[en] Sellafield in NW England was proposed as a candidate site for subsurface disposal in the UK. of Intermediate Level radioactive Waste (ILW). Part of the concept of such a site is that the geosphere functions as one of many barriers against serious leakage. Assessment of overall performance requires predictions of the groundwater flow, which may transport radionuclide into shallow aquifers, or to the surface. This thesis develops a 2-D model, which simulate subsurface fluid flow as a means to aid prediction into the far future. The software uses the finite element method, and is an adaptation of OILGEN (Garven 1989). This permits coupling of rock properties, water properties, and flow resulting from differences of potential- including head, density and heat. Mass transport computations are based on a random walk particle tracking model. Data for this thesis was derived from an extensive site investigation program undertaken by UK NIREX. Conceptually, the regional flow system consists of rainwater falling on 1,000m high ground of the Cumbrian mountains and percolating into the Borrowdale Volcanic Group (BVG), passing westwards by deep flow and returning upwards through the repository site (PRZ), before discharge into overlying sediments and into the Irish Sea. A regional cross section (WSW to ENE) was constructed 115km long and 7.5km deep. This is much longer and deeper than previous studies of hydrogeology in this area. The objective was to reproduce the regional flow and local flow at the repository site. Modelling was carried out progressively, investigating the effects of rock permeability, geometry, anisotropy, faults, salinity and mesh geometry. The approach was to perform a very extensive and prolonged series of sensitivity tests and to adjust each parameter independently to achieve the best fit of predicted groundwater head profiles to head profiles measured in Boreholes 3, 10A and 2. Two sets of best-fit parameters were derived from this calibration exercise. A second stage of model validation used the two calibrated models to predict the streamlines and residence ages of groundwater in the PRZ. These were compared to the in-situ measured chemistry and salinity of groundwater, and to the measured mean residence age of the groundwater. Only one suite of parameters in the modelling was compatible with both head and residence age measured data. This validated model is taken to be the best representation of the natural regional flow system and to simulate the release of radionuclides from the repository and their pathways towards the surface transported by moving groundwater. Modelling shows three flow regimes, similar to measured geochemical data: Shallow Flow (high flux); Inland Flow (small flux); Irish Basin (very small flux). Best fit model parameters are close to the median rock permeability measured in the field. BVG permeability is 0.12m/yr and flow rate at the repository site is 1.0m/yr. Recharge is 16km east of the repository. Critical controls on flow are >2km deep permeabilities of Eskdale Granite and Skiddaw Slate, which have not been sampled by boreholes. Water residence age at the repository is predicted as 0.14-0.15Ma by both streamline and dispersion methods; this compares well with measured 0.03-1.5Ma ages. Leachate from the repository reaches the Calder Sandstone 400m deep aquifer after 25,000yr and the Irish Sea bed at 50,000-80,000yr, 3km west of the repository. It is concluded that the geosphere at this PRZ does not greatly assist performance. Previous local models have not correctly considered very deep flow. A PRZ is better sited on the inflow end, not the outflow end, of a regional groundwater system. (author)

[en] This report discusses the following: (1) An overview of major issues in the downstream oil sector, including oil demand and product export availability, the changing product consumption pattern, and refineries being due for major investment; (2) Recent upstream developments in the oil and gas sector in Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Mexico, Peru, Trinidad and Tobago, and Venezuela; (3) Recent downstream developments in the oil and gas sector in Argentina, Chile, Colombia, Ecuador, Mexico, Peru, Cuba, and Venezuela; (4) Pipelines in Argentina, Bolivia, Brazil, Chile, and Mexico; and (5) Regional energy balance. 4 figs., 5 tabs

[en] For the conventional rolling assisted biaxially textured metallic substrate (RABiTS) process, a large degree of cold rolling deformation and a subsequent high temperature annealing procedure are required to obtain adequately biaxially textured Ni tape. Recently, we have reported a newly developed process, named as ion beam structure modification (ISM), for fabricating biaxially textured Ni tape by use of low energy argon ion beam bombardment. In this paper, the biaxial texture of ISM processed Ni tape and its thermal stability at high temperatures are investigated. Results show that Ni tape processed under optimum ISM conditions, the (2 0 0) rocking curve FWHM is less than 5.7 deg. , and the (1 1 1) phi-scan FWHM is less than 7.5 deg. . High temperature annealing does not impair the biaxial-texture already developed in ISM processed Ni foils, although ISMs should not be regarded as a complete equilibrium process

[en] The aging behavior of SiC whisker reinforced AZ91 magnesium matrix composites was investigated with Vickers hardness measurement, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The precipitation process observed in the monolithic alloy was not altered by the addition of SiC whiskers. The composite exhibited an accelerated hardening response compared with the unreinforced matrix alloy. However, the addition of SiC whiskers altered the distribution of the Mg₁₇Al₁₂ precipitates. Mg₁₇Al₁₂ precipitated preferentially at the SiCw-AZ91 interface, with a definite orientation relationship with SiC whisker: (1-bar10)_Mg17Al12//(111)_SiCw, [111]_Mg17Al12//[011-bar]_SiCw. The preferential interfacial precipitate decreased the Al content in the matrix, resulting in a decrease in the amount of continuous precipitates. As a consequence, the age-hardening efficiency in the composite was lower

[en] The development of high resolution, room temperature semiconductor radiation detectors requires the introduction of materials with increased carrier mobility-lifetime (μτ) product, while having a band gap in the 1.4-2.2 eV range. AlSb is a promising material for this application. However, systematic improvements in the material quality are necessary to achieve an adequate μτ product. We are using a combination of simulation and experiment to develop a fundamental understanding of the factors which affect detector material quality. First principles calculations are used to study the microscopic mechanisms of mobility degradation from point defects and to calculate the intrinsic limit of mobility from phonon scattering. We use density functional theory (DFT) to calculate the formation energies of native and impurity point defects, to determine their equilibrium concentrations as a function of temperature and charge state. Perturbation theory via the Born approximation is coupled with Boltzmann transport theory to calculate the contribution toward mobility degradation of each type of point defect, using DFT-computed carrier scattering rates. A comparison is made to measured carrier concentrations and mobilities from AlSb crystals grown in our lab. We find our predictions in good quantitative agreement with experiment, allowing optimized annealing conditions to be deduced. A major result is the determination of oxygen impurity as a severe mobility killer, despite the ability of oxygen to compensation dope AlSb and reduce the net carrier concentration. In this case, increased resistivity is not a good indicator of improved material performance, due to the concomitant sharp reduction in μτ

[en] Raman microspectroscopy and imaging techniques have been used to investigate key mechanistic features that influence the formation of layered Bi- and Tl-based superconducting phases during the thermal treatment employed to produce BSCCO and TBCCO composite conductors. Seminal information gained from these studies includes the location of lead-rich nonsuperconducting second phases (NSPS) and the identification of the constituent phases in certain NSP agglomerations that tend to resist dissipation as high-Tc phase formation proceeds to completion

[en] For the bone marrow type of radiation sickness, it is possible to describe the injury to whole-body haematopoietic tissue using stem cell dose. In the case of highly non-uniform exposure, an extra-high local dose to certain parts of the body or absorbed dose to critical organs should be additionally described. To obtain objective dosimetric data from objects carried by the irradiated victims, the watch is an easily available accident dosemeter. Watch rubies can be used as thermoluminescence dosemeters, and the watch glass can be used in electron spin resonance dose measurement. (author)

[en] Circularly and linearly polarized radiation from inhomogeneous cyclotron emission regions with uniform magnetic field and temperature but different electron density profiles are studied. Calculations show that the inhomogeneous models generally produce larger polarization for low harmonics and smaller polarization for high harmonics compared to the homogeneous models. Polarization light curves for different inhomogeneous models with a wide variety of parameters are presented, providing handy theoretical results to compare with observations. The observed polarization light curves of ST LMi, EF Eri, and BL Hydri are fitted using an inhomogeneous model for the first time, and good fits are obtained, supporting the hypothesis that the cyclotron emission regions of AM Her systems have a complicated structure. 37 refs

[en] High quality YBa₂Cu₃O_7-x films on metallic substrates with high critical current densities well over 10⁶ A/cm² can be prepared by the rolling assisted biaxially textured substrates (RABiTS) method. Nickel or its alloys have been used as biaxially textured substrates formed through a specific rolling and high temperature annealing procedures. In this paper, we report a newly developed process for developing biaxial texture in rolled Ni tape by argon ion beam bombardment. It is named the ion-beam structure modification (ISM) process. In the ISM processed Ni foils, X-ray diffraction ω scans showed the full width-half maximum (FWHM) value of the (2 0 0) peak was 5.7 deg. . And the electron back scattering diffraction (EBSP) analysis based on scanning electron microscopy showed good {1 0 0} <0 0 1> cubic orientation and the mean grain size was determined as about 25 μm. The texture evolution of rolled Ni foils during ISM process is reported also. For ISM process, local temperature elevation and distribution arises from the ion bombardment, coupled with anisotropic incident ion penetration and propagation as a result of channeling effects in the metal lattice, are expected to play the major roles in the development of grain reorientation in the Ni foil. Due to the simplicity and efficiency of the ISM process, the technique shows a great promise for application in the industrial scale production of long-lengths of superconductor tapes

[en] The effect of high temperature exposure on the interface and tensile properties of Al₁₈B₄O₃₃w/AZ91 magnesium matrix composite fabricated by squeeze casting was studied. The interfaces of the composites were examined using transmission electron microscopy, and the mechanical properties were evaluated by tensile tests. The interfacial region was composed of MgO which was formed by the reaction between the Al₁₈B₄O₃₃ whisker and the Mg matrix. An thin and uniform interfacial reaction layer with a thickness of 10-20 nm formed during squeeze casting could act as a barrier to prevent the further reaction between Al₁₈B₄O₃₃ whisker and Mg alloys. The interfacial reaction rate was very low during thermal exposure below the liquidus temperature of AZ91 matrix alloy. Only after exposure above the liquidus temperature of the AZ91 matrix alloy for a long period, the thickness of the interfacial layer increased obviously. However, the interfacial reaction rate was much slower than that in the Al₁₈B₄O₃₃w/Al-Mg composites. The interfacial reaction kinetics was controlled by the seepage of Mg and release of Al and B along the narrow diffusion channels between the fine MgO particle. The composite did not show a degradation in the tensile properties after exposure below the solidus temperature of AZ91 for long periods, suggesting that the Al₁₈B₄O₃₃w/AZ91 magnesium matrix composite could be subjected to long-term service at elevated temperature