Employing Additive Manufacturing for Fusion High Heat Flux Structures

The commercial realisation of nuclear fusion power will require advanced engineering solutions including high heat flux components with higher performance, greater reliability, and longer lifetimes. Additive manufacturing (AM) provides opportunities to produce components with previously unachievable geometries in new and hard-to-manufacture materials. This project introduces the state of the art of fusion high heat flux components and AM and then focuses on applying laser powder bed fusion to high temperature divertor designs. Much of the work was carried out in parallel to the EU FP7 AMAZE project (Additive Manufacturing Aiming towards Zero waste and Efficient production of high-tech metal products). A review of material selection for divertor applications is carried out with an emphasis on the cooled substructure. A parallel, strengths-based approach is undertaken concluding in a series of SWOT (strengths, weaknesses, opportunities, threats) analyses rather than a traditional linear down-selection. Material properties including strength, ductility, thermal expansion, and thermal conductivity are graphically presented as well as derived figures of merit for thermal stress and thermal mismatch with tungsten armour. Radiation damage and compatibility with operational and manufacturing environments are considered and historical summaries of availability and cost are given. By emphasising high temperature operation and acknowledging the inevitability of some nuclear activation beyond the usual 100 year limit, refractory metals and their alloys present themselves as promising candidates, particularly those based on vanadium, tantalum, and molybdenum. A shortage of data for these materials is highlighted, particularly under fusion neutron irradiation, as well as the need for greater understanding of corrosion under relevant conditions. Two novel divertor cooling schemes are then presented and evaluated via concept-level tile-type geometries. The first is a design with multiple small pipes fed from the rear of the component via an in-built manifold and the second employs an enclosed pin-fin array drawing inspiration from the electronics industry. Both highlight features made feasible only by employing AM and use tantalum as the structural material to demonstrate the effect of high-temperature operation on performance. 1D analytical calculations and simple finite element modelling with 150◦C and 600◦C coolant and up to 10 MWm−2 heat flux loading demonstrate improved heat transfer coefficients and more uniform temperature distributions. Performance improvement over conventional designs is likely to be marginal without significant further design optimisation, but the up to 80% reduction in material use compared with conventional concepts, higher thermal efficiency, and opportunity to reduce or relocate pipe joints are highlighted as more significant advantages. Work to develop laser powder bed fusion of tungsten, molybdenum, and tantalum is then presented. First, a summary of context and recent related work is given. A through-lifecycle approach to component development is detailed with the aim of giving an insight into critical issues related to supply chain, process development, material testing, and component build trials. Basic characterisation of size, morphology, and flowability of a selection of powders is used to demonstrate the high variability of current supply. This is followed by determination of first-order build parameters and energy density required for consolidation. Persistent cracking is found, particularly in tungsten and molybdenum, and causes including oxidation and residual stress are posited with suggestions for possible approaches to mitigating these. The results of material testing of small samples are given, including dilatometry, laser flash, and small punch. Small sample numbers and high variability prevent definitive conclusions from being drawn, but trends towards increased brittleness and decreased thermal conductivity are shown and there are indications that the extreme thermal conditions during processing produce β and ω phases of tantalum. Finally a description of a new facility is given, HIVE (Heating by Induction to Verify Extremes), as well as the results of comparative high heat flux testing of two simple copper components - one produced by electron beam melting (EBM) and the other conventionally manufactured. HIVE can apply a constant 10 MWm−2 to a 30 mm x 30 mm test-piece in vacuum which can be cooled using a 200◦C cooling water supply. Thermocouples, thermography, and water calorimetry provide instrumentation. This facility acts as a strategic and previously unavailable intermediate concept validation step between analytical modelling and plasma-surface interaction testing or in-situ qualification. The results presented suggest that convective heat transfer is enhanced by the rough surface of the AM copper part, but that the component’s lower thermal conductivity through the AM copper and across the brazed joint compared to the conventional results in a higher bulk temperature for the same input power indicating a lower overall heat flux handing capability. The project concludes with a summary of key findings and suggestions for future work

Organizing Our Thoughts: “Global Systems” and the Challenge of Writing a More Complex History

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79334/1/j.1540-5923.2010.00305.x.pd

Mechanisms of Relative Age Effects

Several mechanisms potentially contribute to relative age effects, including sport structure, physical, and social mechanisms. A brief description of each is provided. Sport Structure Mechanisms To maintain fair athletic competition, organizations often institute one- or two-year age bands (e.g., players born in 2008 and 2009 compete in U8 soccer). Even in a one-year age band, athletes’ ages can differ by 364 days. While smaller age bands and rotating cut-off dates have been proposed, these solutions provide many administrative challenges. Thus, the inherent sport structure lends itself to relative age effects. Physical Mechanisms Though not guaranteed, being chronologically older than one’s peers can lead to growth and maturation advantages. The average child who is 8 years and zero days old (e.g., born January 1) weighs 58lbs and stands 51” tall; meanwhile the average child who is 7 years and one day old (e.g., born December 31) weighs 51lbs and stands 48” tall. Both children play in the same age division, but the older child has a distinct physical advantage. Additionally, maturation advantages (e.g., better coordination, advanced cognitive efficiency) often exist for relatively older children. Social Mechanisms Parents appear to register their relatively older children in sport at younger ages. This initial experience results in more practice, competition, and instruction. It has been proposed that such initial advantages lead to later advantages (i.e., a Matthew Effect), including selection to elite teams. Further, it is suggested that parents and coaches place higher expectations on relatively older players, also leading to increased practice, competition, and instruction. These expectations (i.e., a Pygmalion Effect) are then met by players, who show advanced skill development

A Multi Agent System for Flow-Based Intrusion Detection Using Reputation and Evolutionary Computation

The rising sophistication of cyber threats as well as the improvement of physical computer network properties present increasing challenges to contemporary Intrusion Detection (ID) techniques. To respond to these challenges, a multi agent system (MAS) coupled with flow-based ID techniques may effectively complement traditional ID systems. This paper develops: 1) a scalable software architecture for a new, self-organized, multi agent, flow-based ID system; and 2) a network simulation environment suitable for evaluating implementations of this MAS architecture and for other research purposes. Self-organization is achieved via 1) a reputation system that influences agent mobility in the search for effective vantage points in the network; and 2) multi objective evolutionary algorithms that seek effective operational parameter values. This paper illustrates, through quantitative and qualitative evaluation, 1) the conditions for which the reputation system provides a significant benefit; and 2) essential functionality of a complex network simulation environment supporting a broad range of malicious activity scenarios. These results establish an optimistic outlook for further research in flow-based multi agent systems for ID in computer networks

A matrix representation of graphs and its spectrum as a graph invariant

We use the line digraph construction to associate an orthogonal matrix with each graph. From this orthogonal matrix, we derive two further matrices. The spectrum of each of these three matrices is considered as a graph invariant. For the first two cases, we compute the spectrum explicitly and show that it is determined by the spectrum of the adjacency matrix of the original graph. We then show by computation that the isomorphism classes of many known families of strongly regular graphs (up to 64 vertices) are characterized by the spectrum of this matrix. We conjecture that this is always the case for strongly regular graphs and we show that the conjecture is not valid for general graphs. We verify that the smallest regular graphs which are not distinguished with our method are on 14 vertices.Comment: 14 page

Air-Cooled Stack Freeze Tolerance Freeze Failure Modes and Freeze Tolerance Strategies for GenDriveTM Material Handling Application Systems and Stacks Final Scientific Report

Air-cooled stack technology offers the potential for a simpler system architecture (versus liquid-cooled) for applications below 4 kilowatts. The combined cooling and cathode air allows for a reduction in part count and hence a lower cost solution. However, efficient heat rejection challenges escalate as power and ambient temperature increase. For applications in ambient temperatures below freezing, the air-cooled approach has additional challenges associated with not overcooling the fuel cell stack. The focus of this project was freeze tolerance while maintaining all other stack and system requirements. Through this project, Plug Power advanced the state of the art in technology for air-cooled PEM fuel cell stacks and related GenDrive material handling application fuel cell systems. This was accomplished through a collaborative work plan to improve freeze tolerance and mitigate freeze-thaw effect failure modes within innovative material handling equipment fuel cell systems designed for use in freezer forklift applications. Freeze tolerance remains an area where additional research and understanding can help fuel cells to become commercially viable. This project evaluated both stack level and system level solutions to improve fuel cell stack freeze tolerance. At this time, the most cost effective solutions are at the system level. The freeze mitigation strategies developed over the course of this project could be used to drive fuel cell commercialization. The fuel cell system studied in this project was Plug Power's commercially available GenDrive platform providing battery replacement for equipment in the material handling industry. The fuel cell stacks were Ballard's commercially available FCvelocity 9SSL (9SSL) liquid-cooled PEM fuel cell stack and FCvelocity 1020ACS (Mk1020) air-cooled PEM fuel cell stack

The priesthood of Christ in Anglican doctrine and devotion: 1827 - 1900

This thesis traces the history of the interpretation of the doctrine of Christ as priest in the doctrine and devotion of representatives of the Church of England from the publication of Keble's Christian Year in 1827 to the Oxford Conference, 'Priesthood and Sacrifice', of 1899. Between these years the image of Christ as priest was a recurring motif in Anglican thought. Representatives of all shades of Churchmanship were remarkably united in a common enthusiasm for the image, but deeply divided over its interpretation. A composite historico-theological analysis of this hitherto uncharted theme unfolds not only the prevalence of this Christological motif in Anglican doctrine and devotion between these years, but also the potency of this image to shape, direct, and unify crucial features of Victorian religious development and theological controversy. The thesis argues, against the backcloth of a brief examination of the role, content, and significance of the doctrine in Anglican religion prior to 1827, that the prevalence and potency of the image of Christ as priest is to be accounted for as expressing a cardinal article of the Church of England's historic lex orandi. The fact that Tractarians, Evangelicals, the majority of Latitudinarians, Ritualists, Anglo-Catholics, and Biblical Scholars, united in adherence to this one thematic doctrinal image, but were, at times, bitterly divided over their understanding of it, indicates a focal point of Anglican religion, endorsed in its liturgy; namely, that Christ is "a great High Priest", through whom, and with whom, and in whom alone, the Church receives from God His life and gives t« God its life, in worship and service. The thesis seeks to recover the historic, distinctive prominence of this doctrinal and devotional theme in Anglican religion

Urban poachers : cosplay, playful cultures, and the appropriation of urban space

This article considers cosplayers’ use and transformation of urban space. Cosplay provides an important subcultural embodiment of contemporary popular culture, through which we can learn a great deal about contemporary forms of fandom, participatory culture and (mostly notably here) urban appropriation. This article draws on data gathered from a four-year ethnographic study, but here specifically looks at a small cosplay community that regularly meets in a park in Manchester. The article argues that a useful way of understanding cosplay is to consider the relationship between play and culture. In particular, the article sets out a consideration of how cosplayers transform social spaces through the use of process of synecdoche and asyndeton, which link together and edit out parts of the built environment – or what we term ‘urban poaching’