• Coupled systems mechanics
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• 제4권1호
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• pp.37-65
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• 2015

Modeling and simulation of mechanical response of infrastructure object, solids and structures, relies on the use of computational models to foretell the state of a physical system under conditions for which such computational model has not been validated. Verification and Validation (V&V) procedures are the primary means of assessing accuracy, building confidence and credibility in modeling and computational simulations of behavior of those infrastructure objects. Validation is the process of determining a degree to which a model is an accurate representation of the real world from the perspective of the intended uses of the model. It is mainly a physics issue and provides evidence that the correct model is solved (Oberkampf et al. 2002). Our primary interest is in modeling and simulating behavior of porous particulate media that is fully saturated with pore fluid, including cyclic mobility and liquefaction. Fully saturated soils undergoing dynamic shaking fall in this category. Verification modeling and simulation of fully saturated porous soils is addressed in more detail by (Tasiopoulou et al. 2014), and in this paper we address validation. A set of centrifuge experiments is used for this purpose. Discussion is provided assessing the effects of scaling laws on centrifuge experiments and their influence on the validation. Available validation test are reviewed in view of first and second order phenomena and their importance to validation. For example, dynamics behavior of the system, following the dynamic time, and dissipation of the pore fluid pressures, following diffusion time, are not happening in the same time scale and those discrepancies are discussed. Laboratory tests, performed on soil that is used in centrifuge experiments, were used to calibrate material models that are then used in a validation process. Number of physical and numerical examples are used for validation and to illustrate presented discussion. In particular, it is shown that for the most part, numerical prediction of behavior, using laboratory test data to calibrate soil material model, prior to centrifuge experiments, can be validated using scaled tests. There are, of course, discrepancies, sources of which are analyzed and discussed.

• Journal of Radiation Protection and Research
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• 제32권2호
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• pp.71-78
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• 2007

본 연구에서는 원자력 발전소 주변 일시거주자의 방사선 비상시 소개와 관련된 사회행동 특성-특히 소개와 관련된 행동특성을 분석하는데 목적이 있다. 이를 위해 먼저, 이론적 검토 차원에서 비상사태시 소개의 의미와 유형, 그리고 소개를 시작하는데 소요되는 소개준비시간을 살펴보았다. 그리고 소개 대상 주민에 대한 행동특성을 울진, 월성 및 고리원전 방사선비상계획 구역 내에 체류하는 일시거주자를 대상으로 면접설문조사를 통해 실증 분석하였다. 연구의 주요 결과는 다음과 같다. 첫째, 방사선 비상시의 원활한 소개 및 안전 확보를 위하여 일시 거주자에게 소개 경보에 대한 사전 지식을 효율적으로 제공하기 위한 방안을 마련하는 것이 필요하다. 둘째, 방사선 비상시 일시거주자의 교육 훈련 방안을 마련하는 것이 필요하다. 셋째, 일시거주자가 자발적 소개를 하지 않으려는 이유와 배경을 파악하고, 대응 방안을 마련하는 것이 필요하다.

• Animal Bioscience
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• 제34권4호
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• pp.759-769
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• 2021

Objective: This study aimed to investigate the effect of stocking density on the behavior, productivity, and metabolism of periparturient Holstein cows as well as calf performance. Methods: A total of 48 periparturient cows were randomly assigned into three groups at 28 days (±3 days) before their expected calving date. The stocking densities of the groups, relative to the standard cubicle and feed bunk number, were i) 80% (13 cows), ii) 100% (16 cows), and iii) 120% (19 cows). Lying and rumination behavior was recorded using electronic data loggers and HR-Tags from d -21 ("d-" means days before calving) until the calving date, d 0. Lying time was assessed to determine the diurnal total hours spent lying per day. Rumination time was averaged in 2 hours interval periods over 24 hours during the experimental period. Results: Cows in the 80% group spent more time lying and ruminating between d -21 and d -7 and tended to ruminate more between d -14 and d 0. Calcium levels tended to be higher for cows in the 80% group, no other observable differences were found in monitored blood parameters. Moreover, 3.5% fat corrected milk and energy corrected milk yields were higher in 80% group in the first month of lactation. No other observable differences were found in the yield and composition of colostrum and milk in the first 10 months of lactation. The growth and performance of calves in the first week of life was not affected by stocking density of the dams. Conclusion: We concluded that lower stocking density may increase lying and ruminating behavior of prepartum Holstein cows. However, this did not translate into improved productivity and metabolism.

• 한국학교보건학회지
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• 제34권3호
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• pp.179-189
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• 2021

Purpose: The purpose of the study was to investigate health behavior changes in Korean adolescents before and during the COVID-19 pandemic. Methods: A descriptive cross-sectional design was employed. Data were obtained from the 15~16th (2019~2020) Korea Youth Risk Behavior Web-based Survey. Overall, the data of 112,251 students, 57,303 before the COVID pandemic and 54,948 during the pandemic, were included. The data were analyzed using rao-scott 𝝌²-test, t-test, ANCOVA and logistic regression analysis. Results: While sitting time for study decreased, sitting time for leisure increased in the 2020 group compared to the 2019 group. The 2020 group was more likely to skip breakfast and have a higher BMI than the 2019 group. The 2020 group was less likely to consume fruit and engage in moderate and vigorous physical activities than the 2019 group. The 2020 group was less likely to engage in CC, EC, and HTP current smoking and be exposed to secondhand smoke at home, school, and public places than the 2019 group. The 2020 group was more likely to be satisfied with sleep, but less likely to experience stress, depression, suicidal ideation, suicidal plans, and suicidal attempts than the 2019 group. Conclusion: It is necessary to reduce sedentary time, encourage physical activities, manage smoking and drinking rates continuously, and establish a network system to prevent psychological loneliness and isolation for adolescents, which requires participation of experts from the community as a whole.

• 한국학교보건학회지
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• 제36권3호
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• pp.113-125
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• 2023

Purpose: The purpose of this study is to develop a model for predicting mental health risk among adolescents based on health behavior information by employing a hybrid machine learning method. Methods: The study analyzed data of 51,850 domestic middle and high school students from 2022 Youth Health Behavior Survey conducted by the Korea Disease Control and Prevention Agency. Firstly, mental health risk levels (stress perception, suicidal thoughts, suicide attempts, suicide plans, experiences of sadness and despair, loneliness, and generalized anxiety disorder) were classified using the k-mean unsupervised learning technique. Secondly, demographic factors (family economic status, gender, age), academic performance, physical health (body mass index, moderate-intensity exercise, subjective health perception, oral health perception), daily life habits (sleep time, wake-up time, smartphone use time, difficulty recovering from fatigue), eating habits (consumption of high-caffeine drinks, sweet drinks, late-night snacks), violence victimization, and deviance (drinking, smoking experience) data were input to develop a random forest model predicting mental health risk, using logistic and XGBoosting. The model and its prediction performance were compared. Results: First, the subjects were classified into two mental health groups using k-mean unsupervised learning, with the high mental health risk group constituting 26.45% of the total sample (13,712 adolescents). This mental health risk group included most of the adolescents who had made suicide plans (95.1%) or attempted suicide (96.7%). Second, the predictive performance of the random forest model for classifying mental health risk groups significantly outperformed that of the reference model (AUC=.94). Predictors of high importance were 'difficulty recovering from daytime fatigue' and 'subjective health perception'. Conclusion: Based on an understanding of adolescent health behavior information, it is possible to predict the mental health risk levels of adolescents and make interventions in advance.

• 대한수학회지
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• 제47권4호
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• pp.659-674
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• 2010

This paper is concerned with the asymptotic behavior of solutions of the second-order nonlinear perturbed dynamic equation $$(r(t)x^{\Delta}(t))^{\Delta}\;+\;F(t,\;x^{\sigma}))=G(t,\;x^{\sigma},\;(x^{\Delta})^{\sigma})$$ on a time scale $\mathbb{T}$. By using a new technique we establish some sufficient conditions which ensure that every solution oscillates or converges to zero. Our results improve the known oscillation results on the literature for the perturbed dynamic equations on time scales. Some examples illustrating our main results are given.

• 아동학회지
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• 제26권2호
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• pp.121-134
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• 2005

Data were collected by peer nomination and sociometric nomination when children were in 4th grade and again two years later, Concurrent results of peer nominations were that prosocial children were more accepted while overtly/relationally aggressive children were more rejected by peers. Peer acceptance of males at Time 1 affected peer acceptance at Time 2. Peer rejection of females at Time 2 wasn't affected by overt aggression at Time 1. Cross-sectional results of social status were that rejected and controversial children showed higher levels of overt aggression than any other group. Popular children were most prosocial; rejected children were least prosocial. In the prospective view, aggressive males remained more rejected than any other group. Rejected children remained least prosocial.

• International Journal of Industrial Entomology and Biomaterials
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• 제23권1호
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• pp.183-186
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• 2011

The various molecular weight (MW) regenerated silk fibroins were prepared with different dissolution condition and the effect of MW on the gelation behavior of regenerated aqueous silk fibroin (SF) solution was investigated. The result of gelation time measurement indicated that the gelation of SF aqueous solution was accelerated by the increase of MW and SF concentration. When formic acid was added in SF aqueous solution, the gelation time of SFL and SFC30 aqueous solution showed a significant decreaseat 0.03% formic acid addition. In case of the lowest MW sample, SFC180, SF molecules became aggregated and precipitated without gelation after 28 days storage time. These findings indicate that MW control of SF can be utilized to control the gelation time of SF aqueous solution.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2015년도 추계학술대회 논문집
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• pp.289-290
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• 2015

In this experiment, nitriding treatment has been performed at $400^{\circ}C$ with various $N_2$ content and with changing processing time on AISI 420 martensitic stainless steel to investigate the expanded martensite layer (${\alpha}^{\prime}_N$ layer) formation behavior. Nitriding was implemented with changing $N_2$ content from 10% to 25% for 15 hrs and processing time was changed from 4hr to 15hr at 25% $N_2$ content. After treatment, the behavior of the ${\alpha}^{\prime}_N$ layer was investigated by optical microscopy, X-ray diffraction, and micro-hardness testing. Potentiodynamic polarization test was also used to evaluate the corrosion resistance of the samples. It was found that the surface hardness and ${\alpha}^{\prime}_N$ layer thickness increases with increasing $N_2$ percentage and processing time. Although their corrosion behaviors are worse than the bare sample.

• 한국의류학회지
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• 제18권2호
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• pp.234-243
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• 1994

This research has studied situational effects on the perceived risk and store choice behavior. Data were obtained from 388 females with full-time jobs living in Pusan. The results analyzed by Spearman's rank correlation analysis, analysis of variance(ANOVA), 1-test and discriminant analysis. The results of this study were as follows; 1. There were significant differences in percieved risk according to the clothing purchasing situations. Performance risk was perceived high in gift-shopping situation and time-pressured situation, and financial risk was perceived high in self-shoving situation. 2. There were particularly significant differences in store attributes evaluation according to the clothing purchasing situations. In self-shopping situation, price, quality and reliability, store loyalty were evaluated as important store attributes. In gift-shopping situation, quality and reliability, product iuomation and in time-pressured situation, store loyalty and product information were evaluated as important store attributes. 3. Consumers preferred national brand franchise stores in self-shopping situation. They preferred department stores in gift-shopping situation and time-pressured situation. The types of selected store were mainly affetted by shopping convenience and location convenience.