Search Results (3,892)

Stroke is a leading cause of death worldwide, yet current therapeutic strategies remain limited. Among the neuropathological events underlying this disease are multiple cell death signaling cascades, including autophagy. Recent interest has focused on developing agents that target molecules involved in autophagy to modulate this process under pathological conditions. This study aimed to analyze the role of autophagy in cell death induced by an in vitro ischemia–reperfusion (IR) model and to determine whether nitrones, known for their neuroprotective and antioxidant effects, could modulate this process. We focused on key proteins involved in different phases of autophagy: HIF-1α, BNIP3, and BECN1 for induction and nucleation, LC3 for elongation, and p62 for degradation. Our findings confirmed that the IR model promotes autophagy, initially via HIF-1α activation. Additionally, the neuroprotective effect of three of the selected synthetic nitrones (quinolylnitrones QN6 and QN23, and homo-bis-nitrone HBN6) partially derives from their antiautophagic properties, demonstrated by a downregulation of the expression of molecular markers involved in various phases of autophagy. In contrast, the neuroprotective power of cholesteronitrone ChN2 seems to derive from its promoting effects on the initial phases of autophagy, which could potentially help inhibit other forms of cell death. These results underscore the importance of autophagy modulation in neuroprotection, highlighting the potential of inhibiting prodeath autophagy and promoting prosurvival autophagy as promising therapeutic approaches in treating ischemic stroke clinically. Full article

Porous α-Al₂O₃ ceramics are a highly sought-after material with a multitude of applications; for example, they are used as filters, substrates, biomedicine materials, etc. Despite the availability of raw materials, a challenge associated with this technology is the high energy budget caused by sintering above 1500 °C. For the cold sintering processing (CSP) of ceramics, lowering the α-Al₂O₃ sintering temperature is one of the most urgent challenges in the background of its rapid development. This paper is the first to demonstrate a solution to this problem using the CSP of α-alumina ceramics in the presence of pure water as a transient liquid. The manufactured materials were examined using XRD analysis; the evolution of their microstructures during CSP was revealed by SEM; and the porosity was evaluated using the Archimedes method. Ceramics with an open porosity up to 36% were produced at 380–450 °C and 220 MPa in 30 min. An increase in the pressure was found to impede α-Al₂O₃ formation from γ-AlOOH. The development of the microstructure was discussed within the framework of the dissolution–precipitation model and homogenous nucleation. The results of the SEM study pointed to the coalescence of γ-AlOOH grains during CSP. Full article

Coal combustion in power plants for electric power generation produces millions of tons of residues that are generally disposed of in landfills or ponds occupying vast land, resulting in serious environmental pollution. Fly ash (FA) is one of the main solid wastes generated in coal-based thermal power plants, representing the largest fraction of coal combustion residues (65–95%). Unfortunately, the enormous amount of FA residue is utilized only partly, mainly in the cement industry and building materials field. An alternative approach to using FA is its incorporation into ceramic, glass and glass–ceramic production, aligning with circular economy principles and reducing the environmental footprint of both the energy and ceramic sectors. In this review article, the topics of the composition, properties, classification, and utilization of fly ashes from thermal power plants are discussed. The main objective of this work is a critical analysis of the experimental trials directed to the involvement of FA as a raw material in the fabrication of glass–ceramics and porous ceramic composites. Full article

Developing cost-effective methods to synthesize large-size GaN films remains a challenge owing to the high dislocation density during heteroepitaxy. Herein, AlGaN/GaN HEMTs were grown on 6- and 8-inch Si(111) substrates using metal–organic chemical vapor deposition, and their basic properties and dislocation evolution characteristics were investigated thoroughly. With the insertion of a 100 nm thin AlGaN buffer layer, bow–warp analysis of the epitaxial wafers revealed excellent stress control for both the 6- and 8-inch wafers. HR-XRD and AFM analyses validated the high crystal quality and step-flow growth mode of GaN. Further, Hall measurements demonstrated the superior transport performance of AlGaN/GaN heterostructures. It is worth noting that dislocations tended to annihilate in the AlN nucleation layer, the thin AlGaN buffer layer, and the GaN buffer layer in the initial thickness range of 200–300 nm, which was indicated by ADF-STEM. To be specific, the heterointerfaces exhibited a significant effect on the annihilation of c-type (b = <0001>) dislocations, which led to the formation of dislocation loops. The thin inserted layers within the AlGaN buffer layer played a key role in promoting the annihilation of c-type dislocations, while they exerted less influence on a-type (b = 1/3<11$\overline{2}$0>) and (a+c)-type (b = 1/3<11$\overline{2}$3>) dislocations. Within an initial thickness of 200–300 nm in the GaN buffer layer, a-type and (a+c)-type dislocations underwent strong interactions, leading to considerable dislocation annihilation. In addition, the EELS results suggested that the V-shaped pits in the AlN nucleation layer were filled with the AlGaN thin layer with a low Al content. Full article

With the rise in the marine industry and marine tourism, coral powder is increasingly used to make concrete for marine islands. This study proposes a three-parameter hydration model and a hydration kinetic model to predict the performance of coral powder concrete based on previous experimental data. The process of the proposed prediction model is as follows: 1. The input parameters of the three-parameter hydration model are calibrated for the first 7 days using the cumulative hydration heat per gram of cement. The maximum cumulative hydration heat (455.87 J/g cement) and the shape coefficient (−0.87) remain constant. In this study, the hydration rate coefficients for 0%, 10%, and 20% coral powder were 6.91, 6.19, and 5.55, respectively, showing decreases of 10.41% and 19.68% compared with the specimens without coral powder. 2. At 28 days, the cumulative heat release values per gram of cement for 0%, 10%, and 20% coral powder were 389.77, 395.69, and 401.62 J/g, showing increases of 1.52% and 3.04% for the specimens containing 10% and 20% coral powder, respectively. Meanwhile, the hydration degrees for 0%, 10%, and 20% coral powder were 0.855, 0.868, and 0.881, respectively, showing increases of 1.52% and 3.04%. Furthermore, the cumulative heat release values per gram of binder were 389.77, 356.12, and 321.29 J/g, showing decreases of 8.63% and 17.56% for specimens containing 10% and 20% coral powder, respectively. 3. Properties such as compressive strength, ultrasonic pulse velocity (UPV), and surface electrical resistivity were evaluated using the power function and the cumulative hydration heat per gram of binder. 4. At 28 days, the chemically bound water contents for samples with 0%, 10%, and 20% coral powder were 0.2402, 0.2197, and 0.1981 g/g binder, respectively. Moreover, the calcium hydroxide contents were 0.1848, 0.1690, and 0.1524 g/g binder, showing reductions of 8.53% and 17.52% in bound water and 8.54% and 17.53% in calcium hydroxide. 5. A hydration kinetic model is proposed, which can distinguish between the dilution effect and the nucleation effect of coral powder, unlike the three-parameter model, which cannot distinguish between the two effects. Furthermore, the input parameters of the hydration kinetic model remain unchanged for different mixtures, while the input parameters of the three-parameter model must be varied among mixtures. Parameter analysis of the hydration kinetic model indicated that a low water–binder ratio and a high coral powder substitution rate significantly improve the relative reaction level of cement. Full article

In this paper, classical molecular dynamics simulations were used to explore the impact of deposition temperature and bias voltage on the growth of Al2O3 thin films through magnetron sputtering. Ion energy distributions were derived from plasma mass spectrometer measurements. The fluxes of deposited particles (Ar+, Al+, and O−) were categorized into low, medium, and high energies, and the results show that the films are dominated by amorphous Al2O3 at low incident energies without applying bias. As the deposition temperature increased, the crystallinity of the films also increased, with the crystals predominantly consisting of γ-Al2O3. The crystal content of the deposited films increased when biased with −20 V compared to when no bias was applied. Crystalline films were successfully obtained at a deposition temperature of 773 K with a −20 V bias. When biased with −40 V, crystals could be obtained at a lower deposition temperature of 573 K. Increasing the bias enables the particles to have higher energy to overcome the nucleation barrier of the crystallization process, leading to a greater degree of film crystallization. At this stage, the average bond length between Al-O is measured to be approximately 1.89 Å to 1.91 Å, closely resembling that of the crystal. Full article

Diamond as a templating substrate is largely unexplored, and the unique properties of diamond, including its large bandgap, thermal conductance, and lack of cytotoxicity, makes it versatile in emergent technologies in medicine and quantum sensing. Surface termination of an inert diamond substrate and its chemical reactivity are key in generating new bonds for nucleation and growth of an overlayer material. Oxidized high-pressure high temperature (HPHT) nanodiamonds (NDs) are largely terminated by alcohols that act as nucleophiles to initiate covalent bond formation when an electrophilic reactant is available. In this work, we demonstrate a templated synthesis of ultrathin boron on ND surfaces using trigonal boron compounds. Boron trichloride (BCl₃), boron tribromide (BBr₃), and borane (BH₃) were found to react with ND substrates at room temperature in inert conditions. BBr₃ and BCl₃ were highly reactive with the diamond surface, and sheet-like structures were produced and verified with electron microscopy. Surface-sensitive spectroscopies were used to probe the molecular and atomic structure of the ND constructs’ surface, and quantification showed the boron shell was less than 1 nm thick after 1–24 h reactions. Observation of the reaction supports a self-terminating mechanism, similar to atomic layer deposition growth, and is likely due to the quenching of alcohols on the diamond surface. X-ray absorption spectroscopy revealed that boron-termination generated midgap electronic states that were originally predicted by density functional theory (DFT) several years ago. DFT also predicted a negative electron surface, which has yet to be confirmed experimentally here. The boron-diamond nanostructures were found to aggregate in dichloromethane and were dispersed in various solvents and characterized with dynamic light scattering for future cell imaging or cancer therapy applications using boron neutron capture therapy (BNCT). The unique templating mechanism based on nucleophilic alcohols and electrophilic trigonal precursors allows for covalent bond formation and will be of interest to researchers using diamond for quantum sensing, additive manufacturing, BNCT, and potentially as an electron emitter. Full article

This paper reports experimental results concerning the corrosion of 316L austenitic stainless steels produced by ball milling and spark plasma sintering in NaCl electrolyte. Specimens with grain sizes ranging from 0.3 µm to 3 µm, without crystallographic texture, were obtained and compared with a cast that is 110 µm in grain size and an annealed reference. The potentiodynamic experiments showed that the reduction in grain size leads to a degradation of the electrochemical passivation behavior. This detrimental effect can be overcome by appropriate passivation in a HNO₃ concentrated solution before consolidation. The Mott–Schottky measurements showed that the semiconducting properties of the passive layer do not vary significantly on the grain size, especially the donor density, which is responsible for the chemical passivation breakdown by chloride anions. The total electrical resistance of the layer, measured by impedance spectroscopy is always lower than the one of a cast and annealed 316L, but it slightly increases with a reduction in grain size in the ultrafine grain range. This is followed by a slight increase in the thickness of the oxide layer. The effect of chloride ions is very pronounced in terms of passivation breakdown if the powder is not passivated prior to sintering. This leads to the nucleation and growth of subsurface main pits and the formation of secondary satellite pits, especially for the smallest grain sizes. Passivation of the 316L powder before sintering has been found to be an effective way to prevent this phenomenon. Full article

In this paper, the effect of thermomechanical treatment process on the hardening behavior, grain microstructure, precipitated phase, and tensile mechanical properties of the new high-strength and high-ductility Al-10.0Zn-3.0Mg-2.8Cu alloy was studied, and the optimal thermomechanical treatment process was established. The strengthening and toughening mechanisms were revealed, which provided technical and theoretical guidance for the engineering application of this kind of high strength-ductility aluminum alloy. Al-10.0Zn-3.0Mg-2.8Cu alloy cylindrical parts with external longitudinal reinforcement were prepared by a composite extrusion deformation process (reciprocal upsetting + counter-extrusion) with a true strain up to 2.56, and the organizational evolution of the alloys during the extrusion deformation process and the influence of pre-stretching treatments on the subsequent aging precipitation behaviors and mechanical properties were investigated. The results show that firstly, the large plastic deformation promotes the fragmentation of coarse insoluble phases and the occurrence of dynamic recrystallization, which results in the elongation of the grains along the extrusion direction, and the volume fraction of recrystallization reaches 42.4%. Secondly, the kinetic study showed that the decrease in the activation energy of precipitation increased the nucleation sites, which further promoted the diffuse distribution of the second phase in the alloy and a higher number of nucleation sites, while limiting the coarsening of the precipitated phase. When the amount of pre-deformation was increased from 0% to 2%, the size of the matrix precipitated phase decreased from 5.11 μm to 4.1 μm, and when the amount of pre-deformation was increased from 2% to 7%, the coarsening of the matrix precipitated phase took place, and the size of the phase increased from 4.1 μm to 7.24 μm. The finalized heat treatment process for the deformation of the aluminum alloy tailframe was as follows: solution (475 °C/3 h) + 2% pre-stretching + aging (120 °C/24 h), at which the comprehensive performance of the alloy was optimized, with a tensile strength of 634.2 MPa, a yield strength of 571.0 MPa, and an elongation of 15.2%. The alloy was strengthened by both precipitation strengthening and dislocation strengthening. After 2% pre-stretching, the fracture surface starts to be dominated by dense tough nest structure, and most of them are small tough nests, and small and dense tough nests are the main reason for the increase in alloy toughness after 2% pre-stretching deformation. Full article

Ethylene–vinyl acetate copolymer (EVA), a crucial elastomeric resin, finds extensive application in the footwear industry. Conventional chemical foaming agents, including azodicarbonamide and 4,4′-oxybis(benzenesulfonyl hydrazide), have been identified as environmentally problematic. Hence, this study explores the potential of physical foaming of EVA using supercritical nitrogen as a sustainable alternative, garnering considerable interest in both academia and industry. The EVA formulations and processing parameters were optimized and EVA foams with densities between 0.15 and 0.25 g/cm³ were produced. Key findings demonstrate that physical foaming not only reduces environmental impact but also enhances product quality by a uniform cell structure with small cell size (50–100 μm), a wide foaming temperature window (120–180 °C), and lower energy consumption. The research further elucidates the mechanisms of cell nucleation and growth within the crosslinked EVA network, highlighting the critical role of blowing agent dispersion and localized crosslinking around nucleated cells in defining the foam’s cellular morphology. These findings offer valuable insights for producing EVA foams with a more controllable cellular structure, utilizing physical foaming techniques. Full article

Carbon dioxide (CO₂) hydrates have garnered significant interest as a promising technology for CO₂ capture and storage due to its high storage capacity and moderate operating conditions. The kinetics of CO₂ hydrate formation is a critical factor in determining the feasibility of hydrate-based CO₂ capture and storage technologies. This study systematically investigates the promotional effects of the amino acid _L-tryptophan (_L-trp) on CO₂ hydrate formation kinetics and morphology under stirred and unstirred conditions. In the stirred system, experiments were conducted in a high-pressure 100 mL reactor with 0.05, 0.10, and 0.30 wt% _L-trp solution. CO₂ gas uptake kinetics and morphological evolution were monitored using a high-resolution digital camera. Results showed that _L-trp promoted CO₂ hydrate formation kinetics without delay, with rapid CO₂ consumption upon nucleation. Morphological evolution revealed rapid hydrate formation, wall-climbing growth, and dendritic morphology filling the bulk solution. Under unstirred conditions, experiments were performed in a larger 1 L reactor with 0.1 wt% and 0.5 wt% _L-trp solutions to assess the influence of additive concentration on hydrate formation thermodynamics and kinetics. Results demonstrated that _L-trp influenced both thermodynamics and kinetics of CO₂ hydrate formation. Thermodynamically, 0.1 wt% _L-trp resulted in the highest hydrate formation, indicating an optimal concentration for thermodynamic promotion. Kinetically, increasing _L-trp concentration from 0.1 wt% to 0.5 wt% reduced formation time, demonstrating a proportional relationship between _L-trp concentration and formation kinetics. These findings provide insights into the role of _L-trp in promoting CO₂ hydrate formation and the interplay between additive concentration, thermodynamics, and kinetics. The results can inform the development of effective hydrate-based technologies for CO₂ sequestration, highlighting the potential of amino acids as promoters in gas hydrate. Full article

Heavy metal contamination has long been a tough challenge. Recently, enzyme-induced carbonate precipitation (EICP) has been proposed to handle this problem. This paper aims to explore the efficacy, process, and mechanisms of EICP using crude sword bean urease extracts to remediate Zn²⁺, Ni²⁺, and Cr(VI) contamination. A series of liquid batch tests and geochemical simulations, as well as microscopic analyses, were conducted. The liquid batch test results show that Zn²⁺, Ni²⁺, and Cr(VI) can be effectively immobilized by the EICP method, and the highest immobilization percentage was observed for Zn²⁺, reaching up to 99%. Ni²⁺ and Cr(VI) were immobilized at 62.4% and 24.4%, respectively. Additionally, the immobilization percentage of heavy metals increased with the concentration of added Ca²⁺. The simulation results and XRD results reveal that the organic molecules in crude sword bean urease can promote ZnCO₃, Zn(OH)₂, Zn₅(CO₃)₂(OH)₆, and NiCO₃ precipitation. The FTIR and SEM-EDS results provide evidence for heavy metal adsorption by the functional groups in crude urease and calcium carbonate. The liquid batch test results, as well as the simulation results and the microscopic analysis results, indicate that the mechanism of EICP in heavy metal remediation can be summarized as biomineralization to form heavy metal carbonate precipitates and metal hydroxide precipitates, adsorption by calcium carbonate, and adsorption or complexation or promoting nucleation by organic molecules. Full article

In this study, to improve the fatigue strength of the LDED (laser-directed energy deposition) 316L stainless steel, an in situ ultrasonic rolling technology is developed to assist the laser-directed energy deposition process (LDED-UR). The microstructural characteristics and fatigue behavior are comprehensively discussed. The results show that the average size of pores of the LDED-UR alloy is about 10.2 μm, which is much smaller than that of the LDED alloy (34.1 μm). Meanwhile, the density of the LDED alloy is also enhanced from 98.26% to 99.27% via the in situ ultrasonic rolling. With the application of the in situ ultrasonic rolling, the grains are transformed into fully equiaxed grains, and their average grain size is greatly reduced from 84.56 μm to 26.93 μm. The fatigue limit of the LDED-UR alloy is increased by 29% from 210 MPa (LDED alloy) to 270 MPa, which can be ascribed to the decreased porosity and the fine grains. In particular, the crack initiation site of the LDED alloy is located at the surfaces, while it is nucleated from the sub-surface for the LDED-UR alloy. This is mainly attributed to the compression residual stress induced by the in situ ultrasonic rolling. This research offers a valuable understanding of the failure mechanisms in additively manufactured metals, guiding the development of effective strategies to improve their fatigue threshold under severe operating conditions. Full article

The monolithic integration of gallium phosphide (GaP), with its green band gap, high refractive index, large optical non-linearity, and broad transmission range on silicon (Si) substrates, is crucial for Si-based optoelectronics and integrated photonics. However, material mismatches, including thermal expansion mismatch and polar/non-polar interfaces, cause defects such as stacking faults, microtwins, and anti-phase domains in GaP, adversely affecting its electronic properties. Our paper presents a structural and defect analysis using scanning transmission electron microscopy, high-resolution transmission electron microscopy, and scanning nanobeam electron diffraction of epitaxial GaP islands grown on Si nanotips embedded in SiO₂. The Si nanotips were fabricated on 200 mm n-type Si (001) wafers using a CMOS-compatible pilot line, and GaP islands were grown selectively on the tips via gas-source molecular-beam epitaxy. Two sets of samples were investigated: GaP islands nucleated on open Si nanotips and islands nucleated within self-organized nanocavities on top of the nanotips. Our results reveal that in both cases, the GaP islands align with the Si lattice without dislocations due to lattice mismatch. Defects in GaP islands are limited to microtwins and stacking faults. When GaP nucleates in the nanocavities, most defects are trapped, resulting in defect-free GaP islands. Our findings demonstrate an effective approach to mitigate defects in epitaxial GaP on Si nanotip wafers fabricated by CMOS-compatible processes. Full article

Experiments on specimen cooling dynamics and possible film boiling around a body are very important in various industrial applications, such as nucleate boiling, to decrease drag reduction or achieve better surface properties in coating technologies. The objective of this study was to investigate the interaction between the heat transfer processes and cooling dynamics of a sample in different boundary conditions. This article presents new experimental data on specimens coated with Al–TiO₂ film and Leidenfrost phenomenon (LP) formation on the film’s surface. Furthermore, this manuscript presents numerical heat and mass transfer parameter results. The comparative analysis of new experiments on Al–TiO₂ film specimens and other coatings such as polished aluminium, Al–MgO, Al–MgH₂ and Al–TiH₂ provides further detail on oxide and hydride materials. In the experimental cooling dynamics experiments, specimens were heated up to 450 °C, while the sub-cooling water temperatures were 14*‒20 °C (room temperature), 40 °C and 60 °C. The specimens’ cooling dynamics were calculated by applying Newton’s cooling law, and heat transfer was estimated by calculating the heat flux $q$ transferred from the specimens’ surface and the Bi parameter. The metadata results from the performed experiments were used to numerically model the cooling dynamics curves for different material specimens. Approximated polynomial equations are proposed for the polished aluminium, Al–TiO₂, Al–MgO, Al–MgH₂ and Al–TiH₂ materials. The provided comparative analysis makes it possible to see the differences between oxides and hydrides and to choose materials for practical application in the industrial sector. The presented results could also be used in software packages to model heat transfer processes. Full article