Showing papers by "University of Graz published in 1983"

On the shape of a set of points in the plane

Abstract: A generalization of the convex hull of a finite set of points in the plane is introduced and analyzed. This generalization leads to a family of straight-line graphs, " \alpha -shapes," which seem to capture the intuitive notions of "fine shape" and "crude shape" of point sets. It is shown that a-shapes are subgraphs of the closest point or furthest point Delaunay triangulation. Relying on this result an optimal O(n \log n) algorithm that constructs \alpha -shapes is developed.

Vascular protein linkage in various tissue induced by substance P, capsaicin, bradykinin, serotonin, histamine and by antigen challenge.

Abstract: Plasma extravasation was induced in rats or guinea-pigs by intravenous injections of (1) substance P (SP), (2) the C-terminal SP-hexapeptide SP(6--11), (3) serotonin (5-HT), (4) histamine, (5) bradykinin, (6) capsaicin and (7) by antigen challenge. Plasma extravasation induced by SP, SP(6--11), by 5-HT and by capsaicin was, with few exceptions, observed in the same tissues. The effect of SP was not blocked by H1 and H2 histamine receptor antagonists. The effect of i.v. capsaicin was absent in capsaicin desensitized animals. Plasma extravasation upon i.v. SP, SP(6--11), 5-HT and capsaicin was seen in the skin and in all organs containing mucous membranes except the intestinal mucosa. Plasma extravasation by histamine, bradykinin, and antigen challenge of sensitized guinea-pig was, in addition, also observed in the stomach and intestine. Plasma extravasation and bronchoconstriction by antigen challenge with 20 micrograms/kg ovalbumin was completely blocked by combined H1 and H2 histamine receptor blockade. Both responses were reduced to about the half capsaicin desensitized guinea-pigs, although the reduction of the permeability response was statistically not significant in all organs. In conclusion, several substances including anaphylaxis induce protein leakage in many tissues with differing selective distribution patterns. Anaphylactic histamine release leads to protein leakage partly via activation of sensory neurons. SP is a likely mediator of neurogenic protein leakage in many organs.

Substance P and capsaicin-induced contraction of human bronchi

Abstract: Substance P induced a dose-dependent contraction of human segmental bronchi in vitro with a threshold dose of about 10(-6) M. These preparations were obtained from patients undergoing lung tumor surgery. The substance P-induced contractions were resistant to mepyramine and atropine, suggesting a direct effect on the bronchial smooth muscle. Capsaicin (10(-5) M) also induced a slowly developing strong atropine-resistant contraction of human bronchi in vitro. a rapid tachyphylaxis developed for the response to capsaicin. Both substance P and capsaicin were less potent than acetylcholine and histamine in inducing contractions of human bronchi. This finding may however be partly due to the experimental conditions and both substance P and capsaicin were comparatively much more potent in guinea-pig preparations. Transmural field stimulation of the bronchial preparations in man resulted in contractions that were largely sensitive to atropine. The presence of capsaicin-induced bronchial contractions however indicates the existence of a local non-cholinergic axon-reflex control of bronchial smooth muscle tone by substance P in man.

A new approach to rectangle intersections part I

Abstract: Rectangle intersections involving rectilinearly-oriented (hyper-) rectangles in d-dimensional real space are examined from two points of view. First, a data structure is developed which is efficient in time and space and allows us to report all d-dimensional rectangles stored which intersect a d-dimensional query rectangle. Second, in Part II, a slightly modified version of this new data structure is applied to report all intersecting pairs of rectangles of a given set. This approach yields a solution which is optimal in time and space for planar rectangles and reasonable in higher dimensions.

Intracranial pressure oscillations (B-waves) caused by oscillations in cerebrovascular volume.

Abstract: In experiments during stepwise increases in intracranial pressure, B-waves could be provoked synchronously with pial vascular diameter oscillations. The vascular oscillations are known to be a sign of myogenic cerebrovascular regulation. An increase in their amplitude indicates vessel wall relaxation and impending failure of myogenic autoregulation. Therefore, vascular oscillations provoked during intracranial hypertension can be ascribed to a fall in transmural pressure and vessel wall tension. The resulting oscillations in the cerebral blood volume are reflected by ICP oscillations and lead to synchronous variation in ICP, the so-called “B-waves” with a frequency of 0.5 to 2 per minute.

Cubic spline approximation techniques for parameter estimation in distributed systems

Abstract: Approximation schemes employing cubic splines in the context of a linear semigroup framework are developed for both parabolic and and hyperbolic second-order partial differential equation parameter estimation problems. Convergence results are established for problems with linear and nonlinear systems, and a summary of numerical experiments with the techniques proposed is given.

Extraepithelial intraneural endocrine cells as starting-points for gastrointestinal carcinoids

Abstract: Endocrine cells can be demonstrated by light- and electron microscopy in the lamina propria of the mucosa of the appendix They are always in direct contact with a nerve fibre The endocrine cell (type EC1 and EC2 cell) and the polyaxonal non-myelinated nerve fibre are separated from the interstitial connective tissue by a common continous basal lamina The term “ECC-NF complex” (“EC cell — nerve fibre complex”) is suggested by the authors to describe this morphological unit The intraneural endocrine cells may be derived from neuroendocrine-programmed ectoblasts (Pearse, 1977) The electron microscopic demonstration of these “ECC-NF complexes” in carcinoid tumours of the appendix and of similarly structured “eC-NF complexes” (“endocrine cell-nerve fibre complexes”) in carcinoids of the rectum allows us, following the demonstration of small nerve fibres within carcinoids of the appendix, caecum and rectum (and bronchus) to propose a hypothetical parthogenesis of gastrointestinal carcinoid tumours from these intraneural endocrine cells Carcinoid tumours may develop by proliferation of the intraneural endocrine cells with microcarcinoids as intermediate stages In this way the histogenesis of the carcinoids is locateda priori in the subepithelial stroma Nerve fibres are morphological markers of this proposed mechanism Assuming a neuroectodermal cytogenesis for the intraneural endocrine cells we therefore also postulate a histogenesis of the carcinoids from the neuroectoderm

Capsaicin-induced reflex fall in rat blood pressure is mediated by afferent substance P-containing neurones via a reflex centre in the brain stem.

Abstract: Injection of 0.03 micrograms capsaicin into one femoral artery elicited a fall in blood pressure in the rat. This effect was completely and reversibly abolished following intrathecal injection of 1 nmol of the specific substance P antagonist, [D-Pro2,D-Trp7,9] substance P. The capsaicin-evoked depressor reflex is therefore exclusively mediated by substance P-containing primary afferent fibres. Using spinal rats or decerebration experiments, the centre of the capsaicin-evoked reflex fall in blood pressure could be localized in the brain stem.

Cerebral Veins: Fluorescence Histochemistry, Electron Microscopy, and In Vitro Reactivity

Abstract: Pial veins, choroid plexus veins, and the cerebri magna vein were investigated with regard to their ultrastructural organization, adrenergic nerve supply, and in vitro reactivity. The vessel walls consisted of a continuous layer of endothelial cells, large amounts of collagenous material, and occasional pericytes. Smooth muscle cells were observed only in a few specimens from the cerebri magna vein. All veins were surrounded by adrenergic nerve fibres. Potassium (124 mM) and noradrenaline (10−5–10−4M) induced small contractions (0.2–0.5 mN) of isolated veins during in vitro conditions. The magnitude of these responses was less than one-tenth of that obtained in small pial arteries.

Acute surgery of cerebral aneurysms and prevention of symptomatic vasospasm.

Abstract: A treatment protocol for a controlled open study in patients with subarachnoid haemorrhage (SAH) from cerebral aneurysms is presented, applying acute surgery and pharmacological prevention of symptomatic vasospasm: In patients clinically graded I–III (Hunt and Hess), operation is performed within 48 to 72 hours. After aneurysm clipping, the calcium-antagonist Nimodipine is administered 1. topically during operation, 2. intravenously until day 14 after SAH, 3. perorally until day 21 after SAH.

Serum apolipoproteins and lipoprotein (a) during the first week of life.

Abstract: . The levels of apolipoproteins, A-I, A-II, B and E, lipoprotein (a) and of total cholesterol and triglycerides were determined in cord serum and in capillary serum at the fifth day of life in a group of 44 term newborns. Additionally, cord serum lipoproteins were estimated. Sera from 26 healthy adults were studied for comparison. The concentrations of lipids and lipoproteins in cord serum were diminished as compared to adult levels. The occurrence of lipoprotein (a) in cord serum in concentrations significantly lower than in adults could be established. Serum apolipoproteins A-I, A-II and B were significantly lower at birth than in the adult, whereas apolipoprotein E levels did not differ from adult concentrations. During the first five days apolipoprotein B levels more than doubled, apolipoprotein A-I increased moderately and apolipoprotein E rose slightly. In contrast, serum lipoprotein (a) and apolipoprotein A-II did not change signiflcantly. Unlike serum cholesterol, the levels of apolipoproteins B and E at day five were significantly correlated to those measured at birth in the same infants. The changes of the apolipoprotein pattern during the first week of life reflect the evolution of the lipid transport system of the newborn and may be related to the increasing utilisation of fat and to hormonal factors.

Heat loss reaction to capsaicin through a peripheral site of action.

Abstract: The intravenous injection of 15 micrograms capsaicin produced an increase in the temperature of tail skin and paw pad and a fall in the colon temperature in conscious rats. These reactions reflect increased heat dissipation. The increase in skin temperature induced by intravenous capsaicin was absent when the function of small diameter primary afferent neurones was impaired by treatment of the rats with capsaicin as neonates. Thus it appears that intravenous capsaicin triggered the thermoregulatory response predominantly by stimulation of peripheral heat receptors. By means of local application of capsaicin to the nerves of the hind leg and by their chronic denervation, by treatment with phenoxybenzamine and guanethidine, evidence was obtained that reflex withdrawal of sympathetic vasoconstrictor tone mediates the heat loss reaction intravenous capsaicin.

The neuroendocrine system of normal human appendix, ileum and colon, and in neurogenic appendicopathy.

Abstract: Epithelial endocrine cells containing 5-hydroxytryptamine, substance P, somatostatin, enteroglucagon and vasoactive intestinal polypeptide-immunoreactivity were localized by immunocytochemistry in the mucosa of normal appendices, ileum and proximal colon, and in neurogenic appendicopathy. In neurogenic appendicopathy a large number of proliferating nerves were visualized independently of neurotransmitters by immunostaining for neuron-specific enolase. A large number of nerve fibers were shown to contain substance P-immunoreactivity and to be of intrinsic origin. Stromal endocrine cells containing 5-hydroxytryptamine, somatostatin- and possibly substance P-immunoreactivity, were observed in substantial numbers in neurogenic appendicopathy. Substance P may be involved as a neurotransmitter and/or as a paracrine/endocrine peptide in the pathogenesis of spastic contractions and abnormal peristalsis of the appendix, which are characteristic of neurogenic appendicopathy. Stromal endocrine cells may be considered to be the origin of certain carcinoids in the appendix.

Calculation of two-dimensional eddy current problems with the boundary element method

Abstract: Two-dimensional eddy current prblems are formulated by a set of boundary integral equations which are solved by the boundary element method (BEM). The calculations are performed for infinitely long conductors and multiconductor systems with arbitrary cross-sections. The problems are expressed in terms of the axial component A of the magnetic vector potential. The eddy current problems are solved by dividing the boundary of the conductors into three-noded isoparametric, quadratic elements. For the calculation a constant vector potential which is superimposed on the internal magnetic potential of the conductors is assumed. The given conductor currents can be related to the normal derivatives of the magnetic vector potential at the boundaries. In an example the BEM solution is compared with the exact analytical solution for an infinitely long, cylindrical conductor with a circular cross-section showing excellent agreement.

Efficient Method for Calculating Relativistic Corrections for Spin-½ Particles

Abstract: Expanding the Dirac resolvent around its nonrelativistic limit, the authors propose a new method for calculating relativistic corrections to bound-state energies. The present results are more powerful than the expressions obtained by Foldy and Wouthuysen and remain applicable for Coulomb as well as nonlocal interactions.