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Synthetic fibers are adopted to mix with conventional steel fibers (SF) for ultra-high performance concrete (UHPC) to improve chemical resistance and reduce self-weight. Polyoxymethylene fiber (POMF), as a type of lightweight, high-strength, corrosion-resistant synthetic fiber, is expected to replace SF generally used in UHPC. Due to the obvious difference of mechanical properties between POMF and SF, different POMF/SF hybrid ratios may affect the dynamic compression behavior of UHPC. To investigate the dynamic mechanical behavior of hybrid POMF/SF reinforced UHPC (HUHPC), axial compression and split Hopkinson pressure bar (SHPB) tests with strain rate from 40 to 170 s−1 of HUHPC were conducted. The fiber volume fraction was fixed at 3% and four different POMF/SF hybrid ratios (0:3, 1:2, 2:1, 3:0) were adopted. The effects of hybrid POMF/SF ratios on the dynamic compressive properties of HUHPC, including dynamic compressive strength, dynamic elastic modulus, dynamic increase factor (DIF), and impact toughness were discussed. The results show that HUHPC exhibits obvious strain rate sensitivity under impact loading. With the increase of strain rate, the dynamic compressive strength, dynamic elastic modulus, DIF and impact toughness of HUHPC increased. Based on the linear assumption of fiber volume fraction and dynamic compressive strength enhancement of UHPC, the calculated dynamic compressive strength of HUHPC is lower than the experimental values. As the strain rate increases, the propagation path of microcrack transforms from interface of fiber-matrix to penetrating the fiber, resulting in plastic deformation of SF and fracture of POMF, consuming a large amount of impact energy and improving the impact toughness resistance of HUHPC.

Background/purpose: To investigate nerve excitability changes in patients with fibromyalgia and the correlation with clinical severity. Methods: We enrolled 20 subjects with fibromyalgia and 22 sex and age-matched healthy subjects to receive nerve excitability test and nerve conduction study to evaluate the peripheral axonal function. Results: In the fibromyalgia cohort, the sensory axonal excitability test revealed increased superexcitability (%) (P = 0.029) compared to healthy control. Correlational study showed a negative correlation between increased subexcitability (%) (r = −0.534, P = 0.022) with fibromyalgia impact questionnaire (FIQ) score. Computer modeling confirmed that the sensory axon excitability pattern we observed in fibromyalgia cohort was best explained by increased Barrett–Barrett conductance, which was thought to be attributed to paranodal fast K+ channel dysfunction. Conclusion: The present study revealed that paranodal sensory K+ conductance was altered in patients with fibromyalgia. The altered conductance indicated dysfunction of paranodal fast K+ channels, which is known to be associated with the generation of pain.