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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Testing the effects of Bdellovibrio on wheat (Triticum aestivum) and as a food security agent in mushrooms (Agaricus bisporus)

Saxon, Emma B. January 2015 (has links)
Bdellovibrio bacteriovorus is a naturally soil-dwelling, Gram-negative predatory bacterium that attaches to, invades, and replicates within a wide range of other Gram-negative bacterial species, killing such prey in the process. A small number of previous studies testing the effect of B. bacteriovorus against known Gram-negative plant pathogens have suggested that B. bacteriovorus has potential as a ‘food security agent’ against Gram-negative bacterial infections in crop plants. My project built on this knowledge by screening a range of known Gram-negative bacterial plant pathogens and Plant Growth-Promoting Rhizobacteria (PGPRs) for susceptibility to Bdellovibrio predation in vitro; testing predation-susceptible strains in a simple, semi-sterile in vivo system on the surface of Agaricus bisporus mushrooms; and finally testing the effect of Bdellovibrio addition in a more complex, natural Triticum aestivum (wheat) soil rhizosphere mesocosm. An in vitro prey strain growth assay showed that susceptibility to B. bacteriovorus predation varied between a range of 20 Gram-negative (mostly Pseudomonas) bacterial pathogen/PGPR species, isolated from a range of different host crops or soil environments. Four of these species (Pseudomonas avellanae 48, P. syringae pv. phaseolicola, P. tolaasii 2192T and P. agarici 2289) were highly susceptible to predation, and three species (B. vietnamiensis G4, P. marginalis 667, and Pectobacterium atrosepticum SCRI1143) showed apparent resistance to predation. P. tolaasii 2192T, causes dark, pathogenic lesions on post-harvest mushroom host crops; In vivo co-inoculation tests on the surface of A. bisporus mushrooms showed that lesions were significantly reduced with B. bacteriovorus treatment, which was due to B. bacteriovorus predatory killing and reduction of prey cell numbers, preventing symptoms. B. bacteriovorus also preyed upon and killed a putative pathogenic Pseudomonas species isolated from a grey lesion on an organic, garden mushroom, but some likely commensal species isolated from mushroom tissue showed resistance to predation. These data together suggest that B. bacteriovorus could be used commercially to prolong the shelf life of mushrooms, reducing crop losses through spoilage, with minimal negative effects on mushroom PGPR species. Finally, inoculating B. bacteriovorus into the soil around young winter wheat plants in a natural pot soil mesocosm was found to increase plant growth and grain yield at harvest; this was contrary to my initial hypothesis that B. bacteriovorus would reduce wheat plant growth, by preying upon and killing PGPR species such as P. fluorescens that reduce wheat plant infection with Gaeumannomyces graminis var. tritici, the yield-reducing take-all fungal pathogen of wheat. The soil was found to be low in nitrogen; thus B. bacteriovorus inoculation could have increased wheat growth due to B. bacteriovorus death in the soil and subsequent release of nutrients including nitrogen. However, some B. bacteriovorus cells survived in the soil where they could prey upon some Gram-negative bacterial species, reducing their numbers. Some of the wheat growth and yield-producing effects of B. bacteriovorus may be due to the predation of species that are associated with late flowering, and therefore grain development, in wheat, allowing time for more grain to develop. Alternatively, it could be due to processes performed by B. bacteriovorus in the soil that are not related to predation, such as production of the plant hormone IAA, or B. bacteriovorus colonisation of the roots and predation of root-associated pathogenic bacterial species. Further studies are required to identify the mechanisms behind these unexpected crop yield-promoting effects, and the extent of any nutrient ‘boost’ effect due to death of B. bacteriovorus in the wheat soil, to determine whether B. bacteriovorus could be used as a pre-harvest growth and yield-promoting agent. Although most studies of B. bacteriovorus so far have focussed on its predatory activity, it likely performs other functions in its natural soil habitat, which may underlie some of the growth and yield-promoting effects shown here. However, these data show that B. bacteriovorus could be used commercially as a ‘food security agent’ when used as a post-harvest treatment to prevent crop spoilage and loss (as for A. bisporus mushrooms).
42

Development of rapid phage based detection methods for mycobacteria

Swift, Benjamin M. C. January 2014 (has links)
MAP is the causative agent of a wasting disease in ruminants and other animals called Johne’s disease. Culture of the organism can take months and in the case of some sheep strains of MAP, culture can take up to a year. It can take several years for an animal infected with MAP to show clinical symptoms of disease. During this subclinical stage of infection, MAP can be shed into the environment contaminating their surroundings and infecting other animals. As well as this Johne’s disease is particularly difficult to diagnose during the subclinical stage of infection. Culture is very difficult and takes too long to be a viable method to diagnose Johne’s disease. Microscopic methods can be used on histological samples to detect MAP, however common acid-fast stains used are not specific for MAP and other mycobacteria and acid-fast organisms can be detected. Molecular methods, such as PCR, exist to rapidly detect the signature DNA sequences of these organisms, however they have the disadvantage of not being able to distinguish between live and dead organisms. Other immunological methods, such as ELISA tests, exist and are routinely used to diagnose Johne’s disease, however their sensitivity is very poor especially during the subclinical stage of disease. The aim of these studies was to develop novel rapid methods of detecting MAP to act as an alternative to methods already available. Sample processing using magnetic separation was carried out to allow good capture of MAP cells and to allow efficient phage infection. Using the phage assay, a specific, sensitive phage based method was developed that could detect approximately 10 cells per ml of blood within 24 h in the laboratory with a sensitive, specific plaque-PCR. This optimised detection method was then used to determine whether MAP cells could be detected in clinical blood samples of cattle suffering from Johne’s disease. The results suggest that animals experimentally and naturally infected with MAP harboured cells in their blood during subclinical and clinical stages of infection. A novel high-throughput method of detecting mycobacteria was also developed. Using phage D29 as a novel mycobacterial DNA extraction tool, viable MAP cells were detected within 8 h and the format of the assay means that it can be adapted to be used in a high-throughput capacity. Factors affecting phage infection and phage-host interactions were investigated to make sure the phage based methods of detection were as efficient as possible. It was found that periods of recovery were often necessary to not only make sure the phage were not inhibited but to also allow the host cells to be metabolically active as it was found that phage D29 can only infect mycobacteria cells that are metabolically active. A fluorescent fusion-peptide capable of specifically labelling MAP cells was also developed to be used as an alternative to acid-fast staining. Peptides that were found to specifically bind to MAP cells were fused with green fluorescent protein and cells mounted on slides were specifically labelled with the fluorescent fusion protein. This resulted in a good alternative to the generic acid-fast staining methods. The blood phage assay has shown that viable MAP cells can be found in the blood of animals suffering from Johne’s disease within 24 h and this can be confirmed using a MAP specific plaque-PCR protocol. A novel faster method to detect MAP was also developed, to cut down the time to detection of viable MAP cells to 8 h, which can be formatted to be used in a high-throughput capacity. The phage assay was used as a tool to determine different metabolic states of mycobacteria, and helped investigate optimal detection conditions when using the phage assay. Finally a novel fluorescent label was developed to detect MAP as an alternative to insensitive acid-fast staining. The development of these novel methods to rapidly, specifically and sensitively detect MAP will push further the understanding of Johne’s disease and help control it.
43

Análisis hipertextual e interpretación semiótica de la obra de Juan Bautista Sanz García

Quiles Burruezo, Juan Antonio 04 December 2015 (has links)
Este trabajo de investigación se centra en la indagación analítica e interpretativa de la obra artística de Juan Bautista Sanz en su amplio volumen multimodal de alcance humanista, desde un enfoque educativo atento al provecho de integración de lenguajes y perspectivas que proporcionan las actuales corrientes teórico-literarias del hipertexto, el intertexto y la ékfrasis pictórica, donde la originalidad del autor es considerada en su proceso de formación dialógica con otros artistas que inspiraron su mirada personal. Por tanto, el objetivo fundamental se centra en el estudio de toda la obra creada por la poliédrica personalidad de Juan Bautista Sanz a lo largo de su vida (pintura, escritura periodística de perfil ensayístico, cine, televisión y radio) en atención a un enfoque semiótico hipertextual y a su proyección didáctica en la etapa de Educación Secundaria. Y los objetivos específicos que contribuyen a su consecución son: primero, estudiar la literatura científica relevante sobre la semiótica de la hipertextualidad y sus procedimientos intertextuales con la pretensión de establecer las bases teóricas de una metodología de la lectura de textos pictóricos y verbales y su tratamiento ekfrástico; segundo, investigar la producción de índole pictórica, periodística y fílmica de Juan Bautista Sanz para mostrar su itinerario poliédrico en conexión con el contexto artístico-cultural contemporáneo y los vínculos influyentes en su poética personal; tercero, establecer los parámetros poetológicos del ars pictura de Juan Bautista Sanz y un modelo de lectura simbólica y ekfrástica que permitan realizar un análisis interpretativo de una muestra representativa de la producción plástica de Juan Bautista Sanz; cuarto, proponer diversas secuencias de tareas didácticas para Bachillerato destinadas a la lectura de los motivos artísticos presentes en una selección de cuadros de Juan Bautista Sanz y a su recreación ekfrástica. El enfoque metodológico que ha seguido esta tesis doctoral se encuadra dentro de la metodología cualitativa, fundamentada principalmente en la interpretación de datos a través de un análisis triangular: investigación del tesinando, revisión de los directores de la tesis, confrontación con las ideas del autor. La recogida de datos realizada para este estudio se puede dividir en tres grandes apartados: la observación directa por parte del tesinando, las entrevistas en profundidad y el empleo de documentación relacionada con la poliédrica obra de Juan Bautista Sanz. A través de entrevistas con el artista para comprender y acotar los distintos campos de actuación en los que ha materializado su ideología estética y creadora, se ha recopilado, reducido e interpretado la información correspondiente. Igualmente ha sido analizado el conjunto de su producción artística con especial interés en su producción pictórica, y de modo pormenorizado una muestra selecta de sus cuadros más representativos, no solo en atención a la poetología del artista sino también en relación con los principales movimientos artísticos de finales de siglo XIX y principios del siglo XX que presentan interconexiones con su estilo personal: impresionismo, fauvismo y expresionismo. El estudio ha finalizado con el planteamiento de una serie de propuestas didácticas orientadas hacia alumnado de Educación Secundaria en la etapa voluntaria de Bachillerato a partir de la dicotomía lectora de las formas concebidas y las formas recibidas en la serie de cuadros analizados. Tal propuesta didáctica se destina al afianzamiento de las competencias básicas de los estudiantes contempladas en el programa de la asignatura de Lengua Castellana y Literatura, en especial las competencias en comunicación lingüística y las de carácter artístico y cultural. Los resultados de la investigación muestran que se ha contribuido a solventar el problema de investigación mostrado en esta memoria, pues se aporta aquí la primera semblanza completa de la poética que Juan Bautista Sanz ha desarrollado en su obra artística desde las premisas científicas de la semiótica del hipertexto donde han sido analizados los vínculos que sostienen su poliédrica trayectoria. Es indudable el interés didáctico que tiene tal producción de Juan Bautista Sanz en el contexto educativo murciano, pues por él, los jóvenes estudiantes de Bachillerato no solo pueden acceder a los más depurados trayectos artísticos y culturales de esta región, tanto por su labor mediadora en Galería Zero y en los medios de prensa y televisión, como sobre todo en la visión sensual y simbólica de sus pinturas y en la reflexión lúcida, crítica y sincera de sus escritos. Tal es la finalidad de proyección didáctica de esta investigación para uso y deleite estético y comunicativo de los jóvenes estudiantes murcianos. / This research work focuses on an analytical and interpretative inquiry of the work of Juan Bautista Sanz, on its vast humanistic multimodal volume, from a an educational approach for the integration of languages and perspectives that current hyper-text, inter-text and pictorical ekphrasis theoretical and literary trends provide and where the author´s originality is considered through his dialogic learning process with other artist that inspired his personal view. Thus, the fundamental target is centered in the study of all the work created by the polyhedric personality of Juan Bautista Sanz throughout his life (paintings, cinema, television, radio and journalist writings of essay profile) in relation to a semiotic approach of the hypertext and to its didactic projection in secondary education. The specific objectives that contribute to its attainment are: firstly, studying the scientific literature relevant to the semiotic of the hypertext and its intertextual proceedings with the aim of clarifying the theoretical foundations of a methodology of the reading of pictoric and verbal texts and its ekphrastic treatment; secondly, investigate the production of pictoric, journalistic and cinematic work of Juan Bautista Sanz to show his polyhedral itinerary in connection with the artistic and cultural context and the influential points on his personal poetics; thirdly, lay down the poetological parameters of Juan Bautista´s ars pictura and a model of symbolic and ekphrastic reading that allows an interpretative analysis of a sample of the plastic operum of Juan Bautista Sanz; fourthly, suggest various sequences of educational tasks for Bachillerato (A-Levels in the United Kingdom) intended to the reading of the artistic features present in a selection of paintings of Juan Bautista and to its ekphrastic recreation. The methodological perspective followed on this doctoral thesis is framed within the qualitative methodology, mainly based on data interpretation through a triangular analysis: thesis candidate analysis, reviews from the directors of the thesis and comparison with the author ideas. The data collection conducted for this study can be divided in three large sections: direct observation by the thesis candidate, in-depth interviews and the usage of documentation related to the artist's polyhedric work. Through interviews with the artist, it has been collected, reduced and construe the relevant data in order to understand and narrow the different fields of activity in which he has materialized his aesthetic and creative ideology. Similarly, it has been analyzed his artistic production as a whole with an special emphasis on his pictoric work, and in a more detail manner a sample of his most exclusive and representative paintings, not only paying attention to the poetology of the artist but also regarding the main artistic movements of the late XIX century and early XX century that have interconnections with his personal style: impressionism, fauvism and expressionism. The study finalizes with the suggestion of a series of didactic proposals oriented to the secondary education pupils in the voluntary phase of Bachillerato drawn from the reading dichotomy of the conceived and received shapes of the paintings analyzed. Such educational proposal is oriented to the strengthening of the student´s basic competences considered in the syllabus of the subject Lengua y Literatura Castellana (Spanish Language and Literature), particularly in the linguistic communication competences and in the artistic and cultural ones. The results of the research show that it has contributed to solve the research problem shown in this report, since we provide the first complete poetic biographical sketch that Juan Bautista Sanz has developed in his artistic work, from the scientific premises of the semiotics of hyper-text where the links that hold his polyhedric trajectory have been analyzed. It is unquestionable that the work of Juan Bautista Sanz has an important didactic interest in the educational sphere of his hometown, Murcia, since young Bachillerato students can access the finest artistic and cultural paths of Murcia region, as a consequence the artist's mediating work in Galería Zero, in media, as well as the sensual and symbolic views of his paintings and the clear, critical and honest reflection of his writings. Such is the case with didactic projection purpose of this research for the usage and aesthetic and communicative delight of Murcia´s young students.
44

Senyals visuals i creació artística: quotidianitat i referents 1990-2015

Cova, Massimo 20 January 2016 (has links)
Aquesta tesi investiga obres, projectes i models de creació artística contemporània que adopten, com a referents formals i conceptuals, unes senyals visuals espontànies, traces efímeres i transitòries presents en els entorns quotidians i generades pels comportaments i les interaccions de les persones. Vam definir, en el seu inici, l'àmbit d'aquesta recerca des de la nostra experiència docent a secundària, per l'interès envers la varietat de les senyals visuals espontànies generades pels adolescents a l'escola, com també en el seu valor expressiu i comunicatiu. En aquell moment fou el començament d'un projecte artístic personal. A partir d'aquí, el desenvolupament de la pròpia recerca ens va mostrar autors, connexions entre obres i projectes de creació dins d'un espai visual més ampli de materialització i de significació relatiu a la nostra societat global. Hem observat que una part significativa de la producció artística actual té com a referents de creació signes i elements visuals propis d'aspectes de la vida quotidiana, relacionats amb les complexes conseqüències de la internacionalització econòmica i cultural, així com del desenvolupament i de l'expansió de les noves tecnologies. Dins del context artístic contemporani considerem que pot haver-hi un espai per plantejar una reflexió sobre la capacitat que té l'art contemporani de formalitzar i reconfigurar dins de la seva pràctica, a partir d' aquests indicis visuals, emprats com elements de significació oberta, alguns valors culturals d'individus o de col.lectius. La metodologia d'investigació de la tesi s'ha estructurat en dues línies paral•leles: una principal de recerca sobre els processos de creació artística o plàstica, però també de construcció conceptual i projectual, desenvolupada des de les obres de diferents autors relacionades amb els referents considerats, i una segona de producció artística personal annexa. Des del començament hem vist i analitzat, amb visites a exposicions i a manifestacions artístiques internacionals i locals, obres realitzades o vinculades a aquests entorns visuals i culturals. Hem comprovat com els artistes, en les seves pràctiques, han considerat aquestes senyals, petjades i signes visuals, utilitzant llenguatges artístics sovint interdisciplinaris; i, en efecte, de com aquests procediments han definit el procés productiu i la seva conceptualització. Les obres tractades en aquesta tesi s'han organitzat, en certa mesura, per categories de significació destacades en el debat actual, evidenciades i ampliades al llarg de la investigació, com són la virtualitat, el consum, les noves tecnologies, la violència, les migracions o la comunicació mediàtica entre d' altres. Quant a la part productiva personal, s'ha generat certa reconsideració dels materials i dels suports plàstics, així com dels continguts, a través de la creació d'obres vinculades als marcs de referència examinats, que han anat evolucionant fins a concretar un projecte artístic i noves línies experimentals. Amb aquests resultats oberts i sense cap voluntat conclusiva, creiem que podem contribuir a ampliar, ordenar i aprofundir alguns aspectes rellevants de l'experiència artística contemporània, aportant arguments d'anàlisi i de significació, i ordenant recursos productius de la pràctica creativa contemporània, que es troben vinculats i proposats en aquesta tesi.
45

Multi-objective tools for the vehicle routing problem with time windows

Castro-Gutierrez, Juan January 2012 (has links)
Most real-life problems involve the simultaneous optimisation of two or more, usually conflicting, objectives. Researchers have put a continuous effort into solving these problems in many different areas, such as engineering, finance and computer science. Over time, thanks to the increase in processing power, researchers have created methods which have become increasingly sophisticated. Most of these methods have been based on the notion of Pareto dominance, which assumes, sometimes erroneously, that the objectives have no known ranking of importance. The Vehicle Routing Problem with Time Windows (VRPTW) is a logistics problem which in real-life applications appears to be multi-objective. This problem consists of designing the optimal set of routes to serve a number of customers within certain time slots. Despite this problem’s high applicability to real-life domains (e.g. waste collection, fast-food delivery), most research in this area has been conducted with hand-made datasets. These datasets sometimes have a number of unrealistic features (e.g. the assumption that one unit of travel time corresponds to one unit of travel distance) and are therefore not adequate for the assessment of optimisers. Furthermore, very few studies have focused on the multi-objective nature of the VRPTW. That is, very few have studied how the optimisation of one objective affects the others. This thesis proposes a number of novel tools (methods + dataset) to address the above- mentioned challenges: 1) an agent-based framework for cooperative search, 2) a novel multi-objective ranking approach, 3) a new dataset for the VRPTW, 4) a study of the pair-wise relationships between five common objectives in VRPTW, and 5) a simplified Multi-objective Discrete Particle Swarm Optimisation for the VRPTW.
46

Compiling concurrency correctly : verifying software transactional memory

Hu, Liyang January 2013 (has links)
Concurrent programming is notoriously difficult, but with multi-core processors becoming the norm, is now a reality that every programmer must face. Concurrency has traditionally been managed using low-level mutual exclusion /locks/, which are error-prone and do not naturally support the compositional style of programming that is becoming indispensable for today's large-scale software projects. A novel, high-level approach that has emerged in recent years is that of /software transactional memory/ (STM), which avoids the need for explicit locking, instead presenting the programmer with a declarative approach to concurrency. However, its implementation is much more complex and subtle, and ensuring its correctness places significant demands on the compiler writer. This thesis considers the problem of formally verifying an implementation of STM. Utilising a minimal language incorporating only the features that we are interested in studying, we first explore various STM design choices, along with the issue of compiler correctness via the use of automated testing tools. Then we outline a new approach to concurrent compiler correctness using the notion of bisimulation, implemented using the Agda theorem prover. Finally, we show how bisimulation can be used to establish the correctness of a low-level implementation of software transactional memory.
47

An investigation of multi-objective hyper-heuristics for multi-objective optimisation

Maashi, Mashael January 2014 (has links)
In this thesis, we investigate and develop a number of online learning selection choice function based hyper-heuristic methodologies that attempt to solve multi-objective unconstrained optimisation problems. For the first time, we introduce an online learning selection choice function based hyperheuristic framework for multi-objective optimisation. Our multi-objective hyper-heuristic controls and combines the strengths of three well-known multi-objective evolutionary algorithms (NSGAII, SPEA2, and MOGA), which are utilised as the low level heuristics. A choice function selection heuristic acts as a high level strategy which adaptively ranks the performance of those low-level heuristics according to feedback received during the search process, deciding which one to call at each decision point. Four performance measurements are integrated into a ranking scheme which acts as a feedback learning mechanism to provide knowledge of the problem domain to the high level strategy. To the best of our knowledge, for the first time, this thesis investigates the influence of the move acceptance component of selection hyper-heuristics for multi-objective optimisation. Three multi-objective choice function based hyper-heuristics, combined with different move acceptance strategies including All-Moves as a deterministic move acceptance and the Great Deluge Algorithm (GDA) and Late Acceptance (LA) as a nondeterministic move acceptance function. GDA and LA require a change in the value of a single objective at each step and so a well-known hypervolume metric, referred to as D metric, is proposed for their applicability to the multi-objective optimisation problems. D metric is used as a way of comparing two non-dominated sets with respect to the objective space. The performance of the proposed multi-objective selection choice function based hyper-heuristics is evaluated on the Walking Fish Group (WFG) test suite which is a common benchmark for multi-objective optimisation. Additionally, the proposed approaches are applied to the vehicle crashworthiness design problem, in order to test its effectiveness on a realworld multi-objective problem. The results of both benchmark test problems demonstrate the capability and potential of the multi-objective hyper-heuristic approaches in solving continuous multi-objective optimisation problems. The multi-objective choice function Great Deluge Hyper-Heuristic (HHMO_CF_GDA) turns out to be the best choice for solving these types of problems.
48

Identity management policy and unlinkability : a comparative case study of the US and Germany

Rosner, Gilad L. January 2014 (has links)
This study compares the privacy policies of Germany and the US in the field of identity management. It analyses the emergence of unlinkability within the countries’ electronic citizen identity initiatives. The study used qualitative research methods, including semi-structured interview and document analysis, to analyse the policy-making processes surrounding the issue of unlinkability. The study found that unlinkability is emerging in different ways in each country. Germany’s data protection and privacy regimes are more coherent than the US, and unlinkability was an incremental policy change. US unlinkability policies are a more significant departure from its data protection and policy regimes. New institutionalism is used to help explain the similarities and differences between the two countries’ policies. Scholars have long been calling for the use of privacy-enhancing technologies (PETs) in policy-making, and unlinkability falls into this category. By employing PETs in this way, German and US identity management policies are in the vanguard of their respective privacy regimes. Through these policies, the US comes closer to German and European data protection policies, doing so non-legislatively. The digital citizen identities appearing in both countries must be construed as commercial products inasmuch as official identities. Lack of attendance to the commercial properties of these identities frustrates policy goals. As national governments embark on further identity management initiatives, commercial and design imperatives, such as value to the citizen and usability, must be considered for policy to be successful.
49

Semantic methods for functional hybrid modelling

Capper, John January 2014 (has links)
Equation-based modelling languages have become a vital tool in many areas of science and engineering. Functional Hybrid Modelling (FHM) is an approach to equation-based modelling that allows the behaviour of a physical system to be expressed as a modular hierarchy of undirected equations. FHM supports a variety of advanced language features — such as higher-order models and variable system structure — that sets it apart from the majority of other modelling languages. However, the inception of these new features has not been accompanied by the semantic tools required to effectively use and understand them. Specifically, there is a lack of static safety assurances for dynamic models and the semantics of the aforementioned language features are poorly understood. Static safety guarantees are highly desirable as they allow problems that may cause an equation system to become unsolvable to be detected early, during compilation. As a result, the use of static analysis techniques to enforce structural invariants (e.g. that there are the same number of equations as unknowns) is now in use in main-stream equation-based languages like Modelica. Unfortunately, the techniques employed by these languages are somewhat limited, both in their capacity to deal with advanced language features and also by the spectrum of invariants they are able to enforce. Formalising the semantics of equation-based languages is also important. Semantics allow us to better understand what a program is doing during execution, and to prove that this behaviour meets with our expectation. They also allow different implementations of a language to agree with one another, and can be used to demonstrate the correctness of a compiler or interpreter. However, current attempts to formalise such semantics typically fall short of describing advanced features, are not compositional, and/or fail to show correctness. This thesis provides two major contributions to equation-based languages. Firstly, we develop a refined type system for FHM capable of capturing a larger number of structural anomalies than is currently possible with existing methods. Secondly, we construct a compositional semantics for the discrete aspects of FHM, and prove a number of key correctness properties.
50

Truth maintenance in knowledge-based systems

Nguyen, Hai Hoang January 2014 (has links)
Truth Maintenance Systems (TMS) have been applied in a wide range of domains, from diagnosing electric circuits to belief revision in agent systems. There also has been work on using the TMS in modern Knowledge-Based Systems such as intelligent agents and ontologies. This thesis investigates the applications of TMSs in such systems. For intelligent agents, we use a “light-weight” TMS to support query caching in agent programs. The TMS keeps track of the dependencies between a query and the facts used to derive it so that when the agent updates its database, only affected queries are invalidated and removed from the cache. The TMS employed here is “light-weight” as it does not maintain all intermediate reasoning results. Therefore, it is able to reduce memory consumption and to improve performance in a dynamic setting such as in multi-agent systems. For ontologies, this work extends the Assumption-based Truth Maintenance System (ATMS) to tackle the problem of axiom pinpointing and debugging in ontology-based systems with different levels of expressivity. Starting with finding all errors in auto-generated ontology mappings using a “classic” ATMS [23], we extend the ATMS to solve the axiom pinpointing problem in Description Logics-based Ontologies. We also attempt this approach to solve the axiom pinpointing problem in a more expressive upper ontology, SUMO, whose underlying logic is undecidable.

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