Radar Absorption Properties of Ni0.5Zn0.5Fe2O4/PANI/epoxy Nanocomposites

A nitrate? citrate gel was prepared from metallic nitrates and citric acid by sol? gel process and was further used to synthesize Ni_0.5Zn_0.5Fe₂O₄ nanocrystalline powder by auto‐combustion. Then, two novel 15 and 35% (w/w) magnetic Ni_0.5Zn_0.5Fe₂O₄ containing polyaniline nanocomposites, named as PANI‐Ni15 and PANI‐Ni35, respectively, were prepared via in‐situ polymerization of aniline in an aqueous solution containing proper amount of Ni_0.5Zn_0.5Fe₂O₄ magnetic powder. The incorporation of the nanopowders to PANI matrix was confirmed by X‐ray diffraction (XRD), IR and SEM. Synthesized PANI‐NiZn ferrite composite particles were subsequently added to an epoxy resin matrix to produce related nanocomposites. The morphological properties of these nanocomposite materials were investigated by SEM and TEM. The electromagnetic‐absorbing properties were studied by measuring the reflection loss in the frequency range of 8.0 to 12.0 GHz. Results showed the reflection loss of the PANI‐Ni35 composite is higher than pure polyaniline and PANI‐Ni15. The good reflection loss of the nanocomposites suggests their potential applicability as radar absorber.     

塑性减震技术在地下强爆炸环境下的应用研究

本文介绍了地下封闭爆炸中利用塑性减震技术对参试的重要测试仪器进行减震防护研究的基本原理和设计的基本思路，根据振动冲击理论计算和模拟实验实测结果研制的减震装置将63kg重的摄像装置的切向峰值加速度由地表激励的1695m/s^2减至在减震装置上的98m/s^2；将23.5kg重的摄像装置的垂向峰值加速度由地表激励的400m/s^2减至147m/s^2，实测结果表明，本文所研制的塑性减震装置，其减震效果与预计的结果相一致，增强了摄像装置在强冲击、大位移特殊环境下的物理生存能力，保证了拍摄图像的清晰完整，达到了设计的要求，满足了试验研究工作的需要。     

Robust Bayesian analysis in partially ordered plausibility calculi

In Robust Bayesian analysis one attempts to avoid the ‘Dogma of Precision’ in Bayesian analysis by entertaining a set of probability distributions instead of exactly one. The algebraic approach to plausibility calculi is inspired by Cox's and Jaynes' analyses of plausibility assessment as a logic of uncertainty. In the algebraic approach one is not so much interested in different ways to prove that precise Bayesian probability is inevitable but rather in how different sets of assumptions are reflected in the resulting plausibility calculus. It has repeatedly been pointed out that a partially ordered plausibility domain is more appropriate than a totally ordered one, but it has not yet been completely resolved exactly what such domains can look like. One such domain is the natural robust Bayesian representation, an indexed family of probabilities.We show that every plausibility calculus embeddable in a partially ordered ring is equivalent to a subring of a product of ordered fields, i.e., the robust Bayesian representation is universal under our assumptions, if extended rather than standard probability is used.We also show that this representation has at least the same expressiveness as coherent sets of desirable gambles with real valued payoffs, for a finite universe.     

Imprecise random variables,random sets,and Monte Carlo simulation

The paper addresses the evaluation of upper and lower probabilities induced by functions of an imprecise random variable. Given a function g and a family $X_{\lambda }$ of random variables, where the parameter λ ranges in an index set Λ, one may ask for the upper/lower probability that $g(X_{\lambda })$ belongs to some Borel set B. Two interpretations are investigated. In the first case, the upper probability is computed as the supremum of the probabilities that $g(X_{\lambda })$ lies in B. In the second case, one considers the random set generated by all $g(X_{\lambda })$, $\lambda \in \mathrm{\Lambda }$, e.g. by transforming $X_{\lambda }$ to standard normal as a common probability space, and computes the corresponding upper probability. The two results are different, in general. We analyze this situation and highlight the implications for Monte Carlo simulation. Attention is given to efficient simulation procedures and an engineering application is presented.     

基于等离激元多重杂化效应的光吸收结构

近年来,以聚合物为代表的高分子材料由于具有比其他光吸收材料(如半导体材料、碳基材料以及贵金属纳米材料)更好的柔性和粘弹性而受到广泛关注.本文基于等离子体再聚合技术和磁控溅射工艺在聚合物材料层上制备了具有等离激元多重杂化效应的光吸收结构,该结构具有宽谱高吸收特性.该结构的制备工艺简单易行,对不同聚合物材料具有通用性,在光学器件领域具有广泛的应用前景.     

受横向冲击圆环的粘塑性大变形分析

本文采用了受压刚性平板对压圆环的准静态大变形模式,对放置在刚性平板上的圆环受落锤冲击下的动力响应作了粘塑性大变形分析,并考虑了应变强化的影响。由于把问题简化为一个自由度系统的运动,使得整个运动过程可以较方便地计算出来计算结果表明,在运动初期应变率效应对圆环承载力的提高起主要作用,在运动后期应变强化及大变形影响较大,其中应变强化起主导作用。计算结果与实验结果进行了对比。     

Engineering of UV‐absorbing polypropylene films containing poly(2‐(2′‐hydroxy‐5′‐methacryloxyethylphenyl)‐2H‐benzotriazole) nanoparticles

Ultraviolet‐absorbing nanoparticles (NPs) were prepared by emulsion co‐polymerization of the vinylic monomer 2‐(2′‐hydroxy‐5′‐methacryloxyethylphenyl)‐2H‐benzotriazole (Norbloc?, NB) with the crosslinking monomer divinylbenzene. The effect of total monomer, surfactant, crosslinker, and initiator concentrations on the size and size distribution of the formed NPs was elucidated. The NB monomer and the formed polyNB (PNB) NPs of 19 ± 2 nm were then incorporated into polypropylene (PP) films by melt‐compounding technique by using cast film extrusion. Increasing the PNB NP concentrations integrated within the PP films decreased their UV transmittance. Migration of the UV absorbing PNB NPs from the PP films was not observed during 3 years of storage at room temperature or while exposure to extreme conditions. Under the same conditions, a significant migration was observed for the NB monomer‐containing films. Overall, the PNB NP‐containing films are clear and transparent, although the haze was affected by the addition of NB and PNB NPs. Moreover, the films have good mechanical properties and UV‐blocking quality. Copyright © 2017 John Wiley & Sons, Ltd.     

FFT-based spectral analysis methodology for one-dimensional wave propagation in poroelastic media

The general one-dimensional equilibrium equations describing the dynamic behaviour of a porous medium form a system of coupled hyperbolic partial differential equations. A transition from the time to the frequency domain is made by spectral decomposition of the displacements. The equations simplify to a set of coupled ordinary differential equations. A solution can be obtained by solving a frequency-dependent eigenvalue problem. The characteristic equation clarifies the double wave-pattern and the attenuation of each wave. A spectrally formulated element uses the frequency-dependent eivenvectors as shape functions. The mass distribution is treated exactly without the need of subdividing a member into smaller elements and therefore wave propagation within an element is also treated exactly.     

Minimum Vertex Degree Threshold for ‐tiling*

We prove that the vertex degree threshold for tiling (the 3‐uniform hypergraph with four vertices and two triples) in a 3‐uniform hypergraph on vertices is , where if and otherwise. This result is best possible, and is one of the first results on vertex degree conditions for hypergraph tiling.     

A sliding mode approach to robust stabilisation of Markovian jump linear time-delay systems with generally incomplete transition rates

This paper is devoted to investigating the problem of robust sliding mode control for a class of uncertain Markovian jump linear time-delay systems with generally uncertain transition rates (GUTRs). In this GUTR model, each transition rate can be completely unknown or only its estimate value is known. By making use of linear matrix inequalities technique, sufficient conditions are presented to derive the linear switching surface and guarantee the stochastic stability of sliding mode dynamics. A sliding mode control law is developed to drive the state trajectory of the closed-loop system to the specified linear switching surface in a finite-time interval in spite of the existing uncertainties, time delays and unknown transition rates. Finally, an example is presented to verify the validity of the proposed method.