DSpace@RPI
DSpace@RPI is a repository of Rensselaer Polytechnic Institute's theses and dissertations which are available in digital format, largely from 2006 to present, along with other selected resources.
Recent Submissions
Item Design and simulation of cryogenic systems and calibrations techniques for the nexo neutrinoless double beta decay experiment(Rensselaer Polytechnic Institute, Troy, NY, 2024-08)This dissertation presents a study of the dynamics of cryogenic plants and the implementation of radon injection as a calibration strategy for the nEXO neutrinoless double beta decay experiment. The research focused on three main areas: the design and optimization of cryogenic systems, the simulation of \textsuperscript{220}Rn progeny propagation in a xenon flow, and the development of a laboratory test stand to validate these simulations. Simulations of the EXO-200 xenon plant were developed using the Aspen engineering software suite, validating the modeling strategy for application to the nEXO refrigerant plants. Performance evaluations, conducted with Aspen Plus, included steady-state simulations and dynamic modeling of dual-stage heater and condenser systems based on those in EXO-200. These simulations assessed their ability to regulate pressure and temperature during and after transient upset conditions. Ramped pump speed changes were simulated to reflect typical operational variations, with both heater and condenser models utilizing PID controllers for temperature and pressure regulation. The dual-stage heater mitigated temperature excursions to 0.2 K while ensuring full xenon evaporation, achieving a temperature differential of just 0.001 K. The condenser model limited pressure excursions to $\Delta P = 6.21 \times 10^{-4}$ bar, well within the 0.35 bar TPC wall limit. Power consumption for the simulated condenser and heater closely matched theoretical values, confirming the reliability of this simulation strategy. Additionally, data from the LXTS slow control system was used to validate the modeling strategy, further demonstrating its applicability to simulating heat exchanger dynamics in xenon recirculation plants. Models were then created of the nEXO Novec-7000 refrigerant system to explore the viability of different operating conditions and plant configurations. These analyses revealed that using 1-inch piping for the entire Novec-7000 plant was inadequate for meeting the circulation needs of the nEXO system. Moreover, the ``top deck'' configuration, where the xenon circulation pump is placed above the cryostat, was found to be unsuitable due to cavitation issues in the pump caused by insufficient inlet pressure. The effect of incorporating valves with varying flow coefficients was analyzed, ruling out the use of valves with flow coefficient $C_V=13.2$, while indicating that valves with $C_V=26.5$ work under a variety of configurations. Results of these simulations allowed estimates to be placed on the Novec-7000 pump inlet pressure under these different system conditions, specifying which configurations ensure recirculation of refrigerant and which do not. For the unsuitable ``top deck'' configuration, required Novec-7000 vessel operating pressures to prevent recirculation pump cavitation are instead presented. A radon injection simulation model was developed in this study to leverage the entire decay chain of $^{220}$Rn down to stable $^{208}$Pb to understand the flow of calibration radioisotopes through the nEXO xenon plant. Statistical analyses, including z-tests, p-tests, and Kolmogorov-Smirnov tests, demonstrated the infeasibility of using late-chain isotopes for determining velocity and diffusion coefficients in a small-scale test stand. Fitting procedures applied to the model using krypton tracer data yielded best-fit velocity and diffusion parameters, which were $v = 0.635 \pm 0.005 \, \text{m/s}$ and $D = (2.0 \pm 1.9) \times 10^{-2} \, \text{m}^2/\text{s}$, respectively. These parameters were then used to estimate radon arrival times in the nEXO radon injection design, with an estimated arrival time to the TPC of $128 \pm 7_{\text{stat}} \pm 16_{\text{geom}}$ s in agreement with the calculated upper limit of 145 s. The developed simulation code will be made available to the collaboration, ensuring its utility in ongoing and future research. A concentration vs. time trend was determined for an updated TPC model with four outlet lines and a tangentially oriented inlet line using SolidWorks flow simulation. These results were coupled with outputs from the radon injection simulation code to generate a plot of activity vs. time in the TPC. From this plot, it is determined that activity in the TPC reaches a local maximum at 0.08 days, after which point total activity drops to 10\% after 1.41 days and to 1\% after 2.67 days. The updated TPC model is shown to promote effective mixing similar to a previously studied model with tangential inlet and outlet lines called Orientation 6. In contrast, Orientation 2, with radially positioned supply and return lines, demonstrates less effective mixing. Activity trends were determined for each of these configurations, with those encouraging better mixing correlating to higher activites in the TPC. These trends confirm that calibration with $^{220}$Rn is feasible using a standard 20 kBq source as 44\% of the $^{220}$Rn isotopes emanated from the calibration source reach the TPC. A laboratory test stand was constructed to experimentally validate the radon injection simulation model in a dual-phase system. This test stand was designed to be sensitive to xenon scintillation produced by alphas emitted along the $^{220}$Rn decay chain. The characterization of the QDrive and PT-100 components was detailed, ensuring their reliability for experimental use. Helium leak testing was performed to guarantee the integrity of the system, with a global leak rate of $8.37 \times 10^{-10}$ mbar L/s placed on the test stand, with no detection of localized leakage. The leak rate is below the approximate threshold of $\sim 10^{-7}$ mbar L/s which indicates that xenon leakage is dominated by molecular rather than bulk fluid flow, confirming the system's integrity and suitability for commissioning with xenon \cite{pfeiffer2013leak}. Cooling of the xenon condenser was initially achieved with a copper braid in the original design, which was upgraded to a custom thermal link with enhanced cooling capacity calculated to be 67 W for 40-Kelvin temperature differentials across the link. Custom data acquisition software was developed to support the robust operation of the test stand, facilitating efficient data collection and analysis. Argon was studied as a potential inexpensive proxy to xenon for research and development purposes, which necessitated exploring strategies to shift its short-wavelength scintillation light to wavelengths detectable by the photodiode in the test stand. Tetraphenyl butadiene (TPB) spectroscopy studies were conducted to explore the wavelength-shifting efficiency of TPB dissolved in ethanol and toluene for this application. The studies indicated that TPB dissolved in toluene showed markedly higher degrees of wavelength shifting compared to TPB dissolved in ethanol, with TPB coating thickness found to correlate to wavelength shifting efficiency. The TPB-coated slides exhibited flaking over time, making them unsuitable for incorporation in a high purity experimental appartus, indicating that future work must be done to refine the deposition strategy before this material can be used in the test stand.Item Advances in the theory, implementation, and application of mechanistic models in downstream bioprocessing of monoclonal antibodies(Rensselaer Polytechnic Institute, Troy, NY, 2024-07)Mechanistic models are powerful tools for process characterization and optimization. Although their usage in academia is common, their widespread use in the biopharmaceutical industry is hindered by several factors. First, derivation of first-principles models is very difficult, sometimes due to insufficient understanding of the underlying phenomena or limitations in the experimental techniques or instruments. Deriving empirical models also requires instinct and experience in relevant fields. Second, there are many unit operations involved in the production process. There is a lack of a powerful, yet flexible and shared platform to perform these simulations. Third, the workflow for using these developed models is not clear. Applying these models in an already established industry workflow and interpreting the results require advanced knowledge in multiple disciplines. In this thesis, we aim to address these challenges, particularly for protein A chromatography and precipitation capture purification operations in the downstream bioprocessing of monoclonal antibodies. In protein A chromatography, we derived a novel isotherm model and implemented it with the general rate model in well-known chromatography modelling software packages including GoSilico and CADET. Experiments are designed and performed to demonstrate that the model is compatible with an array of resins, mAbs and experimental conditions. We show that the model can be easily trained and that it offers excellent chromatogram predictions. We further established an intuitive workflow showing how to use the model for process development. Beyond these practical applications, we also used models of varying complexity to understand the heterogeneous surface properties of the protein A resins and tried to determine what compromises are needed when applying complicated semi-empirical and first-principles mechanistic models to practical situations where speed, simplicity and accuracy are required simultaneously. In precipitation, we focused on the solution, implementation and benchmarking of a mechanistic model for solid particle formation kinetics called the population balance model in the free and open-source software package CADET. CADET already supports the solution of many models for other unit operations, and introducing population balance model to the CADET family drives integrated in silico process development. In addition to this, we also applied the model to characterize antibody precipitation kinetics: experiments were conducted and a workflow was established to apply the model. The results were further used to inform future process development directions.Item A batch technique for connecting multimodal ligand chemistry to chromatographic separability(Rensselaer Polytechnic Institute, Troy, NY, 2024-08)This dissertation describes the development and utilization of a high-throughput parallel batch adsorption screen with sequential salt step increases to rapidly generate protein elution profiles for multiple resins at different pHs using a protein library. The chromatographic ligand libraries screened using this technique include commercial resins, Bio-Rad prototype small molecule resins, custom synthesized peptide-based ligands, and Solventum prototype membrane adsorbers. The chromatographic sets used in this work includes single, multimodal anion-exchange (MMA), and multimodal cation-exchange resins (MMC). The protein library consists of proteins with isoelectric points ranging from 3.4-11.4 with varying hydrophobicities as determined by their retention on hydrophobic interaction chromatography. The batch sequential experiments are carried out using one protein at a time with a wide set of resins at multiple pH conditions, thus enabling simple microtiter plate detection. A mathematical formulation is then used to determine the first moment of the distributions from each chromatogram (sequential step elution) generated in the parallel batch experiments. Batch data first moments (expressed in salt concentration) were compared to results obtained from column linear salt gradient elution, and the techniques are shown to be consistent. In addition, first moment data was used to calculate one-resin separability scores, which are a measure of a resin’s ability, at a specified pH, to separate the entire set of proteins in the library from one another. Again, the results from the batch and column experiments were shown to be comparable. The first moment data sets were then employed to calculate the two-resin separability scores, which are a measure of the ability of two resins to synergistically separate the entire set of proteins in the library. Importantly, these results based on the two-resin separability performances derived from the batch and column experiments were again shown to be consistent. This analytical approach was applied to all the screened ligand libraries and connections between ligand chemistry/stereochemistry and chromatographic behavior were identified. This approach for rapidly screening large numbers of chromatographic resins and mobile phase conditions for their elution behavior may prove useful for enabling the rapid discovery of new chromatographic ligands and resins.Item Towards generating coherent stories from image sequences: a computational approach using suspension of disbelief(Rensselaer Polytechnic Institute, Troy, NY, 2024-08)This dissertation explores a computational model for generating the connections needed to make a story from a sequence of images. Storytelling is an important cognitive task that humans use to communicate and organize information. Being able to automate storytelling would benefit interactive media such as video games, make it easier to automatically summarize large data sets in a way that people understand, and make AI systems more capable of explaining their actions. One storytelling task that humans perform is visual storytelling, the task of making a story from a sequence of images. To do so, humans establish recurring characters and props, connect actions in different images into a plot, and fit their plot to common emotional arcs, like tragedies. Humans performing visual storytelling reinterpret what actions they see in the images and interpret visually distinct objects in different images as being the same if doing so serves the story they want to make. Existing computational story generation systems do not show these human phenomena and cannot reinterpret the information in images for the sake of the story they aim to create. The aim of this thesis research is to create a computational system that makes the connections between images needed to make a story and can reinterpret the information in those images for the sake of that story. The system accepts the objects and their possible actions in a sequence of images as its input. It then establishes what objects are the same between images to make recurring characters and props, connects actions in different images into sequences to make a plot, and fits its plot to common emotional arcs. The system forms these connections by looking at what evidence supports them and creates different sets of connections depending on how it prioritizes different kinds of evidence. To evaluate the system, human participants were asked to perform the visual storytelling task, and the objects and actions they identified in the images were gathered as input for the system. By varying the system's parameters, diverse sets of connections were generated from the same sequences of images. These sets of connections were examined to see if the system was equating objects and sequencing actions for its plot in a way that was consistent with how the system was expected to form these connections given its different evidence priorities. The results demonstrate the system's ability to vary the extent to which it equates visually distinct objects for the sake of its story and to adapt its interpretation of actions based on its desired emotional story arc.Item Wideband phase locked loop (pll) for sub-mmwave applications(Rensselaer Polytechnic Institute, Troy, NY, 2024-08)Frequency generation is pivotal for the implementation of high-frequency electronic systems. Such circuits must deliver signals with precise frequency locations. The signal source mustalso be tunable over a wide bandwidth. Phase Locked Loops (PLLs) ensure this precision by providing feedback. PLLs are evaluated based on their phase noise, tuning range, output power, and overall DC power consumption. For communication applications, low phase noise is critical due to its impact on signal integrity, frequency stability, and interference mitigation. Enhancing the signal-to-noise ratio (SNR) of communication transceivers necessitates high output power from the local oscillator (LO) to drive mixers into saturation, thereby reducing conversion loss or increasing conversion gain. In sub-mmWave/THz applications, the PLL must offer a broad tuning range to exploit the available bandwidth. This research focuses on the design, implementation, and testing of PLLs operating above 100 GHz using Fully Depleted Silicon on Insulator (FDSOI) technology, targeting future 6G applications in the D-band. These PLLs, when coupled with frequency multipliers, extend into the THz frequency bands, facilitating applications in THz wave sensing and spectroscopy. GlobalFoundries’ 22nm fully depleted silicon on insulator (FDSOI) technology is utilized, offering ultralow power DC consumption and a compact form factor. The technology features thin oxide devices with nominal core voltages as low as 0.4V and provides forward/reverse back gate bias options for threshold voltage control. Additionally, the transistors support different gate pitches and have multiple metal layers to meet electro-migration rules, ensuring reliable long-term operation. This technology’s stack includes ten metal layers, with two thick copper layers and a 2.8µm top aluminum layer, providing high performance for mmWave designs. The thesis objective is to design sub-mmWave PLLs that balance wide tuning range, low phase noise, and relatively high output power while minimizing energy consumption. This challenge is heightened by the limitations of standard silicon technology with low-quality passives at such high frequencies. Research on PLLs above 100 GHz is still in its early stages due to the complexities of designing efficient and robust integrated circuits (ICs) at these frequencies, compounded by device limitations, process variations, and imprecise measurements and device models. Traditional PLL architectures, involving a voltage-controlled oscillator (VCO), frequency divider, phase/frequency detectors, charge pump, and loop filter, must be reconsidered for D-band and higher frequencies due to the limited tuning range of sub-mmWave VCOs and the high power consumption of high-frequency dividers. Therefore, a harmonic PLL is designed that utilizes a dual resonant VCO that generate both 1st and 3rd harmonic signals. Furthermore, a W-band Fundamental PLL is proposed that utilizes a magnetically tuned VCO along with Dynamic latch divider. Both designs are fabricated in 22nm FDSOI technology and tested to validate the performance metrics. The fundamental dual band PLL achieves frequency range of 87 GHz to 104 GHz, delivering a peak output power of -7 dBm while consuming 53.1 mW of DC power. Key components, including the varactorless VCO, a dynamic latch frequency divider, and an implicit reset phasefrequency detector, collectively ensure minimal phase noise at -105 dBc/Hz at a 10 MHz offset and an integrated RMS jitter between 108 and 110 fs. Finally a comparison between two architectures of PLL is presented to summarize performance metrics for the research community.
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