The prediction of turbogenerator behaviour following fault or disturbance conditions has attracted much interest over the past decade, due to the large amplitude torsional oscillations which can be induced. Many simulation studies have been conducted, but the majority have used d-q models to simulate the electrical machines, and have modelled the turbine shaft damping as constant viscous damping. The d-q machine representation is adequate for balanced conditions, whereas the phase coordinate electrical machine model may be used to simulate unbalanced operation. The latter is adopted for the present work. Constant viscous shaft damping is known to be an over simplification which does not truly reflect the stress level dependent, frequency independent nature of shaft material damping. Although small, the mechanical damping can have a decisive influence over the rate of decay of torsional oscillations, and hence on shaft fatigue life expenditure. This project seeks principally to enhance the shaft torsional model formulation by developing methods of simulating variable shaft damping. Two methods are proposed; one in which a stress-strain hysteresis loop is simulated for each shaft section leading to a variable shaft stiffness, and a second simpler method, in which the viscous damping representation is retained, but with variable viscous damping coefficients. It is shown that the effect of incorporating variable damping is to increase the rate of decay of the initial post-fault oscillations, but then to prolong the subsequent oscillations. This is the effect generally observed in practice on full size turbogenerators. Experimental results from a small single shaft rig also show this effect and agree closely with the predictions of the theory. A brief study of the fatigue life expenditure in a turbogenerator shaft during post-fault oscillations is also presented. It is concluded that both the proposed methods of simulating variable mechanical damping have feasible practical applications, and that the use of variable damping in simulation models can significantly improve the prediction of rate of decay of turbogenerator post-fault torsional oscillations.

The topic of this dissertation is the study of the emergence of higher-order correlations in recurrentlyconnected populations of brain cells.Neurons have been experimentally shown to form vast networks in the brain. In these networks, eachbrain cell communicates with tens of thousands of its neighbors by sending out and receiving electricalsignals, known as action potentials or spikes. The effect of a single action potential can propagate throughthe network and cause additional spikes to be generated. Thus, the connectivity of the neuronal networkgreatly influences the network's spiking dynamics. However, while the methods of action potentialgeneration are very well studied, many dynamical features of neuronal networks are still only vaguelyunderstood.The reasons for this mostly have to do with the difficulties of keeping track of the collective, non-linearbehavior of hundreds of millions of brain cells. Even when one focuses on small groups of neurons, all butthe most trivial questions about coordinated activity remain unanswered, due to the combinatorialexplosion that arises in all questions of this sort. In theoretical neuroscience one often needs to resort tomathematical models that try to explain the most important dynamical phenomena while abstractingaway many of the morphological features of real neurons.On the other hand, advances in experimental methods are making simultaneous recording of largeneuronal populations possible. Datasets consisting of collective spike trains of thousands of neurons arebecoming available. With these new developments comes the possibility of finally understanding the wayin which connectivity gives rise to the many interesting dynamical aspects of spiking networks.The main research question, addressed in this thesis, is how connectivity between neurons influences thedegree of synchrony between their respective spike trains. Using a linear model of spiking neurondynamics, we show that there is a mathematical relationship between the network's connectivity and theso-called higher-order cumulants, which quantify beyond-chance-level coordinated activity of groups ofneurons. Our equations describe the specific connectivity patterns that give rise to higher-ordercorrelations. In addition, we explore the special case of correlations of third-order and find that, in large,regular networks, it is the presence of a single subtree that is responsible for third-order synchrony.In summary, the results presented in this dissertation advance our understanding of how higher-ordercorrelations between spike trains of neurons are affected by certain patterns in synaptic connectivity.Our hope is that a better understanding of such complicated neuronal dynamics can lead to a consistenttheory of the network's functional properties. / <p>QC 20161003</p>

Working memory, which enables the temporary storage of information in an active “online” state, is an exceptionally capacity limited system. Given this capacity limit, irrelevant information in our environment must be filtered out, while relevant representation is maintained. Research has shown that neural oscillations in the alpha frequency range (8-12Hz) are greatly influenced by the number of items in memory. Most work has argued that alpha oscillations primarily support working memory processing by suppressing information that could interfere with items already in memory, as indexed by an increase in alpha power. However, other work has shown that decreases in alpha power, with little evidence of concurrent increases, support the maintenance of working memory representations. In this thesis we show that, in the context of visual working memory, the primary role of alpha oscillations is to maintain distinct working memory representations, rather than to suppress irrelevant information. This is shown in a series of three experiments all indicating that as the number of relevant items increases, the power of alpha oscillations systematically decreases. In the first experiment, we use a whole report and change detection task to examine how the number of items in memory influences alpha oscillations. In the second experiment, we use a cuing (Experiment 2A) and filtering (Experiment 2B) paradigm to demonstrate that alpha power tracks the number of remembered items instead of the number of total items on the screen. Lastly, by presenting items sequentially (Experiment 3A) or in overlapping locations (Experiment 3B), we see evidence that decreases in alpha power are related to the maintenance of relevant spatial locations, instead of the number of items in memory. The results of the experiments suggest that alpha power reflects the maintenance of relevant working memory representations, rather than the suppression of irrelevant external distractors or the inhibition of task-irrelevant neural areas. Furthermore, our last experiment indicates that the alpha frequency band is especially sensitive to the maintenance of spatial information.

Ngai Wah Kai = 中微子混合角[theta]₁₃測量的最優化與本底研究 / 魏華佳. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 83-87). / Text in English; abstracts in English and Chinese. / Ngai Wah Kai = Zhong wei zi hun he jiao [theta]₁₃ ce liang de zui you hua yu ben di yan jiu / Wei Huajia. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Puzzle with Beta Decay Spectrum --- p.2 / Chapter 1.2 --- Detection of a Free Neutrino --- p.3 / Chapter 1.3 --- Properties of Neutrinos --- p.5 / Chapter 1.3.1 --- Neutrino Mass --- p.6 / Chapter 1.3.2 --- Dirac and Majorana Neutrinos --- p.7 / Chapter 1.3.3 --- Neutrino Oscillation --- p.8 / Chapter 1.4 --- Background to Underground Neutrino Experiments --- p.10 / Chapter 1.5 --- Outline of the Thesis --- p.12 / Chapter 2 --- The Last Mixing Angle and Daya Bay --- p.14 / Chapter 2.1 --- Current Status of Neutrino Oscillation --- p.14 / Chapter 2.2 --- Measurement of θ13 with Reactors --- p.19 / Chapter 2.3 --- "Daya Bay, the Site and the Detector" --- p.20 / Chapter 2.3.1 --- Overview --- p.20 / Chapter 2.3.2 --- Detector --- p.22 / Chapter 3 --- Detector Baseline Optimization --- p.24 / Chapter 3.1 --- Antineutrino Spectrum and Flux from Reactors --- p.25 / Chapter 3.1.1 --- Antineutrino Production --- p.25 / Chapter 3.1.2 --- Antineutrino Spectrum from Reactors --- p.26 / Chapter 3.2 --- Interaction Rate Analysis --- p.29 / Chapter 3.3 --- Spectral Analysis --- p.30 / Chapter 3.3.1 --- Effect of Three-Neutrino Mixing --- p.33 / Chapter 4 --- Energy Resolution of the Proposed Antineutrino Detector --- p.37 / Chapter 4.1 --- Physical Processes inside the Detector --- p.38 / Chapter 4.2 --- Simulation Algorithm --- p.39 / Chapter 4.3 --- Comparison of Different Detector Geometries and Configurations --- p.43 / Chapter 5 --- Aberdeen Tunnel Laboratory - A Satellite Lab of Daya Bay --- p.53 / Chapter 5.1 --- Geological Properties --- p.54 / Chapter 5.2 --- Research Plan and Methodology --- p.55 / Chapter 5.2.1 --- Detector Configuration --- p.55 / Chapter 5.2.2 --- Front-End Electronics --- p.58 / Chapter 5.2.3 --- Trigger System --- p.60 / Chapter 6 --- Cosmic Ray Muons and Induced Neutron Underground --- p.63 / Chapter 6.1 --- Background to Reactor Antineutrino Experiments --- p.63 / Chapter 6.1.1 --- Origins of the Fast Neutrons --- p.64 / Chapter 6.2 --- Muon Flux and Energy Spectrum Underground --- p.65 / Chapter 6.2.1 --- Muons at the Earth Surface --- p.66 / Chapter 6.2.2 --- Propagating Muons through Rock --- p.67 / Chapter 6.2.3 --- Flat Surface Case --- p.69 / Chapter 6.2.4 --- Aberdeen Mountain Case --- p.69 / Chapter 6.2.5 --- Pyramid Case --- p.72 / Chapter 6.2.6 --- Daya Bay Case --- p.73 / Chapter 6.3 --- Predicting Neutron Production from Cosmic Ray Muons --- p.76 / Chapter 6.3.1 --- Neutron Yield --- p.77 / Chapter 6.3.2 --- Neutron Energy Spectrum --- p.79 / Chapter 6.3.3 --- Neutron Angular Distribution --- p.80 / Chapter 6.3.4 --- Neutron Multiplicity --- p.81 / Bibliography --- p.83 / Chapter A --- Three-neutrino mixing formula --- p.88 / Chapter B --- Sea Level Muon Generator --- p.90 / Chapter B.1 --- Acceptance-rejection Method --- p.90 / Chapter B.2 --- Finding the Comparison Functions --- p.91 / Chapter B.3 --- Checking the Generator --- p.92 / Chapter C --- Circuit Diagrams of the Discrimination Board for Plastic Scintillators --- p.96

No description available.

Wu Jun = 中子星的極性w-模振盪 / 吳俊. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 100-102). / Text in English; abstracts in English and Chinese. / Wu Jun = Zhong zi xing de ji xing w-mo zhen dang / Wu Jun. / Abstract --- p.i / Acknowledgement --- p.iii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background introduction and historical review --- p.1 / Chapter 1.2 --- Outline of the thesis --- p.3 / Chapter 1.3 --- Notations and conventions --- p.4 / Chapter 2 --- Equilibrium and oscillations of Relativistic stars --- p.5 / Chapter 2.1 --- Relativistic stars --- p.5 / Chapter 2.1.1 --- Equilibrium configuration --- p.6 / Chapter 2.1.2 --- Equation of state --- p.7 / Chapter 2.2 --- Oscillations of relativistic stars --- p.9 / Chapter 2.2.1 --- Families of fluid modes --- p.10 / Chapter 2.2.2 --- Families of spacetime modes (w-mode) --- p.11 / Chapter 3 --- Polar oscillations of neutron stars --- p.14 / Chapter 3.1 --- Axial oscillations of neutron stars --- p.14 / Chapter 3.2 --- LD formulation --- p.16 / Chapter 3.2.1 --- Equations inside star --- p.17 / Chapter 3.2.2 --- Boundary conditions at r = 0 and r = R --- p.19 / Chapter 3.2.3 --- Perturbations outside star --- p.21 / Chapter 3.3 --- AAKS formulation --- p.22 / Chapter 3.3.1 --- Equations inside the star --- p.23 / Chapter 3.3.2 --- Behavior at the center and the stellar surface --- p.25 / Chapter 3.3.3 --- Evolution outside star --- p.28 / Chapter 3.3.4 --- Connection formula --- p.29 / Chapter 4 --- QNMs of polar oscillations --- p.31 / Chapter 4.1 --- Solution outside star --- p.31 / Chapter 4.2 --- LD approach --- p.32 / Chapter 4.3 --- Hamiltonian constraint --- p.33 / Chapter 4.4 --- Boundary conditions a.t r = R --- p.37 / Chapter 4.5 --- Direct integration scheme (DIS) --- p.42 / Chapter 4.6 --- Two-way integration scheme (TIS) --- p.43 / Chapter 4.7 --- Connect the interior and exterior solutions --- p.45 / Chapter 4.8 --- Numerical results --- p.46 / Chapter 5 --- Polar oscillations without fluid motions --- p.50 / Chapter 5.1 --- Zero pressure variation approximation (ZPVA) --- p.51 / Chapter 5.1.1 --- Evolution formulas --- p.51 / Chapter 5.1.2 --- Boundary conditions --- p.53 / Chapter 5.1.3 --- Approximate QNMs --- p.55 / Chapter 5.2 --- Zero density variation approximation (ZDVA) --- p.55 / Chapter 5.2.1 --- Single equation formulas --- p.58 / Chapter 5.2.2 --- Numerical results --- p.61 / Chapter 5.2.3 --- Summary --- p.62 / Chapter 5.3 --- Application of ZDVA --- p.65 / Chapter 5.3.1 --- Relation between axial and polar w-modes --- p.65 / Chapter 5.3.2 --- Analysis --- p.66 / Chapter 6 --- Universal behavior of polar QNMs --- p.69 / Chapter 6.1 --- Universal behavior of polar w-modes --- p.70 / Chapter 6.2 --- Ordinary CQM of neutron stars --- p.71 / Chapter 6.2.1 --- TOV parameters of a CQM star --- p.71 / Chapter 6.2.2 --- Stability problem of CQM --- p.73 / Chapter 6.2.3 --- EOS near the surface --- p.75 / Chapter 6.3 --- Scaling behavior of polar oscillations --- p.78 / Chapter 6.3.1 --- Scaling behavior of fluid motions --- p.79 / Chapter 6.3.2 --- Scaled wave equations --- p.80 / Chapter 6.4 --- Scaled Cubic-Quintic Model (SCQM) --- p.82 / Chapter 7 --- Conclusion --- p.85 / Chapter 7.1 --- Summary of Our Work --- p.85 / Chapter 7.2 --- Outlook --- p.86 / Chapter A --- Expansion of Hamiltonian constraint around the center --- p.88 / Chapter B --- Factorization integration scheme (FIS) --- p.92 / Chapter C --- Equivalence of two definitions of the Zerilli function --- p.96

While confirmations of the validity of the Standard Model at low and high energies (reached by present accelerators) continue to be produced, the high-energy physics community is turning towards the search for physics beyond the Standard Model. In chapter 2 we review the evidence for the existence of three neutrino flavors. We proceed by quickly summarizing their properties in the Standard Model and examine the present limits set by experiments on each neutrino's mass. We then move on to some theoretical considerations on neutrino masses, mainly based on cosmology and Grand Unified Theories and the chapter closes by illustrating the remarkable possibility of neutrino oscillations. Interestingly, at the end of 1997 it is in the neutrino physics domain that most inconsistencies with the Standard Model are found. Not in experiments using neutrinos to study the weak and strong interactions, as we see at the start of chapter 3, but definitely when probing the solar and atmospheric neutrino fluxes. This is detailed later in that chapter, without forgetting the only neutrino oscillation appearance evidence found so far (LSND). From the results presented it seems to be clear that neutrinos have opened a window towards new physics. However, solving all the present problems (cosmology, solar, atmospheric, LSND) with our simple neutrino oscillation interpretation seems impossible or difficult and definitely not very elegant. So maybe this window we are opening is really much larger than we think and pushing more could yield some fascinating results. The existing constraints are definitely such that experiments should be built to search for appearance at specific oscillation parameter values. When Chorus was designed and started datataking, these constraints were quite a bit weaker. However, the parameter space area which is being explored is still very relevant in the light of a model solving the Hot Dark Matter and solar problems while satisfying the very elegant see-saw mechanism. We briefly describe the experiment in chapter 4, explaining the chosen tau neutrino detection strategy and the proposed sensitivity to Vµ -> Vtau oscillations. In chapter 5 we start by describing the trackers: purpose, geometry and readout. This is followed by an explanation of the event reconstruction algorithm and its efficiency. Our main contribution to the reconstruction in the Target Trackers consists in their alignment: after introducing a few concepts we give the details of the alignment procedure, the trackers' degrees of freedom and the accuracy obtained for each of these. Two more paragraphs say a few more words on the problem of separation of variables for minimization and the detector stability over time. Next, in chapter 6, we discuss our work on the tagging of muons with the Chorus detector. After explaining the various algorithms used we come to the efficiencies, understanding the found results through event kinematics. A study of non-tagged muons shows that the software efficiency is very close to maximal, and physics is the cause of nearly all the losses. The bulk of our study lies in the determination of the scanning efficiencies. Chapter 7 starts with the description of the interface emulsion sheets and the proof of a method we developed to extract the real scanning efficiency for these sheets from the data itself. We proceed to compare the found results with the results obtained by our simulation and comment on the possible causes for the observed discrepancy. Moving on, we explain how the search for the primary vertex and a possible decay kink is conducted and give the corresponding efficiencies we found using our Monte-Carlo. To close the chapter, we elaborate on the video image simulation, a tool we developed to help improve and determine the efficiency of video image analysis programs. These programs will be used intensively in the future to search for kinks. Last but not least, chapter 8 combines all these numbers with the present scanning status to put a new limit on Vµ -> Vtau oscillations. It also includes a few words on backgrounds and the results from a study of systematic uncertainties. We conclude with a new exclusion plot.

A method is presented for generating shaped command inputs which significantly reduce or eliminate endpoint vibration. Desired system inputs are altered so that the system completes the requested move without residual vibration. A short move time penalty is incurred (on the order of one period of the first mode of vibration). The preshaping technique is robust under system parameter uncertainty and may be applied to both open and closed loop systems. The Draper Laboratory's Space Shuttle Remote Manipulator System simulator (DRS) is used to evaluate the method. Results show a factor of 25 reduction in endpoint residual vibration for typical moves of the DRS.

A problem of interest in the power industry is the mitigation of interarea and torsional oscillations. Interarea oscillations are due to the dynamics of interarea power transfer and often exhibit poor damping when the aggregate power transfer over a corridor is high relative to the transmission strength. These oscillations can severely restrict system operations and, in some cases, can lead to widespread system disturbances. Torsional oscillations are induced due to the interaction between transmission system disturbances and turbine-generator shaft systems. The high torsional stresses induced due to some of these disturbances reduce the life expectancy of the turbine-generators and, in severe cases, may cause shaft damage. <p>This thesis reports the development of novel control techniques for Flexible AC Transmission System (FACTS) devices for the purpose of damping power system interarea and torsional oscillations. In this context, investigations are conducted on a typical three-area power system incorporating FACTS devices. The Genetic Algorithm (GA) and fuzzy logic techniques are used for designing the FACTS controllers. Although attention is focused in the investigations of this thesis on the Unified Power Flow Controller (UPFC), studies are also conducted on two other FACTS devices, a three voltage-source converter Generalized Unified Power Flow Controller (GUPFC) and a voltage-source converter back-to-back HVdc link. <p>The results of the investigations conducted in this thesis show that the achieved control designs are effective in damping interarea oscillations as well as the high torsional torques induced in turbine-generator shafts due to clearing and high-speed reclosing of transmission system faults. The controller design procedures adopted in this thesis are general and can be applied to other FACTS devices incorporated in a power system. The results and discussion presented in this thesis should provide valuable information to electric power utilities engaged in planning and operating FACTS devices.

Interconnection of remotely power systems with large generation capacity and system load is progressively widespread due to the increase of the power exchanges between countries as well as regions within countries in many parts of the world. In the cases of long distance AC transmission, as in interconnected power systems, care has to be taken for maintaining synchronism as well as stable system voltages, particularly in conjunction with system faults and line switching. With series compensation, bulk AC power transmission over very long distances (1000 km and more) is in existence today. These long distance power transfers cause, however, the system low-frequency oscillations, typically within the range of 0.4 to 2 Hz, to become more lightly damped. For this reason, many power network operators and utilities are taking steps to add supplementary controls in their systems to provide extra system damping aiming to improve the system security by damping these undesirable oscillations. This thesis reports the results of time-domain simulation studies that are carried out to investigate the effectiveness of supplemental controls of a phase imbalance hybrid single-phase-Thyristor Controlled Series Capacitor (TCSC) compensation scheme and a static synchronous compensator in damping power system oscillations. In this context, studies are conducted on a typical large power system incorporating several series capacitor compensated transmission lines and large load centers with their reactive power support provided by static synchronous compensators (STATCOM). Several case studies investigating the effects of the location of the hybrid single-phase-TCSC compensation scheme, the degree of compensation provided by the scheme, the stabilizing signals of the supplemental controls, the fault clearing time, as well as the fault location on the damping of power system oscillations are documented. The results of the investigations conducted in this thesis demonstrate that the supplemental controls are very effective in damping power system oscillations resulting from clearing system faults. The time-domain simulation studies are conducted using the ElectroMagnetic Transients program Restructured Version (EMTP-RV).