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A semi-permanent and durable nanoscale-crack-based sensor by on-demand healing
Park, Byeonghak,Lee, Sori,Choi, Hyesu,Kim, Jong Uk,Hong, Haeleen,Jeong, Chanho,Kang, Daeshik,Kim, Tae-il The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.9
<P>Although sensitivity and durability are desirable in a sensor, both of them cannot be easily achieved. Site-specific and effective signal acquisition on the limited area of a sensor inevitably allows fatigue accumulation and contamination. For example, an ultrasensitive nanoscale-crack-based sensor for detecting a mechanical stimulus with tremendous sensitivity (a gauge factor greater than 2000 under 2% strain), yet limited durability (up to a few thousand stretching cycles in tensile tests) has been presented previously. Herein, we suggest a simple yet robust nanoscale-crack-based sensor that achieves remarkable durability through the use of a self-healable polymer. The self-healable polymer helps the crack gap recover and maintain high stability for 1 million cycles under 2% strain. Moreover, site-specific recovery with infrared light irradiation was demonstrated with monolithic arrayed sensors. The proposed strategy provides a unique solution to achieving highly enhanced durability and high mechanosensitivity, which are typically incompatible.</P>
Ultrasensitive mechanical crack-based sensor inspired by the spider sensory system
Kang, Daeshik,Pikhitsa, Peter V.,Choi, Yong Whan,Lee, Chanseok,Shin, Sung Soo,Piao, Linfeng,Park, Byeonghak,Suh, Kahp-Yang,Kim, Tae-il,Choi, Mansoo Nature Publishing Group, a division of Macmillan P 2014 Nature Vol.516 No.7530
Recently developed flexible mechanosensors based on inorganic silicon, organic semiconductors, carbon nanotubes, graphene platelets, pressure-sensitive rubber and self-powered devices are highly sensitive and can be applied to human skin. However, the development of a multifunctional sensor satisfying the requirements of ultrahigh mechanosensitivity, flexibility and durability remains a challenge. In nature, spiders sense extremely small variations in mechanical stress using crack-shaped slit organs near their leg joints. Here we demonstrate that sensors based on nanoscale crack junctions and inspired by the geometry of a spider’s slit organ can attain ultrahigh sensitivity and serve multiple purposes. The sensors are sensitive to strain (with a gauge factor of over 2,000 in the 0–2 per cent strain range) and vibration (with the ability to detect amplitudes of approximately 10 nanometres). The device is reversible, reproducible, durable and mechanically flexible, and can thus be easily mounted on human skin as an electronic multipixel array. The ultrahigh mechanosensitivity is attributed to the disconnection–reconnection process undergone by the zip-like nanoscale crack junctions under strain or vibration. The proposed theoretical model is consistent with experimental data that we report here. We also demonstrate that sensors based on nanoscale crack junctions are applicable to highly selective speech pattern recognition and the detection of physiological signals. The nanoscale crack junction-based sensory system could be useful in diverse applications requiring ultrahigh displacement sensitivity.
안석(An Sok),박대식(Park DaeShik),김경인(Kim KyungIn) 한국농촌경제연구원 2017 한국농촌경제연구원 정책연구보고서 Vol.- No.-
Population aging has become an important social subject for our society to cope with because the number of older adults who need various medical and social supports have increased sharply. Older adults would like to stay in their community as they age; health and social services, home- and communitybased services, help them remain in the community independently. However, rural older adults consistently have been excluded from the public social and health services. In particular, rural older adults with functional disabilities are experiencing difficulties accessing those services because of their limited mobility and rural environment where social resources are insufficient. Previous studies mostly focused on service delivery systems for older adults and linkage of health and social services. Therefore, the present study investigated the current service use of rural older adults with functional disabilities and identified the barriers that hinder them from accessing and using health and social services. To identify the barriers of service use, this study conducted surveys among rural older adults and health and social service providers in rural areas. Additionally, qualitative interviews among rural older adults with functional disabilities were conducted to explore their use of services and difficulties accessing services. Focus group interviews were also carried out to identify the problems delivering services to rural older adults with functional disabilities. This study revealed that the rural older adults with functional disabilities suffer from physical and mental health deterioration. They visited doctor’s office more often than healthy rural older adults. Similarly, they more often used social services than rural older adults without functional disabilities. However, they were more likely to experience unmet service needs compared to their counterparts, which means that rural older adults with functional disabilities receive insufficient health and social services for their health status. The main barriers to access health and social services for rural older adults with functional disabilities were their limited mobility, lack of transportation, insufficiency of services, and financial burden. Therefore, this study suggested building up a regional system to manage various social and health services and deliver the collaborated services to rural older adults. To improve the delivery system, this study suggested future policy directions and proposed several plans for rural older adults with functional disabilities.
Urban-rural Migration and Migrants’ Successful Settlement in Korea
SANGJIN MA,SOK AN,DAESHIK PARK 서울대학교 사회발전연구소 2018 Journal of Asian Sociology Vol.47 No.2
The Republic of Korea, South Korea, was an agricultural country similar to other East Asian countries until the 1950s. As in other developed countries, rural agricultural surplus labor in Korea moved into urban areas for jobs. However, since the late 1990s, urban population movement to rural areas began to be observed and drew policymakers’ attention. Thus, this study aims to describe the trend of urban-rural migration in Korea and identify the factors influencing migrants’ successful settlement. Korea’s urban-rural migration appeared 20 years later than western developed countries and the number of migrants is increasing. Economic and demographic factors and individual preferences are closely related to this trend. To investigate factors influencing successful migration, this study analyzed a data set collected from a nationwide sample of urban-rural migrants. This study argues that personal characteristics, non-economic motives, community life, and government supports are key factors associated with successful migration.