Factors Contributing to Incomplete Charge Collection in Si(Li) X-ray Detectors

This project is concerned with a detailed study of the properties and behaviour of lithium drifted silicon Si(Li) energy dispersive x-ray detectors. In particular, the factors which effect their performance in the detection of low energy x-rays. The Si(Li) detectors used in this project were a new generation of detector. These new detectors were known to exhibit an order of magnitude improvement in the low energy tails associated with the detection process. These low energy tails are caused by the effects of incomplete charge collection (ICC) of the charge carriers created during the detection process. The work discussed in this thesis describes a series of experiments which were performed to primarily investigate why electron generated x-ray spectra obtained from our transmission electron microscope were of a poorer quality, in terms of ICC, than had been predicted by a series of preliminary tests performed with this detector. Chapter 2 discusses the various theoretical considerations required throughout the project. This includes a brief outline of the processes involved during the detection of x-rays and discusses the various cross-sections involved for these processes. Chapter 3 then discusses the design and operation of the Si(Li) energy dispersive x-ray detector. Chapter 4 details the preliminary investigation performed to establish the quality of electron generated spectra obtainable with the Si(Li) detector. The quality of the spectra was established by the accuracy of the theoretical background fit obtainable for a particular spectrum. This investigation clearly showed that the spectra were of an inferior quality to that expected. Chapter's 5 and 6 then detail an investigation into possible reasons to explain why the spectra should have been of such a poor quality. This investigation considers what effects the microscope environment can have on the detectors performance. Whilst in use on the microscope, the detector is immersed in the strong magnetic field from the objective lens (~0.3 T). In addition, the detector is continually subjected to a high energy irradiation from the x-rays created during the collisions between the electron beam and the specimens. In certain applications it is also possible for electrons to be scattered onto the detector. Two similar detectors were studied in detail; this allowed direct comparisons of their performances to be made. This investigation revealed that several interesting phenomena occur with these detectors. Both detectors were found to have regions around their circumference in which a high trap density existed (this leading to the creation of excess ICC). However, the nature of these side regions was found to be different for both detectors. In the first detector, the traps were seen to form by themselves. In the second detector, traps were created by high energy irradiation from terbium characteristic photons. These traps were seen to decay with time. However, both detectors were found to behave in the desired manner when collimated down to a small central region. The performance of the first detector was seen to show a marked deterioration, in terms of the level of ICC, during the time this investigation took. Chapter 7 discusses some of the processes known to be occurring in the detectors which give rise to the low energy tails seen in all spectra. Some of these processes are fundamental and should not be confused with those which give rise to the ICC. The magnitudes of these processes were established whenever possible. This information is valuable to the detector manufacturers who are striving to produce the best detectors that physical constraints will allow. A knowledge of these fundamental limits makes it possible to predict levels in design improvement theoretically possible

Dynamic Interaction Networks in modelling and predicting the behaviour of multiple interactive stock markets

The behaviour of multiple stock markets can be described within the framework of complex dynamic systems. A representative technique of the framework is the dynamic interaction network (DIN), recently developed in the bioinformatics domain. DINs are capable of modelling dynamic interactions between genes and predicting their future expressions. In this paper, we adopt a DIN approach to extract and model interactions between stock markets. The network is further able to learn online and updates incrementally with the unfolding of the stock market time-series. The approach is applied to a case study involving 10 market indexes in the Asia Pacific region. The results show that the DIN model reveals important and complex dynamic relationships between stock markets, demonstrating the ability of complex dynamic systems approaches to go beyond the scope of traditional statistical methods

An innovative virtual reality training tool for orthognathic surgery

Virtual reality (VR) surgery using Oculus Rift and Leap Motion devices is a multi-sensory, holistic surgical training experience. A multimedia combination including 360° videos, three-dimensional interaction, and stereoscopic videos in VR has been developed to enable trainees to experience a realistic surgery environment. The innovation allows trainees to interact with the individual components of the maxillofacial anatomy and apply surgical instruments while watching close-up stereoscopic three-dimensional videos of the surgery. In this study, a novel training tool for Le Fort I osteotomy based on immersive virtual reality (iVR) was developed and validated. Seven consultant oral and maxillofacial surgeons evaluated the application for face and content validity. Using a structured assessment process, the surgeons commented on the content of the developed training tool, its realism and usability, and the applicability of VR surgery for orthognathic surgical training. The results confirmed the clinical applicability of VR for delivering training in orthognathic surgery. Modifications were suggested to improve the user experience and interactions with the surgical instruments. This training tool is ready for testing with surgical trainees

Real-time human action recognition on an embedded, reconfigurable video processing architecture

Copyright @ 2008 Springer-Verlag.In recent years, automatic human motion recognition has been widely researched within the computer vision and image processing communities. Here we propose a real-time embedded vision solution for human motion recognition implemented on a ubiquitous device. There are three main contributions in this paper. Firstly, we have developed a fast human motion recognition system with simple motion features and a linear Support Vector Machine (SVM) classifier. The method has been tested on a large, public human action dataset and achieved competitive performance for the temporal template (eg. “motion history image”) class of approaches. Secondly, we have developed a reconfigurable, FPGA based video processing architecture. One advantage of this architecture is that the system processing performance can be reconfiured for a particular application, with the addition of new or replicated processing cores. Finally, we have successfully implemented a human motion recognition system on this reconfigurable architecture. With a small number of human actions (hand gestures), this stand-alone system is performing reliably, with an 80% average recognition rate using limited training data. This type of system has applications in security systems, man-machine communications and intelligent environments.DTI and Broadcom Ltd

Interferometry with few photons

Optical phase determination is an important and established tool in diverse fields such as astronomy, biology, or quantum optics. There is increasing interest in using a lower number of total photons. However, different noise sources, such as electronic readout noise in the detector, and shot noise, hamper the phase estimation in regimes of very low illumination. Here we report a study on how the quality of phase determination is affected by these two sources of noise. To that end, we experimentally reconstruct different wavefronts by means of a point diffraction interferometer for different mean intensities of illumination, up to $15\ \mathrm{phot/px}$. Our interferometer features a Skipper-CCD sensor, which allows us to reduce the readout noise arbitrarily, thus enabling us to separate the effect of these two sources of noise. For two cases of interest: a spatial qudit encoding phase, consisting of d = 6 uniform phase regions, and a more general continuous phase, we see that reducing the readout noise leads to a clear improvement in the quality of reconstruction. This can be explained by a simple noise model that allows us to predict the expected fidelity of reconstruction and shows excellent agreement with the measurements

Imaging With the Past: Revealing the Complexity of Chimaeroid Pelvic Musculature Anatomy and Development

Chondrichthyans are now widely adopted as models for examining the development and evolution of the stem gnathostome body plan. The fins of some cartilaginous fish are recognized for their plesiomorphic form and mode of muscular development, i.e., epithelial extension. Despite detailed molecular and descriptive examinations of these developmental mechanisms, there has been little contemporary examination of the ontogeny and morphology of the musculature in chondrichthyans including that of the paired fins. This gap represents a need for further examination of the developmental morphology of these appendicular musculatures to gain insight into their evolution in gnathostomes. The elephant shark is a Holocephalan, the sister group of all other chondrichthyans (Holocephali: Callorhinchus milii). Here, we use nano-CT imaging and 3D reconstructions to describe the development of the pelvic musculature of a growth series of elephant shark embryos. We also use historical descriptions from the nineteenth century and traditional dissection methods to describe the adult anatomy. This combined approach, using traditional methods and historical knowledge with modern imaging techniques, has enabled a more thorough examination of the anatomy and development of the pelvic musculature revealing that chimaeroid musculatures are more complex than previously thought. These data, when compared to extant and extinct sister taxa, are essential for interpreting and reconstructing fossil musculatures as well as understanding the evolution of paired fins

Tractarian Objects and Logical Categories

It has been much debated whether Tractarian objects are what Russell would have called particulars or whether they include also properties and relations. This paper claims that the debate is misguided: there is no logical category such that Wittgenstein intended the reader of the Tractatus to understand his objects either as providing examples of or as not providing examples of that category. This is not to say that Wittgenstein set himself against the very idea of a logical category: quite the contrary. However, where Russell presents his logical variety of particulars and the various types of universal, and Frege presents his of objects and the various types of function, Wittgenstein denies the propriety of such a priori expositions. Wittgenstein envisages a variety of logical types of entity but insists that the nature of these types is something to be discovered only through analysis

Ecological risk assessment of the East Coast Otter Trawl Fishery in the Great Barrier Reef Marine Park: Data report

An ecological risk assessment of the East Coast Otter Trawl Fishery in the Great Barrier Reef Region was undertaken in 2010 and 2011. It assessed the risks posed by this fishery to achieving fishery-related and broader ecological objectives of both the Queensland and Australian governments, including risks to the values and integrity of the Great Barrier Reef World Heritage Area. The risks assessed included direct and indirect effects on the species caught in the fishery as well as on the structure and functioning of the ecosystem. This ecosystem-based approach included an assessment of the impacts on harvested species, by-catch, species of conservation concern, marine habitats, species assemblages and ecosystem processes. The assessment took into account current management arrangements and fishing practices at the time of the assessment. The main findings of the assessment were: Current risk levels from trawling activities are generally low. Some risks from trawling remain. Risks from trawling have reduced in the Great Barrier Reef Region. Trawl fishing effort is a key driver of ecological risk. Zoning has been important in reducing risks. Reducing identified unacceptable risks requires a range of management responses. The commercial fishing industry is supportive and being proactive. Further reductions in trawl by-catch, high compliance with rules and accurate information from ongoing risk monitoring are important. Trawl fishing is just one of the sources of risk to the Great Barrier Reef

'Reclaiming the criminal' : the role and training of prison officers in England, 1877-1914

This article examines the role and training of prison officers in England, between 1877 and 1914. It is concerned with the changing penal philosophies and practices of this period and how these were implemented in local prisons, and the duties of the prison officer. More broadly, this article argues that the role of the prison officer and their training (from 1896) reflect wider ambiguities in prison policy and practice during this period