Closed-Loop Force Control by Biorealistic Hand Prosthesis With Visual and Tactile Sensory Feedback.

The ability of a novel biorealistic hand prosthesis for grasp force control reveals improved neural compatibility between the human-prosthetic interaction. The primary purpose here was to validate a virtual training platform for amputee subjects and evaluate the respective roles of visual and tactile information in fundamental force control tasks. We developed a digital twin of tendon-driven prosthetic hand in the MuJoCo environment. Biorealistic controllers emulated a pair of antagonistic muscles controlling the index finger of the virtual hand by surface electromyographic (sEMG) signals from amputees' residual forearm muscles. Grasp force information was transmitted to amputees through evoked tactile sensation (ETS) feedback. Six forearm amputees participated in force tracking and holding tasks under different feedback conditions or using their intact hands. Test results showed that visual feedback played a predominant role than ETS feedback in force tracking and holding tasks. However, in the absence of visual feedback during the force holding task, ETS feedback significantly enhanced motor performance compared to feedforward control alone. Thus, ETS feedback still supplied reliable sensory information to facilitate amputee's ability of stable grasp force control. The effects of tactile and visual feedback on force control were subject-specific when both types of feedback were provided simultaneously. Amputees were able to integrate visual and tactile information to the biorealistic controllers and achieve a good sensorimotor performance in grasp force regulation. The virtual platform may provide a training paradigm for amputees to adapt the biorealistic hand controller and ETS feedback optimally.

Somatotopically Evoked Tactile Sensation via Transcutaneous Electrical Nerve Stimulation Improves Prosthetic Sensorimotor Performance.

Sensory feedback provides critical interactive information for the effective use of hand prostheses. Non-invasive neural interfaces allow convenient access to the sensory system, but they communicate a limited amount of sensory information. This study examined a novel approach that leverages a direct and natural sensory afferent pathway, and enables an evoked tactile sensation (ETS) of multiple digits in the projected finger map (PFM) of participants with forearm amputation non-invasively. A bidirectional prosthetic interface was constructed by integrating the non-invasive ETS-based feedback system into a commercial prosthetic hand. The pressure information of five fingers was encoded linearly by the pulse width modulation range of the buzz sensation. We showed that simultaneous perception of multiple digits allowed participants with forearm amputation to identify object length and compliance by using information about contact patterns and force intensity. The ETS enhanced the grasp-and-transport performance of participants with and without prior experience of prosthetic use. The functional test of transport-and-identification further revealed improved execution in classifying object size and compliance using ETS-based feedback. Results demonstrated that the ETS is capable of communicating somatotopically compatible information to participants efficiently, and improves sensory discrimination and closed-loop prosthetic control. This non-invasive sensory interface may establish a viable way to restore sensory ability for prosthetic users who experience the phenomenon of PFM.

Precision Control of Fingertip Force by a Biorealistic Hand with a Pair of Neuromorphic Muscles.

In this paper, the ability of precision control of fingertip forces was investigated in an antagonistic cable-driven prosthetic hand with neuromorphic twin of muscles. Surface electromyography (sEMG) signals collected from able-bodied subjects' forearm were processed and used as alpha motor commands to drive the neuromorphic muscle models. A pair of antagonistic muscles were cascaded by two servo motors to control the index finger. Force control performance was tested by pressing a spring with a fixed stiffness using the fingertip, where forces with varying target levels were regulated with visual feedback. Two able-bodied subjects performed the precision force control task with the prosthetic index finger by sEMG signals and the intact hand. One subject was tested with force level changes of 0.1N, and another subject with force level changes of 0.2N. The ability of force regulation by the prosthetic finger was compared to that of the intact finger. Results showed that the overall root-mean-squares (RMS) error of the prosthetic finger was low, although significantly higher than the intact finger, 75% higher in subject 1 and 57% in subject 2. However, the correlation coefficient between the forces of prosthetic finger and intact finger was high, 75% for subject 1 and 84% for subject 2, respectively. This preliminary study is encouraging, illustrating the feasibility of accurate and stable control of different levels of fingertip forces by the prosthetic finger, which is comparable to that of the intact finger. This capability may allow the prosthetic hand for fine manipulation tasks, such as grasping brittle objects, or response to object slip during grasp.Clinical Relevance-This work attempts to restore the ability of a prosthetic hand for precision fingertip force control that may enrich the functionality for users in activities of daily living.

Comprehensive Assessment of Pollution Sources and Health Impacts in Suburban Area of Shanghai.

Shanghai, one of China's largest metropolises, faces significant environmental pollution challenges due to rapid economic development. Suburban areas of Shanghai are affected by both long-distance transport and local sources of pollutants. This study conducted an integrated analysis that links health-risk assessment of heavy metals and source apportionment of atmospheric constituents to distinguish the contributions of emission sources and the major sources of health risks. Source-apportionment analysis revealed that secondary sources had the greatest contribution to the local pollutants, indicating the significant influence of peripheral and long-distance transport. Health-risk assessment of Cr, Ni, As, and Cd revealed that local residents were exposed to respiratory health risks, in which Cr is the major contributor. This health risk was primarily associated with emissions from nearby industry-related sources. Our study highlights the significant effects of both long-distance transport and local source emissions on atmospheric composition and human health in large urban agglomerations. The findings can inform future efforts to develop more precise emission-reduction strategies and policy improvements to mitigate environmental pollution and protect public health.

Exposure and health risk assessment of PM2.5-bound polycyclic aromatic hydrocarbons during winter at residential homes: A case study in four Chinese cities.

Residential indoor PM2.5 were concurrently collected in Hong Kong, Guangzhou, Shanghai, and Xi'an during the winter and early spring seasons of 2016-2017, for updating the current knowledge of the spatial variation of indoor air pollution and the potential health risks in China. PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) were characterized, and the associated inhalation cancer risks were assessed by a probabilistic approach. Higher levels of indoor PAHs were identified in Xi'an residences (averaged at 176.27 ng m-3) with those of other cities ranging from 3.07 to 15.85 ng m-3. Traffic-related fuel combustion was identified as a common contributor to indoor PAHs through outdoor infiltration for all investigated cities. Indoor PAHs profiles showed city-specific differences, while distinctions between profiles based on indoor activities or ambient air quality were limited. Similar with the total PAHs concentrations, the estimated toxic equivalencies (TEQ) with reference to benzo[a]pyrene in Xi'an residences (median at 18.05 ng m-3) were above the recommended value of 1 ng m-3 and were magnitudes higher than the other investigated cities with estimated median TEQ ranging from 0.27 to 1.55 ng m-3. Incremental lifetime cancer risk (ILCR) due to PAHs inhalation exposure was identified with a descending order of adult (median at 8.42 × 10-8) > adolescent (2.77 × 10-8) > children (2.20 × 10-8) > senior (1.72 × 10-8) for different age groups. Considering the lifetime exposure-associated cancer risk (LCR), potential risks were identified for residents in Xi'an as an LCR level over 1 × 10-6 was identified for half of the adolescent group (median at 8.96 × 10-7), and exceedances were identified for about 90 % of the groups of adults (10th percentile at 8.29 × 10-7) and seniors (10th percentile at 1.02 × 10-6). The associated LCR estimated for other cities were relatively insignificant.

Sliding nanomechanical resonators.

The motion of a vibrating object is determined by the way it is held. This simple observation has long inspired string instrument makers to create new sounds by devising elegant string clamping mechanisms, whereby the distance between the clamping points is modulated as the string vibrates. At the nanoscale, the simplest way to emulate this principle would be to controllably make nanoresonators slide across their clamping points, which would effectively modulate their vibrating length. Here, we report measurements of flexural vibrations in nanomechanical resonators that reveal such a sliding motion. Surprisingly, the resonant frequency of vibrations draws a loop as a tuning gate voltage is cycled. This behavior indicates that sliding is accompanied by a delayed frequency response of the resonators, making their dynamics richer than that of resonators with fixed clamping points. Our work elucidates the dynamics of nanomechanical resonators with unconventional boundary conditions, and offers opportunities for studying friction at the nanoscale from resonant frequency measurements.

Antagonistic Control of a Cable-Driven Prosthetic Hand with Neuromorphic Model of Muscle Reflex.

In this paper, a novel prototype of a cable-driven prosthetic hand with biorealisitic muscle property was developed. A pair of antagonistic muscles controlled the flexion and extension of the prosthetic index finger. Biorealistic properties of muscle were emulated using a neuromorphic model of muscle reflex in real time. The model output was coupled to a servo motor that tracked the computed muscle force. The servo motor was able to track model output within a frequency range from 0 to 8.29 (Hz) with a phase shift from 2 to 205 (deg). Surface electromyography signals collected from the amputee's forearm were used as α commands to drive the muscle model. With this prototype system, we evaluated its characteristics for force and stiffness control. Results of the force variability test showed that the standard deviation of fingertip force was linear to the mean fingertip force, indicating that force variability was proportional to the background force. At different levels of antagonistic co-contraction, the index finger and muscles displayed different levels of stiffness corresponding to the degree of co-activation. This prototype system showed the similar compliant behaviors of human limbs actuated with biological muscles. In further studies, this prototype system would be thoroughly evaluated for its biorealistic properties, and integrated with sensors to investigate feedback strategies of various sensory information for individuals with amputation. Clinical Relevance- This article established an antagonistic control of a cable-driven prosthetic hand with biorealistic properties of muscle reflex for application to individuals with amputation.

Increased contribution to PM2.5 from traffic-influenced road dust in Shanghai over recent years and predictable future.

Traffic contributes to fine particulate matter (PM2.5) in the atmosphere through engine exhaust emissions and road dust generation. However, the evolution of traffic related PM2.5 emission over recent years remains unclear, especially when various efforts to reduce emission e.g., aftertreatment technologies and high emission standards from China IV to China V, have been implemented. In this study, hourly elemental carbon (EC), a marker of primary engine exhaust emissions, and trace element of calcium (Ca), a marker of road dust, were measured at a nearby highway sampling site in Shanghai from 2016 to 2019. A random forest-based machine learning algorithm was applied to decouple the influences of meteorological variables on the measured EC and Ca, revealing the deweathered trend in exhaust emissions and road dust. After meteorological normalization, we showed that non-exhaust emissions, i.e., road dust from traffic, increased their fractional contribution to PM2.5 over recent years. In particular, road dust was found to be more important, as revealed by the deweathered trend of Ca fraction in PM2.5, increasing at 6.1% year-1, more than twice that of EC (2.9% year-1). This study suggests that while various efforts have been successful in reducing vehicular exhaust emissions, road dust will not abate at a similar rate. The results of this study provide insights into the trend of traffic-related emissions over recent years based on high temporal resolution monitoring data, with important implications for policymaking.

Slower than expected reduction in annual PM2.5 in Xi'an revealed by machine learning-based meteorological normalization.

To evaluate the effectiveness of air pollution control policies, trend analysis of the air pollutants is often performed. However, trend analysis of air pollutants over multiple years is complicated by the fact that changes in meteorology over time can also affect the levels of air pollutants in addition to changes in emissions or atmospheric chemistry. To decouple the meteorological effect, this study performed a trend analysis of the hourly fine particulate matter (PM2.5) observed at an urban background site in Xi'an city over 5 years from 2015 to 2019 using the machine learning algorithm. As a novel way of meteorological normalization, the meteorological parameters were used as constant input for 5 consecutive years. In this way, the impact of meteorological parameters was excluded, providing insights into the "real" changes in PM2.5 due to changes in emission strength or atmospheric chemistry. After meteorological normalization, a decreasing trend of -3.3 % year-1 (-1.9 µg m-3 year-1) in PM2.5 was seen, instead of -4.4 % year-1 from direct PM2.5 observation. Assuming the rate of -1.9 µg m-3 year-1 were kept constant for the next few decades in Xi'an, it would take approximately 25 years (in the year 2045) to reduce the annual PM2.5 level to 5 µg m-3, the new guideline value from World Health Organization. We also show that PM2.5 is primarily associated with anthropogenic emissions, which, underwent aqueous phase chemistry in winter and photochemical oxidation in summer as suggested by partial dependence of RH and Ox in different seasons. Therefore, reducing the anthropogenic secondary aerosol precursors at a higher rate, such as NOx and VOCs is expected to reduce the particulate pollution in this region more effectively than the current -3.3 % year-1 found in this study.

A Biorealistic Computational Model Unfolds Human-Like Compliant Properties for Control of Hand Prosthesis.

Objective: Human neuromuscular reflex control provides a biological model for a compliant hand prosthesis. Here we present a computational approach to understanding the emerging human-like compliance, force and position control, and stiffness adaptation in a prosthetic hand with a replica of human neuromuscular reflex. Methods: A virtual twin of prosthetic hand was constructed in the MuJoCo environment with a tendon-driven anthropomorphic hand structure. Biorealistic mathematic models of muscle, spindle, spiking-neurons and monosynaptic reflex were implemented in neuromorphic chips to drive the virtual hand for real-time control. Results: Simulation showed that the virtual hand acquired human-like ability to control fingertip position, force and stiffness for grasp, as well as the capacity to interact with soft objects by adaptively adjusting hand stiffness. Conclusion: The biorealistic neuromorphic reflex model restores human-like neuromuscular properties for hand prosthesis to interact with soft objects.