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Virginia Tech's open access policy enables researchers to deposit the accepted version of scholarly articles with no embargo.
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More than 50 freely available and openly licensed textbooks are among our most downloaded items.
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Recent Submissions
Modeling of Electrically Controlled Propellant Combustion for Solid-fueled Propulsion
Miller-Smith, Shea Arthur (Virginia Tech, 2026-09-03)
Liquid-fueled rocket propulsion systems are widely used in aerospace and defense applications for their throttle control, shutdown, and restart capabilities. Traditional solid-fueled rocket propulsion systems lack such capabilities, but are comparatively mechanically simple, storable, and less expensive. Electrically controlled solid propellants (ECSPs) seek to address this limitation by applying an electric voltage to regulate ignition and combustion, enabling more complex trajectories and mission plans while retaining many of the advantages of solid propulsion systems. Previous ECSP experiments have demonstrated voltage-dependent ignition delay, control of regression rate, extinguishment, and localized melting and ignition behavior at the electrodes. However, the individual mechanisms involved remain difficult to identify and isolate in ECSP experiments due to the coupling of simultaneous electrical, chemical, and thermal contributions. The objective of the present research is to develop a computational model of ECSPs composed of lithium perchlorate, polyethylene oxide, and carbon-based conductive additives to investigate the mechanisms governing melting, ignition, and combustion. The primary mechanisms considered are ion transport, electronic conduction through additive networks, electrochemical reactions, phase change, heat transfer, and gas-phase combustion. A 3-D Doyle--Fuller--Newman-inspired finite-element model is developed to resolve the coupling among the condensed-phase mechanisms. Experimental results from prior studies are then used to evaluate the mechanistic submodels and the integrated multiphysics model. The primary model results include ignition delay, burn rate, voltage response, and temperature distribution. Sensitivity analyses on electrode kinetics and global ion-transport parameters demonstrate the importance of electrochemistry modeling fidelity, as well as of physical propellant characteristics such as transference number and energetic barriers to electrode reactions. The multiphysics FEM reproduced experimental ignition delay trends as a function of applied voltage, additive concentration, and electrode spacing, and predicted the localization of concentration gradients, current, and heat generation near the electrodes. Butler--Volmer and Marcus-based electrochemical kinetics models were compared, with the Marcus--Hush--Chidsey approach providing the best agreement with spatial experimental observations and capturing the experimentally observed cathode-melting/anode-ignition sequence. Differences between electrode kinetics models were prominent in spatial metrics, such as electrode temperature asymmetry, though differences in global ignition delay metrics were minor. In the model, physical parameters varied in their impact on spatial and global results, demonstrating the sensitivity to input parameters and contributing submodels. These findings also reveal that experimental agreement with global metrics such as ignition delay may be insufficient to validate the spatially dependent ECSP mechanisms.
Multi-Agent Integer Programming Games with Non-Cooperation and Cooperation
Lee, Hyunwoo (Virginia Tech, 2026-09-03)
This dissertation studies integer programming games (IPGs), in which each of several self-interested players solves an integer program whose payoff is coupled to the others' discrete decisions. Because feasible sets are combinatorial and best responses require integer optimization, even deciding whether a pure Nash equilibrium (PNE) exists is computationally intractable in general. The unifying thesis is that the equilibrium of such a game is a computable and leverageable object around which better system-level decisions can be built, and this idea is developed across the non-cooperative, generalized, and cooperative regimes on a common branch-and-cut foundation of globally valid inequalities and best-response oracles. First, to make equilibrium computation scale, round-based random-restart best-response dynamics (RRR-BRD) are introduced with a Las Vegas convergence guarantee and hybridized with the zero-regret cutting-plane method (BZR), lifting tractable PNE computation and sampling from a handful of players to dozens; the methods are instantiated on edge-weighted budgeted maximum coverage games, including a Minnesota aquatic invasive species (AIS) inspection game with up to 84 counties. Second, Nash-informed planning converts computed equilibria into individual-rationality floors and optimizes social welfare above them, improving system outcomes without making any player worse off; the accompanying Price of Individual Rationality is proven to be bounded by the Price of Stability, and the welfare cost of guaranteeing participation is empirically negligible. Third, for generalized IPGs with shared constraints, conditional equilibrium inequalities and a generalized zero-regret algorithm optimize over the equilibrium set, while α-approximate equilibrium certificates and structural (VEST) cuts handle cost-sharing games such as integer splittable bin packing. Fourth, cooperative IPGs define coalition values through pooled integer programs and compute optimal, Core-stable coalition structures via stability inequalities and separation. Computational studies, anchored by the AIS application, demonstrate scalability, interpretability, and concrete policy improvements.
Toxicity of zinc to Schistosoma mansoni cercariae in a chemically defined water medium together with a note on the cercariophagic activity of Macrostomum gigas (Turbellaria: rhabdocoela)
Mecham, John Alvin (Virginia Tech, 1970-11)
A synthetic water medium has been found to support Schistosoma mansoni cercariae for approximately 50 hours, which is the normal life expectancy of cercariae in natural waters.
A partially enclosed slide chamber has proven to be effective in the study of schistosome cercariae where the close observation of a few individual cercariae in a large volume of water otherwise would be extremely difficult.
In low concentrations zinc has little lethal effect on cercariae of Schistosoma mansoni during that period of time in which the cer-cariae are most likely to be infective. Compared to the control groups, concentrations of zinc as low as 0.001 ppm were found to be toxic to schistosome cercariae. Concentrations as high as 57.6 ppm zinc were found to immobilize all cercariae tested within six hours.
A free living flatworm Macrostomum gigas was discovered to be a predator on Schistosoma mansoni cercariae.
Partial resistance to Schistosoma mansoni in mice inoculated with cercarial bodies
Mecham, John Alvin (Virginia Tech, 1972-07)
One group of mice was inoculated with Schistosorna mansoni cercarial bodies. Another group was inoculated with cercarial tails and a third group inoculated with cercarial bodies plus tails in an attempt to determine if schistosome cercarial parts elicit differing immune responses. The mice were then challenged with 100 viable cercariae as were control mice. At six weeks after infection, adult schistosomes were recovered by perfusion. The average worm burden for mice inoculated with cercarial bodies was 9.07 compared to 21.00 for mice inoculated with cercarial tails, 21.90 for mice inoculated with bodies plus tails, and 23.30 for control mice. The number of adults recovered from mice inoculated with cercarial bodies was significantly less than from mice inoculated with cercarial tails, or bodies plus tails, and control mice.
Two serodiagnosic tests, Cercarien-hullen Reaction (CHR) and immunodiffusion, were conducted with sera from experimental and control mice. CHR tests were positive for all experimental mice with strongest reactions occurring with infected mice and with mice inoculated with cercarial bodies. Precipitating antibodies against whole cercarial antigen were shown using anti-body, anti-body-plus-tail, and infected mouse serum. No precipitating antibodies were shown against whole cercarial antigen using anti-tail mouse serum.
The possibility of a cercarial body-tail interaction resulting in stimulation to develop or protection for the developing schistosomulum is indicated.
A late Precambrian resurgent cauldron in the Carolina slate belt of North Carolina, U.S.A.
Newton, Maury Claiborne III (Virginia Tech, 1983-04)
A resurgent cauldron, in the older part of the Carolina slate belt, is part of the lower greenschist-grade Hyco Volcanic-plutonic Group, dated between 620 and 650 Ma. The present dimensions of the cauldron are approximately 45 x 14 km.
The cauldron stratigraphy matches well Smith and Bailey's (1968) seven-stage resurgent cauldron mode!. During Stage (regional tumescence), the ring-fracture system developed, manifested by phreatic explosion breccias and a pre-Stage 11 porphyritic lava dome. The subaqueously-deposited terrane was arched to emergence prior to Stage 11 eruptions. Stage 11 (caldera-forming eruptions) is marked by subaerially-deposited dacitic to rhyolitic ignimbrites and air-fall tuffs. Strongly welded ash-flow tuffs have pumice-flattening ratios of 20-30: 1. Stage 111 (caldera collapse) took place while Stage 11 eruptions were continuing and is recorded by a vertical transition from subaerial pyroclastic facies to subaqueous pyroclastic and epiclastic facies. Stage IV (preresurgence volcanism and sedimentation) is marked by subaqueously-deposited low-Si dacitic to basaltic lavas and epiclastic rocks. Stage V ( resurgent doming), may be represented by a cupola of quartz gabbro to granodiorite that intruded the cauldron block and erupted to form amphibole crystal tuffs. Stage VI (major ring-fracture volcanism) was a second period of regional tumescence culminating in a second cycle of subaerially-deposited dacitic to rhyolitic ignimbrites. Concomitant with rhyolite extrusion, granodiorite to granite intruded the cauldron block. Stage VI I (terminal solfataric activity) resulted in the protoliths of economic pyrophyllite and andalusite deposits.
Stage I I-Stage IV volcanics may represent an inverted compositionally-layered magma chamber with a silicic top and a base of high-alumina basalt to low-Si andesite. Volcanics of the entire cauldron sequence are bimodal with basalt to low-Si andesite and dacite to rhyolite dominant over high-Si andesite. The bimodality suggests there is an apparent compositional gap in the range of high-Si andesite.