2,678 research outputs found
Multi-scale processes in metapopulations : Contributions of stage structure, rescue effect, and correlated extinctions
Peer reviewedPublisher PD
Structural features in the Colorado Plateau margin near Flagstaff, Arizona
The author has identified the following significant results. On ERTS-1 frame 1014-17375, a set of northwest-trending lineaments has been discovered which converge on the north-trending lineament of the Oak Creek Fault near Flagstaff, Arizona. The lineaments are most easily seen in band 7. The region of convergence may mark an area structurally favorable for the location of water in Paleozoic sediments that underlie the basalt cap
Preliminary results in the comparison of Skylab, ERTS and RB-57 images for the detection of lineaments and fractures in Precambrian, Paleozoic, and late Tertiary rocks on and near the Colorado Plateau, North-Central Arizona
There are no author-identified significant results in this report
An IR-Selected Galaxy Cluster at z=1.27
We report the discovery of a galaxy cluster at z=1.27. ClG J0848+4453 was
found in a near-IR field survey as a high density region of objects with very
red J-K colors. Optical spectroscopy of a limited number of 24 < R < 25 objects
in the area shows that 6 galaxies within a 90 arcsec (0.49/h Mpc, q_O = 0.1)
diameter region lie at z=1.273 +/- 0.002. Most of these 6 member galaxies have
broad-band colors consistent with the expected spectral energy distribution of
a passively-evolving elliptical galaxy formed at high redshift. An additional 2
galaxies located ~2 arcmin from the cluster center are also at z=1.27. Using
all 8 of these spectroscopic members, we estimate the velocity dispersion is
700 +/- 180 km/s, similar to that of Abell R=1 clusters in the present epoch. A
deep Rosat PSPC observation detects X-ray emission at the 5 sigma level
coincident with the nominal cluster center. Assuming that the X-ray flux is
emitted by hot gas trapped in the potential well of a collapsed system (no AGN
is known to exist in the area), the resulting X-ray luminosity in the rest
frame 0.1-2.4 keV band of L_x = 1.5 x 10^44 ergs/s suggests the presence of a
moderately large mass. ClG J0848+4453 is the highest redshift cluster found
without targetting a central active galaxy.Comment: Accepted for publication in The Astronomical Journal; 22 pages, 6
figures; corrected titl
Zenithal bistability in a nematic liquid crystal device with a monostable surface condition
The ground-state director configurations in a grating-aligned, zenithally bistable nematic device are calculated in two dimensions using a Q tensor approach. The director profiles generated are well described by a one-dimensional variation of the director across the width of the device, with the distorted region near the grating replaced by an effective surface anchoring energy. This work shows that device bistability can in fact be achieved by using a monostable surface term in the one-dimensional model. This implies that is should be possible to construct a device showing zenithal bistability without the need for a micropatterned surface
Discovery of a Color-Selected Quasar at z=5.50
We present observations of RD J030117+002025, a quasar at z=5.50 discovered
from deep, multi-color, ground-based observations covering 74 square arcmin.
This is the most distant quasar or AGN currently known. The object was targeted
as an R-band dropout, with R(AB)>26.3 (3-sigma limit in a 3 arcsec diameter
region), I(AB)=23.8, and z(AB)=23.4. The Keck/LRIS spectrum shows broad
Lyman-alpha/NV emission and sharp absorption decrements from the
highly-redshifted hydrogen forests. The fractional continuum depression due to
the Lyman-alpha forest is D(A)=0.90. RD J030117+002025 is the least luminous,
high-redshift quasar known (M(B)~-22.7).Comment: 9 pages, 2 figures; to appear in the The Astrophysical Journal
Letter
Geologic applications of ERTS images on the Colorado Plateau, Arizona
Three areas in central and northern Arizona centered on the (1) Verde Valley, (2) Coconino Plateau, and (3) Shivwits Plateau were studied using ERTS photography. Useful applications results include: (1) upgrading of the existing state geologic map of the Verde Valley region; (2) detection of long NW trending lineaments in the basalt cap SE of Flagstaff which may be favorable locations for drilling for new water supplies; (3) tracing of the Bright Angel and Butte faults to twice their previously known length and correlating the extensions with modern seismic events, showing these faults to be present-day earthquake hazards; (4) discovering and successfully drilling perched sandstone aquifers in the Kaibab Limestone on the Coconino Plateau; and (5) determining the relationship between the Shivwits lavas and the formation of the lower Grand Canyon and showing that the lavas should be an excellent aquifer, as yet untapped
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