Transition Phenomena Research Articles

Numerical Simulation of the Hysteresis Phenomenon and Asymmetrical Configuration of Turbulent Gas Flow in an Over-Expanded Nozzle Flows

The turbulent flow within Over-Expanded Nozzles is characterized by shock waves inducing unsteady separation of the boundary layer, which can exhibit both free and restricted detachment. This study investigates various physical phenomena encountered during the expansion regime, including supersonic jet formation, jet separation, adverse pressure gradients, shockwave interactions, turbulent boundary layers, compressible mixture layers, and large-scale turbulence. These complex phenomena significantly influence nozzle performance. Utilizing numerical simulations based on the resolution of Navier-Stokes equations via finite volume methods and employing the CFD-FASTRAN code, this research analyzes detachment characteristics, transition phenomena, and the predictive accuracy of different turbulence models. A test case from the ATAC project CNES-ONERA (Aerodynamics of Hoses and Back-bodies), is examined to elucidate the hysteresis phenomenon and asymmetrical configurations resulting from boundary layer detachment.

Statistical and computational efficiency for smooth tensor estimation with unknown permutations

We consider the problem of structured tensor denoising in the presence of unknown permutations. Such data problems arise commonly in recommendation systems, neuroimaging, community detection, and multiway comparison applications. Here, we develop a general family of smooth tensor models up to arbitrary index permutations; the model incorporates the popular tensor block models and Lipschitz hypergraphon models as special cases. We show that a constrained least-squares estimator in the block-wise polynomial family achieves the minimax error bound. A phase transition phenomenon is revealed with respect to the smoothness threshold needed for optimal recovery. In particular, we find that a polynomial of degree up to ( m − 2 ) ( m + 1 ) / 2 is sufficient for accurate recovery of order-m tensors, whereas higher degrees exhibit no further benefits. This phenomenon reveals the intrinsic distinction for smooth tensor estimation problems with and without unknown permutations. Furthermore, we provide an efficient polynomial-time Borda count algorithm that provably achieves the optimal rate under monotonicity assumptions. The efficacy of our procedure is demonstrated through both simulations and Chicago crime data analysis.

Evolution of linear internal waves over large bottom topography in three-layer stratified fluids

Evolutions of internal waves of different modes, particularly mode 1 and mode 2, passing over variable bathymetry are investigated based on a new numerical scheme. The problem is idealized as interfacial waves propagating on two interfaces of a three-layer density stratified fluid system with large-amplitude bottom topography. The Dirichlet-to-Neumann operators are introduced to reduce the spatial dimension by one and to adapt the three-layer system and significant topographic effects. However, for simplicity, nonlinear interactions between interfaces are neglected. Numerical techniques such as the Galerkin approximation, proven effective in previous works, are applied to save computational costs. Shoaling of linear waves on an uneven bottom is first studied to validate the proposed formulation and the corresponding numerical scheme. Then, for two-dimensional numerical experiments, mode transition phenomena excited by locally confined bottom obstacles and quickly varying topographies, including the Bragg resonance, mode-2 excitation, wave homogenization, etc., are investigated. In three-dimensional simulations, internal wave refraction by a Luneberg lens is considered, and good agreement is found in comparison with the ray theory. Finally, in the limiting case, when the top layer can be negligible (for example, a gas layer of extremely small density), the problem is reduced to a two-and-a-half-layer fluid system, where an interface and a surface are unknown free boundaries. In this situation, the surface signature of an internal wave is simulated and verified by introducing the realistic bathymetry of the Strait of Gibraltar and qualitatively compared with the satellite image.

Glass transition temperature of asphalt binder based on atomistic scale simulation

Glass transition is one of the most crucial physical properties for polymerical materials. As a typical complex polymerical material, the glass transition phenomenon in asphalt binder is directly related to their temperature-related properties. To investigate the glass transition characteristics, this study delves into the glass transition temperature of asphalt binder based on molecular dynamics simulations. It is found that the calculation range for the glass transition temperature sits between 100 and 400 K. The evolution of asphalt binder structure is influenced by different cooling rates, where lower cooling rates allow sufficient microstructural rearrangement, resulting in a smaller volume at the lower temperature. Model size is closely associated with the glass transition region. As the size increases, the transition region significantly expands. Increasing the model size also reduces volume fluctuations after isothermal relaxation, providing more stable volume changes. It is observed that higher cooling rates with a model size over 100 Å can well reproduce the glass transition process of asphalt binders. This work provides atomic-scale insights for the glass transition phenomenon in asphalt binder, which could be beneficial for the design of high-performance asphalt binder.

Dissemination dynamics based on delayed behavior on double-layer networks

Adoption behavior spreads socially due to a variety of variables, and the classic dynamic model is insufficient to fully understand the impact of psychological elements on humans. To illustrate the intricacy of personal decision-making and information dissemination, this paper presents the psychological mechanism of latency. This research analyzes the dynamic process on double-layer networks using an edge division theory based method. The simulation results show the phenomena of phase transition. Global outbreak is possible when latency behavior is weak; global outbreak did not happen when latency behavior becomes strong. There is good agreement between the theoretical analysis and experimental simulation results. It is extremely important for the study of psychology, sociology, and dynamics.

Numerical study on cavitation generation induced by the high-speed jet impact on the water surface

The complex interaction between shock waves and two-phase interfaces can generate cavitation. In this study, the cavitation induced by the high-speed jet impact on the water surface was investigated. The mixture fluid is modeled using the barotropic equation of state under the framework of the two-phase flow model, which can describe the mixture of air, water, and vapor with any proportion. Through constructing a 1D Riemann problem for the impact-induced cavitation phase transition, it indicates that the coupling effect of multiple rarefaction waves emitted from the two-phase interface is responsible for the cavitation phase transition inside the liquid. Then, a 3D (three-dimensional) simulation regarding the impact of a high-speed jet on the water surface was conducted and validated against previous experiments that captured the cavitation phase transition phenomenon in the central region after the jet impact. The 3D simulation results revealed the spatial structure and development process of shock waves in detail. The coupling effects of shock waves and two-phase interfaces generate a ring-shaped rarefaction wave, which develops radially inward and superimposes, resulting in the formation of acorn-shaped cavitation bubble nuclei inside the water. The 3D simulation can provide spatial shock/rarefaction wave structures and internal flow details that have never been obtained in experiments, such as shock generation and propagation, rarefaction wave generation and center convergence, and the internal structure of acorn-shaped cavitation nucleation. Furthermore, the influence of the jet velocity on the cavitation intensity was analyzed, and a quantitative relationship was provided.

Numerical simulations of freezing behaviors of water droplets impacting cold hydrophobic surfaces

Freezing, as a prominent phase transition phenomenon, occurs frequently in nature and industry. This study employs a combination of the Volume of Fluid(VOF) model, solidification model, and a dynamic contact angle model to simulate the dynamics and solidification process of droplets impacting supercooled surfaces. Two distinct freezing morphologies, central-concave and central-convex, are observed. These different morphologies are attributed to the competition between the time scales associated with droplet impact dynamics and solidification (retraction time tr and solidification time tf,p). Thus, we propose a scaling law to predict the occurrence of different morphologies: when tr < tf,p, the final freezing morphology exhibits a central-convex shape, while when tr > tf,p, it exhibits a central-concave shape. In order to explore effects of nucleation on solidification, the classical nucleation theory is adopted to determine the nucleation time, and thus the freezing behaviors can be well captured. Furthermore, we examine the effect of volume expansion during phase transition on the freezing behaviors, and find that the increase in freezing time due to volumetric expansion can be well predicted by the scaling law tf ∼ Δ(H2)/ΔT.

A research of higher-order network emotional phase transitions

This paper explores the law of emotion transmission on the social Internet. By applying higher-order network theory, ER random networks are reconstructed and higher-order network structures with multiple interaction points are generated. The I-state of the SI model is extended to set up the propagation rules of emotions based on higher-order networks. Concepts such as sentiment recession rate are introduced to make sentiment propagate through different simplexes, so as to obtain the propagation rules of higher-order networks. Qualitative analysis of emotional changes during the propagation process verifies the phase transition phenomenon of emotions in the network. By comparing simulated results with actual data, we demonstrate the accuracy of our higher-order network-based emotion propagation model in reflecting real-world trends and outcomes. The study also explores the effects of factors such as the initial proportion of extreme emotions on emotion propagation. This study provides valuable insights into understanding the operation of complex systems and offers important implications for government predictions of opinion development.

A computational analysis on thermodynamic changes in liquid and solid states of carbon at liquid-liquid phase coexistence temperature

The carbon is an important element which belongs to group 14 of the periodic table and shows multiple applications in our daily life as well as at the industrial scale. It is a promising element which represents the liquid–liquid phase transition (LLPT) phenomena. Additionally, it shows interesting anomalous behavior with some usual thermodynamic properties such as heat capacity ([Formula: see text]) near about the liquid–liquid phase coexistence temperature ([Formula: see text]). Hence, it is quite challenging and difficult to simulate carbon at or near the liquid–liquid phase coexistence temperature. This anomalous behavior also creates complications in computing the precise and equilibrated thermodynamic properties close to [Formula: see text]. Therefore, we have studied the thermodynamic behavior of liquid and solid (diamond) states of carbon at liquid–liquid phase coexistence temperature ([Formula: see text]) while transforming from liquid to solid state and achieving the equilibrated liquid and solid states individually. Additionally, we have also performed a similar analysis on melting temperature ([Formula: see text]) to compare the system trends and its thermodynamics behavior in liquid and solid states, respectively. Furthermore, all the predicted thermodynamic results are quite consistent and able to show the equilibrium changes at the liquid–liquid phase coexistence temperature ([Formula: see text]) and melting temperature ([Formula: see text]), respectively.

Multiple spreading phenomena for a multistable reaction-diffusion equation with a free boundary

This paper deals with a nonlinear reaction-diffusion equation with a free boundary, where the nonlinearity has m+1 (m≥2) stable steady states and can be degenerate. Such problems may be used to model invasion phenomena with an expanding front. We focus on the long time dynamical behaviors of the solution, which can be classified into 2m+1 scenarios: vanishing, ith-spreading, and ith-transition for i=1,2,⋯,m. In particular, we observe m distinct types of spreading phenomena that correspond to m stable steady states. Additionally, we observe m different types of transition phenomena that correspond to m varieties of standing waves. Furthermore, by introducing a parameter to describe the initial function's amplitude, we demonstrate that there are m threshold values that guarantee the occurrence of each scenario.

Efficient anti-frosting enabled by femtosecond laser-induced salt-philic and superhydrophobic surface

Frost formation is a normal phase transition phenomenon in cold climates, while it usually brings certain troubles to human lives and production. Therefore, it is of great significance to develop frost resistant materials and key technologies. Here, a salt-philic and superhydrophobic surface is designed on a PDMS substrate by femtosecond laser direct writing technology in combination with salt–ethanol–water mixtures droplet treatment. The laser-treated PDMS embedded salt (LTP-S) surface exhibits superhydrophobicity, which alone is a property that can resist the formation of frost and enables a self-cleaning effect. Meanwhile, the salt coating further enhances the frost resistance of the surface by reducing the freezing point temperature. The LTP-S surface is revealed to perform well in frosting-defrosting cycles, washing resistance, chemical corrosion resistance, heating resistance, and long-term air exposure tests as a highly efficient and stable anti-frosting surface. This work demonstrates a facile strategy to fabricate a salt-philic and superhydrophobic surface for efficient anti-frosting.

Modeling freezing and BioGeoChemical processes in Antarctic sea ice

AbstractThe Antarctic sea ice, which undergoes annual freezing and melting, plays a significant role in the global climate cycle. Since satellite observations in the Antarctic region began, 2023 saw a historically unprecedented decrease in the extent of sea ice. Further ocean warming and future environmental conditions in the Southern Ocean will influence the extent and amount of ice in the Marginal Ice Zones (MIZ), the BioGeoChemical (BGC) cycles, and their interconnected relationships. The so‐called pancake floes are a composition of a porous sea ice matrix with interstitial brine, nutrients, and biological communities inside the pores. The ice formation and salinity are both dependent on the ambient temperature. To realistically model these multiphasic and multicomponent coupled processes, the extended Theory of Porous Media (eTPM) is used to develop Partial Differential Equations (PDEs) based high‐fidelity models capable of simulating the different seasonal variations in the region. All critical variables like salinity, ice volume fraction, and temperature, among others, are considered and have their equations of state. The phase transition phenomenon is approached through a micro‐macro linking scheme. In this paper, a phase‐field solidification model [4] coupled with salinity is used to model the microscale freezing processes and up‐scaled to the macroscale eTPM model. The evolution equations for the phase field model are derived following Landau‐Ginzburg order parameter gradient dynamics and mass conservation of salt allowing to model the salt trapped inside the pores. A BGC flux model for sea ice is set up to simulate the algal species present in the sea ice matrix. Ordinary differential equations (ODE) are employed to represent the diverse environmental factors involved in the growth and loss of distinct BGC components. Processes like photosynthesis are dependent on temperature and salinity, which are derived through an ODE‐PDE coupling with the eTPM model. Academic simulations and results are presented as validation for the mathematical model. These high‐fidelity models eventually lead to their incorporation into large‐scale global climate models.

Promoting green taxation and sustainable energy transition for low-carbon development

Since there is a scientific consensus that the energy sector has brought the planet to the tipping point of climate change, transitioning to sustainable energy sources is inevitable to halt foreseeable climatic adversities. This study looks at how promoting green taxation and sustainable energy transition affected the G7 nations’ goal of low-carbon development between 1994 and 2020. This study used Generalized Least Squares Random Effects Regression and Driscoll-Kraay Standard Errors-based Least Sqaures approaches for empirical analysis. The latter approach accounts for cross-sectional dependence, heteroscedasticity, and autocorrelation to provide robust empirical outcomes. The empirical results are as follows: Firstly, through lowering CO2 intensity and greenhouse gas emissions, the environmental tax revenues have enhanced the condition of the environment. The total tax revenues linked to the environment had a greater overall impact than the tax revenues related to the energy industry. Furthermore, compared to CO2 intensity, both of the environmental tax revenue factors contributed considerably more to greenhouse gas emissions. Second, the sustainable energy transition helped to lower greenhouse gas and CO2 intensity. Among covariates, international trade was supportive of low-carbon development, but industrialization and GDP per capita did the opposite. The panel bootstrap causality revealed a unidirectional causal connection from all independent variables, except foreign direct investment, to CO2 intensity and greenhouse gas emissions. These results demonstrated that the G7 nations’ environmental policies supported their commitment to achieving low-carbon development goals. In this respect, the G7 nations’ environmental emission reduction efforts benefited more from the overall environmental tax revenues. To secure the industrial emissions reduction for a future with net-zero carbon emissions, it is thus advised to continue using policies that price environmental emissions, such as the carbon taxation regulations. Additionally, plans for the sustainable energy transition that includes a quick rise in renewable energy sources in the overall energy mix are successful in lowering environmental emissions. For environmental sustainability and low-carbon development, it is thus advised to divert the taxation burden from renewable energy technologies to the fossil fuel industry to enhance the sustainable energy transition phenomenon for achieving Sustainable Development Goals (especially SDG-7 and SDG-13).

Keeping up with the decarbonization: Conceptualizing and investigating incumbents’ responses to transition pressures in the post-Paris world

Incumbents are central regime actors who simultaneously adapt to transitions and actively shape them. This study has two objectives: advance the conceptualization around these actors’ behaviors in contemporary transition processes and demonstrate a novel research approach to study this behavior in practice. The focus is on incumbents’ responses to transition-related external pressures. These responses are studied by reviewing related work from organization and management literature, as well as conducting an empirical case study in the aviation sector. The theoretical and empirical insights are combined through flexible pattern matching into a conceptual framework, which simultaneously accommodates a holistic view of different types of responses incumbents use to navigate the complex operating environment, while also supporting particularity that goes beyond strategy talk. For the empirical investigation, this research utilizes incumbent airlines’ transition risk work as a source of information on what external pressures these actors themselves perceive and the responses they operationalize. The empirical case study illustrates how by distinguishing between standard, inconsistent, and unconventional response areas that incumbents take part in, even a snapshot analysis of a contemporary transition phenomenon can reveal what is happening in socio-technical regimes. The analysis also pinpoints how responses have two important characteristics that signify the importance of acknowledging the variety of responses that incumbents have at their disposal: multi-functionality and parallelity. Together, the insights of this paper can support the study and understanding of the complex, heterogeneous, and nuanced behavior of incumbent organizations, and encourage more research efforts on transitions in the making.

Synthesis and annealing effect of structural, morphology, optical, and magnetic properties of tin telluride (SnTe)

This study explored the structural, vibrational, morphological, optical, and magnetic characteristics of both as-grown and annealed single crystals of tin telluride (SnTe), employing diverse analytical techniques. X-ray powder diffraction (XRD) analysis shows the cubic lattice structure of SnTe with consistent lattice parameters across different temperatures, along with the phase transition phenomenon. Fourier Transform Infrared Spectroscopy (FTIR) elucidates temperature-induced shifts in vibrational modes, indicating sensitivity to thermal stimuli. Scanning electron microscopy (SEM) reveals layer-by-layer growth patterns and temperature-dependent variations in crystal morphology. Energy-dispersive X-ray analysis (EDAX) confirms the synthesized crystals' high purity and slight tellurium-rich composition. Optical band gap measurements demonstrate an increase in band gap upon annealing, attributed to valence band convergence. Field-dependent magnetization (M − H) curves exhibit ferromagnetic properties at ambient temperature, which escalate with increasing annealing temperature. Electron Paramagnetic Resonance (EPR) spectra reveal spin mobility and exchange coupling, with variations in the g-factor suggesting the presence of additional spin entropy. These observations offer significant insights into the complex properties of SnTe, which are crucial for its potential applications across various technological fields.

Enhanced structural stability of P2-Na0.75Ni0.25Mn0.75-xTixO2 cathodes with high-voltage non-phase transitions property by Mn-sites manipulation strategy

Ni/Mn-based cathode is regarded as a competitive candidate for sodium-ion batteries (SIBs) owing to its high theoretical capacity and low cost. Nevertheless, the issue of its poor cycling stability continues to be a significant obstacle. In this work, P2-Na0.75Ni0.25Mn0.75-xTixO2 (NaNMT-x) cathode materials with high-voltage non-phase transitions property were successfully synthesized. Interestingly, Ti-doping strategy could induce a beneficial reinforcement in the occupancy of stabler Nae sites. Especially, the Nae/Naf ratio of NaNMT-0.15 reached the maximum, which was beneficial for stability. Besides, NaNMT-0.15 with the lowest thermodynamic formation energy and narrower band gap could clearly elaborate excellent structural stability and conductivity via the calculation. The results demonstrated the underlying mechanisms. From the capacity-diffusing factor numerical model and GITT, NaNMT-0.15 have best Na+ diffusion ability. Moreover, ex-situ XRD further demonstrated that NaNMT-0.15 cathode did not undergo obvious P2-O2 phase transition phenomenon in high voltage section. The “no phase transitions” effect enabled NaNMT-0.15 cathode to present distinguished initial capacity (126.0 mAh g−1 at 0.1 C) and stability (85.0 % over 100 cycles). These findings might offer a fresh perspective for designing novel Ni/Mn-based cathode materials with no P2-O2 phase transitions property.

Continuous reduction and phase transformation mechanism of pellets in lumpy zone based on dissected hydrogen blast furnace

The continuous phase transition phenomena and mechanism of pellets in the hydrogen blast furnace is achieved by dissecting the 40m3 hydrogen blast furnace. The results of the dissection reveal that the lumpy zone extends to the bosh of the hydrogen blast furnace (HBF), while it ends at about 2/3 of the stack in traditional blast furnace. The iron oxide (FeOx) began to appear in the upper stack, while the iron started to appear in the lower stack. The reduction rate and metallization rate at the bosh are measured at 95.18% and 95.54%. The content of ferrous oxide (FeO) decreases significantly (measured at 1.73% at the bosh), resulting in an increase in the melting point of the primary slag and a deterioration of its fluidity. FeOx formed in the upper stack continuously diffuses and merges into the gangue, which affects the subsequent transformation of FeOx. FeOx shows a preference for interacting with SiO2, CaO, and MgO, directly influencing the formation of slag in the cohesive zone. These findings offer valuable insights for numerical simulation and research on hydrogen-rich operation.

Experimental investigation on the mode transition characteristics of a phase-change thermofluidic oscillator with external loads

Phase-change thermofluidic oscillator has drawn significant attention thanks to its low operating temperature, which is beneficial for recovering low-grade heat. The vapor–liquid coupling oscillation in the thermofluidic oscillator leads to complex non-linear mode transition phenomenon that affects the steady operation. In this work, the mode transition characteristics of a thermofluidic oscillator with external loads (i.e., a needle valve and a load reservoir) are experimentally investigated through bifurcation analysis. A low-order van der Pol model is employed to examine the effect of acoustic resistance on mode transition. Experimental results demonstrate that modifying the valve opening and load volume under a constant temperature difference can trigger bifurcation, resulting in high-frequency limit cycle, low-frequency limit cycle and quasi-periodic modes. The non-linear features of each mode are revealed through phase space and Poincaré section, with Neimark-Sacker bifurcation, second bifurcation and inverse Neimark-Sacker bifurcation observed. Steady-state performance of oscillator is then characterized under different oscillation modes. The maximum pressure amplitudes measured are 11.54 kPa during the high-frequency oscillation and 1.35 kPa during the low-frequency oscillation, while the maximum displacement amplitudes obtained are 45.5 mm during the high-frequency oscillation and 91.4 mm during the low-frequency oscillation. The oscillation modes can be adjusted by external load to maximize output performance. This study offers comprehensive guidelines for constructing phase-change thermofluidic oscillators.

In Situ Electrochemical Recovery: Sediment Transformation under Chromium Poisoning in Reversible Solid Oxide Cells with La0.6Sr0.4Co0.2Fe0.8O3-σ-Based Oxygen Electrodes.

Reversible solid oxide cells (RSOCs) are an all-solid-state electrochemical device, which can convert H2 into electricity in the fuel cell (SOFC) mode and electrolyze H2O into fuel gas in the electrolytic cell (SOEC) mode, exhibiting good application prospect in the development of carbon neutrality. However, the degradation of the air electrode caused by Cr-containing steel interconnects is a major obstacle that limits the broader application of RSOCs. Herein, the Cr poisoning effect on La0.6Sr0.4Co0.2Fe0.8O3-σ (LSCF)-based oxygen electrodes under the electrolysis mode was systematically investigated. The phase transition of the sediment during the chromium poisoning process was captured and monitored. When tested under the presence of Fe-Cr interconnects at 800 °C for 40 h, SrCrO4 on the surface of LSCF was clearly identified through XRD and Raman analysis as the main deposition, and with the prolonged operating time, LaCrO3 slowly emerged. Due to the much higher electrical conductivity of LaCrO3 compared to SrCrO4, the negative effect induced by Cr poisoning was offset along with test progressing due to the deposition transition phenomenon. Inspired by the interesting discoveries, transition from SrCrO4 to LaCrO3 can be artificially facilitated by switching the operating mode to the SOEC mode, which can partially recover the dramatic degradation caused by the Cr poisoning effect under the SOFC mode. The feasibility of the in situ electrochemical recovery method was also verified by the experimental results. The peak power density of the cells decreased from 0.829 to 0.505 W/cm2 when operating under the SOFC mode with an Fe-Cr metal connector, and after in situ electrochemical recovery in the SOEC mode, the peak power density recovered to 0.630 W/cm2. This study provides a new strategy for achieving high performance and stability of RSOCs.

Alzheimer's Disease Mortality Rate: Correlation with Socio-Economic and Environmental Factors.

The progressive increase in the number of deaths caused by Alzheimer's disease (AD) in Brazil and around the world between 2010 and 2020 raises questions in scientific society. At the same time, there is also an increase in life expectancy at birth (LEB). Thus, the aim of this study was, for the first time, to compare the increase in AD mortality rate (ADMR) in Brazilian regions over the years 2010 to 2020 with the increase in LEB, and investigate the possible correlation between these demographic transition phenomena and pesticide sales and exposure during this period. Data were extracted from the Brazilian Institute of Geography and Statistics (IBGE), from the Department of Informatics and Technology of the Brazilian Ministry of Health (DATASUS) and from the Brazilian Institute of the Environment and Renewable Natural Resources (IBAMA). There was a significant increase in life expectancy at birth and in ADMR over the years between 2010 and 2020 in all Brazilian regions, with the female population in the South region being the most affected. In conclusion, there is a strong positive correlation between the increase in ADMR and LEB; ADMR and Human Development Index (HDI) and ADMR and pesticide sales and exposure in Brazil over the years studied.