• Water for future
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• v.19 no.2
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• pp.131-138
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• 1986

Both hydraulic and dynamic characteristics of a single perforated wall are studied theoretically and experimentally. Theoretically, the effect of evanescent modes on wave force acting on a single perated wall is studied by use of the Horiguchi theory. The wave force on the perforated wall is presented to be insensitive to evanescent modes. According to experimental study, The larger perforation ratio(${\gamma}$) grows, the weaker the wave force on the wall becomes sensitively. And in the small value of l/D (ratio of wall thickness(l) to hole diameter(D)) where the holes on the wall are regarded as orifice, the wave force on the wall is insensitive to the variation of l/D. Energy loss coefficient f is estimated at 1.0 in this small value of l/D by use of Horiguchi theory. But in the large value of l/D where the holes are regarded as pipe, the wave force on the wall is relatively sensitive to the variation of l/D and f is estimated at 1.5 by use of Horiguchi theory.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1427-1439
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• 2008

The quality of track-bed fills of railways has been controlled by field measurements of density (${\gamma}_d$) and the results of plate-load tests. The control measures are compatible with the design procedures whose design parameter is $k_{30}$ for both ordinary-speed railways and high-speed railways. However, one of fatal flaws of the design procedures is that there are no simple laboratory measurement procedures for the design parameters ($k_{30}$ or, $E_{v2}$ and $E_{v2}/E_{v1}$) in design stage. A new quality control procedure, in parallel with the advent of the new design procedure, is being proposed. This procedure is based upon P-wave velocity involving consistently the evaluation of design parameters in design stage and the field measurements during construction. The key concept of the procedure is that the target value for field compaction control is the P-wave velocity determined at OMC using modified compaction test, and direct-arrival method is used for the field measurements during construction. The procedure was verified at a test site and the p-wave velocity turned out to be an excellent control measure. The specifications for the control also include field compaction water content of $OMC{\pm}2%$ as well as the p-wave velocity.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.8
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• pp.19-26
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• 2004

High performance packages must provide excellent transmission characteristics. In face-up ceramic packages, however, parasitic characteristics of bondwires are not negligible at millimeter-wave frequencies. Consequently, the electrical performance of ceramic packages is degraded. In をis paper, we propose a new millimeter-wave ceramic package feed-through having Embedded Metal Sheets (EMS). The package that contains double-bondwire interconnections is analyzed by the FEM (Finite Element Method) and measured from 20 to 50GHz. As a result, the proposed package having Embedded Metal Sheets (EMS) achieved 0.85dB, 0.4dB insertion loss improvement on the conventional and the double bondwires buried in epoxy ( $\varepsilon_{{\gamma}}$/ = 4) ceramic package respectively to 47GHz. This improved ceramic package will be useful for MMICs modules and small ceramic packages developments.amic packages developments.

• Journal of Physiology & Pathology in Korean Medicine
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• v.24 no.4
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• pp.688-695
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• 2010

The aim of this study is to examine the change of Electroencephalogram (EEG) and concentration by practicing acupressure at the GB20 on normal humans. We selected 36 children and divided them into GB20 group and SP6 group. Electrode was measured in Fp1 and Fp2, and EEG was measured before and after practicing acupressure at the GB20 and SP6. Sensorimotor rhythm (SMR) increased significantly at the GB20 group (p=0.043). M-$\beta$ wave increased significantly at the GB20 group (p=0.022). H-$\beta$ wave increased significantly at the GB20 group (p=0.040). $\gamma$ wave increased significantly at the GB20 group (p=0.021). $(SMR+M-\beta)/\Theta$ ratio increased significantly at the GB20 group (p=0.023). $\beta/\Theta$ ratio increased significantly at the GB20 group (p=0.020). On the other hand, $\alpha$ and $\Theta$ wave did not have significant changes. Through this experiment, we conclude that acupressure at the GB20 on normal humans could increase the ability of concentration.

• Publications of The Korean Astronomical Society
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• v.26 no.2
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• pp.71-87
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• 2011

Gravitational waves are predicted by the Einstein's theory of General Relativity. The direct detection of gravitational waves is one of the most challenging tasks in modern science and engineering due to the 'weak' nature of gravity. Recent development of the laser interferometer technology, however, makes it possible to build a detector on Earth that is sensitive up to 100-1000 Mpc for strong sources. It implies an expected detection rate of neutron star mergers, which are one of the most important targets for ground-based detectors, ranges between a few to a few hundred per year. Therefore, we expect that the gravitational-wave observation will be routine within several years. Strongest gravitational-wave sources include tight binaries composed of compact objects, supernova explosions, gamma-ray bursts, mergers of supermassive black holes, etc. Together with the electromagnetic waves, the gravitational wave observation will allow us to explore the most exotic nature of astrophysical objects as well as the very early evolution of the universe. This review provides a comprehensive overview of the theory of gravitational waves, principles of detections, gravitational-wave detectors, astrophysical sources of gravitational waves, and future prospects.

• Journal of Welding and Joining
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• v.33 no.5
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• pp.53-60
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• 2015

Laser surface Melting Process is getting hardening layer that has enough depth of hardening layer as well as no defects by melting surface of substrate. This study used CW(Continuous Wave) Yb:YAG and STD11. Laser beam speed, power and beam interval are fixed at 70mm/sec, 2.8kW and 800um respectively. Hardness in the weld zone are equal to 400Hv regardless of melting zone, remelting zone overlapped by next beam and HAZ. Similarly, microstructures in all weld zone consist of dendrite structure that arm spacing is $3{\sim}4{\mu}m$, matrix is ${\gamma}$(Austenite) and dendrite boundary consists of ${\gamma}$ and $M_7C_3$ of eutectic phase. This microstructure crystallizes from liquid to ${\gamma}$ of primary crystal and residual liquid forms ${\gamma}$ and $M_7C_3$ of eutectic phase by eutectic reaction at $1266^{\circ}C$. After solidification is complete, primary crystal and eutectic phase remain at room temperature without phase transformation by quenching. On the other hand, microstructures of substrate consist of ferrite, fine $M_{23}C_6$ and coarse $M_7C_3$ that have 210Hv. Microstructures in the HAZ consist of fine $M_{23}C_6$ and coarse $M_7C_3$ like substrate. But, $M_{23}C_6$ increases and matrix was changed from ferrite to bainite that has hardness above 400Hv. Partial Melted Zone is formed between melting zone and HAZ. Partial Melted Zone near the melting zone consists of ${\gamma}$, $M_7C_3$ and martensite and Partial Melted Zone near the HAZ consists of eutectic phase around ${\gamma}$ and $M_7C_3$. Hardness is maximum 557Hv in the partial melted zone.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.59.1-59.1
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• 2018

On 2018 February 5 a gamma ray burst with trigger time 04:25:29.3 UT was detected by Swift BAT and this event was named GRB 180205A. We observed the optical afterglow of GRB 180205A starting from about 1 hour after the burst until February 22 in the optical bands with the 1m telescope of Deokheung Optical Astronomy Observatory (DOAO), the 1m telescope at Mt. Lemmon Optical Astronomy Observatory(LOAO) and the 0.8m and 0.25m telescopes at McDonald Observatory. According to the fireball model, which is a well-accepted and conventional model for the afterglow of the GRB, the mechanism of the afterglow is that the expanding external blast wave of the GRB successively collides with the ambient medium and loses its energy, and as a result emits radiation at wavelengths longer than gamma rays. Here we present optical photometry and light curve of the afterglow in the R band and analyze it to characterize GRB 180205A.

• Natural Product Sciences
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• v.18 no.2
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• pp.67-75
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• 2012

Zizyphi Spinosi Semen (ZSS) have been widely used for the treatment of insomnia in Asia. This experiment was performed to investigate whether methanol extract of ZSS (MEZSS) has hypnotic effects through the ${\gamma}$-amino butyric acid (GABA)ergic systems. MEZSS inhibited the locomotor activity. MEZSS enhanced pentobarbital-induced sleep behaviors. However, MEZSS itself did not induce sleep at higher dose, similar to muscimol. On the other hand, both pentobarbital and MEZSS increased the non rapid eye move (NREM) sleep, especially reducing the -wave electroencephalogram (EEG) activity in REM sleep. MEZSS showed similar effects with muscimol on potentiating chloride influx induced by pentobarbital. MEZSS significantly increased GABAA receptors ${\gamma}$-subunit expression and slightly decreased ${\beta}$-subunit expression in hypothalamus and thalamus, showing that subunit-expression was similar to diazepam. In addition, MEZSS enhanced the expression of glutamic acid decarboxylase (GAD). In conclusion, it is suggested that MEZSS might augment pentobarbital-induced sleep behaviors through the modification of GABAergic systems.

• Journal of Ocean Engineering and Technology
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• v.36 no.4
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• pp.251-269
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• 2022

The process-based XBeach model has numerous empirical parameters because of insufficient understanding of hydrodynamics and sediment transport on the nearshore; hence, it is necessary to calibrate parameters to apply to various study areas and wave conditions. Therefore, the calibration process of parameters is essential for the improvement of model performance. Generally, the trial-and-error method is widely used; however, this method is passive and limited to various and comprehensive parameter ranges. In this study, the Generalized Likelihood Uncertainty Estimation (GLUE) method was used to estimate the optimal range of three parameters (gamma, facua, and gamma2) using morphological field data collected in Maengbang beach during the four typhoons that struck from September to October 2019. The model performance and optimal range of empirical parameters were evaluated using Brier Skill Score (BSS) along with the baseline profiles, sensitivity, and likelihood density analysis of BSS in the GLUE tools. Accordingly, the optimal parameter combinations were derived when facua was less than 0.15 and simulated well the shifting shape, from crescentic sand bar to alongshore uniform sand bars in the surf zone of Maengbang beach after storm impact. However, the erosion and accretion patterns nearby in the surf zone and shoreline remain challenges in the XBeach model.

• Journal of the Korean Institute of Intelligent Systems
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• v.23 no.2
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• pp.172-177
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• 2013

With Brain Computer Interface (BCI) system, a person with disabled limb could use this direct brain signal like electroencephalography (EEG) to control a device such as the artifact arm. The precise force control for the artifact arm is necessary for this artificial limb system. To understand the relationship between control EEG signal and the gripping force of hands, We proposed a study by measuring EEG changes of three grades (25%, 50%, 75%) of hand grip MVC (Maximal Voluntary Contract). The acquired EEG signal was filtered to obtain power of three wave bands (alpha, beta, gamma) by using fast fourier transformation (FFT) and computed power spectrum. Then the power spectrum of three bands (alpha, beta and gamma) of three classes (MVC 25%, 50%, 75%) was classified by using PCA (Principal Component Analysis) and LDA (Linear Discriminant Analysis). The result showed that the power spectrum of EEG is increased at MVC 75% more than MVC 25%, and the correct classification rate was 52.03% for left hand and 77.7% for right hand.