773 research outputs found
A ground-based 21cm Baryon acoustic oscillation survey
Baryon acoustic oscillations (BAO) provide a robust standard ruler with which
to measure the acceleration of the Universe. The BAO feature has so far been
detected in optical galaxy surveys. Intensity mapping of neutral hydrogen
emission with a ground-based radio telescope provides another promising window
for measuring BAO at redshifts of order unity for relatively low cost. While
the cylindrical radio telescope (CRT) proposed for these measurements will have
excellent redshift resolution, it will suffer from poor angular resolution (a
few arcminutes at best). We investigate the effect of angular resolution on the
standard ruler test with BAO, using the Dark Energy Task Force Figure of Merit
as a benchmark. We then extend the analysis to include variations in the
parameters characterizing the telescope and the underlying physics. Finally, we
optimize the survey parameters (holding total cost fixed) and present an
example of a CRT BAO survey that is competitive with Stage III dark energy
experiments. The tools developed here form the backbone of a publicly available
code that can be used to obtain estimates of cost and Figure of Merit for any
set of parameters.Comment: ApJ accepted version. Important changes in section 2 and 3 - uses a
more realistic instrument response model and removed the discussion of
aliasing effect. The conclusions remain the same. Typos fixed (including eq
5). 11 emulated apj pages with 7 figures and 1 tabl
BLAST: improvements for better sequence analysis
Basic local alignment search tool (BLAST) is a sequence similarity search program. The National Center for Biotechnology Information (NCBI) maintains a BLAST server with a home page at . We report here on recent enhancements to the results produced by the BLAST server at the NCBI. These include features to highlight mismatches between similar sequences, show where the query was masked for low-complexity sequence, and integrate information about the database sequences from the NCBI Entrez system into the BLAST display. Changes to how the database sequences are fetched have also improved the speed of the report generator
Altered functional connectivity in lesional peduncular hallucinosis with REM sleep behavior disorder
Brainstem lesions causing peduncular hallucinosis (PH) produce vivid visual hallucinations occasionally accompanied by sleep disorders. Overlapping brainstem regions modulate visual pathways and REM sleep functions via gating of thalamocortical networks. A 66-year-old man with paroxysmal atrial fibrillation developed abruptâonset complex visual hallucinations with preserved insight and violent dream enactment behavior. Brain MRI showed restricted diffusion in the left rostrodorsal pons suggestive of an acute ischemic stroke. REM sleep behavior disorder (RBD) was diagnosed on polysomnography. We investigated the integrity of ponto-geniculate-occipital circuits with seed-based resting-state functional connectivity MRI (rs-fcMRI) in this patient compared to 46 controls. Rs-fcMRI revealed significantly reduced functional connectivity between the lesion and lateral geniculate nuclei (LGN), and between LGN and visual association cortex compared to controls. Conversely, functional connectivity between brainstem and visual association cortex, and between visual association cortex and prefrontal cortex (PFC) was significantly increased in the patient. Focal damage to the rostrodorsal pons is sufficient to cause RBD and PH in humans, suggesting an overlapping mechanism in both syndromes. This lesion produced a pattern of altered functional connectivity consistent with disrupted visual cortex connectivity via de-afferentation of thalamocortical pathways
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Mechanisms Underlying Age- and Performance-related Differences in Working Memory
This study took advantage of the subsecond temporal resolution of ERPs to investigate mechanisms underlying age- and performance-related differences in working memory. Young and old subjects participated in a verbal n-back task with three levels of difficulty. Each group was divided into high and low performers based on accuracy under the 2-back condition. Both old subjects and low-performing young subjects exhibited impairments in preliminary mismatch/match detection operations (indexed by the anterior N2 component). This may have undermined the quality of information available for the subsequent decision-making process (indexed by the P3 component), necessitating the appropriation of more resources. Additional anterior and right hemisphere activity was recruited by old subjects. Neural efficiency and the capacity to allocate more resources to decision-making differed between high and low performers in both age groups. Under low demand conditions, high performers executed the task utilizing fewer resources than low performers (indexed by the P3 amplitude). As task requirements increased, high-performing young and old subjects were able to appropriate additional resources to decision-making, whereas their low-performing counterparts allocated fewer resources. Higher task demands increased utilization of processing capacity for operations other than decision-making (e.g., sustained attention) that depend upon a shared pool of limited resources. As demands increased, all groups allocated additional resources to the process of sustaining attention (indexed by the posterior slow wave). Demands appeared to have exceeded capacity in low performers, leading to a reduction of resources available to the decision-making process, which likely contributed to a decline in performance
Expanded HOXA13 polyalanine tracts in a monotreme
The N-terminal region of human HOXA13 has seven discrete polyalanine tracts. Our previous analysis of these tracts in multiple major vertebrate clades suggested that three are mammal-specific. We now report the N-terminal HOXA13 repetitive tract structures in the monotreme Tachyglossus aculeatus (echidna). Contrary to our expectations, echidna HOXA13 possesses a unique set of polyalanine tracts and an unprecedented polyglycine tract. The data support the conclusion that the emergence of expanded polyalanine tracts in proteins occurred very early in the stem lineage that gave rise to mammals, between 162 and 315âMa.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73357/1/j.1525-142X.2008.00254.x.pd
BAC transgenic analysis reveals enhancers sufficient for Hoxa13 and neighborhood gene expression in mouse embryonic distal limbs and genital bud
We previously demonstrated that a âŒ1âMb domain of genes upstream of and including Hoxa13 is co-expressed in the developing mouse limbs and genitalia. A highly conserved non-coding sequence, mmA13CNS, was shown to be insufficient in transgenic mice to direct precise Hoxa13 -like expression in the limb buds or genital bud, although some LacZ expression from the transgene was reproducibly found in these tissues. In this report, we used Î -globin minimal promoter LacZ recombinant BAC transgenes encompassing mmA13CNS to identify a single critical region involved in mouse Hoxa13 -like embryonic genital bud expression. By analyzing the expression patterns of these overlapping BAC clones in transgenic mice, we show that at least two sequences remote to the HoxA cluster are required collectively to drive Hoxa13 -like expression in developing distal limbs. Given that the paralogous posterior HoxD and neighboring genes have been shown to be under the influence of long-range distal limb and genital bud enhancers, we hypothesize that both long-range enhancers have one ancestral origin, which diverged in both sequence and function after the HoxA/D cluster duplication.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73951/1/j.1525-142X.2008.00253.x.pd
Formation dynamics of subsurface hydrocarbon intrusions following the Deepwater Horizon blowout
Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L09602, doi:10.1029/2011GL047174.Hydrocarbons released following the Deepwater Horizon (DH) blowout were found in deep, subsurface horizontal intrusions, yet there has been little discussion about how these intrusions formed. We have combined measured (or estimated) observations from the DH release with empirical relationships developed from previous lab experiments to identify the mechanisms responsible for intrusion formation and to characterize the DH plume. Results indicate that the intrusions originate from a stratification-dominated multiphase plume characterized by multiple subsurface intrusions containing dissolved gas and oil along with small droplets of liquid oil. Unlike earlier lab measurements, where the potential density in ambient water decreased linearly with elevation, at the DH site it varied quadratically. We have modified our method for estimating intrusion elevation under these conditions and the resulting estimates agree with observations that the majority of the hydrocarbons were found between 800 and 1200 m.Funding for this project was supported by
the National Science Foundation under RAPID grants CBETâ1045831,
CBETâ1046890, and OCEâ1048976, and by the U. S. Geological Survey,
Coastal and Marine Geology Program
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ERP correlates of item recognition memory: Effects of age and performance
Decline in episodic memory is a common feature of healthy aging. Event-related potential (ERP) studies in young adults have consistently reported several modulations thought to index memory retrieval processes, but relatively limited work has explored the impact of aging on them. Further, work with functional imaging has demonstrated differential neural recruitment in elderly subjects depending on their level of cognitive performance which may reflect compensatory or, alternatively, inefficient processing. In the present study we examined the effect of aging and level of performance on both early (FN400, LPC) and later [late frontal effect (LFE)] ERP indices of recognition memory. We found that the FN400 and LPC were absent or attenuated in the older group relative to young adults, but that the LFE was actually increased, analogous to findings in the functional imaging literature. Additionally, the latter effect was most prominent in the poorer performing older participants. These findings suggest that weak memory retrieval supported by earlier ERP modulations, may lead to an enhanced LFE in the service of additional retrieval attempts
First-Year Spectroscopy for the SDSS-II Supernova Survey
This paper presents spectroscopy of supernovae discovered in the first season
of the Sloan Digital Sky Survey-II Supernova Survey. This program searches for
and measures multi-band light curves of supernovae in the redshift range z =
0.05 - 0.4, complementing existing surveys at lower and higher redshifts. Our
goal is to better characterize the supernova population, with a particular
focus on SNe Ia, improving their utility as cosmological distance indicators
and as probes of dark energy. Our supernova spectroscopy program features
rapid-response observations using telescopes of a range of apertures, and
provides confirmation of the supernova and host-galaxy types as well as precise
redshifts. We describe here the target identification and prioritization, data
reduction, redshift measurement, and classification of 129 SNe Ia, 16
spectroscopically probable SNe Ia, 7 SNe Ib/c, and 11 SNe II from the first
season. We also describe our efforts to measure and remove the substantial host
galaxy contamination existing in the majority of our SN spectra.Comment: Accepted for publication in The Astronomical Journal(47pages, 9
figures
The Putative Liquid-Liquid Transition is a Liquid-Solid Transition in Atomistic Models of Water
We use numerical simulation to examine the possibility of a reversible
liquid-liquid transition in supercooled water and related systems. In
particular, for two atomistic models of water, we have computed free energies
as functions of multiple order parameters, where one is density and another
distinguishes crystal from liquid. For a range of temperatures and pressures,
separate free energy basins for liquid and crystal are found, conditions of
phase coexistence between these phases are demonstrated, and time scales for
equilibration are determined. We find that at no range of temperatures and
pressures is there more than a single liquid basin, even at conditions where
amorphous behavior is unstable with respect to the crystal. We find a similar
result for a related model of silicon. This result excludes the possibility of
the proposed liquid-liquid critical point for the models we have studied.
Further, we argue that behaviors others have attributed to a liquid-liquid
transition in water and related systems are in fact reflections of transitions
between liquid and crystal
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