Relative Density Distribution Research Articles

Density dependent constitutive model for Bi-2212 powder compression deformation

Bi-2212 HTS materials are fabricated into multi-filamentary wires via powder-in-tube (PIT) method followed by proper heat treatment to obtain superconductivity, but how to predict the large compression deformation behaviors of the Bi-2212 powder is critical to design the processing of the Bi-2212 HTS wire. Drucker Prager/Cap (DPC) model was the most commonly used model for powders including Bi-2212 with soil-like mechanical behavior to consider its shear failure as well as hydrostatic compression. However, the parameters for DPC Cap evolve with densities change and the original model is inadequate to precisely describe the densification process of Bi-2212 powder with large strain. In this study, the modified DPC model with density dependent parameters was introduced for Bi-2212 powder compressions by measuring the failure strength and hydrostatic compressive behavior under different density states. The DPC yield surface was plotted with an evolution trend of non-linear outward expansion with density increased. FEM model of uniaxial compression based on the as-introduced model was built with subroutine VUSDFLD applied. The distribution of Mises stress and relative density were analyzed. The axial stress-density curve for FEM and experimental results were normalized and quantitively evaluated by Mean Square Error (MSE). The introduced model shows good convergence and could match the experimental results well with normalized MSE of 0.000207 and Root Mean Square Error (RMSE) of 0.0144, indicating the mean error percentage of 1.44%. The model introduced in this article provides supports toward large strain deformation simulation of Bi-2212 powder.

Molecular dynamics simulation of the interaction between aggregates and calcium silicate hydrate and influence of ethylene vinyl acetate copolymer modifier

ABSTRACT It is known that the bonding strength of the aggregate/cement interface affects the overall durability of concrete. However, whether the modification of ethylene vinyl acetate (EVA) copolymer affects the interface interaction between aggregates and cementitious materials is unclear. This study analyzed the interface's static structure, dynamic characteristics, and binding energy. The interaction mechanisms between acid and alkali aggregates and hydrated calcium silicate and the modification effect of EVA were compared. The calculation results of relative density distribution and radial distribution function verified the difference in the structure of EVA-modified acidic or alkaline interfaces. EVA polymer chains significantly blocked the flow of Ca atoms in CaO at the CaO/C-S-H interface and weakened the van der Waals effect at the interface. The mean square displacement and time correlation function analysis indicate that all unmodified interfaces have stable interface structures. After EVA modification, the stability of CaCa-HW decreased significantly, hindered the generation of hydration products, and verified the weak Ca atom transport at the CaO/C-S-H interface. In addition, the adhesion energy of SiO2/C-S-H and CaO/C-S-H after EVA modification decreased by 6% and 14.8%, respectively, quantifying the modification effect of EVA.

Molecular Dynamic Simulation Study on Replacement of Methane Hydrates with Carbon Dioxide Under Different Temperatures, Pressures, and Concentrations of Ethylene Glycol.

In order to alleviate the world energy resources crisis, the research and development of natural gas hydrates has a very important economic value and strategic significance. The CH4-CO2 replacement method can not only achieve geological storage of carbon dioxide but also more effectively mine natural gas hydrates. Based on molecular dynamics theory and the properties of natural gas hydrates, this paper delves into the replacement of methane hydrate with carbon dioxide under different temperatures, pressures, and concentrations of ethylene glycol (EG). We established a CO2-Hydrate model and three CO2/EG-Hydrate models with different concentrations of EG, and we simulated the radial distribution function (RDF), mean square displacement (MSD), and relative density distribution of each particle in the system in different conditions. The higher the temperature, the more unstable the methane hydrates are, and the methane hydrates are more prone to decomposition. Compared with 280 and 290 K, the temperature of 270 K is more favorable for carbon dioxide molecules to enter the hydrate layer and form carbon dioxide hydrates. The changes in pressure have little impact on the decomposition of methane hydrates, the rupture of water cages of methane hydrates, and the number of carbon dioxide molecules entering the hydrate layer under temperatures of 280 K and pressures of 1, 4, and 7 MPa. But overall, a pressure of 1 MPa is more conducive for carbon dioxide molecules to enter the hydrate layer and form carbon dioxide hydrates. Adding EG to CO2 molecules can inhibit the decomposition of methane hydrates. However, the higher the concentration of EG, the faster the decomposition of methane hydrates. The degree of fracture of the water cages in methane hydrates is greater under pure CO2 conditions. Adding EG to CO2 molecules is more conducive for CO2 molecules to enter the hydrate layer and form carbon dioxide hydrates. This review is of great significance to improve the mining efficiency and CO2 storage efficiency of the replacement of natural gas hydrates with CO2.

Functionally graded multi-morphology lattice structures as an optimized sandwich core via digital light processing additive manufacturing

This investigation aims to present a high-strength sandwich core with functionally graded multi-morphology lattice inner structures through vat photo-polymerization additive manufacturing (AM). The five better strut-based designs based on [1], are considered here. All printed specimens have been fabricated from photopolymer resin to ensure manufacturability in a digital light processing (DLP) 3D printer. Firstly, the resin and structural characteristics have been examined. Simultaneously, the lattice core is divided into three regions based on the von Mises stress distribution and tensile and compression responses in finite element analysis (FEA). Based on the mechanical responses of the beam-based structures, these topologies have been applied in each region in an optimal fixed relative density distribution, considering different steps and types. This proposed technique is numerically investigated and experimentally validated using a three-point bending test. As a result, the optimized core demonstrated a 96% increase in maximum fracture force and a 174% increase in stiffness compared to the homogeneous body. Additionally, it exhibited a different deformation mode than the single morphology under similar conditions. These significant findings indicate that this approach provides a new perspective on a high-strength design involving more than three morphologies, and it is faster than computational topology optimization processes.

Experimental study on the mechanical behavior and energy absorption capacity of coral sand at high strain rates

This study investigated and compared the compression responses and energy absorption capacities of coral sand and silica sand at a strain rate of approximately 1000 s−1. To this end, the effects of the relative density and particle size distribution on the abovementioned properties were analyzed, and the stress–strain curves, yield stresses, compressibilities, energy absorption curves, and energy absorption ratios were obtained. The experimental results showed that coral sand had a significantly higher energy absorption capacity than silica sand owing to its higher compressibility. The energy absorption curve for sand was primarily influenced by the yield stress and energy absorption ratio. The lower relative density of coral sand contributed to its higher compressibility and energy absorption capacity compared to silica sand. For coral and silica sands with different particle sizes, the intersection of the stress–strain and energy absorption curves was observed and analyzed. Formulas for predicting the yield stress, compressibility, and energy absorption curve of coral sand were derived, considering the variations in the relative density and particle size. The study findings reveal that using poorly graded coral sand with large particle sizes can improve the energy absorption capacity of coral sand.

An acoustic-optic comparison of fish assemblages at a Rigs-to-Reefs habitat and coral reef in the Gulf of Thailand

The number of decommissioned oil and gas platforms will increase over the coming decades. In the tropics and sub-tropics, platforms may operate near biodiverse natural habitats, such as coral reefs. Abundant and diverse fish communities often aggregate around platforms, with different decommissioning options posing variable ecological effects on these assemblages. One decommissioning option is to repurpose platforms into artificial reefs, a process commonly termed “Rigs-To-Reefs” (RTRs). Many RTR programs attempt to retain or enhance habitat availability and associated fish assemblages. To help demonstrate the importance of RTR projects, the fish habitat value of RTRs can be estimated by comparing the fish communities of RTRs to those of adjacent natural habitats. Surveying fish habitats in turbid waters necessitates the use of methods that can quantify the abundance, biomass, and length of fishes irrespective of visibility. Using an imaging sonar (1.2. MHz) and implementing a novel, pixel-based approach analogous to echo-integration, this study estimated the relative biomass density and length distribution of fishes at seven toppled oil and gas platform jackets in a Reefed Jacket Zone (RJZ) in the nearshore western Gulf of Thailand in comparison with a nearby coral reef. Biomass density was comparable at each habitat, despite extreme variability across the RJZ, attributed to the spatiotemporal stochasticity of larger, schooling fishes. However, fishes were larger at the RJZ, a trend supported by simultaneous stereo-video footage. The relative benefits and drawbacks of imaging sonar encountered in this study are also described.

Inverse Identification of Drucker–Prager Cap Model for Ti-6Al-4V Powder Compaction Considering the Shear Stress State

Numerical simulation is an important method to investigate powder-compacting processes. The Drucker–Prager cap constitutive model is often utilized in the numerical simulation of powder compaction. The model contains a number of parameters and it requires a series of mechanical experiments to determine the parameters. The inverse identification methods are time-saving alternatives, but most procedures use a flat punch during the powder-compacting process. It does not reflect the densification behavior under a shearing stress state. Here, an inverse identification approach for the Drucker–Prager cap model parameters is developed by using a hemispherical punch for the powder-compacting experiment. The error between the numerical and experimental displacement–load curves was minimized to identify the Drucker–Prager cap model of titanium alloy powder. The identified model was then verified by powder-compacting experiments with the flat punch. The displacement–load curves acquired by numerical simulation were compared to the displacement–load curves obtained through experiments. The two curves are found to be in good agreement. Meanwhile, the relative density distribution of the powders is similar to the experimental results.

Bayesian areal disaggregation regression to predict wildlife distribution and relative density with low-resolution data.

For species of conservation concern and human-wildlife conflict, it is imperative that spatial population data be available to design adaptive-management strategies and be prepared to meet challenges such as land use and climate change, disease outbreaks, and invasive species spread. This can be difficult, perhaps impossible, if spatially explicit wildlife data are not available. Low-resolution areal counts, however, are common in wildlife monitoring, that is, the number of animals reported for a region, usually corresponding to administrative subdivisions, for example, region, province, county, departments, or cantons. Bayesian areal disaggregation regression is a solution to exploit areal counts and provide conservation biologists with high-resolution species distribution predictive models. This method originated in epidemiology but lacks experimentation in ecology. It provides a plethora of applications to change the way we collect and analyze data for wildlife populations. Based on high-resolution environmental rasters, the disaggregation method disaggregates the number of individuals observed in a region and distributes them at the pixel level (e.g., 5 × 5 km or finer resolution), thereby converting low-resolution data into a high-resolution distribution and indices of relative density. In our demonstrative study, we disaggregated areal count data from hunting bag returns to disentangle the changing distribution and population dynamics of three deer species (red, sika, and fallow) in Ireland from 2000 to 2018. We show an application of the Bayesian areal disaggregation regression method and document marked increases in relative population density and extensive range expansion for each of the three deer species across Ireland. We challenged our disaggregated model predictions by correlating them with independent deer surveys carried out in field sites and alternative deer distribution models built using presence-only and presence-absence data. Finding a high correlation with both independent data sets, we highlighted the ability of Bayesian areal disaggregation regression to accurately capture fine-scale spatial patterns of animal distribution. This study uncovers new scenarios for wildlife managers and conservation biologists to reliably use regional count data disregarded so far in species distribution modeling. Thus, it represents a step forward in our ability to monitor wildlife population and meet challenges in our changing world.

Adsorption mechanism of CO2/CH4/N2 by the synergistic effect of N/S-doped and functional groups in coal at different temperatures and pressures

Doping-modified coal samples can effectively enhance the adsorption of CO2. In order to investigate the micro-mechanism of the adsorption of different gases by the synergistic effect of N/S atomic doping and functional groups in coal, the microporous constructed by N/S doping with different functional groups in coal at different temperatures and pressures were investigated based on a series of grand canonical Monte Carlo (GCMC) computational simulations. The adsorption amount, heat of adsorption, diffusion coefficient, interaction energy and relative density distribution of CO2/CH4/N2 by the model. It was found that coal samples with more N-doped carboxyl groups could adsorb CO2 better, and coal samples with more N-doped aliphatic functional groups should be selected for adsorption of CH4 and N2, and the N-COOH system had the most stable adsorption state of CO2, and the amount of N-modified coal samples adsorbed CO2 was higher than that of CH4 and N2 at the adsorption temperature of 293.15 K.The diffusion coefficients of the gas molecules showed an increasing trend with the adsorption temperature, and the relative density distributions of CO2/CH4/N2 in the N-doped micropore model were larger than those in the S-doped system. These noteworthy findings provide a valuable theoretical foundation for the advancement of novel adsorbent materials.

APPLICATION OF THE TEST-PARTICL STATISTICAL METHOD FOR THE SIMULATION OF RAREFIED PLUME FLOWS IN A VACUUM

The article substantiates the important role of the problem of the supersonic jet outflow into a vacuum to control the motion of the center of mass, orientation, and stabilization of the spacecraft’s position in space. The types of low-thrust engines and microrocket engines viewed have plumes that can pass through all regimes from continuum to free-molecular. In zones where motion is described at the molecular-kinetic level, statistical methods are most often used. The statistical Test Particle Method (TPM) has so far been used only in rarefied homogeneous flows. The aim of this work is to develop the TPM for numerical modelling plume flows. Below are the basic tenets of the TPM and changes in its algorithm. The initial drawing of the trajectories of molecules is carried out either from the nozzle exit (in the absence of a dense core) or from the initial surface, which is the virtual border of the continuity zone. Determining the distributions over the surface of the drawing of the coordinates of the start and the mass velocity of the plume flow is decisive for obtaining adequate results. Among the considered launch options, the most realistic one is uneven, with a concentration on the plume axis. The calculation of the mass velocity of the plume flow at the initial surface can be performed using numerical methods of continuum aerodynamics or using approximate methods. The testing of TPM in the far field of a rarefied nitrogen plume was carried out by comparing the relative density distribution with the data of the approximate method. The results obtained in the presence of the initial sphere and in its absence agree with each other. The TPM testing in the area adjacent to the nozzle was carried out by comparing the isolines of relative density and Mach numbers with the results of direct Monte Carlo simulation for the experimental conditions of helium outflow from a lowthrust engine into a vacuum. Satisfactory agreement has been obtained between the numerical simulation data of the TPM and the compared data

Comparative Analysis of the Hot Isostatic Pressing Densification Behavior of Uniform and Non-Uniform Distributed Powder

Hot isostatic pressing (HIP) technology can directly produce nearly clean shaped workpieces that meet the requirements while ensuring machining accuracy and surface quality. Usually, people use numerical simulation methods to reduce experimental costs. Generally, a uniform powder relative density distribution of about 65% is used in the simulation. However, in practical engineering, we found that even with additional tools such as vibration tables, the powder filling is not uniform. The non-uniform distribution causes uneven shrinkage of the powder and capsule after HIP. In this paper, a numerical model for HIPing of Ti-6Al-4V powder is developed to improve the prediction by comparing the uniform and non-uniform initial powder distribution. The results show that different initial relative density distributions affect the powder densification process and further affect the deformation of the capsule. It also leads to non-uniform stress distribution after HIP, which increases the risk of capsule rupture. The analysis of the numerical simulation results and the comparison with the experimental results highlights that taking into account the non-uniform powder distribution inside the capsule is vital to improve numerical results and produce near-net shape components. The maximum error of the simulation with the usual initial relative density setting of 65% is 4.2%. However, considering the uneven distribution of initial powder, the maximum error is reduced to 3.16%, and the average error is also less than 2%.

High-resolution structural imaging of volcanoes using improved muon tracking

SUMMARY Muography is increasingly used to image the density distribution of volcanic edifices, complementing traditional geophysical tomographies. Here, we present a new muon data processing algorithm, and apply it to a new generation of scintillator-based muon detectors, to image the relative density distribution in La Soufrière de Guadeloupe volcano (Lesser Antilles, France). Our processing method iteratively searches for the best fit of each muon trajectory, accounting for all the hits registered by the detector related to the particular muon event. We test the performance of our algorithm numerically, simulating the interaction of muons with our detector and accounting for its exact assemblage including the scintillator bars and lead shielding. We find that our new data processing mitigates the impact of spurious signals coming from secondary particles, and improves the amount of successfully reconstructed events. The resulting 2-D muon images at La Soufrière have higher angular resolution than previous ones and capture the heterogeneous structure of the dome. They show density anomalies located on the summit southern region, which includes a boiling acid lake and degassing fractures, where the rock is the most porous and fumarolic activity is ongoing. This work shows the importance of combining numerical simulations of muon propagation with precise raw data processing to obtain high-quality results. It is also a first step towards fully assessing the noise contamination sources when performing muon tomography, and their correction, prior to geophysical interpretations.

Migration, breeding location, and seascape shape seabird assemblages in the northern Gulf of Mexico.

The Gulf of Mexico supports many seabird species, yet data gaps describing species composition and habitat use are prevalent. We used vessel-based observations from the Gulf of Mexico Marine Assessment Program for Protected Species to identify and characterize distinct seabird assemblages in the northern Gulf of Mexico (within the U.S. Exclusive Economic Zone; nGoM). Using cluster analysis of 17 seabird species, we identified assemblages based on seabird relative density. Vessel-based surveys documented the location, species, and number of seabirds across the nGoM between 2017-2019. For each assemblage, we identified the (co-)dominant species, spatial distribution, and areas of greater relative density. We also assessed the relationship of the total relative density within each assemblage with environmental, spatial, and temporal covariates. Of the species assessed, 76% (n = 13) breed predominantly outside the nGoM basin. We identified four seabird assemblages. Two assemblages, one dominated by black tern and the other co-dominated by northern gannet/laughing gull, occurred on the continental shelf. An assemblage dominated by sooty tern occurred along the continental slope into pelagic waters. The fourth assemblage had no dominant species, was broadly distributed, and was composed of observations with low relative density ('singles' assemblage). Differentiation of assemblages was linked to migratory patterns, residency, and breeding location. The spatial distributions and relationships of the black tern and northern gannet/laughing gull assemblages with environmental covariates indicate associations with river outflows and ports. The sooty tern assemblage overlapped an area prone to mesoscale feature formation. The singles assemblage may reflect commuting and dispersive behaviors. These findings highlight the importance of seasonal migrations and dynamic features across the seascape, shaping seabird assemblages. Considering the potential far-ranging effects of interactions with seabirds in the nGoM, awareness of these unique patterns and potential links with other fauna could inform future monitoring, research, restoration, offshore energy, and aquaculture development in this highly industrialized sea.

Аналитическая модель равноканального углового прессования титановой губки

Introduction. The use of equal-channel angular pressing (ECAP) of metal powder makes it possible to obtain practically non-porous blanks with high hardness, with a high level of accumulated deformation and with the formation of an ultra-fine-grained structure. A relevant issue for the study of the semi-continuous ECAP process remains a reliable assessment of the energy-power parameters of the process and the prediction of the porosity of compressed materials. This, in turn, is due to the need to develop sufficiently accurate, reliable and simple mathematical models for practical application. The purpose of the work is to develop an analytical model of the process of equal-channel angular pressing of porous material. Powdered screening of spongy titanium of the TG-100 brand was selected as a model of the material for the study. The object of the study is the process of semi-continuous equal-channel angular pressing of axisymmetric porous briquette of titanium sponge in the channel of the mold. It is assumed that the ECAP uses a punch to create back pressure. For the solution, a process scheme, a statically permissible load scheme on a layer of intense deformation and a kinematically permissible flow scheme of a plastically compressible medium in a layer are determined. A system of equations is constructed in accordance with the accepted schemes. The equation power balance is applied. The analytical equation is solved by the method of successive approximations. Finite element simulation of the porous titanium ECAP process was carried out at the angles of intersection of the mold channels at 45°, 50°, 55° and 60°. Results and Discussion. The porosity of the blank is determined at different stages of the ECAP process. A diagram of the change in pressure on the punch using the analytical solution and finite element simulation is obtained. It is revealed that the results of the analytical solution are consistent with the data of the finite element simulation. The highest stress level occurs in the process of equal-channel angular pressing at α = 45°, however, the distribution of relative density over the cross section is most uniform. The maximum value of the pressure on the working punch decreases with an increase in the angle α. Rational technological parameters of pressing porous blanks should provide the maximum permissible pressure on the deforming tool. From this condition, in each specific ECAP process, it is possible to determine the optimal angle value from the analytical solution.

Quantifying the human cost of global warming

AbstractThe costs of climate change are often estimated in monetary terms, but this raises ethical issues. Here we express them in terms of numbers of people left outside the ‘human climate niche’—defined as the historically highly conserved distribution of relative human population density with respect to mean annual temperature. We show that climate change has already put ~9% of people (>600 million) outside this niche. By end-of-century (2080–2100), current policies leading to around 2.7 °C global warming could leave one-third (22–39%) of people outside the niche. Reducing global warming from 2.7 to 1.5 °C results in a ~5-fold decrease in the population exposed to unprecedented heat (mean annual temperature ≥29 °C). The lifetime emissions of ~3.5 global average citizens today (or ~1.2 average US citizens) expose one future person to unprecedented heat by end-of-century. That person comes from a place where emissions today are around half of the global average. These results highlight the need for more decisive policy action to limit the human costs and inequities of climate change.

Multiscale design and experimental verification of Voronoi graded stochastic lattice structures for the natural frequency maximization problem

Additive manufacturing (AM) has gained popularity for its capacity to produce geometrically complicated structures, such as lattice structures. Lattice structures have great advantages in the lightweight design of the aerospace and automotive field, in which frequent vibration is one of the most concerning problems during the structure design process. Consequently, it is necessary to research structural vibration frequency to avoid dynamic failure, especially the natural vibration frequency of the structure. In this work, a multiscale topology optimization method is proposed to design the Voronoi graded stochastic lattice structures for the first-order frequency maximization problem. Firstly, the generation and analysis of the Voronoi stochastic lattice microstructure are carried out on the microscale. Then, the macroscale structural optimization is conducted with a penalty-free density method. Finally, the full-scale Voronoi graded stochastic lattice structure is reconstructed based on the obtained relative density distribution and mapping relationship. Numerical examples are performed to demonstrate the correctness and validity of the proposed method for designing the Voronoi graded stochastic lattice structure. Several dynamic experiments also verify the effectiveness of the developed multiscale method and the advantage of the optimized graded lattice structure in structural dynamic response.

Microstructure and properties of aluminum nitride ceramics prepared by aqueous gelcasting method with nontoxic curdlan as gelling agent

Aluminum nitride ceramics were prepared by aqueous gelcasting method and pressureless sintering technique in N2 atmosphere using Y2O3 as sintering additives with nontoxic curdlan as gel system. The solidification mechanism of curdlan was studied. The effects of curdlan content and solid content on the microstructure, relative density and flexural strength of green bodies were investigated. The influences of Y2O3 content and sintering soaking time on the microstructure and properties of sintered bodies were also studied. The results show that, as the temperature increases to 80 °C, the ceramic powders solidify through three-dimensional gel networks of curdlan during gelling process. The green bodies can be successfully fabricated through aqueous gelcasting method with modified powder as original materials. Suitable curdlan content and solid content contribute to fabricating green body with uniform microstructures and high flexural strength. The relative density and flexural strength of sintered bodies enhance as the Y2O3 content and soaking time increase. The flexural strength and thermal conductivity are about 107.5∼172.3 MPa and 75.2∼112.5 W/(m·K), respectively. The sintered body with 4 wt% Y2O3 soaking for 3 h exhibits the highest thermal conductivity because of appropriate relative density, uniform microstructure and reasonable intergranular phase distribution. The mechanical property and thermal conductivity of sintered bodies can be improved by optimizing the gelcasting process parameter, Y2O3 content, and soaking time. The nontoxic gelling system will have wide application for aqueous gelcasting ceramic with complex shape.

Diatom-inspired stiffness optimization for plates and cellular solids

Diatoms, a class of aquatic autotrophic microorganisms, are characterized by silicified exoskeletons with highly complex architectures. These morphologies have been shaped by the selection pressure that the organisms have been subjected to during their evolutionary history. Two properties which are highly likely to have contributed to the evolutionary success of current diatom species are lightweightness and structural strength. Thousands of diatom species are present in water bodies today, and although each has its unique shell architecture, a strategy that is common across species is the uneven and gradient solid material distribution across their shells. The aim of this study is to present and evaluate two novel structural optimization workflows inspired by material grading strategies in diatoms. The first workflow mimics the Auliscus intermidus diatoms’ surface thickening strategy and generates continuous sheet structures with optimal boundaries and local sheet thickness distributions when applied to plate models subjected to in-plane boundary conditions. The second workflow mimics the Triceratium sp. diatoms’ cellular solid grading strategy, and produces 3D cellular solids with optimal boundaries and local parameter distributions. Both methods are evaluated through sample load cases, and prove to be highly efficient in transforming optimization solutions with non-binary relative density distributions into highly performing 3D models.

Enabling Durable Ultralow-k Capacitors with Enhanced Breakdown Strength in Density-Variant Nanolattices.

Ultralow-k materials used in high voltage devices require mechanical resilience and electrical and dielectric stability even when subjected to mechanical loads. Existing devices with organic polymers suffer from low thermal and mechanical stability while those with inorganic porous structures struggle with poor mechanical integrity. Recently, 3D hollow-beam nanolattices have emerged as promising candidates that satisfy these requirements. However, their properties are maintained for only five stress cycles at strains below 25%. Here,wedemonstrate that alumina nanolattices with different relative density distributions across their height elicit a deterministic mechanical response concomitant with a 1.5-3.3 times higher electrical breakdown strength than nanolattices with uniform density. These density-variant nanolattices exhibit an ultralow-k of ≈1.2, accompanied by complete electric and dielectric stability and mechanical recoverability over 100 cyclic compressions to 62.5% strain.Weexplain the enhanced insulation and long-term cyclical stability by the bi-phase deformation where the lower-density region protects the higher-density region as it is compressed before the higher-density region, allowing to simultaneously possess high strength and ductility like composites. This study highlights the superior electrical performance of the bi-phase nanolattice with a single interface in providing stable conduction and maximum breakdown strength.

Illustrating the atomic structure and formation mechanism of ion tracks in polyethylene terephthalate with molecular dynamics simulations

This work reports molecular dynamics (MD) simulations of the formation of detailed ion track structures at the atomic scale in polymers. To simulate the initial chemical reactions and the subsequent thermal movement of polymer molecules, an adapted thermal spike model was implemented using a charge-implicit reactive force field potential. The MD simulation reproduces the physical–chemical process of ion track formation observed in the experiment, e.g., the bond breakage and creation, gas production and release, carbonization effect, and the relative radial density distributions, which are consistent with small angle X-ray scattering results of ion tracks in polyethylene terephthalate generated with 15.9 keV nm−1 Au and 10.9 keV nm−1 Xe ions, respectively. Based on the MD simulation, the ion tracks in polymers show a heavily-damaged core region with an inhomogeneous nanoporous structure, and a surrounding transition region with the mass density increasing gradually back to the same value as the pristine sample.