Search Results (2,338)

CO₂ geological storage in deep coal seams is a key carbon emission reduction approach, where coal permeability dominates sequestration efficiency. Current studies mainly concentrate on pre-CO₂-adsorption permeability of various coal ranks, while studies on permeability evolution after CO₂ adsorption saturation remain limited, which is vital for optimizing sequestration schemes. This work performed permeability experiments on different-rank coal samples saturated with CO₂ under diverse axial confining pressures and temperatures. The sequestration rate, capacity, and engineering safety were analyzed to propose optimal sequestration conditions. Results reveal that coal permeability decreases significantly after CO₂ saturation. With axial confining pressure increasing from 10 to 30 MPa, the permeability of low-, medium- and high-rank coals declines continuously. Within the temperature range of 20 °C to 60 °C, the permeability of low-rank long-flame coal decreases first then increases, whereas medium-rank coking coal and high-rank anthracite show the opposite trend. At 800 m burial depth, CO₂ injection efficiency first declines then rises. Distinct permeability evolution exists in different coal ranks, so differentiated injection strategies should be adopted to balance sequestration efficiency and safety. By mathematically fitting the permeability variation curves of anthracite saturated with CO₂ under varying axial and confining pressures, combined with the surrounding rock stress formula around the borehole, when CO₂ at approximately 4.7 MPa is injected into anthracite seams, CO₂ can permeate to a distance of 1.35 times the borehole radius from the borehole center around the borehole. The penetration radius ratio of 1.35 is only a qualitative indicator, not a fixed design parameter. Full article

Aerial forest firefighting is a critical technology for wildfire suppression. Recent studies have examined suppression agent drop dynamics, deposition patterns, and optimization strategies. This review synthesizes advances from three perspectives: (i) in-flight suppression agent jet dynamics, (ii) ground deposition patterns, and (iii) suppression effectiveness, while outlining future research directions. Flight altitude, velocity, and momentum ratio govern jet behavior—affecting penetration, expansion, and breakup. Momentum ratio, shaped by drop velocity and aircraft speed, is pivotal in penetration depth and fragmentation. Deposition patterns vary with delivery systems and flight parameters: low-altitude/low-speed drops yield higher coverage density over smaller areas, whereas high-altitude/high-speed drops cover larger areas but less densely. Suppression efficacy depends on fire intensity–vegetation interactions, droplet size–coverage requirements, and operational parameters such as response time, aircraft capacity, and real-time intelligence. Large droplets excel in cooling high-intensity flames, while fine droplets provide efficient area coverage. Adequate resources and integrated data enhance outcomes. Future work should couple multi-physics models of terrain, meteorology, and fire plume dynamics, and develop integrated deposition models including wind, thermodynamics, terrain, and fire behavior to optimize aerial dispersion in diverse wildfire scenarios. Full article

In this paper, a short-term active power curtailment (ST-APC) strategy for doubly-fed induction generator (DFIG) wind farms is proposed to enhance first-swing rotor angle stability under fault disturbances. While wind power is a clean renewable resource that is widely deployed, its large-scale integration heightens concerns about transient stability. After analyzing DFIG operating principles, this study advocates for using short-horizon active power control to mitigate the adverse stability impacts of wind farms. Using the Western System Coordinating Council (WSCC) three-machine nine-bus test system, the effectiveness of the ST-APC strategy across diverse operating conditions was verified. This study is based on the fundamental principle that reducing the output of wind turbines is required for first-swing stability after faults to increase the kinetic energy of synchronous machines. A closed-loop control strategy combining voltage drop, frequency change, and a timer is designed. The correlation laws between various control parameters such as control activation timing, duration, and modulation depth and first-swing stability are analyzed, providing references for parameter selection in engineering applications. The findings indicate that the proposed strategy is practical and adaptable, making it suitable for power systems with high wind power penetration. Full article

To address the difficulty of directionally cutting thick, hard key strata in gob-side entry retaining using conventional blasting or hydraulic fracturing, this paper proposes a high-pressure water-jet slotting-induced pre-cracked weakening belt (PCWB) roof-cutting technology. Several finite-length PCWBs are arranged within the key stratum and designed to coalesce into a plane, inducing through-going roof failure along a pre-determined path. A fixed–fixed key strata beam model combined with linear elastic fracture mechanics shows that the double-belt configuration forces the bending moment and shear force to concentrate in a thin rock bridge, where bending and shear stresses are amplified by about 1.5–2.8 times and 1.2–1.7 times, respectively, for 2–4 m thick key strata, providing a mechanical basis for preferential tensile–shear failure. Two-dimensional RFPA2D simulations reveal “width-dominated, length-assisted” control of cutting performance and identify an optimal weakening belt geometry of about 400 mm in width and 200 mm in length. Three-dimensional numerical modeling of parallel slot pairs indicates that intra-pair spacing of about 40 mm produces a continuous, directional weakening belt, whereas smaller or larger spacing causes, respectively, destructive interference or loss of connectivity. High-pressure water-jet tests (320 MPa, 0.33 mm nozzle, 1.30 mm/s traverse speed) on limestone blocks confirm that single slots can penetrate the full thickness and that cracks from adjacent slots coalesce through the rock bridge, forming a wide, straight fracture band. Field application in the Dongjiang Mine (3.5 m limestone key stratum, ~400 m depth) shows that the first weighting is advanced from the 7th to the 3rd day, peak support resistance is reduced from 8.8 to 7.4 MPa, and periodic weighting becomes more frequent and smoother. The PCWB technology is therefore suitable for panels with 2–4 m thick hard key strata at similar depths, offering precise key stratum severance, active stress relief, and safe, controllable construction. Full article

As a branch of nondestructive testing (NDT), Pulsed Eddy Current Testing (PECT) is characterized by its wide frequency spectrum and high penetration depth. After years of development, it has been widely applied to defect detection and material characterization of key components in industries such as petrochemicals, new energy, and aerospace. With the large-scale application of new energy sources like liquefied natural gas (LNG), methanol, and liquid hydrogen, the demand for NDT of non-ferromagnetic materials (e.g., austenitic stainless steel) has surged. However, challenges such as electromagnetic leakage caused by low magnetic permeability and the lift-off effect induced by protective layers impose stricter requirements on inspection technologies, driving the evolution of PECT towards adaptability in complex scenarios. This paper systematically reviews the latest advances in PECT technology, covering detection sensors, modeling methods, detection signal processing, and engineering applications. With a particular emphasis on research outcomes from the past decade, this paper also proposes potential directions for future development, aiming to provide a reference for innovative research and the industrial promotion of PECT technology. Full article

Zr alloy-shaped charge liners (SCLs) offer broad application prospects due to their multiple post-penetration damage effects. However, research on these liners is still in its early stages. The mechanisms of jet formation and penetration for Zr alloys SCL remain unclear, and the specific contribution of different liner regions to the penetration process is not yet understood. This gap in knowledge has limited their structural design to a black-box correlation between global structural parameters and macroscopic penetration efficiency. To address this gap, a region-tracing Smoothed Particle Hydrodynamics (SPH) simulation was employed. Following a strategy of “wall thickness layering + axial segmentation,” the Zr alloy liner was partitioned into ten characteristic regions. This methodology facilitated the tracking of material transport from each region during jet formation and penetration into an AISI 1045 steel target. The contribution of each region to the penetration depth was then quantitatively assessed via post-processing. For the first time, the “critical region” contributing most to penetration depth was identified, and the influence of the liner’s cone angle and wall thickness on the contribution of each region was revealed. This study enhances the theoretical framework for understanding the damage effects of Zr alloy shaped charge liners. It not only advances the fundamental understanding of jet penetration mechanisms but also provides a theoretical basis for the refined design and performance optimization of these liners. Full article

Asphalt pavements are frequently subjected to fatigue cracking, rutting, and surface wear, which accelerate maintenance needs and shorten service life. This study evaluates the performance enhancement of NHA Class B dense-graded asphalt mixtures (12.5 mm NMAS) prepared with a 60/70 penetration grade binder through carbon fiber (CF) reinforcement. Chopped fibers (~12.7 mm) were incorporated via the dry mixing process at dosages of 0.5%, 1.0%, and 1.5% by binder weight. The results indicate that the 1.0% CF mixture delivered optimal performance, with ITS increasing by 51.9%, Marshall stability improving by 38.4%, resilient modulus rising by 42.6%, and rut depth decreasing by 69.2% compared to the unmodified control. Dynamic stability reached 33,750 passes/mm, demonstrating substantial resistance to permanent deformation. Statistical analysis using one-way ANOVA confirmed that all improvements were significant (p < 0.05). Despite a ~6.7% increase in initial cost, the CF-modified mix exhibited strong economic viability, achieving a benefit–cost ratio of 4.79 and significant life-cycle savings over 20 years. These findings underscore carbon fiber as an effective modifier for developing durable, high-performance asphalt composites with reduced maintenance requirements. This work contributes to the advancement of smart and sustainable pavement technologies for resilient transportation infrastructure. Full article

Marine concrete engineering faces severe service environment challenges, including high hydraulic pressure, large stress, and serious penetration. The evaluation of the durability and safety of these structures depends directly on the damage mechanism of concrete materials submitted to high hydraulic pressures. This paper introduced the experimental research on the mechanical properties and the damage mechanism of concrete submitted to high hydraulic pressures. The permeability tests were carried out on concrete specimens under the effect of different hydraulic pressures (1.2 MPa, 2.4 MPa, 3.6 MPa) and durations (10 d, 20 d, 30 d), after which the compressive strength, micro-cracks, and the ultrasonic velocity were obtained and analyzed. The results show that under the effect of sustained high hydraulic pressure, the micro-cracks in concrete increase, the density decreases, and the harmful pores expand, resulting in a degradation in the mechanical properties of concrete. The damage to concrete is more severe at the near end of the hydraulic head than at the far end. The pore water pressure decays gradually with depth inside the concrete and expands inward when the outer layer of concrete is damaged. The conclusions will provide a scientific basis for the safety evaluation of marine concrete engineering. Full article

Cr₂O₃-based ceramic coatings are widely used in wear-critical applications; however, their tribological performance under dry sliding conditions can be limited by brittleness and frictional instability. In heavy-duty vehicles, the king pin–bushing contact operates under severe dry sliding conditions, motivating the investigation of composite Cr₂O₃–nTiO₂ coatings as a potential surface engineering solution. In this study, Cr₂O₃–TiO₂ coatings containing 0, 10, 20, 30, and 40 wt% TiO₂ were deposited by atmospheric plasma spraying (APS) from mechanically mixed powders. Phase composition was analyzed by X-ray diffraction using an X’Pert PRO MRD diffractometer, while microstructure and elemental distribution were examined by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) on a FEG Quattro C microscope. Mechanical properties were evaluated by Vickers microhardness, instrumented indentation and scratch testing, while dry sliding wear behavior was assessed by pin-on-disc tests performed on a CETR UMT-2 tribometer against a bronze counterbody, with continuous monitoring of the coefficient of friction (COF). The results show that plasma spraying produces lamellar composite coatings with intrinsic porosity and locally modified phase composition. Cr₂O₃-rich coatings exhibit higher hardness (1198 HV2 compared with 877 HV2 for Cr₂O₃–40TiO₂ corresponding to an increase of approximately 36%) and improved resistance to indentation, reflected by lower penetration depths and higher elastic modulus values (134 GPa for S0 compared with 77 GPa for S2). These coatings also exhibit a more stable friction response and reduced material transfer from the bronze counterbody, as confirmed by the lower mass loss of the pins (0.0295 g for S0 compared with 0.0473 g for S4, corresponding to a reduction of about 38%). Increasing TiO₂ content leads to changes in friction stability and wear behavior associated with microstructural heterogeneity. These findings indicate that the sliding wear performance of Cr₂O₃–nTiO₂ coatings is governed by elastic–plastic stability under localized contact loading and support their applicability for dry sliding king pin–bushing systems in heavy-duty vehicles. Full article

The efficiency of railway track maintenance and repair is largely determined by the technological productivity and reliability of track machines operating under conditions of increasing loads and limited time intervals for operational performance. In this regard, the improvement of the working bodies of ballasting machines is an important direction for increasing the efficiency of the repair and track processes. The paper deals with the improvement of the working body of the electric ballasting machine based on parametric optimization methods aimed at increasing the efficiency of the track repair. The study has analyzed the geometric and process parameters of the working body, which have the greatest effect on the quality of the ballast redistribution, energy consumption, and the stress–strain state when interacting with the ballast prism. A parametric model of the working body has been developed, which makes it possible to perform numerical modeling and identify the most sensitive design parameters, including the blade geometry, the angles of their installation, the penetration depth, and the modes of operation. Based on the results of the optimization, the paper suggests a design solution that provides a more uniform load distribution, reduces peak stresses, and improves the quality of the ballast prism profiling. The obtained results demonstrate an increase in the operational productivity of the electric ballasting machine. The proposed approach is linked to the methodology of optimizing the track machine fleet, as the increase in the efficiency of individual machines contributes to downtime reduction, more accurate planning of operations, and increased efficiency of the track maintenance system based on the predicted condition of the railway tracks. Full article

Shaped charge is widely used in petroleum drilling, yet the inherent parametric uncertainty of oil shale introduces significant uncertainties that affect perforation outcomes. The complex coupling of oil shale constitutive parameters under extreme strains poses challenges for uncertainty quantification. A coupled algorithm integrating an improved material point method (MPM) and polynomial chaos expansion (PCE) is presented, and polynomial chaos expansion (PCE) is used to systematically analyze the uncertainty and sensitivity of shaped charge jet penetration depth. Mechanical parameters from oil shale samples at Checun Coal Mine well No. 1 were tested to define key parameter ranges and establish a reliable uncertainty space. A benchmark simulation of a single isolated shaped charge jet validated the algorithm, and Sobol’ global sensitivity analysis identified internal friction angle, density, and Poisson’s ratio as strongly sensitive parameters, while tensile strength, Young’s modulus, and cohesion showed weak sensitivity, supporting surrogate model dimensionality reduction. Composite detonation models of three and five charges further revealed the effects of multi-projectile blast wave coupling on jet dynamics, providing new theoretical insights into cluster effects under high-energy, high-pressure, and extreme-strain conditions. Sensitivity and uncertainty analyses based on surrogate models emphasized the critical influence of internal friction angle alongside Poisson’s ratio and density. A reliable numerical framework is established for multi-physics coupled simulations of geomechanical responses under complex multi-source explosive loading. Full article

Recently, photoacoustic (PA) imaging has made a significant impact on biomedical imaging, providing detailed information on tissue structure and function by integrating optical and acoustic techniques. PA imaging can provide functional information at the cellular (e.g., oxygen saturation, hemoglobin concentration, metabolic rate) and molecular levels, owing to its substantial advantages over conventional imaging techniques. PA imaging is particularly useful for neuroimaging, cancer detection, and cardiovascular studies. Over the last decade, there has been a tremendous amount of research and development dedicated to nanomaterials that are ideal for PA imaging. Examples of nanomaterials include carbon-based and gold nanorods, both of which demonstrate greatly enhanced light absorption capabilities in the near-infrared range. Therefore, the properties of these materials make them perfect for achieving deep penetration into tissues. In addition, they exhibit biocompatibility, tunable optical properties, and enhance the acoustic signal for PA imaging, resulting in greater accuracy and precision in PA results. Researchers working in this area have focused on developing nanomaterials with fabrication capabilities, enabling real-time visualization of therapeutic events and enhancing light absorption. This review critically examines recent advances in nanomaterials for PA imaging, emphasizing strategies for signal enhancement and evaluating their impact on imaging performance, including imaging depth, photostability, and signal intensity, as well as their suitability for biomedical applications. Furthermore, complementary approaches for PA signal enhancement are discussed to provide a broader perspective and guide the selection and design of effective contrast agents for clinical and preclinical use. Full article

Magnetic superconductor EuRbFe₄As₄ is a quite unique system in which macroscopic superconductivity and magnetic ordering coexist, with interesting interactions between Abrikosov vortices and Eu²⁺ spins that were investigated mostly by static (DC) magnetization measurements. Our aim is to study the dynamic interactions between the two sub-systems using AC susceptibility measurements in a wide range of temperatures and superimposed DC fields. In low DC fields, the magnetic transition at 15 K is clearly visible. We have observed very little difference between the AC susceptibility in different cooling regimes, but large difference for different field orientation. For field perpendicular to the superconducting planes, we have observed an anomalous dependence just below the critical temperature, which is absent in the parallel field orientation. We explained the anomaly by the interplay between the sample dimensions and the temperature dependence of the London penetration depth which may allow the paramagnetic Meissner-like response to be detected in the temperature dependence of the AC susceptibility. We stress that the newly reported phenomenon reflects an AC-susceptibility manifestation of a field-stabilized critical state rather than a thermodynamic phase. In addition, we have observed a paramagnetic AC response in the normal phase, in both field orientations, indicative of interactions between Eu²⁺ spins and flux lines. Full article

Reclaimed asphalt pavement (RAP) from polymer-modified asphalt pavements often contains a recovered binder that is stiff and brittle, which reduces workability and increases durability risk. Waste cooking oil (WCO) is a promising circular rejuvenator, but its effectiveness remains inconsistent because oil source and degradation state are often not well controlled, particularly in polymer-modified RAP systems. This study introduced a controlled simulated WCO approach and compared four oil sources (Palm, Soy, Olive, and Rice) as rejuvenators for recovered RAP binder and RAP mixtures. Simulated oils were added at 4% and 8% by mass of recovered RAP binder. The simulated WCOs produced clear dosage-dependent softening of the recovered binder. Penetration increased, while softening point and rotational viscosity decreased, indicating partial restoration of binder mobility and improved workability. At the mixture level, the 4% dosage provided the most balanced performance, improving moisture resistance and reducing Cantabro loss compared with the control mixture. Specifically, tensile strength ratio (TSR) increased from 75% to 80.9–83.7%, while Cantabro loss decreased from 19.8% to 13.2–14.6%, showing better cohesion and resistance to particle loss. However, Hamburg wheel tracking (HWT) results revealed strong oil-source dependence, with Soy showing the lowest rut depth and Olive the highest, indicating that excessive softening can reduce deformation resistance. The results demonstrate that controlled simulated WCO can support practical oil-source selection for polymer-modified RAP mixtures. A moderate dosage is more effective because it improves binder restoration and mixture durability without causing excessive softening, while rutting verification remains essential before field application. Full article

The aim of this work is to investigate the possibility of improving the performance properties of 40CrMnMo7 steel by conducting duplex surface modification treatment. Chemical-thermal treatment processes were used—nitrocarburization and ion-nitriding and subsequent application of a nanostructured multilayer coating, Cr/(Cr-C)ml. The resulting structures and their influence on the adhesion of the applied coating, as well as their influence on the tribological properties of the coating, were studied. By conducting Glow Discharge Optical Emission Spectroscopy (GDOES), it was established that the penetration of nitrogen into the depth is greater in the ion-nitriding process, and the results of the conducted optical metallography and hardness measurement show that after ion-nitriding, the obtained hard layer has a greater thickness and hardness. The data obtained from the studies of the phase composition of the hard layers show that after nitrocarburization the non-stoichiometric, but crystalline phase Fe₃N_1.1 (ξ)—98.4% was formed. In the composition of the hard layer formed after the ion-nitriding process, the presence of Fe₃N (ξ-phase) in an amount of 79.5% and Fe₄N (γ′-phase) in an amount of 19.1% was established. On the chemically and thermally treated surfaces, a Cr/(Cr-C)ml coating was applied through the unbalanced magnetron sputtering technology. The applied coating has a hardness of 17.1 ± 0.6 GPa and a modulus of elasticity of 289 ± 8.7 GPa. The thickness of the coating applied on the test bodies not subjected to diffusion enrichment is 1.967 µm, and the adhesion class is classified as HF-2. It has been established that the profile of the surfaces obtained after the application of the chemical-thermal treatment processes has an impact on the thickness of the applied coating and on its adhesion. After nitrocarburization, the thickness of the coating is 2.9 µm, and the adhesion of the coating is classified as HF-0. The thickness of the applied coating on the test bodies subjected to ion-nitriding is 2.4 µm, and the adhesion class is HF-1. The results of the conducted tribological tests show that the used chemical-thermal treatment processes have an impact on the coefficients of friction and wear of the coating. The coefficient of friction for the combination of the nitriding process and Cr/(Cr-C)ml coating has the highest value (µ ≈ 0.38), while that of the ion-nitrided sample with subsequent coating has a value (µ ≈ 0.21) slightly higher than the COF of the test body with only the coating applied (µ ≈ 0.18). The lowest value of the coating wear coefficient is registered for the combination of the ion-nitriding and coating process (k = 7.96 × 10⁻⁵), while for the combination of nitriding and coating, it is the highest (k = 12.4 × 10⁻⁴). The relevance of the present work is related to the implementation of surface modification of 40CrMnMo7 steel by using established technological processes of chemical-thermal treatment and subsequent deposition of nanostructured multilayer Cr/(Cr-C)ml coating. The other novelty in the present study is related to the use of MF pulsed DC power supplies, operating at a fixed frequency of 100 kHz and a specific pulse shape, similar to the shape of HiPIMS pulses, for the deposition of nanostructured multilayer Cr/(Cr/a-C)ml coatings. Full article