A Novel Stealthy Target Detection Based on Stratospheric Balloon-borne Positional Instability due to Random Wind

A novel detection for stealthy target model F-117A with a higher aspect vision is introduced by using Stratospheric Balloon-borne Bistatic system. The potential problem of proposed scheme is platform instability impacted on the balloon by external wind force. The flight control system is studied in detail under typical random process, which is defined by Dryden turbulence spectrum. To accurately detect the stealthy target model, a real Radar Cross Section (RCS) based on physical optics (PO) formulation is applied. The sensitivity of the proposed scheme has been improved due to increasing PO – scattering field of stealthy model with higher aspect angle comparing to the conventional ground -based system. Simulations demonstrate that the proposed scheme gives much higher location accuracy and reduces location errors

Populations indigènes et inégalités sociales : une approche plurielle à partir du recensement mexicain de 2000

Au Mexique, où l'identification censitaire des populations indigènes sur une base linguistique existe sans interruption depuis le début du vingtième siècle, le recensement de 2000 marque un tournant en introduisant comme second critère l'auto déclaration d'appartenance ethnique qui permet l'expression de leur appartenance communautaire aux indigènes non locuteurs. Cet article étend les catégories d'identification de la population indigène mexicaine à ces nouvelles variables. Ce mode d'identification pluriel nous permet ensuite, à partir de l'ensemble de l'information censitaire, une analyse fouillée des caractéristiques démographiques et socioéconomiques des ménages mexicains, indigènes et non indigènes. A la suite d'une ligne de recherche déjà classique dans le pays, nos résultats conduisent à préciser et enrichir le diagnostic sur l'inégalité sociale et les processus de ségrégation ethnique. L'intérêt est aussi, en multipliant les critères d'identification des populations indigènes et les variables d'analyse, de faire apparaître l'hétérogénéité sociale et économique qui existe dans le monde indigène contemporain ; un aspect beaucoup moins documentée au sein des sciences sociales mexicaines, du moins par des approches quantitatives

Low Complexity V-BLAST MIMO-OFDM Detector by Successive Iterations Reduction

V-BLAST detection method suffers large computational complexity due to its successive detection of symbols. In this paper, we propose a modified V-BLAST algorithm to decrease the computational complexity by reducing the number of detection iterations required in MIMO communication systems. We begin by showing the existence of a maximum number of iterations, beyond which, no significant improvement is obtained. We establish a criterion for the number of maximum effective iterations. We propose a modified algorithm that uses the measured SNR to dynamically set the number of iterations to achieve an acceptable bit-error rate. Then, we replace the feedback algorithm with an approximate linear function to reduce the complexity. Simulations show that significant reduction in computational complexity is achieved compared to the ordinary V-BLAST, while maintaining a good BER performance.Comment: 6 pages, 7 figures, 2 tables. The final publication is available at www.aece.r

First Principles Simulations of Boron Diffusion in Graphite

Boron strongly modifies electronic and diffusion properties of graphite. We report the first ab initio study of boron interaction with the point defects in graphite, which includes structures, thermodynamics, and diffusion. A number of possible diffusion mechanisms of boron in graphite are suggested. We conclude that boron diffuses in graphite by a kick-out mechanism. This mechanism explains the common activation energy, but large magnitude difference, for the rate of boron diffusion parallel and perpendicular to the basal plane. © 2007 The American Physical Society

Ciudad y etnicidad: configuraciones de la etnicidad negra en la ciudad

En un contexto de multiculturalismo que afecta ciertos derechos a ciertas poblaciones, queremos observar cómo se combinan las identidades "étnicas" o otro tipo de identificación, en este caso urbana. ¿Cómo contribuyen las pertenencias raciales y étnicas a la construcción de la ciudad? ¿Cómo son producidas esas pertenencias por la ciudad? El etxto comprara tres contextos urbanos colombianos, desde una metrópolis (Cali), una grande ciudad (Cartagena) y una pequeña ciudad (Tumaco)

A Dip after the Early Emission of Super-Luminous Supernovae: A Signature of Shock Breakout within Dense Circumstellar Media

The origin of super-luminous supernovae (SLSNe), especially the source of their huge luminosities, has not been clarified yet. While a strong interaction between SN ejecta and dense circumstellar media (CSM) is a leading scenario, alternative models have been proposed. In this Letter, we suggest new diagnostics to discriminate the strong SN-CSM interaction scenario from the others: a decline in the luminosity ('dip') before the main peak of the light curve. This dip is an unavoidable consequence of having a dense CSM within which the shock breakout occurs. If a dense CSM shell is located far at large radii from the progenitor inside, it takes time for the SN ejecta to reach it and the early light curve can be powered by the SN ejecta before the collision. Once the SN ejecta collides with the dense CSM, the electron density and thus the Thomson scattering opacity suddenly increase. Photons become unable to go out of the shock even if there is a source of emission inside, which results in the dip in the light curve. This dip is a solid prediction from the strong interaction scenario irrespective of a power source for the early emission. Eventually the forward shock breaks out from within the dense CSM, and the luminosity increases by the continuous strong SN-CSM interaction, resulting in an SLSN. The possible dip observed in the hydrogen-poor SLSN, 2006oz, could be the first example of this signature and give support to the SN-CSM interaction as the power source of SLSN 2006oz.Comment: 5 pages, 1 figure, 1 table, accepted by The Astrophysical Journal Letter

Scientific Computing Meets Big Data Technology: An Astronomy Use Case

Scientific analyses commonly compose multiple single-process programs into a dataflow. An end-to-end dataflow of single-process programs is known as a many-task application. Typically, tools from the HPC software stack are used to parallelize these analyses. In this work, we investigate an alternate approach that uses Apache Spark -- a modern big data platform -- to parallelize many-task applications. We present Kira, a flexible and distributed astronomy image processing toolkit using Apache Spark. We then use the Kira toolkit to implement a Source Extractor application for astronomy images, called Kira SE. With Kira SE as the use case, we study the programming flexibility, dataflow richness, scheduling capacity and performance of Apache Spark running on the EC2 cloud. By exploiting data locality, Kira SE achieves a 2.5x speedup over an equivalent C program when analyzing a 1TB dataset using 512 cores on the Amazon EC2 cloud. Furthermore, we show that by leveraging software originally designed for big data infrastructure, Kira SE achieves competitive performance to the C implementation running on the NERSC Edison supercomputer. Our experience with Kira indicates that emerging Big Data platforms such as Apache Spark are a performant alternative for many-task scientific applications

La répartition régionale des cultures vivrières au Rwanda : analyse statistique

Etant donné les densités exceptionnelles de ses campagnes et le rythme de sa croissance démographique, le Rwanda doit répondre aujourd'hui à un redoutable défi : aménager son territoire et son espace rural de telle sorte qu'il puisse subvenir aux besoins de dix millions d'habitants d'ici une quinzaine d'années. Dans ce but, les services de planification nationale élaborent une stratégie alimentaire dont l'un des éléments est une meilleure répartition régionale des activités agricoles. De nouvelles estimations chiffrées sur l'importance des différentes cultures vivrières dans toutes les communes du pays servent ici de base à une étude méthodologique comportant divers traitement statistiques, informatiques et graphiques qui, d'une part, confirment et précisent l'extrême complexité des systèmes agro-vivriers du pays et, d'autre part, aboutissent à une remise en cause partielle des limites régionales classiques sur lesquelles a été fondée jusqu'ici la planification agricole. (Résumé d'auteur