27,103 research outputs found
Cenozoic extension and magmatism in Arizona
The Basin and Range Province of Arizona was the site of two episodes of Cenozoic extension that can be distinguished on the basis of timing, direction and style of extension, and associated magmatism. The first episode of extension occurred during Oligocene to mid-Miocene time and resulted in the formation of low-angle detachment faults, ductile shear zones (metamorphic core complexes), and regional domains of tilted fault blocks. Evidence for extreme middle Tertiary crustal extension in a NE to SW to SW to ENE to WSW direction has been recognized in various parts of the Basin and Range of Arizona, especially in the Lake Mead area and along the belf of metamorphic core complexes that crosses southern Arizona from Parker to Tucson. New geologic mapping and scrutiny of published geologic maps indicates that significant middle Tertiary extension is more widely distributed than previously thought. The state can be subdivided into regional tilt-block domains in which middle Tertiary rocks dip consistently in one direction. The dip direction in any tilt-block domain is generally toward the breakaway of a low-angle detachment fault that underlies the tilt-block domain; we interpret this an indicating that normal faults in the upper plate of a detechment fault are generally synthetic, rather than antithetic, with respect to the detachment fault
Searching for annihilation radiation from SN 1006 with SPI on INTEGRAL
Historical Type Ia supernovae are a leading candidate for the source of
positrons observed through their diffuse annihilation emission in the Galaxy.
However, search for annihilation emission from individual Type Ia supernovae
has not been possible before the improved sensitivity of \integral. The total
511 keV annihilation flux from individual SNe Ia, as well as their contribution
to the overall diffuse emission, depends critically on the escape fraction of
positrons produced in Co decays. Late optical light curves suggest that
this fraction may be as high as 5%. We searched for positron annihilation
radiation from the historical Type Ia supernova SN 1006 using the SPI
instrument on \integral. We did not detect significant 511 keV line emission,
with a 3 flux upper limit of 0.59 x 10 ergs cm^-2 s^-1 for \wsim
1 Msec exposure time, assuming a FWHM of 2.5 keV. This upper limit corresponds
to a 7.5% escape fraction, 50% higher than the expected 5% escape scenario, and
rules out the possibility that Type Ia supernovae produce all of the positrons
in the Galaxy (~ 12% escape fraction), if the mean positron lifetime is less
than 10 years. Future observations with \integral will provide stronger
limits on the escape fraction of positrons, the mean positron lifetime, and the
contribution of Type Ia supernovae to the overall positron content of the
Galaxy.Comment: 3 pages, 2 figures, accepted for publication in ApJ
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Splanchnic metabolism of nutrients and hormones in steers fed alfalfa under conditions of increased absorption of ammonia and L-arginine supply across the portal-drained viscera
Effects of increased ammonia and/or arginine
absorption on net splanchnic (portal-drained viscera
[PDV] plus liver) metabolism of nonnitrogenous
nutrients and hormones in cattle were examined. Six
Hereford × Angus steers (501 ± 1 kg BW) prepared with
vascular catheters for measurements of net flux across
the splanchnic bed were fed a 75% alfalfa:25% (as-fed
basis) corn and soybean meal diet (0.523 MJ of ME/[kg
BW0.75.d]) every 2 h without (27.0 g of N/kg of DM) and
with 20 g of urea/kg of DM (35.7 g of N/kg of DM) in a
split-plot design. Net flux measurements were made
immediately before and after a 72-h mesenteric vein
infusion of L-arginine (15 mmol/h). There were no treatment
effects onPDVor hepaticO2 consumption. Dietary
urea had no effect on splanchnic metabolism of glucose
or L-lactate, but arginine infusion decreased net hepatic
removal of L-lactate when urea was fed (P < 0.01). Net PDV appearance of n-butyrate was increased by arginine
infusion (P < 0.07), and both dietary urea (P <
0.09) and arginine infusion (P < 0.05) increased net
hepatic removal of n-butyrate. Dietary urea also increased
total splanchnic acetate output (P < 0.06),
tended to increase arterial glucagon concentration (P
< 0.11), and decreased arterial ST concentration (P <
0.03). Arginine infusion increased arterial concentration
(P < 0.07) and net PDV release (P < 0.10) and
tended to increase hepatic removal (P < 0.11) of insulin,
as well as arterial concentration (P < 0.01) and total
splanchnic output (P < 0.01) of glucagon. Despite
changes in splanchnic N metabolism, increased ammonia
and arginine absorption had little measurable effect
on splanchnic metabolism of glucose and other nonnitrogenous
components of splanchnic energy metabolism
Identification of four RXTE Slew Survey sources with nearby luminous active galactic nuclei
Based on RXTE scans and observations with the SWIFT/XRT telescope and
INTEGRAL observatory, we report the identification of four X-ray sources
discovered during the RXTE Slew Survey of the |b|>10deg sky with nearby (z ~
0.017-0.098) luminous (log L_2-10keV ~ 42.7-44 erg/s) active galactic nuclei.
Two of the objects exhibit heavily intrinsically absorbed X-ray spectra
(NHL~10^23 cm^-2).Comment: 4 pages, 2 figures. Sibmitted to Astronomy and Astrophysics Letter
AGN heating and dissipative processes in galaxy clusters
Recent X-ray observations reveal growing evidence for heating by active
galactic nuclei (AGN) in clusters and groups of galaxies. AGN outflows play a
crucial role in explaining the riddle of cooling flows and the entropy problem
in clusters. Here we study the effect of AGN on the intra-cluster medium in a
cosmological simulation using the adaptive mesh refinement FLASH code. We pay
particular attention to the effects of conductivity and viscosity on the
dissipation of weak shocks generated by the AGN activity in a realistic galaxy
cluster. Our 3D simulations demonstrate that both viscous and conductive
dissipation play an important role in distributing the mechanical energy
injected by the AGN, offsetting radiative cooling and injecting entropy to the
gas. These processes are important even when the transport coefficients are at
a level of 10% of the Spitzer value. Provided that both conductivity and
viscosity are suppressed by a comparable amount, conductive dissipation is
likely to dominate over viscous dissipation. Nevertheless, viscous effects may
still affect the dynamics of the gas and contribute a significant amount of
dissipation compared to radiative cooling. We also present synthetic Chandra
observations. We show that the simulated buoyant bubbles inflated by the AGN,
and weak shocks associated with them, are detectable with the Chandra
observatory.Comment: accepted to ApJ, minor change
Imaging extended sources with coded mask telescopes: Application to the INTEGRAL IBIS/ISGRI instrument
Context. In coded mask techniques, reconstructed sky images are
pseudo-images: they are maps of the correlation between the image recorded on a
detector and an array derived from the coded mask pattern. Aims. The
INTEGRAL/IBIS telescope provides images where the flux of each detected source
is given by the height of the local peak in the correlation map. As such, it
cannot provide an estimate of the flux of an extended source. What is needed is
intensity sky images giving the flux per solide angle as typically done at
other wavelengths. Methods. In this paper, we present the response of the
INTEGRAL IBIS/ISGRI coded mask instrument to extended sources. We develop a
general method based on analytical calculations in order to measure the
intensity and the associated error of any celestial source and validated with
Monte-Carlo simulations. Results. We find that the sensitivity degrades almost
linearly with the source extent. Analytical formulae are given as well as an
easy-to-use recipe for the INTEGRAL user. We check this method on IBIS/ISGRI
data but these results are general and applicable to any coded mask telescope.Comment: 9 pages, 6 figures, Accepted for publication in A&
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