Quantitative electron holographic tomography for the 3D characterisation of semiconductor device structures

Electron tomography and electron holography experiments have been combined to investigate the 3D electrostatic potential distribution in semiconductor devices. The experimental procedure for the acquisition and data reconstruction of holographic tilt series of silicon p-n junction specimens is described. A quantitative analysis of the experimental results from specimens of two different thicknesses is presented, revealing the 3D electrostatic potential variations arising from the presence of surfaces and damage generated by focused ion beam (FIB) sample preparation. Close to bulk-like properties are measured in the centre of the tomographic reconstruction of the specimen, revealing higher electrically active dopant concentrations compared to the measurements obtained at the specimen surfaces. A comparison of the experimental results from the different thickness specimens has revealed a 'critical' thickness for this specimen preparation method of 350nm that is required for this device structure to retain 'bulk'-like properties in the centre of the membrane.     

Increased depth of field and stereo pairs of fluorescence micrographs via inverse filtering and maximum-likelihood estimation

Image processing methods are presented for effectively increasing the depth of field and for generating stereo pairs of fluorescence micrographs from a conventional optical microscope. In developing these methods the slice theorem of computed tomography is used. In this way the image reconstruction problem is reduced to one of processing only two-dimensional arrays rather than three-dimensional arrays and the classical difficult problem of restoring missing Fourier components within the missing cone region is circumvented. Two different approaches to such processing are presented. One approach is based on inverse filtering. Another approach is based on previous development of iterative image restoration algorithms for quantum-limited incoherent imagery, founded on maximum-likelihood estimation. Limited experimentation with real micrographs shows that both approaches work well. Some preliminary comparisons are made between the different variations of the methods tested, which point out the advantages and present limitations. Both methods can be implemented on IBM-AT-compatible computers with relatively fast execution times. Advantages that these methods have over confocal microscopy are (i) the optical and computing equipment required is less expensive, and (ii) a conventional microscope when set up properly can have much better light sensitivity than a confocal microscope.     

韩国室内设计专辑——静水流深

静…… 面对群山，出奇的静…… 静的可以听见几百米外，河对岸密林中隐约的鸟鸣……     

Modelling long-term stream acidification in the chemically heterogeneous Upper Severn catchment, Mid-Wales

A two-box version of the long-term acidification model MAGIC is applied to the Upper Severn catchment, Mid-Wales. Comparison between modelled output and the observed stream- and groundwater chemistry points to the limitations of modelling, due to the inherent complexity and variability in the catchment hydrology, soils, geology and chemistry. The MAGIC model is used to produce long-term hind- and forecast predictions of average stream-, soil- and groundwater chemistry, and to simulate long-term changes in sulfate and nitrate deposition, in line with current proposals of reduction. Changes in flow-routing pathways between soil- and groundwater are simulated and the long-term effects on streamwater quality noted. The use of a long-term acidification model enabled the simulation of streamwater quality under these different case scenarios. However, the modelled output is insensitive to depositional and flow routing changes, indicating that catchment processes are not being represented to a sufficient degree. Changes in simulated output as a result of increased acidic deposition are not statistically significant, lying within the variance of long-term observed data. Simulated changes in flow routing suggest a lack of model sensitivity, in terms of the effect on stream chemistry. The need for large amounts of measured data to ensure correct model representation of the hydrology, chemistry and the heterogeneous/variable nature of upland catchments is outlined. It is vital that these long-term data are available to ensure that problems do not arise due to over-reliance by catchment managers on potentially unreliable modelled output.     

Moving from Resource Development to Resource Management: Problems,Prospects and Policy Recommendations for Sustainable Groundwater Management in Bangladesh

Water Resources Management - Increased groundwater accessibility resulting from the expansion of deep and shallow tube wells helped Bangladesh attain near self-sufficiency in rice, with national...     

Study of Organic and Inorganic Binders on Strength of Iron Oxide Pellets

Bentonite is a predominant binder used in iron ore pelletization. However, the presence of a high content of silica and alumina in bentonite is considered undesirable for ironmaking operations. The objective of this study was to identify the alternatives of bentonite for iron ore pelletization. To achieve this goal, different types of organic and inorganic binders were utilized to produce iron oxide pellets. The quality of these iron oxide pellets was compared with pellets made using bentonite. All pellets were tested for physical strength at different stages of pelletization to determine their ability to survive during shipping and handling. The results show that organic binders such as lactose monohydrate, hemicellulose, and sodium lignosulfonate can provide sufficient strength to indurated pellets.     

Ion Exchange in Selected Low Rank Coals. Part II: Kinetics

ABSTRACT

The kinetics of ion exchange in a subbituminous coal have been investigated. The rate determining step in the exchange processes was determined to be intraparticle diffusion for particle sizes of 9,500 × 4,000 μm, 425 × 250 μm and 180 × 125 μm. The kinetics of exchange for the 180 × 125 μm particles was very rapid and approached film diffusion control. A relatively simple mathematical model developed by Helfferich (1) describe adequately ion exchange kinetics. The model was effective in predicting the extent of exchange as a function of time and the time required to reach complete exchange. Interdiffusion coefficients at 298 K obtained from the model for exchange of H for Na ⁺, Mg²⁺and Ca²⁺ranged from 2.0 × 10^10?6to 2.6 × 10^?8cm²/s with the values decreasing in the order:

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Prototypes for Bone Implant Scaffolds Designed via Topology Optimization and Manufactured by Solid Freeform Fabrication

The linking of computational design with precision solid freeform fabrication has tremendous potential for producing tissue scaffolds with tailored properties. We consider a new approach to optimizing the architecture of scaffolds based on jointly maximizing scaffold stiffness and diffusive transport in the interconnected pores. The stiffness of the scaffolds is matched to that of bone by choosing a suitable scaffold porosity. Moreover, the templates can be scaled to achieve target pore sizes whilst preserving their elastic and diffusive properties. The resultant structures have two major design benefits. First, the scaffolds do not have directions of low stiffness. In contrast, the Young's modulus of conventional layered‐grid designs can be 86% less under diagonally‐aligned loads than under axis‐aligned loads. Second, the mass of the scaffold is used efficiently throughout the structure rather than being clumped in non load‐bearing regions. We fabricate prototypes of the implants using selective laser melting and test their elastic properties. Excellent agreement between theory and experiment provides important confirmation of the viability of this route to scaffold design and fabrication.     

Attitudes Towards Growth Management in Florida: Comparing Resident Support in 1985 and 2001

To date, no study has investigated whether resident attitudes towards growth management change over time and, if so, in what ways. This study begins to fill this gap by investigating Floridians' attitudes towards growth management at two key points in time: (i) in 1985, as Florida's groundbreaking growth management legislation was being passed, and (2) in 2001, when substantial revisions to the state's growth management approach were being considered. We found that while overall support for controlling growth remains high, support for government intervention in growth management has diminished. Overall, Florida's experience indicates that popular support for growth management is likely to persist in mature growth management states, even in the face of frustration with government implementation of such efforts and the emergence of political regimes that are less supportive of them.