Showing papers by "University of Ljubljana published in 1992"

Size-biased sampling of Poisson point processes and excursions

Abstract: Some general formulae are obtained for size-biased sampling from a Poisson point process in an abstract space where the size of a point is defined by an arbitrary strictly positive function. These formulae explain why in certain cases (gamma and stable) the size-biased permutation of the normalized jumps of a subordinator can be represented by a stickbreaking (residual allocation) scheme defined by independent beta random variables. An application is made to length biased sampling of excursions of a Markov process away from a recurrent point of its statespace, with emphasis on the Brownian and Bessel cases when the associated inverse local time is a stable subordinator. Results in this case are linked to generalizations of the arcsine law for the fraction of time spent positive by Brownian motion.

Equivalent ductility factors, taking into account low‐cycle fatigue

Abstract: During strong earthquakes, the deformation capacity of structures is reduced due to the cumulative damage caused by cyclic load reversals. In the paper, equivalent (reduced) ductility factors have been proposed, which take into account this effect. They are based on different failure hypotheses. Ductility reduction due to low-cycle fatigue is controlled by a dimensionless parameter γ, which is a function of dissipated hysteretic energy, maximum displacement and the natural frequency of the structural system, and which has been proved to be a relatively stable quantity in the whole period range. If approximate values for γ are used, the determination of equivalent ductility is very simple, and thus appropriate for design purposes. The formulae for equivalent ductility factors include damage indices, and permit the designer to choose acceptable level of structural damage explicitly. As an example, equivalent ductility factors have been used to construct inelastic acceleration spectra, which are proportional to strength demand, for the El Centro 1940 SOOE record. The results have been compared with the ‘exact’ spectra obtained by non-linear dynamic analysis.

Characterization of Dobrava virus: A hantavirus from Slovenia, Yugoslavia

Abstract: Small mammals were collected in natural foci of hemorrhagic fever with renal syndrome (HFRS) in Slovenia, Yugoslavia, and a hantavirus was isolated from the lungs of an Apodemus flavicol lis captured in Dobrava village. This new isolate, Dobrava virus, was compared with representative strains of the Hantavirus genus by serological and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) methods. It was found by cross immunofluorescent and enzyme-linked immunosorbent assays that antigenic properties of Dobrava virus were different from those of other hantaviruses. The RNA of this virus was successfully amplified with hantavirus genus reactive primer sets by reverse transcriptase polymerase chain reaction (RT-PCR); however, PCR-RFLP analysis of the amplified product was shown to be unique among those of the known hantaviruses, further indicating that Dobrava virus represents a new hantavirus serotype. Published 1992 Wiley-Liss, Inc.

Polypeptide cytolytic toxins from sea anemones (Actiniaria)

Abstract: Biochemical and biological properties of 30 cytolytic polypeptide toxins isolated from 18 species of sea anemones (Actiniaria) are presented and classified into three groups according to their molecular mass, isoelectric points and the molecular mechanism of action. Phospholipase A2-like toxins (30 kDa) from Aiptasia pallida are dissimilar to acidic metridiolysin (80 kDa) from Metridium senile and the group of about 27 predominantly basic toxins, having a molecular mass of 16–20 or 10 kDa, inhibited by sphingomyelin. They are lethal for both invertebrates and vertebrates, cardiotoxic, cutolytic and cytotoxic. Pharmacological activities, cytotoxic and cytolytic properties are mediated, at least in part, by forming pores in lipid membranes. Channels, 1–2 nm in diameter, formed in planar lipid membranes are cation selective and rectified. The mechanisms and some characteristics of ion channel formation by the toxins in the cells as well as in artificial lipid membranes are summarized and discussed in view of the structure-function studies of the toxins. Putative biological roles of toxins, based on their channel-forming activity, in the capture and killing of prey, digestion, repelling of predators and intraspecific spatial competition are suggested.

Treatment of chronic wounds by means of electric and electromagnetic fields. Part 1. Literature review.

Abstract: The healing of a cutaneous wound is accompanied by endogeneous electrical phenomena. Not knowing whether they represent merely a side-effect of the physiological processes which take course during healing or whether they play a much more important role as mediators of healing, externally applied electricity was examined as a therapeutic tool for the enhancement of natural regenerative processes. In the present review a historical literature survey dealing with human applications of electric current for wound healing acceleration is given. It presents a complete palette of heterogeneous studies, differing in the parameters of applied electric current, in delivery modes as well as in the types of wounds being stimulated. Because of all these differences, comparing the efficacy of the described methods is difficult and could hardly be objective. Therefore greater stress was laid upon the discussion concerning the problems in designing clinical studies (size of the sample observed, control group, ethics of the procedures), rationales for the employment and possible underlying mechanisms of particular methods, and problems of evaluating their efficacy. In spite of the extensive work performed in the field of electrical wound healing we remain only part way towards explaining the mechanisms by which electricity reinforces the regenerative capabilities of injured tissue as well as only part way towards the selection of the optimal stimulation method from among the published reports.

Fréedericksz transitions in supra-μm nematic droplets

Abstract: The stability of uniaxial nematic-liquid-crystalline structures in supra-\ensuremath{\mu}m-size spherical cavities that impose a weak homeotropic anchoring is studied theoretically. The equilibrium equations are obtained with the minimization of the deformation, surface, and field contributions to the free energy and are solved numerically. The dependencies of the solutions on the ratio of elastic constants ${\mathit{K}}_{33}$/${\mathit{K}}_{11}$, ${\mathit{K}}_{24}$/${\mathit{K}}_{11}$, anchoring strength, and external field strength are discussed, and the stability diagrams with lines of structural (Fr\'eedericksz) transitions are constructed. In the region of strong anchoring and large external field strengths, a triple point, where radial, nonsingular axial, and axial structure with the line defect, is predicted. Particular attention is paid to the inversion point corresponding to the critical-field strength above which radial structure is no longer stable. Two possible methods for saddle-splay elastic constant ${\mathit{K}}_{24}$ determination are suggested.

Structures of the cholesteric liquid crystal droplets with parallel surface anchoring

Abstract: Model structures of cholesteric liquid crystal droplets embedded in a medium which enforces parallel surface anchoring are treated. Structures with disclination lines of integer and half-integer strength are obtained by minimising the Frank free energy. The constant order parameter approximation appropriate for droplets which are large compared to the cores of defects and the approximate ansatz with the molecular director everywhere tangential to the concentric spherical surfaces are used. Within this approach the structure with a diametrical disclination line is the most stable. Its free energy is compared to that of the non-twisted bipolar structure and to that of the two twisted structures. The well-known structure with a radial disclination line and that with a double radial disclination line not found in the known literature are presented. It is shown that surface free energy terms, usually omitted in the minimization, do not influence substantially the stability of the structures discussed....

Direct multicriteria clustering algorithms

Abstract: In a multicriteria clustering problem, optimization over more than one criterion is required. The problem can be treated in different ways: by reduction to a clustering problem with the single criterion obtained as a combination of the given criteria; by constrained clustering algorithms where a selected critetion is considered as the clustering criterion and all others determine the constraints; or by direct algorithms. In this paper two types of direct algorithms for solving multicriteria clustering problem are proposed: the modified relocation algorithm, and the modified agglomerative algorithm. Different elaborations of these two types of algorithms are discussed and compared. Finally, two applications of the proposed algorithms are presented.

Stimulatory effects of jasmonic acid on potato stem node and protoplast culture

Abstract: The effect of jasmonic acid (JA), in a wide range of concentrations (0.01–100 μM), on the development of potato plantlets (Solanum tuberosum L.cv. Vesna) was investigated in order to discriminate between physiological and supraoptimal effects of this growth regulator in vitro. Concentrations from 0.1–1 μM significantly increased the length of developed plants. Application of JA in these concentrations resulted in a very well differentiated root system with many lateral branches. With increasing JA concentrations, the main roots shortened and thickened. Concentrations higher than 10 μM led to the compaction of the stem, roots, and root hairs, giving a stunted appearance to the plants. The effect of JA on cell wall regeneration and callus formation was observed in potato leaf protoplast culture. JA at concentrations from 0.01–1 μM stimulated cell division and microcalli development.

Solitary borrelial lymphocytoma: report of 36 cases.

Abstract: Thirty-six cases of borrelial lymphocytoma were detected during the period 1986 to 1990 in Slovenia. Borrelial lymphocytoma was located on the ear lobe in 17 persons, ten female and seven male, with a median age of 12 years (range 2–56). Fourteen of these 17 were children under 14 years of age. A tick bite was remembered by 15 patients a median of 30 days before borrelial lymphocytoma developed. The most frequent month of onset was September. Erythema migrans preceded or accompanied borrelial lymphocytoma in eight cases. In 15 cases, eight female and seven male, borrelial lymphocytoma was localized on the mamilla. Median age of these patients was 42 years (range 15–72). Twelve had a tick bite about 45 days (median value) before the onset of borrelial lymphocytoma, which occurred most frequently in August. Erythema migrans was reported in 13 patients and preceded borrelial lymphocytoma in ten cases. In another four patients borrelial lymphocytoma was localized on the nose, scrotum, upper arm and shoulder. Antibiotic treatment with phenoxymethyl-penicillin (n=16), ceftriaxone (n=8), doxycycline (n=9), azithromycin (n=2) and penicillin G (1) led to complete recovery within an average of three weeks in all cases.

Thermospray Sample Introduction to Atomic Spectrometry

Abstract: Thermospray aerosols are generated by forcing a liquid sample through a capillary tube that is heated to partially vaporize the solvent, resulting in a blast of vapor that converts the remaining liquid to droplets. The droplet size character of thermospray aerosols can be electrically varied by changing the temperature and degree of solvent vaporization of the liquid stream. The primary droplets produced by thermospray under optimal conditions are smaller on average then those produced by pneumatic nebulizers, particularly of the types used for inductively coupled plasmas (ICPs). Solvent vaporization is enhanced for smaller particles and higher temperatures, with both aspects leading to faster size reduction due to solvent evaporation than would occur with pneumatic sample introduction at room temperature. As smaller droplets are more efficiently transported through sample introduction systems, the use of thermospray aerosol generation provides higher analyte transport, higher sensitivity, and lo...

Erythema migrans: comparison of treatment with azithromycin, doxycycline and phenoxymethylpenicillin.

Abstract: Azithromycin, doxycycline and phenoxymethylpenicillin were compared in a prospective, randomized study of 64 patients with typical erythema migrans. Twenty patients were treated with oral azithromycin, 250 mg bd for two days followed by 250 mg od for eight days, 21 patients were given phenoxymethylpenicillin 1 million IU tds for 14 days and 23 patients received doxycycline, 100 mg bd for 14 days. All patients were followed up for 24 months. There were no significant differences between the groups with respect to the persistence of cutaneous lesions after starting treatment; the mean durations were 10.5 days in the penicillin group, 8.8 days in the doxycycline group and 8.6 days in the azithromycin group. There were statistically significant differences in terms of the resolution of associated local and/or systemic symptoms. The response time was shortest in patients treated with azithromycin. Two patients who received phenoxymethylpenicillin and two given doxycycline subsequently developed major manifestations of Lyme borreliosis; these did not occur in patients receiving azithromycin. Although azithromycin has been shown to be effective in the treatment of erythema migrans, further studies will be needed to determine the optimal dosage and duration of therapy.

Analysis of transient ST segment changes during ambulatory monitoring using the Karhunen-Loeave transform

Abstract: The authors present an algorithm based on the Karhunen-Loeave transform (KLT) for robust automated detection of ischemic ST segment episodes and measurement of the duration of ischemia in two-channel ambulatory electrocardiographic data. The algorithm operates as a postprocessor to an existing arrhythmia detector. The episode detector incorporates a single-scan trajectory recognition technique in the KLT feature space. The algorithm differentiates between true ischemic ST segment changes and non-ischemic ST deviations caused by axis shifts. In evaluations using the European Society of Cardiology ST-T database, the algorithm achieved a gross ST episode sensitivity of 85.2%, with a positive predictivity of 86.2%. The gross ischemic ST duration sensitivity was 75.8%, with a positive predictivity of 78.0%. >

Low-temperature synthesis of sinterable SiC powders by carbothermic reduction of colloidal SiO2

Abstract: β-SiC powders were synthesised by carbothermic reduction of carbon-black doped silica gel. The morphological characteristics of the resulting powders depend on the morphology of precursor carbon black as well as the reaction conditions. A model for particle coarsening during carbothermic reduction is presented, suggesting that surface diffusion may be responsible for the formation of polycrystalline aggregates, while at higher reaction temperatures volume diffusion is operative. Processing consisting of decarburization, HF treatment and sedimentation but no milling is required to convert crude reaction products into sinterable powders. After doping with boron and carbon they can be sintered to 98–99% of theoretical density which, in general, is better than or comparable to results obtained with commercial β-SiC powders which were also included in the present study.

Electrochemical methods in the study of localized corrosion attack

Abstract: Electrochemical methods for determining the characteristic pitting potentials of 90Cu−10Ni alloy in slightly alkaline chloride solutions are summarized and the results of measurements carried out using potentiostatic, quasi-potentiostatic, potentiodynamic and galvanostatic techniques, complemented byex situ techniques — SEM and EDXA — are discussed. In borate buffer solution a passive state is established due to the formation of the oxide film with low ionic conductivity. However, in the presence of Cl− ions, at potentials higher than a certain critical value, breakdown of the anodic passivity occurs, caused by field-stimulated chloride entry into the passive oxide film at singular point defects. The brightening of the pits formed after oxide film breakdown was established to be due to the conversion of the passivating oxide film to one of high ion conductivity “Contaminated oxide” permits the passage of the metal cation into and through it, finally leaving it at the film/solution interface where pitting can proceed. During localized attack two characteristic potentials have to be distinguished: the potential of pit nucleation,E n, above which pit nucleation starts, and the breakdown potential,E b, above which the growth of nucleated pits develops. An attempt is made to compare the values ofE n andE b obtained through different methods, and to determine the factors influencing these values in each particular method.

Modified cell proliferation due to electrical currents.

Abstract: In view of the evidence that electrical currents may enhance healing of chronic wounds and retard tumour growth it is suggested that these currents normalise cell proliferation. Additional support to this contention is given by two reports: one on healing of pressure sores in man and one on tumour growth retardation in mice. The effect of an ionic environment on the cell cycle is analysed. Finally a hypothesis attempting to explain the normalising effect of electrical currents on cell proliferation is proposed. It is known that non-dividing cells, e.g. mature neurons, have high transmembrane potential (TMP) whereas fast-dividing cells, e.g. cancerous cells, have low TMP. When a cell is exposed to an electrical field, one side of the cell becomes hyperpolarised while the opposite side is depolarised. Assuming a nonlinear relationship between TMP and the transmembrane ionic currents, it can be shown that in non-dividing cells their high TMP is lowered; whereas in cells with a high division rate, their low TMP is raised due to cell exposure to the external electrical field. These alterations in transmembrane potential could contribute to the normalisation of abnormal cell proliferation.

Discs in pseudoconvex domains.

Abstract: Let D c C* be a domain in the complex Euclidean space CN (N > 1), and let y be a point in D. There exist many closed complex one-dimensional subvarieties (curves) V cz D passing through y. For instance, it suffices to take the common zero set/i =fi *** =fs 0 of suitably chosen holomorphic functions on D that vanish at y. A special class of closed complex curves in D are the proper analytic dises, Le., the images F(A) of proper holomorphic maps F : A -+D from the open unit dise A cz C into D. A natural question appears [6]: Given a point y e Z>, can we find a proper analytic dise in D passing through y! In this article we give a positive answer to this question for ail bounded pseudoconvex domains in C^ with W2 boundary, and a counterexample for nonpseudoconvex domains with disconnected boundary. More precisely, we prove the following results:

Characterizing vertex-transitive pq -graphs with an imprimitive automorphism subgroup

Abstract: Vertex-transitive graphs with pq vertices, where p and q are primes, having an imprimitive subgroup of automorphisms, are characterized. © 1992 John Wiley & Sons, Inc.