• Sleep Medicine and Psychophysiology
• /
• v.26 no.1
• /
• pp.5-15
• /
• 2019

Chronotype (CT) is defined as an inter-individual difference in sleep-wake cycles and daily activities. Previous studies have suggested that this individual difference can influence our biological and psychological functioning. Literature regarding the psychometric properties and validity of CT measures are reviewed. We provide an overview of biological indicators (sleep-wake cycle, body temperature, cortisol, and melatonin) that are used for distinguishing two chronotypes: morningness (MT) and eveningness (ET). We also review the differences between CT in relation to personality traits and the occurrence of psychopathology. In addition, the methodological limitations of studies on CT are discussed. Finally, future research directions in terms of CT are proposed.

• The Journal of the Korea Contents Association
• /
• v.14 no.8
• /
• pp.319-328
• /
• 2014

The purpose of this study was to investigate circadian rhythms, learning flow, and fatigue of college students. The differences in learning flow and fatigue according to the type of circadian rhythms were also examined. The study used a descriptive survey research design. The convenience sample consisted of 224 college students from five universities. The data were collected from May to June in 2013 using the following instruments: Morningness-Eveningness Questionnaire-Korean (MEQ-K), Flow State Scale, and Fatigue Assessment Inventory. The participants in the study were mostly put in neither-type (51.8%), and only 4.0% in morning-type. The morning-type students had higher learning flow scores and lower fatigue scores than the night-type students. The types of circadian rhythms measured by MEQ-K were compared to the subjective types of circadian rhythm which was based on the participants' self evaluation. There was a difference in the measured type and the subjective type in 32.1% of the participants. The findings of this study suggest that an intervention program to help college students accurately recognize their circadian rhythms might be effective in improving learning flow and decreasing fatigue.

• Journal of the Korean earth science society
• /
• v.37 no.7
• /
• pp.465-475
• /
• 2016

The diurnal and semidiurnal tides in the global atmosphere are examined using 3-hourly geopotential height field of the state-of-the-art reanalysis data. Unlike the previous studies, the spatial structure and seasonality of those tides are analyzed from the surface of the earth to the stratosphere. It is found that, at most levels, diurnal tide is strong in the midlatitudes while semidiurnal tide is predominant in the tropics. The former shows strong seasonal cycle with a larger amplitude in summer than in winter in both hemispheres. This is different from the semidiurnal tide which has essentially no seasonal cycle. In term of the vertical structure, while semidiurnal tide has a barotropic structure, diurnal tide exhibits a distinct vertical structure with increased amplitude and height. Especially tropical diurnal tide exhibits a nearly opposite phase from the surface to the free troposphere, and to the upper stratosphere. Its amplitude also varies nonlinearly with height, possibly influenced by water vapor, ozone, gravity waves and solar radiation.

• Korean Journal of Cognitive Science
• /
• v.33 no.1
• /
• pp.51-75
• /
• 2022

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation that is able to alter neuronal activity in particular brain regions. Many studies have researched how tDCS modulates neuronal activity and reorganizes neural networks. However it is difficult to conclude the effect of brain stimulation because the studies are heterogeneous with respect to the stimulation parameter as well as individual difference. It is not fully in agreement with the effects of brain stimulation. In particular few studies have researched the reason of variability of brain stimulation in response to time so far. The study investigated individual variability of brain stimulation based on circadian rhythm and chronotype. Participants were divided into two groups which are morning type and evening type. The experiment was conducted by Zoom meeting which is video meeting programs. Participants were sent experiment tool which are Muse(EEG device), tdcs device, cell phone and cell phone holder after manuals for experimental equipment were explained. Participants were required to make a phone in frount of a camera so that experimenter can monitor online EEG data. Two participants who was difficult to use experimental devices experimented in a laboratory setting where experimenter set up devices. For all participants the accuracy of 98% was achieved by SVM using leave one out cross validation in classification in the the effects of morning stimulation and the evening stimulation. For morning type, the accuracy of 92% and 96% was achieved in classification in the morning stimulation and the evening stimulation. For evening type, it was 94% accuracy in classification for the effect of brain stimulation in the morning and the evening. Feature importance was different both in classification in the morning stimulation and the evening stimulation for morning type and evening type. Results indicated that the effect of brain stimulation can be explained with brain state and trait. Our study results noted that the tDCS protocol for target state is manipulated by individual differences as well as target state.

• Sleep Medicine and Psychophysiology
• /
• v.1 no.1
• /
• pp.68-75
• /
• 1994

In order to examine the effects of circadian rhythm in subjective alertness on the occurrence of traffic accidents, the authors investigated the occurrence rate of traffic accidents adjusted to traffic volume in Seoul and the relative rate of fatal accidents versus total traffic accidents in Korea at different times of day in 1991. We analyzed these data in relation with the circadian rhythm in subjective alertness. The results were as follows. Both the occurrence rate of traffic accidents adjusted to traffic volume and the relative rate of fatal accidents versus total traffic accidents were the highest at 3-4 a.m., known as the time period of the lowest subjective alertness. They were negatively correlated with subjective alertness (p<0.05, p<0.001). In conclusion, it is suggested that the circadian rhythm of subjective alertness should have a significant effect on the occurrence of traffic accidents despite many confounding factors such as driving environments.

• Information Display
• /
• v.19 no.6
• /
• pp.10-17
• /
• 2018

• Korean journal of applied entomology
• /
• v.30 no.1
• /
• pp.94-99
• /
• 1991

The daily rhythm of sex pheromone production and release by females of the black pine base scale, Matsucoccus thunbergianae Miller and Park, was demonstrated by studying the amounts of pheromone possessed and released by females, periodically after emergence. Cycles of both pheromone production and release had daily peaks between 8 a.m. and 2 p.m., and has marked decreases after 4 p.m. It appeared that the amounts of pheromone gradually decreased three days after the emergence. Significance in synchronization of the daily rhythm of female pheromone release and activities of males and females with reference to reproductive success in this species is discussed.

• Journal of Preventive Medicine and Public Health
• /
• v.25 no.4 s.40
• /
• pp.374-385
• /
• 1992

Some circadian rhythms can become disorgnized due to rotating shift work. This lack of organization, termed desynchronization, can produce a group of symptoms such as insomnia, GI disturbance and fatigue among many rotating shift workers. The magnitude of these symptoms are influenced by personal and environmental factors and the patterns of shift work. This study was carried out to investigate the subjective symptoms related to rotational schedules of shift work after personal and environmental factors adjusted. 182 male workers in rapidly rotating shift system and 86 male workers in weekly rotating shift system were conducted the questionnaire on personal factors and subjective sleep, GI and fatigue symptoms. Major findings obtained from this study are as follows: 1. The symptoms of 'feeling tired at work' and 'being irritable' were more frequent in weekly rotating shift workers (P<0.05), and the mean of symptom score was significantly higher in weekly rotating shift workers(P<0.01). 2. According to 6 hours of sleeping which is a definite elevation point of fatigue, there was not a significant difference between two groups in sleeping hours. Among workers in rapidly rotating shift system, the mean of symptom score was significatly higher in workers of less than 6 hours of sleeping(P<0.05), but it was not different among weekly rotating shift workers. 3. The symptoms of GI disturbance were more frequent in weekly rotating shift workers but statistically not significant. 4. The positive rate of mental and physical fatigue symptoms were significantly higher in weekly rotating shift workers(P<0.01) and mental and physical fatigue symptoms were more frequent in them (P<0.01). 5. After the effect of the factors that were significantly different between two groups by $X^2-test$ were controlled, the mean score of sleep disturbance was significantly higher in weekly rotating shift workers (P<0.01) and mental physical fatigue symptoms were more frequent in them (P<0.01). Based on these study results, subjective symptoms were more common in the weekly rotating shift workers. In future, medical examination and laboratory test will be also administered to evaluate a more accurate health outcomes and the review of current shift schedules will be required.

• Journal of Soil and Groundwater Environment
• /
• v.13 no.1
• /
• pp.43-51
• /
• 2008

Periodic fluctuation of water levels were analyzed for their causes and effects on groundwater movement. Groundwater levels were monitored from two shallow monitoring wells, G1 and G4, located at a headwater catchment in the Gwangneung Ecohydrological Research Site using pressure transducers with automatic data-loggers by five-minute interval from February to October, 2006. The water table fluctuates on a daily basis with a clear diurnal variation, and the fluctuation amplitude increases with time from the winter to the summer. Results from spectral analysis of water-level data show periodic variations in 24.38 hour and in 12.19 hour, indicating $P_1$ diurnal and $L_2$ semidiurnal tidal components, respectively. The diurnal component of the water level in summer has greater power than that in winter, implying that the water table is affected not only by earth tides, but also by evapotranspiration. Right after rain stops, the power of diurnal component of the water level decreases, indicating that evapotranspiration influences significantly diurnal periodicity. The effects of diurnal and semidiurnal components of the water level range from 0.4 to 4.2 cm and from 0.2 to 0.7 cm, respectively.

• Development and Reproduction
• /
• v.12 no.1
• /
• pp.9-18
• /
• 2008

All the organisms on the earth are affected by the repeating signals from the ambient environment caused by the movements of the sun and the earth. Their physiological and behavioral activities such as reproduction, functional pathway of various molecules, and developmental stage, are reflected by the cyclicity whether it is daily(circadian) or annual rhythms. An essential function of circadian rhythms is to provide an internal estimate of the external local time, thereby allowing the organism to program its activities so that they occur at an appropriate time in the daily environment. Of many rhythmic patterns, the circadian rhythms are considered in this review, focusing on the limit cycle, which is a model to investigate the entrainment.