23,535 research outputs found
A survey of stellar X-ray flares from the XMM-Newton serendipitous source catalogue: Hipparcos-Tycho cool stars
The X-ray emission from flares on cool (i.e. spectral-type F-M) stars is
indicative of very energetic, transient phenomena, associated with energy
release via magnetic reconnection. We present a uniform, large-scale survey of
X-ray flare emission. The XMM-Newton Serendipitous Source Catalogue and its
associated data products provide an excellent basis for a comprehensive and
sensitive survey of stellar flares - both from targeted active stars and from
those observed serendipitously in the half-degree diameter field-of-view of
each observation. The 2XMM Catalogue and the associated time-series
(`light-curve') data products have been used as the basis for a survey of X-ray
flares from cool stars in the Hipparcos Tycho-2 catalogue. In addition, we have
generated and analysed spectrally-resolved (i.e. hardness-ratio), X-ray
light-curves. Where available, we have compared XMM OM UV/optical data with the
X-ray light-curves. Our sample contains ~130 flares with well-observed
profiles; they originate from ~70 stars. The flares range in duration from ~1e3
to ~1e4 s, have peak X-ray fluxes from ~1e-13 to ~1e-11 erg/cm2/s, peak X-ray
luminosities from ~1e29 to ~1e32 erg/s, and X-ray energy output from ~1e32 to
~1e35 erg. Most of the ~30 serendipitously-observed stars have little
previously reported information. The hardness-ratio plots clearly illustrate
the spectral (and hence inferred temperature) variations characteristic of many
flares, and provide an easily accessible overview of the data. We present flare
frequency distributions from both target and serendipitous observations. The
latter provide an unbiased (with respect to stellar activity) study of flare
energetics; in addition, they allow us to predict numbers of stellar flares
that may be detected in future X-ray wide-field surveys. The serendipitous
sample demonstrates the need for care when calculating flaring rates.Comment: 26 pages, 24 figures. Additional tables and figures available as 4
ancillary files. To be published in Astronomy and Astrophysic
Acoustic-loads research for powered-lift configurations
Data presented from large-scale model tests with jet engines having thrusts of 9 kN (2000 lb) and 36 kN (8000 lb) include acoustic loads for an externally blown wing and flap induced by a TF34 jet engine, an upper surface blown (USB) aircraft model in a wind tunnel, and two USB models in static tests. Comparisons of these results with results from acoustic loads studies on configurations of other sizes are made and the implications of these results on interior noise and acoustic fatigue are discussed
Feedback in a cavity QED system for control of quantum beats
Conditional measurements on the undriven mode of a two-mode cavity QED system
prepare a coherent superposition of ground states which generate quantum beats.
The continuous system drive induces decoherence through the phase interruptions
from Rayleigh scattering, which manifests as a decrease of the beat amplitude
and an increase of the frequency of oscillation. We report recent experiments
that implement a simple feedback mechanism to protect the quantum beat. We
continuously drive the system until a photon is detected, heralding the
presence of a coherent superposition. We then turn off the drive and let the
superposition evolve in the dark, protecting it against decoherence. At a later
time we reinstate the drive to measure the amplitude, phase, and frequency of
the beats. The amplitude can increase by more than fifty percent, while the
frequency is unchanged by the feedback.Comment: 13 pages, 5 figures, ICAP 2012 23rd International Conference on
Atomic Physic
Color television study Final report, Nov. 1965 - Mar. 1966
Color television camera for transmission from lunar and earth orbits and lunar surfac
Sobre la estratigrafía del singular corte de la Roca de Narieda (parte S de la serie del Cretácico inferior de Organyà). Pirineo catalán, España
El corte de la Roca de Narieda es el único del Pirineo catalán (región de Organyà, NE de España) en el que puede verse la agradación costera de casi todo el ciclo sedimentario del Cretácico inferior: desde el Neocomiense al Aptiense superior.
El solapamiento expansivo (retrogradación) de distintos cuerpos sedimentarios sobre el substrato jurásico corresponde al borde SE de la cuenca sudpirenaica de esta época.
El análisis micropaleontológico ha sido el que ha permitido modificar las ideas erróneas, secuenciales y cronoestratigráficas, que se tenían sobre esta montaña
difícil de explorar.
Palabras clave: Pirineo catalán (España), Región de Organyà, Cretácico inferior, Micropaleontología, Estratigrafía, Paleogeografía
Counter Rotating Open Rotor Animation using Particle Image Velocimetry
This article describes the two accompanying fluid dynamics videos for the
"Counter rotating open rotor flow field investigation using stereoscopic
Particle Image Velocimetry" presented at the 64th Annual Meeting of the APS
Division of Fluid Dynamics in Baltimore, Maryland, November 20-22, 2011.Comment: Videos are include
Rewarding Non-productivity In the Hospitality Industry
The industry has not clearly focused on many important problems, such as rewarding service workers based on productivity. Instead, many industry leaders have focused on straw men issues, issues that are more rhetoric than substance. The authors examine some of these so-called is- sues in detail: governmental wage policies, immigration laws, the quality of the work force, service worker training, and gratuity management, to provide a fresh look at worker productivity beyond the rhetoric and myths that prevai
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