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Natural competence and host adaptation in plant pathogenic bacterium Xylella fastidiosa
No full textThe plant pathogen Xylella fastidiosa is a Gram-negative, fastidious, xylem-limited, vector-
transmitted bacterium, causing severe diseases on numerous economically important plants
including grapes, citrus, coffee, olive and almond, among others. The outbreak of X. fastidiosa in
new geographic regions and the new host-pathogen genotype association present a significant
agricultural challenge. Extensive evidence indicates that homologous recombination (HR) may be
one of the major forces contributing to the appearance of new genotypes, host adaptation and host
shifts in X. fastidiosa. Natural competence has been considered a key mechanism facilitating HR
in this pathogen. However, natural competence has been experimentally confirmed in only a few
strains, and its distribution across diverse X. fastidiosa strains, as well as the underlying regulatory
mechanisms, remains poorly understood. Moreover, while natural competence has been
demonstrated under laboratory conditions, its occurrence in planta and potential metabolic impact
have not yet been confirmed. Additionally, limited information exists regarding the molecular
mechanisms that contribute to plant adaptation in X. fastidiosa. To address these gaps, we
characterized natural competence in 133 X. fastidiosa strains from diverse origins and observed
substantial variation in their ability to acquire foreign DNA. We identified XadA2 as an important
factor influencing natural competence and potentially contributing to its variation among strains.
Furthermore, we assessed the occurrence of natural competence in planta by co-inoculating strains
with differing virulence levels and found that the addition of extracellular DNA slightly altered
disease severity. Pool-seq analysis provided further evidence that genetic exchange via natural
competence likely occurs in planta, contributing to changes in virulence. Additionally, we
investigated the genetic basis of sap adaptation in X. fastidiosa by constructing a partial mutant
2
library using Random-Barcoded Transposon Sequencing (RB-TnSeq) techniques. Several
candidate genes associated with sap adaptation were identified. Interestingly, mutations in type IV
pilus (TIVP) genes significantly increased bacterial fitness, suggesting that TIVP function imposes
a substantial metabolic cost. Similarly, our in vitro growth studies indicate that the DNA uptake
process associated with natural competence may also be metabolically costly. These findings
suggest that natural competence may play distinct roles across different X. fastidiosa populations,
with a potential trade-off between its adaptive benefits and metabolic burden
Interfacial Damage Mechanics and Reliability at Multiple Electronic Interfaces under Harsh Environments
No full textAdvanced electronic assemblies are expected to perform with greater reliability in mission-critical applications under harsh environmental conditions, including high G-shock loads (up to 25,000 g), thermo-mechanical stresses, and long-term exposure to elevated temperatures (up to 150°C) and humidity in various defense, aerospace, and automotive underhood applications. The interfaces at critical junctions Potting/PCB, Resin/Copper, Chip/Underfill, and EMC/Substrate) degrade much faster than the bulk materials. It is necessary to understand these critical interfaces to predict the failure mechanisms, develop mitigation strategies, and optimize material selection for long-term reliability. Through this understanding, this dissertation embarked on a holistic investigation into the degradation of interfacial properties at board-level and component-level assemblies, with particular emphasis on potting material, PCB resin, underfill, and EMC interfaces. In this regard, the cohesive zone parameters used in the finite element simulations are determined by experimental test techniques and predictive modeling to investigate the interfacial fracture behavior. These efforts have been made to assess interface reliability, besides making predictions of failure modes due to harsh mechanical and thermal conditions, thereby helping design reliable electronics. The investigation starts with high-temperature-aged potting/PCB interfaces at 100°C and 150°C from 30 to 360 days and is tested under dynamic four-point bend loading. Stress intensity factors (KI & KII) and energy release rates in a steady state were measured at different aging intervals. The results reveal the degradation in interfacial properties with time due to thermal exposure and an increased tendency for delamination at extended durations of harsh environment exposure. The extracted fracture toughness parameters were used to calculate cohesive zone parameters and validation through finite element modeling. Additionally, shock load orientations at 0°, 30°, and 60° were also investigated, bringing out the sensitivity of the drop orientation to the reliability of potted electronic assemblies. The developed predictive finite element model was validated using experimental data for which high-speed imaging and 3D-Digital Image Correlation (DIC) techniques were employed. This predictive model successfully captured the behavior of potting/PCB interfaces, emphasizing the importance of cohesive zone parameters in understanding damage propagation in potted assemblies. Pad cratering failures at the resin and copper layer of the PCBs due to multiple reflow conditions have been discussed at board–level interfaces. The research characterizes the evolution of bulk resin properties and resin-copper interfacial strength through multiple reflow cycles and their interaction in determining the susceptibility of pad cratering. The interfacial fracture toughness was measured using four-point bend tests for various resin-copper-glass fiber combinations. The results show that multiple reflows degrade bulk resin properties, accelerating the loss of resin-copper interface strength and increasing pad cratering. A predictive regression model to identify material combinations offering superior pad cratering resistance was developed to improve board-level reliability. In flip-chip ball grid array (FCBGA) packages used in automotive applications, the primary focus was the delamination in chip/UF and EMC/substrate interfaces. The thermo-mechanical loads in automotive underhood environments, such as engine control units, advanced driver assistance systems, and safety and critical systems, could degrade the FCBGA interfaces, which have not been studied widely yet. The research reported here has investigated the monotonic and fatigue behavior of chip/UF interfaces after aging at 100°C and 150°C using bi-material specimens aged up to 360 days. The interfacial fracture toughness and Paris law constants are determined to characterize the interfacial strength. Results show that the properties of the cohesive zone evolve with aging, which plays a vital role in crack growth rate and long-term reliability. The presented research follows up with a predictive finite element modeling of the FCBGA packages, the cohesive zone parameters developed from the experiments. To model the interfacial fracture behavior of the FCBGA under thermal cyclic loading (-40°C to 125°C), cohesive elements were used in critical interfaces such as chip/UF, substrate/underfill, and TIM/Cu. The SDEG parameters show that the TIM/Cu interfaces have the highest degradation among the other FCBGA interfaces. These simulations offer predictive insights into possible failure mechanisms occurring during long-term operations. This dissertation embodies significant contributions toward understanding the mechanisms of interfacial degradation and failure in complex electronic assemblies under harsh environments. These findings give critical insights into the evolution of interfacial properties under mechanical and thermal loads, bringing out the importance of cohesive zone modeling for accurately predicting failure behavior. The predictive models developed in this work would go a long way toward being useful to designers and manufacturers for optimizing material selection to ensure electronic component reliability in such a harsh environment. The practical impact of this research is extensive in defense, aerospace, and automotive applications, where long-term electronics reliability is crucial. Herein, a state-of-the-art advance is made in investigating the interfacial fracture toughness and its predictive modeling to enable the development of next-generation electronics for extreme environmental conditions
Gerrymandering: The Impact of Redistricting on State Legislative Election Voter Participation
Get PDFState legislative elections are increasingly shaped by two factors influencing the prospects of winning a majority: the redistricting cycle and partisan tide elections (Makse 2014). Winning control of the redistricting process offers the prospect of shaping elections for the next decade (Makse 2014). State legislators responsible for drawing new district maps can manipulate district lines for maximum partisan advantage without much fear of judicial obstruction. Little research exists that evaluates the effect gerrymandering has on the individual voter. Hayes and McKee (2009) argue that redistricting severs the ties between constituents and their incumbents, raises information costs, and increases nonvoting levels in U.S. House contests. Research indicates that while the overall effects of redistricting on individual voter turnout appear to be substantively low, the effects of changes in partisan composition in a voter's district that result from gerrymandering can decrease turnout (Hunt, 2018). This dissertation aims to determine the impact of incumbent, partisan, and racial gerrymandering on state legislative voter participation
Mesoscale particle-based simulations of flow in expansion-contraction microchannels at low Reynolds number
No full textPolymer flooding is an enhanced oil recovery technique that enables the extraction of significantly more oil than conventional methods. The good performance of polymer flooding is believed to stem from a phenomenon known as elastic turbulence, a hydrodynamic instability that can occur for low Reynolds number flows through expansion-contraction microchannels. Experiments have shown that oil recovery efficiency is influenced by the polymer’s architecture and hydrophobic associations. However, it remains unclear whether these changes are linked to elastic turbulence because little is known about how a polymer's molecular structure impacts this phenomenon. Mesoscale particle-based simulations are a promising approach to address this knowledge gap; however, they have not yet been applied to elastic turbulence. As a first step toward doing so, we have simulated the low-Reynolds-number flow of a Newtonian fluid through an expansion-contraction microchannel. The validity of the simulations was assessed using a theoretical solution derived using a regular perturbation method. The simulations were in good agreement with theory for microchannel geometries in which the theory was expected to be accurate, but the simulations also enabled us to simulate flows for which the theory was not accurate. This work establishes a baseline against which simulations with different polymers can be compared to characterize the presence of elastic turbulence
A Randomized Crossover-Controlled Trial Investigating the Epigenetic Impact of a Greens-Based Supplement in Adults
No full textAging is influenced by genetic, environmental, and lifestyle factors. Preliminary studies suggest that fruit and vegetable-based dietary supplements may reduce inflammation and oxidative stress, key factors in aging. However, limited research has focused on greens-based supplements and their impact on epigenetic markers of aging and metabolic health. This study evaluated the effects of a 30-day greens-based supplement on epigenetic markers of aging and metabolic health in adults aged 50-65 years with body mass index (BMI) >30 kg/m2, using a 60-day randomized crossover design. Participants were randomized to immediate or delayed supplementation. During the 30-day intervention period, participants consumed a daily greens supplement. Primary outcomes included peripheral blood mononuclear cell DNA methylation and epigenetic age (Horvath, PCGrimAge, AdaptAge, and DamAge). Secondary measures included clinical metabolic biomarkers, microbiome diversity, breath hydrogen and methane, body composition, actigraphy, dietary intake, and quality of life questionnaires (RAND 12 item short form questionnaire [SF-12], and 21-item Depression, Anxiety, and Stress Scale [DASS-21]). Twenty participants began the protocol (65% female, mean age 58.4 ± 5.3 years, mean BMI 38.1 ± 8 kg/m2). Nineteen participants completed the study. A significant treatment effect was observed for the Horvath clock (p = 0.015), with an unexpected increase in epigenetic age during supplementation. No significant changes were observed in AdaptAge, PCGrimAge, or DamAge. Gut microbiome alpha diversity remained stable; taxa of interest, including Bilophila (p = 0.037) and Desulfobacterota (p = 0.031) changed with supplementation. Body composition, metabolic biomarkers, dietary intake, breath gases, sleep, and psychosocial measures were unchanged during the study. Exploratory correlations found no significant associations between epigenetic clocks and secondary outcomes, except for an inverse relationship between Faith’s phylogenetic diversity and fasting blood glucose (rₛ = –0.81, p < 0.001). In summary, 30 days of greens-based supplementation led to selective changes in epigenetic aging markers and individual microbial taxa, without significant effects on overall microbiome diversity, metabolic health markers, or body composition. Exploratory correlations suggested links between microbial diversity, glycemic control, and specific taxa with epigenetic clocks. These findings highlight the value of using multiple epigenetic clocks in nutritional studies, given the varied responses observed across different clocks.
Investigating Attachment Bonds in Dogs
Get PDFAs a result of living alongside humans for many centuries, dogs have developed unique social and emotional abilities that allow them to form close relationships with humans. The relationship between dogs and their human caregivers has been described as analogous to that of human parents and their children. There has been recent interest in studying the human-dog relationship from the perspective of attachment theory. Attachment theory suggests that human infants are born with an innate attachment system that ensures proximity of the infant to attachment figures and that attachment figures can serve as a secure base from which to explore the environment. Infants can be classified into one of four attachment styles based upon their secure base use and the balance of proximity seeking behaviors with the attachment figure and exploratory behaviors. Attachment theory has previously been applied to dogs, indicating that dogs indeed form attachment-like bonds with their human caregivers and that these bonds are comparable to the attachment bonds of human children. Behavioral classifications of attachment style have also been applied to dogs. The purpose of the present study is to evaluate the development, stability, and implications of attachment style in dogs. Chapter 1 of this paper provides an introduction to attachment theory and its application to dogs. Chapter 2 compares attachment and social preference across companion and candidate detection dogs. The distribution of attachment security in candidate detection dogs was found to differ significantly from companion dogs, with candidate detection dogs showing more secure attachment than companion dogs. Both companion dogs and candidate detection dogs were found to significantly prefer a familiar caregiver to an unfamiliar stranger. Chapter 3 explores the formation and stability of attachment bonds in the first year of life for a population of candidate detection dogs, as well as possible links between attachment and detection performance for this population. Evidence of attachment was found in some dogs as early as 6 weeks of age, with all dogs showing evidence of attachment by 5 months. Attachment style was found to be largely stable across the first year of life. A significant relationship was observed between attachment style and reward focus and confidence in an unfamiliar location, but there was largely no relationship between attachment style and detection task performance. Chapter 4 evaluates the ability of adult working dogs to form new attachment bonds. Adult working dogs were found to readily form new attachments with new social partners. Chapter 5 explores the role of temperament on attachment in companion dogs. Temperament and attachment were found to be largely independent constructs, however, there is support for the role of differential susceptibility on attachment style formation. Finally, Chapter 6 provides a summary of findings and offers general conclusions on the development, stability, and implications of attachment in dogs
Online Outrage: The Impact of Negative Social Media on Stakeholder Perceptions and Behaviors
No full textStakeholders frequently encounter a diverse array of social media content about firms. Although existing research has examined how organizations use social media to influence stakeholders and vice versa, it has largely overlooked how one stakeholder's post about a firm can influence the perceptions and behaviors of other stakeholders. Furthermore, scholars have given limited attention to the psychological mechanisms that shape stakeholder perceptions and drive subsequent actions. Drawing on stakeholder theory and organizational–stakeholder (O–S) misfit theory, I investigate how two dimensions of perceived misfit, value incongruence and strategic incompatibility, affect the degree of stakeholder behavior in the context of social media backlash. Additionally, I examine how sentiment negativity and post virality interact to shape these misfit perceptions. To test the proposed relationships, I use a 3 × 2 × 2 between-subjects experimental design (N = 1,076) and apply Bayesian ordered logistic regression, structural equation modeling, and response surface methodology. I conclude by discussing the theoretical and practical implications of the findings
God Is Not Making Any New Land: Heirs’ Property, Land Loss, and Black Faith in Alabama’s Black Belt.
No full textThe Black Church has long been recognized as a cornerstone of community life, providing spiritual, social, and economic support to African American communities. While recent scholarship has expanded our understanding of the Black Church’s multifaceted roles, little attention has been given to its relationship with the heirs’ property crisis, a pervasive issue in the Black Belt region of the Deep South. This study employs qualitative methods to explore how Black Church leaders navigate and sustain their communities amidst the social, economic, and cultural challenges posed by a clouded titled property. Central to this investigation is an analysis of how scriptural interpretations of stewardship and the sacredness of land inform their responses to this crisis. By examining the intersection of faith, community resilience, and systemic inequities, this research contributes to broader discussions on the role of religious institutions in addressing rural socio-structural challenges and preserving cultural heritage in marginalized communities
Acculturation, Body Ideals, and Disordered Eating in Latinas
No full textThis study investigated the relationships between acculturation, enculturation, acculturative stress, generational status, body image internalization, and body dissatisfaction among Latina women in the United States. Specifically, we examined how acculturation, enculturation, internalization of thin body ideal, desire for curve, and generational status were related to body dissatisfaction, and whether body ideals mediated the relationships between acculturation, enculturation, and body dissatisfaction. Participants (n = 140) completed measures assessing acculturation and enculturation (Anglo and Mexican Orientation Scales), acculturative stress (SAFE), thin ideal internalization (SATAQ), desire for curve (CDI), and body dissatisfaction (EDI-3).
Results supported our hypothesis that higher levels of acculturative stress were associated with greater internalization of the thin ideal and increased body dissatisfaction. However, no association was found between acculturative stress and desire for curve. Contrary to our predictions, thin and curvy ideal endorsement did not mediate the relationships between acculturation, enculturation, and body dissatisfaction. Notably, thin and curvy ideal endorsement were significant predictors of body dissatisfaction in opposite directions: thin ideal internalization was associated with greater body dissatisfaction, while greater desire for curve was associated with lower dissatisfaction. Acculturation and enculturation (Anglo or Latine orientation) were not significantly related to body ideal internalization or body dissatisfaction. Exploratory analyses revealed generational differences in acculturation and enculturation but not in levels of acculturative stress or body dissatisfaction.
Findings suggest that body image dissatisfaction among Latina women is more strongly influenced by internalized appearance norms than by cultural orientation alone. The results highlight the complex and multidimensional role of acculturative stress in shaping body image concerns, independent of generational status. Limitations include a small first-generation sample and potential measurement constraints. Future research should utilize longitudinal designs, culturally nuanced acculturation and body image measures, and targeted sampling to better capture the diverse experiences of Latina women. Clinically, these findings underscore the need for culturally responsive body image interventions that address both thin and curvy ideal pressures and the role of acculturative stress in shaping body dissatisfaction
A Historical Case Study of Trauma-Informed Leadership During a Natural Disaster
Get PDFThis historical case study examined the trauma-informed leadership practices implemented at
Enterprise High School in Enterprise, Alabama, following the devastating EF4 tornado that struck on
March 1, 2007, which resulted in the loss of eight students’ lives, a community member’s life, and
significant destruction to the school campus. The study investigated how the school’s principal, Rick
Rainer, navigated immediate crisis response, long-term recovery, and community healing through a
trauma-informed lens. The purpose of this research was to explore what principles shaped leadership
decisions in the aftermath of the disaster and to understand how historical, cultural, and institutional
factors influenced the school leader’s response. Using a qualitative historical case study design, data were
collected through interviews with school leaders and current members of faculty who were on campus on
March 1, 2007, as well as archival records, media coverage, and related artifacts. Analysis was guided by
trauma-informed frameworks and historical narrative methods. Findings revealed that the school leader at
Enterprise High School prioritized safety, communication, trust, and decisive decision-making in the
wake of the tragedy. Strategies employed by the school leader indicated that trauma-informed principles
were embedded in navigating the immediate crisis and in supporting the recovery and rebuilding post disaster