136879 research outputs found
Sort by
The Genetic Basis of Seasonal Migration and Its Role in Reproductive Isolation
No full textSeasonal migration has been suggested to play a role in speciation through environmentally induced selection against hybrids. Many migratory divides occur between groups that take different migratory routes. For example, the songbird Swainson���s thrush forms a migratory divide in western North America. This species includes two subspecies; coastal thrushes migrate along the west coast of North America while inland thrushes migrate east of the Rocky Mountains, through central North America to South America. These routes are largely genetically determined and involve navigation around geographic barriers. Hybrids in the divide have been shown to take intermediate routes that lead them through these barriers, potentially reducing their fitness. I used this system, spatial modeling, state-of-the-art tracking and genomic techniques to test the role migratory behavior plays in speciation.
First, I used spatial modeling and habitat preferences of birds on migration to show that hybrids taking intermediate routes have less access to highly suitable habitats and encounter more resistance on their routes compared to parental forms. These findings suggest that intermediate routes are inferior to routes taken by parental birds and there could be selection against hybrids contributing to speciation. Second, I individually tracked over 500 adult and juvenile Swainson���s thrushes from the center of the hybrid zone, obtaining detailed data on several migratory traits (e.g., orientation, timing, and wing morphology). Genomic mapping showed that most migratory traits are highly heritable and genetically correlated. I also mapped these traits to specific genomic regions, gaining insight into how these traits may be co-regulated and generating a list of candidate loci that are associated with these traits. Third, I used genomic data and analyses of viability selection to identify signatures of selection along the genome. I connected these regions with the genes associated with migration and showed that these loci are under selection. Combined, results from this dissertation provide one of the most comprehensive tests of seasonal migration as a driver of environmentally induced selection against hybrids in a free-living population that has ever been conducted. My results also provide insight into additional fields, including behavioral genetics and conservation biology
A State-of-the-Evidence Review: Impacts of Youth Agricultural Education Programs on Global Poverty, Resilience, and Food Security Results
No full textHistorically underestimated, youth can catalyze change towards positive community development. In developing countries, there is tremendous potential to engage youth, not only as passive participants in programming or as a vulnerable population in need of services, but as potential innovators, early adopters, and effective change agents towards the adoption of innovations to improve family and community well-being. However, the body of evidence exploring how youth agricultural education programs impact the necessary global goals of food security, resilience, and nutrition has yet to be systematically evaluated, synthesized, and mapped. This study, the first systematic review of youth agricultural education programs in low- and middle-income countries, employs a mixed methods, theory-based approach to identify evidence of program outcomes and impact, mapping the current state of the evidence to the U.S. Global Food Security Strategy results framework.
With the aim of greater policy and programmatic relevance, this study employs mixed methods theory-based systematic review methodology. The findings provide evidence of how access to information, innovations, and social systems through well-planned, and locally adapted agricultural education can have significant positive influence on individual and family-level changes. However, rigorous evaluation of the outcome and impact-level results of investments in agricultural education is woefully inadequate, and the majority of evaluations of youth agricultural education programs neglect to address dynamics of gender and social inclusion in the evaluation design or reporting. Going beyond the descriptive quantitative systematic review results with the aim of greater policy and programmatic relevance, this paper discusses the results of the qualitative analysis of the 79 included studies, identifying enablers and barriers to positive program outcomes in agricultural education programs, to summarize the individual-level, program-level, and enabling environment factors influencing program outcomes. Ultimately, the paper presents an emerging conceptual framework for the design of youth agricultural education programs in low- and middle-income countries. The detailed results of this study provide insight to build on what we know (scale what is working), improve what we are currently doing (drawing from the lessons learned), and invest in improved evaluation and measurement, presenting recommendations for future programs, policy, and research
The Role of Chondrocyte Transdifferentiation in Midpalatal Sutural Growth in Response to Altered Dietary Load
No full textThe biological mechanism for growth of the midpalatal suture is not fully understood. Chondrocyte transdifferentiation into bone cells has been shown to occur in the condylar cartilage but no study has shown this process to occur in the midpalatal suture.
Twelve Acan-CreErt2; R26RTomato;2.3 Col1a1-GFP (Acan mice) and twelve Col10a1-Cre; R26RTomato; 2.3Col1a1-GFP (Col10a1 mice) were randomly allocated into two groups, respectively; a soft and hard food diet (n=6), fed for 6 weeks and then sacrificed for data collection. One-time tamoxifen injections were given to the Acan mice at 3 weeks. MicroCT, palatal widths, chondrocyte cell proliferation, chondrogenic activity and chondrocyte transdifferentiation were all analyzed and compared between dietary loading groups.
There were no significant differences in palatal widths but a significant decrease in bone quality in the soft diet group. Histologically, there were no significant changes in chondrocyte proliferation, and aggrecan expression. However, soft food diet mice had significantly (p<0.05) lower collagen 10a1 expression, and number of chondrocyte derived bone cells, from the early to late stages of maturation, in the midpalatal suture compared to the control.
Altered dietary loading affects midpalatal sutural bone quality, chondrogenesis and chondrocyte transdifferentiation, which may explain differences in postnatal maxillary transverse development
John Bickham field notebook: AK12001-AK12500.pdf
No full textBound book, each page corresponds to a karyotype slide data.Data pages for AK12501-AK13000 corresponding to unique identifiers of specimens/samples examined for biological research. Specimens are primarily housed at Texas A&M University; Biodiverstiy Research and Teaching Collection
On Fatalism: Revitalizing Durkheim's Theory in the Current Milieu
No full textEmile Durkheim���s fatalistic form of suicide serves as the sociological theory necessary for understanding contemporary social problems with the imbalance of fatalism in society. This has been disastrous throughout the twenty-first century. Specifically, the newer and more virtual the generation, the greater the impact of fatalism as the consequence of modernity from the twentieth century. Fatalism has been neglected or even omitted in both Durkheimian studies and social research on generations. Recontextualizing Durkheim���s theory in the current milieu serves to not only rediscover his works, but to apply them with relevance to the current social malaise that is afflicting society across demographic categories. The current social environment is excessively confining and enforces social behavior through undifferentiating bureaucracy. The increased dehumanization of the average person requires a comprehensive approach to social thought, exemplified by Durkheim and works that are connected to him. Specifically, this thesis draws on Durkheim���s opus, Suicide, and various other literature to study the current generations Millennial and Generation Z. Fatalism linkages impact: public health, suicide, autonomy, mental health, and other social problems. Productivity in sociological research relies on clear, substantive theoretical understanding and policy implications exist in addressing social problems by comprehending their commonalities and clarifying interdisciplinary perspectives
System-Level Rotordynamic Analysis of Centrifugal Compressors Using Computational Fluid Dynamics (CFD), Design and Optimization of Novel Swirl Brakes
No full textThe accurate characterization of compressor rotordynamic coefficients during the design phase reduces the risk of subsynchronous vibration (SSV) problems occurring in the field. Although rotordynamists extensively investigate discrete compressor components (such as seals and front shrouds) to tackle instability issues, integrated or system-level analysis of compressor rotordynamics is very scarce. In reality, the impeller, eye labyrinth seal, and the front shroud heavily influence one another; and the collective dynamic behavior of the system differs from the sum of the dynamic behavior of isolated components. Furthermore, American Petroleum Institute (API) level II vibration stability analysis requires inclusion of all possible destabilizing forces including those that stem from seals and the front shroud cavity.
A CFD-based approach is taken to evaluate the dynamic behavior of the system as a whole. The geometry and operating conditions in this work are based on a recently published experimental study on centrifugal compressor. The commercial CFD code CFX 19.0 is used to resolve Reynolds Averaged Navier-Stokes (RANS) equations to quantify the eye labyrinth seal and front cavity stiffness, damping, and added mass. The entire compressor stage is modeled to uncover the coupled behavior of the components and assess the stability of the whole system instead of just discrete components. In the current work, three CFD approaches, namely quasi-steady, transient static eccentricity, and transient mesh deformation techniques are studied and benchmarked against analytical and experimental results from the literature. Having established the efficacy of the proposed approach, 4 types of swirl brakes are proposed and analyzed for stability. The novel swirl brakes create negative swirls at the brake cavities and stabilize both the front shroud and the eye-labyrinth seal simultaneously. The designed swirl brakes are further investigated to identify contribution of each geometric feature of the brakes to the rotordynamic stability of the whole system/stage. The geometric parameters chosen for the parametric study are the height of the slot cavity, the number of slots, the length of slots, the slot angle and the direction of slot curvature
Targeted Therapeutic Strategies Against Triple-Negative and Metaplastic Breast Cancers
No full textBreast cancer is the second most common cause of cancer mortality in women in the United States. As a heterogenous disease, breast cancer is clinically classified by expression of estrogen receptor (ER), progesterone receptor (PR), and overexpression/amplification of human epidermal growth factor receptor 2 (HER2). Triple-negative breast cancer (TNBC), i.e., those not expressing ER, PR, or HER2, represent ~10-20% of all breast cancer cases, has the worst prognosis in comparison to ER+ or HER2+ breast cancers.
Gene profiling analysis has identified TNBC subtypes with unique molecular signatures that may be therapeutically targeted. Among the six known TNBC molecular subtypes, the mesenchymal subtype comprises 30% of all TNBCs and has the worst disease-free survival compared to other TNBC subtypes. Metaplastic breast cancer (MpBC) is a highly aggressive, and metastatic breast cancer malignancy that typically falls under the mesenchymal TNBC subtype, accounting for <5% of all invasive breast cancers. Patients with MpBC are generally diagnosed at a later age with a more aggressive disease, likely contributing to their dismal median survival of 8 months after metastasis. There are no standardized therapeutic options for patients with MpBC.
MpBC is characterized by one or more cell populations that have undergone metaplastic differentiation, i.e. cells convert from glandular to non-glandular morphology. MpBCs are enriched with epithelial-to-mesenchymal (EMT) and cancer stem cell (CSC) markers, with hyperactivation of phosphoinositide-3-kinase (PI3K) pathway and enhanced nitric oxide (NO) production. Patients diagnosed with metaplastic TNBC have a significantly worse prognosis compared to non-metaplastic TNBC (non-MpTNBC). Thus, the development of effective therapies for women with MpBC and non-MpTNBC represents a significant unmet clinical need.
The focus of my dissertation has been on evaluating novel therapeutic strategies in the preclinical setting to treat MpBC and non-MpTNBC. Using human breast cancer cell lines and patient-derived xenograft (PDX) models, my preclinical studies focused on evaluating targeted therapies, such as utilizing monoclonal antibodies against EGFR to treat TNBC, as well as combining PI3K and nitric oxide synthase (NOS) inhibitors to treat MpBC. I found that combined PI3K and NOS inhibition reverses EMT, decreases CSC populations, rendering MpBC tumors more chemosensitive
Three-Dimensional Simulations of Ductile Fracture Under Arbitrary Loadings
No full textFracture leads to billions of dollars of losses worldwide every year, leading to material waste in manufacturing or disrupting the safe operation of load bearing components. For structures capable of plastic deformation, the ever-increasing demands on performance under extreme environments, combined with the challenges of an-all-experiments based approach, require the development of reliable and predictive failure models under real-world situations. In addition, new design paradigms and the development of strong, lightweight materials for use in thin-walled structures test the limits of classical methods based on linear elastic fracture mechanics. After half a century of porous material yield function development, there is still no sound basis for predicting pore-mediated ductile failure under general loadings. Tremendous progress has been achieved for modeling failure assuming mesoscopically homogeneous deformation at appropriate length scales. The inherent limitations of available theories due to the neglect of what has recently been termed unhomogeneous yielding at such scales are numerous. For example, no existing theory can predict failure in a simple torsion specimen on a sound physical basis, let alone under more general shear-dominant loadings.
In this work, a data-driven approach is followed to develop a porous material plasticity yield function that accounts for porosity, void shape and orientation. High-throughput computational limit load analysis is used to this end. The same dataset is employed to calibrate evolution equations developed on the basis of Eshelby concentration tensors. A comprehensive constitutive theory, named HUNNY, is then formulated which is applicable under general loading conditions. The theory is akin to crystal plasticity but with dependence on the resolved normal stress. In the isotropic limit, dependence upon all stress invariants is rationalized. The predictive capabilities of the theory are assessed against a large set of micromechanical unit cell calculations under combined tension and shear loading. Several realizations of the theory are implemented as user-defined subroutines to enable three-dimensional structural simulations of crack initiation and growth. Illustrations are given to simulate ductile failure in a round notched bar and a top-hat shear specimen developed at the Sandia National Laboratories. Finally, the formulation is extended to deal with more complex hexagonal materials exhibiting plastic anisotropy, such as magnesium alloys
Neoconservatives and Taiwan: Adherents of Conservative Precedent or Advocates for Liberal Interventionism?
No full textDuring the 1990s neoconservatives grew concerned over a burgeoning People���s Republic of China (PRC) threatening the newly democratic government of Taiwan. They wanted the United States to bolster Taiwan���s standing in the international community, commit to defend Taiwan, end strategic ambiguity, prevent further entrenchment of the PRC in international organizations, and push for closer if not official relations between the United States and Taiwan. Neoconservatives frequently employed Wilsonian rhetoric to shore up support for Taiwan. Despite this liberal notion, their foreign policy positions and thinking built on the likes of the China Lobby and New Right. By analyzing neoconservative viewpoints on U.S. policy towards Taiwan one can see how evolved earlier conservative positions despite accusations that they carried on liberal tenets in foreign policy
Addressing Crime as a Root Cause of Migration
No full textMigration is a global challenge driven by push factors in the source countries, pull factors in the destination countries, and migration costs. Among the primary push factors, crime and violence are commonly seen as the root causes, forcing individuals to embark on risky and costly journeys in search of safety and often better economic opportunities. In a recently published paper, the authors examine El Salvador���s 2022 crime crackdown, which resulted in a sharp decline in homicides but raised concerns over human rights violations. They find a significant reduction in Salvadoran encounters at the U.S. border���by approximately 45% to 67% compared to other sending countries. Their findings highlight that addressing the root causes of Central American emigration requires economic and social reforms, along with regional cooperation to combat organized crime, address major human rights issues, and create better jobs for would-be migrants