1,725 research outputs found
Game theory for model et simulate of emergence and dynamics of systems of cities
No full textLa récurrence d’une structure hiérarchique dans les systèmes de villes à travers le monde, caractérisée par le fait que les villes sont d’autant plus nombreuses qu’elles sont petites, et plus précisément qu’il existe globalement une relation entre la taille des villes et leur rang (la taille de la ville de rang r est égale à la population de la plus grosse ville divisée par r) est un phénomène décrit depuis de nombreuses années. Cette régularité statistique, connue sous le nom de loi rang taille, ses variations locales et la recherche de ses explications ont largement été explorées par les géographes depuis plus d’un siècle. Assurément, les économies d’agglomération, qui favorisent la survenue de l’innovation, les modalités de sa diffusion dans la hiérarchie urbaine, elles-mêmes conditionnées par les réseaux de transport dont dépendent les interactions entre villes, jouent un rôle déterminant pour comprendre l’émergence et le maintien de systèmes de villes hiérarchisés.Pour autant, si une nécessaire théorie sur l’évolution des systèmes de villes, qui regroupent à présent plus de la moitié de la population mondiale, est déjà bien avancée, il n’en demeure pas moins qu’il reste impossible de considérer un système de peuplement au temps t et d’en prévoir en détail l’évolution à un horizon donné, en particulier l’émergence de nouvelles concentrations de population, car les systèmes de villes sont à la fois compliqués et complexes.Les gigantesques progrès de l’informatique ont permis, depuis une quarantaine d’années, de développer des modèles de simulation qui permettent de tester différentes hypothèses quant à l’évolution des systèmes de villes et ainsi mieux comprendre leur dynamique. C’est plus particulièrement le cas de la simulation Multi-Agents, mobilisée notamment par l’équipe P.A.R.I.S, qui a permis de grands progrès dans la compréhension de la dynamique des systèmes de villes en rendant possible le test d’hypothèses théoriques, parfois anciennes, concernant notamment la diffusion de l’innovation et ses impacts sur les systèmes de villes. Pour autant, ces modèles, très riches, présentent l’inconvénient de reposer sur de très nombreux paramètres et hypothèses, ce qui les rend difficiles à calibrer et rend leurs résultats parfois difficiles à interpréter. Par ailleurs, si ces modèles permettent d’analyser l’évolution d’un système de villes donné, l’émergence de nouvelles villes demeure assez peu abordée.Dans ce contexte, l’objectif de cette thèse est de contribuer, par la simulation Multi-Agents, à la recherche d’explications de l’émergence et du maintien de systèmes de villes hiérarchisés. Plutôt que de chercher à complexifier encore les modèles existants pour que leurs résultats correspondent le plus possible aux réalités empiriques, le parti pris de ce travail a été de poser une hypothèse centrale, « simple », sans dimension économique et qui s’oppose en cela aux approches les plus fréquentes, et d’en tester la validité. Cette hypothèse consiste à affirmer que la croissance allométrique des systèmes de villes est avant tout fonction de la façon dont s’effectuent les interactions entre villes à l’échelle individuelle. Plus précisément, il s’agit donc de voir dans un premier temps si, selon qu’un individu habitant une ville A choisi de déménager dans une ville B tirée au hasard, ou dont l’attractivité dépendra de l’historique en termes d’échange, de sa centralité et de son accessibilité, on parvient, ou pas, à générer des systèmes de villes hiérarchisés de type rang taille. Cela revient à vouloir confirmer que, bien avant des considérations économiques (profil économique des villes par exemple), ce sont avant tout les modalités de l’interaction spatiale qui président à l’évolution des systèmes de villes.Dans un deuxième temps, toujours en plaçant l’interaction spatiale entre les individus au cœur de notre travail, nous chercherons à mieux comprendre l’émergence des villes.The recurrence of a hierarchical structure in the systems of cities around the world, characterized by the fact that the cities are all the more numerous that they are small, and more precisely that it exist a relation between the size of the cities and their ranks (the size of a city of rank “r” is equal to the population of the biggest city divided by “r”) is a phenomenon which has been described for many years.This statistical regularity, known as the rank size law, its local variations and the research for its explanations, have been widely explored by geographers for more than a century. Certainly, the agglomeration economies, favorizing innovation, its broadcast in urban hierarchy, themselves conditioned by transport networks of which interactions between cities depend, play a crucial role to understand emerging and maintenance systems of hierarchized cities.However, if a necessary theory on the evolution of systems of cities, which regroup now more than half the world population, is already pretty well advanced, it is still impossible to consider a system of settlement at time “t” and to predict in detail the evolution, especially the emergence of new population concentration, because systems of cities are complex.The computer science’s gigantic progresses have been able, since about forty years, to develop simulation models, which can test different hypothesis regarding the evolution of the systems of cities and to better understand their dynamic. It is more especially the case of the Multi-Agent model, created by the P.A.R.I.S team, who allowed huge progresses in understanding the dynamic of systems of cities, allowing the theorical hypothesis test, some old, concerning in particular the innovation diffusion and its impacts on the city system. However, those models, very documented and well used, are presenting the disadvantage to be based on numerous parameters and hypothesis, which makes it difficult to calibrate and render their results sometimes difficult to interpret. Also, if these models allow us to analyze the evolution of a systems of cities, the emergence of new cities is not well studied.In this context, the goal of this thesis is to contribute, using the Multi-Agents simulation, to the research of explanations of the emergence and the maintenance of hierarchized systems of cities. Rather than looking to complexify more the existing models so that their results match the best possible to the empiric realities, it has been decided here to put down a central hypothesis, “simple”, without an economic dimension and which counteract with the most frequent approaches, and to test their validity. This hypothesis state that the allometric growth of the systems of cities is first a function of the way that the interactions between the cities happen at the individual scale. More precisely, it is necessary to look first if, depending if a person living in city A decide to move to the city B, draw at random, or of which the attractiveness’ will depend on its historical past in terms of trade, centrality, accessibility, can one succeed, or not, to generate systems of hierarchized cities type rank size. That is to tend to confirm that, way before economic considerations (economic profile of cities per example), it is before everything the spatial interaction modalities which preside on the evolution of systems of cities.Secondly, always placing the spatial interaction between the individuals at the heart of our work, we are looking to better understand the emergence of the cities
Author Correction: A portrait of the Higgs boson by the CMS experiment ten years after the discovery
No full textIn the version of this article initially published, CMS Collaboration author names, affiliations and acknowledgements were omitted and have now been included in the HTML and PDF versions of the articl
Searches for R-parity-violating supersymmetry in pp collisions at √s=8 TeV in final states with 0–4 leptons
No full textResults are presented from searches for R-parity-violating supersymmetry in events produced in pp collisions at √s=8 TeV at the LHC. Final states with 0, 1, 2, or multiple leptons are considered independently. The analysis is performed on data collected by the CMS experiment corresponding to an integrated luminosity of 19.5 fb−1. No excesses of events above the standard model expectations are observed, and 95% confidence level limits are set on supersymmetric particle masses and production cross sections. The results are interpreted in models featuring R-parity-violating decays of the lightest supersymmetric particle, which in the studied scenarios can be either the gluino, a bottom squark, or a neutralino. In a gluino pair production model with baryon number violation, gluinos with a mass less than 0.98 and 1.03 TeV are excluded, by analyses in a fully hadronic and one-lepton final state, respectively. An analysis in a dilepton final state is used to exclude bottom squarks with masses less than 307 GeV in a model considering bottom squark pair production. Multilepton final states are considered in the context of either strong or electroweak production of superpartners and are used to set limits on the masses of the lightest supersymmetric particles. These limits range from 300 to 900 GeV in models with leptonic and up to approximately 700 GeV in models with semileptonic R-parity-violating couplings
Search for R-parity violating decays of a top squark in proton–proton collisions at √s=8 TeV
No full textThe results of a search for a supersymmetric partner of the top quark (top squark), pair-produced in proton–proton collisions at s=8 TeV, are presented. The search, which focuses on R-parity violating, chargino-mediated decays of the top squark, is performed in final states with low missing transverse momentum, two oppositely charged electrons or muons, and at least five jets. The analysis uses a data sample corresponding to an integrated luminosity of 19.7 fb−1 collected with the CMS detector at the LHC in 2012. The data are found to be in agreement with the standard model expectation, and upper limits are placed on the top squark pair production cross section at 95% confidence level. Assuming a 100% branching fraction for the top squark decay chain, t ̃→tχ ̃1±,χ ̃1±→l±+jj, top squark masses less than 890 (1000) GeV for the electron (muon) channel are excluded for the first time in models with a single nonzero R-parity violating coupling λijk′ (i,j,k≤2), where i,j,k correspond to the three generations
Combined search for the quarks of a sequential fourth generation
No full textResults are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5 fb−1 recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685 GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25 GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about ±20 GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermion
Observation of a diffractive contribution to dijet production in proton-proton collisions at √s=7 TeV
No full textThe cross section for dijet production in proton-proton collisions at √s=7 TeV is presented as a function of ξ˜, a variable that approximates the fractional momentum loss of the scattered proton in single-diffractive events. The analysis is based on an integrated luminosity of 2.7 nb−1 collected with the CMS detector at the LHC at low instantaneous luminosities, and uses events with jet transverse momentum of at least 20 GeV. The dijet cross section results are compared to the predictions of diffractive and nondiffractive models. The low-ξ˜ data show a significant contribution from diffractive dijet production, observed for the first time at the LHC. The associated rapidity gap survival probability is estimated
Measurement of WZ and ZZ production in pp collisions at √s = 8 TeV in final states with b-tagged jets
No full textOpen Access This article is distributed under the terms of the Creative
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reproduction in any medium, provided the original author(s) and the
source are credited.
Funded by SCOAP3 / License Version CC BY 4.0.Measurements are reported of the WZ and ZZ production cross sections in proton-proton collisions at s √ =8 TeV in final states where one Z boson decays to b-tagged jets. The other gauge boson, either W or Z, is detected through its leptonic decay (either W→eν , μν or Z→e + e − , μ + μ − , or νν ¯ ). The results are based on data corresponding to an integrated luminosity of 18.9 fb −1 collected with the CMS detector at the Large Hadron Collider. The measured cross sections, σ(pp→WZ)=30.7±9.3(stat.)±7.1(syst.)±4.1(th.)±1.0(lum.)pb and σ(pp→ZZ)=6.5±1.7(stat.)±1.0(syst.)±0.9(th.)±0.2(lum.)pb , are consistent with next-to-leading order quantum chromodynamics calculationsBMWF and FWF (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil);
MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES and CS (Croatia); RPF (Cyprus); MoER, SF0690030s09 and ERDF (Estonia); Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF(Germany);GSRT(Greece);OTKAand NIH(Hungary);DAEand DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Republic of Korea); LAS (Lithuania);MOE and UM(Malaysia); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Dubna); MON, RosAtom, RAS and RFBR (Russia); MESTD (Serbia); SEIDI and CPAN (Spain); Swiss Funding Agencies (Switzerland);
NSC (Taipei); ThEPCenter, IPST, STAR and NSTDA(Thailand); TUBITAK and TAEK (Turkey); NASU and SFFR (Ukraine); STFC (United Kingdom); DOE and NSF (USA)
Search for supersymmetry in events with b-quark jets and missing transverse energy in pp collisions at 7 TeV
No full textResults are presented from a search for physics beyond the standard model based on events with large missing transverse energy, at least three jets, and at least one, two, or three b-quark jets. The study is performed using a sample of proton-proton collision data collected at √s=7 TeV with the CMS detector at the LHC in 2011. The integrated luminosity of the sample is 4.98 fb−1. The observed number of events is found to be consistent with the standard model expectation, which is evaluated using control samples in the data. The results are used to constrain cross sections for the production of supersymmetric particles decaying to b-quark-enriched final states in the context of simplified model spectra
Measurement of the Pseudorapidity and Centrality Dependence of the Transverse Energy Density in Pb-Pb Collisions at √sNN=2.76 TeV
No full textThe transverse energy (ET) in Pb-Pb collisions at 2.76 TeV nucleon-nucleon center-of-mass energy (√sNN) has been measured over a broad range of pseudorapidity (η) and collision centrality by using the CMS detector at the LHC. The transverse energy density per unit pseudorapidity (dET/dη) increases faster with collision energy than the charged particle multiplicity. This implies that the mean energy per particle is increasing with collision energy. At all pseudorapidities, the transverse energy per participating nucleon increases with the centrality of the collision. The ratio of transverse energy per unit pseudorapidity in peripheral to central collisions varies significantly as the pseudorapidity increases from η=0 to |η|=5.0. For the 5% most central collisions, the energy density per unit volume is estimated to be about 14 GeV/fm3 at a time of 1 fm/c after the collision. This is about 100 times larger than normal nuclear matter density and a factor of 2.6 times higher than the energy density reported at √sNN=200 GeV at the Relativistic Heavy Ion Collider
Search for contact interactions in μ+μ− events in pp collisions at √s=7 TeV
No full textResults are reported from a search for the effects of contact interactions using events with a high-mass, oppositely charged muon pair. The events are collected in proton-proton collisions at √s=7 TeV using the Compact Muon Solenoid detector at the Large Hadron Collider. The data sample corresponds to an integrated luminosity of 5.3 fb−1. The observed dimuon mass spectrum is consistent with that expected from the standard model. The data are interpreted in the context of a quark- and muon-compositeness model with a left-handed isoscalar current and an energy scale parameter Λ. The 95% confidence level lower limit on Λ is 9.5 TeV under the assumption of destructive interference between the standard model and contact-interaction amplitudes. For constructive interference, the limit is 13.1 TeV. These limits are comparable to the most stringent ones reported to date
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