China
Africa
Explore chapters and articles related to this topic
Local Probes of Magnetic Field Distribution
Published in David A. Cardwell, David C. Larbalestier, Aleksander I. Braginski, Handbook of Superconductivity, 2022
Alejandro V. Silhanek, Simon Bending, Steve Lee
Two-sided decoration is also possible and allows the correlation of vortex positions at the top and bottom of a sample (Yao et al., 1994; Yoon et al., 1995). A detailed analysis of the two images allows the dimensionality of the flux line lattice to be probed and estimates of the elastic moduli to be made. The high spatial resolution of the Bitter decoration technique allowed the investigation of geometrical confinement effects in mesoscopic BSCCO structures (Cejas Bolecek et al., 2015) where it was shown that compact planes of the vortex structure align with the sample edge by introducing topological defects. As expected, a larger defect density is observed for circular than for square edge geometries.
Green Synthesis of Graphene and Graphene Oxide and Their Use as Antimicrobial Agents
Published in Sarika Verma, Raju Khan, Avanish Kumar Srivastava, Advanced Nanocarbon Materials, 2022
Roberta Bussamara, Nathália M. Galdino, Andrea A. H. da Rocha, Jackson D. Scholten
The modifications of the structure of graphene are called defects and might be intentional or a consequence of the synthetic method. The defects include sp3 carbons (on the edges, cracks, or functionalities), topological defects (as pentagons and heptagons), adatoms or vacancies, or impurities, among others.
Selection rules and a new model for stable topological defect arrays in nematic liquid crystal
Published in Liquid Crystals, 2021
Topological defects are singularities in ordered material, which are generated during phase transitions, by applying mechanical frustrations or in geometrical confinements. They are important in the science and engineering of optics and soft matter because they generate optical vortices [1], scatter light [2], trap particles [3] or molecules [4,5], and induce huge elastic strain in soft films, leading to structural deformation such as bending [6,7], folding [7,8] and periodic wrinkles [9]. Evenly distributed topological defect in nematic liquid crystal can be utilised as optical diffraction gratings [10,11], micro-array optical vortex generator [12], smart windows [13,14], templates for self-assembled microstructures [5], and origami elastomer accurators [8,9,15,16]. Self-retained large defect array is the essential element of these fascinating devices. Arranging various types of defects into various lattices is the crucial step to new designs. Enormous efforts has been devoted to the creation of new arrangements by trying new surface treatments [8,9,17–20] or new operation modes [20–22], but the selection rules for stable topological defect arrays have never been systematically discussed. In this research, the topological rules in defect arrays are tested and verified experimentally. Surprisingly, the experimental results lead to a new model for director field in stable defect array.
Tailoring surface patterns to direct the assembly of liquid crystalline materials
Published in Liquid Crystals Reviews, 2019
Yu Xia, Apiradee Honglawan, Shu Yang
Topological defects occur when the local alignment of the LC molecules are undefined, as shown in Figure 2. As one approaches the core of the defects, strong director gradients modify the type of ordering of the LCs, which might become isotropic in some cases or biaxial nematic in other cases. There are two major categories of topological defects in the form of points and lines (disclinations). Depending on the different organization of LC molecules surrounding the defect, defects can be divided into different types. Each defect is characterized by a topological charge, often called ‘a strength’ or ‘a winding number’. For point defects in two dimensions (2D) and for disclinations in three dimensions (3D), the topological charge shows how many times the director reorients by 360 degrees when one circumnavigates the core of the defect once. For example, Figure 1(c) shows a point defect of strength −1/2; the number shows that the director reorients by 180 degrees when one completes a path of 360 degrees goes around it; the negative sign shows that the sense of director rotates is opposite to the direction of circumnavigation. The disclination shown in Figure 1(e) is characterized by the same topological charge −1/2.