• Geotechnical Engineering
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• v.2 no.3
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• pp.37-50
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• 1986

The uncertainties encountered in the stability analysis for the foundation of offshore structures on clay are formulated in probabilistic terms and used to evaluate the reliability of the foundation design. The major sources of uncertainty are: soil properties, f.ave loads, and methods of analysis. The major part of the uncertainty in safety factor is contributed by the uncertainty in the undrained shear strength. All sources of uncertainties that affect the shear strength of clay are modeled and systematically analyzed. The in situ undrained shear strengths are evaluated by laboratory tests and cone penetration tests. The undrained shear strengths from the laboratory test and CPT, respectively at Statfjord B site in the North Sea, are used as an example in risk analysis. Using the CPT alone, the failure probability on sliding of gravity platform at Statfjord B is much larger than the failure probability using the laboratory undrained shear strengths. The major uncertainty of using the CPT as the estimate of th2 undrained shear strength of clay results from the correlation between the cone resistance and the undrained shear strength.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.22 no.1
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• pp.33-45
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• 2019

Compound disaster is the type that increases the impact affected by two or more hazard events, and attention to compound disaster and multi-hazards risk is growing due to potential damages which are difficult to predict. The objective of this study is to analyze the possible impacts of post-fire landslide scenario quantitatively by using TRIGRS (Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Analysis), a physics-based landslide model. In the case of wildfire, soil organic material and density are altered, and saturated hydraulic conductivity decrease because of soil exposed to high temperature. We have included the change of soil saturated hydraulic conductivity into the TRIGRS model through literature review. For a case study, we selected the area of $8km^2$ in Pyeongchang County. The landslide modeling process was calibrated before simulate the post-wildfire impact based on landslide inventory data to reduce uncertainty. As a result, the mean of the total factor of safety values in the case of landslide was 2.641 when rainfall duration is 1 hour with rainfall intensity of 100mm per day, while the mean value for the case of post-wildfire landslide was lower to 2.579, showing potential landslide occurrence areas appear more quickly in the compound disaster scenario. This study can be used to prevent potential losses caused by the compound disaster such as post-wildfire debris flow or landslides.

• Structural Monitoring and Maintenance
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• v.10 no.1
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• pp.87-105
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• 2023

Seismic regulations have been updated from time to time to accommodate an increase in seismic hazards. Comparison of seismic fragility of the existing bridges in Indonesia from different historical periods since the era before 1990 will be the basis for seismic assessment of the bridge stock in Indonesia, most of which are located in earthquake-prone areas, especially those built many years ago with outdated regulations. In this study, seismic fragility curves were developed using incremental non-linear time history analysis and more holistically according to the actual strength of concrete and steel material in Indonesia to determine the uncertainty factor of structural capacity, βc. From the research that has been carried out, based on the current seismic load in SNI 2833:2016/Seismic Map 2017 (7% probability of exceedance in 75 years), the performance level of the bridge in the era before SNI 2833:2016 was Operational-Life Safety whereas the performance level of the bridge designed with SNI 2833:2016 was Elastic - Operational. The potential for more severe damage occurs in greater earthquake intensity. Collapse condition occurs at As = F_PGA x PGA value of bridge Era I = 0.93 g; Era II = 1.03 g; Era III = 1.22 g; Era IV = 1.54 g. Furthermore, the fragility analysis was also developed with geometric variations in the same bridge class to see the effect of these variations on the fragility, which is the basis for making bridge risk maps in Indonesia.

• Health Policy and Management
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• v.33 no.3
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• pp.338-354
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• 2023

Background: The influence of social capital on the spread of coronavirus disease 2019 (COVID-19) and related behaviors and perceptions has been recognized during the COVID-19 pandemic. This study aims to analyze the trends in social capital using primary data from the Korean Community Health Survey, which is the only available source in Korea for local-level social capital analysis. It also investigates the relationship between various variables, including social capital, as factors influencing COVID-19-related behaviors and perceptions. Methods: The study analyzed the temporal trends of social capital using raw data from four community health surveys conducted in 2017, 2019, 2020, and 2021. A multilevel analysis was conducted to examine the relationship between social capital and COVID-19-related behaviors and perceptions following the onset of the COVID-19 pandemic in 2020. Results: Social capital consists of trust, bonding social capital, and bridging social capital. Within the trust sub-factor, trust in neighbors (Trust-1) declined after the COVID-19 pandemic, whereas trust in safety and general environment (Trust-2) and trust in medical services and public transportation (Trust-3) increased. Additionally, the gap between municipalities narrowed. COVID-19-related behaviors and perceptions, such as adherence to COVID-19 prevention measures, return to normal activities, and fear of COVID-19, showed improvement in 2021 compared to the previous year. Individual-level trust in neighbors was associated with reduced fear of COVID-19, while community-level trust in neighbors was associated with increased fear of COVID-19. Conclusion: Social capital plays a role in mitigating public health crises, and it is necessary to implement active policies that address the gap in social capital between metropolitan and rural areas. Strengthening risk communication regarding emerging infectious diseases such as COVID-19 is crucial.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.17 no.1
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• pp.67-75
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• 2024

Crosswalks play an important role for the safe movement of pedestrians in a complex urban environment. However, for the visually impaired, crosswalks can be a big risk factor. Although assistive tools such as braille blocks and acoustic traffic lights exist for safe walking, poor management can sometimes act as a hindrance to safety. This paper proposes a method to improve accuracy in a deep learning-based real-time crosswalk detection model that can be used in applications for pedestrian assistance for the disabled at the beginning. The image was binarized by utilizing the characteristic that the white line of the crosswalk image contrasts with the road surface, and through this, the crosswalk could be better recognized and the location of the crosswalk could be more accurately identified by using two models that learned the whole and the middle part of the crosswalk, respectively. In addition, it was intended to increase accuracy by creating a boundary box that recognizes crosswalks in two stages: whole and part. Through this method, additional frames that the detection model did not detect in RGB image learning from the crosswalk image could be detected.

• Journal of radiological science and technology
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• v.31 no.3
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• pp.239-247
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• 2008

In order to study the occurrence of symptoms of musculoskeletal disorders of radio-technologists employed at metropolitan general hospitals and the factors that influence such occurrence, standardized questionnaire by NIOSH that was modified and supplemented to be suitable for conditions in Korea was used. Answers collected from 143 radio-technologists in two weeks from June 13, 2007 were analyzed and the results are as follows. Factor that influence symptoms of musculoskeletal disorders by area were analyzed through multiple logistic regression analysis and the results found that in the neck area, risk increased as the burdening work category 2(Korea ministry of labor)(OR=3.94) and burdening work category 9(Korea ministry of labor)(OR=4.72) increased. In the shoulder region, risk increased as burdening work category 2(Korea ministry of labor)(OR=5.36), burdening work category 7(Korea ministry of labor)(OR=3.90), and burdening work category 9 (Korea ministry of labor)(OR=5.76) increased. In the arm/hand/wrist regions, risk increased as burdening work category 2 (Korea ministry of labor) (OR=6.91), and burdening work category 9 (Korea ministry of labor)(OR=3.76) increased. In the lower back region, risk increased as burdening work category 2 (Korea ministry of labor) (OR=3.06), and burdening work category 8 (Korea ministry of labor)(OR=8.14) increased. In the leg/knees/foot regions, risk increased as burdening work category 2 (Korea ministry of labor) (OR=3.63), and burdening work category 9 (Korea ministry of labor)(OR=2.96) increased. Conclusively, in factors that influence musculoskeletal disorder symptoms in radio-technologists, influence of subjective health conditions, total work experience, experience in current division, and burdening work category 2, 7, 8, and 9 (Korea ministry of labor) were most significant. Therefore, for preventive management, in addition to ergonomic and educational intervention for correcting improper posture during work, efforts for break time adjustment and stress reduction is needed, and encouragement and support for regular exercise is needed.

• Advances in aircraft and spacecraft science
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• v.5 no.2
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• pp.225-237
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• 2018

The difficulties of satellite vibration testing are due to the commonly expressed qualification requirements being incompatible with the limited performance of the entire controlled system (satellite + interface + shaker + controller). Two features cause the problem: firstly, the main satellite modes (i.e., the first structural mode and the high and low tank modes) are very weakly damped; secondly, the controller is just too basic to achieve the expected performance in such cases. The combination of these two issues results in oscillations around the notching levels and high amplitude beating immediately after the mode. The beating overshoots are a major risk source because they can result in the test being aborted if the qualification upper limit is exceeded. Although the abort is, in itself, a safety measure protecting the tested satellite, it increases the risk of structural fatigue, firstly because the abort threshold has been already reached, and secondly, because the test must restart at the same close-resonance frequency and remain there until the qualification level is reached and the sweep frequency can continue. The beat minimum relates only to small successive frequency ranges in which the qualification level is not reached. Although they are less problematic because they do not cause an inadvertent test shutdown, such situations inevitably result in waiver requests from the client. A controlled-system analysis indicates an operating principle that cannot provide sufficient stability: the drive calculation (which controls the process) simply multiplies the frequency reference (usually called cola) and a function of the following setpoint, the ratio between the amplitude already reached and the previous setpoint, and the compression factor. This function value changes at each cola interval, but it never takes into account the sensor signal phase. Because of these limitations, we firstly examined whether it was possible to empirically determine, using a series of tests with a very simple dummy, a controller setting process that significantly improves the results. As the attempt failed, we have performed simulations seeking an optimum adjustment by finding the Least Mean Square of the difference between the reference and response signal. The simulations showed a significant improvement during the notch beat and a small reduction in the beat amplitude. However, the small improvement in this process was not useful because it highlighted the need to change the reference at each cola interval, sometimes with instructions almost twice the qualification level. Another uncertainty regarding the consequences of such an approach involves the impact of differences between the estimated model (used in the simulation) and the actual system. As limitations in the current controller were identified in different approaches, we considered the feasibility of a new controller that takes into account an estimated single-input multi-output (SIMO) model. Its parameters were estimated from a very low-level throughput. Against this backdrop, we analyzed the feasibility of an LQG control in cancelling beating, and this article highlights the relevance of such an approach.

• Journal of Korean Society of Steel Construction
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• v.20 no.6
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• pp.723-730
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• 2008

Due to the higher ratio of live load to total loads of railway bridges, the accumulated damage by cyclic fatigue is significant. Moreover, it is highly possible that the initiated crack grows faster than that of highway bridges. Therefore, it is strongly needed to assess the safety for the accumulated damage analytically. The initiation and growth of fatigue-crack are related with the stress range, number of cycles, and the stiffness of the structural system. The stiffness of the structural system includes uncertainties of the planning, design, construction and maintenance, which varies as time goes. In this study, the authors developed the design and risk assessment techniques based on the reliability theories considering the uncertainties in load and resistance. For the probabilistic risk assessment of crack growth and the remaining life of the structures by the cyclic load of railway and subway bridges, response surface method (RSM) combined with first order second moment method were used. For composing limit state function, the stress range, stress intensity factor and the remaining life were selected as input important random variables to the RSM program. The probabilities of failure and the reliability indices of fatigue life for the considered specimen under cyclic loads were evaluated and discussed.

• Journal of agricultural medicine and community health
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• v.29 no.2
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• pp.249-263
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• 2004

Objectives: The objectives of the present study were to establish the exposure monitoring method of chlorpyrifos and chlorothalonil application to pear and field red pepper by vehicle-mounted sprayer, hand-held sprayer and to assess the risk. Methods and Results: Chlorpyrifos met all of requirements of sampling and analysis method(U.S. EPA), but chlorothalonil met only dermal patch method. Potential dermal and inhalation exposure was evaluated in 42 farmers. Compared with the hand-held sprayer application, vehicle mounted sprayer demonstrated producing relatively lower dermal exposure levels with statistical significance. In dermal exposure during hand-held application, there is no significant difference between pear and red pepper. Conclusions: This results show that application method is the main factor of dermal exposure. There was no statistically significant difference between each group of respiratory exposure level. The margin of safety (MOS) was calculated to assess the risk of pesticide exposure. All Chlorpyrifos MOS values are lower than 0.2, which mean working conditions are unsafe. In order to protect farmers, big efforts to control exposure are needed.

• Journal of Korean Society of Rural Planning
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• v.22 no.2
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• pp.19-29
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• 2016

Disasters that occur most frequently in rural areas are drought, flood, damages from wind and cold weather. Among these, damages from storm and flood and drought are the main disasters and recently, these are occurring on a large scale due to unusual weather conditions. Under such circumstances, projects and researches on disasters in rural areas are under way but they are mostly targeting one area or making approaches focusing on repair facilities, maintenance project of facilities in small streams, and disaster management, so there have not been enough studies on the current status of overall damaged facilities in the rural areas. Against this backdrop, through the analysis of the current status of damaged facilities due to storm and flood in rural areas, this study aims to provide base data for policies needed for disaster recovery planning and maintenance work of rural areas. For the analysis of damaged facilities due to storm and flood in rural areas, using the annual report on disasters issued by Ministry of Public Safety and Security and based on the occurrence rate of estimated damage in each city and district for the past 10 years(2004~2013), 8 areas with the highest number of occurrence and cost of damage were found from each province and target areas were selected. Then, regarding the selected target areas, the General Plan for Reducing Damages from Storm and Flood, which is the report on top-level plan for preventing disasters, was secured and the current status of damaged facilities were analyzed. After organizing the analysis of current status, the tendency of damaged facilities due to storm and flood in rural areas, the items of damaged facilities depending on the types of storm and flood damages, and risk factors were suggested. Based on this result, in order to generalize the results of follow-up researches, it is thought that disaster recovery planning and establishing the system of remodeling items necessary for maintenance work would be possible by analyzing damage investigation items recorded in additional researches on rural areas, researches on natural disasters, and recovery plan instructions and by conducting on-site investigation on the damaged villages from storm and flood in rural areas.