Methodological and empirical challenges in modelling residential location choices

The modelling of residential locations is a key element in land use and transport planning. There are significant empirical and methodological challenges inherent in such modelling, however, despite recent advances both in the availability of spatial datasets and in computational and choice modelling techniques. One of the most important of these challenges concerns spatial aggregation. The housing market is characterised by the fact that it offers spatially and functionally heterogeneous products; as a result, if residential alternatives are represented as aggregated spatial units (as in conventional residential location models), the variability of dwelling attributes is lost, which may limit the predictive ability and policy sensitivity of the model. This thesis presents a modelling framework for residential location choice that addresses three key challenges: (i) the development of models at the dwelling-unit level, (ii) the treatment of spatial structure effects in such dwelling-unit level models, and (iii) problems associated with estimation in such modelling frameworks in the absence of disaggregated dwelling unit supply data. The proposed framework is applied to the residential location choice context in London. Another important challenge in the modelling of residential locations is the choice set formation problem. Most models of residential location choices have been developed based on the assumption that households consider all available alternatives when they are making location choices. Due the high search costs associated with the housing market, however, and the limited capacity of households to process information, the validity of this assumption has been an on-going debate among researchers. There have been some attempts in the literature to incorporate the cognitive capacities of households within discrete choice models of residential location: for instance, by modelling households’ choice sets exogenously based on simplifying assumptions regarding their spatial search behaviour (e.g., an anchor-based search strategy) and their characteristics. By undertaking an empirical comparison of alternative models within the context of residential location choice in the Greater London area this thesis investigates the feasibility and practicality of applying deterministic choice set formation approaches to capture the underlying search process of households. The thesis also investigates the uncertainty of choice sets in residential location choice modelling and proposes a simplified probabilistic choice set formation approach to model choice sets and choices simultaneously. The dwelling-level modelling framework proposed in this research is practice-ready and can be used to estimate residential location choice models at the level of dwelling units without requiring independent and disaggregated dwelling supply data. The empirical comparison of alternative exogenous choice set formation approaches provides a guideline for modellers and land use planners to avoid inappropriate choice set formation approaches in practice. Finally, the proposed simplified choice set formation model can be applied to model the behaviour of households in online real estate environments.Open Acces

Z2SAL: a translation-based model checker for Z

Despite being widely known and accepted in industry, the Z formal specification language has not so far been well supported by automated verification tools, mostly because of the challenges in handling the abstraction of the language. In this paper we discuss a novel approach to building a model-checker for Z, which involves implementing a translation from Z into SAL, the input language for the Symbolic Analysis Laboratory, a toolset which includes a number of model-checkers and a simulator. The Z2SAL translation deals with a number of important issues, including: mapping unbounded, abstract specifications into bounded, finite models amenable to a BDD-based symbolic checker; converting a non-constructive and piecemeal style of functional specification into a deterministic, automaton-based style of specification; and supporting the rich set-based vocabulary of the Z mathematical toolkit. This paper discusses progress made towards implementing as complete and faithful a translation as possible, while highlighting certain assumptions, respecting certain limitations and making use of available optimisations. The translation is illustrated throughout with examples; and a complete working example is presented, together with performance data

A preliminary investigation of additive manufacture to fabricate human nail plate surrogates for pharmaceutical testing

In vitro permeation studies using nail clippings or nail plates are commonly used in the development of transungual formulations. However, there are ethical, safety and cost issues associated with sourcing such tissues. Herein, we describe a preliminary approach is described for the design and manufacture of a human nail model surrogate based on 3D printing. To evaluate these 3D printed constructs, nails were mounted in conventional glass Franz cells and a commercial antifungal lacquer formulation containing ciclopirox olamine was applied daily to the surrogate printed surfaces for a period of 14 days. On days 8 and 14, the surfaces of the 3D printed nails were washed with ethanol to remove excess formulation. Confocal Raman spectroscopy (CRS) was used to profile the drug in the 3D printed nail. At the end of the Franz cell studies, no drug was observed in the receptor phase. CRS studies confirmed penetration of the active into the model nails with reproducible depth profiles. Our ongoing work is focused on synthesising commercial and non-commercial printable resins that can replicate the physical and chemical characteristics of the human nail. This will allow further evaluation of actives for ungual therapy and advance the development of the surrogate nail tissue model

Unlocking the black box: line managers and HRM performance in a call centre context

Purpose – The purpose of this paper is to show the way to unlock the black box of HRM and performance linkages by exploring one of the key variables that mediates the link, namely whether line managers can stimulate improvements in firm performance by eliciting appropriate employee outcomes in a call centre context. Design/methodology/approach – The research draws on Purcell's "People-Performance Model" as a sensitising framework to inform an in-depth case study of a call centre. This provides a mechanism to unlock the HRM-Performance black box by focusing on the ability, motivation and opportunities for line managers to perform and any subsequent impact on employee outcomes. Data were collected over multiple site visits by means of multi-level interviews and a survey of telesales representatives (TSRs). Findings – Research findings indicate that one large client exerted significant control over the HRM policies developed within the call centre. Evidence suggests, however, that line managers'interventions ameliorated some of the negative aspects of work tasks and the HRM imposed by this dependency relationship. Research limitations/implications – This research is an exploratory attempt to better understand HRM-Performance linkages in one specific context. Results are not generalisable across contexts or even within call centres, which can vary extensively. Nonetheless, the research suggests that exploring line management behaviour is a promising avenue for more extensive research. Originality/value – This paper considers HRM-Performance linkages in a service context. Results indicate that both external relations and line managers are critical mediating variables conditioning HRM-Performance linkages, thereby lending support to the notion that hard and soft HRM practices are not necessarily irreconcilable

Speech vocoding for laboratory phonology

Using phonological speech vocoding, we propose a platform for exploring relations between phonology and speech processing, and in broader terms, for exploring relations between the abstract and physical structures of a speech signal. Our goal is to make a step towards bridging phonology and speech processing and to contribute to the program of Laboratory Phonology. We show three application examples for laboratory phonology: compositional phonological speech modelling, a comparison of phonological systems and an experimental phonological parametric text-to-speech (TTS) system. The featural representations of the following three phonological systems are considered in this work: (i) Government Phonology (GP), (ii) the Sound Pattern of English (SPE), and (iii) the extended SPE (eSPE). Comparing GP- and eSPE-based vocoded speech, we conclude that the latter achieves slightly better results than the former. However, GP - the most compact phonological speech representation - performs comparably to the systems with a higher number of phonological features. The parametric TTS based on phonological speech representation, and trained from an unlabelled audiobook in an unsupervised manner, achieves intelligibility of 85% of the state-of-the-art parametric speech synthesis. We envision that the presented approach paves the way for researchers in both fields to form meaningful hypotheses that are explicitly testable using the concepts developed and exemplified in this paper. On the one hand, laboratory phonologists might test the applied concepts of their theoretical models, and on the other hand, the speech processing community may utilize the concepts developed for the theoretical phonological models for improvements of the current state-of-the-art applications

Modelling and verifying dynamic access control policies in workflow-based healthcare systems

Access control system is an important component to protect patients’ information from abuse in a health care system. It is a major concern in the management, design, and development of healthcare systems. Designing access control policies for healthcare systems is complicated due to the dynamic and inherent complexity of the tasks performed by the healthcare personnel. Permissions in access control systems are usually granted on the basis of static policies. However, static policies are not enough to cope with various situations such as emergencies. Most often, the Break-the-glass mechanism is used to bypass static policies to handle emergency situations. Since healthcare systems are critical systems, where errors can be very costly in terms of lives, quality of life, and/or dollars, it is crucial to identify discrepancies between policy specifications and their intended function to implement correctly a flexible access control system. Formal verifications are necessary for exhaustive verification and validation of policy specifications to ensure that the policy specifications truly encapsulate the desires of the policy authors. We present a verifiable framework to enact a dynamic access control model by integrating the ANSI/INCTIS RBAC Reference Model in a workflow and an approach for property verifications of the access control model. Access control policies are expressed by the formal semantics of a model checker and properties are verified by the DiVinE model checker

Computer-aided circuit design during the initial stages

Imperial Users onl