Showing papers by "ParisTech published in 2014"

Theoretical guarantees for approximate sampling from smooth and log-concave densities

Abstract: Sampling from various kinds of distributions is an issue of paramount importance in statistics since it is often the key ingredient for constructing estimators, test procedures or confidence intervals. In many situations, the exact sampling from a given distribution is impossible or computationally expensive and, therefore, one needs to resort to approximate sampling strategies. However, there is no well-developed theory providing meaningful nonasymptotic guarantees for the approximate sampling procedures, especially in the high-dimensional problems. This paper makes some progress in this direction by considering the problem of sampling from a distribution having a smooth and log-concave density defined on \(\RR^p\), for some integer \(p>0\). We establish nonasymptotic bounds for the error of approximating the target distribution by the one obtained by the Langevin Monte Carlo method and its variants. We illustrate the effectiveness of the established guarantees with various experiments. Underlying our analysis are insights from the theory of continuous-time diffusion processes, which may be of interest beyond the framework of log-concave densities considered in the present work.

Effect of inclusion density on ductile fracture toughness and roughness

Abstract: Three dimensional calculations of ductile fracture under mode I plane strain, small scale yielding conditions are carried out using an elastic-viscoplastic constitutive relation for a progressively cavitating solid with two populations of void nucleating second phase particles Larger inclusions that result in void nucleation at an early stage are modeled discretely while smaller particles that require large strains to nucleate voids are homogeneously distributed Full field solutions are obtained for eight volume fractions, ranging from 1% to 19%, of randomly distributed larger inclusions For each volume fraction calculations are carried out for seven random distributions of inclusion centers Crack growth resistance curves and fracture surface roughness statistics are calculated using standard procedures The crack growth resistance is characterized in terms of both J IC and the tearing modulus TR For all volume fractions considered, the computed fracture surfaces are self-affine over a size range of nearly two orders of magnitude with a microstructure independent roughness exponent of 053 with a standard error of 00023 The cut-off length of the scale invariant regime is found to depend on the inclusion volume fraction Consideration of the full statistics of the fracture surface roughness revealed other parameters that vary with inclusion volume fraction For smaller values of the discretely modeled inclusion volume fraction (r7%), there is a linear correlation between several measures of fracture surface roughness and both JIC and TR I n this regime crack growth is dominated by a void-by-void process For greater values of the discretely modeled inclusion volume fraction, crack growth mainly involves multiple void interactions and no such correlation is found

Environmental Feasibility of the Recycling of Carbon Fibers from CFRPs by Solvolysis Using Supercritical Water

Abstract: Originally developed for high-tech applications in the aeronautic and aerospace industry, carbon/epoxy composites have been increasingly used in the automotive, leisure, and sports industries for several years. Nevertheless, the carbon reinforcement is an expensive constituent, and it has been recently shown that it is also the most environmentally impacting in a composite part manufacturing. Recycling these materials (even restricted to the reinforcement recovery) could lead to economic and environmental benefits, while satisfying legislative end-of-life requirements. The solvolysis of the matrix by water under supercritical conditions is an efficient solution to recover the carbon fiber reinforcement with mechanical properties closed to the ones of virgin fibers. This paper aims at demonstrating the environmental feasibility of the recycling of carbon fiber/thermoset matrix composites by solvolysis of the matrix in supercritical water. This demonstration is based on life cycle assessment that evaluates ...

Analogies between Internet network and logistics service networks: challenges involved in the interconnection

Abstract: Logistics networks that are currently formed by supply chains are intertwined but remain heterogeneous and not very interconnected. In computer networks, this stage was overtaken with the arrival of Internet. In this paper we explore the possible analogies and transpositions between computer networks, in particular Internet, and logistic networks. To this end, a new logistical concept was proposed: Physical Internet that aims at the interconnection of networks of logistic services. In fact, there are strong similarities between these networks in spite of the basic differences in the type of objects that prevent an integral transposition. To illustrate the pertinence of this analogy, the authors illustrate the interconnection potential of logistics networks with a stylised model. In view of the exploratory nature of this work, this impact will be assessed by means of an analytic model based on a method of continuous approximations. This illustration provides an indication of the potential inherent in the interconnection of logistics networks.

Invariance property of wave scattering through disordered media

Abstract: A fundamental insight in the theory of diffusive random walks is that the mean length of trajectories traversing a finite open system is independent of the details of the diffusion process. Instead, the mean trajectory length depends only on the system's boundary geometry and is thus unaffected by the value of the mean free path. Here we show that this result is rooted on a much deeper level than that of a random walk, which allows us to extend the reach of this universal invariance property beyond the diffusion approximation. Specifically, we demonstrate that an equivalent invariance relation also holds for the scattering of waves in resonant structures as well as in ballistic, chaotic or in Anderson localized systems. Our work unifies a number of specific observations made in quite diverse fields of science ranging from the movement of ants to nuclear scattering theory. Potential experimental realizations using light fields in disordered media are discussed.

Radiographic Outcomes of Adult Spinal Deformity Correction: A Critical Analysis of Variability and Failures Across Deformity Patterns

Abstract: Study Design: Multicenter, prospective, consecutive, surgical case series from the International Spine Study Group. Objectives: To evaluate the effectiveness of surgical treatment in restoring spinopelvic (SP) alignment. Summary of Background Data: Pain and disability in the setting of adult spinal deformity have been correlated with global coronal alignment (GCA), sagittal vertical axis (SVA), pelvic incidence/lumbar lordosis mismatch (PI-LL), and pelvic tilt (PT). One of the main goals of surgery for adult spinal deformity is to correct these parameters to restore harmonious SP alignment. Methods: Inclusion criteria were operative patients (age greater than 18 years) with baseline (BL) and 1-year full-length X-rays. Thoracic and thoracolumbar Cobb angle and previous mentioned parameters were calculated. Each parameter at BL and 1 year was categorized as either pathological or normal. Pathologic limits were: Cobb greater than 30 � , GCA greater than 40 mm, SVA greater than 40 mm, PI-LL greater than 10 � , and PT greater than 20 � . According to thresholds, corrected or worsened alignment groups of patients were identified and overall radiographic effectiveness of procedure was evaluated by combining the results from the coronal and sagittal planes.

Sealing of hard CrN and DLC coatings with atomic layer deposition.

Abstract: Atomic layer deposition (ALD) is a thin film deposition technique that is based on alternating and saturating surface reactions of two or more gaseous precursors. The excellent conformality of ALD thin films can be exploited for sealing defects in coatings made by other techniques. Here the corrosion protection properties of hard CrN and diamond-like carbon (DLC) coatings on low alloy steel were improved by ALD sealing with 50 nm thick layers consisting of Al2O3 and Ta2O5 nanolaminates or mixtures. In cross sectional images the ALD layers were found to follow the surface morphology of the CrN coatings uniformly. Furthermore, ALD growth into the pinholes of the CrN coating was verified. In electrochemical measurements the ALD sealing was found to decrease the current density of the CrN coated steel by over 2 orders of magnitude. The neutral salt spray (NSS) durability was also improved: on the best samples the appearance of corrosion spots was delayed from 2 to 168 h. On DLC coatings the adhesion of the ALD sealing layers was weaker, but still clear improvement in NSS durability was achieved indicating sealing of the pinholes.

Streamlined ion torrent PGM-based diagnostics: BRCA1 and BRCA2 genes as a model

Abstract: To meet challenges in terms of throughput and turnaround time, many diagnostic laboratories are shifting from Sanger sequencing to higher throughput next-generation sequencing (NGS) platforms. Bearing in mind that the performance and quality criteria expected from NGS in diagnostic or research settings are strikingly different, we have developed an Ion Torrent's PGM-based routine diagnostic procedure for BRCA1/2 sequencing. The procedure was first tested on a training set of 62 control samples, and then blindly validated on 77 samples in parallel with our routine technique. The training set was composed of difficult cases, for example, insertions and/or deletions of various sizes, large-scale rearrangements and, obviously, mutations occurring in homopolymer regions. We also compared two bioinformatic solutions in this diagnostic context, an in-house academic pipeline and the commercially available NextGene software (Softgenetics). NextGene analysis provided higher sensitivity, as four previously undetected single-nucleotide variations were found. Regarding specificity, an average of 1.5 confirmatory Sanger sequencings per patient was needed for complete BRCA1/2 screening. Large-scale rearrangements were identified by two distinct analyses, that is, bioinformatics and fragment analysis with electrophoresis profile comparison. Turnaround time was enhanced, as a series of 30 patients were sequenced by one technician, making the results available for the clinician in 10 working days following blood sampling. BRCA1/2 genes are a good model, representative of the difficulties commonly encountered in diagnostic settings, which is why we believe our findings are of interest for the whole community, and the pipeline described can be adapted by any user of PGM for diagnostic purposes.

Carrier aggregation/channel bonding in next generation cellular networks: methods and challenges

Abstract: To provide cellular systems with additional spectral resources, the wireless industry is considering the aggregation of frequency carriers in licensed, unlicensed, and shared access (SA) bands. In this article, we focus on reliable carrier aggregation/channel bonding (CA/CB) techniques, in which when CA/CB between the licensed, unlicensed, and SA carriers is performed, the licensed carrier is used for the primary and secondary carriers, and the unlicensed and SA carriers operate as additional secondary carriers. We provide a taxonomy of the use of CA/CB in cellular networks and highlight the differences between different CA/CB approaches. We make the case that although the licensed primary carrier can give reliable transmission of control signaling, due to the nature of unlicensed and SA bands, for the efficient aggregation of secondary carriers there is a need for new CA/CB methods. To illustrate our case for novel CA/CB methods, we provide examples for different network environments where intelligent CA/CB decisions can increase throughput compared to the traditional CA/CB methods. Finally, we highlight challenges in the design of novel CA/CB techniques in unlicensed and SA bands.

Statistical axisymmetry of the turbulent sphere wake

Abstract: The turbulent sphere wake is studied experimentally at $${Re}=1.9\,10^4$$ using an axisymmetric support that holds the body from upstream. This setup allows the axisymmetry of the mean wake and preserves the global mode activity at $${St}=0.19$$ . The analysis of the PIV snapshots in a cross-flow plane indicates that this axisymmetry is due to an equal exploration of all the azimuths by the instantaneous wake. Using conditional averaging techniques, we extract the flow topology associated with one azimuthal direction; the obtained wake shows strong similarities with the unsteady planar symmetric flow reported in the laminar regime. In addition, the use of perturbations of the axisymmetry leads to modifications of the azimuthal statistics: The periodicity of the perturbation is recovered in the wake since one or several preferred orientations are identified. Hence, such statistics pave the way to multi-stable behaviors in three-dimensional wakes.

Introduction of variability into pantograph–catenary dynamic simulations

Abstract: In railways, electrical current is generally collected by the train through a complex coupledmechanical system composed of a pantograph and a catenary. Dynamic phenomena that occur duringtheir interaction are still not fully understood. Furthermore, the system behaviour is sensitive to numerousparameters and thus highly variable. The first contribution of this thesis is a detailed analysis of thepantograph-catenary dynamic interaction separating phenomena due to the dynamic response of the pantographto the catenary geometry from wave propagations, reflections and transmissions that occur in thecatenary. The coincidence of frequencies or characteristic times is then shown to explain most variationsin the quantities of interest. Moreover, droppers surrounding the mast have been shown to be particularlyimportant in dynamic interaction. Ratio of wire impedances and sum of wave velocities also appeared tobe dimensioning quantities for catenary design. The second contribution was to reduce epistemic uncertaintylinked with model parameters such as catenary damping, contact stiffness and element size. Thefinal contribution was to use the model in a configuration with random parameters. An initial step was tostatistically characterise physical catenary parameters using available measurements. From this randommodel, ranking of uncertainties using Sobol indices on static and dynamic criteria was shown to be possible.An absence of correlation between geometric and dynamic criteria was also found, which has notableimplications for maintenance policies. The high number of sensitivity studies also gave the occasion tohighlight the maturity of simulation tool and propose directions for further work on design, maintenance orcertification of pantographs and catenaries.

Quantitative Analyses of ROS and RNS Production in Breast Cancer Cell Lines Incubated with Ferrocifens

Abstract: Ferrocifens are an original class of ferrocifen-type breast cancer drugs They possess anti-proliferative effects due to the association of the ferrocene moiety and the tamoxifen skeleton In this work, fluorescence measurements indicated the production of reactive oxygen species (ROS) if hormone-dependent or -independent breast cancer cells were incubated with three hit ferrocifen compounds Additionally, amperometry at ultramicroelectrodes was carried out to identify and quantify ROS and reactive nitrogen species (RNS) under stress conditions Videomicroscopy was used to optimize the conditions employed for electrochemical investigations Amperometry was then performed on two cell lines pre-incubated with each of the three ferrocifens Interestingly, these results demonstrate that the presence of an aminoalkyl chain in the ferrocifen structure may confer a unique behavior toward both cell lines, in comparison with the two other compounds that lack this feature

Strong tip-sample coupling in thermal radiation scanning tunneling microscopy

Abstract: We analyze how a probing particle modifies the infrared electromagnetic near field of a sample. The particle, described by electric and magnetic polarizabilities, represents the tip of an apertureless scanning optical near-field microscope (SNOM). We show that the interaction with the sample can be accounted for by ascribing to the particle dressed polarizabilities that combine the effects of image dipoles with retardation. When calculated from these polarizabilities, the SNOM signal depends only on the fields without the perturbing tip. If the studied surface is not illuminated by an external source but heated instead, the signal is closely related to the projected electromagnetic local density of states (EM-LDOS). Our calculations provide the link between the measured far-field spectra and the sample's optical properties. We also analyze the case where the probing particle is hotter than the sample and evaluate the impact of the dressed polarizabilities on near-field radiative heat transfer. We show that such a heated probe above a surface performs a surface spectroscopy, in the sense that the spectrum of the heat current is closely related to the local electromagnetic density of states. The calculations agree well with available experimental data.

Dealloying of Al2Cu, Al7Cu2Fe, and Al2CuMg intermetallic phases to form nanoparticulate copper films

Abstract: Copper rich intermetallic particles are common in technical aluminum alloys. When exposed to an aggressive electrolyte, these particles undergo a transformation into a pure copper phase due to a selective dissolution or dealloying mechanism. In this work, the kinetics of this transformation have been investigated using synthetic intermetallic phases of Al2Cu, Al7Cu2Fe, and Al2CuMg in 2 M H2SO4 as commonly used in the anodization process. The elementary dissolution rates for Al, Mg, Cu, and Fe were measured as a function of time and potential using atomic emission spectroelectrochemistry (AESEC). From this data, it was possible to measure the degree of selective dissolution for the individual elements in the different potential domains. Mg and Fe dissolve simultaneously with Al during the overall polarization. Al dissolution is activated in the presence of Mg and inhibited in the presence of Fe. This work demonstrates the utility of atomic emission spectroelectrochemistry for the direct measurement of dealloying reactions and the indirect measurement of residual films.

Modelling the impact of climate change on sediment yield in a highly erodible Mediterranean catchment

Abstract: The assessment of climate change impacts on the sediment cycle is currently a primary concern for environmental policy analysts in Mediterranean areas. Nevertheless, quantitative assessment of climate change impacts is still a complex task. The aim of this study was to implement a sediment model by taking advantage of sediment proxy information provided by reservoir bottom deposits and to use it for climate change assessment in a Mediterranean catchment. The sediment model was utilised in a catchment that drains into a large reservoir. The depositional history of the reservoir was reconstructed and used for sediment sub-model implementation. The model results were compared with gauged suspended sediment data in order to verify model robustness. Then, the model was coupled with future precipitation and temperature scenarios obtained from climate models. Climatological model outputs for two emission scenarios (A2 and B2) were simulated and the results compared with a reference scenario. Model results showed a general decrease in soil moisture and water discharge. Large floods, which are responsible for the majority of sediment mobilisation, also showed a general decrease. Sediment yield showed a clear reduction under the A2 scenario but increased under the B2 scenario. The computed specific sediment yield for the control period was 6.33 Mg ha−1 year−1, while for the A2 and B2 scenarios, it was 3.62 and 7.04 Mg ha−1 year−1, respectively. Furthermore, sediment transport showed an increase in its time compression, i.e. a stronger dependence of total sediment yield from the largest event contributions. This study shows a methodology for implementing a distributed sediment model by exploiting reservoir sedimentation volumes. This methodology can be applied to a wide range of catchments, given the high availability of reservoir sedimentation data. Moreover, this study showed how such a model can be used in the framework of a climate change study, providing a measure of the impact of climate change on soil erosion and sediment yields.

Volterra-Based Reconfigurable Nonlinear Equalizer for Coherent OFDM

Abstract: A reconfigurable nonlinear equalizer (RNLE) based on inverse Volterra series transfer function is proposed for dual-polarization (DP) and multiband coherent optical orthogonal frequency-division multiplexing (OFDM) signals. It is shown that the RNLE outperforms by 2 dB the linear equalization in a 260-Gb/s DP-OFDM system at 1500 km. The RNLE improves the tolerance to inter/intraband nonlinearities, being independent on polarization tributaries, modulation format, signal bit rate, subcarrier number, and distance.

Flash flood mitigation as a positive consequence of anthropogenic forcing on the groundwater resource in a karst catchment

Abstract: The Mediterranean coastal region is prone to high-intensity rainfall events that are frequently associated with devastating flash floods. This paper discusses the role of a karst aquifer system in the flash floods of a Mediterranean river, the Lez river. Most of the Lez river watershed is located on karst terrains where interactions between surface water and groundwater take place. During extreme rainfall events, the presence of fractures and well-developed karst features in carbonate terrains enhances the infiltration processes and involves the concentration of the recharge into highly organized and permeable flow paths. The groundwater, therefore, quickly moves towards the natural outlets of the karst system. The influence of the Lez karst aquifer system on the associated river floods dynamics is analysed while considering the spatially distributed rainfall, as well as the time series of the groundwater level within the aquifer and of the Lez river discharge measured at various gauging stations. Special attention is given to the relative importance of the surface and underground processes involved in flash flood genesis. It is shown that the karst groundwater contributes to flash floods under certain conditions, while high-rate pumping within the karst aquifer, which generates significant drawdown, may mitigate flash floods under other conditions.

A physical interpretation of impedance at conducting polymer/electrolyte junctions

Abstract: We monitor the process of dedoping in a planar junction between an electrolyte and a conducting polymer using electrochemical impedance spectroscopy performed during moving front measurements. The impedance spectra are consistent with an equivalent circuit of a time varying resistor in parallel with a capacitor. We show that the resistor corresponds to ion transport in the dedoped region of the film, and can be quantitatively described using ion density and drift mobility obtained from the moving front measurements. The capacitor, on the other hand, does not depend on time and is associated with charge separation at the moving front. This work offers a physical description of the impedance of conducting polymer/electrolyte interfaces based on materials parameters.

3d reconstruction of a multiscale microstructure by anisotropic tessellation models

Abstract: In the area of tessellation models, there is an intense activity to fully understand the classical models of Voronoi, Laguerre and Johnson-Mehl. Still, these models are all simulations of isotropic growth and are therefore limited to very simple and partly convex cell shapes. The here considered microstructure of martensitic steel has a much more complex and highly non convex cell shape, requiring new tessellation models. This paper presents a new approach for anisotropic tessellation models that resolve to the well-studied cases of Laguerre and Johnson-Mehl for spherical germs. Much better reconstructions can be achieved with these models and thus more realistic microstructure simulations can be produced for materials widely used in industry like martensitic and bainitic steels.

The reliability of the anterior pelvic plane for computer navigated acetabular component placement during total hip arthroplasty: Prospective study with the EOS imaging system

Abstract: Introduction Computer navigated total hip arthroplasty is mostly based on the use of the anterior pelvic plane (APP) as a reference. EOS is a new imaging system that provides three-dimensional analysis of the pelvis in a functional position with a low dose of radiation. The aim of this study was to evaluate the reliability of the APP for placement of the cup during computer navigated THA using EOS. Hypothesis The reliability of the APP is limited for the placement of the acetabular cup during computer navigated THA. Materials and methods This was a prospective monocentric study using the EOS imaging system evaluating 44 patients in the standing position three months after computer navigated THA (Orthopilot™). Reproducibility of EOS measurements were analyzed using SterEOS software and the reliability of the navigation data for the position of the cup were assessed. Results Intra and interobserver reproducibility of the measurements of the orientation of the cup by EOS were good with correlation coefficients above 93% and 95% and confidence intervals of less than ± 5°. Mean cup inclination and anteversion were 41.3° and 20.9° and 44.3° and 29.5° respectively in operatively and post-operatively. The differences between measurements of operative cup inclination using computer assisted navigation and the post-operative EOS measurements were significant ( P Discussion Our study confirms the lack of precision of the APP as a reference for positioning of the acetabular component, especially in relation to anteversion. Although for many years the APP was considered to be a global reference, in fact, it is subject to significant inter-individual variations and variations during changes in position. These factors, associated with the difficulty of determining the preoperative APP, explain the lack of reliability of this reference. Preoperative evaluation of the orientation of APP by EOS and its integration into the navigation system could help the operator position these components. Level of evidence Level III Prospective diagnostic case controlled study.

Gait Recognition Based on Modified Phase Only Correlation

Abstract: Clothing, carrying conditions, and other intra-class variations, also referred as ”covariates”, affect the performance of gait recognition systems. This paper proposes a supervised feature extraction method which is able to select relevant features for human recognition to mitigates the impact of covariates and hence improve the recognition performance. The proposed method is evaluated using CASIA Gait Database (Dataset B) and the experimental results suggest that our method yields attractive results.

A Situated Approach of Roles and Participation in Open Source Software Communities

Abstract: Our research aims at understanding the various forms of participation in Open Source Software (OSS) design, seen as distributed design in online spaces of actions - discussion, implementation and boundary between these spaces. We propose a methodology - based on situated analyses of a formal design process used in the Python project- to identify the distribution of actual roles (implementation, interactive, group and design oriented) performed by participants into and between the spaces (defining boundary spaces). This notion of roles is grounded in collaborative design activities performed online by participants. This way, our findings complete the core-periphery model of participation in OSS. Concerning the distribution of roles between spaces, we reveal a map of participation in OSS: the majority of participants are pure discussants but all participants in the implementation spaces do also act in the discussion space and only few participants act at boundary spaces. Concerning the distribution of roles between participants in the discussion space, we reveal that interactions are structured by a central hub (occupied by key-participants) and that, whereas design-oriented roles are spread among all participants, group-oriented roles are performed by one or two participants in the respective spaces and at their boundary. Finally, combination of roles reveals five individual profiles performed by participants. Our approach could be extended to other design situations to explore relationships between forms of participation- in particular those revealing use-oriented contributions- performance, and quality of the design product. Finally, it could be a basis for specifying tools to monitor and manage community activity for both research issues and support of online community.