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
Virginia Tech's open access policy enables researchers to deposit the accepted version of scholarly articles with no embargo.
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
More than 50 freely available and openly licensed textbooks are among our most downloaded items.
Communities in VTechWorks
Select a community to browse its collections.
Recent Submissions
Sales promotions and firm valuation in the airline industry
Sharma, Abhinav; Shin, Hoyoung; Santa-María, María Jesús; Nicolau, Juan Luis (Elsevier, 2026-10-01)
While prior research has shown that sales promotions can erode firm value in industries such as hotels or enhance it in restaurants, their impact in the airline industry remains underexplored despite the strategic use of promotions in this sector. Using an event study methodology, we analyze 369 promotional announcements issued by major publicly traded U.S. passenger airlines from 2000 to 2024. The results show that, on average, promotional activities generate positive and significant abnormal returns, suggesting that investors perceive them as strategic components of revenue management rather than as distress signals. Further analysis reveals that volume discounts, in particular, produce significantly higher abnormal returns than other promotion formats, highlighting their superior signaling and behavioral reinforcement mechanisms. These findings contribute to the marketing-finance interface by demonstrating that not all promotions are equally effective in signaling strategic competence to investors, emphasizing the need to account for promotion type in valuation studies.
Polynomial Time Algorithms for Transportation and Inventory Management in Serial Supply Chain with Multi-Module Capacitated Vehicles
Kulkarni, Kartik Giridhar (Virginia Tech, 2026-04-14)
We study new generalizations of the classical capacitated lot-sizing problem with concave production (or transportation), holding, and subcontracting cost functions, in which the total capacity available in each time period is the sum of capacities of a subset of n heterogeneous modules (machines or vehicles). We refer to this class of problems as the Multi-module Capacitated Lot-Sizing Problem without and with Subcontracting, denoted by MCLS and MCLS-S, respectively. While these problems are NP-hard when n is part of the input and polynomially solvable for n = 1, the complexity status for fixed n ≥ 2 has remained open. We resolve this question by developing exact fixed-parameter tractable algorithms that solve MCLS and MCLS-S in O(T2n+3) time for any fixed n ≥ 2. Our results generalize the algorithm of Atamtürk and Hochbaum [Management Science 47(8):1081–1100, 2001] for the case n = 1. We further extend our framework to two important generalizations:
(i) the lot-sizing problem with piecewise concave production costs (LS-PC-S), for which we propose an O(T2m+3) time algorithm, where m is the number of breakpoints; and (ii) a two-echelon multi-module lot-sizing problem, solved in O(T4n+4) time. Our LS-PC-S algorithm reduces the runtime of the dynamic programming approach of Koca et al. [INFORMS J. on Computing 26(4):767–779, 2014] by up to 93.6%, and our two-echelon results generalize those of van Hoesel et al. [Management Science 51(11):1706–1719, 2005] for the single-module case. Computational experiments demonstrate that our algorithms are both efficient and highly stable compared to Gurobi 9.1, including under parallel implementation.
In addition, our results for MCLS-S establish the existence of a polynomial-time algorithm for optimizing a linear function over the n-mixing set, a significant generalization of the classical 1-mixing set.
We also investigate single-item discrete multi-module capacitated lot-sizing problems without and with backlogging, where production in each period consists of binary multiples of module capacities. For fixed n ≥ 2, we develop exact fixed-parameter tractable algorithms that generalize the results of van Vyve (2007) for n = 1. These algorithms are embedded within a Lagrangian decomposition framework to solve the corresponding multi-item problems. Computational results show substantial improvements over Gurobi 9.0 in both performance and robustness.
Finally, we study serial supply chain models in which goods are transported from a supplier to a warehouse and then to a retailer over a finite planning horizon. These problems fall under the class of two-echelon lot-sizing problems (2-ELS) with capacitated inbound and outbound transportation. We address an open question posed by van Hoesel, Romeijn, Morales, and Wagelmans (2005) concerning the existence of a polynomial-time algorithm for 2-ELS with a single capacitated vehicle in each echelon. We provide polynomial-time exact algorithms for this setting and three further generalizations involving multiple heterogeneous capacitated vehicles, thereby extending the results of Kaminsky and Simchi-Levi (2003) and Sargut and Romeijn (2007).
Architectural Effects on Aqueous Self- Assembly of Bottlebrush Block Copolymers and Synthesis of Degradable Bottlebrush Polymers
Vu, Clark (Virginia Tech, 2026-04-14)
Bottlebrush polymers feature densely grafted side chains along a polymeric backbone. Due to their unusual topology, bottlebrush polymers are an emerging class of materials with unique physical properties and novel applications, including supersoft elastomers, residual-free adhesives, drug delivery or photonic crystals. Among these interesting applications, amphiphilic bottlebrush block copolymers (BCPs) and their solution self-assembly have attracted significant attention over the past decade due to their potentials as drug delivery carriers. Driven by microphase separation, amphiphilic bottlebrush BCPs self-assemble into various nanoaggregates with surface protrusions, including spherical micelles, ellipsoids, cylindrical micelles, and vesicles. Compared to their linear BCP analogues, bottlebrush BCPs exhibit significantly lower critical micelle concentrations and consequently form more stable nanoaggregates. While theoretical and experimental studies on cone-shaped amphiphiles have been widely studied, the solution self-assembly of cone-shaped (tapered) bottlebrush BCPs remains underexplored. To address this knowledge gap, this dissertation presents systematic studies of the aqueous self-assembly of tapered bottlebrush BCPs. A series of eight tapered and four cylindrical bottlebrush BCPs were synthesized via sequential addition of macromonomers ring-opening metathesis polymerization, featuring varying ratios of hydrophobic polystyrene (PS) and hydrophilic poly(acrylic acid) PAA side chains. The nanostructures formed by these bottlebrush BCPs in water were characterized using cryogenic transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS). Results reveal that most BCPs formed multiple nanostructures with surface protrusion, including spherical micelles, cylindrical micelles, and vesicles. Coarse-grained molecular dynamics simulations supported the interpretation of the experimental observations. Collectively, two distinct self-assembly pathways were identified. One pathway involves micelle fusion to form elliptical and cylindrical aggregates that, in some cases, fused further to form Y-junctions. The second pathway proceeded through micelle maturation into semi-vesicles, which subsequently developed into vesicles that, in some cases, fused further to form compound vesicles. Moreover, for the first time, larger spheres that are nanoaggregates with a core radius larger than the average core radius were identified by cryo-TEM tomography. These results provide the first experimental evidence for vesicle formation via semi-vesicle intermediates in bottlebrush BCPs. These findings highlight how structural parameters such as cone directionality govern self-assembly in these large, cone-shaped polymeric amphiphiles.
Extending this work, the effects of cone angle on aqueous self-assembly were systematically investigated using six tapered bottlebrush BCPs—three with hydrophobic tips and three with hydrophobic bases— with estimated cone angles ranging from 6 o to 15o. Cylindrical bottlebrush BCPs with comparable molar masses were also synthesized for comparison. All bottlebrush BCPs maintained a constant mass ratio of hydrophobic PS to hydrophilic deuterated PAA side chains at approximately 50%. Moreover, deuteration of PAA side chains enabled us to employ contrast-variation SANS for characterization of core radius and shell thickness in spherical nanoaggregates. Cylindrical bottlebrush BCPs exhibited similar distributions of self-assembled morphologies regardless of molecular weight. In contrast, tapered bottlebrush BCPs displayed a correlation between morphology distributions and cone angle. Tapered bottlebrush BCPs with a hydrophobic tip favored nearly exclusive formation of spherical micelles at low cone angles. The cone angle exerted a more pronounced effect on morphology in bottlebrush BCPs with hydrophobic bases. Despite similar hydrophobic contents, BCPs with lower cone angles exhibited high populations of spherical micelles, whereas those with higher cone angles led to larger spheres, ellipsoids, vesicles, and work-like structures. Characterization of the core radius and shell thickness by cryo-TEM and contrast-variation SANS showed good agreement between the two techniques, though some discrepancies were observed between theoretical predictions and experimental measurements. This work provides insights into how cone geometry governs the aqueous self-assembly behavior of bottlebrush BCPs.
Bottlebrush polymers have received considerable interest as residual-free pressure-sensitive adhesives (PSAs). Due to their unique topology and entanglement suppression of entanglement, these polymers are naturally soft and flexible without needing chemical additives. This allows them to stick when pressed and peel off cleanly without leaving behind a gummy residue. Unfortunately, most bottlebrush polymers include all-carbon backbones and could contribute to plastic pollution following their intended use. Recent efforts have focused on developing methods to synthesize degradable bottlebrush polymers. However, these methods typically require specialty monomers or cannot make bottlebrush polymers with high molar mass. To address these challenges, we developed an approach that takes advantage of the alternating free-radical copolymerization of sulfur dioxide (SO2) and electron-rich alkenes, including cycloalkenes (e.g., norbornene). We prepared several types of norbornene macromonomers with side chain molecular weights up to 5 kg/mol and successfully copolymerized them with SO2. These poly(olefin sulfone) bottlebrush polymers featured various types of side chains, such as polyacrylates, polymethacrylates, polystyrene, and poly(lactic acid), attached to a poly(norbornene-alt-SO2) backbone and reached number-averaged molar masses of up to 1100 kg/mol. More importantly, these bottlebrush polymers were degradable. Degradation studies with a variety of bases revealed that the sulfone unit with removable protons on neighboring carbons enabled degradation of these high-molecular-weight polymers within hours. Moreover, a bottlebrush polymer synthesized using this approach exhibited pressure-sensitive adhesive properties with a peel strength of approximately 1200 N/m. Collectively, this work offers a versatile approach using inexpensive SO2 gas to synthesize degradable bottlebrush polymers with high molar mass, enabling end-of-life disposal following their intended applications.
Mirtazapine Induced Tardive Dyskinesia in an Older Adult
Syed, Amin; Soni, Karishma; Bankole, Azziza; Ratnakaran, Badr (Elsevier, 2025-10)
Mirtazapine, first sold in the United States as Remeron in 1996, is a noradrenergic and specific serotonergic antidepressant FDA-approved for major depressive disorder.
Its mechanism of action is referred to as NaSSA due to its alpha-2, 5-HT2, and 5-HT3 antagonism. It has also been used off-label as a third-line treatment option for akathisia, appetite stimulation, and SSRIinduced sexual dysfunction. Incidents of hyperkinetic movement disorders caused by mirtazapine have been reported, but even more infrequent for cases involving tardive dyskinesia (TD).
The aim of this presentation is to highlight a case of TD with the use of mirtazapine in an older adult and search for more literature involving mirtazapineinduced tardive dyskinesia.
Land subsidence on Java Island and its contributions to relative sea level change
Ohenhen, Leonard O.; Shirzaei, Manoochehr; Kumar, Praveen; Aditiya, Arif; Tiwari, Ashutosh; Davis, James L.; Kolawole, Folarin; Chaussard, Estelle; Sadhasivam, Nitheshnirmal; Dasho, Oluwaseyi; Zhong, Wen; James, Roselyn H.; Daramola, Samuel; Nicholls, Robert J.; Minderhoud, Philip S. J. (AAAS, 2026-04)
Rising sea levels and land subsidence combine to determine relative sea level (RSL) rise, which is intensifying coastal hazards. However, many densely populated regions lack the observational infrastructure to identify and quantify land subsidence contribution to RSL, hindering effective planning of responses. Here, we used satellite radar observations to generate a high-resolution assessment of land subsidence across Java Island, Indonesia, and evaluate its contribution to 21st-century RSL change. We identify widespread and temporally evolving subsidence with rates ranging from 1 to 15 cm/year in multiple coastal cities. Using machine learning spatiotemporal clustering and ancillary datasets, we attribute the dominant subsidence mechanisms to resource extraction across various geographic and geological settings. We further construct virtual tide gauges at 5-km intervals along the northern coastline, revealing that contemporary subsidence will dominate RSL budgets over the next 25 years along >75% of the coast. These findings underscore the urgent need to integrate subsidence into sea level risk and adaptation assessments in vulnerable coastal regions.