[tel-01135694] Stratégie de fusion pour des signaux écrits et sonores

L’être humain dans sa quête de mise en œuvre d’un dialogue le plus naturel possible avec sa machine s’inspire continuellement de la machine la plus perfectionnée connue à ce jour : l’être humain lui-même. Une caractéristique forte du dialogue entre humains est le recours à la multi-modalité. Le travail rapporté dans ce manuscrit porte sur l’étude, la conception et la validation d’un système de reconnaissance des expressions mathématiques, classe particulière de structures bidimensionnelles. Ce système est développé dans un cadre bimodal où l’on considère de façon complémentaire l’écriture manuscrite et la parole. La complémentarité qui existe entre ces deux modalités a été vérifiée et exploitée à profit dans notre système, d’abord dans un cadre simplifié qui est celui de la reconnaissance des symboles mathématiques isolés, puis dans un cadre plus général et plus réaliste, celui des expressions mathématiques complètes. La mise en place de ce système bimodal et sa validation requérant la disponibilité de données bimodales, nous avons collecté, complètement annoté et mis à disposition une base, nommée HAMEX, contenant 4350 expressions bimodales couvrant différents domaines. Nous montrons comment utiliser la transcription automatique de la dictée d’une expression pour guider le système de reconnaissance du signal manuscrit pour obtenir des résultats supérieurs au système monomodal. Les performances de ce système s’avèrent être meilleures que celles d’un système mono-modal basé uniquement sur le signal manuscrit seul.



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[hal-01136079] CEDIMS: cloud ethical DICOM image Mojette storage

Dicom images of patients will necessarily been stored in Clouds. However, ethical constraints must apply. In this paper, a method which provides the two following conditions is presented: 1) the medical information is not readable by the cloud owner since it is distributed along several clouds 2) the medical information can be retrieved from any sufficient subset of clouds In order to obtain this result in a real time processing, the Mojette transform is used. This paper reviews the interesting features of the Mojette transform in terms of information theory. Since only portions of the original Dicom files are stored into each cloud, their contents are not reachable. For instance, we use 4 different public clouds to save 4 different projections of each file, with the additional condition that any 3 over 4 projections are enough to reconstruct the original file. Thus, even if a cloud is unavailable when the user wants to load a Dicom file, the other 3 are giving enough information for real time reconstruction. The paper presents an implementation on 3 actual clouds. For ethical reasons, we use a Dicom image spreaded over 3 public clouds to show the obtained confidentiality and possible real time recovery.



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[hal-00012830] Comment on 'Quantum Coherence between High Spin Superposition States of Single Molecule Magnet Ni4

In a recent paper, cond-mat/0405331 (Ref. 1), del Barco et al. reported experimental studies on a Ni4 molecular system. They used an experimental method (combining microwave spectroscopy with high sensitivity magnetic measurements) that we have introduced before, cond-mat/0404410 (see also Ref. 2 and 3). Among other things, our technique allows us to monitor spin-state populations in the presence of microwave magnetic fields. Absorption line-widths give rough 'upper bounds' on the decoherence rate similar to 'standard' high frequency electron paramagnetic resonance (HF-EPR) techniques. In the case of quasi continuous radiation our technique does NOT give directly the spin-lattice relaxation time T1. For measurements like those of del Barco et al., it simply gives access to the phonon-bottleneck time, a parameter that is many orders of magnitude longer than the spin-lattice relaxation time. Any conclusion concerning quantum coherence is preliminary.



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[hal-00012829] Comment on 'Pulsed field studies of the magnetization reversal in molecular nanomagnets

In a recent paper, cond-mat/0404041, J. Vanacken et al. reported experimental studies of crystals of Mn12-ac molecular nanomagnets in pulsed magnetic fields with sweep rates up to 4000 T/s. Steps in the magnetization curve were observed. The data were explained by collective dipolar relaxation. We give here an alternative explanation that is based on thermal avalanches triggered by defect molecules (faster relaxing species). These species are always present in Mn12-ac molecular nanomagnets. We propose a simple method to test this interpretation. Note that we do not question the possibility of collective effects that are bassed on spin--spin interactions.



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[hal-00012825] Quantum dynamics of exchange biased Single Molecule Magnets

We present a new family of exchange biased Single Molecule Magnets in which antiferromagnetic coupling between the two components results in quantum behaviour different from that of the individual SMMs. Our experimental observations and theoretical analysis suggest a means of tuning the quantum tunnelling of magnetization in SMMs. See also: W. Wernsdorfer, N. Aliaga-Alcalde, D. Hendrickson, G. Christou, Nature 416 (2002) 406.



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[hal-00743042] Semi-Lagrangian discontinuous Galerkin schemes for some first and second order partial differential equations

Explicit, unconditionally stable, high order schemes for the approximation of some first and second order linear, time-dependent partial differential equations (PDEs) are proposed. The schemes are based on a weak formulation of a semi-Lagrangian scheme using discontinuous Galerkin (DG) elements. It follows the ideas of the recent works of Crouseilles, Mehrenberger and Vecil (2010), Rossmanith and Seal (2011), for first order equations, based on exact integration, quadrature rules, and splitting techniques for the treatment of two-dimensional PDEs. For second order PDEs the idea of the scheme is a blending between weak Taylor approximations and projection on a DG basis. New and sharp error estimates are obtained for the fully discrete schemes and for variable coefficients. In particular we obtain high order schemes, unconditionally stable and convergent, in the case of linear first order PDEs, or linear second order PDEs with constant coefficients. In the case of non-constant coefficients, we construct, in some particular cases, "almost" unconditionally stable second order schemes and give precise convergence results. The schemes are tested on several academic examples.



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[hal-00012823] Spin-spin cross-relaxation in single-molecule magnets

It is shown that dipolar and weak superexchange interactions between the spin systems of single-molecule magnets (SMM) play an important role in the relaxation of magnetization. These interactions can reduce or increase resonant tunneling. The one-body tunnel picture of SMMs is not always sufficient to explain the measured tunnel transitions. We propose to improve the picture by including also two-body tunnel transitions such as spin-spin cross-relaxation (SSCR). A Mn4 SMM is used as a model system to study the SSCR which plays also an important role for other SMMs like Mn12 or Fe8. At certain external fields, SSCRs can lead to quantum resonances which can show up in hysteresis loop measurements as well defined steps. A simple model allows us to explain quantitatively all observed transitions. Including three-body transitions or dealing with the many-body problem is beyond the slope of this paper.



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[hal-01136899] Superhydrophobic surface properties with various nanofibrous structures by electrodeposition of PEDOT polymers with short fluorinated chains and rigid spacers

In the aim to produce superhydrophobic surface properties, the nanofibers are excellent candidates due to the possible control in the water adhesion by the nanofiber characteristics, for example. Here, we report the growth of nanofibers with various assemblies directly on surfaces by electropolymerization. For this purpose, an original 3,4-ethylenediothiophene monomer was synthesized. The monomer contains a short fluorinated chain (C4F9) in order to preserve the nanofiber morphology and a highly rigid methoxybenzothioate spacer for the reduction of the rigidity. In this work, we show that various nanofibrous structures and superhydrophobic properties can be obtained by modifying the electrolyte while the surface roughness can also be controlled by the number of deposition scans. The nanofibrous polymers could be used to control the attachment and growth of cells or bacteria.



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[hal-01136667] Quantitative convergence towards a self similar profile in an age-structured renewal equation for subdiffusion

Continuous-time random walks are generalisations of random walks frequently used to account for the consistent observations that many molecules in living cells undergo anomalous diffusion, i.e. subdiffusion. Here, we describe the subdiffusive continuous-time random walk using age-structured partial differential equations with age renewal upon each walker jump, where the age of a walker is the time elapsed since its last jump. In the spatially-homogeneous (zero-dimensional) case, we follow the evolution in time of the age distribution. An approach inspired by relative entropy techniques allows us to obtain quantitative explicit rates for the convergence of the age distribution to a self-similar profile, which corresponds to convergence to a stationnary profile for the rescaled variables. An important difficulty arises from the fact that the equation in self-similar variables is not autonomous and we do not have a specific analyitcal solution. Therefore, in order to quantify the latter convergence, we estimate attraction to a time-dependent "pseudo-equilibrium", which in turn converges to the stationnary profile.



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[hal-00012651] Magnetization reversal by uniform rotation (Stoner-Wohlfarth model) in f.c.c. cobalt nanoparticles

The combination of high sensitive superconducting quantum interference device (SQUID) with high quality nanoparticles allowed to check the simplest classical model describing the magnetisation reversal by uniform rotation which were proposed more than 50 years ago by Neel, Stoner and Wohlfarth. The micrometer sized SQUIDs were elaborated by electron beam lithography and the nanoparticles were synthesised by arc-discharge. The measured angular dependence of switching fields of nearly all f.c.c. Co nanoparticles revealed a dominating uniaxial magnetic anisotropy. This result suggests that twin boundaries and stacking faults strongly alter the cubic magnetocrystalline anisotropy leading to dominating uniaxial anisotropy. However, few particles were sufficiently \"perfect\" in order to show a more complex switching field surface and a field path dependence of the switching field which is the important signature of the cubic magnetocrystalline anisotropy.



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[hal-00081866] Josephson junctions and superconducting quantum interference devices made by local oxidation of niobium ultrathin films

We present a method for fabricating Josephson junctions and superconducting quantum interference devices (SQUIDs) which is based on the local anodization of niobium strip lines 3 to 6.5 nm-thick under the voltage-biased tip of an Atomic Force Microscope. Microbridge junctions and SQUID loops are obtained either by partial or total oxidation of the niobium layer. Two types of weak link geometries are fabricated : lateral constriction (Dayem bridges) and variable thickness bridges. SQUIDs based on both geometries show a modulation of the maximum Josephson current with a magnetic flux periodic with respect to the superconducting flux quantum h/2e. They persist up to 4K. The modulation shape and depth for SQUIDs based on variable thickness bridges indicate that the weak link size becomes comparable to the superconducting film coherence length which is of the order of 10nm.



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[hal-01136668] Exact bounds of the Möbius inverse of monotone set functions

We give the exact upper and lower bounds of the Möbius inverse of monotone and normalized set functions (a.k.a. normalized capacities) on a finite set of n elements. We find that the absolute value of the bounds tend to 4 n/2 √ πn/2 when n is large. We establish also the exact bounds of the interaction transform and Banzhaf interaction transform, as well as the exact bounds of the Möbius inverse for the subfamilies of k-additive normalized capacities and p-symmetric normalized capacities.



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[hal-01136899] Superhydrophobic surface properties with various nanofibrous structures by electrodeposition of PEDOT polymers with short fluorinated chains and rigid spacers

In the aim to produce superhydrophobic surface properties, the nanofibers are excellent candidates due to the possible control in the water adhesion by the nanofiber characteristics, for example. Here, we report the growth of nanofibers with various assemblies directly on surfaces by electropolymerization. For this purpose, an original 3,4-ethylenediothiophene monomer was synthesized. The monomer contains a short fluorinated chain (C4F9) in order to preserve the nanofiber morphology and a highly rigid methoxybenzothioate spacer for the reduction of the rigidity. In this work, we show that various nanofibrous structures and superhydrophobic properties can be obtained by modifying the electrolyte while the surface roughness can also be controlled by the number of deposition scans. The nanofibrous polymers could be used to control the attachment and growth of cells or bacteria.



from HAL : Dernières publications http://ift.tt/1BVgBEu

[hal-01136667] Quantitative convergence towards a self similar profile in an age-structured renewal equation for subdiffusion

Continuous-time random walks are generalisations of random walks frequently used to account for the consistent observations that many molecules in living cells undergo anomalous diffusion, i.e. subdiffusion. Here, we describe the subdiffusive continuous-time random walk using age-structured partial differential equations with age renewal upon each walker jump, where the age of a walker is the time elapsed since its last jump. In the spatially-homogeneous (zero-dimensional) case, we follow the evolution in time of the age distribution. An approach inspired by relative entropy techniques allows us to obtain quantitative explicit rates for the convergence of the age distribution to a self-similar profile, which corresponds to convergence to a stationnary profile for the rescaled variables. An important difficulty arises from the fact that the equation in self-similar variables is not autonomous and we do not have a specific analyitcal solution. Therefore, in order to quantify the latter convergence, we estimate attraction to a time-dependent "pseudo-equilibrium", which in turn converges to the stationnary profile.



from HAL : Dernières publications http://ift.tt/1bIfy5N

[hal-00012651] Magnetization reversal by uniform rotation (Stoner-Wohlfarth model) in f.c.c. cobalt nanoparticles

The combination of high sensitive superconducting quantum interference device (SQUID) with high quality nanoparticles allowed to check the simplest classical model describing the magnetisation reversal by uniform rotation which were proposed more than 50 years ago by Neel, Stoner and Wohlfarth. The micrometer sized SQUIDs were elaborated by electron beam lithography and the nanoparticles were synthesised by arc-discharge. The measured angular dependence of switching fields of nearly all f.c.c. Co nanoparticles revealed a dominating uniaxial magnetic anisotropy. This result suggests that twin boundaries and stacking faults strongly alter the cubic magnetocrystalline anisotropy leading to dominating uniaxial anisotropy. However, few particles were sufficiently \"perfect\" in order to show a more complex switching field surface and a field path dependence of the switching field which is the important signature of the cubic magnetocrystalline anisotropy.



from HAL : Dernières publications http://ift.tt/1BVgEjo

[hal-00081866] Josephson junctions and superconducting quantum interference devices made by local oxidation of niobium ultrathin films

We present a method for fabricating Josephson junctions and superconducting quantum interference devices (SQUIDs) which is based on the local anodization of niobium strip lines 3 to 6.5 nm-thick under the voltage-biased tip of an Atomic Force Microscope. Microbridge junctions and SQUID loops are obtained either by partial or total oxidation of the niobium layer. Two types of weak link geometries are fabricated : lateral constriction (Dayem bridges) and variable thickness bridges. SQUIDs based on both geometries show a modulation of the maximum Josephson current with a magnetic flux periodic with respect to the superconducting flux quantum h/2e. They persist up to 4K. The modulation shape and depth for SQUIDs based on variable thickness bridges indicate that the weak link size becomes comparable to the superconducting film coherence length which is of the order of 10nm.



from HAL : Dernières publications http://ift.tt/1bIfzXf

[hal-01136668] Exact bounds of the Möbius inverse of monotone set functions

We give the exact upper and lower bounds of the Möbius inverse of monotone and normalized set functions (a.k.a. normalized capacities) on a finite set of n elements. We find that the absolute value of the bounds tend to 4 n/2 √ πn/2 when n is large. We establish also the exact bounds of the interaction transform and Banzhaf interaction transform, as well as the exact bounds of the Möbius inverse for the subfamilies of k-additive normalized capacities and p-symmetric normalized capacities.



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[hal-01136744] D-Sieve: A Novel Data Processing Engine for Efficient Handling of Crises-Related Social Messages

Existing literature demonstrates the usefulness of system-mediated algorithms, such as supervised machine learning for detecting classes of messages in the social-data stream (e.g., topically relevant vs. irrelevant). The classification accuracies of these algorithms largely depend upon the size of labeled samples that are provided during the learning phase. Other factors such as class distribution, term distribution among the training set also play an important role on clas-sifier's accuracy. However, due to several reasons (money / time constraints, limited number of skilled labelers etc.), a large sample of labeled messages is often not available immediately for learning an efficient classification model. Consequently, classifier trained on a poor model often mis-classifies data and hence, the applicability of such learning techniques (especially for the online setting) during ongoing crisis response remains limited. In this paper, we propose a post-classification processing step leveraging upon two additional content features-stable hashtag association and stable named entity association, to improve the classification accuracy for a classifier in realistic settings. We have tested our algorithms on two crisis datasets from Twitter (Hurricane Sandy 2012 and Queensland Floods 2013), and compared our results against the results produced by a " best-in-class " baseline online classifier. By showing the consistent better quality results than the baseline algorithm i.e., by correctly classifying the misclassified data points from the prior step (false negative and false positive to true positive and true negative classes, respectively), we demonstrate the applicability of our approach in practice.



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[hal-00012650] Classical and quantum magnetization reversal studied in nanometer-sized particles and clusters

Nanometer-sized magnetic particles have generated continuous interest as the study of their properties has proved to be scientifically and technologically very challenging. In this article we reviewed the most important theories and experimental results concerning the magnetization reversal of single-domain particles,clusters and molecular clusters. Sect.1 reviews briefly the commonly used measuring techniques. Among them, electrical transport measurements, Hall probes and micro-SQUID techniques seem to be the most convenient techniques for low temperature measurements. Sect.2 discusses the mechanisms of magnetization reversal in single domain particles at zero Kelvin. The influence of temperature on the magnetization reversal is reported in Sect.3. Finally, Sect.4 shows that for very small systems or very low temperature, magnetization can reverse via quantum tunneling. The boundary between classical and quantum physics has become a very attractive field of research. This section discusses detailed measurements which demonstrated that molecular magnets offer an unique opportunity to explore the quantum dynamics of a large but finite spin. We then discussed tunneling in nanoparticles and showed how one might give a definite proof of their quantum character at low temperature.



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[hal-01136764] DIFFUSION HITTING TIMES AND THE BELL-SHAPE

Consider a generalized diffusion on R with speed measure m, in the natural scale. It is known that the conditional hitting times have a unimodal density function. We show that these hitting densities are bell-shaped if and only if m has infinitely many points of increase between the starting point and the hit point. This result can be viewed as a visual corollary to Yamazato's general factorization for diffusion hitting times.



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