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

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.2
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• pp.87-94
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• 2023

As the latest weapon systems and electronic equipments are increasingly demanding stealth technology to improve the survivability of allies, it is necessary to implement low-observability technology that reduces the radar cross section(RCS). In order to implement this stealth technology, a method for low RCS characteristics by applying a shape design or a electromagnetic wave absorber is widely used. However, active phased array antennas have structural limitations in shape design, also when a absorber is applied to it, the performance of the antenna is degraded. Therefore, in this paper, in order to realize the low RCS characteristics of the active phased array antenna operating in the X-band, individual radiating elements suitable for applying the radio wave absorber were selected, and a 13x13 array antenna was designed and manufactured. Next, by comparing the measured results of the relative RCS and electrical performance for the manufactured antenna according to the presence and type of the absorber, it is shown that the electrical performance is maintained at an equal or higher level while obtaining the low RCS characteristics. Thereby the method proposed in this paper for implementing the low RCS characteristics was validated. Finally, it was confirmed that when the wave absorber is applied to the array antenna, the limitation of its performance deterioration can be overcome.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.472-472
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• 2011

탁도는 물의 상대적인 흐림 정도를 나타내는 척도로서 이는 빛이 물을 통과할 때 산란시키는 부유고형물질 때문에 발생한다. 토양침식에 의하여 지표수로 유입된 토사와 광물질은 하천의 수송 및 퇴적 과정을 거치며 이동한다. 이때 하상 퇴적물은 바닥으로부터 먹이를 찾는 유기체에 의해 뒤섞이며 입자들은 일정기간동안 물의 흐름에 의해 부유상태로 남아 있게 되고, 유입되는 영양소와 빛에 의하여 성장하는 조류 또한 탁도를 증가시키는 원인이 된다. 이러한 부유물질의 증가는 수중에 태양복사에너지 전달을 방해하여 수중생태계의 먹이사슬과 저서생물의 서식환경에 많은 영향을 미치고, 수표면 온도 또한 태양으로부터 열을 흡수하는 표면 근처의 부유물질에 의해 증가하여 용존산소의 양에도 영향을 미친다. 따라서 수체내 분포하고 있는 부유물질의 종류와 양 및 공간적 분포 파악은 수질문제와 재난 예방 및 생물의 서식환경 문제를 파악하고 해결하는 데 매우 중요하다. 그러나 부유물질에 부착되어 있는 영양소, 금속, 살충제 등은 물 순환 시스템을 통하여 끊임없이 운반되고 상류유역의 흐름 조건에 따라 시공간적으로 변화하기 때문에 이를 규명하는 것이 매우 어려운 실정이다. 이러한 문제를 해결하기 위하여 광역적인 탁수환경의 분석방법으로 원격탐사(Remote Sensing, 이후 RS) 기법을 이용한 방법이 제안되고 있다. 이미 선진국에서는 광역수계의 수질관리를 위해 RS 기법을 이용하여 신속하고 정확한 수질상태 파악을 시도하고 있으며, 우리나라에서도 KOMPSAT 발사를 계기로 RS 관련 기술이 비약적으로 진화하고 있다. 그러나 RS 데이터를 활용하는데 필수적인 분광학적 특성 규명에 대한 연구는 대부분 식생과 토양에 한정되어 있으며 수체에 대한 연구는 현장조사의 어려움으로 인하여 상당히 제한적인 수준이다. 따라서 본 연구에서는 탁도의 변화에 따른 분광반사 특성을 휴대용 분광복사계를 이용하여 규명하고, 이를 Landsat 위성영상에 적용하여 새만금 유역을 대상으로 완공 직후인 2006년부터 2010년까지의 탁수환경을 모니터링 하였다. 그 결과 새만금 유역 탁수환경을 정성적으로 확인할 수 있었으며, 이를 이용하여 탁수환경 연구에 RS 기법이 효과적임을 제시하고자 한다.

• Electrical & Electronic Materials
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• v.5 no.3
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• pp.284-294
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• 1992

합성용질확산법으로 GaP단결정을 성장시키고 몇가지 성질을 조사하였다. 정지상태에서 결정의 성장속도는 1.75[mm/day]이었고 결정성장용 석영관을 전기로내에서 하강시키므로써 양질의 GaP 단결정을 성장하였다. 에치피트밀도는 결정의 성장축 방향으로 3.8*$10^{4}$[$cm^{-2}$]부터 2.3*$10^{5}$[$cm^{-2}$] 까지 증가하였다. 성장된 GaP결정의 이동도와 캐리어농도는 실온에서 197.49[$cm^{2}$/V.sec]와 6.75*$10^{15}$[$cm^{-3}$]이었고 77K의 온도에서는 266.91[$cm^{2}$ /V.sec]와 3.13*$10^{14}$[$cm^{-3}$]이었다. 에너지갭의 온도의존성은 실험적으로 $E_{g}$(T)=2.3383-(6.082*$10^{-4}$) $T^{2}$/(373.096+T)[eV]로 구하여졌다. 저온에서 측정된 광루미네센스 스펙트럼은 구속된 여기자의 복사재결합과 재결합 과정에 포논의 참여로 인하여 에너지갭 부근의 복잡한 선 스펙트럼이 나타났고 얕은 준위의 Si도너와 Zn억셉터준위 사이에서의 복사재결합 및 이에 대한 1LO, 2LO의 포논복제가 나타났으며 S $i_{Ga}$ -S $i_{p}$의 쌍방출에 의하여 1.8932[eV]에서 넓은 반치전폭의 피크가 나타났다. GaP의 적외선 흡수는 TO, LO, LA, T $A_{1}$, T $A_{2}$ 포논들의 이중결합모드와 G $a_{2}$O의 진동모드 및 Si도너와 Zn억셉터들에 의하여 일어났다. Zn를 확산시키어 제작한 p-n GaP발광다이오드는 실온에서의 발광중심피크가 6250[.angs.]이었고 최대광출력은 0.0916[mW], 양자효율은 0.51%이었다.이었다.

• Journal of the Korean Institute of Telematics and Electronics
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• v.21 no.5
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• pp.90-99
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• 1984

A onetimensional distribution of the temperature and the heat source in the SOI (silicon-on-insulator) multi-layer structure illuminated by tungsten lamps from both sides was obtained by solving the heat equation in steady state on a finite difference grid using successive over-relaxation method. The heat source distribution was obtained by considering such features as spectral components of the light source, multiple reflection at the internal interfaces, temperature and frequency dependence of the light absorption coefficient, etc. The front and back surface temperatures, which are boundary conditions for the heat equation, were derived from a requirement that they satisfy the radiation conditions. The radiation flux as well as the conduction flux was considered in modelling the thermal behaviour at the internal interfaces. Since the temperature and the heat source profiles are strongly dependent upon each other, the calculation of each profile was iterated using the updated profile of the other until they are consistent with each other. The experimental temperature at the front surface of the wafer as measured by Pyrometer was about 1200$^{\circ}$K, while the simulated temperature was 1120$^{\circ}$K.

• Journal of the Korean earth science society
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• v.26 no.3
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• pp.283-296
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• 2005

The effect of ozone and surface temperature on the ozone band at $9.7{\mu}m$ has been investigated from radiative transfer theory together with observations in order to derive empirical methods for remotely sensing ground-ozone concentration. Simultaneous observations of satellite (MODIS Aqua; ECT 13:30) and ground-ozone at 79 stations have been used over the Seoul Metropolitan Area (SMA; 125.7-127.2 E, 37.2-37.7 N) during four ozone-warning days in the year 2003. Cloud effect on the band in the methods was filtered out based on synoptic observations. Upwelling radiance values at $9.6{\mu}m$ which have been estimated at the given ozone concentration of 327-391 DU depend on surface temperature (Ts) showing $5.52\~5.78Wm^{-2}sr^{-1}\;at\;Ts = 290 K,\;and\;9.00\~9.57Wm^{-2}sr^{-1}$ Ts = 325K. Thus, the partitioned contributions of ozone and temperature to intensity of ozone absorption band are $0.26Wm^{-1}sr^{-1}/64\;DU\;and\;0.31 Wm^{-2}sr^{-1}/35K$, respectively. Here the intensity which has been used to remotely detect ground-ozone concentration from infrared satellite measurement is defined as the difference in brightness temperature between $11{\mu} m\;and\;9.7{\mu}m (i.e.,\; T_{11-9.7})$. The methods in this study have been applied to estimate ground-ozone from MODIS data in cases that there are significant correlations between the band intensity and ground-ozone. The values of estimated ozone significantly correlate (0.49-0.63) with ground observations at a significance level of $1\%$. For the improved methods, further study may be required to use tropospheric ozone rather than ground-ozone, considering the variation stratospheric ozone.

• Korean Journal of Optics and Photonics
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• v.9 no.4
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• pp.221-226
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• 1998

Ternary heavy metal oxide glasses in the $PbO-Bi_2O_3-Ga_2O_3$ system doped with $Er_2O_3$ were prepared and their spectroscopic properties, such as radiative transition probability, calculated and measured radiative lifetimes and cross-sections of 1.5 $\mu\textrm{m}$ and 2.7 $\mu\textrm{m}$ emissions were analyzed. Enhanced quantum efficiencies of some electronic transitions were evident mainly because of the low vibrational phonon energy ($~500cm^{-1}$) inherent in the host glasses. This seems to be the main reason for obtaining the 2.7 $\mu\textrm{m}$ luminescence which is normally quenched in the conventional oxide glasses. In addition, green and red fluorescence emissions were observed through the frequency upconversion processes of the 798 nm excitation. Non-radiative transition due to the multiphonon relaxation is a dominant lifetime-shortening mechanism in the 4f-4f transitions in $Er^{3+}$ ion except for the $^4S_{3/2}{\rightarrow}^4I_{15/2}$ transition where a non-radiative transfer to band-gap excitation of the host glasses is dominant. Melting of glasses under an inert gas atmosphere and (or) addition of the typical glass-network former into glasses is necessary in order to enhance the quantum efficiency of the transition.

• Journal of Bio-Environment Control
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• v.28 no.4
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• pp.311-321
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• 2019

Greenhouse farmers often use thermal screens to reduce greenhouse heating expenses during the winter, and for shade during hot, sunny days in the summer, as it is an inexpensive solution to temperature control relative to other available options. However, accurate measurements of their emitted and absorbed radiations are important for the selection of suitable screens that offer maximum performance. Material's ability to save energy is highly dependent on these properties. Limited studies have investigated the measurement of these properties under natural conditions, but they are only applicable to materials having partial porosities. In this work, we describe a new radiation balance method for determining emissive power and absorptive capacity, as well as reflectivity, transmissivity and emissivity of materials having complete and partial transparency by using pyrgeometer and net radiometer. In this study, four materials with zero porosity, were tested. The emissivity value of PE, LD-13, LD-15 and PH-20 was $0.439{\pm}0.020$, $0.460{\pm}0.010$, $0.454{\pm}0.004$, and $0.499{\pm}0.006$, respectively. All tested samples showed high emitted radiation as compared to absorbed radiation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.19-25
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• 2019

The CleanSYS(Clean SYStem) is operated to monitor air pollutants emitted from specific industrial complexes in Korea. So the industrial complexes without the system are directly monitored by the control officers. For efficient monitoring, studies using various sensors have been conducted to monitor air pollutants emitted from industrial complex. In this study, hyperspectral sensors were used to model and verify the equations for estimating the concentration of $NO_2$(nitrogen dioxide) in air pollutants emitted. For development of the equations, spectral radiance were observed for $NO_2$ at various concentrations with different SZA(Solar Zenith Angle), VZA(Viewing Zenith Angle), and RAA(Relative Azimuth Angle). From the observed spectral radiance, the calculated value of the difference between the values of the specific wavelengths was taken as an absorption depth, and the equations were developed using the relationship between the depth and the $NO_2$ concentration. The spectral radiance mixed gas of $NO_2$ and $SO_2$(sulfur dioxide) was used to verify the equations. As a result, the $R^2$(coefficient of determination) and RMSE(Root Mean Square Error) were different from 0.71~0.88 and 72~23 ppm according to the form of the equation, and $R^2$ of the exponential form was the highest among the equations. Depending on the type of the equations, the accuracy of the estimated concentration with varying concentrations is not constant. However, if the equations are advanced in the future, hyperspectral sensors can be used to monitor the $NO_2$ emitted from the industrial complex.

• Progress in Medical Physics
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• v.13 no.4
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• pp.187-194
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• 2002

In this work we investigated through Monte Carlo calculations the physical characteristics of the absorbed dose from the Ir-192 source used in brachytherapy The Monte Carlo calculations were performed using the code EGS4, which was extensively modified in order to handle cylindrical sources, phantoms, and energy distributions to suit out own purpose. From the results of the calculations for the $\beta$ -rays, it was found that they contribute on the average 0.02% to The total absorbed dose in the distance range of 0.5-5.0 cm from the source. This is due to the face that, although most of the primary $\beta$ -rays are absorbed in the source and encapsulation material, the resulting low energy braking radiation from them contribute to such a distance. The absorbed dose in the encapsulation material varied on the average from 2.8% for platinum down to 1.1% for iron. The radial dose functions obtained by our Monte Carlo calculations were consistent within $\pm$3% with those of the TG-43 report for the radial distance interval 0.5-10.0 cm from the source. The user code we wrote in this work can be used for other sources of different sizes and so it can be very useful in designing and producing the sources for brachytherapy.