• Steel and Composite Structures
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• 제34권5호
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• pp.699-713
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• 2020

The aerodynamic performance of long-span cable-stayed bridges is much dependent on its geometrical configuration and countermeasure strategies. In present study, the aerodynamic performance of three composite cable-stayed bridges with different tower configurations and passive aerodynamic countermeasure strategies is systematically investigated by conducting a series of wind tunnel tests in conjunction with theoretical analysis. The structural characteristics of three composite bridges were firstly introduced, and then their stationary aerodynamic performance and wind-vibration performance (i.e., flutter performance, VIV performance and buffeting responses) were analyzed, respectively. The results show that the bridge with three symmetric towers (i.e., Bridge I) has the lowest natural frequencies among the three bridges, while the bridge with two symmetric towers (i.e., Bridge II) has the highest natural frequencies. Furthermore, the Bridge II has better stationary aerodynamic performance compared to two other bridges due to its relatively large drag force and lift moment coefficients, and the improvement in stationary aerodynamic performance resulting from the application of different countermeasures is limited. In contrast, it demonstrates that the application of both downward vertical central stabilizers (UDVCS) and horizontal guide plates (HGP) could potentially significantly improve the flutter and vortex-induced vibration (VIV) performance of the bridge with two asymmetric towers (i.e., Bridge III), while the combination of vertical interquartile stabilizers (VIS) and airflow-depressing boards (ADB) has the capacity of improving the VIV performance of Bridge II.

• Ocean and Polar Research
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• 제25권1호
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• pp.107-118
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• 2003

The axial seamount basalts in the P3 segment of the Phoenix Ridge were obtained from dredging and the K-Ar age determination and whole-rock geochemical analyses have been done for understanding their origin. The K-Ar ages for PRS basalts sampled from 1,000m below sea level are 2.6-2.2 Ma and those for PR3 basalts from 800m are 1.6-1.5 Ma. The younger ages towards the crest of the seamount indicate that this submarine volcano has been grown by central eruptions. The youngest age of about 1.5 Ma for PR3 basalts corresponds to the final eruption period of this volcano. The seamount basalts contain small amounts of normative quartz and olivine. They have transitional geochemical nature between alkaline- and subalkaline-series basalts. Trace and rare earth elements compositions of the seamount basalts are very similar to those of ocean island basalts (OIB), and indicate that this seamount has been formed by a hotspot activity, not in association with a seafloor spreading. The melting degree from the source has decreased with time, and finally the volcanic activity has stopped when the basaltic magma reached mild alkaline composition.

• 응용통계연구
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• 제27권3호
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• pp.387-396
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• 2014

GDP갭(gap)이란 잠재GDP와 실제GDP의 격차로서 산출갭(Output gap)이라고도 한다. 잠재GDP는 노동, 자본 등 생산요소를 완전히 활용하여 달성할 수 있는 최대GDP라고 정의할 수 있다. GDP갭은 수요-공급간 불균형을 의미한다고 할 수 있으며 이러한 특성 때문에 물가 및 고용안정을 추구하는 중앙은행들은 정책수행과정에서 GDP갭을 중요한 정보변수로 활용하고 있다. 본 연구에서는 우리나라의 GDP갭을 그간 선행연구에서 사용하였던 필터링 방법에 의해 분해함으로써 GDP갭 변동을 야기하는 주요 요인이 무엇인지 살펴보았다. Fox 등 (2003)와 Fox와 Zurlinden (2006)에서 사용되었던 Super Smoother 알고리즘을 이용하여 우리나라의 명목GDP갭을 분해해 본 결과 이론적인 설명에 부합하는 것으로 나타났다. 명목GDP갭률 변동의 상당부분은 잔차인 총요소생산성으로 설명됨을 알 수 있었는데, 이는 최근들어 급격한 기술변화 및 환경변화 등 생산성 변화가 GDP변동에 큰 영향을 주고 있음을 의미한다. 다른 나라의 경우와 마찬가지로 국내물가의 영향력도 높은 것으로 나타났지만 대외 의존도가 높은 우리 경제의 특성상 교역조건의 변동 역시 상대적으로 명목GDP 움직임에 큰 영향을 주고 있는 것으로 분석되었다.

• 암석학회지
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• 제7권3호
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• pp.147-160
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• 1998

삼랑진 칼데라에서는 삼랑진응회암의 강하응회암과 회류응회암, 칼데라후 관입체의 유문암 질암과 각섬석 흑운모 화강암, 광역구조 관입체의 세립질 화강섬록암과 흑운모 화강암 등이 관련된다. 화산작용은 먼저 화도에서 어떤 외부물과 상호작용되는 수증기플리니언 분출상으로 주로 강하회를 퇴적시켰으며 점차 물의 유입이 차단됨으로써 일시적으로 플리니언 분출상으로 전환되어 강하부석을 퇴적시켰다. 이는 다시 회류분출상으로 전환되어 고온의 화성쇄설 물질이 회류로 일시에 쏟아져 정치됨으로써 심하게 용결되었다. 분출초기에는 중앙화구로부터 회류가 발생되었지만 후기에는 환상열극화 구로의 전이가 일어났다. 이 결과로 칼데라 내부에 최고 630m 이상 두께의 회류응회암을 축적하였다. 이 회류분출의 결과로 마그마챔버의 지붕이 함몰되어 삼랑진 칼데라를 형성하게 되었다. 칼데라후 화산작용으로서 중앙회구와 환상단열대를 따라 유대상 유문암이 주입되어 중앙관임체와 환상암맥을 형성하고 다시 환상암맥 내측부에 유문대사이트 반암과 대사이트 반암이 정치되었다. 이후 남서측 환상 단열대를 따라 각섬석 흑운모 화강암이 관입되어 환상관입체의 일원이 되었다. 그리고 칼데라의 북동쪽 어영단층대를 따라 세립질 화강섬록암과 흑운모 화강암이 관입되면서 환상암맥을 절단하였다.

• 대한화학회지
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• 제42권6호
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• pp.679-695
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• 1998

A series of ${\alpha}{\omega}-bis[4-(4'-(S)-(+)-2-methylbutylbiphenyl-4-carboxy)phenoxy]alkanes$, were synthesized, and their thermal and liquid crystalline properties were studied. The chain length of the central polymethylene spacers, x, of the chiral twin compounds was varied from 3 to 12. These compounds were characterized by elemental analysis, IR and NMR spectroscopy, differential thermal analysis (DSC), and crosspolarized microscopy. All compounds were found to be enantiotropic liquid crystalline, and the values of melting $(T_m)$ and isotropization temperature $(T_i)$ as well as ${\delta}H_I$ and ${\delta}S_I$ decreased in a zig-zag fashion, revealing the so called odd-even effect as x increased. Their mesomorphic properties fell into four categories depending upon x; (a) compounds with x=3, 4 and 5 formed only a cholesteric phase on heating, while on cooling they went through two transitions of isotropic (I)-to-cholesteric (Ch) and Ch-to-smectic $A\;(S_A)$ phases before crystallization. (b) compounds with x=6, 8 and 10 exhibited only a cholesteric phase both on heating and on cooling. (c) compounds with x=7 and 9 went through three transitions of crystal $(C)-to-S_A,\;S_A-to-Ch,$ and Ch-to-I phases on heating while on cooling they went through four transitions of I-to-Ch, $Ch-to-S_A,\;S_A-to-Smectic\;C\;(S_C),\;and\;S_c-to-C$ phases in that order, and (d) compounds with x=11 and 12 went reversibly through four transitions of $C-to-S_C,\;S_C-to-S_A,\;S_A-to-Ch,$ and Ch-to-I phases.

• 한국수소및신에너지학회논문집
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• 제26권3호
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• pp.234-240
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• 2015

In the face of the world's growing energy storage needs, liquid hydrogen offers a high energy density solution for the storage and transport of energy throughout society. A 5 L liquid hydrogen storage tank has been designed, fabricated and tested to investigate boil-off rate of liquid hydrogen. As the insulation plays a key role on the cryogenic vessels, various insulation methods have been employed. To reduce heat conduction loss, the epoxy resin-based insulation supports G-10 were used. To minimize radiation heat loss, vapor cooled radiation shield, multi-layer insulation, and high vacuum were adopted. Mass flow meter was used to measure boil-off rate of the 5 L cryogenic vessel. A series of performance tests were done for liquid nitrogen and liquid hydrogen to compare with design parameters, resulting in the boil-off rate of 1.7%/day for liquid nitrogen and 16.8%/day for liquid hydrogen at maximum.

• 천문학회보
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• 제41권2호
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• pp.64.2-64.2
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• 2016

Optical variability is one way to probe the nature of the central engine of AGN at smaller linear scales and previous studies have shown that optical variability is more prevalent at longer timescales and at shorter wavelengths. Especially, intra-night variability can be explained through the damped random walk model but small samples and inhomogeneous data have made constraining this model hard. To understand the properties and physical mechanism of optical variability, we are performing the KMTNet Active Nuclei Variability Survey (KANVaS). Test data of KMTNet in the COSMOS field was obtained over 2 separate nights during 2015, in B, V, R, and I bands. Each night was composed of 5 and 9 epochs with ~30 min cadence. To find AGN in the COSMOS field, we applied multi-wavelength selection methods. Different selection methods means we are looking different region in unification model of AGN, and 100~120, 400~500, 50~100 number of AGN are detected in X-ray, mid-infrared, and radio selection of AGN, respectively. We performed image convolution to reflect seeing fluctuation, then differential photometry between the selected AGN and nearby stars to achieve photometric uncertainty ~0.01mag. We employed one of the standard time-series analysis tools to identify variable AGN, chi-square test. Preliminarily results indicate that intra-night variability is found for X-ray selected, Type1 AGN are 23.6%, 26.4%, 21.3% and 20.7% in the B, V, R, and I band, respectively. The majority of the identified variable AGN are classified as Type 1 AGN, with only a handful of Type 2 AGN showing evidence for variability. The work done so far confirms that there are type and wavelength dependence of intra-night optical variability of AGN.

• 한국전자통신학회논문지
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• 제9권9호
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• pp.1043-1049
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• 2014

본 논문은 원격제어 기능의 디지털 LCD 초시계를 설계하고 구현한다. LCD 초시계와 중앙제어기는 ATMEL의 대표적인 AVR계열 중에서 ATmega8 프로세서를 이용하며 8MHz의 크리스털 발진기의 클록 신호를 바탕으로 구현하였고, 기본 통신모듈은 ZBS-100으로 2.4GHz의 ISM 주파수대역을 이용하였다. 제안한 원격제어 초시계는 세 가지 문제를 해결할 수 있다. 첫째, 중앙에 설치된 대형 LCD 초시계 모니터 주시에 따른 토론자와 방송카메라 간의 시각 편차를 해결할 수 있다. 둘째, 카메라 교차 촬영방식의 번거로움을 피할 수 있으며, 셋째, 공개방송에서 방송카메라의 좌우이동 동작에 따른 시청자의 시야방해를 최소화할 수 있다.

• 대한기계학회논문집
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• 제8권5호
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• pp.442-449
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• 1984

본 연구에서는 두 분류가 교우되어 배합이 이루어지는 유동역에서 3차원 방향 에 대하여 평균속도분포, 난류강도분포, 난류전단응력분포, 상관계수의 분포 및 난류 운동에너지와 운동량의 변화 등을 측정 분석하였다.

• Ocean and Polar Research
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• 제26권3호
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• pp.523-529
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• 2004

The seismic monitoring at Syowa Station$(69^{\circ}S,\;39^{\circ}E: SYO)$, located on the continental margin of the Eastern Dronning Maud Land, East Antarctica, began in 1959. Phase readings of the earthquakes have been reported since 1967 and have been annually published as part of the Data Report Series of the National Institute of Polar Research since 1968. An observation of a tripartite seismic network was carried out at SYO for a period of three years from 1987 to 1990. Epicenters of local earthquakes were determined for the first time by using the array network for the three-year period. Many different types of earthquakes, such as the mainshock-aftershock type, twin earthquake, earthquake swarms, etc., were detected during the period. After this, local events around SYO have been detected empirically from their waveforms recorded on seismograms. The seismic activity for the period of 1987-1990 was higher than that of the following decade. Earthquake epicenters, occurring during that period, were highly localized along the coast and in the central part of the $L\"{u}tzow-Holm$ Bay (LHB). Nine local earthquakes, recorded during the period of 1990-1996, showed many different types of events. The seismicity for the period of 1990-1996 was very low and the magnitudes ranged from 0.1 to 1.4. The locations of some events were determined by using the single station method for SYO, i.e., using the particle motions of the initial phase and S-P time. Two local events were detected in 1998 and one event in 2001. It would be estimated that the stress concentration was related to the glacial rebound around the LHB. Afterwards, we will be able to eventually examine the relationship between the seismicity around Antarctica and deglacial phenomena such as crustal uplift, and sea level change within the earth environmental system.