基于飞秒激光等离子体丝诱导击穿光谱探测土壤重金属Cr元素含量

本文基于飞秒激光等离子体丝诱导击穿光谱对土壤重金属Cr元素含量进行了实验研究.利用荧光法对等离子体丝的长度进行测量,给出了在不同焦距聚焦透镜作用下土壤中Cr425.5 nm的谱线强度空间分布,实验给出了Cr元素的定标曲线.实验结果表明,土壤中Cr元素浓度分析测量的相对标准偏差小于5%,土壤中重金属Cr元素的检测极限为7.85 ppm.表明飞秒激光等离子体丝诱导击穿光谱技术在土壤重金属Cr元素含量的定量探测方面是完全可行的.     

Efficient greyscale image compression technique based on vector quantization

In this paper, a novel greyscale image coding technique based on vector quantization (VQ) is proposed. In VQ, the reconstructed image quality is restricted by the codebook used in the image encoding/decoding procedures. To provide a better image quality using a fixed-sized codebook, the codebook expansion technique is introduced in the proposed technique. In addition, the block prediction technique and the relatively address technique are employed to cut down the required storage cost of the compressed codes. From the results, it is shown that the proposed technique adaptively provides better image quality at low bit rates than VQ.     

A first-principle study of the structural and electronic properties of amorphous Cu-Zr alloys

The atomic and electronic structures of amorphous CuxZr100-x(x=36,46,50,56,64) alloys were simulated using first-principle calculations within a 400-atom supercell.The pair correlation function,coordination numbers,local cluster structures and electronic density of states were analyzed.Reasonable agreements between the theory and the experiments were obtained.The amorphous alloys exhibit different local cluster structures and can all be explained with cluster formulas [cluster](glue)1,3,where the clusters a...     

Interfacial microstructure and bonding strength of Sn-3Ag-0.5Cu and Sn-3Ag-0.5Cu-0.5Ce-xZn solder BGA packages with immersion Ag surface finish

Although it has been verified that tin whiskers can be prevented by the addition of 0.5 wt.% Zn into a Sn-3Ag-0.5Cu-0.5Ce solder, no detailed studies have been conducted on interfacial reactions and mechanical properties of Sn-3Ag-0.5Cu-0.5Ce-xZn solder joints with an immersion Ag surface finish. The intermetallic compounds formed during the reflow and aging of Sn-3Ag-0.5Cu and Sn-3Ag-0.5Cu-0.5Ce-xZn solder ball grid array (BGA) packages were investigated. Because more heterogeneous nucleation sites, provided by CeSn₃ intermetallics and Zn atoms, formed in the Sn-3Ag-0.5Cu-0.5Ce-xZn solder matrix, and Cu and Zn have a stronger affinity than Cu and Sn, the Cu-Sn intermetallics growth in Sn-3Ag-0.5Cu-0.5Ce-xZn solder joints with Ag/Cu pads was suppressed. The 0.2% Zn addition for inhibiting rapid whisker growth in RE-doped Sn-Ag-Cu solder joints is more appropriate than 0.5 wt.% additions, as excess Zn addition causes poor oxidation resistance and inferior bonding strength.     

空腔膨胀理论靶体阻力模型及其应用研究进展

从静/动态空腔膨胀模型的理论体系出发,介绍了空腔膨胀模型在不同方向上取得的成果,主要涉及理想侵彻条件的空腔膨胀压力计算模型及数值模拟方法和空腔膨胀模型在典型侵彻问题及复杂弹靶条件下的应用。在理想侵彻条件下的空腔膨胀压力计算模型中,主要讨论了靶体材料、屈服准则和状态方程对空腔边界应力的影响规律及空腔膨胀模型的适用性问题;根据数值模拟中初始条件的不同,介绍了空腔表面恒定速度/恒定压力两种数值模拟方法,证明了数值模拟方法的可靠性;整理了空腔膨胀模型的基本假设、适用范围、工程应用特点,列举了其在典型侵彻问题及多层复合靶板、约束靶体、弹体刻槽和异形截面形状弹体等复杂弹靶条件下的应用。针对空腔膨胀模型的研究现状,总结了目前空腔膨胀模型在冲击动力学领域的应用方向,归纳了空腔膨胀模型应用中尚存在的问题,展望了空腔膨胀模型下一步的重点发展方向。     

Experimental evidence for Efros–Shklovskii variable range hopping in hydrogenated graphene

We have performed transport measurements on a hydrogenated graphene flake. It is found that conventional analysis cannot allow us to determine whether Mott variable range hopping (VRH) or Efros–Shklovskii (ES) VRH is the dominant mechanism in our system. By employing the modified resistance curve derivative analysis (RCDA) method, we are able to unequivocally show that ES VRH dominates and thus Coulomb interaction effects exist in our system at zero magnetic field. Transport data obtained in the intermediate and high field regimes also follow ES VRH based on the RCDA method. Our results suggest that Coulomb interaction effects can play an important role in disordered graphene.     

Evolutionary public goods games based on historical payoffs

We investigate the evolution of cooperation in public goods game based on individuals?? historical payoffs. In particular, the fitness of individuals are characterized by two types of payoffs, which are obtained by acting as cooperators and defectors, respectively. Both of payoffs are the linear combination of the current payoffs and the cumulative historical payoffs. The results show that cooperation is enhanced by an increasing memory effect with a wide range of related factors. To explain this phenomenon, we plot some representative snapshots of the population and scrutinize the mean fitness of cooperators and defectors along the boundary. It is found that increasing memory effect induces a positive feedback mechanism for cooperators to expand their districts. Defectors can just survive through forming narrower clusters to exploit cooperators more widely. The threshold values for cooperators and defectors vanishing under the influence of noise are also investigated.     

Critical importance of current collector property to the performance of flexible electrochemical power sources

The property of current collector is significant to the performance of flexible power supply.     

In situ infrared approach to unravel reaction intermediates and pathways on catalyst surfaces

Research on Chemical Intermediates - Reaction intermediates on catalyst surfaces have often been elucidated on the basis of ex situ observation of adsorbed species and theoretical computations...