Low-density Material Research Articles

Upcycling stale bread into (meso)porous materials: Xerogels and aerogels

This work explores the upcycling of stale bread into bio-based, low-density porous materials with partial mesoporosity, produced through gelatinization and drying, using either supercritical CO2 (aerogels) or low-vacuum conditions (xerogels). Cryogels were also fabricated via freeze-drying for comparison purposes. Stale bread particles (Bread) were subjected to proteolytic gluten depletion (Gluten-Depleted Bread, GDB) or particle size reduction (Finely milled Bread, FB) to investigate the effect of protein removal or particle size on porous materials’ properties. Porous materials made from wheat starch (WS) and wheat flour (Flour) were also examined for comparison. The solvent exchange induced volume shrinkage (SE-VS), which accounted for over 87% of the total shrinkage, ranged from 62% in GDB to 78% in WS. Bread-based porous materials presented comparable specific surface area (∼40 m2/g) and water absorption capacity (∼400%) to WS materials, but outperformed in resistance to volume shrinkage, resulting in lower density. FB porous materials possessed a higher specific surface area than Bread materials, indicating the benefits of particle size reduction. Furthermore, gluten depletion resulted in GDB-aerogels with the highest specific surface area (∼80 m2/g), highlighting the benefits of gluten depletion. However, WS materials exhibited significantly greater maximum compressive stress (>2.0 MPa) and compressive modulus (>6 MPa) than stale bread-based porous materials. Importantly, the porous properties of xerogels and aerogels were similar (differences < 10%), indicating the feasibility of using low vacuum drying to produce new porous materials with partial mesoporosity (surface area 60–80 m2/g) from stale bread at a lower cost.

A novel conceptual design for self-healing of cracked cementitious composites incorporating two bacteria-based capsules

Expanded polystyrene (EPS) is a low-density material prone to float during composite mixing and vibration. Inspired by this, a two-bacteria-capsule system was reported in this study to enhance the self-healing capacity of cracked mortar. Specifically, the BC-A capsule, containing aerobic bacteria, EPS, and superabsorbent polymer (SAP), and the BC-N capsule, containing anaerobic bacteria and SAP, are prepared through granulation using polyethylene glycol. Sulphoaluminate cement and epoxy resin are used to encapsulate the core materials. The BC-A capsules automatically float in the composite preparation process, while the BC-N capsules are distributed in the middle and bottom regions due to extrusion effect. Upon capsule rupture, the two types of bacteria are released in regions favorable for biomineralization, corresponding to the principle that oxygen concentration reduces along the crack depth. The self-healing behaviour was evaluated as well as the healing products were characterized. The results showed that the capsules cracked simultaneously with the composite and the coating effectively avoided premature release of the self-healing materials. Cementitious composites containing double capsules achieved 90 % closure of cracks with initial widths of 50–600 μm. The three-dimensional healing capacity was significantly enhanced, particularly in terms of impermeability and strength recovery ratio. The main healing products in the cracks were calcite and swollen SAP. The swollen SAP provided nucleation sites and enough water for biomineralization in the healing process.

Overview of Multifunctional (Ultra-)Lightweight Materials for a Sustainable Future

Abstract In line with the ongoing advancement of high-performance materials that are multifunctional and environmentally friendly, this paper provides an overview of recent developments in lightweight and ultra-lightweight multifunctional materials. We primarily examine the various types of low-density multifunctional materials, their production techniques, and their applications within the context of a sustainable future. From a structural point of view, ultra-light materials are classified into three main groups: aerogels, foam, and micro/ nanolattice. In terms of composition, they can be derived from ceramic, metallic, or polymeric materials. This overview pays particular attention to silica, carbon and composite aerogels, as well as metal, ceramic (carbon), and polymer foams.

Optimization and characterization of GGBFS-FA based alkali-activated CLSM containing Shield-discharged soil using Box-Behnken response surface design method

With the rapid growth of shield-discharged soil (SDS), there is an increasing demand for effective recycling and transformation methods. This study aims to develop an alkali-activated controlled low-strength material (CLSM) by utilizing ground granulated blast furnace slag (GGBFS) and fly ash (FA) as precursors, SDS as fine aggregate, and sodium hydroxide (NaOH) solution as an activator. The Box-Behnken design (BBD) within the response surface methodology (RSM) framework was employed, considering liquid-to-solid ratio, alkali equivalent, aggregate-to-binder ratio, and foam agent content (FC) in SDS as key factors. Regression models were constructed to analyze the effects of these factors on flowability, bleeding rate, setting time, compressive strength, elastic modulus, and water absorption. The results confirmed the effectiveness of RSM in determining optimal conditions for material performance. In addition, microscopic analyses were conducted to explore hydration products, microstructural characteristics, and pore distribution. The findings revealed that the fresh density of the CLSM ranged from 1460 to 1740 kg/m³, classifying it as a low-density material. The 28-day compressive strength varied from 1.837 to 7.884 MPa, while the setting time ranged between 1.2 and 5.6 hours. These properties comply with the ACI 229 standard and are suitable for practical applications. Interestingly, when the aggregate-to-binder (A/B) ratio was between 0.2 and 0.4, increasing the ratio did not lead to a consistent reduction in mechanical properties. Instead, the properties initially decreased and then improved. Moreover, an increase in foam agent content (FC) extended the setting time and reduced mechanical strength. The correlation coefficients of all models exceeded 0.98, with a coefficient of variation below 10 % and a signal-to-noise ratio greater than 4, demonstrating strong reliability and accuracy of the models. Additionally, the average relative error between predicted and experimental values in six scenarios was under 6 %, validating the feasibility of optimizing the design of alkali-activated CLSM using RSM. The formation of Ca(OH)₂ crystals facilitates early strength development, resulting in final cementitious materials reticular, fibrous C-S-H, C-A-H, and other gel-like hydration products. Calcium promotes the formation of gels such as C-S-H, shortening the setting time and enhancing microstructural density. This study provides valuable insights for optimizing the design of alkali-activated CLSM containing SDS, thereby expanding methods for utilizing construction and demolition waste.

Electrochemistry of Phase-Change Materials in Thermal Energy Storage Systems: A Critical Review of Green Transitions in Built Environments

This article reviews recent research on phase-change materials (PCMs) used in thermal energy storage systems with the aim of enhancing their performance. The study explores various methods to improve heat transfer in PCMs, such as microencapsulation, infill materials, fins and nanofluids. Additionally, it evaluates techniques to boost heat transfer in latent heat thermal energy storage (LHTES) systems and investigates ways to increase thermal conductivity using porous and low-density materials. PCMs store thermal energy, making them suitable for use in solar energy systems when solar energy is not available. The need for eco-friendly alternatives to conventional heating and cooling in global construction and the significant energy consumption of buildings has driven research on this topic. As such, this study additionally examines current advancements in free cooling systems with latent heat storage to identify the key factors affecting their effectiveness. The findings show that using PCMs for overnight cooling maintains the room temperature within the comfort zone and reduces the cooling loads in various climates. Using machine learning methods, this study also compares recent advancements in the use of PCMs in various solar energy systems, including solar thermal power plants, solar air purifiers, solar water heaters and solar appliances. Results derived feature key factors crucial for the optimal selection of PCMs and the challenges associated with sustainable green transitions in built environments. HIGHLIGHTS This review provides an in-depth examination of PCM thermal energy storage systems. This study investigates the use of fillers, nanofluids, and nanoparticles for enhanced heat transfer. Analytical methods for boosting the PCM thermal conductivity are briefly outlined. Geometric design and thermal conductivity enhancement affect the Latent Heat Thermal Energy Storage (LHTES). The assessment also evaluates advanced free-cooling systems using the LHTES. PCMs help to store heat energy in solar systems and bridge supply gaps. GRAPHICAL ABSTRACT

Deactivation of harmful green tide using Ag/SiO2 and Ag/Al2O3 coatings on low-density porous materials

Nowadays harmful bloom tides affect greatly the economy of coastal states. For this reason, the present communication reports on a practical method for synthesizing SiO2 and γ-alumina nanospheres, immobilized by sonochemistry on low-density porous foams and perlite granules, as a solution to this problem. A biostatic AgNP effect was incorporated into both materials, achieving AgSi and AgAl. The green-tide inactivation was performed by using Tetraselmis suecica under aqueous conditions. AgAl/FWGS displayed the best inactivation efficiency performance (94 %). Additionally, foams have significant buoyancy and are easy to handle, being an option for T. suecica inactivation for their easy recovering.

Multifunctional seamless meta-sandwich composite as lightweight, load-bearing, and broadband-electromagnetic-wave-absorbing structure

Engineered porous geometries composed of low-density lossy materials are promising as broadband absorbers due to their tunable structural attenuation that can selectively manipulate electromagnetic (EM) waves. However, the exposed cellular architectures require mechanical reinforcement and additional packaging. Here, we present a multifunctional meta-sandwich structure as one seamlessly integrated component composed of functional faceplates and dielectric lossy material-based octet-truss geometries toward a lightweight, load-bearing, and high-performance broadband EM wave absorber. EM responses are explored in the 4–18 GHz range by varying material combinations and multilayers of the upper-lower faceplates and the octet-truss core, elucidating the absorbing mechanisms of meta-sandwich structures. Multi-material 3D printing that streamlines the production of the seamless meta-sandwich composite into a single step implements the devised design that simultaneously excel in EM wave absorption and mechanical functionalities. The fabricated composite in a thin, single-layer structure comprising a transmitting upper faceplate, a dielectric lossy core, and a reflecting lower faceplate, achieves an average absorption rate of 95.0 % and a broadband reflection loss (≤-10 dB) over the entire measured bandwidth. Furthermore, flexural testing confirms superior bending resistance compared to conventional honeycomb structures. The multi-materials meta-sandwich design will inspire versatile multifunctionalities enabled by rationally combining mechanical metamaterials and functional housing.

High sulfur content cathode composites utilizing the Li(CB9H10)0.7(CB11H12)0.3 superionic conductor for all−solid−state Li−S batteries

Rechargeable batteries are encountering ever−growing demands for further improvements in energy density and safety. All−solid−state lithium−sulfur (Li−S) batteries have the potential to meet these demands, because they employ not only high−energy−density electrodes but also non−flammable inorganic solid electrolytes. However, the sluggish conducting nature of the S cathode results in high electric transfer barriers, making high S content in solid−state cathode composites difficult. In this study, we report the fabrication and reaction behavior of high S content cathode composites using a Li(CB9H10)0.7(CB11H12)0.3 superionic conductor. The lithium superionic conduction, high deformability, and low material density of Li(CB9H10)0.7(CB11H12)0.3 solid electrolyte facilitate intimate and favorable connections with sulfur and carbon, leading to facile electrical migrations within sulfur−Li(CB9H10)0.7(CB11H12)0.3−carbon (S−CH−C) composites. In battery tests, these close interconnections enable the fabrication of S−CH−C cathode composites through simple physical hand−mixing, allowing for reversible discharge−charge cycling of all−solid−state Li−S batteries engaging high energy density (>1,000 Wh kg−1cathode composite) S−CH−C cathode composites with a high S content of 50 wt%. In addition, a comparative investigation using various carbonaceous conductive materials suggests that simultaneously achieving high surface area, nanoparticle size, and non−spherical rough morphology is crucial for developing high S content S−CH−C composites with superior battery performances.

Observations of Igneous Subsurface Stratigraphy during the Jezero Crater Floor Rapid Traverse from the RIMFAX Ground-penetrating Radar

Perseverance traversed the eastern, northern, and western margins of the Séítah formation inlier on the rover’s western fan front approach. Mapping the stratigraphy and extent of the Máaz and Séítah formations is key to understanding the depositional history and timing of crater floor resurfacing events. Perseverance's rapid progress across the Jezero crater floor between the Octavia E. Butler landing site and the western fan front resulted in limited contextual images of the deposits from the Navigation Camera and Mast Camera Zoom. By combining the limited surface images with continuous subsurface sounding by the Radar Imager for Mars’ Subsurface Experiment (RIMFAX) ground-penetrating radar, Jezero crater floor stratigraphy was inferred along this rapid traverse. We produced the first subsurface map of the Máaz formation thickness and elevation of the buried Séítah formation for 2.3 km of the rapid traverse. Three distinct reflector packets were observed in RIMFAX profiles interspersed with regions of low-radar reflectivity. We interpret these reflector packets with increasing depth to be the Roubion member of the Máaz formation (covered in places with regolith), the Rochette member, and the Séítah formation. We found a median permittivity of 9.0 and bulk density of 3.2 g cm−3 from hyperbola fits to RIMFAX profiles, which suggests a mafic composition for Máaz and Séítah. The low-radar reflectivity regions within each reflector packet could indicate potential depositional hiatuses where low-density material like sediment or regolith could have accumulated between successive Máaz formation lava flows and the Séítah formation at depth.

Effects of local bed layer characteristics on separation of low rank oil shale in a dry cascade beneficiation bed

Oil shale is considered a highly significant substitute energy source for the 21st century due to its abundant resources and feasibility for development and utilization. This paper utilizes a dry cascade beneficiation bed to upgrade 25–0 mm oil shale, focusing on the spatial distribution characteristics of local bed layer density and differential density particle spatial distribution rules. The study identifies the formation area of autogenous medium fluidization and systematically analyzes the force characteristics and spatial migration laws of particles in local bed layers. Factors influencing the mixing and separation of oil shale particles are investigated, and stages of the separation process are determined. Experimental results indicate that in area I, the density distribution range of autogenous medium bed layers is 2.21–2.25 g/cm3, representing the formation area of autogenous medium fluidization, predominantly with low-density oil shale particles at ρ = 1.95 g/cm3, ranging from 2.28 % to 4.37 % across particle size grades. Area II predominantly contains intermediate density particles at ρ = 2.20 g/cm3, with upper and lower layer contents of 10.9–11.6 % and 4.7–5.7 %, respectively; the upper bed layer is dominated by 13–25 mm particles, while the lower bed layer by 0–6 mm and 6–13 mm particles. Area III features high-density particles at ρ = 2.40 g/cm3, with upper and lower layer contents of 6.13–6.40 % and 1.86–2.11 %, respectively, showing particle size distribution consistent with area II. When Γ = 13.60–16.28, area I serves as a domain for low-density material separation, with peak forces of 6.95–7.0 mN; area II as a domain for separation of medium to high-density particles, with peak forces of 4.83–4.87 mN; and area III as a domain for high-density material transport, with peak forces of 2.01–2.03 mN. Particle acceleration along the Z-axis relative to the X-axis increases by 0.688 m/s2, 3.791 m/s2, and 4.670 m/s2 in areas I, II, and III, respectively, and relative to the Y-axis by 0.554 m/s2, 3.11 m/s2, and 3.396 m/s2. When U=2.36 m/s and Γ = 17.73–22.04, significant differences in distribution of same-density particles between upper and lower bed layers are observed, with differences in content for low-density materials (ρ = −1.8 g/cm3) of 13.23 %, 0.01 %, and 0.01 % in areas I, II, and III, respectively, and for high-density materials (ρ = +2.5 g/cm3) of 1.21 %, 0.91 %, and 2.17 %. By examining particle mixing and separation processes, three operational stages are defined: Area diffusion, stratified transition, and cascade distribution, and separation tests under optimal conditions achieve a concentrate yield of 39.23 % with an oil content of 10.18 %, and a tailings yield of 60.77 % with an oil content of 0.71 %. The probable error (Ep) is 0.08 g/cm3 achieves high-precision upgrading of oil shale.

A case-history using gravity data to validate alternate interpretations of the material below a deep seismic reflector in the Matheson area of Ontario, Canada

Gravity data are ‘nonunique’ in that a gravity anomaly can be explained by many bodies with different properties. Similarly, in seismic data, the strength of a reflection is dependent on the product of the density and the seismic velocity, so the nature of a reflection cannot be used to determine the density below an interface when the velocity is unknown. In a previous gravity study, we had concentrated on shallow features (model α), which implicitly assumed that a number of deeper reflections were due to an anomalous layer, thick enough to cause reflections from its upper and lower surfaces that do not cancel and that the density above and below this thick layer were the same. An alternate possibility is that the material below some of the reflections is lower density material called the Deloro assemblage. In order to test this hypothesized model (model β), we reinterpreted the seismic sections and repeated the gravity study. In order to allow for the deeper low-density material and account for some shallower reflectors having Deloro below, we had to make the Porcupine assemblage, which is shallow and even lower density than the Deloro, thinner in places. We found that the gravity data could be explained with the Deloro assemblage below the reflectors. The top of this hypothesized Deloro assemblage varies from 7.5 km in the east to 3 km in the west of the study area. Both models and are consistent with the gravity and seismic data, but model is also consistent with the Deloro being mapped outcropping to the west of the study area and a strong reflector (a banded iron formation) often being observed at the top of the Deloro. Our case study illustrates that modelling and interpretation should often be revised when new information becomes known.

Study on particle size and density segregation law in the separating process of poor quality coal with high gangue content under the action of composite force field

ABSTRACT Thin-seam mining frequently captures a significant proportion of gangue and interbedded coal in surface coal mines. Consequently, raw coal has a broad range of particle size distributions and a high percentage of components with intermediate densities, which are complex and challenging to separate. This study aims to determine the method of product division and the segregation law of particle size and density of raw coal during the separation process using a vibration and airflow composite force field. A difference in the particle size segregation of the coal particles was evident. Particle-size segregation primarily occurs in the separation area. Large-particle-size coal has a wide distribution range, spreading over the entire bed and fully utilizing the bed to achieve separation. The material becomes increasingly displaced into the separation area as its particle size decreases, thereby weakening the separation effect. Large coal particles can undergo density segregation in the vertical direction, with low-density material placed in the upper layer. This ensures that low-density material is incorporated into the refined coal product. Regardless of density, the coal tended to tilt more toward the bottom layer as the particle size decreased. This results in a poor density stratification effect with refined coal products mixed with gangue and an increase in the mismatch content. The extent of fine coal discharge was determined to be two-fifths of the entire length of the discharge side. This ensures that the majority of refined coal is recovered and that there is no excessive gangue mixing with the refined coal output. Achieving a 55.54% yield, refined coal lowers its ash content by 16%, increases its calorific value by 1400 kcal/kg, and effectively separates coal with a high gangue concentration.

Artificial High- and Low-density Materials in Bone Mineral Densitometry Using Dual-energy X-ray Absorptiometry: A GATE Monte Carlo Simulation of “Black-hole” Artifact

Objective: The objective of the study was to evaluate the effect of artificial high- and low-density materials on Bone mineral density (BMD)scans in dual-energy X-ray absorptiometry (DXA) method and emergence of black-hole artifact through GATE Monte Carlo simulation. Materials and Methods: GATE Monte Carlo code was utilized to simulate the artifact encountered in clinical scans acquired by HOLOGIC® bone densitometer. Two simplified phantoms were designed. The first one was a rectangular box with six smaller cubes inside and the second one was a body torso. Materials of cubes were spine bone, polymethyl methacrylate (PMMA), barium sulfate suspension in water, stainless steel, titanium alloy, and gold. The torso phantom contained objects of 5 vertebrae, bowel and 3 small spherical objects near the surface of the torso as piercing objects on the abdominal wall, each overlying the vertebrae. Using 100 and 140 kVp, spectral X-rays were generated to simulate DXA. For both phantoms, two simulations were carried out. The pair of projections acquired for each phantom were then subtracted and analyzed by curve fitting techniques. Results: Except for spine bone, in which radio-opacity decreases with increasing spectral X-ray energy (from 100 to 140 kVp), other squares exhibit little changes over different energies. PMMA shows consistently very low radio-opacity. Four other materials (barium sulfate in water, stainless steel alloy, titanium alloy, and gold), all attenuate the X-ray photons substantially. Except for spine bone, other materials are barely noticeable in pairwise subtracted images. In torso phantom, piercing objects are visualized as “holes” in vertebrae. Conclusion: Both artificial high- and low-density materials, compared to bone, are eliminated during the subtraction of dual-energy X-ray profiles and therefore, can create black-hole artifact.

Biodegradable starch foams reinforced by food-chain side streams

Biodegradable starch foam trays offer an eco-friendly substitute for petroleum-based single-use packaging, notably polystyrene foams. However, they lack flexibility, tensile strength, and water-sensitivity, addressable through lignocellulosic reinforcement. This study aimed to develop biodegradable starch foam trays filled with different food-chain side streams for sustainable alternative packaging. Corncob, soybean straw, cassava peel, araucaria seed hull, yerba mate stalks and yerba mate leaves petiole were collected, dried and ground to <250 μm. The trays were filled with 13 % (w/w) of each food-chain side streams and produced by hot molding. The trays morphology, moisture, water activity (aw), thickness, bulk density, tensile strength, elongation at break, Young's modulus, bending strength, maximum deflection, and sorption isotherms were investigated. Reinforcements slightly increased the foams bulk density, reduced the tensile strength and maximum deflection and while bending strength increased from 0.20 MPa to 1.17–1.80 MPa. The elasticity modulus decreased by adding any filling, that resulted in ductility improvement; however, these packaging have moisture-sensitive material especially for aw higher than 0.52, which drives the use recommendation for dry products storage or shipping/transport. The biodegradable starch foam trays filled with side streams were successfully produced and offer excellent alternative to petroleum-based packaging low-density material with bending strength improved.

Numerical relativity simulations of black hole and relativistic jet formation

ABSTRACT We investigate impacts of stellar rotation and magnetic fields on black hole (BH) formation and its subsequent explosive activities, by conducting axisymmetric radiation-magnetohydrodynamics simulations of gravitational collapse of a 70 $\mathrm{M}_\odot$ star with two-moment multi energy neutrino transport in full general relativity for the first time. Due to its dense stellar structure, all models cannot avoid the eventual BH formation even though a strongly magnetized model experiences the so-called magnetorotational explosion prior to the BH formation. One intriguing phenomenon observed in the strongly magnetized model is the formation of a relativistic jet in the post-BH formation. The relativistic jet is the outcome of a combination of strong magnetic fields and low-density materials above the BH. The jet further enhances the explosion energy beyond $\sim 10^{52}$ erg, which is well exceeding the gravitational overburden ahead of the shock. Our self-consistent supernova models demonstrate that rotating magnetized massive stars at the high-mass end of supernova progenitors could be a potential candidate of hypernova and long gamma-ray burst progenitors.

Versatile Landscape of Low-k Polyimide: Theories, Synthesis, Synergistic Properties, and Industrial Integration.

The development of microelectronics and large-scale intelligence nowadays promotes the integration, miniaturization, and multifunctionality of electronic and devices but also leads to the increment of signal transmission delays, crosstalk, and energy consumption. The exploitation of materials with low permittivity (low-k) is crucial for realizing innovations in microelectronics. However, due to the high permittivity of conventional interlayer dielectric material (k ∼ 4.0), it is difficult to meet the demands of current microelectronic technology development (k < 3.0). Organic dielectric materials have attracted much attention because of their relatively low permittivity owing to their low material density and low single bond polarization. Polyimide (PI) exhibits better application potential based on its well permittivity tunability (k = 1.1-3.2), high thermal stability (>500 °C), and mechanical property (modulus of elasticity up to 3.0-4.0 GPa). In this review, based on the synergistic relationship of dielectric parameters of materials, the development of nearly 20 years on low-k PI is thoroughly summarized. Moreover, process strategies for modifying low-k PI at the molecular level, multiphase recombination, and interface engineering are discussed exhaustively. The industrial application, technological challenges, and future development of low-k PI are also analyzed, which will provide meaningful guidance for the design and practical application of multifunctional low-k materials.

Highly Condensed and Super-Incompressible Be2PN3.

Although beryllium and its compounds show outstanding properties, owing to its toxic potential and extreme reaction conditions the chemistry of Be under high-pressure conditions has only been investigated sparsely. Herein, we report on the highly condensed wurtzite-type Be2PN3, which was synthesized from Be3N2 and P3N5 in a high-pressure high-temperature approach at 9 GPa and 1500 °C. It is the missing member in the row of formula type M2PN3 (M=Mg, Zn). The structure was elucidated by powder X-ray diffraction (PXRD), revealing that Be2PN3 is a double nitride, rather than a nitridophosphate. The structural model was further corroborated by 9Be and 31P solid-state nuclear magnetic resonance (NMR) spectroscopy. We present 9Be NMR data for tetrahedral nitride coordination for the first time. Infrared and energy-dispersive X-ray spectroscopy (FTIR and EDX), as well as temperature dependent PXRD complement the analytical characterization. Density functional theory (DFT) calculations reveal super-incompressible behavior and the remarkable hardness of this low-density material. The formation of Be2PN3 through a high-pressure high-temperature approach expands the synthetic access to Be-containing compounds and may open access to various multinary beryllium nitrides.

Multi-scale microstructural construction in ultralight graphene aerogels enables super elasticity and unprecedented durability for impact protection materials

Ultralight graphene aerogels have gained extensive recognition in the impact protection field. However, attaining both elasticity and durability at low material density is challenging due to their intrinsic conflicts. Inspired by the mantis ootheca, we present a simultaneous improvement in the elasticity, durability, and density restrictions of ultralight graphene aerogels via constructing a multiscale honeycomb microstructure (MHM) within the graphene skeleton. This approach enables resulting graphene aerogel to achieve a strength per unit volume of 284.6 cm3 mg−1, the ability to recover its shape within 10 ms after an impact at 3.569 m/s, and maintain 97.2 % of its sample height after 20,000 cycles at 90 % strain. The operand analyses and calculation results reveal that the MHM structure facilitates this aerogel’s dual-stage stress transfer pathway. Initially, the macroscale honeycomb structure (millimeter-scale) of the graphene aerogels bear and transmit stress to the surrounding regions, followed by the microscale honeycomb structure (micron-scale) deformation to convert stress kinetic energy into elastic potential energy. This two-stage stress transition mechanism of the MHM structure can effectively mitigate excessive local stress and suppress strain localization, thus providing remarkable elasticity and durability. Ultimately, the obtained graphene aerogel demonstrates promising applications as a fall height detection device and impact protective material.

Protostellar disk accretion in turbulent filaments

Context. Recent observations of protostellar cores suggest that most of the material in the protostellar phase is accreted along streamers. Streamers in this context are defined as velocity coherent funnels of denser material potentially connecting the large-scale environment to the small scales of the forming accretion disk. Aims. Using simulations that simultaneously resolve the driving of turbulence on the filament scale as well as the collapse of the core down to protostellar disk scales, we aim to understand the effect of the turbulent velocity field on the formation of overdensities in the accretion flow. Methods. We performed a three-dimensional numerical study on a core collapse within a turbulent filament using the RAMSES code and analysed the properties of overdensities in the accretion flow. Results. We find that overdensities are formed naturally by the initial turbulent velocity field inherited from the filament and subsequent gravitational collimation. This leads to streams that are not really filamentary but show a sheet-like morphology. Moreover, they have the same radial infall velocities as the low density material. As a main consequence of the turbulent initial condition, the mass accretion onto the disk does not follow the predictions for solid body rotation. Instead, most of the mass is funneled by the overdensities to intermediate disk radii.

Development of an empirical model for the prediction of the sound absorption coefficient for thin and low-density fibrous materials

Currently, FEA software such as ABAQUS uses empirical models to predict the sound absorption coefficient of poroelastic materials. However, based on a recent review of the literature it was found that the current sound absorption empirical models are inadequate for accurate prediction of thin (t &lt; 20 mm), low-density materials (ρB &lt; 50 kg/m3). Therefore, the predictions of the sound pressure levels in vehicle cabins, using such software, will be inaccurate since the trim materials are thin and have a low density. Thus, this research aimed to develop an empirical model that can accurately predict the sound absorption coefficient of these materials. Hence, polypropylene fibres consisting of four different diameters were manufactured and converted into nonwovens. Thereafter, airflow resistivity and impedance tube experimental testing were performed on the specimens. Subsequently, statistical analysis of the data was performed using SAS software. SAS was used to identify which independent variables should be included in the models to be developed. The empirical models were developed using the regression analysis toolbox in Microsoft Excel. Once the models were developed, various checks were performed to validate the assumptions of linear regression. The software NumXL was used to perform Cook’s distance tests. Thereafter, the models were validated against the validation dataset, where it was found that the developed exponential model performed best. Finally, the exponential model was compared to existing models using two data sets i.e. an internal dataset, and an external dataset derived from the literature. The developed model outperformed all the historic models on both datasets.