• Geomechanics and Engineering
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• 제31권5호
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• pp.529-543
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• 2022

The lattice-spring-based synthetic rock mass model (LS-SRM) technique has been extensively employed in large open-pit mining and underground projects in the last decade. Since the LS-SRM requires a complex and time-consuming calibration process, a robust approach was developed using the Response Surface Methodology (RSM) to optimize the calibration procedure. For this purpose, numerical models were designed using the Box-Behnken Design technique, and numerical simulations were performed under uniaxial and triaxial stress states. The model input parameters represented the models' micro-mechanical (lattice) properties and the macro-scale properties, including uniaxial compressive strength (UCS), elastic modulus, cohesion, and friction angle constitute the output parameters of the model. The results from RSM models indicate that the lattice UCS and lattice friction angle are the most influential parameters on the macro-scale UCS of the specimen. Moreover, lattice UCS and elastic modulus mainly control macro-scale cohesion. Lattice friction angle (flat joint fiction angle) and lattice elastic modulus affect the macro-scale friction angle. Model validation was performed using physical laboratory experiment results, ranging from weak to hard rock. The results indicated that the RSM model could be employed to calibrate LS-SRM numerical models without a trial-and-error process.

• 한국수학교육학회지시리즈D:수학교육연구
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• 제26권4호
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• pp.333-349
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• 2023

Recently, AI has become a crucial tool in mathematics education due to advances in machine learning and deep learning. Considering the importance of AI, examining teachers' beliefs about AI in mathematics education (AIME) is crucial, as these beliefs affect their instruction and student learning experiences. The present study developed a scale to measure preservice teachers' (PST) beliefs about AIME through factor analysis and rigorous reliability and validity analyses. The study analyzed 202 PST's data and developed a scale comprising three factors and 11 items. The first factor gauges PSTs' beliefs regarding their roles in using AI for mathematics education (4 items), the second factor assesses PSTs' beliefs about using AI for mathematics teaching (3 items), and the third factor explores PSTs' beliefs about AI for mathematics learning (4 items). Moreover, the outcomes of confirmatory factor analysis affirm that the three-factor model outperforms other models (a one-factor or a two-factor model). These findings are in line with previous scales examining mathematics teacher beliefs, reinforcing the notion that such beliefs are multifaceted and developed through diverse experiences. Descriptive analysis reveals that overall PSTs exhibit positive beliefs about AIME. However, they show relatively lower levels of beliefs about their roles in using AI for mathematics education. Practical and theoretical implications are discussed.

• Steel and Composite Structures
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• 제50권1호
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• pp.15-24
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• 2024

This research presents dynamical reaction investigation of pore-dependent and nano-thickness beams having functional gradation (FG) constituents exposed to a movable particle. The nano-thickness beam formulation has been appointed with the benefits of refined high orders beam paradigm and nonlocal strain gradient theory (NSGT) comprising two scale moduli entitled nonlocality and strains gradient modulus. The graded pore-dependent constituents have been designed through pore factor based power-law relations comprising pore volumes pursuant to even or uneven pore scattering. Therewith, variable scale modulus has been thought-out until process a more accurate designing of scale effects on graded nano-thickness beams. The motion equations have been appointed to be solved via Ritz method with the benefits of Chebyshev polynomials in cosine form. Also, Laplace transform techniques help Ritz-Chebyshev method to obtain the dynamical response in time domain. All factors such as particle speed, pores and variable scale modulus affect the dynamical response.

• Smart Structures and Systems
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• 제22권1호
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• pp.41-55
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• 2018

Damping ratio and frequency have influence on dynamic serviceability or instability such as vortex-induced vibration and displacement amplification due to earthquake and critical flutter velocity, and it is thus important to make determination of damping ratio and frequency accurate. As bridges are getting longer, small scale model test considering similitude law must be conducted to evaluate damping ratio and frequency. Analysis conditions modified by similitude law are applied to experimental test considering different scale ratios. Generally, Nyquist frequency condition based on natural frequency modified by similitude law has been used to determine sampling rate for different scale ratios, and total time length has been determined by users arbitrarily or by considering similitude law with respect to time for different scale ratios. However, Nyquist frequency condition is not suitable for multimode system with noisy signals. In addition, there is no specified criteria for determination of total time length. Those analysis conditions severely affect accuracy of damping ratio. The focus of this study is made on the determination of minimum analysis conditions for different scale ratios. Influence of signal to noise ratio is studied according to the level of noise level. Free initial value problem is proposed to resolve the condition that is difficult to know original initial value for free vibration. Ambient and free vibration tests were used to analyze the dynamic properties of a system using data collected from tests with a two degree-of-freedom section model and performed on full bridge 3D models of cable stayed bridges. The free decay is estimated with the stochastic subspace identification method that uses displacement data to measure damping ratios under noisy conditions, and the iterative least squares method that adopts low pass filtering and fourth order central differencing. Reasonable results were yielded in numerical and experimental tests.

• Safety and Health at Work
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• 제9권2호
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• pp.159-163
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• 2018

Background: Fatigue and sleepiness are inter-related and common among road transport drivers. In this study, sleep deprivation and fatigue among chemical transportation drivers were examined. Methods: A cross-sectional study surveying 107 drivers from three hazardous types of chemical production and transportation industries (nonflammable gases, flammable gases, and flammable liquids) was conducted. Data on sleep deprivation were collected using questionnaires of the Stanford Sleeping Scale and the Groningen Sleep Quality Scale. Fatigue was assessed using an interview questionnaire and a flicker fusion instrument. Results: Chemical drivers had a mean sleeping scale (Stanford Sleeping Scale) of 1.98 (standard deviation 1.00) and had a mean score of 1.89 (standard deviation 2.06) on the Groningen Sleep Quality Scale. High-risk drivers had higher scores in both the Stanford Sleeping Scale and the Groningen Sleep Quality Scale with a mean score of 2.59 and 4.62, respectively, and those differences reached statistical significance (p < 0.05). The prevalence of fatigue, as assessed through a critical flicker fusion analyzer, subjective fatigue question, and either of the instruments, was 32.32%, 16.16%, and 43.43%, respectively. Drivers who slept <7 hours and had poor sleep quality were found to have more fatigue than those who slept enough and well. Drivers who had a more sleepiness score resulted in significantly more objective fatigue than those who had a less sleepiness score. Conclusion: Sleep quality and sleeping hour can affect a driver's fatigue. Optimization of work-rest model should be considered to improve productivity, driver retention, and road safety.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.797-802
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• 2017

본 연구에서는 하이브리드 추진기관 설계에 중요한 변수인 스케일에 따른 연소특성을 분석하였다. Blow-down 시스템을 사용하는 $LN_2O$/PE 추진제 조합에 대하여 분석을 수행하였으며 현존하는 스케일 관계식을 이용한 스케일 변화에 따른 평균 후퇴율의 변화는 크지 않음을 확인하였다. 특성배기속도 효율은 스케일이 커짐에 따라 증가함을 확인하였다. 그러나 특성배기속도 효율은 후방연소실의 형상 등 복잡한 변수가 포함되어 있어 단순한 스케일의 변화에 따른 영향이라고 단정할 수 없다고 판단된다. 이에 특성속도효율 및 국부적인 후퇴율 예측에 관한 하이브리드 로켓 스케일 관계식에 관해서는 확정적인 결론을 도출하기 어려울 것으로 판단된다.

• Wind and Structures
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• 제38권4호
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• pp.261-275
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• 2024

Before performing an experimental study on the downburst-generated wave, it is necessary to examine the scale effects and corresponding corrections or compensations. Analysis of similarity is conducted to conclude the non-dimensional force ratios that account for the dynamic similarity in the interaction of downburst with wave between the prototype and the scale model, along with the corresponding scale factors. The fractional volume of fluid (VOF) method in association with the impinging jet model is employed to explore the characteristics of the downburst-generated wave numerically, and the validity of the proposed scaling method is verified. The study shows that the location of the maximum radial wind velocity in a downburst-wave field is a little higher than that identified in a downburst over the land, which might be attributed to the presence of the wave which changes the roughness of the underlying surface of the downburst. The impinging airflow would generate a concavity in the free surface of the water around the stagnation point of the downburst, with a diameter of about two times the jet diameter (D_jet). The maximum wave height appears at the location of 1.5D_jet from the stagnation point. Reynolds number has an insignificant influence on the scale effects, in accordance with the numerical investigation of the 30 scale models with the Reynolds number varying from 3.85 × 10⁴ to 7.30 × 10⁹. The ratio of the inertial force of air to the gravitational force of water, which is denoted by G, is found to be the most significant factor that would affect the interaction of downburst with wave. For the correction or compensation of the scale effects, fitting curves for the measures of the downburst-wave field (e.g., wind profile, significant wave height), along with the corresponding equations, are presented as a function of the parameter G.

• 대한가정학회지
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• 제41권2호
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• pp.43-63
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• 2003

The purpose of this study is to investigate how much individual, relational, and contextual variables have an effect on the dating violence of premarital males and females. Researched are 369 male and female residents over 19 years who have experienced dating or were involved in any dating relationships in Daegu. The instruments of measurement are CTSⅡ scale and scales of relation to individual, relational, and contextual variables. The data are analysed through factor analysis, Cronbach's α, frequency, percentile, and stepwise regression analysis. The major findings of this study are as follows: First, individual variables that affect doing and victimization of dating violence are one's permission degree of dating violence, and psychological abuses experienced during childhood from one's mother. Second, relational variables that affect doing and victimization of dating violence are control toward one's partner, communication, conflict, commitment, intimacy, satisfaction of dating relationship, and feeling of inferiority toward one's partner. Third, contextual variables that affect doing and victimization of dating violence are familial relationships, friend relationships, and financial stresses.

• 가정과삶의질연구
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• 제30권2호
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• pp.75-86
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• 2012

The purpose of this study was to investigate the structural relationships school-aged children and related variables. For this study, the respondents were 704 children in elementary schools in the areas of Gyeongsan-Si and Daegu-Si. The questionnaires and psychological tests used in this study surveyed the following concepts: suicide ideation, social support, self-esteem and the scale of depression. The collected data were analyzed with AMOS 19.0, a statistical program for structural equation modeling, to estimate the hypothesized structural equation model. The results were as follows: First, self-esteem, - and depression as perceived by children were found to affect their suicide ideation directly. Second, parental support and teacher support as perceived by children were found to affect children's depression directly. Third, parental support, teacher support, and the support of friend's as perceived by children were found to affect-children's self-esteem directly. Last, parental support and, teacher's support did not show direct effect on children's suicide ideation, though these factors had an indirect effect on suicide ideation through the children's self-esteem and depression. Finally, teacher's support did not direct effectly children's suicide ideation, whereas it had an having indirect effect on suicide ideation through the children's self-esteem.

• 대한간호학회지
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• 제35권2호
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• pp.399-406
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• 2005

Purpose: The purpose of this study was to investigate the factors that affect the psychological well-being in family caregivers of stroke patients. Method: The General Health Perception, short form 36, Health Survey Questionaire was used to measure health perception. The Caregiving Mastery Scale was used to assess the mastery, while the Psychological General Well-Being Index was used to examine the level of well-being. Result: Subjective health, caregiving mastery, patient's ADL and caregiving duration influenced on caregiver's psychological well-being. Subjective health had effect on psychological well-being both directly and indirectly. Caregiving duration and patient's ADL had indirect effect on psychological well-being through caregiving mastery. Conclusion: It is need to develop a health program for the caregivers of stroke patient's and to provide nursing intervention to improve the caregiver's ability, thereby improving the well-being of the family caregivers.