Showing papers by "Conservatoire national des arts et métiers published in 1999"
TL;DR: In this paper, the shape of the S-N curve beyond 10 7 cycles is unknown except in some statistical approaches, and this is also true for the fatigue limit, and the standard deviation applied to the average fatigue limit is certainly not the best way to reduce the risk of rupture in fatigue.
Abstract: Generally, the shape of the S-N curve beyond 10 7 cycles is unknown except in some statistical approaches, and this is also true for the fatigue limit. In the case of a statistical approach, the standard deviation applied to the average fatigue limit is certainly not the best way to reduce the risk of rupture in fatigue. Only the exploration of the life range between 10 6 and 10 10 cycles will create a safer basis for modelling. Today, some piezoelectric fatigue machines are very reliable, capable of producing 10 10 cycles in less than 1 week. We based our research on accelerated fatigue tests which were performed at 20 kHz in the gigacyclic fatigue regime in order to study several typical alloys from the aeronautical and space industries.
462 citations
TL;DR: In this paper, polythiophene (Pth) and polyparafluorophenylthiophen (PFPT) have been chemically synthesized for use as active materials in supercapacitor electrodes.
316 citations
TL;DR: In this paper, the authors determined the very long fatigue life of ferrous alloys up to 1 x 10 10 cycles at an ultrasonic frequency of 20 kHz, and a good agreement was found with the results from conventional tests at a frequency of 25 Hz by Renault between 10 5 and 10 7 cycles for a spheroidal graphite cast iron.
Abstract: The objective of this paper is to determine the very long fatigue life of ferrous alloys up to 1 x 10 10 cycles at an ultrasonic frequency of 20 kHz. A good agreement is found with the results from conventional tests at a frequency of 25 Hz by Renault between 10 5 and 10 7 cycles for a spheroidal graphite cast iron. The experimental results show that fatigue failure can occur over 10 7 cycles, and the fatigue endurance stress S max continues to decrease with increasing number of cycles to failure between 10 6 and 10 9 cycles. The evolution of the temperature of the specimen caused by the absorption of ultrasonic energy is studied. The temperature increases rapidly with increasing stress amplitudes. There is a maximum temperature between 10 6 and 10 7 cycles which may be related to the crack nucleation phase. Observations of fracture surfaces were also made by scanning electron microscopy (SEM). Subsurface cracking has been established as the initiation mechanism in ultra-high-cycle fatigue (> 10 7 cycles). A surface-subsurface transition in crack initiation location is described for the four low-alloy high-strength steels and a SG cast iron.
203 citations
TL;DR: In this article, an attempt has been made to characterize high-cycle fatigue behavior of high-strength spring steel wire by means of an ultrasonic fatigue test and analytical techniques, and the experimental results show that fatigue rupture can occur beyond 107 cycles.
Abstract: An attempt has been made to characterize high-cycle fatigue behaviour of high-strength spring steel wire by means of an ultrasonic fatigue test and analytical techniques. Two kinds of induction-tempered ultra-high-strength spring steel wire of 6.5 mm in diameter with a tensile strength of 1800 MPa were used in this investigation.
The fatigue strength of the steel wires between 106 and 109 cycles was determined at a load ratio R = −1. The experimental results show that fatigue rupture can occur beyond 107 cycles. For Cr–V spring wire, the stress–life (S–N ) curve becomes horizontal at a maximum stress of 800 MPa after 106 cycles, but the S–N curve of the Cr–Si steel continues to drop at a high number of cycles (>106 cycles) and does not exhibit a fatigue limit, which is more correctly described by a fatigue strength at a given number of cycles. By using scanning electron microscopy (SEM), the crack initiation and propagation behaviour have been examined. Experimental and analytical techniques were developed to better understand and predict high-cycle fatigue life in terms of crack initiation and propagation. The results show that the portion of fatigue life attributed to crack initiation is more than 90% in the high-cycle regime for the steels studied in this investigation.
160 citations
TL;DR: In this paper, a two-node adaptive sandwich-beam finite element is presented, capable of dealing with either extension or shear actuation mechanisms, which is reached by coating an elastic core with piezoelectric sheets or sandwiching a core between two elastic faces.
Abstract: We present the formulation and validation of a new adaptive sandwich-beam finite element, capable of dealing with either extension or shear actuation mechanisms, which is reached by coating an elastic core with piezoelectric sheets or sandwiching a piezoelectric core between two elastic faces. The poling direction is taken parallel to the transversely applied electric field for the first mechanism and in the axial direction for the second one. The sandwich construction is made of asymmetric thin faces (Euler-Bernoulli beams) and a relatively thick core (Timoshenko beam). The obtained two-node finite element has only four mechanical degrees of freedom that are the deflection and its derivative and the mean and relative axial displacements of the faces midplanes. Finite element analysis of segmented and continuous cantilever adaptive sandwich beams with active faces (extension actuated) or core (shear actuated) show good comparisons with results found in the Iiterature, Additional parametric studies (actuator's position and thickness, structure's stiffness) with the present element indicate that the shear actuation mechanism presents several promising features over the conventional extension actuation mechanism. In fact, the shear actuation mechanism is better than the extension one for stiff structures and thick piezoelectric actuators.
123 citations
TL;DR: The consumption of breakfast cereals appears to have a positive impact on nutritional status regardless of age, and serum concentrations of vitamin B1, vitamin B2 and beta-carotene were significantly linked to the level of energy provided by breakfast.
Abstract: Objective: to examine associations between the consumption of different types of breakfasts, dietary intakes, and selected indices of nutritional status.Methods: dietary intakes were obtained using the dietary history method, and serum bioassays were used to assess vitamin and mineral status in a representative community-based sample of 1108 French children (ages 2 to 10 years), adolescents (ages 10 to 18 years), and adults (ages 18 to 65 years). Breakfasts were divided into three categories: low-energy ( 25%).Results: High-energy breakfasts were associated with the consumption of ready-to-eat (RTE) cereals. High-energy breakfasts and cereal consumption, both more common among children and adolescents than among adults, were also associated with a greater proportion of daily energy from carbohydrate and lower proportion of energy from fat. High-energy breakfasts and cereal consumption were further associated with higher intakes of vitamins a...
119 citations
TL;DR: In this paper, the first results on the electrochemical behavior of an alkaline solid polymer electrolyte [based on poly(ethylene oxide), potassium hydroxide, and water] medium are presented and show good reversibility of this all-solidstate system for more than 500 cycles, without significant loss of capacity and with a reasonable average discharge efficiency (close to 80%).
Abstract: Sealed alkaline solid polymer electrolyte nickel/metal hydride laboratory cells have been constructed and tested to evaluate their properties. Studies of the cycle life, self‐discharge, and behavior of cells at different temperatures were carried out. The first results on the electrochemical behavior of an alkaline solid polymer electrolyte [based on poly(ethylene oxide), potassium hydroxide, and water] medium are presented here and show good reversibility of this all‐solid‐state system for more than 500 cycles, without significant loss of capacity and with a reasonable average discharge efficiency (close to 80%). The temperature‐dependence study allowed the deremination of optimum operating conditions berween 0 and 40°C. Characteristics of the solid polymer electrolyte based Ni/MH cells are compared to those of several other rechargeable battery systems. © 1999 The Electrochemical Society. All rights reserved.
108 citations
TL;DR: The strong association with refined cereal products is consistent with the hypothesis of a role of hyperinsulinism in colorectal carcinogenesis, and the association with processed but not fresh meat suggests the importance of exogenous carcinogenesis in that area.
Abstract: Although the high meat-low vegetable diet is considered the reference high-risk diet for colorectal cancer, particularly in USA communities, other at-risk dietary patterns, such as high intakes of processed meat and refined carbohydrates are emerging. Little is known about risk factors for colorectal cancer in France, a country at high risk of rectal cancer and moderately high risk of colon cancer. We compared diet of colorectal cancer cases (n = 171) and general population controls (n = 309) in Burgundy (France). Categories of intake were established by sex and based on the distributions of food intakes in controls. Odds ratios for the fourth vs first quartile of intake (OR4) were 2.0 (1.1-3.6) for refined cereal products (rice, pasta and pastry), 2.4 (1.3-4.5) for delicatessen, 2.3 (1.2-4.2) for pates, 1.7 (1.1-2.8) for offal and 2.1 (1.1-4.0) for butter, lard and cream. There was no association with consumption of fresh meat (OR4 = 1.2), fish (OR4 = 1.5), egg (OR4 = 1.1) or dairy products (OR4 = 1.0). A protective effect of vegetables was only observed for left colon cancer (OR3 = 0.3; 0.1-0.6). In men, the most significant risk factors were refined cereal products, seasoning animal fats, chocolate and coffee, whereas risk factors were delicatessen, fat meat, pasta, rice, and chocolate in women. The strong association with refined cereal products is consistent with the hypothesis of a role of hyperinsulinism in colorectal carcinogenesis. The association with processed but not fresh meat suggests the importance of exogenous carcinogenesis in that area.
103 citations
TL;DR: The results of experimental wind-tunnel tests are compared with simulated values for aerodynamic drag coefficient and vortex wake flows at different angles of car rear window inclination, using an Ahmed (AHMED S.R.) reference model.
Abstract: When analysing the topology of turbulent flow systems for alternative vehicle configurations, conventional wind-tunnel tests may not be sufficient. Vehicle development teams investigating this kind of physical phenomenon are increasingly interested in numerical simulation, but reliable implementation of computational techniques in automotive aerodynamics requires validation to confirm that such methods are capable of accurately reproducing experimentally proven physical behaviour. We address this issue by comparing the results of experimental wind-tunnel tests with simulated values for aerodynamic drag coefficient and vortex wake flows at different angles of car rear window inclination, using an Ahmed (AHMED S.R.) reference model.
90 citations
TL;DR: Results clearly showed that the activity and specificity of U. europaeus lectin was preserved after covalent coupling to these biodegradable carriers.
77 citations
TL;DR: In this article, the authors deal with the direct identification of the in-plane elastic properties of orthotropic composite plates from heterogeneous strain fields, where the shape of the tested specimen is that of a T subjected to a complex stress state.
Abstract: This paper deals with the direct identification of the in-plane elastic properties of orthotropic composite plates from heterogeneous strain fields. The shape of the tested specimen is that of a T subjected to a complex stress state. As a result, the entire set of unknown parameters is directly involved in the strain and displacement responses of the sample. No exact analytical solution is available for such a geometry, and a specific strategy is used to identify the different stiffness components from the whole-field displacements measured over the tested specimen with a suitable optical method. The paper focuses mainly on the experimental aspects of the procedure, and an example of mechanical characterization of a fabric-reinforced composite plate is given.
TL;DR: In this paper, results are presented from different binder compositions, such as PTFE and a mixture of CMC/PTFE, that were tested in order to increase the volumetric capacitance of the electrode.
01 Aug 1999
TL;DR: An algorithm is provided, based on Godunov scheme, with a dedicated way of dealing with boundary conditions, to numerically simulate the evolution of the nonlinear system and provide a way of checking the accuracy of the motion planning based on the tangent linear system.
Abstract: We consider a tank containing a fluid. The tank is subjected to a one-dimensional horizontal move and the motion of the fluid is described by Saint-Venant's equations. We show how to parameterize the trajectories of the linearized system thanks to the horizontal coordinate of a particular point in the system — the “flat output”, see figure 2- and a periodic function. The motion planning problem of the linearized model is solved in the general case of joining two steady states. Next we provide an algorithm, based on Godunov scheme, with a dedicated way of dealing with boundary conditions, to numerically simulate the evolution of the nonlinear system. Nonlinear simulations provide a way of checking the accuracy of the motion planning based on the tangent linear system.
TL;DR: In this paper, mixed 10-undecenoyl/phenylaminocarbonyl or benzoyl derivatives of chitosan, differently substituted in the aromatic ring, were prepared, characterized and immobilized on allylsilica gel.
TL;DR: After 2 years of supplementation, biochemical indicators of vitamin and trace element status reach reasonable level without reaching concentrations as high as those observed in intervention studies, which tested relatively high doses of antioxidants, and ended up with higher risk of pathology.
TL;DR: In this article, the photo-induced deprotonation of 7- and 8-hydroxyquinolines (7-and 8-HQ) was investigated in the presence of water molecules as acceptors.
Abstract: When the acidic and basic groups of an amphoteric compound become stronger on excitation, excited-state proton transfers (ESPT) are driven by the photoinduced synergy between the two functions. This is exemplified here by 7- and 8-hydroxyquinolines (7- and 8-HQ), whatever the initially excited form. For instance, the -OH group of the 7-hydroxyquinolinium form undergoes photoinduced deprotonation even in 8M HClO4! This reveals its outstanding photoacidity, confirmed by the value of the deprotonation rate constant k1 at infinite dilution, 5.5 × 1010 s−1. The decrease of k1 on increasing the ionic strength pointed out the key number of 4 water molecules as proton acceptors. In neutral medium, a very efficient photoinduced tautomerization is observed. For 7-HQ in water, a mechanism consisting of three competitive paths was established: A proton translocation via a bridge of water molecules within less than 10 ps for the cis-isomer, and two stepwise competitive reactions for the trans-isomer. Concerning the weakly fluorescent 8-HQ, the photoinduced tautomerization occurs even in organic media. In most solvents, an intrinsic ESPT takes place within intramolecularly H-bonded molecules, but preferential solvation by residual water of the solvent may lead to open structures where ESPT is impaired. In alkanes, a biprotonic ESPT is expected to occur within very stable dimers (Kdim= 7.0 × 107). In all cases, the coupling between proton transfers and an intramolecular electron transfer leads to the ketonic structure of the tautomer. This might be a general feature in phototautomerization reactions.
TL;DR: An evaluation of query execution plans (QEP) in the case of queries with one or two spatial joins, allowing for pipelined QEP execution, thus minimizing memory space required for intermediate results.
Abstract: We provide an evaluation of query execution plans (QEP) in the case of queries with one or two spatial joins. The QEPs assume R*-tree indexed relations and use a common set of spatial joins algorithms, among which one is a novel extension of a strategy based on an on-the-fly index creation prior to the join with another indexed relation. A common platform is used on which a set of spatial access methods and join algorithms are available. The QEPs are implemented with a general iterator-based spatial query processor, allowing for pipelined QEP execution, thus minimizing memory space required for intermediate results.
TL;DR: It is concluded that human tonsillar cells transform DHEA and EPIA, but not PREG, into 7alpha-hydroxylated metabolites which could act on target tonsilar T lymphocytes which in turn act upon B lymphocytes for increasing specific IgG production.
TL;DR: In this article, the hydroxyl group of 7-hydroxyquinoline in acidic media undergoes photoinduced deprotonation even in strongly acidic media, which is evidence of an outstanding photoacidity.
Abstract: The hydroxyl group of 7-hydroxyquinoline in acidic media (i.e., of 7-hydroxyquinolinium cation, 7-HQ(C)) undergoes photoinduced deprotonation even in strongly acidic media. It occurs from dilute perchloric acid solutions up to 8 mol L-1 concentration, which is evidence of an outstanding photoacidity. Excited-state proton ejection was shown to be reversible at acid concentrations greater than 1 mol L-1. Below this value, the proton ejection was not balanced by the proton recombination. Concerning the rates of the excited-state reactions, (i) the proton ejection rate constants k1 increased upon acid dilution, attaining at high dilution the limiting value of (k1)0 = 5.5 × 1010 s-1. k1 was shown to vary with the water activity according to k1 = (k1)0(aH2O)4. The number 4 is then a key number for the ability of water to accept a proton from 7-HQ(C*). (ii) The proton recombination rate constant varies from 3 × 109 to 4 × 1010 s-1 when the acid concentration ranges from 1 to 5 mol L-1. This observation can tenta...
TL;DR: In this paper, a comparative numerical analysis of shear and extension actuation mechanisms for bending vibrations control of sandwich beams is presented, based on Bernoulli-Euler assumptions for the surface layers and Timoshenko ones for the core.
Abstract: This paper presents a comparative numerical analysis of shear and extension actuation mechanisms for the bending vibrations control of sandwich beams. The extension actuation mechanism denotes the use of through-thickness poled piezoelectric actuators bonded on the surfaces of the structure such that, when submitted to a through-thickness applied electric potential, these actuators produce axial stresses or strains. The shear actuation mechanism, in the contrary, is obtained through an embedded longitudinally poled piezoelectric actuator that, subjected to the same electric potential, produces shear stresses or strains. Theoretical and finite element models of a sandwich beam, capable of dealing with both mechanisms, are presented. The models are based on Bernoulli-Euler assumptions for the surface layers and Timoshenko ones for the core. An optimal state feedback control law is used to maximize the damping of the first four natural modes of the sandwich beam. The influence of important parameters variati...
TL;DR: In this article, large electrodes were used to economically prepare large electrodes (32 cm2) in order to assemble mono-cell supercapacitors (100 cm3) of 250 F and reach powers in the range of 120-130 W (2 V/cell) with the structure selected.
TL;DR: In this article, a Monte-Carlo simulation based on the appropriate master equation allowed the calculation of the theoretical anisotropy decay in terms of reduced variables and parameters, showing that the chromophores are randomly oriented.
Abstract: Excitation energy transport in several β-cyclodextrins containing seven appended chromophores was studied theoretically and experimentally by steady-state and time-resolved fluorescence anisotropy. The absorption spectra compared to those of reference chromophores did not reveal significant interactions between the chromophores in the ground state, thus allowing us to assume a very weak coupling regime for energy transfer. The measured long time anisotropies were found to be in all cases close to one-seventh of the fundamental anisotropy, showing that the chromophores are randomly oriented. A realistic model in which the chromophores are in fixed positions but randomly oriented was developed to interpret the steady-state and time-resolved emission anisotropy data. A Monte-Carlo simulation based on the appropriate master equation allowed the calculation of the theoretical anisotropy decay in terms of reduced variables and parameters. The decay contains a wide spectrum of rate constants. A good fit to the e...
22 Sep 1999
TL;DR: A simple mechanism based on the specification of inclusion relationships between thesaurus terms and ontology concepts is presented and it is shown how these relationships can be exploited to create application-specific RDF schemas incorporating the structural views of ontologies and deep classification schemes provided by thesauri.
Abstract: In this paper we present a new approach for building RDF schemas by integrating existing ontologies and structured vocabularies (thesauri). We will present a simple mechanism based on the specification of inclusion relationships between thesaurus terms and ontology concepts and show how these relationships can be exploited to create application-specific RDF schemas incorporating the structural views of ontologies and deep classification schemes provided by thesauri.
TL;DR: Coagulation of Skeletonema costatum biomass was induced at alkaline pH in enriched sea-water to concentrate the microalgal suspensions by decantation and increased the yield of lipid extraction and the 20:5(n-3) fatty acid content of the diatom biomass.
Abstract: Coagulation of Skeletonema costatum biomass was induced at alkaline pH in enriched sea-water to concentrate the microalgal suspensions by decantation Incubation of the concentrated cultures at 15 °C after return at pH 75 preserved cell viability and increased the yield of lipid extraction and the 20:5(n-3) fatty acid content of the diatom biomass
TL;DR: In this article, an optical method based on deflectometry was used to measure the slope fields on the whole surface of a plate specimen under bending testing, which was measured and found to be better than 2.5×10−5 rad.
Abstract: This paper describes an optical method based on deflectometry to measure the slope fields on the whole surface of a plate specimen under bending testing. The phase-stepping procedure used provides an excellent sensitivity on the slope measurement, which was measured and found to be better than 2.5×10−5 rad. Experimental results are presented along with finite element simulations.
TL;DR: In this paper, the authors used the Hamiltonian formulation of systems to derive Lyapunov functions for forced systems with constant input and derived a stabilizing controller for the boost converter.
TL;DR: In this paper, two different ways of electrode preparation were used: spraying a liquid suspension of the electrode materials on a nickel foil, and then filtering and pressing the electrodes materials on to nickel collectors.
10 Jan 1999
TL;DR: It is proved that orthographic dimension preserving Boolean combination of conjunctive queries can be evaluated independently of the global dimension, with operators limited to the Orthographic dimension, in parallel on the components.
Abstract: One of the most important advantages of constraint databases is their ability to represent and to manipulate data in arbitrary dimension within a uniform framework. Although the complexity of querying such databases by standard means such as first-order queries has been shown to be tractable for reasonable constraints (e.g. polynomial), it depends badly (roughly speaking exponentially) upon the dimension of the data. A precise analysis of the trade-off between the dimension of the input data and the complexity of the queries reveals that the complexity strongly depends upon the use the input makes of its dimensions. We introduce the concept of orthographic dimension, which, for a convex object O, corresponds to the dimension of the (component) objects O1; ..., On, such that O = O1 × ... × On. We study properties of databases with bounded orthographic dimension in a general setting of o-minimal structures, and provide a syntactic characterization of first-order orthographic dimension preserving queries.
The main result of the paper concerns linear constraint databases. We prove that orthographic dimension preserving Boolean combination of conjunctive queries can be evaluated independently of the global dimension, with operators limited to the orthographic dimension, in parallel on the components. This results in an extremely efficient optimization mechanism, very easy to use in practical applications.
TL;DR: In this article, the behavior of different exogenous enzymes (soybean lipoxygenase [SLOX], horseradish peroxidase [HPOD], catalase from bovine liver [BCAT], and glucose oxidase [GOX] from Aspergillus niger) added to dough was studied during mixing.
Abstract: The behavior of different exogenous enzymes (soybean lipoxygenase [SLOX], horseradish peroxidase [HPOD], catalase from bovine liver [BCAT], and glucose oxidase [GOX] from Aspergillus niger) added to dough was studied during mixing. The effect of adding these exogenous oxidoreductases on the activity of three oxidative enzymes present in wheat flour (lipoxygenase [WLOX], peroxidase [WPOD], and catalase [WCAT]) was examined. Proper assay conditions were established to differentiate between added WLOX, WPOD, and WCAT and the corresponding activities present in wheat flour. For doughs with added SLOX, an immediate loss of extractable SLOX (≈40%) was observed which remained constant during further mixing. When compared with the control dough, addition of SLOX decreased the losses in WLOX and WCAT activities, whereas WPOD activity was unaffected. With doughs supplemented by HPOD, an immediate loss of 20% in the HPOD activity was observed which did not change after 20 min of mixing. Compared with contro...
TL;DR: Bonded polysaccharide-derived chiral stationary phases were found to be useful for the preparation of the four stereoisomers of the cyclopropane analogue of phenylalanine (c(3)Phe) as well as for the direct determination of the enantiomeric purity of c(3]Phe derivatives by HPLC.