• Geomechanics and Engineering
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• 제10권2호
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• pp.137-154
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• 2016

The purpose of this paper is to study the propagation of Rayleigh waves in an anisotropic heterogeneous crustal layer over a gravitational semi-infinite sandy substratum. It is assumed that the heterogeneity in the crustal layer arises due to exponential variation in elastic coefficients and density whereas the semi-infinite sandy substratum has homogeneous sandiness parameters. The coupled effects of heterogeneity, anisotropy, sandiness parameters and gravity on Rayleigh waves are discussed analytically as well as numerically. The dispersion relation is obtained in determinant form. The proposed model is solved to obtain the different dispersion relations for the Rayleigh wave in the elastic medium of different properties. The results presented in this study may be attractive and useful for mathematicians, seismologists and geologists.

• ALGAE
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• 제21권3호
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• pp.305-310
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• 2006

Succession of artificial seaweed communities in an artificial iron reef at Ikata, southern Japan was studied based on monthly or bimonthly observations from February 1999 to August 2000. Communities were associated with different substrata (40 cm x 60 cm: steel, concrete, wood and stone) as the cover on artificial iron reefs (4.5 m x 4.1 m x 2.5 m, 45.38 m3 and 3.2 ton), which were placed on a sandy substratum at 8 m depth. Within one month diatoms dominated on all substrata with cover of approximately 100%. Enteromorpha intestinalis and Colpomenia sinuosa dominated on the reef within three months after the placement in the spring. Seaweed communities on the reef decreased during the summer. In the winter, the seaweeds on the reef recovered. Sargassum spp., Ecklonia kurome and Padina arborescens dominated on each substratum after one year. Seaweed communities on the artificial reef were similar to those on the rocky substratum around the artificial reef and also similar on different substrata covering the iron artificial reef. These results indicate that seaweed succession was impacted by season and the recruitment of spores and propagules from mature algae around the artificial reefs.

• Structural Engineering and Mechanics
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• 제68권4호
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• pp.443-457
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• 2018

In this article, a comparative study has been made to investigate the scattering behaviour of three layered structure model on torsional surface wave. For such model intermediate layer is taken as fiber reinforced composite, resting over a dry sandy Gibson substratum and underlying by different anelastic media. We consider two distinct mediums for topmost layer. In the first case, topmost layer has been taken as fluid saturated homogeneous porous layer, while in the second case the fluid saturated porous layer has been replaced by a transversely isotropic layer. Simple form expression for the secular equation of torsional surface wave has been worked out in both the cases by executing specific boundary conditions, which comprises Whittaker's function and its derivative, for imminent result that have been elaborated asymptotically. Some special cases have been constituted which are in excellent compliance with recorded literatures. For the sake of comparative study, numerical estimation and graphical illustration have been accomplished to identify the effects of the width ratio of the layers, Biot's gravity parameter, sandy parameter, porosity parameter and other heterogeneity parameters corresponding to the layers and half spaces, horizontal compressive and tensile initial stress on the phase velocity of torsional surface wave.

• Fisheries and Aquatic Sciences
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• 제5권4호
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• pp.281-286
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• 2002

Artificial reefs were set on a sandy bottom substratum at 8m, 10m and 13m depths along the coast in Muronohana, Ikata, Japan. Succession of seaweed communities was observed monthly or bimonthly from February 1999 to August 2000 on artificial reefs. Within one month, the diatom colonized on the reefs with coverage of $100\%$. After three months, Enteromorpha intestinalis and Colpomenia sinuosa dominated on the reef in the spring. Seaweed flora decreased during the summer and the dominant species were several species of Melobesioidea. In the winter, the seaweeds grew up again and the dominant species on the each reef were Sargassum spp., Ecklonia kurome and Padina arborescens after one year. The dominant species in the algal succession process changed from diatoms to the perennial seaweeds such as Sargassum spp., E. kurome and P. arborescens. Thus, the pattern of succession of the dominant species and the degree of domination were changed by the season, water depth and the recruitment of spores and eggs from the mature alga around the reefs.

• Fisheries and Aquatic Sciences
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• 제3권1호
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• pp.1-7
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• 2000

Different substrata fixed as the roof (for shadow) on artificial iron reef had been developed as a tool for valuable fishery resources. The experiment was set up on a sandy bottom substratum at 8m depth in Muronohana, Ikata, Japan. Within one month of placement of the plates, diatoms dominated the experimental plates with a coverage of $100\%$ approximately. Enteromorpha intestinalis and Colpomenia sinuosa dominated within three months after the placement. E. intestinalis coverage on substrata was estimated $7\%$ on the plate shaped iron bar, $12-14\%$ on concrete plates, $18\%$ on the plate fixed pebble, $61\%$ on the plate to accumulated wood, and 80-100% on the steel materials plate. Whereas after four months of placement, C. sinuosa coverage on plates became $1-36\%$ on different plates, and $100\%$ on the plate to accumulated wood. The differences in E. intestinalis and C. sinuosa colonization on the different substrata were probably due to variations in their surface roughness influencing the settlement of zoospores, and thus gametophyte. development. After five months of placement, the above two species slowly disappeared.

• 한국어류학회지
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• 제28권4호
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• pp.239-248
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• 2016

한국고유종 동방종개 Iksookimia yongdokensis의 생태적 특성을 밝히기 위해 2015년 3월부터 2016년 2월까지 경상북도 영덕군 축산군의 축산천에서 서식지와 연령, 산란기 특성 등을 조사하였다. 연령별로 서식지를 분석한 결과 당년생(0+)과 1~4년생은 구별되었는데, 당년생은 유속이 느리고 ($2.4{\pm}2.09\;cm/sec$) 수심이 낮으며 ($29.2{\pm}7.57\;cm$) 모래 바닥 (하상 크기 $0.6{\pm}1.44\;cm$)에 주로 서식하였지만, 1~4년생은 유속이 비교적 빠르고 (3.8~4.6 cm/sec) 수심은 깊은 (50~70 cm) 자갈과 돌 바닥(하상크기 5.5~6.1 cm)에 주로 서식하여 차이를 보였다. 전장빈도분포도로 연령(암컷)을 추정한 결과, 산란기인 6월에 35~64 mm는 만 1년생, 65~94 mm는 만 2년생, 95~119 mm는 만 3년생, 120~145 mm은 만 4년생 이상으로 추정되었다. 생후 13개월 후에 수컷 가슴지느러미 기조에 골질반(lamina circularis)이 형성되어 암 수가 구별되었고, 성비(♂/♀)는 0.69였으며, 암컷이 수컷보다 10~30 mm가 더 컸다. 산란기는 생식소성숙도 (GSI)로 추정한 결과 6~7월 (수온 $20{\sim}25^{\circ}C$)이었고, 포란수는 $2,292{\pm}618$개, 성숙난 크기는 $1.46{\pm}0.02\;mm$였다.

• 생태와환경
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• 제45권4호
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• pp.356-367
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• 2012

본 연구는 금강 지류인 충남 청양군 지천의 어류군집 및 멸종위기종 미호종개와 흰수마자의 서식현황을 파악하기 위하여 2011년 조사를 실시하였다. 지천 상류(St. 1~St. 4)는 하천형이 Aa-Bb형 또는 Bb형이고 하상구조는 자갈과 돌의 비율이 높았으며 10~23종의 어류가 서식하였고, 중류(St. 5~St. 7)는 하천형이 Bb형이고 하상구조는 돌과 큰돌의 비율이 높았으며 16~23종의 어류가 서식하였으며, 하류(St. 8~St. 10)는 하천형이 Bb-Bc형이고 하상구조는 모래의 비율이 높았으며 20~29종의 어류가 서식하였다. 전체 출현한 어종은 모두 9과 44종이었고, 우점종은 피라미 Zacco platypus (37.2%), 아우점종은 돌고기 Pungtungia herzi (5.8%)와 모래무지 Pseudogobio esocinus (5.5%)였으며, 그 다음으로 납자루 Acheilognathus lanceolatus (5.3%)와 참갈겨니 Z. koreanus (5.2%), 참마자 Hemibarbus longirostris (4.9%), 긴몰개 Squalidus gracilis majimae (3.5%) 등의 순으로 우세하게 출현하였다. 출현종 중 고유종은 16종(36.4%)으로 비교적 높게 나타났고, 멸종위기종은 미호종개와 흰수마자 2종이, 외래어종은 배스 Micropterus salmoides 1종이 출현하였다. 지점들 간의 군집유사도를 분석한 결과 상류(St. 1~St. 4)와 중류(St. 5~St. 7), 하류(St. 8~St. 10)로 나누어지고, 우점도는 하류로 갈수록 대체로 낮아지는 반면, 다양도와 균등도, 종풍부도 하류로 갈수록 대체로 높아지는 경향을 보였다. 하류에서 출현한 멸종위기종 미호종개와 흰수마자의 서식현황을 정밀조사한 결과, 두 종 모두 하상이 모래인 곳에 집단을 형성하여 서식하고 있어 주목되었다.