• 소성∙가공
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• 제32권2호
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• pp.74-80
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• 2023

A deformation behavior of commercially pure titanium (CP-Ti) is highly dependent on material and processing parameters, such as deformation temperature, deformation direction, and strain rate. This study aims to predict the multivariable and nonlinear tensile behavior of CP-Ti using machine learning based on three algorithms: artificial neural network (ANN), light gradient boosting machine (LGBM), and long short-term memory (LSTM). The predictivity for tensile behaviors at the cryogenic temperature was lower than those in the room temperature due to the larger data scattering in the train dataset used in the machine learning. Although LGBM showed the lowest value of root mean squared error, it was not the best strategy owing to the overfitting and step-function morphology different from the actual data. LSTM performed the best as it effectively learned the continuous characteristics of a flow curve as well as it spent the reduced time for machine learning, even without sufficient database and hyperparameter tuning.

• Journal of the Korean Academy of Child and Adolescent Psychiatry
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• 제25권4호
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• pp.196-202
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• 2014

Objectives : The purpose of this study is to evaluate the preliminary effects of school-based short term mental health awareness and school bullying prevention programs. Methods : From April to December 2013, the Child and Adolescent Mental Health Promotion team of Seoul National Hospital conducted school-based short term social skill training (N=56, 4 sessions), mental health awareness (N=84, 4 sessions) and school bullying prevention programs (N=171, 1 session) in elementary and junior high schools located in Seoul. The changes in the subjects before and after the program were assessed. Results : The social skills training program improved the 'helping' behaviors in boys (t=-2.355, p<.05) and 'sharing' (t=-3.223, p<.01), 'cooperation' (t=-2.235, p<.05), and 'comforting' (t=-2.830, p<.01) behaviors in girls, assessed using the Prosocial Behavior Questionnaire. The mental health awareness program improved 'general health awareness' (t=2.620, p<.05), measured using the Korean General Health Questionnaire. The school bullying prevention program resulted in decreased 'self esteem' (t=3.769, p<.01), measured using the Self Esteem Scale and decreased 'anger' (t=4.198, p<.01), assessed using the Novaco Anger Scale. Conclusion : The results of our preliminary analysis suggest that school-based mental health awareness and school bullying prevention programs may be effective even when conducted for a short term. Future investigation is necessary in order to validate the long term effects of these programs.

• 대한교통학회지
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• 제17권1호
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• pp.173-185
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• 1999

서울시는 IMF 경제위기 상황으로 교통시설 투자감소에 의한 공급정체 현상이 예상됨에 따라 교통수요관리에 대한 의존도를 높일 수밖에 없는 실정이다. 그러나 교통수요관리에 대한 기대에도 불구하고 기존의 서울시 교통 수요관리 정책은 단기 교통수요관리 목표 및 수요관리정책 시행에 따른 효과 분석체계의 부재, 교통현상 변화에 대한 지속적 모니터링 체계의 결함 등 문제점이 있음에 따라 그동안 정책효과에 대한 정확한 홍보가 미흡했으며 정책의 지속적 수용성 확보가 어려웠다. 이러한 문제점을 해결하기 위해 서울시에서는 교통혼잡관리프로그램(CMP)의 도입이 필요하게 되었다. 이 프로그램은 서울시의 단기교통관리목표를 설정한 뒤 적정교통수준을 넘어서는 수요를 감축하기 위한 종합적 교통수요관리시책을 마련하고 선정된 대안의 기대효과를 예측할 수 있는 방법론을 구축하며, 신속하게 시행, 모니터링함으로써 서울의 교통수준을 단기적으로 항시 적정수준으로 유지하는 것을 목적으로 하고 있다. 본 연구에서는 서울시의 CMP의 실행을 위해 교통수요관리 프로그램의 효과예측모형(Seoul Congestion Management Model: SECOMM)을 개발하였다. SECOMM의 개발을 통해 단기교통관리목표를 달성하기 위한 적정 교통수요관리 프로그램의 실행전략을 보다 효과적으로 마련할 수 있을 것으로 기대된다.

• 복합신소재구조학회 논문집
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• 제6권2호
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• pp.91-96
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• 2015

GRP pipe (Glass-fiber Reinforced Plastic Pipe) lines making use of FRP (Fiber Reinforced Plastic) are generally thinner, lighter, and stronger than the existing concrete or steel pipe lines, and it is excellent in stiffness/strength per unit weight. In this study, we present the result of field test for buried GRP pipes with large diameter(2,400mm). The vertical and horizontal ring deflections are measured for 387 days. The short-term deflection measured by the field test is compared with the result predicted by the Iowa formula. In addition, the long-term ring deflection is predicted by using the procedure suggested in ASTM D 5365(ANNEX) in the range of 40 to 60 years of service life of the pipe based on the experimental results. From the study, it was found that the long-term vertical and horizontal ring deflection up to 60 years is less than the 5% ring deflection limitation.

• 한국해양공학회지
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• 제21권4호
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• pp.28-33
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• 2007

The objective of this paper is to investigate the relationship between the short-term creep rupture time and the creep rupture properties at three different elevated temperatures in STS304 stainless steel. Uniaxial constant stress creep rupture tests were performed on the steel to observe the creep rupture behaviors at the elevated temperatures of 600, 650 and 700, according to the testing matrix. It is very important to predict creep life in practical creep design problems. As one of the series of studies on the statistical modelling of probabilistic creep rupture time and the development of creep life prediction techniques, the relationship between applied stress and creep rupture behaviors, such as creep strain rate and rupture time, were investigated. In addition, the Monkman-Grant relationship was observed between the steady-state creep rate and the creep rupture time. The creep rupture surfaces observed by SEM showed up dimple phenomenon at all conditions.

• 제어로봇시스템학회논문지
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• 제9권7호
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• pp.527-535
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• 2003

A behavior-based control and learning architecture is proposed, where reinforcement learning is applied to learn proper associations between stimulus and response by using two types of memory called as short Term Memory and Long Term Memory. In particular, to solve delayed-reward problem, a knowledge-propagation (KP) method is proposed, where well-designed or well-trained S-R(stimulus-response) associations for low-level sensors are utilized to learn new S-R associations for high-level sensors, in case that those S-R associations require the same objective such as obstacle avoidance. To show the validity of our proposed KP method, comparative experiments are performed for the cases that (ⅰ) only a delayed reward is used, (ⅱ) some of S-R pairs are preprogrammed, (ⅲ) immediate reward is possible, and (ⅳ) the proposed KP method is applied.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 2007년도 학술발표회 논문집
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• pp.393-394
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• 2007

See Full Text

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 2001년도 추계학술발표회요약집
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• pp.304.1-304
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• 2001

• Nuclear Engineering and Technology
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• 제38권6호
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• pp.459-482
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• 2006

A geochemical approach to the long-term safety of waste disposal is discussed in connection with the significance of actinides, which shall deliver the major radioactivity inventory subsequent to the relatively short-term decay of fission products. Every power reactor generates transuranic (TRU) elements: plutonium and minor actinides (Np, Am, Cm), which consist chiefly of long-lived nuclides emitting alpha radiation. The amount of TRU actinides generated in a fuel life period is found to be relatively small (about 1 wt% or less in spent fuel) but their radioactivity persists many hundred thousands years. Geological confinement of waste containing TRU actinides demands, as a result, fundamental knowledge on the geochemical behavior of actinides in the repository environment for a long period of time. Appraisal of the scientific progress in this subject area is the main objective of the present paper. Following the introductory discussion on natural radioactivities, the nuclear fuel cycle is briefly brought up with reference to actinide generation and waste disposal. As the long-term disposal safety concerns inevitably with actinides, the significance of the aquatic actinide chemistry is summarized in two parts: the fundamental properties relevant to their aquatic behavior and the geochemical reactions in nanoscopic scale. The constrained space of writing allows discussion on some examples only, for which topics of the primary concern are selected, e.g. apparent solubility and colloid generation, colloid-facilitated migration, notable speciation of such processes, etc. Discussion is summed up to end with how to make a geochemical approach available for the long-term disposal safety of nuclear waste or for the performance assessment (PA) as known generally.

• 한국대기환경학회지
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• 제19권2호
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• pp.179-189
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• 2003

The concentration of gaseous elemental mercury (Hg) was measured concurrently with relevant environmental parameters from Yang-Jae monitoring station in Seoul during Sept. 1997 to June 2002. Although data collection was disrupted for certain periods, the grand mean concentration of Hg for this five year period was found at 5.32 $\pm$ 3.53 ng m$^{-3}$ (N = 27,170). Because of short resolution of data acquisition, we were able to examine the temporal variability of Hg at varying time scale. The diurnal variability of Hg, when investigated for each of those five years, indicated consistently the dominance of nighttime over daytime. If examined at seasonal scale, Hg level was systematically higher during winter/spring than summer/fall period. The results of this short-term variability were best explained by the combined effects of such factors as meteorological conditions (formation of inversion layer and seasonal changes) and anthropogenic source processes. However, examination of long-term variation Pattern was much more complicated to explain. Thus, extension of our study is needed to diagnose the future direction in long-term trend of Hg behavior.