Search Results (1,164)

Despite the advantages of powder bed fusion–laser beam (PBF-LB), Ti6Al4V components often exhibit high yield strength but limited ductility, which restricts their use in critical structural applications. This study aims to identify the most effective heat treatment to optimize the strength–ductility balance in Ti6Al4V parts produced by PBF-LB and to establish direct correlations between microstructural states, mechanical properties and corrosion behavior. Two distinct post-processing heat treatments were applied, specifically, the first at 500 °C for 5 h and the second at 800 °C for 2 h, both followed by air cooling. The microstructure was characterized using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Mechanical behavior was assessed through Vickers microhardness testing and tensile testing, while corrosion resistance was evaluated via electrochemical measurements. Residual stress profiles were determined using the hole-drilling strain gauge method, in both as-built and heat-treated conditions. The as-built samples displayed a fully martensitic α′ structure with columnar grains aligned parallel to the laser scanning direction, resulting from rapid solidification. Heat treatment at 500 °C caused only partial decomposition of acicular martensite into substructures without altering its acicular morphology, leading to a strengthening effect alongside a reduction in ductility. Conversely, heat treatment at 800 °C offered the most balanced combination of strength and ductility among the conditions studied, albeit with a moderate reduction in corrosion resistance. Full article

This work presents an automated vision-based measurement system designed for the precise dimensional characterization of high-aspect-ratio micro-holes, achieving a relative dimensional error of less than 1% for characterizing high-aspect-ratio damage geometries. The system integrates coaxial microscopic imaging with a precision motorized scanning stage. To ensure high-fidelity measurements in early-stage warning applications, depth is determined using a focus variation method driven by a robust data fusion strategy. By capturing a sequence of images along the Z-axis, the focal planes of the defect’s surface orifice and internal base are automatically identified using a data fusion algorithm based on a consensus evaluation of three parallel sharpness metrics (Tenengrad, Laplacian, and Brenner variants). The Z-axis scanning module, featuring encoder feedback and bi-directional compensation, achieves a repeated positioning error of ±0.5 µm. For lateral damage assessment, the system’s high magnification provides an effective sampling resolution of 0.09 µm. The equivalent diameter of the focused orifice image is calculated through a robust pipeline involving adaptive thresholding, morphological filtering, and sub-pixel ellipse fitting, which serves as a highly sensitive indicator for early-stage structural deformation. The entire process can be completed within five minutes, demonstrating a rapid, highly accurate, and localized optical inspection solution that generates high-precision dimensional data crucial for quality inspection in aerospace and precision engineering. Full article

This work presents a comprehensive review of axion physics through the generative lens of a novel theoretical framework: Real-Now-Front (RNF) cosmology. Moving beyond the standard treatment of the axion as a fundamental particle in a pre-existing spacetime, we systematically reinterpret it as a specific collective excitation, a “twist” mode, arising from the alignment dynamics of the more fundamental Chronon field, from which spacetime itself emerges. Within this paradigm, the axion’s mass, its couplings to photons and matter, and the symmetry-breaking scale $f_a$ are not independent parameters but are derived from the microscopic stiffness and correlation length of the Chronon field, governed by the Temporal Coherence Principle. We re-examine the entire axion landscape, including benchmark models (KSVZ, DFSZ, ALPs) and the full spectrum of experimental constraints from terrestrial haloscopes, helioscopes, and astrophysical environments, translating them into probes of Chronon alignment dynamics. Furthermore,this generative framework yields unique, testable predictions, such as emergent bimetric effects and primordial black hole seeds from closed domain walls, providing independent avenues for falsification. By synthesizing established knowledge with this foundational new perspective, the review aims to establish a unified basis for the next generation of axion searches, positioning them as direct tests of the microscopic architecture of emergent spacetime, leveraginga multi-decade, multi-messenger observational campaign. Full article

This work deals with questions of enhancing the scalability and security of linear chain Bitcoin by introducing a D-BTC (Domino Bitcoin) protocol, supported by a simply connected two-dimensional structure. The paper seeks to answer the question: can the linear topology of Bitcoin be replaced by a richer geometric structure that simultaneously (i) enlarges the number of valid positions where parallel mining can occur, and (ii) strengthens the asymptotic decay of the double-spend reversal probability? In the D-BTC protocol, the blocks, called B-dominoes (Bitcoin dominoes) are organized as a finite connected region subset of ${\mathbb{Z}}^2$ without holes, also called a lattice. Simple connectivity plays a central role in D-BTC and to mine a (valid) B-domino, a miner has to compute four PoW (Proof of Work), corresponding to cardinal directions, allowing them to add it to the frontier of the lattice, under the constraint that the new lattice is simply connected. We introduce a new deterministic consensus based on maximization of the lattice surface. By using a simple version of the isoperimetric inequality, we see that the frontier size grows as $\Omega \left(\sqrt{n}\right)$, where n is the lattice size. Following the Nakamoto’s heuristic, and under the honest majority assumption, a double-spending attack is successful with probability decaying exponentially in $k^2$, where k is the minimum Manhattan distance of the concerned B-domino from the lattice frontier. Additionally, we set up implementations and experiments to demonstrate the practical viability of the protocol with authentic gossip-based message propagation and complete Merkle tree verification. Full article

This study examines a series of organic–inorganic crystal structures containing the periodate anion (IO₄⁻) to clarify the nature of the anion–anion interactions that are frequently referred to as halogen bonds. Our analysis demonstrates that, in many cases, IO₄⁻ does not develop an electrophilic σ-hole on the iodine center, even in the presence of organic cations, and therefore cannot reliably function as a halogen-bond donor. In its discrete (0D) form, the anion retains its character as a Lewis base. In crystal structures where extended architectures are observed—such as one-dimensional chains, two-dimensional layers, or three-dimensional cage-like assemblies—these structures arise predominantly from strong coulombic interactions with surrounding cations, as the interaction between the anions is intrinsically repulsive in the gas phase. Hydrogen bonding, together with other noncovalent interactions including chalcogen, tetrel, and/or pnictogen bonding, plays a dominant role in stabilizing the anionic arrangements and governing their structural organization. Full article

To address challenges such as complex background interference, limited long-range modeling capabilities of CNNs, and poor generalization in steel-concrete cross-material scenarios, this study proposes an enhanced detection framework. This framework integrates a TAPFormer with morphological reasoning rules. The method utilizes TAPFormer as the backbone network. It captures global topological features of cracks through a Task-Aware Query mechanism. This approach compensates for the deficiencies of traditional convolutional operators in modeling the continuity of thin and long cracks. Furthermore, a mask reasoning module based on geometric priors is developed to handle unstructured interferences, such as marker pen marks, welds, and concrete holes. This module defines logical criteria, including edge curvature consistency, axial aspect ratios, and endpoint extension directions. These criteria are used to perform topological repair and filter false positives in the initial segmentation masks. A hybrid dataset containing 4500 cross-material damage images was used for validation. The results show that the proposed method achieves a mean IoU of 86.72% and an F1-score of 90.36%. Notably, the method filters over 91.0% of false positives caused by manual marker pen marks in interference-rich scenarios. Compared to mainstream state-of-the-art models, the IoU improves by at least 5.48%. The results show that the proposed framework improves the robustness and logical self-consistency of crack identification in complex engineering environments. Full article

To improve the directional propagation of blasting-induced cracks in sandstone and reduce over-excavation, under-excavation, and surrounding-rock damage caused by conventional circular blastholes, circular and V-shaped slotted blasthole models were established in LS-DYNA. The ALE fluid–solid coupling algorithm was adopted to investigate the effects of slot angle on the effective stress field, crack propagation pattern, and crack control index. The stress field theory at the tip of the V-shaped slot was further used to explain the directional cracking mechanism. On this basis, a two-hole V-slotted blasting model is established to analyze the influence of hole spacing on crack penetration. The results show that the V-shaped slot can form an obvious stress concentration at the tip, which changes the crack from approximately isotropic extension to directional extension along the direction of the slots. Under the present two-dimensional homogeneous sandstone model with simultaneous initiation, the 60° slot angle corresponds to the highest peak effective stress and crack control index. For the synchronized two-hole model, when the hole spacing is 70–90 cm, namely the ratio of hole spacing to blasthole diameter is approximately 14–18, the inter-hole crack penetration effect is better, and the proportion of effective cracks along the slot direction is about 80%. These results provide baseline numerical references for sandstone-controlled blasting parameter design under the modeling conditions of this study. Full article

Hydrogen oxy-combustion with high CO₂ dilution is a key component of supercritical CO₂ (sCO₂) power cycles, such as the Allam cycle, enabling high-efficiency, near-zero-emission power generation with integrated carbon capture. However, combustion behavior under high-CO₂ conditions remains insufficiently characterized, particularly with respect to mixing and flame stability. In this study, hydrogen combustion in an O₂–CO₂ environment was investigated experimentally and numerically using a custom-designed multi-hole burner. The experiments were conducted in a 1-bar combustion chamber, while the inlet pressures of the reactants were varied between 10 and 50 bar to isolate the effect of injection conditions. Numerical simulations were performed to analyze flow, mixing, and flame structure. The results show that increasing inlet pressure leads to a more compact and localized flame, despite reduced velocity levels in the combustor due to increased reactant density. Higher inlet pressures result in increased peak temperatures but lower mean combustor temperatures, indicating more intense but spatially confined heat release. The flow field remains structurally similar across cases, while reduced radial spreading and longer residence times influence combustion behavior. Stable flame operation was achieved over a wide range of conditions, demonstrating the feasibility of hydrogen oxy-combustion under high CO₂ dilution. The combined experimental and numerical analysis provides insight into the interplay between injection conditions, mixing, and reaction rates in highly CO₂-diluted hydrogen combustion. The obtained results support the development of compact and stable direct-fired combustors for next-generation supercritical CO₂ power cycles and hydrogen-based low-emission energy systems. Full article

Direction-of-arrival (DOA) estimation of cyclostationary signals is an important problem in array signal processing, especially in sensor-limited and underdetermined scenarios. Sparse arrays and cyclostationary statistics can improve virtual degrees of freedom and target selectivity, but incomplete difference coarray information caused by missing lags may degrade virtual covariance reconstruction and reduce the reliability of DOA estimation in closely spaced, coherent, and interference-contaminated environments. To address this issue, this paper proposes a cyclostationary DOA estimation method based on an augmented extended coprime array (AECA), SVT-based hole recovery, and weighted atomic norm minimization (ANM). The proposed method first constructs the cyclic correlation matrix at the target cyclic frequency and maps it into the AECA-based virtual coarray domain. Redundant lag observations are then aggregated, and an iterative hole recovery procedure is applied to obtain an initial structured virtual covariance matrix. On this basis, a weighted ANM-based covariance refinement model is introduced, where directly observed lags and SVT-recovered hole entries are assigned different confidence levels. The final DOA estimates are obtained using MUSIC on the refined virtual covariance matrix. Simulation results under the considered underdetermined, closely spaced, coherent-source, and interference-contaminated scenarios show that the proposed method achieves lower RMSE and clearer spectral responses than the selected baseline methods. Additional ablation, parameter sensitivity, cyclic frequency mismatch, non-Gaussian noise, and runtime analyses further clarify the contribution, robustness range, and computational cost of the proposed framework. Full article

Stable three-dimensional hand landmark reconstruction using low-cost RGB-D sensors is important for human–computer interaction, robot teleoperation, and vision-based motion analysis. RGB-based hand landmark detectors provide stable semantic 2D landmarks, but their depth output is not a metric measurement in the physical camera coordinate system. Stereo cameras can provide metric depth, but direct landmark-level back-projection is sensitive to invalid pixels, local depth holes, boundary noise, and partial occlusion. To address these problems, this paper presents a lightweight RGB-D sensing front-end that combines MediaPipe semantic hand landmarks with ZED2 stereo depth. The proposed pipeline detects 21 semantic hand landmarks in the RGB image, obtains landmark-level metric depth from the aligned ZED2 depth map using local median sampling, reconstructs 3D landmarks by camera back-projection, and further applies exponential moving average filtering and a bone-length consistency constraint. Experiments were conducted on a self-collected SVO dataset containing 13 hand actions and 26 recorded sequences, and an additional checkerboard-based reference-distance validation was performed to evaluate the metric depth sampling and 3D back-projection component. Compared with single-pixel sampling, the $5\times 5$ local median strategy slightly increased the valid-depth ratio from 0.9731 to 0.9738 and reduced the temporal smoothness metric from 1.7163 mm to 1.6902 mm. To further justify the temporal filtering choice, an additional comparison with the 1 Euro Filter was conducted using the reconstructed win5 trajectories. The 1 Euro Filter produced stronger smoothing, reducing the temporal smoothness metric to 0.196 mm, but also reduced the path-length ratio to 0.484, indicating substantial motion attenuation. EMA0.7 was therefore retained as a more balanced setting, reducing the temporal smoothness metric to 0.826 mm while maintaining a path-length ratio of 0.803. The BL0.5 bone-length constraint reduced the bone-length standard deviation from 2.0727 mm to 1.1995 mm with limited trajectory modification. The final configuration provides a practical low-cost RGB-D front-end for stable 3D hand landmark reconstruction under controlled indoor conditions. Full article

This study investigates anion–anion assemblies involving perhalate anions, XO₄⁻ (X = Cl, Br, I), in crystal structures retrieved from the Cambridge Structural Database to clarify the nature of the intermolecular interactions frequently interpreted as halogen bonds. Molecular electrostatic surface potential analysis demonstrates that isolated XO₄⁻ anions do not exhibit electrophilic σ-holes on the halogen or oxygen atoms along the O–X bond extensions, thereby precluding their role as conventional halogen- or chalcogen-bond donors. Gas-phase calculations further show that direct anion–anion assemblies are intrinsically repulsive and unstable in isolation. However, when dielectric screening is introduced through implicit solvation models, metastable dimeric and oligomeric arrangements consistent with crystallographic motifs become accessible. Complementary QTAIM, IGMH, NBO, and SAPT analyses show that the observed X···O and O···O contacts are weak, environment-assisted anti-electrostatic interactions arising from a combination of dielectric screening, polarization, dispersion, and donor–acceptor contributions. The results demonstrate that the structural organization of perhalate anions in crystalline environments is governed primarily by collective environmental and crystal-packing effects rather than intrinsic attractive interactions between isolated anions. Full article

The influence of internal substrate geometry on thermal stability during Laser Directed Energy Deposition Repair (DED-R) remains insufficiently understood, particularly for components containing internal cavities and cooling channels. This study investigates the thermal response of solid (Alpha), blind-hole (Bravo), and channeled (Charlie) AISI 316L substrates using dual infrared thermography, transient finite element modeling, and Short-Time Fourier Transform (STFT)-frequency-domain analysis. Despite substantial differences in internal heat-dissipation pathways, all substrate configurations exhibited similar peak surface temperatures (~1700–2100 °C), indicating that conventional temperature monitoring alone is insufficient to distinguish geometry-dependent melt-pool behavior. To address this limitation, a Spectral Entropy Index (SEI) derived from STFT analysis was proposed to quantify thermal stability. The channeled substrate exhibited the lowest entropy value (H_s = 0.172), compared with the solid (H_s = 0.181) and blind-hole (H_s = 0.183) configurations, indicating a more ordered and predictable thermal response. Furthermore, distinct variations in the spectral stability shadow revealed geometry-dependent oscillatory behavior that was not observable from thermal histories. Finite element simulations showed good agreement with experimental measurements in conduction-dominated regions (RMSE ≈ 46 °C), whereas deviations were observed within the melt-pool region (~250–310 °C), highlighting the increasing influence of fluid-flow phenomena not captured by the conduction-based model. The results demonstrate that internal substrate architecture primarily influences melt-pool stability through frequency-domain thermodynamics rather than significant changes in peak temperature. The proposed STFT method provides a quantitative approach for monitoring thermal stability and assessing the feasibility of L-DED repair over complex internal geometries. Full article

Accurate acoustic emission (AE) source localization in complex structures remains challenging due to non-straight wave propagation paths and the difficulty of obtaining reliable wave velocity models. To address these issues, this study proposes a velocity-free AE source localization method based on an any-angle pathfinding algorithm. The method integrates the Anya algorithm to estimate geometrically optimal propagation paths and a velocity-free objective function formulated under a weak anisotropy assumption. By avoiding the directional limitations of conventional grid-based pathfinding, the proposed approach provides more accurate distance estimates between potential sources and sensors without requiring prior velocity information. The effectiveness of the method was validated through an AE pulse experiment conducted on a granite specimen containing multiple cylindrical holes. The results demonstrate that the average location error of the proposed method is 19.02 mm, which is less than 38.14 mm of the traditional method and 22.90 mm of the velocity-free method using a grid-based search algorithm. Therefore, the proposed framework is applicable to two-dimensional structures or extruded three-dimensional structures, offering a feasible approach for AE source localization in complex environments. Full article

The drilling and blasting method is the mainstream approach for excavating deep-buried tunnels. Nevertheless, a complex static–dynamic coupling environment is formed by the directional high in situ stress and the widely distributed weakly intercalated layers in rock masses, which frequently result in uncontrolled propagation of blasting-induced cracks. In this paper, deep-buried tunnels with weakly intercalated layers are selected as the research subject, and a numerical model for simulating blasting-induced crack evolution is developed using the material point method. After the model’s reliability is verified through single-hole blasting tests, the effects of in situ stress and weakly intercalated layers on the evolution of blasting-induced cracks are investigated using a typical case. The results demonstrate that geostress direction significantly guides and restrains crack propagation, with cracks extending preferentially along the maximum principal stress but being limited in the perpendicular direction. Compared with the zero-confining-pressure condition, the maximum crack length is reduced by more than 80% when an equal biaxial confining pressure of 20 MPa is applied. Weak interlayers attenuate the transmission of blasting energy, and crack propagation at their ends is significantly amplified when the principal in situ stress aligns with the interlayer orientation, leading to over-excavation. In addition, a targeted optimization strategy for blasting parameters was proposed that reduced the particle vibration velocity at the arch shoulder by 49%. Full article

This study examines the effects of jet Reynolds number (Re) and jet hole diameter (d) on flow and heat transfer in the leading-edge full-impingement cooling channel of a gas turbine nozzle guide vanes (NGV). Experiments via transient liquid crystal and numerical simulations were conducted. Results reveal that the peak Nusselt number (Nu) initially increases and then reaches a fixed value from root to tip in the spanwise direction. The area-averaged Nu presents the descending trend of the shower-head surface, pressure surface, and suction surface. In addition, the bleeding from film holes causes significant local flow acceleration and Turbulence Kinetic Energy (TKE) enhancement of 10.69%, resulting in local heat transfer elevation. The heat transfer enhancement region on both pressure and suction surfaces is inclined towards the shower-head at a 5% span region. Increasing the jet hole diameter (d) results in a decrease in both averaged Nu and TKE on the target surface. Simultaneously, the Nu gradient increases. When d = 1.6 mm, there is a recirculation zone near the hub on the suction surface and a strong crossflow near the hub on the pressure surface. The jet flow on the target surface is bending towards the shower-head. When d = 0.8 mm, the overall heat transfer is highest. However, considering heat transfer uniformity, a jet hole diameter of d = 1.2 mm offers better application. Full article