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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
301

A comparison of the reproductive strategies of key species of a prograding dune system in the Mlalazi Nature Reserve, Natal

Todd, Colleen Barbara January 1995 (has links)
The succession on the dunes of the Mlalazi Nature Reserve represents a classical example of primary succession. The reproductive strategies of eight key species were compared to determine some of the mechanisms affecting the community dynamics, at the population level, in the early stages of succession. There is a temporal separation in the flowering and fruiting phenologies. Passerina rigida, Stipagrostis zeyheri and Imperata cylindrica produced small seeds with a low fruit/seed mass ratio within a short cycle. The seeds are suitable for wind-dispersal. The animal-dispersed species; Eugenia capensis, Mimusops caffra and Scaevola plumieri, produced large fleshy seeds with a high fruit/seed mass ratio within cycles of six months and more. Chrysanthemoides monilifera, also an animal-dispersed species, produced a large quantity of small fleshy seeds throughout the year. The fern, Microsorium scolopendrium produced spores throughout the year. The staggered fruiting and flowering phenology ensures a year-round availability of fruit in the dunefield. The key species formed less than half of the species composition of the soil seed bank. The size and range of the soil seed bank differed between the species. P. rigida and S. plumieri formed a high proportion of the seeds in the soil with a wide distribution along the successional gradient. The other species had low soil seed densities with short distribution ranges, or were not present. P. rigida and S. plumieri are easily dispersed species, whereas the other species may have a more restricted and clumped distribution due to the effect of foragers. A high density of P. rigida and E. capensis seeds were found under the parent trees. Only seeds of P. rigida and S. zeyheri were found in the soil in the open. Seeds of P. rigida, S. zeyheri, E. capensis and M. caffra were found under the canopies of P. rigida, E. capensis and M. caffra. No seeds of C. monilifera and I. cylindrica were found in the soil, possibly due to predation. The period of the study (September 1991 to November 1992) was in a dry or drought cycle with only 56.8% of the mean annual rainfall falling. Seed germination and seedling survival of all the species were affected by these dry, warm climatic conditions. The species had seedling densities of less than 4 seeds/m². The environmental conditions along the successional gradient also had an effect on seed germination and seedling survival. Environmental factors of soil pH, light intensity and surface soil temperatures were higher in the open than under canopy. Soil pH and the understorey cover decreased as the light intensity decreased from under the canopy of P. rigida to M. caffra . Litter cover and plant height increased. E. capensis had measurements intermediate to the two species, but had higher surface soil temperatures and plant height than P. rigida. Seedlings of P. rigida in the open and under the canopy of the parent plants had died by the end of the monitoring period. 50% of the seedlings of S. zeyheri under the canopy of P. rigida and M. caffra died. The mortality rate of the seedlings of E. capensis was lower under M. caffra than under the parent plants. I. cylindrica may be propagated vegetatively. However, the mortality of the propagules was greater under the canopy of E. capensis than under P. rigida. M. caffra only germinated under the canopy of E. capensis with a 100% mortality of the seedlings. M. scolopendrium only produced propagules through vegetative propagation under the canopy of E. capensis and M. caffra. The mortality of the young ferns was less than 50% and less under M. caffra than under E. capensis. No seedlings of C. monilifera or S. plumieri were found. The seed distribution range, seed germination requirements and the effect of the environmental conditions on the germination of the seeds and seedling establishment of the species appear to important factors of the reproductive strategies regulating the size of the species populations along the successional gradient.
302

Molecular fungal diversity and its ecological function in sand-dune soils

Gonzalez Gonzalez, Irma January 2015 (has links)
There are about 100,000 described fungal species, however, the diversity could be higher because conventional techniques do not allow identification of all groups of fungi and there are still unexplored geographical areas. High-throughput DNA sequencing methods provide the opportunity to resolve the diversity and distribution of mycelia in soil. Soils are the largest pool of terrestrial carbon and macromolecular materials, such as lignin and cellulose, form an important part of this soil carbon. Saprotrophs (decomposers) fungi degrade lignin and cellulose that is important to the global carbon cycle, although lignin is highly resistant to degradation if compared with cellulose. In this work, we investigated the diversity of fungi in sand-dune soils and their involvement in the decomposition of lignin and cellulose. The key findings of this work were:•A comparison of sand-dune ecosystems from two reserves in the UK showed differences in the ion concentrations, pH and total organic carbon in soils, suggesting that there were different environmental conditions that could potentially affect the distribution/presence of microbial communities in soils, e.g. fungal communities.•Fungi from field samples were identified using 454 pyrosequencing. The identified fungal species belong to groups with different ecologies, among which are wood-rotting fungi that are the main agents responsible for the lignin breakdown. The fungal communities were distributed differently across the different sand-dune ecosystems, sampling times and type of bait materials.•Lignin and cellulose can be degraded in field samples over time. Lignin degradation was shown by the shifts in the [Ac/Al]S, [Ac/Al]G and [S/G] relative lignin decomposition state proxies, and cellulose degradation by the shifts in the [cellulose:cellulose+lignin] ratio. Cellulose degradation was faster than lignin, thus confirming previous studies.•The degradation of both lignin and cellulose was different depending on the type of plant material, ecosystem/soil characteristics where the material was buried and fungal communities present on the bait materials.•Lignin breakdown was most likely to be by white-rot fungi that were identified colonising the bait materials.
303

Vermessung von äolischen Sandrippeln

Beyer, Marcus, Schönfeldt, Hans-Jürgen 22 September 2017 (has links)
Der Transport von Sand ist geprägt durch die Ausbildung von Strukturen. Die kleinste Form bezeichnet man als Rippel. Da die Dimension von äolischen Sandrippeln nicht sehr groß ist, existieren nur wenige Messungen welche direkt am Strand oder in der Wüste durchgeführt wurden. In diesem Artikel wird ein Messverfahren vorgestellt, welches eine Vermessung von Höhenunterschieden im Sandfeld in der Größenordnung von Millimetern ermöglicht. Die durch die sogenannte „Schattenwurf-Methode“ erhaltenen Ergebnisse stehen in guter Übereinstimmung mit der Literatur. Außerdem werden Erkenntnisse aus der Untersuchung von Sandkorngrößenverteilungen an verschiedenen Positionen eines Rippels aufgezeigt. Des Weiteren wird in dieser Arbeit eine Methode vorgestellt, welche es ermöglicht, ein durchgängiges Höhenprofil für ein vermessenes Sandrippelfeld zu erstellen. Das Ergebnis erlaubt eine genauere Betrachtung und Analyse des Verlaufs von Rippelbergen und Rippeltälern. / The transport of sand is affected by the development of structures. The smallest kind of them is called ripple. Owing to the fact that the dimension of aeolian sand ripples is not very large there are only a few measurements that were made directly at the beach or in the desert. This article presents a measurement method that provides the possibility of measuring height differences in the dimension of millimetres. The results achieved by the so called “shadow-cast” method are in good agreement with that found in literature. In addition, findings concerning the investigation of the sand grain size distribution at different positions on the ripple are presented. Furthermore, a possibility of producing continuous profiles of a measured sand ripple field, is presented in this work. The result allows a specified observation and analysis of developing ripple crests and ripple troughs.
304

Mittlere Saltationslänge und deren Bestimmung

Plagemann, S., Schönfeldt, Hans-Jürgen 22 September 2017 (has links)
Diese Studie soll einen näheren Aufschluss über die Ermittlung der mittleren Saltationslänge und somit über den Sandtransport geben. Die Bestimmung der vertikalen und horizontalen Verteilung des Sedimenttransports erfolgte mittels MWAC- und Quaderfallen-Messungen. Das dazugehörige Feldexperiment fand im März 2008 am Zingster Strand (Ostsee/Deutschland) statt. Des Weiteren wurde von Namikas im Juni 1997 in der 'State Vehicular Recreation Area' (SVRA) an der kalifornischen Küste der Transport mithilfe von Vertikal- (VTRAP) und Horizontalfallen (HTRAP) ermittelt (Namikas, 2003). Die Experimente der Quaderfallen und der HTRAP wurden numerisch simuliert und auf Tauglichkeit zur Sprunglängenberechnung geprüft. Die Analyse brachte hervor, dass die vier benutzten Quaderfallen mit unterschiedlicher Länge eine unzureichende Vorhersage für den Massenfluss liefern. Die HTRAP gibt erst durch Differenz der einzelnen Fächer eine nahezu korrekte Prognose. Folglich kann durch eine Korrektur der ermittelten Werte eine zutreffende mittlere Saltationslänge errechnet werden. / This study is giving a near information about ascertaining of mean saltation lenght and consequently about sand transport. The vertical and horizontal distribution of transport of sediment was determined by using MWAC-sampler and cuboid traps measurements. The respective field experiment was processed on the beach of Zingst (Baltic Sea/Germany) in March 2008. Furthermore, the transport was established by using vertical (VTRAP) and horizontal traps (HTRAP) in the 'State Vehicular Recreation Area' (SVRA) on the California coast in July 1997 (Namikas, 2003). The experiments of cuboid traps and HTRAPs have been simulated numerical and checked for efficiency to evaluation of jump lenght. The results generated an insufficient prediction of mass flux by using four cuboid traps with different length. The HTRAP delivered an almost correct prognosis when seperate compartments are subtracted. Consequently a true mean saltation length is calculated by an adjustment of determined values.
305

Development of Portable Undrained Ring Shear Apparatus and Its Application / ポータブル非排水リングせん断試験機の開発とその応用

Maja Ostric 24 September 2013 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17868号 / 工博第3777号 / 新制||工||1577(附属図書館) / 30688 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 寶 馨, 教授 木村 亮, 准教授 立川 康人 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM
306

Evaluation of Producing Sand-Based Sod on a Fine-Textured Native Soil Using Transported Sand

Vanderford, John David 14 December 2013 (has links)
Turfgrass establishment on sand-based rootzones is routinely accomplished by using sod produced on a fine-textured native soil. As a result, soil layering occurs, potentially causing initial reduction in water infiltration, rooting, aeration, and overall turfgrass quality. This research was aimed at determining the feasibility of applying sand over existing native soil to produce hybrid bermudagrass (Cynodon dactylon [L.] Pers. x C. transvaalensis Burtt-Davy) sand-based sod. Factors evaluated were visual quality and scalping. Treatments were harvested and transplanted to a sand-based research green where handle-ability, tensile strength, and infiltration were also evaluated. Results indicate aerify and topdress treatments showed higher quality pre-harvest. Control and 25 mm treatments were best in terms of harvesting, handle-ability, and sod tensile strength. Infiltration data indicated no significant differences between treatments. These outcomes along with further analysis could provide sod producers with a valuable product for use on sand-based rootzones.
307

Sand dune movement and its impact on human activities in the North Western coast region of Libya. An analysis of the sediment characteristics of sand dunes, and their movement using satellite images, and the effects of encroachment on farms assessed by a questionnaire survey.

Koja, Suliman F. January 2012 (has links)
Sand movement is one of the many environmental problems facing humans in the dry and semi-dry areas of the world. This study has investigated the observed changes in sand dune coverage compared to predictions, and has also assessed the impact of sand movement on human activity in the north western coastal region of Libya. The study used three methods. The first was a statistical model proposed by Bagnold, which correlates wind shear velocity with particle size, in order to predict likely sand movement. It was found that 60% of sand grains within the study area have a diameter of less than 0.25 mm, making them liable to be moved by the wind speeds recorded, particularly from March until September, and mostly in a northerly direction. The sand in the western part of the study area had a greater predicted rate of sand transport compared with the sand in the eastern part, which was related to its origin. The second method involved the analysis of satellite images for four different years; from 1986 to 2003. The land cover in the study area was found to have changed over this time. Sand dune area cover had increased, and there were other changes particularly a decline in forest. The third method was the use of a questionnaire (the respondents being land owners), which showed that there was notable loss of crop production (by about a quarter) due to sand movement, and that land owners mostly used afforestation to help control the sand movement in the region. The observed sand movement did not match the predictions based solely on sand grain size and wind speed, and climatic analyses showed no convincing trends which could explain increased sand movement except perhaps an increase in wind gusts. The thesis concludes that the overriding determinant in greater sand movement over the period studied was the loss of forest from the area due to human impacts, which farmers are having to compensate for by planting trees locally to reduce sand movement.
308

Biological treatment of turkey processing wastewater with sand filtration

Kang, Young Woon 11 March 2004 (has links)
No description available.
309

A Process for Manufacturing Metal-Ceramic Cellular Materials with Designed Mesostructure

Snelling, Dean Andrew Jr. 09 March 2015 (has links)
The goal of this work is to develop and characterize a manufacturing process that is able to create metal matrix composites with complex cellular geometries. The novel manufacturing method uses two distinct additive manufacturing processes: i) fabrication of patternless molds for cellular metal castings and ii) printing an advanced cellular ceramic for embedding in a metal matrix. However, while the use of AM greatly improves the freedom in the design of MMCs, it is important to identify the constraints imposed by the process and its process relationships. First, the author investigates potential differences in material properties (microstructure, porosity, mechanical strength) of A356 — T6 castings resulting from two different commercially available Binder Jetting media and traditional 'no-bake' silica sand. It was determined that they yielded statistically equivalent results in four of the seven tests performed: dendrite arm spacing, porosity, surface roughness, and tensile strength. They differed in sand tensile strength, hardness, and density. Additionally, two critical sources of process constraints on part geometry are examined: (i) depowdering unbound material from intricate casting channels and (ii) metal flow and solidification distances through complex mold geometries. A Taguchi Design of Experiments is used to determine the relationships of important independent variables of each constraint. For depowdering, a minimum cleaning diameter of 3 mm was determined along with an equation relating cleaning distance as a function of channel diameter. Furthermore, for metal flow, choke diameter was found to be significantly significant variable. Finally, the author presents methods to process complex ceramic structure from precursor powders via Binder Jetting AM technology to incorporate into a bonded sand mold and the subsequently casted metal matrix. Through sintering experiments, a sintering temperature of 1375 °C was established for the ceramic insert (78% cordierite). Upon printing and sintering the ceramic, three point bend tests showed the MMCs had less strength than the matrix material likely due to the relatively high porosity developed in the body. Additionally, it was found that the ceramic metal interface had minimal mechanical interlocking and chemical bonding limiting the strength of the final MMCs. / Ph. D.
310

Studies of Fungal Antagonism in a Norfolk Fine Sand, Denton County, Texas

Frenzel, Louis D., Jr. 08 1900 (has links)
This investigation has had for its primary purpose the noting of the incidence of antagonists as occurring in a Denton County, Texas, Norfolk Fine Sand. A further interest has been the determination of the effect of these antagonists upon known beneficial soil organisms.

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