Showing papers by "University of Paris published in 1979"

First order quasilinear equations with boundary conditions

Abstract: We solve the initial and boundary condition problem for a general first order quasilinear equation in several space variables by using a vanishing viscosity method and give a definition which chara...

Effects of inertial load and velocity on the braking process of voluntary limb movements.

Abstract: The aim of this study has been to identify, in humans, the braking process underlying voluntary forearm movements performed at various velocities and amplitudes and against different inertial loads. The procedure used to estimate the parameters of the braking process involved kinematic analysis of the movement and measurement of alpha-motoneural input to flexor and extensor muscles by recording electromyographic (EMG) activity. We have shown that when the agonist force does not exceed the passive viscoelastic tension developed by the extensor and flexor muscles, the movement can be braked by the viscoelastic forces alone. In contrast, above this force threshold, it was found that the motor output in agonist and antagonist muscles consists of well defined bursts of EMG activity, first in agonist then in antagonist muscles. The timing of these two bursts (duration of the agonist activity and onset of the antagonist activity) are clearly correlated with the value of the peak velocity. For the same peak velocity, the addition of inertial loads increases the excitation level of both agonist and antagonist muscles but does not change the timing of the EMG bursts. The discussion of these results focuses on the concept of “unit of movement” organized to reduce the large number of possible patterns of activation of the muscles acting on the same joint.

An electrophoretic study of native myosin isozymes and of their subunit content.

Abstract: Myosin polymorphism in muscles has been studied by a variety of electrophoretic techniques, in non-dissociating and in dissociating conditions. The analysis of myosin isozymes in the native state was achieved in pyrophosphate buffer and required only minute amounts of protein; identical results were obtained with purified or crudely extracted myosin. The determination of the subunit content of each isozyme was done in the presence of sodium dodecyl sulphate or urea for light chain, and in a phenol, acetic acid and urea system for heavy chain screening. Electrophoresis in non-dissociating conditions has led to the separation of up to a dozen of myosin isozymes, differing in mobilities by as much as 30%. Muscle specificity of myosin was clearly established. Apart from a few exceptions, all the muscles tested were shown to contain more than one myosin species; fast-twitch muscles for instance all contained the same three isozymes, but in variable ratios. Class specificity of myosin appeared related to the relative proportions of isozymes in a given muscle. A second electrophoresis in dissociating solvents of the myosin bands first resolved in pyrophosphate buffer has then allowed a further characterization of the various isozymes. The differences in mobilities observed in the native state were shown to come either from the light chains, or from the heavy chains, or from both. The first case was illustrated by the three species present in fast muscles, which were shown to correspond to three alkali light-chain isozymes, the heterodimer representing in some instances up to 40% of the total. Next to light-chain muscle type specificity, electrophoresis in the phenol, acetic acid, urea system has led to the detection of differences in the heavy chains of fast, slow and cardiac myosins. The application of these various electrophoretic techniques to the analysis of the modification of myosin isozymes during development or in pathology studies can be considered.

The classical field limit of scattering theory for non-relativistic many-boson systems. II

Abstract: We study the classical field limit of non relativistic many-boson theories in space dimensionn≧3, extending the results of a previous paper to more singular interactions. We prove the expected results: when ħ tends to zero, the quantum theory tends in a suitable sense to the corresponding classical field theory, and the quantum fluctuations are governed by the equation obtained by linearizing the quantum evolution equation around the classical solution. These results hold uniformly in time and therefore apply to scattering theory. The interactions considered here are so singular as to require a change of domain in order to define the generator of the evolution of the fluctuations, but sufficiently regular so that no energy renormalization is needed.

Chemical diabetes in the adult rat as the spontaneous evolution of neonatal diabetes.

Abstract: Injection of streptozotocin in newborn rats induced a severe diabetic syndrome on day 4 after birth, with acute hyperglycaemia and glycosuria Over the next 3 weeks spontaneous recovery occurred as attested by normal basal blood glucose and plasma insulin levels Recovery was, however, incomplete in the adult since a definite impairment in insulin release and glucose disposal was observed This state was characterized by the following features: 1) a 72% decrease in pancreatic insulin stores without change in pancreatic glucagon stores; 2) a slight but consistent elevation of blood glucose in the fasted and fed basal states and especially of blood glucose 90 min after an IV glucose load (2 g/kg) performed under pentobarbitone anaesthesia; 3) a considerable decline in the glucose-induced insulin release with a decrease in the maximal response Both early and late phases of insulin release were impaired, as indicated by in vivo glucose infusion experiments Basal plasma glucagon levels were normal Over a period of 12 months with a normal laboratory diet no aggravation of the chemical diabetic state was observed This new experimental syndrome is a potentially interesting model for the study of the influence of environmental factors on the development of overt diabetes

Darboux transformation and explicit solutions of the Kadomtcev-Petviaschvily equation, depending on functional parameters

Abstract: We present a natural generalization of Wahlquist's results [1] for the two-dimensional KdV equation generating a large family of explicit solutions depending on functional parameters. This family may be fibered into parts invariant with respect to Darboux transformation and corresponding to different choices of the starting solution.

Healthy and atretic human follicles in the preovulatory phase: differences in evolution of follicular morphology and steroid content of follicular fluid.

Abstract: A comparative study was performed on large follicles in the human ovary obtained during the preovulatory period. Size and type of follicle (normal or atretic) and morphology of the granulosa cells were correlated for each follicle with enzymatic activity and steroid content. The true preovulatory follicle was characterized by a pycnotic index which never exceeded 2.0/ml, whereas this index was significantly higher (5–10/ml) in early atretic follicles. For the healthy preovulatory follicle, it was possible to establish a precise chronological sequence of events preceding ovulation. The preovulatory period from day −5 before LH peak (day 0) to ovulation was divided into three discrete phases. In phase I (from the beginning of the estrogen surge to the estrogen peak in plasma), the preovulatory follicle initially contained 4.3 ± 1.6 pmol/μl (mean ± SE; 6 follicles) estradiol, increasing to 9.3 ± 1.1 pmol/μl (mean ± SE; 5 follicles). Progesterone content was 1.6 ± 1.3 pmol/μl (mean ± SE; 11 follicles...

About the stability of the inverse problem in 1-D wave equations—application to the interpretation of seismic profiles

Abstract: This paper is devoted to the study of the following inverse problem: Given the 1-D wave equation: $$\begin{gathered} \rho (z)\frac{{\partial ^2 y}}{{\partial t^2 }} - \frac{\partial }{{\partial z}}\left( {\mu (z)\frac{{\partial y}}{{\partial z}}} \right) = 0 z > 0,t > 0 \hfill \\ + boundary excitation at z = 0 + zero initial conditons \hfill \\ \end{gathered} $$ (1) how to determine the parameter functions (ρ(z),μ(z)) from the only boundary measurementY(t) ofy(z, t)/z=0.

Enzyme collagen membrane for electrochemical determination of glucose

Abstract: A new trace glucose analyzer has been designed using electrochemical sensors. The differential device includes (a) a glucose sensor consisting of a modified gas electrode in which ihe pH detector was replaced by a platinum disk and the porous film by a collagen membrane on which beta-D-glucose oxidase has been covalently bound after an acyl-azide activation process; (b) a compensating electrode mounted with a nonenzymatic collagen membrane. After injection of a glucose containing sample into the reaction vessel, where the probes are immersed, an anodic current is detected at the enzyme working electrode. Current outputs of both electrodes are subtracted and twice differentiated; a steady state is reached and the stationary and dynamic responses are recorded. Both responses are proportional to glucose concentration in the 0.1 µM-2 mM range, and the reproducibility was found to be better than 2% using these conditions. The extreme sensitivity exhibited by our system, i.e., 10 nM, is better than previously reported data by 3 orders of magnitude, and is very favorable for trace glucose assays in food and biological samples.

Relevance of Afar seismicity and volcanism to the mechanics of accreting plate boundaries

Abstract: The seismicity, the horizontal and vertical ground displacements, and the geometry of active faults and fissures during the seismic and volcanic events of November 1978 in Southern Afar are consistent with an accentuation of the pre-existing topography of the Ghoubbet–Asal rift. The zone of sizeable permanent deformation is restricted to several hundred square kilometres. Elastic rebound models seem to explain the observations. The events occurred in the vicinity of the suggested location of the tip of a lithospheric crack which may have been responsible for the progressive opening of the western Gulf of Aden.

An Introduction to Forking

Abstract: The notion of forking has been introduced by Shelah, and a full treatment of it will appear in his book on stability [S1]. The principal aim of this paper is to show that it is an easy and natural notion. Consider some well-known examples of ℵ 0 -stable theories: vector spaces over Q , algebraically closed fields, differentially closed fields of characteristic 0; in each of these cases, we have a natural notion of independence: linear, algebraic and differential independence respectively. Forking gives a generalization of these notions. More precisely, if are subsets of some model and c a point of this model, the fact that the type of c over does not fork over means that there are no more relations of dependence between c and than there already existed between c and . In the case of the vector spaces, this means that c is in the space generated by only if it is already in the space generated by . In the case of differentially closed fields, this means that the minimal differential equations of c with coefficient respectively in and have the same order. Of course, these notions of dependence are essential for the study of the above mentioned structures. Forking is no less important for stable theories. A glance at Shelah's book will convince the reader that this is the case. What we have to do is the following. Assuming T stable and given and p a type on , we want to distinguish among the extensions of p to some of them that we shall call the nonforking extensions of p .

Darboux transformation and the explicit solutions of differential-difference and difference-difference evolution equations I

Abstract: Explicit formulae involving determinants are obtained for the solutions of a class of linear differential-difference and difference-difference evolution equations. The corresponding non-linear problems generated by the conditions of compatibility of those linear equations (the discrete analogues of the Zakharov-Schabat equations) will be discussed in a forthcoming paper. The general idea of this paper is in close analogy with the approach used in the previous works of the author [1, 2] based on the property of the Darboux invariance of the associated linear problem. Surprisingly, for the difference equations, most of the formulae and their derivation are even simpler than the continuous case considered in [1, 2] (see also the works [3–5].