• The Bulletin of The Korean Astronomical Society
• /
• v.43 no.2
• /
• pp.44.3-44.3
• /
• 2018

수성의 대기와 자기장은 매우 희박하여 그 표면이 우주 환경에 거의 그대로 노출되어있다. 표면의 토양은 태양풍입자와 미소유성체 등에 의해 계속해서 밝기가 어두워지고 입자의 크기도 작아진다. 이러한 현상을 종합적으로 '우주풍화'(space weathering)라고 부르는데, 그 정도를 정량화하거나 상대적으로 평가하는 데에는 어려움이 따른다. 왜냐하면 우주풍화의 정도에는 원인이 되는 입자의 입사 플럭스는 물론이고, 표면의 지역 조성비와 토양의 노화도 등이 모두 섞여 영향을 미치기 때문이다. 이를 극복하는 한 가지 방법은 수성 표면을 뒤덮고 있는 수많은 충돌구(impact crater) 내의 광학적 특성 분포를 통계적으로 분석하는 것이다. 충돌구 안쪽의 토양은 충돌 시점에 동시에 형성되었고, 그 성분이 충돌구 밖 임의의 지역에 비교해 상대적으로 균질하며, 지형적으로 충돌구 안팎의 경계가 분명하게 정해져 있다. 또한, 충돌구는 수성 전구(全球)에 걸쳐 어디에서나 발견되므로 각 충돌구의 특성을 경도 위도 연대 등 여러 측면에서 조사할 수 있다. 본 연구에서는, 메신저(MESSENGER) 탐사선의 MDIS 영상기에서 얻은 관측 자료를 활용하여 수성 충돌구의 광학적 특성에 대해 알아본다.

• Journal of the Korean association of regional geographers
• /
• v.22 no.3
• /
• pp.681-702
• /
• 2016

Two different modelling approaches to dune dynamics have been established thus far; continuous models that emphasize the precise representation of wind field, and feedback-based models that focus on the interactions between dunes, rather than aerodynamics. Though feedback-based models have proven their capability to capture the essence of dune dynamics, the compatibility issues on these models have less been addressed. This research investigated, mostly from the theoretical point of view, the algorithmic compatibility of three feedback-based dune models: sand slab models, Nishimori model, and de Castro model. Major findings are as follows. First, sand slab models and de Castro model are both compatible in terms of flux perspectives, whereas Nishimori model needs a tuning factor. Second, the algorithm of avalanching can be easily implemented via repetitive spatial smoothing, showing high compatibility between models. Finally, the wind shadow rule might not be a necessary component to reproduce dune patterns unlike the interpretation or assumption of previous studies. The wind shadow rule, rather, might be more important in understanding bedform-level interactions. Overall, three models show high compatibility between them, or seem to require relatively small modification, though more thorough investigation is needed.

• Geophysics and Geophysical Exploration
• /
• v.12 no.1
• /
• pp.41-48
• /
• 2009

Natural magnetic fields are attenuated by electrically conductive water. For that reason, marine magnetotelluric surveys have collected data at long periods (1000-100 000 s). The mantle structure has been the main target of seafloor magnetotelluric measurements. To ascertain crustal structure, however, electromagnetic data at shorter periods are important, e.g. in investigations of megathrust earthquake zones, or in natural resource surveys. To investigate of the former, for example, electromagnetic data for periods of less than 1000 s are necessary. Because no suitable ocean bottom electromagnetometer (OBEM) has been available, we have developed a small OBEM and ocean bottom electrometer (OBE) system with a high sample rate, which has an arm-folding mechanism to facilitate assembly and recovering operations. For magnetic observation, we used a fluxgate sensor. Field observations were undertaken to evaluate the field performance of our instruments. All instruments were recovered and their electromagnetic data were obtained. Results of the first experiment show that our system functioned well throughout operations and observations. Results of other field experiments off Tottori support the claim that the electromagnetic data obtained using the new OBEM and OBE system are of sufficient quality for the survey target. These results suggest that this device removes all instrumental obstacles to measurement of electromagnetic fields on the seafloor.

• Geophysics and Geophysical Exploration
• /
• v.27 no.2
• /
• pp.119-128
• /
• 2024

Marine magnetic surveys provide a rapid and cost-effective method for pioneer geophysical survey for many purposes. Sea-surface magnetometers offer high accuracy but are limited to measuring the scalar total magnetic field and require dedicated cruise missions. Shipboard three-component magnetometers, on the other hand, can collect vector three components and applicable to any cruise missions. However, correcting for the ship's magnetic field, particularly viscous magnetization, still remains a challenge. This study proposes a new additional correction method for ship's viscous magnetization effect in vector data acquired by shipboard three-component magnetometer. This method utilizes magnetic data collected simultaneously with a sea-surface magnetometer providing total magnetic field measurements. Our method significantly reduces deviations between the two datasets, resulting in corrected vector anomalies with errors as low as 7-25 nT. These tiny errors are possibly caused by the vector magnetic anomaly and its related viscous magnetization. This method is expected to significantly improve the accuracy of shipborne magnetic surveys by providing corrected vector components. This will enhance magnetic interpretations and might be useful for understanding plate tectonics, geological structures, hydrothermal deposits, and more.

• Korean Journal of Agricultural and Forest Meteorology
• /
• v.22 no.1
• /
• pp.26-46
• /
• 2020

An irrigated-maize agroecosystem is viewed as an open thermodynamic system upon which solar radiation impresses a large gradient that moves the system away from equilibrium. Following the imperative of the second law of thermodynamics, such agroecosystem resists and reduces the externally applied gradient by using all means of this nature-human coupled system acting together as a nonequilibrium dissipative process. The ultimate purpose of our study is to test this hypothesis by examining the energetics of agroecosystem growth and development. As a first step toward this test, we employed the eddy covariance flux data from 2003 to 2014 at the AmeriFlux NE1 irrigated-maize site at Mead, Nebraska, USA, and analyzed the energetics of this agroecosystem by scrutinizing its radiation, energy and entropy exchange. Our results showed: (1) more energy capture during growing season than non-growing season, and increasing energy capture through growing season until senescence; (2) more energy flow activity within and through the system, providing greater potential for degradation; (3) higher efficiency in terms of carbon uptake and water use through growing season until senescence; and (4) the resulting energy degradation occurred at the expense of increasing net entropy accumulation within the system as well as net entropy transfer out to the surrounding environment. Under the drought conditions in 2012, the increased entropy production within the system was accompanied by the enhanced entropy transfer out of the system, resulting in insignificant net entropy change. Drought mitigation with more frequent irrigation shifted the main route of entropy transfer from sensible to latent heat fluxes, yielding the production and carbon uptake exceeding the 12-year mean values at the cost of less efficient use of water and light.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2011.05a
• /
• pp.32.1-32.1
• /
• 2011

39 K의 임계온도를 갖는 $MgB_2$ 초전도체를 이용한 전력에너지와 MRI 의료 기기로의 응용 가능성이 높아지고 있다. $MgB_2$ 초전도체 제조에 있어서 마그네슘과 반응성이 좋은 비정질의 붕소 원료 분말 가격이 비싼 반면 상대적으로 경제적인 결정질 분말의 기계적 밀링 공정을 이용하여 비정질화와 나노 입자로의 크기 감소 효과를 얻을 수 있다. 또한 탄소를 이용한 붕소 치환으로부터 고 자기장하에서 초전도 임계 성질을 향상시키고자 유, 무기물 형태의 여러 가지 탄소 소스를 개발하는 연구가 진행되어 왔다. 본 연구에서는 저가의 95~97% 순도, 약 1 ${\mu}m$ 이하 크기를 갖는 준결정상의 붕소 분말을 이용하여 기계적 밀링에 따른 붕소 분말의 비정질화 및 입자 나노화, $MgB_2$ 반응성 향상, $MgB_2$ 결정립 크기 감소 및 결정립계 피닝 증가에 의한 초전도 임계 물성 향상에 대하여 알아보았다. 또한 여러 시간 동안 밀링된 각 붕소 분말에 액체 글리세린을 이용한 탄소 도핑 전처리를 통하여 밀링 시간의 최적화를 알아보았고 이로부터 제조된 $MgB_2$ 초전도 벌크의 경우 적절한 임계온도 감소, 격자 왜곡 결함과 높은 결정립계 밀도 등에 의한 플럭스 피닝 향상으로 $MgB_2$ 초전도체의 임계전류밀도 및 비가역자기장이 증가함을 알 수 있었다. 즉, 경제성 있는 저급의 준결정상을 갖는 붕소 원료 분말의 입자 비정질 나노화 및 탄소 도핑 전처리를 통하여 $MgB_2$ 초전도 임계 물성을 향상시킬 수 있었다.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.125.2-125.2
• /
• 2012

최근 아태지역 국제민간항공기구는 GPS의 항공이행을 위한 전리층 연구 태스크포스(Ionospheric Study Task Force, ISTF)를 결성하였다. 안전한 GPS 항공이행을 위해서는 지역적 그리고 전지구적 전리층 특성을 파악한 후 이를 기반으로 실시간 전리층 모델이 필요하다. 한국천문연구원은 ISTF의 전리층 변화 특성 분석에 관한 기술분과를 담당하고 있으며 GPS 항공이행 실시간 전리층 모델개발을 위한 아태지역 전리층 분석방법 및 표준규범을 수립하고 있다. 아태지역 전리층 연구에 앞서 우리나라 전리층 특성을 파악하고자 한국천문연구원이 1998년부터 운영 중에 있는 대전 국제 GPS 기준점으로부터 관측된 자료를 이용하여 태양 11년 주기에 해당하는 GPS TEC를 분석하였다. 또한, 해당 기간 동안 우리나라 양/음 전리층 폭풍 발생 빈도에 관한 통계분석을 실시하였다. 본 발표에서는 GPS TEC의 태양 극자외선 플럭스와 10.7 cm 태양전파와의 상관관계 차이점, 연변화 및 계절적 변화 그리고 이에 대한 시간 변화에 대해 보고한다. 또한 GPS TEC의 27일 주기 변화에 특성에 대해 토의하며, 우리나라 상공 전리층 폭풍의 계절적 분포에 대해 논의할 것이다. 끝으로 최근 한국천문연구원 GPS TEC 상시 관측자료에 나타난 태양 및 지자기 폭풍에 따른 전리층 폭풍 사례에 대해 고찰하고 이를 바탕으로 고층대기 연구가 GPS로 대표되는 현업에 적용되는 최근 현황을 소개할 것이다.

• The Korean Journal of Food And Nutrition
• /
• v.14 no.1
• /
• pp.34-39
• /
• 2001

The purpose of this study was to examine physical properties of the addition of green tea powder on bread flour and dough rheology of white pan bread. Three levels(0.1, 0.5 and 1.0% ) of each green tea powder with bread flour were tested for their effects in dough mixing using rapid disco analyzer, alveogram and farinogram. Addition of green tea powder tended to reduce initial pasting temperature and increase peak viscosity, break down and set back. L(extensibility) and G(swelling index) value in alveogram showed decrement with increasing green tea powder. These meant that the volume of white pan bread would show same tendency. The use of green tea powder increased consistency and water absorption of the bread flour but decreased development time, salability and degree of softening on farinogram. White pan bread with green tea powder had higher value of hardness and springness than without it. Sensory evaluation determined that the white pan bread with 0.5% green tea powder had the highest score.

• Journal of the Korean earth science society
• /
• v.31 no.7
• /
• pp.673-680
• /
• 2010

A steel pile often utilized to bear heavy loads of the upper sub-structure, e. g., bridge constructions and tall buildings. As the steel piles are driven in the underground, it is not easy to detect the depth of the existing pile foundation when there is no detailed foundation information available. However, accurate informations of the depths of piles becomes critical required when reinforcing the existing structures or constructing new ones at the adjacent stage to assure the safety of existing structures. In this study, we tested the applicability of the three components borehole fluxgate magnetometer for detecting the depths and locations of steel piles which are commonly used in civil engineering. Results showed that the information of location as well as the depth of steel piles could be obtained by using data from the three components borehole fluxgate magnetometer.

• Journal of the Korean earth science society
• /
• v.38 no.4
• /
• pp.251-262
• /
• 2017

The system of magnetic exploration with a drone flight was constructed and applied to the iron mine site. The magnetic probe system installed on the drone used a sensor as Bartington's fluxgate type magnetometer, Mag639 and the A/D converter to collect magnetic intensity values on the tablet PC. The drone flight control module is a highly expandable Pixhawk with allowing 15 minutes of flight by loading 3kg. Experiments on the magnetic field interference range were performed to remove the erroneous effect from the drone with applying RTK GPS to obtain the magnetic intensity value at the accurate position. The accurate location information enabled to obtain the gradient measurement of magnetic field by measuring twice at different altitudes. Also, by using the terrain information, we could eliminate the terrain effect by setting the flight path to fly along the terrain. These results are in line with the field experiments using the nuclear proton magnetometer G-858 of Geometrics Co., Ltd, which adds to the reliability of the drone based aeromagnetic survey system we constructed.