2,600 research outputs found
An Assessment of Four Promising Methods
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The XMM-LSS survey. Survey design and first results
We have designed a medium deep large area X-ray survey with XMM - the XMM
Large Scale Structure survey, XMM-LSS - with the scope of extending the
cosmological tests attempted using ROSAT cluster samples to two redshift bins
between 0<z<1 while maintaining the precision of earlier studies. Two main
goals have constrained the survey design: the evolutionary study of the
cluster-cluster correlation function and of the cluster number density. The
results are promising and, so far, in accordance with our predictions as to the
survey sensitivity and cluster number density. The feasibility of the programme
is demonstrated and further X-ray coverage is awaited in order to proceed with
a truly significant statistical analysis. (Abridged)Comment: Published in Journal of Cosmology and Astroparticle Physic
International Space Station (ISS) Plasma Contactor Unit (PCU) Utilization Plan Assessment Update
The NASA Engineering and Safety Center (NESC) received a request to support the Assessment of the International Space Station (ISS) Plasma Contactor Unit (PCU) Utilization Update. The NESC conducted an earlier assessment of the use of the PCU in 2009. This document contains the outcome of the assessment update
International Space Station (ISS) Plasma Contactor Unit (PCU) Utilization Plan Assessment Update
The International Space Station (ISS) vehicle undergoes spacecraft charging as it interacts with Earth's ionosphere and magnetic field. The interaction can result in a large potential difference developing between the ISS metal chassis and the local ionosphere plasma environment. If an astronaut conducting extravehicular activities (EVA) is exposed to the potential difference, then a possible electrical shock hazard arises. The control of this hazard was addressed by a number of documents within the ISS Program (ISSP) including Catastrophic Safety Hazard for Astronauts on EVA (ISS-EVA-312-4A_revE). The safety hazard identified the risk for an astronaut to experience an electrical shock in the event an arc was generated on an extravehicular mobility unit (EMU) surface. A catastrophic safety hazard, by the ISS requirements, necessitates mitigation by a two-fault tolerant system of hazard controls. Traditionally, the plasma contactor units (PCUs) on the ISS have been used to limit the charging and serve as a "ground strap" between the ISS structure and the surrounding ionospheric plasma. In 2009, a previous NASA Engineering and Safety Center (NESC) team evaluated the PCU utilization plan (NESC Request #07-054-E) with the objective to assess whether leaving PCUs off during non-EVA time periods presented risk to the ISS through assembly completion. For this study, in situ measurements of ISS charging, covering the installation of three of the four photovoltaic arrays, and laboratory testing results provided key data to underpin the assessment. The conclusion stated, "there appears to be no significant risk of damage to critical equipment nor excessive ISS thermal coating damage as a result of eliminating PCU operations during non- EVA times." In 2013, the ISSP was presented with recommendations from Boeing Space Environments for the "Conditional" Marginalization of Plasma Hazard. These recommendations include a plan that would keep the PCUs off during EVAs when the space environment forecast input to the ISS charging model indicates floating potentials (FP) within specified limits. These recommendations were based on the persistence of conditions in the space environment due to the current low solar cycle and belief in the accuracy and completeness of the ISS charging model. Subsequently, a Noncompliance Report (NCR), ISS-NCR-232G, Lack of Two-fault Tolerance to EVA Crew Shock in the Low Earth Orbit Plasma Environment, was signed in September 2013 specifying new guidelines for the use of shock hazard controls based on a forecast of the space environment from ISS plasma measurements taken prior to the EVA [ISS-EVA-312-AC, 2012]. This NESC assessment re-evaluates EVA charging hazards through a process that is based on over 14 years of ISS operations, charging measurements, laboratory tests, EMU studies and modifications, and safety reports. The assessment seeks an objective review of the plasma charging hazards associated with EVA operations to determine if any of the present hazard controls can safely change the PCU utilization plan to allow more flexibility in ISS operations during EVA preparation and execution
Batch discovery of nine z~1 clusters using x-ray and K or R,z' images
We present results of an initial search for clusters of galaxies at z~1 and
above, using data from 2.9 square degrees of XMM-Newton images. By selecting
weak potentially extended X-ray sources with faint or no identifications in
deep, ground-based optical imaging, we have constructed a starting sample of 19
high redshift cluster candidates. Near-IR and R,z' imaging of these fields
identified nine of them as high redshift systems. Six of these were confirmed
spectroscopically, three at z~1.0 and the other three in 0.8<z<0.92 range. The
remaining three systems have solid photometric evidence to be at z_phot ~ 0.8,
1.0 and 1.3. The present sample significantly increases the number of such
clusters. The measured density of z>~1 clusters, after discarding "low"
redshift systems at z <~ 0.92 is about 1.7 /deg2 (with 68 % confidence interval
equal to [1.0,2.9]) for f_X >~2.5 10^{-15} ergs/cm2/s ([0.5-2] keV) and this is
a lower limit, having screened not all potential z~1 candidate clusters.
Coordinates, x-ray measures and evidence for nine x-ray selected high redshift
clusters is given.Comment: MNRAS, in press. Paper with full-resolution figures can be found at
http://www.brera.mi.astro.it/%7Eandreon/MYPUB/hizclus.p
Order-of-magnitude speedup for steady states and traveling waves via Stokes preconditioning in Channelflow and Openpipeflow
Steady states and traveling waves play a fundamental role in understanding
hydrodynamic problems. Even when unstable, these states provide the
bifurcation-theoretic explanation for the origin of the observed states. In
turbulent wall-bounded shear flows, these states have been hypothesized to be
saddle points organizing the trajectories within a chaotic attractor. These
states must be computed with Newton's method or one of its generalizations,
since time-integration cannot converge to unstable equilibria. The bottleneck
is the solution of linear systems involving the Jacobian of the Navier-Stokes
or Boussinesq equations. Originally such computations were carried out by
constructing and directly inverting the Jacobian, but this is unfeasible for
the matrices arising from three-dimensional hydrodynamic configurations in
large domains. A popular method is to seek states that are invariant under
numerical time integration. Surprisingly, equilibria may also be found by
seeking flows that are invariant under a single very large Backwards-Euler
Forwards-Euler timestep. We show that this method, called Stokes
preconditioning, is 10 to 50 times faster at computing steady states in plane
Couette flow and traveling waves in pipe flow. Moreover, it can be carried out
using Channelflow (by Gibson) and Openpipeflow (by Willis) without any changes
to these popular spectral codes. We explain the convergence rate as a function
of the integration period and Reynolds number by computing the full spectra of
the operators corresponding to the Jacobians of both methods.Comment: in Computational Modelling of Bifurcations and Instabilities in Fluid
Dynamics, ed. Alexander Gelfgat (Springer, 2018
The allure of otherness: transnational cult film fandom and the exoticist assumption
Academic scholarship addressing transnational cult fandom, particularly Western cult fans forming attachments to films outside their cultures, has frequently addressed the issue of exoticism. Much attention has been paid to how Western fans are problematically drawn to artefacts outside of their own cultures because of exotic qualities, resulting in a shallow and often condescending appreciation of such films. In this article, I critique a number of such articles for merely assuming such processes without proffering sufficient supporting evidence. In fact, I argue that a number of such exotic-oriented critiques of transnational cultism are actually guilty of practising what they preach against: an insufficient contextualization of fandom and a tendency to downplay the messiness of empirical data in favour of generalized abstractions. Further, I argue that the constant critique of fans as avoiding contextualization has not only been overstated but stringently used as a yardstick to denigrate fan engagements with texts as improper. As such, fans are often ‘othered’ within such articles, a process mirroring the ways they are accused of othering distant cultural artefacts
Glucose tolerance and physical fitness: An epidemiologic study in an entire community
A modification of the Harvard Step Test was administered to approximately 4700 males and females, age 10–69 in Tecumseh, Michigan. Heart rate response to this standardized exercise test is an estimate of capacity for muscular work. A blood sample was drawn 1 h after a glucose challenge on the same day the exercise test was given. Four skinfolds were measured as an index of body fatness. It was the purpose of this analysis to study the relationship of glucose tolerance to heart rate response to exercise.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47419/1/421_2004_Article_BF00421779.pd
Quantum Measurement of a Coupled Nanomechanical Resonator -- Cooper-Pair Box System
We show two effects as a result of considering the second-order correction to
the spectrum of a nanomechanical resonator electrostatically coupled to a
Cooper-pair box. The spectrum of the Cooper-pair box is modified in a way which
depends on the Fock state of the resonator. Similarly, the frequency of the
resonator becomes dependent on the state of the Cooper-pair box. We consider
whether these frequency shifts could be utilized to prepare the nanomechanical
resonator in a Fock state, to perform a quantum non-demolition measurement of
the resonator Fock state, and to distinguish the phase states of the
Cooper-pair box
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