Random Lattices with Fractal Bond Permeabilities

The macroscopic permeability of random lattices has been studied when the permeability of each link is a power law of its length with an exponent . When they are sufficiently long, the link lengths are shown to follow exponential laws which depend on the density. The macroscopic permeability is studied as a function of ; it is compared to a modified effective medium theory (EMT).*Author for correspondence: e-mail: adler@ipgp.jussieu.fr**e-mail: le_chic@mail.ru     

Characterization of the channel walls roughness in photonic crystal fibers

We present electron microscope (FEI NanoSEM) and atomic force microscopy measurements of surface roughness in nanochannels in photonic crystal fibers (PCF). A method was invented to cleave the PCF along the axis without damaging the surface structure in the nanochannels allowing us to characterize the morphology of the nanochannels in the PCF. A multi-wall carbon nanotube mounted onto commercial AFM probes and super sharp silicon non-contact mode AFM probes were used to characterize the wall roughness in the nanochannels. The roughness is shown to have a Gaussian distribution, and has an amplitude smaller than 0.5 nm. The height–height correlation function is an exponential correlation function with an autocorrelation length of 13 nm, and 27 nm corresponding with scan sizes of 200×100 nm², and 1600×200 nm², respectively.     

Uncommon suffix tries

Common assumptions on the source producing the words inserted in a suffix trie with n leaves lead to a height and saturation level. We provide an example of a suffix trie whose height increases faster than a power of n and another one whose saturation level is negligible with respect to . Both are built from VLMC (Variable Length Markov Chain) probabilistic sources and are easily extended to families of tries having the same properties. The first example corresponds to a “logarithmic infinite comb” and enjoys a non uniform polynomial mixing. The second one corresponds to a “factorial infinite comb” for which mixing is uniform and exponential. © 2013 Wiley Periodicals, Inc. Random Struct. Alg., 46, 117–141, 2015     

Emergent geometry experienced by fermions in graphene in the presence of dislocations

In graphene in the presence of strain the elasticity theory metric naturally appears. However, this is not the one experienced by fermionic quasiparticles. Fermions propagate in curved space, whose metric is defined by expansion of the effective Hamiltonian near the topologically protected Fermi point. We discuss relation between both types of metric for different parametrizations of graphene surface. Next, we extend our consideration to the case, when the dislocations are present. We consider the situation, when the deformation is described by elasticity theory and calculate both torsion and emergent magnetic field carried by the dislocation. The dislocation carries singular torsion in addition to the quantized flux of emergent magnetic field. Both may be observed in the scattering of quasiparticles on the dislocation. Emergent magnetic field flux manifests itself in the Aharonov–Bohm effect while the torsion singularity results in Stodolsky effect.     

含裂纹三点弯曲梁起始扩展的动态分析

本文利用高速摄影捕捉含裂纹三点弯曲梁在冲击下裂纹扩展过程，借助动态焦散线对裂纹尖端初始曲线范围内的应力第二不变量分布进行了试验研究，并通过Ｄｅｔ．－准则对动载下裂纹起始扩展的条件和方向进行了分析。结果表明：裂纹扩展的实际方向与理论预测相一致；Ｄｅｔ．－准则与焦散线相结合在动态断裂力学研究中具有广泛的使用价值     

无侧移半刚性连接组合框架的稳定分析:(Ⅰ)柱的有效长度系数方程

本文基于钢结构设计规范GB50017-2003,利用三柱子框架模型,考虑了连接的非线性弯矩-转角关系和楼板组合效应的影响,推导了无侧移半刚性连接组合框架柱的有效长度系数方程式,同时考虑了梁端和柱远端不同约束情况对有效长度系数的影响。另外,分析了GB50017规范附录D表D-1求解的精确性。研究表明,当柱远端刚接时,推导的方程式类似于GB50017规范附录D表D-1给出的无侧移刚接框架柱的有效长度系数计算公式;对于三柱子框架模型,当柱远端铰接时,用GB50017规范附录D表D-1得到的有效长度系数设计柱是不安全的,但最大误差只有11%。     

Fractals — An overview of potential applications to transport in porous media

We present an overview of the potential applicability of fractal concepts to various aspects of transport phenomena in heterogeneous porous media. Three examples of phenomena where a fractal approach should prove illuminating are presented. In the first example we consider pore level heterogeneities as typified by pore surface roughness. We suggest that roughness may be usefully modelled by fractal curves and surfaces and also cite experimental evidence for regarding pores as fractals. In the second example we consider a fractal network approach to modelling large-scale heterogeneities. The presence of features on all length scales in simple fractal models should capture the essential role played by the presence of heterogeneities on many scales in natural reservoirs. Studies of transport phenomena in such models may yield valuable insights into the problems of macroscopic dispersion. The final example concerns dispersion in multiphase flow. Here the fractal character is attributed to the distribution of the fluid phases rather than the porous medium itself. Again studies of transport phenomena in simple fractal models should help to clarify various problems associated with the corresponding phenomena in real reservoirs.     

First- and second-order sensitivities of beams with respect to cross-sectional cracks

This paper deals with a variational formulation for the sensitivity problem of beam systems in the context of deformable solids with cracks. Natural frequencies are defined as state variables involved in the energy functional of the system, while the cracks length and position are treated as system parameters. The hierarchical equation system is formed and solved for the first and second derivatives of the natural frequency functions with respect to the cracks length and position. An analytical procedure for calculations of the second-order sensitivities of natural frequencies is proposed for the non-symmetrical equation system operator. Numerical algorithms are worked out and implemented computationally. Analytical and numerical aspects of the problem are discussed in detail through a number of illustrative results.The support of this work by the State Committee for Scientific Research (KBN) under Grant No. 4-050-0148/17-98-00 is gratefully acknowledged.     

PVDF压电薄膜在应力波测量中的应用

综合介绍了PVDF压力传感器的测试原理、动态标定实验，并采用定制的PVDF压力传感器测量了不同类型分层介质在冲击载荷作用下的压力衰减，说明了PVDF压力传感器在压力测量中有着很好的前景．