Late Quaternary glacial–interglacial variations in sediment supply in the southern Drake Passage     

Jae Il Lee  Ho Il Yoon  Kyu-Cheul Yoo  Hyoun Soo Lim  Yong Il Lee  Donghyun Kim  Young-Suk Bak  Takuya Itaki 《Quaternary Research》2012,78(1):119-129

Geochemical characteristics of marine sediment from the southern Drake Passage were analyzed to reconstruct variations in sediment provenance and transport paths during the late Quaternary. The 5.95 m gravity core used in this study records paleoenvironmental changes during the last approximately 600 ka. Down-core variations in trace element, rare earth element, and Nd and Sr isotopic compositions reveal that sediment provenance varied according to glacial cycles. During glacial periods, detrital sediments in the southern Drake Passage were mostly derived from the nearby South Shetland Islands and shelf sediments. In contrast, interglacial sediments are composed of mixed sediments, derived from both West Antarctica and East Antarctica. The East Antarctic provenance of the interglacial sediments was inferred to be the Weddell Sea region. Sediment input from the Weddell Sea was reduced during glacial periods by extensive ice sheets and weakened current from the Weddell Sea. Sediment supply from the Weddell Sea increased during interglacial periods, especially those with higher warmth such as MIS 5, 9, and 11. This suggests that the influence of deep water from the Weddell Sea increases during interglacial periods and decreases during glacial periods, with the degree of influence increasing as interglacial intensity increases.  相似文献   

A hybrid modeling approach to evaluate the groundwater flow system at the low- and intermediate-level radioactive waste disposal site in Gyeong-Ju, Korea     

Sung-Hoon Ji  Kyung Woo Park  Doo-Hyun Lim  Chunsoo Kim  Kyung Su Kim  William Dershowitz 《Hydrogeology Journal》2012,20(7):1341-1353

The development and implementation of a hybrid discrete fracture network/equivalent porous medium (DFN/EPM) approach to groundwater flow at the Gyeong-Ju low- and intermediate-level radioactive waste (LILW) disposal site in the Republic of Korea is reported. The geometrical and hydrogeological properties of fractured zones, background fractures and rock matrix were derived from site characterization data and implemented as a DFN. Several DFN realizations, including the deterministic fractured zones and the stochastic background fractures, whose statistical properties were verified by comparison with in-situ fracture and hydraulic test data, were suggested, and they were then upscaled to continuums using a fracture tensor approach for site-scale flow simulations. The upscaled models were evaluated by comparison to in-situ pressure monitoring data, and then used to simulate post-closure hydrogeology for the LILW facility. Simulation results demonstrate the importance of careful characterization and implementation of fractured zones. The study highlighted the importance of reducing uncertainty regarding the properties and variability of natural background fractures, particularly in the immediate vicinity of repository emplacement.  相似文献   

Influence of Pore Fluid Chemistry on the Mechanical Properties of Clay-Based Materials     

Sumi Siddiqua  Greg Siemens  James Blatz  Alex Man  Bee Fong Lim 《Geotechnical and Geological Engineering》2014,32(4):1029-1042

The producers of nuclear waste, within all countries exploring options, including Canada, have determined the long-term solution to be a deep geological repository. In the Canadian concept, within the deep geologic repository a number of clay-based barriers will separate the containers from the surrounding geosphere. Following placement the surrounding groundwater will infiltrate into the repository. In order to analyze the performance of the repository under very complex conditions, accurate material properties are required. The chemistry of the host rock is an important aspect as the behaviour of clay-based barrier materials could be affected by the saturating saline groundwater. This paper investigates the saturated mechanical behaviour of light backfill (composed of 50 % silica sand and 50 % Na-bentonite clay) and dense backfill (composed of 70 % crushed granite, 25 % glacial lake clay and 5 % Na-bentonite clay) and the quantifying the effect of pore fluid chemistry on the strength and compressibility behaviour of the materials. The results indicate that light backfill behaviour is strongly influenced by its pore fluid chemistry while dense backfill shows limited effects. The material parameters of light backfill and dense backfill are interpreted for input into numerical simulations. These results and interpretation enrich the understanding of the mechanical response of light and dense backfill, two components of the sealing system of the Canadian deep geologic repository.  相似文献   

Investigating factors driving phytoplankton growth and grazing loss rates in waters around Peninsular Malaysia     

Lim  Joon Hai  Lee  Choon Weng  Bong  Chui Wei 《中国海洋湖沼学报》2021,39(1):148-159

In tropical waters where temperatures are relatively stable,we investigated whether the relationship between phytoplankton growth and grazing loss rate acros s different habitats around Peninsular Malaysia can be attributed to its eutrophication states.We measured phytoplankton growth(μ) and grazing loss(g) rates in waters off Bachok Marine Research Station(BMRS),located northeast of Peninsular Malaysia.Chlorophyll-a(chl-a) concentration ranged from 2.90 to 15.78 μg/L and was dominated by nanoand micro-phytoplankton(2 μm in size).Using the Landry and Hassett dilution method,μ at BMRS ranged from 1.02 to 1.58/d whereas g varied from 0.07 to 0.88/d.Grazing accounted for 35% of the primary production at BMRS.A systematic review of available data in waters around Peninsular Malaysia,revealed how μ fluctuated over a wide range(0.01-1.80/d) and correlated with chl a distribution(R2=0.181,P0.001).However,the relationship was only significant at 9 μg/L chl a for mesotrophic waters and 16 μg/L chl a for eutrophic waters.In contrast,g ranged from 0.00 to 1.01/d,and correlated with μ at all locations.The g/μslope ranged from 19% to 84%,and was generally similar for waters around Peninsular Malaysia.However,all the g/μ slopes had a positive y-intercept except for BMRS,and this seemed to suggest the availability of alternative prey supporting grazing at the other stations.  相似文献   

Relationships between sagittal otolith size and body size of Terapon jarbua (Teleostei,Terapontidae) in Malaysian waters     

Chanthran  Shyama Sundari Devi  Lim  Phaik Eem  Poong  Sze-Wan  Du  Jianguo  Loh  Kar-Hoe 《中国海洋湖沼学报》2021,39(1):372-381

Journal of Oceanology and Limnology - Length-weight relationship provides basic information of a fish’s condition while the morphometric data of otolith has been traditionally used to...  相似文献   

Hypoxia and benthic community recovery in Korean coastal waters   总被引：1，自引：0，他引：1  

Lim HS  Diaz RJ  Hong JS  Schaffner LC 《Marine pollution bulletin》2006,52(11):1517-1526

Low dissolved oxygen (hypoxia and/or anoxia) has become a major cause of change to the benthic component of ecosystems around the world. We present the response of a benthic community to hypoxia in organically enriched environments in Korean coastal waters. Disturbances due to low dissolved oxygen (DO), and organic enrichment altered community dynamics, result in defaunation during summer hypoxia with delayed recolonization occurring in winter. As DO decreased, the number of taxa, their abundance and biomass of macrofauna dropped significantly at inner bay stations in Chinhae Bay and Youngsan River estuarine bay affected by hypoxia. With the return of normoxic conditions in Chinhae Bay, recolonization was initiated by opportunistic species, with a 1-4months lag. The polychaetes, Sigambra tentaculata, Mesochaetopterus sp., and Lumbrineris longifolia, were most persistent under hypoxia. The first recolonizers were the polychaetes Paraprionospio pinnata, S. tantaculata, Glycinde gurjanovae and Nectoneanthes multignatha and the bivalve Theora fragilis. The second group of colonizers included the polychaetes Capitella capitata, Mesochaetopterus sp. and L. longifolia, and the bivalve Raetellops pulchella. Hypoxic and near anoxic conditions resulted in mass mortality in Chinhae Bay and Youngsan River estuarine bay, but communities did partially recover after return to normoxic conditions despite delayed recolonization.  相似文献   

Discrete-time quasi-sliding mode control of an autonomousunderwater vehicle     

Pan-Mook Lee Seok-Won Hong Yong-Kon Lim Chong-Moo Lee Bong-Hwan Jeon Jong-Won Park 《Oceanic Engineering, IEEE Journal of》1999,24(3):388-395

This paper presents a discrete-time quasi-sliding mode controller for an autonomous underwater vehicle (AUV) in the presence of parameter uncertainties and a long sampling interval. The AUV, named VORAM, is used as a model for the verification of the proposed control algorithm. Simulations of depth control and contouring control are performed for a numerical model of the AUV with full nonlinear equations of motion to verify the effectiveness of the proposed control schemes when the vehicle has a long sampling interval. By using the discrete-time quasi-sliding mode control law, experiments on depth control of the AUV are performed in a towing tank. The controller makes the system stable in the presence of system uncertainties and even external disturbances without any observer nor any predictor producing high rate estimates of vehicle states. As the sampling interval becomes large, the effectiveness of the proposed control law is more prominent when compared with the conventional sliding mode controller  相似文献   

Description of feeding apparatus and mechanism innemopilema nomurai kishinouye (scyphozoa: rhizostomeae)     

Hye Eun Lee  Won Duk Yoon  Donghyun Lim 《Ocean Science Journal》2008,43(1):61-65

Feeding apparatus, mechanism and passage of ingested prey were described forNemopilema nomurai (Scyphozoa: Rhizostomeae).N. nomurai medusae without central mouths have developed complicated canal systems connecting the tip of the tentacle and oral arm to the gut cavity. The number of junctions in the canal system increases with the bell diameter. The prey is gathered by paralyzing nematocyst at the tentacles and by adhering cirri at the oral arms and scapulets. They are engulfed into the terminal pore located at the oral arms and scapulets, and entered into the gut cavity via the canal system. The estimated digestion time is 1 hour and 20 min. The diameter of terminal pore is always about 1 mm, implying that they could not eat prey larger than that pore size. On the other hand, ephyrae have central mouths and could swallow prey as large as adults could. Exploitation of the same size of food by adult and ephyra implies thatN. nomurai can affect seriously the whole food web, massively ingesting micro-and mesozoopl a n k t o n and cutting the energy transfer toward the higher level of carnivores.  相似文献   

Homogenization framework for three‐dimensional elastoplastic finite element analysis of a grouted pipe‐roofing reinforcement method for tunnelling     

G. J. Bae  H. S. Shin  C. Sicilia  Y. G. Choi  J. J. Lim 《国际地质力学数值与分析法杂志》2005,29(1):1-24

This paper deals with the grouted pipe‐roofing reinforcement method that is used in the construction of tunnels through weak grounds. This system consists on installing, prior to the excavation of a length of tunnel, an array of pipes forming a kind of ‘umbrella’ above the area to be excavated. In some cases, these pipes are later used to inject grout to strengthen the ground and ‘connect’ the pipes. This system has proven to be very efficient in reducing tunnel convergence and water inflow when tunnelling through weak grounds. However, due to the geometrical and mechanical complexity of the problem, existing finite element frameworks are inappropriate to simulate tunnelling using this method. In this paper, a mathematical framework based on a homogenization technique to simulate ‘grouted pipe‐roofing reinforced ground’ and its implementation into a 3‐D finite element programme that can consider stage construction situations are presented. The constitutive model developed allows considering the main design parameters of the problem and only requires geometrical and mechanical properties of the constituents. Additionally, the use of a homogenization approach implies that the generation of the finite element mesh can be easily produced and that re‐meshing is not required as basic geometrical parameters such as the orientation of the pipes are changed. The model developed is used to simulate tunnelling with the grouted pipe‐roofing reinforcement method. From the analyses, the effects of the main design parameters on the elastic and the elastoplastic analyses are considered. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Relative pointing offset analysis of calibration targets with repeated observations with Herschel-SPIRE Fourier-transform spectrometer     

Ivan Valtchanov  Rosalind Hopwood  Edward Polehampton  Dominique Benielli  Trevor Fulton  Peter Imhof  Tomasz Konopczyński  Tanya Lim  Nanyao Lu  Nicola Marchili  David Naylor  Bruce Swinyard 《Experimental Astronomy》2014,37(2):207-223

We present a method to derive the relative pointing offsets for SPIRE Fourier-Transform Spectrometer (FTS) solar system object (SSO) calibration targets, which were observed regularly throughout the Herschel mission. We construct ratios R _obs(ν) of the spectra for all observations of a given source with respect to a reference. The reference observation is selected iteratively to be the one with the highest observed continuum. Assuming that any pointing offset leads to an overall shift of the continuum level, then these R _obs(ν) represent the relative flux loss due to mispointing. The mispointing effects are more pronounced for a smaller beam, so we consider only the FTS short wavelength array (SSW, 958–1546 GHz) to derive a pointing correction. We obtain the relative pointing offset by comparing R _obs(ν) to a grid of expected losses for a model source at different distances from the centre of the beam, under the assumption that the SSW FTS beam can be well approximated by a Gaussian. In order to avoid dependency on the point source flux conversion, which uses a particular observation of Uranus, we use extended source flux calibrated spectra to construct R _obs(ν) for the SSOs. In order to account for continuum variability, due to the changing distance from the Herschel telescope, the SSO ratios are normalised by the expected model ratios for the corresponding observing epoch. We confirm the accuracy of the derived pointing offset by comparing the results with a number of control observations, where the actual pointing of Herschel is known with good precision. Using the method we derived pointing offsets for repeated observations of Uranus (including observations centred on off-axis detectors), Neptune, Ceres and NGC 7027. The results are used to validate and improve the point-source flux calibration of the FTS.  相似文献