• Korean Journal of Fisheries and Aquatic Sciences
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• v.54 no.4
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• pp.456-466
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• 2021

The distribution and abundance of euphausiids were investigated in Korean waters in 2016. Euphausiids were sampled with a Bongo net. A CTD (Sea Bird Electronics 9 plus) measured the water temperature and salinity while sampling. Mean water temperature ranged from 4.2-31.0℃. The highest temperatures occur in September and lowest temperatures in February. The mean water salinity ranged from 27.9-34.8 psu, with the highest salinities in March and lowest in September. Euphausiid species in group W consisted of four species. Among the euphausiid species, Euphausia pacifica was the dominant species with peak densities in September. The E. pacifica from group W was distributed in the bottom cold water during summer when a thermocline was formed. Five euphausiid species occurred in group S. E. pacifica and E. nana were the dominant species. In group S, E. nana was located in the warm and saline Tsushima Warm Current, a branch of the influential Kuroshio Current. Five euphausiid species occurred in group E. E. pacifica and T. longipes were the dominant species. In group E, E. pacifica and T. longipes were distributed in the deep and cold waters, these species prefer low water temperatures and perform vertical migration. The distribution of euphausiids in Korean waters were highly influenced by mass water characteristics, such as temperature and salinity.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.31 no.5
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• pp.1031-1043
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• 2021

Recently, the importance of information security has become greater. For this reason, the number of departments related to information security at universities and professional educational institutions is increasing. It is analyzed that the curriculum of such educational institutions has a lot to do with the job competency mentioned in NCS in relation to major subjects. This has the advantage of providing a standardized level of education for each job competency. However from the perspective of students there may be limitations on duplicate curriculum quality of education according to the level of teachers and timely acquisition of necessary elemental skills. In this paper we analyze the curriculum of universities and professional educational institutions and propose a cell-based three-dimensional education model to address the limitations of students. We verified based on the college curriculum that the proposed model can effectively improve its limitations.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.1
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• pp.58-66
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• 2019

Paralarvae of the common squid, Todarodes pacificus, were sampled with the bongo net (diameter: 60 cm, mesh: $333{\mu}m$) with a research vessel (Tamgu 20) at 18 stations along the coastal waters of the Yellow Sea in spring and autumn from 2013 to 2015. Over this period, 4 Paralarvae were collected. Paralarval density was $0.1inds./1,000m^3$ and $0.2inds./1,000m^3$ in autumn 2014 and $0.1inds./1,000m^3$ and $0.2inds./1,000m^3$ in autumn 2015. The range of mantle length for paralarvae was from 1.5 to 8.3 mm. Survival temperature ($15-24^{\circ}C$) for embryo stage and paralarvae was found in locations shallower than 56 m of depth at stations which were sampled for paralarvae.

• Journal of Radiation Protection and Research
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• v.44 no.2
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• pp.53-63
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• 2019

Background: As neutron fields are always accompanied by gamma rays, it is essential to distinguish neutrons from gamma rays in the detection of neutrons. Neutrons and gamma rays can be separated by pulse shape discrimination (PSD) methods. Recently, we performed characterization of a stilbene scintillator detector and an EJ-301 liquid scintillator detector with a high-speed digitizer DT5730 and investigated optimized PSD variables for both detectors. This study is for providing a basis for developing fast neutron/gamma-ray dual-particle imager. Materials and Methods: We conducted PSD experiments using stilbene scintillator and EJ-301 liquid scintillator and evaluated neutron and gamma ray discriminability of each PSD method with a $^{137}Cs$ gamma source and a $^{252}Cf$ neutron source. We implemented digital signal processing techniques to apply two PSD methods - the charge comparison (CC) method and the constant time discrimination (CTD) method - to distinguish neutrons from gamma rays. We tried to find optimized PSD variables giving the best discriminability in a given experimental condition. Results and Discussion: For the stilbene scintillator detector, the charge comparison method and the constant time discrimination method both delivered the PSD FOM values of 1.7. For the EJ-301 liquid scintillator detector, both PSD methods delivered the PSD FOM values of 1.79. With the same PSD variables, PSD performance was excellent in $300{\pm}100keVee$, $500{\pm}100keVee$, and $700{\pm}100keVee$ energy regions. This result shows that we can achieve an effective discrimination of neutrons from gamma rays using these scintillator detector systems. Conclusion: We applied both PSD methods to a stilbene and a liquid scintillator and optimized the PSD performance represented by FOM values. We observed a good separation performance of both scintillators combined with a high-speed digitizer and digital PSD. These results will provide reference values for the dual-particle imager we are developing, which can image both fast neutrons and gamma rays simultaneously.

• Ocean and Polar Research
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• v.44 no.3
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• pp.191-207
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• 2022

Using the results of CTD casts made in Spring from 2017 to 2021, in this study we investigated the water mass distribution and occurrence of temperature inversion in the western seas of Jeju Island in spring. The distribution of water masses was characterized by cold and fresh water in the northwest and warm and saline water in the southeast, forming a strong thermohaline front running in the southwest-to-northeast direction. Strong temperature inversion mainly occurred in the frontal boundary when the cold water intrudes beneath the warm water at depths of 30-50 m. Analysis of the mixing ratio demonstrated that Jeju Warm Water is dominantly distributed in the western seas of Jeju Island, but its ratio can be modified depending on the southward extension of Yellow Sea Cold Water (YSCW). Results of in situ measurement showed that in 2020, the YSCW largely expanded to the western seas of Jeju Island, occupying approximately 40 % of the mixing ratio. Due to the expansion of YSCW, a strong thermohaline front was formed in the study area, thereby causing thick and strong temperature inversion. On the other hand, in 2018 the mixing ratio of YSCW was minimum (~18%) during the study period of 2017-2021, and thus a relatively weak frontal boundary was formed, without the occurrence of temperature inversion. The observational results also suggest that the interannual changes of water mass distribution and the associated temperature inversion in the western seas of Jeju Island are closely related with wind-driven Yellow Sea circulation in spring, which is the summer monsoon transition period.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.4
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• pp.334-344
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• 2013

In order to understand the characteristics of oceanic environment in the coastal aquaculture waters of the East Sea, the observation of the CTD (temperature and salinity), dissolved oxygen, chlorophyll a and N/P (DIN ($NO_2$-N, $NO_3$-N, $NH_4$-N) : DIP($PO_4$-P)) ratio was carried out at Sokcho, Jukbyon and Gampo in February, April, June, August, October, December 2013. Based on T(temperature)-S(salinity) diagram analysis, the water masses in the study area were divided into 3 groups; Tsushima Surface Water (TSW: $20-28.3^{\circ}C$ temperatures and 31.04-33.75 salinities), Tsushima Middle Water (TMW: $8.1-16.3^{\circ}C$ and 33.00-34.49), and North Korean Cold Water (NKCW: $1.8-9.4^{\circ}C$ and 33.78-34.42). In winter, DO concentrations in the northern part were higher than those in southern part. In spring and fall, they were low in the surface layer, and increased in summer. Chl-a concentrations < $0.4{\mu}g/L$ dominated in February, April, October and December. Chl-a concentrations were higher in June and August. In particular, the highest Chl-a concentration > $2{\mu}g/L$ was observed in the middle layer of Gampo in August. In February, April, June and December, the N/P ratio in the most of the water masses was less than the Redfield ratio (16), indicating that nitrate did act as a limiting factor in phytoplankton growth. On the contrary, in August and October, the N/P ratio in surface and sub-surface layer was greater than the Redfield ratio, suggesting that phosphate was a limiting factor.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.4
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• pp.255-265
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• 1999

CTD castings and current observations are taken in June, July and October, 1997 and May and July, 1998 to investigate the effect of the Keum River dyke on the structure of physical properties and the type of the Keum River estuary. Tide and tidal current relation shows that the ebbing is longer than the flooding by 1.5 hours with the early current reversing before high tide. In the rainy season (May to July), frequent large fresh water discharge during the ebbing from the dyke changes vertical salinity difference and time variation of salinity greatly near the head of the estuary, where salinity becomes lower than 2‰ in summer fresh water flooding. Halocline developed by the fresh water discharge makes two-layer structure, of which strength and depth increase in the low tide. The relationship between tide phase and surface salinity variation shows the phase lag of 2.5 hours near the head of the estuary but the standing wave relation down the estuary. This phase lag implies that a low salinity water diluted by the fresh water discharge for 2-3 hours in the ebb period moves with tidal excursion. In the dry season, vertical salinity difference reduces significantly. We calculate stratification and circulation parameters using the observed salinity structure, surface current and fresh water discharge. The Keum River estuary shows a partially mixed type, changing the stratification parameter from the rainy to the dry season. Mean flows of observed tidal current at lower and upper layer are landward and seaward, which are consistent with the circulation of a partially mixed estuary. Based upon the estuary type and circulation we suggest that the suspended materials will move toward the upstream due to low-layer mean flow and then the Keum River estuary will be a deposit environment.

• The Journal of Engineering Geology
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• v.25 no.2
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• pp.215-225
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• 2015

We performed injection tests in a deep-seated confined aquifer to assess the potential of artificial recharge as a means of preventing saltwater contamination, thereby securing groundwater resources for the Nakdong Delta area of Busan City, Korea. The study area comprises a confined aquifer, in which a 10-21-m-thick clay layer overlies 31.5-36.5 m of sand and a 2.8-11-m-thick layer of gravel. EC logging of five monitoring wells yielded a value of 7-44 mS/cm, with the transition between saline and fresh water occurring at a depth of 15-38 m. Above 5 m depth, water temperature is 10-15.5℃, whereas between 5 and 50 m depth the temperature is 15.5-17℃. Approximately 950 m³ of fresh water was injected into the OW-5 injection well at a rate of 370 m³/day for 62 hours, after which the fresh water zone was detected by a CTD Diver installed at a depth of 40 m. The persistence of the fresh water zone was determined via EC and temperature logging at 24 hours after injection, and again 21 days after injection. We observed a second fresh water zone in the OW-2 well, where the first injection test was performed more than 20 days before the second injection test. The contact between fresh and saline water in the injection well is represented by a sharp boundary rather than a transitional boundary. We conclude that the injected fresh water occupied a specific space and served to maintain the original water quality throughout the observation period. Moreover, we suggest that artificial recharge via long-term injection could help secure a new alternative water resource in this saline coastal aquifer.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.3
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• pp.143-156
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• 2015

In order to understand the dynamic characteristics of water column environments in the Western Pacific seamount area (approximately $150.2^{\circ}E$, $20^{\circ}N$), we investigated the water mass and the behavior of water column parameters such as dissolved oxygen, inorganic nutrients (N, P), and chlorophyll-a. Physico-chemical properties of water column were obtained by CTD system at the nine stations which were selected along the east-west and south-north direction around the seamount (OSM14-2) in October 2014. From the temperature-salinity diagram, the main water masses were separated into North Pacific Tropical Water and Thermocline Water in the surface layer, North Pacific Intermediate Water in the intermediate layer, and North Pacific Deep Water in the bottom layer, respectively. Oxygen minimum zone (OMZ, mean $O_2$ $73.26{\mu}M$), known as dysoxic condition ($O_2<90{\mu}M$), was distributed in the depth range of 700~1,200 m throughout the study area. Inorganic nutrients typified by nitrite + nitrate and phosphate showed the lowest concentration in the surface mixed layer and then gradually increased downward with representing the maximum concentration in the OMZ, with lower N:P ratio (13.7), indicating that the nitrogen is regarded as limiting factor for primary production. Vertical distribution of water column parameters along the east-west and south-north station line around the seamount showed the effect of bottom water inflowing at around 500 m deep in the western and southern region, and concentrations of water column parameters in the bottom layer (below 2,500 m deep) of the western and southern region were differently distributed comparing to those of the other side regions (eastern and northern). The value of Excess N calculated from Redfield ratio (N:P=16:1) represented the negative value throughout the study area, which indicated the nitrogen sink dominant environments, and relative higher value of Excess N observed in the bottom layer of western and southern region. These observations suggest that the topographic features of a seamount influence the circulation of bottom current and its effects play a significant role in determining the behavior of water column environmental parameters.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.29 no.1
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• pp.56-76
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• 2024

We for the first time made a successful longest continuous sectional observation in the East Sea by an underwater glider during 95 days from September 18 to December 21 2020 in the Korea along the 106 Line (129.1 °E ~ 131.5 °E at 37.9 °N) of the regular shipboard measurements by the National Institute of Fishery Science (NIFS) and obtained twelve hydrographic sections with high spatiotemporal resolution. The glider was deployed at 129.1 °E in September 18 and conducted 88-days flight from September 19 to December 15 2020, yielding twelve hydrographic sections, and then recovered at 129.2 °E in December 21 after the last 6 days virtual mooring operation. During the total traveled distance of 2550 km, the estimated deviation from the predetermined zonal path had an average RMS distance of 262 m. Based on these high-resolution long-term glider measurements, we conducted a comparative study with the bi-monthly NIFS measurements in terms of spatial and temporal resolutions, and found distinguished features. One is that spatial features of sub-mesoscale such as sub-mesoscale frontal structure and intensified thermocline were detected only in the glider measurements, mainly due to glider's high spatial resolution. The other is the detection of intramonthly variations from the weekly time series of temperature and salinity, which were extracted from glider's continuous sections. Lastly, there were deviations and bias in measurements from both platforms. We argued these deviations in terms of the time scale of variation, the spatial scale of fixed-point observation, and the calibration status of CTD devices of both platforms.