Beneficiation of stockpiled fluidized bed coal ash in road base course construction

The presented paper investigates the potential for the utilization of unprocessed, as excavated (i.e. unground), stockpiled coal combustion fluidized bed ash in road base course construction. In addition to functioning as a stabilizer of the fines in the stockpiled material, this ash also permits treating the stockpiled ash agglomerates as an aggregate. Both untreated and cement-treated mix designs were evaluated. The laboratory program included unconfined strength measurements, triaxial, volumetric swell, and moisture susceptibility testing protocols performed on cylindrical specimens compacted at their optimum moisture content.The results have shown that, without breaking down the agglomerates by grinding, the unstabilized stockpiled ash possesses very little residual cementitious activity; whereas, if treated with small amounts of cement (3%), it meets the required strength criteria for cement-treated base courses while minimizing the volumetric swell characteristics.     

Correlation between atomistic morphology and electron transport properties in defect-free and defected graphene nanoribbons: An interpretation through Clar sextet theory

Structural, electronic and transport properties of defect-free, defected and functionalized armchair and zig-zag graphene nanoribbons (GNRs) are investigated with density functional theory and non-equilibrium Green’s function calculations and rationalized in terms of Clar’s theory of the aromatic sextet. Calculations suggest a tight relationship between the transport properties of nanoribbons and the underlying bond patterning as described by valence bond and Clar sextet theory. Namely, armchair GNRs exhibit a strong dependence of the transport properties on the ribbon width, as a consequence of different valence bond representations. The occurrence of localized defects involving electron pairs does not significantly alter this behavior. Conversely, transport properties of zigzag GNRs are less affected by morphological details, such as width and occurrence of defects, as expected from the application of Clar’s theory. However, controlled edge functionalization and morphology modifications in zigzag GNRs can potentially lead to localization of aromatic sextets and, consequently, to strong changes in the transport properties. Our work indicates Clar sextet theory as a powerful and accurate tool to rationalize and predict the electronic and transport properties of complex carbon nanostructures based on GNRs. These principles can be extended to the design of novel systems with potential applications in nanoelectronics.     

混合离散变量模拟退火方法及其应用

基于海洋工程中存在的设计变量为离散型和连续型的混合离散变量的情况,探讨了一种优化设计问题的方法———混合离散模拟退火法.该方法相对常规模拟退火方法有一定改进并且针对混合离散变量进行了特定处理.实际算例计算表明,该方法可用于海洋工程优化设计中,其结果不需圆整,而且其解题可靠性和效率相当高.     

Surface effects on the vibrational frequency of double-walled carbon nanotubes using the nonlocal Timoshenko beam model

Double-walled carbon nanotubes (DWCNTs) are being investigated for use as latent materials for drug carriers. However, the surface effects cannot be ignored when drugs or other functional materials, such as nickel or silver, adhere to the surface of the outer tube of a DWCNT. In this paper, the vibrational frequency of DWCNTs, while accounting for surface effects, is studied using the nonlocal Timoshenko beam model. The influence of the surface elasticity modulus, residual surface stress, nonlocal parameter, axial half-wave number and aspect ratio are investigated in detail. The results show that the vibrational frequency is significantly affected by the surface material, nonlocal parameter, vibration mode and aspect ratio. In short DWCNTs on condition of higher vibrational modes, the influences of the surface and nonlocal effects on vibration are more pronounced.     

柔性被动隔振系统的功率流传递特性研究

对柔性被动隔振系统的功率流传递特性进行研究,建立了隔振器倾斜放置的隔振系统的理论模型,运用机械导纳法推导了系统的功率流传递函数．数值仿真中,分别考虑了无限板和有限板、厚板和薄板的情况,通过大量的数值仿真对这些情况的功率流特性进行了详细研究,得到一些对工程实际具有借鉴意义的结论．     

动力定位系统中桨-船干扰问题研究

该文研究了静水中动力定位系统推进器的桨-船干扰问题。首先对动力定位系统推进器桨-船干扰的影响因素进行分析,如前桨尾流冲击后桨所造成的桨-桨干扰、柯安达效应以及摩擦损失造成的桨-船干扰等,而后利用数值模拟方法和模型试验重点对推进器方位角的变化所造成的推进器桨-船干扰分析研究。经对比分析,动力定位推进系统中桨-船干扰可造成44%的推力损失,是动力定位推进器安装布置不可忽略的因素。该文的研究对提高动力定位推进系统效率,加强动力定位能力具有重要的意义。     

Tunnel waterproofing practices in China

Water ingress in transportation tunnels not only will shorten the durability of concrete lining and reduce the function of establishments in the tunnel, but also will worsen the tunnel surrounding so much that the traffic will be greatly affected. In this situation, therefore, high maintenance costs are compulsory. In many cases, a perfect appearance is strongly recommended to take measures in order to prevent leakage. However, in China, tunnel waterproof requirements and standards for various special uses are considerably different, such that the basis which engineers apply to design in water-control is insufficient. Especially in montanic region, unpleasant geological condition confines engineers in working out more reasonable methods to stop water seepage, even leakage. In this paper, the current waterproofing requirements and measures in different special tunnels adopted in China are reviewed. The limitations of the popular methods in several practical cases applied to prevent water leakage, such as watertight lining, drainage system, as well as grouting, are analyzed at length. Then, some available measures, regarding concrete lining, watertight layer, drainage establishments as well as casting watertight concrete, are proposed, which we think indispensable for tunnel engineering to efficiently control water seepage and even completely prevent water leakage. In the end, to analyze the seepage field in montanic tunnels, the finite element and boundary element coupling analysis method is presented. As an example, the seepage field in Zhenwushan tunnel of Chongqing is simulated. The calculation results coincide with the in-situ data well, and provide credible evidence for the waterproof measures which will be taken in that tunnel project. The method presented in this paper will save expenditures for surveying measures and will enable more reasonable and reliable waterproofing measures to be taken.     

Relay Requirement and Traffic Assignment of Electric Vehicles

This article defines, formulates, and solves a new equilibrium traffic assignment problem with side constraints—the traffic assignment problem with relays. The relay requirement arises from the driving situation that the onboard fuel capacity of vehicles is lower than what is needed for accomplishing their trips and the number and distribution of refueling infrastructures over the network are under the expected level. We proposed this problem as a modeling platform for evaluating congested regional transportation networks that serve plug‐in electric vehicles (in addition to internal combustion engine vehicles), where battery‐recharging or battery‐swapping stations are scarce. Specifically, we presented a novel nonlinear integer programming formulation, analyzed its mathematical properties and paradoxical phenomena, and suggested a generalized Benders decomposition framework for its solutions. In the algorithmic framework, a gradient projection algorithm and a labeling algorithm are adopted for, respectively, solving the primal problem and the relaxed master problem—the shortest path problem with relays. The modeling and solution methods are implemented for solving a set of example network problems. The numerical analysis results obtained from the implementation clearly show how the driving range limit and relay station location reshape equilibrium network flows.     

The Shrinkage Characteristic of a Spherical Cavity in Three-Dimensional Piezoelectric Grain

In this article, an analytical method is presented to solve the shrinkage rate and the healing history of a spherical cavity in three-dimensional piezoelectric grains under electric field, interface pressure, and internal gas pressure. From example calculations, it is seen that because of the influence of piezoelectric characteristics and electric fields, a spherical cavity in three-dimensional piezoelectric grain subjected to hydrostatic interface pressures does not completely eliminate, which is obviously consistent with some experimental observations from the micro-hole healing process. The result is useful to reveal the healing mechanism of defects in piezoelectric materials under electric and mechanical loads.