20,087 research outputs found
Solution to the differential equation for combined radiative and convective cooling for a heated sphere
A solution is presented for the differential equation relating the combined effects of radiative and forced convective cooling for a heated sphere. The equation has the form where T and t are the variables temperature and time, respectively, and K sub o, T sub o, and H are constants. The solution can be used as a guideline for the design and understanding of space processing phenomena
Application of advanced on-board processing concepts to future satellite communications systems
An initial definition of on-board processing requirements for an advanced satellite communications system to service domestic markets in the 1990's is presented. An exemplar system architecture with both RF on-board switching and demodulation/remodulation baseband processing was used to identify important issues related to system implementation, cost, and technology development
Towards a new full-sky list of radial velocity standard stars
The calibration of the Radial Velocity Spectrometer (RVS) onboard the ESA
Gaia satellite (to be launched in 2012) requires a list of standard stars with
a radial velocity (RV) known with an accuracy of at least 300 m/s. The IAU
Commission 30 lists of RV standard stars are too bright and not dense enough.
We describe the selection criteria due to the RVS constraints for building an
adequate full-sky list of at least 1000 RV standards from catalogues already
published in the literature. A preliminary list of 1420 candidate standard
stars is built and its properties are shown. An important re-observation
programme has been set up in order to ensure within it the selection of objects
with a good stability until the end of the Gaia mission (around 2018). The
present list of candidate standards is available at CDS and usable for many
other projects.Comment: Astronomy & Astrophysics, in press, 8 pages, 8 figure
The catalog of radial velocity standard stars for the Gaia RVS: status and progress of the observations
A new full-sky catalog of Radial Velocity standard stars is being built for
the determination of the Radial Velocity Zero Point of the RVS on board of
Gaia. After a careful selection of 1420 candidates matching well defined
criteria, we are now observing all of them to verify that they are stable
enough over several years to be qualified as reference stars. We present the
status of this long-term observing programme on three spectrographs : SOPHIE,
NARVAL and CORALIE, complemented by the ELODIE and HARPS archives. Because each
instrument has its own zero-point, we observe intensively IAU RV standards and
asteroids to homogenize the radial velocity measurements. We can already
estimate that ~8% of the candidates have to be rejected because of variations
larger than the requested level of 300 m/s.Comment: Proceedings of SF2A2010, S. Boissier, M. Heydari-Malayeri, R. Samadi
and D. Valls-Gabaud (eds), 3 pages, 2 figure
Cosmic ray modulation in a random anisotropic magnetic field
Inhomogeneities of the interplanetary magnetic field can be divided into small scale and large scale ones as may be required by the character of the problem of cosmic ray (CR) propagation. CR propagation in stochastic magnetic fields is of diffusion character. The main contribution into the scattering of CR particles is made by their interaction with inhomogeneities of the magnetic field H which have characteristic dimensions 1 of the order of Larmor radius R=cp/eH of particle (p is the absolute value of particle momentum, e is particle charge, c is velocity of light). Scattering of particles on such inhomogeneities leads to their diffusion mostly along a magnetic field with characteristic dimensions of variation in space exceeding the mean free path
All Gifts Large and Small
Much attention has been focused in recent years on the ethical acceptability of physicians receiving gifts from drug companies. Professional guidelines recognize industry gifts as a conflict of interest and establish thresholds prohibiting the exchange of large gifts while expressly allowing for the exchange of small gifts such as pens, note pads, and coffee. Considerable evidence from the social sciences suggests that gifts of negligible value can influence the behavior of the recipient in ways the recipient does not always realize. Policies and guidelines that rely on arbitrary value limits for gift-giving or receipt should be reevaluated
Parameter-free ansatz for inferring ground state wave functions of even potentials
Schr\"odinger's equation (SE) and the information-optimizing principle based
on Fisher's information measure (FIM) are intimately linked, which entails the
existence of a Legendre transform structure underlying the SE. In this
comunication we show that the existence of such an structure allows, via the
virial theorem, for the formulation of a parameter-free ground state's
SE-ansatz for a rather large family of potentials. The parameter-free nature of
the ansatz derives from the structural information it incorporates through its
Legendre properties
Clearing algorithms and network centrality
I show that the solution of a standard clearing model commonly used in
contagion analyses for financial systems can be expressed as a specific form of
a generalized Katz centrality measure under conditions that correspond to a
system-wide shock. This result provides a formal explanation for earlier
empirical results which showed that Katz-type centrality measures are closely
related to contagiousness. It also allows assessing the assumptions that one is
making when using such centrality measures as systemic risk indicators. I
conclude that these assumptions should be considered too strong and that, from
a theoretical perspective, clearing models should be given preference over
centrality measures in systemic risk analyses
Gaia: Organisation and challenges for the data processing
Gaia is an ambitious space astrometry mission of ESA with a main objective to
map the sky in astrometry and photometry down to a magnitude 20 by the end of
the next decade. While the mission is built and operated by ESA and an
industrial consortium, the data processing is entrusted to a consortium formed
by the scientific community, which was formed in 2006 and formally selected by
ESA one year later. The satellite will downlink around 100 TB of raw telemetry
data over a mission duration of 5 years from which a very complex iterative
processing will lead to the final science output: astrometry with a final
accuracy of a few tens of microarcseconds, epoch photometry in wide and narrow
bands, radial velocity and spectra for the stars brighter than 17 mag. We
discuss the general principles and main difficulties of this very large data
processing and present the organisation of the European Consortium responsible
for its design and implementation.Comment: 7 pages, 2 figures, Proceedings of IAU Symp. 24
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