179 research outputs found
A Binary Shaped Mask Coronagraph for a Segmented Pupil
We present the concept of a binary shaped mask coronagraph applicable to a
telescope pupil including obscuration, based on previous works on binary shaped
pupil mask by \citet{Kasdin2005} and \citet{Vanderbei1999}. Solutions with
multi-barcode masks which "skip over" the obscuration are shown for various
types of pupil of telescope, such as SUBARU, JWST, SPICA, and other examples.
The number of diffraction tails in the point spread function of the
coronagraphic image is reduced to two, thus offering a large discovery angle.
The concept of mask rotation is also presented, which allows post-processing
removal of diffraction tails and provides a 360 continuous discovery
angle. It is suggested that the presented concept offers solutions which
potentially allow large telescopes with segmented pupil in future to be used as
platforms for an coronagraph.Comment: 12 pages, 4 figure
High contrast experiment of an AO-free coronagraph with a checkerboard pupil mask
A high contrast coronagraph is expected to provide one of the promising ways
to directly observe extra-solar planets. We present the newest results of our
laboratory experiment investigating "rigid" coronagraph with a binary shaped
checkerboard pupil mask, which should offer a highly stable solution for
telescopes without adaptive optics (AO) for wavefront correction in space
missions. The primary aim of this work was to study the stability of the
coronagraph, and to demonstrate its performance without adaptive wavefront
correction. Estimation of both the raw contrast and the gain of the point
spread function (PSF) subtraction were needed. The limiting factor of the
contrast was also important. A binary shaped pupil mask of a checkerboard type
has been designed. The mask, consisting of an aluminum film on a glass
substrate, was manufactured using nano-fabrication techniques with electron
beam lithography. Careful evaluation of coronagraphic performance, including
PSF subtraction, was carried out in air using the developed mask. A contrast of
was achieved for the raw coronagraphic image by areal
averaging of all of the observed dark regions. Following PSF subtraction, the
contrast reached . Speckles were a major limiting factor
throughout the dark regions of both the raw image and the PSF subtracted image.
A rigid coronagraph with PSF subtraction without AO is a useful method to
achieve high contrast observations. Applications of a rigid coronagraph to a
Space Infrared telescope for Cosmology and Astrophysics (SPICA) and other
platforms are discussed.Comment: 13 pages, 6 figure
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
Laboratory Experiment of Checkerboard Pupil Mask Coronagraph
We present the results of the first laboratory experiment of checkerboard
shaped pupil binary mask coronagraphs using visible light, in the context of
the R&D activities for future mid-infrared space missions such as the 3.5 m
SPICA telescope. The primary aim of this work is to demonstrate the
coronagraphic performance of checkerboard masks down to a
peak-to-peak contrast, which is required to detect self-luminous extra-solar
planets in the mid-infrared region. Two masks, consisting of aluminum films on
a glass substrates, were manufactured using nano-fabrication techniques with
electron beam lithography: one mask was optimized for a pupil with a 30%
central obstruction and the other was for a pupil without obstruction. The
theoretical contrast for both masks was and no adaptive optics system
was employed. For both masks, the observed point spread functions were quite
consistent with the theoretical ones. The average contrast measured within the
dark regions was and . The
coronagraphic performance significantly outperformed the requirement
and almost reached the theoretical limit determined by the mask designs. We
discuss the potential application of checkerboard masks for mid-infrared
coronagraphy, and conclude that binary masks are promising for future
high-contrast space telescopes.Comment: 6 pages, 6 figure
A high dynamic-range instrument for SPICA for coronagraphic observation of exoplanets and monitoring of transiting exoplanets
This paper, first, presents introductory reviews of the Space Infrared
Telescope for Cosmology and Astrophysics (SPICA) mission and the SPICA
Coronagraph Instrument (SCI). SPICA will realize a 3m class telescope cooled to
6K in orbit. The launch of SPICA is planned to take place in FY2018. The SPICA
mission provides us with a unique opportunity to make high dynamic-range
observations because of its large telescope aperture, high stability, and the
capability for making infrared observations from deep space. The SCI is a high
dynamic-range instrument proposed for SPICA. The primary objectives for the SCI
are the direct coronagraphic detection and spectroscopy of Jovian exoplanets in
the infrared region, while the monitoring of transiting planets is another
important target owing to the non-coronagraphic mode of the SCI. Then, recent
technical progress and ideas in conceptual studies are presented, which can
potentially enhance the performance of the instrument: the designs of an
integral 1-dimensional binary-shaped pupil mask coronagraph with general
darkness constraints, a concentric ring mask considering the obscured pupil for
surveying a wide field, and a spectral disperser for simultaneous wide
wavelength coverage, and the first results of tests of the toughness of MEMS
deformable mirrors for the rocket launch are introduced, together with a
description of a passive wavefront correction mirror using no actuator.Comment: 15 pages, 10 figures, 2 table
Potential of an Asymmetrical Agitation in Industrial Mixing
Mixing is one of the most fundamental operations in chemical engineering. Stirred tanks are widely used in the manufacture of such materials as chemicals, paints, inks, electronics materials, ceramics, foods, pharmaceuticals and cosmetics. Suitable mixing is indispensable to the purpose achievement of a process. Eccentric mixing, in which an impeller installed at eccentric position in a vessel, is one of the traditional methods of promoting mixing. An asymmetrical flow which occurs in vessel is complicated, and it promotes mixing, distribution, and mass transfer. In this study, a new mixing method which eccentric mixing using a large type impeller which attracts attention in recent years is shown. The high performance of a large impeller can be combined with the advantages of an eccentric impeller by using the impeller at an eccentric position. The power consumption and mixing time for MAXBLEND, which is a type of large impeller, were investigated. The power consumption, P, and mixing time, θM, were measured under various eccentric conditions. The relation between the power number (Np) and Reynolds number (Re) and that between the dimensionless mixing time (nθM) and Re were investigated. When eccentric mixing is used industrially, we should be concerned about the horizontal load to a agitating shaft. The large oscillating horizontal load causes serious problems, such as the falling off of the impeller or the breakage of the motor, mechanical seal or gearbox. It is, therefore, important to understand the relation between these values and the impeller rotational speed when designing the mixing equipment and determining the operating conditions. In this study, the torque and horizontal load were measured in eccentric mixing under various eccentric conditions. The averages of both, the torque and the horizontal load, and their standard deviations, corresponding to the amplitude of fluctuation, were shown.Doi: 10.12777/ijse.5.2.73-80 [How to cite this article: Nishi, K., Enya, N., Sonoda, K., Misumi, R., Kaminoyama, M. (2013). Potential of an asymmetrical agitation in industrial mixing. International Journal of Science and Engineering, 5(2),73-80. Doi: 10.12777/ijse.5.2.73-80
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
Design, analysis and test of a microdots apodizer for the Apodized Pupil Lyot Coronagraph
Coronagraphic techniques are required to detect exoplanets with future
Extremely Large Telescopes. One concept, the Apodized Pupil Lyot Coronagraph
(APLC), is combining an apodizer in the entrance aperture and a Lyot opaque
mask in the focal plane. This paper presents the manufacturing and tests of a
microdots apodizer optimized for the near IR.
The intent of this work is to demonstrate the feasibility and performance of
binary apodizers for the APLC. This study is also relevant for any coronagraph
using amplitude pupil apodization.
A binary apodizer has been designed using a halftone dot process, where the
binary array of pixels with either 0% or 100% transmission is calculated to fit
the required continuous transmission, i.e. local transmission control is
obtained by varying the relative density of the opaque and transparent pixels.
An error diffusion algorithm was used to optimize the distribution of pixels
that best approximates the required field transmission. The prototype was
tested with a coronagraphic setup in the near IR.
The transmission profile of the prototype agrees with the theoretical shape
within 3% and is achromatic. The observed apodized and coronagraphic images are
consistent with theory. However, binary apodizers introduce high frequency
noise that is a function of the pixel size. Numerical simulations were used to
specify pixel size in order to minimize this effect, and validated by
experiment.
This paper demonstrates that binary apodizers are well suited for being used
in high contrast imaging coronagraphs. The correct choice of pixel size is
important and must be adressed considering the scientific field of view.Comment: A&A accepted, 8 page
The SPICA coronagraphic instrument (SCI) for the study of exoplanets
We present the SPICA Coronagraphic Instrument (SCI), which has been designed
for a concentrated study of extra-solar planets (exoplanets). SPICA mission
provides us with a unique opportunity to make high contrast observations
because of its large telescope aperture, the simple pupil shape, and the
capability for making infrared observations from space. The primary objectives
for the SCI are the direct coronagraphic detection and spectroscopy of Jovian
exoplanets in infrared, while the monitoring of transiting planets is another
important target. The specification and an overview of the design of the
instrument are shown. In the SCI, coronagraphic and non-coronagraphic modes are
applicable for both an imaging and a spectroscopy. The core wavelength range
and the goal contrast of the coronagraphic mode are 3.5--27m, and
10, respectively. Two complemental designs of binary shaped pupil mask
coronagraph are presented. The SCI has capability of simultaneous observations
of one target using two channels, a short channel with an InSb detector and a
long wavelength channel with a Si:As detector. We also give a report on the
current progress in the development of key technologies for the SCI.Comment: 22 pages, 10 figure
Inner Size of a Dust Torus in the Seyfert 1 Galaxy NGC 4151
The most intense monitoring observations yet made were carried out on the
Seyfert 1 galaxy NGC 4151 in the optical and near-infrared wave-bands. A lag
from the optical light curve to the near-infrared light curve was measured. The
lag-time between the V and K light curves at the flux minimum in 2001 was
precisely 48+2-3 days, as determined by a cross-correlation analysis. The
correlation between the optical luminosity of an active galactic nucleus (AGN)
and the lag-time between the UV/optical and the near-infrared light curves is
presented for NGC 4151 in combination with previous lag-time measurements of
NGC 4151 and other AGNs in the literature. This correlation is interpreted as
thermal dust reverberation in an AGN, where the near-infrared emission from an
AGN is expected to be the thermal re-radiation from hot dust surrounding the
central engine at a radius where the temperature equals to that of the dust
sublimation temperature. We find that the inner radius of the dust torus in NGC
4151 is 0.04 pc corresponding to the measured lag-time, well outside
the broad line region (BLR) determined by other reverberation studies of the
emission lines.Comment: Accepted for publication in ApJ Letters, 13 pages, 3 figures;
Corrected typo
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