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
Adaptive Predictive Controllers for Agile Quadrupedal Locomotion with Unknown Payloads
Amanzadeh, Leila (Virginia Tech, 2024-07-12)
Quadrupedal robots play a vital role in various applications, from search and rescue operations to exploration in challenging terrains. However, locomotion tasks involving unknown payload transportation on rough terrains pose significant challenges, requiring adaptive control strategies to ensure stability and performance. This dissertation contributes to the advancement of adaptive motion planning and control solutions that enable quadrupedal robots to traverse unknown rough environments while tasked with transporting unknown payloads.
In the first project, a novel hierarchical planning and control framework for robust payload transportation by quadrupedal robots is developed. This framework integrates an adaptive model predictive control (AMPC) algorithm with a gradient-descent-based adaptive updating law applied to reduced-order locomotion (i.e., template) models. At the high level of the control hierarchy, an indirect adaptive law estimates unknown parameters of the reduced-order locomotion model under varying payloads, ensuring stability during trajectory planning. The optimal trajectories generated by the AMPC are then passed to a low-level and full-order nonlinear whole-body controller (WBC) for tracking. Extensive numerical investigations and hardware experiments on the A1 quadru[pedal robot validate the framework's capabilities, showcasing significant improvements in payload transportation on both flat and rough terrains compared to conventional MPC strategies. Specifically, the robot demonstrates proficiency in transporting unmodeled, unknown static payloads up to 109% of its own mass in experiments on flat terrains and 91% on rough experimental terrains. Moreover, the robot successfully manages dynamic payloads with 73% of its mass on rough terrains.
Adaptive controllers must also address external disturbances inherent in real-world environments. Therefore, the second project introduces a hierarchical planning and control scheme with an adaptive L1 nonlinear model predictive control (ANMPC) at the high level, which integrates nonlinear MPC (NMPC) with an L1 adaptive controller. The prescribed optimal state and control input profiles generated by the ANMPC are then fed to the low-level nonlinear WBC. This approach aims to stabilize locomotion gaits in the presence of parametric uncertainties and external disturbances. The proposed controller is analyzed to accommodate uncertainties and external disturbances. Comprehensive numerical simulations and experimental validations on the A1 quadrupedal robot demonstrate its effectiveness on rough terrains. Numerical results suggest that ANMPC significantly improves the stability of the gaits in the presence of uncertainties and external disturbances compared to NMPC and AMPC. The robot can carry payloads up to 109% of its own mass on its trunk on flat and rough terrains. Simulation results show that the robot achieves a maximum payload capacity of 26.3 (kg), which is equivalent to 211% of its own mass on rough terrains with uncertainties and disturbances.
Hotels' COVID-19 innovation and performance
Sharma, Abhinav; Shin, Hakseung; Santa-María, María Jesús; Nicolau, Juan Luis (Pergamon-Elsevier, 2021-02-25)
To navigate the unchartered terrain that has resulted from the pandemic, there is a palpable need for hotels to re-assess current business practices, and quickly devise new and innovative strategies that safeguard the health and safety of guests as well as employees and, consequently, restore consumer confidence. The objective of this article is to assess the utility of these new innovations by looking at shareholders' perceptions. The empirical application shows that the innovations implemented are seen as effective, although differential effects exist among innovation types. The results could help hotels sustain and expand the innovative responses that work (among which product innovations stand out), and discontinue those that are less effective.
Understanding the dynamics of the quality of airline service attributes: Satisfiers and dissatisfiers
Park, Sangwon; Lee, Jin-Soo; Nicolau, Juan Luis (Elsevier, 2020-06-05)
This research aims to determine the relationship between the quality of airline service attributes and overall satisfaction. Although a number of relevant studies have reported a linear relationship (or symmetric effect) between the two concepts, this work suggests that attribute quality exerts heterogeneous effects on satisfaction or dissatisfaction. A total of 157,035 consumer data from online reviews have been analyzed to achieve the research objective. In accordance with Herzberg, Mausner, and Snyderman's (1959) two-factor theory, the findings of this research have determined that the quality of certain service attributes, such as cleanliness, food and beverages, and in-flight entertainment, affects the variations of positive ratings as a satisfier. Other airline service attributes, such as customer service and check-in and boarding, influence the deviations of negative ratings as a dissatisfier. Apart from airline attributes, the individual features and types of airline products have been estimated to improve the understanding of such relationships. In this regard, this study provides important implications to customer-centric marketing in an airline marketplace.
mSphere of Influence: MmuPV1-a dual tropic papillomavirus, red herring, or novel insight into HPV pathogenesis
Romero-Masters, James (American Society for Microbiology, 2024-06-26)
James Romero-Masters works in the field of tumor virology, focusing on the role of the human papillomavirus oncogenes in pathogenesis. In this mSphere of Influence article, they reflect on how the article "Mouse papillomavirus infection persists in mucosal tissues of an immunocompetent mouse strain and progresses to cancer" impacted them, informing their research strategies, and what it means for the mouse papillomavirus model.
Telling the Extension Story: How to Tell a Good Story for Connection & Advocacy
Haugen, Inga (2024-04-25)
Storytelling for Connection and Advocacy, telling your personal and your professional Extension stories.