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41.
Optically stimulated luminescence (OSL) dating was applied to quartz samples recovered from the gravel sediments of deformed marine terrace at the Suryum site, southeastern Korea, but has yielded stratigraphically inconsistent ages. Micromorphological, chemical, and mineralogical analyses of the gravels indicate the possible influence of chemical weathering on the apparent OSL ages. In the course of weathering after emerging from beach environments, originally permeable gravels underwent infilling by halloysite-rich clays in their voids, export and import of radioactive elements, and loss of mechanical strength with the creation of a porosity within pebbles. Calculation based on the evolution of the weathering profile showed a severe fluctuation of dose rate caused by the change of water content and radioactive element concentrations. Samples recovered from the weathering profile inevitably include quartz grains derived from mechanically weakened pebbles or illuviated from the upper layer, making it difficult to determine the equivalent dose (De) values of exclusively depositional quartz sands. Quantitative evaluation of the change of fabric and chemistry of the sediments on the basis of pedologic insight significantly aids in the derivation of OSL ages consistent with geomorphology and other independent age controls. 相似文献
42.
This study evaluated four possible cases of comparing radar and rain gauge rain rate for the detection of mean‐field bias. These four cases, or detection designs, consider in this study are: (1) design 1‐uses all the data sets available, including zero radar rain rate and zero rain gauge rain rate, (2) design 2—uses the data sets of positive radar rain rate and zero or positive rain gauge rain rate, (3) design 3—uses the data sets of zero or positive radar rain rate and positive rain gauge rain rate and (4) design 4—uses the data sets of positive radar rain rate and positive rain gauge rain rate. A theoretical review of these four detection designs showed that only the design 1 causes no design bias, but designs 2, 3 and 4 can cause positive, negative and negative design biases, respectively. This theoretical result was also verified by applying these four designs to the rain rate field generated by a multi‐dimensional rain rate model, as well as to that of the Mt Gwanak radar in Korea. The results from both applications showed that especially the design 4, which is generally used for the detection of mean‐field bias of radar rain rate, causes a serious design bias; therefore, is inappropriate as a design for detecting the mean‐field bias of radar rain rate. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
43.
Many underwater intervention tasks are today performed using manned submersibles or remotely operated vehicles in teleoperation mode. Autonomous underwater vehicles are mostly employed in survey applications. In fact, the low bandwidth and significant time delay inherent in acoustic subsea communications represent a considerable obstacle to remotely operate a manipulation system, making it impossible for remote controllers to react to problems in a timely manner.Nevertheless, vehicles with no physical link and with no human occupants permit intervention in dangerous areas, such as in deep ocean, under ice, in missions to retrieve hazardous objects, or in classified areas. The key element in underwater intervention performed with autonomous vehicles is autonomous manipulation. This is a challenging technology milestone, which refers to the capability of a robot system that performs intervention tasks requiring physical contacts with unstructured environments without continuous human supervision.Today, only few AUVs are equipped with manipulators. SAUVIM (Semi Autonomous Underwater Vehicle for Intervention Mission, University of Hawaii) is one of the first underwater vehicle capable of autonomous manipulation.This paper presents the solutions chosen within the development of the system in order to address the problems intrinsic to autonomous underwater manipulation. In the proposed approach, the most noticeable aspect is the increase in the level of information transferred between the system and the human supervisor.We describe one of the first trials of autonomous intervention performed by SAUVIM in the oceanic environment. To the best knowledge of the authors, no sea trials in underwater autonomous manipulation have been presented in the literature. The presented operation is an underwater recovery mission, which consists in a sequence of autonomous tasks finalized to search for the target and to securely hook a cable to it in order to bring the target to the surface. 相似文献
44.
Xiaojing Gan Yinting Cai Chiyeung Choi Zhijun Ma Jiakuan Chen Bo Li 《Estuarine, Coastal and Shelf Science》2009,83(2):211-218
Invasive smooth cordgrass (Spartina alterniflora, hereafter Spartina) has been expanding rapidly in the estuarine wetlands at Chongming Dongtan (East China) at the expense of native sea-bulrush (Scirpus mariqueter, hereafter Scirpus) and common reed (Phragmites australis, hereafter Phragmites). To examine the potential impacts of the Spartina invasion on bird diversity, we compared the abundance and species richness of birds in habitats created by Spartina, Phragmites, Spartina mixed with Phragmites, Scirpus, and the bare intertidal zone at Chongming Dongtan in spring 2008. Most birds were recorded in the native habitats, with songbirds and breeding birds being most abundant in the Phragmites habitats, and waterbirds and migrants being most abundant in the Scirpus habitats and bare intertidal zone. Both species number and population densities of birds were lower in the exotic Spartina habitats than in the other four habitats. Although some songbirds and breeding birds used the Spartina-invaded habitats, and even preferred Spartina-invaded habitats to Scirpus habitats and bare intertidal zone, their densities were lower in the Spartina-invaded habitats than in the native Phragmites habitats. This might have resulted from the dense Spartina stands restricting bird movement and providing insufficient useable food for most birds. We conclude that the spread of exotic Spartina has negative impacts on local bird communities. Because Chongming Dongtan is an important stopover site for energy replenishment of shorebirds in the East Asian–Australasian Flyway, urgent measures are needed to control further spread of Spartina and to restore the native habitats for birds. 相似文献
45.
Rare earth elements (REEs) of 91 fine-grained bottom sediment samples from five major rivers in Korea (the Han, Keum, and
Yeongsan) and China (the Changjiang and Huanghe) were studied to investigate their potential as source indicator for Yellow
Sea shelf sediments, this being the first synthetic report on REE trends for bottom sediments of these rivers. The results
show distinct differences in REE contents and their upper continental crust (UCC)-normalized patterns: compared to heavy rare
earth elements (HREEs), light rare earth elements (LREEs) are highly enriched in Korean river sediments, in contrast to Chinese
river sediments that have a characteristic positive Eu anomaly. This phenomenon is observed also in primary source rocks within
the river catchments. This suggests that source rock composition is the primary control on the REE signatures of these river
sediments, due largely to variations in the levels of chlorite and monazite, which are more abundant in Korean bottom river
sediments. Systematic variations in ΣLREE/ΣHREE ratios, and in (La/Yb)–(Gd/Yb)UCC but also (La/Lu)–(La/Y)UCC and (La/Y)–(Gd/Lu)UCC relations have the greatest discriminatory power. These findings are consistent with, but considerably expand on the limited
datasets available to date for suspended sediments. Evidently, the REE fingerprints of these river sediments can serve as
a useful diagnostic tool for tracing the provenance of sediments in the Yellow Sea, and for reconstructing their dispersal
patterns and the circulation system of the modern shelf, as well as the paleoenvironmental record of this and adjoining marginal
seas. 相似文献
46.
47.
In this study, 36 fish species were collected from three coastal cities in Korea to investigate levels and patterns of six arsenicals (arsenite: As (III), arsenate: As (V), arsenocholine: AsC, arsenobetaine: AsB, monomethylarsonic acid: MMA, and dimethylarsinic acid: DMA). The levels of ∑6 As in the different fish species varied substantially, ranging from 0.02 μg As/g ww (Islaeli carp) to 9.65 μg As/g ww (Skate ray) with a median of 0.40 μg As/g ww. All the arsenicals in marine fishes showed higher levels than those in freshwater fishes due to fish feed living in saline water. Overall, marine carnivorous fishes seem to be more contaminated with arsenic. For all the fish samples, AsB (mean fraction: 90.6%) was dominant among the six arsenicals, indicating biomethylation of inorganic arsenic and accumulation of AsB. Fish species with high water contents showed elevated levels of As (III), but there was no further significant correlations between arsenicals and water/lipid contents. Concentrations of As (V) were significantly lower than those of As (III), which implies that As (V) is reduced during biomethylation of inorganic arsenic. Consequently, we hypothesize that the toxicity of arsenic (mainly derived from As (III)) can be increased by the reduction of As (V), especially for the fish species with higher water contents. 相似文献
48.
To understand the temporal and spatial variation of the prokaryotic community in the East Sea, their composition was determined by polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE)-sequencing techniques. The investigations were conducted twice annually in 2007 and 2009 in coastal and offshore stations. Prokaryotic abundance (PA), leucine incorporation rate, and other environmental parameters were also measured. By using the DGGE approach, we obtained 283 bacterial sequences and 160 archaeal sequences. The most frequently detected bacterial phylotypes during the investigations belonged to Alphaproteobacteria, Gammaproteobacteria, and Bacteroidetes. However, their relative compositions differed in time and space. Although Alphaproteobacteria and Bacteroidetes were the dominant groups in the surface water in May 2007 and in May and October 2007, Gammaproteobacteria was dominant in mesopelagic samples. However, Gammaproteobacteria was overwhelmingly dominant in most samples in August 2009. Although Deltaproteobacteria was rarely found as a dominant bacterial group, it occupied the highest fraction in a mesopelagic sample in October 2007. Epsilonproteobacteria also showed a similar trend, although its maximal dominance was found in a mesopelagic sample in August 2009. The archaeal community was dominated overwhelmingly by members of the Euryarchaeota in most of the investigations. However, Nitrosopumilales was dominant in aphotic samples in August 2009. Further, their spatiotemporal composition at the family level changed more dynamically in the East Sea. These temporal and spatial distributions of the prokaryotic community were influenced mainly by seawater temperature and depth in the East Sea. 相似文献
49.
50.