522 research outputs found
Assessing Vegetation Resistace from Observed Temporal Water Surface Profiles of Flood Flows in Rivers
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv
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
Very Long Baseline Array Imaging of Parsec-scale Radio Emissions in Nearby Radio-quiet Narrow-line Seyfert 1 Galaxies
We conducted Very Long Baseline Array (VLBA) observations of seven nearby
narrow-line Seyfert 1 (NLS1) galaxies at 1.7 GHz (18cm) with milli-arcsecond
resolution. This is the first systematic very long baseline interferometry
(VLBI) study focusing on the central parsec-scale regions of radio-quiet NLS1s.
Five of the seven were detected at a brightness temperature of >~5x10^6 K and
contain radio cores with high brightness temperatures of >6x10^7 K, indicating
a nonthermal process driven by jet-producing central engines as is observed in
radio-loud NLS1s and other active galactic nucleus (AGN) classes. VLBA images
of MRK 1239, MRK 705, and MRK 766 exhibit parsec-scale jets with clear linear
structures. A large portion of the radio power comes from diffuse emission
components that are distributed within the nuclear regions (<~300 pc), which is
a common characteristic throughout the observed NLS1s. Jet kinetic powers
limited by the Eddington limit may be insufficient to allow the jets escape to
kiloparsec scales for these radio-quiet NLS1s with low-mass black holes of
<~10^7 M_sun.Comment: 12 pages, 3 figures, 3 tables, accepted for publication in Ap
Atomic scale friction between clean graphite surfaces
We investigate atomic scale friction between clean graphite surfaces by using
molecular dynamics. The simulation reproduces atomic scale stick-slip motion
and low frictional coefficient, both of which are observed in experiments using
frictional force microscope. It is made clear that the microscopic origin of
low frictional coefficients of graphite lies on the honeycomb structure in each
layer, not only on the weak interlayer interaction as believed so far.Comment: 4 pages, 7 figure
Studies on dose distribution, dynamics of DNA repair proteins and radio-sensitization associated with high LET radiation
学位の種別: 課程博士審査委員会委員 : (主査)東京大学教授 上坂 充, 東京大学教授 高橋 浩之, 東京大学教授 鄭 雄一, 東京大学准教授 中島 義和, 東京大学講師 細谷 紀子, 放射線医学総合研究所チームリーダー, 藤森 亮University of Tokyo(東京大学
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