1,556 research outputs found
Liquid crystal light valve structures
An improved photosensor film and liquid crystal light valves embodying said film is provided. The photosensor film and liquid crystal light valve is characterized by a significant lower image retention time while maintaining acceptable photosensitivity. The photosensor film is produced by sputter depositing CdS onto an ITO substrate in an atmosphere of argon/H2S gas while maintaining the substrate at a temperature in the range of about 130 C to about 200 C and while introducing nitrogen gas into the system to the extent of not more than about 1% of plasma mixture. Following sputter deposition of the CdS, the film is annealed in an inert gas at temperatures ranging from about 300 C to about 425 C
Multi-Phase Gas Dynamics in a Weak Barred Potential
The structure of the interstellar medium in the central kpc region of a
galaxy with a weak bar-like potential is investigated taking into account
realistic cooling and heating processes and the self-gravity of the gas. Using
high resolution hydrodynamical simulations, it is revealed that the resonant
structures (e.g. smooth spiral shocks and a nuclear ring) are very different
from those seen in past numerical models where simple models of the ISM, i.e.
non-self-gravitating, isothermal gas were assumed. We find that the pc-scale
filaments and clumps form large scale spirals, which resemble those seen in
real galaxies. The fine structures are different between the arms and in the
nuclear region. The next generation millimeter interferometer (ALMA) may reveal
the fine structures of the cold gas in nearby galaxies. We also find a large
scale anisotropy in the gas temperature, which is caused due to non-circular
velocity field of the gas.The damped orbit model based on the epicyclic
approximation explains the distribution of the hot (> 10^4 K) and cold (< 100
K) gases appearing alternately around the galactic center. Because of the
temperature anisotropy, cold gases observed by molecular lines do not
necessarily represent the real gas distribution in galaxies. Position-Velocity
diagrams depend strongly on the viewing angles. As a result, the rotational
velocity inferred from the PV maps could be two times larger or smaller than
the true circular velocity.Comment: 7 pages, 8 figures, to appear in PASJ, vol. 56, no.6 (2001
The Virgo High-Resolution CO Survey. II. Rotation Curves and Dynamical Mass Distributions
Based on a high-resolution CO survey of Virgo spirals with the Nobeyama
Millimeter-wave Array, we determined the dynamical centers using velocity
fields, and derived position-velocity diagrams (PVDs) along the major axes of
the galaxies across their dynamical centers. We applied a new iteration method
to derive rotation curves (RCs), which reproduce the observed PVDs. The
obtained high-accuracy RCs generally show steep rise in the central 100 to 200
pc regions, followed by flat rotation in the disk. We applied a deconvolution
method to calculate the surface-mass density (SMD) using the RCs based on two
extreme assumptions that the mass distribution is either spherical or thin-disk
shaped. Both assumptions give nearly identical results, agreeing with each
other within a factor of two at any radii. The SMD distributions revealed
central massive cores with peak SMD of 10^4 - 10^5 Msun pc^-2 and total mass
within 200 pc radius of the order of about 10^9 Msun Correlation analysis among
the derived parameters show that the central CO-line intensity is positively
correlated with the central SMD, which suggests that the deeper is the
gravitational potential, the higher is the molecular gas concentration in the
nuclei regardless morphological types.Comment: PASJ 2003 in press, Latex 12 pages, 6 figures (Bigger gif/ps figures
available at http://www.ioa.s.u-tokyo.ac.jp/radio/virgo2
The Virgo CO Survey: VI. Gas Dynamics and Star Formation Along the Bar in NGC 4303
We present CO interferometer observations of the barred galaxy NGC 4303
(M61). This galaxy has a gas concentration at the central region and offset
ridges in the bar. Sharp velocity gradients are apparent across the ridges.
Analyses of the CO data and the newborn stellar clusters revealed in HST images
indicate the existence of unresolved molecular clouds with masses of
10^4-6Msun. The observed shear velocity gradient across the ridges is too small
to break up giant molecular clouds. Therefore, the clouds are likely to survive
passage through the ridges. We discuss a cloud orbit model in a bar potential.
The model reproduces the narrow offset ridges and sharp velocity gradients
across the ridges in NGC 4303. We discuss cloud-cloud collisions (and close
interactions) as a possible triggering mechanism for star formation. The
newborn stellar clusters in NGC 4303 are located predominantly at the leading
sides of the offset ridges, where cloud orbits are densely populated and
suggest a high collisional frequency and possibly a high rate of triggered star
formation. Cloud-based dynamics is less dissipative than smooth hydrodynamic
models, possibly extending the timescales of gas dynamical evolution and gas
fueling to central regions in barred galaxies.Comment: 20 pages, 13 figures, 4 tables. PASJ, accepted (Apr. issue), high
resolution version
"http://www.astro.caltech.edu/~koda/paper/n4303/koda_n4303.pdf
Acceleration Method of Neighbor Search with GRAPE and Morton-ordering
We describe a new method to accelerate neighbor searches on GRAPE, i.e. a
special purpose hardware that efficiently calculates gravitational forces and
potentials in -body simulations. In addition to the gravitational
calculations, GRAPE simultaneously constructs the lists of neighbor particles
that are necessary for Smoothed Particle Hydrodynamics (SPH). However, data
transfer of the neighbor lists from GRAPE to the host computer is time
consuming, and can be a bottleneck. In fact, the data transfer can take about
the same time as the calculations of forces themselves. Making use of GRAPE's
special treatment of neighbor lists, we can reduce the amount of data transfer
if we search neighbors in the order that the neighbor lists, constructed in a
single GRAPE run, overlap each other. We find that the Morton-ordering requires
very low additional calculation and programming costs, and results in
successful speed-up on data transfer. We show some benchmark results in the
case of GRAPE-5. Typical reduction in transferred data becomes as much as 90%.
This method is suitable not only for GRAPE-5, but also GRAPE-3 and the other
versions of GRAPE.Comment: 9 pages, 6 figures, accepted for publication in PAS
A Water Maser and Ammonia Survey of GLIMPSE Extended Green Objects (EGOs)
We present the results of a Nobeyama 45-m water maser and ammonia survey of
all 94 northern GLIMPSE Extended Green Objects (EGOs), a sample of massive
young stellar objects (MYSOs) identified based on their extended 4.5 micron
emission. We observed the ammonia (1,1), (2,2), and (3,3) inversion lines, and
detect emission towards 97%, 63%, and 46% of our sample, respectively (median
rms ~50 mK). The water maser detection rate is 68% (median rms ~0.11 Jy). The
derived water maser and clump-scale gas properties are consistent with the
identification of EGOs as young MYSOs. To explore the degree of variation among
EGOs, we analyze subsamples defined based on MIR properties or maser
associations. Water masers and warm dense gas, as indicated by emission in the
higher-excitation ammonia transitions, are most frequently detected towards
EGOs also associated with both Class I and II methanol masers. 95% (81%) of
such EGOs are detected in water (ammonia(3,3)), compared to only 33% (7%) of
EGOs without either methanol maser type. As populations, EGOs associated with
Class I and/or II methanol masers have significantly higher ammonia linewidths,
column densities, and kinetic temperatures than EGOs undetected in methanol
maser surveys. However, we find no evidence for statistically significant
differences in water maser properties (such as maser luminosity) among any EGO
subsamples. Combining our data with the 1.1 mm continuum Bolocam Galactic Plane
Survey, we find no correlation between isotropic water maser luminosity and
clump number density. Water maser luminosity is weakly correlated with clump
(gas) temperature and clump mass.Comment: Astrophysical Journal, accepted. Emulateapj, 24 pages including 24
figures, plus 9 tables (including full content of online-only tables
- …