2,304 research outputs found
Study of liquid jet impingement on screens
A model is presented for an unconfined flow, such as a free jet, impinging on a screen which incorporates the influence of liquid deflection by the screen. The boundary layer blockage coefficient is introduced. This coefficient depends on the screen weave geometry and the jet impingement angle, and essentially accounts for the increase in fluid particle trajectory length through the screen resulting from the flow deflection. Comparisons were made with previous experimental studies to determine empirical values of the blockage coefficient. It is concluded that the new model reliably predicts the bulk flow and penetration characteristics of an impinging liquid jet interacting with a screen
Probing Satellite Quenching With Galaxy Clustering
Satellites within simulated massive clusters are significantly spatially
correlated with each other, even when those satellites are not gravitationally
bound to each other. This correlation is produced by satellites that entered
their hosts relatively recently, and is undetectable for satellites that have
resided in their hosts for multiple dynamical timescales. Therefore, a
measurement of clustering statistics of cluster satellites may be used to
determine the typical accretion redshifts of those satellites into their
observed hosts. We argue that such measurements may be used to determine the
fraction of satellite galaxies that were quenched by their current hosts,
thereby discriminating among models for quenching of star formation in
satellite galaxies.Comment: 7 page
Water Quality Project Evaluation A Handbook for Objectives-Based Evaluation of Water Quality Projects
PDF pages: 5
Observation and implications of the Epeak - Eiso correlation in Gamma-Ray Bursts
The availability of a few dozen GRB redshifts now allows studies of the
intrinsic properties of these high energy transients. Amati et al. recently
discovered a correlation between Epeak, the intrinsic peak energy of the spectrum, and Eiso, the isotropic equivalent energy radiated by the
source. Lamb et al. have shown that HETE-2 data confirm and extend this
correlation. We discuss here one of the consequences of this correlation: the
existence of a 'spectral standard candle', which can be used to construct a
simple redshift indicator for GRBs.Comment: Proceedings of the GRB 2003 Conference in SantaFe, 5 pages, 4 figure
Discovery and Characterization of Transiting SuperEarths Using an All-Sky Transit Survey and Follow-up by the James Webb Space Telescope
Doppler and transit surveys are finding extrasolar planets of ever smaller
mass and radius, and are now sampling the domain of superEarths (1-3 Earth
radii). Recent results from the Doppler surveys suggest that discovery of a
transiting superEarth in the habitable zone of a lower main sequence star may
be possible. We evaluate the prospects for an all-sky transit survey targeted
to the brightest stars, that would find the most favorable cases for
photometric and spectroscopic characterization using the James Webb Space
Telescope (JWST). We use the proposed Transiting Exoplanet Survey Satellite
(TESS) as representative of an all-sky survey. We couple the simulated TESS
yield to a sensitivity model for the MIRI and NIRSpec instruments on JWST. We
focus on the TESS planets with radii between Earth and Neptune. Our simulations
consider secondary eclipse filter photometry using JWST/MIRI, comparing the 11-
and 15-micron bands to measure CO2 absorption in superEarths, as well as
JWST/NIRSpec spectroscopy of water absorption from 1.7-3.0 microns, and CO2
absorption at 4.3-microns. We project that TESS will discover about eight
nearby habitable transiting superEarths. The principal sources of uncertainty
in the prospects for JWST characterization of habitable superEarths are
superEarth frequency and the nature of superEarth atmospheres. Based on our
estimates of these uncertainties, we project that JWST will be able to measure
the temperature, and identify molecular absorptions (water, CO2) in one to four
nearby habitable TESS superEarths.Comment: accepted for PASP; added discussion and figure for habitable planets;
abridged Abstrac
A q-deformed nonlinear map
A scheme of q-deformation of nonlinear maps is introduced. As a specific
example, a q-deformation procedure related to the Tsallis q-exponential
function is applied to the logistic map. Compared to the canonical logistic
map, the resulting family of q-logistic maps is shown to have a wider spectrum
of interesting behaviours, including the co-existence of attractors -- a
phenomenon rare in one dimensional maps.Comment: 17 pages, 19 figure
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Bibliographical database of radiation biological dosimetry and risk assessment: Part 1, through June 1988
This database was constructed to support research in radiation biological dosimetry and risk assessment. Relevant publications were identified through detailed searches of national and international electronic databases and through our personal knowledge of the subject. Publications were numbered and key worded, and referenced in an electronic data-retrieval system that permits quick access through computerized searches on publication number, authors, key words, title, year, and journal name. Photocopies of all publications contained in the database are maintained in a file that is numerically arranged by citation number. This report of the database is provided as a useful reference and overview. It should be emphasized that the database will grow as new citations are added to it. With that in mind, we arranged this report in order of ascending citation number so that follow-up reports will simply extend this document. The database cite 1212 publications. Publications are from 119 different scientific journals, 27 of these journals are cited at least 5 times. It also contains reference to 42 books and published symposia, and 129 reports. Information relevant to radiation biological dosimetry and risk assessment is widely distributed among the scientific literature, although a few journals clearly dominate. The four journals publishing the largest number of relevant papers are Health Physics, Mutation Research, Radiation Research, and International Journal of Radiation Biology. Publications in Health Physics make up almost 10% of the current database
MHD Simulations of AGN Jets in a Dynamic Galaxy Cluster Medium
We present a pair of 3-d magnetohydrodynamical simulations of intermittent
jets from a central active galactic nucleus (AGN) in a galaxy cluster extracted
from a high resolution cosmological simulation. The selected cluster was chosen
as an apparently relatively relaxed system, not having undergone a major merger
in almost 7 Gyr. Despite this characterization and history, the intra-cluster
medium (ICM) contains quite active "weather". We explore the effects of this
ICM weather on the morphological evolution of the AGN jets and lobes. The
orientation of the jets is different in the two simulations so that they probe
different aspects of the ICM structure and dynamics. We find that even for this
cluster that can be characterized as relaxed by an observational standard, the
large-scale, bulk ICM motions can significantly distort the jets and lobes.
Synthetic X-ray observations of the simulations show that the jets produce
complex cavity systems, while synthetic radio observations reveal bending of
the jets and lobes similar to wide-angle tail (WAT) radio sources. The jets are
cycled on and off with a 26 Myr period using a 50% duty cycle. This leads to
morphological features similar to those in "double-double" radio galaxies.
While the jet and ICM magnetic fields are generally too weak in the simulations
to play a major role in the dynamics, Maxwell stresses can still become locally
significant.Comment: 20 pages, 14 figures, accepted for publication in the Astrophysical
Journa
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