• 대한원격탐사학회지
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• 제32권4호
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• pp.383-401
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• 2016

In this paper, we described the statistical modeling of crop yields using satellite images, climatic datasets, soil property maps, and fertilizer data for the Midwestern United States during 2001-2012. Satellite images were obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS), and climatic datasets were provided by the Parameter-elevation Regressions on Independent Slopes Model (PRISM) Climate Group. Soil property maps were derived from the Harmonized World Soil Database (HWSD). Our multivariate regression models produced quite good prediction accuracies, with differences of approximately 8-15% from the governmental statistics of corn and soybean yields. The unfavorable conditions of climate and vegetation in 2012 could have resulted in a decrease in yields according to the regression models, but the actual yields were greater than predicted. It can be interpreted that factors other than climate, vegetation, soil, and fertilizer may be involved in the negative biases. Also, we found that soybean yield was more affected by minimum temperature conditions while corn yield was more associated with photosynthetic activities. These two crops can have different potential impacts regarding climate change, and it is important to quantify the degree of the crop sensitivities to climatic variations to help adaptation by humans. Considering the yield decreases during the drought event, we can assume that climatic effect may be stronger than human adaptive capacity. Thus, further studies are demanded particularly by enhancing the data regarding human activities such as tillage, fertilization, irrigation, and comprehensive agricultural technologies.

• 한국음향학회지
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• 제24권2호
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• pp.78-86
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• 2005

진단용 초음파에 의해 가진된 초음파 조영제에서 방사하는 하모닉 성분의 크기를 이론적으로 고찰하였다. 본 연구에서는 2 MHz 진단용 초음파 펄스에 의한 초음파 조영제의 비선형 동적 반응을 Gilmore Model을 이용하여 수치 해석하였다. 초음파 조영제의 탄성 효과는 무시하였다. 초음파 조영제 반경의 크기 (1-9 $\mu$m)와 초음파의 MI 값 (0.125-8)을 변화시키면서 발생된 서브, 울트라. 2차 하모닉 성분의 파워를 기본 주파수 성분과 비교하였다. 시뮬레이션 결과, 초음파 조영제가 공진 반경 (2 $\mu$m) 보다 클 경우, 초음파 조영제에서 방출하는 서브 하모닉의 파워가 기본 주파수 것 보다 압도적으로 크게 나타났다. 특히 하모닉 영상에서 사용하는 2차 하모닉의 파워는 서브 및 울트라 하모닉 성분 보다 낮은 값을 가지는 것으로 예측되었다. 본 연구 결과는 초음파 조영제를 이용하여 하모닉 영상을 구현할 경우, 서브 및 울트라 하모닉 성분이 2차 하모닉 성분 보다 우수한 영상 변수가 될 수 있음을 시사한다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.78-78
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• 2015

Metamaterials, artificially structured nanomaterials, have enabled unprecedented phenomena such as invisibility cloaking and negative refraction. Especially, hyperbolic metamaterials also known as indefinite metamaterials have unique dispersion relation where the principal components of its permittivity tensors are not all with the same signs and magnitudes. Such extraordinary dispersion relation results in hyperbolic dispersion relations which lead to a number of interesting phenomena, such as super-resolution effect which transfers evanescent waves to propagating waves at its interface with normal materials and, the propagation of electromagnetic waves with very large wavevectors comparing they are evanescent waves and thus decay quickly in natural materials. In this abstract, I will focus discussing our efforts in achieving the unique optical property overcoming diffraction limit to achieve several extraordinary metamaterials and metadevices demonstration. First, I will present super-resolution imaging device called "hyperlens", which is the first experimental demonstration of near- to far-field imaging at visible light with resolution beyond the diffraction limit in two lateral dimensions. Second, I will show another unique application of metamaterials for miniaturizing optical cavity, a key component to make lasers, into the nanoscale for the first time. It shows the cavity array which successfully captured light in 20nm dimension and show very high figure of merit experimentally. Last, I will discuss the future direction of the hyperbolic metamaterial and outlook for the practical applications. I believe our efforts in sub-wavelength metamaterials having such extraordinary optical properties will lead to further advanced nanophotonics and nanooptics research.

• 천문학회보
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• 제38권2호
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• pp.88.2-88.2
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• 2013

Exploration of the wave-mode identification and its propagating property in the solar pore is desirable to study the energy transfer in the solar atmosphere. The Fast Imaging Solar Spectrograph (FISS) installed at the New Solar Telescope (NST) is a unique system that can do imaging of H-alpha and Ca II 8542 band simultaneously, which is quite suitable for studying of dynamics of chromosphere. In this study, we inspect a relationship between the cross-sectional area and intensity of the pore at continuum (-0.4 nm) near the Ca II line. We find coherent oscillations of the area and intensity. They shows out-of-phase (~ 180 degree difference) in photosphere, which implies that the oscillation is fast sausage mode. We also investigate a relationship between LOS velocities above the pore obtained from the Ca II and the Ha line cores, and find no significant difference of the phase (~10 degree) between the formation heights of the lines in chromosphere.

• 비파괴검사학회지
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• 제26권2호
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• pp.115-121
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• 2006

유한 요소 해석을 위해서는 형상과 경계, 하중 조건 그리고 물성을 결정하여야 한다. 그러나 살아 있는 인체에 대해서는 실험이 어렵기 때문에 정확한 형상과 물성을 얻기가 매우 어렵다. 본 논문에서는 한국인 표준체형을 가진 젊은 남성의 생체 자기 공명 영상(MRI : magnetic resonance imaging)을 이용하여 내부 장기를 38가지로 구역화 하고 이것을 이용하여 정밀 유한 요소 모델을 만들었다. 또한 인체를 이루고 있는 다양한 물질들 가운데 뼈에 대한 물성을 얻기 위한 연구를 시행하였다. 인체 뼈의 이방성을 표현할 수 있는 물성을 얻기 위해 성인 남성과 여성의 사체에서 얻은 대퇴골두 시편을 RUS(resonant ultrasound spectroscopy)를 사용하여 탄성 계수 행렬을 얻을 수 있었다.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2007년도 특별 심포지엄 논문집
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• pp.31-42
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• 2007

Dc resistivity monitoring has been increasingly used in order to understand the changes of subsurface conditions in terms of conductivity. The commonly adopted interpretation approach which separately inverts time-lapse data may generate inversion artifacts due to measurement error. Eventually the contaminated error amplifies the artifacts when reconstructing the difference images to quantitatively estimate the change of ground condition. In order to alleviate the problems, we defined the subsurface structure as four dimensional (4-D) space-time model and developed 4-D inversion algorithm which can calculate the reasonable subsurface structure continuously changing in time even when the material properties change during data measurements. In this paper, we discussed two case histories of resistivity monitoring to study the ground condition change when the properties of the subsurface material were artificially altered by injecting conductive materials into the ground: (1) dye tracer experiment to study the applicability of electrical resistivity tomography to monitoring of water movement in soil profile and (2) the evaluation of cement grouting performed to reinforce the ground. Through these two case histories, we demonstrated that the 4-D resistivity imaging technique is very powerful to precisely delineate the change of ground condition. Particularly owing to the 4-D inversion algorithm, we were able to reconstruct the history of the change of subsurface material property.

• Current Optics and Photonics
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• 제2권4호
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• pp.368-377
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• 2018

In this paper, we evaluate cryptographic properties of a double random phase encoding (DRPE) scheme in the discrete Gyrator domain with avalanche and bit independence criterions. DRPE in the discrete Gyrator domain is reported to have higher security than traditional DRPE in the Fourier domain because the rotation angle involved in the Gyrator transform is viewed as additional secret keys. However, our numerical experimental results demonstrate that the DRPE in the discrete Gyrator domain has an excellent bit independence feature but does not possess a good avalanche effect property and hence needs to be improved to satisfy with acceptable avalanche effect that would be robust against statistical-based cryptanalysis. We compare our results with the avalanche and bit independence criterion (BIC) performances of the conventional DRPE scheme, and improve the avalanche effect of DRPE in the discrete Gyrator domain by integrating a photon counting imaging technique. Although the Gyrator transform-based image cryptosystem has been studied, to the best of our knowledge, this is the first report on a cryptographic evaluation of discrete Gyrator transform with avalanche and bit independence criterions.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.361-361
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• 2007

A lot of efforts have been paid to develop infrared imaging systems in last decades. Bolometer has a wide range of applications from military to commercial, such as military night vision, medical imaging system and so on. Bolometer is a resistive sensor that detects temperature changes through resistance change. To improve detecting ability, bolometer should have a good resistive film which has high temperature coefficient of resistance (TCR) value. Colossal magnetoresistance (CMR) $L_{1-x}A_xMnO_3$ (where L and A are trivalent rare-earth ions and divalent alkaline earth ions, respectively.) are received attention to apply bolometer resistive film because it has a high TCR property which was discovered in the metal to semiconductor phase transition temperature region. In this work, CMR films were deposited on various substrates in relative low substrate temperature by RF magnetron sputtering. The influence of deposition parameters such as substrate temperature, gas partial pressure, and so on have been studied. The structural and TCR properties of the films were also investigated for applying to microbolometer.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.781-789
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• 2008

The fluorescence ratio method for processing planar laser induced fluorescence(PLIF) data was generalized for quantitative imaging of the injectant mole-fraction in supersonic mixing flowfields. The original fluorescence ratio approach was introduced by Hartfield et al. for tests in a special closed-loop wind tunnel to eliminate the effects of thermodynamic property variations in compressible flowfields and to provide a quantitative means of mole-fraction measurement. However, they implicitly assumed that the tracer molecules were seeded at the same fraction in both main and secondary flows. In the present study, we proposed generalizing the Hartfield method by considering differences in the tracer seeding rates. We examined the generalized method in a mixing flowfield formed by sonic transverse injection into a Mach 1.8 supersonic air stream. The injectant molefraction distribution obtained from PLIF data processed by our new approach showed better agreement with the gas chromatograph than one based on the Hartfield method.

• Molecules and Cells
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• 제44권11호
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• pp.851-860
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• 2021

Label-free optical diffraction tomography (ODT), an imaging technology that does not require fluorescent labeling or other pre-processing, can overcome the limitations of conventional cell imaging technologies, such as fluorescence and electron microscopy. In this study, we used ODT to characterize the cellular organelles of three different stem cells-namely, human liver derived stem cell, human umbilical cord matrix derived mesenchymal stem cell, and human induced pluripotent stem cell-based on their refractive index and volume of organelles. The physical property of each stem cell was compared with that of fibroblast. Based on our findings, the characteristic physical properties of specific stem cells can be quantitatively distinguished based on their refractive index and volume of cellular organelles. Altogether, the method employed herein could aid in the distinction of living stem cells from normal cells without the use of fluorescence or specific biomarkers.