Effect of submicron admixtures on mechanical and self‐healing properties of cement‐based composites

This study presents the development of novel submicron super absorbent polymers (SAPs) used as admixtures in cement‐based matrices with significant advantages over conventional products. The produced SAPs were characterized in respect of their morphology and composition, while their water absorption capacity was determined in different electrolyte solutions. The hybrid core‐shell spherical structure of the fabricated materials offered significant compatibility enhancement with cement while the workability of the mixture was maintained. The assessment of the cement‐based composites including SAPs revealed that their flexural strength increased by 78%. Self‐healing/sealing behavior was assessed by monitoring the crack sealing via SEM, elemental analysis of the healing products, and determination of the water absorbance coefficient for different times of treatment. The cement/SAPs composites with a concentration of SAPs 2% by weight of cement exhibited self‐healing/sealing responsive capability when an artificial crack was induced. According to the SEM characterization, the crack demonstrated complete healing for the better part of its length after 28 days of treatment.     

Analysis of the effect of structural defects on the fatigue strength of RFSSW joints using C‐scan scanning acoustic microscopy and SEM

Solid‐state refill friction stir spot welding (RFSSW) technology offers significant benefits in the fabrication of aluminium structures in the transport and aerospace industries. In this paper, the joining of 1.6‐mm‐thick Alclad 7075‐T6 aluminium alloy sheets is investigated. High‐cycle fatigue strength tests of single‐lap welded joints were carried out on an Instron E10000 testing machine with a limited number of cycles equal to 2 × 10⁶. The welding of overlap fatigue specimens was conducted using an RPS100 spot welder by Harms & Wende GmbH & Co KG. C‐mode scanning acoustic microscopy (C‐SAM) and scanning electron microscopy (SEM) were utilised to evaluate the joint quality and characterise the microstructure. The paper discusses the effect of the maximum load force and defects (voids, hook, kissing bond, bonding ligament, etc) associated with the material flow in the weld on the failure mechanism. Insufficient plasticisation of sheet material and mixing of the material in the weld area are crucial defects that influence the number of destructive cycles. The weld defects in the joint structure are a source of a decrease in the fatigue life compared with the fatigue life of defect‐free welds. It was also found that RFSSW joint defects can be effectively detected by the nondestructive C‐SAM method.     

All‐hexahedral element meshing: automatic elimination of self‐intersecting dual lines

There has been some degree of success in all‐hexahedral meshing. Standard methods start with the object geometry defined by means of an all‐quadrilateral mesh, followed by the use of the combinatorial dual to the mesh in order to define the internal connectivities among elements. For all of the known methods using the dual concept, it is necessary to first prevent or eliminate self‐intersecting (SI) dual lines of the given quadrilateral mesh. The relevant features of SI lines are studied, giving a method to remove them, which avoids deforming the original geometry. Some examples of resulting meshes are shown where the current meshing method has been successfully applied. Copyright © 2002 John Wiley & Sons, Ltd.     

Fatigue properties of self‐piercing riveted multi‐rivet joints in steel and aluminum sheets

Self‐piercing riveting (SPR) is an important joining technology for connecting steel and aluminum sheets. In this paper, AA6111 aluminum alloy and DP780 high‐strength steel were adopted to study the influence of fatigue on remaining static strength and energy absorption properties on self‐piercing riveting multi‐rivet joints. The results showed that energy absorption capacity of the specimens decreased significantly after high cycle fatigue. Fatigue reduced the remaining static lap shear strength of riveted specimens. Scanning electron microscopy (SEM) was used to analyze the cross section of fatigue specimens fractured by static tension. The results showed that fretting wear was found at the contact area between rivet and aluminum sheets. Fatigue bands and fatigue cracks appeared in fatigue specimens after high cycle fatigue, while those with low cycle fatigue specimens did not appear. Small cracks weaken the strength of the aluminum sheet, resulting in the static tensile strength of the riveted specimen with high cycle fatigue is lower than that of other fatigue specimens.     

The effect of T‐stress on crack‐tip plastic zones under mixed‐mode loading conditions

In this paper, the influence of T‐stress on crack‐tip plastic zones under mixed‐mode I and II loading conditions is examined. The crack‐tip stress field is defined in terms of the mixed‐mode stress intensity factors and the T‐stress using William's series expansion. The crack‐tip stress field is incorporated into the Von Mises yield criteria to develop an expression that determines the crack‐tip plastic zone. Using the resultant expression, the plastic zone is plotted for various combinations of mode II to mode I stress intensity factor ratios and levels of T‐stress. The properties of the plastic zone affected by T‐stress and mixed‐mode phase angle are discussed. The observations obtained on plastic zones variations are important for further fatigue and fracture analyses for defects in engineering structures under mixed‐mode loading conditions.     

Virtual view synthesis method and self‐evaluation metrics for free viewpoint television and 3D video

Virtual view synthesis is one of the most important techniques to realize free viewpoint television and three‐dimensional (3D) video. In this article, we propose a view synthesis method to generate high‐quality intermediate views in such applications and new evaluation metrics named as spatial peak signal‐to‐noise ratio and temporal peak signal‐to‐noise ratio to measure spatial and temporal consistency, respectively. The proposed view synthesis method consists of five major steps: depth preprocessing, depth‐based 3D warping, depth‐based histogram matching, base plus assistant view blending, and depth‐based hole‐filling. The efficiency of the proposed view synthesis method has been verified by evaluating the quality of synthesized images with various metrics such as peak signal‐to‐noise ratio, structural similarity, discrete cosine transform (DCT)‐based video quality metric, and the newly proposed metrics. We have also confirmed that the synthesized images are objectively and subjectively natural. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 378–390, 2010     

转镜-振镜扫描的非线性及非对称性研究

根据几何光学原理,推导出转镜-振镜扫描系统物镜前振镜上光斑移动速度的解析表达式。 系统本身的结构特点是产生扫描非线性和非对称性的根源,并会引起图像畸变。对设计的40面,半径40mm,转速为23437.5rmin-1的转镜-振镜系统的数值计算结果表明,行扫描中最大速度差约为6m.s-1,时间对称中心从32祍改变到约30.7477祍。此结果可作图像畸变修正的参考。     

Magnetic Imaging of Cyanide‐Bridged Co‐ordination Nanoparticles Grafted on FIB‐Patterned Si Substrates

Prussian blue CsNiCr nanoparticles are used to decorate selected portions of a Si substrate. For successful grafting to take place, the Si surface needs first to be chemically functionalized. Low‐dose focused ion beam patterning on uniformly functionalized surfaces selects those portions that will not participate in the grafting process. Step‐by‐step control is assured by atomic force and high‐resolution scanning electron microscopy, revealing a submonolayer distribution of the grafted nanoparticles. By novel scanning Hall‐probe microscopy, an in‐depth investigation of the magnetic response of the nanoparticles to varying temperature and applied magnetic field is provided. The magnetic images acquired suggest that low‐temperature canted ferromagnetism is found in the grafted nanoparticles, similar to what is observed in the equivalent bulk material.     

Algebraic grid generation on trimmed parametric surface using non‐self‐overlapping planar Coons patch

Using a Coons patch mapping to generate a structured grid in the parametric region of a trimmed surface can avoid the singularity of elliptic PDE methods when only C¹ continuous boundary is given; the error of converting generic parametric C¹ boundary curves into a specified representation form is also avoided. However, overlap may happen on some portions of the algebraically generated grid when a linear or naïve cubic blending function is used in the mapping; this severely limits its usage in most of engineering and scientific applications where a grid system of non‐self‐overlapping is strictly required. To solve the problem, non‐trivial blending functions in a Coons patch mapping should be determined adaptively by the given boundary so that self‐overlapping can be averted. We address the adaptive determination problem by a functional optimization method. The governing equation of the optimization is derived by adding a virtual dimension in the parametric space of the given trimmed surface. Both one‐ and two‐parameter blending functions are studied. To resolve the difficulty of guessing good initial blending functions for the conjugate gradient method used, a progressive optimization algorithm is then proposed which has been shown to be very effective in a variety of practical examples. Also, an extension is added to the objective function to control the element shape. Finally, experiment results are shown to illustrate the usefulness and effectiveness of the presented method. Copyright © 2004 John Wiley & Sons, Ltd.     

Perspective Measurement of the Out‐of‐plane Displacement and Normal Strain Field Distributions Inside Glass Fibre‐reinforced Resin Matrix Composite

A depth‐resolved wavenumber‐scanning interferometer (DRWSI) was built up to measure the out‐of‐plane displacement and normal strain field distributions on the front surface, rear surface and internal glass fibres of a glass fibre‐reinforced resin matrix composite before and after loading. Series of the fringe patterns were recorded, while the wavenumber of the laser, monitored online by an optical wedge, was scanned by tuning the temperature. Random sampling Fourier transform is used to overcome the non‐linearity of the wavenumber series. In the end, the distributions of the out‐of‐plane displacements and normal strain field are presented as the applied loads were 10 µm, 20 µm and 30 µm, respectively. In conclusion, DRWSI is a suitable method to measure the mechanical properties inside resin composite non‐destructively.     

Level‐Sets fields,placement and velocity based formulations of contact‐impact problems

By introducing unknown Sign‐like fields of Level‐Sets type, the Signorini‐Moreau dynamic contact conditions are set merely as boundary equations. From this setting, a continuous hybrid weak–strong formulation for dynamic contact between deformable solids is derived and a new Lagrangian formulation (we call stabilized) generalizing both the classical and augmented ones is obtained. Friction phenomena are treated similarly. In the global problem, the irregular Sign‐like fields stand for the intrinsic contact unknown ones. This problem is discretized by means of time, space and collocation schemes. Some numerical experimentations are carried out, showing the potential of our developments. Copyright © 2006 John Wiley & Sons, Ltd.     

On‐Surface Synthesis of 8‐ and 10‐Armchair Graphene Nanoribbons

Armchair graphene nanoribbons (AGNRs) with 8 and 10 carbon atoms in width (8‐ and 10‐AGNRs) are synthesized on Au (111) surfaces via lateral fusion of nanoribbons that belong to different subfamilies. Poly‐para‐phenylene (3‐AGNR) chains are pre‐synthesized as ladder ribbons on Au (111). Subsequently, synthesized 5‐ and 7‐AGNRs can laterally fuse with 3‐AGNRs upon annealing at higher temperature, producing 8‐ and 10‐AGNRs, respectively. The synthetic process, and their geometric and electronic structures are characterized by scanning tunneling microscopy/spectroscopy (STM/STS). STS investigations reveal the band gap of 10‐AGNR (2.0 ± 0.1 eV) and a large apparent band gap of 8‐AGNRs (2.3 ± 0.1 eV) on Au (111) surface.     

The effect of heat treatment on superconductivity of Zn‐doped YBa2Cu3‐xZnxO7‐y

YBa₂Cu_3‐xZn_xO_7‐y compounds with x = 0, 0.05, 0.15, and 0.30 have been synthesized by standard solid state reaction method. The crystal structure, lattice parameters, and oxygen content are not changed by the substitution of Zn for Cu since both valence state and ionic radius are almost identical for Zn and Cu elements in YBa₂Cu_3‐xZn_xO_7‐y. However, the superconducting transition temperature T_c decreases with the increase of Zn content, reflecting the T_c‐suppression effect of Zn substitution. Heat treatment experiments indicate that the heat treatment at low temperature is beneficial to improve the superconductivity of the sample. But T_c decreases with the increase of annealing temperature when the treatment temperature is above 300°C, and finally the superconductivity disappears at approximately 920°C, 700°C and 550°C for the samples with x = 0.0, 0.05 and 0.15, respectively. Our experiments indicate that the superconductivity of the sample with higher Zn content is more sensitive to the oxygen content, and a small decrease in the oxygen content can lead to a considerable decrease of T_c.     

Micrometer‐sized DNA–Single‐Fluorophore–DNA Supramolecule: Synthesis and Single‐Molecule Characterization

The synthesis of single‐fluorophore‐bis(micrometer‐sized DNA) triblock supramolecules and the optical and structural characterization of the construct at the single‐molecule level is reported. A fluorophore‐bis(oligodeoxynucleotide) triblock is synthesized via the amide‐coupling reaction. Subsequent protocols of DNA hybridization/ligation are developed to form the supramolecular triblock structure with λ‐DNA fragments on the micrometer length scale. The successful synthesis of the micrometer‐sized DNA–single‐fluorophore–DNA supramolecule is confirmed by agarose gel electrophoresis with fluorescence imaging under UV excitation. Single triblock structures are directly imaged by combined scanning force microscopy and single‐molecule fluorescence microscopy, and provide unambiguous confirmation of the existence of the single fluorophore inserted in the middle of the long DNA. This type of triblock structure is a step closer to providing a scaffold for single‐molecule electronic devices after metallization of the DNAs.     

Temperature‐Enhanced Solvent Vapor Annealing of a C3 Symmetric Hexa‐peri‐Hexabenzocoronene: Controlling the Self‐Assembly from Nano‐ to Macroscale

Temperature‐enhanced solvent vapor annealing (TESVA) is used to self‐assemble functionalized polycyclic aromatic hydrocarbon molecules into ordered macroscopic layers and crystals on solid surfaces. A novel C₃ symmetric hexa‐peri‐hexabenzocoronene functionalized with alternating hydrophilic and hydrophobic side chains is used as a model system since its multivalent character can be expected to offer unique self‐assembly properties and behavior in different solvents. TESVA promotes the molecule's long‐range mobility, as proven by their diffusion on a Si/SiO_x surface on a scale of hundreds of micrometers. This leads to self‐assembly into large, ordered crystals featuring an edge‐on columnar type of arrangement, which differs from the morphologies obtained using conventional solution‐processing methods such as spin‐coating or drop‐casting. The temperature modulation in the TESVA makes it possible to achieve an additional control over the role of hydrodynamic forces in the self‐assembly at surfaces, leading to a macroscopic self‐healing within the adsorbed film notably improved as compared to conventional solvent vapor annealing. This surface re‐organization can be monitored in real time by optical and atomic force microscopy.     

Uzawa and Newton algorithms to solve frictional contact problems within the bi‐potential framework

This paper is concerned with the numerical modeling of three‐dimensional unilateral contact problems in elastostatics with Coulomb friction laws. We propose a Newton‐like algorithm to solve the local contact non‐linear equations within the bi‐potential framework. The piecewise continuous contact tangent matrices are explicitly derived. A comparative study is made between the Newton algorithm and the previously developed Uzawa algorithm. A test example is included to demonstrate the developed algorithms and to highlight their performance. Copyright © 2007 John Wiley & Sons, Ltd.     

Stabilization of bi‐linear mixed finite elements for tetrahedra with enhanced interpolation using volume and area bubble functions

In order to overcome the oscillatory effects of the mixed bi‐linear Galerkin formulation for tetrahedral elements, a stabilization approach is presented. To this end the mixed method of incompatible modes and the mixed method of enhanced strains are reformulated, thus giving both the interpretation of a mixed finite element method with stabilization terms. For non‐linear problems, these are non‐linearly dependent on the current deformation state and therefore are replaced by linearly dependent stabilization terms. The approach becomes most attractive for the numerical implementation, since the use of quantities related to the previous Newton iteration step, typically arising for mixed‐enhanced elements, is completely avoided. The stabilization matrices for the mixed method of incompatible modes and the mixed method of enhanced strains are obtained with volume and area bubble functions. Various numerical examples are presented, which illustrate successfully the stabilization effect for bi‐linear tetrahedral elements. Copyright © 2007 John Wiley & Sons, Ltd.