arXiv subjects

Ali Yawar

Publications and source records attributed to Ali Yawar.

3 recordsLinked to original sources

arXiv2025

Non-invasive load measurement in the human tibia via spectral analysis of flexural waves

Forces transmitted by bones are routinely studied in human biomechanics, but it is challenging to measure them non-invasively, especially outside of laboratory settings. We introduce a technique for non-invasive, in vivo measurement of tibial compressive force using flexural waves propagating in the tibia. Modelling the tibia as an axially compressed Euler-Bernoulli beam, we show that tibial flexural waves have load-dependent frequency spectra. Specifically, under physiological conditions, peak locations in the wave acceleration spectra vary linearly with the compressive force on the tibia and may be used as proxies for the compressive force. We test the validity of this technique using a proof-of-concept wearable system that generates flexural waves via a skin-mounted mechanical transducer and measures the spectra of these waves using a skin-mounted accelerometer. In agreement with beam theory, data from 9 participants demonstrate linear relationships between tibial compressive force and spectral peak location, with Pearson correlation coefficients $r=0.82 - 0.99$ (mean $r=0.93$) for medial-lateral swaying and $r=0.81 - 0.98$ (mean $r=0.93$) for walking trials. This flexural wave-based technique could give rise to a new class of wearable sensors for non-invasive physiological bone load monitoring and measurement, impacting research in human locomotion and sports medicine.

q-bio.QM↗

arXiv2017

Transverse contributions to the longitudinal stiffness of the human foot

Humans rely on foot stiffness to withstand the propulsive forces of walking and running. Skeletal adaptations that increase foot stiffness include the medial longitudinal arch (MLA) and the transverse tarsal arch (TTA). The TTA has been hypothesized to stiffen the foot through cross-axis coupling of transverse intermetatarsal stiffness with sagittal-plane midfoot stiffness, but this has been tested only in cadaveric specimens. In vivo testing is essential because muscle contraction substantially modulates MLA function and may similarly affect the TTA's cross-axis coupling. Here we provide in vivo evidence for the TTA's contribution to foot stiffness by externally increasing intermetatarsal stiffness and measuring its effects on midfoot elasticity during walking. As predicted by the cross-axis coupling hypothesis, increasing intermetatarsal stiffness with an elastic tape wrapped around the forefoot reduced the energy absorbed in midfoot flattening and increased sagittal-plane midfoot stiffness concomitantly (mean,$\pm$,standard error of the mean (SEM): $13.9\% \pm 3\%$ and $16.8\% \pm 5.8\%$, respectively). However, taping did not change the curvature of the TTA, thereby isolating the effects of cross-axis coupling from morphological changes to the TTA. Thus, forefoot taping modulates midfoot stiffness through cross-axis coupling and could provide a non-invasive means to manage pathological foot flexibility or enhance athletic performance.

physics.bio-ph↗

arXiv2017

On angled bounce-off impact of a drop impinging on a flowing soap film

Small drops impinging angularly on thin flowing soap films frequently demonstrate the rare emergence of bulk elastic effects working in-tandem with the more common-place hydrodynamic interactions. Three collision regimes are observable: (a) drop piercing through the film, (b) it coalescing with the flow, and (c) it bouncing off the film surface. During impact, the drop deforms along with a bulk elastic deformation of the film. For impacts that are close-to-tangential, the bounce-off regime predominates. We outline a reduced order analytical framework assuming a deformable drop and a deformable three-dimensional film, and the idealization invokes a phase-based parametric study. Angular inclination of the film and the ratio of post and pre impact drop sizes entail the phase parameters. We also perform experiments with vertically descending droplets impacting against an inclined soap film, flowing under constant pressure head. Model predicted phase domain for bounce-off compares well to our experimental findings. Additionally, the experiments exhibit momentum transfer to the film in the form of shed vortex dipole, along with propagation of free surface waves. On consulting prior published work, we note that for locomotion of water-walking insects using an impulsive action, the momentum distribution to the shed vortices and waves are both significant, taking up respectively 2/3-rd and 1/3-rd of the imparted streamwise momentum. In view of the potentially similar impulse actions, this theory is applied to the bounce-off examples in our experiments, and the resultant shed vortex dipole momenta are compared to the momenta computed from particle imaging velocimetry data. The magnitudes reveal identical order ($10^{-7}$ N$\cdot$s), suggesting that the bounce-off regime can be tapped as a simple analogue for interfacial bio-locomotion relying on impulse reactions.

physics.flu-dyn↗