• 한국수소및신에너지학회논문집
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• 제23권6호
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• pp.628-633
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• 2012

It was found that the pure hydrogen-air pre-mixture was self-ignited at a high compression ratio without any assisting method in room temperature, thus refuting the preconception that compression ignition of hydrogen engine was impossible. Therefore, in order to analyze the correlation of compression ignition condition at cold start with hydrogen HCCI engine clearly, the possibility of compression igniting compression ratio is investigated with the change of equivalence ratio and engine speed, experimentally. As the results, it is confirmed that the possibility of compression-igniting compression ratio at cold start was decreased by increasing equivalence ratio due to decreasing auto-ignition temperature. In addition, it is grasped that the possibility of compression-igniting compression ratio at cold start is decreased around 14.9% by increasing engine speed at same supply energy.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2010년도 춘계학술대회 논문집
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• pp.510-510
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• 2010

우리나라에서 고속철도는 이미 중요한 대중교통수단 중 하나가 되었으며 향후에도 운행구간을 확대할 예정인 만큼 승객수도 더욱 증가할 것으로 보인다. 또한 승객수가 증가하는 만큼 정숙한 실내환경의 조성 또한 요구되고 있다. 하지만 현재 철도차량 소음에 관한 연구는 대부분 철도 외부에서 방사되는 소음에 한정되어 있으며 철도차량의 내부 소음 특성에 대한 연구는 미비한 상황이다. 현재 국내 환경소음에 대한 규정은 음압레벨만을 기준으로 하고 있지만 실제로 사람이 소음에 대하여 느끼는 청감특성을 나타내기에는 음압레벨만으로는 부족하다. 사람의 청감특성을 효과적으로 반영하기 위하여 음질(Sound Quality)평가의 방법에 대해 현재 활발하게 연구되고 있다. 본 연구에서는 국내에서 운행중인 고속철도 실내 소음의 특성에 대하여 연구하였다. 음압레벨과 loudness의 관계에 대하여 분석하였고 Zwicker parameter과 ACF, IACF 분석을 통하여 객관적인 음질평가를 실시하였다. 또한 청감실험을 통하여 주관적인 음질평가를 수행하여 청감특성에 대하여 분석하고 객관적 평가의 결과를 검증하였다.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1998년도 추계학술대회
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• pp.121-122
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• 1998

To induce perturbed magnetic field variations in the range of auto prescans permitted, we chose artificially shim values and applied manualy as DC offsets to X, Y, Z gradient amplifiers. The STEAM spectra were obtained from a localized region (8ml) of phantom's center and a Marquart Algorithm is employed to quantify MRS spectra. Results indicated that Creatine (Cr) which had a good correlation between a signal intensity and an area, changed little bit and showed extremly a stabilized state in perturbed magnetic field variations. Therefore, during the MRS experiments, to minimize the SNR reduction by means of unavoidable inhomogeneous magnetic fields, the present study suggested that the quantification method of relative ratios produced by replacing Cr concentration with standard quantify was most desirable.

• 한국소음진동공학회논문집
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• 제20권11호
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• pp.995-1000
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• 2010

With the development of the auto industry, the automobile manufacturers demand to shorten development period and reduce the cost. Compared with the traditional method, applying the virtual prototype is more economical. This paper presents a method for parameters sensitivity analysis and optimizing the performance of vehicle noise and vibration. The existing design processes were repeatedly analyzed with a focus on vehicle performance to decide the design parameters of dimension, thickness, mounting type of body and chassis systems in the vehicle development period. This paper describes the prediction technique of vehicle performance using L18 orthogonal array layout, quality deviation analysis and parameter sensitivity analysis for robust design. This paper analyzed the performance correlation equation through the frequency and sensitivity database according to a design factor change. The new concept is that the performance prediction is possible without repeated activities of test and analysis. This paper described the parameter analysis applications such as bush dynamic stiffness and bush void direction of rear suspension. Design engineer could efficiently decide the design variable using parameter analysis database in early design stage. These improvements can reduce man hour and test development period as well as to achieve stable NVH performance.

• 한국지하수토양환경학회지:지하수토양환경
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• 제15권6호
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• pp.1-8
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• 2010

The groundwater level distribution and characteristics of responses to rainfall were examined in the Haean basin of Yangu that has a single stream exit to the east. The groundwater levels showed a circular or elliptical distribution converging the center of the basin with different hydraulic gradients in the north and south regions. The waterlevel elevations exhibited a perfect correlation with topographic elevation ($r^2=0.99$) while the depth to water showed a rather weak correlation ($r^2=0.49$). The water table fluctuation (WTF) method yielded recharge ratios of 6.1~12.65% ($S_y=0.02$) and 15.2~28.5% ($S_y=0.05$). The waterlevels of HG3 well, which is much proximal to a stream, were weakly auto-correlated but they were highly sensitive to direct infiltration from the rainfall event. The shorter regulation times of the HG3 represented a quicker dissipation of the input stress (rainfall).

• 산경연구논집
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• 제8권1호
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• pp.5-13
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• 2017

Purpose - In this article, a dynamic model like a VAR is an appropriate choice for estimating the possible interrelationship between ownership structure and firm performance as a dynamic process. Research design, data, and methodology - Data of this work are collected from Chinese stock exchange including 350 Chinese-listed firms during the period of 1999-2012. We hypothesize that this interrelationship dynamically exists between ownership structure and firm performance. To examine the correlation, a panel Vector Auto-regression (PVAR) approach generated by GMM method is utilized to test the possible dynamic relation embedded in corporate governance. Another two dynamic analysis solutions such as orthogonalized impulse-response function and variance decomposition are also used simultaneously. Results - Findings of this study indicate the evidence that dynamically endogenous relationship exists between ownership structure and firm performance. Further, there is a dynamical correlation between investment and performance. Impulse response and variance decomposition illustrate that impact of a shock to variables themselves is the main source for their variability. Conclusions - The conclusion in this study is that there is a bidirectional and inter-temporal effect between proportion of ownership and corporate performance for a long run in accordance with impulse response function. Overall, our results suggest that corporate governance in China is more market oriented.

• 물과 미래
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• 제14권4호
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• pp.19-26
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• 1981

자연하천에서의 수질은 유량의 변화에 많은 영향을 받을 것으로 기대되는 바, 유량과 각 수질인자의 통계적 특성 및 유량변화와 수질인자간의 상관관계를 조사하기 위하여 자기 및 상호상관함수 power spectrum, coherence 함수 및 Markov 모형을 적용하였다. 일부 자료만이 입수 가능한 한강 하류부 인도교 지점에서의 유량, 용존산소, 전기전도도는 명백한 1년 주기와 6, 4, 3개월의 약한 주기를 가지며, 유량과 용존산소, 유량과 전도도 사이의 상관은 약하게 나타났고 상호상관함수에서 첨두가 지체 1일에서 발생하여 미약하지만 유량의 변화에 의한 영향이 1일 정도 차이로 수질인자에게 미치는 것으로 해석된다. 계열 발생 및 예측수단인 선형회귀모형의 검토에서 유량은 1차 및 2차 Markov 모형과, 용존산소와 전도도는 1차 Markov 모형과 흡사하게 나타났다.

• International Journal of Automotive Technology
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• 제7권1호
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• pp.43-49
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• 2006

In this paper, an index for the evaluation of a vehicle intake booming noise and intake sound quality were developed through a correlation analysis and a multiple factor regression analysis of objective measurement and subjective evaluation data. At first, an intake orifice noise was measured at the wide-open throttle test condition. And then, an acoustic transfer function between intake orifice noise and interior noise at the steady state condition was estimated. Simultaneously, subjective evaluation was carried out with a 10-scale score by 8 intake noise and vibration expert evaluators. Next, the correlation analysis between the psychoacoustic parameters derived from the measured data and the subjective evaluation was performed. The most critical factor was determined and the corresponding index for intake booming noise and sound quality are obtained from the multiple factor regression method. And, the optimal design of intake system was studied using the booming noise and the sound quality evaluation index for expectation performance of intake system. Conclusively, the optimal designing parameters of intake system from noise level and sound quality whose point of view were extracted by adapting comparative weighting between the booming noise and sound quality evaluation index, which optimized the process. These work could be represented guideline to system engineers, designers and test engineers about optimization procedure of system performance by considering both of noise level and sound quality.

• Journal of Power Electronics
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• 제5권3호
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• pp.198-205
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• 2005

The mechanical system of a drive can often be modeled as a two- or three-mass-system. The load is coupled to the driving motor by a shaft able to perform torsion oscillations. For the automatic tuning of the control, it is necessary to know the mathematical description of the system and the corresponding parameters. As the manpower and setup-time necessary during the commissioning of electrical drives are major cost factors, the development of self-operating identification strategies is a task worth pursuing. This paper presents an identification method which can be utilized for the assisted commissioning of electrical drives. The shaft assembly can be approximated as a two-mass non-rigid mechanical system with four parameters that have to be identified. The mathematical background for an identification procedure is developed and some important implementation issues are addressed. In order to avoid the excitation of the system with its natural resonance frequency, the frequency response can be obtained by exciting the system with a Pseudo Random Binary Signal (PRBS) and using the cross correlation function (CCF) and the auto correlation function (ACF). The reference torque is used as stimulation and the response is the mechanical speed. To determine the parameters, especially in advanced control schemes, a numerical algorithm with excellent convergence characteristics has also been used that can be implemented together with the proposed measurement procedure in order to assist the drive commissioning or to achieve an automatic setting of the control parameters. Simulations and experiments validate the efficiency and reliability of the identification procedure.

• Bulletin of the Korean Chemical Society
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• 제19권4호
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• pp.422-428
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• 1998

In the present paper, we report a molecular dynamics (MD) simulation of non-rigid zeolite-A framework only as the base case for a consistent study of the role of intraframework interaction on several zeolite-A systems using the same technique in our previous studies of rigid zeolite-A frameworks. Usual bond stretching, bond angle bending, torsional rotational, and non-bonded Lennard-Jones and electrostatic interactions are considered as intraframework interaction potentials. The comparison of experimental and calculated structural parameters confirms the validity of our MD simulation for zeolite-A framework. The radial distribution functions of non-rigid zeolite-A framework atoms characterize the vibrational motion of the framework atoms. Mean square displacements are all periodic with a short period of 0.08 ps and a slow change in the amplitude of the vibration with a long period of 0.53 ps. The displacement auto-correlation (DAC) and neighbor-correlation (DNC) functions describe the up-and-down motion of the framework atoms from the center of α-cage and the back-and-forth motion on each ring window from the center of each window. The DAC and DNC functions of the framework atoms from the center of α-cage at the 8-ring windows have the same period of the up-and-down motion, but those functions from the center of 8-ring window at the 8-ring windows are of different periods of the back-and-forth motion.