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Title: MODELING OF A DCFC ANODE IN CONNECTION WITH THE EXPERIMENTAL RESEARCH ON THE WETTING BEHAVIOR OF A GRAPHIC ROD IN MOLTEN CARBONATE
Creator: Li, Yue
Date: 2013, 2013-12
Description: Not available
M.S. in Civil Engineering, July 2013

Title: INVESTIGATION OF NIOBIUM SURFACE STRUCTURE AND COMPOSITION FOR IMPROVEMENT OF SUPERCONDUCTING RADIO-FREQUENCY CAVITIES
Creator: Trenikhina, Yulia
Date: 2014, 2014-12
Description: Nano-scale investigation of intrinsic properties of niobium near-surface is a key to control performance of niobium superconducting radio...
Show moreNano-scale investigation of intrinsic properties of niobium near-surface is a key to control performance of niobium superconducting radio-frequency cavities. Mechanisms responsible for the performance limitations and their empirical remedies needs to be justified in order to reproducibly control fabrication of SRF cavities with desired characteristics. The high field Q-slope and mechanism behind its cure (120◦C mild vacuum bake) were investigated by comparison of the samples cut out of the cavities with high and low dissipation regions. Material evolution during mild field Q-slope nitrogen treatment was characterized using the coupon samples as well as samples cut out of nitrogen treated cavity. Evaluation of niobium near-surface state after some typical and novel cavity treatments was accomplished. Various TEM techniques, SEM, XPS, AES, XRD were used for the structural and chemical characterization of niobium near-surface. Combination of thermometry and structural temperature-dependent comparison of the cavity cutouts with different dissipation characteristics revealed precipitation of niobium hydrides to be the reason for medium and high field Q-slopes. Step-by-step effect of the nitrogen treatment processing on niobium surface was studied by analytical and structural characterization of the cavity cutout and niobium samples, which were subject to the treatment. Low concentration nitrogen doping is proposed to explain the benefit of nitrogen treatment. Chemical characterization of niobium samples before and after various surface processing (Electropolishing (EP), 800◦C bake, hydrofluoric acid (HF) rinsing) showed the differences that can help to reveal the microscopic effects behind these treatments as well as possible sources of surface contamination.
Ph.D. in Physics, December 2014
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Title: SURVIVAL AND ATTACHMENT OF SALMONELLA ENTERICA ON ALMOND, HAZELNUT, AND BLACK PEPPER
Creator: Zhai, Yang
Date: 2016, 2016-05
Description: S. Enteritidis (SE) and S. Typhimurium (ST) are the two most common Salmonella enterica serovars that cause foodborne illnesses in U.S....
Show moreS. Enteritidis (SE) and S. Typhimurium (ST) are the two most common Salmonella enterica serovars that cause foodborne illnesses in U.S. Outbreaks of these serovars have been attributed to low moisture foods such as nuts and spices. However, little is known about the mechanisms of attachment on low moisture food surfaces. This study evaluated the associations between attachment and survival of Salmonella enterica serovars, storage temperatures, and surface characteristics of selected food samples. In the study, S. Enteritidis PT4 and S. Typhimurium LT2 were inoculated onto the surfaces of black peppercorns, almonds and hazelnuts at ~108 CFU/g. After 2 h air-drying, samples were stored at 4 and 25°C with 58 ± 2% relative humidity for up to 14 d. At specific time points, the food sample were washed two times in 1 × Phosphate Buffered Saline (PBS) to remove attached bacterial cells. The bacterial suspensions were serially diluted and plated on Brain Heart Infusion (BHI) and Xylose Lysine Deoxycholate (XLD) agar plates for enumeration. Significant differences (P<0.05) were found in the survival and attachment of SE and ST under all the conditions. ST can survive and attach better than SE at both 4 and 25°C. The decline rates on almonds, hazelnuts, and black peppercorns at 25°C were 0.348 ± 0.017, 0.273 ± 0.015, and 0.196 ± 0.017 log CFU/g per day for SE and 0.077 ± 0.008, 0.157 ± 0.008, and 0.048 ± 0.005 log CFU/g per day for ST, respectively. The attachment rates on almonds, hazelnuts and black peppercorns at 25°C were 18.71 ± 14.38, 1.56 ± 1.50, and 4.68 ± 0.76% for SE and 38.46 ± 11.32, 18.45 ± 7.73, and 56.30 ± 14.72% for ST, respectively. In addition, low temperature (i.e. 4°C) may contribute more to the survival of Salmonella than ambient temperature (i.e. 25°C). Certain surface characteristics (roughness & hydrophobicity) of hazelnut may probably result in weaker attachment of both Salmonella serovars. The results can be used to better understand the physiology of Salmonella enterica on low moisture foods and aid in developing effective control measures to reduce pathogen contamination.
M.S. in Food Safety and Technology, May 2016
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Title: OPERATION AND PLANNING OF COORDINATED NATURAL GAS AND ELECTRICITY INFRASTRUCTURES
Creator: Zhang, Xiaping
Date: 2015, 2015-07
Description: Natural gas is becoming rapidly the optimal choice for fueling new generating units in electric power system driven by abundant natural gas...
Show moreNatural gas is becoming rapidly the optimal choice for fueling new generating units in electric power system driven by abundant natural gas supplies and environmental regulations that are expected to cause coal-fired generation retirements. The growing reliance on natural gas as a dominant fuel for electricity generation throughout North America has brought the interaction between the natural gas and power grids into sharp focus. The primary concern and motivation of this research is to address the emerging interdependency issues faced by the electric power and natural gas industry. This thesis provides a comprehensive analysis of the interactions between the two systems regarding the short-term operation and long-term infrastructure planning. Natural gas and renewable energy appear complementary in many respects regarding fuel price and availability, environmental impact, resource distribution and dispatchability. In addition, demand response has also held the promise of making a significant contribution to enhance system operations by providing incentives to customers for a more flat load profile. We investigated the coordination between natural gas-fired generation and prevailing nontraditional resources including renewable energy, demand response so as to provide economical options for optimizing the short-term scheduling with the intense natural gas delivery constraints. As the amount and dispatch of gas-fired generation increases, the long-term interdependency issue is whether there is adequate pipeline capacity to provide sufficient gas to natural gas-fired generation during the entire planning horizon while it is widely used outside the power sector. This thesis developed a co-optimization planning model by incorporating the natural gas transportation system into the multi-year resource and transmission system planning problem.This consideration would provide a more comprehensive decision for the investment and accurate assessment for system adequacy and reliability. With the growing reliance on natural gas and widespread utilization of highly efficient combined heat and power (CHP), it is also questionable that whether the independent design of infrastructures can meet potential challenges of future energy supply. To address this issue, this thesis proposed an optimization framework for a sustainable multiple energy system expansion planning based on an energy hub model while considering the energy efficiency, emission and reliability performance. In addition, we introduced the probabilistic reliability evaluation and flow network analysis into the multiple energy system design in order to obtain an optimal and reliable network topology.
Ph.D. in Electrical and Computer Engineering, July 2015
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Title: OIL RECOVERY IN SINGLE CAPILLARIES AND POROUS MEDIA USING WETTING NANOFLUIDS
Creator: Zhang, Hua
Date: 2016, 2016-05
Description: Recent experiments and modeling conducted in our laboratory have demonstrated that the spreading of nanofluids, liquid suspensions of...
Show moreRecent experiments and modeling conducted in our laboratory have demonstrated that the spreading of nanofluids, liquid suspensions of nanosized particles, on solids are enhanced due to self-structuring of nanoparticles in the confined three-phase oil-nanofluid-solid contact region. Nanofluids have recently been proposed as agents for enhanced oil recovery (EOR). Despite recently widely conducted research using nanofluids for EOR, the underlying operating mechanism is not well understood. In this thesis, we attempt to understand the mechanism of nanofluid based EOR and evaluate its performance from reservoir core samples and model systems (glass capillary and sintered bead-pack). To visualize how oil displacement in the rock pores by nanofluid, we conducted model study using hexadecane and single glass capillary and showed the oil film dynamics in air and nanofluid after oil was displaced in the capillary. Based on the understanding of the role of nanofluid on oil displacement in capillaries, we conducted imbibition tests using Berea sandstones and flooding experiments in sintered glass-beads. X-ray microtomography was used to visualize and analyze fluid distribution and to see the effect of nanofluid in EOR. We finally considered fractured media by fabricating such structures. The dynamics of a cylindrical hexadecane layer deposited inside glass capillaries after the oil/air displacement was studied experimentally and by modeling. The oil layer subject to surface perturbation becomes unstable forming uniform, regularly-spaced double concave menisci across the capillary that are bridged with dimples (collars). In order to reveal the phenomena of the film thinning and stability between the double concave meniscus and the dimple, we monitored an air bubble approaching a flat glass surface in hexadecane. We found that the oil film thinning in a cylindrical glass capillary and on a flat glass substrate were similar; We adapted the model proposed by Gauglitz and Radke for our system (oil-air displacement) and solved it numerically. The numerical result shows a stable film between the liquid bridge and the dimple, which is consistent with our experimental observations. We also estimated the meniscus-film-dimple thickness profile and found it was in fair agreement with the model prediction. The dynamics of cylindrical hexadecane film after displacement by a nanofluid in a glass capillary was studied. We found the thick hexadecane film is unstable, and over time it breaks and forms a thin film. Once the thick film ruptures, it retracts and forms an annular rim (liquid ridge) that collects liquid. As the volume of the annular rim increases over time, it forms a double concave meniscus across the capillary and dewetting stops. The thin film on the right side of the double concave meniscus then breaks and the contact angle increases. The process repeats until droplets build along the capillary wall. Finally, the droplets are displaced from the capillary wall by the nanofluid and spherical droplets appear inside the capillary. This is a novel phenomenon not observed during dewetting by a solution without nanoparticles. The theoretical model based on the lubrication approximation using the capillary pressure gradient was developed to estimate the annular rim dewetting velocity. The predicted dewetting velocity is found to be in fair agreement with the experimental value. We conducted imbibition tests using a reservoir crude oil and a reservoir brine solution with a high salinity and a suitable nanofluid that displaces crude oil from Berea sandstone and single glass capillaries. We present visual evidence of the underlying mechanism based on the structural disjoining pressure for the crude oil displacement using a polymeric nanofluid (our definition of such a fluid means a suspension of polymeric particles in an aqueous substrate) in high salinity brine. The polymeric nanofluid is specially formulated to survive in a high salinity environment and is found to result in an increased efficiency of 50% for Berea sandstone compared to 17% using the brine alone at a reservoir temperature of 55 oC. These results aid our understanding of the role of the nanofluid in displacing crude oil from the rock especially in a high salinity environment containing Ca++ and Mg++ ions. Results are also reported using Berea sandstone and a nanofluid containing silica nanoparticles. We conducted a series of flooding experiments at different capillary numbers to quantify the performance of a polymeric nanofluid compared to brine using the sintered glass-beads. A high resolution X-ray microtomography (microCT) was used to visualize oil and brine distribution in a sintered bead-pack before and after nanofluid flooding. The results of flooding experiments showed that an additional oil recovery of approximately 15% is possible with nanofluids compared to brine at low capillary numbers, and is as effective as high capillary number brine flooding. Nanofluid induced additional oil recovery decreases as we increase the capillary number and the total oil recovered shows a marginal decrease. At first glance, these results are opposite of what one expects in the conventional EOR, where oil recovery is known to increase progressively with increasing capillary number. These results cannot be explained based on mobilization theories due to the reduced capillarity. Our results however are consistent with the mechanism of wettability alteration caused by structural disjoining pressure leading to the formation of the wetting nanofluid film between oil and substrate.We presented experimental studies of nanofluid flooding in fractured porous media formed with sintered glass-beads. The nanofluid injection is conducted at a rate where structural disjoining pressure driven recovery is operational. We found an additional 23.8% oil can be displaced using nanofluid after brine injection with an overall displacement efficiency of 90.4% provided the matrix was in its native wettability state. In summary, nanofluids are excellent EOR agents and their economic viability needs to be examined.
Ph.D. in Chemical Engineering, May 2016
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Title: TOWARDS THE EXACT CALCULATIONS OF THE FREE ENERGY FOR ENTANGLED SEMIFLEXIBLE POLYMER CHAIN
Creator: Pilyugina, Ekaterina
Date: 2015, 2015-05
Description: This work consists of two separate projects unified by the idea to extend the Discrete Slip-Link Model, which has been being successfully...
Show moreThis work consists of two separate projects unified by the idea to extend the Discrete Slip-Link Model, which has been being successfully developed in this group to predict rheological behavior of entangled flexible polymers, to new applications. The first project was dedicated to application of the Discrete Slip-Link Model to dielectric relaxation in order to simultaneously predict linear rheology and dielectric relaxation experiments of entangled polyisoprenes. Linear monodisperse, linear bidisperse and star-branched monodisperse systems were studied. It was found that all circumstances save one are well described. Namely, dilute long chains in a sea of short chains can be predicted rheologically, but dielectric relaxation data show a reduction in the relaxation time of long chains greater than that predicted by either the DSM or the expected Rouse motion. The second project was focused on the derivation of the exact free energy expression for semiflexible chains in the presence of entanglements in order to implement the DSM for semiflexible polymers. The special cases of chains with one, two and three strands are examined. An additional implementation of obtained results for one and two strands to buckling instability was performed. It is believed that in two dimensional case the critical buckling force is increased by thermal fluctuations in comparison to classical Euler buckling. However, how the critical buckling force is influenced by thermal fluctuations in three dimensions remains unclear. Some research groups calculate the critical buckling force approximately and conclude that, in opposite to 2D case, in 3D the force is decreased by thermal fluctuations. In this work the critical buckling force for semiflexible chain under compression was calculated exactly. It was shown that thermal fluctuations significantly increase the critical force over classical Euler buckling force in both two and three dimensions.
Ph.D. in Chemical Engineering, May 2015
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Title: FLOW DISTRIBUTION AND TURBULENCE CHARACTERISTICS IN AN URBAN ENVIRONMENT
Creator: Goudarzi, Sepehr Aboutorabi
Date: 2014, 2014-12
Description: The amount of the urban flow studies has been excessively increased during past decade. Pollutant dispersion quality has been the main...
Show moreThe amount of the urban flow studies has been excessively increased during past decade. Pollutant dispersion quality has been the main motivation in these investigations. Besides, a more recent goal is to provide a spatial map of the flow distribution which can be used for micro aerial vehicles (MAV) flight control. These all have developed advanced methodologies in both computational and experimental researches. In this study flow distribution and characteristics are investigated in a 7×5 urban array model (blocks are representing buildings) in a low-speed wind tunnel. Stereoscopic Particle Image Velocimetry (SPIV) is employed as the velocimetry method to acquire three-dimensional velocity filed in the three-dimensional region of street areas. A large amount of SPIV data was acquired in four consecutive streets for four wind incidence angle. The evolution of the three-dimensional coherent structures is investigated. Also, flow characteristics are studied using parameters such as mean velocity, turbulent kinetic energy (TKE), vorticity magnitude and Reynolds stress tensor components. All flow characteristics are studied in four consecutive streets of the array. Also, the effects of the wind direction on the flow characteristics and arch vortex location are studied. A valuable achievement of this study is to suggest a method to find the location of the arch vortex legs, and find the angle between the arch horizontal axis with the spanwise direction (𝜑). It is shown that this angle is increasing significantly in variation of angle of incidence (AOI) in the range of 𝐴𝑂𝐼=0° to 𝐴𝑂𝐼=15°. The rate of increment of 𝜑 is much slower between 𝐴𝑂𝐼=15° and 𝐴𝑂𝐼=30° but the 𝜑 range is still greater than AOI. Existence of geometrical symmetry in 𝐴𝑂𝐼=0° case, brings unique features for this condition such as zero spanwise flow velocity in streets.. Increasing AOI to higher magnitudes will cause severe change in flow distribution and turbulence level, in the sense that turbulence intensity starts to impoverish.
M.S. in Mechanical and Aerospace Engineering, December 2014
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Title: DELAYING THE ONSET OF ROTATING STALL IN AN AXIAL COMPRESSOR
Creator: Thomas, Seth
Date: 2011-04-12, 2011-05
Description: The optimal performance of axial compressors is crucial in a number of appli- cations, including power plants and gas turbine engines. Their...
Show moreThe optimal performance of axial compressors is crucial in a number of appli- cations, including power plants and gas turbine engines. Their efficiency is limited by the onset of stall, when the pressure rise across the compressor drops suddenly and destructive flow patterns emerge. Because of this, all compressors operate at conditions away from the stall point, but with an accompanying penalty in efficiency. The objective of this study is to examine the detailed fluid dynamic processes lead- ing to stall and devise a scheme of active flow control to delay stall onset, allowing compressors to operate safely much closer to the stall point and at greater efficiency. This is done on the low speed axial compressor rig in the Fluid Dynamics Research Center at the Illinois Institute of Technology. Results indicated that the stall cell appears at a flow coefficient, φ = 0.292 and that it is small, located close to the casing, rotating with the rotor blade row, but at 55% of the rotor rotation rate. Detailed stall inception investigation revealed that small amplitude modal waves instigated flow breakdown upstream of the rotor blade row, causing a spike stall cell to develop. This spike cell rotates very quickly (70%) and grows rapidly into a finite stall cell, slowing its rotation rate as it becomes fully developed. Stagnation pressure in the wake of the rotor blades was phase locked to both the rotor and stall cell rotation, allowing phase-averaging techniques to reveal the averaged stall cell structure. A new actuator was designed for rotating stall control. Based on the stall inception results, a disturbance rejection scheme was devised to interact with the incipient stall cell, preventing its growth into a finite stall cell. The single blade was studied in a number of open loop control experiments, which indicated that pulsing at 2psi over a range of frequencies can inhibit stall inception, extending the operating range by 0.4% mass flow, thus stabilizing a previously unstable operating point.
M.S. in Mechanical and Aerospace Engineering, May 2011
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Title: NEW TOOLS FOR JET ANALYSIS IN HIGH ENERGY COLLISIONS
Creator: Duffty, Daniel
Date: 2015, 2015-05
Description: Our understanding of the fundamental interactions of particles has come far in the last century, and is still pushing forward. As we build...
Show moreOur understanding of the fundamental interactions of particles has come far in the last century, and is still pushing forward. As we build ever more powerful machines to probe higher and higher energies, we will need to develop new tools to not only understand the new physics objects we are trying to detect, but even to understand the environment that we are searching in. We examine methods of identifying both boosted objects and low energy jets which will be shrouded in a sea of noise from other pasts of the detector. We display the power of boosted-b tagging in a simulated W' search. We also examine the effetc of pile up on low energy jet reconstructions. For this purpose we develop a new priority-based jet algorithm, "p-jets", to cluster the energy that belongs together, but ignore the rest.
Ph.D in Physics, May 2015
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Title: FLOW FIELD STRUCTURE AND UNSTEADY AERODYNAMIC LOADS ON AN AIRFOIL IN SURGING FLOW
Creator: Iliev, Simeon Milenov
Date: 2015, 2015-05
Description: Airfoils subject to unsteady freestream velocity as in the case of helicopter rotor blades and vertical axis wind turbines have been observed...
Show moreAirfoils subject to unsteady freestream velocity as in the case of helicopter rotor blades and vertical axis wind turbines have been observed to exhibit very interesting lift behavior. Depending on the frequency of the oscillating freestream velocity, the uctuating lift amplitude can reach values as much as twice of that predicted by a quasi-steady approximation or as low as only one-half of that. Experimental data and analysis presented in this study provide the exact relationship between surging ow frequency and amplitude of the uctuating lift force for a range of reduced fre- quencies between k=0.1 and k=1.5. Furthermore, surface pressure measurements on the suction surface of the airfoil are used to supplement the measured lift force data and provide a measure of the level of unsteady ow e ects. Finally, experimental particle image velocimetry ow eld data is presented for the two surging ow cases corresponding to the maximum and minimum uctuating lift amplitude and is used to extract coherent ow eld structures which are related to the respective lift be- havior. Both the experimental lift force data and ow eld structures are compared to corresponding, low Reynolds number numerical simulation results.
M.S. in Mechanical and Aerospace Engineering, May 2015
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Title: RECONFIGURABLE ANALOG FRONT-END SYSTEM FOR ULTRASONIC IMAGING APPLICATIONS
Creator: Vasudevan, Vidya
Date: 2014, 2014-12
Description: Ultrasonic systems, applied in the field of Medical Imaging and Non-Destructive Testing, have evolved from the trolley-based units to more...
Show moreUltrasonic systems, applied in the field of Medical Imaging and Non-Destructive Testing, have evolved from the trolley-based units to more portable, hand-held devices. These systems are built to suit a specific application or aim at specific target material. In order to make these systems portable and adaptable to the testing environment, a flexible and programmable hardware is built. A fully configurable Analog Front-End (AFE) is presented, which possesses the capability for dynamic re-configuration by using ARM processing core for real-time control, data acquisition and signal analysis in a Linux environment. This system supports up to 8 ultrasonic sensors. The flexibility built into the AFE allows for various beamforming and signal conditioning requirements. This reconfigurable system enables ultrasonic researchers to efficiently prototype different experiments and to incorporate high performance ultrasonic signal and image processing algorithms. This system provides real-time signal processing for nondestructive evaluation (NDE) and imaging applications using ultrasonic sensors ranging from 60 KHz to 15 MHz operating frequencies. A dynamically reconfigurable sensor interface is presented for ultrasonic pulse-echo measurements targeting flaw detection and parametric echo classification applications. For real-time implementation, a SoC-based system is developed on an ARM platform. For a working system, a BCM2835 SoC on a Raspberry Pi hardware system is explored with a further upgrade to Xilinx Zynq 7020 SoC in order to achieve a higher throughput.
M.S. in Electrical Engineering, December 2014
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Title: SPATIO-TEMPORAL RECONSTRUCTION FOR GATED CARDIAC SPECT
Creator: Niu, Xiaofeng
Date: 2011-07, 2011-07
Description: In myocardial perfusion imaging using single photon emission computed tomography (SPECT), gated acquisition is often used in order to deal...
Show moreIn myocardial perfusion imaging using single photon emission computed tomography (SPECT), gated acquisition is often used in order to deal with blur caused by cardiac motion in the resulting images. While this can provide useful information about the myocardial function, it also inevitably leads to reduced signal-to-noise ratio in the acquired data due to gating. In this work, we aim to investigate and evaluate image reconstruction methods for improving the quality of the reconstructed images in cardiac gated SPECT imaging. First, we propose a spatio-temporal (aka 4D) reconstruction procedure for gated images based on use of discrete Fourier transform (DFT) basis functions, wherein the image activity at each spatial location is regulated by a Fourier representation along the gate dimension. The gated images are then reconstructed through determination of the coefficients of the Fourier representation. We explore two different reconstruction algorithms, one is a penalized least-square approach and the other is a maximum a posteriori approach. Our simulation results demonstrate that use of DFT-basis functions in gated imaging can improve the accuracy of the reconstruction. While in gated imaging the tracer distribution is traditionally treated as constant, a recent development is gated dynamic imaging where the goal is to obtain an image sequence from a single acquisition which shows simultaneously both cardiac motion and tracer distribution change over the course of imaging. In this work, we further develop and demonstrate a fully 5D (3D space plus time plus gate) reconstruction procedure for cardiac gated, dynamic SPECT imaging, where the challenge is even greater without the use of multiple fast camera rotations. We develop and compare two iterative reconstruction algorithms: one is based on the modified block sequential regularized EM (BSREM-II) algorithm, and the other is based on the Bsplines algorithm. Our simulation results demonstrate that the 5D reconstruction xiii procedure can yield gated dynamic images which show quantitative information for both perfusion defect detection and cardiac motion. Based upon the success of 5D reconstruction, we also study the saliency of 5D images for detection of perfusion defects. We explore efficient ways for characterization and visualization of information pertinent to perfusion defects in a 5D image sequence. We apply various metrics to quantify the degree to which perfusion deficits can be detected. We show that these metrics can be used to produce new types of visualizations, showing wall motion and perfusion information, that may potentially be useful for clinical evaluation. Finally, with the ultimate goal of effective detection of lesion defect for clinical use, we also investigate a direct reconstruction approach to determine a sequence of gated, kinetic parameter images from a single acquisition, which can provide information simultaneously for both tracer kinetics and wall motion. To combat the greatly under-determined nature of the problem, we apply smoothness constraints to exploit the similarity both among the different gates and among the local spatial neighborhood. The parameter images of the different gates are then determined jointly using maximum a posteriori estimation from all the available image data.
Ph.D. in Electrical Engineering, July 2011
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Title: SURFACE CHARACTERIZATION OF NIOBIUM FOR SUPERCONDUCTING RF CAVITIES
Creator: Cao, Chaoyue
Date: 2014, 2014-07
Description: Surface characterization techniques including point contact tunneling (PCT) spectroscopy and Raman spectroscopy have been employed to study...
Show moreSurface characterization techniques including point contact tunneling (PCT) spectroscopy and Raman spectroscopy have been employed to study the surface of niobium (Nb) superconducting radio frequency (SRF) cavities. PCT spectroscopy provides a direct means of measuring the surface superconductivity, which is closely correlated with the cavity’s performance characterized by the quality factor Q. Cavities with remarkably high Q show near ideal tunneling spectra with sharp coherent peaks and low zero bias conductance, consistent with the Bardeen-Cooper-Schrie↵er (BCS) density of states (DOS), and bulk gap parameter, " = 1.55 -1.6 meV. Cavities with Q-drop often exhibit strong non-uniform heating during RF operations, with high loss regions identified as hot spots. PCT spectra on hot spots reveal suppressed superconductivity, broadened DOS and Kondo tunneling, consistent with magnetic impurities on the surface. Raman spectra on hot spots indicate the presence of various impurities on the surface including amorphous carbon, C-H chain compounds and NbC, providing insights into the formation of hot spots. The origin of the impurities is unclear at present but it is suggested that particular processing steps in SRF cavity fabrication may be responsible.
Ph.D. in Physics, July 2014
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Title: PROBING THE PAN-GENOME OF LISTERIA MONOCYTOGENES
Creator: Deng, Xiangyu
Date: 2011-04-26, 2011-05
Description: Bacterial pathogens often show significant intra-species variations in ecological fitness, host preference and pathogenic potential to cause...
Show moreBacterial pathogens often show significant intra-species variations in ecological fitness, host preference and pathogenic potential to cause infectious disease. The species of Listeria monocytogenes, a facultative intracellular pathogen and the causative agent of human listeriosis, consists of at least three distinct genetic lineages. Two of these lineages predominantly cause human sporadic and epidemic infections, whereas the third lineage has never been implicated in human disease outbreaks despite its overall conservation of many known virulence factors. The genomes of 26 L. monocytogenes strains representing the three lineages are compared based on both in silico comparative genomic analysis and high-density, pan-genomic DNA microarray hybridizations. We uncover 86 genes and 8 small regulatory RNAs that likely make L. monocytogenes lineages differ in carbohydrate utilization and stress resistance during their residence in natural habitats and passage through the host gastrointestinal tract. We also identify 2,330 to 2,456 core genes that define this species along with an open pan-genome pool that contains more than 4,052 genes. Phylogenomic reconstructions based on 3,560 homologous groups allowed robust estimation of phylogenetic relatedness among L. monocytogenes strains. The pan-genome approach enables accurate co-analysis of DNA sequence and hybridization array data for both core gene estimation and phylogenomic reconstruction. Application of our method to the pan-genome of L. monocytogenes sheds new insights into the intra-species genomic diversification, niche expansion and evolution of this important foodborne pathogen.
Ph.D. in Biology, May 2011
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Title: IMPROVED SPATIAL-TEMPORAL RECONSTRUCTION FOR CARDIAC AND RESPIRATORY GATED SPECT
Creator: Qi, Wenyuan
Date: 2014, 2014-12
Description: Myocardial perfusion single photon emission computed tomography (SPECT) is an important imaging technique for evaluating coronary artery...
Show moreMyocardial perfusion single photon emission computed tomography (SPECT) is an important imaging technique for evaluating coronary artery disease. It can provide information of both myocardial perfusion and ventricular function. However, SPECT images su er from both cardiac and respiratory motion blur. In order to reduce the motion degrading, cardiac and respiratory gated SPECT imaging is used. In gated SPECT imaging, due to the lowered counts, the gated images will be more noisy than the ungated ones. Spatiotemporal (4D) processing is often used to reduce the noise level in gated images. In this thesis, we aim to investigate spatial and temporal processing techniques for improving the quality in cardiac and respiratory gated SPECT imaging. First, we will investigate a piecewise spatial smoothing prior based on totalvariation (TV) in 4D cardiac SPECT image reconstruction. In previous studies, it was found that spatial smoothing could adversely a ect the accuracy of 4D reconstruction in cardiac gated SPECT when temporal smoothing was applied, even though it could suppress the noise level. Our goal is to explore whether a piecewise spatial smoothing prior will improve the image accuracy while reducing the noise. Toward this goal, we will compare TV based piecewise spatial smoothing with quadratic spatial smoothing with simulated imaging, in which we will evaluate the lesion detectability. Clinical data will also be used to compare the results as a preliminary test. Motion-compensated temporal smoothing is known to play a key role in 4D cardiac gated SPECT reconstruction. Next, we will investigate whether better motion estimation could further improve the accuracy of reconstructed images. We will consider two di erent motion estimation models and the known motion in simulated experiments. The motion estimation methods are the classic optical ow estimation (OFE) and a periodic motion estimation method. We will evaluate the reconstruction from di erent motion models using several numerical quanti cation metrics. Furthermore, we will demonstrate reconstruction with the two motion estimation models using clinical acquisitions. Respiratory motion is known to cause motion blur in SPECT image reconstruction, and respiratory gated SPECT imaging can be e ective to combat its e ect. We will develop reconstruction techniques in respiratory gated SPECT. We will consider two reconstruction schemes for respiratory gated SPECT. The rst scheme is a post motion compensated reconstruction, in which images at di erent respiratory phases are reconstructed seperately, and afterwards are averaged over all the respiratory gates by motion compensation. The second scheme is a model based motion compensated reconstruction approach, in which one reference gate is used to describe the acquisition data of all the respiratory gates. Due to irregular respiratory motion, the data acquisition in each respiratory gate is not uniformly distributed among the acquisition angles, which would lead to limited-angle artifacts. To correct such artifacts, we propose an angle compensation method in the reconstruction. In order to deal with both cardiac and respiratory motion, we will investigate a 4D reconstruction approach for dual cardiac-respiratory gated SPECT reconstruction. This approach can accommodate the acquired data simultaneously from di erent cardiac and respiratory gates. It can exploit the correlation in the signal component among both the cardiac and respiratory phases. Both simulated experiments and clinical reconstruction will be used for evaluating this reconstruction approach. Due to the radiation risk of myocardial perfusion imaging (MPI) scans, there is an urgent need to lower the radiation dose used in SPECT. However, lower radiation dose will lead to more noisy reconstruction, which is even more serious in gated SPECT. We would explore the potential of using 4D reconstruction for lowering the dose in dual cardiac-respiratory gated SPECT.
Ph.D. in Electrical and Computer Engineering, December 2014
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Title: COMPRESSIVE SENSING AND RECONSTRUCTION : THEORY AND APPLICATIONS
Creator: Krishnamurthy, Ritvik Nadig
Date: 2014, 2014-07
Description: Conventional approach in acquisition and reconstruction of images from frequency domain strictly follow the Nyquist sampling theorem. The...
Show moreConventional approach in acquisition and reconstruction of images from frequency domain strictly follow the Nyquist sampling theorem. The principle states that the sampling frequency required for complete reconstruction of a signal is at least twice the maximum frequency of the original signal. This dissertation studies an emerging theory called Compressive Sensing or Compressive Sampling which goes against the conventional wisdom. Theoretically, it is possible to reconstruct images or signals accurately from a number of samples which is far smaller than the Nyquist samples. Compressive Sensing has proven to have farther implications than merely reducing sampling frequency of the signal. Possibility of new data acquisition methods from analog domain to digital form using fewer sensors, image acquisition using much smaller sensors array, to name a few. This novel theory combines sampling and compression methods thereby reducing the data acquisition resources, such as number of sensors, storage memory for collected samples and maximum operating frequency. This dissertation presents some insights into reconstruction of grey scale images and audio signals using OMP and CoSaMP algorithms. It also delves into some of the key mathematical insights underlying this new theory and explains some of the interactions between Compressive Sensing and related elds such as statistics, coding theory and theoretical computer science. viii
M.S. in Computer Engineering, July 2014
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Title: SYSTEM SUPPORT FOR RESILIENCE IN LARGE-SCALE PARALLEL SYSTEMS: FROM CHECKPOINTING TO MAPREDUCE
Creator: Jin, Hui
Date: 2012-05-31, 2012-05
Description: High-Performance Computing (HPC) has passed the Petascale mark and is moving forward to Exascale. As the system ensemble size continues to...
Show moreHigh-Performance Computing (HPC) has passed the Petascale mark and is moving forward to Exascale. As the system ensemble size continues to grow, the occurrence of failures is the norm rather than the exception during the execution of parallel applications. Resilience is widely recognized as one of the key obstacles towards Exascale computing. Checkpointing is currently the de-facto fault tolerant mechanism for parallel applications. However, parallel checkpointing at scale usually generates bursts of concurrent I/O requests, imposes considerable overhead to I/O subsystems, and limits the scalability of parallel applications. Despite the doubt in the feasibility of checkpointing continues to increase, there is still no promising alternative on the horizon yet to replace checkpointing. MapReduce is a new programming model for massive data processing. It has demonstrated a compelling potential in reshaping the landscape of HPC from various perspectives. The resilience of MapReduce applications and its potential in benefiting HPC fault tolerance are active research topics that require extensive investigation. This thesis work targets at building a systematic framework to support resilience in large-scale parallel systems. We address the identified checkpointing performance issue through a three-fold approach: reduce the I/O overhead, exploit storage alternatives, and determine the optimistic checkpointing frequency. This three-fold approach is achieved with three different mechanisms, namely system coordination and scheduling, the utilization of MapReduce framework, and stochastic modeling. To deal with the increasing concerns about MapReduce resilience, we also strive to improve the reliability of MapReduce applications, and investigate the tradeoffs in the programming model selection (e.g., MPI v.s. MapReduce) from the perspective of resilience. This thesis provides a thorough study and a practical solution for solving the outstanding resilience problem of large-scale MPI-based HPC applications and beyond. It makes a noticeable contribution to the state-of-the-art and opens a new research direction for many to follow.
Ph.D. in Computer Science, May 2012
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Title: SEARCHING ENCRYPTED CLOUD DATA
Creator: Urs, Karthik Mahendra Raje
Date: 2011-05-04, 2011-05
Description: The major setback of the cloud is its inability to induce strong trust in its users. For us, the users of the cloud, to be sure of the...
Show moreThe major setback of the cloud is its inability to induce strong trust in its users. For us, the users of the cloud, to be sure of the security of the data from other users, we have to trust cloud. In most of the cases, say if the data were to be hosted on Microsoft’s servers, we can trust Microsoft in its policies to prevent unauthorized access to it from other users (via hacking). But, the issue that is haunting the cloud is this - ”How can we be sure that our data is safe from Cloud service providers themselves?” The most intuitive solution for the cloud service provider to gain trust is to insist we encrypt our data. That is an irrefutable act of honesty from the cloud. But this has some obvious setbacks, few of which would negate the very advantages of cloud. One such issue that dictates the scope of this thesis is this - Typical cryptographic algorithms are not amenable to search. Now, if we were to implement a search engine on cloud (which has the data encrypted), the native search techniques have to be extended on to the cryptographic domain so that the cloud can perform the tasks of a search engine. This thesis explores the solutions to the above mentioned problem of searching over encrypted data, specifically using a secure pre-processed index approach. Though significant ideas have been proposed in the area, there is no concrete implementation to analyze if it can be used in the industrial setting. The main goal of the thesis is to implement a system which supports a variety of searching techniques. We make use of Amazon EC2 and test out the designed systems to evaluate how feasible they are for immediate consumption by the industry.
M.S. in Computer Engineering, May 2011
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Title: MICROCALCIFICATION DETECTION WITH DEEP BELIEF NETWORK
Creator: Liu, Lu
Date: 2012-04-24, 2012-05
Description: In this thesis, deep belief net (DBN) is applied for detection of microcalcification (MC) clusters in digital mammograms. DBN is a relatively...
Show moreIn this thesis, deep belief net (DBN) is applied for detection of microcalcification (MC) clusters in digital mammograms. DBN is a relatively new type of neural network in machine learning which can learn complex structures from data by using a deep architecture. Based on a database of 200 clinical mammograms, a 3-level unsupervised network followed by a supervised back-propagation fine-tuning classifier is trained and tested. For each location in the image, the classifier is applied to decide whether there is an MC, and subsequently all the detected MCs are grouped into clusters. Free-response receiver operating characteristic (FROC) curves are used to evaluate the performance. The performance of DBN is compared to a well-known support vector machine (SVM) detector. Experimental results show that DBN can outperform SVM. In particular, DBN can achieve a detection rate of 83% at the cost of only one false positive cluster per image. These promising results show that DBN can be adopted in the study of object detection in medical image.
M.S. in Electrical Engineering, May 2012
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Title: SURVIVAL AND GROWTH OF LISTERIA MONOCYTOGENES IN CHOPPED GREEN AND RED BELL PEPPERS USING PREDICTIVE MODELING
Creator: Zhang, L1jie
Date: 2015, 2015-07
Description: Listeria monocytogenes (L. monocytogenes) is a Gram-positive pathogenic organism and the causative agent of human and animal listeriosis....
Show moreListeria monocytogenes (L. monocytogenes) is a Gram-positive pathogenic organism and the causative agent of human and animal listeriosis. Listeriosis is a gastrointestinal or invasive systemic illness resulting from consumption of contaminated food products, mainly cheese, deli meats, and fresh produce, by L. monocytogenes. In recent years, several foodborne outbreaks have been reported that were associated with fresh produce, such as cantaloupe, celery and sprouts. Temperature is considered a major factor that affects L. monocytogenes growth during storage. The proliferation of L. monocytogenes varies on different produce items based on storage temperature. In this study, the persistence and population dynamics of three L. monocytogenes strains, LS806 (cheese isolate), LS810 (cantaloupe isolate) and LS808 (celery isolate) were evaluated by incubating inoculated fresh-cut green bell pepper and red bell pepper at various temperatures (5oC, 10oC, and 25oC) for 14 days. To assess the risk of L. monocytogenes in these fresh-cut vegetable items, a primary predictive model was fitted for L. monocytogenes growth data using DMFit. Green bell pepper had significantly (P<0.05) higher pH and aw, and higher amounts of yeast and mold and Enterobacteriaceae than did red bell pepper. In green bell pepper, all three strains showed no significant difference (P>0.05) in growth rate when incubated at the same temperature. In red bell peppers, LS808 had the highest (P<0.05) growth rate at both 5°C and 25°C out of the three strains. All of the three strains grew significantly faster (P<0.01) at 25°C than either 5°C or 10°C in both green and red bell peppers. All three strains obtained less than 1 log10 growth increase after incubating at 25°C for 6 hours on pre-chilled produce. Some strains (LS806 and LS810) significantly increased (P<0.01) during two 5-hour 25°C incubations, but did not reach 1 log10 growth increase. The results indicate that L. monocytogenes not only persists, but also grows in chopped green and red bell peppers at 5, 10, and 25°C, and strains grew faster at the higher temperature (25°C). Data obtained could be further evaluated for determining whether Time/temperature control for safety (TCS) designation should be applied to chopped green and red bell peppers.
M.S. in Food Safety and Technology, July 2015
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