16 research outputs found
Potts models in the continuum. Uniqueness and exponential decay in the restricted ensembles
No full textIn this paper we study a continuum version of the Potts model, where particles are points in R-d supercript stop, d >= 2, with a spin which may take S >= 3 possible values. Particles with different spins repel each other via a Kac pair potential of range gamma(-1), gamma > 0. In mean field, for any inverse temperature beta there is a value of the chemical potential lambda (beta) at which S+1 distinct phases coexist. We introduce a restricted ensemble for each mean field pure phase which is defined so that the empirical particles densities are close to the mean field values. Then, in the spirit of the Dobrushin-Shlosman theory (Dobrushin and Shlosman in J. Stat. Phys. 46(5-6):983-1014, 1987), we prove that while the Dobrushin high-temperatures uniqueness condition does not hold, yet a finite size condition is verified for gamma small enough which implies uniqueness and exponential decay of correlations. In a second paper (De Masi et al. in Coexistence of ordered and disordered phases in Potts models in the continuum, 2008), we will use such a result to implement the Pirogov-Sinai scheme proving coexistence of S+1 extremal DLR measures
Dobrushin Interfaces via Reflection Positivity
No full text48 pages, 4 figures; updated for publication (to appear in CMP)We study the interfaces separating different phases of 3D systems by means of the Reflection Positivity method. We treat discrete non-linear sigma-models, which exhibit power-law decay of correlations at low temperatures, and we prove the rigidity property of the interface. Our method is applicable to the Ising and Potts models, where it simplifies the derivation of some known results. The method also works for large-entropy systems of continuous spins
Interfaces rigides des modèles sur réseau : une application de la positivité par réflexion
No full textWe study interfaces for four spin models on a lattice: the Ising model at low temperature, the Potts model at critical point, a continuous symmetry model and its associated clock approximation. For each model, we use specific boundary conditions that force the existence of an interface; related Gibbs measures then satisfy the so-called chessboard estimates, which are powerful correlation inequalities. These estimates are a simple way to show that such interfaces are rigid, in the sense that they deviate only locally from a perfect hyperplane. This method is a restricted version of the so-called reflection positivity method, since reflections in certain directions are forbidden by the chosen boundary conditions.In the case of Ising and Potts models, our method drastically simplifies historical proofs respectively since its requires neither Pirogov-Sinai theory nor cluster expansions. Besides, PS-theory is not directly available for the continuous model and its clock approximation, their ground states being infinitely degenerated; our method is thus a real alternative to such techniques.Nous étudions les interfaces de quatre modèles de spins sur réseau: le modèle d'Ising à basse température, le modèle de Potts à la température critique, un modèle à symétrie continue et son approximation d'horloge.Pour chacun de ces modèles, nous imposons des conditions au bord spécifiques qui assurent l'existence d'une interface ; les mesures de Gibbs associées à de telles conditions au bord satisfont alors de puissantes inégalités de corrélation. Ces inégalités nous permettent de montrer que les interfaces considérées sont rigides, au sens où ce sont des hyperplans légèrement déformés par des aspérités locales. Cette méthode est une version restreinte de la méthode de positivité par réflexion, l'une des directions de réflexion étant prohibée par les conditions au bord choisies.Pour Ising et Potts, notre méthode simplifie considérablement les démonstrations historiques, puisque ni la théorie de Pirogov-Sinai, ni les développements en amas ne sont nécessaires à son application. Par ailleurs, la théorie-PS n'est directement envisageable ni pour le modèle continu ni son approximation car leurs états fondamentaux sont infiniment dégénérés; notre méthode est donc une réelle alternative à ces techniques
An Old Unknown Map of America. The First to Show the Future Bering Strait
No full text"This map is found without title, date, or the name of the author, in an atlas of the sixteenth century which we have had the pleasure of studying in the Americana library of M. Chadenat, a library rich in cartographical documents… Although this map in its condition does not give the author's name, we have no hesitation in attributing it to Gastaldi because it is clearly designed by the same author as two of the other maps in the collection... What characterizes this map and gives it exceptional historical importance is that contrary to all other maps by Gastaldi one sees America clearly separated from Asia.
Hydrodynamic limit for the Ginzburg–Landau <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="mml1" display="inline" overflow="scroll" altimg="si1.gif"><mml:mo>∇</mml:mo><mml:mi>ϕ</mml:mi></mml:math> interface model with non-convex potential
No full text
Le Verglas, analyse et réemploi des images d’une catastrophe
No full textMémoire en recherche-création.À partir d’archives diffusées sur YouTube, ce mémoire s’intéresse à la catastrophe naturelle du Verglas de 1998. Les vidéos sont l’occasion d’une réflexion sur l’esthétique des images d’information journalistique de catastrophes naturelles, sur le support VHS qui a permis leur premier enregistrement (la création d’une mémoire), et sur la télévision, médium qui les a d’abord diffusées. Conjointement à l’analyse de ces images est exposée la démarche de leur réemploi qui a mené à la réalisation d’un essai filmique. Le réemploi s’est notamment effectué en altérant des archives avec des magnétoscopes, fruits de la technologie de l’époque, qui avaient permis d’enregistrer les images télévisées. Avec ce geste de réemploi sont apparues des perspectives esthétiques qui permettent de voir la catastrophe autrement. D’autre part, ce projet a conduit l’auteur, muni d’une caméra VHS, à aller sur les lieux de l’événement, filmer les pylônes reconstruits, mais aussi au-delà, à la Baie James. Ce travail de recherche-création procède d’une méthode non systématique mais qui suit des chemins ouverts par les archives, par les technologies rencontrées ou par les images créées. Il envisage la question fondamentale que posent les catastrophes naturelles : celle du rapport qu’entretient l’homme avec la nature.From archives released on YouTube, this thesis aims to explore the natural disaster of Ice Storm
of 1998. The videos offer an opportunity to reflect on the aesthetic images of journalistic
information on natural disasters, but also on the VHS medium that allowed their first recording
(the creation of a memory), as well as on television, the medium that first distributed them.
Alongside the analysis of these images, this thesis presents the process for reusing them, which
led to the production of a film essay. Archives were altered thanks to video recorders, the
technological advancement of the time, which allowed the recording of televised images. With
reuse, came aesthetic perspectives that allow us to see the disaster differently. On the other
hand, this project led the author, equipped with a VHS camera, to go to the scene of the event,
to film the reconstructed pylons, but also to go beyond, to James Bay. This research-creation
work was developed through a non-systematic method, rather following the paths opened up
by the archives, technologies encountered or images created. It considers the fundamental
question posed by natural disasters : that of the relationship between man and nature
Interfaces rigides des modèles sur réseau (une application de la positivité par réflexion)
No full textNous étudions les interfaces de quatre modèles de spins sur le réseau Zd, d>= 3 : le modèle d Ising à basse température, le modèle de Potts à la température critique, un modèle à symétrie continue et son approximation d horloge ; les interfaces de ces deux derniers modèles n ont jamais été étudiées auparavant. Pour chacun de ces modèles, nous imposons des conditions au bord spécifiques qui assurent l existence d une interface ; les mesures de Gibbs associées à de telles conditions au bord satisfont alors de puissantes inégalités de corrélation, dites de l échiquier. Ces inégalités nous permettent de montrer que les interfaces conside rées sont rigides, au sens où ce sont des hyperplans légèrement déformés par des aspérités locales. Cette méthode est une version restreinte de la méthode de positivité par réflexion, l une des directions de réflexion étant prohibée par les conditions au bord choisies. Pour Ising et Potts, notre méthode simplifie considérablement les démonstrations historiques respectivement dues à Dobrushin et Messager et al., puisque ni la théorie de Pirogov-Sina ı, ni les développements en amas ne sont nécessaires à son application. Par ailleurs, la théorie-PS n est directement envisageable ni pour le modèle continu ni pour son approximation car leurs états fondamentaux sont infiniment dégénérés ; notre méthode est donc une réelle alternative à ces techniques.We study interfaces for four spin models on the lattice Zd, d >= 3: the Ising model at low temperature, the Potts model at critical point, a continuous symmetry model and its associated clock approximation. Interfaces of the last two models were not previously dealt with. For each model, we use specific boundary conditions that force the existence of an interface; related Gibbs measures then satisfy the so-called chessboard estimates, which are powerful correlation inequalities. These estimates are a simple way of showing that such interfaces are rigid, in the sense that they deviate only locally from a perfect hyperplane. This method is a restricted version of the so-called reflection positivity method, since reflections in certain directions are forbidden by the chosen boundary conditions. In the case of Ising and Potts models, our method drastically simplifies historical proofs respectively devised by Dobrushin and Messager et al., since its requires neither Pirogov-Sina ı theory nor cluster expansions. Besides, PS-theory is not directly available for the continuous model and its clock approximation, their ground states being infinitely degenerated; our method is thus a true alternative to such techniques.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF
Influence of growth conditions on the structural, optical and electrical quality of MBE grown InAlAs/InGaAs metamorphic HEMTs on GaAs
No full textInAlAs/InGaAs metamorphic HEMTs on GaAs have demonstrated low noise figures and high output powers with obvious advantages over structures grown on InP substrates. Indeed, from a processing viewpoint, the GaAs substrate is less brittle, less expensive, available in size up to 6 inches in diameter and then it is preferred for the production of high performance monolithic integrated circuits. Furthermore, the metamorphic scheme allows one to arbitrary choose the indium content in the InAlAs/InGaAs layers, which is a supplementary degree of freedom for the optimization of the active layers. Various buffer layers have been developed to accommodate the lattice mismatch between the active layers and the substrate. Production tools allows the growth of ternary as well as quaternary graded buffer layers; although the growth of a ternary alloy is more simple, it still requires the optimization of growth parameters like temperatures and arsenic fluxes. The layers presented here are based on thick InAlAs with a graded indium content from 1%-10% to 49% and terminated with an inverse step to obtain a highly relaxed In/sub 0.42/Al/sub 0.58/As/In/sub 0.43/Ga/sub 0.57/As structure. In the present work, the quality of the metamorphic HEMT structures is investigated by varying the growth parameters for the graded buffer layer as well as for the active layers. The structural quality is studied with high resolution X-ray diffraction, transmission electron microscopy (TEM) and atomic force microscopy, while the optical quality and the electrical quality of the HEMTs are studied with photoluminescence and Hall effect measurements respectively
Differential response of skeletal muscles to mTORC1 signaling during atrophy and hypertrophy
No full textBACKGROUND: Skeletal muscle mass is determined by the balance between protein synthesis and degradation. Mammalian target of rapamycin complex 1 (mTORC1) is a master regulator of protein translation and has been implicated in the control of muscle mass. Inactivation of mTORC1 by skeletal muscle-specific deletion of its obligatory component raptor results in smaller muscles and a lethal dystrophy. Moreover, raptor-deficient muscles are less oxidative through changes in the expression PGC-1alpha, a critical determinant of mitochondrial biogenesis. These results suggest that activation of mTORC1 might be beneficial to skeletal muscle by providing resistance to muscle atrophy and increasing oxidative function. Here, we tested this hypothesis by deletion of the mTORC1 inhibitor tuberous sclerosis complex (TSC) in muscle fibers. METHOD: Skeletal muscles of mice with an acute or a permanent deletion of raptor or TSC1 were examined using histological, biochemical and molecular biological methods. Response of the muscles to changes in mechanical load and nerve input was investigated by challenging the mice by denervation or ablation of synergistic muscles. RESULTS: Genetic deletion or knockdown of raptor, causing inactivation of mTORC1, was sufficient to prevent muscle growth and enhance muscle atrophy. Conversely, short-term activation of mTORC1 by knockdown of TSC induced muscle fiber hypertrophy and atrophy-resistance upon denervation, in both fast tibialis anterior (TA) and slow soleus muscles. Surprisingly, however, sustained activation of mTORC1 by genetic deletion of Tsc1 caused muscle atrophy in all but soleus muscles. In contrast, oxidative capacity was increased in all muscles examined. Consistently, TSC1-deficient soleus muscle was atrophy-resistant whereas TA underwent normal atrophy upon denervation. Moreover, upon overloading, plantaris muscle did not display enhanced hypertrophy compared to controls. Biochemical analysis indicated that the atrophy respo of muscles was based on the suppressed phosphorylation of PKB/Akt via feedback inhibition by mTORC1 and subsequent increased expression of the E3 ubiquitin ligases MuRF1 and atrogin-1/MAFbx. In contrast, expression of both E3 ligases was not increased in soleus muscle suggesting the presence of compensatory mechanisms in this muscle. CONCLUSIONS: Our study shows that the mTORC1- and the PKB/Akt-FoxO pathways are tightly interconnected and differentially regulated depending on the muscle type. These results indicate that long-term activation of the mTORC1 signaling axis is not a therapeutic option to promote muscle growth because of its strong feedback induction of the E3 ubiquitin ligases involved in protein degradation
