3,785 research outputs found
An evaluation of the development and use of a microcomputer assisted system for planning individualised adult literacy programmes in an adult basic education unit
The thesis describes the development, implementation and evaluation of a computer assisted system for planning individualised adult literacy programmes in an adult basic education (ABE) unit located in an English College of Further Education. After examining past and current developments of Computer Based Applications in Education, both in general and in Literacy Teaching Applications, conclusions as to the appropriate use of computer-based learning in the proposed context are drawn. Human and hardware resources available in the ABE unit are detailed and appropriate aims for a proposed system based on the earlier conclusions are set out. A possible system instructional model is discussed via details of the current teaching, monitoring and evaluation activities of the unit. An examination of the current theory, practice and literature relating to literacy and adult literacy teaching enables a conclusion that a student-centred approach, in a real world context, using a common core curriculum, is most suitable. A detailed common-core curriculum model for teaching adult literacy is then proposed, following which a Warnier-Orr design exercise of a computer-based system known as MALCM, using the model, is described, from initial considerations through to system testing. The implementation and evaluation of the MALCM system in the setting of the ABE Unit is then described in the form of a case study. The reported and observed experiences of staff involved are analysed and the appropriateness of the case study as a means for evaluation is discussed. The thesis concludes by endorsing the potential for a system such as MALCM but underlines the need for user involvement in any CBL learning management development; It suggests that further development of the MALCM system as currently constituted is non-viable without considerable refinements to take account of developments in the field of hardware and intelligent knowledge-based systems
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Study of External Kink Modes in Shaped HBT-EP Plasmas
The first study of magnetohydrodynamic (MHD) equilibria and external kink modes in shaped plasmas on the High Beta Tokamak - Extended Pulse (HBT-EP) is described. A new poloidal field coil and high-current, low-voltage capacitive power supply was designed and installed. The new coil significantly modifies the shape of the plasma cross section and provides a new research tool for the study of kink mode structure and control. When fully energized, the coil creates a magnetic separatrix, which defines the boundary between confined and unconfined plasma. The separatrix is set by a poloidal field null called an “X-point”, which is on the inboard side of the torus, above the midplane. Several arrays of magnetic sensors observe and characterize the plasma equilibrium and the MHD fluctuations from kink modes. Free-boundary plasma equilibria are reconstructed using standard methods that minimize the mean-square error between the numerically reconstructed equilibria and various measurements. Reconstructions of shaped plasma equilibria show the creation of fully diverted plasmas with shaped outer boundaries. The reconstructions are confirmed by direct measurements using arrays of magnetic sensors and a moveable Langmuir probe to measure the outermost closed flux surface. Measurements of individual kink modes are obtained from the magnetic fluctuations using a technique known as biorthogonal decomposition. External kink modes that naturally arise in shaped plasmas are observed and described. The poloidal structure of modes in shaped plasmas are found to be similar to those that arise in circular plasmas, except near the X-point. The magnetic signature of kink modes on the surface of the plasma are calculated using the ideal MHD code DCON. For plasmas with an X-point, DCON shows a short-wavelength, low amplitude structure near the X-point. The code VALEN is used to calculate the perturbed magnetic field measured at the sensors due to the DCON mode at the plasma surface. VALEN includes the effects of sensor/plasma separation and eddy currents induced in conducting structures by rotation of the modes. Good agreement is found between the measured mode structures and the ideal kink mode structures calculated at the sensors by VALEN. A distributed array of forty active control coils was used to perturb the plasma equilibria, and for both shaped and circular equilibria, the structure of the response to the perturbation was found to be the same as the that of the dominant naturally occurring mode in that equilibrium. Finally, the magnitude of the plasma’s response to applied magnetic perturbations was found to be comparable between shaped and unshaped plasmas, even though separation between the sensors and the boundary of the shaped plasmas increases relative to circular plasmas with the same plasma current and radial positions. In addition to demonstrating a new research tool for study of kink modes on HBT-EP, this research demonstrates the importance of accurate electromagnetic calculations, including eddy currents, when comparing measured and predicted mode structure
Fundamentals of Fluid Film Thrust Bearing Operation and Modeling
TutorialsWidely used in turbomachinery, the fluid film thrust bearing is critical to the overall reliability of a machine. Their design complexity and application severity continue to increase, making it challenging for the plant engineer to evaluate their reliability. This tutorial first provides practical knowledge on their basic physics, including hydrodynamic pressure generation, temperature rise due to internal viscous shearing and elastic deformation, as well as how those aspects interact with each other during operation. Examples are given to demonstrate how common design and operational parameters affect a bearing’s key performance parameters, such as the minimum film thickness and pad temperature. Then, this tutorial reviews the analytical models used to simulate the various physical aspects. The state of the art techniques for modeling important aspects are presented, along with discussions on their capabilities and limitations. Also covered in this tutorial are subjects including flooded versus evacuated housing design and direct lubrication, as well as a brief discussion on dynamics
Validity of the Cauchy-Born rule applied to discrete cellular-scale models of biological tissues.
The development of new models of biological tissues that consider cells in a discrete manner is becoming increasingly popular as an alternative to continuum methods based on partial differential equations, although formal relationships between the discrete and continuum frameworks remain to be established. For crystal mechanics, the discrete-to-continuum bridge is often made by assuming that local atom displacements can be mapped homogeneously from the mesoscale deformation gradient, an assumption known as the Cauchy-Born rule (CBR). Although the CBR does not hold exactly for noncrystalline materials, it may still be used as a first-order approximation for analytic calculations of effective stresses or strain energies. In this work, our goal is to investigate numerically the applicability of the CBR to two-dimensional cellular-scale models by assessing the mechanical behavior of model biological tissues, including crystalline (honeycomb) and noncrystalline reference states. The numerical procedure involves applying an affine deformation to the boundary cells and computing the quasistatic position of internal cells. The position of internal cells is then compared with the prediction of the CBR and an average deviation is calculated in the strain domain. For center-based cell models, we show that the CBR holds exactly when the deformation gradient is relatively small and the reference stress-free configuration is defined by a honeycomb lattice. We show further that the CBR may be used approximately when the reference state is perturbed from the honeycomb configuration. By contrast, for vertex-based cell models, a similar analysis reveals that the CBR does not provide a good representation of the tissue mechanics, even when the reference configuration is defined by a honeycomb lattice. The paper concludes with a discussion of the implications of these results for concurrent discrete and continuous modeling, adaptation of atom-to-continuum techniques to biological tissues, and model classification
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