O uso de comportas ou válvulas em condutos para efetuar o controle de fluxo em estruturas hidráulicas é bastante usual. Uma das aplicações deste tipo de dispositivo de controle de vazões é para fazer o enchimento e esvaziamento de câmaras de eclusas de navegação. Entretanto, a sua aplicação deve ser feita com cuidado em função da complexidade do escoamento, o qual pode apresentar grandes variações de velocidade e pressões junto à base e ao teto da galeria a jusante da comporta. O gradiente de pressão pode variar no tempo e no espaço podendo vir a ocasionar danos por erosão (desgaste) e/ou cavitação. Assim, torna-se fundamental obter critérios para a estimativa de previsão do valor dessas pressões para, então, poder inferir a possibilidade de danos junto à superfície sólida, permitindo que se determinem as condições críticas de operação que devem ser evitadas ou minimizadas durante as operações de esvaziamento ou de enchimento da câmara da eclusa. Esta pesquisa procura apresentar o estado da arte em relação à distribuição longitudinal das pressões a jusante de comportas tipo segmento invertida e os resultados e análises desenvolvidas em um modelo físico de laboratório. Estes estudos permitiram compreender o comportamento das pressões e verificar se o método sugerido por Batistton (2013), para estimar os valores da distribuição longitudinal das pressões junto à base e o teto da galeria a jusante da comporta, podem ser aplicados para todas as aberturas da comporta. As análises desenvolvidas consentiram observar que as situações críticas ocorrem para aberturas entre 40% e 60% e que as pressões mínimas ocorrem em uma distância adimensional ( ) em torno de 2 a 6. Destaca-se que todos os resultados apresentados na presente pesquisa são válidos para coeficiente de pressão média para abertura de 100% da comporta, CP* 100%, entre 2,8 e 65,9. / The practice of using of gates or valves in conduits to control the flow in hydraulic structures is a common one. One of the applications for this type of device is the flow control for filling and emptying navigation locks. However proper care should be taken when applying those due to the inherit complexity of the flows, which can present significant pressure and velocity fluctuation in the regions next to the floor and ceiling downstream of these gates. Fluctuations in the pressure gradients can cause damage by erosion and/or cavitation. For these reasons its of interest the understanding of criteria for the estimative of those pressures to then infer the possibility of damage in the solid boundaries, allowing the determination of critical operation conditions which to avoid or minimize during the emptying and filling operations of lock chambers. This research aims to present the state of art regarding the longitudinal pressure distribution downstream of inverted tainter gates and the results of experimental data obtained in a physical model. These study allowed to comprehend the behavior of the aforementioned pressures and to verify the method proposed by Battiston (2013) to estimate longitudinal pressure distributions next to the ceiling and floor of those types of structures. The developed analysis showed that the critical conditions occur in between the 40% and 60% opening and that the minimum pressures occur in between a dimensionless distance (Ladm) 2 and 6. The presented results are valid for a mean pressure coefficient of 100% gate opening, CP*100%, between 2,81 and 65,9.

Institutional theory has been used to explain the duality of multinational companies and the need to establish legitimacy both internally- within the organisation and externally- with the external operating environment. The concept of liability of foreignness explains the legitimacy pressures posed by the duality of environments that MNCs are exposed to and the strategic responses taken in this context. However it remains unclear how MNCs respond appropriately to the conundrum, more so in the emerging market context. Using deductive qualitative research grounded on institutional theory, the research study sought to establish which liability of foreignness issues posed the greatest challenge for MNC executives in emerging markets, their response to emergent issues and additionally how they deal with conflicting outcomes, if any from the strategic responses taken. The findings support institutional theory precepts that external institutional pressures pose the greatest challenge for MNCs but conversely the firm’s response to the challenges puts the overall efficiency of the firm at risk. Executives of MNCs focused on emerging markets will find the outcome of the research useful as it identifies key LOF issues and the appropriate strategic response. More importantly it also addresses albeit to a limited extent how to mitigate the conflicting outcomes of such actions. An attempt is also made at establishing an optimal mix of strategic actions. / Dissertation (MBA)--University of Pretoria, 2013. / ccgibs2014 / Gordon Institute of Business Science (GIBS) / MBA / Unrestricted

<div>Nitrous oxide (N₂O) has gained popularity as a unique oxidizer due to its ability to decompose exothermically, producing nitrogen and oxygen. Additionally, there are concerns about the safety of nitrous oxide in the nuclear industry where it has been observed that stored nuclear waste generates and retains large amounts of flammable</div><div>gases such as hydrogen and ammonia along with nitrous oxide. These gases are at risk of explosion even in the presence of a weak ignition source which can result in detonations more violent than those initiated directly. Nitrous oxide is also finding an application in the geothermal industry where it is being tested in combination with ethylene as a stimulant mixture to fracture rock. The detonations initiated in this mixture have the ability to produced a network of fractures in the rock formation. In the rocket industry, nitrous oxide has been used for propulsion in multiple systems, but never in a detonative mode. In order to use nitrous oxide in these areas, its detonation properties in combination with a fuel require quantification. Available literature on nitrous oxide-hydrocarbon detonations is mainly restricted to initial pressures below one atm or with dilution. Therefore, detonations with nitrous oxide as the oxidizer are far from being completely characterized. In addition to this lack of general knowledge, understanding of nitrous oxide-fuel detonations at higher pressures, more typical of practical combustion systems is either extremely limited or</div><div>non-existent.</div><div><br></div><div>In the current work, the flame acceleration, deflagration-to-detonation transition (DDT), and detonation properties of a bipropellant mixture of ethylene (C₂H₄) and N₂O are studied as a function of initial pressures. These properties are compared to those in mixtures of ethylene-oxygen (O₂). these detonations are investigated in a combustion tube designed and fabricated in-house. The performances of these two mixtures are also investigated using theoretical Chapman-Jouguet detonation calculations as a basis of comparison with the measured properties. Additionally, detonation properties in a mixture of acetylene (C₂H₂) and nitrous oxide are also investigated to compare the two fuels. While C₂H₂ is a highly energetic fuel with theoretically high performance, it presents serious practical storage concerns when considered for propulsion applications. These practical issues motivates the investigation of C₂H₄as a potential alternative fuel, which is relatively easy to manage. </div><div><br></div><div>A critical requirement for the application of bipropellant mixtures to detonation systems is rapid flame acceleration to achieve significant chamber pressure rise in a short distance with the potential for a prompt transition to detonation. This DDT behavior of mixtures using N₂O and O₂ with C₂H₄ and C₂H₂ is investigated for increasing initial pressures in the experimental portion of this work. This behavior is quantified by measuring the run-up distances leading to DDT. The pre-compression of the bipropellant mixtures during flame acceleration caused by the accelerating flame is also estimated and directly measured using appropriate instrumentation. These direct measurements of pre-compression are further used to estimate the path of the</div><div>accelerating flame in the combustion tube. These estimates are compared with the flame tracked by high-speed imaging in an optically accessible combustion tube.</div>

Gas turbine engines are an efficient and flexible way of power generation and aircraft propulsion. Even though different combustion systems can be implemented in these engines, more stringent regulations on pollutant emissions have been imposed throughout the years, especially in regard to nitrogen oxides (NOx). A very promising technology to reduce NOx emissions is lean premixed combustion (LPC), however, it is plagued by intense flame dynamics. Thermoacoustic instabilities, lean blow-off and lean instabilities are examples of dynamical phenomena that are detrimental to the gas turbines. In view of this, the present thesis presents the experimental investigation of the response of lean premixed swirl flames to acoustic perturbations at atmospheric and elevated pressures. The results of this investigation may be used to understand the thermoacoustic instabilities and further could be helpful in their prediction. Moreover, this work addresses the effects of non-thermal plasma discharges on the lean blow-off and stability limits of premixed swirl flames at elevated pressures. For the analysis of the flame response to acoustic fluctuations, the flame transfer functions, the flame dynamics, phase-locked velocity fields, and phase-locked measurements of flame curvature are collected through heat release and velocity fluctuations measurements, phase-locked images of the flame, particle image velocimetry, and planar laser-induced fluorescence, respectively. For the analysis of the effects of plasma discharges on the stability limits, electrical measurements and direct imaging of the flame are performed. The results include the development of an empirical relation based on the laminar burning velocity and on the circulation of the acoustically generated vortex to predict the response of the flame to acoustic fluctuations in different operating conditions. Moreover, the results show that the pressure has a strong impact on the response of lean premixed swirl flames to acoustic oscillations and on the flame-plasma interactions. Therefore, extrapolating results obtained at atmospheric conditions to elevated pressures may result in erroneous conclusions. Furthermore, it is shown that non-thermal plasma discharges can effectively extend the stability limits of lean premixed swirl flames at elevated pressures, underlining the potential of these discharges at conditions relevant for gas turbines.

Experiments were performed to determine to what extent increments in esophageal and abdominal pressure would have on arterial blood pressure during fatiguing isometric exercise. Arterial blood pressure was measured during handgrip and leg isometric exercise performed with both a free and occluded circulation to active muscles. Handgrip contractions were exerted at 33 and 70% MVC (maximum voluntary contraction) by 4 volunteers in a sitting position and calf muscle contractions at 50 and 70% MVC with the subjects in a kneeling position. Esophageal pressure measured at the peak of inspirations did not change during either handgrip or leg contractions but peak expiratory pressures increased progressively during both handgrip and leg contractions as fatigue occurred. These increments were independent of the tensions of the isometric contractions exerted. Intra-abdominal pressures measured at the peak of either inspiration or expiration did not change during inspiration with handgrip contractions but increased during expiration. During leg exercise, intraabdominal pressures increased during both inspiration and expiration, reaching peak levels at fatigue. The arterial blood pressure also reached peak levels at fatigue, independent of circulatory occlusion and tension exerted, averaging 18.5-20 kPa (140-150 mm Hg) for both handgrip and leg contrations. While blood pressure returned to resting levels following exercise with a free circulation, it declined by only 2.7-3.8 kPa after leg and handgrip exercise, respectively, during circulatory occlusion. These results indicate that straining maneuvers contribute 3.5 to 7.8 kPa to the change in blood pressure depending on body position.

Aims: The peak transmitral velocity/peak mitral annular velocity (E/e′) ratio has been used as a left ventricular (LV) filling pressure (LVFP) correlate. However, the E/e′ and its changes with haemodynamic alterations have not always correlated with changes in LVFP's. We hypothesized that indexing E/e′ to a measure of LV filling volume may enhance the correlation with LVFP and LVFP changes. Methods and results: We summarized previously obtained haemodynamic and Doppler echo data in 137 dogs with coronary microsphere embolization induced-chronic LV dysfunction prior to and following haemodynamic induced alterations in LVFP's. E/e′ values were obtained as E∗tau where tau is the inverse logarithmic LV pressure decay. E∗tau was indexed to LV filling volume by dividing by the diastolic time velocity integral (DVI) and correlated with LV mean diastolic pressure (LVmDP). Similarly, the relationship of E/e′ and E/e′/DVI to LV pre A wave pressure was evaluated in 84 patients by invasive haemodynamics and Doppler echo. Combining data from all interventions, LVmDP correlated with E∗tau (r = 0.408) but more strongly with E∗tau/DVI (r = 0.667, z = 3.03, P = 0.0008). The change in LVmDP correlated with the change in E∗tau/DVI (r = 0.742) more strongly than E∗Tau (r = 0.187, Z = 4.01, P < 0.0001). In the patient cohort, E/e′ was modestly correlated with LV pre A wave pressure (r = 0.301) but more strongly correlated with E/e′/DVI (r = 0.636, z = 2.36, P = 0.0161). Conclusion: Indexing E to both LV relaxation and filling volume results in a more robust relation with LVFP's and with LVFP changes.

Although there is a wealth of research knowledge related to risk behavior engagement of the general student population, there is less specifically reported about honors students. To address this gap in research, non-honors and honors students were surveyed to determine possible differences in risk behavior engagement. Students were recruited through the East Tennessee State University psychology subject pool and via direct email messages to an honors student-specific listserv. We hypothesized that honors students would have differences in terms of GPA and number of credit hours, endorse more substance use and have more perceived stress compared to non-honors students. The survey sample was majority non-honors students (90.5%; n = 383), with 9.5% (n = 40) honors undergraduate students. After conducting chi-square tests of independence and independent t-tests we determined that there were no significant differences in substance use, life events, or emotional dysregulation between groups. However, upon analyzing demographic information honors students reported significantly higher GPAs (M = 3.77, SD = 0.32) than non-honors students (M = 3.53, SD = 0.53), t(404) = -2.72, p = .007. Additionally, honors students reported a higher number of credit hours than non-honors students, t(403) =-4.26, p < .001, with non-honors students taking an average of 14.67 (SD = 2.63) credit hours and honors students an average of 16.53 (SD = 1.81) credit hours. No other significant demographic differences were observed. Our findings did not show significant differences within populations, but rather, that honors students likely encounter stress and engage in risk behaviors just as much as non-honors students.

Primary angiitis of the central nervous system (PACNS) is a rare form of vasculitis. It is a diagnosis of exclusion and often diagnosed post mortem on pathologic evaluation. Cerebral angiography can be suggestive, but biopsy is required. Symptoms can vary from headache to focal cranial nerve deficits. On the more severe spectrum, patients can present with ischemic and vary rarely hemorrhagic stroke. We present in this case report key clinical pearls regarding suspected diagnosis. Younger patients with cortical hemorrhages may have PACNS instead of the more common cerebral amyloid angiopathy. Early suspicion may aid in initiating effective treatment as we highlight in the discussion.

<p> A series capillary viscometer has been used to measure the viscosity of nitrogen and air over a temperature range of 100 to 400°K and to pressures of 150 atmospheres. </p> <p>The low pressure results have been correlated using a modified Sutherland equation of the form: n = C1T^C2 / T+C3 </p> <p> Intermolecular force constants have been computed for nitrogen using the Chapman Enskog collision theory approach.</p> <p> The viscosity in the dense gas region was correlated using equations of the form n-no = A1ρ + A2ρ^2 and thus overall equations for viscosity as a function of temperature and density were formulated as n = C1T^C2 / T+C3 +A1ρ + A2ρ^2 </p> <p> These equations were used to generate tables of smoothed values of viscosity as a function of pressure and temperature.</p> / Thesis / Master of Engineering (MEngr)

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