• Communications for Statistical Applications and Methods
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• 제19권1호
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• pp.23-32
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• 2012

본 논문은 유한모집단에서 회귀계수추정량의 근사편향과 근사분산을 다루고 있다. 유한모집단에서 고정크기 포함확률비례표본을 추출하고 이 표본에서 조사된 데이터에 기초하여 회귀계수를 일반최소제곱추정량과 가중최소제곱추정량으로 추정할 때 두 추정량의 편향, 분산 그리고 평균제곱오차의 근사식을 유도하였다. 그리고 두 추정량의 효율을 비교하기 위하여 두 추정량의 분산을 비교하는 필요충분조건을 제시하였다. 또한 수치적인 비교를 위하여 간단한 예제를 소개하였다.

• 열처리공학회지
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• 제20권2호
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• pp.78-83
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• 2007

CrN coatings were deposited by cathodic arc ion plating method on the SKD11 steel substrates. Atmosphere temperature of $350^{\circ}C$, arc current of 90 A, nitrogen partial pressure of 1.0-5.3 Pa, and negative bias voltage of 30-135 V were selected. The characteristics of microstructure were investigated with XRD. Hardness, adhesion and friction coefficient measured by microhardness tester, scratch tester, and ball on disk tribometer. Microstructures depended on nitrogen partial pressure and bias voltage. The preferred orientation of the films was changed from (200) to (111) with decreasing pressure and increasing bias voltage. Adhesion properties related with microstructure, but microstructure changes slightly influenced on hardness and friction properties. The critical load.($Lc_1$) and hardness of CrN films deposited at 5.3 Pa, -30 V condition were 55 N(HF1), $2157{\pm}47\;Hk_{0.025}$. The friction coefficient were about 0.5 under dry condition.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 추계학술대회 논문집 학회본부
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• pp.200-202
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• 1996

MgO film was deposited on the glass substrate by the hollow cathode discharge ion plating method and the characteristics of the MgO thin film such as deposition rate, crystalline orientation, surface morphology and secondary electron coefficient were investigated. The deposition rate of MgO thin films were $430^{\sim}1270{\AA}$/min at various temperatures and biases. The crystalline orientation of the MgO thin film changed from (200) to (220) upon increasing the HCD current from 100A to 200A. These results indicated that the crystallin orientation of the MgO thin film was determined by the super-saturation ratio. The (200) peak decreased and the (220) peak increased as the substrate bias increased, while both peaks increased as the substrate temperature increased. The grain size increased as the substrate bias increased and the secondary electron emission coefficient increased as the substrate bias increased.

• Journal of the Korean Statistical Society
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• 제35권3호
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• pp.331-341
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• 2006

An approximate distribution of the plug-in estimator of the squared coefficient of variation ($CV^2$) is derived by using Edgeworth expansions under general population models. Also bias of the estimator is investigated for several important distributions. Under the normal distribution, we proposed the new estimator for $CV^2$ based on median of the sampling distribution of plug-in estimator.

• 한국표면공학회지
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• 제35권3호
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• pp.121-126
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• 2002

WC/C multilayered films were deposited by arc ion plating and magnetron sputter hybrid system with various $C_2$H$_2$ flow rates and bias voltages. The coatings have been characterized with respect to their chemical composition (Glow Discharge Optical Emission Spectroscopy), hardness(Knoop micro-hardness), residual stress(Laser beam bending) and friction coefficient(Ball on disc type wear test). Deposition rate, microhardness and residual stress of WC/C films were observed to increase with increasing the $C_2$$H_2$ flow rates. The highest hardness and residual stress were measured to be 26.5 GPa and 1.1GPa for, WC/C film deposited at substrate bias of -100V. WC/C multilayered film was obtained very low friction coefficient(~0.1).

• 한국세라믹학회지
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• 제40권10호
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• pp.921-924
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• 2003

A current-voltage relation for Positive Temperature Coefficient of Resistance (PTCR) ceramic was derived and compared with the experimental data. The new current-voltage relation was developed based on Heywangs double Schottky barrier model and a bias distribution across the grain boundary. The voltage limitation V < 4${\Phi}$$\sub$b/ suggested by Heywang is no longer necessary in the new expression for the voltage dependence of the resistance. The pulsed voltages were applied to the PTCR ceramic specimen in order to avoid possible temperature variation during the measurement.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2006년도 하계종합학술대회
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• pp.635-636
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• 2006

A self-biased CMOS current reference is described which provides supply and temperature independent bias current. The supply independency is obtained by subtracting two bias currents which have the same supply dependency. Unlike the conventional self-bias CMOS current reference, excellent supply independency can be obtained even with the minimum channel length devices and thus smaller area implementation becomes possible. The supply independent bias current is then applied to a temperature compensating circuit and as a result supply and temperature independent bias current is obtained. The current reference has been implemented in a $0.25{\mu}m$ standard CMOS technology. The active silicon area is only $45{\mu}m{\times}45{\mu}m$. The simulated temperature coefficient is 64ppm/$^{\circ}C$ in temperature range between $0^{\circ}C$ and $120^{\circ}C$. Supply voltage can be as low as 1.3V and the supply dependency of the current reference is measured to be smaller than 4500ppm/V. While providing $10.25{\mu}A$ output current, the current reference consumes $160{\mu}W$.

• 한국전기전자재료학회논문지
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• 제34권5호
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• pp.382-385
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• 2021

Electrical poling is a crucial step to convert ferroelectrics to piezoelectrics. Nevertheless, no systematic investigation on the effect of poling has been reported. Given that the poling involves an alignment of spontaneous polarization, the condition for poling should be different when a material has an internal bias field that influences the domain stability. Here, we present the effect of poling profile on the dielectric and piezoelectric properties in Mn-doped Pb(Mg_1/3Nb_2/3)O₃-29 mol%PbTiO₃ single crystal with an internal bias field. We showed that both the dielectric permittivity and the piezoelectric coefficient were further enhanced when the poling procedure ends with a field application along the opposite direction to the internal bias field. We expect that the current finding would give a clue to understanding the true mechanism for the electrical poling.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
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• pp.361-365
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• 2002

Rain-rate retrieval using the NOAA/AMSU (Advanced Microwave Sounding Unit) (Zaho et al., 2001) has been implemented at METRI/KMA since 2001. Here, we present the results of the AMSU derived rain-rate and validation result, especially for the rainfall associated with the tropical cyclone for 2001. For the validation, we use rain-rate derived from the ground based radar and/or rainfall observation from the rain gauge in Korea. We estimate the bias score, threat score, bias, RMSE and correlation coefficient for total of 16 tropical cyclone cases. Bias score shows around 1.3 and it increases with the increasing threshold value of rain-rate, while the threat score extends from 0.4 to 0.6 with the increasing threshold value of precipitation. The averaged rain-rate for at all 16 cases is 3.96mm/hr and 1.41mm/hr for the retrieved from AMSU and the ground observation, respectively. On the other hand, AMSU rain-rate shows a much better agreement with the ground based observation over inner part of tropical cyclone than over the outer part (Correlation coefficient for convective region is about 0.7, while it is only about 0.3 over the stratiform region). The larger discrepancy of tile correlation coefficient with the different part of the tropical cyclone is partly due to the time difference in between ice water path and surface rainfall. This results indicates that it might be better to develop the algorithm for different rain classes such as convective and stratiform.

• 한국강구조학회 논문집
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• 제19권2호
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• pp.139-146
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• 2007

국내 LRFD 도로교설계규정의 휨에 대한 재료 저항계수 정립 시 기초 통계자료로 활용하기 위하여 국산 강재를 적용한 강합성 플레이트 거더 단면의 정모멘트 및 부모멘트 하 휨저항강도를 통계적으로 분석하였다. 최근 국내에서 생산된 16,000여 표본의 구조용 강재와 철근에 대한 항복강도와 인장강도 등의 기계적 특성을 통계적으로 분석하여, 공칭강도에 대한 편심계수(bias factor)와 변동계수(coefficient of variation)를 구하였다. 이들 국산 강재와 철근을 적용하여 정 부모멘트를 받는 도로교 강합성 플레이트 거더교 대표단면에 대한 재료 비선형 소성해석을 수행하였으며, 해석결과로부터 모멘트-곡률 곡선을 구하고 단면의 휨저항강도를 산정하였다. 공칭휨강도와 극한휨저항강도를 비교하고 대표적 강합성 단면에 대한 편심계수와 변동계수 통계치를 제시하였다.