9 research outputs found
Decaying Neutrinos in Galaxy Clusters
Davidsen et al. (1991) have argued that the failure to detect uv photons from
the dark matter DM) in cluster A665 excludes the decaying neutrino hypothesis.
Sciama et al. (1993) argued that because of high central concentration the DM
in that cluster must be baryonic. We study the DM profile in clusters of
galaxies simulated using the Harrison--Zel'dovich spectrum of density
fluctuations, and an amplitude previously derived from numerical simulations
(Melott 1984b; Anninos et al. 1991) and in agreement with microwave background
fluctuations (Smoot et al. 1992). We find that with this amplitude
normalization cluster neutrino DM densities are comparable to observed cluster
DM values. We conclude that given this normalization, the cluster DM should be
at least largely composed of neutrinos. The constraint of Davidsen et al. can
be somewhat weakened by the presence of baryonic DM; but it cannot be
eliminated given our assumptions.Comment: 14 pages, requires aaspp.sty. All latex, style files, and postscript
files included in a uuencoded compressed-tar file.
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Demonstrating Discreteness and Collision Error in Cosmological N-body Simulations of Dark Matter Gravitational Clustering
Two-body scattering and other discreteness effects are unimportant in
cosmological gravitational clustering in most scenarios, since the dark matter
has a small particle mass. The collective field should determine evolution:
Two-body scattering in simulations violates the Poisson-Vlasov equations. We
test this in PM, PM, Tree, and NGPM codes, noting that a collisionless code
will preserve the one-dimensional character of plane wave collapse. We find
collisionality vanishing as the softening parameter approaches the mean
interparticle separation. Solutions for the problem are suggested, involving
greater computer power, PM-based nested grid codes, and a more conservative
approach to resolution claims.Comment: Final version accepted for ApJ Letters. Minor revisions, including
due to bug fix in tree code. Uses aasms4.sty. 15 pages. Higher resolution
figures available at ftp://kusmos.phsx.ukans.edu/preprints/discret
The Ellipticity and Orientation of Clusters of Galaxies from N-Body Experiments
In this study we use simulations of 128 particles to study the
ellipticity and orientation of clusters of galaxies in N-body simulations of
differing power-law initial spectra (P(k) \propto k^n ,n = +1, 0, -1, -2\Omega_0 = 0.2nD < 15 h^{-1}n-$dependent way.Comment: 22 pages, requires aaspp4.sty, flushrt.sty, and epsf.sty Revised
manuscript, accepted for publication in Ap
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Coastal vulnerability across the Pacific dominated by El Niño/Southern Oscillation
To predict future coastal hazards, it is important to quantify any links between climate drivers and spatial patterns of coastal change. However, most studies of future coastal vulnerability do not account for the dynamic components of coastal water levels during storms, notably wave-driven processes, storm surges and seasonal water level anomalies, although these components can add metres to water levels during extreme events. Here we synthesize multi-decadal, co-located data assimilated between 1979 and 2012 that describe wave climate, local water levels and coastal change for 48 beaches throughout the Pacific Ocean basin. We find that observed coastal erosion across the Pacific varies most closely with El Niño/Southern Oscillation, with a smaller influence from the Southern Annular Mode and the Pacific North American pattern. In the northern and southern Pacific Ocean, regional wave and water level anomalies are significantly correlated to a suite of climate indices, particularly during boreal winter; conditions in the northeast Pacific Ocean are often opposite to those in the western and southern Pacific. We conclude that, if projections for an increasing frequency of extreme El Niño and La Niña events over the twenty-first century are confirmed, then populated regions on opposite sides of the Pacific Ocean basin could be alternately exposed to extreme coastal erosion and flooding, independent of sea-level rise.The published article is copyrighted by the author(s) and published by Nature Publishing Group. The published article can be found at: http://www.nature.com/ngeo/index.htm
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Coastal vulnerability across the Pacific dominated by El Nino/Southern Oscillation
Recommended from our members