无阀压电泵的流固耦合仿真及试验验证

提出利用结构分析软件ANSYS和流体分析软件ANSYS CFX对无阀压电泵进行流固耦合仿真分析,以研究无阀压电泵的输出性能。分别对进口在中间出口在一侧、出口在中间进口在一侧、进出口对称布置的3种不同结构形式的无阀压电泵进行了流固耦合仿真分析。结果显示,上述3种无阀压电泵中,出口在中间进口在一侧结构形式的无阀压电泵的宏观输出流量最大。制作了3种无阀压电泵的试验样机,并搭建了相应的试验测试系统,在幅值为45 V、频率为0~700Hz的正弦信号激励下对其输出流量进行了测试。结果表明,3种不同结构形式的无阀压电泵的最大输出流量分别为3.8、6.0和4.0ml/min,出口在中间进口在一侧的压电泵输出流量最大,与流固耦合仿真分析的结果相吻合,验证了本文提出的流固耦合仿真分析的方法可以指导压电泵的设计。     

Complexity of CO2 adsorption on nanoporous sulfur-doped carbons – Is surface chemistry an important factor?

Nanoporous S-doped carbon and its composites with graphite oxide were tested as adsorbents of CO₂ (1 MPa at 0 °C) after degassing either at 120 °C or 350 °C. The adsorption capacities were over 4 mmol/g at ambient pressure and 8 mmol/g at 0.9 MPa in spite of a low volume of micropores. The nitrogen adsorption experiments showed an increase in porosity upon an increase in the degassing temperature. The extent of this effect depends on the stability of surface groups. Interestingly, the CO₂ adsorption, especially at low pressure, was not affected. The good performance is due to the presence of ultramicropores similar in sizes to CO₂ molecule and to sulfur in various functionalities. Sulfur incorporated to aromatic rings enhances CO₂ adsorption via acid–base interactions in micropores. Moreover, sulfonic acids, sulfoxides and sulfones attract CO₂ via polar interactions. Hydrogen bonding of CO₂ with acidic groups on the surface can also play an important role in the CO₂ retention. These carbons have high potential for application as CO₂ removal media owing to their high degree of pore space utilization. The results obtained also show that high degassing temperatures might result in the decomposition of surface groups and thus in changes in surface interactions.     

Graphene oxide–TiO2 composite filtration membranes and their potential application for water purification

Graphene oxide-particle composite films with filtration function have been successfully synthesized by a two-step method. First, graphene oxide–TiO₂ composite sheets are prepared, which can form stable dispersion in water. Then, by assembling these composite sheets, graphene oxide–TiO₂ films are obtained. In these as-prepared films, dilated space and channels are desirably formed by introducing nanoparticles between these carbon sheets, making them promising separation membranes. We used these films as filtration membranes to remove dye molecules (methyl orange and rhodamine B) from water. The results show that apart from the adsorption capacities of these dyes, these graphene oxide–TiO₂ films can also capture additional amount of dye molecules, indicating their potential applications in water purification areas.     

Luminescence of Eu‐Doped Transparent LuPO4 Glass‐Ceramics

Dual valence Eu‐doped transparent glass‐ceramics containing LuPO₄ nanocrystals were fabricated by melt‐quenching technique in air atmosphere. Their luminescent properties were systematically investigated by excitation, emission spectra, and decay lifetime measurements. The prominent Stark splitting, low forced electric‐dipole ⁵D₀ – ⁷F₂ transition and long decay lifetimes of Eu^{3 +} emission for glass‐ceramics reveal the incorporation of Eu^{3 +} into LuPO₄ nanocrystals. The enhanced Eu^{2 +} emission and reduction mechanism of Eu^{3 +} to Eu^{2 +} after crystallization are discussed briefly. Our results indicate that transparent LuPO₄ glass‐ceramics may find applications in photonics.     

聚磷酸铵聚合度影响因素的研究

聚磷酸铵具有良好的热稳定性和优良的阻燃性能,是应用领域十分广泛的添加型阻燃剂,不产生二次污染。但聚合度的大小直接影响到其与阻燃基材的相容性,以磷酸和尿素为原料,控制适宜的聚合条件,合成了高聚合度的聚磷酸铵,得到了在此实验范围内最佳工艺条件:T=175℃,反应时间t=2～3 h,配样比为:H3PO4(70%)∶CO(NH2)2=1∶1.84。即得粉末状的APP聚合物,通过端基滴定法测定聚合度,其平均聚合度大于20。     

MnO anchored reduced graphene oxide nanocomposite for high energy applications of Li-ion batteries: The insight of charge-discharge process

In the present work, a new class of anode material for high energy applications of Li-ion battery is prepared by easy and large-scale producible process. Herein, the nanocomposite of MnO and reduced graphene oxide (rGO) is prepared by anchoring MnO nanoparticles into 3D matrix of rGO hydrogel followed by annealing process. The composite which has homogeneous distribution of MnO particles on conducting rGO layers demonstrated superior electrochemical performance such as high reversible capacity, stable cycle life and better rate capability. It has shown initial discharge capacity of 2358 mAh g⁻¹ and retained 570 mAh g⁻¹ after 100 cycles as compared to pristine MnO which shown initial discharge capacity of 820 mAh g⁻¹ and retained only 45 mAh g⁻¹ after 100 cycles. The retained capacity of new MnO/rGO anode is much higher than the theoretical capacity of conventional graphite anode. Moreover, the MnO/rGO nanocomposite shows six times higher Li⁺ ion diffusion of 4.18 × 10⁻¹² cm² s⁻¹ as compared to 6.84 × 10⁻¹³ cm² s⁻¹ of MnO. In addition, the study provides insight of charge-discharge process, which conducted in initial, discharge and charge states of pristine MnO and MnO/rGO composite using ex-situ X-ray diffraction and X-ray photon spectroscopy techniques.     

A novel nonlinear algorithm for typhoon cloud image enhancement

A novel nonlinear gray transform method is proposed to enhance the contrast of a typhoon cloud image. Generally, the typhoon cloud image obtained by a satellite cannot be directly used to make an accurate prediction of the typhoon’s center or intensity because the contrast of the received typhoon cloud image may be bad. Our aim is to extrude the typhoon’s eye in the typhoon cloud image. A normalized arc-tangent transformation operation is designed to enhance global contrast of the typhoon cloud image. Differential evolution algorithm is used to choose the optimal nonlinear transform parameter. Finally, geodesic activity contour model is used to extract the typhoon’s eye to verify the performance of the proposed method. Experimental results show that the proposed method can efficiently enhance the global contrast of the typhoon cloud image while greatly extruding the typhoon’s eye.     

基于EMD-DCS的滚动轴承伪故障特征识别方法

伪故障特征是健康零部件振动信号中具有的故障特征,伪故障特征是由系统内故障零部件引起的。由于滚动轴承伪故障特征与故障特征具有相似性,针对转子-轴承系统中滚动轴承伪故障特征识别问题,提出一种基于经验模式分解(Empirical Mode Decomposition,EMD)和循环平稳度(Degree of Cyclostationarity,DCS)的伪故障特征识别方法。利用滚动轴承健康信号和伪故障信号对比分析基于单通道伪故障信号进行滚动轴承故障诊断的技术难点;建立了考虑滚动轴承打滑率的转子-轴承系统动力学模型;利用时频分析方法和循环平稳分析方法对滚动轴承伪故障特征进行分析;给出了基于EMD-DCS的滚动轴承伪故障特征识别流程;在滚动轴承故障模拟实验台上开展了滚动轴承伪故障特征识别实验。实验结果表明:基于EMD-DCS的滚动轴承伪故障信号识别方法可以有效区分滚动轴承故障特征与伪故障特征。该研究工作对于提高滚动轴承故障诊断准确率、保障设备安全运行具有理论意义和实际应用价值。     

Algebraic conditions on the controllability for a type of discrete‐continuous systems with delays

In this paper, the controllability for a type of discrete‐continuous systems with delays is investigated. The solution of such systems based on variation of parameters is derived. Several sufficient and necessary algebraic conditions for the controllability of the system as well as the relation among these conditions are established. It is also shown that the delayed input contributes to achieving the controllability of discrete‐continuous systems. A numerical example is provided to illustrate the effectiveness of the proposed methods. Copyright © 2011 John Wiley & Sons, Ltd.