• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 하계종합학술대회 논문집(1)
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• pp.211-214
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• 2002

In this paper, we present a simple method for characterizing a rectangular waveguide to circular waveguide transition Three standard loads consisting of a short circuit, an offset short circuit 1, and an offset short circuit 2 are sequentially connected to the circular waveguide port and the reflection coefficient at port 1 Is measured for each case. From known reflection coefficients, of standard loads and measured reflection coefficients, the scattering matrix of the transition Is obtained. The proposed method Is verified by the numerical experiment using a commercial software HFSS and by measurments of a actual rectangular-to-circular waveguide transition.

• Journal of electromagnetic engineering and science
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• 제18권2호
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• pp.136-140
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• 2018

We propose an improved semi-empirical scattering model for X-band radar backscattering from rough sea surfaces. This new model has a wider validity range of wind speeds than does the existing semi-empirical sea spectrum (SESS) model. First, we retrieved the small-roughness parameters from the sea surfaces, which were numerically generated using the Pierson-Moskowitz spectrum and measurement datasets for various wind speeds. Then, we computed the backscattering coefficients of the small-roughness surfaces for various wind speeds using the integral equation method model. Finally, the large-roughness characteristics were taken into account by integrating the small-roughness backscattering coefficients multiplying them with the surface slope probability density function for all possible surface slopes. The new model includes a wind speed range below 3.46 m/s, which was not covered by the existing SESS model. The accuracy of the new model was verified with two measurement datasets for various wind speeds from 0.5 m/s to 14 m/s.

• 한국해양공학회지
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• 제28권1호
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• pp.55-63
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• 2014

In this paper, we propose an threshold-based Schur algorithm for estimating the media characteristics of sub-bottom multi-layers by using the signal generated by a parametric array transducer. We use the KZK model to generate a parametric array signal, and use the proposed threshold-based Schur algorithm for estimating the reflection coefficients of multiple sea bottom layers. Using computer simulation, we verify that the difference frequency component generated by the KZK model prevails over the signals of primary frequencies at long range. For the simulation, we use the transmit signal generated by the KZK and the reflected signal obtained from a lattice filter model for the seawater and sub-bottom of multi-level non-homogeneous layers. Through the simulation, we verify that the proposed threshold-based Schur algorithm can give much more accurate and efficient estimates of the reflection coefficients than methods using received signal, matched filter output signal, and normal Schur algorithm output.

• 한국응용과학기술학회지
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• 제19권4호
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• pp.339-348
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• 2002

Self-diffusion coefficients of colloidal ass9Ciation structures in the aqueous solutions of anionic ammonium dodecyl sulfate (ADS) and cationic octadecyltrimethylammonium chloride (OTAC) surfactants were measured by pulsed-gradient spin echo NMR. The results were interpreted on the basis of the ADS/OTAC/water phase diagram. Crossing the phase boundaries, significant changes in self diffusion coefficients were observed and well correlated to the phase diagram. For the micelles their apparent radii were obtained from Stokes-Einstein equation. Their values were 15 for the ADS micelles and 54 ${{\AA}}$ for the OTAC micelles, respectively. For vesicles which were formed spontaneously at different relative amounts of the surfactants and total surfactant concentrations, the radius was measured as 50 to 200 nm. This result is in fair agreement with those by TEM and light scattering.

• 한국전자파학회논문지
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• 제27권7호
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• pp.660-663
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• 2016

본 논문에서는 초목 층 산란모델과 지표면 산란 모델을 이용하여 초목 층에서 수분함유량 측정에 초목 층과 레이다 파라미터가 갖는 영향에 대하여 분석하였다. $1^{st}$-order RTM(Radiative Transfer Model)을 이용하여 여러 상태의 초목 층 밀도와 입사각, 주파수, 편파를 갖는 데이터베이스를 생성하고, WCM(Water Cloud Model)과 Oh 모델을 이용하여 후방산란계수로부터 지표면 수분함유량을 추출하였다. 수분함유량 추출 에러를 예측하기 위해 추출한 수분함유량과 RTM의 입력 변수인 수분함유량을 비교하였다. 수분함유량 추출 에러로부터 초목 층에서의 수분함유량 측정에서 초목 층 밀도와 입사각, 주파수, 편파에 따른 초목 층과 레이다 파라미터의 영향을 분석하였다.

• Journal of Radiation Protection and Research
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• 제43권2호
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• pp.75-84
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• 2018

Background: Gamma-ray spectrometry helps in radiation shielding problems and different applications of radioisotopes. Experimental arrangements including broad beam geometries are widely used. The aim is to investigate and evaluate the ${\gamma}-ray$ spectra via attenuation by environmental materials. Materials and Methods: The photo peak to nominated parts in the ${\gamma}-ray$ spectra and the attenuation coefficients ${\mu}_b/{\rho}$ from broad beam geometries are measured for the materials water, soil, sand and cement at the energies 0.662, 1.25, and 1.332 MeV with a $3{^{\prime}^{\prime}}{\times}3{^{\prime}^{\prime}}$ NaI(Tl) detector. Results and Discussion: The ${\gamma}-ray$ spectra vary according to changes in the effective atomic number $Z_{eff}$ of the attenuator, the photon energy and the solid angle. The peak to total ratios are the most sensitive parts to variations in the experimental conditions and overturn in the region 0.663 MeV to 1.332 MeV. This is indicated as inversion trend. The results are discussed in view of $Z_{eff}$ and the experimental conditions. The intensity build-up is larger at the lower energy and larger scattering angles in agreement with Klein-Nishina formula and other results. The build-up factor B is$${\sim_=}$$1 at high ${\gamma}-energies$ and small scattering angles. Conclusion: The sensitivity to material characteristics decrease gradually from peak: to total, to Compton valley, to Compton plateau ratios. Rigorous collimation is necessary at small energies. Cement, of the largest $Z_{eff}$, is characterized by the maximum broad beam mass attenuation coefficients ${\mu}_b/{\rho}$. The obtained results provide information to decide for the suitable experimental set-up based on aim of the work.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2000년도 춘계종합학술대회
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• pp.460-464
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• 2000

임팩트이온화현상은 소자의 크기가 점점 작아지면서, 높은 에너지에 있는 hot carrier 전송을 해석하기 위해 매우 중요하므로 소자의 시뮬레이션에 정확한 임팩트이온화모델이 필수적이다. 본 연구에서는 의사포텐셜방법을 사용하여 full 밴드모델을 구하고, 임팩트이온화율은 수정된 Keldysh 공식을 이용하여 유도하였다. 본 연구에서는 GaAs 임팩트이온화의 온도와 전계에 대한 의존특성을 조사하기 위하여 Monte Carlo 시뮬레이터를 제작하여 임팩트이온화계수를 구하였다. 결과적으로, 임팩트이온화계수는 300K에서 실험 값과 잘 일치하였다. 또한 에너지는 전계가 증가할수륵 증가하고, 높은 온도에서는 포논산란의 emission mode가 높기 때문에 에너지가 감소함을 알 수 있었다. 임팩트 이온화의 대수 fitting 함수 식은 온도와 전계에 대해 2차 식으로 표현하였다. 대수 fitting 함수의 오차는 대부분 5%이내에 머물렀다. 그러므로 대수 식으로 표현된 임팩트이온화계수는 온도와 전계에 의존함을 알았고, 온도와 전계에 의존하는 임팩트이온화계수를 구하는데 시간을 절약할 수 있다

• 천문학회지
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• 제42권6호
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• pp.161-174
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• 2009

Observation of standard stars is of crucial importance in stellar photometry. We have studied the standard transformation relations of the UBV RI CCD photometric system at the Maidanak Astronomical Observatory in Uzbekistan. All observations were made with the AZT-22 1.5m telescope, SITe 2k CCD or Fairchild 486 CCD, and standard Bessell UBV RI filters from 2003 August to 2007 September. We observed many standard stars around the celestial equator observed by SAAO astronomers. The atmospheric extinction coefficients, photometric zero points, and time variation of photometric zero points of each night were determined. Secondary extinction coefficients and photometric zero points were very stable, while primary extinction coefficients showed a distinct seasonal variation. We also determined the transformation coefficients for each filter. For B, V, R, and I filters, the transformation to the SAAO standard system could be achieved with a straight line or a combination of two straight lines. However, in the case of the U filter and Fairchild 486 CCD combination, a significant non-linear correction term - related to the size of Balmer jump or the strength of the Balmer lines - of up to 0:08 mags was required. We found that our data matched well the SAAO photometry in V, B - V, V - I, and R - I. But in U - B, the difference in zero point was about 3.6 mmag and the scatter was about 0.02 mag. We attribute the relatively large scatter in U -B to the larger error in U of the SAAO photometry. We confirm the mostly small differences between the SAAO standard UBV RI system and the Landolt standard system. We also attempted to interpret the seasonal variation of the atmospheric extinction coefficients in the context of scattering sources in the earth's atmosphere.

• 한국전자파학회논문지
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• 제14권5호
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• pp.458-465
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• 2003

본 논문에서는 3차원 유전체로부터의 전자기 과도 응답을 해석하기 위하여 시간 영역 전장 적분방정식을 이용한 새로운 해법을 제안한다. 이를 위하여 공간 및 시간 시험 과정으로 분리한 갤러킨 방법을 적용한다. 3차원임의 형태의 유전체 표면을 삼각형으로 분할한 다음, 공간에 대한 등가 전류의 전개 및 시험 함수로서 삼각형 벡터 함수를 사용한다. 시간 영역의 미지 계수를 라게르 함수로부터 유도된 기저함수로 근사하며, 이 함수를 시간 영역의 시험 함수로도 사용한다 제안된 방법에 의하여 계산된 등가 전류 및 원거리장의 수치 결과들을 제시한다.

• 한국응용과학기술학회지
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• 제22권2호
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• pp.182-190
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• 2005

The propagation of light radiation within tissues is an important problem that confronts the dosimetry of therapeutic laser delivery and the development of diagnostic spectroscopy. In the clinical application of photodynamic therapy(PDT) and in photobiology, the photon deposition within a tissue determines the spatial distribution of photochemical reactions. Scattered light is measured as a function of the distance (r) between the axis of the incident beam and the detection spot. Consequently, knowledge of the photosensitizer(Chlorophyll-a) function that characterizes a phantom is important. To obtain the results of scattering coefficients(${\mu}s$) of a turbid material from diffusion described by experimental approach. It was measured the energy fluency of photon radiation at the position of penetration depth. From fluorescence experimental method obtained the analytical expression for the scattered light as the values of $(I\;/I_o)_{wavelength}$ vs the distance between the center of the incident beam and optical fiber in terms of the condition of "in situ spectroscopy(optically thick)" and real time by fluorometric measurements.