5,755 research outputs found
Skylab mission planning support through the use of a hybrid simulation
The manner in which a hybrid simulation was used in support of Skylab operations in the area of dynamics and control is described. Simulation results were used in the development of acceptable vehicle maneuvers and in the verification of acceptability when the maneuvers were integrated into daily flight plans. The criterion of acceptability was based on vehicle controllability and the minimization of thruster system propellant usage. A simulation of a representative daily flight plan containing three experimental maneuvers is included, along with thruster attitude control system propellant usage tables which show predicted and actual usage for each mission. The inherent characteristics of quick turnaround and flexibility afforded by the hybrid computer proved invaluable in the operations support required throughout the Skylab mission
A search for gravitational lensing in 38 X-ray selected clusters of galaxies
We present the results of a CCD imaging survey for gravitational lensing in a
sample of 38 X-ray-selected clusters of galaxies. Our sample consists of the
most X-ray luminous (Lx>= 2x10^{44} erg s^{-1}) clusters selected from the
Einstein Observatory Extended Medium Sensitivity Survey (EMSS) that are
observable from Mauna Kea (dec > -40deg). The sample spans a redshift range of
0.15 0.5. CCD images of the
clusters were obtained in excellent seeing. There is evidence of strong
gravitational lensing in the form of giant arcs (length l > 8'', axis ratio l/w
> 10) in 8 of the 38 clusters. Two additional clusters contain shorter arclets,
and 6 more clusters contain candidate arcs that require follow-up observations
to confirm their lensing origin. Since the survey does not have a uniform
surface brightness limit we do not draw any conclusion based on the statistics
of the arcs found. We note, however, that 60% (3 of 5) of the clusters with Lx
> 10^{45} erg s^{-1}, and none of the 15 clusters with Lx < 4x10^{44} erg
s^{-1} contain giant arcs, thereby confirming that high X-ray luminosity does
identify the most massive systems, and thus X-ray selection is the preferred
method for finding true, rich clusters at intermediate and high redshifts. The
observed geometry of the arcs, most of which are thin, have large axis ratios
(l/w > 10), and are aligned orthogonal to the optical major axes of the
clusters, indicate the cluster core mass density profiles must be compact
(steeper than isothermal). In several cases, however, there is also some
evidence, in the form of possible radial arcs, for density profiles with finite
core radii.Comment: Latex file, 17 pages, 7 jpeg figures, to be published in Astronomy
and Astrophysics Supplement
The CANADA-FRANCE REDSHIFT SURVEY XIII: The luminosity density and star-formation history of the Universe to z ~ 1
The comoving luminosity density of the Universe is estimated from the CFRS
faint galaxy sample in three wavebands (2800A, 4400A and 1 micron) over the
redshift range 0 < z < 1. In all three wavebands, the comoving luminosity
density increases markedly with redshift. For a (q_0 = 0.5, Omega = 1.0)
cosmological model, the comoving luminosity density increases as at 1 micron, as at 4400A and as at 2800A, these exponents being reduced by 0.43 and 1.12 for (0.05,0.1)
and (-0.85,0.1) cosmological models respectively. The variation of the
luminosity density with epoch can be reasonably well modelled by an actively
evolving stellar population with a Salpeter initial mass function (IMF)
extending to 125 M_sun, a star-formation rate declining with a power 2.5, and a
turn-on of star-formation at early epochs. A Scalo (1986) IMF extending to the
same mass limit produces too many long-lived low mass stars. This rapid
evolution of the star-formation rate and comoving luminosity density of the
Universe is in good agreement with the conclusions of Pei and Fall (1995) from
their analysis of the evolving metallicity of the Universe. One consequence of
this evolution is that the physical luminosity density at short wavelengths has
probably declined by two orders of magnitude since z ~ 1.Comment: uuencoded compressed tar file containing 8 page Tex file, 2
postscript figures and 2 tables. Ap J Letters, in press. Also available at
http://www.astro.utoronto.ca/~lilly/CFRS/papers.htm
Deranged calcium signaling and neurodegeneration in spinocerebellar ataxia type 3
Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease (MJD), is
an autosomal-dominant neurodegenerative disorder caused by a polyglutamine
expansion in ataxin-3 (SCA3, MJD1) protein. In biochemical experiments we demonstrate
that mutant SCA3exp specifically associated with the type 1 inositol 1,4,5-trisphosphate
receptor (InsP3R1), an intracellular calcium (Ca2+) release channel. In electrophysiological
and Ca2+ imaging experiments we show that InsP3R1 are sensitized to activation by InsP3
in the presence of mutant SCA3exp. We found that feeding SCA3-YAC-84Q transgenic
mice with dantrolene, a clinically relevant stabilizer of intracellular Ca2+ signaling,
improved their motor performance and prevented neuronal cells loss in pontine nuclei
and substantia nigra regions. Our results indicate that deranged Ca2+ signaling may play
an important role in SCA3 pathology and that Ca2+ signaling stabilizers such as
dantrolene may be considered as potential therapeutic drugs for treatment of SCA3
patients
GIRAFFE multiple integral field units at VLT: a unique tool to recover velocity fields of distant galaxies
The GIRAFFE spectrograph is unique in providing the integral field
spectroscopy of fifteen distant galaxies at the same time. It has been
successfully implemented at the second VLT unit within the FLAMES facility. We
present GIRAFFE observations acquired during the Guaranteed Time Observation of
the Paris Observatory, using total exposure times ranging from 6 to 12 hours.
The reduced 3D cube of each galaxy has been deconvolved using our new package
DisGal3D. This software has been written using the only assumption that UV
light traces the emission line regions. The comparison between GIRAFFE spectra
and HST imagery allows us to recover details on velocity fields as small as
0.3-0.4 arcsec. It has been successfully tested using Fabry Perot observations
of nearby galaxies purposely redshifted to large distances. We present here
preliminary results for three distant galaxies at 0.45< z < 0.65, whose
velocity fields have been derived with exquisite spectral (R=10000) and spatial
resolutions. Observed velocity fields range from disturbed fields expected in
major merger events to those of regular spiral with minor perturbations. For
the latter, one could accurately derive the dynamical major axis and the
maximal rotational velocity. We conclude that dynamical properties of a large
number of distant galaxies can be routinely derived at VLT. This opens a new
avenue towards the understanding of the galaxy formation and evolution during
the last 8 Gyr.Comment: 4 pages, 3 jpeg figures. to appear in A&
A recent rebuilding of most spirals ?
Re-examination of the properties of distant galaxies leads to the evidence
that most present-day spirals have built up half of their stellar masses during
the last 8 Gyr, mostly during several intense phases of star formation during
which they took the appearance of luminous infrared galaxies (LIRGs). Distant
galaxy morphologies encompass all of the expected stages of galaxy merging,
central core formation and disk growth, while their cores are much bluer than
those of present-day bulges. We have tested a spiral rebuilding scenario, for
which 75+/-25% of spirals have experienced their last major merger event less
than 8 Gyr ago. It accounts for the simultaneous decreases, during that period,
of the cosmic star formation density, of the merger rate, of the number
densities of LIRGs and of compact galaxies, while the densities of ellipticals
and large spirals are essentially unaffected.Comment: (1) GEPI, Obs. Meudon, France ;(2)Max-Planck Institut fuer
Astronomie, Germany (3) National Astronomical Observatories, CAS, China. Five
pages, 1 figure. To be published in "Starbursts: From 30 Doradus to Lyman
Break Galaxies", held in Cambridge, ed. R. de Grijs & R. M. Gonzalez Delgado
(Dordrecht: Kluwer
Interference between magnetic field and cavity modes in an extended Josephson junction
An extended Josephson junction consists of two superconducting electrodes
that are separated by an insulator and it is therefore also a microwave cavity.
The superconducting phase difference across the junction determines the
supercurrent as well as its spatial distribution. Both, an external magnetic
field and a resonant cavity intrafield produce a spatial modification of the
superconducting phase along the junction. The interplay between these two
effects leads to interference in the critical current of the junction and
allows us to continuously tune the coupling strength between the first cavity
mode and the Josephson phase from 1 to -0.5. This enables static and dynamic
control over the junction in the ultra-strong coupling regime.Comment: 4 pages, 3 figure
Subject-oriented plural method meets BPMN: a case study
Subject-oriented approach to business process management focuses on the subjects and their interactions with the aim to capture more accurate process information with increased fidelity. In a common setting, business processes are modeled by process engineers or modeling experts who often create their processes in a top-down fashion. However, this may pose risks to the acceptance and adoption of these models in practice, particularly in knowledge-centric environments. The Plural method follows a subject-oriented approach and allows process participants, rather than a centralized group of process engineers, to model and maintain their processes in a decentralized way. It guides process participants to focus on the roles and their interactions in terms of message exchanges. This study investigates the use of BPMN 2.0 for the Plural method. With the aim to show the applicability of the notation for a subject-oriented approach and report on the benefits and limitations of the new edition of the Plural method in general, we performed a case study in an industry company. Guided by a coordinator, 11 process participants modeled four processes that they participate by following the Plural method. These models were also compared with the classical models developed prior to the application of the Plural method to better understand the influence. Analyses showed that the application of the Plural resulted in more complete process models. However, there are concerns regarding the understandability of these models when compared with their classical counterparts. It has been shown that the Plural method is a powerful tool for process discovery and modeling, but an improvement on its models is needed to obtain full value of the framework
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