Interfacial behavior of phospholipid monolayers revealed by mesoscopic simulation

A mesoscopic model with molecular resolution is presented for dipalmitoyl phosphatidylcholine (DPPC) and pal-mitoyl oleoyl phosphatidylcholine (POPC) monolayer simulations at the air-water interface using many-body dissipative particle dynamics (MDPD). The parameterization scheme is rigorously based on reproducing the physical properties of water and alkane and the interfacial property of the phospholipid monolayer by comparison with experimental results. Using much less computing cost, these MDPD simulations yield a similar surface pressure-area isotherm as well as similar pressure-related morphologies as all-atom simulations and experiments. Moreover, the compressibility modulus, order parameter of lipid tails, and thickness of the phospholipid monolayer are quantitatively in line with the all-atom simulations and experiments. This model also captures the sensitive changes in the pressure-area isotherms of mixed DPPC/POPC monolayers with altered mixing ratios, indicating that the model is promising for applications with complex natural phospholipid monolayers. These results demonstrate a significant improvement of quantitative phospholipid monolayer simulations over previous coarse-grained models

热处理对铜基粉末冶金刹车片的摩擦性能的影响

本文对铜基粉末冶金刹车片进行热处理,首先利用销盘定速摩擦磨损试验机检验摩擦材料的短时摩擦学性能,同时通过SAE2台架试验研究实际工况下的长时接合摩擦性能。采用扫描电子显微镜(SEM)及维氏硬度实验分析了表面摩擦层热处理处理前后的微观结构和磨损形貌以及宏观硬度变化。结果表明,热处理试样摩擦区域表面相对光滑和平整,并未出现明显的犁沟状损伤;试样的宏观硬度增加,且硬度分布更均匀。动摩擦因数显著提高,且随时间的变化趋势更加平稳。这说明热处理对铜基摩擦层的短时摩擦性能以及实际工况下的长时摩擦性能有一定的改善

Deformation patterns in Zr-based and Ti-based metallic glasses under scratch processes

采用痕法研究了Zr_(47.9)Ti_(0.3)Ni_(3.1)Cu_(39.3)Al_(9.4)与Ti_(40)Zr_(25)Be_(30)Cr_5两种非晶合金的塑性变特征,考查了载荷与痕速度对塑性变特征的影响.结果表明两种铸态非晶合金样品的剪切带表现出同的特征:Ti非晶合金在痕两侧剪切带现分枝特征,随着载荷和痕速度的增加,出现多重分枝和混乱分特征;而Zr非晶合金的剪切带特征以一次剪切带为主,随载荷和痕速度增加,剪切带特征向单一、平滑趋势转变.进一研究了弛豫对Zr非晶合金痕变特征的影响,发现弛豫使Zr非晶合金剪切带向分枝特征转变.从自由体积观点探讨了两种合金中同剪切带特征的和演制

Machine learning assisted fast prediction of inertial lift in microchannels

Inertial effect has been extensively used in manipulating both engineered particles and biocolloids in microfluidic platforms. The design of inertial microfluidic devices largely relies on precise prediction of particle migration that is determined by the inertial lift acting on the particle. In spite of being the only means to accurately obtain the lift forces, direct numerical simulation (DNS) often consumes high computational cost and even becomes impractical when applied to microchannels with complex geometries. Herein, we proposed a fast numerical algorithm in conjunction with machine learning techniques for the analysis and design of inertial microfluidic devices. A database of inertial lift forces was first generated by conducting DNS over a wide range of operating parameters in straight microchannels with three types of cross-sectional shapes, including rectangular, triangular and semicircular shapes. A machine learning assisted model was then developed to gain the inertial lift distribution, by simply specifying the cross-sectional shape, Reynolds number and particle blockage ratio. The resultant inertial lift was integrated into the Lagrangian tracking method to quickly predict the particle trajectories in two types of microchannels in practical devices and yield good agreement with experimental observations. Our database and the associated codes allow researchers to expedite the development of the inertial microfluidic devices for particle manipulation

不同石墨含量铜基摩擦材料耐热特性及摩擦性能研究

针对铜基摩擦材料耐热性能不足导致的摩擦片服役寿命受限这一问题，采用粉末冶金方法压烧了3种不同质量分数石墨的摩擦材料试样，主要研究了石墨含量对材料耐热性能及摩擦磨损性能的影响及其作用机制。表面形貌分析表明，随着石墨含量的增加基体连续性先增加后降低；热分析结果表明，石墨含量对热学性能的主要影响在于因石墨过量产生的团聚现象导致的界面传热下降；摩擦磨损试验结果证实，随着石墨含量的增加，试样耐热性能明显提升，材料基体的强度得到增强，但是却导致试样磨损率及动摩擦因数上升