Dynamical analysis of spatial interaction models

We develop a novel dynamical method to examine spatial interaction models (SIMs). For each SIM, we use our dynamical framework to model emigration patterns. We look at the resulting population distributions to see if they are realistic or not. We use the US census data from 2010 and various spatial statistics to access the success or failure of each model. While we looked at over eighty different SIMs, we will focus here on two examples: the production constrained gravity model and the Radiation model. The results suggest that all these models fail to produce realistic population distributions and we identify the flaws within existing models. This leads us to suggest that we should define site attractiveness in terms of a second short range SIM leading to a new spatial interaction model - the Two-Trip model - which offers significant improvements when examined via our method. We also note that our Two-Trip adaptation can be used in any spatial modelling contexts, not just emigration

Type-Inference Based Short Cut Deforestation (nearly) without Inlining

Deforestation optimises a functional program by transforming it into another one that does not create certain intermediate data structures. In [ICFP'99] we presented a type-inference based deforestation algorithm which performs extensive inlining. However, across module boundaries only limited inlining is practically feasible. Furthermore, inlining is a non-trivial transformation which is therefore best implemented as a separate optimisation pass. To perform short cut deforestation (nearly) without inlining, Gill suggested to split definitions into workers and wrappers and inline only the small wrappers, which transfer the information needed for deforestation. We show that Gill's use of a function build limits deforestation and note that his reasons for using build do not apply to our approach. Hence we develop a more general worker/wrapper scheme without build. We give a type-inference based algorithm which splits definitions into workers and wrappers. Finally, we show that we can deforest more expressions with the worker/wrapper scheme than the algorithm with inlining

Contactless payments :usability at the cost of security?

PhD ThesisEMV (Europay, MasterCard, Visa), commonly termed “Chip & PIN”, is becoming the dominant card based payment technology globally. The EMV Chip & PIN transaction protocol was originally designed to operate in an environment where the card was physically inserted into the POS terminal / ATM and used a wired connection to communicate. The introduction of EMV contactless payments technology raises an interesting question “has usability been improved at the cost of security?”. Specifically, to make contactless payments more convenient / usable, a wireless interface has been added to EMV cards and PIN entry has been waived for contactless payments. Do these new usability features make contactless cards less secure? This PhD thesis presents an analysis of the security of the EMV contactless payments. It considers the security of the EMV contactless transaction protocols as stand-alone processes and the wider impact of contactless technology upon the security of the EMV card payment system as a whole. The thesis contributes a structured analysis methodology which identifies vulnerabilities in the EMV protocol and demonstrates the impact of these vulnerabilities on the EMV payment system. The analysis methodology comprises UML diagrams and reference tables which describe the EMV protocol sequences, a protocol emulator which implements the protocol, a Z abstract model of the protocol and practical demonstrations of the research results. Detailed referencing of the EMV specifications provide a documented link between the exploitable vulnerabilities observed in real EMV cards and the source of the vulnerability in the EMV specifications. Our analysis methodology has identified two previously undocumented vulnerabilities in the EMV contactless transaction protocol. The potential existence of these vulnerabilities was identified using the Z abstract model with the protocol emulator providing experimental confirmation of the potential for real-world exploitation of the vulnerabilities and test results quantifying the extent of the impact. Once a vulnerability has been shown to be exploitable using the protocol emulator, we use practical demonstrations to show that these vulnerabilities can be exploited in the real-world using off-the-shelf equipment. This presents a stronger impact message when presenting our research results to a nontechnical audience. This has helped to raise awareness of security issues relating to EMV contactless cards, with our work appearing in the media, radio and TV

Optimal management of an insurer's exposure in a competitive general insurance market

The qualitative behavior of the optimal premium strategy is determined for an insurer in a finite and an infinite market using a deterministic general insurance model. The optimization problem leads to a system of forward-backward differential equations obtained from Pontryagin’s Maximum Principle. The focus of the modelling is on how this optimization problem can be simplified by the choice of demand function and the insurer’s objective. Phase diagrams are used to characterize the optimal control. When the demand is linear in the relative premium, the structure of the phase diagram can be determined analytically. Two types of premium strategy are identified for an insurer in an infinite market, and which is optimal depends on the existence of equilibrium points in the phase diagram. In a finite market there are four more types of premium strategy, and optimality depends on the initial exposure of the insurer and the position of a saddle point in the phase diagram. The effect of a nonlinear demand function is examined by perturbing the linear price function. An analytical optimal premium strategy is also found using inverse methods when the price function is nonlinear

Exploring the anthelmintic properties of Australian native shrubs with respect to their potential role in livestock grazing systems

We measured in vitro anthelmintic activity in extracts from 85 species of Australian native shrub, with a view to identifying species able to provide a degree of worm control in grazing systems. Approximately 40% of the species showed significant activity in inhibiting development of Haemonchus contortus larvae. The most active extracts showed IC50 values of 60–300 mg/ml. Pre-incubation with polyvinylpolypyrrolidine removed the activity from some extracts, implicating tannins as the bioactive agent, while in other cases the pre-incubation had no effect, indicating the presence of other anthelmintic compounds. Plant reproductive maturity (onset of flowering or fruiting) was associated with increasing anthelmintic activity in some species. Variability was observed between plants of the same species growing in different environments, while variation between individual plants of the same species within a single field suggests the existence of distinct chemotypes. Significant activity against adult H. contortus worms in vitro was also demonstrated in a limited number of extracts tested against this life stage. Our study indicates that there is potential for Australian native shrubs to play an anthelmintic role in grazing systems, and highlights some plant biology factors which will need to be considered in order to maximize any anthelmintic effects.A. C. Kotze, J. O’Grady, J. Emms, A. F. Toovey, S. Hughes, P. Jessop, M. Bennell P. E. Vercoe and D. K. Revel

Making Decisions to Identify Forage Shrub Species for Versatile Grazing Systems

Grazing systems in many parts of the world face large challenges, including a declining natural resource base (e.g. soil fertility), marked fluctuations in feed production across seasons and years, climate change (including the contribution of greenhouse gases from livestock), and market demands for sustainable and ethical production systems. The ‘Enrich’ project was established in Australia (Revell et al. 2008; Bennell et al. 2010) within this broad context of emerging challenges to explore the potential of using Australian native perennial shrub species as part of the feedbase for sheep and cattle in southern Australia. The underlying rationale was to: add perennial shrub species into the existing annual-based pasture feedbase so that the forage system could tolerate extended dry periods but provide green edible plant material during periods where a ‘feed gap’ would otherwise exist; be productive on marginal soils where other productive options are limited (Masters et al. 2010); and have a positive effect on gut function and health (Vercoe et al. 2007); i.e. a versatile grazing system. This paper outlines the research approach that was taken, and reports on a ‘decision tree’ to prioritise species from an initial large list, based on a wide range of plant characteristics and how they can be used in a grazing system

Mitigation of carbon using Atriplex nummularia revegetation

The use of abandoned or marginally productive land to mitigate greenhouse gas emissions may avoid competition with food and water production. Atriplex nummularia Lindl. is a perennial shrub commonly established for livestock forage on saline land, however, its potential for carbon mitigation has not been systematically evaluated. Similarly, although revegetation is an allowable activity to mitigate carbon within Article 3.4 of the United Nations Framework Convention on Climate Change's Kyoto Protocol, there is a paucity of information on rates of carbon mitigation in soils and biomass through this mechanism. For six sites where A. nummularia had been established across southern Australia four were used to assess changes in soil carbon storage and four were used to develop biomass carbon sequestration estimates. A generalised allometric equation for above and below ground biomass was developed, with a simple crown volume index explaining 81% of the variation in total biomass. There were no significant differences in soil organic carbon storage to 0.3 m or 2 m depth compared to existing agricultural land-use. Between 2.2 and 8.3 Mg C ha−1 or 0.2–0.6 Mg C ha−1 yr−1 was sequestered in above and below ground biomass and this translates to potential total sequestration of 1.1–3.6 Tg C yr−1 on saline land across Australia. Carbon income and forage grazing may thus provide a means to finance the stabilization of compromised land

Simulation of water-limited growth of the forage shrub saltbush (Atriplex nummularia Lindl.) in a low-rainfall environment of southern Australia

Old man saltbush (Atriplex nummularia Lindl.) is a useful forage shrub for livestock in the low-rainfall areas of the world, and particularly in Australia. In these semi-arid and arid environments, saltbush is valuable for increasing the production from otherwise marginal areas of the farm and during drought periods when there are few feed alternatives. The ability to predict the growth and development of perennial forages such as old man saltbush in response to rainfall, soils and farm management is necessary for farming system planning and design purposes. A field experiment was conducted at Waikerie, South Australia, to inform the development of a new forage shrub model for use in the APSIM framework. The model takes into account the common setup of saltbush plantations in alley systems, by simulating light interception and water uptake for interacting shrub and inter-row zones separately. This is done by modelling the canopy and root system development. Field data across three soil types along a landscape catena showed that the model was able to satisfactorily predict daily biomass accumulation, partitioning into leaf and woody biomass, and regrowth after grazing. The model was sensitive to properties associated with the root system, and with limited parameterisation can be tailored to simulate different clonal cultivars. The model can now be used in the APSIM framework to assess temporal and spatial dynamics of forage systems combining shrubs with herbaceous pasture components