Showing papers by "Ghent University published in 1987"

Numerical Methods for Bifurcations of Dynamical Equilibria

Abstract: Preface Notation Introduction 1. Examples and Motivation 2. Manifolds and Numerical Continuation 3. Bordered Matrices 4. Generic Equilibrium Bifurcations in One-Parameter Problems 5. Bifurcations Determined by the Jordan Form of the Jacobian 6. Singularity Theory 7. Singularity Theory with a Distinguished Bifurcation Parameter 8. Symmetry-Breaking Bifurcations 9. Bifurcations with Degeneracies in the Nonlinear Terms 10. An Introduction to Large Dynamical Systems Bibliography Index.

Generalized quadrangles and flocks of cones

Abstract: A flock of the quadratic cone K of PG(3, q) is a partition of K but its vertex into disjoint conics. If the planes of the q conics of such a flock all contain a common line, then the flock is called linear. With any flock there corresponds a translation plane which is Desarguesian iff the flock is linear. W. M. Kantor showed that with a set of q upper triangular 2 × 2-matrices over GF(q) of a certain type, there corresponds a generalized quadrangle of order (q2, q). We prove that with such a set of q matrices there corresponds a flock of the quadratic cone of PG(3, q), and conversely that with each flock of the quadratic cone there corresponds such a set of matrices. Using this relationship, new flocks, new generalized quadrangles, and probably new translation planes are obtained.

Two-dimensional hot-electron models for short-gate-length GaAs MESFET's

Abstract: A detailed hot-electron device model suitable for modeling short-gate-length GaAs MESFET's is described. A two-dimensional numerical simulation is used to solve a set of semiclassical carrier transport equations, including a full rigorous solution of the energy conservation equation. The importance of the hot-electron effects is demonstrated and in particular the role of the electron temperature gradient in addition to velocity overshoot is emphasized. The influence of doping and mobility profiles are investigated and found to have a very significant effect on the device characteristics. The model is applied to a range of submicrometer-gate-length devices and is shown to be useful for characterizing devices with gate lengths down to less than 0.1 µm. The dependence of saturated drain current on gate length is quantified.

Estimation of active soil microbial biomass by mathematical analysis of respiration curves: Calibration of the test procedure

Abstract: The biokinetic properties of the active component of the soil biomass were estimated in a range of soils by mathematical simulation of the respiration curve obtained after the soil was amended with glucose. Microbial communities appeared to vary considerably with regard to their affinity for substrate, their maintenance coefficient and particularly the amount of active microbial biomass they contain. In soils from undisturbed natural ecosystems, the active biomasss component was on average about half that in arable agricultural soils. In a wheat field, the active but not the total microbial biomass was significantly stimulated by the growth of the crop. In the soils examined, the active biomass comprised 4% to 49% of the total soil biomass. A 10 h procedure is described for estimating the active soil biomass component, by monitoring either O 2 consumption or CO 2 production.

Electrical needle therapy of uremic pruritus.

Abstract: Six patients with intractable uremic pruritus were treated with a modified acupuncture technique, the electrical needle stimulation (ENS). Results were followed with a pruritic score scale based on severity, frequency and distribution of itching, together with sleeping hours and waking up at night. The results were encouraging: pruritus was drastically improved during or after ENS in several patients. A control treatment with superficial electrical stimulation was ineffective.

A critical review of some liquid chromatography systems for the separation of sugars

Abstract: This contribution to the problems of carbohydrate (sugar) column liquid chromatography, evaluates several currently used systems (reversed phase octadecylated silica gel, amino modified silica gel, cation exchangers on polystyrene and on silica gel basis, polyol derivatised silica gel and anion exchange systems). The elution pattern, analysis time, column efficiency and column life time expectancy are considered to be the important points for this comparison. The application of silica gel-based cation exchanger and of polyol derivatised silica gel is new to this field. The comparison and/or evaluation tries to be critical and to come to a conclusion for the choice of a recommended system.

Reassessment of the accuracy of traditional sperm characteristics and adenosine triphosphate (ATP) in estimating the fertilizing potential of human semen in vivo

Abstract: Receiver operating characteristic curves and accuracy parameters were computed for traditional sperm characteristics (concentration, motility, morphology) and the number of peroxidase negative cells, and the concentration of adenosine triphosphate (ATP) in semen from populations of fertile and infertile men, and men who achieved a pregnancy after varicocele treatment. The percentage and concentration per millilitre of spermatozoa with rapid linear progressive motility, and the ATP concentration, provided the best discrimination between fertile and treated fertile from infertile men. The misclassification rate was higher for sperm morphology, total progressive motility and viability, whereas sperm concentration and the total sperm count per ejaculate had the worst discriminating power. The number of peroxidase negative cells per 100 spermatozoa was highly specific in identifying men who achieved pregnancy after varicocele treatment. The lower limit of normality of sperm characteristics was remarkably different between fertile men and men achieving pregnancy after treatment or during infertility work-up.

Clinical pharmacokinetics of glyceryl trinitrate following the use of systemic and topical preparations.

Abstract: Glyceryl trinitrate has been used for more than a century for the treatment of angina pectoris and, more recently, for the treatment of congestive heart failure. The introduction of transdermal delivery systems has renewed the controversy regarding the efficacy of the drug, mainly in the light of the development of tolerance. With concentrations of the order of 1 microgram/L or less, the measurement of glyceryl trinitrate in plasma is not easy: gas chromatography with electron capture detection has been used widely but recently gas chromatography-mass spectrometry has provided satisfactory results. Assay problems are most likely to be responsible for some of the unexpected results reported. Further factors which may confound the results of the study of plasma concentrations are the rapid metabolism of glyceryl trinitrate in blood in vitro, adsorption to containers and infusion sets, and the uptake and/or metabolism in vessel walls. From the intravenous infusion data, the large interindividual variability in plasma concentrations of glyceryl trinitrate is apparent. The plasma half-life is about 2 to 3 minutes; plasma clearance values reported vary from 216 to 3270 L/h, indicating extensive non-hepatic metabolism. With transdermal administration, mainly with the transdermal controlled delivery systems, plasma concentrations of glyceryl trinitrate appear to be maintained for up to 24 hours, with large interindividual variations. Despite the ability to maintain, for example with the transdermal delivery systems, relatively constant concentrations of glyceryl trinitrate, it has not been possible to find a relationship between plasma concentrations and pharmacological or clinical effects. This is in part due to the attenuation of the effects with time; from the available data it is clear that this attenuation occurs at a pharmacodynamic level (reflex adaptation and tolerance) and not at the pharmacokinetic level.

Estimation of active soil microbial biomass by mathematical analysis of respiration curves: development and verification of the model

Abstract: A new method is proposed for estimating the amount of biomass that is capable of directly metabolizing a given substrate A sample, containing a given amount of active biomass is amended with the substrate and oxygen uptake monitored continuously for 120 h From this information, supplemented by the substrate removal curve, the time-course of the biomass may be calculated This calculation is based on a set of four biokinetic equations comprising of the following arbitrary constants: maximum specific growth rate, substrate affinity, biomass growth yield coefficient and biomass maintenance coefficient In this paper, the validity of the method is verified for liquid axenic cultures and mixed cultures The method is also shown to be applicable to soils amended with acetate or glucose

Effect of seed inoculation with the rhizopseudomonad strain 7NSK2 on the root microbiota of maize (Zea mays) and barley (Hordeum vulgare)

Abstract: The addition of sugars or amino acids to the soil gave rise to the development of different groups of microorganisms. The increase in the number of different groups of microorganisms in the soil had an influence on the microbiota in the rhizoplane and endorhizosphere of maize and barley grown in that soil. Furthermore, growth of maize and barley decreased with increasing microbial activity and density in soil. This effect could be counteracted effectively by the rhizopseudomonad strain 7NSK2. The beneficial effect of the strain 7NSK2 correlated inversely with the microbial activity, as measured by soil respiration, in the bulk-pretreated soil. The effect of seed inoculation with the rhizopseudomonad strain 7NSK2 on the root microbiota of maize and barley was evaluated. The strain 7NSK2 was capable of colonizing the rhizoplane and endorhizosphere of the maize cultivar Beaupre and barley cultivar Than very effectively and of considerably altering their composition. The number of total bacteria, fungi, pseudomonads and coliform bacteria in the rhizoplane and endorhizosphere of both plants was strongly reduced by inoculating the seeds with the strain 7NSK2.

Model of jaw depression during feeding in Astatotilapia elegans (Teleostei Cichlidae). Mechanisms for energy storage and triggering.

Abstract: Suction feeding in Astatotilapia elegans occurs by a series of rapid, coupled movements of various head parts. The lower jaw rotates with respect to the neurocranium through an angle of 62° in less than 15 ms. The power requirements for jaw depression are calculated from a mathematical model and may reach a peak of ±4 watt in a 12-cm-long specimen. Data from the literature on mechanical output of fish muscle suggest that a muscular volume equal to 44% of the volume of the fish (= 45 cm3 ) should be required, if it is premised that movement and muscle shortening are directly coupled. Therefore, we assumed that storage and release of strain energy must be considered. The work demands for depression equal 0.014 J. The amount of energy storable in only three pairs of head ligaments can be estimated between 0.008 J and 0.05 J. The use of strain energy implies initial blocking and subsequent triggering of the movement. The position of the hyalomandibular connection, dorsal to the mandibular-suspensorial articulation, appears to be of crucial importance in balancing the forces of sternohyoideus and the body muscles. Triggering at the onset of jaw depression occurs by the contraction of the levator operculi. The line of action of the hyalomandibular connection is lowered beneath the jaw suspension, which raises the equilibrium of forces. Elastic recoil can occur thereafter.

Propofol combined with nitrous oxide-oxygen for induction and maintenance of anaesthesia

Abstract: After a bolus of 2 mg/kg, propofol was given by continuous infusion (150 micrograms/kg/minute for 30 minutes and then 100 micrograms/kg/minute) supplemented with nitrous oxide for anaesthesia during ear surgery in 12 patients. Cardiovascular changes were not significant except for a decrease in heart rate after 60 minutes. Acid-base balance was unaffected by the amount of fatty emulsion. Cortisol levels showed a nonsignificant decrease during the prolonged administration of propofol but had recovered completely by one hour following anaesthesia. Mean blood concentrations of propofol were 10.5 micrograms/ml (SEM 1.2) at the onset of unconsciousness, between 3.4 and 4.5 micrograms/ml during continuous infusion and 2.9 micrograms/ml (SEM 0.3) on awakening. Patients opened their eyes 6 minutes (SEM 1) after discontinuation of the infusion, and were responsive at 7.5 minutes (SEM 0.5), which suggests that propofol infusion can be used safely for surgery of 2 hours' duration.

Behavioural Responses to Stress in Farm Animals

Abstract: If applied ethology has other aims than fundamental behavioural sciences and deserves acknowledgement on its own, it should also strengthen its contact with them, as it has worked too much in a theoretical vacuum with sometimes a deficient methodology; hence maybe its slowness in giving concrete advise to zootechnicians and lawyers.

Clinical manifestations in HLA-B27-positive patients.

Abstract: The clinical manifestations of rheumatic diseases have been studied in a population of 440 HLA-B27-positive patients. Fifty-eight per cent had peripheral joint involvement. After statistical analysis and clustering of characteristics, three patterns of peripheral joint involvement were found. They were referred to as the X, Y and Z type for mnemotechnical reasons. The X type includes male patients with sacroiliitis, spondylitis, uveitis and uni- or bilateral arthritis of hip and/or shoulder. Y type patients present sacroiliitis, pauci-articular asymmetrical joint involvement and tendinitis. Z type patients are characterized by sacroiliitis, polyarticular symmetrical joint involvement and a positive IgM rheumatoid factor. This classification enables a new approach to the pathology, diagnosis and therapy of the seronegative spondyloarthropathies.

Judges, Legislators and Professors: Chapters in European Legal History

Abstract: Part I. The Common Law is Different: Ten Illustrations: 1. The ambiguity of the term 'law' 2. Appeal: a recent development 3. English law is a 'seamless web' 4. The rule of exclusion 5. A land without a constitution? 6. The consequences of parliamentary absolutism 7. The haphazard development of criminal law 8. Prosecution and verdict in criminal trials 9. A law uncodified Jurists are dispensable Part II. The Mastery of the Law: Judges, Legislators and Professors: 10. Some facts 11. Explanations: the 'national spirit'? 12. Explanations: authoritarian Roman law and democratic England? 13. Explanations: political history Part III. The Divergent Paths of Common Law and Civil Law: 14. Common law and civil law: the parting of the ways 15. The ways remain separate 16. Which diverged from which? Part VI. Which is Best, Case Law, Statute Law, Or Book Law: 17. The judges: amateurs and professionals 18. The courts and their creators 19. Codification: a weapon against the judiciary 20. Law professors serve the powers that be 21. Eight criteria of good law.

Influence of α‐chymotrypsin and trypsin on the non‐adrenergic non‐cholinergic relaxation in the rat gastric fundus

Abstract: Relaxations of the rat gastric fundus were induced by electrical stimulation of the non-adrenergic non-cholinergic (NANC) neurones, by vasoactive intestinal polypeptide (VIP), by noradrenaline and by isopropylnoradrenaline. The influence of alpha-chymotrypsin and trypsin thereupon was studied. alpha-Chymotrypsin 2 u ml-1, present for 30 min, antagonized completely the VIP-induced relaxation, but not the stimulation-induced relaxation; alpha-chymotrypsin 10 u ml-1 also partially antagonized the stimulation-induced relaxation. When alpha-chymotrypsin 2 u ml-1 was added after the relaxation had occurred, it antagonized completely the VIP-induced relaxation, but it also partially antagonized the stimulation-induced relaxation. The partial antagonism of the stimulation-induced relaxation was more pronounced with alpha-chymotrypsin 10 u ml-1. Trypsin, 10(-6) M and 3 X 10(-6) M, had effects on VIP- and stimulation-induced relaxations similar to those of alpha-chymotrypsin. The relaxations induced by noradrenaline and isopropylnoradrenaline were not influenced by alpha-chymotrypsin or trypsin, respectively. The results suggest that a peptide, possibly VIP, is involved in the NANC relaxation of the rat gastric fundus.

Invasiveness of human glioma cell lines in vitro: relation to tumorigenicity in athymic mice.

Abstract: Five established cell lines derived from human anaplastic astrocytomas or glioblastoma multiforme were tested for invasiveness into precultured chick heart fragments in vitro. Four of the cell lines (U118 MG, D54 MG, U373 MG and A172) were strongly invasive into the heart tissue. A fifth cell line, U251 MG sp, which was only tumorigenic at doses of greater than 1×108 cells in athymic mice, was non-invasive in vitro. One line, A172, was invasive but not tumorigenic in athymic mice, although a related invasive subline, D54 MG, at later passage levels was tumorigenic even at low cell doses. Invasion of the glioma cells was characterized by progressive and irreversible replacement of the precultured chick heart tissue. Both by light and transmission electron microscopy, a similar pattern of invasion was observed as earlier found with experimental rat glioma cells in the same system. Some human cell lines established from human gliomas retain invasive properties after a prolonged culture period in vitro.

Hyperglycaemia and diuresis during sedation with detomidine in the horse.

Abstract: Summary In four horses (mares), the effect of atropine (1 mg/100 kg of body weight I. V.) and detomidine (4 mg/100 kg of body weight I. V.) on several electrolytes and other parameters in serum and urine was studied. A marked hyperglycaemia was noted in all cases; none of the investigated serum electrolytes, metabolites or enzyme concentrations changed significantly. An initial increase of PCV and RBC count was followed by a decrease. Increased production of urine accompanied by a significant increase in sodium excretion was noted in all mares. In two horses, small amounts of glucose could be detected in the urine. The arterial partial oxygen pressure showed a significant decrease, possibly due to the use of atropine. Zusammenfassung Hyperglykamie und Diurese wahrend der Sedierung mit Detomidin beim Pferd: Bei vier Pferden wurde der Effekt von Atropin (1 mg/100 kg Korpergewicht, i. v.) und Detomidin (4 mg/100 kg Korpergewicht, i. v.) auf mehrere Elektrolyt- und andere Parameter im Serum und Harn untersucht. In allen Fallen wurde eine ausgepragte Hyperglykamie beobachtet; die Konzentrationen der daruber hinaus untersuchten Serum-Elektrolyte, -Metabolite und -Enzyme waren nicht signifikant verandert. Auf die anfangliche Zunahme des Hamatokrits und der Zahl der Erythrozyten folgte eine Abnahme. Eine von einer signifikanten Zunahme der Na-Ausscheidung begleitete vermehrte Harnbildung wurde bei allen Stuten beobachtet. Bei zwei Stuten wurden geringe Mengen von Glucose im Harn nachgewiesen. Der arterielle Blutdruck nahm wahrscheinlich wegen der Applikation von Atropin signifikant ab.

Microbial Sucrose Phosphorylase: Fermentation Process, Properties, and Biotechnical Applications

Abstract: Publisher Summary Relatively few microorganisms are known to produce sucrose phosphorylase might be related to the fact that so far no simple direct screening test is available for such strains. Microbial fermentations related to sucrose phosphorylase production are described in the chapter. Apart from the strain involved and the medium used, further information concerning process control and parameter changes (pH, temperature, D.O.) during the fermentation cycle is lacking. All fermentation media reported are based on sucrose as a carbon source. Media for sucrose phosphorylase production based on corn steep liquor and molasses have also been tested. Slower growth and a much lower enzyme activity were obtained. Sucrose phosphorylase is an “intracellular” enzyme, though it is not known whether the enzyme is cell wall bound, periplasmic, or truly intracellular. Because several strains producing this enzyme also display phosphatase and invertase or mannitol dehydrogenase activity, cell disruption and enzyme extraction and purification procedures were needed to obtain homogeneous sucrose phosphorylase preparations. Comparison of pure sucrose phosphorylase from different strains revealed differences in molecular weight, substrate specificity, and substrate inhibition pattern. Applications of sucrose phosphorylase include production of sucrose from starch, production of fructose and glucose-1-phosphate from sucrose or molasses, synthesis of labeled sucrose, and formation of high-energy- bonds without the need for ATP.

Rotifers from Turkey

Abstract: Seventy-eight rotifer species are reported from 19 localities in Turkey. About half are first records for that country. Some interesting species are illustrated and the composition of the regional fauna is discussed. Wide-ranging taxa are dominant, with notbale additions of tropical, subtropical, afrotropical and circumboreal species. Many are restricted to saline environments, where some show an unusual vertical distribution. Endemism is suspected in a few taxa.

Recombinant tumor necrosis factor can induce interleukin 2 receptor expression and cytolytic activity in a rat × mouse T cell hybrid

Abstract: Tumor necrosis factor (TNF), an endotoxin-induced macrophage monokine, is known for its cytotoxic and cytostatic effect on some tumor cell lines. Here we show that highly purified recombinant TNF, in combination with interleukin 2 (IL 2), can induce IL 2 receptor expression and cytolytic activity in a rat × mouse T cell hybrid (PC60). Previously, it was shown that IL 1 had a similar effect on PC60 cells. The ability of TNF to co-induce IL 2 receptor expression suggests that it may play a role in the activation of certain lymphoid effector cells. This observation augments the growing list of biological activities attributed to TNF.