Bits through queues with feedback

In their $1996$ paper Anantharam and Verd\'u showed that feedback does not increase the capacity of a queue when the service time is exponentially distributed. Whether this conclusion holds for general service times has remained an open question which this paper addresses. Two main results are established for both the discrete-time and the continuous-time models. First, a sufficient condition on the service distribution for feedback to increase capacity under FIFO service policy. Underlying this condition is a notion of weak feedback wherein instead of the queue departure times the transmitter is informed about the instants when packets start to be served. Second, a condition in terms of output entropy rate under which feedback does not increase capacity. This condition is general in that it depends on the output entropy rate of the queue but explicitly depends neither on the queue policy nor on the service time distribution. This condition is satisfied, for instance, by queues with LCFS service policies and bounded service times

Fonctions double Gamma liées aux systèmes de racines

Cette thèse, composée de 11 chapitres, répartis en trois parties, aborde les fonctions double Gamma liées aux systèmes de racines. La première partie regroupe les théorèmes classiques sur la fonction G d'Euler ; y sont ajoutés des résultats spécifiquement développés pour ce travail, qui seront utilisés dans les deux autres parties. Sont également étudiées sur un modèle similaire (relation fonctionnelle, formules intégrales, valeurs limites) la fonction double Gamma et la fonction Gamma q- analogue. La deuxième partie expose les variantes de Double Gamma en physique : sont ainsi étudiées, la fonction Gammab, double-sinus Sb, la fonction gamma des frères Zamolodchikov, la fonction de Lukyanov-Zamolodchikov et les fonctions de Fateev liées aux matrices de Cartan. Une partie de ces résultats, énoncés par les physiciens, est démontrée. La dernière partie s'intéresse aux formules de Fateev et donne une preuve par calcul, du théorème de Fateev pour les systèmes du type A,D,E et aussi B,C,F,G en n'utilisant que la formule classique du produit de Gamma. Le chapitre 9 donne un théorème de Fateev q-analogue pour A, B, C, D, G2. Le chapitre 10 permet d'exprimer certains vecteurs propres de matrices de Cartan en termes de produits de valeurs de la fonction G. Les cas affines et finis sont démontrés.This thesis, consisting of 11 chapters, is divided into three parts and addresses the double Gamma functions associated with root systems. The first part includes the classical theorems on the Euler G function ; added are results, specifically developed for this work, which will be used in the other two parts. According a similar pattern (functional equation, integral formulas, limiting values) the double Gamma function and the q-Gamma function are also studied. The second part describes the Double Gamma versions in physics : the Gammab function, double sine Sb function, the gamma function of the brothers Zamolodchikov, the Lukyanov-Zamolodchikov and Fateev functions related to Cartan matrices, are studied. A part of these results, expressed by the physicists, is demonstrated. The last part deals with Fateev formulas and gives proof of the Fateev theorem by direct calculation, for systems of type A, D, E, B, C, F, G, using only the classical formula of the product of Gamma. Chapter 9 gives a q-analogue theorem of the Fateev formula for the systems of type A, B, C, D, G2. Chapter 10 allows us to express some eigenvectors of the Cartan matrix in terms of products of values of the G function. Finite and affine cases are demonstrated

Comparaison de deux systèmes de rotation de postes dans le cadre de la prévention des troubles musculosquelettiques

La rotation est souvent perçue par les entreprises comme une des réponses à la prévention des troubles musculosquelettiques (TMS) car elle apporte une variabilité à la fois biomécanique et psychosociale dans les exigences des postes de travail. Deux systèmes de rotation de postes sont comparés dans le cadre d’une démarche de prévention des TMS du membre supérieur (MS). Pour ce faire, deux outils sont utilisés, l’un basé sur la cotation des efforts et des postures de l’épaule dominante et l’autre, sur l’évaluation subjective des difficultés dans l’exécution du travail (cadence, apprentissage et risque d’erreur). Il s’agit de réaliser un parallèle entre ces évaluations et les plaintes de TMS évoquées par les opérateurs. À l’issue de la mise en œuvre des deux outils, l’un des deux systèmes de rotation de postes se distingue par une contrainte posturale et un risque d’erreur importants. Il en découle un certain nombre de recommandations pour la rotation de postes dans un objectif de prévention des TMS.Rotation is often perceived by companies as one answer to preventing musculoskeletal disorders (MSD) because it offers both biomechanical and psychosocial variability in job requirementsTwo job rotation systems were compared in the context of an upper-limb MSD prevention process. Two methods were used, one assessing the efforts and postures of the dominant shoulder, and the other, the subjective evaluation of the difficulties in job performance (work pace, learning and risk of error). These evaluations and the MSD complaints expressed by the operators were compared. After these two methods were implemented, one of the two job rotation systems stood out due to a significant postural risk factor and a significant risk of error. The outcome of the project was some recommendations for job rotation in order to prevent MSD.La rotación suele percibirse como una de las respuestas a la prevención de los trastornos musculoesqueléticos (TMS) porque proporciona una variabilidad a la vez mecánica y psicosocial en las exigencias de los puestos de trabajo. Dos sistemas de rotación en el empleo se comparan en el contexto de un trámite de prevención de los TMS del miembro superior (MS). Para esto, se utilizan dos instrumentos : uno basado en la cotización de los esfuerzos y de las posturas de la espalda dominante y la otra sobre la evaluación subjetiva de las dificultades en la execución del trabajo (cadencia, aprendizaje y riesgo de error). Se trata de establecer un paralelo entre estas evaluaciones y las quejas de TMS reveladas por los operadores. Sobre la base de la realización de los dos instrumentos, uno de ambos sistemas de rotación en el empleo se distingue por una coacción postural y un riesgo de error importantes. Se derivan de esto ciertas recomendaciones para la rotación en empleos en un objetivo de prevención de TMS

Retinal Vessel Phenotype In Patients With Primary Open-Angle Glaucoma

International audiencePURPOSE: To characterize the phenotype of retinal vessels using central retinal artery equivalent (CRAE), central retinal vein equivalent (CRVE), tortuosity and fractal dimension (FD) in primary open-angle glaucoma (POAG) subjects. METHODS: This prospective case-control multicentre study included 61 POAG subjects and 61 controls matched for age, systemic hypertension and body mass index. Fundus images of the right eye were acquired using a non-mydriatic camera. Central retinal artery equivalent (CRAE), CRVE, arteriole-to-venule ratio, FD and tortuosity of the vascular network were measured using VAMPIRE software (Vessel Assessment and Measurement Platform for Images of the Retina). Primary open-angle glaucoma (POAG) patients underwent 24.2 sita-standard visual field and peri-papillary optical coherence tomography (OCT) examinations. Data were expressed as median and interquartile range (75-25th percentiles). RESULTS: The control group was comparable to the POAG group for sex ratio, refraction and intraocular pressure. The mean CRAE and the mean CRVE were significantly lower in the POAG group than in the control group [150.5 (137.9; 157.1) mum versus 161.3 (154.0; 168.4) mum and 204.8 (190.1; 218.1) mum versus 233.5 (222.3; 246.9) mum, respectively; p < 0.001] and for fractal parameters as well. No significant difference was found for tortuosity between the two groups. There was a significant correlation between CRAE and retinal nerve fibre layer (RNFL) thickness (r = 0.27; p = 0.03). VAMPIRE parameters were not correlated with visual field indices. CONCLUSION: Primary open-angle glaucoma (POAG) was associated with a narrowing of arterial and venous retinal vessels, a higher arteriole-to-venule ratio and lower values of FD. The relationship between CRAE and RNFL thickness needs further investigation

Fractal dimension and degree of order in sequential deposition of mixture

We present a number models describing the sequential deposition of a mixture of particles whose size distribution is determined by the power-law $p(x) \sim \alpha x^{\alpha-1}$, $x\leq l$ . We explicitly obtain the scaling function in the case of random sequential adsorption (RSA) and show that the pattern created in the long time limit becomes scale invariant. This pattern can be described by an unique exponent, the fractal dimension. In addition, we introduce an external tuning parameter beta to describe the correlated sequential deposition of a mixture of particles where the degree of correlation is determined by beta, while beta=0 corresponds to random sequential deposition of mixture. We show that the fractal dimension of the resulting pattern increases as beta increases and reaches a constant non-zero value in the limit $\beta \to \infty$ when the pattern becomes perfectly ordered or non-random fractals.Comment: 16 pages Latex, Submitted to Phys. Rev.