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Creative writing.Bachelor of Art

Field oriented control of single and cascaded doubly-fed induction machines

PhD ThesisA single doubly-fed induction machine (SDFM) is a wound rotor induction machine with the stator connected to a supply network and the rotor fed by a bi-directional converter. A cascaded doubly-fed induction machine (CDFM) is a. connection of two wound rotor induction machines with the rotors connected electrically and mechanically thus avoiding brushes. One stator is connected to the supply network and the other is fed by a bidirectional converter. Both schemes, the SDFM and the CDFM, have in common that the VA-rating of the power converter is reduced compared to a singly-fed system. This thesis presents investigations of the field oriented control for the SDFM and the CDFM. - After reviewing and categorising doubly-fed machines a thorough steady state analysis and stator flux oriented control treatment of the SDFM is presented. Although the steady state analysis and the field oriented control of a SDFM is well established it is necessary that this is included as foundation for the CDFM control behaviour and for the sensorless control investigations. Steady state analysis of the CDFM highlights similarities to the SDFM. Two different field oriented control schemes are applied to the CDFM. A previously developed combined flux oriented scheme is modified to be applicable to a CDFM consisting of any machine combination. Furthermore, the scheme is simplified by removing a mathematical control extension in the q-axis, which has a stabilising effect on the control performance. Justified by steady state analysis the stator flux oriented control structure initially developed for the SDFM is applied to the CDFM. Two variations of a position sensorless scheme taking advantage of the proportionalitics between stator and rotor quantities are applied to the SDFM. Differentiating the estimated position angle allows the schemes to be extended for speed control purposes. The performance of the scnsorless field oriented control methods are also investigated on the CDFM. Harmonic analysis of the SDFM / CDFM systeme stablishes harmonic sources and harmonic current propagation through the system. A theoretical harmonic current prediction process incorporating simulation and steady state modeling delivers good results. All theoretical investigations are confirmed by experimental results. The experimental realtime controlled drive system consists of two 2.25 kW wound rotor induction machines, a bidirectional IGBT converter and the control hardware comprises two 8OC167 microcontrollers.Department of Electrical and Electronic Engineerin

EFFECTS OF ANNUAL AND PERENNIAL COMMUNITY DYNAMICS ON TIDAL FRESHWATER MARSH ECOSYSTEM FUNCTIONING

Tidal freshwater marshes are complex systems with many linkages between the physical, chemical, and biological components. Understanding how the community dynamics of a tidal freshwater marsh affect ecosystem processes may be applicable towards restoring properly functioning wetlands that improve the filtration of excess nutrients and toxins, subsequently improving water quality for downstream areas. The first question explored is why annual species exist in a marsh dominated by perennials. Annual species may exist through facilitation or competition with neighboring species, or through relationships with abiotic variables including elevation and seed rain. Through many field and greenhouse studies, I have determined that competition between annual and perennial species may exist, but abiotic factors are driving the vegetative composition of the marsh. Understanding if annual patches move through time is imperative for relating the plant community to ecosystem processes. To explore the temporal community dynamics, I examined the composition of the belowground marsh seed bank and the aboveground vegetation composition for three years. I have learned that the seed bank partially drives the vegetation composition. Furthermore, additional environmental factors may play a role in determining aboveground vegetation composition. I examined differences in the ecosystem processes of denitrification and its influencing variables among communities dominated by annual species, perennial species, and a mixture of the two. No differences in denitrification rates existed among community types; however organic nitrogen, which is driven by vegetation increased with denitrification rates. Communities readily move through space and time and may influence nutrient cycling in tidal freshwater marshes. Therefore, restoration managers should take into consideration species that maximize nitrogen removal and the variables that control their spatial and temporal movement when planning restoration designs and alternatives

Noise sensitivities in dogs: a new licensed treatment option

Review of noise sensitivities and new product for treating them

Andean Land Use And Biodiversity: Humanized Landscapes In A Time Of Change

Some landscapes Cannot be understood without reference., to the kinds. degrees, kinds, degrees, and history of human-caused modifications to the Earth's surface. The tropical latitudes of the Andes represent one such place, with agricultural land-use systems appearing in the Early Holocene. Current land use includes both intensive and extensive grazing and crop- or tree-based agricultural systems found across virtually the, entire range of possible elevations and humidity regimes. Biodiversity found in or adjacent to such humanized landscapes will have been altered in abundance. composition, and distribution in relation to the resiliency of the native Species to harvest, hold cover modifications, and other deliberate or inadvertent human land uses. In addition, the geometries of land cover, resulting flout difference among the shapes, sizes, connectivities, and physical structures of the patches, corridors, and matrices that compose landscape mosaics, will constrain biodiversity, often in predictable ways. This article proposes a conceptual model that alter ins that the Continued persistence of native species may depend as much oil the shifting Of Andean landscape mosaics as on species characteristics, themselves. Furthermore, mountains such as the Andes display long gradients of environmental Conditions that after in relation to latitude, soil moisture, aspect, and elevation. Global environmental change will shift these, especially temperature and humidity regimes along elevational gradients, causing Changes outside the historical range of variation for some species. Both land-use systems and Conservation efforts will need to respond spatially to these shifts in the future, at both landscape and regional scales.Geography and the Environmen

MiFID II Unbundling and Sell Side Analyst Research

We examine the effect of MiFID II, which mandated the unbundling and separate pricing of analyst research in Europe beginning in 2018. We find that the requirements of MiFID II were associated with a reduction in analyst following for European firms relative to US firms, with decreases in coverage greatest for firms that were larger, older and less volatile, and had greater coverage and more accurate consensus forecasts. Remaining analysts follow fewer firms and issue fewer forecasts, consistent with increased focus, and appear to increase their efforts on the firms they continue to cover. In particular, forecasts become more accurate, are more likely to be disaggregated and include recommendations, and are accompanied by larger stock price reactions. Consistent with increased effort to curry favor with management, analysts issue more optimistic recommendations and beatable earnings forecasts. While individual forecasts are more informative, the overall information environment for the average firm tends to deteriorate, with less aggregate information conveyed by analyst forecasts, a greater proportion of information delayed to earnings announcements and higher average bid-ask spreads. Taken as a whole, results are consistent with a reduction in analyst following mitigated by an increase in focus and effort by remaining analysts, but with an overall negative effect on the information environment

Evolutionary plasticity of SH3 domain binding by Nef proteins of the HIV-1/SIVcpz lentiviral lineage

The accessory protein Nef of human and simian immunodeficiency viruses (HIV and SIV) is an important pathogenicity factor known to interact with cellular protein kinases and other signaling proteins. A canonical SH3 domain binding motif in Nef is required for most of these interactions. For example, HIV-1 Nef activates the tyrosine kinase Hck by tightly binding to its SH3 domain. An archetypal contact between a negatively charged SH3 residue and a highly conserved arginine in Nef (Arg77) plays a key role here. Combining structural analyses with functional assays, we here show that Nef proteins have also developed a distinct structural strategy-termed the "R-clamp"-that favors the formation of this salt bridge via buttressing Arg77. Comparison of evolutionarily diverse Nef proteins revealed that several distinct R-clamps have evolved that are functionally equivalent but differ in the side chain compositions of Nef residues 83 and 120. Whereas a similar R-clamp design is shared by Nef proteins of HIV-1 groups M, O, and P, as well as SIVgor, the Nef proteins of SIV from the Eastern chimpanzee subspecies (SIVcpzP.t.s.) exclusively utilize another type of Rclamp. By contrast, SIV of Central chimpanzees (SIVcpzP.t.t.) and HIV-1 group N strains show more heterogenous R-clamp design principles, including a non-functional evolutionary intermediate of the aforementioned two classes. These data add to our understanding of the structural basis of SH3 binding and kinase deregulation by Nef, and provide an interesting example of primate lentiviral protein evolution.Peer reviewe

HIV-1 Vpu is a potent transcriptional suppressor of NF-κB-elicited antiviral immune responses

Many viral pathogens target innate sensing cascades and/or cellular transcription factors to suppress antiviral immune responses. Here, we show that the accessory viral protein U (Vpu) of HIV-1 exerts broad immunosuppressive effects by inhibiting activation of the transcription factor NF-κB. Global transcriptional profiling of infected CD4 +T cells revealed that vpu-deficient HIV-1 strains induce substantially stronger immune responses than the respective wild type viruses. Gene set enrichment analyses and cytokine arrays showed that Vpu suppresses the expression of NF-κB targets including interferons and restriction factors. Mutational analyses demonstrated that this immunosuppressive activity of Vpu is independent of its ability to counteract the restriction factor and innate sensor tetherin. However, Vpu-mediated inhibition of immune activation required an arginine residue in the cytoplasmic domain that is critical for blocking NF-κB signaling downstream of tetherin. In summary, our findings demonstrate that HIV-1 Vpu potently suppresses NF-κB-elicited antiviral immune responses at the transcriptional level