188 research outputs found
Example Based Learning for View-Based Human Face Detection
We present an example-based learning approach for locating vertical frontal views of human faces in complex scenes. The technique models the distribution of human face patterns by means of a few view-based "face'' and "non-face'' prototype clusters. At each image location, the local pattern is matched against the distribution-based model, and a trained classifier determines, based on the local difference measurements, whether or not a human face exists at the current image location. We provide an analysis that helps identify the critical components of our system
The large-scale Quasar-Lyman \alpha\ Forest Cross-Correlation from BOSS
We measure the large-scale cross-correlation of quasars with the Lyman
\alpha\ forest absorption in redshift space, using ~ 60000 quasar spectra from
Data Release 9 (DR9) of the Baryon Oscillation Spectroscopic Survey (BOSS). The
cross-correlation is detected over a wide range of scales, up to comoving
separations r of 80 Mpc/h. For r > 15 Mpc/h, we show that the cross-correlation
is well fitted by the linear theory prediction for the mean overdensity around
a quasar host halo in the standard \Lambda CDM model, with the redshift
distortions indicative of gravitational evolution detected at high confidence.
Using previous determinations of the Lyman \alpha\ forest bias factor obtained
from the Lyman \alpha\ autocorrelation, we infer the quasar bias factor to be
b_q = 3.64^+0.13_-0.15 at a mean redshift z=2.38, in agreement with previous
measurements from the quasar auto-correlation. We also obtain a new estimate of
the Lyman \alpha\ forest redshift distortion factor, \beta_F = 1.1 +/- 0.15,
slightly larger than but consistent with the previous measurement from the
Lyman \alpha\ forest autocorrelation. The simple linear model we use fails at
separations r < 15 Mpc/h, and we show that this may reasonably be due to the
enhanced ionization due to radiation from the quasars. We also provide the
expected correction that the mass overdensity around the quasar implies for
measurements of the ionizing radiation background from the line-of-sight
proximity effect.Comment: 24 pages, 6 figures, published in JCA
Detection of Ly\beta auto-correlations and Ly\alpha-Ly\beta cross-correlations in BOSS Data Release 9
The Lyman- forest refers to a region in the spectra of distant quasars
that lies between the rest-frame Lyman- and Lyman- emissions.
The forest in this region is dominated by a combination of absorption due to
resonant Ly and Ly scattering. When considering the 1D Ly
forest in addition to the 1D Ly forest, the full statistical
description of the data requires four 1D power spectra: Ly and
Ly auto-power spectra and the Ly-Ly real and imaginary
cross-power spectra. We describe how these can be measured using an optimal
quadratic estimator that naturally disentangles Ly and Ly
contributions. Using a sample of approximately 60,000 quasar sight-lines from
the BOSS Data Release 9, we make the measurement of the one-dimensional power
spectrum of fluctuations due to the Ly resonant scattering. While we
have not corrected our measurements for resolution damping of the power and
other systematic effects carefully enough to use them for cosmological
constraints, we can robustly conclude the following: i) Ly power
spectrum and Ly-Ly cross spectra are detected with high
statistical significance; ii) the cross-correlation coefficient is
on large scales; iii) the Ly measurements are contaminated by the
associated OVI absorption, which is analogous to the SiIII contamination of the
Ly forest. Measurements of the Ly forest will allow extension of
the usable path-length for the Ly measurements while allowing a better
understanding of the physics of intergalactic medium and thus more robust
cosmological constraints.Comment: 26 pages, 10 figures; matches version accepted by JCA
New approach for precise computation of Lyman-alpha forest power spectrum with hydrodynamical simulations
Current experiments are providing measurements of the flux power spectrum from the Lyman-α forests observed in quasar spectra with unprecedented accuracy. Their interpretation in terms of cosmological constraints requires specific simulations of at least equivalent precision. In this paper, we present a suite of cosmological N-body simulations with cold dark matter and baryons, specifically aiming at modeling the low-density regions of the inter-galactic medium as probed by the Lyman-α forests at high redshift. The simulations were run using the GADGET-3 code and were designed to match the requirements imposed by the quality of the current SDSS-III/BOSS or forthcoming SDSS-IV/eBOSS data. They are made using either 2 × 7683 1 billion or 2 × 1923 14 million particles, spanning volumes ranging from (25 Mpc h−1)3 for high-resolution simulations to (100 Mpc h−1)3 for large-volume ones. Using a splicing technique, the resolution is further enhanced to reach the equivalent of simulations with 2 × 30723 58 billion particles in a (100 Mpc h−1)3 box size, i.e. a mean mass per gas particle of 1.2 × 105M⊙ h−1. We show that the resulting power spectrum is accurate at the 2% level over the full range from a few Mpc to several tens of Mpc. We explore the effect on the one-dimensional transmitted-flux power spectrum of four cosmological parameters (ns, σ8, Ωm and H0) and two astrophysical parameters (T0 and γ) that are related to the heating rate of the intergalactic medium. By varying the input parameters around a central model chosen to be in agreement with the latest Planck results, we built a grid of simulations that allows the study of the impact on the flux power spectrum of these six relevant parameters. We improve upon previous studies by not only measuring the effect of each parameter individually, but also probing the impact of the simultaneous variation of each pair of parameters. We thus provide a full second-order expansion, including cross-terms, around our central model. We check the validity of the second-order expansion with independent simulations obtained either with different cosmological parameters or different seeds. Finally, a comparison to the one-dimensional Lyman-α forest power spectrum obtained with BOSS by [1] shows an excellent agreement
Probing the Circumgalactic Medium at High-Redshift Using Composite BOSS Spectra of Strong Lyman-alpha Forest Absorbers
We present composite spectra constructed from a sample of 242,150 Lyman-alpha
(Lya) forest absorbers at redshifts 2.4<z<3.1 identified in quasar spectra from
the Baryon Oscillation Spectroscopic Survey (BOSS) as part of Data Release 9 of
the Sloan Digital Sky Survey III. We select forest absorbers by their flux in
bins 138 km/s wide (approximately the size of the BOSS resolution element). We
split these absorbers into five samples spanning the range of flux -0.05 <
F<0.45. Tests on a smaller sample of high-resolution spectra show that our
three strongest absorption bins would probe circumgalactic regions (projected
separation < 300 proper kpc and |Delta v| < 300km/s) in about 60% of cases for
very high signal-to-noise ratio. Within this subset, weakening Lya absorption
is associated with decreasing purity of circumgalactic selection once BOSS
noise is included. Our weaker two Lya absorption samples are dominated by the
intergalactic medium.
We present composite spectra of these samples and a catalogue of measured
absorption features from HI and 13 metal ionization species, all of which we
make available to the community. We compare measurements of seven Lyman series
transitions in our composite spectra to single line models and obtain further
constraints from their associated excess Lyman limit opacity. This analysis
provides results consistent with column densities over the range 14.4 <~ Log
(N_HI) <~ 16.45. We compare our measurements of metal absorption to a variety
of simple single-line, single-phase models for a preliminary interpretation.
Our results imply clumping on scales down to ~30 pc and near-solar
metallicities in the circumgalactic samples, while high-ionization metal
absorption consistent with typical IGM densities and metallicities is visible
in all samples.Comment: 23 pages, 15 figures, 5 tables, link to downloadable data included.
Accepted by MNRAS 2014 March 20. New sections 3.4 and 6.1 limiting the
occurrence and impact of Lyman limit system
Constraint on neutrino masses from SDSS-III/BOSS Ly-alpha forest and other cosmological probes
International audienceWe present constraints on the parameters of the CDM cosmologicalmodel in the presence of massive neutrinos, using the one-dimensionalLy forest power spectrum obtained with the Baryon OscillationSpectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS) byPalanque-Delabrouille et al. (2013), complemented by additional cosmologicalprobes. The interpretation of the measured Ly spectrum is done using asecond-order Taylor expansion of the simulated power spectrum. BOSS Ly data alone provide better bounds than previous Ly results,but are still poorly constraining, especially for the sum of neutrino masses, for which we obtain an upper bound of 1.1~eV (95\% CL), includingsystematics for both data and simulations. Ly constraints onCDM parameters and neutrino masses are compatible with CMB bounds fromthe Planck collaboration. Interestingly, the combination of Ly with CMBdata reduces the uncertainties significantly, due to very different directionsof degeneracy in parameter space, leading to the strongest cosmological boundto date on the total neutrino mass, ~eV at 95\% CL (with abest-fit in zero). Adding recent BAO results further tightens this constraintto ~eV at 95\% CL. This bound is nearly independent of thestatistical approach used, and of the different combinations of CMB and BAOdata sets considered in this paper in addition to Ly. Given themeasured values of the two squared mass differences , this resulttends to favor the normal hierarchy scenario against the inverted hierarchyscenario for the masses of the active neutrino species
Ethnic differences in receipt of psychological interventions in Early Intervention in Psychosis services in England – a cross-sectional study
There is some evidence of differences in psychosis care provision by ethnicity. We investigated variations in the receipt of CBTp and family intervention across ethnic groups in Early Intervention in Psychosis (EIP) teams throughout England, where national policy mandates offering these interventions to all.
We included data on 29,610 service users from the National Clinical Audit of Psychosis (NCAP), collected between 2018 and 2021. We conducted mixed effects logistic regression to examine odds ratios of receiving an intervention (CBTp, family intervention, either intervention) across 17 ethnic groups while accounting for the effect of years and variance between teams and adjusting for individual- (age, gender, occupational status) and team-level covariates (care-coordinator caseload, inequalities strategies).
Compared with White British people, every minoritized ethnic group, except those of mixed Asian-White and mixed Black African-White ethnicities, had significantly lower adjusted odds of receiving CBTp. People of Black African, Black Caribbean, non-African/Caribbean Black, non-British/Irish White, and of “any other” ethnicity also experienced significantly lower adjusted odds of receiving family intervention.
Pervasive inequalities in receiving CBTp for first episode psychosis exist for almost all minoritized ethnic groups, and family intervention for many groups. Investigating how these inequalities arise should be a research priority
Baryon Acoustic Oscillations in the Ly{\alpha} forest of BOSS DR11 quasars
We report a detection of the baryon acoustic oscillation (BAO) feature in the
flux-correlation function of the Ly{\alpha} forest of high-redshift quasars
with a statistical significance of five standard deviations. The study uses
137,562 quasars in the redshift range from the Data Release
11 (DR11) of the Baryon Oscillation Spectroscopic Survey (BOSS) of SDSS-III.
This sample contains three times the number of quasars used in previous
studies. The measured position of the BAO peak determines the angular distance,
and expansion rate, , both on a scale set by the sound
horizon at the drag epoch, . We find
and
where . The optimal
combination, is determined with a precision of
. For the value , consistent with the CMB power
spectrum measured by Planck, we find
and . Tests with mock
catalogs and variations of our analysis procedure have revealed no systematic
uncertainties comparable to our statistical errors. Our results agree with the
previously reported BAO measurement at the same redshift using the
quasar-Ly{\alpha} forest cross-correlation. The auto-correlation and
cross-correlation approaches are complementary because of the quite different
impact of redshift-space distortion on the two measurements. The combined
constraints from the two correlation functions imply values of and
that are, respectively, 7% low and 7% high compared to the
predictions of a flat CDM cosmological model with the best-fit Planck
parameters. With our estimated statistical errors, the significance of this
discrepancy is .Comment: Accepted for publication in A&A. 17 pages, 18 figure
Mock Quasar-Lyman-{\alpha} Forest Data-sets for the SDSS-III Baryon Oscillation Spectroscopic Survey
We describe mock data-sets generated to simulate the high-redshift quasar
sample in Data Release 11 (DR11) of the SDSS-III Baryon Oscillation
Spectroscopic Survey (BOSS). The mock spectra contain Ly{\alpha} forest
correlations useful for studying the 3D correlation function including Baryon
Acoustic Oscillations (BAO). They also include astrophysical effects such as
quasar continuum diversity and high-density absorbers, instrumental effects
such as noise and spectral resolution, as well as imperfections introduced by
the SDSS pipeline treatment of the raw data. The Ly{\alpha} forest BAO analysis
of the BOSS collaboration, described in Delubac et al. 2014, has used these
mock data-sets to develop and cross-check analysis procedures prior to
performing the BAO analysis on real data, and for continued systematic cross
checks. Tests presented here show that the simulations reproduce sufficiently
well important characteristics of real spectra. These mock data-sets will be
made available together with the data at the time of the Data Release 11.Comment: 35 pages, 19 figures, Accepted by JCA
The SDSS-III Baryon Oscillation Spectroscopic Survey: Quasar Target Selection for Data Release Nine
The SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), a five-year
spectroscopic survey of 10,000 deg^2, achieved first light in late 2009. One of
the key goals of BOSS is to measure the signature of baryon acoustic
oscillations in the distribution of Ly-alpha absorption from the spectra of a
sample of ~150,000 z>2.2 quasars. Along with measuring the angular diameter
distance at z\approx2.5, BOSS will provide the first direct measurement of the
expansion rate of the Universe at z > 2. One of the biggest challenges in
achieving this goal is an efficient target selection algorithm for quasars over
2.2 < z < 3.5, where their colors overlap those of stars. During the first year
of the BOSS survey, quasar target selection methods were developed and tested
to meet the requirement of delivering at least 15 quasars deg^-2 in this
redshift range, out of 40 targets deg^-2. To achieve these surface densities,
the magnitude limit of the quasar targets was set at g <= 22.0 or r<=21.85.
While detection of the BAO signature in the Ly-alpha absorption in quasar
spectra does not require a uniform target selection, many other astrophysical
studies do. We therefore defined a uniformly-selected subsample of 20 targets
deg^-2, for which the selection efficiency is just over 50%. This "CORE"
subsample will be fixed for Years Two through Five of the survey. In this paper
we describe the evolution and implementation of the BOSS quasar target
selection algorithms during the first two years of BOSS operations. We analyze
the spectra obtained during the first year. 11,263 new z>2.2 quasars were
spectroscopically confirmed by BOSS. Our current algorithms select an average
of 15 z > 2.2 quasars deg^-2 from 40 targets deg^-2 using single-epoch SDSS
imaging. Multi-epoch optical data and data at other wavelengths can further
improve the efficiency and completeness of BOSS quasar target selection.
[Abridged]Comment: 33 pages, 26 figures, 12 tables and a whole bunch of quasars.
Submitted to Ap
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