Modified 9Cr-1Mo 강의 항온변태처리에 따른 미세조직 및 경도변화

유정훈,주성욱,허성강,신기삼,이수,정연길 국립7개대학공동논문집간행위원회 2003 공업기술연구 Vol.3 No.-

Evolution of microstructure and its relation with hardness in the modified 9%Cr-1%Mo steel which was isothermally heat-treated has been investigated in various heat-treatment temperatures and time of duration. For microstructural and crystallographic analyses, optical microscope, scanning and transmission electron microscopes, energy dispersive spectrometer, and X-ray diffractometer were used. Vickers microhardness tester were used for the measurement of hardness. Precipitates of the complex M23C6, M(C,N) formed at grain boundaries and interiors of grains had led to the secondary hardening. Normalized specimen and all of the isothermally heat-treated ones showed no evidence of retained austenite.

Al-Mg합금(Al-5wt%Mg-3wt%Zn-1wt%Mn)의 T6 열처리에 따른 미세조직 및 기계적 특성변화

유정훈,신기삼,허성강,김정민 국립7개대학공동논문집간행위원회 2005 공업기술연구 Vol.5 No.-

Al-Mg base alloys are attractive for aircraft. automobile and leisure applications because of their properties of low density, high intensity and wear resistance. The effect of Zn and Mn on the properties was studied in an Al-Mg base alloy. After T6 heat-treatment, the change of the microstructure and mechanical property was examined. Our investigations show that after T6 heat-treatment, the elongation was improved. The microstructures are investigated by TEM, which shows that the size of Al6Mn, Al57Mn12 phase is 100~500nm, and it also appears presence of the very small size MgZn₂ phase about 30nm.

9-12%Cr강의 첨가원소 및 열처리에 따른 미세조직거동과 경도변화

주성욱,유정훈,신기삼,허성강,이재현,석진익,김병훈,김정태 국립7개대학공동논문집간행위원회 2004 공업기술연구 Vol.4 No.-

9-12%Cr steel are getting increasing attention for expanded application as high temperature materials applicable for gas turbine compressors, steam turbine rotors, blade and casing. For efficient and extensive application of 9-12%Cr steel, the data in addition to the improvement of mechanical properties on the correlation of microstructural evolution and mechanical properties are inevitable and thus the investigation in this study is performed for the determination for the specimens heat-treated at 600, 650 and 700℃ for 1000, 3000 and 5000hrs. The microstructure of as-received specimen was tempered martensite, with a high dislocation density and secondary phases. Upon high temperature heat-treatment, the martensite lath got larger and dislocation density decreased resulting the reduction of the strength. In addition, sharp growth of secondary phases was observed in the specimen heat-treated at 700℃ for 5000hrs. A specimen aged at 600℃ and 650℃ Laves phase was observed. The hardness showed close relationship with the secondary phase particle and dislocation density.

주요우울증에 대한 Milnacipran의 효과 및 안정성 : Fluoxetine과의 비교

이민수,함병주,기백석,김정범,연병길,오강섭,오병훈,이철,정한용,지익성,최병무,백인호 大韓神經精神醫學會 2004 신경정신의학 Vol.43 No.4

Objectives : This 6-week, open label randomized, multicenter study was conducted to evaluate the antidepressant effect and safety of milnacipran and fluoxetine in patients with major depression. Methods : The study was done in patients with major depression diagnosed by DSM-IV who score ≥17 in 17 items Hamilton Rating Scale for Depression (17-item HAM-D) and score ≥25 in Montgomery and Asberg Depression Rating Scale (MADRS). A total of 87 patients were randomized to milnacipran group and fluoxetine group. In cases of the patients taking other antidepressants, 6 weeks of each medication was administered after 7 days of drug excretion period. The evaluation was done using 17 item HAM-D, MADRS, Clinical Global Impression Scale (CGI), and COVI scale after baseline, 1 week, 2 weeks, 4 weeks, and 6 weeks. The side effects that had occurred during the period of our study were put in records by developed/disappeared time, severities, incidences, managements and results. Results : A total of 87 patients were enrolled. 70 (mitnacipran group 39 ; fluoxetine group 31) of them were included for the 6 weeks of research and 17 of them dropped out with in the first week, not due to adverse reactions or deficiency of effects. Total 17 item HAM-D scores, total points of MADRS, and CGI showed significant decrease after 1 week in each treatment group and continued decrease after 2 weeks and 4, 6 weeks. But there was no difference between milnacipran group and fluoxetine group in the antidepressant effect. There were no significant changes in vital sign, CBC, chemistry, and EKG in each treatment group. The commonly reported side elfects of minlacipran were nausea (25.0%), headache (10.7%), vomiting (7.1%),constipation (7.1%), dizziness (7.1%) and those of fluoxetne were GI trouble (11.1%), diarrhea (11.1%), insomnia (11.1%),agitation (5.6%), and dizziness (5.6%). Conclusion : Milnacipran was effective for the improvement of depressive symptoms and was well tolerated and safe in patients with depression.

An Iterative Algorithm for Data Sharpening in Density Estimation

Kang, Kee-Hoon 한국외국어대학교 기초과학연구소 2001 기초과학연구 Vol.12 No.-

Data sharpening is an useful tool for enhancing statistical properties of conventional nonparametric curve estimators. We propose a simple numerical algorithm for dada sharpening in density estimation. It does not need the estimation procedures of density and its derivative. Numerical results reveal that our algorithm works well and computationally efficient.

Study on mold sterilization using High Electric field generation system

Kang-Hoon Koh,Kee-Yeon Joe,Wook-Jung Kang,Hyun-Woo Lee 전력전자학회 2000 전력전자학술대회 논문집 Vol.2000 No.11

There are several electricity applied sterilizers such as sterilizer with high frequency, sterilizer with ozone, sterilizer with high voltage, and so on. Those sterilizers feature "because there IS no chemical process, there is no secondly environmental pollution" At the power conversion part, ZVS and ZCS methods have been used that it results in reduced switching loss, miniaturized size, and lightened weight. Besides, the current in the device is smaller than that of existing method. Thus, it is expected that the cost of sterilization process, when quality of the device is measured by power consumption, will be reduced.

NONPARAMETRIC ESTIMATION OF THE VARIANCE FUNCTION WITH A CHANGE POINT

Kang Kee-Hoon,Huh Jib The Korean Statistical Society 2006 Journal of the Korean Statistical Society Vol.35 No.1

In this paper we consider an estimation of the discontinuous variance function in nonparametric heteroscedastic random design regression model. We first propose estimators of the change point in the variance function and then construct an estimator of the entire variance function. We examine the rates of convergence of these estimators and give results for their asymptotics. Numerical work reveals that using the proposed change point analysis in the variance function estimation is quite effective.

Versions of Data Sharpening in Density Estimation

KANG, KEE-HOON 한국외국어대학교 외국학종합연구센터 부설 기초과학연구소 2004 기초과학연구 Vol.17 No.-

There are several ways of reducing bias in kernel density estimation. One possible way is introducing the idea of data shapening, which is an useful tool for enhancing statistical properties of conventional nonparaiuetric density estimators. hi this article, we review a i d combine sonie versions of data sharpening approach in density estimation. Those include reducing bias. cross-validation and estimation under constraints.

NONPARAMETRIC ESTIMATION OF THE VARIANCE FUNCTION WITH A CHANGE POINT

KEE-HOON KANG,JIB HUH 한국통계학회 2006 Journal of the Korean Statistical Society Vol.35 No.1

In this paper we consider an estimation of the discontinuous variancefunction in nonparametric heteroscedastic random design regression model.We rst propose estimators of the change point in the variance functionand then construct an estimator of the entire variance function. We exam-ine the rates of convergence of these estimators and give results for theirasymptotics. Numerical work reveals that using the proposed change pointanalysis in the variance function estimation is quite eective.AMS 2000 subject classications.Primary 62G08; Secondary 62G20.Keywords.Discontinuity point, jump size, nonparametric regression, variance estimation,one-sided kernel, rate of convergence.1. IntroductionIn most nonparametric regression function estimation, the variance of errorsis assumed to be a homogeneous or a heterogeneous smooth function. Estima-tion of this variance function has great meaning because it is important in itsown right and in various applications. An estimation of the variance functionis needed in some bandwidth selection procedures, weighted least squares esti-mation, constructions of condence and prediction intervals for mean functions,quality control,etc:These applications are discussed in Carroll (1982), Carrolland Ruppert (1988) and Muller (1988). Variance function estimation is impor-tant for inference purposes as well as risk management based on second momentsof nancial data. Volatility in nancial markets corresponds to variance in con-ventional statistical research areas. Recently, relative high attention is paid tocapture and explain the variation of the second moments of nancial data.Received October 2005; accepted December 2005.1Corresponding author. Department of Statistics, Hankuk University of Foreign Studies,Yongin 449-791, Korea (e-mail : khkang@hufs.ac.kr)

Comparison of Bootstrap Methods for LAD Estimator in AR(1) Model

Kang, Kee-Hoon,Shin, Key-Il 한국통계학회 2006 Communications for statistical applications and me Vol.13 No.3

It has been shown that LAD estimates are more efficient than LS estimates when the error distribution is double exponential in AR(1) model. In order to explore the performance of LAD estimates one can use bootstrap approaches. In this paper we consider the efficiencies of bootstrap methods when we apply LAD estimates with highly variable data. Monte Carlo simulation results are given for comparing generalized bootstrap, stationary bootstrap and threshold bootstrap methods.