751 research outputs found
Computing automorphic forms on Shimura curves over fields with arbitrary class number
We extend methods of Greenberg and the author to compute in the cohomology of
a Shimura curve defined over a totally real field with arbitrary class number.
Via the Jacquet-Langlands correspondence, we thereby compute systems of Hecke
eigenvalues associated to Hilbert modular forms of arbitrary level over a
totally real field of odd degree. We conclude with two examples which
illustrate the effectiveness of our algorithms.Comment: 15 pages; final submission to ANTS I
On the existence of abelian surfaces with everywhere good reduction
Let be a positive discriminant such that has narrow class one, and an abelian surface of -type with everywhere good reduction. Assuming that is modular, we show that is either an -surface or is a base change from of an abelian surface such that , except for and . In the latter case, we show that there are indeed abelian surfaces with everywhere good reduction over for and , which are non-isogenous to their Galois conjugates. These are the first known such examples
An intriguing hyperelliptic Shimura curve quotient of genus 16
Let be the maximal totally real subfield of , the cyclotomic field of nd roots of unity. Let be the quaternion algebra over ramified exactly at the unique prime above and 7 of the real places of . Let be a maximal order in , and the Shimura curve attached to . Let , where is the unique Atkin-Lehner involution on . We show that the curve has several striking features. First, it is a hyperelliptic curve of genus , whose hyperelliptic involution is exceptional. Second, there are Weierstrass points on , and exactly half of these points are CM points; they are defined over the Hilbert class field of the unique CM extension of class number contained in , the cyclotomic field of th roots of unity. Third, the normal closure of the field of -torsion of the Jacobian of is the Harbater field , the unique Galois number field unramified outside and , with Galois group . In fact, the Jacobian has the remarkable property that each of its simple factors has a -torsion field whose normal closure is the field . Finally, and perhaps the most striking fact about is that it is also hyperelliptic over
A three DOF linear ultrasonic motor for transport and micropositionning.
International audienceThe paper deals with the study and use of a linear ultrasonic motor at low voltages. Standing waves are generated in a 64 x 38 x 2.5 mm3 vibrator by 20 piezoelectric ceramics and converted into sliding motions by the friction between four legs and the worktop : translations and rotations are achieved. The speed of the motor is studied according to the amplitude and frequency of the driving voltage as well as the mass of the load. Then, a model of the system is retrieved for some set points and validated using a position control. According to its interesting performances for transport and positioning, the motor is used to motorize a moving palet for the transfer of parts in a microassembly workcell
Contribution du SIG Ă la PrĂ©vention et Ă la Gestion des Risques dâinondation dans le District de Bamako au Mali
En raison de sa situation gĂ©ographique, la ville de Bamako reste fortement vulnĂ©rable aux risques dâinondations. La prĂ©sente Ă©tude a pour objectif de mettre en exergue un outil opĂ©rationnel et Ă©volutif dâaide Ă la prise de dĂ©cisions en matiĂšre de prĂ©vention et de gestion des risques dâinondations dans le District de Bamako en RĂ©publique du Mali. Il sâagit dâĂ©laborer Ă partir du SystĂšme dâInformation GĂ©ographique des grilles dâanalyse et dâĂ©valuation permettant aux dĂ©cideurs de mieux apprĂ©hender les risques naturels. La mĂ©thodologie adoptĂ©e sâest appuyĂ©e sur une approche par tĂ©lĂ©dĂ©tection appuyĂ©e par des enquĂȘtes et relevĂ©s de terrain. Les rĂ©sultats de lâĂ©tude ont montrĂ© que les nombreux amĂ©nagements rĂ©alisĂ©s Ă travers la ville grĂące aux politiques publiques urbaines, ont entrainĂ© dâimportants changements spatiaux-temporels. Toutefois, des occupations anarchiques rĂšgnent toujours dans la ville de Bamako, notamment sur les berges des cours dâeau qui constituent Ă priori des zones inondables. Des constructions existent dans les zones Ă risque oĂč la vulnĂ©rabilitĂ© des populations reste forte. Les cartes rĂ©alisĂ©es indiquent les zones Ă stress et orientent les dĂ©cideurs dans les options dâamĂ©nagement pour une rĂ©duction des risques dâinondation dans les annĂ©es Ă venir au travers de la planification urbaine et de la participation des populations touchĂ©es dans lâĂ©laboration des stratĂ©gies dâadaptation.
Due to its geographical location, the city of Bamako remains highly vulnerable to flood risk. The objective of this study is to highlight an operational and evolving decision support tool for flood risk prevention and management in the Bamako District of the Republic ofMali. This is to develop from the Geographic Information System grids analysis and evaluation for decision-makers to better understand natural risks. The methodology adopted was based on an exploratory approach sustained by field surveys and the analysis of cartographic data. The results of the study showed that the numerous developments carried out throughout the city by urban public policies have led to a great spatial "metamorphosis". However, anarchic occupations are still a reality in the city of Bamako, especially on the banks of rivers are a priori vulnerable areas. Buildings exist in risk areas where people's vulnerability remains high. The maps produced indicate areas of stress and guide decision makers in management options for flood risk reduction in the coming years through urban planning and the participation of affected populations in the development of adaptation strategies
- âŠ