A deterministic algorithm for fitting a step function to a weighted point-set

Given a set of n points in the plane, each point having a positive weight, and an integer k>0, we present an optimal O(n \log n)-time deterministic algorithm to compute a step function with k steps that minimizes the maximum weighted vertical distance to the input points. It matches the expected time bound of the best known randomized algorithm for this problem. Our approach relies on Cole's improved parametric searching technique.Comment: 5 pages, 2 figure

Morphologie et reproduction des plantes le long des gradients altitudinaux

Sites valaisans: Salgesch, Mont Rogneux

Plant traits co-vary with altitude in grasslands and forests in the European Alps

Biological traits that are advantageous under specific ecological conditions should be present in a large proportion of the species within an ecosystem, where those specific conditions prevail. As climatic conditions change, the frequency of certain traits in plant communities is expected to change with increasing altitude. We examined patterns of change for 13 traits in 120 exhaustive inventories of plants along five altitudinal transects (520-3,100m a.s.l.) in grasslands and in forests in western Switzerland. The traits selected for study represented the occupation of space, photosynthesis, reproduction and dispersal. For each plot, the mean trait values or the proportions of the trait states were weighted by species cover and examined in relation to the first axis of a PCA based on local climatic conditions. With increasing altitude in grasslands, we observed a decrease in anemophily and an increase in entomophily complemented by possible selfing; a decrease in diaspores with appendages adapted to ectozoochory, linked to a decrease in achenes and an increase in capsules. In lowlands, pollination and dispersal are ensured by wind and animals. However, with increasing altitude, insects are mostly responsible for pollination, and wind becomes the main natural dispersal vector. Some traits showed a particularly marked change in the alpine belt (e.g. the increase of capsules and the decrease of achenes), confirming that this belt concentrates particularly stressful conditions to plant growth and reproduction (e.g. cold, short growing season) that constrain plants to a limited number of strategies. One adaptation to this stress is to limit investment in dispersal by producing capsules with numerous, tiny seeds that have appendages limited to narrow wings. Forests displayed many of the trends observed in grasslands but with a reduced variability that is likely due to a shorter altitudinal gradien

Genealogical Population-Based Training for Hyperparameter Optimization

HyperParameter Optimization (HPO) aims at finding the best HyperParameters (HPs) of learning models, such as neural networks, in the fastest and most efficient way possible. Most recent HPO algorithms try to optimize HPs regardless of the model that obtained them, assuming that for different models, same HPs will produce very similar results. We break free from this paradigm and propose a new take on preexisting methods that we called Genealogical Population Based Training (GPBT). GPBT, via the shared histories of "genealogically"-related models, exploit the coupling of HPs and models in an efficient way. We experimentally demonstrate that our method cuts down by 2 to 3 times the computational cost required, generally allows a 1% accuracy improvement on computer vision tasks, and reduces the variance of the results by an order of magnitude, compared to the current algorithms. Our method is search-algorithm agnostic so that the inner search routine can be any search algorithm like TPE, GP, CMA or random search

Matériau composite à base de matière naturelle lignocellulosique

L'invention concerne un matériau composite à base de particules d'une matière naturelle lignocellulosique, notamment de bois. Ces particules sont dispersées dans une matrice d'un polymère thermoplastique choisi parmi les polyamides et les copolymères à blocs comprenant au moins un bloc polyamide. Un procédé de préparation de ce matériau composite comprend le mélange desdites particules et dudit polymère thermoplastique et la mise en forme de ce mélange

Approche probabiliste pour l'analyse des tolérances des produits hyperstatiques – application à une pompe

International audienceL'analyse des tolérances des mécanismes a pour but d'évaluer la qualité du produit lors de sa phase de conception. La technique consiste à déterminer si, dans une production de grandes séries, le taux de rebuts des mécanismes défaillants est acceptable. Deux conditions doivent être vérifiées: une condition d'assemblage et une condition fonctionnelle. La méthode existante se base sur le couplage de la simulation de Monte Carlo avec un algorithme d'optimisation qui est très couteuse en temps de calcul. De ce fait, nous proposons une méthode plus efficace basée sur des approches probabilistes. Ces travaux ont permis le développement d'une nouvelle méthode de résolution basée sur la méthode de fiabilité système FORM (First Order Reliability Method) système. Cette méthode permet de traiter uniquement le problème fonctionnel. Ces performances sont illustrées sur un cas industriel : une pompe à débit variable

Behavior of epoxy bonded bars in concrete affected by alkali-silica reaction

Installation of drilled-in epoxy-bonded reinforcing bars is generally an effective strengthening method to increase the flexural and shear capacities of deficient concrete structures. However, most of the available studies characterizing the bond behavior of epoxy bonded bars in concrete have been carried out on sound concrete elements—that is, without any pathological material damage. This raises the question of bond capacities in existing damaged elements. This study investigates the influence of alkali-silica reaction (ASR) on the capacity of post-installed reinforcing bars. ASR is a deleterious mechanism that causes expansion and cracking in the affected concrete elements. Pullout tests on post-installed reinforcing bars having embedded lengths of 2db, 4db, and 5db with 15M reinforcing bars (db = 15.9 mm [0.626 in.]) have demonstrated a drop-in bond strength when concrete is affected by ASR. In addition, the study revealed that the progression of concrete expansion due to ASR may lead to some confinement of the post-installed reinforcing bar and possibly increases the bond strength

Modelling a Multi-Modal Logistic Network with Agents and Dynamic Graphs

International audienceThis paper presents a model of a logistic system. Our goal is to understand how such a system (with numerous stakeholders) behaves and evolves according to different constraints or scenarios. We adopted a complex system approach which leads us to propose an agent-based model coupled with dynamic graphs. It allows us to represent the properties, constraints and behaviours at a local level of a logistic system in order to reproduce the global behaviours thanks to the simulation in a dynamic context. The simulation (which uses data about the Seine axis) allows to test different scenarios in order to understand how local decisions impact the whole system. For example, this work presents the evolution of the system at the opening of the Seine-Nord Europe Canal. Indeed, this canal is a real major project for Europe, and has numerous economical stakes. So, we first describe the traffic evolution on the multi-modal transportation network (see figures 1 to 4). Then, we observe different other measures (evolution of costs, transportation mode share). Thanks to these analyses, we show that the Seine-Nord Europe Canal should promote the use of the river barges and reduce financial costs. In the same time, it could modify the respective shares of the northern European ports

Study of bond between epoxy, steel reinforcing bars and concrete affected by alkali-silica reaction

Installation of drilled-in epoxy bonded reinforcing barsis generally an effective strengthening method for deficient concretestructures. However, this method of rehabilitation has largely been studied and tested on sound concrete elements, i.e. without any pathological damage, which raisesthe question of bond capabilities inexisting damaged elements. This investigation studies the influence of alkali-silica reaction (ASR) onthe capacity of epoxy bonded anchors. ASR, which is very common in eastern Canada, results from the chemical reaction between the alkali hydroxides in the concrete’s pore solution and some siliceous mineral phases inthe aggregates. Pull-out tests on epoxy bonded anchors havingembedded lengths offourtimes the bar diameter(Ø= 16 mm)have demonstrated a drop in bond strength when concrete is affected by ASR. In addition, the study revealed that the progression of concrete expansion due to ASR, leads to a confinement of the epoxy bonded anchor and increases the bond strength. These conclusions are therefore considered for the development of a model for the design of epoxy bonded anchors in existing concrete infrastructure affected by ASR

Current-Based Detection of Mechanical Unbalance in an Induction Machine Using Spectral Kurtosis with Reference

This article explores the design, on-line, of an electrical machine’s healthy reference by means of statistical tools. The definition of a healthy reference enables the computation of normalized fault indicators whose value is independent of the system’s characteristics. This is a great advantage when diagnosing a broad range of systems with different power, coupling, inertia, load, etc. In this paper, an original method called spectral kurtosis with reference is presented in order to designa system’s healthy reference. Its principle is first explained on asynthetic signal. This approach is then evaluated for mechanicalunbalance detection in an induction machine using the stator currents instantaneous frequency. The normalized behaviour ofthe proposed indicator is then confirmed for different operatingconditions and its robustness with respect to load variationsis demonstrated. Finally, the advantages of using a statisticalindicator based on a healthy reference compared to a raw faultsignature are discussed