Miombo woodlands near human settlements are under significant pressures from human activities,with negative consequences on their structure and composition.As studies are limited,we assessed the structure and species ...Miombo woodlands near human settlements are under significant pressures from human activities,with negative consequences on their structure and composition.As studies are limited,we assessed the structure and species composition of a portion of miombo woodland along an increasing disturbance gradient from a national park,through a buffer zone to communal lands in northeast Zimbabwe.Five concentric plots of 2 and 11 m radii were established in each area to record woody species composition,diameter,height,basal area,density and volume as well as evidence of disturbance.Effects of site,growth stage and their interaction on vegetation diversity and structural parameters were tested using a general linear model(GLM).Principal component analysis(PCA) tested the association between species and site and ANOVA the differences in the level of disturbance across strata.Species diversity did not differ between sites except for evenness,which increased with disturbance.Evenness and richness were greater in seedlings and saplings than mature trees across sites,respectively.Sapling and mature tree diameters differed significantly between sites.Volume and density of mature trees declined with increasing disturbance while seedling densities peaked at intermediate disturbance levels(buffer zone).Tree harvesting,was more evident in the buffer zone and in the communal area relative to the national park.In contrast,fire frequency was greater in the national park and in the buffer zone relative to the communal area.The results of this study identify a true miombo woodland dominated by Brachystegia boehmii with a stable population,as illustrated by an inverse-J shape in diameter class distribution on all sites,and that these woodlands are generally resilient to disturbances,maintaining similar species composition and structure at various levels of disturbance.However,continued monitoring of disturbance levels and miombo woodland response is recommended to ensure sustainable utilisation of these resources.展开更多
With assistance of Mo interlayer, joining of Cf/SiC composite to GH783 superalloy was carried out using NiPdPtAu-Cr filler alloy. Under the brazing condition of 1200 C for 10 min, the maximum joint strength of 98.5 MP...With assistance of Mo interlayer, joining of Cf/SiC composite to GH783 superalloy was carried out using NiPdPtAu-Cr filler alloy. Under the brazing condition of 1200 C for 10 min, the maximum joint strength of 98.5 MPa at room temperature was achieved when the thickness of Mo interlayer was 0.5 mm. Furthermore, the corresponding joint strength tested at 800 ℃ and 900℃ was even elevated to 123.8 MPa and 133.0 MPa, respectively. On one hand, the good high-temperature joint strength was mainly attributed to the formation of the refractory Mo-Ni-Si ternary compound within the joint. On the other hand, the residual Mo interlayer as a hard buffer, can release the residual thermal stresses within the dissimilar joint. The Cf/SiC-Mo bonding interface was still the weak link over the whole joint, and the cracks propagated throughout the whole reaction zone between the Cf/SiC composite and the Mo interlayer.展开更多
Theinvestigation of physicometallurgicalphenomena forthe CC formingof WCP/ Fe Ccom posites wasperformed. Resultsshow that underthe patentcondition, WCP/ Fe Ccomposite surfacelayerof16 20 m m heavycross sectio...Theinvestigation of physicometallurgicalphenomena forthe CC formingof WCP/ Fe Ccom posites wasperformed. Resultsshow that underthe patentcondition, WCP/ Fe Ccomposite surfacelayerof16 20 m m heavycross sectioncan beacquiredintheoutsideofa hollow cylin der. The surface of CTC particlescould be partially dissolved by Fe containing melt. Thefineshortstick like WCcrystallitesarein situseparated neartothesurfaceof CTC particles.Far from the CTC particles,someseparated, finetungsten carbidecrystallitesand Fe, W,Mo and Cretc. containing web composite carbides, are distributed on the matrix of WCP/ Fe Ccomposite. Fe Calloy matrix of the hollow composite cylinder is alloyed in differenthigh levels.展开更多
Urchin-like Sn–ZnO–C composite have been successfully prepared by thermal annealing of ZnSn(OH)6precursor in acetylene/argon gas(1/9;v/v).The phase of the urchin-like Sn–ZnO–C has been characterized by X-ray diffr...Urchin-like Sn–ZnO–C composite have been successfully prepared by thermal annealing of ZnSn(OH)6precursor in acetylene/argon gas(1/9;v/v).The phase of the urchin-like Sn–ZnO–C has been characterized by X-ray diffraction(XRD)and Raman spectrum.The images of scanning electron microscopy(SEM)and transmission electron microscope(TEM)demonstrate that the Sn–ZnO–C composite with an average of 3 lm in diameter is composed of many core–shell nanowires and carbon nanotubes emanated from the center.The thermal annealing temperature and time have crucial effects on the formation of urchin-like structure and carbon content of the Sn–ZnO–C composites.As an anode for lithium-ion batteries,the urchin-like Sn–ZnO–C composite delivers a discharge capacity of 1,034.5 mAh/g in initial cycle and 571.9 mAh/g reversible discharge capacity after 25 cycles at a current density of 50 mA/g.The superior energy storage properties highlight the urchin-like Sn–ZnO–C composite as a potential alternative anode material in lithium-ion batteries.展开更多
文摘Miombo woodlands near human settlements are under significant pressures from human activities,with negative consequences on their structure and composition.As studies are limited,we assessed the structure and species composition of a portion of miombo woodland along an increasing disturbance gradient from a national park,through a buffer zone to communal lands in northeast Zimbabwe.Five concentric plots of 2 and 11 m radii were established in each area to record woody species composition,diameter,height,basal area,density and volume as well as evidence of disturbance.Effects of site,growth stage and their interaction on vegetation diversity and structural parameters were tested using a general linear model(GLM).Principal component analysis(PCA) tested the association between species and site and ANOVA the differences in the level of disturbance across strata.Species diversity did not differ between sites except for evenness,which increased with disturbance.Evenness and richness were greater in seedlings and saplings than mature trees across sites,respectively.Sapling and mature tree diameters differed significantly between sites.Volume and density of mature trees declined with increasing disturbance while seedling densities peaked at intermediate disturbance levels(buffer zone).Tree harvesting,was more evident in the buffer zone and in the communal area relative to the national park.In contrast,fire frequency was greater in the national park and in the buffer zone relative to the communal area.The results of this study identify a true miombo woodland dominated by Brachystegia boehmii with a stable population,as illustrated by an inverse-J shape in diameter class distribution on all sites,and that these woodlands are generally resilient to disturbances,maintaining similar species composition and structure at various levels of disturbance.However,continued monitoring of disturbance levels and miombo woodland response is recommended to ensure sustainable utilisation of these resources.
基金sponsored by the National Natural Science Foundation of China (Grant Nos. 59905022, 50475160 and 51275497)Aeronautical Science Foundation of China (Grant No. 2008 ZE21005)
文摘With assistance of Mo interlayer, joining of Cf/SiC composite to GH783 superalloy was carried out using NiPdPtAu-Cr filler alloy. Under the brazing condition of 1200 C for 10 min, the maximum joint strength of 98.5 MPa at room temperature was achieved when the thickness of Mo interlayer was 0.5 mm. Furthermore, the corresponding joint strength tested at 800 ℃ and 900℃ was even elevated to 123.8 MPa and 133.0 MPa, respectively. On one hand, the good high-temperature joint strength was mainly attributed to the formation of the refractory Mo-Ni-Si ternary compound within the joint. On the other hand, the residual Mo interlayer as a hard buffer, can release the residual thermal stresses within the dissimilar joint. The Cf/SiC-Mo bonding interface was still the weak link over the whole joint, and the cracks propagated throughout the whole reaction zone between the Cf/SiC composite and the Mo interlayer.
文摘Theinvestigation of physicometallurgicalphenomena forthe CC formingof WCP/ Fe Ccom posites wasperformed. Resultsshow that underthe patentcondition, WCP/ Fe Ccomposite surfacelayerof16 20 m m heavycross sectioncan beacquiredintheoutsideofa hollow cylin der. The surface of CTC particlescould be partially dissolved by Fe containing melt. Thefineshortstick like WCcrystallitesarein situseparated neartothesurfaceof CTC particles.Far from the CTC particles,someseparated, finetungsten carbidecrystallitesand Fe, W,Mo and Cretc. containing web composite carbides, are distributed on the matrix of WCP/ Fe Ccomposite. Fe Calloy matrix of the hollow composite cylinder is alloyed in differenthigh levels.
基金supported by the National Natural Science Foundation of China (91022033 and 21201158)the National Basic Research Program of China (2011CB935901)+1 种基金Anhui Provincial Natural Science Foundation (1208085QE101)the Fundamental Research Funds for the Central Universities (WK 2340000027)
文摘Urchin-like Sn–ZnO–C composite have been successfully prepared by thermal annealing of ZnSn(OH)6precursor in acetylene/argon gas(1/9;v/v).The phase of the urchin-like Sn–ZnO–C has been characterized by X-ray diffraction(XRD)and Raman spectrum.The images of scanning electron microscopy(SEM)and transmission electron microscope(TEM)demonstrate that the Sn–ZnO–C composite with an average of 3 lm in diameter is composed of many core–shell nanowires and carbon nanotubes emanated from the center.The thermal annealing temperature and time have crucial effects on the formation of urchin-like structure and carbon content of the Sn–ZnO–C composites.As an anode for lithium-ion batteries,the urchin-like Sn–ZnO–C composite delivers a discharge capacity of 1,034.5 mAh/g in initial cycle and 571.9 mAh/g reversible discharge capacity after 25 cycles at a current density of 50 mA/g.The superior energy storage properties highlight the urchin-like Sn–ZnO–C composite as a potential alternative anode material in lithium-ion batteries.
