• Fisheries and Aquatic Sciences
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• 제24권7호
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• pp.243-259
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• 2021

The spatial and temporal behaviors and fluctuations of the cold water that appeared in the South East Sea and the East Sea coast from 2016 to 2017 were investigated. The water temperature drop was large in the east coast from April to June and the southeast coast from July to September, and the temperature drop period was longer in the southeast coast. The water temperature fluctuated sensitively to the wind direction, and it gradually decreased in the southwest wind but rose as if jumping in the northeast wind. Wind stress and surface water temperature had an inverse correlation, which was larger in Bukhang-Idukseo, and decreased toward the north of Guryongpo. The cold water appeared mainly in Geojedo-Pohang after 1 to 2 days when the southwest wind was strong, but when the wind became weak, it shrank to the Idukseo (Ulgi-Gampo) and extended into the open sea in a tongue shape. Cold water was distributed only in Samcheok-Toseong in mid-May, Idukseo-Guryongpo and Hupo-Jukbyeon-Samcheok from late May to mid-July, and Bukhang-Idukseo in August-September. The intensity of cold water was greatest in mid-August, and the center of cold water descended from the east coast to the southeast coast from spring to summer. The water temperature fluctuation was dominant at the periods of 1 d and 7-21 d. In wavelet spectrum analysis of water temperature and wind, wind speed increase-water temperature decrease showed phase difference of 12 h in 2 d, 18 h in 3 d, 1.5 d in 4-8 d, and 2-3 d in 8-24 d period. The correlation between the two parameters was large in Geojedo and Namhang, Bukhang-Idukseo, Guryongpo-Jukbyeon, and Samcheok-Toseong. Monitoring stations with high correlation in all periods were generally parallel to the monsoon direction.

• 한국환경보건학회지
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• 제23권2호
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• pp.89-97
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• 1997

Most of urban streams in Korea have been changed channel forms and suffered from direct inflow of domestic sewage, etc. Therefore, maintenance of structure and function of those ecosystem are hard. The present study was carried out to examine the life survival maintenance ability of the stream by community analysis of aquatic animals in typical urban stream (Jungrang stream) in Seoul. The aquatic animals were composed of 31 species, 18 families, 8 orders, 5 classes in 4 phyla. Seasonal species number showed big fluctuation between 8 species in Winter and 24 species in Autumn. Major dominant species in Jungrang stream were Tubificidae sp.1, Chironomidae sp.1, Chironomidae sp.2 and Physa acuta, and above endurance species for water pollution occupied very high dominance indices. But, Cercion hieroglyphicum, Ischnura asiatica, Rantra chinensis, Herochares striatus, Agabus japonicus in benthic macroinvertebrates of a few individuals are appeared. Also, fry of Carassius auratus and Silurus asotus in fish are occurred. Therefore, we can be inferred on posibility of growth and spawning of above species in the stream. Jungrang stream has a small quantity of natural riffle areas, ponds and watergrass areas by channel form of water course. Aquatic animals in Jungrang stream has been suffered by reduction of self-purification reaction ability and have mass production of attached algae on the stream bed. For analysis of fluctuation of life survival maintenance ability in Jungrang stream, long-term survey is needed.

• The Korean Journal of Ecology
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• 제16권2호
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• pp.209-227
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• 1993

Aquatic insects were collected from 18 sites in the Yongsan River System from August, 1988 to July, 1989. The monthly fluctuation and distributional pattern of the aquatic insects along the environmental factors were investigated. Quantitatively collected aquatic insects were identified, and numbers, standing biomass, dominance indices and diversity indices in each site and month were determined. The aquatic insect faun of the Yongsan River System was composed of 146 species, 82 genera, 38 families in 7 orders including 44 species of mayflies, 32 species of caddisflies, 24 species of stoneflies, 21 species of flies, 16 species of beetles, 6 species of dragonflies and 3 species of dobsonflies. Seasonal occurrence of species were more diversified in winter and spring than in summer. Also, the number of individuals occurred was higher in winter and spring than in summer while it was the highest in upper stream and the lowest in Kwang-ju stream. Component ratio of the number of individuals according to the insect orders was as follows: Mayflies 38.71%, Flies 36.97%, Stoneflies 10.21%, Caddisflies 6.80%, Beetles 2.96%, Dobbsonflies 2.74%, Dragonflies 0.95%. Percentage of standing biomass according to insect orders were as follows: Mayfiles 32.81%, Stoneflies 26.51%, Caddisflies 17.58%, Dobbsonflies 14.84%, Flies 3.74%, Beetles 3.08%, Dragonflies 1.45%, The highest standing biomass occurred in spring and the lowest in summer.

• 수산해양기술연구
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• 제56권1호
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• pp.18-25
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• 2020

Monthly fluctuation in abundance and species composition of fish in coastal waters off Oenaro island, Goheung were investigated using seasonal samples collected by a shrimp beam trawl in 2018. A total of 5,981 fishes were sampled and classified into 48 species, 32 families, and 9 orders. The dominant species was Engraulis japonicus (993 individuals, 16.60%), Amblychaeturichthys hexanema (844 individuals, 14.11%), and Thryssa kammalensis (674 individuals, 11.27%). The highest number of individuals was found in August (958 individuals), while the lowest number of individuals was found in January (136 individuals). The diversity index was the highest in November (H' = 2.37) and the lowest in January (H' = 1.77).

• Ocean and Polar Research
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• 제32권1호
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• pp.41-52
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• 2010

Daily samples were collected during summer in order to analyse changes in the mesozooplankton community and to identify the major environmental factors that may influence mesozooplankton abundance in Jangmok Bay. A single site in the bay was sampled 47 times from July to September 2003. Mesozooplankton community, hydrographic (watertemperature, salinity, dissolvedoxygen) and biological (chlorophyll-a, ciliates densities, Noctiluca scintillans densities) factors were determined. The mesozooplankton abundance varied remarkably from 954 to $14,816\;inds.\;m^{-3}$. The six taxa of Evadne tergestina, barnacle nauplii and cypris, Paracalanus parvus s.1., Acartia omorii, Penilia avirostris and Sagitta crassa dominated numerically, contributing 86% of total mesozooplankton abundance. Stepwise multiple linear regression analysis was applied to find correlation between environmental factors and fluctuation in the abundance of dominant species and mesozooplankton. A. omorii was significantly correlated with temperature and N. scintillans densities. E. tergestina was correlated with temperature, salinity, and ciliate densities, whereas P. avirostris was correlated with temperature and dissolved oxygen. Among the environmental factors, mesozooplankton abundance correlated most strongly with N. scintillans densities. Accordingly, N. scintillans may be a key player in controlling the fluctuation of mesozooplankton abundance as a strong competitor for same food resources.

• The Korean Journal of Ecology
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• 제11권1호
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• pp.1-15
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• 1988

Studies on species compostion, promary production of benthic algal assemblage were carried out along a channel of the salt marsh near Inch'on, Kyonggi Bay, Korea. Possible biological, physical and KDICical factors controlling the aglal assemblage were also examined. The oveall diatoms were encountered one hundred and thirty-seven taxa, of which the dominant species were Paralia sulcata and Cymatosira belgica. These two species accounted for 32.6% relative abundance throughout the study period. Diatom taxa had no clear seasonal pattern in abundance analysis. But at the algal blooming period in spring, euglenoids occurred with a high abundance. The chlorophyll a content of benthic algae showed definite seasonal pattern. The algal biomass of the appeared to influence the spatial fluctuation in the algal biomass of the channel was regulated primarily by water content of sediment. Grazing by zoobenthos apperaed to influence the spatial fluctuation in the algal biomass of the sediment surface. The algal photosynthesis was measured in the laboratory with oxygen method. Photo-synthetic rate was independent of the temperature under the lower irradiance. The gross production from March to November was estimated to be 190g C/m2 at the channel slope. Photosynthetic efficiency was 0.37% on the basis of the photosyntherically active radiation for the study period.

• 한국해양바이오학회지
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• 제13권1호
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• pp.58-65
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• 2021

In 2012, fishes caught by three-side fyke net in the coastal waters of Jedo were assessed for species composition and seasonal fluctuation in their abundance. The fish were caught at two research stations (St.) and were found to comprise 53 species, 39 families, and 9 orders. The dominant species were Takifugu niphobles, Lateolabrax maculatus, and Acanthopagrus schlegelii. To gain a measure of their biodiversity, all the species were assessed for their number, richness, diversity, evenness, and dominance. The highest and lowest number of total caught fish individuals was recorded in summer and winter, respectively. The diversity index was the highest in summer and lowest in winter. The evenness index was the highest in summer and lowest in spring. The richness index was highest in summer and lowest in winter. Furthermore, the dominance index was highest in spring and lowest in autumn.

• 한국해양바이오학회지
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• 제12권1호
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• pp.59-65
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• 2020

Fish, caught by bottom trawling in the middle of the Yellow sea (east of Korea), in the spring and summer of 2016 were assessed for species composition and fluctuation in their abundance. The fish were studied at four research stations (St.) and were found to be composed of 46 species, 31 families, and 14 orders. The dominant species caught were Engraulis japonicus, Larimichthys polyactis, Johnius grypotus, Liparis tanakae, and Larimicthys crocea. All the species were assessed for their numbers, richness, diversity, and dominance to gain a measure of the biodiversity. The highest number of individuals was recorded at St. 4 (50,053 individuals), while the lowest number of individuals was recorded at St. 1 (44,090 individuals). The evenness index was the highest at St. 2 (E = 0.65) and lowest at St. 3 (E = 0.62). The diversity index was the highest at St. 4 (H' = 2.31) and lowest at St. 3 (H' = 2.23). Furthermore, the dominance index was the highest at St. 3 (D = 54.9%) and lowest at St. 2 (D = 47.7%).

• Journal of Electrical Engineering and Technology
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• 제10권5호
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• pp.2018-2030
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• 2015

A two stage ac drive configuration consisting of a single-phase line commutated rectifier and a three-phase voltage source inverter (VSI) is very common in low and medium power applications. The deterministic pulse width modulation (PWM) methods like sinusoidal PWM (SPWM) could not be considered as an ideal choice for modern drives since they result mechanical vibration and acoustic noise, and limit the application scope. This is due to the incapability of the deterministic PWM strategies in sprawling the harmonic power. The random PWM (RPWM) approaches could solve this issue by creating continuous harmonic profile instead of discrete clusters of dominant harmonics. Insufficient filtering at dc link results in the amplitude distortion of the input dc voltage to the VSI and has the most significant impact on the spectral errors (difference between theoretical and practical spectra). It is obvious that the sprawling effect of RPWM undoubtedly influenced by input fluctuation and the discrete harmonic clusters may reappear. The influence of dc link fluctuation on harmonics and their spreading effect in the VSI remains invalidated. A case study is done with four different filter capacitor values in this paper and results are compared with the constant dc input operation. This paper also proposes an ingenious RPWM, a ripple dosed sinusoidal reference-random carrier PWM (RDSRRCPWM), which has the innate capacity of suppressing the effect of input fluctuation in the output than the other modern PWM methods. MATLAB based simulation study reveals the fundamental component, total harmonic distortion (THD) and harmonic spread factor (HSF) for various modulation indices. The non-ideal dc link is managed well with the developed RDSRRCPWM applied to the VSI and tested in a proto type VSI using the field programmable gate array (FPGA).

• Progress in Superconductivity
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• 제3권1호
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• pp.23-27
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• 2001

We have investigated the mixed-state magnetoresistance of high quality c-axis-oriented MgB2 thin film for magnetic field from 0.5 T to 5.0 T, applied normal to ab-plane. The temperature dependence of magnetoresistance was well described by vortex glass and fluctuation theories for different temperature regimes. We observed glassy exponent of v(z-1)~3 and upper critical field of $H_{c2}$(0)~35 T, which is consistent with previous data obtained from direct $H_{c2}$(0) measurements. Interestingly, the thermally activated flux flow region was observed to be very narrow, suggesting that the pinning strength of this compound is very strong. This finding is closely related to the recent reports that the bulk pinning is dominant in $MgB_2$and the critical current density of $MgB_2$ thin film is very high, comparable to that of cuprate superconductor. The present results further suggest that $MgB_2$is beneficial to technical applications.ons.