An in-situ TiCp/Al composite was prepared by a thermal explosion/quick pressure method （TE/QP）. The effect of Al content on the reaction temperature as well as the reaction rate has been studied. Phase constituents ...An in-situ TiCp/Al composite was prepared by a thermal explosion/quick pressure method （TE/QP）. The effect of Al content on the reaction temperature as well as the reaction rate has been studied. Phase constituents and the microstructure of the composites and the particle size of the reinforcement were analysed using X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results have shown that TiCp/Al composite with 40～70 vol. pct TiC particle reinforcement and high relative density can be directly obtained by TE/QP. TiC is the only reaction product when Al content in Al-Ti-C system is no more than 60 vol. pct, but Al3Ti phase will also form when Al content is more than 60 vol. pct. Increasing Al content prolongs the initial reaction time, reduces the highest reaction temperature and the reaction rate, and decreases the size of TiC particles. In addition, the microstructure of TiCp/Al composite and the structure of interface between TiCp and Al are studied using SEM and transmission electron microscopy （TEM）. The results show that the in-situ synthesized TiC particle has fcc cubic structure. The orientation between TiC particles and Al matrix can be described as （220）Al//（022）TiC and [112]Al//[011]TiC. Results of the mechanical property tests reveal that the ultimate strength （σ） and modulus （E） are 687 MPa and 142 GPa respectively when the Al content is 40 vol. pct. On contrary, 6 elongation increases by 3.2% with increasing Al content.展开更多
Background To investigate the relationship of age at first separation from parents(AFSP)with suicidal ideation(SI),suicide planning(SP)and suicide attempts(SA)among left-behind children(LBC)in China and the mediating ...Background To investigate the relationship of age at first separation from parents(AFSP)with suicidal ideation(SI),suicide planning(SP)and suicide attempts(SA)among left-behind children(LBC)in China and the mediating effect of traumatic events(TEs).Methods This cross-sectional study employed a multistage sampling method to conduct questionnaire surveys in six high-concentrated LBC provinces.Logistic regression and restricted cubic splines were performed to investigate the association of AFSP with SI,SP and SA,and meta-analysis(I2)was used to assess the heterogeneity.Causal mediation analysis(structural equation modelling)was used to evaluate the mediating effect of TEs,and bootstrap resampling was employed to assess the robustness of the causal mediation analysis.Results A total of 12162(6269 LBC)participants were included in this study;the prevalence rates of SI,SP and SA among LBC were 30.7%,18.6%and 11.9%;and LBC had a higher risk of SI(OR:1.32),SP(OR:1.40)and SA(OR:1.25)than non-LBC,all p<0.001.AFSP was negatively associated with SI,SP and SA,particularly peaking before 2 years old.LBC with AFSP<2 years old had a higher risk of SI(OR 2.65;95%CI 2.17 to 3.24;p<0.001),SP(OR 2.63;95%CI 3.36 to 4.29;p<0.001)and SA(OR 2.04;95%CI 2.73 to 3.63;p<0.001).TEs mediated the increased risk of SI(average causal mediation effect(ACME)0.03–0.07;proportion(Prop)40–54%;all p<0.001),SP(ACME 0.03–0.06;Prop 39–61%;all p<0.001)and SA(ACME 0.02–0.04;Prop 53–80%;all p<0.01).Conclusions We found that AFSP was associated with SI,SP and SA,mediated by TEs.Our findings supported the necessity of reducing SI,SP and SA risks among LBC and highlighted the need to consider AFSPs and TEs in intervention strategies.展开更多
文摘An in-situ TiCp/Al composite was prepared by a thermal explosion/quick pressure method （TE/QP）. The effect of Al content on the reaction temperature as well as the reaction rate has been studied. Phase constituents and the microstructure of the composites and the particle size of the reinforcement were analysed using X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results have shown that TiCp/Al composite with 40～70 vol. pct TiC particle reinforcement and high relative density can be directly obtained by TE/QP. TiC is the only reaction product when Al content in Al-Ti-C system is no more than 60 vol. pct, but Al3Ti phase will also form when Al content is more than 60 vol. pct. Increasing Al content prolongs the initial reaction time, reduces the highest reaction temperature and the reaction rate, and decreases the size of TiC particles. In addition, the microstructure of TiCp/Al composite and the structure of interface between TiCp and Al are studied using SEM and transmission electron microscopy （TEM）. The results show that the in-situ synthesized TiC particle has fcc cubic structure. The orientation between TiC particles and Al matrix can be described as （220）Al//（022）TiC and [112]Al//[011]TiC. Results of the mechanical property tests reveal that the ultimate strength （σ） and modulus （E） are 687 MPa and 142 GPa respectively when the Al content is 40 vol. pct. On contrary, 6 elongation increases by 3.2% with increasing Al content.
基金supported by the National Social Science Fund of China(NSSFC)(Grant No 20BSH066,JZ).
文摘Background To investigate the relationship of age at first separation from parents(AFSP)with suicidal ideation(SI),suicide planning(SP)and suicide attempts(SA)among left-behind children(LBC)in China and the mediating effect of traumatic events(TEs).Methods This cross-sectional study employed a multistage sampling method to conduct questionnaire surveys in six high-concentrated LBC provinces.Logistic regression and restricted cubic splines were performed to investigate the association of AFSP with SI,SP and SA,and meta-analysis(I2)was used to assess the heterogeneity.Causal mediation analysis(structural equation modelling)was used to evaluate the mediating effect of TEs,and bootstrap resampling was employed to assess the robustness of the causal mediation analysis.Results A total of 12162(6269 LBC)participants were included in this study;the prevalence rates of SI,SP and SA among LBC were 30.7%,18.6%and 11.9%;and LBC had a higher risk of SI(OR:1.32),SP(OR:1.40)and SA(OR:1.25)than non-LBC,all p<0.001.AFSP was negatively associated with SI,SP and SA,particularly peaking before 2 years old.LBC with AFSP<2 years old had a higher risk of SI(OR 2.65;95%CI 2.17 to 3.24;p<0.001),SP(OR 2.63;95%CI 3.36 to 4.29;p<0.001)and SA(OR 2.04;95%CI 2.73 to 3.63;p<0.001).TEs mediated the increased risk of SI(average causal mediation effect(ACME)0.03–0.07;proportion(Prop)40–54%;all p<0.001),SP(ACME 0.03–0.06;Prop 39–61%;all p<0.001)and SA(ACME 0.02–0.04;Prop 53–80%;all p<0.01).Conclusions We found that AFSP was associated with SI,SP and SA,mediated by TEs.Our findings supported the necessity of reducing SI,SP and SA risks among LBC and highlighted the need to consider AFSPs and TEs in intervention strategies.
