Showing papers by "Pierre-and-Marie-Curie University published in 1990"

Inversion of field data in fault tectonics to obtain the regional stress—III. A new rapid direct inversion method by analytical means

Abstract: SUMMARY A new method for determining the reduced stress tensor with four degrees of freedom (the orientations of the three principal stress axes as well as the ratio of principal stress differences) using fault slip data (or focal mechanisms of earthquakes) is presented. From a computational point of view, the inversion of fault slip data is made in a direct way by purely analytical means; as a result, the determination process is extremely fast and adaptable on small microcomputers. From a physical point of view, the method aims at simultaneously (i) minimizing the angles between theoretical shear stress and actual slip vector and (ii) having relative magnitudes of shear stress large enough to induce slip despite rock cohesion and friction. Examples of application to actual fault slip data sets with good or poor variety of fault slip orientations are shown. The double significance of the basic criterion adopted results in a more realistic solution of the inverse problem than the single minimization of the shear-stria angle.

Random particle model for fracture of aggregate or fiber composites

Abstract: A particle model for brittle aggregate composite materials such as concretes, rocks, or ceramics is presented. The model is also applicable to the behavior of unidirectionally reinforced fiber composites in the transverse plane. A method of random computer generation of the particle system meeting the prescribed particle size distribution is developed. The particles are assumed to be elastic and have only axial interactions, as in a truss. The interparticle contact layers of the matrix are described by a softening stress‐strain relation corresponding to a prescribed microscopic interparticle fracture energy. Both two‐ and three‐dimensional versions of the model are easy to program, but the latter poses, at present, forbidding demands for computer time. The model is shown to simulate realistically the spread of cracking and its localization. Furthermore, the model exhibits a size effect on: (1) The nominal strength, agreeing with the previously proposed size effect law; and (2) the slope of the post‐peak l...

Spectral absorption coefficients of living phytoplankton and nonalgal biogenous matter: A comparison between the Peru upwelling areaand the Sargasso Sea

Abstract: Absorption coefficients of total particulate (biogenous) matter were determined in the mesotrophic waters of the Peruvian upwelling and the oligotrophic waters of the Sargasso Sea. A method based on spectral criteria was used to partition these coefficients into absorption by living algal cells and by nonalgal (mainly detrital) material. This method was tested by independently measuring absorption by nonalgal material for samples from the Sargasso Sea. The average Chl-specific absorption coefficients measured in the Sargasso Sea are significantly higher than in the Peruvian upwelling and also higher in the surface layer than in the deep Chl maximum layer. These systematic variations appear to be mainly due to differences in sizes and intracellular pigment concentrations ofthe cells, inducing differences in the amplitude ofthe package effect. In the open ocean, particulate biogenous matter dominates the optical variability of the water column. This suspended matter includes two types of particles present in variable proportions and having different spectral properties: living pigmented algal cells, and weakly pigmented or unpigmented particles mainly derived from phytoplankton as well as other living heterotrophs such as bacteria. These two categories will hereafter be referred to as the “algal” and “nonalgal” fractions. Unlike the absorption coefficients of the pigments extracted from natural popula

Genetic linkage studies suggest that Alzheimer's disease is not a single homogeneous disorder

Abstract: Alzheimer's disease, a fatal neurodegenerative disorder of unknown aetiology, is usually considered to be a single disorder because of the general uniformity of the disease phenotype. Two recent genetic linkage studies revealed co-segregation of familial Alzheimer disease with the D21S1/S11 and D21S16 loci on chromosome 21. But two other studies, one of predominantly multiplex kindreds with a late age-of-onset, the other of a cadre of kindreds with a unique Volga German ethnic origin, found absence of linkage at least to D21S1/S11. So far it has not been possible to discern whether these conflicting reports reflect aetiological heterogeneity, differences in methods of pedigree selection, effects of confounding variables in the analysis (for example, diagnostic errors, assortative matings), or true non-replication. To resolve this issue, we have now examined the inheritance of five polymorphic DNA markers from the proximal long arm of chromosome 21 in a large unselected series of pedigrees with familial Alzheimer's disease. Our data suggest that Alzheimer's disease is not a single entity, but rather results from genetic defects on chromosome 21 and from other genetic or nongenetic factors.

Tectonic erosion along the Japan and Peru convergent margins

Abstract: The volume of material removed by subduction erosion can be estimated quantitatively if the position of the volcanic arc, the position of the paleotrench axis, and a paleo-depth reference surface are known. Estimates based on these parameters along the Japan and Peru Trenches indicate rates of erosion comparable to well-known rates of accretion. Proposed erosional mechanisms along the plate boundary, where horsts on the lower plate abrade the upper one, appear insufficient to handle the minimum volumes of eroded material. Some mechanisms of tectonic erosion at the base of the trench slope can be observed at colliding seamounts and ridges where structures are large enough to be seismically imaged. Local tectonic erosion of the lower slope of the Japan Trench resulted when seamounts entered the subduction zone, uplifted the slope, and oversteepened it. The oversteepened slope failed, debris slumped into the trench axis, and much of it was then subducted. Where a seamount was subducted, a large re-entrant was left in the slope, which filled rapidly by local accretion of abundant sediment. Subduction of the oblique-trending Nazca Ridge off Peru produced many similar structures. Erosion is dominated by uplift and breakup of the lower slope, with subduction of the debris rather than abrasion under high-stress conditions. Another form of tectonic erosion occurs along the base of the upper plate. Its magnitude is indicated by massive subsidence along the margin; however, because of deep burial, the structure resulting from basal erosion is rarely imaged in seismic records. The volume of material eroded along the base of the upper plate exceeds that eroded from the front of the lower slope.

An operator-integration-factor splitting method for time-dependent problems: application to incompressible fluid flow

Abstract: In this paper we present a simple, general methodology for the generation of high-order operator decomposition (“splitting”) techniques for the solution of time-dependent problems arising in ordinary and partial differential equations. The new approach exploits operator integration factors to reduce multiple-operator equations to an associated series of single-operator initial-value subproblems. Two illustrations of the procedure are presented: the first, a second-order method in time applied to velocity-pressure decoupling in the incompressible Stokes problem; the second, a third-order method in time applied to convection-Stokes decoupling in the incompressible Navier-Stokes equations. Critical open questions are briefly described.

Free-energy density functional for the inhomogeneous hard-sphere fluid: Application to interfacial adsorption.

Abstract: We propose a simplified version of the free-energy density functional for the inhomogeneous hard-sphere fluid mixture recently derived by Rosenfeld [Phys. Rev. Lett. 63, 980 (1989)]. This new functional, which requires four distinct weight functions, generates a triplet-direct-correlation function for the one-component fluid, which is in good agreement with Monte Carlo simulation results. It also performs well in describing the density profile of the hard-sphere fluid in contact with hard and soft walls. Yet, it is not suitable for studying the freezing transition.

Production of hollow atoms by the excitation of highly charged ions in interaction with a metallic surface.

Abstract: The capture of many electrons by ${\mathrm{Ar}}^{17+}$ ions, at low velocity, near a metallic surface, has been studied. Multiexcited bound states with many electrons in the outermost shells (hollow atoms) have been observed. The surrounding of an ionic excited core by many outermost electrons greatly decreases the lifetimes of the states. This characteristic decrease explains the main striking features of the relaxation of the ions.

Aqueous ferrofluids based on manganese and cobalt ferrites

Abstract: Synthesis of two new aqueous ferrofluids is performed chemically according to Massart's procedure. Manganese and cobalt ferrite magnetic particles are precipitated and treated in order to obtain colloidal sols by creating a charge density on their surface. Such “ionic” ferrofluids can be prepared in an acidic (after a treatment by ferric nitrate) or in an alkaline medium at a concentration as high as 17moll−1, i.e. a volumic fraction of 0.26. This result makes these new compounds of great interest.

Estimate of organic matter turnover rate in a savanna soil by 13C natural abundance measurements.

Abstract: The medium-term dynamics of organic matter in a sandy savanna soil has been investigated at Lamto (Ivory Coast) through changes in the 13C/12C ratio induced by vegetation changes from the C4 to the C3 photosynthetic pathway. After 25 yr of protection from fire, a soil previously covered by C4 grassland vegetation had been progressively colonized by C3 woody plants. Although the total C content did not show significant changes. 52–70% of the original C4 carbon was turned over when vegetation cover was changed. Turnover of coarse organic debris (> 250 μm) was much greater (97%) than the mineralization (50%) of clay-associated fractions (< 20 μm).

Seed-dispersal of Vouacapoua americana (Caesalpiniaceae) by caviomorph rodents in French Guiana

Abstract: A possible mutualistic dispersal system between a large-seeded tree of French Guiana, Vouacapoua americana (Caesalpiniaceae), and caviomorph rodents, Myoprocta exilis and Dasyprocta leporina, is described. Mast fruiting of Vouacapoua at the beginning of the wet season coincides with scatter-hoarding seed dispersal. During the wet season, almost 100% of marked seeds on three sites were removed: nearly 70% were buried and the rest were eaten by mammals. Unburied seeds were attacked by insects and/or lost their ability to germinate. Rodents preferred ungerminated seeds, and had no interest in germinated seeds. Seeds were buried individually near natural objects such as palms, branches, logs, lianas, roots and trees. After predation by rodents, seedling distribution did not differ from seed distribution. Most seeds were transported less than 5 m from the feeding plots but some were carried as far as 22.4 m. Between 40 and 85% of dispersed seeds were retrieved during the following month by rodents and eaten. The disinterest of caviomorph rodents in germinated seeds, because of rapid exhaustion of endosperm reserves, prevents feeding from hoarded Vouacapoua during the long dry season when resources are scarce. Seedlings emerging from forgotten or abandoned cached seeds appear to increase the recruitment of Vouacapoua americana.

Quantum Limits in Interferometric Measurements

Abstract: Quantum noise limits the sensitivity of interferometric measurements. It is generally admitted that it leads to an ultimate sensitivity, the "standard quantum limit". Using a semi-classical analysis of quantum noise, we show that a judicious use of squeezed states allows one in principle to push the sensitivity beyond this limit. This general method could be applied to large-scale interferometers for gravitational wave detection.

Flow in powders: From discrete avalanches to continuous regime.

Abstract: The flow under gravity of a granular material can exhibit either intermittent avalanches or a steady regime. The transition from the discrete to the steady regime is shown experimentally to display hysteresis. Next, a relationship between the current and the slope is established and interpreted.

Magnetic Field Effects on Mass Transport

Abstract: It has been shown that the stationary limiting diffusion current on a steady electrode is proportional to {ital B}{sup 1/3}{ital C}{sup 4/3} where {ital C} is the electroactive species concentration and {ital B} the magnetic field intensity. A new impedance technique is developed which consists of the frequency response analysis of the limiting diffusion current to a sinusoidal magnetic field perturbation. In the low frequency range, all the impedance diagrams can be reduced, in Bode coordinates, by {omega}{ital B}{sup {minus}2/3}{ital C}{sup {minus}2/3}. This response is due to convective mass transport and is similar to the electrohydrodynamical impedance obtained through the modulation of the rotation speed of a rotating disk electrode.

Alcohol adducts of alkoxides: intramolecular hydrogen bonding as a general structural feature

Abstract: Characterization of Zr{sub 2}(O{sup i}Pr){sub 8}({sup i}PrOH){sub 2} by {sup 1}H and {sup 13}C NMR spectroscopy, ir spectroscopy, and single-crystal x-ray diffraction ({minus}100{degree}C) is reported. The unit cell contains four half-dimers in the asymmetric unit, all of which differ only in the rotational conformation about Zr-O and O-C bonds. In each dimer, the edge-shared bioctahedron has two {mu}-O{sup i}Pr groups. On opposite sides of this Zr{sub 2}({mu}-OR){sub 2} plane, each dimer forms two hydrogen bonds, one each between a coordinated alcohol and a terminal alkoxide. The NMR spectra at 25{degree}C are so simple as to be structurally uninformative, a result of rapid fluxionality which includes, as one component, proton migration among all O{sup i}Pr units. At {minus}80{degree}C in toluene, the NMR spectra are now too complex to be accounted for by a single edge-shared bioctahedral structure. The hafnium analogue is isomorphous with the zirconium compound. Although Ce{sub 2}(O{sup i}Pr){sub 8}({sup i}PrOH){sub 2} is not isomorphous, it exhibits an analogous hydrogen-bonded structure in which the O{hor ellipsis}O distance is as short as it is in the Zr analogue, in spite of a metal-metal separation which is longer by 0.28 {angstrom}. The generality of hydrogen bonding between M-OR and M-O(H)R groups whenmore » they are aligned parallel in a metal cluster is reviewed. 44 refs., 2 figs., 4 tabs.« less

Multiconfiguration Dirac-Fock calculations of transition energies with QED corrections in three-electron ions.

Abstract: We present accurate calculations of the 1${\mathit{s}}^{2}$2s and 1${\mathit{s}}^{2}$2p energy levels of lithiumlike ions for 15\ensuremath{\le}2Z\ensuremath{\le}92. The multiconfiguration Dirac-Fock method has been used to calculate relativistic effects. One-electron radiative corrections and estimated screening corrections have been calculated. These results are in good agreement with relativistic many-body calculations. General agreement with experimental transition energies (available up to Z=92) is very good.

Swelling of anionic and cationic starch-based superabsorbents in water and saline solution

Abstract: Starch graft superabsorbents were prepared by graft copolymerization either with polyacrylonitrile (PAN) and saponification of the resulting copolymer or with trimethyl–aminoethylacrylate chloride (CMA) and methylene bisacrylamide as crosslinking agent. The influence of several structural parameters on the swelling properties of these absorbents have been studied: crosslink density, ionic content, and composition of the starch. As expected, the absorbency decreases with an increase of the crosslink density. It increases with the ionic content of the graft copolymer up to a maximum, an excess of charges leading to a swelling decrease. The PAN branch length depends on the origin of the starch. High molar weight PAN was grafted onto waxy corn, a starch with high amylopectin content. The swelling increases with increasing molar weight of PAN up to 5 × 105. In saline solution the absorbency of both ionic gels decreases significantly. However, in the presence of multivalent ions their behavior is different. For cationic absorbents the swelling depends on the ionic strength but not on the ion valency. On the other hand, anionic absorbents are significantly affected by multivalent cations.

The energy-momentum tensor and material uniformity in finite elasticity

Abstract: Eshelby's elastic energy-momentum tensor is shown to satisfy a differential identity which, in the general case of a uniform elastic body with inhomogeneities, is expressible in terms of the torsion of the material connection.

Implications of shear-sense criteria for the tectonic evolution of the Central Rhodope massif, southern Bulgaria

Abstract: A systematic record of sense-of-shear criteria associated with peak conditions of amphibolite facies metamorphism from the Central Rhodope massif, Bulgaria, gives evidence for superposition of two distinct terranes. The lower terrane is characterized by south-vergent, flat-lying thrusting that involved eclogites. The upper terrane is characterized by east-vergent, flat-lying shearing possibly associated with crustal extension. We suggest that both regional metamorphism and deformation may be Cretaceous in age. There was erosion prior to emplacement of several crystalline sheets at shallow depths during the early Cenozoic. This was followed by Oligocene extension and rhyolitic volcanism. The Rhodope massif can no longer be regarded as a stable Paleozoic or older microcontinent.

Simple Liquid Metals

Abstract: Liquid metals differ from the other classes of liquids considered so far primarily through the presence of the conduction electrons. Although the theory of liquid metals has much in common with that of the other ionic liquids discussed in Chapter 10, the problem is complicated by the fact that the electronic component requires a quantum-mechanical treatment. Many elements show metallic behaviour in the liquid state, but their electronic band structures can differ widely. We shall restrict ourselves to the so-called “simple” metals. The class of simple metals comprises those in which the electronic valence states are well separated in energy from the tightly-bound core states; their properties are reasonably well described by the nearly-free-electron model. Metals that are classified as simple in this sense include the alkali metals, magnesium, zinc, mercury, gallium and aluminium. Other liquid metals (noble and transition metals, alkaline earths, lanthanides and actinides) have more complicated electronic structures, and the theory of such systems is correspondingly less well advanced. More complete accounts of the properties of liquid metals than we are able to give here can be found in a number of excellent monographs (Faber, 1972; Shimoji, 1977) and review articles (Ashcroft and Stroud, 1978; Evans, 1978), and in the proceedings of regular conferences on the subject (Takeuchi, 1973; Evans and Greenwood, 1977; Cyrot-Lackmann and Desre, 1980).

The ocean-continent boundary off the western continental margin of Iberia—I. Crustal structure at 40°30′N

Abstract: SUMMARY The western continental margin of the Iberian peninsula has the characteristics of a rifted non-volcanic margin with half-graben and tilted fault blocks seen in several places. The ocean-continent boundary (OCB) is therefore expected to be where thinned continental crust and oceanic crust are juxtaposed, as at many similar margins worldwide. It is particularly useful to locate the OCB off western Iberia in order to constrain the pre-rift fit of North America to Iberia and, by implication, the shape of the proto-Bay of Biscay. The fit is only marginally constrained by sea-floor spreading magnetic anomalies because anomaly 34 is believed to be far to the west of the OCB and it is even possible that all older oceanic crust was created during the Cretaceous constant polarity interval. The best way to distinguish oceanic crust from thinned continental crust appears to be the crustal seismic velocity structure. Therefore in 1986 a series of seismic refraction lines was shot parallel to, and normal to, the continental margin. These lines enabled us to bracket the location of the OCB. A further constraint on the location was obtained by modelling an east-west magnetic profile which included the enigmatic J-anomaly. This anomaly can be explained as either just pre-anomaly MO or as part of the Cretaceous constant polarity interval, depending on whether spreading began about 127 or after 118 Myr ago, respectively. The evidence favours the former explanation. Lastly the depth to acoustic basement was contoured from a compilation of seismic reflection profiles. This indicated a new fracture zone at 41"15'N which offsets the OCB. A few key reflection profiles also suggest that the OCB can be identified by an abrupt landward step-down in acoustic basement. We conclude that the OCB in the eastern Iberia Abyssal Plain lies between 12'10' and 12'30'W and has a trend just east of north. This westerly location is consistent with recent estimates of the location of the OCB off the Grand Banks but brings into question the proposed location at about 11"W of the OCB in the Tagus Abyssal Plain.