• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.213-216
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• 2000

본 연구에서는 마이크로폰 어레이를 이용하여 화자의 음성신호로부터 화자의 위치를 추정하는 기존의 대표적인 알고리듬인 CPSP(Cross Power Spectrum Phase)로부터 보다 반향에 강인한 알고리듬인 저주파 위상 복원 알고리듬을 제안한다. CPSP 함수는 상호 상관관계(Cross Correlation)가 정규화 되어있는 형태를 갖는데, CPSP 함수의 최대 값 인덱스로부터 화자의 공간정보인 TDOA(Time Difference Of Arrival)를 추출한다. 그러나 CPSP 함수를 이용한 공간정보 추정 알고리듬은 실내환경에서 심각하게 일어나는 반향신호에 대해서 취약한 단점을 갖고 있다. 본 논문에서 제안하는 저주파 위상복원 알고리듬은 주파수 측면에서 반향신호가 CPSP 함수에 미치는 영향을 분석하여 반향으로 인하여 왜곡된 위상 성분을 복원함으로써 보다 신뢰도 있는 TDOA 추정을 가능하게 한다. 반향신호로 인한 CPSP의 위상은 저주파보다 고주파에서 심하게 왜곡되는데, 각각의 반향신호의 도달 시간을 기하학적 분포를 갖는 확률변수로 모델링하여 이를 수학적으로 증명하였다. 또한 실제 환경에서 채집한 음성신호를 이용한 모의 실험을 통해 개선된 알고리듬의 성능 개선을 확인하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.8
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• pp.85-90
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• 2003

To control spacecraft including satellite, we should understand precisely the performance of propulsion system and the program logic with appropriate format for satellite operations. In this study, the thruster performance functions was generated by using the best curve fitting for performance data from bi-propellant thrusters. Detailed thruster performance data are, in general, company proprietary information, therefore real firing tests were performed to understand the basic characteristics of the performance curve. Experimental rocket motor utilize liquid oxygen and kerosine as propellant and designed average thrust was 100 pound.

• Solar Energy
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• v.12 no.3
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• pp.107-115
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• 1992

An experiment was performed to study solidification of binary mixture with double-diffusive convection in the liquid. A rectangular enclosure was filled with ammonium chloridewater solution. The phase change and convection process were studied through shadowgraph. Becasuse of the double-diffusive convection, the temperature field and concentration filed were stratified very rapidly. Correlation between solidified mass fraction and the dimensionless numbers was found; solidified mass concentration can be expressed as a linear function of $(Ste{\cdot}Ra^{1/4})^{2-Ste}{\cdot}Fo^{1/2}$.

• Journal of the Korean Wood Science and Technology
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• v.28 no.2
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• pp.3-9
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• 2000

This study concerns the distribution and dependence of moisture content(MC) in wood for same thickness in different vapor transmission conditions. The specimens were disks of 70-mm in diameter and 20-mm in thickness from quartersawn lumber of Korean red pine(Pinus densiflora S. et Z.). The experiments were conducted in ten different conditions on the difference of the vapor pressures by the JIS Z-0208. The distribution of moisture content in wood can be illustrated by two straight lines intersecting at the point of about ten percent Me. On the other hand, when more or less than about 10 percent, the distribution of the Me can be illustrated by one straight lines. Therefore, it is considered that the values of 10 percent Me has no relation to the wood and experimental conditions. It's assumed that 10 percent is the boundary point at which the moisture sorption energy changes. In a previous study, diffusion coefficient is almost constant with no relation to a thickness of the woods for the constant experimental conditions. But, in this study, it seems that diffusion coefficient from the moisture gradient vary with the Me of wood in different vapor transmission conditions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.4
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• pp.511-517
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• 1998

In this paper a new technique to generate spreading code sequences in the CDMA communication is introduced. It is an effective method to generate optimal code sequences using the orthogonality of wavelet packet basis set of subspaces. With a three-stage Quadrature Mirror Filter(QMF), generation of optimal code sequences has been demonstrated. Since these generated optimal code sequences are non-binary and have an arbitrary waveform which is different from that of the conventional PN-based Gold code sequences, a strong security against the intended interceptor is feasible. Encouraging good correlation properties are also achieved with this new method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.122-124
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• 2006

Ta-Mo를 co-sputtering으로 증착하여 MOS-C(Capacitor)를 제작하였다. 열적 화학적 안정성을 판별하기 위해 $600^{\circ}C$, $700^{\circ}C$, $800^{\circ}C$ 에서 급속 열처리를 행하였고, C-V 측정으로 얻은 데이터로 평탄 전압, 일함수, EOT값을 계산 하였다. I-V 측정으로 누설 전류 특성을 파악 하였다. 위의 실험 데이터를 종합하여 폴리 실리콘 게이트를 대체할 차세대 게이트 물질로써 Ta-Mo 게이트 물질을 제안하였다.

• Journal of the Korean Data and Information Science Society
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• v.22 no.1
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• pp.89-97
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• 2011

The aims of this study were to propose a method of estimation for mean residual life function (MRLF) from conditional survival function using the Buckley and James's (1979) pseudo random variables, and then to assess the performance of the proposed method through the simulation studies. The mean squared error (MSE) of proposed method were less than those of the Cox's proportional hazard model (PHM) and Beran's nonparametric method for non-PHM case. Futhermore in the case of PHM, the MSE's of proposed method were similar to those of Cox's PHM. Finally, to evaluate the appropriateness of practical use, we applied the proposed method to the gastric cancer data. The data set consist of the 1, 192 patients with gastric cancer underwent surgery at the Department of Surgery, K-University Hospital.

• The Korean Journal of Applied Statistics
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• v.24 no.2
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• pp.269-278
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• 2011

There are many researches that have considered the distribution functions and appropriate covariates corresponding to the scores in order to improve the accuracy of a diagnostic test, including the ROC curve that is represented with the relations of the sensitivity and the specificity. The ROC analysis was used by the regression model including some covariates under the assumptions that its distribution function is known or estimable. In this work, we consider a general situation that both the distribution function and the elects of covariates are unknown. For the ROC analysis, the mixtures of normal distributions are used to estimate the distribution function fitted to the credit evaluation data that is consisted of the score random variable and two sub-populations of parameters. The AUC measure is explored to compare with the nonparametric and empirical ROC curve. We conclude that the method using normal mixtures is fitted to the classical one better than other methods.

• Journal of the Korean Society for Railway
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• v.16 no.4
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• pp.318-330
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• 2013

It is necessary to estimate the operating cost for constructing an urban railway system. The present study was thus carried out to develop an estimation function of the operating cost for a MRT(Medium-sized Rapid Transit) system. We selected seven independent variables that could influence the operating cost: the rolling stocks, the number of trains in operation, the length of the lines, the number of stations, the number of passengers per day, the frequency of train operation, and the number of depots. We performed a multiple regression using Excel. Three types of regression functions were thereupon developed. All of them proved to be appropriate after comparing the results of the estimated cost. It will therefore be possible to use one of these three types, depending on the assumptions of the independent variables.

• The Journal of the Acoustical Society of Korea
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• v.27 no.7
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• pp.350-356
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• 2008

In this paper, we propose shading functions to the appropriate focused beamforming for near-field target estimation. This near field shading functions are based on Chebychev and Manning windows. In order to obtain the optimum sensor weighting values with the help of the proposed shading technique, we assume that the sensor positions associated to the non-uniformly distributed array are precisely known. We calculate a series of sensor weighting values from the FFT operation of given shading functions in time domain. By applying the shading weights on the sensor array, we can see that the level of sidelobe becomes diminished and the performance of estimating range and azimuth gets improved. In addition, we propose a non-uniform structure in terms of frequency bands, which may minimize the attenuation of incoming signals.