Vibration Damping of Carbon Nanotube Assembly Materials

Vibration reduction is of great importance in various engineering applications, and a material that exhibits good vibration damping along with high strength and modulus has become more and more vital. Owing to the superior mechanical property of carbon nanotube (CNT), new types of vibration damping material can be developed. This paper presents recent advancements, including our progresses, in the development of high-damping macroscopic CNT assembly materials, such as forests, gels, films, and fibers. In these assemblies, structural deformation of CNTs, zipping and unzipping at CNT connection nodes, strengthening and welding of the nodes, and sliding between CNTs or CNT bundles are playing important roles in determining the viscoelasticity, and elasticity as well. Towards the damping enhancement, strategies for micro-structure and interface design are also discussed

厌氧条件在不同Fe( II) 浓度测定方法中必要性的比较研究

厌氧是目前Fe(II)测定方法中常选择的处理方式,但是不可避免会给实验操作带来不便。为了方便、准确地测定铁还原体系中的Fe(II)浓度,对比研究了厌氧条件对草酸—草酸铵和盐酸两种典型浸提方法测定Fe(II)浓度的影响。结果表明:对于草酸—草酸铵浸提法,厌氧条件是必须的,以防止提取液中的Fe(II)被氧化,而且样品浸提1 h 便可用于Fe(II)的测定;然而对于盐酸浸提法,厌氧条件却并不是必须的,对Fe(II)浓度测定基本不产生影响。因此,为简化实验操作或在没有厌氧条件的情况,可利用盐酸浸提法测定铁还原体系中Fe(II)浓度

Wide-Range Tunable Dynamic Property of Carbon Nanotube-Based Fibers

Carbon nanotube (CNT) fiber is formed by assembling millions of individual tubes. The assembly feature provides the fiber with rich interface structures and thus various ways of energy dissipation, as reflected by the non-zero loss tangent (>0.028--0.045) at low vibration frequencies. A fiber containing entangled CNTs possesses higher loss tangents than a fiber spun from aligned CNTs. Liquid densification and polymer infiltration, the two common ways to increase the interfacial friction and thus the fiber's tensile strength and modulus, are found to efficiently reduce the damping coefficient. This is because the sliding tendency between CNT bundles can also be well suppressed by the high packing density and the formation of covalent polymer cross-links within the fiber. The CNT/bismaleimide composite fiber exhibited the smallest loss tangent, nearly as the same as that of carbon fibers. At a higher level of the assembly structure, namely a multi-ply CNT yarn, the inter-fiber friction and sliding tendency obviously influence the yarn's damping performance, and the loss tangent can be tuned within a wide range, as similar to carbon fibers, nylon yarns, or cotton yarns. The wide-range tunable dynamic properties allow new applications ranging from high quality factor materials to dissipative systems

洱海流域水生态分区

分区边界的确定是生态分区的重要步骤,但目前多数水生态分区的边界确定以定性分析、专家判断为主。本研究以洱海流域为例,建立了一套两级分区体系。该体系基于GIS技术,用子流域作为分区基本单元,并用相关分析法,定量筛选一、二级分区指标。其中,一级分区指标为高程、坡度和植被归一化指数(NDVI),二级分区指标为农田百分比和城镇百分比。通过指标图层的叠加和重分类,合并同质性子流域,从而将洱海流域划分为5个一级区和9个二级区。藻类群落分布的验证结果表明分区合理。本研究将定量分析和子流域边界应用于水生态分区,使分区边界的确定更科学,在实际管理中更具有可操作性。本研究结果为水生态分区研究提供了新的方法,为洱海流域水生态管理提供了基本管理单元

Randomized Approximation Algorithm for MAX-CNF

已有的Johnson算法是求解组合问题的一种随机近似算法,可以用于求解MAX-CNF问题。基于该算法,提出新的随机近似算法RCNF求解MAX-CNF问题。概率推导和实验数值均表明,RCNF具有良好的近似比和稳定的性能。在构成难可满足问题的CNF实例上,将新算法与演化算法结合,进一步提出扩展算法E-RCNF。扩展算法利用演化算法的并行性,可以在较短时间内,简单有效地求出最多可满足子句数的近似值。Johnson's algorithm is a known randomized approximation algorithm for combinatorial problems including MAX-CNF problem.Based on it,this paper proposes a new algorithm RCNF,which has a steady performance and improves Johnson's algorithm on approximation ratio.On a class of instance of CNF,which constitutes hard-SAT problem,a further improvement is proposed which combines the RCNF algorithm with parallel evolutionary algorithm.Computational experiments show that this algorithm is faster and better than another given hybrid algorithm.“985工程”项目(0000-X07204)

求解MAX- CNF 问题的一种随机近似算法

已有的Johnson 算法是求解组合问题的一种随机近似算法, 可以用于求解MAX- CNF 问题。基于该算法, 提出新 的随机近似算法RCNF 求解MAX- CNF 问题。概率推导和实验数值均表明, RCNF 具有良好的近似比和稳定的性能。在 构成难可满足问题的CNF 实例上, 将新算法与演化算法结合, 进一步提出扩展算法E- RCNF。扩展算法利用演化算法的 并行性, 可以在较短时间内, 简单有效地求出最多可满足子句数的近似值。“985 工程”项目( 0000- X07204

Bio-Inspired Aggregation Control of Carbon Nanotubes for Ultra-Strong Composites

High performance nanocomposites require well dispersion and high alignment of the nanometer-sized components, at a high mass or volume fraction as well. However, the road towards such composite structure is severely hindered due to the easy aggregation of these nanometer-sized components. Here we demonstrate a big step to approach the ideal composite structure for carbon nanotube (CNT) where all the CNTs were highly packed, aligned, and unaggregated, with the impregnated polymers acting as interfacial adhesions and mortars to build up the composite structure. The strategy was based on a bio-inspired aggregation control to limit the CNT aggregation to be sub 20--50 nm, a dimension determined by the CNT growth. After being stretched with full structural relaxation in a multi-step way, the CNT/polymer (bismaleimide) composite yielded super-high tensile strengths up to 6.27--6.94 GPa, more than 100% higher than those of carbon fiber/epoxy composites, and toughnesses up to 117--192 MPa. We anticipate that the present study can be generalized for developing multifunctional and smart nanocomposites where all the surfaces of nanometer-sized components can take part in shear transfer of mechanical, thermal, and electrical signals

浅析巨灾期权在我国的运用

我国是一个自然灾害多发的国家,巨大自然灾害的破坏力不言而喻,多年来我国也一直在寻找着有效的解决办法。本文从目前我国巨灾风险的现状出发,以巨灾期权为例剖析了我国应如何应对巨灾风险,并相应提出了建议及对策

台湾社会“统独”意识消长成因及发展新态势

台湾社会存在的“统独“意识是构成岛内“统独“矛盾的要素之一,而“统独“矛盾的变迁既是观察台湾民意走向及两岸关系发展变化的重要因素,也是考察两岸关系和平发展长期趋势时不得不深入研究的一个课题。台湾学者施正锋援引西方政治学的解释也认为,意识的产生可以归纳为三大类型:原生论认为人群的集体认同建立于有形文化或是自然的生物特征上;结构论认为集体认同的产生,主要是因为不满自身