Superhumps in Low-Mass X-Ray Binaries

We propose a mechanism for the superhump modulations observed in optical photometry of at least two black hole X-ray transients (SXTs). As in extreme mass-ratio cataclysmic variables (CVs), superhumps are assumed to result from the presence of the 3:1 orbital resonance in the accretion disc. This causes the disc to become non-axisymmetric and precess. However the mechanism for superhump luminosity variations in low mass X-ray binaries (LMXBs) must differ from that in CVs, where it is attributed to a tidally-driven modulation of the disc's viscous dissipation, varying on the beat between the orbital and disc precession period. By contrast in LMXBs, tidal dissipation in the outer accretion disc is negligible: the optical emission is overwhelming dominated by reprocessing of intercepted central X-rays. Thus a different origin for the superhump modulation is required. Recent observations and numerical simulations indicate that in an extreme mass-ratio system the disc area changes on the superhump period. We deduce that the superhumps observed in SXTs arise from a modulation of the reprocessed flux by the changing area. Therefore, unlike the situation in CVs, where the superhump amplitude is inclination-independent, superhumps should be best seen in low-inclination LMXBs, whereas an orbital modulation from the heated face of the secondary star should be more prominent at high inclinations. Modulation at the disc precession period (10s of days) may indicate disc asymmetries such as warping. We comment on the orbital period determinations of LMXBs, and the possibility and significance of possible permanent superhump LMXBs.Comment: 6 pages, 1 encapsulated figure. MNRAS in press; replaced to correct typographical error

Evaluation of Spacecraft Technology Programs (Effects on Communication Satellite Business Ventures), Volume 2

The computational procedures used in the evaluation of spacecraft technology programs that impact upon commercial communication satellite operations are discussed. Computer programs and data bases are described

NASA'S Simulant Development Program Evolution and Overview

Since its origination under NASA's previous Human System Research and Technology program, the Lunar Simulant Development Program has undergone several changes. NASA recognized as early as the Apollo Program, and even more so as a result of the Apollo missions, that a viable dust and lunar simulant program is critical to the success of its space exploration goals. Unfortunately, this program has suffered the same problems that all programs share from time to time including uncertain budgets, shifting of priorities, and schedule fluctuations. To compound the problem, the process for developing simulants is being redefined and is not a trivial pursuit. Before now, NASA had not attempted to develop a suitable standard simulant since the 1990s when JSC-1 was produced. Although several other simulants have been developed by various groups both before and after the production of JSC-1, JSC-1 had become the de facto standard even though it has some limitations. The development and production of new simulants will address some of these limitations by starting with an assessment of NASA's needs and understanding the required processing in order to make these simulants

Gas and stellar dynamics in NGC 1068. Probing the galactic gravitational potential

We present Sauron 2D spectrography of the central 1.5 kpc of the nearby Sey2 galaxy NGC1068, encompassing the well-known NIR inner bar. We have successively disentangled the respective contributions of the ionized gas and stars, thus deriving their 2D distribution and kinematics. The [OIII] and Hbeta emission lines exhibit very different spatial distribution and kinematics, the latter following inner spiral arms with clumps associated with star formation. Strong inwards streaming motions are observed in both the Hbeta and [OIII] kinematics. The stellar kinematics also exhibit clear signatures of a non-axisymmetric tumbling potential, with a twist in both the velocity and h3 fields. We re-examined the long-slit data of Shapiro et al (2003) using pPXF: a strong decoupling of h3 is revealed, and the central decrease in h4 hinted in the Sauron data is confirmed. These data also suggest that NGC1068 is a good candidate for a so-called sigma-drop. We confirm the possible presence of two pattern speeds. We also examine the stellar kinematics of bars formed in N-body+SPH simulations built from axisymmetric initial conditions. These successfully reproduce a number of properties observed in the 2D kinematics of NGC1068, and the long-slit data, showing that the kinematic signature of the NIR bar is imprinted in the stellar kinematics. The remaining differences between the models and the observed properties are mostly due to the exclusion of star formation and the lack of the primary large-scale oval/bar in the simulations. These models suggest that the inner bar could drive a significant amount of gas down to a scale of ~300 pc. This is consistent with the interpretation of the sigma-drop in NGC1068 being the result of central gas accretion followed by an episode of star formation.Comment: accepted for publication in MNRAS, 20 pages, 17 figures (high res version available at www-obs.univ-lyon1.fr/eric.emsellem/preprints/NGC1068_Emsellemetal_final.pdf

Multiphysics modeling of ceramic-matrix composites processing by thermal-gradient chemical vapor infiltration

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Three-dimensional modeling of a thermal dendrite using the phase field method with automatic anisotropic and unstructured adaptive finite element meshing

International audienceDendritic growth is computed with automatic adaptation of an anisotropic and unstructured finite element mesh. The energy conservation equation is formulated for solid and liquid phases considering an interface balance that includes the Gibbs-Thomson effect. An equation for a diffuse interface is also developed by considering a phase field function with constant negative value in the liquid and constant positive value in the solid. Unknowns are the phase field function and a dimensionless temperature, as proposed by [1]. Linear finite element interpolation is used for both variables, and discretization stabilization techniques ensure convergence towards a correct non-oscillating solution. In order to perform quantitative computations of dendritic growth on a large domain, two additional numerical ingredients are necessary: automatic anisotropic unstructured adaptive meshing [2,[3] and parallel implementations [4], both made available with the numerical platform used (CimLib) based on C++ developments. Mesh adaptation is found to greatly reduce the number of degrees of freedom. Results of phase field simulations for dendritic solidification of a pure material in two and three dimensions are shown and compared with reference work [1]. Discussion on algorithm details and the CPU time will be outlined

Ground water and surface water under stress

Presented at Ground water and surface water under stress: competition, interaction, solutions: a USCID water management conference on October 25-28, 2006 in Boise, Idaho.Includes bibliographical references.Conventional irrigation practices are predicated on maximizing crop yield - a biological objective. As worldwide competition for water intensifies a fundamentally new paradigm for irrigation management is emerging predicated on maximizing net returns to water - an economic objective. Maximizing returns to water generally involves some degree of deficit irrigation, particularly when water supplies or system constraints limit the availability of water, but few farmers are well equipped to deal with the analytical challenges associated with managing water deficits. This paper presents a web based advisory service for irrigation management now in use in a pilot program in Oregon. While the system can be used for conventional irrigation scheduling it is designed explicitly to assist irrigation managers with planning and implementing optimum irrigation strategies when water supplies are limited or expensive. Though originally developed for use in Oregon, discussions with other states have been initiated to make the system available nationally. This paper provides an overview of the analytical framework and demonstrates primary features of the user interface

Projet Collège+ : validation d’un assistant numérique pour l’inclusion scolaire de collégiens porteurs d’autisme

International audienceLe projet propose un outil d'assistance à l'inclusion scolaire permettant d'organiser et de soutenir les activités pédagogiques et communicationnelles d'élèves autistes en milieu ordinaire (i.e., collège). Cette assistance s'articule autour d'une tablette numérique. Celle-ci sera utilisable par les élèves et leurs aidants (enseignants, auxiliaires de vie scolaire, éducateurs, rééducateurs, etc.) dans leur travail d'accompagnement des élèves autistes. Les tablettes numériques de nouvelle génération, munies d'un écran tactile, du réseau sans fil et de camera, représentent un support très prometteur pour une assistance multifonctions de la personne en situation de handicap et à un cout raisonnable. La versatilité de ces tablettes permet une utilisation adaptée aux capacités de l'utilisateur. Dans ce projet, la tablette s'appuiera sur un catalogue ouvert d'applications gratuites, destinées aux élèvesavec désordres du spectre de l'autisme : ralenti vidéo, communication augmentée, gestion des routines scolaires, gestion du temps, aide-mémoire, enregistrement contextuel, gestion des émotions, scenarios d'interaction sociale, etc

Access to Educational Opportunities for Latino Students in Four Massachusetts School Districts

This report was prompted by the pressing concerns over the high failure rates of Latino students on the Massachusetts Comprehensive Assessment System (MCAS) exam. While 27% of White students failed the English portion of the MCAS test and 38% failed the Mathematics portion in 2000, the corresponding rates for Latino students were 66% and 79% respectively (Massachusetts Department of Education, 2000a). There is a great urgency to understand why Latino students score substantially behind students from other racial/ethnic groups. This urgency stems from the reality that students currently enrolled in the 10th grade will be required to pass this exam in order to receive a high school diploma in 2003

Sex steroid dynamics during embryogenesis and sexual differentiation in Eurasian perch, Perca fluviatilis

It is widely accepted that sex steroid hormones play an important and a specific role during the process of sex differentiation in fish. In order to describe the role of the three main sex steroid hormones (testosterone--T, 17beta-estradiol--E2 and 11keto-testosterone--11KT) during embryogenesis and sex differentiation in Eurasian perch, Perca fluviatilis, eggs, larvae and juveniles originating from two mixed-sex and two all-female progenies were regularly sampled from fertilization to hatching (D0) and from hatching to day 70 post-hatching (D70). Just after spawning, a significant amount of sex steroids [T (1634.2pgg(-1)), E2 (554.4pgg(-1)) and 11KT (1513.2pgg(-1))] was measured in non-fertilised eggs suggesting a maternal transmission of these steroids. From D2 to D70 post-hatching, E2 levels were significantly higher in mixed-sex progenies (median: 725.7pgg(-1)) than in all-female progenies (156.2pgg(-1)) and significantly increased after the onset of the histological differentiation of the gonad in both progenies (D35). Levels of 11KT were significantly higher in mixed-sex (median: 431.5pgg(-1)) than in all-female progenies (below the limit of assay detection) and significantly increased at D35 in all-female progenies (median value: 343.2pgg(-1)). Mean 11KT to E2 ratio was six-fold higher in mixed-sex progenies (1.35) than in all-female progenies (0.24). The data suggest that the 11-oxygenated androgen (11KT) plays a major role in the male differentiation process, and that sex differentiation in Eurasian perch is probably determined by the 11KT to E2 ratio