Graphs with flexible labelings allowing injective realizations

We consider realizations of a graph in the plane such that the distances between adjacent vertices satisfy the constraints given by an edge labeling. If there are infinitely many such realizations, counted modulo rigid motions, the labeling is called flexible. The existence of a flexible labeling, possibly non-generic, has been characterized combinatorially by the existence of a so called NAC-coloring. Nevertheless, the corresponding realizations are often non-injective. In this paper, we focus on flexible labelings with infinitely many injective realizations. We provide a necessary combinatorial condition on existence of such a labeling based also on NAC-colorings of the graph. By introducing new tools for the construction of such labelings, we show that the necessary condition is also sufficient up to 8 vertices, but this is not true in general for more vertices.     

5G数据机房高密度光纤布线系统的升级改造设计与实践

本文重点介绍了适应于5G数据机房改造过程中的光纤布线系统的升级改造实践,建设固网基础设施具备高性能计算、网络架构扁平化、模块化、智能化、集中式管理、可实现交叉连接等特点,在保证高密度的同时,也确保整体布线系统的灵活性和可维护性,实现网络重构与运营重构.5G网络技术的推动以及国家"互联网+"产业需求,数据信息的传输数量和...     

Static analysis of Euler–Bernoulli beams with multiple unilateral cracks under combined axial and transverse loads

The paper deals with the static analysis of pre-damaged Euler–Bernoulli beams with any number of unilateral cracks and subjected to tensile or compression forces combined with arbitrary transverse loads. The mathematical representation of cracks with a bilateral behaviour (i.e. always open) via Dirac delta functions is extended by introducing a convenient switching variable, which allows each crack to be open or closed depending on the sign of the axial strain at the crack centre. The proposed model leads to analytical solutions, which depend on four integration constants (to be computed by enforcing the boundary conditions) along with the Boolean switching variables associated with the cracks (whose role is to turn on and off the additional flexibility due to the presence of the cracks). An efficient computational procedure is also presented and numerically validated. For this purpose, the proposed approach is applied to two pre-damaged beams, with different damage and loading conditions, and the results so obtained are compared against those given by a standard finite element code (in which the correct opening of the cracks is pre-assigned), always showing a perfect agreement.     

云计算趋势对网络基础架构的影响

针对云计算的变革,文章分析云计算发展的几大趋势,阐述适应云计算的关键是要提供高弹性、高扩展性、易管理和开放的网络,并建议未来理想的云计算网络架构应是一个无阻塞、可自愈、即插即用的黑盒网络平台,它可持续演进,并能提供开放的网络业务。     

Exact closed-form solutions for the static analysis of multi-cracked gradient-elastic beams in bending

Cracks and other forms of concentrated damage can significantly affect the performance of slender beams under static and dynamic loads. The computational model for such defects often consists of a localised reduction in the flexural stiffness, which is macroscopically equivalent to a beam where the undamaged parts are hinged at the position of the crack, with a rotational spring taking into account the residual stiffness (“discrete spring” model). It has been recently demonstrated that this model is equivalent to an inhomogeneous Euler–Bernoulli beam in which a Dirac’s delta is added to the bending flexibility at the position of each damage (“flexibility crack” model). Since these models concentrate the increased curvature at a single abscissa, a jump discontinuity appears in the field of rotations. This study presents an improved representation of cracked slender beams, based on a general class of gradient elasticity with both stress and strain gradient, which allows smoothing the singularities in the flexibility crack model. Exact closed-form solutions are derived for the static response of slender gradient-elastic beams in flexure with multiple cracks, and the numerical examples demonstrate the effects of the nonlocal mechanical parameters (i.e. length scales of the gradient elasticity) in this context.     

Flexible microporous coordination polymers

In a decade, many porous coordination polymers have been synthesized, providing a variety of properties ranging from storage, separation and exchange of guests in their cavities, magnetism, conductivity and catalysis by their frameworks. Recent advent of flexible porous coordination polymers, which exhibit elastic guest accommodation in contrast to rigid three-dimensional (3-D) frameworks of conventional porous materials, have acquired a position as a new class of porous materials. Such flexible porous properties induce highly selective guest accommodation and magnetic modulation, which could now be a unique class of practical materials. In this review, we introduce recent flexible porous coordination polymers (3-17) and their functional properties, categorizing with the four types of pores with framework deformation.     

柔性超级电容器电极材料与器件研究进展

超级电容器,也称电化学电容器,它具有比锂离子电池更高的功率密度和更长的循环寿命,与此同时,其能量密度也高于传统的电介质电容器,因此成为了一类具有很大应用前景的能量储存设备。随着人们对智能电子设备性能要求的提高,各类柔性可穿戴电子设备相继出现,柔性超级电容器作为一类便携式能量储存设备也受到了许多研究者的关注。在持续的研究中,二维平面结构的柔性超级电容器得到较大发展并日益成熟,与此同时,随着对柔性电子设备可穿戴性能要求的提高,一维纤维结构的柔性超级电容器应运而生,并且得到了初步发展。本文首先介绍了超级电容器的储能原理和重要性能的评估方法;接着,重点概述了二维平面结构和一维纤维结构两类柔性超级电容器器件结构和电极材料的研究进展;最后,总结了两类柔性超级电容器仍然存在并亟待解决的问题以及未来发展所面临的关键技术挑战,期望能为柔性超级电容器的研究提供参考和借鉴。     

轻质柔性聚酰亚胺纸基电磁屏蔽材料的制备与性能

基于聚酰亚胺纤维纸基导电骨架(PI-CP)的三维网络结构, 通过聚吡咯(PPy)的气相沉积及无钯化学镀工艺在PI-CP上进行镍基金属的层层组装, 制备了夹芯结构的镍/聚吡咯@聚酰亚胺纤维纸基电磁屏蔽材料 (Ni/PPy@PI-CP); 对其形貌、 结构、 导电性能、 力学性能及电磁屏蔽性能进行了表征; 并考察了温度、 弯曲牢度和折叠次数对Ni/PPy@PI-CP导电性能和电磁屏蔽性能的影响. 研究结果表明, Ni/PPy@PI-CP-3的电磁屏蔽性能可达到70 dB以上; Ni/PPy@PI-CP-3在弯曲变形下表现出优良的导电稳定性, 其电导率损失可以忽略不计, 经过200次的反复弯曲测试, 其电导率仍保持在92.4%以上. 此外, Ni/PPy@PI-CP还具有轻质及易于加工的特性, 并具有稳定的热性能, 于300 ℃下处理后电磁屏蔽性能仍保持在80％以上.     

Electromechanical properties of graphene transparent conducting films for flexible electronics

We report a systematic study of the electromechanical properties of graphene films for flexible transparent conducting electrodes. The flexibility of graphene films, which were grown using a chemical vapor deposition (CVD) method and transfer process on polyethylene terephthalate (PET) substrates, was investigated using a lab-made inner/outer bending, twisting and stretching test system. The electromechanical properties as a function of the change of bending radius, twisting angle and strain distance were evaluated by measuring the change in resistance. The change in resistance during the inner bending test was less than 8% even when the bending radius was 3 mm. Additionally, the results of the inner bending fatigue test showed a constant resistance throughout 2000 bending cycles. However, in the outer bending test, the resistance increased substantially when the bending radius was smaller than 10 mm. Therefore, we can expect that more cracks form between the grains of graphene during the outer bending test. The twistability and stretchability of the graphene film were also investigated. Both twisting and stretching tests show gradually increasing resistances according to the twisting angle and stretching distance. These results provide useful information regarding the electromechanical properties of graphene transparent conducting films for the development of flexible electronics.