6,815 research outputs found
Dependence of the High Latitude Middle Atmosphere Ionization on Structures in Interplanetary Space
The precipitation of high energetic electrons during and after strong geomagnetic storms into heights below 100 km in middle and subauroral latitudes is markedly modulated by the structure of the interplanetary magnetic field (IMF). Under relative quiet conditions the D-region ionization caused by high energetic particle precipitation (energies greater than 20 to 50 keV) depends on changes of the interplanetary magnetic field and also on the velocity of the solar wind. To test this assumption, the influence of the IMF-sector boundary crossings on ionospheric absorption data of high and middle latitudes by the superposed-epoch method was investigated
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Arterial-portal fistula treated with hepatic arterial embolization and portal venous aneurysm stent-graft exclusion complicated by type 2 endoleak.
Intrahepatic arterioportal fistulas may be complicated by portal hypertension. An associated portal venous aneurysm (PVA) may impinge upon adjacent structures or rupture. We present a 65-year-old man with an intrahepatic Intrahepatic arterioportal fistula and 6.4 × 5.8 cm right portal vein aneurysm extending within 0.4 cm of the hepatic margin, associated with pain concerning for impending rupture. The PVA was refractory to transarterial embolization due to recruitment of arterial collaterals. Therefore, it was additionally excluded from the portal vein with a 12 mm × 9.5 cm venous stent graft. Although endovascular therapy thrombosed the aneurysm and improved symptoms, it was complicated by a type 2 endoleak into the PVA
The Physical Properties of LBGs at z>5: Outflows and the "pre-enrichment problem"
We discuss the properties of Lyman Break galaxies (LBGs) at z>5 as determined
from disparate fields covering approximately 500 sq. arcmin. While the broad
characteristics of the LBG population has been discussed extensively in the
literature, such as luminosity functions and clustering amplitude, we focus on
the detailed physical properties of the sources in this large survey (>100 with
spectroscopic redshifts). Specifically, we discuss ensemble mass estimates,
stellar mass surface densities, core phase space densities, star-formation
intensities, characteristics of their stellar populations, etc as obtained from
multi-wavelength data (rest-frame UV through optical) for a subsample of these
galaxies. In particular, we focus on evidence that these galaxies drive
vigorous outflows and speculate that this population may solve the so-called
``pre-enrichment problem''. The general picture that emerges from these studies
is that these galaxies, observed about 1 Gyr after the Big Bang, have
properties consistent with being the progenitors of the densest stellar systems
in the local Universe -- the centers of old bulges and early type galaxies.Comment: 4 pages, to appear in "Pathways Through an Eclectic Universe", J. H.
Knappen, T. J. Mahoney, and A. Vazedekis (Eds.), ASP Conf. Ser., 200
Detection of X-ray emission from the host clusters of 3CR quasars
We report the detection of extended X-ray emission around several powerful
3CR quasars with redshifts out to 0.73. The ROSAT HRI images of the quasars
have been corrected for spacecraft wobble and compared with an empirical
point-spread function. All the quasars examined show excess emission at radii
of 15 arcsec and more; the evidence being strong for the more distant objects
and weak only for the two nearest ones, which are known from other wavelengths
not to lie in strongly clustered environments. The spatial profiles of the
extended component is consistent with thermal emission from the intracluster
medium of moderately rich host clusters to the quasars. The total luminosities
of the clusters are in the range 4x10^44 - 3x10^45 erg/s, assuming a
temperature of 4keV. The inner regions of the intracluster medium are, in all
cases, dense enough to be part of a cooling flow.Comment: 21 pages including 4 figures and 4 tables. To be published in MNRA
A Parkes half-Jansky sample of GPS galaxies
This paper describes the selection of a new southern/equatorial sample of
Gigahertz Peaked Spectrum (GPS) radio galaxies, and subsequent optical CCD
imaging and spectroscopic observations using the ESO 3.6m telescope. The sample
consists of 49 sources with -4020 degrees, and
S(2.7GHz)>0.5 Jy, selected from the Parkes PKSCAT90 survey. About 80% of the
sources are optically identified, and about half of the identifications have
available redshifts. The R-band Hubble diagram and evolution of the host
galaxies of GPS sources are reviewed.Comment: Latex, 12 pages, 8 figures, accepted for publication in MNRA
The Air Littoral: Another Look
Assessing threats to the air littoral, the airspace between ground forces and high-end fighters and bombers, requires a paradigm change in American military thinking about verticality. This article explores the consequences of domain convergence, specifically for the Army and Air Force’s different concepts of control. It will assist US military and policy practitioners in conceptualizing the air littoral and in thinking more vertically about the air and land domains and the challenges of domain convergence
Modeling Urban Hydrology: A Comparison of New Urbanist and Traditional Neighborhood Design Surface Runoff
Urban development affects the amount of potential surface runoff generated during storms by changing the amount of impervious cover across the landscape. However, the degree of surface runoff alteration depends on the type of urban development in place. New urbanist developments are designed with higher densities and encourage a diversity of land uses, while traditional neighborhood developments have a monotone land use pattern with medium-to- low densities. Two neighborhoods within the city of Austin, Texas- Mueller, a new urbanist development, and Circle C Ranch, a traditional neighborhood development- were used to study the effect of development type on potential surface runoff. Using satellite imagery coupled to the HEC-HMS model nested within the Watershed Modeling System (WMS), potential surface runoff was calculated for the two different neighborhoods for a 10-year 24 hour storm scenario. Results initially suggest that total runoff volume and peak surface runoff significantly increase for the new urbanist neighborhood over the traditional development as a function of the higher density urban footprint associated with the new urbanist design. However a higher number of residential units are available at Mueller over the same area as Circle C Ranch. When taking this into account the increased potential surface runoff is negated at the new urbanist site. Although new urbanist neighborhoods will usually contain more residential units than traditional developments when compared at the same scale, the higher urban density associated with these developments necessitates the construction of more efficient stormwater retention measures within these neighborhoods
Effects of Home Value, Home Age, and Lot Size on Lawn Watering Practices of Residential Homeowners
Lawn care and lawn watering practices of residential homeowners were significantly affected by home value and home age, but lot size was less a factor
Faint Gigahertz peaked spectrum sources and the evolution of young radio sources
GPS sources are the objects of choice to study the initial evolution of
extragalactic radio sources, since it is most likely that they are the young
counterparts of large scale radio sources. Correlations found between their
peak frequency, peak flux density and angular size provide strong evidence that
synchrotron self absorption is the cause of the spectral turnovers, and
indicate that young radio sources evolve in a self-similar way. The difference
in redshift distribution between young and old radio sources must be due to a
difference in slope of their luminosity functions, and we argue that this slope
is strongly affected by the luminosity evolution of the individual sources. A
luminosity evolution scenario is proposed in which GPS sources increase in
luminosity and large scale radio sources decrease in luminosity with time. It
is shown that such a scenario agrees with the local luminosity function of GPS
galaxies.Comment: Late, 6 pages, 2 figs. To appear in the proceedings of EVN/JIVE
Symposium No 4, New Astronomy Reviews (eds. Garrett et al.). For related
papers, see http://www.ast.cam.ac.uk/~snelle
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