In our earlier experiment, we observed intact force-control capabilities in individuals post-stroke during locomotion without postural influence. We sought to better understand the mechanisms underlying the interaction of locomotor and postural control and the role of postural control as an interactive mechanism that might interfere with appropriate foot-force generation. We designed an experiment in which subjects performed biomechanically-controlled locomotion, under posturally challenged pedaling while generating force outputs comparable to pedaling without postural challenge, thus allowing us to monitor the different strategies by the nervous system when postural conditions were manipulated. We hypothesized that with postural influence, individuals post-stroke will generate inappropriate shear forces accompanied by inappropriate coupling of muscle activity, and will be exaggerated with increased postural loading. Methods: Post-stroke (n=11) and non-impaired (n=5) individuals pedaled on a cycle ergometer under (1)seated, and (2)non-seated postural-loaded conditions, generating matched pedal normal force, with the motor-driven crank moving at 40rpm. Forces and EMG were recorded and analyzed offline. Results: During seated pedaling, we observed comparable shear pedal forces in both groups. During non-seated postural-loaded pedaling, we observed greater forward-directed shear forces in individuals post-stroke, but not in controls, which were exaggerated with increased postural loading. With postural influence, individuals post-stroke showed increased SOL and RF activities, whereas, in non-impaired controls we observed decreased VM, RF and BF activity. Conclusion: Reduced force-control capabilities during locomotion only when postural mechanisms were involved, suggests impaired interaction between locomotion and posture in the post-stroke nervous system. This inability to regulate postural loads may compromise the ability to adapt and react to changes in environmental conditions during walking, and could result in slips and falls.

Guided wave structural health monitoring (SHM) is being considered to assess the integrity of plate-like structures for many applications. Prior research has investigated how guided wave propagation is affected by applied loads, which induce anisotropic changes in both dimensions and phase velocity. In addition, it is well-known that applied tensile loads open fatigue cracks and thus enhance their detectability using ultrasonic methods. Here we describe load-differential methods in which signals recorded from different loads at the same damage state are compared without using previously obtained damage-free data. Changes in delay-and-sum images are considered as a function of differential loads and damage state. Load-differential features are extracted from these images that capture the effects of loading as fatigue cracks are opened. Damage detection thresholds are adaptively set based upon the load-differential behavior of the various features, which enables implementation of an automated fatigue crack detection process. The efficacy of the proposed approach is examined using data from a fatigue test performed on an aluminum plate specimen that is instrumented with a sparse array of surface-mounted ultrasonic guided wave transducers.

This paper presents an ultra-low power wireless strain sensor consuming about 9 mW. To achieve such a low power operation, a voltage-controlled oscillator (VCO) is utilized to convert the direct-current (DC) strain signal to a high frequency oscillatory signal. This oscillatory signal is then transmitted using an unpowered wireless transponder (Huang et al. 2011). A photocell based energy harvester was developed to power the wireless strain sensor. The energy harvested from a flash light placed at 65 cm away is sufficient to power the wireless strain sensor continuously. The implementation of the wireless strain sensor and its characterization are presented.