Biodegradable Zn alloy interference screws are promising for anterior cruciate ligament reconstruction.How-ever,previous in vitro studies not only predominantly focus on short-term(≤30 days)immersion,but also neglect...Biodegradable Zn alloy interference screws are promising for anterior cruciate ligament reconstruction.How-ever,previous in vitro studies not only predominantly focus on short-term(≤30 days)immersion,but also neglect influence of crevice corrosion in bone tunnel.This study develops a Zn-0.45Mn-0.2 Mg alloy with yield strength of 288.3 MPa,ultimate tensile strength of 325.4 MPa and elongation of 26.3%.The alloy is fabricated into screws,inserted into polyurethane bone blocks and immersed in Hank’s balanced salt solution for 180 days.The alloy degraded at a corrosion rate of 0.07 mm/y,with its yield strength and elongation eventually decreasing to 229 MPa and 4.3%,respectively.Second phase detachment during long-term corrosion reduces alloy’s surface fracture toughness(KIC)and increases stress intensity(KI)at corrosion pits.This causes premature fracture of the alloy(KI>KIC)and a larger decrease in the alloy’s ductility(70%)than that in strength(30%).Crevice corrosion of the screws originates deep within the bone tunnel and spreads outward over time.Accumulation of Clions exacerbates corrosion severity in the narrow thread tops of the screws.This study provides a foundation for quasi-equivalent in vitro studies of Zn alloy implants,and highlights the necessity of developing ductility-attenuation-resistant Zn alloys.展开更多
The input aggregation strategy can reduce the online computational burden of the model predictive controller. But generally aggregation based MPC controller may lead to poor control quality. Therefore, a new concept, ...The input aggregation strategy can reduce the online computational burden of the model predictive controller. But generally aggregation based MPC controller may lead to poor control quality. Therefore, a new concept, equivalent aggregation, is proposed to guarantee the control quality of aggregation based MPC. From the general framework of input linear aggregation, the design methods of equivalent aggre- gation are developed for unconstrained and terminal zero constrained MPC, which guarantee the actual control inputs exactly to be equal to that of the original MPC. For constrained MPC, quasi-equivalent aggregation strategies are also discussed, aiming to make the difference between the control inputs of aggregation based MPC and original MPC as small as possible. The stability conditions are given for the quasi-equivalent aggregation based MPC as well.展开更多
Based on the first part of this paper (Science in China, 33(1990), 982—995), further research has been done on quasi-equivalence relation and asymmetrical character of axisymmetrical phase-conjugatlon resonator(PCR)....Based on the first part of this paper (Science in China, 33(1990), 982—995), further research has been done on quasi-equivalence relation and asymmetrical character of axisymmetrical phase-conjugatlon resonator(PCR). A series of calculations for axisymmetrical PCR(hundreds of transverse modes in 66 axisymmetrical PCRs) have been carried out, and the results are compared with those of corresponding conventional laser resonators. Fundamental properties of the transverse modes (TEMs) in PCR are summarized. This makes possible a rough estimation of the properties of various TEMs in these simple PCR, including different geometrical structures.展开更多
基金Financial supports from National Natural Science Foundation of China(No.52231010)the project selected through the open competi-tion mechanism of Ministry of Industry and Information Technology of P.R.China(Biodegradable Zn alloys for interference screws in sports medicine,2023.09-2026.09)the Beijing Outstanding Young Sci-entist Program(JWZQ20240101016)are appreciated.
文摘Biodegradable Zn alloy interference screws are promising for anterior cruciate ligament reconstruction.How-ever,previous in vitro studies not only predominantly focus on short-term(≤30 days)immersion,but also neglect influence of crevice corrosion in bone tunnel.This study develops a Zn-0.45Mn-0.2 Mg alloy with yield strength of 288.3 MPa,ultimate tensile strength of 325.4 MPa and elongation of 26.3%.The alloy is fabricated into screws,inserted into polyurethane bone blocks and immersed in Hank’s balanced salt solution for 180 days.The alloy degraded at a corrosion rate of 0.07 mm/y,with its yield strength and elongation eventually decreasing to 229 MPa and 4.3%,respectively.Second phase detachment during long-term corrosion reduces alloy’s surface fracture toughness(KIC)and increases stress intensity(KI)at corrosion pits.This causes premature fracture of the alloy(KI>KIC)and a larger decrease in the alloy’s ductility(70%)than that in strength(30%).Crevice corrosion of the screws originates deep within the bone tunnel and spreads outward over time.Accumulation of Clions exacerbates corrosion severity in the narrow thread tops of the screws.This study provides a foundation for quasi-equivalent in vitro studies of Zn alloy implants,and highlights the necessity of developing ductility-attenuation-resistant Zn alloys.
基金Supported by the National Natural Science Foundation of China (Grant No. 60674041)the Specialized Research Fund for the Doctoral Program of Higher Education (Grant No. 20070248004)
文摘The input aggregation strategy can reduce the online computational burden of the model predictive controller. But generally aggregation based MPC controller may lead to poor control quality. Therefore, a new concept, equivalent aggregation, is proposed to guarantee the control quality of aggregation based MPC. From the general framework of input linear aggregation, the design methods of equivalent aggre- gation are developed for unconstrained and terminal zero constrained MPC, which guarantee the actual control inputs exactly to be equal to that of the original MPC. For constrained MPC, quasi-equivalent aggregation strategies are also discussed, aiming to make the difference between the control inputs of aggregation based MPC and original MPC as small as possible. The stability conditions are given for the quasi-equivalent aggregation based MPC as well.
文摘Based on the first part of this paper (Science in China, 33(1990), 982—995), further research has been done on quasi-equivalence relation and asymmetrical character of axisymmetrical phase-conjugatlon resonator(PCR). A series of calculations for axisymmetrical PCR(hundreds of transverse modes in 66 axisymmetrical PCRs) have been carried out, and the results are compared with those of corresponding conventional laser resonators. Fundamental properties of the transverse modes (TEMs) in PCR are summarized. This makes possible a rough estimation of the properties of various TEMs in these simple PCR, including different geometrical structures.
