Search Results (779)

The aim of this paper is to characterize a relativistic bulk viscous fluid string spacetime whose energy–momentum tensor satisfying certain geometric symmetries. At first, it is shown that a relativistic bulk viscous fluid string spacetime is a generalized quasi-Einstein manifold. Then, we characterize such a spacetime, satisfying Codazzi type of energy–momentum tensor (denoted by ${\mathcal{T}}^{\oslash }$), covariant constant ${\mathcal{T}}^{\oslash }$, recurrent and generalized recurrent ${\mathcal{T}}^{\oslash }$, and almost pseudo-symmetric and weakly symmetric ${\mathcal{T}}^{\oslash }$, respectively. Next, we consider quadratic Killing ${\mathcal{T}}^{\oslash }$ in such a spacetime. Finally, we provide a concrete example using partial differential equations. Full article

Background: Acute focal neurological deficits require rapid differentiation between ischemic stroke and stroke mimics to avoid treatment delays and inappropriate therapy. Seizures, including ictal deficits, status epilepticus, and post-ictal/Todd’s phenomena, are among the most challenging mimics. This review summarizes the role of multimodal neuroimaging in distinguishing acute ischemic stroke from seizure-related deficits. Methods: We performed a focused narrative review of neuroimaging findings in acute stroke mimics, emphasizing non-contrast computed tomography (CT), CT angiography, CT perfusion, magnetic resonance imaging (MRI), including diffusion weighted imaging (DWI), apparent diffusion coefficient (ADC), fluid attenuated inversion recovery (FLAIR), and arterial spin labeling (ASL) sequences. Imaging patterns, diagnostic pitfalls, and practical clues for hyperacute stroke pathways were synthesized. Results: Acute ischemic stroke is typically suggested by vascular-territorial abnormalities, including arterial occlusion or stenosis, territorial hypoperfusion, and congruent DWI/ADC restriction. Seizure-related deficits more often show non-territorial cortical perfusion changes, ictal or status-related hyperperfusion, reversible MRI abnormalities, and absence of arterial occlusion. However, post-ictal hypoperfusion, peri-ictal diffusion restriction, and reperfusion-related hyperperfusion may overlap with ischemic patterns. Conclusions: A multimodal approach integrating vascular imaging, perfusion distribution, DWI/ADC, ASL, clinical timing, and EEG findings can improve diagnostic accuracy in the stroke–seizure differential without delaying treatment in true acute ischemic stroke. Full article

Verification of the blast resistance capacity of military protective structures is generally conducted through experimental testing; however, repeated experiments are limited due to spatial, temporal, economic, and safety constraints. Accordingly, this study evaluated the global deformation-based protective performance of the entrance-side front wall of a covered artillery position (double-door type) using three-dimensional numerical analysis based on ANSYS AUTODYN. The blast scenario was defined as a frontal standoff blast using a 00.0 kg TNT-equivalent charge, corresponding to a 000 kg class munition with a charge-to-weight ratio of 00%, at a standoff distance of 0.0 m. A coupled fluid–structure interaction analysis was applied to consider the interaction between the blast pressure transmission medium and the reinforced concrete structure. The entrance-side front wall surrounding the double-door opening was selected as the primary evaluation member because it is directly exposed to the incoming blast wave and forms part of the entrance zone of the facility. The analysis results showed that the maximum wall-applied reflected pressure was 1487.6 kPa at approximately 5.8 ms, and the maximum front-wall displacement was 0.505 mm at approximately 7.0 ms. The support rotation angle calculated from the maximum displacement was 0.012° based on a wall height of 2.3 m, which was within the elastic design limit of 0–2° specified in UFC 3-340-02. Therefore, under the specified numerical scenario, the entrance-side front wall was assessed to remain within the Protection Level A limit based on the UFC support rotation criterion. (The standoff distance and TNT charge weight are masked under the restriction on disclosure due to military secrets). Full article

Background: Neovascular age-related macular degeneration (nAMD) remains a leading cause of irreversible central vision loss. Although anti-vascular endothelial growth factor (anti-VEGF) therapy has transformed management, pivotal trials enrolled exclusively treatment-naïve patients, leaving clinicians without pooled evidence to guide switching decisions in previously treated eyes. This systematic review and meta-analysis assessed real-world visual, anatomical, durability, and safety outcomes following switching to aflibercept 8 mg in previously treated nAMD. Methods: Following PRISMA 2020 guidelines, we searched PubMed, Embase, Web of Science, CENTRAL, Scopus, and Google Scholar through April 2026. Studies reporting switching to aflibercept 8 mg with change in best-corrected visual acuity (BCVA), central subfield thickness (CST), or treatment interval were included. Continuous outcomes were pooled using random-effects models with Hartung–Knapp–Sidik–Jonkman adjustment; proportions were estimated using generalized linear mixed models. Methodological quality was evaluated using the JBI Critical Appraisal Checklist for Case Series. Certainty of evidence was assessed using GRADE. The protocol was registered with PROSPERO (CRD420261371334). Results: Twenty-one studies met inclusion criteria. BCVA remained stable (WMD: −0.017 logMAR; 95% CI: −0.027 to −0.007; +0.83 ETDRS letters; I² = 0%). CST decreased significantly (WMD: −21.5 µm; 95% CI: −29.3 to −13.7; I² = 56.0%), and treatment intervals extended by +1.79 weeks (95% CI: +1.32 to +2.27; I² = 74.3%). Intraretinal and subretinal fluid each resolved in 37.5% of eyes. Intraocular inflammation was rare across 9959 treated eyes, though this pool was not restricted to switched eyes, with no confirmed retinal vasculitis. Sensitivity analyses confirmed robustness across all co-primary estimates. GRADE certainty was low for BCVA and very low for CST and treatment interval. Conclusions: Low-certainty evidence suggests that switching to aflibercept 8 mg preserves visual acuity, while very-low-certainty evidence suggests reductions in central subfield thickness and modest extension of treatment intervals. Intraocular inflammation was rare, though safety denominators included non-switch eyes. These findings provide preliminary pooled estimates to inform switch decisions in previously treated eyes. Full article

Mineral exploration in the Iberian Pyrite Belt follows increasingly deeper targets. The present study introduces an innovative methodology for the detection and identification of blind metallic mineral deposits, in particular volcanogenic massive sulfides based on surface rock coatings. This approach follows the identification pathways of upward metal escape routes and metal distribution in rock fractures located in different anisotropic or isotropic planes above the Neves-Corvo VMS deposit ore lenses, using VP-SEM-EDS and XRD. Coatings are dominated by poorly crystalline to amorphous phases, with goethite and birnessite as the main Fe- and Mn-bearing minerals. Copper, zinc and lead are systematically enriched in coatings developed above or near the ore bodies, reflecting chalcopyrite, sphalerite and galena acidic leaching. Tin shows a restricted and heterogeneous distribution, while Ni and Co display no systematic relationship with the ore bodies. Barium and late Ba–Pb–(Zn) mineralization along fault zones record VMS mineralization. Lead isotopic coating signatures overlap those of IPB massive sulfide deposits, confirming a dominant VMS-derived contribution. Fe–Mn coatings were formed by precipitation from ascending meteoric fluids that leached metals from massive sulfides, their alteration halos, and surrounding lithologies, preserving the geochemical footprint of buried mineralization. This approach constitutes a new patented exploration tool. Full article

Optimizing flapping-foil kinematics for underwater propulsion is challenging due to strong temporal coupling and nonlinear fluid–structure interactions. Most existing approaches rely on parameterized motion profiles, which restrict the accessible design space. A non-parametric kinematic optimization framework based on the discrete adjoint method is developed, enabling direct optimization of time-resolved motions without predefined functional forms. A Morison-based low-order hydrodynamic model, calibrated against Computational Fluid Dynamics (CFD), is employed for efficient evaluation within a validated regime. Results show that optimized motions substantially enhance propulsion performance over conventional sinusoidal motions, yielding non-sinusoidal, high-efficiency kinematics. In thrust-maximization cases, the optimized kinematics achieve a 50.29% increase in mean thrust by redistributing heave and pitch amplitudes and timing. Under balanced thrust–power conditions, the optimized motions consistently outperform sinusoidal counterparts. In power-minimization cases, a “generator-like” regime emerges, indicating a reversal of net energy transfer enabled by the non-parametric formulation. These results demonstrate that non-parametric optimization provides enhanced design flexibility and improved propulsion performance, offering a practical framework for biomimetic underwater propulsion design. Full article

Background: Glucagon-like peptide-1 receptor agonists (GLP-1RAs) and dual glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 receptor agonists have transformed obesity treatment, producing substantial weight loss during active therapy. However, real-world effectiveness may be limited by gastrointestinal adverse events, reduced dietary intake, fat-free mass loss as part of total weight reduction, and weight regain after discontinuation. Methods: This narrative review synthesizes current pharmacological, nutritional, gastrointestinal, body-composition, and implementation evidence to propose an evidence-informed nutrition-first framework for patients receiving incretin-based therapy for obesity. Results: We translate pharmacologic mechanisms into practical dietary strategies, including protein prioritization, structured meal patterns, hydration and fiber management, symptom-targeted interventions, resistance-training support, and maintenance planning. Because direct trials of structured nutrition interventions in GLP-1RA- or dual incretin-treated populations remain limited, several recommendations are extrapolated from the broader obesity, caloric restriction, body-composition, gastrointestinal, and expert-consensus literature. Conclusions: Integrating structured nutrition care into pharmacotherapy pathways may help address meal-related symptom burden, support protein and fluid adequacy, identify patients at higher nutritional or body-composition risk, and prepare patients for long-term weight-management behaviors. Embedding practical nutrition management within multidisciplinary obesity care may help translate pharmacologic efficacy into durable, patient-centered outcomes. Full article

The spatiotemporal evolution of seepage fields and the associated hydrodynamic risk of subsequent internal erosion pose a critical threat to the structural integrity of marine and hydraulic infrastructure. To quantify these complex fluid–solid interactions, this study develops a high-fidelity numerical model—coupling the Navier–Stokes equations with the Darcy–Forchheimer resistance model and the Volume of Fluid (VOF) method—to investigate transient hydrodynamics within porous foundations under complex geometric and geological boundary conditions. Parametric analyses reveal that spatial porosity distribution fundamentally dictates the system’s seepage capacity; notably, relocating a highly permeable stratum to the shallow sub-surface eliminates upper hydraulic bottlenecks and significantly escalates total volumetric discharge. Furthermore, the study systematically evaluates the hydrodynamic efficacy of multi-dimensional seepage control structures. Results demonstrate that while increasing the vertical depth of a cutoff wall is highly efficient in restricting bulk volumetric flux, it inadvertently induces intense localized streamline convergence and flow acceleration at the structural tip. Conversely, lateral expansion of the wall base, though yielding only a moderate reduction in total seepage, successfully diffuses this concentrated flow and substantially attenuates peak pore fluid velocities. Ultimately, a combined design paradigm is proposed for practical coastal engineering applications: prioritizing vertical penetration to optimize bulk seepage reduction, concurrently integrated with moderate lateral base expansion to redistribute concentrated hydrodynamic shear stresses, thereby minimizing the hydrodynamic potential for localized piping and ensuring long-term stability against seepage-induced degradation. Full article

Background: Sepsis is a time-critical condition requiring early recognition and intervention. Many emergency departments (EDs) have adopted clinical pathways to standardise sepsis care; however, the impact of these pathways on patient outcomes remains unclear. Methods: A systematic review and meta-analysis was conducted in November 2024 searching PubMed, Embase, and Scopus. Studies were included if they assessed the impact of a clinical pathway on adult or paediatric patients with sepsis presenting to the ED. Results: Thirty-three studies were included, of which the majority were retrospective cohort designs and were rated serious overall risk of bias. Pathway implementation was associated with faster time to antibiotics across all subgroups (135 min before vs. 93 min after; MD −43 min, p < 0.001). In-hospital mortality appeared reduced in the primary analysis (RD −2.4%, p = 0.032); however, this finding was fragile under sensitivity analysis and was not observed in prospective or randomised designs. The apparent reduction in hospital length of stay was driven by paediatric and low- and middle-income country studies and was non-significant when restricted to adult studies. ICU admission rate, ED length of stay, and time to IV fluid resuscitation were not significantly reduced. Conclusions: ED sepsis pathway implementation is associated with improved time to antibiotics across clinical settings and populations. Current evidence is insufficient to demonstrate a reduction in mortality; the apparent signal in retrospective studies is attributable to secular improvements in sepsis care and asymmetric patient identification rather than a true pathway effect. Future research should prioritise prospective controlled studies with standardised screening methods, time zero definitions and control of confounding variables. Full article

Porosity is a key parameter controlling reservoir storage capacity and fluid flow behavior, and its accurate prediction remains a major challenge in complex reservoirs with limited well control. Traditional methods based on well logs and rock physics modeling are often restricted by sparse spatial coverage, while purely data-driven approaches lack physical interpretability and geological consistency. To address these limitations, this study proposes a model–data coupled framework for seismic porosity prediction in sandstone reservoirs. The approach integrates rock physics constraints into a deep learning architecture by embedding relationships derived from the Gassmann equation and critical porosity model into an LSTM-UNet network. This design enables the model to simultaneously capture spatial features and temporal dependencies from seismic data while maintaining physical consistency. Synthetic experiments based on the SEAM model demonstrate that the proposed method achieves stable and accurate porosity predictions under both noise-free and noisy conditions. Application to field data from a real-world study area further demonstrates the effectiveness of the proposed method, with predicted porosity showing strong agreement with well-log data and improved lateral continuity relative to conventional approaches. The results indicate that the proposed framework effectively combines the flexibility of data-driven learning with the interpretability of physics-based modeling, providing a robust and reliable solution for porosity prediction in complex sandstone reservoirs. Full article

Thermo-electromagnetic force plays a crucial role in tailoring the solidification microstructure by altering thermal-solutal buoyancy. However, while in situ synchrotron experiments offer some observations of microstructural evolution, their restricted spatial resolution and beam intensity prevent the full characterization of fluid flow and solute transport during solidification. To address this limitation, a calibrated model of a cellular automaton method coupled with a Eulerian multiphase approach is employed in this study to comprehensively investigate the impact of solute distribution on grain evolution during the directional solidification of an Al-2.5 wt.% Cu alloy under varying steady magnetic fields from 0.5 T to 4.0 T. The model incorporates heat and solute transport, nucleation, grain growth, and complex melt flows driven by thermal-solutal buoyancy, alongside thermo-electromagnetic effects and induced Lorentz forces. Simulations reveal that under a steady 0.5 T magnetic field, an elliptical copper-rich region forms near the solidification front. This solute redistribution significantly influences the development of a tilted solid–liquid interface, consistent with experimental observations. As the magnetic field strength increases, this copper-rich region transitions from an elliptical to a circular morphology. Notably, under a 4.0 T magnetic field, the tilted interface is effectively stabilized due to the suppression of grain growth. Furthermore, significant grain refinement is observed under a steady magnetic field, as the average grain size decreases from 209.3 μm without magnetic field to 122.5 μm of 0.5 T. This refinement is driven by redistribution of the copper concentration, which increases the undercooling from 1.4 K to 3.7 K and generates new nucleation zones. This solute-driven mechanism is identified as the primary cause of grain refinement under steady magnetic fields and is successfully validated by experimental results. These results shed new light on the mechanism of grain growth evolution under a steady magnetic field. Full article

Multi-cluster perforation staged fracturing in horizontal wells has become an important means of completion stimulation for unconventional oil and gas reservoirs. However, the non-uniform propagation of multi-cluster hydraulic fractures remains one of the key challenges restricting efficient reservoir stimulation. In this study, based on the finite element method and considering factors such as frictional pressure drop along the wellbore for power-law fluid, perforation friction, and stress interference, a fracture propagation model with dynamic multi-stage flow distribution coupling formation, perforation, and wellbore flow was constructed. The effects of non-uniform perforation schemes, total number of perforations, and perforation non-uniformity coefficient on multi-cluster fracture propagation behavior were systematically investigated, and the characteristics of dynamic flow distribution were clarified. The results show that the order of fluid intake uniformity among different perforation schemes is as follows: spindle-shaped perforation, uniform perforation, and Tapered perforation. Reducing the number of perforations and decreasing the perforation non-uniformity coefficient can improve the uniformity of fracture propagation to a certain extent. The findings of this study can provide a theoretical basis and practical reference for efficient fracturing stimulation of shale oil in the Cangdong Sag. Full article

Accurate prediction of hydrodynamic forces on confined oscillating structures is essential in applications related to nuclear engineering, energy systems, offshore devices, and mechanical components subjected to flow-induced vibrations. In this work, two computational fluid dynamics (CFD) methodologies implemented in ANSYS CFX are compared to determine the added-mass coefficients for a square cross-section cylinder confined within a square container: a deforming-mesh method (DMM) and an immersed-boundary method (IBM). Unlike previous studies restricted either to concentric square cylinders or to eccentric configurations treated with potential flow, the present study addresses eccentric confined configurations by solving the incompressible Navier–Stokes equations and focuses primarily on the prediction of added mass under strong confinement. Horizontal, vertical, and combined eccentric displacements are analyzed in detail. Mesh-independence, domain-size sensitivity, and temporal-convergence analyses are performed. Results show that both methods provide closely matching added-mass predictions over a wide range of eccentricities, with relative differences typically below 1% for moderate eccentricities, although discrepancies increase under extreme confinement. Relative to the concentric configuration, the added-mass coefficient increases by about 44% for the most eccentric vertical case and by about 87% for the most eccentric corner-approach case. Force decomposition and pressure-field analysis show that this increase is governed primarily by pressure-induced inertial effects, whereas viscous shear plays a secondary role under the conditions considered. From a practical standpoint, the immersed-boundary method reduced the computational time by approximately 92% in the most demanding case. Full article

This study presents an AI-assisted thermodynamic and computational fluid dynamics (CFD) evaluation of a β-type Stirling engine to improve its thermal efficiency and indicated power output. The engine performance was investigated using Restricted Dimensions Thermodynamics (RDT), the Schmidt thermodynamic model, and three-dimensional CFD simulations under various operating and geometric conditions. Key parameters including rotational speed, phase angle, piston diameter, displacer stroke, porosity, and charged pressure were systematically analyzed to determine their influence on engine behavior. A feed-forward artificial neural network (ANN) trained using the Levenberg–Marquardt optimization algorithm was integrated with CFD-generated datasets to predict engine performance and accelerate the optimization process. The AI-assisted optimization was coupled with the Variable Step-size Simplified Conjugate Gradient Method (VSCGM) to identify near-optimal operating conditions while reducing computational cost. Simulation results demonstrated that the optimization process improved the indicated power from 180.33 W to 185.44 W and increased thermal efficiency from 10.32% to 11.54%. The results also showed close agreement between predicted and experimental pressure–temperature profiles, confirming the reliability of the proposed methodology. Furthermore, CFD analyses revealed that increasing piston diameter and optimizing porosity enhanced heat transfer and pressure distribution within the engine chambers, resulting in improved thermodynamic performance. The proposed AI-driven framework provides a reliable and computationally efficient approach for the design and optimization of advanced β-type Stirling engines operating under realistic thermal conditions. Full article

This paper introduces a topology optimization framework for steady incompressible Stokes flow based on the non-conforming Virtual Element Method, VEM. The proposed framework combines the geometric flexibility of VEM with an optimality criteria update scheme to minimize viscous and Darcy dissipation under a prescribed volume constraint. The method is applied to the Stokes-flow pipe bend benchmark with parabolic inlet velocity, no-slip wall, and prescribed outlet velocity boundary conditions. By allowing general polygonal elements, including concave and semi-structured polygonal meshes, the method alleviates mesh-related restrictions commonly encountered in conventional finite element discretizations. The methodology is demonstrated through Stokes-flow benchmark problems on different polygonal meshes. The numerical results show that the proposed VEM-based formulation can obtain stable and mesh-insensitive optimized flow channels for Stokes-flow topology optimization. This work offers a systematic approach to obtaining accurate, efficient, and mesh-independent optimal designs for complex fluid systems, providing a stable numerical tool for low-energy-consumption flow channel design in microfluidics, heat exchangers, and biomedical engineering. Extensions to Navier–Stokes and non-Newtonian flow models are left for future work. It should be clarified that the proposed method is only validated for steady Stokes flow and has not been validated for complex fluid models including unsteady Navier–Stokes and non-Newtonian flow models; extensions to these complex models are left for future work. Full article