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Double-walled carbon nanotubes (DWNTs), produced by a catalytic chemical vapor deposition method, have been fluorinated using a volatile mixture of BrF3 and Br2. Optical absorption spectroscopic study on the product detected nonfluorinated nanotubes, which could correspond to the inner walls of DWNTs. The fluorinated DWNTs have been annealed in vacuum at fixed temperatures, and X-ray photoelectron spectroscopy showed almost no fluorine in the sample heated to 300 °C. Comparison between X-ray fluorescent C KR spectra of the pristine DWNT sample and the annealed fluorinated sample revealed change of the atomic structure of graphitic shells in the process of thermal defluorination.
L'objectif de cette thèse est de concevoir une chimiothèque à partir de synthons C-glycosidiques. Les composés obtenus sont destinés à l'identification de modulateurs de l'activité des protéines pour comprendre leur rôle dans les mécanismes cellulaires. Pour réaliser ce travail, nous nous sommes basés sur le concept de la Synthèse Orientée vers la Diversité (SOD) pour générer une collection de molécules par des réactions à plusieurs composants. A partir de glycals peracétylés, nous avons préparés les C-glycosides de départ qui portent une fonction aldéhyde sur l'aglycone. Nous avons montré qu'il était possible de synthétiser ces produits en irradiant le milieu réactionnel par les micro-ondes. Puis ces synthons ont été traité par une amine et un alcyne ce qui a permis de générer une série de propargylamines. Parmi les propargylamines synthétiseés nous avons pu montrer que la L-proline avait une activité auto catalytique et qu'elles conduisaient a une addition stéréosélective de l'alcyne sur l'iminium intermédiaire. Nous avons alors utilisé cette propriété pour combiner la réaction à 3 composants avec la chimie click pour obtenir en quatre étapes une banque de 40 C-glycosides complexes hautement fonctionnalisées. Dans la deuxième partie de ce travail nous avons mis à profit la présence d'un alcool allylique sur le cycle pyranne pour mettre au point une nouvelle réaction tandem, la réaction A3M. Ce nouveau procédé permet d'obtenir en une seul étape des pyridino pyrannes par une réaction à trois composants. Après oxydation de l'alcool en cétone, le C-glycoside est irradie par les micro ondes en présence d'une amine primaire, et d'une alcyne (couplage A3). Cette première réaction est suivie d'une addition de Michael intramoléculaire sur la double liaison activée pour donner stéréo sélectivement le composé bicyclique
We assess a variant of linear-response range-separated time-dependent density-functional theory (TDDFT), combining a long-range Hartree-Fock (HF) exchange kernel with a short-range adiabatic exchange-correlation kernel in the local-density approximation (LDA) for calculating isotropic C6 dispersion coefficients of homodimers of a number of closed-shell atoms and small molecules. This range-separated TDDFT tends to give underestimated C6 coefficients of small molecules with a mean absolute percentage error of about 5%, a slight improvement over standard TDDFT in the adiabatic LDA which tends to overestimate them with a mean absolute percentage error of 8%, but close to time-dependent Hartree-Fock which has a mean absolute percentage error of about 6%. These results thus show that introduction of long-range HF exchange in TDDFT has a small but beneficial impact on the values of C6 coefficients. It also confirms that the present variant of range-separated TDDFT is a reasonably accurate method even using only a LDA-type density functional and without adding an explicit treatment of long-range correlation.
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.
This paper describes a machine-checked proof of the Jordan- Hölder theorem for finite groups. This purpose of this description is to discuss the representation of the elementary concepts of finite group the- ory inside type theory. The design choices underlying these representa- tions were crucial to the successful formalization of a complete proof of the Odd Order Theorem with the Coq system.
The interaction of 784 intergenic (ig-miRNA), 686 intronic (in-miRNA) and 49 exonic miRNAs (ex-miRNA) with mRNAs of 51 oncogenes coding in-miRNAs was investigated. Out of the studied genes, 44 were targets for 94 ig-miRNAs, 29 were targets for 44 in-miRNAs and 7 were targets for 7 ex-miRNAs. The density of miRNA binding sites was higher in 5'-untranslated regions than it was in coding sequences and 3'-untranslated regions. Three types of miRNA interaction with mRNA were revealed: 5'-dominant canonical, 3'-compensatory and complementary types. In-miRNAs do not interact with mRNAs of host genes (where in-miRNA is encoded). Linkage between some mRNAs of genes encodes in-miRNAs via other in-miRNAs was revealed. These data promote the understanding of interaction mechanism of miRNA with mRNA genes participating in gastrointestinal and breast cancers.
This paper targets the autonomic management of dynamically partially reconfigurable hardware architectures based on FPGAs. Such hardware-level autonomic computing has been less often studied than at software-level. We consider control techniques to model the considered behaviours of the computing system and derive a controller for the control objective enforcement. Discrete Control modelled with Labelled Transition Systems is employed in this paper. Such models are amenable to Discrete Controller Synthesis algorithms that can automatically generate a controller enforcing the correct behaviours of a controlled system. A general modelling framework is proposed for the control of FPGA based computing systems. We consider system application described as task graphs and FPGA as a set of reconfigurable areas that can be dynamically partially reconfigured to execute tasks. We encode the computation of an autonomic manager as a DCS problem w.r.t. multiple constraints and objectives e.g., mutual exclusion of resource uses, power cost minimization. We validate our models and manager computations by using the BZR language and an experimental demonstrator implemented on a Xilinx FPGA platform.
We prove a Lieb-Thirring type inequality for a complex perturbation of a d-dimensional massive Dirac operator $D_m, m\geq 0$ whose spectrum is $]-\infty , -m]\cup[m , +\infty[$. The difficulty of the study is that the unperturbed operator is not bounded from below in this case, and, to overcome it, we use the methods of complex function theory. The methods of the article also give similar results for complex perturbations of the Klein-Gordon operator.
Let T be a tilting object in a triangulated category which is equivalent to the bounded derived category of a finite-dimensional hereditary algebra. The text investigages the strong global dimension, in the sense of Ringel, of the opposite algebra A of the endomorphism algebra of T. This invariant is expressed in terms of the lengths of the sequences of tilting objects with last term equal to T, such that each term arises from the preceding one by a tilting mutation, and such that the opposite of the endomorphism algebra of the first term is a tilted algebra. It is also expressed in terms on the hereditary abelian subcategories of the triangulated category.
Very few results are known about the topology of the strata of the moduli space of quadratic differentials. In this paper, we prove that any connected component of such strata has only one topological end. A typical flat surface in a neighborhood of the boundary is naturally split by a collection of parallel short saddle connections, but the discrete data associated to this splitting can be quite difficult to describe. In order to bypass these difficulties, we use the Veech zippered rectangles construction and the corresponding (extended) Rauzy classes.
The selective laser melting process (SLM), belonging to the family of additive manufacturing processes, can create complex geometry parts from a CAD file. Previously, only prototypes were created by SLM, but now this process is used to manufacture quickly and directly functional parts. For example, in the PEP (Centre Technique de la Plasturgie), this process is used to manufacture tooling parts or injection molds with cooling channels that can't be obtained by conventional routes. During the process, the laser beam generates violent heating and cooling cycles in the material inducing important thermal gradients in the consolidated part. The cyclic thermal expansions and contractions exceeding the maximum elastic strain of the material induce heterogeneous plastic strains and generate internal stresses the level of which can reaches the yield stress of the material and cracks may appear during the process. This paper deals with the measurement and analysis of residual stresses during the selective laser melting of a simple part in maraging steel. The objective of this study is the analysis of experimental results to validate the numerical model previously presented in [1]. A new method is proposed to evaluate the residual stresses induced during the SLM process, a rosette is fixed on the bottom face of the support. The residual stresses in the created part are calculated from strain and temperature variations when the fused layer is consolidating during the cooling between two layers. Process parameters like the powder thickness or the cooling time between successive layers are studied in this paper.
Selective laser melting (SLM) first developed for rapid prototyping (RP) is now used for rapid manufacturing of parts with inner complex shapes that cannot be made by more conventional routes. For example, production of injection moulds with cooling channels is of special interest. In this paper, a numerical model of SLM process was investigated to simulate the genesis of residual stresses. The proposed numerical modelling is based upon a double meshing with a multi-step birth and death technique of manufactured part. The influence of the mesh size is analysed with element as small as the powder layer thickness for 2D and 3D geometries of simple parts. Comparisons between plane stress, plane strain, and 3D analysis are presented in order to propose a simplified approach.
We derive an exact formula for the complex frequency in spatio-temporal stability analysis that is valid for arbitrary complex wave numbers. The usefulness of the formula lies in the fact that it depends only on purely temporal quantities, which are easily calculated. We apply the formula to two model dispersion relations: the linearized complex Ginzburg-Landau equation, and a model of wake instability. In the first case, a quadratic truncation of the exact formula applies; in the second, the same quadratic truncation yields an estimate of the parameter values at which the transition to absolute instability occurs; the error in the estimate decreases upon increasing the order of the truncation. We outline ways in which the formula can be used to characterize stability results obtained from purely numerical calculations, and point to a further application in global stability analyses.
Modern soil and litter samples from southeastern Cameroon, collected along a continuous forest-savanna transect were analysed for pollen content to define modern pollen-vegetation relationships. The pollen results, completed and compared with botanical inventories, leaf area index and basal area measurements performed in the same area, clearly registered the physiognomy, the main floristic composition and floral richness of the two sampled ecosystems. Distortions were observed between sampled vegetations and their pollen rain, related to important differences in pollen production and dispersal of plant species: this is a general feature in many tropical regions. The pollen data in the area studied reflected well the recent transgression of forest versus savanna. This permitted us to define inside the forest ecosystem more successional vegetation communities than the botanical surveys allowed.
Instruments for surface missions to extraterrestrial bodies should be cross-calibrated using a common suite of relevant materials. Such work is necessary to improve instrument performance and aids in the interpretation of in-situ measurements. At the CNRS campus in Orléans, the Observatoire des Sciences de l'Univers en région Centre (OSUC) has created a collection of well-characterised rocks and minerals for testing and calibrating instruments to be flown in space missions. The characteristics of the analogue materials are documented in an accompanying online database. In view of the recent and upcoming rover missions to Mars (NASA's 2011 Mars Science Laboratory (MSL) and ESA/Roscosmos' 2018 ExoMars), we are concentrating initially on materials of direct relevance to the red planet. The initial collection consists of 15 well-studied rock and mineral samples, including a variety of basalts (ultramafic, weathered, silicified, primitive), sediments (volcanic sands, chert, and a banded iron formation -BIF-), and the phyllosilicate nontronite (a clay). All the samples were characterised petrographically, petrologically, and geochemically using the types of analyses likely to be performed during in-situ missions, in particular ExoMars: hand specimen description; optical microscopy; mineralogical analysis by XRD, Raman and IR spectrometry; iron phase analysis by Mössbauer spectroscopy (MBS), elemental analysis by Energy-Dispersive X-ray spectroscopy (EDX), microprobe, Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and Mass Spectrometry (ICP-MS); and reduced carbon analysis by Raman spectrometry.
This Thesis presents the results of a study of the "High Zagros", the most internal part of the Zagros-Fold-Thrust-Belt (ZFTB). On map view, the High Zagros is exposed in two separated domains (Western and Eastern High Zagros respectively) and partly hidden as an under-plated region beneath the Sanandaj-Sirjan Domain. The High Zagros is the only place in the ZFTB where the Paleozoic rocks are widely exposed.A primary objective was to reevaluate the structural style and kinematic evolution of the High Zagros. It is shown that the most significant geological elements within this area are large scale faulted detachment folds, associated with a complex system of thrust faults segmented by strike-slip faults. This work suggests that the existence of active Ordovician and/or Silurian décollements led to the development of duplex structures which are confined in the core of the anticlines. A two-step kinematic scenario, similar to the one already proposed elsewhere in the belt, is proposed for the High Zagros. Firstly, a thin-skinned phase led to establish detachment folding over the basal Hormuz salt. Then, a thick-skinned phase resulted in the basement thrusting and allowed the exhumation of Lower Paleozoic succession.After this presentation of the tectonic context of the High Zagros, the thesis focuses on the tectonic significance of the pre-Permian unconformity, which was known through a major hiatus between Cambro-Ordovicien to Early Permian and between Devonian to Permian rocks in the western and eastern High Zagros respectively. It is shown that (1) the High Zagros presents below the unconformity a large "Arch-and-Basin" geometry; and that (2) only extensional features such as normal faults and rotated blocks, without evidence of contractional deformation, can be observed below the unconformity. Thermal uplift of possible Late Devonian is proposed as a probable mechanism explaining both the uplift and the diffuse extensional deformation. This proposal strongly modifies the "classical" interpretation of the pre-Permian hiatus as a far effect of the Variscan Orogeny.Thermal modeling based on maturity data from potential source rocks cropping out in the High Zagros has been performed. The most probable modeled scenario suggests an important heat flow during the Devonian and the erosion of ~3900m of the sedimentary pile prior to the deposition of Permian sequence. This outcome reinforces our interpretation of a thermal uplift scenario responsible for pre-Permian vertical movements. On the other hand, a set of new (U-Th)/He ages obtained from the Lower Paleozoic, Devonian and early Permian clastic rocks show a partial reset of zircon grains. These two results are fairly consistent with the published data describing a major thermo-tectonic event during Late Devonian-Early Carboniferous in the Levant Arch (Israel, Jordan) and suggest a common mechanism at the scale of the Arabian Plate.
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.
Les tâches d'empan de mémoire de travail sont des tâches dans lesquelles des items doivent être maintenus en mémoire à court terme pendant qu'un traitement concurrent est effectué. Le but de la présente étude était de déterminer si, comme le soutient le modèle de partage temporel des ressources (Barrouillet, Bernardin, & Camos, 2004), les traitements gênent le maintien parce que les deux composantes entrent en compétition pour des processus communs ou plus simplement parce que les stratégies de maintien des items à rappeler sont perturbées par l'intrusion de l'information à traiter simultanément. Quatre-vingt sujets adultes étaient soumis à une tâche d'empan où ils devaient maintenir des lettres en même temps qu'ils devaient juger soit de la parité soit de la position spatiale de nombre présentés successivement à l'écran. Par ailleurs, ces nombres apparaissaient à un rythme régulier et donc prévisible ou bien aléatoire. Conformément à nos attentes, et contrairement à l'hypothèse d'une perturbation des stratégies de maintien, les jugements de parité qui nécessitent des récupérations en mémoire entraînaient de plus faibles empans que la tâche spatiale qui ne requiert qu'une sélection de réponse alors que le rythme de réalisation de la tâche secondaire n'avait pas d'effet sur les empans.
The functional organization of the PFC from anterior to posterior regions reflects a hierarchy of cognitive control whereby progressively anterior sub-regions are associated with higher-order control. The present study aimed at providing behavioral evidence for two predictions issuing from this cascade model. First, even the lower-most sub-part of the cognitive control hierarchy, i.e. motor programming, should interfere with higher controlled processes such as maintenance in working memory. Second, this effect should be commensurate with the time during which control is required. In a computer-paced complex span task, adults had to maintain letters while they performed a secondary task. The demand imposed by this task was manipulated either at the selection or at the motor programming stage of response preparation. Results revealed that both manipulations have a disruptive effect on verbal memory, and that this effect is commensurate with the extra-time during which response selection and motor programming require cognitive control.
Memorizing is crucial for human beings because it constitutes the fundamental step in acquiring knowledge. Among the different memory systems, the one called "working memory" works continuously to simultaneously memorize and process information. It is particularly important in children who are continually confronted to learning situations. It has long been considered that memorizing required verbalizing and repeating. The present paper offers an alternative conception: working memory relies on attentional mechanisms constrained by time and do not depend on verbal characteristics. The empirical analyses we present here do not only conduct to important theoretical conclusions, they also give a glimpse of practical applications for preventing school failure.
Modern soil and litter samples from southeastern Cameroon, collected along a continuous forest-savanna transect were analysed for pollen content to define modern pollen-vegetation relationships. The pollen results, completed and compared with botanical inventories, leaf area index and basal area measurements performed in the same area, clearly registered the physiognomy, the main floristic composition and floral richness of the two sampled ecosystems. Distortions were observed between sampled vegetations and their pollen rain, related to important differences in pollen production and dispersal of plant species: this is a general feature in many tropical regions. The pollen data in the area studied reflected well the recent transgression of forest versus savanna. This permitted us to define inside the forest ecosystem more successional vegetation communities than the botanical surveys allowed.
Depuis bientôt un siècle, on utilise des systèmes différentiels pour représenter la dynamique des populations de différentes espèces dans des écosystèmes. Les nombres réels prédits par ces modèles mathématiques peuvent être si petits qu'il n'ont plus de sens dans la théorie physique représentée. La notion classique de persistance qui exige que les quantités manipulées restent strictement positives n'est pas satisfaisante car dans la représentation de populations en interaction par des systèmes différentiles, il faut se souvenir que les nombres réels manipulés sont en fait des nombres d'individus comptés avec une unité assez grande. Nous étudions et critiquons la notion de persistance à travers le modèle classique de "ressource-consommateur" et des simulations sur ordinateur.
In the Water Framework Directive (European Union) context, a multimetric fish based index is required to assess the ecological status of French estuarine water bodies. A first indicator called ELFI was developed, however similarly to most indicators, the method to combine the core metrics was rather subjective and this indicator does not provide uncertainty assessment. Recently, a Bayesian method to build indicators was developed and appeared relevant to select metrics sensitive to global anthropogenic pressure, to combine them objectively in an index and to provide a measure of uncertainty around the diagnostic. Moreover, the Bayesian framework is especially well adapted to integrate knowledge and information not included in surveys data. In this context, the present study used this Bayesian method to build a multimetric fish based index of ecological quality accounting for experts knowledge. The first step consisted in elaborating a questionnaire to collect assessments from different experts then in building relevant priors to summarize those assessments for each water body. Then, these priors were combined with surveys data in the index to complement the diagnosis of quality. Finally, a comparison between diagnoses using only fish data and using both information sources underlined experts knowledge contribution. Regarding the results, 68% of the diagnosis matched demonstrating that including experts knowledge thanks to the Bayesian framework confirmed or slightly modified the diagnosis provided by survey data but influenced uncertainty around the diagnostic and appeared especially relevant in terms of risk management.
Etude de l'activité accomplie en discussions à visée philosophique sous différents angles relativement aux spécificités de chaque équipe impliquée dans l'opération 2LAPRÉ. Celle-ci permettra de fournir une modélisation de la pratique enseignante dans ce type de contexte. Cela constituera un support au développement d'un processus de formation qui ne pourra se faire qu'en partenariat avec les acteurs institutionnels impliqués de près ou de loin dans ce type de discussion (formateur, enseignants, parents...).
This paper examines the causality relationship between immigration, unemployment and economic growth of the host country. We employ the panel Granger causality testing approach of Konya (2006) that is based on SUR systems and Wald tests with country specific bootstrap critical values. This approach allows to test for Granger-causality on each individual panel member separately by taking into account the contemporaneous correlation across countries. Using annual data over the 1980-2005 period for 22 OECD countries, we find that, only in Portugal, unemployment negatively causes immigration, while in any country, immigration does not cause unemployment. On the other hand, our results show that, in four countries (France, Iceland, Norway and the United Kingdom), growth positively causes immigration, whereas in any country, immigration does not cause growth.
The vita of Saint Francis contained in the Speculum historiale of Vincent of Beauvais is a compilation of the Vita Sancti Francisci of Julian of Speyer, and is not often consulted in Franciscan studies. Yet the editor's revision of the Speculum reveals that even a digest of the saint's life posed a challenge to an increasingly Dominican agenda, and had to be adjusted. This paper explores the portrayal of Francis in the Speculum historiale alongside with the ps-Vincentian Speculum morale, composed by a Franciscan but revealing a similar manipulation of the saint's vita. I argue that both specula are threatened by the visionary and charismatic nature of the saint -- the Historiale by the shadow he cast over Dominic and the Morale by the potentially dangerous zeal his example could inspire -- and both construct a Francis that is an acceptable compromise fitting their particular needs. The analysis of the construction of the persona of Francis in the two works associated with Vincent of Beauvais provides further evidence for the fluid perception and pragmatic use of Francis in the second half of the thirteenth and early fourteenth centuries, and new understanding of the context surrounding the appearance of the Speculum morale.
Super-resolution (SR) aims at combining a number of aliased images of the same scene into a higher resolution image by using the difference in sampling caused by camera motion. As the problem of SR is generally ill-posed, techniques developed in the literature often rely on hypotheses on the regularity of the image. In this paper, we try to minimize these assumptions for the interpolation part of super-resolution. We describe situations where super-resolution interpolation is invertible and/or well conditioned. We first study the interpolation problem for large numbers of images when motions are pure translations. Then, we look at the more generic problem of super-resolution interpolation with translations and rotations. We give a simple condition on the number of images and zoom factor for perfect recovery of the high resolution image. We also study the conditioning in the critical case and propose regularization methods which adapts to local sampling variations. Thus, we avoid the generation of artifacts when the acquired data is noisy.
The selective laser melting process (SLM), belonging to the family of additive manufacturing processes, can create complex geometry parts from a CAD file. Previously, only prototypes were created by SLM, but now this process is used to manufacture quickly and directly functional parts. For example, in the PEP (Centre Technique de la Plasturgie), this process is used to manufacture tooling parts or injection molds with cooling channels that can't be obtained by conventional routes. During the process, the laser beam generates violent heating and cooling cycles in the material inducing important thermal gradients in the consolidated part. The cyclic thermal expansions and contractions exceeding the maximum elastic strain of the material induce heterogeneous plastic strains and generate internal stresses the level of which can reaches the yield stress of the material and cracks may appear during the process. This paper deals with the measurement and analysis of residual stresses during the selective laser melting of a simple part in maraging steel. The objective of this study is the analysis of experimental results to validate the numerical model previously presented in [1]. A new method is proposed to evaluate the residual stresses induced during the SLM process, a rosette is fixed on the bottom face of the support. The residual stresses in the created part are calculated from strain and temperature variations when the fused layer is consolidating during the cooling between two layers. Process parameters like the powder thickness or the cooling time between successive layers are studied in this paper.
Selective laser melting (SLM) first developed for rapid prototyping (RP) is now used for rapid manufacturing of parts with inner complex shapes that cannot be made by more conventional routes. For example, production of injection moulds with cooling channels is of special interest. In this paper, a numerical model of SLM process was investigated to simulate the genesis of residual stresses. The proposed numerical modelling is based upon a double meshing with a multi-step birth and death technique of manufactured part. The influence of the mesh size is analysed with element as small as the powder layer thickness for 2D and 3D geometries of simple parts. Comparisons between plane stress, plane strain, and 3D analysis are presented in order to propose a simplified approach.
The interaction of 784 intergenic (ig-miRNA), 686 intronic (in-miRNA) and 49 exonic miRNAs (ex-miRNA) with mRNAs of 51 oncogenes coding in-miRNAs was investigated. Out of the studied genes, 44 were targets for 94 ig-miRNAs, 29 were targets for 44 in-miRNAs and 7 were targets for 7 ex-miRNAs. The density of miRNA binding sites was higher in 5'-untranslated regions than it was in coding sequences and 3'-untranslated regions. Three types of miRNA interaction with mRNA were revealed: 5'-dominant canonical, 3'-compensatory and complementary types. In-miRNAs do not interact with mRNAs of host genes (where in-miRNA is encoded). Linkage between some mRNAs of genes encodes in-miRNAs via other in-miRNAs was revealed. These data promote the understanding of interaction mechanism of miRNA with mRNA genes participating in gastrointestinal and breast cancers.
Following Kimura's neutral theory of molecular evolution [M. Kimura, The Neutral Theory of Molecular Evolution (Cambridge University Press, Cambridge, 1983) (reprinted in 1986)], it has become common to assume that the vast majority of viable mutations of a gene confer little or no functional advantage. Yet, in silico models of protein evolution have shown that mutational robustness of sequences could be selected for, even in the context of neutral evolution. The evolution of a biological population can be seen as a diffusion on the network of viable sequences. This network is called a "neutral network." Depending on the mutation rate mu and the population size N, the biological population can evolve purely randomly (muN<1) or it can evolve in such a way as to select for sequences of higher mutational robustness (muN>1). The stringency of the selection depends not only on the product muN but also on the exact topology of the neutral network, the special arrangement of which was named "superfunnel." Even though the relation between mutation rate, population size, and selection was thoroughly investigated, a study of the salient topological features of the superfunnel that could affect the strength of the selection was wanting. This question is addressed in this study. We use two different models of proteins: on lattice and off lattice. We compare neutral networks computed using these models to random networks. From this, we identify two important factors of the topology that determine the stringency of the selection for mutationally robust sequences. First, the presence of highly connected nodes ("hubs") in the network increases the selection for mutationally robust sequences. Second, the stringency of the selection increases when the correlation between a sequence's mutational robustness and its neighbors' increases. The latter finding relates a global characteristic of the neutral network to a local one, which is attainable through experiments or molecular modeling.
BACKGROUND: Protein fold recognition usually relies on a statistical model of each fold; each model is constructed from an ensemble of natural sequences belonging to that fold. A complementary strategy may be to employ sequence ensembles produced by computational protein design. Designed sequences can be more diverse than natural sequences, possibly avoiding some limitations of experimental databases. METHODOLOGY/PRINCIPAL FINDINGS: WE EXPLORE THIS STRATEGY FOR FOUR SCOP FAMILIES: Small Kunitz-type inhibitors (SKIs), Interleukin-8 chemokines, PDZ domains, and large Caspase catalytic subunits, represented by 43 structures. An automated procedure is used to redesign the 43 proteins. We use the experimental backbones as fixed templates in the folded state and a molecular mechanics model to compute the interaction energies between sidechain and backbone groups. Calculations are done with the Proteins@Home volunteer computing platform. A heuristic algorithm is used to scan the sequence and conformational space, yielding 200,000-300,000 sequences per backbone template. The results confirm and generalize our earlier study of SH2 and SH3 domains. The designed sequences ressemble moderately-distant, natural homologues of the initial templates; e.g., the SUPERFAMILY, profile Hidden-Markov Model library recognizes 85% of the low-energy sequences as native-like. Conversely, Position Specific Scoring Matrices derived from the sequences can be used to detect natural homologues within the SwissProt database: 60% of known PDZ domains are detected and around 90% of known SKIs and chemokines. Energy components and inter-residue correlations are analyzed and ways to improve the method are discussed. CONCLUSIONS/SIGNIFICANCE: For some families, designed sequences can be a useful complement to experimental ones for homologue searching. However, improved tools are needed to extract more information from the designed profiles before the method can be of general use.
We consider supervised learning problems within the positive-definite kernel framework, such as kernel ridge regression, kernel logistic regression or the support vector machine. With kernels leading to infinite-dimensional feature spaces, a common practical limiting difficulty is the necessity of computing the kernel matrix, which most frequently leads to algorithms with running time at least quadratic in the number of observations n, i.e., O(n^2). Low-rank approximations of the kernel matrix are often considered as they allow the reduction of running time complexities to O(p^2 n), where p is the rank of the approximation. The practicality of such methods thus depends on the required rank p. In this paper, we show that in the context of kernel ridge regression, for approximations based on a random subset of columns of the original kernel matrix, the rank p may be chosen to be linear in the degrees of freedom associated with the problem, a quantity which is classically used in the statistical analysis of such methods, and is often seen as the implicit number of parameters of non-parametric estimators. This result enables simple algorithms that have sub-quadratic running time complexity, but provably exhibit the same predictive performance than existing algorithms, for any given problem instance, and not only for worst-case situations.
To take account of the uncertainties introduced on the soft magnetic materials properties (magnetic behavior law, iron losses) during the manufacturing process, the present work deals with the stochastic modeling of the magnetic behavior law B-H and iron losses of claw pole stator generator. Twenty eight (28) samples of slinky stator (SS) coming from the same production chain have been investigated. The used approaches are similar to those used in mechanics. The accuracy of existing anhysteretic models has been tested first using cross validation techniques. The well known iron loss separation model has been implemented to take into account the variability of the losses. Then, the Multivariate Gaussian distribution is chosen to model the variability and dependencies between identified parameters, for both behavior law and iron loss models. The developed stochastic models allow predicting a 98% confidence interval for the considered samples
Using an approach recently developed by Nourdin and Poly, we improve the rate in an inequality for the total variation distance between two double Wiener-Itô integrals originally due to Davydov and Martynova. An application to the rate of convergence of a functional of a correlated two-dimensional fractional Brownian motion towards the Rosenblatt random variable is then given, following a previous study by Maejima and Tudor.
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