• Sleep Medicine and Psychophysiology
• /
• v.6 no.2
• /
• pp.116-125
• /
• 1999

Objectives: The purpose of this study is to investigate the effect of exercise load on sleep structure and stress hormone secretion during sleep. Methods: Five male physical education students were included in this study after giving their written, informed consents in the Research Institute for Sports Science at the University of Hanyang. All subjects have performed for at least 3 years in a regular aerobic exercises such as football, basketball, and running. The subjects were divided into three groups ; NOE(non-exercise), MDE(middle duration exercise), LDE(long duration excercise). MDE group maintained a total of 120 min exercise, and LDE group maintained a total of 300 min exercise by football, basketball or badminton. All subjects were acclimatized to the experimental sleep condition by spending one night under expermental conditions, including the placement of an intravenous catheter. During the subsequent night(24:00-08:00), somnopolygraphic sleep recordings were obtained, and blood for measuring growth hormone, cortisol, testosterone, and $\beta$-endorphin was collected every 120 min throughout the night. Blood samples were obtained from prominent forearm veins of subjects. Then, the samples were immediately placed in ice and centrifuged within 10 min at 3000 rpm at $4^{\circ}C$. Statistical analyses were performed using the SPSS/$PC^+$. Data were analyzed by one-way ANOVA with repeated measures. Results: No significant differences among groups were observed in sleep latency, total sleep time, stage 2 sleep, and slow wave sleep. However, daytime exercise produced significant changes in stage 1 sleep, REM sleep, stage 2 sleep latency, REM sleep latency and sleep efficiency. Stage 1 sleep, stage 2 sleep latency, and REM sleep latency significantly increased in LDE compared to those of NOE and MDE groups. But the amount of REM sleep significantly decreased in LDE. Sleep efficiency of MDE was higher than those of NOE and LDE. The blood concentrations of growth hormone, testosterone, and cortisol during night sleep were significantly lower in LDE than in NOE. $\beta$-endorphin concentrations in blood during night sleep were not different among groups. Conclusion: The daytime exercise load was significantly related to sleep structure and stress hormone secretion during night sleep. Long duration exercise showed a harmful effect on sleep structure and hormone secretion. However, middle duration exercise had a beneficial effect on sleep structure and hormone secretion during sleep.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.32 no.5
• /
• pp.287-296
• /
• 2019

In this study, the effect of ground boundary conditions on the evaluation of blast resistance performance of precast arch structures was evaluated by a numerical analysis method. Two types of boundary conditions, namely, fixed boundary conditions and a perfectly matched layer (PML) were applied to numerical models. Blast loads that were much higher than the design load of the target structure were applied to compare the effects of the boundary conditions. The distribution and path of the ground explosion pressure, structural displacement, fracture of concrete, stress of concrete, and reinforcing bars were compared according to the ground boundary condition settings. As a result, the reflecting pressure shock wave at the ground boundaries could be effectively eliminated using PML elements; furthermore, the displacement of the foundation was reduced. However, no distinct difference could be observed in the overall structural behavior including the fracture and stress of the concrete and rebar. Therefore, when blast simulations are performed in the design of protective structures, it is rational to apply the fixed boundary condition on the ground boundaries as conservative design results can be achieved with relatively short computation times.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.48 no.3
• /
• pp.269-279
• /
• 2021

The purpose of this study is to evaluate the effect of the spread of a new type of coronavirus infection (COVID-19) on the mental state in school-age children and parents focusing on the aspects of sleep disorders and depression. A questionnaire survey was conducted for 123 parents and 108 school-age children who visited Department of Pediatric Dentistry, Kyung Hee University Dental Hospital at Gangdong from April 2, 2020 through April 25, 2020, via the direct writing method. Participants were assessed with Pittsburgh Sleep Quality Index, Generalized Anxiety Disorder (GAD)-7, Center for Epidemiology Scale for Depression. Logistic regressions were used with a level of significance of 5%. The prevalence of GAD, depression, and poor sleep in parents were 34.1%, 17.1% and 44.7%, respectively. The prevalence of GAD in children was 20.4%. Logistic regression showed that stress from Emergency Alert Messages about COVID-19 was associated with GAD and depression in parents. In children, the degree of emotional change after COVID-19 was associated with GAD. This study confirmed that there was a change in the psychological status of children and guardians due to the epidemic of coronavirus disease-2019, and it would be necessary to consider their psychological status during dental treatment.

• Journal of the Korean GEO-environmental Society
• /
• v.22 no.12
• /
• pp.41-50
• /
• 2021

This study investigated the changes in engineering characteristics of sand-tire chip mixtures during repetitive loading. To quantify the changes in the maximum shear modulus according to the tire chip content in the mixtures and the particle size ratio between sand particle and tire chip, the samples were prepared with tire chip content of TC = 0, 10, 20, 40, 60, and 100%, and the particle size ratios SR were also set to be SR = 0.44, 1.27, 1.87, and 4.00. The stress of the prepared sample was applied through a pneumatic cylinder. The experiment was conducted in the order of static loading (= 50 kPa), cyclic loading (= 50-150 kPa), static loading (= 400 kPa) and unloading. The stress applied to tested mixtures was controlled by a pressure panel and a pneumatic valve by using an air compressor. The shear wave velocity was measured during static and cyclic loadings by installing bender elements at the upper and lower caps of the mold. The results demonstrated that the change in maximum shear modulus of all tested materials with varying SR during repetitive loading is the most significant when TC ~ 40%. In addition, the mixture with smaller SR at a given TC shows greater increase in maximum shear modulus during repetitive loading.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2004.05a
• /
• pp.337-341
• /
• 2004

Engineering ceramics have superior heat resistance, corrosion resistance, and wear resistance. Consequently, these art significant candidates for hot-section structural components of heat engine and the inner containment of nuclear fusion reactor. Besides, some of them have the ability to heal cracks and great benefit can be anticipated with great benefit the structural engineering field. Especially, law fracture toughness of ceramics supplement with self-healing ability. In the present study, we have been noticed some practically important points for the healing behavior of silicon nitride, alumina, mullite with SiC particle and whisker. The presence of silicon carbide (SiC) in ceramic compound is very important for crack-healing behavior. However, self-healing of SiC has not been investigated well in detail yet. In this study, commercial SiC was selected as sample, which can be anticipated in the excellent crack healing ability. The specimens were produced three-point bending specimen with a critical semi-circular crack of which size that is about $50-700{\mu}m$. Three-point bending test and static fatigue test were performed cracked and healed SiC specimens. A monotonic bending load was applied to cracked specimens by three-point loading at different temperature. The purpose of this paper is to report Strength Properties and Elastic Waves Characteristics of Silicon Carbide with Crack Healing Ability.

• Journal of the Society of Naval Architects of Korea
• /
• v.49 no.4
• /
• pp.359-366
• /
• 2012

This is the final one of the two companion papers dealing with accuracy of accumulated fatigue damage estimation under wide band process. It is stated that four kinds of wide band models exist: typed of equivalent stress, combined PDF, correction factor, and damage combination. For the idealized ESDs from full scale measurement data on an 8100TEU container vessel, fatigue damages are compared for a narrow band prediction model based on Rayleigh PDF and five wide band fatigue prediction models of Dirlik, Wirsching-Light, Jiao-Moan, Benasciutti and DNV. DNV model consistently overestimates fatigue damages regardless of variation of ESDs. Predictions by Jiao-Moan model, which is understood as standard method for design of offshore platforms, are also in conservative side. Best accuracy is found from the results by Dirlik and Benasciutti models, but Benasciutti model is preferred since it can easily combined with narrow band fatigue damage based on Rayleigh PDF.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.9
• /
• pp.831-837
• /
• 2015

Many persons and electronic devices are exposed to electromagnetic (EM) waves generated from magnetic resonance imaging (MRI) equipment, EM pulses (EMPs), and many other kinds of EM wave devices. Finger strips are used to provide shielding from these EM waves. Because of the high thermal conductivity of finger strips, they are used in the design of specialized doors that are installed in shielded rooms. In this study, we perform an accelerated life test using the load acceleration stress, which affects the main failure mode of finger strips. We predict the life of the finger strip under normal usage conditions based on the results of the accelerated life test. We compare the results with those predicted from the life test under normal usage conditions to evaluate the validity of accelerated life testing.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2009.11a
• /
• pp.112-112
• /
• 2009

In this study, the effect of a long post-deposition thermal annealing(600 and 1000 $^{\circ}C$) on the surface acoustic wave (SAW) properties of polycrystalline (poly) aluminum-nitride (AlN) thin films grown on a 3C-SiC buffer layer was investigates. The poly-AlN thin films with a (0002) preferred orientation were deposited on the substrates by using a pulsed reactive magnetron sputtering system. Experimental results show that the texture degree of AlN thin film was reduced along the increase in annealing temperature, which caused the decrease in the electromechanical coupling coefficient ($k^2$). The SAW velocity also was decreased slightly by the increase in root mean square (RMS) roughness over annealing temperature. However, the residual stress in films almost was not affect by thermal annealing process due to small lattice mismatch different and similar coefficient temperature expansion (CTE) between AlN and 3C-SiC. After the AlN film annealed at 1000 $^{\circ}C$, the insertion loss of an $IDT/AlN/3C-SiC/SiO_2/Si$ structure (-16.44 dB) was reduced by 8.79 dB in comparison with that of the as-deposited film (-25.23 dB). The improvement in the insertion loss of the film was fined according to the decrease in the grain size. The characteristics of AlN thin films were also evaluated using Fourier transform-infrared spectroscopy (FT-IR) spectra and X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) images.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.13 no.5
• /
• pp.23-29
• /
• 2009

On December 13, 1996, an earthquake with local magnitude (M$_L$) 4.5 occurred in the Yeongwol area of South Korea. The epicenter was 37.2545$^{\circ}$N and 128.7277$^{\circ}$E, which is located inside the Okcheon Fold Belt. The waveform inversion analysis was carried out to estimate source parameters of the event according to the filtering bandwidth of seismic data. Using 0.02$\sim$0.2 Hz filtering bandwidth, focal depth and seismic moment were estimated to be 6 km and 1.3$\times$10$^{16}$ N$\cdot$m, respectively. This seismic moment corresponds to the moment magnitude (M$_W$) 4.7. The focal mechanism by the waveform inversion and P wave first motion polarity analysis is a strike slip faulting including a small thrust component, and the direction of P-axis is ENE-WSW. The moment magnitude estimated by spectral analysis was 4.8, which is similar to that estimated by waveform inversion. Average stress drop was estimated to be 14.3 MPa.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.9 no.4
• /
• pp.418-428
• /
• 2017

In offshore area, newly deposited Quaternary loose seabed soils are widely distributed. There are a great number of offshore structures has been built on them in the past, or will be built on them in the future due to the fact that there would be no very dense seabed soil foundation could be chosen at planed sites sometimes. However, loosely deposited seabed foundation would bring great risk to the service ability of offshore structures after construction. Currently, the understanding on wave-induced liquefaction mechanism in loose seabed foundation has been greatly improved; however, the recognition on the consolidation characteristics and settlement estimation of loose seabed foundation under offshore structures is still limited. In this study, taking a semi-coupled numerical model FSSI-CAS 2D as the tool, the consolidation and settlement of loosely deposited sandy seabed foundation under an offshore breakwater is investigated. The advanced soil constitutive model Pastor-Zienkiewics Mark III (PZIII) is used to describe the quasi-static behavior of loose sandy seabed soil. The computational results show that PZIII model is capable of being used for settlement estimation problem of loosely deposited sandy seabed foundation. For loose sandy seabed foundation, elastic deformation is the dominant component in consolidation process. It is suggested that general elastic model is acceptable for subsidence estimation of offshore structures on loose seabed foundation; however, Young's modulus E must be dependent on the confining effective stress, rather than a constant in computation.