• 소음진동
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• 제8권5호
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• pp.887-899
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• 1998

It has been resulted that Lagrange multiplier method with statistical approach was superior to traditional harmonic balance method in identifying the nonlinear loudspeaker parameters when output signals were contaminated with Gaussian random noise. We have known that the displacement-dependent characteristic values of nonlinear parameters identified by traditional harmonic balance method were estimated less than original values by the increase of output noise and the stiffness coefficients were very sensitive to output noise. Also, by the sensitivity analysis we have verified that the harmonic distortions in acoustic radiation was mainly due to nonlinearity of force factor caused by uneven magnetic fields and that reducing the nonlinearity of damping coefficients were very effective for improving second harmonic distrotion of acoustic radiation.

• 천문학회보
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• 제35권1호
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• pp.69.2-69.2
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• 2010

The far-ultraviolet (FUV) H2 and C IV emission images and spectra of Orion Eridanus Superbubble (OES) is hereby presented. The OES seems to consists of multiple phase through the detection of highly-ionized gas and pervasive neutral hydrogen. The former is traced by hot gas while the latter is traced by cold medium. A spectral image made with H2 fluorescent emission shows that the spatial distribution of hydrogen molecule is well correlated with the dust map. The model spectra was taken from a photodissociation region (PDR) radiation code which find a best suitable parameter such as hydrogen density, gas temperature and incident uv intensity of the radiation field. C IV emission is caused by intermediate temperature ISM about 10^4.5 K~10^6 K. Therefore we could get more clear evidence to reveal the structure of OES. Feature of spectra for the each sub region is also presented and discussed. The data were obtained with the Far-Ultraviolet Imaging Spectrograph (FIMS) and the whole data handling were followed by previous FIMS analysis.

• 천문학회보
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• 제35권2호
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• pp.71.1-71.1
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• 2010

The far-ultraviolet (FUV) C IV and H2 emission spectra of Orion-Eridanus Superbubble (OES) is hereby presented. The OES seems to consist of multiple phase through the detection of highly-ionized gas and pervasive neutral hydrogen. The former is traced by hot gas while the latter is traced by cold medium. A spectral image made with H2 fluorescent emission shows that the spatial distribution of hydrogen molecule is well correlated with the dust map. The model spectra was taken from a photodissociation region (PDR) radiation code which finds a best suitable parameter such as hydrogen density and intensity of the radiation field. C IV emission is caused by intermediate temperature ISM about 10^5 K. Therefore we could get more clear evidence to reveal the morphology of OES. In this process, the hydrogen density and gas temperature were also estimated. The data were obtained with the Far-Ultraviolet Imaging Spectrograph (FIMS) and the whole data handling were followed by previous FIMS analysis.

• Nuclear Engineering and Technology
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• 제49권8호
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• pp.1636-1644
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• 2017

The main purpose of this article is to describe the magnetohydrodynamic stagnation point flow of Walter-B nanofluid over a stretching sheet. The phenomena of heat and mass transfer are based on the involvement of thermal radiation and chemical reaction. Characteristics of Newtonian heating are given special attention. The Brownian motion and thermophoresis models are introduced in the temperature and concentration expressions. Appropriate variables are implemented for the transformation of partial differential frameworks into sets of ordinary differential equations. Plots for velocity, temperature, and nanoparticle concentration are displayed and analyzed for governing parameters. The skin friction coefficient and local Nusselt and Sherwood numbers are studied using numerical values. The temperature and heat transfer rate are enhanced within the frame of the thermal conjugate parameter.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.317-322
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• 2004

In this paper, It was describe the processes of development of HiFi speaker system. Woofer and tweeter were fabricated by unskilled students and their 1.5 parameters were identified by known mass method. Based on T-S parameters port enclosure was designed and built by means of software. Acoustic radiation phenomena of port enclosure were simulated and compared to test result. Acoustic pressure difference between lower frequency and higher frequency was flattened by adopting optimal crossover network. Finally, built HiFi speaker system was showed good sound quality and sound pressure and electrical impedance was well agreed with test results each other.

• 한국전자파학회논문지
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• 제27권12호
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• pp.1059-1068
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• 2016

본 논문에서는 프린트 다이폴의 지향성 증가와 동시에 부엽 레벨을 억제하는 기능을 가진 저속파 구조를 제안하고 구성 설계변수의 변화에 따른 전기적 특성의 변화를 알아보고자 한다. 유전체 기판과 도체 막대의 배열로 구성된 프린트 형태의 저속파 구조는 프린트 다이폴 안테나의 여기 방향에 위치하며 안테나의 방사 패턴 및 세기에 영향을 미친다. 이 도체 막대로 된 기생소자는 좁은 간격을 가지고 일정하게 배열되며 소자의 길이는 점차 줄어드는 형상을 가진다. 따라서 본 연구에서는 저속파 구조에서 방사 성능에 영향을 줄 수 있는 변수로 기생소자 배열 간격, 소자 길이, 소자 길이의 테이퍼 각도가 고려되며, 변수들의 변화에 따른 전기장 세기 및 위상 분포가 관찰 및 분석된다. 이를 기반으로 방사패턴이 분석이 되며, 고지향성 특성을 위한 저속파 구조의 기생소자 배열 방안이 제공된다. 제안된 안테나는 Wifi 대역(5.15~5.85 GHz)에서 동작하도록 설계되며, 안테나의 이득을 극대화하고 부엽을 억제하도록 저속파 기생소자의 설계변수가 최적화된다. 제작된 안테나의 시뮬레이션 및 측정 결과 넓은 대역폭 특성을 나타내며, 높은 효율과 이득, 낮은 부엽 레벨을 갖는 것을 확인할 수 있다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
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• pp.12-16
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• 2002

The clear sky radiative forcings of aerosols were evaluated over East Asia. We first investigated optical characteristics of aerosol using sky radiation measurements. An algorithm of Nakajima et al. (1996) is used for retrieving aerosol parameters such as optical thickness, ${\AA}$ngstr$\"{O}$m exponent, single scattering albedo, and size distribution from sky-radiation measurements, which then can be used for examining spatial and temporal variations of aerosol. Obtaining aerosol radiative forcing at TOA and surface, a radiative transfer model is used with inputs of obtained aerosol parameters and GMS-5 satellite-based cloud optical properties. Results show that there is a good agreement of simulated downwelling radiative flux at the surface with observation within 10 W m$^{-2}$ rms errors under the clear sky condition. However, a relatively large difference up to 40 W m$^{-2}$ rms error is found under the cloudy sky condition. The computed aerosol radiative forcing at the surface shows downward flux changes ranging from -100 to -170 W m$^{-2}$ per unit aerosol optical thickness at 0.7 $\mu$m. The different values of aerosol radiative forcing among the stations is mainly due to the differences in single scattering albedo ($\omega$$_{0.7}$) and asymmetric parameter (g$_1$) related to the geographical and seasonal variations.

• 대한기계학회논문집B
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• 제35권5호
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• pp.467-472
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• 2011

본 연구는 LED 조명기구와 같은 원형 모양에 적합한 원형 히트싱크의 주위의 열유동을 실험 및 해석적으로 분석하였다. 기존 복사 열전달을 고려하지 않은 상관식을 이용하여, 추가적으로 복사 열전달을 해석적으로 계산하였다. 본 해석 모델의 타당성을 실험적으로 확인하였다. 이 모델을 바탕으로 휜의 형상 및 열유속을 인자로 하여 히트싱크 평균 온도의 변화를 살펴보았다. 그 결과 열전달 성능을 최대로 할 수 있는 최적 휜의 길이가 존재하였고, 방사율이 클수록 형상 인자의 변화가 복사 열전달 변화에 미치는 영향이 상대적으로 감소하였다.

• 한국광학회지
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• 제11권4호
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• pp.221-226
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• 2000

MOT에 포획된 원자 구름의 분포가 포획광의 편광, 어긋난 정렬에 따라 구형, 막대형, 고리형, 가운데 구를 포함한 고리형, 구-구형, 구-고리형 등으로 다양하게 변하는 것을 관측하였다. 이는 포획광의 어긋난 정렬 등에 의한 좌표의존 비대칭 광압(Coordinate-dependent asymmetry radiation force ; CDARF)으로 설명할 수 있었다. 루비듐-87 원자의 S1/2(F=2), P3/2(F=3)준위에 축퇴된 제만 부준위에 대하여 제만 주파수 이동, 자기장과 포획광 방향에 따른 전이 확률, 편광에 따른 전이 확률, 레이저광의 편광, 레이저 광의 공간 분포 등을 고려하여 가능한 정확한 운동방정식을 세우고, 이를 풀어 다양한 형태의 원자구름 분포를 설명하였다.

• Journal of electromagnetic engineering and science
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• 제15권4호
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• pp.224-231
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• 2015

A comparison of the antenna parameters for R-band (1.7-2.6 GHz) and S-band (2.6-3.95 GHz) standard gain horn antennas has been performed by the Korea Research Institute of Standards and Science (KRISS), together with seven domestic participants from private companies and public institutions. Its purpose, as a proficiency test program of the 'Antenna Measurement Club' of KRISS, was to check equivalences in antenna parameter measurements between KRISS and the participants, particularly in the R-/S-band, to support antenna manufacturers and end users in Korea. The measurement parameters of this comparison are the power gain, radiation pattern, and reflection coefficient of the traveling standards for R-/S-band pyramidal standard gain horn antennas. The comparison used a gain comparison method and an extrapolation method to measure the power gain of the two traveling standards; the radiation patterns were measured in the far-field region of the transmitting and receiving antennas.