• Geophysics and Geophysical Exploration
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• v.11 no.2
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• pp.99-108
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• 2008

To extend our detailed knowledge for the Hwasan caldera, we carried out magnetotelluric (MT) survey, which is pretty sensitive to electrical property variation in both horizontal and vertical direction of subsurface, across the Hwasan caldera with the direction of EW. The 2-D inversion results of observed MT data lead to following conclusions. Firstly, the depth of the basin basement inferred by the MT inversion results matches well with that suggested by previous potential studies, but the basement resistivity seems fairly low when compared to that of general case. This feature might be related with the large-scaled, highly conductive layer beneath the Euisung Sub-basin suggested by the previous MT study. Secondly, the high resistivity zones reaching to 4000 $\Omega{\cdot}m$ are imaged around two external ring fault boundaries. These zones are thought of as the response of the rhyolitic dykes intruding along the ring fault, and in the previous gravity data correspond to relatively high density anomalies. Thirdly, low resistivity zone reaching to 200 $\Omega{\cdot}m$ is detected around a depth of 1km beneath the central part of the caldera, which has not been yet reported in korean geophysical literatures. If we take account of the evolution model of the Hwasan caldera, this zone is regarded as the past sedimentary layer that subsided during the period of forming external ring fault system. In addition, the relatively low density anomaly observed in the central part of the caldera may be attributed to this sedimentary layer.

• Geophysics and Geophysical Exploration
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• v.21 no.3
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• pp.150-161
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• 2018

Recently, unmanned aircraft EM (electromagnetic) survey based on ICT (Information and Communication Technology) has been widely utilized because of the efficiency in regional survey. We performed the theoretical study on the unmanned airship EM system developed by KIGAM (Korea Institute of Geoscience and Mineral resources) as part of the practical application of unmanned aircraft EM survey. Since this system has different configurations of transmitting and receiving loops compared to the conventional aircraft EM systems, a new technique is required for the appropriate interpretation of measured responses. Therefore, we proposed a method to calculate the EM field for the arbitrary shaped transmitter and verified its validity through the comparison with analytic solution for circular loop. In addition, to simulate the magnetic responses by three-dimensionally (3D) distributed anomalies, we have adapted our algorithm to 3D frequency-domain EM modeling algorithm based on the edge-FEM (finite element method). Though the analysis on magnetic field responses from a subsurface anomaly, it was found that the response decreases as the depth of the anomaly increases or the flight altitude increases. Also, it was confirmed that the response became smaller as the resistivity of the anomaly increases. However, a nonlinear trend of the out-of-phase component is shown depending on the depth of the anomaly and the used frequency, that makes it difficult to apply simple analysis based on the mapping of the magnitude of the responses and can cause the non-uniqueness problem in calculating the apparent resistivity. Thus, it is a prerequisite to analyze the appropriate frequency band and flight altitude considering the purpose of the survey and the site conditions when conducting a survey using the unmanned aircraft EM system.

• Management & Information Systems Review
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• v.30 no.4
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• pp.147-173
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• 2011

It is generally accepted that there are momentum effects in the short term and reversal effects in the long term, which makes abnormal excess returns in the major stock markets in the world. In Korea stock market, however, the previous studies demonstrate that contrarian strategies based on reversal effects are more effective than momentum strategies following momentum effects in the short term as well as in the long term. This paper examines wether contrarian strategies are still effective In Korea stock market from 1980 to 2009, and the short term reversals may be changed after the foreign exchange crisis in 1997-1998. Moreover, this paper investigates how contrarian profits are shown considering the state of market. In my research, unlike previous studies, I find that both of contrarian strategies using price change and price level cannot gain excess risk adjusted returns in Korea stock market from 1980 to 2009, but this result is due to the fact that reversal effects existed before the foreign exchange crisis but momentum effects does after the foreign exchange crisis in 1997-1998. Specially, after the foreign exchange crisis, it is confirmed momentum strategies using 52 week high price, that is, price level are more effective than momentum strategies using price change. And following the strategies using 52 week high price after the foreign exchange crisis, the momentum is not only observed in the up market but also in the down market, which is different with the results of the studies regarding to American market, where the momentum is just found in the up market.

• The Journal of the Petrological Society of Korea
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• v.18 no.1
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• pp.31-47
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• 2009

We performed petrological, geochemical, and geochronological study for the Pyeonghae granite gneiss and the Hada leuco-granite gneiss intruding the Paleoproterozoic meta-sedimentary rocks (pyeonghae formation and Wonnam formation) of the Pyeonghae area located in northeastem part of the Yeongnam (Sobaeksan) massif. The Pyeonghae granite gneiss generally has higher abundance of mafic minerals (biotite etc.), and posesses higher ${Fe_2}{O_3}^t$, MgO, CaO, $TiO_2$, $P_{2}O_{5}$ contents but lower $SiO_2$ and $K_{2}O$ contents than the Hada leuco-granite gneiss which tends to have slightly high $Al_{2}O_{3}$ and $Na_{2}O$ contents and slightly high larger negative Eu anomalies. However both gneisses reveal very similar REE concentrations and chondrite-normalized patterns and apparently show differentiation trend affected by crystallization of biotite, plagioclase, apatite and sphene. Their peraluminous and calc-alkaline chemistry suggests tectonic environment of volcanic arc. SHRIMP Zircon U-Pb age determinations yield upper intercept ages of $1990{\pm}23\;Ma$ ($2{\sigma}$) and $1939{\pm}41\;Ma$ ($2{\sigma}$), and weighted mean $^{207}Pb/^{206}Pb$ ages of $1982{\pm}6.3\;Ma$ ($2{\sigma}$) and $1959{\pm}28\;Ma$ ($2{\sigma}$) for the Pyeonghae granite gneiss and the Hada leuco-granite gneiss respectively, showing overlapping ages within the error. Our study suggests that the Precambrian granitoids in this area intruded contemporaneously with the Buncheon granite gneissin volcanic arc environment.

• Journal of radiological science and technology
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• v.32 no.4
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• pp.419-426
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• 2009

Purpose : The aim of this study was to evaluate the difference of bone mineral density according to distal radius rotation and to develop the supporting tool to measure rotation angles. Materials and Methods : CT scanning and the measurement of BMD by DXA of the appropriate position of the forearm were performed on 20 males. Twenty healthy volunteers without any history of operations, anomalies, or trauma were enrolled. The CT scan was used to evaluate the cross sectional structure and the rotation angle on the horizontal plane of the distal radius. The rotational angle was measured by the m-view program on the PACS monitor. The DXA was used in 20 dried radii of cadaveric specimens in pronation and supination with five and ten degrees, respectively, including a neutral position (zero degrees) to evaluate the changes of BMD according to the rotation. Results : The mean rotation angle of the distal radius on CT was 7.4 degrees of supination in 16 cases (80%), 3.3 degrees of pronation in three cases (15%), and zero degree of neutral in one case (9%), respectively. The total average rotation angle in 20 people was 5.4 degrees of supination. In the cadaveric study, the BMD of the distal radius was different according to the rotational angles. The lowest BMD was obtained at 3.3 degrees of supination. Conclusion : In the case of the measurement of BMD in the distal radius with a neutral position, the rotational angle of the distal radius is close to supination. Pronation is needed for the constant measurement of BMD in the distal radius with the rotation angle measuring at the lowest BMD and about five degrees of pronation of the distal radius is recommended.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.7
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• pp.881-897
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• 2019

We reconstructed and digitized the National Institute of Fisheries Science (NIFS) Serial Oceanographic observations (NSO) and Coastal Oceanographic observations (NCO) data attained prior to 1961 through historical oceanographic observation data rescue projects. Increasing trends of long-term sea surface temperature (SST) were shown from the NSO data of 21 available stations for the past 80 to 92 years. In general agreement with previous research results used in the data of the past 50 years, we calculated the rate of temperature rise. As a result of analyzing the spatial distribution of SST change rate in the Korean of shore region using selected oceanographic data, the West Sea and South Sea showed a higher tendency of temperature rise in the offshore area than in the coastal area. However, unlike the results of previous studies, the East Sea (Gangwon Line and Ulsan Line) showed a lower water temperature rise than the coastal stations. Annual fluctuations of NCO's SST data from 1989 to 1998 for three stations representing the East Sea, South Sea, and West Sea, (Jumunjin, Geomundo and Budo, respectively) revealed that the East Sea showed the highest SST increase for the 10 years. The increases were 1.63 ℃ at Jumunjin, 1.16 ℃ at Geomundo, and 0.79 ℃ at Budo. As a result of the investigation, it can be concluded that SST is repeatedly rising and falling with a period of 3 ~ 6 years. Especially, since the 1980s, most of the stations show positive anomalies of SST. Lastly, to understand ocean_atmosphere interactions, we analyzed the correlations between SST of the NCO stations and air temperature around them and the results were 0.76 for the South Sea (Geomundo), 0.34 for the West Sea (Budo), and 0.32 for the East Sea (Jumunjin) with the highest correlation in the South Sea.

• Journal of Chest Surgery
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• v.39 no.4 s.261
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• pp.275-280
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• 2006

Background: Aortopulmonary window (APW) is a very rare congenital heart anomaly, often associated with other cardiac anomalies. It causes a significant systemic to pulmonary artery shunt, which requires early surgical correction. Accurate diagnosis and surgical correction will bring good outcomes. The purpose of this study was to describe our 20-year experience of aortopulmonary window. Material and Method: Between March 1985 and January 2005, 16 patients with APW underwent surgical repair. Mean age at operation was $157.8{\pm}245.3$ ($15.0{\sim}994.0$) days and mean weight was $4.8{\pm}2.5$ ($1.7{\sim}10.7$) kg. Patent ductus arteriosus (8), atrial septal defect (7), interruptedaortic arch (5), ventricular septal defect (4), patent foramen ovate (3), tricuspid valve regurgitation (3), mitral valve regurgitation (2), aortic valve regurgitation (1), coarctation of aorta (1), left superior vena cavae (1), and dextrocardia (1) were associated. Repair methods included 1) division of the APW with primary closure or patch closure of aorta and pulmonary artery primary closure or patch closure (11) and 2) intra-arterial patch closure (3). 3) Division of the window and descending aorta to APW anastomosis (2) in the patients with interrupted aortic arch or coarctation. Result: There was one death. The patient had 2.5 cm long severe tracheal stenosis from carina with tracheal bronchus supplying right upper lobe. The patient died at 5th post operative day due to massive tracheal bleeding. Patients with complex aortopulmonary window had longer intensive care unit and hospital stay and showed more morbidities and higher reoperation rates. 5 patients had reoperations due to left pulmonary artery stenosis (4), right pulmonary artery stenosis (2), and main pulmonary artery stenosis (1). The mean follow-up period was $6.8{\pm}5.6$ (57.0 days$\sim$16.7 years)years and all patients belonged to NYHA class 1. Conclusion: With early and prompt correction of APW, excellent surgical outcome can be expected. However, optimal surgical method needs to be established to decrease the rate of stenosis of pulmonary arteries.

• Journal of Chest Surgery
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• v.42 no.6
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• pp.749-756
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• 2009

Background: Vascular ring is a rare anomaly of the aortic arch. We did surgical repair procedures on 16 cases of vascular ring over the past 12 years. This article reviews our results. Material and Method: Between 1995 and 2007, 16 patients (5 with double aortic arch, 7 with right aortic arch-left ligamentum, 4 with pulmonary artery sling) underwent surgical repair. Mean age at the time of the operation were as follows: double aortic arch, $5.7{\pm}5.5$ years; right aortic arch-left ligamentum, $6.1{\pm}13.4$ years; pulmonary artery sling, $2.9{\pm}2.6$ years. Five patients (71%) with right aortic arch-left ligamentum had an associated Kommerell's diverticulum. Two patients (40%) with double aortic arch, 2 patients (28.6%) with right aortic arch-left ligament and 4 patients (100%) with pulmonary artery sling had associated airway stenosis. Cardiac anomalies were present in 8 of 16 patients. Result: There was no peri-operative or post-operative mortality. The mean hospital stay was $27.1{\pm}38.2$ days. None of our patients underwent reoperation. Conclusion: Vascular ring is rare, but, it needs surgical correction. It is important to suspect the diagnosis and to validate with echocardiography. Preoperative and postoperative computed tomography and bronchoscopy are useful to evaluate the airway and surrounding structures.

• Journal of Chest Surgery
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• v.40 no.2 s.271
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• pp.83-89
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• 2007

Background: The surgical repair of an isolated coarctation of the aorta, without complex cardiac anomalies, has improved, with very good results. However, despite the success of surgical repair, many long-term complications, such as hypertension, re-coarctation and an aortic aneurysm, still exist. Material and Method: Between 1991 and 2006, 50 patients diagnosed with an isolated coarctation of the aorta were reviewed retrospectively. The incidence of re-coarctation and hypertension were compared with respect to age and surgical methods. Result: There were no early & late mortality, or post operative aortic aneurysms. Hypertension developed in 11 patients (22%). A greater number of patients in the child/adult group had hypertension (52.4%) than in the neonate/infant group (0%). With respect to the surgical methods, the patients in the graft interposition group suffered more hypertension (88.9%) than those in the EEEA (extended end to end anastomosis) group (5.3%). Post operative re-coarctation developed in 2 out of the 29 patients (6.9%) in the neonate/infant group and 2 out of the 21 patients (9.5%) in the child/adult group, but without any statistical difference. There were no statistical differences between the operative type-related groups. Conclusion: Even though the surgical outcomes have greatly improved, an isolated coarctation of the aorta still has many long-term problems, such as hypertension and re-coarctation. An isolated coarctation is accepted as a systemic vascular dysfunction, and often progresses to other cardiovascular diseases. Therefore, patients with a coarctation of the aorta have to be carefully followed-up, and aggressive management must be given when required.

• Childhood Kidney Diseases
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• v.10 no.1
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• pp.27-32
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• 2006

Purpose : Conservative management of multicystic dysplastic kidney(MCDK) without nephrectomy has recently been advocated. The purpose of this study was to determine the clinical course of conservatively managed MCDK and to find out possible predictive factors for involution of MCDK by ultrasonography(US). Methods : A retrospective analysis was made on 45 patients(26 boys and 20 girls) in whom MCDK was detected and had been traced by US between Dec. 1993 and Aug. 2005 at Severance Hospital. Results : Median follow-up time was 30 months(range 2-102 months). All patients under-went radionuclide scans and voiding eystourethrograms. The serial follow-up US showed complete involution in 11(24%), partial involution in 19(41%), and no interval change or increased in cyst size in 13(28%) patients. Nephrectomy was done in 3 patients(7%) due to relapsing urinary tract infection(UTI) and severe abdominal distension. The mean age of complete involution of MCDK was 37 months(range 12-84 months). Episodes of UTI were present in 17 patients(37%) and additional genitourinary(GU) abnormalities were found in 22 patients(44%). Hypertension and renal insufficiency was complicated in one patient. No child developed malignant tumor. Univariate analysis showed that five variables were associated with complete involution of the MCDK; gender, site, UTI episode, additional GU abnormalities, and renal length on initial US. After adjusting using the Pearson model, the presence of additional GU abnormalities was exclusively associated with complete involution among the 5 variables(P=0.034). Conclusion : In our review of 46 cases of MCDK, non-surgical approach for patients with MCDK was advisable and we could predict poor prognosis when MCDK is associated with other GU anomalies.