The advancement of wireless technology has led to an increase in the employment of wireless sensor networks (WSNs). Traditionally, WSNs are powered by batteries. However, the high power consump- tion and the need to change the batteries regularly has made these networks costly to maintain. The nodes in the WSNs are increasingly strained as power consumption increases and the batteries are depleted faster. This has consequently decreased the overall lifetime of the WSNs. Although many energy-conserving techniques exist, for example energy-efficient medium access control and energy-efficient routing protocols, energy consumption remains one of the significant constraints in the development of WSNs. A natural solution to this constraint is harvesting energy from the environment. However, unlike conventional energy, energy harvested from the environment is random in nature, making it challenging to realise energy-harvesting transmission schemes. Although energy harvesting might be considered a solution to many problems, it brings about new challenges with regard to the usage and management of the energy harvested. Some of these challenges include uneven consumption of power in the network, resulting in dead nodes in some portion of the network and the batteries used in the network are being affected negatively by the energy usage; they may consequently sustain the nodes for long or short periods. To analyse the usage and consumption of energy, a number of techniques have been proposed, namely; information theory, game theory and queueing theory. By this time, the performance of the sensor nodes in WSNs has been analysed making use of a queueing-theoretic model for each sensor. The aforementioned model inadequately expresses the physical constraints, namely, the energy drawing process and the finite battery capacity. This research focuses on developing a model that captures the harvesting, accumulation and dissipation of energy, utilising queueing theory. A rechargeable battery with a finite storage capacity will be used. To ensure that the battery does not lose its capability to store charge after being recharged repeatedly, the leaky bucket model is proposed to check the network data flow as the harvested energy in the WSN is analysed. To capture real-world WSNs with energy harvesting in which there is energy leakage, the energy- harvesting sensor node performance is analysed with two assumptions: data transmission and energy leakage occurring and the token buffer being subjected to a threshold. The system had finite buffers for the data and energy. To make it possible to have some influence over the system performance measures a threshold is imposed on the token buffer. Four models are developed: a basic model, a basic model with leakage incorporated, a basic model with leakage and priority incorporated and a basic model with leakage, priority and threshold incorporated. The developed models are simulated and results for the performance measures are obtained. / Dissertation (MEng (Computer Engineering))--University of Pretoria, 2021. / BWMC, NRF / Electrical, Electronic and Computer Engineering / MEng (Computer Engineering) / Unrestricted

The thesis deals with the presentation of an overview of the methods used for leak detection set by technical standards. Following the analysis of the pressure records from the pipeline, a new method is proposed, which is based on existing methods and uses the determination of the direction of arrival of the wave directly at the measurement station. The proposed concept was subsequently developed in Matlab, where the ability to detect was also verified. The whole algorithm was then implemented in programmable logic controllers and a suitable communication between them was designed. The entire solution was then tested in terms of functionality.

The (BMN) bulk materials were sintered at 1050°C, 1100°C, 1150°C, 1200°C by the conventional ceramic process, and their microstructure and dielectric properties were investigated by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Transmission electron microscopy (TEM) (including the X-ray energy dispersive spectrometry EDS and high resolution transmission electron microscopy HRTEM) and dielectric impedance analyzer. We systematically investigated the structure, dielectric properties and voltage tunable property of the ceramics prepared at different sintering temperatures. The XRD patterns demonstrated that the synthesized BMN solid solutions had cubic phase pyrochlore-type structure when sintered at 1050°C or higher, and the lattice parameter (a) of the unit cell in BMN solid solution was calculated to be about 10.56Å. The vibrational peaks observed in the Raman spectra of BMN solid solutions also confirmed the cubic phase pyrochlore-type structure of the synthesized BMN. According to the Scanning Electron Microscope (SEM) images, the grain size increased with increasing sintering temperature. Additionally, it was shown that the densities of the BMN ceramic tablets vary with sintering temperature. The calculated theoretical density for the BMN ceramic tablets sintered at different temperatures is about 6.7521 . The density of the respective measured tablets is usually amounting more than 91% and 5 approaching a maximum value of 96.5% for sintering temperature of 1150°C. The microstructure was investigated by using Scanning Transmission Electron Microscope (STEM), X-ray diffraction (XRD). Combined with the results obtained from the STEM and XRD, the impact of sintering temperature on the macroscopic and microscopic structure was discussed. The relative dielectric constant ( ) and dielectric loss ( ) of the BMN solid solutions were measured to be 161-200 and (at room temperature and 100Hz-1MHz), respectively. The BMN solid solutions have relative high dielectric constant and low dielectric loss. With increasing sintering temperature, the dielectric constant showed the maximum at 1150°C. The leakage current of BMN ceramic material is extraordinary small. When the voltage and thickness of the BMN capacitor are 4000V and 300um, the leakage current amounts only about 0.13-0.65 . The excellent physical and electrical properties make BMN thin films promising for potential tunable capacitor applications.

Acute lung injury (ALI) is a critical manifestation of sepsis/septic shock. Heat shock protein A12B (HSPA12B), an endothelial cell-expressed heat shock protein, shows a negative regulation of lipopolysaccharide (LPS)-induced inflammation in myocardium and endothelial cells. However, it is unclear whether HSPA12B exerts protective effects against ALI during sepsis/septic shock. In this study, we treated HSPA12B transgenic mice (Tg) and wild type littermates (WT) with LPS for 6 h to induce endotoxemia. LPS treatment significantly caused pulmonary injuries as evidenced by microarchitecture destruction, vascular leakage and neutrophil recruitment in lungs of WT mice. However, the LPS-induced pulmonary injuries were significantly attenuated in Tg mice. Moreover, the LPS-induced activation of extracellular signal-regulated kinases (ERKs) and upregulation of intercellular adhesion molecule-1 (ICAM-1) and Cyclooxygenase-2 (Cox-2) were inhibited in Tg lungs compared with that in WT mice. Additionally, Tg lungs showed a significant lower level of vascular endothelial growth factor (VEGF) compared with WT mice. Our results demonstrate a pulmonary protective effect of HSPA12B against endotoxin challenge, which indicates management of HSPA12B expression could serve as a potential therapeutic target for ALI during sepsis/septic shock.

Indiana University-Purdue University Indianapolis (IUPUI) / Gopinath, Anoop. M.S.E.C.E., Purdue University, May 2018. Low-Power Hybrid TFET-CMOS Memory. Major Professor: Maher E. Rizkalla. The power consumption and the switching speed of the current CMOS technology have reached their limits. In contrast, architecture design within computer systems are continuously seeking more performance and e ciency. Advanced technologies that optimize the power consumption and switching speed may help deliver this e ciency. Indeed, beyond CMOS technology may be a viable approach to meeting the ever increasing need for low-power design. These technology includes devices such as Tunnel Field E ect Transistor (TFET), Graphene based devices such as GFET and GRNFET and FinFET. However, the low cross-sectional area of the channel asso- ciated with smaller technology nodes brings with it the challenges associated with leakage current below the threshold. Mitigating these challenges with devices such as TFETs may allow higher levels of integration, faster switching speed and lower power consumption. This thesis investigates the use of Gallium Nitride (GaN) TFET devices at 20nm for memory cells. These cells can be used in the L1 data cache of the Graphic Processing Units (GPU) thereby minimizing the static power and the dynamic power within these memory systems. The TFET technology was chosen since it has a low subthreshold slope of nearly 30mV/decade. This enables the TFET-based cells to function with a 0.6V supply voltage leading to reduced dynamic power consumption and leakage current when compared to the current CMOS technology. The results suggest that there are bene ts in pursuing an integrated TFET-based technology for Very Large Scale Integrated Circuit (VLSI) design. These bene ts are demonstrated using simulation at the schematic-level using Cadence Virtuoso.

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The great challenge of the 21st century to mitigate climate change requires generation of green electricity to be an achievable goal. One way of producing green electricity is through usage of wave energy converters which are devices that use the energy of the ocean waves to produce electricity.   W4P Waves4Power AB is a company from Sweden, devoted to commercializing their wave energy converter called the WaveEl buoy. The WaveEl buoy is a point absorber that produces electricity by using the energy of the waves to run a hydraulic motor connected to a generator. The working principle of the buoy is to let a water piston oscillate in a tube with a water column. The water column exerts flow resistance forces on the piston as it oscillates, and these forces create a frame of reference upon which the hydraulic motor system may operate. There are leakage clearances at the sides of the water piston that allow for flow of water past the piston and associated with this flow are parts of the flow resistance forces. The flow resistance forces that are present due to water flow in the leakage clearances are calculated with the use of a flow resistance parameter and, in the literature, there is little investigation conducted as to the importance of this parameter.  The goal of present thesis work was to investigate the effect on 4 parameters of the WaveEl buoy system (power captured from the waves, flow resistance force acting on the piston, mean piston position, and number of bumper hits) due to adoption of 3 different values of the flow resistance parameter. One of these values was the currently assigned value by Waves4Power at the time when this study was conducted. The value was the constant 0.75 and was a guess by Waves4Power. The other two values were received from a parallel thesis work done at Karlstad University by Linnéa Tebelius where, with the use of CFD, Tebelius calculated the flow resistance parameter with different levels of accuracy.  The results of present thesis work were generated from simulations in a MATLAB Simulink model describing the dynamics of the WaveEl buoy system. Simulated time varied from 5.5 to 8.5 minutes per simulation. Generated results were compared to the results from using 0.75 as the value for the flow resistance parameter and showed that the energy captured from the waves was, at most, overestimated by approximately 13 % and underestimated by 6 %, depending on applied level of accuracy for description of the dynamic flow resistance parameter and simulated wave state. Furthermore, it was found that number of bumper hits varied extensively, in some cases from 0 to 47, between simulations where the only difference was applied value of the flow resistance parameter – further indicating that assigning a more accurate value on the dynamic flow resistance parameter may be of great importance when modelling the dynamics of the WaveEl buoy system.

The growing popularity of additive manufacturing in commercial applications has al- lowed for new ideas and new ways of thinking when designing components. Further optimization at the component level is possible, though powder metallurgy is in its infancy. This study explores the possibility of using additive manufacturing to develop better labyrinth seals in turbomachinery. Labyrinth seals have a torturous fluid path with high losses, thus limiting the amount of fluid leakage. These types of seals can be non-rotating, allowing them to better take advantage of the additive manufacturing process due to the absence of rotating stresses. Labyrinth seal performance is defined by its ability to limit leakage through a seal. Investigations on the ability to reduce this leakage using the inherent roughness from the additive manufacturing process and the addition of complex geometry only capable of being produced by additive manufacturing are explored. Incompressible and compressible fluid models are utilized in the study. Perfectly smooth seals with tooth counts of four, six, and eight are first simulated using ANSYS FLUENT and compared to theoretical models to determine accuracy. Roughness is then applied to the seals and leakage decreases of 0.5% to 1.5% are experienced for the incompressible model. Decreases of 1.0% to 3.5% are experienced for the compressible model. Flow visualization and line analysis are conducted for all seals tested to understand how fluid flow is behaving within the clearance region of the seal and seal chambers. Several additive manufacturing geometries are simulated against a control seal to determine geometries with the largest effect on leakage rates. These geometries are then adapted to a six tooth seal and simulated with roughness. This additively manufactured seal is then compared to the smooth and rough six tooth seal for both incompressible and compressible fluids. Leakage was decreased by 5% to 8% for the incompressible model and 5% to 7% reductions for the compressible model when compared to the smooth seal. Flow visualization and line analysis were also conducted for the additively manufactured six tooth seal. A basic outline for an experiment and test stand were developed for future work.

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Cavitation is detrimental to the performance of ships and submarines, causing noise, erosion, and vibration. This study seeks to understand cavitation inception and delay on a typical ducted propulsor by utilizing the SimCenter's unstructured simulation and design system: U2NCLE. Specifically, three fundamental questions are addressed: 1. What are the macroscale flow physics causing cavitation inception? 2. How does cavitation inception scale with Reynolds number? 3. How can tip-leakage vortex cavitation inception be suppressed? To study the physics of cavitation inception, a ducted propulso simulation is developed and extensively validated with experimental results. The numerical method is shown to agree very well with experimental measurements made in the vortex core. It was discovered that the interaction of the leakage and trailing edge vortices cause the pressure to drop to a local minimum, providing ideal conditions for inception to occur. However, experimental observation shows that inception does not occur at the minimum pressure location, but rather at the point where the two vortices completely coalesce. At the point of coalescence, the simulation reveals that the streamwise core velocity decelerates, causing the air nuclei to stretch and burst. A Reynolds number scaling analysis is performed for the minimum pressure and maximum velocity in the vortex core. First, the numerical method is validated on a flate plate at various Reynolds numbers to assess the ability of typical turbulence models to predict Reynolds numbers ranging from one million to one billion. This scaling analysis methodology is then applied to the propulsor simulation, revealing that the minimum pressure in the vortex core is much less dependent on Reynolds number than was previously hypothesized. Lastly, to investigate means of delaying cavitation inception, the propulsor is parameterized and studied using design optimization theory. Concepts of vortex alleviation evident in nature are used to suggest suitable parameterizations. Also, dimension reduction is used to reduced the number of design variables. Finally, the concepts are implemented, evaluated, and shown to completely decouple the two vortices causing cavitation inception. Moreover, the minimum pressure in the vortex core is significantly increased.