2,190 research outputs found
Political Integration Through Jurisprudence: An Analysis of the European Court of Justice’s Ruling on Freedom of Movement for Workers
Source, Path and Site Effects on Loma Prieta Strong Motions
The amplitudes of strong ground motions from the Loma Prieta earthquake recorded in the San Francisco and Oakland areas exceeded the levels predicted by standard empirical attenuation relations. Preliminary analysis of accelerograms having known trigger times suggests that the elevation of ground motion amplitudes in the distance range of approximately 40 to 100 km was due to critical reflections from the base of the crust. These reflections were large and occurred at relatively close range because of the deep focal depth of the earthquake and the strong velocity gradient at the base of the crust, and were enhanced by rupture directivity. These motions were further amplified, presumably by impedance contrast effects, at soft soil sites in San Francisco and Oakland. The effect of the critical reflections in amplifying peak accelerations of the Loma Prieta earthquake in the San Francisco and Oakland regions was as large as the effect of soft soil site conditions
The merger rate of massive galaxies
We calculate the projected two point correlation function for samples of
luminous and massive galaxies in the COMBO-17 photometric redshift survey,
focusing particularly on the amplitude of the correlation function at small
projected radii and exploring the constraints such measurements can place on
the galaxy merger rate. For nearly volume-limited samples with 0.4<z<0.8, we
find that 4+/-1% of luminous M_B<-20 galaxies are in close physical pairs (with
real space separation of <30 proper kpc). The corresponding fraction for
massive galaxies with M_*>2.5e10 M_sun is 5+/-1%. Incorporating close pair
fractions from the literature, the 2dFGRS and the SDSS, we find a fairly rapid
evolution of the merger fraction of massive galaxies between z=0.8 and the
present day. Assuming that the major merger timescale is of order the dynamical
timescale for close massive galaxy pairs, we tentatively infer that ~50% (70%)
of all galaxies with present-day masses M_*>5e10 M_sun (remnants of mergers
between galaxies with M_*>2.5e10 M_sun) have undergone a major merger since
z=0.8(1): major mergers between massive galaxies are a significant driver of
galaxy evolution over the last eight billion years.Comment: ApJ, in press. 8 pages, 3 figures. Expanded discussion section with
explicit discussion of merger fraction vs. close pair fraction. Change of
typical close pair timescale results in increased inferred merger rat
Modeling the red sequence: Hierarchical growth yet slow luminosity evolution
We explore the effects of mergers on the evolution of massive early-type
galaxies by modeling the evolution of their stellar populations in a
hierarchical context. We investigate how a realistic red sequence population
set up by z~1 evolves under different assumptions for the merger and star
formation histories, comparing changes in color, luminosity and mass. The
purely passive fading of existing red sequence galaxies, with no further
mergers or star formation, results in dramatic changes at the bright end of the
luminosity function and color-magnitude relation. Without mergers there is too
much evolution in luminosity at a fixed space density compared to observations.
The change in color and magnitude at a fixed mass resemble that of a passively
evolving population that formed relatively recently, at z~2. Mergers amongst
the red sequence population ("dry mergers") occurring after z=1 build up mass,
counteracting the fading of the existing stellar populations to give smaller
changes in both color and luminosity for massive galaxies. By allowing some
galaxies to migrate from the blue cloud onto the red sequence after z=1 through
gas-rich mergers, younger stellar populations are added to the red sequence.
This manifestation of the progenitor bias increases the scatter in age and
results in even smaller changes in color and luminosity between z=1 and z=0 at
a fixed mass. The resultant evolution appears much slower, resembling the
passive evolution of a population that formed at high redshift (z~3-5) and is
in closer agreement with observations. Measurements of the luminosity and color
evolution alone are not sufficient to distinguish between the purely passive
evolution of an old population and cosmologically motivated hierarchical
growth, although these scenarios have very different implications for the mass
growth of early-type galaxies over the last half of cosmic history.Comment: 14 pages, 4 figures. Final version accepted for publication in ApJ
(2012, ApJ 753, 44
Letter from John F. Somerville, D.W. Osborn, S.E. Hustlin & G.B. Read to James B. Finley
The Committee of Arrangements for the Troy Division #20, Sons of Temperance, invites Finley to speak at their celebration on June 30th. They apologize for the lateness of the request. Abstract Number - 1173https://digitalcommons.owu.edu/finley-letters/2155/thumbnail.jp
Urosemiotik: The Pathological Chemistry of The Urine, The Complete Quantitative Analysis of The Urine, a Valuable Aid to Clinical Diagnosis
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