2,112 research outputs found
Proper Motion of H2O Masers in IRAS 20050+2720 MMS1: An AU Scale Jet Associated with An Intermediate-Mass Class 0 Source
We conducted a 4 epoch 3 month VLBA proper motion study of HO masers
toward an intermediate-mass class 0 source IRAS 20050+2720 MMS1 (d=700 pc).
From milli-arcsecond (mas) resolution VLBA images, we found two groups of H2O
maser spots at the center of the submillimeter core of MMS1. One group consists
of more than intense maser spots; the other group consisting of
several weaker maser spots is located at 18 AU south-west of the intense group.
Distribution of the maser spots in the intense group shows an arc-shaped
structure which includes the maser spots that showed a clear velocity gradient.
The spatial and velocity structures of the maser spots in the arc-shape did not
significantly change through the 4 epochs. Furthermore, we found a relative
proper motion between the two groups. Their projected separation increased by
1.13+/-0.11 mas over the 4 epochs along a line connecting them. The spatial and
velocity structures of the intense group and the relative proper motions
strongly suggest that the maser emission is associated with a protostellar jet.
Comparing the observed LSR velocities with calculated radial velocities from a
simple biconical jet model, we conclude that the most of the maser emission are
likely to be associated with an accelerating biconical jet which has large
opening angle. The large opening angle of the jet traced by the masers would
support the hypothesis that poor jet collimation is an inherent property of
luminous (proto)stars.Comment: 14 pages, 10 figures, Fig.3 was downsized significantly. accepted for
publication in A&
First results from a VLBA proper motion survey of H2O masers in low-mass YSOs: the Serpens core and RNO15-FIR
This article reports first results of a long-term observational program aimed
to study the earliest evolution of jet/disk systems in low-mass YSOs by means
of VLBI observations of the 22.2 GHz water masers. We report here data for the
cluster of low-mass YSOs in the Serpens molecular core and for the single
object RNO~15-FIR. Towards Serpens SMM1, the most luminous sub-mm source of the
Serpens cluster, the water maser emission comes from two small (< 5 AU in size)
clusters of features separated by ~25 AU, having line of sight velocities
strongly red-shifted (by more than 10 km/s) with respect to the LSR velocity of
the molecular cloud. The two maser clusters are oriented on the sky along a
direction that is approximately perpendicular to the axis of the radio
continuum jet observed with the VLA towards SMM1. The spatial and velocity
distribution of the maser features lead us to favor the interpretation that the
maser emission is excited by interaction of the receding lobe of the jet with
dense gas in the accretion disk surrounding the YSO in SMM1. Towards
RNO~15-FIR, the few detected maser features have both positions and (absolute)
velocities aligned along a direction that is parallel to the axis of the
molecular outflow observed on much larger angular scales. In this case the
maser emission likely emerges from dense, shocked molecular clumps displaced
along the axis of the jet emerging from the YSO. The protostar in Serpens SMM1
is more massive than the one in RNO~15-FIR. We discuss the case where a high
mass ejection rate can generate jets sufficiently powerful to sweep away from
their course the densest portions of circumstellar gas. In this case, the
excitation conditions for water masers might preferably occur at the interface
between the jet and the accretion disk, rather than along the jet axis.Comment: 18 pages (postscript format); 9 figures; to be published into
Astronomy & Astrophysics, Main Journa
Optimal Layout Design for Agricultural Facility Using Simulated Annealing
Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is a Technical Paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 5 (2003): T. Satake, O. Sataka, Y. Ohta, and T. Furuya. Optimal Layout Design for Agricultural Facility Using Simulated Annealing. Vol. V. May 2003
WWP1 knockout in mice exacerbates obesity-related phenotypes in white adipose tissue but improves whole-body glucose metabolism
Impact of pre-existing immunity on live attenuated influenza vaccine-induced cross-protective immunity
The efficacy of the intranasally (i.n.) delivered live attenuated influenza vaccine (LAIV) is variable and, in some seasons, suboptimal. In this study, we report that LAIV exhibits cross-protective efficacy in mice, potentially associated with cellular immunity as opposed to antigen-specific antibody responses. However, pre-exposure to the intramuscularly (i.m.) delivered inactivated influenza vaccine (IIV) severely impaired LAIV-induced cross-protection against heterologous challenge, potentially by inhibiting replication of LAIV. Our findings suggest that pre-existing immunity afforded by IIV suppresses cross-protective T cell immunogenicity of LAIV
Microscopic and Macroscopic Signatures of Antiferromagnetic Domain Walls
Magnetotransport measurements on small single crystals of Cr, the elemental
antiferromagnet, reveal the hysteretic thermodynamics of the domain structure.
The temperature dependence of the transport coefficients is directly correlated
with the real-space evolution of the domain configuration as recorded by x-ray
microprobe imaging, revealing the effect of antiferromagnetic domain walls on
electron transport. A single antiferromagnetic domain wall interface resistance
is deduced to be of order at a
temperature of 100 K.Comment: 3 color figure
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