2,192 research outputs found
A Correlation Between Circumstellar Disks and Rotation in the Upper Scorpius OB Association
We present projected rotational velocities for 20 early-type (B8-A9) and 74
late-type (F2-M8) members of the ~5 Myr old Upper Scorpius OB Association
derived from high dispersion optical spectra obtained with the High Resolution
Echelle Spectrometer (HIRES) on Keck I and the Magellan Inamori Kyocera Echelle
(MIKE) on the Magellan Clay telescope. The spectroscopic sample is composed of
stars and brown dwarfs with infrared signatures of circumstellar disks, both
primordial and debris, and non-excess sources of comparable spectral type. We
merge projected rotational velocities, accretion diagnostics, and Spitzer Space
Telescope Infrared Array Camera (IRAC) and Multiband Imaging Photometer for
Spitzer (MIPS) 24 micron photometry to examine the relationship between
rotation and circumstellar disks. The rotational velocities are strongly
correlated with spectral type, a proxy for mass, such that the median vsini for
B8-A9 type stars is: 195(+/-)70 km/s, F2-K4: 37.8(+/-)7.4 km/s, K5-K9:
13.8(+21.3/-8.2) km/s, M0-M5: 16.52(+/-)5.3 km/s, and M5.5-M8: 17.72(+/-)8.1
km/s. We find with a probability of >0.99 that M-type stars and brown dwarfs
having infrared excess suggestive of circumstellar disks rotate more slowly
than their non-excess counterparts. A similar correlation is present among
F2-K9 type stars, but only at the ~97% confidence level. Among the early-type
(B8-A9) members, rotational velocities of the debris-disk and non-disk
populations are indistinguishable. Considering the late-type (F2-M8) stars and
brown dwarfs, we find a low fraction of slowly rotating, non-excess sources
relative to younger star forming regions, suggesting that most have spun up
following disk dissipation. The few late-type (F2-M5) debris disk sources,
which may be representative of stars that have recently dispersed their inner
disks, are evenly divided between slow and moderate rotators.Comment: 41 pages, 11 figures, accepted for publication in the Astrophysical
Journa
Size Matters: Microservices Research and Applications
In this chapter we offer an overview of microservices providing the
introductory information that a reader should know before continuing reading
this book. We introduce the idea of microservices and we discuss some of the
current research challenges and real-life software applications where the
microservice paradigm play a key role. We have identified a set of areas where
both researcher and developer can propose new ideas and technical solutions.Comment: arXiv admin note: text overlap with arXiv:1706.0735
Ensuring transparency and minimization of methodologic bias in preclinical pain research: PPRECISE considerations
The formation of free radicals by cardiac myocytes under oxidative stress and the effects of electron-donating drugs
Distribution of [3H]trans-resveratrol in rat tissues following oral administration
Resveratrol has been widely investigated for its potential health properties, although little is known about its metabolism in vivo. Here we investigated the distribution of metabolic products of [H-3]trans-resveratrol, following gastric administration. At 2 h, plasma concentrations reached 1 center dot 7 % of the administered dose, whilst liver and kidney concentrations achieved 1 center dot 0 and 0 center dot 6 %, respectively. Concentrations detected at 18 h were lower, being only 0 center dot 5 % in plasma and a total of 0 center dot 35 % in tissues. Furthermore, whilst kidney and liver concentrations fell to 10 and 25 %, respectively, of concentrations at 2 h, the brain retained 43 % of that measured at 2 h. Resveratrol-glucuronide was identified as the major metabolite, reaching 7 mu m in plasma at 2 h. However, at 18 h the main form identified in liver, heart, lung and brain was native resveratrol aglycone, indicating that it is the main form retained in the tissues. No phenolic degradation products were detected in urine or tissues, indicating that, unlike flavonoids, resveratrol does not appear to serve as a substrate for colonic microflora. The present study provides additional information about the nature of resveratrol metabolites and which forms might be responsible for its in vivo biological effects
Surface Structure of Liquid Metals and the Effect of Capillary Waves: X-ray Studies on Liquid Indium
We report x-ray reflectivity (XR) and small angle off-specular diffuse
scattering (DS) measurements from the surface of liquid Indium close to its
melting point of C. From the XR measurements we extract the surface
structure factor convolved with fluctuations in the height of the liquid
surface. We present a model to describe DS that takes into account the surface
structure factor, thermally excited capillary waves and the experimental
resolution. The experimentally determined DS follows this model with no
adjustable parameters, allowing the surface structure factor to be deconvolved
from the thermally excited height fluctuations. The resulting local electron
density profile displays exponentially decaying surface induced layering
similar to that previously reported for Ga and Hg. We compare the details of
the local electron density profiles of liquid In, which is a nearly free
electron metal, and liquid Ga, which is considerably more covalent and shows
directional bonding in the melt. The oscillatory density profiles have
comparable amplitudes in both metals, but surface layering decays over a length
scale of \AA for In and \AA for Ga. Upon controlled
exposure to oxygen, no oxide monolayer is formed on the liquid In surface,
unlike the passivating film formed on liquid Gallium.Comment: 9 pages, 5 figures; submitted to Phys. Rev.
Extreme infrared variables from UKIDSS-I. A concentration in star-forming regions
We present initial results of the first panoramic search for high-amplitude near-infrared variability in theGalactic plane.We analyse the widely separated two-epoch K-band photometry in the fifth and seventh data releases of the UKIDSS Galactic plane survey.We find 45 stars with δK > 1 mag, including two previously known OH/IR stars and a Nova. Even though the midplane is not yet included in the data set, we find the majority (66 per cent) of our sample to be within known star-forming regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (12 stars). Sources in SFRs show spectral energy distributions that support classification as young stellar objects (YSOs). This indicates that YSOs dominate the Galactic population of high-amplitude infrared variable stars at low luminosities and therefore likely dominate the total high-amplitude population. Spectroscopic follow up of the DR5 sample shows at least four stars with clear characteristics of eruptive premain- sequence variables, two of which are deeply embedded. Our results support the recent concept of eruptive variability comprising a continuum of outburst events with different timescales and luminosities, but triggered by a similar physical mechanism involving unsteady accretion. Also, we find what appears to be one of the most variable classical Be stars. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Spectroscopy of new brown dwarf members of rho Ophiuchi and an updated initial mass function
To investigate the universality hypothesis of the initial mass function in
the substellar regime, the population of the rho Ophiuchi molecular cloud is
analysed by including a new sample of low-mass spectroscopically confirmed
members. To that end, we have conducted a large spectroscopic follow-up of
young substellar candidates uncovered in our previous photometric survey. The
spectral types and extinction were derived for a newly found population of
substellar objects, and its masses estimated by comparison to evolutionary
models. A thoroughly literature search was conducted to provide an up-to-date
census of the cluster, which was then used to derive the luminosity and mass
functions, as well as the ratio of brown dwarfs to stars in the cluster. These
results were then compared to other young clusters. It is shown that the study
of the substellar population of the rho Ophiuchi molecular cloud is hampered
only by the high extinction in the cluster ruling out an apparent paucity of
brown dwarfs. The discovery of 16 new members of rho Ophiuchi, 13 of them in
the substellar regime, reveals the low-mass end of its population and shows the
success of our photometric candidate selection with the WIRCam survey. The
study of the brown dwarf population of the cluster reveals a high disk fraction
of 76 (+5-8)%. Taking the characteristic peak mass of the derived mass function
and the ratio of brown dwarfs to stars into account, we conclude that the mass
function of rho Ophiuchi is similar to other nearby young clusters.Comment: Accepted to A&A (30 December 2011); v2 includes language editin
Valence Fluctuations Revealed by Magnetic Field Scan: Comparison with Experiments in YbXCu_4 (X=In, Ag, Cd) and CeYIn_5 (Y=Ir, Rh)
The mechanism of how critical end points of the first-order valence
transitions (FOVT) are controlled by a magnetic field is discussed. We
demonstrate that the critical temperature is suppressed to be a quantum
critical point (QCP) by a magnetic field. This results explain the field
dependence of the isostructural FOVT observed in Ce metal and YbInCu_4.
Magnetic field scan can lead to reenter in a critical valence fluctuation
region. Even in the intermediate-valence materials, the QCP is induced by
applying a magnetic field, at which the magnetic susceptibility also diverges.
The driving force of the field-induced QCP is shown to be a cooperative
phenomenon of the Zeeman effect and the Kondo effect, which creates a distinct
energy scale from the Kondo temperature. The key concept is that the closeness
to the QCP of the FOVT is capital in understanding Ce- and Yb-based heavy
fermions. It explains the peculiar magnetic and transport responses in CeYIn_5
(Y=Ir, Rh) and metamagnetic transition in YbXCu_4 for X=In as well as the sharp
contrast between X=Ag and Cd.Comment: 14 pages, 9 figures, OPEN SELECT in J. Phys. Soc. Jp
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