1,573 research outputs found
Teaching Notes for CHAPTER 7: Leading Healing in a Broken Unit
Teaching Notes for Leading Healing in a Broken Unit, by Edward H. Powley and Scott N. Taylor.
Source material for this case study comes from the following: the first-hand experiences of an officer embedded within the ground combat element of a Marine Air Ground Task Force; reports on the use of improvised explosive devices (IEDs) in Iraq and Afghanistan; and first-hand knowledge of military officers recently returned from combat operations. Specific names, dates, and locations have been changed and descriptive background information added.
The announcement of increased deployments meant additional preparations for many military units that anticipated deployment to the U.S. Central Command (CENTCOM) area of operations. This case is about one ground combat element for a Marine Air Ground Task Force deployed into the CENTCOM area of operations. Excitement for the mission remained high, but extended deadlines well beyond the return date caused Marines and sailors to become wary. On top of their fatigue, a suicide bomber detonated himself at an entry control point, significantly affecting the morale and welfare of the unit. The blast killed several individuals and severely wounded nearly a dozen others. One of those killed in the blast was the well-known and well-respected senior enlisted leader of the ground combat element. In life, as in death, his presence affected the morale and productivity of the entire unit. Would his loss paralyze the unit? How would the unit rebound, pick up the pieces, and return with honor? How would the officers lead the unit toward healing in the remaining weeks of the deployment? These questions were in the forefront of the officers’ minds as they struggled to keep the unit moving forward
Evolution of the stellar mass function and infrared luminosity function of galaxies since z = 1.2
© 2019. The American Astronomical Society. All rights reserved. We measured evolution of the K-band luminosity function and stellar mass function (SMF) for red and blue galaxies at z 0.4 luminosity and mass function measurements. Using an evolving relation for K-band mass-to-light ratios as a function of (B-V) color, we found a slowly decreasing rate of growth in red galaxy stellar mass density of ×2.3 from z ∼ 1.1 to z ∼ 0.3, indicating a slowly decreasing rate of migration from the blue cloud to the red sequence. Unlike some studies of the SMF, we find that massive red galaxies grow by a factor of ×1.7 from z ∼ 1.1 to z ∼ 0.3, with the rate of growth due to mergers decreasing with time. These results are comparable with measurements of merger rates and clustering, and they are also consistent with the red galaxy stellar mass growth implied by comparing K-band luminosity evolution with the fading of passive stellar population models
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Optical Spectroscopy Of X-Ray Sources In The Extended Chandra Deep Field South
We present the first results of our optical spectroscopy program aimed to provide redshifts and identifications for the X-ray sources in the Extended Chandra Deep Field South. A total of 339 sources were targeted using the IMACS spectrograph at the Magellan telescopes and the VIMOS spectrograph at the VLT. We measured redshifts for 186 X-ray sources, including archival data and a literature search. We find that the active galactic nucleus (AGN) host galaxies have on average redder rest-frame optical colors than nonactive galaxies, and that they live mostly in the "green valley." The dependence of the fraction of AGNs that are obscured on both luminosity and redshift is confirmed at high significance and the observed AGN spatial density is compared with the expectations from existing luminosity functions. These AGNs show a significant difference in the mid-IR to X-ray flux ratio for obscured and unobscured AGNs, which can be explained by the effects of dust self-absorption on the former. This difference is larger for lower luminosity sources, which is consistent with the dust opening angle depending on AGN luminosity.National Aeronautics and Space Administration PF8-90055, NAS8-03060NSF AST0407295Spitzer JPL RSA1288440Natural Science and Engineering Research Council of Canada (NSERC)National Academy of SciencesNASA/INTEGRAL NNG05GM79GAstronom
Analyses of space environment effects on active fiber optic links orbited aboard the LDEF
The results of the 'Preliminary Analysis of WL Experiment no. 701, Space Environment Effects on Operating Fiber Optic Systems,' is correlated with space simulated post retrieval terrestrial studies performed on the M0004 experiment. Temperature cycling measurements were performed on the active optical data links for the purpose of assessing link signal to noise ratio and bit error rate performance some 69 months following the experiment deployment in low Earth orbit. The early results indicate a high correlation between pre-orbit, orbit, and post-orbit functionality of the first known and longest space demonstration of operating fiber optic systems
Strong lensing selection effects
Context. Strong lenses are a biased subset of the general population of
galaxies.
Aims. The goal of this work is to quantify how lens galaxies and lensed
sources differ from their parent distribution, namely the strong lensing bias.
Methods. We first studied how the strong lensing cross-section varies as a
function of lens and source properties. Then, we simulated strong lensing
surveys with data similar to that expected for Euclid and measured the strong
lensing bias in different scenarios. We focused particularly on two quantities:
the stellar population synthesis mismatch parameter, , defined as
the ratio between the true stellar mass of a galaxy and the stellar mass
obtained from photometry, and the central dark matter mass at fixed stellar
mass and size.
Results. Strong lens galaxies are biased towards larger stellar masses,
smaller half-mass radii and larger dark matter masses. The amplitude of the
bias depends on the intrinsic scatter in the mass-related parameters of the
galaxy population and on the completeness in Einstein radius of the lens
sample. For values of the scatter that are consistent with observed scaling
relations and a minimum detectable Einstein radius of , the strong
lensing bias in is , while that in the central dark matter
mass is . The bias has little dependence on the properties of the source
population: samples of galaxy-galaxy lenses and galaxy-quasar lenses that probe
the same Einstein radius distribution are biased in a very similar way.
Conclusions. Given current uncertainties, strong lensing observations can be
used directly to improve our current knowledge of the inner structure of
galaxies, without the need to correct for selection effects. Time-delay
measurements of from lensed quasars can take advantage of prior
information obtained from galaxy-galaxy lenses with similar Einstein radii.Comment: Published on Astronomy & Astrophysics. A two-minute summary video of
this paper is available at https://youtu.be/UmS9jRHTmZ
Spontaneous synchronization of coupled oscillator systems with frequency adaptation
We study the synchronization of Kuramoto oscillators with all-to-all coupling
in the presence of slow, noisy frequency adaptation. In this paper we develop a
new model for oscillators which adapt both their phases and frequencies. It is
found that this model naturally reproduces some observed phenomena that are not
qualitatively produced by the standard Kuramoto model, such as long waiting
times before the synchronization of clapping audiences. By assuming a
self-consistent steady state solution, we find three stability regimes for the
coupling constant k, separated by critical points k1 and k2: (i) for k<k1, only
the stable incoherent state exists; (ii) for k>k2, the incoherent state becomes
unstable and only the synchronized state exists; (iii) for k1<k<k2, both the
incoherent and synchronized states are stable. In the bistable regime
spontaneous transitions between the incoherent and synchronized states are
observed for finite ensembles. These transitions are well described as a
stochastic process on the order parameter r undergoing fluctuations due to the
system's finite size, leading to the following conclusions: (a) in the bistable
regime, the average waiting time of an incoherent-to-coherent transition can be
predicted by using Kramer's escape time formula and grows exponentially with
the number of oscillators; (b) when the incoherent state is unstable (k>k2),
the average waiting time grows logarithmically with the number of oscillators.Comment: 8 page Tex file, 6 figure
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