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Efficient stabilization strategies for polymeric materials are critical to guarantee them to withstand decades of service in multiple aggressive environments. Graphene oxide (GO) has been identified as a kind of promising antioxidant to improve the oxidative stability of polymers; however, a comprehensive understanding of the multifunctional stabilization mechanisms of GO for polymeric materials subjected to various weathering factors is still missing. Here, we explored the effect of the thermally reduced GO (TrGO) on the thermo‐ and photo‐oxidation of isotactic polypropylene (iPP), respectively. The addition of TrGO could simultaneously suppress the thermo‐ and photo‐oxidation of iPP, and the stabilization effects became stronger with increasing TrGO content. While similar carbonyl species were formed under both thermo‐oxidation and photo‐oxidation of iPP, the proportion of ketone was much higher under thermal‐oxidation. The incorporation of TrGO did not change the proportion of the degradation products under thermo‐oxidation; however, the proportion of lactone was risen under photo‐oxidation, suggesting a different degradation mechanism. Versatile stabilization mechanisms of TrGO were further revealed by UV–Vis spectroscopy and oxygen permeability tests, which were related to the extraordinary ability of TrGO in the block of UV light (deter), suppression of oxygen diffusion (delay), and scavenging of free radicals (defend). In this contribution, we clearly demonstrated different multifunctional and synergistic stabilization functions of TrGO for thermo‐ and photo‐oxidation respectively, which shall be useful for the practical design of next‐generation GO‐based stabilizers with superior efficiency. [ABSTRACT FROM AUTHOR]

Influences of silica nanoparticles on the microstructural evolution of polyamide 6 (PA6)/polystyrene (PS) blends with varying blend ratios were investigated in confined shear flow. Hydrophilic silica nanoparticles were found to promote the formation of PA6 strings with excellent shape stability during shearing. It was ascribed to the promoted coalescence of PA6 droplets induced both by the significantly increased droplet viscoelasticity and confinement, and the reduced interfacial tension by adding silica nanoparticles. Additionally, the width and aspect ratio of droplets obtained by experiments were compared with the predictions of Maffettone-Minale, Minale, Shapira-Haber, MMSH, and modified M models. Good agreements were found in the droplet width in blends with low nanoparticle concentrations, whereas the experimental aspect ratio showed a negative deviation to model predictions, which was attributed to the enhanced droplet viscoelasticity and the omitted droplet orientation angle in these models. © 2015 American Institute of Chemical Engineers AIChE J, 62: 564-573, 2016 [ABSTRACT FROM AUTHOR]

Muscle synergy is a fundamental mechanism of motor control. Despite a number of studies focusing on muscle synergy during power grip and pinch at high-level force, relatively less is known about the functional interactions between muscles within low-level force production during precision pinch. Traditional analytical tools such as nonnegative matrix factorization or principal component analysis have limitations in processing nonlinear dynamic electromyographic signals and have confined sensitivity particularly for the low-level force production. In this study, we developed a novel method - multiplex muscle networks, to investigate the dynamical coordination of muscle activities at low-level force production during precision pinch. The multiplex muscle network was constructed based on multiplex limited penetrable horizontal visibility graph (MLPHVG). Seven forearm and hand muscles, including brachioradialis (BR), flexor carpi ulnaris (FCU), flexor carpi radialis (FCR), flexor digitorum superficialis (FDS), extensor digitorum communis (EDC), abductor pollicis brevis (APB) and first dorsal interosseous (FDI), were examined using surface electromyography (sEMG). Eight healthy subjects were instructed to perform a visuomotor force tracking task by producing higher (10% MVC) and lower (1% MVC) precision pinch. Interlayer mutual information I, average edge overlap ω weighted clustering coefficient C W , weighted characteristic path length L W were selected as network metrics. We assessed the undirected weighted network generated from multiplex muscle network after taking the I between paired muscle network layers as edge. There are significant differences between higher and lower force level with higher I, ω, C W and lower L W at higher force level. Advanced efficiency of information processing in the regional and global perspective indicated dynamical alterations when human faces the higher force tracking task. It suggested that ω may be an important characteristic to classify different force control states with the average classification accuracy of 82.21%. These findings reveal related alterations of functional interactions between muscles involved in precision pinch. The novel method for constructing multiplex muscle network may provide insights into muscle synergies during precision pinch force control.

Precision grip requires accurate but dynamic control of the magnitude and direction of fingertip forces. It is still not well known whether directed information flow across activated cortical regions could change with different force outputs during precision grip. This study aimed to investigate the directed connectivity in large-scale brain networks for precision grip force control. Eight healthy volunteers participated in the experiment. Totally 32 channel electroencephalography (EEG) signals were recorded during a precision grip task that requires accurate force control following a dynamically changed visual target. The force target changed between 10% and 1% Maximal Voluntary Contraction (MVC). Horizontal visibility graph transfer entropy (HVG-TE) was used to measure the directed connectivity between pairs of EEG channels. In addition, the relative HVG-TE (rHVG-TE) was applied to evaluate the activation of each EEG channel. Results showed relatively higher rHVG-TE values in the posterior brain region but lower rHVG-TE values in the anterior brain region within the whole spectrum (4-70Hz), indicating a posterior-to-anterior information flow. This study revealed that the activation of posterior region is higher than the anterior region. There is a directed functional connectivity of cortex from posterior to anterior region for precision grip force control. This study shed light on how to quantify activation and large-scale connectivity of cortical regions, and reveal the in-depth central mechanisms for peripheral fine motor control.