41,786 research outputs found
Mixed-Morphology Supernova Remnants in X-rays: Isothermal Plasma in HB21 and Probable Oxygen-Rich Ejecta in CTB 1
(Abridged) We present an analysis of X-ray observations made of the Galactic
supernova remnants (SNRs) HB21 (G89.0+4.7) and CTB 1 (G116.9+0.2), two
well-known mixed-morphology (MM) SNRs. We find a marked contrast between the
X-ray properties of these SNRs: for HB21, the extracted ASCA spectra of the
northwest and southeast regions of the X-ray emitting plasma can be fit with a
single thermal model with marginally enhanced silicon and sulfur abundances.
For both of these regions, the derived column density and temperature are
N_H~0.3x10^22 cm^-2 and kT~0.7 keV, respectively. No significant spatial
differences in temperature or elemental abundances between the two regions are
detected and the X-ray-emitting plasma in both regions is close to ionization
equilibrium. Our Chandra spectral analysis of CTB 1 reveals that this source is
likely an oxygen-rich SNR with enhanced abundances of oxygen and neon. The
extracted ASCA spectra for the southwestern and northeastern regions of CTB 1
cannot be fit with a single thermal component. Based on our fits to these
spectra, we derive a column density N_H~0.6x10^22 cm^-2 and a temperature for
the soft thermal component of kT_soft~0.28 keV. The hard emission from the
southwest may be modeled with either a thermal component (kT_hard~3 keV) or by
a power law component (Gamma~2-3) while the hard emission from the northeast
may be modeled with a power law component (Gamma~1.4). We have also extracted
ASCA GIS spectra of the discrete X-ray source 1WGA J0001.4+6229 which is seen
in projection toward CTB 1. These spectra are best fit using a power-law model
with a photon index Gamma=2.2^{+0.5}_{-1.2} which is typical for featureless
power-law continua produced by rotation-powered pulsars. This source may be a
neutron star associated with CTB 1.Comment: 46 pages, 16 figures, accepted for publication in the Astronomical
Journa
Non-Thermal X-ray Emission from the Northwestern Rim of the Galactic Supernova Remnant G266.2-1.2 (RX J0852.0-4622)
We present a detailed spatially-resolved spectroscopic analysis of two X-ray
observations (with a total integration time of 73280 seconds) made of the
luminous northwestern rim complex of the Galactic supernova remnant (SNR)
G266.2-1.2 (RX J0852.0-4622) with the Chandra X-ray Observatory. G266.2-1.2 is
a member of a class of Galactic SNRs which feature X-ray spectra dominated by
non-thermal emission: in the cases of these SNRs, the emission is believed to
have a synchrotron origin and studies of the X-ray spectra of these SNRs can
lend insights into how SNRs accelerate cosmic-ray particles. The Chandra
observations have clearly revealed fine structure in this rim complex and the
spectra of these features are dominated by non-thermal emission. We have
measured the length scales of the upstream structures at eight positions along
the rim and derive lengths of 0.02-0.08 pc (assuming a distance of 750 pc to
G266.2-1.2). We have also extracted spectra from seven regions in the rim
complex and fit these spectra with such models as a simple power law as well as
the synchrotron models SRCUT and SRESC. We have constrained our fits to the
latter two models using estimates for the flux densities of these filaments at
1 GHz as determined from radio observations made with the Australia Telescope
Compact Array (ATCA). Statistically-acceptable fits to all seven regions are
derived using each model: differences in the fit parameters (such as photon
index and cutoff frequency) are seen in the different regions, which may
indicate variations in shock conditions and the maximum energies of the
cosmic-ray electrons accelerated at each region. Finally, we estimate the
maximum energy of cosmic-ray electrons accelerated along this rim complex to be
approximately 40 TeV. We include a summary of estimated maximum energies for
both Galactic SNRs as well as SNRs located in the Large Magellanic Cloud.Comment: 56 Pages, 11 Figures, Accepted for publication in the Astrophysical
Journa
The X-ray Properties of Five Galactic Supernova Remnants Detected by the Spitzer GLIMPSE Survey
(Abbreviated) We present a study of the X-ray properties of five Galactic
supernova remnants (SNRs) -- Kes 17 (G304.60.1), G311.50.3, G346.60.2,
CTB 37A (G348.50.1) and G348.50.0 -- that were detected in the infrared
by Reach et al. (2006) in an analysis of data from the Galactic Legacy Infrared
Mid-Plane Survey Extraordinaire (GLIMPSE) that was conducted by the Spitzer
Space Telescope. We present and analyze archival ASCA observations of Kes 17,
G311.50.3 and G346.60.2, archival XMM-Newton observations of Kes 17, CTB
37A and G348.50.0 and an archival Chandra observation of CTB 37A. All of the
SNRs are clearly detected in the X-ray possibly except for G348.50.0. Our
study reveals that the four detected SNRs all feature center-filled X-ray
morphologies and that the observed emission from these sources is thermal in
all cases. We argue that these SNRs should be classified as mixed-morphology
SNRs (MM SNRs): our study strengthens the correlation between MM SNRs and SNRs
interacting with molecular clouds and suggests that the origin of
mixed-morphology SNRs may be due to the interactions between these SNRs and
adjacent clouds. Our ASCA analysis of G311.50.3 reveals for the first time
X-ray emission from this SNR: the X-ray emission is center-filled within the
radio and infrared shells and thermal in nature ( 0.98 keV), thus
motivating its classification as an MM SNR. We find considerable spectral
variations in the properties associated with the plasmas of the other
X-ray-detected SNRs, such as a possible overabundance of magnesium in the
plasma of Kes 17. Finally, we also estimate such properties as electron density
, radiative age and swept-up mass for each of the
four X-ray-detected SNRs.Comment: 78 pages, 26 figures, Astronomical Journal, in pres
Evolutionary Centrality and Maximal Cliques in Mobile Social Networks
This paper introduces an evolutionary approach to enhance the process of
finding central nodes in mobile networks. This can provide essential
information and important applications in mobile and social networks. This
evolutionary approach considers the dynamics of the network and takes into
consideration the central nodes from previous time slots. We also study the
applicability of maximal cliques algorithms in mobile social networks and how
it can be used to find the central nodes based on the discovered maximal
cliques. The experimental results are promising and show a significant
enhancement in finding the central nodes
Sandstone and Chisel: Three Historic Ohio "Indian" Rock Carvings
Three historic petroglyphs (rock carvings) are described from Ohio, including the Jobes Indian head Rock, Washington Co.; Baughman Park carvings, Licking Co.; the Portsmouth Indian Head Rock, originally in the Ohio River and currently located at Portsmouth, Ohio
Rewriting the How-To of Parenting: What Is Really Modern about ABC’s Modern Family
Despite its unconventional family structures and playful gestures at redefining traditional gender scripts, ABC’s domestic comedy, Modern Family, perpetuates perceived notions of femininity and masculinity within the context of three families whose differences from the nuclear family are far from radical. Reassuring even its most conservative viewers on these counts, the show does, however, portray a potentially unsettling approach to parenting. The dynamics of parenting are unstable, bending gender rules and disregarding boundaries normally set by age, race, and social class. As normative notions of parenting are questioned and expanded, parenthood is no longer an immutable institution built on hard rules and clear hierarchies. However chaotic in appearance, such parenting takes a tremendous burden off the shoulders of viewer-parents and, particularly, viewer-mothers who, in a climate that equates the decline of family values with the failure of society as a whole, are culturally mandated to be unshakeable sources of stability, consistency, and guidance. Rather than blaming parents for their inability to follow a socially sanctioned parenting protocol, Modern Family grants fathers and especially mothers leeway to approach parenthood and family according to their individual abilities and limitations
2003-2004 graduate catalog
The SNHU graduate catalog features information for graduate certificate and continuing education programs, admission and program requirements, tuition and fee information, financial aid information, academic support services, and information about non-academic on-campus features such as athletics and residence life
Detection of Network Structure in the Las Campanas Redshift Survey
We employ a percolation technique developed for pointwise distributions to analyze two-dimensional projections of the three northern and three southern slices in the Las Campanas Redshift Survey. One of the goals of this paper is to compare the visual impressions of the structure within distributions with objective statistical analysis. We track the growth of the largest cluster as an indicator of the network structure. We restrict our analysis to volume limited subsamples in the regions from 200 to 400 Mpc where the number density of galaxies is the highest. As a major result, we report a measurement of an unambiguous signal, with high signal-to-noise ratio (at least at the level of a few ), indicating significant connectivity of the galaxy distribution which in two dimensions is indicative of a filamentary distribution. This is in general agreement with the visual impression and typical for the standard theory of the large-scale structure formation based on gravitational instability of initially Gaussian density fluctuations
Holocene Biogeochemical and Pollen History of a Lake Erie, Ohio, Coastal Wetland
Author Institution: Department of Biological and Environmental Sciences, Morehead State University and Byrd Polar Research Center, The Ohio State UniversityA five meter sediment core was taken from Old Woman Creek National Estuarine Research Reserve and State Natural Area and Preserve along the western basin of Lake Erie, U.S.A., to determine the historical biogeochemistry of the wetland. Analysis of pollen and sediment chemistry revealed that the area has remained a wetland since ca. 5,500 yr BP, despite changing lake levels. Pollen stratigraphy indicates a distinctive local succession, which has been divided into three zones. Sediments from sometime after glaciation to 5,500 yr BP were characterized by low concentrations of herb pollen; the next zone showed an establishment of hardwood forest vegetation. The modern local vegetation developed after deforestation (about 200 years ago), when sedimentation increased an order of magnitude, phosphorus deposition increased, and the ecosystem changed from a macrophyte dominated wetland to a plankton dominated marsh. After European settlement, the wetland retained its ability to act as a sink and biotic transformer of bioavailable phosphorus; however, abiotic processes seemed to be more important than the biotic transformations that dominated before deforestation
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