Jurnal Edukasi
Not a member yet
4879 research outputs found
Sort by
Measurement of top quark-antiquark pair production in association with a W or Z boson in pp collisions at sqrt(s) = 8 TeV
No full textSubmitted to Eur. Phys. J. C ; see paper for full list of authorsA measurement of the cross section for the production of top quark-antiquark pairs (ttbar) in association with a vector boson V (W or Z) in proton-proton collisions at sqrt(s) = 8 TeV is presented. The results are based on a dataset corresponding to an integrated luminosity of 19.5 inverse femtobarns recorded with the CMS detector at the LHC. The measurement is performed in three leptonic (e and mu) channels: a same-sign dilepton analysis targeting ttbar W events, and trilepton and four-lepton analyses designed for ttbar Z events. In the same-sign dilepton channel, the ttbar W cross section is measured as sigma[ttbar W] = 170 +90/-80 (stat) +/- 70 (syst) fb, corresponding to a significance of 1.6 standard deviations over the background-only hypothesis. Combining the trilepton and four-lepton channels, a direct measurement of the ttbar Z cross section, sigma[ttbar Z] = 200 +80/-70 (stat) +40/-30 (syst) fb, is obtained with a significance of 3.2 standard deviations. The measured cross sections are compatible with standard model predictions within their experimental uncertainties. The inclusive ttbar V process is observed with a significance of 3.7 standard deviations from the combination of all three leptonic channels
Multiple satellites in materials with complex plasmon spectra: From graphite to graphene
No full textInternational audienceThe photoemission spectrum of graphite is still debated. To help resolve this issue, we present photoemission measurements at high photon energy and analyze the results using a Green's function approach that takes into account the full complexity of the loss spectrum. Our measured data show multiple satellite replicas. We demonstrate that these satellites are of intrinsic origin, enhanced by extrinsic losses. The dominating satellite is due to the π+σ plasmon of graphite, whereas the π plasmon creates a tail on the high-binding energy side of the quasiparticle peak. The interplay between the two plasmons leads to energy shifts, broadening, and additional peaks in the satellite spectrum. We also predict the spectral changes in the transition from graphite towards graphene
Peeking Through the BitTorrent Seedbox Hosting Ecosystem
No full textInternational audienceIn this paper, we propose a lightweight method for detecting and classifying BitTorrent content providers with a minimal amount of resources. While heavy methodologies are typically used (which require long term observation and data exchange with peers of the swarm and/or a semantic analysis of torrent websites), we instead argue that such complexity can be avoided by analyzing the correlations between peers and torrents. We apply our methodology to study over 50K torrents injected in ThePirateBay during one month, collecting more than 400K IPs addresses. Shortly, we find that exploiting the correlations not only enhances the classification accuracy keeping the technique lightweight (our methodology reliably identifies about 150 seedboxes), but also uncovers seeding behaviors that were not previously noticed (e.g., as multi-port and multi-host seeding). Finally, we correlate the popularity of seedbox hosting in our dataset to criteria (e.g., cost, storage space, Web popularity) that can bias the selection process of BitTorrent content providers
Unirational threefolds with no universal codimension cycle
No full textFurther typos corrected. Introduction reorganizedWe prove that the general quartic double solid with nodes does not admit a Chow theoretic decomposition of the diagonal, or equivalently has a nontrivial universal group. The same holds if we replace in this statement "Chow theoretic" by "cohomological". In particular, it is not stably rational. We also prove that the general quartic double solid with seven nodes does not admit a universal codimension cycle parameterized by its intermediate Jacobian, and even does not admit a parametrization with rationally connected fibres of its Jacobian by a family of -cycles. This implies that its third unramified cohomology group is not universally trivial
Bloch's conjecture for Catanese and Barlow surfaces
No full textTo appear in Journal of Differential GeometryInternational audienceCatanese surfaces are regular surfaces of general type with . They specialize to double covers of Barlow surfaces. We prove that the group of a Catanese surface is equal to , which implies the same result for the Barlow surfaces. We will also give a conditional application (more precisely, assuming the variational Hodge conjecture) of the same method to the Chow motive of low degree surfaces
Une théorie de la moyenne pour les équations aux dérivées partielles non linéaires
No full textThis Ph.D thesis focuses on studying the long-time behavior of solutions for non-linear PDEs that are close to a linear or an integrable Hamiltonian PDE. An averaging theory for nonlinear PDEs is presented. The model equations are the perturbed Korteweg-de Vries (KdV) equations and some weakly nonlinear partial differential equations.Cette thèse se consacre aux études des comportements de longtemps des solutions pour les EDPs nonlinéaires qui sont proches d'une EDP linéaire ou intégrable hamiltonienne. Une théorie de la moyenne pour les EDPs nonlinéaires est presenté. Les modèles d'équations sont les équations Korteweg-de Vries (KdV) perturbées et quelques équations aux dérivées partielles nonlinéaires faiblement
Spectroscopie résolue en temps de la femtoseconde à la milliseconde
No full textThe aim of the work was the development of a time-resolved pump-probe measurement system allowing temporal scanning from femtosecond to millisecond time scale. An original method for asynchronous optical sampling, named AD-ASOPS, was developed, patented, and is now undergoing the industrialization phase. The method can be applied to couples of lasers oscillating at arbitrary repetition rates, which is a novelty and opens up many experimental possibilities. Two specific set-ups were realized in the case of laser oscillators (MHz AD-ASOPS) or in the case of amplified laser systems (kHz AD-ASOPS). A feasibility study confirmed many application possibilities. Different tests were performed for a complete characterization and demonstrated a sub-picosecond time resolution of about 400 fs for temporal sampling windows only limited by the period of the pump laser.The implementation flexibility related to AD-ASOPS allowed a pump-probe experiment on biological samples (reaction centre of Rhodobacter Sphaeroides), by using a conventional Ti:Sapphire oscillator at 74.5 MHz as probe and a CPO oscillator at 5.1 MHz as pump. The multi-scale dynamics for returning to the fundamental state, from picoseconds to about fifty nanoseconds, could be recorded into only a few minutes of acquisition time with one test bench. The results are in agreement with the literature. Finally, a demonstration experiment of the kHz AD-ASOPS version was performed with two amplified laser systems, by comparison with Fourier transform spectral interferometry. A sub-picosecond time resolution was confirmed over 1 millisecond temporal window.L'objet de ce travail a été le développement d'un système de mesure pompe-sonde résolue en temps permettant d'atteindre des fenêtres temporelles allant de la centaine de femtosecondes à la milliseconde. Une méthode de balayage optique asynchrone originale, appelée AD-ASOPS, a été développée et a donné lieu à un dépôt de brevet avec valorisation industrielle. La méthode peut être appliquée avec deux lasers de fréquences de répétition arbitraires, ce qui est une nouveauté et ouvre de nombreuses possibilités expérimentales. Une mise en œuvre spécifique a été réalisée selon que les systèmes lasers utilisés soient deux oscillateurs (AD-ASOPS MHz) ou bien deux lasers amplifiés (AD-ASOPS kHz). Une étude de faisabilité a été faite pour confirmer les larges possibilités d’applications. Une caractérisation complète a été menée avec plusieurs tests qui ont démontré une résolution sub-picoseconde d’environ 400 fs pour des balayages temporels réalisés sur des fenêtres temporelles uniquement limitées par la période du laser pompe. Grâce à la flexibilité d’utilisation introduite par l’AD-ASOPS une expérience pompe-sonde sur échantillon biologique (centre réactionnel de Rhodobacter Sphaeroides) a été réalisée en utilisant comme sonde un oscillateur Ti:Saphire conventionnel à 74.5 MHz et comme pompe un oscillateur CPO à 5.1 MHz. La dynamique de retour à l’état fondamental, se développant sur plusieurs ordres de grandeur, de la picoseconde à la cinquantaine de nanosecondes, a pu être enregistrée en seulement quelques minutes d’acquisitions sur un banc de test unique. Les résultats obtenus sont en accord avec les résultats de la littérature.Enfin une expérience de démonstration de la variante AD-ASOPS kHz a été effectuée sur deux systèmes laser amplifiés, par comparaison avec la méthode d’interférométrie spectrale par transformée de Fourier. Une résolution sub-picoseconde a été confirmée sur une fenêtre de balayage d’une milliseconde
Filamentation d'impulsions laser ultra-courtes dans l'air et dans l'eau : étude des processus de transfert d'énergie
No full textWith the development of ultrashort lasers, pulses with peak power in the gigawatt level are easily obtained. In this intensity range, the propagation is no longer linear. Due to the Kerr effect, the beam self-focuses and tends to collapse until the intensity is high enough to ionize the medium, an effect that defocuses the beam. A dynamic competition takes place between Kerr effect, ionization and diffraction, resulting in a spectacular reshaping of the beam in an intense core propagating over many Rayleigh lengths. During this phenomenon, called laser filamentation, a thin and weakly ionized plasma channel is left in the trail of the pulse. This propagation mode strongly affects the pulse and the medium where it happens. Through several collaborations, I focus this work on experimental studies of the impact of the filamentary propagation in gases and liquids. I thus mapped the spatio-temporal distortions of the pulse during its propagation in water and identified their signatures in the spatial, spectral and energetic domain. I then characterized the energy losses in water and the shock wave generated by the plasma relaxation in different power ranges and focalisation geometries, for the generation of acoustic waves by femtosecond laser pulses. On the other hand, I studied the plasma generated at the intersection of two crossing filaments in molecular and atomic gases. I demonstrated that its spatial properties and transient behaviour can spatially and temporally filter a laser pulse, and could potentially offer a new alternative to generate femtosecond laser pulses with a high contrast and good quality beam profile. Finally I characterized the compression of high energy femtosecond pulses with a planar hollow waveguide and demonstrated that the time compressed pulses can be used to generate high order harmonics, and in general for high field physics.Le développement des chaines laser femtoseconde amplifiées a permis de mettre à la disposition des chercheurs des impulsions dont la puissance crête excède quelques Gigawatts. Dans ce régime de puissance, la propagation du faisceau laser est fortement non-linéaire. L'effet Kerr auto-focalise le faisceau qui s'effondre sur lui-même jusqu'à ce que l'intensité soit suffisante pour générer un plasma à effet défocalisant. La compétition dynamique entre l'effet Kerr, l'ionisation et la diffraction permet de conserver une intensité élevée dans le cœur du faisceau sur une grande distance. Dans ce processus, dit de filamentation, l'impulsion lumineuse laisse dans son sillage une mince colonne de plasma faiblement ionisé. Le phénomène de filamentation peut affecter fortement l'impulsion laser et le milieu dans lequel elle se propage. Par le biais de multiples collaborations, je me suis attachée au cours de cette thèse à étudier expérimentalement plusieurs effets liés à la propagation non-linéaire dans les gaz et dans les liquides. Ainsi j'ai réalisé une cartographie des déformations spatio-temporelles de l'impulsion au cours de sa propagation dans l'eau et mis en évidence leurs signatures dans le domaine spatial, spectral, et énergétique. J'ai ensuite caractérisé le dépôt d'énergie dans l'eau liquide et l'onde de choc induite par la relaxation du plasma dans différents régimes de puissance et de focalisation, dans le but d'analyser la génération d'ondes acoustiques par des impulsions laser femtoseconde. Par ailleurs, j'ai étudié le plasma formé à l'intersection de deux filaments dans différents gaz moléculaires et atomiques. J'ai mis en évidence que ses propriétés spatiales et transitoires permettent un filtrage spatio-temporel d'une impulsion incidente, ce qui pourrait constituer une nouvelle alternative aux techniques de filtrage d'impulsions femtoseconde. Enfin, j'ai caractérisé la compression d'impulsions énergétiques dans un guide plan creux et démontré que les impulsions comprimées temporellement pouvaient être utilisées pour la génération d'harmoniques d'ordres élevés, et plus généralement pour la physique de haute intensité
A Behavioral Congruence for Concurrent Constraint Programming with Non-deterministic Choice
No full textInternational audienceConcurrent constraint programming (CCP) is a well-established model of concurrency for reasoning about systems of multiple agents that interact with each other by posting and querying partial information on a shared space. (Weak) bisimilarity is one of the most representative notions of behavioral equivalence for models of concurrency. A notion of weak bisimilarity, called weak saturated bisimilarity (WSB), was recently proposed for CCP. This equivalence improves on previous bisimilarity notions for CCP that were too discriminating and it is a congruence for the choice-free fragment of CCP. In this paper, however, we show that WSB is not a congruence for CCP with nondeterministic choice. We then introduce a new notion of bisimilarity, called weak full bisimilarity (FB), and show that it is a congruence for the full language of ccp. We also show the adequacy of FB by establishing that it coincides with the congruence induced by closing WSB under all contexts. The advantage of the new definition is that, unlike the congruence induced by WSB, it does not require quantifying over infinitely many contexts