Effects of ocean acidification driven by elevated CO<Subscript>2</Subscript> on larval shell growth and abnormal rates of the venerid clam, <Emphasis Type="Italic">Mactra veneriformis</Emphasis>     

Jee-Hoon Kim  Ok Hwan Yu  Eun Jin Yang  Sung-Ho Kang  Won Kim  Eun Jung Choy 《中国海洋湖沼学报》2016,34(6):1191-1198

The venerid clam (Mactra veneriformis Reeve 1854) is one of the main cultured bivalve species in intertidal and shallow subtidal ecosystems along the west coast of Korea. To understand the effects of ocean acidification on the early life stages of Korean clams, we investigated shell growth and abnormality rates and types in the D-shaped, umbonate veliger, and pediveliger stages of the venerid clam M. veneriformis during exposure to elevated seawater pCO₂. In particular, we examined abnormal types of larval shell morphology categorized as shell deformations, shell distortions, and shell fissures. Specimens were incubated in seawater equilibrated with bubbled CO₂-enriched air at (400±25)×10^-6 (ambient control), (800±25)×10^-6 (high pCO₂), or (1 200±28)×10^-6 (extremely high pCO₂), the atmospheric CO₂ concentrations predicted for the years 2014, 2084, and 2154 (70-year intervals; two human generations), respectively, in the Representative Concentration Pathway (RCP) 8.5 scenario. The mean shell lengths of larvae were significantly decreased in the high and extremely high pCO₂ groups compared with the ambient control groups. Furthermore, under high and extremely high pCO₂ conditions, the cultures exhibited significantly increased abundances of abnormal larvae and increased severity of abnormalities compared with the ambient control. In the umbonate veliger stage of the experimental larvae, the most common abnormalities were shell deformations, distortions, and fissures; on the other hand, convex hinges and mantle protuberances were absent. These results suggest that elevated CO₂ exerts an additional burden on the health of M. veneriformis larvae by impairing early development.  相似文献   

Semi-empirical Model for Estimating the Small-Strain Shear Modulus of Unsaturated Non-plastic Sandy Soils     

Won Taek Oh  Sai K. Vanapalli 《Geotechnical and Geological Engineering》2014,32(2):259-271

The shear modulus at small-strain, G _max is a maximum value of shear modulus for a given stress state and void ratio, and is a key parameter to evaluate the dynamic response of geotechnical structures. However, the laboratory testing procedures for determining G _max are time-consuming, cumbersome and require elaborate equipment especially for unsaturated soil samples. A semi-empirical model is proposed in this paper that can be used to estimate the variation of G _max with respect to matric suction for non-plastic sandy soils (i.e. I _p  = 0 %). The proposed model uses the Soil–Water Characteristic Curve (SWCC) and the shear modulus at saturation condition along with two fitting parameters ζ and ξ. The proposed model permits estimation of the variation of G _max with respect to matric suction over different zones of the SWCC (i.e. boundary effect, transition, and residual zones) for various non-plastic sandy soils. The fitting parameters ζ and ξ required for the proposed semi-empirical model can be estimated from simple relationships derived from the grain size distribution curve.  相似文献   

GNSS integration with vision-based navigation for low GNSS visibility conditions   总被引：1，自引：1，他引：0  

Dae Hee Won  Eunsung Lee  Moonbeom Heo  Sangkyung Sung  Jiyun Lee  Young Jae Lee 《GPS Solutions》2014,18(2):177-187

In urban canyons, buildings and other structures often block the line of sight of visible Global Navigation Satellite System (GNSS) satellites, which makes it difficult to obtain four or more satellites to provide a three-dimensional navigation solution. Previous studies on this operational environment have been conducted based on the assumption that GNSS is not available. However, a limited number of satellites can be used with other sensor measurements, although the number is insufficient to derive a navigation solution. The limited number of GNSS measurements can be integrated with vision-based navigation to correct navigation errors. We propose an integrated navigation system that improves the performance of vision-based navigation by integrating the limited GNSS measurements. An integrated model was designed to apply the GNSS range and range rate to vision-based navigation. The possibility of improved navigation performance was evaluated during an observability analysis based on available satellites. According to the observability analysis, each additional satellite decreased the number of unobservable states by one, while vision-based navigation always has three unobservable states. A computer simulation was conducted to verify the improvement in the navigation performance by analyzing the estimated position, which depended on the number of available satellites; additionally, an experimental test was conducted. The results showed that limited GNSS measurements can improve the positioning performance. Thus, our proposed method is expected to improve the positioning performance in urban canyons.  相似文献   

Comparison Between Shear Behaviors of Overconsolidated Nakdong River Sandy Silt and Silty Sand     

Khin Swe Tint  Seung Rae Lee  Young Su Kim 《Marine Georesources & Geotechnology》2013,31(3):217-229

From this research, overconsolidated undrained and drained behaviors of specimens with high sand content were highly dilatant. According to the comparison results of laboratory tests, the deviator stresses of silty sand were greater than sandy silt due to high sand content under increasing OCRs, and both silty sand and sandy silt were presented strain softening tendency after failure under undrained loading. The pore water pressure increased with increasing fines content under increasing OCRs. Silty sand exhibited more dilatancy and increasing shear strength than sandy silt because pore water pressures of silty sand were lower than sandy silt under higher OCRs. In overconsolidated drained tests, silty sand is higher strength than sandy silt because silty sand has a lower volumetric strain and higher deviator stress than sandy silt under increasing OCRs. As the degree of overconsolidation increased, similar behaviors of silty sand and sandy silt observed that volumetric strain decreased to negative values due to dilatancy effect and low-cohesion under current effective confining pressures.  相似文献   

Marine-Derived Fungi in Korea     

Kwon  Yong Min  Bae  Seung Sub  Choi  Grace  Lim  Ji Yeon  Jung  Yoon-Hee  Chung  Dawoon 《Ocean Science Journal》2021,56(1):1-17

Ocean Science Journal - Studies on marine fungi (termed as ‘marine-derived fungi’ in this paper) have been significantly increasing worldwide because of the critical role displayed by...  相似文献   

Distribution of small plastic debris in cross-section and high strandline on Heungnam beach, South Korea     

Nak Won Heo  Sang Hee Hong  Gi Myung Han  Sunwook Hong  Jongmyoung Lee  Young Kyung Song  Mi Jang  Won Joon Shim 《Ocean Science Journal》2013,48(2):225-233

The spatial distribution of small plastic debris on Heungnam beach in February 2011 was investigated. The abundances of small plastic debris over 2 mm in size along the high strandline and cross-sectional line of the beach were determined. The mean abundances of small plastics were 976 ± 405 particles/m² at the high strandline in the upper tidal zone along the shoreline and 473 ± 866 particles/m² at the cross-section perpendicular to the shoreline. Specifically, styrofoam (expanded polystyrene) spherules accounted for 90.7% of the total plastic abundance in the high strandline and 96.3% in the cross-section. The spatial distribution patterns of small plastic debris differed between the high strandline and cross-sectional line. The cross-sectional distribution of small plastic abundance differed among plastic types, indicating that representative sampling of small plastic debris on a beach is necessary.  相似文献   

Seasonal variations in the low-salinity intermediate water in the region south of sub-polar front of the East Sea (Sea of Japan)     

Chang-Woong Shin  Sang-Kyung Byun  Cheolsoo Kim  Jae Hak Lee  Bong-Chae Kim  Sang-Chull Hwang  Young Ho Seung  Hong-Ryeol Shin 《Ocean Science Journal》2013,48(1):35-47

Seasonal variations in the low-salinity intermediate water (ESIW) in the region south of the sub-polar front of the East Sea were investigated by using historical hydrographic data. The salinity of the representative density (sigma-0=27.2) of the ESIW was minimal in summer and maximal in winter in the region south of the sub-polar front. The selected four subregions showed different salinity variations. In the west of Oki Spur and the Yamato Basin, salinity fluctuated similarly, with a minimum during summer. In the Ulleung Basin and northwest of Sado Island, however, variations in salinity showed two minima, one is in winter and the other is in summer. These results imply differences in the flow path of the ESIW into the region south of the sub-polar front over time.  相似文献