Bubble Phenomena Research Articles

Analysis of bearing capacity of consolidated clay under the track load of deep-sea mining vehicle

Analysis of bearing capacity of seabed consolidation foundation is conducted. Two types of bearing capacity along the vertical and horizontal directions are derived. The stress distribution between tooth plates is analyzed using the slip line field theory, and the soil between the tooth plates is divided into wedge-shaped rigid zones, passive slip zones, and transition zones. The analysis results show that the ratio of tooth depth to tooth spacing significantly affects the formation pattern of the failure zone between the tooth plates. When the depth-to-spacing ratio is small, all three zones are present, while as the ratio gradually increases, the rigid wedge-shaped zone also increases, the transition zone becomes smaller, and the passive zone disappears. Therefore, it is advisable to arrange a smaller depth-to-spacing ratio to fully exploit the strength potential of the soil between the tooth plates. The results of the finite element method (FEM) analysis also show the existence of active and passive zones beneath the crawler tracks, and due to the combination of orthogonal loadings in the vertical and horizontal directions, there is a phenomenon of skewed stress bubbles in the foundation soil beneath and correctness of the derived bearing capacity of the foundation in this study.

Wetting phenomena of droplets and gas bubbles: Contact angle hysteresis based on varying liquid-solid and solid-gas interfacial tensions.

Wetting phenomena have been widely observed in our daily lives, such as dew on lotus leaf, and applied in technical applications, e.g., ink-jet printing. In contrast to constant liquid-solid and solid-gas interfacial tensions in Young's law, we here focus on the wetting phenomena by considering varying fluid-solid interfacial tensions. We analyze the energy landscape, the map of Young's contact angle, the number and corresponding contact angle of local energy minima, and the contact angle hysteresis for a liquid droplet on a solid substrate in a gas phase. In addition, a gas bubble on a solid substrate in a liquid phase has been scrutinized from the aspect of surface energy minimization. The wetting effect has been regarded, where the liquid and gas species penetrate into the solid phase on the microscopic scale [F. Wang and B. Nestler, Phys. Rev. Lett. 132, 126202 (2024)]. We assume the liquid-solid and the solid-gas interfacial tensions to be a function dependent on the volume fraction of the liquid and the gas species and investigate the impact of the size ratio of the droplet to the solid surface that is overlooked in existing theories on the wetting phenomena. Our finding sheds light on the microscopic origin of the contact angle hysteresis and the droplet size effect on the wetting phenomena.

INFERENCE IN MILDLY EXPLOSIVE AUTOREGRESSIONS UNDER UNCONDITIONAL HETEROSKEDASTICITY

Mildly explosive autoregressions have been extensively employed in recent theoretical and applied econometric work to model the phenomenon of asset market bubbles. An important issue in this context concerns the construction of confidence intervals for the autoregressive parameter that represents the degree of explosiveness. Existing studies rely on intervals that are justified only under conditional homoskedasticity/heteroskedasticity. This paper studies the problem of constructing asymptotically valid confidence intervals in a mildly explosive autoregression where the innovations are allowed to be unconditionally heteroskedastic. The assumed variance process is general and can accommodate both deterministic and stochastic volatility specifications commonly adopted in the literature. Within this framework, we show that the standard heteroskedasticity- and autocorrelation-consistent estimate of the long-run variance converges in distribution to a nonstandard random variable that depends on nuisance parameters. Notwithstanding this result, the corresponding t-statistic is shown to still possess a standard normal limit distribution. To improve the quality of inference in small samples, we propose a dependent wild bootstrap-t procedure and establish its asymptotic validity under relatively weak conditions. Monte Carlo simulations demonstrate that our recommended approach performs favorably in finite samples relative to existing methods across a wide range of volatility specifications. Applications to international stock price indices and U.S. house prices illustrate the relevance of the advocated method in practice.

Experimental investigation of heat transfer and pressure drop in copper manifold microchannel heat sinks

Over the past decade, various two-phase cooling solutions have been implemented to dissipate power in high heat flux electronic components. The manifold microchannel heat sink is an efficient thermal management solution that reduces heat resistance while also limiting the pumping power. However, there is limited work available on small form factor manifold microchannels with traditional heat sinking materials like copper. In this study, an experimental investigation is conducted to evaluate the heat transfer and pressure drop performance of copper manifold microchannel heat sinks using an environmentally friendly refrigerant, R1233zd(E), as the working fluid. A microchannel plate and a manifold plate, both made of oxygen-free copper, are sandwiched together to form the manifold microchannel test sample assembly. To compare the effects of geometric parameters, a total of six manifold microchannel test samples are investigated, including two types of manifold plates and three types of microchannel plates. The experiments are performed with refrigerant mass flow rates ranging from 5 to 15 g/s and inlet subcooling temperatures ranging from 3 to 10 K. The heat transfer coefficient increases with a decreasing number of manifolds and with an increase in the number and width of the microchannels. The pressure drop decreases in configurations with more microchannels, more manifolds, and larger microchannel widths. Compared to traditional microchannels, manifold microchannels significantly reduce the total pressure drop. However, their heat transfer performance at higher heat flux conditions is limited by the trapped bubbles phenomena. In comparison to traditional microchannels, manifold microchannels demonstrate much higher performance in dissipating the same amount of heat flux while limiting pumping power, as indicated by the COP.

Filter Bubble Trap: The Effect of TikTok Media on Language Use and Interaction Among Communication Science Students at UINSU

This article aims to explore the impact of the filter bubble created by the social media algorithm of TikTok on the language use and social interactions of Communication Studies students at the State Islamic University of North Sumatra (UINSU). The urgency of this research lies in the increasing dominance of TikTok in students' daily lives and how this platform shapes their behavioral and communication patterns. This study employs a qualitative method with a field research approach. The primary data sources are 10 key informants selected through purposive sampling, while secondary data are derived from books, scholarly articles, and reports. Data collection techniques include interviews, observations, documentation, and literature study. Data analysis is carried out through data reduction, data display, and conclusion drawing, with the validity of the data tested using triangulation techniques. The findings indicate that the filter bubble phenomenon has varied effects on students. On one hand, some students feel that the filter bubble limits their views on social and cultural issues, while others find it helpful in obtaining relevant and beneficial information. Additionally, TikTok also influences the language usage of students, with some reporting an expansion in their vocabulary and an increase in creativity, although it also leads to the use of more colloquial and less formal language. The discussion highlights the importance of digital literacy and critical awareness in utilizing social media. These findings align with the filter bubble theory by Eli Pariser, which emphasizes the need for exposure to diverse views to avoid intellectual isolation. Overall, the research suggests that students should be trained to use social media wisely, enabling them to maximize its benefits without falling into the shackles of the filter bubble.

Self-adaptive and time divide-and-conquer physics-informed neural networks for two-phase flow simulations using interface tracking methods

Physics-informed neural networks (PINNs) are emerging as a promising artificial intelligence approach for solving complex two-phase flow simulations. A critical challenge in these simulations is an accurate representation of the gas–liquid interface using interface tracking methods. While numerous studies in conventional computational fluid dynamics (CFD) have addressed this issue, there remains a notable absence of research within the context of PINNs-based two-phase flow simulations. Therefore, this study aims to develop a robust and generic PINNs for two-phase flow by incorporating the governing equations with three advanced interface tracking methods—specifically, the Volume of Fluid, Level Set, and Phase-Field method—into an improved PINN framework that has been previously proposed and validated. To further enhance the performance of the PINNs in simulating two-phase flow, the phase field constraints, residual connection and the time divide-and-conquer strategies are employed for restricting neural network training within the scope of physical laws. This self-adaptive and time divide-and-conquer (AT) PINNs is then optimized by minimizing both the residual and loss terms of partial differential equation. By incorporating the three different interface tracking methods, it efficiently handles high-order derivative terms and captures the phase interface. The case of single rising bubble in two-phase flow is simulated to validate the robustness and accuracy of the AT PINNs. The simulation's accuracy is evaluated by comparing its performance in terms of velocity, pressure, phase field, center of mass, and rising velocity with that of conventional PINNs and CFD benchmarks. The results indicate that the AT PINNs coupled with these interface tracking methods offers a satisfactory performance in simulating rising bubble phenomenon.

Bifurcation Analysis and Spatiotemporal Dynamics in a Diffusive Predator–Prey System Incorporating a Holling Type II Functional Response

This study aims to investigate a diffusive predator–prey system incorporating additional food for predators, prey refuge, fear effect, and its carry-over effects. For the temporal model, the well-posedness and persistence of the system have been discussed. We investigated the existence and the stability behavior of the various equilibria. Furthermore, we explored the bifurcations of codimension-1 including transcritical, saddle-node, and Hopf, concerning the crucial parameters. The system also presents codimension-2 bifurcations such as Bogdanov–Takens and cusp bifurcation along with the global homoclinic bifurcation. We observed the bubbling phenomena, which illustrate the fluctuations in the amplitudes of the periodic oscillations. For the spatiotemporal system, we established the non-negativity and boundedness of the solutions. We derived the conditions for the diffusion-driven instabilities in a confined region with Neumann boundary conditions. Extensive numerical simulations have been conducted to depict the various stationary patterns in Turing space. It is observed that incorporating cross-diffusion divides the bi-parametric plane into various sub-regions and dynamic patterns are analyzed in these different regions. The intricate spatiotemporal dynamics exhibited by prey–predator interactions are crucial for unraveling the intricacies within ecological systems.

Determining the Ebullient Phases in EFTA Stock Markets

Previous empirical literature supports the idea that stock bubbles have impacts on the efficient allocation of wealth. Researchers targeted various economies in the past using various methods to explore the bubble phenomenon. This study uses the generalized SADF test, which is admitted by empirical literature to be the most successful technique, to explore stock bubbles in three countries included in the European Free Trade Association (EFTA) that have not been studied before. This paper takes the lead and tests for the existence of bubbles in the monthly end index prices of respective countries based on the latest available time series data from January 2001 to September 2019. Based on empirical results, it is concluded that the stock markets of all three countries experienced multiple bubbles during the study period. The case of Iceland is worse, where comparatively more fluctuations in stock prices are seen. To avoid the occurrence of further stock price bubbles in these countries, policy recommendations are provided as well.

A Moving Least-Squares/Level-Set Particle Method for Bubble and Foam Simulation.

We present a novel particle-grid scheme for simulating bubble and foam flow. At the core of our approach lies a particle representation that combines the computational nature of moving least-squares particles and particle level-set methods. Specifically, we assign a dedicated particle system to each individual bubble, enabling accurate tracking of its interface evolution and topological changes in a foaming fluid system. The particles within each bubble's particle system serve dual purposes. Firstly, they function as a surface discretization, allowing for the solution of surfactant flow physics on the bubble's membrane. Additionally, these particles act as interface trackers, facilitating the evolution of the bubble's shape and topology within the multiphase fluid domain. The combination of particle systems from all bubbles contributes to the generation of an unsigned level-set field, further enhancing the simulation of coupled multiphase flow dynamics. By seamlessly integrating our particle representation into a multiphase, volumetric flow solver, our method enables the simulation of a broad range of intricate bubble and foam phenomena. These phenomena exhibit highly dynamic and complex structural evolution, as well as interfacial flow details.

Identifying price bubbles in global carbon markets: Evidence from the SADF test, GSADF test and LPPLS method

Amid growing climate concerns, Emissions Trading Schemes (ETS) serve as key mechanisms for reducing greenhouse gas emissions through market forces. This study delves into the phenomenon of price bubbles within six major ETSs globally: the European Union Emissions Trading Scheme (EU ETS), the New Zealand Emissions Trading Scheme (NZ ETS), the California-Québec Emissions Trading Scheme (CQ ETS), the South Korea Emissions Trading Schemes (K-ETS), the China Emissions Trading Scheme (C-ETS), and the United Kingdom Emissions Trading Schemes (UK ETS). Employing the sup augmented Dickey-Fuller (SADF) test, generalized sup ADF (GSADF) test, and log-periodic power law singularity (LPPLS) model, our analysis aims to uncover the dynamics and implications of these bubbles. Our findings reveal varied patterns of price bubbles across the schemes, with the EU ETS showing the highest frequency and the NZ ETS exhibiting the longest durations. The period of 2021 and 2022 marked a significant increase in bubble occurrences across all ETSs, suggesting the influence of post-COVID-19 economic recovery and geopolitical tensions on market stability. These bubbles are attributed to factors including carbon market policies, macroeconomic conditions, energy price fluctuations, and market uncertainties. The study offers valuable insights for compliance firms, policymakers, and investors on navigating carbon market volatility. Understanding bubble dynamics can aid in formulating more effective emission reduction strategies, carbon pricing policies, and investment decisions. This research underscores the importance of integrating monetary policy considerations with environmental objectives within ETS frameworks, paving the way for future research on predictive bubble detection and the development of robust carbon market regulations.

Effects of porous transport layer wettability on performance of proton exchange membrane water electrolyzer: Mass transport overvoltage and visualization of oxygen bubble dynamics with high-speed camera

For producing hydrogen from renewable energy, a proton exchange membrane water electrolyzer (PEMWE) is an appealing method offering higher current density and purity of generated hydrogen than other electrolyzers. However, this technique should be further developed to have higher efficiency for utilization. The main issue on reducing the PEMWE performance is the management of generated oxygen bubbles near the reaction site. They persist near the reaction site, inhibit the water supply, and significantly reduce the reaction efficiency. Therefore, how oxygen bubbles are removed from the reaction site should be optimized, however, the mechanism of transport phenomena of oxygen bubbles through the porous transport layer (PTL) has not been clarified. Therefore, in this study, an original cell was developed which allowed us to observe bubble movements inside PTL with a high-speed camera, and the effects of PTL wettability on the oxygen bubble movement were investigated. The PTL wettability drastically affected the PEMWE performance and bubble movement, and hydrophobic PTL reduced the PEMWE performance. The oxygen bubbles tended to stay inside hydrophobic PTL, which might cause lower PEMWE performance.

Electrical tree degradation of MgO/epoxy resin composites at different voltage frequencies

AbstractElectrical tree degradation is one of the main causes of insulation failure in high‐frequency transformers. Electrical tree degradation is studied on pure epoxy resin (EP) and MgO/EP composites at frequencies ranging from 50 Hz to 130 kHz. The results show that the tree initiation voltage of EP decreases, while the growth rate and the expansion coefficient increase with frequency. Moreover, the bubble phenomenon at high frequencies in EP composites is discussed. Combined with trap distribution characteristics within the material, the intrinsic mechanism of epoxy composites to inhibit the growth of the electrical tree at different frequencies is discussed. It can be concluded that more deep traps and blocking effect are introduced by doping nano‐MgO into EP bulks, which can improve the electrical tree resistance performance of EP composites in a wide frequency range.

The Degree of Homogeneity Versus Heterogeneity in Individuals’ Political News Consumption

Abstract: This work investigated the prevalence of filter bubble or echo chamber-related phenomena, psychological factors rendering individuals resilient or vulnerable to them, and their associations to political views focusing on extremity and polarization. For this, a cross-cultural replication of a study by Sindermann et al. (2021) was conducted. As an extension, multiple political views variables were assessed to examine whether the application of different conceptualizations of political views explains heterogeneous findings across previous studies. Two samples were recruited: 390 ( n = 135 males) US college students and a quota sample of 489 ( n = 243 males) US adults. Participants completed personality scales and measures on political news consumption homogeneity versus heterogeneity and political views. Consistent with previous research, results revealed few individuals consume political news absolutely homogeneously. Openness was negatively related to the degree of political news consumption homogeneity, and the relationship between political news consumption homogeneity and political views yielded inconsistent, often statistically nonsignificant, results. These findings challenge the prevailing notion of filter bubbles and echo chambers as widespread phenomena and indicate that relationships between political news consumption homogeneity and political views are not necessarily deleterious with respect to extremization and polarization. As such, the results suggest that these phenomena might not be as significant for the general population as previously thought. Nonetheless, certain individuals might still find themselves in filter bubbles or echo chambers and suffer from accompanying consequences. In this regard, the present work replicates findings underscoring that individuals with lower Openness exhibit greater political news consumption homogeneity.

Carbon-based electrocatalysts for water splitting at high-current-densities: A review

Electrocatalytic water splitting is a promising strategy to generate hydrogen using renewable energy under mild conditions. Carbon-based materials have attracted attention in electrocatalytic water splitting because of their distinctive features such as high specific area, high electron mobility and abundant natural resources. Hydrogen produced by industrial electrocatalytic water splitting in a large quantity requires electrocatalysis at a low overpotential at a large current density. Substantial efforts focused on fundamental research have been made, while much less attention has been paid to the high-current-density test. There are many distinct differences in electrocatalysis to split water using low and high current densities such as the bubble phenomenon, local environment around active sites, and stability. Recent research progress on carbon-based electrocatalysts for water splitting at low and high current densities is summarized, significant challenges and prospects for carbon-based electrocatalysts are discussed, and promising strategies are proposed.

Characterization of microbubble aggregation in a double-T microfluidic chip

The coalescence phenomenon of air bubbles affects the flow field, bubble morphology, bubble velocity, and mass transfer efficiency in bioreactors, air bubble generators, and other devices. This article combines the level set method with COMSOL to simulate the formation process of two-phase fluid bubbles in microfluidic chips. The result shows that when the contact angle exceeds 90°, significant agglomeration occurs and the size of bubbles decreases with the increase in liquid flow velocity. However, as the gas velocity increases, agglomeration does not occur at liquid flow rates below 0.1 m/s. In addition, the agglomeration phenomenon occurs above the threshold, and when the gas flow rate is less than 0.02 m/s, there is no agglomeration phenomenon. The numerical simulation results exhibit an error rate of less than 10% compared to the experimental values, indicating that microfluidic chips can accurately predict the process of bubble coalescence.

Bubble nucleation and growth on microstructured surfaces under microgravity

Understanding the dynamics of surface bubble formation and growth on heated surfaces holds significant implications for diverse modern technologies. While such investigations are traditionally confined to terrestrial conditions, the expansion of space exploration and economy necessitates insights into thermal bubble phenomena in microgravity. In this work, we conduct experiments in the International Space Station to study surface bubble nucleation and growth in a microgravity environment and compare the results to those on Earth. Our findings reveal significantly accelerated bubble nucleation and growth rates, outpacing the terrestrial rates by up to ~30 times. Our thermofluidic simulations confirm the role of gravity-induced thermal convective flow, which dissipates heat from the substrate surface and thus influences bubble nucleation. In microgravity, the influence of thermal convective flow diminishes, resulting in localized heat at the substrate surface, which leads to faster temperature rise. This unique condition enables quicker bubble nucleation and growth. Moreover, we highlight the influence of surface microstructure geometries on bubble nucleation. Acting as heat-transfer fins, the geometries of the microstructures influence heat transfer from the substrate to the water. Finer microstructures, which have larger specific surface areas, enhance surface-to-liquid heat transfer and thus reduce the rate of surface temperature rise, leading to slower bubble nucleation. Our experimental and simulation results provide insights into thermal bubble dynamics in microgravity, which may help design thermal management solutions and develop bubble-based sensing technologies.

Поведінка фінансових ринків в експериментальному економічному аналізі

Behavioral aspects play an important role, and an experimental analysis of financial markets allows studying the psychological and behavioral factors that are affecting participants. The aim of the article is to analyze the interaction of financial market participants in a controlled experimental environment in order to identify and reveal the peculiarities of their behavior, strategies and mutual influence. The information base of the research is official information and scientific publications. Research was conducted using the following methods: monographic; analysis, synthesis, induction, deduction; system analysis. Systematic changes in consumer demand, production and other spheres of economy determine not only household habits, but also affect decision-making by participants in economic relations. The identified calendar anomalies indicate that economic entities react to time factors and seasonal changes, which is important for management and forecasting strategies. Price bubbles are an expression not only of objective market conditions, but also of psychological and socio-cultural influences on the behavior of market participants. Understanding and predicting price bubbles requires a comprehensive approach that combines economic, psychological and social aspects. This will allow more accurate analysis and management of risks associated with price fluctuations and their possible consequences for economic stability. As part of the experimental economic analysis, it is found that calendar and seasonal effects play a significant role in the formation of economic trends. The study of the phenomenon of price bubbles and adaptive expectations in experimental economic analysis reveals deep structures of market dynamics.

Influences of the wall distance and initial shape on the dynamic behaviors of near-wall bubbles

The phenomenon of buoyancy-driven bubbles near a fluid-solid interface is common in both natural settings and industrial processes, such as oil and gas exploration and production. The intricate dynamics of bubbles are profoundly shaped by their interactions with adjacent solid walls. In this study, a direct numerical simulation of bubbles rising near a wall is conducted using the volume of fluid method. The motion behavior and wake vortex structure of bubbles with three types of migration trajectories (linear, zigzag, and spiral) are analyzed. The influences of the initial shape and wall distance of the bubbles on their motion trajectory, rising velocity, and wake structure is investigated. The results show that the presence of a nearby wall obstructs the diffusion of eddies across a bubble surface, and the repulsive force induced by the wall increases as the distance between the bubble and the wall decreases. Remarkably, at a dimensionless wall distance of 0.6, a change in the lateral lift direction triggers a collision between a zigzagging bubble and the wall, consequently setting the bubble into a bouncing motion mode. In the case of spiral-moving bubbles, proximity to the wall enhances the likelihood of oscillations within the bubble's migration trajectory along the x-y plane while maintaining stability along the z-y plane. While variations in the initial aspect ratio of bubbles have marginal impacts on the migration paths of linear and zigzagging bubbles, the initial shape affects the migration trajectory of spiral bubbles to some extent. The bubble migration trajectory first experiences oscillations when the initial deformation reaches its maximum.

Application of the unified equation of bubble dynamics for simulating the large-scale air-gun bubble with migration effect

How to effectively reduce the high-frequency output caused by excessively steep initial peak slope and enhance the low-frequency output generated by bubble oscillation has become present research interest in seismic source design. The most effective way to improve the low-frequency content of a seismic source is to increase its chamber volume. However, the size of air-gun bubbles generated by large-volume air-gun sources has increased by several hundred times compared to traditional high-pressure air guns, which has made the migration phenomenon of bubbles no longer negligible. The previous air-gun bubble dynamics models did not comprehensively account for the effects caused by bubble migration phenomenon. In this paper, we have developed an air-gun bubble dynamics model based on unified equation for bubble dynamics, and the newly established model demonstrates a closer alignment with experimental data compared to models based on the Gilmore and Keller equations. Based on this, the influence of the design parameters of air-gun seismic source on the bubble migration is studied. It explores the ramifications of migration on the dynamic properties of air-gun bubbles and the signatures of seismic sources. Additionally, we examine how incoming flow velocity magnitude and air-gun design parameters influence the signatures of air-gun seismic sources. Finally, we investigate the impact of both the spacing between dual guns and the horizontal movement of bubbles caused by mutual attraction on the signatures of dual-gun sources.

Vibrations Analysis of Bubble Evolution in Liquids of Varying Physical Properties

In recent years there is an attempt to control the gas stirring intensity in metal-making ladles with the aid of vibration measurements. Understanding better the induced vibrations in two-phase flows can substantially improve the existing models for gas stirring control. In this work, highly sensitive accelerometers were used for the vibration measurements in a liquid metal alloy; Sn–40 wt pctBi alloy at 200 °C and water at 20 °C. The examination of the liquids was conducted in the ladle mockup integrated into the Liquid Metal Model for Steel Casting facility at Helmholtz-Zentrum Dresden Rossendorf. Single bubbles were generated in the respective liquids by controlled argon injection at low flow rates in the range of 0.01 to 0.15 NL min−1 through a single nozzle installed at the bottom of the ladle. Obtained results demonstrate differences between the induced vibrations in the examined liquids in terms of the magnitude of the root mean square values of vibration amplitude and the shape of the resulting curves with increasing flow rate. Furthermore, continuous wavelet transform reveals variations in the duration and vibrational frequency of the evolved bubble phenomena. The findings suggest that differences in the physical properties of the examined liquids result in variations in the vibrations induced during bubble evolution.