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Sub-Finsler structures from the time-optimal control viewpoint for some nilpotent distributions
No full text24 pages, 17 figuresIn this paper we study the sub-Finsler geometry as a time-optimal control problem. In particular, we consider non-smooth and non-strictly convex sub-Finsler structures associated with the Heisenberg, Grushin, and Martinet distributions. Motivated by problems in geometric group theory, we characterize extremal curves, discuss their optimality, and calculate the metric spheres, proving their Euclidean rectifiability
Ultrafast filling of an electronic pseudogap in photoexcited (LaS) 1.196 VS 2
No full textWe investigate by angle and time resolved photoemission spectroscopy the unusual insulating state of strongly distorted triangular V slabs in (LaS)1.196VS2. We show that the electronic structure is dominated by the lowest band of the V t2g manifold, which disperses over 0.7 eV and is nearly filled. Hence, (LaS)1.196VS2 is not a Mott insulator. The spectra are strongly temperature dependent, shifting by 100 meV upon cooling to 50 K. The sudden photoexcitation at 50K induces a partial filling of the electronic pseudogap within less than 80 fs. The electronic energy flows into the lattice modes on a comparable timescale. We conclude that a very strong electron-phonon coupling makes this state extremely sensitive to small perturbations of the V clusters distortions
The effect of irradiation on the magnetic properties of rock and synthetic samples: Implications to irradiation of extraterrestrial materials in space
No full textInternational audienceWe report here the results of laboratory analog experiments to consider the potential effects of solar energetic particles (SEP or solar-flare-associated particles) and galactic cosmic rays (GCR) on the magnetic properties of extraterrestrial materials. We carried out proton bombardment experiments (with irradiation energies E (1)=400, E (2) =850 keV and three irradiation fluences in 10(14)-10(16) p/cm(2) range) and lead-ion bombardment experiments (E =1 GeV) on (previously demagnetized by 120 mT alternating magnetic field) rock and synthetic samples with the following magnetic carriers: metallic iron and nickel iron, Ti-rich and Ti-free magnetite, pyrrhotite. Irradiation experiments resulted in either further demagnetization or magnetization of irradiated samples depending on the type of magnetic mineralogy and type of ionizing radiation involved. Apart for the formation of radiation-induced remanent magnetization (RIRM), we observed major changes in bulk magnetic properties, i.e., a moderate to dramatic decrease (up to 93%) in the coercivity of remanence B (cr) for all iron-bearing phases (iron-in-epoxy and Bensour meteorite samples). Contrary to iron-bearing samples, several magnetite-bearing samples experienced a radiation-induced magnetic hardening (increase in B (cr) ). Magnetic hardening was also observed for Ar2+ ion-irradiated nickel iron-bearing HED meteorites, measured for comparison with the previously stated results. Therefore, the combined effect of SEP with GCR may magnetically soften iron-bearing materials and harden magnetite-bearing materials. In order to answer the question wether RIRM may account for natural remanent magnetization of meteorites and lunar samples, physical mechanism of RIRM formation and potential dependence of RIRM intensity on the background magnetic field present during irradiation event should be investigated
Donor/Acceptor Dihydroindeno[1,2-a]fluorene and Dihydroindeno[2,1-b]fluorene: Towards New Families of Organic Semiconductors
No full textInternational audienceNew families of donor/acceptor semiconductors based on dihydroindeno[1,2-a]fluorene and dihydroindeno[2,1-b]fluorene are reported. Due to the spiro bridges, this new generation of dihydroindenofluorenes allows a spatial separation of HOMO and LUMO, which retains the high ET value of the dihydroindenofluorene backbone and excellent physical properties. This control of the electronic and physical properties has allowed a second generation of dihydroindeno[1,2-a]fluorene to be obtained with strongly enhanced performance in green and sky-blue phosphorescent organic light-emitting diodes (PhOLEDs) relative to the first generation of materials. To date, this is the highest performance ever reported for a blue PhOLED by using a dihydroindenofluorene derivative. Through this structure-property relationship study, a remarkable difference of performance between syn and anti isomers has also been highlighted. This surprising behaviour has been attributed to the different symmetry of the two molecules, and highlights the importance of the geometry profiles in the design of host materials for PhOLEDs
Search for neutral color-octet weak-triplet scalar particles in proton-proton collisions at sqrt(s) = 8 TeV
No full textsee paper for full list of authorsInternational audienceA search for pair production of neutral color-octet weak-triplet scalar particles (Theta) is performed in processes where one Theta decays to a pair of b quark jets and the other to a Z boson plus a jet, with the Z boson decaying to a pair of electrons or muons. The search is performed with data collected by the CMS experiment at the CERN LHC corresponding to an integrated luminosity of 19.7 inverse femtobarns of proton-proton collisions at sqrt(s) = 8 TeV. The number of observed events is found to be in agreement with the standard model predictions. The 95% confidence level upper limit on the product of the cross section and branching fraction is obtained as a function of the Theta mass. The 95% confidence level lower bounds on the Theta mass are found to be 623 and 426 GeV, for two different octo-triplet theoretical scenarios. These are the first direct experimental bounds on particles predicted by the octo-triplet model
Introduction: dossier : Décrire les marchés, un impératif scientifique
No full textInternational audienceThe first financial market in the world was the 17th-century stock exchange in Amsterdam. Joseph de la Vega’s description of it in his mythic Confusion of Confusions (1688) was the very first analysis of a stock market. As the title states, this writer, a trader in securities, saw the market as a vast disorder that normally produces order but also potentially generates chaos, since the first crashes soon followed on the market’s creation. Instead of a single account of this chaos, various viewpoints are presented. For this purpose, the author chose the form of a dialog between a subtle philosopher, a circumspect merchant and a clever shareholder.Les théories des marchés ne manquent pas : en économie, en sociologie, en anthropologie. Mais manquent des descriptions fines, qui permettent de mettre en lumière les différences dans les fonctionnements et les institutions. La description doit retrouver son statut d’instrument scientifique. Pour cela, il faut la repenser, dans ses techniques et dans son rôle. Il n’existe pas une description, objective, d’un phénomène ou d’un objet, seuls existent des « voir comme » (au sens de Wittgenstein). Ce sont ceux des acteurs eux-mêmes (dont il faut tenir compte, tout en leur faisant subir un examen critique) et ceux que peut construire le chercheur. Il ne s’agit pas de subjectivité qui s’affronteraient, mais de points de vue construits. Quant à l’objectif scientifique d’une description, il n’est évidemment pas d’illustrer une théorie, mais de discuter les théories et de faire émerger de nouvelles idées
Combinatorial RNA Design: Designability and Structure-Approximating Algorithm
No full textAccepted (To appear)International audienceIn this work, we consider the Combinatorial RNA Design problem, a minimal instance of the RNA design problem which aims at finding a sequence that admits a given target as its unique base pair maximizing structure. We provide complete characterizations for the structures that can be designed using restricted alphabets. Under a classic four-letter alphabet, we provide a complete characterization of designable structures without unpaired bases. When unpaired bases are allowed, we provide partial characterizations for classes of designable/undesignable structures, and show that the class of designable structures is closed under the stutter operation. Membership of a given structure to any of the classes can be tested in linear time and, for positive instances, a solution can be found in linear time. Finally, we consider a structure-approximating version of the problem that allows to extend bands (helices) and, assuming that the input structure avoids two motifs, we provide a linear-time algorithm that produces a designable structure with at most twice more base pairs than the input structure
Sports Ballistics
No full textInternational audienceThis review describes and classifies the trajectories of sports projectiles that have spherical symmetry, cylindrical symmetry, or (almost) no symmetry. This classification allows us to discuss the large diversity observed in the paths of spherical balls, the flip properties of shuttlecocks, and the optimal position and stability of ski jumpers
Search for physics beyond the standard model in dilepton mass spectra in proton-proton collisions at sqrt(s) = 8 TeV
No full textSubmitted to JHEP, see paper for full list of authorsInternational audienceDimuon and dielectron mass spectra, obtained from data resulting from proton-proton collisions at 8 TeV and recorded by the CMS experiment, are used to search for both narrow resonances and broad deviations from standard model predictions. The data correspond to an integrated luminosity of 20.6 (19.7) inverse femtobarns for the dimuon (dielectron) channel. No evidence for non-standard-model physics is observed and 95% confidence level limits are set on parameters from a number of new physics models. The narrow resonance analyses exclude a Sequential Standard Model Z'[SSM] resonance lighter than 2.90 TeV, a superstring-inspired Z'[psi] lighter than 2.57 TeV, and Randall-Sundrum Kaluza-Klein gravitons with masses below 2.73, 2.35, and 1.27 TeV for couplings of 0.10, 0.05, and 0.01, respectively. A notable feature is that the limits have been calculated in a model-independent way to enable straightforward reinterpretation in any model predicting a resonance structure. The observed events are also interpreted within the framework of two non-resonant analyses: one based on a large extra dimensions model and one based on a quark and lepton compositeness model with a left-left isoscalar contact interaction. Lower limits are established on M[S], the scale characterizing the onset of quantum gravity, which range from 4.9 to 3.3 TeV, where the number of additional spatial dimensions varies from 3 to 7. Similarly, lower limits on Lambda, the energy scale parameter for the contact interaction, are found to be 12.0 (15.2) TeV for destructive (constructive) interference in the dimuon channel and 13.5 (18.3) TeV in the dielectron channel
Ergodicity conditions for zero-sum games
No full textSee also arXiv: 1405.4658International audienceA basic question for zero-sum repeated games consists in determining whether the mean payoff per time unit is independent of the initial state. In the special case of "zero-player" games, i.e., of Markov chains equipped with additive functionals, the answer is provided by the mean ergodic theorem. We generalize this result to repeated games. We show that the mean payoff is independent of the initial state for all state-dependent perturbations of the rewards if and only if an ergodicity condition is verified. The latter is characterized by the uniqueness modulo constants of non-linear harmonic functions (fixed point of the recession operator of the Shapley operator), or, in the special case of stochastic games with finite action spaces and perfect information, by a reachability condition involving conjugated subsets of states in directed hypergraphs. We show that the ergodicity condition for games only depend on the support of the transition probability, and that it can be checked in polynomial time when the number of states is fixed