Results for "Nicolas Bousquet"

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A polynomial version of Cereceda's conjectureMar 13 2019Let $k$ and $d$ be such that $k \ge d+2$. Consider two $k$-colourings of a $d$-degenerate graph $G$. Can we transform one into the other by recolouring one vertex at each step while maintaining a proper coloring at any step? Cereceda et al. answered that ... More
EPTAS for Max Clique on Disks and Unit BallsMar 05 2018Apr 11 2018We propose a polynomial-time algorithm which takes as input a finite set of points of $\mathbb R^3$ and compute, up to arbitrary precision, a maximum subset with diameter at most $1$. More precisely, we give the first randomized EPTAS and deterministic ... More
Induced magnetoelectric response in Pnma perovkitesAug 30 2011We use symmetry analysis to show that the G, C and A-type antiferromagnetic Pnma perovskites can exhibit magnetoelectric (ME) responses when a ferroelectric instability is induced with epitaxial strain. Using first-principles calculations we compute the ... More
Reconfiguration of graphs with connectivity constraintsSep 14 2018A graph $G$ realizes the degree sequence $S$ if the degrees of its vertices is $S$. Hakimi gave a necessary and sufficient condition to guarantee that there exists a connected multigraph realizing $S$. Taylor later proved that any connected multigraph ... More
Well-posedness conditions in stochastic inversion problemsJun 09 2018Stochastic inversion problems arise when it is wanted to estimate the probability distribution of a stochastic input from indirect observable and noisy information and the limited knowledge of an operator that connects the inputs to the observable output. ... More
Issues with J-dependence in the LSDA+U method for non-collinear magnetsNov 03 2010We re-examine the commonly used density functional theory plus Hubbard \textit{U} (DFT$+U$) method for the case of non-collinear magnets. While many studies neglect to explicitly include the exchange correction parameter \textit{J}, or consider its exact ... More
VC-dimension and Erdős-Pósa propertyDec 04 2014Let $G=(V,E)$ be a graph. A $k$-neighborhood in $G$ is a set of vertices consisting of all the vertices at distance at most $k$ from some vertex of $G$. The hypergraph on vertex set $V$ which edge set consists of all the $k$-neighborhoods of $G$ for all ... More
Token Sliding on Chordal GraphsMay 02 2016Let I be an independent set of a graph G. Imagine that a token is located on any vertex of I. We can now move the tokens of I along the edges of the graph as long as the set of tokens still defines an independent set of G. Given two independent sets I ... More
Fast Recoloring of Sparse GraphsNov 25 2014In this paper, we show that for every graph of maximum average degree bounded away from $d$, any $(d+1)$-coloring can be transformed into any other one within a polynomial number of vertex recolorings so that, at each step, the current coloring is proper. ... More
Colorful paths for 3-chromatic graphsMar 03 2015In this paper, we prove that every 3-chromatic connected graph, except $C_7$, admits a 3-vertex coloring in which every vertex is the beginning of a 3-chromatic path. It is a special case of a conjecture due to S.~Akbari, F.~Khaghanpoor, and S.~Moazzeni, ... More
Excluding cycles with a fixed number of chordsApr 05 2013Trotignon and Vuskovic completely characterized graphs that do not contain cycles with exactly one chord. In particular, they show that such a graph G has chromatic number at most max(3,w(G)). We generalize this result to the class of graphs that do not ... More
The Erdős-Hajnal Conjecture for Paths and AntipathsMar 21 2013Jun 26 2014We prove that for every k, there exists $c_k>0$ such that every graph G on n vertices not inducing a path $P_k$ and its complement contains a clique or a stable set of size $n^{c_k}$.
Strain-induced ferroelectricity in simple rocksalt binary oxidesJun 23 2009The alkaline earth binary oxides adopt a simple rocksalt structure and form an important family of compounds because of their large presence in the earth's mantle and their potential use in microelectronic devices. In comparison to the class of multifunctional ... More
Coalition Games on Interaction Graphs: A Horticultural PerspectiveFeb 26 2015We examine cooperative games where the viability of a coalition is determined by whether or not its members have the ability to communicate amongst themselves independently of non-members. This necessary condition for viability was proposed by Myerson ... More
Estimating Discrete Markov Models From Various Incomplete Data SchemesSep 07 2010Feb 22 2012The parameters of a discrete stationary Markov model are transition probabilities between states. Traditionally, data consist in sequences of observed states for a given number of individuals over the whole observation period. In such a case, the estimation ... More
Frozen $(Δ+1)$-colourings of bounded degree graphsNov 30 2018Let $G$ be a graph of maximum degree $\Delta$ and $k$ be an integer. The $k$-recolouring graph of $G$ is the graph whose vertices are $k$-colourings of $G$ and where two $k$-colourings are adjacent if they differ at exactly one vertex. It is well-known ... More
Multicut is FPTOct 25 2010Nov 23 2010Let $G=(V,E)$ be a graph on $n$ vertices and $R$ be a set of pairs of vertices in $V$ called \emph{requests}. A \emph{multicut} is a subset $F$ of $E$ such that every request $xy$ of $R$ is cut by $F$, \i.e. every $xy$-path of $G$ intersects $F$. We show ... More
A Near-Optimal Mechanism for Impartial SelectionJul 31 2014We examine strategy-proof elections to select a winner amongst a set of agents, each of whom cares only about winning. This impartial selection problem was introduced independently by Holzman and Moulin and Alon et al. Fisher and Klimm showed that the ... More
The Erdős-Hajnal Conjecture for Long Holes and Anti-holesAug 08 2014Erd\H{o}s and Hajnal conjectured that, for every graph $H$, there exists a constant $c_H$ such that every graph $G$ on $n$ vertices which does not contain any induced copy of $H$ has a clique or a stable set of size $n^{c_H}$. We prove that for every ... More
Non collinear magnetism and single ion anisotropy in multiferroic perovskitesJun 04 2012The link between the crystal distortions of the perovskite structure and the magnetic exchange interaction, the single-ion anisotropy (SIA) and the Dzyaloshinsky-Moriya (DM) interaction are investigated by means of density-functional calculations. Using ... More
An adaptive kriging method for solving nonlinear inverse statistical problemsAug 23 2015In various industrial contexts, estimating the distribution of unobserved random vectors Xi from some noisy indirect observations H(Xi) + Ui is required. If the relation between Xi and the quantity H(Xi), measured with the error Ui, is implemented by ... More
Welfare and Rationality Guarantees for the Simultaneous Multiple-Round Ascending AuctionOct 01 2015The simultaneous multiple-round auction (SMRA) and the combinatorial clock auction (CCA) are the two primary mechanisms used to sell bandwidth. Under truthful bidding, the SMRA is known to output a Walrasian equilibrium that maximizes social welfare provided ... More
Clique versus Independent SetJan 11 2013Jun 27 2014Yannakakis' Clique versus Independent Set problem (CL-IS) in communication complexity asks for the minimum number of cuts separating cliques from stable sets in a graph, called CS-separator. Yannakakis provides a quasi-polynomial CS-separator, i.e. of ... More
Lipschitz regularity for orthotropic functionals with nonstandard growth conditionsOct 09 2018We consider a model convex functional with orthotropic structure and super-quadratic nonstandard growth conditions. We prove that bounded local minimizers are locally Lipschitz, with no restrictions on the ratio between the highest and the lowest growth ... More
The degree distribution in bipartite planar maps: applications to the Ising modelNov 04 2002May 20 2003We characterize the generating function of bipartite planar maps counted according to the degree distribution of their black and white vertices. This result is applied to the solution of the hard particle and Ising models on random planar lattices. We ... More
The importance of the electronic contribution to linear magnetoelectricityDec 07 2009Sep 07 2010We demonstrate that the electronic contribution to the linear magnetoelectric response, usually omitted in first-principles studies, can be comparable in magnitude to that mediated by lattice distortions, even for materials in which responses are strong. ... More
Parameterized Complexity of Independent Set in H-Free GraphsOct 10 2018Feb 20 2019In this paper, we investigate the complexity of Maximum Independent Set (MIS) in the class of $H$-free graphs, that is, graphs excluding a fixed graph as an induced subgraph. Given that the problem remains $NP$-hard for most graphs $H$, we study its fixed-parameter ... More
Shortest Reconfiguration of MatchingsDec 13 2018Imagine that unlabelled tokens are placed on the edges of a graph, such that no two tokens are placed on incident edges. A token can jump to another edge if the edges having tokens remain independent. We study the problem of determining the distance between ... More
A Polynomial Kernel For Multicut In TreesFeb 06 2009The MULTICUT IN TREES problem consists in deciding, given a tree, a set of requests (i.e. paths in the tree) and an integer k, whether there exists a set of k edges cutting all the requests. This problem was shown to be FPT by Guo and Niedermeyer. They ... More
Identifying codes in hereditary classes of graphs and VC-dimensionJul 22 2014Apr 22 2015An identifying code of a graph is a subset of its vertices such that every vertex of the graph is uniquely identified by the set of its neighbours within the code. We show a dichotomy for the size of the smallest identifying code in classes of graphs ... More
On a conjecture of Mohar concerning Kempe equivalence of regular graphsOct 23 2015Sep 22 2016Let $G$ be a graph with a vertex colouring $\alpha$. Let $a$ and $b$ be two colours. Then a connected component of the subgraph induced by those vertices coloured either $a$ or $b$ is known as a Kempe chain. A colouring of $G$ obtained from $\alpha$ by ... More
On the number of planar Eulerian orientationsOct 31 2016The number of planar Eulerian maps with n edges is well-known to have a simple expression. But what is the number of planar Eulerian orientations with n edges? This problem appears to be difficult. To approach it, we define and count families of subsets ... More
Detecting and modeling worst-case dependence structures between random inputs of computational reliability modelsApr 27 2018Uncertain information on input parameters of reliability models is usually modeled by considering these parameters as random, and described by marginal distributions and a dependence structure of these variables. In numerous real-world applications, while ... More
Parameterized Complexity of Independent Set in H-Free GraphsOct 10 2018In this paper, we investigate the complexity of Maximum Independent Set (MIS) in the class of $H$-free graphs, that is, graphs excluding a fixed graph as an induced subgraph. Given that the problem remains $NP$-hard for most graphs $H$, we study its fixed-parameter ... More
On the Economic Efficiency of the Combinatorial Clock AuctionJul 23 2015Since the 1990s spectrum auctions have been implemented world-wide. This has provided for a practical examination of an assortment of auction mechanisms and, amongst these, two simultaneous ascending price auctions have proved to be extremely successful. ... More
On the practical interest of discrete Inverse Polya and Weibull-1 models in industrial reliability studiesNov 03 2014Engineers often cope with the problem of assessing the lifetime of industrial components, under the basis of observed industrial feedback data. Usually, lifetime is modelled as a continuous random variable, for instance exponentially or Weibull distributed. ... More
A Vizing-like theorem for union vertex-distinguishing edge coloringMay 09 2016We introduce a variant of the vertex-distinguishing edge coloring problem, where each edge is assigned a subset of colors. The label of a vertex is the union of the sets of colors on edges incident to it. In this paper we investigate the problem of finding ... More
Distributed coloring in sparse graphs with fewer colorsFeb 15 2018Dec 19 2018This paper is concerned with efficiently coloring sparse graphs in the distributed setting with as few colors as possible. According to the celebrated Four Color Theorem, planar graphs can be colored with at most 4 colors, and the proof gives a (sequential) ... More
$χ$-bounded families of oriented graphsMay 24 2016A famous conjecture of Gy\'arf\'as and Sumner states for any tree $T$ and integer $k$, if the chromatic number of a graph is large enough, either the graph contains a clique of size $k$ or it contains $T$ as an induced subgraph. We discuss some results ... More
Density modification based reliability sensitivity analysisOct 03 2012Mar 09 2014Sensitivity analysis of a numerical model, for instance simulating physical phenomena, is useful to quantify the influence of the inputs on the model responses. This paper proposes a new sensitivity index, based upon the modification of the probability ... More
Parameterized Domination in Circle GraphsMay 16 2012A circle graph is the intersection graph of a set of chords in a circle. Keil [Discrete Applied Mathematics, 42(1):51-63, 1993] proved that Dominating Set, Connected Dominating Set, and Total Dominating Set are NP-complete in circle graphs. To the best ... More
Linear Magnetoelectric Effect by Orbital MagnetismJul 12 2012Aug 01 2012We use symmetry analysis and first principles calculations to show that the linear magnetoelectric effect can originate from the response of orbital magnetic moments to the polar distortions induced by an applied electric field. Using LiFePO4 as a model ... More
The macroscopic monopolization in diagonal magnetoelectricsJun 23 2013Jun 29 2013We develop the formalism of the macroscopic monopolization -- that is the monopole moment per unit volume -- in periodic solids, and discuss its relationship to the diagonal magnetoelectric effect. For the series of lithium transition metal phosphate ... More
Strong coupling of Jahn-Teller distortion to oxygen-octahedron rotation and functional properties in epitaxially-strained orthorhombic LaMnO$_3$Jul 12 2013First-principles calculations reveal a large cooperative coupling of Jahn-Teller (JT) distortion to oxygen-octahedron rotations in perovskite LaMnO$_3$. The combination of the two distortions is responsible for stabilizing the strongly orthorhombic $A$-AFM ... More
Weak approximation by bounded Sobolev maps with values into complete manifoldsJan 26 2017We have recently introduced the trimming property for a complete Riemannian manifold $N^{n}$ as a necessary and sufficient condition for bounded maps to be strongly dense in $W^{1, p}(B^m; N^{n})$ when $p \in \{1, \dotsc, m\}$. We prove in this note that ... More
Strong approximation of fractional Sobolev mapsOct 22 2013Brezis and Mironescu have announced several years ago that for a compact manifold $N^n \subset \mathbb{R}^\nu$ and for real numbers $0 < s < 1$ and $1 \le p < \infty$ the class $C^\infty(\overline{Q}^m; N^n)$ of smooth maps on the cube with values into ... More
Eulerian orientations and the six-vertex model on planar mapFeb 20 2019We address the enumeration of planar 4-valent maps equipped with an Eulerian orientation by two different methods, and compare the solutions we thus obtain. With the first method we enumerate these orientations as well as a restricted class which we show ... More
The generating function of planar Eulerian orientationsMar 22 2018The enumeration of planar maps equipped with an Eulerian orientation has attracted attention in both combinatorics and theoretical physics since at least 2000. The case of 4-valent maps is particularly interesting: these orientations are in bijection ... More
Dynamical coupling during collective animal motionNov 06 2013The measurement of information flows within moving animal groups has recently been a topic of considerable interest, and it has become clear that the individual(s) that drive collective movement may change over time, and that such individuals may not ... More
Quantum cryptography with and without entanglementDec 01 2003Quantum cryptography is reviewed, first using entanglement both for the intuition and for the experimental realizations. Next, the implementation is simplified in several steps until it becomes practical. At this point entanglement has disappeared. This ... More
Dark soliton past a finite-size obstacleJan 04 2005Sep 05 2005We consider the collision of a dark soliton with an obstacle in a quasi-one-dimensional Bose condensate. We show that in many respects the soliton behaves as an effective classical particle of mass twice the mass of a bare particle, evolving in an effective ... More
Anderson localization of elementary excitations in a one dimensional Bose-Einstein condensateFeb 27 2006Aug 01 2006We study the elementary excitations of a transversely confined Bose-Einstein condensate in presence of a weak axial random potential. We determine the localization length (i) in the hydrodynamical low energy regime, for a domain of linear densities ranging ... More
High-accuracy first-principles determination of the structural, vibrational and thermodynamical properties of diamond, graphite, and derivativesDec 22 2004The structural, dynamical, and thermodynamical properties of diamond, graphite and layered derivatives (graphene, rhombohedral graphite) are computed using a combination of density-functional theory (DFT) total-energy calculations and density-functional ... More
An elementary solution of Gessel's walks in the quadrantMar 30 2015Aug 25 2016Around 2000, Ira Gessel conjectured that the number of lattice walks in the quadrant N^2, starting and ending at the origin (0,0) and taking their steps in {E,NE,W,SW} had a simple hypergeometric form. In the following decade, this problem was recast ... More
Limit laws for embedded trees. Applications to the integrated superBrownian excursionJan 18 2005We study three families of labelled plane trees. In all these trees, the root is labelled 0, and the labels of two adjacent nodes differ by $0, 1$ or -1. One part of the paper is devoted to enumerative results. For each family, and for all $j\in \ns$, ... More
Clusters of proteins in bio-membranes: insights into the roles of interaction potential shapes and of protein diversityJun 07 2011It has recently been proposed that proteins embedded in lipidic bio-membranes can spontaneously self-organize into stable small clusters, or membrane nano-domains, due to the competition between short-range attractive and longer-range repulsive forces ... More
Families of prudent self-avoiding walksApr 30 2008Oct 09 2009A self-avoiding walk (SAW) on the square lattice is prudent if it never takes a step towards a vertex it has already visited. Prudent walks differ from most classes of SAW that have been counted so far in that they can wind around their starting point. ... More
The expected number of inversions after n adjacent transpositionsSep 01 2009Mar 02 2010We give a new expression for the expected number of inversions in the product of n random adjacent transpositions in the symmetric group S_{m+1}. We then derive from this expression the asymptotic behaviour of this number when n scales with m in various ... More
$C^1$ regularity of orthotropic $p-$harmonic functions in the planeJul 18 2016We prove that local weak solutions of the orthotropic $p-$harmonic equation in $\mathbb{R}^2$ are $C^1$ functions.
A property of dominance of partitionsMar 18 2008Given an integer partition $\la=(\la_1, ..., \la_\ell)$ and an integer k, denote by $\la^{(k)}$ the sequence of length $\ell$ obtained by reordering the values $|\la_i-k|$ in non-increasing order. If $\la$ dominates $\mu$ and has the same weight, then ... More
Generating functions for generating treesNov 11 2004Certain families of combinatorial objects admit recursive descriptions in terms of generating trees: each node of the tree corresponds to an object, and the branch leading to the node encodes the choices made in the construction of the object. Generating ... More
Rational and algebraic series in combinatorial enumerationMay 05 2008Let A be a class of objects, equipped with an integer size such that for all n the number a(n) of objects of size n is finite. We are interested in the case where the generating fucntion sum_n a(n) t^n is rational, or more generally algebraic. This property ... More
Walks in the quarter plane: Kreweras' algebraic modelJan 08 2004Jan 21 2006We consider planar lattice walks that start from (0,0), remain inthe first quadrant i, j >= 0, and are made of three types of steps: North-East, West and South. These walks are known to have remarkable enumerative and probabilistic properties: -- they ... More
The equation div$u$+$\langle a, u \rangle=f$Jan 17 2019We study the solutions $u$ to the equation $$ \begin{cases} \operatorname{div} u + \langle a , u \rangle = f & \textrm{ in } \Omega,\\ u=0 & \textrm{ on } \partial \Omega, \end{cases} $$ where $a$ and $f$ are given. We significantly improve the existence ... More
Global Lipschitz continuity for minima of degenerate problemsApr 23 2015We consider the problem of minimizing the Lagrangian $\int [F(\nabla u)+f\,u]$ among functions on $\Omega\subset\mathbb{R}^N$ with given boundary datum $\varphi$. We prove Lipschitz regularity up to the boundary for solutions of this problem, provided ... More
Unveiling the room temperature magnetoelectricity of troilite FeSNov 04 2015The amazing possibility of magnetoelectric crystals to cross couple electric and magnetic properties without the need of time-dependent Maxwell's equations has attracted a lot of interest in material science. This enthusiasm has re-emerged during the ... More
New derived symmetries of some hyperkähler varietiesDec 02 2011Aug 18 2016We construct a new autoequivalence of the derived category of the Hilbert scheme of n points on a K3 surface, and of the variety of lines on a smooth cubic 4-fold. For Hilb^2 and the variety of lines, we use the theory of spherical functors; to deal with ... More
Some Ontological Principles for Designing Upper Level Lexical ResourcesSep 09 1998The purpose of this paper is to explore some semantic problems related to the use of linguistic ontologies in information systems, and to suggest some organizing principles aimed to solve such problems. The taxonomic structure of current ontologies is ... More
On the bounded cohomology of semi-simple groups, S-arithmetic groups and productsOct 29 2007We prove vanishing results for Lie groups and algebraic groups (over any local field) in bounded cohomology. The main result is a vanishing below twice the rank for semi-simple groups. Related rigidity results are established for S-arithmetic groups and ... More
Perfect graphs: a surveyJan 22 2013May 22 2015Perfect graphs were defined by Claude Berge in the 1960s. They are important objects for graph theory, linear programming and combinatorial optimization. Claude Berge made a conjecture about them, that was proved by Chudnovsky, Robertson, Seymour and ... More
Neutron conduction in the inner crust of a neutron star in the framework of the band theory of solidsMar 01 2012Even though the "free" neutrons in the inner crust of a neutron star are superfluid, they are still strongly coupled to nuclei due to non-dissipative entrainment effects. These effects have been systematically studied in all regions of the inner crust ... More
Opinion dynamics with confidence threshold: an alternative to the Axelrod modelFeb 27 2010Dec 25 2010The voter model and the Axelrod model are two of the main stochastic processes that describe the spread of opinions on networks. The former includes social influence, the tendency of individuals to become more similar when they interact, while the latter ... More
Inhomogeneous diffusion model for recent data on high-energy cosmic raysOct 30 2015The AMS Collaboration has recently released precision data on cosmic ray (CR) leptons and protons at high energies. Interesting progresses have also been made on the measurement of CR nuclei, such as the boron-to-carbon ratio or the lithium spectrum, ... More
Origin of the spectral upturn in the cosmic-ray C/Fe and O/Fe ratiosSep 18 2015The observed spectrum of Galactic cosmic rays has several exciting features such as the rise in the positron fraction above ~10 GeV of energy and the spectral hardening of protons and helium at ~300 GeV/nucleon of energy. The ATIC-2 experiment has recently ... More
Tradeoffs for reliable quantum information storage in surface codes and color codesJan 28 2013The family of hyperbolic surface codes is one of the rare families of quantum LDPC codes with non-zero rate and unbounded minimum distance. First, we introduce a family of hyperbolic color codes. This produces a new family of quantum LDPC codes with non-zero ... More
Inclusive Hadronic Results at BaBar: ISR and Pentaquark SearchesOct 15 2005We present recent measurements of hadronic cross-sections from the BaBar experiment and report preliminary results on searches for pentaquark states.
A synthesis and a practical approach to complex systemsJun 15 2006Mar 05 2008This document is both a synthesis of current notions about complex systems, and a practical approach description. A disambiguation is proposed and exposes possible reasons for controversies related to causation and emergence. Theoretical considerations ... More
The Semisimplicity Conjecture for A-MotivesSep 01 2008We prove the semisimplicity conjecture for A-motives over finitely generated fields K. This conjecture states that the rational Tate modules V_p(M) of a semisimple A-motive M are semisimple as representations of the absolute Galois group of K. This theorem ... More
Remarques a propos de l'operateur de Dirac cubiqueJun 21 2010Remarks on the Kostant Dirac operator In 1999, Kostant [Kos99] indroduces a Dirac operator D_g/h associated to any triple (g, h,B), where g is a complex Lie algebra provided with an ad g-invariant non degenerate nsymetric bilinear form B, and h is a Lie ... More
Large values of modular formsJul 25 2012Sep 19 2013We show that there are primitive holomorphic modular forms f of weight two and arbitrary large level N such that $|f(z)| \gg N^{1/4}$ for some point z. Thereby we disprove a folklore conjecture that the sup-norm of such forms would be as small as $N^{o(1)}$. ... More
Determination of the a0-a2 pion scattering length from K->pi+ pi0 pi0 decayMay 03 2004May 04 2004We present a new method for the determination of the pion-pion scattering lenght combination a0-a2, based on the study of the pi0-pi0 spectrum in K->pi+ pi0 pi0 in the vicinity of the pi+ pi- threshold. The method requires a minimum of theoretical input, ... More
Are There Quantum Effects Coming from Outside Space-time? Nonlocality, free will and "no many-worlds"Nov 15 2010Observing the violation of Bell's inequality tells us something about all possible future theories: they must all predict nonlocal correlations. Hence Nature is nonlocal. After an elementary introduction to nonlocality and a brief review of some recent ... More
The Free Will Theorem, Stochastic Quantum Dynamics and True Becoming in Relativistic Quantum PhysicsFeb 06 2010In Bell inequality tests, the evolution of the wavefunction is not covariant, i.e. not invariant under velocity boost that change the time ordering of events, but the laws that govern the probability distribution of possible results are. In this note ... More
Non-realism : deep thought or a soft option ?Jan 27 2009Aug 18 2009The claim that the observation of a violation of a Bell inequality leads to an alleged alternative between nonlocality and non-realism is annoying because of the vagueness of the second term.
On p-rank representationsFeb 20 2004Feb 20 2004The p-rank of an algebraic curve X over an algebraically closed field k of characteristic p>0 is the dimension of the first etale cohomology vector space H^1(X,Z/pZ). We study the representations of finite groups G of automorphisms of X induced on the ... More
Semi-classical measures for inhomogeneous Schrödinger equations on toriSep 17 2012Dec 20 2012The purpose of this note is to investigate the high frequency behaviour of solutions to linear Schr\"odinger equations. More precisely, Bourgain and Anantharaman-Macia proved that any weak-* limit of the square density of solutions to the time dependent ... More
Global Strichartz Estimates for nontrapping Geometries: About an Article by H. Smith and C. SoggeOct 17 2002The purpose of this note is to present an alternative proof of a result by H. Smith and C. Sogge showing that in odd dimension of space, local (in time) Strichartz estimates and exponential decay of the local energy for solutions to wave equations imply ... More
Global temperatures and sunspot numbers. Are they related? Yes, but non linearly. A reply to Gil-Alana et al. (2014)Jul 27 2014Gil-Alana et al. (Physica A: 396, 42-50, 2014) compared the sunspot number record and the temperature record and found that they differ: the sunspot number record is characterized by a dominant 11-year cycle while the temperature record appears to be ... More
Total solar irradiance satellite composites and their phenomenological effect on climateAug 06 2009Herein I discuss and propose updated satellite composites of the total solar irradiance covering the period 1978-2008. The composites are compiled from measurements made with the three ACRIM experiments. Measurements from the NIMBUS7/ERB and the ERBS/ERBE ... More
A shared frequency set between the historical mid-latitude aurora records and the global surface temperatureMay 25 2012Herein we show that the historical records of mid-latitude auroras from 1700 to 1966 present oscillations with periods of about 9, 10-11, 20-21, 30 and 60 years. The same frequencies are found in proxy and instrumental global surface temperature records ... More
Empirical evidence for a celestial origin of the climate oscillations and its implicationsMay 25 2010We investigate whether or not the decadal and multi-decadal climate oscillations have an astronomical origin. Several global surface temperature records since 1850 and records deduced from the orbits of the planets present very similar power spectra. ... More
Dirac operators on Lagrangian submanifoldsMay 14 2004We study a natural Dirac operator on a Lagrangian submanifold of a K\"ahler manifold. We first show that its square coincides with the Hodge-de Rham Laplacian provided the complex structure identifies the Spin structures of the tangent and normal bundles ... More
A new extrinsic estimate for the spectrum of the Dirac operatorApr 28 2003We prove a new upper bound for the smallest eigenvalues of the Dirac operator on a compact hypersurface of the hyperbolic space.
Spherical homogeneous spaces of minimal rankSep 03 2009Let $G$ be a complex connected reductive algebraic group and $G/B$ denote the flag variety of $G$. A $G$-homogeneous space $G/H$ is said to be {\it spherical} if $H$ acts on $G/B$ with finitely many orbits. A class of spherical homogeneous spaces containing ... More
Reconstructing Dark Matter Properties via Gamma-Rays with Fermi-LATDec 01 2010We study the capabilities of the Fermi-LAT instrument for identifying particle Dark Matter properties as mass, annihilation cross section and annihilation channels, with gamma-ray observations from the Galactic Center. For the potential Dark Matter signal, ... More
La Notion D'irrationalitÉ Selon Un MathÉmaticien Du Xe SiÈcle: Abū Ja'far Al-KhāzinJan 27 2013The treatise of Ab\=u Ja'far al-Kh\=azin (Xth century), entitled "Commentary on the introduction of the tenth book of the treatise of Euclid" ("tafs\={i}r sadr al-maq\={a}la al-'\={a}shira min kit\={a}b Uql\={i}dis") exists in eight manuscripts. In this ... More
Bremsstrahlung corrections to the decay $b \to s γ$Dec 07 1995Jun 28 1996We calculate the O($\alpha_s$) gluon Bremsstrahlung corrections to the inclusive decay $b \rightarrow s \gamma$, involving the full operator basis $\hat O_1$ -- $\hat O_8$. Confirming and extending earlier calculations of Ali and Greub, we give formulas ... More
Frankenstein's Glue: Transition functions for approximate solutionsNov 23 2006Aug 17 2007Approximations are commonly employed to find approximate solutions to the Einstein equations. These solutions, however, are usually only valid in some specific spacetime region. A global solution can be constructed by gluing approximate solutions together, ... More
Trace formula for an ensemble of bumpy billiards.May 16 1995We study the semiclassical quantization of an ensemble of billiards with a small random shape deformation. We derive a trace formula averaged over shape disorder. The results are illustrated by the study of supershells in rough metal clusters.
Discrete Symmetries in the Weyl Expansion for Quantum BilliardsNov 15 1994We consider two and three-dimensional quantum billiards with discrete symmetries. We derive the first terms of the Weyl expansion for the level density projected onto the irreducible representations of the symmetry group. As an illustration the method ... More