Search Results (7,939)

Low-temperature Cu sintering is used as a die-bonding strategy for the third-generation power device, and the Cu-sintered joints require long-term stability at elevated temperature. In this work, we investigate the thermal stability and microstructural evolution of the Cu interconnect joints with an ultra-thin sintered layer at the temperature of 250 °C in air. The as-prepared joint shows a dense well-bonded interface with low porosity before the thermal aging test. The average shear strength of the joints increases from 85.5 MPa to 91.3 MPa after aging up to 300 h. With further increase in aging time, the shear strength begins to decrease. However, the strength remains at a high level of 69.8 MPa even after 500 h of aging, satisfying the requirements for high-temperature stability. At short aging times, the porosity within the interface reduces slightly, and the fracture exhibits distinct ductile characteristics. When the aging time exceeds 300 h, the oxide content at the interface increases from the outer region toward the inner part, and aging cracks eventually appear at the edge of the sintered layer. Therefore, it is demonstrated that the dense and thin sintered layer limits oxygen diffusion, guaranteeing the high-temperature stability of the sintered joint. Full article

Carbon fiber-reinforced polyimide composites are critical for aerospace applications in high-temperature environments of 300–500 °C. However, conventional PMR-15- and PEPA-terminated polyimides are limited by their insufficient glass transition temperatures (T_g) and low crosslinking densities. This study proposes a reactive backbone construction strategy by employing 4,4′-(ethyne-1,2-diyl)diphthalic anhydride (EBPA) as a difunctional monomer copolymerized with asymmetric 2,3,3′,4′-biphenyl tetracarboxylic dianhydride (α-BPDA) and 4,4′-oxydianiline to synthesize polyimide resins containing both backbone ethynyl and terminal phenylethynyl groups. The effects of EBPA content on the curing behavior, thermomechanical properties, and elevated temperature mechanical performance were systematically investigated. The incorporation of EBPA significantly elevated T_g from 378 °C to 486 °C. Compared to the EBPA-0 control, the optimized EBPA-2 composite exhibited 7.3% and 3.6% improvements in room temperature flexural strength and modulus, respectively. Notably, at 400 °C, EBPA-2 demonstrated retention rates of 69.9%, 93.7%, and 61.6% for flexural strength, flexural modulus, and interlaminar shear strength, exceeding EBPA-0 by 16.9, 8.9, and 18.6 percentage points. SEM analysis confirmed the effective suppression of interfacial debonding at elevated temperatures. These findings elucidate the structure–property relationships between molecular structure, T_g, and short-term high-temperature mechanical retention, providing a promising resin matrix for advanced aerospace carbon fiber composites. Full article

Creep is one of the main failure mechanisms of materials at elevated temperatures, and the creep rate curve is a key descriptor of creep deformation and damage evolution. However, existing creep models are mainly phenomenological or stage-wise, and the physical origin of the bathtub-shaped creep rate curve over the full creep process has not been systematically clarified. In this study, creep damage is treated as an aging failure process of a material system, and a physically interpretable hierarchical model is established based on statistical physics for disordered complex systems. By linking the evolution and interaction of microscopic material units with macroscopic creep behavior, the proposed model provides a unified description of the primary, secondary, and tertiary creep stages and offers a theoretical explanation for the bathtub-shaped creep rate curve. Validation using representative metallic and composite material cases shows that the model can reasonably reproduce the overall three-stage creep rate evolution, with residual sums of squares of 1.3088 and 0.5369, respectively. These results demonstrate the ability of the model to capture full-process creep behavior in different material systems. The main advantage of the proposed approach is its physical interpretability within a unified framework, while its current limitation is that the validation remains limited in scale and broader benchmark comparisons with conventional methods are still needed. This work provides a statistical perspective for creep behavior modeling and for understanding the microscopic mechanisms and interactions underlying creep degradation in structural materials. Full article

Vacuum drying is a promising alternative to conventional dehydration for heat-sensitive vegetables, although process temperature can significantly affect both drying behavior and product quality. In this study, vacuum drying of cauliflower florets (Brassica oleracea) was evaluated at 40, 50, 60, 70, and 80 °C under 10 kPa, using freeze-drying as a reference. Desorption isotherms were determined at 50 and 70 °C and fitted to common models, where the GAB model provided excellent fits (R² = 0.9999 and 0.9997, respectively). The drying kinetics were successfully described by four thin-layer models, with the Midilli–Kucuk and Weibull models performing best overall. Color was significantly affected, with total color differences (ΔE) ranging from 15.9 to 20.6 and higher browning indices at elevated temperatures. Bioactive compounds (total phenols, flavonoids, and glucosinolates) and antioxidant potential (by DPPH and ORAC assays) were quantified to assess changes in functional quality across treatments. Bioactive compounds showed the highest values at the highest temperatures (60–80 °C). The DPPH assay remained stable between 50 and 80 °C, but ORAC assay decreased with increasing temperature, suggesting that vacuum drying at 60–70 °C offers the best balance between overall bioactive retention and functionality for producing cauliflower powder. Full article

Identifying the heterogeneous characteristics of habitat quality (HQ) trajectories is a key prerequisite for refined ecological spatial management. We used kernel Normalized Difference Vegetation Index (kNDVI) to correct the highly sensitive parameters, validated the correction results based on their consistency with the prior study findings, developed a framework for the evolution of HQ using Sen+MK and Pettitt’s tests, and utilized XGBoost and partial correlation analysis to identify the primary drivers of dynamic changes in HQ from both spatiotemporal perspectives. Our findings include the following: (1) between 2000 and 2023, the average annual rate of change in the HQ index was 0.0037 per year, indicating a continuous improvement in HQ. Compared with the period from 2011 to 2023 (0.0026 per year), the rate of improvement in HQ was faster during 2000–2011 (0.0047 per year). (2) Mutational improvement and progressive improvement were the main evolutionary trajectories, accounting for over 50.33% of the total. (3) Precipitation, land-use intensity (LUI), temperature, and elevation show a strong correlation with HQ distribution. The magnitude of HQ variation is related to HQ status, LUI, precipitation, and elevation. This study establishes a scientific foundation for developing differentiated regulatory strategies for YRB. Full article

Modern dentistry increasingly relies on light-curing units (LCUs) and lasers in essential clinical procedures such as composite resin polymerization, caries treatment, and periodontal therapy. This review aims to outline the evolution of light-emitting technologies and to assess their potential biological risks, with particular emphasis on effects on the visual system, oral tissues, and microbiome. The development of curing devices is presented chronologically, from the first-generation ultraviolet (UV-A) lamps introduced in the 1970s to current light-emitting diode (LED-LCU) systems and dental lasers (e.g., Er:YAG, Nd:YAG). The progressive increase in light intensity—now exceeding 3000 mW/cm²—has shortened curing times but simultaneously raised safety concerns. Major hazards include the so-called blue-light hazard, where exposure to high-energy visible (HEV) blue light may accelerate macular degeneration, and temperature elevations in the pulp chamber, which may damage the dentin–pulp complex. Laser radiation also exerts significant microbiological effects: Er:YAG and diode lasers demonstrate bactericidal activity against biofilms and oral pathogens (e.g., P. gingivalis), although therapeutic outcomes depend on wavelength, dose, and exposure time. Suboptimal parameters may lead to microbiome disturbances, whereas low-level laser therapy (LLLT; 600–1200 nm) supports tissue regeneration and helps restore microbial balance. The individualization of irradiation parameters, combined with thorough theoretical knowledge, operator expertise, and technical understanding of LCUs and lasers, is essential for maximizing clinical benefits while minimizing health risks and preserving oral microbiome homeostasis. Full article

This study investigates the effects of tempering temperature on the microstructural evolution and mechanical properties of Cr-Ni-Mo-V steel designed for pressure vessel applications. The microstructure was characterized via scanning electron microscopy (SEM), transmission electron microscopy (TEM, Thermo Fisher Talos F200X), electron backscatter diffraction (EBSD), and physicochemical phase analysis. Mechanical performance was evaluated through tensile and impact tests, followed by a detailed discussion of the underlying strengthening mechanisms. The results demonstrate that the microstructure after tempering is fully tempered martensite. Samples tempered between 425 °C and 525 °C exhibit significant tempering resistance, maintaining a tensile strength of approximately 1300 MPa. This is primarily attributed to the synergistic effect of dislocation strengthening and the precipitation of MC-type carbides. As the tempering temperature increases to 625 °C, the dislocation density decreases sharply from 3.71 × 10¹¹ cm⁻² to 1.18 × 10¹¹ cm⁻², leading to a decline in strength. Concurrently, the impact energy increases significantly from 71 J to 132 J. The improvement in toughness is mainly attributed to the significant elevation of the crack initiation threshold, which is dominated by the reduction in matrix dislocation density, the coarsening and spheroidization of carbides, and the alleviation of local stress concentration. The relative proportion of high-angle grain boundaries (HAGBs, misorientation > 15°) increases from 51.9% to 57.7% during tempering, which is a result of the massive elimination of low-angle grain boundaries rather than an increase in the absolute length per unit area of HAGBs. Full article

Monolithic ceramic catalysts are a key technology for the industrial treatment of coal mine ventilation air methane (VAM). The preparation of straight-channel NiO/CeO₂ monolithic ceramic catalysts via phase inversion addresses critical bottlenecks for industrial VAM abatement. However, high-temperature sintering leads to irreversible NiO agglomeration and coarsening, severely reducing catalytic activity. In this study, an in situ reduction–oxidation reconstruction method is developed to regenerate sinter-degraded NiO. The reconstructed catalyst increases methane conversion from below 70% after sintering to over 95% at 550 °C and achieves full conversion at 600 °C. The catalyst maintains near 100% conversion during 400 h of continuous operation at 600 °C and shows no performance degradation over 15 thermal cycles. Moreover, the reconstructed catalyst exhibits excellent steam tolerance with fully reversible deactivation. The reconstructed catalyst presents a refined porous structure with BET surface area rising from 4.5 to 11.4 m² g⁻¹, an elevated Ni³⁺/Ni²⁺ ratio (1.47 to 1.97), a higher surface adsorbed oxygen proportion (36.8% to 48.7%) and significantly strengthened NiO-CeO₂ interfacial interaction. This work provides a facile and efficient in situ regeneration strategy, greatly enhancing the VAM oxidation activity and stability of sinter-degraded monolithic ceramic catalysts. Full article

Aquatic ecosystems worldwide are increasingly threatened by invasive species, with water hyacinth [Eichhornia crassipes (Mart.) Solms] being among the most destructive aquatic weeds. Despite numerous regional studies, a global assessment integrating climatic and hydrological drivers remains lacking. Here, we assessed current and future invasion risks across 55,945 freshwater lakes using the maximum entropy (MaxEnt) model. Climatic variables and key aquatic parameters, including biological oxygen demand (BOD), water depth, and discharge, were incorporated under two shared socioeconomic pathways (SSP2-4.5 and SSP5-8.5). Annual mean temperature, annual precipitation, and BOD were the strongest predictors of habitat suitability. Under current conditions, 5524 lakes, primarily in tropical and subtropical regions, were identified as being suitable habitats, with medium-sized lakes exhibiting the highest proportional suitability (16.54%). Although small lakes were most frequently classified as suitable due to their abundance, larger lakes showed higher suitability intensity. Future projections indicated marked habitat expansion, especially under SSP5-8.5, with suitable lake surface area increasing to 18.12% by 2061–2080. Moreover, 543 currently unsuitable lakes, including Lake Erie, Lake Huron, and Lake Ontario, were projected to face elevated invasion risk, particularly in Africa, South Asia, Southeast Asia, and North America. This global, lake-specific assessment supports early warning, targeted management, and climate-responsive policy planning. Full article

Perfluorosulfonic acid (PFSA) membranes, exemplified by Nafion, suffer dehydration-induced degradation at elevated temperatures, although modifications enhance their conductivity and performance. Sulfonated aromatic polymers (SAPs) exhibit weaker phase separation, yielding narrow, tortuous ion channels and lower conductivity than their PFSA membrane counterparts at equivalent ion exchange capacity; however, excessive sulfonation causes swelling and mechanical instability, offset by cost advantages. Phosphoric acid-doped polybenzimidazole (PBI) offers superior thermal stability and high conductivity, with recent advances in polybenzimidazole derivatives and composites driving medium-to-high temperature proton-exchange membrane fuel cell innovation. This review summarizes progress in three major medium-to-high temperature proton-exchange membrane fuel cell categories—perfluorosulfonic acid, sulfonated polymers, and PBI-based membranes—while addressing challenges and future goals for enhanced performance. Full article

Wind energy is an important form of clean energy, and its rational utilization represents a crucial solution for mitigating the energy crisis and global warming. In this study, wind energy potential and its long-term changes in the South China Sea (SCS) are evaluated using ERA5 100 m wind data from 1944 to 2023, validated against ASCAT observations. High wind speeds and high wind power density (WPD) are concentrated southwest of Taiwan and southeast of Vietnam. Annual wind availability exceeds 6457 h across most regions, reaching up to 8283 h in optimal locations. WPD and capacity factor peak in winter (up to 2.4 × 10⁸ Wh·m⁻² and >50% capacity factor), with the most stable conditions occurring in the southwestern Taiwan Strait, southeast of the Pearl River Delta, and the Beibu Gulf. Empirical orthogonal function analysis reveals that the first mode of winter WPD accounts for 65.7% of the total variance, with a statistically significant increasing trend since 1990. The interannual variation in wind energy resources in the SCS during winter is controlled by the combined effects of sea surface temperature (SST) anomalies in the tropical Pacific and the Arctic Barents Sea. Specifically, in the years with strong wind anomalies in the SCS, mega-La Niña-type SST patterns in the tropical Pacific trigger anomalous cyclonic circulation in the SCS and the eastern Philippine Sea, while warm anomalies in the Arctic Barents Sea surface drive a wave-like structure of “anticyclone–cyclone–anticyclone” from Siberia to South China. The coupling of the two systems jointly promotes the strengthening of the South China Sea monsoon, leading to increased wind speeds and elevated WPD in the northern SCS. These findings provide a scientific basis for wind farm siting and long-term operational planning in the region. Full article

Preparing a highly wear-resistant AlTiN coating on a powder metallurgy (PM) M42 high-speed steel substrate is a key strategy to enhance tool performance and meet the demands of efficient machining. This study adopted a process route comprising substrate preparation, heat treatment regulation, and arc-PVD deposition of AlTiN coatings to systematically investigate the influence of sintering temperature (1130, 1160, and 1190 °C) and austenitizing time (1150 °C for 0, 15, 60, and 120 min) on the microstructure and mechanical properties of the substrate, as well as on the tribological performance of the AlTiN coatings. The results indicate that elevating the sintering temperature promotes densification of the matrix, with Vickers hardness increasing from 366 HV to 462 HV and bending strength (σ) increasing from 1064 MPa to 1310 MPa. The predominant carbide phases identified are MC, M₂C, and M₆C. During austenitizing, microstructural changes consistent with a progressive transformation from M₂C to MC and M₆C carbides were indicated by SEM and XRD analyses. Precipitation strengthening was most evident after 60 min, with hardness reaching 868 HV. In contrast, bending strength (σ) exhibited a progressive decline with increasing austenitizing time, decreasing from 1310 MPa to 1015 MPa after 120 min, illustrating a clear trade-off between hardness and toughness. The wear behavior of the coating is governed synergistically by substrate hardness, bending strength (σ), coating–substrate interfacial adhesion strength (L_C), and carbide phase transformation. Elevated substrate hardness enhances anti-wear performance; bending strength influences crack propagation and spallation tendency; and L_C determines the efficiency of interfacial load transfer. The carbide phase evolution appears to modulate the coating’s wear behavior by regulating both the microstructure and mechanical properties of the substrate. Among the six sample conditions evaluated, the A3 sample (sintered at 1190 °C and austenitized for 120 min) exhibited the lowest wear rate (2.38 × 10⁻⁶ mm³·N⁻¹·m⁻¹), demonstrating superior wear resistance. These findings provide a reference for process optimization and rational design of M42/AlTiN composite coating systems. Full article

Global warming and increasing heatwaves elevate the risk of exertional heat illnesses, particularly heatstroke, in endurance athletes and outdoor workers. This study developed and validated a wearable heatstroke warning system integrating physiological and environmental monitoring with a real-time web dashboard. The wrist- and finger-worn prototype comprised an ESP32 microcontroller and heart rate (MAX30101), skin temperature (MAX30205), ambient temperature and humidity (SHT31), and galvanic skin response (Grove-GSR v1.2) sensors with dual acoustic–visual alerts and WiFi transmission. Fifteen triathletes (18–39 years) completed 30 min of cycling in a climatic chamber: 0–15 min at 24 ± 1 °C, 70 ± 10% RH, and 16–30 min at 27 ± 1 °C, 90 ± 10% RH, with the workload rising from 40%HRmax by 10% every 10 min. Heart rate, estimated core temperature, ambient temperature, relative humidity, and GSR were recorded every 30 s and compared with standard devices using Spearman correlation (p = 0.01) and Wilcoxon signed-rank tests (p < 0.05). Heart rate, skin temperature (used a linear model to calculate core body temperature), ambient temperature, and humidity sensors showed fair–very good validity (r = 0.692, 0.995, 0.994, 0.952), while GSR was low (r = 0.298). No significant differences were observed for heart rate, skin temperature, and humidity (p > 0.05), but body temperature (p = 0.003) and GSR (p < 0.001) differed. The system showed promising validity for real-time heatstroke risk monitoring, with further refinement needed for skin temperature and GSR sensing. Full article

This paper presents a collaborative optimization design methodology aimed at improving heat dissipation efficiency through the modulation of microstructural variations. The approach addresses the thermal protection requirements of high-temperature components, such as ceramic matrix composite turbine blades, which are subjected to complex and elevated thermal loads. Through the integration of numerical simulation and experimental validation, a bidirectional mapping model linking carbon nanotube (CNT) content with the macroscopic anisotropic thermal conductivity of the material was developed. Furthermore, a thermal conduction analysis and optimization framework for Ceramic Matrix Composite (CMC) high-temperature components under non-uniform thermal loads was established. This study expands the adjustable range of the material’s thermal conductivity by allowing flexible modulation of carbon nanotube content. The results demonstrate that this methodology effectively enhances the heat dissipation capacity of CMC materials in extreme thermal environments: the maximum surface temperature of the optimized flat plate is reduced by 8.96%, the peak temperature gradient is lowered by 46.64%, and the maximum thermal stress is decreased by 38.17%. This research provides new insights into the comprehensive integration of thermal dissipation requirements for CMC hot components. Full article