National Technical University of Athens

About: National Technical University of Athens is a education organization based out in Athens, Attiki, Greece. It is known for research contribution in the topics: Large Hadron Collider & Nonlinear system. The organization has 13445 authors who have published 31259 publications receiving 723504 citations. The organization is also known as: Athens Polytechnic & NTUA.

Interference-Based Topology Control Algorithm for Delay-Constrained Mobile Ad Hoc Networks

Abstract: As the foundation of routing, topology control should minimize the interference among nodes, and increase the network capacity. With the development of mobile ad hoc networks (MANETs), there is a growing requirement of quality of service (QoS) in terms of delay. In order to meet the delay requirement, it is important to consider topology control in delay constrained environment, which is contradictory to the objective of minimizing interference. In this paper, we focus on the delay-constrained topology control problem, and take into account delay and interference jointly. We propose a cross-layer distributed algorithm called interference-based topology control algorithm for delay-constrained (ITCD) MANETs with considering both the interference constraint and the delay constraint, which is different from the previous work. The transmission delay, contention delay and the queuing delay are taken into account in the proposed algorithm. Moreover, the impact of node mobility on the interference-based topology control algorithm is investigated and the unstable links are removed from the topology. The simulation results show that ITCD can reduce the delay and improve the performance effectively in delay-constrained mobile ad hoc networks.

Measurement of Higgs boson production in the diphoton decay channel in pp collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector

Abstract: A measurement of the production processes of the recently discovered Higgs boson is performed in the two-photon final state using 4.5 fb(-1) of proton-proton collisions data at root s = 7 TeV and 20.3 fb(-1) at root s = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. The number of observed Higgs boson decays to diphotons divided by the corresponding Standard Model prediction, called the signal strength, is found to be mu = 1.17 +/- 0.27 at the value of the Higgs boson mass measured by ATLAS, m(H) = 125.4 GeV. The analysis is optimized to measure the signal strengths for individual Higgs boson production processes at this value of m(H). They are found to be mu(ggF) = 1.32 +/- 0.38, mu(VBF) = 0.8 +/- 0.7, mu(WH) = 1.0 +/- 1.6, mu(ZH) = 0.1(-0.1)(+3.7), and mu t (t) over barH = 1.6(-1.8)(+2.7), for Higgs boson production through gluon fusion, vector-boson fusion, and in association with a W or Z boson or a top-quark pair, respectively. Compared with the previously published ATLAS analysis, the results reported here also benefit from a new energy calibration procedure for photons and the subsequent reduction of the systematic uncertainty on the diphoton mass resolution. No significant deviations from the predictions of the Standard Model are found.

To Aggregate or Not to aggregate: Selective Match Kernels for Image Search

Abstract: This paper considers a family of metrics to compare images based on their local descriptors. It encompasses the VLAD descriptor and matching techniques such as Hamming Embedding. Making the bridge between these approaches leads us to propose a match kernel that takes the best of existing techniques by combining an aggregation procedure with a selective match kernel. Finally, the representation underpinning this kernel is approximated, providing a large scale image search both precise and scalable, as shown by our experiments on several benchmarks.

Statistics of extremes and estimation of extreme rainfall: I. Theoretical investigation

Abstract: La distribution de Gumbel a longtemps ete le modele regnant pour la quantification du risque associe aux precipitations extremes. Plusieurs arguments comprenant a la fois un raisonnement theorique et des faits empiriques sont censes soutenir la pertinence de la distribution de Gumbel. Ces arguments sont examines exhaustivement dans ce travail et sont mis en question. Specifiquement, des analyses theoriques montrent que la distribution de Gumbel est peu susceptible de s'appliquer aux valeurs extremes de variables hydrologiques et que son application peut conduire a une mauvaise estimation du risque par une serieuse sous-estimation des plus grandes valeurs extremes de precipitations. En outre, il est montre que les series hydrologiques de longueur typique (quelques decennies) peuvent montrer une image deformee de la distribution reelle, ce qui suggere que la distribution de Gumbel est le modele approprie pour les precipitations extremes alors qu'elle ne l'est pas. En outre, on montre que la distribution de valeurs extremes du type II (EV2) est une alternative plus coherente. Dans la deuxieme partie de cette etude, une recherche empirique etendue est effectuee, en se basant sur l'analyse theorique, avec une collection de 169 series de precipitations, parmi les plus longues de celles qui sont disponibles dans le monde entier, comportant chacune 100-154 ans de donnees. Ceci permet de verifier la non-pertinence de la distribution de Gumbel et la pertinence de la distribution EV2 pour les precipitations extremes.