An expansion of the field modulus suitable for the description of strong field gradients in axisymmetric magnetic fields: Application to single-sided magnet design, field mapping and STRAFI

International audienceMapping (or plotting) the magnetic field has a critical importance for the achievement of the homogeneous magnetic field necessary to standard MR experiments. A powerful tool for this purpose is the Spherical Harmonic Expansion (SHE), which provides a simple way to describe the spatial variations of a field in free space. Well-controlled non-zero spatial variations of the field are critical to MRI. The resolution of the image is directly related to the strength of the gradient used to encode space. As a result, it is desirable to have strong variations of the field. In that case, the SHE cannot be used as is, because the field modulus variations are affected by the variations of all components of the field. In this paper, we propose a method based on the SHE to characterize such variations, theoretically and experimentally, in the limit of an axisymmetric magnetic field. Practical applications of this method are proposed through the examples of single-sided magnet design and characterization, along with Stray-Field Imaging (STRAFI)

Simple method for the generation of multiple homogeneous field volumes inside the bore of superconducting magnets

International audienceStandard Magnetic Resonance magnets produce a single homogeneous field volume, where the analysis is performed. Nonetheless, several modern applications could benefit from the generation of multiple homogeneous field volumes along the axis and inside the bore of the magnet. In this communication, we propose a straightforward method using a combination of ring structures of permanent magnets in order to cancel the gradient of the stray field in a series of distinct volumes. These concepts were demonstrated numerically on an experimentally measured magnetic field profile. We discuss advantages and limitations of our method and present the key steps required for an experimental validation

La production porcine dans la Loire et le rôle des groupements de producteurs : compte-rendu d'enquête

Diffusion du document : INRA Station d'Economie et Sociologie rurales 65 rue de Saint-Brieuc 35042 Rennes Cedex (FRA)Ce document est le rapport d'une enquête effectuée dans le département de la Loire en juillet 1978 sur la situation de la production porcine et particulièrement la place des groupements de producteurs

Late-glacial and postglacial fluctuations of the tree limits in the Mediterranean Pyrenees : the use of pollen ratios

International audienceThe use of pollen ratios to estimate the fluctuations of the late-glacial and holocene tree-limits and the timber line is discussed. An attempt is made with fossil data from some sites from the eastern part of the Pyrenees. Comparisons with the records of Pinus stomata indicating local occurence of Pinus show a good correlation between the two complementary approaches and emphasize the value of the pollen ratio. However, in all cases, the components of the ratio have to be discussed. For reconstructing the timber line, local floristic studies are necessary so that the most appropriate pollen indicators can be chosen

Type regions F-zg and F-r, the northen slope of the Pyrenees

From the Atlantic Ocean to the Mediterranean Sea, the Pyrenees form the westernmost mountain chain of E-W orientation in the south of western Europe. We can distinguish two regions : an Atlantic zone and a Pyrenean zone. The Pyrenean chain shows in each of these zones a great diversity of local climatic characteristics. This paper attempts to illustrate the methodological approach we need to reach a palaeoecological synthesis. Five or six studied sites in different vegetation belts of the Chaîne des Hurtières are presented

AMCIS 2021 Awards and Closing Ceremony

This is a video recording of the AMCIS 2021 Awards and Closing Ceremony

Quark-Squark Alignment Revisited

We re-examine the possibility that the solution to the supersymmetric flavor problem is related to small mixing angles in gaugino couplings induced by approximate horizontal Abelian symmetries. We prove that, for a large class of models, there is a single viable structure for the down quark mass matrix with four holomorphic zeros. Consequently, we are able to obtain both lower and upper bounds on the supersymmetric mixing angles and predict the contributions to various flavor changing neutral current processes. We find that the most likely signals for alignment are $\Delta m_D$ close to the present bound, significant CP violation in $D^0-\bar{D^0}$ mixing, and shifts of order a few percent in various CP asymmetries in $B^0$ and $B_s$ decays. In contrast, the modifications to radiative B decays, to $\epsilon^\prime/\epsilon$ and to $K\to\pi\nu\bar\nu$ decays are small. We further investigate a new class of alignment models, where supersymmetric contributions to flavor changing processes are suppressed by both alignment and RGE-induced degeneracy.Comment: 20 pages, 3 figure

Histoire des forêts du versant nord des Pyrénées au cours des 30000 dernières années

Les recherches playnologiques réalisées dans le versant nord des Pyrénées ainsi que les données anthracologiques disponibles et les études de macrorestes végétaux permettent de décrire les étapes de la mise en place des principales essences forestières au cours des 30000 dernières années. Dans les Pyrénées centrales, avant 30000 BP, l'épicéa était bien développé. Les données anthracologiques permettent de penser qu'il a disparu des Pyrénées vers 18000-17000 BP. Entre 11000 BP et 10000 BP, l'ultime phase de dégradation climatique de la fin du dernier épisode glaciaire, le Dryas récent, a davantage affecté la couverture végétale des Pyrénées méditerranéennes que celle de la moitié nord occidentale. Au Postglaciaire, le sapin se développe précocement dans la partie orientale de la chaîne et beaucoup plus tard dans la partie occidentale. L'homme agit très tôt sur le milieu montagnard, dès 6200 BP dans les Pyrénées méditerranéennes. Son ection s'accentue particulièrement vers 4000 BP, au Moyen Age, puis au 16è-17è et 18 è siècles lors du développement des forges, déterminant d'importantes modifications phytogéographiques, notamment une extension du hêtre aux dépens du sapin