A durabilidade de estruturas de concreto armado é altamente dependente das características do concreto de cobrimento das armaduras e sua espessura. O fracasso na obtenção do cobrimento é o fator de maior influência na corrosão prematura de armaduras que, por sua vez, é a principal forma de deterioração de estruturas de concreto armado. Pesquisas indicam que o cobrimento mínimo normatizado não tem sido alcançado em sua totalidade nas atuais obras que adotam esta solução estrutural, tratando-se de um problema crônico e não esporádico. Esta situação foi constatada através de um levantamento realizado in loco do cobrimento obtido em obras de Porto Alegre/RS e Cuiabá/MT. Dentre os elementos estruturais mais prejudicados, encontram-se as lajes e o fundo das vigas que, em determinadas ocasiões, apresentaram a totalidade dos valores medidos de cobrimento abaixo do valor mínimo especificado em norma. Uma das causas observadas para falha na obtenção do cobrimento mínimo normatizado é o uso incorreto de espaçadores e a utilização de espaçadores inadequados, bem como a falta de uma norma brasileira que regulamente o produto e seu uso e, consequentemente, a falta de certificação de qualidade pelo órgão responsável. Tendo este trabalho como foco o espaçador propriamente dito, foram propostos requisitos e critérios de desempenho para os espaçadores, assim como métodos para avaliação dos mesmos. A maioria dos requisitos e critérios propostos foram compilados e adaptados a partir de normas internacionais. Depois de estabelecidos os requisitos, critérios e métodos de avaliação, alguns espaçadores plásticos disponíveis no mercado foram efetivamente testados segundo a metodologia proposta. Nenhum modelo de espaçador avaliado provou-se satisfatório segundo a abordagem de desempenho estabelecida. Entretanto, ficou claro que os requisitos, critérios e métodos de avaliação propostos são adequados para avaliação de desempenho de espaçadores plásticos. Diante da diversidade de modelos e de desempenho dos espaçadores ofertados, ficou comprovada a necessidade de uma norma brasileira regulamentadora para este produto, a fim de balizar a qualidade dos espaçadores disponíveis no mercado e eliminar esta variável das causas da não obtenção do correto cobrimento. Desta forma, este trabalho visa colaborar com melhorias na questão da durabilidade de estruturas de concreto armado com foco na obtenção da correta espessura de cobrimento. / The reinforced concrete structures durability is highly dependent on the concrete cover to reinforcement characteristics and its thickness. The failure on achieving the specified cover thickness is the most influential factor in premature reinforcement corrosion, which is the main deterioration form of reinforced concrete structures. Researches indicate that the minimum standardized cover has not been completely achieved in current constructions that adopt this structural solution, which is a chronic problem and not sporadic. This situation was reaffirmed through a survey conducted in loco of the cover obtained in Porto Alegre/RS and Cuiabá/MT constructions. Among the most damaged structural elements are the slabs and beams bottom that, sometimes, showed one hundred percent probability of unsatisfactory standard cover levels. One of the failure causes observed to obtain the minimum standardized cover is the incorrect use of spacers and the use of inappropriate spacers, not to mention the lack of a Brazilian standard for regulating its manufacturing and, therefore, the lack of quality certification by the responsible agency. Having this work focused on the spacers themselves, requirements and performance criteria for the spacers, as well as methods for their evaluation, were proposed. Most of them were compiled and adapted from international standards. After established the requirements, criteria and evaluation methods, some plastic spacers available in the market were effectively tested according to the proposed methodology. No model spacers evaluated proved to be satisfactory according to the established performance approach. However, it was clear that any requirements, criteria and set evaluation methods can be satisfied. Given the diversity of spacers models and offered performances, it has been stated the need for a Brazilian regulatory standard for this product, in order to gauge the quality of the ones commercially available and to eliminate this variable among the causes of failure in obtaining the correct cover. Thus, this work aims to collaborate with improvements on the durability issue of reinforced concrete structures with a focus on getting the right cover thickness.

Master of Science / Department of Agronomy / Johanna A. Dille / Palmer amaranth and horseweed are problematic weeds in no-till soybeans in Kansas. Integrating cover crops and herbicide programs could suppress weed populations. To determine the emergence pattern and survival of horseweed, a study was conducted across six locations in eastern KS in 2014-2015 and 2015-2016. Horseweed seedlings and leaf number per seedling were recorded at two-week intervals. Cumulative GDDs required to reach 50% horseweed emergence increased from north to south. Horseweed survival ranged from 4 to 90%, and majority of horseweed emerged in the fall. Field studies were conducted to determine effects of cover crops and herbicide programs on Palmer amaranth near Manhattan, KS in 2014-2015 and 2015-2016. Five cover crop treatments included no cover, fall-sown winter wheat, spring-sown oat, pea, and mixture of oat and pea. Cover crops were terminated in May with glyphosate and 2,4-D alone or with residual herbicides of flumioxazin and pyroxasulfone. By 10 weeks after termination in 2014-2015, Palmer amaranth biomass and density, averaged across cover crops. was 95 and 69% less with residual herbicides than without, respectively, and Palmer amaranth biomass was 98% less in winter wheat and 91% less in spring oat, averaged across termination methods, compared to no cover. Time to 50% Palmer amaranth emergence was delayed with winter wheat, spring oat, and spring oat/pea mix without residual herbicide. Soybean yields were greater with residual herbicide and greater with winter wheat or spring oat cover crop in 2014-2015. A field study was conducted to determine suppression effects of cover crop and herbicide programs on horseweed and Palmer amaranth near Manhattan, KS in 2015-2016. Three fall treatments included fall-sown rye, a residual herbicide tank mix of glyphosate, dicamba, chlorimuron-ethyl, tribenuron-methyl, and AMS, and no fall application. Four spring treatments included no spring application or three herbicide tank mixes: glyphosate, dicamba, and AMS alone or with flumioxazin and pyroxasulfone as early preplant, or as split applied with 2/3 preplant and 1/3 at soybean planting. Similar levels of horseweed suppression were observed when some control measure was used in fall or spring. Fall rye completely suppressed horseweed while the fall herbicide suppressed biomass by 93% and density by 86% compared to no fall application. Palmer amaranth suppression was observed when a spring herbicide application was used. In rye, total weed biomass was reduced by 97% or more across all spring treatments. Total weed biomass was reduced with a spring herbicide was used. Soybean yields were least when no herbicide treatment was used in the spring. An integrated program of fall cover crops or herbicide applications together with spring herbicide applications maintained soybean yields.

Repeat photography, the process of retaking an existing photograph from the same vantage point, can give insight into long-term land cover dynamics. I advance the use of repeat photography to quantify landscape change in two ways: first, I demonstrate that rigorous field and post-processing methods can lead to highly accurate co-registration of images; second, I show that oblique photographs can provide land cover composition information similar to conventional satellite (Landsat) imagery for dominant land cover types, and that oblique photographs are better at resolving narrow or steep landscape features. I then present a novel approach to evaluate long-term biodiversity change using repeat photography: I measure land cover composition in 46 historical and modern photograph pairs in the Willmore Wilderness Park, Alberta, Canada, and use that land cover information as input into species-habitat models to predict the probability of occurrence of 15 songbird species. I show that coniferous forest cover increased over the past century, leading to a homogenization of the landscape which increased the probability of occurrence of forest-adapted species but negatively impacted non-forest-adapted species. / Graduate / 2019-04-18

Validation of global forest change detection databases Abstract The main aim of the thesis is to validate selected databases of changes in forest areas based on the analysis of satellite imagery time series in the Czech Republic. For this purpose we are using databases of M. C. Hansen and P. V. Potapov which are mapping the evolution of forest areas internationally. For the purposes of validation, we have proposed a methodology primarily based on historical ortophotographs from 2000-2012, the same time period which is documented in the validated databases. The results obtained were statistically processed, allowing to assess the accuracy of validated databases. At the end of the thesis, we are discussing the causes of identified inaccuracies and presented with recommendations for future improvements of detection of changes in forest areas. Keywords: validation, forest, land cover, change detection, Hansen, Potapov

Master of Agribusiness / Department of Agricultural Economics / Jason S. Bergtold / Cover crops can be used as forage for cattle and other grazing animals. This research investigated the net returns of using cover crops for forage or grazing under four scenarios. These scenarios were: 1) a mixed crop and livestock producer who owns a herd of cattle and has both dry or pregnant cows and weaned calves available to graze corn stover and cover crops; 2) a crop farmer who purchases stocker cattle for the purpose of grazing the cover crop and corn stover; 3) a crop farmer who leases out a corn stover and cover crop field to a livestock producer (and who provides value-added services to the livestock producer for a fee); and 4) an integrated operation with crops and cattle where cover crops are not grown and hay is fed to cattle during the winter months. Each of these scenarios had different budgets, risks, and profit potentials. The research aimed to address the risks and profit potentials for each scenario. The stocking density was initially set at three cows and 31 steers for a period of 90 days, and alternatively, three cows and 25 steers for a period of 120 days. Two sets of cattle pricing data were used: the average historical prices from 1992 to 2011 and reported prices from a regional stockyard for the period of November 2016 to March 2017. The results showed that the initial stocking densities used for scenarios one and two were too low to provide profitable net returns regardless of pricing data used. Net returns for scenario three were also not profitable based on the services rendered and the management fee charged. Scenario four was profitable on one occasion. November steers with a 500 lb. average starting weight fed hay and concentrate for 120 days resulted in a positive net return of $375. A second analysis was done using stocking rates of 50, 75, or 100 steers to determine if increasing stocking density would result in a positive net return using only the 2016/2017 pricing data and only evaluating net returns on 2.0 and 2.5 lbs. of average daily gain. Positive net returns were achieved at various start weights and average daily gain rates at stocking rates of 75 and 100 animals. No positive net returns were realized at the stocking rate of 50 animals/100 acre field. The management fee charged for providing management services under scenario three was adjusted based on stocking densities to determine if a positive net return could be achieved at the set fee rate of $0.875/head/day. At that rate, no stocking rate resulted in a positive net return. Using the cost data, less the $900 field lease income, a breakeven pricing point for the management fee was determined for each stocking density and grazing duration within the scenario. Management of cost factors to achieve greater chances of profitability and additional research needs are discussed.

Investors rely on secondary information sources, like cover stories, as market indicators due to time, information and resources constraints. However, studies in the US market gave mixed results about the potential use of cover stories while no publish research could be found in South Africa related to investors reaction to cover stories or whether an understanding of investment periods, company specific characteristics or bounded rational behaviour would yield superior abnormal returns from cover stories.In total, 1218 cover stories related to publicily listed companies were recorded from FinWeek and Financial Mail for the period 1985 to 2008 and categorised based on the Likert scale developed by Arnold et al. (2007). Event study methodology was used in the research.The research found evidence that investors did pay attention to very optimistic cover stories. Positive an neutral cover stories were contrarian indicators, while negative cover stories were momentum indicators of future company investment performances and the abnormal returns for an investment portfolio based on these cover story effects were optimised by short-selling cover story companies from healthcare, general retail and general mining industries and buying shares in control companies from the same industries and company sizes. The ability to earn long-term abnormal returns proofed weak form market inefficiency for the JSE. Copyright / Dissertation (MBA)--University of Pretoria, 2012. / Gordon Institute of Business Science (GIBS) / unrestricted

Intensive tillage and monoculture cropping practices reduce soil C accumulation hence increasing soil vulnerability to chemical, physical and biological degradation. This study focussed on enhancing biomass production of wheat and oat winter cover crops as a means of increasing C sequestration in the low organic C soils of the central part of Eastern Cape Province. The specific objectives were (i) to evaluate the short-term effects of no till and cereal-fallow based crop rotations on; soil organic matter related parameters, pH and electrical conductivity, (ii) soil bulk density, water retention and aggregate stability, (iii) soil microbial biomass C and N, mineralizable N, soil respiration, and dehydrogenase enzyme activity, (iv) grain yield, soil nutrient concentration (N, P and K) and their uptake by maize, and (v) to identify soil parameters with high sensitivity to tillage under maize-fallow-maize, maize-wheat-maize and maize-oat-maize rotational cover cropping practices. The experiment was laid out as a split-plot arrangement in a randomized complete block design with 4 replicates. Tillage treatments (CT and NT) were applied on the main plots which measured 8 × 18 m while crop rotation treatments were applied in the subplots which measured 8 × 6 m. The rotation treatments were maize-fallow-maize (MFM), maize-wheat-maize (MWM) and maize-oat-maize (MOM). Weed control in NT plots involved preplant application of glyphosate to control mainly the grass weeds while post emergence weed management was done using Atrazine (485 atrazine and 15 g l-1 triazines). Initial weed control in CT plots was achieved through ploughing to a depth of 20 cm followed by disking while post emergence weed iii management was done by hand hoeing. Soil parameters measured were; (i) particulate organic matter (POM), soil organic carbon (SOC), total nitrogen (TN), pH and electrical conductivity (EC), (ii) soil bulk density (b), moisture at field capacity (FC), aggregate mean weight diameter (MWD) determined by fast wetting (FW), slow wetting (SW), mechanical breakdown by shaking (MB) and the stability index (SI), (iii) soil microbial biomass C (MBC) and N (MBN), mineralizable N (MN), soil respiration (SR), and dehydrogenase enzyme activity (DHEA). No-till increased POM and TN compared to CT in Lenye and Burnshill, respectively. The MWM and the MOM rotations increased TN relative to the MFM rotation in Lenye. The MWM and MOM rotations enhanced SOC relative to MFM in all sampled soil depths at Burnshill and similar observations were made under MOM rotation in the 5-20 cm depth in Lenye. The MWM and MOM rotations tended to depress soil pH relative to the MFM rotation in both sampled soil depths in Lenye while NT reduced soil pH relative to CT on the surface soil layer in Burnshill. Soil EC and pH varied with depth across tillage practices but both parameters remained within the ideal range for successful crop production over the study period. Soil stability index (SI) and aggregate MWD determined by FW, SW and MB were higher in Lenye compared to Burnshill. The MOM rotation enhanced the SI relative to MFM and MWM rotations at both sites. Scanning electron microscope (SEM) showed that more organic C was incorporated into the soil under NT and MOM rotation compared to CT and MFM rotation which had few organic coatings on the soil particles. Microbial properties varied with plant biomass input as influenced by tillage and type of rotational cover crop at both sites. Like in other past studies, NT showed higher levels of MBC, MBN, NM and SR at the soil surface layer compared to CT in Burnshill. No till increased MN iv relative to CT in both sampled soil depths in Lenye and resulted in higher DHEA compared to CT in Burnshill. The MOM rotation increased MBC, MBN, MN relative to MFM rotation especially within surface soil layer. Similar observations were made with respect to MN and SR in both sampled soil layers at Lenye. By contrast, the DHEA was higher under the MFM relative to the MWM and MOM rotations in Lenye but similar under the MFM and MOM rotations in Burnshill. Maize grain yield was not affected by both tillage and crop rotations but varied with cropping season. Comparable grain yields observed under the two tillage practices with similar fertilizer application rates indicated the advantage of NT over CT in saving on labour costs in maize production without compromising yields. High plant biomass retention under NT relative to CT contributed to high soil N and P levels under the former compared to the latter tillage practice especially on soil surface layer at both study sites. Principal component analysis (PCA) revealed that soil chemical and biological parameters closely linked to organic matter, namely SOC, MN, MBC and MBN showed the highest sensitivity to tillage and crop rotation treatments. Soil aggregate MWD determined by SW and b were the physical parameters which were highly altered by agronomic management practice. The MWM and MOM rotations were clustered together and clearly separated from the MFM rotation and this observed trend only applied to the 0-5 and 5-20 cm depths in Lenye site only. No till, MWM and MOM rotations enhanced POM, SOC and TN relative to CT and MFM rotation suggesting these practices have greater potential to improve soil chemical properties compared to intensive tillage and maize monoculture based production practices. Reduced soil b under MOM rotation and improved SI under NT compared to MFM and CT, respectively v indicate that these practices have the potential to improve degraded soils. Although not significantly different, NT values for MBC, MBN, MN, SR and DHEA were higher compared to CT indicating the potential of the practice to improve soil biotic activity relative to conventional tillage practices. No till enhanced surface soil nitrate N and extractable P compared to CT at both sites revealing the long-term potential of NT in improving the supply of these essential plant nutrients compared to CT. Principal component analysis showed that SOC, MN, K, P, MBC, MBN, soil aggregate MWD determined by SW and b were the most sensitive parameters to tillage and crop rotations. Therefore, these parameters could constitute the minimum data set for assessments of the impact of selected CA practices on soil quality attributes.

In this thesis, I survey 11 approximation algorithms for unweighted set cover problem. I have also implemented the three algorithms and created a software library that stores the code I have written. The algorithms I survey are: 1. Johnson's standard greedy; 2. f-frequency greedy; 3. Goldsmidt, Hochbaum and Yu's modified greedy; 4. Halldorsson's local optimization; 5. Dur and Furer semi local optimization; 6. Asaf Levin's improvement to Dur and Furer; 7. Simple rounding; 8. Randomized rounding; 9. LP duality; 10. Primal-dual schema; and 11. Network flow technique. Most of the algorithms surveyed are refinements of standard greedy algorithm.

Magister Scientiae - MSc / The complex nature and composition of regolith cover in Southern Africa is a major challenge to geochemical mapping for concealed mineralization. Some of the setbacks to successful geochemical exploration may be ascribed to the use of various partial extraction techniques,without a profound understanding of the regolith components and their composition. This investigation therefore focuses on the use of hydroxylamine partial extraction geochemistry for geochemical mapping in regolith over two contrasting environments viz; aeolian sand-calcrete regolith over Au mineralization at Amalia Blue Dot Mine in South Africa and lateritic regolith covering the Ni-Cu deposit at Kabanga Main and Luhuma in Tanzania. Regolith samples from the above areas were sieved and extracted with hydroxylamine hydrochloride solution and analyzed for multi-element by AAS and ICP-MS techniques. A stepwise optimization of the hydroxylamine extraction technique of samples from both areas was carried out and incorporated into the analytical programme (in a pilot study). Results of hydroxylamine partial extraction generally gave better anomaly contrast and reflection of bedrock mineralization than the conventional aqua regia techniques that were previously used in the region. The results however show that lateritic regolith may be best extracted using 0.25M hydroxylamine while 0.1M concentration appears most suitable for extraction of aeolian-calcrete regolith. The above results are corroborated by principal component analysis of the analytical data that show various element associations, e.g. with Fe-Mn oxides while others possibly belong to the loosely adsorbed or exchangeable group. The gochemical maps in the pilot study areas at Amalia, Kabanga and Luhuma show elevated element contents or clusters of anomalies of diverse elements associated with Fe-Mn oxides. Geochemical mapping at Kabanga with deeply concealed mineralization however shows variability of subdued element patterns over mineralized areas. Geochemical signatures associated with hydroxylamine hydrochloride partial leach are therefore characterized by a lower geochemical background than that using conventional aqua regia leach. This study leads recommending for further investigations into partial extraction of the exchangeable group of elements, possibly using ammonium acetate. / South Africa

Greenhouse and microplot studies were conducted for understanding the effects of cover crop species/cultivars for hosts and population reduction of soybean cyst nematode (SCN; Heterodera glycines) from the fields of North Dakota. Moreover, early-maturing soybean [Glycine max (L.)] accessions from different countries of origin were screened for resistance against two common SCN populations for finding new sources of resistance. Thirty-eight cover crop species/cultivars were evaluated for their hosting ability of two SCN populations (SCN103 and SCN2W) from two fields of North Dakota in greenhouse experiments. The majority of the tested crops were non-hosts for both SCN populations. However, a few of them, such as Austrian winter pea (Pisum sativum L.), crimson clover (Trifolium incarnatum L. cv. Dixie), crambe (Crambe abyssinica, cv. BelAnn), field pea, cvs. Aragorn and Cooper, hairy vetch (Vicia villosa Roth), turnip (Brassica rapa L. cv. Purple top), and white lupine (Lupinus albus L.) were poor-hosts/hosts of both SCN populations. Furthermore, thirteen of them were tested for the SCN population reduction either or both in the greenhouse and microplot experiments. Out of 13, at least four crops, such as annual ryegrass (Lolium multiflorum L.), brown mustard (Brassica juncea L. cv. Kodiak), daikon radish (Raphanus sativus L.), and turnip cv. Pointer showed more than 50% population reduction compared with initial population densitiy, consistently in the greenhouse or microplot experiments. The resistance screening of 152 early-maturing soybean accessions showed that a majority of the accessions were susceptible/moderately susceptible to both SCN populations (SCN HG type 0 and 2.5.7), while a few (n=18) showed good resistance responses to both or either of the SCN populations. The cover crops, which were non-hosts/poor-hosts and have a greater ability for the SCN population reduction have great potential to be included in an integrated SCN management strategy. The novel resistant accessions identified in this study have the potential to be used in soybean breeding for developing SCN-resistant cultivars after confirming their resistance response and identifying the resistance genes/loci. The results obtained from this study helps in developing a sustainable SCN management strategy in the northern Great Plains.