Correlation between the strength of fiber-reinforced plastics and the adhesive strength of fiber—Matrix joints

The relationship between the strength (σc) of unidirectional fiber-reinforced plastics in different stressed states and the interfacial strength of their components is investigated. The shear adhesive strength (τ0) of fiber—matrix joints determined by the pull-out technique is used as a measure of the interfacial strength. To obtain the correlation curves betweenσc andτ0, the experimental results are used, where both the plastic and adhesive strength change under the influence of a single factor. In this case, such factors are the fiber surface treatment, nature and composition of polymer matrices, and test temperature. It is shown that the strength of the glass, carbon, and boron plastics increases practically linearly with increased interfacial strength. Such a behavior is observed in any loading conditions (tension, shear, bending, and compression). Sometimes, a small (10–20%) increase in the adhesive strength induces a significant (50–70%) growth in the material strength. Therefore, the interface is the “weak link” in these composites. The shape of theσc—τ0 curves for composites based on the high-strength and high-modulus aramid fibers and different thermoreactive matrices depends on the nature of the fiber and the type of stress state. In many cases, the composite strength does not depend on the interfacial strength. Then, the fiber itself is the “weak link” in these composites. Submitted to the 11th International Conference on Mechanics of Composite Materials (Riga, June 11–15, 2000). Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 3, pp. 291–304, May–June, 2000.     

Scattering Invisibility With Free‐Space Field Enhancement of All‐Dielectric Nanoparticles

Simultaneous scattering invisibility and free‐space field enhancement have been achieved based on multipolar interferences among all‐dielectric nanoparticles. The scattering properties of all‐dielectric nanowire quadrumers are investigated and two sorts of scattering invisibilities have been identified: the trivial invisibility where the individual nanowires are not effectively excited; and the nontrivial invisibility with strong multipolar excitations within each nanowire, which results in free‐space field enhancement outside the particles. It is revealed that such nontrivial invisibility originates from not only the simultaneous excitations of both electric and magnetic resonances, but also their significant magnetoelectric cross‐interactions. We further show that the invisibility obtained is both polarization and direction selective, which can probably play a significant role in various applications including non‐invasive detection, sensing, and non‐disturbing medical diagnosis with high sensitivity and precision.     

负反馈放大器的单向化条件

从单向化条件的三个基本准则出发，以电压串联型负反馈为例，采用了广义ｈ参数对反馈网络的负载效应作了定量分析，得出负反馈放大器放大倍数一般表达式的适用条件，同时强调了反馈系数与信号源内阻及负载电阻无关。     

Design method of reusable reciprocal invisibility and phantom device

Reusable reciprocal invisibility and phantom device is proposed and designed based on multi-folded transformation optics and equivalent components. In comparison with the reported reciprocal invisibility cloaks, the material parameters of the device presented here are homogeneous, and the hiding of the target object does not require any "anti-object" at all, which dramatically breaks through the limitations of the "anti-object" design in previous reciprocal cloak design. Perfectly illusion effect is also found by reasonably setting the material parameters of the restored medium of the device, which can be used to confuse detection radars while hiding target objects. Last but not least, the proposed device has an open structure, which enables the target object enclosed by the device to perform material exchange and simplex transfer of information with the outside world through open channels. In other words, the proposed device has a reusable function, enabling stealth or phantom of new target objects without changing any parameters of the device.     

On regularized full- and partial-cloaks in acoustic scattering

The aim of this work is to derive sharp quantitative estimates of the qualitative convergence results developed by Li et al. (2015) for regularized full- and partial-cloaks through transformation optics approach. Let Γ₀ be a compact set in ?³ and Γ_δ be a δ-neighborhood of Γ₀ for δ∈?₊. Γ_δ represents the virtual domain used for the blow-up construction. By incorporating suitably designed lossy layers, it is shown that if the generating set Γ₀ is a generic curve, then one would have an approximate full-cloak within δ² to the perfect full-cloak, whereas if Γ₀ is the closure of an open subset on a flat surface, then one would have an approximate partial-cloak within δ to its perfect counterpart. The estimates derived are independent of the contents being cloaked; that is, the cloaking devices are capable of nearly cloaking an arbitrary content. Furthermore, as a significant by-product, our argument allows the relaxation of the convexity requirement on Γ₀ by Li et al. (2015), which is critical for the Mosco convergence argument therein.     

定向凝固宏微观热质传递及双扩散流作用

针对氯化铵水溶液定向凝固实验,从枝晶微尺度到宏观尺度耦合模拟了相变热质传递过程,并考察了双扩散流的影响.研究结果表明,NH4CI-H2O溶液的枝晶微界面浓度变化与非平衡态的谢尔方程趋于一致.两相区内液相率较高,易于流动的产生;热浮升力形成逆时针回流,溶质浮升力形成顺时针回流;热浮升力作用大于溶质浮升力.但双扩散流几乎不影响凝固沿着结晶室高度方向进行的一维定向特性.数值模拟中低估了两相区的渗透率,是造成两相区厚度模拟结果小于实验值的原因.     

Resonant Transmission through Topological Metamaterial Grating

Recently, artificial photonic structures that exhibit nontrivial topological properties have attracted growing attention due to their capability of achieving one‐way backscatter immune transport of light. While photonic crystals are predominantly employed for achieving nontrivial topologies, effective medium approach based on metamaterials has been recently proposed for realizing topologically protected unidirectional surface states. In this article, a microscopic model to investigate the transmission of topological metamaterial grating is constructed based on the scattering processes involving unidirectional surface states. The numerically simulated transmission efficiency of the grating can be precisely reproduced by the model. The model demonstrates that the sharp transmission resonance of the grating results from the constructive interference of the topologically protected one‐way surface states. The present work provides an intuitive picture for understanding the scattering processes and resonance behaviors of the topologically protected one‐way surface states. Benefitting from the sharp spectral features of the supported resonances, the proposed grating structure may be potentially used for sensing applications.