Showing papers by "Mines ParisTech published in 2000"

Alpha emission and spontaneous fission through quasi-molecular shapes

Abstract: The potential energy governing α emission has been determined within a liquid drop model including proximity effects between the α particle and the daughter nucleus and adjusted to reproduce the experimental Qα. The α emission half-lives have been deduced from the WKB barrier penetration probability as for a spontaneous asymmetric fission. The RMS deviation between the theoretical and experimental values of log 10[T1/2(s)] is only 0.63 for a recent data set of 373 α emitters and 0.35 for the subset of even-even nuclides. Predictions for the heaviest and superheavy elements are presented as well as simple analytical formulae for log 10[T1/2(s)].

A smooth Lyapunov function from a class- ${\mathcal{KL}}$ estimate involving two positive semidefinite functions

Abstract: We consider dierential inclusions where a positive semidenite function of the solutions satises a class-KL estimate in terms of time and a second positive semidenite function of the initial condition. We show that a smooth converse Lyapunov function, i.e., one whose derivative along solutions can be used to establish the class-KL estimate, exists if and only if the class-KL estimate is robust, i.e., it holds for a larger, perturbed dierential inclusion. It remains an open question whether all class-KL estimates are robust. One sucient condition for robustness is that the original dierential inclusion is locally Lipschitz. Another sucient condition is that the two positive semidenite functions agree and a backward completability condition holds. These special cases unify and generalize many results on converse Lyapunov theorems for dierential equations and dierential inclusions that have appeared in the literature.

Palladium sorption on glutaraldehyde-crosslinked chitosan

Abstract: The high nitrogen content of chitosan is the main reason for its ability to sorb metal ions through several mechanisms including ion-exchange or chelation, depending on the metal and the pH of the solution. Glutaraldehyde is used to crosslink chitosan through imine linkage between amine groups of chitosan and aldehyde groups of the crosslinking agent. This modified biosorbent was studied for palladium recovery in acidic medium (around pH 2). The influence of several parameters such as pH and competitor anions were studied with respect to sorption equilibrium. Sorption isotherms were obtained and modeled using the Langmuir and the Freundlich model. This study also examines the effect of palladium concentration, particle size, sorbent dosage, and the extent of crosslinking on sorption kinetics. Kinetic curves are modeled using single diffusion model equations to evaluate the predominance of either external or intraparticle mass transfer resistance. The influence of the acid used to control the pH of the solution was examined in conjunction with the influence of competitor anions. Sulfuric acid proves to be unfavorable to palladium sorption, in comparison with hydrochloric acid. However, the addition of chloride anions in a palladium solution, whose pH is controlled with sulfuric acid, enhances metal anion sorption: results are interpreted with reference to chloropalladate speciation.

Motion planning for the heat equation

Abstract: SUMMARYThe paper gives an explicit open-loop control, able to approximately steer the one-dimensional heatequationwith control onthe boundaryfromanystate to any otherstate. The controlisobtained thankstoaparametrizationofthesolutionsoftheheatequationbyaseriesinvolvingin"nitelymanyderivativesofthesystem &#at output’. Copyright ( 2000 John Wiley & Sons, Ltd. KEY WORDS : heat equation; boundary control; motion planning; #atness; Gevrey functions; approximatecontrollability 1. INTRODUCTIONMotion planning, i.e. the construction of an open-loop control connecting an initial state toa "nal state, is a fundamental problem of control theory both from a practical and theoreticalpointofview.Forsystemsgovernedby ordinary di!erentialequationsthenotionof- atness [1,2]providesaconstructivesolutiontothisproblem.AsnoticedinReference[2],theideaunderlyingequivalence and #atness*the existence of a one-to-one correspondence between trajectories ofsystems*can be adapted to partial di!erential equations [3}5] with boundary control.In this paper, which develops ideas introduced in [2, 6], we study in this spirit the heat equationwithonespacedimension and controlontheboundary.Wegive anexplicitparametrizationofthetrajectoriesasapower series inthespacevariablewithcoe $cients involvingtimederivatives ofthe&#at’ output. This series is convergent when the #atoutput is restricted to be a Gevrey function (i.e.asmoothfunctionwitha¬ too divergent’ Taylor expansion). This parameterization

Low-temperature plasma-assisted nitriding

Abstract: Plasma-assisted nitriding is an attractive surface treatment for metallurgical surface modification to improve wear, hardness and fatigue resistance of ferrous and non-ferrous materials. For this purpose, ion nitriding by a d.c. glow discharge is generally efficient for numerous materials. However, for some metals and alloys, the processing temperature, dominated by the discharge parameters, is too high and cannot be controlled independently from the plasma reactivity. This paper reviews the following solutions for low-temperature plasma-assisted nitriding: pulsed d.c. discharge, thermionically assisted d.c. triode arrangements, plasma implantation, electron cyclotron resonance systems and thermionic arc discharges. We focus on metallurgical results obtained by these techniques on austenitic stainless steel and aluminium.

Rapid on-line sampler-injector : a reliable tool for HT-HP sampling and on-line GC analysis

Abstract: Withdrawing of representative and reliable microsamples down to 1/100th mg is far from trivial, especially for extreme conditions such as high temperature and high pressure conditions or very corrosive media. The new Rapid On-Line Sampler- Injector presented herein was designed and set-up to largely extend sampling capabilities in hazardous media. It is largely use d in our laboratory to measure vapour-liquid equilibria. It has a lot of applications, both in production (process control in pet ro- leum, chemical, nuclear plants, etc.) and academic and industrial researches and development (laboratory instruments, pilot plants…).

Mechanical properties and non-homogeneous deformation of open-cell nickel foams: application of the mechanics of cellular solids and of porous materials

Abstract: The mechanical properties of open-cell nickel foams are investigated for the range of densities used in industrial applications for energy storage. The obtained Young’s modulus, compression yield stress and tensile fracture stress are compared to the predictions of models based on periodic, Penrose and Voronoi beam networks. It is found that Gibson and Ashby’s model [L.J. Gibson, M.F. Ashby, Cellular Solids, Cambridge University Press, Cambridge, 1998] provides the proper scaling laws with respect to relative density for almost all investigated properties. The strong anisotropy of the observed overall responses can also be accounted for. The two-dimensional strain field during the tension of a nickel foam strip has been measured using a photomechanical technique. Non-homogeneous deformation patterns are shown to arise. The same technique is used to obtain the strain field around a circular hole in a nickel foam strip. The observed deformation fields are compared to the results of a finite element analysis using anisotropic compressible continuum plasticity.

Interstitial glucose concentration and glycemia: implications for continuous subcutaneous glucose monitoring.

Abstract: The changes in plasma glucose concentration and in interstitial glucose concentration, determined with a miniaturized subcutaneous glucose sensor, were investigated in anesthetized nondiabetic rats. Interstitial glucose was estimated through two different calibration procedures. First, after a glucose load, the magnitude of the increase in interstitial glucose, estimated through a one-point calibration procedure, was 70% of that in plasma glucose. We propose that this is due to the effect of endogenous insulin on peripheral glucose uptake. Second, during the spontaneous secondary decrease in plasma glucose after the glucose load, interstitial glucose decreased faster than plasma glucose, which may also be due to the effect of insulin on peripheral glucose uptake. Third, during insulin-induced hypoglycemia, the decrease in interstitial glucose was less marked than that of plasma glucose, suggesting that hypoglycemia suppressed transfer of glucose into the interstitial tissue; subsequently, interstitial glucose remained lower than plasma glucose during its return to basal value, suggesting that the stimulatory effect of insulin on peripheral glucose uptake was protracted. If these observations obtained in rats are relevant to human physiology, such discrepancies between plasma and interstitial glucose concentration may have major implications for the use of a subcutaneous glucose sensor in continuous blood glucose monitoring in diabetic patients.

New prospects from potential applications of quasicrystalline materials

Abstract: Since 1984, several quasicrystalline materials were selected for possible technological applications as coatings and composites. A few examples of products derived from such materials are now on the market. The aim of this review is along several key points raised by the technological prospects of quasicrystals, namely composition tailoring and industrial processing of thick coatings, surface preparation and properties, and new potential applications.

Incremental Mining of Sequential Patterns in Large Databases.

Abstract: In this paper, we consider the problem of the incremental mining of sequential patterns when new transactions or new customers are added to an original database. We present a new algorithm for mining frequent sequences that uses information collected during an earlier mining process to cut down the cost of finding new sequential patterns in the updated database. Our test shows that the algorithm performs significantly faster than the naive approach of mining the whole updated database from scratch. The difference is so pronounced that this algorithm could also be useful for mining sequential patterns, since in many cases it is faster to apply our algorithm than to mine sequential patterns using a standard algorithm, by breaking down the database into an original database plus an increment.

Fine diameter ceramic fibres

Abstract: Two families of small diameter ceramic fibres exist. The oxide fibres, based on alumina and silica, which were initially produced as refractory insulation have also found use as reinforcements for light metal alloys. The production of SiC based fibres made possible the development of ceramic matrix composites. Improved understanding of the mechanisms which control the high temperature behaviour of these latter fibres has led to their evolution towards a near stoichiometric composition which results in strength retention at higher temperatures and lower creep rates. The SiC fibres will however be ultimately limited by oxidation so that there is an increasing interest in complex two phase oxide fibres composed of α-alumina and mullite as candidates for the reinforcement of ceramic matrices for use at very high temperatures. These fibres show low creep rates, comparable to the SiC based fibres but are revealed to be sensitive to alkaline contamination.

Le Guide rouge Michelin

Abstract: A guidebook serves the economics of quality in markets where what is traded is quite singular, and where goods and services cannot be fully compared. It provides a meeting-place for supply and demand and also, redefines consumers and producers. The red guidebook, which has served as the bible for travelers and gastronomes –and which is now celebrating its hundredth birthday – has assumed three forms over time. These forms differ owing to both the object of transactions and the way they ‘regulate’ the market. Focused on interchangeable technical goods, the ‘technical’ one (1900–1908) was intended for a neoclassical market; it was not a guidebook. The ‘tourist’ one (1909–1933), which concentrated on ‘cultural objects’, and the ‘gastronomic’ one (1934–1998), which focuses on restaurants and on cultural products, both establish a quality market, despite their differing methods. Without these two guidebooks (or their equivalents), these two variants of the quality market would not have been able to take shape or last.

Can we quantitatively image complex structures with rays

Abstract: Ray‐based prestack depth migration fails to image quantitatively complex structures when a single arrival—for example, the first or the strongest one—is taken into account. In this paper, we investigate whether accounting for multiple arrivals in ray‐based preserved amplitude prestack depth migration allows one to improve quantitative imaging of complex media. The asymptotic ray‐Born migration/inversion, originally designed to process one single arrival, is extended to the case of multiple arrivals by accounting for the cross‐contributions of all the source and receiver raypaths. Multiple arrivals in the folded ray fields are computed by a dynamic ray tracing based on a wavefront construction technique. With an application to the complex Marmousi model, we demonstrate that ray‐Born inversion can provide a reliable quantitative estimation of the relative impedance perturbation even in the complex deep part of the model, for which the amplitudes were underestimated drastically when only a single arrival was...

Magnesium hydroxide/zinc borate/talc compositions as flame-retardants in EVA copolymer

Abstract: The fire-resistance of EVA filled with ternary systems (magnesium hydroxide/zinc borate/ talc) has been investigated. The release of water from Mg(OH) 2 seemed to be the predominant phenomenon which acts in relation to fire-resistance. The presence of talc as a minor component, mainly in binary compositions by partial substitution of Mg(OH) 2 , appeared to enhance the flame-retardant properties. It acts by forming a diffusion barrier which is able to limit the transfer of degradation products and oxygen. Synergism was also noticed between talc and zinc borate at constant Mg(OH) 2 loading in ternary compositions.

Shear-induced crystallization of polypropylene : Influence of molecular weight

Abstract: Three series of isotactic polypropylene characterized by different molecular weights and the same isotactic index have been studied during crystallization under static and shearing conditions. The shear is induced by the displacement of a glass fiber in the molten polymer. The monoclinic α-phase is here formed under shear with a columnar organization at the surface of the glass fiber, and does not appear under static condition. The growth-rate, constant during the shear-induced crystallization experiment, is compared with the result obtained from static crystallization. An important increase of the growth-rate due to the shear flow is observed. This increase depends on the molecular structure. The average molecular weights ―Mw and ―Mz seem to be the most important molecular parameters, for which an excellent correlation is obtained. The increase of these parameters ―Mw and ―Mz leads to a significant enhancement of the growth-rate, which can be multiplied by a factor of 10 in the present conditions.

Synthesis and characterization of a thiourea derivative of chitosan for platinum recovery

Abstract: Chitosan is effective at removing platinum from dilute solutions, but sorption properties are significantly affected by the presence of competitor anions, such as chloride and, especially, sulfate anions. Sorption capacities in such complex solutions are enhanced by grafting thiourea through glutaraldehyde linkage. The influence of the amount of glutaraldehyde and thiourea in the impregnation bath was investigated and optimized with special attention to the composition of the solution and the type of acid used for pH control. This modification involves a change in the sorption mechanism: While glutaraldehyde-crosslinked chitosan adsorbs platinum through an ion-exchange mechanism, the thiourea derivative of chitosan acts as a chelating resin, less sensitive to ionic strength and competitor anions. Platinum sorption is also less sensitive to pH, and increasing the sulfate anion concentration has a limited effect on platinum sorption in comparison with the crosslinked sorbent. Thiourea grafting seems to increase sorption kinetics, especially in solutions controlled with sulfuric acid. SEM–EDAX techniques as well as FTIR analyses were used to characterize chemical modifications of the sorbent. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 119–134, 2000

Random texture models for material structures

Abstract: We consider the construction and properties of some basic random structure models (point processes, random sets and random function models) for the description and for the simulation of heterogeneous materials. They can be specialized to three dimensional Euclidean space. Their implementation requires the use of image analysis tools.

A fast algorithm for the estimation of the equivalent hydraulic conductivity of heterogeneous media

Abstract: Fast upscaling of hydraulic conductivity is a recurrent problem in modeling flow through heterogeneous porous media. We propose a new renormalization technique. It is based on the iterative application of the Cardwell and Parsons (1945) bounds on elementary groups of cells. The combination of the bounds with a heuristic formula allows anisotropy to be taken into account. The new technique is tested and compared with other fast techniques. Among the tested techniques the two most reliable ones are the tensorial renormalization and the new simplified renormalization. The numerical efficiency of the simplified renormalization leads us to recommend it when a diagonal tensor of equivalent conductivity is sufficient.

Connections for sets and functions

Abstract: Classically, connectivity is a topological notion for sets, often introduced by means of arcs. An algebraic definition, called connection, has been proposed by Serra to extend the notion of connectivity to complete sup-generated lattices. A connection turns out to be characterized by a family of openings parameterized by the sup-generators, which partition each element of the lattice into maximal components. Starting from a first connection, several others may be constructed; e.g., by applying dilations. The present paper applies this theory to numerical functions. Every connection leads to segmenting the support of the function under study into regions. Inside each region, the function is r-continuous, for a modulus of continuity r given a priori, and characteristic of the connection. However, the segmentation is not unique, and may be particularized by other considerations (self-duality, large or low number of point components, etc.). These variants are introduced by means of examples for three different connections: flat zone connections, jump connections, and smooth path connections. They turn out to provide remarkable segmentations, depending only on a few parameters. In the last section, some morphological filters are described, based on flat zone connections, namely openings by reconstruction, flattenings and levelings.