• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1B
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• pp.66-78
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• 2002

In this paper, we propose a new symbol offset estimation technique for an orthogonal frequency-division multiplexing (OFDM)-based wireless LAN. When both inter-symbol interference (ISI) and inter-channel interference (ICI) do not exist in an OFDM symbol, symbol offsets cause circular shifts in the estimated channel impulse response (CIR) by the amount of symbol offset. Also, the power delay profile of a typical multipath wireless channel can be modeled by exponentially decaying function, and most energy of multipath channel is concentrated at the beginning part of the CIR. Based on these properties, the proposed symbol offset estimation technique estimates the CIR, which is circularly shifted by the amount of symbol offset, and then calculates the partial mean power from the estimated impulse response by using a moving window with a finite length. And, symbol offset can be estimated from the index of a moving window having the maximal partial mean power. The proposed technique can reduce noise effect in the process of the CIR estimation, and remove ISI and ICI using repetitive training symbol structure in time-domain for minimum training overhead. The performances of the proposed symbol offset estimation technique in typical indoor channels are demonstrated by computer simulation.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2000.11a
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• pp.63-63
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• 2000

저급의 고지 원료를 두께 방향으로 고온 압착을 가하여 건조함으로써 전반적인 종이 물성 을 향상시키는 콘디벨트 건조 방식은 70년대 중반부터 80년대에 이르는 10여년에 걸친 개발 과정을 거쳤으며 90년대에 들어서 핀랜드의 Inkeroinen에 위치한 V alemt- Tarnpella의 연구 소에 최초의 파일로트 설비가 설치되었으며 그 후 1996년에는 핀랜드 ENSO사의 P Pank밟oski 판지공장에 설치됨으로써 세계 최초의 상업생산설비를 이루게 되었다. 기존의 실린더 건조 기술과 비교할 때 콘디벨트 건조방식은 건조속도를 약 5-15배 향상시킬 수 있 으며, 건조 에너지 절감에 큰 효과가 있을 뿐만 아니라 기존의 실린더 건조시 종이가 폭방 향으로 수축되 어 인장 stiffness와 압축 강도 동의 종이 물성 이 저 하되 는 반면 습윤상태 의 섬유를 120도씨이상에서 가열에 의해 리그닌을 연화시킴과 동시에 섬유의 유연성을 증가시켜 준다. 그리고 높은 압력을 가해줌으로써 섬유간의 결합 면적을 증가시키고 건조시 종이의 폭방향의 수축을 감소시켜 인장강도, 내부결합강도, 밀도, 표면평활성, 투기저항성 등 종이의 물성을 대폭 향상시켜주는 혁신적인 제지기술로 인정받고 있으며 국내의 경우 현재 1998년 부터 상업생산을 이루어짐으로써 그 공헌도는 매우 크다고 할 수 있다. 골판지의 주원료가 되는 국산 골판지 고지 (Korean old corrugated container, K KOCC)의 거듭된 재생처리로 인하여 미세분의 함량이 전체 지료의 절반 이상에 달할 뿐만 아니라, 섬유가 각질화와 단섬유화로 인하여 고온압착 건조처리 만으로는 골판지 고지로 생 산된 원지의 강도를 버진펄프로 생산된 원지가 가지는 강도에 준하는 강도로 향상시키는데 한계점을 가지게 된다. 유럽의 제지선진국들은 골판지 원지의 강도를 향상시키는 방편으로 표변에 전분 사이즈 프레스 처리를 도입하였으며 본 연구에서는 고온 압착 건조 처리 설비를 활용한 전분 표면처리의 가능성을 검토하고 골판지 원지의 강도를 향상시키기 위한 표면처리조건을 탐색하였다.

• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.548-553
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• 2002

We have investigated the output characteristics of a Nd:YAG oscillator with a Stimulated Brillouin Scattering phase conjugation mirror (SBS-PCM). FC-75 is used as an SBS gain medium and Cr:YAG (T=50%) as a Q-switcher. The SBS-PCM consists of an SBS-cell and a simple plano-convex focusing lens system. For the case of not using a Q-switcher, an SBS-cell doesn't work as a phase conjugation mirror. For the case of using a Q-switcher, the energy characteristics remains nearly the same whether using the SBS-cell or not using it. The pulse width is reduced from 50 ns to 40 ns by an SBS-PCM. When the SBS-cell is used with a Q- switcher, the SBS-cell works very well as a phase conjugation mirror and its beam-profile is improved dramatically. And in order to explain the progression of beam-profile, we propose a simple model based on the nonlinear reflectivity of the SBS-PCM, whose reflectivity is dependent on the pumping intensity at the focal plane.

• Nuclear Engineering and Technology
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• v.27 no.1
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• pp.74-83
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• 1995

The accurate determination of the fast neutron flux/fluence onto the pressure vessel is an essential part of the reactor pressure vessel surveillance program. It has been reported recently that the iron cross section data in ENDF/B versions III through V might underestimate the flux/fluence of fast neutrons in steel structures such as reactor pressure vessel. In this study, for the comparison of iron data of ENDF/B-IV and VI we produced two 47-group cross section sets, CXFe-IV and CXFe-Ⅵ, which are based on Yonggwang nuclear unit-3/4 model and the iron data of ENDF/B-IV and VI, respectively. A comparison was made of the results obtained from DOT4.3 calculation using CXFe-IV and CXFe-VI. From the results, it was found that the fast flux(E 〉 1.0 MeV), which is important for the pressure vessel embrittlement analysis, increases by about 7.6％ at the inner wall and 20％ at the outer wall of the vessel, if the iron data are used from ENDF/B-VI instead of ENDF/B-IV.

• Journal of the Institute of Convergence Signal Processing
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• v.5 no.1
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• pp.66-72
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• 2004

PID control has been well used for several decades. For PID algorithms, some tuning methods are used for selecting PID parameters and with these selected parameters, PID control system is designed. But in some cases various kinds of performance indices are used instead of well-known tuning rules, and so variable type of performance index must be tested so that the designed control system meets the some specifications. For 2 DOF PID controller design this paper presents a linear combinational type of performance indices constituting of index for robust performance, which is obtained by h infinity norm of a weighted complementary sensitivity function, including other time domain indices such as error, energy and changing rate of control input. By numerical methods, the optimal 2 DOF PID parameters are obtained. Therefore various types of 2 degree of freedom PID controllers such as I-PD controller are used so that this two degree of freedom PID controllers may give more desirable output characteristics. Simulations are done with MATLAB m file and mdl files.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.11a
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• pp.880-883
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• 2002

In this paper, we propose the synchronization recovery algorithm which is suitable to wireless multimedia of wireless channel situation which is being used OFDM signaling method. The basic of the suggested clock synchronization. restoration Algorithm is to getting the shock response of channel or getting the multipath strength profile through IFFT after the getting the frequency, response of deducted channel from channel deductor of receiver and to trace the location in the channel energy concentrated area of timing area. And it also analysis the start point of 64-QAM and 16-QAM if the sampling clock offset has the sample of $\pm$1-3, and we identified the occurance of performance deterioration when occures more than 2 samples of offset to compare with star point and BER performance in optimum sampling point result of BER performance checking, and we know that the recovery algorithm proposed algorithm also provide excellent synchronization characteries under frequency, selecting fading channel as result of simulation.

• Clean Technology
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• v.18 no.1
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• pp.31-37
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• 2012

Biomass has become a major feedstock for bioenergy and other bio-based products because of its renewability and environmental benefits. Various researches have been done in the prediction of crucial characteristics of biomass, including the active utilization of spectroscopy data. Near infrared (NIR) spectroscopy has been widely used because of its attractive features: it's non-destructive and cost-effective producing fast and reliable analysis results. This work developed the multivariate statistical scheme for predicting weight loss profiles based on the utilization of NIR spectra data measured for six lignocellulosic biomass types. Wavelet analysis was used as a compression tool to suppress irrelevant noise and to select features or wavelengths that better explain NIR data. The developed scheme was demonstrated using real NIR data sets, in which different prediction models were evaluated in terms of prediction performance. In addition, the benefits of using right pretreatment of NIR spectra were also given. In our case, it turned out that compression of high-dimensional NIR spectra by wavelet and then PLS modeling yielded more reliable prediction results without handling full set of noisy data. This work showed that the developed scheme can be easily applied for rapid analysis of biomass.

• Journal of the Korean Institute of Gas
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• v.17 no.5
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• pp.58-63
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• 2013

LNG(Liquefied Natural Gas) has been considered as the green energy. Thus, the demand of natural gas is keep increasing around the world, and various studies are actively under progress about the LNG storage tank. To calculate the seismic forces of actual LNG storage tank, FEM model has to include inner tank, outer tank, pile and soil to implement the interaction between structure and ground. So, this paper is represent the study about inner tank model of three cases using Malhotra method in EN 1998-4(European Standard). The results of calculation were compared, and the most suitable to inner tank model was suggested.

• Tunnel and Underground Space
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• v.20 no.6
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• pp.446-454
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• 2010

CAES-G/T (Compressed Air Energy Storage - Gas Turbine) power generation is a likely option for the buffer facility stabilizing the fluctuation of the renewable powers, such as wind and solar powers. Considering the geological conditions, the underground CAES facility is most probable if the CAES-G/T generation is planed in Korea. In this kind of facility, a concrete plug is installed to seal the compressed air in the container, so that the selection of the shape and dimension of concrete plug could be a critical design factor. The stability evaluation of two types of plug was carried out by investigating the distribution of the factor of safety in the plugs and the distribution of contact pressure over the contact surface. The analysis result shows that the taper-shaped plug is more structurally stable than the wedge-shaped plug for the given geological condition. Possible separation of the rock-concrete interface around the spring line of the wedge-shaped plug is anticipated, which means the possible leakage of compressed air through the side wall and also means the poor mobilization of frictional resistance on that area.

• Journal of Aerospace System Engineering
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• v.17 no.4
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• pp.18-27
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• 2023

In this paper, the structural-thermal-optical performance analysis of the mirror was performed by setting the laser heat source as the boundary condition of the thermal analysis. For the laser heat source model, the Beer-Lambert model considering semi-transparent optical material based on Gaussian beam was selected as the boundary condition, and the mechanical part was not considered, to analyze the performance of only the mirror. As a result of the thermal analysis, thermal stress and thermal deformation data due to temperature change on the surface of the mirror were obtained. The displacement data of the surface due to thermal deformation was fitted to a Zernike polynomial to calculate the optical performance, through which the performance of the mirror when a high-energy laser was incident on the mirror could be predicted.