Search Results (749)

Composite integrative and conjugative elements (ICEs) frequently mediate the co-transfer of multiple antibiotic resistance genes during horizontal gene transfer, but their formation mechanisms remain unclear. This study investigated the site-specific integration of Tn1806 into ICESa2603-family ICEs in Streptococcus agalactiae by conjugation experiments. PCR screening of 161 S. agalactiae clinical isolates identified potential Tn1806-like ICE carriers; whole-genome sequencing was performed to further characterize the macrolide-resistance isolates from this group. PCR detection resulted in 24 carrying Tn1806-like ICEs being found, five of which were macrolide-resistant. Genomic analysis for these five revealed distinct Tn1806-like ICEs (ICESag16, ICESag57, ICESag139, ICESag167, and ICESag220), three of which were found nested within another ICE (ICESpy009, an ICESa2603-family ICE). Conjugation experiments confirmed ICESag167 could integrate into the snf2 (methyltransferase containing a SNF2 helicase domain) of ICESpy009 in recipient cells, generating a composite ICE. Re-conjugation verified the transferability of composite ICE at low frequencies (8.63 × 10⁻⁸), during which some nested ICESag167 were excised and transferred independently. This work provides first experimental evidence supporting Tn1806 nesting within another ICE as a mechanism for resistance accumulation and mobile element evolution in S. agalactiae. The spread of such composite ICEs may confer multiple forms of resistance to new hosts, challenging infection treatment and raising public health concerns. Full article

Background: The pressure reduction range in traditional protective coal mining is often set conservatively, resulting in diminished actual pressure reduction effects near the mining boundary. Therefore, analyzing the stress and permeability evolution patterns at the mining boundary is particularly essential. Method: A three-dimensional numerical model was established according to the mining conditions of the 864 working face in T Mine to study the stress evolution, fissure development, and permeability evolution of the coal and rock mass overlying the protective seam mining, especially those near the mining boundary. Results: The overlying coal and surrounding rock mass near the mining boundary are in the state of increasing vertical stress and decreasing horizontal stress, and under this mechanical path of “increasing axial pressure and decreasing peripheral pressure”, the coal mass is damaged and destroyed, fissures are developed, and the permeability is increased; as a result, the coal and surrounding rock mass near the mining boundary mainly produce vertical longitudinal fissures, and the permeability can be increased 900 times compared with that of the overlying coal and surrounding rock mass in the mining boundary. After ground drilling and enhanced depressurization, the measured maximum gas content of the coal mass at the strike boundary is 3.25 m³/t, and the measured maximum gas content of the coal mass at the inclination boundary is 2.63 m³/t. Conclusions: After mining the protective layer, the permeability enhancement effect diminishes from the center toward the sides, yet remains sufficient to eliminate the risk of gas outbursts. This validates the importance of verifying permeability enhancement effects at coal seam boundaries. Full article

With the increasing density of urban underground space development, the soil disturbance induced by large-section rectangular pipe jacking poses a significant threat to the safety of underlying subway tunnels. Taking the Lihe Road utility tunnel project in Wuhan, which crosses over Metro Line 4, as the engineering background, a three-dimensional finite element (FE) model was established using Midas GTS NX to simulate the entire pipe jacking process. Field monitoring data from caisson excavation, ground improvement, pipe jacking, and backfill grouting were introduced for validation, enabling a systematic investigation of the influence mechanism of pipe jacking on existing tunnels. In the numerical simulation, the modified Mohr–Coulomb constitutive model was adopted for the soil, and a “portal-type” reinforcement system was introduced. The pipe jacking process was simulated equivalently with a 1.2 m advance per cycle. The results indicate that the ground settlement induced by pipe jacking exhibits a stage-wise accumulation pattern and eventually develops into a stable settlement trough. The vertical settlement of the tunnel follows an evolutionary law of “early occurrence in the near field, delayed response in the far field, and final convergence,” with peak settlements of 2.44 mm and 2.53 mm for the left and right lines, respectively. Ground improvement significantly mitigates soil deformation, reducing the maximum surface settlement from 45.5 mm to 11.1 mm, decreasing the tunnel’s peak vertical settlement by 37%, and reducing horizontal displacement by 64%, thereby effectively suppressing lateral soil extrusion. The proposed closed-loop analysis method of “numerical simulation–monitoring validation–measure evaluation” reveals the spatiotemporal evolution law of soil–tunnel interaction during pipe jacking construction and provides valuable reference for risk control in similar engineering projects. Full article

The anisotropic properties of wood make timber beams prone to developing longitudinal cracks. Notably, cracks occurring at the mid-height position are both highly common and critically detrimental to structural load-bearing capacity. This study focuses on the influence mechanisms of such cracks through four-point bending tests on 860 specimens, finite element simulations, and fracture morphology analyses. By introducing a horizontal crack location parameter called crack eccentricity (e), the influence of cracks at different horizontal positions on timber beam load-bearing capacity was investigated. The experimental results show that the horizontal position of the crack has a “critical eccentricity effect”: when e is below the critical value, cracks will not propagate and will have a minor impact on the load-bearing performance of timber beams; when e exceeds the critical value, cracks will propagate and their harmfulness will increase dramatically. As a special case, specimens with side-opening cracks (e = 1) exhibit “damage saturation” characteristics. That is, when the crack length exceeds the threshold (half of the beam span), regardless of further lengthening, the bearing capacity is unchanged and the damage evolution reaches a saturation plateau. The above analysis results suggest that the influence of cracks on the bearing capacity of timber beams may be counterintuitive. The calculation method for the “crack hazard coefficient” proposed in this study can provide a reference for crack hazard assessments. Full article

To enhance the assessment accuracy of tunnel face instability risks of active collapse during shield tunneling, this study establishes a novel unified analytical framework that couples the effects of unsaturated transient seepage induced by excavation drainage with soil stratification and heterogeneity. Grounded in unsaturated effective stress theory, the framework explicitly incorporates matric suction into the Mohr–Coulomb failure criterion via suction stress and apparent cohesion. By employing a horizontal two-layer nonhomogeneous soil model and solving the one-dimensional vertical Richards’ equation, an analytical solution for the face drainage boundary is derived to quantify the spatiotemporal evolution of suction stress and apparent cohesion. Subsequently, the critical support pressure is evaluated using the upper bound theorem of limit analysis, incorporating a horizontal layer-discretized rotational failure mechanism and the power balance equation. The validity of the proposed framework is confirmed through comparative analyses. Parametric studies reveal that in the upper hard and lower soft strata, the critical support pressure decreases and converges over time, indicating that unsaturated transient seepage exerts a significant influence in the short term that stabilizes over the long term. Additionally, sand–silt stratum exhibits lower overall stability and higher sensitivity to groundwater levels and temporal factors compared to silt–clay stratum. Conversely, silt–clay stratum displays a non-monotonic evolution with increasing cover-to-diameter ratios (C/D), reaching a minimum critical support pressure at approximately C/D = 1.1. Regarding heterogeneity, the internal friction angle of the lower layer exerts dominant control over the critical support pressure compared to seepage velocity, while the influence of other strength parameters remains secondary. These findings provide a theoretical basis for the time-dependent design of tunnel face support pressure under excavation drainage conditions. Full article

The development of urban underground spaces has led to an increasing number of projects involving super-large-diameter shield tunnels, making research on their impact on existing structures particularly significant. This paper investigated the numerical simulation on deformation and damage mechanism of existing underground structures induced by adjacent construction of super-large-diameter tunnels. A 3D finite element model using ABAQUS (version 2022) software incorporating the Concrete Damaged Plasticity (CDP) constitutive model was established, and this paper was used to systematically analyze the deformation, internal force response, and damage evolution of existing tunnels. The results showed the following: (1) The double-line tunnel excavation intensified settlement superposition, increasing the maximum settlement from −19.70 mm (single-line) to −24.51 mm (double-line) and transforming the settlement trough from a V shape to a W shape. (2) The vertical bending moment evolved from a single peak to double peaks being the dominant loading mode, with the maximum horizontal moment only about 1/8 of the vertical value. (3) During the construction, the peak tensile stress at the tunnel bottom reached 2.655 MPa, exceeding the C50 concrete tensile strength, but later decreased to 2.097 MPa. Damage was primarily caused by bending-induced tension. (4) Tunnel damage was triggered by the historical peak stress and accumulated irreversibly, resulting in a final state of low-stress and high-damage, with a maximum tensile damage of 92.4%. This research can provide a theoretical basis for safety control in similar adjacent engineering projects. Full article

With the continuous growth of highway traffic volume and the increasing proportion of heavy vehicles, vehicle–bridge collisions have emerged as a significant accidental hazard threatening the safe operation of bridge infrastructure. Systematic investigation of the collision resistance of critical bridge components is therefore essential for the development of rational anti-collision design strategies and reliable risk assessment methods. Focusing on the representative disaster scenario of high-speed heavy vehicles impacting concrete bridge piers, this study first develops a finite element model of an RPC beam and validates its reliability through impact experiments. The validated modeling approach is then extended to bridge piers, where a high-fidelity finite element model established using ANSYS/LS-DYNA 2020 is employed to simulate the vehicle–pier collision process and to systematically investigate collision force characteristics, bridge damage evolution, and collision response behavior. The results show that the established reactive powder concrete (RPC) beam model, validated through drop hammer impact tests, reliably captures the impact-induced damage and dynamic response of concrete members. During heavy-vehicle impacts, the vehicle head and cargo compartment successively interact with the pier, generating two distinct collision force peaks, with the peak force induced by the cargo compartment being approximately 38.2% higher than that caused by the vehicle head. Severe damage is mainly concentrated within the impact region, characterized by punching shear failure on the impact face, tensile damage on the rear face, and shear failure near the pier top. The collision-induced structural response is dominated by horizontal displacement, which remains below 10 mm during the vehicle head impact but exceeds 260 mm under the cargo compartment impact. Significant displacements are also observed in the cap beam, with maximum horizontal and vertical values of 24 mm and 19 mm, respectively. These findings provide valuable insights into the impact behavior and failure mechanisms of concrete bridge piers, offering a sound theoretical basis and technical support for anti-vehicle collision design, collision-resistant structural optimization, bridge damage assessment, and the refinement of relevant design specifications. Full article

To address the depletion of shallow coal resources, mining activities have progressed to greater depths, where rock masses contain numerous fractures due to complex geological conditions, making grouting reinforcement essential for ensuring stability. Using digital image correlation, this study investigated the strain evolution characteristics of grouted fractured specimens of three rock types—mudstone, coal–rock, and sandstone—under uniaxial compression. Analysis of the strain evolution process focused on two typical fracture inclinations of 0° and 60°, while examination of the peak strain characteristics covered five inclinations, namely 0°, 15°, 30°, 45°, and 60°. The findings indicate that the mechanical response varies systematically with lithology and fracture inclination. The post-peak curves differ significantly among rock types: coal–rock shows a gentle descent, mudstone exhibits a rapid strength drop but higher residual strength, and sandstone is characterized by “serrated” fluctuations. The failure mode transitions from tensile splitting at a horizontal inclination of 0° to shear failure at inclinations of 15°, 30°, 45°, and 60°. Strain nephograms corresponding to the peak stress point D reveal sharp, band-shaped zones of strain localization. The maximum principal strain exhibits a non-monotonic trend, first increasing and then decreasing with increasing inclination angle. For grouted coal–rock and sandstone, the peak values of 47.47 and 45.00 occur at α = 45°. In contrast, grouted mudstone reaches a maximum value of 26.80 at α = 30°, indicating its lower susceptibility to damage. The study systematically clarifies the strain evolution behavior of grouted fractured rock masses, providing a theoretical basis for evaluating the effectiveness of reinforcement and predicting failure mechanisms. Crucially, the findings highlight mudstone’s role as a high-integrity medium and the particular vulnerability of horizontal fractures, offering direct guidance for the targeted grouting design in stratified rock formations. Full article

Investigating the spatial distribution and dynamics of terrestrial carbon storage is vital for climate change mitigation. However, horizontal spatial analyses often overlook heterogeneity in complex terrains. Here, we focused on the Gonghe Basin on the northeastern margin of the Qinghai–Tibet Plateau, where resource exploitation and ecological conservation interact. By using land use and DEM data and integrating the InVEST model, Geoda, and a geographical detector, we showed the altitudinal gradient effect and spatiotemporal evolution of carbon storage in the Gonghe Basin from 2000 to 2020 and identified the key factors influencing these patterns. Results show the following: (1) From 2000 to 2020, carbon storage in the Gonghe Basin exhibited a distinct pattern of “high at mid-elevations, low at both summit and valley” along the elevation gradient. High-value areas were concentrated in the forest–grassland zone between 2800–4400 m, while low-value areas were distributed in the human activity-intensive zone of 2100–2800 m and the alpine desert zone of 4400–5000 m. (2) The synergistic drivers of carbon storage differed markedly across elevation gradients. The low-elevation zone (2100–2800 m) was characterized by strengthened interactions between vegetation cover and precipitation as well as human activity variables, indicating a coupled natural–anthropogenic driving regime. In the mid-elevation zone (2800–4400 m), interactive effects shifted from vegetation–natural factor coupling to enhanced synergy with social factors such as population density. In the high-elevation zone (4400–5000 m), stable long-term interactions between vegetation and temperature predominated, while sensitivity to interactions involving human activity factors increased. (3) Although natural factors remained dominant, the explanatory power of human activity factors—including GDP density, land-use intensity, and grazing intensity—increased over time across all elevation gradients, suggesting progressively stronger human intervention in carbon cycling. (4) Based on these findings, this study proposes a “three belts–three strategies” synergistic governance framework—“regulation and restoration” for the low-elevation belt, “conservation and efficiency enhancement” for the mid-elevation belt, and “monitoring and early warning” for the high-elevation belt—aiming to enhance regional carbon sink capacity and ecological resilience through zone-specific, targeted interventions. These findings offer a scientific basis for reinforcing regional ecological security and improving carbon sink management. Full article

The Longmaxi from the Anchang Syncline in northern Guizhou exhibits a high degree of thermal evolution of organic matter and significant variation in gas content. Because the synclinal is narrow, steep, and internally faulted, the mechanisms controlling shale gas preservation and escape remain poorly understood, complicating development planning and engineering design. Research on oil and gas migration and accumulation mechanisms in synclinal structures is therefore essential. To address this issue, three proportionally scaled strata—pure shale, gray shale, and sandy shale—were fabricated, and faults and artificial fractures with different displacements and inclinations were introduced. The simulation system consisted of two glass tanks (No. 1 and No. 2). Each tank had three rows of eight transmitting electrodes on one side, and a row of eight receiving electrodes on the opposite side. Tank 1 remained fixed, while Tank 2 could be hydraulically tilted up to 65° to simulate air and water migration under varying formation inclinations. A gas-water injection device was connected at the base. Gas was first injected slowly into the model. After injecting a measured volume (recorded via the flowmeter), the system was allowed to rest for 24–48 h to ensure uniform gas distribution. Water was then injected to displace the gas. During displacement, Tank 1 remained horizontal, and Tank 2 was inclined at a preset angle. An embedded monitoring program automatically recorded resistivity data from the 48 electrodes, and water-driven gas migration was analyzed through resistivity changes. A gas escape rate parameter (G_d), based on differences in gas saturation, was developed to quantify escape velocity. The simulation results show that gas escape increased with formation inclination. Beyond a critical angle, the escape rate slowed and approached a maximum. Faults and fractures significantly enhanced gas escape. Full article

During layered mining of extra-thick coal seams in deep rock-burst-prone mines, a thick bottom coal layer facilitates the accumulation of elastic strain energy in the floor strata. This stored energy may be released under mining-induced disturbances during retreat, thereby triggering rock-burst events. To mitigate floor energy accumulation at the lower-slice working face of extra-thick coal seams, previous studies have primarily adopted floor blasting for pressure relief. However, conventional blasting is often associated with poor energy utilization and limited controllability of the pressure-relief range, which hampers achieving the intended relief performance. Accordingly, this study proposes a shaped charge blasting scheme to reduce floor energy accumulation. ANSYS/LS-DYNA simulations and UDEC-based energy analyses, together with theoretical analysis and field validation, were conducted to clarify the mechanism of directional fracture propagation and the evolution of floor elastic energy before and after blasting. The results showed that the synergistic effects of the high-velocity jet and quasi-static pressure in shaped charge blasting generated a through-going fracture aligned with the maximum horizontal principal stress. This fracture effectively segmented the high-stress region in the floor and increased the maximum fracture length along the shaped charge direction to 10–13 times that achieved by conventional blasting. UDEC simulations and theoretical analysis indicated that the peak elastic energy in the floor was reduced by up to 54.08% after shaped charge blasting. Field measurements further showed that shaped charge blasting limited the maximum roadway floor heave to 300 mm and reduced floor deformation by 35–42% compared with the case without pressure relief. Overall, shaped charge blasting effectively blocks stress-transfer pathways and improves energy dissipation efficiency, providing theoretical support and a practical technical paradigm for safe and efficient mining of deep extra-thick coal seams. Full article

Cardinium endosymbionts are obligate intracellular bacteria found in a wide range of invertebrate hosts. In this study, we generated ten new Cardinium genomes from plant-parasitic nematodes of the genera Amplimerlinius, Bursaphelenchus, Cactodera, Ditylenchus, Globodera, Meloidoderita, and Rotylenchus, revealing their broad ecological and phylogenetic distribution. Using an expanded set of genes, we clarified the relationship between previously defined Cardinium groups B and F from nematodes, showing that they are closely related and likely share a single evolutionary origin within nematode-associated Cardinium. Among the newly assembled Cardinium genomes obtained in this study, two genomes originating from strains associated with wood-inhabiting Bursaphelenchus species exhibited remarkable genome reduction, with estimated sizes of approximately 695 kb. Functional annotation of Cardinium genomes indicated an absence of or a reduction in several central metabolic pathways, including the biotin biosynthetic pathway. A complete biotin pathway was found only in D. weischeri, and this pathway is only partially encoded in Cactodera sp. The polA gene, which encodes DNA polymerase I, showed partial loss in several Cardinium strains. Phylogenetic and comparative genomic analyses provided strong evidence that several carbohydrate, glycerophospholipid, and biotin metabolism genes in these endosymbionts have been acquired through horizontal gene transfer. Future research that integrates high-quality genome assemblies with functional analyses of host–symbiont interactions will be essential to elucidate how metabolic dependency, genome reduction, and horizontal gene transfer collectively shape the evolution and ecological diversification of Cardinium across nematode hosts. Full article

In response to the critical demand for improved characterization of atmospheric stability effects in wind turbine wake prediction, this study proposes and systematically validates a new analytical wake model that incorporates atmospheric stability effects. In recent years, research on wake models with atmospheric stability effects has primarily followed two approaches: incorporating stability through high-fidelity numerical simulations or modifying classical analytical wake models. While the former offers clear mechanical insights, it incurs high computational costs, whereas the latter improves efficiency yet often suffers from near-wake prediction biases under stable stratification, lacks a unified framework covering the entire wake region, and relies heavily on case-specific calibration of key parameters. To overcome these limitations, this study introduces a stability-dependent turbulence expansion term with a square of a cosine function and the stability sign parameter, enabling the model to dynamically respond to varying atmospheric conditions and overcome the reliance of traditional models on neutral atmospheric assumptions. It achieves physically consistent descriptions of turbulence suppression under stable conditions and convective enhancement under unstable conditions. A newly developed far-field decay function effectively coordinates near-wake and far-wake evolution, maintaining computational efficiency while significantly improving prediction accuracy under complex stability conditions. The Present model has been validated against field measurements from the Scaled Wind Farm Technology (SWiFT) facility and the Alsvik wind farm, demonstrating superior performance in predicting wake velocity distributions on both vertical and horizontal planes. It also exhibits strong adaptability under neutral, stable, and unstable atmospheric conditions. This proposed framework provides a reliable tool for wind turbine layout optimization and power output forecasting under realistic atmospheric stability conditions. Full article

As the retrieval of unconventional oil and gas resources extends to the deep and ultra-deep domains, the issue of cement sheath failure in shale oil wellbores seriously endangers wellbore safety, making it imperative to uncover the relevant damage mechanism and develop effective assessment approaches. In response to the limitations of conventional finite element methods in representing mesoscopic damage, in this study, we determined the mesoscopic parameters of cement paste via laboratory calibrations; constructed a 3D casing–cement sheath–formation composite model using the discrete element method; addressed the restriction of the continuum assumption; and numerically simulated the microcrack initiation, propagation, and interface debonding behaviors of cement paste from a mesomechanical viewpoint. The model’s reliability was validated using a full-scale cement sheath sealing integrity assessment apparatus, while the influences of fracturing location, stage count, and internal casing pressure on cement sheath damage were analyzed systematically. Our findings indicate that the DEM model can precisely capture the dynamic evolution features of microcracks under cyclic loading, and the results agree well with the results of the cement sheath sealing integrity evaluation. During the first internal casing pressure loading phase, the microcracks generated account for 84% of the total microcracks formed during the entire loading process. The primary interface (casing–cement sheath interface) is fully debonded after the second internal pressure loading, demonstrating that the initial stage of cyclic internal casing pressure exerts a decisive impact on cement sheath integrity. The cement sheath in the horizontal well section is subjected to high internal casing pressure and high formation stress, resulting in more frequent microcrack coalescence and a rapid rise in the interface debonding rate, whereas the damage progression in the vertical well section is relatively slow. Full article

The impact and solidification of multiple molten droplets on a cold substrate critically influence the quality and performance of thermally sprayed coatings. We present a Smoothed Particle Hydrodynamics (SPH) model that couples fluid-solid interaction, wetting, heat transfer and phase change to simulate multi-droplet impact and freezing. The model is validated against benchmark cases, including the Young–Laplace relation, wetting dynamics, single-droplet impact and the Stefan solidification problem, showing good agreement. Using the validated model, we investigate two droplets—either centrally or off-centrally—impacting on a cold surface. Simulations reveal two distinct solidification patterns: convex pattern (CVP), which results in a mountain-like splat morphology, and concave pattern (CCP), which leads to a valley-like shape. The criterion for the two patterns is explored with two dimensionless numbers, the Reynolds number $Re$ and the Stefan number $Ste$. When $Re\le 17.8$, droplets tend to solidify in CVP; at higher Reynolds numbers $Re\ge 18.8$, they tend to solidify in CCP. The transition between the two patterns is primarily governed by $Re$, with $Ste$ exerting a secondary influence. For example, when droplets have $Re=9.9$ and $Ste=5.9$, they tend to solidify in a convex pattern, whereas at $Re=19.8$ and $Ste=5.9$, they tend to solidify in a concave pattern. Also, the solidification state of the first droplet greatly influences the subsequent spreading and solidification of the second droplet. A parametric study on CCP cases with varying vertical and horizontal offsets shows that larger vertical offsets accelerate solidification and reduce the maximum spreading factor. For small vertical distances, the solidification time increases with horizontal offset by more than 29%; for large vertical distances the change is minor. These results clarify how droplet interactions govern coating morphology and thermal evolution during thermal spraying. Full article