In a world where money often is the main controlling factor, everything that can be tends to be more and more optimized. Regarding electrical machines, developers have always had the goal to make them better. The latest trend is to make machines as efficient as possible, which calls for accurate simulation models where different designs can be tested and evaluated. The finite element method is probably the most popular approach since it makes it possible to, in an easy and accurate way, get numerical solutions to a variety of physics problems with complex geometries and non-linear materials. This licentiate thesis includes two different projects in which finite element methods have had a central roll. In the first project, the goal was to develop a simulation model to be able to predict demagnetization of permanent magnets. It is of great importance to be able to predict if a permanent magnet will be demagnetized or not in a certain situation. In the worst case, the permanent magnets will be completely destroyed and the machine will be completely useless. However, it is more probable that the permanent magnets will not be completely destroyed and that the machine still will be functional but not as good as before. In a time where money is more important than ever, the utilization has to be as high as possible. In this study the demagnetization risk for different rotor geometries in a 12 kW direct driven permanent magnet synchronous generator was studied with a proprietary finite element method simulation model. The demagnetization study of the different rotor geometries and magnet grades showed that here is no risk for the permanent magnets in the rotor as it is designed today to be demagnetized. The project also included experimental verification of the simulation model. The simulation model was compared with experiments and the results showed good agreement. The second project treated the redesign of the rotor in the generator previously mentioned. The goal was to redesign the surface mounted NdFeB rotor to use a field concentrating design with ferrite permanent magnets instead. The motivation was that the price on NdFeB magnets has fluctuated a lot the last few years as well as to see if it was physically possible to fit a ferrite rotor in the same space as the NdFeB rotor. A new rotor design with ferrite permanent magnets was presented together with an electromagnetic and a mechanical design.

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Thermal modelling is of great importance in all electric machines but especially in permanent magnet synchronous machines (PMSMs). The thermally fragile permanent magnets (PMs) can more easily be demagnetized at high temperatures. When high speed machines are considered, heat extraction surfaces are small due to the higher energy density. This thesis focuses on the thermal modelling of a high speed slotless PMSM using analytical techniques. From literature it is clear that analytical distributed models have not reached its full potential in thermal modelling of electric machines. Thermal experiments on high speed electric machine, including rotor PM temperature measurements are not commonly found in literature. The thermal behaviour of each component of the machine is influenced by the overall temperature distribution. The widely used lumped parameter (LP) cylindrical component model derived by Mellor et al. is used to derive a LP model of the entire machine. A two dimensional (2-D) analytical distributed model is derived for the rotor PM using the separation of variables method. Three of the boundaries are assumed to be of the convection type and the fourth of constant heat flow type. Different convection coefficients are assumed to exist in the radial and axial directions. The distributed model is verified using COMSOL R and good correlation is shown. The distributed model is used to determine the temperature distribution in the PM and the convection heat flow in the axial direction. Loss calculation is an integral part of thermal modelling. Temperature changes in an electric machine is due to the interaction between the heat generation (losses) and heat removal. The losses found in a high speed slotless PMSM are investigated. A 2-D analytical magnetic model is used to determine the stator lamination loss as well as the stator winding eddy current loss. A simple LP model is derived for the rotor eddy current loss. Due to the relatively large resistivity of the shielding cylinder and PM material, the rotor eddy current loss is a significant part of the total machine loss. The tangential current width is determined empirically in this thesis but a 3-D distributed model which includes end space effects and skin depth could also be used. A large part of thermal modelling is empirically based. The convection and interface resistances are determined through a set of experiments in this thesis. The measured and calculated convection coefficients correlated well for both forced and natural convection cooling. A large temperature increase found during the no-load test can be attributed to large bearing loss, possibly due to axial loading. The LP model is modified to include the phenomena found during the experiments. The thermal model is used to predict the temperatures of a high speed PMSM at rated load and speed. Although the PM is not heated above the Curie temperature, demagnetization is still possible. According to the model, the machine will not be able to operate at full load and speed for extensive periods due to mechanical stress limits being exceeded. The temperature distribution of the PM could not be verified since the temperatures in the air gap and end space could not be measured. It is expected that axial heat flow will be larger than what is currently predicted by the distributed model. A sensitivity analysis was used to investigate the influence of the thermal resistances and losses on the machine temperatures. Methods for reducing the rotor eddy current loss and interface resistances are also discussed. The first contribution of this thesis is the 2-D analytical distributed model for the PM of a high speed PMSM. Hot spots and 2-D heat flow can be analysed using this model. Combining the LP and 2-D analytical distributed models is another contribution. This combines the simplicity and fast solution times of the LP model with the 2-D thermal distribution of the analytical distributed model. The systematic experimental investigation of the thermal behaviour of a high speed PMSM is a further contribution. / Thesis (Ph.D. (Electrical Engineering))--North-West University, Potchefstroom Campus, 2011.

If A is an nxn matrix, then the permanent of A is the sum of all products of entries on each of n! diagonals of A. Also, A is called doubly stochastic if it has non-negative entries and the row and column sums are all equal to one. A conjecture on the minimum of the permanent on the set of doubly stochastic matrices was stated by van der Waerden in 1926 and became one of the most studied conjectures for permanents. It was open for more than 50 years until, in 1981, Egorychev and Falikman independently settled it. Another conjecture (which, if it were true, would imply the van der Waerden conjecture) was originally stated by Holens in 1964 in his M.Sc. thesis at the University of Manitoba. Three years later, Dokovic independently introduced an equivalent conjecture. This conjecture is now known as the Holens-Dokovic conjecture, and while known not to be true in general, it still remains unresolved for some specific cases. This thesis is devoted to the study of these and other conjectures on permanents.

Thermal modelling is of great importance in all electric machines but especially in permanent magnet synchronous machines (PMSMs). The thermally fragile permanent magnets (PMs) can more easily be demagnetized at high temperatures. When high speed machines are considered, heat extraction surfaces are small due to the higher energy density. This thesis focuses on the thermal modelling of a high speed slotless PMSM using analytical techniques. From literature it is clear that analytical distributed models have not reached its full potential in thermal modelling of electric machines. Thermal experiments on high speed electric machine, including rotor PM temperature measurements are not commonly found in literature. The thermal behaviour of each component of the machine is influenced by the overall temperature distribution. The widely used lumped parameter (LP) cylindrical component model derived by Mellor et al. is used to derive a LP model of the entire machine. A two dimensional (2-D) analytical distributed model is derived for the rotor PM using the separation of variables method. Three of the boundaries are assumed to be of the convection type and the fourth of constant heat flow type. Different convection coefficients are assumed to exist in the radial and axial directions. The distributed model is verified using COMSOL R and good correlation is shown. The distributed model is used to determine the temperature distribution in the PM and the convection heat flow in the axial direction. Loss calculation is an integral part of thermal modelling. Temperature changes in an electric machine is due to the interaction between the heat generation (losses) and heat removal. The losses found in a high speed slotless PMSM are investigated. A 2-D analytical magnetic model is used to determine the stator lamination loss as well as the stator winding eddy current loss. A simple LP model is derived for the rotor eddy current loss. Due to the relatively large resistivity of the shielding cylinder and PM material, the rotor eddy current loss is a significant part of the total machine loss. The tangential current width is determined empirically in this thesis but a 3-D distributed model which includes end space effects and skin depth could also be used. A large part of thermal modelling is empirically based. The convection and interface resistances are determined through a set of experiments in this thesis. The measured and calculated convection coefficients correlated well for both forced and natural convection cooling. A large temperature increase found during the no-load test can be attributed to large bearing loss, possibly due to axial loading. The LP model is modified to include the phenomena found during the experiments. The thermal model is used to predict the temperatures of a high speed PMSM at rated load and speed. Although the PM is not heated above the Curie temperature, demagnetization is still possible. According to the model, the machine will not be able to operate at full load and speed for extensive periods due to mechanical stress limits being exceeded. The temperature distribution of the PM could not be verified since the temperatures in the air gap and end space could not be measured. It is expected that axial heat flow will be larger than what is currently predicted by the distributed model. A sensitivity analysis was used to investigate the influence of the thermal resistances and losses on the machine temperatures. Methods for reducing the rotor eddy current loss and interface resistances are also discussed. The first contribution of this thesis is the 2-D analytical distributed model for the PM of a high speed PMSM. Hot spots and 2-D heat flow can be analysed using this model. Combining the LP and 2-D analytical distributed models is another contribution. This combines the simplicity and fast solution times of the LP model with the 2-D thermal distribution of the analytical distributed model. The systematic experimental investigation of the thermal behaviour of a high speed PMSM is a further contribution. / Thesis (Ph.D. (Electrical Engineering))--North-West University, Potchefstroom Campus, 2011.

There is a general assumption that permanent teeth in children are emerging into the oral cavity earlier than the dates given in published scientific studies conducted many years ago. In the course of this research a rigorous experimental protocol was devised to provide reliable data collection and analysis methods and give contemporary emergence rate estimations with a strong scientific basis. In addition equations are presented to predict the chronological age of children using only the sex of the child and the number of permanent teeth present. Data was collected between April 1998 and July 2001 from 12,395 children between 4 and 15 years of age, in the Colchester area of the UK. The results show that the ages of emergence of the permanent teeth are later than previously assumed. This research also confirms previous research showing that girl's teeth emerge before boy's teeth, that there is no statistical difference in the age of emergence contra-lateral teeth in the same arch and that there is a statistical difference in the age of emergence of ipsi-lateral teeth in opposing arches.

Electromagnetic microactuators with permanent magnets have many potential applications such as micro-energy scavengers, microswitches, micromirrors and microfluidics. However, many electromagnetic microactuator designs utilize either external permanent magnet or external coil, which do not allow tight integration to other MEMS components and further miniaturization. Furthermore, all of the available permanent magnet microfabrication technologies have some drawbacks and improvements are required. Thus the integrated monolithic electromagnetic microactuator is investigated in this project. The three main components of the electromagnetic actuator have been investigated separately. A novel microfabrication technology called ???Template printing???for the fabrication of polymer bonded permanent magnet has been investigated and developed. It is based on ???Screen printing??? which has its drawbacks on alignment accuracy and poor line definition. This is eliminated in ???Template printing??? by photolithography of the photoresist template. The shape and location of the permanent magnet is defined by the template. A new approach based on the filling of dry magnetic powder and vacuum impregnation has been developed to form the polymer bonded permanent magnet. This allows the use of short pot-life matrix material and the elimination of homogenous mixing. A monolithic electromagnetic microactuator has been fabricated successfully. It consists of a 2-layer planar copper microcoil, surface micromachined polyimide beam and Strontium ferrite/EPOFIX permanent magnet (diameter of 460 ??m and 30 ??m thickness). Large deflection in excess of 100 ??m at 35 mA driving current and magnetic force of 0.39 ??N/mA have been achieved. It compares favourably with other much larger electromagnetic actuators that have been reported. ???Template printing??? has the potential of being a low temperature batch process for the microfabrication of thick polymer bonded permanent magnets with high magnetic properties and low residual stress. The fabrication consistency and the quality of template printed magnet can be improved in future studies.

Many high performance drive applications require wide Constant Power Speed Range (CPSR) for efficient use of energy. The examples of such applications are the starter alternator system of automobiles proposed for the 42V PowerNet, traction in the hybrid/electric vehicle, wind power generator etc. The Permanent Magnet (PM) machine is the natural choice of such niche applications because of their higher efficiency and compact size. However, the Surface Permanent Magnet (SPM) machine with sine distributed winding and radially-laminated Interior Permanent Magnet (IPM) machine with conventional structure has very limited or zero flux-weakening capability. The flux-weakening capability of the SPM machine can be improved by using concentrated, fractional-slot stator but here well-known advantages of the sine distributed winding are needed to be compromised. In the IPM machine, fluxweakening was improved using axial lamination and more than two magnet layers per pole. However, the construction of such IPM machine is complicated and expensive. This thesis presents design and analysis of a new type of the Interior Permanent Magnet (IPM) machine that have a very wide Constant Power Speed Range (CPSR) without compromising simplicity of construction and advantages of the distribution winding. In the new IPM machine, the magnet poles were segmented in the radially direction and the iron bridges between magnet segments provide for additional paths of flux-canalization to give the rotor an inherent capability of fluxweakening. Consequently, a very wide constant power speed range can be achieved in such machines. The proposed IPM machine of this work was referred as the Segmented IPM machine. The thesis focuses on the optimization of the Segmented IPM machine in a 42V environment of the automobile. First, for the conceptual evaluation a 4 pole, 550W Segmented Magnet IPM machine was optimized using finite element analysis. The parameters were calculated for prediction of the steady-state and transient performances. The torque- and power-speed capability were estimated using time-step, circuit-coupled finite element analysis. The cogging torque and variation of iron loss with frequency were also investigated during the design process. A prototype machine was constructed on the basis of the optimized design. The steady-state and transient performances of the prototype machine were measured and compared with the predicted results for experimental verification. The measured performance analysis was found to match very well with the predicted results. The measured torque- and power-speed capability of the Segmented IPM machine was also compared to those of a conventional, non-segmented IPM machine of similar rating and size. The thesis also presents the optimized design of a 6kW, 12 pole Segmented Magnet IPM machine for application in the Integrated Starter Alternator (ISA) of the electric/hybrid vehicle. It can be concluded from the predicted steady-state analysis of the 6 kW, 12 pole Segmented Magnet IPM machine that it should be able to satisfy most of the required criteria of an ISA with appropriate design optimization.

This research study examines the psychological and emotional experiences of children and parents as they embark on a permanent placement living arrangement. A permanent placement living arrangement is entered into when a child is no longer able to reside with their family of origin. Three family groups participated in the study and separate interviews were conducted with both the children and placement parents. Overall, three interviews were conducted, with the first interview taking place prior to the child’s transition into the family. A further two interviews were conducted with the participants after the transition had taken place. The findings of this study indicate that both the parents and children were profoundly affected by the experience of permanent placement. The common themes that emerged from the data were the hopes, anxieties and coping strategies of the participants which became the focal point of analysis. The parents experienced a mixture of fulfilment, tempered with anxieties of whether they would be able to provide adequate care for the child placed with them. Whereas, the children appeared to find it difficult to trust that this experience would be any different from their previous experiences. The study concludes that further attention is needed in the preparation for the transition into permanent placement. It further concludes that ‘after transition’ support is important to the stability of the placement.

Thesis (Ed. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.