Showing papers by "Katholieke Universiteit Leuven published in 1987"

The Total Least Squares Problem: Computational Aspects and Analysis

Abstract: Introduction Basic principles of the total least squares problem Extensions of the basic total least squares problem Direct speed Improvement of the total least squares computations Iterative speed Improvement for solving slowly varying total least squares problems Algebraic Connections Between total least squares and least squares problems Sensitivity analysis of total least squares and least squares problems in the presence of errors in all data Statistical properties of the total least squares problem Algebraic connections between total least squares estimation and classical linear regression in Multicollinearity problems Conclusions.

The wetting of solids by molten metals and its relation to the preparation of metal-matrix composites composites

Abstract: This review aims at making a bridge between the fundamentals of the wetting of solids by liquid metals and the practice of the preparation of metal-matrix composites. One recalls first the significance of concepts such as surface tension, work of adhesion, adsorption and the relation between these concepts, the phenomenon of wetting and the process of liquid metal infiltration. Thereafter, the wetting of various types of solids is considered: metals, oxides, carbon and carbides. !n the !light of this body of science, one proposes finally a critical evaluation of the literature concerning the preparation of metal-matrix composites by liquid metal infiltration techniques. Particular emphasis is devoted to reinforcements made of graphite, alumina or silicon carbide multifilament fibres; the use of coatings and the addition of alloying elements to the metal are successively discussed.

Deficient t-PA release and elevated PA inhibitor levels in patients with spontaneous or recurrent deep venous thrombosis.

Abstract: The fibrinolytic system was investigated in 120 patients with spontaneous or recurrent deep vein thrombosis (DVT) without any known organic disease able to explain by itself the occurrence of a thrombosis and without any known defect of antithrombin III, Heparin Cofactor II, Protein C, or Protein S. The assays included: Euglobulin fibrinolytic activity (EFA), tissue-type plasminogen activator related antigen (t-PA-Ag) and plasminogen activator inhibitor activity (PA inhibitor), which were measured before and after 10 min of venous occlusion (V.O.). On the basis of the results, the patients could be classified in 3 groups: good responders with an at least two-fold increase of EFA after venous occlusion (n = 76), poor responders with a lesser increase of EFA due to deficient release of t-PA (n = 12), and poor responders with a normal t-PA release but an increased level of PA-Inhibitor (n = 32). The poor responders due to deficient t-PA release (10% of total) had a higher incidence of recurrence of deep vein thrombosis, than the other groups (p less than 0.01). An overall correlation was found between the level of PA-Inhibitor activity and the triglyceride level (r = 0.40, p less than 0.01), suggesting that these elevations may be due to a common cause, at least in some of the patients. It is concluded that a poor fibrinolytic response to venous occlusion occurs in 35 percent of DVT patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Affective consequences of mere ownership: The name letter effect in twelve European languages

Abstract: The hypothesis is tested that mere ownership of an object is a sufficient condition to enhance its likelihood to become one of the most attractive items of the entire set of similar objects. Evidence is presented that isolated visual letter stimuli belonging to one's own name are more often ranked among the six most preferred letters of the entire alphabet than identical not-own name letters. Across 12 different European languages, an (own) name letter effect was found for (initial and/or not-initial) letters belonging to own first and/or family name. The fundamental theoretical relevance of the effect is outlined as well as its heuristic value for research on individual versus collective ownership and on affective asymmetry. A cross-lingual analysis of the six least preferred letters-while also confirming the mere ownership hypothesis-calls for a critical reformulation of Zajonc's mere exposure theory.

A mathematical-model for the electrolytic codeposition of particles with a metallic matrix

Abstract: Over the last decade the general knowledge of the electrolytic codeposition of inert particles with metals has increased markedly, and a few models have been proposed. In this paper a new model that overcomes several of the shortcomings of the previously proposed models is developed starting from a statistical approach of the incorporation of particles. The validity of the new model is shown for two experimental codeposition systems, namely, from acidic sulfate baths and from additive‐free potassium cyanide baths.

The Effect of Semantic Structure on First Graders' Strategies for Solving Addition and Subtraction Word Problems

Abstract: In a longitudinal investigation, data were collected on the problem representations and solution strategies of 30 first graders who were given a series of simple addition and subtraction word problems (Verschaffel, 1984). The children were interviewed three times during the school year, and data obtained on their solution strategies and on the influence of problem structure on the strategies. The results complement those of recent related research, especially the work of Carpenter and Moser (1982, 1984). More precisely, the influence of problem structure on children's solution strategies appears even more extensive and decisive than that described by previous researchers.

Transposon Mutagenesis of Azospirillum brasilense and Azospirillum lipoferum: Physical Analysis of Tn5 and Tn5-Mob Insertion Mutants

Abstract: Tn5-induced insertion mutants were generated in Azospirillum brasilense Sp7 and A. lipoferum SpBr17 by mating with Escherichia coli strains carrying suicide plasmid vectors. The sources of Tn5 were the suicide plasmids pGS9 and pSUP2021. Kanamycin-resistant Azospirillum colonies appeared from crosses with E. coli at maximum frequencies of 10 per recipient cell. Transposon Tn5 also conferred streptomycin resistance on Azospirillum colonies as was observed earlier for Rhizobium sp. Eight Tn5-induced Km SmA. brasilense Sp7 mutants with reduced nitrogen-fixing capacity were isolated. The potential use of Tn5-Mob for labeling and mobilization of Azospirillum-indigenous plasmids was demonstrated by isolating Tn5-Mob insertions in the megaplasmids of A. brasilense Sp7.

Evidence for functional communication between folliculo-stellate cells and hormone-secreting cells in perifused anterior pituitary cell aggregates.

Abstract: Dispersed anterior pituitary cells from adult female rats were separated by gradient sedimentation at unit gravity. The small-sized cell population on top of the gradient consisted of 65.6 ± (SE) 4.2% (n = 8) cells immunoreactive to antiserum against S-100 protein, a marker of folliculo-stellate (FS) cells in rat pituitary. The corresponding fraction derived from adult male or immature female rats were also enriched in S-100 positive cells but to a lower extent. Only small numbers of S-100 positive cells were found in medium- and large-sized cell populations. Coaggregating the S-100 cell-enriched populations from adult females with other pituitary cell populations resulted in a clear-cut inhibition of the GH response to rat GHreleasing factor and /3-adrenergic agents, of the PRL response to TRH and angiotensin II (All) and the LH response to LHRH. The magnitude of inhibition increased with the number of FS cells put into the coaggregates. In perifused aggregates prepared from different gradient fractions ...

Slow inactivation of the sodium current in rabbit cardiac Purkinje fibres.

Abstract: An analysis of the slowly inactivating Na current in rabbit cardiac Purkinje fibres was made, using the twomicroelectrode voltage clamp technique. The existence of the slowly inactivating Na current was demonstrated by recording TTX-sensitive currents. The current was sensitive to Na withdrawal and could be blocked by 0.1 mM Cd. The current-voltage relation extended over a broad range of potentials, as negative as −85 mV. The time course of inactivation consisted of different phases, with time constants differing as much as three orders of magnitude. Time constants of the first phase of slow inactivation increased at more positive potentials. Non-inactivating Na currents were observed in the threshold region. Recovery from inactivation was less complex. The voltage dependency of inactivation could be described by a sigmoidal curve with a half maximum potential of −75.6 mV and a slope factor of 6.3 mV. Deactivation was fast. The results suggest that at the microscopic level the Na channel shows multiple states of inactivation. At the macroscopic level the slowly inactivating Na current plays an important role in determining diastolic potential, pacemaker activity and plateau duration, and is fundamental in explaining the effect of local anesthetics and frequency of stimulation on action potential duration.

Some Trends in European Sociology of Religion: The Secularization Debate*

Abstract: The very flattering invitation to deliver the Paul Hanly Furfey Lecture for 1986 was accompanied by a suggestion that caused me to hesitate before accepting this notable honor. That suggestion was that the subject of my discourse should be the research traditions in the sociology of religion in Europe, and I was all too well aware that no one has a total overview of the European contribution to our discipline. There are too many barriers, the major one being the language barrier. Fortunately, a few internationally oriented journals help us by inviting colleagues and research teams to present important research findings and theoretical insights, some of which have originally been published in national journals. They also publish wide

Intrinsic framework electronegativity: A novel concept in solid state chemistry

Abstract: The charge‐dependent ‘‘effective’’ electronegativity χα of an atom α in a molecule or crystal, i.e., χα=(χ0α+Δχα)+2(η0α +Δηα)qα +∑β≠α qβ/Rαβ differs from the expression for the isolated atom (χ0α+2η0αqα) because of corrections to the electronegativity (Δχα) and hardness (Δηα), respectively, and due to the external potential generated by the surrounding charges qβ at distances Rαβ (new quantum‐mechanical proof given). After calibration of Δχα and Δηα for all atom types, ab initio charges can be reproduced to within a few hundredths of an electron by the electronegativity equilization method (using χav=χα=χβ⋅⋅⋅ and ∑β qβ=constant). Application of this algorithm to the solid state (i.e., charges and external potential being generated in a self‐consistent way and using Ewald’s method for determining the Madelung potential) leads to a novel method for determining ‘‘ab initio quality’’ charges and the value of the average electronegativity. If applied to SiO2 polymorphs, a relation between the refractive index ...

Reading a message when the same message is available auditorily in another language: the case of subtitling

Abstract: In Experiment 1 , subjects reported on the speed of three presentation times of subtitles (4-, 6- and 8-seconds rules), with the 6-seconds rule as the one used by most TV stations (normal presentation time). In Experiment 2 , three time rules (2-, 4- and 6-seconds rule) were used in three different tapes of the same movie and the eye movements were recorded. Subjects did or did not master the spoken language; a third group did not receive the sound track. The findings suggest that, under normal presentation time, time spent in reading the subtitle does not change as a function of the knowledge and the availability of the spoken language, due to the longstanding experiences of our subjects with such a presentation time. A number of episodic effects of the movie are to be explained by their confounding with the number of lines in the subtitle: As the time to switch from the movie to the subtitle is more or less the same in all cases, more viewing time is available with two lines. In general, processing of subtitles seems to be an automatic or “encapsulated” activity, at least if it is not disturbed by abnormal presentation times.

Control of glycogen synthesis in health and disease.

Abstract: Investigations in our laboratory have shown that the activity of glycogen synthase phosphatase in the liver is shared by at least two functionally distinct proteins: a G-component, which is tightly associated with glycogen particles, and a soluble S-component. Most preparations of glycogen synthase-b that are isolated from the liver of fed glucagon-treated animals require the presence of both components in order to be converted to synthase-a. The G-component is subject to control mechanisms that do not affect the S-component. Its activity is strongly inhibited by phosphorylase-a. This feature explains why glycogen synthesis and glycogenolysis do not normally occur simultaneously, except in the glycogen-depleted liver, where a futile cycle may occur. Experiments in vitro have shown that a minimal glycogen concentration is required to ensure the interaction between the G-component and phosphorylase-a. The G-component is also selectively inhibited by Ca2+, and the magnitude of this inhibition depends markedly on the glycogen concentration. The latter inhibition is probably one of the mechanisms by which cyclic adenosine monophosphate (cAMP)-independent glycogenolytic agents achieve the inactivation of glycogen synthase in the liver. Glucocorticoid hormones and insulin are required for the induction and/or maintenance of the G-component in the liver. During the development of the fetal rat, glucocorticoids induce the G-component in the liver. This is an essential event in the glucocorticoid-triggered deposition of glycogen in the fetal liver. A functional adrenal cortex is also required in the adult animal to prevent a loss of the capacity for hepatic glycogen storage during starvation. The latter capacity depends on the concentration of functional G-component in the liver. Chronic diabetes causes a similar functional loss. However, the effect of glucocorticoids is not mediated by a putative secretion of insulin.

Trigger factors in migraine: a study conducted by the Belgian Migraine Society.

Abstract: SYNOPSIS Information on trigger factors provoking a migraine attack, was collected in 217 migraineurs (176 women, 41 men). In this selected group of patients, most patients were spontaneously aware of one or more trigger factors; 184 (85%) of the patients reported trigger factors with a median number of 3 different trigger factors. The main trigger factors were menstruation (48%) or ovulation (8.5%) in women, certain food (44.7%), alcoholic beverages (51.6%) and stress 148.8%). After excluding the menstrual cycle as a trigger factor, trigger factors were more frequent in women, in older patients and in patients with a longer duration of disease. Women with a menstrual cycle-related migraine reported more trigger factors, other than the menstrual cycle itself, than women in whom the menstrual cycle had no influence on this migraine: this was especially so for food and beverages. The number and type of trigger factors in the women in whom the migraine was not menstrual cycle-related, were fully comparable with those in men. Patients in whom alcohol acts as a trigger factor had also significantly more other trigger factors, especially food. The same holds true for patients reporting stress as a trigger factor, but the latter difference is not significant when the different subgroups of trigger factors (food, beverages, other)are considered. Certain trigger factors may be mutually related.

Role of proaggregatory and antiaggregatory prostaglandins in hemostasis. Studies with combined thromboxane synthase inhibition and thromboxane receptor antagonism.

Abstract: Thromboxane synthase inhibition can lead to two opposing effects: accumulation of proaggregatory cyclic endoperoxides and increased formation of antiaggregatory PGI2 and PGD2. The elimination of the effects of the cyclic endoperoxides by an endoperoxide-thromboxane A2 receptor antagonist should enhance the inhibition of hemostasis by thromboxane synthase blockers. We have carried out a series of double-blind, placebo-controlled, crossover studies in healthy volunteers to check if this hypothesis may be operative in vivo in man. In a first study, in 10 healthy male volunteers, the combined administration of the thromboxane receptor antagonist BM 13.177 and the thromboxane synthase inhibitor dazoxiben gave stronger inhibition of platelet aggregation and prolonged the bleeding time more than either drug alone. In a second study, in 10 different healthy male volunteers, complete inhibition of cyclooxygenase with indomethacin reduced the prolongation of the bleeding time by the combination BM 13.177 plus dazoxiben. In a third study, in five volunteers, selective cumulative inhibition of platelet TXA2 synthesis by low-dose aspirin inhibited platelet aggregation and prolonged the bleeding time less than the combination BM 13.177 plus dazoxiben. In vitro, in human platelet-rich plasma stimulated with arachidonic acid, the combination of BM 13.177 and dazoxiben increased intraplatelet cAMP while the single drugs did not affect it. Our results indicate that prostaglandin endoperoxides can partly substitute for the activity of TXA2 in vivo in man and that an increased formation of endogenous antiaggregatory and vasodilatory prostaglandins, as obtained with selective thromboxane synthase inhibitors, may contribute to the impairment of hemostasis.

Regulation of the cAMP Level in the Yeast Saccharomyces cerevisiae: Intracellular pH and the Effect of Membrane Depolarizing Compounds

Abstract: SUMMARY: Addition of plasma membrane depolarizing agents, such as dinitrophenol (DNP) and azide, to cells of Saccharomyces cerevisiae under aerobic conditions, is known to cause an increase in the cAMP level within 15 s. We found that both compounds lowered the intracellular pH (measured by in vivo 3P-NMR) drastically within the same time period. Plasma membrane depolarization, however, was much slower: DNP and azide had no effect on the membrane potential during, respectively, the first 2 min and the first 10 min after addition. Apparently, the intracellular pH of yeast is much more sensitive to perturbation than the membrane potential. The effect of both compounds on the cAMP level was highly dependent on the extracellular pH: when the latter was raised, the effect disappeared completely between pH 6 and 7. A similar dependence on the extracellular pH was observed for the lowering of intracellular pH. Addition of organic acids, such as acetate and butyrate, at low pH and under aerobic conditions, also caused an immediate increase in the cAMP level and an immediate drop in the intracellular pH. These results suggest that agents such as DNP and azide do not raise the cAMP level in yeast cells because of their membrane depolarizing properties but because they lower the intracellular pH. Under anaerobic conditions, DNP. azide and organic acids were much less effective in increasing the cAMP level. Addition of a small amount of glucose, however, restored their capacity to enhance the cAMP level. This suggests that under anaerobic conditions and in the absence of glucose the ATP level is a limiting factor for cAMP synthesis.

Fibrinolytic response and fibrin fragment D-dimer levels in patients with deep vein thrombosis.

Abstract: An enzyme-linked immunosorbent assay for fragment D-dimer was developed with the use of two monoclonal antibodies directed against specific non-overlapping antigenic determinants, present in fragment D-dimer of crosslinked fibrin but not in fragment D of non crosslinked fibrin or of fibrinogen. The lower limit of sensitivity of the assay when applied to human plasma, is 25 ng/ml. Concentration of fragment D-dimer in plasma from healthy individuals was 177 +/- 83 ng/ml (mean +/- SD). In plasma of 11 out of 12 patients with phlebographically confirmed acute deep vein thrombosis, fragment D-dimer levels were significantly increased. Fragment D-dimer was not increased in 9 out of 10 patients with recurrent idiopathic deep vein thrombosis during clinically silent episodes. Total t-PA antigen and free t-PA antigen concentrations were measured using previously developed ELISAs. Nine of the 12 patients with acute deep vein thrombosis showed a significant increase of total t-PA antigen (from 8.6 +/- 6.9 ng/ml to 21 +/- 16 ng/ml) after venous occlusion but in 3 of these free t-PA remained undetectable. Five of the 10 patients with recurrent deep vein thrombosis responded to venous occlusion with a significant increase of total t-PA antigen (from 6.7 +/- 3.2 ng/ml to 14 +/- 7.9 ng/ml) but, in all patients, free t-PA antigen remained undetectable. It is concluded that the combined assays of total and free t-PA antigen and of fragment D-dimer may be useful for the evaluation of the dynamics of the fibrinolytic system in physiological and pathological conditions.