157 research outputs found
Dust from Comet 209P/LINEAR during its 2014 Return: Parent Body of a New Meteor Shower, the May Camelopardalids
We report a new observation of the Jupiter-family comet 209P/LINEAR during
its 2014 return. The comet is recognized as a dust source of a new meteor
shower, the May Camelopardalids. 209P/LINEAR was apparently inactive at a
heliocentric distance rh = 1.6 au and showed weak activity at rh < 1.4 au. We
found an active region of <0.001% of the entire nuclear surface during the
comet's dormant phase. An edge-on image suggests that particles up to 1 cm in
size (with an uncertainty of factor 3-5) were ejected following a differential
power-law size distribution with index q=-3.25+-0.10. We derived a mass loss
rate of 2-10 kg/s during the active phase and a total mass of ~5x10^7 kg during
the 2014 return. The ejection terminal velocity of millimeter- to
centimeter-sized particles was 1-4 m/s, which is comparable to the escape
velocity from the nucleus (1.4 m/s). These results imply that such large
meteoric particles marginally escaped from the highly dormant comet nucleus via
the gas drag force only within a few months of the perihelion passage.Comment: 18 pages, 4 figures, accepted on 2014 December 11 for publication in
the Astrophysical Journal Letter
The Hyper Suprime-Cam Software Pipeline
In this paper, we describe the optical imaging data processing pipeline
developed for the Subaru Telescope's Hyper Suprime-Cam (HSC) instrument. The
HSC Pipeline builds on the prototype pipeline being developed by the Large
Synoptic Survey Telescope's Data Management system, adding customizations for
HSC, large-scale processing capabilities, and novel algorithms that have since
been reincorporated into the LSST codebase. While designed primarily to reduce
HSC Subaru Strategic Program (SSP) data, it is also the recommended pipeline
for reducing general-observer HSC data. The HSC pipeline includes high level
processing steps that generate coadded images and science-ready catalogs as
well as low-level detrending and image characterizations.Comment: 39 pages, 21 figures, 2 tables. Submitted to Publications of the
Astronomical Society of Japa
Cosmology from cosmic shear power spectra with Subaru Hyper Suprime-Cam first-year data
We measure cosmic weak lensing shear power spectra with the Subaru Hyper
Suprime-Cam (HSC) survey first-year shear catalog covering 137deg of the
sky. Thanks to the high effective galaxy number density of 17
arcmin even after conservative cuts such as magnitude cut of
and photometric redshift cut of , we obtain a high
significance measurement of the cosmic shear power spectra in 4 tomographic
redshift bins, achieving a total signal-to-noise ratio of 16 in the multipole
range . We carefully account for various uncertainties
in our analysis including the intrinsic alignment of galaxies, scatters and
biases in photometric redshifts, residual uncertainties in the shear
measurement, and modeling of the matter power spectrum. The accuracy of our
power spectrum measurement method as well as our analytic model of the
covariance matrix are tested against realistic mock shear catalogs. For a flat
cold dark matter (CDM) model, we find for
( for ) from our HSC tomographic
cosmic shear analysis alone. In comparison with Planck cosmic microwave
background constraints, our results prefer slightly lower values of ,
although metrics such as the Bayesian evidence ratio test do not show
significant evidence for discordance between these results. We study the effect
of possible additional systematic errors that are unaccounted in our fiducial
cosmic shear analysis, and find that they can shift the best-fit values of
by up to in both directions. The full HSC survey data
will contain several times more area, and will lead to significantly improved
cosmological constraints.Comment: 43 pages, 21 figures, accepted for publication in PAS
Towards HCP-Style macaque connectomes: 24-Channel 3T multi-array coil, MRI sequences and preprocessing
© 2020 The Author(s) Macaque monkeys are an important animal model where invasive investigations can lead to a better understanding of the cortical organization of primates including humans. However, the tools and methods for noninvasive image acquisition (e.g. MRI RF coils and pulse sequence protocols) and image data preprocessing have lagged behind those developed for humans. To resolve the structural and functional characteristics of the smaller macaque brain, high spatial, temporal, and angular resolutions combined with high signal-to-noise ratio are required to ensure good image quality. To address these challenges, we developed a macaque 24-channel receive coil for 3-T MRI with parallel imaging capabilities. This coil enables adaptation of the Human Connectome Project (HCP) image acquisition protocols to the in-vivo macaque brain. In addition, we adapted HCP preprocessing methods to the macaque brain, including spatial minimal preprocessing of structural, functional MRI (fMRI), and diffusion MRI (dMRI). The coil provides the necessary high signal-to-noise ratio and high efficiency in data acquisition, allowing four- and five-fold accelerations for dMRI and fMRI. Automated FreeSurfer segmentation of cortex, reconstruction of cortical surface, removal of artefacts and nuisance signals in fMRI, and distortion correction of dMRI all performed well, and the overall quality of basic neurobiological measures was comparable with those for the HCP. Analyses of functional connectivity in fMRI revealed high sensitivity as compared with those from publicly shared datasets. Tractography-based connectivity estimates correlated with tracer connectivity similarly to that achieved using ex-vivo dMRI. The resulting HCP-style in vivo macaque MRI data show considerable promise for analyzing cortical architecture and functional and structural connectivity using advanced methods that have previously only been available in studies of the human brain
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