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 40 freely available and openly licensed textbooks are among our most downloaded items.
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Recent Submissions
Using Passive Acoustic Monitoring to Estimate Bird Community Response to Land Management in Southeastern Georgia
Watson III, Daniel Hays (Virginia Tech, 2025-02-28)
Working lands, such as mine reclamation and timber production sites, may be able to provide supplementary habitat for declining disturbance-dependent birds, such as Bachman's Sparrow (Peucaea aestivalis) and Northern Bobwhite (Colinus virginianus). However, habitat use is likely contingent on specifics of land-use practices, especially those that could alter understory vegetation. My first research objective was to use autonomous recording units (ARUs) and BirdNET algorithms to compare the relative abundance of eight focal bird species across site treatments representing land management types: surface mine reclamation, timber production, young savanna, and mature savanna. All sites were established in upland pine (Pinus spp.) habitat throughout the southeastern Coastal Plain region of Georgia, USA from May-June 2024. I hypothesized that the mine reclamation site would support similar focal species, but in lower abundances than timber production and both savanna sites, and vegetation characteristics would also influence relative abundance along with site treatment. Model selection showed site treatment influenced relative abundance for all species and explained more variation in relative abundance than measured vegetation characteristics. The mine reclamation site had similar relative abundances for focal species when compared to the timber production site, suggesting these treatments provide comparable habitat. The young savanna site exhibited the highest abundances for most species, whereas the mature savanna site had lower abundances, suggesting some focal species may prefer habitat lacking overstories. Focal species responded differently to vegetation characteristics; for example, Common Nighthawk showed a positive response to grass cover, whereas Prairie Warbler responded negatively. My results provide strong evidence that site treatment influences the relative abundance of all focal species and highlight the need for future studies to parse out the exact mechanisms underlying these differences. Additionally, this study highlights the potential for working lands to provide habitat for disturbance-dependent birds and the effectiveness of using ARUs to assess the effects of land management on bird relative abundances.
My second research objective assessed optimal survey frequency when using Royle-Nichols (RN) models to estimate abundance or relative abundance from ARU data. Passive acoustic monitoring with ARUs can enable efficient monitoring of avian populations. RN models may be well suited for estimating abundance or relative abundance from ARU detection/non-detection data; as repeated surveys can easily be conducted with ARUs. Yet, optimal survey effort using these methods remains unexplored. Using ARU data from four site treatments in southeastern Georgia, I assessed how survey frequency and mean cumulative detection probability influenced estimates for Blue Grosbeak (Passerina caerulea) and Bachman's Sparrow from May–June 2024. A baseline dataset of 50 daily surveys was subsampled into reduced frequencies: 25 surveys every 2nd day, 17 every 3rd day, 13 every 4th day, 8 every 7th day, and 5 every 10th day. RN models were fitted to each subsample. Abundance estimates decreased with subsampling, showing survey frequency arbitrarily influences estimates and RN models should be viewed as relative, not absolute, abundance estimates. However, the specific order of relative abundance across site treatments remained consistent for both species during subsampling, indicating RN models can still reliably infer effects across sites. Mean cumulative detection probability decreased with subsampling yet remained >70% for both species. Subsampling reduced precision in relative abundance estimates for both species; particularly for Bachman's Sparrow, emphasizing species-specific sensitivity to survey effort. However, subsampling every 2nd day or every 3rd day resulted in moderate losses of precision (≤ 34%) for both species, suggesting reduced survey frequency may be a viable strategy for efficient data collection depending on species detectability and study goals. Together, these findings from my research objectives highlight the potential of working lands to support disturbance-dependent bird conservation and demonstrate how passive acoustic monitoring with ARUs can be an effective tool for the conservation and management of bird populations.
Essays on Dynamic Optimization for Forest Resource Management
Chong, Fayu (Virginia Tech, 2025-02-28)
The dissertation consists of three essays in forestry resource management, with focuses on investigating the ecosystem collapse and invasive species control problems. The first two papers consider the shift from primary forests to cleared land and secondary forests in the context of deforestation. This process is known to lead to irreversible tipping points that lead to the loss of ecosystem services. The past literature has discussed forest rotations under stochastic prices, timber volume, and amenity values. I extend this body of work to show how stochastic processes concerning primary forests could lead to ecological collapse. Drift and volatility in these processes explain different types of long-term and short-term shocks in tropical forest systems, such as fire, drought, or climate changes, all mechanisms that can drive ecosystem function to collapse. Common examples of severe ecosystem damage include the irreversible change from tropical forests to grassy savanna, fire events, and other climate problems. However, another case of uncertainty happens when ecosystem service production of primary and secondary forests itself is stochastic, so that there is a more complicated relationship between deforestation and reaching a point where ecosystem functions collapse. I compare and contrast these two cases to determine how drift and volatility determines the timing of a tipping point in a deforestation model where primary and secondary forests, as well as agricultural land, influence ecosystem function. I examine the sensitivity of the timing of collapse in both model variants to critical market and land-use parameters. The third chapter of this dissertation explores the connection between landowners' risk preferences, invasive species spread, and optimal control efforts. This study analyzes the control effort involved in neighboring infested and uninfested municipalities, which may have differing risk preferences. In the context of an application to the spread of Emerald ash borer (EAB) in the Twin Cities, Minnesota, I develop a simulation to explore the level of control and spread in a myopic policy scenario versus that in a first-best problem, where the two municipalities may be either risk neutral or risk averse. The results suggest that heterogeneity in risk aversion across the municipalities leads to lower control efforts and a longer time to drive the probability of spread to zero.
Space Network (SpaceNet) Testbed - Development of a Multi-Functional Testbed for Simulating Space Communication Networks
Downs, John S.; Barbour, Bruce; Kedrowitsch, Alexander; Mhadgut, Deven; Aryan, Suryansh; Kenyon, Samantha P. (American Institute of Aeronautics and Astronautics, 2025-01-03)
Low Earth Orbit mega-constellations make up a large portion of modern developments in space communications. The ability to simulate and properly research these complex systems is currently being developed to answer questions on the capabilities of the rapidly expanding industry. The development and improvement of a simulation-based platform for satellite network testing can help research efforts to enable industry and government entities to work together in the growing enterprise. The ongoing development of the SpaceNet Testbed is investigated, detailing its use of orbit-based constellation dynamics modeling, software-based emulation, and a hardware-in-the-loop integration design. An overview of the testbed’s software infrastructure design is described alongside details regarding the make-up of its hardware components. Use cases are presented comparing the differences in performance between the satellite network of an actual Starlink mega-constellation currently in orbit and a custom constellation with the same quantity of satellites, but with ideal node spacing and initial orbital positioning. Results of these use cases are then discussed, focusing on the latency of the data traffic and how it differs when varying the testbed’s user-defined configurations. In the future, resiliency testing and ground station to satellite link behavior analysis can be included into the testbed. The testbed has potential to help lead efforts in simulating complex space communication systems.
Low-Power mm-Wave Frequency Quadrupler Using Deep Class-C Doublers
Darban, Meysam Sohani; Ha, Dong Sam; Walling, Jeffrey Sean (2024-09-01)
In this paper, a low-power mm-wave frequency quadrupler is introduced. The proposed quadrupler comprises two push-push frequency doublers operating in deep class-C mode to ensure minimal static power consumption. The quadrupler is fabricated in the 22-nm FD-SOI process technology and uses an area of 0.5 × 0.41mm2. It generates a ≈ 60 GHz signal with a Pout of -10 dBm from a 15 GHz input signal and provides 10.8 GHz output bandwidth (18% fractional bandwidth). Its low power consumption and wide bandwidth make it attractive for many operations in the 60 GHz spectrum, including advanced communication with a high data rate. Operating from 54.9 − 65.7 GHz, its total power consumption is 12 mW, which includes the output pad driver; however, the core frequency quadrupler consumes only 5 mW due to deep class-C operation.
Virginia Tech Magazine, Fall 2024
(Virginia Tech, 2025)
The official magazine of Virginia Tech, dedicated to its motto, Ut Prosim (That I May Serve).