Showing papers by "ParisTech published in 2012"

Seed Germination and Vigor

Abstract: Germination vigor is driven by the ability of the plant embryo, embedded within the seed, to resume its metabolic activity in a coordinated and sequential manner. Studies using “-omics” approaches support the finding that a main contributor of seed germination success is the quality of the messenger RNAs stored during embryo maturation on the mother plant. In addition, proteostasis and DNA integrity play a major role in the germination phenotype. Because of its pivotal role in cell metabolism and its close relationships with hormone signaling pathways regulating seed germination, the sulfur amino acid metabolism pathway represents a key biochemical determinant of the commitment of the seed to initiate its development toward germination. This review highlights that germination vigor depends on multiple biochemical and molecular variables. Their characterization is expected to deliver new markers of seed quality that can be used in breeding programs and/or in biotechnological approaches to improve crop yields.

Transformation optics and subwavelength control of light

Abstract: Our intuitive understanding of light has its foundation in the ray approximation and is intimately connected with our vision. As far as our eyes are concerned, light behaves like a stream of particles. We look inside the wavelength and study the properties of plasmonic structures with dimensions of just a few nanometers, where at a tenth or even a hundredth of the wavelength of visible light the ray picture fails. We review the concept of transformation optics that manipulates electric and magnetic field lines, rather than rays; can provide an equally intuitive understanding of subwavelength phenomena; and at the same time can be an exact description at the level of Maxwell's equations.

High Accuracy and Visibility-Consistent Dense Multiview Stereo

Abstract: Since the initial comparison of Seitz et al. [48], the accuracy of dense multiview stereovision methods has been increasing steadily. A number of limitations, however, make most of these methods not suitable to outdoor scenes taken under uncontrolled imaging conditions. The present work consists of a complete dense multiview stereo pipeline which circumvents these limitations, being able to handle large-scale scenes without sacrificing accuracy. Highly detailed reconstructions are produced within very reasonable time thanks to two key stages in our pipeline: a minimum s-t cut optimization over an adaptive domain that robustly and efficiently filters a quasidense point cloud from outliers and reconstructs an initial surface by integrating visibility constraints, followed by a mesh-based variational refinement that captures small details, smartly handling photo-consistency, regularization, and adaptive resolution. The pipeline has been tested over a wide range of scenes: from classic compact objects taken in a laboratory setting, to outdoor architectural scenes, landscapes, and cultural heritage sites. The accuracy of its reconstructions has also been measured on the dense multiview benchmark proposed by Strecha et al. [59], showing the results to compare more than favorably with the current state-of-the-art methods.

Spreading of the Western Mediterranean Deep Water after winter 2005: Time scales and deep cyclone transport

Abstract: This work is dedicated to the study of the propagation of the Western Mediterranean Deep Water (WMDW) formed in the Gulf of Lions during the exceptional winter 2005 A simulation of the 1998-2008 period has been carried out with an eddy-resolving Ocean General Circulation Model of the Mediterranean Sea, driven by interannual high-resolution air-sea fluxes This study first presents a validation of the recently improved model configuration against satellite observations Then, we assess the ability of the model to reproduce the particularly intense deep convection event of winter 2005 in the Gulf of Lions A huge volume of very dense water is formed in the simulations at that time (annual formation rate of about 3 Sv) The thermohaline characteristics of the new WMDW allow a monitoring of its deep propagation We identify several deep cyclones as mainly responsible of the fast spreading of the WMDW southwards in the Western Mediterranean By comparing Eulerian and Lagrangian approaches, we estimate different transport times of the WMDW by these cyclonic eddies and compare them to those deduced from several observations Finally, we argue that these cyclones favour the propagation of the WMDW thermohaline characteristics towards the Channel of Sardinia and decrease the volume of WMDW which can reach the Strait of Gibraltar

Quantitative elastography of renal transplants using supersonic shear imaging: a pilot study

Abstract: Purpose To evaluate the reliability of quantitative ultrasonic measurement of renal allograft elasticity using supersonic shear imaging (SSI) and its relationship with parenchymal pathological changes.

Genetic structure and local adaptation of European wheat yellow rust populations: the role of temperature-specific adaptation

Abstract: Environmental heterogeneity influences coevolution and local adaptation in host-parasite systems. This also concerns applied issues, because the geographic range of parasites may depend on their capacity to adapt to abiotic conditions. We studied temperature-specific adaptation in the wheat yellow/stripe rust pathogen, Puccinia striiformis f.sp. tritici (PST). Using laboratory experiments, PST isolates from northern and southern France were studied for their ability to germinate and to infect bread and durum wheat cultivars over a temperature gradient. Pathogen origin × temperature interactions for infectivity and germination rate suggest local adaptation to high- versus low-temperature regimes in south and north. Competition experiments in southern and northern field sites showed a general competitive advantage of southern over northern isolates. This advantage was particularly pronounced in the southern 'home' site, consistent with a model integrating laboratory infectivity and field temperature variation. The stable PST population structure in France likely reflects adaptation to ecological and genetic factors: persistence of southern PST may be due to adaptation to the warmer Mediterranean climate; and persistence of northern PST can be explained by adaptation to commonly used cultivars, for which southern isolates are lacking the relevant virulence genes. Thus, understanding the role of temperature-specific adaptations may help to improve forecast models or breeding programmes.

The Imaclim-R model: infrastructures, technical inertia and the costs of low carbon futures under imperfect foresight

Abstract: This paper analyzes the transition costs of moving towards a low carbon society when the second-best nature of the economy is accounted for. We emphasize the consequences on mitigation costs of considering the interplay between a) technical systems inertia, including slow infrastructure turnover in transportation and construction; and b) imperfect foresight influencing investment decisions. To this end, the hybrid general equilibrium modeling framework I maclim-R is employed as it allows for transitory partial adjustments of the economy and captures their impact on the dynamics of economic growth. The modeling exercise quantitatively emphasizes the a) specific risks that the interplay between inertia and imperfect foresight leads to high macroeconomic costs of carbon abatement measures; b) opportunities of co-benefits from climate policies permitted by the correction of sub-optimalities in the reference scenarios. The article draws insights for the framing of future climate architectures by studying the role of measures that act complementarily to carbon pricing in the transport sector. In particular, reallocating public investment towards low-carbon transport infrastructure significantly reduces the overall macroeconomic costs of a given GHG stabilization target and even creates the room for long-term net economic benefits from climate policies. © 2012 Springer Science+Business Media B.V.

A theoretical analysis of creativity methods in engineering design: casting and improving ASIT within C–K theory

Abstract: Approaches to supporting creativity are diverse and numerous. Making sense of these methods, including the comparative benefits of one approach over another is highly significant to both research and practice of creative design. This paper demonstrates the benefit of conducting analyses of methods with the aid of a theory. Such an approach provides a clear basis for analysing different methods that could in turn be compared with each other. This approach is demonstrated through the critical analysis of advanced systematic inventive thinking (ASIT) – a practical method – using the C–K theory, a design theory that offers a formal model of creative thinking. The analysis uncovers a paradox in ASIT operation: being creative while ‘staying in the box’. While confirming that ASIT could be perceived as an implementation of some of the C–K constructs, the analysis further resolves the paradox by explaining how creative solutions could be created with ASIT. Finally, the analysis also exposes the capabilities and l...

Obstructed breakup of slender drops in a microfluidic T junction.

Abstract: In this Letter we present a theoretical analysis of the droplet breakup with ``permanent obstruction'' in a microfluidic $T$ junction [M.-C. Jullien et al., Phys. Fluids 21, 072001 (2009)]. The proposed theory is based on a simple geometric construction for the interface shape combined with Tanner's law for the local contact angle. The resulting scaling of the droplet deformation with time and capillary number is in excellent agreement with the results of direct numerical simulations and prior experiments. More rigorous analysis based on the lubrication approximation reveals a self-similar behavior analogous to the classical problem of a droplet spreading over a preexisting liquid film.

Robust Nonlinear Controls of Model-Scale Helicopters Under Lateral and Vertical Wind Gusts

Abstract: A helicopter maneuvers naturally in an environment where the execution of the task can easily be affected by atmospheric turbulence, which leads to variations of its model parameters. This paper discusses the nature of the disturbances acting on the helicopter and proposes an approach to counter the effects. The disturbance consists of vertical and lateral wind gusts. A 7-degrees-of-freedom (DOF) nonlinear Lagrangian model with unknown disturbances is used. The model presents quite interesting control challenges due to nonlinearities, aerodynamic forces, under actuation, and its non-minimum phase dynamics. Two approaches of robust control are compared via simulations with a Tiny CP3 helicopter model: an approximate feedback linearization and an active disturbance rejection control using the approximate feedback linearization procedure. Several simulations show that adding an observer can compensate the effect of disturbances. The proposed controller has been tested in a real-time application to control the yaw angular displacement of a Tiny CP3 mini-helicopter mounted on an experiment platform.

The Imaclim-R model: infrastructures, technical inertia and the costs of low carbon futures under imperfect foresight

Abstract: This paper analyzes the transition costs of moving towards a low carbon society when the second-best nature of the economy is accounted for. We emphasize the consequences on mitigation costs of considering the interplay between a) technical systems inertia, including slow infrastructure turnover in transportation and construction; and b) imperfect foresight influencing investment decisions. To this end, the hybrid general equilibrium modeling framework Imaclim-R is employed as it allows for transitory partial adjustments of the economy and captures their impact on the dynamics of economic growth. The modeling exercise quantitatively emphasizes the a) specific risks that the interplay between inertia and imperfect foresight leads to high macroeconomic costs of carbon abatement measures; b) opportunities of co-benefits from climate policies permitted by the correction of sub-optimalities in the reference scenarios. The article draws insights for the framing of future climate architectures by studying the role of measures that act complementarily to carbon pricing in the transport sector. In particular, reallocating public investment towards low-carbon transport infrastructure significantly reduces the overall macroeconomic costs of a given GHG stabilization target and even creates the room for long-term net economic benefits from climate policies.

Model of the Regional Coupled Earth system (MORCE): Application to process and climate studies in vulnerable regions

Abstract: The vulnerability of human populations and natural systems and their ability to adapt to extreme events and climate change vary with geographic regions and populations. Regional climate models (RCM), composed by an atmospheric component coupled to a land surface scheme and driven over ocean areas by prescribed sea surface temperature, have been developed to produce fine scale regional climate change information useful for impact assessment and adaptation studies. Although RCM can be sufficient for many applications, the Earth system is composed of the physical, chemical, biological, and social components, processes, and interactions that together determine the state and dynamics of Earth, including its biota and human occupants. Developing regional Earth system models has thus two primary motivations: (1) with respect to climate science, to improve modeling capabilities and better understand coupled processes at regional scales and (2) to support stakeholders who aim to use climate information for regionally-specific impact assessment and adaptation planning. IPSL in collaboration with ENSTA-ParisTech, LOPB, and CERFACS developed the MORCE (Model of the Regional Coupled Earth system) platform for process and climate studies of the regional Earth system. The original aspects of the MORCE platform are (1) the integration of a large number of coupled compartments and processes (physical and biogeochemical processes in the ocean, atmosphere and continent), (2) the transferability of the numerical platform to different locations in the world, (3) the use of a non-hydrostatic model for the atmospheric module which allows an accurate representation of kilometric scale processes. The present article describes the MORCE platform, detailing its various modules and their coupling and illustrating its potential with results obtained in the Mediterranean region and over the Indian Ocean.

Volatility and covariation estimation when microstructure noise and trading times are endogenous

Abstract: This paper considers practically appealing procedures for estimating intraday volatility measures of financial assets. The underlying microstructure model accommodates the inherent properties of ultra high-frequency data with the assumption of continuous efficient price processes. In this model, microstructure noise and trading times are endogenous but do not only depend on the prices. Using the (observed) last traded prices of the assets, we develop a new approach that enables to approximate the values of the efficient prices at some random times. Based on these approximated values, we build an estimator of the integrated volatility and give its asymptotic theory. We also give a consistent estimator of the integrated covariation when two assets (asynchronous by construction of the model) are observed.

Cooperative multi-vehicle localization using split covariance intersection filter

Abstract: Vehicle localization (ground vehicles) is an important task for intelligent vehicle systems and vehicle cooperation may bring benefits for this task. A new cooperative multi-vehicle localization method using split covariance intersection filter is proposed in this paper. In the proposed method, each vehicle maintains an estimate of a decomposed group state and this estimate is shared with neighboring vehicles; the estimate of the decomposed group state is updated with both the sensor data of the ego-vehicle and the estimates sent from other vehicles; the covariance intersection filter which yields consistent estimates even facing unknown degree of inter-estimate correlation has been used for data fusion. A comparative study based simulations demonstrate the effectiveness and the advantage of the proposed cooperative localization method.1

Method for small signal stability analysis of VSC-MTDC grids

Abstract: This paper deals with small signal stability analysis of Voltage Source Converter based Multitermial HVDC grids (VSC-MTDC). First, a simplified model is used to predict the voltage dynamic behavior. Next, a modular method to build the state space model of the overall MTDC system is described. Model validation is achieved in time domain by a comparison with an electromagnetic simulation in EMTP-rv. As concrete example of effective application, a parametric study on the droop value is carried on a 3-terminal meshed HVDC grid. This example attests to the effect of the droop parameter on the stability of the overall system.

Oxygen hole doping of nanodiamond

Abstract: Surface-graphitized nanodiamonds (NDs) are promising hybrid nanomaterials which appear to combine core properties of diamond with surface properties of graphene-based materials. Here we demonstrate that NDs covered by graphene islands, so-called Fullerene-Like Reconstructions (FLRs), are sensitive to hole doping by molecular oxygen in water. NDs covered by FLRs (NDs-FLRs) are prepared by annealing under vacuum of detonation NDs at 750 °C. We propose that oxygen hole doping is promoted on FLRs due to a unique electronic interaction between the diamond core and the outer graphene layer. As a consequence, NDs-FLRs exhibit positive zeta potential in water, unlike NDs surrounded by several graphitic layers. Surface hole-doped NDs may be promising nanomaterials for new electronic and biomedical applications.

Pilus biogenesis in Lactococcus lactis: molecular characterization and role in aggregation and biofilm formation.

Abstract: The genome of Lactococcus lactis strain IL1403 harbors a putative pilus biogenesis cluster consisting of a sortase C gene flanked by 3 LPxTG protein encoding genes (yhgD, yhgE, and yhhB), called here pil. However, pili were not detected under standard growth conditions. Over-expression of the pil operon resulted in production and display of pili on the surface of lactococci. Functional analysis of the pilus biogenesis machinery indicated that the pilus shaft is formed by oligomers of the YhgE pilin, that the pilus cap is formed by the YhgD pilin and that YhhB is the basal pilin allowing the tethering of the pilus fibers to the cell wall. Oligomerization of pilin subunits was catalyzed by sortase C while anchoring of pili to the cell wall was mediated by sortase A. Piliated L. lactis cells exhibited an auto-aggregation phenotype in liquid cultures, which was attributed to the polymerization of major pilin, YhgE. The piliated lactococci formed thicker, more aerial biofilms compared to those produced by non-piliated bacteria. This phenotype was attributed to oligomers of YhgE. This study provides the first dissection of the pilus biogenesis machinery in a non-pathogenic Gram-positive bacterium. Analysis of natural lactococci isolates from clinical and vegetal environments showed pili production under standard growth conditions. The identification of functional pili in lactococci suggests that the changes they promote in aggregation and biofilm formation may be important for the natural lifestyle as well as for applications in which these bacteria are used.

Harmonic Balance-Based Approach for Quasi-Periodic Motions and Stability Analysis

Abstract: Quasi-periodic motions and their stability are addressed from the point of view of different harmonic balance-based approaches. Two numerical methods are used: a generalized multidimensional version of harmonic balance and a modification of a classical solution by harmonic balance. The application to the case of a nonlinear response of a Duffing oscillator under a bi-periodic excitation has allowed a comparison of computational costs and stability evaluation results. The solutions issued from both methods are close to one another and time marching tests showing a good agreement with the harmonic balance results confirm these nonlinear responses. Besides the overall adequacy verification, the observation comparisons would underline the fact that while the 2D approach features better performance in resolution cost, the stability computation turns out to be of more interest to be conducted by the modified 1D approach.

Random Projection Depth for Multivariate Mathematical Morphology

Abstract: The open problem of the generalization of mathematical morphology to vector images is handled in this paper using the paradigm of depth functions. Statistical depth functions provide from the “deepest” point a “center-outward ordering” of a multidimensional data distribution and they can be therefore used to construct morphological operators. The fundamental assumption of this data-driven approach is the existence of “background/foreground” image representation. Examples in real color and hyperspectral images illustrate the results.

A cell formation problem considering machine utilization and alternative process routes by scatter search

Abstract: Cell formation (CF) is the first step in the design of cellular manufacturing systems (CMSs), which has been recognized as an effective way to enhance the productivity in a factory. There is a set of criteria on which to judge route of product, machine grouping and part family simultaneously in terms of the effective utilization of these cells. In this study, we consider four objectives simultaneously: (1) Minimizing the total fixed and variable cost including costs of purchasing, operation, and maintenance; (2) minimizing cost of intercellular movements; (3) maximizing the utilization of machines in the system; and (4) minimizing deviations among the levels of the cell utilization (i.e., balancing the workload between cells). In this paper, these objectives are first weighted by their relative importance and then a new mathematical model is presented. To solve this model, a scatter search (SS) algorithm is proposed to select a process plan for each part with the minimum cost along with forming the part family and machine grouping simultaneously. The performance of the proposed SS is compared with the Lingo 8.0 software. A number of test problems are carried out to verify the good ability of the proposed SS in terms of the solution quality and computational time. The computational results reveal that the SS finds promising results, especially in the case of large-sized problems.

Analysis of laser shock waves and resulting surface deformations in an Al-Cu-Li aluminum alloy

Abstract: Laser shock processing is now a recognized surface treatment for improving fatigue or corrosion behaviour of metallic materials through the generation of a compressive stress field. In turn, the analysis of shock wave propagation is of primary importance to predict numerically morphological and mechanical surface modifications.Considering experimental and numerical analyses of shock wave propagation, and surface deformations induced by single impacts, a 2050 aluminum alloy having different microstructures was investigated under laser-shock loading. In a first step, the evolution of shock wave attenuation and elastic precursor amplitude was correctly reproduced by finite element simulations, and in a second step, surface deformations induced by 1–6 local impacts were also compared satisfactorily with experiments. This allowed us to validate mechanical loading and materials' constitutive law, but did not allow accurate determination of residual stress fields on a single impact.