8,375 research outputs found
Measuring Galactic Extinction: A Test
We test the recently published all-sky reddening map of Schlegel, Finkbeiner
& Davis (1998 [SFD]) using the extinction study of a region in the Taurus dark
cloud complex by Arce & Goodman (1999 [AG]). In their study, AG use four
different techniques to measure the amount and structure of the extinction
toward Taurus, and all four techniques agree very well. Thus we believe that
the AG results are a truthful representation of the extinction in the region
and can be used to test the reliability of the SFD reddening map. The results
of our test show that the SFD all-sky reddening map, which is based on data
from COBE/DIRBE and IRAS/ISSA, overestimates the reddening by a factor of 1.3
to 1.5 in regions of smooth extinction with A_V > 0.5 mag. In some regions of
steep extinction gradients the SFD map underestimates the reddening value,
probably due to its low spatial resolution. We expect that the astronomical
community will be using the SFD reddening map extensively. We offer this Letter
as a cautionary note about using the SFD map in regions of high extinction (A_V
> 0.5 mag), as it might not be giving accurate reddening values there.Comment: 14 pages (which include 2 pages of figures
Investigations of Protostellar Outflow Launching and Gas Entrainment: Hydrodynamic Simulations and Molecular Emission
We investigate protostellar outflow evolution, gas entrainment, and star
formation efficiency using radiation-hydrodynamic simulations of isolated,
turbulent low-mass cores. We adopt an X-wind launching model, in which the
outflow rate is coupled to the instantaneous protostellar accretion rate and
evolution. We vary the outflow collimation angle from =0.01-0.1 and
find that even well collimated outflows effectively sweep up and entrain
significant core mass. The Stage 0 lifetime ranges from 0.14-0.19 Myr, which is
similar to the observed Class 0 lifetime. The star formation efficiency of the
cores spans 0.41-0.51. In all cases, the outflows drive strong turbulence in
the surrounding material. Although the initial core turbulence is purely
solenoidal by construction, the simulations converge to approximate
equipartition between solenoidal and compressive motions due to a combination
of outflow driving and collapse. When compared to a simulation of a cluster of
protostars, which is not gravitationally centrally condensed, we find that the
outflows drive motions that are mainly solenoidal. The final turbulent velocity
dispersion is about twice the initial value of the cores, indicating that an
individual outflow is easily able to replenish turbulent motions on sub-parsec
scales. We post-process the simulations to produce synthetic molecular line
emission maps of CO, CO, and CO and evaluate how well
these tracers reproduce the underlying mass and velocity structure.Comment: Accepted to ApJ, 17 pages, 15 figure
Suicide Terrorism and the Weakest Link
In this paper we examine a model of terrorism which focuses on the tradeoffs facing a terrorist organization that has the ability to utilize either or both suicide and conventional terrorism tactics. The terrorist organization’s objective is to successfully attack at least one target. Success for the target government is defined as defending all targets from any and all attacks. In this context, we examine how terrorist entities strategically utilize suicide attacks when other modes of attack are available, and the optimal anti-terrorism measures.conflict, suicide terrorism, weakest link, Colonel Blotto
Security-Induced Lock-In in the Cloud
Cloud services providers practice security-induced lock-in when employing cryptography and tamper-resistance to limit the portability and interoperability of users’ data and applications. Moreover, security-induced lock-in and users’ anti-lock-in strategies intersect within the context of platform competition. When users deploy anti-lock in strategies, such as using a hybrid cloud, a leader–follower pricing framework increases profits for cloud services providers relative to Nash equilibrium prices. This creates a second-mover advantage, as the follower’s increase in profits exceeds that of the leader owing to the potential for price undercutting. By contrast, introducing or enhancing security-induced lock-in creates both an increase in profits and a first-mover advantage. Cloud services providers therefore favor security-induced lock-in over price leadership. More broadly, we show why standardization of semantics, technologies, and interfaces is a nonstarter for cloud services providers
Music genre classification via joint sparse low-rank representation of audio features
A novel framework for music genre classification, namely the joint sparse low-rank representation (JSLRR) is proposed in order to: 1) smooth the noise in the test samples, and 2) identify the subspaces that the test samples lie onto. An efficient algorithm is proposed for obtaining the JSLRR and a novel classifier is developed, which is referred to as the JSLRR-based classifier. Special cases of the JSLRR-based classifier are the joint sparse representation-based classifier and the low-rank representation-based one. The performance of the three aforementioned classifiers is compared against that of the sparse representation-based classifier, the nearest subspace classifier, the support vector machines, and the nearest neighbor classifier for music genre classification on six manually annotated benchmark datasets. The best classification results reported here are comparable with or slightly superior than those obtained by the state-of-the-art music genre classification methods
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