• 천문학회지
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• 제36권spc1호
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• pp.93-99
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• 2003

Various attempts have been made to explain the: pronounced seasonal and universal time (UT) variations of geomagnetic indices. As one of such attempts, we analyze the hourly-averaged auroral electroject indices obtained during the past 20 years. The AU and AL indices maximize during summer and equinoctial months, respectively. By normalizing the contribution of the solar conductivity enhancement to the AU index, or to the eastward electrojet, it is found that the AU also follows the same semiannual variation pattern of the AL index, suggesting that the electric field is the main modulator of the semiannual magnetic variation. The fact that the variation pattern of the yearly-mean AU index follows the mirror image of the AL index provides another indication that the electric field is the main modulator of magnetic disturbance. The pronounced UT variations of the auroral electrojet indices are also noted. To determine the magnetic activity dependence, the probability of recording a given activity level of AU and AL during each UT is examined. The UT variation of the AL index, thus obtained, shows a maximum at around 1200-1800 UT and a minimum around 0000-0800 UT particularly during winter. It is closely associated with the rotation of the geomagnetic pole around the rotational axis, which results in the change of the solar-originated ionospheric conductivity distribution over the polar region. On the other hand the UT variation is prominent during disturbed periods, indicating that the latitudinal mismatch between the AE stations and the auroral electrojet belt is responsible for it. Although not as prominent as the AL index, the probability distribution of the AU also shows two UT peaks. We confirm that the Dst index shows more prominent seasonal variation than the AE indices. However, the UT variation of the Dst index is only noticeable during the main phase of a magnetic storm. It is a combined result of the uneven distribution of the Dst stations and frequent developments of the partial ring current and substorm wedge current preferentially during the main phase.

• Geomechanics and Engineering
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• 제22권5호
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• pp.449-460
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• 2020

The double-lane arrangement model is frequently used in underground coal mines because it is beneficial to improve the mining efficiency of the working face. When the double-lane arrangement is used, the service time of the reserved roadway increases by twice, which causes several difficulties for the maintenance of the roadway. Given the severe non-uniform deformation of the reserved roadway in the Buertai Coal Mine, the stress distribution law in the mining area, the failure characteristics of roadway and the control effect of support resistance (SR) were systematically studied through on-site monitoring, FLAC 3D numerical simulation, mechanical model analysis. The research shows that the deformation and failure of the reserved roadway mainly manifested as asymmetrical roof sag and floor heave in the region behind the working face, and the roof dripping phenomenon occurred in the severe roof sag area. After the coal is mined out, the stress adjustment around goaf will happen to some extent. For example, the magnitude, direction, and confining pressure ratio of the principal stress at different positions will change. Under the influence of high-stress rotation, the plastic zone of the weak surrounding rock is expanded asymmetrically, which finally leads to the asymmetric failure of roadway. The existing roadway support has a limited effect on the control of the stress field and plastic zone, i.e., the anchor cable reinforcement cannot fully control the roadway deformation under given conditions. Based on obtained results, using roadway grouting and advanced hydraulic support during the secondary mining of the panel 22205 is proposed to ensure roadway safety. This study provides a reference for the stability control of roadway with similar geological conditions.

• Journal of Astronomy and Space Sciences
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• 제33권4호
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• pp.287-293
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• 2016

The equatorial region of the Earth's ionosphere exhibits large temporal variations in electron density that have significant implications on satellite signal transmissions. In this paper, the first observation results of the variations in the trough of the equatorial ionospheric anomaly at the permanent Global Navigation Satellite System (GNSS) site in Chuuk (Geographic: $7.5^{\circ}N$, $151.9^{\circ}E$; Geomagnetic: $0.4^{\circ}N$) are presented. It was found that the daytime Global Positioning System (GPS) total electron content (TEC) values vary according to the 27 day period of solar rotation, and that these trends show sharp contrast with those of summer. The amplitudes of the semi-annual anomaly were 12.4 TECU (33 %) on $19^{th}$ of March and 8.8 TECU (23 %) on $25^{th}$ of October respectively, with a yearly averaged value of 38.0 TECU. The equinoctial asymmetry at the March equinox was higher than that at the October equinox rather than the November equinox. Daily mean TEC values were higher in December than in June, which could be interpreted as annual or winter anomalies. The nighttime GPS TEC enhancements during 20:00-24:00 LT also exhibited the semi-annual variation. The pre-midnight TEC enhancement could be explained with the slow loss process of electron density that is largely produced during the daytime of equinox. However, the significant peaks around 22:00-23:00 LT at the spring equinox require other mechanisms other than the slow loss process of the electron density.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2015년도 학술발표회
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• pp.53-53
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• 2015

Basin-scale motions in a stratified lake rely on interactions of spatially and temporally varying wind force, bathymetry, density variation, and earth's rotation. These motions provide a major driving force for vertical and horizontal mixing of inorganic and organic materials, dissolved oxygen, storm water and floating debris in stratified lakes. In Lake Tahoe, located between California and Nevada, USA, basin-scale circulations are obviously important because they are directly associated with the fate of the suspended particulate materials that degrade the clarity of the lake. A three-dimensional hydrodynamic model, ELCOM, was applied to Lake Tahoe to investigate the underlying mechanisms that determine the characteristics of basin-scale circulations. Numerical experiments were designed to examine the relative effects of various mechanisms responsible for the horizontal circulations for two different seasons, summer and winter. The unique double gyre, a cyclonic northern gyre and an anti-cyclonic southern gyre, occurred during the winter cooling season when wind stress curl, stratification, and Coriolis effect were all incorporated. The horizontal structure of the upwelling and downwelling formed due to basin-scale internal waves found to be closely related to the rotating direction of each gyre. In the summer, the spatially varying wind field and the Coriolis effect caused a dominant anti-cyclonic gyre to develop in the center of the lake. In the winter, a significant wind event excited internal waves, and a persistent (2 week long) cyclonic gyre formed near the upwelling zone. Mechanism of the persistent cyclonic gyre is explained as a geostrophic circulation ensued by balancing of the baroclinc pressure gradient (or baroclinic instability) and Coriolis effect. Topographic effect, examined by simulating a flat bathymetry with constant depth of 300m, was found to be significant during the winter cooling season but not as significant as the wind curl and baroclinic effects.

• Journal of Astronomy and Space Sciences
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• 제30권4호
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• pp.315-320
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• 2013

Space geodetic techniques can be used to obtain precise shape and rotation information of the Earth. To achieve this, the representative combination solution of each space geodetic technique has to be produced, and then those solutions need to be combined. In this study, the representative combination solution of very long baseline interferometry (VLBI), which is one of the space geodetic techniques, was produced, and the variations in the position coordinate of each station during 7 years were analyzed. Products from five analysis centers of the International VLBI Service for Geodesy and Astrometry (IVS) were used as the input data, and Bernese 5.0, which is the global navigation satellite system (GNSS) data processing software, was used. The analysis of the coordinate time series for the 43 VLBI stations indicated that the latitude component error was about 15.6 mm, the longitude component error was about 37.7 mm, and the height component error was about 30.9 mm, with respect to the reference frame, International Terrestrial Reference Frame 2008 (ITRF2008). The velocity vector of the 42 stations excluding the YEBES station showed a magnitude difference of 7.3 mm/yr (30.2%) and a direction difference of $13.8^{\circ}$ (3.8%), with respect to ITRF2008. Among these, the 10 stations in Europe showed a magnitude difference of 7.8 mm/yr (30.3%) and a direction difference of $3.7^{\circ}$ (1.0%), while the 14 stations in North America showed a magnitude difference of 2.7 mm/yr (15.8%) and a direction difference of $10.3^{\circ}$ (2.9%).

• 한국발생생물학회지:발생과생식
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• 제7권1호
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• pp.1-7
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• 2003

사람을 비롯한 대부분의 동물들은 주변 환경의 영향을 받아 주기적인 생활을 영위하고 있다. 지구의 자전 및 공전으로 그리고 국소적으로 발생되는 주기적인 변화는 생명체의 행동으로 뚜렷하게 표출된다. 이러한 환경의 주기적인 변화는 오랜 기간의 진화과정을 통하여 생명체 내의 유전자로 각인되었으며, 이 유전자들은 발생 과정을 포함하는 성장 과정에서 리듬으로 발현된다. 환경의 변화는 결국 유전자로 정착하여 생체 시계로서 작용하며, 시상하부의 시신경교차상핵(suprachiasmatic nucleus, SCN)이 유력한 해부학적 위치이다. 따라서 생체 시계는 지구상에 살고 있는 생명체의 각종 리듬을 지배하여, 출생 및 사망, 수명, 행동, 생리, 세포 분열, 생화학적 반응 등등에 영향을 미친다. 리듬은 서서히 변화하는 환경의 변화에 맞도록 재조정된다. 생체 시계는 규칙적인 환경 변화를 예측하고 이에 미리 대비하게 하는 장점을 지니고 있다.

• Earthquakes and Structures
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• 제2권3호
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• pp.233-256
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• 2011

This paper investigates the applicability of newly developed Cu-Al-Mn shape memory alloy (SMA) bars to retrofitting of historical masonry constructions by performing quasi-static tests of half-scale brick walls subjected to cyclic out-of-plane flexure. Problems associated with conventional steel reinforcing bars lie in pinching, or degradation of stiffness and strength under cyclic loading, and in their inability to restrain residual deformations in structures during and after intense earthquakes. This paper attempts to resolve the problems by applying newly developed Cu-Al-Mn SMA bars, characterized by large recovery strain, low material cost, and high machinability, as partial replacements for steel bars. Three types of brick wall specimens, unreinforced, steel reinforced, and SMA reinforced specimens are prepared. The specimens are subjected to quasi-static cyclic loading up to rotation angle enough to cause yielding of reinforcing bars. Corresponding nonlinear finite element models are developed to simulate the experimental observations. It was found from the experimental and numerical results that both the steel reinforced and SMA reinforced specimens showed substantial increment in strength and ductility as compared to the unreinforced specimen. The steel reinforced specimen showed pinching and significant residual elongation in reinforcing bars while the SMA reinforced specimen did not. Both the experimental and numerical observations demonstrate the superiority of Cu-Al-Mn SMA bars to conventional steel reinforcing bars in retrofitting historical masonry constructions.

• 전자공학회논문지S
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• 제35S권10호
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• pp.64-76
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• 1998

본 논문에서 4-구륜 2-자유도 이동 로보트의 체계적인 동적 모델링과 경로설계 및 추적 알고리즘을 제안한다. 실시간에서 이동 로보트의 위치 측정을 위해 관성측정장치중의 3가지 요소를 이용한다. 이러한 장치들은 지구의 회전속도 및 중력가속도 등의 여러 요인으로 인해 초기 오차를 가진다. 그래서 초기오차 모델을 유도하고, 실제 데이터와 유도된 모델의 추정 데이터의 확률적 특성을 분석 ${\cdot}$ 비교하여 적합도를 판정하여 사용한다. 관성측정장치의 동작특성은 오차모델과 칼만 필터와 연계된 경우와 배제된 일반적인 경우와 비교한다. 모의실험 결과들은 제안된 경로설계 및 추적 알고리즘이 기존의 방식과 비교하여 보다 유용함을 입증한다.

• 한국초등과학교육학회지:초등과학교육
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• 제32권4호
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• pp.423-436
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• 2013

This research purports to analyze released items and G4 students' science achievement from TIMSS 2011 according to their academic achievement levels and gender. By doing so, it aims to draw educational implications for Korea from analyses results. Korea showed a lower rate of students at the advanced international benchmark - the highest achievement level - compared to Singapore. The difference was the smallest in Life Science among three content domains and knowing among three cognitive domains. The results of analysis according to gender showed that male students' achievement was significantly higher in Physical Science and Earth Science, and their achievement was also higher in the cognitive domains of Knowing and Applying. From the analysis of the released items, it was revealed that the students' achievement was low in items related to classification of organisms, functions of heart, matters that combust or emit light, and the concept of rotation. Moreover, students drew some illogical conclusions based on their personal experience. Male students were found to show high achievements in items that were not included in curriculum, constructed-response items in the form of short-answer questions, and multiple-choice items in the Knowing domain. Female students were found to show high achievement in items that were included in curriculum, constructed-response items that require reasons and methods, and items that represent experimental situations. Male students showed high achievement in forces concept and movements concept of bodies in the universe, while female students showed high achievement in solubility concept.

• 한국측량학회지
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• 제19권4호
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• pp.415-423
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• 2001

본 연구는 GPS상시관측소의 기준좌표계별 절대좌표 산정을 위한 적합한 방안의 결정을 위해 수행되었으며, 성균관대학교 구내에 설치된 상시관측소를 연구대상으로 하였다. 본 논문에서 ITRF97성과는 정밀도 0.001ppm의 정밀단독측위기법으로 GPS 데이터를 해석하여 산정하였고. WGS84와 대한민국 좌표계 성과는 결정된 ITRF97성과를 이미 제공되어 있는 파라메터들로 변환하여 산정하였다. ITRF97 성과의 경우 제트추진연구소에서 개발한 위치결정 알고리즘과 GIPSY-OASIS II(이하 GOA II)를 사용하여 산정하였다. WGS84와 대한민국 좌표계 성과는 IERS에서 전 지구적으로 계산한 좌표변환 계수와 2000년도 국립지리원에서 시행한 사업인 한국 지구중심 기준좌표계의 결정 사업을 통해 산정된 좌표변환 계수를 이용하여 산정하였으며, 이를 지역적인 GPS 데이터 해석을 통해 산정된 성과와 비교하여 그 활용성을 검증하였다.