3,204 research outputs found
Satellite microwave observations of soil moisture variations
The electrically scanning microwave radiometer (ESMR) on the Nimbus 5 satellite was used to observe microwave emissions from vegetated and soil surfaces over an Illinois-Indiana study area, the Mississippi Valley, and the Great Salt Lake Desert in Utah. Analysis of microwave brightness temperatures (T sub B) and antecedent rainfall over these areas provided a way to monitor variations of near-surface soil moisture. Because vegetation absorbs microwave emission from the soil at the 1.55 cm wavelength of ESMR, relative soil moisture measurements can only be obtained over bare or sparsely vegetated soil. In general T sub B increased during rainfree periods as evaporation of water and drying of the surface soil occurs, and drops in T sub B are experienced after significant rainfall events wet the soil. Microwave observations from space are limited to coarse resolutions (10-25 km), but it may be possible in regions with sparse vegetation cover to estimate soil moisture conditions on a watershed or agricultural district basis, particularly since daily observations can be obtained
The Emergence of the Modern Universe: Tracing the Cosmic Web
This is the report of the Ultraviolet-Optical Working Group (UVOWG)
commissioned by NASA to study the scientific rationale for new missions in
ultraviolet/optical space astronomy approximately ten years from now, when the
Hubble Space Telescope (HST) is de-orbited. The UVOWG focused on a scientific
theme, The Emergence of the Modern Universe, the period from redshifts z = 3 to
0, occupying over 80% of cosmic time and beginning after the first galaxies,
quasars, and stars emerged into their present form. We considered
high-throughput UV spectroscopy (10-50x throughput of HST/COS) and wide-field
optical imaging (at least 10 arcmin square). The exciting science to be
addressed in the post-HST era includes studies of dark matter and baryons, the
origin and evolution of the elements, and the major construction phase of
galaxies and quasars. Key unanswered questions include: Where is the rest of
the unseen universe? What is the interplay of the dark and luminous universe?
How did the IGM collapse to form the galaxies and clusters? When were galaxies,
clusters, and stellar populations assembled into their current form? What is
the history of star formation and chemical evolution? Are massive black holes a
natural part of most galaxies? A large-aperture UV/O telescope in space
(ST-2010) will provide a major facility in the 21st century for solving these
scientific problems. The UVOWG recommends that the first mission be a 4m
aperture, SIRTF-class mission that focuses on UV spectroscopy and wide-field
imaging. In the coming decade, NASA should investigate the feasibility of an 8m
telescope, by 2010, with deployable optics similar to NGST. No high-throughput
UV/Optical mission will be possible without significant NASA investments in
technology, including UV detectors, gratings, mirrors, and imagers.Comment: Report of UV/O Working Group to NASA, 72 pages, 13 figures, Full
document with postscript figures available at
http://casa.colorado.edu/~uvconf/UVOWG.htm
Unquenching the Quark Model and Screened Potentials
The low-lying spectrum of the quark model is shown to be robust under the
effects of `unquenching'. In contrast, the use of screened potentials is shown
to be of limited use in models of hadrons. Applications to unquenching the
lattice Wilson loop potential and to glueball mixing in the adiabatic hybrid
spectrum are also presented.Comment: 6 pages, 3 ps figures, revtex. Version to appear in J. Phys.
Hartree-Fock and Many-Body Perturbation Theory with Correlated Realistic NN-Interactions
We employ correlated realistic nucleon-nucleon interactions for the
description of nuclear ground states throughout the nuclear chart within the
Hartree-Fock approximation. The crucial short-range central and tensor
correlations, which are induced by the realistic interaction and cannot be
described by the Hartree-Fock many-body state itself, are included explicitly
by a state-independent unitary transformation in the framework of the unitary
correlation operator method (UCOM). Using the correlated realistic interaction
V_UCOM resulting from the Argonne V18 potential, bound nuclei are obtained
already on the Hartree-Fock level. However, the binding energies are smaller
than the experimental values because long-range correlations have not been
accounted for. Their inclusion by means of many-body perturbation theory leads
to a remarkable agreement with experimental binding energies over the whole
mass range from He-4 to Pb-208, even far off the valley of stability. The
observed perturbative character of the residual long-range correlations and the
apparently small net effect of three-body forces provides promising
perspectives for a unified nuclear structure description.Comment: 14 pages, 8 figures, 3 tables, using REVTEX
Pair decay width of the Hoyle state and carbon production in stars
Electron scattering off the first excited 0+ state in 12C (the Hoyle state)
has been performed at low momentum transfers at the S-DALINAC. The new data
together with a novel model-independent analysis of the world data set covering
a wide momentum transfer range result in a highly improved transition charge
density from which a pair decay width Gamma_pi = (62.3 +- 2.0) micro-eV of the
Hoyle state was extracted reducing the uncertainty of the literature values by
more than a factor of three. A precise knowledge of Gamma_pi is mandatory for
quantitative studies of some key issues in the modeling of supernovae and of
asymptotic giant branch stars, the most likely site of the slow-neutron
nucleosynthesis process.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Let
Ultrafast sublattice pseudospin relaxation in graphene probed by polarization-resolved photoluminescence
Electronic pseudospin degrees of freedom in two-dimensional materials exhibit unique carrier-field interactions which allow for advanced control strategies. Here, we investigate ultrafast sublattice pseudospin relaxation in graphene by means of polarization-resolved photoluminescence spectroscopy. A comparison with microscopic Boltzmann simulations allows us to determine a lifetime of the optically aligned pseudospin distribution of 12±2fs. This experimental approach extends the toolbox of graphene pseudospintronics, providing additional means to investigate pseudospin dynamics in active devices or under external fields
Sub-Relativistic Radio Jets and Parsec-Scale Absorption in Two Seyfert Galaxies
The Very Long Baseline Array has been used at 15 GHz to image the
milliarcsecond structure of the Seyfert galaxies Mrk 231 and Mrk 348 at two
epochs separated by about 1.7 yr. Both galaxies contain parsec-scale double
radio sources whose components have brightness temperatures of 10^9-10^{11} K,
implying that they are generated by synchrotron emission. The nuclear
components are identified by their strong variability between epochs,
indicating that the double sources represent apparently one-sided jets.
Relative component speeds are measured to be ~0.1c at separations of 1.1 pc or
less (for H_0 = 65 km/s/Mpc), implying that parsec-scale Seyfert jets are
intrinsically different from those in most powerful radio galaxies and quasars.
The lack of observed counterjets is most likely due to free-free absorption by
torus gas, with an ionized density n_e > 2 X 10^5 cm^{-3} at T~8000 K, or n_e >
10^7 cm^{-3} at T~10^{6.6} K, in the inner parsec of each galaxy. The lower
density is consistent with values found from X-ray absorption measurements,
while the higher temperature and density are consistent with direct radio
imaging of the NGC 1068 torus by Gallimore et al.Comment: 12 pages, 2 postscript figures, LaTeX file in AASTeX format, accepted
by ApJ Letter
O VI Observations of the Onset of Convection Zones in Main-Sequence A Stars
If magnetic activity in outer stellar atmospheres is due to an interplay
between rotation and subsurface convection, as is generally presumed, then one
would not expect to observe indicators of activity in stars with T_eff > 8300
K. Any X-ray or ultraviolet line emission from hotter stars must be due either
to a different mechanism or to an unresolved, active, binary companion. Due to
their poor spatial resolution, X-ray instruments have been especially
susceptible to source confusion. At wavelengths longward of 1216 Angstroms, the
near ultraviolet spectra of stars hotter than this putative dividing line are
dominated by photospheric continuum. We have used FUSE to obtain spectra of the
subcoronal O VI emission lines, which lie at a wavelength where the
photospheric continuum of the mid- and early-A stars is relatively weak. We
observed 14 stars spanning a range in T_eff from 7720 to 10,000 K. Eleven of
the 14 stars showed O VI emission lines, including 6 of the 8 targets with
T_eff > 8300 K. At face value, this suggests that activity does not fall off
with increasing temperature. However, the emission lines are narrower than
expected from the projected rotational velocities of these rapidly-rotating
stars, suggesting that the emission could come from unresolved late-type
companions. Furthermore, the strength of the O VI emission is consistent with
that expected from an unseen active K or M dwarf binary companinon, and the
high x-ray to far uv luminosity ratios observed indicate that this must be the
case. Our results are therefore consistent with earlier studies that have shown
a rapid drop-off in activity at the radiative/convective boundary expected at
T_eff about 8300 K, in agreement with conventional stellar structure models
Conversion of barley SNPs into PCR-based markers using dCAPS method
Molecular genetic research relies heavily on the ability to detect polymorphisms in DNA. Single nucleotide polymorphisms (SNPs) are the most frequent form of DNA variation in the genome. In combination with a PCR assay, the corresponding SNP can be analyzed as a derived cleaved amplified polymorphic sequence (dCAPS) marker. The dCAPS method exploits the well-known specificity of a restriction endonuclease for its recognition site and can be used to virtually detect any SNP. Here, we describe the use of the dCAPS method for detecting single-nucleotide changes by means of a barley EST, CK569932, PCR-based marker
The Local Universe as Seen in Far-Infrared and in Far-Ultraviolet: A Global Point of View on the Local Recent Star Formation
We select far-infrared (FIR-60 microns) and far-ultraviolet (FUV-1530 A)
samples of nearby galaxies in order to discuss the biases encountered by
monochromatic surveys (FIR or FUV). Very different volumes are sampled by each
selection and much care is taken to apply volume corrections to all the
analyses. The distributions of the bolometric luminosity of young stars are
compared for both samples: they are found to be consistent with each other for
galaxies of intermediate luminosities but some differences are found for high
(>5 10^{10} L_sun) luminosities. The shallowness of the IRAS survey prevents us
from securing comparison at low luminosities (<2 10^9 L_sun). The ratio of the
total infrared (TIR) luminosity to the FUV luminosity is found to increase with
the bolometric luminosity in a similar way for both samples up to 5 10^{10}
L_sun. Brighter galaxies are found to have a different behavior according to
their selection: the L_TIR/L_FUV ratio of the FUV-selected galaxies brighter
than 5 10^{10} L_sun reaches a plateau whereas L_TIR/L_FUV continues to
increase with the luminosity of bright galaxies selected in FIR. The
volume-averaged specific star formation rate (SFR per unit galaxy stellar mass,
SSFR) is found to decrease toward massive galaxies within each selection. The
SSFR is found to be larger than that measured for optical and NIR-selected
sample over the whole mass range for the FIR selection, and for masses larger
than 10^{10} M_sun for the FUV selection. Luminous and massive galaxies
selected in FIR appear as active as galaxies with similar characteristics
detected at z ~ 0.7.Comment: 32 pages, 9 figures, to be published in the Astrophysical Journal
Supplement series dedicated to GALEX result
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