Showing papers by "Mines ParisTech published in 2004"

Correlations between the calculated stacking fault energy and the plasticity mechanisms in Fe–Mn–C alloys

Abstract: A model is proposed for the evaluation of the stacking fault energy (SFE) in Fe–Mn–C austenitic alloys, at different temperatures. It accounts for the variation of the Gibbs energy of each element during the austenite to e martensite transformation, plus their interactions. The Gibbs energy due to the antiferromagnetic to paramagnetic transition is also taken into account. The required data have been obtained from the literature. The result shows a decrease of the SFE with temperature, with a saturation below the austenite Neel temperature. The result agrees with the mechanical and thermal martensitic transformation limits proposed by Schumann. The plasticity mechanisms depend on the SFE. The mechanical martensitic transformation occurs below 18 mJ/m 2 , and twinning between 12 and 35 mJ/m 2 , in agreement with the tensile tests and the deformation microstructures observed in an Fe–22 wt.% Mn–0.6 wt.% C alloy at 77, 293 and 693 K.

A physical model of the twinning-induced plasticity effect in a high manganese austenitic steel

Abstract: The steel Fe–22 wt.% Mn–0.6 wt.% C exhibits a low stacking fault energy (SFE) at room temperature. This rather low value promotes mechanical twinning along with strain which is in competition with dislocation gliding, the so called twinning-induced plasticity effect. The proposed modeling of the mechanical behavior introduces the formation of mechanical microtwins in a viscoplasticity framework based on dislocation glide at the mesoscopic scale in the case of a simple tensile test. The important parameter is the mean free path of the dislocations between twins, whose reduction explains the high hardening rate (by a dynamical Hall–Petch-like effect). It takes into account the typical organization of microtwins observed in electron microscopy (geometrical organization by using a twin-slip intersection matrix). To take into account the polycrystalline disorder, the macroscopic flow stress is calculated by assuming that the deformation work is equal in each grain for each strain step. This model gives an intermediate rule between Taylor and Sachs approximations and is simpler to compute than self-consistent methods. The parameters for gliding are first fitted on results at intermediate temperatures (without twinning), and the whole modeling is then correlated at room temperature. The simulated results (microstructure and mechanical properties) are in good agreement with experience.

Protein homology detection using string alignment kernels

Abstract: Motivation: Remote homology detection between protein sequences is a central problem in computational biology. Discriminative methods involving support vector machines (SVMs) are currently the most effective methods for the problem of superfamily recognition in the Structural Classification Of Proteins (SCOP) database. The performance of SVMs depends critically on the kernel function used to quantify the similarity between sequences. Results: We propose new kernels for strings adapted to biological sequences, which we call local alignment kernels. These kernels measure the similarity between two sequences by summing up scores obtained from local alignments with gaps of the sequences. When tested in combination with SVM on their ability to recognize SCOP superfamilies on a benchmark dataset, the new kernels outperform state-of-the-art methods for remote homology detection. Availability: Software and data available upon request.

A strict Lyapunov function for boundary control of hyperbolic systems of conservation laws

Abstract: We present a strict Lyapunov function for hyperbolic systems of conservation laws that can be diagonalized with Riemann invariants. The time derivative of this Lyapunov function can be made strictly negative definite by an appropriate choice of the boundary conditions. It is shown that the derived boundary control allows to guarantee the local convergence of the state towards a desired set point. Furthermore, the control can be implemented as a feedback of the state only measured at the boundaries. The control design method is illustrated with an hydraulic application, namely the level and flow regulation in an horizontal open channel

Mechanisms and modeling of cleavage fracture in simulated heat-affected zone microstructures of a high-strength low alloy steel

Abstract: The effect of the welding cycle on the fracture toughness properties of high-strength low alloy (HSLA) steels is examined by means of thermal simulation of heat-affected zone (HAZ) microstructures. Tensile tests on notched bars and fracture toughness tests at various temperatures are performed together with fracture surface observations and cross-sectional analyses. The influence of martensite-austenite (M-A) constituents and of “crystallographic” bainite packets on cleavage fracture micromechanisms is, thus, evidenced as a function of temperature. Three weakest-link probabilistic models (the “Master-curve” (MC) approach, the Beremin model, and a “double-barrier” (DB) model) are applied to account for the ductile-to-brittle transition (DBT) fracture toughness curve. Some analogy, but also differences, are found between the MC approach and the Beremin model. The DB model, having nonfitted, physically based scatter parameters, is applied to the martensite-containing HAZ microstructures and gives promising results.

Globalized Nelder–Mead method for engineering optimization

Abstract: One of the fundamental difficulties in engineering design is the multiplicity of local solutions. This has triggered great efforts to develop global search algorithms. Globality, however, often has a prohibitively high numerical cost for real problems. A fixed cost local search, which sequentially becomes global is developed. Globalization is achieved by probabilistic restart. A spatial probability of starting a local search is built based on past searches. An improved Nelder-Mead algorithm makes the local optimizer. It accounts for variable bounds. It is additionally made more robust by reinitializing degenerated simplexes. The resulting method, called Globalized Bounded Nelder-Mead (GBNM) algorithm, is particularly adapted to tackle multimodal, discontinuous optimization problems, for which it is uncertain that a global optimization can be afforded. Different strategies for restarting the local search are discussed. Numerical experiments are given on analytical test functions and composite laminate design problems. The GBNM method compares favorably to an evolutionary algorithm, both in terms of numerical cost and accuracy.

Protein network inference from multiple genomic data: a supervised approach

Abstract: Motivation: An increasing number of observations support the hypothesis that most biological functions involve the interactions between many proteins, and that the complexity of living systems arises as a result of such interactions. In this context, the problem of inferring a global protein network for a given organism, using all available genomic data about the organism, is quickly becoming one of the main challenges in current computational biology. Results: This paper presents a new method to infer protein networks from multiple types of genomic data. Based on a variant of kernel canonical correlation analysis, its originality is in the formalization of the protein network inference problem as a supervised learning problem, and in the integration of heterogeneous genomic data within this framework. We present promising results on the prediction of the protein network for the yeast Saccharomyces cerevisiae from four types of widely available data: gene expressions, protein interactions measured by yeast two-hybrid systems, protein localizations in the cell and protein phylogenetic profiles. The method is shown to outperform other unsupervised protein network inference methods. We finally conduct a comprehensive prediction of the protein network for all proteins of the yeast, which enables us to propose protein candidates for missing enzymes in a biosynthesis pathway. Availability: Softwares are available upon request.

Extensions of marginalized graph kernels

Abstract: Positive definite kernels between labeled graphs have recently been proposed. They enable the application of kernel methods, such as support vector machines, to the analysis and classification of graphs, for example, chemical compounds. These graph kernels are obtained by marginalizing a kernel between paths with respect to a random walk model on the graph vertices along the edges. We propose two extensions of these graph kernels, with the double goal to reduce their computation time and increase their relevance as measure of similarity between graphs. First, we propose to modify the label of each vertex by automatically adding information about its environment with the use of the Morgan algorithm. Second, we suggest a modification of the random walk model to prevent the walk from coming back to a vertex that was just visited. These extensions are then tested on benchmark experiments of chemical compounds classification, with promising results.

Gino’s lesson on humanity: genetics, mutual entanglements and the sociologist’s role

Abstract: The identification of the genes responsible for certain serious diseases and the development of tests for identifying carriers of those genes help to put the individuals concerned in the forefront of ethical decisions. These decisions are unavoidable, especially when available knowledge and techniques have already been broadly disseminated. This article presents the case of a limb-girdle muscular dystrophy patient in Reunion Island who refuses to comprehend the lessons of genetics and to become part of the medical and associative networks that implement and diffuse that knowledge. His refusal is interpreted as the rejection of a form of agency and subjectivity, in which the individual is considered as an autonomous subject forced to choose between a number of pre-established options and responsible for the consequences of his choices. Using definitions of humanity and morality presented by Francois Jullien in his commentary on Mencius, the authors propose to consider that, by refusing, the patient is opti...

Investigation of porosity and permeability effects from microstructure changes during limestone dissolution

Abstract: We studied experimentally the dissolution of a porous limestone core during CO2-enriched water injection. We measured the changes in porosity and permeability arising from modifications of the pore network geometry and the fluid-rock interface. A methodology based on periodic X-ray microtomography imaging was implemented to record the evolution of the time- and scale-dependent microstructures with a spatial resolution of 4.91 μm. Two processes were successively involved in the rapid permeability increase of the sample, as documented from microscale to core-scale measurements...

Metal anion sorption on chitosan and derivative materials: a strategy for polymer modification and optimum use

Abstract: The affinity of chitosan for several metal anions (molybdate, vanadate, arsenate, chloro-platinate and chloro-palladate) was investigated with the objective of identifying the controlling parameters (related to intrinsic polymer properties, diffusion properties and the properties of the metal in solution). Better understanding of sorption mechanisms and controlling steps may help not only in optimizing the use of these biosorbents but also in designing new chitosan-based sorbents. Some examples of physical modification (gel bead conditioning) and chemical modification (grafting of polyethyleneimine, sulfur compounds, impregnation with metal ions) are given to illustrate the versatility of the polymer and its promising performances for the recovery of toxic and/or valuable metal anions.

Modeling of mechanical twinning in a high manganese content austenitic steel

Abstract: We propose a 2D simulation of the formation of twins, in correlation with their microstructure observed in a Fe–22 wt.% Mn–0.6 wt.% C austenitic steel deformed at room temperature. TEM observations show that microtwins of a few tens of nanometer thick develop in between grain and twin boundaries, and are stored into stacks of a few tenth of micron wide. We first use a model of the emission of an isolated microtwin, based on the critical stress required to develop successive Shockley dislocation loops along parallel slip planes. As the first loop drags a stacking fault, while the following ones only thicken it, when the critical stress is reached, several dislocations are emitted until the backstress shuts down the source at the equilibrium state. After, the twin thickens stably with the increase of the applied stress. The same model is reproduced to simulate numerically the simultaneous formation of interacting microtwins in a stack. We give a general law correlating the average thickness of the twins with the stacking fault energy, their length, their number and their distance. The thickness is a key parameter in our physically based model presented during this congress.

Effect of substitutions and defects in half-Heusler FeVSb studied by electron transport measurements and KKR-CPA electronic structure calculations

Abstract: The structural and electron transport properties of the pure and $\mathrm{Co}\text{\ensuremath{-}}$, $\mathrm{Ti}\text{\ensuremath{-}},$ and $\mathrm{Zr}\text{\ensuremath{-}}$substituted $\mathrm{FeVSb}$ half-Heusler phases have been investigated using x-ray diffraction, M\"ossbauer spectroscopy, and Electron Probe Microscopy Analysis as well as resistivity, thermopower, and Hall effect measurements in the $80--900\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ temperature range. In a parallel study, the electronic structures of $\mathrm{FeVSb}$ and the aforementioned alloys were calculated using the Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA) in the LDA framework. The electronic densities of states and dispersion curves were obtained. The crystal structure stability and site preference analysis were addressed using total energy computations. Most of these experimental results correspond to electronic structure computations only if they take into account extra crystal defects such as antisite defects or vacancies present to various extents in the samples. Indeed a remarkable variation of KKR-CPA density of states occurring both in $\mathrm{FeVSb}$ and ${\mathrm{FeV}}_{1\ensuremath{-}x}{\mathrm{Zr}}_{x}\mathrm{Sb}$ including defects may explain why $\mathrm{FeVSb}$ is not fully semiconducting as well as why there is a change of the thermopower sign in the ${\mathrm{FeV}}_{1\ensuremath{-}x}{\mathrm{Zr}}_{x}\mathrm{Sb}$ versus $\mathrm{x}$ content.

Generalization of the strategies in differential evolution

Abstract: Summary form only given. Differential evolution, is a recently invented global optimization algorithm. Originally proposed as a method for the global continuous optimization differential evolution has been easily modified for handling mixed (continuous and discrete) variables. In order to have a better choice of the differentiation's formula, we introduce a generalization of the differential evolution's strategies. This is done by dividing them into four groups according to their differentiation principle. Such approach leads us to the new universal formula of differentiation. Some examples of strategies are demonstrated and compared on the De Jong test functions.

Biosorption of palladium and platinum by sulfate‐reducing bacteria

Abstract: The biosorption capacities of palladium and platinum were studied in three different species of Desulfovibrio: Desulfovibrio desulfuricans, Desulfovibrio fructosivorans and Desulfovibrio vulgaris. The influence of several parameters such as pH, acidic background and competitor anions on biosorption equilibria and biosorption kinetics were evaluated. Differences were observed between the three strains of Desulfovibrio with respect to the optimum biosorption parameters of both metals, suggesting differences in the metal speciation–dependent sorption mechanisms involved. The most promising Pd and Pt biosorption results were obtained using D desulfuricans with rapid achievement of equilibrium (90% of total sorption was achieved in 5–15 min) and a maximum value of 190 mg g−1 dry biomass and 90 mg g−1 dry biomass for Pd and Pt accumulation respectively, at pH 3. Copyright © 2003 Society of Chemical Industry

Preparation of polyurethane-based aerogels and xerogels for thermal superinsulation

Abstract: Previous work has demonstrated the feasibility of synthesizing low-density polyurethane- and polyisocyanurate-based aerogels that exhibit low effective thermal conductivity. On the basis of this literature, the present study synthesized and characterized nanostructured polyurethane aerogel-like materials processed via subcritical drying routes. Two families of polyurethane gels were studied. Wet gels were synthesized with two polyols of different functionality. The influence of the composition of the reaction media is discussed. Depending on the solubility of the precursors, macroporous foam-like or mesoporous aerogel-like materials can be obtained as observed by scanning electron microscopy coupled with mercury porosimetry. Prior to drying, specific washing steps were performed. Preliminary results obtained by evaporative and freeze-drying were then compared to reference aerogel materials dried through a direct supercritical route. Only a slight density increase was observed. Effective thermal conductivities were also measured and discussed.

From rifting to spreading in the eastern Gulf of Aden: a geophysical survey of a young oceanic basin from margin to margin

Abstract: A geophysical survey in the eastern Gulf of Aden, between the Alula–Fartak (52°E) and the Socotra (55°E) transform faults, was carried out during the Encens–Sheba cruise. The conjugate margins of the Gulf are steep, narrow and asymmetric. Asymmetry of the rifting process is highlighted by the conjugate margins (horst and graben in the north and deep basin in the south). Two transfer fault zones separate the margins into three segments, whereas the present-day Sheba Ridge is divided into two segments by a transform discontinuity. Therefore segmentation of the Sheba Ridge and that of the conjugate margins did coincide during the early stages of oceanic spreading. Extensive magma production is evidenced in the central part of the western segment. Anomaly 5d was identified in the northern and southern parts of the oceanic basin, thus confirming that seafloor spreading in this part of Gulf of Aden started at least 17.6 Ma ago.