• Nuclear Engineering and Technology
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• v.46 no.5
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• pp.619-632
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• 2014

The Best Estimate Plus Uncertainty (BEPU) method has been widely used to evaluate the uncertainty of a best-estimate thermal hydraulic system code against a figure of merit. This uncertainty is typically evaluated based on the physical model's uncertainties determined by expert judgment. This paper introduces the application of data assimilation methodology to determine the uncertainty bands of the physical models, e.g., the mean value and standard deviation of the parameters, based upon the statistical approach rather than expert judgment. Data assimilation suggests a mathematical methodology for the best estimate bias and the uncertainties of the physical models which optimize the system response following the calibration of model parameters and responses. The mathematical approaches include deterministic and probabilistic methods of data assimilation to solve both linear and nonlinear problems with the a posteriori distribution of parameters derived based on Bayes' theorem. The inverse problem was solved analytically to obtain the mean value and standard deviation of the parameters assuming Gaussian distributions for the parameters and responses, and a sampling method was utilized to illustrate the non-Gaussian a posteriori distributions of parameters. SPACE is used to demonstrate the data assimilation method by determining the bias and the uncertainty bands of the physical models employing Bennett's heated tube test data and Becker's post critical heat flux experimental data. Based on the results of the data assimilation process, the major sources of the modeling uncertainties were identified for further model development.

• Nuclear Engineering and Technology
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• v.51 no.7
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• pp.1853-1859
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• 2019

The two-thermocouple method was investigated experimentally to evaluate its accuracy for the measurement of local wall temperature and heat flux on a heat transfer tube with an electric heater rod installed in an annulus channel. This work revealed that a thermocouple flush-mounted in a surface groove serves as a good reference method for the accurate measurement of the wall temperature, whereas two thermocouples installed at different depths in the tube wall yield large bias errors in the calculation of local heat flux and wall temperature. These errors result from conductive and convective changes due to the fin effect of the thermocouple sheath. To eliminate the bias errors, we proposed a calibration method based on both the local heat flux and Reynolds number of the cooling water. The calibration method was validated with the measurement of local heat flux and wall temperature against experimental data obtained for single-phase convection and two-phase condensation flows inside the tube. In the manuscript, Section 1 introduces the importance of local heat flux and wall temperature measurement, Section 2 explains the experimental setup, and Section 3 provides the measured data, causes of measurement errors, and the developed calibration method.

• Korean Journal of Materials Research
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• v.8 no.10
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• pp.961-968
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• 1998

In order to investigate the effects of substrate bias voltage on the formation of$ZnS-SiO_2$ protective film in phase change optical disk by R.F. magnetron sputtering method, thin dielectric film was formed on Si wafer and Corning glass by using ZnS(80mol%)-$SiO_2$(20mol%)t arget under argon gas. In this study, the Taguchi experimental method was applied in order to obtain optimum conditions with reduced number of experiments and to control numerous variables effectively. At the same time this method can assure the reproducibility of experiments. Optimum conditions for film formation obtained by above method were target RF power of 200 W. substrate RF power of 20 W, Ar pressure of 5 mTorr. sputtering time of 20 min.. respectively. The phase of specimen was determined by using XRD and TEM. The compositional analysis of specimen was performed by XPS test. In order to measure the thermal resistivity of deposited specimen, annealing test was carried out at $300^{\circ}C$ and $600^{\circ}C$. For the account of void fraction in thin film, the Bruggeman EMA(Effective Medium Approximation) method was applied using the optical data obtained by Spectroscopic Ellipsometry. According to the results of this work, the existence of strong interaction between bias voltage and sputtering time was confirmed for refractive index value. According to XRD and TEM analysis of specimen, the film structure formed in bias voltage resulted in more refined structures than that formed without bias voltage. But excess bias voltage resulted in grain growth in thin film. It was confirmed that the application of optimum bias voltage increased film density by reduction of void fraction of about 3.7%.

• The Journal of the Korea Contents Association
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• v.13 no.4
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• pp.53-63
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• 2013

This paper presents an importance sampling(IS) embedded experimental frame(EF) design for efficient Monte Carlo (MC) simulation. To achieve IS principles, the proposed EF contains two embedded sub-models, which are classified into Importance Sampler(IS) and Bias Compensator(BC) models. The IS and BC models stand between the existing system model and EF, which leads to enhancement of model reusability. Furthermore, the proposed EF enables to achieve fast stochastic simulation as compared with the crude MC technique. From the abstract two case studies with the utilization of the proposed EF, we can gain interesting experimental results regarding remarkable enhancement of simulation performance. Finally, we expect that this work will serve various content areas for enhancing simulation performance, and besides, it will be utilized as a tool to understand and analyze social phenomena.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.3
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• pp.383-390
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• 2018

Piezoelectric micro-machined ultrasonic transducers for highly directional speaker need DC bias voltage. Most existing power amplifiers are not suitable for use in highly directional transducers because they are based on AC. In addition, since the piezoelectric micro-machined ultrasonic transducer has a large capacitive reactance, the power efficiency of the power amplifier is very low. Thus this paper proposes a new high efficiency power amplifier with DC bias voltage. In addition, by designing a matching circuit to compensate the capacitive reactance of the micro-machined ultrasonic transducer, the power efficiency of the power amplifier increases. The operating characteristics of the proposed power amplifier was verified by an experimental prototype. The proposed power amplifier is expected to be widely used in designing and implementing other related power amplifiers.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.5
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• pp.1-9
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• 2003

To predict the powering performance of full scale ships from the towing tank tests, resistance, propeller open water and self-propulsion tests are conducted. Model tests inevitably include the experimental error defined as the sum of two types of uncertainties, bias and precision errors. The induced errors in each element of model test are propagated through various routes and correlated with one another. The correlation coefficients are very important in the uncertainty analysis. The coefficient gives a direction(increase or decrease) for a value of error in individual elements. If the coefficient is not used accurately, the error bounds of the individual elements are overestimated or underestimated. In this study, the new methodology is applied to the uncertainty analysis of HMRI's towing tank tests, thus error bounds of each element is suggested and verified by several repetitive experiments.

• Journal of Advanced Marine Engineering and Technology
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• v.9 no.3
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• pp.250-256
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• 1985

With the advant of thryistors having large peak inverse voltages, current-source inverters are becoming very popular to feed induction motors. But it is very difficult to analysis the commutation. Since the actual variation of current during commutation is neither instantaneous nor linear and is effected by many parameters. Minimized bias-time of reverse voltages during commutation is expressed in term of machine parameters, capacitor voltage, load current and so on. The minimized bias-time is computed with y and z and also the commuation mechanism is tested on 2.2 kw induction motor. The computed results are compared with the experimental results, and the results give a good information for designing the commutation mechanism.

• The Korean Journal of Applied Statistics
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• v.22 no.1
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• pp.107-114
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• 2009

The present study was carried out to summarize the effect of ginseng in the experimental diabetic rats by meta-analysis related studies. The association measure to test effect of ginseng was the mean difference(MD) between group of rats induced streptozotocin(STZ) and group of rats induced STZ treated with ginseng about the considered effect factors. The level of FI, glucose and TG were significantly reduced(< 0.01), and the level of glycogen was significantly increased by treatment with ginseng (< 0.01) After checking the indication of publication bias for the combined MDs by using the funnel plots, the anti-diabetic effects of ginseng is clearly presented in FI, glucose, TG and glycogen (< 0.05).

• Proceedings of the KIEE Conference
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• 2008.10b
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• pp.165-168
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• 2008

The experimental results of exposing IGBT (Insulated Gate Bipolar Transistor) samples to gamma radiation source show shifting of threshold voltages in the MOSFET and degradation of carrier mobility and current gains. At low total dose rate, the shift of threshold voltage is the major contribution of current increases, but for more than some total dose, the current is increased because of the current gain degradation occurred in the vertical PNP at the output of the IGBTs. In the paper, the collector current characteristics as a function of gate emitter voltage (VGE) curves are tested and analyzed with the model considering the radiation damage on the devices for gate bias and different dose. In addition, the model parameters between simulations and experiments are found and studied.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.8
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• pp.1075-1079
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• 2014

In this paper, we describe the analysis and the compensation method of the g-sensitivity error for MEMS vibratory gyroscopes. Usually, the g-sensitivity error has been ignored in the commercial MEMS gyroscope, but it deserves our attention to apply for the missile application as a tactical grade performance. Thus, it is necessary to compensate for the g-sensitivity error to reach a tactical grade performance. Generally, the g-sensitivity error seems intuitively to be a gyroscope bias error proportional to the linear acceleration. However, we assert that the g-sensitivity error mainly causes not a bias error but a scale-factor error. And we verify that the g-sensitivity scale-factor error occurs due to the non-linearity of parallel plate electrodes. Therefore, we propose the compensation method to remove the g-sensitivity scale-factor error. The experimental result showed that a proposed compensation method improved successfully the performance of the MEMS vibratory gyroscope.