148 research outputs found
Unilateral vs. bilateral STN DBS effects on working memory and motor function in Parkinson disease
Bilateral subthalamic nucleus deep brain stimulation (STN DBS) can reduce working memory while improving motor function in Parkinson disease (PD), but findings are variable. One possible explanation for this variability is that the effects of bilateral STN DBS on working memory function depend in part on functional or disease asymmetry. The goal of this study was to determine the relative contributions of unilateral DBS to the effects seen with bilateral DBS. Motor (Unified Parkinson Disease Rating Scale Part III, UPDRS) and working memory function (Spatial Delayed Response, SDR) were measured in 49 PD patients with bilateral STN DBS while stimulators were Both-off, Left-on, Right-on and Both-on in a randomized, double-blind manner. Patients were off PD medications overnight. Effects of unilateral DBS were compared to effects of bilateral STN DBS. Mean UPDRS and SDR responses to Left-on vs. Right-on conditions did not differ (p>.20). However, improvement in contralateral UPDRS was greater and SDR performance was more impaired by unilateral DBS in the more affected side of the brain than in the less affected side of the brain (p=.008). The effect of unilateral DBS on the more affected side on contralateral UPDRS and SDR responses was equivalent to that of bilateral DBS. These results suggest that motor and working memory function respond to unilateral STN DBS differentially depending on the asymmetry of motor symptoms
Testing Models of Intrinsic Brightness Variations in Type Ia Supernovae, and their Impact on Measuring Cosmological Parameters
For spectroscopically confirmed Type Ia supernovae we evaluate models of
intrinsic brightness variations with detailed data/Monte Carlo comparisons of
the dispersion in the following quantities: Hubble-diagram scatter, color
difference (B-V-c) between the true B-V color and the fitted color (c) from the
SALT-II light curve model, and photometric redshift residual. The data sample
includes 251 ugriz light curves from the 3-season Sloan Digital Sky Survey-II,
and 191 griz light curves from the Supernova Legacy Survey 3-year data release.
We find that the simplest model of a wavelength-independent (coherent) scatter
is not adequate, and that to describe the data the intrinsic scatter model must
have wavelength-dependent variations. We use Monte Carlo simulations to examine
the standard approach of adding a coherent scatter term in quadrature to the
distance-modulus uncertainty in order to bring the reduced chi2 to unity when
fitting a Hubble diagram. If the light curve fits include model uncertainties
with the correct wavelength dependence of the scatter, we find that the bias on
the dark energy equation of state parameter is negligible. However,
incorrect model uncertainties can lead to a significant bias on the distance
moduli, with up to ~0.05 mag redshift-dependent variation. For the recent SNLS3
cosmology results we estimate that this effect introduces an additional
systematic uncertainty on of ~0.02, well below the total uncertainty.
However, this uncertainty depends on the samples used, and thus this small
-uncertainty is not guaranteed in future cosmology results.Comment: accepted by Ap
Hubble Residuals of Nearby Type Ia Supernovae Are Correlated with Host Galaxy Masses
From Sloan Digital Sky Survey u'g'r'i'z' imaging, we estimate the stellar
masses of the host galaxies of 70 low redshift SN Ia (0.015 < z < 0.08) from
the hosts' absolute luminosities and mass-to-light ratios. These nearby SN were
discovered largely by searches targeting luminous galaxies, and we find that
their host galaxies are substantially more massive than the hosts of SN
discovered by the flux-limited Supernova Legacy Survey. Testing four separate
light curve fitters, we detect ~2.5{\sigma} correlations of Hubble residuals
with both host galaxy size and stellar mass, such that SN Ia occurring in
physically larger, more massive hosts are ~10% brighter after light curve
correction. The Hubble residual is the deviation of the inferred distance
modulus to the SN, calculated from its apparent luminosity and light curve
properties, away from the expected value at the SN redshift. Marginalizing over
linear trends in Hubble residuals with light curve parameters shows that the
correlations cannot be attributed to a light curve-dependent calibration error.
Combining 180 higher-redshift ESSENCE, SNLS, and HigherZ SN with 30 nearby SN
whose host masses are less than 10^10.8 solar masses in a cosmology fit yields
1+w=0.22 +0.152/-0.143, while a combination where the 30 nearby SN instead have
host masses greater than 10^10.8 solar masses yields 1+w=-0.03 +0.217/-0.108.
Progenitor metallicity, stellar population age, and dust extinction correlate
with galaxy mass and may be responsible for these systematic effects. Host
galaxy measurements will yield improved distances to SN Ia.Comment: 16 pages, 6 figures, published in ApJ, minor change
Core-Collapse Supernovae and Host Galaxy Stellar Populations
We have used images and spectra of the Sloan Digital Sky Survey to examine
the host galaxies of 519 nearby supernovae. The colors at the sites of the
explosions, as well as chemical abundances, and specific star formation rates
of the host galaxies provide circumstantial evidence on the origin of each
supernova type. We examine separately SN II, SN IIn, SN IIb, SN Ib, SN Ic, and
SN Ic with broad lines (SN Ic-BL). For host galaxies that have multiple
spectroscopic fibers, we select the fiber with host radial offset most similar
to that of the SN. Type Ic SN explode at small host offsets, and their hosts
have exceptionally strongly star-forming, metal-rich, and dusty stellar
populations near their centers. The SN Ic-BL and SN IIb explode in
exceptionally blue locations, and, in our sample, we find that the host spectra
for SN Ic-BL show lower average oxygen abundances than those for SN Ic. SN IIb
host fiber spectra are also more metal-poor than those for SN Ib, although a
significant difference exists for only one of two strong-line diagnostics. SN
Ic-BL host galaxy emission lines show strong central specific star formation
rates. In contrast, we find no strong evidence for different environments for
SN IIn compared to the sites of SN II. Because our supernova sample is
constructed from a variety of sources, there is always a risk that sampling
methods can produce misleading results. We have separated the supernovae
discovered by targeted surveys from those discovered by galaxy-impartial
searches to examine these questions and show that our results do not depend
sensitively on the discovery technique.Comment: Accepted by the Astrophysical Journal (22 July 2012), conclusions not
changed, extended discussion of sample construction and updated SN
spectroscopic type
Current cosmological bounds on neutrino masses and relativistic relics
We combine the most recent observations of large-scale structure (2dF and
SDSS galaxy surveys) and cosmic microwave anisotropies (WMAP and ACBAR) to put
constraints on flat cosmological models where the number of massive neutrinos
and of massless relativistic relics are both left arbitrary. We discuss the
impact of each dataset and of various priors on our bounds. For the standard
case of three thermalized neutrinos, we find an upper bound on the total
neutrino mass sum m_nu < 1.0 (resp. 0.6) eV (at 2sigma), using only CMB and LSS
data (resp. including priors from supernovae data and the HST Key Project), a
bound that is quite insensitive to the splitting of the total mass between the
three species. When the total number of neutrinos or relativistic relics N_eff
is left free, the upper bound on sum m_nu (at 2sigma, including all priors)
ranges from 1.0 to 1.5 eV depending on the mass splitting. We provide an
explanation of the parameter degeneracy that allows larger values of the masses
when N_eff increases. Finally, we show that the limit on the total neutrino
mass is not significantly modified in the presence of primordial gravitational
waves, because current data provide a clear distinction between the
corresponding effects.Comment: 13 pages, 6 figure
The UV-Optical Color Dependence of Galaxy Clustering in the Local Universe
We measure the UV-optical color dependence of galaxy clustering in the local
universe. Using the clean separation of the red and blue sequences made
possible by the NUV - r color-magnitude diagram, we segregate the galaxies into
red, blue and intermediate "green" classes. We explore the clustering as a
function of this segregation by removing the dependence on luminosity and by
excluding edge-on galaxies as a means of a non-model dependent veto of highly
extincted galaxies. We find that \xi (r_p, \pi) for both red and green galaxies
shows strong redshift space distortion on small scales -- the "finger-of-God"
effect, with green galaxies having a lower amplitude than is seen for the red
sequence, and the blue sequence showing almost no distortion. On large scales,
\xi (r_p, \pi) for all three samples show the effect of large-scale streaming
from coherent infall. On scales 1 Mpc/h < r_p < 10 Mpc/h, the projected
auto-correlation function w_p(r_p) for red and green galaxies fits a power-law
with slope \gamma ~ 1.93 and amplitude r_0 ~ 7.5 and 5.3, compared with \gamma
~ 1.75 and r_0 ~ 3.9 Mpc/h for blue sequence galaxies. Compared to the
clustering of a fiducial L* galaxy, the red, green, and blue have a relative
bias of 1.5, 1.1, and 0.9 respectively. The w_p(r_p) for blue galaxies display
an increase in convexity at ~ 1 Mpc/h, with an excess of large scale
clustering. Our results suggest that the majority of blue galaxies are likely
central galaxies in less massive halos, while red and green galaxies have
larger satellite fractions, and preferentially reside in virialized structures.
If blue sequence galaxies migrate to the red sequence via processes like
mergers or quenching that take them through the green valley, such a
transformation may be accompanied by a change in environment in addition to any
change in luminosity and color.Comment: accepted by MNRA
Weighing the Giants - I. Weak-lensing masses for 51 massive galaxy clusters: project overview, data analysis methods and cluster images
This is the first in a series of papers in which we measure accurate
weak-lensing masses for 51 of the most X-ray luminous galaxy clusters known at
redshifts 0.15<z<0.7, in order to calibrate X-ray and other mass proxies for
cosmological cluster experiments. The primary aim is to improve the absolute
mass calibration of cluster observables, currently the dominant systematic
uncertainty for cluster count experiments. Key elements of this work are the
rigorous quantification of systematic uncertainties, high-quality data
reduction and photometric calibration, and the "blind" nature of the analysis
to avoid confirmation bias. Our target clusters are drawn from RASS X-ray
catalogs, and provide a versatile calibration sample for many aspects of
cluster cosmology. We have acquired wide-field, high-quality imaging using the
Subaru and CFHT telescopes for all 51 clusters, in at least three bands per
cluster. For a subset of 27 clusters, we have data in at least five bands,
allowing accurate photo-z estimates of lensed galaxies. In this paper, we
describe the cluster sample and observations, and detail the processing of the
SuprimeCam data to yield high-quality images suitable for robust weak-lensing
shape measurements and precision photometry. For each cluster, we present
wide-field color optical images and maps of the weak-lensing mass distribution,
the optical light distribution, and the X-ray emission, providing insights into
the large-scale structure in which the clusters are embedded. We measure the
offsets between X-ray centroids and Brightest Cluster Galaxies in the clusters,
finding these to be small in general, with a median of 20kpc. For offsets
<100kpc, weak-lensing mass measurements centered on the BCGs agree well with
values determined relative to the X-ray centroids; miscentering is therefore
not a significant source of systematic uncertainty for our mass measurements.
[abridged]Comment: 26 pages, 19 figures (Appendix C not included). Accepted after minor
revisio
Approaches to lowering the cost of large space telescopes
New development approaches, including launch vehicles and advances in
sensors, computing, and software, have lowered the cost of entry into space,
and have enabled a revolution in low-cost, high-risk Small Satellite (SmallSat)
missions. To bring about a similar transformation in larger space telescopes,
it is necessary to reconsider the full paradigm of space observatories. Here we
will review the history of space telescope development and cost drivers, and
describe an example conceptual design for a low cost 6.5 m optical telescope to
enable new science when operated in space at room temperature. It uses a
monolithic primary mirror of borosilicate glass, drawing on lessons and tools
from decades of experience with ground-based observatories and instruments, as
well as flagship space missions. It takes advantage, as do large launch
vehicles, of increased computing power and space-worthy commercial electronics
in low-cost active predictive control systems to maintain stability. We will
describe an approach that incorporates science and trade study results that
address driving requirements such as integration and testing costs,
reliability, spacecraft jitter, and wavefront stability in this new
risk-tolerant "LargeSat" context.Comment: Presented at SPIE, Optics+Photonics 2023, Astronomical Optics:
Design, Manufacture, and Test of Space and Ground Systems IV in San Diego,
CA, US
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