• Physical Therapy Rehabilitation Science
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• v.9 no.4
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• pp.302-308
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• 2020

Objective: The endurance and strength of deep neck flexor (DNF) muscles have a major role on the function and stability of the cervical spine. In recent years, there has been a lack of research that have investigated the muscle tone of the superficial neck muscles. The purpose of this study was to examine the relationship of between contraction ratio of the DNF and sternocleidomastoid (SCM) muscles, DNF endurance, and muscle tension of the neck muscles. Design: Cross-sectional study. Methods: Forty-seven subjects (male=20, female=27) participated in this study. The muscle tone of the upper trapezius (UT), SCM, and suboccipital (SO) muscle was measured using a contact soft tissue tone-measuring instrument. For the contraction ratio of the SCM and longus colli muscle, the thickness of the relaxation and maximum contraction state of the SCM and longus colli muscles were assessed using a diagnostic ultrasound measuring instrument and a pressure biofeedback unit. The deep neck flexor endurance test (DNFET) was performed in a cranio-cervical flexion posture. The correlations between the measured variables were investigated. Results: The relationship between the DNFET and SO tone showed a significant negative correlation (p<0.05). The relationship between the DNFET and contraction ratio showed a significant positive correlation (p<0.01). There was no significant correlation between the DNFET and SCM and UT tone. Conclusions: This study confirmed that there is a relationship between DNF endurance, DNF activation, and SO tone. The information on the results of this study may be used as a reference that can be actively applied in the clinical environment.

• Tribology and Lubricants
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• v.35 no.4
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• pp.222-228
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• 2019

As rubber products such as O-rings, which are also known as packings or toric joints, come in regular, long term contact with liquid fuel, they can eventually swell, become mechanically weakened, and occasionally crack; this diminishes both their usefulness and intrinsic lifetime and could cause leaks during the steady-state flow condition of the fuel. In this study, we evaluate the lifetime of such products through compression set tests of FKM, a family of fluorocarbon elastomer materials defined by the ASTM international standard D141; these materials have great compression, sunlight, and ozone resistance as well as a low gas absorption rate. In this process, O-rings are immersed in the liquid fuel of airtight containers that can be expressed as a compression set, and the liquid fuel leakage in a flow rig tester at variable temperatures over 12 months is investigated. Using the Power Law model, our study determined a theoretical O-ring lifetime of 2,647 years, i.e. a semi-permanent lifespan, by confirming the absence of liquid fuel leakage around the O-ring assembled fittings. These results indicate that the FKM O-rings are significantly compatible for fuel tests to evaluate long-term sealing conditions.

• Tribology and Lubricants
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• v.35 no.1
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• pp.30-36
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• 2019

The tribological properties of paper-based friction materials are crucial to the performance of a wet clutch system. In this work, the friction and wear characteristics of a paper-based friction material in boundary lubrication state was experimentally investigated using a pin-on-reciprocating tribotester under various normal forces and temperatures. It was found that the wear rate of the friction material increased from $5.8{\times}10^{-6}mm^3/N/cycle$ to $5.5{\times}10^{-5}mm^3/N/cycle$ after 1,700 cycles of testing at $80^{\circ}C$ as normal force increased from 2 N to 7 N. The friction coefficient was also found to increase from 0.135 to 0.155 with increasing normal force from 2 N to 7 N. The increase in contact pressure with increasing normal force may be responsible for these results. In addition, as temperature increased from $20^{\circ}C$ to $80^{\circ}C$, the wear rate of the friction materials increased from $2.0{\times}10^{-5}mm^3/N/cycle$ to $3.6{\times}10^{-5}mm^3/N/cycle$ while the friction coefficient decreased from 0.163 to 0.146. This result may be associated with the decrease in the hardness of friction materials with increasing temperature. Furthermore, plastic deformation on the friction materials was mainly observed after the test. The outcome of this work may be useful to gain a better understanding of the tribological properties of friction materials, and therefore can contribute to the development of friction materials with enhanced performance for wet clutch systems.

• Advances in concrete construction
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• v.7 no.2
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• pp.117-126
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• 2019

When designing reinforced concrete (RC) members, the rebar is assumed to resist all tensile forces, but the resistance of the concrete in the tension area is neglected. However, concrete can also resist tensile forces and increase the tensile stiffness of RC members, which is called the tension stiffening effect (TSE). Therefore, this study assessed the TSE, particularly after yielding of the steel bars and the effects of the steel ratio on the TSE. For this purpose, RC member specimens with steel ratios of 2.87%, 0.99%, and 0.59% were fabricated for uniaxial tensile tests. A vision-based non-contact measurement system was used to measure the behavior of the specimens. The cracks on the specimen at the stabilized cracking stage and the fracture stage were measured with the image analysis method. The results show that the number of cracks increases as the steel ratio increases. The reductions of the limit state and fracture strains were dependent on the ratio of the rebar. As the steel ratio decreased, the strain after yielding of the RC members significantly decreased. Therefore, the overall ductility of the RC member is reduced with decreasing steel ratio. The yielding plateau and ultimate load of the RC members obtained from the proposed equations showed very good agreement with those of the experiments. Finally, the image analysis method was possible to allow flexibility in expand the measurement points and targets to determine the strains and crack widths of the specimens.

• Journal of Korean society of Dental Hygiene
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• v.19 no.5
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• pp.845-858
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• 2019

Objectives: This study aims to contribute to devising systems for family caregivers of dementia patients by examining the state of oral care of dementia patients, and depression and social support among family caregivers of dementia patients. Methods: Family caregivers of dementia patients in the metropolitan area were selected in this study. The inclusion criteria were individuals who have provided care for a dementia patient at home for at least six months and those who come in contact (including phone calls) with the patient at least twice a week. Results: Oral health knowledge of the elderly, caregiving burden, depression, and social support were examined. The mean scores for oral health knowledge of the elderly and caregiving burden were $57.11{\pm}16.94$ out of 100 and $17.33{\pm}8.61$ out of 48, respectively. Further, the mean caregiving behavior score, depression score, and social support score were $8.49{\pm}13.71$ out of 100, $5.11{\pm}3.05$ out of 10, and $72.75{\pm}17.03$ out of 100, respectively. Factors affecting oral health knowledge of the elderly were examined. The results showed that the level of oral health knowledge of the elderly increased with an increasing perception of a need for oral health education (p<0.05), caregiving burden (p<0.01), and social support (p<0.01). Conclusions: These findings suggest that developing and popularizing oral care intervention programs for family caregivers of dementia patients are necessary to ensure systematic oral care for dementia patients.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.10
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• pp.1427-1434
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• 2021

In this paper, we propose a psychological state estimation process that computes children's attention and tension in response to training stimuli. Joint attention was adopted as the training stimulus required for behavioral intervention, and the Discrete trial training (DTT) technique was applied as the training protocol. Three types of training stimulation contents are composed to check the user's attention and tension level and provided mounted on a character-shaped tabletop robot. Then, the gaze response to the user's training stimulus is estimated with the vision-based head pose recognition and geometrical calculation model, and the nervous system response is analyzed using the PPG and GSR bio-signals using heart rate variability(HRV) and histogram techniques. Through experiments using robots, it was confirmed that the psychological response of users to training contents on joint attention could be quantified.

• Advances in nano research
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• v.10 no.3
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• pp.253-261
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• 2021

Polydimethylsiloxane (PDMS) is one of the most widely adopted silicon-based organic polymeric elastomers. Elastomeric nanostructures are normally required to accomplish an explicit mechanical role and correspondingly their mechanical properties are crucial to affect device and material performance. Despite its wide application, the mechanical properties of PDMS are yet fully understood. In particular, the time dependent mechanical response of PDMS has not been fully elucidated. Here, utilizing state-of-the-art PeakForce Quantitative Nanomechanical Mapping (PFQNM) together with Force Volume (FV) and Fast Force Volume (FFV), the elastic moduli of PDMS samples were assessed in a time-dependent fashion. Specifically, the acquisition frequency was discretely changed four orders of magnitude from 0.1 Hz up to 2 kHz. Careful calibrations were done. Force data were fitted with a linearized DMT contact mechanics model considering surface adhesion force. Increased Young's modulus was discovered with increasing acquisition frequency. It was measured 878 ± 274 kPa at 0.1 Hz and increased to 4586 ± 758 kPa at 2 kHz. The robust local probing of mechanical measurement as well as unprecedented high-resolution topography imaging open new avenues for quantitative nanomechanical mapping of soft polymers, and can be extended to soft biological systems.

• Journal of Advanced Navigation Technology
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• v.25 no.1
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• pp.108-114
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• 2021

In recent years, human is experiencing an 'untact' era that has not been existed before. A remarkable features of an untact era is a limited or no interaction with other people and things in a daily life. In order to overcome this special situation, diverse state-of-the-art technologies like ICT technology are being used to give the effect of face-to-face and contact. In particular, Virtual Reality technology allows users to actively interact with virtual environments, objects, and other people, thereby providing effects that are as similar as possible to experience in real life. School freshmen are also experiencing various inconveniences because they are not experiencing the environment or academic management of newly admitted schools in the untact era. This research is a study and implementation of 'Virtual School Life Experience Content' which provides new students to tour campus, to utilize the school buildings facilities, to experience of academic schedules including course registration, and to participate in school events in an environment that is as close as possible to the real campus. Freshmen will be able to easily adapt to a new school through the implemented VR content.

• Journal of the Korean Dietetic Association
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• v.28 no.3
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• pp.205-217
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• 2022

School meals are prepared based using the HACCP system, which is designed to ensure the physical and mental health of students. However, operational recommendations in school cafeterias have changed due to COVID-19 and include delays in serving time to restrict the number of meals and the installation of screens to prevent droplet transmission. Unfortunately, these changes may have detrimentally affected hygiene practices and generated new food poisoning sources. This study aimed to determine the hygiene state of school cafeterias in the Gyeongnam area from December 2020 to September 2021 based on the monitoring of total aerobic and coliform bacteria. Kitchen floors were the most contaminated areas with an average number of total aerobic bacteria of 4.3 log CFU/100 cm², whereas counts in dining areas were relatively low at 0.1~3.5 log CFU/100 cm². Newly installed partitioned areas had the lowest contamination level of 0.1~2.8 log CFU/100 cm². Escherichia coli was not detected on any surface, while coliform was detected on workbenches and floors. In conclusion, hygienic practices appear to have been adequately managed in school cafeterias despite COVID-19 driven changes. Nonetheless, continuous monitoring is recommended to ensure prompt response to changing environments.

• Safety and Health at Work
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• v.13 no.2
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• pp.141-147
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• 2022

Background: On the basis of its role for the development of occupational health research, information, good practices, the International Commission on Occupational Health (ICOH) launched the present survey to collect information on public health and prevention policies put in place by the governments of the countries in the world to contain the pandemic. Methods: A cross-sectional study was conducted through an online questionnaire focused on COVID-19 data, public health policies, prevention measures, support measures for economy, work, and education, personal protective equipment, intensive care units, contact tracing, return to work, and the role of ICOH against COVID-19. The questionnaire was administered to 113 ICOH National Secretaries and senior OSH experts. Collected data refer to the period ranging from the beginning of the pandemic in each country to June 30, 2020. Results: A total of 73 questionnaires from 73 countries around the world were considered valid, with a 64.6% response rate. Most of the respondents (71.2%) reported that the state of emergency was declared in their country, and 86.1% reported lockdown measures. Most of the respondents (66.7%) affirmed that the use of face masks was compulsory in their country. As for containment measures, 97.2% indicated that mass gatherings (meetings) were limited. Regarding workplace closing, the most affected sector was entertainment (90.1%). Conclusion: The results of this survey are useful to gain a global view on COVID-19 policy responses at country level.