• 제목/요약/키워드: Long-term deterioration

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Monitoring moisture content of timber structures using PZT-enabled sensing and machine learning

  • Chen, Lin;Xiong, Haibei;He, Yufeng;Li, Xiuquan;Kong, Qingzhao
    • Smart Structures and Systems
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    • v.29 no.4
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    • pp.589-598
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    • 2022
  • Timber structures are susceptible to structural damages caused by variations in moisture content (MC), inducing severe durability deterioration and safety issues. Therefore, it is of great significance to detect MC levels in timber structures. Compared to current methods for timber MC detection, which are time-consuming and require bulky equipment deployment, Lead Zirconate Titanate (PZT)-enabled stress wave sensing combined with statistic machine learning classification proposed in this paper show the advantage of the portable device and ease of operation. First, stress wave signals from different MC cases are excited and received by PZT sensors through active sensing. Subsequently, two non-baseline features are extracted from these stress wave signals. Finally, these features are fed to a statistic machine learning classifier (i.e., naïve Bayesian classification) to achieve MC detection of timber structures. Numerical simulations validate the feasibility of PZT-enabled sensing to perceive MC variations. Tests referring to five MC cases are conducted to verify the effectiveness of the proposed method. Results present high accuracy for timber MC detection, showing a great potential to conduct rapid and long-term monitoring of the MC level of timber structures in future field applications.

Deterioration of Mental Health in Children and Adolescents During the COVID-19 Pandemic

  • Eunkyung Jo;Kyoil Seo;Boram Nam;Deokyong Shin;Seohyun Kim;Youngil Jeong;Aeju Kim;Yeni Kim
    • Journal of the Korean Academy of Child and Adolescent Psychiatry
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    • v.34 no.1
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    • pp.21-29
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    • 2023
  • This paper reviews the global effect of the coronavirus disease 2019 (COVID-19) pandemic on the mental health of children and adolescents in South Korea, the U.S., Japan, and China. We reviewed research on deteriorated mental health, including increased suicide, suicidal thoughts, and self-harm. Various studies have shown that students' mental health issues, such as depression and anxiety, have worsened during the COVID-19 pandemic. Furthermore, the number of students who committed suicide has significantly increased in the U.S. and Japan. Factors such as prior mental health status, change in daily routine, reduced physical activity, excessive screen time, overuse of electronic devices, and reduced social support have been reported to have a significant effect. The chain of deteriorating mental health among the youth began at the onset of COVID-19, social distancing, and school closure. As youths began to stay at home instead of going to school, they lost opportunities to connect with their friends or teachers, who could provide support outside of their homes. Young people spent less time on physical activity and more time online, which damaged their sleeping schedule and daily routine. In preparing for the post-pandemic phase, we should thoroughly analyze the long-term effects of the pandemic on youth mental health, while simultaneously tackling current imminent issues.

Optimal Replacement Scheduling of Water Pipelines

  • Ghobadi, Fatemeh;Kang, Doosun
    • Proceedings of the Korea Water Resources Association Conference
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    • 2021.06a
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    • pp.145-145
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    • 2021
  • Water distribution networks (WDNs) are designed to satisfy water requirement of an urban community. One of the central issues in human history is providing sufficient quality and quantity of water through WDNs. A WDN consists of a great number of pipelines with different ages, lengths, materials, and sizes in varying degrees of deterioration. The available annual budget for rehabilitation of these infrastructures only covers part of the network; thus it is important to manage the limited budget in the most cost-effective manner. In this study, a novel pipe replacement scheduling approach is proposed in order to smooth the annual investment time series based on a life cycle cost assessment. The proposed approach is applied to a real WDN currently operating in South Korea. The proposed scheduling plan considers both the annual budget limitation and the optimum investment on pipes' useful life. A non-dominated sorting genetic algorithm is used to solve a multi-objective optimization problem. Three decision-making objectives, including the minimum imposed LCC of the network, the minimum standard deviation of annual cost, and the minimum average age of the network, are considered to find optimal pipe replacement planning over long-term time period. The results indicate that the proposed scheduling structure provides efficient and cost-effective rehabilitation management of water network with consistent annual budget.

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Durability of Photocatalytic Cementitious Materials Exposed to Nitrogen Dioxide (광촉매 시멘트의 이산화질소 분해에 따른 내구성에 관한 연구)

  • Lee, Bo Yeon
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2014.05a
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    • pp.248-249
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    • 2014
  • Photocatalytic cement is receiving attention due to its high oxidation power that oxidizes nitrogen oxides (NOx), thus contributing to clean atmospheric environment. However, there has not been a thorough investigation on durability of a parent material, cementitious material, as a result of photocatalytic reactions. In this study, durability of photocatalytic cementitious materials exposed to nitrogen dioxide (NO2) gas was examined. Titanium dioxide (TiO2) nanoparticles containing cement paste samples were exposed to cycles of NO2 with UV light, followed by wetting and drying to simulate environmental condition. The surface of samples was characterized mechanically, chemically, and visually during the cycling. The results indicate that the photocatalytic efficiency decreased with continued NO2 oxidation due to calcium carbonate formation. The pits found from SEM demonstrate that chemical deterioration have occurred, such as acid attack or leaching. In conclusion, the photocatalytic reactions and its product could alter cementitious materials chemically and mechanically which could further affect long-term durability.

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Development of Tunnel Asset Management (TAM) Program

  • Hamed Zamenian;Dae-Hyun (Dan) Koo
    • International conference on construction engineering and project management
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    • 2013.01a
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    • pp.576-582
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    • 2013
  • Typical highway infrastructure systems include roadway pavement, drainage systems, tunneling, and other hardware components such as guardrails, traffic signs, and lighting. Tunnels in a highway system have provided significant advantages to overcoming various natural challenges including crossing underneath bodies of water or through mountainous areas. While only a few tunnel failure cases have been reported, the failure rate is likely to increase as these assets age and because agencies have not emphasized tunneling asset management. A tunnel system undergoes a deterioration life cycle pattern that is similar to other infrastructure systems. There are very few agencies in the United States implementing comprehensive tunnel asset management programs. While current tunnel asset management programs focus on inspection, maintenance, and operation safety, there is an increasing need for the development of a comprehensive life cycle tunnel asset management program. This paper describes a conceptual framework for a comprehensive tunnel asset management program. The framework consists of three basic phases including a strategic plan, a tactical plan, and an operational plan to provide better information to the decision makers. The strategic plan is a basic long term approach of tunnel asset management. The tactical plan determines specific objectives and the operational plan actually applies asset management objectives in practice. The information includes operational condition, structural condition, efficiency of the system, emergency response, and life cycle cost analysis for tunnel capital improvement project planning.

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A Study on Performance Evaluation of Masonry Thermal Bridge Blocking Brackets for Building Energy Efficiency (건축물에너지 효율을 위한 조적조 열교 차단 브라켓의 성능 평가 연구)

  • Kim, Woong-Hoi;Kim, Hyung-Kyu;Lee, Tae-Gyu;Lee, Jae-Hyun;Kim, Gyu-Yong
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2023.05a
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    • pp.175-176
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    • 2023
  • The masonry structure is constructed by cement mortar binding material of brick objects and uses reinforced hardware(connected hardware or wall tie) together when building. However, over time, the corrosion of reinforced steel and the deterioration of joint mortar as well as bricks cause the risk of collapse. In particular, when the externally decorated brick wall is installed on the concrete girder for each floor, the angle bracket is not constructed or corroded, the full-layer weight load is applied to the wall of 0.5B, which is an example of full-scale or collapse. As a result of the evaluation, it was confirmed that the performance was improved compared to the existing bracket, and we plan to carry out a real-life test and long-term performance review of the building using the bracket in the future.

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Capacitor Failure Detection Technique for Microgrid Power Converter (마이크로그리드 전력변환장치용 커패시터 고장 검출 기법)

  • Woo-Hyun Lee;Gyang-Cheol Song;Jun-Jae An;Seong-Mi Park;Sung-Jun Park
    • Journal of the Korean Society of Industry Convergence
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    • v.26 no.6_2
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    • pp.1117-1125
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    • 2023
  • The DC part of the DC microgrid power conversion system uses capacitors for buffers of charge and discharge energy for smoothing voltage and plays important roles such as high frequency component absorption, power balancing, and voltage ripple reduction. The capacitor uses an aluminum electrolytic capacitor, which has advantages of capacity, low price, and relatively fast charging/discharging characteristics. Aluminum electrolytic capacitors(AEC) have previous advantages, but over time, the capacity of the capacitors decreases due to deterioration and an increase in internal temperature, resulting in a decrease in use efficiency or an accident such as steam extraction due to electrolyte evaporation. It is necessary to take measures to prevent accidents because the failure diagnosis and detection of such capacitors are a very important part of the long-term operation, safety of use, and reliability of the power conversion system because the failure of the capacitor leads to not only a single problem but also a short circuit accident of the power conversion system.

Laboratory Performance Evaluation of Recycled Asphalt Binders with Differing Rejuvenators (재생 첨가제를 활용한 재활용 아스팔트 바인더의 실내 공용성 평가)

  • Kim, Yeong Min;Im, Jeong Hyuk;Hwang, Sung Do;Jeong, Kyu Dong;Rhee, Suk Keun
    • International Journal of Highway Engineering
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    • v.17 no.6
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    • pp.55-63
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    • 2015
  • PURPOSES : The objective of this study is to investigate the properties of recycled asphalt binders with five different rejuvenators, in order to evaluate the applicability of the recycled asphalt binders compared with the original asphalt binder. METHODS : In order to simulate recycled asphalt binders, fresh asphalt binders are aged by various Superpave aging procedures, such as the rolling thin-film oven (RTFO) and the pressure aging vessel (PAV). Then, selected rejuvenators are added to the aged asphalt binders in the amount of 5%, 10%, and 15%. The asphalt binder properties are evaluated by the dynamic shear rheometer (DSR), the rotational viscometer (RV), and the bending beam rheometer (BBR). In this study, AP-5 (penetration grade 60-80, PG 64-16) asphalt binder is used. A total of five types of rejuvenators are employed. RESULTS AND CONCLUSIONS : When considering aged asphalt without a new asphalt binder, it seems that the percentage of rejuvenator used in Korea is a bit too low, and that it fails to possess the characteristics of the original binder. From the current practice of evaluating the properties of recycled binder based on penetration ratio only, the amount of rejuvenator required is similar for the long-term-aged binder, but is excessive for the longest-term aged binder, causing deterioration of workability and stiffness of the recycled binder.

Sustainable Utilization and Management Scheme in Wangdol-cho Surrounding Sea Area (동해 왕돌초 어장의 지속적 이용 및 관리 방안)

  • Lee, Kwang-Nam;Myoung, Jung-Goo
    • Ocean and Polar Research
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    • v.25 no.3
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    • pp.331-345
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    • 2003
  • The fishing ground surrounding Wangdol-cho is not only overexploited by the littering of dilapidated fishing net and equipment, but also by fishermen's overfishing, surpassing optimum fisheries resources. In addition, increasing fishing efforts (number of fishing vessel and fishing net, etc) contribute to the deterioration of fishing ground, and it is urgently required that schemes to tackle the problems should be taken. To effectively address the problems as such, this paper aims to propose sustainable utilization and management scheme of fishing ground through classification of fishing ground surrounding Wangdol-cho as one area which is less than 50m deep, measuring $13.66km^2$ and the other, permission fishing area of Gill Net fishery, measuring $347.23km^2$. The analysis shows that, for the water area less than 50m deep, implementation from a short-term perspective includes autonomous management fishery by gill net and trap fishery. For the permission fishing area of Gill Net fishery, implementation includes limit on fishing period, real name system of fishing equipment and limit on fishing equipment. Implementation from a medium and long-term perspective includes limit on scuba diving, designation of underwater sightseeing zone, sea farming, facilities of surveillance, adoption of approval system for the permission fishing area of Gill Net fishery and introduction of report system for fishing.

Changes of Toxicological Factors in Rats Short-Term Treated with Two Feeding Methods at Low Level of Microcystin-LR (저농도의 Microcystin-LR를 단기간 처리한 흰쥐에서 투여방법에 따른 독성 지표의 변화)

  • 함영국;김성완
    • Environmental Analysis Health and Toxicology
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    • v.18 no.3
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    • pp.209-217
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    • 2003
  • To investigate the effects of low dosed microcystin -LR (MCLR) on the initial stage of subacute hepatotoxicity in vivo, male Sprague-Dawley rats after weanling were divided in four groups. The orally treated group (OG) was administered orally by 1 $\mu\textrm{g}$/kg B.W. at an interval of three days. The free group (FG) has taken the drinking water including 1 $\mu\textrm{g}$/L freely and the control group (CC) was only treated with 0.9% saline solution All groups were treated for a period of 3 weeks. There was a significant correlation in body growth rate between OG and FC and especially, a deterioration of the growth of spleen was observed in the FG after 5 days. The protein levels were also decreased in OG and FG after 9 days. Level of total fat was increased to the 9th day but again decreased up to the initial level. High hemolysis of the isolated erythrocytes occurred only in OG. Activities of ${\gamma}$-G7 of 0G and FG were higher twice-fold than CG, but the values of OG were already higher at the first treatment day. No significant change in aspartate aminotransferase (AST) activity was shown in all groups, but the activity of alanine aminotransferase (ALT) was slightly increased at the beginning state. There were much similarities in the results of OG and FG. except the growth inhibition of spleen in FG. It may be concluded that long -term effects of the low doses of mycrocystins in animals including human being can lead to serious health problems, especially to liver and spleen.