Dense Material Research Articles

Microarchitectural properties of compacted cancellous bone allografts: A morphology micro-computed tomography analysis

Massive bone loss poses a significant challenge in defect reconstruction. The use of compacted allografts is a valuable technique to reconstruct bone stock. This study aimed to assess the impact of compression on the microstructure of native cancellous bone chips with a micro-CT analysis.Bone samples were harvested from 15 femoral heads donated by patients who underwent total hip arthroplasty. Bone chips were prepared using a bone mill. All samples with the same weight were compressed by 25% and 50% of their original volume and subsequently scanned with a micro-CT scanner to determine the microarchitectural morphology of the bone chips. Uniaxial compression test was carried out before and after a standardized compaction procedure.Comparing the samples without compaction to 50% , the number of trabeculae doubled, the volume ratio doubled, and the trabeculae spacing was reduced, showing voids of 800 μm on average. The number of interlocking possibilities tripled, while no differences were seen in the trabeculae morphology. Uniaxial compression test showed a yield limit after compaction of 0.125 MPa.Interlocking might occur three times more with a denser material than in a non-compacted sample. The increase in density comparable to manual intraoperative compaction did not lead to significant fragmentation of the allograft material. The assessed microarchitecture should, therefore, reassemble the intraoperative situation during a manual bone impaction procedure.

Benzofuroxan‐Based Energetic Materials with Alternating Nitro and Hydroxyl Groups: Synthesis, Characterization, and Energetic Properties

AbstractDue to its good stability, density and oxygen balance, the benzofuroxan fused ring framework has attracted particular attention in the field of high energy density materials. The planar structure of the benzofuroxan facilitates the straightforward derivatization with explosophores and contributes to molecular stability. In this work, a benzofuroxan scaffold was utilized to develop a highly dense energetic material, namely 5,7‐dihydroxy‐4,6‐dinitrobenzo[c][1,2,5]oxadiazole 1‐oxide (DHDNBF). The successive inclusion of explosophores like nitro (−NO2) and oxidative functionality like hydroxyl (−OH) on benzofuroxan resulted in an impressive density (ρ=1.91 g cm−3) and a positive oxygen balance (6.20 %) in DHDNBF (2). Furthermore, the hydroxy groups on DHDNBF enable the formation of dicationic energetic salts 3–7, contributing to additional modifications in the overall performance. Energetic salts 3, 4, and 5 exhibit significantly higher densities ranging from 1.84 (5) to 1.87 (3) g cm−3 and possess a favorable oxygen balance approaching zero or equal to zero. A marked improvement in thermal stabilities was observed in all the energetic salts (3–7) compared to their neutral counterparts, DHDNBF. Energetic salts 4 (Dv=8459 m s−1, P=32.10 GPa) and 5 (Dv=8539 m s−1, P=30.37 GPa) possess good energetic performance, comparable to that of well‐known explosives such as LLM‐105 (Dv=8560 m s−1, P=33.4 GPa). Overall, the favorable characteristics of energetic salts 4 and 5 make them potential candidates for use as benzofuroxan‐based secondary and primary explosives, respectively, in various military and civilian applications.

Deep mantle plumes feeding periodic alignments of asthenospheric fingers beneath the central and southern Atlantic Ocean

High-resolution full waveform seismic tomography of the Earth's mantle beneath the south and central Atlantic Ocean brings into focus a series of asthenospheric low shear velocity channels, or "fingers" on both sides of the southern and central mid-Atlantic ridge (MAR), elongated in the direction of absolute plate motion with a spacing of [Formula: see text]1,800 to 2,000 km, and associated with bands of shallower residual seafloor depth anomalies that suggest channeled flow over thousands of kilometers. Each of the three most clearly resolved fingers on the African side of the MAR corresponds to a separate group of whole mantle plumes rooted in distinct patches at the core-mantle boundary, feeding hotspots, and volcanic lines with distinct isotopic signatures. Plumes of a given group appear to merge at the top of the lower mantle before separating again, suggesting interaction of deep mantle flow with a more vigorous mesoscale circulation in the upper mantle. The corresponding hotspots are generally offset from the location of the deep mantle plume roots. The distinct isotopic signatures of these hotspot groups are also detected in the mid-ocean ridge basalts at the location where the fingers meet the ridge. Meanwhile, at least some of the variability within each plume group could originate in the upper mantle and extended transition zone where plumes in a given group appear to merge and pond. This study also adds to mounting evidence that the African large low shear velocity province is not a uniform, unbroken pile of dense material rising high above the core-mantle boundary, but rather a collection of mantle plumes rooted in patches of distinct composition.

Evaluation of emergency nurses’ knowledge of medical response in nuclear and radiological emergencies : a cross-sectional study

BackgroundEvaluating emergency room nurses’ knowledge of radiation protection, health effects, and decontamination procedures is crucial for preparedness in nuclear and radiological emergencies. This study aims to evaluate the level of knowledge among emergency nurses in Saudi Arabia regarding medical responses to nuclear and radiological emergencies.MethodsA multicenter cross-sectional study was conducted via a self-structured questionnaire with 15 true‒false questions divided into three domains, namely, radiation protection measures, radiation health effects, and decontamination procedures, each with five items and a possible score of 1 point per correct answer. The collected data were analyzed via descriptive and inferential statistics. The study followed the STROBE checklist for methodological rigor.ResultsA total of 594 emergency nurses participated in this study, with the majority being young (64.50% aged ≤ 30), female (68.69%), bachelor’s degree-holding (67.68%), single (63.64%), having ≤ 4 years of experience (56.06%), working in public health facilities (88.89%), and lacking training in medical response (85.35%). The mean knowledge scores for participants were highest for radiation exposure effects (3.27 ± 0.91), followed by radiation protective measures (2.32 ± 0.99), and lowest for decontamination procedures (1.46 ± 1.07). Overall knowledge was measured at a mean score of 7.06 ± 1.68, with 97.47% of the nurses categorized as having poor knowledge level. Nurses in private hospitals scored higher (7.77 ± 1.82) than those in public hospitals (6.97 ± 1.65) on overall mean knowledge (P = 0.034). Concerning findings include emergency nurses’ misconceptions about the protection provided by dense materials, the effectiveness of increasing distance from a radiation source, and prioritizing decontamination of victims over life-saving measures. Additionally, they were unaware of the immediate symptoms following radiation exposure and misunderstood that the primary threat in a radioactive bomb event is the explosion rather than the radiation itself.ConclusionThis study revealed poor knowledge among emergency nurses regarding medical responses to radiation emergencies and highlighted the critical need for enhanced and standardized training in radiation emergency preparedness among nurses. The gaps in knowledge identified in this study could significantly impact the effectiveness of healthcare responses in radiation emergency scenarios. Therefore, targeted educational interventions and policy changes are recommended to address these shortcomings.

Statistical modeling of soft magnetic composites’ permeability

Soft magnetic composites (SMC) also known as powder cores are widely used in many applications because of their linearity, controllable permeability and isotropy. Because of the distributed air gap, the permeability is governed by the inner demagnetizing fields. To model the permeability dependence on the filling fraction, essentially two approaches are used both based on spatial periodicity hypothesis: the non magnetic grain boundary model and the effective medium theory. Actually, the first one works only for dense materials and the second works at low concentration. Both need fitting of two parameters, the inner demagnetizing factor and the particle susceptibility, just because the periodicity hypothesis is never verified for magnetic filling factors larger than 20%. A breakaway model is proposed based on the computation of mathematical esperance of the statistical distribution of magnetic chains and the subsequent determination of demagnetizing coefficient of an ellipsoid of equivalent aspect ratio. The model is collated with permeability data from the literature for spherical or non-spherical particles based SMCs and shows a excellent agreement with only one or even without fitting parameter in the whole concentration range.

The Nusselt number of a hot sphere levitated by a volatile pool

When placed at the surface of a volatile liquid, a sphere of hot dense non-volatile material remains suspended until it cools sufficiently. The duration of this ‘inverse Leidenfrost’ phenomenon depends on the Nusselt number $Nu$ of the sphere, itself determined by flow in the film of vapour separating particle and liquid. It is shown that provided the Nusselt number is large, it can be calculated numerically using only the Laplace relation and the equations governing the thin film; patching to a solution for the outer thick film is not necessary. This method is demonstrated by using it to determine $Nu$ for a sphere sufficiently small that in the governing equations, the acceleration due to gravity is negligible except where multiplied by the density of the sphere. Numerical results giving $Nu$ as a function of a dimensionless measure of sphere weight are supplemented with analysis showing that, when the weight is of the order of the maximum supportable by surface tension alone, the film consists of a spherical bubble cap bounded by its contact rim. The solutions for these regions are coupled: although the apparent contact angle $\chi$ for the cap is determined within the rim, its value depends on the flow rate arriving from the cap as well as on the additional evaporation from the rim. The latter acts to reduce $\chi$ from the value it would otherwise have, thereby reducing the thickness of the entire cap. For the example treated here, the value of $Nu$ is doubled by this mechanism.

Discovery and characterization of a dense sub-Saturn TOI-6651b

We report the discovery and characterization of a transiting sub-Saturn exoplanet TOI-6651b using PARAS-2 spectroscopic observations. The host, TOI-6651 (mV ≈ 10.2), is a sub-giant, metal-rich G-type star with [Fe / H] = 0.225−0.0450.044[Fe/H] = 0.225−0.045+0.044, Teff = 5940 ± 110 K, and log g = 4.087−0.032+0.035. Joint fitting of the radial velocities from PARAS-2 spectrograph and transit photometric data from Transiting Exoplanet Survey Satellite (TESS) reveals a planetary mass of 61.0−7.9+7.6 M⊕ and radius of 5.09−0.26+0.27 R⊕, in a 5.056973−0.000018+0.000016 day orbit with an eccentricity of 0.091−0.062+0.096. TOI-6651b has a bulk density of 2.52−0.44+0.52 g cm−3, positioning it among the select few known dense sub-Saturns and making it notably the densest detected with TESS. TOI-6651b is consistent with the positive correlation between planet mass and the host star’s metallicity. We find that a considerable portion ≈87% of the planet’s mass consists of dense materials such as rock and iron in the core, while the remaining mass comprises a low-density envelope of H/He. TOI-6651b lies at the edge of the Neptunian desert, which will be crucial for understanding the factors shaping the desert boundaries. The existence of TOI-6651b challenges conventional planet formation theories and could be a result of merging events or significant atmospheric mass loss through tidal heating, highlighting the complex interplay of dynamical processes and atmospheric evolution in the formation of massive dense sub-Saturns.

CLASSY. X. Highlighting Differences between Partial Covering and Semianalytic Modeling in the Estimation of Galactic Outflow Properties

Feedback-driven massive outflows play a crucial role in galaxy evolution by regulating star formation and influencing the dynamics of surrounding media. Extracting outflow properties from spectral lines is a notoriously difficult process for a number of reasons, including the possibility that a substantial fraction of the outflow is carried by dense gas in a very narrow range in velocity. This gas can hide in spectra with insufficient resolution. Empirically motivated analysis based on the apparent optical depth method, commonly used in the literature, neglects the contribution of this gas, and may therefore underestimate the true gas column density. More complex semianalytical line transfer (e.g., SALT) models, on the other hand, allow for the presence of this gas by modeling the radial density and velocity of the outflows as power laws. Here we compare the two approaches to quantify the uncertainties in the inferences of outflow properties based on 1D “down-the-barrel” spectra, using the UV spectra of the CLASSY galaxy sample. We find that empirical modeling may significantly underestimate the column densities relative to SALT analysis, particularly in the optically thick regime. We use simulations to show that the main reason for this discrepancy is the presence of a large amount of dense material at low velocities, which can be hidden by the finite spectral resolution of the data. The SALT models in turn could overestimate the column densities if the assumed power laws of the density profiles are not a property of actual outflows.

CFD Modeling of HBI/scrap Melting in Industrial EAF and the Impact of Charge Layering on Melting Performance.

The melting of scrap and hot briquetted iron (HBI) in an AC electric arc furnace (EAF) is simulated by an advanced 3D computational fluid dynamics (CFD) model that captures the arc heating, the scrap/HBI melting process, and the solid collapse mechanisms. The CFD model is used to simulate a scenario where charge layering and EAF power profiles are provided by a real EAF operation. CFD simulation of the EAF operation shows proper prediction of the charge melting when compared with standard industry practice. Namely, the CFD model predicts a 32.5%/67.5% ratio of solid/liquid steel at the beginning of refining, which approaches the 30%/70% ratio used in standard practice. Based on this prediction, the melting rate in the CFD results differs by 8.3% from actual EAF operation. The impact of charge layering on melting is also investigated. CFD results show that distributing charge material into a greater number of layers in the first bucket (10 layers as compared to 4) enhances the melting rate by 12%. However, including dense material at the bottom of the furnace deteriorates melting performance, reducing the impact of the number of layers of the charge. The CFD platform can be used to optimize the use of HBI/scrap in real EAF operations and to determine best recipe practices.

Novel insights into the synthesis and tribo-mechanical performance of high-entropy (Hf0.2Zr0.2Ti0.2W0.2Mo0.2)B2 ceramics

High-entropy (Hf0.2Zr0.2Ti0.2W0.2Mo0.2)B2 ceramics were synthesized using a two-step spark plasma sintering process, with densification at 1600 °C followed by sintering at 1850 °C. This method produced dense materials with excellent mechanical and tribological properties. Hardness values ranged from 18.85 GPa to 39.65 GPa, with a maximum Young’s modulus of 319 GPa. Micro-scratch tests showed high resistance to plastic deformation and minimal surface damage, highlighting durability under mechanical stress. Tribological tests at 15 N and 20 N loads demonstrated exceptional wear resistance, attributed to hard primary phases and lubricating soft secondary phases. These findings confirm the material’s robustness and show the effectiveness of the two-step synthesis in optimizing microstructure and enhancing properties, making it suitable for high-stress and wear-intensive applications.

Controlled Release of Diborane from Alkali Metal Borohydride using Ionic Liquid-Based Lewis Acids.

Alkali metal borohydrides present a rich source of energy dense materials of boron and hydrogen, however their potential in propellants has been hitherto untapped. Potassium borohydride is a promising fuel with high gravimetric energy density and relatively low sensitivity to air and moisture. Problems arise due to the dehydrogenation of the borohydride on heating with minimal energy release. Common methods to extract both boron and hydrogen by means of borane species involve direct reaction of boron trifluoride species with alkali borohydrides. However, these methods face storage and safety issues due to rapid release of diborane on mixing the reactants. We propose a method of diborane release through controlled release of boron trifluoride by means of a tetrafluoroborate based ionic liquid. The trifluoride is released from the ionic liquid at elevated temperatures and enables safe mixture of the reactants at room temperature. It was found that the reaction between borohydride and boron trifluoride proceeds well above room temperature with potassium borohydride releasing diborane and potassium fluoride. The reaction pathway shows a primary reaction releasing diborane and potassium fluoride and a second less energy efficient step leading to the formation of potassium tetrafluoroborate. A 3D printed propellant formulation was also tested.

Controlled Release of Diborane from Alkali Metal Borohydride using Ionic Liquid‐Based Lewis Acids

AbstractAlkali metal borohydrides present a rich source of energy dense materials of boron and hydrogen, however their potential in propellants has been hitherto untapped. Potassium borohydride is a promising fuel with high gravimetric energy density and relatively low sensitivity to air and moisture. Problems arise due to the dehydrogenation of the borohydride on heating with minimal energy release. Common methods to extract both boron and hydrogen by means of borane species involve direct reaction of boron trifluoride species with alkali borohydrides. However, these methods face storage and safety issues due to rapid release of diborane on mixing the reactants. We propose a method of diborane release through controlled release of boron trifluoride by means of a tetrafluoroborate based ionic liquid. The trifluoride is released from the ionic liquid at elevated temperatures and enables safe mixture of the reactants at room temperature. It was found that the reaction between borohydride and boron trifluoride proceeds well above room temperature with potassium borohydride releasing diborane and potassium fluoride. The reaction pathway shows a primary reaction releasing diborane and potassium fluoride and a second less energy efficient step leading to the formation of potassium tetrafluoroborate. A 3D printed propellant formulation was also tested.

Deep learning based x-ray spectrometer for high repetition rate characterization of betatron radiation

Betatron radiation produced from a laser-wakefield accelerator is a broadband, hard x-ray (>1 keV) source that has been used in a variety of applications in medicine, engineering, and fundamental science. Further development and optimization of stable, high repetition rate (HRR) (>1 Hz) betatron sources will provide a means to extend their application base to include single-shot dynamical measurements of ultrafast processes or dense materials. Recent advances in laser technology used in such experiments have enabled increases in shot-rate and system stability, providing improved statistical analysis and detailed parameter scans. However, unique challenges exist at high repetition rate, where data throughput and source optimization are now limited by diagnostic acquisition rates and analysis. Here, we present the development of a machine-learning algorithm for the real-time analysis of betatron radiation. We report on the fielding of this deep learning algorithm for online source characterization at the Institut National de la Recherche Scientifique's Advanced Laser Light Source. By fine-tuning an algorithm originally trained on a fully synthetic dataset using a subset of experimental data, the algorithm can predict the betatron critical energy with a percent error of 7.2 % with a reconstruction time of 1.5 ms, providing a valuable tool for real-time, multi-objective optimization at HRR.

Rapid cargo verification with cosmic ray muon scattering and absorption tomography

Cosmic ray muon tomography is considered a promising method for the non-invasive inspection of shipping containers and trucks. It utilizes highly penetrating cosmic-ray muons and their interactions with various materials to generate three-dimensional images of large and dense materials, like inter-modal shipping containers, typically not transparent with conventional X-ray radiography techniques. The commonly used methods for imaging with muons are based on muon scattering or absorption-transmission data analysis. Due to large thickness of cargo material in shipping container substantial scattering and absorption occur when muons are passing through cargo. One of the key tasks of customs and border security is to verify shipping container declarations to prevent illegal trafficking, and muon tomography could be a viable choice for this task. In this paper, we demonstrate through Monte Carlo simulations using the GEANT4 toolkit that a combined analysis of muon scattering and absorption data can improve the identification of cargo materials compared to using scattering or absorption data alone. The statistical differences in scattering and absorption data for several cargo materials are quantified. For a particular smuggling scenario where tobacco declared as paper towel rolls, it is demonstrated that the combined analysis can accurately distinguish between tobacco and paper towel rolls with 5.5σ accuracy for detector spatial resolution (FWHM) of 0.235 mm, 4.5σ for 1.175 mm resolution (FWHM), and 3.9σ accuracy for 2.35 mm spatial resolution (FWHM), in a short scanning time of 10 seconds. This rapid detection capability has significant implications for anti-smuggling efforts and cargo inspection.

Densification and properties of WC-CoCrFeNi/Co cemented carbide fabricated via spark plasma sintering

The spark plasma sintering (SPS) technique was used to employe WC-CoCrFeNi/Co cemented carbides, incorporating CoCrFeNi and Co as low-coercivity binder phases, resulting in the development of cemented carbides with exceptional mechanical properties. The densification mechanism varying with increasing sintering temperature and the effect of densification on the mechanical properties were investigated using the creep deformation model. In the temperature range of 1100 °C–1300 °C, the main factors contributing to densification behavior are particle rearrangement and grain boundary diffusion due to the viscous flow of the binder phase. The densification mechanism gradually transforms into dislocation climbing with increasing temperature. When the sintering temperature exceeded 1300 °C, the WC grain size increased significantly with increasing temperature and holding time, and the dominant mechanism for grain growth was grain boundary diffusion. The high densification resulted in a substantial increase in effective grain boundary area, thereby increasing both hardness and fracture toughness of the material. Benefiting from the fine grain strengthening effect of the high-entropy alloys (HEAs) and the excellent wettability of Co, a highly dense cemented carbide material with excellent hardness and fracture toughness is achieved at the sintering temperature of 1300 °C, characterized by a relative density of 99.3 %, a hardness of 2064.9 MPa, and a fracture toughness of 11.5 MPa m−2.

Conduit armouring preceding explosive activity at an andesitic stratovolcano, an example from Taranaki Mounga, New Zealand

The strength and permeability of volcanic conduits can directly influence eruption dynamics via moderating the outgassing of ascending magma and the density of eruption plumes. Lithic clasts in pyroclastic ejecta can be used to understand the dynamic evolution of conduit walls because they are incorporated into the ascending melt-gas-particle mixture during volcanic eruptions. We examine the 1655 CE Burrell eruption of Taranaki Mounga, which transitioned from effusive activity to an explosive sub-Plinian phase and ended in unsteady columns. This episode was followed by a series of effusive eruptions of lower explosivity. Using textural analysis and physical properties, we distinguish five dominant lithic clast types within Burrell deposits that represent different regions of the shallow conduit and vent. Lithic types 1–3 represent juvenile (‘intrusive cognate’) and older (‘intrusive accessory’) conduit-filling plug materials. Lithic type 4 represents juvenile (‘extrusive cognate’) vent-filling lava dome extruded at the eruption onset, while Type 5 lithics (‘extrusive cognate’) represent sintered/compacted cognate material from the shallow vent accumulated during transitions in eruptive style. Crystalline andesite lithics (type 1) show a microlite-dominated groundmass. Hydrothermally altered andesite lithics (type 2) show breakdown of phenocrysts and increased seismic velocity relative to type 1 lithics. Brecciated andesite lithics (type 3) comprise fractured and sintered clasts of crystalline andesite. Glassy andesite lithics (type 4) show sub-rounded vesicles and glass-hosted microlites. Banded vitrophyre lithics (type 5) show bands of varying vesicularity, crystallinity and clast load. Physical property data reveals porosity, fracturing, sintering and alteration extent dictate dynamic changes in conduit permeability and potentially strength. Our results show how, during the explosive phase of the Burrell eruption, the conduit was lined with juvenile and remnant shallow plug material that was variably fractured, sintered and altered before being eroded and ejected. Comparison with previous work on Taranaki and dome-plug material from around the world shows how fracturing and sintering of conduit walls, combined with lining with dense juvenile material, cause overall permeability reduction and strengthening of the conduit. This inhibits outgassing and preserves conduit structure, facilitating the transition to explosive activity and the establishment of a stable eruption column.

EWOCS-II: X-ray properties of the Wolf–Rayet stars in the young Galactic super star cluster Westerlund 1

Context. Wolf–Rayet (WR) stars are massive evolved stars that exhibit particularly fast and dense stellar winds. Although they constitute a very short phase near the end of a massive star’s life, they play a crucial role in the evolution of massive stars and have a substantial impact on their surrounding environment. Aims. We present the most comprehensive and deepest X-ray study to date of the properties of the richest Wolf–Rayet population observed in a single stellar cluster, Westerlund 1 (Wd1). By examining the X-ray signatures of WR stars, we aim to shed light on the hottest plasma in their stellar winds and gain insights into whether they exist as single stars or within binary systems. Methods. This work is based on 36 Chandra observations obtained from the “Extended Westerlund 1 and 2 Open Clusters Survey” (EWOCS) project, plus 8 archival Chandra observations. The overall exposure depth Ms) and baseline of the EWOCS observations extending over more than one year enable us to perform a detailed photometric, colour, and spectral analysis, as well as to search for short- and long-term periodicity. Results. In X-rays, we detect 20 out of the 24 known Wolf–Rayet stars in Wd1 down to an observed luminosity of ~7 × 1029 erg s−1 (assuming a distance of 4.23 kpc to Wd1), with 8 WR stars being detected in X-rays for the first time. Nine stars show clear evidence of variability over the year-long baseline, with clear signs of periodicity. The X-ray colours and spectral analysis reveal that the vast majority of the WR stars are hard X-ray sources (kT≥2.0 keV). The Fe XXV emission line at ~6.7 keV, which commonly originates from the wind–wind collision zone in binary systems, is detected for the first time in the spectra of 17 WR stars in Wd1. In addition the ~6.4 keV fluorescent line is observed in the spectra of three stars, which are among the very few massive stars exhibiting this line, indicating that dense cold material coexists with the hot gas in these systems. Overall, our X-ray results alone suggest a very high binary fraction (≥80%) for the WR star population in Wd1. When combining our results with properties of the WR population from other wavelengths, we estimate a binary fraction of ≥92%, which could even reach unity. This suggests that either all the most massive stars are found in binary systems within Wd1, or that binarity is essential for the formation of such a rich population of WR stars.

Short-term interactions between Longmaxi shale and carbon dioxide-based fracturing fluids

The shale is a dense quarried rock material containing abundant shale oil/gas. Extracting shale gas usually requires fracturing the rock formation to speed up gas desorption and migration. Supercritical carbon dioxide fracturing, as an environmentally friendly and waterless fracturing technique of reservoir stimulation, gains increasing recognition in commercial exploitation of shale oil and gas. However, there is insufficient understanding on the interaction between carbon dioxide-based fracturing fluids and shale, as well as its influence on the mechanical parameters of shale, which are pivotal for determining injection parameters and forming the fracture network. This study focuses on the injection of carbon dioxide-based fracturing fluids to enhance shale gas extraction and carbon dioxide sequestration. Simulation tests of injection were conducted to investigate the influence of different fracturing fluids (deionized water, gaseous/supercritical carbon dioxide, gaseous/supercritical carbon dioxide mixed with brine) injected into shale reservoirs on the microstructure and mechanical properties of shale after short-term physicochemical interaction. This article adopts research methods such as uniaxial compression and uniaxial tensile mechanical experiments based on acoustic emission monitoring and various physical characterizations such as scanning electron microscopy, X-ray diffraction, X-ray fluorescence spectrometer, etc. Results show that following treatment with different carbon dioxide-based fluids, the uniaxial tensile/compressive strength, elastic modulus, fractal dimension of pore structure, and the brittleness index of shale exhibit varying degrees of decrease compared to those of dry untreated shale samples. After interacting with different carbon dioxide-based fracturing fluids, the mechanical parameters and brittleness index of shale decrease more significantly than that of the others as the addition of brine. This study shows that the water in carbon dioxide-based fracturing fluids is a controlling factor affecting the elastic modulus of shale. Additionally, the ductility of the shale increases and the acoustic emission emitting lag due to the coupling effects of brine and carbon dioxide. The change law of the elemental and mineral composition of the shale is consistent with the mechanical strength; and the change of element content and mineral composition is the most significant. Compared to gaseous carbon dioxide, the supercritical carbon dioxide has a greater impact on mineral composition of the shale. The change of mechanical strength and microstructure evolution mechanism caused by the short-term interactions between the shale and fracturing fluids provide theoretical references and implications for the determination of injection parameters and permeability transformation of the Longmaxi shale reservoirs.

The sound of porosity: Suitability of the impulse excitation technique (IET) to determine the Young's modulus of 2D macroporous ceramics

The presence of pores in a ceramic leads to a lower Young's modulus compared to dense material. For the development of porous ceramics with tailored elastic properties, an exact determination of the Young's modulus is required, especially for industrial applications. Therefore, we investigated the suitability of the non-destructive impulse excitation technique for measuring the dynamic Young's modulus of two-dimensional ceramics with low porosity (P < 19 %). For rectangular samples it was shown that the measurement results depend on the geometric pore position, as added pores outside the nodal lines of the fundamental flexural vibration had no influence on the result. Pores in the inner part of the sample led to a decrease of the Young's modulus that is in good agreement with empirical and analytical models. For the investigated interval of porosity range, the influence of pore size and geometric position on the reduction of the Young's modulus was determined.

Reconfigurable ultrasound focusing effect through acoustic barriers

The low transmission efficiency of ultrasonic waves in waveguides of a high acoustic impedance (referred to as dense materials), due to the impedance mismatch between the background media and the dense materials, poses a significant obstacle to practical applications of high-intensity focused ultrasound (HIFU) such as ultrasound therapy or medical imaging. To address this challenge, we present an inverse optimization scheme for fabrication of novel acoustic meta-lenses, enabling strengthened penetration and enhanced focusing of ultrasonic waves when the waves traverse barriers. Both simulation and experiment validate the effectiveness of the developed meta-lenses which are annexed to hemispherical plates, and demonstrate an enhanced transmission of the sound power by an order of magnitude compared to a scenario without the use of the meta-lens. The focal distance is reconfigurable by adjusting the geometric parameters of the meta-lenses. The proposed design philosophy is not restricted by the complexity of the target structures, and it allows the ultrasonic waves to pass through acoustic barriers with a non-uniform thickness yet maintaining efficient wave focusing. This study holds appealing applications in HIFU-enabled ultrasound imaging and therapy.