658 research outputs found
Effects of Sediment Supply on Low-Flow Channel Formation
Sediment Transport and Morphodynamic
A Setup Method of Tide Level Variations at Open Boundary in Estuaries for Numerical Tidal Flow Analysis
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv
Horikawa Sen-Nin Chosatai(HSC) (Horikawa River Thousand-Citizen Survey Network 2010)
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv
MgII Absorption Lines in z=2.974 Damped Lyman-alpha System toward Gravitationally Lensed QSO APM 08279+5255: Detection of Small-scale Structure in MgII Absorbing Clouds
1.02-1.16 micron spectra (R ~ 7,000) of the gravitationally lensed QSO APM
08279+5255 at z_em=3.911 were obtained during the commissioning run of IRCS,
the 1-5 micron near-infrared camera and spectrograph for the Subaru 8.2 m
Telescope. Strong MgII doublet at 2976,2800 angstrom and FeII (2600 angstrom),
FeII (2587 angstrom) absorption lines at z_abs=2.974 were clearly detected in
the rest-frame UV spectra, confirming the presence of a damped Lyman-alpha
system at the redshift as suggested by Petitjean et al. Also MgI (2853
angstrom) absorption line is probably detected. An analysis of the absorption
lines including velocity decomposition was performed. This is a first detailed
study of MgII absorption system at high redshift (z > 2.5) where the MgII
doublet shifts into the near-infrared in the observer's frame.
The spectra of the lensed QSO pair A and B with 0.38 arcsec separation were
resolved in some exposure frames under excellent seeing condition. We extracted
the MgII doublet spectra of A and B separately. Although three velocity
components (v ~ -28, +5, +45 km/s) are known to exist in this MgII system
(Petitjean et al.), the v ~ +45 km/s absorption line was not detected toward
source B, showing that the +45 km/s MgII cloud lies only in the line of sight
to the source A. Our results suggests that the size of the MgII absorbing
clouds is as small as 200 pc, which corresponds to the separation of A and B at
the redshift of the absorber. This is the first direct detection of the
small-scale structure of MgII clouds at high-redshift, confirming the estimated
cloud sizes from photoionization model by Churchill and Charlton.Comment: ApJ in press (Vol.569, 20 April 2002 issue
Infrared Spectroscopy of CO Ro-vibrational Absorption Lines toward the Obscured AGN IRAS 08572+3915
We present high-resolution spectroscopy of gaseous CO absorption in the
fundamental ro-vibrational band toward the heavily obscured active galactic
nucleus (AGN) IRAS 08572+3915. We have detected absorption lines up to highly
excited rotational levels (J<=17). The velocity profiles reveal three distinct
components, the strongest and broadest (delta_v > 200 km s-1) of which is due
to blueshifted (-160 km s-1) gas at a temperature of ~ 270 K absorbing at
velocities as high as -400 km s-1. A much weaker but even warmer (~ 700 K)
component, which is highly redshifted (+100 km s-1), is also detected, in
addition to a cold (~ 20 K) component centered at the systemic velocity of the
galaxy. On the assumption of local thermodynamic equilibrium, the column
density of CO in the 270 K component is NCO ~ 4.5 x 10^18 cm-2, which in fully
molecular gas corresponds to a H2 column density of NH2 ~ 2.5 x 10^22 cm-2. The
thermal excitation of CO up to the observed high rotational levels requires a
density greater than nc(H2) > 2 x 10^7 cm-3, implying that the thickness of the
warm absorbing layer is extremely small (delta_d < 4 x 10-2 pc) even if it is
highly clumped. The large column densities and high radial velocities
associated with these warm components, as well as their temperatures, indicate
that they originate in molecular clouds near the central engine of the AGN.Comment: 13 pages, 7 figures, accepted for publication in PASJ (Vol.65 No.1
2013/02/25
Low-Waterway Variation Due to Change of Water and Sediment Supply Conditions
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv
Step length formula of bed-load sediment and its application to dune-bed
Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732A stochastic sediment transport model consists of a pick-up rate and a step length of sediment
particles. Einstein (1950) assumed that the mean step length of uniform bed-load sediment particle is
approximately 100 times of its diameter. After that, some estimation methods and formulas have
been presented. As for graded sediments, Nakagawa et al. (1982b) found that the mean step length
of each particle is approximately 10-30 times of its diameter. Almost all of the previous works for
step length have been conducted for coarse particles on flat beds. Therefore, step lengths for fine
particles and non-flat bed have been not always discussed. Since the particle diameter and status of
bed influence to the grain-size Reynolds number and variation coefficient of velocity, we propose
the mean step length formula which considers these two parameters. The proposed step length
formula is applied to sediments on flat bed and dune-bed, and is verified with the direct and indirect
measurement values
Observing Dynamic State of River-Mouth Bar and its Control in the Yuragawa River
Sediment Transport and Morphodynamic
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