Secondary radiation force can be an attractive force causing aggregates of encapsulated microbubbles in ultrasonic molecular imaging. The influence of the secondary radiation force on aggregation between two coated bu...Secondary radiation force can be an attractive force causing aggregates of encapsulated microbubbles in ultrasonic molecular imaging. The influence of the secondary radiation force on aggregation between two coated bubbles is investigated in this study. Numerical calculations are performed based on four simultaneous differential equations of radial and translational motions. Results show that the secondary force can change from attraction to repulsion during approach, and stable microbubble pairs can be formed in the vicinity of resonant regions; the possibility of microbubble aggregations can be reduced by using low exciting amplitude, ultrasonic frequencies deviating from the resonant frequencies or microbubbles with small compressibility.展开更多
This paper investiages the secondary Bjerknes force for two oscillating bubbles in various pressure amplitudes in a concentration of 95% sulfuric acid. The equilibrium radii of the bubbles are assumed to be smaller th...This paper investiages the secondary Bjerknes force for two oscillating bubbles in various pressure amplitudes in a concentration of 95% sulfuric acid. The equilibrium radii of the bubbles are assumed to be smaller than 10 μm at a frequency of 37 kHz in various strong driving acoustical fields around 2.0 bars （1 bar=10^5 Pa）. The secondary Bjerknes force is investigated in uncoupled and coupled states between the bubbles, with regard to the quasi-adiabatic model for the bubble interior. It finds that the value of the secondary Bjerknes force depends on the driven pressure of sulfuric acid and its amount would be increased by liquid pressure amplitude enhancement. The results show that the repulsion area of the interaction force would be increased by increasing the driven pressure because of nonlinear oscillation of bubbles.展开更多
背景:前交叉韧带重建后肌肉功能的恢复通常评估肌肉的最大力量,最近的研究认为还应考虑神经肌肉功能,比如肌肉等长发力率,即在肌肉等长收缩条件下测量不同时间间隔的力-时间曲线斜率。目的:阐述前交叉韧带重建后患者肌肉等长发力率的研...背景:前交叉韧带重建后肌肉功能的恢复通常评估肌肉的最大力量,最近的研究认为还应考虑神经肌肉功能,比如肌肉等长发力率,即在肌肉等长收缩条件下测量不同时间间隔的力-时间曲线斜率。目的:阐述前交叉韧带重建后患者肌肉等长发力率的研究现状与不足,分析术后不同时间内股四头肌和腘绳肌等长发力率的缺陷程度;等长发力率对术后患者功能表现的影响,为优化前交叉韧带重建后康复、减少患者二次损伤以及降低膝骨关节炎发生率提供重要信息。方法:检索中国知网、维普、万方和PubMed数据库,以“前交叉韧带,发力率”为中文检索词,以“anterior cruciate ligament,rate of force development,rate of torque development”为英文检索词,按照纳入和排除标准最终纳入69篇文献。结果与结论:(1)大多数研究发现前交叉韧带重建后半年内患者双侧肌肉等长发力率存在缺陷,双侧腘绳肌早期等长发力率(即肌肉收缩100 ms时间段内任意时间间隔的力-时间曲线斜率)在半年后有显著改善,但双侧股四头肌早期等长发力率长期缺陷,表明术后股四头肌神经肌肉功能长期受损。(2)有关晚期等长发力率(肌肉收缩100 ms后时间段内任意时间间隔的力-时间曲线斜率)的相关研究较少,无法得出确切结论。(3)关于着陆运动(跳跃落地和侧切等)和日常生活活动(走、跑),股四头肌早期等长发力率比等长峰值力矩相关性更强,运动过程中生物力学的异常改变被认为是患者二次损伤以及创伤性膝骨关节炎发生的重要风险因素,积极改善股四头肌早期等长发力率可能会降低二次损伤以及创伤性膝骨关节炎的发生率。(4)目前仅有很少的证据表明,全身振动训练能改善前交叉韧带重建后患者股四头肌早期等长发力率,建议今后在术后早期阶段应用神经肌肉电刺激干预股四头肌和腘绳肌,而在术后晚期阶段实施爆发力、高阻力训练,这可能会改善患者等长发力率。(5)短时间产生足够的肌肉力量才能有效保护前交叉韧带,而腘绳肌等长发力率与功能表现的关系尚不清楚,这可能会提供有关预防患者二次损伤的信息。(6)作者建议将等长发力率作为指导康复以及恢复运动的评估指标之一,除了关注对称性的改善以及与正常人的差异,还要考虑腘绳肌与股四头肌力量的比值,合适的比值范围才能保证肌肉快速发力时的平衡,这可能会降低再次损伤的发生,但比值的正常范围尚不清楚。(7)未来研究要考虑移植物类型和膝关节屈曲角度对等长发力率的影响,以尽可能找出患者存在的神经肌肉功能障碍,帮助患者更好地康复。展开更多
The secondary flow attracts wide concerns in the aeroengine compressors since it has become one of the major loss sources in modern high-performance compressors.But the research about the quantitative relationship bet...The secondary flow attracts wide concerns in the aeroengine compressors since it has become one of the major loss sources in modern high-performance compressors.But the research about the quantitative relationship between secondary flow and inviscid blade force needs to be more detailed.In this paper,a database of 889 three-dimensional linear cascades was built.An indicator,called Secondary Flow Intensity(SFI),was used to express the loss caused by secondary flow.The quantitative relationship between the SFI and inviscid blade force deterioration was researched.Blade oil flow and Computation Fluid Dynamics(CFD)results of some cascades were also used to cross-validate.Results suggested that all numerical cascade cases can be divided into 3 clusters by the SFI,which are called Clusters A,B and C in the order of the increasing SFI indicator.The corner stall,known as the strong corner separation,only happens when the SFI is high.Both calculations and oil flow experiments show that the SFI would stay at a low level if the vortex core at the endwall surface does not appear.The strong interaction of Kutta condition and endwall cross-flow is considered the dominant mechanism of higher secondary flow losses,rather than the secondary flow penetration depth on the suction surface.In conclusion,the inviscid blade force spanwise deterioration is strongly related to the SFI.The correlation of the SFI and spanwise inviscid blade force deterioration is given in this paper.The correlation could provide a quantitative reference for estimating secondary flow losses in the design.展开更多
基金supported by the National Basic Research Program of China(Grant No.2011CB707900)the National Natural Science Foundation of China(Grant Nos.10974093,11011130201,and 10904094)+2 种基金the Fundamental Research Funds for the Central Universities of China(Grant Nos.1103020402,1116020410,and 1112020401)the Prior Academic Program Development of Jiangsu Higher Education Institutions,Chinathe State key Laboratory of Acoustics of Ministry of Education,China
文摘Secondary radiation force can be an attractive force causing aggregates of encapsulated microbubbles in ultrasonic molecular imaging. The influence of the secondary radiation force on aggregation between two coated bubbles is investigated in this study. Numerical calculations are performed based on four simultaneous differential equations of radial and translational motions. Results show that the secondary force can change from attraction to repulsion during approach, and stable microbubble pairs can be formed in the vicinity of resonant regions; the possibility of microbubble aggregations can be reduced by using low exciting amplitude, ultrasonic frequencies deviating from the resonant frequencies or microbubbles with small compressibility.
基金Project supported by Sharif University of Technology
文摘This paper investiages the secondary Bjerknes force for two oscillating bubbles in various pressure amplitudes in a concentration of 95% sulfuric acid. The equilibrium radii of the bubbles are assumed to be smaller than 10 μm at a frequency of 37 kHz in various strong driving acoustical fields around 2.0 bars （1 bar=10^5 Pa）. The secondary Bjerknes force is investigated in uncoupled and coupled states between the bubbles, with regard to the quasi-adiabatic model for the bubble interior. It finds that the value of the secondary Bjerknes force depends on the driven pressure of sulfuric acid and its amount would be increased by liquid pressure amplitude enhancement. The results show that the repulsion area of the interaction force would be increased by increasing the driven pressure because of nonlinear oscillation of bubbles.
文摘背景:前交叉韧带重建后肌肉功能的恢复通常评估肌肉的最大力量,最近的研究认为还应考虑神经肌肉功能,比如肌肉等长发力率,即在肌肉等长收缩条件下测量不同时间间隔的力-时间曲线斜率。目的:阐述前交叉韧带重建后患者肌肉等长发力率的研究现状与不足,分析术后不同时间内股四头肌和腘绳肌等长发力率的缺陷程度;等长发力率对术后患者功能表现的影响,为优化前交叉韧带重建后康复、减少患者二次损伤以及降低膝骨关节炎发生率提供重要信息。方法:检索中国知网、维普、万方和PubMed数据库,以“前交叉韧带,发力率”为中文检索词,以“anterior cruciate ligament,rate of force development,rate of torque development”为英文检索词,按照纳入和排除标准最终纳入69篇文献。结果与结论:(1)大多数研究发现前交叉韧带重建后半年内患者双侧肌肉等长发力率存在缺陷,双侧腘绳肌早期等长发力率(即肌肉收缩100 ms时间段内任意时间间隔的力-时间曲线斜率)在半年后有显著改善,但双侧股四头肌早期等长发力率长期缺陷,表明术后股四头肌神经肌肉功能长期受损。(2)有关晚期等长发力率(肌肉收缩100 ms后时间段内任意时间间隔的力-时间曲线斜率)的相关研究较少,无法得出确切结论。(3)关于着陆运动(跳跃落地和侧切等)和日常生活活动(走、跑),股四头肌早期等长发力率比等长峰值力矩相关性更强,运动过程中生物力学的异常改变被认为是患者二次损伤以及创伤性膝骨关节炎发生的重要风险因素,积极改善股四头肌早期等长发力率可能会降低二次损伤以及创伤性膝骨关节炎的发生率。(4)目前仅有很少的证据表明,全身振动训练能改善前交叉韧带重建后患者股四头肌早期等长发力率,建议今后在术后早期阶段应用神经肌肉电刺激干预股四头肌和腘绳肌,而在术后晚期阶段实施爆发力、高阻力训练,这可能会改善患者等长发力率。(5)短时间产生足够的肌肉力量才能有效保护前交叉韧带,而腘绳肌等长发力率与功能表现的关系尚不清楚,这可能会提供有关预防患者二次损伤的信息。(6)作者建议将等长发力率作为指导康复以及恢复运动的评估指标之一,除了关注对称性的改善以及与正常人的差异,还要考虑腘绳肌与股四头肌力量的比值,合适的比值范围才能保证肌肉快速发力时的平衡,这可能会降低再次损伤的发生,但比值的正常范围尚不清楚。(7)未来研究要考虑移植物类型和膝关节屈曲角度对等长发力率的影响,以尽可能找出患者存在的神经肌肉功能障碍,帮助患者更好地康复。
基金the National Science and Technology Major Project,China(Nos.2017-I-0005-0006&2019-II-0020-0041).
文摘The secondary flow attracts wide concerns in the aeroengine compressors since it has become one of the major loss sources in modern high-performance compressors.But the research about the quantitative relationship between secondary flow and inviscid blade force needs to be more detailed.In this paper,a database of 889 three-dimensional linear cascades was built.An indicator,called Secondary Flow Intensity(SFI),was used to express the loss caused by secondary flow.The quantitative relationship between the SFI and inviscid blade force deterioration was researched.Blade oil flow and Computation Fluid Dynamics(CFD)results of some cascades were also used to cross-validate.Results suggested that all numerical cascade cases can be divided into 3 clusters by the SFI,which are called Clusters A,B and C in the order of the increasing SFI indicator.The corner stall,known as the strong corner separation,only happens when the SFI is high.Both calculations and oil flow experiments show that the SFI would stay at a low level if the vortex core at the endwall surface does not appear.The strong interaction of Kutta condition and endwall cross-flow is considered the dominant mechanism of higher secondary flow losses,rather than the secondary flow penetration depth on the suction surface.In conclusion,the inviscid blade force spanwise deterioration is strongly related to the SFI.The correlation of the SFI and spanwise inviscid blade force deterioration is given in this paper.The correlation could provide a quantitative reference for estimating secondary flow losses in the design.
