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The YSTAR program is a general sky survey looking for variability. The main equipments are three 0.5-m telescopes. These telescopes have fast F/2 optics covering nearly 3.5 square degree field onto a 2K CCD. They also have very fast slew capability, which exceeds 10 degrees per second. These two factors make them most suitable for rapid target acquisition and wide-field surveys of various kinds. Our primary objective is to identify and monitor variable stars down to 18th R-magnitude, and our observing mode allows the same data set to be also useful in identifying asteroids. Our first telescope has just begun regular automated operation, and the second telescope will be installed in South Africa within this year to provide coverage of the southern sky.
In 2000, Korea Astronomy Observatory launched the Near-Earth Object Patrol (NEOPAT) program. NEOPAT has conducted follow-up observations of NEOCP (NEO Confirmation Page) objects and discovered 52 new main-belt asteroids during the observation runs. We initiated collaboration with the Yonsei Survey Telescopes for Astronomical Research (YSTAR) team for NEO search. Wide-field of view, fast read-out time, and fully autonomous data pipeline will enable us to detect and track NEOs with a high efficiency. Scheduled to begin active operations in mid-2001, our survey system is going to be the first network of robotic telescopes for NEO search with automatic access to both hemispheres.
Abstract:GaN thin films on sapphire were grown by RF magnetron sputtering with ZnO buffer layer. The tremendous mismatch between the lattices of GaN and sapphire can be partly overcome by the use of thin buffer layer of ZnO. The dependence of GaN film quality on ZnO buffer layer was investigated by X-ray diffraction(XRD). The properties of the sputtered GaN are strongly dependent on ZnO buffer layer thickness. The optimum thickness of ZnO buffer layer is around 30nm. Using XRD analysis, we have found the optimal substrate temperature which can grow high quality GaN thin film. In addition, the effect of excimer laser annealing(ELA) on structural and electrical properties of GaN thin films was investigated. The surface roughness and images according to the laser energy density were investigated by atomic force microscopy(AFM) and it was confirmed that the crystallization was improved by increasing laser energy density.
Pt thin films were deposited by a DC magnetron sputtering with Ar/O2 gas mixtures. Due to the oxygen incorporation into the Pt films, deposition rate and resistivity of as-deposited Pt thin films increased with oxygen fraction in the sputtering gas. No peaks from crystalline Pt oxides were observed by x-ray diffraction (XRD) and excessive oxygen incorporation into Pt lead to an amorphous Pt oxide formation. More oxygen could be incorporated in the Pt thin films deposited at lower temperatures and at higher total pressures. Incorporated oxygen was completely removed after an annealing at 800 °C for an hour in air ambient, as the resistivity of the Pt thin films recovered their bulk resistivity values. Tensile stress of the Pt films decreased with oxygen incorporation, and approached a saturation level at high resistivity of the films, presumably due to the formation of amorphous Pt oxides.
III-nitride films were grown on the corrugated interface substrate using a metalorganic chemical vapor deposition system to increase the optical power of white LEDs. The patterning of a substrate for enhancing the extraction efficiency was processed using an inductively coupled plasma reactive ion etching system and the surface morphology of the etched sapphire wafer and that of the non-etched one were investigated using an atomic force microscope. The structural and optical properties of GaN on CIS were characterized by a high-resolution x-ray diffraction, transmission electron microscopy, AFM and photoluminescence. The roughness of the etched sapphire wafer was higher than that of the non-etched one. The GaN layer didn't grow locally over the surface of the cone shape pattern. The reason is that (0001) c-plane which is favor for GaN growth doesn't exist on the cone shape patterned region. The lateral growth of the GaN layer that was initially grown on the (0001) c-plane among pattern regions, was enhanced by raising the growth temperature and lowering the reactor pressure, resulting in the smooth surface over the pattern region. The (102) FWHM of GaN layer on the patterned substrate was better than that of GaN on the conventional substrate and no defect was detected at the interface of the cone shape pattern. The optical power of the LED on the patterned substrate was 20% higher than that on the conventional substrate due to the increased extraction efficiency.
Although electrical pacing is of great utility in many cardiovascular diseases, its effects on the combined cardiac cell therapy have not been established. We hypothesised that mesenchymal stem cell transplantation changes cardiac sympathetic nerve and gap junction, and concomitant pacing has additional biological effects.
We monitored cardiac rhythm for 4 weeks after human mesenchymal stem cell transplantation (1 × 107, epicardial injection) in 18 dogs in vivo, seven human mesenchymal stem cell with pacing, six human mesenchymal stem cell, and five sham, and evaluated the sympathetic innervation, nerve growth factor-β; tyrosine hydroxylase, angiogenesis, von Willebrand factor, and connexin43 expressions by real time (RT)–polymerase chain reaction and immunostaining. We also measured mRNA expressions of nerve growth factor-β, von Willebrand factor, and connexin43 in vitro culture of human mesenchymal stem cell with or without pacing.
Human mesenchymal stem cell transplanted hearts expressed higher mRNA of nerve growth factor-β (p < 0.01) with sympathetic nerves (p < 0.05), higher mRNA of von Willebrand factor (p < 0.001) with angiogenesis (p < 0.001), but lower mRNA of connexin43 (p < 0.0001) with reduced gap junctions (p < 0.001) than sham. Pacing with human mesenchymal stem cell transplantation resulted in higher expression of mRNA of connexin43 (p < 0.02) and gap junctions (p < 0.001) compared with sham. In contrast, in vitro paced mesenchymal stem cell reduced expression of connexin43 mRNA (p < 0.02).
Human mesenchymal stem cell transplantation increased cardiac sympathetic innervation and angiogenesis, but reduced gap junction after transplanted in the canine heart. In contrast, concomitant electrical pacing increased gap junction expression by paracrine action.
Perimesencephalic subarachnoid hemorrhage (PSH) is a relatively benign clinical entity with a low risk of recurrent bleeding. The precise etiology of PSH has not yet been determined. We report here three cases of PSH with clinical and radiological features that support a venous system as a cause.
The first patient, a 72-year-old woman, had PSH and venous hemorrhagic infarct in the left thalamus on non-contrast CT. Subsequent cerebral angiography revealed widespread thrombosis in the cerebral venous system, a potential cause for reflux overflow hemorrhage. The second patient, a 55-year-old man with an established diagnosis of neuro-Behçet's disease, a well-known cause for cerebral venulitis, presented with PSH one year later. The third patient, a 39-year-old female, with incomplete Behçet's disease was admitted with PSH.
Current concepts on the anatomic origin and the possible pathophysiologic mechanism leading to PSH are discussed. The underlying pathological conditions in the venous system in our cases provide theoretical clues to the anatomic origin of PSH in general.
The purpose of the present study was to characterize the Ca2+ channels in smooth
muscle cells from human stomach and to examine the effects of osmotic swelling on
the channel activity. Ca2+ channel current with either Ca2+ or Ba2+ as charge carrier
was recorded from freshly isolated smooth muscle cells using the conventional
whole-cell patch clamp technique. The degree of cell swelling as a result of hypotonic
challenge was monitored using a video image analysis system. The changes in
intracellular Ca2+ concentration ([Ca2+]i) were measured by microfluorimetry. The
pharmacological and voltage activation profile suggests a typical
dihydropyridine-sensitive L-type Ca2+ current. Cell swelling, induced by hypotonic
challenge, enhanced the amplitude of currents through L-type Ca2+ channels without
significant effects on steady-state voltage dependency. After treatment with the
L-type Ca2+ channel agonist Bay K 8644 (0.1-2 µM), no further significant increase in
calcium channel current or corresponding [Ca2+]i transients were provoked by the
swelling. The above results demonstrated that the presence of L-type Ca2+ current in
smooth muscle cells of the human stomach and the augmentation of the current are
closely associated with the volume increase resulting from hypotonic swelling.
Experimental Physiology (2000) 85.5, 497-504.
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