. Increasing insulin concentrations (1–1000 nM) elicited a progressive elevation in isometric force and free, cytosolic Ca2+. In contrast, in the presence of IGF-1, the maximal rise in isometric force and free cytosolic Ca2+ were both observed at 10 ng/ml. Recent reports have suggested that IGF-1 may act on the mammalian myocardium when administered chronically, but this study is amongst the first to demonstrate an acute effect of IGF-I on the mammalian heart. IGF-1 may prove then to be a novel cardioactive agent in both normal and pathophysiological states.

The ecology of anchihaline caves

Abstract: The dark, mostly brackish, aquatic habitats along the coasts are inhabited by a number of phylogenetically and/or biogeographically interesting animal taxa, whose ecology is poorly known. We are especially ignorant about the nature of the deoxygenated strata that occur in most of these habitats. Are these strata anoxic or only dysoxic? And how are their inhabitants adapted to low oxygen tensions?

Evidence for ideal insulating or conducting state in a one-dimensional integrable system.

Abstract: Using numerical diagonalization techniques we analyze the finite temperature/frequency conductance of a one-dimensional model of interacting spinless fermions. Depending on the interaction, the observed finite temperature charge stiffness and low-frequency conductance indicate a fundamental difference between integrable and nonintegrable cases. The integrable systems behave as ideal conductors in the metallic regime and as ideal insulators in the insulating one. The nonintegrable systems are, as expected, generic conductors in the metallic regime and activated ones in the insulating regime. \textcopyright{} 1996 The American Physical Society.

Self-buffering, self-balancing, self-flushing production lines

Abstract: This research addresses a system of flexible worker assignments in a setting where there are more workers than machines. When organized using this system, a production line balances itself by shifting the workloads continuously and automatically in response to changes in the state of the system. The system is, in effect, buffering itself against variation by altering the work assignments on the fly. This allows the system to operate with very low levels of work-in-process inventory WIP. In this paper, the workers rather than machines are the factor that limits the rate of output. We also assume that the line has a "U" shape, but many of the results do not depend on this topology. An industrial example is described. The system has some interesting and counter-intuitive properties which we demonstrate under a variety of circumstances through an exploratory approach that uses both Markovian and simulation models. Several different policies are compared under conditions of processing time uncertainty. We demonstrate that a flexible assignment system can outperform fixed assignments in a variety of circumstances. Of particular interest is the near absence of balance delay, even when the tasks cannot be divided equally among the workers.

Shapes of bilayer vesicles with membrane embedded molecules

Abstract: The interdependence of the lateral distribution of molecules which are embedded in a membrane (such as integral membrane proteins) and the shape of a cell with no internal structure (such as phospholipid vesicles or mammalian erythrocytes) has been studied. The coupling of the lateral distribution of the molecules and the cell shape is introduced by considering that the energy of the membrane embedded molecule at a given site of the membrane depends on the curvature of the membrane at that site. Direct interactions between embedded molecules are not considered. A simple expression for the interaction of the membrane embedded molecule with the local membrane curvature is proposed. Starting from this interaction, the consistently related expressions for the free energy and for the distribution function of the embedded molecules are derived. The equilibrium cell shape and the corresponding lateral distribution of the membrane embedded molecules are determined by minimization of the membrane free energy which includes the free energy of the membrane embedded molecules and the membrane elastic energy. The resulting inhomogeneous distribution of the membrane embedded molecules affects the cell shape in a nontrivial manner. In particular, it is shown that the shape corresponding to the absolute energy minimum at given cell volume and membrane area may be elliptically non-axisymmetric, in contrast to the case of a laterally homogeneous membrane where it is axisymmetric.

On the kinetics of phenol oxidation in supercritical water

Abstract: Phenol oxidation in supercritical water was carried out in a tubular laboratory-scale reactor operated at a temperature range of 380 C to 450 C and pressures between 230 and 265 bar The phenol feed concentrations were between 500 and 1,000 mg/L, while oxygen was fed into the reactor at 50 to 1,000% of the stoichiometric amount needed to oxidize phenol completely to carbon dioxide Phenol conversions from 16 to 96% were attained as the reactor residence times varied from 15 to 203 s The oxidation obeys a parallel-consecutive reaction scheme that involves multi-ring, intermediate products such as phenoxyl-phenol, biphenol, dibenzo-dioxin, maleic acid, and succinic acid Experimental results showed that the phenol disappearance rate is represented well by a power-law kinetic model in which the rate is proportional to the 04 power of the oxygen mole fraction and roughly linearly proportional to the phenol mole fraction The pressure effect on the disappearance rate was appropriately accounted for by introducing the molar volume of the reaction mixture, which was readily calculated by an equation of state Total organic carbon reduction can be estimated by a lumped kinetic equation In the P-T region the activation energy of the phenol disappearance was 1247 kJ/mol

Transport processes in fibrinolysis and fibrinolytic therapy

Abstract: Transport of fibrinolytic agents into thrombi represents a rate limiting step in therapeutic thrombolysis. Mathematical modeling predicts and in vitro experiments demonstrate that effective delivery of fibrinolytic agents into clots is the most important determinant of fibrinolytic rate. Transport by diffusion is slow and limited by the need for a high concentration gradient. Transport by convection is more efficient and depends on both the intrinsic resistance of the thrombus and on the effective pressure gradient. Animal experiments indicate that delivery of activator into a thrombus accelerates fibrinolysis and that fibrinolytic rate is dependent on the pressure gradient to which the clot is exposed. Clinical observations are consistent with a dominant role of transport in determining thrombolytic efficacy. Systemic thrombolysis is most successful in short clots exposed to a high pressure gradient, such as coronary artery thrombi in normotensive or hypertensive patients. Rapid lysis is also achieved by intrathrombic delivery of plasminogen activator into peripheral arterial clots and thrombosed dialysis access fistulas. In contrast, systemic thrombolysis is much less successful in clots that are exposed to an insufficient pressure gradient, such as venous thrombi and coronary thrombi of patients in cardiogenic shock.

Consistent gradient formulation for a stable enhanced strain method for large deformations

Abstract: Considers the problem of stability of the enhanced strain elements in the presence of large deformations. The standard orthogonality condition between the enhanced strains and constant stresses ensures satisfaction of the patch test and convergence of the method in case of linear elasticity. However, this does not hold in the case of large deformations. By analytic derivation of the element eigenvalues in large strain states additional orthogonality conditions can be derived, leading to a stable formulation, regardless of the magnitude of deformations. Proposes a new element based on a consistent formulation of the enhanced gradient with respect to new orthogonality conditions which it retains with four enhanced modes volumetric and shear locking free behaviour of the original formulation and does not exhibit hour‐glassing for large deformations.

On the distribution of Brownian areas

Abstract: We study the distributions of the areas under the positive parts of a Brownian motion process B and a Brownian bridge process U: with $A^+ = \int_0^1 B^+ (t) dt$ and $A_0^+ = \int_0^1 U^+ (t) dt$, we use excursion theory to show that the Laplace transforms $\Psi^+ (s) = E \exp (-sA^+)$ and $\Psi_0^+ (s) = E \exp (-sA_0^+)$ of $A^+$ of $A_0^+$ satisfy $$\int_0^{\infty} e^{-\lambda s \Psi +} (\sqrt{2} s^{3/2}) ds = \frac{\lambda^{-1/2} Ai(\lambda) + (1/3 - \int_0^{\lambda} Ai(t) dt)}{\sqrt{\lambda} Ai(\lambda) - Ai (\lambda)}.$$ and $$\int_0^{\infty} \frac{e^{-\lambda s}{\sqrt{s}} \Psi_0^+ (\sqrt{2} s^{3/2}) ds = 2 \sqrt{\pi} \frac{Ai(\lambda)}{\sqrt{\lambda} Ai'(\lambda) - Ai(\lambda)}.$$ where Ai is Airy's function. At the same time, our approach via excursion theory unifies previous calculations of this type due to Kac, Groeneboom, Louchard, Shepp and Takacs for other Brownian areas. Similarly, we use excursion theory to obtain recursion formulas for the moments of the "positive part" areas. We have not yet succeeded in inverting the double Laplace transforms because of the structure of the function appearing in the denominators, namely, $\sqrt{\lambda} Ai(\lambda) - Ai'(\lambda)$.