982 research outputs found
Gamma-Ray Emission from Arp 220: Indications of an Active Galactic Nucleus
Extragalactic cosmic ray populations are important diagnostic tools for
tracking the distribution of energy in nuclei and for distinguishing between
activity powered by star formation versus active galactic nuclei (AGNs). Here,
we compare different diagnostics of the cosmic ray populations of the nuclei of
Arp 220 based on radio synchrotron observations and the recent gamma-ray
detection. We find the gamma-ray and radio emission to be incompatible; a joint
solution requires at minimum a factor of 4 - 8 times more energy coming from
supernovae and a factor of 40 - 70 more mass in molecular gas than is observed.
We conclude that this excess of gamma-ray flux in comparison to all other
diagnostics of star-forming activity indicates that there is an AGN present
that is providing the extra cosmic rays, likely in the western nucleus.Comment: 5 pages, 3 figures, 1 table, accepted for publication in MNRAS
Letter
Touching the Rock:An Experience of Blindness (1990)
Touching the Rock comprises the autobiographical reflections of Anglo-Australian theologian and educator John M. Hull in the period shortly after losing his sight, from summer 1983 to summer 1986. In the book, Hull discusses coming to terms with his impairment, his loss of memory of the visual, his damaged recollection of those things that were once familiar, and the diversity of reactions from those around him. Touching the Rock is a transcript of Hull's taped diary entries on various topics related to his blindness, including dream analyses; altered practices with familiar objects and the environment; reflections on sections of literature, including the Bible and other religious texts; his trials while forming a young family as a man without sight; and the kindness and cruelty of people during his initial three years of living in complete darkness.<br/
VV 655 and NGC 4418: Implications of an interaction for the evolution of a LIRG
VV 655, a dwarf irregular galaxy with HI tidal debris, is a companion to the
lenticular luminous infrared galaxy (LIRG) NGC 4418. NGC 4418 stands out among
nearby LIRGs due to its dense central concentration of molecular gas and the
dusty, bi-polar structures along its minor axis suggestive of a wind driven by
a central starburst and possible nuclear activity. We seek to understand the
consequences of the ongoing minor interaction between VV 655 and NGC 4418 for
the evolution of the LIRG, including the origin of the gas supply responsible
for its unusual nuclear properties. We investigate the structural, kinematic,
and chemical properties of VV 655 and NGC 4418 by analyzing archival imaging
data and optical spectroscopic observations from the SDSS-III and new spectra
from SALT-RSS. We characterize their gas-phase metal abundances and spatially
resolved, ionized gas kinematics, and demonstrate that the gas-phase
metallicity in NGC 4418 significantly exceeds that in VV 655. No kinematic
disturbances in the ionized gas are observed along the minor axis of NGC 4418,
but we see evidence for ionized gas outflows from VV 655 that may increase the
cross-section for gas stripping in grazing collisions. A faint, asymmetric
outer arm is detected in NGC 4418 of the type normally associated with
galaxy-galaxy interactions. The simplest model suggests that the minor
interaction between VV 655 and NGC 4418 produced the unusual nuclear properties
of the LIRG via tidal torquing of the interstellar medium of NGC 4418 rather
than through a significant gas transfer event. In addition to inducing a
central concentration of gas in NGC 4418, this interaction also produced an
enhanced star formation rate and an outer tidal arm in the LIRG. The VV 655-NGC
4418 system offers an example of the potential for minor collisions to alter
the evolutionary pathways of giant galaxies.Comment: 9 pages, 4 figures, accepted for publication in Astronomy &
Astrophysic
Sediment Movement Within a Strip Intercropping System
This study was conducted to identify sediment movement within a strip intercropping system in southwestern Iowa during the third year of a three-year crop rotation. Soil loss, resulting from the application of simulated rainfall to a Monona silt loam soil, was measured from individual corn (Zea mays L.), soybean (Glycine max (L.) Merr), and winter wheat (Triticum aestivum L.) strips, and from multiple strips which included all three crops. Because of the crop rotation and residue management procedures, used at the study site, a substantial amount of surface cover and vegetative mass was present on each of the strips. As a result, soil loss resulting from simulated rainfall applied for a one-hour duration at an intensity of approximately 64 mm/hr (2.5 in/hr) was less than or equal to 1.5 Mg/ha (0.67 tons/acre) from each of the individual and multiple strips. Thus, the strip intercropping system established on this highly erodible site provided effective erosion control
A Trapped Field of 17.6 T in Melt-Processed, Bulk Gd-Ba-Cu-O Reinforced with Shrink-Fit Steel
The ability of large grain, REBaCuO [(RE)BCO; RE =
rare earth] bulk superconductors to trap magnetic field is determined by their
critical current. With high trapped fields, however, bulk samples are subject
to a relatively large Lorentz force, and their performance is limited primarily
by their tensile strength. Consequently, sample reinforcement is the key to
performance improvement in these technologically important materials. In this
work, we report a trapped field of 17.6 T, the largest reported to date, in a
stack of two, silver-doped GdBCO superconducting bulk samples, each of diameter
25 mm, fabricated by top-seeded melt growth (TSMG) and reinforced with
shrink-fit stainless steel. This sample preparation technique has the advantage
of being relatively straightforward and inexpensive to implement and offers the
prospect of easy access to portable, high magnetic fields without any
requirement for a sustaining current source.Comment: Updated submission to reflect licence change to CC-BY. This is the
"author accepted manuscript" and is identical in content to the published
versio
Post-Test Analysis of a 10-Year Sodium Heat Pipe Life Test
High-temperature heat pipes are being evaluated for use in energy conversion applications such as fuel cells, gas turbine re-combustors, Stirling cycle heat sources; and with the resurgence of space nuclear power both as reactor heat removal elements and as radiator elements. Long operating life and reliable performance are critical requirements for these applications. Accordingly, long-term materials compatibility is being evaluated through the use of high-temperature life test heat pipes. Thermacore, Inc., has carried out a sodium heat pipe 10-year life test to establish long-term operating reliability. Sodium heat pipes have demonstrated favorable materials compatibility and heat transport characteristics at high operating temperatures in air over long time periods. A representative one-tenth segment Stirling Space Power Converter heat pipe with an Inconel 718 envelope and a stainless steel screen wick has operated for over 87,000 hr (10 years) at nearly 700 C. These life test results have demonstrated the potential for high-temperature heat pipes to serve as reliable energy conversion system components for power applications that require long operating lifetime with high reliability. Detailed design specifications, operating history, and post-test analysis of the heat pipe and sodium working fluid are described. Lessons learned and future life test plans are also discussed
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