• 한국지진공학회논문집
• /
• 제27권2호
• /
• pp.101-109
• /
• 2023

Steel brace strengthening is the most popular seismic rehabilitation method for school buildings. This is because the design can be conducted by using relatively easy nonlinear pushover analysis and standard modeling in codes. An issue with steel brace strengthening is that the reinforced building should behave elastically to satisfy performance objectives. For this, the size of steel braces should be highly increased, which results in excessive strengthening cost by force concentration on existing members and foundations due to the considerable stiffness and strength of the steel braces. The main reason may be the brittle failure mode of columns, so this study investigated the relationship between the efficiency of steel brace strengthening and column failure modes. The result showed that the efficiency is highly dependent on the shear capacity ratio of columns and structural analysis methods. School buildings reinforced by steel braces do not need to behave elastically when the shear capacity ratio is low, and pushover analysis is used, which means reducing steel material is possible.

• Environmental Analysis Health and Toxicology
• /
• 제29권
• /
• pp.15.1-15.7
• /
• 2014

Objectives This paper tried to review a recent research trend for the environmental exposure of engineered nanomaterials (ENMs) and its removal efficiency in the nanowaste treatment plants. Methods The studies on the predicted environmental concentrations (PEC) of ENMs obtained by exposure modeling and treatment (or removal) efficiency in nanowaste treatment facilities, such as wastewater treatment plant (WTP) and waste incineration plant (WIP) were investigated. The studies on the landfill of nanowastes also were investigated. Results The Swiss Federal Laboratories for Materials Science and Technology group has led the way in developing methods for estimating ENM production and emissions. The PEC values are available for surface water, wastewater treatment plant effluents, biosolids, sediments, soils, and air. Based on the PEC modeling, the major routes for the environmental exposure of the ENMs were found as WTP effluents/sludge. The ENMs entered in the WTP were 90-99% removed and accumulated in the activated sludge and sludge cake. Additionally, the waste ash released from the WIP contain ENMs. Ultimately, landfills are the likely final destination of the disposed sludge or discarded ENMs products. Conclusions Although the removal efficiency of the ENMs using nanowaste treatment facilities is acceptable, the ENMs were accumulated on the sludge and then finally moved to the landfill. Therefore, the monitoring for the ENMs in the environment where the WTP effluent is discharged or biomass disposed is required to increase our knowledge on the fate and transport of the ENMs and to prevent the unintentional exposure (release) in the environment.

• 대한기계학회논문집A
• /
• 제29권1호
• /
• pp.59-66
• /
• 2005

In this paper, a robust stationary Kalman filter is designed by minimizing selected performance indices so that it is less sensitive to uncertainties. The uncertainties include not only stochastic factors such as process noise and measurement noise, but also deterministic factors such as unknown initial estimation error, modeling error and sensing bias. To reduce the effect on the uncertainties, three performance indices that should be minimized are selected based on the quantitative error analysis to both the deterministic and the stochastic uncertainties. The selected indices are the size of the observer gain, the condition number of the observer matrix, and the estimation error variance. The observer gain is obtained by optimally solving the multi-objectives optimization problem that minimizes the indices. The robustness of the proposed filter is demonstrated through the comparison with the standard Kalman filter.

• Nutrition Research and Practice
• /
• 제17권2호
• /
• pp.341-355
• /
• 2023

BACKGROUND/OBJECTIVES: The consumption of dietary supplements has shown an increase among young people in their 20s. We aimed to compare the use of dietary supplements and related factors between Chinese international and Korean college students living in South Korea. SUBJECTS/METHODS: We conducted online surveys of 400 Chinese international students and 452 Korean college students from January to February 2021. We analyzed the factors related to the use of dietary supplements by these students using multi-group structural equation modeling and logistic regression analysis. RESULTS: Approximately 65% of the Chinese international students and 93% of the Korean college students consumed dietary supplements at least once in the year preceding the survey. The common types of dietary supplements consumed by both groups of students were vitamin and mineral supplements, Lactobacillus products, and red ginseng products. Structural equation modeling showed that perception of the consumption of dietary supplements by family and friends positively influenced attitude toward dietary supplements. This effect was higher for Korean college students than for Chinese international students (P < 0.01). Attitude toward dietary supplements positively influenced their use, and this effect was higher for Chinese international students than for Korean college students (P < 0.001). Logistic regression analysis showed that the use of dietary supplements by Chinese international students was significantly associated with age, self-reported health status, interest in health, perception of and attitude toward dietary supplements, and length of residence in South Korea. Among Korean college students, it was associated with exercise frequency and attitude toward dietary supplements. CONCLUSION: This study showed significant differences in the use of dietary supplements and related factors between Chinese international and Korean college students. Therefore, nutrition education programs on dietary supplements need to have differentiated content for each group. Such differences also suggest that the industry should consider the relevant characteristics of college students while developing and marketing dietary supplements.

• Safety and Health at Work
• /
• 제1권1호
• /
• pp.43-50
• /
• 2010

Objectives: The objective of this study was to investigate the effect of chain installation condition on stress distribution that could eventually cause disastrous failure from sudden deformation and geometric rupture. Methods: Fractographic method used for the failed chain indicates that over-stress was considered as the root cause of failure. 3D modeling and finite element analysis for the chain, used in a crane hook, were performed with a three-dimensional interactive application program, CATIA, commercial finite element analysis and computational fluid dynamic software, ANSYS. Results: The results showed that the state of stress was changed depending on the initial position of the chain that was installed in the hook. Especially, the magnitude of the stress was strongly affected by the bending forces, which are 2.5 times greater (under the simulation condition currently investigated) than that from the plain tensile load. Also, it was noted that the change of load state is strongly related to the failure of parts. The chain can hold an ultimate load of about 8 tons with only the tensile load acting on it. Conclusion: The conclusions of this research clearly showed that a reduction of the loss from similar incidents can be achieved when an operator properly handles the installation of the chain.

• Journal of Preventive Medicine and Public Health
• /
• 제55권2호
• /
• pp.134-143
• /
• 2022

Objectives: Many governments have imposed-and are still imposing-mobility restrictions to contain the coronavirus disease 2019 (COVID-19) pandemic. However, there is no consensus on whether policy-induced reductions of human mobility effectively reduce the effective reproduction number (Rt) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Several studies based on country-restricted data reported conflicting trends in the change of the SARS-CoV-2 Rt following mobility restrictions. The objective of this study was to examine, at the global scale, the existence of regional specificities in the correlations between Rt and human mobility. Methods: We computed the Rt of SARS-CoV-2 using data on worldwide infection cases reported by the Johns Hopkins University, and analyzed the correlation between Rt and mobility indicators from the Google COVID-19 Community Mobility Reports in 125 countries, as well as states/regions within the United States, using the Pearson correlation test, linear modeling, and quadratic modeling. Results: The correlation analysis identified countries where Rt negatively correlated with residential mobility, as expected by policymakers, but also countries where Rt positively correlated with residential mobility and countries with more complex correlation patterns. The correlations between Rt and residential mobility were non-linear in many countries, indicating an optimal level above which increasing residential mobility is counterproductive. Conclusions: Our results indicate that, in order to effectively reduce viral circulation, mobility restriction measures must be tailored by region, considering local cultural determinants and social behaviors. We believe that our results have the potential to guide differential refinement of mobility restriction policies at a country/regional resolution.

• 한국항공운항학회지
• /
• 제13권3호
• /
• pp.34-42
• /
• 2005

The objectives of the study are to present simple physical and mathematical models of liquid fuel in the tank of an aerospace vehicle such launch vehicle or missile and to investigate its dynamic stability for a parameter space. In this paper, liquid in the container is modeled as multi-mass system subject to parametric excitations, and a stability diagram for determination of stable-unstable regions of the motion is obtained by using an analytical method. Also, computer simulations are conducted at various parameter points to verify the analytical results, and time histories of motion are compared to explain the effect of variation of parameters of the system.

• 정보관리학회지
• /
• 제35권3호
• /
• pp.77-100
• /
• 2018

본 연구는 텍스트 마이닝 기법을 활용하여 대량의 데이터로부터 학제 간 융합 기술을 발굴하는 일련의 과정을 제시하는 것을 목표로 한다. 바이오공학 기술(BT) 분야와 정보통신 기술(ICT) 분야 간의 융합 연구를 위해 (1) BT 분야의 기술용어 목록을 작성하여 대량의 학술논문 메타데이터를 수집한 후 (2) 패스파인더 네트워크 척도 알고리즘을 이용해 유망 기술의 지식 구조를 생성하고 (3) 토픽 모델링 기법을 사용하여 BT분야 중심의 내용 분석을 수행하였다. 다음 단계인 BT-ICT 융합 기술 아이템 도출을 위해, (4) BT-ICT 관련 정보를 얻기 위해 BT 기술용어 목록을 상위 개념으로 확장한 후 (5) OpenAPI 서비스를 이용하여 두 분야가 관련된 학술 정보의 메타데이터를 자동 수집하여 (6) BT-ICT 토픽 모델의 내용 분석을 실시하였다. 연구를 통해 첫째, 융합 기술의 발굴을 위해서는 기술 용어 목록의 작성이 중요한 지식 베이스가 된다는 점과 둘째, 대량의 수집 문헌을 분석하기 위해서는 데이터의 차원을 줄여 분석을 용이하게 해주는 텍스트 마이닝 기법이 필요하다는 점을 확인하였다. 본 연구에서 제안한 데이터 처리 및 분석 과정이 학제 간 융합 연구의 가능성이 있는 기술 요소들을 발굴하는 데 효과적이었음을 확인할 수 있었다.

• 자동차안전학회지
• /
• 제12권2호
• /
• pp.27-32
• /
• 2020

This paper presents steering system requirements to ensure the stabilized lateral control of autonomous driving vehicles. The two main objectives of a lateral controller in autonomous vehicles are maintenance of vehicle stability and tracking of the desired path. Even if the desired steering angle is immediately determined by the upper level controller, the overall controller performance is greatly influenced by the specification of steering system actuators. Since one of the major inescapable traits that affects controller performance is the time delay of the steering actuator, our work is mainly focused on finding adequate parameters of high level control algorithm to compensate these response characteristics and guarantee vehicle stability. Actual vehicle steering angle response was obtained with Electric Power Steering (EPS) actuator test subject to various longitudinal velocity. Steering input and output response analysis was performed via MATLAB system identification toolbox. The use of system identification is advantageous since the transfer function of the system is conveniently obtained compared with methods that require actual mathematical modeling of the system. Simulation results of full vehicle model suggest that the obtained tuning parameter yields reduced oscillation and lateral error compared with other cases, thus enhancing path tracking performance.

• Geomechanics and Engineering
• /
• 제17권6호
• /
• pp.583-595
• /
• 2019

In this paper, a comprehensive investigation of the dynamic response of a long-bridge subjected to spatially varying earthquake ground motions (SVEGM) is performed based on a proposed analytical model which includes the effect of soil-structure interaction (SSI). The spatial variability of ground motions is simulated by the powerful record generator, SIMQKE II. Modeling of the SSI in the system is simplified by replacing the pile foundations and soil with sets of independent equivalent linear springs and dashpots along the pile groups. One of the most fundamental objectives of this study is to examine how well the proposed model simulates the dynamic response of a bridge system. For this purpose, the baseline data required for the evaluation process is derived from analyzing a 3D numerical model of the bridge system which is validated in this paper. To emphasize the importance of the SVEGM and SSI, bridge responses are also determined for the uniform ground motion and fixed base cases. This study proposing a compatible analytical model concerns the relative importance of the SSI and SVEGM and shows that these effects cannot be neglected in the seismic analysis of long-bridges.