Search Results (405)

In this study, we analyzed the lithospheric seismic background of the Tianshan and adjacent areas by combining various geophysical methods (effective elastic thickness, time-varying gravity, apparent density, and InSAR), and explored the genesis mechanism of the Wushi Ms7.1 earthquake as an example, which led to the following conclusions: (1) The effective elastic thickness (Te) of the Tianshan lithosphere is low (13–28 km) and weak, while the Tarim and Junggar basins have Te > 30 km with high intensity, and the loads are all mainly from the surface (F < 0.5). Earthquakes occur mostly in areas with low values of Te. (2) Medium and strong earthquakes are prone to occur in regions with alternating positive and negative changes in the gravity field during the stage of large-scale reverse adjustment. It is expected that the risk of a moderate-to-strong earthquake occurring again in the vicinity of the survey area between 2025 and 2026 is relatively high. (3) Before the Wushi earthquake, the positive and negative boundaries of the apparent density of the crust at 12 km shifted to be approximately parallel to the seismic fault, and the earthquake was triggered after undergoing a “solidification” process. (4) The Wushi earthquake is a leptokurtic strike-slip backwash type of earthquake; coseismic deformation shows that subsidence occurs in the high-visual-density zone, and vice versa for uplift. The results of this study reveal the lithosphere-conceiving environment of the Tianshan and adjacent areas and provide a basis for regional earthquake monitoring, early warning, and post-disaster disposal. Full article

Driven by stringent emission regulations, advanced combustion modes utilizing turbulent jet ignition technology are pivotal for enhancing the performance of marine low-speed natural gas dual-fuel engines. This review focuses on three novel combustion modes, yielding key conclusions: (1) Compared to the conventional DJCDC mode, the TJCDC mode exhibits a significantly higher swirl ratio and turbulence kinetic energy in the main chamber during initial combustion. This promotes natural gas jet development and combustion acceleration, leading to shorter ignition delay, reduced combustion duration, and a combustion center (CA50) positioned closer to the Top Dead Center (TDC), alongside higher peak cylinder pressure and a faster early heat release rate. Energetically, while TJCDC incurs higher heat transfer losses, it benefits from lower exhaust energy and irreversible exergy loss, indicating greater potential for useful work extraction, albeit with slightly higher indicated specific NOx emissions. (2) In the high-compression ratio TJCPC mode, the Liquid Pressurized Natural Gas (LPNG) injection parameters critically impact performance. Delaying the start of injection (SOI) or extending the injection duration degrades premixing uniformity and increases unburned methane (CH₄) slip, with the duration effects showing a load dependency. Optimizing both the injection timing and duration is, therefore, essential for emission control. (3) Increasing the excess air ratio delays the combustion phasing in TJCPC (longer ignition delay, extended combustion duration, and retarded CA50). However, this shift positions the heat release more optimally relative to the TDC, resulting in significantly improved indicated thermal efficiency. This work provides a theoretical foundation for optimizing high-efficiency, low-emission combustion strategies in marine dual-fuel engines. Full article

We investigate how collisional interactions between the condensate and the thermal cloud influence the distinct dynamical regimes (Josephson plasma, phase-slip-induced dissipative regime, and macroscopic quantum self-trapping) emerging in ultracold atomic Josephson junctions at non-zero subcritical temperatures. Specifically, we discuss how the self-consistent dynamical inclusion of collisional processes facilitating the exchange of particles between the condensate and the thermal cloud impacts both the condensate and the thermal currents, demonstrating that their relative importance depends on the system’s dynamical regime. Our study is performed within the full context of the Zaremba–Nikuni–Griffin (ZNG) formalism, which couples a dissipative Gross–Pitaevskii equation for the condensate dynamics to a quantum Boltzmann equation with collisional terms for the thermal cloud. In the Josephson plasma oscillation and vortex-induced dissipative regimes, collisions markedly alter dynamics at intermediate-to-high temperatures, amplifying damping in the condensate imbalance mode and inducing measurable frequency shifts. In the self-trapping regime, collisions destabilize the system even at low temperatures, prompting a transition to Josephson-like dynamics on a temperature-dependent timescale. Our results show the interplay between coherence, dissipation, and thermal effects in a Bose–Einstein condensate at a finite temperature, providing a framework for tailoring Josephson junction dynamics in experimentally accessible regimes. Full article

To explore the influence of mine roof on the damage and failure of sandstone surrounding rock under different pressure rates, mechanical experiments with different strain rates were carried out on sandstone rock samples. The strength, deformation, failure, energy and damage characteristics of rock samples with different strain rates were also discussed. The research results show that with the increases in the strain rate, peak stress, and elastic modulus show a monotonically increasing trend, while the peak strain decreases in the reverse direction. At a low strain rate, the proportion of the mass fraction of complete rock blocks in the rock sample is relatively high, and the shape integrity is good, while rock samples with a high strain rate retain more small-sized fragmented rock blocks. This indicates that under high-rate loading, the bifurcation phenomenon of secondary cracks is obvious. The rock samples undergo a failure form dominated by small-sized fragments, with severe damage to the rock samples and significant fractal characteristics of the fragments. At the initial stage of loading, the primary fractures close, and the rock samples mainly dissipate energy in the forms of frictional slip and mineral fragmentation. In the middle stage of loading, the residual fractures are compacted, and the dissipative strain energy keeps increasing continuously. In the later stage of loading, secondary cracks accelerate their expansion, and elastic strain energy is released sharply, eventually leading to brittle failure of the rock sample. Under a low strain rate, secondary cracks slowly expand along the clay–quartz interface and cause intergranular failure of the rock sample. However, a high strain rate inhibits the stress relaxation of the clay, forces the energy to transfer to the quartz crystal, promotes the penetration of secondary cracks through the quartz crystal, and triggers transgranular failure. A constitutive model based on energy damage was further constructed, which can accurately characterize the nonlinear hardening characteristics and strength-deformation laws of rock samples with different strain rates. The evolution process of its energy damage can be divided into the unchanged stage, the slow growth stage, and the accelerated growth stage. The characteristics of this stage reveal the sudden change mechanism from the dissipation of elastic strain energy of rock samples to the unstable propagation of secondary cracks, clarify the cumulative influence of strain rate on damage, and provide a theoretical basis for the dynamic assessment of surrounding rock damage and disaster early warning when the mine roof comes under pressure. Full article

In the present study, the mechanical properties of high-strength steel rebar with different crossrib spacing that affect the bond behavior between steel rebar and concrete is investigated. To reveal the effects of crossrib spacing on the bond behavior of 630 MPa high-strength steel rebar (T63) in concrete, 42 bonding specimens were designed using T63 rebars and T63 rebars with increased crossrib spacing (TB63). The bond properties of two kinds of steel rebar with concrete were investigated by pull-out test and the failure modes, bond strengths, relative slippages, and bond-slip curves were obtained. Based on analysis of bond-slip curves, the applicability of the existing bond-slip constitutive model to describe T63 and TB63 rebars was discussed. It was found that 30–50% increase in crossrib spacing had little effect on the bond failure mode and bond strength of T63 rebar. The bond-slip curves of the two types of bonding specimens were similar and there is a 1.3 to 1.5-fold increase in peak slippage with TB63. The calculation method of critical bond length in Chinese code (GB 50010-2010) is applicable to T63 and TB63 rebars, and the bond-slip characteristics of T63 rebar with different crossrib spacings was reliably described by the bond-slip constitutive model. The research results can be used as the basis for the application of T63 reinforcement and can also be used as a reference for optimizing of rebar ribs outline. Full article

The morphologic dating of single-event fault scarps along the dextral strike-slip Valley Fault System (VFS) yielded distinct clusters of relative ages (kt), which we interpret as evidence of independent surface ruptures. The boundaries between structural and geometric segments of the East Valley Fault (EVF) appear to have been nonpersistent during the recent rupture cycle. We associate the youngest cluster with the largest historical earthquake (M > 7 in 1863) felt in Manila, which is believed to have come from three segments of the EVF. Thus, future multiple-segment events, M > 7, could occur on the EVF. Our results do not support rupturing of the entire length of the West Valley Fault (WVF), but its northern segment (segment I) is capable of generating an M > 7 earthquake. This is the first time that diffusivity and relative ages of fault scarps are determined from this part of the world and is one of the few studies applying analysis of recent fault scarps to rupture segmentation studies. The recent scarps along the WVF’s segment II are due to aseismic creep and occur along pre-existing tectonic structures. Continued groundwater overextraction within the creeping zone could induce seismicity and modulate the natural timing of future earthquakes along the WVF. Full article

Accurately modeling fractures in wave-propagation simulations is challenging due to their small scale relative to other features. While equivalent-media models can approximate fracture-induced anisotropy, they fail to capture their discrete influence on wave propagation. To address this limitation, the Interior-Penalty Discontinuous Galerkin Method (IP-DGM) can be adapted to incorporate the Linear-Slip Model (LSM) to represent fractures explicitly. In this study, we apply IP-DGM to elastic wave propagation in fractured cylindrical domains using realistic fracture compliances obtained from laboratory experiments (using ultrasonic-pulse transmission) to simulate the effects of fluid-filled fractures. We analyze how fracture spacing and fluid type influence P- and S-wave behavior, focusing on amplitude attenuation and wave-front delays. Our numerical results align with experimental and theoretical predictions, demonstrating that higher-density fluids enhance wave transmission, reducing the impedance contrast and improving coupling across fracture surfaces. These findings highlight the capability of IP-DGM to accurately model wave propagation in realistic fractured and saturated media, providing a valuable tool for seismic monitoring in fractured reservoirs and other applications where fluid-filled fractures are prevalent. Full article

Quench–polish–quench (QPQ) nitro-carburizing of AISI 4140 steel in a salt bath was performed in this study. Nitro-carburizing in a salt bath enhanced the formation of Fe-nitride on the outer surface layer. Moreover, the oxidizing treatment formed a thin oxide layer decorated on the outermost part of the QPQ-treated sample. The dense compound layer formed after nitro-carburizing in a salt bath consisted of refined granular Fe₃N and transformed to Fe₂N after post-oxidation treatment. Micro-shot peening (MSP) was adopted before QPQ treatment to increase the treated steel’s fatigue performance. The results indicated that MSP slightly increased the thickness of the compound layer and harden depth, but it had little effect on improving the fatigue strength/life of the QPQ-treated sample (SP-QPQ) compared to the non-peened one (NP-QPQ). A deep compressive residual stress (CRS) field (about 200 μm) and a hard nitrided layer showed a noticeable improvement in the fatigue performance of the QPQ-treated ones relative to the 4140 substrates tempered at 570 °C. The ease of slipping or deforming on the substrate surface was responsible for its poor resistance to fatigue failure. The cracking and spalling of the brittle surface layer were the causes for the fatigue crack initiation and growth of all of the QPQ-treated samples fatigue-loaded at/above 875 MPa. It was noticed that fatigue crack initiation at the subsurface inclusions was more likely to occur in the SP-QPQ sample fatigue-loading at 850 MPa or slightly above the fatigue limit. Full article

Pallet-type end-effectors robots are widely used for airport baggage handling, because of their better adaptability to different types of baggage. A novel attitude-variable high acceleration motion planning method is presented for improving the handling efficiency, which is to move a pallet with non-fixed baggage as fast as possible under a given path, such that the baggage does not slip at any time. Firstly, the motion state model, which focuses on the friction force between the pallet and baggage during handling, is established. The influence of handling attitude on maximum handling acceleration is analyzed, which is verified by a real robot system made up of an IRB-6700 robot and a pallet. Then, a high acceleration motion planning method is proposed by changing the pallet attitude to avoid relative sliding. Finally, three numerical simulations are implemented to verify the proposed motion planning method. The results show that this method can at least improve handling efficiency by 17.64% in linear motion and up to 34.55% in curved motion compared with the horizontal fixed-attitude handling. Full article

Laser shock peening (LSP) is an effective method to improve the fatigue property of metallic materials, and a thorough understanding of its strengthening mechanism is crucial for technology application. In this study, the LSP and fatigue tests of TC4 titanium alloy have been carried out. Combined with the structural characterization and the crystal plasticity finite element (CPFE) simulation, the relationship of stress distribution, microstructure evolution and fatigue performance caused by LSP is revealed. The results indicate that the material’s fatigue life initially increases and subsequently declines with the rising pulse energy. At the optimal pulse energy condition, the laser-shocked specimen demonstrates a 126% increase in fatigue life relative to the untreated specimen, which is accompanied by the higher residual compressive stress along the depth. Meanwhile, the grains become more refined with a uniform size change gradient, and the β phase content drops from 4.1% to 2.2%. Notably, regions with <$\stackrel{-}{1}$2$\stackrel{\mathrm{-}}{1}$0> crystal orientation can be selectively achieved. With the favorable <$\stackrel{\mathrm{-}}{1}$2$\stackrel{\mathrm{-}}{1}$0> slip direction orthogonal to the applied fatigue loading axis, the generation and propagation of dislocations are effectively constrained, thereby significantly enhancing the material’s fatigue performance. The stress distribution and fatigue life in models with different grain sizes and phase contents are further analyzed by the CPFE method, showing good consistency with the experimental results. Theoretically, the excessively high pulse energy causes the transient temperature (1769 °C) to surpass the melting point (1660 °C), which can affect the recrystallization structure and stress distribution. Full article

The bond between steel bars and concrete is a fundamental aspect of reinforced concrete, ensuring the efficient transfer of forces between the two materials and guaranteeing their compatibility and composite action. The conventional equation for calculating bond stress does not account for slip effects. However, significant slip can lead to considerable errors, which are disadvantageous when analyzing bond performance using finite element methods. To address this issue, this study proposed a modified bond stress calculation model, whose reliability was systematically validated through pull-out tests and comparative analysis with a CEB-FIP model. The experimental program employed a universal testing machine for load application, with a static strain measurement system continuously monitoring stress–strain data throughout the loading process. The experimental results indicated that the failure process of the specimens could be categorized into the following, four distinct stages: micro-slip stage, slip stage, descent stage, and residual stage. The discrepancy between bond stresses calculated by the modified and conventional equations increased with the increasing relative slip, reaching its maximum value in the residual stage. A comparative analysis of 23 groups of experimental data from the literature was performed, revealing that the difference in bonding stress reached a maximum of 20.45% in the residual stage, with a standard deviation (S) of 0.006 and a coefficient of variation (C_v) of 0.321, reflecting small fluctuations but large dispersion. In contrast, the S of the residual bonding stress was 0.016, and the C_v was 0.080, showing lower dispersion but greater volatility. Further comparison with the CEB-FIP model confirmed the superior applicability and computational accuracy of the proposed modified model. Therefore, the modified equation should be utilized for calculating bond stress when significant slip occurs, particularly during the residual stage. Full article

The cutting of leaf stems is a critical step in the mechanized harvesting of tuber mustard (Brassica juncea L.). This study focuses on the calibration of parameters for the discrete element model of mustard leaf stems to visualize the cutting process and facilitate numerical simulations. Intrinsic material properties were measured based on mechanical testing, and EDEM2022 simulation software was utilized to calibrate the model parameters. The Hertz–Mindlin (no-slip) model was employed to simulate the stacking angle of mustard leaf stems, and the contact parameters for the discrete element model were determined using a combination of two-level factorial design, steepest ascent, and CCD (central composite design) tests. The results showed that the coefficient of restitution, coefficient of static friction, and coefficient of rolling friction for the leaf stems were 0.45, 0.457, and 0.167, respectively, while for interactions between the leaf stems and the working parts, these values were 0.45, 0.55, and 0.175, respectively. Based on the Hertz–Mindlin with bonding model, the primary bonding parameters were calculated, and a BBD (Box–Behnken design) test was applied for optimization. The comparison between the simulation and experimental results showed that the relative error in the maximum shear force was within 5%, indicating that the calibrated model can serve as a reliable theoretical reference for the design and optimization of tuber mustard harvesting and cutting equipment. Full article

The real-time surface thermal monitoring of thermal protection structures (TPSs) is crucial for hypersonic vehicle safety. This study proposes an effective approach for real-time temperature reconstruction by integrating embedded sensor arrays with an enhanced full-time domain inversion algorithm, utilizing the overlapping sliding window method. An array of three evenly spaced sensors is used for TPS monitoring. Notably, the inversion approach eliminates the need for prior knowledge of the TPS’s thermal parameters. It exhibits remarkable practicality with low-frequency sampling requirements (1 Hz) and robust noise resistance. Through numerical simulations and a quartz lamp side heating experiment, it is demonstrated that the window size and data noise have great influence on the temperature reconstruction accuracy, but the window slip step has little influence. The mean relative error of the inversion temperature decreases exponentially as the window size increases, and the optimal window duration is equal to the thermal hysteresis time. The study investigates the impact of three noise filtering methods on the inversion accuracy, finding that the Savitzky-Golay filtering significantly enhances measurement precision, reducing mean relative error from 18.4% to 6.7%. These results highlight the potential of the proposed real-time sensor method for practical engineering applications, offering a reliable and efficient solution for real-time TPS temperature monitoring. Full article

The Muong La–Bac Yen–Cho Bo fault is one of the seismic faults in the northwest region of Vietnam. Neo-tectonic activities and exogenous processes have influenced the drainage system and topographic–geomorphologic features on both walls of the fault. The results of topographic analysis and geomorphological indices have confirmed the active tectonics of the fault during the Neo-tectonic period (Pliocene–Quaternary, about 5 million years). The valley floor width-to-height ratio (V_f) of less than 0.5 indicates the “rejuvenation” of the streams and the obvious influence of tectonic activities on the two walls of the studied fault. The Hypsometric curve (HC) in the study area has a straight–convex shape and the basins on the northeast wall have hypsometric integral index values ranging from 0.46 to 0.481, which are lower and more convex than those of the southwest wall. The Mountain-front sinuosity index (S_mf) from 1.92 to 3.28 along the foot slope of the Hoang Lien Son range (the segment from Than Uyen to Bac Yen and Phu Yen) and the highly variable stream-length gradient index (SL) value on the northeast wall signify the relative tectonic uplift on the northeast wall of the fault. The deformed geomorphological indications (steep cliffs, slip surfaces, etc.) in the field confirm the active tectonics of the Muong La–Bac Yen–Cho Bo fault during the Neo-tectonic period. Full article

The primary objective of this study is to establish an innovative theoretical framework for analyzing the behavior of an end-bearing pile-supported embankment. This proposed methodology extensively investigates various aspects, including the characteristics of relative slip at the interface between the pile and soil, the distinctive non-uniform deformation patterns typically observed in soft soils, and the substantial influence of pile–soil interaction on the evolution of soil arching phenomena. To precisely capture the frictional relationship and relative displacement within the pile–soil system, we introduce an enhanced ideal elastic-plastic model. Additionally, a deformation function is incorporated to simulate the non-uniform deformation of soft soils, and an improved soil arching model is developed to assess its impact on the overall behavior. The analytical solution is derived through the implementation of a stress and volume deformation continuity condition, and its validity is effectively demonstrated through numerical simulations. The results indicate that under the load of the embankment, relative slip at the pile–soil contact surface is a significant phenomenon and should not be neglected in theoretical calculations. The relative displacement between the pile and soil initially exhibits a linear relationship with depth, and later follows a quadratic function as depth increases. Full article