888 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
Detection of Dense Molecular Gas in Inter-Arm Spurs in M51
Spiral arm spurs are prominent features that have been observed in extinction
and 8m emission in nearby galaxies. In order to understand their molecular
gas properties, we used the Owens Valley Radio Observatory to map the
CO(J=1--0) emission in three spurs emanating from the inner northwestern spiral
arm of M51. We report CO detections from all three spurs. The molecular gas
mass and surface density are M M_{\sun} and
50 M_{\sun} pc. Thus, relative to the spiral arms,
the spurs are extremely weak features. However, since the spurs are extended
perpendicular to the spiral arms for 500 pc and contain adequate fuel for
star formation, they may be the birthplace for observed inter-arm HII regions.
This reduces the requirement for the significant time delay that would be
otherwise needed if the inter-arm star formation was initiated in the spiral
arms. Larger maps of galaxies at similar depth are required to further
understand the formation and evolution of these spurs and their role in star
formation - such data should be forthcoming with the new CARMA and future ALMA
telescopes and can be compared to several recent numerical simulations that
have been examining the evolution of spiral arm spurs.Comment: 6 pages, 3 figures, emulate-apj format, accepted in Ap
Cu-spin dynamics in the overdoped regime of La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ probed by muon spin relaxation
Muon-spin-relaxation measurements have been performed for the partially
Zn-substituted La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ with y=0-0.10 in the overdoped
regime up to x=0.30. In the 3 % Zn-substituted samples up to x=0.27,
exponential-like depolarization of muon spins has been observed at low
temperatures, indicating Zn-induced slowing-down of the Cu-spin fluctuations.
The depolarization rate decreases with increasing x and almost no fast
depolarization of muon spins has been observed for x=0.30 where
superconductivity disappears. The present results suggest that the dynamical
stripe correlations exist in the whole superconducting regime of
La_2-x_Sr_x_CuO_4_ and that there is no quantum critical point at x~0.19.Comment: 6 pages, 5 figure
Multi-Transition Study of M51's Molecular Gas Spiral Arms
Two selected regions in the molecular gas spiral arms in M51 were mapped with
the Owens Valley Radio Observatory (OVRO) mm-interferometer in the 12CO(2-1),
13CO(1-0), C18O(1-0), HCN(1-0) and HCO+(1-0) emission lines. The CO data have
been combined with the 12CO(1-0) data from Aalto et al. (1999) covering the
central 3.5kpc to study the physical properties of the molecular gas. All CO
data cubes were short spacing corrected using IRAM 30m (12CO(1-0): NRO 45m)
single dish data. A large velocity gradient (LVG) analysis finds that the giant
molecular clouds (GMCs) are similar to Galactic GMCs when studied at 180pc
(120pc) resolution with an average kinetic temperature of T_kin = 20(16)K and
H_2 density of n(H_2) = 120(240)cm^(-3) when assuming virialized clouds (a
constant velocity gradient dv/dr. The associated conversion factor between H_2
mass and CO luminosity is close to the Galactic value for most regions
analyzed. Our findings suggest that the GMC population in the spiral arms of
M51 is similar to those of the Milky Way and therefore the strong star
formation occurring in the spiral arms has no strong impact on the molecular
gas in the spiral arms. Extinction inferred from the derived H_2 column density
is very high (A_V about 15 - 30 mag), about a factor of 5-10 higher than the
average value derived toward HII regions. Thus a significant fraction of the
ongoing star formation could be hidden inside the dust lanes of the spiral
arms. A comparison of MIPS 24um and H_alpha data, however, suggests that this
is not the case and most of the GMCs studied here are not (yet) forming stars.
We also present low (4.5") resolution OVRO maps of the HCN(1-0) and HCO+(1-0)
emission at the location of the brightest 12CO(1-0) peak.Comment: 41 pages, 12 figures, 7 tables; accepted for publication by Ap
The HST Cosmos Project: Contribution from the Subaru Telescope
The Cosmic Evolution Survey (COSMOS) is a Hubble Space Telescope (HST)
treasury project.The COSMOS aims to perform a 2 square degree imaging survey of
an equatorial field in (F814W) band, using the Advanced Camera for Surveys
(ACS). Such a wide field survey, combined with ground-based photometric and
spectroscopic data, is essential to understand the interplay between large
scale structure, evolution and formation of galaxies and dark matter. In 2004,
we have obtained high-quality, broad band images of the COSMOS field ( and ) using Suprime-Cam on the Subaru
Telescope, and we have started our new optical multi-band program, COSMOS-21 in
2005. Here, we present a brief summary of the current status of the COSMOS
project together with contributions from the Subaru Telescope. Our future
Subaru program, COSMOS-21, is also discussed briefly.Comment: 4 pages, 3 figures, to appear in the Proceedings of the 6th East
Asian Meeting on Astronomy, JKAS, 39, in pres
Time-Reversal Symmetry-Breaking Superconductivity in Heavy Fermion PrOs4Sb12 detected by Muon Spin Relaxation
We report on muon spin relaxation measurements of the 4f^2-based
heavy-fermion superconductor filled-skutterudite PrOs4Sb12. The results reveal
the spontaneous appearance of static internal magnetic fields below the
superconducting transition temperature, providing unambiguous evidence for the
breaking of time-reversal symmetry in the superconducting state. A discussion
is made on which of the spin or orbital component of Cooper pairs carries a
nonzero momentum.Comment: 5 pages with 3 figure
Dynamically Driven Evolution of the Interstellar Medium in M51
We report the highest-fidelity observations of the spiral galaxy M51 in CO
emission, revealing the evolution of giant molecular clouds (GMCs) vis-a-vis
the large-scale galactic structure and dynamics. The most massive GMCs
(so-called GMAs) are first assembled and then broken up as the gas flow through
the spiral arms. The GMAs and their H2 molecules are not fully dissociated into
atomic gas as predicted in stellar feedback scenarios, but are fragmented into
smaller GMCs upon leaving the spiral arms. The remnants of GMAs are detected as
the chains of GMCs that emerge from the spiral arms into interarm regions. The
kinematic shear within the spiral arms is sufficient to unbind the GMAs against
self-gravity. We conclude that the evolution of GMCs is driven by large-scale
galactic dynamics --their coagulation into GMAs is due to spiral arm streaming
motions upon entering the arms, followed by fragmentation due to shear as they
leave the arms on the downstream side. In M51, the majority of the gas remains
molecular from arm entry through the inter-arm region and into the next spiral
arm passage.Comment: 6 pages, including 3 figures. Accepted, ApJ
Starbursting Nuclear CO Disks of Early-type Spiral Galaxies
We have initiated the first CO interferometer survey of early-type spiral
galaxies (S0-Sab). We observed five early-type spiral galaxies with HII nuclei
(indicating circumnuclear starburst activities). These observations indicate
gas masses for the central kiloparsec of \sim 1-5% of the dynamical masses.
Such low gas mass fractions suggest that large-scale gravitational instability
in the gas is unlikely to be the driving cause for the starburst activities.
The Toomre Q values were >1 (mostly >3) within the central kiloparsec,
indicating that the gas disks are globally gravitationally stable. The area
filling factor of the gas disks is estimated to be about 0.05. This small value
indicates the existence of lumpy structure, i.e. molecular clouds, in the
globally-gravitationally stable disks. The typical surface density of the
molecular clouds is as high as \sim 3000 Msun pc^{-2}. We reconsider the nature
of the Toomre Q criterion, and conclude that the Q derived from CO observations
indicates neither star formation nor molecular cloud formation. This argument
should be valid not only for the circumnuclear disks but also for any region in
galactic disks. We tentatively explore an alternative model, i.e. cloud-cloud
collisions, as an initiating mechanism of star formation.Comment: 7pages, including 2 figures ; A&A accepted (19 Oct. 2004
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