VTechWorks

VTechWorks provides global access to Virginia Tech scholarship, including journal articles, books, theses, dissertations, conference papers, slide presentations, technical reports, working papers, administrative documents, videos, images, and more by faculty, students, and staff. Faculty can deposit items to VTechWorks from Elements, including journal articles covered by the University open access policy. Email vtechworks@vt.edu for help.


 
Open Access Policy

Open Access Policy

Virginia Tech's open access policy enables researchers to deposit the accepted version of scholarly articles with no embargo.


Theses and Dissertations

Theses and Dissertations

Virginia Tech was first in the world to require ETDs in 1997, and continues to add scans of older theses and dissertations.


Open Textbooks

Open Textbooks

More than 40 freely available and openly licensed textbooks are among our most downloaded items.


Recent Submissions

Educational Leadership Impact on Early Career Teacher Retention:  Making Meaning of School Principal and Classroom Educator Perceptions
Riganti, Heather Victoria (Virginia Tech, 2025-02-07)
Teacher retention, specifically early career teacher retention, is a prominent issue facing educational leaders. This dissertation addresses the impact high early career teacher attrition has on student academic achievement, establishes the purpose of my qualitative research study, and clarifies the problem of study. Integrated into Chapter 1 is a conceptual framework that outlines leadership and non-leadership factors impacting early career teacher retention. The literature review in Chapter 2 examines current teacher attrition trends as well as practices and policies implemented to improve teacher retention. Literature included in the review is peer reviewed and published between 2012 and 2024. Articles produced from the search criteria were derived from the Virginia Tech remote library's Education Research Complete from EBSCO host, ERIC from EBSCOhost, Educators Reference Complete from Gale, and Teacher Reference Center from EBSCOhost in addition to articles referred to me by Virginia Tech faculty. The connection between leadership practices or behaviors and new teacher retention is supported by current literature. Teacher retention is discussed as a global and national issue as well as an issue facing educational leaders in the state of Virginia. Monetary and non-monetary costs of teacher attrition are discussed in addition to the monetary and non-monetary factors impacting teacher retention. School leadership and the connection to mentorship literature are analyzed to determine the connection between leadership behaviors and new teacher retention. Using the identified research questions in Chapter 1, I outlined my research methodology and framework for my qualitative research study in Chapter 3. The purpose of this study was to investigate the influence educational leadership has, specifically building level principals, on early career teacher retention decisions. The study specifically focused on the secondary level in a medium sized school division in southwest Virginia. I wanted to gain a better understanding of how principals at the secondary level positively contribute to the retention of early career teachers within their schools. New teacher, beginning teacher, novice teacher, and early career teacher are used interchangeably throughout this dissertation. Chapter 4 presents an analysis of individual semi-structured early career teacher interviews and principal interviews. Chapter 5 presents implications and meanings generated from this research study. Meanings made and implication from early career teacher interviews and principal interviews are presented in this study. This study has value in its potential to inform school policy makers, drive future leadership practices, or influence the practice of future school leaders.
Muscle Loading Treatments for Achilles Tendinopathy
Easley, Dylan Cole (Virginia Tech, 2025-02-07)
Tendinopathies are common, painful, and debilitating injuries that can be challenging to treat. Current treatment methods are limited to surgery, nonsteroidal anti-inflammatory drugs, dry needling, and injectable therapeutics, platelet rich plasma and corticosteroids. Unfortunately, these existing treatments display poor long-term outcomes and have an increased risk of reinjury. Additionally, the healing mechanism for injured tendons forms scar tissue which is characterized by disrupted extracellular matrix rather than complete injury resolution. These structural changes impact the mechanical properties of tendon, reducing their capacity to transfer and store energy, making them inferior to uninjured tendons. The reduced mechanical properties increase the risk of rupture, exacerbating this debilitating disease and decreasing quality of life. Physical therapy (eccentric loading) decreases the symptoms of tendinopathy and restores Achilles tendon functionality. However, the mechanism by which these mechanical stimulations induce healing is poorly understood. There is a clinically relevant motivation to better understand the healing cascade in response to eccentric exercises. We aim to identify and characterize the effects of eccentric rehabilitative muscle loading on the Achilles tendon and gastrocnemius muscle complex using our preclinical TGF-ß1-induced murine model of Achilles tendinopathy. To accomplish our objective, we tested three muscle loading magnitudes (50%, 75%, and 100% body weight), over three treatment durations (1, 2, and 4 weeks) to determine their effects on tendon healing. Age-matched injured/untreated and naïve groups accompanied each loading magnitude and duration period. The functional biomechanical properties, morphological adaptations, transcriptomic response, and muscle strength of the Achilles tendon were assessed. Injured/untreated tendons had a significantly increased cross-sectional area compared to naïve and all loading groups at 2 and 4 weeks. Maximum stress and elastic modulus of injured/untreated tendons were significantly lower compared to naïve and all loading groups after 4 weeks. Gastrocnemius muscle strength was maintained over time as loading magnitude increased. Force output was lower after 2 weeks at 100% body weight loading compared to the naïve group, then recovered to naïve levels after 4 weeks. Histological findings included increased cross-sectional area, matrix disorganization, and increased cellular density of injured/untreated tendons. The transcriptomic evaluation revealed several patterns of expression among exercised groups. Biological processes associated with exercised groups revealed genes responsible for inflammation, extracellular matrix organization, and cell to cell signaling. Overall, eccentric muscle loading improved tendon geometry and material properties compared to naïve levels and improved muscle strength over time. Morphological evaluation also showed improvements in cross-sectional area, and collagen orientation, and cell appearance after 2 and 4 weeks of eccentric loading. Similarly, the transcriptomic changes showed an effect from exercise and upregulation of genes essential for extracellular matrix organization, inflammatory regulation, and cell to cell signaling.
Plasma SOMAmer proteomics of postoperative delirium
Leung, Jacqueline M.; Rojas, Julio C.; Sands, Laura P.; Chan, Brandon; Rajbanshi, Binita; Du, Zhiyuan; Du, Pang (Wiley, 2024-02-12)
Background: Postoperative delirium is prevalent in older adults and has been shown to increase the risk of long-term cognitive decline. Plasma biomarkers to identify the risk for postoperative delirium and the risk of Alzheimer's disease and related dementias are needed. Methods: This biomarker discovery case–control study aimed to identify plasma biomarkers associated with postoperative delirium. Patients aged ≥65 years undergoing major elective noncardiac surgery were recruited. The preoperative plasma proteome was interrogated with SOMAmer-based technology targeting 1433 biomarkers. Results: In 40 patients (20 with vs. 20 without postoperative delirium), a preoperative panel of 12 biomarkers discriminated patients with postoperative delirium with an accuracy of 97.5%. The final model of five biomarkers delivered a leave-one-out cross-validation accuracy of 80%. Represented biological pathways included lysosomal and immune response functions. Conclusion: In older patients who have undergone major surgery, plasma SOMAmer proteomics may provide a relatively non-invasive benchmark to identify biomarkers associated with postoperative delirium.
Tissue-specific responses to oxidative fuel source preference during heat stress in lactating dairy cows
Ellett, Mark D.; Daniels, Kristy M.; Hanigan, Mark D.; Corl, Benjamin A.; Perez-Hernandez, G.; Parsons, Catherine L. M.; Melvin, J. A.; Fausnacht, D. W.; McMillan, R. P.; Baumgard, L. H.; Rhoads, Robert P. (American Dairy Science Association, 2024-09-18)
Prolonged exposure to high environmental temperatures results in an accumulated heat load that induces a heat stress (HS) response in dairy cattle. Heat stress compromises dairy farm profitability by reducing milk yield, altering milk composition, and hindering reproductive performance. The ability to alternate between carbohydrate and lipid sources for energy production is termed metabolic flexibility (Met Flex). The objective of this study was to evaluate the Met Flex of mammary, muscle, and liver tissue in lactating dairy cows under HS and thermoneutral (TN) conditions. Sixteen Holstein cows were assigned to 1 of 2 treatment groups: pair-feeding in TN conditions (PFTN) or HS conditions. All cows experienced a 4-d TN period with ad libitum intake followed by a 4-d treatment period. Heat stress cows were exposed to a temperature-humidity index (THI) ranging from 76 to 80 and the PFTN cows were exposed to a THI of 64. Milk production and health data were recorded twice daily. Semitendinosus biopsies were obtained on d 4 of each period and postmortem mammary and liver samples were obtained on d 4 of period 2. All tissue samples were assayed for Met Flex. Activity of mitochondrial (Mit) enzymes were assessed in skeletal muscle only. Four days of HS decreased milk yield, altered milk composition, and increased respiration rate and rectal temperatures. No differences in Met Flex were observed in mammary or liver tissue during period 2. However, HS, but not PFTN conditions, lowered Met Flex of skeletal muscle by 18.3% when compared with TN ad libitum feed intake conditions of period 1. No treatment differences were observed in skeletal muscle Mit enzyme activity indicating the decrease in Met Flex occurred independently of changes in Mit function. The reduction in Met Flex of skeletal muscle during HS may contribute to reduced milk yield and warrants further investigation.
Cyclical heat stress during lactation influences the microstructure of the bovine mammary gland
Perez-Hernandez, G.; Ellett, Mark D.; Banda, L. J.; Dougherty, D.; Parsons, Catherine L. M.; Lengi, A. J.; Daniels, Kristy M.; Corl, Benjamin A. (Elsevier, 2024-05-31)
This study aimed to evaluate the effect of heat stress on mammary epithelial cell (MEC) losses into milk, secretory mammary tissue structure, and mammary epithelial cell activity. Sixteen multiparous Holstein cows (632 ± 12 kg BW) approximately 100 DIM housed in climate-controlled rooms were paired by BW and randomly allocated to one of 2 treatments, heat stress (HS) or pair-feeding thermoneutral (PFTN) using 2 cohorts. Each cohort was subjected to 2 periods of 4 d each. In period 1, both treatments had ad libitum access to a common TMR and were exposed to a controlled daily temperature-humidity index (THI) of 64. In period 2, HS cows were exposed to controlled cyclical heat stress (THI: 74–80), while PFTN cows remained at 64 THI and daily DMI was matched to that of the HS cows. Cows were milked twice daily, and milk yield was recorded at each milking. Individual milk samples on the last day of each period were used to quantify MEC losses by flow cytometry using butyrophilin as a cell surface marker. On the final day of period 2, individual bovine mammary tissue samples were obtained for histomorphology analysis, assessment of protein abundance, and evaluation of gene expression of targets associated with cellular capacity for milk and milk component synthesis, heat response, cellular proliferation, and autophagy. Statistical analysis was performed using the GLIMMIX procedure of SAS. Milk yield was reduced by 4.3 kg by HS (n = 7) compared with PFTN (n = 8). Independent of treatment, MEC in milk averaged 174 cells/mL (2.9% of total cells). There was no difference between HS and PFTN cows for MEC shed or concentration in milk. Alveolar area was reduced 25% by HS, and HS had 4.1 more alveoli than PFTN. The total number of nucleated MEC per area was greater in HS cows (389 ± 1.05; mean ± SE) compared with PFTN (321 ± 1.05); however, cell number per alveolus was similar between groups (25 ± 1.5 vs. 26 ± 1.4). There were no differences in relative fold expression for GLUT1, GLUT8, CSN2, CSN3, LALBA, FASN, HSPA5, and HSPA8 in HS cows compared with PFTN cows. Immunoblotting analyses showed a decrease in abundance for phosphorylated STAT5 and S6K1, and an increase in LC3 II in HS cows compared with PFTN cows. These results suggest that even if milk yield differences and histological changes occur in the bovine mammary gland after 4 d of heat exposure, MEC loss into milk, nucleated MEC number per alveolus, and gene expression of nutrient transport, milk component synthesis, and heat-stress-related targets are unaffected. In contrast, the abundance of proteins related to protein synthesis and cell survival decreased significantly, whereas proteins associated with autophagy were upregulated in HS cows compared with PFTN cows.