Showing papers by "École Normale Supérieure published in 1988"

Muscarinic activation of ionic currents measured by a new whole-cell recording method

Abstract: A new method is described as an alternative to whole-cell recording in order to prevent "wash-out" of the muscarinic response to acetylcholine (ACh) in rat lacrimal gland cells. The membrane of a cell-attached patch is permeabilized by nystatin in the patch pipette, thus providing electrical continuity between the pipette and the cytoplasm of the cell without the loss or alteration of cytoplasmic compounds necessary for the maintenance of the response to ACh. With normal whole-cell recording in these cells, the response to ACh, seen as the activation of Ca-activated K and Cl currents, lasts for approximately 5 min. With the nystatin method, the response is not diminished after 1 h. Nystatin, applied extracellularly, is shown to cause a rapid and reversible increase of membrane conductance to cations. In the absence of wash-out, we were able to obtain dose-response curves for the effect of ACh on Ca-activated K currents. An increase of [ACh] caused an increase in the K current, with apparent saturation at concentrations above approximately 1 microM ACh. The delay between ACh application and the activation of K current was inversely related to [ACh] and reached a minimum value of 0.7-1.0 s at high [ACh].

Notes towards a description of Social Representations

Abstract: The theory of social representations occupies a place apart in social psychology both by the problems it raises and the scale of the phenomena with which it deals. This provokes many a criticism and misunderstanding. Such a theory may not correspond with the model of social psychology as it is defined at present. One attempts however to show that it answers important social and scientific questions, in what it differs from the classical conception of collective representations and, from the very beginning, adopts a constructivist perspective which has spread in social psychology since. Several trends of research have confirmed its vision of the relations between social and cognitive phenomena, communication and thought. More detailed remarks aim at outlining the nature of social representations, their capacity to create information, their function which is to familiarize us with the strange, according to the categories of our culture. Going farther, one insists on the diversity of methodological approaches. If the experimental method is useful to understand how people should think, higher mental and social processes must be approached by different methods, including linguistic analysis and observation of how people think. No doubt, social representations have a relation with the more recent field of social cognition. But inasmuch as the former depend on content and context, i.e. subjectivity and sociability of people, they approach the phenomena differently from the latter. Referring to child psychology and anthropology, one can contend, despite appearances, that it is also a more scientific approach. There is however much to be learned from criticisms and there is still a long way to go before we arrive at a satisfactory theory of social thinking and communication.

Food, self and identity:

Abstract: Food is central to our sense of identity. The way any given human group eats helps it assert its diversity, hierarchy and organisation, but also, at the same time, both its oneness and the otherness of whoever eats differently. Food is also central to individual identity, in that any given human individual is constructed, biologically, psychologically and socially by the foods he/she choses to incorporate. This paper is intended as a speculative survey of the ways in which food is related to identity formation.

The role of divalent cations in the N-methyl-D-aspartate responses of mouse central neurones in culture.

Abstract: 1. Single-channel currents activated by N-methyl-D-aspartate (NMDA) agonists were analysed in the presence of various extracellular concentrations of divalent cations in outside-out patches from mouse neurones in primary culture. 2. In nominally Mg2+-free solutions the opening and closing of the channels leads to rectangular current pulses, the mean duration of which varies little with membrane potential. After addition of Mg2+, the single-channel currents recorded at negative potentials appear in bursts of short openings separated by brief closures. 3. The duration of the short openings decreases with increasing Mg2+ concentration, while the duration of the short closures is independent of the Mg2+ concentration. Depolarization increases the duration of the short openings and decreases the duration of the short closures. 4. The dependence of the burst structure on the Mg2+ concentration and on membrane potential is compatible to a first approximation with a model in which Mg2+ ions enter the open channel and block it by binding at a deep site. A better approximation requires, however, additional assumptions such as Mg2+ permeation and/or interactions between Ca2+ and Mg2+. 5. Increasing the extracellular Ca2+ concentration from 1 to 100 mM produces three effects on the currents flowing through NMDA channels. It shifts the reversal potential towards a positive value (+30 mV); it reduces the outward current flowing through the NMDA channels at very positive potentials; it reduces the inward current flowing at negative potentials. 6. The interpretation of the effects of Ca2+ appears to require three hypotheses: that Ca2+ permeates the NMDA channel, that there exists a significant surface potential at the entrance of the NMDA channel in physiological solutions and that both Ca2+ and monovalent cations bind to the channel, binding being stronger in the case of Ca2+ ions. 7. While Co2+ and, to a lesser extent, Mn2+ mimic the effects of Mg2+ on the NMDA channel, Ca2+, Ba2+ and Cd2+ do not. The distinction between Mg2+-like and Ca2+-like divalent cations corresponds to a difference in the speed of exchange of the water molecules surrounding the cations in solutions. Thus, it is possible that permeation occurs for all the divalent cations, but is slower for those which are slowly dehydrated.

Managerial influence in the implementation of new technology

Abstract: In the implementation of an organizational innovation, managers are usually presumed to influence the extent to which the innovation is adopted and used by their subordinates. However, the findings presented in this paper suggest that the managerial influence is not equally perceived by all subordinates. Rather, certain context-specific characteristics of individual employees mediate the managerial influence. Users of the expert system studied herein who were low in personal innovativeness toward this class of innovations, for whom the subjective importance of the task being computerized was low, whose task-related skills were low or who were low performers in their sales job-all these user groups perceived their management had encouraged them to adopt. In contrast, users who rated high on any of these measures did not perceive any management influence in their adoption decision. Moreover, although access to the innovation was in fact highly similar for all users, high performers also were inclined to perceive the system as more accessible than were low performers. These findings suggest that the diffusion of an innovation within an organization perhaps could be viewed as a two-step managerial process. Employees whose characteristics incline them to adopt an innovation will do so without management support or urging if it is simply made available. Employees low on these characteristics will await a managerial directive before adopting. Implications for future research are discussed.

Laser cooling below the one-photon recoil by velocity-selective coherent population trapping.

Abstract: We present a new laser-cooling scheme based on velocity-selective optical pumping of atoms into a nonabsorbing coherent superposition of states. This method has allowed us to achieve transverse cooling of metastable $^{4}\mathrm{He}$ atoms to a temperature of 2 \ensuremath{\mu}K, lower than both the usual Doppler cooling limit (23 \ensuremath{\mu}K) and the one-photon recoil energy (4 \ensuremath{\mu}K). The corresponding de Broglie wavelength (1.4 \ensuremath{\mu}m) is larger than the atomic-transition optical wavelength.

Supernode partitioning

Abstract: Supercompilers must reschedule computations defined by nested DO-loops in order to make an efficient use of supercomputer features (vector units, multiple elementary processors, cache memory, etc…). Many rescheduling techniques like loop interchange, loop strip-mining or rectangular partitioning have been described to speedup program execution. We present here a class of partitionings that encompasses previous techniques and provides enough flexibility to adapt code to multiprocessors with two levels of parallelism and two levels of memory.

$4$-dimensional black holes from Kaluza-Klein theories

Abstract: In this paper we consider generalizations in 4 dimensions of the Einstein-Maxwell equations which typically arise from Kaluza-Klein theories. We specify conditions such that stationary solutions lead to non-linearσ-models for symmetric spaces. Using both this group theoretic structure and some properties of harmonic maps we are able to generalize many of the known existence and uniqueness theorems for black holes in Einstein-Maxwell theory to this more general setting.

Earthworm activities and the soil system.

Abstract: Earthworms find in soil the energy, nutrient resources, water and buffered climatic conditions that they need. According to the food resource they exploit and the general environmental conditions, earthworms can be grouped into different functional categories which differ essentially in morphology, size, pigmentation, distribution in the soil profile, ability to dig galleries and produce surface casts, demographic profiles and relationships with the soil microflora. Soil characteristics are both the determinant and the consequence of earthworm activities, since these animals greatly influence the functioning of the soil system. When present, they build and maintain the soil structure and take an active part in energy and nutrient cycling through the selective activation of both mineralization and humification processes. By their physical activities and resultant chemical effects, earthworms promote short and rapid cycles of nutrients and assimilable carbohydrates. Thus earthworms represent a key component in the biological strategies of nutrient cycling in soils and the structure of their communities gives a clear indication of the type of soil system that they inhabit.

Pillared Clays as Catalysts

Abstract: Clays have long been used as catalysts [1] and they retain a continuing important role since they constitute the matrix of many industrial catalysts based on zeolites. Intercalated clays are a new class of materials, in which an homogeneous distribution of micropores can be obtained with pore openings varying from 4 A to 18 A according to the type of pillars. These solids are then attractive because they can adsorb and convert large molecules.

Plant models faithful to botanical structure and development

Abstract: Some very impressive results have been obtained in the past few years in plants and trees image synthesis. Some algorithms are largely based on the irregularity and fuzziness of the objects, and use fractals, graftals or particle systems. Others focus on the branching pattern of the trees with emphasis on morphology. Our concern here is the faithfulness of the models to the botanical nature of trees and plants. We present a model which integrates botanical knowledge of the architecture of the trees: how they grow, how they occupy space, where and how leaves, flowers or fruits are located, etc. The very first interest of the model we propose is its great richness: the same procedural methods can produce "plants" as different as weeping willows, fir trees, cedar trees, frangipani trees, poplars, pine trees, wild cherry trees, herbs, etc. Another very important benefit one can derive from the model is the integration of time which enables viewing the aging of a tree (possibility to get different pictures of the same tree at different ages, accurate simulation of the death of leaves and branches for example). The ease to integrate physical parameters such as wind, the incidence of factors such as insects attacks, use of fertilizers, plantation density, and so on makes it a useful tool for agronomy or botany.

Factors of success for end-user computing

Abstract: A two-phase study concerned with the factors of success associated with the development of computer applications by end users was conducted in 10 large organizations. During the first phase, in-depth interviews were used to refine a preliminary model of the factors of success for user development of computer applications (UDA). In the second phase, a questionnaire was administered to 272 end users experienced in developing applications. Statistical tests of the relationships in the model indicated that all but one of the derived hypotheses were substantiated. The result of this study is a field-verified model of the factors of success of UDA that provides a basis for implementation of UDA practices and policies in organizations, as well as for further research in end-user computing.

COMPLICATIONS RELATED TO ANAESTHESIA IN INFANTS AND CHILDREN A Prospective Survey of 40240 Anaesthetics

Abstract: A prospective survey of anaesthesia-related mortality and morbidity in infants and children was carried out in a representative sample of anaesthetics performed in 440 institutions chosen at random in France. A total of 40240 anaesthetics were administered to patients younger than 15 yr, 2103 (5%) involving infants (younger than 1 yr). Twenty-seven major complications related to anaesthesia occurred during or within 24 h of the anaesthesia—an incidence of 0.7 per 1000 anaesthetics. Nine, of which four were associated with cardiac arrest, were observed in infants, whereas in children there were 18 complications of which eight were associated with cardiac arrest, one with fatal outcome. The risk of complications was significantly higher (P

Arbitrarily shaped microstrip structures and their analysis with a mixed potential integral equation

Abstract: The author gives a comprehensive description of the mixed potential integral equation (MPIE) as applied to microstrip structures. This technique uses Green's functions associated with the scalar and vector potential which are calculated by using stratified media theory and are expressed as Sommerfeld integrals. Several methods of moments allowing the study of irregular shapes are described. It is shown that the MPIE includes previously published static and integral equations. Hence, it can be used at any frequency ranging from DC to higher-order resonances. Several practical examples including an L-shaped patch have been numerically analyzed and the results are found to be in good agreement with measurements. >

Electric-field-induced localization and oscillatory electro-optical properties of semiconductor superlattices.

Abstract: We show that the application of an electric field $F$ along the growth axis of a semiconductor superlattice results in a strong localization of the eigenstates, a blue shift of the optical-absorption edge, and the presence of oscillations periodic in ${F}^{\ensuremath{-}1}$. These unique electro-optical properties are derived here within the framework of a tight-binding description of the envelope functions and also from numerical solutions of the Schr\"odinger equation for a finite set of coupled quantum wells.

Observation of the Wannier-Stark quantization in a semiconductor superlattice.

Abstract: When an electric field $F$ is applied parallel to the growth axis of a semiconductor superlattice, the eigenstates are quantized and strongly localized. This Wannier-Stark quantization manifests itself as an effective blue shift of the optical-absorption edge and is accompanied by a new type of electro-optical oscillation of the absorption coefficient which is periodic in ${F}^{\ensuremath{-}1}$. We report experimental evidences for these theoretical predictions from the study of the low-temperature electroreflectance of a GaAs-AlGaAs superlattice.

Localized structures generated by subcritical instabilities

Abstract: We report the existence of structurally stable pulse-like solutions in the vicinity of an inverted Hopf bifurcation. These localized structures correspond to droplets in first order phase transitions, where they are known to be unstable. We show that the stabilisation mechanism is a non variational effect, i.e. is due to the non existence of a «free-energy» to minimize in the instability problem we consider. We propose this mechanism as an explanation for the existence of localized waves in shear flows or in convection experiments in binary fluid mixtures Etude de l'existence de solutions stables en forme d'impulsion au voisinage d'une bifurcation de Hopf inverse. On montre que le mecanisme de stabilisation est un effet non variationnel. On propose ce mecanisme pour expliquer l'existence de paquets d'ondes localises dans certains ecoulements paralleles ou dans des experiences de convection dans les fluides binaires

Improvement and simplification of low-background silver staining of proteins by using sodium dithionite

Abstract: High sensitivity and low background, the attractive characteristics of the procedure of Blum et al., Electrophoresis 1987, 8, 93-99, for silver staining of proteins in polyacrylamide gels have been improved by sensitizing the gels with sodium dithionite instead of sodium thiosulfate and by equilibration in water after fixation and prior to sensitization. These modifications decrease the background and allow for a longer development period, which in turn increases sensitivity and color contrast. In addition, the colors of the spots are shifted toward colder tones when compared with the original method.

The Hidden Symmetries of Multi-Centre Metrics

Abstract: We discuss the dynamical symmetries of the multi-centre metrics and apply our results to the scattering of BPS monopoles and fluctuations around such monopoles In particular, we give a detailed account of the hidden symmetries of the Taub-NUT metric

N‐methyl‐D‐aspartate‐activated channels of mouse central neurones in magnesium‐free solutions.

Abstract: 1 The whole-cell and outside-out configurations of the patch-clamp method were used to investigate the properties of the channels activated by N-methyl-D-aspartate (NMDA channels) in mouse central neurones in culture Recording was made in Mg2+-free solutions 2 In the whole-cell recording mode the currents induced by both NMDA and L-glutamate were accompanied by a large increase in noise In both cases the noise power spectra were well fitted by single Lorentzian functions and the corresponding mean time constant, tau, was about 6 ms at room temperature The single-channel conductance, gamma n, estimated from the ratio of the noise variance to the total current, varied between 22 and 40 pS 3 Endogenous amino acids known to activate NMDA receptors (L-glutamate, L-aspartate, L-cysteine sulphinate and quinolinate) as well as exogenous NMDA agonists such as ibotenate and trans-2,3-piperidine dicarboxylate (trans-PDA) all produced similar responses In particular, analysis of the current noise yielded tau values between 4 and 8 ms in all cases 4 NMDA responses were antagonized by 2-amino-5-phosphonovalerate (APV) without any effect on gamma n or tau values measured by noise analysis; NMDA responses were also diminished by D-alpha-aminoadipate and cis-2,3-piperidine dicarboxylate 5 In outside-out patches, it was observed that the single-channel current amplitude varies linearly as a function of membrane potential between -80 and +60 mV The reversal potential is near 0 mV NMDA channels are permeable to Na+, K+ and Cs+, but blocked by choline The single-channel conductance, gamma e, varies between 40 and 50 pS at room temperature 6 The NMDA channels open in bursts of short openings interrupted by brief closures At -60 mV, the closures had a mean duration, tc, of 04 +/- 02 ms The mean channel open time, to, was 59 +/- 10 ms for NMDA and 53 +/- 17 ms for L-glutamate The mean burst duration, tb, was 105 +/- 07 ms for NMDA and 85 +/- 20 ms for L-glutamate 7 When the temperature was increased between 14 and 24 degrees C, the NMDA channel conductance increased with a Q10 of 16 while the mean open time decreased with a Q10 close to 2 8 The NMDA channel showed, in addition to the 'main' conductance state (40-50 pS), smaller conductance states of 15 and 35 pS(ABSTRACT TRUNCATED AT 400 WORDS)

A new method for monitoring ultra-fast photopolymerizations by real-time infra-red (RTIR) spectroscopy

Abstract: An original method based on IR spectroscopy has been developed in order to follow real-time photopolymerizations that take place in less than one second. Conversion versus time curves were directly recorded for various multiacrylic monomers irradiated in condensed phase, thus allowing an immediate evaluation of both the rate of polymerization and the amount of residual unsaturation in the UV-cured polymer. This method proved well suited to study the effect on the polymerization rate of the photoinitiator efficiency, the monomer reactivity, the light intensity, the film thickness, and the O2 inhibition. The dark polymerization that develops just after the UV exposure was investigated as a function of the degree of conversion and was shown to represent up to 60% of the total process. A comparison with other methods of kinetic analysis shows the unique advantages of real-time infra-red (RTIR) spectroscopy which permits to follow quantitatively and in situ ultra-fast polymerizations.

High-Resolution Numerical Experiments for Forced Two-Dimensional Turbulence

Abstract: Forced two-dimensional turbulence is simulated by high-resolution (5122) numerical integrations of the Navier-Stokes equations. Small-scale behaviour differs significantly from the one previously observed at lower resolutions. Coherent structures are observed at the injection scale with spontaneous formation of dipolar and tripolar structures here analysed for the first time.

Intrinsic bending force in anisotropic membranes made of chiral molecules.

Abstract: A linear term linked to molecular chirality occurs in the bending energy of membranes with C/sub 2/ or D/sub 2/ symmetry. We find it to alternate in sign, depending on the direction of a cylindrical curvature, and discuss consequences for anisotropic solid membranes, tilted fluid bilayers, and ferroelectric smectic liquid crystals.

Prokaryotic hopanoids: the biosynthesis of the bacteriohopane skeleton. Formation of isoprenic units from two distinct acetate pools and a novel type of carbon/carbon linkage between a triterpene and D-ribose.

Abstract: Incorporation of 13C-labelled acetate into the hopanoids of the purple non-sulfur bacteria Rhodopseudomonas palustris and Rhodopseudomonas acidophila and the facultative methylotroph Methylobacterium organophilum showed that the bacteriohopane skeleton is built from an unique carbon/carbon linkage between the triterpenic hopane moiety and the C-5 carbon of a D-ribose derivative arising from the non-oxidative pentose phosphate pathway. Furthermore a probable compartmentation of the acetate metabolism could be observed in these bacteria. Whereas exogenous acetate was directly incorporated into the glucose derivatives and poly-(3-hydroxybutyrate), the isoprenic units were apparently solely synthesized from two acetate units arising from the glyoxylate cycle and a third one issued either from the glyoxylate cycle or from the Entner-Doudoroff pathway of glucose catabolism. Although an unknown biosynthetic pathway different from that usually proposed for isoprenoid biosynthesis can not be excluded, the former hypothesis explained all labelling patterns observed on the triterpenic skeleton.