The Electronically Steered Phased Array is one of the most versatile antennas used in radars applications. Some of the advantages of electronic steering are faster scan, no moving parts and higher reliability. However, the cost of phased arrays has always been prohibitive - in the order of $1M per square meter. The cost of a phased array is largely impacted by the cost of the high frequency electronics at each element and the cost of packaging. Advances in IC integration will allow incorporating multiple elements such as low noise amplifier, power amplifier, phase shifters and up/down-conversion into one or two ICs. Even though the cost for large quantities of ICs (both Silicon and GaAs) has lowered, the high cost of IC packaging and the array backplane still make the use of phase arrays for radar applications costly. The focus of this research is on techniques that reduce the packaging and the backplane cost of large electronically steered arrays. These techniques are based on simplified signal distributions schemes, reduction of layers in the backplane and use of inexpensive materials. Two architectures designed based on these techniques, as well as a novel BGA active antenna package for dual polarized phased arrays are presented. The first architecture, called the series fed row-column architecture, focuses on the reduction of phase shifters and control signals used in the backplane of the array. The second architecture, called the parallel plate feed architecture, is based on a simplified scheme for distribution of the local oscillator signal. A prototype making use of each one of these architectures is presented. Analysis of advantages and disadvantages of each of these architectures is described. The necessity of cost reduction is a factor that can possibly impact the polarization performance of the antenna. This factor is a motivation to study and develop calibration techniques that reduce the cross-polarization of electronically steered phased arrays. Advances on Interleaving Sparse Arrays, a beam forming technique for polarization improvement/correction in phased arrays, are also presented.

Aneurysms are a deadly asymptomatic cardiovascular disease that may occur especially where there are bends and bifurcations in the cerebral vasculature. A region where these features are especially prominent is the Circle of Willis (COW) in the brain, where aneurysms are known to occur. In the carotid artery, which feeds into the COW, the Reynolds number of blood flow is typically around 200-500. Even with such a low Reynolds number, turbulent-like flow, or tortuous flow, can occur due to bends, bifurcations and highly pulsatile flow which lower the effective Reynolds number where tortuous flow can occur. Highly pulsatile flow is unsteady flow that is high in magnitude and changes over time. Endothelial cells (ECs) line the inner wall of the blood vessel and experience the friction force of blood flow. This work is focused on designing a device that can expose ECs to forces they would undergo in an aneurysm-susceptible site. This is accomplished by exposing ECs to physiologically relevant Wall Shear Stress (WSS) and vibrations simultaneously. Vibrations in the body occur due to flow separation at the vessel wall, which leads to pressure changes. These pressure changes induce vibrations onto ECs. The fluid flow in the designed Parallel Plate Flow Chamber (PPFC) is laminar to induce a predictable WSS onto the cells, while the vibrations will induce a rapid cyclical force to simulate pressure fluctuations that may occur in vivo. The aneurysm-susceptible flow will simulate a more turbulent-like flow in the carotid artery; higher maximum WSS (around 2.2 Pa) with vibrations. The aneurysm-protective flow will have a lower WSS maximum (around 0.5 Pa). The PPFC, made of polycarbonate, is small and light enough to be conveniently vibrated using an electromagnetic vibration stage. The PPFC can be driven by a syringe or peristaltic pump, allowing for either steady or transient waveforms. The PPFC’s fluid domain will not change upon vibration, isolating the effect of vibration on the cells. Also, two side-by-side glass slide slots were included to allow for both protein and mRNA quantification from the same experiment, increasing experimental efficiency and flow-related consistency between the two cell areas. Simulations using ANSYS Fluent verified the flow field and WSS waveform on the cells for the designed geometry for 3D and 2D cases, as well as verified equal WSS values throughout all areas of ECs. Then, Particle Image Velocimetry (PIV) was done to verify the predicted flow rate in the machined PPFC given a steady flow rate driven by a syringe pump. Preliminary cell experiments were performed in an incubator under flow and vibration conditions to demonstrate cell survivability.

No description available.

No description available.

Due to the fact that bone cells are highly responsive to mechanical stimuli, shear stress has been extensively studied for its ability to enhance osteogenic differentiation through mechanotransduction. In addition, thermal stress has also been explored as a conditioning method to stimulate cellular proliferation, differentiation, and cytoprotection through heat shock protein induction. Despite the beneficial effects observed with individual stress on cells, there has been little focus on the potential of a combination of stresses to improve cellular response. Therefore, the aim of this study was to investigate the effect of combined shear and thermal stress on preosteoblasts to stimulate an enhanced osteogenic response. To achieve this, MC3T3-E1 cells were exposed to one of the following protocols for an hour: no stress (control), shear stress at 1 dyne/cm2 using a parallel plate flow chamber, thermal stress in a 42°C incubator, or combined shear and thermal stress (1 dyne/cm2 at 42°C). Stress treatments were applied on Day 2, Day 6, and Day 10. To assess the early response of cells to stress treatments, we measured metabolic activity, expression of signaling factors, and HSPs following stress on Day 2. Despite an initial decrease in metabolism, combined stress stimulated a strong response in VEGF (12.49 RFI) COX-2 (12.32 RFI), HSPs (2-4 RFI) and increased PGE accumulation. The long-term cellular response to stress treatments was measured on Day 15 by evaluating the ability of combined stress to stimulate late stage markers of differentiation. Combined stress increased OPN gene and protein expression, yet OCN was minimally affected by stress treatments. However, mineralization was significantly decreased with combined stress. Overall, combined stress was able to stimulate an enhanced effect across a majority of the bone-related markers measured, whereas individual shear stress or thermal stress were limited in their response. This suggests that combined stress can provide the appropriate cues to modify osteoblast differentiation and generate an enhanced osteogenic response. / Master of Science

Yes / A numerical study of natural convection heat transfer in water filled cavity has been examined in 3-D for single phase liquid cooling system by using an array of parallel plate fins mounted to one wall of a cavity. The heat generated by a heat source represents a computer CPU with dimensions of 37.5∗37.5mm mounted on substrate. A cold plate is used as a heat sink installed on the opposite vertical end of the enclosure. The air flow inside the computer case is created by an exhaust fan. A turbulent air flow is assumed and k-ε model is applied. The fins are installed on the substrate to enhance the heat transfer. The applied power energy range used is between 15 - 40W. In order to determine the thermal behaviour of the cooling system, the effect of the heat input and the number of the parallel plate fins are investigated. The results illustrate that as the fin number increases the maximum heat source temperature decreases. However, when the fin number increases to critical value the temperature start to increase due to the fins are too closely spaced and that cause the obstruction of water flow. The introduction of parallel plate fins reduces the maximum heat source temperature by 10% compared to the case without fins. The cooling system maintains the maximum chip temperature at 64.68°C when the heat input was at 40W that is much lower than the recommended computer chips limit temperature of no more than 85°C and hence the performance of the CPU is enhanced.

Many new applications are being proposed and developed for use in the terahertz (THz) frequency region. Similarly, many new materials are being characterized for possible use in this area. Nanostructured forms are of particular interest since they may yield desirable properties, but they remain especially challenging to characterize. This work focuses on the characterization of zinc oxide (ZnO) in bulk and nanowire form. A method for characterizing nanostructures at THz by use of a parallel-plate waveguide (PPWG) is presented. This method is novel in that it is simple, both in theory and practice, and does not require the use of complex measurement techniques such as differential and double modulated terahertz time-domain spectroscopy (THz-TDS). To enable easy evaluation of the quality of the result the maximum deviation in the material response measurement is presented. The dielectric properties of bulk and nanowire ZnO as determined by THz-TDS measurements are reported, and the electrical conductivity extracted from both are presented for comparison. Experimental results are compared to the well established pseudo-harmonic phonon dielectric model. Shortcomings in the pseudo-harmonic phonon model are resolved when coupled with a modified Drude model. This work will enable the determination of THz material properties from nano-scale and very-thin film materials with better reliability and practicality than what has been possible until now.

X-ray computed tomography (CT) holds a critical role in current medical practice for the evaluation of patients, particularly in the emergency department and intensive care units. Expensive high resolution stationary scanners are available in radiology departments of most hospitals. In many situations however, a small, inexpensive, portable CT unit would be of significant value. Several mobile or miniature CT scanners are available, but none of these systems have the range, flexibility or overall physical characteristics of a truly portable device. The main challenge is the design of a geometry that optimally trades image quality for system size. The goal of this work has been to develop analysis tools to help simulate and evaluate novel system geometries. To test the tools we have developed, three geometries have been considered in the thesis, namely, parallel projections, clam-shell and parallel plate geometries. The parallel projections geometry is commonly used in reconstruction of images by filtered back projection technique. A clam-shell structure consists of two semi-cylindrical braces that fold together over the patient's body and connect at the top. A parallel plate structure uses two fixed flat or curved plates on either side of the patient's body and image from fixed sources/detectors that are gated on and off so as to step the X-ray field through the body. The parallel plate geometry has been found to be the least reliable of the three geometries investigated, with the parallel projections geometry being the most reliable. For the targeted application, the clam-shell geometry seems to be the solution with more chances to succeed in the short term. We implemented the Van Cittert iterative technique for the reconstruction of images from projections. The thesis discusses a number of variations on the algorithm, such as the use of the Conjugate Gradient Method, several choices for the initial guess, and the incorporation of a priori information to handle the reconstruction of images with metal inserts.

In the quest for reliable, repeatable and stable field electron emission that has commercial potential, whilst many attempts have been made, none yet has been truly distinguishable as being successful. Whilst I do not claim within this thesis to have uncovered the secret to success, fundamental issues have been addressed that concern the future directions towards achieving its full potential. An exhaustive comparison is made across the diverse range of materials that have, over the past 40-50 years, been postulated and indeed tested as field emitters. This has not previously been attempted. The materials are assessed according to the important metrics of turn on voltage, Eon, and maximum current density, Jmax, where low Eon and high Jmax are seen as desirable. The nano-carbons, carbon nanotubes (CNTs), in particular, perform well in both these metrics. No dependency was seen between the material work function and its performance as an emitter, which might have been suggested by the Fowler Nordheim equations. To address the issues underlying the definition of the local enhancement factor, β, a number of variations of surface geometry using CNTs were fabricated. The field emission of these emitters was measured using two different approaches. The first is a Scanning Electrode Field Emission Microscope, SAFEM, which maps the emission at individual locations across the surface of the emitter, and the parallel plate that is more commonly encountered in field emission measurements. Finally, an observed hysteretic behaviour in CNT field emission was explored. The field emitters were subjected to a number of tests. These included; in-situ residual gas analysis of the gas species in the emitter environment, a stability study in which the emitters were exposed to a continuing voltage loop for 50 cycles, differing applied voltage times to analyse the effects on the emitted current, and varying maximums of applied field in a search for hysteresis onset information. These studies revealed the candidate in causing the hysteresis is likely to be water vapour that adsorbs on the CNT surface. A six step model if the emission process was made that details how and when the hysteresis is caused.

Submitted by Cristhiane Guerra (cristhiane.guerra@gmail.com) on 2017-01-26T13:30:08Z No. of bitstreams: 1 arquivototal.pdf: 7840328 bytes, checksum: 74229a382309ea0fcf42de5818cc899a (MD5) / Made available in DSpace on 2017-01-26T13:30:08Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 7840328 bytes, checksum: 74229a382309ea0fcf42de5818cc899a (MD5) Previous issue date: 2016-08-25 / The aim of this work deals with the analysis of the mutual interaction between flow and magnetic fields that develops in a parallel-plate channel as soon as an external magnetic field is applied transversely to the plates. The fluid, electrically conductive, enters the channel under any velocity profile and will have its natural development within the channel changed by the applied magnetic field. With a coupled two-way interaction, the field will also be affected by the flow. The study of these interactions will be made from the two-dimensional version of the steady-state Navier-Stokes equations in the stream function formulation, coupled with the transport equation of the magnetic field. The solution of the governing equations will be obtained by the Generalized Integral Transform Technique (GITT). The results obtained for the velocity field, magnetic field and temperature field, as well as the associated scalar functions, are produced and compared with the literature on the basis of the main parameters of government: Reynolds number (Re), magnetic Reynolds number (Rem) and Hartmann number (Ha). In order to illustrate the consistency of the generalized integral transform technique, convergence analysis, are also performed and presented. / O objetivo do presente trabalho trata da análise da interação mútua escoamento/campo magnético que se desenvolve no interior de um canal de placas planas e paralelas ao se aplicar um campo magnético externo transversal. O fluido, eletricamente condutor, entra no canal sob um perfil qualquer de velocidade, e terá seu desenvolvimento natural afetado pelo campo magnético aplicado. Com uma interação acoplada de duas vias, o campo também será afetado pelo escoamento. O estudo dessas interações será efetuado a partir de uma formulação bidimensional das equações de Navier-Stokes, na formulação em função corrente, para escoamento em regime permanente, acoplada à equação de transporte do campo magnético. A solução das equações governantes será obtida através da Técnica da Transformada Integral Generalizada (GITT). Os resultados obtidos para o campo de velocidade e campo magnético, bem como suas funções escalares associadas, são produzidos e comparados aos da literatura em função dos principais parâmetros de governo: número de Reynolds (Re), número de Reynolds magnético (Rem) e número de Hartmann (Ha). Com o objetivo de ilustrar a consistência da técnica da transformada integral generalizada, análises de convergência são também efetuadas e apresentadas.