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Small-scale morphologic properties of martian gullies: insights from analysis of HiRISE images
Abstract not available
Is the EGRET source 3EG J1621+8203 the radio galaxy NGC 6251?
We discuss the nature of the unidentified EGRET source 3EG J1621+8203. In an
effort to identify the gamma-ray source, we have examined X-ray images of the
field from ROSAT PSPC, ROSAT HRI, and ASCA GIS. Of the several faint X-ray
point sources in the error circle of 3EG J1621+8203, most are stars or faint
radio sources, unlikely to be counterparts to the EGRET source. The most
notable object in the gamma-ray error box is the bright FR I radio galaxy NGC
6251. If 3EG J1621+8203 corresponds to NGC 6251, then it would be the second
radio galaxy to be detected in high energy gamma rays, after Cen A, which
provided the first clear evidence of the detection above 100 MeV of an AGN with
a large-inclination jet. If the detection of more radio galaxies by EGRET has
been limited by its threshold sensitivity, there exists the exciting
possibility that new high energy gamma-ray instruments, with much higher
sensitivity, will detect a larger number of radio galaxies in the future.Comment: 7 pages, 6 figures. Accepted for publication in The Astrophysical
Journal, August 2002 issu
Cloud Structure and Physical Conditions in Star-forming Regions from Optical Observations. I. Data and Component Structure
We present high-resolution optical spectra (at ~0.6--1.8 km s-1) of
interstellar CN, CH, CH^+, \ion{Ca}{1}, \ion{K}{1}, and \ion{Ca}{2} absorption
toward 29 lines of sight in three star-forming regions, \rho Oph, Cep OB2, and
Cep OB3. The observations and data reduction are described. The agreement
between earlier measurements of the total equivalent widths and our results is
quite good. However, our higher resolution spectra reveal complex structure and
closely blended components in most lines of sight. The velocity component
structure of each species is obtained by analyzing the spectra of the six
species for a given sight line together. The tabulated column densities and
Doppler parameters of individual components are determined by using the method
of profile fitting. Total column densities along lines of sight are computed by
summing results from profile fitting for individual components and are compared
with column densities from the apparent optical depth method. A more detailed
analysis of these data and their implications will be presented in a companion
paper.Comment: 66 pages, 15 figures, accepted to ApJ
Multi-State Trials of Bt Sweet Corn Varieties for Control of the Corn Earworm (Lepidoptera: Noctuidae)
Field tests in 2010-2011 were performed in New York, Minnesota, Maryland, Ohio, and Georgia to compare Bt sweet corn lines expressing Cry1A.105 + Cry2Ab2 and Cry1Ab with their non-Bt isolines, with and without the use of foliar insecticides. The primary insect pest in all locations during the trial years was Heliocoverpa zea (Boddie), which is becoming the most serious insect pest of sweet corn in the United States. At harvest, the ears were measured for marketability according to fresh market and processing standards. For fresh market and processing, least squares regression showed significant effects of protein expression, state, and insecticide frequency. There was a significant effect of year for fresh market but not for processing. The model also showed significant effects of H. zea per ear by protein expression. Sweet corn containing two genes (Cry1A.105 + Cry2Ab2) and a single gene (Cry1Ab) provided high marketability, and both Bt varieties significantly outperformed the traditional non-Bt isolines in nearly all cases regardless of insecticide application frequency. For pest suppression of H. zea, plants expressing Bt proteins consistently performed better than non-Bt isoline plants, even those sprayed at conventional insecticide frequencies. Where comparisons in the same state were made between Cry1A.105 + Cry2Ab2 and Cry1Ab plants for fresh market, the product expressing Cry1A.105 + Cry2Ab2 provided better protection and resulted in less variability in control. Overall, these results indicate Cry1A.105 + Cry2Ab2 and Cry1Ab plants are suitable for fresh market and processing corn production across a diversity of growing regions and years. Our results demonstrate that Bt sweet corn has the potential to significantly reduce the use of conventional insecticides against lepidopteran pests and, in turn, reduce occupational and environmental risks that arise from intensive insecticide us
Abundances and Physical Conditions in the Interstellar Gas toward HD 192 639
We present a study of the abundances and physical conditions in the
interstellar gas toward the heavily reddened star HD 192639 [E_(B-V) = 0.64],
based on analysis of FUSE and HST/STIS spectra covering the range from 912 to
1361 A. This work constitutes a survey of the analyses that can be performed to
study the interstellar gas when combining data from different instruments.
Low-velocity (-18 to -8 km/s) components are seen primarily for various neutral
and singly ionized species such as C I, O I, S I, Mg II, Cl I, Cl II, Mn II, Fe
II and Cu II. Numerous lines of H2 are present in the FUSE spectra, with a
kinetic temperature for the lowest rotational levels T_(01) = (90 +/- 10) K.
Analysis of the C I fine-structure excitation implies an average local density
of hydrogen n_H = (16 +/- 3) cm^-3. The average electron density, derived from
five neutral/first ion pairs under the assumption of photoionization
equilibrium, is n_e = (0.11 +/- 0.02) cm^-3. The relatively complex component
structure seen in high-resolution spectra of K I and Na I, the relatively low
average density, and the measured depletions all suggest that the line of sight
contains a number of diffuse clouds, rather than a single dense, translucent
cloud. Comparisons of the fractions of Cl in Cl I and of hydrogen in molecular
form suggest a higher molecular fraction, in the region(s) where H2 is present,
than that derived considering the average line of sight. In general, such
comparisons may allow the identification and characterization of translucent
portions of such complex lines of sight. The combined data also show
high-velocity components near -80 km/s for various species which appear to be
predominantly ionized, and may be due to a radiative shock. A brief overview of
the conditions in this gas will be given.Comment: 37 pages, accepted for publication in Ap
The Velocity Distribution of the Nearest Interstellar Gas
The bulk flow velocity for the cluster of interstellar cloudlets within about
30 pc of the Sun is determined from optical and ultraviolet absorption line
data, after omitting from the sample stars with circumstellar disks or variable
emission lines and the active variable HR 1099. Ninety-six velocity components
towards the remaining 60 stars yield a streaming velocity through the local
standard of rest of -17.0+/-4.6 km/s, with an upstream direction of l=2.3 deg,
b=-5.2 deg (using Hipparcos values for the solar apex motion). The velocity
dispersion of the interstellar matter (ISM) within 30 pc is consistent with
that of nearby diffuse clouds, but present statistics are inadequate to
distinguish between a Gaussian or exponential distribution about the bulk flow
velocity. The upstream direction of the bulk flow vector suggests an origin
associated with the Loop I supernova remnant. Groupings of component velocities
by region are seen, indicating regional departures from the bulk flow velocity
or possibly separate clouds. The absorption components from the cloudlet
feeding ISM into the solar system form one of the regional features. The
nominal gradient between the velocities of upstream and downstream gas may be
an artifact of the Sun's location near the edge of the local cloud complex. The
Sun may emerge from the surrounding gas-patch within several thousand years.Comment: Typographical errors corrected; Five tables, seven figures;
Astrophysical Journal, in pres
High-Resolution Observations of Interstellar Ca I Absorption -- Implications for Depletions and Electron Densities in Diffuse Clouds
We present high-resolution (FWHM ~ 0.3-1.5 km/s) spectra of interstellar Ca I
absorption toward 30 Galactic stars. Comparisons of the column densities of Ca
I, Ca II, K I, and other species -- for individual components identified in the
line profiles and also when integrated over entire lines of sight -- yield
information on relative electron densities and depletions. There is no obvious
relationship between the ratio N(Ca I)/N(Ca II) [equal to n_e/(Gamma/alpha_r)
for photoionization equilibrium] and the fraction of hydrogen in molecular form
f(H2) (often taken to be indicative of the local density n_H). For a smaller
sample of sightlines for which the thermal pressure (n_H T) and local density
can be estimated via analysis of the C I fine-structure excitation, the average
electron density inferred from C, Na, and K (assuming photoionization
equilibrium) seems to be independent of n_H and n_H T. While the n_e obtained
from the ratio N(Ca I)/N(Ca II) is often significantly higher than the values
derived from other elements, the patterns of relative n_e derived from
different elements show both similarities and differences for different lines
of sight -- suggesting that additional processes besides photoionization and
radiative recombination commonly and significantly affect the ionization
balance of heavy elements in diffuse IS clouds. Such additional processes may
also contribute to the (apparently) larger than expected fractional ionizations
(n_e/n_H) found for some lines of sight with independent determinations of n_H.
In general, inclusion of ``grain-assisted'' recombination does reduce the
inferred n_e, but it does not reconcile the n_e estimated from different
elements. The depletion of calcium may have a much weaker dependence on density
than was suggested by earlier comparisons with CH and CN.Comment: aastex, 70 pages, accepted to ApJ
Self-aligned nanoscale SQUID on a tip
A nanometer-sized superconducting quantum interference device (nanoSQUID) is
fabricated on the apex of a sharp quartz tip and integrated into a scanning
SQUID microscope. A simple self-aligned fabrication method results in
nanoSQUIDs with diameters down to 100 nm with no lithographic processing. An
aluminum nanoSQUID with an effective area of 0.034 m displays flux
sensitivity of 1.8 \mu_B/\mathrm{Hz}^{1/2}$ and high bandwidth, the SQUID on a tip is a highly
promising probe for nanoscale magnetic imaging and spectroscopy.Comment: 14 manuscript pages, 5 figure
Hubble Space Telescope Observations of Element Abundances in Low-redshift Damped Lyman-alpha Galaxies and Implications for the Global Metallicity-Redshift Relation
Most models of cosmic chemical evolution predict that the mass-weighted mean
interstellar metallicity of galaxies should rise with time from a low value
solar at to a nearly solar value at . In the
absence of any selection effects, the damped Lyman-alpha absorbers (DLAs) in
quasar spectra are expected to show such a rise in global metallicity. However,
it has been difficult to determine whether or not DLAs show this effect,
primarily because of the very small number of DLA metallicity measurements at
low redshifts. In an attempt to put tighter constraints on the low-redshift end
of the DLA metallicity-redshift relation, we have observed Zn II and Cr II
lines in four DLAs at , using the Space Telescope Imaging
Spectrograph (STIS) onboard the Hubble Space Telescope (HST). These
observations have provided the first constraints on Zn abundances in DLAs with
. In all the three DLAs for which our observations offer meaningful
constraints on the metallicity, the data suggest that the metallicities are
much lower than the solar value. These results are consistent with recent
imaging studies indicating that these DLAs may be associated with dwarf or low
surface brightness galaxies. We combine our results with higher redshift data
from the literature to estimate the global mean metallicity-redshift relation
for DLAs. We find that the global mean metallicity shows at most a slow
increase with decreasing redshift. ...(Please see the paper for the complete
abstract).Comment: 56 pages, including 13 figures. Accepted for publication in the
Astrophysical Journa
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