12,059 research outputs found
The Effects of Clumping and Substructure on ICM Mass Measurements
We examine an ensemble of 48 simulated clusters to determine the effects of
small-scale density fluctuations and large-scale substructure on X-ray
measurements of the intracluster medium (ICM) mass. We measure RMS density
fluctuations in the ICM which can be characterized by a mean mass-weighted
clumping factor C = /^2 between 1.3 and 1.4 within a density
contrast of 500 times the critical density. These fluctuations arise from the
cluster history of accretion shocks and major mergers, and their presence
enhances the cluster's luminosity relative to the smooth case. We expect,
therefore, that ICM mass measurements utilizing models which assume uniform
density at a given radius carry a bias of order sqrt(C) = 1.16. We verify this
result by performing ICM mass measurements on X-ray images of the simulations
and finding the expected level of bias.
The varied cluster morphologies in our ensemble also allow us to investigate
the effects of departures from spherical symmetry on our measurements. We find
that the presence of large-scale substructure does not further bias the
resulting gas mass unless it is pronounced enough to produce a second peak in
the image of at least 1% the maximum surface brightness. We analyze the subset
of images with no secondary peaks and find a bias of 9% and a Gaussian random
error of 4% in the derived mass.Comment: To appear in ApJ
Workplace Organization and Innovation
This study uses data on Canadian establishments to test whether particular organizational structures are correlated with the likelihood of adopting process and product innovations, controlling for the endogeneity of the predictors. We find that establishments with decentralized decision-making, information-sharing programs, or incentive pay plans are significantly more likely to innovate than other establishments. Larger establishments and those with a high vacancy rate are also more likely to innovate. These findings are consistent with a model in which workers hold information about production inefficiencies or consumer demands that can lead to productive innovations and that workplace organization attributes facilitate the communication and implementation of those ideas.Innovation, Decision-Making, Information-Sharing
Investigation of continental drift, phase 1 effort Progress report, 1 Apr. - 30 Sep. 1968
Feasibility of using ultrashort pulse laser ranging and independent clock radio interferometry distance measurement methods to test for existence of continental drif
Investigation of planetary ionospheres
Feasibility of using radio sounding techniques to investigate ionospheric properties of planet
- …