• Development and Reproduction
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• v.9 no.2
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• pp.95-103
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• 2005

Reproductive cycle, gonadosomatic index(GSI), egg diameter composition, first sexual maturity, sexually matured length(50% of first sexual maturity), and sex ratio of Amusium japonicum japonicum, were investigated by histological observations and morphometric data. Samples were collected monthly from the subtidal zone of Sogwipo, Jejudo, Korea, for two years. The sun and moon scallop Amusium japonicum japonicum is dioecious. Monthly variation in the GSI showed similar patterns with the reproductive cycle. Ripe oocytes were about $70{\sim}90\;{\mu}m$ in diameter and had thick egg membranes. The spawning period was from November to January, and the main spawning occurred between November and December when the seawater temperature was relatively low. From monthly changes in egg diameter composition, the spawning period was once a year, although the number of spawning frequencies is assumed to occur more than twice during the spawning season. The reproductive cycle of this species could be divided into five successive stages: early active stage(April to June), late active stage(June to September), ripe stage(October to November), spawning stage(November to January), and spent/resting stage(February to April). First sexual maturities in female and male scallops ranging from 85.1 to 90.0mm in shell length were over 50% and they were 100% for scallops over 90.0mm in shell length. In this population, sexually matured shell lengths(50% of rate of group maturity) in females and males were 86.96 and 86.59mm, respectively. The female to male sex ratio among individuals over 85.1mm in shell length was not significantly different from 1:1($X^2=0.18$, p>0.05). No evidence of hermaphrodite was found in histological sections of any scallop examined.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.2
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• pp.49-63
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• 1989

Wave drift forces which are small in magnitudes compared to the first order wave exciting forces can cause very large motion of a vessel in waves. In this paper a theoretical and experimental analysis is made of the mean and slowly varying wave dirft forces on the semi-submersible platform. Theoretical calculations are performed by using near field method with three dimensional diffraction theory and model tests are carried out in regular and irregular waves with a 1/60 semi model. Test results are compared with theoretical calculations and the mooring spring effects in the test are discussed.

• 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.

• The Korean Journal of Malacology
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• v.31 no.3
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• pp.171-178
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• 2015

The reproductive ecology of freshwater bivalve, Unio douglasiae in Lake Uiam were examined from March 2014 to February 2015. The gonads distributed in reticular connective tissue, the dioecious clams take an internal fertilization and fertilized eggs are stored in the foster-sack in the gills, then the hatched juveniles are released outside after an ovoviviparous process. The gonad index (GI) began to increase in April, reached the maximum value in July and to decrease in August. The reproductive cycle of U. douglasiae can be divided into five successive stages: multiplicative stage (November to January), growing stage (February to March), mature stage (February to May), spawning stage (April to September), recovery stage (August to December). The spawning periods were from April to September, and the main spawning occurred between April and July. The shell length at 50% group maturity was estimated to be 29.4 mm.

• Journal of the Korean Vacuum Society
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• v.3 no.2
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• pp.179-185
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• 1994

음극에 DLC 필름이 놓여져 있는 용량결합형의 RF 플라즈마 장치에서 Ar가스에 의한 방전에서 발생된 입자의 분포를 레이져 산란에 의하여 관측하였다. 발생된 입자들은 플라즈마와 sheath의 경계면 에서 높은 밀도의 구름을 이루었으며 시간에 따라 주기적인 분포의 변화가 반복되었다, 입자 구름의 발 생은 플라즈마 물성의 변화를 야기하였으며 그 결과로 심한 self-bias 전위의 감소현상이 관측되었다. 입자 구름분포의 시간에 따른 변화와 같은 주기의 self-bias 플라즈마전위의 진동현상이 가열된 fast-scanning langmuir 탐침에 의하여 관측되었다. 이결과는 입자 표면에로의 음전하 누적에 따른 전체 음전하의 이동도 감소에 의한 것으로 해석된다. 또한 방출 분광법에 의하여 입자오염상태의 Ar 플라즈 마와 정상상태의 Ar 플라즈마의 방출 선세기의 변화를 관측하였는데 입자구름 오염시의 2차전자 차폐 현상에 의해 높은 문턱 에너지를 가진 Ar II 선의 세기 감소현상이 나타났다.

• The Korean Journal of Malacology
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• v.14 no.2
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• pp.91-102
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• 1998

새꼬막은 자웅이체로서 난생이었다. 생식소는 내장낭의 간중장선에서부터 족부까지 외측의 대부분을 싸고 있으며, 난소는 난자형성소낭, 정소는 정자형성소낭으로 구성되어 있었다. 완숙란의 세포질에는 많은 난황과립을 축적하고 있으며, 난막의 외측은 얇은 젤라틴상의 피막으로 싸여 있었다. 정자형성소낭벽에는 정원, 정모, 정세포 및 변태한 정자 순으로, 소낭의 내강을 향하여 충상배열을 하며 성숙 발달되었다. 생식주기는 초기 활성기(11-5월), 후기 활성기(5-7월), 완숙기(6-9월), 부분 방출기(7-9월), 방출 및 비활성기(9-4월)로 구분할 수 있었다. 방란, 방정은 수온이 21$^{\circ}C$ 이상으로 상승하는 7월초순부터 9월까지 지속되며, 산란 최성기는 8월이었다. 비만도지수의 월별 변화는 생식주기와 아주 밀접ㅎ나 관계가 있었다. 난자형성소낭과 정자형성소낭에는 eosin에 강하게 염색되는 과립세포와 간충직들이 나타나는데, 이들은 생식소 및 생식세포형성과 발달에 영양을 공급하는 영양세포로 생각되었다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1996.06a
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• pp.33-36
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• 1996

해양에서 내부파 (internal wave)는 수직적으로 밀도가 크게 다른 두 층의 경계면에서 생성되는데, 일반적으로 경계면은 수온약층 (thermocline)에 해당된다. 본 연구에서는 간단한 단주기(하나의 주기만을 갖는)내부파를 가정하고 이 내부파에 의해서 야기될 수 있는 저주파 (100-400 HZ) 전파손실의 변동 정도를 모델링을 통해 추정하였다. 내부파의 파장은 1Km이고 진폭은 25m이며 수심 50-100m 사이에 존재하는 것으로 가정하였다. 전파손실 계산은 PE (parabolic equation) 기법을 도입한 모델을 이용하였다.수층의 두께는 2000m로 균일하고 퇴적층 및 기반암층의 두께는 각각 500m로 가정하였다. 모델링 결과 단주기 내부파의 1 파장이 진행하는 동안 고정된 수신 깊이별로 20km 거리에서 10 dB 이상의 큰 변동이 야기 될 수 있음을 확인하였다. 이는 내부파 내에서 큰 굴절을 변화로 인한 음파의 산란 때문으로 볼 수 있다. 실제 해양에서는 내부파가 단주기 파동 형태로 나타나기 보다는 여러 주기의 파동이 중첩되어 나타나므로 정확한 내부파 영향을 추정하기 위해서는 보다 실제에 가까운 내부파를 모델링할 필요가 있다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.6
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• pp.629-635
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• 1997

The theory of characteristic modes for coaxial waveguide with periodic axial slots is used to derive the weighted eigenvalue equation for calculating the characteristic values and the characteristic currents. Once the characteristic values and the characteristic currents are obtained, the important quantities such as the equivalent magnetic current, radiation patterns, and RCS are determined. Numerical results of the equivalent magnetic currents, radiation patterns, and RCS are compared with those obtained by use of the method of moments. A fairly good correspondence is observed between them.

• Journal of the Korean Vacuum Society
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• v.1 no.3
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• pp.395-399
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• 1992

In0.5Al0.5As와 같은 조성을 갖는 합금인 n=1~4인 (InAs)n(AlAs)n 형태의 완벽한 층 상구조의 단주기 초격자를 MBE 방법으로 성장하였다. 저온 PL 측정을 통하여 광학적 특성 을 조사하였으며, Raman 산란실험을 통하여 구조적 특성을 조사하였다. X선화질 실험을 통하여 홀수 번호의 회적을 관측할 수 있었는데 이것은 초격자에 의한 새로운 주기의 형성 을 직접적으로 보여 주는 것이다.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.211-214
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• 1999

Periodical surfaces with the sawtooth profile are studied on their backscattering by the TE plane wave incident. The backscattering is calculated by the mode-matching method. The surfaces are perfect conductor and are covered with dielectric materials to make a flat surface. It is observed that a cover filled with multiple dielectric layers can be used to reduce the backscattering at an arbitrary incident angle.