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Minho Lee,Yurim Jeong,Man-Young Choi,Mun-Il Ryoo 한국응용곤충학회 2010 한국응용곤충학회 학술대회논문집 Vol.2010 No.05
In many cases over the years, we failed to forecast accurately outbreak of Rice stripe virus (RSV) disease using population density of overwintering small brown planthopper (SBPH), Laodelphax striatellus. What is the source of error in this viral disease assessment? For answering the question, spatial distribution of RSV in paddy fields was investigated in relation to the yield of rice grain, and the population density of overwintering SBPH in ridge of paddy fields. Total 14 paddy fields in 5 regions were surveyed in June, 2008. Disease assessment was carried out with each of 30 rice plants in the one of the borders, 5th, 10th line from ridge, and 90 rice plants in diagonal line for conventional method. The ears of rices from 18 plants in the same surveyed line were collected in the late of August for the weights of 100 rice grains. The infection rate of RSV was decreased by the distance from ridge; on the contrary, the increase tendency was shown in the yield of rice grains in the middle of paddy field. It is suggested that the border effect of viral distribution between ridge and paddy field is caused by the spatial distribution of the vector insect. Thus, in this case, the narrow border effect could represent that the SBPH migrated short distance from the ridge to paddy field. The conventional method, observing the disease in middle area of diagonal line, showed no correlation to the population density of overwintering vector generation in ridge. It might cause underestimation of the regional disease rate. The counting of RSV-diseased plant in border line only overestimated it also. However, the RSV infection rate in the near border had highly positive linear relationship (R2=0.91) to the regional average values by regression analysis. Therefore, the near border sampling method can improve the RSV disease risk assessment.
ROTATION OF THE NGC 1333 IRAS 4A2 PROTOSTELLAR JET
Choi, Minho,Kang, Miju,Tatematsu, Ken'ichi IOP Publishing 2011 ASTROPHYSICAL JOURNAL LETTERS - Vol.728 No.2
<P>The bipolar jet of the NGC 1333 IRAS 4A2 protostar shows a velocity gradient in the direction perpendicular to the jet axis. This lateral velocity gradient can be seen throughout the jet imaged in a silicon monoxide line, 2500-8700 AU from the driving source, and is consistent with the rotation of the accretion disk. If this gradient is caused by the rotation of the jet around its axis, the average specific angular momentum is about 1.5 x 10(21) cm(2) s(-1). Comparison of the kinematics between the jet and the disk suggests that the jet-launching region on the disk has a radius of about 2 AU, which supports the disk-wind models. The angular momentum transported away by the jet seems to be large enough for the protostar to accrete matter from the disk, confirming the crucial role of jets in the early phase of the star formation process.</P>
Imaging the Dense Core Obstructing the NGC 1333 IRAS 4A Outflow
Minho Choi 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.2
The NGC 1333 IRAS 4A region was imaged in the HCO+ and HCN J = 1 ! 0 lines by combining the data previously obtained from single-dish observations and from interferometric observations. Visibility data were generated from the single-dish maps and combined with the interferometric data in the visibility domain. The resulting combined data were used to produce synthesized maps. These maps reveal the cloud structure with an angular resolution (≫900) higher than that of the single-dish maps while recovering the °ux resolved out by the interferometer. At VLSR = 6 km s¡1, the HCO+ and HCN maps show the IRAS 4 dense core and other extended structures to the west. At 8 km s¡1, the maps show a very extended cloud complex with a dense core located just north of the bending point of the northeastern out°ow driven by the protostar IRAS 4A. The relative location suggests that the IRAS 4A out°ow is making a nearly head-on collision with the core, and the morphology and the density of the bstructing core is consistent with predictions of jet-core collision models. The obstructing core is probably part of the large cloud associated with the HH 7 - 11 complex.0
WATER AND METHANOL MASER ACTIVITIES IN THE NGC 2024 FIR 6 REGION
Choi, Minho,Kang, Miju,Byun, Do-Young,Lee, Jeong-Eun IOP Publishing 2012 The Astrophysical journal Vol.759 No.2
<P>The NGC 2024 FIR 6 region was observed in the water maser line at 22 GHz and the methanol class I maser lines at 44, 95, and 133 GHz. The water maser spectra displayed several velocity components and month-scale time variabilities. Most of the velocity components may be associated with FIR 6n, while one component was associated with FIR 4. A typical lifetime of the water maser velocity components is about eight months. The components showed velocity fluctuations with a typical drift rate of about 0.01 km s(-1) day(-1). The methanol class I masers were detected toward FIR 6. The methanol emission is confined within a narrow range around the systemic velocity of the FIR 6 cloud core. The methanol masers suggest the existence of shocks driven by either the expanding H II region of FIR 6c or the outflow of FIR 6n.</P>