• Journal of Astronomy and Space Sciences
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• 제21권4호
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• pp.329-342
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• 2004

In this paper, we present preliminary feasibility studies on three types of solar observation payloads for future Korean Science and Technology Satellite (STSAT) programs. The three candidates are (1) an UV imaging telescope, (2) an UV spectrograph, and (3) an X-ray spectrometer. In the case of UV imaging telescope, the most important constraint seems to be the control stability of a satellite in order to obtain a reasonably good spatial resolution. Considering that the current pointing stability estimated from the data of the Far ultraviolet Imaging Spectrograph (FIMS) onboard the Korean STSAT-1, is around 1 arc minutes/sec, we think that it is hard to obtain a spatial resolution sufficient for scientific research by such an UV Imaging Telescope. For solar imaging missions, we realize that an image stabilization system, which is composed of a small guide telescope with limb sensor and a servo controller of secondary mirror, is quite essential for a very good pointing stability of about 0.1 arcsec. An UV spectrograph covering the solar full disk seems to be a good choice in that there is no risk due to poor pointing stability as well as that it can provide us with valuable UV spectral irradiance data valuable for studying their effects on the Earth's atmosphere and satellites. The heritage of the FIMS can be a great advantage of developing the UV spectrograph. Its main disadvantage is that two major missions are in operation or scheduled. Our preliminary investigations show that an X-ray spectrometer for the full disk Sun seems to be the best choice among the three candidates. The reasons are : (1) high temporal and spectral X-ray data are very essential for studying the acceleration process of energetic particles associated with solar flares, (2) we have a good heritage of X-ray detectors including a rocket-borne X-ray detector, (3) in the case of developing countries such as India and Czech, solar X-ray spectrometers were selected as their early stage satellite missions due to their poor pointing stabilities, and (4) there is no planned major mission after currently operating Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) mission. Finally, we present a preliminary design of a solar X-ray spectrometer covering soft X-ray (2 keV) to gamma ray (10 MeV).

• 천문학회지
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• 제36권3호
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• pp.81-87
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• 2003

It is suggested that a flying-by star in a hot accretion disk may cool the hot accretion disk by the Comptonization of the stellar emission. Such a stellar cooling can be observed in the radio frequency regime since synchrotron luminosity depends strongly on the electron temperature of the accretion flow. If a bright star orbiting around the supermassive black hole cools the hot disk, one should expect a quasi-periodic modulation in radio, or even possible an anti-correlation of luminosities in radio and X-rays. Recently, the unprecedentedly accurate infrared imaging of the Sagittarius A$\ast$ for about ten years enables us to resolve stars around it and thus determine orbital parameters of the currently closest star S2. We explore the possibility of using such kind of observation to distinguish two quite different physical models for the central engine of the Sagittarius A$\ast$, that is, a hot accretion disk model and a jet model. We have attempted to estimate the observables using the observed parameters of the star S2. The relative difference in the electron temperature is a few parts of a thousand at the epoch when the star S2 is near at the pericenter. The relative radio luminosity difference with and without the stellar cooling is also small of order $10^{-4}$, particularly even when the star S2 is near at the pericenter. On the basis of our findings we tentatively conclude that even the currently closest pass of the star S2 is insufficiently close enough to meaningfully constrain the nature of the Sagittarius A$\ast$ and distinguish two competing models. This implies that even though Bower et al. (2002)have found no periodic radio flux variations in their data set from 1981 to 1998, which is naturally expected from the presence of a hot disk, a hot disk model cannot be conclusively ruled out. This is simply because the energy bands they have studied are too high to observe the effect of the star S2 even if it indeed interacts with the hot disk. In other words, even if there is a hot accretion disk the star like S2 has imprints in the frequency range at v $\le$ 100 MHz.

• Imaging Science in Dentistry
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• 제31권4호
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• pp.185-192
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• 2001

Purpose: To evaluate the condylar movement at maximal mouth opening on MRI in patients with internal derangement. Materials and Methods: MR images and transcranial views for 102 TMJ s in 51 patients were taken in closed and maximal opening positions, and the amount of condylar movement was analyzed quantitatively and qualitatively. Results: For MR images, the mean condylar movements were 9.4 mm horizontally, 4.6 mm vertically and 10.9 mm totally, while those for transcranial views were 12.5 mm, 4.6 mm, and 13.7 mm respectively. The condyle moved forward beyond the summit of the articular eminence in 41 TMJs (40.2%) for MR images and 56 TMJs (54.9%) for transcranial views. Conclusion: The horizontal and total condylar movements were smaller in MR images than in transcranial views.

• 천문학회지
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• 제36권spc1호
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• pp.145-149
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• 2003

LIST is the Lyman-$\alpha$ Imaging Solar Telescope, a project funded by the Korean government to fly on the second Korean Science and Technology research Satellite (STSat-2) due to launch in December 2005. The Principal Investigator is Dr. Minhwan Jang of Kyung-Hee University and of the Space Payload Research Center (SPARC), a consortium of Korean universities and institutions formed to develop scientific research projects in space. The purpose of the LIST project is to design, build, and operate an instrument on STSat-2 which will make images of the Sun from Earth orbit at the wavelength of the Hydrogen Lyman-a emission line at 121.6 nm. LIST has a simple design concept comprised of a small telescope to image the full disk of the Sun onto a CCD detector and a set of filters to isolate the 121.6 nm wavelength.

• 천문학회보
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• 제38권2호
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• pp.45.2-45.2
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• 2013

We studied recent evolution of M31 and M33 with star-forming regions and hot massive stars. We use GALEX far-UV and near-UV imaging to detect the star-forming regions and trace the recent star formation across the entire disk of galaxies. The GALEX imaging, combining deep sensitivity and entire coverage of these galaxies, provides a complete picture of the recent star formation in M31 and M33, and its variation with environment throughout these galaxies. We also show results from recent extensive surveys in M31 and M33 with Hubble Space Telescope multi-wavelength data including UV filters, which imaged several regions at a linear resolution of less than half a pc in these galaxies. Both datasets allow us to study the hierarchical structure of star formation: the youngest stellar groups are the most compact, and are often arranged withing broader, sparser structures. The derived recent star-formation rates are rather similar for the two galaxies, when scaled for the respective areas.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.480-483
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• 1997

In this paper, we have proposed an automatic inspection system for cracks on the surface of a structure. The proposed system consists of the imaging system and the veh~cle system. The imaging system. a set of optical sensor, lens, illuminator, storage and their configuration, images the scene and store it on the hard disk. We adopted a linescan camera of 5000 pixel density to achieve high resolution without loss of simplicity. The vehicle system that moves the optical system IS ~mplemented by an AGV. The AGV moves forward at constant velocity and avoid obstacles to acquire a stable image. We have cmplemented an experimental system and have acquired images of the wall of hallway. The image is of 0.1-mmipixel resolution and the scanning time IS about 1 mlsec. The allow able scan.

• 천문학회보
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• 제37권2호
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• pp.69.1-69.1
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• 2012

We present a comprehensive study of star-forming regions and young star clusters in M33. We use GALEX far-UV and near-UV imaging to detect these young stellar populations tracing recent star formation across the disk of M33. The GALEX imaging, combining deep sensitivity and entire coverage of the galaxy, provides a complete view of the recent star formation in M33 and its variation with environment throughout the galaxy. We discuss variation of various properties (e.g., age, mass, spatial distribution) of star-forming regions and young star clusters in M33 which allow to provide constraints of recent star formation history of this galaxy.

• Current Optics and Photonics
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• 제6권6호
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• pp.550-564
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• 2022

Optical microscopy is a useful tool for study in the biological sciences. With an optical microscope, we can observe the micro world of life such as tissues, cells, and proteins. A fluorescent dye or a fluorescent protein provides an opportunity to mark a specific target in the crowd of biological samples, so that an image of a specific target can be observed by an optical microscope. The optical microscope, however, is constrained in resolution due to diffraction limit. Super-resolution microscopy made a breakthrough with this diffraction limit. Using a super-resolution microscope, many biomolecules are observed beyond the diffraction limit in cells. In the case of volumetric imaging, the super-resolution techniques are only applied to a limited area due to long imaging time, multiple scattering of photons, and sample-induced aberration in deep tissue. In this article, we review recent advances in super-resolution microscopy for volumetric imaging. The super-resolution techniques have been integrated with various modalities, such as a line-scan confocal microscope, a spinning disk confocal microscope, a light sheet microscope, and point spread function engineering. Super-resolution microscopy combined with adaptive optics by compensating for wave distortions is a promising method for deep tissue imaging and biomedical applications.

• 대한의용생체공학회:의공학회지
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• 제8권2호
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• pp.118-122
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• 1987

The medical image processing system is intended for a diverse set of users in the medical Imaging Parts. This system consists of a 640 Kbyte IBM-PC/AT with 30 Mbyte hard disk, special purpose image processor with video input devices and display monitor. Image may be recorded and processed in real time at sampling rate up to 10 MHz. This system provides a wide range of image enhancement processing facilities via a menu-driven software packages. These facilities include point by point processing, image averaging, convolution filter and subtraction.

• 한국가시화정보학회지
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• 제22권1호
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• pp.28-33
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• 2024

We visualized the rupturing of liquid films flowing over a disk rotating with large angular velocity. A setup of high speed imaging for liquid flows on dark and reflective surfaces are suggested. From the result, rivulet structures are revealed to be strongly governed by three-dimensional surface structures developed in the film flow. Additionally, unique flow structures including the rivulet sliding and internal meandering are investigated. Generation mechanism of such structures are discussed in terms of the dynamic contact angle theory.