Correlation of spectroscopic properties and substitutional sites of Cr3+ in aluminosilicates: I. Kyanite

Using the superposition model in conjunction with our crystal field analysis package recently developed for 3d ions doped at arbitrary low symmetry sites in crystals, the energy levels and statevectors have been predicted within the whole 3d ³ configuration of Cr³⁺ at the four possible triclinic sites in kyanite (Al₂O₃∶SiO₂). The values of the ground state zero-field splitting for each of the four Al sites are evaluated. The splittings of the lower excited state ² E as well as the admixture of ⁴ T ₂ state into ² E have also been determined. The predicted results are compared with the available experimental data on the four possible, but so far not uniquely identified, substitutional Cr³⁺ sites in kyanite thus enabling correlation of the spectroscopic properties and substitutional sites.     

Phosphorus and organic carbon in the sediments of a polluted subtropical estuary,and the influence of coastal reclamation

In July 1978, total phosphorus and organic carbon were determined in the sediments of Tolo Harbour, a sewage-polluted estuary in north-east Hong Kong. Concentrations were correlated with % silt-clay in each of three areas. Phosphorus concentrations were highest in central Tolo Harbour, lower by about 1.5μg at. P g^?1 in the outer estuary, Tolo Channel, and lowest in the polluted inner reaches near large coastal reclamations. The latter values, about 3.0 μg at. P g^?1 lower than in central Tolo Harbour, might reflect a selective adsorption of phosphate by reclamation sediments. Organic carbon concentrations were high in the inner reaches and decreased towards the outer channel. Correlations between phosphorus and organic carbon were compared with a published correlation for the east coast of England: in Hong Kong, phosphorus concentrations showed a smaller increase as organic carbon increased, and reached only one-third of the English values as organic carbon approached 2.0%.     

Response of tension-leg platforms to vertical seismic excitations

Presented is a systematic approach, for analysing the vertical motion, tendon force and foundation uplift of a tension-leg platform (TLP) when the subsea soil is excited by vertical seismic waves. The complex problem of multiple interactions among the soil, foundation, fluid and platform can be mathematically modelled using the substructure technique. Having obtained the frequency dependent impedance function for each substructure, the total system is then solved in the frequency domain. A specific TLP is analysed to show the application of the procedures developed and the importance of response to vertical seismic excitation.     

Analysis of cylindrical cavity expansion in a strain weakening material

A numerical technique is suggested that allows a prediction of the behaviour of a single phase, strain softening material during the expansion of a long cylindrical cavity. The method provides the entire pressure-expansion relationship, including the identification of the limit pressure at large deformations.The numerical solutions, obtained using the finite element technique and allowing for finite deformations, show very good agreement with closed form answers that are available for a restricted class of material models. Results are also presented for the more general, dilatant (or collapsing), strain softening materials for which closed form solutions do not exist. The importance of the rate of dilation and rate of softening in determining the behaviour during cavity expansion is illustrated.     

An assessment of the bearing capacity of calcareous and silica sands

A spherical cavity expansion model has been used to study the bearing capacity of foundations on calcareous and silica sands. Two constitutive models have been used to represent each sand: an elastoplastic, collapse-softening model, and a computationally simpler, elastic/perfectly plastic material. The predictions of the limit pressures for spherical cavity expansion are compared with laboratory data on the bearing capacities obtained from model footing tests. It is shown that the numerical predictions of the limit pressures correlate well with the experimental values of bearing capacity, particularly at higher effective overburden pressures.     

Analysis of bacterial diversity and metals in produced water, seawater and sediments from an offshore oil and gas production platform

Produced water is one of the largest waste products routinely discharged into the ocean from offshore oil and gas platforms. This study analyzed bacterial communities and metals in the produced water, surrounding seawater, and sediment around the Thebaud platform. The bacterial community within the produced water was different from the seawater (SAB = 13.3), but the discharge had no detectable effect on the bacterial communities in the seawater (SAB > 97). In contrast, genomic analysis of sediments revealed that the bacterial community from 250 m was different (SAB = 70) from other locations further from the discharge, suggesting that the produced water had a detectable effect on the bacterial community in the sediment closest to the discharge. These near-field sediments contained elevated concentrations of manganese and iron that are associated with the produced water effluent. The results suggested that the discharge of produced water has influenced the bacterial community structure of sediments adjacent to the platform.     

Land-use and land tenure explain spatial and temporal patterns in terrestrial net primary productivity (NPP) in Southern Africa

Net primary productivity (NPP) is an important indicator of ecosystem health and its estimation and understanding of factors determining its spatial and temporal variations is critical. It is important to note that biophysical factors and human induced factors are interlinked in determining NPP patterns. Nevertheless, it is difficult to consider some aspects of human management systems in relation to NPP variations on a global scale analysis than on a local scale analysis. In this study, we tested the hypothesis that, at the local scale, particularly in highly intensive systems, land-use/land tenure types influence NPP variations by altering the biophysical conditions of the land. We estimated NPP between 2000 and 2009 using MODIS data and used ANOVA to test the abovementioned hypotheses. Results showed that NPP significantly (p < 0.05) varied by land-use/land tenure type. We also found that biophysical factors remained essential in explaining NPP variations even at local scales. These results exhibit the intricacies that exist between the biophysical and human-induced factors in explaining NPP variations within ecological landscapes.     

Performance of ground penetrating radar in root detection and its application in root diameter estimation under controlled conditions

A plant is stabilized by its root system. In congested urban cities such as Hong Kong, ground trenching is frequently seen due to the installation of utility lines along the roadside. Soil nailing, which involves soil coring in slopes, is a common solution to improve the slope stability. However, both activities inevitably pose a risk to the integrity of any root systems present, and thus reduce the root anchorage. To prevent or minimize such damage, a careful design of the excavation/drilling location is of prime importance. Ground penetrating radar (GPR) provides a non-destructive method for locating roots by examining the contrast between the dielectric properties of the roots and the surrounding soil. To examine the performance of GPR and promote its use in Hong Kong, a test bed was prepared using local materials to create a controlled environment in which to conduct a series of systematic tests evaluating the performance of a 900 MHz GPR. The reflected radargrams were subject to the influence of the following factors: size and depth of roots, horizontal distance between roots, and contrast between the root and soil water content. Correlations between root size and a number of waveform parameters were also explored. Limiting values for root size, root embedded depth, horizontal separation distance between roots, and water content contrast between root and soil were obtained. A significant correlation was found between the root diameter and time travel parameter T ₂ (p<0.001, r=0.795). Because GPR root detection is highly site-specific, this study provides a local reference for GPR performance in the Hong Kong environment. The findings demonstrate that the 900 MHz GPR is applicable in Hong Kong for the detection of main roots.     

Nodal-based three-dimensional discontinuous deformation analysis (3-D DDA)

This paper presents a new numerical model that can add a finite element mesh into each block of the three-dimensional discontinuous deformation analysis (3-D DDA), originally developed by Gen-hua Shi. The main objectives of this research are to enhance DDA block’s deformability. Formulations of stiffness and force matrices in 3-D DDA with conventional Trilinear (8-node) and Serendipity (20-node) hexahedral isoparametric finite elements meshed block system due to elastic stress, initial stress, point load, body force, displacement constraints, inertia force, normal and shear contact forces are derived in detail for program coding. The program code for the Trilinear and Serendipity hexahedron elements have been developed, and it has been applied to some examples to show the advantages achieved when finite element is associated with 3-D DDA to handle problems under large displacements and deformations. Results calculated for the same models by use of the original 3-D DDA are far from the theoretical solutions while the results of new numerical model are quite good in agreement with theoretical solutions; however, for the Trilinear elements, more number of elements are needed.