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A predator-prey model with age-structured role reversal
No full textWe propose a predator-prey model with an age-structured predator population that exhibits a functional role reversal. The structure of the predator population in our model embodies the ecological concept of an "ontogenetic niche shift", in which a species' functional role changes as it grows. This structure adds complexity to our model but increases its biological relevance. The time evolution of the age-structured predator population is motivated by the Kermack-McKendrick Renewal Equation (KMRE). Unlike KMRE, the predator population's birth and death rate functions depend on the prey population's size. We establish the existence, uniqueness, and positivity of the solutions to the proposed model's initial value problem. The dynamical properties of the proposed model are investigated via Latin Hypercube Sampling in the 15-dimensional space of its parameters. Our Linear Discriminant Analysis suggests that the most influential parameters are the maturation age of the predator and the rate of consumption of juvenile predators by the prey. We carry out a detailed study of the long-term behavior of the proposed model as a function of these two parameters. In addition, we reduce the proposed age-structured model to ordinary and delayed differential equation (ODE and DDE) models. The comparison of the long-term behavior of the ODE, DDE, and the age-structured models with matching parameter settings shows that the age structure promotes the instability of the Coexistence Equilibrium and the emergence of the Coexistence Periodic Attractor
Hallucinations in Multimodal Large Language Models: Evaluation, Mitigation, and Future Directions
No full textMultimodal Large Language Models (MLLMs) have achieved impressive performance across a wide array of tasks. Despite these promising developments, MLLMs often generate outputs that are inconsistent with the visual content, a challenge known as hallucination, which poses substantial obstacles to their practical deployment and raises concerns regarding their reliability in real-world applications. This problem has attracted increasing attention, prompting efforts to detect and mitigate such inaccuracies.
This thesis makes four key contributions to the study of hallucinations in MLLMs. First, we provide a clear definition and taxonomy of hallucinations. Second, we propose a systematic evaluation framework that quantifies hallucinations across different modalities and task settings, employing a suite of metrics specifically designed to capture real-world failure modes. Third, we introduce a set of novel mitigation strategies that integrate architectural enhancements, finetuning with targeted objectives, and data augmentation. These approaches collectively reduce hallucination rates while maintaining the model’s generalization ability. Finally, we conduct an in-depth analysis to uncover the underlying causes of hallucination.
By consolidating evaluation, diagnosis, and mitigation into a unified investigation, this thesis advances the understanding of hallucinations in MLLMs and offers actionable guidance for building more reliable and trustworthy multimodal AI systems in both the architecture and data perspectives. Our findings provide a foundation for future research and practical deployment in the multimodal learning domain
Practical Applications for Partial Quantum Error Correction
No full textQuantum computers have the theoretical potential to solve problems intractable for classical computers. However, realizing this potential requires dealing with the noise inherent in near and far-term devices. One way of doing this is to redundantly encode the quantum information in a quantum error-correcting code and manipulate the encoded states to do computation. Protecting quantum information in this way incurs additional space overhead in the form of extra qubits; this is problematic since qubits are a scarce resource, especially for near-term quantum computers. Reducing these overheads could significantly accelerate the arrival of large-scale, fault-tolerant quantum computation.
In this thesis, we address this topic of research and present techniques which aim to practically reduce the space and time overheads of implementing quantum error correction. The overarching motivation for the works presented in this thesis is the belief that it is advantageous, perhaps even essential, to measure every stabilizer generator when performing quantum error correction. To address this claim, we introduce partial quantum error correction, which we broadly define to be using incomplete syndrome information from the code or neglecting to correct errors on some part of the system. We show that it is not necessary to measure every stabilizer generator in order to obtain a threshold, and we will describe several situations where we obtain better logical performance and/or reduced overheads by not doing so.
In particular, we present an error correction protocol built on a bilayer architecture that aims to reduce operational overheads when restricted to 2D local gates by measuring some generators less frequently than others. We show through numerical simulations that high-rate quantum error correcting codes implemented with this protocol achieve logical error rates comparable to the surface code while using fewer physical qubits. We then introduce adaptive syndrome extraction as a scheme to improve code performance and reduce the quantum error correction cycle time by measuring only the stabilizer generators that are likely to provide useful syndrome information. We describe and numerically evaluate a concrete example of the scheme instantiated using a concatenated code and a syndrome extraction cycle that uses quantum error detection to modify the syndrome extraction circuits in real time
EFFECTS OF AGING PROCESSES AND CO-EXISTING SUBSTANCES ON THE PERFORMANCE OF COLLOIDAL ACTIVATED CARBON FOR IN SITU REMEDIATION OF PERFLUOROALKYL ACIDS
No full textPer- and polyfluoroalkyl substances (PFAS) are emerging organic contaminants that are ubiquitous and persistent in environments, bioaccumulative in ecosystems, and pose potential risks to human health and wildlife. PFAS have been detected in human tissues, raising concerns about their potential impacts on public health. Among PFAS, perfluoroalkyl acids (PFAAs) are particularly challenging to remediate due to their high detection rates, greater water solubility, and widespread mobility in the environment, especially in soil and groundwater. Colloidal activated carbon (CAC), characterized by its small size ( 1000 m2/g), has gained attention as an injectable adsorbent for in-situ remediation technology for PFAA-contaminated groundwater. However, the long-term effectiveness of CAC for in-situ PFAA removal is challenged by the complexity of the subsurface environment. Environmental factors, such as fluctuations in humidity, chemical reactions, and biological activity (e.g., biofilm formation) in the subsurface area, can lead to aging effects that alter the surface properties of CAC. Additionally, the presence of co-existing substances can influence the adsorption behavior of PFAAs, collectively diminishing the performance of CAC. Limited information is available on the extent and mechanisms by which these factors influence CAC’s effectiveness, posing a barrier to its widespread implementation for remediating PFAA-impacted sites. However, over time, the complex and variable environmental conditions can induce aging (mechanical, chemical, and/or biochemical) processes in CAC, altering its surface properties and potentially affecting its PFAA removal efficiency during the long-term in-situ application. These aging processes include physical aging (i.e., driven by mechanical stresses such as wet-dry cycles), chemical aging (i.e., through oxidative reactions involving oxidants or mineral catalysts), and biological aging (i.e., caused by microbial colonization and biofilm formation). Those processes might affect the adsorption efficiency of CAC for PFAA by altering the availability of effective surface sites and accessibility of pore structure, and changing surface elementary composition and charge. Currently, there is little information on how aging processes affect the removal of PFAA by CAC. In this project, controlled laboratory physical (i.e., wet-dry cycling, W/D), chemical (i.e., H2O2 (H), Fenton reaction (F), and acid treatment (A)), and biological (i.e., bacterial inoculation on CAC surface (B)) aging processes were applied to CAC at the laboratory scale to simulate the aging processes in the subsurface environments. The impact of controlled laboratory aging treatments, designed to stimulate the aging processes of CAC, on the effectiveness of CAC in removing PFAA compounds were evaluated by characterizing aged CACs for surface properties, including specific surface area, pore structure, surface morphology, elemental composition, surface functional groups, point of zero charge, and anion exchange capacity). Adsorption parameters (including the Freundlich exponent (n), the Freundlich constant (KF), and the partition coefficient (Log Kd)) were determined from adsorption isotherm experiments using a mixed PFAA solution containing perfluorobutanoic acid (PFBA), perfluorobutanesulfonic acid (PFBS), perfluoro-n-pentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), and perfluorooctanesulfonic acid (PFOS). These results were compared with unaged CAC to elucidate mechanisms by which aging affect CAC performance in mitigating PFAA contamination.
Physical and chemical aging treatments induced varying changes in CAC surface properties, including surface area, pore structure, surface oxygen content, and surface charge. H₂O₂ and physical aging treatments caused minor changes on CAC compared to unaged CAC, whereas Fenton-reagent and acid aging treatments markedly increased surface oxygen content, reduced surface area, and enhanced surface negativity. These changes collectively suggest a reduction in the adsorption capacity of CAC for PFAA removal. Consistent with the observed aging effects on surface properties, the results from adsorption isotherm experiments indicated the tendency of reduction in the adsorption of all tested PFAAs, except for PFOS, on CAC following both physical and chemical aging. Especially for short-chain PFAAs, such as PFPeA and PFBA, Fenton-aging treatment led to decreases in KF and Log Kd by up to 63%-76% and 45%-53%, respectively. Surface characterization analyses of CAC after biological aging treatment revealed a significant reduction in the effective surface area of CAC, primarily due to biofilm or biological residue occupying adsorption sites and blocking pores. Additionally, biological aging treatment increased the contents of oxygen and hydrophilic functional groups on CAC surface, such as carboxyl/carboxylate and amino groups, leading to decreased surface hydrophobicity and reduced sorption capacity for most PFAAs, with the exception of PFOS. Similar to physical and chemical aging treatments, biological aging posed a greater challenge to the adsorption capacity of CAC for shorter-chain PFAA, such as PFPeA and PFBA, with reductions in KF and Log Kd reaching 56%-74% and 37%-47%, respectively. These results suggest that the aging process is an important, yet often overlooked, factor in determining the long-term effectiveness of the CAC sorptive barrier for PFAS removal, especially for shorter-chain, hydrophilic PFAA. The presence of co-existing substances in the subsurface environments, such as dissolved organic matters (DOM), inorganic ions, and other co-contaminants (e.g., diesel range organics (DRO)), may exacerbate the impacts of aging processes on CAC’s performance for PFAS removal. In this study, the combination effects of aging and various environmental solutes (i.e., DOM, DRO, or inorganic ions like Cl- and Ca2+) on CAC performance were assessed in a multi-PFAA solution containing PFOS, PFOA, PFHxA, PFPeA, PFBS, and PFBA. Batch and column adsorption experiments were utilized to evaluate the adsorption coefficients (i.e., n, KF, and Log Kd), adsorption capacity (Qm) and accumulative desorption ratio). The results indicated that adsorption affinities of each tested PFAA generally aligned with their hydrophobicity, with the observed trend: PFOS > PFOA >> PFHxA ~ PFBS > PFPeA > PFBA, suggesting that hydrophobic interactions play a key role in PFAA adsorption. This ranking remained invariant across fresh or aged CAC and different aqueous environmental conditions, suggesting that the relative affinities among PFAA are primarily governed by their physiochemical properties, particularly their fluorinated carbon chain length and functional groups. Meanwhile, batch isotherm experiments demonstrated that high ionic strength (101 mM adjusted by NaCl), DOM (1 or 10 ppm), and DRO (1.73 ppm) inhibit PFAA adsorption by altering electrostatic interactions and suppressing effective adsorption sites on both fresh and aged CAC. The adverse effects of aging processes, such as Fenton reagent and biological aging, compounded these inhibitory mechanisms of co-existing substances by altering CAC surface properties, particularly reducing its effectiveness in removing short-chain PFAA adsorption. Notably, the presence of 10 ppm DOM or 1.73 ppm DRO completely suppressed the adsorption capacities of Fenton reagent and biological aged CAC for PFPeA and PFBA, leading to non-detectable adsorption occurred. Column experiments revealed that aged CAC exhibited reduced adsorption capacities and enhanced desorption. Particularly, in the column filled with Fenton’s reagent aged and biologically aged CAC, short-chain PFAAs (C<7) that had initially adsorbed were fully desorbed and remobilized. These findings suggest that complex environmental solutes, particularly with the presence of DOM and DRO, can diminish the long-term effectiveness of CAC barriers. Moreover, aging processes such as Fenton-induced reaction and biological aging might intensify these inhibitory effects, further reducing the long-term effectiveness of CAC for in-situ PFAA removal and accelerating the remobilization of PFAAs from adsorbed CAC sorptive barrier.
While previous studies have investigated the aging effects on other carbon-based adsorbents (e.g., granular and powdered activated carbon, and biochar) in various contexts, this study is the first to evaluate the potential effects of in-situ aging on the performance of CAC for PFAA removal under controlled laboratory conditions. By examining combined impacts of aging and environmental solutes on PFAA adsorption by CAC particles, and how aging processes influence PFAA adsorption-desorption behaviors, this work provides valuable insights into the long-term operation of in-situ CAC barriers for remediating PFAA in subsurface environment. The findings underscore the critical need for comprehensive characterization of aging effects on CAC, refinement of predictive models of CAC barrier for considering aging effects, and the development of improved guidance for site-specific CAC barrier applications
Novel Precision Measurement Methods for Probing Dark Matter
No full textThe nature of dark matter (DM) remains one of the most profound open questions in fundamental physics. In this thesis, we develop and apply novel precision measurement techniques to probe DM across a broad range of candidate masses and interaction strengths. For weakly interacting massive particle (WIMP) DM, we present a new directional detection scheme based on solid-state quantum sensing in diamond. For ultralight bosonic DM, we introduce a novel experimental concept--GALILEO--which employs electro-optics and resonant interferometry to search for DM–induced oscillating electric fields. To probe ultra-heavy DM, we develop a geological detection method that maps extended damage tracks in ancient quartz using electron microscopy, leveraging billion-year exposure times for enhanced sensitivity. Finally, we analyze gravitational wave signals from double white dwarf binaries, treating them as a distributed array of galactic accelerometers capable of dynamically measuring the Milky Way’s gravitational potential. Together, these complementary approaches demonstrate the potential of precision measurement science to expand the search for DM. They highlight the powerful interplay between quantum technologies, materials science, and astrophysics in tackling some of the most fundamental mysteries of the universe
DROP DURABILITY ASSESSMENT OF ELECTRONIC ASSEMBLIES UNDER OFF-AXIS LOADING WITH SKEWED FIXTURES
No full textThis thesis studies drop durability of electronic assemblies when the acceleration vector is oriented at 45° to the out-of-plane direction of the circuit card. The off-axis drop tests are accomplished with a skewed fixture and are conducted as a proxy for multiaxial drop testing. Advanced shock testing and vibration test methods have been developed over the last few decades to better represent real-world field environments during ground-based laboratory testing. However, many of these test methods require expensive and specialized equipment not available in most laboratories. An alternative approach for approximating simultaneous loading along multiple axes on conventional equipment utilizes skewed fixtures which have seen use in off-axis random vibration and drop impact testing. These methods generally rely on the conversion of a uniaxial input load from the test equipment (using a uniaxial drop tower or shaker) into a multiaxial load when resolved in the reference frame of the test article (mounted on a skewed fixture).Skewed fixture design is presented and recommendations for conducting skewed angle drop testing are introduced based on local measurements along the skewed face of the fixture to accurately monitor the impact event. Characterization tests were performed with a skewed fixture, at simultaneous acceleration loads from 500 to 3,000 g in two (in-plane and out-of-plane) directions, while meeting standard time domain tolerances. Upon experimental characterization, drop shock durability tests were conducted on a printed circuit assembly (PCA). Mean drops-to-failure were measured and quantified with Weibull statistics. Dominant solder joint failure modes were identified via failure analysis.
Prior work on inclined angle impact testing is limited, and the majority of solder joint interconnect level fatigue studies are conducted considering perpendicular loading normal the circuit card. Low-cycle fatigue curves are generated based on plastic strain and plastic work density within the solder joint. A multiscale nonlinear finite element model is used to relate board-level flexure to solder joint interconnect level plastic strain. A high strain rate solder constitutive model allows for accurate modeling of solder plasticity resulting from high-impact drop shock. Fatigue parameters are computed from the Coffin-Manson relation and Palmgren-Miner damage accumulation. This work serves to apply established low-cycle fatigue methods for conventional drop shock loading (impact normal to circuit card) to non-perpendicular loading with a skewed fixture
Desarrollo: A Community-based Organization, Hispanic Youth, and Postsecondary Transitions
No full textABSTRACT
Title of Dissertation: DESARROLLO: A COMMUNITY-BASED ORGANIZATION, HISPANIC YOUTH, AND POSTSECONDARY TRANSITIONS
Staci Lynn Pippin-Kottkamp, Doctor of Philosophy, 2025
Dissertation directed by: Sophia Rodriguez, Associate Professor, Educational Leadership & Policy Studies
Historically, the children of immigrants have utilized schools to obtain the knowledge and skills needed for economic mobility into the middle class. Scholarship suggests that, in recent decades, children of immigrants have followed nonlinear paths of assimilation, with some groups experiencing downward assimilation into lower socioeconomic classes. Evidence indicates that immigrant youth experience barriers to academic achievement and economic opportunities in K-12 schools. These barriers limit their access to capital for transition to higher education. In this context, capital is defined as the resources, knowledge, discourse, information, or forms of interpersonal support that youth utilize to meet their postsecondary goals, including college. Our modern economic structure generally requires a postsecondary education for individuals to avoid menial labor and enter professional, higher-wage employment. Thus, barriers to higher education contribute to a lack of economic mobility for immigrant youth. Outside of K-12 schools, some immigrant youth develop relationships with adults in community-based organizations. There is evidence that CBOs can support immigrant youth in academic achievement and accessing higher education. There is also evidence that immigrant youth find ways to access capital to access higher education despite barriers. An area of understudied research is the extent to which community-based organizations impact immigrant youth’s ability to transition to college by providing college related capital. Also understudied is how immigrant youth access and enact both traditional and non-traditional forms of college related capital and how they use this capital in tandem with capital from a CBO program to reach their postsecondary goals.
My dissertation addresses these gaps in the literature by using a qualitative conceptual framework and a qualitative instrumental case study design to examine how a community-based organization, Desarrollo, develops and provides capital related to postsecondary goals to Hispanic immigrant youth. Desarrollo is ideal for study as an instrumental case in that understanding how the organization provides capital related to postsecondary goals, contributes to understanding the larger research question of how community-based organizations contribute to economic mobility for children of immigrants. Furthermore, Desarrollo only serves children of immigrants, so it allows insight into how this population accesses capital for economic mobility through the CBO and enacts this capital in tandem with other capital they possess to meet their postsecondary goals.
I find that Desarrollo promotes college attendance as the surest path for economic mobility. I find that Desarrollo adults perceive the needs of youth as primarily related to college access and act as institutional agents, shaping the CBO program to provide college related capital to a Hispanic youth. I find that youth possess significant traditional and non-traditional capital outside of the Desarrollo program that shapes decisions and beliefs related to postsecondary goals and their perceptions of the overall impact of the CBO. I find that youth’s perceptions of the overall impact of the CBO are related to forms of capital the CBO provides that youth cannot access through other social connections. Ultimately, the findings suggest that the CBO supports economic mobility through access to college related capital for youth who already possess significant capital outside of the CBO and that youth strategically identify these forms of capital, using this capital collectively with outside capital, to meet their postsecondary goals
BOARDWALK NATURE TRAILS: A STRATEGY TO MITIGATE THE NEGATIVE IMPACT OF HUMAN ACTIVITY ON THE LANDSCAPE
No full textUrban natural areas provide critical opportunities for recreation, education, and human-nature connection, but their high usage also presents major challenges to ecological sustainability. This thesis explores the need to establish a balance between recreational use and environmental conservation. It focuses on the design and implementation of sustainable trails that preserve ecological integrity while enhancing accessibility. Using Lake Roland’s Field Loop Path in Ruxton Maryland, this design thesis proposes a boardwalk trail that will minimize soil compaction, erosion, and prevent the spread of invasive species, all of which are common consequences of unmanaged trail use and off-trail trampling. The literature review examines trail-induced ecological disturbance, the spread of invasive species, the impacts of weather and soil types on trial durability, and best practices for sustainable trail design. The central research question investigates how landscape architects can create accessible nature trails that support community use while effectively mitigating environmental degradation. Findings support the boardwalk as a viable solution that offers both ecological protection and inclusive access, representing a practical balance between human use and the conservation of our natural environments
ETERNAL REST DISRUPTED: TECHNIQUES FOR LOCATING IMPERMANENT GRAVES OF LOST INSTITUTIONAL CEMETERIES: STATE FARM CEMETERY OF CRANSTON RHODE ISLAND
No full textThe State Farm Cemetery is a lost cemetery that is located under Route 37 in Cranston, Rhode Island. Historic burials include people from the State Almshouse and State Infirmary of Rhode Island. These institutions housed the poor, the mentally ill, and those sick from tuberculosis. These individuals were considered of a low social class and had to seek habitation within the State Almshouse. This thesis is focused on how the Rhode Island State values and characteristics can be seen in institutions, specifically the Rhode Island State Almshouse and how there may be evidence in the burial practices. It also provides information on how to locate and identify lost cemeteries through historic records and GIS. There are many institutions across the nation that have buried individuals without an identifying headstone, or with no grave marker at all. This can lead to lack of recognition and the reversion to nature to the point where a cemetery becomes lost. Poor or mentally ill people were kept hidden from the public eye, and neglect can render their cemeteries hidden as well. Since Roger Williams, Thomas Hazard, and Henry Jones had an interest in protecting those of a different belief or lifestyle, I am interested if the Rhode Island State Almshouse differentiated treatment of individuals of different genders or ethnicities. I analyzed available data representing the State Farm Cemetery for any evidence of segregation or different burial practices done between the various ethnicities, gender, and patient types.
I want to recognize and give a name to those who remain under State Route 37 in the State Farm Cemetery. Using my skills with GIS, and historic maps and records of the State Farm Cemetery and State Almshouse, I placed points on the graves of the individuals and attaching their information to each point. I hope to make an example for Rhode Island, to show that we can make a difference and help give justice and a voice to those who may not be able to speak for themselves. Social class may affect the cemeteries and burials of people in an institution, but we can make a change and give them the recognition that they always deserved.
I hope my thesis is a forerunner for those in the Cultural Resource Management and Archaeology / History field. Whether it is a project carried out for regulatory compliance, or someone in their free time, hopefully we can map and locate more forgotten people in lost cemeteries. This will lead to the prevention of disturbances of the lost human remains
The "Church" in the Diaspora
No full textThe basis of this thesis surrounds the uprooting of a community from its church whose experiences already lived through displacement. What results then is a removal that strips an established community of its identity, leaving the church building vacant or to be redeveloped. What has taken place in North America are historic churches reaching a decline, similar to the subject, that often succumb to economic pressures as demands such as housing persist. Developers and architects have followed suit to convert churches into heavily privatized uses, which presents some challenges in perceptions around newly repurposed churches. Some find converted churches trendy, while there are those, whether Christian or related, who see churches as original temples for spiritual practice. The disconnect offers the opportunity to repurpose former churches, not only for housing but for critically-thought programs that can strengthen neighborhoods. Despite adaptations configured into a new use, considerations to translate a church’s past fall short beyond its external expression. These adaptations, thus leave another question unanswered: how do we deal with a translation of a church’s sanctity? Any associations of its meaning are challenged by a church’s shifting identity related to its communities. Through a study of a diaspora church, I will explore ways to reconcile church adaptations that serve the community of parishioners and neighbors while addressing economic demands. What I offer is a chance to reclaim and repurpose the church to be a renewed anchor that stems from former attributes of fellowship and a memory of the place