Reduction of aircraft loads, arising as a result of manoeuvre commands or atmospheric turbulence, by means of active control is an important problem in flight control. A variety of methods of designing appropriate control systems to achieve such reduction are available, but not every method is effective. A feature of this research work is the use of an eigenvalue/eigenvector assignment method using full state variable feedback, to design aircraft load alleviation control systems.

A study of the response of submerged mast-like structures to shock loads has been carried out. An analytical model has been developed which uses a lumped parameter system whose equations of motion are solved by the use of finite difference time integration techniques. The effects of the stiffness and damping inherent in the supporting restraints are successfully included into the analysis by assuming that they provide linear rotational stiffness and a viscous type of damping. An analysis of hydrodynamic interaction effects has been developed in order to investigate how the frequency response of the structure is affected by submergence. Changes in both the frequency and the damping characteristics are predicted as a function of the depth of submergence. Methods of incorporation of these hydrodynamic forces into the time domain solution of the lumped mass system are investigated and are found to be most accurate for slender structures. In order to develop a fuller understanding of the hydrodynamic response, two experimental investigations have been carried out. The first is laboratory based and uses carefully controlled free vibration tests to excite a number of modal frequencies of a rigidly clamped vertical mast in both submerged and partially submerged conditions. Results show that the frequency changes are closely predicted by the hydrodynamic analysis developed in this thesis and also show that hydrodynamic damping is a linear function of amplitude of deflection for the first natural response mode over the mast's elastic range of response. To investigate the shock response of submerged structures, a second test rig is used to subject a slender mast to a shock load radiating from an underwater explosion. The structural significance of the higher modal frequencies is evaluated through the use of Fourier Analysis and digital filtering techniques. The instrumentation performance including both damped and undamped transducers is assessed in order to make recommendations for future shock trials. The experimental investigation has shown that both the direct pressure loading and the movement of the supports are important factors in the mast response and that their combination produces important high frequency response modes.

Current environmental and economic trends have forced grid operators to maximize the utilization of the existing assets, which is causing systems to be operated closer to their stability limits than ever before. This requires, among other things, better knowledge and modelling of the existing power system equipment to increase the accuracy of the assessment of current stability margins.This research investigates the possibility of improving the quality of load modeling. The thesis presents a review of the traditional methods for estimation of load model parameters and proposes to use Improved Particle Swarm Optimization. Different algorithms are tested and compared in terms of accuracy, reliability and CPU requirements using computer simulations and real-data captured in a power system.Estimation of frequency and power components has also been studied in this thesis. A review of the existing methods has been provided and the use of an Unscented Kalman Filter proposed. This nonlinear recursive algorithm has been thoroughly tested and compared against selected traditional techniques in a number of experiments involving computer-generated signals as well as measurements obtained in laboratory conditions.

Abstract Natriuretic peptide hormones secreted from the heart are important in maintaining the volume and electrolyte balance and in regulation of blood pressure. The secretion of natriuretic peptides is stimulated by myocyte stretch and paracrine factors. However, the intracellular actions of these stimuli and the cellular and molecular mechanisms involved in the processing and secretion of natriuretic peptides are still largely unknown. In this study, a new model for studies of the natriuretic peptide system was developed using a novel natriuretic peptide from salmon. Salmon (Salmo salar) maintains its water and salt homeostasis despite the volume gain in fresh water and electrolyte gain in sea water. Thus, salmon is an ideal model to study the mechanisms regulating the extracellular volume and salt balance, like natriuretic peptides. Furthermore, comparative studies revealing the common characteristics in phylogenetically distinct species suggest the importance of these factors in the regulation of the natriuretic peptide system. A novel natriuretic peptide, salmon cardiac peptide (sCP), was cloned from salmon heart. Distribution of sCP was studied in a variety of vertebrates and its physiological effects were examined in in vitro and in vivo experiments in salmon and rats. The storage and release of sCP was studied using a salmon ventricle perfusion system and by analysing the molecular forms of stored and secreted forms. Factors modulating the secretion and circulating concentration of sCP, and cardiac peptide and sCP mRNA level in salmon were examined as well. The biosynthesis of sCP is strictly restricted to the heart. sCP is stored in myocytes in the prohormone form, while the secreted form is a 29-amino acid peptide in salmon. Mechanical load on isolated salmon ventricle and volume overload in intact salmon induced a rapid release of sCP. Exposure to hyperosmotic environment decreased the plasma sCP level. sCP increased diuresis and natriuresis, as well as relaxed preconstricted arteries from salmon and rats. Thus the storage, processing and release of sCP resembles those of mammalian ANP. The circulating level of sCP in salmon was markedly upregulated at increased temperatures. Upregulation resulted from decreased elimination rather than increased secretion of sCP, providing the first direct evidence that elimination is used for the regulation of the natriuretic peptide system. In conclusion, sCP is a promising model for studying the general factors regulating the cardiac natriuretic peptides.

In this study, the author investigated factors that influence the direct measurement of cognitive load using the dual-task method. The dual-task method is an unambiguous and objective technique to measure cognitive load. The primary task was to master content in a lesson about the Autonomic Nervous System. The secondary task was to respond to a symbol that changed colour by pressing the Enter key. The time between the symbol changing colour and the response of the student was measured. Two versions of the multimedia program tested the influence of the presentation format and instructional strategy on cognitive load. Each version of the program was further subdivided into four lessons, which were used to test the influence of the position of the secondary task on the cognitive load. All the data was collected electronically. The statistical analysis revealed that the position of the secondary task does not influence cognitive load (F (1, 2661) = 3.25, p = 0.071). The presentation format and instructional strategy used in this study however did result in a significant difference between the cognitive load of the two versions. The mean cognitive load of the version using animation was 6.408 and that of the version using predominantly static images and text was 5.684. This difference was found to be highly significant (F (1, 2661) = 52.39, p <.0001). It was concluded that using animation to present content required more mental effort by participants than using images and text to present the same content. / Dissertation (MEd (Computer-Integrated Education))--University of Pretoria, 2007. / Curriculum Studies / unrestricted

Many aircraft are designed using the Damage-Tolerance concept. This concept assumes that a structural component is flawed during the manufacturing process. A central feature in this concept is the fatigue-crack-growth-rate properties of the material used in its construction. ASTM E-647 standard describes how fatigue crack growth tests are to be conducted. In the late 1960’s, Wolf Elber discovered the concept of crack closure. He showed that the crack would close prematurely even while under tensile loading. A central feature in this concept is called the crack opening load. The method in ASTM E-647 used to calculate the crack opening load has been found to be inadequate for high load ratios R (Pmin/Pmax>0.4) tests. Herein, an algorithm implementing the least squares method was developed to determine the crack-opening load for low and high R tests on a variety of materials for fatigue crack growth tests conducted on compact C(T) specimens.

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