Precise nanoscale characterisation of novel Heusler thermoelectrics via analytical electron microscopy

Thermoelectric power generation presents an opportunity to `scavenge' energy that would otherwise be wasted as heat. Heusler alloys, a class of materials often comprising inexpensive, non-toxic elements, are promising for practical use in a new generation of thermoelectric devices. Recently, efficient thermoelectric Heusler alloys have overcome a performance-limiting thermal conductivity through the introduction of nanostructures that scatter phonons and impede thermal transport. However, the nature and stability of nanostructures can be difficult to discern, especially the minor compositional variations that derive from inhomogeneous phase segregation. Throughout this thesis TiNiSn, which forms the basis for some of the most promising n-type half-Heusler thermoelectrics, is studied through a unique combination of elemental and diffractive analysis in the scanning transmission electron microscope (STEM). Epitaxial thin films of TiNiSn are grown by pulsed laser deposition and FIB-prepared cross-sections of these are characterised in STEM with a focus on aberration-corrected STEM-EELS spectrum imaging and scanning precession electron diffraction (SPED), yielding precise chemical and structural quantification with nanoscale spatial resolution. The results throughout this thesis demonstrate the importance of STEM for quantitative studies of thermoelectric materials, as it can provide the analytical precision required for accurate identification of minority phases in TiNiSn specimens that would otherwise be overlooked in bulk analytical techniques. Sensitivity to very small elemental concentrations is a cornerstone of the use of STEM-EELS for chemical characterisation. Precisions of 0.3 % were achieved through adoption and development of refined, reference-based, absolute elemental quantification protocols which were essential in overcoming difficulties with large uncertainties posed by conventional methods. The success of this approach, in part, is due to advances made in characterisation of experimental conditions including, for the first time, an automated, standard-less approach to the measurement and correction of energy dispersion non-uniformities. Dispersion correction enables reliable, absolute calibration of energy-loss in spectra to yield a precision better than 0.1 eV. These developments in STEM-EELS were then used in three investigations of TiNiSn thin films exploring aspects of nanostructuring, phase segregation and crystrallographic strain and coherency. We discovered the spontaneous formation of nanostructures during thin film growth, gaining some insight into the phase segregation mechanisms that lead to their nucleation. Novel in situ STEM studies of phase segregation facilitated direct observations of the thermal evolution of nanoscale phases and results enabled characterisation of diffusion rates of Ni migration between full- and half-Heusler phases, for which the activation energy was calculated as 0.3~eV. Combining SPED with advances in detector technology, STEM structural investigations highlighted an interesting strain texture associated with nanostructuring of the half-Heusler thin films. Finally, combining SPED results with STEM-EELS measurements is proposed as a route to `correlative-STEM' analysis, which unifies nanoscale chemical and structural information for greater insights into the impact of nanostructures in thermoelectrics

Control Software for Reconfigurable Coprocessors

On-line data processing at the ATLAS general purpose particle detector, which is currently under construction at Geneva, generates demands on computing power that are difficult to satisfy with commodity CPU-based computers. One of the most demanding applications is the recognition of particle tracks that originate from B-quark decays. However, this and many others applications can benefit from parallel execution on field programmable gate arrays (FPGA). After the demonstration of accelerated track recognition with big FPGA-based custom computers, the development of FPGA based coprocessors started in the late 1990's. Applications of FPGA coprocessors are usually partitioned between the host and the tightly coupled coprocessor. The objective of the research that I present in this thesis was the development of software that mediates to applications the access to FPGA coprocessors. I used a software process based on iterative prototyping to cope with the expected changing requirements. Also, I used a strict bottom-up design to create classes that model devices on the coprocessors. Using these low-level classes, I developed tools which were used for bootstrapping, debugging, and firmware update of the coprocessors during their development and maintenance. Measurements show that the software overhead introduced by object-oriented programming and software layering is small. The software-support for six different coprocessors was partitioned into corresponding independent packages, which reuse a set of packages that provide common and basic functions. The steady evolution and use of the software during more than four years shows that the software is maintainable, adaptable, and usable

Pervasive handheld computing systems

The technological role of handheld devices is fundamentally changing. Portable computers were traditionally application specific. They were designed and optimised to deliver a specific task. However, it is now commonly acknowledged that future handheld devices need to be multi-functional and need to be capable of executing a range of high-performance applications. This thesis has coined the term pervasive handheld computing systems to refer to this type of mobile device. Portable computers are faced with a number of constraints in trying to meet these objectives. They are physically constrained by their size, their computational power, their memory resources, their power usage, and their networking ability. These constraints challenge pervasive handheld computing systems in achieving their multi-functional and high-performance requirements. This thesis proposes a two-pronged methodology to enable pervasive handheld computing systems meet their future objectives. The methodology is a fusion of two independent and yet complementary concepts. The first step utilises reconfigurable technology to enhance the physical hardware resources within the environment of a handheld device. This approach recognises that reconfigurable computing has the potential to dynamically increase the system functionality and versatility of a handheld device without major loss in performance. The second step of the methodology incorporates agent-based middleware protocols to support handheld devices to effectively manage and utilise these reconfigurable hardware resources within their environment. The thesis asserts the combined characteristics of reconfigurable computing and agent technology can meet the objectives of pervasive handheld computing systems

Real-time power system dynamic simulation

The present day digital computing resources are overburdened by the amount of calculation necessary for power system dynamic simulation. Although the hardware has improved significantly, the expansion of the interconnected systems, and the requirement for more detailed models with frequent solutions have increased the need for simulating these systems in real time. To achieve this, more effort has been devoted to developing and improving the application of numerical methods and computational techniques such as sparsity-directed approaches and network decomposition to power system dynamic studies. This project is a modest contribution towards solving this problem. It consists of applying a very efficient sparsity technique to the power system dynamic simulator under a wide range of events. The method used was first developed by Zollenkopf (^117) Following the structure of the linear equations related to power system dynamic simulator models, the original algorithm which was conceived for scalar calculation has been modified to use sets of 2 * 2 sub-matrices for both the dynamic and algebraic equations. The realisation of real-time simulators also requires the simplification of the power system models and the adoption of a few assumptions such as neglecting short time constants. Most of the network components are simulated. The generating units include synchronous generators and their local controllers, and the simulated network is composed of transmission lines and transformers with tap-changing and phase-shifting, non-linear static loads, shunt compensators and simplified protection. The simulator is capable of handling some of the severe events which occur in power systems such as islanding, island re-synchronisation and generator start-up and shut-down. To avoid the stiffness problem and ensure the numerical stability of the system at long time steps at a reasonable accuracy, the implicit trapezoidal rule is used for discretising the dynamic equations. The algebraisation of differential equations requires an iterative process. Also the non-linear network models are generally better solved by the Newton-Raphson iterative method which has an efficient quadratic rate of convergence. This has favoured the adoption of the simultaneous technique over the classical partitioned method. In this case the algebraised differential equations and the non-linear static equations are solved as one set of algebraic equations. Another way of speeding-up centralised simulators is the adoption of distributed techniques. In this case the simulated networks are subdivided into areas which are computed by a multi-task machine (Perkin Elmer PE3230). A coordinating subprogram is necessary to synchronise and control the computation of the different areas, and perform the overall solution of the system. In addition to this decomposed algorithm the developed technique is also implemented in the parallel simulator running on the Array Processor FPS 5205 attached to a Perkin Elmer PE 3230 minicomputer, and a centralised version run on the host computer. Testing these simulators on three networks under a range of events would allow for the assessment of the algorithm and the selection of the best candidate hardware structure to be used as a dedicated machine to support the dynamic simulator. The results obtained from this dynamic simulator are very impressive. Great speed-up is realised, stable solutions under very severe events are obtained showing the robustness of the system, and accurate long-term results are obtained. Therefore, the present simulator provides a realistic test bed to the Energy Management System. It can also be used for other purposes such as operator training

An institution-based enquiry into concepts of proficiency, automaticity and second-language learning among dyslexic students

It is, for some, 'common knowledge' that dyslexic students cannot master a foreign language 'because' they cannot master their own. This study enquires into the assumption, and the 'because', above, and seeks other explanatory routes for dyslexic university students' difficulties with foreign language learning. Building on earlier work concerned with notions of 'automaticity' in relation to concepts of 'proficiency' in proficiency and dyslexia literatures, it relates these directly to second language teaching/learning concepts and discusses this in relation to 'phronetic', 'professional' and tacit' views of knowledge. The empirical part of the study comprises cross-comparison of four narrative sources: the narratives of a dozen dyslexic students engaged in a semi-structured, in-depth interview concerning their language difficulty and how they view it; a second narrative relating the voices of the advisors most directly linked to dyslexic language learners in the institution, also including past and future difficulties of some dyslexic students who may face a study year abroad, e.g. on Erasmus and similar schemes; a third interview with the then current head of the unit dealing with both English as a Foreign Language, and Modern Foreign Languages; and the over-arching narrative of the researcher – his story in conducting this study. Within this framework, the research uncovers how, at a practical level as well as theoretically, phronetic, teaching-learning and exceptional language-acquisition 'knowledge' may be open to subversion from several quarters: the pragmatics and economics of 3rd-level EFL and MFL1 language teaching; transposing child language acquisition concepts onto adult language learning ones; the cross- and/or mismatching of these with dyslexia ones; and the possible collision between some areas of professional knowledge – tacit or otherwise. The research shows how for the 'institutional dyslexics' concerned, and sometimes despite their advisors, the unit's academic director and the institution, automaticity is anterior to proficiency and agency is anterior to automaticity. Moreover reversing this, discovering or rediscovering their sense of agency allows certain of the dyslexic participants to attain a qualified measure of automaticity in their language studies and hence, of proficiency. These findings have important implications for those engaged in second language teaching and learning. The organisation of the thesis is as follows: in a first chapter which the researcher introduces with a short autobiography and an account of how the research came about, a broadly descriptive and factual introduction to the piece then summarises previous work in the doctoral degree particularly the critical analytical study, focusing the research questions, and discussing the relationship between methodology and methods, and begins a consideration of what a 'case' is, and what is the case here. Chapter 2 expands the theoretical focus with a discussion of the notion of coherentism and the notion of 'fit', and introduces issues in narrativity and in phronesis. Chapter 3 addresses understandings and terminologies in 'communicative' language teaching, cross-mapping these to both dyslexia and 'proficiency' issues previously discussed. Chapter 4 explores the data, and begins an assessment of the 'fit' between the respondents. Finally, Chapter 5 summarises and discusses the 'findings' of the research – what emerges from the research questions and what from their interpretation; how theoretical understandings now 'fit', or not; what else emerged during the study; what constitutes a finding; and returning to Chapter 1, asks to what extent the study is a foundationalist 'case' which can or should be 'generalisable'. A short discussion of further research avenues is presented

Intelligent electronic design for mechatronic systems

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Studies Towards the Development of a Novel Anti-Cancer Agent

This project has been a collaborative effort involving the design, synthesis and testing of analogues of the fungal metabolites viridin, demethoxyviridin and wortmannin. Extraction methods of viridin, from Trichoderma viride were developed and initially provided a lead compound for testing. Data relating to the anti-inflammatory activity of wortmannin analogues was available in the literature and was used in a computer modelling program SYBYL to build a structure activity relationship from which activity of new analogues could be predicted. The crystal structure determination of demethoxyviridin provided detailed structural information about these molecules. This was used in modelling studies to guide the synthesis of new compounds, leading to the synthesis of an analogue several hundred times more active than the original lead compound. A patent has been applied for this compound and it is presently being forwarded for cinical trials in animals for toxicity testing. The compounds were shown to be cytotoxic in vitro and inhibit specific enzymes in the signal transduction pathway. Preferential inhibition of mitogen stimulated cells was shown, indicating that some degree of selectivity was built into the molecules, suggesting that future compounds may have relatively few side effects due to their novel mechanism of action