• 보건교육건강증진학회지
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• 제26권4호
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• pp.1-10
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• 2009

Objectives: The purpose of this study is to find the determinants of suicide impulse of residents living in mining region and other areas in one city. The past studies did not examine the suicide related attitudes or behaviors in mining region. This study also examines how coping resources and behaviors moderate the suicide impulse. Methods: For this purpose, hierarchical logistic regression method was used to predict the likelihood of suicide impulse. The personal characteristics, depression, coping resources and behaviors were considered as the independent variables. The data collected in this study was gathered through questionnaire survey with 502 residents in other areas as well as mining area in one city. Results and Conclusion: The results and conclusions are as follows: 1. The chi-square test revealed that residents living mining region showed higher percentage of suicide impulse compared to other areas. 2. The t-test revealed that those with suicide impulse had higher level of depression compared to those without it. This pattern was consistent in other areas as well as mining region. 3. The hierarchical logistic regression revealed that age, education, depression showed positive effect on suicide impulse in mining region. However, in other areas, education, illness, and depression showed positive effect on suicide impulse. Also, this result implies that suicide prevention efforts should be actively made in mining region.

• Journal of Power Electronics
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• 제18권2호
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• pp.511-521
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• 2018

Proportional capacitor current feedback active damping (CCFAD) has a limited valid damping region in the discrete time domain as (0, $f_s/6$. However, the resonance frequency ($f_r$) of an LCL-type filter is usually designed to be less than half the sampling frequency ($f_s$) with the symmetry regular sampling method. Therefore, ($f_s/6$, $f_s/2$) becomes an invalid damping region. This paper proposes an improved CCFAD method to extend the valid damping region from (0, $f_s/6$ to (0, $f_s/2$), which covers all of the possible resonance frequencies in the design procedure. The full-valid damping region is obtained and the stability margin of the system is analyzed in the discrete time domain with the Nyquist criterion. Results show that the system can operate stably with the proposed CCFAD method when the resonance frequency is in the region (0, $f_s/2$). The performances at the steady and dynamic state are enhanced by the selected feedback coefficient H and controller gain $K_p$. Finally, the feasibility and effectiveness of the proposed CCFAD method are verified by simulation and experimental results.

• Geomechanics and Engineering
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• 제37권1호
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• pp.9-19
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• 2024

This study presents an energy analysis for large-strain cavity expansion problem based on the general strength criterion and energy theory. This study focuses on the energy dissipation problem during the cavity expansion process, dividing the soil mass around the cavity into an elastic region and a plastic region. Assuming compliance with the small deformation theory in the elastic region and the large deformation theory in the plastic region, combined with the general strength criterion of soil mass and energy theory, the energy dissipation solution for cavity expansion problem is derived. Firstly, from an energy perspective, the process of cavity expansion in soil mass is described as an energy conversion process. The energy dissipation mechanism is introduced into the traditional analysis of cavity expansion, and a general analytical solution for cavity expansion related to energy is derived. Subsequently, based on this general analytical solution of cavity expansion, the influence of different strength criterion, large-strain, expansion radius, cavity shape and characteristics of soil mass on the stress distribution, displacement field and energy evolution around the cavity is studied. Finally, the effectiveness and reliability of theoretical solution is verified by comparing the results of typical pressure-expansion curves with existing literature algorithms. The results indicate that different strength criterion have a relatively small impact on the displacement and strain field around the cavity, but a significant impact on the stress distribution and energy evolution around the cavity.

• 자원환경지질
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• 제57권3호
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• pp.293-303
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• 2024

River mining, the extraction of sand and gravel from riverbeds, is rising at an alarming rate to keep pace with the increasing demand for construction materials worldwide. The far-reaching deleterious effects of river mining include the lowering of water levels, the augmentation of turbidity, and the erosion of riverbanks, i.e., the disruption of water flow and alteration of river morphology. Aggregates demand, geolocation, and the economy of Bangladesh accelerated illegal extraction. However, limited research has been carried out in this region, despite the severe impact on aquatic and terrestrial ecosystems. To address the corresponding consequences and direct the scope for further research, it is required to evaluate existing studies of other countries having similarities in river morphology, climate, economy, and other related parameters. In this respect, based on previous studies, the effects of sand extraction are particularly prominent in India, having 54 cross-boundary rivers with Bangladesh. The geological profile of numerous rivers in the past decades has been altered due to natural aggregate mining in the Indian subcontinent. Hence, this study focused on relevant research in this region. However, the existing research only focuses on the regional portion of the aforementioned international rivers, which lacks proper assessments of these rivers, taking into account especially the mining effects. Moreover, several global rivers that have similarities with Bangladeshi rivers, considering different parameters, are also included in this study. The findings of this article underline the pressing need for more efficacious measures to address the adverse effects of river mining and safeguard ecosystems and communities globally, especially in the Indian subcontinent, where the situation is particularly vulnerable. For this reason, targeting the aforementioned region, this review highlights the global evidence in assessing the future effects of river mining and the need for further research in this field.

• Journal of Power Electronics
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• 제17권6호
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• pp.1480-1489
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• 2017

In this study, a carrier-based pulse-width modulation (PWM) method for two-level voltage source inverters in the over-modulation region is proposed. Based on the superposition principle, the reference voltage vectors outside the linear modulation boundary are adjusted to relocate to the vector hexagon, while their fundamental magnitudes are retained. In accordance with the adjusted reference vector, the corresponding modulated waves are respectively deduced in over-modulation mode I and II to generate the gate signals of the power switches, guaranteeing the linearity of the fundamental output phase voltage in the over-modulation region. Moreover, due to the linear relationship between the voltage vector and the duty ratios, the complicated sector identification and holding angle calculation found in previous methods are avoided in the modulated wave synthesis, which provides great simplicity for the proposed carrier-based over-modulation strategy. Experimental results demonstrate the effectiveness and validity of the proposed method.

• Journal of Power Electronics
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• 제17권5호
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• pp.1317-1326
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• 2017

The cascaded H-bridge (CHB) multilevel converter is a promising topology for large-scale photovoltaic (PV) systems. The output voltage over-modulation derived by the inter-module active power imbalance is one of the key issues for CHB PV systems. This paper proposed a dynamic power distribution strategy to eliminate the over-modulation in a CHB PV system by suitably redistributing the reactive power among the inverter modules of the CHB PV system. The proposed strategy can effectively extend the operating region of the CHB PV system with a simple control algorithm and easy implementation. Simulation and experimental results carried out on a seven-level CHB grid-connected PV system are shown to validate the proposed strategy.

• 디지털융복합연구
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• 제17권4호
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• pp.49-55
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• 2019

본 연구는 빅데이터 분석방법인 텍스트마이닝을 이용한 부동산시장 동향분석에 관한 연구로 자료는 2016년 8월부터 2017년 8월까지의 포털사이트인 네이버에 게시된 인터넷 뉴스를 통해 수집하였다. TF-IDF 분석결과, 주택, 분양, 가구, 시장, 지역 순으로 빈도가 높게 나타났고 대출, 정부, 대책, 규제 등 정책과 관련된 단어들도 많이 추출되었으며 지역관련 단어는 서울의 출현빈도가 가장 많은 것으로 나타났다. 지역과 관련된 단어 조합은 '서울-강남', '서울-수도권', '강남-재건축', '서울-재건축'의 출현빈도가 많은 것으로 나타나 강남지역 재건축에 대한 사람들의 관심과 기대가 높은 것을 알 수 있다.

• Safety and Health at Work
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• 제12권3호
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• pp.317-323
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• 2021

Background: The surface mining industry has one of the highest fatality rates among private industries in the United States. Despite recent decreases in the fatality rates of comparable industries, the fatality rate in the surface mining industry has increased. Meanwhile, a lack of safety research in surface mining has hindered efforts to improve safety strategies in the surface mining workplace. Method: This study examined quarry workers' hazard identification skills by conducting a case study of a surface mining facility in the Mid-Atlantic region of the United States. Semistructured interviews were conducted with eight quarry workers who were employed at the mine facility. In addition to the interviews, data were collected through field notes, notes from an expert meeting with safety managers, and site photographs to explore quarry workers' safety behaviors in the workplace. Results: The results showed that quarry workers identified hazards and improved their safety performance by translating safety knowledge learned from training into practice, acquiring hands-on work experience, learning from coworkers, and sharing responsibilities among team members. Conclusion: This study contributes to understanding quarry workers' safe performance beyond what they have learned in safety training to include their interaction with other workers and hand-on experience in the workplace. This study informs practitioners in the surface mining industry to build a safe work environment as they design effective safety programs for employees.

• 대한환경공학회지
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• 제32권12호
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• pp.1102-1110
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• 2010

갯벌 퇴적토는 미생물 다양성이 매우 높다고 알려져 있다. 하지만 인위적인 교란에 의해 갯벌 퇴적토 내 미생물 다양성이 달라질 수 있다. 지속적인 퇴적토 내 미생물 다양성 모니터링을 위해서는 대표성을 지닌 시료의 채취가 중요하다. 본 연구에서는 강화도 여차리 갯벌을 대상으로 식생이 있는 지역과 식생이 없는 지역의 미생물 다양성과 이화학적 특성치를 지구 통계학적으로 비교분석 하였다. 갯벌 시료에서 측정된 미생물 다양성과 다양한 이화학적 특성치를 지구통계학적으로 분석한 결과, 식생이 존재하는 지역에서의 상관거리가 식생이 존재하지 않는 지역에 비하여 대체로 짧다는 것을 알 수 있었다. 이는 식생이 존재하는 지역의 높은 생태학적 및 이화학적 복잡성과 이질성으로 인해 식생이 존재하는 지역에서는 식생이 존재하지 않는 지역에서 보다 비교적 좁은 간격으로 시료를 채취해야 한다는 것을 의미한다. 데이터 마이닝 기법을 사용하여 미생물 다양성에 영향을 주는 주요 환경영향 인자를 분석한 결과, 식생이 존재하는 지역에서는 유기물 함량과 질산염이온, 식생이 존재하지 않는 지역에서는 pH와 황산염이온이 미생물 다양성에 영향을 끼친다는 것을 알 수 있었다. 이러한 지구통계학 및 데이터 마이닝 분석 결과들을 활용해서 갯벌 퇴적토 내 미생물 다양성 측정을 위한 시료 채취 간격 및 개수 선정 지침을 본 연구에서 제안하였다.

• 국제학술발표논문집
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• The 9th International Conference on Construction Engineering and Project Management
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• pp.11-17
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• 2022

Design-bid-build (DBB) is the most common project delivery method among highway projects. State Highway Agencies (SHAs) usually apply a low-bid approach to select contractors for their DBB projects. In this approach, the Federal Highway Agency suggests SHAs heighten contractors' competition to lower bid prices. However, these attempts may become ineffective due to collusive bidding arrangements among certain contractors. One common strategy is the rotation of winning bidders of a group of contractors who bid on many of the same projects. These arrangements may also be specific to a particular region or vary in time. Despite the practices' adverse effects on bidding outcomes, an effective model to detect red-flag bidding patterns is lacking. This study fills the gap by proposing a novel framework that utilizes pattern mining techniques and statistical tests for unusual pattern detection. A case study with historical data from an SHA is conducted to illustrate the proposed framework.