On the semiclassical Laplacian with magnetic field having self-intersecting zero set

This paper is devoted to the spectral analysis of the Neumann realization of the 2D magnetic Laplacian with semiclassical parameter h > 0 in the case when the magnetic field vanishes along a smooth curve which crosses itself inside a bounded domain. We investigate the behavior of its eigenpairs in the limit h $\rightarrow$ 0. We show that each crossing point acts as a potential well, generating a new decay scale of h 3/2 for the lowest eigenvalues, as well as exponential concentration for eigenvectors around the set of crossing points. These properties are consequences of the nature of associated model problems in R 2 for which the zero set of the magnetic field is the union of two straight lines. In this paper we also analyze the spectrum of model problems when the angle between the two straight lines tends to 0

Méthode de correction des erreurs de mesure appliquée à un système FASTRAK 3SPACE

La méthode de correction développée au LIO permet de réduire l’erreur de mesure en translation et en rotation produites par des distorsions électromagnétiques et qui affectent la précision des capteurs Fastrak. La méthode permet la caractérisation des erreurs de mesure d’un champ électromagnétique et l’étalonnage d’un volume de 0,458 m3 en moins de 35 secondes. Il est possible de réduire l’erreur moyenne d’un ensemble de mesures, sans en augmenter la variabilité, pour autant que l’erreur de mesure ne dépasse pas 35 mm en translation. Nous avons réussi à réduire cette erreur à 6,1 mm +/- 3,0 mm en translation et à 0,49° +/- 0,17° en rotation avec seulement 1000 étalons sur un ensemble de 712 mesures. La méthode fonctionne sur un nombre illimité de mesures pouvant se situer jusqu’à 115 cm de l’émetteur. Le nombre de mesures étalons utilisées à montrer qu’il influence les performances de la méthode de correction, ce nombre se situant entre 100 et 1000 mesures. À 115 cm de l’émetteur, les meilleurs résultats ont été obtenus en divisant le volume global d’étalonnage en deux sous volumes distinctes. Dans ce cas, le calcul des polynômes se fait donc sur les sections plus petites, ce qui permet d’éliminer les distorsions aux frontières du volume d’étalonnage dans les conditions optimales de la méthode de correction du LIO. Pour des distances inférieures à 75 cm de l’émetteur, l’utilisation d’un seul ensemble de polynômes est possible

The Vestibular Implant: Quo Vadis?

Objective: To assess the progress of the development of the vestibular implant (VI) and its feasibility short-term. Data sources: A search was performed in Pubmed, Medline, and Embase. Key words used were “vestibular prosth*” and “VI.” The only search limit was language: English or Dutch. Additional sources were medical books, conference lectures and our personal experience with per-operative vestibular stimulation in patients selected for cochlear implantation. Study selection: All studies about the VI and related topics were included and evaluated by two reviewers. No study was excluded since every study investigated different aspects of the VI. Data extraction and synthesis: Data was extracted by the first author from selected reports, supplemented by additional information, medical books conference lectures. Since each study had its own point of interest with its own outcomes, it was not possible to compare data of different studies. Conclusion: To use a basic VI in humans seems feasible in the very near future. Investigations show that electric stimulation of the canal nerves induces a nystagmus which corresponds to the plane of the canal which is innervated by the stimulated nerve branch. The brain is able to adapt to a higher baseline stimulation, while still reacting on a dynamic component. The best response will be achieved by a combination of the optimal stimulus (stimulus profile, stimulus location, precompensation), complemented by central vestibular adaptation. The degree of response will probably vary between individuals, depending on pathology and their ability to adapt

The effect of semi-natural habitats on aphids and their natural enemies across spatial and temporal scales

Semi-natural habitats in agricultural landscapes are generally assumed to enhance the biological control of insect pests based on native beneficial insects, by providing alternative prey and hosts, resources and refuges for overwintering. We hypothesized that natural enemies of winter wheat aphids should arrive sooner in fields near semi-natural habitats. We compared aphid, hoverfly (larvae and eggs) and parasitized aphid (mummies) abundances in 54 winter wheat fields located in southern France from 2003 to 2007. Six surveys were recorded each spring and were split into the early period (defined as the period before the peak of aphid growth) and the late period (after the peak). The wheat fields differed by their surrounding landscape composition measured as the proportion of semi-natural habitats (woods, hedges and grasslands), at three different spatial scales: 200 m, 500 m, and 1200 m. Despite great variability in abundance data between years, the abundance of hoverflies appeared more sensitive to landscape composition than aphid abundance was. Early abundance for both aphids and hoverflies was positively related to wood cover, but not late abundance in spring. The abundance of hoverflies was positively related to hedge and grassland cover at all spatial scales and both periods considered. Aphid parasitism was higher near hedges at the small spatial scale late in the spring. Our results confirmed that higher proportions of semi-natural habitats in agricultural landscapes enhance the biological control of pests, but this effect depends on the spatial scale, the time period in the spring and the natural enemies considered

Dispositifs de gouvernance territoriale durable en agriculture Analyse de trois situations en France et au Brésil

La question de la gouvernance est devenue depuis quelques années une préoccupation grandissante des acteurs territoriaux qui cherchent à associer l’ensemble des parties-prenantes à la définition des actions de développement durable. C’est aussi un nouveau champ d’investigation pour les chercheurs qui essaient de comprendre pourquoi et comment les acteurs de terrain passent d’un mode de coordination hiérarchique à un mode plus participatif. Ce passage ne va pas de soi, il nécessite une recomposition. Les acteurs vont soit s’approprier des dispositifs et outils déjà existants et les « bricoler », soit en inventer de nouveaux pour répondre aux enjeux de développement durable. Nous proposons une analyse des comportements d’acteurs agricoles vis-à-vis de dispositifs et outils de gouvernance. Nous illustrons ce travail à partir de trois études de cas. Cette mise en perspective nous amène à conclure que le développement durable, pour qu’il soit mis en œuvre localement, nécessite que les acteurs (ré)définissent ses enjeux et ses objectifs à leur propre niveau d’action.For the last decade, governance issues become of a growing interest for local actors which seek to gather stakeholders around sustainable development actions. Likewise researchers try to understand why and how local actors move from hierarchical modes of co-ordination to a distributed and more participating ones. The shift is not so obvious and involve recombining processes. Local actors have two alternatives: to appropriate existing devices and tools and “tinker” them or to invent new ones to deal with the sustainable development stakes. The paper suggest an analysis of farming actors behaviour facing governance devices and tools, through three case studies. The authors conclude that carrying out sustainable development at the local scale involve local actors planning out its stakes and objectives at the action local level

Dispositifs de gouvernance territoriale durable en agriculture Analyse de trois situations en France et au Brésil

La question de la gouvernance est devenue depuis quelques années une préoccupation grandissante des acteurs territoriaux qui cherchent à associer l’ensemble des parties-prenantes à la définition des actions de développement durable. C’est aussi un nouveau champ d’investigation pour les chercheurs qui essaient de comprendre pourquoi et comment les acteurs de terrain passent d’un mode de coordination hiérarchique à un mode plus participatif. Ce passage ne va pas de soi, il nécessite une recomposition. Les acteurs vont soit s’approprier des dispositifs et outils déjà existants et les « bricoler », soit en inventer de nouveaux pour répondre aux enjeux de développement durable. Nous proposons une analyse des comportements d’acteurs agricoles vis-à-vis de dispositifs et outils de gouvernance. Nous illustrons ce travail à partir de trois études de cas. Cette mise en perspective nous amène à conclure que le développement durable, pour qu’il soit mis en œuvre localement, nécessite que les acteurs (ré)définissent ses enjeux et ses objectifs à leur propre niveau d’action.For the last decade, governance issues become of a growing interest for local actors which seek to gather stakeholders around sustainable development actions. Likewise researchers try to understand why and how local actors move from hierarchical modes of co-ordination to a distributed and more participating ones. The shift is not so obvious and involve recombining processes. Local actors have two alternatives: to appropriate existing devices and tools and “tinker” them or to invent new ones to deal with the sustainable development stakes. The paper suggest an analysis of farming actors behaviour facing governance devices and tools, through three case studies. The authors conclude that carrying out sustainable development at the local scale involve local actors planning out its stakes and objectives at the action local level

Spherical deconvolution of multichannel diffusion MRI data with non-Gaussian noise models and spatial regularization

Spherical deconvolution (SD) methods are widely used to estimate the intra-voxel white-matter fiber orientations from diffusion MRI data. However, while some of these methods assume a zero-mean Gaussian distribution for the underlying noise, its real distribution is known to be non-Gaussian and to depend on the methodology used to combine multichannel signals. Indeed, the two prevailing methods for multichannel signal combination lead to Rician and noncentral Chi noise distributions. Here we develop a Robust and Unbiased Model-BAsed Spherical Deconvolution (RUMBA-SD) technique, intended to deal with realistic MRI noise, based on a Richardson-Lucy (RL) algorithm adapted to Rician and noncentral Chi likelihood models. To quantify the benefits of using proper noise models, RUMBA-SD was compared with dRL-SD, a well-established method based on the RL algorithm for Gaussian noise. Another aim of the study was to quantify the impact of including a total variation (TV) spatial regularization term in the estimation framework. To do this, we developed TV spatially-regularized versions of both RUMBA-SD and dRL-SD algorithms. The evaluation was performed by comparing various quality metrics on 132 three-dimensional synthetic phantoms involving different inter-fiber angles and volume fractions, which were contaminated with noise mimicking patterns generated by data processing in multichannel scanners. The results demonstrate that the inclusion of proper likelihood models leads to an increased ability to resolve fiber crossings with smaller inter-fiber angles and to better detect non-dominant fibers. The inclusion of TV regularization dramatically improved the resolution power of both techniques. The above findings were also verified in brain data

Genome-wide gene expression profiling analysis of Leishmania major and Leishmania infantum developmental stages reveals substantial differences between the two species

<p>Abstract</p> <p>Background</p> <p><it>Leishmania </it>parasites cause a diverse spectrum of diseases in humans ranging from spontaneously healing skin lesions (e.g., <it>L. major</it>) to life-threatening visceral diseases (e.g., <it>L. infantum</it>). The high conservation in gene content and genome organization between <it>Leishmania major </it>and <it>Leishmania infantum </it>contrasts their distinct pathophysiologies, suggesting that highly regulated hierarchical and temporal changes in gene expression may be involved.</p> <p>Results</p> <p>We used a multispecies DNA oligonucleotide microarray to compare whole-genome expression patterns of promastigote (sandfly vector) and amastigote (mammalian macrophages) developmental stages between <it>L. major </it>and <it>L. infantum</it>. Seven per cent of the total <it>L. infantum </it>genome and 9.3% of the <it>L. major </it>genome were differentially expressed at the RNA level throughout development. The main variations were found in genes involved in metabolism, cellular organization and biogenesis, transport and genes encoding unknown function. Remarkably, this comparative global interspecies analysis demonstrated that only 10–12% of the differentially expressed genes were common to <it>L. major </it>and <it>L. infantum</it>. Differentially expressed genes are randomly distributed across chromosomes further supporting a posttranscriptional control, which is likely to involve a variety of 3'UTR elements.</p> <p>Conclusion</p> <p>This study highlighted substantial differences in gene expression patterns between <it>L. major </it>and <it>L. infantum</it>. These important species-specific differences in stage-regulated gene expression may contribute to the disease tropism that distinguishes <it>L. major </it>from <it>L. infantum.</it></p