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Browsing by Author "Zhang, Zheng"

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    It's tricky: Rating alleviating maneuvers in cervical dystonia
    (Elsevier, 2020) Cisneros, Elizabeth; Stebbins, Glenn T.; Chen, Qiyu; Vu, Jeanne P.; Benadof, Casey N.; Zhang, Zheng; Barbano, Richard L.; Fox, Susan H.; Goetz, Christopher G.; Jankovic, Joseph; Jinnah, Hyder A.; Perlmutter, Joel S.; Adler, Charles H.; Factor, Stewart A.; Reich, Stephen G.; Rodriguez, Ramon; Severt, Lawrence L.; Stover, Natividad P.; Berman, Brian D.; Comella, Cynthia L.; Peterson, David A.; University of California San Diego; Rush University; University of Rochester; University of Toronto; University Health Network Toronto; Baylor College of Medicine; Emory University; Washington University (WUSTL); Mayo Clinic; University of Maryland Baltimore; Harvard University; Beth Israel Deaconess Medical Center; University of Alabama Tuscaloosa; Virginia Commonwealth University; Salk Institute
    Objectives: To investigate hypothesized sources of error when quantifying the effect of the sensory trick in cervical dystonia (CD) with the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS-2), test strategies to mitigate them, and provide guidance for future research on the sensory trick. Methods: Previous analyses suggested the sensory trick (or "alleviating maneuver", AM) item be removed from the TWSTRS-2 because of its poor clinimetric properties. We hypothesized three sources of clinimetric weakness for rating the AM: 1) whether patients were given sufficient time to demonstrate their AM; 2) whether patients' CD was sufficiently severe for detecting AM efficacy; and 3) whether raters were inadvertently rating the item in reverse of scale instructions. We tested these hypotheses with video recordings and TWSTRS-2 ratings by one "site rater" and a panel of five "video raters" for each of 185 Dystonia Coalition patients with isolated CD. Results: Of 185 patients, 23 (12%) were not permitted sufficient testing time to exhibit an AM, 23 (12%) had baseline CD too mild to allow confident rating of AM effect, and 1 site- and 1 video-rater each rated the AM item with a reverse scoring convention. When these confounds were eliminated in step-wise fashion, the item's clinimetric properties improved. Conclusions: The AM's efficacy can contribute to measuring CD motor severity by addressing identified sources of error during its assessment and rating. Given the AM's sensitive diagnostic and potential pathophysiologic significance, we also provide guidance on modifications to how AMs can be assessed in future CD research.
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    Static and dynamic characteristics of membrane wings at low Reynolds number
    (University of Alabama Libraries, 2014) Zhang, Zheng; Hubner, James Paul; University of Alabama Tuscaloosa
    To lessen the deterioration of fixed-wing aerodynamic performance associated with Reynolds numbers (Re) below 100,000, flexible membrane wing designs have been studied and proposed as an alternative for micro air vehicle (MAV) use. The beneficial effects of a flexible membrane can include higher lift, steeper lift-curve slope, delayed stall, gentle stall characteristics, and greater efficiency. These benefits have been attributed to both the time-averaged and dynamic deformation of the membrane. The background literature search shows that few investigations regarding membrane wings have focused on low aspect ratio (AR) wings (AR < 2) with a free (or unattached) trailing edge (TE), where the spanwise flow over the wing surface is dominant. Additionally, no study has looked at introducing membrane vibration at the leading edge (LE), which could potentially improve the aerodynamic performance by reducing the LE separation for the thin airfoil. Therefore, this work discusses the static and dynamic characteristics of a simplified membrane wing and airfoil configuration in the low Re flow (Re = 40,000 - 70,000). The global aerodynamic forces on the free TE membrane wing with varying wing AR, cell AR, and pre-strain level were measured. The result shows that the aerodynamic advantages of the flexible membrane are retained for the low AR wings. The optimal membrane cell AR is found to be approximately one. The comparison of the aerodynamic forces between the low AR membrane wings and the corresponding 3D- printed wings with the time-averaged deformation indicates the importance of membrane dynamic motion for the derived aerodynamic benefits. The effect of LE vibration was studied by performing wake velocity profile scans and aerodynamic load measurements on a spanwise tensioned, tip-bounded membrane cell. The LE vibration increased the lift coefficient in pre-stall region, but also resulted in a deeper wake, greater momentum loss, and less peak aerodynamic efficiency and power efficiency. Because the aerodynamic benefits by the membrane are attributed to the static and dynamic characteristics, the nondimensional deformation scaling and frequency scaling are proposed. For the stiff membrane, as the aerodynamic-induced strain is small, the membrane deflection can be reasonably predicted using a wave equation with a constant tension. For the flexible membrane, the trend of aerodynamic-induced strain with respect to dynamic pressure and angle-of-attack is qualitatively predicted using a catenary curve model. Compared with the traditional Strouhal scaling, the proposed nondimensional frequency scaling with the linear combination of applied strain and aerodynamic-induced strain better characterizes the fluid-structure interaction.