• Journal of Fisheries and Marine Sciences Education
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• v.27 no.3
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• pp.747-756
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• 2015

Brown alga Undaria peterseniana has been interested in the commercial scale aquaculture for warm water species development in southern coastal area of Korea. However, this species was classified an endangered species caused by a decrease in habitat and natural population. In this study, inhabit characteristics of U. peterseniana was investigated in their natural habitat of Ulleung Island, Korea. The U. peterseniana population was occurred dense patches at 20~30m depth. Total length of the alga reached 1.0~2.0m and the largest width ranged 10.0~35.0cm during the study. In 2013, habitats of this species increased two sites compared with the previous year and their distribution extended to low depth (10m) of coastal area. In long-term data, seawater temperature revealed a continuous increment by strong going north of East Korea Warm Current or Ulleung Warm Eddy turning around the coast of Ulleung Island. It suggested that habitat extension of U. peterseniana may be caused by suitable settlement condition and increase of warm water around the coastal area. Current studies of this species may be continuously required in the possibility of fisheries resources as aquaculture species and index species of increment of water temperature at the fixed monitoring site in East Sea. This is the first study to research ecological feature U. peterseniana population at the natural habitat of Ulleung Island.

• Korean Journal of Remote Sensing
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• v.25 no.3
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• pp.225-231
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• 2009

The characteristics of morphological shapes, wave heights, tidal ranges and sediment sizes are observed and compared between intertidal beach and mudflat. The Mohang sand beach, southwest coast of Korea, is located just next to the large mudflat and has tidal range over 5 meters. Wave measurements are conducted at each entrance of the beach and mudflat as well as at the outside waters representing the incident waves to these different coastal environments. The morphological characteristics are also examined including the sediment size and the slope of the bathymetry, For the observation of morphological shapes, camera monitoring technique is used to measure the spatial information of intertidal bathymetry. The water lines moving on the intertidal flat/beach durinq a flood indicate depth contours between low and high water lines. The water lines extracted from the consecutive images are rectified to get the ground coordinates of each depth contours and integrated to provide three dimensional information of intertidal topography. The wave data show that sand beach is in the condition of severer wave forcing but tidal range is almost identical in both environment. The slope of the mudflat is much milder than the sand beach with finer sediment.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.719-722
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• 2005

The watertightness of concrete is judged by the depth of penetration of water forced in under pressure with the mechanism of flow of seepage water examined theoretically and experimentally. As a result, it is found that in the case of low water pressure approximately 0.15Mpa or less, the flow is Darcy seepage flow, the same as flow in an ordinary sand stratum, whereas in the case of high water pressure, the flow is diffused seepage flow accompanied by internal deformation of concrete. It is suggested that the watertightness of concrete be evaluated by seepage coefficient in the case of the former and diffusion coefficient in the case of the latter.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.254-256
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• 2009

The performances of proton exchange membrane (PEM) water electrolysis depend on many factors such as materials, geometries, fabrication methods, operating conditions, and so forth. The fabrication method is concerned, membrane electrode assemblies (MEA) are a most important part to show different performances by different fabrication methods. The performance change of PEM water electrolysis was experimentally measured according to the fabrication differences of the anode electrodes. One point of view is the catalyst intrusion rate to the anode gas diffusion layer (GDL), and the other point of view is the catalyst loading distribution in depth of the anode GDL. Results show that the performances of MEA with deep intrusion of the catalysts are better in the range of low current densities but worse at higher current densities. The catalyst loading distribution does not affect significantly to the performance of PEM water electrolyser.

• The Journal of the Acoustical Society of Korea
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• v.6 no.4
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• pp.64-73
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• 1987

Low frequency sound propagation in a range-dependent shallow water environment of the Korea Strait has been studied by using the adiabatic coupled mode, ADIAB. The range-dependent environment is unique in terms of horizontal variations of sound velocity profiles, sediment thickness and attenuation coefficients and water depths. For shallow source and receiver depths, the most important mechanism involved in the propagation loss is the depth changing character of mode functions that strongly depends on the local sound velocity profile. Application of the adiabatic coupled mode theory to shallow water environment is reasonable when higher modes are attenuated due to bottom interaction effects. Underwater sound propagation in a range-dependent shallow-water environment.

• New & Renewable Energy
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• v.5 no.4
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• pp.75-78
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• 2009

The performances of proton exchange membrane (PEM) water electrolysis depend on many factors such as materials, geometries, fabrication methods, operating conditions, and so forth. The fabrication method is concerned, membrane electrode assemblies (MEA) are a most important part to show different performances by different fabrication methods. The performance change of PEM water electrolysis was experimentally measured according to the fabrication differences of the anode electrodes. One point of view is the catalyst intrusion rate to the anode gas diffusion layer (GDL), and the other point of view is the catalyst loading distribution in depth of the anode GDL. Results show that the performances of MEA with deep intrusion of the catalysts are better in the range of low current densities but worse at higher current densities. The catalyst loading distribution does not affect significantly to the performance of PEM water electrolyser.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.30 no.1
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• pp.25-32
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• 1994

An underwater speaker was made of a moving coil driver unite of usual speaker, acryl-boards, polyester resin, rubber and castor oil and it's frequency characteristics was measured in range of 250~600Hz in air water tank and sea. The results of measurements are follows: 1. Transmitting and receiving frequency of measurement frequency were similar in air, water tank and sea. 2. The input and output wave forms of a manufactured speaker which is not water-proof in air were similar to each other in 300~450Hz, but other frequencies showed distorted wave forms. 3. The input and output wave forms of an underwater speaker in water thank and sea were similar to each other in 250~600Hz. But output wave forms showed combination waves with very low frequency. 4. Transmitting and receiving frequency wave forms and resisting pressure of an underwater speaker at 80m in the depth of water were in good condition. Therefore it can be possible to use it as an underwater speaker.

• Korean Journal of Environment and Ecology
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• v.34 no.4
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• pp.334-344
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• 2020

A total of 24 families, 44 species, and 658 benthic macroinvertebrates were identified, and Ecdyonurus dracon Kluge (13%) was the dominant species in forested streams within the Yeonyeopsan (Mt.). A total of four habit categories (i.e., clingers (56%), burrowers (19%), swimmers (14%), and sprawlers (56%)) were identified, and clingers were the dominant habit at all survey points except point one (UP1). Habitat characteristics were depended on the hydraulic factors (e.g., flow velocity, depth, and substrates), water quality (e.g., DO and water temperature), and the habitat characteristics were differed in the riffle, which has a faster the flow velocity, compared by in the stagnant pool. In other words, in riffles, the clingers dominated in high flow velocity with the large maximum and median grain size for substrates in the habitats regardless of depth, but the burrowers and sprawlers were dominant in low flow velocity with the small maximum and median grain size for substrates in the habitats. Moreover, DO and flow velocity were in positive correlation (y = 0.6666x - 0.659, R² = 0.0851), and the habitat for burrowers was wider than that for sprawlers or clingers. The water depth was negatively correlated with water temperature (y = -26.397x + 283.87, R² = 0.1802) since the water temperature is more sensitive to insolation in shallow depth. pH was positively correlated with water temperature. The investigation of the habitat characteristics by separating the relations between pH and DO in upstream and downstream showed the low pH and high DO in the upstream with a high crown density of 68%, regardless of community composition. On the other hand, high pH and low DO in the downstream with a relatively low crown density of 51%. It was considered that the riparian forest played a role in suppressing the growth of attached algae and the controlling water temperature in headwater streams. Our findings identified the habitat characteristics of benthic macroinvertebrates in a headwater stream. We expected that the finding can provide reference data for suggesting conservation and management plans in a headwater stream and increasing academic value.

• 한국해양학회지
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• v.11 no.1
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• pp.1-8
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• 1976

This work concerns ecological studies on the larvae of the ark shell, Anadara broughtonii(SCHRENCK), in the aea adjacent to Gajyo-do in Jinhae Bay. Marine environmental factors, namely, temperatue, salinity, depth, and tidal current were observed in connection with the larval distributions. Water temperature appeared to be one of the main factors that influence the spawning activity. The numbers of the drifting larvae fluctuated greatly during the study period. The trend, however, was for numbers to be low in early summern, increasing in mid summer, and reaching a peak in late summer, at high bottom water temperature and low bottom salinities. Significantly increased numbers of the drifting larvae were observed during the period in which the bottom water temperatures and salinities were very close to those at the surface. the numbers of the drifting larvae showed a positive relationship with velocities of the water mass within the range of 0∼20 cm/sec. It was also noticed that the drifting larvae were relatively abundant in the area of eddy motion.

• Nuclear Engineering and Technology
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• v.54 no.4
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• pp.1526-1533
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• 2022

Small modular reactors have garnered considerable attention in the recent years. Plate fuel elements exhibit a good application prospect in small modular pressurized water reactors for marine applications. Further, improved economic benefits can be achieved by extending the core lifetime of small modular reactors. However, it is necessary to realize a large initial residual reactivity for achieving a relatively long burnup depth finally. Thus, the selection of a suitable burnable poison (BP) is a crucial factor that should be considered in the design of small modular reactors. In this study, some candidate BPs are selected to realize the effective control of reactivity. The results show that ²³¹Pa₂O₃, ²⁴⁰Pu₂O₃, ¹⁶⁷Er₂O₃, PACS-J, and PACS-L are ideal candidates of BP, and since the characteristics of BP can increase the final burnup depth of assembly, the economic benefits are gained. Additionally, an optimal combination scheme of BPs is established. Specifically, it is proved that through a reasonable combination of BPs, a low reactivity fluctuation during the lifetime can be achieved, leading to a large final burnup depth.