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This work presents the synthesis and studies of a red-NIR luminescent liquid crystal compound based on an octahedral metallic cluster core orthogonally bounded to six non-mesogenic organic ligands. It evidences synergetic effects between the organic and inorganic parts of the hybrid, resulting in the generation of liquid crystal properties on cooling from the isotropic melt.
The intermolecular potential for the van der Waals complex of the carbon monoxide cation with helium is studied by means of the partially spin adapted coupled cluster RCCSD(T) method and the aug-cc-pVXZ family of basis sets. In the ground electronic state, correlated with the lowest electronic asymptote $X {^2\Sigma^+}$ of the monomer CO$^+$, the complex He($^1S$)-CO$^+$($^2\Sigma^+$) has a nonlinear equilibrium structure with a Jacobi angle of about 46 deg and a binding energy of about 275 cm$^{-1}$. For the complex He($^1S$)-CO$^+$($A {^2\Pi}$) we find equilibrium Jacobi angles of 78 deg and 90 deg and electronic binding energies of about 160 cm$^{-1}$ and 303 cm$^{-1}$ for the $A^{\prime\prime}$ and $A^{\prime}$ components, respectively, coalescing into the $\Pi$ state at linearity. Two-dimensional intermolecular potential energy surfaces are constructed for the ground electronic state and used to compute rotation-vibration states up to J=10 with the numerically exact discrete variable representation (DVR) technique. The He-CO$^+$ complex is found to have 19 bound even-parity J=0 states and 16 bound odd-parity J=1 states and to exhibit strong angular-radial coupling and quasilinear behaviour.
A RCCSD(T)/cc-pVQZ potential energy surface is constructed for the HOCO radical in the ground electronic state and used to compute rotation-vibration levels of HOCO and DOCO. Two numerical strategies are employed to study in detail the wave function properties. The importance of stretch−bend coupling, such as ν4/ν5 and ν3/ν4, for the internal dynamics is demonstrated. The rotational constants computed for the vibrational ground state of trans and cis conformers are in good agreement with experimental values.
We present a mathematical study of the order book as a multidimensional continuous- time Markov chain where the order ow is modeled by independent Poisson processes. Our aim is to bridge the gap between the microscopic description of price formation (agent- based modeling), and the Stochastic Di erential Equations approach used classically to describe price evolution at macroscopic time scales. To do this, we rely on the theory of in nitesimal generators and Foster-Lyapunov stability criteria for Markov chains. We motivate our approach using an elementary example where the spread is kept constant (\perfect market making"). Then we compute the in nitesimal generator associated with the order book in a general setting, and link the price dynamics to the instantaneous state of the order book. In the last section, we prove that the order book is ergodic| in particular it has a stationary distribution|that it converges to its stationary state exponentially fast, and that the large-scale limit of the price process is a Brownian motion.
In this paper, we consider a discrete time economy where we assume that the short term interest rate follows a quadratic term structure of a regime switching asset process. The possible non-linear structure and the fact that the interest rate can have different economic or financial trends justify the interest of Regime Switching Quadratic Term Structure Model (RS-QTSM). Indeed, this regime switching process depends on the values of a Markov chain with a time dependent transition probability matrix which can well captures the different states (regimes) of the economy. We prove that under this modelling that the conditional zero coupon bond price admits also a quadratic term structure. Moreover, the stochastic coefficients which appear in this decomposition satisfy an explicit system of coupled stochastic backward recursions.
In this note, we cast a Hawkes process-based order book model into a markovian setting, and using techniques from the theory of Markov chains and stochastic stability [16], show that the order book is stable and leads to a di usive price limit at large time scales.
We have developed a patch implementing multivariate polynomials seen as a multi-base algebra. The patch is to be released into the software Sage and can already be found within the Sage-Combinat distribution. One can use our patch to define a polynomial in a set of indexed variables and expand it into a linear basis of the multivariate polynomials. So far, we have the Schubert polynomials, the Key polynomials of types A, B, C, or D, the Grothendieck polynomials and the non-symmetric Macdonald polynomials. One can also use a double set of variables and work with specific double-linear bases like the double Schubert polynomials or double Grothendieck polynomials. Our implementation is based on a definition of the basis using divided difference operators and one can also define new bases using these operators.
Attributes are an intermediate representation which enables parameter sharing between classes, a must when training data is scarce. We propose to view attribute-based image classification as a label-embedding problem: each class is embedded in the space of attribute vectors. We introduce a function which measures the compatibility between an image and a label embedding. The parameters of this function are learned on a training set of labeled samples to ensure that, given an image, the correct classes rank higher than the incorrect ones. Results on the fine-grained Caltech-UCSD-Birds dataset show that the proposed framework outperforms the standard Direct Attribute Prediction baseline in a zero-shot learning scenario.
Self-service bike sharing systems experience often imbalance problems: in some stations there is a lack of bikes while in others there are too many bikes, leaving no empty rack for a user willing to park his bike. Imbalance problems can be partially settled by the actions of vehicles moving bikes during the night in order to prepare the forthcoming day. We speak then of static regulation, since bikes can be assumed to be not moving. These problems can also be partially countered by actions of the vehicles during the day. This is dynamic regulation and forms the topic of our present work. We build a precise theoretical framework for studying this dynamic problem and discuss the kind of impact vehicles moving bikes can have on the system. We prove moreover the inherent hardness of the dynamic regulation problem and present some ways to circumvent it by the use of heuristics. A pricing technique, not involving vehicles, is also proposed. An open-source and versatile simulator is also briefly described and used to compare the aforementioned methods.
We have developed a patch implementing multivariate polynomials seen as a multi-base algebra. The patch is to be released into the software Sage and can already be found within the Sage-Combinat distribution. One can use our patch to define a polynomial in a set of indexed variables and expand it into a linear basis of the multivariate polynomials. So far, we have the Schubert polynomials, the Key polynomials of types A, B, C, or D, the Grothendieck polynomials and the non-symmetric Macdonald polynomials. One can also use a double set of variables and work with specific double-linear bases like the double Schubert polynomials or double Grothendieck polynomials. Our implementation is based on a definition of the basis using divided difference operators and one can also define new bases using these operators.
We consider a Bernoulli bond percolation on a random recursive tree of size $n\gg 1$, with supercritical parameter $p_n=1-c/\ln n$ for some $c>0$ fixed. It is known that with high probability, there exists then a unique giant cluster of size $G_n\sim \e^{-c}$, and it follows from a recent result of Schweinsberg \cite{Sch} that $G_n$ has non-gaussian fluctuations. We provide an explanation of this by analyzing the effect of percolation on different phases of the growth of recursive trees. This alternative approach may be useful for studying percolation on other classes of trees, such as for instance regular trees.
We start an analysis of geometric properties of a structure relative to a reduct. In particular, we look at definability of groups and fields in this context. In the relatively one-based case, every definable group is isogenous to a subgroup of a product of groups definable in the reducts. In the relatively CM-trivial case, which contains certain Hrushovski amalgamations (the fusion of two strongly minimal sets or the expansions of a field by a predicate), every definable group allows a homomorphism with virtually central kernel into a product of groups definable in the reducts.
A Local/Global non-intrusive coupling algorithm is proposed for the analysis of mixed-mode crack propagation. It is based on a three scale multigrid and extended finite element method, that was proposed recently for the direct estimation of stress intensity factors of static cracks. The algorithm couples a linear elastic global model (possibly performed by a industrial software) with an enhanced local model capable of modeling a crack and accurately estimating SIFs (performed by a separate research code). It is said non-intrusive since it does not modify the global mesh, its connectivity and solver. For the global model, the contribution of the local patch consists in additional nodal efforts near the crack, which makes it compatible with most softwares. Further the shape of the domain over which the local model is applied is automatically adapted during propagation.
Despite remarkable accomplishment, the classical hydrodynamic stability theory fails to predict transition in wall-bounded shear ow. The shortcoming of this modal approach was found 20 years ago and is linked to the non-orthogonality of the eigenmodes of the linearised problem, de noted by the Orr Sommerfeld and Squire equations. The associated eigenmodes of this linearised problem are the normal velocity and the normal vorticity eigenmodes, which are not dimensionally homogeneous quantities. Thus non-orthogonality condition between these two families of eigenmodes have not been clearly demonstrated yet. Using an orthogonal decomposition of solenoidal velocity fields, a velocity perturbation is expressed as an L2 orthogonal sum of an OrrSommerfeld velocity field (function of the perturbation normal velocity) and a Squirevelocity field (function of the perturbation normal vorticity). Using this decomposition,a variational formulation of the linearised problem is written, that is equivalent to the Orr Sommerfeld and Squire equations, but whose eigenmodes consist of two families of velocity eigenmodes (thus dimensionally homogeneous). We demonstrate that these two sets are non-orthogonal and linear combination between them can produce large transient growth. Using this new formulation, the link between optimal mode and continuous mode transition will also be clari fied, as the role of direct resonance. Numerical solutions are presented to illustrate the analysis in the case of thin boundary layers developing between two parallel walls at large Reynolds number. Characterisations of the destabilizing perturbations will be given in that case.
La morphogenèse tissulaire est encore mal comprise. Nous présentons ici un modèle biomécanique de tissu composé de cellules ayant des comportements reproduisant ceux observés expérimentalement (croissance, division et mort cellulaire). Les tissus sont générés selon deux modes : accrétion et prolifération. Les topologies obtenues concordent avec les observations expérimentales et permettent d'étudier l'impact des modes de formation sur la morphogénèse des tissus biologiques.
Fully dynamic numerical simulations have been designed in order to asses how the orientation of mechanical layering in rocks controls the orientation of shear bands and the depth of penetration of strain in the footwall of detachment zones. Two parametric studies are presented. In the first one, the influence of stratification orientation on the occurrence and mode of strain localisation is tested. The second parametric study shows that results are length-scale independent and that orientation of shear bands is not sensitive to the viscosity contrast or the strain rate. Based on the results, a conceptual model for strain localisation under detachment faults is presented. In the early stages, strain localisation occurs at slow rates by viscous shear instabilities but as the layered media is exhumed, the temperature drops and the strong layers start yielding plastically, forming shear bands and localising strain at the top of the shear zone. Once strain localisation has occured, the deformation in the shear band becomes extremely penetrative but the strength cannot drop since the shear zone has a finite thickness.
Subduction zones are places where one hydrated oceanic plate goes underneath another plate, and releases its fluids into the overlying mantle wedge. Slab-derived fluids play a key role in subduction zone processes. They serpentinize the cold forearc mantle at shallow depths; and deeper, they trigger hydrous mantle melting beneath the arc volcanoes and sometimes at backarc basin (BAB) spreading center. Examining the composition of arc and BAB magmas helps understanding genesis of subduction-related magmas, nature and composition of their mantle sources and slab-derived fluids. However, investigating such processes at shallow subduction zones is challenging, because the cold forearc mantle generally does not melt. Here, I investigate an unusual region in the southernmost Mariana convergent margin in the Western Pacific, near the Challenger Deep. The SE Mariana forearc stretched to accommodate opening of the southernmost Mariana Trough ~5Ma ago, opening the SE Mariana forearc rift (SEMFR) and causing seafloor spreading ~2.7-3.7Ma ago. The subducted slab beneath SEMFR deepens from <50km to ~100km, thus studying SEMFR lavas provides a unique opportunity to understand shallow subduction processes. By examining the major and trace element composition, the Pb-Nd-Sr isotopic ratios and the volatile contents (H2O, CO2, Cl, S, F) of SEMFR basalts, associated glassy rinds and olivine-hosted melt inclusions (Ol-MI) collected during three cruises (YK08-08, YK10-12, TN273), I show that: (i) SEMFR lavas were produced by adiabatic decompression melting of depleted asthenospheric BAB-like mantle at ~30±6.6 km depth and 1224±40oC; (ii) Ol-MI represent hydrous melts trapped by forearc mantle olivines. Xenocrysts were entrained with SEMFR basalts during ascent; (iii) SEMFR mantle flowed from the forearc towards the arc volcanoes and was metasomatized by shallow aqueous fluids; (iv) SEMFR shallow fluids are more aqueous than the fluids released beneath the Mariana arc and Mariana BAB; (v) the aqueous slab-derived fluids and the volatile fluxes are greatest at ~50-100km slab depth, suggesting that the minerals from the subducting plate mostly broke down beneath the arc to release their fluids. Such results provide new insights into shallow subduction processes, as previous studies showed that volatile fluxes and aqueous slab-derived fluids should increase toward the trench.
The Korba aquifer on the east coast of Cape Bon has been overexploited since the 1960s with a resultant reversal of the hydraulic gradient and a degradation of the quality due to seawater intrusion. In 2008, the authorities introduced integrated water resources planning based on a managed aquifer recharge with treated wastewater. Water quality monitoring was implemented in order to determine the different system components and trace the effectiveness of the artificial recharge. Groundwater samples taken from recharge control piezometers and surrounding farm wells were analyzed for their chemical contents, for their boron isotopes, a proven tracer of groundwater salinization and domestic sewage, and their carbamazepine content, an anti-epileptic known to pass through wastewater treatment and so recognized as a pertinent tracer of wastewater contamination. The system equilibrium was permanently disturbed by the different temporal dynamics of continuous processes such as cation exchange, and by threshold processes linked to oxidation-reductive conditions. The boron isotopic compositions significantly shifted back-and-forth due to mixing with end-members of various origins. Under the variable contribution of meteoric recharge, the Plio-Quaternary groundwater (δ11B of 35-40.6‰, a mean B concentration of 30 µmol/L, no carbamazepine, n=7) was subject to seawater intrusion that induced a high δ11B level (δ11B of 41.5-48.0‰, a mean B concentration of 36 µmol/L, and n=8). Fresh groundwater (δ11B of 19.89‰, B concentration of 2.8 µmol/L, no carbamazepine) was detected close to the recharge site and may represent the deep Miocene pole which feeds the upper Plio-Quaternary aquifer. The managed recharge water (δ11B of 10.67-13.8‰, n=3) was brackish and of poor quality with a carbamazepine content showing a large short term variability with an average daily levels of 328 ± 61 ng/L. A few piezometers in the vicinity of the recharge site gradually acquired a B isotopic composition close to the wastewater signature and showed an increasing carbamazepine content (from 20 to 910 ng/L). The combination of boron isotopic signatures with boron and carbamazepine contents is a useful tool to assess sources and mixing of treated wastewaters in groundwaters. Effluent quality needs to be greatly improved before injection to prevent further degradation of groundwater quality.
An improved Lozi function with alternate coefficients has been proposed. The modifications in the model allow to remove the holes in the attractor which are not desirable, but appeared in the previous Lozi function; in this way, an everywhere dense attractor can be obtained. Moreover, the strong sensitivity to the type of binarisation (conversion of real values to 0 and 1) has been demonstrated; this conversion to binary numbers is instrumental to apply the NIST tests for randomness. The results have been validated and compared via NIST tests, for the different methods of quantization. Finally, is has been verfied that the multi-random properties of the output signal have been improved thanks to the following strategies : under-sampling of the output signal, and the system order increasing. Keywords. Nonlinear dynamical system, ring-coupled map, Lozi function, NIST tests, discrete-time map, dense chaotic attractor, pseudo random number generator 1 I
The extreme characteristics of long wave run-up are studied in this paper. First we give a brief overview of the existing theory which is mainly based on the hodograph transformation (Carrier & Greenspan, 1958). Then, using numerical simulations, we build on the work of Stefanakis et al. (2011) for an infinite sloping beach and we find that resonant run-up amplification of monochromatic waves is robust to spectral perturbations of the incoming wave and resonant regimes do exist for certain values of the frequency. In the setting of a finite beach attached to a constant depth region, resonance can only be observed when the incoming wavelength is larger than the distance from the undisturbed shoreline to the seaward boundary. Wavefront steepness is also found to play a role in wave run-up, with steeper waves reaching higher run-up values.
The water wave theory traditionally assumes the fluid to be perfect, thus neglecting all effects of the viscosity. However, the explanation of several experimental data sets requires the explicit inclusion of dissipative effects. In order to meet these practical problems, the theory of visco-potential flows has been developed (see P.-F. Liu & A. Orfila (2004) and D. Dutykh & F. Dias (2007)). Then, usually this formulation is further simplified by developing the potential in an entire series in the vertical coordinate and by introducing thus, the long wave approximation. In the present study we propose a derivation of dissipative Boussinesq equations which is based on asymptotic expansions of the Dirichlet-to-Neumann (D2N) operator. Both employed methods yield the same system by different ways.
According to the time-based resource-sharing model (P. Barrouillet, S. Bernardin, & V. Camos, 2004), the cognitive load a given task involves is a function of the proportion of time during which it captures attention, thus impeding other attention-demanding processes. Accordingly, the present study demonstrates that the disruptive effect on concurrent maintenance of memory retrievals and response selections increases with their duration. Moreover, the effect on recall performance of concurrent activities does not go beyond their duration insofar as the processes are attention demanding. Finally, these effects are not modality specific, as spatial processing was found to disrupt verbal maintenance. These results suggest a sequential and time-based function of working memory in which processing and storage rely on a single and general purpose attentional resource needed to run executive processes devoted to constructing, maintaining, and modifying ephemeral representations.
The time-based resource-sharing model of working memory assumes that memory traces suffer from a time-related decay when attention is occupied by concurrent activities. Using complex continuous span tasks in which temporal parameters are carefully controlled, P. Barrouillet, S. Bernardin, S. Portrat, E. Vergauwe, & V. Camos (2007) recently provided evidence that any increase in time of the processing component of these tasks results in lower recall performance. However, K. Oberauer and R. Kliegl (2006) pointed out that, in this paradigm, increased processing times are accompanied by a corollary decrease of the remaining time during which attention is available to refresh memory traces. As a consequence, the main determinant of recall performance in complex span tasks would not be the duration of attentional capture inducing time-related decay, as Barrouillet et al. (2007) claimed, but the time available to repair memory traces, and thus would be compatible with an interference account of forgetting. The authors demonstrate here that even when the time available to refresh memory traces is kept constant, increasing the processing time still results in poorer recall, confirming that time-related decay is the source of forgetting within working memory.
Working memory is usually defined in cognitive psychology as a system devoted to the simultaneous processing and maintenance of information. However, although many models of working memory have been put forward during the last decades, they often leave underspecified the dynamic interplay between processing and storage. Moreover, the account of their interaction proposed by the most popular A. D. Baddeley and G. Hitch's (1974) multiple-component model is contradicted by facts, leaving unresolved one of the main issues of cognitive functioning. In this article, the author derive from the time-based resource-sharing model of working memory a mathematical function relating the cognitive load involved by concurrent processing to the amount of information that can be simultaneously maintained active in working memory. A meta-analysis from several experiments testing the effects of processing on storage corroborates the parameters of the predicted function, suggesting that it properly reflects the law relating the 2 functions of working memory.
The Korba aquifer on the east coast of Cape Bon has been overexploited since the 1960s with a resultant reversal of the hydraulic gradient and a degradation of the quality due to seawater intrusion. In 2008, the authorities introduced integrated water resources planning based on a managed aquifer recharge with treated wastewater. Water quality monitoring was implemented in order to determine the different system components and trace the effectiveness of the artificial recharge. Groundwater samples taken from recharge control piezometers and surrounding farm wells were analyzed for their chemical contents, for their boron isotopes, a proven tracer of groundwater salinization and domestic sewage, and their carbamazepine content, an anti-epileptic known to pass through wastewater treatment and so recognized as a pertinent tracer of wastewater contamination. The system equilibrium was permanently disturbed by the different temporal dynamics of continuous processes such as cation exchange, and by threshold processes linked to oxidation-reductive conditions. The boron isotopic compositions significantly shifted back-and-forth due to mixing with end-members of various origins. Under the variable contribution of meteoric recharge, the Plio-Quaternary groundwater (δ11B of 35-40.6‰, a mean B concentration of 30 µmol/L, no carbamazepine, n=7) was subject to seawater intrusion that induced a high δ11B level (δ11B of 41.5-48.0‰, a mean B concentration of 36 µmol/L, and n=8). Fresh groundwater (δ11B of 19.89‰, B concentration of 2.8 µmol/L, no carbamazepine) was detected close to the recharge site and may represent the deep Miocene pole which feeds the upper Plio-Quaternary aquifer. The managed recharge water (δ11B of 10.67-13.8‰, n=3) was brackish and of poor quality with a carbamazepine content showing a large short term variability with an average daily levels of 328 ± 61 ng/L. A few piezometers in the vicinity of the recharge site gradually acquired a B isotopic composition close to the wastewater signature and showed an increasing carbamazepine content (from 20 to 910 ng/L). The combination of boron isotopic signatures with boron and carbamazepine contents is a useful tool to assess sources and mixing of treated wastewaters in groundwaters. Effluent quality needs to be greatly improved before injection to prevent further degradation of groundwater quality.
The extreme characteristics of long wave run-up are studied in this paper. First we give a brief overview of the existing theory which is mainly based on the hodograph transformation (Carrier & Greenspan, 1958). Then, using numerical simulations, we build on the work of Stefanakis et al. (2011) for an infinite sloping beach and we find that resonant run-up amplification of monochromatic waves is robust to spectral perturbations of the incoming wave and resonant regimes do exist for certain values of the frequency. In the setting of a finite beach attached to a constant depth region, resonance can only be observed when the incoming wavelength is larger than the distance from the undisturbed shoreline to the seaward boundary. Wavefront steepness is also found to play a role in wave run-up, with steeper waves reaching higher run-up values.
A high-resolution sedimentological and geochemical study of a high-altitude proglacial lake (Lake Blanc, Aiguilles Rouges, 2352m a.s.l.) revealed 195 turbidites, 190 of which are related to flood events over the last 1400 years. We used the coarsest sediment fraction of each turbidite as a proxy for the intensity of each flood event. Because most flood events at this locality are triggered by localized summer convective precipitation events, the reconstructed sedimentary record reveals changes in the frequency and intensity of such events over the last millennium. Comparisons with other temperature, palaeohydrological and glacier reconstructions in the region suggest that the most intense events occurred during the warmest periods, i.e. during the Medieval Climate Anomaly (AD 800-1300) and the current period of global warming. On a multi-decadal time scale, almost all the flood frequency peaks seem to correspond to warmer periods, whereas multi-centennial variations in flood frequency appear to follow the regional precipitation pattern. Consequently, this new Alpine flood record provides further evidence of a link between climate warming and an increase in the frequency and intensity of flooding on a multidecadal time scale, whereas the centennial variability in flood frequencies is related to regional precipitation patterns.
Une revue des principaux modèles de la Conscience de la Situation dégage deux points de vue : * Issue de la psychologie ergonomique, la "vue du sujet" identifie la Conscience de la Situation à une représentation fonctionnelle dont la construction renvoie à un critère de pertinence pragmatique. Par anticipation partielle du contexte et pré-activation d'invariants internes, la Conscience de la Situation favorise l'inscription de l'activité dans la dynamique de l'environnement. * Issue de l'ingénierie et de la psychologie écologique, la "vue de l'environnement" renverse la perspective en associant la Conscience de la Situation aux invariants externes du couplage sujet/environnement, notion élaborée à partir des affordances de la psychologie écologique. Son objet principal n'est donc pas tant la situation que les interactions possibles en situation. L'enjeu de notre recherche est l'étude du couplage entre ces deux approches, l'objectif applicatif sous-jacent étant l'utilisation des invariants externes en tant qu'extension représentationnelle de l'environnement afin de faciliter l'adaptation des opérateurs aux environnements dynamiques.
Force-feedback and physical modeling technologies now allow to achieve the same kind of relation with virtual instruments as with acoustic instruments, but the design of such elaborate models needs guidelines based on the study of the human sensory-motor system and behaviour. This article presents a qualitative study of a simulated instrumental interaction in the case of the virtual bowed string, using both waveguide and mass-interaction models. Subjects were invited to explore the possibilities of the simulations and to express themselves verbally at the same time, allowing us to identify key qualities of the proposed systems that determine the construction of an intimate and rich relationship with the users.
[extraits du début de l'article] Lorsque des troubadours, dès la fin du XIIe siècle, prennent le chemin de l'Italie et de ses cours, ils emmènent avec eux une lyrique destinée à y connaître une nouvelle floraison. Cette implantation en Italie du Nord de la lyrique occitane explique le rôle joué par la Vénétie comme " conservatoire " de la poésie des troubadours. Elle induit également le besoin d'explicitation et de contextualisation des poèmes de la lyrique occitane, causé par un décalage à la fois chronologique, géographique et linguistique, qui donne naissance à un corpus de textes que nous qualifions de biographies des troubadours depuis Raynouard, et qui regroupe des commentaires d'un poème particulier, les razos, et des biographies générales des troubadours, les vidas. Ces dernières tirent leurs informations des poèmes d'un troubadour et d'un nombre restreint d'autres sources pour en retour expliciter les poèmes, en fixer une interprétation, une exégèse presque, fondée sur la vie de leur auteur, dans un mouvement que Laura Kendrick qualifie de " circularité herméneutique ". C'est dans ce contexte de développement d'un canon que se déroule un phénomène de mise par écrit de la lyrique occitane, qui donne naissance, au cours de la deuxième moitié du XIIIe siècle, aux premiers chansonniers occitans que nous ayons conservés. Parmi ceux-ci, un groupe se distingue par la présence de vidas, de miniatures et par un modèle de mise en page particulier. Il s'agit des chansonniers AIK, tous trois vénètes, voire, d'après les développements historiographiques les plus récents, originaires de Venise même, et datant du dernier quart du XIIIe siècle, auxquels on pourrait ajouter le chansonnier B, quoique son lieu d'origine soit sujet à débat et qu'en dépit des espaces réservés les miniatures n'y aient jamais été ajoutées. (...) La division en trois grandes sections et l'ordre dans lequel se suivent les sous-sections consacrées à chaque auteur sont conçus comme un moyen d'établir une hiérarchie entre les genres, les textes et les auteurs. (...) Vidas et miniatures participent également de ce mouvement, comme on peut le voir dans la structuration des sections d'auteurs, qui débutent par la vida à l'encre rouge, et une miniature représentant le troubadour, souvent décrite comme un portrait, et contenue dans l'initiale du premier poème. Maria-Luisa Meneghetti qualifie de " doppio filtro metatestuale " cette biographie, qui emprunte la majeure partie de ses éléments aux œuvres du troubadour, et ce portrait, " che trasforma il racconto biografico in una sorta di flash esemplare ". La question demeure toutefois des modalités de cette transformation, des outils employés par l'image, et des sources autres que la vida auxquelles elle pourrait puiser. En quelques mots : peut-on superposer ces deux filtres ?
An optimized giant magneto-impedance effect magnetometer has been developed, based upon an overall analysis of the measurement chain, including physical material properties, associated detection coil parameters, and equivalent magnetic noise performances. The field response model for the sensing element and the noise model yield good agreement with experimental results. The noise performance of the magnetometer, approximately 1.7pT/√Hz in the white noise region, with a band-pass of about 70kHz, is competitive with that of other technologies. Present limitations are clearly established, leaving room for further improvements.
Considering the viscoelastic behavior of polymer foams a new plate theory based on the direct approach is introduced and applied to plates composed of functionally graded materials (FGM). The governing two-dimensional equations are formulated for a deformable surface, the viscoelastic stiffness parameters are identified assuming linear-viscoelastic material behavior. The material properties are changing in the thickness direction. Solving some problems of the global structural analysis it will be demonstrated that in some cases the results significantly differ from the results based on the Kirchhoff-type theory.
A Local/Global non-intrusive coupling algorithm is proposed for the analysis of mixed-mode crack propagation. It is based on a three scale multigrid and extended finite element method, that was proposed recently for the direct estimation of stress intensity factors of static cracks. The algorithm couples a linear elastic global model (possibly performed by a industrial software) with an enhanced local model capable of modeling a crack and accurately estimating SIFs (performed by a separate research code). It is said non-intrusive since it does not modify the global mesh, its connectivity and solver. For the global model, the contribution of the local patch consists in additional nodal efforts near the crack, which makes it compatible with most softwares. Further the shape of the domain over which the local model is applied is automatically adapted during propagation.
Nonribosomal peptides (NRPs) are molecules produced by microorganisms that have a broad spectrum of biological activities and pharmaceutical applications (e.g., antibiotic, immunomodulating, and antitumor activities). One particularity of the NRPs is the biodiversity of their monomers, extending far beyond the 20 proteogenic amino acid residues. Norine, a comprehensive database of NRPs, allowed us to review for the first time the main characteristics of the NRPs and especially their monomer biodiversity. Our analysis highlighted a significant similarity relationship between NRPs synthesized by bacteria and those isolated from metazoa, especially from sponges, supporting the hypothesis that some NRPs isolated from sponges are actually synthesized by symbiotic bacteria rather than by the sponges themselves. A comparison of peptide monomeric compositions as a function of biological activity showed that some monomers are specific to a class of activities. An analysis of the monomer compositions of peptide products predicted from genomic information (metagenomics and high-throughput genome sequencing) or of new peptides detected by mass spectrometry analysis applied to a culture supernatant can provide indications of the origin of a peptide and/or its biological activity.
Il y a une dizaine d'années, de nouvelles flavoenzymes nommées hydroxylases flavine-dépendantes à deux composants ont été identifiées chez certains microorganismes. Le rôle physiologique de ces enzymes est maintenant bien connu. Elles sont impliquées dans les processus de biosynthèse et de biodégradation d'une multitude de molécules organiques. Ces hydroxylases sont composées de deux enzymes distinctes. La première est une flavine réductase qui catalyse la formation de flavine réduite nécessaire au fonctionnement de la seconde enzyme, une monooxygénase flavine-dépendante. Au début de notre projet, le mécanisme enzymatique de ces nouvelles hydroxylases était encore inconnu. Pour comprendre le détail de leur fonctionnement, nous avons choisi d'étudier le système ActVA-ActVB, un nouveau membre de la famille des hydroxylases flavine-dépendantes impliqué dans la dernière étape de biosynthèse de l'actinorhodine, un antibiotique naturel synthétisé par Streptomyces coelicolor. La caractérisation préalable de ActVB avait permis de montrer que cette enzyme était une NADH:FMN oxydoréductase capable de catalyser la réduction du FMN par le NADH selon un mécanisme de type séquentiel ordonné. Nos résultats ont permis d'identifier ActVA-Orf5, une monooxygénase flavine-dépendante capable d'utiliser la flavine réduite fournie par ActVB pour catalyser l'hydroxylation du précurseur de l'actinorhodine, la DHK. Le mécanisme de transfert de flavine entre les deux protéines a été étudié. Pour cela, les constantes de dissociation du FMNox et FMNred vis-à-vis de ActVA et ActVB ont été déterminées. Nos donnés montrent clairement qu'à l'état réduit, la flavine est bien plus affine pour la monooxygénase ActVA que pour la réductase ActVB alors qu'à l'état oxydé, elle possède une meilleure affinité pour la réductase que pour la monooxygénase. Cette différence d'affinité permet d'orienter le transfert de flavine d'une protéine à l'autre sans nécessiter d'interaction entre les deux protéines. Nous avons montré de plus que ActVA avait la capacité de stabiliser un intermédiaire activé de l'oxygène, une espèce électrophile nommée C(4a)-hydroperoxyflavine, au sein de son site actif. Cet intermédiaire réagit très rapidement avec la DHK nucléophile pour former son analogue hydroxylé : la DHK-OH. En accord avec ce mécanisme, il semble que le pouvoir nucléophile du substrat est très important pour cette réaction car seule la forme réduite à deux électrons de DHK (hydroquinone) est hydroxylée. D'autre part, ActVA ne semble pas être très spécifique car elle parvient également à catalyser l'hydroxylation de l'énantiomère de la DHK, la NNM-A et de l'analogue lactonique de la NNM-A, la NNM-D. Finalement le système ActVA-ActVB n'a pas la capacité de dimériser la DHK-OH pour former l'actinorhodine et l'enzyme intervenant dans la dernière étape de cette biosynthèse reste à identifier.
Compressed sensing (CS) is a theory which guarantees the exact recovery of sparse signals from a few number of linear projections. The sampling schemes suggested by current CS theories are often of little relevance since they cannot be implemented on practical acquisition systems. In this paper, we study a new random sampling approach that consists in selecting a set of blocks that are predefined by the application of interest. A typical example is the case where the blocks consist in horizontal lines in the 2D Fourier plane. We provide theoretical results on the number of blocks that are required for exact sparse signal reconstruction in a noise free setting. We illustrate this theory for various sensing matrices appearing in applications such as time-frequency bases. A typical result states that it is sufficient to acquire no more than $O\left( s \ln^2(n) \right)$ lines in the 2D Fourier domain for the perfect reconstruction of an $s$-sparse image of size $\sqrt{n} \times \sqrt{n}$ . The proposed results have a large number of potential applications in systems such as magnetic resonance imaging, radio-interferometry or ultra-sound imaging.
Wavelet analysis has been found to be a powerful tool for the nonparametric estimation of spatially-variable objects. We discuss in detail wavelet methods in nonparametric regression, where the data are modelled as observations of a signal contaminated with additive Gaussian noise, and provide an extensive review of the vast literature of wavelet shrinkage and wavelet thresholding estimators developed to denoise such data. These estimators arise from a wide range of classical and empirical Bayes methods treating either individual or blocks of wavelet coefficients. We compare various estimators in an extensive simulation study on a variety of sample sizes, test functions, signal-to-noise ratios and wavelet filters. Because there is no single criterion that can adequately summarise the behaviour of an estimator, we use various criteria to measure performance in finite sample situations. Insight into the performance of these estimators is obtained from graphical outputs and numerical tables. In order to provide some hints of how these estimators should be used to analyse real data sets, a detailed practical step-by-step illustration of a wavelet denoising analysis on electrical consumption is provided. Matlab codes are provided so that all figures and tables in this paper can be reproduced.
This paper is concerned with the problem of the alignment of multiple sets of curves. We analyze two real examples arising from the biomedical area for which we need to test whether there are any statistically significant differences between two subsets of subjects. To synchronize a set of curves, we propose a new nonparametric landmark-based registration method based on the alignment of the structural intensity of the zero-crossings of a wavelet transform. The structural intensity is a multiscale technique recently proposed by Bigot (2003, 2005) which highlights the main features of a signal observed with noise. We conduct a simulation study to compare our landmark-based registration approach with some existing methods for curve alignment. For the two real examples, we compare the registered curves with FANOVA techniques, and a detailed analysis of the warping functions is provided.
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