Search Results (5,853)

The linear stability of convection in a vertical two-layer porous structure representing a building external wall is studied. The wall is confined by two open vertical boundaries kept at different but uniform temperatures and is composed of two homogeneous porous layers, characterized by different values of permeability and thermal conductivity. The aim of this paper is investigating whether the wall can undergo the transition to thermal instability, namely, the onset of a multicellular convective pattern. The basic stationary state, given by the fully developed buoyant flow in the vertical direction, is perturbed by means of small-amplitude disturbances, and the resulting eigenvalue problem for neutrally stable modes is studied numerically. The solution of the perturbed governing equations shows that, for suitable values of the governing parameters, thermal instability can arise. The results highlight that the ratio of the permeabilities of the two layers as well as the ratio of their thermal conductivities, together with the aspect ratio between their thicknesses, are key parameters for the possible onset of instability. The temperature difference between the two open boundaries that can trigger instability is determined with reference to practical cases, namely, insulated walls that fulfill the Italian requirements in terms of overall thermal transmittance. Full article

The Allen-Cahn equation is a fundamental model in materials science for describing phase separation phenomena. This paper introduces an Energy-Stabilized Scaled Deep Neural Network (ES-ScaDNN) framework to solve the Allen-Cahn equation by energy minimization. Unlike traditional numerical methods, our approach directly approximates the solution of steady-state solution the Allen-Cahn equation by minimizing the associated energy functional using a deep neural network. ES-ScaDNN incorporates two key innovations. The first is a scaling layer designed to map the network output to the physical range of the Allen-Cahn phase variable. The second is a variance-based regularization term designed to promote clear phase separation. We demonstrate the accuracy and efficiency of ES-ScaDNN through comprehensive numerical experiments in both one and two dimensions. Our results show that ReLU activation functions are particularly well-suited for one-dimensional cases, while tanh functions are more suitable for two-dimensional problems due to their superior ability to maintain solution smoothness. Furthermore, we investigate how training epochs and the interface parameter ε influence the behavior of the solution. ES-ScaDNN provides a novel, accurate, and efficient deep learning framework for solving the Allen-Cahn equation, paving the way for tackling more complex phase-field problems. Full article

Quantitative Geometrical Thermodynamics (QGT) exploits the entropic Lagrangian–Hamiltonian canonical equations of state as applied to entities obeying the holographic principle and exhibiting Shannon information, the creation of which measures the (validly defined) “entropic purpose” of the system. QGT provides a physical description for what we might consider the true “atoms” of physical science and has also recently enabled a number of significant advances: accounting ab initio for the chirality of DNA and the stability of Buckminsterfullerene; the size of the alpha particle (and other nuclear entities) and the lifetime of the free neutron; and the shape, structure, and stability of the Milky Way galaxy. All these entities, ranging in size over more than 38 orders of magnitude, can each be considered to be an “atom”; in particular, the size of the alpha is calculated from QGT by assuming that the alpha is a “unitary entity” (that is, than which exists no simpler). The surprising conclusion is that clearly compound entities may also be physically treated as unitary (“uncuttable”) according to a principle of scale relativity, where a characteristic size for such an entity must be specified. Since QGT is entropic, and is therefore described using a logarithmic metric (involving hyperbolic space), it is not surprising that the length scale must be specified in order to account for unitary properties and for an entity to be appropriately considered an “atom”. The contribution to physics made by QGT is reviewed in the context of the related work of others. Full article

The Laplace equation is an important partial differential equation, typically used to describe the properties of steady-state distributions or passive fields in physical phenomena. Its Cauchy problem is one of the classic, serious, ill-posed problems, characterized by the fact that minor disturbances in the data can lead to significant errors in the solution and lack stability. Secondly, the determination of the parameters of the classical Laplace equation is difficult to adapt to the requirements of complex applications. For this purpose, in this paper, the Laplace equation with uncertain parameters is defined, and the uncertainty is represented by fuzzy numbers. In the case of granular differentiability, it is transformed into a granular differential equation, proving its serious ill-posedness. To overcome the ill-posedness, the Fourier regularization method is used to stabilize the numerical solution, and the stability estimation and error analysis between the regularization solution and the exact solution are given. Finally, numerical examples are given to illustrate the effectiveness and practicability of this method. Full article

Digital Twin (DT) technology has rapidly matured from pilot projects to integral components of advanced asset management and process optimization in the oil and gas (O&G) industry. This review provides a structured synthesis of the current state of digital twin frameworks, with a focus on offshore and topside gas-processing systems, such as those found on Floating Production Storage and Offloading (FPSO). Emphasis is placed on high-fidelity process simulations and scalable architectures integrating real-time data with advanced analytics. Drawing on over 85 peer-reviewed sources and industrial frameworks, the paper outlines modular DT architectures, encompassing steady-state and dynamic process simulations (e.g., Aspen HYSYS), reduced-order and hybrid machine learning models, co-simulation environments, and advanced equation-of-state packages (e.g., GERG-2008). Special attention is given to compressor map integration, Equations of State (EOS) selection, ISO/IEC standard compliance, and digital thread continuity. Additionally, the review explores economic and sustainability-driven DT implementations, including flare and methane mitigation, ISO 50001-aligned energy optimization, and lifecycle/decommissioning strategies. It concludes with a technical and economic assessment of DT maturity for gas compression facilities, identifying research gaps in standardization, long-term validation, and cybersecurity integration. The insights provided are intended to support decision-makers, engineers, and researchers in deploying scalable, auditable, and high-impact DT solutions across the O&G value chain. Full article

Probiotic enumeration in foods and beverages remains anchored in culture dependent colony-forming unit (CFU) counts, the regulatory gold standard for label compliance. However, culturability does not fully equate to viability as environmental stresses can convert probiotic cells into a viable but non-culturable (VBNC) state, where they remain metabolically active but undetectable by CFU counts. Microencapsulation can provide a degree of protection to probiotics against stress; nevertheless, this blind spot in quantification forces manufacturers to overdose formulations or risk non-compliance with health benefits claims. Thus, the efficacy of probiotics may be underestimated when evaluation relies solely on CFU, creating a false dichotomy between VBNC and non-viable cells. Culture-independent methods, including flow cytometry quantification of active fluorescent units (AFUs), viability PCR/dPCR, and rRNA-targeted Flow-FISH, can aid closing this gap by detecting metabolically active cells non-detectable by culturing, providing complementary quantification data to CFU counts alone. Understanding the relationship between quantification by culture and culture-independent methods provides a more accurate measure of probiotic dose delivery in functional foods and beverages. This review covers the current understanding of VBNC state, including induction, detection, and resuscitation in probiotics, with emphasis on experimental controls that differentiate true VBNC resuscitation from population growth. Case studies in Lactobacillus and Bifidobacterium illustrate triggers, molecular mechanisms, and methodological advances. Finally, guidance is provided for the development of an integrated quantification approach that reconciles culture-dependent and culture-independent data, ultimately aiming to improve CFU count accuracy through the controlled resuscitation of VBNC cells. Full article

Bellows compensators are critical components in pipeline systems, designed to absorb thermal expansions, vibrations, and pressure reflections. Ensuring their operational reliability requires accurate prediction of the stress–strain state (SSS) and stability under internal pressure. This study presents a comprehensive mathematical model for analyzing corrugated bellows compensators, formulated as a boundary value problem for a system of partial differential equations (PDEs) within the Kirchhoff–Love shell theory framework. Two numerical approaches are developed and compared: a finite difference method (FDM) applied to a reduced axisymmetric formulation to ordinary differential equations (ODEs) and a finite element method (FEM) for the full variational formulation. The FDM scheme utilizes a second-order implicit symmetric approximation, ensuring stability and efficiency for axisymmetric geometries. The FEM model, implemented in Ansys 2020 R2, provides high fidelity for complex geometries and boundary conditions. Convergence analysis confirms second-order spatial accuracy for both methods. Numerical experiments determine critical pressures based on the von Mises yield criterion and linearized buckling analysis, revealing the influence of geometric parameters (wall thickness, number of convolutions) on failure mechanisms. The results demonstrate that local buckling can occur at lower pressures than that of global buckling for thin-walled bellows with multiple convolutions, which is critical for structural reliability assessment. The proposed combined approach (FDM for rapid preliminary design and FEM for final verification) offers a robust and efficient methodology for bellows design, enhancing reliability and reducing development time. The work highlights the importance of integrating rigorous PDE-based modeling with modern numerical techniques for solving complex engineering problems with a focus on structural integrity and long-term performance. Full article

Türkiye is one of the most vulnerable countries in the Mediterranean Basin; the assessment of changes in soil erosion driven by both climate variability and anthropogenic factors is of great importance. This study aims to examine the current state and potential future changes in soil erosion in Sakarya Province, situated in the eastern part of the Mediterranean Basin, by employing the GIS-based RUSLE (Revised Universal Soil Loss Equation) model. Considering the impact of climate change on precipitation regimes, rainfall projections for the 2061–2080 period under the high-emission SSP5-8.5 scenario were evaluated. The analysis revealed that the current average annual soil loss in Sakarya is 2.9 t/ha, with the highest erosion risk occurring on steep slopes, bare surfaces, and agricultural lands. By 2080, under the SSP5-8.5 scenario, the annual average soil loss is projected to be 2.6 t/ha, while slight and very slight erosion levels are expected to increase. These results provide important insights for identifying current risk areas and critical zones for conservation, as well as for projecting future erosion scenarios, thus contributing to sustainable land management policies at the watershed scale. The study suggests that strategies to reduce erosion risk in Sakarya should particularly focus on land management practices such as slope stabilization, afforestation, land cover improvement, and terracing. These approaches are crucial for mitigating land degradation (SDG 15.3) and ensuring sustainable agricultural production (SDG 2.4) within the framework of the Sustainable Development Goals. Full article

This paper explores the optimal control issue for a linear–quadratic–Gaussian (LQG) system under the conditions of imperfect feedback and constraints related to energy harvesting. The system is equipped with various energy options, which allow it to gather energy for information transmission while also receiving imperfect feedback from an auxiliary filter that estimates packet loss. The primary goal of this study is to jointly design the energy selector and the controller to achieve an optimal balance between transmission costs and control performance. Initially, we separate the controller’s synthesis task from the energy selection task. The subproblem of optimal controller synthesis is characterized by a Riccati equation that takes continuous packet loss into account. Simultaneously, the energy selection task, influenced by imperfect feedback and constraints on energy costs, is reformulated as a Markov decision process (MDP) that operates with perfect acknowledgments through iterative updates of state information. Ultimately, the optimal energy selection policy that guarantees filtering performance is derived by solving a Bellman equation. The effectiveness of the proposed approach is confirmed through simulation results. Full article

Polycystic Ovary Syndrome (PCOS) is a widespread hormonal disorder affecting women of reproductive age, often leading to infertility and associated complications. This study presents a comprehensive stochastic mathematical framework to analyze the dynamics of PCOS with a particular focus on infertility and treatment outcomes. Here, the transitions between compartments represent progression of women through clinical states of PCOS (risk, diagnosis, treatment, recovery) rather than infection or transmission, since PCOS is a non-communicable disorder. The model incorporates probabilistic elements to break the symmetric and predictable assumptions inherent in deterministic approaches. This allows it to reflect the randomness and asymmetry in hormonal regulation and ovulation cycles, enabling a more realistic representation of disease progression. By utilizing stochastic differential equations, the study evaluates the impact of treatment adherence on fertility restoration. We establish the conditions for disease extinction versus the existence of an ergodic stationary distribution, which represents a form of long-term statistical symmetry. The results emphasize the importance of early diagnosis and consistent treatment. Furthermore, the proposed approach provides a valuable tool for clinicians to predict patient-specific trajectories and optimize individualized treatment plans, accounting for the asymmetric nature of patient responses. Full article

This study investigates how urban tourism contributes to sustainable development, with a focus on SDGs 8.9 and 17 in Nanyang City. Drawing on a reflective measurement model and employing Partial Least Squares Structural Equation Modeling (PLS-SEM), this study examines the impact of urban tourism on cultural promotion, employment creation, and multi-stakeholder collaboration. A total of 300 surveys were collected from locals and visitors across Nanyang City to analyze these relationships. The results suggest that urban tourism promotes economic development but is also a means to preserve cultural heritage, and in turn directly supports SDG 8.9 for sustainable tourism, leading to job creation and local culture preservation. The analysis also shows that collaboration among governments, private organizations, and local communities is needed to achieve effective urban tourism governance, as stated in SDG 17. This study contributes a novel theoretical development to the literature, relating SDG-based governance with local tourism dynamics whilst providing an emic perspective of how mid-sized Chinese cities like Nanyang City, through collaborative and inclusive governance of tourism, put SDGs 8.9 and 17 into practice. The results contribute to current tourism–SDG frameworks by showing how the presence of local cultural endowments and decentralized governance structures homogenizes a specific pathway toward sustainable urban tourism. Additionally, the results provided practical guidance for tourism practitioners and policymakers on how to increase urban tourism systems’ diversity, inclusiveness, and resilience. This study’s limitations, being restricted to a single city with a small sample and a lack of longitudinal follow-up, may make findings difficult to generalize. Full article

The main motivation of this research is the semi-analytical exploration of the dynamics of an asteroid that is attacked while approaching a planet (with an inelastic collision of the projectile normally to the surface of the asteroid occurring just before approaching). Namely, the particular case of the spin dynamics of the asteroid that has been struck by a projectile almost perpendicularly to the maximal-inertia principal axis, with further perturbing the dynamics of rotation due to gravitational torques during close approach to the planet, is investigated. The initial surface of the asteroid is assumed to be a rubble pile, but preferably with a quasi-rigid internal structure, with circa constant distances between various parts of the asteroid as a first approximation. As a result of an inelastic collision with the surface of the asteroid, the rubble-pile material should be thrown off the surface into outer space in large amounts; thus, the mass of the asteroid and the moments of inertia along its principal axes should be changed (as well as the regime of angular rotation around its maximal-inertia principal axis). The updated Euler’s equations, stemming from the conservation of angular momentum, have been presented with gravitational torques acting during the approach of the asteroid to the planet (taking into account the impact on the asteroid that occurs just before it enters the zone of close approach). The evolution of the non-linear spin dynamical state is studied, along with kinematical findings for Euler angles via the governing equations, in accordance with two main rotational stages: first, immediately after the impact on the asteroid’s surface; and second, at the regime of asteroid rotation during its close approach to the planet, with perturbations caused by gravitational torques (just after being struck by the projectile). Full article

A simplified kinetic model for the quantitative analysis of a potentiometric, pH-based urea biosensor is presented. The device was an electrolyte–insulator–semiconductor capacitor (EISCAP) with a pH-sensitive Ta₂O₅ gate functionalized by a polyallylamine hydrochloride (PAH)/urease bilayer. Within the steady-state approximation, the kinetic equations yielded an implicit algebraic relation linking the bulk urea concentration to the local pH at the sensor surface. Numerical solution of this equation, combined with a fitting routine, provides the apparent Michaelis–Menten constant ($K_M$) and the normalized maximum reaction rate (${\overline{k}}_V$). Validation against the literature data confirmed the reliability of the approach. Experimental results were then analyzed in both phosphate buffer (PBS) and artificial urine (AU), covering urea concentrations of 0.1–50 mM. The fitted parameters showed comparable $K_M$ values of 10.9 mM (PBS) and 32.4 mM (AU), but strongly different ${\overline{k}}_V$ values: $2.2\times {10}^{-4}$ (PBS) versus $8.6\times {10}^{-7}$ (AU). The three-order reduction in AU was attributed to the inhibitory effects inherent to complex biological fluids. These findings highlight the importance of the model-based quantitative analysis of EISCAP biosensors, enabling the accurate characterization of immobilized enzyme layers and guiding optimization for applications in realistic sample matrices. Full article

This work presents a method for simulating balanced gliding trajectories of high-hypersonic flight vehicles, circumventing the challenges associated with trajectory modeling for these advanced vehicles. A typical hypersonic vehicle is used as a case study to create an external shape prototype. Aerodynamic simulations are performed using atmospheric data corresponding to various altitudes throughout the hypersonic flight. This process generates aerodynamic characteristic models for the vehicle across various Mach numbers and altitude conditions. Subsequently, ballistic modeling is conducted using the simulated aerodynamic data. The ballistic curve is refined iteratively during critical flight stages, taking into account the missile’s terminal guidance towards the target. As a result, the ballistic modeling curve is made relatively precise. Simulation results demonstrate that, compared to conventional equation-based ballistic curve modeling, the proposed iteration method yields ballistic curves that more accurately reflect actual flight conditions. This enhances flight state parameters and facilitates missile simulation for targeting moving objects. Notably, the terminal guidance accuracy error decreases from 0.12° to 0.03°, establishing a robust foundation for accurate ballistic modeling of hypersonic vehicles. Full article

The present theoretical work is devoted to the construction of a model of the equation of state for matter, where the specific volume is used as the thermodynamic potential, and the entropy and the thermal part of the internal energy act as thermodynamic variables. Based on the proposed model, called STEC, calculations were carried out for aluminum in the region of high internal energies and entropies. A comparison of the calculated shock adiabats with the available data from shock-wave experiments indicates that the constructed equation of state describes well the thermodynamic properties of aluminum up to a shock compression pressure of about 1 TPa. The proposed STEC equation-of-state model can be used in numerical simulations of various processes under extreme conditions at high energy densities. Full article