A note on the divergence problem arising in calculation of Green’s function for a 2D piezoelectric thin film strip containing straight line defects and free boundaries: Fourier approach for bodies of unrestricted anisotropy

In this paper we derive a set of novel formulas for computation of the Green’s function and the coupled electro-elastic fields in a 2D piezoelectric strip with free boundaries and containing a distribution of straight line defects. The strip is assumed to be of unrestricted anisotropy, but allowing piezoelectricity, and in this sense situation is more general than in the available literature where only cubic symmetry was investigated. We employ a set of already known analytic formulas for the Fourier amplitude of the Green’s function and the corresponding electro-elastic fields. The key novelty of this paper is solution for the divergence problem occurring during integration of the Fourier amplitude. This problem is caused by poles at k = 0 in various matrix components of the amplitude. From purely mathematical point of view such poles lead to quantities which do not tend to zero at infinity, and this situation is clearly unphysical. To resolve this issue it is demonstrated by means of rigorous analysis that when some additional physical conditions are imposed, physical fields exhibit regular behavior at infinity - the poles do not contribute. Nevertheless, they lead to irremovable numerical ∞ − ∞ uncertainties spreading over the whole domain of integration. This motivates us to compute exact formulas for all these poles to enable engineering calculations involving the system in question.     

Accelerated convergence for a normal state layered superconductor’s transverse resistance expression,measured with strip contacts

The expression of the transverse resistance for an ohmic parallelepipedic layered conductor, measured with strip contacts, extended along its width, is a slowly convergent series. This series is reworked and transformed to the sum of an analytical part and an exponentially convergent series, which reduces considerably the number of terms needed for the numerical evaluation. In addition, an asymptotic formula is obtained, valid for Γ < 2, Γ is the effective anisotropy. This formula is used to determine the room temperature resistivity anisotropy of two small Γ layered superconductors, which are 2H–NbSe₂ and 2H–TaSe₂.     

A simple strategy to generate light-responsive azobenzene-containing epoxy networks

Azobenzene containing epoxy networks are a class of photosensitive materials characterized by high thermal, optical and mechanical stability, promising for reversible optical storage applications. Here, we propose an encouraging two-step method to fabricate crosslinked coatings by simply reacting an amine-functionalized azobenzene and an epoxy resin in bulk for specified times to get soluble products (network precursors). Thin films based on these precursors were prepared, and thermally crosslinked in order to obtain high-T_g materials. The optical response of the materials was determined, both before and after crosslinking. In the case of the samples as prepared, the dynamic time response of the system is fast, as well as the relaxation of the photoinduced birefringence, as expected due to the high mobility of the chromophore. On the other hand, crosslinked systems have a slightly slower response, but higher values of remnant birefringence, providing stability of the photoinduced orientation, what makes them promising materials to use in optical storage applications. Besides, further analysis on the effect of temperature on the induced birefringence of the polymeric networks was also conducted to help optimization of material design. Finally, we had presented some preliminary investigations of surface relief grating recording in the obtained new materials.     

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Abstract

This work proposes a hypothesis for the interpretation of shrinkage anisotropy during sintering of an Fe–Cu–C alloy based on the effect of the structural modifications of the powder, due to the prior compaction, on the mass transport phenomena. Dislocations are introduced by cold compaction in the contact regions between particles, with different densities along the compaction direction and the transversal one. Therefore, the mass transport by volume diffusion is strongly activated in both directions, and a prevailing effect in the compaction direction is shown. The volume diffusion coefficients derived from the kinetic model correspond to the dislocation pipe diffusion mechanism.     

泌阳北部斜坡地区复杂断块群成像技术探讨

泌阳凹陷北部斜坡是河南油田的重点勘探区块之一,其构造产状复杂,断层发育；根据高精度勘探思路,提出多域数据重构体去噪方法进行规则干扰压制,层析反演静校正解决该区复杂地表条件引起的静校正方面的问题；然后基于各向异性双谱速度分析技术,进一步提高该区成像速度模型的精度；通过分析偏移孔径、去假频参数等处理参数对成像效果的影响,确...     

An experimental and theoretical study of the carbazole to carbazole intramolecular energy transfer in N‐vinylcarbazole/vinyl tert‐butyl‐benzoate copolymers of different molar compositions

Fluorescence depolarization and quenching measurements of N‐vinyl carbazole/vinyl tert‐butyl‐benzoate copolymers in dilute solution of several fluid solvents and in a rigid poly(methyl methacrylate) matrix were performed to study the effect of copolymer composition on the intramolecular energy transfer (IET) between carbazole groups (Cz) along the polymer chain. IET efficiency, as the amount of Cz? Cz intramolecular excimer formation, monotonically increases with Cz content up to a number average sequence length of carbazole of ca 12 (Cz molar content ≥ 90%). After this value, IET efficiency remains almost constant. Molecular dynamics simulations on isotactic and syndiotactic copolymer fragments of several monomer compositions were used for obtaining different parameters related to the efficiency for the IET process between Cz units along the polymer chain. Copyright © 2011 Society of Chemical Industry     

Biomimetic surfaces with controlled direction-dependent adhesion

We propose a novel design of a biomimetic micro-structured surface, which exhibits controlled strongly direction-dependent adhesion properties. The micro-system consists of parallel elastic wall-like structures covered by a thin layer. Numerical calculations have been carried out to study the adhesive properties of the proposed system and to provide design criteria with the aim of obtaining optimized geometries. A numerically equivalent version of the double cantilever beam fracture experiment is, then, simulated by means of finite element analysis to investigate the anisotropic adhesion of the structure. We find that, because of inherent crack trapping properties of these types of structures, the wall-like geometry allows us to strongly enhance adhesion when the detachment direction is perpendicular to the walls. On the other hand, when the detachment occurs parallel to the walls, the system shows low adhesion. This controlled direction-dependent adhesive property of the proposed structure solves one of the key problems of biomimetic adhesive surfaces, which usually show very strong adhesion, even larger than biological systems, but are not suitable for object manipulation and locomotion, as detachment always occurs at high loads and cannot be controlled.     

Magnetic and optical properties of cobalt nanowires fabricated in polycarbonate ion-track templates

Cobalt nanowires with diameter 75 nm were synthesized in ion track-etched membranes by electrochemical deposition. Scanning electron microscopy displays cylindrical wires with smooth and homogeneous contours. X-ray diffraction studies indicate that the wires possess a face centered cubic structure and a preferred growth orientation along the [1 1 0] direction. The wires exhibit magnetic anisotropy, which is observed and is ascribed to shape anisotropy. The optical extinction spectrum shows a band which probably originates from a surface plasmon resonance.     

Implementation of Two-Dimensional Polycrystalline Grains in Object Oriented Micromagnetic Framework

In response to the growing need for a more accurate micromagnetic model to understand switching phenomenon in nanoscale magnets, we developed the capability to simulate two-dimensional polycrystalline grains using the Object Oriented Micromagnetic Framework (OOMMF). This addition allows users full flexibility in determining the magnetocrystalline anisotropy and axe in each grain as well as the inter- and intragranular exchange coupling strength.     

金属薄板带应变硬化指数和厚向异性指数测定方法

介绍了应变硬化指数n值和厚向异性指r值的物理意义和几种不同的测定方法，具有一定的实践指导意义。