Yes / This paper presented a new circular polarization reconfigurable antenna for 5G wireless communications. The antenna, containing a semicircular slot, was compact in size and had a good axial ratio and frequency response. Two PIN diode switches controlled the reconfiguration for both the right-hand and left-hand circular polarization. Reconfigurable orthogonal polarizations were achieved by changing the states of the two PIN diode switches, and the reflection coefficient |S11| was maintained, which is a strong benefit of this design. The proposed polarization-reconfigurable antenna was modeled using the Computer Simulation Technology (CST) software. It had a 3.4 GHz resonance frequency in both states of reconfiguration, with a good axial ratio below 1.8 dB, and good gain of 4.8 dBic for both modes of operation. The proposed microstrip antenna was fabricated on an FR-4 substrate with a loss tangent of 0.02, and relative dielectric constant of 4.3. The radiating layer had a maximum size of 18.3 18.3 mm2, with 50 W coaxial probe feeding. / European Union’s Horizon 2020 research and innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424.

Yes / A planar dual-polarized phased array is proposed for 5G cellular communications. The array has the properties of dual-polarization, wideband and quasi end-fire radiation, which is printed on one side of a single-layer substrate. The design contains two 8-element sub-arrays including horizontally polarized end-fire dipole antennas and vertically polarized end-fire periodic slot antennas, employed on the PCB ground plane of the 5G mobile platform. Both sub-arrays provide wide bandwidth to cover 28 and 38 GHz (promising 5G candidate bands). The -10 dB impedance bandwidth of the proposed CPW-fed dipole and slot antennas are 26.5-39.5 GHz and 27.1-45.5 GHz, respectively. Moreover, for -6 dB impedance bandwidth, these values could be more than 20 GHz (24.4-46.4 GHz for the dipole antenna) and 70 GHz (22.3-95 GHz for the slot antenna). The fundamental characteristics of the proposed dual-polarized 5G antenna array in terms of the impedance bandwidth, realized gain, polarization, radiation pattern, and beam steering are investigated and good results are obtained. The clearance of the proposed dual-polarized 5G antenna array is less than 4.5 mm which is sufficient for cellular applications. / This work is partially supported by the InnovationsFonden project of Reconfigurable Arrays for Next Generation Efficiency (RANGE), AAU Young Talent Program, and European Union’s Horizon 2020 research and innovation programme under grant agreement H2020-MSCA-ITN-2016SECRET-722424.

The dynamic nuclear polarization of hydrogen nuclei by the solid effect in single crystals of samarium doped lanthanum magnesium nitrate (Sm:LMN) has been studied theoretically and experimentally. The equations of evolution governing the dynamic nuclear polarization by the solid effect have been derived in detail using the spin temperature theory and the complete expression for the steady-state enhancement of the nuclear polarization has been calculated. For well-resolved solid effect transitions at microwave frequencies Ï ~ Ï _e ± Ï _n, the expression for the steady-state enhancement differs from the expression obtained by the rate equation approach by small terms which become zero at Ï ~ Ï _e ± Ï _n Experimental enhancements of the proton polarization were obtained for eight crystals at 9.2 GHz and liquid helium temperatures. The samarium concentration ranged from 0.1 percent to 1.1 percent as determined by X-ray fluorescence. A peak enhancement of 181 was measured for a 1.1 percent Sm:LMN crystal at 3.0^" K. The maximum enhancements extrapolated with the theory using the experimental data for peak enhancement versus microwave power and correcting for leakage, agree with the ideal enhancement (24O in this experiment) within experimental error for three of the crystals. The calculated satellite separation was within 6 percent of the measured separation for each of the enhancement curves and the peak positive and negative enhancements were equal for all but two of the crystals. The nuclear spin"lattice relaxation time was measured for one of the crystals between l.6^" K and 4.2^" K. To account for nuclear spin"lattice relaxation, spin diffusion theory in the rapid airrusion limit was incorporated into the results of the spin temperature theory of the solid effect. The experimental results indicate that the spin temperature theory is a quantitatively correct approach for the description of dynamic nuclear polarization by the solid effect for well"resolved solid effect transitions. / Ph. D.

The charged pion production reactions d(gamma,pi⁺n), d(gamma,pi^-p), HD(gamma,pi⁺n)X were studied using linearly polarized gamma-rays with energies in the range from 260 MeV to 370 MeV at the Laser Electron Gamma Source (LEGS). A solid HD target was used in this experiment for the first time. The beam asymmetry data for the d(gamma,pi^-p) reaction significantly add to the previously available data. This gives new input to multipole analysis of pion production. A slight deviation from the beam asymmetry predicted for the free neutron is observed. The cross sections in the d(gamma,pi^-p) channel agree with previous measurements. / Ph. D.

Broadband wireless communications require wideband antennas to support large number of users and higher data rates. Desirable features of a wideband antenna are low-profile, dual-polarization and wide bandwidth in a compact size. Many existing wideband antennas are large in size and some have only circular polarization. On the other hand low-profile, dual-polarized antennas frequently have limited bandwidth. This dissertation reports on results from original research into several new wideband antennas. All are compact and planar, and many are low-profile and dual-polarized. Since 1994, Virginia Tech Antenna Group (VTAG) has performed research on the wideband, low-profile and dual-polarized antennas of compact size. This research resulted in the following antenna innovations: the Fourpoint, Fourtear, PICA (Planar Inverted Cone Antenna), diPICA (dipole PICA) and LPdiPICA (Low-Profile diPICA) antennas. They are all planar in geometry so one can easily construct them in a compact size. The antennas were characterized and investigated with extensive simulations and measurements. The computed and measured data demonstrates that some of the antennas appear to have the characteristics of the self-complementary antenna and most of the proposed antennas provide more than a 10:1 impedance bandwidth for a VSWR < 2. Patterns, however, are degraded at the high end of the frequency. Several tapered ground planes were proposed to improve the radiation pattern characteristics without degrading the impedance performance. A simulation result proposed a possibility of another antenna inventions providing 10:1 pattern bandwidth with the 10:1 impedance bandwidth. Research into wideband antennas demonstrated that the newly invented antennas are closely related each other and are evolved from a primitive element, PICA. Not only the comprehensive investigation but also a practical antenna design has been done for commercial base-station array antennas and to phased array antennas for government applications. This dissertation presents results of comprehensive investigation of new planar wideband antennas and its usefulness to the broadband wireless communications. / Ph. D.

Subclinical endotoxemia (low levels of circulating bacterial endotoxin) has been observed in patients suffering from chronic inflammatory diseases such as atherosclerosis, diabetes, and obesity. However, the link between this condition and chronic inflammation is poorly understood. Previous work from our lab has shown that chronic exposure to super-low doses of bacterial endotoxin (LPS) aggravates atherosclerosis resulting in increased plaque size and instability in a macrophage-dependent manner in a mouse model of atherosclerosis. Further, we showed that super-low dose LPS (SLD-LPS) treatment was able to inhibit lysosomal fusion in immortalized macrophages. However, this was done under more acute treatment conditions. The aim of this project was to examine the molecular mechanisms by which chronic SLD-LPS may polarize macrophages to a non-resolving pro-inflammatory state consistent with chronic inflammation. This was carried out in two projects, the first a more broad phenotypic paper showing the disruption in homeostasis by chronic SLD-LPS in immortalized macrophages, while the second uses primary bone marrow-derived mouse macrophages to identify specific molecular signaling pathways used by chronic SLD-LPS. Here we show that chronic SLD-LPS led to the novel upregulation of pro-inflammatory mediators p62 and ccl2 with simultaneous downregulation of homeostatic mediators Nrf2 and slc40a1 in immortalized wild-type mouse macrophages. Further we showed this effect was reversed using the homeostatic restorative agent sodium phenylbutyrate (4-PBA), a newly reported activity for this reagent in mouse macrophages. This indicated that a disruption in homeostasis, possibly involving autophagy, may be responsible for the non-resolving pro-inflammatory polarization of macrophages. Therefore, in our second project, we further explored the effect of chronic SLD-LPS treatment on the homeostatic arm of the response by focusing on the Nrf2 inhibitor Keap1. Here we show that chronic SLD-LPS results in an accumulation of Keap1 in mouse bone marrow-derived macrophages, an effect specific to chronic SLD-LPS, as high doses of LPS failed to induce Keap1. We suggest that this effect may be related to a disruption in lysosomal fusion as evidenced by accumulation of autophagy flux markers MLKL and p62. Further, we show that these effects are dependent on the non-traditional TLR4 adaptor TRAM, suggesting an alternative dose-dependent signaling pathway for LPS. Together this work identifies novel signaling mechanisms involved in non-resolving pro-inflammatory polarization of murine macrophages, providing new insight behind how chronic super-low dose LPS exposure may lead to chronic inflammation. / Doctor of Philosophy / Inflammation is the body's natural response to injury or insult and can be beneficial in certain contexts such as pathogen clearance. However, left un-checked, chronic inflammation can exacerbate or even lead to disease pathology, such as is the case with modern diseases such as atherosclerosis, obesity, diabetes, etc. Despite the high prevalence of these diseases, effective treatments and therapies are still lacking. Recently it was discovered that many patients suffering from chronic inflammatory diseases had low levels bacterial endotoxin (LPS) in their circulation, a condition referred to as subclinical endotoxemia. However, possible links between this condition and chronic inflammatory disease remain poorly understood. Using a mouse model of atherosclerosis, previous research from our lab showed that persistent exposure to super-low doses of bacterial endotoxin (similar to those observed in humans) lead to aggravated atherosclerosis with both increased plaque size and instability. Further, we showed that this effect was primarily mediated by pro-inflammatory polarized immune cells called macrophages, but the molecular mechanism behind this polarization is still unclear. Further research into these molecular mechanisms may provide better targets for the development of future chronic inflammatory disease treatments. Here using a combination of mouse cell line and primary cell cultures, we discuss how chronic exposure to super-low doses of bacterial endotoxin leads to the chronic non-resolving pro-inflammatory polarization of macrophage immune cells, with particular emphasis on the distinct molecular signaling mechanisms induced by chronic super-low dose LPS.

Liquid phase ¹³C DNP experimental data were collected in a flow transfer system for different organic molecules, such as acetone, acetaldehyde, diethyl malonate, ethyl acetoacetate, diphenylmethane, and triphenylmethane. These molecules represent a wide range of functional groups with different acidities of the respective carbon-hydrogen bonds. The ¹³C DNP results demonstrated that the scalar dominated enhancement is sensitive to the acidity of carbon-hydrogen bonds as well as to the correlation times of the sample molecules. A hydrogen bonding spin polarization model is used, for the first time, to interpret the scalar components induced by the nitroxide free radical at the carbon sites of the acidic carbon-hydrogen bonds. Three aromatic molecules: nitrobenzene, 1, 2-dichlorobenzene, and toluene, are studied by the solution ¹³C DNP technique. The scalar components for the ring carbons are sensitive to the electronic environment of these carbon sites. A spin delocaliztion model is used, for the first time, to explain the scalar contribitions for the ¹³C DNP enhancements of the ring carbons. Both ¹H and ¹³C DNP experiments are performed for the Taxol/TEMPO (2, 2, 6, 6-tetramethyl-1-piperidinyloxy) system. The different ¹H enhancements for the hydrogens in the two acetyl groups indicate the different accessibility of these groups to the free radical. The ¹³C DNP results for the skeleton carbons of Taxol show the different accessibility of these carbon sites to the free radical. The solution ¹³C DNP result of adamantane indicates that the DNP enhancements and thus the correlation times for the two different carbon sites are very close under the high free radical concentration. The ¹³C DNP study of C₇₀ empty cage fullerene suggests that the endcap carbons are more accessible than those at the center of the cage, and that the scalar coupling between the cage carbons and the free radical is very weak. / Ph. D.

In recent years, the ferroelectric oxides belonging to the family of layered perovskite, e.g., SrBi₂(Ta₁₋_xNb_x)₂O₉ (or SBTN), were identified as promising candidates for nonvolatile memory applications. SrBi₂Ta₂O₉ (or SBT) thin films were found to exhibit no fatigue up to 10¹² switching cycles, very good retention properties and low leakage current densities on Pt electrodes. However, high temperature processing, ie. 750 - 800°C, is needed for SBT to exhibit ferroelectric properties. Moreover, the fundamental properties of SBTN have not been fully characterized. In this research, SBTN solid solutions were studied from two aspects: the technical aspect and scientific aspect. From the technical point of view, low temperature processing of SBTN ferroelectric thin films was developed. In this part of study, SBTN thin films were made by metalorganic decomposition method (MOD) and were deposited on Pt-electrodes. The structure development study by a non-destructive optical method, spectroscopic ellipsometry, was proposed to determine nucleation and grain growth temperatures. The information on structure development can be obtained by observing how the refractive indices and film thicknesses change as functions of annealing temperature. The results of structure development study for SBT thin films suggest that the ferroelectric properties are controlled by grain growth process rather than nucleation process. The critical factor for ferroelectric properties was to have grain size exceeding a critical value, i.e., 0.1 µm. Applying this concept, low temperature processing can be achieved by growing larger grains at lower temperature. The processing temperature of SBTN thin films was reduced by 50 - 100°C by adding excess Bi or increasing Nb/Ta ratio. The optimum excess Bi content in SBT was 30 - 50%; within this range, limited solid solution of Bi₂O₃ and SBT was formed. From the scientific aspect of view, optical properties and ionic transport phenomena of SBTN bulk ceramics were investigated for the first time. The reason of using bulk ceramics is to exclude the difficulties associated with thin film technology, e.g., grain size effect and electrode-ferroelectric interface effect. These bulk property studies provide fundamental understanding of SBTN materials and provide a guideline for process development in device applications. The optical dispersion functions of bulk SBTN were obtained by using various angle spectroscopic ellipsometry with a surface layer correction. The values of refractive indices were found to vary with composition, which are possibly associated with crystallographic orientation. Using the Lorentz Oscillator model, the approximate energy band gaps of SBTN solid solutions were estimated to be about 5 eV. The ionic transport phenomena of SBT and SrBi₂Nb₂O₉ (or SBN) were investigated by using impedance spectroscopy. This technique allows to separate the effect of ion transport in grain, grain boundary and electrode-ferroelectric interface. In this study, the fatigue model of bismuth layered oxides was discussed through ionic conductivity and interface absorption effect. One conducting species, oxygen vacancies with positive charges, was assumed in the model. High ionic conductivities of SBT and SBN (~ 10¯⁷ S/cm) comparing to Pb(Zr₁₋_xTi_x)O₃ (~ 10¯¹¹-10¯¹⁰ S/cm) suggests high defect concentration and high charge mobility in bismuth layered oxide materials. As a result, the most possible model to explain high resistance to fatigue of SBT/SBN was the easy recovery of oxygen vacancies from the entrapment at electrode-ferroelectric interfaces. / Ph. D.

Ferroelectric materials show a spontaneous electrical polarization that can be reversed in sense by an applied external electric field. It should, therefore, be feasible to build a ferroelectric memory device that can store information in digital form. Ascertaining the suitability of a ferroelectric material for use in memory devices requires an understanding of electrical properties of the thin-film capacitor. There are a number of electrical characterization methods which can be used to investigate these electrical properties. The polarization mechanism can be studied by the most fundamental characterization technique for ferroelectrics, the hysteresis loop, which is derived by plotting polarization against applied field. Fatigue, retention and imprint, which are specific ferroelectric lifetime characterization methods, are employed to determine the rate of capacitor degradation as well as the mechanisms responsible for it. The DC conductivity characterization techniques, including leakage current, resistivity degradation and time dependent dielectric breakdown (TDDB) are used to study the electrical current properties and charge transport mechanism in memory applications. Finally, the AC conductivity (complex impedance) characterization method, introduced here for the first time for ferroelectric capacitors, permits further understanding of the charge transport mechanism of ferroelectric materials. However, this characterization method is not directly used to evaluate the application of ferroelectrics in memory devices, but it can provide a further physical understanding of ferroelectric capacitors, such as the understanding of fatigue. PbZr_xTi_1-xO₃ (PZT), a ferroelectric material with a pseudo-cubic perovskite-type structure, has been the material of choice in all major ferroelectric random access memory (FRAM) development programs to date. However, degradation problems such as fatigue and imprint that affect the lifetime of ferroelectric capacitors have moderated the progress of using PZT in commercial ferroelectric memories. Recently, SrBi₂Ta₂O₉ (SBT), a ferroelectric material that crystallizes in a layered structure, has been identified as a promising candidate for FRAM applications as a result of its fatigue-free behavior. In this research, the performance of PZT and SBT as ferroelectric memory materials is compared by using the aforementioned electrical characterization methods. / Master of Science

Interference between the modes of an optical fiber generates specific mode (intensity) patterns which get modulated by disturbances in the optical fiber system. Mode-mode interference has been analyzed from first principles and a model based on differential phase modulation presented. Mode-mode interference effects such as intensity modulation of the mode patterns are directly related to differential phase modulation between modes which arises due to the difference between the propagation constants of the constituent modes. Practical implementation of modal methods involves selective launching of modes and processing of the output pattern to demodulate the information. Axial strain has been chosen as the modulating mechanism in experiments designed to quantify mode-mode interference effects. Quasi-statically varying strain as well as vibrational strain was used to study 'dc' and 'ac' mechanisms. Specific mode combinations have been excited and their radiation patterns identified. Mode pattern changes have been described. Experimental observations and results correlate very well with analysis. / Master of Science