Showing papers by "Mines ParisTech published in 1995"
TL;DR: In this paper, the authors introduce flat systems, which are equivalent to linear ones via a special type of feedback called endogenous feedback, which subsumes the physical properties of a linearizing output and provides another nonlinear extension of Kalman's controllability.
Abstract: We introduce flat systems, which are equivalent to linear ones via a special type of feedback called endogenous. Their physical properties are subsumed by a linearizing output and they might be regarded as providing another nonlinear extension of Kalman's controllability. The distance to flatness is measured by a non-negative integer, the defect. We utilize differential algebra where flatness- and defect are best defined without distinguishing between input, state, output and other variables. Many realistic classes of examples are flat. We treat two popular ones: the crane and the car with n trailers, the motion planning of which is obtained via elementary properties of plane curves. The three non-flat examples, the simple, double and variable length pendulums, are borrowed from non-linear physics. A high frequency control strategy is proposed such that the averaged systems become flat.
3,025 citations
TL;DR: The problem of tracking with stability of a reference trajectory is solved by means of linearizing "static" and "dynamic" state feedback laws by giving conditions to avoid possible singularities of the feedback laws.
Abstract: We are concerned in this article with the control of wheeled mobile robots, which constitute a class of nonholonomic mechanical systems. More precisely, we are interested in solving the problem of tracking with stability of a reference trajectory, by means of linearizing ''static'' and ''dynamic'' state feedback laws. We give conditions to avoid possible singularities of the feedback laws.
346 citations
TL;DR: In this article, the authors studied the use of an electrochemical destabilization coupled to a process of flotation (DAF) in waste water treatment, and the results obtained on an urban waste water treated by electrocoagulation and dissolved air flotation.
259 citations
TL;DR: In this article, the individual behavior of α- and β-spherulites in polypropylene samples which have been subjected to tensile and shear loading is reported.
250 citations
TL;DR: The Beauvoir rare metal granite as mentioned in this paper was mined from two distinct intrusions within a short time interval, and its geochemical and mineralogical data established its similarity to pegmatite melts.
Abstract: The Beauvoir rare metal granite, at the southern edge of the Echassieres granite massif, French Massif Central, is mineralized by disseminated Ta, Sn, and Li. The granite body formed from an independent melt which was emplaced soon after the main granite facies of the massif. The geochemistry of the Beauvoir granite relates it to the phosphorus-rich type of Ta-bearing granites, and geochemical and mineralogical data establish its similarity to pegmatite melts. The Beauvoir granite results built up from two distinct intrusions. Both intrusions are cogenetic and were emplaced within a short time interval. A geochemical study of a deep drill hole bored down to 900 m under the surface to the floor of the granite sheet, with selected key zones observed in greater detail, has allowed the recreation step by step of a long process leading to the economic concentration of Ta, Sn, and Li. The comparison of major element, trace element, and isotopic geochemistry with the petrology makes it possible to unravel the numerous processes contributing to the ore formation. Local events need to be determined before main events can be identified. Constraints on the interpretation of the ore genesis are provided by a careful observation of data; interpretations of these observations are strongly backed up by experimental data (e.g., Keppler, 1993). The source rock was most likely enriched in Sn and W at about 10 ppm, precluding a slightly enriched granitic melt by partial melting; it is not known whether the melt was already enriched in Ta, but this is not a prerequisite. Subsequently, deep-seated fractional crystallization produced granitic magma similar in composition (Ta nearly equal 9 m) to the adjacent Colettes granite, and further fractionation processes led to a melt already strongly enriched in Ta (ca. 40 ppm), strongly peraluminous, and enriched in the depolymerizing elements F and P. The viscosity was therefore very low, allowing easy ascent. During transport, small-scale fluctuations in the viscosity were amplified by upward movement, leading to an F- and P-rich melt preceding the magma batch. This less viscous melt again underwent crystallization while moving through the upper..
195 citations
TL;DR: In this paper, the authors present a theoretical study which could open the way to new plasma-assisted processes for converting natural gas resources into carbon and water without any external energy supply.
179 citations
TL;DR: In this paper, a laboratory study was conducted on weathered tailings collected from the Nickel Rim mine tailings impoundment near Sudbury, Ontario, Canada, which indicated that high concentrations of potentially toxic metals are potentially available for release by reductive dissolution of the ferric-bearing secondary minerals.
167 citations
TL;DR: The focus of the research is on the combination, by means of the sup- and inf-operations, of alternating filters by reconstruction when their component filters belong to a granulometry and an antigranulometry (by reconstruction).
166 citations
TL;DR: In this article, the mechanisms of ion nitriding are discussed, with particular attention being paid to d.c. diode nitriders, emphasizing the importance of the cathode fall region.
Abstract: In this paper the mechanisms of ion nitriding are discussed, particular attention being paid to d.c. diode nitriding. Recent trends in the analysis of the mechanisms of d.c. diode nitriding are reviewed, emphasizing the importance of the cathode fall region. Diagnostics of active species and calculation of their densities in the plasma are presented and related to modelling. The hydrogen effect and plasma-solid interaction are also discussed. New developments and alternatives to d.c. diode nitriding such as triode nitriding are highlighted.
147 citations
TL;DR: In this article, the role of the ceramic particles in the wear behavior of particulate composites was investigated by minimizing the influence of the often intricate metallic matrix (high speed steel, Al alloys, Mg alloys).
136 citations
TL;DR: In this article, a general framework for the development of plastic or viscoplastic constitutive equations is described, which is restricted to the case of quadratic criteria, and specially to the study of various interactions which can be introduced between the mechanisms.
TL;DR: In this article, the role played by the distribution of the current lines around the blockers and by the dielectric properties of these blockers is stressed. And when the matrix conductivity is low enough, isolated spaces appear on both sides of the blockers.
TL;DR: In this article, potato starch was extruded under various thermomechanical conditions in order to elucidate its behavior in two screw extruders, and extensive macromolecular degradation was found to be linked to thermOMEchanical treatment as evaluated through the measurement of specific mechanical energy.
TL;DR: In this article, a singular perturbation formulation for mechanical systems not exactly satisfying velocity constraints is proposed, and the robustness of static-state linearizing feedback laws which have been obtained to solve a point tracking problem is studied.
Abstract: We propose in this paper a singular perturbation formulation for mechanical systems not exactly satisfying velocity constraints. We particularize to 'wheeled mobile robots' which do not satisfy ideal pure rolling and nonslipping constraints. We study the robustness of static-state linearizing feedback laws which have been obtained to solve a point tracking problem in the ideal case when constraints were satisfied.
01 Jan 1995
TL;DR: This lecture is devoted to the survey of some recent results on feedback stabilization of nonlinear systems and introduces the notion of assignable Lyapunov function and presents some techniques for designing feedback based on L ∞ stability properties.
Abstract: This lecture is devoted to the survey of some recent results on feedback stabilization of nonlinear systems. This text can be seen as a prolongation of the overview written by E. Sontag in 1990 [83] in several directions where progress has been made. It consists of three parts:
The first part is devoted to sufficient conditions on the stabilization problem by means of discontinuous or time-varying state or output feedback.
In the second part, we present some techniques for explicitly designing these feedbacks by using Lyapunov’s method. This introduces us with the notion of assignable Lyapunov function and leads us to concentrate our attention on systems having some special recurrent structure.
The third part presents some techniques for designing feedback based on L ∞ stability properties. This last section also addresses robustness through a small gain theorem.
TL;DR: A review of the results reported up to now concerning the phase behavior and the microstructure of these novel systems can be found in this paper, where the experimental techniques and the theoretical explanations provided for the various phenomena that have been observed.
TL;DR: In this paper, the tensile behavior of a commercial grade of isotactic polypropylene was tested in a temperature range between 20 and 150 °C with a video-controlled testing system which is capable of imposing a constant true strain-rate within the neck automatically.
Abstract: The tensile behaviour of a commercial grade of isotactic polypropylene was tested in a temperature range between 20 and 150 °C with a video-controlled testing system which is capable of imposing a constant true strain-rate within the neck automatically. The results are displayed in the form of effective stress-strain curves and modelled by a constitutive equation in a multiplicative form. It is thus shown that, for each temperature, the plastic response can be described up to very large strains (ɛ ≃ 2.0) by a set of four parameters. The assumptions introduced in this modelling are critically discussed in order to check the validity of the simplifying hypotheses (strain homogeneity, isochoric deformation, etc.). The constitutive equation thus obtained was utilized in a finite difference code in order to predict the development of stretching instabilities of polypropylene. The simulation gives access to the engineering stress-strain response of the stretched test piece and to the detailed kinetics of the incipient neck. It is found that the severity of the instabilities is less at room temperature than near the melting point because of the decrease of the strain-hardening and of the strain-rate sensitivity with temperature.
01 Dec 1995
TL;DR: In this article, an enhancement to the classical numerical methods, which, up to now, are the only ones that apply to the general case, is proposed to solve geometric constraints, all of them having their own advantages and drawbacks.
Abstract: Numerous methods have been proposed in order to solve geometric constraints, all of them having their own advantages and drawbacks. In this article, we propose an enhancement to the classical numerical methods, which, up to now, are the only ones that apply to the general case.
TL;DR: In this article, the authors measured the transport properties of single crystal solid solutions with x = 0.025 and x =0.05 as a function of deviations from stoichiometry and obtained a maximum in the figure of merit Z = 2.9 × 10 3 K −1 for the solid solution containing 2.5% Bi 2 Se 3.
TL;DR: In this paper, the transformations induced by dry ball milling in an argon atmosphere have been investigated in various oxides by X-ray diffraction, Mossbauer spectroscopy and transmission electron microscopy.
TL;DR: In this article, a mathematical method is given to approximate the curve and determine the critical load where the derivative d(frictional force)/d(load) is maximum, where the first contact of the diamond with the substrate, total failure, is marked by an inflection point in the measured frictional force.
Abstract: During a scratch adhesion test, the plot of the frictional force against the normal applied load on the diamond can indicate different types of failure: small oscillations in the measured friction correspond to chipping, bigger variations show the presence of flaking. The first contact of the diamond with the substrate, total failure, is marked by an inflection point in the measured frictional force. A mathematical method is given to approximate the curve and determine the critical load where the derivative d(frictional force)/d(load) is maximum.
TL;DR: In this article, the macroscopic behavior of single-crystal superalloys under torsion or tension-torsion loadings was investigated at room temperature, on tubular specimens equipped with micro strain-gages for local deformation measurements.
TL;DR: In this paper, the influence of nitrogen incorporation into the coatings reactively sputter-deposited in different Ar-N2 mixtures was discussed, and the effect of their composition upon their mechanical characteristics such as intrinsic stress, microhardness or wear resistance as well as upon their corrosion resistance.
Abstract: Aluminium-based alloy films are potential candidates for anodic corrosion protection of construction steels. However, the mechanical properties of such coatings must be reinforced, for example by addition of transition elements. In this paper, we will first present some results concerning Al-Cr and Al-Ti coatings synthesized by r.f. sputtering of composite targets. We will further discuss the influence of nitrogen incorporation into the coatings reactively sputter-deposited in different Ar-N2 mixtures. After a description of the structural and microstructural features of Al-Cr-(N) and Al-Ti-(N) coatings, we will link the effect of their composition upon their mechanical characteristics such as intrinsic stress, microhardness or wear resistance as well as upon their corrosion resistance. The as-sputtered Al-Cr and Al-Ti coatings always remain microcrystalline or amorphous solid solutions, and their microhardness can reach about 10 000 MPa. Nitrogen incorporation favours the amorphization of the coatings. An extensive-to-compressive stress transition, which is clearly related to a densification of the coatings, is also observed as the Cr or Ti content increases and when nitrogen is incorporated into the reactor. Owing to the mechanical properties obtained for coatings remaining anodic compared with the construction steel substrate, future applications in mechanics are expected.
TL;DR: In this article, Kramers et Croockewit (1952) and Ronco et Ronco (1965) proposed an equation for the distribution of the time of day and the profil de profondeur du lit.
Abstract: On a mene des experiences dans un four rotatif a l'echelle pilote avec des particules de charbon et de coke en vue d'etudier le temps de sejour, la distribution du temps de sejour, le profil de profondeur du lit et le temps passe a la surface du lit. L'influence du coefficient de remplissage sur le temps de sejour a ete etudiee avec une profondeur de lit uniforme dans le four. Des mesures de la distribution du temps de sejour et du profil de profondeur du lit ont ete effectuees dans un four sans constriction finale, a differente vitesses de rotation et a differents apports en solides. On a mesure la fraction du temps de sejour correspondant au passage des particules a la surface du lit en photographiant le mouvement d'une particule coloree. Differentes equations ont ete testees pour representer les resultats experimentaux. L'equation de Kramers et Croockewit (1952) et celle de Ronco (1965) se sont revelees adequates pour calculer les temps de sejours moyens, tandis que seule la premiere a pu representer correctement le profil de profondeur du lit. On propose une equation qui s'est averee suffisamment precise pour predire la fraction du temps de sejour dans la couche superieure du lit
TL;DR: In this article, experiments were carried out on pure iron and low alloyed steels without palladium coating and it was shown clearly that in this case surface phenomena are not controlled.
TL;DR: In this article, a video-controlled stress-strain analysis of poly(etherether ketone) (PEEK) was performed under uniaxial tension and simple shear loading.
Abstract: Samples of poly(etherether ketone) (PEEK) were subjected to large plastic deformations under uniaxial tension and simple shear by means of a new video-controlled testing method at constant true strain rate. The “equivalent” stress-strain curves obtained under the two loading modes are close at the yield point, but diverge drastically at large strains, with a rapidly increasing hardening in tension and a moderate hardening under simple shear. X-ray diffraction goniometry shows that these contrasting behaviors are associated with the different textures developed in the crystallite orientations. Under tension, the PEEK lamellae are progressively tilted in such a way that the chain axis becomes oriented parallel to the tensile axis; in the other mode, the final chain orientation is near to the shear axis. DSC analyses of deformed samples in both modes are carried out. The results show that the tension loading induces a fragmentation of the thin lamellae, while the shear mode generates less fragmentation. A quantitative model is presented that involves a composite approach: (i) the viscoplastic deformation of the crystalline lamellae, which is controlled by chain slip and transverse slip systems on planes parallel to the c axis, and (ii) the hyperelastic deformation of the amorphous phase, which depends on the affine unfolding of statistically distributed subchains. A discussion of the influence of the CRSS values on the stress-strain curves and textures is developed by means of this model.
TL;DR: A Hadamard's experimental matrix was used to determine the main effects of 11 physico-chemical factors on malolactic activity of three Leuconostoc œnos strains and one Lactobacillus plantarum strain, and this methodology could be used for the selection of strains formalolactic starters.
Abstract: The ability of selected lactic acid bacteria to carry out malolactic fermentation depends on the level of numerous wine characteristics. A Hadamard's experimental matrix was used to determine the main effects of 11 physico-chemical factors on malolactic activity of three Leuconostoc œnos strains and one Lactobacillus plantarum strain. Ethanol had the greatest inhibitory effect on the achievement of malolactic fermentation for all Leuc. œnos strains. An inhibitory effect of the L-malic acid was also found in the operating conditions. These strains show different degrees of sensitivity to pH. One of these strains was inhibited by SO2. Malolactic activity of the Lact. plantarum strain is mainly affected by a low pH, and this strain is often less efficient than Leuc. œnos strains. This methodology could be used for the selection of strains for malolactic starters. Further work is in progress using factorial design in order to determine the interactions between influential factors.
TL;DR: In this paper, the performance of multifunctional coatings combining a nitriding treatment and physical vapour deposition was evaluated on a construction steel 35NCD16 and a hot working steel Z38CDV5-1.
Abstract: Multifunctional coatings combining a nitriding treatment and physical vapour deposition allow the performance of cutting and forging tools to be boosted, since the improved mechanical support of the coating makes them withstand higher loads. This treatment can also be used for wear parts made from construction steels to increase their fatigue and wear resistance. Hard coatings applied on nitrided layers can replace or enhance the e or γ′ layers currently used. These treatments can be made in a discontinuous mode using a dedicated equipment for the nitriding and coating treatment or in a continuous mode, i.e. directly in the coating reactor. These treatments were applied and optimized for a construction steel 35NCD16 and a hot working steel Z38CDV5-1. Coating conditions have a decisive impact on the thermal stability of the iron nitride layers. This aspect was studied in detail and several technical solutions have been identified. Finally, it will be shown that in contradiction to previous findings the coatings have only a negligible influence on the stress intensity in the nitrided zone.
TL;DR: In this article, the high-temperature mechanical behaviour of alumina-based ceramic fibres has been investigated by the comparison of a dense pure alumina fiber, a porous pure aluminifera fiber and a zirconia-reinforced dense fiber.
Abstract: The high-temperature mechanical behaviour of alumina-based ceramic fibres has been investigated by the comparison of a dense pure alumina fibre, a porous pure alumina fibre and a zirconia-reinforced dense fibre. Tensile and creep tests have been conducted up to 1300°C in air in parallel with microstructural investigations on the as-received and tested fibres. Room-temperature behaviour of the fibres is close to that of bulk materials having the same microstructure, but the fibre form allows higher failure stresses to be attained. High-temperature deformation of the three fibres is achieved by grain-boundary sliding (\(\dot \varepsilon \propto \sigma ^2 \)), and is accompanied by isotropic grain growth. The specific microstructures of each fibre induce differences in the creep threshold levels as a function of temperature and stress and also in creep rates and resistance to damage. Despite better resistance to creep and damage of the zirconia-reinforced fibre, alumina-based fibres are limited to applications below 1100°C. Grain boundaries are the principal cause of mechanical degradation at high temperature with these fibres.
TL;DR: An analysis of the problems of production scheduling in the dairy product industry where variety and sell-by-date constraints have to be taken into account using the formalization of priorities as a basis is presented in this article.
Abstract: Analyses the problems of production scheduling in the dairy product industry where variety and sell‐by date constraints have to be taken into account Using the formalization of priorities as a basis, attempts to demonstrate that a thorough understanding of the relation between a formal scheduling model and its implementation permits one to grasp the profound changes in industrial processing systems at present With this analysis new representations of possible changes can be created and the idea of a transformation of work organization based on a new form of production management can be developed