It is well known that real op-amps do not share most of the desirable characteristics of an ideal one, particularly those of gain and output impedance. When presented with a capacitive load, such as a MOSFET or ADC, feedback in an op-amp circuit can quickly become unstable. This thesis studies and characterizes an op-amp’s output impedance and how its interaction with this type of load creates a parasitic pole which leads to instability. Applying ideas from feedback control theory, a model for studying the problem is developed from which a generalized method for compensating the undesirable circumstance is formulated. Even in a zero-input state, many real op-amps driving capacitive loads can experience unforced oscillations. A case study is performed with three commonly used devices. First, the output impedance is determined by its dependence on the unity-gain bandwidth, load capacitance, and oscillation frequency. It is fitted into a second-order feedback control model that allows for an analytical study of the problem. It is then shown that a carefully designed passive network can be introduced between the load and op-amp to obtain a properly damped system free of oscillation and well-behaved. Using a shunt resistor is a known and commonly used method for lowering an op-amp’s output impedance to gain stability. This work considers the converse addition of a series capacitor to instead lower the load capacitance seen by the op-amp, a seemingly complementary method that achieves the same goal. A generalized, composite compensation method is developed that uses both the shunt resistor and series capacitor– a strategy not yet found in literature. Relevant formulas for damping ratio and natural frequency are derived that allow the design of a passive compensation network. Furthermore, tradeoffs between compensation, voltage swing, current consumption, and power usage are considered. An emphasis is placed on comparing simulated versus real circuits to highlight the fact that any problem is much worse in real-life than in a simulation. SPICE models and programs aim to de-idealize certain device characteristics, but often cannot account for environmental conditions and manufacturing variance. Thus, an importance is placed on experimental verification guided by simulations.

<p>The goal of this project was to develop part of the environment that would allow the creation of distributed applications in ACT++. ACT++ is a programming framework in which concurrent object-oriented programs can be written in C++. The concurrent objects in ACT ++ are called actors. Specifically, the project is concerned with the development of a communication infrastructure that configures a collection of heterogeneous machines for use in the distributed version of ACT++.</p> <p> A utility, "ActorControl," was implemented through which the user can specify how ACT ++ is to run on each of the nodes by means of a configuration file. The "ActorControl" utility starts a process on each of the nodes specified in the configuration file and establishes TCP socket based connections among all of them. To simplify the communication between the different nodes, a special type of actor called an interface actor is used. Instead of issuing communication requests directly to sockets, a request is directed to an interface actor that is responsible for that socket. A related project is concerned with the problems of creation, destruction and invocation of the methods on the remote machine.</p> <p> Thus the project consists of two parts. The first part is the implementation of the "Actor Control" utility that establishes socket connections among all the nodes participating in the distributed ACT ++. The second part is the implementation of the interface actors that are present at each end of the connection between any pair of machines.</p> / Master of Science

Ligand-activated signal transduction is a process critical to cell survival and function as it serves as a means of communication between the cells and their environment. Endocytosis is generally thought to down-regulate incoming signals by reducing the surface availability of receptors. However, increasing evidence in many systems suggests a notion which is referred to as the „signalling endosome" hypothesis - that endocytosis can also actively contribute to signalling apart from clearance of activated receptors and thereby attenuation of signalling. The functional aspect of signalling endosomes has been well-characterized in several pathways including RTK and TGF-β signalling. There are, however, various other signalling pathways where the active mechanism of endocytotic regulation is yet to be understood. In this study, we probe this aspect in the cytokine signalling system, where the receptors are known to internalize but the significance of such internalization and precise mechanism is unclear. My thesis aims to elucidate the function and molecular details of internalization of cytokine receptor using interleukin-4 receptor (IL-4R) signalling as a model. IL-4 and IL-13 ligands can induce assembly of three distinct complexes: IL4 induced IL-4Rα – IL-2Rγ (type I), IL-4 induced IL-4Rα – IL-13Rα1 (type II) or the IL-13 induced IL-13Rα1-IL-4Rα (type II). The formation of any of these complexes triggers signalling through the JAK/STAT pathway. However, models of how the oligomerization of the transmembrane receptors and activation takes place are very diverse and lack a clear molecular and biophysical understanding of the underlying receptor dynamics. Previous results of the lab had shown that the affinities between subunits are low, precluding complex formation at the plasma membrane at physiological concentrations. In addition, IL-4R subunits localize in to endosomal structures adjacent to the plasma membrane. It had already been shown that the shared IL-4R subunit IL-2Rγ is internalized by a specific, actin dependent, Rac1/Pak1 regulated endocytosis route in the IL-2 context. We could show that pharmacological suppression of this endocytosis pathway also prevented IL-4 induced JAK/STAT signalling, placing endocytosis upstream of signalling. Here I show using immuno-EM techniques that these endosomal structures are multivesicular bodies. Importantly, I could show that receptor subunits are highly enriched in the limiting membrane of these endosomes relative to the adjacent plasma membrane. Using quantitative loading assays I could furthermore demonstrate that this enrichment is achieved by constitutive internalization of receptors from the cell surface into cortical endosomes. The trafficking kinetics of the receptor subunits is independent of ligand occupancy. Pharmacological inhibition shows that receptors and ligand traffic via the previously identified Rac1/Pak1 pathway. Finally, Vav2 was identified as a candidate Guanine Exchange Factor (GEF) that may regulate Rac1 activity and thereby control the actin polymerization cascade driving IL-4R endocytosis. Immunoprecipitations showed that Vav2 interacts both with the cytoplasmic tail region of the receptors and the receptor associated 2 kinase JAK3. Vav2 may thus couple the receptor/JAK complexes to the Rac1/Pak1 mediated endocytosis route. Taken together, our results suggests that stable „signalling endosomes‟ adjacent to the plasma membrane act as enrichment centres, where ligand and receptor concentrations are locally increased by constitutive trafficking. The confined environment of the endosome then compensates for the weak affinities between the ligand and receptor and facilitates ligand-mediated receptor dimerization. Importantly, overexpression of both type II IL-4R subunits renders signal transduction resistant to endocytosis inhibition, strongly suggesting that the critical factor effecting signalling is sufficient concentration, which the endosomes facilitate achieving. The endosomes are thus dispensable as signalling scaffolds when the receptors are in sufficient concentration, where activated receptors could interact with downstream pathway components. Endocytosis thus provides a crucial means for the signalling process to overcome the thermodynamic hurdles for receptor oligomerization. In conclusion, our data propose a novel, purely thermodynamic role of endosomes in regulating cytokine receptor signalling not seen in any other signalling pathway.

The number of unanswered questions on Community based Question Answering (CQA) websites has increased significantly due to the rising number of duplicate questions. This is a serious problem, one that could lead to the decline of such beneficial websites. This thesis presents novel avenues that use gaze tracking technology and behavioral testing to tackle this problem. Based on prior studies on web search behaviors, we assumed that adding contextual information (snippets) to proposed related questions displayed on the `Ask a Question' page of the CQA website iFixit would improve the asker experience and reduce their tendency to post a new duplicate question. The first lab experiment where this web page was redesigned and compared to the original one was conducted on 8 participants. Results confirmed that participants were more likely to find an answer to their question on the redesigned page. A second experiment, conducted remotely and on a larger sample of 74 participants, aimed to discover strategic attributes that increase the perceived similarity of question pairs. These attributes were used in the third lab experiment (20 participants) to redesign and assess the snippets from Experiment 1. Results indicated that snippets containing `symptom(s)' and `cause(s)' attributes constitute an incremental improvement over basic snippets: they are perceived as slightly more relevant and require significantly less gaze fixations on the asker's part.

The development of appropriate technologies aimed at improving the livelihoods of people living in poverty has been a focal area of international aid. These technologies can have a transformative impact on economic growth and individual health when designed and implemented properly. Long-term usage and performance of these products are difficult to measure accurately through self-reporting, and the use of low-cost sensors allows researchers and designers to better assess their overall impact. The first part of the thesis presents a methodology for implementing sensor technologies in lowresource settings. The second part of the thesis presents the design of a novel sensorbased data collection system that was developed for design and impact research. The third part of this thesis presents three case studies where this system is used to evaluate wheelchairs, improved cookstoves, and evaporative coolers. The wheelchair case study in Indonesia compares the performance of different wheelchairs ranging in cost from $100 to $300 and finds little variation between improved wheelchairs in frequency of use and distance traveled. All of the improved wheelchairs show significant benefits when compared to hospital style chairs. The improved cookstove case study demonstrates the effectiveness of using a household air pollution monitor in combination with a stove use monitor to identify cooking events and measure cookstove adoption in a research pilot in India. Particulate matter concentrations in all of the households using improved cookstoves were significantly higher than World Health Organization (WHO) recommended levels. The evaporative cooling case study demonstrates that clay pot coolers are effective at keeping fresh produce more than 5°C cooler than ambient temperatures in the hottest months of the year in Mali. The final part of this thesis examines the ethical challenges that may arise from incorporating sensors for field research and best practices for addressing some of these concerns. / Ph.D.

Indiana University-Purdue University Indianapolis (IUPUI) / Electronic health records collect an enormous amount of data about patients. However, the information about the patient’s illness is stored in progress notes that are in an un- structured format. It is difficult for humans to annotate symptoms listed in the free text. Recently, researchers have explored the advancements of deep learning can be applied to pro- cess biomedical data. The information in the text can be extracted with the help of natural language processing. The research presented in this thesis aims at automating the process of symptom extraction. The proposed methods use pre-trained word embeddings such as BioWord2Vec, BERT, and BioBERT to generate vectors of the words based on semantics and syntactic structure of sentences. BioWord2Vec embeddings are fed into a BiLSTM neural network with a CRF layer to capture the dependencies between the co-related terms in the sentence. The pre-trained BERT and BioBERT embeddings are fed into the BERT model with a CRF layer to analyze the output tags of neighboring tokens. The research shows that with the help of the CRF layer in neural network models, longer phrases of symptoms can be extracted from the text. The proposed models are compared with the UMLS Metamap tool that uses various sources to categorize the terms in the text to different semantic types and Stanford CoreNLP, a dependency parser, that analyses syntactic relations in the sentence to extract information. The performance of the models is analyzed by using strict, relaxed, and n-gram evaluation schemes. The results show BioBERT with a CRF layer can extract the majority of the human-labeled symptoms. Furthermore, the model is used to extract symptoms from COVID-19 tweets. The model was able to extract symptoms listed by CDC as well as new symptoms.

Crystallization is a key unit operation in the fine chemical and pharmaceutical industries, many of which employ batch stirred vessels for crystallization. Although using stirred vessels for crystallization has advantages such as better mixing and faster cooling, one of the disadvantages is that due to the presence of mechanical parts in the vessel such as baffles, impeller etc., crystals break up while stirring and generate unwanted secondary nucleation. This process contributes to a wide crystal size distribution with a smaller than desired mean crystal size. For studying crystal breakage phenomenon, experimentalists choose to use nonsolvents for crystal breakage experiments to isolate breakage from simultaneously occurring phenomena such as Ostwald-ripening, aging and agglomeration. Although performing experiments in non-solvents eliminates other phenomena and helps isolate breakage, the results can not always be correlated to saturated solutions due to density and viscosity differences between the two conditions. In this research, the effects of Ostwald ripening, aging and agglomeration on the crystal size and shape distributions are quantitatively measured. Micro and macro scale experiments were performed in both non-solvents and saturated solutions and the results were compared to determine the effects. Both in situ focused beam reflectance method (FBRM) and off-line analyses were performed to characterize the crystal size distributions. Results from experiments show that there is significant difference between the breakage behavior of crystals in non-solvents and in saturated solutions, mplying significant impacts of Ostwald ripening, aging, agglomeration and dissolution in saturated solutions. Calculations using Zwietering correlation also show that the difference between the viscosities and densities in the two systems may also be a contributing factor to the difference in the breakage profiles. It was also found that growth rates of crystals can differ when they are subjected to stress and strain. In macroscale experiments, dissolution was found to have a significant impact on the crystal size distribution. Abrasion was found to be the dominating fracture mechanism for most systems. Extent of breakage and morphological changes were found to be dependent on stirring rates, suspension density, shape and hardness of crystals and the type of system.

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As UASs (Uncrewed Aerial System) are further integrated into operations, the need for on-board environmental perception and sensing is necessitated. An accurate and reliable creation of a 3D map resembling an aircraft's surrounding is crucial for accurate collision avoidance and path planning. Consumer UASs are now being equipped with sensors to fulfill such a requirement – but no system has been proven as capable of being fully relied upon. With many sensing options available, there are several constraints regarding size, weight, and cost that must be considered when developing a sensing solution. Additionally, the robustness of the system must not be diminished when moving to a system that minimizes size, weight, or cost. An analysis of different sensing technologies that small rotary-wing aircraft (below 25kg) can be outfitted with for collision avoidance is performed. Several sensing technologies are initially compared through technology analyses and controlled experiments. The topmost systems were then further integrated onto a small low-cost quadcopter for flight testing and data acquisition. Ultimately, a fusion between stereo vision imagery and radar was deemed the most reliable method for providing environmental data needed for collision avoidance. / Master of Science / As drones become further integrated in several industries, it is important that their operations are conducted in a safe manner. Most drones today have a limited ability to sense and react to the environment around them. This results in the risk of the drone colliding with people or obstacles such as buildings, trees, light poles, etc. Thus, an accurate and reliable creation of a 3D map resembling a drone's surrounding is crucial for collision avoidance. This would allow for the avoidance of people and obstacles during automated flights where the drone may encounter obstacles during flight. With many sensing options available, there are several constraints regarding size, weight, and cost that must be considered when developing a sensing solution. Additionally, the reliability of the system must be of the topmost priority to ensure safe operations. An analysis of different sensing technologies that small rotary-wing aircraft (below 25kg) can be outfitted with for collision avoidance is performed. Rotary-wing aircraft are a specific subset of drones that are capable of vertical takeoff, landing, and hover (i.e not planes). An analysis regarding the several sensing technologies was first conducted to select the three topmost solutions. These solutions were then integrated onto a small low-cost quadcopter for data collection and flight testing. Ultimately, a combination of stereo vision imagery and radar was deemed the most reliable method for collecting collision avoidance data.

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