Measurement of the charge asymmetry in top quark pair production in pp collisions at s=7\sqrt s = 7 TeV using the ATLAS detector

We present a measurement of the charge asymmetry in top-antitop production using data corresponding to an integrated luminosity of $0.70 fb^{-1}$ of proton-proton collisions at $\sqrt s = 7$ TeV collected by the ATLAS detector. The top pair events decaying semileptonically (lepton+jets channel) to either an electron or muon, missing transverse energy and at least four jets are selected. The reconstruction of the $t\bar{t}$ events was performed using a kinematic likelihood approach. The difference of absolute values of top and antitop rapidities is used to define the charge asymmetry: $A_{C} = (N(|\Delta Y|>0) - N(|\Delta Y|0) + N(|\Delta Y|<0))$. To allow comparisons with theory calculations, a Bayesian unfolding technique is applied to correct the measured $|\Delta Y|$ distributions for acceptance and detector effects. The top charge asymmetry in both channels (e and mu) after correction is measured to be: $A_{C} = -0.009 \pm 0.023 (stat) \pm 0.032 (syst)$ (e+jets channel) and $A_{C} = -0.028 \pm 0.019 (stat) \pm 0.022 (syst)$ ($\mu$+jets channel) giving a combined result of : $A_{C} = -0.024 \pm 0.016 (stat) \pm 0.023 (syst)$. These results are compatible with the Standard Model predictions of $A_{C}=0.006$.Comment: Presented at the 2011 Hadron Collider Physics symposium (HCP-2011), Paris, France, November 14-18 2011, 3 pages, 4 figure

Context-Aware Adaptive System For M- Learning Personalization

International audienceContext-aware mobile learning is becoming important because of the dynamic and continually changing learning settings in learner's mobile environment, giving rise to many different learning contexts that are difficult to apprehend. To provide personalization of learning content, we aim to develop a recommender system based on semantic modeling of learning contents and learning context. This modeling is complemented by a behavioral part made up of rules and metaheuristics used to optimize the combination of pieces of learning contents according to learner's context. All these elements form a new approach to mobile learning

Comparative Study of the Mobile Learning Architectures

International audienceWith the emergence of mobile devices (Smart Phone, PDA, UMPC, game consoles, etc.), learning is changing from electronic learning (e-Learning) to mobile learning (m-learning). In fact, due to the mobility feature, it seems that the m-learning have to be adapted with the change within the context. Several researches addressed this issue and implemented a mobile learning environment to prove its usefulness and feasibility in various domains. In this article, we conduct a comparative study between a list of mobile learning architectures and methods that are presented in the literature. The performance of these architectures is evaluated based on several criteria, such as the adaptation management, which is an important parameter for the management and customization of the learning resources for the learners, as well as the environment, which is a core part of mobile learning systems

Algorithmes heuristiques et exacts pour le problème de l’ensemble dominant connexe minimum

Dans ce mémoire, nous abordons le problème de l’ensemble dominant connexe de cardinalité minimale. Nous nous penchons, en particulier, sur le développement de méthodes pour sa résolution basées sur la programmation par contraintes et la programmation en nombres entiers. Nous présentons, en l’occurrence, une heuristique et quelques méthodes exactes pouvant être utilisées comme heuristiques si on limite leur temps d’exécution. Nous décrivons notamment un algorithme basé sur l’approche de décomposition de Benders, un autre combinant cette dernière avec une stratégie d’investigation itérative, une variante de celle-ci utilisant la programmation par contraintes, et enfin une méthode utilisant uniquement la programmation par contraintes. Des résultats expérimentaux montrent que ces méthodes sont efficaces puisqu’elles améliorent les méthodes connues dans la littérature. En particulier, la méthode de décomposition de Benders avec une stratégie d’investigation itérative fournit les résultats les plus performants.In this work, we address the minimum connected dominating set problem. We focus, in particular, on the development of solution methods based on constraint programming and integer programming, including one heuristic and some exact methods that can be used as heuristics if we limit their running time. These are based on Benders decomposition and exploit a stand-alone and an iterative probing strategy. In particular, we develop a method based on the stand-alone Benders decomposition, another combining this one with an iterative probing strategy, a variant of the latter using constraint programming, and finally, a method using only constraint programming. Experimental results show that these methods are effecient, since they perform better than those known in the literature. In particular, iterative probing Benders decomposition provides the best results overall

Production of Neutral Pions in Pb+Au collisions at 158 AGeV/c

Direkte Photonen sind ein besonders gute Probe zum Nachweis eines Quark-Gluon-Plasmas in ultrarelativistischen Kollisionen von Schwerionen. Sie können experimentell nach der Messung des erheblichen Untergrundes aus Zerfällen von neutralen Pionen und Eta-Mesonen extrahiert werden. Die vorliegende Arbeit stellt die Erzeugung von neutralen Pionen vor, die innerhalb des CERES-Experimentes bei der topSPS-Energie von 158 AGeV/c Pb-Au-Kollisionen gemessen wurden. Die Analyse basiert auf der Datennahme des Jahres 2000. Das CERES-Experiment kann Photonen, die kurz vor der TPC konvertieren, durch die Messung von e+e-Paaren nachweisen. Der in dieser Arbeit verwendete Hauptkonverter ist der RICH2-Spiegel. Die hier vorgestellte Rekonstruktionsmethode beschreibt detailliert die Auswahl der e+e- Spuren, wobei ausschliesslich TPC-Informationen zur Rekonstruktion konvertierter Photonen benutzt wurden. Eine Sekundär-Vertex-Technik wurde entwickelt und zur Auswahl von konvertierten Photonen im Bereich des RICH2-Spiegels verwendet. Zur Extraktion der neutralen Pionen ist eine sorgfältige Studie des kombinatorischen Untergrundes erforderlich, welcher mittels Mixed-Event-Technik bestimmt wurde. Die Verteilung der invarianten Massen von Photonpaaren zeigt den Peak bei der Pion-Masse sehr deutlich. Der Vergleich des hier ermittelten transversalen Spektrums für neutrale Pionen mit phänomenologischen Modellen und anderen Experimenten verifizieren diese Analysemethode

Heavy Metals Assessment in the Medjerda River Basin (Northeastern Algeria): A Preliminary Water Analysis and Toad Skin Biopsy

AbstractOur study attempted to monitor the quality of water in Medjarda basin (Northeastern Algeria) and to provide baseline information of heavy metals in the water as well as in a potential amphibian biosentinel, the spiny toad, Bufo spinosus. We measured pH, temperature, dissolved oxygen and biological oxygen demand of water and levels of heavy metals in toad skin using an atomic absorption flame spectrophotometer. Lead (Pb) concentration in water and in toad skin at all sites exceeded respectively 60 and 96 times the standard reference values. The heavy metal concentrations, in descending order, in water and in male toad skin were as follows: Pb > Fe > Cu > Zn and Fe > Pb > Zn > Cu respectively. This study highlights the ecological status of the surrounding areas upstream of the Medjarda basin as being a point source of heavy metal pollution. It is further stated that a non-invasive skin removal is an ethically sound technique to evaluate heavy metal accumulation in aquatic animals like toad, without euthanizing the specimens and making any loss to biodiversity of the species