Showing papers by "Université catholique de Louvain published in 1980"

Stimulation of the superior colliculus in the alert cat. I. Eye movements and neck EMG activity evoked when the head is restrained.

Abstract: Electrical stimulation of the cat superior colliculus (SC), in conjunction with the accurate measurement of elicited eye movements and histologically verified electrode positions, has revealed a striking antero-posterior variation in collicular organization. Three zones could be defined in the SC on the basis of eye movement patterns and associated neck muscle EMG activity evoked from the deeper layers. The Anterior zone was coextensive with the central 25 degrees of the visual retinotopically coded map contained in the superficial layers. Saccades evoked from this zone were also retinotopically coded, and the latency of EMG activity depended on the position of the eye in the orbit. A similar observation applies to the entire monkey SC. The Intermediate zone was coextensive with the 25 degrees--70 degrees of visual projections. Saccades evoked from this region were "goal-directed" and were associated with invariant, short latency EMG responses. The Posterior zone was found in the extreme caudo-lateral portion of the SC. Eye movements evoked from this zone were centering saccades associated with constant latency EMG activity. The present results in conjunction with previously demonstrated antero-posterior variations in projections to the SC, suggest that the motor strategies controlling gaze shifts toward visual targets vary depending on the location of the target in the visual field.

Comparison of several methods for the determination of arsenic compounds in water and in urine. Their application for the study of arsenic metabolism and for the monitoring of workers exposed to arsenic.

Abstract: Several arsenic species (inorganic tri- or pentavalent arsenic, mono-and dimethylated arsonic acids) can be determined in water samples by electrothermal atomic absorption spectrometry after appropriate acidification procedures (concentrated HCl or a mixture HCl/HClO4/HBr) and extraction by toluene in the presence or absence of KI; the determination of aromatic derivatives and of arsenic thiol complexes needs a wet or dry ashing step. The procedures for water analysis are not directly applicable to urine samples; in the best conditions, total inorganic plus 85% on the average of the methylated arsenicals present in urine are measured after acidification with concentrated HCl and extraction by toluene in the presence of KI. Total arsenic content (including arsenic from marine origin) is measured only after a drastic mineralization step like MgO treatment at 600°C. The results obtained by the electrothermal atomic absorption technique and those obtained by neutron activation analysis are in excellent agreement. When the presence of arsenic of marine origin is suspected in urine, the analysis of inorganic arsenic and its metabolites is preferably performed by an arsine generation technique. The sum of inorganic arsenic and of its mono and dimethylated derivatives determined by such a technique is identical with the results obtained by electrothermal atomic absorption spectrometry after complete mineralization of the samples as long as no arsenic from marine origin is present. After oral ingestion of As2O3 by man, the urinary excretion of inorganic arsenic and its metabolites is important and rapid (approximately 60% are eliminated by the oral route with a half life of 30 h). While the excretion occurs in the form of inorganic species during the first hours following the ingestion, a methylating process is rapidly triggered and leads to a preponderant excretion of dimethylarsinic acid 1 day after ingestion. In the case of ingestion of seafood containing arsenic, the urinary excretion occurs at a higher rate (half life 18 h) apparently without transformation. The absence of interference of arsenic from marine origin and the capacity of measuring separately inorganic arsenic and its main urinary metabolites makes the arsine generation technique the best suited for the monitoring of workers exposed to inorganic arsenic. However, since the technique may sometimes be too elaborate and time-consuming for routine work, the biological monitoring of workers can be performed by determining total arsenic concentration in urine after mineralization with MgO. Samples with high arsenic content are then re-analyzed to distinguish between occupational exposure and ingestion of the organic arsenic present in marine organisms. This is carried out either by the arsine generation method or, if this technique is not available, by a direct extraction procedure in the presence of KI of a sample acidified with HCI. With the latter procedure, 85% of the methylated arsenic is measured on average without interference of arsenic from marine origin.

Die Swell of a Maxwell Fluid - Numerical Prediction

Abstract: Numerical results are presented on the calculation of die swell at the exit of slit, circular and annular dies. The material is an upper-convected Maxwell fluid (rubberlike liquid); the numerical method is of the mixed finite element type.

Molecular and Kinetic Properties of the Purified Plasma Membrane ATPase of the Yeast Schizosaccharomyces pombe

Abstract: This paper reports the properties of the purified plasma-membrane ATPase of the yeast Schizo-saccharomyces pombe which appears to transport H+ across the cellular membrane. The rate of sedimentation of the purified ATPase, estimated by the computation model of McEwen, yields a sedimentation coefficient s0.78420, w of 24 S. Calculation of the corresponding molecular weight shows that the ATPase is purified in an oligomeric form of molecular weight 800000 to 1000000 corresponding to 8 to 10 monomers of molecular weight 100000. Eadie-Hofstee plots for the purified ATPase activity are linear when tested with or without lysophosphatidylcholine showing that strict Michaelis-Menten kinetics apply within a large range of ATP and Mg2+ concentrations. Addition of egg lyso-phosphatidylcholine increases V from 1.4 to 26.8 μmol × min−1× mg−1 whereas Km is less modified. The lipid-reconstituted purified ATPase activity is strictly specific for ATP and is inhibited competitively by ADP with a Ki of 2.5 mM. The optimum pH of 5.6 for the purified enzyme is shifted to pH 6.0 in the presence of lysophosphatidylcholine. The optimum temperature of the purified ATPase is 30 and 32.5 °C in absence or presence of lysophosphatidylcholine, respectively. The lipid-reconstituted purified ATPase activity is cation-dependent with the following specificity: Zn2+ > Co2+ > Mg2+ > Mn2+ > Ni2+ for cation concentrations below 2 mM (M2+/ATP 1), Mg2+ is the most efficient cofactor followed by Co2+ > Mn2+ > Zn2+ > Ni2+. These properties are qualitatively similar to those of the membrane-bound ATPase activity indicating that the integrity of the lipid-reconstituted purified ATPase is not appreciably modified by the extraction, purification and reconstitution procedures.

Subcellular Location of Semicarbazide-sensitive Amine Oxidase in Rat Aorta

Abstract: With tyramine as substrate, a considerable part of the amine oxidase activity of rat aorta was inhibited by 0.1 mM semicarbazide. The residual activity was little affected by 1 mM semiicarbazide. Oxidation of 5-hydroxytryptamine was not inhibited by 0.1 mM semicarbazide. The subcellular location of the semicarbazide-sensitive and semicarbazide-resistant amine oxidases was investigated by analytical density gradient centrifugation. The semicarbazide-resistant enzyme was identified with the mitochondrial monoamine oxidase, located in the outer envelope of mitochondria. The semicarbazide-sensitive amine oxidase was ascribed to the plasma membrane because it was distributed like 5′-nucleotidase and (oligomycin-insensitive) Mg2+-ATPase in various fractionation experiments, and markedly shifted by digitonin towards higher equilibrium densities in sucrose gradient.

Models With Several Regimes and Changes in Exogeneity

Abstract: In recent years, increasing attention has been devoted to models with a finite (usually small) number of regimes. Various strategies have been discussed in the literature to handle situations where each regime is characterized by a different value of a common parameter vector. See e.g. Barten and Bronsard (1970), Goldfeld and Quandt (1973), Poirier (1976),... . It appears however that no satisfactory treatment has yet been given to cases where the partitioning between " endogenous " and " exogenous " variables changes over time. Our objective is therefore to define a class of models with several regimes which is flexible enough to cover such situations. For convenience, we shall illustrate our argument by reference to an economy which is "controlled " by a policy maker shifting between instruments at some, possibly unknown, points of time. For tractability we shall mainly restrict our attention to a class of dynamic linear models although the concepts we introduce apply in a much broader framework. The possibility that the switching times could be endogenous to the model, such as in disequilibrium models will not be investigated here: work in progress indicates however that our approach can be extended in such directions. The paper is organized as follows: In Section 2 we shall discuss at length the issues to be faced by means of a simple example, taken from Goldfeld and Quandt (1973). In Section 3 we shall introduce the concepts which are needed for our analysis; linear dynamic models, LIML estimation and exogeneity. In Section 4, we shall discuss models with several regimes and concentrate in particular on imposing appropriate restrictions on the parameters characterizing different regimes. It will be shown that it is possible to preserve some of the operational features of LIML procedures.

Intergroup alliances and rejections within a protest movement (analysis of the social representations)

Abstract: Studied the development of a student protest movement which, after an initial success, rapidly declined. Opinion surveys were conducted simultaneously with an analysis of the social representations which our population (i.e. male and female university students) held about itself, its potential partners and the proposed strategies. For this latter method, different words related to the protest movement were used as stimuli for a free association task. Similarities between dictionaries were analysed according to Johnson's clustering method and Kruskal's multidimensional scaling method. The structure of social representations allows us to explain the lack of success of the protest movement in terms of intergroup differentiation: the students refused an alliance with the leaders of the movement and rejected their strategies because they progressively defined them and their culture as foreign to and incompatible with themselves. The concept of social representation is discussed in light of the findings.

Biological surveillance of workers exposed to dimethylformamide and the influence of skin protection on its percutaneous absorption.

Abstract: Two studies were carried out among workers exposed to dimethylformamide (DMF) in an acrylic fiber factory. The first study involved 22 exposed workers and 28 control workers. Blood was examined at the beginning and at the end of a working week for the presence of biological signs of liver dysfunction. Pre- and post-shift urine samples were also collected during 1 week for determination of N-methylformamide (NMF) concentration. The airborne concentration of DMF was determined at different work places during the same period. On prevention of direct skin contact with DMF solution a significant correlation was found on a group basis between the concentration of DMF vapor and the NMF concentration in post-shift urine samples. When the concentration of NMF in post-shift urine samples from a group of workers does not exceed 30 mg/g creatinine, then their integrated exposure is probably below 60 mg/m3 × h (10 mg/m3 for 6 h). This exposure appears to be safe with regard to the risk of liver damage but does not necessarily preclude episodes of alcohol intolerance in some workers.

Controlled trial of cimetidine in reflux esophagitis.

Abstract: In an eight-week double-blind trial, the effectiveness of cimetidine (1.6 g/day) was compared to placebo in 34 patients with symptomatic esophagitis confirmed by endoscopy with biopsies and/or by acid infusion test. Patients treated with cimetidine had significantly less symptomatic days during the first six weeks and less symptomatic nights during the first two weeks, and they consumed less antacids during the whole trial period. Endoscopic evaluation of 17 patients on cimetidine and of 15 patients on placebo did not show any significant difference in severity and extent of esophageal lesions after eight weeks, but histological assessment of 16 patients on cimetidine and 13 patients on placebo showed a significant improvement after eight weeks of cimetidine (P<0.025). These results show that cimetidine has a rapid effect on symptoms of reflux esophagitis and that, in some cases, it may reduce the esophageal lesions after eight weeks.

High-accuracy MOS models for computer-aided design

Abstract: This paper presents accurate device models (1-3 percent) to describe the I_{D}-V_{D} electrical characteristics of surface-channel PMOS transistors in strong inversion, and ion-implanted depletion-mode buried-channel PMOS transistors. The primary emphasis is an accurate description of the transverse carrier mobility with distance and normal electrical field in long-channel structures. The influence of substrate bias on carrier mobility in the surface-channel device is modeled theoretically and verified by experiment. The carrier mobility in the buried-channel devices is constant as determined experimentally with gated-diode C-V and conductance measurements. The modeling parameters are determined at V_{D} = 0 with an automated data-acquisition micro-processor-controlled system. The models are analyzed with a least squares estimation criterion and a high degree of internal consistency is apparent from the statistical significance of the results.

Primaquine liposomes in the chemotherapy of experimental murine malaria

Abstract: Due to a significant reduction of toxicity, 100% curative (causal prophylactic) doses of primaquine diphosphate entrapped in liposomes (60 and 70 mg/kg body weight) can be administered in a single intravenous injection to treat sporozoite-induced Plasmodium berghei infections of mice.Although drug activity is not enhanced as compared to free drug, a simplified experimental therapy scheme could be developed, which may facilitate comparative pharmacokinetic studies of various drug delivery systems.

A New Concept Explaining Catalytic Synergy Between 2 Solid-phases

Abstract: We propose a new mechanism for explaining the synergy between MoS2 and Co9S8 in hydrodesulfurization. We suppose that spill-over hydrogen produced by Co9S8 exerts an effect ofremote control on the active center of MoS2, a slight reduction leading to hydrogenation centers and stronger reduction to hydrodesulfurization centers.

Cell-to-cell interactions in the secretion of enzymes of connective tissue breakdown, collagenase and proteoglycan-degrading neutral proteases. A review

Abstract: Cell and tissue culture techniques provide valuable tools for investigating cell-to-cell interactions leading to the secretion of connective-tissue degrading enzymes, collagenase and proteoglycan-degrading neutral proteases, in inflammatory situations. These interactions, which might constitute a major regulatory mechanism, are reviewed here. Taken together, the available data strongly suggest that fibroblasts and related mesenchymal cells (such as chondrocytes, fibroblast-like or type B synovial lining cells, corneal stromal cells, etc.) could be the main suppliers of collagenase within tissues. These cells can secrete collagenase in response to factors produced by other cells, mainly macrophages and related cells (monocytes, synovial cells — presumably the macrophage-like, type A synovial lining cells), possibly also epithelial cells. Lymphocytes are able to modulate factor production by macrophages so that, through the macrophage link the secretory behavior of the fibroblastic cells may be under the control of the immune defense system and serve as an effector of immune reactions leading to connective tissue destruction.

Extraction, Purification and Properties of Soil Hydrolases

Abstract: Invertase, cellulase, phosphatases, protease and β-glucosidase were extracted from permanent pasture soil with 0.2 M phosphate buffer (pH 8) in the presence of 0.2 M EDTA. This extract was further treated with ammonium and salmine sulphates. Attempts were made to fractionate these enzyme activities by gel and anion-exchange chromatography. Specific activities were estimated in all fractions and some characteristics of the purified enzymes (optimum pH, temperature and substrate concentration, and K m and V max ) were investigated. The results indicated that extracted enzyme activities occurred partly in soil as a carbohydrate-enzyme complex and partly as a humo-carbohydrate complex.

Intertemporal Price-discrimination and Sticky Prices

Abstract: It is shown that potential entry leads to a marginal-revenue-below-marginal-cost rule, while the possibility of building up inventories (voluntarily!) leads to the intertemporal price discrimination rule, which provides a formal rationalization for normal costing. Equilibrium conditions for a group of firms are derived, using the intertemporal discrimination rule. These conditions can be written as linear estimating equations, with regression coefficients explicitly linked with parameters representing market structure. They imply that, in more concentrated industries, cost increases are less fully transmitted and changes in demand are more fully transmitted into prices than in less concentrated industries.

Relations between substrate feeding pattern and development of filamentous bacteria in activated sludge processes

Abstract: Laboratory scale activated sludge systems were operated under regimes of continuous or intermittent feeding of substrate. In a previous paper it was shown that continuously operated systems resulted in the development of filamentous bacteria and bulking sludges. Intermittently fed sludges resulted in good settling. These results are now confirmed when substrates other than glucose are present in the influent, such as nutrient broth, acetate and starch. With casein deflocculation occurred. For intermittent systems the substrate removal rates were higher than for continuous systems. Based on the results a theory is presented to account for the growth of filamentous bacteria (and bulking) in continuous systems (completely mixed systems). This theory assumes that in intermittently fed systems (plug flow systems) floc forming bacteria become dominant as a result of higher substrate uptake rates and the possibility to survive a starvation phase by thriving on accumulated intracellular metabolites.

Uricosuric Effect of Fenofibrate in Healthy-volunteers

Abstract: The uricosuric properties of a single oral dose (300 mg) of fenofibrate, or isopropyl-[4'-(p-chlorobenzoyl)-2-phenoxy-2-methyl] propionate (LF 178), a new hypolipidemic drug, have been investigated versus placebo, benzbromarone, with and without urine alkalinization, in ten normouricemic male volunteers, following a crossover design. Twofold increased uric acid clearance values were obtained after fenofibrate and fourfold increased values after benzbromarone. The ratio urinary uric acid/urinary creatinine (UUA/UCr) was enhanced after fenofibrate and benzbromarone versus placebo. The urine alkalinization with fenofibrate intake did increase this ratio to a higher extent.