Search Results (726)

Underwater optical images often exhibit severe color distortion, weak texture, and uneven illumination due to light absorption and scattering in water. These issues result in unstable feature detection and inaccurate image registration. To address these challenges, this paper proposes an underwater image stitching method that integrates ORB (Oriented FAST and Rotated BRIEF) feature extraction with a fixed-ratio constraint matching strategy. First, lightweight color and contrast enhancement techniques are employed to restore color balance and improve local texture visibility. Then, ORB descriptors are extracted and matched via a KNN (K-Nearest Neighbors) nearest-neighbor search, and Lowe’s ratio test is applied to eliminate false matches caused by weak texture similarity. Finally, the geometric transformation between image frames is estimated by incorporating robust optimization, ensuring stable homography computation. Experimental results on real underwater datasets show that the proposed method significantly improves stitching continuity and structural consistency, achieving 40–120% improvements in SSIM (Structural Similarity Index) and PSNR (peak signal-to-noise ratio) over conventional Harris–ORB + KNN, SIFT (scale-invariant feature transform) + BF (brute force), SIFT + KNN, and AKAZE (accelerated KAZE) + BF methods while maintaining processing times within one second. These results indicate that the proposed method is well-suited for real-time underwater environment perception and panoramic mapping on low-cost, micro-sized underwater robotic platforms. Full article

Background/Objectives: Optimizing routine neurointerventional workflow and minimizing exposure to ionizing radiation during coil-only endovascular treatment of intracranial aneurysms depend on operator experience, reduced frame rates during both fluoroscopy and digital subtraction angiography (DSA), and the use of advanced angiographic systems. The low-dose protocol implemented in this study used the lowest available fluoroscopy frame rate (3.125 frames per second [fps]) and a nominal acquisition rate of 2 fps (actual = 2.45 fps) for DSA, three-dimensional (3D) rotational angiography, two-dimensional (2D)/3D mapping, and roadmapping. Methods: This retrospective analysis encompassed 245 coil-only procedures performed at a single tertiary center from 2018 to 2024. Data collected for each procedure included dose-area product (DAP), reference air kerma (K_a,r), fluoroscopy time (FT), and the total number of DSA frames. Local diagnostic reference levels (DRLs; 75th percentile [P75]) and typical values (50th percentile [P50]) were determined and descriptively compared with values reported in the literature. Results: The P75 values, representing DRLs, were 22.4 Gy·cm² for DAP (literature range, 123–272.8 Gy·cm²), 268 mGy for K_a,r (1171–4240 mGy), 18 min 56 s for FT, and 285 DSA frames. The P50 values were 13.8 Gy·cm² for DAP (78.7–179.0 Gy·cm²), 196 mGy for K_a,r (801–2804 mGy), 13 min 25 s for FT, and 208 DSA frames. Conclusions: In this single-center cohort, dose metrics for coil-only intracranial aneurysm treatment were within the lower range of published values. Cross-study comparisons are descriptive and require cautious interpretation. The proposed local DRLs may support quality assurance, dose optimization, and patient safety in comparable clinical settings. Further multi-center and multi-operator studies are warranted to evaluate transferability and applicability beyond coil-only procedures. Full article

Underwater images often suffer from luminance attenuation, structural degradation, and color distortion due to light absorption and scattering in water. The variations in illumination and color distribution across different water bodies further increase the uncertainty of these degradations, making traditional enhancement methods that rely on fixed parameters, such as underwater dark channel prior (UDCP) and histogram equalization (HE), unstable in such scenarios. To address these challenges, this paper proposes a multi-operator underwater image enhancement framework with adaptive parameter optimization. To achieve luminance compensation, structural detail enhancement, and color restoration, a collaborative enhancement pipeline was constructed using contrast-limited adaptive histogram equalization (CLAHE) with highlight protection, texture-gated and threshold-constrained unsharp masking (USM), and mild saturation compensation. Building upon this pipeline, an adaptive multi-operator parameter optimization strategy was developed, where a unified scoring function jointly considers feature gains, geometric consistency of feature matches, image quality metrics, and latency constraints to dynamically adjust the CLAHE clip limit, USM gain, and Gaussian scale under varying water conditions. Subjective visual comparisons and quantitative experiments were conducted on several public underwater datasets. Compared with conventional enhancement methods, the proposed approach achieved superior structural clarity and natural color appearance on the EUVP and UIEB datasets, and obtained higher quality metrics on the RUIE dataset (Average Gradient (AG) = 0.5922, Underwater Image Quality Measure (UIQM) = 2.095). On the UVE38K dataset, the proposed adaptive optimization method improved the oriented FAST and rotated BRIEF (ORB) feature counts by 12.5%, inlier matches by 9.3%, and UIQM by 3.9% over the fixed-parameter baseline, while the adjacent-frame matching visualization and stability metrics such as inlier ratio further verified the geometric consistency and temporal stability of the enhanced features. Full article

Top-and-seat angle connections (TSACs) exhibit inherently asymmetric and nonlinear moment–rotation behavior, which can significantly influence the global response of steel frames subjected to combined gravity and lateral loading. In this study, a three-dimensional finite element model of an unstiffened TSAC is developed and validated against experimental moment–rotation data from the literature under monotonic loading conditions. The validated model is then used to investigate the influence of key geometric parameters, including top angle thickness, bolt diameter, and beam depth, on the connection’s moment–rotation response in both positive and negative bending directions. Subsequently, the monotonic connection behavior is incorporated into nonlinear static analyses of steel portal frames to examine the effects of asymmetric connection response and moment reversal on frame-level stiffness degradation and capacity. A practical SAP2000 modeling workflow is proposed in which the finite element-derived monotonic moment–rotation curves are implemented using zero-length rotational link elements, allowing combined consideration of material, geometric, and connection nonlinearities at the structural level. The comparisons between Abaqus and SAP2000 results demonstrate consistent frame-level responses when identical monotonic connection characteristics are employed, highlighting the ability of the proposed workflow to reproduce detailed finite element predictions at the structural analysis level. The results indicate that increasing top angle thickness, bolt diameter, and beam depth enhances the lateral stiffness and base shear resistance of steel frames. Positive and negative bending directions are defined consistently with the applied gravity-plus-lateral loading sequence. Full article

In Minkowski 3-space, we establish a geometric framework to osculate Type-II ruled surfaces by utilizing the Type-II Bishop frame in $\left({\mathbb{E}}_1^3\right)$. Our analysis extends to higher-order singularities such as butterflies and pyramids, including explicit singularity loci. We also compare Type-II Bishop frames with rotation-minimizing frames using timelike base curves and spacelike normals. With RK4 integration, we develop a robust computational model for Weingarten surfaces and subclasses with constant curvature. The theoretical foundation for Type-II Bishop frames is extended to higher-dimensional Minkowski spaces ${\mathbb{E}}_1^n$ for $n>3$ through generalized Frenet-type equations and curvature functions. We determine exact stability conditions under perturbations of Bishop curvature using advanced singularity theory. The numerical implementations of our methods, including geometric modeling and relativistic geometry, demonstrate their effectiveness in both theoretical and applied contexts. Full article

A lens-coupled high-speed X-ray camera, “Hayaka”, was developed for quick imaging of X-ray absorption fine structure (XAFS) and time-resolved high-speed computed tomography (CT) using synchrotron radiation (SR). This camera is a lens-coupled type, composed of a scintillator, an imaging lens system, and a high-speed visible light sCMOS, capable of imaging with a minimum exposure time of 1 μs and a maximum frame rate of 5000 frames/s (fps). A feasibility study using white and monochromatic SR at the beamline BL07 of the SAGA Light Source showed that fine X-ray images with a spatial resolution of 77 μm can be captured with an exposure time of 10 μs. Furthermore, quick imaging XAFS, combined with high-speed energy scanning of a small Ge double crystal monochromator of the same beamline, enabled spectral image data to be acquired near the Cu K-edge in a minimum of 0.5 s. Additionally, an in coquendo 4DCT (time-resolved 3D observation of cooking processes) observation combined with a high-speed rotation table revealed the boiling process of Japanese somen noodles over 150 s with a time resolution of 0.5 s. Full article

In this study, equidistant ruled surfaces generated by the Darboux vector, which has significant kinematic importance and characterizes the instantaneous rotation of a moving frame, are investigated specifically for the Frenet frame. By establishing a structural relationship between a surface and its equidistant ruled surface, transition formulas are provided for shape operators, Gaussian and mean curvatures, and fundamental forms, revealing that the equidistant surface is a scaled transformation of the original one. The obtained results demonstrate that both surfaces are developable and that the geometric properties of the equidistant ruled surfaces can be expressed dependently on each other. Furthermore, it is shown that the geometric character of the equidistant surface, including the invariance of asymptotic lines and the preservation of umbilical points under constant angle conditions, is determined by the rotational dynamics of the base curve. These findings constitute a theoretical foundation for cases involving the use of Darboux axes of different frames in higher dimensions or the investigation of similar structures in different geometric spaces. The geometric interpretation of this theoretical framework is elucidated through the fundamental properties of the surfaces. Finally, a concrete example is presented, where the symmetry of the central planes of the equidistant ruled surfaces at appropriate points is visualized using Maple 2017 software. Full article

Objectivity is a fundamental requirement for vortex identification, ensuring that vortex structures observed remain invariant under changes in the reference frame. However, although most conventional vortex identification methods, including Liutex, are Galilean invariant, they are not objective. Since the accelerated motion of the observer does not affect the velocity gradient tensor at an instant of time, the rotational motion is only considered for the non-inertial frame. This paper proposes a method to recover the angular velocity of a rotating observer directly from flow field data measured in the rotating frame. The approach exploits the observation that, in an inertial frame, zero-vorticity points tend to dominate the region with an almost identical nonzero vorticity in the observer’s non-inertial coordinate system. By identifying the most frequently occurring vorticity within the domain, the observer’s angular velocity can be uniquely determined, enabling reconstruction of the objective velocity gradient tensor and, consequently, the objective Liutex. The key issue is to find a reference point (RP). The RP should have zero vorticity in the inertial coordinate system, and then the RP has the same angular speed as the observer. The RP can be found by comparing the vorticity of all points in the computational domain and the RP will correspond to the vorticity vector with the highest percentage in the non-inertial coordinate system. The proposed method is validated using DNS data of the boundary layer transition over a flat plate with an artificially imposed angular velocity. The recovered angular velocity agrees closely with the true value within an acceptable margin of error. Furthermore, the objective Liutex reconstructed from the rotating frame data is visually indistinguishable from the original inertial frame Liutex. These results demonstrate that the method provides a simple and accurate way to restore objectivity for Liutex and other vortex identification techniques. The objective Liutex will be equal to the original Liutex in an inertial coordinate system when the observer does not have rotational motion. Full article

To enable automatic extraction of high-precision paths for intelligent orchard operations, a path detection method targeting the fruit-tree dripline is proposed. The method integrates 2D-LiDAR, RTK-GNSS, and an electronic compass, achieving time synchronization, coordinate-frame construction, and extrinsic calibration. Point clouds are rotation-normalized via least-squares trajectory fitting; ground segmentation and statistical filtering suppress noise; segment-wise extremal edge points, together with an α-shape-based concave hull algorithm, fit and generate the dripline path; and inverse rotation restores the result to the orchard-local coordinate frame. Field experiments demonstrated that the method accurately extracts dripline paths in orchard environments; relative to manual measurements, the overall mean absolute error was 0.23 m and the root-mean-square error was 0.30 m. Across different travel speeds, the system exhibited good adaptability and stability, meeting the path-planning requirements of precision orchard operations. Full article

Background: The development of CAD, FEA, and biomechanical models of the shoulder is challenging due to the joint’s complexity. The spatial relationships between bones, muscles and ligaments are difficult to parameterize, both statically and dynamically, because these structures move three-dimensionally and synergistically. Methods: An assembly of the shoulder joint was developed, including parameterisation of the positional relationships among the rotator cuff structures, with particular focus on the bone components: Humerus, Scapula, Clavicle, and Sternum. Discussion: The abundance of existing CAD models of the shoulder makes it difficult to compare numerical results. Variability in reference frames, positioning assumptions and geometric relationships often hinders reproducibility and cross-study interpretation. Conclusions: The presented methodology supports standardised assembly of a shoulder joint model, ensuring consistent assumptions about the relative positioning of the bony structures. This standardization enables more accurate numerical comparisons across studies and improves the reliability of biomechanical research on the shoulder. Full article

Accurate extrinsic calibration between radar and camera sensors is essential for reliable multi-modal perception in robotics and autonomous navigation. Traditional calibration methods often rely on artificial targets such as checkerboards or corner reflectors, which can be impractical in dynamic or large-scale environments. This study presents a fully targetless calibration framework that estimates the rigid spatial transformation between radar and camera coordinate frames by aligning their observed trajectories of a moving object. The proposed method integrates You Only Look Once version 5 (YOLOv5)-based 3D object localization for the camera stream with Density-Based Spatial Clustering of Applications with Noise (DBSCAN) and Random Sample Consensus (RANSAC) filtering for sparse and noisy radar measurements. A passive temporal synchronization technique, based on Root Mean Square Error (RMSE) minimization, corrects timestamp offsets without requiring hardware triggers. Rigid transformation parameters are computed using Kabsch and Umeyama algorithms, ensuring robust alignment even under millimeter-wave (mmWave) radar sparsity and measurement bias. The framework is experimentally validated in an indoor OptiTrack-equipped laboratory using a Skydio 2 drone as the dynamic target. Results demonstrate sub-degree rotational accuracy and decimeter-level translational error (approximately 0.12–0.27 m depending on the metric), with successful generalization to unseen motion trajectories. The findings highlight the method’s applicability for real-world autonomous systems requiring practical, markerless multi-sensor calibration. Full article

Indoor localization remains a challenging task due to the unavailability of reliable global navigation satellite system (GNSS) signals in most indoor environments. One way to overcome this challenge is through visual–inertial odometry (VIO), which enables real-time pose estimation by fusing camera and inertial measurements. However, VIO suffers from performance degradation under high-speed motion and in poorly lit environments. In such scenarios, motion blur, sensor noise, and low temporal resolution reduce the accuracy and robustness of the estimated trajectory. To address these limitations, we propose a motion-aware event-based VIO (MA-EVIO) system that adaptively fuses asynchronous event data, frame-based imagery, and inertial measurements for robust and accurate pose estimation. MA-EVIO employs a hybrid tracking strategy combining sparse feature matching and direct photometric alignment. A key innovation is its motion-aware keyframe selection, which dynamically adjusts tracking parameters based on real-time motion classification and feature quality. This motion awareness also enables adaptive sensor fusion: during fast motion, the system prioritizes event data, while under slow or stable motion, it relies more on RGB frames and feature-based tracking. Experimental results on the DAVIS240c and VECtor benchmarks demonstrate that MA-EVIO outperforms state-of-the-art methods, achieving a lower mean position error (MPE) of 0.19 on DAVIS240c compared to 0.21 (EVI-SAM) and 0.24 (PL-EVIO), and superior performance on VECtor with MPE/mean rotation error (MRE) of 1.19%/1.28 deg/m versus 1.27%/1.42 deg/m (EVI-SAM) and 1.93%/1.56 deg/m (PL-EVIO). These results validate the effectiveness of MA-EVIO in challenging dynamic indoor environments. Full article

Direct ink writing (DIW) deposits viscous, shear-responsive inks at low temperature, enabling hydrogels and cell-laden bioinks for biomedical fabrication. Access to DIW remains limited by the cost of dedicated systems and the complexity of custom motion control. Repurposing fused deposition modeling (FDM) printers lowers these barriers by using accurate motion stages, open firmware, and familiar workflows while preserving build volume. In this study, three DIW actuator designs were implemented on an FDM frame. The first used a gear-and-rail transmission that converted stepper rotation to plunger travel. The second used a direct trapezoidal-screw pusher that increased force but reduced build-space clearance. The third relocated actuation to a remote piston-driven module that decoupled force generation from the printhead. The final architecture integrates the remote piston with partitioned control, where the printer executes motion and a programmable logic controller (PLC) manages extrusion. This arrangement reduces carried mass, preserves build space, and enables precise volumetric dosing with fast response. On a standard desktop frame, the system achieved controllable deposition of an agar/alginate ink using off-the-shelf electronics and modest modifications. This approach promotes sustainable and accessible innovation by repurposing existing FDM printers with open-source hardware and modular components. The resulting platform supports biomimetic biofabrication by combining mechanical efficiency, environmental responsibility, and cost-effective design. Full article

Background: Seated shot put is a core Paralympic event in which lower-limb-impaired athletes generate throwing power primarily through the trunk and upper limbs. The configuration of the throwing frame may influence performance stability and biomechanics. This study aimed to evaluate the effect of two seated orientations on throwing performance, kinematics, and within-subject reliability in a Paralympic F55 athlete using markerless motion capture. Methods: A para-athlete F55-class (age: 37 years; body mass: 93 kg; height: 180 cm; training experience: 20 years) performed 20 throws (10 per seat position: perpendicular and 54.5° rotated). Kinematic data were recorded with an eight-camera, 250 Hz markerless motion capture system. Variables included throw distance, trial time, release angle, wrist acceleration and velocity, and torso angular velocities. Reliability was assessed using intraclass correlation coefficients (ICC), standard error of measurement (SEM), coefficient of variation (CV%), Bland–Altman analysis, and ROC curve discrimination. Results: Throw distance did not differ significantly between positions (p = 0.1086), but trial duration was significantly shorter in the rotated position (p = 0.0114). Most kinematic variables showed poor-to-moderate reliability (ICC = −0.51 to 0.40). Bland–Altman and ROC analyses indicated stable performance measures but higher variability in torso motion, with torso rotation (AUC = 0.72) showing the strongest discriminative ability. Conclusions: Seated orientation minimally affected performance but influenced trunk kinematics and reliability, emphasizing the need for individualized biomechanical assessment in Paralympic shot put training. Full article

In this paper, a stability analysis was conducted of the lateral torsional buckling of the beam of a braced portal frame. The elastic critical resistance (ECR) of the frame was estimated for: (a) a volumetric 3D model (Abaqus/CAE 2017) including the interaction of the component members (beam, columns) in welded corner joints and (b) a simplified 1D bar model (LTBeamN, v 1.0.3) including the parameters of elastic restraint (at support nodes) for the so-called critical member extracted from the structure. In the case of the analysed portal frame, the critical member that determines the lowest elastic critical load of the frame was the transversely bent beam. The following parameters of the elastic restraint of the beam in the support members were taken into account: (1) restraint against warping, (2) restraint against lateral rotation, and (3) restraint against rotation in the bending plane M_y. The paper demonstrates that the use of a simplified model can enable an efficient and, from an engineering point of view, sufficiently accurate estimation of the ECR of the analysed braced portal frame. The underestimation of the calculated elastic critical resistance of the structure in the simplified 1D model (discrepancies of −10.3% to −18.8%) is compensated for by the lack of the need to prepare a relatively complex volumetric 3D model of the frame (Abaqus). Warping restraint, when neglected, reduces ECR by up to 25% for HEA300 columns. Full article