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Coop, Lisa Jane. "The diurnal cycle of cloud cover over southern and central Africa." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/4838.
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The current understanding of the temporal and spatial distribution of clouds over southern and central Africa is poor and the regional processes governing cloud occurrence is only weakly understood. This study seeks to improve the current understanding of cloud diurnal variability over this region by providing a base-line diurnal climatology of lowlevel, mid-level and high-level cloud cover. Diurnal variations of cloudiness are examined using ten years of cloud data from latest version of the International Satellite Cloud Climatology Project (ISCCP-D1). The broad seasonal average diurnal variability is explored across the region. Thereafter a more detailed analysis of regionally specific variability is made using a Self-Organising Map. The findings of this study are in broad agreement with previous work. Cloud over the southern and central African region shows clear spatial organisation, most significantly associated with the location of the Intertropical Convergence Zone. The diurnal variation of high-level cloud is large, closely correlated to its mean and is enhanced by orographic features. Minimum high-level cloud occurs at 1100 LST and maximum extent is reached during the evening around 1800 LST, except in locations experiencing deep convection which displayed a redevelopment of cloud in the early morning (0300 LST). This redevelopment of HLCA is hypothesised to be due to the destabilization of the upper troposphere through nighttime cloud radiative cooling. Mid-level cloud exhibits smaller diurnal variations, reaching maximum coverage at approximately 0300 LST. Clouds at this level are severely obscured by higher clouds and therefore the detected diurnal variation is due to both real and artificial signals and care needs to be taken in interpreting the results. Low-level cloud shows strong diurnal variations when not obscured by higher clouds, reaching a maximum just after midday. The results of this study are interpreted in terms of the life-cycle of deep convective cloudiness. A number of mechanisms are suggested to explain the regional differences in diurnal variations with land surface heating being the primary mechanism.
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Couedel, Antoine. "Analysis of performances of crucifers-legumes cover crop mixtures to provide multiple-ecosystem services." Thesis, Toulouse, INPT, 2018. http://www.theses.fr/2018INPT0097/document.
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Les cultures intermédiaires multi-services (CIMS) implantées en interculture entre deux cultures de rente permettent de produire de nombreux services écosystémiques. Parmi les familles d’espèces utilisées comme CIMS, les crucifères réduisent efficacement la lixiviation de nitrate et de sulfate en captant l’azote (N) et le soufre (S) minéral du sol (services de piège à N et à S). Les crucifères ont aussi la capacité de contrôler les pathogènes via des composés biocides issus de l’hydrolyse de métabolites secondaires appelés glucosinolates (GSL). L’objectif de nos travaux de recherche est d’évaluer les performances en termes de services écosystémiques liés à l’azote, au soufre et au potentiel de bio-contrôle d’une grande diversité de mélanges bispécifiques de crucifères et de légumineuses en comparaison aux CIMS pures. Nous avons réalisé des expérimentations sur 2 sites contrastés (région de Toulouse et Orléans, France) et sur 2 années pour tester les performances de mélanges crucifère-légumineuse en comparaison aux espèces pures. Les espèces testées sont i) pour les crucifères : colza, moutarde blanche, moutarde brune, moutarde éthiopienne, navet, navette, radis, roquette, et ii) pour les légumineuses : trèfle Egyptien, trèfle incarnat, vesce commune, vesce pourpre, vesce velue, pois, soja, féverole et lupin blanc. Nos travaux de recherche montrent que les mélanges crucifère-légumineuse peuvent produire simultanément divers services écosystémiques avec un haut niveau d’expression, allant de 2/3 (production de GSL, engrais vert à N et S), à quasiment 100% (piège à N et S) du service produit par la famille d’espèce pure la plus performante. La concentration et les types de GSL ne changeant pas en mélanges, les interactions des crucifères avec leurs pathogènes restent identiques. Via une revue de littérature nous concluons également que le service de bio-contrôle des cultures pures de crucifères peut être maintenu en mélanges crucifère-légumineuse sur une grande diversité de pathogènes et adventices tout en réduisant les potentiels dis-services sur les auxiliaires et sur le cycle de l’azoteMulti-services cover crops (MSCC) grown during fallow period between two cash crops provide various ecosystem services. Among species used as MSCC, crucifers can efficiently prevent nitrate and sulphate leaching by catching residual soil mineral nitrogen (N) and sulphur (S) afterthe preceding cash crop (N and S catch crop services). Crucifers also have a unique capacity to suppress pathogens due to the biocidal hydrolysis products of endogenous secondary metabolites called glucosinolates (GSL). The aim of our study was to assess the provision of various ecosystem services linked to N, S cycles and biocontrol potential for a wide range of bispecific crucifer-legume mixtures in comparison to sole cover crops of legume and crucifer. We carried out experiments in 2 contrasted sites (Toulouse and Orléans regions, France) during 2 years in order to assess these services and the compatibility of various bi-specific crucifer-legume mixtures. We tested a great diversity of species, such as i) crucifers : rape, white mustard, Indian mustard, Ethiopian mustard, turnip, turnip rape, radish and rocket, and ii) legumes: Egyptian clover, crimson clover, common vetch, purple vetch, hairy vetch, pea, soya bean, faba bean, and white lupin. Our study demonstrated that crucifer-legume mixtures can provide and mutualize various ecosystem services by reaching from 2 thirds (GSL production, S and N green manure) to the same level ofservice (N and S catch crop) than the best sole family of species. GSL profile and concentration did not change in mixtures meaning that crucifer-pests interactions were identical. Through a literature review we also illustrated that biocontrol services of crucifers could be largely maintained in crucifer-legume mixtures for a wide range of pathogens and weeds while reducing potential disservices on beneficials and increasing N related service
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Hägglund, Jonas. "Snarks : Generation, coverings and colourings." Doctoral thesis, Umeå universitet, Institutionen för matematik och matematisk statistik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-53337.
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For a number of unsolved problems in graph theory such as the cycle double cover conjecture, Fulkerson's conjecture and Tutte's 5-flow conjecture it is sufficient to prove them for a family of graphs called snarks. Named after the mysterious creature in Lewis Carroll's poem, a \emph{snark} is a cyclically 4-edge connected 3-regular graph of girth at least 5 which cannot be properly edge coloured using three colours. Snarks and problems for which an edge minimal counterexample must be a snark are the central topics of this thesis. The first part of this thesis is intended as a short introduction to the area. The second part is an introduction to the appended papers and the third part consists of the four papers presented in a chronological order. In Paper I we study the strong cycle double cover conjecture and stable cycles for small snarks. We prove that if a bridgeless cubic graph $G$ has a cycle of length at least $|V(G)|-9$ then it also has a cycle double cover. Furthermore we show that there exist cyclically 5-edge connected snarks with stable cycles and that there exists an infinite family of snarks with stable cycles of length 24. In Paper II we present a new algorithm for generating all non-isomorphic snarks with a given number of vertices. We generate all snarks on 36 vertices and less and study these with respect to various properties. We find that a number of conjectures on cycle covers and colourings holds for all graphs of these orders. Furthermore we present counterexamples to no less than eight published conjectures on cycle coverings, cycle decompositions and the general structure of regular graphs. In Paper III we show that Jaeger's Petersen colouring conjecture holds for three infinite families of snarks and that a minimum counterexample to this conjecture cannot contain a certain subdivision of $K_{3,3}$ as a subgraph. Furthermore, it is shown that one infinite family of snarks have strong Petersen colourings while another does not have any such colourings. Two simple constructions for snarks with arbitrary high oddness and resistance is given in Paper IV. It is observed that some snarks obtained from this construction have the property that they require at least five perfect matchings to cover the edges. This disproves a suggested strengthening of Fulkerson's conjecture.
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Germer, Sonja. "Near-surface hydrology and hydrochemistry under contrasting land-cover." Phd thesis, Universität Potsdam, 2008. http://opus.kobv.de/ubp/volltexte/2008/1904/.
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Human transformation of the Earth’s land surface has far-reaching and important consequences for the functioning of hydrological and hydrochemical processes in watersheds. In nowadays land-use change from forest to pasture is a major issue in particular in the tropics. A sustainable management of deforested areas requires an in-depth understanding of the water and nutrient cycle. On this basis we compared the involved hydrological pathways for rainfall to reach streams and the nutrient budgets of a tropical rainforest and a pasture. In addition we studied the links of hydrochemical differences to differences of the relative importance of flowpaths. This study was conducted in the southwestern part of the Brazilian Amazon basin. An intensive hydrological and hydrochemical sampling and monitoring network was set up. The results indicate that the hydrology was modified in many ways due to land-use change. The most important alteration was the increased importance of the fast flowpath overland flow. Solute exports were in particular linked to the increased volume of overland flow that resulted from the land-use change. An additional reason for the increased nutrient exports from the pasture are the high concentrations of these nutrients in pasture overland flow probably as a due to cattle excrements. Tight nutrient cycles with minimal nutrient losses could not be maintained after the land-use change. This study provides the first attempt to quantify the respective nutrient losses.Die Zerstörung von natürlicher Vegetation kann weit reichende Folgen auf den Wasser- und Nährstoffhaushalt von Ökosystemen haben. Der Landnutzungswandel vom Wald zur Weide ist heute in den Tropen ein wichtiges Thema. Eine nachhaltige Nutzung abgeholzter Gebiete setzt ein fundiertes Wissen des Wasser- und Nährstoffhaushaltes voraus. Darauf aufbauend wurden in dieser Studie das Abflussverhalten und die Nährstoffbilanzen von einem tropischem Regenwald und einer Weide verglichen. Außerdem wurde untersucht inwieweit die Nährstoffbilanzen vom Abflussverhalten abhängen. Die Untersuchungsgebiete liegen im südwestlichen brasilianischen Amazonasgebiet. Ein umfangreiches System zur Aufnahme von hydrologischen Daten und zum Sammeln von Wasserproben wurde aufgebaut. Die Ergebnisse haben gezeigt, dass sich das Abflussverhalten durch die Landnutzung geändert hat. Die wichtigste Änderung vom Wald zur Weide war der gesteigerte Anteil des schnellen Wasserabflusses auf der Geländeoberfläche. Hieraus resultierten gesteigerte Nährstoffausträge aus der Weide gegenüber dem Wald. Ein weiterer Grund für die gesteigerten Nährstoffausträge sind die hohen Konzentrationen dieser Stoffe im Oberflächenabfluss der Weide, die vermutlich mit den Ausscheidungen des Viehs zusammenhängen. Es hat sich also gezeigt, dass der quasi-geschlossene Nährstoffkreislauf nach der Landnutzungsänderung nicht aufrecht erhalten werden konnte. Diese Arbeit liefert den ersten Versuch diese Nährstoffverluste zur quantifizieren.
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Valayamkunnath, Prasanth. "Understanding the Role of Vegetation Dynamics and Anthropogenic induced Changes on the Terrestrial Water Cycle." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/105061.
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The land surface and atmosphere interact through complex feedback loops that link energy and water cycles. Effectively characterizing these linkages is critical to modeling weather and climate extremes accurately. Seasonal variability in vegetation growth and human-driven land cover changes (LCC) can alter the biophysical properties of the land surface, which can in turn influence the water cycle. We quantified the impacts of seasonal variability in vegetation growth on land surface energy and water balances using ecosystem-scale eddy covariance and large aperture scintillometer observations. Our results indicated that the monthly precipitation and seasonal vegetation characteristics such as leaf area index, root length, and stomatal resistance are the main factors influencing ecosystem land surface energy and water balances when soil moisture and available energy are not limited. Using a regional-scale climate model, we examined the effect of LCC and irrigation on summer water cycle characteristics. Changes in biophysical properties due to LCC reducing the evapotranspiration, atmospheric moisture, and summer precipitation over the contiguous United States (CONUS). The combined effects of LCC and irrigation indicated a significant drying over the CONUS, with increased duration and decreased intensity of dry spells, and reduced duration, frequency, and intensity of wet spells. Irrigated cropland areas will become drier due to the added effect of low-precipitation wet spells and long periods (3-4% increase) of dry days, whereas rainfed croplands are characterized by intense (1-5% increase), short-duration wet spells and long periods of dry days. An analysis based on future climate change projections indicated that 3–4 °C of warming and an intensified water cycle will occur over the CONUS by the end of the 21st century. The results of this study highlighted the importance of the accurate representation of seasonal vegetation changes and LCC while forecasting present and future climate.Doctor of Philosophy
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Lytle, William. "Coupled Evaluation of Below- and Above-Ground Energy and Water Cycle Variables from Reanalysis Products Over Five Flux Tower Sites in the U.S." Thesis, The University of Arizona, 2015. http://hdl.handle.net/10150/595636.
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Reanalysis products are widely used to study the land-atmosphere exchanges of energy, water, and carbon fluxes, and have been evaluated using in situ data above or below ground. Here measurements for several years at five flux tower sites in the U.S. (with a total of 315,576 hours of data) are used for the coupled evaluation of both below- and above-ground processes from three global reanalysis products and six global land data assimilation products. All products show systematic errors in precipitation, snow depth, and the timing of the melting and onset of snow. Despite the biases in soil moisture, all products show significant correlations with observed daily soil moisture for the periods with unfrozen soil. While errors in 2 meter air temperature are highly correlated with errors in skin temperature for all sites, the correlations between skin and soil temperature errors are weaker, particularly over the sites with seasonal snow. While net shortwave and longwave radiation flux errors have opposite signs across all products, the net radiation and ground heat flux errors are usually smaller in magnitude than turbulent flux errors. On the other hand, the all-product averages usually agree well with the observations on the evaporative fraction, defined as the ratio of latent heat over the sum of latent and sensible heat fluxes. This study identifies the strengths and weaknesses of these widely-used products, and helps understand the connection of their errors in above- versus below-ground quantities.
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Silvestri, Selene. "Models and Algorithms for Some Covering Problems on Graphs." Thesis, Universita degli studi di Salerno, 2016. http://hdl.handle.net/10556/2303.
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2014 - 2015Several real-life problems as well as problems of theoretical importance within the field of Operations Research are combinatorial in nature. Combinatorial Optimization deals with decision-making problems defined on a discrete space. Out of a finite or countably infinite set of feasible solutions, one has to choose the best one according to an objective function. Many of these problems can be modeled on undirected or directed graphs. Some of the most important problems studied in this area include the Minimum Spanning Tree Problem, the Traveling Salesman Problem, the Vehicle Routing Problem, the Matching Problem, the Maximum Flow Problem. Some combinatorial optimization problems have been modeled on colored (labeled) graphs. The colors can be associated to the vertices as well as to the edges of the graph, depending on the problem. The Minimum Labeling Spanning Tree Problem and the Minimum Labeling Hamiltonian Cycle Problem are two examples of problems defined on edge-colored graphs. Combinatorial optimization problems can be divided into two groups, according to their complexity. The problems that are easy to solve, i.e. problems polynomially solvable, and those that are hard, i.e. for which no polynomial time algorithm exists. Many of the well-known combinatorial optimization problems defined on graphs are hard problems in general. However, if we know more about the structure of the graph, the problems can become more tractable. In some cases, they can even be shown to be polynomial-time solvable. This particularly holds for trees...[edited by Author]
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Loucaides, Socratis. "Human impact on the silica cycle : reduction of dissolved silica inputs into the ocean as a result of the increasing impervious cover /." Electronic version (PDF), 2003. http://dl.uncw.edu/etd/2003/loucaidess/socratisloucaides.pdf.
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Summers, Percy M. "The Post-frontier: Land use and social change in the Brazilian Amazon (1992 - 2002)." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/27903.
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Deforestation of tropical forests is one of the most pressing environmental problems of the twenty-first century, leading to the loss of environmental services such as climate regulation and biodiversity. The expansion of the agricultural frontier by small landholder farmers continues to be one of the major drivers of land use change in the Amazon region. Much of the recent research in the Brazilian Amazon has been focused on modeling their behavior in order to prescribe policies that can curb current deforestation rates and promote more sustainable land use practices. The availability of more sophisticated remote sensing and economic modeling tools has led to the proliferation of agricultural household level models that attempt to explain land use change processes at the farm level. This dissertation tests the household life cycle theory in one of the oldest colonization fronts in the Brazilian Amazon: Rondônia, now a post-frontier.
The study examines household and farm level changes over time for specific aspects of the frontier process that can be tested using the household life cycle theory. This study introduces important additions to the life cycle theory in order to consider the more dynamic and complex set of factors that characterize modern frontier processes. Specifically the study examines: (1) property fragmentation and expansion processes, (2) property ownership, turnover and change, and (3) land use change processes at the property level. These are linked to changes in the social and economic features of the smallholder farmer as it moves along its life cycle. The central hypothesis is that these changes in property and land use dynamics can be explained by the corresponding changes in the life cycle of the household as the frontier evolves over time into a post-frontier.
It was found that the household life cycle theory did not adequately explain land use change processes over time. As the frontier evolved into the modern post-frontier, the labor and drudgery constraints associated with the initial frontier processes, as exemplified in the household life cycle theory, became less relevant. The Sauerian concept of cultural successions and the concept of scale from hierarchical ecology are used in order to explain the apparent inconsistencies found between the household life cycle theory and land use change processes over time and at different scales of analysis. The household life cycle theory is a useful theoretical framework from which to examine the effects of household level factors on land use; however, this must be embedded within concepts of time and scale that determine their differentiated impact and behavior.
Existing plans to expand road infrastructure into the Amazon region will open-up previously inaccessible rainforest regions to agricultural frontier expansion at a scale unprecedented since the mid-eighties. Findings from this study reveal that policies based on household life cycle postulates will have limited impacts in reducing deforestation rates and promoting sustainable land use practices. Appropriate accounting of the social and environmental costs of future infrastructure development projects should consider associated frontier agricultural expansion costs to discourage further deforestation.Ph. D.
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Klec, Martin. "Analýza nákladů inženýrských staveb." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2017. http://www.nusl.cz/ntk/nusl-295665.
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The thesis titled "Cost analysis of engineering structures" presents a comparison of the life cycle costs of linear structures with an asphalt surface against the life cycle cost of linear structures with a concrete surface. The thesis deals with prices, costs, calculations and budgets in its theoretical part. The following chapters present history and current status, road constructions, life cycle of the construction and differences between concrete and asphalt covering. Practical part of the thesis is divided into three parts. In each sub-section, there is a practical example of comparing the costs of the life cycle of linear structure with the asphalt surface against the costs of the life cycle of linear structure with the concrete surface. Everything is expressed in graphs.
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Fish, Jocelyn M. "Small cycle double covers and line graphs." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ38584.pdf.
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Schmidt, Anja. "Time series analysis of ground frost conditionsat Abisko, sub-Arctic Sweden, 1985-2010." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-301910.
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Observed climatic change may result in modification of the ground thermal regime.The causes of shallow ground temperature variability, however, are not well documented.This thesis reports ground temperatures from Absiko Scientific Research Station, measured ata site currently not underlain by permafrost to illustrate the response of shallow groundtemperatures to changes in climatic parameters. Both air temperature and precipitationincreased at Abisko from 1985-2010. The strongest increase in air temperature occurred inwinter, whereas the precipitation increased mainly during the summer months. There was asignificant trend towards later onset of permanent snow cover, as well as a steadily earlierdisappearance of permanent snow cover in spring, resulting in reduced snow cover duration.Also the snow thickness decreased at Abisko during the study period. The ground experiencedapproximately five months of frost at 5 and 20 cm depth and approx. four, respectively two,months at 50 and 100 cm depth. Annual ground temperatures were found to be increasingfrom 1985-2010 with approx. 0.31 °C, 0.64 °C, 0.82 °C and 0.94 °C at 5, 20, 50, respectively100 cm depth from the surface. The duration and intensity of the seasonal frost cycles weredecreasing, which would reflect the increasing ground temperatures. Changes in short-termfrost cycles were not found to be significant. The changes in mean annual and winter groundtemperature were significantly correlated to the changes in mean annual and winter airtemperature, but surprisingly not to the changes in snow cover. However, seasonally theincreasing trend of ground temperatures was found in autumn and winter, whereas thesummer ground temperatures were decreasing. The cooling of ground temperature in summerat increasing air temperatures may be explained by increased precipitation totals and henceincreased soil moisture due to the so called soil-moisture feedback. From this fact, it can bededuced that the changes in air temperature alone cannot explain all variances in groundtemperatures. However, the results of the study may suggest that in sub-Arctic Swedenchanges in air temperatures may be used as indicator for changes in shallow groundtemperatures.perioden 1985-2010 ökade både lufttemperatur och nederbörd i Abiskoområdet. Denstörsta ökningen av lufttemperatur skedde under vinterhalvåret medan nederbörden ökademest under sommarhalvåret. En signifikant förkortning i längden av vintersnötäckets existensunder året observerades under studieperioden. Reduceringen av vintesnötäcket skedde genomatt den första snön kom senare och bortsmältningen på våren skedde tidigare. Snötäcketstjocklek minskade också under studieperioden. Marktemperaturmätningarna visar frysgraderpå 5 och 20 cm djup fem månader och fyra respektive två månader på 50 och 100cm djup.Den årliga medeltemperaturen i marken ökade under perioden med 0.31 °C, 0.64 °C, 0.82 °Coch 0.94 °C vid 5, 20, 50 och 100 cm djup. Den årliga längden och intensiteten avfrysförhållandena i marken minskade vilket förmodligen är en konsekvens av de ökandemarktemperaturerna. Ingen trend i förekomsten av kortare svängningar i frysförhållandenakunde observeras. Förändringarna i årsmedetemperaturen i marken är signifikant korrelerademed förändringen i den årliga medeltemperaturen och vintertemperaturen i luften, men ingenkorrelation mellan marktemperaturen och förändringar i snötäckets tjocklek och längdobserverades. Studien avslöjade också att temperaturen i marken ökade under vinternhalvåretmedan den sjönk under sommaren. Avkylningen av marken under sommaren kan förklaras avökad nederbörd under sommaren som ger högre markfuktighet som ger en kylande effektgenom den så kallade jord-fuktighets återkopplingsmekanismen (soil-moisture feedback).Från detta kan vi dra slutsatsen att förändringar i enbart lufttemperatur inte kan förklara denhela observerade variansen av marktemperatur men att lufttemperaturen har en domineranderoll. Resultaten från denna studie indikerar således att förändringar lufttemperatur kananvändas som en indikator på marktemperaturförändringar i Abisko området.
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Perron, Mary Ann. "The Value of Urban Ponds for Odonata and Plant Biodiversity." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40522.
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Urbanization involves the conversion of natural areas to impervious surfaces, which can lead to an increase in the frequency and severity of flood events in cities. To mitigate flood risk, stormwater ponds are constructed to manage urban runoff. Stormwater ponds can also be colonized by wildlife, but their suitability as habitat is disputed due to potential toxicological risks. This study assessed the suitability of stormwater ponds as habitat for the bioindicators Odonata (dragonflies and damselflies) and determined environmental factors that impact their community structure. Odonata (adults, nymphs and exuviae) were sampled at 41 stormwater ponds and 10 natural reference ponds across the National Capital Region of Canada, with a subset of ponds sampled over four years (2015-2018). Plant communities, water quality and surrounding land cover were analyzed at each pond to determine their impacts on Odonata community structure. Overall, stormwater ponds had lower Odonata abundance and a greater variation in species richness and community structure compared to natural ponds but had comparable dragonfly reproduction rates. Plants were the most significant driver of Odonata communities, as stormwater ponds with a high richness of native wetland plants had higher Odonata abundance and community structures similar to natural ponds. Water quality was the second most important driver of Odonata communities with dragonflies showing greater sensitivity to urban contaminants than damselflies. While stormwater ponds had higher concentrations of trace elements than natural ponds (e.g. Ni, V, As), concentrations were generally below toxic levels for all elements except copper and chloride, the latter likely an input from winter road salting. Surrounding land cover was the least important factor affecting Odonata communities. In conclusion, this research demonstrated the importance of local-scale factors related to plants and water quality in sustaining Odonata communities and specifies recommendations for stormwater pond design and maintenance that enhance urban biodiversity.
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Streib, Noah Sametz. "Planar and hamiltonian cover graphs." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43744.
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This dissertation has two principal components: the dimension of posets with planar cover graphs, and the cartesian product of posets whose cover graphs have hamiltonian cycles that parse into symmetric chains. Posets of height two can have arbitrarily large dimension. In 1981, Kelly provided an infinite sequence of planar posets that shows that the dimension of planar posets can also be arbitrarily large. However, the height of the posets in this sequence increases with the dimension. In 2009, Felsner, Li, and Trotter conjectured that for each integer h at least 2, there exists a least positive integer c(h) so that if P is a poset with a planar cover graph (the class of posets with planar cover graphs includes the class of planar posets) and the height of P is h, then the dimension of P is at most c(h). In the first principal component of this dissertation we prove this conjecture. We also give the best known lower bound for c(h), noting that this lower bound is far from the upper bound. In the second principal component, we consider posets with the Hamiltonian Cycle--Symmetric Chain Partition (HC-SCP) property. A poset of width w has this property if its cover graph has a hamiltonian cycle which parses into w symmetric chains. This definition is motivated by a proof of Sperner's theorem that uses symmetric chains, and was intended as a possible method of attack on the Middle Two Levels Conjecture. We show that the subset lattices have the HC-SCP property by showing that the class of posets with the strong HC-SCP property, a slight strengthening of the HC-SCP property, is closed under cartesian product with a two-element chain. Furthermore, we show that the cartesian product of any two posets from this strong class has the (weak) HC-SCP property.
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Manthey, Bodo. "Approximability of cycle covers and smoothed analysis of binary search trees." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=978602366.
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Tarasca, Nicola. "Geometric cycles on moduli spaces of curves." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, 2012. http://dx.doi.org/10.18452/16518.
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Ziel dieser Arbeit ist die explizite Berechnung gewisser geometrischer Zykel in Modulräumen von Kurven. In den letzten Jahren wurden Divisoren auf $\Mbar_{g,n}$ ausgiebig untersucht. Durch die Berechnung von Klassen in Kodimension 1 konnten wichtige Ergebnisse in der birationalen Geometrie der Räume $\Mbar_{g,n}$ erzielt werden. In Kapitel 1 geben wir einen Überblick über dieses Thema. Im Gegensatz dazu sind Klassen in Kodimension 2 im Großen und Ganzen unerforscht. In Kapitel 2 betrachten wir den Ort, der im Modulraum der Kurven vom Geschlecht 2k durch die Kurven mit einem Büschel vom Grad k definiert wird. Da die Brill-Noether-Zahl hier -2 ist, hat ein solcher Ort die Kodimension 2. Mittels der Methode der Testflächen berechnen wir die Klasse seines Abschlusses im Modulraum der stabilen Kurven. Das Ziel von Kapitel 3 ist es, die Klasse des Abschlusses des effektiven Divisors in $\Mbar_{6,1}$ zu berechnen, der durch punktierte Kurven [C, p] gegeben ist, für die ein ebenes Modell vom Grad 6 existiert, bei dem p auf einen Doppelpunkt abgebildet wird. Wie Jensen gezeigt hat, erzeugt dieser Divisor einen extremalen Strahl im pseudoeffektiven Kegel von $\Mbar_{6,1}$. Ein allgemeines Ergebnis über gewisse Familien von Linearsystemen mit angepasster Brill-Noether-Zahl 0 oder -1 wird eingeführt, um die Berechnung zu vervollständigen.The aim of this thesis is the explicit computation of certain geometric cycles in moduli spaces of curves. In recent years, divisors of $\Mbar_{g,n}$ have been extensively studied. Computing classes in codimension one has yielded important results on the birational geometry of the spaces $\Mbar_{g,n}$. We give an overview of the subject in Chapter 1. On the contrary, classes in codimension two are basically unexplored. In Chapter 2 we consider the locus in the moduli space of curves of genus 2k defined by curves with a pencil of degree k. Since the Brill-Noether number is equal to -2, such a locus has codimension two. Using the method of test surfaces, we compute the class of its closure in the moduli space of stable curves. The aim of Chapter 3 is to compute the class of the closure of the effective divisor in $\M_{6,1}$ given by pointed curves [C,p] with a sextic plane model mapping p to a double point. Such a divisor generates an extremal ray in the pseudoeffective cone of $\Mbar_{6,1}$ as shown by Jensen. A general result on some families of linear series with adjusted Brill-Noether number 0 or -1 is introduced to complete the computation.
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Gordon, Line. "Land Use, Freshwater Flows and Ecosystem Services in an Era of Global Change." Doctoral thesis, Stockholm : Univ, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-16.
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Liao, Julia Den-Yue. "Woodland development and soil carbon and nitrogen dynamics and storage in a subtropical savanna ecosystem." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1560.
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Woody plant invasion of grasslands is prevalent worldwide, but the biogeochemical consequences of this vegetation shift remain largely unquantified. In the Rio Grande Plains, TX, grasslands and savannas dominated by C4 grasses have undergone succession over the past century to subtropical thorn woodlands dominated by C3 trees/shrubs. To elucidate mechanisms of soil organic carbon (SOC) and soil total N (STN) storage and dynamics in this ecosystem, I measured the mass and isotopic composition (δ13C, δ15N) of C and N in whole-soil and soil size/density fractions in chronosequences consisting of remnant grasslands (Time 0) and woody plant stands ranging in age from 10-130 years. Rates of SOC and STN storage
averaged 10-30 g C m-2yr-1 and 1-3 g N m-2yr-1, respectively. These accumulation rates increased soil C and N pools 80-200% following woody encroachment. Soil microbial biomass (SMB-C) also increased after woody invasion. Decreasing Cmic/C org and higher qCO2 in woodlands relative to grasslands suggests that woody litter is of
poorer quality than grassland litter. Greater SOC and STN following woody invasion
may also be due to increased protection of organic matter by stable soil structure. Soil
aggregation increased following woody encroachment; however, most of the C and N
accumulated in free particulate organic matter (POM) fractions not protected within
aggregates. Mean residence times (MRTs) of soil fractions were calculated based on
changes in their δ13C with time after woody encroachment. Free POM had the shortest
average MRTs (30 years) and silt+clay the longest (360 years). Fine POM had MRTs
of about 60 years, reflecting protection by location within aggregates. δ15N values of
soil fractions were positively correlated with their MRTs, suggesting that higher δ15N
values reflect an increased degree of humification. Increases in SOC and STN are
probably being sustained by greater inputs, slower turnover of POM (some
biochemical recalcitrance), and protection of organic matter in aggregates and
association with silt and clay. Grassland-to-woodland conversion during the past
century has been geographically extensive in grassland ecosystems worldwide,
suggesting that changes in soil C and N dynamics and storage documented here could have significance for global C and N cycles.
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連敏筠. "Cycle Cover of Graphs." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/7za764.
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碩士國立交通大學
應用數學系所
96
A cycle cover of a graph G is a collection of cycles of G which covers all edges of G. The size of a cycle cover is the sum of the lengths of the cycles in the cover. A flow in G under orientation D is an integer-valued function on E(G) such that the output value is equal to the input value for each v in V(G). The support of ph(i) is defined by S(ph(i)) = {e in E(G) : phi(e) not equalto 0}. For a positive integer k, if −k < (e) < k for every e in E(G), then is called a k-flow, and furthermore, if S(phi) = E(G), then is called a nowhere-zero k-flow. In this thesis we prove: (1) if Tutte’s 3-Flow Conjecture is true, then every (k − 1)-edge-connected graph G with minimum degree = k has a nowhere-zero 6-flow such that when k is odd |Eodd(phi)| not less than (k-1)\k |E(G)| and when k is even |Eodd(phi)| not less than (k-2)\(k-1) |E(G)| ; (2) If a (k−1)-edge-connected graph G with minimum degree = k has a nowhere-zero 6-flow such that when k is odd |Eodd(phi)| not less than (k-1)\k |E(G)|, then G has a cycle cover in which the size of the cycle cover is at most (13k+5)\9k |E(G)| and when k is even |Eodd(phi)| not less than (k-2)\(k-1) |E(G)|, then G has a cycle cover in which the size of the cycle cover is at most (13k−8)\9(k−1) |E(G)|, where Eodd(phi)={e in E(G) : phi(e) is odd }.
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Lin, Chia-Hui, and 林家暉. "Three Types of Two-disjoint-cycle-cover Pancyclicity And Their Applications to Cycle Embedding in Locally Twisted Cubes." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/47777454426457619950.
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碩士靜宜大學
資訊工程學系
104
A graph G = (V, E) is two-disjoint-cycle-cover [r1, r2]-pancyclic if for any integer l satisfying r1 ≤ l ≤ r2, there exist two vertex-disjoint cycles C1 and C2 in G such that the lengths of C1 and C2 are l and |V|− l, respectively, where |V| denotes the total number of vertices in G. On the basis of this definition, we further propose Ore-type conditions for graphs to be two-disjoint-cycle-cover vertex/edge [r1, r2]-pancyclic. In addition, we study cycle embedding in the n-dimensional locally twisted cube LTQn under the consideration of two-disjoint-cycle-cover vertex/edge pancyclicity.
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Fei-Hung, Lin. "A Cost-effective Minimum Cycle Cover (MCC) Algorithm in WDM Networks with Automatic Protection Switching." 2006. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0009-2501200721295700.
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Lin, Fei-Hung, and 林飛宏. "A Cost-effective Minimum Cycle Cover (MCC) Algorithm in WDM Networks with Automatic Protection Switching." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/77943824012377364343.
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碩士元智大學
資訊工程學系
95
In networks with planar topologies, this paper proposes a heuristic method based on routing which is the Minimum Cycle Cover (MCC) algorithm for performing Automatic Protection Switching (APS) in optical networks. The algorithm provide for restoration inherit many advantages of Double Cycle Cover (DCC). The protection process proposed is fast, full restoration, distributed, and autonomous. It restores the network in real time, without relying on a central manager or a centralized database, but the drawback of this DCC scheme needs constructing of fault tolerant environment cost is not accord with the economic benefits. Therefore, the MCC can establish an efficient construction of many decomposition cycles from the architecture of DCC. That can really protect single failure and multiple failures. The MCC algorithm of performance with single and two link faults are similar to DCC. Comparisons are made by introduction of metrics that measure a protection scheme’s effectiveness in handling link failures. The cost-effective of link fault obtained using MCC is higher than using DCC and the protection probability value is approximation between the two algorithms.
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Briber, Brittain. "Urbanization, the carbon cycle, and ecosystems: an exploration of coupled dynamics and feedbacks." Thesis, 2015. https://hdl.handle.net/2144/14023.
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Urban areas are responsible for the majority of global anthropogenic CO2 emissions. Urbanization has altered the structure and function of terrestrial ecosystems and is increasing rapidly, further modifying global carbon cycling. The three research papers in this dissertation explore the role of urban vegetation in the carbon cycle using a combination of atmospheric observation, field measurements, remote sensing, and modeling. First, I characterized the spatiotemporal patterns of observed atmospheric CO2 mixing ratios and compared these data to estimated CO2 fluxes at three sites across Boston's urban-to-rural gradient. Total fossil fuel emissions estimates ranged from 1.5 to 37.3 Mg C ha-1 yr-1 between rural Harvard Forest and urban Boston. Despite large differences in emissions, atmospheric CO2 concentrations only differed by approximately 5%. The growing season length in Boston was approximately 31 days longer than in Harvard Forest, enhancing the period for biological carbon uptake. In Boston, gross primary production was 3.8 Mg C ha-1 yr-1, which was ~75% lower than gross primary production at Harvard Forest and ~10% of total anthropogenic carbon fluxes in Boston. Second, I assessed how forest-to-urban land cover change affected both aboveground biomass and productivity across eastern Massachusetts. I found that urban land covers contained less than half the biomass of adjacent forests, but the mean basal area increment of existing trees nearly doubled with development over time from 17.1 ± 3.0 to 35.8 ± 4.7 cm2 yr-1. Scaling this increase in growth suggests an aboveground biomass growth rate of 1.8 ± 0.4 Mg C ha-1 yr-1, a rate similar to that found in Harvard Forest, despite having only ~1/3 the standing aboveground biomass. Last, I assessed how above- and belowground ecosystem characteristics changed as a function of time since development and development intensity. I found that soil C and aboveground biomass showed significant differences with time since development. My data suggests that soil C, N, and bulk density are dependent on land use history, with previously agricultural sites consistently showing higher rates of soil N and C accumulation than previously forested and grassland sites. Taken as a whole, this dissertation highlights the potential consequences of altered ecological and environmental conditions on tree growth, the legacy effects of land use history, climate, and land management practices on below ground soil C and N, and the importance of vegetation in the C cycle in urban areas.
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Matthews, H. Damon. "Land cover change, vegetation dynamics and the global carbon cycle : experiments with the UVic earth system climate model." 2004. http://hdl.handle.net/1828/484.
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This thesis explores the role of terrestrial vegetation in the global climate system in a series of modelling studies using the University of Victoria Earth System Climate Model (UVic ESCM). The ways that vegetation affects climate, as well as the feedbacks that operate between changing climate and vegetation distributions, are investigated within the framework of three foci: 1) historical land cover changes that have resulted from human modification of natural vegetation cover; 2) historical land cover change and the dynamics of terrestrial vegetation in the context of anthropogenic and natural climate change; and 3) the role of terrestrial vegetation in the global carbon cycle. First, the radiative effect of changing human land-use patterns on the climate of the past 300 years is discussed through analysis of a series of equilibrium and transient climate simulations using the UVic ESCM. These experiments highlight the biogeophysical effects of historical land cover change on climate: those that result from physical changes to the land surface under altered vegetation cover. Results show a global cooling in the range of -0.06 to -0.22 "C, though this effect is not found to be detectable in observed temperature trends. Using a global carbon cycle the climatic effects of land cover change emissions (the biogeochemical effect of historical land cover change) are assessed. The resultant warming is found to exceed the biogeophysical cooling by 0.15 "C. Second, the effect of historical land cover change is compared with the effects of natural forcings (volcanic aerosols, solar insolation variability and orbital changes) and other anthropogenic forcings (greenhouse gases and sulphate aerosols). Transient model runs from the year 1700 to 2000 are presented for each forcing individually as well as for combinations of forcings. I find that the UVic model reproduces well the global temperature data when all forcings are included. In the context of these anthropogenic and natural climate influences, the response of vegetation distributions to changing climate is explored through the use of a dynamic global vegetation model coupled interactively to the UVic ESCM. Transient simulations of the past 300 years are repeated using this new model so as to isolate the biogeophysical feedbacks that operate between vegetation and climate. Dynamic vegetation is found to act as a positive feedback to climate, amplifying both warming and cooling climate trends. Third, the development of a global carbon cycle model allows for investigation of the role of terrestrial carbon cycle dynamics under past and future climate change. When forced by historical emissions of C02 from fossil fuels and land-use change, the coupled carbon cycle model accurately reproduces historical atmospheric C02 trends, as well as terrestrial and oceanic uptake for the past two decades. Under six 21St century C02 emissions scenarios, both terrestrial and oceanic carbon sinks continue to increase, though terrestrial uptake slows in the latter half of the century. The modelled positive feedback between the carbon cycle and climate is relatively small, resulting in an increase in simulated C02 of 60 ppmv at the year 2100. Including non- C02 greenhouse gas forcing and increasing the model's climate sensitivity increases the effect of this feedback to 140 ppmv. The UVic model does not, however, simulate a switch from a terrestrial carbon sink to a source during the 2lSt century, as earlier studies have suggested. This can be explained by a lack of substantial reductions in simulated vegetation productivity due to climate changes.
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Thapa, Chandra. "Graphical approaches to single-sender and two-sender index coding." Thesis, 2018. http://hdl.handle.net/1959.13/1388175.
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Research Doctorate - Doctor of Philosophy (PhD)In index coding, a sender broadcasts messages through a noiseless broadcast channel to multiple receivers, each possessing a subset of the messages a priori, known as side-information. The sender knows the side-information available at each receiver, and uses that information to broadcasts coded messages, called an index code, such that all receivers can decode their requested messages using their side-information and the received index code. The aim is to find an index code with the minimum information bits per received message bits, called the optimal broadcast rate. The index-coding problem is applicable in many real-world contexts such as content-distribution networks (e.g., a network providing video-on-demand services), satellite communications, and distributed storage (e.g., data centers). In this dissertation, we investigate unicast-index-coding (UIC) problems, where each message is requested by only one receiver, each receiver requests only one message and each receiver has a subset of messages except its requested messages in side-information. These problems can be modeled by directed graphs. We apply graph-based approaches to the two types of the UIC problems based on the number of senders, namely single-sender unicast-index-coding (SSUIC) and two-sender unicast-index-coding (TSUIC) problems. In SSUIC, we propose a new scheme, called interlinked-cycle-cover (ICC) scheme, that exploits interlinked-cycle (IC) structures (a form of overlapping cycles that generalizes cliques and cycles) in directed graphs. This scheme provides an upper bound on the optimal broadcast rate for any SSUIC instance, and construct a linear index code. We prove that the ICC scheme is optimal over all linear and non-linear index codes for a class of infinitely many digraphs. We show that the ICC scheme can outperform existing schemes for some SSUIC instances with six receivers. Further, we extend the IC structures and the scheme. We find that the ICC scheme (including the extended scheme) provides the optimal broadcast rates for all message alphabet sizes for all SSUIC instances up to five receivers except eight problems. In TSUIC, firstly, we extend the existing SSUIC graph-based schemes, namely clique-cover, cycle-cover, and local-chromatic-number schemes to TSUIC. Then we investigate the TSUIC problems by its structural characterization. By considering three sub-problems of a TSUIC problem based on whether the receivers' requests are available at only one sender or both senders, we formulate its optimal broadcast rate as a function of the optimal broadcast rates of its three sub-problems. Furthermore, for this formulation, we extend the notion of confusion graphs and graph coloring to TSUIC. We characterize a class of infinitely many TSUIC instances where a certain type of side-information can be removed without affecting their optimal broadcast rates.
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Wang, Pei-Ling. "Modeling global human-induced soil degradation and its impacts on water balance." Thesis, 2021. http://hdl.handle.net/1828/13361.
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Soils are a critical resource for supporting ecosystems, agricultural systems, and human wellbeing. However, these same soils have been degraded by human activities throughout human history. Despite the rapid development of global models that include dynamic changes in land use and land cover (LULC) and biogeochemical processes to assess climate and hydrological impacts, soil properties are often assumed to be spatially or temporally constant. These assumptions can affect the results of model projections, impact assessments and underestimate the human impact on Earth systems. This study reveals the physical impacts of human-altered soil conditions on the global water balance through a meta-analysis study and soil degradation modeling. We link major global LULCs to four hydrologic soil groups: sandy (sand, sandy loam, and loamy sand), loamy (loam, silty loam, and silt)), clayey soils (clay, sandy clay, clay loam, silty clay, and silty clay loam), and sandy clay loam) from 850 to 2015 AD, and identified loamy and clayey soils as the preferred soils for most human land uses. Humans selectively use those soils for intensive agriculture and pasture activities, while grazing occurs on sandier soils.
To simulate the impact of human activities on soils, several soil change models were built for soil organic carbon (SOC) content, soil texture (sand, silt, and clay), and soil bulk density from meta-analyses of site observations. The models were applied globally based on the LULC and soil relations, global environmental and soil conditions, and LULC distributions. Pedotransfer functions were applied to estimate soil water-holding capacity using those soil properties, then a Thornthwaite-type water balance model was used to assess the impacts of soil degradation on the global water balance. Results show that under a high-intensity LULC scenario (conventional tillage on croplands and heavy grazing), SOC decreases by 363 Pg and water deficit increases 78 km3 globally. The impacts on SOC and deficit are reduced to 213 Pg and 51 km3, respectively, when reducing land-use intensity by substituting animal ploughing/no-till and light grazing for conventional tillage and heavy grazing. Impacts from other LULC types are identical for these two LULC scenarios. Development of this history between LULC and soil properties allows for improved simulation of human impacts on global water, energy, and biogeochemical cycles. The results of the water balance simulations demonstrate how different soils representations in models can significantly alter the estimates of global evapotranspiration, water deficit, and surplus. This study contributes to developing a better understanding of the processes by which human-induced soil degradation impacts climate/hydrological models and providing a mechanism to better assess the impacts of humans on the Earth system. The outcome will also complement numerous ongoing global studies that evaluate the impacts of climate change on water resources and society.Graduate
2022-08-09
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Wang, Chun-Kai, and 王俊凱. "Two Edge-Disjoint Hamiltonian Cycles and One Isometric Path Cover in Augmented Cubes." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/10688943365551438099.
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碩士朝陽科技大學
資訊工程系碩士班
100
The n-dimensional hypercube network Qn is one of the most popular interconnection networks since it has simple structure and is easy to implement. The n-dimensional augmented cube AQn, an important variation of the hypercube, possesses several embedding properties that hypercubes and other variations do not possess. The advantages of AQn are that the diameter is only about half of the diameter of Qn and it is node-symmetric. Recently, some interesting properties of AQn have been investigated in the literature. The presence of edge-disjoint Hamiltonian cycles provides an advantage when implementing algorithms that require a ring structure by allowing message traffic to be spread evenly across the interconnection network. A network G contains one isometric path cover and is called isometric path coverable if for any two distinct pairs of nodes us, ut and vs, vt of G, there exist two node-disjoint paths P and Q satisfying that (1) P joins us and ut , and Q joins vs and vt , (2) |P| = |Q|, and (3) every node of G appears in P and Q exactly once. In this thesis, we first prove that the augmented cube AQn contains two edge-disjoint Hamiltonian cycles for n is equal or greater than 3. We then prove that AQn, with n is equal or greater than 2, is isometric path coverable. Based on the proofs of existences, we further present linear time algorithms to construct two edge-disjoint Hamiltonian cycles and one isometric path cover in an n-dimensional augmented cube AQn.
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Manthey, Bodo [Verfasser]. "Approximability of cycle covers and smoothed analysis of binary search trees / Bodo Manthey." 2005. http://d-nb.info/978602366/34.
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Hosney, Mohamed. "PERFORMANCE OF GEOSYNTHETIC CLAY LINERS IN COVER, SUBSURFACE BARRIER, AND BASAL LINER APPLICATIONS." Thesis, 2014. http://hdl.handle.net/1974/8641.
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The use of geosynthetic clay liners (GCLs) as (i) covers for arsenic-rich gold mine tailings and landfills, (ii) subsurface barrier for migration of hydrocarbons in the Arctic, and (iii) basal liner for sewage treatment lagoons were examined.
After 4 years in field and laboratory experiments, it was found that best cover configuration above gold mine tailings might include a layer of GCL product with polymer-enhanced bentonite and a geofilm-coated carrier geotextile serving above the tailings under ≥ 0.7 m overburden. However, acceptable performance could be achieved with using a standard GCL with untreated bentonite provided that there is a minimum of 0.7 m of cover soil above the GCL.
When GCL samples were exhumed from experimental landfill test cover with complete replacement of sodium in the bentonite with divalent cations in the adjacent soil, it was observed that the (i) hydraulic head across the GCLs, (ii) size of the needle-punched bundles, and (iii) structure of the bentonite can all significantly affect the value of the inferred in-situ hydraulic conductivity measured at the laboratory. The higher the hydraulic head and the larger the size of the needle-punched bundles, the higher the likelihood of internal erosion/structural change of bentonite at bundles that will cause a preferential flow for liquids to occur. A key practical implication was that GCLs can perform effectively as a single hydraulic barrier in covers provided that the water head above the GCL kept low.
The hydraulic performance of a GCL in the Arctic was most affected by the location within the soil profile relative to the typical groundwater level with the highest increase in the hydraulic conductivity (by 1-4 orders of magnitude) for GCL below the water table. However, because the head required for jet fuel to pass through the GCL was higher than that present under field conditions, there was no evidence of jet fuel leakage through the barrier system.
The leakage through GCLs below concrete lined sewage treatment lagoons was within acceptable limits, in large part, due to the low interface transmissivity between GCLs and the overlying poured concrete.Thesis (Ph.D, Civil Engineering) -- Queen's University, 2014-02-28 08:53:29.171