On-the-fly Approximation of Multivariate Total Variation Minimization

In the context of change-point detection, addressed by Total Variation minimization strategies, an efficient on-the-fly algorithm has been designed leading to exact solutions for univariate data. In this contribution, an extension of such an on-the-fly strategy to multivariate data is investigated. The proposed algorithm relies on the local validation of the Karush-Kuhn-Tucker conditions on the dual problem. Showing that the non-local nature of the multivariate setting precludes to obtain an exact on-the-fly solution, we devise an on-the-fly algorithm delivering an approximate solution, whose quality is controlled by a practitioner-tunable parameter, acting as a trade-off between quality and computational cost. Performance assessment shows that high quality solutions are obtained on-the-fly while benefiting of computational costs several orders of magnitude lower than standard iterative procedures. The proposed algorithm thus provides practitioners with an efficient multivariate change-point detection on-the-fly procedure

Unveiling Groups of Related Tasks in Multi - Task Learning

A common approach in multi-task learning is to encourage the tasks to share a low dimensional representation. This has led to the popular method of trace norm regularization, which has proved effective in many applications. In this paper, we extend this approach by allowing the tasks to partition into different groups, within which trace norm regularization is separately applied. We propose a continuous bilevel optimization framework to simultaneously identify groups of related tasks and learn a low dimensional representation within each group. Hinging on recent results on the derivative of generalized matrix functions, we devise a smooth approximation of the upper-level objective via a dual forward-backward algorithm with Bregman distances. This allows us to solve the bilevel problem by a gradient-based scheme. Numerical experiments on synthetic and benchmark datasets support the effectiveness of the proposed method

réaction des Etats est-asiatiques au défi de la piraterie sur les mers de l’après-Guerre froide. The Reaction of East Asian States to the Challenge of Post Cold War Maritime Piracy.

Au lendemain de la Guerre froide, l’Asie orientale est marquée par un regain de la piraterie maritime. Il ne s’agit plus de littérature. Les rapports policiers remplacent les chroniques de Joseph Conrad ; les voyous et autres oubliés du miracle asiatique supplantent les fiers héros Bugis du XIXe siècle. Petits bandits des mers, mafias et occasionnellement terroristes : tous usent à leur manière des abordages, vols, détournements et kidnappings, des détroits malais jusqu’à la mer de Chine méridionale. Les gouvernements sont défiés et les piliers des Etats fragilisés. Leur autorité paraît bafouée. Ce fléau criminel peut-il être fatal pour les pouvoirs en place ? En contestant sur mer le modèle d’organisation politique inspiré des traités de Westphalie et adopté par les gouvernements locaux, que dit la piraterie sur le statut de l’Etat moderne en Asie orientale ? A première vue, sur le terrain, l’Etat semble perdre pied et ne plus contrôler ni ses approches maritimes, cibles des pirates, ni les modes de luttes gérés et encadrés dès le début des années quatre-vingt-dix par des acteurs concurrents et souvent privés, comme le Bureau maritime international. Pourtant, à plus long terme, la piraterie offre aux Etats est-asiatiques l’occasion de s’affirmer sur la scène régionale. Tous savent résister pour prendre leur revanche. Pressés de toutes parts, ils s’équipent et s’organisent pour finalement imposer leur autorité en mer. Mieux : par la coopération, ils trouvent auprès de leurs voisins un surplus de légitimité et d’efficacité. Au terme de cette fable asiatique mettant en scène le pirate et l’Etat, le plus affaibli des deux n’est pas celui qu’on pense.Piraterie maritime;Terrorisme;Asie orientale;Association des nations d’Asie du Sud-est;

Relax and penalize: a new bilevel approach to mixed-binary hyperparameter optimization

In recent years, bilevel approaches have become very popular to efficiently estimate high-dimensional hyperparameters of machine learning models. However, to date, binary parameters are handled by continuous relaxation and rounding strategies, which could lead to inconsistent solutions. In this context, we tackle the challenging optimization of mixed-binary hyperparameters by resorting to an equivalent continuous bilevel reformulation based on an appropriate penalty term. We propose an algorithmic framework that, under suitable assumptions, is guaranteed to provide mixed-binary solutions. Moreover, the generality of the method allows to safely use existing continuous bilevel solvers within the proposed framework. We evaluate the performance of our approach for a specific machine learning problem, i.e., the estimation of the group-sparsity structure in regression problems. Reported results clearly show that our method outperforms state-of-the-art approaches based on relaxation and roundin

Étude de quelques liens entre les groupes de rang de Morley fini et les groupes algébriques linéaires

Cette thèse traite essentiellement des liens qui peuvent exister entre les groupes de rang de Morley fini et les groupes algébriques linéaires. En effet, nous y établissons quelques propriétés algébriques aux K-groupes ; d'ailleurs une étude de linéarité sur ces groupes est dressée et permet en particulier d'obtenir une généralisation du théorème de Levi sur la décomposition des groupes algébriques. Ensuite, nous étudions dans ununivers de rang de Morley fini, une action définissable de SL2(K) sur un groupe abélien SL2(K)-minimal V où K est un corps définissable de caractéristique positive p > 0. À cet effet, nous montrons que le rang de Morley rk(V ) de V est pair et multiple de rk(K). Enfin, nous analysons sous quelles conditions, étant donné G un groupe algébrique sur un corps algébriquement clos de caractéristique non nulle, le quotient G=Z(G) est définissablement linéaire. Par ailleurs, nous montrons sous certaines hypothèses le groupe des automorphismes définissables d'un K*-groupe simple est interprétable.This thesis essentially focuses on relationships that may exist between groups of finite Morley rank and linear algebraic groups. Indeed, we establish some algebraic properties to K-groups; while a linearity study on these groups is drawn and allows in particular to obtain an analogue to Levi decomposition theorem of algebraic groups. Next, in a univers of finite Morley rank, we study a definable action of SL2(K) on an abelian group V such as V is SL2(K)-minimal, where K is an definable field of non zero characteristic. For that purpose, we show that Morley rank of V denoted rk(V ) is even and multiple of rk(K). Finally, we analyze the conditions under which, given an algebraic group G over an algebraically field of non zero characteristic, the quotient G=Z(G) is definably linear. Besides, we show under certain assymptions that the group of definable automorphism of a simple K*-group is interpretable.POITIERS-SCD-Bib. électronique (861949901) / SudocSudocFranceF

Hydraulic disruption and passive migration by a bacterial pathogen in oak tree xylem

Xylella fastidiosa (Xf) is a xylem-limited bacterial pathogen that causes leaf scorch symptoms in numerous plant species in urban, agricultural, and natural ecosystems worldwide. The exact mechanism of hydraulic disruption and systemic colonization of xylem by Xf remains elusive across all host plants. To understand both processes better, the functional and structural characteristics of xylem in different organs of both healthy and Xf-infected trees of several Quercus species were studied. Hydraulic conductivity (Ks) in Xf-infected petioles of Q. palustris and Q. rubra decreased significantly compared with healthy trees as the season progressed and plummeted to zero with the onset of scorch symptoms. Prior to the onset of symptoms, embolism was as much as 3.7 times higher in Xf-infected petioles compared with healthy controls and preceded significant reductions in Ks. Embolism likely resulted from pit membrane degradation during colonization of new petiole xylem and triggered the process that eventually led to vessel occlusion. Pit membrane porosity was studied using the following four methods to determine if a pathway exists in the xylem network of woody stems that allows for passive Xf migration: (i) calculations based on vulnerability to cavitation data, (ii) scanning electron micrographs, (iii) microsphere injections, and (iv) air seeding thresholds on individual vessels. All four methods consistently demonstrated that large pit membrane pores (i.e. greater than the diameter of individual Xf) occur frequently throughout the secondary stem xylem in several Quercus species. These large pores probably facilitate systemic colonization of the secondary xylem network and contribute to the high susceptibility to bacterial leaf scorch exhibited among these species

Threshold Bound States

Relationships between the coupling constant and the binding energy of threshold bound states are obtained in a simple manner from an iterative algorithm for solving the eigenvalue problem. The absence of threshold bound states in higher dimensions can be easily understood

Tangible Teleconferencing

This paper describes a teleconferencing application that uses real objects to interact with virtual on-screen content. A variety of tangible interaction techniques can be used to load, translate, rotate and scale shared virtual models. In addition, snapshots of real documents can be easily introduced into the system and enlarged using a tangible lens. We describe the teleconferencing interface and present results from a pilot user study