Showing papers by "ParisTech published in 2011"

Algorithms for nonnegative matrix factorization with the β-divergence

Abstract: This letter describes algorithms for nonnegative matrix factorization (NMF) with the β-divergence (β-NMF). The β-divergence is a family of cost functions parameterized by a single shape parameter β that takes the Euclidean distance, the Kullback-Leibler divergence, and the Itakura-Saito divergence as special cases (β = 2, 1, 0 respectively). The proposed algorithms are based on a surrogate auxiliary function (a local majorization of the criterion function). We first describe a majorization-minimization algorithm that leads to multiplicative updates, which differ from standard heuristic multiplicative updates by a β-dependent power exponent. The monotonicity of the heuristic algorithm can, however, be proven for β ∈ (0, 1) using the proposed auxiliary function. Then we introduce the concept of the majorization-equalization (ME) algorithm, which produces updates that move along constant level sets of the auxiliary function and lead to larger steps than MM. Simulations on synthetic and real data illustrate the faster convergence of the ME approach. The letter also describes how the proposed algorithms can be adapted to two common variants of NMF: penalized NMF (when a penalty function of the factors is added to the criterion function) and convex NMF (when the dictionary is assumed to belong to a known subspace).

Ultrafast compound doppler imaging: providing full blood flow characterization

Abstract: Doppler-based flow analysis methods require acquisition of ultrasound data at high spatio-temporal sampling rates. These rates represent a major technical challenge for ultrasound systems because a compromise between spatial and temporal resolution must be made in conventional approaches. Consequently, ultrasound scanners can either provide full quantitative Doppler information on a limited sample volume (spectral Doppler), or averaged Doppler velocity and/or power estimation on a large region of interest (Doppler flow imaging). In this work, we investigate a different strategy for acquiring Doppler information that can overcome the limitations of the existing Doppler modes by significantly reducing the required acquisition time. This technique is called ultrafast compound Doppler imaging and is based on the following concept: instead of successively insonifying the medium with focused beams, several tilted plane waves are sent into the medium and the backscattered signals are coherently summed to produce high-resolution ultrasound images. We demonstrate that this strategy allows reduction of the acquisition time by a factor of up to of 16 while keeping the same Doppler performance. Depending on the application, different directions to increase performance of Doppler analysis are proposed and the improvement is quantified: the ultrafast compound Doppler method allows faster acquisition frame rates for high-velocity flow imaging, or very high sensitivity for low-flow applications. Full quantitative Doppler flow analysis can be performed on a large region of interest, leading to much more information and improved functionality for the physician. By leveraging the recent emergence of ultrafast parallel beamforming systems, this paper demonstrates that breakthrough performances in flow analysis can be reached using this concept of ultrafast compound Doppler.

Arabidopsis Roots and Shoots Show Distinct Temporal Adaptation Patterns toward Nitrogen Starvation

Abstract: Nitrogen (N) is an essential macronutrient for plants. N levels in soil vary widely, and plants have developed strategies to cope with N deficiency. However, the regulation of these adaptive responses and the coordinating signals that underlie them are still poorly understood. The aim of this study was to characterize N starvation in adult Arabidopsis (Arabidopsis thaliana) plants in a spatiotemporal manner by an integrative, multilevel global approach analyzing growth, metabolites, enzyme activities, and transcript levels. We determined that the remobilization of N and carbon compounds to the growing roots occurred long before the internal N stores became depleted. A global metabolite analysis by gas chromatography-mass spectrometry revealed organ-specific differences in the metabolic adaptation to complete N starvation, for example, for several tricarboxylic acid cycle intermediates, but also for carbohydrates, secondary products, and phosphate. The activities of central N metabolism enzymes and the capacity for nitrate uptake adapted to N starvation by favoring N remobilization and by increasing the high-affinity nitrate uptake capacity after long-term starvation. Changes in the transcriptome confirmed earlier studies and added a new dimension by revealing specific spatiotemporal patterns and several unknown N starvation-regulated genes, including new predicted small RNA genes. No global correlation between metabolites, enzyme activities, and transcripts was evident. However, this multilevel spatiotemporal global study revealed numerous new patterns of adaptation mechanisms to N starvation. In the context of a sustainable agriculture, this work will give new insight for the production of crops with increased N use efficiency.

A Survey of Terahertz Applications in Cultural Heritage Conservation Science

Abstract: The authors present a review of the advances that have been made to establish terahertz applications in the cultural heritage conservation sector over the last several years. This includes material spectroscopy, 2D and 3D imaging and tomographic studies, using a broad range of terahertz sources demonstrating the breadth and application of this burgeoning community.

Exploring Electronic versus Steric Effects in Stereoselective Ring‐Opening Polymerization of Lactide and β‐Butyrolactone with Amino‐alkoxy‐bis(phenolate)–Yttrium Complexes

Abstract: A series of methoxy-amino-bis(phenol)s (ONOO(R(1),R(2)))H(2) possessing on the phenol rings R(1) ortho substituents with variable steric and electronic properties (R(1)=CMe(2)Ph, 1; CMe(2)tBu, 3; CMe(2)(4-CF(3)C(6)H(4)), 5; CPh(3), 9; Cl, 10) has been synthesized and further reacted with [Y{N(SiHMe(2))(2)}(3)](THF)(2) to give cleanly the corresponding yttrium compounds [Y(ONOO(R(1),R(2))){N(SiHMe(2))(2)}(thf)(n)] (Y-x); the solid-state structures of Y-3 and Y-10 have been determined. These amido complexes have been used as initiators for the ring-opening polymerization (ROP) of rac-lactide (LA) and rac-β-butyrolactone (BBL) to provide heterotactically enriched poly(lactic acid)s (PLAs) and syndiotactically enriched poly(3-hydroxybutyrate)s (PHBs), respectively, by means of a chain-end control mechanism. Most of these polymerizations proceeded in a controlled fashion, giving polymers with narrow polydispersities and experimental molecular weights in good agreement with calculated values. The nature of the R(1) ortho substituents has a profound impact on the rates and, more spectacularly, on the stereocontrol of the polymerizations. The heterotactic stereocontrol in the ROP of rac-LA appears to be governed essentially by steric considerations; the larger the substituent, the higher the heterotacticity: R(1)=Cl (P(r)=0.56)≪CMe(3) (P(r)=0.80)≪CMe(2)Ph (P(r)=0.90)

Wrinkling hierarchy in constrained thin sheets from suspended graphene to curtains.

Abstract: The drive towards miniaturization in technology is demanding for increasingly thinner components, raising new mechanical challenges. Thin films are however unstable to boundary or substrate-induced compressive loads. Moderate compression results in regular wrinkling while further confinement can lead to crumpling. Regions of stress focusing can be a hindrance, acting as nucleation points for mechanical failure. Conversely, they can be exploited constructively for tunable thin structures. For example, singular points of deformation dramatically affect the electronic properties of graphene. Here, we show that thin sheets under boundary confinement spontaneously generate a universal self-similar hierarchy of wrinkles; from strained suspended graphene to ordinary hanging curtains. We develop a formalism based on "wrinklons", a localized transition zone in the merging of two wrinkles, as building-blocks to describe these wrinkled patterns. Our approach may find applications in domains such as graphene-based electronics, fuel cell technology, thin-film solar cells or draping in virtual reality.

Wrinkling Hierarchy in Constrained Thin Sheets from Suspended Graphene to Curtains

Abstract: We show that thin sheets under boundary confinement spontaneously generate a universal self-similar hierarchy of wrinkles. From simple geometry arguments and energy scalings, we develop a formalism based on wrinklons, the localized transition zone in the merging of two wrinkles, as building blocks of the global pattern. Contrary to the case of crumpled paper where elastic energy is focused, this transition is described as smooth in agreement with a recent numerical work [R.D. Schroll, E. Katifori, and B. Davidovitch, Phys. Rev. Lett. 106, 074301 (2011)]. This formalism is validated from hundreds of nanometers for graphene sheets to meters for ordinary curtains, which shows the universality of our description. We finally describe the effect of an external tension to the distribution of the wrinkles.

Asf1b, the necessary Asf1 isoform for proliferation, is predictive of outcome in breast cancer

Abstract: Mammalian cells possess two isoforms of the histone H3–H4 chaperone anti-silencing function 1 (Asf1), Asf1a and Asf1b. However to date, whether they have individual physiological roles has remained elusive. Here, we aim to elucidate the functional importance of Asf1 isoforms concerning both basic and applied aspects. First, we reveal a specific proliferation-dependent expression of human Asf1b unparalleled by Asf1a. Strikingly, in cultured cells, both mRNA and protein corresponding to Asf1b decrease upon cell cycle exit. Depletion of Asf1b severely compromises proliferation, leads to aberrant nuclear structures and a distinct transcriptional signature. Second, a major physiological implication is found in the applied context of tissue samples derived from early stage breast tumours in which we examined Asf1a/b levels. We reveal that overexpression of Asf1b mRNA correlate with clinical data and disease outcome. Together, our results highlight a distribution of tasks between the distinct Asf1 isoforms, which emphasizes a specialized function of Asf1b required for proliferation capacity. We discuss the implications of these results for breast cancer diagnosis and prognosis.

Early stages of surface graphitization on nanodiamond probed by x-ray photoelectron spectroscopy

Abstract: We have investigated the early stages of graphitization on detonation nanodiamond during sequential annealing treatments under vacuum using x-ray photoelectron spectroscopy. Two different temperature-dependent regimes were observed. Below 900 \ifmmode^\circ\else\textdegree\fi{}C, the nanodiamond surface reconstructs into graphitic domain but does not alter the diamond core. Above 900 \ifmmode^\circ\else\textdegree\fi{}C, graphitization, i.e., carbon hybridization changes from $s{p}^{3}$ to $s{p}^{2}$, occurs from the nanodiamond surface toward the diamond core. Graphitization is observed at much lower temperatures on nanodiamonds than on bulk diamond due to the high concentration of structural defects on their surface. These results indicate that low-temperature annealing under vacuum is an efficient method to uncouple surface and bulk graphitization. Hybrid nanocarbons formed in these conditions, constituted of a diamond core with a thin graphitic outer shell, may have interesting catalytic and chemical properties.

Random-walk-based stochastic modeling of three-dimensional fiber systems

Abstract: For the simulation of fiber systems, there exist several stochastic models: systems of straight nonoverlapping fibers, systems of overlapping bending fibers, or fiber systems created by sedimentation. However, there is a lack of models providing dense, nonoverlapping fiber systems with a given random orientation distribution and a controllable level of bending. We introduce a new stochastic model in this paper that generalizes the force-biased packing approach to fibers represented as chains of balls. The starting configuration is modeled using random walks, where two parameters in the multivariate von Mises--Fisher orientation distribution control the bending. The points of the random walk are associated with a radius and the current orientation. The resulting chains of balls are interpreted as fibers. The final fiber configuration is obtained as an equilibrium between repulsion forces avoiding crossing fibers and recover forces ensuring the fiber structure. This approach provides high volume fractions up to $72.0075%$.

Surface chemical modifications and surface reactivity of nanodiamonds hydrogenated by CVD plasma

Abstract: The present study focuses on the interaction of hydrogen microwave CVD plasma with nanodiamonds (NDs). Hydrogen treated NDs (H-NDs) were characterized using electron spectroscopies (XPS, AES) without air exposure. A surface temperature higher than 700 °C is needed to remove the oxygen present on raw NDs. The kinetics of oxygen removal were investigated. Moreover, UHV annealings of H-NDs after ageing in ambient air clearly underline that 75% of the oxygen is related to physisorbed species. Finally, H-NDs were efficiently grafted using photochemical reaction with alkenes and a spontaneous coupling of aryldiazonium salts. These results confirm similar electronic surface properties between bulk and nano diamond materials.

GeoBrush: Interactive Mesh Geometry Cloning

Abstract: We propose a method for interactive cloning of 3D surface geometry using a paintbrush interface, similar to the continuous cloning brush popular in image editing. Existing interactive mesh composition tools focus on atomic copy-and-paste of preselected feature areas, and are either limited to copying surface displacements, or require the solution of variational optimization problems, which is too expensive for an interactive brush interface. In contrast, our GeoBrush method supports real-time continuous copying of arbitrary high-resolution surface features between irregular meshes, including topological handles. We achieve this by first establishing a correspondence between the source and target geometries using a novel generalized discrete exponential map parameterization. Next we roughly align the source geometry with the target shape using Green Coordinates with automatically-constructed cages. Finally, we compute an offset membrane to smoothly blend the pasted patch with C continuity before stitching it into the target. The offset membrane is a solution of a bi-harmonic PDE, which is computed on the GPU in real time by exploiting the regular parametric domain. We demonstrate the effectiveness of GeoBrush with various editing scenarios, including detail enrichment and completion of scanned surfaces.

Guaranteed estimation of the parameters of nonlinear continuous‐time models: Contributions of interval analysis

Abstract: This paper is about guaranteed parameter estimation in two contexts, namely bounded-error and optimal estimation. In bounded-error estimation, one looks for the set of all parameter vectors that are consistent with some prior bounds on the errors deemed acceptable between the model behavior and that of the system. In optimal estimation, one looks for the set of all parameter vectors that minimize some cost function quantifying the discrepancy between the behaviors of the system and its model. In both cases, guaranteed means that proven statements are made about the set of interest. The situation is made much more difficult when the model output is assumed to depend nonlinearly in the parameters to be estimated and when dealing with continuous-time models, as here. Important tools based on interval analysis (IA) that contribute to allowing guaranteed estimation in these challenging conditions are presented. Some are absolutely classical in the context of IA but not so well known in the community of parameter estimation at large. Others have been developed recently and were mainly presented in conferences. Some, such as the use of sensitivity functions to reduce more quickly the size of outer approximations of the sets of interest, are new. Challenges for future research in the context of guaranteed nonlinear estimation are mentioned. Copyright © 2010 John Wiley & Sons, Ltd.

Calcium phosphate grafts produced by rapid prototyping based on laser cladding

Abstract: Rapid prototyping based on laser cladding by powder injection has been used to produce calcium phosphate three-dimensional grafts without using molds. Precursor material comprising of hydroxyapatite (HA) powder was irradiated by means of an infrared Nd:YAG laser. The processing parameters and the thermal history of the processed material have been assessed and the process has been optimized to obtain solid parts. Processing by laser cladding lead to complete dehydroxylation of the precursor HA, the obtained microstructure is composed by an alpha-tricalcium phosphate (α-TCP) matrix with nucleated tetracalcium phosphate (TTCP) grains, in coexistence with oxyapatite and amorphous calcium phosphate. The produced bioceramic grafts were observed to be bioactive, leading to calcium-deficient hydroxyapatite precipitation and promoting pre-osteoblastic cell attachment and proliferation during “ in vitro ” cell culture test.

Benchmark of experimental techniques for measuring and controlling suction

Abstract: The paper presents a benchmarking study carried out within the ‘Mechanics of Unsaturated Soils for Engineering' (MUSE) network aimed at comparing different techniques for measurement and control of suction. Techniques tested by the eight ‘Mechanics of Unsaturated Soils for Engineering' research teams include axis-translation (pressure plate and suction-controlled oedometer), high-capacity tensiometer and osmotic technique. The soil used in the exercise was a mixture of uniform sand, sodium bentonite (active clay) and kaolinite (non-active clay), which were all commercially available. Samples were prepared by one team and distributed to all other teams. They were normally consolidated from slurry under one-dimensional conditions (consolidometer) to a given vertical stress. The water retention characteristics of the initially saturated specimens were investigated along the main drying path. Specimens were de-saturated by applying suction through the liquid phase when using an axis-translation technique or o...

Variation in breast cancer risk with mutation position, smoking, alcohol, and chest X-ray history, in the French National BRCA1/2 carrier cohort (GENEPSO)

Abstract: Germline mutations in BRCA1/2 confer a high risk of breast cancer (BC), but the magnitude of this risk varies according to various factors Although controversial, there are data to support the hypothesis of allelic-risk heterogeneity We assessed variation in BC risk according to the location of mutations recorded in the French study GENEPSO Since the women in this study were selected from high-risk families, oversampling of affected women was eliminated by using a weighted Cox-regression model Women were censored at the date of diagnosis when affected by any cancer, or the date of interview when unaffected A total of 990 women were selected for the analysis: 379 were classified as affected, 611 as unaffected For BRCA1, there was some evidence of a central region where the risk of BC is lower (codons 374–1161) (HR = 059, P = 004) For BRCA2, there was a strong evidence for a region at decreased risk (codons 957–1827) (HR = 035, P = 0005) and for one at increased risk (codons 2546–2968) (HR = 356, P = 001) Moreover, we found an important association between radiation exposure from chest X-rays and BC risk (HR = 429, P < 10−3) and a positive association between smoking more than 21 pack-years and BC risk (HR = 209, P = 004) No significant variation in BC risk associated with chest X-ray exposure, smoking, and alcohol consumption was found according to the location of the mutation in BRCA1 and BRCA2 Our findings are consistent with those suggesting that the risk of BC is lower in the central regions of BRCA1/2 A new high-risk region in BRCA2 is described Taking into account environmental and lifestyle modifiers, the location of mutations might be important in the clinical management of BRCA mutation carriers

Multi-vehicle cooperative perception and augmented reality for driver assistance: A possibility to ‘see’ through front vehicle

Abstract: A typical scenario where a front vehicle (the first vehicle) occludes the view of another vehicle (the second vehicle) is often encountered in traffic environment and can be potentially dangerous. For enhancing traffic safety in this scenario, multi-vehicle cooperative perception between the two vehicles is useful. Besides, better visualization of the cooperative perception result might be needed for driver assistance. Based on these motivations, a method of multi-vehicle cooperative perception which realizes an effect of augmented reality is proposed in this paper; the effect of augmented reality here means a direct and natural visualization of the occluded environment for the second vehicle, as if a person at the second vehicle can see through the front vehicle and directly perceive the environment occluded. The proposed cooperative perception method can be used for applications of completely automated mode while the effect of augmented reality would also be convenient for driver assistance. Theoretical and technical details of the proposed method are described; field tests results are given to demonstrate the performance of the proposed method.1

Genetic diversity of the wheat yellow rust population in Pakistan and its relationship with host resistance

Abstract: Yellow rust, caused by Puccinia striiformis f.sp. tritici (PST), is an important disease that threatens wheat production in Pakistan. This study was designed to explore the virulence and simple sequence repeat (SSR) diversity of the Pakistani PST population and the ongoing selective pressures of widely grown wheat cultivars. Analyses of 49 isolates sampled from the North-West Frontier Province of Pakistan led to the identification of 12 distinct pathotypes. The virulence frequencies of v2 (virulent against Yr2), v6, v7, v9, vSU and v27 ranged from 63% to 100%. Virulences v3, v4, v17 and vSD were uncommon, whilst v5, v10, v15, v24, v32 and vSp were not detected. The pathotypes thus described were then classified into 27 distinct genotypes. Bayesian structure analysis clustered these genotypes into five groups (in addition to one hybrid isolate) which represent three distinct lineages of the SSR-based phylogenetic tree. Of the studied isolates, 80%, represented by three predominant pathotypes (P1–P3), belonged to the same characteristic Pakistani lineage, whilst the other isolates were close to either a Mediterranean lineage or a Northern European lineage. Genetic recombination was detected within P2 isolates. Resistance genes postulated in 40 Pakistani wheat cultivars indicated the high frequency of Yr2, Yr6, Yr7, Yr9, Yr27 and YrSU. Only 11 cultivars were found to be resistant to P1–P3. Migration and varietal diversity factors might contribute to maintaining the currently high genetic diversity in Pakistani PST, and have serious regional implications for wheat improvement programmes.

SIR distribution analysis in cellular networks considering the joint impact of path-loss, shadowing and fast fading

Abstract: In this paper, we propose an analysis of the joint impact of path-loss, shadowing and fast fading on cellular networks. Two analytical methods are developed to express the outage probability. The first one based on the Fenton-Wilkinson approach, approximates a sum of log-normal random variables by a log-normal random variable and approximates fast fading coefficients in interference terms by their average value. We denote it FWBM for Fenton-Wilkinson based method. The second one is based on the central limit theorem for causal functions. It allows to approximate a sum of positive random variables by a Gamma distribution. We denote it CLCFM for central limit theorem for causal functions method. Each method allows to establish a simple and easily computable outage probability formula, which jointly takes into account path-loss, shadowing and fast fading. We compute the outage probability, for mobile stations located at any distance from their serving BS, by using a fluid model network that considers the cellular network as a continuum of BS. We validate our approach by comparing all results to extensive Monte Carlo simulations performed in a traditional hexagonal network and we provide the limits of the two methods in terms of system parameters. The proposed framework is a powerful tool to study performances of cellular networks, e.g., OFDMA systems (WiMAX, LTE).

How different steel grades react to a salt bath nitrocarburizing and post-oxidation process: Influence of alloying elements

Abstract: Two different grades of steel, DC 04 (non alloyed steel) and 15 CrMoV 6 (alloyed steel) were studied; both of them were salt bath nitrided with QPQ process. They were subjected to different durations of nitriding sequences, 2 h, 3 h and 8 h while the duration for the last sequence, i.e. oxidation remained the same. Microhardness measurements showed that the alloying elements had a strong influence on the profile and on the surface hardness value. For each grade, the maximum surface hardness value was already obtained after a 2 h treatment. The surface constitution was observed by XRD; the presence of Fe 3 O 4 was noticed above the compound layers made up of e and γ′ nitrides. Cross sectional observations by SEM revealed that the growth kinetics of compound layers follows a parabolic law. The layers' thickness and constitution have also been confirmed by EDS analysis. On increasing nitriding duration, γ′ nitride content decreases while e nitride content increases. For longer nitriding durations, mostly e nitride and Fe 3 O 4 are observed on the surface of both grades. It seems that for long nitriding sequences, additional elements are not essential for compound layers' nature.

Absorption spectra of azobenzenes simulated with time-dependent density functional theory

Abstract: Using time-dependent density functional theory and the polarizable continuum model, we have simulated the absorption spectra of an extended series of azobenzene dyes. First, we have determined a theoretical level optimal for this important class of dyes, and it turned out that a C-PCM-CAM-B3LYP/6-311+G(d,p)//C-PCM-B3LYP/6-311G(d,p) approach represents an effective compromise between chemical accuracy and computational cost. In a second stage, we have compared the theoretical and experimental transition energies for 46 n π☆ and 141 π π☆ excitations. For the full set, that spans over a 302–565 nm domain, we obtained a mean absolute deviation of 13 nm (0.10 eV) and a linear correlation coefficient of 0.95, illustrating the accuracy of our approach, though some significant outliers pertained. In a last step, the impact of several modifications, that is, trans/cis isomerization, variation of the acidity of the medium and azo/hydrazo tautomerism have been modeled with two functionals. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Minimum d-blockers and d-transversals in graphs

Abstract: We consider a set V of elements and an optimization problem on V: the search for a maximum (or minimum) cardinality subset of V verifying a given property ?. A d-transversal is a subset of V which intersects any optimum solution in at least d elements while a d-blocker is a subset of V whose removal deteriorates the value of an optimum solution by at least d. We present some general characteristics of these problems, we review some situations which have been studied (matchings, s---t paths and s---t cuts in graphs) and we study d-transversals and d-blockers of stable sets or vertex covers in bipartite and in split graphs.