Longitudinal permeability determination of dual-scale fibrous materials

In this work, the longitudinal permeability of squarely packed dual-scale fiber preforms is studied theoretically. These fiber preforms are composed of aligned porous tows and the tows are tightly packed. The effective permeability is calculated as a parallel-like network of intra-tow permeability and inter-tow permeability, which are quantified by Darcy’s law and the inscribed radius between tows, respectively. The jump velocity at the interface between inter-tow fluids and porous tows is considered, as derived by substituting Beavers and Joseph’s correlation into Brinkman’s equation. We further examine the effects of intra-tow permeability on the effective permeability of the fibrous system with three interface conditions: (1) interface velocity = 0, (2) interface velocity = mean intra-tow velocity, and (3) interface velocity = jump velocity. The jump-velocity-based model is found to be closest to numerical data. The influence of the fiber volume fraction of tows on the effective permeability is also analyzed.     

A review on spindle thermal error compensation in machine tools

Thermal error caused by the thermal deformation is one of the most significant factors influencing the accuracy of the machine tool. Among all the heat sources which lead to the thermal distortions, the spindle is the main one. This paper presents an overview of the research about the compensation of the spindle thermal error. Thermal error compensation is considered as a more convenient, effective and cost-efficient way to reduce the thermal error compared with other thermal error control and reduction methods. Based on the analytical calculation, numerical analysis and experimental tests of the spindle thermal error, the thermal error models are established and then applied for implementing the thermal error compensation. Different kinds of methods adopted in testing, modeling and compensating are listed and discussed. In addition, because the thermal key points are vital to the temperature testing, thermal error modeling, and even influence the effectiveness of compensation, various approaches of selecting thermal key points are introduced as well. This paper aims to give a basic introduction of the whole process of the spindle thermal error compensation and presents a summary of methods applied on different topics of it.     

Structural performance of ballastless track slabs reinforced with BFRP and SFCB

Because of the inductive impedance caused by steel meshes in traditional reinforced ballastless track slabs, the electrical properties, primarily the rail resistance and inductance, of jointless track circuits are affected by electromagnetic induction between the slabs and the electric current in the rail. This problem results in poor transmission performance throughout the track circuit. Insulating sleeves or cards between the steel meshes have been used to improve the insulation capability of steel meshes in slabs; however, they reduce the bonding performance between the steel bars and concrete. Because of the good insulation properties of fiber-reinforced polymer composite bars (FRPs) and steel-fiber reinforced polymer composite bars (SFCBs), these composite materials have shown potential to overcome this insulation problem. However, the structural performance of the ballastless track slabs reinforced by basalt fiber reinforced polymer composite bars (BFRPs) and SFCBs, which play a key role in the structure and transportation safety, needs to be investigated. In this paper, six ballastless track slabs reinforced with BFRPs, SFCBs, and steel bars were constructed and tested. The following results were obtained. (1) Shear failures were observed for all slabs, both the BFRP and SFCB slabs meet the load level requirements, and SFCBs reinforcements have higher strength utilization compared with BFRPs reinforcements. (2) The bond-quality of SFCBs and BFRPs reinforcements proved slightly poorer than that of the steel bars. Because of the good corrosion resistance of the FRP, the maximum crack width limits can be slightly larger than that of the RC slabs. (3) Bischoff’s equation was initially used to calculate the deflection of partially prestressed concrete slabs under service loads. The results demonstrated a good agreement between the theoretical and experimental analysis. (4) Considering the tensile stiffness, the modified ACI equation was used to calculate the slabs’ crack width and the theoretical and experimental results showed a good agreement.     

Hygrothermal deformation of orthotropic nanoplates based on the state-space concept

This paper deals with the investigation of the effect of hygrothermal conditions on the bending of nanoplates using Levy type solution model employing the state-space concept. The nanoplates are assumed to be subjected to a hygrothermal environment. The two-unknown function plate theory is used to derive the governing differential equations on the basis of Eringen's nonlocal elasticity theory. The governing equations contain the small scale effect as well as hygrothermal and mechanical effects. These equations are converted into a set of first-order linear ordinary differential equations with constant coefficients. Analytical solution of bending response for nanoplates under combinations of simply supported, clamped and free boundary conditions is obtained. Comparison of the results with those being in the open literature is made. The influences played by small scale parameter, temperature rise, the degree of moisture concentration, boundary conditions, plate aspect ratio and side-to-thickness ratio are studied.     

Research on the relationship between cephalosporin structure,solution clarity,and rubber closure compatibility using volatile components profile of butyl rubber closures

Objective: Establish an effective experimental strategy to determine the compatibility of rubber closures for drugs.

Significance: Various types of rubber closures with different compositions are available for drug packaging. Many additives of rubber closures can be released from rubber closures and may affect the quality of drugs and pose a risk to human health. In this study, we aimed to determine the relationship between cephalosporin structure, solution clarity, and rubber closure compatibility using volatile components profile of butyl rubber closures.

Methods: Two opposite polarity gas chromatography (GC) systems and GC-mass spectrometry (MS) were used to achieve rapid qualitative determination of the main volatile components in rubber closures. Simulated adsorption experiment was performed to investigate the adsorption of main volatile components in rubber closures by cephalosporins with different side chain structures, and to determine the effects of adsorption on solution clarity.

Results: A volatile components screening library of rubber closures was established and the structures of some volatile component were confirmed. The specific adsorption of the structure of cephalosporins on volatile components from rubber closures was studied.

Conclusion: Based on the results of this study, rubber closures with good compatibility for cephalosporins with different side chain structures can be selected rapidly. This experimental strategy not only facilitates the screening of suitable rubber closures more effectively, but also enables the quick determination of volatile components adsorbed by drugs.     

Optimized techniques for driving and control of the switched reluctance motor to improve efficiency

This work presents modeling, driving and classical speed control techniques for the switched reluctance motor. The aim is to improve the computational model, the control response and the machine efficiency. A parametric regression model was used to find the inductance profile of the switched reluctance motor and from the new inductance profile model. The drive and control techniques are shown: (i) with speed control acting on the excitation voltage and fixed switching angles, (ii) with speed control acting on the switching angles and fixed excitation voltage and (iii) with speed control acting on the excitation voltage, in this case, with dynamic switching angles and controller parameters. The inductance profile is represented by expression and inserted into the machine computer model, allowing greater precision and low computational cost. The speed control acting on the excitation voltage with dynamic controller parameters and dynamic switching angles allowed: (i) shorter response time for a wide range of control, (ii) higher efficiency, (iii) low computational cost and (iv) simplified implementation and maintenance. The techniques proposed in this work obtained precision of the computational model with respect to the system (in workbench) and optimized parameters in a wide range of the speed control, allowing an improvement of switched reluctance motor efficiency.     

大新锰矿复杂空区群三维数值模型构建方法及胶结充填治理研究

矿山岩土工程数值分析中研究复杂空区群三维数值模型构建方法对空区治理具有现实意义。为精确分析矿山地下工程围岩移动和应力变化规律，特别是不同采矿方法形成的复杂空区的稳定性和矿柱应力变化，提出了3DMine-Surfer-Rhino-ANSYS-FLAC3D多软件联合建模方法，解决了复杂空区群三维数值模型构建和大数量小尺寸矿房矿柱网格剖分问题。以广西大新锰矿矿体开采为案例，构建了留矿法与房柱法形成的采空区的三维数值模型，模拟分析空区的稳定性和决策胶结充填治理方案。研究结果表明：（1）大新锰矿留矿法开采的空区部分顶柱有垮落风险；（2）房柱法开采的空区部分矿柱变形大，有塑性破坏；（3）对于胶结充填留矿法的空区，隔一充一充填方案治理效果更好，在治理初期地表沉降更小。     

仿人机器人的机械结构设计与控制系统构建

文章研发了一款适用于机器人教育教学的多功能、多用途、普适性的19自由度的小型仿人机器人,主要完成了该机器人的机械结构设计与控制系统构建工作[1]。所设计的机器人机械结构可靠性高、工艺性好、结构紧凑、样式新颖；所构建的机器人控制系统鲁棒性高、稳定性好、控制准确、反应迅速,圆满地实现了预期的设计任务。通过对优缺点的综合对比,得出组合式构型方案在功能性、实用性和稳定性等方面具有明显优势,有望通过后续软件系统的开发提高其运动效能,真正在青少年机器人教育中发挥重要作用[2]。     

低分子量聚丙烯酸钾的合成及其应用

采用水溶液聚合法制备了低分子量聚丙烯酸钾（PAAK），并作为新型消焰剂加入单基发射药中。通过火焰原子吸收光谱法测试了PAAK中钾的含量；用乌氏黏度计测定了特性黏度；采用DSC法研究不同pH值的PAAK与硝化棉（NC）的相容性；利用充氮氧弹法对添加PAAK、硝酸钾KNO₃、硫酸钾K₂SO₄的单基发射药的燃烧残渣进行了对比研究。结果表明，合成的PAAK中，钾的质量分数为15.21%，相对分子量在3 000左右，有利于和NC均匀混合，且在中性或微碱性（pH＝7.0~7.5）的情况与NC相容性良好。与传统的KNO₃、K₂SO₄消焰剂相比，PAAK能够和NC均匀混合，制备均质透明的单基发射药；PAAK发射药的燃烧残渣最少，占发射药质量的0.18%。