Search Results (2,237)

Since Reynolds’ work, turbulence has been one of the most important subjects in fluid dynamics. Although its complete understanding seems still out of reach, there is at least one established physical basis that turbulence is a phenomenon of a random but non-trivially correlated assembly of vortices. The knowledge of vortices has thus become a prerequisite for promoting our understanding of the nature of turbulence. In this article, we first review the simple, compact vortex solutions to the Navier–Stokes equations for incompressible viscous fluids and a unified view of a certain type of vortices including Burgers, Sullivan and Bellamy-Knights solutions. The non-equivalence of the inviscid limit of the Navier–Stokes equations and the Euler equations is emphasized. Introducing the notion of observational non-uniqueness, which differs from the non-uniqueness in a certain class of differential equations, of solutions to the Navier–Stokes equations, the observation problem associated with the dense distribution of non-equivalent solutions is argued. The origin of the extreme sensitivity of the solutions to the boundary conditions is clarified. A few examples of vortex phenomena in the real world are also surveyed. We next review the works of constructing turbulence as a random assembly of simple, compact vortices. An attempt to combine the vortex model of turbulence with the Kármán–Howarth equation for the velocity correlation functions of anisotropic turbulence is presented. It is pointed out that the studies in this direction suggested that Kolmogorov’s 2/3 scaling law was generally compatible with anisotropy. A few quantities are proposed as candidates to measure anisotropy in turbulence experiments. Full article

Grassland degradation, exacerbated by climate change and anthropogenic disturbances, poses a substantial barrier to ecological restoration, largely due to the invasion of toxic weeds. In the degraded grasslands of the Ili River Valley, Xinjiang, Sophora alopecuroides has emerged as the dominant toxic species; yet, its expansion mechanisms and sensitivity to management interventions remain poorly understood. This study utilized a three-year (2023–2025) field experiment to evaluate the impacts of nitrogen addition (N), mowing (M), and their combination (NM) on the stoichiometric characteristics and homeostasis of the plant–soil system. The results demonstrated that while M suppressed aboveground biomass, it facilitated the accumulation of root carbon (RC) and phosphorus (RP). Nitrogen enrichment significantly lowered soil C:N and C:P ratios, thereby alleviating phosphorus limitation. Crucially, the NM treatment effectively counteracted N-induced weed proliferation and mitigated M-induced biomass reductions. Analysis of stoichiometric homeostasis revealed that NM optimized plant adaptive strategies, maintaining strict homeostasis for RC and RP (H > 4) while preserving the sensitivity of the root N:P ratio of S. alopecuroides (RN:P). Structural equation modeling further indicated that soil C:P and N:P indirectly regulated total biomass by modulating the root C:P ratio of S. alopecuroides (RC:P). Consequently, stoichiometric coupling within the plant–soil system is essential for maintaining ecosystem functions. Integrated management (NM) optimizes soil nutrient balance and harnesses compensatory growth to suppress weed expansion, providing a robust scientific framework for the restoration of S. alopecuroides-invaded grasslands. Full article

High-water material (HWM) is widely used for roadside filling in gob-side entry retaining (GER), where its creep behavior under sustained loading critically influences the long-term stability of the roadway. To enhance the long-term mechanical performance of HWM, this study modified it with polyethylene (PE) fiber and conducted uniaxial compression creep tests to investigate the effects of fiber content on time-dependent deformation, long-term strength, and failure time. The results indicate that when the applied stress remains below the long-term strength, the creep deformation of PE fiber-modified HWM stabilizes over time. In contrast, under higher stress levels, the deformation of HWM continuously develops over time and progresses through three stages: attenuation, steady-state, and accelerated creep, ultimately resulting in failure. Compared with pure HWM, the fiber-modified material exhibits a significant improvement in long-term strength, which increases linearly with fiber content. Furthermore, a higher fiber content raises the stress threshold for creep failure and substantially extends the time to failure. To predict the creep response of PE fiber-modified HWM, a viscoelastic-plastic creep damage model was developed using the component combination method, incorporating the Riemann–Liouville fractional-order integral operator and a time-dependent damage evolution equation. The reliability of the model was verified by utilizing the experimental data, and a sensitivity analysis of the model parameters was carried out based on the fitting results. The proposed model can not only describe the creep behavior of HWM across all loading stages, including the accelerated creep phase, but also accounts for the effect of fiber content on long-term strength. These findings can provide a theoretical foundation for the design and stability assessment of fiber-reinforced HWM roadside backfills in GER engineering. Full article

Carbon capture and storage (CCS) is essential for achieving net-zero emissions, yet amine-based capture systems face significant challenges including high energy penalties (20–30% of power plant output) and operational costs ($50–120/tonne CO${}_2$). This study develops and validates a novel multi-scale Digital Twin (DT) framework integrating Physics-Informed Neural Networks (PINNs) to address these challenges through real-time optimization. The framework combines molecular dynamics, process simulation, computational fluid dynamics, and deep learning to enable real-time predictive control. A key innovation is the sequential training algorithm with domain decomposition, specifically designed to handle the nonlinear transport equations governing CO${}_2$ absorption with enhanced convergence properties.The algorithm achieves prediction errors below 1% for key process variables (R${}^2$> 0.98) when validated against CFD simulations across 500 test cases. Experimental validation against pilot-scale absorber data (12 m packing, 30 wt% MEA) confirms good agreement with measured profiles, including temperature (RMSE = 1.2 K), CO${}_2$ loading (RMSE = 0.015 mol/mol), and capture efficiency (RMSE = 0.6%). The trained surrogate enables computational speedups of up to four orders of magnitude, supporting real-time inference with response times below 100 ms suitable for closed-loop control. Under the conditions studied, the framework demonstrates reboiler duty reductions of 18.5% and operational cost reductions of approximately 31%. Sensitivity analysis identifies liquid-to-gas ratio and MEA concentration as the most influential parameters, with mechanistic explanations linking these to mass transfer enhancement and reaction kinetics. Techno-economic assessment indicates favorable investment metrics, though results depend on site-specific factors. The framework architecture is designed for extensibility to alternative solvent systems, with future work planned for industrial-scale validation and uncertainty quantification through Bayesian approaches. Full article

Background and Objectives: Primary open-angle glaucoma (POAG) is one of the leading ocular diseases leading to irreversible blindness and is often asymptomatic until advanced cases. While intraocular pressure reduction remains the cornerstone of treatment, neuroprotective strategies targeting retinal ganglion cell metabolism are actively investigated. Niacinamide (nicotinamide, vitamin B3), a precursor of NAD+, has shown neuroprotective potential in preclinical models. This exploratory study evaluated the short-term functional, structural, and electrophysiological effects of oral niacinamide supplementation in POAG. Materials and Methods: In this interventional study, patients with POAG received oral niacinamide 500 mg daily for six months. Visual field (VF) global and localized sensitivity (Mean Deviation [MD], Pattern Standard Deviation [PSD]), Optic Coherence Tomography (OCT)-derived peripapillary retinal nerve fiber layer (RNFL) and macular ganglion cell complex (GCC), and Visual evoked potentials (VEP) latency parameters (P2 1.4 Hz, P100 1°, and P100 15′) were assessed at baseline and at six months. Because both eyes from some participants were included, primary longitudinal inference was based on clustered analyses using generalized estimating equations and linear mixed-effects models to account for inter-eye correlation. Eye-level paired analyses were used for exploratory comparison. Change–change relationships across modalities were explored using Spearman correlation. Results: After accounting for inter-eye correlation, no statistically significant change in MD was detected (mean ΔMD +0.43 dB; GEE p = 0.099; LME p = 0.101), and PSD remained stable. RNFL thickness showed a small decrease (−1.26 µm; GEE p = 0.046), while GCC did not change significantly. VEP P100 latencies remained stable, whereas P2 latency showed a small increase (+3.9 ms; GEE p = 0.039). Correlation analysis revealed a moderate association between changes in GCC and MD (ρ = 0.44), suggesting concordance between macular structural stability and global visual field performance. Conclusions: When inter-eye correlation is appropriately accounted for, six months of niacinamide supplementation in POAG is associated with overall functional, structural, and electrophysiological stability, without evidence of clinically meaningful improvement or progression. These findings support short-term safety and highlight the importance of clustered analytical approaches and macular-centered biomarkers in future glaucoma neuroprotection trials. Full article

Design optimization is a computational tool that can enable a designer to investigate the effectiveness of a design concept in an organized format. However, this design process requires the design variables, constraints, and objective function to be properly defined and expressed in mathematical forms. Post-optimality analysis thus becomes a necessary step to investigate different variations in the problem formulation and parameters to ensure that optimization produces a stable and trustworthy outcome. One efficient way to achieve this aim is to compute the local derivative of the optimized objective function with respect to the optimization problem parameters, such as bounds on the constraints and the material properties in the state equation. This method is referred to as post-optimality sensitivity analysis. In this study, we derived the post-optimal sensitivity equation to explicitly include the derivatives of state variables with respect to problem parameters and to broaden its applications to minimax and goal attainment design optimization problems. Full article

Hemolysis rate is usually used as the acceptance criterion for stored red blood cells (RBCs) in clinical practice. However, there is a current lack of parameters for the characterization of hemoglobin quality. This study aimed to incorporate oxygen affinity, cooperativity, and the Bohr effect into a parameter system to monitor oxygen supply efficiency in stored RBCs, potentially serving as a basis for quality assessment. Han Chinese blood from plains, Tibetan blood from plateau, bovine hemoglobin (bHb), and a dextran–bovine hemoglobin conjugate (Dex20-bHb) were analyzed using the BLOODOX-2018. Oxygen affinity (P₅₀) was determined by oxygen dissociation curves (ODCs) at pH = 7.4. Cooperativity was assessed through the Hill coefficient, calculated from the fitting range of the Hill equation. The Bohr effect was evaluated by the acid-base sensitivity index (SI) under simulated pH conditions of the lungs (pH = 7.6) and tissues (pH = 7.2) to calculate corresponding P₅₀ values. Oxygen partial pressures (PO₂) simulating lungs (PO₂ = 100 mmHg for plains and 60 mmHg for plateau) and tissues (PO₂ = 40 mmHg for plains and 30 mmHg for plateau) were used to calculate theoretical oxygen-release capacities in both environments. Multiple regression analysis explored relationships among parameters, constructing a system to assess changes in rat RBCs during storage. Optimized test methods determined P₅₀, Hill coefficient, SI, and theoretical oxygen-release capacities for Han Chinese blood, Tibetan blood, bHb, and Dex20-bHb samples in various environments. We constructed a parameter system to characterize blood’s oxygen supply efficiency, revealing the significant influence of the Bohr effect. This influence varied with environmental changes in oxygen affinity. We validated the system using stored rat RBCs, finding consistent P₅₀ trends with predictions, and initial increases in Hill coefficient and SI followed by decreases. Theoretical oxygen-release capacities varied significantly between plateau and plain environments. These results support using oxygen supply efficiency to assess RBC storage quality for developing transfusion strategies. P₅₀, Hill coefficient, SI, and theoretical oxygen-release capacity in different environments can be incorporated into blood oxygen supply efficiency characterization systems to assess the quality changes in RBCs during storage. Full article

In this study, we address a coupled system of nonlinear fractional delay differential equations subject to cross-coupled multi-point boundary conditions. By utilizing the generalized power Caputo fractional derivative, we present a unified theoretical framework that encompasses several operators—including the Atangana–Baleanu, Caputo–Fabrizio, and weighted Hattaf derivatives—as special cases. This generality ensures that our results remain applicable across a broad family of fractional kernels. We transform the complex delay system into an equivalent integral form to derive sufficient criteria for the existence and uniqueness of solutions via fixed-point theory. Furthermore, we rigorously establish the Ulam–Hyers stability of the system, a critical property for ensuring robustness in the presence of perturbations. Finally, the theoretical findings are validated through a detailed numerical study employing a predictor–corrector scheme adapted for fractional delay systems. The simulations highlight the sensitivity of solutions to the memory kernel and fractional orders and include a systematic exploration of delay effects. Full article

Sustainable packaging has become a major area of academic and practical interest, reflecting growing environmental awareness, regulatory pressure, and changing consumer expectations. This study aims to synthesize existing knowledge on consumers’ behavior toward sustainable packaging and their willingness to pay (WTP) for environmentally friendly solutions. Following PRISMA guidelines, a systematic literature review was conducted, encompassing 78 peer-reviewed publications from 2019 to 2025. Bibliometric mapping using VOSviewer (version 1.6.20) identified three main research streams: consumer attitudes and determinants of behavior, willingness to pay for sustainable packaging, and perception of packaging materials and systems. The reviewed studies, conducted across Europe, Asia, Australia, and North America, employed diverse methods, including surveys, discrete choice experiments, structural equation modeling, and mixed designs. Results indicate that consumer behavior is shaped by environmental awareness, self-identity, perceived usefulness, and trust in labeling, while packaging material and functionality remain decisive for acceptance. Most studies show that consumers are willing to pay a premium of about 10–20% for sustainable packaging, though price sensitivity and hygiene concerns limit actual adoption. The findings highlight the conditional nature of consumer acceptance and emphasize the need for transparent communication, credible certification, and functional design. This study provides guidance for policymakers and businesses seeking to promote sustainable packaging solutions. Full article

Developing the analytical model of a multibody system is often the initial step in control and optimization. The analytical model (equations of motion) describes a system’s time evolution under specified forcing conditions. Although developing these equations is easy for simple systems, this process becomes more complex for systems composed of multiple bodies. Deriving equations of motion for complex multibody systems requires specialized expertise in multibody dynamics, is time-consuming, and is susceptible to error. To address this issue, this paper presents an open-source, easy-to-use, systematic framework to derive symbolic equations of motion in both Python and MATLAB using the joint coordinate formulation. This formulation results in a set of ordinary differential equations that use the minimum set of coordinates needed to model a system. The symbolic representation provides better insight into the influence of design parameters on system performance, facilitates sensitivity analysis and parameter studies, and supports direct implementation of control and optimization routines. The tool enables numerical simulation for specified parameter sets, is modular for straightforward integration with other tools and libraries, and allows incorporation of hydrodynamics, mooring, and other external forces. The result is a reproducible, extensible pipeline for modeling, simulation, and design of complex multibody systems. The proposed tool is versatile and can be applied to domains such as robotics, control, and design. In addition, we integrated external libraries that provide capabilities for modeling offshore systems such as underwater robots and marine energy converters. Full article

This study examines the impact of role overload on female hoteliers’ intention to quit, highlighting the mediating role of work–family conflict and the moderating role of co-worker support. Drawing on Conservation of Resources (COR) theory, the research conceptualizes role overload as a key job demand that depletes employees’ personal and emotional resources, triggering strain and turnover intentions. Data were collected from 255 full-time female employees working in five-star hotels in Egypt and analyzed using Partial Least Squares Structural Equation Modeling (PLS-SEM) via WarpPLS software version 8. The findings reveal that role overload significantly increases both work–family conflict and intention to quit, while work–family conflict partially mediates the relationship between role overload and turnover intentions. Moreover, co-worker support plays a crucial buffering role, weakening the positive effects of both role overload and work–family conflict on intention to quit. The study contributes to hospitality research by providing a gender-sensitive understanding of how high-demand hotel environments affect female employees’ retention and highlights the importance of co-worker support as a practical intervention to mitigate turnover among women employees. These insights offer valuable guidance for hotel managers aiming to enhance employee well-being and reduce attrition in luxury hotel settings. Full article

Prediction accuracy for complex flexible support systems is often limited by insufficiently characterized thermo-mechanical couplings and nonlinearities. To address this, we propose a multilevel hybrid parallel–serial model that integrates the thermo-viscous effects of a Squeeze Film Damper (SFD) via a coupled Reynolds–Walther equation, the structural flexibility of a squirrel-cage support using Finite Element analysis, and the load-dependent stiffness of a four-point contact ball bearing based on Hertzian theory. The resulting state-dependent system is solved using a force-controlled iterative numerical algorithm. For validation, a dedicated bidirectional excitation test rig was constructed to decouple and characterize the support’s dynamics via frequency-domain impedance identification. Experimental results indicate that equivalent damping is temperature-sensitive, decreasing by approximately 50% as the lubricant temperature rises from 30 °C to 100 °C. In contrast, the system exhibits pronounced stiffness hardening under increasing loads. Theoretical analysis attributes this nonlinearity primarily to the bearing’s Hertzian contact mechanics, which accounts for a stiffness increase of nearly 240%. This coupled model offers a distinct advancement over traditional linear approaches, providing a validated framework for the design and vibration control of aero-engine flexible supports. Full article

Food waste remains a significant challenge in the European Union, reflecting structural differences across economic sectors and member states. This study examines how macroeconomic conditions relate to sectoral food waste using harmonized Eurostat data for the EU-27, covering five stages of the food chain and three economic indicators: GDP (Gross Domestic Product) per capita, adjusted gross disposable income per capita, and the Harmonized Index of Consumer Prices for food. The research design integrates factor analysis, structural equation modeling, and hierarchical clustering. Results show that income-related variables have a positive, statistically significant effect on overall food waste, particularly in manufacturing and distribution. In contrast, food prices show a negative, statistically non-significant relationship with waste generation. Cluster analysis identifies two statistically distinct country groups; however, substantial internal heterogeneity indicates that these clusters reflect structural economic configurations rather than typological or behavioral categories. The findings suggest that macroeconomic factors partially explain cross-country differences in food waste and support the need for context-sensitive, sector-specific policy interventions. Full article

This paper presents an analytical model for the hereditary vibrations of a coupled circular plate system interconnected by viscoelastic creep layers. The system is represented as a discrete-continuous chain of thin, isotropic plates with time-dependent material properties. Based on the theory of hereditary viscoelasticity and D’Alembert’s principle, a system of partial integro-differential equations is derived and reduced to ordinary integro-differential equations using Bernoulli’s method and Laplace transforms. Analytical expressions for natural frequencies, mode shapes, and time-dependent response functions are obtained. The results reveal the emergence of multi-frequency vibration regimes, with modal families remaining temporally uncoupled. This enables the identification of resonance conditions and dynamic absorption phenomena. The fractional parameter serves as a tunable damping factor: lower values result in prolonged oscillations, while higher values cause rapid decay. Increasing the kinetic stiffness of the coupling layers raises vibration frequencies and enhances sensitivity to hereditary effects. This interplay provides deeper insight into dynamic behavior control. The model is applicable to multilayered structures in aerospace, civil engineering, and microsystems, where long-term loading and time-dependent material behavior are critical. The proposed framework offers a powerful tool for designing systems with tailored dynamic responses and improved stability. Full article