Nearly sign-nonsingular matrices

AbstractA real matrix A is nearly sign-nonsingular if every term in the expansion of det A but one has the same sign. We show such matrices can be put into a normal form in which all diagonal entries are negative, all other nonzero entries are positive, and the directed graph of the matrix is intercyclic. With the help of recent results of Metzlar, McCuaig, and Thomassen on intercyclic digraphs, we are able to separate the nearly sign-nonsingular matrices into five classes and to characterize each of these classes. We also obtain two results showing where real matrices having intercyclic digraphs can or cannot be signed in such a way as to belong both to the class of sign-nonsingular matrices and the class of nearly sign-nonsingular matrices

Information literacy and informed learning: conceptual innovations for IL research and practice futures

Our paper draws together conceptual innovations emerging from the work of a group of researchers focussed on the relational approach to information literacy, more recently labelled ‘informed learning’. Team members have been working together in various configurations for periods ranging from seven to seventeen years. Our collaborative approach continues to yield new concepts and constructs which we believe to be of value to ongoing research and practice. Some of the ideas discussed have been previouly published, while others are being put forward for the first time. All are significant in that they together form new constructs that have emerged from a focus on the relational approach to information literacy. In this paper, Christine Bruce introduces the background to this work and the contributing researchers. Then the individual authors present the key directions which they have developed and are leading, typically working with one or more of the wider network. The key ideas presented are: The expressive window for information literacy (Mandy Lupton); information experience design (Elham Sayyad Abdi); cross-contextuality and experienced identity (Andrew Demasson); informed learning design (Clarence Maybee); spaces for inclusive informed learning (Hilary Hughes); and informed systems (Mary Somerville and Anita Mirjamdotter). In each piece, authors reflect on what the idea is about, where it came from and what it might mean for research and practice

Motivating learners through information literacy

This paper is included in the Information Literacy: Key to an Inclusive Society, the proceedings of the European Conference on Information Literacy, 2016. The paper introduces a model for creating information literacy learning activities that motivate students. The model draws from informed learning, an approach to information literacy that emphasizes the role that information plays in fostering learning about a subject. Self-determination theory, a motivational theory that focuses on enabling self-determined learners, is applied within the informed learning framework. The results of the investigation outline characteristics of motivating learning activities that enable learning subject content through engagement with information. The model is intended to be used by librarians when working with classroom teachers to foster greater student learning gains through creative and reflective engagement with information

Wind shear effects in convection–permitting models influence MCS rainfall and forcing of tropical circulation

Mesoscale Convective Systems (MCSs) play a critical role in tropical rainfall patterns and circulations. To reduce persistent biases and improve understanding of the climate system, international groups have called for unprecedented investment in global convection–permitting (CP) climate models. It is essential such models accurately represent MCSs, and in particular environmental interactions such as dynamical control by wind shear. We show that in representative current generation CP simulations, MCS updraft entrainment decreases with shear, leading to a realistic increase of extreme rainfall. We find the control of environmental shear extends to mean storm rainfall and anvil heights. The simulation of these effects depends strongly on model physics in both CP and parameterized models. We show that in West Africa, MCS shear response influences the zonal distribution of storm diabatic heating, modifying upscale impacts of convection. Our results demonstrate key tests for focused process–based assessment of CP model fidelity

Topology and Wilson lines: global aspects of the double copy

The Kerr-Schild double copy relates exact solutions of gauge and gravity theories. In all previous examples, the gravity solution is associated with an abelian-like gauge theory object, which linearises the Yang-Mills equations. This appears to be at odds with the double copy for scattering amplitudes, in which the non-abelian nature of the gauge theory plays a crucial role. Furthermore, it is not yet clear whether or not global properties of classical fields - such as non-trivial topology - can be matched between gauge and gravity theories. In this paper, we clarify these issues by explicitly demonstrating how magnetic monopoles associated with arbitrary gauge groups can be double copied to the same solution (the pure NUT metric) in gravity. We further describe how to match up topological information on both sides of the double copy correspondence, independently of the nature of the gauge group. This information is neatly expressed in terms of Wilson line operators, and we argue through specific examples that they provide a useful bridge between the classical double copy and the BCJ double copy for scattering amplitudes.Comment: 31 pages, 4 figures. Some minor corrections have been implemente

The Weyl double copy from twistor space

The Weyl double copy is a procedure for relating exact solutions in biadjoint scalar, gauge and gravity theories, and relates fields in spacetime directly. Where this procedure comes from, and how general it is, have until recently remained mysterious. In this paper, we show how the current form and scope of the Weyl double copy can be derived from a certain procedure in twistor space. The new formalism shows that the Weyl double copy is more general than previously thought, applying in particular to gravity solutions with arbitrary Petrov types. We comment on how to obtain anti-self-dual as well as self-dual fields, and clarify some conceptual issues in the twistor approach

Power investment decisions under uncertain carbon policy: The effect of anticipated repeal and reinstatement of regulations

Political uncertainty over global greenhouse gas (GHG) mitigation policy is likely to defer investment in cleaner technologies. It may also incentivise short-lived, high-cost interim investments while businesses wait for the uncertainty to subside. The range of possible policy responses to the issue has created uncertainty over the future of national mitigation pathways. Given that the electricity sector, globally, is a major emitter of GHGs, this represents a systematic risk to investment in electricity generation assets. This paper uses a real options analysis framework informed by a survey of experts conducted in Australia - used as a proxy to model the degree of the uncertainty- to investigate the optimal timing for investment in the conversion of a coal plant to a combined cycle gas turbine plant using the American-style option valuation method. The effect of market and political uncertainty is studied for the Clean Energy Act 2011 in Australia. Political uncertainty is addressed bimodally in terms of: (1) uncertainty over the repeal of the carbon pricing policy, and (2) if it is repealed, uncertainty over the reinstatement of the policy, to represent the effect of electoral cycles and the possibility of more stringent future global mitigation efforts. Results of the analysis show that although political uncertainty with respect to GHG mitigation policy may delay investment in the conversion of the coal plant, expectations over the reinstatement of the carbon pricing reduces the amount of option premium to defer the conversion decision

An extension of portfolio theory in selecting projects to construct a preferred portfolio of petroleum assets

Advances in decision analysis have seen the oil and gas sector adapt its approach to project evaluation and selection through the inclusion of the principles of modern portfolio theory (MPT). Several studies have highlighted how MPT can be applied to optimise a portfolio of upstream oil and gas projects. This provides a useful framework for E&P managers who are seeking to identify the combination of projects that lie on the efficient frontier, where portfolios are structured to maximise total return for a given level of risk. This paper builds on previous research undertaken in this area. It expands the investment set and incorporates real life constraints associated with the available capital budget and investment size in the portfolio optimisation. These are not considered in traditional Markowitz portfolio theory and are typically overlooked in its application within the upstream oil and gas sector.Producing projects are significantly de-risked relative to exploration projects. While their standard deviation is not absolutely zero, producing projects have significantly lower variability in their returns than exploration projects, and can be likened to risk-free assets. Their inclusion in the portfolio optimisation results in the construction of a capital market line (CML) that dominates over portfolios along the efficient frontier. The subsequent introduction of the available capital budget and investment size constraints is shown to modify the CML, and we introduce the concept of a ‘Limited CML’. Unlike the CML or traditional efficient frontier, not all portfolios along this curve are efficient. Instead, efficient portfolios are only observed up to a given level of risk (referred to as the ‘vertex’). Beyond this level, additional risk is no longer value-accretive, and the expected return for these portfolios can be replicated by portfolios with lower standard deviations. Following construction of the ‘Limited CML’, a single preferred portfolio can be identified through the application of preference decision theory. We demonstrate how a company’s risk tolerance can be quantified for the purpose of constructing certainty equivalent curves. By overlaying these curves with the ‘Limited CML’ it is possible to identify a single preferred portfolio of E&P assets that is not only efficient, but also matches the targeted risk tolerance