1,206 research outputs found
Internal Motility in Stiffening Actin-Myosin Networks
We present a study on filamentous actin solutions containing heavy meromyosin
subfragments of myosin II motor molecules. We focus on the viscoelastic phase
behavior and internal dynamics of such networks during ATP depletion. Upon
simultaneously using micro-rheology and fluorescence microscopy as
complementary experimental tools, we find a sol-gel transition accompanied by a
sudden onset of directed filament motion. We interpret the sol-gel transition
in terms of myosin II enzymology, and suggest a "zipping" mechanism to explain
the filament motion in the vicinity of the sol-gel transition.Comment: 4 pages, 3 figure
Optimising Spectroscopic and Photometric Galaxy Surveys: Efficient Target Selection and Survey Strategy
The next generation of spectroscopic surveys will have a wealth of
photometric data available for use in target selection. Selecting the best
targets is likely to be one of the most important hurdles in making these
spectroscopic campaigns as successful as possible. Our ability to measure dark
energy depends strongly on the types of targets that we are able to select with
a given photometric data set. We show in this paper that we will be able to
successfully select the targets needed for the next generation of spectroscopic
surveys. We also investigate the details of this selection, including
optimisation of instrument design and survey strategy in order to measure dark
energy. We use color-color selection as well as neural networks to select the
best possible emission line galaxies and luminous red galaxies for a
cosmological survey. Using the Fisher matrix formalism we forecast the
efficiency of each target selection scenario. We show how the dark energy
figures of merit change in each target selection regime as a function of target
type, survey time, survey density and other survey parameters. We outline the
optimal target selection scenarios and survey strategy choices which will be
available to the next generation of spectroscopic surveys.Comment: 16 pages, 22 figures, accepted to MNRAS in dec 201
The Global Star Formation Rate from the 1.4 GHz Luminosity Function
The decimetric luminosity of many galaxies appears to be dominated by
synchrotron emission excited by supernova explosions. Simple models suggest
that the luminosity is directly proportional to the rate of supernova
explosions of massive stars averaged over the past 30 Myr. The proportionality
may be used together with models of the evolving 1.4 GHz luminosity function to
estimate the global star formation rate density in the era z < 1. The local
value is estimated to be 0.026 solar masses per year per cubic megaparsec, some
50% larger than the value inferred from the Halpha luminosity density. The
value at z ~ 1 is found to be 0.30 solar masses per year per cubic megaparsec.
The 10-fold increase in star formation rate density is consistent with the
increase inferred from mm-wave, far-infrared, ultra-violet and Halpha
observations.Comment: 10 pages, 2 figures, Astrophysical Journal Letters (in press); new PS
version has improved figure placemen
Onset of collective and cohesive motion
We study the onset of collective motion, with and without cohesion, of groups
of noisy self-propelled particles interacting locally. We find that this phase
transition, in two space dimensions, is always discontinuous, including for the
minimal model of Vicsek et al. [Phys. Rev. Lett. {\bf 75},1226 (1995)] for
which a non-trivial critical point was previously advocated. We also show that
cohesion is always lost near onset, as a result of the interplay of density,
velocity, and shape fluctuations.Comment: accepted for publication in Phys. Rev. Let
Optically Faint Microjansky Radio Sources
We report on the identifications of radio sources from our survey of the
Hubble Deep Field and the SSA13 fields, both of which comprise the deepest
radio surveys to date at 1.4 GHz and 8.5 GHz respectively. About 80% of the
microjansky radio sources are associated with moderate redshift starburst
galaxies or AGNs within the I magnitude range of 17 to 24 with a median of I =
22 mag. Thirty-one (20%) of the radio sources are: 1) fainter than 25 mag,
with two objects in the HDF 28.5, 2) often identified with very red
objects 4, and 3) not significantly different in radio properties than
the brighter objects. We suggest that most of these objects are associated with
heavily obscured starburst galaxies with redshifts between 1 and 3. However,
other mechanisms are discussed and cannot be ruled out with the present
observations.Comment: to appear in Astrophysical Journal Letters, 3 figures, 1 tabl
Optical Morphologies of Millijansky Radio Galaxies Observed by HST and in the VLA FIRST Survey
We report on a statistical study of the 51 radio galaxies at the millijansky
flux level from the Faint Images of the Radio Sky at Twenty centimeters,
including their optical morphologies and structure obtained with the Hubble
Space Telescope. Our optical imaging is significantly deeper (~2 mag) than
previous studies with the superior angular resolution of space-based imaging.
We that find 8/51 (16%) of the radio sources have no optically identifiable
counterpart to AB~24 mag. For the remaining 43 sources, only 25 are
sufficiently resolved in the HST images to reliably assign a visual
classification: 15 (60%) are elliptical galaxies, 2 (8%) are late-type spiral
galaxies, 1 (4%) is an S0, 3 (12%) are point-like objects (quasars), and 4
(16%) are merger systems. We find a similar distribution of optical types with
measurements of the Sersic index. The optical magnitude distribution of these
galaxies peaks at I~20.7+-0.5 AB mag, which is ~3 mag brighter than the depth
of our typical HST field and is thus not due to the WFPC2 detection limit. This
supports the luminosity-dependent density evolutionary model, where the
majority of faint radio galaxies typically have L*-optical luminosities and a
median redshift of z~0.8 with a relatively abrupt redshift cut-off at z>~2. We
discuss our results in the context of the evolution of elliptical galaxies and
active galactic nuclei.Comment: 20 pages, 8 figures, 51 galaxy images, and 5 tables. Uses
emulateapj.cls and natbib.sty. Accepted to ApJS. High resolution images are
available upon reques
CEDIM Risk Explorer ? a map server solution in the project "Risk Map Germany"
International audienceThe project "Risk Map Germany" at the Center for Disaster Management and Risk Reduction Technology (CEDIM) aims at visualizing hazards, vulnerabilities and risks associated with natural and man made hazards. CEDIM as an interdisciplinary project unified various expertise like earthquake, storm and flood disaster research. Our aim was to visualize the manifold data exploration in thematic maps. The implemented Web-GIS solution "CEDIM Risk Explorer" represents the map visualizations of the different risk research. This Web-GIS integrates results from interdisciplinary work as maps of hazard, vulnerability and risk in one application and offers therefore new cognitions to the user by enabling visual comparisons. The present paper starts with a project introduction and a literature review of distributed GIS environments. Further the methods of map realization and visualization in the selected technical solution is worked out. Finally, the conclusions give the perspectives for future developments to the "CEDIM Risk Explorer"
Dynamic Critical Behavior of an Extended Reptation Dynamics for Self-Avoiding Walks
We consider lattice self-avoiding walks and discuss the dynamic critical
behavior of two dynamics that use local and bilocal moves and generalize the
usual reptation dynamics. We determine the integrated and exponential
autocorrelation times for several observables, perform a dynamic finite-size
scaling study of the autocorrelation functions, and compute the associated
dynamic critical exponents . For the variables that describe the size of the
walks, in the absence of interactions we find in two dimensions
and in three dimensions. At the -point in two dimensions
we have .Comment: laTeX2e, 32 pages, 11 eps figure
Cl 1205+44, a fossil group at z = 0.59
This is a report of Chandra, XMM-Newton, HST and ARC observations of an
extended X-ray source at z = 0.59. The apparent member galaxies range from
spiral to elliptical and are all relatively red (i'-Ks about 3). We interpret
this object to be a fossil group based on the difference between the brightness
of the first and second brightest cluster members in the i'-band, and because
the rest-frame bolometric X-ray luminosity is about 9.2x10^43 h70^-2 erg s^-1.
This makes Cl 1205+44 the highest redshift fossil group yet reported. The
system also contains a central double-lobed radio galaxy which appears to be
growing via the accretion of smaller galaxies. We discuss the formation and
evolution of fossil groups in light of the high redshift of Cl 1205+44.Comment: 21 pages, 13 figures, minor corrections to match published ApJ
versio
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