压缩载荷下微缺损关节软骨流体场变化的数值分析

背景:长久以来关节软骨的力学研究以固相的变形为重心,间质流动的研究相对较少,而间质流动是维持软骨正常力学行为和生理功能的核心机制。目的:研究压缩载荷作用下微缺损关节软骨流体场的变化规律,为软骨损伤力学机制的完善提供理论依据。方法:建立微缺损的纤维增强多孔黏弹性的二维关节软骨数值模型,对压缩载荷作用下间质流动过程进行模拟和参数研究,获得微缺损关节软骨的流体场分布变化规律。结果与结论:压缩载荷下,缺损部位两侧底角处间质液压的增大,会增大此处的承载能力,阻止损伤向深处扩展,而缺损两侧间质液压的减小以及该处间质流动的加快,会促进缺损向两侧扩展;此外由于缺损部位两侧底角处的应力集中处与四周存在间质液压差,会使得缺损部位的间质液以应力集中处为中心向四周流动。此研究结果表明损伤软骨具有自我调节能力,能够延缓损伤加剧。

Analysis of the Influence of Type, Amount and Way of Introduction of Anti-foaming Admixture （AFA） on the Properties of Self-compacting Concrete （SCC） Mix

The properties of the self-compacting concrete mix depend on an automatic introduction of air bubbles caught during the process of mixing. What is interesting, the criterion for self-compactibility is not taken into consideration in commonly used self-compacting tests. On the basis of different tests concerning self-compacting concrete mixes, it has been found out that too high air content in their volume was the result of superplasticizer, in spite of meeting the self-compactibility criteria （i.e., self-venting）. For the decrease of too high air volume in SCC, the use of anti-foaming admixture （AFA） is proposed. As a result, the effect of AFA mix flow diameter is increased and the flow time is decreased. Moreover, the workability loss is lower. In case of mix incorporating AFA, their high flowability does not cause segregation of the mix, what is possible in case of SCC incorporating only superplasticizer. However, the time of the introduction of AFA and its type is essential to get higher flowability degree, but it is not important to achieve low air volume in SCC.

Bloodletting at Jing-well points decreases interstitial fluid flow in the thalamus of rats

OBJECTIVE：To investigate the changes in the neuronal microenvironment of the middle cerebral artery （MCA） territory induced by Jing-well points bloodletting acupuncture （WPBA） and to explore the neuroprotective mechanism of WPBA in stroke. METHODS： Adult male Sprague Dawley （n = 32） rats were randomly divided into four groups of eight animals each： WPBA-thalamus group （WT）, WPBA-caudate nucleus group （WC）, sham-control thalamus group （ST） and sham-control caudate nucleus group （SC）. Animals in the WT and WC groups received 2 I-μL of the extracellular tracer gadolinium-diethylene triamine pentaacetic acid （Gd-DTPA） injected into the thalamus or caudate nucleus, respectively, and 12 Jing-well points in the distal ends of the rats＇ digits were used for WPBA. Although 2 μL of Gd-DTPA was injected into the thalamus or caudate nucleus, respectively, for animals in the two sham groups （ST and SC）, no acupuncture or bloodletting was performed. Brain extracellular space and interstitial fluid flow parameters were measured using Gd-DTPA-enhanced magnetic reso- nance imaging. RESULTS： The brain interstitial fluid flow speed was decreased in the thalamus after WPBA, with a significantly lower Gd-DTPA clearance rate and longer half-life of Gd-DTPA in the thalamus of treated rats than those in sham-control rats [WPBA-treated rats＇clearance rate, （7.47 ± 3.15） x 10^-5/s （P = 0.009）; half-life, （1.52 ± 0.13） h, P = 0.000]. By contrast, no significant changes in brain extracellular space and interstitial fluid flow parameters were detected in the caudate nucleus after WPBA （P = 0.649）. In addi- tion, no differences in the morphology of the brain extracellular space or the final distribution of the traced brain interstitial fluid were demonstrated be- tween theWT and WC groups （P = 0.631, P = 0.970, respectively）. CONCLUSION： The WPBA decreased the speed of the local thalamic ISF flow in rats, which is assumed to be a beneficial protection by down-modulated the metabolic rate of the attacked neurons under stroke.

Low Speed Axial Compressor Stall Margin Improvement by Unsteady Plasma Actuation

This research investigates the use of single dielectric barrier discharge(SDBD) actuators for energizing the tip leakage flow to suppress rotating stall inception and extend the stable operating range of a low speed axial compressor with a single rotor.The jet induced by the plasma actuator adds momentum to the flow in the tip region and has a significant impact on the tip-gap flow.Experiments are carried out on a low speed axial compressor with a single rotor.The static pressure is measured at both the rotor inlet and outlet.The flow coefficient and pressure rise coefficient are calculated.Then the characteristic line is acquired to show the overall performance of the compressor.With unsteady plasma actuation of 18kV and 60W the compressor stability range improvement is realized at rotor speed of 1500 r/min – 2400 r/min.

A COMBINATORIAL PROPERTY OF PALLET-CONSTRAINED TWO MACHINE FLOW SHOP PROBLEM IN MINIMIZING MAKESPAN

We consider the problem of scheduling n jobs in a pallet-constrained flow shop so as to minimize the makespan.In such a flow shop environment,each job needs a pallet the entire time,from the start of its first operation until the completion of the last operation,and the number of pallets in the shop at any given time is limited by a positive integer,K≤n.Generally speaking,the optimal schedules may be passing schedules.In this paper,we present a combinatorial property which shows that for two machines,K(K≥3）pallets,there exists a no-passing schedule which is an optimal schedule for n≤2K-1 and 2K-1 is tight.