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Title: Essays on Empirical Corporate Finance
Creator: Yang, Zihao
Date: 2020
Description: This thesis consists of two essays on empirical corporate finance. The first essay examines the influence of corporate tax on corporate social...
Show moreThis thesis consists of two essays on empirical corporate finance. The first essay examines the influence of corporate tax on corporate social responsibility (CSR) investment. This essay takes advantage of the dynamic changes on state corporate taxes from 2003 to 2016 and explores the causal effects of the tax changes on firms’ CSR outcomes. Applying a difference-in-difference approach, I find that tax effects on CSR are asymmetric. Tax cuts lead to significant improvement of CSR ratings, especially in the concern issues. Tax hikes, on the other hand, lead to deterioration of CSR strength, but have no effect on CSR concerns. I also find that CSR investment from financial constrained firms is more sensitive to tax changes. The second essay studies the financial effect of suppliers’ initial public offering (IPO) on their customer companies. By analyzing matched supplier companies and their large customers, I find that customer companies lose value in both short-run and long-run time periods after suppliers’ IPO events. These customer companies also have higher risk compared to those whose suppliers do not go public. Moreover, I explore the channels of suppliers’ IPO effect on their customers. The results show that suppliers diversify customers and reduce trade credit after IPO. Finally, I find that the supply chain relationships are more likely to terminate after suppliers going public.
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Title: PREPARATION OF MG3SB2-XBIX THERMOELECTRIC MATERIAL AND THEIR LASER SINTERING BEHAVIOR
Creator: Xiao, Xudong
Date: 2020
Description: In the introduction part, a novel thermoelectric material, Zintl compounds were introduced due to its potential high thermoelectric...
Show moreIn the introduction part, a novel thermoelectric material, Zintl compounds were introduced due to its potential high thermoelectric performance in low-temperature applications as thermoelectric devices. Recent researches focused on Mg3Sb2-based Zintl Compounds was summarized in this article, and the general methods and its limitations to fabricate Mg3Sb2-based thermoelectric modules were introduced. Thus, a novel selective laser melting process was introduced, and it has enormous potential to fabricate Mg3Sb2-based thermoelectric modules in commercial applications. What’s more, the challenges of selective laser melting method were also discussed in the articles. For developing selective laser melting as the mature method to fabricate Mg3Sb2-based thermoelectric modules, many works and researches need to be done. In my project, the powder of Mg3.1(Sb0.3Bi0.7)1.99Te0.01 thermoelectric material was synthesized by using the mechanical alloying process and the proper particle size and distribution of powder using for selective laser melting was obtained by increasing the time of mechanical alloying. The thermoelectric properties of the powder prepared by mechanical alloying were measured, and it shows the powder still in a good performance after a long-time mechanical alloying particle reduction process. Finally, the obtained powder was treated by different parameters of continued wave fiber laser. The morphology and composition of the sintered area were analyzed to better understanding the process of laser sintering. More work needs to be done for using a selective laser melting method to fabricate Mg3Sb2-based thermoelectric modules in the future.
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Title: PURIFICATION AND ANALYSIS OF BAXΔ2 PROTEIN AGGREGATES FROM MAMMALIAN CELLS
Creator: Wang, Xiling
Date: 2020
Description: BaxΔ2 is a unique isoform of the proapoptotic protein Bax that does not target mitochondria. The proapoptotic function of BaxΔ2 is through...
Show moreBaxΔ2 is a unique isoform of the proapoptotic protein Bax that does not target mitochondria. The proapoptotic function of BaxΔ2 is through forming cytotoxic aggregates in the cytosol. The cytotoxicity of BaxΔ2 is known as associated with the BH3 killing domain and the C-terminus, which recruits caspase 8. BaxΔ2 proteins without C-terminal form large cytosolic protein aggregates unable to induce caspase 8-dependent cell death. Since abnormal cytosolic protein aggregates often contain complexes of proteins that involved in many diseases, we would like to purify BaxΔ2 aggregates and examine their components. In this study, we expressed GFP-tagged BaxΔ2(Δ6) in the Bax-negative HCT116 cell line and purified the aggregates via different digestion processes. We found that most aggregates were trapped into a DNA pellet after cell lysis. Digestion with DNase could release the aggregates, which were susceptible to detergent solvent. The yield of purification is very low and needed improvement. The results from Western Blot showed that, in addition to BaxΔ2 proteins, stress granule protein TIAR was also potentially in the aggregates. Identification of the components inside aggregates will help us to understand the mechanism of BaxΔ2 cytotoxicity.
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Title: Electronically Assisted Direct Current Circuit Breakers
Creator: Feng, Yanjun
Date: 2019
Description: DC power is gaining tractions recently, however, DC fault protection remains a major technical challenge. Popular and cost-effective AC...
Show moreDC power is gaining tractions recently, however, DC fault protection remains a major technical challenge. Popular and cost-effective AC mechanical circuit breakers do not offer sufficient DC interruption capability. Solid state circuit breakers have drawbacks of high cost and high conduction loss. The reported hybrid circuit breakers solutions require fast responding current sensors and mechanical actuation mechanism vastly different from and far more complex than the conventional AC circuit breakers.This thesis introduces a new DC hybrid circuit breaker concept termed Electronically Assisted Circuit Breaker (EACB). A conventional AC mechanical circuit breaker (MCB) is used to interrupt DC fault currents with the assistance of an electronic commutation circuit, which is activated for a short time period only during the late phase of the breaking process. Unlike other prior art HCB concepts, an EACB uses (1) a conventional thermal-magnetic AC baseline breaker design with minimal modification; and (2) an electronic commutation circuit which only needs to commutate a fault current already reduced from its peak for a very short duration (~100µs), both contributing to significant cost savings. While an EACB does not facilitate arc-free or ultrafast breaking, it does provide a simple and cost-effective way to enhance the DC current interruption capability of conventional thermal-magnetic AC circuit breakers currently dominating the low voltage circuit breaker market. The EACB concept has been validated both experimentally and by simulation. A 600VDC/250A (nominal) EACB prototype is designed and tested. It has experimentally demonstrated a fault current interruption capability of over 8kA at a DC voltage of 600V within 6 milliseconds.
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Title: FAST AUTOMATIC BAYESIAN CUBATURE USING MATCHING KERNELS AND DESIGNS
Creator: Rathinavel, Jagadeeswaran
Date: 2019, 2019-12-20
Publisher: Chicago
Description: Automatic cubatures approximate multidimensional integrals to user-specified...
Show moreAutomatic cubatures approximate multidimensional integrals to user-specified error tolerances. In many real-world integration problems, the analytical solution is either unavailable or difficult to compute. To overcome this, one can use numerical algorithms that approximately estimate the value of the integral. For high dimensional integrals, quasi-Monte Carlo (QMC) methods are very popular. QMC methods are equal-weight quadrature rules where the quadrature points are chosen deterministically, unlike Monte Carlo (MC) methods where the points are chosen randomly. The families of integration lattice nodes and digital nets are the most popular quadrature points used. These methods consider the integrand to be a deterministic function. An alternate approach, called Bayesian cubature, postulates the integrand to be an instance of a Gaussian stochastic process.
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Title: Impact of powder heterogeneity on particle collection behaviors in a cylindrical electrostatic precipitator
Creator: Lee, Eric Monsu
Date: 2019
Description: Injection of powdered activated carbon (PAC) upstream of electrostatic precipitators (ESPs) has been the most commonly used strategy for post...
Show moreInjection of powdered activated carbon (PAC) upstream of electrostatic precipitators (ESPs) has been the most commonly used strategy for post-combustion mercury emissions control at coal-fired power plants. However, as PAC injection rate increases, the darkening filters with particulate matter (PM) samples collected downstream of ESPs indicates an unidentified performance anomaly. It has been hypothesized that injection of PAC can introduce unexpected heterogeneity to the PM collection process in ESPs as PAC differs greatly from fly ash in both physical and electrical properties and can potentially pose challenges to ESPs that were initially operated for coal fly ash removal. The present study is carried out by an experimental study and a numerical study. The experimental study centers on the differential collection of PAC-fly ash admixtures and shows increasing trends of unaccounted-for particles as PAC concentration increases in the admixtures. In addition, measurement of powder resistivity of the ESP-collected powder samples infers that the unaccounted-for particles become more PAC-concentrated as PAC concentration becomes higher in the admixtures. The numerical study aims to extract additional variable(s) leading to higher percentage of unaccounted-for particles by using COMSOL Multiphysics. The Euler-Lagrange numerical scheme enables the modeling of the cylindrical ESP used during the experimental study and allows for solving the interrelated physics, including electric field coupled with charge conservation, electro-hydro-dynamics (EHD) fluid velocity field, and particle tracing. The model shows that the induced EHD vortex flow field due to the inhomogeneous current density along the collection electrode can result in continue entrainment of sub-micrometer particles of both fly ash and PAC. The experimental and numerical results provide new understanding for explaining the increasingly darkening PM filters as PAC injection rate increases.
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Title: Implementation of a multisensor wearable artificial pancreas platform: ensuring safety with communication robustness and cyber security
Creator: Lazaro Martinez, Carmen Caterina
Date: 2019
Description: Advances in IoT technologies and new sensor capabilities contributed to the rapid growth of wearable medical devices. Today, mobile sensor...
Show moreAdvances in IoT technologies and new sensor capabilities contributed to the rapid growth of wearable medical devices. Today, mobile sensor platforms can be effectively, cost efficiently integrated in healthcare applications. However, the increased risks of these devices, inherent vulnerabilities of mobile operating systems and open nature of the wireless protocols call for improved safety and security measures to prioritize patient's well-being. In the field of type 1 diabetes, blood glucose level management with insulin control algorithms are available in diabetes therapy systems, though none are fully automated and require extra announcements (such as meal and exercise) to operate. A mobile artificial pancreas (AP), based on Android smartphone, is developed: such a platform relies on off-the-shelf components and receives in real-time the physiological measurements from the wrist worn physical activity tracker and the glucose measurements, then used in a predictive control algorithm (originally developed and tested on a laptop), to compute the optimal amount of insulin to administer via an insulin pump. A dedicated remote server provides additional support for registration, authentication and data backup.The nature of the algorithm required a fast, reliable method to translate its inherent functions. Therefore, we implement a new semi-automatic conversion mechanism which ports MATLAB to Android as native C code. Validation tests of the mobile version confirm there are no deviations in the results.Moreover, in order to enhance safety guarantees for the patient, this cyber-physical system needs a robust implementation also resilient to attacks and failures. A central monitor module is introduced, wherein wireless devices and communications channels are integrated with complementary alarm and safety subsystems. The parameterization of the AP as a state machine demonstrates the efficiency to detect and react to possible errors, since any state change triggers the appropriate correcting response. The result is a protected and fail-safe environment, further expanded with security modules enforcing encryption, authenticated access and data-flow rules for intrusion detection.Overall, this research demonstrates, in the case of an AP, how challenges in diverse fields such as sensor fusion, control systems, wireless communications and cybersecurity can be addressed with a holistic approach for mobile health (mHealth).
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Title: An adaptive personalized multivariable, multimodule artificial pancreas system based on a plasma insulin cognizant model predictive control
Creator: Hajizadeh, Iman
Date: 2019
Description: An adaptive and personalized multivariable artificial pancreas system is proposed for effective glycemic control and disturbance rejection...
Show moreAn adaptive and personalized multivariable artificial pancreas system is proposed for effective glycemic control and disturbance rejection without manual user announcements for meals and exercise. Adaptive models identified through system identification techniques are integrated with a physiological compartment model to characterize the time-varying glucose-insulin dynamics. The real-time estimation of plasma insulin concentration to quantify the insulin in the bloodstream in patients with type 1 diabetes mellitus is presented. The identified time-varying models are employed for the design of an adaptive model predictive control formulation that is cognizant of the plasma insulin concentration. A feature extraction method based on glucose measurements is used to detect rapid deviations from the desired set-point caused by significant disturbances and subsequently modify the constraints of the optimization problem for negotiating between the aggressiveness and robustness of the controller to suggest the required amount of insulin. A predictive hypoglycemia module with carbohydrate suggestion is also designed to prevent any potential hypoglycemia events. A controller performance assessment algorithm is developed to analyze the closed-loop behavior and modify the parameters of the artificial pancreas control system. To this end, various performance indices are defined to quantitatively evaluate the controller efficacy in real-time. The controller assessment and modification module also incorporates on-line learning from historical data to anticipate impending disturbances and proactively counteract their effects.
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Title: Electron Cloud studies at Fermilab
Creator: Ji, Yichen
Date: 2019
Description: The presence of unwanted electrons in an accelerator vacuum chamber, known as E-cloud (E-cloud) can potentially cause operational problems in...
Show moreThe presence of unwanted electrons in an accelerator vacuum chamber, known as E-cloud (E-cloud) can potentially cause operational problems in the Fermilab Main Injector (MI) and Recycler Ring (RR). E-cloud has caused instability in the RR in the past, and although it is not currently a problem, there is measurable E-cloud in the MI accelerator. There are planned beam intensity increases due to upgrades of the Fermilab accelerator complex, so E-cloud could become a problem. Some work has been done by others previously to understand how low SEY (Secondary Electron Yield coefficient) coatings might mitigate production of E-cloud, and to model the mechanism whereby E-cloud causes beam instability. Using previous studies as a base, this research took several approaches toward understanding the risk of E-cloud at Fermilab. The evolution of the SEY of the SS316L (stainless steel), TiN coated SS316L, and amorphous carbon coated SS316L were measured in-situ using a SEY measurement station in the MI tunnel. The SEY of these materials change over time either due to bombardment of the E-cloud, or disruption of vacuum conditions. The SEY evolution was tracked over a several year period to find out how long it takes for the SEY of each material to reach its lowest level, and how much the SEY rises during deconditioning periods of poor vacuum. The SEY measurement results can be used to determine whether the SS316L will be a problem at upgrade intensities, and if so, whether or not TiN and A-Carbon coatings can mitigate E-cloud related problems sufficiently. Direct measurements of the E-cloud were done as well, and compared to simulation. The E-cloud bombardment rate was measured at different beam intensities and bunch lengths. It was possible to get detailed information on how the E-cloud varies over the acceleration cycle, where sensitivity to bunch length is reflected in the evolution of the E-cloud. The Retarding Field Analyzer (RFA) measuring the E-cloud bombardment rate was near the instrument that is used to measure the SEY of the beam pipe material. This proximity provided an accurate SEY value for simulations, so that the simulated E-cloud bombardment rate could be better compared to measurement. Bunch length measurements and computations generated accurate bunch length information also needed as input for simulations. After this careful control of the input parameters, the POSINST simulations of E-cloud were a good match to direct measurements. This gave confidence that predictions could be made concerning the E-cloud densities at upgrade intensities. These densities were compared against corresponding proton densities to predict the SEY required to avoid instabilities. That prediction and the information provided by the SEY measurements provide helpful information regarding the risks of E-cloud effects at future beam intensities at Fermilab.
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Title: Measuring Maternal-Fetal Attachment: Model Fit and Measurement Invariance of a New Assessment Tool
Creator: Hedrick, Laura
Date: 2019
Description: The importance of studying Maternal-Fetal Attachment (MFA) as part of the system of maternal-child perinatal functioning is well established...
Show moreThe importance of studying Maternal-Fetal Attachment (MFA) as part of the system of maternal-child perinatal functioning is well established in the literature, as MFA relates to health-related and psychosocial variables both during pregnancy and after the infant is born (e.g., positive health behaviors in pregnancy; levels of maternal stress, anxiety, and depressive symptoms; positive parenting behaviors after the child is born; and secure infant attachment at age one year). Despite the apparent value of studying MFA, there is no acceptable measurement tool for the construct. Existing assessment tools often do not meet minimum psychometric standards, may not be practical for broad research application, and have demonstrated inconsistent results in correlational research. Therefore, a clear need exists for a measurement scale with strong psychometric properties that is based on empirically supported development strategies. The present line of research sought to fill this need. The process of developing a new measurement tool began in a previous study, Hedrick (2015), which used Exploratory Factor Analyses to identify options for a potential measurement scale from subsets of a large pool of items intended to measure MFA. In Hedrick (2015), three options were identified as acceptable, then compared based on ranges of communalities, percentage of variance explained, internal consistency, and performance on two measures of concurrent and discriminant validity. However, these assessments failed to differentiate a single option as most preferable. Therefore, the first aim of present study was to complete the task of differentiating among the working measures to choose a measurement scale. Confirmatory Factor Analysis (CFA) was used to attempt to determine which working measure from the EFA study had the factor structure that fit best in a second sample of participants. The CFA process was not able to differentiate a superior working measure from the options. Therefore, the most theoretically sound of the three was chosen to use as a measurement tool, with some small adjustments made based on the CFA results. To continue to establish the validity of the new questionnaire measure, the second aim of the study was to assess its measurement invariance among different administration methods and populations. The measurement tool was found to be non-invariant in both areas. Specifically, the results of the measurement invariance analyses indicated that the measure should be administered on paper rather than online, would be best applied in research in African American/Black populations than in research with other racial/ethnic groups, and should not be used to compare MFA scores among racial/ethnic groups. Measurement invariance analyses also revealed that the scale was non-invariant at the metric level regarding parity groups. The implications of these findings for further research is discussed.
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Title: Security analysis in device-to-device wireless networks
Creator: Liu, Kecheng
Date: 2019
Description: Device-to-device (D2D) network has now become a standardized feature in many mobile devices, by which mobile devices can communicate with each...
Show moreDevice-to-device (D2D) network has now become a standardized feature in many mobile devices, by which mobile devices can communicate with each other even when internet access is not available. Because D2D network is expected to be an intrinsic part of the Internet of Things (IoT) and mobile device is the smartest and the most advanced commercial device in everyday usage, the D2D feature and related security protocols can influence the design and implementation of many other IoT devices. While D2D network provides tangible benefits to users, it also raises the security risks of information leaking. Our work performs an in-depth systematical security analysis on 802.11 based D2D network among commercial devices, including personal mobile devices such as phones and tablet, as well as business POS and printers. In this paper, we focus on most popular apps in the Google Play Store, the best selling printers in the market and the most widely adopted commercial POS devices for small businesses. Our analysis reveals some critical vulnerabilities. The key findings are multi-fold. First, the current mobile D2D network framework established on 802.11 protocol has significant flaw of over-privileged issue. Second, we have identified that data transfer over D2D network can be eavesdropped. Furthermore, we exploit the identified framework flaws to construct multiple proof-of-concept attacks and we conclude the paper with security lessons and suggestions of possible solutions against the identified security issues.
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Title: SODIUM-BASED ENERGY METABOLISM AND DYNAMIC ENERGY DEPENDENCY OF CHLAMYDIA TRACHOMATIS
Creator: Liang, Pingdong
Date: 2019
Description: Chlamydia trachomatis is an obligate intracellular bacterium that is responsible for various human diseases including trachoma, genital tract...
Show moreChlamydia trachomatis is an obligate intracellular bacterium that is responsible for various human diseases including trachoma, genital tract infections, and lymphogranuloma venereum. Energy metabolism consists many essential pathways to generate energy for every organism. However, it remains much unknown in C. trachomatis. For decades, C. trachomatis has been considered as an “energy parasite”, which needs the energy supply from the host cells entirely. In contrast, genomic studies show that this bacterium is capable of encoding enzymes that involve energy metabolism. However, no experimental data were provided to support the genomic information due to the peculiar developmental cycle of C. trachomatis inside the host cells. In this project, the oxidative phosphorylation pathway of C. trachomatis is first identified with experimental results. This pathway starts with the sodium pumping NADH:Ubiquinone oxidoreductase enzyme complex (NQR) transferring the electrons along the respiratory chain and generating a sodium gradient across the membrane. C. trachomatis contains an A-type ATPase that can utilize this sodium gradient to generate ATP. In vitro experiments in mammalian cells with different respiratory inhibitors show that C. trachomatis is not an obligate energy parasite. Instead, it has a dynamic energy dependency on the host metabolism that the bacterium switches from entirely to partially relying on the host energy metabolism for its energy requirement. The sodium gradient established by NQR and/or other transporters is of great importance to chlamydial metabolism. Further, the respiratory inhibitors test on interferon-γ-induced persistence of C. trachomatis in mammalian cell cultures shows that an inhibited energy metabolism prevents and eliminates the persistent form. This study provides new insights about antibiotics development and therapeutic methods against C. trachomatis infections.
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Title: Silkworm silk - CNT composite fibers: fabrication, characterization and application in cell stimulation for tissue regeneration
Creator: Zheng, Shuyao
Date: 2019
Description: Silk fibroin, a structural protein of the Bombyx mori cocoons, is widely studied for biomedical applications because of its strong mechanical...
Show moreSilk fibroin, a structural protein of the Bombyx mori cocoons, is widely studied for biomedical applications because of its strong mechanical property, biocompatibility, low degradation rate and ease of processing. In this study, we incorporated functionalized CNT in silkworm silk proteins to generate biocomposite fibers by electrospinning. The electro-spun (E-spun) fibers were unidirectionally aligned with a diameter at the sub-micrometer scale, mimicking the locally oriented ECM proteins in native tissues. The addition of a minute amount of CNT not only reinforced the stability and the mechanical strength of the flexible scaffolds, but also rendered the fibers electrical conductivity to not only facilitate the E-spun fiber formation but also grant the fibers an additional functionality that can be utilized for cell stimulation. It is known that endogenous electric field is present in the human body at various locations and plays critical physiological roles through its effect on cell proliferation, migration and activation mediated by its interference with growth factor secretion and intracellular signaling pathways. Electrical stimulation (ES) has been widely investigated as a potential method to regulate cell functions for the treatment of a number of diseases. It has been reported that in dermal fibroblasts, ES induces the secretion of FGF-1 and FGF-2 which promotes cell proliferation, contraction, migration, and activation/differentiation into myofibroblasts for increased collagen synthesis in favor of tissue repair. In this work, the modulation effect of the aligned E-spun SWS-CNT fibers was examined by their application in inducing polarization and activation of fibroblasts with cellular deficit, like those from pelvic organ prolapse (POP) patients. These cells are characterized by low productivity of collagen with abnormally high COLI/COLIII ratio, leading to a loose and fragile collagen network, decreased integration among the tissue constituents and reduced tissue strength. Electrical stimulation boosted the collagen productivity by 20 folds in cells on silk-CNT than on pure silk due to silk-CNT’s high electrical conductivity. The developed approach can be potentially utilized to remedy the dysfunctional fibroblasts for therapeutic treatment of diseases and health conditions associated with collagen disorder.
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Title: Energy Scale Study for PROSPECT's Measurement of the Antineutrino Spectrum of 235U
Creator: Zhang, Xianyi
Date: 2019
Description: Neutrinos from nuclear fission reactors have been widely studied in particle and nuclear physics. In the last ten years, the antineutrino flux...
Show moreNeutrinos from nuclear fission reactors have been widely studied in particle and nuclear physics. In the last ten years, the antineutrino flux and spectrum were measured independently by short baseline reactor experiments. Both flux and spectrum measurements showed discrepancies compared to theoretical models based on historical measurements and nuclear databases. These discrepancies hint at sterile neutrino oscillation at the eV mass scale, as well as an incomplete theoretical model. PROSPECT, the Precision Reactor Oscillation and Spectrum experiment, was built to probe for sterile neutrino oscillations and precisely measure the reactor antineutrino spectrum from a highly 235U enriched reactor. The PROSPECT antineutrino detector is an optically segmented liquid scintillator detector deployed at seven meters to nine meters from the High Flux Isotope Reactor at Oak Ridge National Laboratory. This dissertation details the analysis to calibrate the energy scale of the PROSPECT antineutrino detector, an essential step for both the oscillation and spectrum measurements. To characterize the nonlinear detector energy response, a unique calibration and analysis strategy was developed to overcome challenges brought on by particle multi-segment scattering within the PROSPECT detector. With the calibrated scale for energy reconstruction, PROSPECT measured of the antineutrino spectrum from a 235U-burning reactor.
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Title: ENGINEERING HUMAN ADIPOSE TISSUE WITHIN A MICROFLUIDIC DEVICE
Creator: Yang, Feipeng
Date: 2019
Description: Adipose tissue models can be used for in vitro drug screening of therapeutics designed for the treatment of obesity or adipose tissue-related...
Show moreAdipose tissue models can be used for in vitro drug screening of therapeutics designed for the treatment of obesity or adipose tissue-related diseases. This work aimed to engineer functional three-dimensional (3D) adipose microtissue models that could be incorporated within a microfluidic system. To support the on-chip 3D culture, a microfluidic device consisted of cell culture chambers flanked by two side channels was designed. The mold for the microfluidic device was manufactured using computer numeric control (CNC) micro-milling. Soft lithography with polydimethylsiloxane (PDMS) was used to construct the microchannels and chambers in the microfluidic device. A model was developed by the monoculture of adipocytes within the microfluidic device. Human adipose-derived stem cells (ADSCs) were differentiated toward adipocyte in the cell culture chambers and formed a 3D adipose microtissue. The effect of interstitial flow on the adipogenic differentiation of ADSCs was explored. Adipocytes showed decreased adiponectin secretion and increased lipolysis in response to increased interstitial shear stress. Meanwhile, multiple adipogenic genes were downregulated with the increase in shear stress.To engineer vascularized adipose tissue, a co-culture system with ADSCs, human umbilical vein endothelial cells (HUVECs) and normal human lung fibroblasts (NHLFs) was applied. Culture conditions (media, cell ratios, temporal conditions, etc.) for optimal differentiation of ADSCs and induction of network formation were identified. ADSCs were induced toward adipogenesis before mixed with HUVECs and NHLFs. The cell mixture was loaded into the microfluidic device and formed an adipose microtissue with a vessel network in a mixed culture media. An interconnected vascular network was established within 2 weeks and formed anastomoses with the side channels. Perfusion of fluorescent dextran confirmed the interconnections and lumen formation of the vascular network. Perfusion of fluorescently labeled fatty acid analog through vessels resulted in the accumulation of the fatty acid in adipocytes, confirming the functionality of the adipose microtissue. In conclusion, this work presented adipose tissue models within a microfluidic device that can potentially be utilized for on-chip drug screening, as well as provide insights into the engineering of complex tissues.
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Title: Control Surface Synthesis of Propane Dehydrogenation Catalysts
Creator: Zhao, Yiqing
Date: 2019
Description: Alkane dehydrogenation is one of the primary chemical reactions to convert light alkanes into light olefins. The conversion of small alkanes...
Show moreAlkane dehydrogenation is one of the primary chemical reactions to convert light alkanes into light olefins. The conversion of small alkanes to alkenes by dehydrogenation reactions is important for polymer and chemical industrial process because it makes direct producing the possible alkenes. Controlled synthesis of single-site catalysts are still challenges. This makes tuning of the catalysts structure and active sites difficult. We developed method of Zirconium modified SiO2 to support single-site catalysts. My research is focusing on the synthesis new single-site heterogeneous catalysts for high selectivity alkane dehydrogenation reaction and the general principles to design better preformed catalysts (e.g., more active, more selective, more stable) for dehydrogenation reaction, especially on propane dehydrogenation. The study described in this thesis was conducted to understand how zirconium ions can modify the electronic properties and catalytic performance.In this study, with the Zr promoted cobalt catalysts show high propane conversion and propene selectivity compared to the previous reported Co/SiO2 catalyst by our group previous work. The Co/Zr/SiO2 material exhibited good catalytic activity, stability and high propylene selectivity which can reach up to 97% for catalytic propane dehydrogenation at 550 ℃. The catalyst was characterized by TEM, STEM, EPR, DRIFTS, UV-vis, XANES and EXAFS for synthesized material, under reaction conditions and post reaction samples. We hypothesized the reason behind is due to the π donation of Zr will lead to ease of heterolytic cleavage of the propane by have a lower metal-oxygen bond dissociation energy in the rate-determining step which is consistent with the previous calculations found that weaker catalyst-oxygen bonds led to facile heterolytic cleavage. A varieties of single-site Ga catalysts supported on Zr modified SiO2 were synthesized by different methods. The Ga/Zr/SiO2 catalysts prepared by the difference method also exhibit higher or similar activity and selectivity. Those catalysts have more isolated active sites show that rational catalyst design method, such as surface organometallic chemistry synthesize, can be applied in heterogeneous systems using homogeneous catalyst design method. But the origin of those effects is unclear, some discussion of possible origins of observation of catalysts behavior are discussed in Chapter 4. And we will do more characterization to find the origins behind.
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Title: NUMERICAL ANALYSIS ON MAXIMUM LIKELIHOOD ESTIMATORS FOR LINEAR PARABOLIC STOCHASTIC PARTIAL DIFFERENTIAL EQUATIONS
Creator: Zhang, Jun
Date: 2019
Description: The thesis contributes to the numerical analysis on statistical inference for stochastic partial differential equations (SPDEs). We study the...
Show moreThe thesis contributes to the numerical analysis on statistical inference for stochastic partial differential equations (SPDEs). We study the maximum likelihood estimation problem of the drift parameter for a large class of linear parabolic SPDEs. As in the existing literature on statistical inference for SPDEs, we take a spectral approach, and assume that one path of the first N Fourier modes is observed continuously in a fixed finite time interval [0, T]. We first provide a review of the asymptotic properties of the maximum likelihood estimator (MLE) of the drift parameter in the large number of Fourier modes regime, N  ∞, while the time horizon T > 0 is fixed. The main part of this thesis is dedicated to the numerical study of the asymptotic properties of the MLEs for two examples of linear parabolic SPDEs: the one-dimensional stochastic heat equation and a d-dimensional linear, diagonalizable, parabolic SPDE, where d  ℕ. For the one-dimensional stochastic heat equation, we perform the sensitivity analysis to assess the effect of changes in model parameters on the speed of convergence of the MLE. For the second linear parabolic SPDE, our simulations verify the theoretical results in the literature that both the consistency and asymptotic normality of the MLE hold for such equation only when d ≥ 2.
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Title: Physics at the MeV-Scale in Liquid Argon Time Projection Chambers
Creator: Lepetic, Ivan Thomas
Date: 2020
Description: The liquid argon time projection chamber (LArTPC) is the detection technology chosen for several Fermilab-based neutrino experiments. This...
Show moreThe liquid argon time projection chamber (LArTPC) is the detection technology chosen for several Fermilab-based neutrino experiments. This technology will be used in studies of neutrino cross-sections and oscillations, neutrinos from supernovae as well as a variety of studies of beyond the Standard Model physics. This thesis explores the use of these detectors to study MeV-scale activity. MeV-scale electrons arising from Compton scatters of deexcitation photons and photons from inelastic neutron scattering in neutrino-nucleus interactions are reconstructed using novel methods presented here. This work represents the first demonstration of MeV-scale physics capabilities in a LArTPC neutrino experiment as well as the first observation of neutrino-produced photons from nuclear de-excitation and inelastic neutron scattering. A search for millicharged particles, postulated by theories of beyond the standard model physics, is also performed using data from a LArTPC and the low-energy reconstruction techniques developed. The results set world-leading bounds on the parameter space of millicharged particles. The work in this thesis demonstrates that studies of MeV-scale activity and new physics are possible with LArTPC technology and provides the foundation for future LArTPC studies of low energy neutrinos and new physics.
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Title: Gradient Hydrogels for Neovascularization of Engineered Tissues
Creator: He, Yusheng Jason
Date: 2020
Description: The inability to induce extensive and perfusable microvasculature within complex engineered tissues that possess spatial variations in...
Show moreThe inability to induce extensive and perfusable microvasculature within complex engineered tissues that possess spatial variations in mechanical properties, physical architecture and biochemical composition remains as a major hurdle to their clinical translation. Biomaterial strategies focused on designing scaffolds with physiologically relevant gradients provide a promising means for elucidating 3D vascular cell responses to spatial and temporal variations in matrix properties. This work developed a cell-laden hydrogel platform with tunable decoupled and combined gradients of multiple matrix properties critical for maintenance of long term-vascular cell viability, adhesion, migration and invasion outgrowth to elucidate the impact of gradient matrix cues on 3D neovascularization in culture. This was achieved through the completion of three specific aims. First, a novel ascending frontal polymerization (AFP) technique was developed to generate gradient-based PEG hydrogel scaffolds with tunable individual and combined matrix gradients. Using programmable syringe pumps to control the delivery of precursors with distinct composition during crosslinking, we were able to generate gradient scaffolds with decoupled spatial variations in the immobilized concentration of the RGD cell adhesion peptide ligand and elastic modulus. Using this approach, the slope and magnitude of the imposed RGD gradients were readily manipulated without inducing variations in elastic modulus. Vascular spheroids inserted into gradient hydrogel scaffolds supported 3D vascular sprout formation, while the immobilized RGD gradient promoted an increase in sprout length towards the imposed gradient. Next, to create cell-laden scaffolds photopolymerization conditions were optimized to enable viable cell encapsulation during scaffold fabrication. To achieve this, an experimental sensitivity analysis combined with the design of experiments (DOE) was implemented to design isotropic hydrogel scaffolds with a broad range of matrix properties (elastic modulus, immobilized RGD and proteolytic degradation) that supported vascular sprouting in 3D culture. We examined the individual and interaction effects of each matrix property and demonstrated that an optimal combination associated with increases in immobilized RGD and proteolytic degradation of mediate synergistic enhancements in 3D vascular sprouting. Based on the findings from this in vitro study with isotropic hydrogel scaffolds, we designed scaffolds with 5 types of gradient combinations in immobilized RGD, stiffness and protease-sensitivity and explored the impact of spatial variations these matrix cues on vascular sprouting within the constructs in 3D culture. Specifically, we created hydrogel scaffolds with gradients in immobilized RGD with (1) steep and (2) shallow slopes, (3) gradients in elastic modulus, (4) gradients in protease-sensitivityand and (5) opposing gradients of RGD and modulus and concurrent gradients of protease sensitivity and RGD. By encapsulating vascular spheroids in different regions of each gradient scaffold, we observed spatial variations in total sprout length within all gradient scaffolds. We also found that RGD gradient and combined gradient scaffolds induced biased vascular sprouting toward increased RGD concentration and that biased sprouting was enhanced by gradient magnitude and slopes of immobilized RGD concentration. Conversely, directional sprouting responses diminished in scaffolds possessing opposing gradients in RGD (with concurrent gradients of degradation) and modulus. The presented work is the first to demonstrate the use of a cell-laden biomaterial platform to explore the impact of gradients in RGD, proteolytic degradation, and stiffness on vascular sprouting responses in 3D culture. The presented platform and findings of this thesis work hold great potential in the fields of tissue engineering specifically for prevascularization of complex tissues that possess spatial variations in mechanical properties, degradation rate and adhesion ligand composition to facilitate their regeneration.
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Title: THREE ESSAYS IN ENTREPRENEURIAL FINANCE AND COMMODITY MARKETS
Creator: Jia, Jian
Date: 2020
Description: This dissertation includes three essays with a series of empirical investigations in areas of entrepreneurial finance and commodity markets.In...
Show moreThis dissertation includes three essays with a series of empirical investigations in areas of entrepreneurial finance and commodity markets.In the first essay, I study the impact of General Data Protection Regulation (GDPR) on investment in new and emerging technology firms. My findings indicate negative post-GDPR effect after its 2018 rollout on EU ventures, relative to their US counterparts, but no such effects following its 2016 enactment.In the second essay, I examine how investors’ tendency to prefer investing in local ventures interacts with the effects of the GDPR on venture investment in EU. I demonstrate that GDPR’s enactment and rollout differentially affect investors as a function of their proximity to ventures. Specifically, I show that GDPR’s rollout in 2018 has a negative effect on EU venture investment and the effects are higher when ventures and lead investors are not in the same country or union. The relationship manifests in the number of deals per month and in the amount invested per deal, and is particularly pronounced for newer and data-related ventures.In the third essay, I formulate two claims about spot and futures return prediction in industrial metal futures market. These claims lead to testable hypotheses, and provide theory-based restrictions for the coefficients of spot and futures return regression. I investigate six industrial metals and find empirical support for my hypotheses. The in-sample and out-of-sample evidence shows that financial variables, proxies for global economic activities, and the basis predict futures and spot price returns consistently with my hypotheses. Furthermore, my out-of-sample trading experiments document economic significance of the restrictions.
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