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Title: COMPUTATION OF THIN AIRFOIL AERODYNAMICS FOR MICRO AIR VEHICLE APPLICATIONS
Creator: Baez Guada, Alejandro
Date: 2013-04-29, 2013-05
Description: With the significant interest in the development of micro air vehicles with gust resistant capabilities, active flow control has become a main...
Show moreWith the significant interest in the development of micro air vehicles with gust resistant capabilities, active flow control has become a main challenge in enhancing flight conditions. The current flow control techniques are limited at suppressing fluctuations in the lift induced by unsteady freestreams and while undergoing fast maneuvers. As a result of the time delay associated with the actuation input and formation of the leading edge vortex, closed-loop controllers are limited by the bandwidth to suppress fluctuation in the lift under unsteady freestreams. Therefore, the recognition of the direct interaction of the controller with the formation of vortex shedding suggests the development of new techniques for flow control. For the sinusoidal oscillating freestream, the knowledge of the time scales in response to actuation and the phase between the unsteady freestream and lift time series are useful in the implementation of the feed forward controllers suppressing lift fluctuations. Moreover, prospective solutions have been conceptualized in the implementation of the leading edge separation sensor and the gust load alleviation controller that would allow the instantaneous response to enhance lift under unsteady freestreams conditions. With the increasing computational power and reliance on turbulence models, the numerical simulations facilitate the investigation of thin airfoil aerodynamics at post-stall angles of attack under steady and unsteady freestreams. The computations of turbulent flows for external flow aerodynamics are challenging as a result of the presence of separated flow. The detachment of boundary layers is by nature three-dimensional and time dependent. Therefore, simulating these flows is problematic and requires high computational cost. Thin shear layers are common in external aerodynamic flows demanding very fine near-wall discretization to solve for separation points. The growth of the boundary layer, separation, and mixing length scales require complex approaches for accurate results. xviii In the present study, the performance of the turbulence models is investigated in numerical predictions of thin airfoil aerodynamics at post-stall angles of attack. The results suggest that low computational cost turbulence models fail at treating separated flows. Moreover, the instantaneous locations of separation and stagnation points in response to the changes in the lift for steady and unsteady flows were investigated. The amplitude and frequency of the time series of the separation and stagnation point location are highly correlated with the characteristics of the lift oscillations. Therefore, the recognition of separation or stagnation point locations at the leading edge of the wing could provide the direct information of the gains and drops in the lift for active flow control applications.
M.S. in Aerospace and Mechanical Engineering, May 2013
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Title: DOUBLE AGING AND THERMOMECHANICAL HEAT TREATMENT OF ALUMINUM EXTRUSIONS
Creator: Emani, Satyanarayana
Date: 2012-08-27, 2012-12
Description: Double aging and thermo mechanical treatment of AA7075 and AA6061 aluminum alloys was studied and optimized to accelerate the kinetics of...
Show moreDouble aging and thermo mechanical treatment of AA7075 and AA6061 aluminum alloys was studied and optimized to accelerate the kinetics of aging process. This novel process is highly energy efficient and reduces the time of heat treatment of AA7075 alloys by 96%. It also achieves excellent mechanical properties compared to the conventional T6 heat treatment while improving ductility and energy efficiency. Hardness curves for different aging times and temperatures and TEM analysis was used to develop an empirical model was which explains the precipitation mechanism of η’ precipitates on GP zones and the effect of time and temperature on the double aging process.
PH.D in Materials Science, December 2012
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Title: SINTER B0NDING TITANIUM POWDER COMPONENTS: AN UNCONVENTIONAL ADDITIVE MANUFACTURING APPROACH
Creator: Montonera, Darrell R
Date: 2018, 2018-05
Description: Titanium and its alloys are desirable for many applications. The cost of producing titanium parts that also have needed microstructure for a...
Show moreTitanium and its alloys are desirable for many applications. The cost of producing titanium parts that also have needed microstructure for a given application limit where titanium is used. Methods of reducing the cost of titanium parts have been to use powder metallurgy processing routes. However, not all powder processing routes are cost effective, as additive manufacturing and powder injection molding processes are costly and require expensive spherical powder. Cheaper processing Press and Sinter utilizes cheaper non-spherical powder. Powder titanium components made through Press and Sinter have complexity, size, and geometrical constraints and have detrimental mechanical properties unless further post processing is done. To utilize the simple geometries from Press and Sinter, pressed powder components are bonded to examine the possibility of creating higher complexity parts. To achieve this, the dimensional sintering behavior of powders were quanti- ed using dilatometry. Grade 5 titanium alloys were created by blending hydridedehydride (HDH) commercially pure powder with master alloy (MA) 60/40 wt%. The dimensional effect of varying master alloy produced a maximum difference of 0.341% between an alloy with lower MA content compared to higher content during sintering. The sintering behavior of powder HDH+MA reached a nal shrinkage of 4.59%. Other powders TiH2, TiH2+MA, and Armstrong pre-alloyed had fi nal shrinkages of 9.85, 9.64, and 8.31%. The larger shrinkage powders were pressed into a peripheral component to be bonded to a HDH+MA core. Samples were sintered under a vacuum of 2x10􀀀6 torr by heating from room temperature to 1370 oC at 15 oCmin􀀀1 and holding at 1370 oC for 90 minutes. Sinter Bonded sample interfaces were examined showing the best bond to be the Armstrong j HDH+MA combination. This bond was tested using a push out test achieving shear stresses of 423 60 MPa using a pre-sintering tolerance between components of 0.065 mm and 444 37 MPa using a pre-sintering tolerance of 0.03 mm. Wrought material tested in the same manner as the sinter bonded components had a strength of 517 8 MPa. Sinter bonded samples achieved on average 82% the strength of wrought tested in the same manner. Strong bond strengths lead to a fatigue analysis of sinter bonded samples. Under various applied cyclic compressive stresses the number of cycles to failure were measured using an applied stress ratio R = 0.1. Determination of fatigue properties was done by simulating and probing in Abaqus the max tension stresses located at the bottom center of the sample. Simulations produced steady state tension stresses measured at maximum, mean, and minimum applied compressive stresses. These stresses were used to plot a S-N curve. True stress amplitudes were calculated from probed maximum and minimum stresses and the fatigue data were fi t to the Basquin empirical relation 2 = 810:4(2Nf )􀀀0:055 for sinter bonded samples and 2 = 1290:9(2Nf )􀀀0:065 for wrought samples. As a proof of concept several pressed titanium parts were combined in the green state and successfully sintered into a single component.
Ph.D. in Materials Science and Engineering, May 2018
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Title: SYNTHESIS AND EVALUATION OF STABILIZED ALGINATE MICROBEADS
Creator: Soma, Sami Isaac
Date: 2018, 2018-05
Description: Alginate hydrogels have been investigated for a broad variety of medical applications. The ability to assemble hydrogels at neutral pH and...
Show moreAlginate hydrogels have been investigated for a broad variety of medical applications. The ability to assemble hydrogels at neutral pH and mild temperatures makes alginate a popular choice for the encapsulation and delivery of cells and proteins. Alginate has been studied extensively for the delivery of islets as a treatment for type 1 diabetes. However, stability of the encapsulation systems after implantation remains a challenge. The broad goal of this proposal was to develop and investigate methods for enhancing the stability of alginate-based encapsulation systems. First, a method was developed to create dual crosslinked alginate microbeads. Alginate was modified with 2-aminoethyl methacrylate hydrochloride (AEMA) to introduce groups that can be photoactivated to generate covalent bonds. This enabled formation of dual crosslinked structure upon exposure to ultraviolet light following initial ionic crosslinking into bead structures. The degree of methacrylation was varied and in vitro stability, long term swelling, and cell viability examined. At low levels of methacrylation, the beads could be formed by first ionic crosslinking followed by exposure to ultraviolet light to generate covalent bonds. The methacrylated alginate resulted in more stable beads and cells were viable following encapsulation. Alginate microbeads, ionic (unmodified) and dual crosslinked, were implanted into a rat omentum pouch model. Implantation was performed with a local injection of Lipopolysaccharide (LPS) to stimulate a robust in inflammatory challenge in vivo. Implants were retrieved at 1 and 3 weeks for analysis. The unmodified alginate microbeads had all failed by week 1, whereas the dual-crosslinked alginate microbeads remained stable up through 3 weeks. The modified alginate microbeads may provide a more stable alternative to current alginate-based systems for cell encapsulation. In the next set of studies, multilayered alginate microbeads (Alginate-Poly-l-ornithine-Alginate (APA)) were investigated for cell encapsulation. The APA microbeads were generated with a thick outer alginate layer that is present in order to reduce inflammation post implantation. The dual crosslinking approach was applied to the outer layer APA microbeads. Dual crosslinked outer layer multilayered alginate microbeads remained intact in presence of chelating agents. APA alginate microbeads, ionic (unmodified) and dual crosslinked were tested using omentum pouch model with local injection of LPS. Dual crosslinked microbeads remained intact up to three weeks without significant change in outer layer size. In conclusion, alginate was modified with methacrylate groups to enhance stability when subjected to an inflammatory challenge. APA microbeads with methacrylated outer layer hold a great potential for cell encapsulation therapies.
Ph.D. in Biomedical Engineering, May 2018
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Title: CHARACTERIZING GPS PHASE LOCK LOOP PERFORMANCE IN WIDEBAND INTERFERENCE USING THE DISCRIMINATOR OUTPUT DISTRIBUTION
Creator: Stevanovic, Stefan
Date: 2018, 2018-05
Description: The use of the Global Positioning System (GPS) has accelerated in recent years. In its inception, GPS was used exclusively by the military for...
Show moreThe use of the Global Positioning System (GPS) has accelerated in recent years. In its inception, GPS was used exclusively by the military for navigation. Today, with the emergence of extremely capable electronics and microprocessors, GPS has been integrated into many aspects of life. It is currently widely used by both the military and various civilian industries for applications that require navigation as well as precise timing. Some applications of GPS include ground vehicle and aircraft navigation, banking, power transmission, and agriculture. As a result, disruptions in GPS availability have the potential to disrupt many services and industries around the globe, and even threaten the safety of life. Reliable operation can be interrupted by radio frequency interference (RFI), which can come from natural and manufactured sources. This work describes new techniques to evaluate the performance of GPS receivers that may be subjected to RFI events. The example application motivating this work is Ground Based Augmentation System (GBAS) reference station receivers subjected to broadband interference, for example, from nearby use of personal privacy devices (PPDs). PPDs most commonly emit broadband interference, and GBAS ground based reference receivers have expe- rienced tracking discontinuities as a result [Pul12]. These events can cause navigation service interruptions to aircraft on nal approach. To ensure continuity of the nav- igation service, GBAS reference stations must be able to track GPS signals in the presence of wideband interference. The objective of this work is to develop the PLL analysis tools required to design PLLs capable of tracking through RFI events, while reducing the need for time-consuming simulations and experimental validation. Instead, simulation and experimental validation can be reserved for PLL designs which are much more likely to be successful. The techniques described in this work are valid for any GPS application in which the receiver cannot tolerate cycle slips in the phase-lock loop (PLL). The methodology is directly applicable to ground-based reference receivers for differential GPS systems, as well as other ground-based receivers that require high continuity of service. It is also relevant to moving receivers, if the additional dynamic stresses on the PLL are also taken into account. The PLL discriminator output (DO) distribution is used to characterize GPS PLL tracking performance, in contrast to the phase jitter metric widely used in prior work and literature. Both the DO variance and the bias on the mean of the DO distribution are shown to be superior to the jitter metric in predicting phase-lock. And, it is shown that the bias in the DO mean is the most effective measure of cycle slip probability. Studying the discriminator output distribution also provides a means of comparing different techniques to extend PLL averaging time beyond the length of a navigation data bit, without time-consuming direct simulation and experimental validation. Experimental results are presented to validate the theoretical analysis and simulations. The observed tracking results are consistent with the theoretically predicted system performance. The DO bias is superior to the variance metric in its ability to predict loss of phase-lock.
Ph.D. in Mechanical and Aerospace Engineering, May 2018
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Title: CHARACTERIZATION OF GATE-ALL-AROUND FIELD EFFECT TRANSISTORS BASED ON BSIM-CMG MODEL
Creator: Yang, Muyu
Date: 2018, 2018-05
Description: The objective of this thesis is to analyze the characteristics of gate-all-around (GAA) field-effect-transistors (FETs) based on BSIM-CMG ...
Show moreThe objective of this thesis is to analyze the characteristics of gate-all-around (GAA) field-effect-transistors (FETs) based on BSIM-CMG (Berkeley Short-channel IGFET Model Common Multi-Gate) compact model. As devices continue scaling according to Moore’s Law, traditional planar multi-gated MOSFET cannot suppress the short-channel effects (SCE). The GAA FETs structure is a good candidate for sub-7nm technology nodes because of its’ electrostatic gate control and the ability to suppress the SCE. In this thesis, two different kinds of GAA FETs, Lateral GAA FETs (LGAA FETs) and Vertical GAA FETs (VGAA FETs), are characterized and compared with multi-gate FinFETs. The devices implemented in this thesis are all based on BSIM-CMG compact models from Berkeley BSIM Group and PTM-MG compact models from Nanoscale Integration and Modeling (NIMO) Group. In this dissertation, LGAA FETs and VGAA FETs are compared with double-gate FinFETs, triple-gate FinFETs and quadruple-gate FinFETs. Firstly, both N-type and P-type of devices are characterized for a variety of parameters to investigate their properties. Then basic logic gates, i.e. Inverter, NOR and NAND, are created based on GAA FETs and multi-gate FinFETs, and simulated for comparison. Finally, an extended datapath study was done by implementing several full adder designs, including the traditional 28T mirror adder, the 9A adder, the 13A adder, the SERF adder, the CLRCL adder, the HULPFA adder, and the ULPFA adder. Simulation results confirm that LGAA FETs and VGAA FETs have substantially smaller leakage current and dynamic power consumption but slightly increased delay when compared with traditional planar multi-gate FinFETs.comparison. Finally, an extended datapath study was done by implementing several full adder designs, including the traditional 28T mirror adder, the 9A adder, the 13A adder, the SERF adder, the CLRCL adder, the HULPFA adder, and the ULPFA adder. Simulation results confirm that LGAA FETs and VGAA FETs have substantially smaller leakage current and dynamic power consumption but slightly increased delay when compared with traditional planar multi-gate FinFETs.
M.S. in Electrical Engineering, May 2018
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Title: ENSURING NAVIGATION INTEGRITY AND CONTINUITY USING MULTI-CONSTELLATION GNSS
Creator: Zhai, Yawei
Date: 2018, 2018-05
Description: Global navigation satellite system (GNSS) measurements are vulnerable to faults including satellite and constellation failures, which can...
Show moreGlobal navigation satellite system (GNSS) measurements are vulnerable to faults including satellite and constellation failures, which can potentially lead to catastrophic consequences in safety-critical applications. To mitigate their impact, receiver autonomous integrity monitoring (RAIM) fault detection has been designed and used in aviation as a backup navigation tool. Future GNSS has been foreseen to provide dramatically increased measurement redundancy and reduced measurement error. These revolutionary developments, together with important advancements in the RAIM concept itself, will open the possibility to independently support aircraft navigation using GNSS, from takeoff, through en-route flight and final approach to landing, with minimal investment in ground infrastructure. Therefore, this research focuses on developing new dual-frequency, multi-constellation advanced RAIM (ARAIM) fault detection and exclusion methods to ensure high navigation integrity and continuity. In this thesis, the theoretical basis is established to quantify the contributions of fault events and unscheduled satellite outages on continuity risk. Accordingly, the need for airborne fault exclusion is assessed, and the requirements for the exclusion function itself are speci fied. To improve continuity, a new fault exclusion scheme is developed, for which the real-time implementation of the algorithm is described and the associated integrity risk bound is derived. With the theoretical methods being fully characterized, this thesis comprehensively quanti es the achievable ARAIM navigation performance over various numbers and qualities of constellations. The results show high service availability can be achieved using multi-constellation GNSS, while meeting both integrity and continuity requirements. Furthermore, this work investigates the impact of test statistic time correlation on integrity and continuity risk, and rigorously derives the new methods to evaluate the actual risk over the exposure time. The results show that the false alarm probability is two orders of magnitude higher than previously thought. A feasible solution to resolve this issue at the user receiver is provided, and the performance is analyzed. The most signifi cant new feature of ARAIM is the integrity support message (ISM), which provides assertions on the GNSS signal-in-space performance. This dissertation describes the design, analysis, and evaluation of the offline ground monitor, which aims at validating the ISM broadcast to the users. The proposed architecture utilizes a worldwide network of sparsely distributed reference stations, and paramet- ric satellite orbital models to estimate the satellite position and clock. Two separate analyses, covariance analysis and model delity evaluation, are carried out to respec- tively quantify the impact of measurement errors and of residual model errors on the estimation. The results indicate this ground monitor design is adequate for ARAIM ISM validation.
Ph.D. in Mechanical and Aerospace Engineering
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Title: Technical and Business Analysis of Challenges and Opportunities Associated with Guitar String Products (Spring 2002) IPRO 306: Technical_and_Business_Analysis_of_Challenges_and_Opportunities_Associated_with_Guitar_String_Products_IPRO306_Spring2002_Final_Presentation
Creator: Alaniz Iii, Jesus, Flores, Antonio, Havens, Brad, Khalid, Usman, Oleszkiewicz, Anthony, Salam, Basel
Date: 2002, 2002-05
Description: Gibson USA, Nashville, Tennessee, is a recognized leader in the design and manufacture of acoustic and electric guitars for the entertainment...
Show moreGibson USA, Nashville, Tennessee, is a recognized leader in the design and manufacture of acoustic and electric guitars for the entertainment industry. Gibson has a rich and respected history that began with the design and manufacture of mandolins in 1894. Its innovations in guitars have generated tremendous market loyalty, and have helped to transform the music industry in partnership with generations of musicians. A great deal of interesting information about Gibson USA is available at http://www.gibson.com. Gibson USA is also a prominent manufacturer and marketer of aftermarket guitar strings and accessories through its dedicated facilities in Elgin, Illinois. At this time, the Gibson Strings & Accessories division of Gibson USA is interested in supporting an IIT IPRO team that would study the complex relationships between its products, manufacturing operations, marketing strategy and competitive position. Gibson Strings & Accessories, located in Elgin, Illinois, manufactures strings, amplifiers, pickups and other accessories. This IPRO project will concentrate on issues related to the acoustic and electric guitar strings manufactured under the Gibson or Epiphone brand names. This initial IPRO project for Gibson will give students great experience in working closely with its young and energetic management to review current operations and select an appropriate initial focus for the project. This may include developing test and measurement methods and equipment to analyze string performance across product lines and competitive offerings, observing manufacturing operations to identify factors that affect product performance, evaluating marketing and competitive issues that offer opportunities or challenges, and developing an understanding of the user purchase decision process associated with the aftermarket for guitar strings. Projects could also include fine-tuning an integrated Internet strategy for marketing guitar strings and accessories and supporting the dealer network.
Sponsorship: Gibson Strings & Accessories, Gibson USA
Project Plan for IPRO 306: Technical and Business Analysis of Challenges and Opportunities Associated with Guitar String Products for the Spring 2002 semester
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Title: RECURRENT PREGNANCY LOSS: PSYCHOLOGICAL SEQUELAE AND COPING
Creator: Grathouse, Heidi Richelle
Date: 2016, 2016-05
Description: Recurrent pregnancy loss has received little attention in the research literature despite being recognized as a source of distress. This study...
Show moreRecurrent pregnancy loss has received little attention in the research literature despite being recognized as a source of distress. This study examined 126 participants who were either in a recurrent pregnancy loss group (as defined by the ASRM guidelines of 2 or more miscarriages occurring within the first trimester of pregnancy) or a nonpregnancy loss community group. This study tested the hypothesis that depression and anxiety symptoms, as measured by the IDAS would be different for the group of persons that had experienced RPL as compared to the community sample. It was expected that individuals who had experienced RPL would have significantly higher levels of depression and anxiety than the community group. This hypothesis was based upon the finding that elevated anxiety and depressive symptoms are common, and major depressive disorder has been reported at a rate of 10-50% following a miscarriage (Conway & Russell, 2000; LaRoche, et al. 1984). The findings failed to support this hypothesis. The second hypothesis stated that coping styles, as measured by the COPE, would be related to levels of distress as measured by the IDAS. Specifically, active-emotion-focused coping and avoidant coping would be related strongly to negative affect, consistent with research by Folkman and Lazarus (1986), in which it was shown that depressed individuals used relatively less problem-focused coping than non-depressed individuals. Results from this study partially supported this hypothesis and the previous findings.
Ph.D. in Psychology, May 2016
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Title: DEVELOPMENT OF A HYDROGEL NANOPARTICLE SYSTEM FOR SUSTAINED DELIVERY OF ANIGOGENIC FACTORS FOR THERAPEUTIC NEOVASCULARIZATION
Creator: Young, Daniel A
Date: 2018, 2018-05
Description: Neovascularization requires controlled and sustained delivery of proangiogenic factors to stimulate reperfusion of ischemic tissues. Tissue...
Show moreNeovascularization requires controlled and sustained delivery of proangiogenic factors to stimulate reperfusion of ischemic tissues. Tissue engineering strategies for therapeutic neovascularization have used proangiogenic, recombinant growth factors to direct vessel development. Recently, peptides that mimic the bioactivity of growth factors have emerged as therapeutics for a variety of drug delivery applications, including therapeutic neovascularization. We designed hydrogel nanoparticles to provide sustained and tunable di usion-based release of a proangiogenic peptide, QK, and a vessel stabilizing peptide, Vasculotide (VT). These nanoparticles were combined with a tissue engineering sca old to promote tissue neovascularization. We used this nanocomposite system, utilizing peptide loaded hydrogel nanoparticles embedded in an implantable sca old, to investigate the e cacy of a dual peptide delivery strategy for therapeutic neovascularization. Inverse phase mini-emulsion polymerization (IPMP) was used to generate crosslinked poly(ethylene) glycol (PEG) hydrogel nanoparticles. We characterized the nanoparticles in terms of their swelling ratio, mesh size, surface charge ( -potential), and particle size distributions. We developed several nanoparticle formulations using various sizes and molar concentrations of PEG chains to study the e ects of crosslink density on peptide release kinetics. This resulted in the formation of nanoparticles with low and high crosslink density as well as time-dependent variations in network density due to hydrolysis. We utilized two di erent loading techniques, peptide entrapment during IPMP and peptide post-loading into the nanoparticles, and found both to be e ective via peptide loading measurements and release kinetic studies. In the case of entrapment loading, peptides were included in the aqueous precursor during nanoparticle IPMP. Peptide release kinetics were tuned through adjustments in nanoparticle crosslink density. The resulting nanoparticle crosslink density impacted both peptide loading and fractional release, as studies showed higher crosslink density nanoparticles resulted in slower peptide release. The IPMP process preserved QK secondary structure and bioactivity, as con rmed with released peptide using circular dichroism spectroscopy and a Matrigel tubulogenesis assay, respectively. In the case of the post-loading method, pristine nanoparticles were soaked in various concentrations of either QK or VT. Unlike with the entrapment loading method, crosslink density of the nanoparticles had little e ect on release kinetics. However, much higher mass amounts of peptide could be loaded using this method and thus this method was chosen for the in vivo studies. Next, we developed a hydrogel nanocomposite sca old system to sequester nanoparticles for implantation. We characterized the nanocomposite sca old system experimentally and theoretically using one-dimensional transport models of molecular di usion. We estimated peptide di usion coe cients from nanoparticles and the nanocomposites under perfect sink conditions. Importantly, we found this system capable of providing previously reported therapeutic thresholds of QK and VT. Finally, the in uence of sustained release of QK and VT on neovascularization was evaluated using a subcutaneous rat implant model. Results demonstrated statistically higher increases in perfused vessel density from peptide loaded nanocomposite sca olds as compared to sca olds where peptide was simply entrapped. These results suggest that controlled release of proangiogenic peptides from the developed nanoparticle system holds great potential for ischemic tissue repair.
Ph.D. in Biomedical Engineering, May 2018
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Title: THE ASSOCIATION BETWEEN DEPRESSIVE SYMPTOM FACTORS AND CANNABIS USE
Creator: Miner, Jacob L.
Date: 2018, 2018-05
Description: Substance use and mood disorders are the most common co-occurring psychiatric disorders, with cannabis use and depression being the most...
Show moreSubstance use and mood disorders are the most common co-occurring psychiatric disorders, with cannabis use and depression being the most prevalent. Despite the growing body of evidence examining the relationship between depression and cannabis use, the association is still not well understood. The purpose of the present study was to determine if depressive symptom type (i.e., somatic vs. cognitive) was differentially associated with severity of past month cannabis use. Due to inconsistencies in the literature, no a priori hypothesis was made. Data for this study were obtained from the 2015 national survey sample sponsored by the Substance Abuse and Mental Health Services Administration (SAMHSA). Depression variables used for the analysis consisted of the 9 symptoms related to a diagnosis of Major Depressive in the DSM-IV. Confirmatory Factor Analyses indicated that the best fitting measurement models was a two-factor model of depression, with a 4-symptom somatic factor and a 5-symptom cognitive factor. Results of the full structural equation model indicated that neither somatic nor cognitive symptom factors significantly predicted past month cannabis use. There is a need for a better understanding of the way depressive symptoms are associated with cannabis use.
M.S. in Psychology, May 2018
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Title: COMPREHENSIVE ALWAYS-ON SENSING (CAS) PLATFORM FOR MOBILE CONTEXTUAL AWARENESS
Creator: Lautner, Douglas
Date: 2018, 2018-05
Description: From conception and for decades, a cell phone was used solely for wireless communication purposes [1]. Recently however, over the past nine...
Show moreFrom conception and for decades, a cell phone was used solely for wireless communication purposes [1]. Recently however, over the past nine years after the Android™ and iOS™ operating systems were released to the market, its definition has changed. With increasing capabilities, importance of data generation, data collection and processing functionalities, a cell phone has evolved into a mobile smart device e.g. smartphone. Smart devices are emerging into new roles such as a portable computing devices [2], sensor hubs [3] and Internet access terminals [4]. As embedded technologies and systems advance, not only smartphones, but all commercial smart devices [5], such as wearables, smartwatches or head mounted displays, extend with these capabilities. Amongst all, the function of contextual sensing is unique on a mobile smart device more than on any other commercial computing platform. Mobile smart devices are carried in close proximity of users, traveling with them throughout a day sensing what the user experiences. Ambient and on-body contexts are shared with the user and hence the sensing data can accurately reflect an individual’s real environment better than any other computing or sensing device. It is likely that most domesticated living beings i.e. humans, pets, livestock, etc. would be associated with a mobile smart device in the future [6]. As the Internet of Things (IoT) wireless capabilities become more cost effective and are connected to more objects [7][8], pervasive deployment can be realized and hence becomes an important information source in contextual sensing. More important, as IoT wireless items can be equipped with various sensing techniques, such as geofencing data [10] or information acquired from any kind of sensor attached to them e.g. temperature, force, strain, pressure, etc. [11][12], the sensing result is comprehensive and highly configurable which is impractical for traditional sensors. The following three challenges are the major causes of limited IoT contextual sensing in smart devices. First, if implementing such sensing capability on a traditional smart device platform, its high current drain becomes intolerable. Second, prevailing smart device platforms are not able to accommodate all IoT contextual sensors and their requirements. Third, there is no solution for the smart device to schedule sensing tasks from different IoT contextual sensors and pre-process sensing raw data at the system’s low layer. To conquer these three problems, and the goal of the thesis is to research, design and implement a novel platform in between a smart device’s system’s hardware layer and operation system layer to accommodate IoT contextual sensors and conduct always-on sensing tasks.
Ph.D. in Computer Science, May 2018
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Title: SYNTHESIS OF NEW CATHODE AND ANODE STRUCTURES FOR LITHIUM-SULFUR BATTERIES
Creator: Lin, Yiwei
Date: 2018, 2018-05
Description: One of the greatest technological success stories in recent years has been that of the development and commercialization of the Li-ion battery...
Show moreOne of the greatest technological success stories in recent years has been that of the development and commercialization of the Li-ion battery (LIB) technology. It has been predicted that the silicon anode technology will be the next evolution in LIBs, due to its potential to enable cheaper, higher capacity batteries. To attain its immense storage capacity, the silicon particles in the anode must expand to accommodate the lithium ions. In this expansion lies the technological challenge facing further development of silicon anode technology. The consequences of the expansion can be simplified into the following issues: swelling and rupture, loss of mechanical stability due to pulverization of the electrode, and cell drying. In this thesis work, we have designed a novel nanostructured anode material that will address some of the key issues preventing commercial applicability of silicon anode. We have also designed a novel nanostructured cathode material that will store high percentage of sulfur and exhibit high capacity retention. While the synthesis of these novel nanostructured materials was the primary objective, some preliminary electrochemical data have also been presented in the thesis. These two materials (lithiated silicon as the anode and sulfur as the cathode) can be combined to construct lithium-sulfur batteries (LSBs), which have potential to provide 3-5 times more energy than that of current LIBs at lower cost. Moreover, sulfur is environmentally benign and one of the most abundant elements on earth. More importantly, its low operating voltage of 2.1 V could offer safety advantages over high-voltage intercalation cathodes (>4 V) used in LIBs. Thus, realization of a practical Li-S technology can move the U.S. rapidly toward a more sustainable transportation future.
M.S. in Chemistry, May 2018
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Title: CORANNULENE η(ETA)5-COORDINATION WITH TRANSITION METALS: A THEORETICAL STUDY
Creator: Lu, Xiang
Date: 2018, 2018-05
Description: Planar polyaromatic molecules η5-coordinated to transition metal complexes are well-studied and applied in organometallic chemistry. Much less...
Show morePlanar polyaromatic molecules η5-coordinated to transition metal complexes are well-studied and applied in organometallic chemistry. Much less attention is paid to curved polyaromatic systems, so-called buckybowls or fullerene fragments. Here we present results of theoretical investigation of η5-adducts of corannulene as representative model for buckybowls with VIIIB group transition metals (Co, Rh, Ir and Fe, Ru, Os). Natural bonding orbital (NBO) analysis revealed that corannulene acts as a π-donor whereas transition metal center behaves as an acceptor, using its empty dxy orbital. Additionally, relatively weak back-donation from transition metals to corannulene was also observed. Energetics of the bonding was further explored with help of Energy Decomposition Analysis (EDA), which includes repulsive Pauli and attractive electrostatic (ionic) and orbital (covalent) components. Combined with EDA, NOCV (Natural Orbitals for Chemical Valence) analysis of donor-acceptor pairs associated with shape of charge flow and quantification of its magnitude in terms of energy confirmed the aforementioned nature of the orbital interactions. For comparison, η6-coordination mode of corannulene was also analyzed.
M.S. in Chemistry, May 2018
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Title: EXPERIMENTAL AND COMPUTATIONAL STUDIES OF STRUCTURAL DIFFERENCES BETWEEN ALTERNATIVE EXON SKIPPED REPAIRS FOR DUCHENNE MUSCULAR DYSTROPHY
Creator: Ma, Manyuan
Date: 2018, 2018-05
Description: Exon skipping is a therapy that seeks to correct or mitigate defects in proteins by masking of a specific exon during mRNA maturation. The...
Show moreExon skipping is a therapy that seeks to correct or mitigate defects in proteins by masking of a specific exon during mRNA maturation. The first approved exon skipping compound in humans is eteplirsen, which targets exon 51 of dystrophin, the protein defective in the common and devastating genetic disease, Duchenne muscular dystrophy, DMD. DMD is most often caused by deletions that create a frame shift in the gene; this abolished protein expression so that the dystrophin protein is totally absent. Exon skipping therapy corrects the reading frame, restoring protein expression and hopefully mitigating this disease. However, this creates an edited protein, missing both the original defect as well as the therapeutically skipped region. Crucially, it is possible to correct many defects in alternative ways, typically by skipping and exon either before, or after the patient’s defect. This results in different, alternatively edited proteins, of possibly different properties and therapeutic consequences. Currently, there is only one exon skipping drug available, but many others are in late stage clinical trials and it is expected that in the near future for some patients there will be a choice of which exon to skip. Since at the edit site regions of the protein that are normally not in contact are juxtaposed, structural disturbances may result in instability and potentially loss of function. This has been the focus of our work. In this study we examined three such dystrophin exon skipped edits, comprising two pairs of alternative repairs of the same underlying DMD defect. We found that in both cases, one member of each alternative was clearly more stable than the other by a variety of thermodynamic and biochemical measures. We also examined the origin of these differences by molecular dynamics, MD, simulation. Here, we found that these stability differences manifested in different types of structural perturbations. In one case, the edit site was partially unfolded, and this resulted in additional perturbations in the protein domain in which it was localized. However, in the other reduced stability case, the edit site was well-structured, but unfolding was see distal to the edit site, at protein domain junctions which were severely unfolded resulting in excess molecular flexibility. This demonstrates that alternative exon skip repairs of the same underlying defect can have very different consequences at the level of protein structure and stability, and furthermore that these can arise either locally, or by more-subtle long-range perturbations.
M.S. in Molecular Biochemistry and Biophysics, May 2018
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Title: THE EFFECT OF RUTHENIUM ADDITION ON THE PHASE EQUILIBRIA, MECHANICAL PROPERTIES AND OXIDATION RESISTANCE OF TIAL-BASED ALLOYS
Creator: Liu, Qizheng
Date: 2012-05-11, 2011-12
Description: The high temperature phase equilibria in the Ti-Al-Ru ternary system have been investigated but there remain some ambiguous regions. In this...
Show moreThe high temperature phase equilibria in the Ti-Al-Ru ternary system have been investigated but there remain some ambiguous regions. In this work arc-melted alloys were studied using scanning electron microscopy, X-ray diffraction and optical microscopy to determine the isothermal section of Ti-Al-Ru system at 1200°C. The lattice parameters were calculated from X-ray diffraction pattern for some compounds, including LI, 8-Ruso(TixAlso-x) and (AI6o-xTix)Ru4o. The lattice parameter of these three phases generally increases with Ti content. Enthalpy of formation was also measured for LI and 8-Ruso(TixAlso_x) with direct synthesis calorimeter to compare with the lattice parameter change. The enthalpy of formation of LI matches its lattice parameter change, but 8-Ruso(TixAlso_x) shows a reversed trend. It suggests that addition of Ti introduces a stronger bonding in the 8-B2 phase super-lattice. The phase equilibria are discussed in comparison with published research work. A new three phase region was detected for L t, Y and Til_xAl 1+x by X-ray diffraction. The homogeneity region of (AI6o-xTix)RU4o was found to be much higher than previously reported, with almost constant Ru content. The results from the ternary isothermal section also help to clarify the uncertain parts of the binary Ti-Al phase diagram. Three ternary eutectic reaction temperatures were measured with differential scanning calorimetry and the results were compared with the published liquidus projection. The high temperature compression behavior of TiAl-Ru alloys was studied at different temperatures and strain rates. Ru was found to have a strong strengthening effect on TiAI alloys. However the Ru addition amount was limited by its low solubility in y-TiAI and U2-Ti3AI, and the detrimental effect of excessive ternary phase precipitation. Furthermore, the melting temperature decreases when Ru 2:0.6at% as the alloy composition approaches a ternary eutectic point. The strengthening mechanism is discussed and two separate mechanisms are proposed, viz. solid solution strengthening and refined colony strengthening. Intergranular cracks were found in the alloys with low Ru or no Ru addition, but were barely detected as Ru content increased to above 0.6 at.%. It was suggested that Ru showed a beneficial effect on both strength and ductility of TiAI alloys due to the refined colony size. Three-point bend test results showed that the Ru addition can also improve the room temperature ductility of TiAl alloys. Hot workability was increased according to the compression tests. Thermal-mechanically treated TiAI-Ru had much smaller grain size than the heat-treated samples due to dynamic recrystallization. But it did not show superior strength in the compression test compared to the heat-treated samples. The Zener-Hollomon parameter was calculated from the compression strength of heat-treated TiAI-Ru alloys. Its relationship with dynamic recrystallization and hot work is discussed. The mechanical properties of TiAI-Ru alloys are compared with TiAI-Nb samples and demonstrate a promising combination of strength and ductility. The high-temperature oxidation resistance ofTiAI alloys with constant AI content and different alloying elements was tested with thermogravimetric calorimeter. Both Ru and Nb additions were found to have beneficial effect on the oxidation resistance ofTiAI alloys. While TiAI-Ru showed a slight improvement on the oxidation behavior, TiAI-Nb alloys had much better performance in comparison with TiAI alloys. Complicated oxide scale structure was characterized with the assistance of X-ray diffraction, scanning electron microscopy and Energy-dispersive X-ray spectroscopy analysis. The different oxide scale structure among the TiAl, TiAl-Ru and TiAl-Nb alloys were discussed with respect to their thickness, spatial pattern and composition gradient. The poor oxidation resistance of TiAI alloys at the testing temperature was determined to be attributed to the competition growth between Ah03 as well as Ti02, and the lack of a thick continuous Ah03 layer. The outward diffusion of Ti was found to be the controlling factor and the growth of Ti02 on top level of the oxide scale destroyed the initial Ah03 protection. RU02 was found to be the natural marker of the oxidation process in TiAl-Ru alloys due to its slow diffusion. The repartitioning of Ru in the oxide/substrate boundary was revealed to be the reason of its slight beneficial effect. Nb20 S layer was observed in the oxide scale of TiAl-Nb alloys and it played the role of blocking the outward diffusion of Ti. Thus Nb addition can suppress the growth of Ti02 and promote the formation of a continuous AI 20 3 layer. Treating the TiAI alloys by dipping in hydrofluoric (HF) acid was found to have a dramatic beneficial effect on TiAI alloys. Alloying elements have reversed effect on the HF dipping due to the reduced reaction rate with HF acid. The oxidation rate constant and activation energy were calculated for TiAI alloys with/without alloying addition. They were compared with the published data and the trend with composition change was discussed.
Ph.D. in Materials Science and Engineering, December 2011
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Title: MINIATURE SHOCK TUBE ACTUATORS FOR HIGH SPEED FLOW CONTROL APPLICATIONS
Creator: Ramachandran, Rakesh Chandran
Date: 2011-04-11, 2011-05
Description: In the field of aero-acoustics, one of the primary areas of interest has always been centered around the resonant flows. The fluid structure...
Show moreIn the field of aero-acoustics, one of the primary areas of interest has always been centered around the resonant flows. The fluid structure interactions gives rise to a reverberant field, which results in high amplitude fluctuating pressures associated with the resonant tones that could lead to sonic fatigue failure of sensitive components in the vicinity of such flows. One such fluid structure interaction is the cavity flow problem. Several flow control technologies exist to suppress cavity tones but most of them lose efficacy at off-design conditions and particularly at higher subsonic and supersonic flows. It is due to this fact that there is a high demand for high control authority flow control actuators. In order for an actuator to have higher control authority, one must be able to use a mechanism that has sufficient energy to disrupt the cavity tone generation mechanism at higher subsonic Mach numbers. One such mechanism is the shock tube generating high strength shock waves. To the best of our knowledge, there does not appear to be any use of shock waves to suppress noise emitted by cavity in aircrafts. The main challenge lied in developing the miniature shock tubes that could produce high intensity shock waves. In the present work, we designed, developed and tested these miniature shock tube flow control actuators. The initial part of this work involved a detailed study of the theory behind producing shock waves using a shock tube. The designing and development part included a lot of trial and error adjustments to produce shock waves as predicted by the 1D shock wave theory. Two shock tube actuators were developed, one having a single shock tube and another with three shock tubes but with the same exit area as the previous one. We carried out various characterization experiments measuring the unsteady pressure at the exit of these shock tubes and also the walls of the shock tube. The experimental investigation of the shock tubes revealed that miniature version of the shock tubes indeed produced high intensity shock waves as predicted by the shock wave theory. Apart from the shock tube actuators, fast acting solenoid valves which does not produce any shock were also tested, to compare the efficacy of both types of actuators. The later part of the work focuses on the actual application of these actuators as flow control devices. First, we delve into the acoustic suppression results which show the amount of tonal noise suppression achieved by using these actuators. For the M = 0.6 case the valves produced very good suppression up to 20 dB but the mass flow rate of these valves were about 26% of the main jet mass flow rate. In the M = 0.8 flows the valves produced negligible suppression. The multiple shock tube performed better than the single shock tube in both cases with a tonal noise suppression of up to 12 dB and 10 dB for M = 0.6 and M = 0.8 flows, respectively. The effect of the shock wave on the cavity tone was evident from the results and had a memory effect on the cavity tone suppression. Due to this the mass flux and the momentum coefficient for the shock tube actuators were considerably low. In order to better understand the mechanism through which the actuators suppress cavity tones, mean velocity measurements and phase averaged pressure measurements were carried out. Based on these results, it was observed that the lifting of the shear layer was the dominant mechanism behind steady and pulsed mass injection. In addition to this beamforming, used for locating the noise sources, was also used to study the cavity tones. Detailed discussion of the results are presented in this report.
M.S. in Mechanical and Aerospace Engineering, May 2011
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Title: LOCALIZATION OF WIND TURBINE NOISE USING A COMPACT MICROPHONE ARRAY WITH ADVANCED BEAMFORMING ALGORITHMS
Creator: Ramachandran, Rakesh Chandran
Date: 2014, 2014-12
Description: The knowledge of noise source location on a wind turbine is crucial for de- signing low noise wind turbines. Even though there has been...
Show moreThe knowledge of noise source location on a wind turbine is crucial for de- signing low noise wind turbines. Even though there has been considerable e ort to theoretically predict the noise from wind turbines in the past, very few experimental investigations have been performed to validate these models. Currently, compliance standards for wind turbine noise are based on single microphone measurements at various designated locations around a wind turbine. This only provides amplitude and frequency data of the overall wind turbine noise. However, it is impossible to locate noise sources, and to understand the dominant noise generation mechanism, using single microphone measurements. A sophisticated method, namely, the use of a microphone phased array with beamforming is necessary to locate the noise sources. Even though microphone arrays have been widely used to study aircraft yover and jet noise, it has just recently found application in locating wind turbine noise. Typical microphone arrays that have been used in the past for monitoring aircraft noise and wind turbine noise are very large ranging up to 270 m2 in area with about 148 mi- crophones. The setup is xed for a particular wind turbine and takes a considerable amount of time. In this thesis it is shown that a compact microphone array (with 24 microphones spread over 1.5 m2) is su cient to locate and separate wind turbine noise sources successfully. It is also shown that in order to use a compact micro- phone array, advanced deconvolution based beamforming methods such as DAMAS, CLEAN-SC, LP, and TIDY are necessary. However, before attempting to validate our idea, it is necessary to understand the concept of array resolution and di erent methods to improve it. We start with an in-depth study on the microphone array resolution and the e ect of di erent beamforming algorithms on it. This study has resulted in several interesting results: (i) The resolution limits that govern the resolution of the imaging system in optics also govern the resolution of microphone array. (ii) The resolution is a function of source frequency, diameter of the array, separation distance between sources, and the distance between the array and the sources. (iii) The resolution lost due to the compact microphone array can be recovered by using deconvolution algorithms. (iv) Di erent algorithms are useful for di erent scenarios; CLEAN-SC is most e cient in extracting the dominant noise source from the source map, LP is e cient in locating multiple or extended noise sources, and TIDY is e cient in locating moving sources. (v) LP and DAMAS show superresolution. (vi) The dynamic range of source maps could be improved by eliminating the diagonal elements of CSM or CCM but care should be take as this could also eliminate weak sources. Following this study, we discuss the results from the full scale large wind tur- bine noise measurements. Our study focuses on the ability of a compact microphone array to successfully locate both mechanical and aerodynamic noise sources on the wind turbine. Several interesting results have emerged from this study: (i) A compact microphone array is su cient to perform a detailed study on wind turbine noise if advanced deconvolution methods are applied. (ii) Noise sources on the blade and on the nacelle can clearly be separated. (iii) Noise of the blades is dominated by trailing edge noise which is frequency dependent and is distributed along the length of the blade with the dominant noise source closer to the tip of the blade. (iv) The LP and DAMAS algorithms represent the distributed trailing edge noise source better than CLEAN-SC and conventional beamforming. (v) Additional tonal noise produced dur- ing yawing operation is believed to be radiating from the tower of the wind turbine that acts like a resonator. (vi) Ground re ection is not believed to have a signi cant e ect on noise source location estimates in this study. (vii) The asymmetry in the aerodynamic noise is attributed to the Doppler ampli cation e ect. Finally, the noise measurements made on the small scale wind turbine showed that the compact array was successfully able to separate out the mechanical and aerodynamic noise. The mechanical noise from the nacelle was found to be the dominant noise source below 3000 Hz and the aerodynamic noise from the blades was found to be dominant above 3000 Hz. The asymmetry in the aerodynamic noise was also present in this case. The study on mechanical noise found that gear box was the dominant noise source. It is hoped that the work presented in this thesis will serve as a guide to researchers who intend to use compact microphone arrays with advanced beamforming algorithms in the future and also to those who intend to validate theoretical models of wind turbine noise.
Ph.D. in Mechanical and Aerospace Engineering, December 2014
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Title: CREDIT DERIVATIVES AND COUNTERPARTY CREDIT RISK UNDER VOLATILE MARKETS
Creator: Li, Dan
Date: 2012-11-20, 2012-12
Description: Both counterparty credit risk and credit derivatives have come under greater scrutiny under volatile markets especially after the 2007’s...
Show moreBoth counterparty credit risk and credit derivatives have come under greater scrutiny under volatile markets especially after the 2007’s credit crunch and the 2008’s global recession. This dissertation covers three essays topics that reflect different perspectives in credit derivatives and counterparty credit risk under volatile markets. In the first essay topic, we focuses on the modeling challenge after the 2007/2008 crisis in counterparty risks measurement by introducing a 4-factor model for simplicity with extensive comparison with a 2-factor model for both pre-crisis and post-crisis scenarios. Besides the correlation effects and basis risks concluded from the experimental results, those also implied the urgent needs for regulatory standardization (and transparency) for counterparty risk management (e.g. CVA, CSA, collateralization, etc.). Since CDS is one of the main hedging instruments for counterparty risks, therefore, we then tackle CDS in volatile market in our second essay topic. We will review some common practices in handling CDS since the standard bootstrapping failed using conventional JPM (2001). We will also examine the corresponding assumptions and limitations of the latest CDS standardization (ISDA (2009)). And we will compare this with the conventional CDS model. The third essay topic is a modeling survey on CDS with a special underlying – loan (LCDS) that unveils the potential usage and corresponding limitations of each prevailing modeling approach.
PH.D in Management Science, December 2012
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Title: DEVELOPMENT OF PERMEABLE REACTIVE FILTER SYSTEMS (PRFS) FOR TREATMENT OF URBAN STORMWATER RUNOFF
Creator: Prabhukumar, Giridhar
Date: 2013, 2013-05
Description: Urban stormwater runoff is a major contributor of pollutants to nearshore beach water of Lake Michigan and other water bodies. Reduction of...
Show moreUrban stormwater runoff is a major contributor of pollutants to nearshore beach water of Lake Michigan and other water bodies. Reduction of pollutants levels to within safe limits in urban runoff from near shore areas by means of filtration using low-impact reactive multi-media systems is the subject of research in this dissertation. The key research issues addressed are the identification of effective filter materials and laboratory-scale testing of the selected materials for permeable reactive filter systems (PRFS) that are feasible for installation in urban environment. The focus was to evaluate different media materials for removal of total suspended solids (TSS), nutrients (nitrate and phosphate), heavy metals (Cd, Cr, Cu, Pb, Ni and Zn), polycyclic aromatic hydrocarbons (naphthalene and phenanthrene) and microbial (E. coli.) contaminants from stormwater runoff to levels below standard discharge criteria. Eight different media materials were initially selected, including calcite, anthracite coal, zeolite, sand, iron-oxide coated sand (IOCS), iron filings, perlite and biochar. Of these, calcite (C), zeolite (Z), sand (S) and iron filings (Fe0) were screened based on preliminary column experiment results and used for further studies. Physical and chemical characterization studies were carried out to understand the material properties. Contaminant attenuation studies with lab-scale column experiments for the four individual media materials (C, Z, S and Fe0) were conducted with synthetic stormwater solution containing all the aforementioned pollutants. Results showed that calcite and sand were efficient in TSS, nutrients and polycyclic aromatic hydrocarbons (PAHs) removal, zeolite was efficient for metals removal and the only material that was able to lower E. coli level to below its safe xv limit of 126 most probable number (MPN) per 100ml, and iron filings was efficient in nutrients and metals removal. Column experiments were also conducted with three mixed media compositions, C-Z-S, C-Z-Fe0 and C-Z-S-Fe0. The results indicated that a multi-media based filtration system can perform efficiently to treat a wide range of pollutants and runoff flow conditions. Finally, several conceptual designs for PRFS were proposed that are suitable for application at various urban locations.
PH.D in Environmental Engineering, May 2013
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