This paper is concerned with the problem of computing approximate D-optimal design for polynomial regression with analytic weight function on the interval [m_0-a,m_0+a]. It is shown that the problem of constructing D-optimal designs for weighted polynomial regression is equivalent to that of finding D-optimal designs for polynomial regression with weight function |x|^s on the interval [-1,1] as a to 0. By using Taylor expansion we provide a recursive algorithm such that the D-optimal designs for weighted polynomial regression on a neighborhood of m_0 can be determined.

The South African Competition Commission has analysed most levels of the food supply chain by investigation of alleged anti-competitive behaviour by producers, input suppliers, storage companies, processors and retailers. The numbers of these cases include cartels and, to a lesser extent, restrictive vertical constraints and abuse of dominance position. Sexton (2012) states that the recent development in the agricultural market, where large companies are vertically integrating, renders the perfect competition model inappropriate. This brings doubt that the law based on perfect competition will work in oligopolistic markets. Despite the identified number of detected cartels in the grain industry, it might be possible that some cartels in other food chains are still undetected. Through the application of the market screening approach, the aim of this study is to establish whether the National Agricultural Marketing Council (“NAMC”) and the Competition Commission could have detected the bread cartel using secondary data in the absence of the information from the whistle-blower. As the first step, the study carried out a structural assessment of the bread industry. This assessment indicated that the bread market has a number of factors that may facilitate collusive behaviour. The study found that the history of information sharing played a crucial role for bakeries to coordinate their conduct. The second step was to conduct an in-depth behavioural assessment that focused on bread prices to see whether there has been a structural break in the period under investigation. The idea was to estimate the price equation of brown bread as a function of the SAFEX wheat price, petrol price (cost shifters), and 1 kg of maize meal (demand shifters). The study used the OLS to estimate three regressions using the data for the whole period and two sub-breaks (before the break point, and after the break point) to perform a Chow test. The question that the Chow test asked is: was there a structural break in March 2007, after the Competition Commission received the information from the whistle-blower? In other words, had the price of bread increased or decreased at a certain period without any changes in the demand or cost variable. The Null hypothesis states that there was no structural break, while the alternative hypothesis states that there was a structural break in March 2007. The Chow test result shows that at a 5 per cent significant level, the F-critical value is F_5, 90 = 2.68 and the F test statistics is 20.59 with a p value of 0.00. This indicates that we cannot reject the null hypothesis and conclude that a structural break did not occur in March 2007. The screening approached failed to prove the existence of cartel in the bread industry. Therefore, the study concludes that in the absence of the whistle-blower, it would not have been easy for the Competition Commission and the NAMC (2009) to detect a cartel by just using secondary data. This proves that screening alone cannot prove the existence of cartel without prior knowledge of the conduct and of the industry as a whole. Nevertheless, a market screening approach is important as it can be used as a warning mechanism to detect an emerging cartel, since it can flag potentially suspicious behaviour. Nevertheless, this calls for the policy makers to combine the scoping study by the Competition Commission and the monitoring of food prices by the NAMC, as this will provide the best enforcement tool in detecting cartel behaviour in the food industry. / Dissertation (MInst Agrar)--University of Pretoria, 2014. / tm2015 / Agricultural Economics, Extension and Rural Development / MInst Agrar / Unrestricted

Automatic text summarization can efficiently and effectively save users¡¦ time while reading text documents. The objective of automatic text summarization is to extract essential sentences that cover almost all the concepts of a document so that users are able to comprehend the ideas the document tries to address by simply reading through the corresponding summary. This research focuses on developing a hybrid automatic text summarization approach, KCS, to enhancing the quality of summaries. This approach basically consists of two major components: first, it employs the K-mixture probabilistic model to calculate term weights in a statistical sense; it then identifies the term relationship between nouns and nouns as well as nouns and verbs, which results in the connective strength (CS) of nouns. With the connective strengths available scores of sentences can be calculated and ranked to be extracted. We conduct three experiments to justify the proposed approach. The quality of summary is examined by its capability of increasing accuracy of text classification,while the classifier employed, the Naïve Bayes classifier, is kept the same through all experiments. The results show that the K-mixture model is more contributive to document classification than traditional TFIDF weighting scheme. It, however, is still no better than CS, a more complex linguistic-based approach. More importantly, our proposed approach, KCS, performs best among all approaches considered. It implies that KCS can extract more representative sentences from the document and its feasibility in text summarization applications is thus justified.

Determining the minimum distance between two objects is a problem that has been solved using many different approaches. Most methods proposed so far are, in essence, limited to solve the problem amongst convex polyhedra. Thus, to deal with concave objects, these methods partition concave objects into convex sub-objects and solve the convex problem between all possible sub-object combinations. This adds a large computational expense, especially when the concave objects in the scene are complicated, or when concave quadratically bound objects are to be linearized. In this work, two optimization-based formulations are proposed to solve the minimum distance problem without the need for partitioning concave objects into convex sub-objects. The first one, referred to as the continuous approach, uses concepts of computational solid geometry in order to represent objects with concavities. On the other hand, in the second formulation, referred to as the combinatorial approach, the geometries of the objects are replaced by large sets of points arranged in surface meshes. Since the optimization problem is not unimodal (i.e., has more than one local minimum point), global optimization techniques are used. Simulated Annealing and Genetic Algorithms, with constraint handling techniques such as penalty and repair strategies are used in the continuous approach. In order to eliminate the computational expense of determining the feasibility of every trial point, the combinatorial approach replaces the objects' geometry by a set of points on the surface of each object. This reduces the minimum distance problem to an unconstrained combinatorial optimization problem where the combination of points (one on each object) that minimizes the distance between objects is the solution. Additionally, Genetic Algorithms with niche formation techniques were developed in order to allow the distance algorithm to track multiple minima. In a series of numerical examples, a preliminary implementation of the proposed algorithms has proven to be robust and equivalent, in terms of computational efficiency, to some conventional approaches. / Graduate

This dissertation comprises an introduction, seven previously published papers dealing with aspects of psychodrama and the person-centred approach, criticisms of the person-centred approach, an assessment of my contribution to person-centred theory and practice and an 'afterword' which brings my exploration up to date. Although each of the papers draws on my practical experience as a therapist, researcher and educator, two of them are accounts of research, the others are broadly 'conceptual'. They are presented in the context of an heuristic journey which demonstrates my development as a person-centred thinker and practitioner. The introduction establishes this over-arching heuristic framework and gives my rationale for including these papers. The papers are followed by a consideration of the criticisms of the person-centred approach in which I show (with reference to the literature) how, if I can, I answer these criticisms. In the penultimate chapter I examine my papers in the light of some of the 'critical issues' with respect to the person-centred approach.

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Les recherches sur les processus d’acquisition et de développement de compétences de lecture et d’écriture s’accordent sur l’idée qu’ils s’opèrent par le contact et l’exposition continue du jeune lecteur à des textes et genres discursifs normées. Cette théorie trouve un écho particulier lorsqu’il s’agit de récits de fiction qui reposent sur une structure générique et textuelle à la fois conventionnelle et récurrente dont le traitement serait facilité par l’activation d’un « déjà là ». Il serait intéressant de savoir d’où vient « ce déjà là ». La réponse à cette question nous amène à interroger les caractéristiques de l’action didactique conjointe en nous focalisant sur trois formes de médiation : la culture éducative scolaire et non scolaire des élèves, les médiations textuelles et celles assurée par les enseignants. Ce choix trouve sa justification dans le contexte de notre recherche qui concerne des classes de 6ème et de 4ème au Sénégal, où l’acquisition de la lecture et de l’écriture se fait à l’école et en français langue officielle, langue d’enseignement au demeurant, mais aussi et surtout, langue seconde. Pour analyser les effets conjugués ces médiations, nous nous appuyons sur un corpus constitué de deux types de données. Il s’agit d’une part, d’enregistrements vidéo de séances d’enseignement-apprentissage organisées autour d’activités scolaires ouvertement orientées vers le développement de compétences narratives chez les élèves. D’autre part, nous disposons des productions écrites des élèves prélevées avant et après la séquence didactique portant sur l’enseignement du récit. Dans une approche plurielle, nous avons cherché à comprendre la manière dont la co-action entre le professeur et les élèves autour de textes modèles explique les performances de ces derniers lorsqu’ils sont placés en situation de production autonome. Notre démarche a permis de montrer que l’efficacité de l’agir enseignant dans ces conditions relève de trois paramètres. A l’enseignement systématique des savoirs, qui se mesure à leur niveau de concentration dans la conduite des activités scolaires, il faut associer la maturité didactique des élèves, leur participation à l’action didactique conjointe et l’étayage de leurs actions à travers des stratégies centrées sur les connaissances procédurales et pragmatiques. / The researches on the process of acquisition and development of reading and writing skills agree on the idea that these are implemented by the pupils’ continuous contact and exposure to texts and discursive genres. This theory finds a particular echo when it comes to narrative fiction based on a conventional and recurring generic and textual structure, whose treatment of which should be facilitated by the activation of prior learning. It would be interesting to know where this prior knowledge comes from. The answer to this question brings us to examine the characteristics of the joint didactic action. Thus we focus on three forms of mediation: the pupils’ educational culture in and outside school, the textual and the teacher mediation. This choice finds its justification in the context of our research which concerns first and forth year students of a Senegalese secondary school. In this context, the acquisition of the reading and the writing is made in school and in French; official language, teaching language, but also and especially, second language. In order to analyze the combined effects of these semiotic mediations we use a corpus constituted by two types of data. On the one hand, we have at our disposal video recordings of sessions of learning organized around didactical activities openly directed to the development of narrative competences in the pupils. On the other hand, we have collected written productions of these students before and after the didactical sequence concerning the teaching of narrative fiction. Through a multifaceted approach, we describe how the co-action between the professor and the pupils around model texts explains the performances of the latter ones when they are placed in situation of autonomous production. Our approach allowed us to demonstrate that we can explain the effectiveness of the teaching act by the correlation of three variables. Firstly, a systematic teaching of an object of knowledge measured by their level of concentration in the action learning. Secondly, we have the organization system of the participation of the students, prepared in advance to play their role in the co-construction of the knowledge. Finally, we underline the importance of the shoring up of their actions through strategies centred on the procedural and pragmatic knowledge.