Šiuo metu daugumoje automatinio valdymo sistemų struktūrų yra įtaisų kurie pagerina šių sistemų kokybines charakteristikas. Šie įtaisai yra vadinami reguliatoriais. Reguliatoriai formuoja objekto valdymo dėsnį, todėl panaudojant reguliatorius galima originalios sistemos valdymo kokybinius parametrus nustatytu tikslumu priartinti prie norimos sistemos charakteristikų. Šio darbo tikslas ištirti elektromechaninės greičio stabilizavimo sistemos dinamikos kokybės pagerinimo metodą pagrįstą keičiamos struktūros greičio reguliatoriumi. Šiame darbe buvo sudarytas elektromechaninės greičio stabilizavimo sistemos su keičiamos struktūros reguliatoriumi imitacinis modelis MATLAB/SIMULINK programa. Pagal tiesioginį kokybės rodiklį – reguliavimo trukmę, buvo nustatyta geriausioji greičio reguliatoriaus valdymo dėsnio perjungimo momento priklausomybė nuo greičio nustatymo signalo bei statinės apkrovos, tuo užtikrinant geriausią elektromechaninės greičio stabilizavimo sistemos dinamikos kokybę. Tiriamos sistemos statinės apkrovos nustatymui pereinamajame režime pritaikytas Luenbergerio stebiklis. Gauti rezultatai yra universalūs ir buvo sėkmingai pritaikyti nuolatinės srovės elektros pavarai, panaudojant programuojamą duomenų lentelę Lookup Table, imituojant automatinį reguliatoriaus valdymo dėsnio keitimą iš proporcinio (P) į proporcinį integruojantį (PI). / Currently in the majority of automatic control systems are the devices that improve the qualitative characteristics of these systems. These devices – controllers. Controllers form the object's control law, so using controllers is possible quality parameters of the original control system to place closer to the desired characteristics of the system. The aim of this work is the investigation of the dynamical quality improvement method of the electromechanical velocity stabilization system based on the variable structure velocity controller. The MATLAB/SIMULINK model of the electromechanical speed stabilization system with variable structure controller has been created. According to the quality indicator – settling time, it has been determined the control law switching parameter dependence on the static load and the command input ensuring the best dynamical quality of the electromechanical speed stabilization system. The Luenberger observer has been applied for the static load estimation during the transient regime of the electromechanical speed stabilization system. The obtained results are universal and have been successfully applied for the DC electric drive model simulaiting the automatic control law change from the proportional (P) to the proportional integral (PI) using Lookup Table.

The main project was an assessment of the effect that colonization by five different Vesicular-arbuscular mycorrhiza (VAM) cultures have on the growth of the indigenous-grasses Themeda triandra and Trachypogon spicatus, when grown on coalmine topsoil. With unamended topsoil, VAM showed the ability to significantly increase the growth of the grasses compared to non-VAM control plants. The amount of effect varied with the VAM inoculum culture type, with a VAM culture originally from the Cape Flats being the most effective. In a second trial, soil fertilized with nitrogen, potassium and low concentrations of phosphate (P) was used. Again VAM displayed the ability to improve grass plant growth. The increase in P caused the Large spore inoculum to become the most effective. This indicated that different VAM cultures are inhibited to different degrees by an increase in phosphate fertilization. The low level of VAM infection, in both trials, seemed to preclude most of the VAM associated nutrient uptake control. Varying reports have been published on the effect of fertilization on VAM infection and colonization. In an attempt to further elucidate the role of fertilizer in VAM inhibition, rhizosphere soil from a long term fertility trial near Witbank, S.A. was sampled. Amcoal environmental services fertilized forty-two plots with varying concentrations of nitrogen, potassium, phosphate and lime to assess the growth of a variety of grasses. The trial had been maintained for ten years before sampling was completed for this project. Samples from each plot were taken from the rhizosphere soil of the most prominent grass (Digitaria eriantha). VAM spores were extracted from all the samples and five different types of spores were identified and counted for each sample. By comparing spore counts from each plot, the effect that the fertilizer regime had on the VAM on that plot could be assessed. Variation in the concentrations of nitrogen (N) and potassium had no significant effect on VAM colonization. Very low concentrations of N could not be assessed as all plots had been initially top dressed with nitrogen fertilizer. Phosphate (P) fertilizer concentration had a marked effect on spore concentrations. There was a significant increase in spore concentration as P levels were increased from zero P fertilization to 80kgs P/ha. Further increase in P to ≥ 60kgs P/ha resulted in a significant decrease in spore concentrations. From this it would appear that a low level of soil P is needed to give maximum VAM colonization and further increase in soil P causes VAM inhibition. Lime ameliorated the VAM inhibition caused by high concentrations of P. Increase in P caused spore concentrations of low abundance propagules (LAP) too decreased more rapidly than high abundance propagules (HAP). In high P soils VAM with LAP would eventually be eliminated from the system resulting in a decrease in VAM diversity. A project was attempted to use the recently developed Randomly Amplified Polymorphic DNA in conjunction with the Polymerase Chain Reaction (RAPD PCR) techniques to identify different VAM families. The technique causes the amplification of segments of DNA which can be visualized by gel electrophoresis and staining. Band patterns formed can be related to the VAM of origin and hence used in identification of that VAM. An attempt was made to amplify DNA from a single spore in this manner which would, in conjunction with morphological observations, make identification of VAM easier and more accurate. Problems with either releasing the DNA from the spores, or substances in the spore inhibiting the PCR reaction made obtaining band patterns difficult. After many PCR attempts, varying extraction methods and PCR conditions, no repeatable results could be obtained and work on this project was discontinued. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1997.

Zimbabwe's economy has shrunk by 40 percent over five years (Bratton and Masununngure 2006:23). The country currently faces an unemployment rate of at least 80 percent, and an inflation rate of 165 000 per cent (BBC News, 8 /10/2008). Many Zimbabweans have turned to the informal sector as a source of livelihood and survival with formal employment estimated to constitute only 16 percent of the labour force in 2006 (Tibaijuka, 2005). The violation of political and civil rights as well as the state's approach to regulation of the economy has translated into low investor confidence. In addition the country has serious foreign currency shortages. The sheer scale of informality combined with radical attempts by the state to regulate these and other economic activities make Zimbabwe a unique context within which to understand the nature of the informal economy. Recent research on the Zimbabwean informal economy has focused on its destruction through the Operation Murambatsvina (Potts, 2007; Tibaijuka, 2005) as well as the nature and extent of cross border trading (Muzvidziwa, 1998). Other authors have explored the nature of the informal economy in crisis states in particular Zaire / Democratic Republic of Congo (MacGaffey, 1997; Dehart and Marysse, 1997). There however is no research which explores the dynamics of informal foreign currency trading in this or other contexts. The objective of this study is to explore the nature of informal foreign currency trading in Zimbabwe. The research aims to investigate the dynamics of informal foreign currency trading by tracing the role of state regulation in these operations, linkages between the formal sector and informal currency traders, the role of social networks, the lived experiences of traders involved and the social-economic benefits derived by these operations. The research approach drew on ethnographic methods. The researcher spent considerable time with the people whose realities the research aims to understand. In total 10 traders were observed and interviewed in January 2008. This research shows that excessive state intervention in the foreign exchange market leads to the emergence of informal foreign currency trading on the 'black market'. As the black market premium widens, the intensity of informality with regards to foreign currency trading increases. The existence of informal—formal linkages is strongly demonstrated by this research. It shows that there is a strong relationship between the informal currency traders and the private sector including other government entities. In order for this relationship to be sustained the research also reveals that social networks are essential for informal foreign currency traders. The study shows that informal foreign currency traders operate mainly from the streets and rented office space although deals can done from any environment as long as it is secured from law enforcement agencies. The benefits of informal foreign currency trading accrue more at the household level (micro level) rather than the macro level. This research reveals that in a state of economic crisis the formal economy fails to provide adequate basic services and commodities. As a result, an informal economy is created to ensure the supply of scarce goods and services. The study shows that Zimbabwe's economy has managed to sustain itself despite economic collapse. Informal activities are identified as playing critical role in sustaining the population of the country. The study shows that foreign currency is being traded entirely on the parallel market. Private sector and government entities totally rely on informal foreign currency traders for their supplies of foreign currency. Chapter 2 reviews the literature on the informal economy. Various theoretical approaches to the informal economy are outlined. Much of the research on informality draws attention to the role of networks of trust and reciprocity - social capital. Debates about this notion are also reviewed. In Chapter 3 the background to the Zimbabwean economic and political crisis generally and the foreign currency problems facing the country particularly is outlined. The foreign currency regulations of Zimbabwe and how they have changed over time are also considered. International experience of parallel exchange rate regimes and currency crises are also reviewed. Chapter 4 reflects the research methodology. This chapter explains how the data was collected, analyzed and interpreted. The ethical concerns and potential biases arising from the methodology are explored. Chapter 5 presents the findings from the interviews. It analyses and interprets the various views gathered from the participants. The concluding chapter, Chapter 6 reflects back on the literature and outlines the policy recommendations drawing from the research findings. / Thesis (M.A.)-University of KwaZulu-Natal, Durban, 2008.

River stage or flow rates are required for the design and evaluation of hydraulic structures. Most river reaches are ungauged and a methodology is needed to estimate the stages, or rates of flow, at specific locations in streams where no measurements are available. Flood routing techniques are utilised to estimate the stages, or rates of flow, in order to predict flood wave propagation along river reaches. Models can be developed for gauged catchments and their parameters related to physical characteristics such as slope, reach width, reach length so that the approach can be applied to ungauged catchments in the region. The objective of this study is to assess Muskingum-based methods for flow routing ill ungauged river reaches, both with and without lateral inflows. Using observed data, the model parameters were calibrated to assess performance of the Muskingum flood routing procedures and the Muskingum-Cunge method was then assessed using catchment derived parameters for use in ungauged river reaches. The Muskingum parameters were derived from empirically estimated variables and variables estimated from assumed river cross-sections within the selected river reaches used. Three sub-catchments in the Thukela catchment in KwaZulu-Natal, South Africa were selected for analyses, with river lengths of 4, 21 and 54 km. The slopes of the river reaches and reach lengths were derived from a digital elevation model. Manning roughness coefficients were estimated from field observations. Flow variables such as velocity, hydraulic radius, wetted perimeters, flow depth and top flow width were determined from empirical equations and cross-sections of the selected rivers. Lateral inflows to long river reaches were estimated from the Saint-Venant equation. Observed events were extracted for each sub-catchment to assess the Muskingum-Cunge parameter estimation method and Three-parameter Muskingum method. The extracted events were further analysed using empirically estimated flow variables. The performances of the methods were evaluated by comparing both graphically and statistically the simulated and observed hydrographs. Sensitivity analyses were undertaken using three selected events and a 50% variation in selected input variables was used to identify sensitive variablesThe performance of the calibrated Muskingum-Cunge flood routing method using observed hydrographs displayed acceptable results. Therefore, the Muskingum-Cunge flood routing method was applied in ungauged catchments, with variables estimated empirically. The results obtained shows that the computed outflow hydrographs generated using the Muskingum-Cunge method, with the empirically estimated variables and variables estimated from cross-sections of the selected rivers resulted in reasonably accurate computed outflow hydrographs with respect to peak discharge, timing of peak flow and volume. From this study, it is concluded that the Muskingum-Cunge method can be applied to route floods in ungauged catchments in the Thukela catchment and it is postulated that the method can be used to route floods in other ungauged rivers in South Africa. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2005.

No description available.

Soil organic matter (SOM) is a dynamic soil property, sensitive and responsive to many factors. The possibility of increasing soil carbon (C) sequestration by changing land use and management practices has been of great interest recently due to concerns with global changes in the atmospheric carbon dioxide (CO2) balance. Nonetheless, as a result of the complex dynamics of SOM, there is still the need for SOM characterization procedures capable of monitoring SOM stabilization, taking into account all the factors involved. This study characterized SOM stabilization as affected by management practices in three long-term field experiments, considering physical, chemical and biological components. The field experiments are located near Lexington, Kentucky, on a Maury silt loam (fine, mixed, mesic Typic Paleudalfs). The first experiment evaluates tillage and nitrogen (N) rate effects. The second experiment studies manure and N rate effects. The third experiment evaluates the five corn components of three crop rotations [continuous (monoculture) corn, corn-wheat/double crop soybean, and hay-hay-corn-corn-corn]. Soil organic matter content, stability, and composition, for physically separated fractions, were assessed using δ13C natural abundance and diffuse reflectance Fourier transformed infrared (DRIFT) spectroscopy. In addition, management effects on microbial biomass and microbial function as indicated by phenol oxidase enzyme activity were evaluated. The results indicate that management practices affect SOM content, stability, and composition, and these effects differ by the soil aggregate fraction. No-tillage (NT), N fertilization, manure application and increased corn in crop rotations enhanced SOM levels. However, the effect of NT was observed mainly at the soil surface. Soil organic matter storage was determined by the aggregate size distribution. The proportion of recently deposited C was generally positively related to aggregate size, especially for the first and third experiments. Most of the recently deposited C was stabilized in microaggregates within macroaggregates, across the management treatments and field experiments. In addition, this fraction consistently exhibited low to medium SOM reactivity. These results suggest that SOM stabilization, as influenced by management practices, required achieving a specific composition and location within the soil matrix. This implies that soil C forms and aggregate size and stability are closely interrelated.

Electromagnetic compatibility (EMC) standards for an accredited test laboratory require that the measurement uncertainty of the measuring instruments be characterized. The CISPR 16-4 standard gives guidance to the magnitude of this uncertainty, but no method of characterization. This thesis describes a method to perform this characterization on a conducted emissions measurement system, taking advantage of full system analysis techniques to reduce the uncertainty to exceptionally low levels. In addition, a framework is introduced whereby uncertainty can decomposed into its constituent parts such that the laboratory operator can identify methods to improve the systems performance.

This thesis concerns new hydrogen- and polarity-related effects in the photoluminescence of ZnO single crystal wafers and the relationship between surface electron accumulation and surface hydroxyl coverage on different ZnO surfaces. A comparative study of the low temperature photoluminescence of various types of hydrothermal and melt-grown ZnO wafers revealed several new hydrogen-related exciton recombination lines and a number of consistent polarity-related differences in the PL emission from different crystallographic surfaces. Temperature-dependent PL measurements were extensively used to distinguish the ground and excited state transitions involved in these effects. ZnO samples of different surface polarity were annealed in oxygen and nitrogen gases and in hydrogen-containing forming gas mixtures in an attempt to identify the origin of these new PL features. The well known aluminium-related I_₆ recombination line was resolved into two separate features in hydrothermal ZnO, and the new component I6-H (3.36081 eV) was found to repeatedly quench and then re-emerge after annealing in oxygen and forming gas, respectively. A model involving an aluminium - lithium - hydrogen defect complex was proposed for I6-H and further tested via hydrogen and deuterium implantation experiments on hydrothermal ZnO wafers with different lithium concentrations. These experiments also provided evidence for the involvement of a different lithium-hydrogen defect complex in other hydrogen-related emission lines I₄b,c (3.36219 eV and 3.36237 eV) unique to hydrothermal ZnO. In addition, a broad Gaussian-shaped feature observed in the near-band-edge PL emission from the O-polar (000‾1), a-plane (11‾20) and r-plane (1‾102) faces of ZnO was shown to be surface sensitive and also related to hydrogen. The involvement of hydrogen in the chemical and electronic properties of different ZnO surfaces was also investigated. The thermal stability of the hydroxyl termination and the associated downward surface band bending on the polar and non-polar surfaces of ZnO was studied by synchrotron and real-time photoelectron spectroscopy, both during and after annealing and subsequent H₂O/H₂ dosing in ultra-high vacuum conditions. On the O-polar face, the band bending could be reversibly switched over a range of approximately 0.8 eV by adjusting the surface H-coverage using simple UHV heat treatments and atmospheric exposure. A transition from electron accumulation to electron depletion on the O-polar face was observed at a H-coverage of approximately 0.9 monolayers. In contrast, the downward band bending on the Zn-polar face was significantly more resilient and electron-depleted surfaces could not be prepared by heat treatment alone. This was also the case for in situ cleaving in UHV conditions which failed to produce hydroxyl-free surfaces due to migration of hydrogen from the bulk to the cleaved surface. Interestingly, the thermal stability of the hydroxyl termination on the a-plane (11‾20) and m-plane (10‾10) surfaces was signiifcantly lower than on the polar faces due to the availability of a lower energy desorption pathway and the electrostatic stability of these non-polar surfaces in their clean, bulk terminated form. The surface band bending on the non-polar ZnO surfaces was also found to be directly related to their OH coverage with a transition from downward to upward band bending, similar to that observed on the O-polar face, as the OH coverage was reduced. Thermal admittance spectroscopy and deep level transient spectroscopy was used to investigate the effect of lithium removal on the defect nature of hydrothermal ZnO. A number of new defects were introduced by the high temperature (1100-1400°C) annealing/re-polishing process used to reduce the lithium concentration, particularly E₁₉₀ (also known as T2) which is thought to be related to Zn vacancies. Significantly, both the E₅₀ defect level and the I6-H PL emission line were absent after lithium (and hydrogen) removal suggesting an association of both these features with the same aluminium - lithium - hydrogen defect complex.

Muddringsprojekt är en global företeelse och görs av flera olika anledningar, till exempel för miljömässiga aspekter och för breddning av farleder. För att få en hållbar utveckling är det viktigt att finna bra lösningar på frågan hur förorenade sediment skall hanteras . I Mälaren kommer olika muddringsprojekt att genomföras för att bredda farleden från slussen i Södertälje till hamnarna i Köping och Västerås. Muddringsprojekten skall genomföras av Sjöfartsverket, Köpings kommun och Västerås stad. En metod för att omhänderta muddermassorna är att stabilisera/solidifiera dem genom att blanda i ett bindemedel bestående av en blandning av cement, masugnsslagg och aktivt kol och låta dem härda. Detta görs för att förbättra materialets geotekniska egenskaper samt för att immobilisera föroreningar. Syftet med detta examensarbete var att undersöka om det går att använda krossade stabiliserade/solidifierade muddermassor ovan vattenytan till exempel i vägkonstruktioner alternativt som fyllnadsmaterial. Möjligheten för användandet av de stabiliserade/solidifierade materialet utvärderades genom att materialets geotekniska och miljömässiga egenskaper undersöktes. Den miljöpåverkan som de stabiliserade/solidifierade materialet skulle kunna ha på den omgivning där de används har undersökts genom analyser av totala föroreningshalter samtkoncentrationer vid lakning. Detta gjordes dels genom egna skakförsök och dels genom utvärdering av resultat från undersökningar som Statens geotekniska instituts (SGI)miljölaboratorium gjort. När det gäller materialets geotekniska egenskaper utvärderades resultat från undersökningar genomförda av SGIs geotekniska laboratorium. Stabiliseringen/solidifiering gjorde att de undersökta metallerna som förekommer som katjoner immobiliserades, vilket ledde till att lakningen minskade. Däremot fungerade imobiliseringen inte för anjoner; om det skulle ha förekommit höga halter av toxiska anjoner som till exemple arsenik, vanadin och molybden skulle dessa ha lakats ut. Ur ett miljömässigt perspektiv skulle det gå bra att använda det undersökta materialet då koncentrationen i lakvätskan låg under de båda gränsvärden som används; gränsvärden för inert avfall och gränsvärden för mindre än ringa risk vid användning av avfall för anläggningsändamål. När det gäller hållfasthet uppfyllde materialet efter 28 dagars härdning inte kraven som ställs för användning i vägkonstruktion. Däremot hade materialets geotekniska egenskaper förbättrats jämfört med de obehandlade sedimenten. / Dredging is a global phenomenon carried out for several different reasons, e.g. environmental remediation and expansion of shipping lanes. A sustainable solution to the problem of how contaminated sediment should be handled is thus important to achieve a more sustainable development. Several dredging projects will be implemented in the lake Mälaren to widen the shipping lane from the lock in Södertälje to the ports of Köping and Västerås. The dredging will be carried out as a joint effort by the Swedish Maritime Administration, the City of Västerås and Köping municipality. One method used for treating dredged sediments is stabilization/solidification. This is carried out to improve the geotechnical properties of the material and to immobilize contaminants. The method works as follows: Sediments are dragged form the lake, mixed with a binding agent consisting of cement, granulated blastfurnace slag and active carbon and then left to harden. The objective of this master thesis was to investigate the feasibility of using the stabilized/solidified material on land above the water surface. Examples of applications for the crushed material are in road construction or as fillers for vegetation surfaces. The stabilized/solidified material was evaluated with respect to environmental factors and geotechnical properties to determine if it was appropriate to use for these applications. To investigate the potential impact of the stabilized/solidified material on the surrounding environment, analysis of total contamination content and leaching tests were evaluated. In this thesis, batch-leaching tests for metals were performed as well as evaluation of lab results from surveys conducted in the environmental laboratory at the Swedish Geotechnical Institute. The geotechnical properties of the material were evaluated based on results from experimentsconducted by the geotechnical laboratory at the Swedish Geotechnical Institute. The results from the treatment with stabilization/solidification showed that most of the studied metals were immobilized, and the leaching of these metals decreased. From an environmental perspective it would be feasible to use the material, as the results of the leaching test were below the limit values used in the assessment; limits for inert waste and limits for less than small risk (‘mindre än ringa risk’) in use of waste for construction purposes. In terms of the geotechnical features, after 28 days of hardening the material did not meet the requirements for use in road construction. However, the material's geotechnical properties such as strength had improved compared to the untreated sediments.

Bakalauro darbe, analizuojama 11- 15 metų netaisyklingos laikysenos vaikų, liemens raumenų ištvermės ir stuburo paslankumo kaita, taikant stuburo stabilizavimo pratimus. Tyrimo tikslas: įvertinti stuburo stabilizavimo pratimų įtaką liemens raumenų ištvermei ir stuburo paslankumui 11- 15 metų netaisyklingos laikysenos vaikams. Tyrimui atskleisti buvo iškelti šie uždaviniai: išanalizuoti laikysenos formavimosi, jos sutrikimų ir korekcijos ypatumus remiantis mokslinės literatūros analize; taikant S. McGill statinės liemens raumenų ištvermės testus įvertinti ir palyginti liemens raumenų ištvermės kaitą kontrolinei ir eksperimentinei grupei; taikant stuburo paslankumo testus įvertinti ir palyginti stuburo paslankumo kaitą kontrolinei ir eksperimentinei grupei. Tyrime dalyvavo 11 – 15 metų vaikai, besigydantys Palangos vaikų reabilitacijos sanatorijoje „Palangos Gintaras“ ir turintys laikysenos sutrikimų. Buvo sudarytos dvi grupės vienodos pagal vaikų skaičių (kontrolinė ir eksperimentinė). Eksperimento pagalba buvo siekiama išsiaiškinti stuburo stabilizavimo pratimų poveikį tiriamųjų liemens raumenų ištvermei ir stuburo paslankumui. Eksperimentinei grupei papildomai buvo taikoma stuburo stabilizavimo pratimų programa. Tyrimas vyko nuo 2013 12 09 iki 2014 02 28. Tyrimo rezultatai atskleidė stuburo stabilizavimo pratimų poveikį, kuris buvo matomas išanalizavus tiriamųjų testo rezultatus. Eksperimentinės grupės tiriamųjų, kuriai buvo taikomi stuburo stabilizavimo pratimai, nugaros... [toliau žr. visą tekstą] / This study analyzed the change trunk muscles endurance and spinal flexibility of children with poor posture using spinal stabilization exercises. The aim of the research was: to evaluate spinal stabilization exercise’s effect for trunk muscles endurance and spine flexibility of 11 – 15 year old children with poor posture. For carrying out the research the following objectives were pursued: To analyze the posture formation, its problems and the correction peculiarities referring to scientific literature; to assess and compare trunk muscles endurance changes in control and experimental groups using S. McGill static trunk muscle endurance test; to assess and compare the changes in spinal flexibility of both control and experimental groups using spinal flexibility tests. 11 - 15-year-old children with poor posture from Children’s Rehabilitation Sanatorium “Palangos Gintaras” took part in the research. There were two identical groups – experimental and control. With the help of this experiment it was aimed to clear out the effect of spinal stabilization exercises for the trunk muscles endurance and spinal flexibility. An additional stabilization exercise program was applied to the experimental group. The investigation was going from the 9 December, 2013 to 28 February, 2014. The results of the research revealed the impact of the experiment on the children. It was clear after analyzing the data. The experimental group which experienced the spinal stabilization exercises, endurance... [to full text]