22282 research outputs found
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The evolution of cooperation and diversity in public good producing organisms
No full textIn a population of altruists, all individuals thrive. But altruists are exploited by cheating individuals which do not perform altruistic acts but still benefit from those. In these conditions cooperation cannot easily evolve. This issue is resolved by kin recognition: altruists recognise each other through the use of a conspicuous tag. These altruists do well until cheaters acquire the signalling tag and disrupt the cooperation. But altruists using a different tag can then invade the population, followed by new cheaters. This mechanism can lead to a diversity of tags coexisting in the population. However it has not yet been applied in realistic biological systems. In this thesis, I formulated mathematical and simulation models to investigate the effect of diversity on the evolutionary dynamics in systems where different altruists compete with cheaters. In particular, I focused on organisms producing public goods, i.e. goods that can profit to the whole population. I considered two biological systems models: gynodioecious populations of plants, where hermaphrodites produce pollen that can be used by female-only individuals, and bacteria producing an iron-chelating molecule, called siderophore, that can be exploited by both producers and non-producers. I found that diversity in gynodioecious plants is dependent on population structure. In particular, I found that the maximal level of diversity occurs when the population structure does not favour altruists or cheaters. Next, I found a number of important results in siderophore-producing bacteria. By considering a detailed ecological model, I derived Hamilton's rule in a metapopulation and found that the level of cooperation in a population depends on the length of interaction between strains. Finally, I discovered a novel evolutionary mechanism generating and maintaining diversity and showed that it results from non-equilibrium mechanisms. These findings explain why cheaters appear readily in experiments but are rare in natural populations. My results demonstrate the importance of integrating ecological details in order to understand the mechanisms leading to cooperation and diversity, and will provide a basis and framework for future studies on the emergence and maintenance of diversity
A Middle Devensian woolly rhinoceros from Whitemoor Haye Quarry, Staffordshire (UK): palaeoenvironmental context and significance
No full textThis paper reports the discovery of a rare partial skeleton of a woolly rhinoceros (Coelodonta antiquitatis Blumenbach, 1799) and associated fauna from a low Pleistocene terrace of the River Tame at Whitemoor Haye, Staffordshire, UK. A study of the sedimentary deposits around the rhino skeleton and associated organic-rich clasts containing pollen, plant and arthropod remains suggests that the animal was rapidly buried on a braided river floodplain surrounded by a predominantly treeless, herb-rich grassland. Highlights of the study include the oldest British chironomid record published to date and novel analysis of the palaeoflow regime using caddisfly remains. For the first time, comparative calculations of coleopteran and chironomid palaeotemperatures have been made on the same samples, suggesting a mean July temperature of 8–11 8C and a mean December temperature of between -22 and -16 °C. Radiocarbon age estimates on skeletal material, supported by optically stimulated luminescence ages from surrounding sediments, indicate that the rhino lived around 41–43 k cal a BP. The combined geochronological, stratigraphic and palaeoenvironmental evidence places the assemblage firmly within the Middle Devensian (Marine
Oxygen Isotope Stage 3). This would agree with other regional evidence for the timing of aggradation for the lowest terrace of the Trent and its tributary systems
An Exploration of the Identities and Gender Discourses of a Taiwanese Woman: A Case Study of a Working Mother
No full textThis exploratory study sets out to examine the identities of a Taiwanese woman in the 21st century. Adopting the case study as a research strategy, I probe into a working mother’s life story to understand firstly a Taiwanese working mother’s perspectives on her family roles as a wife, mother and daughter-in-law. Secondly, I investigate how social institutions, which transmit different and often-conflicting Confucian and non-Confucian “gender discourses” influence her identities. This thesis adopts narrative interviews as the major method to probe into the life story of a Taiwanese working mother. The dimensions of domestic work and childcare, verbal communication, marital sex and looking after parents-in-law are examined in order to understand how she has taken on gender discourses and developed identities through her contact with different social institutions. Informed by post-structuralism and feminist theories, I consider the Taiwanese working mother as an individual who has “agency”, meaning she recognizes and values her ability to use and integrate gender discourses into her sense of self through the process of self-attribution. My research results found that “differentiation” “reflection” and “reflexivity” are themes that play important roles in affecting how a Taiwanese working mother perceives herself as an individual and defines her social and family roles. The findings also show that a working mother is able to negotiate different gender discourses. Despite the influence of the Taiwanese Confucian gendered binary, her interactions with different social institutions, especially her native family, counselling services and women’s self-help groups, enable her to develop a sense of “who I am”. She is able to reflect on her life experiences and perceive gender discourses in a critical manner and thus take on gender discourses that she identifies with to develop her own identities
Accounting and the absence of a business economics tradition in the United Kingdom
No full textThe chapter explains why business economics did not emerge as a distinct discipline in the UK, and examines the extent to which accounting filled the gap left by this in UK universities
Monoidal Computer I: Basic Computability by String Diagrams
No full textWe present a new model of computation, described in terms of monoidal categories. It conforms the Church-Turing Thesis, and captures the same computable functions as the standard models. It provides a succinct categorical interface to most of them, free of their diverse implementation details, using the ideas and structures that in the meantime emerged from research in semantics of computation and programming. The salient feature of the language of monoidal categories is that it is supported by a sound and complete graphical formalism, string diagrams, which provide a concrete and intuitive interface for abstract reasoning about computation. The original motivation and the ultimate goal of this effort is to provide a convenient high level programming language for a theory of computational resources, such as one-way functions, and trapdoor functions, by adopting the methods for hiding the low level implementation details that emerged from practice. In the present paper, we make the initial step towards this ambitious goal, and sketch the ideas how to reach it. These ideas will be elaborated in the three sequel papers, that are in preparation
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