3,053 research outputs found
High-precision CTE measurement of hybrid C/SiC composite for cryogenic space telescopes
This paper presents highly precise measurements of thermal expansion of a
"hybrid" carbon-fiber reinforced silicon carbide composite,
HB-Cesic\textregistered - a trademark of ECM, in the temperature region of
\sim310-10K. Whilst C/SiC composites have been considered to be promising for
the mirrors and other structures of space-borne cryogenic telescopes, the
anisotropic thermal expansion has been a potential disadvantage of this
material. HB-Cesic\textregistered is a newly developed composite using a
mixture of different types of chopped, short carbon-fiber, in which one of the
important aims of the development was to reduce the anisotropy. The
measurements indicate that the anisotropy was much reduced down to 4% as a
result of hybridization. The thermal expansion data obtained are presented as
functions of temperature using eighth-order polynomials separately for the
horizontal (XY-) and vertical (Z-) directions of the fabrication process. The
average CTEs and their dispersion (1{\sigma}) in the range 293-10K derived from
the data for the XY- and Z-directions were 0.8050.003\times10
K and 0.837\pm0.001\times10 K, respectively. The absolute
accuracy and the reproducibility of the present measurements are suggested to
be better than 0.01\times10 K and 0.001\times(10)^{-6} K^{-1},
respectively. The residual anisotropy of the thermal expansion was consistent
with our previous speculation regarding carbon-fiber, in which the residual
anisotropy tended to lie mainly in the horizontal plane.Comment: Accepted by Cryogeincs. 12 pages, 3 figures, 1 tabll
Large-scale distributions of mid- and far-infrared emission from the center to the halo of M82 revealed with AKARI
The edge-on starburst galaxy M82 exhibits complicated distributions of
gaseous materials in its halo, which include ionized superwinds driven by
nuclear starbursts, neutral materials entrained by the superwinds, and
large-scale neutral streamers probably caused by a past tidal interaction with
M81. We investigate detailed distributions of dust grains and polycyclic
aromatic hydrocarbons (PAHs) around M82 to understand their interplay with the
gaseous components. We performed mid- (MIR) and far-infrared (FIR) observations
of M82 with the Infrared Camera and Far-Infrared Surveyor on board AKARI. We
obtain new MIR and FIR images of M82, which reveal both faint extended emission
in the halo and very bright emission in the center with signal dynamic ranges
as large as five and three orders of magnitude for the MIR and FIR,
respectively. We detect MIR and FIR emission in the regions far away from the
disk of the galaxy, reflecting the presence of dust and PAHs in the halo of
M82. We find that the dust and PAHs are contained in both ionized and neutral
gas components, implying that they have been expelled into the halo of M82 by
both starbursts and galaxy interaction. In particular, we obtain a tight
correlation between the PAH and H emission, which provides evidence
that the PAHs are well mixed in the ionized superwind gas and outflowing from
the disk.Comment: 12 pages, 8 figures, accepted for publication in A&
Large-scale distributions of mid- and far-infrared emission from the center to the halo of M82 revealed with AKARI
The edge-on starburst galaxy M82 exhibits complicated distributions of
gaseous materials in its halo, which include ionized superwinds driven by
nuclear starbursts, neutral materials entrained by the superwinds, and
large-scale neutral streamers probably caused by a past tidal interaction with
M81. We investigate detailed distributions of dust grains and polycyclic
aromatic hydrocarbons (PAHs) around M82 to understand their interplay with the
gaseous components. We performed mid- (MIR) and far-infrared (FIR) observations
of M82 with the Infrared Camera and Far-Infrared Surveyor on board AKARI. We
obtain new MIR and FIR images of M82, which reveal both faint extended emission
in the halo and very bright emission in the center with signal dynamic ranges
as large as five and three orders of magnitude for the MIR and FIR,
respectively. We detect MIR and FIR emission in the regions far away from the
disk of the galaxy, reflecting the presence of dust and PAHs in the halo of
M82. We find that the dust and PAHs are contained in both ionized and neutral
gas components, implying that they have been expelled into the halo of M82 by
both starbursts and galaxy interaction. In particular, we obtain a tight
correlation between the PAH and H emission, which provides evidence
that the PAHs are well mixed in the ionized superwind gas and outflowing from
the disk.Comment: 12 pages, 8 figures, accepted for publication in A&
Mapping of Large Scale 158 micron [CII] Line Emission: Orion A
We present the first results of an observational programme undertaken to map
the fine structure line emission of singly ionized carbon ([CII] 157.7409
micron) over extended regions using a Fabry Perot spectrometer newly installed
at the focal plane of a 100cm balloon-borne far-infrared telescope. This new
combination of instruments has a velocity resolution of ~200 km/s and an
angular resolution of 1.5'. During the first flight, an area of 30'x15' in
Orion A was mapped. The observed [CII] intensity distribution has been compared
with the velocity-integrated intensity distributions of 13CO(1-0), CI(1-0) and
CO(3-2) from the literature. The observed line intensities and ratios have been
analyzed using the PDR models by Kaufman et al. 1999 to derive the incident UV
flux and volume density at a few selected positions.Comment: To appear in Astronomy & Astrophysic
High Precision CTE-Measurement of SiC-100 for Cryogenic Space-Telescopes
We present the results of high precision measurements of the thermal
expansion of the sintered SiC, SiC-100, intended for use in cryogenic
space-telescopes, in which minimization of thermal deformation of the mirror is
critical and precise information of the thermal expansion is needed for the
telescope design. The temperature range of the measurements extends from room
temperature down to 10 K. Three samples, #1, #2, and #3 were
manufactured from blocks of SiC produced in different lots. The thermal
expansion of the samples was measured with a cryogenic dilatometer, consisting
of a laser interferometer, a cryostat, and a mechanical cooler. The typical
thermal expansion curve is presented using the 8th order polynomial of the
temperature. For the three samples, the coefficients of thermal expansion
(CTE), \bar{\alpha}_{#1}, \bar{\alpha}_{#2}, and \bar{\alpha}_{#3} were
derived for temperatures between 293 K and 10 K. The average and the dispersion
(1 rms) of these three CTEs are 0.816 and 0.002 (/K),
respectively. No significant difference was detected in the CTE of the three
samples from the different lots. Neither inhomogeneity nor anisotropy of the
CTE was observed. Based on the obtained CTE dispersion, we performed an
finite-element-method (FEM) analysis of the thermal deformation of a 3.5 m
diameter cryogenic mirror made of six SiC-100 segments. It was shown that the
present CTE measurement has a sufficient accuracy well enough for the design of
the 3.5 m cryogenic infrared telescope mission, the Space Infrared telescope
for Cosmology and Astrophysics (SPICA).Comment: in press, PASP. 21 pages, 4 figure
Slow-roll inflation in (R+R*4) gravity
We reconsider the toy-model of topological inflation, based on the
R*4-modified gravity. By using its equivalence to the certain scalar-tensor
gravity model in four space-time dimensions, we compute the inflaton scalar
potential and investigate a possibility of inflation. We confirm the existence
of the slow-roll inflation with an exit. However, the model suffers from the
eta-problem that gives rise to the unacceptable value of the spectral index n_s
of scalar perturbations.Comment: 12 pages, 3 figures, LaTeX, misprints corrected and references
update
Structure of Critical Lines in Quenched Lattice QCD with the Wilson Quark Action
The structure of critical lines of vanishing pion mass for the Wilson quark
action is examined in quenched lattice QCD. The numerical evidence is presented
that critical lines spread into five branches beyond beta=5.6-5.7 at zero
temperature. It is also shown that critical lines disappear in the deconfined
phase for the case of finite temperatures.Comment: 11 pages, Latex, 7 Postscript figures, uses epsf.st
Non-perturbative renormalization factors of bilinear quark operators for Kogut-Susskind fermions and light quark masses in quenched QCD
Light quark masses are computed for Kogut-Susskind fermions by evaluating
non-perturbatively the renormalization factor for bilinear quark operators.
Calculations are carried out in the quenched approximation at \beta=6.0, 6.2,
and 6.4. For the average up and down quark mass we find in the continuum limit, which is significantly larger than
() or () obtained with the
one-loop perturbative renormalization factor.Comment: LATTICE98(matrixelement), 3 pages, 4 eps figure
Form Factors with NRQCD Heavy Quark and Clover Light Quark Actions
We report results on semileptonic decay form factors
near using NRQCD heavy quark and clover light quark actions and
currents improved through . An inconsistency with the soft pion
relation found in a previous work is
confirmed, and a possible solution with nonperturbative renormalization is
discussed. We find that is well described by the pole near
, and its scaling is also consistent with the prediction
of the pole dominance model.Comment: LATTICE99, 3 pages, 3 figure
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