Chemical and Biomolecular Engineering Theses and Dissertations

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13C and 15N Metabolic Flux Analysis on the Marine Diatom Phaeodactylum tricornutum to Investigate Efficient Unicellular Carbon and Nitrogen Assimilation Mechanisms
(2013) Zheng, Yuting; Sriram, Ganesh; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Photosynthesis is indispensable in carbon cycling and obtaining renewable carbon. Operated by cyanobacteria, algae and plants, this process provides reduced carbon and molecular oxygen, consumes atmospheric CO₂ and harnesses solar energy. Photosynthesis is also central to the production of biofuels. Diatoms, a class of marine algae, contribute 20% to 40% of global photosynthetic productivity despite surviving in CO₂-depleted and nitrogen-limited environments. This makes diatoms ideal models to study efficient photosynthetic, specifically carbon concentrating mechanisms (CCM). It has been long debated that whether the unicellular marine diatom Phaeodactylum tricornutum operates a CCM, and whether the CCM is biophysical or biochemical (C4) in nature, with existing (circumstantial) experimental evidence divided amongst the two possibilities. Through isotope labeling experiments (ILE) and metabolic flux analysis (MFA), we provide for the first time significant, direct evidence for a biochemical CCM and the potential combined operation of a biochemical and a biophysical CCM. Additionally, we shed light on how genes regulating this complex process respond to critical environmental variables. Furthermore, we report the use of isotope-assisted metabolic flux analysis to study organic carbon (especially glucose) assimilation in P. tricornutum. Our steady state ILEs reveal glucose assimilation under light and potentially which genes may be responsible for glucose metabolism. We then studied nitrogen (mainly urea) assimilation through instationary 15N and 13C labeling experiments, to find indications of an unusual pathway of urea assimilation. Gene expression trends under various environmental conditions suggest the possible participation of the urea cycle in assimilating nitrogen in P. tricornutum, and how this metabolically differs from nitrate and ammonium assimilation. We anticipate that this work will not only improve understanding of unicellular C4 CCMs, but provide insights to explain the ecological success of diatoms in adapting to challenging environments.
2-DIMENSIONAL ZEOLITES FOR ADSORPTIVE DESULFURIZATION
(2018) Fang, Jingyu; Liu, Dongxia; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The removal of sulfur-containing compounds from transportation fuels is of growing urgency due to the increasingly government stringent regulations. Adsorptive desulfurization at ambient conditions is a promising strategy for sulfur-containing compound removal compared to traditional hydrodesulfurization (HDS) that requires high temperature and pressure. In this thesis, we studied zeolite adsorbents for adsorptive desulfurization of model fuels. Three zeolite frameworks (MFI, MWW and FAU) in both 2-dimensional (2D) and 3D structures were synthesized and ion-exchanged to both proton-form and Ag+-form. The adsorption of thiophene and benzothiophene, respectively, in n-octane was done using both H+- and Ag+-form zeolites in both 2D and 3D structures. The results show that 2D zeolites have high adsorption capacity than 3D analogues in removal of benzothiophene. The Ag+-form zeolites increase the adsorption capacity compared with that of H+-form. In terms of zeolite framework effects, MWW zeolites possesses the highest adsorption capacity.
Ab initio determination of kinetics for atomic layer deposition modeling
(2014) Remmers, Elizabeth; Adomaitis, Raymond A; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
A first principles model is developed to describe the kinetics of atomic layer deposition (ALD) systems. This model requires no fitting parameters, as it is based on the reaction pathways, structures, and energetics obtained from quantum-chemical studies. Using transition state theory and partition functions from statistical mechanics, equilibrium constants and reaction rates can be calculated. Several tools were created in Python to aid in the calculation of these quantities, and this procedure was applied to two systems- zinc oxide deposition from diethyl zinc (DEZ) and water, and alumina deposition from trimethyl aluminum (TMA) and water. A Gauss-Jordan factorization is used to decompose the system dynamics, and the resulting systems of equations are solved numerically to obtain the temporal concentration profiles of these two deposition systems.
ACTIVE AND PASSIVE MICROFLUIDICS FOR SAMPLE DISCRETIZATION, MANIPULATION AND MULTIPLEXING
(2020) Padmanabhan, Supriya; DeVoe, Don L; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The use of microfluidic technology to compartmentalize an initial sample into discrete and isolated volumes is an important step for many biological and chemical applications, that allows molecules, cells, particles, reagents, and analytes to be spatially constrained, providing unique benefits for their characterization, sorting, and manipulation with low reagent consumption. Discretization can also increase the overall throughput and enable multiplexing. In this dissertation, two platforms are described to enable microfluidic sample discretization and manipulation. First, (2D) microwell arrays fabricated in thermoplastic cyclic olefin copolymer (COP) are explored as a new approach toward the development of high throughput, low-cost components in disposable diagnostics by utilizing a passive discretization technique. Performance of various 2D array designs is characterized numerically and experimentally to assess the impact of thermoplastic surface energy, fluid flow rate, and device geometry on sample filling and discretization. The design principles are used to successfully scale up the platform without affecting device performance. Loop-mediated isothermal amplification (LAMP) on chip is used to demonstrate the platform’s potential for discretized nucleic acid testing. Next, pin spotting in nanoliter-scale 2D arrays is demonstrated as technique for high resolution reagent integration to enable multiplexed testing in diagnostics. The potential for nucleic-acid diagnostics is evaluated by performing rolling circle amplification (RCA) on chip with integrated reagents. Finally, an innovative platform enabling complex discretization and manipulation of aqueous droplets is presented. The system uses simple membrane displacement trap elements as an active technique to perform multiple functions including droplet discretization, release, metering, capture, and merging. Multi-layer polydimethylsiloxane (PDMS) devices with membrane displacement trap (MDT) arrays are used to discretize sample into nanoliter scale droplet volumes, and reliably manipulate individual droplets within the arrays. Performance is characterized for varying capillary number flows, membrane actuation pressures, trap and membrane geometries, and trapped droplet volumes, with operational domains established for each platform function. The novel approach to sample digitization and droplet manipulation is demonstrated through discretization of a dilute bacteria sample, metering of individual traps to generate droplets containing single bacteria, and merging of the resulting droplets to pair the selected bacteria within a single droplet.
Adsorption Humidity Effects, Microparticle Rate Behavior, and Thermal Swing Adsorption
(2005-12-06) mahle, john; Harris, Michael T.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Application of adsorption processes for air purification requires an approach, which accounts for the presence of humidity. Four separate but related studies are conducted to examine the adsorption processes. A new pure component adsorption isotherm is developed to describe Type 5 adsorption. The results are used to correlate data of water on activated carbon. This model derives from the concept that capillary condensation accounts for Type 5 behavior and is strongly dependent on the pore size distribution. The new model has the advantage over all other prior models of being invertible in terms of loading and partial pressure. The Henry's law limit and heat of adsorption effects are discussed. A study of coadsorption of water and immiscible organics is also presented. Data for the system chloroethane water on two activated carbons is measured. A new coadsorption model is developed to describe immiscible vapors and water. This model has the advantage of at most one adjustable parameter and can also be solved without iteration. Good agreement is demonstrated between this new model, data measured here and literature data. The use of thermal swing adsorption for air purification is examined in this work. An experimental system is used to perform cycling experiments under dry and humid conditions. A dynamic simulation model is developed to describe several of cycling runs. Using the coadsorption model developed above the good agreement is found between the data and simulation profiles. Optimization of cycle parameters was investigated to show that some moderation of the feed water content is required to obtain high purification of a light vapor challenge at ambient temperature conditions. The internal rate effects of commercial adsorbents have been reported in the literature. There is seldom an attempt to review the many approaches. Data was measured using a gravimetric technique for chloroethane and hexane on BPL activated carbon and 13X molecular sieve. A distributed parameter micropore diffusion model was solved to simulate this data. Regression of the adsorption and desorption data was used to determined micropore diffusion coefficients. These values were shown to compare well with literature values.
ADVANCED REACTION ENGINEERING FOR THE NONOXIDATIVE VALORIZATION OF METHANE
(2023) Cheng, Sichao; Liu, Dongxia; Zhang, Chen; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Non-oxidative methane conversion (NMC) represents a promising pathway that directly transforms methane into higher hydrocarbons such as ethane, ethylene, acetylene, aromatics, and hydrogen in a single-step synthesis. This process holds particular appeal due to its potential for remote operation and its status as a carbon-neutral process, given that it does not produce carbon dioxide in the product effluent. As such, NMC could serve as a viable alternative to existing multi-step, energy-intensive processes like the Fischer-Tropsch synthesis and liquid petroleum gas production. Despite its potential, NMC faces significant challenges. The thermodynamic stability of methane, attributed to its strong C-H bonds, poses a considerable obstacle. Other challenges include low selectivity towards desired products, rapid catalyst deactivation, and kinetic hindrance, all of which complicate the process. As of now, these challenges have prevented the development of a commercially viable NMC process. This dissertation aims at overcoming these hurdles to unlock the full potential of NMC, paving the way for a more efficient and sustainable method of methane conversion from the perspective of both catalyst design and reaction engineering. The impact of hydrogen activation on NMC using a hydrogen-permeable SrCe0.8Zr0.2O3-δ (SCZO) perovskite oxide material over the iron/silica catalyst was explored. The SCZO oxide, with its mixed ionic and electronic conductivity, facilitates H2 activation into protons and electrons. The SCZO's ability to absorb H2 in-situ lowers its local concentration, promoted the improvement of NMC reaction thanks to the Le Chaterlie’s principle. To further improve the NMC reaction performance, an innovative autothermal catalytic wall reactor (ACWR) designed for self-sustaining NMC with high hydrocarbon product yield (>21% C2 & >27% Aromatics) and minimal coke formation. The system, potentially powered by combusting the sole co-product H2, offers a self-sustained and negative neutral operation of NMC. Further operando studies via Spatial Resolved Capillary Inlet Mass Spectrometry (SpaciMS) have demonstrated that the increased local concentration and the volcanic axial concentration profile of ethylene within the ACWR highlight its effectiveness in comparison to traditional reactor designs. With the detection of a higher ethylene concentration near the reactor wall, SpaciMS studies have also provided experimental evidence that ethylene is a surface product of the Fe/SiO2 catalyst. A novel Pulsed Heating and Quenching (PHQ) thermochemical synthesis technique was applied to methane pyrolysis to demonstrate high selectivity to valuable C2 products. The technique's salient features include rapid activation of reactants at high temperatures for increased rates and conversions, and precise control over the heating process, enhancing the selectivity of desired products.
Advanced Sulfide Solid Electrolyte Enabled by Nitrogen Doping
(2017) Zhu, Xiangyang; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
All-solid-state lithium batteries (ASSLBs) are being considered as the ultimate solution to the safety issue of current lithium ion batteries which use flammable organic electrolyte. The properties of the solid electrolyte, the most important component in ASSLBs, largely affect the electrode/electrolyte interfacial behavior and eventually the performance of ASSLBs. Sulfide electrolytes are considered as one of the most promising solid electrolyte for ASSLBs because of its excellent mechanical properties. However, they suffer from poor electrochemical stability and lithium dendrite formation. In this thesis, I demonstrated that the nitrogen-doped sulfide solid electrolyte system (75-1.5x)Li2S-25P2S5-xLi3N showed comprehensive performance improvements. The ionic conductivity is enhanced and the interfacial resistance between Li anode and solid electrolyte gets reduced by over 80%. The dendrite formation in solid electrolyte could also be effectively suppressed with the critical current density enhanced by 70%. The simultaneous improvement make it a promising solid electrolyte for ASSLBs.
Advancements in Label-free Biosensing Using Field-Effect Transistors and Aided by Molecular Dynamics Simulations
(2019) Guros, Nicholas; Klauda, Jeffery B; Balijepalli, Arvind; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Biosensors are used to characterize or measure concentrations of physiologically or pathologically significant biomarkers that indicate the health status of a patient, for example, a biomarker associated with a specific disease or cancer. Presently, there is a need to improve the capabilities of biosensors, which includes their rate of detection, limit of detection, and usability. With respect to usability, it is advantageous to develop biosensors that can detect a biomarker that is not labeled, such as with a conventional fluorescent, magnetic, or radioactive label, prior to characterization or measurement by that biosensor. Such biosensors are known as label-free biosensors and are the primary focus of this work. Biosensors are principally evaluated by two standards: their sensitivity to detect a target biomarker at physiologically relevant concentrations and their specificity to detect only the target biomarker in the presence of other molecules. The elements of biosensing critical to improving these two standards are: biorecognition of the biomarker, immobilization of the biorecognition element on the biosensor, and transduction of biomarker biorecognition to a measurable signal. Towards the improvement of sensitivity, electrostatically sensitive field-effect transistors (FET) were fabricated in a dual-gate configuration to enable label-free biosensing measurements with both high sensitivity and signal-to-noise ratio (SNR). This high performance, quantified with several metrics, was principally achieved by performing a novel annealing process that improved the quality of the FET’s semiconducting channel. These FETs were gated with either a conventional oxide or an ionic liquid, the latter of which yielded quantum capacitance-limited devices. Both were used to measure the activity of the enzyme cyclin-dependent kinase 5 (Cdk5) indirectly through pH change, where the ionic-liquid gated FETs measured pH changes at a sensitivity of approximately 75 times higher than the conventional sensitivity limit for pH measurements. Lastly, these FETs were also used to detect the presence of the protein streptavidin through immobilization of a streptavidin-binding biomolecule, biotin, to the FET sensing surface. To study the biomolecular factors that govern the specificity of biomarker biorecognition in label-free biosensing, molecular dynamics (MD) simulations were performed on several proteins. MD simulations were first performed on the serotonin receptor and ion channel, 5-HT3A. These simulations, which were performed for an order of magnitude longer than any previous study, demonstrate the dynamic nature of serotonin (5-HT) binding with 5-HT3A. These simulations also demonstrate the importance of using complex lipid membranes to immobilize 5-HT3A for biosensing applications to adequately replicate native protein function. The importance of lipid composition was further demonstrated using MD simulations of the ion channel alpha-hemolysin (αHL). The results of these simulations clearly demonstrate the lipid-protein structure-function relationship that regulates the ionic current though a lipid membrane-spanning ion channel. Finally, to demonstrate the impact of MD simulations to inform the design of FET biosensing, a strategy to use FETs to measure the ultra-low ionic currents through the ion channel 5-HT3A is outlined. This strategy leverages critical elements of 5-HT biorecognition and ion channel immobilization extracted from MD simulations for the design of the proposed FET sensing surface interface.
AEROSOL SYNTHESIS OF CATHODE MATERIALS FOR NA-ION AND LI-ION BATTERIES
(2014) Langrock, Alex; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Energy production and storage are important issues that play a key role in our daily lives. There is a need for high energy and high power systems for portable electronic devices and zero-emission vehicles. Lithium-ion batteries are crucial in addressing these needs. However, for the smart electric grid and renewable energy storage where cost is critical but weight and footprint requirement is less important, the sodium-ion battery is the most suitable power sources. To achieve both high power density and high energy density, nanostructured sphere particles with controlled porosity and high tapping density are desired for both Li-ion and Na-ion batteries. The versatile and facile ultrasonic spray pyrolysis method allows for the synthesis of a variety of electrode materials with sphere morphology. Work has been done to develop electrode materials through an aerosol method that can be readily applied to industry. Two classes of high energy cathodes suitable for lithium-ion batteries were studied. These include the 5V spinels and lithium-rich materials. The 5V spinels are a promising class of electrodes for secondary lithium batteries. This class of material has the highest intrinsic rate capability of the intercalation cathodes with high safety, low toxicity, and low cost making it ideal for high-power applications such as electric vehicles, while the lithium-rich compounds exhibit high capacity and reasonable cycle stability. Two classes of stable cathodes suitable for sodium-ion batteries were studied. The first was carbon coated porous hollow Na2FePO4F spheres with 500 nm diameter and 80 nm wall thickness synthesized by a one-step template-free ultrasonic spray pyrolysis process using sucrose as the carbon source. Nano-sized porous hollow Na2FePO4F spheres allow electrolyte to penetrate into the hollow structure, and thus the electrochemical reaction can take place on both the outside and inside surface and in the pores. Also, the carbon coating on Na2FePO4F hollow spheres enhances the electronic conductivity and charge transfer reaction kinetics. The exceptional performance of hollow Na2FePO4F spheres combined with mature aerosol spray synthesis technology make these carbon coated porous hollow Na2FePO4F spheres very promising as cathode materials for practical applications in Na-ion batteries. Finally, P2-type earth abundant layered oxides with high energy density and long cycling stability were also developed and studied. These layered materials were investigated due to their high theoretical capacity. A novel ultrasonic spray pyrolysis system has been developed to effectively coat any cathode, including layered oxides, with a thin layer of carbon to improve the kinetics and increase the electronic conductivity. The residence time in air is sufficiently short to allow the decomposition of the carbon source (sucrose) without further reduction of the cathode material. A vertical configuration allows the solid particles to reach the filter for collection with high efficiency. As a test sample, lithium-rich cathodes have been successfully carbon coated and compared with the bare material.
AEROSOL-CLOUD-CLIMATE INTERACTIONS DUE TO CARBONACEOUS AEROSOLS
(2022) Gohil, Kanishk; Asa-Awuku, Akua A; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Aerosols can affect the net radiation budget and global climate of the Earth either “directly” – through their radiative properties, or “indirectly” – through their cloud-forming abilities by acting as Cloud Condensation Nuclei (CCN). The interactions between aerosols and clouds are the most significant sources of uncertainty in the overall radiative forcing from due to a lack of understanding related to the droplet formation mechanism of aerosols. These uncertainties are majorly associated with the carbonaceous aerosols present in the atmosphere, notably due to their compositional diversity, vastly variable physicochemical properties, and unique water uptake characteristics. In this dissertation, new lab-based measurement techniques and computational methods have been developed to resolve the CCN activity and water uptake behavior of pure and mixed carbonaceous aerosol particles.The first part of this dissertation accomplishes two goals: 1. The development and application of a new CCN measurement method, and 2. The formulation of a new computational framework for CCN activity analysis of aerosols. The results in this dissertation demonstrate the significance of size-resolved morphology and dissolution properties of aerosol particles in improving their CCN activity analysis under varying ambient conditions. Furthermore, these results suggest that in the future, more comprehensive CCN analysis frameworks can be developed by explicitly treating other physical and chemical properties of the aerosols to further improve their CCN activity analysis. The second part of this dissertation focuses on large-scale analysis. The CCN analysis framework is implemented into a climate model to quantify the water uptake behavior of carbonaceous aerosols, and then study the subsequent variabilities associated with the physical and radiative properties of ambient aerosols and clouds. Statistical techniques are also developed in this work for chemical characterization of ambient aerosols. The characterization results show large regional compositional variations in ambient aerosol populations. These results also suggest that the knowledge of chemical species is necessary to quantify the water uptake properties of the aerosol population.
An Analysis of a New Approach to Sol-gel Synthesis: The Reaction of Formic Acid with Teos
(2005-08-09) Brown, Kimberly; Harris, Michael T; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
FTIR spectroscopy was investigated as a means of monitoring the reactions of formic acid and tetraethoxy silane, TEOS, at different temperatures and molar ratios of formic acid to TEOS, r. FTIR spectra of the reactions at r values of 1, 2, and 6 showed that increasing the molar ratio and temperature significantly increased the rates of hydrolysis and condensation. An activation energy of 10.5 0.6 kcal/mole was determined for the r= 6 system. 29Si NMR was used to monitor the reaction of formic acid with TEOS at molar ratios of 1, 2, and 6. The increase in reaction rate with increasing molar ratio was clearly evident in the silica NMR spectra. The low concentration of monomeric species containing hydroxy groups was deduced from NMR spectra. Proton NMR spectroscopy was utilized in identifying the byproducts of the reaction of formic acid with TEOS. Ethanol, ethyl formate, and SiOOCH groups were easily identified by NMR. Ethyl formate was initially the major byproduct; however, ethanol became the major low molecular weight species as the reaction proceeded. Information on the oligomeric structures was gathered using USAXS and mass spectrometry. USAXS was used to obtain radii of gyration for the r = 6 system which increased from 5.4 nm to 9.6 nm as the reaction progressed. An analysis was performed on the mass spectrum of the reaction of formic acid with TEOS at r =6, 35 minutes. Most oligomeric species contained at least one ring, and the maximum number of silicons was 11. Furthermore, the mass spectrum indicated that OR groups were the predominant groups attached to the silica oligomers. The analyses performed on the reaction of TEOS with formic acid provided possible explanations for the increased rate of gelation. The presence of fewer cyclic oligomers in the early stages of reactions was observed in 29Si NMR spectroscopy. 29Si NMR spectroscopy also indicated an increase in the rates of condensation for the reaction of formic acid with TEOS. The results of the analyses on the reaction of formic acid with TEOS were used to propose a kinetic model.
Analysis of Air Quality with Numerical Simulation (CMAQ), and Observations of Trace Gases
(2009) Castellanos, Patricia; Ehrman, Sheryl H; Dickerson, Russell R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Ozone, a secondary pollutant, is a strong oxidant that can pose a risk to human health. It is formed from a complex set of photochemical reactions involving nitrogen oxides (NO_x) and volatile organic compounds (VOCs). Ambient measurements and air quality modeling of ozone and its precursors are important tools for support of regulatory decisions, and analyzing atmospheric chemical and physical processes. I worked on three methods to improve our understanding of photochemical ozone production in the Eastern U.S.: a new detector for NO₂, a numerical experiment to test the sensitivity to the timing to emissions, and comparison of modeled and observed vertical profiles of CO and ozone. A small, commercially available cavity ring-down spectroscopy (CRDS) NO₂ detector suitable for surface and aircraft monitoring was modified and characterized. The CRDS detector was run in parallel to an ozone chemiluminescence device with photolytic conversion of NO₂ to NO. The two instruments measured ambient air in suburban Maryland. A linear least- squares fit to a direct comparison of the data resulted in a slope of 0.960±0.002 and R of 0.995, showing agreement between two measurement techniques within experimental uncertainty. The sensitivity of the Community Multiscale Air Quality (CMAQ) model to the temporal variation of four emissions sectors was investigated to understand the effect of emissions' daily variability on modeled ozone. Decreasing the variability of mobile source emissions changed the 8-hour maximum ozone concentration by ±7 parts per billion by volume (ppbv). Increasing the variability of point source emissions affected ozone concentrations by ±6 ppbv, but only in areas close to the source. CO is an ideal tracer for analyzing pollutant transport in AQMs because the atmospheric lifetime is longer than the timescale of bound- ary layer mixing. CO can be used as a tracer if model performance of CO is well understood. An evaluation of CO model performance in CMAQ was carried out using aircraft observations taken for the Regional Atmospheric Measurement, Mod- eling and Prediction Program (RAMMPP) in the summer of 2002. Comparison of modeled and observed CO total columns were generally in agreement within 5-10%. There is little evidence that the CO emissions inventory is grossly overestimated. CMAQ predicts the same vertical profile shape for all of the observations, i.e. CO is well mixed throughout the boundary layer. However, the majority of observations have poorly mixed air below 500 m, and well mixed air above. CMAQ appears to be transporting CO away from the surface more quickly than what is observed. Turbulent mixing in the model is represented with K-theory. A minimum K_z that scales with fractional urban land use is imposed in order to account for subgrid scale obstacles in urban areas and the urban heat island effect. Micrometeorological observations suggest that the minimum K_z is somewhat high. A sensitivity case where the minimum K_z was reduced from 0.5 m2/s to 0.1 m2/s was carried out. Model performance of surface ozone observations at night increased significantly. The model better captures the observed ozone minimum with slower mixing, and increases ozone concentrations in the residual layer. Model performance of CO and ozone morning vertical profiles improves, but the effect is not large enough to bring the model and measurements into agreement. Comparison of modeled CO and O₃ vertical profiles shows that turbulent mixing (as represented by eddy diffusivity) appears to be too fast, while convective mixing may be too slow.
Analysis of Drug Delivery in the Eye Using Magnetic Resonance Imaging
(2007-11-19) Kim, Heekyong Stephanie; Wang, Nam S; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
With the rapid increase in the elderly population, the number of Americans afflicted with vision impairment due to ocular disease is projected to rise substantially by the year 2020. Ocular disorders are becoming a major public health problem, and efforts have increased in recent years to develop methods of efficient drug delivery. Currently, the most effective method for treating serious ocular disorders is to inject drug solutions directly into the vitreous. However, injecting in this manner carries a high risk of severe side effects. As a safer alternative, researchers in recent years have been investigating transscleral drug delivery, in which the drug is administered to the outer coat of the eye. Various methods of transscleral drug delivery have been proposed, but it is still clinically not as effective as intravitreal drug delivery. In order to design improved transscleral drug delivery systems, the ocular barriers to drug transport must be accurately understood. While various barrier types have been identified in the eye, the significance and contribution of individual barriers have not been investigated and are still widely unknown. A reason for this lack of understanding is due to the inability to acquire concentration measurements in the eye in vivo. In this study, magnetic resonance imaging (MRI) was employed to obtain drug concentration measurements in vivo after transscleral drug delivery. To address the current needs of the ocular drug delivery community, several goals have been achieved in this work: (1) to evaluate transscleral drug delivery in vivo using MRI, (2) to assess MRI as a technique for evaluating drug delivery in the eye, and (3) to better understand the significance of individual barriers in the eye by quantitatively analyzing experimental (MRI) data and by pharmacokinetic modeling. While encompassing many advantages, it is found that MRI has limitations in spatial and temporal resolution that may restrict its use in measuring parameters with low sensitivity. However, the MRI results in parallel with analysis from the pharmacokinetic model give new insight into the barriers to drug transport in the eye.
ANALYSIS OF OBJECTIVES AND CONSTRAINTS TOWARDS PREDICTIVE MODELING OF COMPLEX METABOLISM
(2020) Boruah, Navadeep; Sriram, Ganesh; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The central theme of this dissertation is predictive modeling of metabolism in complex biological systems with genome-scale stoichiometric metabolic models to (i) gain nontrivial insight on cellular metabolism and (ii) provide justifications for hitherto unexplained metabolic phenomena. The crux of high-quality predictive modeling with genome-scale stoichiometric metabolic models is appropriate selection of (i) a biologically relevant objective function and (ii) a set of constraints based on experimental data. However, in many complex systems, like a plant tissue with its wide array of specialized cells, a biological objective is not always apparent. Additionally, generation of experimental data to develop biochemically relevant constraints can be nearly impossible in systems that cannot be cultured under a controlled environment for the duration of an experiment. Such limitations necessitate careful reformulation of the biological question, development of novel methods and data analysis strategies. Here, we push the boundaries of predictive modeling by demonstrating its first application in deciphering hitherto unexplained metabolic phenomena and in developing novel hypotheses on metabolism. Towards achieving this goal, we developed several novel approaches and employed them in diverse biological systems. Firstly, we investigated the selection of carbohydrate degrading pathway employed by Saccharophagus degradans, an aerobic cellulosic marine bacterium. Flux balance analyses of its growth in nutrient rich hypoxic marine environment predicted that the selection of carbohydrate degrading pathway is possibly influenced by inorganic nutrient availability. Secondly, multi-tissue genome-scale metabolic modeling of Populus trichoparpa, a perennial woody tree, and analyses with a novel strategy based on multiple biologically relevant metrics provided a metabolic justification for the predominance of glutamine as the predominant nitrogen transport amino acid for internal nitrogen recycling. Thirdly, predictive modeling of maize grain filling predicted amino acid fermentation as a mechanism for expending excess reductant cofactors for continual starch synthesis in the hypoxic environment of endosperm. Finally, we developed bilevel optimization framework to integrate publicly available transcriptome datasets with metabolic networks. This framework predicted accumulation of specific classes of maize endosperm storage protein at distinct stages of grain filling. We anticipate that the employment of these aforementioned approaches in other biological systems will lead to the generation of a wide array of nontrivial hypothesis on cellular metabolism and to develop targeted experiments to validate them.
Analysis of rheological properties and molecular weight distributions in continuous polymerization reactors
(2004-12-06) Dave, Kedar Himanshu; Choi, Kyu Yong; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This work explores the possibility of exploiting structure-property relationships to manufacture tailor-made polymers with target end-use properties. A novel framework which aims to improve upon current industrial practices in polymerization process and product quality control is proposed. The strong inter-relationship between the molecular architecture and rheological properties of polymers is the basis of this framework. The melt index is one of the most commonly used industrial measures of a polymer's processibilty. However, this single-point non-Newtonian viscosity is inadequate to accurately reflect the polymer melt's flow behavior. This justifies monitoring the entire viscosity-shear rate behavior during the polymerization stage. In addition, the crucial role played by the polymer melt's elastic characteristics is not reflected in it's shear viscosity and so elasticity meaurements are also warranted. In this study, rheological models available in the open literature are utillized to demonstrate these critical issues at industrially relevant operating conditions. The observations made are also compared with published experimental results and found to be qualitatively similar. Two case studies are presented. The first one is the free-radical solution polymerization of styrene with binary initiators in a cascade of two CSTRs. In the second case, the solution polymerization of ethylene in a single CSTR with a mixture of two single-site transition metal catalysts is considered. The feasibility of the proposed framework to tailor the product's MWD, irrespective of the underlying reactor configuration or kinetic mechanism, is demonstrated via steady state simulations. Relative gain analysis reveals the non-linearity and interactions in the control loops. Although the main contributions of this study primarily deal with the viscoelastic behavior of linear homopolymers, potential extensions to systems involving polymers with small amounts of long chain branching or the control of other end-use properties are also discussed.
ANALYSIS OF TEMPERATURE AND SPECIFIC HUMIDITY DEPENDENCE OF MOVES OUTPUT FOR MOTOR VEHICLE EMISSIONS
(2017) Varada, Sai Sreedhar; Ehrman, Sheryl H; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Air pollution and climate change are some of the important consequences of modern industrialization. In a large developed country like the United States of America, these changes have a greater impact due to the country’s high energy demands. This project focuses on air pollution caused by emissions released by combustion of fuels in automobile engines. The mobile emissions inventory for the National Emissions Inventory (NEI) is based on the estimates from MOtor Vehicle Emissions Simulator (MOVES), which is a software program used to model automobile emissions. Analysis of in-situ roadside monitor observations shows that emissions from automobile sources, especially CO and NOx emissions are correlated with ambient temperature and humidity. In this research, I compared the MOVES model output dependence on ambient temperature and specific humidity to observations from an Air quality Monitoring Site which is located in Maryland on Interstate-95 (I-95) and adjusted the model output to nearly match the observations. The adjusted model was used to obtain emissions estimates of another month (here, Nov 2014) and these estimated ratios nearly matched with the observations.
ANALYSIS, QUANTIFICATION AND SIMULATION OF THE RISK FROM AIRBORNE INFLUENZA
(2016) YAN, JING; Ehrman, Sheryl H; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Despite the development of effective vaccines, influenza still remains as a global concern. For appropriate public health intervention, it is crucial to accurately determine the routes of transmission. Influenza is believed to have three primary modes of transmission: big droplet, direct contact and aerosol particles. Considerable evidence points to both aerosol and droplet transmission routes as being significant. Because of the limitation of sampling and analysis, the quantitative dynamics of the aerosol mode of transmission are not completely understood. In this dissertation I have characterized the physical and biological collection efficiency of a novel exhaled breath aerosol collector named Gesundheit II (G-II). The device was proven to successfully collect and preserve infectivity with different types of influenza virus. I have also been involved in epidemiological data analysis, experimental quantification and numerical modeling. On experimental quantification, I have been part of a multi-member team that has conducted a study of characterization of respiratory droplets from influenza infected individuals at the University of Maryland campus during the flu seasons of 2012-2013. The exhaled breath was collected with the G-II for accurate quantification of the influenza virus. 218 pairs of fine (< 5 µm) and coarse (≥ 5µm) exhaled breath samples were obtained from 142 subjects and analyzed. The relationship between culturability, coughing frequency, and symptoms were investigated. The high rate of RNA detection and the frequent recovery of influenza virus by culture from fine aerosol samples suggest a contribution of fine particle aerosols in the transmission of influenza. Given these new findings, to understand the risk of influenza infection from these finer droplets, we have modified an existing mathematical risk analysis model and studied the effect of these droplets on subjects in presence or absence of a respiratory protective device (RPD). Two of the major enhancements in our model are (1) the ability to account for subject-to-subject variability over a wide range of age groups and (2) the heterogeneous population was introduced into the model with some infectees or susceptibles not wearing RPDs.
Application of Dynamic Light Scattering to Chemical and Biomolecular Engineering: Polymers, Proteins, and Liquid Crystals
(2008-05-02) Linegar, Kirtland Lee; Anisimov, Mikhail A; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Dynamic Light Scattering (DLS) is a powerful tool for probing soft-matter. The history, equipment, and basic theory of DLS is outlined. Three applications of DLS representing contemporary problems in chemical and biomolecular engineering are presented: polymers, proteins, and liquid crystals. DLS was performed on the polymer poly(ethylene glycol) in aqueous solutions to discern a conformational change from a coil to a helix when dissolved in isobutyric acid and to compare DLS and small angle neutron scattering (SANS) measurements. DLS experiments were conducted on the protein GroEL to determine the aggregation kinetics of the protein in solution. Finally, we observed a phenomenon never before seen associated with the relaxation of fluctuations of anisotropy and concentration fluctuations in a lyotropic chromonic liquid crystal solution of cromolyn. This phenomenon causes a significant increase of the effective relaxation time of the anisotropy fluctuations with an increase of the wave-number of the fluctuations.
Assembly and Combustion Properties of Energetic Mesoparticles
(2015) Wei, Boran; Zachariah, Micheal R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Energetic materials are materials which can release large amounts of energy in a short time interval. When the size of energetic materials is reduced from micro into nanoscale, the reactivity of energetic materials increases dramatically due to increase in intimate contact and faster mass and heat transfer. Finding an efficient way to synthesize energetic nanocomposites has become an import research topic. Here I demonstrate the use of electrospray methods to generate mesostructured microparticles containing nanomaterials and a gas generator. The system was designed for characterization of the size distribution as well as combustion properties. In this thesis, size distribution of the Al/NC mesoparticles is tuned from 0.7-2.0 µm, and the ignition delay is shown significantly decrease (15 ms to 3 ms) compared to nano-size Al. The burn time is also decreased significantly (4036 µs to 366 µs) by using electrospray assembly. This demonstrated that assembly of nanocomponents can significantly impact combustion performance.
Assembly of Quorum Sensing Pathway Enzymes onto Patterned Microfabricated Devices
(2007-07-31) Lewandowski, Angela; Bentley, William; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
I report patterned protein assembly onto microfabricated devices using our unique assembly approach. This approach is based on electrodeposition of the aminopolysaccharide chitosan onto a selected electrode pattern of the device, and covalent conjugation of a target protein to chitosan upon biochemical activation of a genetically fused C-terminal pentatyrosine "pro-tag." With this approach, assembly is "spatially selective", occurring only at selected electrode patterns, and the entire process occurs under mild experimental conditions. Additionally, assembly is reversible and the devices reusable, as the deposited chitosan can be removed by simple incubation in dilute acid. Finally, the protein is covalently and robustly linked to chitosan through the pro-tag versus the native tyrosines, and thus our approach confers "orientational control". I have examined patterned assembly of metabolic pathway enzymes onto both flat microfabricated chips and into 3-dimensional microfluidic devices. The assembled enzymes retain reproducible catalytic activities and protein recognition capabilities for antibody binding. Additionally, catalytic activity is retained over multiple days, demonstrating enzyme stability over extended time. Finally, substrate catalytic conversion can be controlled and manipulated through the assembly patterned area, or in the case of microfluidic devices, through the substrate flow rate over the assembled enzyme. I specifically examined the patterned assembly of Pfs and LuxS enzymes, members of the bacterial autoinducer-2 (AI-2) biosynthesis pathway. AI-2 is a small signaling molecule that mediates interspecies bacterial communication termed type II "quorum sensing", which is involved in regulating the pathogenesis of a bacterial population. Significantly, this is the first time that Pfs and LuxS have been assembled onto devices. More significantly, Pfs and LuxS have both been assembled onto the same chip; that is, the quorum sensing pathway has been assembled onto a single device. This device could be used to screen inhibitors of AI-2 biosynthesis and discover novel "anti-pathogenic" drugs. In summary, I have demonstrated patterned enzyme assembly onto microfabricated devices. The assembled enzymes retain reproducible catalytic activities and are capable of recognizing and binding antibodies. Importantly, patterned device-assembly of multiple enzymes representing a metabolic pathway is possible. I envision many potential biosensing, bioMEMS, drug screening, and metabolic engineering applications.

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