• Nutrition Research and Practice
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• v.18 no.2
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• pp.269-281
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• 2024

BACKGROUND/OBJECTIVES: The objective of this study was to compare dietary habits and mental health among middle school students in urban and rural areas based on bedtime, and to provide evidence supporting appropriate bedtime for Korean middle school students in relation to their healthy dietary habits and mental well-being. SUBJECTS/METHODS: The study population consisted of 25,681 second-year middle school students who participated in the Korea Youth Risk Behavior Survey in 2020-2022. Participants were asked about their bedtime and wake-up time during the past 7 days and were classified into five categories. The study compared the general characteristics, academic factors, dietary habits, and mental health of urban and rural students based on their bedtime. RESULTS: Bedtime was found to be later in the following order: urban female students, rural female students, urban male students, and rural male students. As bedtime got later, the rates of smoking and alcohol consumption increased. Students who went to bed before 11 p.m. had lower academic performance, while rural male students who went to bed after 2 a.m. had lower academic performance. Later bedtime was associated with increased smartphone usage, skipping breakfast, consuming fast food, and drinking carbonated beverages. Later bedtime was also associated with higher perceived stress levels, particularly among students who went to bed after 2 a.m., higher rates of suicidal ideation, experiencing sadness and despair, as well as the prevalence of clinically significant anxiety disorders. CONCLUSION: These results suggest that middle school students who go to bed too late have higher rates of smoking and alcohol drinking, as well as unhealthy eating habits, stress, suicidal ideation, sadness, and anxiety. Therefore, it is necessary to provide educational and social institutional support to promote adequate sleep for the health of adolescents.

• Journal of Korean Society of Rural Planning
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• v.22 no.3
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• pp.71-80
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• 2016

Korea is becoming a model country for the developing countries' agricultural and rural development. Drawing implications for Vietnam from Korea's experiences can help make development strategies and policies for other developing countries including North Korea as well as for Vietnam itself. Vietnam is facing an inefficiency in agricultural production and the gap between urban and rural growth has been widening. Farm sizes per household are small and farmlands are scattered. Diversification in rural industry is very restricted. To attack these problems, investment is urgently needed for rural infrastructure building as well as agricultural structure adjustment. In the process of rural development, there have been also encountered such problems as financial procurement, community's spontaneous participation, manpower development for adjusting to industrial structural change. Korea's experiences may be helpful for establishing rural development strategies and policies in Vietnam. Benchmark scopes can go beyond Saemaul Undong in 1970s. Korea's pre- and post-Saemaul Undong era as well as the Saemaul Undong era can be referred. In the wake of globalization, Vietnam has not only experienced compressed rapid economic growth but also encountered policy tasks to eradicate poverty, to realize self-reliance and income increase, and to lessen urban-rural development gap, at the same time. Korea's experiences show that priority needs to be put on the establishment of national and rural development strategies based on Vietnam-specific conditions, utilization of village's resources including community tradition and social capital, fund raising for rural development, farmland development and mobilization, production and living infrastructure building, technology transfer for farmers and vocational training for new job seekers.

• Sleep Medicine and Psychophysiology
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• v.13 no.1
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• pp.15-21
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• 2006

Introduction: The objective of the present study was to investigate bedtime, rise time and time-in-bed of Korean college students, separately on weekday and on weekend and to compare them. In addition, this study also aimed to evaluate the influence of gender, age and grade on the above sleep parmeters in Korean college students. Methods: Information regarding bedtime and rise time, separately on weekday and on weekend, of Korean college students were obtained by self-administered questionnaire. Questionnaires of 1,825 students (1,416 females and 409 males, age 18-30；mean age $21.1{\pm}2.2$) were used for statistical analyses. Results: Korean college students retired to bed 50 minutes later (00：49 on weekday；01：40 on weekend；t=39.67, p<0.001), rose 1 hour 58 minutes later (07：52 on weekday；09：50 on weekend；t=39.46, p<0.001), and slept 1 hour 8 minutes longer (t=13.33, p<0.001) on weekend. Compared to male students, female students had earlier rise time (t=8.96, p<0.01；t=3.89, p<0.01) and earlier bedtime both on weekday and weekend (t=7.10, p<0.01；t=6.04, p<0.01), and shorter time-in-bed on weekday (t=1.99, p<0.01). In addition, rise time delay and time-in-bed increase on weekend were more prominent in female students than in male students (t=3.41, p<0.01; t=3.68, p<0.01). Grade was correlated with bedtime and rise time on weekday (${\beta}=0.1022$, p<0.01；${\beta}=0.1009$, p<0.01), bedtime and time-in-bed on weekend (${\beta}=0.1096$, p<0.01；${\beta}=-0.0990$, p<0.01), and differences between week-day and weekend of the rise time and the time-in-bed (${\beta}=-0.0906$, p<0.01；${\beta}=-0.1115$, p=0.02). Conclusions: In this study, Korean college students had earlier bedtime/rise time and shorter time-in-bed on weekday than on weekend. These findings suggest that weekday sleep-wake schedule of Korean college students may be advanced relative to their biological sleep-wake cycle and that this discrepancy may be associated with weekday sleep deprivation. In addition, differences of sleep patterns between weekday and weekend were more prominent in female students and students with lower grade. Therefore, discrepancy between weekday sleep-wake schedule and biological sleep-wake cycle, as well as weekday sleep deprivation, might be more serious in female or lower-grade students.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.10 no.4
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• pp.95-108
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• 2007

Test application of revegetation measure was made on the roadside slope damaged by Nongseo-Eomo national road improvement project in a bid to prevent the soil from being washed out as well as to restore the ecological environment, and the survey for assessment of the effect of slope revegetation measures was conducted, beginning May 11 through Nov 7, 2006. In the wake of comprehensive reviewing and evaluating the surrounding topographic environment, physical and chemical characteristics of soil, germination of revegetation plants, analysis of bio mass, covering ratio and the plants appeared, measure b was found to have been most appropriate to cut blasting rock slope, and alternatively measure c. For cut ripping rock slope, measure c-1 appeared to be effective in revegetation effect, and alternatively, b-1.When it comes to cut soil slope, measure c-2 was found to be effective, and b-2 to be a good alternative. And for embankment soil slope, measure b-3 appeared to be most efficient in revegetation effect and measure f as alternative.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.10 no.4
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• pp.83-94
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• 2007

Test application of revegetation measure was made on the roadside slope damaged by Gimcheon-Eomo national road improvement project in a bid to prevent the soil from being washed out as well as to restore the ecological environment, and the survey for assessing the effect of slope revegetation measures was conducted, beginning Sep 7 through Sep 20, 2006. In the wake of comprehensive reviewing and evaluating the surrounding topographic environment, physical and chemical characteristics of soil, germination of revegetation plants, analysis of bio mass, covering ratio and the plants appeared, revegetation measure C was found to have been most effective and desirable for further application in the area. Viewing the specific applicability by the area, revegetation measure C and C-1 appeared to be appropriate for blasting rock slope and ripping rock slope as they are efficient in preventing the slope from being washed out and in early revegetating. And revegetation measure B deemed to be effective to blasting rock slope or ripping rock slope as an alternative. And for cut slope, vegetation measure C-2 was judged to be more effective than measure D or E, while measure C-3 would be appropriateto embankment slope.

• Journal of the Korean Ceramic Society
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• v.33 no.5
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• pp.602-615
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• 1996

The purpose of the present study is to investigate the microstructural effect on the R-curve behavior in three aluminas with different grain size distributions by analyzing the bridging stress distribution. The crack opening displacement (COD) according to the distance behind the stationary crack tip was measured using an in situ SEM fracture method. The measured COD values in the fine-grained alumina agreed well with Wiederhorn's sollution while they deviated from Wiederhorn's solution in the two coarse-grained aluminas because of the increase of the crack closure due to the grain interface bridging in the crack wake. A numerical fitting procedure was conducted by the introduction of the power-law relation and the current theoretical model together with the measured COD's in order to obtain the bridging stress distribution. The results indicated that the bridging stress function and the R-curve computed by the current model were consistent with those computed by the power-law relation providing a reliable evidence for the bridging stress analysis of the current model. The strain-softening exponent in the power-law relation n, was calculated to be in the range from 2 to 3 and was closely related to the grain size distribution. Thus it was concluded from the current theoretical model that the grain size distribution affected greatly the bridging stress distribution thereby resulting in the quantitative analysis of microfracture of polycrystalline aluminas through correlating the local-fracture-cont-rolling microstructure.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.3 s.147
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• pp.275-284
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• 2006

In recent years, many environmentally disastrous maritime accidents resulted from oil or fuel spills from damaged vessels. The situation becomes worse especially when the early counter treatment is not prompt enough. To properly handle this type of accidents and prevent further disasters, the propulsive performance of damaged vessels must be better understood for salvage operations, as well as for containing oil spills while the vessels are being towed or self-propelled. Until now, many hydrodynamic studies have focused on the propulsive performance of undamaged vessels but only a few studies on that of damaged vessels. in this paper, both experimental and computational methods are used to study the propulsive performance of a VLCC in heeled and/or trimmed conditions. For experimental studies, measurement systems should be modified to adapt to the variations of attitude of a damaged vessel. For numerical studies, CFD programs should be also extended to be applied to asymmetrically floating conditions.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.38-47
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• 2017

This paper presents experimental data on water droplet breakup in high-speed air flows. Exact-time-dependent evolution of wave and droplet interaction as well as breakup processes were optically visualized using a shadowgraph technique. Droplet experiments were conducted in a shock tube. Five flow conditions were used with an incident shock wave Mach number from 1.40 to 2.19 with Weber number based on the droplet initial diameter from 2300 to 38000, respectively. This corresponds to post-shock flow speeds varying from subsonic to supersonic. The considered droplet diameters were 2.0 mm to 3.6 mm. Some interesting wave patterns in the near wake were found. The present data shows that with an increase in the Weber number the droplet acceleration coefficient decreases and the level of decrease was weaker for the case of higher Mach numbers. This state of affair is different to the existing data in literature. Possible reasons are discussed.

• Wind and Structures
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• v.13 no.2
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• pp.127-144
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• 2010

Pressure measurements on static and autorotating flat plates have been recently reported by Lin et al. (2006), Holmes, et al. (2006), and Richards, et al. (2008), amongst others. In general, the variation of the normal force with respect to the angle of attack appears to stall in the mid attack angle range with a large scale separation in the wake. To date however, no surface pressures have been measured on auto-rotating plates that are typical of a certain class of debris. This paper presents the results of an experiment to measure the aerodynamic forces on a flat plate held stationary at different angles to the flow and allowing the plate to auto-rotate. The forces were determined through the measurement of differential pressures on either side of the plate with internally mounted pressure transducers and data logging systems. Results are presented for surface pressure distributions and overall integrated forces and moments on the plates in coefficient form. Computed static force coefficients show the stall effect at the mid range angle of attack and some variation for different Reynolds numbers. Normal forces determined from autorotational experiments are higher than the static values at most pitch angles over a cycle. The resulting moment coefficient does not compare well with current analytical formulations which suggest the existence of a flow mechanism that cannot be completely described through static tests.

• Korean Journal of Biological Psychiatry
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• v.29 no.1
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• pp.9-14
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• 2022

Objectives Sleep is fundamental to maintaining homeostatic control and has behavioral and psychological effects on humans. To better understand the function and pathophysiology of sleep, specific gene expressions in reference to sleep deprivation have been studied. In this study, we investigated the gene expression of peripheral blood mononuclear cells after sleep deprivation to better understand the functional consequence of sleep. Methods In eight healthy men, 24 h sleep deprivation was induced. Blood was sampled at 14:00, before and after sleep deprivation. mRNA was isolated and analyzed via microarrays. cDNAs before and after sleep deprivation were coupled to Cy3 or Cy5, respectively, and normalized cDNAs were selected with a ratio greater than two as a significant gene. Results are expressed as mean. Results Among 41174 transcripts, 38852 genes were selected as reliable, and only a small minority (< 1%) of the genes were up-or down-regulated. Total six and eleven genes were selected as significant upregulated and downregulated genes, respectively. Protein tyrosine phosphatase receptor type O was most upregulated (6.9-fold), and low-density lipoprotein receptor-related protein 5-like protein showed the most substantial inhibition (0.06-fold). Conclusions This study showed significant associations between sleep deprivation and the immune system. Acute sleep deprivation affects pathways in proinflammatory cytokines as well as metabolic pathways of glutamate and purine, neurotransmitters related to sleep and wake cycle.