73 research outputs found
Mature neurons dynamically restrict apoptosis via redundant premitochondrial brakes
Apoptotic cell death is critical for the early development of the nervous system, but once the nervous system is established, the apoptotic pathway becomes highly restricted in mature neurons. However, the mechanisms underlying this increased resistance to apoptosis in these mature neurons are not completely understood. We have previously found that members of the miR-29 family of microRNAs (miRNAs) are induced with neuronal maturation and that overexpression of miR-29 was sufficient to restrict apoptosis in neurons. To determine whether endogenous miR-29 alone was responsible for the inhibition of cytochrome c release in mature neurons, we examined the status of the apoptotic pathway in sympathetic neurons deficient for all three miR-29 family members. Unexpectedly, we found that the apoptotic pathway remained largely restricted in miR-29-deficient mature neurons. We therefore probed for additional mechanisms by which mature neurons resist apoptosis. We identify miR-24 as another miRNA that is upregulated in the maturing cerebellum and sympathetic neurons that can act redundantly with miR-29 by targeting a similar repertoire of pro-death BH3-only genes. These results reveal that mature neurons engage redundant brakes to restrict the apoptotic pathway and ensure their long-term survival
Cross-correlation Weak Lensing of SDSS Galaxy Clusters III: Mass-to-light Ratios
We present measurements of the excess mass-to-light ratio measured
aroundMaxBCG galaxy clusters observed in the SDSS. This red sequence cluster
sample includes objects from small groups with masses ranging from ~5x10^{12}
to ~10^{15} M_{sun}/h. Using cross-correlation weak lensing, we measure the
excess mass density profile above the universal mean \Delta \rho(r) = \rho(r) -
\bar{\rho} for clusters in bins of richness and optical luminosity. We also
measure the excess luminosity density \Delta l(r) = l(r) - \bar{l} measured in
the z=0.25 i-band. For both mass and light, we de-project the profiles to
produce 3D mass and light profiles over scales from 25 kpc/ to 22 Mpc/h. From
these profiles we calculate the cumulative excess mass M(r) and excess light
L(r) as a function of separation from the BCG. On small scales, where \rho(r)
>> \bar{\rho}, the integrated mass-to-light profile may be interpreted as the
cluster mass-to-light ratio. We find the M/L_{200}, the mass-to-light ratio
within r_{200}, scales with cluster mass as a power law with index 0.33+/-0.02.
On large scales, where \rho(r) ~ \bar{\rho}, the M/L approaches an asymptotic
value independent of cluster richness. For small groups, the mean M/L_{200} is
much smaller than the asymptotic value, while for large clusters it is
consistent with the asymptotic value. This asymptotic value should be
proportional to the mean mass-to-light ratio of the universe . We find
/b^2_{ml} = 362+/-54 h (statistical). There is additional uncertainty in
the overall calibration at the ~10% level. The parameter b_{ml} is primarily a
function of the bias of the L <~ L_* galaxies used as light tracers, and should
be of order unity. Multiplying by the luminosity density in the same bandpass
we find \Omega_m/b^2_{ml} = 0.02+/-0.03, independent of the Hubble parameter.Comment: Third paper in a series; v2.0 incorporates ApJ referee's suggestion
Changes in Statin Adherence Following an Acute Myocardial Infarction Among Older Adults: Patient Predictors and the Association With FollowâUp With Primary Care Providers and/or Cardiologists
BACKGROUND: Hospitalizations for acute myocardial infarctions (AMIs) are associated with changes in statin adherence. It is unclear to what extent adherence changes, which patients are likely to change, and how post-discharge follow-up is associated with statin adherence change.
METHODS AND RESULTS: This retrospective study used Medicare data for all fee-for-service beneficiaries 66Â years and older with an AMI hospitalization in 2008-2010 and statin use before their index AMI. Multivariable multinomial logistic regression models (odds ratio [OR] and 99% confidence interval [CI]) were applied to assess associations between both patient characteristics and follow-up with a primary care provider and/or cardiologist with the outcome of statin adherence change (increase or decrease) from the 6-month pre- to 6-month post-AMI periods. Of 113Â 296 patients, 64.0% had no change in adherence, while 19.7% had increased and 16.3% had decreased adherence after AMI hospitalization. Black and Hispanic patients were more likely to have either increased or decreased adherence than white patients. Patients who required coronary artery bypass graft surgery (OR, 1.34; 99% CI, 1.21-1.49) or percutaneous transluminal coronary angioplasty/stent procedure (OR, 1.25; 99% CI, 1.17-1.32) during their index hospitalization were more likely to have increased adherence. Follow-up with a primary care provider was only mildly associated with increased adherence (OR, 1.08; 99% CI, 1.00-1.16), while follow-up with a cardiologist (OR, 1.15; 99% CI, 1.05-1.25) or both provider types (OR, 1.21; 99% CI, 1.12-1.30) had stronger associations with increased adherence.
CONCLUSIONS: Post-AMI changes in statin adherence varied by patient characteristics, and improved adherence was associated with post-discharge follow-up care, particularly with a cardiologist or both a primary care provider and a cardiologist
Photometric Redshifts of Quasars
We demonstrate that the design of the Sloan Digital Sky Survey (SDSS) filter
system and the quality of the SDSS imaging data are sufficient for determining
accurate and precise photometric redshifts (``photo-z''s) of quasars. Using a
sample of 2625 quasars, we show that photo-z determination is even possible for
z<=2.2 despite the lack of a strong continuum break that robust photo-z
techniques normally require. We find that, using our empirical method on our
sample of objects known to be quasars, approximately 70% of the photometric
redshifts are correct to within delta z = 0.2; the fraction of correct
photometric redshifts is even better for z>3. The accuracy of quasar
photometric redshifts does not appear to be dependent upon magnitude to nearly
21st magnitude in i'. Careful calibration of the color-redshift relation to
21st magnitude may allow for the discovery of on the order of 10^6 quasars
candidates in addition to the 10^5 quasars that the SDSS will confirm
spectroscopically. We discuss the efficient selection of quasar candidates from
imaging data for use with the photometric redshift technique and the potential
scientific uses of a large sample of quasar candidates with photometric
redshifts.Comment: 29 pages, 8 figures, submitted to A
Evolution of Galaxy Luminosity Function Using Photometric Redshifts
We examine the impact of using photometric redshifts for studying the
evolution of both the global galaxy luminosity function (LF) and that for
different galaxy types. To this end we compare LFs obtained using photometric
redshifts from the CFHT Legacy Survey (CFHTLS) D1 field with those from the
spectroscopic survey VIMOS VLT Deep Survey (VVDS) comprising ~4800 galaxies. We
find that for z<2, in the interval of magnitudes considered by this survey, the
LFs obtained using photometric and spectroscopic redshifts show a remarkable
agreement. This good agreement led us to use all four Deep fields of CFHTLS
comprising ~386000 galaxies to compute the LF of the combined fields and
estimate directly the error in the parameters based on field-to-field
variation. We find that the characteristic absolute magnitude M* of Schechter
fits fades by ~0.7mag from z~1.8 to z~0.3, while the characteristic density
phi* increases by a factor of ~4 in the same redshift bin. We use the galaxy
classification provided by the template fitting program used to compute
photometric redshifts and split the sample into galaxy types. We find that
these Schechter parameters evolve differently for each galaxy type, an
indication that their evolution is a combination of several effects: galaxy
merging, star formation quenching and mass assembly. All these results are
compatible with those obtained by different spectroscopic surveys such as VVDS,
DEEP2 and zCosmos, which reinforces the fact that photometric redshifts can be
used to study galaxy evolution, at least for the redshift bins adopted so far.
This is of great interest since future very large imaging surveys containing
hundreds of millions of galaxies will allow to obtain important precise
measurements to constrain the evolution of the LF and to explore the dependence
of this evolution on morphology and/or color helping constrain the mechanisms
of galaxy evolution.Comment: 29 pages, 10 figures. Approved for publication in The Astronomical
Journa
The Angular Correlation Function of Galaxies from Early SDSS Data
The Sloan Digital Sky Survey is one of the first multicolor photometric and
spectroscopic surveys designed to measure the statistical properties of
galaxies within the local Universe. In this Letter we present some of the
initial results on the angular 2-point correlation function measured from the
early SDSS galaxy data. The form of the correlation function, over the
magnitude interval 18<r*<22, is shown to be consistent with results from
existing wide-field, photographic-based surveys and narrower CCD galaxy
surveys. On scales between 1 arcminute and 1 degree the correlation function is
well described by a power-law with an exponent of ~ -0.7. The amplitude of the
correlation function, within this angular interval, decreases with fainter
magnitudes in good agreement with analyses from existing galaxy surveys. There
is a characteristic break in the correlation function on scales of
approximately 1-2 degrees. On small scales, < 1', the SDSS correlation function
does not appear to be consistent with the power-law form fitted to the 1'<
theta <0.5 deg data. With a data set that is less than 2% of the full SDSS
survey area, we have obtained high precision measurements of the power-law
angular correlation function on angular scales 1' < theta < 1 deg, which are
robust to systematic uncertainties. Because of the limited area and the highly
correlated nature of the error covariance matrix, these initial results do not
yet provide a definitive characterization of departures from the power-law form
at smaller and larger angles. In the near future, however, the area of the SDSS
imaging survey will be sufficient to allow detailed analysis of the small and
large scale regimes, measurements of higher-order correlations, and studies of
angular clustering as a function of redshift and galaxy type
Cosmological parameters from SDSS and WMAP
We measure cosmological parameters using the three-dimensional power spectrum
P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in
combination with WMAP and other data. Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt,
tensor modes or massive neutrinos. Adding SDSS information more than halves the
WMAP-only error bars on some parameters, tightening 1 sigma constraints on the
Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter
density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on
neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when
dropping prior assumptions about curvature, neutrinos, tensor modes and the
equation of state. Our results are in substantial agreement with the joint
analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive
consistency check with independent redshift survey data and analysis
techniques. In this paper, we place particular emphasis on clarifying the
physical origin of the constraints, i.e., what we do and do not know when using
different data sets and prior assumptions. For instance, dropping the
assumption that space is perfectly flat, the WMAP-only constraint on the
measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to
t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running
tilt, neutrino mass and equation of state in the list of free parameters, many
constraints are still quite weak, but future cosmological measurements from
SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt
figures available at http://www.hep.upenn.edu/~max/sdsspars.htm
Percolation Galaxy Groups and Clusters in the SDSS Redshift Survey: Identification, Catalogs, and the Multiplicity Function
We identify galaxy groups and clusters in volume-limited samples of the SDSS
redshift survey, using a redshift-space friends-of-friends algorithm. We
optimize the friends-of-friends linking lengths to recover galaxy systems that
occupy the same dark matter halos, using a set of mock catalogs created by
populating halos of N-body simulations with galaxies. Extensive tests with
these mock catalogs show that no combination of perpendicular and line-of-sight
linking lengths is able to yield groups and clusters that simultaneously
recover the true halo multiplicity function, projected size distribution, and
velocity dispersion. We adopt a linking length combination that yields, for
galaxy groups with ten or more members: a group multiplicity function that is
unbiased with respect to the true halo multiplicity function; an unbiased
median relation between the multiplicities of groups and their associated
halos; a spurious group fraction of less than ~1%; a halo completeness of more
than ~97%; the correct projected size distribution as a function of
multiplicity; and a velocity dispersion distribution that is ~20% too low at
all multiplicities. These results hold over a range of mock catalogs that use
different input recipes of populating halos with galaxies. We apply our
group-finding algorithm to the SDSS data and obtain three group and cluster
catalogs for three volume-limited samples that cover 3495.1 square degrees on
the sky. We correct for incompleteness caused by fiber collisions and survey
edges, and obtain measurements of the group multiplicity function, with errors
calculated from realistic mock catalogs. These multiplicity function
measurements provide a key constraint on the relation between galaxy
populations and dark matter halos.Comment: 26 emulateapj pages including 19 figures. Replaced with final ApJ
versio
The Fifth Data Release of the Sloan Digital Sky Survey
This paper describes the Fifth Data Release (DR5) of the Sloan Digital Sky
Survey (SDSS). DR5 includes all survey quality data taken through June 2005 and
represents the completion of the SDSS-I project (whose successor, SDSS-II will
continue through mid-2008). It includes five-band photometric data for 217
million objects selected over 8000 square degrees, and 1,048,960 spectra of
galaxies, quasars, and stars selected from 5713 square degrees of that imaging
data. These numbers represent a roughly 20% increment over those of the Fourth
Data Release; all the data from previous data releases are included in the
present release. In addition to "standard" SDSS observations, DR5 includes
repeat scans of the southern equatorial stripe, imaging scans across M31 and
the core of the Perseus cluster of galaxies, and the first spectroscopic data
from SEGUE, a survey to explore the kinematics and chemical evolution of the
Galaxy. The catalog database incorporates several new features, including
photometric redshifts of galaxies, tables of matched objects in overlap regions
of the imaging survey, and tools that allow precise computations of survey
geometry for statistical investigations.Comment: ApJ Supp, in press, October 2007. This paper describes DR5. The SDSS
Sixth Data Release (DR6) is now public, available from http://www.sdss.or
Detection of the Baryon Acoustic Peak in the Large-Scale Correlation Function of SDSS Luminous Red Galaxies
We present the large-scale correlation function measured from a spectroscopic
sample of 46,748 luminous red galaxies from the Sloan Digital Sky Survey. The
survey region covers 0.72 h^{-3} Gpc^3 over 3816 square degrees and
0.16<z<0.47, making it the best sample yet for the study of large-scale
structure. We find a well-detected peak in the correlation function at
100h^{-1} Mpc separation that is an excellent match to the predicted shape and
location of the imprint of the recombination-epoch acoustic oscillations on the
low-redshift clustering of matter. This detection demonstrates the linear
growth of structure by gravitational instability between z=1000 and the present
and confirms a firm prediction of the standard cosmological theory. The
acoustic peak provides a standard ruler by which we can measure the ratio of
the distances to z=0.35 and z=1089 to 4% fractional accuracy and the absolute
distance to z=0.35 to 5% accuracy. From the overall shape of the correlation
function, we measure the matter density Omega_mh^2 to 8% and find agreement
with the value from cosmic microwave background (CMB) anisotropies. Independent
of the constraints provided by the CMB acoustic scale, we find Omega_m = 0.273
+- 0.025 + 0.123 (1+w_0) + 0.137 Omega_K. Including the CMB acoustic scale, we
find that the spatial curvature is Omega_K=-0.010+-0.009 if the dark energy is
a cosmological constant. More generally, our results provide a measurement of
cosmological distance, and hence an argument for dark energy, based on a
geometric method with the same simple physics as the microwave background
anisotropies. The standard cosmological model convincingly passes these new and
robust tests of its fundamental properties.Comment: Submitted to the ApJ. Additional pedagogical material and numerical
data at http://cmb.as.arizona.edu/~eisenste/acousticpea
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