• Progress in Medical Physics
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• v.22 no.2
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• pp.85-91
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• 2011

The energy spectra for electron beam of medical linear accelerator were calculated using a GEANT4 Medical Linac 2 example code. The incident electron mean energy were 6, 9, 12, 16, 20 MeV. This code was designed to calculate electron beam energy spectra according to material, thickness and location of electron scattering foil affecting electron beam characteristic. Lead, Copper, Aluminum and Gold were used for scattering foil. The energy distribution for electron and photon were analyzed by changing position of scattering foil in the head of linear accelerator. The effect of electron scattering foil on energy spectra which is basic data of simulation for medical linear accelerator were presented. The calculated results would be used in design of medical accelerator head.

• The Korean Journal of Malacology
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• v.23 no.2
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• pp.199-208
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• 2007

The gonad index, gonadosomatic index, the condition index, reproductive cycle, first sexual maturity, and sex ratio of the hard shelled mussel, Mytilus coruscus were investigated by using histological analysis and morphometric data. Specimens were collected monthly in Kyeokpo, western Korea from January to December, 2006. The gonad index reached a maximum in February, and minimum in September. Both the monthly variations of the gonad index (GI) and the gonadosomatic index (GSI) reached a maximum in February. After that, their values continually decreased between March and April because of spawning. The monthly variation of the condition index coincides with the GI and the GSI. The spawning period was from February to April, with the main spawning occurring between February and March. The reproductive cycle of this species could be classified into six stages: early active stage (November to January), late active stage (November to February), ripe stage (December to April), partially spawned stage (February to April), degenerative stage (April to October), and resting stage (June to December ). Percentages of sexual maturity was over 50% for the female and male hard shelled mussels that ranges from 40.1 to 50.0 mm in shell length. The percentage was 100% for those that are over 50.1 mm. The sex ratios of females to males over 40.1 mm in shell length were not significantly different from a 1:1 sex ratio $(x^2\;=\;0.63,\;p\;>\;0.05)$. No evidence of hermaphroditism was found in histological sections of any hard shelled mussel examined.

• Journal of Aquaculture
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• v.16 no.4
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• pp.245-251
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• 2003

Sexual maturation and gametogenic cycle of the hard shelled mussel, Mytilus coruscus were investigated by means of histological method. Specimens were collected monthly in Hansan Bay of south coast, Korea from January to December 2002. Sex of the clam was dioecious. The gonads are composed of a number of gametogenic follicles. The gonad index (GI) was reached the maximum in February (3.40), and the minimum in August (1.18). The monthly variation of condition index (CI) coincides with gonad index. The main spawning occurs between February and March. The gametogenic cycle of the clam could be divided into six stages: resting (August to November), multiplicative (November to December), growing (December to January), maturation (January to February), partially spent (February to April) and completely spent/degenerative stage (April to July). Sex ratio (♀/♂) was 1:0.96.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.2
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• pp.195-205
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• 2020

Oceanic conditions in walleye pollock habitat in the East Sea have shown decadal fluctuations between warm and cold periods in turn. Specifically, sea surface temperature (SST) has shown a dramatic increase between the late 1980s and the middle 2000s, and abrupt decreasing patterns after the late 2000s. Oceanic conditions in the Dong-han Bay (spawning ground) and middle eastern coastal waters (fishing ground), however, indicated different fluctuation trends in SST, increasing in the Dong-han Bay after the late 1980s, and decreasing after the late 2000s. These fluctuation patterns were especially clear in February and March. Sea surface temperature in the middle eastern coastal waters of Korea soared continuously after the late 1980s, but did not show a distinct decreasing pattern after the late 2000s compared with Dong han Bay, except for February SST values. These long term water temperature changes in both walleye pollock spawning and fishing ground are related to variation in walleye pollock landings. Especially, abrupt changes in spawning ground SST can be one of the factors influencing survival in the early ontogenesis of walleye pollock, including egg and yolk larval stages. During the 1980s, the area of suitable spawning temperature (2-5℃) was wider, and the length of Walleye pollock egg and larval stages greater compared with past and present oceanographic environments. However, such patterns did not correspond with the optimal spawning temperature range and greater length of development of walleye pollock during the late 1980s likely triggering a decline in pollock stock. In conclusion, it has been supposed that the dramatic decrease in walleye pollock landings in the East Sea since the late 1980s was caused by increasing water temperature leading to both early mortality and unsuitable spawning conditions.

• Development and Reproduction
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• v.11 no.1
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• pp.43-47
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• 2007

Smad proteins mediate transforming growth $factor(TGF)-{\beta}$ signaling and play a pivotal role in embryonic development. The estrogen receptor-related receptors(ERRs), which are structurally similar to estrogen receptors, are members of orphan nuclear receptor in the nuclear receptor superfamily and their functions are known to be involved in the formation of extra-embryonic ectoderm. To investigate the involvement of Smad3 and $ERR{\beta}$ like 1 in reproductive activities and embryogenesis in marine invertebrate, we examined gene expression of Smad3 and $ERR{\beta}$ like 1 in Strongylocentrotus nudus during their seasonal changes and embryonic development using real-time polymerase chain reaction. The Smad3 mRNA levels in gonad showed an increasing pattern from February to June 2004 but decreased at August(spawning season) followed by an elevation of the levels at October and December 2004. The mRNA levels of the $ERR{\beta}$ like 1 significantly elevated during the spawning season. During embryonic development, Smad3 mRNA levels at $8{\sim}16$ cell stages were significantly higher than those of other stages, whereas the mRNA of the $ERR{\beta}$ like 1 was significantly high levels at late development stages, i.e., blastular, gastrula and plutei stages. These results suggest that the Smad3 could be involved at least in part in the early cleavage stages and the $ERR{\beta}$ like 1 may play an important role in the spawning season and late developmental stage in the sea urchin.

• Korean Journal of Ichthyology
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• v.10 no.2
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• pp.176-183
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• 1998

Spawning ecology and feeding habits of Maurolicus muelleri in the Korean waters were studied. M. muelleri spawned continuously throughout the year showing a peak in August. Major spawning ground of this species was the southeastern sea of Korea. The fecundity observed from the ovaries of M. muelleri showed a range of 5,072 to 32,117, and the average number of eggs per one spawning time was approximately 250. M. muelleri was a zooplanktivore which fed mainly on copepods. Its diets also included various crustaceans such as amphipods, euphausiids, shrimps and mysids.

• KOREAN POULTRY JOURNAL
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• v.36 no.7 s.417
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• pp.70-74
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• 2004

최근 육종개량의 발전과 성과로 인하여 대형화되었지만 고밀도 사육에 의해서 하절기 열사병과 심한 더위로 인한 생산성 저하가 큰 문제로 혹서기에 대두되고 있어 그 대응책을 반드시 세워야 할 것이다. 하절기 온도관리 대책으로서는 계사내의 공기유통을 좋게 하는 것이 가장 기본이므로 충분한 환기에 의해 닭의 체감온도를 낮추어 주게 되는 것이다. 그러나 우리나라와 같이 여름철의 기후 특성이 고온다습한 경우는 습도가 높아지게 되면 체감온도는 낮아지지 않는다. 그러므로 계사내의 습도를 저하시키기 위해서 환기휀 등을 이용해 깔짚과 계분을 건조시키는 것도 한가지방법이다. 일반적으로 열사병 대책으로 실시하고 있는 방법으로서는 입기구에 물 분무, 지붕에 물 분무, 계사내의 미세한 분무냉각 등 물을 이용하는 방법이나, 환풍기의 설치, 닥트송풍을 이용한 방법, 거칠고 얇은 그물에 의한 차광 등의 방법으로 온도를 낮게 할 수가 있다. 특히 산란계의 경우 여러 연구보고 자료에 의하면 산란계를 고온 환경에서 사육할 경우 난각질이 저하된다고 하는 보고가 많이 있다. 1일 중에 환경온도를 주기적으로 변화시킨 경우는 일정하게만 유지해 주는 환경온도에 비해서 난각질과 난각강도는 낮아지게 된다. 또한 산란계에 있어서 간헐점등에 대해서는 에너지 수준을 줄이는 기술, 또는 사료절감을 유도하는 방법은 계속 연구되고 있다. 따라서 다음은 하절기 산란$\cdot$육계사의 적온유지를 위한 온도관리 사례에 대하여 이야기하고자 한다.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2000.05a
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• pp.84-85
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• 2000

1996년도 우리나라 굴 총생산량은 약 20만여톤으로 일반 패류 생산량의 절반 이상을 차지하고 있으며, 대부분이 양식에 의존하고 있다(Korean Fisheries Associati 1997). 양식산 굴은 대략 11월부터 출하하기 시작하여 3월까지는 주로 생식용으로 내수 또는 수출되고 있고, 산란기로 접어드는 4월부터 6월까지는 통조림용으로 대부분이 이용되고 있다. 굴 통조림의 제조를 위한 원료 굴은 뻘 등의 제거를 위한 수세, 레토르트에서 자숙 및 탈각한 후 탈각 이물질, 껍질 조각 등을 제거하기 위하여 탈각굴에 대하여 수세 및 탈수와 같은 전처리 공정을 반드시 거친다. (중략)

• Korean Journal of Environment and Ecology
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• v.35 no.2
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• pp.115-125
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• 2021

This study surveyed the population ecology of Acheilognathus chankaensis (Pisces: Acheilognathinae) in the vicinity of the Churyeongcheon (Stream) and Seomjingang (River) in Jeonbuk, Korea, from February 2006 to May 2007. The survey found the habits mainly in the slow-flowing waters having sand, mud, and gravel bottoms. Age groups estimated by the standard length-frequency distribution of the population indicated that the one-year-olds were 30-46 mm long, the two-year-olds were 47-58 mm long, the three-year-olds were 59-68 mm long, and the four-year-olds were longer than 69 mm. The gonadosomatic index (GSI) and the ratio of ovipositor length/standard length were the highest in March (♀: 12.9%, ♂: 5.0%) and in April (46.3%), respectively. The ratio of mature egg diameters that were 1.6 mm was highest in May (13.2%). The comprehensive analysis of spawning characteristics showed that the spawning season was from March to June with water temperatures in 11.5-22.5℃, and the sex ratio of female:male was 1:1.13. The fecundity in the ovaries and the number of mature eggs were 318±174.5 (50~583) and 220±139.2 (50~406), respectively. The size of the mature eggs was 2.04±0.110 mm on the long axis and 1.55±0.100 mm on the short axis for the study period. Gut contents of A. chankaensis were mainly phytoplankton such as the genera Fragilaria, Synedra, Navicular, Cymbella (Bacillariophyceae), and Cosmarium (Chlorophyceae).

• Korean Journal of Ichthyology
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• v.23 no.2
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• pp.111-118
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• 2011

The maturation and spawning of filefish, Stephanolepis cirrhifer were investigated using samples randomly collected in the East Sea of Korea from August 2009 to July 2010. The total length at 50% group maturity of filefish was estimated to be 11.7 cm. Based on monthly changes in maturity stages and gonadosomatic index (GSI), the spawning period was estimated to be from June to September, and the peak spawning from August to September. The fecundity (F) ranged from 693,981 eggs to 7,383,429 eggs at 23.6 cm between minimum and maximum total length (TL) 13.3 cm and 23.6 cm respectively. The relationship between TL and F was expressed as F=$12.19TL^{4.208}$ ($R^2$=0.727). The sex ratio of male to female was 1 to 0.9.