Showing papers by "ParisTech published in 2007"

The fungal dimension of biological invasions

Abstract: Fungi represent an essential component of biodiversity, not only because of the large number of species, but also for their ecological, evolutionary and socio-economic significance. Yet, until recently, fungi received scant consideration in ecology, especially invasion ecology. Their under-representation is largely the result of a lack of scientific knowledge of fungal biodiversity and ecology. With the exception of pathogenic fungi, which cause emergent infectious diseases, the impact of fungal invasions is often difficult to quantify owing to limited baseline data on fungal communities. Here, we aim to raise awareness among mycologists and ecologists of the fungal dimension of invasions and of the need to intensify research in fungal ecology to address issues of future introductions.

Both caffeoyl Coenzyme A 3-O-methyltransferase 1 and caffeic acid O-methyltransferase 1 are involved in redundant functions for lignin, flavonoids and sinapoyl malate biosynthesis in Arabidopsis

Abstract: Two methylation steps are necessary for the biosynthesis of monolignols, the lignin precursors. Caffeic acid O-methyltransferase (COMT) O-methylates at the C5 position of the phenolic ring. COMT is responsible for the biosynthesis of sinapyl alcohol, the precursor of syringyl lignin units. The O-methylation at the C3 position of the phenolic ring involves the Caffeoyl CoA 3-O-methyltransferase (CCoAOMT). The CCoAOMT 1 gene (At4g34050) is believed to encode the enzyme responsible for the first O-methylation in Arabidopsis thaliana. A CCoAOMT1 promoter-GUS fusion and immunolocalization experiments revealed that this gene is strongly and exclusively expressed in the vascular tissues of stems and roots. An Arabidopsis T-DNA null mutant named ccomt 1 was identified and characterised. The mutant stems are slightly smaller than wild-type stems in short-day growth conditions and has collapsed xylem elements. The lignin content of the stem is low and the S/G ratio is high mainly due to fewer G units. These results suggest that this O-methyltransferase is involved in G-unit biosynthesis but does not act alone to perform this step in monolignol biosynthesis. To determine which O-methyltransferase assists CCoAOMT 1, a comt 1 ccomt1 double mutant was generated and studied. The development of comt 1 ccomt1 is arrested at the plantlet stage in our growth conditions. Lignins of these plantlets are mainly composed of p-hydroxyphenyl units. Moreover, the double mutant does not synthesize sinapoyl malate, a soluble phenolic. These results suggest that CCoAOMT 1 and COMT 1 act together to methylate the C3 position of the phenolic ring of monolignols in Arabidopsis. In addition, they are both involved in the formation of sinapoyl malate and isorhamnetin.

Cortical Surface Shape Analysis Based on Spherical Wavelets

Abstract: In vivo quantification of neuroanatomical shape variations is possible due to recent advances in medical imaging and has proven useful in the study of neuropathology and neurodevelopment. In this paper, we apply a spherical wavelet transformation to extract shape features of cortical surfaces reconstructed from magnetic resonance images (MRIs) of a set of subjects. The spherical wavelet transformation can characterize the underlying functions in a local fashion in both space and frequency, in contrast to spherical harmonics that have a global basis set. We perform principal component analysis (PCA) on these wavelet shape features to study patterns of shape variation within normal population from coarse to fine resolution. In addition, we study the development of cortical folding in newborns using the Gompertz model in the wavelet domain, which allows us to characterize the order of development of large-scale and finer folding patterns independently. Given a limited amount of training data, we use a regularization framework to estimate the parameters of the Gompertz model to improve the prediction performance on new data. We develop an efficient method to estimate this regularized Gompertz model based on the Broyden-Fletcher-Goldfarb-Shannon (BFGS) approximation. Promising results are presented using both PCA and the folding development model in the wavelet domain. The cortical folding development model provides quantitative anatomic information regarding macroscopic cortical folding development and may be of potential use as a biomarker for early diagnosis of neurologic deficits in newborns

Ensemble averaging stress–strain fields in polycrystalline aggregates with a constrained surface microstructure – Part 2: crystal plasticity

Abstract: The effect of three-dimensional (3D) grain morphology on the deformation at a free surface in polycrystalline aggregates is investigated by means of a large-scale finite element and statistical approach. For a given two-dimensional surface at z = 0 containing 39 grains with given crystal orientations, eight 3D random polycrystalline aggregates are constructed having different 3D grain shapes and orientations except at z = 0, based on an original 3D image analysis procedure. They are subjected to overall tensile loading conditions. The continuum crystal plasticity framework is adopted and the resulting plastic strain fields at the free surface z = 0 are analyzed. Ensemble average and variance maps of the plastic strain field at the observed free surface are computed. In the case of elastoplastic copper grains, fluctuations ranging between 2% and 80% are found in the equivalent plastic slip level at a given material point of the observed surface from one realization of the microstructure to another. The obt...

Eigentongue Feature Extraction for an Ultrasound-Based Silent Speech Interface

Abstract: The article compares two approaches to the description of ultrasound vocal tract images for application in a "silent speech interface," one based on tongue contour modeling, and a second, global coding approach in which images are projected onto a feature space of Eigentongues. A curvature-based lip profile feature extraction method is also presented. Extracted visual features are input to a neural network which learns the relation between the vocal tract configuration and line spectrum frequencies (LSF) contained in a one-hour speech corpus. An examination of the quality of LSFs derived from the two approaches demonstrates that the Eigemongues approach has a more efficient implementation and provides superior results based on a normalized mean squared error criterion.

Is a management framework based on spawning-stock biomass indicators sustainable? A viability approach

Abstract: Fisheries management agencies have to drive resources on sustainable paths, i.e. within defined boundaries for an indefinite time. The viable-control approach is proposed as a relevant method to deal with sustainability. We analyse the ICES precautionary approach (PA) by means of the notion of viability domain, and provide a mathematical test for sustainability. It is found that the PA based on spawning-stock biomass (SSB) and fishing mortality (F) indicators is sustainable only when recruits make a significant contribution to SSB. In this case, advice based upon SSB, with an appropriate reference point, is sufficient to ensure sustainability. In all other cases, SSB is not a sufficient metric of stock productivity and must be complemented with other management indicators to ensure sustainability. The approach is illustrated with numerical applications to the northern hake and Bay of Biscay anchovy.

Ensemble averaging stress–strain fields in polycrystalline aggregates with a constrained surface microstructure – Part 1: anisotropic elastic behaviour

Abstract: The effect of three-dimensional (3D) grain morphology on the deformation at a free surface in polycrystalline aggregates is investigated by means of a large-scale finite element and statistical approach. For a given two-dimensional surface at z = 0 containing 39 grains with given crystal orientations, 17 random 3D polycrystalline aggregates are constructed having different 3D grain shapes and orientations except at z = 0, based on an original 3D image analysis procedure. They are subjected to overall tensile loading conditions. The resulting stress–strain fields at the free surface z = 0 are analyzed. Ensemble average and variance maps of the stress field at the observed surface are computed. In the case of an anisotropic elastic behaviour of the grains, fluctuations ranging between 5% and 60% are found in the equivalent stress level at a given material point of the observed surface from one realization of the microstructure to another. These results have important implications in the way of comparing fin...

Progressive mixture rules are deviation suboptimal

Abstract: We consider the learning task consisting in predicting as well as the best function in a finite reference set G up to the smallest possible additive term. If R(g) denotes the generalization error of a prediction function g, under reasonable assumptions on the loss function (typically satisfied by the least square loss when the output is bounded), it is known that the progressive mixture rule ĝ satisfies ER(ĝ) ≤ ming∈G R(g) + Cst log|G|/n, (1) where n denotes the size of the training set, and E denotes the expectation w.r.t. the training set distribution. This work shows that, surprisingly, for appropriate reference sets G, the deviation convergence rate of the progressive mixture rule is no better than Cst/√n: it fails to achieve the expected Cst/n. We also provide an algorithm which does not suffer from this drawback, and which is optimal in both deviation and expectation convergence rates.

Growth of small cracks and prediction of lifetime in high-temperature alloys

Abstract: The lifetime to initiate an engineering crack is usually predicted from S–N curves in high cycle fatigue or Coffin–Manson curves in low-cycle fatigue. This paper investigates how to predict the engineering life to initiate an engineering crack from the growth of small cracks. Small cracks can nucleate from defects and especially ceramic inclusions in superalloys produced by powder metallurgy. The behavior of short cracks nucleated from artificial defects was investigated under small scale yielding. A deterministic prediction of the life of smooth specimens was made using the growth law measured in air or in vacuum. The distribution of real defects was then used in a probabilistic life prediction model. The growth of small cracks under large scale yielding was investigated in stainless steels. A modified Tomkins equation can account for the behavior of small cracks and provide an estimate of the lifetime under low-cycle fatigue or thermal fatigue. A damage model based on the propagation of micro-cracks originating at casting defects has been developed for single crystal turbine blades, operating under thermo-mechanical creep–fatigue conditions. The model used the process zone concept introduced by Mc Clintock. Weakening of material due to localized oxidation embrittlement is shown to account for oxidation–creep–fatigue interactions. The model gives satisfactory life predictions under various thermo-mechanical loading conditions. A local approach to fracture is proposed for fatigue crack growth using a fracture criterion as a post-processor of a finite element model, for two-dimensional long cracks.

New Solubility Data of Hydrocarbons in Water and Modeling Concerning Vapor−Liquid−Liquid Binary Systems

Abstract: Solubility data in water of ethane, propane, isobutane, n-butane, n-pentane, and n-hexane have been obtained as a function of temperature in vapor−liquid−liquid equilibrium (VLLE) conditions. The minimum temperature of experiments is 288 K, while the maximum temperature, for each system, is lower than the critical temperature of the corresponding hydrocarbon. New solubility vs temperature correlations are given herein for the studied hydrocarbons in water. Henry's law and activity coefficients at infinite dilution are deduced from the experimental solubility data. Good agreement is found with available literature data.

Laser Shock Flier Impact Simulation of Particle-Substrate Interactions in Cold Spray

Abstract: Coating-substrate adhesion in cold spray is a paramount property, the mechanisms of which are not yet well elucidated. To go into these mechanisms, due to the intrinsic characteristics of the cold spray process (particle low-temperature and high velocity) direct observation and control of inflight particles and related phenomena cannot be done easily. For this reason, an experimental simulation of the particle-substrate reactions at the particle impingement was developed. This simulation is based on original flier impact experiments from laser shock acceleration. Relevant interaction phenomena were featured and studied as a function of shearing, plastic deformation, phase transformation primarily. These phenomena were shown to be similar to those involved in cold spray. This was ascertained by the study of the Cu-Al metallurgically reactive system using SEM, TEM, EPMA, and energy balance and diffusion calculations. This simulation could also be used to feed finite element modeling of cold spray and laser shock flier impact.

Risk Aversion, Road Choice, and the One-Armed Bandit Problem

Abstract: This paper provides a theoretical analysis of advanced traveler information systems for road choice with risk-averse drivers who rationally learn over time, in a simple setting. For this purpose, we study the one-armed bandit problem where a driver selects, day after day, either a safe or a random road. Four information regimes are envisaged. The visionary driver knows beforehand, with certainty, the travel time on the random road, while the locally informed driver needs to select a road to acquire information on it. Two intermediary information regimes (fully and globally) are also envisaged. We analyze these four regimes and compare the optimal strategies and the individual benefits with respect to individual risk aversion. A numerical example also illustrates the impact of risk aversion on dynamic optimal strategies.

Analysis of Yarrowia lipolytica extracellular lipase Lip2p glycosylation

Abstract: Wild-type (WT) Yarrowia lipolytica strain secretes a major extracellular lipase Lip2p which is glycosylated. In silico sequence analysis reveals the presence of two potential N-glycosylation sites (N113IS and N134NT). Strains expressing glycosylation mutant forms were constructed. Esterase activities for the different forms were measured with three substrates: p-nitrophenol butyrate (p-NPB), tributyrin and triolein. Sodium dodecyl sulfate polacrylamide gel electrophoresis analysis of supernatant indicated that the suppression of the two sites of N-glycosylation did not affect secretion. S115V or N134Q mutations led to lipase with similar specific activity compared with WT lipase while a T136V mutation reduced specific activity toward p-NPB and tributyrin. Electrospray ionization MS of the WT entire protein led to an average mass of 36 950 Da, higher than the mass deduced from the amino acid sequence (33 385 Da) and to the observation of at least two different mannose structures: Man(8)GlcNAc(2) and Man(9)GlcNAc(2). LC-tandem MS analysis of the WT Lip2p after trypsin and endoproteinase Asp-N treatments led to high coverage (87%) of protein sequence but the peptides containing N113 and N134 were not identified. We confirmed that the presence of N-glycosylation occurred at both N113 and N134 by MS of digested proteins obtained after enzymatic deglycosylation or from mutant forms.

Finite element simulations of the cyclic elastoplastic behaviour of copper thin films

Abstract: A large-scale computational and statistical strategy is presented to investigate the development of plastic strain heterogeneities and plasticity induced roughness at the free surface in multicrystalline films subjected to cyclic loading conditions, based on continuum crystal plasticity theory. The distribution of plastic strain in the grains and its evolution during cyclic straining are computed using the finite element method in films with different ratios of in-plane grain size and thickness, and as a function of grain orientation (grains with a {1 1 1} or a {0 0 1} plane parallel to the free surface and random orientations). Computations are made for 10 different realizations of aggregates containing 50 grains and one large aggregate with 225 grains. It is shown that overall cyclic hardening is accompanied by a significant increase in strain dispersion. The case of free-standing films is also addressed for comparison. The overall surface roughness is shown to saturate within 10 to 15 cycles. Plasticity induced roughness is due to the higher deformation of {0 0 1} and random grains and due to the sinking or rising at some grain boundaries.

A methodology for assessing the risk posed by the deliberate and harmful use of plant pathogens in Europe

Abstract: L'utilisation volontaire et malveillante d'agents phytopathogenes, i.e. agroterrorisme lato sensu (bioterrorisme anti-cultures et emploi d'armes biologiques contre le secteur agricole), represente une menace contre les cultures et les forets europeennes qu'il ne faut pas negliger. Afin d'evaluer ce risque de maniere objective, une methodologie s'appuyant sur une analyse critique des schemas d'Analyse de Risques Phytosanitaires existants a ete elaboree et est decrite dans le present article. Dans cette methodologie, trois etapes interdependantes sont proposees : i) elaboration d'une liste a priori constituee d'agents phytopathogenes potentiellement dangereux pour l'Europe, ii) redaction detaillee et analyse de scenarios theoriques d'actes d'agroterrorisme potentiels, iii) conception et application d'un schema d'analyse de risque adapte a l'agroterrorisme.

High-Pressure Vapor−Liquid Equilibria, Liquid Densities, and Excess Molar Volumes for the Carbon Dioxide + 2-Propanol System from (308.10 to 348.00) K

Abstract: Vapor−liquid equilibrium data and volumetric properties (density and excess molar volumes) of the carbon dioxide (1) + 2-propanol (2) system have been determined for seven molar compositions, z1, close to 0.15, 0.20, 0.42, 0.60, 0.80, 0.95, and 0.97, using a vibrating tube densimeter, which takes advantage of a forced path mechanical calibration model. The Peng−Robinson equation of state including Panagiotopoulos and Reid mixing rules is used to correlate the data. Comparison of the new data with selected literature data and correlated results shows good consistency agreement, demonstrating the reliability of the data presented herein.

A Simple Proof of the Entropy-Power Inequality via Properties of Mutual Information

Abstract: While most useful information theoretic inequalities can be deduced from the basic properties of entropy or mutual information, Shannon's entropy power inequality (EPI) seems to be an exception: available information theoretic proofs of the EPI hinge on integral representations of differential entropy using either Fisher's information (FI) or minimum mean-square error (MMSE). In this paper, we first present a unified view of proofs via FI and MMSE, showing that they are essentially dual versions of the same proof, and then fill the gap by providing a new, simple proof of the EPI, which is solely based on the properties of mutual information and sidesteps both FI or MMSE representations.

Storing events to retell them

Abstract: Episodic memory is certainly a unique endowment, but its primary purpose is something other than to provide raw material for creative synthesis of future scenarios. Remembered episodes are exactly those which are worth telling. The function of episodic memory, in our view, is to accumulate stories that are relevant to recount in conversation.

Shipping the good beef out: EU trade liberalization to Mercosur exports

Abstract: The European Union tariff schedule includes a large number of specific and composite tariffs as well as many tariff-rate quotas (TRQs), which affect the composition of imports. By altering price ratios between products with different unit values, both can generate the typical Alchian-Allen 'shipping the good apples out' effect in foreign countries' exports to the EU. Different patterns of trade liberalization, either through tariff reduction or an expansion in preferential-access quotas, might have different consequences for producers and consumers because of changes in the composition of trade. We illustrate the issues at stake in the beef sector, focusing on Mercosur exports to the EU. We model import demand for different qualities in the presence of a TRQ and we derive comparative statics results for changes in various policy variables.

Accounting for biological variability and sampling scale: a multi-scale approach to building epidemic models

Abstract: When one considers the fine-scale spread of an epidemic, one usually knows the sources of biological variability and their qualitative effect on the epidemic process. The force of infection on a susceptible unit depends on the locations and the strengths of the infectious units, and on the environmental and intrinsic factors affecting infectivity and/or susceptibility. The infection probability for the susceptible unit can then be modelled as a function of these factors. Thus, one can build a conceptual model at the fine scale. However, the epidemic is generally observed at a larger scale and one has to build a model adapted to this larger scale. But how can the sources of variation identified at the fine scale be integrated into the model at the larger scale? To answer this question, we present, in the context of plant epidemiology, a multi-scale approach which consists of defining a base model built at the fine scale and upscaling it to match the scale of the sampling and the data. This approach will enable comparing experiments involving different observational processes.

Use of a Modification of the Patel-Teja Equation of State + van der Waals-Platteeuw Theory Based Model for Predicting Hydrate Phase Boundary of Methane - Ethylene Glycol - Water System from Ice Point Data of Aqueous Solution

Abstract: A major concern with the oil/gas pipelines and production/processing facilities is the possibility of flow restriction and blockage due to gas hydrate formation, which can lead to serious operational, economic and safety problems. Organic inhibitors such as methanol and ethylene glycol are normally used for preventing gas hydrate formation. Accurate knowledge of hydrate phase equilibrium in the presence of inhibitors is therefore crucial to avoid gas hydrate formation problems and to design/optimize production, transportation and processing facilities. Experimental data are needed for developing models capable of predicting hydrate phase behavior. In general, measuring hydrate phase equilibrium in the presence of inhibitor is more difficult than measuring ice point of inhibitor aqueous solution, particularly at high concentrations of inhibitor. This is partly due to the fact that the presence of inhibitor shifts hydrate phase boundaries to high pressures, which leads to difficulties in hydrate phase equilibria measurements. In this work, we examine the need for hydrate phase equilibrium data in the presence of inhibitor (ethylene glycol) aqueous solutions for tuning parameters of a thermodynamic model based on a modification of the Patel-Teja equation of state + van der Waals-Platteeuw theory. We consider two cases for tuning: use of ice point data or, using hydrate phase equilibrium data. The results show that using only ice point data of inhibitor aqueous solution for tuning thermodynamic model can lead to acceptable predictions of hydrate phase equilibrium in the presence of inhibitor and therefore experimental hydrate phase equilibrium data are not strictly indispensable.