• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.11
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• pp.873-877
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• 2012

The effect of oxygen pressure in the synthesis of ZnO nanostructures through thermal evaporation of Zn powder was investigated. The thermal evaporation process was carried out in oxygen ambient for 1 hr at $1,000^{\circ}C$ under different pressures. The oxygen pressure was changed in range of 0.5 ~ 900 Torr. Any nanostructure was not formed on the specimens prepared at oxygen pressures lower than 10 Torr. When oxygen pressure was 100 Torr, ZnO nanowires were observed. With increasing the oxygen pressure to 500 Torr, the morphology of ZnO nanostructures changed from wire to tetrapod. For all the samples, room temperature photoluminescence spectra show a strong green emission peak at around 550 nm.

• Journal of Ocean Engineering and Technology
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• v.29 no.1
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• pp.62-69
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• 2015

Coastlines are protected by breakwater structures against the erosion of sand or other materials along beaches due to wave action. This research examined the use of physical modeling to determine the effects of the tetrapod size and vertical walls of a rubble mound on the volume of wave overtopping under irregular wave conditions in coastal areas in Busan Yacht Harbor. In this analysis model, the structures were studied using irregular waves and the JONSWAP wave energy spectrum. To understand the effects of the tetrapod size and heights of the vertical wall, the study considered vertical walls of 0, 1.78, 6.83, and 9.33 cm with armor double layered material tetrapods of 8, 12, 16, and 20 tons. An extensive number of experiments covering a relatively large range of variables enabled a comprehensive discussion. First, in the presence of a short vertical wall, the water level played a key role in the overtopping discharge. In such circumstances, the values of the wave overtopping discharge decreased with increasing freeboard size. In the presence of a tall freeboard and middle, the value of the wave overtopping discharge was equally influenced by the vertical wall factor. Moreover, the tetrapod size decreased by an increase in the vertical wall factor, and relationship between them resulted in a short wall height. From an engineering point of view, considering a small water level may allow the choice of a shorter vertical wall, which would ultimately provide a more economical design.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.389-398
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• 2017

The re-analysis on the stable weight of the concrete armor unit (CAU) at the roundhead and the suggestion of the covering range at the roundhead with the increased weight of CAU were conducted. Tetrapods were applied to the tests and the three dimensional hydraulic tests were performed. The test results for the stable weight at the roundhead area were similar to the guides from Korean Design Standard for Harbour and Fishery Port (MOF, 2014) and Coastal Engineering Manual (USACE, 2005). The investigation of covering range at the roundhead of rubble mound structures armoured with Tetrapods was suggested that the length of five times of the design wave height from the tip of the superstructure was needed and appropriate. Both sides of the superstructure should be covered with increasing weighted CAU to satisfy the stability at roundhead area.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.6
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• pp.397-404
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• 2010

Laboratory tests of wave overtopping rates for a rubble mound breakwaters armoured Tetrapod were carried out, with varying design waves, crest berm widths and crest freeboards. The objective of this study is to investigate overtopping performance and to examine the characteristics of the widely used overtopping prediction models through the results of laboratory tests. Laboratory tests show that structure slope and wave periods have a considerable influence on overtopping rates, but the difference of overtopping rates related to crest berm widths is slight. Owen(1980)'s prediction considerably overestimates compared to the measured valued. Prediction of Van der Meer et al.(1998) underestimates only for steep slope($cot{\alpha}$=1.5). Besley(1999)'s and Pedersen(1996)'s predictions have a relatively good agreement with the measured results for slopes with a broader crest berm width. In general, best agreement between measured and predicted overtopping rates is observed using modified Pedersen(1996)'s formula for all test conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.35-40
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• 2020

The ballast layers play a key role in distributing and supporting a trainload. On the other hand, it settles down by dynamic train loading due to large void ratios. Consequently, it requires continuous maintenance. In this paper, ballast layers mixed with three types of specially shaped artificial ballast (AB) (Rectangular, Tetrapod, Hexagonal) were modeled by using a two dimensional DEM (Discrete Element Method). Repeated loading tests were performed to evaluate the settlement behavior of the ballast layers. The smallest settlement was observed in the case of the ballast layer mixed with Tetrapod AB than in other cases, according to an analysis of the force transfer routes. In addition, contact force analysis showed that the Tetrapod AB, which has a concave shape, could easily make small and multi-channel force-transfer routes. This means that the stress in the ballast layer by the train loading transferred through the sleeper uniformly was distributed well by the AB. Therefore, the settlement of the ballast layer mixed with the concave-shaped Tetrapod AB could be reduced effectively under a repeated train loading. The effects of a decrease in settlement of the ballast layer highlight the possibility of a maintenance-free ballasted track.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.1013-1016
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• 2005

ZnO nanostructure was fabricated by catalyst-free method using Zn powder in air. The growth temperature was controlled from 450$^{\circ}$C to 600$^{\circ}$C, and the structural and optical properties were investigated by scanning electron microscopy (SEM), photoluminescence (PL), energy dispersive X-ray spectroscopy (EDX) and cathodoluminescence (CL). From all samples both ZnO tetrapods and clusters were observed. No significant dispersion was observed from the ZnO tetrapods, however, ZnO clusters show considerable change in density and size. From the EDX results, atomic composition difference was found. The clusters have O-deficiencies, while tetrapods have stoichiometric composition. Strong luminescence was observed at room temperature. From room temperature PL, UV emission at 380 nm and green emission at 500 nm were observed, and the intensity ratio ($I_{uv}/I_{green}$) increased as growth temperature increases. CL measurements show that the UV emission is closely related with tetrapods and the green emission is dominated from the clusters.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.1
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• pp.43-49
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• 2020

In this study, the stability of the low crested structure armoured by Tripod block has been investigated using two-dimensional hydraulic model tests. The effect of wave steepness and freeboard on the rock stability on crest, front, and the rear slope has been investigated. From the experimental data, the new empirical formula for the stability coefficients of the Tripod block was proposed. But Tripod is not proper to use the armour block of the low crested structure because the uplift force of this block is greater than that of Tetrapod and rock.

• Korean Journal of Materials Research
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• v.28 no.10
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• pp.578-582
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• 2018

ZnO crystals with different morphologies are synthesized through thermal evaporation of the mixture of Zn and Cu powder in air at atmospheric pressure. ZnO crystals with wire shape are synthesized when the process is performed at $1,000^{\circ}C$, while tetrapod-shaped ZnO crystals begin to form at $1,100^{\circ}C$. The wire-shaped ZnO crystals form even at $1,000^{\circ}C$, indicating that Cu acts as a reducing agent. As the temperature increases to $1,200^{\circ}C$, a large quantity of tetrapod-shaped ZnO crystals form and their size also increases. In addition to the tetrapods, rod-shaped ZnO crystals are observed. The atomic ratio of Zn and O in the ZnO crystals is approximately 1:1 with an increasing process temperature from $1,000^{\circ}C$ to $1,200^{\circ}C$. For the ZnO crystals synthesized at $1,000^{\circ}C$, no luminescence spectrum is observed. A weak visible luminescence is detected for the ZnO crystals prepared at $1,100^{\circ}C$. Ultraviolet and visible luminescence peaks with strong intensities are observed in the luminescence spectrum of the ZnO crystals formed at $1,200^{\circ}C$.

• Journal of Aquaculture
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• v.22 no.1
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• pp.83-91
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• 2009

The Korean doty barbel Hemibarbus mylodon (Cypriniformes; Cyprinidae) is a critically endangered freshwater fish species mainly because of its natural habitat degradation. Three full-length complementary DNA (cDNA) clones representing different muscle actin isoforms were isolated and characterized. The three muscle actin isoforms were 1,294-1,601 bp long with the identical open reading frames of 1,134 bp with the deduced amino acid residues of 377. They showed 83.9-87.2% identities in the coding nucleotide level and 96.8-98.1% identities in the amino acid level. Phylogenetic analysis with the coding nucleotide sequences revealed that three muscle actin isoforms of H. mylodon formed strongly supported monophyletic groups with one of cypriniform skeletal $\alpha$-actin (acta1), cypriniform aortic $\alpha$-actins (acta2), and uncharacterized Danio rerio muscle actin isoform/Salmo trutta slow muscle actin (a novel muscle actin type). Our phylogenetic tree further suggested that cypriniform acta2 only showed the orthologous relationship to tetrapod acta2. Other multiple actin isoforms from diverse teleostean taxa were however clustered to no tetrapod orthologs, i.e., acta1, cardiac $\alpha$-actins (aetc1), acta2, and enteric $\gamma$-actin (actg2). This result strongly suggested that teleostean muscle actins have experienced different and complicated evolutionary history in comparison to mammalian counterparts.

• Journal of Ocean Engineering and Technology
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• v.18 no.4 s.59
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• pp.23-32
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• 2004

Specially shaped concrete blocks are used for the armor layer of rubble structure for breakers, seawalls, or other shore protection work. In this study, the hydraulic characteristics of the Modified-Tribar(MTB), which addresses the shortcomings of the Arch-Tribar, and the most widely used Tetrapod(TTP) in Korea are examined through hydraulic model tests. The MTB are much more stable than the TTP, as shown through the stability model tests under non-breaking and non-overtopping condition. The value of the stability coefficient(KD) was obtained at around 30. The model tests show that the TTP random two layers and MTB uniform 1.5 layers have similar effects, but the MTB one layer shows slightly low effects in dissipating wave energy. The TTP random two layer model is the most effective in reducing wave overtopping rate, under overtopping condition, while the MTB uniform one layer and the MTB uniform 1.5 layer models follow respectively.