• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.7
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• pp.992-1001
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• 2023

OWEC (Overtopping Wave Energy Converter) is a wave power generation system using the wave overtopping. The performance and safety of the OWEC are affected by wave characteristics, such as wave height, period. To mitigate this issue, optimal OWEC designs based on wave characteristics must be investigated. In this study, the environmental conditions along the Ulleungdo coast were used. The hydraulic efficiency of the OWEC was calculated using SPH (Smoothed Particle Hydrodynamics) by comparing 4 models that changed the substructure. As a result, it was possible to change the substructure. Through design optimization, a new truss-type structure, which is a substructure capable of carrying the design load, was proposed. Through a case study using member diameter and thickness as design variables, structural safety was secured under allowable stress conditions. Considering wave load, the natural frequency of the proposed structure was compared with the wave period of the relevant sea area. Harmonic response analysis was performed using wave with a 1-year return period as the load. The proposed substructure had a reduced response magnitude at the same exciting force, and achieved weight reduction of more than 32%.

• Korean Journal of Food Science and Technology
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• v.32 no.3
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• pp.590-597
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• 2000

The rheological properties of ${\beta}-glucans$ isolated from non-waxy and waxy barley were investigated. ${\beta}-Glucan$ solutions showed pseudoplastic properties and their behaviors were explained by applying Power law model in the range of concentrations$(1{\sim}4%)$ and temperatures$(20{\sim}65^{\circ}C)$. The effects of temperature and concentration on the apparent viscosity at $700\;s^{-1}$ shear rate were examined by applying Arrhenius equation and power law equation, and their effect was more pronounced in waxy ${\beta}-glucan$ solutions. The activation energy for flow of ${\beta}-glucan$ solutions decreased with the increase of concentration, and the concentration-dependent constant A increased with the increase of temperature. The intrinsic viscosity of waxy ${\beta}-glucan$ was higher than that of non-waxy ${\beta}-glucan$. The transition from dilute to concentrate region occurred at a critical coil overlap parameter $C^*[{\eta}]=0.02.$ The slopes of non-waxy and waxy ${\beta}-glucan$ at $C[{\eta}] were similar, but the slope of waxy ${\beta}-glucan$ at $C[{\eta}]>C^*[{\eta}]$ was higher than that of non-waxy ${\beta}-glucan$. Dynamic viscoelasticity measurement showed that cross-over happened, and storage modulus was higher than loss modulus at frequency range above cross-over. ${\beta}-Glucan$ solutions formed weak gels after stored for 24 hr.

• Geophysics and Geophysical Exploration
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• v.17 no.1
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• pp.1-10
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• 2014

To reveal and classify site characteristics in densely populated areas in Chuncheon, Korea, Rayleigh-waves were recorded at 50 sites including four sites in the forest area using four 1-Hz velocity sensors and 24 4.5-Hz vertical geophones during the period of January 2011 to May 2013. Dispersion curves of the Rayleigh waves obtained by the extended spatial autocorrelation method were inverted to derive shear-wave velocity ($v_s$) models comprising 40 horizontal layers of 1-m thickness. Depths to weathered rocks ($D_b$), shear wave velocities of these basement rocks ($v_s^b$), average velocities of the overburden layer ($\bar{v}_s^s$), and the average velocity to a depth of 30 m ($v_s30$), were then derived from those models. The estimated values of $D_b$, $v_s^b$, $\bar{v}_s^s$, and $v_s30$ for 46 sites at lower altitudes were in the ranges of 5 to 29 m, 404 to 561 m/s, 208 to 375 ms/s, and 226 to 583 m/s, respectively. According to the Korean building code for seismic design, the estimated $v_s30$ indicates that the lower altitude areas in Chuncheon are classified as $S_C$ (very dense soil and soft rock) or $S_D$ (stiff soil). To determine adequate proxies for $v_s30$, we compared the computed values with land cover, lithology, topographic slope, and surface elevation at each of the measurement sites. Due to a weak correlation (r = 0.41) between $v_s30$ and elevation, the best proxy of them, applications of this proxy to Chuncheon of a relatively small area seem to be limited.

• The Journal of Korean Academy of Prosthodontics
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• v.51 no.3
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• pp.167-174
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• 2013

Purpose: This study was conducted to evaluate the roughness and surface alternations of three differently blasted titanium discs treated by $Nd:YVO_4$ Laser irradiation in different conditions. Materials and methods: Thirty commercially pure titanium discs were prepared and divided into three groups. Each group was consisted of 10 samples and blasted by $ZrO_2$ (zirconium dioxide), $Al_2O_3$ (aluminum oxide), and RBM (resorbable blasted media). All the samples were degreased by ultrasonic cleaner afterward. Nine different conditions were established by changing scanning speed (100, 300, 500 mm/s) and repetition rate (5, 15, 35 kHz) of $Nd:YVO_4$ Laser (Laser Pro D-20, Laserval $Korea^{(R)}$, Seoul, South Korea). After laser irradiation, a scanning electron microscope, X-ray diffraction analysis, energy dispersive X-ray spectroscopic analysis, and surface roughness analysis were used to assess the roughness and surface alternations of the samples. Results: According to a scanning electron microscope (SEM), titanium discs treated with laser irradiation showed characteristic patterns in contrast to the control which showed irregular patterns. According to the X-ray diffraction analysis, only $Al_2O_3$ group showed its own peak. The oxidation tendency and surface roughness of titanium were similar to the control in the energy dispersive X-ray spectroscopic analysis. The surface roughness was inversely proportional to the scanning speed, whereas proportional to the repetition rate of $Nd:YVO_4$. Conclusion: The surface microstructures and roughness of the test discs were modified by the radiation of $Nd:YVO_4$ laser. Therefore, laser irradiation could be considered one of the methods to modify implant surfaces for the enhancement of osseointegration.

• Geophysics and Geophysical Exploration
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• v.10 no.3
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• pp.183-190
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• 2007

The site effects of seismic stations were evaluated by conducting a simultaneous inversion of the stochastic point-source ground-motion model (STGM model; Boore, 2003) parameters based on the accumulated dataset of horizontal shear-wave Fourier spectra. A model parameter $K_0$ and frequency-dependent site amplification function A(f) were used to express the site effects. Once after a H/V ratio of the Fourier spectra was used as an initial estimate of A(f) for the inversion, the final A(f) which is considered to be the result of combined effect of the crustal amplification and loca lsite effects was calculated by averaging the log residuals at the site from the inversion and adding the mean log residual to the H/V ratio. The seismic stations were classified into five classes according to $logA_{1-10}^{max}$(f), the maximum level of the site amplification function in the range of 1 Hz < f < 10 Hz, i.e., A: $logA_{1-10}^{max}$(f) < 0.2, B: 0.2 $\leq$ $logA_{1-10}^{max}$(f) < 0.4, C: 0.4 $\leq$ $logA_{1-10}^{max}$(f) < 0.6, D: 0.6 $\leq$ $logA_{1-10}^{max}$(f) < 0.8, E: 0.8 $\leq$ $logA_{1-10}^{max}$(f). Implication of the classified result was supported by observing a shift of the dominant frequency of average A(f) for each classified stations as the class changes. Change of site classes after moving seismic stations to a better site condition was successfully described by the result of the station classification. In addition, the observed PGA (Peak Ground Acceleration)-values for two recent moderate earthquakes were well classified according to the proposed station classes.

• Journal of the Korean Society of Food Science and Nutrition
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• v.43 no.12
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• pp.1942-1947
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• 2014

Nutritional compositions of Korean traditional actinidia (Actinidia arguta) cultivars, such as Otumsense, Chiak, and Skinny green, were investigated as high value-added food substances. Among minerals, K content of three cultivars was the highest, and P, Ca, and Na contents were relatively higher than those of other minerals. Contents of essential amino acids were analyzed as follows: Otumsense (198.48 mg/100 g), Chiak (413.50 mg/100 g), and Skinny green (270.07 mg/100 g). Total amino acids of Chiak were the highest among the three cultivars, and major amino acids of the three cultivars were glutamic acid and aspartic acid. Analysis of fatty acids showed that major fatty acids were palmitic acid as a saturated fatted acid and ${\alpha}$-linoleic acid as an unsaturated fatty acid in the three cultivars. Glucose and fructose were major free sugar constituents in the three cultivars. Total free sugar content of Otumsense was relatively higher than others. Finally, niacin and vitamin $B_6$ of Skinny green (1.55 mg/100 g, 1.92 mg/100 g) were the highest among the cultivars. However, ${\beta}$-carotene as a vitamin A precursor ($3.82{\mu}g/100g$) and vitamin C as a natural antioxidant substance (47.18 mg/100 g) of Otumsense cultivar were the highest.