Search Results (926)

Background: Favorable attitudes toward regular leisure-time physical activity may not always translate into intention if adolescents feel ambivalent about the behavior. This study tested whether felt ambivalence weakens the prospective attitude–intention association and the indirect effect of attitude on later behavior through intention. Methods: Chinese adolescents (N = 1714; Grades 7–12; mean age = 15.0 years) completed a three-wave survey at approximately two-week intervals. Wave 1 assessed attitudes toward regular leisure-time moderate-to-vigorous physical activity, felt ambivalence, and physical activity habit; Wave 2 assessed intention; and Wave 3 assessed leisure-time physical activity. Moderated mediation was tested in a structural equation model adjusting for habit, gender, and grade. Results: More favorable baseline attitudes predicted stronger intention two weeks later, and intention predicted greater self-reported leisure-time physical activity at follow-up. Felt ambivalence significantly moderated the attitude–intention pathway such that the association was weaker at higher levels of ambivalence. The conditional indirect effect of attitude on later leisure-time physical activity through intention was significant at low, mean, and high ambivalence, but decreased as ambivalence increased. Conclusions: Favorable attitudes may be insufficient when adolescents remain conflicted about physical activity. The present study provides prospective support for a theoretically relevant moderation pattern in which felt ambivalence weakens the attitude–intention pathway, but it does not establish ambivalence as a key explanatory mechanism. Full article

Asymptotic solutions that can describe the incidence and reflection of waves have been used in various situations. They can also be applied to inverse problems and provide useful information in situations where a precise evaluation is required. However, the construction of standard asymptotic solutions requires higher regularity with respect to the boundaries of the observation target. This article proposes a “modified asymptotic solution” to overcome this weakness. To demonstrate its usefulness, it is applied to the analysis of the indicator function in the enclosure method for the inverse problem of the wave equation in a mixed-type medium. Full article

Drifting fish aggregating devices (DFADs) are central to tropical tuna purse-seine fisheries, yet their hydrodynamic performance under realistic seas has not been adequately addressed, particularly for emerging eco-friendly designs. A three-dimensional framework based on computational fluid dynamics is developed to assess the motion response and mooring loads of full-scale DFADs comprising raft buoys, biodegradable cotton rope, and iron sinkers, using four buoy layouts (Models A to D). Unsteady Reynolds-averaged Navier–Stokes (URANS) simulations are performed with a realizable k–ε closure, volume of fluid (VOF) free-surface capturing, the Euler overlay method, dynamic overset meshes, and catenary mooring coupling. Regular waves representative of operational conditions (T = 1.40 to 2.40 s, H = 0.10 to 0.40 m) are imposed via a VOF wave-forcing technique, and mesh/time-step sensitivity analyses demonstrate the accurate reproduction of the first-order wave elevation (error < 0.8%). Surge drift per cycle and heave response amplitude operators, with the relative mooring force, are evaluated as functions of the relative wavelength (λ/L_a) and wave steepness (H/λ). The results reveal that the buoy layout exerts first-order control on DFAD dynamics, whereas short, steep waves dominate motion and line loads. The intermediate end-point sinker mass achieves a favorable balance between motion suppression and mooring load control, whereas distributing a fixed total sinker mass along the rope reduces heave response and mooring force by improving the tension redistribution and overall stability. Across all sea states, Models A and D reduced motion envelopes and mooring forces, indicating their suitability as robust, low-impact configurations. The proposed framework and design recommendations provide quantitative guidance for optimizing eco-DFAD geometry and deployment strategies, supporting safer and more sustainable DFAD-based tuna fisheries. Full article

The classical Neumann–Kelvin (NK) theory of potential flow around a free-surface-piercing ship that steadily advances in calm water or through regular waves is considered. Specifically, this study presents an elementary ‘no-equation interpretation’ of the rigid-waterplane linear flow model and the related modification of the NK theory recently presented by the authors and complements the detailed mathematical analysis given in that earlier study. Specifically, the NN (Neumann–Noblesse) integral equation obtained in that previous study by applying Green’s fundamental identity to an alternative linear flow model called the rigid-waterplane flow model, in which an open free-surface-piercing ship hull is closed by a rigid waterplane slightly submerged under the free surface, is interpreted in light of Saint-Venant’s principle. Briefly, the present study argues that the NK integral equation obtained in the classical NK theory of potential flow around a ship contains a singularity at the ship waterline and that this singularity is removed—in the spirit of the classical Saint-Venant principle—in the rigid-waterplane flow model and the related weakly-singular NN integral equation, which can then be viewed as a ‘regularization’ of the NK integral equation. This study also presents variants of the NN integral equation in which a function defined in terms of the ship hull surface geometry by an integral over the ship waterplane or an integral around the ship waterline is expressed as equivalent integrals over the ship hull surface. Like the NN integral equation given previously, the equivalent variants of the weakly-singular NN integral equation obtained in this study do not involve a waterline integral and hold for a ship that steadily advances in calm water or through regular waves, as well as for an offshore structure or a moored ship in regular waves. Full article

The Korteweg–de Vries (KdV) equation is a foundational model in geophysical fluid dynamics (GFD), governing the propagation of long internal and surface gravity waves in stratified and shallow ocean environments where the interplay between nonlinear steepening and frequency-dependent dispersion gives rise to solitons. Although the analytical tractability of the KdV equation through inverse scattering is well established, systematic numerical exploration of multi-soliton interactions remains valuable for benchmarking solvers, probing conservation properties under varied oceanic initial conditions, and building intuition for more complex ocean wave phenomena. This article presents sangkuriang, an open-source Python library that solves the KdV equation using Fourier pseudo-spectral spatial discretization and adaptive eighth-order Runge–Kutta time integration. The implementation leverages just-in-time (JIT) compilation to achieve research-grade computational efficiency on standard hardware, making it readily accessible for coastal and ocean engineering applications, including idealized modeling of internal solitary waves on continental shelves, rapid parameter studies for solitary wave propagation in stratified basins, and pedagogical investigations of nonlinear dispersive wave dynamics. The solver is validated through four progressively complex idealized scenarios motivated by oceanic wave dynamics: isolated soliton propagation, symmetric interactions, overtaking collisions, and three-body interactions. High-fidelity conservation of mass, momentum, and energy is demonstrated, with relative errors remaining below $\mathcal{O}\left({10}^{-4}\right)$ across all test cases. Measured soliton velocities align with theoretical predictions within 5%, confirming the capture of the amplitude-dependent dispersion characteristic of oceanic solitary waves. Complementary diagnostics, including spectral entropy and recurrence quantification analysis (RQA), verify that the numerical solutions preserve the regular phase-space structure characteristic of integrable Hamiltonian systems. These results establish sangkuriang as a robust, lightweight platform for reproducible numerical investigation of idealized nonlinear dispersive wave dynamics relevant to coastal and ocean engineering applications. Full article

When two floating bodies are engaged in side-by-side operations, gap resonance is prone to occur. This phenomenon leads to violent, large-amplitude fluid motions inside the gap, posing a serious threat to operational safety. To address this issue, the present study establishes a numerical wave tank based on a two-way coupled potential–viscous flow method. In the vicinity of the floating bodies, viscous flow is solved to capture nonlinear effects; in the far field, a potential flow solver is employed to simulate wave propagation. Information exchange between the two domains is achieved through a two-way coupling strategy involving coupling interfaces and relaxation zones. Then, the numerical method is validated by simulating the gap wave elevation and the sway motion of a floating body under regular waves, with computed results compared against experimental data. Subsequently, to reveal the distinct roles of fixed and moving bodies in modulating gap resonance behavior, the hydrodynamic interactions between two identical floating bodies in regular waves are investigated under two representative configurations, one in which both bodies remain fully fixed, and another in which the upstream body is held fixed while the downstream body is allowed coupled motion in three degrees of freedom. The results demonstrate that the multi-degree-of-freedom (DOF) motion of the downstream floating body has a significant effect on the behavior of the resonance frequency and amplitude of the gap resonance. Full article

Following successful applications in inland water bodies, floating photovoltaics (FPV) developers are now targeting offshore sites. This advancement requires numerical tools that can quantify the hydrodynamic performance of large-scale FPV farms. The existing wave-diffraction solver DIFFRAC was extended to simulate the response of a large number of interconnected floating objects on a supercomputer. The applicability is demonstrated by simulating a 2 MWp offshore solar farm, consisting of 3660 FPV modules moored inside a protective ring of 32 interconnected floating breakwaters (FBWs). The FPV motions and loads on FPV connectors in regular and irregular waves are compared to a reference case without FBW protection. Results show an average reduction in axial FPV connector loads in the setup with FBW ring, but local load enhancements occur due to dynamic amplifications of horizontal FPV module motions. Vertical loads and overturning moments onto FPV connectors are globally reduced by up to 50% in steep irregular seas but are locally enhanced due to standing waves that develop inside the ring. The insights of the hydrodynamic behaviour lead to recommendations for improving the farm configuration to further reduce fatigue and survival loads onto FPV modules and connectors. Full article

This paper presents a computational study of wave–bathymetry and wave–structure interaction problems using advanced numerical techniques based on high-fidelity, two-phase Navier–Stokes (TpNS) flow and reduced-order, fully nonlinear potential flow models. For high-fidelity simulations, the TpNS equations are discretized using the finite-element method, with free-surface evolution captured through a hybrid level-set (LS) and volume-of-fluid (VOF) formulation. A monolithic, phase-conservative LS equation is introduced to mitigate mass loss and interface smearing, combined with a semi-implicit projection scheme. Hydrodynamic forces are resolved using a high-order, phase-resolving cut finite-element method (CutFEM), which enables the representation of complex solid geometries within a fixed background mesh. An equivalent polynomial of Heaviside and Dirac distributions ensures accurate evaluation of surface and volume integrals. Hence, no explicit generation of cut cell meshes, adaptive quadrature, or local refinement is required. For reduced-order modeling, a fast regularized boundary integral method (RBIM) is employed to solve the fully nonlinear potential flow. Singular and near-singular integrals are treated using a subtract-and-addition technique based on auxiliary functions derived from Stokes’ theorem, allowing direct application of high-order quadrature without conventional boundary element discretization. An arbitrary Lagrangian–Eulerian (ALE) formulation is adopted to enforce free-surface boundary conditions while avoiding excessive mesh distortion. The proposed approaches are applied to investigate highly nonlinear wave transformation over complex bathymetry and wave-induced dynamics of floating structures, including eddy-making damping effects. Numerical results are validated against experimental measurements. These two modeling approaches represent complementary levels of physical fidelity and computational efficiency, and their systematic comparison clarifies the trade-offs between computational accuracy, efficiency, and cost for practical marine problems. Full article

Unlike traditional marine floating platforms, floating offshore wind turbines (FOWTs) are subjected to larger overturning moments. This study presents a novel floating offshore wind turbine concept—termed the Multi-Body Anti-Pitching Floating Wind Turbine (MAFWT)—designed to mitigate excessive pitching motion of semi-submersible FOWTs. The MAFWT integrates three Wave-star-like appendages arranged in the UMaine VolturnUS-S platform. A fully coupled dynamic model is developed within the FAST-to-AQWA (F2A) simulation framework. Parametric time- and frequency-domain analyses are subsequently conducted under both regular wave/steady wind and irregular wave/turbulent wind conditions to investigate the influence of stiffness parameter K and damping parameter B on system dynamics. Results demonstrate that increasing stiffness enhances the restoring moment, thereby reducing the static pitching offset and overall dynamic response (with the maximum and average values decreasing by 27.6% and 31.9%, respectively). However, it may amplify low-frequency slow-drift motions (with the maximum and average values of surge increasing by 9.4% and 9.5%, respectively). In contrast, damping primarily dissipates kinetic energy, yielding up to a 25.5% reduction in pitch angular velocity and significantly mitigating power output fluctuations (the standard deviation decreased by 16.4%). Furthermore, increases in the stiffness coefficient and damping coefficient result in respective slight increments of 0.12% and 0.18% in the average power output. This work elucidates the distinct physical mechanisms through which stiffness and damping govern pitch suppression. Full article

We analyze the spectral stability of travelling waves in a $\delta$-regularized dissipative sine-Gordon equation modelling refined long Josephson junction dynamics. Linearization about a wave yields a singularly perturbed fourth-order spectral problem with intrinsic slow–fast spatial structure. Using an Evans-function formulation on a domain of consistent spatial splitting, we establish a local factorization separating slow and fast modes and prove that the $\delta$-induced fast subsystem remains uniformly hyperbolic and does not generate an additional point spectrum near $\lambda =0$. Hence, the local point spectrum coincides with that of the classical dissipative sine-Gordon equation. Numerical computations of the essential spectrum and Evans winding numbers confirm the analysis and show that the higher-order terms enhance high-frequency damping without altering low-frequency spectral stability. Full article

Gait is a sensitive marker of mobility decline and fall risk, motivating unobtrusive sensing methods that can extract spatiotemporal parameters outside specialized gait laboratories. This paper presents a physics-based comparison of two millimeter-wave frequency-modulated continuous-wave (FMCW) radar deployment paradigms using a low-cost, system-on-chip (SoC) 60 GHz Infineon BGT60TR13C radar sensor: (i) a fixed (tripod-mounted) corridor observer and (ii) a shoe-mounted body-centric configuration attached to the medial side of the left shoe. Four healthy adult author-participants performed repeated 30 s corridor trials under five gait styles (regular, slow, fast, simulated festination, and simulated freezing-of-gait), including brief pauses during turns; an empty-corridor recording was acquired to characterize static clutter. Step events were detected using peak-picking on foot-related velocity envelopes with adaptive thresholds, and step count, cadence, step time, and step-time variability were derived. Performance of the fixed and shoe-mounted configurations was quantitatively compared to video ground truth using mean absolute percentage error (MAPE) for step count estimation. Across all gait styles, the shoe-mounted FMCW radar consistently reduced step-count error relative to the fixed corridor-mounted configuration, with the largest gains under irregular patterns (e.g., festination: 37.1% fixed vs. 9.6% shoe-mounted). These findings highlight the advantages of body-centric millimeter-wave radar sensing and support low-cost SoC radar as a pathway toward wearable, privacy-preserving gait monitoring in real-world environments. Full article

Examining the mechanism of two-way interaction between the air turbine and generator is essential for accurately predicting the performance of oscillating water column (OWC) devices. This study developed a fully integrated model for a back-bent duct buoy device, which incorporated the chamber, impulse turbine, permanent magnet synchronous generator, PI controller, and speed control strategies. The models of chamber–turbine and turbine-control systems were validated separately against wave-flume experimental results under regular and irregular wave conditions. In addition, a comparative study of two control strategies based on Best Efficiency Point Tracking was conducted by analysing key performance parameters at each energy conversion. The mechanism of two-way interaction between the turbine and the generator was elucidated. The integrated model demonstrated a great potential in predicting the conversion performance of wave energy to electrical energy under real sea conditions, as well as testing control strategies and algorithms before physical deployment. Full article

Objectives: To strengthen the recognition of juvenile xanthogranuloma (JXG) by analyzing ultrasound findings. Methods: This study retrospectively enrolled these patients with pathologically confirmed JXG from January 2011 to March 2025. The clinical, imaging, pathological features, and prognosis of all included patients were analyzed. All the imaging features were evaluated in consensus by two radiologists. Results: Fourteen patients were included in the study. A total of 78.6% presented with solitary masses. The age of the patients ranged from 2 months to 48 years. Those aged ≤1 year accounted for 64.3% of the sample. The lesions were predominantly located on the head and face, and the skin of most patients was yellowish-orange. The ultrasound manifestations are mostly hypoechoic masses with clear boundaries and regular shapes. Contrast-enhanced ultrasound shows a slight homogeneous enhancement, and on shear wave elastography, it appears to be relatively hard. Conclusions: JXGs are more common in infants or young children and present with yellowish-orange, cutaneous lesions. Ultrasound revealed homogeneous, well-circumscribed, regular hypoechoic nodules. Multimodal imaging may be helpful for preoperative diagnosis. Full article

Cardiovascular disease has become the leading cause of death worldwide, underscoring the urgent need for widespread cardiac monitoring, while the Electrocardiogram (ECG) remains the diagnostic gold standard, the complexity of its acquisition limits its long-term feasibility. In contrast, Photoplethysmography (PPG), ubiquitous in wearable devices, is increasingly adopted due to its accessibility. However, synthesizing ECG from PPG poses an intrinsically ill-posed inverse problem. Existing purely data-driven paradigms often neglect underlying biophysical mechanisms, resulting in a lack of physical constraints and interpretability, which renders them prone to generating non-physiological hallucinations. To address this, we propose PhysDiff-LBM, a novel physics-aware framework that incorporates Lattice Boltzmann hemodynamic constraints into a conditional diffusion model. Employing a dual-stream architecture, our framework captures high-frequency morphological details via a cross-attention-guided diffusion model with region-wise adaptability. Synergistically, we physically regularize the ECG synthesis by leveraging the mesoscopic streaming and collision operators of LBM. By forcing the synthesized waveform gradients to evolve consistently with hemodynamic momentum, this mechanism constrains the model to strictly adhere to the fluid dynamic conservation laws governing pulse wave propagation. Experimental results demonstrate that our method achieves superior signal fidelity and exhibits significant advantages in downstream clinical applications. Full article

For $\mathbb{D}:=\{z\in \mathbb{C}:|z|<1\}$, this paper derives refined conditions for the inclusion of special functions in lemniscate and nephroid domains focusing on solutions to the differential equations of the form $z^n{F}^{″}(z)+a\left(z\right)z^{n-1}{F}^{\prime }\left(z\right)+b\left(z\right)F\left(z\right)+d\left(z\right)=0,n\in \{1,2\},z\in \mathbb{D},$ with normalization $F\left(0\right)=1$, where $a\left(z\right)$, $b\left(z\right)$ and $d\left(z\right)$ are analytic in $\mathbb{D}$. Using advanced techniques from geometric function theory, we generalize and improve existing results, particularly for classes of functions defined by differential equations. Specific applications include generalized Bessel functions, regular Coulomb wave functions, and associated Laguerre polynomials, where we derive improved bounds for their inclusion in lemniscate domains. Additionally, we present open problems, supported by numerical experiments, to guide future research in this direction. Full article