Mechanical and Electrical Properties of Direct Spun Carbon Nanotube Fibers Exposed to Ultrahigh Temperatures in Vacuum.

Carbon nanotube (CNT) fibers are promising reinforcements in ceramic matrix composites where the service environments involve extremely high temperatures that are generally beyond 1000 °C. This work focuses on the thermal stability of a direct spun CNT fiber in vacuum and in a wide temperature (25-2000 °C). The microstructure, mechanical and electrical properties of the fibers as a function of the heat-treatment temperature were investigated. The results show that high temperature exposure could increase the defect density and loosen the packing state of the fiber, but enhance the graphitization degree of the CNTs. Accordingly, there was a ductile-to-brittle transition in the uniaxial tensile response as the heat-treatment temperature increased, and this was mainly a consequence of the failure mode transitions from localized shear to defect dominant fracture. The tensile modulus was enhanced, but the tensile strength was decreased after the heat-treatment. The former can be explained by the enhanced graphitization degree of CNT and the latter should be a result of the increased defect density. Finally, the electrical property of the fiber was degraded, due to the increased contact resistance of mutual CNTs.

Increased concentration of sialidases by HeLa cells might influence the cytotoxic ability of NK cells.

OBJECTIVE: Cancer cells reportedly have the ability to escape from the immune system, mainly from natural killer (NK) cells. Although the real mechanisms are complicated, some inhibitors that are secreted from the cancer cells might play an important role. This study's aim was to investigate the potential mediator released by cancer cells (HeLa) that contributes to the decreased cytotoxicity of NK cells. METHODS AND MATERIALS: An NK-HeLa coculture system was used to test the hypothesis that the presence of the potential mediator from cancer cells contributes to the decreased cytotoxicity of NK cells. RESULTS: After coculturing with HeLa cancer cells, the cytotoxicity of NK cells was decreased. When the coculture medium and culture medium containing commercialized sialidase were used to culture NK cells, the cytotoxicity of the NK cells was also inhibited. However, cytotoxicity was partially restored by a sialidase inhibitor (DANA). Western blot analysis of the HeLa cells after coculturing with NK cells demonstrated increased Neu2 and Neu3 expression in HeLa cells. CONCLUSIONS: The finding that Neu2 and Neu3 expression in cancer cells might be involved in the impaired function of NK cells, which could be restored by a sialidase inhibitor, provides a new concept that could be applied to the management of cancer.