ABSTRACT
Acetylene production from mixed α-olefins emerges as a potentially green and energy-efficient approach with significant scientific value in the selective cleavage of C-C bonds. On the Pd(100) surface, it is experimentally revealed that C2 to C4 α-olefins undergo selective thermal cleavage to form surface acetylene and hydrogen. The high selectivity toward acetylene is attributed to the 4-fold hollow sites which are adept at severing the terminal double bonds in α-olefins to produce acetylene. A challenge arises, however, because acetylene tends to stay at the Pd(100) surface. By using the surface alloying methodology with alien Au, the surface Pd d-band center has been successfully shifted away from the Fermi level to release surface-generated acetylene from α-olefins as a gaseous product. Our study actually provides a technological strategy to economically produce acetylene and hydrogen from α-olefins.
ABSTRACT
In this study, a novel multi-walled carbon nanotubes reinforced nanocrystalline copper matrix composite with super high strength and moderate plasticity was synthesized. We successfully overcome the agglomeration problem of the carbon nanotubes and the grain growth problem of the nanocrystalline copper matrix by combined use of the electroless deposition and spark plasma sintering methods. The yield strength of the composite reach up to 692 MPa, which is increased by 2 and 5 times comparing with those of the nanocrystalline and coarse copper, respectively. Simultaneously, the plasticity of the composite was also significantly increased in contrast with that of the nanocrystalline copper. The increase of the density of the carbon nanotubes after coating, the isolation effect caused by the copper coating, and the improvement of the compatibility between the reinforcements and matrix as well as the effective control of the grain growth of the copper matrix all contribute to improving the mechanical properties of the composite. In addition, a new strengthening mechanism, i.e., the series-connection effect of the nanocrystalline copper grains introduced by carbon nanotubes, is proposed to further explain the mechanical behavior of the nanocomposite.
ABSTRACT
OBJECTIVE: To explore the protective effect of propofol on liver during hepatic ischemia/reperfusion injury (HIRI) and its mechanisms in patients undergoing liver surgery. METHODS: Eighteen patients who were scheduled for selective hepatic surgery were randomly divided into control group (n=9) and propofol treatment group (n=9). Changes of several parameters in plasma and effects of propofol on them were observed before liver ischemia, at end of ischemia and at reperfusion for 25 minutes, parameters of which included superoxide dismutase (SOD), xanthine oxidase (XO), lipid peroxide (LPO) and alanine aminotransferase (ALT) activity, and the ultrastructure changes in liver tissue were observed under electron microscope at 25 minutes after reperfusion. RESULTS: SOD activity decreased remarkably (P<0.01); XO activity, LPO concentration and ALT value increased significantly (P<0.01) during HIRI, and there were abnormal changes of the hepatic ultrastructure at 25 minutes after reperfusion. Afer treatment with propofol, the variation of all parameters were alleviated markedly (P<0.05 and P<0.01). CONCLUSION: Propofol has protective effects on HIRI by reducing oxygen free radical level and inhibiting lipid peroxidation after hepatic ischemia/reperfusion in patients undergoing liver cancer surgery.
