Uranium in coastal sediments of Tokyo Bay and Funka Bay

The sediment cores from Tokyo Bay and Funka Bay were analyzed for U and its isotopic ratio,²³⁴U/²³⁸U, after dissolving them in 0.1 M HCl, and 30% H₂O₂ in 0.05 M HCl. A small fraction of U in the anoxic sediments was dissolved in 0.1M HCl and even the added yield tracer,²³²U, was lost. The isotopic ratio of H₂O₂ soluble U in the sediments was equal to that of seawater, suggesting that the H₂O₂ soluble U in the sediments is authigenic. The 6M HCl solution dissolved part of the lithogenic U besides the authigenic U. The depth profiles of U from the two bays resembled each other. The authigenic U comprised more than half of the total U even at the surface and increased with depth down to 70 cm, showing small maxima at about 20 cm. The concentration of refractory U was nearly constant with depth and similar to that of the pelagic sediments. The highest U concentration, 6 µg g^–1 which was about 5 times that of the pelagic sediments, was observed in the layer between 70 and 160 cm depth in Tokyo Bay. The annual sedimentation rates of U in the Tokyo Bay sediments were 2.6 tons at the surface and 7.0 tons at the 70–160 cm depth. The increase in U with depth should be due to the deposition of interstitial U either diffusing downward from the surface indicating the trapping of seawater U, or otherwise diffusing upward from the deeper layer indicating the internal cycling of U within the sediments.     

The effect of particle shape and hydrophobicity in flotation

The effect of particle shape on the flotation process has been investigated in laboratory experiments with monosized spherical ballotini and ground ballotini. The particles were treated by partial methylation with trimethylchlorosilane to achieve varying degrees of hydrophobicity. In flotation, the process of film thinning and liquid drainage is critical in the formation of stable bubble–particle attachments and this is affected by the particle shape and surface hydrophobicity. Flotation tests with different particle sizes were conducted in a modified batch Denver cell. Predictions from a computational fluid dynamic model of the flotation cell that incorporates fundamental aspects of bubble–particle attachment were compared with data from flotation tests. Contact angles of the particles were measured using a capillary rise technique to indicate surface hydrophobicity. Ground ballotini generally has higher flotation rates than spherical ballotini; the results are consistent with effects from faster film thinning and rupture at rough surfaces and are well correlated by the sphericity index.     

Factors controlling groundwater chemistry in an agricultural area with complex topographic and land use patterns in mid‐western South Korea

Shallow and bedrock groundwater from granitic aquifers were investigated for the hydrogeochemistry of major and minor constituents in an agricultural area. Nitrate concentrations were observed up to 49 mg/l as NO₃‐N, with 22% of samples exceeding the drinking water standard, which could pose a significant threat because most residents rely on groundwater as their drinking water source. Principal component analysis revealed three principal components (PCs): (1) nitrate contamination, contributed by major cations, Cl^?, SO and NO , (2) reduction processes positively involving Fe, Mn and B, and negatively involving dissolved oxygen and NO and (3) natural mineralization, involving HCO and F^?. Cluster analysis, performed on the PC scores, resulted in seven sample groups, which were successfully identified by total depth, elevation and land use. The nitrate‐contaminated groups had mixed land uses, with locally concentrated residential areas. Uncontaminated groundwater groups were found in the natural environment, including high‐altitude spring water and bedrock groundwater with a higher degree of natural mineralization. Shallow groundwater groups in paddy fields in lowlands were affected by reducing environments, of which one group was characterized by high Fe, Mn and B, and negligible nitrate. Groundwater with intermediate nitrate and lower Cl^? and SO was found primarily in hilly terrains with orchards and vegetable gardens, indicating lower contaminant loadings than lowland areas. Higher concentrations of F^? and nitrate were observed in the nitrate‐contaminated water, which seemed unlikely to be explained by groundwater mixing. The strong acidity generated from nitrification may infiltrate deeper into the aquifer, induce accelerated weathering of bedrock and result in the coexistence of F^? and nitrate, which may be an evidence of intense nitrate loading, leading to soil acidification. Multivariate statistical analysis successfully delineated hydrochemical characteristics of groundwater attained by natural and anthropogenic processes in an agriculturally stressed area with complex topographic land use patterns. Copyright © 2009 John Wiley & Sons, Ltd.     

Frequency domain substructural identification for arbitrary excitations

Structural identification based on analysis of vibration signals is usually formulated as an optimization problem. Nevertheless, identifying a structural system as a whole often involves a great number of unknowns and degrees of freedom, resulting in considerable convergence difficulty and expensive evaluation of objective function. To handle these issues, this paper aims to propose a frequency domain substructural identification method applicable to arbitrary excitations. This is done by introducing the exponential window method in the formulation so that the effect caused by initial condition is alleviated without using zero padding. The proposed identification method is verified through both numerical and experimental studies. It is shown that significant reduction in computer time can be achieved in addition to remarkable identification accuracy. The experimental study also indicates that the proposed strategy is effective in identifying small structural changes. Copyright © 2011 John Wiley & Sons, Ltd.     

Substructural first‐ and second‐order model identification for structural damage assessment

This paper presents two methods to perform system identification at the substructural level, taking advantage of reduction in the number of unknowns and degrees of freedom (DOFs) involved, for damage assessment of fairly large structures. The first method is based on first‐order state space formulation of the substructure where the eigensystem realization algorithm (ERA) and the observer/Kalman filter identification (OKID) are used. Identification at the global level is then performed to obtain the second‐order model parameters. In the second method, identification is performed at the substructural level in both the first‐ and second‐order model identification. Both methods are illustrated using numerical simulation studies where results indicate their significantly better performance than identification using the global structure, in terms of efficiency and accuracy. A 12‐DOF system and a fairly large structural system with 50 DOFs are used where the effects of noisy data are considered. In addition to numerical simulation studies, laboratory experiments involving an eight‐storey frame model are carried out to illustrate the performance of the proposed method. The identification results presented in terms of the stiffness integrity index show that the proposed methodology is able to locate and quantify damage fairly accurately. Copyright © 2005 John Wiley & Sons, Ltd.     

Contamination of polychlorinated biphenyls (PCBs) in sediments from Kyeonggi Bay and nearby areas, Korea

To elucidate the characteristic distribution and contamination of polychlorinated biphenyls (PCBs) in sediments, 63 sediments and five benthic organisms from Kyeonggi Bay, Namyang Bay and Lake Shihwa, West coast of Korea, were analysed. Characterization of PCBs distribution in sediments was conducted by correlation between PCBs concentrations and environmental parameters, comparison of contamination level and composition of PCBs homologs between Kanechlor mixture (KC-mix) and sediments. The residues of PCBs in sediments were correlated with total organic carbon (TOC) and particulate organic carbon (POC) contents, not with mud contents and grain size distributions. Elevated concentrations of T-PCBs were found in sediments from Incheon North Harbor (INH) in Kyeonggi Bay. T-PCBs concentrations were decreased with distance increase from inner site of INH. The residues of T-PCBs in sediments from Namyang Bay were either non-detectable or near to detection limit. The contamination by PCBs in sediments from Lake Shihwa was also low. The PCBs congener profiles in INH were similar to those of KC-mix, while those in less contaminated sites showed relatively high percentage of lower chlorinated biphenyls. Sites K18 (580 ng/g or 48 ug/g-OC dry wt) and K19 (330 ng/g or 38 ug/g-OC dry wt) within INH exceeded the sediment quality criteria (SQC) (16 micrograms/g-OC as a KC-mix) derived from equilibrium partitioning (EqP) approach.     

Electron-microprobe dating of monazites from Western Carpathian basement granitoids: plutonic evidence for an important Permian rifting event subsequent to Variscan crustal anatexis

Accessory monazites from 35 granitoid samples from the Western Carpathian basement have been analysed with the electron microprobe in an attempt to broadly constrain their formation ages, on the basis of their Th, U and Pb contents. The sample set includes representative granite types from the Tatric, Veporic and Gemeric tectonic units. In most cases Lower Carboniferous (Variscan) ages have been obtained. However, a much younger mid-Permian age has been recorded for the specialised S-type granites of the Gemeric Unit, and several small A- and S-type granite bodies in the Veporic Unit and the southern Tatric Unit. This distinct Permian plutonic activity in the southern part of the Western Carpathians is an important, although previously little considered geological feature. It appears to be not related to the Variscan orogeny and is interpreted here to reflect the onset of the Alpine orogenic cycle, with magma generation in response to continental rifting. The voluminous Carboniferous granitoid bodies in the Tatric and Veporic units comprise S- and I-type variants which document crustal anatexis accompanying the collapse of a compressional Variscan orogen sector. The Variscan magmas were most likely produced through the remelting of a subducted Precambrian volcanic arc-type crust which included both igneous and sedimentary reworked volcanic-arc material. Although the 2C errors of the applied dating method are quite large and typically ᆞ-20 Ma for single samples, it would appear from the data that the Variscan S-type granitoids (333-367 Ma) are systematically older than the Variscan I-type granitoids (308-345 Ma). This feature is interpreted in terms of a prograde temperature evolution in the deeper parts of the post-collisional Variscan crust. In accordance with recently published zircon ages, this study shows that the Western Carpathian basement must be viewed as a distinct "eastern" tectonomagmatic province in the Variscan collision zone, where the post-collisional crustal melting processes occurred ~20 Ma earlier than in the central sector (South Bohemian Batholith, Hohe Tauern Batholith).