5,465 research outputs found
A Measurement of Proper Motions of SiO Maser Sources in the Galactic Center with the VLBA
We report on the high-precision astrometric observations of maser sources
around the Galactic Center in the SiO J=1--0 v=1 and 2 lines with the VLBA
during 2001 -- 2004. With phase-referencing interferometry referred to the
radio continuum source Sgr A*, accurate positions of masers were obtained for
three detected objects: IRS 10 EE (7 epochs), IRS 15NE (2 epochs), and SiO 6
(only 1 epoch). Because circumstellar masers of these objects were resolved
into several components, proper motions for the maser sources were derived with
several different methods. Combining our VLBA results with those of the
previous VLA observations, we obtained the IRS 10EE proper motion of 76+-3 km
s^{-1} (at 8 kpc) to the south relative to Sgr A*. Almost null proper motion of
this star in the east--west direction results in a net transverse motion of the
infrared reference frame of about 30+-9 km s^{-1} to the west relative to Sgr
A*. The proper-motion data also suggests that IRS 10EE is an astrometric binary
with an unseen massive companion.Comment: High-res. figures are available at
ftp://ftp.nro.nao.ac.jp/nroreport/no656.pdf.gz . PASJ 60, No. 1 (2008) in
pres
How Does Longitudinal Interaction Promote Second Language Speech Learning? Roles of Learner Experience and Proficiency Levels
This study examined how longitudinal interaction impacts the development of second language
(L2) oral proficiency in relation to learners’ different experience and proficiency levels. Japanese
English-as-a-Foreign-Language learners participated in weekly conversation exchanges with
native speakers (NSs) in the US via videoconferencing tools over one academic semester (12
weeks). The participants’ spontaneous speech, elicited from a story telling task before and after
the treatment, was analyzed via a set of linguistic measures. In line with the componential view
of L2 oral proficiency (De Jong et al., 2012) and development (Bundgaard-Nielsen et al., 2011),
our results hinted L2 learners’ experience and proficiency levels as a mediating factor for
determining the link between interaction and its impact on different dimensions of L2 speech
learning. While the longitudinal interaction equally improved the participants’ grammatical
complexity and articulation rate—a fundamental component for defining L2 oral proficiency, the
development of less experienced/proficient learners was observed across a wide range of
lexicogrammar and fluency features (lexical appropriateness/richness, grammatical accuracy,
pause ratio). It was only more experienced/proficient learners that significantly enhanced
phonological accuracies (segmentals, word stress) which are thought to gradually develop in the
later stages of L2 speech learning. These findings add another piece of evidence for the
differential effects of long-term interaction relative to L2 learners’ developmental stages
Subdiffusive axial transport of granular materials in a long drum mixer
Granular mixtures rapidly segregate radially by size when tumbled in a
partially filled horizontal drum. The smaller component moves toward the axis
of rotation and forms a buried core, which then splits into axial bands. Models
have generally assumed that the axial segregation is opposed by diffusion.
Using narrow pulses of the smaller component as initial conditions, we have
characterized axial transport in the core. We find that the axial advance of
the segregated core is well described by a self-similar concentration profile
whose width scales as , with . Thus, the
process is subdiffusive rather than diffusive as previously assumed. We find
that is nearly independent of the grain type and drum rotation rate
within the smoothly streaming regime. We compare our results to two
one-dimensional PDE models which contain self-similarity and subdiffusion; a
linear fractional diffusion model and the nonlinear porous medium equation.Comment: 4 pages, 4 figures, 1 table. Submitted to Phys Rev Lett. For more
info, see http://www.physics.utoronto.ca/nonlinear
LHR band emissions at mid-latitude and their relationship to ionospheric ELF hiss and relativistic electrons
LHR band emissions observed at mid-latitude were investigated using data from the EXOS-C (Ohzora) satellite. A typical feature of the LHR band emissions is a continuous banded structure without burst-like and cut-off features whose center frequency decreases as the satellite moves to higher latitudes. A statistical analysis of the occurrence characteristics of the phenomena showed that mid-latitude LHR emissions are distributed inside the plasmapause during magnetically quiet periods, and the poleward boundary of the emission region moves to lower latitudes as the magnetic activity increases. The altitude distribution of the waves suggests that the propagation in the LHR duct formed horizontally in the mid-latitude upper-ionosphere. The emission is closely related to the occurrence of ionospheric ELF hiss. It is also shown that LHR emissions are commonly observed in the slot region of the radiation belt, and they sometimes accompany the enhancement of the ionospheric electron temperature. The generation of the LHR band emissions is discussed based on the observed characteristics
Pressure-driven instability in auroral images to create auroral patches
第3回極域科学シンポジウム/第36回極域宙空圏シンポジウム 11月27日(火) 国立極地研究所 2階大会議
Comparative Study of MHD Instabilities in LHD and JT-60U - Instability at t ~ 0.5 during Counter-NB -
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