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Examination of Listeria monocytogenes survival in refrigerated chopped hard-boiled eggs and deli salads containing this ingredient
No full textPeeled hard-boiled eggs (HBEs) are widely favored by both consumers and food services due to their convenience. These HBEs are often chopped and incorporated into
various dishes such as deli salads. However, recent recalls of hard-boiled eggs have brought
attention to the risk of contamination with Listeria monocytogenes. Prepared HBEs are
typically subjected to antibacterial treatment to maintain product safety and quality. Citric
acid is a common antibacterial used in the food industry to treat the HBEs. Previous
research has determined that 2% citric acid treatment is effective against L. monocytogenes
on whole HBEs. This study examined the efficacy of citric acid on the reduction of L.
monocytogenes on chopped HBEs and in deli salads containing chopped HBEs. HBEs were
treated with 2% citric acid or water (untreated) by submersion for 24 h at 5°C. HBEs were
dried for 10 min, inoculated with a 4-strain cocktail of rifampicin-resistant L.
monocytogenes, at 1 (low-level inoculation) or 4 log CFU/HBE (high level-inoculation),
and allowed to dry for 10 min. Low-level inoculated HBEs were chopped and stored at 5,
10, or 15°C for 28 d. High-level inoculated HBEs were chopped and stored at 5, 10, and
25°C for 14 d. Low-level inoculated HBEs were also chopped and incorporated into potato,
tuna, chicken, or macaroni salad at a 1:6 ratio (HBE to other ingredients), or into egg salad
at a 7:1 ratio. Salads were stored at 5, 10, or 15°C for 28 d. The presence of L.
monocytogenes was determined at intervals during storage by enrichment with BLEB
and/or enumerated on BHIArif throughout storage. Triplicate samples were assessed for
each time point, and three independent trials were conducted. Data was analyzed by
Student’s T-test, ANOVA, and Fisher’s exact test, p≤0.05. For low-level inoculated
chopped HBEs, the L. monocytogenes population was significantly higher in untreated chopped HBEs (1.86±0.33 log CFU/g) as compared to treated chopped HBEs (1.47±0.27
log CFU/g) on day 14 at 15°C. On both untreated and treated chopped HBEs, there was no
significant difference in the population of L. monocytogenes up to 7 d. However, from 14
d, there was a significant increase in the growth of L. monocytogenes (1.86±0.33 to
2.18±0.35 log CFU/g on untreated chopped HBEs and 1.47±0.27 to 1.94±0.47 log CFU/g
for treated, respectively). For high-level inoculated HBEs, a higher L. monocytogenes
growth rate was observed on untreated chopped HBEs as compared to treated chopped
HBEs at 10 and 25°C. It was observed that treated chopped HBEs at 5°C took the longest
to reach 1 log CFU/g increase in the L. monocytogenes population (50 d) whereas,
untreated chopped HBEs at 25°C took the shortest (0.22 d). Untreated chopped HBEs
showed a significantly higher population of L. monocytogenes as compared to treated
chopped HBEs on 14 d at all storage temperatures. In deli salads containing chopped HBEs,
potato salad showed the highest growth of L. monocytogenes after 14 d, followed by
macaroni, egg, chicken, and tuna salad. The population of L. monocytogenes was the lowest
in tuna salad. L. monocytogenes was present throughout the storage period at all storage
temperatures. It was observed that 2% citric acid is more efficient in controlling the growth
of L. monocytogenes in chopped HBEs as compared to when those HBEs are incorporated
into deli salads. The findings contribute to the formulation of preventive measures and
standards aimed at guaranteeing the safety of HBEs
Two Essays on Mergers and Acquisitions
No full textThis dissertation is composed of two self-contained chapters that both relate to mergers and acquisitions (M&A). In the first essay, we examine the Delaware (DE) reincorporation effect on firms’ post-IPO behaviors on mergers and acquisitions. We find that firms’ DE reincorporation decisions enhance the likelihood of engaging in M&A as targets. However, as a tradeoff, DE reincorporated firms get lower takeover valuations compared to stay-at-home-state firms, and the acquisition of reincorporated firms is less likely to be successful. Our second essay aims to explore the role of the options market in price discovery for M&A. We find that the predictive power of the changes in implied volatility of the target firm stock for the takeover outcome is statistically and economically significant. The risk arbitrage portfolios incorporating filters derived from the options on stocks of the target firms generate annualized risk-adjusted abnormal returns between 2.6% and 5%, depending on the portfolio weighting method, the threshold of filters for the implied volatility change, and the asset pricing models applied for abnormal returns. The results are robust to different empirical setups and are not explained by traditional factors
Design and Optimization of Air-Core High Temperature Superconducting (HTS) Pulse Transformer for Series Type Hybrid Circuit Breaker (S-HCB)
No full textDC 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
A Wireless Intraspinal Microstimulation Interface for the Recovery of Motor Function Following Spinal Cord Injury
No full textRecovery of function following spinal cord injury (SCI) remains a daunting medical challenge. There are 270,000 people living in the US with SCI, and 17,800 additional injuries occur each year. Over half of people with SCI do not recover the ability to walk. In the US, the estimated cost amounts to nearly $14.5 billions of dollars. Attempts to recover function have included surgically implanting polymer scaffolding and stem cells to cause repair of the spinal cord, but to date, these approaches have not been efficacious. Following a SCI, the muscles, their innervating neurons, and the segmental spinal circuitry below the level of injury remain largely intact. Therefore, rehabilitation interventions that activate the surviving neural elements have been investigated. A well-known approach for restoring a large range of functions, even following a SCI, is functional electrical stimulation (FES). FES of muscles, peripheral nerves and spinal sacral roots can restore independent respiration, arm and hand function, and bladder voiding. FES also improves bone and muscle health, increases circulatory function, reduces spasticity, prevents pressure ulcers, and induces functional recovery. Nerve cuff, epimysial, or intramuscular electrodes are used to stimulate nerve fibers innervating various muscles. Notable limitations have compromised their effectiveness in restoring functional walking, including lead breakage, reduced fatigue resistance (due to reversed recruitment order of muscles), widespread implantation of electrodes throughout the legs, and challenges in the activation of multiple muscles. The challenges encountered with applying FES to the periphery for restoring standing and walking led to the investigating the application of electrical stimulation to the lumbosacral enlargement of the spinal cord. While most clinical spinal stimulators are pacemaker-style devices with epidural electrodes, intraspinal microstimulation (ISMS), has emerged as an alternative with the potential to restore functional over-ground walking. ISMS was initially used in improving bladder function after SCI in the 1970s. Mushahwar (one of our collaborators) has pioneered the use of ISMS to restore movement of the legs, and ISMS has produced sustained stepping in severe (ASIA A) SCI in animal models. Moreover, ISMS produced similar movements in other species including pigs and monkeys, strongly suggesting that similar outcomes may also be obtained with ISMS in humans in the future.
Current ISMS implant concepts consist of fine penetrating microelectrodes placed with the tips targeting lamina IX bilaterally. Despite experimental results in acute animal models, the literature currently presents no implantable ISMS system capable of providing this type of interface in a form suitable for chronic deployment in a clinical setting. Moreover, emerging ISMS implant designs use wires that connect to the electrodes and cross the dura. Spinal cord electrode wires are known to be problematical due to the chronic adverse tissue responses, tethering forces on the electrodes (with spinal cord movement), and cerebrospinal fluid leakage caused by the transdural conduits. For the latter, it is well known that wires exiting through the dura are a major surgical complication.
To overcome the current ISMS limitations, we aimed to develop and test a wireless intraspinal microstimulation interface which eliminates both tethering forces on the electrodes and the transdural conduit. The feasibility of the proposed system is supported using an existing 5mm-diameter wireless floating microelectrode array (WFMA) developed by Troyk and his team (our lab) which is now in use in an FDA-approved clinical trial for intracranial occipital cortex stimulation for visual restoration. Combined with a wireless extension lead (to magnetically reach from the surface of the back to the cord), multiple WFMA devices were implanted into the spinal cord with no transdural lead or conduit; communication across the dura was accomplished via magnetic coupling. The subdural WFMA devices served as a platform for developing a novel wireless ISMS system.
Initial experiments demonstrated the system’s mechanical stability and the feasibility of using microelectrode arrays to achieve controlled motor responses. Although early chronic trials led to neural deficits, subsequent surgical refinements—including duroplasty, hemostatic agents, and a redesigned wireless extension wire—successfully preserved motor function in spinally intact animals. These modifications significantly improved neural recovery outcomes, highlighting the impact of precise surgical adjustments on the system's efficacy.
The research underscores the spinal cord’s vulnerability and the importance of precise, individualized implantation strategies for ISMS systems. Suggested improvements for future studies include preoperative MRI-guided electrode positioning and use of flexible implant materials to reduce tissue disruption. This work establishes foundational insights for ISMS technology, with potential applications extending beyond motor restoration to include pain management, sensory feedback, and neural regeneration, laying a path toward therapeutic human use
Improving Localization Safety for Landmark-Based LiDAR Localization System
No full textAutonomous ground robots have gained traction in various commercial applications, with established safety protocols covering subsystem reliability, control algorithm stability, path planning, and localization. This thesis specifically delves into the localizer, a critical component responsible for determining the vehicle’s state (e.g., position and orientation), assessing compliance with localization safety requirements, and proposing methods for enhancing localization safety.Within the robotics domain, diverse localizers are utilized, such as scan-matching techniques like normal distribution transformations (NDT), the iterative closest point (ICP) algorithm,probabilistic maps method, and semantic map-based localization.Notably, NDT stands out as a widely adopted standalone laser localization method, prevalent in autonomous driving software such as Autoware and Apollo platforms.In addition to the mentioned localizers, common state estimators include variants of Kalman Filter, particle filter-based, and factor graph-based estimators. The evaluation of localization performance typically involves quantifying the estimated state variance for these state estimators.While various localizer options exist, this study focuses on those utilizing extended Kalman filters and factor graph methods. Unlike methods like NDT and ICP algorithms, extended Kalman filters and factor graph based approaches guarantee bounding of estimated state uncertainty and have been extensively researched for integrity monitoring.Common variance analysis, employed for sensor readings and state estimators, has limitations, primarily focusing on non-faulted scenarios under nominal conditions. This approach proves impractical for real-world scenarios and falls short for safety-critical applications like autonomous vehicles (AVs).To overcome these limitations, this thesis utilizes a dedicated safety metric: integrity risk. Integrity risk assesses the reliability of a robot’s sensory readings and localization algorithm performance under both faulted and non-faulted conditions. With a proven track record in aviation, integrity risk has recently been applied to robotics applications, particularly for evaluating the safety of lidar localization.Despite the significance of improving localization integrity risk through laser landmark manipulation, this remains an under explored territory. Existing research on robot integrity risk primarily focuses on the vehicles themselves. To comprehensively understand the integrity risk of a lidar-based localization system, as addressed in this thesis, an exploration of lidar measurement faults’ modes is essential, a topic covered in this thesis.The primary contributions of this thesis include: A realistic error estimation method for state estimators in autonomous vehicles navigating using pole-shape lidar landmark maps, along with a compensatory method; A method for quantifying the risk associated with unmapped associations in urban environments, enhancing the realism of values provided by the integrity risk estimator; a novel approach to improve the localization integrity of autonomous vehicles equipped with lidar feature extractors in urban environments through minimal environmental modifications, mitigating the impact of unmapped association faults. Simulation results and experimental results are presented and discussed to illustrate the impact of each method, providing further insights into their contributions to localization safety
Case Study: A Comparison of Pedagogical Content Knowledge Between Coaches and Coaches/Mentees
No full textThis multiple case study dissertation aimed to examine one of the domains of pedagogical content knowledge, knowledge of content and students, between different types of elementary coaches and between coach and their respective collaborating teachers. It also investigated the impact a coaches’ background experiences have on the dynamic between coaches and teachers and the perceptions' teacher have on the effectiveness of coaching. The theoretical framework used in this qualitative study was Ball, Thames, and Phelps’ (2008) definition of PCK. Data was collected from six coaches–four instructional coaches and two math coaches–and eleven k-5th grade teachers. Data collection involved a survey, LMT assessment, and semi-structured interviews, and a thematic analysis method was conducted. The findings from the cross-case analysis resulted in ten themes, with the majority having multiple categories. One finding to one of the research questions was that there were no differences in knowledge of content and students between mathematics coaches and general instructional coaches, but other areas to further investigate emerged. Another finding was that coaches were either within the same capacity as their respective teachers or had extra knowledge of content and students. Although the majority of the coaches’ knowledge of content and students was at a higher level according to their LMT score, it does not necessarily mean that coaches are working with teachers in improving knowledge of content and students. In addition, more research is recommended in creating a pedagogical content knowledge instrument that is specific for coaches
Characterization of Novel Concrete Formulations: High-Volume Fly Ash for Precast Industry Use and Non-Proprietary UHPC
No full textThe use of high-volume fly ash concretes can be challenging for high-early strength applications, such as in precast construction, largely due to potential delays in strength gain resulting from relatively lower heats of hydration of the underlying binder formulations. Considering that the use of higher levels of available fresh or landfilled fly ash as a replacement for traditional ordinary Portland cement (OPC) could result in more sustainable mix designs, a framework to develop novel, high-volume fly ash mixes with optimized dosages of commercial grade gypsum and accelerating admixtures to enhance early-age strength performance. Early-age mechanical properties such as compressive strength, modulus of rupture, and modulus of elasticity were evaluated starting within 24 hours of specimen preparation. Experimental test results were then characterized and subsequently analyzed relative to current design provisions to highlight the best performing trial mixes (with respect to the early-age strength target) and cases where current design provisions are either unconservative or overly-conservative with respect to the test data. Additionally, thermal properties of concrete produced with fly ash were tested with two different curing environments, along with using code equations to determine if high volume fly ash provides a higher thermal resistance compared to OPC concrete. Wrapping up cementitious replacement with non-proprietary ultra high-performance concrete (UHPC) for transportation structures. Then reproducing mixtures to ensure target compressive strength values could be reached. Followed by increasing batch size to a larger quantity using a large mixer to create full-size specimens
Estimation of Platinum Oxide Degradation in Proton Exchange Membrane Fuel Cells
No full textThe performance and durability of Proton Exchange Membrane Fuel Cells (PEMFCs) can be significantly hampered due to the degradation of the platinum catalyst. The production of platinum oxide is a major cause of the degradation of the fuel cell system, negatively affecting its performance and durability. In order to predict and prevent this degradation, this research examines a novel method to estimate degradation due to platinum oxide formation and predict the level of platinum oxide coverage over time. Mechanisms of platinum oxide formation are outlined and two methods are compared for platinum oxide estimation. Linear regression and two Artificial Neural Network (ANN) models, including a Recurrent Neural Network (RNN) and Feed-forward Back Propagation Neural Network (FFBPNN), are compared for estimation. The estimation model takes into account the influence of cell temperature and relative humidity.Evaluation of relative errors (RE) and root mean square error (RMSE) illustrates the superior performance of RNN in contrast to GT-Suite and FFBPNN. However, both RNN and GT-Suite showcase an average error rate below 5% while the FFBPNN had a higher error rate of approximately 7%. The RMSE of RNN shows mostly less compared to FFBPNN and GT-Suite, however, at 50% training data, GT-Suite shows lowest RMSE. These findings indicate that GT-Suite can be a valuable tool for estimating platinum oxide in fuel cells with a relatively low RE, but the RNN model may be more suitable for real-time estimation of platinum oxide degradation in PEM fuel cells, due to its accurate predictions and shorter computational time. This comprehensive approach provides crucial insights for optimizing fuel cell efficiency and implementing effective maintenance strategies
Optimization of Large-Scale NOMA With Incidence Matrix Design and Physical Layer Security
No full textThe Non-Orthogonal Multiple Access (NOMA) system is recognized for its capability to achieve higher spectral efficiency and massive connectivity. NOMA is intended to transmit massive user communications. The incidence matrix governs the relationship between users and resources for the Code domain NOMA (CD-NOMA). However, NOMA studies focus less on the design and optimization of the incidence matrix.Therefore, this thesis aims to investigate the development of a secure and large-scale NOMA system based on incidence matrix design. The main contributions are outlined as follows:
Firstly, this research introduces a novel NOMA system. Distinct from existing studies, the NOMA system is based on combinatorial design. This innovative approach, coupled with a unique constellation design, eliminates the surjective mapping from the linear adding data of multiusers, reducing the complexity of constellation design and Multiuser Detection (MUD). The characteristics of the incidence matrix designs, Simple Orthogonal Multi-Arrays (SOMA), are explored, which display a distinct Latin Square pattern. The SOMA design's unique structure allows for the creation of a highly flexible and fair resource allocation matrix. The NOMA system's theoretical performance analysis equations are established, supporting dynamic adaptability and optimization. The design is validated by Monte Carlo simulation. Compared to other NOMA schemes, it offers higher degrees of freedom and lower complexity while maintaining graceful error rates to transmit a larger number of users.
Secondly, a novel NOMA system utilizing incidence matrix information in the uplink is investigated. The incidence matrix pattern is exploited for MUD to achieve large-scale user connectivity. The incidence matrix is designed based on two critical mathematical concepts: parallel classes in hypergraph theory and orthogonal arrays (OAs) in combinatorial designs. Unlike other NOMA schemes, which require modification of their receiver and transmitter to decode superimposed multiuser signals, the unique pattern of the OA structure enables the use of conventional modulators. Consequently, the system load increases and the complexity and latency are reduced. The order of magnitude of the decoding complexity can be significantly reduced from O(N^3) to O(N) compared to the conventional minimum mean-square estimation (MMSE) decoder. Monte Carlo simulation validates that this novel NOMA system outperforms other NOMA designs in terms of error rate, data rate, and system size.
Finally, a reconfigurable convolutional encoder design that integrates security and error correction based on physical layer security (PLS) and randomness is developed. This design addresses concerns over privacy, security, and reliability of Internet of Things devices in edge computing networks. The lightweight Convolutional encoders are designed to ensure security by updating the transfer function dynamically with user data. The reconfigurability of the design is achieved by replacing the fixed adder that represents the generator polynomials with the switch adder, enabling the use of 87 billion distinct updating structures, thereby enhancing the versatility of the design. BER-based PLS paradigms are demonstrated in the simulation. In the simulation, the robustness and randomness of this design are further validated through tests suggested by the National Institute of Standards and Technology for cryptographically secure pseudorandom number generators, such as the monobits, longest one, and run tests
Capital Design: The Role of Design in Institutional Capital Allocation
No full textThere is a paradox within the $100 trillion institutional investment industry: the more choices an institutional investor has, the more challenging it becomes to make investment decisions. This paradox is significant because capital is one of the most transformational elements of the 21st century, driven by financialization, universal ownership, and increasing systemic risks. The direction of capital flows significantly influences the approach to addressing climate change, aging populations, and the transition to sustainable energy, in addition to supporting the essential physical and social infrastructure supported by institutional capital. This research proposes and substantiates a novel hypothesis: design can significantly influence capital allocation in institutional investment contexts. Through an institutional case study, expert interviews, workshops with master’s level design students, and systems-informed reflective practice, this research identifies asset classes as an important and changeable lens through which institutions engage with the future. It explores how these asset classes shape choices in the capital allocation process and identifies eight design capabilities particularly suited for institutional investment contexts. In doing so, it introduces a framework termed Capital Design. This framework illustrates how design can influence institutional capital allocation by integrating these design capabilities with investment tools through informational lenses within a choice/knowledge map. As a result, Capital Design offers an innovative approach for investors and investees to reorient toward emergent asset categories that directly meet the most urgent societal needs