942 research outputs found
Minimum energy configurations of classical charges: Large N asymptotics
We study minimum energy configurations of particles in of charge
-1 (`electrons') in the potential of particles of charges
(`atomic nuclei'). In a suitable large-N limit, we determine the asymptotic
electron distribution explicitly, showing in particular that the number of
electrons surrounding each nucleus is asymptotic to the nuclear charge
("screening"). The proof proceeds by establishing, via Gamma-convergence, a
coarse-grained variational principle for the limit distribution, which can be
solved explicitly.Comment: To appear in Applied Mathematics Research Expres
Antenna Gain and Link Budget for Waves Carrying Orbital Angular Momentum (OAM)
This paper addresses the RF link budget of a communication system using
unusual waves carrying an orbital angular momentum (OAM) in order to clearly
analyse the fundamental changes for telecommunication applications. The study
is based on a typical configuration using circular array antennas to transmit
and receive OAM waves. For any value of the OAM mode order, an original
asymptotic formulation of the link budget is proposed in which equivalent
antenna gains and free-space losses appear. The formulations are then validated
with the results of a commercial electromagnetic simulation software. By this
way, we also show how our formula can help to design a system capable of
superimposing several channels on the same bandwidth and the same polarisation,
based on the orthogonality of the OAM. Additional losses due to the use of this
degree of freedom are notably clearly calculated to quantify the benefit and
drawback according to the case.Comment: 33 pages, 11 figure
William Morris et les arts du livre
La derniĂšre partie de la vie de William Morris est associĂ©e Ă lâimage de la Kelmscott Press, qui peut ĂȘtre perçue comme une synthĂšse entre lâamour des livres quâil a eu toute sa vie et la passion tout aussi longue quâil a entretenue vis-Ă -vis des techniques de fabrication manuelles. Son sens de la beautĂ©, issu de lâarchitecture mĂ©diĂ©vale, a dictĂ© les choix esthĂ©tiques effectuĂ©s pour les livres, qui Ă leur tour ont dictĂ© les techniques retenues par la Kelmscott Press, caractĂ©risĂ©es par le soin extrĂȘme apportĂ© aux dĂ©tails. Il a su combiner la grande connaissance quâil avait des techniques traditionnelles du livre avec le savoir-faire de certains des plus grands artistes et artisans de son temps pour produire des ouvrages qui sâapprochaient de trĂšs prĂšs de sa dĂ©finition exigeante du « livre idĂ©al ».The last phase of William Morrisâs life is associated with the Kelmscott Press, which can be seen as providing a synthesis between his life-long love of books and his equally durable passion for manual methods of production. His sense of beauty, derived from medieval architecture, dictated the choices made for the appearance of the books, which in turn dictated the technical choices made by the Press, characterised by extreme attention to detail. He was able to combine his own extensive knowledge of traditional book techniques with the skills of some of the most prominent artists and craftsmen of his time to produce volumes which were the nearest thing to his exacting definition of âthe ideal bookâ
Juliette Pattinson, Behind Enemy Lines: Gender, Passing and the Special Operations Executive in the Second World War, Cultural History of Modern War Series, Manchester: Manchester University Press, 2007
Les crĂ©cibistes qui sâintĂ©ressent au domaine baptisĂ© War Studies (Ă ne pas confondre avec Military History, Ă la fois plus facile Ă saisir et plus aisĂ© Ă traduire) savent quâil est en pleine expansion dans les universitĂ©s britanniques. Autrefois, le Kingâs College de Londres en avait le quasi monopole. Aujourdâhui, il existe des centres trĂšs actifs Ă Birmingham, Ădimbourg et Glasgow. Indirectement, Ă©galement, des dĂ©pĂŽts dâarchive comme Mass Observation Ă Brighton et des groupes de recherche d..
Amélioration du découplage inter-éléments par surface haute impédance pour des antennes réseaux GNSS compactes
L'objectif de cette thÚse est de proposer une solution à base de Surface Haute Impédance (HIS) permettant de découpler les éléments rayonnants d'un réseau GNSS pour améliorer un systÚme CRPA (Controlled Reception Pattern Antenna). Nous concevons alors une HIS possédant une taille de cellule élémentaire inférieure à lambda0/14 et caractérisons sa bande interdite électromagnétique (EBG). Un patch est choisi comme antenne élémentaire du réseau CRPA. Différentes configurations de mise en réseau incorporant des HIS idéales ou non sont étudiées pour affiner la conception de notre antenne élémentaire. Nous menons ensuite une étude détaillée des phénomÚnes résonants dans les HIS. Nous proposons alors l'utilisation de résonateurs originaux et compacts inspirés des HIS. Finalement, nous concevons et réalisons différentes antennes patchs en cavité environnées par des résonateurs. Des résultats de simulations et de mesures mettent en évidence le trÚs fort potentiel de découplage de ces structures.This thesis addresses the problem of mutual coupling reduction between the elements of a compact GNSS array - using High Impedance Surfaces (HIS) - to improve Controlled Reception Pattern Antenna (CRPA) performances. We first design a HIS, which elementary cell size is smaller than lambda0/14. Its Electromagnetic Band Gap (EBG) properties are characterised numerically and experimentally. A patch antenna is chosen as the elementary antenna of the CRPA. Ideal HIS are proposed to study different array configurations in order to define the elementary antenna. Resonant mechanisms occurring at the frequencies of the band gap in the HIS are then studied in detail. As a result, we propose the use of new compact HIS like resonators. Finally, different prototypes are designed and built. They consist of cavity backed patch elements surrounded or not by the proposed HIS like resonators. Numerical and experimental results demonstrate the mutual coupling drastic reduction achieved with these structures
Contributions to the understanding of meso/submesoscale turbulence and their impact on the ocean functioning
The ocean is variable on a broad range of scales and for a variety of reasons. The role of mesoscale subinertial currents has been known for a long time to be an important aspect of the ocean circulation. At the other end of the spectrum superinertial motions (near-inertial waves, inertial-gravity waves) are also important to the ocean functioning. In between, subinertial turbulent processes termed âsubmesoscaleâ exist, with time and space scales that largely overlap with those of superinertial motions. Submesoscale activity results from the intensification of fronts in the upper ocean. In this manuscript I strive to describe my research contribution from 1998 to 2015 on mesoscale and submesoscale turbulence. Some of their interactions with superinertial processes on which I have also worked are also discussed. This work is put into the proper scientific context through a substantial review effort.L'ocĂ©an est variable sur une large gamme d' Ă©chelles et pour une variĂ©tĂ© de raisons. Le rĂŽle des courants subinertiels mĂ©soĂ©chelle est connu depuis longtemps pour ĂȘtre un aspect important de la circulation ocĂ©anique. A l'autre extrĂ©mitĂ© des spectre en Ă©chelles, les mouvements superinertiels (ondes quasi-inertielles, ondes d'inertie-gravitĂ©) sont Ă©galement importants pour le fonctionnement de l'ocĂ©an. Entre les deux existent des processus turbulents subinertiels appelĂ©s "sous-mĂ©soĂ©chelle", dont les Ă©chelles de temps et d'espace recouvrent en grande partie celles des mouvements superinertiels. L'activitĂ© sous-mĂ©soĂ©chelle rĂ©sulte de l'intensification des fronts dans l'ocĂ©an supĂ©rieur. Dans ce manuscrit, je prĂ©sente ma contribution Ă la recherche sur la turbulence mĂ©soĂ©chelle et sous-mĂ©soĂ©chelle. Certaines de leurs interactions avec les processus superinertiels sur lesquelles j'ai rĂ©cemment travaillĂ© sont Ă©galement discutĂ©es. Ces travaux sont mis en perspective grĂące Ă un effort de revue couvrant l'essentiel des Ă©tudes produites depuis 20 ans sur les sujets concernĂ©es
Full-Metal Reflectarray for Space Applications
This paper proposes a new full-metal unit cell for reflectarray antenna for space applications. It can be scaled to operate from X-band to Ka-band with the same manufacturing process. In this paper, An X-band 3-panel reflectarray for small satellite has been designed in this paper. The reflectarray has been simulated on the [8-8.4] GHz band and shows a good stability on the band. The maximum gain is 28 dB and the half-power beamwidth is 8°
3-Allyl-1-{[3-(4-nitroÂphenÂyl)-4,5-dihydro-1,3-oxazol-5-yl]methÂyl}-1H-anthra[1,2-d]imidazole-2,6,11(3H)-trione
The molÂecular structure of the title compound, C28H20N4O6, consists of three fused six-membered rings (A,B,C) and one five-membered ring (D). The latter is linked to an isoxazole ring (E) via a methylÂene unit. A 4-nitro-phenyl substituent (F) is attached to the isoxazole. The fused five and six-membered rings (C,D) are almost coplanar with an r.m.s. deviation of 0.0345â
Ă
and make a dihedral angle of 9.40â
(8)° with ring A. The isoxazole and 4-nitro-phenyl rings (E,F) are also almost coplanar with the imidazole and the fused adjacent ring (C,D), forming a dihedral angle of 11.4â
(6)°. The crystal packing displays interÂmolecular CâHâŻO hydrogen bonding. An intraÂmolecular CâHâŻO interÂaction also occurs
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