Showing papers by "Centre national de la recherche scientifique published in 1976"

A dual algorithm for the solution of nonlinear variational problems via finite element approximation

Abstract: For variational problems of the form Inf v∈ V {f(Av)+g(v)} , we propose a dual method which decouples the difficulties relative to the functionals f and g from the possible ill-conditioning effects of the linear operator A. The approach is based on the use of an Augmented Lagrangian functional and leads to an efficient and simply implementable algorithm. We study also the finite element approximation of such problems, compatible with the use of our algorithm. The method is finally applied to solve several problems of continuum mechanics.

Strong MHD helical turbulence and the nonlinear dynamo effect

Abstract: To understand the turbulent generation of large-scale magnetic fields and to advance beyond purely kinematic approaches to the dynamo effect like that introduced by Steenbeck, Krause & Radler (1966)’ a new nonlinear theory is developed for three-dimensional, homogeneous, isotropic, incompressible MHD turbulence with helicity, i.e. not statistically invariant under plane reflexions. For this, techniques introduced for ordinary turbulence in recent years by Kraichnan (1971~~)’ Orszag (1970, 1976) and others are generalized to MHD; in particular we make use of the eddy-damped quasi-normal Markovian approximation. The resulting closed equations for the evolution of the kinetic and magnetic energy and helicity spectra are studied both theoretically and numerically in situations with high Reynolds number and unit magnetic Prandtl number. Interactions between widely separated scales are much more important than for non-magnetic turbulence. Large-scale magnetic energy brings to equipartition small-scale kinetic and magnetic excitation (energy or helicity) by the ‘AlfvBn effect ’; the small-scale ‘residual’ helicity, which is the difference between a purely kinetic and a purely magnetic helical term, induces growth of largescale magnetic energy and helicity by the ‘helicity effect’. In the absence of helicity an inertial range occurs with a cascade of energy to small scales; to lowest order it is a - power law with equipartition of kinetic and magnetic energy spectra as in Kraichnan (1965) but there are - 2 corrections (and possibly higher ones) leading to a slight excess of magnetic energy. When kinetic energy is continuously injected, an initial seed of magnetic field willgrow to approximate equipartition, at least in the small scales. If in addition kinetic helicity is injected, an inverse cascade of magnetic helicity is obtained leading to the appearance of magnetic energy and helicity in ever-increasing scales (in fact, limited by the size of the system). This inverse cascade, predicted by Frisch et aZ. (1975), results from a competition between the helicity and Alfvh effects and yields an inertial range with approximately - 1 and - 2 power laws for magnetic energy and helicity. When kinetic helicity is injected at the scale Zinj and the rate k (per unit mass), the time of build-up of magnetic energy with scale L 9 Zinl is t % L( prp;nj)-k 21 FLM 77

Observation of Near-Infrared Dicke Superradiance on Cascading Transitions in Atomic Sodium

Abstract: We report the observation of near-infrared Dicke superradiant pulses. The active medium (atomic Na vapor) is optically pumped in the $5{S}_{\frac{1}{2}}$ state and superradiates on transitions cascading down from this level at 3.41, 2.21, and 9.10 \ensuremath{\mu}m. The superradiant character of the emission is checked by studying variations of pulse heights and delays versus initial population inversion density.

Plio—Pleistocene hominid discoveries in Hadar, Ethiopia

Abstract: The International Afar Research Expedition has now recovered remains of twelve hominid individuals from geological deposits estimated to be ∼ 3.0 Myr in Hadar, Ethiopia. A partial skeleton represents the most complete hominid known from this period. The collection suggests that Homo and Australopithecus coexisted as early as 3.0 Myr ago.

Fuzzy sets for man-machine interaction

Abstract: A new type of experiment is'proposed to better understand the fuzzy behaviour of a human operator in a man-machine system. The published applications of fuzzy set theory to the control of a simple steam engine are used as a convenient example to illustrate how some of the current applications of fuzzy set theory may be modified to carry out this type of experiment. The rationale for this proposal is developed by reviewing studies of the classification of human height and applications of fuzzy set theory to handwritten character recognition and control system design. Based on this brief review, both the results to be expected from such an experiment and how they might be analyzed are discussed. A key result is that such experiments ought to provide a much better understanding of the operator's fuzzy algorithm for adapting his experience to the development of the fuzzy algorithm for the new task.

Analytic continuation of the holomorphic discrete series of a semi-simple Lie group

Abstract: O. Introduction In this paper, we are mainly interested in the construction of certain Hilbert spaces of holomorphic functions on an irreducible hermitian symmatric space D = G/K on which G acts by a natural unitary representation. Our construction will produce some new irreducible representations of the simple group G. In this introduction we shall indicate the nature of our methods and results, leaving the full statements to the text. We shall be looking at the unbounded realization of G/K, as a Siegel domain D = D(~2, Q) of type II; however our methods are here more easily explained for tube domains. Thus, in this introduction, we shall consider G/K as a tube domain D =R~§ c C ~, where ~2 is a homogeneous irreducible self-dual convex cone in R ~. We reiterate that our results appear, in the text, for the general case. Let G(~2)= {g E GL(R~), g(~)= ~}. Let G(D) be the connected component of the group of holomorphie transformations of D and ~(D) the universal covering of G(D). There is a natural unitary irreducible representation of G(D) on the I-Iilbert space of holomorphic functions on D which are square integrable, i.e., the Bergman space

Recent Progress in the Theory of Atomic Isotope Shift

Abstract: Publisher Summary This chapter discusses the recent developments in the theory of atomic isotope shift. The understanding of atomic isotope shifts relies partly on the knowledge of nuclear structure. Conversely, it can provide some information of the structure of nuclei. The phenomenological analyses of isotope shifts are similar to those of hyperfine structures in that they consist of two steps. First, through the parametric study of the level energies, the angular wavefunctions of the levels in intermediate coupling are determined, with possible allowance for configuration mixing; using those wavefunctions, the isotope shift of each level can be written as a numerical expansion in terms of isotope-shift formal parameters. Second, through least-squares fitting procedure, the values of the isotope shift parameters are adjusted so that experimental shift values can be reproduced in the most accurate way. Moreover, the isotope shift of an optical transition is the sum of two terms: the mass effect and the field effect. If only one isotope pair is available, the experiment only yields this sum but not the respective contributions of the two effects. The situation is then much less favorable than for hyperfine structure, because, in the latter case, the Casimir formula allows a separation of the magnetic-dipole and electric-quadrupole contributions.

Conformation of Met5-enkephalin determined by high field PMR spectroscopy

Abstract: THE discovery by Hughes et al.1 that peptides (the enkephalins) could be the endogenous agonists of opiates in brain represents a challenge to medical chemistry both in its fundamental aspects and for the possible development of new therapeutic approaches. To understand how non-peptidic substances belonging to various chemical classes can mimic the action of the pentapeptide enkephalins it is first necessary to determine the spatial arrangement of the latter. We have thus synthesised large quantities of Met5-enkephalin (H–Tyr–Gly–Gly–Phe–Met–OH) and determined its preferential conformation in solution using high field proton magnetic resonance (PMR) spectroscopy at variable temperatures, coupling constants in relation with Karplus–Bystrov curves2 and conformational energy steric maps3.

Covariant Newtonian limit of Lorentz space-times

Abstract: The formulation of this limit given by Dautcourt [1] is slightly improved using the notions of Galilei manifold and Newtonian connection. It is then shown under what conditions the conservation equations ▽μ μα = 0 for an arbitrary relativistic continuum have the correct (also covariantly formulated) Newtonian limit. For electromagnetism one obtains a curved space generalization of the electric or magnetic Galileian theory of LeBellac and Levy-Leblond [4] depending on whether the contravariant or the covariant Maxwell tensor is required to have a regular Galileian limit.

Energy levels of neutral atomic uranium (Ui)

Abstract: High-resolution grating and Fourier transform spectroscopy measurements, using hollow-cathode and electrodeless discharge lamp sources, have resulted in a list of 92000 lines of Ui and Uii. The wave-number accuracy is about 0.003 cm−1. With this list and new Zeeman structure, isotope-shift, and 233U hyperfine-structure spectrograms, we have found 500 new Ui levels. We now know 1240 even levels between 7020 and 42000 cm−1 and 360 odd levels up to 38000 cm−1. All levels expected to lie below 10000 cm−1 have been found. Levels of five odd configurations (f3ds2, f3d2s, f4sp, f3ds8s, f4dp) and seven even configurations (f4s2, f2d2s2, f3s2p, f3dsp, f4ds, f3d2p, f3ds8p) are now known.

Anisotropy of defect creation in electron-irradiated iron crystals

Abstract: Single crystals of \ensuremath{\alpha}-iron were irradiated perpendicularly to the (100), (110), and (111) planes with electrons in the range 0.35-1.7 MeV and their electrical resistivity change rates were measured. A geometrical model of the threshold-energy surface for atomic displacement in a bcc lattice produces a fit to the experimental data leading to the following values for the threshold energies in the principal crystal directions: ${T}_{d}^{〈100〉}=17\ifmmode\pm\else\textpm\fi{}1$ eV, ${T}_{d}^{〈111〉}=20\ifmmode\pm\else\textpm\fi{}1.5$ eV, and ${T}_{d}^{〈110〉}\ensuremath{\gtrsim}30$ eV. The specific resistivity of a Frenkel pair is deduced to $\ensuremath{\rho}_{F}^{\mathrm{Fe}}=(30\ifmmode\pm\else\textpm\fi{}5)$ \ensuremath{\mu}\ensuremath{\Omega}cm/at.%. From the obtained ${T}_{d}'\mathrm{s}$ we derived an interatomic potential of the Born-Mayer type, valid in the range $1.2\ensuremath{\le}r\ensuremath{\le}2.5$ \AA{}. We propose as a good choice: $V(r)=8900{e}^{\ensuremath{-}4.5r}$ eV. The recovery due to isochronal annealing during stage I, after irradiation at different electron energies, was measured and related to specific recovery mechanisms. Thus, the first important substage, ${I}_{B}$ (\ensuremath{\sim} 66 K), is due to the recovery of close Frenkel pairs created in the $〈100〉$ direction, while a comparison of calculated cross sections suggests that ${I}_{C}$ (\ensuremath{\sim} 87 K) possibly stems from $〈111〉$ close pairs. Substage ${I}_{D}$ (90-110 K) is complex; its first part, below 100 K, originates mostly from defects produced in the $〈100〉$ direction and the second part, above 100 K, together with ${I}_{E}$, principally originates from defects produced in the $〈111〉$ direction.

Biological role of alcohol dehydrogenase in the tolerance of Drosophila melanogaster to aliphatic alcohols: Utilization of an ADH-null mutant

Abstract: The toxicity of the first eight primary alcohols and of four secondary alcohols was compared in a wild-type strain (having active ADH) and an ADH-negative mutant. Differences between lc 50 measured in the two strains allowed an evaluation of the biological activity of the enzyme. In vitro, ADH is mainly active on secondary alcohols, while in vivo its main role is the detoxification and metabolism of ethanol. These observations suggest that originally ADH was involved in unknown metabolic pathways and that its utilization in ethanol metabolism could be a recent event.

Theoretical investigation on photoionization from Rydberg states of lithium, sodium and potassium

Abstract: Cross sections for s, p and d have been computed in the framework of a single-electron model (non-relativistic) by using a parametric central potential. The evolution of the non-hydrogenic behaviour of photoionization cross sections near threshold is studied along Rydberg series; non-hydrogenic characters are particularly large for all the ns series and for the np series of K. The validity of the method is discussed and it appears that sigma sigma np and sigma nd values are more reliable than sigma ns. The results are compared to experimental data and other theoretical results, mainly provided by the quantum-defect theory. The agreement between the various results is generally very good for sigma np and sigma nd; the agreement is satisfactory even for the most unfavourable cases provided by sigma ns of Na and K.

Geological and palaeontological background of Hadar hominid site, Afar, Ethiopia

Abstract: The hominid-bearing Plio–Pleistocene sequence of the west central Afar sedimentary basin in Hadar contains 120–140 m of fossiliferous lacustrine and lake margin sediments. The Hadar sequence is described and divided into four members. The mammalian fauna indicates an age of ∼ 3.0 Myr which is confirmed under the Hadar formation by K–Ar determinations on a basalt.

Programs of Gene Action and Progressive Evolution

Abstract: Structural genes and their products have captured much of the attention of a number of contributors to this volume on molecular anthropology. It seems to me that, in addition, we must not fail to discuss the role of gene regulation and of genetic regulatory networks in evolution, in particular with respect to conditions that paved the way to man.

Subtropical convergence fluctuations and quaternary climates in the middle latitudes of the Indian ocean.

Abstract: Oxygen isotopic and microfaunal analyses and shell size variations of Orbulina universa in two Indian Ocean cores indicate that the position of the Subtropical Convergence has fluctuated between a northern limit north of 31°S during glacial stages and its present, maximum southern limit. The northward displacement of the Subtropical Convergence to a position off Durban, South Africa, reflects the general weakness of the Agulhas Current during glacial stages and parts of interglacial stages, representing about 65 percent of the past 540,000 years.