6,187 research outputs found
Unexpected Magnetism of Small Silver Clusters
The ground-state electronic, structural, and magnetic properties of small
silver clusters, Ag (2n22), have been studied using a linear
combination of atomic Gaussian-type orbitals within the density functional
theory. The results show that the silver atoms, which are diamagnetic in bulk
environment, can be magnetic when they are grouped together in clusters. The
Ag cluster with icosahedral symmetry has the highest magnetic moment per
atom among the studied silver clusters. The cluster symmetry and the reduced
coordination number specific of small clusters reveal as a fundamental factor
for the onset of the magnetism.Comment: 4 pages, 4 figure
Evaluating the Effectiveness of Iron Chelates in Managing Iron Deficiency Chlorosis in Grain Sorghum
Grain sorghum production in alkaline or calcareous soils is frequently affected by iron (Fe) chlorosis. Soil conditions such as high pH, high free calcium carbonate (lime), and low organic matter favor development of Fe deficiency chlorosis (IDC), which can delay crop maturity and reduce yields. Field experiments were conducted in the summer of 2014 and 2015 to determine the effectiveness of Fe chelate application in alleviating IDC in grain sorghum. Treatments were four Fe chelate application rates (0, 3, 6, and 9 lb product/a) applied either in-furrow with the seed at the time of planting or 2 weeks after planting in 2014. A split treatment of 3 lb/a applied at planting and another 3 lb/a applied 2 weeks after planting was included. The study in 2015 had four Fe chelate rates (0, 3, and 6 lb product/a, and split treatment of 3 lb/a applied at planting and another 3 lb/a applied 2 weeks after planting) as main plots and five commercial sorghum hybrids as sub-plots. Results in 2014 showed IDC scores among the treatments were significant only in the early stages of growth. Iron chelate application did improve sorghum yield, with the highest yield occurring when Fe chelate was split-applied at 6 lb product/a. Grain sorghum hybrids differed in their response to IDC in 2015. Application of Fe chelates suppressed IDC and increased grain yield, particularly in susceptible hybrids in both dryland and irrigated sites. Our findings indicate that sorghum hybrids 86G32 and 87P06 showed promise for tolerance to IDC and that Fe chelate application to reduce IDC is economically feasible at current grain prices
Physical Properties of the X-ray Luminous SN 1978K in NGC 1313 from Multiwavelength Observations
We update the light curves from the X-ray, optical, and radio bandpasses
which we have assembled over the past decade, and present two observations in
the ultraviolet using the Hubble Space Telescope Faint Object Spectrograph. The
HRI X-ray light curve is constant within the errors over the entire observation
period. This behavior is confirmed in the ASCA GIS data obtained in 1993 and
1995. In the ultraviolet, we detected Ly-alpha, the [Ne IV] 2422/2424 A
doublet, the Mg II doublet at 2800 A, and a line at ~3190 A we attribute to He
I 3187. Only the Mg II and He I lines are detected at SN1978K's position. The
optical light curve is formally constant within the errors, although a slight
upward trend may be present. The radio light curve continues its steep decline.
The longer time span of our radio observations compared to previous studies
shows that SN1978K is in the same class of highly X-ray and radio-luminous
supernovae as SN1986J and SN1988Z. The [Ne IV] emission is spatially distant
from the location of SN1978K and originates in the pre-shocked matter. The Mg
II doublet flux ratio implies the quantity of line optical depth times density
of ~10^14 cm^-3 for its emission region. The emission site must lie in the
shocked gas.Comment: 32 pages, 13 figs; LaTeX with AASTEXv5; paper accepted, scheduled for
AJ, Dec 199
Chandra and ASCA X-ray Observations of the Radio Supernova SN1979C IN NGC 4321
We report on the X-ray observation of the radio selected supernova SN1979C
carried out with ASCA in 1997 December and serendipitously available from a
Chandra Guaranteed Time Observation in 1999 November. The supernova, of type SN
II-Linear (SN IIL), was first observed in the optical and occurred in the
weakly barred, almost face on spiral galaxy NGC 4321 (M100). The galaxy, a
member of the Virgo S cluster, is at a distance of 17.1 Mpc, and contains at
least three other supernovae discovered in this century. The useful exposure
time was ~25 ks for the Solid-State Imaging Spectrometer (SIS), ~28 ks for the
Gas Scintillation Imaging Spectrometer (GIS), and ~2.5 ks for Chandra's
Advanced CCD Imaging Spectrometer (ACIS). No point source was detected at the
radio position of SN1979C in a 3' diameter half power response circle in the
ASCA data. The background and galaxy subtracted SN signal had a 3sigma upper
limit to the flux of 6.3x10^-14 ergs/s/cm^-2 in the full ASCA SIS band
(0.4-10.0 keV) and a 3sigma upper limit of <3-4x10^-14 erg/s/cm^2 in the 2-10
keV band. In the Chandra data, a source at the position of SN1979C is
marginally detected at energies below 2 keV at a flux consistent with the ROSAT
HRI detection in 1995. At energies above 2 keV, no source is detected with an
upper limit of ~3x10^-14 erg/s/cm^-2. These measurements give the first ever
x-ray flux limit of a Type IIL SN above 2 keV which is an important diagnostic
of the outgoing shock wave ploughing through the circumstellar medium.Comment: 8 pages, 2 figures, accepted A
Pinto Beans (\u3ci\u3ePhaseolus vulgaris\u3c/i\u3e L.) as a Functional Food: Implications on Human Health
Most foods are considered functional in terms of providing nutrients and energy to sustain daily life, but dietary systems that are capable of preventing or remediating a stressed or diseased state are classified as functional foods. Dry beans (Phaseolus vulgaris L.) contain high levels of chemically diverse components (phenols, resistance starch, vitamins, fructooligosaccharides) that have shown to protect against such conditions as oxidative stress, cardiovascular disease, diabetes, metabolic syndrome, and many types of cancer, thereby positioning this legume as an excellent functional food. Moreover, the United States has a rich dry bean history and is currently a top producer of dry beans in the world with pinto beans accounting for the vast majority. Despite these attributes, dry bean consumption in the US remains relatively low. Therefore, the objective of this manuscript is to review dry beans as an important US agricultural crop and as functional food for the present age with an emphasis on pinto beans
The Ultraluminous X-ray Sources NGC 1313 X-1 and X-2
We present a detailed analysis of XMM archival data of two Ultraluminous
X-ray Sources (ULXs) in the nearby spiral galaxy NGC 1313: NGC 1313 X-1 and
X-2. The spectral continuum of these sources was modeled with a soft thermal
component plus a power-law. If the soft component originates from an accretion
disk, the inferred mass of the compact remnant is > 100 M_sun, making it an
Intermediate Mass Black Hole (IMBH). A detailed analysis of the residuals of
the XMM EPIC-pn spectrum shows some evidence for the presence of an Oxygen
emission line in NGC 1313 X-1. The simultaneous presence of an excess in
emission, although at a much reduced significance level, at different energies
in the X-ray spectra of NGC 1313 X-1 and X-2 is suggestive of typical emission
lines from young supernova remnants. An optical counterpart for NGC 1313 X-2
was also identified. On an ESO 3.6 m image, the Chandra error box embraces a R
\~ 23 mag stellar-like object and excludes a previously proposed optical
counterpart.Comment: 7 pages, 2 figures, to be published in Advances in Space Researc
AX J1749.1-2733 and AX J1749.2-2725 - the close pair of X-ray pulsars behind the Galactic Center: an optical identification
Two faint X-ray pulsars, AX J1749.2-2725 and AX J1749.1-2733, located in the
direction to the Galactic Center, were studied in detail using data of
INTEGRAL, XMM-Newton and Chandra observatories in X-rays, the SOFI/NTT
instrument in infrared and the RTT150 telescope in optics. X-ray positions of
both sources were determined with the uncertainty better than ~1 arcsec, that
allowed us to identify their infrared counterparts. From the subsequent
analysis of infrared and optical data we conclude that counterparts of both
pulsars are likely massive stars of B0-B3 classes located behind the Galactic
Center at distances of 12-20 kpc, depending on the type, probably in further
parts of galactic spiral arms. In addition, we investigated the extinction law
towards the galactic bulge and found that it is significantly different from
standard one.Comment: 6 pages, 7 figures, will be published in MNRA
A second glance at SN 2002ap and the M74 field with XMM-Newton
We have re-observed the field of M74 in January 2003 with XMM-Newton, 11
months after the X-ray detection of SN 2002ap. From a comparison of the two
XMM-Newton observations we obtain more accurate values for the X-ray luminosity
and colours of the source five days after the event, and a limit on its decline
rate. We compare its X-ray behaviour (prompt soft X-ray emission, relatively
low luminosity) with that of other Type Ic SNe, and speculate that SN 2002ap
may share some physical properties (low mass-loss rate and high-velocity
stellar wind from the progenitor star) with the candidate hypernova/GRB
progenitor SN 1998bw, but with a lower (non-relativistic) speed of the ejecta.
We suggest that the X-ray emission observed in 2002 is likely to come from the
radiatively-cooling reverse shock, at a temperature kT ~ 0.8 keV, and that this
soft component was already detected 5 d after the event because the absorbing
column density of the cool shell between the forward and reverse shocks was
only ~ 10^{20} cm^{-2}, ie, the shell was optically thin in the soft X-ray
band. The new XMM-Newton data also allowed us to continue monitoring two bright
variable sources in M74 that had reached peak luminosities > 10^{39} erg s^{-1}
in previous XMM-Newton and Chandra observations. Finally, we used two Chandra
observations from 2001 to investigate the luminosity and colour distribution of
the X-ray source population of M74, typical of moderately-active late-type
spirals.Comment: 13 pages, A&A, in press. Revised version with an expanded discussion
of the X-ray behaviour of SN2002a
The Blue Tip of the Stellar Locus: Measuring Reddening with the SDSS
We present measurements of reddening due to dust using the colors of stars in
the Sloan Digital Sky Survey (SDSS). We measure the color of main sequence
turn-off stars by finding the "blue tip" of the stellar locus: the prominent
blue edge in the distribution of stellar colors. The method is sensitive to
color changes of order 18, 12, 7, and 8 mmag of reddening in the colors u-g,
g-r, r-i, and i-z, respectively, in regions measuring 90' by 14'. We present
maps of the blue tip colors in each of these bands over the entire SDSS
footprint, including the new dusty southern Galactic cap data provided by the
SDSS-III. The results disfavor the best fit O'Donnell (1994) and Cardelli et
al. (1989) reddening laws, but are well described by a Fitzpatrick (1999)
reddening law with R_V = 3.1. The SFD dust map is found to trace the dust well,
but overestimates reddening by factors of 1.4, 1.0, 1.2, and 1.4 in u-g, g-r,
r-i, and i-z, largely due to the adopted reddening law. In select dusty regions
of the sky, we find evidence for problems in the SFD temperature correction. A
dust map normalization difference of 15% between the Galactic north and south
sky may be due to these dust temperature errors.Comment: 18 pages, 22 figure
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