An offline-online strategy for multiscale problems with random defects

In this paper, we propose an offline-online strategy based on the Localized Orthogonal Decomposition (LOD) method for elliptic multiscale problems with randomly perturbed diffusion coefficient. We consider a periodic deterministic coefficient with local defects that occur with probability $p$. The offline phase pre-computes entries to global LOD stiffness matrices on a single reference element (exploiting the periodicity) for a selection of defect configurations. Given a sample of the perturbed diffusion the corresponding LOD stiffness matrix is then computed by taking linear combinations of the pre-computed entries, in the online phase. Our computable error estimates show that this yields a good approximation of the solution for small $p$, which is illustrated by extensive numerical experiments. This makes the proposed technique attractive already for moderate sample sizes in a Monte Carlo simulation.

Creation and annihilation of mobile fractional solitons in atomic chains

Localized modes in one-dimensional (1D) topological systems, such as Majonara modes in topological superconductors, are promising candidates for robust information processing. While theory predicts mobile integer and fractional topological solitons in 1D topological insulators, experiments so far have unveiled immobile, integer solitons only. Here we observe fractionalized phase defects moving along trimer silicon atomic chains formed along step edges of a vicinal silicon surface. By means of tunnelling microscopy, we identify local defects with phase shifts of 2π/3 and 4π/3 with their electronic states within the band gap and with their motions activated above 100 K. Theoretical calculations reveal the topological soliton origin of the phase defects with fractional charges of ±2e/3 and ±4e/3. Additionally, we create and annihilate individual solitons at desired locations by current pulses from the probe tip. Mobile and manipulable topological solitons may serve as robust, topologically protected information carriers in future information technology.

Influence of phosphorus diffusion modes on the formation of defects in an oxide

Using optical microscopy, SEM, atomic force microscope and profilometer, the shape, size and impurity composition of local defects occurring in the silicon dioxide layer during phosphorus diffusion were determined. The reason for the formation of defects in the passivating oxide during phosphorus diffusion is the local melting of SiO2 in interaction with liquid drops of phosphoric-silicate glass. A decrease in the temperature of the phosphorus deposition process and the concentration of POCL3 in the gas stream leads to a decrease in the density of oxide defects.

Fault Dynamic Modeling and Characteristic Parameter Simulation of Rolling Bearing with Inner Ring Local Defects

To further study the fault mechanism and fault features of rolling bearings, a two-DOF rolling bearing fault dynamic model with inner ring local defects considering the bearing radial clearance and time-varying displacement excitation is established based on Hertz contact theory. By comparing the simulated fault signal with bearing fault test data in the time domain and frequency domain, the accuracy of the established fault dynamic model is verified. Finally, the change rules of the characteristic parameters of the bearing inner ring fault signal, including effective value, absolute mean value, square root amplitude, peak value, kurtosis factor, pulse factor, peak factor, and shape factor, are simulated by the fault dynamic model. The results highlight that the proposed fault dynamic model is in good agreement with the experimental results. The model can simulate the fault signal characteristic parameters with the change of defect width, external load, and rotating speed effectively. The study in this paper is of engineering application value for bearing condition monitoring and fault diagnosis.

EVALUATION OF SURFACE DEFECTS OF PRODUCTS USING DIGITAL TECHNOLOGIES

The suggested approach provides an opportunity under the conditions of enterprises to give a comprehensive view of products defects and functional coatings imperfections. The application of the computer program developed in the Microsoft Visual Studio environment, which allows digital image processing of the studied surfaces to estimate the area of external defects of materials, regardless of the nature of the origin of defects and the method of image acquisition, is proved. Research methods. Digital images of metal surfaces and coatings obtained by energy dispersive microanalysis, electron and optical microscopy have been tested. Research results and novelty. The possibility of using the program for evaluation of surface bands with local chemical and morphological inhomogeneities, determination of the porosity of materials is shown. The possibility of express evaluation of digital images of objects at macro-, meso- and microstructural levels for automated diagnostic control of surface defects within 1-2 seconds is implemented. Disaggregation of brightness, texture and color components of the image significantly increases the speed and efficiency of image processing structures. Conclusions: The proposed program is versatile, does not require special user skills and serves as a convenient tool for analyzing and controlling the quality of objects of various physico-chemical nature. The results of the study indicate that the application of the developed computer program makes effective quantitative calculation of the area of local defects, areas of distribution of chemical elements, various inclusions, surface porosity of products and coatings possible.

Near-field optical imaging and spectroscopy of 2D-TMDs

Two-dimensional transition metal dichalcogenides (2D-TMDs) are atomically thin semiconductors with a direct bandgap in monolayer thickness, providing ideal platforms for the development of exciton-based optoelectronic devices. Extensive studies on the spectral characteristics of exciton emission have been performed, but spatially resolved optical studies of 2D-TMDs are also critically important because of large variations in the spatial profiles of exciton emissions due to local defects and charge distributions that are intrinsically nonuniform. Because the spatial resolution of conventional optical microscopy and spectroscopy is fundamentally limited by diffraction, near-field optical imaging using apertured or metallic probes has been used to spectrally map the nanoscale profiles of exciton emissions and to study the effects of nanosize local defects and carrier distribution. While these unique approaches have been frequently used, revealing information on the exciton dynamics of 2D-TMDs that is not normally accessible by conventional far-field spectroscopy, a dedicated review of near-field imaging and spectroscopy studies on 2D-TMDs is not available. This review is intended to provide an overview of the current status of near-field optical research on 2D-TMDs and the future direction with regard to developing nanoscale optical imaging and spectroscopy to investigate the exciton characteristics of 2D-TMDs.

DAMAGE DETECTION IN LAMINATED COMPOSITES BY NEURAL NETWORKS AND HIGH ORDER FINITE ELEMENTS

In the aerospace industry, machine learning techniques are becoming more and more important for Structural Health Monitoring (SHM). In fact, they could be useful in giving a precise and complete mapping of damage distribution in a structure, including low-intensities or local defects, which cannot be detected via traditional tests. In this work, feedforward artificial neural networks (ANN) are employed for vibration-based damage detection in composite laminates. In the framework of Carrera Unified formulation (CUF), one-dimensional refined models in conjunction with layer-wise (LW) theory are adopted. CUF-based Monte Carlo simulations have been used for the creation of a dataset of damage scenarios for the training of the ANN. Therefore, the latter is fed with the vibrational characteristics of these structures. The trained ANN, given these dynamic parameters, is able to predict location and intensity of all damages in the laminated composite structures.