Impact resistance analysis of flexible fabric by 3D shape of impact basin in low-speed impact test

Hopkinson non-penetrating low-speed impact test was carried out on Kevlar flexible fabrics. The impact basin was formed by the clay on the back of the fabric, and the ultimate deformation of the fabric was recorded completely. The 3D shape of the clay impact basin was measured by fringe projection profilometry and converted into the impact basin volume. At the same time, the relationship between the indentation volume and the deformation energy of the clay was calibrated using the clay intrusion test. The clay impact basin volume is then converted into the residual energy of the flexible fabric subjected to the low-speed impact, and a new index of the impact basin volume is established to evaluate the energy absorption efficiency of fabric under the low-speed impact. Finally, combined with the deformation of single-layer fabric, the stress wave propagation in the impact deformation process of fabric is discussed, which is helpful to understand the impact energy absorption mechanism of flexible fabric.     

Nanocomposites induced by two-dimensional titanium carbide nanosheets for highly efficient energy storage

Surface group-rich titanium carbide nanosheets (TCNSs) were successfully fabricated by simply etching Ti₃AlC₂ powders and used as dielectric fillers to promote the dielectric and energy storage performances of poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP)-based composites. The PVDF-HFP/TCNS composites realize a high dielectric constant and low dielectric loss of 16.3 and 0.034 at 10² Hz, respectively. Importantly, a high energy storage density (U_e) of 0.367 J cm⁻³ at 900 kV cm⁻¹ and a high energy storage efficiency (η ≥ 78.9%) at a TCNS content of only 0.5 wt% are obtained, which indicates that incorporating TCNS is an efficient route in enhancing U_e while maintaining a high level η of the PVDF-HFP-based composites. According to detailed characterization results, a mechanism related to the reduction of lamellar crystals in the PVDF-HFP matrix is suggested. The above mechanism restricts the movement of polymer chains near the filler-matrix interface and is proposed to be responsible for the outstanding dielectric and energy storage performances. Consequently, this work provides a simple and effective method for fabricating highly efficient energy storage nanocomposites.     

Single-Molecule Magnetism in Dy2 Cluster Based on a Schiff Base Ligand

Two dinuclear Ln^III-based clusters, namely [Dy₂L₂(NO₃)₂(DME)₄] ( 1 ) and [Gd₂L₂(NO₃)₂(DME)₄] ( 2 ) [H₂L = (E)-2-((2-hydroxybenzylidene)amino)phenol] were obtained under hydrothermal condition. Two Ln^III ions are bridged by two phenolic hydroxyl oxygen atoms, and the distances of them are 3.829 Å (Dy1–Dy1A) and 3.860 Å (Gd1–Gd1A). Two Dy1–O–Dy1A and Gd1–O–Gd1A angles are 109.4° and 109.8°, respectively. Magnetic studies reveal a weak antiferromagnetic interaction between Gd ions in complex 2 , and single-molecule magnet behavior for 1 with U_eff = 49.9 K and τ₀ = 1.54 × 10^–6 s.     

Research progress on transition metal oxide based electrode materials for asymmetric hybrid capacitors

In the past few years, the increasing energy consumption of traditional fossil fuels has posed a huge threat to human health. It is very imperious to develop the sustainable and renewable energy storage and conversion devices with low cost and environment friendly features. Hybrid supercapacitors are emerging as one of the promising energy devices with high power density, fast charge-discharge process and excellent cycle stability. However, morphology and structure of the electrode materials exert serious effect on their electrochemical performances. In this review, we summarized recent progresses in transition metal oxide based electrode materials for supercapacitors. Different synthesis routes and electrochemical performances of electrode materials and storage mechanisms of supercapacitor devices have been presented in details. The future developing trends of supercapacitor based on metal oxide electrode materials are also proposed.     

基于拟相对内部集值优化问题弱有效元的最优性条件

本文研究了基于拟相对内部的非凸集值优化问题弱有效元的最优性条件.首先,讨论了弱有效元与线性子空间之间的关系,利用涉及拟相对内部的凸集分离定理,获得了弱有效元的最优性条件.其次,给出了基于拟相对内部弱有效元的Lagrange乘子定理.     

序线性空间中向量优化问题的K-T型定理

本文在广义凸性条件下,研究实线性空间中一类向量优化问题的最优性条件,我们引入F ritz-John鞍点,、“K-T鞍点”讨论它们与有效解、弱有效解之间的关系.     

852.3 nm激光线共振激发Cs蒸气的荧光光谱

研究了Cs蒸气被单模半导体激光器的852.3 nm线激发产生的荧光光谱。由Cs,Cs₂的荧光及其强度确定了在受激Cs-Cs₂系统中的若干碰撞和辐射过程。高位态原子线是由Cs(6P_3/2)+ Cs(6P_3/2)到Cs(6D,8S)的碰撞能量合并形成的,Cs₂(B 1∏_u)带则由Cs(6P)+Cs₂(X 1Σ+_g)碰撞转移产生。通过激发转移、能量碰撞合并和Cs₂-Cs碰撞传能研究了6 2P原子的精细结构混合,得到了6P_3/2→6P_1/2碰撞转移速率系数是(5.2±2.1)×10-11 cm3·s-1,给出了过程Cs₂(B 1∏_u)+Cs(6S)→Cs₂(X 1Σ+_g)+Cs(6P_1/2)的速率系数是(1.0±0.4)×10-9 cm3·s-1。     

Ba2SiO4荧光粉中Ce3+和Eu2+的光谱性质和能量传递

采用高温固相法合成了绿色荧光粉Ba2SiO4:Ce3 ,Eu2 .测量了它们的吸收光谱、激发光谱和发射光谱,观察到了Ba2SiO4中Ce3 对Eu2 发光的敏化现象,发光的敏化作用缘于Ce3 和Eu2 之间的高效无辐射能量传递.     

Energy transport in boundary driven quantum spin systems: One-way street phenomenon in models with long range interactions

We address the investigation of non trivial properties of the energy current in boundary driven XXZ quantum spin models. In specific, we focus on the occurrence of the one-way street phenomenon in asymmetrical chains, a phenomenon stronger than rectification, which establishes the existence of a unique way for the energy current in the absence of external magnetic field, that is, the magnitude and direction of the energy flow does not change as we invert the baths at the boundaries. For general target polarizations at the boundaries, we show that such a phenomenon holds in the presence of long range interactions, ingredient which increases the flow and the rectification in chains of classical oscillators, and so, of interest in the study of manipulation and control of the energy flow.     

Nonlinear energy harvesting from vibratory disc-shaped piezoelectric laminates

Implementing resonators with geometrical nonlinearities in vibrational energy harvesting systems leads to considerable enhancement of their operational bandwidths. This advantage of nonlinear devices in comparison to their linear counterparts is much more obvious especially at small-scale where transition to nonlinear regime of vibration occurs at moderately small amplitudes of the base excitation. In this paper the nonlinear behavior of a disc-shaped piezoelectric laminated harvester considering midplane-stretching effect is investigated. Extended Hamilton's principle is exploited to extract electromechanically coupled governing partial differential equations of the system. The equations are firstly order-reduced and then analytically solved implementing perturbation method of multiple scales. A nonlinear finite element method(FEM) simulation of the system is performed additionally for the purpose of verification which shows agreement with the analytical solution to a large extent. The frequency response of the output power at primary resonance of the harvester is calculated to investigate the effect of nonlinearity on the system performance. Effect of various parameters including mechanical quality factor, external load impedance and base excitation amplitude on the behavior of the system are studied. Findings indicate that in the nonlinear regime both output power and operational bandwidth of the harvester will be enhanced by increasing the mechanical quality factor which can be considered as a significant advantage in comparison to linear harvesters in which these two factors vary in opposite ways as quality factor is changed.