Coarse Structure Research Articles

Suppression of melt flow instabilities by amplifying high-frequency melt waves in laser fusion cutting

High-frequency resonant melt waves locally increase the stability of melt flow and enhance cut flank quality. To amplify these waves along the melt flow, an acoustically tuned cutting nozzle, termed the cutting whistle, generates gas flow oscillations based on a resonant cavity. The nozzle cavity is designed for 6 mm thick sheets, causing the gas flow to oscillate at 15 kHz within the kerf, creating a uniform melt flow with synchronized oscillating melt waves. Performance evaluations on stainless steel sheets show that, compared to a standard conical nozzle, the cutting whistle reduces surface roughness across the entire cutting depth and prevents coarse structures near the upper sheet surface and at the bottom in burr-free cuts.

On Wavelet Coorbit Spaces Associated to Different Dilation Groups

This paper develops methods based on coarse geometry for the comparison of wavelet coorbit spaces defined by different dilation groups, with emphasis on establishing a unified approach to both irreducible and reducible quasi-regular representations. We show that the use of reducible representations is essential to include a variety of examples, such as anisotropic Besov spaces defined by general expansive matrices, in a common framework. The obtained criteria yield, among others, a simple characterization of subgroups of a dilation group yielding the same coorbit spaces. They also allow to clarify which anisotropic Besov spaces have an alternative description as coorbit spaces associated to irreducible quasi-regular representations.

GS‐Octree: Octree‐based 3D Gaussian Splatting for Robust Object‐level 3D Reconstruction Under Strong Lighting

AbstractThe 3D Gaussian Splatting technique has significantly advanced the construction of radiance fields from multi‐view images, enabling real‐time rendering. While point‐based rasterization effectively reduces computational demands for rendering, it often struggles to accurately reconstruct the geometry of the target object, especially under strong lighting conditions. Strong lighting can cause significant color variations on the object's surface when viewed from different directions, complicating the reconstruction process. To address this challenge, we introduce an approach that combines octree‐based implicit surface representations with Gaussian Splatting. Initially, it reconstructs a signed distance field (SDF) and a radiance field through volume rendering, encoding them in a low‐resolution octree. This initial SDF represents the coarse geometry of the target object. Subsequently, it introduces 3D Gaussians as additional degrees of freedom, which are guided by the initial SDF. In the third stage, the optimized Gaussians enhance the accuracy of the SDF, enabling the recovery of finer geometric details compared to the initial SDF. Finally, the refined SDF is used to further optimize the 3D Gaussians via splatting, eliminating those that contribute little to the visual appearance. Experimental results show that our method, which leverages the distribution of 3D Gaussians with SDFs, reconstructs more accurate geometry, particularly in images with specular highlights caused by strong lighting. The source code can be downloaded from https://github.com/LaoChui999/GS-Octree.

Nanoscale stress and microstructure gradients across a buckled Mo-Cu bilayer: Cu self-annealing triggered by interface delamination

Residual stresses in thin film structures significantly impact their mechanical properties and affect interface delamination. Highly compressively stressed thin films buckling is the predominant interfacial failure mode due to strain energy release. In the present study the effect of cross-sectional stress and microstructural gradients of thin films on the buckling behavior are explored in a model material system consisting of a thin Cu film sputtered onto glass and a highly compressively stressed 500 nm thick Mo overlayer causing buckling delamination at the Cu-glass interface. Employing synchrotron cross-sectional X-ray nano-diffraction, multiaxial X-ray elastic strain and microstructure distributions were explored across the cross-section of the adhering and buckled bilayer, respectively. In the adhering state, a gradual thickness evolution of columnar microstructure and residual stress was found for Mo, while in Cu, no microstructure changes and only minimal stress variations were detected along the film thickness. After delamination, diffraction peak broadening and changes in unstrained lattice parameters in the Cu sublayer indicated structural defect annihilation and grain coarsening. These microstructural changes were further validated via cross-sectional transmission electron microscopy. The evaluated residual stress distributions across the two sublayers of the pristine and buckled bilayer were used to quantify the released strain energy per unit area due to buckling, amounting to 0.61 J/m². Further cross-validation of experimental stress results with finite element simulations strengthened the experimental findings, providing a comprehensive understanding of the stress distribution across the buckled bilayer.

Atomic Level Understanding of the Structural Stability and Catalytic Activity of Nanoporous Gold/Titania Cluster Inverse Catalysts at Ambient and High Temperatures.

Nanoporous gold (NPG) exhibits exceptional catalytic performance at low temperatures, but its activity declines at elevated temperatures due to structural coarsening. Loading metal oxide nanoparticles onto NPG can enhance its catalytic activity at high temperatures. In this work, we used NPG-supported titania nanoparticles as a model system (denoted as Ti2O4/NPG) to study their catalytic activity at ambient and high temperatures with CO oxidation as a probe reaction by density functional theory (DFT) calculation and ab initio molecular dynamics (AIMD) simulations. The possible factors that may affect the CO oxidation reaction pathways and energy profiles on the Ti2O4/NPG, such as oxygen vacancies; silver impurities; Mars-van Krevelen (MvK), Eley-Rideal (ER), or trimolecular Eley-Rideal (TER) mechanisms; and catalytic active sites, were comprehensively investigated. The results showed that reaction energy barriers on Ti2O4/NPG were not significantly decreased compared to the pristine NPG, indicating that their catalytic activities at ambient temperature were comparable. At the evaluated temperature (400 °C), the Ti2O4/NPG exhibited superior thermal stability and maintained its active sites, while the NPG reduced active sites due to surface coarsening. The strong oxide-metal interaction (SOMI) effect between the NPG and Ti2O4 nanoparticles is found to be a main factor for the high structural stability and catalytic activity at high temperatures.

Carbon sequestration in earth-based alkali-activated mortar: phase changes and performance after natural exposure

This research investigates the effect of carbon sequestration via accelerated carbon curing (ACC) in alkali-activated earth-based alkali-activated mortar (25S-AAM) on the long-term engineering performance, chemical bonding and microstructure. The addition of clay accelerates hydration kinetics and promotes the formation of more cross-linked calcium–(sodium) alumino silicate hydrates (N-A-S-H and C-(N)-A-S-H). This contributes to early strength and a 25% reduction in total shrinkage after 60 days. Although ACC promotes higher carbon sequestration and increases 1-d compressive strength by 13%, it leads to severe decalcification of 25S-AAM after 365 days of natural exposure, resulting in coarsening of the pore structure in the mesoporous size range of 10–100 nm. Due to a relatively low Ca/Si ratio, 25S-AAM is more adversely affected by natural carbonation during the 365-d exposure period than the control (without clay). In summary, ACC is not recommended for earth-based AAM products especially if they are applied for outdoor constructions.

Realizing Ultrahigh Cycle Life Anode for Sodium-Ion Batteries through Heterostructure Design and Introducing Electro Active Polymer Coating.

Bi2S3 has attracted increasing attention in sodium-ion batteries (SIBs) for its high theoretical capacity and low discharge platform. However, the sodium storage performance of Bi2S3 is limited by poor electrical conductivity and volume expansion during cycling. Herein, we report a special polypyrrole (PPy)-coated MoS2/Bi2S3 (MBS@PPy) heterostructure composite obtained by hydrothermal reaction as an anode material for SIB. As a result, the MBS@PPy composites demonstrate exceptional electrochemical performance in SIB, exhibiting a high capacity of 361.1 mA h g-1 at 10 A g-1 and showcasing remarkable rate performance. Even under a high current density of 35 A g-1, the specific capacity remains stable at 280 mA h g-1 after 2,000 cycles. Furthermore, a successfully assembled Na3V2(PO4)3//MBS@PPy sodium-ion full cell can achieve an impressive specific capacity of approximately 400 mA h g-1 after 300 cycles at 0.5 A g-1. In MBS@PPy composites, the polypyridine coating not only improves the interfacial conductivity of nanorods but also effectively inhibits the agglomeration between nanorods due to large volume changes. The MoS2 heterostructure further inhibits the coarsening of the internal structure, improves electron transport and reaction kinetics, and increases the rate capability of the material. This work provides an effective strategy to develop energy storage materials with superior electrochemical properties.

EXPERIMENTAL AND OPTIMIZATION-BASED ANALYSIS TO MAXIMIZE MECHANICAL-RELATED ATTRIBUTES OF FRICTION STIR WELDED CDA101 CU ALLOY JOINTS

This paper deals with the identification of optimized process parameters for FSW of 6[Formula: see text]mm thick CDA 101 Cu alloy plates. Three distinctive parameters, the tool’s traverse speed, rotational speed, axial load, have been considered as self-reliant variables for formulating a numerical model based on nonlinear regression-type approach, with the objective of anticipating mechanical attributes of joints. From the surface- and contour-type plots, it was revealed that the axial load in combination with rotational speed has played a dominant role in influencing the tensile and yield strength of the CDA101 Cu alloy joints. At the same time, the traverse speed of the tool has played a dominant role in enhancing the ductility of the CDA101 joints through the generation of ample volumes of frictional heat, which in turn have facilitated both coarsening of grain structures and softening of materials in an ideal manner. Employing tool rotational speed, traverse speed and axial load in the ranges of 1750–1900[Formula: see text]rpm, 23–27[Formula: see text]mm/min and 5.75–6.5[Formula: see text]kN, respectively, was found to enhance the tensile strength of the CDA101 Cu alloy joints. FSW process parameters attained through the numerical meta-model of RSM have led to the attainment of the highest value of tensile strength of 209.5[Formula: see text]MPa together with a 141.4[Formula: see text]MPa yield strength with very minimal fitting errors of 0.28% and 0.52%, respectively. A collection of additional experimental data has been employed to verify the formulated empirical-based formula and additionally, an entirely different optimization technique namely PSO (i.e. particle swarm optimization) was implemented for comparison and validation purposes. The formulated meta-model of RSM generated the largest value of % of elongation of 14.23%, though the relative percent error was around 1.988%, which was slightly larger than that of the value (i.e. 14.11%) generated by PSO, with a relative error of 0.58%.

Study on the influence of early frost attack on the performance of cement mortar

The loss of strength and durability caused by early frost attack is the macro performance of internal microstructure deterioration. Understanding the influence mechanism of early frost attack at the micro level is necessary to avoid or minimize the early frost attack to macro performance. In this study, the influence of early frost attack on the strength, water sorptivity, chloride permeability, and microstructure of cement mortar was investigated. The fresh mortars were pre-cured for 10, 12, 14, and 16 h and then frozen at −10 °C for 7 days to simulate an early frost attack. After freezing, the standard curing (20 °C) was carried out until the testing. It is found that after standard curing of 28 days, the strength of early-frozen mortar can reach more than 95 % of the 28-day strength of unfrozen mortar. Interestingly, the sorptivity coefficient and total charge passed of early-frozen mortar are much higher than the level of unfrozen mortar, and the loss of resistance to water penetration and chloride ion penetration exceeds 20 %, indicating that early frost attack causes more severe damage to the durability than to the strength of mortar. Mercury intrusion porosimetry (MIP) results show that early frost attack can increase the pore volume of >50 nm and coarsen the pores within 10–50 nm. Correspondingly, key pore parameters (critical pore diameter, threshold pore diameter, and tortuosity) that affect the durability of mortar are also negatively affected. Energy dispersive spectroscopy (EDS) analysis also shows that after suffering early frost attack, the interfacial transition zone (ITZ) thickness of mortar is increased from 4 to 10 μm to 8–13 μm, and the probability of high Ca/Si ratios (4–10) in the ITZ is also increased. Finally, it is concluded that the coupling effect of pore structure coarsening and ITZ degradation leads to more severe durability loss.

Coarse entropy of metric spaces

Coarse geometry studies metric spaces on the large scale. The recently introduced notion of coarse entropy is a tool to study dynamics from the coarse point of view. We prove that all isometries of a given metric space have the same coarse entropy and that this value is a coarse invariant. We call this value the coarse entropy of the space and investigate its connections with other properties of the space. We prove that it can only be either zero or infinity, and although for many spaces this dichotomy coincides with the subexponential–exponential growth dichotomy, there is no relation between coarse entropy and volume growth more generally. We completely characterise this dichotomy for spaces with bounded geometry and for quasi-geodesic spaces. As an application, we provide an example where coarse entropy yields an obstruction for a coarse embedding, where such an embedding is not precluded by considerations of volume growth.

SmoGSI: smoothed multiscale iterative geostatistical seismic inversion

Iterative geostatistical seismic inversion is a vital technique for estimating subsurface properties. However, a conventional single-scale strategy faces challenges in preserving large-scale geological features due to the limited restoration of the type of data template, and conventional multiscale strategies face the challenge in that it is easy to lose the large-scale structure that was previously preserved. This paper introduces a novel smoothed multiscale strategy aimed at overcoming these limitations, which comprises two components: Simulated annealing at the coarsest scale and smooth conversation between two scale grids. This approach offers a smoother way to simultaneously retain large-scale and small-scale structures, improving the overall accuracy of the subsurface property estimations. To validate the effectiveness of our approach, we apply it to both synthetic and real examples. The results show that the simulated annealing strategy at the coarsest scale grid explores the prior space and finds the best large structures to avoid the generated models trapping in the local minimal. Meanwhile, the smooth conversation strategy between two scale grids helps us avoid the damage of the coarser structure. It can be explained that a large weight is assigned to the coarse structure at the beginning of the conversation of two grid scale, reducing the likelihood of the replacing proposed local small-scale geological patterns, which prone to be accepted in the conventional multiscale strategies. The combination of the two strategies used in the proposed smoothed multiscale strategy displays a significant improvement in subsurface property estimation accuracy compared to traditional multiscale strategies. This innovation can have far-reaching implications, benefiting a wide range of geophysical applications and contributing to more accurate and informed decision-making in geological and hydrogeological assessments.

Functionalized flattened bamboo board: In-situ immersion assembly of flame-retardant, waterproof and anti-mold composite coatings

The flattened bamboo board (FB) represents a promising innovation in the bamboo industry. To address the challenges of flammability and hygroscopicity, composite coatings consisting of melamine (MEL), phytic acid (PA), cerium ions (Ce3+), and sodium laurate (La) are assembled on the FB surface through an in-situ impregnation strategy. The resulting MEL/PA-Ce3+@La FB exhibits exceptional flame retardancy. It achieves a V-0 rating in the vertical burning test (UL-94) and boasts a high limiting oxygen index (LOI) value of 38.5 %. The coated FB exhibits superhydrophobicity, evidenced by a water contact angle of 156.5°, which can be attributed to the in-situ growth of PA-Ce3+ complexes (for constructing micro/nanoscale coarse structures) and the modification with La (for reducing surface energy).This superhydrophobic surface imparts both self-cleaning and anti-mold properties to the coated FB. Moreover, the coated FB exhibits excellent mechanical stability, withstanding 36 cycles of sandpaper abrasion and tape peeling without losing its hydrophobicity. In summary, this work provides an innovative strategy for the bamboo processing industry to produce flattened bamboo boards with combined flame retardancy, superhydrophobic and anti-mold properties. Such versatility holds significant potential to facilitate the utilization of flattened bamboo boards in the construction and decorative materials industries.

Book Review: Coarse geometry of topological groups

Book Review: Coarse geometry of topological groups

Corrosion properties of submerged friction stir modified as-cast nickel-aluminum bronze (NAB) compositions

This study aimed to analyze the effects of adding alloying elements and cooling medium during friction stirring on the electrochemical and immersion corrosion properties. The results showed that the addition of nickel and iron prevented the formation of an unfavorable phase γ2 and instead produced intermetallic compounds κ in the microstructure. Friction stir processing (FSP) helped refine and homogenize the coarse and inhomogeneous structure of the casting, and also eliminated casting defects, whether performed in air or underwater conditions. The polarization and electrochemical impedance tests revealed that, in most cases, FSP led to a decrease in electrochemical and short-term corrosion behaviors as compared to the as-cast specimens, under the impact of alloy composition and active cooling. However, the weight loss immersion tests indicated that the friction stir processed alloys, particularly those processed underwater, demonstrated the best long-term corrosion properties. It was observed that the corrosion product film created on all models after immersion had a similar composition.

Mechanism of recalcification and its effects on the microstructure and transport properties of cement paste

Calcium leaching involves the removal of calcium ions from the pore solution and hydration products, leading to a decrease in pH, coarsening of pore structure, and, in severe cases, loss of cohesion, shrinkage, and cracking. Recalcification is a restoration process aiming at repairing degraded C-S-H structures by externally supplying calcium ions. However, our understanding of recalcification mechanism, its potential to reverse calcium leaching, and its effects on deteriorated cementitious matrices remains limited. This study aims at enhancing the understanding of the impact of recalcification on calcium leached cement pastes. Our findings demonstrate that calcium leaching can be partially reversed by immersion in a saturated calcium hydroxide solution. Recalcification functions by introducing calcium ions to the degraded matrix, triggering a reaction with the degraded C-S-H. This process reverses silicate polymerization, increases the Ca/Si ratio in the degraded zone’s, and densifies the pore structure. After only 14 days of recalcification, the degraded portion experienced a 50 % reduction in porosity, an increase in pH. By day 28, recalcification halved the permeability of the treated sample and completely consumed all silica gel. Additionally, our findings reveal that higher temperatures adversely affect the structure of C-S-H, hindering the beneficial structural modifications facilitated by recalcification.

Hot deformation and dynamic recrystallization of Mg-Gd-Y-Zn-Zr alloy containing high volume fraction 18R-LPSO phase

The deformation behavior including flow behavior, hot workability and dynamic recrystallization (DRX) mechanism of as-cast Mg-9Gd-3Y-3.75Zn-0.6Zr alloy containing 26.5 % volume fraction 18R long-period stacking ordered (LPSO) phase distributed in continuous network morphology were studied by hot compression experiments at deformation condition of 350 ℃-500 ℃, 0.01–1 s−1 strain rate and 0.75 true strain. The influence of deformation conditions on the microstructural evolution was analyzed by using optical microscopy (OM), scanning electron microscope (SEM), electron back scatter diffraction (EBSD) and transmission electron microscope (TEM). Results display that stress exponent and deformation activation energy are 5.58 and 241.39 kJ·mol−1 correspondingly, which suggested that dislocation climb is the principal deformation mechanism. The Arrhenius type constitutive equation is established as ε̇=4.09×1016sinh(9.922×10−3σ)5.58exp(−241394RT). Microstructure evolution can be characterized by Zener-Holomon parameter (Z) which reflects the combining effect of temperature and strain rate on microstructure. At low lnZ (lnZ<36), the 18R-LPSO phase dissolves from continuous network to blocks and high DRX volume (>50 %) is realized by particle-stimulated nucleation and discontinuous dynamic recrystallization. At moderate lnZ (36≤lnZ<40), a fine and coarse grains bimodal structure is formed at the original grain boundary by continuous dynamic recrystallization resulting in a DRX volume between 10 % and 50 %. At high lnZ (lnZ≥40), layered 14H‐LPSO phase precipitates and inhibits DRX (DRX volume＜10 %) by absorbing dislocations. With combination of dissipation coefficient, instability factor and microstructure analysis, 400 ℃/0.01–0.05 s−1 and 450 ℃/0.01 s−1 are confirmed as optimal hot working domains for the as-cast alloy, under which conditions bimodal microstructure and equiaxed grains microstructure (average grain size 10.3 μm) can be formed correspondingly.

Realistic Facial Age Transformation with 3D Uplifting

AbstractWhile current facial re‐ageing methods can produce realistic results, they purely focus on the 2D age transformation. In this work, we present an approach to transform the age of a person in both facial appearance and shape across different ages while preserving their identity. We employ an α‐(de)blending diffusion network with an age‐to‐α transformation to generate coarse structure changes, such as wrinkles. Additionally, we edit biophysical skin properties, including melanin and hemoglobin, to simulate skin color changes, producing realistic re‐ageing results from ages 10 to 80 years. We also propose a geometric neural network that alters the coarse scale facial geometry according to age, followed by a lightweight and efficient network that adds appropriate skin displacement on top of the coarse geometry. Both qualitative and quantitative comparisons show that our method outperforms current state‐of‐the‐art approaches.

Influence of low vacuum and high temperature condition on moisture transport and dry shrinkage of mature concrete

Low vacuum and high temperature typically promote the evaporation of moisture and exacerbate concrete shrinkage cracking, which highlights the issue of volume stability for concrete materials in some engineering environments (e.g. the operational environment of ultra-high-speed train in the low-vacuum tube). To evaluate its impact on moisture transport and drying shrinkage of mature concrete, different air pressure and temperature conditions were selected and the correspondent experiments of investigating moisture loss, internal relative humidity, and drying shrinkage after exposure were conducted. And the evolution of different types of moisture, hydration degree, pore structure, and morphology of matrix was analyzed through microscopic testing methods. Experimental results present that compared to the standard drying condition, the moisture loss and drying shrinkage of concrete under low vacuum and high temperature condition increased by more than 48.5 % and 77.4 % respectively. There exists a strong correlation between moisture loss and drying shrinkage of matrix after low vacuum and high temperature exposure. Besides, compared to the sole effect of low vacuum, the coupling effect of low vacuum and high temperature has a more significant impact on the moisture transport and drying shrinkage of concrete. Among them, after prolonged exposure to low vacuum and high temperature, the internal relative humidity of matrix drops to 50 %∼60 %, and the corresponding critical aperture reduces to 1.0–1.5 nm, thereby significantly increasing the shrinkage stress of concrete. Furthermore, low vacuum and high temperature condition reduces the content of capillary water, gel water, and chemically combined water, and leads to the loss of moisture in smaller pores. In addition, for mature concrete, low vacuum and high temperature condition not only impedes cement hydration but also induces the coarsening of pore structure, resulting in an increase in the number of macropores and pores around 50 nm, which correlates highly with the evolution of drying shrinkage.

Microstructure and properties of metal inert gas welded joints in a novel Al–Mg–Zn–Er–Zr alloy

Metal inert gas (MIG) welding of a novel Al-5.82Mg-0.61Zn-0.14Er-0.11Zr alloy was performed using ER5E61 and ER5B71 filler wires. The effect of the two filler wires on microstructures and mechanical properties of MIG welded joints was investigated. The study shows that fully penetrated joints are obtained by MIG welding process filled with ER5E61 and ER5B71 wires. Compared with ER5B71, the weld metal (WM) with ER5E61 exhibits a coarse structure and high solid solution of Mg and Mn elements. After the tensile test, the WM with ER5E61 and ER5B71 wires is composed of elongated coarse grains with a higher proportion of low angle grain boundaries (LAGBs). In addition, the lattice rotation occurring within the grains, indicating that single grain has an unevenly plastic deformation after the tensile test. The average microhardness of the WM is 83.4 HV and 82.9 HV for ER5E61 and ER5B71 wire, which is the lowest microhardness in the MIG welded joint. The average ultimate tensile strength (UTS) and elongation index (EI) of the MIG joints are 327.7 MPa and 8.5% for ER5E61 wire, and 314.3 MPa and 8.2% for ER5B71 wire, suggesting the MIG welded joint with ER5E61 wire achieves a good combination of strength and ductility. Quantitative assessments of the effects of different strengthening mechanisms on the strength reveal that dislocation strengthening and solid solute strengthening are the main factors to obtain a higher strength of welded joints with ER5E61.

Microstructural transformation and corrosion–cavitation behavior of ultrasonic nanocrystal surface modified nickel aluminum bronze (NAB)

In this study, nickel–aluminum bronze (NAB) is optimized by ultrasonic nanocrystal surface modification (UNSM), and its surface microstructural evolution, surface hardness, electrochemical corrosion behavior, and cavitation erosion behavior are investigated. The potentiodynamic polarization curves and electrochemical impedance spectra before and after UNSM treatment of NAB are measured using a typical three-electrode system. The cavitation erosion process is simulated through the vibration of ultrasonic waves underwater, and the cavitation erosion resistance performance of various specimens is evaluated. UNSM significantly refines the coarse and heterogeneous multi-phase structure of the cast NAB, providing a relatively uniform and dispersed structure. Simultaneously, severe plastic deformation rapidly increases micro-strains on the NAB surface, which effectively improves its surface hardness from 211 to 360 Hv. After UNSM treatment, the corrosion potential increases slightly; and the passivation potential and current decrease considerably, dropping from 207 to 103 mV and from 5.23 to 2.41 mA/cm2, respectively. This is primarily because of the slowdown of selective-phase corrosion and the uniform formation of an oxide film. Additionally, UNSM parameters affect corrosion potential by regulating surface roughness. A smoother surface corresponds to a higher corrosion potential at the same load. UNSM treatment significantly improves the cavitation corrosion resistance of NAB, primarily because an increase in hardness and uniform distribution of structure effectively slows the speed of crack formation and propagation, which is a result of the synergistic improvement of mechanical and corrosion resistance properties.