Local Geometric Distortions Research Articles

Local Geometric Distortion to Stimulate Oxygen Reduction Activity of Atomically Dispersed Zn‐Nx Sites for Zn–Air Batteries

AbstractLocal geometric strain engineering is useful for modulating the performance of nitrogen‐coordinated transition metal‐carbon catalysts. However, realizing the nano‐level strain is technically challenging. Additionally, the structure‐property relationship between strain degree and performance remains poorly understood. Herein, it is conceptually predict that geometric bending induces more electron transfer from Zn to the coordinated N in Zn─N─C, leading to a positive shift of the d‐band center of the Zn atom, which promotes the adsorption reduction process of the O2 molecule and thus increases the intrinsic oxygen reduction reaction (ORR) activity. Moreover, a low‐temperature non‐saturated coordination strategy is proposed to prepare spherical porous carbon catalysts with surface‐enriched geometrically bent (20‐50°) Zn─N─C sites. Benefiting from the highly active Zn─N─C sites, large specific surface area and abundant pore structure, the optimized catalyst (S─Zn─N─C‐950) exhibited excellent intrinsic alkaline ORR activity (half‐wave potential E1/2 = 0.89 V) and high zinc‐air battery performance (peak power density of 229.2 mW cm−2), exceeding that of commercial Pt/C catalysts. Density functional theory (DFT) calculations show that when the geometrical bending angle is 30–45°, Zn centers with suitable charge transfer to the surrounding N can produce a moderate adsorption strength to the oxygen intermediate state, resulting in optimal ORR activity.

A multiscale electrochemo-mechanical model of porous electrode in lithium-ion batteries: The coupling of reaction and finite deformation

In this study, we present a novel multiscale electrochemo-mechanical model for porous electrodes in lithium-ion batteries (LIBs). Building upon the theory of finite deformation and the pseudo-two-dimensional framework introduced by Doyle et al. (Journal of the Electrochemical Society, 140, 6(1993)), our model incorporates the interaction between particle deformation and multiscale electrochemical processes, which has been lacking in previous research. The model is validated by the rate performance tests on SiO-based electrodes. By utilizing the model, we analyze the coupling effects among reaction distribution, porosity variation, and local geometrical distortion of the electrode at high current rates. We also investigate the relative importance of different electrochemo-mechanical coupling paths for materials with large volume expansion ratios. Comparing the comprehensive model with simplified versions, we find that diffusion stress is a priority due to its significant impact on ionic diffusion within particles. Porosity variation becomes equally significant at high current rates, as ionic transport in the electrolyte becomes the rate-limiting step. This work contributes to enhance understanding of the interplay between electrochemical and mechanical phenomena in LIB electrodes, especially for silicon-based materials.

Does the Rational Function Model’s Accuracy for GF1 and GF6 WFV Images Satisfy Practical Requirements?

The Gaofen-1 (GF-1) and Gaofen-6 (GF-6) satellites have acquired many GF-1 and GF-6 wide-field-view (WFV) images. These images have been made available for free use globally. The GF-1 WFV (GF-1) and GF-6 WFV (GF-6) images have rational polynomial coefficients (RPCs). In practical applications, RPC corrections of GF-1 and GF-6 images need to be completed using the rational function model (RFM). However, can the accuracy of the rational function model satisfy practical application requirements? To address this issue, a geometric accuracy method was proposed in this paper to evaluate the accuracy of the RFM of GF-1 and GF-6 images. First, RPC corrections were completed using the RFM and refined RFM, respectively. The RFM was constructed using the RPCs and Shuttle Radar Topography Mission (SRTM) 90 m DEM. The RFM was refined via affine transformation based on control points (CPs), which resulted in a refined RFM. Then, an automatic matching method was proposed to complete the automatic matching of GF-1/GF-6 images and reference images, which enabled us to obtain many uniformly distributed CPs. Finally, these CPs were used to evaluate the geometric accuracy of the RFM and refined RFM. The 14th-layer Google images of the corresponding area were used as reference images. In the experiments, the advantages and disadvantages of BRIEF, SIFT, and the proposed method were first compared. Then, the values of the root mean square error (RSME) of 10,561 Chinese, French, and Brazilian GF-1 and GF-6 images were calculated and statistically analyzed, and the local geometric distortions of the GF-1 and GF-6 images were evaluated; these were used to evaluate the accuracy of the RFM. Last, the accuracy of the refined RFM was evaluated using the eight GF-1 and GF-6 images. The experimental results indicate that the accuracy of the RFM for most GF-1 and GF-6 images cannot meet the actual use requirement of being better than 1.0 pixel, the accuracy of the refined RFM for GF-1 images cannot meet practical requirement of being better than 1.0 pixel, and the accuracy of the refined RFM for most GF-6 images meets the practical requirement of being better than 1.0 pixel. However, the RMSE values that meet the requirements are between 0.9 and 1.0, and the geometric accuracy can be further improved.

Heteroatom inducing local geometrical configuration transformation of metallic oxygen clusters in metal hydroxide-organic frameworks with optimized hydrogen evolution performance

Various heteroatom doped metal organic frameworks (MOFs) and MOFs derived materials with high activity are designed as electrochemical water splitting catalysts. However, local geometrical configuration transformation or local structure distortion on account of heteroatom doping are usually neglected. Herein, this work firstly investigated local structure transformation of metallic oxygen clusters to β-Ni(OH)2-like geometrical configuration (edge-shared octahedrons) in heteroatom (Ru, Cr, Sn and Ce) doped nickel based metal hydroxide-organic frameworks (MHOFs). The transformation process, atomic/electronic structure and composition are investigated via spectroscopy methods such as X-ray absorption structure spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Hereinto, Ru doped Ni-MHOFs with high local geometrical configuration transformation as a representative one was deeply studied to reveal hydrogen evolution reaction properties. Density functional theory calculations provided a deep understanding of the effect of organic linker defect on local structure and descriptor of p-band center of O. This work provides a sight into local structural transformation in heteroatom doped MHOFs and proposes a novel strategy to modulate structural microenvironment of MOFs materials towards electrochemical applications.

Fluorination-Induced Asymmetry in Vacancy-Ordered Brownmillerite: Route to Multiferroic Behavior

Four distinct classes of multiferroics are usually being discussed in the literature, in which ferroelectricity is respectively driven by electronic lone pairs, geometry, charge ordering, and magnetism. Each class has its own shortcomings for technological applications. Here, through a combined experimental and theoretical investigation, we propose a mechanism to achieve multiferroicity in a single phase by engineering the anionic network and creating local geometric distortions in fluorinated, vacancy-ordered brownmillerite Ca2Mn2O5–xFy. The system exhibits both ferroelectricity and an antiferromagnetic order above room temperature, pointing toward a novel route to multiferroicity by anion mixing.

Effects of short-range order on phase equilibria and opto-electronic properties of ternary alloy ZnxCd1-xTe

We employ first principles methods based on density functional theory and beyond to study ZnxCd1-xTe, 0≤x≤1, alloys in the zinc blende (B3) crystal structure. Cluster Expansion and Monte Carlo formalisms were deployed to provide a phase diagram determining consolute temperature of 387 K at 40% Zn concentration. Opto-electronic properties are computed with the hybrid HSE06 functional for disordered ZnxCd1-xTe alloys, which were simulated using special quasi-random structures. Bowing effects in the bandgap and effective carrier masses were observed in alloying which can be attributed to local geometrical distortions as portrayed by bond length distributions. Downward bowing in the electronic bandgap will be beneficial in photovoltaic applications through increased net photocurrent. Absorption coefficients show robust absorption in ZnxCd1-xTe as indicated by substantial optical absorption throughout all Zn concentrations, aided by low reflectivity that ensures a high absorption. Presence of short-range order in Zn0.25Cd0.75Te was observed through clustering and anti-clustering among different cationic species of Zn and Cd. It has a value of 0.11 at 1000 K compared to −0.79 at 400 K. The bandgap of Zn0.25Cd0.75Te at 1000 K was found to be slightly higher, 0.05 eV, than at 400 K, consistent with the value of short-range order. Thus, short-range order and possibly composition can be used in the design and synthesis of the appropriate solar cell, thereby improving the performance in this system.

Tuning Fe Spin Moment in Fe-N-C Catalysts to Climb the Activity Volcano via a Local Geometric Distortion Strategy.

As the most promising alternative to platinum-based catalysts for cathodic oxygen reduction reaction (ORR) in proton exchange membrane fuel cells, further performance enhancement of Fe-N-C catalysts is highly expected to promote their wide application. In Fe-N-C catalysts, the single Fe atom forms a square-planar configuration with four adjacent N atoms (D4h symmetry). Breaking the D4h symmetry of the FeN4 active center provides a new route to boost the activity of Fe-N-C catalysts. Herein, for the first time, the deformation of the square-planar coordination of FeN4 moiety achieved by introducing chalcogen oxygen groups (XO2 , X=S, Se, Te) as polar functional groups in the Fe-N-C catalyst is reported. The theoretical and experimental results demonstrate that breaking the D4h symmetry of FeN4 results in the rearrangement of Fe 3d electrons and increases spin moment of Fe centers. The efficient spin state manipulation optimizes the adsorption energetics of ORR intermediates, thereby significantly promoting the intrinsic ORR activity of Fe-N-C catalysts, among which the SeO2 modified catalyst lies around the peak of the ORR volcano plot. This work provides a new strategy to tune the local coordination and thus the electronic structure of single-atom catalysts.

Unveiling the boson peak from local geometric distortion in a metallic glass

The origin of boson peaks is vital for understanding the nature of glasses, but remains unsettled. Applying molecular dynamics simulations, we clearly demonstrate that this mystery can be cracked by scrutinizing the individual vibration mode and the local symmetry of structure in glasses. The intensity of boson peaks can be significantly enhanced by vibrational modes with large vibrational amplitudes and high vibrational anisotropy. Furthermore, these vibrational modes are correlated to the structural motifs with a large number of types of local symmetry, which results in extensive local distortion. This local distortion contributes to the excess low-frequency vibration around the boson peak. Therefore, our findings shed light on the roles of local geometric distortion in understanding the structural origin of boson peaks.

LGGD+: Image Retargeting Quality Assessment by Measuring Local and Global Geometric Distortions

Numerous image retargeting algorithms have been proposed to achieve adaptive image resizing during the past years. To compare different image retargeting algorithms, reliable objective image retargeting quality assessment (IRQA) metrics are highly desired. Given that image retargeting usually introduces geometric distortions, this paper presents an objective IRQA metric by measuring both local and global geometric distortions (LGGD). Since human visual system perception is highly dependent on edges and the geometric distortions caused by image retargeting usually cause edge deformation, a sketch token-based local edge descriptor (ST-LED) is introduced to represent geometric-aware features in LGGD. First, ST-LED is first applied on both source and retargeted images for edge pattern representation. Second, pixel-level backward registration is conducted to enable estimating local geometric distortion (LGD) and a spatial pyramid-improved Bag-of-Token (BoT) model is built to enable estimating global geometric distortion (GGD). Since the proposed LGGD metric only focuses on geometric distortion while image retargeting quality is related with more aspects, we further fuse LGGD and an existing (EXT) IRQA metric to build a final version called LGGD+ for IRQA. Experiments on two benchmark databases demonstrate the superiority of LGGD+ and the excellent compatibility of our proposed LGGD for further improving a wide range of existing IRQA metrics (including both geometric distortion and non-geometric distortion metrics). In addition, the effectiveness of our LGGD metric is also demonstrated in another relevant task, i.e., quality evaluation of depth-image-based rendering (DIBR)-synthesized images, which also calls for accurate estimation of geometric distortion.

Unveiling the Boson Peak from Local Geometric Distortion in a Metallic Glass

Unveiling the Boson Peak from Local Geometric Distortion in a Metallic Glass

Study on Correction Method of Local Geometric Distortion in Projection Phantom Imaging

Study on Correction Method of Local Geometric Distortion in Projection Phantom Imaging

Free-Boundary Conformal Parameterization of Point Clouds

With the advancement in 3D scanning technology, there has been a surge of interest in the use of point clouds in science and engineering. To facilitate the computations and analyses of point clouds, prior works have considered parameterizing them onto some simple planar domains with a fixed boundary shape such as a unit circle or a rectangle. However, the geometry of the fixed shape may lead to some undesirable distortion in the parameterization. It is therefore more natural to consider free-boundary conformal parameterizations of point clouds, which minimize the local geometric distortion of the mapping without constraining the overall shape. In this work, we develop a free-boundary conformal parameterization method for disk-type point clouds, which involves a novel approximation scheme of the point cloud Laplacian with accumulated cotangent weights together with a special treatment at the boundary points. With the aid of the free-boundary conformal parameterization, high-quality point cloud meshing can be easily achieved. Furthermore, we show that using the idea of conformal welding in complex analysis, the point cloud conformal parameterization can be computed in a divide-and-conquer manner. Experimental results are presented to demonstrate the effectiveness of the proposed method.

DIBR-Synthesized Image Quality Assessment With Texture and Depth Information.

Accurately predicting the quality of depth-image-based-rendering (DIBR) synthesized images is of great significance in promoting DIBR techniques. Recently, many DIBR-synthesized image quality assessment (IQA) algorithms have been proposed to quantify the distortion that existed in texture images. However, these methods ignore the damage of DIBR algorithms on the depth structure of DIBR-synthesized images and thus fail to accurately evaluate the visual quality of DIBR-synthesized images. To this end, this paper presents a DIBR-synthesized image quality assessment metric with Texture and Depth Information, dubbed as TDI. TDI predicts the quality of DIBR-synthesized images by jointly measuring the synthesized image's colorfulness, texture structure, and depth structure. The design principle of our TDI includes two points: (1) DIBR technologies bring color deviation to DIBR-synthesized images, and so measuring colorfulness can effectively predict the quality of DIBR-synthesized images. (2) In the hole-filling process, DIBR technologies introduce the local geometric distortion, which destroys the texture structure of DIBR-synthesized images and affects the relationship between the foreground and background of DIBR-synthesized images. Thus, we can accurately evaluate DIBR-synthesized image quality through a joint representation of texture and depth structures. Experiments show that our TDI outperforms the competing state-of-the-art algorithms in predicting the visual quality of DIBR-synthesized images.

Effective Local Geometry Descriptor for 29Si NMR Q4 Anisotropy

The nuclear shielding anisotropy, ζ, is a useful nuclear magnetic resonance (NMR) shielding tensor parameter in describing the extent of electron cloud distortion about an atom. Despite the advantages afforded by NMR in structural characterization, the relationship between ζ and local structure of an atom in high-symmetry environments, such as Si–Q4 sites, is poorly understood. Here, we use a data-driven approach combining random forest feature ranking and the Sure Independence Screening and Sparsifying Operator (SISSO) approach to derive a simple and accurate geometric descriptor for ζ with a root-mean-squared prediction error of 6.77 ppm and an R2 of 0.761. We then apply this descriptor to describe the local geometric distortion of zeolites Sigma-2 and silica-ZSM-5 whose chemical shift anisotropy tensor has been reported. We envision that this geometric descriptor will allow for structural description and refinement in previously difficult-to-describe materials.

Defect-Induced Magnetic Skyrmion in a Two-Dimensional Chromium Triiodide Monolayer.

Chromium iodide monolayers, which have different magnetic properties in comparison to the bulk chromium iodide, have been shown to form skyrmionic states in applied electromagnetic fields or in Janus-layer devices. In this work, we demonstrate that spin-canted solutions can be induced into monolayer chromium iodide by select substitution of iodide atoms with isovalent impurities. Several concentrations and spatial configurations of halide substitutional defects are selected to probe the coupling between the local defect-induced geometric distortions and orientation of chromium magnetic moments. This work provides atomic-level insight into how atomically precise chemical doping can be used to create and control complex magnetic patterns in chromium iodide layers and lays out the foundation for investigating the field- and geometric-dependent magnetic properties in similar two-dimensional materials.

Rationalize the Significantly Enhanced Photocatalytic Efficiency of In3+-doped α'-Ga2S3 by Bond Theory and Local Structural Distortion.

Mechanistic understanding on the electronic structure of α'-Ga2S3 unravel that the electrons in nonbonding 3pz orbitals of two-coordinated S2- anions are photoexcited to the adjacent σ-type antibonding orbitals (Ga-4s and S-3p) and migrate thereafter to the surface along the a-axis. By introduction of the In-S antibonding on the one hand and modifying the local dipole moment on the other hand, the light absorption ability and charge separation efficiency can be both enhanced by In3+-to-Ga3+ substitution, and the photocatalytic H2 evolution rate can be significantly promoted. Local geometric distortion is common in solid solutions, but its effect on charge migration behavior has yet been considered in semiconducting photocatalysis. Our case study on In3+-doped Ga2S3 is a good reminder of such the importance.

Local Geometric Distortions Resilient Watermarking Scheme Based on Symmetry

As an efficient watermark attack method, geometric distortions destroy the synchronization between watermark encoder and decoder. And the local geometric distortion is a famous challenge in the watermark field. Although a lot of geometric distortions resilient watermarking schemes have been proposed, few of them perform well against local geometric distortion like random bending attack (RBA). To address this problem, this paper proposes a novel watermark synchronization process and the corresponding watermarking scheme. In our scheme, the watermark bits are represented by random patterns. The message is encoded to get a watermark unit, and the watermark unit is flipped to generate a symmetrical watermark. Then the symmetrical watermark is embedded into the spatial domain of the host image in an additive way. In watermark extraction, we first get the theoretically mean-square error minimized estimation of the watermark. Then the auto-convolution function is applied to this estimation to detect the symmetry and get a watermark units map. According to this map, the watermark can be accurately synchronized, and then the extraction can be done. Experimental results demonstrate the excellent robustness of the proposed watermarking scheme to local geometric distortions, global geometric distortions, common image processing operations, and some kinds of combined attacks.

High‐resolution optical‐to‐SAR image registration using mutual information and SPSA optimisation

The high-resolution optical and synthetic aperture radar (SAR) images are widely used in many remote sensing application areas such as image fusion and change detection where image registration is a fundamental step. The latest high-resolution optical and SAR satellites and airborne systems provide geometrically corrected images which do not contain global deformations. Though the images do not have global differences, still, registration differences exist between these optical and SAR images. These registration differences should be minimised through an automatic registration method before using the images for the aforementioned applications. However, an automatic optical-to-SAR image registration is a challenging task due to the presence of significant nonlinear intensity differences as well as local geometric distortions between the images. In order to solve these problems, an automatic optical-to-SAR image registration method is proposed which can effectively handle the registration differences between the globally corrected high-resolution images. In the proposed method, initially, a coarse registration is performed by using a discrete simultaneous perturbation stochastic approximation (SPSA) optimisation. Then, a smooth continuous SPSA optimisation is utilised for the fine registration of the images. Experiments are performed on six sets of high-resolution optical-SAR image pairs and the results show the effectiveness of the proposed method.

Quality Assessment of Free-Viewpoint Videos by Quantifying the Elastic Changes of Multi-Scale Motion Trajectories.

Virtual viewpoints synthesis is an essential process for many immersive applications including Free-viewpoint TV (FTV). A widely used technique for viewpoints synthesis is Depth-Image-Based-Rendering (DIBR) technique. However, such technique may introduce challenging non-uniform spatial-temporal structure-related distortions. Most of the existing state-of-the-art quality metrics fail to handle these distortions, especially the temporal structure inconsistencies observed during the switch of different viewpoints. To tackle this problem, an elastic metric and multi-scale trajectory based video quality metric (EM-VQM) is proposed in this paper. Dense motion trajectory is first used as a proxy for selecting temporal sensitive regions, where local geometric distortions might significantly diminish the perceived quality. Afterwards, the amount of temporal structure inconsistencies and unsmooth viewpoints transitions are quantified by calculating 1) the amount of motion trajectory deformations with elastic metric and, 2) the spatial-temporal structural dissimilarity. According to the comprehensive experimental results on two FTV video datasets, the proposed metric outperforms the state-of-the-art metrics designed for free-viewpoint videos significantly and achieves a gain of 12.86% and 16.75% in terms of median Pearson linear correlation coefficient values on the two datasets compared to the best one, respectively.

Automated layerwise detection of geometrical distortions in laser powder bed fusion

In-situ layerwise imaging in laser powder bed fusion (L-PBF) has been implemented by many system developers to monitor the powder bed homogeneity. Increasing attention has been recently devoted to the possibility of using the same sensing approach to detect also in-plane and out-of-plane geometrical distortions of the part while it is being produced. To this aim, seminal works investigated the suitability of various image segmentation algorithms and assessed the accuracy of layerwise dimensional and geometrical measurements. Nevertheless, there is a lack of automated methods to identify, in-situ and in-process, geometrical defects and out-of-control deviations from the nominal geometry. This study presents a methodology that combines an active contours methodology for image segmentation with a statistical process monitoring approach suitable to deal with complex geometries that change layer by layer. The proposed approach enables a data-driven and automated alarm rule to detect the onset of geometrical distortions during the build by comparing the slice contour reconstruction with the nominal geometry in each layer. Moreover, by coupling edge-based and region-based segmentation techniques, the method is sufficiently robust to be applied to imaging and illumination setups that are already available on industrial L-PBF systems. The effectiveness of the proposed approach was tested on a real case study involving the L-PBF of complex Ti6Al4V parts that exhibited local geometrical distortions.