River-ice break-up in high-latitude regions, despite its brevity, is a fundamental process, representing the most dynamic and complex period of fluvial processes. Moreover, ice break-up has significant cascading ecological effects, with a different severity for mechanical vs. thermal break-up, and thus, motivates the importance of monitoring efforts. Classical research methods, such as fieldwork or analysis of photographs and aerial imagery, offer a general perspective on the timing of ice break-up but have safety and logistic issues caused by the dangers of unstable ice cover, the lag times between event occurrence and observation, and the frequent low visibilities. The emerging field of environmental seismology, which studies surface processes through seismic signals, provides an alternative solution to these shortcomings by continuously recording high temporal resolution data. Seismic sensing can potentially record any event within a set distance if the produced signal is powerful enough. Three geophones had monitored the subarctic Sävar River reach for 185 days to test the efficiency of seismic methods to capture ice-cracking events, and based on their characteristics, to identify thermal vs. mechanical ice break-up. With visual and multivariate analysis, seismic methods provided a conservative set of 2 228 events, detected at milliseconds precision, described, and located. Besides, both trigger lag times and principal component analysis depicted correlations between environmental drivers and ice-cracking events. The automatic picker based on duration and trigger thresholds required manual supervision because of the initial numerous false signals that accounted for 96% of total initial events. Ice-cracking signals as short as 0.2s and frequencies of 8-40 Hz with an average power of -117 dB were statistically defined, classified, and described by case events as two types, associated, based on their spectral and temporal patterns, with the two ice break-up modes. With an estimated Rayleigh wave velocity of 680 m/s, all ice-cracking signals' locations were within the instrumented area. Trigger lag times analysis improved detection and showed a strong link between ice-cracking events and drivers of lag times less than three hours, including near-immediate responses (< 2s). With multivariate analysis, the lag times showed a mainly climatic control for thermal melting and a primarily fluvial control in mechanical ice break-up. The combination of statistical and seismic analysis provides, despite the considerable manual screening, a valid and potentially site-transferable method to extract and describe ice-cracking signals and thus identify ice break-up modes in northern rivers.

Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Natural draught wet-cooling tower rain zone performance can be significantly enhanced by reducing the mean drop size in the rain zone with the installation of specially designed grids below the cooling tower fill. Drops enter the rain zone in the form of a polydisperse drop distribution, dripping from below the cooling tower fill, comprising relatively large drops. In order to design and optimize a grid for breaking up these drops, the mechanisms of drop break-up after impingement on the grid surface, referred to as splashing, straddling and dripping, need to be clearly understood. Two of these mechanisms, splashing and straddling, are therefore investigated experimentally using high speed video cameras to measure initial drop sizes, mass fractions and drop size distributions after impingement on different horizontal slats covered with a thin layer of water. The following parameters are varied independently for these experiments: drop fall distance, initial drop size, slat width and the water film thickness on the slats. Dripping from below the grid, is investigated theoretically. The effect of drop interaction on the drop size distribution in the rain zone is also investigated experimentally by measuring the drop distributions at the top and bottom of rain zones with a height of approximately 7.05 m to 7.65 m for different inlet distributions. The experimental drop break-up data, numerically obtained splash drop trajectory data and drop interaction data found in literature are used to develop a theoretical model of a purely counter flow cooling tower rain zone with and without installed grids. The model is compared to experimental data and theoretical data from literature and the predicted thermal and dynamic behaviour of the rain zone are generally found to be in good agreement with these results. Ultimately, this model is used for the optimization of the grid layout in terms of variables such as distance between the grid and the fill, slat width, slat spacing and slat height. It is found that the best drop break-up is achieved for grids comprising narrower slats with lower grid porosities as opposed to grids comprising wider slats. For the determined optimal grid layout it is found that a significant improvement in cooling tower performance can be achieved. / AFRIKAANSE OPSOMMING: Nat-koeltoringreënsonevermoë kan aansienlik verhoog word deur die druppelgrootte in hierdie gebied te verklein deur roosters, wat spesifiek vir hierdie doel ontwerp is, onder die pakkingsmateriaal te installeer. Die inlaatdruppelverdeling aan die bokant van die reënsone bestaan uit ‘n verdeling van relatief groot druppels wat drip van die onderkant van die pakkingsmateriaal. Ten einde ‘n rooster te ontwerp en te optimeer wat hierdie druppels kan opbreek moet die meganismes van druppelopbreking, bekend as spatting, vurking en drip goed verstaan word. Spatting en vurking is om hierdie rede eksperimenteel ondersoek, met behulp van hoëspoed videokameras. Die volgende veranderlikes is onafhanklik verander tydens hierdie eksperimente: valafstand van die druppel, aanvanklike druppelgrootte, latwydte en die dikte van die lagie water bo-op die lat. Die dripmeganisme aan die onderkant van die rooster is slegs teoreties ondersoek. Die effek wat druppelinteraksie in die reënsone het op die druppelgrootte is ondersoek deur die druppelgroottes aan die bo- en onderkant van ‘n 7.05 m tot 7.65 m reënsone te meet vir verskillende druppelinlaatverdelings. Die eksperimentele druppeldata, sowel as numeries berekende data wat die snelheid en trajek van spatdruppels beskryf, tesame met data vir druppelinteraksies wat uit die literatuur verkry is word gebruik om ‘n teoretiese model te ontwikkel vir ‘n suiwer teenvloei koeltoringreënsone met en sonder roosters. Hierdie model word vergelyk met eksperimentele data en data wat uit die literatuur verkry is en daar is gevind dat daar oor die algemeen ‘n goeie ooreenstemming is tussen die voorspelde en gemete termiese en dinamiese gedrag van die reënsone. Uiteindelik word die model gebruik vir die optimering van die rooster in terme van die volgende veranderlikes: afstand tussen rooster en pakkingsmateriaal, latwydte, latspasiëring en lathoogte. Daar word gevind dat beter druppelopbreking verkry word deur gebruik te maak van smaller latte en ‘n laer roosterporeusiteit. Daar is gevind dat die bepaalde optimale roosteruitleg in die reënsone van ‘n koeltoring ‘n wesenlike verbetering in koeltoringvermoë tot gevolg kan hê.

Den första februari år 2015 infördes, i linje med motsvarande reglering i engelska Takeover Code, ett förbud mot budrelaterade arrangemang i takeover-reglerna. Vilka avtal förbudet omfattar och i vilka fall dispens kan beviljas utreds i det här arbetet. Bland annat på grund av dess nära relation till den svenska regleringen har dess engelska förebild getts en central roll i analysen. Några av de viktigaste slutsatserna är att irrevocables inte torde omfattas av förbudet och att vissa krav för hur budrelaterade arrangemang får utformas torde gälla även i de situationer då dispens enligt kommentaren till förbudet kan beviljas.

Por meio de ensaios em reatores estáticos (em equipamento de jarteste) foram estudados os efeitos da ruptura e da refloculação na sedimentação dos flocos, para diferentes velocidades de sedimentação. A água de estudo foi preparada com substâncias húmicas aquáticas (SHA) extraídas de água coletada do rio Itapanhaú - Bertioga/SP, resultando cor verdadeira de 100 uH, e coagulada com sulfato de alumínio e cloreto férrico. Para os dois coagulantes, foram realizadas as etapas de coagulação, mistura rápida, floculação, ruptura (G=50, 100 e 150/s) e refloculação (G=10 e 20/s). Na sedimentação sem a ocorrência de ruptura o cloreto férrico teve um desempenho superior ao sulfato de alumínio, principalmente nas velocidades de sedimentação mais altas. Isso se deve ao fato da floculação da água coagulada com o cloreto férrico ter gerado flocos de tamanho muito superior aos flocos gerados com o sulfato de alumínio. A ruptura, em poucos segundos, prejudicou a remoção dos flocos por sedimentação. Quanto maior o gradiente de velocidade na ruptura, maiores foram os valores da cor aparente remanescente, mesmo após a refloculação. A refloculação, mesmo nos primeiros minutos, diminuiu a cor aparente remanescente se comparada a logo após a ruptura. O menor gradiente de velocidade durante a refloculação testado (10/s) apresentou menores valores da cor aparente remanescente. Tanto na água coagulada com o sulfato de alumínio quanto na coagulada com o cloreto férrico a refloculação se comportou de modo semelhante, havendo recuperação na eficiência de remoção de cor sem, porém, atingir os resultados obtidos antes da ruptura. / By using the jar test equipment, the effects of breakage and reflocullation on the efficiency of floc sedimentation were studied, using different settling velocities. Water of study was prepared with aquatic humic substances (AHS) extracted from the Itapanhaú river (Bertioga, SP, Brazil), resulting a true color of 100 uH. Coagulation was performed by using aluminum sulfate and ferric chloride. For both coagulants, coagulation, flocculation, breakage (G=50, 100 and 150/s) and reflocculation (G=10 and 20/s) tests were carried out. In the sedimentation without the floc breakage occurrence the ferric chloride had a superior performance to aluminum sulphate, mainly in higher settling velocities. This occurred because of flocculation of the ferric chloride coagulated water have generated higher size flocs than that generated with aluminum sulphate. The breakage of flocs, in few seconds, hindered the settling removal. The higher the average shear rate in the break-up, the higher result the residual turbidity even after the reflocculation. The reflocculation, even in the first minutes, decreased the apparent color if compared to the results just after the break-up and sedimentation. The lower average share rate used during the reflocculation (10/s) resulted lower values of the remaining apparent color. During the flocculation, the aluminum sulphate coagulated water as well as in the ferric chloride coagulated water held in similar way, recovering the efficiency of removal of color without, however, reach the results gotten before the breakage.

Durante a floculação, a agitação promove dois efeitos simultaneamente, a agregação e a ruptura. A ruptura ocorre devido à atuação de forças de cisalhamento sobre os flocos. O aumento da agitação com, conseqüentemente, aumento do gradiente de velocidade médio, em água com flocos formados, promove o aumento das forças de cisalhamento e a degradação parcial ou total dos mesmos, em poucos segundos. Retornando à condição anterior de agitação, pode ocorrer o recrescimento dos flocos. Através de ensaios em reatores estáticos (em equipamento de jarteste) foram estudados os efeitos da ruptura e da refloculação na sedimentação dos flocos, para velocidades de sedimentação entre 0,9 e 7,0 cm/min. A água de estudo foi preparada com caulinita, resultando turbidez de 100 uT, e coagulada com sulfato de alumínio. Foram realizadas as etapas de coagulação, mistura rápida, floculação, ruptura (G=75, 150 e 250 \'S POT.-1\') e refloculação (G=25, 20 e 15 \'S POT.-1\'). A ruptura, em poucos segundos, prejudicou a remoção dos flocos por sedimentação. Quanto maior o gradiente de velocidade na ruptura, maiores foram os valores da turbidez remanescente do sobrenadante, mesmo após a refloculação. A refloculação, mesmo nos primeiros minutos, diminuiu a turbidez remanescente do sobrenadante se comparada a logo após a ruptura. Quanto menor o gradiente de velocidade durante a refloculação, menores foram os valores da turbidez remanescente do sobrenadante. Apenas para velocidades de sedimentação, gradientes de velocidade de ruptura e gradientes de velocidade de refloculação menores ou iguais a 2,5 cm/min, 75 \'S POT.-1\' e 15 \'S POT.-1\', respectivamente, foi possível obter sobrenadante com valores de turbidez remanescente similares aos encontrados inicialmente, sem ruptura. / During the flocculation, the shear rate promotes two effects simultaneously, growth and breakage of flocs. The break up of flocs is caused as a result of disruptive forces. The increase of the shear rate in water with formed flocs increases the disruptive forces and it also can break the flocs partial or totally in a few seconds. Restoring the previous low shear conditions, flocs can grow back. By using the jar test equipment, the effects of breakage and reflocullation on the efficiency of floc sedimentation were studied, using settling velocities between 0.9 e 7.0 cm/min. Water of study was prepared with groundwater and kaolin, resulting a turbidity of approximately 100 NTU. Coagulation was performed by using aluminum sulfate. Coagulation, flocculation, breakage (G=75, 150 e 250 \'S POT.-1\') and reflocculation tests were carried out. In a few seconds the breakage of flocs hindered the settling removal of turbidity. The higher the average shear rate in the break-up, the higher result the residual turbidity even after the reflocculation. In the first minutes, the reflocculation decreased the residual turbidity after sedimentation if compared to the residual turbidity just after the break-up and sedimentation. The lower the average shear rate during the reflocculation, the lower result the supernatant values of residual turbidity. Supernatant could only be obtained with the value of residual turbidity similar to the values found initially (without breakage of flocs) for the settling velocity, the average velocity gradient of break-up and the average velocity gradient of reflocculation equal or less than 2.5 cm/min, 75 \'S POT.-1\' e 15 \'S POT.-1\', respectively.

Many daily life products consist of mixtures of oil and water. When an immiscible material is dispersed an interface in-between the two phases is created which gives rise to rheological phenomena which can be exploited for product formulation; this is the case in products such as hand-creams and food products. Furthermore emulsions are used to transport hydrophobic materials, for example, many pharmaceuticals are injected as emulsions into the bloodstream. The performance of such products depends on their microstructure, which is determined by its formulation and how its constituents are mixed together; therefore the microstructure depends on the properties of the dispersed phases, the emulsifier used, the equipment used and its processing conditions. Emulsified products are seldom mono-dispersed due to the complex drop breakup mechanism in the turbulent fields inside the equipment in which the phases are forced together. The chaotic breakup mechanism of highly viscous dispersed phases yield complex and broad drop size distributions (DSD) as a result of the dominating viscous cohesive stresses inside the parent drop. Former studies have used the Sauter mean diameter and/or the size of the largest drop as the characteristic measure of central tendency of the DSD to correlate their results and to prove mechanistic or phenomenological models; however these parameters in isolation are insufficient to characterise the whole DSD of highly polydisperse emulsions. In this dissertation a vast amount of silicon oils of different viscosity were used as dispersed phase to study the effect of various processing conditions and formulations on the resulting DSD. The effect of several formulation and processing parameters were studied for two different mixing devices: stirred vessels and in-line high-shear mixers. (1) For stirred vessels, the effect of stirring speed, continuous phase viscosity and dispersed phase volume fraction were studied in combination with the viscosity of the dispersed phase for steady-state systems. (2) For in-line high-shear mixers a model that links batch and multi-pass continuous emulsification for multimodal DSD was derived from a transient mass balance. Processing parameters such as time and volume, flow rate and number of passes through the mixer, and stirring speed were studied for a wide dispersed phase viscosity range. The analytical methodology implemented included the use of one or more probability density functions to describe the shape of the DSD. The models proposed gave reasonable approximations of the Sauter mean diameter and allowed to study the drop size changes and the relative amount of different types of drops resulting from different breakup mechanisms.

<p>The objective of this project is to study the production of Li, Be and B isotopes emitted in the interaction of 12C with 12C at incident energies of 200 and 400 MeV.<br /> The energies of these produced fragments were measured with a detector telescope consisting of two silicon detectors at the incident energy of 200 MeV while a third silicon detector was added for the measurements at 400 MeV.</p>

<p>The objective of this project is to study the production of Li, Be and B isotopes emitted in the interaction of 12C with 12C at incident energies of 200 and 400 MeV.<br /> The energies of these produced fragments were measured with a detector telescope consisting of two silicon detectors at the incident energy of 200 MeV while a third silicon detector was added for the measurements at 400 MeV.</p>

The frequency, magnitude, and atmospheric drivers of winter hydroclimatic conditions conducive to snowmelt in western Canada were evaluated. These hydroclimatic variables were linked to the mid-winter break-up of river ice that included the creation of a comprehensive database including 46 mid-winter river ice break-up events in western Canada (1950-2008) and six events in Alaska (1950-2014). Widespread increases in above-freezing temperatures and spatially diverse increases in rainfall were detected over the study period (1946-2012), particularly during January and March. Critical elevation zones representing the greatest rate of change were identified for major river basins. Specifically, low-elevation (500-1000 m) temperature changes dominated the Stikine, Nass, Skeena, and Fraser river basins and low to mid-elevation changes (700-1500 m) dominated the Peace, Athabasca, Saskatchewan, and Columbia river basins. The greatest increases in rainfall were seen below 700 m and between 1200-1900 m in the Fraser and at mid- to high-elevations (1500-2200 m) in the Peace, Athabasca, and Saskatchewan river basins. Daily synoptic-scale atmospheric circulation patterns were classified using Self-Organizing Maps (SOM) and corresponding hydroclimatic variables were evaluated. Frequency, persistence, and preferred shifts of identified synoptic types provided additional insight into characteristics of dominant atmospheric circulation patterns. Trend analyses revealed significant (p < 0.05) decreases in two dominant synoptic types: a ridge of high pressure over the Pacific Ocean and adjacent trough of low pressure over western Canada, which directs the movement of cold, dry air over the study region, and zonal flow with westerly flow from the Pacific Ocean over the study region. Conversely, trend analyses revealed an increase in the frequency and persistence of a ridge of high pressure over western Canada over the study period. However, step-change analysis revealed a decrease in zonal flows and an increase in the occurrence of high-pressure ridges over western Canada in 1977, coinciding with a shift to a positive Pacific Decadal Oscillation regime. A ridge of high pressure over western Canada was associated with a high frequency and magnitude of above-freezing temperatures and rainfall in the study region. This pattern is highly persistent and elicits a strong surface climate response. A ridge of high pressure and associated above-freezing temperatures and rainfall was also found to be the primary driver of mid-winter river ice break-up with rainfall being a stronger driver west of the Rocky Mountains and temperature to the east. These results improve our understanding of the drivers of threats to snowpack integrity and the generation of extreme hydrologic events. / Graduate

Durante a floculação, a agitação promove dois efeitos simultaneamente, a agregação e a ruptura. A ruptura ocorre devido à atuação de forças de cisalhamento sobre os flocos. O aumento da agitação com, conseqüentemente, aumento do gradiente de velocidade médio, em água com flocos formados, promove o aumento das forças de cisalhamento e a degradação parcial ou total dos mesmos, em poucos segundos. Retornando à condição anterior de agitação, pode ocorrer o recrescimento dos flocos. Através de ensaios em reatores estáticos (em equipamento de jarteste) foram estudados os efeitos da ruptura e da refloculação na sedimentação dos flocos, para velocidades de sedimentação entre 0,9 e 7,0 cm/min. A água de estudo foi preparada com caulinita, resultando turbidez de 100 uT, e coagulada com sulfato de alumínio. Foram realizadas as etapas de coagulação, mistura rápida, floculação, ruptura (G=75, 150 e 250 \'S POT.-1\') e refloculação (G=25, 20 e 15 \'S POT.-1\'). A ruptura, em poucos segundos, prejudicou a remoção dos flocos por sedimentação. Quanto maior o gradiente de velocidade na ruptura, maiores foram os valores da turbidez remanescente do sobrenadante, mesmo após a refloculação. A refloculação, mesmo nos primeiros minutos, diminuiu a turbidez remanescente do sobrenadante se comparada a logo após a ruptura. Quanto menor o gradiente de velocidade durante a refloculação, menores foram os valores da turbidez remanescente do sobrenadante. Apenas para velocidades de sedimentação, gradientes de velocidade de ruptura e gradientes de velocidade de refloculação menores ou iguais a 2,5 cm/min, 75 \'S POT.-1\' e 15 \'S POT.-1\', respectivamente, foi possível obter sobrenadante com valores de turbidez remanescente similares aos encontrados inicialmente, sem ruptura. / During the flocculation, the shear rate promotes two effects simultaneously, growth and breakage of flocs. The break up of flocs is caused as a result of disruptive forces. The increase of the shear rate in water with formed flocs increases the disruptive forces and it also can break the flocs partial or totally in a few seconds. Restoring the previous low shear conditions, flocs can grow back. By using the jar test equipment, the effects of breakage and reflocullation on the efficiency of floc sedimentation were studied, using settling velocities between 0.9 e 7.0 cm/min. Water of study was prepared with groundwater and kaolin, resulting a turbidity of approximately 100 NTU. Coagulation was performed by using aluminum sulfate. Coagulation, flocculation, breakage (G=75, 150 e 250 \'S POT.-1\') and reflocculation tests were carried out. In a few seconds the breakage of flocs hindered the settling removal of turbidity. The higher the average shear rate in the break-up, the higher result the residual turbidity even after the reflocculation. In the first minutes, the reflocculation decreased the residual turbidity after sedimentation if compared to the residual turbidity just after the break-up and sedimentation. The lower the average shear rate during the reflocculation, the lower result the supernatant values of residual turbidity. Supernatant could only be obtained with the value of residual turbidity similar to the values found initially (without breakage of flocs) for the settling velocity, the average velocity gradient of break-up and the average velocity gradient of reflocculation equal or less than 2.5 cm/min, 75 \'S POT.-1\' e 15 \'S POT.-1\', respectively.