DSpace Community:https://dspace.lboro.ac.uk/2134/832016-12-02T04:30:55Z2016-12-02T04:30:55ZOn restricting the ambiguity in morphic images of wordsDay, Joel D.https://dspace.lboro.ac.uk/2134/231712016-11-22T14:49:54Z2016-01-01T00:00:00ZTitle: On restricting the ambiguity in morphic images of words
Authors: Day, Joel D.
Abstract: For alphabets Delta_1, Delta_2, a morphism g : Delta_1* to Delta_2* is ambiguous with respect to a word u in Delta_1* if there exists a second morphism h : Delta_1* to Delta_2* such that g(u) = h(u) and g not= h. Otherwise g is unambiguous. Hence unambiguous morphisms are those whose structure is fully preserved in their morphic images.
A concept so far considered in the free monoid, the first part of this thesis considers natural extensions of ambiguity of morphisms to free groups. It is shown that, while the most straightforward generalization of ambiguity to a free monoid results in a trivial situation, that all morphisms are (always) ambiguous, there exist meaningful extensions of (un)ambiguity which are non-trivial - most notably the concepts of (un)ambiguity up to inner automorphism and up to automorphism.
A characterization is given of words in a free group for which there exists an injective morphism which is unambiguous up to inner automorphism in terms of fixed points of morphisms, replicating an existing result for words in the free monoid. A conjecture is presented, which if correct, is sufficient to show an equivalent characterization for unambiguity up to automorphism. A rather counterintuitive statement is also established, that for some words, the only unambiguous (up to automorphism) morphisms are non-injective (or even periodic).
The second part of the thesis addresses words for which all non-periodic morphisms are unambiguous. In the free monoid, these take the form of periodicity forcing words. It is shown using morphisms that there exist ratio-primitive periodicity forcing words over arbitrary alphabets, and furthermore that it is possible to establish large and varied classes in this way. It is observed that the set of periodicity forcing words is spanned by chains of words, where each word is a morphic image of its predecessor. It is shown that the chains terminate in exactly one direction, meaning not all periodicity forcing words may be reached as the (non-trivial) morphic image of another. Such words are called prime periodicity forcing words, and some alternative methods for finding them are given.
The free-group equivalent to periodicity forcing words - a special class of C-test words - is also considered, as well as the ambiguity of terminal-preserving morphisms with respect to words containing terminal symbols, or constants. Moreover, some applications to pattern languages and group pattern languages are discussed.
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.2016-01-01T00:00:00ZOn the decidability and complexity of problems for restricted hierarchical hybrid systemsBell, Paul C.Chen, ShangJackson, Lisa M.https://dspace.lboro.ac.uk/2134/231322016-11-11T10:39:31Z2016-01-01T00:00:00ZTitle: On the decidability and complexity of problems for restricted hierarchical hybrid systems
Authors: Bell, Paul C.; Chen, Shang; Jackson, Lisa M.
Abstract: We study variants of a recently introduced hybrid system model, called a Hierarchical Piecewise Constant Derivative (HPCD). These variants (loosely called Restricted HPCDs) form a class of natural models with similarities to many other well known hybrid system models in the literature such as Stopwatch Automata, Rectangular Automata and PCDs. We study the complexity of reachability and mortality problems for variants of RHPCDs and show a variety of results, depending upon the allowed powers. These models form a useful tool for the study of the complexity of such problems for hybrid systems, due to their connections with existing models.
We show that the reachability problem and the mortality problem are co-NP-hard for bounded 3-dimensional RHPCDs (3-RHPCDs). Reachability is shown to be in PSPACE, even for n-dimensional RHPCDs. We show that for an unbounded 3-RHPCD, the reachability and mortality problems become undecidable. For a nondeterministic variant of 2-RHPCDs, the reachability problem is shown to be PSPACE-complete.
Description: This paper is closed access until 13th September 2017.2016-01-01T00:00:00ZNeural plasticity for rich and uncertain robotic information streamsSoltoggio, Andreavan der Velde, Frankhttps://dspace.lboro.ac.uk/2134/231242016-11-10T14:30:12Z2016-01-01T00:00:00ZTitle: Neural plasticity for rich and uncertain robotic information streams
Authors: Soltoggio, Andrea; van der Velde, Frank
Abstract: Models of adaptation and neural plasticity are often demonstrated in robotic scenarios with heavily pre-processed and regulated information streams to provide learning algorithms with appropriate, well timed, and meaningful data to match the assumptions of learning rules. On the contrary, natural scenarios are often rich of raw, asynchronous, overlapping and uncertain inputs and outputs whose relationships and meaning are progressively acquired, disambiguated, and used for further learning. Therefore, recent research efforts focus on neural embodied systems that rely less on well timed and pre-processed inputs, but rather extract autonomously relationships and features in time and space. In particular, realistic and more complete models of plasticity must account for delayed rewards, noisy and ambiguous data, emerging and novel input features during online learning. Such approaches model the progressive acquisition of knowledge into neural systems through experience in environments that may be affected by ambiguities, uncertain signals, delays, or novel features.
Description: Closed access. This is an edited book. It is available at: http://dx.doi.org/10.3389/978-2-88919-995-2 and the individual papers are available to download. The editorial article by Soltoggio and van der Velde is available on the Institutional Repository at: https://dspace.lboro.ac.uk/2134/194732016-01-01T00:00:00ZMeasuring the credibility of student attendance data in Higher Education for data miningDawson, Christian W.Alsuwaiket, MohammedBatmaz, Firathttps://dspace.lboro.ac.uk/2134/230052016-11-02T14:06:16Z2016-01-01T00:00:00ZTitle: Measuring the credibility of student attendance data in Higher Education for data mining
Authors: Dawson, Christian W.; Alsuwaiket, Mohammed; Batmaz, Firat
Abstract: Educational Data Mining (EDM) is a developing discipline, concerned with expanding the classical Data Mining (DM) methods and developing new methods for discovering the data that originate from educational systems. It aims to use those methods to achieve a logical understanding of students, and the educational environment they should have for better learning.
These data are characterized by their large size and randomness and this can make it difficult for educators to extract knowledge from these data. Additionally, knowledge extracted from data by means of counting the occurrence of certain events is not always reliable, since the counting process sometimes does not take into consideration other factors and parameters that could affect the extracted knowledge.
As a case example of the above problem, student attendance in higher education has always been dealt with in a classical way, i.e. educators rely on counting the occurrence of attendance or absence building their knowledge about students as well as modules based on this count. This method is neither credible nor does it necessarily provide a real indication of a student’s performance.
This study explores the above problem and tries to formulate the extracted knowledge in a way that guarantees achieving accurate and credible results. Student attendance data, gathered from the educational system, were first cleaned in order to remove any randomness and noise, then various attributes were studied so as to highlight the most significant ones that affect the real attendance of students. The next step was to derive an equation that measures the Student Attendance’s Credibility (SAC) considering the attributes chosen in the previous step. The reliability of the newly developed measure was then evaluated in order to examine its consistency. Finally, the J48 DM classification technique was utilized in order to classify modules based on the strength of their SAC values.
Results of this study were promising, and credibility values achieved using the newly derived formula gave accurate, credible, and real indicators of student attendance, as well as accurate classification of modules based on the credibility of student attendance on those modules.
Description: This paper is closed access until publication. It was presented at the 5th International Conference on Knowledge and Education Technology (ICKET 2016) and subsequently published in the International Journal of Information and Education Technology.2016-01-01T00:00:00Z