SHAREOK Repository
Not a member yet
49261 research outputs found
Sort by
Synthesis and Characterizations of Lightweight, Highly Flexible Porous Polydimethylsiloxane (PDMS) Structures with Piezoresistive Strain Sensing Capabilities Using Solvent Evaporation Technique
Get PDFConsidering their specific structure, porous polymers have high adsorptive capacity, high flexibility, and high surface area compared to solid material. Highly flexible, deformable, and ultralightweight structures are required for advanced sensing applications such as wearable electronics and robotics. Hence, porous conductive polymer nanocomposites (CPNCs) have attracted significant attention for developing flexible piezoresistive sensors. In the first part of this dissertation, the application of solvent evaporation-induced phase separation (EIPS) as a promising technique to create porous polymer structures is investigated. The ternary polymer solution consisting of polymer/solvent/nonsolvent is explored. The ternary phase diagram is constructed, showing the thermodynamic equilibrium state for polymeric solutions consisting of Polydimethylsiloxane (PDMS)/Water/Tetrahydrofuran (THF). The possible composition path during the heat treatment and phase separation procedure is obtained. Moreover, the fabrication and characterization of porous PDMS structures developed by the EIPS technique are explored. The porous PDMS structures are formed by phase separation induced by removing the solvent, leading to water enriched droplets formation and removal during the stepping heat treatment procedure. The results show that the isolated pores with the adjustable pore size ranging from 330 µm to 1900 µm are obtained by tuning the water to the THF ratio. A wide range of elastic modulus ranging between 0.49-1.05 MPa was achieved without affecting the density of the porous sample by adjusting the solvent and non-solvent content in the solution.
The second part of the dissertation proposes a two-step phase separation synthesis protocol based on a ternary polymer solution. THF and Toluene with various mixing ratios are utilized as the solvent phase. Two distinct pore size distributions were observed in the cast PDMS sheets. The large pores with an average of 509 µm are formed during the first step of the phase separation after THF is evaporated. The second phase separation occurs later at higher temperatures by the evaporation of Toluene, resulting in much smaller pores with an average size of 28 µm. The experiments reveal that raising the THF/solvent ratio increases the large pore concentration, and the small pore density is reduced. The elastic modulus is varied between 0.64-0.95 MPa, indicating that the proposed method can create porous structures with a wide range of flexibility while keeping the density constant.
In the third part of the dissertation, a novel approach to synthesizing highly flexible and ultralightweight piezoresistive sensors is developed by combining the direct ink writing (DIW) and EIPS method. CPNC is prepared by dispersing carbon nanotubes (CNTs) at various concentrations in PDMS polymer, followed by mixing with solvent and nonsolvent phases to achieve a homogenous solution. Macroscale pores are established by designing structural printing patterns with adjustable infill densities, while the microscale pores are developed by EIPS of the deposited CPNC solution ink. Silica nanoparticles are utilized to modify the rheological properties of the DIW, evaluated by rheology experiments. A tunable porosity of up to 84% is achieved by controlling macroscale (infill density) and microscale porosity (polymer weight). The effect of macroscale/microscale porosity and printing nozzle sizes on the mechanical and piezoresistive behavior of the CPNC structures is explored. The electrical and mechanical testing demonstrate a durable, extremely deformable, and sensitive piezoresistive response without sacrificing mechanical performance. The flexibility and sensitivity of the CPNC structure are enhanced up to 900% and 67% with the development of dual-scale porosity. The application of the developed porous piezoresistive sensor for detecting human motion is also evaluated
Fusion Of Multiple Inertial Measurements Units And Its Application In Reduced Cost, Size, Weight, And Power Synthetic Aperture Radars
Get PDFPosition navigation and timing (PNT) is the concept of determining where an object is on the Earth (position), the destination of the object (navigation), and when the object is in these positions (timing). In autonomous applications, these three attributes are crucial to determining the control inputs required to control and move the platform through an area. Traditionally, the position information is gathered using mainly a global positioning system (GPS) which can provide positioning sufficient for most PNT applications. However, GPS navigational solutions are limited by slower update rates, limited accuracy, and can be unreliable. GPS solutions update slower due to the signal having to travel a great distance from the satellite to the receiver. Additionally, the accuracy of the GPS solution relies on the environment of the receiver and the effects caused by additional reflections that introduce ambiguity into the positional solution. As result, the positional solution can become unstable or unreliable if the ambiguities are significant and greatly impact the accuracy of the positional solution. A common solution to addressing the shortcomings of the GPS solution is to introduce an additional sensor focused on measuring the physical state of the platform. The sensors popularly used are inertial measurement units (IMU) and can help provide faster positional accuracy as the transmission time is eliminated. Furthermore, the IMU is directly measuring physical forces that contribute to the position of the platform, therefore, the ambiguities caused by additional signal reflections are also eliminated. Although the introduction of the IMU helps mitigate some of the shortcomings of GPS, the sensors introduce a slightly different set of challenges. Since the IMUs directly measure the physical forces experienced by the platform, the position is estimated using these measurements. The estimates of position utilize the previously known position and estimate the changes to the position based on the accelerations measured by the IMUs. As the IMUs intrinsically have sensor noise and errors in their measurements, the noise errors
directly impact the accuracy of the position estimated. These inaccuracies are further compounded as the erroneous position estimate is now used as the basis for future position calculations. Inertial navigation systems (INS) have been developed to pair the IMUs with the GPS to overcome the challenges brought by each sensor independently. The data provided from each sensor is processed using a technique known as data fusion where the statistical likelihood of each positional solution is evaluated and used to estimate the most likely position solution given the observations from each sensor. Data fusion allows for the navigation solution to provide a positional solution at the sampling rate of the fastest sensor while also limiting the compounding errors intrinsic to using IMUs. Synthetic aperture radar (SAR) is an application that utilizes a moving radar to synthetically generate a larger aperture to create images of a target scene. The larger aperture allows for a finer spatial resolution resulting in higher quality SAR images. For synthetic aperture radar applications, the PNT solution is fundamental to producing a quality image as the range to a target is only reported by the radar. To form an image, the range to each target must be aligned over the coherent processing interval (CPI). In doing so, the energy reflected from the target as the radar is moving can be combined coherently and resolved to a pixel in the image product. In practice, the position of the radar is measured using a navigational solution utilizing a GPS and IMU. Inaccuracies in these solutions directly contribute to the image quality in a SAR system because the measured range from the radar will not agree with the calculated range to the location represented by the pixel. As a result, the final image becomes unfocused and the target will be blurred across multiple pixels.
For INS systems, increasing the accuracy of the final position estimate is dependent on the accuracy of the sensors in the system. An easy way to increase the accuracy of the INS solution is to upgrade to a higher grade IMU. As a result,
the errors compounded by the IMU estimations are minimized because the intrinsic noise perturbations are smaller. The trade-off is the IMU sensors increase in cost, size, weight, and power (C-SWAP) as the quality of the sensor increases. The
increase in C-SWAP is a challenge of utilizing higher grade IMUs in INS navigational solutions for SAR applications. This problem is amplified when developing miniaturized SAR systems. In this dissertation, a method of leveraging the benefits of data fusion to combine multiple IMUs to produce higher accuracy INS solutions is presented. Specifically, the C-SWAP can be reduced when utilizing lower-quality IMUs. The use of lower quality IMUs presents an additional challenge of providing positional solutions at the rates required for SAR. A method of interpolating the position provided by the fusion algorithm while maintaining positional accuracy is also presented in this dissertation.
The methods presented in this dissertation are successful in providing accurate positional solutions from lower C-SWAP INS. The presented methods are verified in simulations of motion paths and the results of the fusion algorithms are evaluated for accuracy. The presented methods are instrumented in both ground and flight tests and the results are compared to a 3rd party accurate position solution for an accuracy metric. Lastly, the algorithms are implemented in a miniaturized SAR system and both ground and airborne SAR tests are conducted to evaluate the effectiveness of the algorithms. In general, the designed algorithms are capable of producing positional accuracy at the rate required to focus SAR images in a miniaturized SAR system
Effects of water and aluminum distribution on catalytic performance of zeolites
Get PDFZeolites are used in numerous industrially relevant reactions such as cracking, isomerization, and alkylation. The activity of Brønsted acid sites contained within the microporous zeolite channels might be influenced by the location and resulting local confining environment that stabilizes reaction intermediates and transition states. The presence of active sites nearby and extra-lattice species may modify the environment surrounding active sites, which have been proposed to alter reaction rates significantly. Thus, understanding the effect of these factors on the reactivity of zeolites is essential for the design and synthesis of solid acid catalysts to improve their catalytic performance.
It is well-known that extra-framework Al species generated due to the exposure of zeolites to water at high temperatures can significantly modify the catalytic reactivity of neighboring Brønsted acid sites. Hydrothermal treatment and steaming might lead to the generation of synergistic sites between Brønsted acid sites and extra-framework Al species with high activity for alkane cracking reaction. The generation of these synergistic sites is strongly influenced by the formation, diffusion, and stabilization of extra-framework Al species inside the zeolite pores. Thus, this dissertation aims to reveal the influence of water and other structural properties of zeolites, including the density and the distribution of framework and non-framework Al species in the generation of highly active sites that regulate the catalytic performance of catalysts. In particular, newly developed treatment methods by pulsing water are employed to decouple the rate enhancement due to the generation of highly active sites without the hydrolysis of framework Al sites. The experiment results combined with Density Functional Theory calculations show that cations such as sodium and calcium prefer to exchange with protons associated with highly active sites in zeolites. These cations inhibit the generation of these sites under water treatment. This approach allows quantifying the number of highly active sites and accesses the activation energies for cracking reactions on different types of active sites. Various pre-treatments of catalysts are conducted to modify the cracking rate via enhancement of mobility of extra-framework Al species inside zeolite pores or transformation of these species leading to the generation of new actives sites. Conclusions regarding the generation of highly active sites in MFI zeolite are expanded to other zeolite topologies (FAU, BEA, MOR, MEL, FER, and TON) to understand the impact of confinement and topologies on the reactivity of the catalyst
Engineering a peptide-based tool for biomedical applications
Get PDFNumerous technological and scientific advancements have been developed by the structural organization and functional capabilities of natural materials. A field known as "biomaterials" focuses on adapting engineering concepts found in biological models to create materials that can solve enduring issues in the biomedical engineering field. The fundamental molecules in a living organism are comprised of proteins. Protein structures are guided by combined and complex intermolecular interactions of peptides which ultimately influence the functionality of proteins. Synthetic engineering approaches of peptides can overcome the limitations of the complexity of protein intermolecular interactions and provide scalable technological solutions.
In the current dissertation, an engineering platform called CoOP (co-assembled oppositely charged peptides) was introduced and studied to understand the complex intermolecular interactions of proteins. Inspired by naturally found amyloid-beta (Ab) protein, a hexapeptide framework was designed to determine the effect of pi- stacking, hydrophobic and electrostatic interactions. By using computational and experimental approaches, this unique framework showed the importance of electrostatic interactions to initiate peptide assembly and enhanced stability due to hydrophobic interactions. The usability of this framework was first tested by changing the hydrophobic interactions. Then, assembly kinetics and structural organizations were studied depending on hydrophobicity indexes of amino acids. It was found that the highest hydrophobicity in the framework called [II], formed by co-assembly of KFFIIK and EFFIIE, resulted in the fastest assembly kinetics, showed the most organized secondary structure and similar physical properties as in Ab protein. Given that there is a strong correlation between different aggregated states (fibrillar or globular aggregates) and toxicity of Ab, [II] a platform is provided to study and model these aggregated states. Similar to Ab, oligomeric and fibrillar forms of [II] resulted in a difference in cell membrane damage. However, unlike Ab, [II] platform was implemented to modulate the aggregation where each aggregated state provided different toxicity levels depending on biophysical features. A change in aggregation had control over cell membrane damage, leading to differential and synergistic release of immune system-related molecules. This approach was tested with model antigen Ovalbumin, and antigen-specific antibody production was achieved based on aggregation kinetics. Furthermore, a change of aggregation of [II] was applied to the prophylactic tumor vaccine application, which shows the potential of system for cancer-related applications.
Based on the aggregation kinetics, an engineering platform, CoOP, can be applied to correlate structural changes with a biological effect. In this thesis, biological effect is limited based on the applications related to cell membrane damage. However, CoOP provides the discovery of new peptides and functionalities with an understanding of intermolecular interactions
Track-Initiated Beam Spoiling for Improved Tracking with Digital Phased-Array Radars
Get PDFRadar systems have become highly dynamic with the advancements in all-digital radar architectures. All-digital radar architectures introduce the potential for dynamic beamforming. This thesis will detail the fundamentals that are the foundation of radar signal processing (RSP) and modeling a digital phased array radar. This thesis will detail the techniques used for digital beamspoiling. The intentional beamspoiling is intended to improve the trackers’ ability to track a target continuously. When a high-speed target falls out of a beam due to a maneuver, the radar will spoil the transmit beam illuminating a wider scene. The wider illuminated scene allows for a higher likelihood of accurately detecting the target, allowing the tracker to track the target continuously. This thesis will discuss the theory and application of the trackers used in the simulation. With the beamspoiling and trackers, this thesis will analyze the ability of an all-digital phased array to track a target utilizing dynamic beamforming to improve the tracking performance. Finally, it will detail the improvement of the trackers’ ability to track when utilizing beamspoiling for specific situations, allowing the radar to track targets for a more extended time. The results varied based on the amount a transmit beam was spoiled due to the loss in SNR that naturally occurs from the decrease in power density
A Typology of Local and State Government Responses to Racism: A Case of Anti-Asian Hate in the COVID-19 Pandemic
Get PDFWe examine local and state government responses to anti-Asian hate during the initial months of the coronavirus (COVID-19) pandemic in the United States. Formal state and municipal government statements and websites were examined for fifty states and 104 of the largest municipalities using critical discourse analysis and racial formation theory to understand how government agencies racialized Asian Americans and reacted to their responsibility to address racism. We develop a typology of racist, race-neutral, and anti-racism to categorize the responses. Government statements are important for planners because they affect resident safety and willingness to report hate crimes.YesThis is an Accepted Manuscript of an article published by SAGE in the Journal of Planning Education and Research, Copyright © 2022 C. Aujean Lee & John C. Arroyo DOI: https://doi.org/10.1177/0739456X221084592
Molecular Divergence with Major Morphological Consequences: Development and Evolution of Organ Size and Shape
Get PDFUnderstanding the causes of the morphological diversity among organisms is a topic of great interest to evolutionary developmental biologists. Although developmental biologists have had great success in identifying the developmental mechanisms and molecular processes that specify organ size and shape within species, only relatively recently have the molecular tools become available to study how variation in these mechanisms gives rise to the phenotypic differences that are observed among closely related species. In addition to these technological advances, researchers interested in understanding how molecular variation gives rise to phenotypic variation have used three primary strategies to identify the molecular differences underlying species-specific traits: the candidate gene approach, differential gene expression screens, and between-species genetic mapping experiments. In this review, we discuss how these approaches have been successful in identifying the genes and the cellular mechanisms by which they specify variation in one of the most recognizable examples of the evolution of organ size, the adaptive variation in beak morphology among Darwin’s finches. We also discuss insect reproductive structures as a model with great potential to advance our understanding of the specification and evolution of organ size and shape differences among species. The results from these two examples, and those from other species, show that species-specific variation in organ size and shape typically evolves via changes in the timing, location, and amount of gene/protein expression that act on tissue growth processes.YesThis is the accepted manuscript version of the following article: Masly, J. & Azom, M. (2022). Molecular divergence with major morphological consequences: Development and evolution of organ size and shape. Essays in Biochemistry, 66 (6). https://doi.org/10.1042/EBC20220118
