化学增透膜激光疲劳损伤效应

疲劳效应是诱导高功率固体激光装置中光学元件激光损伤的因素之一,目前对SiO₂化学增透膜激光诱导疲劳损伤的研究鲜见报道。基于此,本文采用单一激光能量多发次辐照和多梯度激光能量多发次辐照两种不同的激光辐照方式,研究1064 nm化学增透膜层的激光疲劳损伤效应及特征。研究结果表明,在单一激光能量多发次脉冲激光辐照下,膜层最易发生疲劳损伤; 采用多梯度激光能量多发次辐照的方式,可以有效地提升膜层的损伤阈值,进而提升膜层的抗激光疲劳损伤性能。     

EZ模型中的有限尺寸效应

研究EZ模型中的有限尺寸效应.当经纪人数目N足够大及发生交易的概率a1/N，发现有限尺 寸效应是重要的.此时，系统几乎变成包含所有经纪人的单一集团.而对较小集团，尺寸分布 仍然服从幂函数律，但是指数因涨落效应而改变.但当a1/N时，可以论证涨落效应不重要 ，因而平均场理论是严格成立的. 关键词： EZ模型 有限尺寸效应 涨落 平均场理论     

Stage-I fatigue crack studies in order to validate the dislocation-free zone model of fracture for bulk materials

Stage-I fatigue cracks are commonly described by the model of Bilby, Cottrell and Swinden (BCS model). However, since several experimental investigations have shown a dislocation-free zone (DFZ) in front of crack-tips, it is necessary to validate the new DFZ model and to examine the deviations to the BCS model. Therefore, the dislocation density distribution is derived from height profiles of slip lines in front of stage-I fatigue cracks in CMSX4® single crystals measured by contact-mode atomic force microscopy. This is possible, because the cracks are initiated at notches milled by focused ion beam technique directly on slip planes with a high Schmid factor. Consequently, the directions of the Burgers vectors are well known; it is possible to calculate the dislocation density distributions from the height profiles. The measured distributions are compared to the calculated distribution function of the DFZ model proposed by Chang et al. The additionally measured microscopic friction stress of the dislocations is then used to calculate the influence of grain boundaries on the dislocation density distribution in front of stage-I cracks. The calculation is done by the extended DFZ model of Shiue et al. and compared with the measured distribution function in polycrystalline specimens. Finally, the crack-tip sliding displacement as a measure for the crack propagation rate is compared for the DFZ model and the BCS model with the experimentally revealed values. The important result: the often used BCS model does not reflect the experimental measurements. On the contrary, the DFZ model reflects the measurements at stage-I cracks qualitatively and quantitatively.     

An improved EEHEMT model for kink effect on AlGaN/GaN HEMT

In this paper, a new current expression based on both the direct currect(DC) characteristics of the AlGaN/GaN high election mobility transistor(HEMT) and the hyperbolic tangent function tanh is proposed, by which we can describe the kink effect of the AlGaN/GaN HEMT well. Then, an improved EEHEMT model including the proposed current expression is presented. The simulated and measured results of I–V, S-parameter, and radio frequency(RF) large-signal characteristics are compared for a self-developed on-wafer AlGaN/GaN HEMT with ten gate fingers each being 0.4-μm long and 125-μm wide(Such an AlGaN/GaN HEMT is denoted as AlGaN/GaN HEMT(10 × 125 μm)). The improved large signal model simulates the I–V characteristic much more accurately than the original one, and its transconductance and RF characteristics are also in excellent agreement with the measured data.     

An improved EEHEMT model for kink effect on AIGaN/GaN HEMT

In this paper, a new current expression based on both the direct currect （DC） characteristics of the A1GaN/GaN high election mobility transistor （HEMT） and the hyperbolic tangent function tanh is proposed, by which we can describe the kink effect of the A1GaN/GaN HEMT well. Then, an improved EEHEMT model including the proposed current expression is presented. The simulated and measured results of Ⅰ-Ⅴ, S-parameter, and radio frequency （RF） large-signal characteristics are compared for a self-developed on-wafer A1GaN/GaN HEMT with ten gate fingers each being 0.4-μm long and 125-p-m wide （Such an A1GaN/GaN HEMT is denoted as A1GaN/GaN HEMT （10 × 125 μm））. The improved large signal model simulates the Ⅰ-Ⅴ characteristic much more accurately than the original one, and its transconductance and RF characteristics are also in excellent agreement with the measured data.     

An analytic model for gate-all-around silicon nanowire tunneling field effect transistors

An analytical model of gate-all-around(GAA) silicon nanowire tunneling field effect transistors(NW-TFETs) is developted based on the surface potential solutions in the channel direction and considering the band to band tunneling(BTBT) efficiency. The three-dimensional Poisson equation is solved to obtain the surface potential distributions in the partition regions along the channel direction for the NW-TFET, and a tunneling current model using Kane’s expression is developed. The validity of the developed model is shown by the good agreement between the model predictions and the TCAD simulation results.     

A statistical model of fatigue failure incorporating effects of specimen size and load amplitude on fatigue life

Among many contributing factors, the load range, number of load cycles and specimen geometry (including configuration and size) are three major variables for fatigue failure. Most existing statistical fatigue models deal with only one or two of these three variables. According to the statistical distribution of microcracks with respect to their size and spatial location, a weakest-link probabilistic model for fatigue failure is established to incorporate the combined effect of load range, number of load cycles and specimen size. The model reveals a compound parameter of load range and number of load cycles reminiscent of the empirical formulae of fatigue stress-life curve and its correlation with another compound parameter of cumulative failure probability and specimen size. Four sets of published fatigue test data are adopted to validate the model.     

加载应力幅值对高纯铜动态损伤演化特性研究

研究了加载应力幅值对延性金属高纯无氧铜动态损伤演化特性的影响. 层裂实验在一级轻气炮上开展, 利用不同的飞片击靶速度实现不同加载应力幅值(2.5 GPa, 2.75 GPa和3.75 GPa), 采用DISAR位移干涉诊断技术测量样品自由面的速度剖面, 利用基于白光轴向色差的表面轮廓测试技术测试软回收的样品截面. 结果显示: 随着加载应力幅值的升高, 层裂强度几乎没有变化, 但自由面速度剖面上Pull back信号后的回跳速率和幅值显著增大, 损伤演化速率显著升高.进一步分析表明: 延性金属动态损伤演化过程中微孔洞成核对加载应力幅值单一因素不敏感, 但加载应力幅值是微孔洞长大和聚集的主导因素之一.     

Effect of surface treatment for steel adherends on static and fatigue crack growth of epoxy adhesives

The fracture toughness of unmodified, glass-bead-reinforced and CNBR-modified epoxy adhesives under mode I loading is not improved by acid surface treatment of steel adherends since cohesive failure always occurs for all adhesives with or without acid surface treatment. On the other hand, the fatigue crack growth resistance greatly increases due to acid surface treatment of steel adherends. Especially, the threshold dramatically increases. The crack grows cohesively at all stages of crack velocity for DCB specimens treated with acids while it grows at the interface between the adherend and the adhesive layer for the specimens whose polished surface of adherends is only decreased with solvent. An optical microscope observation revealed that adherend surfaces treated with acids were rougher than ones without acid treatment, although XPS examination for the surfaces did not show significant difference in their chemical elements among the specimens with and without acid treatment.     

Effect of molecular structure on bias stress effect in organic thin-film transistors

Two thiophene-phenylene semiconductors, bis(2-phenylethynyl) end-substituted oligothiophenes (diPhAc-nTs, n = 2, 3), were studied as active layers in organic thin film transistors (OTFTs). Structural and electrical properties of such high vacuum evaporated thin films were compared to pentacene. All three oligomers behave as p-type semiconducting layers into OTFTs. In the same preparation and measurement conditions, diPhAc-3T possesses two of incontrovertible attributes of OTFTs for low cost applications, a high air-stable mobility at low substrate temperature (T_sub), i.e. typically 25 °C together with a reduced bias stress effect compared to the well-known pentacene semiconductor. This study brings to light on the role of the molecular structure involved in the active layer in thin-film devices and describes effects as thin film morphology as important parameters when optimizing the structure of OTFTs.     

光学薄膜残余应力分配预测模型计算方法研究

残余应力是光学薄膜研究的一个重要组成部分，它对光学元器件有很大的影响。根据弹性力学原理，基于应变不匹配，提出了一种可以预测薄膜残余应力分配的理论模型计算方法，并将计算结果与干涉仪测量值进行了对比。利用所建立的模型分析了薄膜参数变化时基底残余应力的变化情况。结果表明：所建模型合理；随着镀膜温度的增加，基底总残余应力随镀膜温度升高而呈增大的趋势;本征应力变化不太大；随着基底厚度的减小，基底上下表面应力呈增大的趋势，而薄膜应力则呈减小趋势，但变化趋势很小。基底的中心轴约位于基底上表面以下2／3处。     

An LCOR model for suppressing cascading failure in weighted complex networks

Based on the relationship between capacity and load, cascading failure on weighted complex networks is investigated, and a load-capacity optimal relationship (LCOR) model is proposed in this paper. Compared with three other kinds of load-capacity linear or non-linear relationship models in model networks as well as a number of real-world weighted networks including the railway network, the airports network and the metro network, the LCOR model is shown to have the best robustness against cascading failure with less cost. Furthermore, theoretical analysis and computational method of its cost threshold are provided to validate the effectiveness of the LCOR model. The results show that the LCOR model is effective for designing real-world networks with high robustness and less cost against cascading failure.     

An extended improved global structure model for influential node identification in complex networks

Accurate identification of influential nodes facilitates the control of rumor propagation and interrupts the spread of computer viruses. Many classical approaches have been proposed by researchers regarding different aspects. To explore the impact of location information in depth, this paper proposes an improved global structure model to characterize the influence of nodes. The method considers both the node's self-information and the role of the location information of neighboring nodes. First, degree centrality of each node is calculated, and then degree value of each node is used to represent self-influence, and degree values of the neighbor layer nodes are divided by the power of the path length, which is path attenuation used to represent global influence. Finally, an extended improved global structure model that considers the nearest neighbor information after combining self-influence and global influence is proposed to identify influential nodes. In this paper, the propagation process of a real network is obtained by simulation with the SIR model, and the effectiveness of the proposed method is verified from two aspects of discrimination and accuracy. The experimental results show that the proposed method is more accurate in identifying influential nodes than other comparative methods with multiple networks.     

A Dugdale–Barenblatt model for a strip with a semi-infinite crack embedded in decagonal quasicrystals

The present study is to determine the solution of a strip with a semi-infinite crack embedded in decagonal quasicrystals, which transforms a physically and mathematically daunting problem. Then cohesive forces are incorporated into a plastic strip in the elastic body for nonlinear deformation. By superposing the two linear elastic fields, one is evaluated with internal loadings and the other with cohesive forces, the problem is treated in Dugdale-Barenblatt manner. A simple but yet rigorous version of the complex analysis theory is employed here, which involves conformal mapping technique. The analytical approach leads to the establishment of a few equations, which allows the exact calculation of the size of cohesive force zone and the most important physical quantity in crack theory: stress intensity factor. The analytical results of the present study may be used as the basis of fracture theory of decagonal quasicrystals.     

Theoretical study on interaction of cytochrome f and plastocyanin complex by a simple coarse-grained model with molecular crowding effect

ABSTRACT

We present a simple coarse-grained model with the molecular crowding effect in solvent to investigate the structure and dynamics of protein complexes including association and/or dissociation processes and investigate some physical properties such as the structure and the reaction rate from the viewpoint of the hydrophobic intermolecular interactions of protein complex. In the present coarse-grained model, a function depending upon the density of hydrophobic amino acid residues in a binding area of the complex is introduced, and the function involves the molecular crowding effect for the intermolecular interactions of hydrophobic amino acid residues between proteins. We propose a hydrophobic intermolecular potential energy between proteins by using the density-dependent function. The present coarse-grained model is applied to the complex of cytochrome f and plastocyanin by using the Langevin dynamics simulation to investigate some physical properties such as the complex structure, the electron transfer reaction rate constant from plastocyanin to cytochrome f and so on. We find that for proceeding the electron transfer reaction, the distance between metals in their active sites is necessary within about 18 Å. We discuss some typical complex structures formed in the present simulation in relation to the molecular crowding effect on hydrophobic interactions.     

用横场伊辛模型研究应力对铁电薄膜的热力学性质的影响

用横场伊辛模型研究了铁电薄膜的热力学性质.在体系的哈密顿量中引入一个两维的在平面内的应力，并假设应力从基底材料和薄膜材料之间的界面层到薄膜的表面层是呈指数形式衰减的.结果显示：压应力有利于极化，使居里温度向高温区移动，而张应力对极化和居里温度的影响正好相反.扩散长度对铁电薄膜的热力学性质有很大的影响. 关键词： 铁电薄膜 应力 横场伊辛模型     

A review of a phenomenological model for magnetocaloric effect in ferromagnetic materials

The present work is devoted to a review of the phenomenological model proposed by Mahmoud Aly Hamad (M. Aly Hamad, Phase Transitions 85 (2012) 106–112) to predict the magnetocaloric effect in ferromagnetic material from the only measure of its magnetization as a function of temperature under an applied magnetic field. We questioned the reliability of that model. Based on some experimental data available in the literature, we have shown that, contrary to what is expected, the prediction of the magnetocaloric effect by this model is poor.     

基于Jiles-Atherton理论的铁磁材料塑性变形磁化模型修正

Jiles-Atherton(J-A)模型在磁化建模领域应用广泛,但不同文献给出的J-A模型并不一致,致使采用不同表达式建立的塑性变形磁化模型存在多种版本,其正确性难以甄别.通过对无磁滞磁化方程、能量守恒方程和等效磁场强度方程的梳理与比较,发现原有模型中存在将磁化强度和无磁滞磁化强度混用、将不可逆磁化能量等效于全部的磁化能量、等效磁场强度中应力磁化项界定不清等问题.在此基础上,对上述方程进行了修正,推导了基于J-A模型的塑性变形磁化修正模型.将修正模型计算结果与原模型计算结果、相关文献中的试验结果进行对比,结果表明:与原有计算模型相比,修正模型计算结果的饱和磁化强度和剩余磁化强度随塑性变形增加而减小,矫顽力随塑性变形增大而增大,达到饱和磁化强度时的外磁场强度随塑性变形增大而增大的趋势有所减弱,更符合试验结果,可更准确地反映塑性变形对材料磁化的影响.