178 research outputs found
Resonant transmission line drivers
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.Includes bibliographical references (leaves 71-72).by Matthew E. Becker.Ph.D
Fast arbitration in dilated routers
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (p. 84-85).by Matthew E. Becker.M.Eng
Cross-correlation Weak Lensing of SDSS galaxy Clusters II: Cluster Density Profiles and the Mass--Richness Relation
We interpret and model the statistical weak lensing measurements around
130,000 groups and clusters of galaxies in the Sloan Digital Sky Survey
presented by Sheldon et al. 2007 (Paper I). We present non-parametric
inversions of the 2D shear profiles to the mean 3D cluster density and mass
profiles in bins of both optical richness and cluster i-band luminosity. We
correct the inferred 3D profiles for systematic effects, including non-linear
shear and the fact that cluster halos are not all precisely centered on their
brightest galaxies. We also model the measured cluster shear profile as a sum
of contributions from the brightest central galaxy, the cluster dark matter
halo, and neighboring halos. We infer the relations between mean cluster virial
mass and optical richness and luminosity over two orders of magnitude in
cluster mass; the virial mass at fixed richness or luminosity is determined
with a precision of 13% including both statistical and systematic errors. We
also constrain the halo concentration parameter and halo bias as a function of
cluster mass; both are in good agreement with predictions of LCDM models. The
methods employed here will be applicable to deeper, wide-area optical surveys
that aim to constrain the nature of the dark energy, such as the Dark Energy
Survey, the Large Synoptic Survey Telescope and space-based surveys
A GMBCG Galaxy Cluster Catalog of 55,424 Rich Clusters from SDSS DR7
We present a large catalog of optically selected galaxy clusters from the
application of a new Gaussian Mixture Brightest Cluster Galaxy (GMBCG)
algorithm to SDSS Data Release 7 data. The algorithm detects clusters by
identifying the red sequence plus Brightest Cluster Galaxy (BCG) feature, which
is unique for galaxy clusters and does not exist among field galaxies. Red
sequence clustering in color space is detected using an Error Corrected
Gaussian Mixture Model. We run GMBCG on 8240 square degrees of photometric data
from SDSS DR7 to assemble the largest ever optical galaxy cluster catalog,
consisting of over 55,000 rich clusters across the redshift range from 0.1 < z
< 0.55. We present Monte Carlo tests of completeness and purity and perform
cross-matching with X-ray clusters and with the maxBCG sample at low redshift.
These tests indicate high completeness and purity across the full redshift
range for clusters with 15 or more members.Comment: Updated to match the published version. The catalog can be accessed
from: http://home.fnal.gov/~jghao/gmbcg_sdss_catalog.htm
Cosmological Constraints from the SDSS maxBCG Cluster Catalog
We use the abundance and weak lensing mass measurements of the SDSS maxBCG
cluster catalog to simultaneously constrain cosmology and the richness--mass
relation of the clusters. Assuming a flat \LambdaCDM cosmology, we find
\sigma_8(\Omega_m/0.25)^{0.41} = 0.832\pm 0.033 after marginalization over all
systematics. In common with previous studies, our error budget is dominated by
systematic uncertainties, the primary two being the absolute mass scale of the
weak lensing masses of the maxBCG clusters, and uncertainty in the scatter of
the richness--mass relation. Our constraints are fully consistent with the WMAP
five-year data, and in a joint analysis we find \sigma_8=0.807\pm 0.020 and
\Omega_m=0.265\pm 0.016, an improvement of nearly a factor of two relative to
WMAP5 alone. Our results are also in excellent agreement with and comparable in
precision to the latest cosmological constraints from X-ray cluster abundances.
The remarkable consistency among these results demonstrates that cluster
abundance constraints are not only tight but also robust, and highlight the
power of optically-selected cluster samples to produce precision constraints on
cosmological parameters.Comment: comments welcom
Precision Measurements of the Cluster Red Sequence using an Error Corrected Gaussian Mixture Model
The red sequence is an important feature of galaxy clusters and plays a
crucial role in optical cluster detection. Measurement of the slope and scatter
of the red sequence are affected both by selection of red sequence galaxies and
measurement errors. In this paper, we describe a new error corrected Gaussian
Mixture Model for red sequence galaxy identification. Using this technique, we
can remove the effects of measurement error and extract unbiased information
about the intrinsic properties of the red sequence. We use this method to
select red sequence galaxies in each of the 13,823 clusters in the maxBCG
catalog, and measure the red sequence ridgeline location and scatter of each.
These measurements provide precise constraints on the variation of the average
red galaxy populations in the observed frame with redshift. We find that the
scatter of the red sequence ridgeline increases mildly with redshift, and that
the slope decreases with redshift. We also observe that the slope does not
strongly depend on cluster richness. Using similar methods, we show that this
behavior is mirrored in a spectroscopic sample of field galaxies, further
emphasizing that ridgeline properties are independent of environment.Comment: 33 pages, 14 Figures; A typo in Eq.A11 is fixed. The C++/Python codes
for ECGMM can be downloaded from:
https://sites.google.com/site/jiangangecgmm
Cosmological Constraints from the Large Scale Weak Lensing of SDSS MaxBCG Clusters
We derive constraints on the matter density \Om and the amplitude of matter
clustering \sig8 from measurements of large scale weak lensing (projected
separation R=5-30\hmpc) by clusters in the Sloan Digital Sky Survey MaxBCG
catalog. The weak lensing signal is proportional to the product of \Om and the
cluster-mass correlation function \xicm. With the relation between optical
richness and cluster mass constrained by the observed cluster number counts,
the predicted lensing signal increases with increasing \Om or \sig8, with mild
additional dependence on the assumed scatter between richness and mass. The
dependence of the signal on scale and richness partly breaks the degeneracies
among these parameters. We incorporate external priors on the richness-mass
scatter from comparisons to X-ray data and on the shape of the matter power
spectrum from galaxy clustering, and we test our adopted model for \xicm
against N-body simulations. Using a Bayesian approach with minimal restrictive
priors, we find \sig8(\Om/0.325)^{0.501}=0.828 +/- 0.049, with marginalized
constraints of \Om=0.325_{-0.067}^{+0.086} and \sig8=0.828_{-0.097}^{+0.111},
consistent with constraints from other MaxBCG studies that use weak lensing
measurements on small scales (R<=2\hmpc). The (\Om,\sig8) constraint is
consistent with and orthogonal to the one inferred from WMAP CMB data,
reflecting agreement with the structure growth predicted by GR for an LCDM
cosmological model. A joint constraint assuming LCDM yields \Om=0.298 +/- 0.020
and \sig8=0.831 +/- 0.020. Our cosmological parameter errors are dominated by
the statistical uncertainties of the large scale weak lensing measurements,
which should shrink sharply with current and future imaging surveys.Comment: 20 pages, 12 figures, MNRAS Submitted. For a brief video explaining
the key result of this paper, see http://www.youtube.com/user/OSUAstronomy,
or http://v.youku.com/v_show/id_XNDI3ODA3NzY4.html in countries where YouTube
is not accessibl
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
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
Pan-Cancer Analysis of lncRNA Regulation Supports Their Targeting of Cancer Genes in Each Tumor Context
Long noncoding RNAs (lncRNAs) are commonly dys-regulated in tumors, but only a handful are known toplay pathophysiological roles in cancer. We inferredlncRNAs that dysregulate cancer pathways, onco-genes, and tumor suppressors (cancer genes) bymodeling their effects on the activity of transcriptionfactors, RNA-binding proteins, and microRNAs in5,185 TCGA tumors and 1,019 ENCODE assays.Our predictions included hundreds of candidateonco- and tumor-suppressor lncRNAs (cancerlncRNAs) whose somatic alterations account for thedysregulation of dozens of cancer genes and path-ways in each of 14 tumor contexts. To demonstrateproof of concept, we showed that perturbations tar-geting OIP5-AS1 (an inferred tumor suppressor) andTUG1 and WT1-AS (inferred onco-lncRNAs) dysre-gulated cancer genes and altered proliferation ofbreast and gynecologic cancer cells. Our analysis in-dicates that, although most lncRNAs are dysregu-lated in a tumor-specific manner, some, includingOIP5-AS1, TUG1, NEAT1, MEG3, and TSIX, synergis-tically dysregulate cancer pathways in multiple tumorcontexts
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