2,050 research outputs found
Cognitive impairment and decline in cognitively normal older adults with high amyloid-β: A meta-analysis
AbstractIntroductionThis meta-analysis aimed to characterize the nature and magnitude of amyloid (Aβ)-related cognitive impairment and decline in cognitively normal (CN) older individuals.MethodMEDLINE Ovid was searched from 2012 to June 2016 for studies reporting relationships between cerebrospinal fluid or positron emission tomography (PET) Aβ levels and cognitive impairment (cross-sectional) and decline (longitudinal) in CN older adults. Neuropsychological data were classified into domains of episodic memory, executive function, working memory, processing speed, visuospatial function, semantic memory, and global cognition. Type of Aβ measure, how Aβ burden was analyzed, inclusion of control variables, and clinical criteria used to exclude participants, were considered as moderators. Random-effects models were used for analyses with effect sizes expressed as Cohen's d.ResultsA total of 38 studies met inclusion criteria contributing 30 cross-sectional (N = 5005) and 14 longitudinal (N = 2584) samples. Aβ-related cognitive impairment was observed for global cognition (d = 0.32), visuospatial function (d = 0.25), processing speed (d = 0.18), episodic memory, and executive function (both d's = 0.15), with decline observed for global cognition (d = 0.30), semantic memory (d = 0.28), visuospatial function (d = 0.25), and episodic memory (d = 0.24). Aβ-related impairment was moderated by age, amyloid measure, type of analysis, and inclusion of control variables and decline moderated by amyloid measure, type of analysis, inclusion of control variables, and exclusion criteria used.DiscussionCN older adults with high Aβ show a small general cognitive impairment and small to moderate decline in episodic memory, visuospatial function, semantic memory, and global cognition
Constraining the HI-Halo Mass Relation From Galaxy Clustering
We study the dependence of galaxy clustering on atomic gas mass using a
sample of 16,000 galaxies with redshift in the range of
and HI mass of , drawn from the 70% complete sample
of the Arecibo Legacy Fast ALFA survey. We construct subsamples of galaxies
with above different thresholds, and make volume-limited
clustering measurements in terms of three statistics: the projected two-point
correlation function, the projected cross-correlation function with respect to
a reference sample selected from the Sloan Digital Sky Survey, and the
redshift-space monopole moment. In contrast to previous studies, which found
no/weak HI-mass dependence, we find both the clustering amplitude on scales
above a few Mpc and the bias factors to increase significantly with increasing
HI mass for subsamples with HI mass thresholds above . For HI
mass thresholds below , while the measurements have large
uncertainties caused by the limited survey volume and sample size, the inferred
galaxy bias factors are systematically lower than the minimum halo bias factor
from mass-selected halo samples. The simple halo model, in which galaxy content
is only determined by halo mass, has difficulties in interpreting the
clustering measurements of the HI-selected samples. We extend the simple model
by including the halo formation time as an additional parameter. A model that
puts HI-rich galaxies into halos that formed late can reproduce the clustering
measurements reasonably well. We present the implications of our best-fitting
model on the correlation of HI mass with halo mass and formation time, as well
as the halo occupation distributions and HI mass functions for central and
satellite galaxies. These results are compared with the predictions from
semi-analytic galaxy formation models and hydrodynamic galaxy formation
simulations.Comment: Accepted for publication in ApJ. The 2PCF measurements are available
at http://sdss4.shao.ac.cn/guoh
Africa as an evolutionary arena for large fruits
Strong paleoclimatic change and few Late Quaternary megafauna extinctions make mainland Africa unique among continents. Here, we hypothesize that, compared with elsewhere, these conditions created the ecological opportunity for the macroevolution and geographic distribution of large fruits. We assembled global phylogenetic, distribution and fruit size data for palms (Arecaceae), a pantropical, vertebrate-dispersed family with > 2600 species, and integrated these with data on extinction-driven body size reduction in mammalian frugivore assemblages since the Late Quaternary. We applied evolutionary trait, linear and null models to identify the selective pressures that have shaped fruit sizes. We show that African palm lineages have evolved towards larger fruit sizes and exhibited faster trait evolutionary rates than lineages elsewhere. Furthermore, the global distribution of the largest palm fruits across species assemblages was explained by occurrence in Africa, especially under low canopies, and extant megafauna, but not by mammalian downsizing. These patterns strongly deviated from expectations under a null model of stochastic (Brownian motion) evolution. Our results suggest that Africa provided a distinct evolutionary arena for palm fruit size evolution. We argue that megafaunal abundance and the expansion of savanna habitat since the Miocene provided selective advantages for the persistence of African plants with large fruits.</p
Core-Clickable PEG-Branch-Azide Bivalent-Bottle-Brush Polymers by ROMP: Grafting-Through and Clicking-To
The combination of highly efficient polymerizations with modular "click" coupling reactions has enabled the synthesis of a wide variety of novel nanoscopic tructures. Here we demonstrate the facile synthesis of a new class of clickable, branched nanostructures, polyethylene glycol (PEG)-branch-azide bivalent-brush polymers, facilitated by "graft-through" ring-opening metathesis polymerization of a branched norbornene-PEG-chloride macromonomer followed by halide-azide exchange. The resulting bivalent-brush polymers possess azide groups at the core near a polynorbornene backbone with PEG chains extended into solution; the structure resembles a unimolecular micelle. We demonstrate copper-catalyzed azide-alkre cycloaddition (CuAAC) "click-to" coupling of a photocleavable doxorubicin (DOX)-alkyne derivative to the azide core. The CuAAC coupling was quantitative across a wide range of nanoscopic sizes (similar to 6-similar to 50 nrn); UV photolysis of the resulting DOX-loaded materials yielded free DOX that was therapeutically effective against human cancer cells
Early Outbreak of 2009 Influenza A (H1N1) in Mexico Prior to Identification of pH1N1 Virus
10.1371/journal.pone.0023853PLoS ONE68
Interferometric 12CO(J=2-1) image of the Nuclear Region of Seyfert 1 Galaxy NGC 1097
We have mapped the central region of the Seyfert 1 galaxy NGC 1097 in
12CO(J=2-1) with the Submillieter Array (SMA). The 12CO(J=2-1) map shows a
central concentration and a surrounding ring, which coincide respectively with
the Seyfert nucleus and a starburst ring. The line intensity peaks at the
nucleus, whereas in a previously published 12CO(J=1-0) map the intensity peaks
at the starburst ring. The molecular ring has an azimuthally averaged
12CO(J=2-1)/(J=1-0) intensity ratio (R21) of about unity, which is similar to
those in nearby active star forming galaxies, suggesting that most of the
molecular mass in the ring is involved in fueling the starburst. The molecular
gas can last for only about 1.2\times10^8 years without further replenishment
assuming a constant star formation rate and a perfect conversion of gas to
stars. The velocity map shows that the central molecular gas is rotating with
the molecular ring in the same direction, while its velocity gradient is much
steeper than that of the ring. This velocity gradient of the central gas is
similar to what is usually observed in some Seyfert 2 galaxies. To view the
active nucleus directly in the optical, the central molecular gas structure can
either be a low-inclined disk or torus but not too low to be less massive than
the mass of the host galaxy itself, be a highly-inclined thin disk or clumpy
and thick torus, or be an inner part of the galactic disk. The R21 value of
~1.9 of the central molecular gas component, which is significantly higher than
the value found at the molecular gas ring, indicates that the activity of the
Seyfert nucleus may have a significant influence on the conditions of the
molecular gas in the central component.Comment: 22 pages, 4 figures, accepted by Ap
The Cenozoic history of palms:Global diversification, biogeography and the decline of megathermal forests
10.1111/geb.13436GLOBAL ECOLOGY AND BIOGEOGRAPHY313425-43
Nanoscale cuticle density variations correlate with pigmentation and color in butterfly wing scales
How pigment distribution correlates with cuticle density within a microscopic
butterfly wing scale, and how both impact final reflected color remains
unknown. We used ptychographic X-ray computed tomography to quantitatively
determine, at nanoscale resolutions, the three-dimensional mass density of
scales with pigmentation differences. By comparing cuticle densities with
pigmentation and color within a scale, we determine that the lower lamina
structure in all scales has the highest density and lowest pigmentation. Low
pigment levels also correlate with sheet-like chitin structures as opposed to
rod-like structures, and distinct density layers within the lower lamina help
explain reflected color. We propose that pigments, in addition to absorbing
specific wavelengths, can affect cuticle polymerization, density, and
refractive index, thereby impacting reflected wavelengths that produce
structural colors
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