Showing papers by "Mines ParisTech published in 1989"

The chemical abstract machine

Abstract: We introduce a new kind of abstract machine based on the chemical metaphor used in the G language of Banâtre & al. States of a machine are chemical solutions where floating molecules can interact according to reaction rules. Solutions can be stratified by encapsulating subsolutions within membranes that force reactions to occur locally. We illustrate the use of this model by describing the operational semantics of the TCCS and CCS process calculi. We also show how to extract a higher-order concurrent l-calculus out of the basic concepts of the chemical abstract machine.

Algebraic tools for the performance evaluation of discrete event systems

Abstract: It is shown that a certain class of Petri nets called event graphs can be represented as linear time-invariant finite-dimensional systems using some particular algebras. This sets the ground on which a theory of these systems can be developed in a manner which is very analogous to that of conventional linear system theory. Some preliminary basic developments in that direction are shown. Several ways in which one can consider event graphs as linear systems are described. These correspond to approaches in the time domain, in the event domain, and in a two-dimensional domain. In each of these approaches, a different algebra has to be used for models to remain linear, but the common feature of these algebras is that they all fall into the axiomatic definition of 'dioids'. A unified presentation of basic algebraic results on dioids is provided. >

The metamorphism in the Central Himalaya

Abstract: All along the Himalayan chain an axis of crystalline rocks has been preserved, made of the Higher Himalaya crystalline and the crystalline nappes of the Lesser Himalaya. The salient points of the metamorphism, as deduced from data collected in central Himalaya (central Nepal and Kumaun), are: 1 The Higher Himalaya crystalline, also called the Tibetan Slab, displays a polymetamorphic history with a first stage of Barrovian type overprinted by a lower pressure and/or higher temperature type metamorphism. The metamorphism is due to quick and quasi-adiabatic uplift of the Tibetan Slab by transport along an MCT ramp, accompanied by thermal refraction effects in the contact zone between the gneisses and their sedimentary cover. The resulting metamorphic pattern is an apparent (diachronic) inverse zonation, with the sillimanite zone above the kyanite zone. 2 Conversely, the famous inverted zonation of the Lesser Himalaya is basically a primary pattern, acquired during a one-stage prograde metamorphism. Its origin must be related to the thrusting along the MCT, with heat supplied from the overlying hot Tibetan Slab, as shown by synmetamorphic microstructures and the close geometrical relationships between the metamorphic isograds and the thrust. 3 Thermal equilibrium is reached between units above and below the MCT. Far behind the thrust tip there is good agreement between the maximum temperature attained in the hanging wall and the temperature of the Tibetan Slab during the second metamorphic stage; but closer to the MCT front, the thermal accordance between both sides of the thrust is due to a retrogressive metamorphic episode in the basal part of the Tibetan Slab.

Isothermal crystallization kinetics in a limited volume. A geometrical approach based on Evans' theory

Abstract: A new theoretical approach of the isothermal crystallization of a thin polymer film is proposed. This model, derived from Evans' theory, is in very good agreement with a previous one, but is much more interesting because it makes it possible to calculate the transformed volume fraction anywhere in the film. The main effects of decreasing thickness are a slower average crystallization of the film and a decrease in the Avrami exponent caused by a slower crystallization of the polymer close to the surfaces.

Mechanical alloying of Fe and V powders: Intermixing and amorphous phase formation

Abstract: Mossbauer spectrometry and x-ray diffractometry were used to characterize the microstructural changes that occurred during the mechanical alloying of Fe and V powders, After 3 h of essentially no interatomic intermixing, an Fe–V alloy began to form. At first the chemical composition of this alloy was highly inhomogeneous, having large variations over distance scales of less than 100 A. After about 24 h of ball milling, the alloy homogenized and then became at least partly amorphous.

Qualitative models, quantitative tools and network analysis

Abstract: One model for knowledge development is the network interaction model. Insofar as socio-technical networks may have some structural properties, does knowledge development reflect this? The hypothesis that it does may enable us to make some forecasts of science development from a description of the state of a field. One condition necessary for testing this hypothesis is that of adopting a model for these networks. Co-word analysis is such a tool. It gives us key-words networks derived from scientific and technical texts. The author checks for network properties in the area of knowledge development through a case study of Polymer Science and Technology from 1973 to 1978.

Relationship between mechanical properties and wear resistance of alumina-zirconia ceramic composites

Abstract: Mechanical behavior of Al2O3-based ceramics can be improved by dispersion of pure or partially stabilized ZrO2 particles. The effective toughening or strengthening effect, which is operating in these composite materials, is determined by microstructural characteristics (composition, processing conditions) and environmental conditions (temperature, loading rate,…). The objective of this work has been to make a correlation between mechanical properties and wear resistance of alumina-zirconia composites. Wear tests were conducted employing a bloc-on-ring tribometer which consists of a steel ring rotating against plane ceramic specimens. Different environmental conditions were investigated: ambient air, and water. The wear volume is determined as a function of sliding distance. The dispersion of ZrO2 particles in Al2O3 matrix improves the fracture behavior but reduces the wear resistance. However, the addition of ZrO2 limits the water corrosion effect observed in Al2O3 materials. Wear seems to be controlled b...

Overall crystallization kinetics of thin polymer films. General theoretical approach. I. Volume nucleation

Abstract: A general theoretical approach of the overall crystallization kinetics of thin polymer films is developed. This new model makes it possible to calculate the evolution of the transformed volume fraction anywhere in the film, whatever the cooling conditions are. In its isothermal limit this model is equivalent to previous approaches which have been well verified by a computer simulation. In conclusion, it is pointed out that both isothermal and anisothermal determinations of crystallization kinetic parameters are greatly dependent on the sample thickness.

Effect of plastic deformation on the microstructure and properties of amorphous polycarbonate

Abstract: Polycarbonate specimens were subjected to a plastic strain cycle at room temperature by means of a computer-controlled shear apparatus. The strain-cycling has several consequences: it softens the further plastic behaviour of the material, it increases the β relaxation peak observed between 300 and 400 K by dynamic mechanical analysis, and it generates an exothermic shoulder in the differential scanning calorimetry plot at 350 K. The experimental results are analysed in terms of a model which, during shear straining, involves the nucleation of quasi-point defects of higher molecular mobility. These defects persist in large density after strain cycling and are responsible for the changes in material behaviour reported. In particular, the evolution of the loss tangent spectra was analysed quantitatively by means of a computer simulation based on the elimination of the defects.

Adaptive nonlinear regulation: equation error from the Lyapunov equation

Abstract: An adaptive controller for nonlinear, linearly parameterized systems is presented. The new features introduced in the design are: (1) parameter estimation is performed on the scalar Lyapunov equation instead of the n-dimensional equation of the system itself. This allows non-Lipschitz uncertainties to be tolerated, especially when the stabilizing laws are not feedback linearization plus linear control. (2) Double estimation is used. One estimate is used for the stabilizing control, and the other is used to cancel the perturbation terms introduced by the adaptation, if possible. This is proposed to solve the problem of the implicit definition of the controller which arises when one tries to do this cancellation. >

Modelling and analysis of lead acid battery operation

Abstract: A model of the lead-acid battery is presented based on a simple description of electrochemical reactions. Models of the electromotive force, the internal resistance, and the gassing phenomenon are detailed. Good agreement between simulation and measurement has led to the validation of a model for discharge and for the charge preceding gassing at constant temperature. As regards the calculation of the state of charge, modeling of the gas emission is necessary to minimize drift over a long period of operation. >

Heterogeneities and geometry of sedimentary bodies in a fluvio-deltaic reservoir

Abstract: This paper gives the initial results of a two- and three-dimensional (2D and 3D) geological study that aimed at describing reservoir heterogeneities. This study serves as a basis for the conditional simulation of the geometry of a fluvio-deltaic reservoir presented in a companion paper. These two studies should solve the difficult problems of interpolating between wells and thereby the problem of forecasting the extension of sedimentary bodies. The research is being carried out by Inst. Francais du Petrole and Center of Geostatistics, Paris School of Mines. The study was made in the middle Jurassic in Yorkshore, which is very similar to the Brent formation in the North Sea. In the 2D phase, an outcrop consisting of a 1-km (0.6-mile) -long and approximately 30-m (100-ft) -high cliff was described with a photogeological interpretation. The sedimentological representation was carried out by means of several vertical cross sections. In the 3D phase, 36 boreholes were continuously cored and logged behind the cliff over an area of 1 km/sup 2/ (0.4 sq miles). The boreholes were about 300 m (985 ft) apart except in one grid where the distance was progressively reduced to 20 m (66 ft). This phase was designed to follow themore » evolution of the sedimentary bodies and their physical properties and to compare the correlation that could have been made (1) with fewer boreholes and (2) without the existence of the cliff. These studies provide new tools for understanding and describing the shape and heterogeneities of a reservoir.« less

Neutron-diffraction approach to the atomic decoration of the Al-Mn icosahedral quasicrystal.

Abstract: Neutron-diffraction data were obtained from single-phase icosahedral powder of the system ${\mathrm{Al}}_{74}$${\mathrm{Si}}_{5}$${\mathrm{Mn}}_{21}$ and its modification by isomorphous substitution on the Mn sites. Amplitudes and phase differences of the partial structure factors (${F}_{\mathrm{Al}}, {F}_{\mathrm{Mn}}$) were determined. From their ${Q}_{\ensuremath{\perp}}$ dependences, and within a strip-projection approach, phases were reconstructed. Atomic densities calculated in the physical 3D space show that Mackay icosahedra, the structural units usually invoked for quasicrystal models, do not emerge as the basic ingredients of the atomic arrangements.

The use of review articles in the analysis of a research area

Abstract: Review articles in the field of polymer science in the seventies are analyzed in order to check their usefulness in describing at a very low cost the development or the state of the art of a field. Results are compared with those obtained through a quantitative study of scientific articles published at the same time in the field. Review articles can be regarded as defining a research programme attempting to link together two networks: polymer properties—as being desirable from market considerations—and polymer structure—as being analyzable by means of academic science, through three kinds of “translation” strategies. If we thus define a research programme in terms of the mobilization of networks, it is possible to say of review articles that they provide a good representation of the development of networks of problems whose evolution they sketch.

Boolean random functions

Abstract: SUMMARY A Boolean function f in Rn is the supremum of upper semi-continuous random functions f'i which are almost surely positive, bounded with compact support and centred at the Poisson points (i). They generalize to functions of classical Boolean model for sets. The Boolean function f may be studied via its subgraph, i.e. as a random set in Rn x R. The key notion is then the functional Q(Bt), i.e. the probability that a compact set Bt centred at altitude t misses the subgraph of f. The general expression of Q(Bt) is given, and followed by a series of important derivations (volumes, gradients, numbers of summits, etc). Theorems of structure are given: they concern the properties of infinite divisibility for the sup, and domains of attraction for Boolean functions. The last sections are devoted to the study of two particular Boolean functions; emphasis is put on the stereological implications of the approach. A critical example illustrates the theory.

Self-diffusion in Mg2SiO4 (forsterite) at high temperature

Abstract: The use of neutral primary particles for secondary ion mass spectrometry (NPB-SIMS) makes it possible to analyse the isotope concentration profiles of all constituent elements in Mg2SiO4 simultaneously. The results indicate

Models with orthogonal indicator residuals

Abstract: In this paper, a new isofactorial model is presented. At each point of a random function it is possible to define the residuals of the regressions between successive indicators. These residuals are precisely the factors of this model. This leads to a simple expression for indicator cokriging, i.e. for Disjunctive Kriging.