9,760 research outputs found
Discovery of hard X-ray features around hotspots of Cygnus A
We present results of analysis of a Chandra observation of Cygnus A in which
the X-ray hotspots at the ends of the jets are mapped in detail. A hardness map
reveals previously unknown structure in the form of outer and inner hard arcs
around the hotspots, with hardness significantly enhanced compared with the
hotspot central regions. The outer hard arcs may constitute the first detection
of the bow shock; the inner hard arcs may reveal where the jets impact on the
hotspots. We argue that these features cannot result from electrons radiating
by the synchrotron self-Compton process. Instead we consider two possible
sources of the hard emission: the outer arcs may be due to thermal radiation of
hot intracluster gas compressed at the bow shock. Alternatively, both outer and
inner arcs may be due to synchrotron radiation of electrons accelerated in
turbulent regions highly perturbed by shocks and shear flows. Comparison of
measured hardness ratios with simulations of the hardness ratios resulting from
these processes show that it is more diffcult to explain the observations with
a thermal model. Although we cannot rule out a thermal model, we argue in
favour of the non-thermal explanation. The hard regions in the secondary
hotspots suggest that jet activity is still powering these hotspots.Comment: MNRAS in press; 5 pages, 3 figures (2 figures in colour in jpeg
format should be printed separately
Development of a machine protection system for the Superconducting Beam Test Facility at Fermilab
Fermilab's Superconducting RF Beam Test Facility currently under construction
will produce electron beams capable of damaging the acceleration structures and
the beam line vacuum chambers in the event of an aberrant accelerator pulse.
The accelerator is being designed with the capability to operate with up to
3000 bunches per macro-pulse, 5Hz repetition rate and 1.5 GeV beam energy. It
will be able to sustain an average beam power of 72 KW at the bunch charge of
3.2 nC. Operation at full intensity will deposit enough energy in niobium
material to approach the melting point of 2500 {\deg}C. In the early phase with
only 3 cryomodules installed the facility will be capable of generating
electron beam energies of 810 MeV and an average beam power that approaches 40
KW. In either case a robust Machine Protection System (MPS) is required to
mitigate effects due to such large damage potentials. This paper will describe
the MPS system being developed, the system requirements and the controls issues
under consideration.Comment: 3 pp. 13th International Conference on Accelerator and Large
Experimental Physics Control Systems (ICALEPCS 2011). 10-14 Oct 2011.
Grenoble, Franc
Benchmark ages for the Gaia benchmark stars
In the era of large-scale surveys of stars in the Milky Way, stellar ages are
crucial for studying the evolution of the Galaxy. But determining ages of field
stars is notoriously difficult; therefore, we attempt to determine benchmark
ages for the extensively studied Gaia benchmark stars which can be used for
validation purposes. By searching the literature for age estimates from
different methods and deriving new ages based on Bayesian isochrone fitting, we
are able to put reliable limits on the ages of 16 out of the 33 benchmark
stars. The giants with well-defined ages are all young, and an expansion of the
sample to include older giants with asteroseismic ages would be beneficial.
Some of the stars have surface parameters inconsistent with isochrones younger
than 16 Gyr. Including -enhancement in the models when relevant
resolves some of these cases, but others clearly highlight discrepancies
between the models and observations. We test the impact of atomic diffusion on
the age estimates by fitting to the actual surface metallicity of the models
instead of the initial value and find that the effect is negligible except for
a single turn-off star. Finally, we show that our ability to determine
isochrone-based ages for large spectroscopic surveys largely mirrors our
ability to determine ages for these benchmark stars, except for stars with
dex since their location in the HR diagram is almost age
insensitive. Hence, isochrone fitting does not constrain their ages given the
typical uncertainties of spectroscopic stellar parameters.Comment: Accepted in MNRAS. 69 pages (18 for main text, 11 for appendix, and
40 for extra figures
Posture : a 4-H club activity
Cooperative Extension Work in Agriculture and Home Economics, University of Missouri, College of Agriculture and the United States Department of Agriculture cooperating."... Material in quotations has been taken from material by Miss Ella Gardner, Recreation Specialist, Extension Service, U. S. Department of Agriculture, Washington, D.C."--Page 3."June, 1939."Title from cover
Hips Unsocketed, Names Changed
This collection of poems represents my work from the past two years. I experiment with a variety of forms and measures, though most of these poems are in free verse. Two images serves as a cipher for understanding them as a whole: a peach tree and a red fox. Every year, I would wait in anticipation for the hard green buds to appear on the peach tree in my backyard, then, for them to change color, swelling with sweetness. By the time the ones that escaped the frost and insects were ripe enough to eat, I had forgotten about them and was surprised to see them on the kitchen table or catch a glimpse of red or orange in the leaves. Poetry has become my way of holding up my life’s fruits, my memories, to the sun to see how they have ripened. This metaphorical process of waiting and the renewed sense of discovery that comes with the long-awaited harvest define my experience of writing poetry. The second image, a red fox, has come to signify for me spiritual awareness and encounters with God in unexpected places. I have often seen red foxes in unlikely places. Poetry, for me, is a movement towards a deeper understanding of God. Poetry is searching for shalom in the midst of alienation, severed relationships, and ruptured selves. In summary, I seek a balanced and honest treatment of human heart-terrain, open to all emotions and experiences, with the ultimate aim of participating in God’s work of redemption and restoration
Oxygen Cost of Recreational Horse-Riding in Females
Version: as accepted for publication.BACKGROUND: The purpose of this study was to characterize the physiological demands of a riding session comprising different types of recreational horse riding in females. METHODS: Sixteen female recreational riders (aged 17 to 54 years) completed an incremental cycle ergometer exercise test to determine peak oxygen consumption (VO₂peak) and a 45-minute riding session based upon a British Horse Society Stage 2 riding lesson (including walking, trotting, cantering and work without stirrups). Oxygen consumption (VO₂), from which metabolic equivalent (MET) and energy expenditure values were derived, was measured throughout. RESULTS: The mean VO₂ requirement for trotting/cantering (18.4 ± 5.1 ml·kg⁻¹·min⁻¹; 52 ± 12% VO₂peak; 5.3 ± 1.1 METs) was similar to walking/trotting (17.4 ± 5.1 ml·kg⁻¹·min⁻¹; 48 ± 13% VO₂peak; 5.0 ± 1.5 METs) and significantly higher than for work without stirrups (14.2 ± 2.9 ml·kg⁻¹·min⁻¹; 41 ± 12% VO₂peak; 4.2 ± 0.8 METs) (P = .001). CONCLUSIONS: The oxygen cost of different activities typically performed in a recreational horse riding session meets the criteria for moderate intensity exercise (3-6 METs) in females, and trotting combined with cantering imposes the highest metabolic demand. Regular riding could contribute to the achievement of the public health recommendations for physical activity in this population
Discovery of narrow X-ray absorption features from the dipping low-mass X-ray binary X 1624-490 with XMM-Newton
We report the discovery of narrow X-ray absorption features from the dipping
low-mass X-ray binary X 1624-490 during an XMM-Newton observation in 2001
February. The features are identified with the K alpha absorption lines of Fe
xxv and Fe xxvi and have energies of 6.72 +/- 0.03 keV and 7.00 +/- 0.02 keV
and equivalent widths (EWs) of -7.5 +1.7 -6.3 eV and -16.6 +1.9 -5.9 eV,
respectively. The EWs show no obvious dependence on orbital phase, except
during a dip, and correspond to a column of greater than 10^17.3 Fe atom /cm2.
In addition, faint absorption features tentatively identified with Ni xxvii K
alpha and Fe xxvi K beta may be present. A broad emission feature at 6.58 +0.07
-0.04 keV with an EW of 78 +19 -6 eV is also evident. This is probably the 6.4
keV feature reported by earlier missions since fitting a single Gaussian to the
entire Fe-K region gives an energy of 6.39 +0.03 -0.04 keV. A deep absorption
feature is present during the dip with an energy consistent with Fe xxv K
alpha. This is the second dipping LMXRB source from which narrow Fe absorption
features have been observed. Until recently the only X-ray binaries known to
exhibit narrow X-ray absorption lines were two superluminal jet sources and it
had been suggested that these features are related to the jet formation
mechanism. It now appears likely that ionized absorption features may be common
characteristics of accreting systems with accretion disks.Comment: 6 pages. To appear in A&
A comparison of consumer behavior of coin laundry users and beliefs about this behavior held by coin laundry owners
Thesis (M.B.A.)--Boston Universit
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