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Historically, the Minor Planet Center (MPC) has concentrated on improving the quality of the astrometric observations and the resulting orbits of minor planets. In light of long-standing complaints in the literature about the quality of the photometric parameters for the minor planets, there has been a need to improve the quality of the absolute magnitudes, H, and slope parameters, G. However, this task is complex, as the bulk of the minor-planet magnitude estimates are suppl ied by the astrometric observers. These observations are not made through standard fillers and are made with respect to the (indifferent) magnitudes in numerous astrometric reference catalogues. Such magnitude estimates are labelled "astrophotometry", to reflect their low quality. This thesis describes a method for correcting the catalogue- and observer-specific errors present in the astrophotometry. This method was applied to more than 70 million astrometric observations with magnitude estimates. New H determinations have been made for 322 607 numbered minor planets, while new G determinations have been made for 64 348 numbered minor planets. New assumed G values have been determined for 258 259 numbered minor planets. Analysis of the results shows that the problems identified in the literature have been removed, particularly the -0.5 magnitude offset at H14 that is present in the current MPC HG data set. Implications of the new H magnitudes on the albedos determined by the WISE space mission and on the differential H distributions of various types of solar-system object are discussed.

In this thesis, I use an experimental model to investigate the role of social pressures in stimulating language divergence. Research into the evolution of cooperation has emphasised the usefulness of ingroup markers for swiftly identifying outsiders, who pose a threat to cooperative networks. Mechanisms for avoiding cheats and freeriders, which tend to rely on reputation, or on (explicit and implicit) contracts between individuals, are considerably less effective against short-term visitors. Outsiders, moreover, may behave according to different social norms, which may adversely affect cooperative interactions with them. There are many sources of markers by which insiders and outsiders can be distinguished, but language is a particularly impressive one. If human beings exploit linguistic variation for this purpose, we might expect the exploitation to have an influence on the cultural evolution of language, and to be involved in language divergence, since it introduces a selective pressure, by which linguistic variants are selected on the basis of their social significance. However, there is also a neutral, mechanistic model of dialect formation that relies on unconscious accommodation between interlocutors, coupled with variation in the frequency of interaction, to account for divergence. In studies of real-world communities, these factors are difficult to tease apart. The model described in this thesis put real speakers in the artificial environment of a computer game. A game consisted of a series of rounds in which players were paired up with each other in a pseudo-random order. During a round, pairs of players exchanged typed messages in a highly restricted artificial "alien language". Each player began the game with a certain number of points, distributed between various resources, and the purpose of sending messages was to negotiate to exchange these resources. Any points given away were worth double to the receiver, so, by exchanging resources, players could accumulate points for their team. However, the pairings were anonymous: until the end of a round, players were not told who they had been paired with. This basic paradigm allowed the investigation of the major factors influencing language divergence, as well as the small-scale individual strategies that contribute to it. Two major factors were manipulated: frequency of interaction and competitiveness. In one condition, all players in a game were working together; in another condition, players were put into teams, such that giving away resources to teammates was advantageous, but giving them to opponents was not. This put a pressure on players to use variation in the alien language to mark identity. A combination of this pressure and a minimum level of interaction between teammates was found to be sufficient for the alien language to diverge into "dialects". Neither factor was sufficient on its own. The results of these experiments suggest that a pressure for the socially based selection of linguistic variants can lead to divergence in a very short time, given sufficient levels of interaction between members of a group.

Open hypermedia concerns itself with finding ways to provide links between information using systems that allow the direct manipulation of links. These systems are generally built in component fashion, a major component will be the Link Service. This thesis extends previous work on building link services for the World Wide Web in order to improve the quality of linking that can be provided. A link service delivers links into Web pages dynamically, this allows the system the opportunity to adapt the links to suit the user and content. The more general form of this adaption is to deliver links in some context. The core of this work is to examine how to generalise the delivery of links in context so that new context models and techniques can be introduced without writing a new link service each time. This thesis examines the problem of defining models of context and how different models are often incompatible. It introduces a new architecture for exploring methods of providing links in context. The architecture consists of a core infrastructure along with a method for dynamically changing the components of the system concerned with the link model and the computation process for generating the final link to deliver. The effectiveness of the architecture is explored through the undertaking of a number of projects using real-world data. The limits of the design are explored and the analysis focuses on how successful it is possible to be given the goals set.