Showing papers by "University of Paris published in 1978"

An extension of the self-consistent scheme to plastically-flowing polycrystals

Abstract: T he general formulation of the self-consistent scheme is specified for an isotropic elasto-plastic approximation of the “constraint” tensor. This leads to an explicit interaction law, modified from that of E. k roner (1961), which takes elasto-plastic accommodation into account via a simple scalar “accommodation function”. This model is applied to uniaxial tension tests for fee polycrystals. Both plastic flow and texture development are investigated. Internal stresses are shown to be significantly lowered with respect to the Kroner model predictions, due to the occurrence of plastic stress relaxation. As a result, the specific plastic properties of the material which are studied, as expressed by a single crystal “hardening matrix”, are found to have a significant influence on the final results.

Ground state of the fermion one-component plasma: A Monte Carlo study in two and three dimensions

Abstract: We have performed fermion Monte Carlo variational calculations to determine the equation of state of the uniform electron one-component plasma in two and three dimensions. The ground-state excess energies calculated by the Monte Carlo method are very precise and in agreement with those of other calculations in the metallic density range and in the very-low-density Wigner crystals. Three phases have been investigated: the Wigner crystal, the normal or unpolarized fluid, and the polarized fluid. The Wigner crystal has the lowest energy for ${r}_{s}g67$ in three dimensions and ${r}_{s}g33$ in two dimensions. The totally polarized quantum fluid is stable for $26l{r}_{s}l67$ in three dimensions and for $13l{r}_{s}l33$ in two dimensions, and the normal or unpolarized fluid is stable at higher densities ${r}_{s}l26$ in three dimensions and ${r}_{s}l13$ in two dimensions. A pseudopotential with no adjustable parameters, derived from the random-phase approximation, is found to give excellent energies. The present results lend support to earlier conjectures that the ground state of the electron gas will be spin polarized at intermediate densities.

A new method for the detection of singlet oxygen in aqueous solutions

Abstract: — In experiments on the interception of reactive intermediates of strongly oxidizing character in dye (S) sensitized photooxidations using p-nitrosodimethylaniline (RNO) as a selective scavenger, it has been observed that some substrates (A) or 1O2 acceptors (like imidazole derivatives) induce the bleaching of RNO as followed spectrophotometrically at 440 nm. Since singlet oxygen (1O2) does not react chemically with RNO, this bleaching is a consequence of 1O2 capture by the imidazole ring which results in the formation of a trans-annular peroxide intermediate [1O2] capable of inducing the bleaching of RNO (-RNO). In the absence of RNO, [1O2] decomposes or rearranges into the final oxygenation product 1O2: 1Δg Thus, the system imidazole plus RNO can be used as a sensitive and selective test for the presence of 1O2 in aqueous solutions. The method can also be applied in the presence of sensitizing dyes which, under visible irradiation, can partially bleach RNO even in the absence of imidazole derivatives. In such a case, the bleaching of RNO is strongly increased by the presence of imidazoles with a characteristic dependence on their concentration. The separation of the product of RNO bleaching by thin layer chromatography can serve as additional proof of the presence of 1O2 in the system. The imidazole plus RNO method has been applied to a number of sensitizing and non-sensitizing dyes.

Rheology of concentrated disperse systems II. A model for non-newtonian shear viscosity in steady flows

Abstract: A relative viscosity — volume concentration relationship,η r =η r (φ) deduced from an energy principle, which operates in newtonian range, is phenomenologically extended to the description of non-newtonian behaviour. Such an extension is performed, using a structural intrinsic viscosity $$\tilde k$$ , which depends on volume concentrationφ and shear rate $$\dot \gamma $$ . At constant $$\dot \gamma $$ , some new results concerningk(φ) are given, leading to determination of the thickness of a surfactant layer onto particle surface, and allowing good agreement to the semi-empirical viscosity relation given byThomas. At constantφ, a rate equation governs the evolution of $$\tilde k$$ as a structural parameter. In steady conditions ( $$\dot \gamma $$ = const.), an equilibrium value $$\tilde k(\dot \gamma _r )$$ is reached, $$\dot \gamma _r $$ being a relative shear rate, depending on the overall time relaxation of the structure. A non-newtonian shear viscosity for steady flows is then obtained, depending on $$(\dot \gamma _r )^p $$ . For systems of non-spherical particles, an empirical determination ofp givesp ≈ 0.5.

Produits infinis de resolvantes

Abstract: This paper is concerned with the convergence of the sequence χ n =(I+λ n A)−1χ n−1 whereA is maximal monotone and λ n >0. Various assumptions onA and λ n are considered.

Purification of mouse interferon by sequential affinity chromatography on poly(U)--and antibody--agarose columns.

Abstract: Mouse interferon has been purified to homogeneity by two-step affinity chromatography. Two polypeptide bands were obtained on sodium dodecyl sulphate–polyacrylamide gel electrophoresis migrating at molecular weights 35,000 and 22,000, both having antiviral activity. The 35,000 but not the 22,000 band, also stained with periodic acid–Schiff. The specific activity was 8×109 of our laboratory units, corresponding to 2.4×109 NIH reference units.

Shear deformation zones along major transform faults and subducting slabs

Abstract: Summary. Narrow zones of intense shear deformation, i.e. viscous slip zones, are studied analytically with a one-dimensional time-dependent model of two half-spaces of identical or contrasting rheologies and ambient temperatures in relative motion. The rheologies of the half-spaces are strongly temperature-dependent and viscous heating maintains a thin zone of high temperature, low viscosity and large strain rate. The mathematical model is used to describe the structures of slip zones at ridge and plate-boundary transform faults, major continental strike—slip faults and at the top of subducting oceanic crust. No a priori assumption about slip-zone width or shear-stress magnitude is necessary; the thermal-mechanical structure of the slip zone evolves in time and all its characteristics are self-consistently determined. Slip-zone widths and shear stresses depend on the ambient temperatures, the relative velocity, the rheology and the length of time following the onset of relative motion; for reasonable geologic times, 0.1–10 M yr for example, slip zones are generally several kilometres wide and shear stresses are several hundred bars (tens of MPa). The region of intense shear in a viscous slip zone is an order of magnitude narrower than the width of the accompanying thermal anomaly. The maximum temperature generated by viscous dissipation in a slip zone depends only on the relative motion and the creep properties of the rocks; it is independent of slip-zone age and ambient temperature. Maximum temperatures associated with frictional heating are always less than those required for partial melting. The slip zone on a descending slab is influenced most strongly by the contrast in creep behaviour between the relatively soft oceanic crustal rocks and the hard, overlying mantle rocks; as a result, the slip zone is confined entirely within the oceanic crustal layer. Oceanic crustal rocks deform so readily that frictional heating in a slip zone on a descending slab cannot by itself lead to partial melting and thermal conduction from the hotter overriding mantle must play an essential role in heating the descending crust if melting is to occur therein. Because of the increase in the mantle temperature with depth, narrow slip zones in oceanic regions probably do not exist below depths of about 100 km; they may extend to greater depths beneath continents.

Enhanced diffusion mechanisms

Abstract: The phenomenology is reviewed for several enhanced diffusion mechanisms: the normal ionization-enhanced diffusion mechanism, the Bourgoin mechanism, the energy-release mechanism and some recoil mechanisms. Application of these mechanisms are discussed for crystalline and amorphous semiconductors, super-ionic materials and insulators in radiation damage, impurity and self-diffusion, ion-implantation, and dislocation-motion-experiments.

Experimental determination of the isotopic fractionation between gaseous CO2 and carbon dissolved in tholeiitic magma

Abstract: Isotope fractionation of carbon between CO2 and carbon dissolved in a tholeiitic magma measured in the range 1120–1280 ° C, 7.0–8.4 Kb varies from 4.6 to 4‰ in favor of CO2. These results make possible to explain all deep seated 13C values from a restricted range of primary mantle 13C concentrations. They also suggest that carbon could be dissolved in basaltic magmas in a reduced form.

Laser intensity and the comparative method for determination of triplet quantum yields

Abstract: — In the comparative method of determining the triplet quantum yield oT by laser flash absorption spectroscopy, general equations are established (1) for describing the dependence of oT with laser intensity and (2) for absolute actionometry of a laser pulse. Applications to specific examples are discussed.

The regulation of working methods as a function of work-load among air traffic controllers.

Abstract: A series of field studies among air traffic controllers is reviewed. It largely concentrated on regulatory aspects of operational behaviour, using a model based on the concept of ‘ economy ’ in the individual's selection of operating procedures. Attention is directed at processes involving reasoning, the receipt and transmission of information, and the division of tasks between controllers at the same station. The basic hypothesis, which is supported by numerous data, is that for a given task and a given controller certain operating procedures are less costly than others; that is, they generate lower levels of load. These procedures will therefore be more and more employed as work demand increases, together with the relaxation of certain, self-imposed, qualitative criteria. This regulatory feedback between work-load and operating methods is used by the controller to avoid the abrupt onset of overload conditions and to delay satiation. For the investigator, these progressive changes in operating p...

Rheology of concentrated disperse systems III. General features of the proposed non-newtonian model. Comparison with experimental data

Abstract: A non-newtonian viscosity equation\(\eta _r = (1 - \tfrac{1}{2} \cdot \tilde k\phi )^{ - 2} \) whereφ is the volume concentration and\(\tilde k = (k_0 + k_\infty \dot \gamma _r^p )/(1 + \dot \gamma _r^p )\) is an intrinsic viscosity, function of a relative shear rate\(\dot \gamma _r = \dot \gamma /\dot \gamma _c , k_0 , k_\infty \) and\(\dot \gamma _c \) being structural parameters, has been proposed in a previous paper (1). From empirical grounds, the valuep = 1/2 holds for a large class of systems, like suspensions of rodand disc-shaped particles. In the high shear rate limit, aCasson law-type is recovered and discussed, especially the concentration dependence of the yield stress. However, the latter disappears in the low shear limit, and must be considered as a pseudo-yield stress. Good agreement is found in this low shear limit with some theoretical results ofBueche for polymers. More generally, the viscosity equation displays pseudo-plastic behaviour and fitting it on experimental data allows the determination of the structural parameters. Some examples (especially Red Blood Cell suspensions and Blood) are studied and support the model. Nevertheless, for spherical particle suspensions, the best fitting is reached forp = 1. Accurate values of particle diameters can be deduced from the structural parameter\(\dot \gamma _c \), in this case.