Counterexample Guided Abstraction Refinement Algorithm for Propositional Circumscription

Circumscription is a representative example of a nonmonotonic reasoning inference technique. Circumscription has often been studied for first order theories, but its propositional version has also been the subject of extensive research, having been shown equivalent to extended closed world assumption (ECWA). Moreover, entailment in propositional circumscription is a well-known example of a decision problem in the second level of the polynomial hierarchy. This paper proposes a new Boolean Satisfiability (SAT)-based algorithm for entailment in propositional circumscription that explores the relationship of propositional circumscription to minimal models. The new algorithm is inspired by ideas commonly used in SAT-based model checking, namely counterexample guided abstraction refinement. In addition, the new algorithm is refined to compute the theory closure for generalized close world assumption (GCWA). Experimental results show that the new algorithm can solve problem instances that other solutions are unable to solve

Deciding to enter tertiary education and taking on debt : a longitudinal perspective

This thesis describes a program of research designed to investigate longitudinally the role of debt in a cohort of 1232 final-year New Zealand secondary school students, their tertiary entry decisions and their attitudes towards tertiary education and student debt. It follows some of these students into their first year out of school into tertiary education or otherwise. Two surveys were conducted that employed the Attitude to Debt Scale (Davies and Lea, 1995) to address students’ debt and savings behaviour and estimates, tertiary education entry decisions, and attitudes to tertiary education and term-time working. Debt attitudes are found to be more complex than previously proposed, and this has significant ramifications for debt attitude theory and research. Longitudinal comparisons suggest students’ views regarding debt necessity does not change but their attitude to avoiding does. Students become more or less avoidant of debt depending on their circumstances. However, debt attitude results still support many of the findings of earlier research such as debt acquisition preceding a more tolerant attitude change. Debt and tertiary education attitudes are not well predicted. Students report engaging in term-time working to limit their student loans, but engaging in term-time working results in lower grades in their studies. Those from the middle and higher socio-economic classes are more likely to be positive towards tertiary education, and thus entrants, compared with the lower socio-economic classes. However, the results do not suggest this is due to debt attitudes or fear of debt

The moderating influences on the relationship of corporate reputation with its antecedents and consequences: a meta-analytic review

Through a meta-analytical approach, we test the antecedents and consequences of corporate reputation, examining specifically the moderating roles of three study variables: country of study, stakeholder group, and reputational measure. The study presents a comprehensive overviewof threemoderating factors for the relationship of corporate reputation with its antecedents and consequences in the literature from 101 quantitative studies. Our findings suggest that practitioners need to exercise considerable caution when developing and managing the reputation of their organizations through the use of research evidence from various countries, with different stakeholder groups and when employing diverse reputational measures

On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM