Nanotubes, such as boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs), exhibit excellent mechanical properties. In this work, high-quality BNNTs were synthesized by ball milling and annealing. Subsequently, w...Nanotubes, such as boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs), exhibit excellent mechanical properties. In this work, high-quality BNNTs were synthesized by ball milling and annealing. Subsequently, well-dispersed 3vol%BNNTs/Cu and 3vol%CNTs/Cu composites were successfully prepared using ball milling, spark plasma sintering, and followed by hot-rolling. Moreover, the mechanical properties and strengthening mechanisms of BNNTs/Cu and CNTs/Cu composites were compared and discussed in details. At 293 K,both BNNTs/Cu and CNTs/Cu composites exhibited similar ultimate tensile strength (UTS) of~404 MPa, which is approximately 170%higher than pure Cu. However, at 873 K, the UTS and yield strength of BNNTs/Cu are 27%and 29%higher than those of CNTs/Cu, respectively.This difference can be attributed to the stronger inter-walls shear resistance, higher thermomechanical stability of BNNTs, and stronger bonding at the BNNTs/Cu interface as compared to the CNTs/Cu interface. These findings provide valuable insights into the potential of BNNTs as an excellent reinforcement for metal matrix composites, particularly at high temperature.展开更多
Methods for measuring functional diversity are essential for functional studies of plant communities. A useful method, the PCA index, based on principal component analy- sis ordination of functional trait data was int...Methods for measuring functional diversity are essential for functional studies of plant communities. A useful method, the PCA index, based on principal component analy- sis ordination of functional trait data was introduced and applied to functional diversity analysis of Juglans mandshurica communities in the Beijing Mountains. Thirty-five 10 m×10 m quadrats were established in Juglans mandshurica communities. Species composition, functional traits and environmental factors were measured and recorded. The four common indices, FAD, MFAD, FDp and FDc, were used and compared with the PCA index in the analysis. The results showed that the PCA index was successful in quantifying functional diversity and describing its relationships with environmental variables; therefore, it was an effective index in functional diversity analyses. Functional diversity in Juglans mandshurica communities varied widely. Elevation and aspect were the key factors affecting functional diversity in communities. Functional diversity increased with elevation increases and with the change in aspect from North to South. Functional diversity was significantly correlated with species richness and heterogeneity.展开更多
As we know,thus far,there has appeared no definition of bilinear spectral multipliers on Heisenberg groups.In this article,we present one reasonable definition of bilinear spectral multipliers on Heisenberg groups and...As we know,thus far,there has appeared no definition of bilinear spectral multipliers on Heisenberg groups.In this article,we present one reasonable definition of bilinear spectral multipliers on Heisenberg groups and investigate its boundedness.We find some restrained conditions to separately ensure its boundedness from C0(H^(n))×L^(2)(H^(n))to L^(2)(H^(n)),from L2(H^(n))×C0(H^(n))to L^(2)(H^(n)),and from L^(p)×L^(q) to L^(r) with 2<p,q<∞,2≤r≤∞.展开更多
基金financially supported by the National Natural Science Foundation of China (No.52171144)。
文摘Nanotubes, such as boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs), exhibit excellent mechanical properties. In this work, high-quality BNNTs were synthesized by ball milling and annealing. Subsequently, well-dispersed 3vol%BNNTs/Cu and 3vol%CNTs/Cu composites were successfully prepared using ball milling, spark plasma sintering, and followed by hot-rolling. Moreover, the mechanical properties and strengthening mechanisms of BNNTs/Cu and CNTs/Cu composites were compared and discussed in details. At 293 K,both BNNTs/Cu and CNTs/Cu composites exhibited similar ultimate tensile strength (UTS) of~404 MPa, which is approximately 170%higher than pure Cu. However, at 873 K, the UTS and yield strength of BNNTs/Cu are 27%and 29%higher than those of CNTs/Cu, respectively.This difference can be attributed to the stronger inter-walls shear resistance, higher thermomechanical stability of BNNTs, and stronger bonding at the BNNTs/Cu interface as compared to the CNTs/Cu interface. These findings provide valuable insights into the potential of BNNTs as an excellent reinforcement for metal matrix composites, particularly at high temperature.
文摘Methods for measuring functional diversity are essential for functional studies of plant communities. A useful method, the PCA index, based on principal component analy- sis ordination of functional trait data was introduced and applied to functional diversity analysis of Juglans mandshurica communities in the Beijing Mountains. Thirty-five 10 m×10 m quadrats were established in Juglans mandshurica communities. Species composition, functional traits and environmental factors were measured and recorded. The four common indices, FAD, MFAD, FDp and FDc, were used and compared with the PCA index in the analysis. The results showed that the PCA index was successful in quantifying functional diversity and describing its relationships with environmental variables; therefore, it was an effective index in functional diversity analyses. Functional diversity in Juglans mandshurica communities varied widely. Elevation and aspect were the key factors affecting functional diversity in communities. Functional diversity increased with elevation increases and with the change in aspect from North to South. Functional diversity was significantly correlated with species richness and heterogeneity.
基金Supported by National Natural Science Foundation of China(11471040 and 11761131002)。
文摘As we know,thus far,there has appeared no definition of bilinear spectral multipliers on Heisenberg groups.In this article,we present one reasonable definition of bilinear spectral multipliers on Heisenberg groups and investigate its boundedness.We find some restrained conditions to separately ensure its boundedness from C0(H^(n))×L^(2)(H^(n))to L^(2)(H^(n)),from L2(H^(n))×C0(H^(n))to L^(2)(H^(n)),and from L^(p)×L^(q) to L^(r) with 2<p,q<∞,2≤r≤∞.
