Showing papers by "Pierre-and-Marie-Curie University published in 1980"

Parametrization of the Paris N-N potential

Abstract: In view of practical nuclear structure calculations the Paris $N\ensuremath{-}N$ potential is parametrized in a simple analytical form. This parametrization consists of a regularized discrete superposition of Yukawa-type terms. Results for phase shifts and deuteron parameters are presented as well as nuclear matter binding energy obtained with this potential.NUCLEAR REACTIONS Nucleon-nucleon interaction, parametrization of the Paris $N\ensuremath{-}N$ potential. 0 to 330 MeV $N\ensuremath{-}N$ phase shifts.

A note on limiting cases of sobolev embeddings and convolution inequalities

Abstract: (1980). A note on limiting cases of sobolev embeddings and convolution inequalities. Communications in Partial Differential Equations: Vol. 5, No. 7, pp. 773-789.

The method of virtual power in continuum mechanics: Application to coupled fields

Abstract: Using as main tools the principle of virtual power — in the form recently favored by French mechanicians - and continuum thermodynamics, this work of a synthetic nature develops in a “rational” manner and from a unified viewpoint the fully dynamical (albeit not relativistic) theory of electromagnetic continua. The resulting equations are those to be used by theoretical mechanicians, applied physicists and electronic engineers alike to study coupled electro-magneto-mechanical effects in electronic components. A fairly long account of the formal structure underlying the principle of virtual power is first given. Following then a simple purely mechanical application, a full illustration is given of the application of this principle to the theory of coupled fields in deformable continua, all states of magnetism and dielectricity being representable if one makes the appropriate adjustments. Other illustrations of the method concern the case of complicated schemes of elastic dielectrics, liquid crystals and ferrofluids. To end with a comparison with other energy approaches used nowadays in continuum physics is given.

A justification of the von Kármán equations

Abstract: The method of asymptotic expansions, with the thickness as the parameter, is applied to the nonlinear, three-dimensional, equations for the equilibrium of a special class of elastic plates under suitable loads. It is shown that the leading term of the expansion is the solution of a system of equations equivalent to those of von Karman. The existence of solutions of this system is established. It is also shown that the displacement and stress corresponding to the leading term of the expansion have the specific form generally assumed in the usual derivations of the von Karman equations; in particular, the displacement field is of Kirchhoff-Love type. This approach also clarifies the nature of admissible boundary conditions for both the von Karman equations and the three-dimensional model from which these equations are obtained. A careful discussion of the limitations of this approach is given in the conclusion.

Sprouting and regression of the nerve at the frog neuromuscular junction in normal conditions and after prolonged paralysis with curare.

Abstract: A light microscopical, histochemical and electron microscopical investigation of the frog neuromuscular junction has been performed on muscles from animals in different functional states of activity. The combined staining of axon terminals and cholinesterase (ChE) allows a precise description of the nerve terminal arborization and its synaptic contacts. Most terminal arborizations form long continuous contacts with the muscle cell. Distinguishable from these are nerve branches (usually of small diameter) or distal endings of branches with one or several small and isolated contacts. It is assumed that these are sprouts with newly-formed synaptic sites. Other sprouts end without apparent synaptic contact. At the ultrastructural level, nerve sprouts growing into empty, well-differentiated synaptic gutters or inducing the formation of new synaptic sites were observed. In other sites, ChE is apparently located at postsynaptic gutters with no nerve present. Similarly, in the electron microscope, well-differentiated synaptic gutters lacking any nerve or Schwann cell elements were observed. In addition, synaptic gutters only partially occupied by the nerve were frequently seen. These features have been interpreted as signs of regression of the nerve terminals. Nerve regression and sprouting were found in animals chronically paralysed with curare over several weeks as well as in untreated frogs (winter and summer frogs, laboratory frogs, fed and unfed). When quantitatively evaluating the occurrence of presumed features of nerve sprouting and nerve regression, differences were found between different experimental groups. From this it is concluded that, in addition to developmental changes, the degree of nerve sprouting and regression is controlled by external factors such as muscle activity and seasonal variations. Signs of sprouting and nerve regression can be simultaneously present in a single synapse. It appears that the frog neuromuscular synapse is not a static structure, but is in a state of permanent remodelling.

Long range control circuits within mitochondria and between nucleus and mitochondria. I. Methodology and phenomenology of suppressors.

Abstract: To uncover the functional circuitry both within the mitochondrial genome and between the mitochondrial and the nuclear genome, we have developed a general method for selecting and characterizing genetically suppressor mutations that restore the respiratory capacity of mit- mitochondrial mutants. Several hundreds of pseudo-wild type revertants due to a second unlinked mutation which suppresses a target mit- mutation were isolated. The suppressor mutations were found located either in the nuclear (abbreviated NAM for 'nuclear accommodation of mitochondria') or in the mitochondrial genome (abbreviated MIM for 'mitochondrial-mitochondrial interaction'). The specificity of action of various suppressors upon some 250 different mit- mutations located in several genes was tested. According to this specificity of action, suppressors were subdivided into two major classes: allele specific or gene specific suppressors. Because the cob-box mitochondrial gene has a mosaic organization, we were able to find a novel third class of extragenic suppressors specific for mit- mutations within the introns of this gene. Four examples of suppressors showing various specificities of action illustrate our approach. (1) a nuclear gene controlling specific alleles of different mitochondrial genes; (2) a nuclear gene controlling selectively one intron of a split mitochondrial gene; (3) a mitochondrial gene controlling specific alleles of different mitochondrial genes; (4) a region in one complex mitochondrial gene which controls selectively one intron of another split mitochondrial gene. Different mechanisms of suppression are discussed stressing the alleviation of splicing deficiencies of intron mutations.

Multiple innervation of cerebellar purkinje cells by climbing fibres in staggerer mutant mouse.

Abstract: Multiple innervation of cerebellar Purkinje cells by climbing fibres in staggerer mutant mouse

187 Re– 187 Os systematics in meteorites: early chronology of the Solar System and age of the Galaxy

Abstract: Using isotope dilution mass spectrometry, we have determined the 187Re/186Os, 187Os/186Os ratios of five iron meteorites of various groups, and one ordinary chondrite. These results show that iron meteorites and ordinary chondrites were formed within a short time. We determine the 187Re decay constant as 1.62 ± 0.0310−11 yr−1 and the 187Os/186Os isotopic ratio at the origin of the Solar System as 0.805 ± 0.011. These values are used to compute limits for the age of the Galaxy between 13,300 and 22,400 Myr.

Periodic Oscillations of the Frequency-Dependent Photoelectric Cross Sections of Surface States: Theory and Experiment

Abstract: High-resolution angle-resolved photoemission spectroscopy is employed to study surface states on the Cu(111) surface, with use of synchrotron radiation in the energy range $18l~\ensuremath{\hbar}\ensuremath{\omega}l~120$ eV. The results reveal a novel periodic oscillatory behavior in surface-state emission intensity which leads to identification of additional new surface states. A spectral decomposition theory is proposed to explain the physical origin of the oscillations. It describes the measured intensity profiles and predicts that the oscillations are universal for all surface states.

The effect of a thin inclusion of high rigidity in an elastic body

Abstract: We study an elastic body comprising an inclusion whose thickness is 2ϵ and for which Lame's constants are λϵ and μ. We are interested in the limit behaviour of the inclusion, when ϵ 0 and μϵ ϵ; that is when the inclusion becomes thiner and more rigid. Different behaviours are possible, according to the rate at which μϵ converges to infinity; the limit inclusion may “vanish” if it is not very rigid, but also it may be entirely solid.

Leg 67: The Deep Sea Drilling Project Mid-America Trench transect off Guatemala

Abstract: Drill cores from a transect of the Mid-America Trench off Guatemala were obtained at three sites on the oceanic Cocos plate, and at four sites on the continental Caribbean plate. An ocean sub-bottom seismometer was successfully emplaced in the deepest hole in the trench landward slope where it was left to record data after departure of the drill ship. Drilling on the Cocos plate recovered a basal chalk sequence deposited during early and mid-Miocene time, a short interval of abyssal red clay, and an upper sequence of late Miocene and younger sediment deposited within an area influenced by a terrigenous source. In the trench, a mud and sand fill less than 400,000 yr old overlies the oceanic sequence. The entire section shows no evidence of compressive deformation even at holes drilled against the trench9s landward slope. In contrast, the section cored on the trench9s landward slope 3 km from the trench axis is affected by tectonism. The section contains a Cretaceous to Pliocene claystone sequence, broken by hiatuses but in a normal stratigraphic succession that is capped by Pliocene to Quaternary hemipelagic slope deposits. Seismic records show that the section overlies probable igneous oceanic crust from which it is separated by a few hundred metres. That thickness of undrilled section is insufficient to accommodate the potential offscraped volume of oceanic sediment carried into the trench during Neogene plate convergence. At the estimated 10 cm/yr rate of convergence, much of the oceanic sediment must have been subducted rather than tectonically accreted to the Guatemalan margin. Current models for convergent margin tectonics do not satisfactorily explain the surprising occurrence of Cretaceous to Miocene mudstone at the base of this trench slope. The recovery of gas hydrates prevented drilling to some landward-dipping reflections presumed to be imbricate thrust slices at two sites near the middle of the trench landward slope.

Molecular Evolution of Biologically Active Polypeptides

Abstract: Any biological function is at least bimolecular and involves primarily a specific recognition between the shapes (conformations) of the reacting molecules. The selective pressure of evolution therefore acted on the interaction so that coordinated changes probably occurred in two lines of molecules. Because the structure of the specific partner (receptor, macromolecular substrate, naturally occurring inhibitor, antigen, etc.) is rarely known, evolutionary speculations are often arbitrarily limited to the active polypeptide. During the life of a polypeptide chain, its conformation can be modified by ligands, by `conformers' or by morphogenic cleavages. Inactive preprohormones and prohormones (e.g. preproparathyrin, proopiocortin) are successively split by specific proteolytic enzymes. Several modulator- or activator-binding sites can be distinguished in addition to the active site, so that the chain can be regarded as the result of a multiple evolution. The conformation of an active polypeptide chain on the one hand displays a variable degree of flexibility, and on the other may include a hierarchy of organized substructures: secondary ($\alpha $-helix, $\beta $-pleated sheet, $\beta $-bend), super-secondary and domain. The amino acid sequence appears to program largely the organized substructures and the potential adaptability. However, general architectural rules on which selective pressure could primarily act remain unknown. Duplication seems to be a fundamental mechanism for increasing both the size and the number of polypeptide chains. Duplication without fusion may lead to parallel lines of peptides which differentiate functionally by subsequent mutations (e.g. neurohypophysical hormones and neurophysins). Duplication with fusion may give single-chain proteins with internal homology between two or several domains (e.g. somatotrophin). Repetitive duplication could involve fusion in the first steps and not in the last step so that several lines of homologous proteins, each with internal homology, could arise (e.g. somatotrophin, prolactin, choriomammotrophin). The assembly of polypeptide chains, whether covalent or not, is likely to represent a higher level of evolution. Each chain or subunit may have a distinct function, as in dimeric hormones (e.g. lutrophin, follitrophin, thyrotrophin, choriogonadotrophin), or the association may determine new cooperative properties (allostery). The integration of molecular evolution at the organelle, cellular and organismal levels raises the problem of the evolution of regulatory mechanisms.