505 research outputs found
Irrigated lands assessment for water management: Technique test
A procedure for estimating irrigated land using full frame LANDSAT imagery was demonstrated. Relatively inexpensive interpretation of multidate LANDSAT photographic enlargements was used to produce a map of irrigated land in California. The LANDSAT and ground maps were then linked by regression equations to enable precise estimation of irrigated land area by county, basin, and statewide. Land irrigated at least once in California in 1979 was estimated to be 9.86 million acres, with an expected error of less than 1.75% at the 99% level of confidence. To achieve the same level of error with a ground-only sample would have required 3 to 5 times as many ground sample units statewide. A procedure for relatively inexpensive computer classification of LANDSAT digital data to irrigated land categories was also developed. This procedure is based on ratios of MSS band 7 and 5, and gave good results for several counties in the Central Valley
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Food Insecurity and Metabolic Control Among U.S. Adults With Diabetes
OBJECTIVE We sought to determine whether food insecurity is associated with worse glycemic, cholesterol, and blood pressure control in adults with diabetes. RESEARCH DESIGN AND METHODS We conducted a cross-sectional analysis of data from participants of the 1999–2008 National Health and Nutrition Examination Survey. All adults with diabetes (type 1 or type 2) by self-report or diabetes medication use were included. Food insecurity was measured by the Adult Food Security Survey Module. The outcomes of interest were proportion of patients with HbA1c >9.0% (75 mmol/mol), LDL cholesterol >100 mg/dL, and systolic blood pressure >140 mmHg or diastolic blood pressure >90 mmHg. We used multivariable logistic regression for analysis. RESULTS Among the 2,557 adults with diabetes in our sample, a higher proportion of those with food insecurity (27.0 vs. 13.3%, P 9.0% (75 mmol/mol). After adjustment for age, sex, educational attainment, household income, insurance status and type, smoking status, BMI, duration of diabetes, diabetes medication use and type, and presence of a usual source of care, food insecurity remained significantly associated with poor glycemic control (odds ratio [OR] 1.53 [95% CI 1.07–2.19]). Food insecurity was also associated with poor LDL control before (68.8 vs. 49.8, P = 0.002) and after (1.86 [1.01–3.44]) adjustment. Food insecurity was not associated with blood pressure control. CONCLUSIONS Food insecurity is significantly associated with poor metabolic control in adults with diabetes. Interventions that address food security as well as clinical factors may be needed to successfully manage chronic disease in vulnerable adults
Low-loss criterion and effective area considerations for photonic crystal fibers
We study the class of endlessly single-mode all-silica photonic crystal
fibers with a triangular air-hole cladding. We consider the sensibility to
longitudinal nonuniformities and the consequences and limitations for realizing
low-loss large-mode area photonic crystal fibers. We also discuss the
dominating scattering mechanism and experimentally we confirm that both macro
and micro-bending can be the limiting factor.Comment: Accepted for Journal of Optics A - Pure and Applied Optic
The ALHAMBRA photometric system
This paper presents the characterization of the optical range of the ALHAMBRA
photometric system, a 20 contiguous, equal-width, medium-band CCD system with
wavelength coverage from 3500A to 9700A. The photometric description of the
system is done by presenting the full response curve as a product of the
filters, CCD and atmospheric transmission curves, and using some first and
second order moments of this response function. We also introduce the set of
standard stars that defines the system, formed by 31 classic spectrophotometric
standard stars which have been used in the calibration of other known
photometric systems, and 288 stars, flux calibrated homogeneously, from the
Next Generation Spectral Library (NGSL). Based on the NGSL, we determine the
transformation equations between Sloan Digital Sky Survey (SDSS) ugriz
photometry and the ALHAMBRA photometric system, in order to establish some
relations between both systems. Finally we develop and discuss a strategy to
calculate the photometric zero points of the different pointings in the
ALHAMBRA project.Comment: Astronomical Journal on the 14th of January 201
Ionized gas and stellar kinematics of seventeen nearby spiral galaxies
Ionized gas and stellar kinematics have been measured along the major axes of
seventeen nearby spiral galaxies of intermediate to late morphological type. We
discuss the properties of each sample galaxy distinguishing between those
characterized by regular or peculiar kinematics. In most of the observed
galaxies ionized gas rotates more rapidly than stars and have a lower velocity
dispersion, as is to be expected if the gas is confined in the disc and
supported by rotation while the stars are mostly supported by dynamical
pressure. In a few objects, gas and stars show almost the same rotational
velocity and low velocity dispersion, suggesting that their motion is dominated
by rotation.
Incorporating the spiral galaxies studied by Bertola et al. (1996), Corsini
et al. (1999, 2003) and Vega Beltran et al. (2001) we have compiled a sample of
50 S0/a-Scd galaxies, for which the major-axis kinematics of the ionized gas
and stars have been obtained with the same spatial (~1'') and spectral
(~50km/s) resolution, and measured with the same analysis techniques. This
allowed us to address the frequency of counterrotation in spiral galaxies. It
turns out that less than 12% and less than 8% (at the 95% confidence level) of
the sample galaxies host a counterrotating gaseous and stellar disc,
respectively. The comparison with S0 galaxies suggests that the retrograde
acquisition of small amounts of external gas gives rise to counterrotating
gaseous discs only in gas-poor S0s, while in gas-rich spirals the newly
acquired gas is swept away by the pre-existing gas. Counterrotating gaseous and
stellar discs in spirals are formed only from the retrograde acquisition of
large amounts of gas exceeding that of pre-existing gas, and subsequent star
formation, respectively.Comment: 14 pages, 33 figures, A&A accepte
Dynamical Constraints on The Masses of the Nuclear Star Cluster and Black Hole in the Late-Type Spiral Galaxy NGC 3621
NGC 3621 is a late-type (Sd) spiral galaxy with an active nucleus, previously
detected through mid-infrared [Ne V] line emission. Archival Hubble Space
Telescope (HST) images reveal that the galaxy contains a bright and compact
nuclear star cluster. We present a new high-resolution optical spectrum of this
nuclear cluster, obtained with the ESI Spectrograph at the Keck Observatory.
The nucleus has a Seyfert 2 emission-line spectrum at optical wavelengths,
supporting the hypothesis that a black hole is present. The line-of-sight
stellar velocity dispersion of the cluster is sigma=43+/-3 km/s, one of the
largest dispersions measured for any nuclear cluster in a late-type spiral
galaxy. Combining this measurement with structural parameters measured from
archival HST images, we carry out dynamical modeling based on the Jeans
equation for a spherical star cluster containing a central point mass. The
maximum black hole mass consistent with the measured stellar velocity
dispersion is 3*10^6 solar masses. If the black hole mass is small compared
with the cluster's stellar mass, then the dynamical models imply a total
stellar mass of ~1*10^7 solar masses, which is consistent with rough estimates
of the stellar mass based on photometric measurements from HST images. From
structural decomposition of 2MASS images, we find no clear evidence for a bulge
in NGC 3621; the galaxy contains at most a very faint and inconspicuous
pseudobulge component (M_K>-17.6 mag). NGC 3621 provides one of the best
demonstrations that very late-type spirals can host both active nuclei and
nuclear star clusters, and that low-mass black holes can occur in disk galaxies
even in the absence of a substantial bulge.Comment: 13 pages, 10 figures. Accepted for publication in Ap
The ACS Nearby Galaxy Survey Treasury VI. The Ancient Star Forming disk of NGC 404
We present HST/WFPC2 observations across the disk of the nearby isolated
dwarf S0 galaxy NGC 404, which hosts an extended gas disk. Our deepest field
reaches the red clump and main-sequence stars with ages <500 Myr. Although we
detect trace amounts of star formation at times more recent than 10 Gyr for all
fields, the proportion of red giant stars to asymptotic giants and main
sequence stars suggests that the disk is dominated by an ancient (>10 Gyr)
population. Detailed modeling of the color-magnitude diagram suggests that ~70%
of the stellar mass in the NGC 404 disk formed by z~2 (10 Gyr ago) and at least
~90% formed prior to z~1 (8 Gyr ago). These results indicate that the stellar
populations of the NGC 404 disk are on average significantly older than those
of other nearby disk galaxies, suggesting that early and late type disks may
have different long-term evolutionary histories, not simply differences in
their recent star formation rates. Comparisons of the spatial distribution of
the young stellar mass and FUV emission in GALEX images show that the brightest
FUV regions contain the youngest stars, but that some young stars (<160 Myr)
lie outside of these regions. FUV luminosity appears to be strongly affected by
both age and stellar mass within individual regions. Finally, we use our
measurements to infer the relationship between the star formation rate and the
gas density of the disk at previous epochs. We find that most of the history of
the NGC 404 disk is consistent with star formation that has decreased with the
gas density according to the Schmidt law. However, 0.5-1 Gyr ago, the star
formation rate was unusually low for the inferred gas density, consistent with
the possibility that there was a gas accretion event that reignited star
formation ~0.5 Gyr ago. Such an event could explain why this S0 galaxy hosts an
extended gas disk.Comment: 28 pages, 20 figures, 1 table, accepted for publication in Ap
Harmonic analysis of iterated function systems with overlap
In this paper we extend previous work on IFSs without overlap. Our method
involves systems of operators generalizing the more familiar Cuntz relations
from operator algebra theory, and from subband filter operators in signal
processing.Comment: 37 page
The stellar host in blue compact dwarf galaxies: the need for a two-dimensional fit
The structural properties of the low surface brightness stellar host in blue
compact dwarf galaxies are often studied by fitting r^{1/n} models to the outer
regions of their radial profiles. The limitations imposed by the presence of a
large starburst emission overlapping the underlying component makes this kind
of analysis a difficult task. We propose a two-dimensional fitting methodology
in order to improve the extraction of the structural parameters of the LSB
host. We discuss its advantages and weaknesses by using a set of simulated
galaxies and compare the results for a sample of eight objects with those
already obtained using a one-dimensional technique. We fit a PSF convolved
Sersic model to synthetic galaxies, and to real galaxy images in the B, V, R
filters. We restrict the fit to the stellar host by masking out the starburst
region and take special care to minimize the sky-subtraction uncertainties. In
order to test the robustness and flexibility of the method, we carry out a set
of fits with synthetic galaxies. Furthermore consistency checks are performed
to assess the reliability and accuracy of the derived structural parameters.
The more accurate isolation of the starburst emission is the most important
advantage and strength of the method. Thus, we fit the host galaxy in a range
of surface brightness and in a portion of area larger than in previous
published 1D fits with the same dataset. We obtain robust fits for all the
sample galaxies, all of which, except one, show Sersic indices n very close to
1, with good agreement in the three bands. These findings suggest that the
stellar hosts in BCDs have near-exponential profiles, a result that will help
us to understand the mechanisms that form and shape BCD galaxies, and how they
relate to the other dwarf galaxy classes.Comment: 22 pages, 15 figures (low resolution), accepted for publication in
A&A. A higher resolution version of the figures can be provided upon reques
Compensation or displacement of physical activity in middle-school girls: the Trial of Activity for Adolescent Girls
The “activitystat” hypothesis suggests that increases in moderate-to-vigorous physical activity (MVPA) are accompanied by a compensatory reduction in light physical activity (LPA) and/or an increase in inactivity in order to maintain a consistent total physical activity level (TPA).ObjectiveThe purpose of this study was to identify evidence of compensation in middle school girls.SubjectsParticipants were 6,916, 8th grade girls from the Trial of Activity for Adolescent Girls (TAAG).DesignInactivity and physical activity were measured over 6- consecutive days using accelerometry (MTI Actigraph). A within-girl, repeated measures design was used to assess associations between physical activity and inactivity using general linear mixed models.ResultsWithin a given day, for every one MET-minute more of inactivity, there was 3.18 MET-minutes (95% confidence interval: −3.19, −3.17) less of TPA (activity > 2 METS) on the same day. Daily inactivity was also negatively associated with TPA on the following day. Each additional minute of MVPA was associated with 1.85 minutes less of inactivity on the same day (95% confidence interval: −1.89, −1.82). Daily MVPA was also negatively associated with inactivity the following day.ConclusionOur results, based on 6-days of observational data, were not consistent with the “activitystat” hypothesis, and instead indicated that physical activity displaced inactivity, at least in the short term. Longer intervention trials are needed, nevertheless our findings support the use of interventions to increase physical activity over discrete periods of time in middle school girls
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