• 한국태양에너지학회 논문집
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• 제32권3호
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• pp.104-113
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• 2012

A set of candela distribution curves(CDCs) were generated for a fiber optic dish daylighting system by Photopia under clear sky conditions at different solar altitudes. The candela distribution curves were then exported to Radiance for photometric analysis of a windowless lecture room. Observations were made on the Radiance rendered illuminance images, which provided photo realistic scenes varying with solar altitudes. If no tracking error were assumed, the daylight collection efficiency of the system remained at a constant value of 68.4% during its operation. Higher the solar altitude angle, greater in photometric quantities were observed, which are represented by candela(cd) and total lumens(lm). In all cases considered, however, the angle of light distribution remained fixed reflecting the solar tracking feature of the system. The illuminance uniformity on the workplane lingered around 0.12, which is quite low. This is quite a contrast to its average value of 0.68 of the $2.7m^2$ area directly below the terminal device (diffuser) of the system. The maximum illuminance of 1,340lux was obtained at a solar altitude of 80 degrees.

• 한국태양에너지학회 논문집
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• 제30권1호
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• pp.19-24
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• 2010

At the altitudes above 3km, the wind is three to four time faster and less variable than at the current MW sized wind turbine hub height of around 100m. In addition, power generation from wind turbines installed on the ground is intermittent because local wind conditions are affected by local topography and artificial structures. The wind energy researchers and engineers are now looking for revolutionary ideas to utilize high altitude wind resources in-creasing the capabilities of wind turbine installations. This article presents and discusses several concepts for wind energy exploitation from wind at high altitudes. The concepts presented in this paper make use of lifting bodies, called wings or kites, connected to a tether that stetches into the higher regions of the atmosphere.

• 한국전자통신학회논문지
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• 제17권3호
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• pp.433-440
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• 2022

고고도 장기체공 태양광 무인기는 성층권에서 태양광을 에너지원으로 장기간 비행하며 임무를 수행하는 무인기를 의미하며 고고도에서 장기적으로 임무 수행이 가능하여 지역적으로 통신위성 대체, 군사적 목적으로 임시 통신망 구축, 지상 촬영을 통한 감시 정찰 기능 등으로 사용할 수 있다. 이런 임무특성상 임무 수행 가용시간을 분석하는 것은 무인기를 상용화하는 데 매우 중요한 요소이다. 하지만 고고도에서 태양광 전력의 획득은 운용 위도와 계절에 영향을 받고 여러 요소가 복합적으로 작용하여 가용일수의 분석이 쉽지 않다. 본 논문에서는 고고도 장기체공 무인기의 설계 파라미터를 바탕으로 가용시간의 분석 모델 및 로직을 제시하고 태양광 획득 조건에 따른 고고도 장기체공 태양광 무인기의 가용시간을 분석하였다.

• 대한지구과학교육학회지
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• 제5권1호
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• pp.88-94
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• 2012

This study was created to resolve the problems embedded in the formal measuring experiments to determine the earth's size in the current curriculum, to develop an updated measuring experiment to determine the earth's size and to establish its effect. For this study, pre-service elementary teachers, who had attempted the experiment of measuring the size of the earth when they were in middle school, performed the experiments in the existing national curriculum, and their responses, collected through in-depth interviews, were examined. To begin with, the pre-service elementary teachers conducted the experiment of measuring the earth size and they recorded the problems while performing it. At the end, an in-depth interview was administered. Based on the problems, an updated measuring experiment to determine the earth's size was suggested to be applied to the same contents and be analyzed through the in-depth interviews. Common themes which were mutually categorized and analyzed by the two researchers were obtained based on the records produced while conducting the experiment and the in-depth interview data. The teachers mentioned that the experiments for measuring the size of the earth in the current curriculum gave rise to difficulties in measuring precisely the angles between the string and the post. Also, there has been a scientific contradiction that solar altitudes were increased in a high latitude region, instead of decreased. For this reason, an alternative method has been developed to measure the earth's size using the distance and the solar altitude difference of two places. The teachers all agreed that by using the updated measuring experiment, they can acquire more precise measurements and it is easier, faster and consequently more effective than the existing methods. Through the results of this study, I suggest that the newly developed experiment by the researchers can overhaul the problems of the current experiments and it can be an effective alternative to the current experiment.

• 천문학회보
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• 제36권2호
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• pp.82.2-82.2
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• 2011

Major solar eruptive events, consisting of both a large flare and a near simultaneous fast coronal mass ejection (CME), are the most powerful explosions in the solar system, releasing $10^{32}-10^{33}$ ergs in ${\sim}10^{3-4}\;s$. They are also the most powerful and energetic particle accelerators, producing ions up to tens of GeV and electrons up to hundreds of MeV. For flares, the accelerated particles often contain up to ~50% of the total energy released, a remarkable efficiency that indicates the particle acceleration is intimately related to the energy release process. Similar transient energy release/particle acceleration processes appear to occur elsewhere in the universe, in stellar flares, magnetars, etc. Escaping solar energetic particles (SEPs) appear to be accelerated by the shock wave driven by the fast CME at altitudes of ~1 40 $R_s$, with an efficiency of ~10%, about what is required for supernova shock waves to produce galactic cosmic rays. Thus, large solar eruptive events are our most accessible laboratory for understanding the fundamental physics of transient energy release and particle acceleration in cosmic magnetized plasmas. They also produce the most extreme space weather - the escaping SEPs are a major radiation hazard for spacecraft and humans in space, the intense flare photon emissions disrupt GPS and communications on the Earth, while the fast CME restructures the interplanetary medium with severe effects on the magnetospheres and atmospheres of the Earth and other planets. Here I review present observations of large solar eruptive events, and future space and ground-based measurements needed to understand the fundamental processes involved.

• 천문학회지
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• 제43권3호
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• pp.55-64
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• 2010

We investigate how plasma structures in the solar chromosphere and corona can extend to altitudes much above hydrostatic scale heights from the solar surface even under the force of gravity. Using a simple modified form of equation of motion in the vertical direction, we argue that there are two extreme ways of non-hydrostatic support: dynamical support and magnetic support. If the vertical acceleration is downward and its magnitude is a significant fraction of gravitational acceleration, non-hydrostatic support is dynamical in nature. Otherwise non-hydrostatic support is static, and magnetic support by horizontal magnetic fields is the only other possibility. We describe what kind of observations are needed in the clarification of the nature of non-hydrostatic support. Observations available so far seem to indicate that spicules in the quiet regions and dynamic fibrils in active regions are dynamically supported whereas the general chromosphere as well as prorninences is magnetically supported. Moreover, it appears that magnetic support is required for plasma in some coronal loops as well. We suspect that the identification of a coronal loop with a simple magnetic flux tube might be wrong in this regard.

• Journal of Astronomy and Space Sciences
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• 제14권1호
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• pp.87-93
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• 1997

Radiometers in UV and visible wavelengths were onboard the Korean Sounding Rocket(KSR)-1 and 2 which were launched on June 4th and September 1st, 1993. These radiometers were designed to capture the solar radiation during the ascending period of the rocket flight. The purpose of the instrument was to measure the vertical profiles of stratospheric ozone densities. Since the instrument measured the solar radiation from the ground to its apogee, it is possible to investigate the altitude variation of the measured intensity and to estimate the effect of atmospheric scattering by comparing the UV and visible intensity. The visible channel was a reference because the 450-nm wavelength is in the atmospheric window region, where the solar radiation is transmitted through the atmosphere without being absorbed by other atmospheric gases. The use of 450-nm channel intensity as a reference should be limited to the altitude ranges above the certain altitudes, say 20 to 25km where the signals are not perturbed by atmospheric scattering effects.

• 천문학회보
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• 제37권2호
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• pp.105.2-105.2
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• 2012

The upper ionosphere of Mars has been explored by many spacecraft like Mariners, Mars, Viking, and recently by MGS and MEX. MARSIS (Mars Advanced Radar for Subsurface and Ionospheric Sounding) aboard Mars Express Orbiter is operating from August 2005. MARSIS provides topside ionospheric traces, of which yield electron density profiles for altitudes above the primary ionospheric peak. A large amounts of data is useful for investigation of the Martian ionospheric environments under the changing conditions like solar activity, seasons, and solar zenith angle. We studied the characteristics of the Martian ionosphere through analysis of MARSIS data in the various conditions. We expect that our results contribute for understanding of the Martian ionospheric environment.

• 천문학논총
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• 제15권spc2호
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• pp.21-25
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• 2000

The ionosphere, the atmosphere of the earth ionized by solar radiations, has been strongly varied with solar activity. The ionosphere varies with the solar cycle, the seasons, the latitudes and during any given day. Radio wave propagation through or in the ionosphere is affected by ionospheric condition so that one needs to consider its effects on operating communication systems normally. For examples, sporadic E may form at any time. It occurs at altitudes between 90 to 140 km (in the E region), and may be spread over a large area or be confined to a small region. Sometimes the sporadic E layer works as a mirror so that the communication signal does not reach the receiver. And radiation from the Sun during large solar flares causes increased ionization in the D region which results in greater absorption of HF radio waves. This phenomenon is called short wave fade-outs. If the flare is large enough, the whole of the HF spectrum can be rendered unusable for a period of time. Due to events on the Sun, sometimes the Earth's magnetic field becomes disturbed. The geomagnetic field and the ionosphere are linked in complex ways and a disturbance in the geomagnetic field can often cause a disturbance in the F region of the ionosphere. An enhancement will not usually concern the HF communicator, but the depression may cause frequencies normally used for communication to be too high with the result that the wave penetrates the ionosphere. Ionospheric storms can occur throughout the solar cycle and are related to coronal mass ejections (CMEs) and coronal holes on the Sun. Except the above mentioned phenomena, there are a lot of things to affect the radio communication. Nowadays, radio technique for probing the terrestrial ionosphere has a tendency to use satellite system such as GPS. To get more accurate information about the variation of the ionospheric electron density, a TEC measurement system is necessary so RRL will operate the system in the near future.

• 한국항공우주학회지
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• 제40권6호
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• pp.523-535
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• 2012

태양광 추진 항공기는 감시, 지구 모니터링, 통신 등에 대기 오염 없이 그리고 가까운 장래에 인공위성과의 가격 경쟁력까지 갖추게 될 수 있어 미래의 고고도 장기체공 임무수행을 위해 더욱더 그 중요성이 증대되고 있다. 그러나 전통적인 항공기 사이징 방법들은 태양광 추진 항공기에 바로 적용될 수 없다. 본 연구에서는 다양한 동력 시스템 구성품들이 태양광 추진 장기 체공 항공기의 사이징에 어떤 영향을 미치는지를 파악하기 위하여 에너지 균형 및 구속조건 연구를 수행하였다. 본 연구에서는 동력 생성과 연료전지의 재생 에너지 저장을 위한 광전지 모듈을 동력 시스템 구성품으로 고려하였다. 또한 본 연구 결과를 검증하기 위해 고고도 무인기에 이 새로운 사이징 기법을 적용하여 결과를 제시하였다.