10,746 research outputs found

    Beam scanning by liquid-crystal biasing in a modified SIW structure

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    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    Novel 129Xe Magnetic Resonance Imaging and Spectroscopy Measurements of Pulmonary Gas-Exchange

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    Gas-exchange is the primary function of the lungs and involves removing carbon dioxide from the body and exchanging it within the alveoli for inhaled oxygen. Several different pulmonary, cardiac and cardiovascular abnormalities have negative effects on pulmonary gas-exchange. Unfortunately, clinical tests do not always pinpoint the problem; sensitive and specific measurements are needed to probe the individual components participating in gas-exchange for a better understanding of pathophysiology, disease progression and response to therapy. In vivo Xenon-129 gas-exchange magnetic resonance imaging (129Xe gas-exchange MRI) has the potential to overcome these challenges. When participants inhale hyperpolarized 129Xe gas, it has different MR spectral properties as a gas, as it diffuses through the alveolar membrane and as it binds to red-blood-cells. 129Xe MR spectroscopy and imaging provides a way to tease out the different anatomic components of gas-exchange simultaneously and provides spatial information about where abnormalities may occur. In this thesis, I developed and applied 129Xe MR spectroscopy and imaging to measure gas-exchange in the lungs alongside other clinical and imaging measurements. I measured 129Xe gas-exchange in asymptomatic congenital heart disease and in prospective, controlled studies of long-COVID. I also developed mathematical tools to model 129Xe MR signals during acquisition and reconstruction. The insights gained from my work underscore the potential for 129Xe gas-exchange MRI biomarkers towards a better understanding of cardiopulmonary disease. My work also provides a way to generate a deeper imaging and physiologic understanding of gas-exchange in vivo in healthy participants and patients with chronic lung and heart disease

    Southern Adventist University Undergraduate Catalog 2022-2023

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    Southern Adventist University\u27s undergraduate catalog for the academic year 2022-2023.https://knowledge.e.southern.edu/undergrad_catalog/1121/thumbnail.jp

    Investigation of Inorganic Salt Hydrate Phase Change Materials for Thermal Energy Storage Integrated into Heat Pump Systems

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    Thermal energy storage (TES) is a promising technology for the Energy Transition. Low grade heat is valuable for many everyday applications: indoor heating and cooling, hot water, refrigeration, etc. Heat pumps (HPs) move heat up a thermal gradient (from cold to hot) with an input of energy. Integrating TES into a HP grants flexibility to dispatch the stored heat as needed. When operating a HP against a fluctuating temperature body (i.e., outdoor ambient air temperature), TES provides an isothermal heat source that enables more efficient HP operation to its reduce energy consumption without sacrificing thermal comfort. This work explores the thermodynamic limits of HP-TES and it was found that TES temperatures equal to the application temperature leads to the highest potential for energy savings and peak demand reduction. This HP-TES system was then modeled in a building thermal energy simulation where the same findings emerge: a TES temperature near the application temperature shows the highest potential. A common method of achieving an isothermal TES is to incorporate phase change materials (PCMs) that store heat through the enthalpy of phase change. Salt hydrates are valued for their high volumetric storage density and low cost. This work explores the Brunauer-Emmett-Teller method to model sodium sulfate, but this salt was found to be incompatible with this reduced order method. Salt hydrates also exhibit low thermal conductivity which limits their direct use in TES. This work develops salt hydrate-graphite composite PCMs with improved thermal conductivity, however a tradeoff between energy storage capacity and thermal power density was seen. The composite PCMs were experimentally tested in a TES device and the improved thermal properties demonstrate their potential for use in simple TES architectures. Overall, this work evaluated TES systems from a holistic perspective, spanning several orders of magnitude, both energetically and spatially.Ph.D

    A New Wave in Robotics: Survey on Recent mmWave Radar Applications in Robotics

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    We survey the current state of millimeterwave (mmWave) radar applications in robotics with a focus on unique capabilities, and discuss future opportunities based on the state of the art. Frequency Modulated Continuous Wave (FMCW) mmWave radars operating in the 76--81GHz range are an appealing alternative to lidars, cameras and other sensors operating in the near visual spectrum. Radar has been made more widely available in new packaging classes, more convenient for robotics and its longer wavelengths have the ability to bypass visual clutter such as fog, dust, and smoke. We begin by covering radar principles as they relate to robotics. We then review the relevant new research across a broad spectrum of robotics applications beginning with motion estimation, localization, and mapping. We then cover object detection and classification, and then close with an analysis of current datasets and calibration techniques that provide entry points into radar research.Comment: 19 Pages, 11 Figures, 2 Tables, TRO Submission pendin

    Impact of aortic acceleration on haemodynamics

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    The aortic valve apparatus (AVA) is a complicated structure continuously moving throughout the cardiac cycle such that it may be regarded as a live organ. Different studies previously focused on analysing the dynamism or local deformations of the AVA; however, the effect of the axial movement of the AVA on blood flow or aortic valve loading remains uncharted. In this study we propose analysing the axial acceleration of the AVA and its effect on blood flow. After mathematically decomposing the deformations of healthy AVA’s from CT image tracking, it was deduced that the dominant component is the axial movement towards and away from the left ventricle. Using the 1D water hammer approximation we hypothesised a theory tying the previously inexplicable dicrotic notch seen on the arterial pressure waveform to the AVA acceleration during valve closure. The next intermediate step was to use an idealised model replicating the anatomy of the AVA in order to study the effect of axial acceleration on blood flow combined with steady inflow conditions. A series of non-dimensional parameters describing the underlying physics were derived in order to enable an appropriate comparison with a patient specific anatomy. The final step was to analyse a stationary and an accelerating patient specific AVA using high fidelity Fluid-Structure Interaction (FSI) simulations. The results showed qualitative and quantitative differences between both cases especially in valvular dynamics and loading. Moreover, the FSI simulation results confirmed the presence of a sudden reactive force on the aortic valve in the accelerating AVA case at the time of peak acceleration during valve closure; where the same phenomenon was not present in the stationary AVA case. The calculated force of 0.6 N along with the aortic valve wetted area of 0.0013 m2 yield ≈ 3.5 mmHg which is in the same ball park as previously measured dicrotic notch pressure rises. As a result, we propose that the axial acceleration of the AVA may be a crucial parameter in diagnosing aortic or ventricular disease since it has a significant effect on aortic valve function. We also propose a future plan of investigation in order to strengthen our hypothesis and enable the use of the acceleration of the AVA as a non-invasive diagnostic parameter.Open Acces

    Children's Community-Based Guided Active Play; Influence on Physical Activity Participation and Cardiovascular Responses

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    It is well established that the decline in children’s physical activity (PA) participation contributes to increases in the prevalence of paediatric obesity, risks for developing cardiovascular disease and decreases in physical fitness. PA interventions that are regimented and conducted in structured environments, such as laboratories, hospitals and school-based curricula, have shown to improve healthy PA behaviours and health- related fitness (i.e., health-enhancing PA). The increased costs and labour intensiveness of these programs have raised questions about their attractiveness in recreational/community summer camps and/or after-school settings. The importance of community-based programming where play (i.e., free play [FP], active play [AP], guided active play [GAP]) may provide increased opportunities for children to be active and facilitate social interactions should not be overlooked when considering children’s PA participation. Previous studies have shown that in a simulated AP environment using cooperative games, children elicit a wide range of energy expenditures and percentage of time spent in moderate-to-vigorous PA (%MVPA). The overarching purpose of this dissertation was to use cooperative games in community summer camp programs for school-aged children to determine if select health PA behaviour outcomes (energy expenditure, intensity) and health-related fitness (blood pressure, aerobic fitness, body composition) improvements are associated with long-term GAP programs. The major findings are that: 1) energy expenditure (EE) and %MVPA associated with children’s GAP using cooperative games over an 8-week community summer camp are maintained and sufficient to improve blood pressure and estimated maximal oxygen consumption (VO2max; Ch. 3.2); 2) following a shorter (5-wk) GAP program, school-aged children showed statistically higher forearm vascular perfusion controlled by endothelial independent processes that preceded changes in estimated VO2max (Ch. 3.3); and 3) during development, PA tracking over 1 year intervals were moderately high when assessed by GAP and using cooperative games (Ch. 3.1). In conclusion, cooperative games within a longer-term community summer camp GAP program are effective in sustaining health-enhancing PA and improving school-aged children’s health and fitness. PA participation over a one-year period for GAP using cooperative games is stable in children 5-12 years. A community camp that includes GAP programming with cooperative games seems to be an effective strategy to engage children in health-enhancing PA during time away from school (i.e., afterschool, weekends, summer)

    Multi-Character Motion Retargeting for Large Scale Changes

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