The construction and testing of an IR absorption metric for high speed sintering

High Speed Sintering (HSS) is a new and innovative Rapid Manufacturing (RM) process that enables the manufacture of complex 3D geometries from polymer powders. The process utilises an ink jet print-head, which selectively deposits a Radiation Absorbing Material (RAM) onto a preheated bed of Duraform Polyamide (PA) powder, thus creating regions of increased emissivity. These printed regions are then sintered using a short burst of thermal energy from an Infra-Red (IR) lamp; conversely, due to the difference in emissivity, unprinted regions remain as powders. The work presented within this thesis expands the knowledge surrounding the HSS process; wherein its main contribution is a validated procedure which tests the suitability of new RAMs for HSS through the analysis of their spectral emissivity. In developing the procedure for selecting new RAMs, it was first identified that for efficient energy transmission from one surface to another, the spectral emissivity of the transmitting surface must be well matched with that of the absorbing surface. This finding was applied to HSS, and consequently, it was suggested that for sintering to occur, the spectral emissivity of the IR lamp must be well matched with the spectral emissivity of the RAM and not the polymer powder. In order to investigate this, the spectral characteristics of the HSS IR lamp and a selection of RAMs were then determined, and an Energy Absorption Value (EAV), a value which quantified how well the spectra overlapped, was defined. The EAV was then validated through the manufacture of a series of tensile test specimens using each RAM, which were then tested for their mechanical properties and Degree of Particle Melt (DPM). Strong correlations were found between the EAV, DPM and each mechanical property. These results consequently validated the effectiveness of the EAV and its potential use to select new RAMs for HSS

A method for solving systems of non-linear differential equations with moving singularities

We present a method for solving a class of initial valued, coupled, non-linear differential equations with `moving singularities' subject to some subsidiary conditions. We show that this type of singularities can be adequately treated by establishing certain `moving' jump conditions across them. We show how a first integral of the differential equations, if available, can also be used for checking the accuracy of the numerical solution.Comment: 9 pages, 7 eps figures, to appear in Comput. Phys. Co

Phenomena exposure from the large scale gas injection test (Lasgit) dataset using a bespoke data analysis toolkit

The Large Scale Gas Injection Test (Lasgit) is a field-scale experiment designed to study the impact of gas buildup and subsequent migration through an engineered barrier system. Lasgit has a substantial experimental dataset containing in excess of 21 million datum points. The dataset is anticipated to contain a wealth of information, ranging from long-term trends and system behaviours to small-scale or ‘second-order’ features. In order to interrogate the Lasgit dataset, a bespoke computational toolkit, designed to expose difficult to observe phenomena, has been developed and applied to the dataset. The preliminary application of the toolkit, presented here, has resulted in a large number of phenomena being indicated/quantified, including highlighting of second-order events (small gas flows, perturbations in stress/pore-water sensors, etc.) and quantification of temperature record frequency content. Localized system behaviour has been shown to occur along with systematic aberrant behaviours that remain unexplained

Nucleon Generalized Parton Distributions and Holographic Models

Using ideas from Light Front Holography, we discuss the calculation of the nucleon helicity-independent generalized parton distributions of quarks in the zero skewness case.Comment: Prepared for LIGHTCONE 2011, 23 - 27 May, 2011, Dalla

Effect of infra-red power level on the sintering behaviour in the high speed sintering process

Purpose: To investigate the effects of the infra-red power level on sintering behaviour in the High Speed Sintering process. Design/methodology/approach: Single-layer parts were produced using the High Speed Sintering process, in order to determine the effect of the infra-red power level on the maximum achievable layer thickness, and the degree of sintering. The parts were examined using both optical microscopy and contact methods. Findings: Whilst it was expected that an increase in the infra-red lamp powder might allow an increase in the depth of sintering that could be achieved, as a result of increased thermal transfer through the powder, results in fact indicated that there is a maximum layer thickness that can be achieved, as a result of part shrinkage in the z direction. Optical microscopy images have shown that a greater degree of sintering occurs at higher power levels, which would be expected to correspond to an improvement in the mechanical properties of the parts produced. These images also indicate that the RAM forms in small ‘islands’ on the powder bed surface. However, these islands begin to merge as sintering progresses, to a greater degree as the infra-red lamp power is increased. Research limitations/implications: These results are based only on single layer parts. Further work will examine the sintering characteristics of multiple layer parts. Practical implications: Results have shown that, whilst it is not possible to increase the achievable layer thickness of the parts produced by modifying the infra-red lamp power, the degree of sintering can be improved greatly by increasing the power. Originality/value: High Speed Sintering is an entirely new process which is currently still under development; the results presented here will directly impact the direction of further development and research into this process

A fly in the buttermilk: Descriptions of university life by successful Black undergraduate students at a predominately white southeastern university

Although many predominantly white universities exert great effort to recruit minority students, statistics regarding retention and graduation for these students are disturbing. Previous research indicates that academic concerns are not paramount in the attrition of minority students, suggesting that greater attention must be given educational experiences of black students over and above academic matters. Using in-depth phenomenological interviewing, 11 graduating seniors from diverse majors were asked to describe salient incidents of their university experience. These interviews were transcribed verbatim and subjected to hermeneutic interpretation by an interdisciplinary research group. Dominant in student descriptions of their experiences were five themes: (1) It happens every day : Unfairness/Sabotage/Condescension; (2) You have to initiate the conversation ; (3) They seem the same; I\u27m the one who\u27s different ; (4) I have to prove I\u27m worthy to be here ; and (5) Sometimes I\u27m not even here/Sometimes I have to represent every black student : Invisibility and Supervisibility

Определение оптимальных параметров источника рентгеновского излучения на базе малогабаритного ускорителя электронов

Проведено моделирование спектров рентгеновского излучения, генерируемого электронами с энергией 4…10 МэВ в мишенях из различных материалов и разной толщины. Определены оптимальные параметры мишени-конвертора для использования ее в медицинских источниках монохроматического рентгеновского излучения на базе малогабаритных электронных ускорителей. Проведены оценки интенсивности излучения и сравнение источников на базе разных ускорителей

Beyond locutionary denotations: exploring trust between practitioners and policy

This study reports the findings of a research on the trust relationship between practitioners in the Skills for Life (SfL) area and the policy that informs their practice. The exploration of this relationship was premised on an extended notion of trust relationship which draws from the Speech Act theory of Austin (1962; Searle 1969; Kissine 2008), leading to the claim that the existence of different layers of imports in textual analysis makes it possible for a trust relationship to exist between the human/physical and the non human/non physical. The study found that the majority of practitioners in the SfL field trust policy to deliver its inherent policy only to a limited extent. Amongst others, the study identified the impact of the perlocutionary import of policy text on practitioners as a viable reason for this limited level of trust. Such perlocutionary imports, it also found, have adverse impact on practitioners who are considered to have drawn from previous experience to mediate the import of contemporary policies

SAT-Based Synthesis Methods for Safety Specs

Automatic synthesis of hardware components from declarative specifications is an ambitious endeavor in computer aided design. Existing synthesis algorithms are often implemented with Binary Decision Diagrams (BDDs), inheriting their scalability limitations. Instead of BDDs, we propose several new methods to synthesize finite-state systems from safety specifications using decision procedures for the satisfiability of quantified and unquantified Boolean formulas (SAT-, QBF- and EPR-solvers). The presented approaches are based on computational learning, templates, or reduction to first-order logic. We also present an efficient parallelization, and optimizations to utilize reachability information and incremental solving. Finally, we compare all methods in an extensive case study. Our new methods outperform BDDs and other existing work on some classes of benchmarks, and our parallelization achieves a super-linear speedup. This is an extended version of [5], featuring an additional appendix.Comment: Extended version of a paper at VMCAI'1