Using Hybrid Agent-Based Systems to Model Spatially-Influenced Retail Markets

One emerging area of agent-based modelling is retail markets; however, there are problems with modelling such systems. The vast size of such markets makes individual-level modelling, for example of customers, difficult and this is particularly true where the markets are spatially complex. There is an emerging recognition that the power of agent-based systems is enhanced when integrated with other AI-based and conventional approaches. The resulting hybrid models are powerful tools that combine the flexibility of the agent-based methodology with the strengths of more traditional modelling. Such combinations allow us to consider agent-based modelling of such large-scale and complex retail markets. In particular, this paper examines the application of a hybrid agent-based model to a retail petrol market. An agent model was constructed and experiments were conducted to determine whether the trends and patterns of the retail petrol market could be replicated. Consumer behaviour was incorporated by the inclusion of a spatial interaction (SI) model and a network component. The model is shown to reproduce the spatial patterns seen in the real market, as well as well known behaviours of the market such as the "rocket and feathers" effect. In addition the model was successful at predicting the long term profitability of individual retailers. The results show that agent-based modelling has the ability to improve on existing approaches to modelling retail markets.Agents, Spatial Interaction Model, Retail Markets, Networks

The impact of repetitive unclamped inductive switching on the electrical parameters of low-voltage trench power nMOSFETs

The impact of hot-carrier injection (HCI) due to repetitive unclamped inductive switching (UIS) on the electrical performance of low-voltage trench power n-type MOSFETs (nMOSFETs) is assessed. Trench power nMOSFETs with 20- and 30-V breakdown voltage ratings in TO-220 packages have been fabricated and subjected to over 100 million cycles of repetitive UIS with different avalanche currents IAV at a mounting base temperature TMB of 150°C. Impact ionization during avalanche conduction in the channel causes hot-hole injection into the gate dielectric, which results in a reduction of the threshold voltage VGSTX, as the number of avalanche cycles N increases. The experimental data reveal a power-law relationship between the change in the threshold voltage ΔVGSTX and N. The results show that the power-law prefactor is directly proportional to the avalanche current. After 100 million cycles, it was observed in the 20-V rated MOSFETs that the power-law prefactor increased by 30% when IAV was increased from 160 to 225 A, thereby approximating a linear relationship. A stable subthreshold slope with avalanche cycling indicates that interface trap generation may not be an active degradation mechanism. The impact of the cell pitch on avalanche ruggedness is also investigated by testing 2.5- and 4- m cell-pitch 30-V rated MOSFETs. Measurements showed that the power-law prefactor reduced by 40% when the cell pitch was reduced by 37.5%. The improved VGSTX stability with the smaller cell-pitch MOSFETs is attributed to a lower avalanche current per unit cell resulting in less hot-hole injection and, hence, smaller VGSTX shift. The 2.5-m cell-pitch MOSFETs also show 25% improved on -state resistance RDSON, better RDSON stability, and 20% less subthreshold slope compared with the 4-m cell-pitch MOSFETs, although with 100% higher initial IDSS and less IDSS stability with avalanche cycling. These results are important for manufacturers of automotive MOSFETs where multiple avalanche occurrences over the lifetime of the MOSFET are expected

Creating realistic synthetic populations at varying spatial scales: A comparative critique of population synthesis techniques

There are several established methodologies for generating synthetic populations. These include deterministic reweighting, conditional probability (Monte Carlo simulation) and simulated annealing. However, each of these approaches is limited by, for example, the level of geography to which it can be applied, or number of characteristics of the real population that can be replicated. The research examines and critiques the performance of each of these methods over varying spatial scales. Results show that the most consistent and accurate populations generated over all the spatial scales are produced from the simulated annealing algorithm. The relative merits and limitations of each method are evaluated in the discussion

Modelling Individual Evacuation Decisions during Natural Disasters: A Case Study of Volcanic Crisis in Merapi, Indonesia

As the size of human populations increases, so does the severity of the impacts of natural disasters. This is partly because more people are now occupying areas which are susceptible to hazardous natural events, hence, evacuation is needed when such events occur. Evacuation can be the most important action to minimise the impact of any disaster, but in many cases there are always people who are reluctant to leave. This paper describes an agent-based model (ABM) of evacuation decisions, focusing on the emergence of reluctant people in times of crisis and using Merapi, Indonesia as a case study. The individual evacuation decision model is influenced by several factors formulated from a literature review and survey. We categorised the factors influencing evacuation decisions into two opposing forces, namely, the driving factors to leave (evacuate) versus those to stay, to formulate the model. The evacuation decision (to stay/leave) of an agent is based on an evaluation of the strength of these driving factors using threshold-based rules. This ABM was utilised with a synthetic population from census microdata, in which everyone is characterised by the decision rule. Three scenarios with varying parameters are examined to calibrate the model. Validations were conducted using a retrodictive approach by performing spatial and temporal comparisons between the outputs of simulation and the real data. We present the results of the simulations and discuss the outcomes to conclude with the most plausible scenario

The unseen cost of falls: the environmental impact of attending falls call out by the emergency ambulance services

Falls in older people are a major public health problem. This has major consequences to the individual, which can ultimately lead to injury, functional decline, psycho-social impairment and increased risk of mortality. It is also a major burden on healthcare resources. In the United Kingdom (UK), falls account for 3% (about £980 million) of the total National Health Service (NHS) expenditure [1] and the prevention of falls in older people has been highlighted as a priority area [2] and [3]. Older people commonly call out an emergency ambulance following a fall. This group account for 8% of emergency ambulance responses, which is similar to the proportion reported in Australia [4] and an urban Emergency Medical Service system in USA [5]. Transfer of these patients to the emergency department is also high, close to 60% and account for 60,000 of attendances in the UK [6], with similar proportions in the USA [7] and as high as 75% in Australia [4]. Previous studies examining healthcare cost of falls suggest costs of approximately £2000–£3000 per faller, with hospital costs accounting from 50% to 80% of these costs [8] and [9]. Global warming is becoming an increasing concern. In a natural carbon cycle, carbon dioxide is re-absorbed by plants and trees but this excess has now reached dangerous levels not seen in the last 3 million years and has led to an overall rise in atmospheric temperature-global warming. The transportation sector is the second largest source of anthropogenic carbon dioxide emissions. Transporting goods and people around the world produced 22% of fossil fuel related carbon dioxide emissions in 2010. Since the 1990s, transport related emissions have grown rapidly, increasing by 45% in less than 2 decades. Road traffic accounts for 74% of this sector's carbon dioxide emissions. Automobiles, freight and light-duty trucks are the main sources of emissions for the whole transport sector and emissions from these three have steadily grown since 1990 [10]. The NHS itself accounts for 3% of the UK's carbon footprint, which makes it a bigger polluter than some small countries [11]. The direct contribution related to the ambulance service and more specifically to falls is unknown. The aim of this study was to assess the environmental implication of falls in older people who call out an emergency ambulance

An assessment of the welfare of non-human primates used in neuroscience research

The Animals (Scientific Procedures) Act 1986 governs the use of animals in scientific research in the UK. Embedded within this is a requirement to implement the 3Rs: replacement, reduction, and refinement; a key mechanism for minimising the pain, suffering, distress, and lasting harm of research models. To adhere fully to these principles, it is imperative to assess animal welfare. Non-human primates (NHP) human similarities make them both an essential biomedical research model and a species particularly vulnerable to welfare challenges. This thesis investigates non-invasive, objective methods of welfare assessment and applies them alongside neuroscience research to monitor the welfare of rhesus macaques (Macaca mulatta). Accelerometers monitored changes in activity levels following general anaesthesia (GA) and revealed a decline in activity for 5.7 days following GA alone. Additionally, 2.6 days of activity decline were observed after surgery under GA, followed by an activity increase, suggesting post-operative behavioural change. Additionally, accelerometers were used to create a rule-based model for automated behavioural assessment. This model groups macaque activity into 5 species-typical behavioural categories with an overall 69% accuracy. Physiological welfare parameters were assessed by detecting cortisol in faeces and hair. Faecal cortisol levels were significantly elevated for several days following GA, with a longer and more profound increase after surgery. Hair samples are a valuable measure of chronic stress and cumulative experience, facilitating longitudinal cortisol assessment without influence from transient stressors. Hair cortisol levels were significantly elevated post-surgery and, in some cases, following social disruption. A customised, neck-based ECG was designed to monitor heart rate variability. The ECG was trialled on anaesthetised and restrained NHPs, dogs, and sheep. Proof of concept was achieved, with R-waves detectable in all species. Overall, this thesis demonstrates how welfare and neuroscience research can be conducted in parallel for a better understanding of the life-time experience of animal models. This is an essential step towards implementing refinements and improving welfare, which may ultimately improve public perception and help to form the evidence-base required to inform and drive policy change

When is rotational angiography superior to conventional single-plane angiography for planning coronary angioplasty?

Objectives: To investigate the value of rotational coronary angiography (RoCA) in the context of percutaneous coronary intervention (PCI) planning. Background: As a diagnostic tool, RoCA is associated with decreased patient irradiation and contrast use compared with conventional coronary angiography (CA) and provides superior appreciation of three-dimensional anatomy. However, its value in PCI remains unknown. Methods: We studied stable coronary artery disease assessment and PCI planning by interventional cardiologists. Patients underwent either RoCA or conventional CA pre-PCI for planning. These were compared with the referral CA (all conventional) in terms of quantitative lesion assessment and operator confidence. An independent panel reanalyzed all parameters. Results: Six operators performed 127 procedures (60 RoCA, 60 conventional CA, and 7 crossed-over) and assessed 212 lesions. RoCA was associated with a reduction in the number of lesions judged to involve a bifurcation (23 vs. 30 lesions, P < 0.05) and a reduction in the assessment of vessel caliber (2.8 vs. 3.0 mm, P < 0.05). RoCA improved confidence assessing lesion length (P = 0.01), percentage stenosis (P = 0.02), tortuosity (P < 0.04), and proximity to a bifurcation (P = 0.03), particularly in left coronary artery cases. X-ray dose, contrast agent volume, and procedure duration were not significantly different. Conclusions: Compared with conventional CA, RoCA augments quantitative lesion assessment, enhances confidence in the assessment of coronary artery disease and the precise details of the proposed procedure, but does not affect X-ray dose, contrast agent volume, or procedure duration. © 2015 Wiley Periodicals, Inc

Page Ranking Systems: Axiomatisation and Experimentation

Ranking a set of objects based on the relationships between them is fundamental for use with search engines, e-commerce websites and in the field of bibliometrics. Two of the most prominent search ranking algorithms are PageRank and SALSA (Stochastic Approach to Link-Structure Analysis). In this thesis, we further explore the connections between page ranking algorithms and the theory of social choice, providing a basis for theoretical assessment of a weighted version of PageRank and we create and assess a new page ranking al- gorithm, combining ideas from both PageRank and SALSA which we call Query- Independent SALSA. We justify the use of weighted PageRank from a theoretical perspective by providing a set of axioms which characterize the algorithm. We provide a tighter bound for our derivation than that of Altman et al and show that each of our axioms are independent. We describe a query-independent version of SALSA, using ideas from the PageRank algorithm and test this on a real-world subgraph of the web graph. We find that our new algorithm, Query-Independent Stochastic Approach to Link-Structure Analysis (QISALSA) slightly outperforms PageRank on two measures and under-performs on one measure. We suggest that the approach of combining aspects of both algo-rithms may be less eective than precomputational methods for query-dependent algorithms