5,274 research outputs found
Galactic centre star formation writ large in gamma-rays
We have modelled the high-energy astrophysics of the inner 200 pc of the
Galaxy with a view to explaining the diffuse, broad-band (radio continuum to
TeV gamma-ray), non-thermal signal detected from this region. Our modelling
pins down the ISM parameters for the environment wherein cosmic ray (CR)
electrons and ions reside in the Galactic centre (GC). We find that the
magnetic field in this region is 100-300 microG, the gas density < 60 cm^-3,
and that a powerful (> 200 km/s) 'super'-wind acts to remove > 95% of the
cosmic rays accelerated in the region before they have time to lose their
energy in situ. The ~ 10^39 erg/s carried away by the GC cosmic ray protons is
precisely enough to energise the ~GeV gamma-ray emission from the Fermi
'bubbles' recently found to extend north and south of the GC out to distances
of ~10 kpc, provided that the bubbles constitute thick targets to the GC
protons and that the situation has reached steady state. In such a situation of
'saturation' the hard, uniform spectrum of the bubbles are explained and
secondary electron synchrotron explains the non-thermal microwave emission
found in WMAP data mirroring the bubbles. Given the very low density of the
bubble plasma ( 5 Gyr. Our
scenario thus has the startling implication that a GC source of nonthermal
particles of time-averaged power 10^39 erg/s has persisted since the youth of
the Galaxy.Comment: 7 pages, 1 figure. Accepted to the Proceedings of the 25th Texas
Symposium on Relativistic Astrophysics (Heidelberg, 2010). References updates
and abstract typo corrected: "100-300 mG" -> "100-300 microG
The influence of the scene on linguistic expectations: Evidence from cross-model priming in visual worlds
- Numerous studies of utterance mediated gaze in visual scenes have demonstrated that sentence processing is not only incremental but also eager: During processing, listeners form expectations about upcoming arguments and make anticipatory eye movements to relevant displayed objects. - In particular, selectional information from verbs has been shown to guide visual attention to appropriate objects; upon hearing “the boy will eat”, listeners start looking at edible objects even before they are mentioned [1, 2]. - While these studies provide valuable insights into semantic processing, it is not clear whether anticipatory eye movements indeed reflect the purely linguistic activation of likely arguments or whether these anticipatory processes are influenced by the circumscribed visual context. - We present a German cross-modal priming experiment in which we examined listeners sensitivity to selectional restrictions between verbs and their object arguments
Measurement of damping of graphite expoxy materials
During this period damping measurements were made on the cylindrical graphite epoxy specimen using the forced-vibration test method. The specimen was carefully mounted directly on the shaker through the supporting ring and the impedance head. This was done to simulate an idealized free-free boundary condition at the two edges. The damping ratio value and the natural frequency (first mode) obtained in this experiment were 0.13% and 508.75 Hz respectively. In order to check the damping induced by the supporting ring, measurements were made with the top half of the ring removed. The specimen then was supported only by the bottom half of the ring (half ring). It was observed that the natural frequency of the specimen (first mode) increased of a value of 552.5 Hz due to the influence of the reduced mass of the supporting ring. But the damping ratio value obtained was the same as that obtained with full supporting ring, namely 0.13%
The Galactic Centre - A Laboratory for Starburst Galaxies (?)
The Galactic centre - as the closest galactic nucleus - holds both intrinsic
interest and possibly represents a useful analogue to star-burst nuclei which
we can observe with orders of magnitude finer detail than these external
systems. The environmental conditions in the GC - here taken to mean the inner
200 pc in diameter of the Milky Way - are extreme with respect to those
typically encountered in the Galactic disk. The energy densities of the various
GC ISM components are typically ~two orders of magnitude larger than those
found locally and the star-formation rate density ~three orders of magnitude
larger. Unusually within the Galaxy, the Galactic centre exhibits
hard-spectrum, diffuse TeV (=10^12 eV) gamma-ray emission spatially coincident
with the region's molecular gas. Recently the nuclei of local star-burst
galaxies NGC 253 and M82 have also been detected in gamma-rays of such
energies. We have embarked on an extended campaign of modelling the broadband
(radio continuum to TeV gamma-ray), non- thermal signals received from the
inner 200 pc of the Galaxy. On the basis of this modelling we find that
star-formation and associated supernova activity is the ultimate driver of the
region's non-thermal activity. This activity drives a large-scale wind of hot
plasma and cosmic rays out of the GC. The wind advects the locally-accelerated
cosmic rays quickly, before they can lose much energy in situ or penetrate into
the densest molecular gas cores where star-formation occurs. The cosmic rays
can, however, heat/ionize the lower density/warm H2 phase enveloping the cores.
On very large scales (~10 kpc) the non-thermal signature of the escaping GC
cosmic rays has probably been detected recently as the spectacular 'Fermi
bubbles' and corresponding 'WMAP haze'.Comment: Invited talk to appear in Proceedings of IAU Symposium No. 284, 2011
(R.J. Tuffs & C.C. Popescu, eds.) `The Spectral Energy Distribution of
Galaxies
Fixing Advising: A Model for Faculty Advising
This paper addresses mandates to fix the advising process with a focus on faculty advising systems. Measures of student success and satisfaction, administrative issues, and faculty concerns are among the many factors discussed. Regression analysis is used to explore long-voiced faculty complaints that students do not follow advice. A case study is used to illustrate changes in one department’s advising process and measures of student satisfaction are reported. A model of advising components is offered to illustrate practices suggested to realize the full potential of the advising process
Acoustic prediction methods for rocket engines, including the effects of clustered engines and deflected exhaust flow
Acoustic prediction methods for rocket engine
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