Stackings and One-Relator Products of Groups

The theory of one-relator groups (groups admitting a presentation with a single relator) has a selection of interesting open questions. For example, it is unknown exactly which torsion-free one-relator groups are coherent, or which are hyperbolic. One way in which these questions are currently being studied is by considering immersions of 2-complexes into a group’s presentation complex. The specific properties of interest are called non-positive immersions and negative immersions, which put restrictions on the Euler characteristic of the immersing space. In this thesis, we look more closely at these properties, and see how they have been used to study one-relator groups. We also consider one-relator products of groups, a generalisa- tion of one-relator groups where a defining relator is taken over a free product of groups rather than just a free group. We prove that one-relator products admit a stacking, which is a geometric object containing information about the relationship between the defining relator and the underlying free product of groups. We go on to use these stackings to prove that torsion-free one-relator products have the non- positive immersions property. This is a result that has also recently been proved by James Howie and Hamish Short. We discuss how our proof differs and how by using stackings we can find improvements for some of their results. Finally, we discuss the negative immersions property, its conjectural link to hyperbolicity, and how stackings may allow progress in the classification of which one-relator products have negative immersions

Re -inventing the "cry for help": attempted suicide in Britain in the mid-twentieth centuary c 1937-1969

PhDAfter 1945 in Britain there emerges an ‘epidemic’ of ‘attempted suicide’ that is read as not aiming at death exclusively, but is instead a form of communication – a ‘cry for help’. This ‘epidemic’ consists predominantly of young people (increasingly gendered female) who present at general hospitals after having taken an amount of medication that is deemed excessive, but insufficient to kill them. This thesis places this ‘epidemic’ into historical context by looking at two interlinked developments in healthcare provision in Britain. First, models of mental healthcare provision change. With mental health included in the NHS, provision slowly and unevenly moves away from the geographically remote asylum, and into general hospitals and ‘the community’. The legislative high point of this process is the 1959 Mental Health Act, removing all legal barriers to mental treatment in general hospitals. This enables consistent psychological scrutiny upon patients presenting at general hospitals. This is cemented by the Suicide Act 1961 which decriminalises suicide and attempted suicide, and is swiftly followed by a government memorandum asking hospitals to ensure that all ‘attempted suicide’ patients presenting at casualty receive psychiatric assessment. The second development is in psychiatric thought, moving towards a socially-focused model of the causation of mental disorder. This is underpinned by broad concepts of ‘mental stress’ which enable pathology to be located in social relationships and social situations. This is achieved through much intellectual and practical labour, with psychiatric social workers carrying out home visits and follow-up, as well as interviewing friends, relatives and even employers, in order to construct a ‘social constellation’ around the ‘overdose’. Thus, the increased scrutiny at general hospitals recasts that presenting ‘physical injury’ as a symptom of a disordered social situation, and a communication with a social circle: ‘a cry for help’, newly possible on a nationwide scale.Wellcome Trus

Facebook and the People in the Iron House: 非死不可？

“Maybe we will block content in some countries, but not others,” Adam Conner, a Facebook lobbyist, told the [Wall Street] Journal. “We are occasionally held in uncomfortable positions because now we’re allowing too much, maybe, free speech in countries that haven’t experienced it before,” he said

Predictive Fault Tolerance for Autonomous Robot Swarms

Active fault tolerance is essential for robot swarms to retain long-term autonomy. Previous work on swarm fault tolerance focuses on reacting to electro-mechanical faults that are spontaneously injected into robot sensors and actuators. Resolving faults once they have manifested as failures is an inefficient approach, and there are some safety-critical scenarios in which any kind of robot failure is unacceptable. We propose a predictive approach to fault tolerance, based on the principle of preemptive maintenance, in which potential faults are autonomously detected and resolved before they manifest as failures. Our approach is shown to improve swarm performance and prevent robot failure in the cases tested.Comment: This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

Conversational human-swarm interaction using IBM Cloud

Swarm robotics is an approach to the coordination of large numbers of robots that has become an increasingly popular field of research in recent years, not least because properly engineered robot swarms are scalable, flexible, and robust, making them an attractive alternative to single-robot systems in many application domains. Since its inception, the field of swarm robotics has grown beyond its roots in purely decentralised control inspired by social insect behaviour, now often utilising hybrid centralised/decentralised control architectures that incorporate human operators who guide swarm actions during tasks such as firefighting, or the localisation of radiation sources. This kind of human-swarm interaction has attracted significant interest from the research community, spawning an entire sub-field of its own that investigates how human operators, supervisors, and team-mates can interact with robot swarms and receive feedback from them. To date, human-swarm control methods such as the use of graphical user interfaces and spatial gestures have received much attention, but there has been little investigation into the potential of controlling swarm robotic systems with an operator’s voice. The few studies that have explored this idea are restricted to the use of specific predefined phrases that the human operator is required to learn, resulting in interactions that are unnatural in comparison to the way a human would normally express themselves in speech. In this paper, we present a novel architecture for conversational human-swarm interaction that addresses these issues, allowing swarm robotic systems to be engineered in such a way that a human operator can guide a swarm using spoken dialogue in a more natural manner

Inflation dynamics with labour market matching: assessing alternative specifcations

This paper reviews recent approaches to modeling the labour market and assesses their implications for inflation dynamics through both their effect on marginal cost and on price-setting behavior. In a search and matching environment, we consider the following modeling setups: right-to-manage bargaining vs. efficient bargaining, wage stickiness in new and existing matches, interactions at the firm level between price and wage-setting, alternative forms of hiring frictions, search on-the-job and endogenous job separation. We find that most specifications imply too little real rigidity and, so, too volatile inflation. Models with wage stickiness and right-to-manage bargaining or with firm-specific labour emerge as the most promising candidates.Inflation Dynamics, Labour Market, Business Cycle, Real Rigidities

Inflation dynamics with labour market matching: assessing alternative specifications

This paper reviews recent approaches to modeling the labour market and assesses their implications for inflation dynamics through both their effect on marginal cost and on price-setting behavior. In a search and matching environment, we consider the following modeling setups: right-to-manage bargaining vs. efficient bargaining, wage stickiness in new and existing matches, interactions at the firm level between price and wage-setting, alternative forms of hiring frictions, search on-the-job and endogenous job separation. We find that most specifications imply too little real rigidity and, so, too volatile inflation. Models with wage stickiness and right-to-manage bargaining or with firm-specific labour emerge as the most promising candidates.Labor market ; Business cycles

Inflation dynamics with labour market matching : assessing alternative specifications

This paper reviews recent approaches to modeling the labour market, and assesses their implications for inflation dynamics through both their effect on marginal cost and on price-setting behavior. In a search and matching environment, we consider the following modeling setups: right-to-manage bargaining vs. efficient bargaining, wage stickiness in new and existing matches, interactions at the firm level between price and wage-setting, alternative forms of hiring frictions, search on-the-job and endogenous job separation. We find that most specifications imply too little real rigidity and, so, too volatile inflation. Models with wage stickiness and right-to-manage bargaining or with firm-specific labour emerge as the most promising candidatesInflation Dynamics, Labour Market, Business Cycle, Real Rigidities

Inflation dynamics with labour market matching: assessing alternative specifications

This paper reviews recent approaches to modeling the labour market and assesses their implications for inflation dynamics through both their effect on marginal cost and on price-setting behaviour. In a search and matching environment, we consider the following modeling setups: right-to-manage bargaining vs. efficient bargaining, wage stickiness in new and existing matches, interactions at the firm level between price and wage-setting, alternative forms of hiring frictions, search on-the-job and endogenous job separation. We find that most specifications imply too little real rigidity and, so, too volatile inflation. Models with wage stickiness and right-to-manage bargaining or with firm-specific labour emerge as the most promising candidates. JEL Classification: E31, E32, E24, J64business cycle, Inflation Dynamics, labour market, real rigidities