144 research outputs found
Study of A Permanent-Magnet Dipole with Variable Field Strength and Polarity(Abstracts of Doctoral Dissertations,Annual Report (from April 1995 to March 1996))
H2O maser motions and the distance of the star forming region G192.16-3.84
We present the results of astrometic observations of H2O masers associated
with the star forming region G192.16-3.84 with the VLBI Exploration of Radio
Astrometry (VERA). The H2O masers seem to be associated with two young stellar
objects (YSOs) separated by \sim1200 AU as reported in previous observations.
In the present observations, we successfully detected an annual parallax of
0.66 \pm 0.04 mas for the H2 O masers, which corresponds to a distance to
G192.16-3.84 of D = 1.52 \pm 0.08 kpc from the Sun. The determined distance is
shorter than the estimated kinematic distance. Using the annual parallax
distance and the estimated parameters of the millimeter continuum emission, we
estimate the mass of the disk plus circumstellar cloud in the southern young
stellar object to be 10.0+4.3M\cdot. We also estimate the galactocentric
distance and the peculiar motion -3.6 of G192.16-3.84, relative to a circular
Galactic rotation: R\star = 9.99 \pm 0.08 kpc, Z\star = -0.10 \pm 0.01 kpc, and
(U\star,V\star,W\star)=(-2.8\pm1.0,-10.5\pm0.3,4.9\pm2.7)[kms-1]respectively.
The peculiar motion of G192.16-3.84 is within that typically found in recent
VLBI astrometric results. The angular distribution and three-dimensional
velocity field of H2O maser features associated with the northern YSO indicate
the existence of a bipolar outflow with a major axis along the
northeast-southwest direction.Comment: 9 pages, 2 figures and 4 tables. Accepted for publication on PAS
Recent increase of genetic diversity in Plasmodium vivax population in the Republic of Korea
<p>Abstract</p> <p>Background</p> <p>The reemergence of <it>Plasmodium vivax </it>in South Korea since 1993 represents a serious public health concern. Despite the importance in understanding genetic diversity for control strategies, however, studies remain inconclusive with the general premise that due to low rate of malaria transmission, there is generally low genetic diversity with very few strains involved. In this study, the genetic diversity and population structure of <it>P. vivax </it>in South Korea were explored by analysing microsatellite polymorphism.</p> <p>Methods</p> <p>Sequences for 13 microsatellite loci distributed across the twelve chromosomes of <it>P. vivax </it>were obtained from 58 South Korean isolates collected during two sampling periods, namely 1997-2000 and 2007. The sequences were used for the analysis of expected heterozygosity and multilocus genotype diversity. Population structure was evaluated using STRUCTURE version 2.3.2. Linkage disequilibrium was also analysed to investigate the extent of outbreeding in the <it>P. vivax </it>population.</p> <p>Results</p> <p>Mean expected heterozygosity significantly increased from 0.382 in 1997-2000 to 0.545 in 2007 (<it>P </it>< 0.05). The number of multilocus genotypes was 7 and 27; and genotype diversity was statistically significant (<it>P </it>< 0.01) at 0.661 and 0.995 in 1997-2000 and 2007, respectively. Analysis by STRUCTURE showed a more complex population structure in 2007 than in 1997-2000. Linkage disequilibrium between 13 microsatellites, although significant in both time points, was notably lower in 2007.</p> <p>Conclusions</p> <p>The present microsatellite analysis clearly showed recent increase of genetic diversity and recent relaxation of the strong population structure observed in 1997-2000. These results suggest that multiple genotypes not present previously recently migrated into South Korea, accompanied by substantial outbreeding between different genotypes.</p
Bigradient Phase Referencing
We propose bigradient phase referencing (BPR), a new radio-observation
technique, and report its performance using the Japanese
very-long-baseline-interferometry network (JVN). In this method, a weak source
is detected by phase-referencing using a primary calibrator, in order to play a
role as a secondary calibrator for phase-referencing to a weak target. We will
be given the opportunity to select a calibrator from lots of milli-Jansky
sources, one of which may be located at the position closer to the target. With
such a smaller separation, high-quality phase-referencing can be achieved.
Furthermore, a subsequent more-sophisticated calibration can relocate array's
focus to a hypothetical point much closer to the target; a higher quality of
phase referencing is available. Our demonstrative observations with strong
radio sources have proved the capabilities of BPR in terms of image dynamic
ranges and astrometric reproducibility. The image dynamic range on a target has
been improved with a factor of about six compared to that of normal
phase-referencing; the resultant position difference of target's emission
between two epochs was only 62+-50 micro-arcsecond, even with less than 2300-km
baselines at 8.4 GHz and fast-switching of a target-calibrator pair of a
2.1-degree separation.Comment: 10 pages, 4 figures, accepted for publication in PAS
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