Natural convection as a heat transfer mechanism plays a major role in the functioning of many heat transfer devices, such as heat exchangers, energy storage, thermal management and solar collectors. All of these have a large impact on the generation of solar power. Considering how common these devices are not only in power generation cycles, but in a majority of other thermal uses it is clear that increased performance for natural convection heat transfer will have consequences of a high impact. As such, the purpose of this study is to experimentally study the natural convection heat transfer behaviour of a relatively new class of fluids where nano-sized particles are mixed into a base fluid, also known as a nanofluids. Nanofluids have attracted widespread interest as a new heat transfer fluid due to the fact that the addition of nanoparticles considerably increases the thermophysical properties of the nanofluids when compared to those of the base fluid. Furthermore, if these nanoparticles show magnetic behaviour, huge increases in the thermal conductivity and viscosity of the nanofluid can be obtained if the fluid is exposed to a proper magnetic field. With this in mind, the study aimed to experimentally show the behaviour of these so-called magnetic nanofluids in natural convection heat transfer applications. In this study, the natural convection heat transfer of a magnetic nanofluid in a differentially heated cavity is investigated with and without an applied external magnetic field. The effects of volume concentration and magnetic field configuration are investigated. Spherical nanoparticles with a diameter of 20 nm are used with a volume concentration ranging between 0.05% and 0.3%, tested for the case with no magnetic field, while only a volume concentration of 0.1% was used in the magnetic cases. The experiments were conducted for a range of Rayleigh numbers in . The viscosity of the nanofluid was determined experimentally, while an empirical model from the literature was used to predict the thermal conductivity of the nanofluids. An empirical correlation for the viscosity was determined, and the stability of various nanofluids was investigated. Using heat transfer data obtained from the cavity, the average heat transfer coefficient, as well as the average Nusselt number for the nanofluids, is determined. It was found that a volume concentration of 0.05% showed an increase of 3.75% in heat transfer performance. For the magnetic field study, it was found that the best-performing magnetic field enhanced the heat transfer performance by 1.58% compared to the 0.1% volume concentration of the nanofluid with no magnetic field. / Dissertation (MEng)--University of Pretoria, 2017. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

The ideal two-fluid plasma model is a more generalized plasma model compared to the ideal MHD and it couples the ion and electron Euler equations via Maxwell's equations. Two-fluid plasma model is essential when the ion and electron fluids are at different temperatures. In this work, a fundamental investigation on the effect of non-dimensional light speed, ion-to-electron mass ratio and plasma beta on the plasma dynamics in the Brio-Wu shock tube Riemann problem is presented. A one dimensional finite volume code is developed based on the macroscopic governing equations, with second order accuracy in space and time. The source terms are treated implicitly and the homogeneous flux terms are treated explicitly. The credibility of the numerical results is assessed by performing several linear and nonlinear tests. Realistic light speed results in increasing the stiffness of the equations and severe time step restriction, which poses a challenge to the numerical simulations. In the context of the Brio-Wu shock tube problem, it is observed that the light speed is not important with respect to the hydrodynamics. However, light speed does affect the magnitude of the self generated electric field. Mass ratio affects the electron plasma dynamics. The speed of the fast moving electron plasma waves changes with the mass ratio. The results obtained using a mass ratio of 500 are in close agreement with that of realistic mass ratio of 1836. Increasing plasma beta suppresses the amplitude of the fast moving electron plasma waves.

The objective of the study was to investigate the effect of increased volumes of milk feeding as well as the effect different group sizes may have on the growth and health of Jersey calves. One hundred and twenty 3-day old heifer calves were randomly assigned to one of four treatment groups (30 calves each) and calves in groups one and two were assigned into four subgroups (15 calves each). Two groups received unrestricted volumes of milk (HMV), while two groups received restricted volumes of milk (RMV) during the preweaning period. The calves were weaned after 6 weeks. Feed intake, growth rates, health and cross-sucking behaviour of calves were monitored until all the calves in the trial reached at least 60 days of age. The effects of milk volume and group size on growth rates and the risks of diseases were evaluated using multiple linear- and logistic-regression models. During the milk-fed stage, the HMV calves drank 72% more milk than calves fed conventionally. Probably as a result of the much higher intake of milk, the HMV calves gained 154 g/d more weight than the RMV calves before weaning (P < 0.001), resulting in a 6.3 kg weight advantage on d 42. Birth weight of the HMV calves showed a strong linear relationship with milk intake (Pearson’s r = 0.696, P < 0.001) and preweaning ADG (Pearson’s r = 0.426, P < 0.001). Calves that were provided with more milk consumed less calf starter, reflecting effective substitution of milk with concentrate. However, after the calves were weaned, the difference in starter intakes disappeared. This resulted in no treatment differences in weight gains over the postweaning period, and on d 60 the HMV calves maintained an advantage in mean (± SD) body weight (67.6 ± 7.9 kg vs. 60.8 ± 6.6 kg for the HMV vs. RMV calves). With the exception of keratoconjunctivitis, the incidence of disease in milk-fed calves was low and did not differ between HMV and RMV treatment groups. Days of treatment for keratoconjunctivitis (birth to d 42) was significantly higher (P < 0.05) for calves in the large HMV group compared with calves in other groups. Smaller groups showed a higher incidence of diarrhoea during the preweaning period (OR = 3.23; P < 0.01). Over the whole trial period, the gain-to-feed ratio of HMV calves was 9.6% better than calves receiving restricted milk volumes. However, the cost per kg body mass gain was 12% higher for HMV calves. Cross-sucking observations showed that the incidence in the preweaning period differed greatly between the groups (1.7% vs. 75.5% for HMV vs. RMV groups; P < 0.001). During the last 10 days of the trial, this difference decreased, but was still significant (10.0% vs. 19.1% for HMV vs. RMV groups; P < 0.001). The conclusion was that the feeding of high volumes of milk to dairy calves will have a significant positive effect on growth rates, without compromising their health or the intake of solid food after weaning. Additionally it allows calves to be housed in groups with less problems of cross-sucking. Copyright / Dissertation (MSc)--University of Pretoria, 2008. / Production Animal Studies / unrestricted

Spaceborne scatterometers have measured the normalized radar cross section (RCS) of the earth's surface for several decades. Two frequencies, C- and Ku-band, have been used in designing scatterometers, such as with the Ku-band NASA Scatterometer (NSCAT) and the C-band Advanced Scatterometer (ASCAT). The scatterometer data record between C- and Ku-band has been disjoint for several decades due to the difficulties in cross calibration of sensors that operate at different frequencies and incidence angles. A model for volume scattering over the Amazon rainforest canopy that includes both the incidence angle and frequency dependence is developed to overcome this challenge in cross calibration. Several models exist for the σ0 incidence angle dependence, however, none of them are based on backscatter physics. This thesis develops a volume scattering model from a simple EM scattering model for cultural vegetation canopies and applies it to the volume scattering of the Amazon rainforest. It is shown that this model has lower variance than previously used models for the incidence angle dependence of σ0, and also enables normalization of σ0 with respect to the incidence angle. In addition, the frequency dependence of σ0 is discovered to be quite sensitive at Ku-band due to the distribution of leaf sizes in the Amazon rainforest. This may limit the accuracy of the model of the frequency dependence of σ0. Although the proposed frequency dependence model may be limited for cross calibrating between C- and Ku-band, it provides the groundwork for future studies.

No description available.

Background: Cervical cancer is the most common gynecological malignant disorder worldwide. Activated platelets play a key role in cancer development and progression. Mean platelet volume (MPV) is an early indicator of platelet activation. The aim of the present study was to evaluate MPV levels in patients with cervical cancer. Materials and methods: A total of 181 patients with cervical cancer and 181 controls between January 2015 and June 2015 were included in the study. Patient characteristics and hematologic test data at initial diagnosis were collected and odds ratios (ORs) and 95% confidence intervals (CIs) for risk of cervical cancer were calculated using multivariate logistic regression analyses across MPV quartiles. Results: MPV levels were decreased in patients with cervical cancer compared with control subjects. A significant correlation between MPV and FIGO stage was found. Moreover, after adjusting for other risk factors, the ORs (95%CIs) for cervical cancer according to MPV quartiles were 4.450 (1.975-10.026), 2.505 (1.206-5.202), 0.573 (0.261-1.259), and 1.000, respectively. Conclusions: MPV was found to be independently associated with the presence of cervical cancer. Our results suggest that MPV could be potential diagnostic screening tool.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Glycine-arginine-alpha-ketoisocaproic acid calcium (GAKIC) is an amino acid combination postulated to improve dynamic performance of skeletal muscle during acute, anaerobic exercise in healthy individuals. Purpose: The purpose of this study was to determine the ergogenic effects of GAKIC ingestion on resistance training performance in both trained male and female participants. Methods: Utilizing a double-blinded, crossover design, male participants completed a lower body leg press resistance exercise protocol and female participants completed a lower body leg extension resistance exercise protocol once using 10.2 g GAKIC and the other with a placebo. Results: A significant increase in TLV after GAKIC supplementation was observed in both male and female participants performing a lower body resistance exercise. No significant differences were found in lower body 1RM, HR, BLa, and Glucose between conditions in both groups. Conclusion: We concluded with the specific exercise protocols that were implemented, GAKIC increased TLV in the lower body exercises.

An aircraft may experience inlight ice accretion and corresponding reductions in performance and control when the vehicle encounters clouds of super-cooled water droplets. The EADS-IW Surface Engineering Group is investigating passive anti-icing possibilities, such as functional and ice phobic coatings. Ice-resistant coatings require investigating droplet impact on dry surfaces and wet films, including microscopic effects such as droplet splashing. To investigate droplet impacts, a volume of fluid (VOF) flow solver was used for droplets impacting dry and wetted hydrophobic and superhydrophobic surfaces, focusing on meso-scale simulations. The effects of structured, micro-scale surface roughness and the effects of a thin wet film on the surface, corresponding to a saturated surface under high humidity conditions, were investigated. Axisymmetric domains produced acceptable results for smooth, dry surfaces. It was determined that in order to properly predict behavior of droplets impacting surfaces with structured micro-scale roughness, three-dimensional simulations are recommended.

Large eddy simulation (LES) suffers from two primary sources of error: the numerical discretization scheme and the subgrid stress model (SGS). An attempt has been made to determine optimum combinations of SGS models and numerical schemes for use in performing practical LES for engineering-relevant problems. A formal quantification of numerical error present in finite-volume/finite-difference simulations was conducted. The effect of this error was explicitly added to a pseudospectral LES solver, and the modified pseudospectral solver was used to compute LES of decaying turbulence. In this way SGS modeling error and numerical error could be separately assessed. Verification of results was carried out using a commercially available finite-volume solver (FLUENT). Results showed that some combinations of SGS model and discretization scheme are more suitable for performing LES than others. Favorable combinations from the above findings were tested for an axisymmetric jet at Mach number 0.2. Results indicate good agreement with prior findings.