Quasiperiodicity and non-computability in tilings

We study tilings of the plane that combine strong properties of different nature: combinatorial and algorithmic. We prove existence of a tile set that accepts only quasiperiodic and non-recursive tilings. Our construction is based on the fixed point construction; we improve this general technique and make it enforce the property of local regularity of tilings needed for quasiperiodicity. We prove also a stronger result: any effectively closed set can be recursively transformed into a tile set so that the Turing degrees of the resulted tilings consists exactly of the upper cone based on the Turing degrees of the later.Comment: v3: the version accepted to MFCS 201

Composite mirror facets for ground based gamma ray astronomy

Composite mirrors for gamma-ray astronomy have been developed to fulfill the specifications required for the next generation of Cherenkov telescopes represented by CTA (Cherenkov Telescope Array). In addition to the basic requirements on focus and reflection efficiency, the mirrors have to be stiff, lightweight, durable and cost efficient. In this paper, the technology developed to produce such mirrors is described, as well as some tests that have been performed to validate them. It is shown that these mirrors comply with the needs of CTA, making them good candidates for use on a significant part of the array.Comment: 16 pages, 13 figures, accepted to be published on NIM

A double continuum hydrological model for glacier applications

Peer reviewedPublisher PD

Cocaine Addiction as a Homeostatic Reinforcement Learning Disorder

Drug addiction implicates both reward learning and homeostatic regulation mechanisms of the brain. This has stimulated 2 partially successful theoretical perspectives on addiction. Many important aspects of addiction, however, remain to be explained within a single, unified framework that integrates the 2 mechanisms. Building upon a recently developed homeostatic reinforcement learning theory, the authors focus on a key transition stage of addiction that is well modeled in animals, escalation of drug use, and propose a computational theory of cocaine addiction where cocaine reinforces behavior due to its rapid homeostatic corrective effect, whereas its chronic use induces slow and long-lasting changes in homeostatic setpoint. Simulations show that our new theory accounts for key behavioral and neurobiological features of addiction, most notably, escalation of cocaine use, drug-primed craving and relapse, individual differences underlying dose-response curves, and dopamine D2-receptor downregulation in addicts. The theory also generates unique predictions about cocaine self-administration behavior in rats that are confirmed by new experimental results. Viewing addiction as a homeostatic reinforcement learning disorder coherently explains many behavioral and neurobiological aspects of the transition to cocaine addiction, and suggests a new perspective toward understanding addiction

Simulating nitrogen budgets in complex farming systems using INCA: calibration and scenario analyses for the Kervidy catchment (W. France)

International audienceThe integrated nitrogen model INCA (Integrated Nitrogen in Catchments) was used to analyse the nitrogen dynamics in a small rural catchment in Western France. The agrosystem studied is very complex, with: extensive use of different organic fertilisers, a variety of crop rotations, a structural excess of nitrogen (i.e. more animal N produced by the intensive farming than the N requirements of the crops and pastures), and nitrate retention in both hydrological stores and riparian zones. The original model features were adapted here to describe this complexity. The calibration results are satisfactory, although the daily variations in stream nitrate are not simulated in detail. Different climate scenarios, based on observed climate records, were tested; all produced a worsening of the pollution in the short term. Scenarios of alternative agricultural practices (reduced fertilisation and catch crops) were also analysed, suggesting that a reduction by 40% of the fertilisation combined with the introduction of catch crops would be necessary to stop the degradation of water quality. Keywords: diffuse pollution, nitrate, climate change, mode

Planting material : what strategy for planters ? : DxP seed is not only DxP seed

For a tropical plant, the oil palm commodity chain includes the peculiarity of possessing a major seed production sector for reasons that are primarily genetic. Planters are always concerned about the reliability and value of the material they plant. Most oil palm plantations (around 70%) belong to large agroindustrial enterprises, but family smallholdings are also developing strongly and are in the majority in numerous countries. However, access to seeds and to information on seeds is not organized in the same way for agro-industries as for smallholders, especially if the latter are in isolated locations. In fact, it is difficult to organize seed distribution to smallholders, and very often they will depend on agro-industry strategy or middlemen networks for their own plantation. Another peculiarity of the oil palm seed market is, despite state or public organization attempts to organize the market, the virtual total absence of guarantees for buyers. It is difficult, if not impossible, to evaluate the quality of the research conducted by breeders. Have commercial seeds, based on scientific criteria, such as yield components, resistance to diseases, to drought, to altitude, to low temperatures, been really developed on these criteria with well-defined and adapted experimental designs? In addition, the seed production strategies, necessary for transferring genetic progress observed in research stations into the commercial seeds, are not all reliable. And, last but not least, the technical quality of production can lead to a not inconsiderable percentage of weak seeds due to uncontrolled pollen contamination. The only guarantee today comes from the relationships of confidence established year after year between breeders/distributors and growers. In this respect, the initial strategy for agro-industry is very often to diversify supply sources in order to guarantee their plantations an "average" value. In a second step, these groups almost always aim to become seed producers themselves. To that end, they can either link-up with breeders to acquire production licences, or if they are seeking greater independence they may attempt to procure parent material and become breeders in their own right. In either case, they must take on a major risk of ending up with a planting material that might not perform well, as the different materials available on the market display substantial production differences that can exceed 20%. In such a case, the very future of a major industrial group could be jeopardized. In these fields, research can lead to some proposals: to help public institutions to define a seed certification policy, molecular biology offers some interesting prospects for certifying seed quality (contamination rates and genetic origin), and social science could develop effective communication methods towards planters. (Résumé d'auteur