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
The Perspective of University Instructors About COVID Pandemic-Related Changes in Instructional Delivery Methods
Roark, Shannan Marie (Virginia Tech, 2025-12-12)
The Perspective of University Instructors About COVID Pandemic-Related Changes in Instructional Delivery Methods Shannan M. Roark Abstract In March of 2020, colleges and universities closed their doors due to the onset of the COVID-19 pandemic. As a result of this unexpected event, approximately 200 million students worldwide were transitioned from traditional face-to-face lectures to online courses (Salmi, 2020). On the college and university levels, numerous instructors were unprepared to convert long-standing lecture courses into viable synchronous and asynchronous classes (Pavlidou, 2021; Salmi, 2020). This action prompted instructors to redefine their courses and the way instruction was presented.
This qualitative research study examined how instructors addressed the sudden transition to online teaching, what they gained from the experience, and how this knowledge influenced their subsequent teaching styles. As revealed in the study, after the pandemic, instructors were more willing to incorporate elements of online learning into their courses, including, but not limited to, learning software used in conjunction with classes notated as blended/hybrid or courses completely online in a full asynchronous format. Due to the increase in online and digital instruction, the study revealed a dramatic rise in the number of higher education instructors attending professional development workshops and participating in training on technological innovations. These changes have also compelled colleges and universities to adjust policies, adapt course offerings, and provide incentives to encourage the development of courses with a stronger technological focus. This shift involves greater reliance on learning management systems and the transition of course offerings from traditional formats to various learning modalities, including synchronous, asynchronous, and hybrid/blended learning formats
Characterizing Natural Frequencies of the Hybrid III and NOCSAE Headforms
Dingelstedt, Kristin J.; Rowson, Steven (Springer, 2024-10-01)
The vibrational characteristics of the Hybrid III and NOCSAE headforms are not well understood. It is hypothesized that they may perform differently in certain loading environments due to their structural differences; their frequency responses may differ depending on the impact characteristics. Short-duration impacts excite a wider range of headform frequencies than longer-duration (padded) impacts. While headforms generally perform similarly during padded head impacts where resonant frequencies are avoided, excitation of resonant frequencies during short-duration impacts can result in differences in kinematic measurements between headforms for the matched impacts. This study aimed to identify the natural frequencies of each headform through experimental modal analysis techniques. An impulse hammer was used to excite various locations on both the Hybrid III and NOCSAE headforms. The resulting frequency response functions were analyzed to determine the first natural frequencies. The average first natural frequency of the NOCSAE headform was 812 Hz. The Hybrid III headform did not exhibit any natural frequencies below 1000 Hz. Comparisons of our results with previous studies of the human head suggest that the NOCSAE headform's vibrational response aligns more closely with that of the human head, as it exhibits lower natural frequencies. This insight is particularly relevant for assessing head injury risk in short-duration impact scenarios, where resonant frequencies can influence the injury outcome.
Malicious RIS Versus Massive MIMO: Securing Multiple Access Against RIS-Based Jamming Attacks
de Sena, Arthur Sousa; Kibilda, Jacek; Mahmood, Nurul Huda; Gomes, Andre; Latva-aho, Matti (IEEE, 2024-04-01)
In this letter, we study an attack that leverages a reconfigurable intelligent surface (RIS) to induce harmful interference toward multiple users in massive multiple-input multiple-output (mMIMO) systems during the data transmission phase. We propose an efficient and flexible weighted-sum projected gradient-based algorithm for the attacker to optimize the RIS reflection coefficients without knowing legitimate user channels. Simulation results demonstrate that our malicious algorithm outperforms baseline strategies while offering adaptability for targeting specific users. To counter such a threat, we propose two reception strategies, which we show to be effective even if only an imperfect estimate of the cascade RIS channel is available.
Development of a hard cider flavor wheel using free word sorting and multivariate statistical techniques
Calvert, Martha D.; Neill, Clinton L.; Ac-Pangan, Marlon F.; Stewart, Amanda C.; Lahne, Jacob (Wiley, 2024-04-01)
Flavor wheels are visual tools built from standardized sensory lexicons that are used in many different industries to improve communication, marketing, and quality discrimination among products. To date, flavor wheels have been developed for spices, coffee, wine, beer, and many other foods and beverages-yet no flavor wheel has been constructed for hard cider. While there is no single established method for constructed flavor wheels, most approaches are based on sensory descriptive analysis (DA) and free word sorting activities that investigate the semantic similarity and dissimilarity of descriptive terms. This research study utilized multiple DA studies for the generation of a sensory lexicon, followed by independent word sorting tasks with cider industry professionals (N = 40) and untrained consumers (N = 58) to establish two flavor wheels that are broadly understandable to a variety of industry stakeholders. Based on the results of DISTATIS and additive tree partitioning, this research showcases a workflow for developing and refining flavor wheels that incorporate both stakeholder and researcher input and can be built upon by other analysts.Practical ApplicationsThis research demonstrates an accessible methodology for developing flavor wheels that incorporates input from diverse parties and considers the semantic associations of terms used by cider consumers and industry professionals. The proposed methodology is a useful framework for other sensory scientists seeking to efficiently develop flavor wheels for multiple audiences. As a demonstration, this research also delivers two flavor wheels-one that highlights discrepancies in how industry consumers and producers semantically understand sensory experiences compared to trained sensory personnel, and a second wheel that showcases how hard cider can more objectively be described. Together, these flavor wheels are tools for improving sensory communication, education, and marketing in the US hard cider industry.
Structured interpolation for multivariate transfer functions of quadratic-bilinear systems
Benner, Peter; Gugercin, Serkan; Werner, Steffen W. R. (Springer, 2024-04-01)
High-dimensional/high-fidelity nonlinear dynamical systems appear naturally when the goal is to accurately model real-world phenomena. Many physical properties are thereby encoded in the internal differential structure of these resulting large-scale nonlinear systems. The high dimensionality of the dynamics causes computational bottlenecks, especially when these large-scale systems need to be simulated for a variety of situations such as different forcing terms. This motivates model reduction where the goal is to replace the full-order dynamics with accurate reduced-order surrogates. Interpolation-based model reduction has been proven to be an effective tool for the construction of cheap-to-evaluate surrogate models that preserve the internal structure in the case of weak nonlinearities. In this paper, we consider the construction of multivariate interpolants in frequency domain for structured quadratic-bilinear systems. We propose definitions for structured variants of the symmetric subsystem and generalized transfer functions of quadratic-bilinear systems and provide conditions for structure-preserving interpolation by projection. The theoretical results are illustrated using two numerical examples including the simulation of molecular dynamics in crystal structures.