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
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Recent Submissions
Subsidy-stress responses of ecosystem functions along experimental freshwater salinity gradients
DeVilbiss, Stephen E.; Badgley, Brian D.; Hotchkiss, Erin R.; Steele, Meredith K. (Springer, 2024-05-01)
Human activity is increasing salt concentrations in freshwaters worldwide, but effects of freshwater salinity gradients on biogeochemical cycling are less understood than in saline, brackish, or marine environments. Using controlled microcosm experiments, we characterized (1) short-term (one to five days) biogeochemical responses and (2) water column metabolism along a freshwater salinity gradient of multiple salt types. After one day, microcosms were oxic (4.48-7.40 mg O2 L-1) but became hypoxic (1.20-3.31 mg L-1) by day five. After one day in oxic conditions, microbial respiration in magnesium-, sodium-, and sea salt-based salinity treatments showed a subsidy-stress response, with respiration increasing by over 100% as salinity increased from 30 to 350-800 mu S cm-1. Conversely, respiration consistently increased along a calcium-based salinity gradient, peaking at 1500 mu S cm-1. By day five, an inverse subsidy-stress response was observed with elevated respiration at upper or lower ends of the gradient except for the magnesium treatment, which had the lowest respiration at the highest salinity. Calcium- and magnesium-based salinity treatments also caused considerable changes in phosphorus concentrations and C:P and N:P. In a separate experiment, microbial respiration and water column primary production also displayed subsidy-stress responses, but imbalances in effect sizes caused consistently declining net community production with increasing salinity. Collectively, our results establish that short-term exposure to different salt ion concentrations can enhance freshwater biogeochemical cycling at relatively low concentrations and alter resource stoichiometry. Furthermore, the nature of effects of freshwater salinization may also change with oxygen availability.
Optimizing indoor air quality and energy efficiency in multifamily residences: Advanced passive pipe system parametrics study
Obeidat, L. M.; Jones, James R.; Mahaftha, D. M.; Amhamed, A. I.; Alrebei, O. F. (Springer, 2024-12-01)
This research focuses on enhancing natural ventilation in multifamily residential buildings to improve air quality and minimize reliance on mechanical ventilation, thereby reducing energy consumption. The study pioneers the integration of passive pipe systems within structural floor slabs and building envelopes, aiming to overcome the inherent challenges of indoor environmental quality (IEQ) related to design constraints, occupant behavior, and urban context. Our innovative approach, utilizing a novel application of Grasshopper for precise architectural modeling and Ansys for advanced multiphysics simulation, enables a detailed comparative analysis of airflow dynamics across various system configurations. A comprehensive literature review underscores the significance of natural ventilation as a key passive cooling strategy, vital for reducing energy use and enhancing IEQ in the face of urbanization challenges. Our empirical findings reveal that configurations with more inlet and outlet pipes significantly outperform simpler ones, with a notable configuration of 11 pipes (5 x 6) achieving an actual-to-required ventilation rate increase in 158.15%. This evidence highlights the substantial benefits of adopting complex system configurations for improved ventilation efficiency. The study's outcomes include impactful design recommendations for adopting enhanced natural ventilation strategies in multifamily residential buildings. These recommendations promise to inform sustainable urban planning and building management strategies, offering a scalable solution for cities seeking to balance growth with environmental sustainability. By demonstrating the clear advantages of targeted passive cooling interventions, this research contributes valuable insights toward achieving energy efficiency and superior IEQ in residential buildings, paving the way for future exploration in diverse climatic and urban contexts.
Enhancing Electrical Conductivity of Stretchable Liquid Metal-Silver Composites through Direct Ink Writing
Zu, Wuzhou; Carranza, Hugo E.; Bartlett, Michael D. (American Chemical Society, 2024-04-30)
Structure-property-process relationships are a controlling factor in the performance of materials. This offers opportunities in emerging areas, such as stretchable conductors, to control process conditions during printing to enhance performance. Herein, by systematically tuning direct ink write (DIW) process parameters, the electrical conductivity of multiphase liquid metal (LM)-silver stretchable conductors is increased by a maximum of 400% to over 1.06 x 10(6) Sm(-1). This is achieved by modulating the DIW print velocity, which enables the in situ elongation, coalescence, and percolation of these multiphase inclusions during printing. These DIW printed filaments are conductive as fabricated and are soft (modulus as low as 1.1 MPa), stretchable (strain limit >800%), and show strain invariant conductivity up to 80% strain. These capabilities are demonstrated through a set of electromagnetic induction coils that can transfer power wirelessly through air and water, even under deformation. This work provides a methodology to program properties in stretchable conductors, where the combination of material composition and process parameters leads to greatly enhanced performance. This approach can find use in applications such as soft robots, soft electronics, and printed materials for deformable, yet highly functional devices.
Assessing the importance of sediment characterization on seabed embedment predictions of cylindrical objects
Shrestha, Saurav; Stark, Nina; Green, Brendan; Stilwell, Dan; Kim, Mingyu (Elsevier, 2024-07-01)
The prediction of object embedment into the seabed is important for the deployment and efficacy of submerged sensors and sensor networks, as well as for other applications such as unexploded ordnance risk assessment, subaquatic search and rescue efforts, or anchors and moorings. The embedment of objects into the seabed during placement depends on the strength parameters of the seabed sediment. However, a detailed characterization of seabed strength can be complex and costly since quality seabed samples and/or in situ testing are required. This study evaluates the importance of a detailed geotechnical seabed sediment characterization over seabed classification from geoacoustic surveying or accepting unknown seabed conditions for the prediction of seabed embedment of cylindrical objects. Monte Carlo simulation was applied to model the uncertainty of sediment strength parameters. The results suggest that prior knowledge of the general sediment type (e.g., fine-grained versus coarse-grained as determined from side scan sonar imaging) significantly improves the precision of the embedment predictions over unknown conditions, reducing the coefficient of variation (CV) in prediction of percent embedment (PE) by about 50 % to 65 %. Performing a detailed geotechnical testing of sediment strength represented a further improvement by 15 % to 35 % over the knowledge of sediment type. Both the mean and standard deviation of PE in fine-grained sediments are at least about 3 times the values for coarse-grained sediments indicating a wider distribution of PE with deeper embedment for cohesive fine-grained soils. The embedment behavior is a function of the method of deployment (free fall with a certain speed versus placement with no speed) in stiff cohesive sediments but is less relevant in soft sediments since PE values are always greater than 100 % (i.e., full embedment). Similarly, in cohesionless sediments, PE is always less than 50 %.
Tarazu: An Adaptive End-to-end I/O Load-balancing Framework for Large-scale Parallel File Systems
Paul, Arnab K.; Neuwirth, Sarah; Wadhwa, Bharti; Wang, Feiyi; Oral, Sarp; Butt, Ali R. (ACM, 2024-05-01)
The imbalanced I/O load on large parallel file systems affects the parallel I/O performance of high-performance computing (HPC) applications. One of the main reasons for I/O imbalances is the lack of a global view of system-wide resource consumption. While approaches to address the problem already exist, the diversity of HPC workloads combined with different file striping patterns prevents widespread adoption of these approaches. In addition, load-balancing techniques should be transparent to client applications. To address these issues, we propose Tarazu, an end-to-end control plane where clients transparently and adaptively write to a set of selected I/O servers to achieve balanced data placement. Our control plane leverages real-time load statistics for global data placement on distributed storage servers, while our design model employs trace-based optimization techniques to minimize latency for I/O load requests between clients and servers and to handle multiple striping patterns in files. We evaluate our proposed system on an experimental cluster for two common use cases: the synthetic I/O benchmark IOR and the scientific application I/O kernel HACC-I/O. We also use a discrete-time simulator with real HPC application traces from emerging workloads running on the Summit supercomputer to validate the effectiveness and scalability of Tarazu in large-scale storage environments. The results show improvements in load balancing and read performance of up to 33% and 43%, respectively, compared to the state-of-the-art.