Techniques for power system simulation using multiple processors

The thesis describes development work which was undertaken to improve the speed of a real-time power system simulator used for the development and testing of control schemes. The solution of large, highly sparse matrices was targeted because this is the most time-consuming part of the current simulator. Major improvements in the speed of the matrix ordering phase of the solution were achieved through the development of a new ordering strategy. This was thoroughly investigated, and is shown to provide important additional improvements compared to standard ordering methods, in reducing path length and minimising potential pipeline stalls. Alterations were made to the remainder of the solution process which provided more flexibility in scheduling calculations. This was used to dramatically ease the run-time generation of efficient code, dedicated to the solution of one matrix structure, and also to reduce memory requirements. A survey of the available microprocessors was performed, which concluded that a special-purpose design could best implement the code generated at run-time, and a design was produced using a microprogrammable floating-point processor, which matched the code produced by the earlier work. A method of splitting the matrix solution onto parallel processors was investigated, and two methods of producing network splits were developed and their results compared. The best results from each method were found to agree well, with a predicted three-fold speed-up for the matrix solution of the C.E.G.B. transmission system from the use of six processors. This gain will increase for the whole simulator. A parallel processing topology of the partitioned network and produce the necessary structures for the remainder of the solution process

Constructing Gravity Amplitudes from Real Soft and Collinear Factorisation

Soft and collinear factorisations can be used to construct expressions for amplitudes in theories of gravity. We generalise the "half-soft" functions used previously to "soft-lifting" functions and use these to generate tree and one-loop amplitudes. In particular we construct expressions for MHV tree amplitudes and the rational terms in one-loop amplitudes in the specific context of N=4 supergravity. To completely determine the rational terms collinear factorisation must also be used. The rational terms for N=4 have a remarkable diagrammatic interpretation as arising from algebraic link diagrams.Comment: 18 pages, axodraw, Proof of eq. 4.3 adde

On the number of sides necessary for polygonal approximation of black-and-white figures in a plane

A bound on the number of extreme points or sides necessary to approximate a convex planar figure by an enclosing polygon is described. This number is found to be proportional to the fourth root of the figure's area divided by the square of a maximum Euclidean distance approximation parameter.An extension of this bound, preserving its fourth root quality, is made to general planar figures. This is done by decomposing the general figure into nearly convex sets defined by inflection points, cusps, and multiple windings.A procedure for performing actual encoding of this type is described. Comparisons of parsimony are made with contemporary figure encoding schemes

Modeling the Spatial Distribution of Fragments Formed from Tidally Disrupted Stars

Roughly once every 104 years, a star passes close enough to the supermassive black hole Sgr A* at the center of the Milky Way to be pulled apart by the black holes tidal forces. The star is then spaghettified into a long stream of mass, with approximately one half being bound to Sgr A* and the other half unbound. Hydrodynamical simulations of this process have revealed that within this stream, the local self-gravity dominates the tidal field of Sgr A*. This residual self-gravity allows for planetary-mass fragments to form along the stream that are then shot out into the galaxy at velocities determined by a spread of binding energies. We develop a Monte Carlo code in Python that models and plots the evolving position of these fragments for a variety of initial conditions that are likely realized in nature. This code utilizes an n-body integrator based in Mathematica to differentially solve for the position, velocity, and acceleration of each fragment at every time step. From the produced data we determine the probability distribution of bound and unbound fragments, along with a possible fraction of fragments end up within a 8 kpc shell around the galactic center. This enables the calculation of the distance at which the nearest fragment to our sun could potentially lie, which turns out to be approximately 200 parsecs

Qualitative Phytochemical Analysis and Microbial Inhibitory Activities of Pacific Rain Tree (Samanea saman (Jacq.) Merr.) Pods

Background: Crop diseases and human health are always at stake and the emerging problem on the use of synthetic anti-pathogens and medicine is one of the most difficult to combat. The first step towards determining such capabilities among plants is to determine their phytochemicals.Methods: Eight preliminary phytochemical tests was done on Samanea saman which includes, test for alkaloids saponins, flavonoids, tannins, glycosides, steroids, terpenoids and resins. Powdered pods were subjected to ethanol and aqueous extraction. Extracts were also tested for its antifungal and anti-microbial properties against Fusarium oxysporum, E. coli and S. aureus,respectively.Results: Out of the eight phytochemical tests done, seven (7) were found to be present both on the ethanol and aqueous extracts namely, alkaloids, saponins, tannins, glycosides, steroids, terpenoids and resins. However, flavonoids is absent. The statistical results exhibited that there is a significant difference on the inhibitory effects against in-vitro bioassay of Fusarium oxysporumwhich is known to cause crop wilts and the two bacterial pathogens E. coli and S. aureus.Conclusions: The presence of such phytochemicals in Samanea saman pods revealed that it can be a basis of new, natural and non-synthetic treatments. This finding suggests that its pods can be used as antibacterial and antifungal source

Developing a real time sensing system to monitor bacteria in wound dressings

Infection control is a key aspect of wound management strategies. Infection results in chemical imbalances and inflammation in the wound and may lead to prolonged healing times and degradation of the wound surface. Frequent changing of wound dressings may result in damage to healing tissues and an increased risk of infection. This paper presents the first results from a monitoring system that is being developed to detect presence and growth of bacteria in real time. It is based on impedance sensors that could be placed at the wound-dressing interface and potentially monitor bacterial growth in real time. As wounds can produce large volumes of exudate, the initial system reported here was developed to test for the presence of bacteria in suspension. Impedance was measured using disposable silver-silver chloride electrodes. The bacteria Staphylococcus aureus were chosen for the study as a species commonly isolated from wounds. The growth of bacteria was confirmed by plate counting methods and the impedance data were analysed for discernible differences in the impedance profiles to distinguish the absence and/or presence of bacteria. The main findings were that the impedance profiles obtained by silver-silver chloride sensors in bacterial suspensions could detect the presence of high cell densities. However, the presence of the silver-silver chloride electrodes tended to inhibit the growth of bacteria. These results indicate that there is potential to create a real time infection monitor for wounds based upon impedance sensing

Hrs- and CD63-dependent competing mechanisms make different sized endosomal intraluminal vesicles.

Multivesicular endosomes/bodies (MVBs) contain intraluminal vesicles (ILVs) that bud away from the cytoplasm. Multiple mechanisms of ILV formation have been identified, but the relationship between different populations of ILVs and MVBs remains unclear. Here, we show in HeLa cells that different ILV subpopulations can be distinguished by size. EGF stimulation promotes the formation of large ESCRT-dependent ILVs, whereas depletion of the ESCRT-0 component, Hrs, promotes the formation of a uniformly sized population of small ILVs, the formation of which requires CD63. CD63 has previously been implicated in ESCRT-independent sorting of PMEL in MVBs and transfected PMEL is present on the small ILVs that form on Hrs depletion. Upregulation of CD63-dependent ILV formation by Hrs depletion indicates that Hrs and CD63 regulate competing machineries required for the generation of distinct ILV subpopulations. Taken together our results indicate that ILV size is influenced by their cargo and mechanism of formation and suggest a competitive relationship between ESCRT-dependent and -independent mechanisms of ILV formation within single MVBs