107 research outputs found
Multi-Epoch VERA Observations of Sagittarius A*: I. Images and Structural Variability
We report the results of multi-epoch observations of Sgr A* with VLBI
Exploration of Radio Astrometry (VERA) at 43 GHz, carried out from 2004 to
2008. We detected a time variation of flux at 11 % level and intrinsic size at
19 %. In addition, comparisons with previous Very Long Baseline Array (VLBA)
results shows that Sgr A* underwent the flaring event at least longer than 10
days in May 2007. The intrinsic size of Sgr A* remained unchanged within 1
level from the size before/after the flaring event, indicating that
the brightness temperature of Sgr A* was increased. The flaring event occurred
within 31 d, which is shorter than the refractive time scale. Moreover it is
difficult to explain the increase in the spectral index at the flaring event by
the simple interstellar scattering model. Hence, the flaring event is most
likely associated with the changes in intrinsic properties of Sgr A*. We
considered the origin of the brightness temperature variation, and concluded
that the flaring event of Sgr A* could be explained by the continuous heating
of electrons, such as a standing shock in accretion flow.Comment: 13 pages, 7 figures, published in Publications of the Astronomical
Society of Japan (PASJ
Increased Rac1 activity and Pak1 overexpression are associated with lymphovascular invasion and lymph node metastasis of upper urinary tract cancer
<p>Abstract</p> <p>Background</p> <p>Lymphovascular invasion (LVI) and lymph node metastasis are conventional pathological factors associated with an unfavorable prognosis of urothelial carcinoma of the upper urinary tract (UC-UUT), but little is known about the molecular mechanisms underlying LVI and nodal metastasis in this disease. Rac1 small GTPase (Rac1) is essential for tumor metastasis. Activated GTP-bound Rac1 (Rac1 activity) plays a key role in activating downstream effectors known as Pak (21-activated kinase), which are key regulators of cytoskeletal remolding, cell motility, and cell proliferation, and thus have a role in both carcinogenesis and tumor invasion.</p> <p>Methods</p> <p>We analyzed Rac1 activity and Pak1 protein expression in matched sets of tumor tissue, non-tumor tissue, and metastatic lymph node tissue obtained from the surgical specimens of 108 Japanese patients with UC-UUT.</p> <p>Results</p> <p>Rac1 activity and Pak1 protein levels were higher in tumor tissue and metastatic lymph node tissue than in non-tumor tissue (both <it>P </it>< 0.0001). A high level of Rac1 activity and Pak1 protein expression in the primary tumor was related to poor differentiation (<it>P </it>< 0.05), muscle invasion (<it>P </it>< 0.01), LVI (<it>P </it>< 0.0001), and lymph node metastasis (<it>P </it>< 0.0001). Kaplan-Meier survival analysis showed that an increase of Rac1 activity and Pak1 protein was associated with a shorter disease-free survival time (<it>P </it>< 0.01) and shorter overall survival (<it>P </it>< 0.001). Cox proportional hazards analysis revealed that high Rac1 activity, Pak1 protein expression and LVI were independent prognostic factors for shorter overall and disease-free survival times (<it>P </it>< 0.01) on univariate analysis, although only Pak1 and LVI had an influence (<it>P </it>< 0.05) according to multivariate analysis.</p> <p>Conclusions</p> <p>These findings suggest that Rac1 activity and Pak1 are involved in LVI and lymph node metastasis of UC-UUT, and may be prognostic markers for this disease.</p
Multifrequency VLBI Observations of the Broad Absorption Line Quasar J1020+4320: Recently Restarted Jet Activity?
This paper reports very-long-baseline interferometry observations of the
radio-loud broad absorption line (BAL) quasar J1020+4320 at 1.7, 2.3, 6.7, and
8.4 GHz using the Japanese VLBI network (JVN) and European VLBI network (EVN).
The radio morphology is compact with a size of ~10 pc. The convex radio
spectrum is stable over the last decade; an observed peak frequency of 3.2 GHz
is equivalent to 9.5 GHz in the rest frame, suggesting an age of the order of
~100 years as a radio source, according to an observed correlation between
linear size and peak frequency of compact steep spectrum (CSS) and giga-hertz
peaked spectrum (GPS) radio sources. A low-frequency radio excess suggests
relic of past jet activity. J1020+4320 may be one of the quasars with recurrent
and short-lived jet activity during a BAL-outflowing phase.Comment: 7 pages, 2 figures, 2 tables, accepted for publication in PAS
Astrometry of Water Maser Sources in Nearby Molecular Clouds with VERA - II. SVS 13 in NGC 1333
We report on the results of multi-epoch VLBI observations with VERA (VLBI
Exploration of Radio Astrometry) of the 22 GHz H2O masers associated with the
young stellar object SVS 13 in the NGC 1333 region. We have carried out
phase-referencing VLBI astrometry and measured an annual parallax of the maser
features in SVS 13 of 4.25+/-0.32 mas, corresponding to the distance of
235+/-18 pc from the Sun. Our result is consistent with a photometric distance
of 220 pc previously reported. Even though the maser features were detectable
only for 6 months, the present results provide the distance to NGC 1333 with
much higher accuracy than photometric methods. The absolute positions and
proper motions have been derived, revealing that the H2O masers with the LSR
(local standard of rest) velocities of 7-8 km s-1 are most likely associated
with VLA4A, which is a radio counterpart of SVS 13. The origin of the observed
proper motions of the maser features are currently difficult to attribute to
either the jet or the rotating circumstellar disk associated with VLA4A, which
should be investigated through future high-resolution astrometric observations
of VLA4A and other radio sources in NGC 1333.Comment: 9 pages, 5 figures. PASJ, in press (2008, Vol. 60, No. 1
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