The thermal behavior, miscibility, crystallite conformation and thermal stability ofcrosslinked(CL-) PVA/PVP blends were studied by DSC and TG methods, respectively. DSCresults showed that in the blend, the crystallin...The thermal behavior, miscibility, crystallite conformation and thermal stability ofcrosslinked(CL-) PVA/PVP blends were studied by DSC and TG methods, respectively. DSCresults showed that in the blend, the crystallinity,T_m and T_c of PVA were obviously lower thanthose of pure PVA; the crystal growth changed from three dimensional to two dimensional andonly a single T_g was detected. These facts demonstrated that this crystalline and amorphousblend have good miscibility. TG curves showed that providing the quantity of K_2S_2O_8 added ismore than 3 wt%,in the blends PVA will form a stable CL-network, whose thermal degradationtemperature was near to that of PVP. But crosslinking reaction will not take place for PVP. Theprocesses of thermal degradation of CL-blends are based on combining both the thermaldegradation of PVP and that of PVA crosslinked with corresponding quantity of K_2S_2O_8 CL-agent, respectively. The UV measurements showed that 75 wt% of PVP may be remained in CL-blend hydrogelscrosslinked by adding (3--5 wt% )K_2S_2O_8. This is mainly due to the stable CL-network formed and the good compatibility and properentanglement between the composites in the CL-blends.展开更多
Safety monitoring and stability analysis of high slopes are important for high dam construction in high mountainous regions or precipitous gorges. In this paper, deformation characteristics of toppling block at upper ...Safety monitoring and stability analysis of high slopes are important for high dam construction in high mountainous regions or precipitous gorges. In this paper, deformation characteristics of toppling block at upper abutment, deforming tensile rip wedge in the middle part and deep fractures are comprehensively analyzed based on the geological conditions, construction methods and monitoring results of left abutment slope in Jinping Ⅰ hydropower station. Safety analyses of surface and shallow-buried rock masses and the corresponding anchorage system are presented. The monitoring results indicate that the global stability of the large wedge block in the left abutment is effectively under control, and the abutment slope is stable in a global sense. After the completion of excavation, the deformations of toppling block at the top of the slope and deep fracture zone continue at a very low rate, which can be explained as 'rock mass creep'. Further monitoring and analysis are needed.展开更多
Small-diameter ZnO nanorods with lengths of 35-50 nm were synthesized by solvothermal treatment route at low temperature(70℃)for 48,96 and 144 hours using polyvinylpyrrolidone(PVP)as stabilizing agent.The optical ban...Small-diameter ZnO nanorods with lengths of 35-50 nm were synthesized by solvothermal treatment route at low temperature(70℃)for 48,96 and 144 hours using polyvinylpyrrolidone(PVP)as stabilizing agent.The optical band gap energy of nanorods was calculated by Tauc’s approximation,obtaining values of 3.30-3.21 eV.By X-ray diffraction(XRD)it was determined that ZnO samples crystallize in Wurtzite hexagonal structure and present changes in lattice parameters.Also XRD patterns reveal a preferential growth of ZnO nanostructures along the plane with Miller indices(002).Stabilization process of ZnO nanoparticles and nanorods was studied by Fourier-transform infrared(FT-IR)spectroscopy,determining that the presence of amide group in polymer structure confers the ability to interact electrostatically with ZnO nanostructures surface.FT-IR results revealed that O and N atoms of amide group interact strongly with the surface of ZnO nanostructures.The length/diameter ratio of ZnO nanorods at 48 and 96 hours of reflux was 2.3 and 2.7,respectively.展开更多
文摘The thermal behavior, miscibility, crystallite conformation and thermal stability ofcrosslinked(CL-) PVA/PVP blends were studied by DSC and TG methods, respectively. DSCresults showed that in the blend, the crystallinity,T_m and T_c of PVA were obviously lower thanthose of pure PVA; the crystal growth changed from three dimensional to two dimensional andonly a single T_g was detected. These facts demonstrated that this crystalline and amorphousblend have good miscibility. TG curves showed that providing the quantity of K_2S_2O_8 added ismore than 3 wt%,in the blends PVA will form a stable CL-network, whose thermal degradationtemperature was near to that of PVP. But crosslinking reaction will not take place for PVP. Theprocesses of thermal degradation of CL-blends are based on combining both the thermaldegradation of PVP and that of PVA crosslinked with corresponding quantity of K_2S_2O_8 CL-agent, respectively. The UV measurements showed that 75 wt% of PVP may be remained in CL-blend hydrogelscrosslinked by adding (3--5 wt% )K_2S_2O_8. This is mainly due to the stable CL-network formed and the good compatibility and properentanglement between the composites in the CL-blends.
文摘Safety monitoring and stability analysis of high slopes are important for high dam construction in high mountainous regions or precipitous gorges. In this paper, deformation characteristics of toppling block at upper abutment, deforming tensile rip wedge in the middle part and deep fractures are comprehensively analyzed based on the geological conditions, construction methods and monitoring results of left abutment slope in Jinping Ⅰ hydropower station. Safety analyses of surface and shallow-buried rock masses and the corresponding anchorage system are presented. The monitoring results indicate that the global stability of the large wedge block in the left abutment is effectively under control, and the abutment slope is stable in a global sense. After the completion of excavation, the deformations of toppling block at the top of the slope and deep fracture zone continue at a very low rate, which can be explained as 'rock mass creep'. Further monitoring and analysis are needed.
文摘Small-diameter ZnO nanorods with lengths of 35-50 nm were synthesized by solvothermal treatment route at low temperature(70℃)for 48,96 and 144 hours using polyvinylpyrrolidone(PVP)as stabilizing agent.The optical band gap energy of nanorods was calculated by Tauc’s approximation,obtaining values of 3.30-3.21 eV.By X-ray diffraction(XRD)it was determined that ZnO samples crystallize in Wurtzite hexagonal structure and present changes in lattice parameters.Also XRD patterns reveal a preferential growth of ZnO nanostructures along the plane with Miller indices(002).Stabilization process of ZnO nanoparticles and nanorods was studied by Fourier-transform infrared(FT-IR)spectroscopy,determining that the presence of amide group in polymer structure confers the ability to interact electrostatically with ZnO nanostructures surface.FT-IR results revealed that O and N atoms of amide group interact strongly with the surface of ZnO nanostructures.The length/diameter ratio of ZnO nanorods at 48 and 96 hours of reflux was 2.3 and 2.7,respectively.
文摘目的 :探讨坚固内固定 ( RIF)技术用于 Le Fort 型截骨固定的优越性。方法 :利用头影测量技术对家兔模型进行术后骨稳定性的定量分析。结果 :通过头影测量发现 ,用 RIF固定的家兔上颌骨位置在术后 2个月时没有明显改变 ( P>0 .0 5)。结论 :RIF用于 L e Fort 型截骨骨间固定 。
