Search results

Title: WEB-BASED CONTEMPORANEOUS DELAY ANALYSIS
Creator: Pektas, Murat
Date: 2011-11-22, 2011-12
Description: The construction industry is fragmented due to the many stakeholders and the diverse phases involved in a construction project. On time,...
Show moreThe construction industry is fragmented due to the many stakeholders and the diverse phases involved in a construction project. On time, within budget, with required quality are essentials of a successful project. However, most construction projects are faced with delays, which obstruct success. To recover the damage caused by delays, both the delays and the parties responsible for them should be identified accurately. Daily window delay analysis outperforms other delay analysis methods, but it requires intensive day-by-day information. The information flow among the project stakeholders must be smooth and speedy at all stages of the production process not only to achieve the basic project objectives but also to let project stakeholders recognize the delays and the parties responsible for them in order to recover time and cost. The Internet is attractive for transferring information promptly and economically with no regional or temporal borders. To merge the power of the Internet and to ease time consuming delay analysis, a web-based application is proposed to analyze delays effectively and contemporaneously, to reduce time and cost, and to provide historical data. The application considers the day-by-day variation in critical path(s) during the project life cycle. The application gives accurate and repeatable results for apportioning project delays, accelerations and decelerations among involved parties. The manual effort required by traditional systems is minimized with the application’s simple, easy to use, yet effective and highly automated features. Moreover, the database structure of the application is designed to store and manage more than one project at a time to let its users calculate the overall performance of the company including all projects, and to calculate average durations for activities that can come up in future projects.
M.S. in Civil Engineering, December 2011
Show less

Title: TASK/STAFFING-TECHNOLOGY FIT IN CONSTRUCTION SCHEDULING
Creator: Yang, Juneseok
Date: 2015, 2015-07
Description: Construction managers use scheduling methods such as the critical path method (CPM) and linear scheduling methods (LSM) to improve the outcome...
Show moreConstruction managers use scheduling methods such as the critical path method (CPM) and linear scheduling methods (LSM) to improve the outcome of their project. CPM is a popular scheduling method that is mostly based on precedence relationships and the identification of the longest path through a network. LSMs are based on a continuous flow of resources and are used mostly on projects that exhibit repetitive characteristics. Despite the many obvious advantages of CPM, its use in construction has been limited. LSMs are much less frequently used than CPM, although the general consensus is that LSMs are quite effective in projects composed of activities of repetitive nature. Understanding the reasons why these methods are not used as extensively as expected could improve their level of acceptance in the construction industry. The link between construction scheduling methods and the tasks expected to be performed by schedulers has been an on-going concern in the construction industry. The link between construction scheduling methods and the capabilities of the scheduling staff has also been an important issue. This study proposes a combined task/staffing-technology fit model to understand why CPM and LSM are not used as extensively as expected in construction scheduling: (1) a task-technology fit model that aims to measure the extent to which a construction scheduling method functionally matches the tasks expected to be performed by the scheduling staff; (2) a staffing-technology fit model that aims to measure the extent to which a construction scheduling method matches the staff`s experience, know-how and capabilities. The models that are proposed are an answer to the lack of proper instruments for evaluating the extent to which scheduling methods are used in the industry. A questionnaire survey was administered to professionals listed in the directory of the Construction Management Association of America (CMAA) who have many years of experience in construction scheduling. Statistical analyses were performed to determine statistical significance of the differences between the level of agreement concerning task-technology fit and staffing-technology fit for CPM and LSM applications. Findings indicate that there are significant differences between the opinions of CPM users and LSM users. This means that task-technology fit is much different in CPM and LSM applications. Similarly, staffing-technology fit is also quite different in CPM and LSM applications.
M.S. in Civil Engineering, July 2015
Show less

Title: Technology News, February 16, 1951
Collection: Technology News Microfilm collection, 1928-1981

Title: Simulation, design and applications of a table top analyzer-based phase contrast mammography system
Creator: Caudevilla Torras, Oriol
Date: 2019
Description: Analyzer-based Imaging is a promising phase contrast technology with huge potential for soft tissue imaging. Unlike absorption-contrast...
Show moreAnalyzer-based Imaging is a promising phase contrast technology with huge potential for soft tissue imaging. Unlike absorption-contrast methods, phase-contrast modalities measure refraction and scatter properties of the tissue. Such images are particularly suitable for applications such as mammography.The potential advantages of the Analyzer-Based Imaging technology are three fold. First, it shows exceptional contrast when imaging soft tissue, which produces extremely sharp images of the breast compared to absorption images. Second, it provides additional insights about the breast. In particular, the density and scatter images of breast micro-calcifications can help assessing their malignancy better than common mammograms. Third, it has shown potential to reduce the radiation dose deposited in the breast tissue by an order of magnitude compared to common mammography procedures.In the past, Analyzer-Based Imaging has been mainly developed with synchrotron light sources and focused on obtaining micro-resolution images. For such applications, quasi-monoenergetic beams are required. Nevertheless, monochromatic radiation can be easily obtained in synchrotron setups by filtering the source’s spectrum with crystal optics. Since synchrotrons are very brilliant sources, most of their radiation can be filtered out and still obtain low noise phase contrast images. Nowadays, there is a lot of interest in transitioning the technology to a table-top system using compact X-ray sources for mammography. However, compact sources are several orders of magnitude less brilliant, which causes extremely long exposure times. Additionally, the trade-off between exposure time (throughput) and resolution in compact analyzer-based imaging systems is yet to be completely understood.In this thesis, we lay down the principles to develop compact analyzer-based imaging systems capable of imaging a full-sized breast under ten seconds, while ensuring a resolution under 100 microns. This represents a major breakthrough towards obtaining a clinical analyzer-based mammography system. Additionally, we explore a unique application of the analyzer-based technology for breast diagnosis consisting on the assessment of the chemical composition of micro-calcifications. In conjunction with ABI’s unparalleled image quality, determining the chemical composition of micro- calcifications can help to mitigate the high false positive rate in common mammography.
Show less

Title: ON THE FLOW AND PERFORMANCE OF MUTUAL FUNDS
Creator: Zhang, Jingqi
Date: 2019
Description: ABSTRACTThis dissertation consists of three essays on mutual funds. I first discuss the flow of active ETFs. And then I focus on the...
Show moreABSTRACTThis dissertation consists of three essays on mutual funds. I first discuss the flow of active ETFs. And then I focus on the performance of mutual funds. Finally, I evaluate the timing ability of mutual fund investors.Using a data set from 2000 to 2016, this thesis first studies the behavior of active ETF investors from the perspective of fund flows. The results show that the investors chase past returns as they do for mutual funds. Furthermore, I find that the return-chasing behavior can be influence by other considerations, such as fee changes. However, the evidence of performance persistence is weak for active ETFs. Therefore, I propose that the return-chasing behavior is not smart, and the flows of active ETFs instead behave more like “dumb money”, which are demonstrated by the data.I continue to study the performance of the mutual funds. To avoid the bias caused by pricing models themselves, I introduce a model-independent method to assess the mutual fund performance relative to the portfolios constructed by ordinary investors, assuming they are following a naive strategy. Using a data set from October 1984 to September 2017, I find that the majority of mutual funds have higher buy-and-hold returns than the T-bill returns as well as the market returns in the long run. And employing the model-independent measure of performance, I find that the mutual fund industry creates value for individual investors for that mutual funds on average exceed the performance of the majority of the portfolios constructed by the investors selecting stocks randomly.To measure the timing ability of mutual fund investors, I use the difference between the internal rate of return realized by investors and the buy-and-hold return of the funds. Different from the existing literature, I modify the cash flows used to generate the internal rate of return, in which way I can capture the realized return of investors more accurately. I find that investors show timing skills in short horizon. And on average, investors of mutual funds have worse timing skills than those of ETFs. And compared with active fund investors, passive fund investors have better timing skills. I also find that investors who simply chase past winners would show worse timing skills.
Show less

Title: Buried in stigma: Experimental investigation of the impact of hoarding depictions in reality television on public perception
Creator: Bates, Sage
Date: 2019
Description: Hoarding disorder (HD) has been newly classified as a distinct mental disorder and is a considerable public health concern. Treatment...
Show moreHoarding disorder (HD) has been newly classified as a distinct mental disorder and is a considerable public health concern. Treatment ambivalence is a problem in this clinical population, and stigma of HD may be one potential factor contributing to an unwillingness to seek treatment. However, stigma of HD has been understudied, despite the media often perpetuating severe and negative representations of individuals with HD. This study is the first to investigate experimentally the impact of a popular reality television show on attitudes and beliefs about individuals with HD. Participants were randomly assigned to one of three conditions in which they watched popular television shows with varying degrees of clutter: Hoarders (high clutter depiction), Clean House (medium clutter depiction), and House Hunters (low clutter depiction). Participant attitudes and beliefs were evaluated before and after the episode viewing. Results of the study showed that participants who viewed A&E’s Hoarders desired more social distance from individuals with HD—an index of stigma—after viewing the television show, compared to the other groups. The interaction effects of two additional indices of stigma based on watching Hoarders approached statistical significance. There were also significant effects found for other indices of stigma. The present experimental study contributes to the very small body of research investigating stigma of HD and possible causes of treatment ambivalence in individuals living with HD.
Show less

Title: Design and Optimization of Air-Core High Temperature Superconducting (HTS) Pulse Transformer for Series Type Hybrid Circuit Breaker (S-HCB)
Creator: Alashi, Mahmoud
Date: 2024
Description: DC power has been gaining much attention and traction due to its superior benefits over AC power in terms of better system stability, better...
Show moreDC power has been gaining much attention and traction due to its superior benefits over AC power in terms of better system stability, better transmission efficiency, and compatibility with the modern DC electric loads. However, DC fault protection is a major challenge in DC power systems due to the lack of current zero crossings that are necessary for arcless current interruption. The reported Solid State Circuit Breakers (SSCB) suffer from the high conduction power loss and the cost of the cooling systems of the power switches. The Hybrid Circuit Breakers (HCBs) offer low conduction loss in the normal operation but a slow fault interruption response due to the complex mechanical switching mechanism.Recently, a new class of circuit breakers termed Series Type Hybrid Circuit Breaker (S-HCB) was proposed to achieve a µs-scale fault interruption faster than the fast-acting SSCB with ultra-low power loss in the normal operation like an HCBand minimal cost and weight. The S-HCB uses a series pulse transformer to inject a transient counter pulse voltage (higher than the main DC voltage) to bring the fault current down to zero within 10µs and maintain the fault current at near zero for 250µs until the series mechanical switch opens arclessly. The transformer secondary winding made of High Temperature Superconducting (HTS) material carries the nominal 100A DC current offering ultra-low power loss in the normal operation.This thesis discusses the design and optimization of a unique HTS air-core pulse transformer for the S-HCB operating in the Liquid Nitrogen (LN2) under cryogenic environment. The HTS pulse transformer is a key component playing a fundamental role in the S-HCB operation and therefore must be uniquely designed to meet the system level S-HCB performance within a set of constraints defined by the cryogenic environment conditions. Unlike in the prior-art HTS AC power transformers,the HTS windings of the new pulse transformer carries a DC load current without any concerns on AC power losses. On the other hand, the S-HCB operation imposes several unique requirements on the HTS pulse transformer design, including an exceedingly large pulse current up to a few kA, potentially causing core saturation, loss of superconductivity (quenching) of the HTS winding, or extremely high mechanical stress. The HTS transformer is comprehensively modeled using COMSOL. The FEM model of the transformer is coupled with a power electronic circuit to perform a time domain mixed mode simulation and optimization of S-HCB.A 10kV/150A HTS transformer prototype is built and LCR parameters are extracted and found consistent with the simulated values. The S-HCB with the HTS transformer is experimentally tested up to 7kV/150A to validate the design. Experimental results show a fault current of 150A was forced down to zero within 7µs and remains as a small ripple current for 200µs before a series mechanical switch opens arclessly.
Show less

Title: Learning with Contextual Feature Annotations
Creator: Wang, Juanyan
Date: 2024
Description: Machine learning models have been increasingly used for prediction across a wide range of domains, including medical diagnosis, loan approvals...
Show moreMachine learning models have been increasingly used for prediction across a wide range of domains, including medical diagnosis, loan approvals, intrusion detection, autonomous driving, and many others. However, their development and application face several challenges. One major issue is that labeled data is often scarce; acquiring high-quality labeled data can require specialized knowledge, making the labeling process time-consuming and costly. Additionally, the internal mechanisms of these models are often highly complex and opaque, meaning their decision-making processes are not easily interpretable by humans. While some models can provide explanations for their decisions, these explanations still do not align well with human reasoning. To address these issues, I propose models that can learn more efficiently from additional domain knowledge and can mimic humans in decision-making by utilizing contextual feature annotations.First, I introduce an approach that allows humans to provide additional domain knowledge for learning in text classification tasks. Specifically, we ask human annotators to highlight segments of the text, called rationales, that serve as the evidence for their labeling decisions. In my approach, I define a new loss function that incorporates the rationale-based supervision, where a document containing rationales has a higher probability of being correctly classified than the same document with the rationales removed. The model leverages rationales in addition to the document labels during the training stage, and thus is able to learn effectively even with a limited number of labeled documents and also has the benefit of acting like humans.Second, I introduce a framework that mimics typical human decision-making behavior in predictive processes, where the model skims the full feature vector, decides which features are relevant for the case at hand, and makes a classification decision using only the selected features. The model utilizes class labels and additional contextual feature annotations to support the classification decisions during training. At test time, the model is able to perform context-aware feature selection and classification: providing both the classification decision and the human-understandable feature-level explanation for each specific sample.In the final chapter, I address the problem of imbalance in context-aware feature selection tasks by incorporating different costs for various types of feature selection errors into the training process. I propose three cost-sensitive strategies tailored to preferences in diverse real-world scenarios and also conduct an extensive study to analyze their behavior. Consequently, the model improves its ability to reduce balanced errors in both feature selection and classification tasks while offering greater flexibility to achieve the desired trade-off between False Positive and False Negative errors.
Show less

Title: Explaining the Predictions of Image Classifiers
Creator: Yang, Ruo
Date: 2024
Description: With the deployment of deep neural network (DNN) models for safety-critical applications such as autonomous driving and medical diagnosis,...
Show moreWith the deployment of deep neural network (DNN) models for safety-critical applications such as autonomous driving and medical diagnosis, explaining the decisions of DNNs has become a critical concern. For humans to trust the decision of DNNs, not only the model must perform well on the specified task, it must also generate explanations that are easy to interpret. There is a significant amount of research that investigates the contributions of features, in a given instance, to the model’s prediction, where the contribution constitutes the explanation for the model’s decision. Specifically, in the computer vision domain, the explanation method often generates a saliency map that indicates the importance of the pixels for DNNs to make the prediction from the original input image. I propose explanation approaches that generate better saliency maps that represent the importance of the pixels more accurately and evaluate models’ decision-making reasoning from a human perspective.First, I investigate the source of the noise generated by a well-known explanation method, Integrated Gradient (IG), and its variants. Specifically, I propose the Important Direction Gradient Integration (IDGI) framework, which can be incorporated into all IG-based explanation methods and reduce the noise in their outputs. Additionally, I proposed a novel measurement for assessing the attribution techniques’ quality, i.e., the Accuracy Information Curve (AIC) and the Softmax Information Curve (SIC) using the Multi-scale Structural Similarity Index Measure (MS-SSIM). We show that this metric offers a more precise measurement than the original AIC and SIC. Extensive experiments show that IDGI can drastically improve the quality of saliency maps generated by the underlying IG-based approaches.Second, I introduce Information Propagation, IProp, a novel explanation method that leverages the local structural relationships of pixels. Specifically, IProp considers each pixel as the source of information in a saliency map, and formulates the model explanation through information propagation among pixels. Hence, IProp constructs the saliency map by considering all pixels’ contributions to the prediction jointly. I prove that IProp is guaranteed to converge to the unique solution and is compatible with any existing explanation method. The extensive evaluations show the advantage of applying IProp to the existing explanation methods.In the final chapter, I present a methodology for generating meaningful explanations from a human perspective and evaluate if the model’s rationale agrees with human reasoning. We propose a new framework for evaluating how models make decisions in comparison to humans. We propose a novel evaluation metric to measure the model misalignment with the human decision-making process. We show empirically that complex models have more misalignment with humans than simpler models.
Show less

Title: Marine Biology Research Center
Creator: Pehlivan, Nurullah
Date: 2012-05-02, 2012-05
Description: This project tried to achieve 3 things. First urban integration to bigger master plan by being destination or starting point of journey at...
Show moreThis project tried to achieve 3 things. First urban integration to bigger master plan by being destination or starting point of journey at water front of Hudson river. Second finding an appropriate narrative to create a architectural language for Marine biology research center. And last but not least energy analysis to evaluate best orientation and form of the building.
Show less

Title: Marine Biology Research Center: 17x11- Master Project_NAP
Creator: Pehlivan, Nurullah
Date: 2012-05-02, 2012-05
Description: This project tried to achieve 3 things. First urban integration to bigger master plan by being destination or starting point of journey at...
Show moreThis project tried to achieve 3 things. First urban integration to bigger master plan by being destination or starting point of journey at water front of Hudson river. Second finding an appropriate narrative to create a architectural language for Marine biology research center. And last but not least energy analysis to evaluate best orientation and form of the building.
Show less

Title: Marine Biology Research Center: 40x30 Final Poster
Creator: Pehlivan, Nurullah
Date: 2012-05-02, 2012-05
Description: This project tried to achieve 3 things. First urban integration to bigger master plan by being destination or starting point of journey at...
Show moreThis project tried to achieve 3 things. First urban integration to bigger master plan by being destination or starting point of journey at water front of Hudson river. Second finding an appropriate narrative to create a architectural language for Marine biology research center. And last but not least energy analysis to evaluate best orientation and form of the building.
Show less

Title: DESIGN OF WOUND FIELD SYNCHRONOUS MACHINES AND HYBRID EXCITATION SYNCHRONOUS MACHINES FOR ELECTRIC VEHICLE TRACTION WITH BRUSHLESS CAPACITIVE FIELD EXCITATION
Creator: Di Gioia, Antonio
Date: 2018, 2018-05
Description: The focus of this dissertation is to describe the electromagnetic modeling and optimization, mechanical modeling, thermal simulation and...
Show moreThe focus of this dissertation is to describe the electromagnetic modeling and optimization, mechanical modeling, thermal simulation and experimental characterization of two prototype permanent magnet-free high power density wound eld synchronous machines (WFSMs) and one prototype of permanent magnet-wound eld hybrid excitation synchronous machine (HESM) for electric and hybrid-electric vehicle traction applications. The WFSMs and HESM are designed for brushless rotor eld excitation using an axial ux hydrodynamic capacitive power coupler (CPC) but can also be operated with a brush and slip rings excitation system. A exible design environment has been developed for large scale multi-objective optimization of the machines, particularly focusing on the use of a static electro-magnetic solver, FEMM, and the extension of the software routines to reconstruct the transient behavior of rotating electrical machines. The prototypes are designed to operate with a spray cooling system with automatic transmission uid (ATF Dexron VI) in order to reach power densities comparable to the commercial permanent magnet synchronous machines (PMSMs) for similar applications. The spray cooling system was simulated with a commercial software (MotorCAD) and the modeling approach validated with experimental characterization. The spray cooling system was modi ed to include thermal circuit paths that emerged during the testing of the prototypes and integrated in the current release of the software. The experimental characterization shows promising results, with peak output power at a base speed of 4,000 RPM exceeding 80 kW for the WFSM prototypes, and a continuous power output of 60 kW with the spray cooling system. The prototyped WFSMs achieve volumetric and speci c torque and power densities of 17.22 Nm/l, 4.69 Nm/kg, 7.19 kW/l, and 1.95 kW/kg. The experimental data collected for the HESM prototype shows a no-load rotor-side ux weakening capability that enables constant power speed ratio of 10:1 during operation and provides a exible platform for machine characterization and advanced control development for one monoaxial and one biaxial hybrid excitation synchronous machine con gurations. The design of the HESM prototype was obtained with an integration of analytical sizing equations for the initial exploration of the design space and FEA methods for detailed modeling of the nal prototype features.
Ph.D. in Electrical Engineering, May 2018
Show less

Title: International Bond Portfolio: Evidence from Emerging Markets
Creator: Wang, Jinghua
Date: 2012-08-20, 2012-07
Description: Allocating capital to fixed income instruments issued by emerging markets (EMs), governments may provide significant benefits to both the...
Show moreAllocating capital to fixed income instruments issued by emerging markets (EMs), governments may provide significant benefits to both the investors and issuers of these instruments. For investors, emerging market instruments may offer a significant risk premium relative to conventional investments in developed markets (DMs) bonds. Furthermore, EMs bonds offer potential diversification benefits because these bonds are not strongly correlated with DMs instruments. For emerging market government issuers, access to global fixed income markets is likely to improve liquidity and offer lower borrowing costs relative to a strategy focused purely on the domestic market. Access to global capital provides these governments with the opportunity to invest in infrastructure projects that promote economic growth and development. Over the past fifty years, economic growth in emerging markets has been supported by investments in capital and technology from the developed world. The benefit of this development for the emerging markets, as measured by growth in income, employment, and wealth, is immediately apparent. There have also been significant advantages for the developed world through opportunities for higher risk adjusted returns from investments in emerging markets. For the most part, the benefits of diversification into emerging markets have focused on equity markets. In this dissertation, the focus is on investments in fixed income instruments. Specifically, the dissertation explores the performance benefits of DMs combined with EMs. It first identifies the potential diversification and describes the financial integration for incorporating EMs bonds into DMs government bond portfolios. In the second phase, it constructs the dynamic linear regression models and conducts the mean-variance tests to demonstrate the incremental benefit of the strategy. In the last phase, a robust test examines the strength of bond portfolio performance between DMs with EMs and the U.S. 7-10 year government bond index. The empirical analysis in this dissertation focuses on three DMs sources of bonds and four EMs regions. Since the EMs are evolving rapidly, and since the global financial markets have also been subject to erratic fluctuations during the global financial crisis, the empirical models employed in the dissertation do not rely on stationarity assumptions. Instead, Kalman Filter (KF) procedures are employed that generate the time-varying coefficients in the multi-factor models in response to new conditions in the markets. The outputs from the KF are used as inputs in the factor model, and the outputs from the factor models are used as inputs in a Markowitz style mean-variance optimization model. This study explores the benefits of the diversification of global government bond portfolio, and provides complete performance evaluations of DMs with or without EMs. The study examines: i) the benefits of inclusion of EMs bonds in DMs; ii) the degrees of financial integration among the research markets; iii) the correlation of the macro-economic factors in the multi-factor models; iv) the relative bond returns of dynamic factor models with time-varying coefficients; and v) the robust tests of bond portfolio performance between DMs with EMs and bond index. The results of this study provide important implications for global investors by identifying diversification gains in EMs.
Ph.D. in Management Science in Finance, July 2012
Show less

Title: ADVANCED MATERIALS ENABLED BY ATOMIC LAYER DEPOSITION FOR HIGH ENERGY DENSITY RECHARGEABLE BATTERIES
Creator: Chen, Lin
Date: 2017, 2017-05
Description: In order to meet the ever increasing energy needs of society and realize the US Department of Energy (DOE)’s target for energy storage,...
Show moreIn order to meet the ever increasing energy needs of society and realize the US Department of Energy (DOE)’s target for energy storage, acquiring a fundamental understanding of the chemical mechanisms in batteries for direct guidance and searching novel advanced materials with high energy density are critical. To realize rechargeable batteries with superior energy density, great cathodes and excellent anodes are required. LiMn2O4 (LMO) has been considered as a simpler surrogate for high energy cathode materials like NMC. Previous studies demonstrated that Al2O3 coatings prepared by atomic layer deposition (ALD) improved the capacity of LMO cathodes. This improvement was attributed to a reduction in surface area and diminished Mn dissolution. However, here we propose a different mechanism for ALD Al2O3 on LMO based on in-situ and ex-situ investigations coupled with density functional theory calculations. We discovered that Al2O3 not only coats the LMO, but also dopes the LMO surface with Al leading to changes in the Mn oxidation state. Different thicknesses of Al2O3 were deposited on nonstoichiometric LiMn2O4 for electrochemical measurements. The LMO treated with one cycle of ALD Al2O3 (1×Al2O3 LMO) to produce a sub-monolayer coating yielded a remarkable initial capacity, 16.4%higher than its uncoated LMO counterpart in full cells. The stability of 1×Al2O3 LMO is also much better as a result of stabilized defects with Al species. Furthermore, 4×Al2O3 LMO demonstrates remarkable capacity retention. Stoichiometric LiMn2O4 was also evaluated with similar improved performance achieved. All superior results, accomplished by great stability and reduced Mn dissolution, is thanks to the synergetic effects of Al-doping and ALD Al2O3 coating.Turning our attention to the anode, we again utilized aluminum oxide ALD to form conformal films on lithium. We elaborately designed and studied, for the first time, the growth mechanism during Al2O3 ALD on lithium metal in-situ quart crystal microbalance (QCM) measurements and found larger growth than expected during the initial cycles. Besides, we discovered that electrolytes show much enhanced wettability on Li with Al2O3 coating, leading to uniform and dense solid electrolyte interphase formation as well as less electrolyte required for battery operations. Also, we achieved more than 2 times longer cycling life with protected Li and obtained Coulombic efficiencies as high as ~98% at a practical current rate of 1 mA/cm2, compared to bare Li. More significantly, when the electrolyte volume is limited (10 μL and 5 μL), the cycling life is about 4 times longer. X-ray photoelectron spectroscopy (XPS) for electrodes after cycles and in-situ transmission electron microscopy (TEM) demonstrate that most of lithium is deposited beneath the film. The more uniform Al2O3 coated lithium after cycling observed by scanning electron microscopy (SEM) verifies that ALD Al2O3 isexceptionally effective to prevent lithium dendrite formation. These results demonstrate that ALD Al2O3 coatings offer a promising route towards energy storage devices that utilize lithium metal anodes, such as Li-S batteries.
Ph.D. in Materials Science and Engineering, May 2017
Show less

Title: PERFORMANCE ANALYSIS OF ENERGY HARVESTING IN WIRELESS NETWORKS USING STOCHASTIC GEOMETRY
Creator: Chen, Ziru
Date: 2017, 2017-07
Description: As the era of Internet of things (IoT) approaches, energy harvesting over radio frequency (RF) energy, has been proposed recently as a...
Show moreAs the era of Internet of things (IoT) approaches, energy harvesting over radio frequency (RF) energy, has been proposed recently as a promising solution to charge an ever increasing number of users for wireless communications. Exploiting the wireless signals in the surrounding environment coming from TV towers, Wi-Fi networks and cellular base stations (BSs), wireless devices such as wireless sensors scavenge ambient RF energy and operate self-sustainably without replacing or recharging their batteries. In this dissertation, the downlink performance of wireless networks with RF energy harvesting is investigated. We consider a large scale cellular network, where BSs and RF energy powered mobile users (MUs) are deployed as a homogeneous Poisson Point Process (HPPP) with different spatial densities. Downlink transmissions for multiple MUs associated with one BS are scheduled in a time division multiple access (TDMA) manner, which allows each MU to harvest the ambient RF energy from concurrent transmissions in other cells when it is not transmitting. Applying stochastic geometry, we develop an analytical model to investigate the energy harvesting performance of MUs and the throughput performance of the wireless network under different densities of BSs and MUs. The successful transmission probability of MUs, i.e., when an MU has charged enough energy for one transmission and the achieved signal to interference ratio is larger than a threshold, is derived. Based on the analysis, the conditions that MUs can be fully energy sustainable with RF charging are further quantified. Finally, the analytical results and the full sustainability conditions of the proposed network model have been verified by extensive simulations with Matlab.
M.S. in Electrical Engineering, July 2017
Show less

Title: Cardiolipin Modulates the Insertion of Adsorbed Helical Amyloid Beta Peptide Into Model Mitochondrial Membranes
Creator: Kaczmarek, Julia A.
Date: 2023
Description: The loss of mitochondrial phospholipid cardiolipin (CL) may play a role in both the pathogenesis of Alzheimer's Disease (AD) and its treatment...
Show moreThe loss of mitochondrial phospholipid cardiolipin (CL) may play a role in both the pathogenesis of Alzheimer's Disease (AD) and its treatment. An effector molecule of the disease, amyloid-beta (Aβ), has been observed to interact with lipid membranes, but its relevance to mitochondrial membranes containing CL remained elusive. The present study investigated if the presence of CL modulated the insertion of adsorbed helical amyloid beta (Aβ14-40) into model mitochondrial membranes, and if this effect was more pronounced for its N-terminus or C-terminus. I conducted a coarse-grained computer simulation using well-tempered metadynamics to traverse the free energy landscape that maps the translocation of Aβ14-40. Insertion into CL-containing bilayers created larger local membrane deformations and modulated the location of the transition path but had an inconclusive impact on the free energy cost of translocation. Since the generation of toxic calcium-permeable pores depends on the insertion of Aβ into the bilayer, the loss of CL seen in AD may prime the inner mitochondrial membrane for pore formation, but more research is needed to pursue this hypothesis.
Show less

Title: MULTIFUNCTIONAL BIOMATERIAL SYSTEM FOR DRUG DELIVERY AND SCAFFOLDING TO PROMOTE NEOVASCULARIZATION IN TISSUE ENGINEERING
Creator: Jiang, Bin
Date: 2013, 2013-05
Description: The successful development of engineered tissues requires extensive vascular network formation. The overall goal of this work is to develop a...
Show moreThe successful development of engineered tissues requires extensive vascular network formation. The overall goal of this work is to develop a multifunctional biomaterial system for scaffolding and drug delivery to promote neovascularization in engineered tissue. Firstly, a drug delivery system was developed for molecules of different properties. Poly(lactic-co-glycolic acid) (PLGA) was prepared into microspheres using a double emulsion process for delivery of hydrophobic chlorhexidine (CHX) and hydrophilic platelet-derived growth factor-BB (PDGF-BB). Both drugs exhibited bioactivity after release and the efficacy of dual drug delivery was evaluated with an infected wound animal model. The simultaneous delivery of CHX and PDGF-BB improved wound healing and neovascularization while reducing bacteria levels. Therefore, the PLGA microspheres can be used for long-term active delivery of both hydrophobic and hydrophilic molecules in tissue engineering applications. Secondly, a 3D scaffold was developed for tissue engineering applications. Poly(ethylene glycol) (PEG) hydrogels with interconnected pores were generated with a salt leaching technique. Fibrin was filled in the pores by adding fibrinogen solution to hydrogel scaffolds pre-loaded with thrombin. The hydrogels were evaluated in a rodent subcutaneous implant model, showing that tissue invasion with a higher vascular density occurred when the hydrogels were loaded with fibrin. This composite hydrogel supports vascularized tissue ingrowth, and thus holds potential for tissue engineering applications. Thirdly, approaches from the previous studies were combined to develop a multifunctional biomaterial system for tissue engineering scaffolding and sequential xi growth factor delivery. PLGA microspheres were incorporated into a fibrin loaded porous hydrogel, in which the PEG based scaffold was modified to allow controlled degradation via hydrolysis. Different growth factors were encapsulated in fibrin and PLGA microspheres to provide temporal control of delivery. Growth factors released with the appropriate sequence promoted stable and functional blood vessel formation. In conclusion, a multifunctional biomaterials system was developed to provide structural and mechanical support for tissue regeneration, as well as delivery of signals that stimulate neovascularization. The system holds great potential for tissue engineering applications. Future work will require the extensive collaboration from interdisciplinary fields towards the successful development of engineered tissue substitutes.
PH.D in Biomedical Engineering, May 2013
Show less

Title: vVIENER-HOPF FACTORIZATION FOR TIME-INHOMOGENEOUS MARKOV CHAINS AND STATISTICAL INFERENCE FOR STOCHASTIC PARTIAL DIFFERENTIAL EQUATIONS
Creator: Huang, Yicong
Date: 2018, 2018-05
Description: The thesis consists of two major parts, and it contributes to two topics in stochastic analysis – Wiener-Hopf factorization (WHf) for Markov...
Show moreThe thesis consists of two major parts, and it contributes to two topics in stochastic analysis – Wiener-Hopf factorization (WHf) for Markov chains and statistical inference for Stochastic Partial Differential Equations (SPDEs). The first part deals with Wiener-Hopf factorization for finite state time inhomogeneous Markov chains. To the best of our knowledge, this study is the first attempt to investigate the WHf for the time-inhomogeneous Markov chains. In this work we only deal with a special class of time-inhomogeneous Markovian generators, namely piece-wise constant, which allows to derive the corresponding WHf by using an appropriately tailored randomization technique. Besides the mathematical importance of the WHf methodology, there is also an important computational aspect: it allows for efficient computation of important functionals of Markov chains. In this work, we also provide an efficient algorithm to compute the quantities in the Wiener-Hopf factorization for the time-inhomogeneous Markov chains. Finally, we provide a comparison (based on numerical simulations) between our algorithm and the brute-force Monte Carlo simulations. The second part is dedicated to statistical inference for Stochastic Partial Differential Equations (SPDEs). First, we study the problem of estimating the drift/viscosity coefficient for a large class of linear, parabolic SPDEs driven by an additive space-time noise. We propose a new class of estimators, called trajectory fitting estimators (TFEs). The estimators are constructed by fitting the observed trajectory with an artificial one, and can be viewed as an analog to the classical least squares estimators from the time-series analysis. As in the existing literature on statistical inference for SPDEs, we take a spectral approach, and assume that we observe the first N Fourier modes of the solution, and we study the consistency and the asymptotic normality of the TFE, as N ₀₀. Next we consider a parameter estimation problem for one dimensional stochastic heat equation, when data is sampled discretely in time or spatial component. We establish some general results on derivation of consistent and asymptotically normal estimates based on computation of the p-variations of stochastic processes and their smooth perturbations. We apply these results to the considered SPDEs, by using some convenient representations of the solutions. For some equations such representations were ready available, while for others classes of SPDEs we derived the needed representations along with their statistical asymptotic properties. We prove that the real valued parameter next to the Laplacian, and the positive parameter in front of the noise can be consistently estimated by observing the solution at a fixed time and on a discrete spatial grid, or at a fixed space point and at discrete time instances of a finite interval, assuming that the mesh size goes to zero.
Ph.D. in Applied Mathematics, May 2018
Show less

Title: BIOMATERIAL SYSTEMS WITH PERSISTENT GROWTH FACTOR GRADIENTS IN VIVO FOR TISSUE ENGINEERING APPLICATIONS
Creator: Akar, Banu
Date: 2016, 2016-12
Description: Tissue engineering aims to develop strategies for the replacement of damaged, injured or missing tissues with biologically compatible...
Show moreTissue engineering aims to develop strategies for the replacement of damaged, injured or missing tissues with biologically compatible substitutes such as bioengineered tissues. However, generating tissues of su cient volume for clinical application requires the formation of stable and extensive vasculature within the tissue constructs. The overall goal of this work is to enhance vascularization using a gradient biomaterial system and apply this research to engineering vascularized bone of clinical size. First, a method was developed to create persistent growth factor gradients with an adjustable gradient magnitude in vivo. This method generated persistent gradients of platelet-derived growth factor (PDGF-BB) within brin/poly (ethylene glycol) (PEG) sca olds. The presence of a growth factor gradient within the system was veri ed in vivo using near-infrared imaging. Also, a computational model was developed to investigate gradient characteristics within the system. Gradient properties can be controlled by varying the degradation rate of the gradient layer components or dose of PDGF-BB delivered. The angiogenic potential of gradient sca olds was tested in rodents using a subcutaneous implantation model. The depth of tissue invasion and density of blood vessels formed in response to the biomaterial increased with dose of the growth factor. The gradient biomaterial system allows formation of persistent gradients that can be in uenced by biomaterial characteristics, and enhances vascularization. Therefore, this biomaterial system can be used for tissue engineering applications. Second, the brin/PEG-based sca olds were modi ed to be degradable via hydrolysis and to include bioactive ceramic particles (hydroxyapatite and -tri-calcium phosphate). Characteristics of the hydrogel ceramic composites were investigated in vitro and in vivo. The presence of ceramic particles extended degradation time of thehydrogels in vitro and in vivo. Hydrogel ceramic composites were tested in a rodent cranial defect model and enhanced bone tissue regeneration. Third, strategies developed from the previous studies were combined to prepare ceramic supplemented gradient sca olds for bone tissue engineering applications. A gradient layer was applied to the hydrogel-ceramic composites and bone tissue response was evaluated in a periosteum guided large animal model. Ceramic supplemented gradient sca olds augmented vascularization and bone regeneration in vivo. In conclusion, a biomaterial system with persistent growth factor gradients was developed and enhanced vascularization and bone regeneration in vivo. This system holds a great potential for tissue engineering applications.
Ph.D. in Biomedical Engineering, December 2016
Show less

repository.iit

Search the repository

Pages

Pages