In the past few years, a possible new population of sources emitting fast and bright transient radio bursts have been discovered. To explore this new transient phase space, the next generation of radio telescopes, typically interferometers, provide wide observing bandwidths in order to achieve high sensitivity for the detection of weak sources and multi-beaming capabilities to increase the field of view. In comparison to a traditional single beam radio dish, these telescopes collect vast volumes of data and still rely on the traditional observing techniques. Localising transient events during their discovery is essential as these events might not be repeatable by nature. I describe the development and construction of a prototype phased array, the Manchester University Student Telescope (MUST), capable of multi-beam operation. I present results of the Yagi antenna beam measurements and the optimum antenna separations; the investigation of the radio frequency interference spectrum around the preferred observing band and setting the subsequent bandpass filter specifications; simulations of the optimum configurations of the MUST tiles; and finally I describe implementation of the digital back-end. For the joint task of discovery and simultaneous localisation, the advantages of single dishes and interferometers are combined in a beam forming approach. I present an investigation into the wide-bandwidth time-domain signal processing techniques for time-domain beamforming that can be used in transient and pulsar observations. I discuss the efficient polyphase decomposition for interpolation digital filters and multiplication-free fractional delay filters that can be used to reduce the complexity of the beamformer implementation and avoid high sampling rates. This reduced complexity allows more simultaneous beams to be formed using time-domain techniques. This analysis was performed for the MUST array, but is applicable to a wide range of interferometers. I have developed and analysed a new proof-of-concept non-imaging method to localise transient sources observed with interferometers or phased array feeds. It utilises the additional spectral and comparative spatial information obtained from multiple overlapping tied array beams. This allows us to estimatea transient source location with up to arc second accuracy in almost real time and allows the required high time resolution to be preserved. We demonstrate that this method can work for a variety of interferometric configurations, including for LOFAR and MeerKAT, and that the estimated angular position may be sufficient to identify a host galaxy, or other related object, without reference to other simultaneous or follow-up observations.

Techniques for modelling of synchronous generators in the simulation of electromagnetic transients are described. First of all, an adequate mathematical model of the generator is established. It uses the conventional set of generator data only, which are readily available, but it is flexible enough to accommodate additional data, if and when such become available. The resulting differential equations of the generator are then transformed into linear algebraic equations, with a time varying coefficient matrix, by using the numerically stable trapezoidal rule of integration. These equations can be interfaced with the equations of an electromagnetic transients program in one of two ways: (a) Solve the equations of the generator simultaneously with the equations of a three-phase Thevenin equivalent circuit of the transmission network seen from the generator terminals. (b) Replace the generator model with a modified Thevenin equivalent circuit and solve the network equations with the generator treated as known voltage sources e[sup red][sub ph] (t-Δt) behind constant resistances [R [sup red][sub ph]]. After the network solution at each time step, the stator quantities are known and used to solve the equations for the rotor windings. These two methods cover, in principle, all possible interfacing techniques. They are not tied to the trapezoidal rule of integration, but can be used with any other implicit integration technique. The results obtained with these two techniques are practically identical. Interfacing by method (b), however, is more general since it does not require a Thevenin equivalent circuit of the network seen from the generator terminals. The numerical examples used in this thesis contain comparisons with field test results in order to verify the adequacy of the generator model as well as the correctness of the numerical procedures. A short discussion of nonlinear saturation effects is also presented. A method of including these effects into the model of the generator is then proposed. Typical applications of the developed numerical procedures include dynamic overvoltages, torsional vibrations of the turbine-generator shaft system, resynchronization of the generator after pole slipping and detailed assessment of generator damping terms in transient stability simulations. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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Transient stability analysis is an important part of power system planning and operation. For large power systems, such analysis is very demanding in computation time. On-line transient stability assessment will be necessary for secure and reliable operation of power systems in the near future because systems are operated close to their maximum limits. In the last two decades, a vast amount of research work has been done in the area of fast transient stability assessment by direct methods. The major difficulties associated with direct methods are the limitations in the power system model, determination of transient stability regions and adaptation to changes in operating conditions. In this thesis catastrophe theory is used to determine the transient stability regions. Taylor series expansion is used to find the energy balance equation in terms of clearing time and system transient parameters. The energy function is then put in the form of a catastrophe manifold from which the bifurcation set is extracted. The bifurcation set represents the transient stability region in terms of the power system transient parameters bounded by the transient stability limits. The transient stability regions determined are valid for any changes in loading conditions and fault location. The transient stability problem is dealt with in the two dimensions of transient stability limits and critical clearing times. Transient stability limits are given by the bifurcation set and the critical clearing times are calculated from the catastrophe manifold equation. The method achieves a breakthrough in the modelling problem because the effects of exciter response, flux decay and systems damping can all be included in the transient stability analysis. Numerical examples of one-machine infinite-bus and multi-machine power systems show very good agreement with the time solution in the practical range of first swing stability analysis. The method presented fulfills all requirements for on-line assessment of transient stability of power systems. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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Thesis (Ph. D.)--Naval Postgraduate School, 2002. / Thesis advisor(s): Herschel H. Loomis, Jr., Alan A. Ross. Includes bibliographical references (p. 157-161). Also available online.

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Neurotransmitter release is modulated by multiple regulatory mechanisms that control several stages of synaptic vesicle (SV) exocytosis. At the final stage, SV fusion with the presynaptic membrane requires calcium influx through voltage-gated calcium channels, and regulatory mechanisms that alter the surface expression or conductance of calcium channels have large effects on neurotransmitter release. To determine how these mechanisms contribute to synapse-specific modulations of neurotransmitter release and synaptic strength, we require a means to monitor presynaptic calcium transients at individual synapses. Genetically encoded calcium indicators (GECIs), engineered proteins that change their fluorescence emission properties upon calcium binding, generally lack the sensitivity to measure such transients in response to isolated stimuli. Therefore, we modified the GECI, GCaMP3, by altering its sensitivity for calcium. Our results suggest the modified GCaMP-based presynaptically targeted GECIs are excellent tools to quantify presynaptic calcium transients at individual synapses in response to isolated action potentials.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 53-56). Also available via the Internet.