Showing papers by "Centre national de la recherche scientifique published in 1985"

Weak localization and coherent backscattering of photons in disordered media.

Abstract: On trouve que l'intensite diffusee est augmentee jusqu'a 75% a l'interieur d'un cone etroit centre sur la direction de retrodiffusion

Early steps of lymphocyte activation bypassed by synergy between calcium ionophores and phorbol ester

Abstract: Although it has been proposed that the activation of T lymphocytes is mediated by an early rise in cytosolic calcium concentration, it has not been possible to mimic antigen- or mitogen-induced mouse lymphocyte activation by calcium ionophores that bypass receptor-mediated processes. There is now evidence from other systems that the rise in cytosolic calcium which follows receptor triggering is preceded by the breakdown of phosphatidylinositol bisphosphate into 1,2-diacylglycerol and inositol trisphosphate. The latter is known to cause release of calcium from intracellular stores. The cellular target for the former is now widely accepted to be protein kinase C. Therefore, ligand-induced cellular response follows a rise in cytosolic calcium concentration and protein kinase C activation. Here we confirm that the calcium ionophores A23187 and ionomycin do not activate mouse T lymphocytes. However, either one in combination with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA), which is structurally related to 1,2-diacylglycerol, induces in lymphoid cell populations the expression of receptors for interleukin-2 (IL-2), the secretion of IL-2 and cell proliferation as measured by 3H-thymidine uptake. The growth-promoting effect of IL-2 on an exogenous IL-2-dependent clone could not be substituted for by ionomycin either alone or with TPA. Thus, the combination of calcium ionophores and TPA bypasses the requirement for antigen- or lectin-induced signal at the onset of lymphocyte activation.

Position referencing and consistent world modeling for mobile robots

Abstract: In order to understand its environment, a mobile robot should be able to model consistently this environment, and to locate itself correctly. One major difficulty to be solved is the inaccuracies introduced by the sensors. The approach proposed in this paper to cope with this problem relies on 1) defining general principles to deal with uncertainties : the use of a multisensory system, favo ring of the data collected by the more accurate sensor in a given situation, averaging of different but consistent measurements of the same entity weighted with their associated uncertainties, and 2) a methodology enabling a mobile robot to define its own reference landmarks while exploring its environment. These ideas are presented together with an example of their application on the mobile robot HILARE.

Fruit characters as a basis of fruit choice and seed dispersal in a tropical forest vertebrate community.

Abstract: Interactions between a large community of vertebrate frugivore-granivores (including 7 species of large canopy birds, 19 species of rodents, 7 species of ruminants, and 6 species of monkeys), and 122 fruit species they consume, were studied for a year in a tropical rainforest in Gabon. The results show how morphological characters of fruits are involved in the choice and partitioning of the available fruit spectrum among consumer taxa. Despite an outstanding lack of specificity between fruit and consumer species, consideration of simple morphological traits of fruits reveals broad character syndromes associated with different consumer taxa. Competition between distantly related taxa that feed at the same height is far more important than has been previously supposed. The results also suggest how fruit characters could have evolved under consumer pressure as a result of consumer roles as dispersers or seed predators. Our analyses of dispersal syndromes show that fruit species partitioning occurs more between mammal taxa than between mammals and birds. There is thus a bird-monkey syndrome and a ruminant-rodent-elephant syndrome. The bird-monkey syndrome includes fruit species on which there is no pre-dispersal seed predation. These fruits (berries and drupes) are brightly colored, have a succulent pulp or arillate seeds, and no protective seed cover. The ruminant-rodent-elephant syndrome includes species for which there is pre-dispersal predation. These fruits (all drupes) are large, dull-colored, and have a dry fibrous flesh and well-protected seeds.

3d x-ray-absorption lines and the 3d94fn+1 multiplets of the lanthanides.

Abstract: We have measured and calculated the 3d (${M}_{4}$,5) absorption spectra for all the rare-earth metals, as well as the full 3${d}^{9}$4${f}^{n+1}$ multiplets for the early and late rare earths. The quality of agreement between theory and experiment is excellent, except for Sm. In x-ray-absorption spectroscopy (XAS), only dipole selected lines are seen but all multiplet effects can be observed in x-ray photoemission spectroscopy. The line shapes and 3d-4f interactions are discussed. Our results provide an improved basis for use of the 3d XAS spectra for studies of ``mixed-valence'' systems.

A 150,000-year climatic record from Antarctic ice

Abstract: During much of the Quaternary, the Earth's climate has undergone drastic changes most notably successive glacial and interglacial episodes. The past 150 kyr includes such a climatic cycle: the last interglacial, the last glacial and the present holocene interglacial. A new climatic–time series for this period has been obtained using δ18 O data from an Antarctic ice core.

The two-dimensional resonance of sediment-filled valleys

Abstract: This paper presents a numerical study of the response of relatively embanked sediment-filled valleys to incident plane SH , SV , and P waves, in the two-dimensional case. The Aki-Larner technique used here is shown to be reliable even for steep interface slopes. Numerical results show the existence and the importance in such valleys of specific two-dimensional resonance patterns, which may be classified in three categories: the antiplane shear modes, corresponding to SH motion; the in-plane shear modes ( SV ); and the in-plane bulk modes ( P ). Each of them is characterized by the consistency of the peak frequencies, and the in-phase motion (modulo 180°) across the whole valley. They induce a very large amplification, even in the case of significant damping (up to 4 times the corresponding one-dimensional prediction), a very long duration of motion, and large differential motion. The characteristics of the fundamental modes are in good qualitative agreement with the relevant experimental observations. The existence of this two-dimensional resonance is controlled by the shape ratio (thickness to half-width ratio) and the velocity contrast: a quantitative relationship is proposed in the SH case. The frequency of these resonance modes, for each pattern, is shown to depend only on two parameters: the one-dimensional resonance frequency at the valley center and the shape ratio. A simple model of a soft rectangular inclusion is shown to provide satisfactory quantitative formulas to estimate the fundamental resonance frequencies of any valley. As to the amplitude of this two-dimensional resonance, the general trends of its dependence on the different valley parameters (shape ratio, velocity contrast, Poisson ratio, damping) and on the incident wave field characteristics (wave type, incidence angle) are indicated. An important result, however, for earthquake engineering purposes is that both the two-dimensional resonant frequencies and amplification values differ a lot from their “classical” one-dimensional estimates.

The internal structure of phonological elements: a theory of charm and government *

Abstract: In this article we have two primary objectives: (1) to elaborate in some detail a theory of phonological representations embedded within a parametric framework, and (2) to apply this theory to a particular vowel system which displays some rather interesting properties. This work is a continuation of a collaboration on a programme of research on phonological theory begun in 1982 (cf. Vergnaud 1982; Kaye & Vergnaud 1984; Kaye et al. 1984, 1985, in preparation).This programme incorporates the view that phonology is to be regarded as a system of universal principles defining the class of human phonological systems. These principles underdetermine given phonologies in certain specific areas. A complete phonological system consists, then, of these principles along with sets of parameter values. Taken together, the principles and language-specific parameter settings give a complete characterisation of the phonological system under study. In this model, a phonological system contains no rule component. The observed phonological phenomena result from a combination of the general principles governing phonological representations and structures and the parameter values in operation in the particular language. We view this line of research as a continuation of the development of a theory of markedness (cf. Chomsky & Halle 1968 (SPE); Kean 1975, 1979). At the moment of writing, this view of phonology remains a long-term objective of our research programme. However, an increasing number of phonological processes which were formerly considered to be manifestations of rules are now successfully derivable from the principles of Universal Phonology (UP) (cf. Kaye & Lowenstamm 1984, to appear).

Families of finite sets in which no set is covered by the union ofr others

Abstract: Letfr(n, k) denote the maximum number ofk-subsets of ann-set satisfying the condition in the title. It is proved that $$f_1 (n,r(t - 1) + 1 + d)\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{ \leqslant } (_{ t}^{n - d} )/(_{ t}^{k - d} )$$ wheneverd=0, 1 ord≦r/2t2 with equality holding iff there exists a Steiner systemS(t, r(t−1)+1,n−d). The determination offr(n, 2r) led us to a new generalization of BIBD (Definition 2.4). Exponential lower and upper bounds are obtained for the case if we do not put size restrictions on the members of the family.

Dressed-atom approach to atomic motion in laser light: the dipole force revisited

Abstract: We show that the dressed-atom approach provides a quantitative understanding of the main features of radiative dipole forces (mean value, fluctuations, velocity dependence) in the high-intensity limit where perturbative treatments are no longer valid. In an inhomogeneous laser beam, the energies of the dressed states vary in space, and this gives rise to dressed-state-dependent forces. Spontaneous transitions between dressed states lead to a multivalued instantaneous force fluctuating around a mean value. The velocity dependence of the mean force is related to the modification, induced by the atomic motion, of the population balance between the different dressed states. The corresponding modification of the atomic energy is associated with a change of the fluorescence spectrum emitted by the atom. The particular case of atomic motion in a standing wave is investigated, and two regimes are identified in which the mean dipole force averaged over a wavelength exhibits a simple velocity dependence. The large values of this force achievable with reasonable laser powers are pointed out with view to slowing down atoms with dipole

The Improved Initialization Inversion Method: A High Resolution Physical Method for Temperature Retrievals from Satellites of the TIROS-N Series.

Abstract: The Improved lnitialization Inversion (3I) procedure is a physico-statistical algorithm for retrieving meteorological parameters from TIROS-N satellite data at a special resolution of 100 × 100 km. This procedure accounts for the physics of the phenomena involved, explicitly taking into consideration the local properties of each terrain observed, such as surface elevation, surface emissivity, percentage of water, and viewing angle. Considerable effort is put into the optimization of the initial guess solution which is retrieved from a large precomputed TOVS Initial Guess Retrieval (TIGR) data set. TIGR describes the physical and statistical properties of a large number of well-sampled atmospheric situations with which the observed situation may be compared. Retrieval of the initial guess also relies upon operational forecast of the temperature and gepotential altitude of the lowest atmospheric levels. The quality of the initial solution obtained is demonstrated by the fact that only one iteration...

Persistent Anomalies, Blocking and Variations in Atmospheric Predictability

Abstract: The fully nonlinear, equivalent-barotropic vorticity equation on the sphere, with simplified forcing, dissipation and topography, is the model used in the present consideration of low frequency variability regimes in large scale atmospheric dynamics. The solutions obtained are studied as a function of the nondimensional intensity of the forcing and dissipation. The number of modes retained in the analysis allows the multiple equilibria thus obtained, which exhibit blocked and zonal flow patterns very similar to synoptically defined zonal and blocked Northern Hemisphere midlatitude flows, to appear for realistic values of the forcing. The number of episodes of blocked or zonal flow decreases monotonically as their duration increases, in agreement with observations.

DNA probe localization at 18p113 band by in situ hybridization and identification of a small supernumerary chromosome

Abstract: Recombinant plasmid clone B74 (also named D18S3) containing a human single-copy DNA segment of 6 kilobases (kb) was localized by in situ hybridization on band p113 of chromosome 18. This probe was then used in cytogenetic diagnosis to identify precisely a small supernumerary chromosome as an isochromosome i(18p).

Mitochondrial class II introns encode proteins related to the reverse transcriptases of retroviruses.

Abstract: Organelle introns share several distinctive features that set them apart from their counterparts in nuclear-encoded pre-messenger RNAs (reviewed in ref 1): their termini do not obey the GUAG rule; the introns are 'structured' (members of the same family or 'class' can theoretically adopt very similar RNA secondary conformations and several of the postulated pairings have been confirmed by studies of splicing mutants and their revertants (see, for example, ref 4); many introns from both classes contain long open reading frames We report here that the proteins potentially encoded by four class II introns are related to several RNA-dependent polymerases of viral and transposable element origins

Critical slowing down in spin glasses and other glasses: Fulcher versus power law.

Abstract: We propose a new objective criterion potentially capable of discriminating between the different laws which aim at describing the frequency dependence of the temperature of the susceptibility maximum in spin glasses. By applying this criterion to different systems, we found that the power law (which follows from dynamic scaling theory) gives a better account of the available experimental evidence.

The DNA sequence of the gene for the secreted Bacillus subtilis enzyme levansucrase and its genetic control sites.

Abstract: We present the sequence of a 2 kb fragment of the Bacillus subtilis Marburg genome containing sacB, the structural gene of levansucrase, a secreted enzyme inducible by sucrose. The peptide sequence deduced for the secreted enzyme is very similar to that directly determined by Delfour (1981) for levansucrase of the non-Marburg strain BS5. The peptide sequence is preceded by a 29 amino acid signal peptide. Codon usage in sacB is rather different from that in the sequenced genes of other secreted enzymes in B. subtilis, especially α-amylase. Genetic evidence has shown that the sacB promotor is rather far from the beginning of sacB (200 bp or more). The 200 bp region preceding sacB shows some of the features of an attenuator. A preliminary discussion of the putative workings and roles of this attenuator-like structure is proposed. sacR c mutations, which allow constitutive expression of levansucrase, have been located within the 450 bp upstream of sacB. It is shown that sacR c and sacR + alleles control in cis the expression of the adjacent sacB gene.