Delay-dependent exponential stabilization for uncertain linear systems with interval non-differentiable time-varying delays

In this paper, the problem of exponential stabilization for a class of linear systems with time-varying delay is studied. The time delay is a continuous function belonging to a given interval, which means that the lower and upper bounds for the time-varying delay are available, but the delay function is not necessary to be differentiable. Based on the construction of improved Lyapunov-Krasovskii functionals combined with Leibniz-Newton’s formula, new delay-dependent sufficient conditions for the exponential stabilization of the systems are first established in terms of LMIs. Numerical examples are given to demonstrate that the derived conditions are much less conservative than those given in the literature.     

带有二元连接函数的半参数模型

提出了一种新的带有二元连接函数的广义半参数模型,即二元连接模型(简称为BLM).使用轮廓似然方法估计模型的参数和非参数部分,并给出了计算算法.证明了所得的未知参数的估计量为n~(1/2)-相合,渐近正态且具有渐近最小方差,给出了实际数据分析和模拟研究,最终采用局部功效方法来检验非参数部分的线性性.     

Resonant Leading Term Geometric Optics Expansions with Boundary Layers for Quasilinear Hyperbolic Boundary Problems

We construct and justify leading order weakly nonlinear geometric optics expansions for nonlinear hyperbolic initial value problems, including the compressible Euler equations. The technique of simultaneous Picard iteration is employed to show approximate solutions tend to the exact solutions in the small wavelength limit. Recent work [2 Coulombel, J.-F., Gues, O., and Williams, M., 2011. Resonant leading order geometric optics expansions for quasilinear hyperbolic fixed and free boundary problems, Comm. Part. Diff. Eqs. 36 (2011), pp. 1797–1859.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]] by Coulombel et al. studied the case of reflecting wave trains whose expansions involve only real phases. We treat generic boundary frequencies by incorporating into our expansions both real and nonreal phases. Nonreal phases introduce difficulties such as approximately solving complex transport equations and result in the addition of boundary layers with exponential decay. This also prevents us from doing an error analysis based on almost periodic profiles as in [2 Coulombel, J.-F., Gues, O., and Williams, M., 2011. Resonant leading order geometric optics expansions for quasilinear hyperbolic fixed and free boundary problems, Comm. Part. Diff. Eqs. 36 (2011), pp. 1797–1859.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]].     

Experimental shift allowance in the deconvolution of SIMS depth profiles

We study the deconvolution of the secondary ion mass spectrometry (SIMS) depth profiles of silicon and gallium arsenide structures with doped thin layers. Special attention is paid to allowance for the instrumental shift of experimental SIMS depth profiles. This effect is taken into account by using Hofmann's mixing‐roughness‐information depth model to determine the depth resolution function. The ill‐posed inverse problem is solved in the Fourier space using the Tikhonov regularization method. The proposed deconvolution algorithm has been tested on various simulated and real structures. It is shown that the algorithm can improve the SIMS depth profiling relevancy and depth resolution. The implemented shift allowance method avoids significant systematic errors of determination of the near‐surface delta‐doped layer position. Copyright © 2013 John Wiley & Sons, Ltd.     

Viscosities of Binary and Ternary Mixtures of Water,Alcohol, Acetone,and Hexane

This articles studied and determined the viscosities of the binary mixtures of water–methanol, water–ethanol, water–propanol, water–acetone, acetone–ethanol, methanol–ethanol, and acetone–hexane and the ternary mixtures of water–methanol–ethanol and water–ethanol–acetone at 20°C. It is shown that the mixing of water with the alcohols and acetone resulted in a positive deviation of viscosity, which reached the maximum value at the water mole fraction x ₁ ～ 0.7 for water–methanol, x ₁ ～ 0.72 for water–ethanol, x ₁ ～ 0.74 for water–propanol, and x ₁ ～ 0.83 for water–acetone binary mixture. This viscosity deviation can be mainly attributed to the formation of micelles of alcohol or acetone molecules in water because of the hydrophobic attraction between the hydrocarbon chains. The micelle surfaces are surrounded by hydration layers, leading to the positive viscosity deviation in the liquid mixtures because the water in hydration layers has a much higher viscosity than bulk water. Also, the contrary observation was found in the binary mixtures of acetone–ethanol and acetone–hexane, having a negative viscosity deviation.     

Nanoscale imaging of oxidized copper foil covered with chemical vapor deposition-grown graphene layers

Characterization of the geometrical and structural characteristics of oxidized Cu area in high resolution is crucial for tracking the change in morphology, exploring interactions between graphene layers and Cu substrates and revealing the mechanism for the orientation-dependent oxidation of Cu. Here, we reported experimental results on nanoscale imaging of natural oxidation of the polycrystalline Cu substrate coated by partial-coverage chemical vapor deposition (CVD)-grown graphene stored in dryer under ambient conditions for up to 10 months. Scanning electron microscope (SEM), together with atomic force microscope (AFM), Raman, and X-ray photoelectron spectroscopy (XPS), was used for systematically studying the morphological and compositional changes at nanoscale during oxidation. The appearance of oxidized Cu substrates could be unambiguously distinguished from the unoxidized regions based on their distinctly different morphologies in SEM images, and the underlying mechanism was discussed in detail. By analyzing a millimeter-seized polycrystalline Cu substrate, we found that the oxidation of polycrystalline Cu substrate depends sensitively on both orientation of graphene layers and Cu substrates. Furthermore, the time-dependent oxidation evolution of Cu substrate was also established, and the oxidation rate was readily determined. The findings reported here will have important implications for developing protection coatings for Cu.     

反式钙钛矿电池超薄空穴传输层研究进展

空穴传输层(HTLs)厚度对反式钙钛矿太阳能电池(PSCs)性能具有重大影响,因其显著影响太阳光透过和HTLs的空穴传输性能。几个纳米至十几个纳米厚度的超薄HTLs在减少伴生吸收、电荷传输损失和材料消耗等方面具有明显优势。目前,有许多成熟的制备超薄无机HTLs的方法,并在反式和叠层PSCs中得到广泛研究与应用。最近,一些关于有机超薄HTLs的新型制备方法也展现出良好的性能并逐渐引起相关领域研究者关注。在此,本文主要总结反式PSCs中超薄HTLs的研究进展与应用,关注其未来发展的挑战和方向,为该领域进一步的研究提供参考。     

Back contact–absorber interface modification by inserting carbon intermediate layer and conversion efficiency improvement in Cu2ZnSn(S,Se)4 solar cell

Carbon layers have been employed as intermediate layers between Mo back contact and Cu₂ZnSn(S_1–xSe_x)₄(CZTSSe) absorber film prepared by sol–gel and post‐selenization method. Carbon layers with appropriate thickness can significantly inhibit the formation of MoSe₂ and voids at bottom region of the absorber, and therefore reduce the series resistance remarkably. The conversion efficiency can be boosted by the introducing of the carbon layer from 6.20% to 7.24% by enhancement in short current density, fill factor and open voltage in comparison to the reference sample without carbon layer. However, excess thickness of carbon layer will worse device performance due to the deteriorated absorber crystallinity. In addition, the time‐resolved photoluminescence analysis shows that inserting the carbon layer with suitable thickness does not introduce recombination and lower minority lifetime. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

PEFC catalyst layers: Effect of support microstructure on both distributions of Pt and ionomer and cell performance and durability

In order to improve the performance and durability of polymer electrolyte fuel cells (PEFCs), various improvements in the microstructures of cathode catalyst layers (CLs) were initiated in the early 1990s. More recent advances in CL materials are highlighted, including carbon supports for improved accessibility of Pt nanoparticles (NPs), adsorption of ionomer on the Pt surface, high-oxygen-permeability ionomers, corrosion resistance of mesoporous and microporous carbons, and conductive ceramic supports with a fused-aggregate network structure. These approaches are summarized as stepwise improvements. The influences of the support structure on the distribution of Pt NPs and ionomer are reviewed, as well as their effects on performance and durability. These approaches for carbon supports are extended to conductive ceramic supports and the unique advantages are discussed.