No description available.

Master of Science / Department of Biological & Agricultural Engineering / Stacy L. Hutchinson / A field study was conducted at Fort Riley, Kansas from late spring to early winter of 2007 to investigate the ability of vegetated filter strips (VFS) to attenuate pollutants resulting from military activities, the impact of different management practices (i.e. burning and mowing) on VFS performance, and the effects of vegetation on hydrological components of VFS, especially infiltration and runoff. Two native tallgrass VFS sites, each comprising three plots, located in the military training area of Fort Riley were used for this study. Fifteen rainfall events were simulated on each site along with overland application of water containing nitrogen (N), phosphorous (P) and sediment. At the end of the season both VFS were managed by mowing or burning and a final rainfall simulation was done. Variables including rainfall, infiltration, runon, runoff, above ground biomass density, pollutant concentrations of runon and runoff, and soil moisture were measured and used in the data analysis. Hydrograph development, water balance, and mass balance calculations were carried out in order to calculate the pollutant trapping efficiencies (PTE) of the VFS. Statistical analysis was done by fitting several regression models. Mean comparisons were also done for variables and variance was decomposed into time, plot and site effects at an alpha = 0.05. Results showed that on average the VFS attenuated 84 % of total nitrogen, 24 % of total phosphorous and 95 % of sediments. Regression models showed that infiltration percentage and biomass density have a positive correlation with PTE. Runoff volume and PTE were negatively correlated. Soil moisture was negatively correlated with infiltration and time to runoff. With increasing biomass density, percentage of water infiltrating and time of concentration increased. Management practices, especially burning, tended to reduce PTE. Also, both management practices reduced infiltration percentage and time of concentration. PTE reduced with intensifying rainfall and increased when rainfall faded off. Phosphorous was the most sensitive pollutant for intense storm conditions followed by nitrogen, while sediment was comparatively insensitive.

Background: In PET/MRI, linear photon attenuation coefficients for attenuation correction (AC) cannot be directly derived, and cortical bone is, so far, usually not considered. This results in an underestimation of the average PET signal in PET/MRI. Recently introduced MR-AC methods predicting bone information from anatomic MRI or proton density weighted zero-time imaging may solve this problem in the future. However, there is an ongoing debate if the current error is acceptable for clinical use and/or research. Methods: We examined this feature for [18F] fluorodeoxyglucose (FDG) brain PET in 13 patients with clinical signs of dementia or movement disorders who subsequently underwent PET/CT and PET/MRI on the same day. Multiple MR-AC approaches including a CT-derived AC were applied. Results: The resulting PET data was compared to the CT-derived standard regarding the quantification error and its clinical impact. On a quantitative level, −11.9 to +2 % deviations from the CT-AC standard were found. These deviations, however, did not translate into a systematic diagnostic error. This, as overall patterns of hypometabolism (which are decisive for clinical diagnostics), remained largely unchanged. Conclusions: Despite a quantitative error by the omission of bone in MR-AC, clinical quality of brain [18F]FDG is not relevantly affected. Thus, brain [18F]FDG PET can already, even now with suboptimal MR-AC, be utilized for clinical routine purposes, even though the MR-AC warrants improvement.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: In recent years, breakwater design has been governed not only by structural stability, but by cost effectiveness as well. Breakwater designers are constantly trying to find the perfect balance between low-risk design and low-cost design. The combination of a main rubble mound breakwater and a submerged offshore reef, that are designed to function together, is known as a tandem breakwater. The reef structure is responsible for dissipating some of the energy by causing wave breaking. Thereafter, the area between the reef and the main structure - the tranquillity zone - allows for natural energy dissipation. The combination of the effects of the reef and tranquillity zone results in reduced significant wave heights at the main rubble mound structure, which allows it to be designed with lighter armour units. This study investigates the application of a tandem breakwater, based on the conditions at the port of Mossel Bay, by achieving the following set of objectives: (1) to determine the influence of the tandem breakwater‟s submerged reef crest elevation on the damage level of the main rubble mound structure, (2) to determine the relationship between the relative wave attenuation distance and the percentage wave attenuation, and (3) to compare the abovementioned parameters for rock and geotube reefs. A physical model test series was conducted to gain the data required for achieving the objectives. A rubble mound structure that makes use of dolos armour units, resembling the one at Mossel Bay, was constructed inside a concrete flume equipped with a single-paddle wavemaker. Two reef structure types (rock and geotube) were tested at three crest elevations (below-LAT, LAT and ML), against combinations of two significant wave heights (2.5 m and 3 m) and two peak periods (8 s and 12 s), at one water level (ML) and one offshore reef distance (50 m). From the model test results, it is evident that the presence of a reef structure significantly affects the wave conditions that reach the main structure. When comparing significant wave heights measured at a prototype distance of 20 m in front of the main breakwater, a reduction of as high as 42% can be observed for a reef structure made from rocks and 54% for a geotube structure. In all cases, the geotube structure causes more wave attenuation due to its lower permeability, which enables it to reflect more wave energy. However, it should be noted that the stability of the geotube reef was not considered during testing. Generic graphs are presented, that aim to provide guidance in the design process of such a tandem breakwater system. The graphs are produced for a case where dolos armour units are used and might not be exactly the same when a different type of armour unit is used. One graph shows the relationship between the damage reduction at the main breakwater and the relative reef submergence. The other shows the relationship between wave attenuation and the relative wave attenuation distance. Unfortunately, the implementation of geotube reefs of the nature described in this investigation is not likely in the South African context at present. This, however, does not eliminate the possibility of future applications. As geotextile technology develops and greater operational experience and equipment is gained, tandem breakwaters that incorporate geotube reefs could provide an alternative that is both cost-effective and more environmentally friendly with regards to transport emissions. Until then, tandem breakwaters that incorporate rock reefs may be able to provide a desired alternative design for certain scenarios. / AFRIKAANSE OPSOMMING: In die afgelope jare, word breekwater ontwerp nie net beheer deur strukturele stabiliteit nie, maar ook koste effektiwiteit. Ontwerpers poog alewig om die perfekte balans tussen lae-risiko ontwerp en lae-koste ontwerp na te streef. Die kombinasie van 'n hoof ruklipgolfbreker en 'n sekondêre onderwater rif breekwater, wat ontwerp is om as 'n eenheid te funksioneer, staan bekend as „n tandem breekwater. Die rif struktuur is verantwoordelik vir die verlies van 'n gedeelte van die golf energie deur golf breking te veroorsaak. Daarna veroorsaak die area tussen die rif en die hoof struktuur – die kalmeringsone – verdere natuurlike energie verlies. Die gekombineerde effek van die rif en kalmeringsone veroorsaak dat kleiner branders die hoof breekwater bereik, wat toelaat dat dit ontwerp kan word met kleiner pantser eenhede. Dié studie ondersoek die toepassing van 'n tandem breekwater, gebaseer op die kondisies by die Mosselbaai hawe, deur die volgende doelwitte te bewerkstellig: (1) om die invloed van die onderwater rif kruinhoogte op die vlak van skade aan die hoof breekwater te bepaal, (2) om die verhouding tussen die relatiewe golfhoogte-verminderings-afstand en die golfhoogte vermindering te bepaal, en (3) om die bogenoemde parameters vir rots en geo-buis riwwe te vergelyk. 'n Fisiese model toets reeks is uitgevoer sodat die benodigde data ingesamel kan word om die doelwitte te bereik. „n Rotsvul breekwater wat gebruik maak van dolos pantser eenhede, soortgelyk aan dié by Mosselbaai, is gebou in 'n beton kanaal wat toegerus is met 'n enkel-spaan golfmasjien. Twee tipes riwwe (rots en geo-buis) is getoets met drie kruin hoogtes (onder-LAG, LAG en GV), teen kombinasies van twee beduidende golfhoogtes (2.5 m en 3 m) en twee spitsperiodes (8 s en 12 s), by een watervlak (GV) en een sekondêre breekwater afstand (50 m). Uit die model toets resultate is dit duidelik dat die teenwoordigheid van 'n rif struktuur, die golfkondisies wat die hoof breekwater bereik, beduidend beïnvloed. Wanneer beduidende golfhoogtes, gemeet op 'n prototipe afstand van 20 m voor die hoof breekwater, vergelyk word, word 'n vermindering van so hoog as 42% waargeneem vir 'n rif bestaande uit rots en 54% vir 'n rif bestaande uit geo-buise. In alle gevalle veroorsaak die geo-buis struktuur meer golfhoogte vermindering, as gevolg van sy laer deurlaatbaarheid, wat dit in staat stel om meer golfenergie te reflekteer. Die stabiliteit van die geo-buis struktuur is egter nie in ag geneem tydens die toetse nie. Generiese grafieke word weergegee, met die doel om leiding te gee tydens die ontwerpsproses van só 'n tandem breekwater struktuur. Die grafieke hou verband met die geval waar dolos pantser eenhede gebruik word, en mag verskil vir ander tipes pantser eenhede. Een van die grafieke dui die verhouding tussen skadevermindering aan die hoof breekwater en die relatiewe posisie van die onderwater rif se kruinhoogte aan. Die ander grafiek dui die verhouding tussen die golfhoogte vermindering en die relatiewe golfhoogte-verminderings-afstand aan. Huidiglik is die toepassing van die tipe geo-buis riwwe soos beskryf in hierdie ondersoek, ongelukkig onwaarskynlik in die Suid-Afrikaanse konteks. Dit skakel egter nie die moontlikheid van toekomstige toepassings van dié aard uit nie. Soos geo-tekstiel tegnologie ontwikkel en meer operasionele ervaring en toerusting bekom word, kan die effektiewe implementasie van geo-buis riwwe 'n alternatief bied wat beide koste effektief en omgewingsvriendelik is met betrekking tot die vrystelling van uitlaatgasse tydens die vervoer van materiale. Tot dan, kan tandem breekwaters wat van rots riwwe gebruik maak, moontlik die gewenste alternatiewe ontwerp bied vir sekere situasies.

The entire stretch of the Ohio River is under fish consumption advisories due to contamination with polychlorinated biphenyls (PCBs). In this study, natural attenuation and biostimulation of PCBs and microbial communities responsible for PCB transformations were investigated in Ohio River sediments. Natural attenuation of PCBs was negligible in sediments, which was likely attributed to low temperature conditions during most of the year, as well as low amounts of available nitrogen, phosphorus, and organic carbon. Moreover, surface sediments were relatively oxidized, as indicated by the prevalence of aerobic bacteria such as beta- Proteobacteria, alpha-Proteobacteria, Sphingobacteria, and Nitrospira in 16S rRNA sediment clone libraries. On the other hand, several reductive dechlorinators were detected in sediments, including Dehalococcoides, Desulfitobacterium spp. which suggested that reductive dechlorination might be possible in sediments under certain biogeochemical conditions. Considerable amounts of PCBs were transformed by reductive dechlorination (80% in 177 days by pattern N) when sediments were maintained under anaerobic conditions, amended with nutrients and organic carbon, and incubated at 25 ºC in lab microcosms. Analysis of 16S rRNA clone libraries from these treatments revealed that Bacteroidetes, Chloroflexi and Firmicutes were enriched and Proteobacteria were depleted compared to clone libraries from treatment without organic amendments. Reductive dechlorination was decreased in sediments incubated at 10 and 40 ºC, and was not affected by FeSO4 amendments compared to unamended sediments incubated at 25 ºC. Transformations of PCB-153 were investigated in sediments under anaerobic, aerobic and sequential anaerobic and aerobic conditions. Transformations were only observed in treatments with an anaerobic phase, which occurred by reductive dechlorination by pattern N. Neither PCB-153 nor dechlorination products PCB-99 or PCB-47 were transformed under aerobic conditions. Analysis of 16S rRNA clone libraries revealed that Bacteoridetes, Chloroflexi, and Firmicutes were enriched under anaerobic conditions and Proteobacteria were enriched under aerobic conditions. Results from this study revealed that natural attenuation and biostimulation were not effective at removing PCBs from Ohio River sediments. Hence, other remediation methods will need to be employed to decrease PCB levels in this ecosystem.

Single frame ultrasound B-mode image quality is largely governed by the ability to focus the ultrasound beam over a range in depths both in transmission and reception. By developing a comprehensive understanding of acoustic wave propagation two signal processing methods were identified for solving the transmission problem. We made use of both the impulse response using the classical point spread function (PSF) and the spatial sensitivity function (SSF) which describes the spatial distribution at a particular time. Using the angular spectrum method, an accurate analytical model was developed for the field distribution arising from a finite geometry, apodized and focused, plane piston transducer. While there is a thorough understanding of the radiated field arising from uniformly excited plane piston transducers, the focused equivalent (i.e., one that allows a continuous change in phase over the plane piston surface) is incomplete and assumes the Fresnel approximation. Our model addresses the effects of diffraction and evanescent waves without the use of the Fresnel approximation and is applicable at all near- and far-field locations in a lossless medium. The model was analyzed to identify new insights into wave propagation and compared with the Fresnel approximation and the spherically-focused, concave transducer. The piston transducer model was then extended to an attenuating and dispersive medium. After analysing existing models of power-law frequency dependent attenuation, a causal, spherical wave Green’s function was derived from the Navier-Stokes equation for a classical viscous medium. Modifications to the angular spectrum method were presented and used to analyze the radiated field of a focused, planar piston transducer. Finally, after presenting our signal processing strategy for improving imaging spatial resolution through minimization of the SSF, two signal processing methods were derived and analysed in simulation: a deconvolution technique to remove the effects of the ultrasound excitation wave and suppress additive noise from the received ultrasound signal, and a retrospective transmit focusing method that changed the response from a predefined transmit focus to an arbitrary transmit focal depth. Proof-of-concept simulations were presented using a variable number of scatterers and compared with the traditional matched filtering and envelope detection technique.

Numerical modelling currently cannot accurately reproduce the onshore-offshore transport asymmetry observed on gravel beaches. The role of the impulsive pressure response generated by plunging waves has been hypothesised to aid mobilisation of sediment, and thus may contribute to transport asymmetry. This process is not currently included in models. Laboratory tests were conducted across a range of wave conditions to investigate the role of plunging wave-breaker impacts on the mobilisation of sediment of gravel beaches. Pressure records were obtained at positions close to the plunging impact locations, to monitor the localised pressures that lead to sediment mobilisation. The correction of the recorded pressure to the bed surface, for further analysis, was achieved through a two stage approach. Adoption of a new technique for separating the pressure records into two components, each determined by different processes is presented. Each component is then corrected to the bed surface with the application of a pragmatic prediction of the experienced attenuation. Data covering a wide range of Iribarren values was assessed, and the impact pressure was parameterised against the wave-breaker type. This procedure identified a potential peak in the impact pressure-Iribarren space in the plunging breaker region, consistent with the previous hypothesis. Comparison of cross-shore profile records provides further limited evidence that morphological prediction fails to reproduce specific characteristics associated with profiles generated under plunging breaker action. Finally, a brief discussion is provided on how the role of the additional pressure generated under plunging impacts can be incorporated into future numerical models.

No description available.

Conventional AVO analysis has been used for the past 4 decades to aid in locating oil and gas reservoirs for extraction. It is, however, not possible to use it to acquire information on the porosity of the rock, the fluid saturation or other important petrophysical parameters. In this thesis, I study the effects of attenuation on seismic waveform signatures, due to wave induced fluid-flow. In the first part of the thesis, 2 models were used to synthetically model the attenuation caused by the wave induced fluid-flow: White's model and the double-porosity dual-permeability (DPDP) model. The parameters used for modeling were both synthetic and acquired from real well data of a known oil field off the coast of Norway. White's model was found to model relatively high attenuation (5%) for intermediately consolidated gas reservoirs while oil saturated intermediately consolidated reservoirs showed such low attenuation (0.3%) that it is easy to say that for the real-world situation it would not be detected. The DPDP model seemed to be able to better describe the attenuation and gave attenuations up to 10% for an intermediately consolidated oil reservoir, but due to lack of parameters from well data it was not sufficiently able to model the real-world situation. The synthetic data, however, show interesting characteristics and it is therefore recommended that more and detailed well parameters be acquired if the research should continue. For the second part, Svenska Petroleum Exploration AB and Det Norske Oljeselskap ASA provided stacked seismic data that were spectrally analyzed for hints of attenuation variation with frequency (using Fourier Transform and Complex Spectral Decomposition). Twelve locations, on the stacked seismic cube, were analyzed; six oil saturated; and six (assumed) water saturated. At each location, a main trace was selected along with the two nearby traces on each side of it (five in total). The Complex Spectral Decomposition method seemed unable to correctly break down the stacked section's signal, which is why Fourier Transform was used for further analysis. The frequency analysis showed a peak at ~30 Hz for both oil and water saturated reservoirs which seems like a characteristic frequency of the source, but that was unfortunately not confirmed and not enough time was available to test the assumption. The Fourier transform seems to show some difference between oil and water saturated traces, but that could well be because of lithological differences and not the pore fluid. It is therefore recommended, if research is to be continued, that 4D seismic data is used to analyze the same location with respect to time. It is also recommended that pre-stack or shot data be used as information is lost in stacked data. / Konventionell AVO-analys har använts under fyra deceniär som ett hjälpmedel för att finna olje- och gasreserver, men tekniken kan även användas för att erhålla information om bergets porositet, vätskemättnaden och andra viktiga petrofysiska parametrar. I denna avhandlingen har jag studerat hur våginducerat vätskeflöde påverkar dämpningen av den seismiska vågformssignaturen. I den första delen av avhandlingen användes två metoder för att syntetisk modellera dämpning orsakad av våginducerat vätskeflöde: "White's modell" och "double-porosity dual-permeability (DPDP) modellen". Både syntetiska parametrar och verkliga parametrar från borrhålsdata från ett känt norskt oljefält användes vid modelleringen. White's modell visade sig modellera relativt kraftig dämpning (5%) för medelstarkt konsoliderade gasreservoarer medan för oljereservoarer med motsvaranda konsolidering dämpningen var så låg (0.3%) att det är uppenbart att i en verklig situation skulle dämpningen inte vara mätbar. DPDP modelleringen verkar vara bättre på att beskriva dämpningen och gav dämpningar upp till 10% för en medelstarkt konsoliderad oljereservoar. Brist på parametrar från borrhålsdata gjorde att det inte var möjligt att på ett tillfredställande sätt modellera en verklig situation.Dock visade syntetisk data intressant karaktäristik och det rekommenderas därför att mer och detaljerade borrhålsparametrar mäts om ytterligare forskning om detta ska genomföras. För den andra delen av avhandlingen har Svenska Petroleum Exploration AB och Det Norske Oljeselskap ASA bidragit med stackad seismisk data som även var spectralanalyserad för indikationer på frekvensberoende dämpningsvariationer (utfört med fouriertransform och komplex spectraldekomposition). Tolv områden på den stackade kuben analyserades; sex oljemättade och sex som antogs vara vattenmättade. I varje område valdes en huvudtracé och de två närmaste tracéerna på vardera sida (totalt fem tracéer). Metoden med komplex spectraldekomposition klarade inte att analysera signalen från den stackade sektionen, varför fouriertransform användes för vidare analys. Frekvensanalysen gav en topp vid ~30 Hz för både olje- och vattenmättade reservoarer vilket tycks vara en karaktäristisk frekvens för källan. Detta kunde tyvärr inte bekräftas och tiden räckte inte till för att testa antagandet. Fouriertransformen tycks visa en viss skillnad mellan olje- och vattenmättade tracéer, men det kan också bero på skillnad i litologin snarare än porvätskan. Där för rekommenderas vid fortsättning på denna forskning att 4D seismisk data används för att analysera samma område men med data från olika tidpunkter. Det rekommenderas även att ostackad eller råa skott-data används eftersom väsentlig information kan försvinna när data stackas. / <p>Advisor present: Dr. Chris Juhlin</p><p>Examiner: Dr. Milovan Urosevic</p><p>Opponent: Álvaro Polín Tornero</p>

[pt] A disponibilidade é o parâmetro chave no dimensionamento de sistemas de comunicação. Em sistema via rádio diversos fatores reduzem esta disponibilidade, entre os quais se podem citar o desvanecimento, as atenuações adicionais, as interferências externas e a ocorrência de falhas dos equipamentos. A atenuação por chuvas é o principal fenômeno de atenuação adicional para sistemas que operam em frequências superiores a 10 GHz. A chuva é um fenômeno aleatório que apresenta grande variação no espaço e no tempo. Diversos modelos teóricos e semi-empíricos foram propostos na literatura à medida que crescia a utilização de frequências mais elevadas na faixa de micro-ondas. A principal diferença entre os modelos está na maneira de representar a variação espaço-temporal da chuva e o seu efeito na onda eletromagnética em propagação. No trabalho é investigada a influência de parâmetros meteorológicos de direção e velocidade do vento, e testado o conceito de taxa de precipitação efetiva na modelagem. Dois modelos semi-empíricos são desenvolvidos com base em distribuições cumulativas de atenuação e taxas de precipitação pontuais disponíveis no banco de dados da União Internacional de Telecomunicações (UIT-R). Os testes de comparação demonstram que os modelos obtidos apresentam desempenho superior se comparados aos modelos atualmente recomendados para previsão da atenuação por chuvas. Em outra linha de investigação, foi desenvolvido um modelo estatisticamente consistente para previsão da distribuição da atenuação a partir da representação da distribuição cumulativa complementar da taxa de precipitação. A distribuição cumulativa da atenuação foi obtida a partir da suposição de um relacionamento com significado físico entre a taxa de precipitação e atenuação por chuvas. A comparação dos modelos demonstra que o modelo obtido apresenta resultados comparáveis a modelos de Recomendações do UIT-R. / [en] Availability is the key parameter in the communication systems design. In radio system many factors impact the availability, including fading, additional loss, external interference and equipment availability. The rain attenuation is the main impairments in systems operating at frequencies above 10 GHz. The rain is a random phenomenon that is highly variable in space and time. Several theoretical and semi-empirical models have been proposed in the literature as the growing use of higher frequencies in the microwave range. The main difference between the models is the way to represent the rain variation effect on electromagnetic waves. This work investigates the meteorological parameters direction and speed of wind influence in modeling. Two semi-empirical models are developed based on attenuation and rainfall rates cumulative distributions available at International Telecommunication Union (ITU-R) database. ITU-R testing criteria shows that the obtained models have superior performance compared to currently recommended models for rain attenuation prediction. In another line of investigation, a statistically consistent model to predict attenuation distribution from the complementary cumulative distribution of rainfall rate was developed. The attenuation cumulative distribution was obtained from rainfall rate and rain attenuation physical relationship assumption. ITU-R testing criteria show that the obtained model has results comparable with Recommendations ITU-R models.