Noncovalent Functionalized Graphene-Filled Polyimides with Improved Thermal,Mechanical, and Wear Resistance Properties

A facile method is proposed to prepare poly-o-phenylenediamine (PoPD) noncovalent functionalized graphene (G)-reinforced polyimide (PI) nanocomposites. PoPD-G exhibited excellent dispersibility in various organic solvents. The structures of PoPD-G were characterized by Raman and UV spectrum, which verified the π–π interactions between PoPD and G. The effective exfoliation of graphene nanosheets was investigated by observation of the morphology of PoPD-G with SEM, SPM, and TEM. Compared to PI/G composites, the interfacial adhesion between graphene nanosheets and PI matrices promoted efficient stress transfer from PI chains to PoPD-G nanofillers. Polyimide nanocomposites with different incorporations of PoPD-G exhibited outstanding thermal properties. It is interesting to note that only 0.5 wt% PoPD-G-reinforced PI composites increased by 20.8% in hardness, enhanced by 84.0% in storage modulus, and reduced by 72.8% in wear rate compared with neat PI. The eminent enhancement was attributed to the facile dispersion of graphene nanosheets and strong interface adhesion between PI and PoPD-G.     

Kinetic theory for aquatic animal distribution simulation

Identifying the underlying mechanisms that influence the spatial patterns in populations improves the forecasts of the alternative management strategies on the spatial dynamics of the populations, which are critical for assessing and managing the fisheries and improving the water resource management. This paper described a new approach of the numerical model for the prediction of the aquatic animal distribution in the flows. The model was developed based on the kinetic theory of gases, the mechanism of the aquatic animal movement and the flow hydrodynamic patterns. The model was validated using the available experimental data and an acceptable agreement was obtained. A comprehensive parameter study was then conducted to help understand the impact and the sensitivity of each parameter to the aquatic animal distribution. The promising results of the model reveal the prospect of applying this model to the reliable prediction of the aquatic animal distribution within a relatively large water area.     

An efficient equivariant adaptive separation via independence algorithm for acoustical source separation and identification

To balance the convergence rate and steady-state error of blind source separation (BSS) algorithms, an efficient equivariant adaptive separation via independence (Efficient EASI) algorithm is proposed based on separating indicator, which was derived from the convergence condition of EASI, and can be used to evaluate the separation degree of separated signals. Furthermore, a nonlinear monotone increasing function between suitable step sizes and separating indicator is constructed to adaptively adjust step sizes, and forgetting factor is employed to weaken effects of data at the initial stage. Numerical case studies and experimental studies on a test bed with shell structures are provided to validate the efficiency improvement of the proposed method. This study can benefit for vibration & acoustic monitoring and control, and machinery condition monitoring and fault diagnosis.     

双三相永磁同步电动机一相绕组短路故障性能分析

对双三相永磁同步电动机发生一相短路故障时的磁场分布、磁链、电流以及输出转矩等电磁性能进行分析,并与传统三相电机进行比较.结果表明,双三相电机相与相之间的耦合较弱,故障相几乎不影响非故障相的正常运行,电机依然能够在可接受的范围内继续工作,具有一定的容错能力,适用于对电机连续运行有特殊要求的场合.     

Dynamic observation of bainite transformation in a Fe-C-Mn-Si superbainite steel

The dynamic observations of bainitic transformation in a Fe-C-Mn-Si superbainite steel were conducted on a high temperature laser scanning confocal microscope. It is indicated that the mutual intersection of bainite sheaves often occurs during growth of bainite ferrite, resulting in an interlocked bainite microstructure. Moreover, bainite transformation is promoted by higher austenization temperature and the longer and finer bainite platelets are obtained. Further, The average growth rate of bainite after austenization at 1 100 ° is calculated as 5.8 µm·s^?1. In situ observation investigation makes it possible to identify bainite transformation in real time during isothermal holding.     

Improved visible transparency of SIO<Subscript>2</Subscript>/ZNO:AL /CEO<Subscript>2</Subscript>-TIO<Subscript>2</Subscript>/SIO<Subscript>2</Subscript> multilayer films with high UV absorption and infrared reflection rate

New visible transparent, UV absorption, and high infrared reflection properties have been realized by depositing multilayer SiO₂/ZnO: Al/CeO₂-TiO₂/SiO₂ films onto glass substrates at low temperature by radio frequency magnetron sputtering. Optimum thickness of SiO₂, ZnO: Al (ZAO) and CeO₂-TiO₂ (CTO) films were designed with the aid of thin film design software. The degree of antireflection can be controlled by adjusting the thickness and refractive index. The outer SiO₂ film can diminish the interference coloring and increase the transparency; the inner SiO₂ film improves the adhesion of the coating on the glass substrate and prevents Ca²⁺, Na⁺ in the glass substrate from entering the ZAO film. The average transmittance in the visible light range increases by nearly 18%-20%, as compared to double layer ZAO/CTO films. And the films display high infrared reflection rate of above 75% in the wavelength range of 10-25 μm and good UV absorption (> 98%) properties. These systems are easy to produce on a large scale at low cost and exhibit high mechanical and chemical durability. The triple functional films with high UV absorption, antireflective and high infrared reflection rate will adapt to application in flat panel display and architectural coating glass, automotive glass, with diminishing light pollution as well as decreasing eye fatigue and increasing comfort.     

Microstructure and properties of cement foams prepared by magnesium oxychloride cement

Microstructural features including pore size distribution, cell walls and phase compositions of magnesium oxychloride cement foams (MOCF) with various MgO powders and water mixture ratios were studied. Their influences on compressive strength, water absorption and resistance of MOCF were also discussed in detail. The experimental results indicated that moderate and slight excess MgO powders (MgO/MgCl₂ molar ratios from 5.1 to 7) were beneficial to the formation of excellent microstructure of MOCF, but increasing water contents (H₂O/MgO mass ratios from 0.9 to 1.29) might result in opposite conclusions. The microstructure of MOCF produced with moderate and slight excess MgO powders could enhance the compressive strength, while serious excess MgO powders addition (MgO/MgCl₂ molar ratios = 9) would destroy the cell wall structures, and therefore decrease the strength of the system. Although MOCF produced with excess MgO powders could decrease the water absorption, its softening coefficient was lower than that of the material produced with moderate MgO powders. This might be due to the instability of phase 5, the volume expansion and cracking of cell walls as immersed the sample into water.     

Head Orientation Stability of Underwater Snake-Like Robot Swimming

In prior research,the orientation of head of the snake-like robot is changed according to the sinusoidal wave. To solve this problem,we propose Central Pattern Generator( CPG)-based control scheme with head-controller to stabilize the head of the underwater snake-like robot. The advantage of the CPG-based control scheme with head-controller is that the head of the underwater snake-like robot is direct to the target orientation during swimming. The relation between CPG parameters and orientation stability of head is discussed.The adaptation of the proposed method to environment changes is tested. The influences of CPG parameters and hydrodynamic forces on the orientation offset of head are investigated. The target orientation( the input of headcontroller) with an experimental optimization is calculated through a convenient method. To prove the feasibility of the proposed methodology,the different swimming modes have been implemented in our simulation platform.The results show that the oscillation of head’s orientation is inhibited effectively,and the proposed method has strong adaptation to environment and CPG parameters changes.     

Numerical Simulation of Energy Saving Potential in Dispersing Process of Blasted Smoke in Mines

The dispersing process of the blasted smoke in underground mines by ventilation is very important for the safety of personnel, and its energy consumption is also worthy of concern. In this study, the impact of supply air flow rate on the decay process of harmful gases and fan energy, and the role of harmful gases buried by blasted pile in the smoke dispersing process is analyzed with three-dimensional numerical simulation. According to the results, air flow facilitates quick smoke dispersion and the gas emits from the blasted pile is only significant at the beginning of ventilation. It is thus recommended that large amount of air supply is taken to disperse the smoke quickly until the concentration of harmful gases reaches relevant standards, and reduce the amount of air in the remain time with frequency conversion technology to save energy. In the given study, 12 m/s air flow rate is taken for dispersing smoke and 3 m/s air flow rate is taken for the waiting time. The energy consumption for ventilation is reduced by about 50％. In addition, due to the gases in the blasted pile remains very high concentration after the dispersing process, it is recommended to keep suitable amount of ventilation in the consequent process.     

一维炉系统的测试实验

一维炉是一种研究煤的热解燃烧和结渣等方面的实验系统,可用于模拟电厂煤粉的燃烧特性。以元宝山褐煤为燃料,介绍了一维炉的结构和功能,并对系统的可靠性进行了验证,利用烟气分析仪及热重分析仪对燃烧后的尾部烟气及灰渣进行了分析测定。结果表明:尾部烟气含氧量与灰渣可燃部分剩余量均在理论计算值的误差允许范围内,说明一维炉密封良好,系统内各部分正常运行,对维炉的调试和研究具有一定的参考意义。