Structural analysis for tensile behavior of silicon-carbon core-shell nanotube

This paper presents a molecular dynamics study on the tensile behavior of carbon nanotubes (CNT) with or without nanowire of Si (SiNW) encapsulated. Compared to the CNT without SiNW, the CNT with the SiNW (denoted as SiNW@CNT) shows a decreased tensile strength but an increased maximum tensile deformation rate. The micromechanisms of the different tensile behaviors were explored through the structural analysis including the radial distribution function, the bond angle distribution function, and the statistics of the polygon defects. The results showed that the C-C bond in the CNT under the maximum tensile deformation becomes longer and more uniform due to the van der Waals force between the SiNW and the CNT, which accounts for the change in the macroscopical tensile behavior. Moreover, it has been found that after tensile fracture, the CNT mainly form long chains consisting of triangle, pentagon, and heptagonal defects, while SiNW@CNT cannot form long chains due to the lack of triangular defects. These differences in the microstructures are probably because the C-C bonds in the SiNW@CNT can be strengthened by the SiNW. The results provide a better understanding of the fracture of the CNT and its nano composites, and have certain reference value for the application of the SiNW@CNT

Three-dimensional topological structures and formation processes of dislocations in Au nanowire under tension loading

Dislocation is an important microstructural configuration in most crystalline materials, but it is still difficult for experiments to detect its local atomic structures and formation processes. Molecular dynamics simulation provides a powerful tool to investigate the dislocation by means of some geometrical structural analysis methods, but most of these methods cannot accurately distinguish the nuances of local configurations. Herein, we propose a new microstructural analysis method of cluster-type-index method (CTIM). The three-dimensional (3D) topological structures and formation processes of dislocations during tensioning Au nanowire are illuminated by means of CTIM. It is found that the favourite local atomic structures in dislocations are the defective FCC clusters represented by the CTIM indexes (13, 3/1421 2/1431 2/1441 4/1541 2/1661). The vector analysis method based on the accumulation of lattice distortions cannot identified the aggregation of disordered atoms in the initial nucleation of dislocation. In the formation processes of dislocation atoms, three trajectories of T1: FCC→(13, 3/1421 2/1431 2/1441 4/1541 2/1661), T2: FCC→(12, 2/1311 1/1411 9/1421) and T3: FCC→(11, 4/1311 7/1421) are favorite. The dislocation atoms following the T1 trajectory are mainly located at the core of dislocations, while that following the T2 and T3 trajectories is at the front of dislocations. CTIM would provide an effective tool to investigate the defective structures and their interactions in nanocrystalline structures

LaSCA: A Visualization Analysis Tool for Microstructure of Complex Systems

Over the past few decades, plenty of visualization software for the structural analysis of disordered/complex systems has been developed, but the uniqueness and correctness of structural quantification for such systems are still challenging. This paper introduces a visualization analysis tool based on the largest standard cluster analysis (LaSCA), which satisfies the three essential requirements for general structural analysis: physical correctness, objective identification, and injective representation. The specific functionalities of LaSCA include the directed graph model of complex systems, novel structural parameters, topologically close-packed structures, arbitrary partial pair distribution functions, the identification of long-range ordered structures, the adaptive selection of graphical elements, the tracking display of atom ID, user-defined view angles, various options for atom selection, and so on. The program is efficiently based on OpenGL hardware acceleration, employing special algorithms to treat bonds as cylinders or lines and treat atoms as spheres, icosahedrons, tetrahedrons, or points. LaSCA can process more than 1.2 million atoms within 50 s on a PC with 1 GB memory and four cores (Intel Core i7-9700). It is robust and low-cost for surveying short-, medium-, and long-range ordered structures and tracking their evolutions

Structural evolution in the packing of uniform spheres

Structural analysis is very important to understanding the physics of atomic or particle systems of various types. However, properly characterizing the structures at different packing fraction ρ is still a challenge. Here we analyze the local structure, in terms of the so-called common-neighbor-subcluster (CNS), of sphere packings with ρ ∈ (0.2, 0.74). We show that although complicated in structure, there are totally 39 kinds of CNSs of which 12 are dominant. The evolution of these CNSs with the increase of ρ is quantified, and the rules governing the evolution are explored. The results are found to be useful in constructing a comprehensive picture about the critical states and their transition in sphere packing

A method for structural analysis of disordered particle systems

We present a brief overview of a method which can identify different 3D local structures in ordered and disordered systems. Its effectiveness is demonstrated in the analysis of the structures of sphere packings, the structural evolution of a rapid cooling process of silver liquid, and the inner structure of a metal nanocluster. Quantifying local structures by means of a topological criterion, this method is parameter-free and scale-independent, and can generally be used for structural analysis of amorphous systems involving atoms or particles at different length scales

Local rotational symmetry in the packing of uniform spheres

Local rotational symmetry (LRS) of a particulate system is important for understanding its structure and phase transition. However, how to properly characterize LRS for this system is still a challenge as the system normally includes both ordered and disordered local structures. Herein, based on the so-called common neighbour subcluster (CNS), we proposed a method to characterize the LRS of uniform spheres packings with the packing fraction ρ ranging within 0.20 and 0.74. It was found that different fold LRSs coexist in most packings, and their maximum degree increases at ρ < 0.64, except for the 2-fold LRS held by 6-sphere CNS that continuously increases to form the fcc crystal at ρ = 0.74. The overall LRS involving all the CNSs monotonically increases with two critical changes at ρ = (0.35–0.40) and 0.64; the evolution of individual LRSs held by specific CNS groups critically changes at ρ ≈ (0.35–0.40), 0.50, 0.55–0.60, and 0.64. The physics corresponding to these critical changes has also been discussed. The findings will significantly enrich the understanding of the structural symmetry of materials including atoms and particles

Removal of Artifacts from EEG Signals: A Review

Electroencephalogram (EEG) plays an important role in identifying brain activity and behavior. However, the recorded electrical activity always be contaminated with artifacts and then affect the analysis of EEG signal. Hence, it is essential to develop methods to effectively detect and extract the clean EEG data during encephalogram recordings. Several methods have been proposed to remove artifacts, but the research on artifact removal continues to be an open problem. This paper tends to review the current artifact removal of various contaminations. We first discuss the characteristics of EEG data and the types of different artifacts. Then, a general overview of the state-of-the-art methods and their detail analysis are presented. Lastly, a comparative analysis is provided for choosing a suitable methods according to particular application

Structural evolution in the crystallization of rapid cooling silver melt

The structural evolution in a rapid cooling process of silver melt has been investigated at different scales by adopting several analysis methods. The results testify Ostwald’s rule of stages and Frank conjecture upon icosahedron with many specific details. In particular, the cluster-scale analysis by a recent developed method called LSCA (the Largest Standard Cluster Analysis) clarified the complex structural evolution occurred in crystallization: different kinds of local clusters (such as ico-like (ico is the abbreviation of icosahedron), ico-bcc like (bcc, body-centred cubic), bcc, bcc-like structures) in turn have their maximal numbers as temperature decreases. And in a rather wide temperature range the icosahedral short-range order (ISRO) demonstrates a saturated stage (where the amount of ico-like structures keeps stable) that breeds metastable bcc clusters. As the precursor of crystallization, after reaching the maximal number bcc clusters finally decrease, resulting in the final solid being a mixture mainly composed of fcc/hcp (face-centred cubic and hexagonal-closed packed) clusters and to a less degree, bcc clusters. This detailed geometric picture for crystallization of liquid metal is believed to be useful to improve the fundamental understanding of liquid–solid phase transition

A Simple Parallel Chaotic Circuit Based on Memristor

This paper reports a simple parallel chaotic circuit with only four circuit elements: a capacitor, an inductor, a thermistor, and a linear negative resistor. The proposed system was analyzed with MATLAB R2018 through some numerical methods, such as largest Lyapunov exponent spectrum (LLE), phase diagram, Poincaré map, dynamic map, and time-domain waveform. The results revealed 11 kinds of chaotic attractors, 4 kinds of periodic attractors, and some attractive characteristics (such as coexistence attractors and transient transition behaviors). In addition, spectral entropy and sample entropy are adopted to analyze the phenomenon of coexisting attractors. The theoretical analysis and numerical simulation demonstrate that the system has rich dynamic characteristics

The topologically close-packed Fe70Cu15Ni15 nanoparticles : a simulation study

The classical molecular dynamics simulation is performed to investigate the frozen structure obtained by rapid cooling Fe70Cu15Ni15 nanodroplets, in terms of the system energy, the pair distribution function (PDF), and the largest standard cluster analysis (LaSCA). Interestingly, all frozen nanodroplets have a core-shell structure with copper atoms on the surface, whether they are amorphous or crystalline nanoparticles. Besides the familiar body-centered cubic (BCC) structure, a topologically close-packed (TCP) nanoparticle is observed for the first time. For a type of nanodroplets, the larger the size, the higher the onset temperature of crystallization, and the lower the potential energy of the nanoparticles at 300 K. For BCC nanoparticles crystallinity increases with size, but this is not the case for TCP nanoparticles. These findings indicate a simple and efficient way to produce core-shell nanoparticles