Search Results (4,205)

Deep joint source-channel coding (DeepJSCC) has emerged as a promising paradigm for semantic-aware wireless image transmission, achieving strong performance under challenging channel conditions. However, MSE-trained DeepJSCC systems typically achieve high peak signal-to-noise ratio (PSNR) values but suppress high-frequency details, resulting in perceptually blurry reconstructions that fail to capture fine textures and edge information. Existing perceptual enhancement approaches for JSCC systems face significant practical limitations: full transceiver redesign methods require replacing both the transmitter and the receiver with large models (19–31 million parameters), incurring substantial deployment costs; diffusion-based refinement approaches require over 1700 million additional parameters and introduce inference latency exceeding 13 s, rendering them unsuitable for latency-constrained wireless applications; and generic image restoration networks lack channel state awareness and cannot adapt to varying signal-to-noise ratio (SNR) conditions. This paper proposes a lightweight receiver-only perceptual enhancer designed for use with frozen DeepJSCC backbones. The proposed module adopts residual learning with feature-wise linear modulation (FiLM)-based SNR-adaptive modulation to dynamically adjust the enhancement strength under varying channel conditions. A radially weighted FFT magnitude loss is further introduced to guide high-frequency recovery. The enhancer adds only 0.29 million trainable parameters (<1% of the backbone) and requires neither transmitter modification nor backbone retraining. Extensive experiments on the Kodak24 and DIV2K datasets demonstrate a 34.4–37.5% LPIPS reduction over the frozen DeepJSCC baseline under AWGN channels. Supplementary robustness evaluations further show a 30–33% LPIPS reduction under Rayleigh fading, and stable generalization to unseen SNR levels. The receiver-side decoder-plus-enhancer pipeline requires 43 ms at 768 × 512 resolution, corresponding to approximately 23 frames per second. Full article

The seismic performance of reinforced concrete (RC) beam–column joints depends on both shear strength and failure mechanisms, the assessment of which remains challenging because of complex interactions among geometric, material, loading, and reinforcement parameters. This study presents a data-driven framework for assessing the shear strength and failure mechanisms of exterior RC beam–column joints. A database comprising 210 experimental specimens was systematically compiled from published studies. Seventeen input variables were selected based on structural mechanics, seismic design provisions, and previous experimental investigations. Machine learning models were developed for shear strength prediction and failure mode classification. SHAP was employed to interpret the trained models, while symbolic regression derived an interpretable design-oriented equation. On the independent test set, XGBoost achieved the highest shear strength prediction (R² = 0.973, RMSE = 40.09 kN), whereas the Support Vector Machine achieved 80.5% classification accuracy. The results indicate that the governing parameters for failure mechanisms differ from those controlling shear strength. Joint shear capacity was primarily influenced by geometric dimensions and longitudinal reinforcement ratios, whereas axial load ratio and joint transverse reinforcement had a greater influence on failure mechanisms. These findings highlight the importance of simultaneously assessing shear strength and failure mode in RC beam–column joints. Full article

Vertical joints are commonly required in precast concrete shear walls when large wall panels are divided for fabrication, transportation, and erection. To reduce on-site work and improve assembly efficiency, this study proposes and investigates a hybrid steel–grout vertical joint, namely a steel-anchor-ring grouted connection, which uses embedded threaded sleeves, steel anchor rings, an inserted vertical bar, and high-strength grout to transfer shear between adjacent wall panels. Monotonic direct shear tests, cyclic shear tests under normal tension and compression, and cyclic loading tests on precast shear wall specimens were conducted to investigate its mechanical behavior. The load–slip behavior, observed interface debonding, and final shank fracture in the direct shear tests suggested that grout–panel interface bond contributed substantially to the pre-peak response, whereas anchor-ring action became increasingly important after bond degradation. Comparison of the cyclic shear specimens suggested that normal tension promoted interface opening and bond degradation, leading to slip-dominated behavior, whereas normal compression enhanced interface contact and post-peak stability. For the specimens tested, the measured-to-calculated resistance ratios based on the code-based expression were 1.97–2.70 under direct shear and compression–shear conditions, but decreased to 1.20–1.31 under tension–shear loading. Wall-level demand analysis showed that the shear transferred across the vertical joint was significantly affected by both joint location and wall shear span ratio; larger shear span ratios increased the joint shear demand, whereas offset joint layouts reduced the demand. The wall specimens, designed relative to the code-based resistance, exhibited limited joint-related cracking and stable hysteretic behavior, and failed by wall-base flexural damage, indicating the shear-transfer effectiveness of the proposed joint under the tested configurations. Full article

The mechanical interpretation of impact traces on historical masonry structures offers a promising pathway for identifying the typology of ancient projectiles used in past conflicts. In recent years, inverse analysis approaches have been increasingly employed to infer projectile characteristics from residual damage patterns observed on archaeological remains. However, the reliability of such reconstructions strongly depends on the mechanical representation adopted for the impacted masonry. Ancient masonry walls, particularly those composed of tuff blocks and mortar joints, exhibit a marked heterogeneity that cannot always be adequately captured through simplified homogeneous material models. In this study, a numerical framework is developed to investigate how different assumptions regarding masonry homogenization influence the identification of projectile parameters derived from impact evidence. The mechanical response of the masonry is modeled through a homogenization procedure based on representative volume elements (RVE), allowing the heterogeneous brick—mortar assemblage to be translated into an equivalent macroscopic constitutive description. The resulting elastic and limit mechanical properties are then employed within a Finite Element Limit Analysis (FELA) formulation grounded in Melan’s lower bound theorem to evaluate collapse mechanisms and energy dissipation during impact.The methodology is applied to a case study inspired by the masonry walls of Pompeii, where parametric variations in mortar thickness are considered to assess their influence on the homogenized stiffness and strength domain. The results highlight how even simplified yet mechanically consistent models are capable of capturing the anisotropic behavior of masonry and its implications for energy absorption. In particular, the study shows that adopting a homogenization-based representation leads to more reliable inverse estimates of projectile velocity and momentum compared to purely homogeneous approximations. Overall, the proposed approach provides a computationally efficient yet mechanically grounded framework for supporting archaeological interpretations of impact traces, contributing to a more quantitative understanding of ancient warfare technologies. Full article

This paper investigates the stress corrosion cracking (SCC) behavior under constant loading conditions and the early-stage grain-scale deformation mechanisms of a friction-stir-welded (FSW) joint of 7A52 aluminum alloy. The results show that when a constant load equivalent to 1.0 times the yield strength (439.43 MPa) of the base metal is applied, the joint fractures after 72 days of immersion in a 3.5 wt% NaCl solution, with the fracture located in the heat-affected zone on the advancing side (AS-HAZ). The fracture surface exhibits a mixed-mode morphology characterized by both brittle and ductile features. Observations suggest that cracks mainly initiate at the bottom of corrosion pits, at grain boundaries, and at the interfaces between precipitates (such as Mg-Si-rich, Al-Fe-rich, or Al-(FeMn)-rich) and the Al matrix. It is suggested that the initiation mechanisms are closely related to galvanic corrosion, interfacial weakening, and mechanical property mismatch. In situ tensile and EBSD results indicate that the AS-HAZ is the first region to undergo deformation. As the load increases from 400 N to 1500 N, the degree of strain localization intensifies, with high-strain regions preferentially concentrated at grain boundaries. Grain boundary damage is likely a key mechanism responsible for the initial failure on the advancing side of the FSW joint. Further in situ SEM observations reveal that during the early stage of tensile deformation, as the load increases from 300 N to 455 N, the grain surface in the AS-HAZ evolves from a flat morphology to a typical orange peel appearance. Meanwhile, grain boundaries change from clearly visible to blurred, slip traces increase, and multiple slip systems are activated within the grains. The continuous pile-up of dislocations at grain boundaries leads to a sharp increase in local stress concentration, ultimately inducing grain boundary instability and crack nucleation. Full article

Coal dust carried by open-top freight trains can undergo complex transport and redistribution in confined railway tunnels, where train-induced airflow links in-tunnel particle motion to near-portal dispersion. However, how particle size and source position jointly influence transport across the train–tunnel–portal system remains insufficiently understood. A three-dimensional transient CFD–DPM model was developed for an open-top coal train traveling at 80 km/h through a 200 m local tunnel section and adjoining portal air domains. Four controlled cases combined two prescribed particle sources—a coal-surface source and a near-ground source—with representative diameters of 10 and 350 μm. In the simulated cases, the maximum air speed over the exposed coal surface increased from approximately 24 to 39 m/s during tunnel entry. The 350 μm particles exhibited stronger inertial settling and preferential migration toward the lower tunnel, whereas the 10 μm particles were more strongly coupled to the airflow and transported toward the portal by the train wake. Under the same prescribed source strength, the near-ground-source cases produced higher source-normalized concentration responses than the coal-surface-source cases, indicating a stronger suspended-transport response for particles introduced near the tunnel floor. In the 10 μm near-ground-source case, fine particles passed through the outlet portal and formed a transient elevated plume that spread downstream and laterally. Within the prescribed-input cases examined here, the simulations illustrate the joint influence of particle size and source position on cross-region coal-dust transport and organize the transport pathways into four particle-transport regions: the coal-surface, lower-tunnel, train-wake, and near-portal regions. Full article

To enhance the seismic performance of existing reinforced concrete (RC) buildings during retrofitting, the study introduces a new type of joint connected by a T-shaped steel plate. Compared with previous similar strengthening methods, this novel structure incorporating a post-installed beam not only effectively improves the mechanical properties of RC columns, but the connectors also further enhance the integrity of the post-installed beam. Low-cycle reversed loading tests on one cast-in-place specimen (RC) and three T-shaped steel plate connection specimens (TRC1–TRC3) were conducted to evaluate failure modes, hysteresis and skeleton curves, and energy dissipation. Results show that the novel joint failure concentrates at beam-end–column steel jacket weld seams and column-side steel plate cracking, while the core-zone concrete remains intact. Compared with RC, the novel joints TRC1–TRC3 exhibit bearing capacity variations of −1.03%~+15.80% and significantly enhanced energy dissipation. The thickness of the beam’s wrapped steel improves the carrying capacity and energy dissipation, whereas the T-shaped connector thickness has limited influence on bearing capacity. ABAQUS parametric analysis indicates that bolt quantity, concrete strength, and connector thickness have limited influence and serve as secondary design factors. These findings provide a theoretical basis for retrofitting existing buildings. Full article

This study investigates the influence of joining technology on the microstructural evolution and mechanical properties of joints produced from extruded AA2017 aluminum alloy rods. Rotary Friction Welding (RFW) was compared with conventional TIG welding to evaluate the effects of solid-state and fusion-based joining mechanisms. The joints were characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), hardness measurements, tensile testing, and fracture analysis. TIG welding produced a coarse-grained cast microstructure within the fusion zone, whereas RFW generated a fine-grained microstructure formed through intense thermomechanical deformation accompanied by crystallographic texture evolution. These distinct microstructural characteristics resulted in markedly different mechanical behavior. The RFW joints achieved an ultimate tensile strength of 247 MPa and an elongation to failure of 12.5%, compared with 160 MPa and 1.7%, respectively, for the TIG-welded joints. The results demonstrate that the joint formation mechanism is the primary factor governing the microstructural evolution and mechanical performance of AA2017 alloy joints. Full article

Prefabricated post-pouring UHPC (ultra-high performance concrete) beam–column joints have the advantages of strong integrity, excellent seismic performance and good durability, but there are also problems of easy cracking of old and new concrete interfaces and concrete near the interface. Therefore, a new type of post-cast UHPC joint is designed in this paper. The joint is connected by post-cast UHPC at the beam and column sections far from the core area, and the keyway is set in the connection section to solve the defect that the old and new interfaces easily crack. The refined finite element model of the joint was established by using the finite element software ABAQUS (2023). Through the simulation of 10 working conditions, the typical failure modes and seismic performance of the joint were discussed in depth, and the influence of key parameters such as the lap length of steel bars, the strength of steel bars and the strength of post-pouring UHPC was analyzed. The results show that the joint cracks first appear at the junction of the beam–column core area and develop along the cut-off interface between ordinary concrete and UHPC. No macroscopic cracks were observed in the post-pouring UHPC connection section, and the structure was finally destroyed due to the crushing of ordinary concrete. Increasing the lap length of the steel bar can improve the peak bearing capacity and stiffness of the joint, but it will accelerate the stiffness degradation. Increasing the strength grade of steel bars can significantly improve the bearing capacity and stiffness of the joints, but the energy dissipation capacity is slightly reduced. In addition, the improvement effect of UHPC strength is closely related to the strength of steel bars: when an HRB500 steel bar is used, high-strength UHPC can show better bearing capacity, stiffness and energy dissipation performance, while the improvement effect is not significant when an HRB400 steel bar is used. The research results can effectively inhibit the development of interface cracks and provide a theoretical reference for the subsequent full-scale test and the seismic design of precast joints with post-cast UHPC connections. Full article

The mechanical performance of CFRP/2024 Al alloy hybrid laminates joined by transverse ultrasonic vibration-assisted riveting (TUVAR) was investigated. The experiments were conducted on a self-developed ultrasonic riveting system with a power of 3000 W and a vibration frequency of 19.8 kHz, covering ultrasonic amplitudes from 0 to 24 μm. Test specimens were fabricated from T300/CFRP laminates, 2024 Al alloy sheets, and 2A10 Al alloy rivets. The influences of ultrasonic amplitudes (12 μm, 16 μm, 20 μm, and 24 μm) on riveting load, driven head geometry, interference, static tensile strength, and cyclic loading behavior were systematically analyzed. The results showed that TUVAR reduced the riveting force and promoted rivet deformation. As the amplitude increased, the driven head diameter increased, and the driven head height decreased, with a maximum reduction of 6.62%. The mean interference generally increased up to 20 μm and then decreased slightly at 24 μm; the relative interference variance coefficient ranged from 0.070 to 0.155 under TUVAR. Static tensile tests showed that the joint strength first increased and then decreased with increasing amplitude, with the highest mean static tensile load obtained at 20 μm. Cyclic tensile tests indicated that load-bearing capacity was improved with increasing amplitude, while the maximum deviation was maintained within 3.5%. These findings demonstrate that TUVAR can enhance both the forming quality and the mechanical performance of CFRP/2024 Al alloy riveted joints, and provide a useful reference for the high-performance joining of composite-metal hybrid structures in aerospace applications. Full article

Climate change may redistribute forest pests, pathogens, natural enemies, and host trees, yet these components are still often projected independently. We used ensemble species distribution models (SDMs) to map potential climatic suitability for Monochamus alternatus, Dastarcus helophoroides, Scleroderma guani, Bursaphelenchus xylophilus, and a genus-level Pinus host layer, and then summarized niche overlap, range overlap, and multispecies co-suitability under SSP1-2.6, SSP3-7.0, and SSP5-8.5 for the 2050s and 2090s. A structural equation model (SEM) fitted to thresholded binary layers was retained only as an exploratory description of conditional spatial associations. Because its inputs were suitability classifications rather than abundance, infection, parasitism, nematode load, or transmission data, neither arrow direction nor coefficient sign is interpreted causally. The strongest joint modeled suitability for the vector, pathogen, host, and at least one natural enemy occurred in East Asia, whereas B. xylophilus alone also showed potential climatic suitability in parts of the Americas and Africa. Importantly, the current model underpredicted the established occurrence of B. xylophilus in Portugal and western Spain, demonstrating that mapped unsuitable cells cannot be interpreted as confirmed absence. The genus-level Pinus layer similarly represents broad host availability rather than species-specific susceptibility. Because the future maps are based on averages across three general circulation models and the archived outputs do not permit retrospective estimation of inter-model variability, these projections should be treated as screening-level, scenario-conditioned summaries rather than uncertainty-bounded forecasts. The results identify priorities for surveillance and field validation, but they do not quantify disease incidence, interaction strength, or biological-control efficacy. Full article

This study proposes a novel friction-based beam-to-column shear connection designed to behave as a nominally pinned joint while avoiding any perforation of the connected members. The connection relies on frictional resistance to transfer shear forces, enabling full reversibility and preserving the integrity of the structural elements for future reuse. A comprehensive design methodology is first introduced, addressing key parameters such as clamping force, friction coefficient, and slip resistance. Subsequently, an extensive numerical investigation is carried out using refined finite-element models, i.e., considering multiple geometric configurations and loading conditions. The local behaviour of the connection is hence assessed in terms of stiffness, strength, and slip capacity. Results show that—with proper sizing—plastic deformation localises in the beam while the joint remains elastic and slip is limited, confirming the conservativeness of the approach. The joints behave as nominally pinned in terms of resistance while showing moderate stiffness. Derived findings highlight the feasibility of adopting friction-based, non-invasive connections as a viable alternative for circular steel construction, contributing to the ongoing transition toward more sustainable structural systems. Full article

This study investigates the mechanical performance and non-destructive evaluation of oak (Quercus spp.) glued-laminated timber (GLT), manufactured from predominantly low-quality lamellae (five layers of 20 mm thick lamellae). The other GLT type tested was a veneer-reinforced configuration (4 mm thick veneers in the first and third layers on both sides of the reinforced GLT, combined with five layers of 15 mm thick low-quality lamellae). 18 basic GLT and 5 reinforced GLT beams, with nominal lengths of 2000 mm were produced using polyurethane adhesive and tested under four-point bending, according to EN 408. Their average densities and standard deviations were 759 ± 23 kg/m³ for basic GLT and 781 ± 6 kg/m³ for reinforced GLT. The reinforced GLT exhibited a substantially higher modulus of rupture (70.9 ± 4.6 MPa) compared to the basic GLT (37.6 ± 6.2 MPa), representing an increase of 89%. The bending modulus of elasticity also increased by 17.2% (12.0 ± 0.6 vs. 10.3 ± 0.6 GPa). The 11.4–12.0 GPa dynamic modulus of elasticity values were consistent with static results. Strain increased by +66.7% from 0.15% to 0.25% with reinforcement. Despite similar densities, adhesive-related failures governed performance in basic GLT. Veneer reinforcement significantly improved their strength, stiffness, and structural reliability. Full article

In this paper, we investigated the capability of Yukawa gravity to explain the Schwarzschild precession of S-stars as a probe for General Relativity and to map the allowed parameter space of a potential fifth force. We simulated the S38 star orbit in a Yukawa gravity model and fitted it into the observed astronomical data of the S38 star using the Markov Chain Monte Carlo method in order to constrain the parameters (strength $\delta$ and range $\lambda$) of the Yukawa interaction. Comparing these findings with previous results for the S2 star reveals that the best-fit values for $\lambda$ are remarkably close, while the magnitudes of $\delta$ are slightly smaller for S38. These results map the joint statistical boundaries of a fifth force at the Galactic Center. Although the General Relativity limit ($\delta =0$) falls well within the reported $1\sigma$ uncertainties, rendering potential nominal deviations statistically insignificant, the interaction range $\lambda$ exhibits a highly stable spatial scale across different stellar orbits. This cross-consistency between independent datasets, with stable clusters near 360, 1900, and 7000 AU, keeps a viable physical window open for a fifth force. This agreement demonstrates that the interaction scale is robust against individual single-orbit systematic errors, ensuring that this parameter domain remains a prime target for future high-precision astrometric observations. Ultimately, analyzing S-star kinematics within Yukawa gravity provides a powerful independent tool for testing General Relativity and bounding non-standard gravitational effects at the Galactic Center. Full article

As piston rods for excavator boom hydraulic cylinders shift from integral forging to welded assemblies of separately manufactured rod bodies and rod heads, joint reliability becomes critical to load-bearing performance. In this study, 60 mm diameter quenched-and-tempered/as-rolled 1045 steel joints were fabricated by continuous-drive friction welding under three coupled secondary-friction pressure–time conditions. Joints made with two quenched-and-tempered base metals were compared under the same high-pressure/short-time condition. Optical microscopy, electron backscatter diffraction, microhardness testing, tensile testing, and scanning electron microscopy were used to characterize microstructure and failure behavior. Fine, multi-oriented reconstructed microstructures formed in all weld zones, while a hardness valley developed in the heat-affected zone on the quenched-and-tempered side. As the machine-displayed secondary-friction pressure increased from 1.43 to 2.14 MPa, the actual secondary-friction time decreased from 57.3 to 37.5 s. Under the corresponding high-pressure/short-time condition, heat-affected-zone softening was slightly mitigated and tensile strength increased from 743.37 to 755.78 MPa. Different elongations were observed between the two joint types. All specimens fractured in the softened heat-affected zone on the quenched-and-tempered side and exhibited dimple-dominated fracture surfaces. Under the present tensile-testing conditions, the weld zone was not the fracture-controlling region. Full article