We have previously demonstrated that natural killer (NK) cells are the primary immune effectors with the ability to mediate selection and differentiation of several different cancer stem cells/undifferentiated tumors via lysis and secreted or membrane-bound IFN-γ and TNF-α, respectively, leading to growth inhibition and curtailment of tumor metastasis. Here, we present an overview of our recent findings on the biology and significance of NK cells in the selection/differentiation of stem-like tumors using in vitro and in vivo studies conducted in the NSG and humanized-BLT mice. To establish the phenotypic and functional differences between primary NK and super-charged NK cells in vitro and in vivo, we analyzed their surface receptors, cytotoxicity, and cytokine secretion in either NK cells culture, NK-tumor co-culture, and CD34+ humanized mouse model condition. In in vitro studies, super-charged NK cells were more polyfunctional. They expressed higher surface receptors, performed higher cytotoxicity, and secreted higher IFN-γ compared to primary NK cells in vitro. When cultured with tumor tissues, super-charged NK cells were also more resistant to immunosuppression by the tumor tissues. Moreover, we observed similar inhibition of tumor growth by super-charged NK cells in the NSG-CD34+ humanized mouse model as we saw in hu-BLT mice. Therefore, due to their indispensable role in targeting cancer stem-like/undifferentiated tumors and various other vital functions of NK cells which are presented in this thesis, NK cells should be placed high in the armamentarium of tumor immunotherapy.

As a key passivation layer that governs battery operation, the solid electrolyte interphase (SEI) has long been credited for enabling high performing batteries or blamed for their eventual death. However, qualitative descriptions of the SEI often found in the literature (e.g., “conductive”, “passivating”) highlight our incomplete understanding, where even the most basic properties foundational to SEI function (e.g., ionic and electronic conductivity) remain difficult to determine. Here, we propose a methodology to quantify SEI conductivities using a separatorfree Cu|SEI|Li architecture that treats the SEI as a solid-state electrolyte. Although the non-ideal experimental setup leads to inconsistent and widespread SEI conductivity measurement, several improvement and failure analysis are discussed in this work. Perhaps most striking, we find that reversible Li metal deposition is possible in our separator-less Cu|SEI|Li cell with additional liquid electrolyte, demonstrating that the SEI might be able to function like a solid-state electrolyte. However, the excess liquid electrolyte in the Cu|SEI|Li cell makes the argument of using SEI as solid state electrolyte somewhat questionable since SEI solely function as a passivated film and the lithium ions only come from the additional liquid electrolyte. Indeed, using SEI as solid state electrolyte remain challenging, but several future improvements are also discussed in this work. Our work provides quantitative measurement for how “conductive” and “passivating” SEI films and further enrich our understanding of the SEI, not just as a passivation layer to enable battery operation, but as a functional structure that can potentially have important implications for solid-state batteries.

This dissertation accentuates the significance of high-power gallium nitride (GaN) camel diode varactors for RF transmitter applications. Modern RF transmitters favor compact adaptive circuits for cost and power efficiency. Adaptive circuits include tunable filters, tunable matching networks, and antenna tuners, facilitating adjustments in resonate frequency or impedance. Crucially, these components need to exhibit robust power handling capability when operating below 6 GHz. Vertical Schottky diodes stand out as tuning elements in these high-power adaptive circuits due to their compactness, high power handling, and superior quality factor, with GaN holds promise for achieving the highest quality factor figure of merit (QFOM) owing to its outstanding breakdown electric field and favorable electron mobility.Popularly pursued GaN Schottky diode varactors suffer from leakage currents at high reverse voltage biases at their junctions and because of inherent threading dislocations in thin GaN layers on foreign substrates. We devised a novel device architecture to address these limitations. We employ an interdigitated anti-series multi-Fin camel diode structure composed of a thin p+-GaN top layer situated between the Schottky metal and an n-type GaN drift layer. The p-GaN layer raises the barrier height to suppress reverse leakage current to maintain a high Q factor at higher reverse biases than Schottky diodes. Additionally, we utilize GaN on Qromis Substrate Technology (QST) wafers that permit the growth of thick GaN layers with lower dislocation densities and lower leakage currents than GaN-on-Si and that are comparable to GaN-on-GaN. In this dissertation, we first propose a universal design flow for power varactors. Secondly, we experimentally validate the proposed methods for suppressing leakage current. Subsequently, a significant portion of this dissertation is dedicated to device optimizations encompassing epi-structure and device aspects. Detailed iterations of experiments and subsequent improvements are documented. The finalized fabrication flow and the DC, RF S-parameters of these diodes are reported, signifying their potential to outperform other power varactor technologies. Lastly, we demonstrate prototype bandpass filters using these diodes, underscoring the feasibility of real-world applications with further refinement and development efforts.

Millisecond pulsars are extremely stable and rapidly rotating neutron stars that emit electromagnetic radiation along their magnetic axes. Due to the misalignment between the rotational and the magnetic axes, the observed pulsar signals are analogous to the light beams of distant lighthouses. The predictable pulsing behavior is the fundamental mechanism that allows researchers to use pulsars as tools for science and engineering. This research focused on the analysis, simulation, estimation, and verification associated with pulsar-based navigation and clock calibration.

The autonomous pulsar-based navigation problem is formulated in terms of a nonlinear filtering problem where a single filter is used to estimate the spacecraft position and velocity. The positioning accuracy of a spacecraft traveling at known constant velocity was analyzed to build insights into the general navigation problem. An analytical comparison between the measurement noises of X-ray based and radio based pulsar timing/navigation system is discussed. A variation of the Extended Kalman Filter was developed and implemented to track simulated X-ray pulsar measurements collected by an orbiting spacecraft. This filter uses a multirate structure to more efficiently process pulsar measurements. The ephemeris of the DAWN spacecraft was used to investigate the performance of pulsar-based navigation in a more realistic mission scenario.

In order to show the feasibility of pulsar-based navigation, several existing pulsar tim- ing software packages and publicly available radio millisecond pulsar data were used to experimentally verify the concept. An Unscented Kalman Filter was used to process the time-of-arrival measurements from 5 isolated millisecond pulsars in order to estimate the position of the radio telescope in Earth fixed coordinate system.

This research also investigated the theoretical frequency stability of pulsar-aided atomic clocks from power spectral densities. Hadamard variance was used to analyze the unfiltered and the filtered clock systems. The result of the analysis shows that pulsars have the potential of enhancing the long-term frequency stability of stand-alone compact atomic clocks.

The last chapter of this dissertation discusses relative positioning using differential phase measurement. The proposed method can be used to eliminate common mode errors embed- ded in the pulsar measurements when the two observed signal frequencies are known.

Cervical cancer is a common malignancy worldwide and is one of the leading causes of death for women. Vaginal stenosis is a common long-term side effect of pelvic radiation. Vaginal dilator therapy is the most common and universally accepted strategy to prevent vaginal stenosis, as it can promote epithelialization and increased vascularity of the tissues after brachytherapy. However, many patients feel uncomfortable with using commercial vaginal dilators that are manufactured using hard latex materials, struggle with transitioning from one dilator size to another, and have difficulty dilating the apex of the vaginal canal. In this thesis, an inflatable vaginal dilator made from silicone polymers was developed to overcome the problems inherent with hard plastic dilators. Silicone polymers are soft and inflatable materials and ideally suited for this application. In this thesis, we have investigated the stress-strain characteristics of silicone material used for manufacturing vaginal dilators. We have determined a two-term Mooney-Rivlin equation to describe the behavior of silicone. Finite element analysis was used to simulate the dilator inflation and determine the force that the dilator exerts on the vaginal wall. In addition, experimental studies were conducted to verify the finite element simulation. Silicone dilator balloons of various wall thicknesses were fabricated.

In this dissertation, we study the stability of self-similar blow-up for two nonlinear wave equations: the equation of motion of the strong-field Skyrme model and the quadratic wave equation.

We begin by studying the stability of an explicitly known, self-similar solution of the equation of motion of the strong-field Skyrme model in the lowest energy supercritical dimension. This model originates from the Skyrme model which is itself a quasilinear modification of wave maps into a sphere. The strong-field Skyrme model restores the scaling invariance not present in the Skyrme model which allows for the existence of self-similar solutions. This equation is a semilinear wave equation that is, in particular, nonlinear in the derivatives of the unknown. As a consequence, standard techniques for establishing linear stability of this solution do not apply. Via application to a toy model, we present techniques that will be used to establish linear stability of this solution in a forthcoming paper.

Next, we study the stability of an explicitly known, self-similar solution of the quadratic wave equation in the lowest energy supercritical dimension. For radial data close to this self-similar blowup solution with blowup time $T=1$ adjusted along a one-dimensional subspace, we are able to prove convergence of the corresponding solution to another self-similar blowup solution with blowup time close to $T=1$. In particular, this result holds true in a region of spacetime that can be made arbitrarily close to the Cauchy horizon of the singularity. This will be achieved via hyperboloidal similarity coordinates.