Epoxy resins are widely used materials in the industry as electrical insulators, adhesives and in aircrafts structural components because of their high mechanical stiffness, strength and high temperature and chemical resistance properties. But still, the influence of water uptake due to moisture adsorption is not fully understood as it detrimentally modifies the electrical and chemical properties of the material. Here ,we investigate the influence of water moisture uptake on the neat epoxy material by monitoring the change in the volume resistivity and dielectric properties of epoxy material at three different thickness configurations: 0.250 mm, 0.50 mm and 1 mm thicknesses. Gravimetric analysis was done to monitor the mass uptake behaviour, Volume Resistivity was measured to monitor the change in conductivity of the material, and the dielectric properties were mapped to characterise the type of water mechanism available within the material during two ageing processes of sorption and desorption. Two-stage behaviours of diffusion and reaction have been identified by the mass uptake analysis. Moreover, the plot of volume resistivity versus mass uptake has indicated a non-uniform relationship between the two quantities. However, the analysis of the dielectric spectrum at medium range of frequency and time has showed a change in the dipolar activities and also showed the extent to which the water molecules can be segregated between bounding to the resin or existing as free water

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第22076号 / 農博第2368号 / 新制||農||1072(附属図書館) / 学位論文||R1||N5230(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 近藤 直, 准教授 小川 雄一, 教授 飯田 訓久 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(医学) / 甲第23076号 / 医博第4703号 / 新制||医||1049(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 花川 隆, 教授 古川 壽亮, 教授 髙橋 良輔 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Improved knowledge of human nerve function and recruitment would enable innovation in the Biomedical Engineering field. Better understanding holds the potential for greater integration between devices and the nervous system as well as the ability to develop therapeutic devices to treat conditions affecting the nervous system. This work presents a three-dimensional volume conductor model of the human arm for coupling with code describing nerve membrane characteristics. The model utilizes an inhomogeneous medium composed of bone, muscle, skin, nerve, artery, and vein. Dielectric properties of each tissue were collected from the literature and applied to corresponding material subdomains. Both a fully anatomical version and a simplified version are presented. The computational model for this study was developed in COMSOL and formatted to be coupled with SPICE netlist code. Limitations to this model due to computational power as well as future work are discussed. The final model incorporated both anatomically correct geometries and simplified geometries to enhance computational power. A stationary study was performed implementing a boundary current source through the surface of a conventionally placed electrode. Results from the volume conductor study are presented and validated through previous studies.

The thermophysical properties of nanofluids have attracted the attention of researchers to a far greater extent than the heat transfer characteristics of nanofluids have. Contradictory results on the thermal-fluid behaviour of nanofluids have been numerically and experimentally reported on in the open literature. Natural convection has not been investigated experimentally as much as the other properties of nanofluids. In this study, the characteristics and stability of Al2O3-water nanofluids (d = 20 30 nm) were analysed using a Malvern zetasizer, zeta potential and UV-visible spectroscopy. The natural convection of Al2O3- water nanofluids (formulated with a single-step method) was experimentally studied in detail for the volume fractions 0, 0.05, 0.1, 0.2, 0.4 and 0.6% in a rectangular cavity with an aspect ratio of 1, heated differentially on two opposite vertical walls for the Rayleigh number (Ra) range 3.49 x 10⁸ to 1.05 x 10⁹. The viscosity of Al2O3-water nanofluids measured between 15 and 50 °C. The effect of temperature and volume fraction on viscosity was also investigated. A detailed study of the nanoparticle concentration effect on the natural convection heat transfer coefficient was performed. It was found that increasing the concentration of nanoparticles improves the heat transfer coefficient by up to 15% at a 0.1% volume fraction. Further increasing the concentration of nanoparticles causes the natural convection heat transfer coefficient to deteriorate. This research also supports the idea that "for nanofluids with thermal conductivity more than the base fluids an optimum concentration may exist that maximises heat transfer in an exact condition as natural convection, laminar force convection or turbulence force convection". / Dissertation (MEng)--University of Pretoria, 2016. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

This Master of Engineering investigation focuses on the natural convection of nanofluids in rectangular cavities. The governing equations applied to analyse the heat transfer and fluid flow occurring within the cavity are given and discussed. Special attention is given to the models that were developed to predict the thermal conductivity and dynamic viscosity of such nanofluids. A review concerning past investigations into the field of natural convection of nanofluids in cavities is made. The investigation is divided into experimental works and computational fluid dynamics (CFD) numerical investigations. Through the literature review, it was discovered that many numerical models exist for the prediction of the thermophysical properties of nanofluids, specifically thermal conductivity and viscosity. Depending on the nanofluid and the application, different models can be used. The literature study also revealed that most previous works were done in the CFD field. Very few experimental studies have been performed. Numerical CFD investigations, however, need experimental results for validation purposes, leading to the conclusion that more experimental work is needed. The heat transfer capability and thermophysical properties of the nanofluid are investigated based on models found in literature. The investigation incudes measuring the heat transfer inside a cavity filled with a nanofluid and subjected to a temperature gradient. The experiment is performed for several volume fractions of particles. An optimum volume fraction of 0.005 is obtained. At this volume fraction the heat transfer enhancement reaches a maximum for the present investigation. The investigation is repeated as a numerical investigation using the commercially available CFD software ANSYS-FLUENT. The same case as used in the experimental investigation is modelled as a two-dimensional case and the results are compared. The same optimum volume fraction and maximum heat transfer is obtained with an insignificantly small difference between the two methods of investigation. This error can be attributed to the minor heat losses experienced from the experimental setup as in the CFD adiabatic walls considered. It is concluded that, through the inclusion of TiO2 particles in the base fluid (deionised water), the thermophysical properties and the heat transfer capability of the fluid are altered. For a volume fraction of 0.005 and heat transfer at a temperature difference of 50 °C, the heat transferred through the fluid in the cavity is increased by more than 8%. From the results, it is recommended that the investigation is repeated with TiO2 particles of a different size to determine the dependency of the heat transfer increase on the particle size. Various materials should also be tested to determine the effect that material type has on the heat transfer increase. / Dissertation (MEng)--University of Pretoria, 2016. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

Post tensioning bridges is an efficient way of construction where segments of a bridge are strung together using small diameter high strength strands. The steel strands are passed through internal and/or external ducts within the concrete segments, jacked to high levels of stress, anchored using steel wedges, and then filled with a corrosion inhibiting filler. A cementitious material called grout has been widely used for over 50 years as this filler. The Federal Highway Administration design and construction manual provides recommendations in the properly filling techniques to ensure the tendons are full of grout. Despite the level of detail the manual provides, several Florida bridges that used this construction technique have seen severe corrosion related failures due to poor grout quality. Oil based products have been developed for the express purpose of reducing the corrosion rate in previously grouted tendons. Utilizing the interstitial spaces in the steel strands, low viscosity fluid is pumped through the strand which can also penetrate the surrounding grout and fill unintentional voids. However, by doing so, there is the concern that the bond strength could be compromised and increase the risk of failure. This study presents the findings of small scale grouted mono-strand tendons which determined the bond effects of defective grout, evaluated the injection capabilities of various penetrants, and determined whether or not the penetrant adversely affects bond after impregnation. No appreciable variation in bond was found.

Magister Scientiae (Medical Bioscience) - MSc(MBS) / The incidence of non-communicable diseases is increasing worldwide, with South Africa being no exception. Non-communicable diseases are classified as non-infectious and are often referred to as lifestyle diseases as they are caused by common, modifiable risk factors such as unhealthy diet, obesity, tobacco use and lack of physical activity. Due to the increasing prevalence of childhood obesity diseases such as fatty pancreas and fatty liver are becoming more common. Cardiovascular disease, and more specifically atherosclerosis is the underlying cause in most adult deaths. Disease pathogenesis starts in childhood and can be detected via Aortic intima-media thickness (IMT). The developmental origins of health and disease hypothesis (DOHaD) proposes that exposures in-utero may result in persistent adaptations including alterations in metabolism.

The resolutions of acquired image and volume data are ever increasing. However, the resolutions of commodity display devices remain limited. This leads to an increasing gap between data and display resolutions. To bridge this gap, the standard approach is to employ output-sensitive operations on multi-resolution data representations. Output-sensitive operations facilitate interactive applications since their required computations are proportional only to the size of the data that is visible, i.e., the output, and not the full size of the input. Multi-resolution representations, such as image mipmaps, and volume octrees, are crucial in providing these operations direct access to any subset of the data at any resolution corresponding to the output. Despite its widespread use, this standard approach has some shortcomings in three important application areas, namely non-linear image operations, multi-resolution volume rendering, and large-scale image exploration. This dissertation presents new multi-resolution representations for large-scale images and volumes that address these shortcomings. Standard multi-resolution representations require low-pass pre-filtering for anti- aliasing. However, linear pre-filters do not commute with non-linear operations. This becomes problematic when applying non-linear operations directly to any coarse resolution levels in standard representations. Particularly, this leads to inaccurate output when applying non-linear image operations, e.g., color mapping and detail-aware filters, to multi-resolution images. Similarly, in multi-resolution volume rendering, this leads to inconsistency artifacts which manifest as erroneous differences in rendering outputs across resolution levels. To address these issues, we introduce the sparse pdf maps and sparse pdf volumes representations for large-scale images and volumes, respectively. These representations sparsely encode continuous probability density functions (pdfs) of multi-resolution pixel and voxel footprints in input images and volumes. We show that the continuous pdfs encoded in the sparse pdf map representation enable accurate multi-resolution non-linear image operations on gigapixel images. Similarly, we show that sparse pdf volumes enable more consistent multi-resolution volume rendering compared to standard approaches, on both artificial and real world large-scale volumes. The supplementary videos demonstrate our results. In the standard approach, users heavily rely on panning and zooming interactions to navigate the data within the limits of their display devices. However, panning across the whole spatial domain and zooming across all resolution levels of large-scale images to search for interesting regions is not practical. Assisted exploration techniques allow users to quickly narrow down millions to billions of possible regions to a more manageable number for further inspection. However, existing approaches are not fully user-driven because they typically already prescribe what being of interest means. To address this, we introduce the patch sets representation for large-scale images. Patches inside a patch set are grouped and encoded according to similarity via a permutohedral lattice (p-lattice) in a user-defined feature space. Fast set operations on p-lattices facilitate patch set queries that enable users to describe what is interesting. In addition, we introduce an exploration framework—GigaPatchExplorer—for patch set-based image exploration. We show that patch sets in our framework are useful for a variety of user-driven exploration tasks in gigapixel images and whole collections thereof.

Objective To determine the cardiopulmonary and blood gas status of elephants during chemical capture (immobilisation) with a thiafentanil-azaperone drug combination kept in lateral recumbency. Study design Prospective descriptive study. Animal population Ten free-ranging adult African elephant bulls (estimated weight range 3000 to 6000 kg). Methods Elephants were immobilised using a thiafentanil (15-18 mg) and azaperone (75-90 mg) by darting from a helicopter. Once recumbent, the tidal volume, minute volume, end-tidal carbon dioxide, arterial blood pressure and pulse rate were recorded immediately after instrumentation and at five-minute intervals until T20. Arterial and venous blood gases were analysed at the time of initial instrumentation and at 20 minutes. On completion of the data collection, the thiafentanil was antagonised using naltrexone (10 mg mg-1 thiafentanil). A stopwatch was used to record time to recumbency (dart placement to recumbency) and time to recovery (administering antagonist to standing). Data was checked for normality and was found to be parametric. Data were compared using a one-way analysis of variance and reported as mean (± SD). Results All elephants were successfully immobilised and all physiological variables remained constant with minimal non-significant variation over time. Average time to recumbency was 12.5 minutes. The estimated expiratory tidal volume was 21 (± 6) L breath-1 or 4.8 ± 0.8 mL kg-1, and the measured minute volume was 103 (± 31) L minute-1. The heart and respiratory rates were 49 (±6) beats and 5 (± 1) breaths minute-1, respectively. The mean arterial blood pressure was 153 (± 31) mmHg. The elephants were acidaemic (pH 7.18 ±0.06; bicarbonate ion 20 ±4 mmol L-1; lactate 11 ± 4 mmol L-1), mildly hypoxemic (PaO2 68 ± 15 mmHg) and mildly hypercapnic (PaCO2 52 ± 7 mmHg). Average time to recovery was 2.2 minutes. Conclusion and clinical relevance African elephant bulls can be successfully immobilised using thiafentanil-azaperone. Recumbency was rapid, the cardiopulmonary variables were stable and within acceptable ranges, and recovery was rapid and complete. Mild hypoxaemia and hypercapnia were evident, but does not necessarily require oxygen supplementation. / Dissertation (MSc)--University of Pretoria, 2020. / Companion Animal Clinical Studies / MSc / Unrestricted