Showing papers by "ParisTech published in 2010"

Modeling the Mediterranean Sea interannual variability during 1961–2000: Focus on the Eastern Mediterranean Transient

Abstract: [1] This work is dedicated to the study of the climate variability of the Mediterranean Sea, in particular the study of the Eastern Mediterranean Transient (EMT) which occurred in the early 1990s. Simulations of the 1961–2000 period have been carried out with an eddy-permitting Ocean General Circulation Model of the Mediterranean Sea, driven by realistic interannual high-resolution air-sea fluxes. Using different databases for the river runoff, Black Sea inflow, and Atlantic thermohaline characteristics at climatological or interannual scales, we assess the effects of the non-atmospheric hydrological forcings on the simulation of the interannual variations of the Mediterranean circulation. The evolution of the basin-scale heat content is in very good agreement with the observations (especially in the surface and intermediate layers), while the agreement is lower for the evolution of the salt content. Convection events in the Aegean Sea are noticed in the simulations between 1972 and 1976, in the late 1980s, and around the EMT period. The formation rates of Cretan Deep Water (CDW) are different during these periods, allowing or preventing the spreading of CDW into the eastern Mediterranean. The sequence of the EMT events is well reproduced: the high winter oceanic surface cooling and net evaporation over the Aegean Sea in the early 1990s, the high amount of dense CDW formed during these winters, and then the overflow and the spreading of this CDW in the eastern Mediterranean. Among the preconditioning processes suggested in the literature, we find that changes in the Levantine surface circulation, possibly induced by the presence in the Cretan Passage of anticyclonic eddies and a lasting period with reduced net precipitation over the eastern Mediterranean, lead to an increase of the salt content of the Aegean Sea. Changes in the Black Sea freshwater inflow or in the characteristic of the Atlantic Water entering at the Gibraltar Strait also modify the thermohaline state of the Aegean Sea before the EMT. But, as none of these preconditioning factors has a lasting impact on lowering the vertical stratification of the Aegean Sea, we conclude that concerning the EMT, the major triggering elements are the atmospheric fluxes and winds occurring in winters 1991–1992 and 1992–1993.

Radiative corrections to the polarizability tensor of an electrically small anisotropic dielectric particle

Abstract: Radiative corrections to the polarizability tensor of isotropic particles are fundamental to understand the energy balance between absorption and scattering processes. Equivalent radiative corrections for anisotropic particles are not well known. Assuming that the polarization within the particle is uniform, we derived a closed-form expression for the polarizability tensor which includes radiative corrections. In the absence of absorption, this expression of the polarizability tensor is consistent with the optical theorem. An analogous result for infinitely long cylinders was also derived. Magneto optical Kerr effects in non-absorbing nanoparticles with magneto-optical activity arise as a consequence of radiative corrections to the electrostatic polarizability tensor.

On the Convergence of a Greedy Rank-One Update Algorithm for a Class of Linear Systems

Abstract: In this paper we study the convergence of the well-known Greedy Rank-One Update Algorithm. It is used to construct the rank-one series solution for full-rank linear systems. The existence of the rank one approximations is also not new, but surprisingly the focus there has been more on the applications side more that in the convergence analysis. Our main contribution is to prove the convergence of the algorithm and also we study the required rank one approximation in each step. We also give some numerical examples and describe its relationship with the Finite Element Method for High-Dimensional Partial Differential Equations based on the tensorial product of one-dimensional bases. We illustrate this situation taking as a model problem the multidimensional Poisson equation with homogeneous Dirichlet boundary condition.

Generalization of the cavity method for adiabatic evolution of Gibbs states

Abstract: Mean-field glassy systems have a complicated energy landscape and an enormous number of different Gibbs states. In this paper, we introduce a generalization of the cavity method in order to describe the adiabatic evolution of these glassy Gibbs states as an external parameter, such as the temperature, is tuned. We give a general derivation of the method and describe in details the solution of the resulting equations for the fully connected $p$-spin model, the XOR-satisfiability (SAT) problem and the antiferromagnetic Potts glass (coloring problem). As direct results of the states following method we present a study of very slow Monte Carlo annealings, the demonstration of the presence of temperature chaos in these systems and the identification of an easy/hard transition for simulated annealing in constraint optimization problems. We also discuss the relation between our approach and the Franz-Parisi potential, as well as with the reconstruction problem on trees in computer science. A mapping between the states following method and the physics on the Nishimori line is also presented.

Constitutive modeling of the creep behavior of single crystal superalloys under non-isothermal conditions inducing phase transformations

Abstract: The prediction of the viscoplastic behavior of Ni-based single crystal superalloy is still a challenging issue due to the non-isothermal loadings which can be encountered by aeronautical engines components such as high pressure turbine blades. Under particular in-service conditions, these materials may experience temperature cycles which promote the dissolution of the strengthening γ′ phase of the material on (over)heating, and subsequent precipitation on cooling, leading to a transient viscoplastic behavior. New internal variables representing the microstructural changes under those specific thermal loadings have been introduced in the framework of crystal plasticity using a macroscopic approach (no representation of the γ/γ′ microstructure of the alloy) to account for the transient creep behavior induced by microstructure changes. This modeling approach captures first order effects on the creep behavior due to (a) γ′ precipitates volume fraction evolution of each kind of particles of a bimodal distribution of precipitates (which evolves according to thermal history), (b) recovery of the dislocation density and, (c) material orientation. In addition, a damage law keeping in memory all the thermal history and recovery processes has been introduced to account for the unconventional post-overheating creep life. This model is calibrated on non-isothermal creep experiments on [0 0 1] oriented single crystals made of MC2 alloy. It is able to predict creep strain (primary, secondary, tertiary), whatever the temperature history of the material. In addition, it can be used to quantify the effect of slight variation of the as-received γ′ volume fraction on the creep behavior.

Synthesis, capping and binding of colloidal gold nanoparticles to proteins

Abstract: Bovine serum albumin (BSA) was used as a stabilizing agent and biofunctionalized layer for water-dispersed gold nanoparticles (NPs) synthesized from metal precursor HAuCl4. The BSA binding to gold NPs was characterized qualitatively and quantitatively by transmission electron microscopy, UV-VIS and FTIR spectrophotometers. HER2 (human epidermal growth factor receptor 2) specific phage antibodies were attached to BSA stabilized gold NPs to form a gold‐antibody complex. An ELISA (enzyme-linked immunosorbent assay) test was done to confirm the bioactivity of antibodies attached to gold NPs.

On the cation dependence of interlamellar and interparticular water and swelling in smectite clays.

Abstract: The osmotic character of long-range interlamellar swelling in smectite clays is widely accepted and has been evidenced in the interlayer space by X-ray diffraction. Such a behavior in mesopores was not experimentally confirmed until the determination of the mesopore size distribution in Na−montmorillonite prepared from MX80 bentonite using thermoporometry experiments. This is confirmed here for other montmorillonite samples where the interlayer cations are alkaline and Ca2+ cations. The nature of the interlayer cation is found as strongly influencing the behavior of the size and the swelling of mesopores. These results are supported by the BJH (Barrett, Joyner and Halenda) pore radius values issued from the nitrogen adsorption−desorption isotherms at the dry state. Thermoporometry results as a function of relative humidity ranging from 11% to 97% have shown an evolution of the mesopore sizes for a purified Na−montmorillonite. New thermoporometry data are presented in this article and confirm that the inte...

Photothermal heterodyne holography of gold nanoparticles.

Abstract: We report a method based on heterodyne numerical holography associated to photothermal excitation for full field and three-dimensional localisation of metallic nanoparticles. A modulated pump laser (lambda = 532 nm) heats several particles, creating local refractive index changes. This modulation is detected using a probe and a local oscillator beam (lambda = 785 nm), frequency-shifted to create a hologram beating at low frequency. Tens of particles, down to diameters of 10 nm, can be localised simultaneously and selectively in three dimensions with near- diffraction resolution by a numerical reconstruction of a single hologram acquired in 5 s.

Direct Fabrication of a Ti-47Al-2Cr-2Nb Alloy by Selective Laser Melting and Direct Metal Deposition Processes

Abstract: A Ti-47Al-2Cr-2Nb (at.%) material was fabricated using two laser-based methods, “Selective Laser Melting” (SLM) and “Direct Metal Deposition” (DMD), for potential uses in aircraft jet engines. Experiments were conducted under controlled atmosphere by changing the processing parameters. Optimal parameters were searched for this relatively low ductility material to prevent cracking due to built-up residual stresses during fast cooling. It was observed that these non-equilibrium cooling conditions were fast enough to generate ultra fine and metastable structures exhibiting high microhardness values. Post heat-treatments were successfully used to restore homogeneous lamellar or duplex microstructures and to relieve the residual stresses. A comparison of these two methods is provided in terms of powder requirements and of process parameters to achieve noncracked structures and fully dense materials.

Thermocapillary actuation by optimized resistor pattern: bubbles and droplets displacing, switching and trapping

Abstract: We report a novel method for bubble or droplet displacement, capture and switching within a bifurcation channel for applications in digital microfluidics based on the Marangoni effect, i.e. the appearance of thermocapillary tangential interface stresses stemming from local surface tension variations. The specificity of the reported actuation is that heating is provided by an optimized resistor pattern (B. Selva, J. Marchalot and M.-C. Jullien, An optimized resistor pattern for temperature gradient control in microfluidics, J. Micromech. Microeng., 2009, 19, 065002) leading to a constant temperature gradient along a microfluidic cavity. In this context, bubbles or droplets to be actuated entail a surface force originating from the thermal Marangoni effect. This actuator has been characterized (B. Selva, I. Cantat, and M.-C. Jullien, Migration of a bubble towards a higher surface tension under the effect of thermocapillary stress, preprint, 2009) and it was found that the bubble/droplet (called further element) is driven toward a high surface tension region, i.e. toward cold region, and the element velocity increases while decreasing the cavity thickness. Taking advantage of these properties three applications are presented: (1) element displacement, (2) element switching, detailed in a given range of working, in which elements are redirected towards a specific evacuation, (3) a system able to trap, and consequently stop on demand, the elements on an alveolus structure while the continuous phase is still flowing. The strength of this method lies in its simplicity: single layer system, in situ heating leading to a high level of integration, low power consumption (P < 0.4 W), low applied voltage (about 10 V), and finally this system is able to manipulate elements within a flow velocity up to 1 cm s−1.

Localization for intelligent vehicle by fusing mono-camera, low-cost GPS and map data

Abstract: The localization of intelligent vehicle is an important research topic in the field of intelligent transportation systems. This paper proposes a new vehicle localization method by fusing mono-camera, low-cost GPS and map data. The basic idea is: a possible position range of the vehicle is determined by fusing low-cost GPS output and the map data; Lateral spatial information for high-accuracy localization is provided frequently by vision based lane detection module; both longitudinal and lateral spatial information for high accuracy localization is provided by vision based traffic sign detection module. The proposed method is economically feasible, is reliable and does not need any construction work or change on current traffic environments. Simulation based experiments have shown the effectiveness of the proposed method in achieving high-accuracy localization result (accuracy of centimeter-level) and have also shown apparent better performance of the proposed method over the performance of former method which is similar to the proposed method.

Depth sensitivity analysis of functional near-infrared spectroscopy measurement using three-dimensional Monte Carlo modelling-based magnetic resonance imaging

Abstract: Theoretical analysis of spatial distribution of near-infrared light propagation in head tissues is very important in brain function measurement, since it is impossible to measure the effective optical path length of the detected signal or the effect of optical fibre arrangement on the regions of measurement or its sensitivity. In this study a realistic head model generated from structure data from magnetic resonance imaging (MRI) was introduced into a three-dimensional Monte Carlo code and the sensitivity of functional near-infrared measurement was analysed. The effects of the distance between source and detector, and of the optical properties of the probed tissues, on the sensitivity of the optical measurement to deep layers of the adult head were investigated. The spatial sensitivity profiles of photons in the head, the so-called banana shape, and the partial mean optical path lengths in the skin-scalp and brain tissues were calculated, so that the contribution of different parts of the head to near-infrared spectroscopy signals could be examined. It was shown that the signal detected in brain function measurements was greatly affected by the heterogeneity of the head tissue and its scattering properties, particularly for the shorter interfibre distances.

Drop production and tip-streaming phenomenon in a microfluidic flow-focusing device via an interfacial chemical reaction.

Abstract: Microfluidic flow-focusing technology is used to investigate the effect on drop formation due to the production of a surfactant via an interfacial chemical reaction. The reactants are an aqueous so...

Oxidation-assisted creep damage in a wrought nickel-based superalloy: Experiments and modelling

Abstract: Creep damage investigation was carried out in wrought nickel-based superalloy Udimet 720LI in air at 850 °C using multiple cross-sections specimens in order to be able to make interrupted tests. In all tests conducted on this material, creep curves showed only tertiary stage and the surface connected intergranular cracking was found to be dominant in creep fracture. It was shown that γ′ precipitate coarsening occurs in the bulk of the specimens and obeys the LSW kinetics. Metallographic analysis led to the conclusion that creep does not alter oxidation, except at grain boundaries, where oxide spikes can be developed under creep. Therefore grain boundary oxidation was found to be creep strain-assisted. A constitutive model accounting for precipitate coarsening was proposed. The oxidation-assisted intergranular damage and the oxidation embrittlement of the microstructure elements phenomena were successfully described using the continuum damage mechanics and the local ductility exhaustion laws, respectively. Creep rupture and elongation curves were taken into account by the model with suitable accuracy, as well. The model was found able to figure the specimen's geometry variations effects on lifetime and creep elongation curves.

Lower limb coordination in hemiparetic subjects: impact of botulinum toxin injections into rectus femoris.

Abstract: Background. Botulinum toxin (BTX) injection into rectus femoris (RF) is a therapeutic modality used to improve knee flexion during the swing phase of gait in hemiparesis. The impact of this treatment on lower limb coordination is unknown. The authors evaluated whether BTX injection into RF is associated with modifications of intersegmental coordination in hemiparesis. Methods. The authors evaluated gait in 10 control and 14 hemiparetic subjects with low peak knee flexion associated with inappropriate RF activity in mid-swing, using 3-dimensional analysis before and 1 month after BTX injection into RF (Botox, 200 units). Thigh—shank coordination was measured in the sagittal plane by averaging the continuous relative phase (CRPThigh— Shank) during each phase of the gait cycle in both lower limbs. The CRP is a validated metric that integrates angle positions and velocities of 2 limb segments to quantify their temporal—spatial coordination. Results. Before treatment, the low peak knee flexion in hemiparetic s...

The Effect of Aiding/Opposing Buoyancy on Two-Dimensional Laminar Flow Across a Circular Cylinder

Abstract: The effect of thermal buoyancy on the upward flow and heat transfer characteristics around a heated/cooled circular cylinder is studied. A two-dimensional finite-volume model is deployed for the analysis. The influence of aiding/opposing buoyancy is studied for the range of parameters −0.5 ≤ Ri ≤ 0.5, 50 ≤ Re ≤ 150, and the blockage ratios of B = 0.02 and 0.25. The flow shows unsteady periodic nature in the chosen range of Reynolds numbers for the forced convective cases (Ri = 0), and the vortex shedding stops completely at some critical values of Richardson numbers.

Homogeneous Dispersion of Magnetic Nanoparticles Aggregates in a PS Nanocomposite: Highly Reproducible Hierarchical Structure Tuned by the Nanoparticles’ Size

Abstract: We present here the synthesis and structural characterization of new nanocomposites made of spherical magnetic nanoparticles of maghemite (γ-Fe2O3) dispersed in a polystyrene (PS) matrix. The γ-Fe2O3 nanoparticles, synthesized in aqueous media, were first gently transferred by dialysis in dimethylacetamide (DMAc), a polar solvent which is a good solvent for PS. Electrostatic repulsions enable to keep colloidal stability in DMAc. The nanocomposites were then processed by a controlled evaporation of DMAc of binary mixtures of γ-Fe2O3 nanoparticles and PS chains. The size of the nanoparticles ranges from 3.5 to 6.5 nm and can be changed without any modification of the nanoparticles’ surface. The structural organization of the nanoparticles inside the polymer was determined as a function of the nanoparticles’ size. It was performed by combining very high resolution SAXS measurements which permit to decrease the nanoparticles content down to very low values (Φmag ∼ 10−5) and TEM microscopy. Whatever the size, ...

The role of disc-type crystal shape for micromechanical predictions of elasticity and strength of hydroxyapatite biomaterials.

Abstract: The successful design of ceramic bone biomaterials is challenged by two competing requirements: on the one hand, such materials need to be stiff and strong, which would suggest a low porosity (of pore sizes in the 10-100 microm range) to be targeted; on the other hand, bone biomaterials need to be bioactive (in particular vascularized), which suggests a high porosity of such materials. Conclusively, reliable information on how porosity drives the stiffness and strength properties of ceramic bone biomaterials (tissue engineering scaffolds) is of great interest. In this context, mathematical models are increasingly being introduced into the field. Recently, self-consistent continuum micromechanics formulations have turned out as expressedly efficient and reliable tools to predict hydroxyapatite biomaterials' stiffness and strength, as a function of the biomaterial-specific porosity, and of the 'universal' properties of the individual hydroxyapatite crystals: their stiffness, strength and shape. However, the precise crystal shape can be suitably approximated by specific ellipsoidal shapes: while it was shown earlier that spherical shapes do not lead to satisfactory results, and that acicular shapes are an appropriate choice, we here concentrate on disc-type crystal shape as, besides needles, plates are often reported in micrographs of hydroxyapatite biomaterials. Disc-based model predictions of a substantial set of experimental data on stiffness and strength of hydroxyapatite biomaterials almost attain the quality of the very satisfactory needle-based models. This suggests that, as long as the crystal shape is clearly non-spherical, its precise shape is of secondary importance if stiffness and strength of hydroxyapatite biomaterials are predicted on the basis of continuum micromechanics, from their micromorphology and porosity.

Algorithmic Information Theory-Based Analysis of Earth Observation Images: An Assessment

Abstract: Earth observation image-understanding methodologies may be hindered by the assumed data models and the estimated parameters on which they are often heavily dependent. First, the definition of the parameters may negatively affect the quality of the analysis. The parameters could not be captured in all aspects, and those resulting superfluous or not accurately tuned may introduce nuisance in the data. Furthermore, the diversity of the data, as regards sensor type, spatial, spectral, and radiometric resolution, and the variety and regularity of the observed scenes make it difficult to establish enough valid and robust statistical models to describe them. This letter proposes algorithmic information theory-based analysis as a valid solution to overcome these limitations. We will present different applications on satellite images, i.e., clustering, classification, artifact detection, and image time series mining, showing the generalization power of these parameter-free data-driven methods based on the computational complexity analysis.

Strip flatness modelling including buckling phenomena during thin strip cold rolling

Abstract: This paper describes the application of a steady state elastic-viscoplastic finite element model to the prediction of strip flatness and out of bite buckling during cold rolling of thin strips. This model is applied here to the last stand of a tinplate tandem cold mill. Results show that strip buckling reshuffles the non-homogeneous strip velocity profile just at the roll bite exit; strip stresses inside the roll bite are little impacted, so that roll stack deformation and roll force profile are not modified. The paper focuses on 'latent strip flatness', i.e. the profile in the transverse direction of the stress in the rolling direction. The profile predicted by the model far downstream the roll bite is in good agreement with shapemeter measurements only if strip buckling (i.e. manifest flatness) just at the roll bite exit and its interaction with the roll bite are considered, using a strong coupling of bite model and post-bite buckling model.