84 research outputs found
Development of an Ultra-Lightweight Buckling-Restrained Brace Using Analytical and Numerical Methods
An ultra-lightweight buckling-restrained brace (ULWBRB) is developed using a highly ductile aluminum core and FRP restrainer. Utilization of lightweight materials results in a BRB that is 25% the weight of traditional mortar-filled tube varieties allowing easy installation in small to medium sized buildings requiring seismic retrofit without the need for heavy equipment. Construction utilizes commonly stocked materials able to be customized for required strength, drift, and geometry limitations. Analytical single degree of freedom (SDOF) and Euler buckling models are compared with published equations to determine the required restrainer stiffness (RRS). SDOF models yield RRS values 200% higher than the Euler model. Applied end moments due to frame deformation are incorporated into a modified design method that gives RRS values 50% higher than Euler model without eccentricity. RRS is provided using a bundled and wrapped FRP tube configuration using a developed shear flow method considering composite action. Uniaxial low-cycle fatigue (LCF) testing of a 6061-T6 candidate alloy provides data for a constitutive model using combined kinematic-isotropic hardening. LCF testing of round short gage coupons indicates the candidate alloy is capable of stable cycling to 2%, 3%, and 4% total strain with excellent ductility. Early fracture of specimens at 24, 18, and 11 cycles, respectively, also indicates that other candidate alloys should be examined for improved fatigue life. However, inconsistency is noted between similar tests of 6061-T6 that were able to achieve up to 76 cycles at 2.5% total strain. ULWBRB FEA models loaded monotonically consistently give higher RRS values as compared to the analytical methods. This is due to assignment of initial imperfections, longer more realistic unbraced length, higher axial loads achieved through the post-yield region, and plastic hinging potential. Cyclic simulations of braces with the same RRS values are also able to achieve reliable and stable hysteretic behavior through 21 cycles. If a less stiff restrainer is used, cumulative energy dissipation potential is reduced considerably due to pinched hysteresis loops and strain ratcheting. Applied end moments are found to have a linear effect on the RRS that can be modeled by superposition of the buckling effect plus end moment
Climate-driven change in the North Atlantic and Arctic Ocean can greatly reduce the circulation of the North Sea
We demonstrate for the first time a direct oceanic link between climate‐driven change in the North Atlantic and Arctic oceans and the circulation of the northwest European shelf‐seas. Downscaled scenarios show a shutdown of the exchange between the Atlantic and the North Sea, and a substantial decrease in the circulation of the North Sea in the second half of the 21st Century. The northern North Sea inflow decreases from 1.2‐1.3Sv (1Sv=106 m3s‐1) to 0.0‐0.6Sv with Atlantic water largely bypassing the North Sea. This is traced to changes in oceanic haline stratification and gyre structure, and to a newly identified circulation‐salinity feedback. The scenario presented here is of a novel potential future state for the North Sea, with wide‐ranging environmental management and societal impacts. Specifically, the sea would become more estuarine and susceptible to anthropogenic influence with an enhanced risk of coastal eutrophication
The Atacama Cosmology Telescope: Physical Properties and Purity of a Galaxy Cluster Sample Selected via the Sunyaev-Zel'dovich Effect
We present optical and X-ray properties for the first confirmed galaxy
cluster sample selected by the Sunyaev-Zel'dovich Effect from 148 GHz maps over
455 square degrees of sky made with the Atacama Cosmology Telescope. These
maps, coupled with multi-band imaging on 4-meter-class optical telescopes, have
yielded a sample of 23 galaxy clusters with redshifts between 0.118 and 1.066.
Of these 23 clusters, 10 are newly discovered. The selection of this sample is
approximately mass limited and essentially independent of redshift. We provide
optical positions, images, redshifts and X-ray fluxes and luminosities for the
full sample, and X-ray temperatures of an important subset. The mass limit of
the full sample is around 8e14 Msun, with a number distribution that peaks
around a redshift of 0.4. For the 10 highest significance SZE-selected cluster
candidates, all of which are optically confirmed, the mass threshold is 1e15
Msun and the redshift range is 0.167 to 1.066. Archival observations from
Chandra, XMM-Newton, and ROSAT provide X-ray luminosities and temperatures that
are broadly consistent with this mass threshold. Our optical follow-up
procedure also allowed us to assess the purity of the ACT cluster sample.
Eighty (one hundred) percent of the 148 GHz candidates with signal-to-noise
ratios greater than 5.1 (5.7) are confirmed as massive clusters. The reported
sample represents one of the largest SZE-selected sample of massive clusters
over all redshifts within a cosmologically-significant survey volume, which
will enable cosmological studies as well as future studies on the evolution,
morphology, and stellar populations in the most massive clusters in the
Universe.Comment: 20 pages, 15 figures, 6 tables. Accepted for publication in ApJ.
Higher resolution figures available at:
http://peumo.rutgers.edu/~felipe/e-prints
The Atacama Cosmology Telescope: Dynamical Masses and Scaling Relations for a Sample of Massive Sunyaev-Zel'dovich Effect Selected Galaxy Clusters
We present the first dynamical mass estimates and scaling relations for a
sample of Sunyaev-Zel'dovich effect (SZE) selected galaxy clusters. The sample
consists of 16 massive clusters detected with the Atacama Cosmology Telescope
(ACT) over a 455 sq. deg. area of the southern sky. Deep multi-object
spectroscopic observations were taken to secure intermediate-resolution
(R~700-800) spectra and redshifts for ~60 member galaxies on average per
cluster. The dynamical masses M_200c of the clusters have been calculated using
simulation-based scaling relations between velocity dispersion and mass. The
sample has a median redshift z=0.50 and a median mass M_200c~12e14 Msun/h70
with a lower limit M_200c~6e14 Msun/h70, consistent with the expectations for
the ACT southern sky survey. These masses are compared to the ACT SZE
properties of the sample, specifically, the match-filtered central SZE
amplitude y, the central Compton parameter y0, and the integrated Compton
signal Y_200c, which we use to derive SZE-Mass scaling relations. All SZE
estimators correlate with dynamical mass with low intrinsic scatter (<~20%), in
agreement with numerical simulations. We explore the effects of various
systematic effects on these scaling relations, including the correlation
between observables and the influence of dynamically disturbed clusters. Using
the 3-dimensional information available, we divide the sample into relaxed and
disturbed clusters and find that ~50% of the clusters are disturbed. There are
hints that disturbed systems might bias the scaling relations but given the
current sample sizes these differences are not significant; further studies
including more clusters are required to assess the impact of these clusters on
the scaling relations.Comment: 15 pages, 4 figures. Accepted for publication in The Astrophysical
Journal; matches published version. Full Table 8 with complete spectroscopic
member sample available in machine-readable form in the journal site and upon
request to C. Sif\'o
The Atacama Cosmology Telescope: Cosmology from Galaxy Clusters Detected via the Sunyaev-Zel'dovich Effect
We present constraints on cosmological parameters based on a sample of
Sunyaev-Zel'dovich-selected galaxy clusters detected in a millimeter-wave
survey by the Atacama Cosmology Telescope. The cluster sample used in this
analysis consists of 9 optically-confirmed high-mass clusters comprising the
high-significance end of the total cluster sample identified in 455 square
degrees of sky surveyed during 2008 at 148 GHz. We focus on the most massive
systems to reduce the degeneracy between unknown cluster astrophysics and
cosmology derived from SZ surveys. We describe the scaling relation between
cluster mass and SZ signal with a 4-parameter fit. Marginalizing over the
values of the parameters in this fit with conservative priors gives sigma_8 =
0.851 +/- 0.115 and w = -1.14 +/- 0.35 for a spatially-flat wCDM cosmological
model with WMAP 7-year priors on cosmological parameters. This gives a modest
improvement in statistical uncertainty over WMAP 7-year constraints alone.
Fixing the scaling relation between cluster mass and SZ signal to a fiducial
relation obtained from numerical simulations and calibrated by X-ray
observations, we find sigma_8 = 0.821 +/- 0.044 and w = -1.05 +/- 0.20. These
results are consistent with constraints from WMAP 7 plus baryon acoustic
oscillations plus type Ia supernoava which give sigma_8 = 0.802 +/- 0.038 and w
= -0.98 +/- 0.053. A stacking analysis of the clusters in this sample compared
to clusters simulated assuming the fiducial model also shows good agreement.
These results suggest that, given the sample of clusters used here, both the
astrophysics of massive clusters and the cosmological parameters derived from
them are broadly consistent with current models.Comment: 12 pages, 7 figures. Submitted to Ap
Riflessioni su alcune scelte traduttive in lingua inglese (Morris, Tinker, Tolkien, Heaney e Porter)
This essay takes into account some English translations of the Old English poem Beowulf. Matter of specific investigation is the passage of the coming of Grendel to the Danes' court Heorot. As the translations of Beowulf are countless, only specific and emblematic cases – both in prose and verse – are analysed. Then, the translations by William Morris, Chancey Brewster Tinker, J.R.R. Tolkien, Seamus Heaney and John Porter are compared trying to ascertain the approach of those translators to the Old English text and furthermore the intentions they had in rendering the poem into Modern English. The big problem that all the translators consciously tackled was the chronological and linguistic distance of Beowulf that had to be solved in some way. Choices and strategies differ from one version to another, but every solution demonstrates a specific attention to the musicalness of the original together with a deep awareness for the tradition that the Old English poem embodies
The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic
data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data
release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median
z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar
spectra, along with the data presented in previous data releases. These spectra
were obtained with the new BOSS spectrograph and were taken between 2009
December and 2011 July. In addition, the stellar parameters pipeline, which
determines radial velocities, surface temperatures, surface gravities, and
metallicities of stars, has been updated and refined with improvements in
temperature estimates for stars with T_eff<5000 K and in metallicity estimates
for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars
presented in DR8, including stars from SDSS-I and II, as well as those observed
as part of the SDSS-III Sloan Extension for Galactic Understanding and
Exploration-2 (SEGUE-2).
The astrometry error introduced in the DR8 imaging catalogs has been
corrected in the DR9 data products. The next data release for SDSS-III will be
in Summer 2013, which will present the first data from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) along with another year of
data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at
http://www.sdss3.org/dr
The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III
The Sloan Digital Sky Survey (SDSS) started a new phase in August 2008, with
new instrumentation and new surveys focused on Galactic structure and chemical
evolution, measurements of the baryon oscillation feature in the clustering of
galaxies and the quasar Ly alpha forest, and a radial velocity search for
planets around ~8000 stars. This paper describes the first data release of
SDSS-III (and the eighth counting from the beginning of the SDSS). The release
includes five-band imaging of roughly 5200 deg^2 in the Southern Galactic Cap,
bringing the total footprint of the SDSS imaging to 14,555 deg^2, or over a
third of the Celestial Sphere. All the imaging data have been reprocessed with
an improved sky-subtraction algorithm and a final, self-consistent photometric
recalibration and flat-field determination. This release also includes all data
from the second phase of the Sloan Extension for Galactic Understanding and
Evolution (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars
at both high and low Galactic latitudes. All the more than half a million
stellar spectra obtained with the SDSS spectrograph have been reprocessed
through an improved stellar parameters pipeline, which has better determination
of metallicity for high metallicity stars.Comment: Astrophysical Journal Supplements, in press (minor updates from
submitted version
The Baryon Oscillation Spectroscopic Survey of SDSS-III
The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the
scale of baryon acoustic oscillations (BAO) in the clustering of matter over a
larger volume than the combined efforts of all previous spectroscopic surveys
of large scale structure. BOSS uses 1.5 million luminous galaxies as faint as
i=19.9 over 10,000 square degrees to measure BAO to redshifts z<0.7.
Observations of neutral hydrogen in the Lyman alpha forest in more than 150,000
quasar spectra (g<22) will constrain BAO over the redshift range 2.15<z<3.5.
Early results from BOSS include the first detection of the large-scale
three-dimensional clustering of the Lyman alpha forest and a strong detection
from the Data Release 9 data set of the BAO in the clustering of massive
galaxies at an effective redshift z = 0.57. We project that BOSS will yield
measurements of the angular diameter distance D_A to an accuracy of 1.0% at
redshifts z=0.3 and z=0.57 and measurements of H(z) to 1.8% and 1.7% at the
same redshifts. Forecasts for Lyman alpha forest constraints predict a
measurement of an overall dilation factor that scales the highly degenerate
D_A(z) and H^{-1}(z) parameters to an accuracy of 1.9% at z~2.5 when the survey
is complete. Here, we provide an overview of the selection of spectroscopic
targets, planning of observations, and analysis of data and data quality of
BOSS.Comment: 49 pages, 16 figures, accepted by A
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