2,542 research outputs found
Comparing Segmentation by Time and by Motion in Visual Search: An fMRI Investigation
Abstract
Brain activity was recorded while participants engaged in a difficult visual search task for a target defined by the spatial configuration of its component elements. The search displays were segmented by time (a preview then a search display), by motion, or were unsegmented. A preparatory network showed activity to the preview display, in the time but not in the motion segmentation condition. A region of the precuneus showed (i) higher activation when displays were segmented by time or by motion, and (ii) correlated activity with larger segmentation benefits behaviorally, regardless of the cue. Additionally, the results revealed that success in temporal segmentation was correlated with reduced activation in early visual areas, including V1. The results depict partially overlapping brain networks for segmentation in search by time and motion, with both cue-independent and cue-specific mechanisms.</jats:p
Herschel evidence for disk flattening or gas depletion in transitional disks
Transitional disks are protoplanetary disks characterized by reduced near-
and mid-infrared emission with respect to full disks. This characteristic
spectral energy distribution indicates the presence of an optically thin inner
cavity within the dust disk believed to mark the disappearance of the
primordial massive disk. We present new Herschel Space Observatory PACS spectra
of [OI] 63 micron for 21 transitional disks. Our survey complements the larger
Herschel GASPS program "Gas in Protoplanetary Systems" (Dent et al. 2013) by
quadrupling the number of transitional disks observed with PACS at this
wavelength. [OI] 63 micron traces material in the outer regions of the disk,
beyond the inner cavity of most transitional disks. We find that transitional
disks have [OI] 63 micron line luminosities two times fainter than their full
disk counterparts. We self consistently determine various stellar properties
(e.g. bolometric luminosity, FUV excess, etc.) and disk properties (e.g. disk
dust mass, etc.) that could influence the [OI] 63 micron line luminosity and we
find no correlations that can explain the lower [OI] 63 micron line
luminosities in transitional disks. Using a grid of thermo-chemical
protoplanetary disk models, we conclude that either transitional disks are less
flared than full disks or they possess lower gas-to-dust ratios due to a
depletion of gas mass. This result suggests that transitional disks are more
evolved than their full disk counterparts, possibly even at large radii.Comment: Accepted for publication in ApJ; 52 pages, 16 figures, 8 table
Boundary crossing Random Walks, clinical trials and multinomial sequential estimation
A sufficient condition for the uniqueness of multinomial sequential unbiased
estimators is provided generalizing a classical result for binomial samples.
Unbiased estimators are applied to infer the parameters of multidimensional or
multinomial Random Walks which are observed until they reach a boundary. An
application to clinical trials is presented
Eotvos bounds on couplings of fundamental parameters to gravity
The possible dependence of fundamental couplings and mass ratios on the
gravitational potential has been bounded by comparing atomic clock frequencies
over Earth's elliptical orbit. Here we evaluate bounds on such dependence from
E"otv"os-type experiments that test the Weak Equivalence Principle, including
previously neglected contributions from nuclear binding energy. We find that
variations of fundamental parameters correlated with the gravitational
potential are bounded at 10^-8--10^-9, an improvement of 2--3 orders of
magnitude over atomic clock bounds.Comment: To be published (Phys.Rev.Lett.), minor changes and corrections,
equivalent to journal versio
Constraining the time variation of the coupling constants from cosmic microwave background: effect of \Lambda_{QCD}
We investigate constraints on the time variation of the fine structure
constant between the recombination epoch and the present epoch,
\Delta\alpha/\alpha \equiv (\alpha_{rec} - \alpha_{now})/\alpha_{now}, from
cosmic microwave background (CMB) taking into account simultaneous variation of
other physical constants, namely the electron mass m_{e} and the proton mass
m_{p}. In other words, we consider the variation of Yukawa coupling and the QCD
scale \Lambda_{QCD} in addition to the electromagnetic coupling. We clarify
which parameters can be determined from CMB temperature anisotropy in terms of
singular value decomposition. Assuming a relation among variations of coupling
constants governed by a single scalar field (the dilaton), the 95% confidence
level (C.L.) constraint on \Delta\alpha/\alpha is found to be -8.28 \times
10^{-3} < \Delta\alpha/\alpha < 1.81 \times 10^{-3}, which is tighter than the
one obtained by considering only the change of \alpha and m_{e}. We also obtain
the constraint on the time variation of the proton-to-electron mass ratio \mu
\equiv m_{p}/m_{e} to be -0.52 < \Delta\mu/\mu < 0.17 (95% C.L.) under the same
assumption. Finally, we also implement a forecast for constraints from the
PLANCK survey.Comment: 25 pages, 4 figures; references adde
Dust in the 55 Cancri planetary system
The presence of debris disks around 1-Gyr-old main sequence stars
suggests that an appreciable amount of dust may persist even in mature
planetary systems. Here we report the detection of dust emission from 55
Cancri, a star with one, or possibly two, planetary companions detected through
radial velocity measurements. Our observations at 850m and 450m imply
a dust mass of 0.0008-0.005 Earth masses, somewhat higher than that in the the
Kuiper Belt of our solar system. The estimated temperature of the dust grains
and a simple model fit both indicate a central disk hole of at least 10 AU in
radius. Thus, the region where the planets are detected is likely to be
significantly depleted of dust. Our results suggest that far-infrared and
sub-millimeter observations are powerful tools for probing the outer regions of
extrasolar planetary systems.Comment: 8 pages and 2 figures, to appear in the Astrophysical Journa
The JCMT 12CO(3-2) Survey of the Cygnus X Region: I. A Pathfinder
Cygnus X is one of the most complex areas in the sky. This complicates
interpretation, but also creates the opportunity to investigate accretion into
molecular clouds and many subsequent stages of star formation, all within one
small field of view. Understanding large complexes like Cygnus X is the key to
understanding the dominant role that massive star complexes play in galaxies
across the Universe.
The main goal of this study is to establish feasibility of a high-resolution
CO survey of the entire Cygnus X region by observing part of it as a
Pathfinder, and to evaluate the survey as a tool for investigating the
star-formation process.
A 2x4 degree area of the Cygnus X region has been mapped in the 12CO(3-2)
line at an angular resolution of 15" and a velocity resolution of ~0.4km/s
using HARP-B and ACSIS on the James Clerk Maxwell Telescope. The star formation
process is heavily connected to the life-cycle of the molecular material in the
interstellar medium. The high critical density of the 12CO(3-2) transition
reveals clouds in key stages of molecule formation, and shows processes that
turn a molecular cloud into a star.
We observed ~15% of Cygnus X, and demonstrated that a full survey would be
feasible and rewarding. We detected three distinct layers of 12CO(3-2)
emission, related to the Cygnus Rift (500-800 pc), to W75N (1-1.8 kpc), and to
DR21 (1.5-2.5 kpc). Within the Cygnus Rift, HI self-absorption features are
tightly correlated with faint diffuse CO emission, while HISA features in the
DR21 layer are mostly unrelated to any CO emission. 47 molecular outflows were
detected in the Pathfinder, 27 of them previously unknown. Sequentially
triggered star formation is a widespread phenomenon.Comment: 18 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
A deep submillimetre survey of the Galactic Centre
We present first results from a submillimetre continuum survey of the
Galactic Centre `Central Molecular Zone' (CMZ), made with SCUBA on the James
Clerk Maxwell Telescope. SCUBA's scan-map mode has allowed us to make extremely
wide-field maps of thermal dust emission with unprecedented speed and
sensitivity. We also discuss some issues related to the elimination of
artefacts in scan-map data. Our simultaneous 850/450 micron maps have a total
size of approximately 2.8 x 0.5 degrees (400 x 75 pc) elongated along the
galactic plane. They cover the Sgr A region-including Sgr A*, the circumnuclear
disc, and the +20 km/s and +50 km/s clouds; the area around the Pistol; Sgr
B2-the brightest feature on the map; and at their Galactic Western and Eastern
edges the Sgr C and Sgr D regions. There are many striking features such as
filaments and shell-like structures, as well as point sources such as Sgr A*
itself. The total mass in the Central Molecular Zone is greater than that
revealed in previous optically-thin molecular line maps by a factor of ~3, and
new details are revealed on scales down to 0.33 pc across this 400 pc wide
region.Comment: 12 pages, 3 figures, (figures now smaller, in paper body), accepted
by ApJ
The combined tensile and torsional behavior of irregular fibers
Most fibers are irregular, and they are often subjected to combined loading conditions during processing and end-use. In this paper, polyester and wool fibers under the combined tensile and torsional loads have been studied for the first time, using the finite element method (FEM). The dimensional irregularities of these fibers are simulated with sine waves of different magnitude and frequency. The breaking load and breaking extension of the fibers at different twist or torsion levels are then calculated from the finite element model. The results indicate that twist and level of fiber irregularity have a major impact on the mechanical properties of the fiber and the effect of the frequency of irregularity is relatively small.<br /
A polymerase chain reaction/ligase detection reaction fluorescent microsphere assay to determine Plasmodium falciparum MSP-119 haplotypes
The merozoite surface protein-1 (MSP-1) is a blood stage antigen currently being tested as a vaccine against Plasmodium falciparum malaria. Determining the MSP-1(19) haplotype(s) present during infection is essential for assessments of MSP-1 vaccine efficacy and studies of protective immunity in human populations. The C-terminal fragment (MSP-1(19)) has four predominant haplotypes based on point mutations resulting in non-synonymous amino acid changes: E-TSR (PNG-MAD20 type), E-KNG (Uganda-PA type), Q-KNG (Wellcome type), and Q-TSR (Indo type). Current techniques using direct DNA sequencing are laborious and expensive. We present an MSP-1(19) allele-specific polymerase chain reaction (PCR)/ligase detection reaction-fluorescent microsphere assay (LDR-FMA) that allows simultaneous detection of the four predominant MSP-1(19) haplotypes with a sensitivity and specificity comparable with other molecular methods and a semi-quantitative determination of haplotype contribution in mixed infections. Application of this method is an inexpensive, accurate, and high-throughput alternative to distinguish the predominant MSP-1(19) haplotypes in epidemiologic studies
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