<p>Breast cancer is the most common cancer among women, with effective treatments if the disease stays local. However, if the tumor metastasizes, patient outcomes are significantly reduced. Mesenchymal stem cells (MSC) have been shown to enhance metastasis by facilitating invasion and tumor outgrowth. MCF10A Ca1h cells, a mesenchymal-like cell line, have been shown to promote metastasis in a murine model and enhance the survival and proliferation of their epithelial counterpart (Ca1a) in coculture. We have established the presence of the classic MSC markers, CD90, CD105, and CD73, on the Ca1h cells and observe a decrease in the CD90⁺ population in the Ca1a and fibronectin knockdown Ca1h cells. To examine the effects of this decreased expression, a CD90 knockdown of Ca1h cells was created using lenti-viral transduction. A decrease in fibronectin levels was seen in the CD90 knockdowns, along with a change in morphological characteristics of the cells. To investigate the influence of a 3D microenvironment on cell phenotype, they were also cultured on fibronectin coated scaffolds and evaluated for CD44/CD24 expression. Lastly, the knockdowns were cocultured with the Ca1a cells in a 3D hydrogel to assess the impact of coculture on survival and proliferation. We found that the CD90 knockdowns take on epithelial-like characteristics and decrease survival of Ca1a cells in coculture. These findings suggest that CD90 is necessary to maintain a mesenchymal phenotype and could be used as a target for therapies to prevent metastasis. </p>

Effective collaboration in a team is a crucial skill. When people interact together to perform physical tasks, they rely on gestures to convey instructions. This thesis explores gestures as means to assess physical collaborative task understanding. This research proposes a framework to represent, compare, and assess gestures’ morphology, semantics, and pragmatics, as opposed to traditional approaches that rely mostly on the gestures’ physical appearance. By leveraging this framework, functionally equivalent gestures can be identified and compared. In addition, a metric to assess the quality of assimilation of physical instructions is computed from gesture matchings, which acts as a proxy metric for task understanding based on gestural analysis. The correlations between this proposed metric and three other task understanding proxy metrics were obtained. Our framework was evaluated through three user studies in which participants completed shared tasks remotely: block assembly, origami, and ultrasound training. The results indicate that the proposed metric acts as a good estimator for task understanding. Moreover, this metric provides task understanding insights in scenarios where other proxy metrics show inconsistencies. Thereby, the approach presented in this research acts as a first step towards assessing task understanding in physical collaborative scenarios through the analysis of gestures.

<p>Failure along rock discontinuities can result in economic losses as well as loss of life. It is essential to develop methods that monitor the response of these discontinuities to shear loading to enable prediction of failure. Laboratory experiments are performed to investigate geophysical techniques to monitor shear failure of a pre-existing discontinuity to detect signatures of impending failure. Previous studies have detected precursors to shear failure in the form of maxima of transmitted waves across a discontinuity under shear. However, those experiments focused on well-matched discontinuities. However, in nature, rock discontinuities are not always perfectly matched because the asperities may be weathered by chemical, physical or mechanical processes. Further, the specific shear mechanism of mismatched discontinuities is still poorly understood. In this thesis, the ability to detect seismic precursors to shear failure for various discontinuity conditions—well-matched (rough and saw-tooth), mismatched (rough), and nonplanar (discontinuity profile with a half-cycle sine wave (HCS))—was assessed. The investigation was carried out through a coupled geophysical and mechanical experimental program that integrated detailed laboratory observations at the micro- and meso-scales. Shear experiments on gypsum discontinuities were conducted to observe changes in compressional (P) and shear (S) waves transmitted across the discontinuity. Digital Image Correlation (DIC) was used to quantify the vertical and horizontal displacements along the discontinuity during shearing to relate the location and magnitude of slip with the measured wave amplitudes. </p> <p>Results from the experiments conducted on planar, well-matched rough discontinuities (grit 36 sandpaper roughness) showed that seismic precursors to failure took the form of peaks in the normalized transmitted amplitude prior to the peak shear stress. Seismic wave transmission detected non-uniform dilation and closure of the discontinuity at a normal stress of 1 MPa. The results showed that large-scale roughness (presence of a HCS) could mask the generation of precursors, as it can cause non-uniform closure/dilation along the fracture plane at low normal stress. </p> <p>The experiments on idealized saw-toothed gypsum discontinuities showed that seismic precursors to failure appeared as maxima in the transmitted wave amplitude and conversely as minima in the reflected amplitudes. Converted waves (S to P & P to S) were also detected, and their amplitudes reached a maximum prior to shear failure. DIC results showed that slip occurred first at the top of the specimen, where the load was applied, and then progressed along the joint as the shear stress increased. This process was consistent with the order of emergence of precursors, i.e., precursors were first recorded near the top and later at the center, and finally at the bottom of the specimen. </p> <p>Direct shear experiments conducted on specimens with a mismatched discontinuity did not show any precursors (in the transmitted amplitude) to failure at low normal stresses (2 MPa), while those precursors appeared at higher normal stresses (5 MPa). The interplay between wave transmission, the degree of mismatch, and the discontinuity’s micro-physical, -chemical and -mechanical properties was assessed through: (1) 3D CT in-situ Xray scans to quantify the degree of mismatch at various normal stresses; (2) micro-indentation testing, to measure the micro-strength of the asperities; and (3) Scanning Electron Microscopy (SEM) and Electron Xray Diffraction (EDX), to study the micro-structure and chemical composition of the discontinuity. The X-ray results showed that contact between asperities increased with normal stress, even when the discontinuity was mismatched. The results indicated that: (1) at 2 MPa, the void aperture was large, so significant shear displacement was needed to interlock and damage the asperities; and (2) the micro-hardness of the asperities of the mismatched discontinuity was larger than that of the well-matched discontinuity, which points to inducing less damage for the same shear displacement. Both mechanisms contribute to the need for larger shear displacements to the mismatched discontinuity asperities to cause damage, which is consistent with the inability to detect seismic precursors to failure. The experimental results suggest that monitoring changes in transmitted wave amplitude across a discontinuity is a promising method for predicting impending failure for well-matched rock discontinuities. Precursor monitoring for mismatched rock discontinuities seems only possible when there is sufficient contact between the two rock surfaces, which occurs at large normal stresses. </p>

<p>Increasing demand for higher power density in many applications such as Hybrid Electric Vehicles (HEVs) and renewable power generation has led to great technological advances in power electronics. To meet this increasing demand, a power semiconductor device needs to have low on resistance, increased switching speeds and reduced total system cost. Silicon (Si) power devices have been used for several decades but they are fundamentally limited by material properties. Silicon carbide (SiC) as a power semiconductor material offers superior electrical and thermal properties compared to silicon, which it can replace in a large spectrum of applications. Because of a lower critical electric field, drift regions in Si power transistors need to be much thicker and more lightly doped, which in turn increases the specific onresistance Ron,sp. To combat the drift resistance component for higher blocking voltages, superjunction MOSFETs for medium voltages and Si IGBTs for high voltages are used. Since IGBTs are bipolar transistors, they exhibit much higher switching energy losses than MOSFETs. The SiC MOSFET is an excellent candidate in the medium to high voltage range, which mainly targets the HEV market.</p><p><br></p><p>Due to their low channel mobility, SiC MOSFETs have not reached the theoretical limit below 1200 V where channel resistance is dominant. Planar DMOSFETs dominate the</p><p>commercial SiC market today because of higher yield and relatively simpler fabrication process, but trench MOSFETs can be made with a smaller cell area and thus lower Ron,sp. Due to lower cell-pitch and high integration density of trench-gate devices, they offer an opportunity to reduce the size and weight of HEV power control units by replacing IGBTs with MOSFETs. The single-trench UMOSFET was first reported in 1994 by CREE and the first oxide protected trench MOSFET in 1998 by Purdue. This structure inserts a grounded p-type region below the gate trench to protect the oxide in the blocking state. In 2012, Rohm Semiconductor reported a novel double-trench UMOSFET with separate gate and</p><p>field-protection trenches. In 2017, Infineon published their new trench UMOSFET, known as Cool-SiC, with high gate oxide reliability. In this work a deeply-scaled, fully-self-aligned trench MOSFET is fabricated and characterized. The innovative process described enables a record cell-pitch of 0.5 μm per channel, equivalent to a channel density 6Å~ higher than currently available commercial UMOSFETs.</p>

<p>Fabricating complex submicron 3D structures can be achieved by multi-photon lithography, especially two-photon lithography is commonly used to obtain precision and flexibility in printing sophisticated sub-micron 3D structures. Several disadvantages stemmed from a two-photon lithography experiment setup, including cost, the necessity of a large laboratory space to use a femtosecond laser and a high-order process. A two-step absorption is chosen instead of two-photon lithography as a primary excitation process achieving the same degree of quadratic optical non- linearity as two-photon lithography at a lower cost with a relatively compact laboratory size. The working mechanism of Two-step absorption is the following. Quadratic nonlinearity comes from radicals from excited triplet states photoinitiators. Ground states of photoinitiators get excited by the incident laser. Those excited singlet photoinitiators go through the intersystem crossing, becoming the ground triplet state of photoinitiators. There are two branches after the ground triplet states, especially for photoinitiator benzil molecules with the incident laser on. Either it becomes a radical without photons received from the incident laser or gets excited again to an excited triplet state by the incident laser. Those excited triplet-state photoinitiator molecules become radicals that occur in polymerization. However, those from the ground triplet states add linearity to polymerization. When it comes to multiple exposures, the linearity becomes problematic, especially outside the region and tails of the voxel. For example, suppose the intensity at two tails of the voxel is 1% relative to the maximum intensity at the focal point. In that case, the absorbed dose will be added up to the maximum intensity at the focal point when it comes to 100 exposures. Quadratic nonlinearity and linearity are jumbled together in the current two-step absorption process. In this work, optimization of photoinitiator concentration was conducted to reduce the linearity. Confined and high throughput 3D structure fabrications are achieved by controlling initiator depletion. Simulations are also developed with multi-physics models to compare with the empirical results.</p>

<p>Dielectric breakdown in gases is an important criterion for device reliability when designing various electronic devices such as sensors, medical plasma jets and fusion applications. As devices become smaller and more compact, microscale gap distances need to be considered and Paschen’s law, which dictates typical breakdown behavior when electron avalanche dominates, fails. The stronger electric fields for microscale gaps induce field emission, which generates additional electrons that further enhance the electric field at the cathode and the resulting secondary emission to reduce breakdown voltages below those predicted by Paschen’s law. Field emission is governed by the Fowler-Nordheim equation, which mathematically describes the quantum tunneling that occurs. Many studies have examined breakdown voltage in the Paschen’s and field emission regimes but recent theories have unified the two regimes for DC gas breakdown at microscale gaps [A. L. Garner, A. M. Loveless, J. N. Dahal, and A. Venkattraman (2020)]. However, although microwave and RF fields are used in many microelectronics systems and microplasmas, they have been less studied. This thesis derives a breakdown condition that unifies avalanche and field emission for RF fields. The derivation includes analysis of potential secondary emission representations for AC fields. The breakdown condition is then benchmarked to simulations that accounts for both avalanche and field emission for user-defined AC fields.</p> <p>We use a modified version of XPDP1, which is a one-dimensional in space and three-dimensional in velocity (1D/3v) particle-in-cell (PIC) code that incorporates field emission. The resulting breakdown depends on several parameters, most notably gap size d, pressure p and frequency f. We determine breakdown voltages in terms of d and pd scalings for 1-10 𝜇m gap distances, 10-1000 GHz frequencies, and 180-760 Torr pressures. Additional scalings that were studied include the work function, field enhancement factor, secondary emission, and ionization coefficients. PIC demonstrated that the breakdown voltage varied linearly with gap distance up to ~4 𝜇m from DC to 10 GHz for a secondary electron emission coefficient 𝛾𝑆𝐸=0.05. For DC fields, the breakdown voltage decreases with increasing gap distance; the breakdown voltage increases with increasing frequency, approaching linearly with increasing gap distance.</p>

<p>Advancements on flexible radiofrequency (RF) coils have been made to accommodate a variety of body sizes with great image quality and a comfortable imaging process. RF coils are magnetic field antennas for magnetic resonance imaging (MRI) that broadcast the RF signal to the patient and receive the returning signal to affect the image quality. The conventional neck RF coil is rigid and requires the patients to be in supine position. Due to its characteristics, the patients who have difficulties to move their neck experience an uncomfortable imaging process. The novel 4-channel neck RF coil is made of conductive silver thread embroidered on stretchable fabric to provide patients a more comfortable experience with lightweight and flexible materials. A wide range of neck sizes can be covered with the stretchable materials and great image quality can be acquired due to the RF coil positioned close to the source. The stretchable RF coil was built as non-overlapping 4 channels in zigzag stitch pattern and tested on a dielectric phantom, which was made to have the permittivity and conductivity of muscle at 128 MHz. The research can be extended to stretchable RF coils with more channels and different stitching patterns. It also has potential to be applied on joints such as wrist and ankle due to its flexibility to cover the curved surface. </p>

<p>The morphologies and growth behavior of Cu₆Sn₅ intermetallic compound (IMC) formed between Sn-based solder and large-grain polycrystalline Cu substrate were systematically investigated. Hexagonal Cu₆Sn₅ grains were observed to form at certain reflow condition, which matches well with the literature results for IMC growing on single crystal substrate. The kinetics of IMC growth was also investigated and different mechanisms were proposed for different evolution stages. It was observed that facet formation should be a growth shape rather than an equilibrium shape, and the orientation relationship between Cu and Cu₆Sn₅ was studied using scanning electron microscope (SEM) and Electron backscatter diffraction (EBSD), and were visualized on inverse pole figure. </p>

<p>The aim of the project is to collect empirical data on contact line motion in vibrating tanks under zero-gravity (zero-g) conditions. This study is particularly focused on the behavior of current green propellants, which have a high contact angle compared to traditional stores like water. As a result, the non-linear contact line and angle is expected to have a significant impact on zero-g behavior. The thesis focuses on the dynamic experiment of developing an experimental payload designed to fly on Blue Origin\textquotesingle s New Shepherd suborbital flight. The data collected from this experiment will provide a benchmark case for developers of zero-g fluid dynamics simulations to compare or improve their simulation results. The results will also be useful for testing non-linear hysteresis contact line simulations.</p> <p><br></p> <p>The design of the experiment mainly focuses on conducting oscillatory motion in zero gravity to observe the contact line at varying speeds. Two different liquids are intended to be tested on the same payload. The liquid is to be filled so that the free surface has a height of 1 inch, and the vibration amplitude is to be 0.1 inches. The liquid chosen closely simulates the current green propellants under development or other poorly-wetting liquids. The purpose of each of the components used in the experiment is justified with respect to the given flight design constraints, along with how the constraints impacted the experiment. The experiment is designed to sustain the forces in case of hard landing during the flight and autonomous control of motion. The experiment is staged to be ready for flight on the New Shepherd, and any future works are mentioned. </p> <p><br></p> <p>To meet these constraints, the experimental payload is designed with a variety of components, each chosen for its ability to perform under the given conditions. The payload includes a custom-built system, which generates the oscillatory motion necessary to observe the contact line behavior. The system is designed to be compact and lightweight, yet robust enough to withstand the forces of launch and landing. In addition, the payload includes a custom-built tank designed to hold the liquids being tested. The study of contact line motion in vibrating tanks under zero-g conditions is important in understanding the behavior of liquids in space. This study will provide crucial data that will help in the development of more accurate fluid dynamic simulations for future space missions.</p>

<p> The use of smart devices such as smartphones, tablets, and laptops skyrocketed in the last decade. These devices enable ubiquitous applications for entertainment, communication, productivity, and healthcare but also introduce big concern about user privacy and data security. In addition to various authentication techniques, automatic and immediate device locking based on user leaving detection is an indispensable way to secure the devices. Current user leaving detection techniques mainly rely on acoustic ranging and do not work well in environments with multiple moving objects. In this paper, we present mmLock, a system that enables faster and more accurate user leaving detection in dynamic environments. mmLock uses a mmWave FMCW radar to capture the user’s 3D mesh and detects the leaving gesture from the 3D human mesh data with a hybrid PointNet-LSTM model. Based on explainable user point clouds, mmLock is more robust than existing gesture recognition systems which can only identify the raw signal patterns. We implement and evaluate mmLock with a commercial off-the-shelf (COTS) TI mmWave radar in multiple environments and scenarios. We train the PointNet-LSTM model out of over 1 TB mmWave signal data and achieve 100% true-positive rate in most scenarios. </p>