Showing papers by "University of Nice Sophia Antipolis published in 2002"

Computing iceberg concept lattices with TITANIC

Abstract: We introduce the notion of iceberg concept lattices and show their use in knowledge discovery in databases. Iceberg lattices are a conceptual clustering method, which is well suited for analyzing very large databases. They also serve as a condensed representation of frequent itemsets, as starting point for computing bases of association rules, and as a visualization method for association rules. Iceberg concept lattices are based on the theory of Formal Concept Analysis, a mathematical theory with applications in data analysis, information retrieval, and knowledge discovery. We present a new algorithm called TITANIC for computing (iceberg) concept lattices. It is based on data mining techniques with a level-wise approach. In fact, TITANIC can be used for a more general problem: Computing arbitrary closure systems when the closure operator comes along with a so-called weight function. The use of weight functions for computing closure systems has not been discussed in the literature up to now. Applications providing such a weight function include association rule mining, functional dependencies in databases, conceptual clustering, and ontology engineering. The algorithm is experimentally evaluated and compared with Ganter's Next-Closure algorithm. The evaluation shows an important gain in efficiency, especially for weakly correlated data.

Processing of the β‐Amyloid Precursor Protein and Its Regulation in Alzheimer's Disease

Abstract: One of the majorhistopathological hallmarks in Alzheimer's disease is the senile plaque that is constituted mainly by an insoluble peptide, the amyloid 3-peptide (A3) . The purification and partial sequencing of Aß (Glenner and Wong, 1984; Masters et al ., 1985) have allowed the molecular cloning of its precursor, the ßamyloid precursor protein (ßAPP) cDNA. These crucial advances concerning the structural features of these proteins have allowed the development of very useful tools and, thus, given rise to numerous studies aimed at better understanding the physiopathological mechanisms underlying 6APP processing . In this review, we present the various products derived from ßAPP proteolysis, we discuss the possible cellular compartments and routes for their production, and we examine some proteases that can be considered as putative candidates responsible for their formation . Finally, we describe some recent studies concerning the regulation of 6APP processing . Senile plaques can be found in the brain of normal elderly subjects but accumulate greatly in subjects with Alzheimer's disease (AD) neuropathology . This extracellular deposit is composed mainly of a small insoluble protein of 40-42 amino acids called amyloid 3-peptide (A3) that derives from a precursor, the ,ß-amyloid precursor protein (ßAPP). Several 6APP isoforms can be generated by alternative splicing of a single gene located on chromosome 21 (for review, see Mullan and Crawford, 1993) . As shown in Fig. IA, ßAPP exhibits the structural features of a transmembrane protein, with the Aß sequence partly embedded in the membrane domain . The production of Aß is thought to derive from proteolytic attacks at its Nand C-termini by ,ßand y-secretases, respectively (Fig . IA) . In physiological conditions, another enzyme called a-secretase cleaves 6APP inside the Aß sequence (Fig . 1A) and liberates a secreted N-terminal product named soluble 3APP (,6APPs) . Particularly interesting was the demonstration that some 3APPs that derive from 3APP,51 and 3APP o contain a Kun-

Histone deacetylases inhibitors as anti-angiogenic agents altering vascular endothelial growth factor signaling

Abstract: Angiogenesis is a complex biological process involving the coordinated modulation of many genes. Histone deacetylases (HDAC) are a growing family of enzymes that mediate the availability of chromatin to the transcriptional machinery. Trichostatin-A (TSA) and suberoylanilide hydroxamic acid (SAHA), two HDAC inhibitors known to relieve gene silencing, were evaluated as potential antiangiogenic agents. TSA and SAHA were shown to prevent vascular endothelial growth factor (VEGF)-stimulated human umbilical cord endothelial cells (HUVEC) from invading a type I collagen gel and forming capillary-like structures. SAHA and TSA inhibited the VEGF-induced formation of a CD31-positive capillary-like network in embryoid bodies and inhibited the VEGF-induced angiogenesis in the CAM assay. TSA also prevented, in a dose-response relationship, the sprouting of capillaries from rat aortic rings. TSA inhibited in a dose-dependent and reversible fashion the VEGF-induced expression of VEGF receptors, VEGFR1, VEGFR2, and neuropilin-1. TSA and SAHA upregulated the expression by HUVEC of semaphorin III, a recently described VEGF competitor, at both mRNA and protein levels. This effect was specific to endothelial cells and was not observed in human fibroblasts neither in vascular smooth muscle cells. These observations provide a conspicuous demonstration that HDAC inhibitors are potent anti-angiogenic factors altering VEGF signaling.

Prefrontal Cortex Long-Term Potentiation, But Not Long-Term Depression, Is Associated with the Maintenance of Extinction of Learned Fear in Mice

Abstract: Considerable efforts have been made to identify changes of brain synaptic plasticity associated with fear conditioning. However, for both clinical applications and our fundamental understanding of memory processes, it appears also necessary to investigate synaptic plasticity related to extinction. We previously showed that extinction of freezing to a tone conditioned stimulus (CS; previously paired with footshock) in mice results in a sequence of depression and potentiation of synaptic efficacy in the medial prefrontal cortex (mPFC). These data as well as those from lesion studies suggest that the direction of changes in prefrontal synaptic plasticity may modulate extinction of learned fear. To test this, we analyzed the effects of low-frequency stimulation (LFS) and high-frequency stimulation (HFS) of the mediodorsal thalamic nucleus, known to induce prefrontal long-term depression (LTD) and potentiation (LTP), respectively, on extinction. We found that maintenance of the depression phase, using thalamic LFS, was associated with resistance to extinction. Thalamic HFS applied before extinction testing had no effect on the rate of extinction. However, 1 week follow-up tests revealed that the memory of extinction was intact in these mice (with prefrontal LTP) and in control mice displaying prefrontal LTP-like changes, whereas control mice that did not exhibit such changes displayed a return of freezing to the CS. The results suggest that after extinction the lack of depression-LTP-like conversion sequence in the mPFC synaptic efficacy may profoundly alter the process of consolidation.

Field dependence of viscoelastic properties of mr elastomers

Abstract: A magnetoactive elastomer made of micronic carbonyl iron particles, structured in elongated clusters and embedded in a silicon elastomer matrix is studied under traction both in static and dynamic modes. The application of a magnetic field of 120 kA/m induces a change in elastic moduli of about 0.6 MPa at strains of 4 to 5%. Still higher changes (4 MPa) are observed in dynamic storage modulus at low strains (10-4 to 10-3). The shape of the stress-strain curves are explained by taking into account the existence of a fiber like structure.

Arthroscopic biceps tenodesis: a new technique using bioabsorbable interference screw fixation.

Abstract: Purpose: To report a new technique of arthroscopic biceps tenodesis using bioabsorbable interference screw fixation and the early results. Type of Study: Prospective, nonrandomized study. Methods: Technique: The principle of arthroscopic biceps tenodesis is simple: after biceps tenotomy, the tendon is exteriorized and doubled on a suture; the biceps tendon is then pulled into a humeral socket (7 or 8 mm × 25 mm) drilled at the top of the bicipital groove, and fixed using a bioabsorbable interference screw (8 or 9 mm × 25 mm) under arthroscopic control. Patients: 43 patients treated with this technique between 1997 and 1999 were followed-up for at least 1 year. The technique was indicated in 3 clinical situations: (1) with arthroscopic cuff repair (3 cases), (2) in case of isolated pathology of the biceps tendon with an intact cuff (6 cases), and (3) as an alternative to biceps tenotomy in patients with massive, degenerative and irreparable cuff tears (34 cases). The biceps pathology was tenosynovitis (4 cases), prerupture (15 cases), subluxation (11 cases), and luxation (13 cases). Results: The absolute Constant score improved from 43 points preoperatively to 79 points at review ( P Conclusions: Arthroscopic biceps tenodesis using bioabsorbable screw fixation is technically possible and gives good clinical results. This technique can be used in cases of isolated pathologic biceps tendon or a cuff tear. A very thin, fragile, almost ruptured biceps tendon is the technical limit of this arthroscopic technique. Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 9 (November-December), 2002: pp 1002– 1012

Subcritical and supercritical regimes in epidemic models of earthquake aftershocks

Abstract: We present an analytical solution and numerical tests of the epidemic-type aftershock (ETAS) model for aftershocks, which describes foreshocks, aftershocks and mainshocks on the same footing. The occurrence rate of aftershocks triggered by a single mainshock decreases with the time from the mainshock according to the modified Omori law K/(t+c)^p with p=1+theta. A mainshock at time t=0 triggers aftershocks according to the local Omori law, that in turn trigger their own aftershocks and so on. The effective branching parameter n, defined as the mean aftershock number triggered per event, controls the transition between a sub-critical regime n 1. In the sub-critical regime, we recover and document the crossover from an Omori exponent 1-theta for t0, we find a novel transition from an Omori decay law with exponent 1-theta fot tt*. The case theta<0 yields an infinite n-value. In this case, we find another characteristic time tau controlling the crossover from an Omori law with exponent 1-theta for t

Identification of novel fusion partners of ALK, the anaplastic lymphoma kinase, in anaplastic large-cell lymphoma and inflammatory myofibroblastic tumor.

Abstract: ALK-positive anaplastic large-cell lymphoma (ALCL) has been recognized as a distinct type of lymphoma in the heterogeneous group of T/Null-ALCL. While most of the ALK-positive ALCL (ALKomas) are characterized by the presence of the NPM-ALK fusion protein, the product of the t(2;5)(p23;q35), 10–20% of ALKomas contain variant ALK fusions, including ATIC-ALK, TFG-ALK, CLTC-ALK (previously designated CLTCL-ALK), TMP3-ALK, and MSN-ALK. TMP3-ALK and TMP4-ALK fusions also have been detected in inflammatory myofibroblastic tumors (IMTs), making clear that aberrations of the ALK gene are not associated exclusively with the pathogenesis of ALK-positive ALCL. Here we report results of molecular studies on two lymphoma cases and one IMT case with variant rearrangements of ALK. Our study led to the detection of the CLTC-ALK fusion in an ALCL case and to the identification of two novel fusion partners of ALK: ALO17 (KIAA1618), a gene with unknown function, which was fused to ALK in an ALCL case with a t(2;17)(p23;q25), and CARS, encoding the cysteinyl-tRNA synthetase, which was fused to ALK in an IMT case with a t(2;11;2)(p23;p15;q31). These results confirm the recurrent involvement of ALK in IMT and further demonstrate the diversity of ALK fusion partners, with the ability to homodimerize as a common characteristic. © 2002 Wiley-Liss, Inc.

Methods to determine aerobic endurance

Abstract: Physiological testing of elite athletes requires the correct identification and assessment of sports-specific underlying factors. It is now recognised that performance in long-distance events is determined by maximal oxygen uptake (.VO2max), energy cost of exercise and the maximal fractional utilisation of.VO2max in any realised performance or as a corollary a set percentage of.VO2max that could be endured as long as possible. This later ability is defined as endurance, and more precisely aerobic endurance, since.VO2max sets the upper limit of aerobic pathway. It should be distinguished from endurance ability or endurance performance, which are synonymous with performance in long-distance events. The present review examines methods available in the literature to assess aerobic endurance. They are numerous and can be classified into two categories, namely direct and indirect methods. Direct methods bring together all indices that allow either a complete or a partial representation of the power-duration relationship, while indirect methods revolve around the determination of the so-called anaerobic threshold (AT). With regard to direct methods, performance in a series of tests provides a more complete and presumably more valid description of the power-duration relationship than performance in a single test, even if both approaches are well correlated with each other. However, the question remains open to determine which systems model should be employed among the several available in the literature, and how to use them in the prescription of training intensities. As for indirect methods, there is quantitative accumulation of data supporting the utilisation of the AT to assess aerobic endurance and to prescribe training intensities. However, it appears that: (i) there is no unique intensity corresponding to the AT, since criteria available in the literature provide inconsistent results; and (ii) the non-invasive determination of the AT using ventilatory and heart rate data instead of blood lactate concentration ([La- ]b) is not valid. Added to the fact that the AT may not represent the optimal training intensity for elite athletes, it raises doubt on the usefulness of this theory without questioning, however, the usefulness of the whole [La- ]b-power curve to assess aerobic endurance and predict performance in long-distance events.

PPLN waveguide for quantum communication

Abstract: We report on energy-time and time-bin entangled photon-pair sources based on a periodically poled lithium niobate (PPLN) waveguide. Degenerate twin photons at 1314 nm wavelength are created by spontaneous parametric down-conversion and coupled into standard telecom fibers. Our PPLN waveguide features a very high conversion efficiency of about 10^(-6), roughly 4 orders of magnitude more than that obtained employing bulk crystals. Even if using low power laser diodes, this engenders a significant probability for creating two pairs at a time - an important advantage for some quantum communication protocols. We point out a simple means to characterize the pair creation probability in case of a pulsed pump. To investigate the quality of the entangled states, we perform photon-pair interference experiments, leading to visibilities of 97% for the case of energy-time entanglement and of 84% for the case of time-bin entanglement. Although the last figure must still be improved, these tests demonstrate the high potential of PPLN waveguide based sources to become a key element for future quantum communication schemes

Mott Domains of Bosons Confined on Optical Lattices

Abstract: In the absence of a confining potential, the boson-Hubbard model exhibits a superfluid to Mott insulator quantum phase transition at commensurate fillings and strong coupling. We use quantum Monte Carlo simulations to study the ground state of the one-dimensional bosonic Hubbard model in a trap. Some, but not all, aspects of the Mott insulating phase persist. Mott behavior occurs for a continuous range of incommensurate fillings, very different from the unconfined case, and the establishment of the Mott phase does not proceed via a traditional quantum phase transition. These results have important implications for interpreting experiments on ultracold atoms on optical lattices.

Magnetorheology: Fluids, Structures and Rheology

Abstract: Magnetorheological suspensions are complex fluids which show a transition from a liquid behavior to a solid one upon application of a magnetic field. This transition is due to the the attractive dipolar forces between the particles which have been magnetized by the applied field. The formation of a network of particles or aggregates throughout the suspension is the basic phenomena which is responsible for the strength of the solid phase. In this paper we shall give an overview on the fluids and their properties and we shall especially emphasize the interplay between magnetic forces which are responsible for the gelling of the suspension and on the other hand of hydrodynamic and thermal forces which contribute to break this gel and allow the suspension to flow. The combination of these three forces gives rise to a very rich rheology whose many aspects are still not understood.

Diffusion of epicenters of earthquake aftershocks, Omori's law, and generalized continuous-time random walk models.

Abstract: The epidemic-type aftershock sequence (ETAS) model is a simple stochastic process modeling seismicity, based on the two best-established empirical laws, the Omori law (power-law decay approximately 1/t(1+theta) of seismicity after an earthquake) and Gutenberg-Richter law (power-law distribution of earthquake energies). In order to describe also the space distribution of seismicity, we use in addition a power-law distribution approximately 1/r(1+mu) of distances between triggered and triggering earthquakes. The ETAS model has been studied for the last two decades to model real seismicity catalogs and to obtain short-term probabilistic forecasts. Here, we present a mapping between the ETAS model and a class of CTRW (continuous time random walk) models, based on the identification of their corresponding master equations. This mapping allows us to use the wealth of results previously obtained on anomalous diffusion of CTRW. After translating into the relevant variable for the ETAS model, we provide a classification of the different regimes of diffusion of seismic activity triggered by a mainshock. Specifically, we derive the relation between the average distance between aftershocks and the mainshock as a function of the time from the mainshock and of the joint probability distribution of the times and locations of the aftershocks. The different regimes are fully characterized by the two exponents theta and mu. Our predictions are checked by careful numerical simulations. We stress the distinction between the "bare" Omori law describing the seismic rate activated directly by a mainshock and the "renormalized" Omori law taking into account all possible cascades from mainshocks to aftershocks of aftershock of aftershock, and so on. In particular, we predict that seismic diffusion or subdiffusion occurs and should be observable only when the observed Omori exponent is less than 1, because this signals the operation of the renormalization of the bare Omori law, also at the origin of seismic diffusion in the ETAS model. We present predictions and insights provided by the ETAS to CTRW mapping which suggest different ways for studying seismic catalogs. Finally, we discuss the present evidence for our predicted subdiffusion of seismicity triggered by a main shock, stressing the caveats and limitations of previous empirical works.

Retinoic acid activation of the ERK pathway is required for embryonic stem cell commitment into the adipocyte lineage.

Abstract: Mouse embryonic stem (ES) cells are pluripotent cells that differentiate into multiple cell lineages. The commitment of ES cells into the adipocyte lineage is dependent on an early 3-day treatment with all-trans retinoic acid (RA). To characterize the molecular mechanisms underlying this process, we examined the contribution of the extracellular-signal-regulated kinase (ERK) pathway. Treatment of ES cell-derived embryoid bodies with RA resulted in a prolonged activation of the ERK pathway, but not the c-Jun N-terminal kinase, p38 mitogen-activated protein kinase or phosphoinositide 3-kinase pathways. To investigate the role of ERK activation, co-treatment of RA with PD98059, a specific inhibitor of the ERK signalling pathway, prevented both adipocyte formation and expression of the adipogenic markers, adipocyte lipid-binding protein and peroxisome-proliferator-activated receptor gamma. Furthermore, we show that ERK activation is required only during RA treatment. PD98059 does not interfere with the commitment of ES cells into other lineages, such as neurogenesis, myogenesis and cardiomyogenesis. As opposed to the controversial role of the ERK pathway in terminal differentiation, our results clearly demonstrate that this pathway is specifically required at an early stage of adipogenesis, corresponding to the RA-dependent commitment of ES cells.

Random laser in the localized regime

Abstract: We present detailed calculations of laser action in two-dimensional disordered systems in the localized regime. The systems are made of circular particles imbedded in an active dielectric medium, described by a population of four-level atoms. Without pumping the active medium, the existence of localized modes is studied as a function of the filling fraction and of the radius of the scattering particles. When pumping the active medium above threshold, we find that the localized modes of the passive system act as the regular modes of a conventional cavity. They are not modified by the presence of gain. By introducing local pumping of the atomic system, the spectrum of the laser emission is found to depend on the position of the pump in agreement with recent experimental results. It is shown that local pumping allows a selective excitation of individual localized modes.

Periapical status, prevalence and quality of endodontic treatment in an adult French population.

Abstract: Lupi-Pegurier L, Bertrand M-F, Muller-Bolla M, Rocca JP, Bolla M. Periapical status, prevalence and quality of endodontic treatment in an adult French population. International Endodontic Journal, 35, 690^697, 2002. Aim The aim of this study was to determine the periapical status and the quality of root-canal treatment amongst an adult population attending the dental school in Nice, France during 1998. Methodology Patients who attended the dental school for the ¢rst time during 1998 were included. Panoramic radiographs, taken by a trained radiology assistant, were used in this study. The periapical areas of all teeth with the exception of third molars, were examined and the technical quality of root ¢llings were evaluated for both apical extension and density. Statistical analyses were conducted using anova, Chi-square, Fisher’s PLSD and Cohen’s Kappa tests. Results The survey involved 344 patients: 180 females and 164 males. Males had signi¢cantly fewer natural remaining teeth than females (P < 0.03). Similarly, the average number of root-¢lled teeth was lower for males (P < 0.01). Nonroot-¢lled teeth (n ¼ 6126) had signi¢cantly fewer signs of periapical pathology than root-¢lled teeth (n ¼ 1429) (1.7% vs. 31.5%, P < 0.0001). The majority of root ¢llings were poorly executed. There was a signi¢cant correlation between the presence of periapical pathology and inadequate root-canal ¢llings (P < 0.001). Conclusions The results of the present study indicate that many root-canal treatments were technically unsatisfactory in terms of quality and treatment outcome. There is a need for endodontic retreatment in the population examined.

Relation between anomalous and normal diffusion in systems with memory.

Abstract: We present a simple criterion based on the Einstein relation for determining whether diffusion in systems governed by a generalized Langevin equation with long-range memory is normal, superdiffusive, or subdiffusive. We support our analysis with numerical simulations.

Oscillatory finite-time singularities in finance, population and rupture

Abstract: We present a simple two-dimensional dynamical system where two nonlinear terms, exerting respectively positive feedback and reversal, compete to create a singularity in finite time decorated by accelerating oscillations. The power law singularity results from the increasing growth rate. The oscillations result from the restoring mechanism. As a function of the order of the nonlinearity of the growth rate and of the restoring term, a rich variety of behavior is documented analytically and numerically. The dynamical behavior is traced back fundamentally to the self-similar spiral structure of trajectories in phase space unfolding around an unstable spiral point at the origin. The interplay between the restoring mechanism and the nonlinear growth rate leads to approximately log-periodic oscillations with remarkable scaling properties. Three domains of applications are discussed: (1) the stock market with a competition between nonlinear trend-followers and nonlinear value investors; (2) the world human population with a competition between a population-dependent growth rate and a nonlinear dependence on a finite carrying capacity; (3) the failure of a material subjected to a time-varying stress with a competition between positive geometrical feedback on the damage variable and nonlinear healing.

Total coronagraphic extinction of rectangular apertures using linear prolate apodizations

Abstract: This paper presents a theoretical study of stellar coronagraphy with apodized entrance apertures. The study is restricted to a perfect telescope operating in space, and a monochromatic on-axis unresolved star. It is shown that linear prolate functions are the optimal apodizers for rectangular apertures in stellar coronagraphy. With the phase mask technique (Roddier & Roddier 1997), prolate functions can produce a total extinction of the star light. For Lyot's coronagraphy, the extinction is not complete, but prolate apodizations lead to an optimal star residual intensity with surprising interesting properties: the residual star light and the planet enjoy the same apodized intensity pattern (but dierent dynamic) with the optimal light concentration. With this technique, very high rejection rates can be obtained for Lyot's coronagraphy, with smaller mask sizes.