Showing papers by "Mines ParisTech published in 1991"

Watersheds in digital spaces: an efficient algorithm based on immersion simulations

Abstract: A fast and flexible algorithm for computing watersheds in digital gray-scale images is introduced. A review of watersheds and related motion is first presented, and the major methods to determine watersheds are discussed. The algorithm is based on an immersion process analogy, in which the flooding of the water in the picture is efficiently simulated using of queue of pixel. It is described in detail provided in a pseudo C language. The accuracy of this algorithm is proven to be superior to that of the existing implementations, and it is shown that its adaptation to any kind of digital grid and its generalization to n-dimensional images (and even to graphs) are straightforward. The algorithm is reported to be faster than any other watershed algorithm. Applications of this algorithm with regard to picture segmentation are presented for magnetic resonance (MR) imagery and for digital elevation models. An example of 3-D watershed is also provided. >

Co-word analysis as a tool for describing the network of interactions between basic and technological research: The case of polymer chemsitry

Abstract: The goal of this paper is to show how co-word analysis techniques can be used to study interactions between academic and technological research. It is based upon a systematic content analysis of publications in the polymer science field over a period of 15 years. The results concern a.) the evolution of research in different subject areas and the patterns of their interaction; b.) a description of subject area “life cycles”; c.) an analysis of ”research trajectories” given factors of stability and change in a research network; d.) the need to use both science push and technology pull theories to explain the interaction dynamics of a research field. The co-word techniques developed in this paper should help to build a bridge between research in scientometrics and work underway to better understand the economics of innovation.

Finite difference computation of traveltimes in very contrasted velocity models: a massively parallel approach and its associated tools

Abstract: SUMMARY We present a new massively parallel method for computation of first arrival times in arbitrary velocity models. An implementation on conventional sequential computers is also proposed. This method relies on a systematic application of Huygens’ principle in the finite difference approximation. Such an approach explicitly takes into account the existence of different propagation modes (transmitted and diffracted body waves, head waves). Local discontinuities of the time gradient in the first arrival time field (e.g., caustics) are built as intersections of locally independent wavefronts. As a consequence, the proposed method provides accurate first traveltimes in the presence of extremely severe, arbitrarily shaped velocity contrasts. Associated with a simple procedure which accurately traces rays in the obtained time field, this method provides a very fast tool for a large spectrum of seismic and seismological problems. We show moreover that this method may also be used to obtain several arrivals at a given receiver, when the model contains reflectors. This possibility significantly extends the domain of potential geophysical applications.

Semantic file systems

Abstract: A semantic file system is an information storage system that provides flexible associative access to the system's contents by automatically extracting attributes from files with file type specific transducers. Associative access is provided by a conservative extension to existing tree-structured file system protocols, and by protocols that are designed specifically for content based access. Compatiblity with existing file system protocols is provided by introducing the concept of a virtual directory. Virtual directory names are interpreted as queries, and thus provide flexible associative access to files and directories in a manner compatible with existing software. Rapid attribute-based access to file system contents is implemented by automatic extraction and indexing of key properties of file system objects. The automatic indexing of files and directories is called "semantic" because user programmable transducers use information about the semantics of updated file system objects to extract the properties for indexing. Experimental results from a semantic file system implementation support the thesis that semantic file systems present a more effective storage abstraction than do traditional tree structured file systems for information sharing and command level programming.

An Assessment of the Fe-C-Si System

Abstract: Precise knowledge of the Fe-C-Si system has been the subject of numerous previous studies because of the importance of this system for steelmaking processes and cast iron foundry. How-ever, the most recent articles on this subject still reveal uncertainties or insufficient information. The purpose of this work was to assess this system and to give it a precise description, but one which was simple enough for practical applications. An evaluation of the parameters describing the thermodynamic properties of the phases involved in the binary Fe-Si system has been achieved, mainly based on values of the silicon activity in the body-centered cubic (bcc) phase and on knowledge of the phase diagram. The A2-B2 ordering reaction of the bcc phase has been included. It has been shown that this reaction is of paramount importance for the description of the thermodynamic properties of this phase and its field of stability. This preliminary work and previous similar studies of the Fe-C and Si-C systems were used as a base for the evaluation of the ternary stable and metastable Fe-C-Si systems. Optimization of the parameters describing the properties of the phases involved in both of these systems was achieved using experimental thermodynamic data and the critical assessment of the phase diagrams.

Semantical interprocedural parallelization: an overview of the PIPS project

Abstract: PIPS is an experhnental FORTRAN source-to-source parallelizer that combines the goal of exploring interprocedural and semantical analysis with a requirement for compilation speed. We present in this paper the main features of PIPS, i.e., demand-driven architecture, automatic support for multiple implementation languages, structured control graph, predicates and regions for interprocedural analysis and global nested loop paralle~lzation, with an emphasis on its core data structures and transformation phases. Some preliminary results on the practical impact of our design choices are discussed. This research is partially funded by DRET, under contract 87-017.

Algebraic reconstruction of types and effects

Abstract: We present the rst algorithm for reconstructing the types and e ects of expressions in the presence of rst class procedures in a polymorphic typed language. E ects are static descriptions of the dynamic behavior of expressions. Just as a type describes what an expression computes, an effect describes how an expression computes. Types are more complicated to reconstruct in the presence of e ects because the algebra of e ects induces complex constraints on both e ects and types. In this paper we show how to perform reconstruction in the presence of such constraints with a new algorithm called algebraic reconstruction, prove that it is sound and complete, and discuss its practical import. This research was supported by DARPA under ONR Contract N00014-89-J-1988.

Room-Temperature Mechanosynthesis of Carbides by Grinding of Elemental Powders

Abstract: The direct room-temperature synthesis (mechanochemical synthesis or mechanosynthesis—MS) of most metal carbides by milling metal—carbon powders (size some tens of micrometers) mixtures is described. The particle size of the carbides obtained is of the order of 20 nm. Stable, metastable, mixed, and new carbides can be formed. Moreover, metal—carbon alloys can be obtained, such as in the Fe—C system. The synthesized compounds have been characterized by X-ray diffraction and Mossbauer spectroscopy for iron-containing systems. Carbides of the following elements were obtained: Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, Hf, Ta, W, Re, Al and Si.

Modelling and control of non-holonomic wheeled mobile robots

Abstract: A general dynamical model is derived for three-wheel mobile robots with nonholonomic constraints by using a Lagrange formulation and differential geometry. It is shown that a static state feedback allows one to reduce the dynamics of the system to a form in which stabilizing input-output linearizing control is possible. >

Adaptive Stabilization of Nonlinear-systems

Abstract: An overview of the various parametric approaches which can be adopted to solve the problem of adaptive stabilization of nonlinear systems is presented. The Lyapunov design and two estimation designs —equation error filtering and regressor filtering— are revisited. This allows us to unify and generalize most of the available results on the topic and to propose a classification depending on the required extra assumptions — matching conditions or growth conditions.

Ergodicity and integral range

Abstract: SUMMARY When attempting to estimate stereological parameters starting from measurements in a limited domain, the question has to be addressed of how large the domain size must be in order to ensure representative measurements. To answer that question, the concept of ‘integral range’ is introduced. It allows a comparison between the scale of the phenomenon under study and the scale of observation. The integral range can be assessed using curves of dispersion variance, which can also yield empirical laws of change of scale.

Properties of sputtered stainless steel-nitrogen coatings and structural analogy with low temperature plasma nitrided layers of austenitic steels

Abstract: Structural analogies are revealed between 310 stainless steel-nitrogen deposits prepared by reactive sputtering and diffusion layers resulting from low temperature plasma nitriding of the same grade of stainless steel Both the coatings and the diffusion layers show high nitrogen supersaturations in the fcc lattice of austenite and present a rather favourable compressive stress and a good level of microhardness An interesting corrosion resistance is also expected With these properties, future applications can be considered

Peak load reduction by preconditioning buildings at night

Abstract: Cooling loads during the peak period can be reduced if a building is subcooled a few degrees below its normal thermostat set-point during the preceding night. During the day the thermostat must control the warm-up in such a way that the stored energy is released when it brings maximum benefit. This strategy exploits the heat capacity of the building itself; it can be implemented at low cost and without sacrifice of comfort. To evaluate the strategy for a given building and to control the thermostat, one needs to know the thermal behaviour of the building. Building temperature, internal load and solar data are used to determine a small number of thermal parameters which characterize the building. Several thermostat control strategies, distinguished by their knowledge of the building dynamics, are described and simulated, with a data-based dynamic model. Universal graphs for effective storage capacity and storage efficiency are developed. A simple economic analysis shows that subcooling is likely to be cost-effective for many commercial buildings, with current electric rate schedules.

Orientation splitting of cube-oriented face-centred cubic crystals in plane strain compression

Abstract: Orientation splitting of cube-oriented f.c.c. crystals during plane strain compression is analysed by assuming the development of deformation bands in the direction of extension. The bands are considered to undergo the macroscopic normal strain components but are allowed to shear in opposite senses along the elongation direction (local relaxed constraints model). It is shown that this local deformation banding leads, for both the (001)[010] and (001)[110] orientations, to large lattice rotations of opposite sign about the transverse axis and hence the formation of transition bands. Analytical expressions are derived for the lattice rotations up to true strains of about unity. Experimental plane strain compression tests on (001)[010] and (001)[110] aluminium single crystals confirm the predicted behaviour and indicate the spatial distribution of the bands and their slip systems. It is shown that the bands in the (001)[110] orientation are characterized by double coplanar slip while those in the cube crystals behave according to a single-slip model.

Lyapunov design of stabilizing controllers for cascaded systems

Abstract: The design of a state feedback law for an affine nonlinear system to render a (as small as possible) compact neighborhood of the equilibrium of interest globally attractive is discussed. Following Z. Artstein's theorem (1983), the problem can be solved by designing a so-called control Lyapunov function. For systems which are in a cascade form, a Lyapunov function meeting Artstein's conditions is designed, assuming the knowledge of a control law stabilizing the equilibrium of the head nonlinear subsystem. In particular, for planar systems, this gives sufficient and necessary conditions for a compact neighborhood of the equilibrium to be stabilized. >

Reduction of haematite with carbon by room temperature ball milling

Abstract: The solid state reduction of haematite (α-Fe2O3) to mainly nanocrystalline wustite by room temperature dry ball milling of haematite and carbon, in an inert atmosphere, is described. In addition to wustite, a smaller amount of nanocrystalline magnetite is also formed, possibly by a disproportionation reaction of wustite. The reaction is completed in about 70 h in a Spex vibratory ball mill. Haematite alone is converted by dry milling for 70 h into nanocrystalline magnetite with an average crystallite size of 10 nm as shown by X-ray diffraction and Mossbauer spectroscopy.

Quasicrystals and crystalline phases in Al65Cu20Fe10Cr5 alloy

Abstract: An alloy of compositon Al65Cu20Fe10Cr5 forms a mixture of icosahedral and decagonal quasicrystals upon rapid solidification from the liquid state. These quasicrystals are highly faulted as revealed by electron microscopy studies. After heat treatment, the alloy transforms into a new orthorhombic modification. This crystal is studied by X-ray and transmission electron microscopy and emphasis is put on its close resemblance to the decagonal phase.

STUDY OF DYNAMIC ABSORPTIVITY AT 10.6 µm (CO2) AND 1.06 µm (Nd-YAG) WAVELENGTHS AS A FUNCTION OF TEMPERATURE

Abstract: One of the main advantages of Nd-YAG lasers compared to CO2 lasers consists of easy beam handling using optical silica fibers. However, up to now Nd-YAG applications for material processing were limited due to a rather low available mean output power (less than about 500 W). A Eureka project (termed "EU-226") which consequently aimed at developing the so called "High Power Solid State Laser (HPSSL)" capable of 1 to 3 kW, involved absorptivity studies results of which are given in this contribution. Metallic surfaces exhibit a higher absorptivity at 1.06 µm (Nd-YAG) than at 10.6 µm which improves the energy transfer with a Nd-YAG laser and decreases the thermal runaway. This was acertained by measurements of absorptivity as a function of temperature and by thermal cycle calculations. This permits laser surface hardening of steels without any coating or gas shielding, which prevents in particular pollution. Various materials, I. e. pure nickel, Inconel 718 and AISI 1045 steel, were studied, featuring in particular the influence of surface roughness, oxidation and initial absorptivity on laser-material interaction.

Perfect and modulated quasicrystals in the system Al─Fe─Cu

Abstract: The occurrence of a reversible phase transformation from a rhombohedral crystalline structure to a perfect quasicrystalline state of chemical composition Al63·5Fe12·5Cu24 has been studied by transmission electron microscopy. Both direct in situ heating experiments and thermal treatments of bulk dodecahedral particles have been carried out in order to characterize the various intermediate stages of this transformation and its reversibility. The most spectacular intermediate state can be considered as a modulated quasicrystalline structure which, depending on the thermal treatment, appears either at about 550°C or at about 750°C. Under fast cooling, it may be retained as a metastable state at room temperature. A modulation mechanism of the perfect icosahedral phase is proposed based on a phason field theory. It has been shown that the observed wavelength of the modulated quasicrystalline structure can be deduced, to first order, from a dynamical phason condition applied to atomic displacements defi...

The structure of the icosahedral AlPdMn quasicrystal

Abstract: Neutron diffraction data were obtained from quasicrystals of the AlPdMn system and the isomorphic modifications AlPd(FeCr). From contrast variation effects, partial structure factors were determined. In the high-dimensional periodic description, the structure can be viewed as a six-dimensional cubic lattice belonging to the Pm space group, with a superstructure due to a chemical order which somewhat induces an F-type lattice.

Microstructural and analytical characterization of Al2O3(AlMg) composite interfaces

Abstract: Mechanical properties of composite materials depend on the reactions taking place at the ceramic-matrix interface. This study was devoted to the identification of the mechanisms of interaction for a Saffil-(AlMg) composite during squeeze casting and heat treatment. Transmission electron microscopy characterization and microanalysis clearly show migration of magnesium to the interface and reactions during processing of the composite and appropriate heat treatments allowed MgO and MgAl 2 O 4 clusters to be identified along the interface. Additionally, structural hardening of matrix through Mg 2 Si precipitation was made clear. Some evidence of macroheterogeneity in composition is also given.

A Review on Theoretical Analyses of Rolling in Europe

Abstract: A review of works on modelling of hot and cold rolling in the European area during the last few years is presented. First, the mechanical and mathematical features of the papers reviewed are presented (rheological assumptions; friction law and contact treatment; time integration schemes; thermomechanical coupling; methods of solutions). Then the results obtained by the various research groups are presented. First hot rolling is investigated; the major problems addressed are then product geometry and thermal evolution with some applications to metallurgical evolution. Finally, papers about cold strip rolling are discussed; these mainly analyze elastic roll deformation (flattening by plane strain approaches, 3D roll bending studies) and its consequences on strip profile and flatness.