30 research outputs found
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Numerical Modelling of Dynamic Resistance in a Parallel-Connected Stack of HTS Coated-Conductor Tapes
Dynamic resistance is observed in type-II superconductors carrying a DC transport current while simultaneously exposed to an alternating magnetic field. The appearance of a nonzero resistance is attributed to the interaction between the transport current and moving fluxons. This effect is relevant to many superconductor applications such as high-temperature-superconductor (HTS) flux pumps, DC / AC magnets, synchronous machines, and persistent current switches. Here, we present a finite element method (FEM) analysis of both the time averaged dynamic resistance and the instantaneous current sharing behaviour
in a cable comprised of a stack of four YBCO thin films connected in parallel. Numerical modelling was performed using the H-formulation method implemented in the commercial software COMSOL. The model employs experimentally measured values of the angular dependence of the critical current Ic(B, θ) and the flux creep exponent n(B, θ). A single threshold field is observed, above which a finite dynamic resistance is observed in all tapes simultaneously. The time-averaged dynamic resistance of individual tapes tends to be larger for the exterior tapes than the interior tapes, but this difference decreases as the total transport current in the cable increases. We attribute this to shielding currents flowing in the exterior tapes during the majority of the cycle, which displace net DC current into the interior tapes. However, the relative proportion of DC transport current flowing in the exterior and interior
tapes is also observed to vary periodically once per half cycle of the
applied field. This is due to the periodic trapping of return screening currents in the interior tapes.New Zealand MBIE Endeavour Grant No. RTVU1707 and NZ Royal Society Marsden Grant No. MFP-VUW180
The Role of Individual Variables, Organizational Variables and Moral Intensity Dimensions in Libyan Management Accountants’ Ethical Decision Making
This study investigates the association of a broad set of variables with the ethical decision making of management accountants in Libya. Adopting a cross-sectional methodology, a questionnaire including four different ethical scenarios was used to gather data from 229 participants. For each scenario, ethical decision making was examined in terms of the recognition, judgment and intention stages of Rest’s model. A significant relationship was found between ethical recognition and ethical judgment and also between ethical judgment and ethical intention, but ethical recognition did not significantly predict ethical intention—thus providing support for Rest’s model. Organizational variables, age and educational level yielded few significant results. The lack of significance for codes of ethics might reflect their relative lack of development in Libya, in which case Libyan companies should pay attention to their content and how they are supported, especially in the light of the under-development of the accounting profession in Libya. Few significant results were also found for gender, but where they were found, males showed more ethical characteristics than females. This unusual result reinforces the dangers of gender stereotyping in business. Personal moral philosophy and moral intensity dimensions were generally found to be significant predictors of the three stages of ethical decision making studied. One implication of this is to give more attention to ethics in accounting education, making the connections between accounting practice and (in Libya) Islam. Overall, this study not only adds to the available empirical evidence on factors affecting ethical decision making, notably examining three stages of Rest’s model, but also offers rare insights into the ethical views of practising management accountants and provides a benchmark for future studies of ethical decision making in Muslim majority countries and other parts of the developing world
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Processing and application of high-temperature superconducting coated conductors
Synthesis of Highly Magnetic Iron Carbide Nanoparticles via a Biopolymer Route
In this article, we report a facile, one-pot route to phase-pure Fe3C nanoparticles (mean diameter = 20 nm) that show a remarkably high saturation magnetization (∼130 emu/g), higher than iron oxide (Fe3O4) and comparable to that of bulk Fe3C (∼140 emu/g). A readily available biopolymer (gelatin) is used as a matrix to disperse an aqueous iron acetate precursor. On heating, the biopolymer induces nucleation of magnetite (Fe3O4) nanoparticles before decomposing to form a carbon-rich matrix. This then acts as a reactive template for carbothermal reduction of the magnetite nanoparticles to Fe3C at a moderate temperature of 650 °C. This method represents a considerable advance over previous reports that often use high-energy procedures or costly and hazardous precursors. These homogeneous, highly magnetic nanoparticles have many potential applications in biomedicine and catalysis