Thesis (Ph.D. (Education))--North-West University, Potchefstroom Campus, 2008

The purpose of this research is to survey and describe some science teachers’ conceptions of which assessment criteria they use at the marking process. Questions which are relevant for this research are the following: 1. Which assessment methods form the basis for science teachers’ marking process? 2. Which knowledge qualities are assessed and marked by science teachers? 3. How do science teachers use national curriculum and marking criterions? Five qualitative interviews of science teachers were performed. The interview material was analyzed by a phenomenographical analysis method. The result from the first problem consists of the descriptive categories: Science methodology and Oral and written use of language. The result from the second problem consists of the descriptive categories: The students´ ability to use science knowledge in different contexts, The students´ ability to use science vocabulary, The students´ ability to develop science knowledge, and The students´ behavior. The result from the third problem consists of the descriptive categories: As a support in the marking process, As a material for discussion, and As a way to communicate objects to students. / Undersökningens syfte är att kartlägga och beskriva några NO-lärares uppfattningar om vilka bedömningskriterier de använder vid betygssättning. Frågor som är relevanta för den här undersökningen är följande: 1. Vilka bedömningsformer utgör underlag för NO-lärares betygssättning? 2. Vilka kunskapskvaliteter bedömer och betygssätter NO-lärare? 3. Hur använder NO-lärare nationella kursplaner och betygskriterier? Fem kvalitativa intervjuer genomfördes med NO-lärare. Intervjumaterialet analyserades med en fenomenografisk analysmetod. Resultatet av den första frågeställningen består av beskrivningskategorierna: Det naturvetenskapliga arbetssättet och Muntlig och skriftlig språkanvändning. Resultatet av den andra frågeställningen består av beskrivningskategorierna: Elevens förmåga att använda den naturvetenskapliga kunskapen i olika sammanhang, Elevens förmåga att använda det naturvetenskapliga språket, Elevens förmåga att utveckla sin naturvetenskapliga kunskap och Elevens beteende. Resultatet i den tredje frågeställningen består av beskrivningskategorierna: Som ett stöd för betygssättningen, Som ett diskussionsunderlag och Som ett sätt att förmedla målen till eleverna.

The application of Art. 87(1) EC to taxes above all is connected to the application of the derogation method, which appears to be part of the selectivity criterion. This dissertation examines the application of the derogation method and the assessment of the selectivity criterion applied to taxes, primarily de lege lata, but also de lege ferenda. It begins with an analysis of the relationship among the criteria of Article 87(1) EC and continues with an analysis of the relationship between the derogation method and the assessment of the selectivity criterion applied to taxes. Several scholars have criticised the application of the derogation method because of the difficulty of identifying a derogation and of establishing the benchmark against which the derogation should be assessed. In this dissertation both the benchmark and the establishment of a derogation is analysed, partly with reference to the tax expenditure debate that occurred in the subject area of international taxation during the 1970s and 1980s. The selectivity criterion applied to taxes contains an assessment of justification, whereby the selective nature of a measure can be justified on the basis of the nature or general scheme of the system: Therfore the meaning and implications of this assessment are also examined. After all these issues have been examined de lege lata, the extents to which the application of the derogation method and the assessment of the selectivity criterion follow a logical system are discussed and recommendations for eliminating the identified deficiences are put forward.

A main aspect of wellbore stability analysis is the selection of an appropriate rock failure criterion. The most commonly used criterion for brittle failure of rocks is the Mohr-Coulomb criterion. This criterion involves only the maximum and minimum principal stresses, s1 and s3, and therefore assumes that the intermediate stress s2 has no influence on rock strength. When the Mohr-Coulomb criterion had been developed, it was justified by experimental evidence from conventional triaxial tests (s1>s2=s3). Based on triaxial failure mechanics, the Mohr-Coulomb criterion has been extensively used to represent rock failure under the polyaxial stress state (s1>s2>s3). In contrast to the predictions of Mohr-Coulomb criterion, much evidence has been accumulating to suggest that s2 does indeed have a strengthening effect. In this research, I have shown that Mohr-Coulomb failure criterion only represents the triaxial stress state (s2=s3 or s2=s1), which is a special case that will only occasionally be encountered in situ. Accordingly, I then developed a new true-triaxial failure criterion called the Mogi-Coulomb criterion. This failure criterion is a linear failure envelope in the Mogi domain (toct-sm,2 space) which can be directly related to the Coulomb strength parameters, cohesion and friction angle. This linear failure criterion has been justified by experimental evidence from triaxial tests as well as polyaxial tests. It is a natural extension of the classical Coulomb criterion into three dimensions. As the Mohr-Coulomb criterion only represents rock failure under triaxial stress states, it is expected to be too conservative in predicting wellbore instability. To overcome this problem, I have developed a new 3D analytical model to estimate the mud pressure required to avoid shear failure at the wall of vertical, horizontal and deviated boreholes. This has been achieved by using linear elasticity theory to calculate the stresses, and the fully-polyaxial Mogi-Coulomb criterion to predict failure. The solution is achieved in closed-form for vertical wellbores, for all stress regimes. For deviated or horizontal wellbores, Mathcad programs have been written to evaluate the solution. These solutions have been applied to several field cases available in the literature, and the new model in each case seems to be consistent with the field experience. / QC 20100629

Failure of bi-material interfaces is studied with the aim to quantify the influence of the induced stress concentrations on the strength of the interfaces. A simple point-stress criterion, used in conjunction with finite element calculations, is evaluated to provide strength predictions for bi-material bonded joints and inserts in polymer foam. The influence of local stress concentrations on the initiation of fracture at open and closed wedge bi-material interfaces is investigated. The joint combinations are analysed numerically and the strength predictions obtained from the point-stress criterion are verified in experiments. The predictions are made using a simple point-stress criterion in combination with highly accurate finite element calculations. The point-stress criterion was known from earlier work to give accurate predictions of failure at cracks and notches but had to be slightly modified to become applicable for the studied configurations. The criterion showed to be generally applicable to the bi-material interfaces studied herein. Sensible predictions for the tendentious strength behaviour could be made with reasonable accuracy, including the prediction of crossover from local, joint-induced failure to global failure. To study the micromechanical properties of a cellular solid with arbitrary topology, various models of a closed-cell foam are created on the basis of random Voronoi tessellations. The foam models are analysed using the finite element method and the effective elastic properties of the model cellular solids are determined. The calculated moduli are compared to the properties of a real reference foam and the numerical results show to be in very good agreement. The mechanical properties of closed-cell, low-density cellular solids are governed by the stiffnesses of the cell edges and the cell faces. Models of idealised foam models with planar cell faces, cannot account for the curved faces found on some metal and polymer foams. Finite element models of closed-cell foams were created to analyse the influence of cell face curvature on the stiffness of the foam. By determining the elastic modulus for foams with non-planar cell faces, the effect of cell face curvature could be analysed as a function of the relative density and the distribution of solid material between cell edges and faces. Foam models were generated from disturbed point distribution lattices and compared to models obtained from random distributions. The aim was to analyse if and how the geometry of the cells and their spatial arrangement influences the mechanical properties of a foam. The results suggest that the spatial arrangement and the geometry of the cells have significant influence on the properties of a foam. The elastic properties calculated for models from disturbed foam structures underestimated the elastic moduli of the foam, whereas models from random structures provided results which were in very good agreement with a reference foam. / QC 20101011

This thesis presents a model that simulates and solves power system dispatch problems utilizing stochastic linear programming. The model features the ability to handle single period, multiple bus, linear DC approximated systems. It determines capacity, energy, and reserve quantities while accounting for N-1 contingency scenarios (single loss of either generator or line) on the network. Market systems applying to this model are also proposed, covering multiple real-time, day-ahead, and hybrid versions of consumer costing, transmission operator payment, and generator remuneration schemes. The model and its market schemes are applied to two test systems to verify its viability: a small 6-bus system and a larger 66-bus system representing the Ontario electricity network.

This thesis presents a model that simulates and solves power system dispatch problems utilizing stochastic linear programming. The model features the ability to handle single period, multiple bus, linear DC approximated systems. It determines capacity, energy, and reserve quantities while accounting for N-1 contingency scenarios (single loss of either generator or line) on the network. Market systems applying to this model are also proposed, covering multiple real-time, day-ahead, and hybrid versions of consumer costing, transmission operator payment, and generator remuneration schemes. The model and its market schemes are applied to two test systems to verify its viability: a small 6-bus system and a larger 66-bus system representing the Ontario electricity network.

Syfte: Undersöka den kriterierelaterade validiteten, mellanbedömarreliabiliteten och användarvänligheten för MEONF, ett screeninginstrument för bedömning av risk för undernäring. Metoder: Hundra patienter inkluderades och nutritionsstatus bedömdes med Mini Nutritional Assessment (MNA) som här anses vara golden standard samt screenades med Malnutrition Universal Screening Tool (MUST) och Minimal Eating Observation and Nutrition Form (MEONF). Resultat: Sjuksköterskorna ansåg MEONFs instruktioner och frågor lätta att förstå, svara på (100 %) samt att frågorna var angelägna (98 %). Instrumentet hade acceptabel sensitivitet (0.83) och specificitet (0.78) jämfört med MNA. Sensitiviteten var högre än den som fanns mellan MUST och MNA (0.57). När BMI ersattes med vadomkrets erhölls likvärdiga resultat (sensibilitet 0.83 specificitet 0.79) för MEONF i förhållande till MNA. Mellanbedömarreliabiliteten var hög (kappa 0.81). Sammanfattning: MEONF har bra validitet jämfört med MNA, med hög mellanbedömarreliabilitet. När BMI ersattes med vadomkrets bibehölls precisionen vilket är viktigt när vikt och längd är svåra att erhålla. Hög sensitivitet är angeläget vid screening för undernäring och i det avseendet fungerar MEONF bättre än MUST. En fundamental vinst med MEONF är att instrumentets kriterier upplevs som meningsfulla, för att vissa svårigheter kan avhjälpas med omvårdnadsåtgärder. Syfte: Undersöka den kriterierelaterade validiteten, mellanbedömarreliabiliteten och användarvänligheten för MEONF, ett screeninginstrument för bedömning av risk för undernäring. Metoder: Hundra patienter inkluderades och nutritionsstatus bedömdes med Mini Nutritional Assessment (MNA) som här anses vara golden standard samt screenades med Malnutrition Universal Screening Tool (MUST) och Minimal Eating Observation and Nutrition Form (MEONF). Resultat: Sjuksköterskorna ansåg MEONFs instruktioner och frågor lätta att förstå, svara på (100 %) samt att frågorna var angelägna (98 %). Instrumentet hade acceptabel sensitivitet (0.83) och specificitet (0.78) jämfört med MNA. Sensitiviteten var högre än den som fanns mellan MUST och MNA (0.57). När BMI ersattes med vadomkrets erhölls likvärdiga resultat (sensibilitet 0.83 specificitet 0.79) för MEONF i förhållande till MNA. Mellanbedömarreliabiliteten var hög (kappa 0.81). Sammanfattning: MEONF har bra validitet jämfört med MNA, med hög mellanbedömarreliabilitet. När BMI ersattes med vadomkrets bibehölls precisionen vilket är viktigt när vikt och längd är svåra att erhålla. Hög sensitivitet är angeläget vid screening för undernäring och i det avseendet fungerar MEONF bättre än MUST. En fundamental vinst med MEONF är att instrumentets kriterier upplevs som meningsfulla, för att vissa svårigheter kan avhjälpas med omvårdnadsåtgärder. / Rationale: Analyse the criterion related validity, interrater reliability and the usefulness of MEONF, an instrument for undernutrition risk screening. Methods: 100 patients were included and assessed with Mini Nutritional Assessment (MNA) regarded as golden standard and screened with Malnutrition Universal Screening Tool (MUST) as well as Minimal Eating Observation and Nutrition Form (MEONF). Results: Nurses regarded MEONF instructions and questions easy to understand, easy to answer (100%) and questions as being important (98%). It had acceptable sensitivity (0.83) and specificity (0.78) in relation to MNA. Sensitivity was higher than found between MUST and MNA (0.57). Replacing BMI with Calf Circumference (CC) gave equivalent results (sensibility 0.83, specificity 0.79) in relation to MNA. Interrater reliability was high (kappa 0.81). Conclusions: MEONF has good validity in relation to MNA and high interrater reliability. If replacing BMI with CC the precision is maintained, which is important in cases were weight or height is difficult to obtain. Having high sensitivity is a major concern for nutritional screening instruments and in that respect MEONF works better than MUST. One fundamental gain with MEONF is that the instruments criteria are experienced as clinically meaningful, in that some observed difficulties can be managed by nursing interventions.

The paper deals with the problem of finding an optimal one-time rebalancing strategy for the Bachelier model, and makes some remarks for the similar problem within Black-Scholes model. The problem is studied on finite time interval under mean-square criterion of optimality. The methods of the paper are based on the results for optimal stopping problem and standard mean-square criterion. The solution of the problem, considered in the paper, let us interpret how and - that is more important for us -when investor should rebalance the portfolio, if he wants to hedge it in the best way.

The design of clinical trials is one of the important problems in medical statistics. Its main purpose is to determine the methodology and the sample size required of a testing study to examine the safety and efficacy of drugs. It is also a part of the Food and Drug Administration approval process. In this thesis, we first study the comparison of the efficacy of drugs in clinical trials. We focus on the two-sample comparison of proportions to investigate testing strategies based on two-stage design. The properties and advantages of the procedures from the proposed testing designs are demonstrated by numerical results, where comparison with the classical method is made under the same sample size. A real example discussed in Cardenal et al. (1999) is provided to explain how the methods may be used in practice. Some figures are also presented to illustrate the pattern changes of the power functions of these methods. In addition, the proposed procedure is also compared with the Pocock (1997) and O¡¦Brien and Fleming (1979) tests based on the standardized statistics. In the second part of this work, the operating room scheduling problem is considered, which is also important in medical studies. The national health insurance system has been conducted more than ten years in Taiwan. The Bureau of National Health Insurance continues to improve the national health insurance system and try to establish a reasonable fee ratio for people in different income ranges. In accordance to the adjustment of the national health insurance system, hospitals must pay more attention to control the running cost. One of the major hospital's revenues is generated by its surgery center operations. In order to maintain financial balance, effective operating room management is necessary. For this topic, this study focuses on the model fitting of operating times and operating room scheduling. Log-normal and mixture log-normal distributions are identified to be acceptable statistically in describing these operating times. The procedure is illustrated through analysis of thirteen operations performed in the gynecology department of a major teaching hospital in southern Taiwan. The best fitting distributions are used to evaluate performances of some operating combinations on daily schedule, which occurred in real data. The fitted distributions are selected through certain information criteria and bootstrapping the log-likelihood ratio test. Moreover, we also classify the operations into three different categories as well as three stages for each operation. Then based on the classification, a strategy of efficient scheduling is proposed. The benefits of rescheduling based on the proposed strategy are compared with the original scheduling observed.