Crown evolution kinematics of a camellia oil droplet impacting on a liquid layer

The phenomenon of droplet impact on an immiscible liquid is encountered in a variety of scenarios in nature and industrial production. Despite exhaustive research, it is not fully clear how the immiscibility of the liquid on which a droplet impacts affects the crown evolution. The present work experimentally investigates the evolution kinematics of a crown formed by the normal impact of a camellia oil droplet on an immiscible water layer. Based on discussion of dynamic impact behaviors for three critical Weber numbers (We), the radius of the crown and its average spreading velocity are compared with those of previous theoretical models to discuss their applicability to the immiscible liquid. The evolution kinematics (morphology and velocity) are analyzed by considering the effects of the We and layer thickness. Furthermore, the ability of crown expansion in radial and vertical directions is characterized by a velocity ratio. The results show that our experimental crown radius still follows a square-root function of evolution time, which agrees with the theoretical predictions. The dimensionless average spreading velocity decreases with We and follows a multivariate power law, while the dimensionless average rising velocity remains constant. The velocity ratio is shown to linearly increase with We, demonstrating that the rising movement in crown evolution gradually enhances with We. These results are helpful for further investigation on the droplet impact on an immiscible liquid layer.     

纳米流体液滴撞击壁面铺展动力学特性研究

纳米流体液滴撞击固体壁面的铺展动力学特性是基于液滴沉积实现高效传热传质过程的关键因素,然而由于纳米流体的非牛顿流变特性及液滴内微流动与纳米颗粒的耦合作用,目前对纳米流体液滴撞击固体壁面的铺展动力学行为缺乏足够的认识.本研究利用了两步法分别配制了分散有3种纳米颗粒的均匀稳定纳米流体(碳纳米管、石墨烯、纳米石墨粉),并对流体的流变特性进行了测量分析.利用显微高速数码摄像技术捕捉了液滴撞击固体壁面的动态过程,通过图像处理技术分析铺展过程中液滴的无量纲高度、铺展因子及动态接触角,探究了液滴在韦伯数约为200及800时撞击壁面后铺展沉积形态的演变规律.研究表明,3种不同纳米颗粒的加入均使基液表现出明显的剪切变稀特性,在液滴撞击壁面的铺展过程中,流体的剪切黏度起重要作用,液滴的无量纲高度和铺展因子的变化幅度随着纳米流体剪切黏度的增大而减小.纳米流体液滴撞击疏水表面时能更快的达到平衡状态,液滴的惯性力主导着液滴的初始铺展阶段,液滴的铺展范围和速度随撞击速度的增大而增大.开展该研究能够为基于液滴沉积的增益冷却技术以及微型高导热及导电材料的制造提供理论依据和技术指导.      

正电子冲击下氦电离三重微分截面的理论计算

我们发展了一种正电子碰撞原子电离的畸变波Born近似方法， 在这个方法中，正负电子偶素通道通过一个ab initio的光学势附加到入射粒子和靶的相互作用势上，且通道对电离作用被第一次被考虑在正电子碰撞原子电离的过程中. 应用这个方法计算了在50 eV入射能量范围氦的电离的三重微分截面，计算结果和实验数据很好的符合.     

Experimental investigation of hydrodynamic loads and pressure distribution during a pyramid water entry

In the maritime environment slamming is a phenomenon known as short duration impact of water on a floating or sailing structure. Slamming loads are local and could induce very high local stresses. This paper reports a series of impact test results and investigate the slamming loads and pressures acting on a square based pyramid. In this study the slamming tests have been conducted at constant velocity impact with a hydraulic high speed shock machine. This specific experimental equipment avoids the deceleration of the structure observed usually during water entry with drop tests. Three velocities of the rigid pyramid have been used (10, 13 and 15 m s⁻¹). Time-histories of local pressures, accelerations and slamming loads were successfully measured. The relationship between the pressure magnitude and the impact velocity is obtained and the spatial distribution of pressures on pyramid sides is characterized. The impact velocity was found to have a negligible influence in predicting the maximum pressure coefficient.     

Enhanced interfacial adhesion between PMMA and carbon fiber by graphene oxide coating

The purpose of this study is to increase the interfacial properties in PMMA/carbon fiber (PMMA/CF) composites Graphene oxide (GO) and brached polyethyleneimine were coated onto the surface of carbon fiber by layer-by-layer assembly in this work. Compared with the origin PMMA/CF composite, the composites reinforced by PMMA/CF–GO showed significant enhancement in interFacial shear strength (IFSS). The improved fiber–matrix adhesion was proved by fracture morphology observation of scanning electron microscopy and almost unaffected mechanical properties of the fiber itself during the coating process. The optimal assembly time was found to be 10 for enhancing the overall composite mechanical performance.     

轴向冲击载荷下薄壁折纹管的屈曲模态与吸能

在方管的基础上引入折纹结构, 利用几何关系建立折纹管的折角公式。采用LS-DYNA软件研究了6种折纹管在轴向冲击下的屈曲模态与能量吸收性能, 并与方管进行对比分析。结果表明, 折纹管在冲击载荷作用下屈曲变形过程可分为3个阶段, 初始峰值阶段、稳定渐进屈曲阶段和密实化阶段。折角是影响初始峰值载荷和平均载荷的重要因素之一, 折纹结构的引入有效的降低了初始峰值载荷, 减小了冲击力的波动幅度; 折纹管的比吸能低于方管, 但是在特定折角下, 折纹管的压缩力效率和比总体效率高于方管。     

REBOUNDING OF GALILEAN CANNON FROM A RIGID WALL1)

研究了Galilean炮——即若干个直径递增的弹性球组成的球链---撞击刚性壁回弹的问题。采用三种力学模型：分离刚体的多次"弹性"碰撞、多刚体的接触碰撞、以及有限元模拟，对球链撞击问题进行了分析，旨在给出碰撞结束后末端小球的飞离速度与入射速度的比值。研究表明：球链碰撞反弹后将会散开，末端小球的飞离速度明显大于球链入射速度；当入射球链间存在间隙时，末端小球的速度增幅更加明显。通过实验展现了这种末端小球回弹速度增加的现象。     

Logging damage and injured tree mortality in tropical forest management

Using insights from the forest ecology literature, we analyze the effect of injured trees on stand composition and carbon stored in above‐ground biomass and the implications for forest management decisions. Results from a Faustmann model with data for a tropical forest on Kalimantan show that up to 50% of the basal area of the stand before harvest can consist of injured trees. Considering injured trees leads to an increase in the amount of carbon in above‐ground biomass of up to 165%. These effects are larger under reduced impact logging than under conventional logging. The effects on land expectation value and cutting cycle are relatively small. The results suggest that considering injured trees in models for tropical forest management is important for the correct assessment of the potential of financial programs to store carbon and conserve forest ecosystem services in managed tropical forests, such as reducing emissions from deforestation and forest degradation and payment for ecosystem services. Recommendations for Resource Managers

• Considering the role of injured trees is important for managing tropical forests
• These trees can cover up to 50% of basal area and contain more than 50% of the carbon stored in above‐ground biomass
• Reduced impact logging leads to a larger basal area of injured trees and more carbon stored in injured trees than conventional logging
• Injured trees play an important role when assessing the potential for carbon storage in the context of payment for forest ecosystem services.

     

BrCN分子的电子碰撞离子对解离

离子对解离是一类重要的分子过程，常发生于分子被激发到超激发态. 与光激发的离子对解离实验研究不同，电子碰撞的相关过程研究尚存在实验挑战，特别是在测定其阈值方面. 本文报道了相关的利用单色化电子碰撞分子的实验研究进展. 以BrCN→Br^-+CN⁺离子对解离为例，根据CN⁺离子出现能测定其解离阈值为13.78 eV，同时在16.09 eV获得了CN⁺离子的时间切片速度影像且显示出动量分布的各向异性.     

Biological and catalytic evaluation of Ru(II)‐p‐cymene complexes of Schiff base ligands: Impact of ligand appended moiety on photo‐induced DNA and protein cleavage,cytotoxicity and C‐H activation

Two organometallic Ru(II)‐p‐cymene complexes of the type [Ru(η⁶‐p‐cymene)(L)Cl]PF₆ 1 and 2 , where L is N,N‐bis(4‐isopropylbenzylidene)ethane‐1,2‐diamine (bien, L1 ) or N,N‐bis (pyren‐2‐ylmethylene)ethane‐1,2‐diamine (bpen, L2 ) have been prepared and characterized well. Because of appended pyrenyl groups in coordinated bpen ligand, the complex 2 exhibits higher DNA and protein binding than complex 1 in which isopropylbenzyl groups are incorporated. Interestingly, the luminescent characteristic complex 2 is unique in displaying DNA cleavage after light activation by UVA light at 365 nm through oxygen dependent mechanism. AFM analysis attests the photo‐induced DNA fragmentation ability of complex 2 . Also, the complex 2 cleaves the protein after light exposure in a non‐specific manner suggesting that it can act as a protein photo cleaving agent. In contrast to the trend of DNA and protein interaction of complexes, the complex 1 exhibits cytotoxic activity against human breast carcinoma ( MCF‐7 ) and liver carcinoma ( HepG2 ) with potency higher than that of complex 2 due to enhanced hydrophobicity of isopropyl groups present in p‐cymene and bien ligands. Indeed, complex 2 is inactive against MCF‐7 and HepG2 cancer cell lines even up to 200 μM concentration. The AO/EB staining assay reveals that the complex 1 is able to induce late apoptotic mode of cell death in breast cancer cells, which is further confirmed by inter‐nucleosomal DNA cleavage. Furthermore, the complexes 1 and 2 are evaluated for their catalytic activities and found to be working well for the β‐carboline directed C–H arylation to afford the desired products in good yield (40–47%).