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This article is devoted to the investigation of gaseous bubble dynamics in oscillating viscous liquids of different density values. The study is conducted numerically using the level-set method with a non-stationary approach. The bubble is initially located near the upper wall of the container. The effects of the inclusion and host liquid viscosities on interaction of the bubble with the wall are analysed. The calculations show that in the absence of gravity, for low-viscosity fluids the bubble is attracted to the nearest wall, which is consistent with previous analytical and experimental results. With increasing viscosity, the vibrational attraction to the wall becomes weaker and is then replaced by repulsion, which can be explained by the decelerative effect of viscosity in the boundary layer near the rigid surface, where the average flow becomes less intensive. The dependencies of the repulsion force on the parameter values are obtained by using the balance method (investigation of the gravity level needed to attain the quasi-equilibrium state at a certain distance between the bubble and the wall). The calculations show that the repulsion force grows with decreasing Reynolds number (increase of the viscosity). This article is part of the theme issue 'New trends in pattern formation and nonlinear dynamics of extended systems'. [ABSTRACT FROM AUTHOR]

In this research, the effects of ultrasonic cavitation bubbles on the transesterification process were investigated utilizing a modified Rayleigh–Plesset model. Furthermore, the influence of some operating parameters on ultrasound biodiesel production from rapeseed oil and waste oil were evaluated containing operating temperature, reaction time, and catalyst (LiOH) concentration. According to researches, the several cycles of collapse and rebound of cavitation bubble are the basis of intense sound effects especially acoustic micro-streaming and shock waves. The results of this study revealed that the operating conditions of reaction were effective on the behavior of micro bubbles and the yield of transesterification. The results confirmed the enhancement and intensification of the transesterification process by sonication. The high temperature and pressure inside bubble induced operating parameters similar to supercritical conditions. This condition around hotspots could offer the presence of micro-reactors that speed up the rate of reaction. Moreover, cultivating the interfacial area between viscous films containing gas-filled bubbles and the liquid phase of reactants could be one of the effective parameters to increase the yield of ultrasonic method comparing with conventional mechanical stirring transesterification. The catalyst concentration amount had a significant influence on the reaction yield. The highest conversion efficiency (approximately 99.4%) was observed at 35 °C, after a reaction time of 35 min with alcohol to oil molar ratio of 6:1 and 0.5%wt of catalyst (LiOH). [ABSTRACT FROM AUTHOR]

Experimental investigations of Marangoni flow in micro-foams have faced challenges due to the inherent difficulties in detecting and measuring this flow. The Marangoni flow manifests as small spots within the lamellae films, which makes it hard to accurately analyze. Hence, to elucidate Marangoni flow characteristics, this study introduces and investigates comprehensive three-dimensional models of flow in microscale foams. The geometric models contained Plateau Borders (PB), nodes, and films. The recirculating Marangoni flow was simulated and studied for different interfacial mobilities. Inside the foams, the Marangoni flow velocities were at the same scale with the PB flow velocity for mobile interfaces. However, for a more rigid interface, the magnitude of the Marangoni flow was considerably less than that of the PB owing to the combined effect of high surface hydraulic resistance on the Marangoni flows and nature of the Marangoni flow as a surface-only flow type. Furthermore, the effect of the film thickness on the Marangoni flow was analyzed. Thicker films have a stronger effect in reducing the Marangoni flow than PB flow. This is due to the higher ratio of gravity body force to the Marangoni-driven surface force for thicker films. Finally, the combined effect of the liquid–air interfacial mobility and film thickness on the Marangoni velocity was studied. [ABSTRACT FROM AUTHOR]

Enhanced gas-liquid mass transfer is significant for the desulfurization and denitration of ship exhaust gases. As a fluid device, the special structure of the fluidic oscillator generates self-excited oscillations that can effectively enhance the mass transfer process of gas-liquid. But there are few studies on the internal gas-liquid flow. The transportation of individual bubbles in the fluidic oscillator was investigated by a high-speed camera and digital image analysis. The results show that the bubble experienced a significant deceleration process in the chamber region of the fluidic oscillator. In addition, the maximum bubble offset increased with the diameter of the initial bubble. The trajectory of the bubble showed zigzag movement due to the deflecting oscillation of the fluidic oscillator. At the same time, the deformation of the bubble was intensified by the deflecting oscillation. The deformation ratio of the bubble increased with the increase of Reynolds number. By studying the transport process of a single bubble in the fluid oscillator, it is considered that the fluid oscillator has the potential to be a new bubble generator. [ABSTRACT FROM AUTHOR]

Background: This paper sets out to design a device for removing bubbles during the process of hemodialysis. The concept is to guide the bubbles while traveling through the device and eventually the bubbles can be collected. The design focuses on the analysis of various parameters i.e. inlet diameter, inlet velocity and size of the pitch. The initial diameters of Models 1 and 2 have thread regions of 6 and 10 mm, respectively. Parameters: Swirl number, Taylor number, Lift coefficient along with pressure field are also implemented. Results: Based on computational fluid dynamics analysis, the bubbles' average maximum equilibrium position for Model 1 reached 1.995 mm, being greater than that of Model 2, which attained 1.833 mm. Then, 16,000 bubbles were released into Model 1 to validate the performance of the model. This number of bubbles is typically found in the dialysis. Thus, it was found that 81.53% of bubbles passed through the radial region of 2.20 ± 0.30 mm. The appropriate collecting plane was at 100 mm, as measured from the inlet position along the axial axis. The Taylor number, Lift coefficient, and Swirl number proved to be significant parameters for describing the movement of the bubbles. Results were based on multiple inlet velocities. It is seen that Model 3, the improved model with unequal pitch, reached a maximum equilibrium position of 2.24 mm. Conclusion: Overall, results demonstrated that Model 1 was the best design compared to Models 2 and 3. Model 1 was found capable of guiding the bubbles to the edge location and did not generate extra bubbles. Thus, the parametric study, herein, can be used as a prototype for removing bubbles during the process of hemodialysis. [ABSTRACT FROM AUTHOR]

A mathematical model was developed to investigate the refining process through using slot-porous matched dual tuyeres. In this model, the bubble expansion is considered through the ideal gas state equation. The density variation of bubbles is calculated through the mass conservation equation. The coalescence and breakup of bubbles are tracked using the discrete particle model (DPM). The transient flow is computed through the k-ε model with three continuous phases (air–slag–steel). Comparisons were made between traditional porous–porous and the new slot–porous tuyeres, mainly focusing on the mixing behavior and inclusion removement ratio. The results show that, for traditional porous–porous matched tuyeres (P-P mode), the inclusion removement ratio is 34.14%; by comparison, after employing the slot–porous matched tuyeres (S-P mode), the inclusion removements ratio rises to 36.34%. The mixing time is also shortened by 18.74% by using the S-P mode. The reason for this phenomenon is because the slot tuyere produces a strong asymmetry that drives more liquid at the bottom of the ladle. The new tuyere match takes advantage of porous and slot tuyeres, and the mixing behavior and inclusion removements are improved. The result is beneficial for future refining. [ABSTRACT FROM AUTHOR]

Due to their long history and extensive applications within modern society, foams have always been a popular topic of study. These systems are present everywhere in our life. They are also valuable in many industrial applications. For this reason, it is essential to continue investigating their properties and develop new materials to fabricate them. In this paper, we demonstrate a new way to create 3D foams by using an ordered viscoelastic material, the smectic liquid crystal (LC). Because of their lamellar structure, which is similar to soap, and their tunable properties that can be controlled via geometric confinement and external fields, smectic LCs are suitable for the fabrication of bubbles and foams. In this work, we present a compelling study of the parameters that influence the fabrication of LC foams in 3D. Particularly, we analyze the effects of the airflow rate and the geometry of confining boundaries on the assembly of their cells. We also compare our results to foams made with sodium dodecyl sulfate (SDS) and discuss the difference between their behaviors. Finally, we discuss how LC elasticity can substantially affect the stability and organization of foams. This work paves the way to exploiting new materials to fabricate foams with better monodispersity, uniformity, and controlled ordering that are useful in a wide range of industrial applications for which the tuning of properties is required. This includes the fields of oil recovery, decontamination, architecture, and design. [ABSTRACT FROM AUTHOR]

The influence of n-alkanol (C2–C10) water solutions on bubble motion was studied in a wide range of concentrations. Initial bubble acceleration, as well as local, maximal and terminal velocities during motion were studied as a function of motion time. Generally, two types of velocity profiles were observed. For low surface-active alkanols (C2–C4), bubble acceleration and terminal velocities diminished with the increase in solution concentration and adsorption coverage. No maximum velocities were distinguished. The situation is much more complicated for higher surface-active alkanols (C5–C10). In low and medium solution concentrations, bubbles detached from the capillary with acceleration comparable to gravitational acceleration, and profiles of the local velocities showed maxima. The terminal velocity of bubbles decreased with increasing adsorption coverage. The heights and widths of the maximum diminished with increasing solution concentration. Much lower initial acceleration values and no maxima presence were observed in the case of the highest n-alkanol concentrations (C5–C10). Nevertheless, in these solutions, the observed terminal velocities were significantly higher than in the case of bubbles moving in solutions of lower concentration (C2–C4). The observed differences were explained by different states of the adsorption layer in the studied solutions, leading to varying degrees of immobilization of the bubble interface, which generates other hydrodynamic conditions of bubble motion. [ABSTRACT FROM AUTHOR]

Two-phase flow boiling is the preferred method for efficient heat dissipation in electronic equipment, so the bubble dynamics and heat transfer characteristics of flow boiling in a single pentagonal rib channel are numerically analyzed by the volume of fluid (VOF) model. Three typical rib structures are obtained, whose block ratios are 0.4, 0.75, and 0.25, and the corresponding length-diameter ratios are 1.72, 0.59, and 12.70, respectively. The Reynolds number is 14,000 and 28,000. The heat flux is set from 50 to 150 kW/m². The results show that the starting position of the bubble is at the cone and sides of the rib, and its moving direction is related to the configuration of the rib, the heat flux, and fluid velocity. Additionally, the bubbles are shedding at the corner of the rib, and the short rib does not appear to be the vortex shedding phenomenon. The wall temperature and temperature fluctuation increase with the increase of heat flux and with the decrease of fluid velocity. The heat transfer coefficient decreases with the increase of heat flux and with the decrease of fluid velocity. The short rib channel has a higher heat transfer coefficient, approximately 14% and 50% higher than that of the median and long rib channels, respectively. Compared with the single-phase flow, the main frequency of the lift coefficient increases with the increase of the fluid velocity while decreasing with the increase of heat flux. The main frequency of the median rib without harmonic signal keeps constant, and that for long rib decreases by 38%. The study of the instantaneous characteristics of bubble growth in pentagonal rib channels is instructive to the efficient heat dissipation in electronic equipment. [ABSTRACT FROM AUTHOR]

To avoid the simulation error caused by the consistent solid-liquid energy transfer rate in the boiling heat transfer LB (lattice Boltzmann) model, different energy transfer rates of solid and liquid are successfully distinguished by tentatively introducing the physical parameters λ, cp of solid and liquid into the temperature relaxation time τT, as a result, a novel solid-liquid conjugate boiling heat transfer LB model is proposed in this paper. After verifying the accuracy, stability and rationality of the model, boiling heat transfer at different wettability surfaces are simulated by the solid-liquid conjugate model and the original pseudo-potential model. The results show that the unintentional neglection of different heat transfer capacities of solid and liquid regions in the original pseudo-potential model leads to the appearance of large low-density phase transition region around the bubble root. The existence of low-density phase transition region produces additional interphase forces and greatly changes the wall contact angle of bubbles. However, the solid-liquid conjugate heat conduction model realized characterization of different thermophysical properties of solid and liquid regions by introducing a temperature relaxation time function. The low-density phase transition region only appears in a very small range and at very low level, the actual bubble wall contact angles obtained by the conjugate heat transfer model are closer to the setting bubble contact angle. For other wettable surfaces except superhydrophilic surfaces, the maximum relative error of the actual contact angle obtained by the conjugate heat transfer model is 8.6%, which is 9.8% lower than that of the original pseudopotential model. The solid-liquid conjugate boiling heat transfer LB model can more accurately describe the actual microscopic process of boiling heat transfer. [ABSTRACT FROM AUTHOR]

A series of industrial trials of argon injection into ladle shroud (AIILS) with different argon-blowing rates were conducted in this study. Firstly, bubbles in actual liquid steel of the tundish were captured by the method of "cold steel plate dipping" and characterized by microscope examination. A detailed investigation on the three-dimension morphology of bubbles was carried out by using industrial computerized tomography (ICT). Then, the two-phase flow of liquid steel and argon gas in the tundish was numerically simulated to further investigate the motion behaviors of bubbles in liquid steel of the tundish. The simulated results showed that bubbles in the size range of this investigation had a large enough filtration rate to demonstrate a good performance on inclusion removal. Finally, the effect of AIILS on inclusion removal was analyzed by detecting the variations of inclusions as well as total oxygen content in steels taken from the ladle, tundish, and casting billet. The method of AIILS was more effective at improving the removal of inclusions in the range of 5 to 10 μm and obviously increased the removal rate of total oxygen content. [ABSTRACT FROM AUTHOR]

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Based on the recent development of underwater sound absorption coatings, this paper analyzes the evolution of underwater sound absorption coatings from two aspects: traditional structures and metamaterials. The traditional structures are divided into three types: cavity structures, composite structures, and impedance‐matching structures. First, the development history of traditional structures, from cavities to hybrid structures, is presented, and the optimization and recent improvements in sound absorption fundamentals are explained. For different types of structures, the sound absorption effects of their respective structures are presented. At the same time, recent development progress of underwater coating metamaterials is summarized, and the sound absorption fundamentals and effects of local and nonlocal resonance types are compared. In addition, typical underwater sound absorption metamaterials are described in detail, and the application prospect of the acoustic bubble structure in practice is summarized. Moreover, this paper compares and discusses various structural types of underwater sound absorption coatings and points out the shortcomings of recent related research. Finally, it points out current open issues in the field and suggests future development directions of underwater sound absorption coatings, defining the possible development focus of underwater sound absorption coatings.

Abstract Bubbles in air are ephemeral because of gravity‐induced drainage and liquid evaporation, which severely limits their applications, especially as intriguing bio/chemical reactors. In this work, a new approach using acoustic levitation combined with controlled liquid compensation to stabilize bubbles is proposed. Due to the suppression of drainage by sound field and prevention of capillary waves by liquid compensation, the bubbles can remain stable and intact permanently. It has been found that the acoustically levitated bubble shows a significantly enhanced particle adsorption ability because of the oscillation of the bubble and the presence of internal acoustic streaming. The results shed light on the development of novel air‐purification techniques without consuming any solid filters.

In hydrogen evolution reaction, inefficient mass transfer caused by bubble adhesion on electrode, bubble dispersion in electrolyte and slow H2 diffusion, has greatly impeded the reaction process. Existing techniques can only resolve bubble adhesion or bubble dispersion problems. Strategy that simultaneously solve bubble adhesion, bubble dispersion and poor hydrogen diffusion problems is rarely reported. Recently, an article reported a new electrode with special wettability design, which can efficiently promote bubble transfer and dissolved H2 diffusion. This design can simultaneously solve above mentioned three mass transfer issues and improve electrode efficiency. We summarize the remaining challenges of this work and outlook potential approaches to promote mass transfer in gas-evolution reactions.

A 3D manipulation technique based on two optothermally generated and actuated surface-bubble robots is proposed. A single laser beam can be divided into two parallel beams and used for the generation and motion control of twin bubbles. The movement and spacing control of the lasers and bubbles can be varied directly and rapidly. Both 2D and 3D operations of micromodules were carried out successfully using twin bubble robots. The cooperative manipulation of twin bubble robots is superior to that of a single robot in terms of stability, speed, and efficiency. The operational technique proposed in this study is expected to play an important role in tissue engineering, drug screening, and other fields.

Microchannel flow boiling is an efficient cooling method for high-heat-flux electronic devices. To understand the flow boiling regime in a T-shaped microchannel, this paper prepared T-shaped microchannels of different sizes and designed an experimental platform for the visualization of flow boiling in microchannels, and aimed to study the evolution characteristics of two-phase flow patterns in T-shaped microchannels. The influences of the flow rate and channel size on the boiling flow pattern inside a T-shaped microchannel were experimentally observed and quantitatively described. The results indicate that the occurrence position of the vaporization core gradually migrates from branch channel to main channel as the wall temperature increases. The flow boiling at the bifurcation of the T-shaped microchannel mainly includes the extrusion fracture flow, bubble flow, plug–annular alternating flow and annular flow, in which the annular flow can be further divided into the intermittent annular flow and the stable annular flow. In addition, a high flow rate and small channel size can lead to the disappearance of the bubble flow, and the presence of the bubble flow delays the appearance of the annular flow.

In this study, we focused on the effect of the underwater explosion parameters of multi-point array explosion. The shock wave and bubble parameters of aggregate charge, two charges, and four charges were measured through an underwater explosion test, and their influence on the explosion power field of charge quantity and array distance was analyzed. Results show that the multi-shock wave collision of array explosion can be approximated to a linear superposition, and the interaction of delayed shock wave can be deemed as the increase of the shock wave baseline. Shock wave focusing and delayed superposition increase the shock wave peak pressure. Compared with the aggregate charge, the greater the number of array explosion points is, the higher the impulse and the gain of the bubble peak pressure are. At the same array distance, the smaller the charge quantity is, the higher the bubble impulse will be. At the same charge quantity, the smaller the array distance is, the higher the bubble impulse will be. The bubble period decreases gradually with the increase of the charge quantity, but the test orientation has little effect on the bubble period.

This research uses a swirl type MBG (MBG) with the gap variation between the air nozzle and the outlet of 1, 5 and10 mm. In this experiment, we used a tangential inlet of 25 mm and an outlet of 20 mm with a water flow rate of 20 – 70 l/min and an air flow rate range of 0.1 – 0.8 l/min, to determine the characteristics of MBG which include bubble distribution, pressure drop, hydraulic power, and efficiency. The probability of the diameter of the microbubble formed was in the range of 90 – 150 µm for all variations of the air nozzle gap. The larger the incoming water flow rate, the smaller the diameter of the bubbles formed, whereas if the water flow rate decreases, the diameter of the bubbles formed will increase. In contrast to the water flow rate, if the air flow rate increases, the diameter of the bubbles formed will increase, whereas if it decreases, the diameter of the bubbles will decrease. From the signal processing data, information was obtained about the comparison of the pressure drop of the three variations of the air nozzle gap, as follows: The higher the water flow rate, the pressure drop and hydraulic values increase significantly, while for air flow rate, the higher the air flow rate, the pressure drop and hydraulic power values will increase albeit not significantly. As for MBG efficiency, it will decrease significantly with increasing water flow rate and will increase insignificantly with decreasing water flow rate.

Using bubbles to remove inclusions in steel is rapidly becoming a popular method for refining. Fine bubbles are thought to be more effective on inclusion removal than big bubbles. The fine bubbles can be formed in molten steel using the argon injection into ladle shroud technology. There are two stages during the formation of fine bubbles in ladle shroud: bubble detachment from wall orifice and detached bubbles splitting into smaller ones in turbulent steel. Many reports have been published on the water model of the argon injection into ladle shroud technology, but industrial experimental research is in its early stage. In this study, high argon flow was injected into a ladle shroud and adopted in continuous casting production to produce fine argon bubbles in a tundish. The bubbles were captured by dipping a cold steel sheet into molten steel. The captured bubbles at the surface of a hot-dipped steel sheet, with a size of 1.0–3.0 mm, characterized the argon bubbles at steel/slag interface and slag phase in the upper part of a tundish rather than those inside molten steel in tundish. The bubbles inside molten steel in tundish were characterized by the captured bubbles in the interior of a hot-dipped steel sheet, and their morphology, size, and number were analyzed using scanning electron microscopy and confocal microscopy. The bubbles inside molten steel in tundish have a spherical shape and occasionally adhere to each other. These bubbles rang in size from 100 to 1000 μm, with an average of 500 μm. They are dispersed at the exit of a ladle shroud in its lower position, with a density of 15.2 cm–2. Moreover, it was observed that a bubble could adhere to inclusion, even multiple inclusions for part of bubbles. Bubbles adhered more strongly to Al2O3 inclusions than that to CaO(‒MgO)‒Al2O3‒SiO2 complex inclusions.

Aeration becomes an essential aspect of biofilter performance to reduce ammonia nitrogen in the Recirculating Aquaculture System (RAS). Efficient aeration introduces air into water media and offers an aerobic environment in the biofilter for microbial degradation of organic matter and ammonia nitrogen. The efficiency of the bubble aeration depends on the size of the bubbles; these include coarse bubble, microbubble, fine bubble, and ultrafine bubble or nanobubble. This review highlights an overview of bubble aeration features in a biofilter to reduce ammonia nitrogen. Moreover, key aspects responsible for the ammonia nitrogen removal efficiencies, such as oxygen transfer, microbial community, and biofilm thickness, are evaluated in this review. In conclusion, the bubble size of aeration affects the microbial community of nitrifying bacteria, consequently determining the growth and thickness of biofilm to improve ammonia removal efficiency. It is emphasized that fine bubble and nanobubble aeration have very positive prospects on improving biofilter performance, though they are currently not widely used in RAS. [ABSTRACT FROM AUTHOR]

Flotation process of micro-fine minerals have historically been hampered by slow flotation rate, poor selectivity, high reagent consumption, and low recovery. These disadvantages are mainly due to the large specific surface area attributed to the small-sized mineral particles. As such, research have revolved around enhancing their recovery by process intensification as one of the known effective methods. Micro/nanoparticles, on the other hand, possess many attributes, for instance, strong chemical activity, high reactivity, high surface free energy, and large adsorption capacity, all of which can contribute to improve the separation of micro-fine minerals. The mechanisms and preparation methods of nanoparticle collectors (NPCs) as well as ultrafine bubbles (UFBs) are described in this paper. Furthermore, the influences of NPCs and UFBs on the flotation of micro-fine minerals are also discussed. NPCs and UFBs are capable of providing hydrophobicity selectivity to the desired minerals to improve the flotation performance of mineral particles. This paper offers an overview of the underlying properties of NPCs and UFBs in intensifying flotation applications. [ABSTRACT FROM AUTHOR]

Theoretical results of studying thermodynamic and structural characteristics of free droplets and bubbles around nanosized solid heterogeneous spherical inclusions using phenomenological thermodynamic approach and various versions of the molecular density functional method are reviewed. In the case of a droplet in an undersaturated or supersaturated vapor, the central solid particle is assumed to be lyophilic and can be either electrically charged, or uncharged. In the case of a vapor bubble in a stretched liquid, the central particle is assumed to be lyophobic and, as in the previous case, can be electrically charged or uncharged. The structure of droplets and bubbles is described by equilibrium molecular density profiles. Thermodynamic characteristics imply the chemical potential of molecules in a droplet or bubble as a function of their size, the work of formation of equilibrium droplets or bubbles as a function of the chemical potential of molecules in the system, and the surface tension and disjoining pressure in droplets or bubbles as functions of its radius. [ABSTRACT FROM AUTHOR]

The present study examined the pool boiling process in a specific geometry by designing and constructing a laboratory complex. Investigation of pool boiling process, electrical resistance, critical heat flux, heat transfer coefficient, bubble growth and departure, bubble growth frequency, and nucleation site density by applying heat flux to critical heat flux was carried out on a ring wire in deionized water at different temperatures. According to the results, increasing the number of rings and fluid temperature decreased the critical heat flux. In the case of a ring wire with a constant number of rings, a fluid with a constant temperature, and the use of heat flux values less than the critical heat flux, the wire temperature increased, but it decreased in the case of increasing the number of rings, a fluid with a constant temperature and applying critical heat flux values. In a ring wire with a constant number of rings, the heat transfer coefficient was constant by increasing fluid temperature at values of heat flux less than the critical heat flux, but the heat transfer coefficient decreased at critical heat flux values. The diameters of the produced bubbles were enhanced by increasing heat flux and they separated from the rings when combined. At the beginning of the reddening of the ring wire, a critical heat flux occurred, and considering 110% of the time required for the critical heat flux, the images of the state of the ring wire after the critical heat flux are presented. [ABSTRACT FROM AUTHOR]

Bubbles in subsurface porous media spontaneously coarsen to reduce free energy. Bubble coarsening dramatically changes surface area and pore occupancy, which affect the hydraulic conductivity, mass and heat transfer coefficients, and chemical reactions. Coarsening kinetics in porous media is thus critical in modeling geologic CO2 sequestration, hydrogen subsurface storage, hydrate reservoir recovery, and other relevant geophysical problems. We show that bubble coarsening kinetics in porous media fundamentally deviates from classical Lifshitz‐Slyozov‐Wagner theory, because porous structure quantizes the space and rescales the mass transfer coefficient. We develop a new coarsening theory that agrees well with numerical simulations. We identify a pseudo‐equilibrium time proportional to the cubic of pore size. In a typical CO2 sequestration scenario, local equilibrium can be achieved in 1s for media consisting of sub‐micron pores, while in decades for media consisting of 1 mm pores. This work provides new insights in modeling complex fluid behaviors in subsurface environment. Plain Language Summary: In modeling fluid behaviors during geologic CO2 sequestration, hydrogen subsurface storage, hydrocarbon recovery and magma kinetics, the evolution of bubbles in subsurface porous media should be resolved to quantify hydraulic conductivity, mass and heat transfer coefficients, and reactional surface area. However, classical Lifshitz‐Slyozov‐Wagner theory qualitatively fails to predict bubbles' coarsening kinetics, as porous structure fundamentally reshapes the mass transfer pattern. A new coarsening theory is derived that perfectly matches numerical simulation. The evolution of free energy, pore occupancy, and surface area can be predicted, and an equilibrium time is identified that determines the validity of the local thermodynamic equilibrium presumption. This work helps to model complex fluid behaviors in many geophysical applications. Key Points: Bubbles in subsurface porous media coarsen toward equilibrium, which modifies local thermodynamics, transport, and reactive propertiesClassical Lifshitz‐Slyozov‐Wagner theory fails for bubbles coarsening in porous media, as porous geometry reshapes the concentration profileA new theory is derived that predicts the bubble population evolution during coarsening, which helps in modeling complex subsurface flow [ABSTRACT FROM AUTHOR]

The track circuit reader (TCR) is an important part of train control systems. This paper reports a failure of the TCR antenna baffle, which is used to prevent the TCR antenna from being struck by foreign objects. The designed service life of the baffle is 4.8 million kilometers, but serious cracking was found during routine maintenance after only 0.67 million kilometers of operation. In order to avoid the hidden danger brought by the incident to the safe operation of the train, it is necessary to conduct a complete failure analysis of the failed TCR antenna baffle. Therefore, a comprehensive investigation of the base material, cleaning agents, crack morphologies, etc., was carried out, and the failure environment of the antenna baffle was verified by experiment. The final results show that the environmental stress cracking is the root cause of the failed antenna baffle, and the multiple bubbles produced by the formed process of the antenna baffle are another important cause. According to the conclusions, the solutions to prevent the reoccurrence of such failures are proposed. After these solutions are adopted, the number of failed antenna baffles is greatly reduced, which fully proves the correctness of this analysis. [ABSTRACT FROM AUTHOR]

For many years, global researches that focus on improving soil fertility have been conducted. Nowadays, innovative inculcations of environmentally (ecologically) friendly organic agriculture are becoming quite popular. One of the most effective indicators is the use of alternative types of fertilizers. As part of large-scale experiments, researchers propose to use fertilizers made from organic sapropel concentrated in freshwater lakes. Analysis of such studies shows that the impact of sapropel on soil fertility is significant and complex. The main problem they faced is the extraction of these deposits from underwater deposits (fields). Ukrainian scientists have proven the effectiveness of sapropel extraction by means of a pneumatic intake device. To substantiate the rational parameters of this device and visualize the processes, experimental studies of the work of the pneumatic working body were carried out. Namely, experimental studies of the determination of the trajectories of air bubbles in liquids of different viscosity were carried out. According to received trajectories, the boundaries of airflow and its shape are determined. Limpid liquids of different viscosities were used specially in order to see and fix the flow parameters, because it is impossible to observe such a phenomenon in sapropels placed in underwater deposits, due to their opacity and change of viscosity with depth of the bedding. Therefore, the experiment was considered as close as possible to the real one, and the environment of realization of the experiment was simulated. Water, industrial oil and concentrated detergent were selected as investigated liquids. Research data indicate that one can use a whirling airflow for better loosening of deposits of reduced humidity. Whirling occurs when there is a horizontal position of the outlet axis with a diameter in the range of 1-1.5 mm and air pressure of 300-400 kPa. [ABSTRACT FROM AUTHOR]

To study the effect of the length of the second inclined section of the inclined vane on the vortex structure and pressure distribution inside a vortex pump, this paper uses a combination of numerical simulations (CFD) and experimental verification methods to analyze the static pressure distribution of the internal flow field and the volume fraction distribution of the impeller bubble at different total inlet pressures as well as to analyze the volume and streamline of the distribution of the impeller bubble of the vortex pump at different instants. The results show that as the length of the second inclined section of the inclined vane increases, both the low-pressure area and the volume fraction of the vapor bubbles inside the impeller of the vortex pump increase, and the resistance to cavitation becomes worse. When the total inlet pressure of the impeller is low, a large number of vortices will be generated inside the flow channel of the vortex pump, leading to vortex cavitation; the longer the length of the inclined section, the larger the velocity gradient of the fluid and the more serious the phenomenon of deliquescence, leading to more intense cavitation, while a shorter inclined section length can effectively improve the anti-cavitation performance of the vortex pump. [ABSTRACT FROM AUTHOR]

Copyright of Nonferrous Metals (Mineral Processing Section) is the property of Beijing Research Institute of Mining & Metallurgy Technology Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Effect of water flow velocity (≤3 m/s) on bubbles detaching from bitumen was examined in a water channel at room temperature. The results showed different behaviours of bubble–bitumen detachment for different sizes of bubbles. With increasing water flow speed, a larger bubble (>0.15–0.2 cm) underwent the following steps before detaching from the bitumen layer: deformation; neck formation; the bubble broke up from the neck, with the top portion sheared away, leaving the bottom portion as a small bubble stuck to bitumen; and then, the small bubble detached from the bitumen and was carried away by further increasing water flow. Smaller bubbles (<0.1–0.15 cm) detached from bitumen after deformation without breaking up, with increasing water flow. An empirical correlation between the size of bubbles detaching from bitumen with water flow velocity/shear rate was established. At a flow velocity of 3 m/s, only bubbles smaller than 250–300 μm might be able to stay attached to bitumen, or a shear rate higher than 2500 s−1 is needed to detach a 250–300 μm bubble from bitumen. [ABSTRACT FROM AUTHOR]

The impeded mass transfer rate by on-site-generated gas bubbles at both cathode and anode dramatically reduces the energy conversion efficiency of the proton exchange membrane water electrolyzer (PEMWE). Herein, we report a surfactant-assistant method to accelerate the nano/micro-bubble detachment and the mass transfer rate by reducing the surface tension, resulting in an increase in overall efficiency. Four kinds of surfactants are studied in this work. Only potassium perfluorobutyl sulfonate (PPFBS), which has the structural similarity to Nafion, shows a significant promotion of activity and stability for both hygrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the acidic medium at the high current density region. The HER overpotential at 0.1 A·cm−2 decreased 22%, and the current density at −0.4 V increased 31% by adding PPFBS. The promotion of overall efficiency by PPFBS on a homemade PEMWE was also proven. The reduced surface tension and electrostatic repulsion were the probable origins of the accelerated bubble detachment. [ABSTRACT FROM AUTHOR]

Electrochemical machining (ECM), an advanced manufacturing technology, is widely used in aero-engine blades machining. In traditional ECM, the electrolyte flows through the inter-electrode gap (IEG), generating hydrogen bubbles and heat, which affect the conductance and thus influence the machining quality. This paper focuses on the effect of bubble movement on the flow field and the machining quality of ECM. A novel vertical flow mode of electrolyte is proposed according to the bubbles dynamics analysis. Multi-physical fields simulations of blade ECM using vertical and horizontal flows were carried out. With an initial gas void fraction, flow rate, and temperature at the inlet of 0, 19.7 m/s, and 302.65 K, respectively, in both flow modes, the vertical flow reduces the gas void fraction, flow rate, and temperature at the outlet by 2.4%, 0.4 m/s, and 0.6 K, and increases the conductance by 0.47 S/m. Thus, the vertical flow of the electrolyte is beneficial in reducing the gas void fraction and controlling the temperature rise, while enhancing the conductance. Then, the corresponding experiments using a vertical flow were carried out. The maximum machining deviation ranges from 3.4 to 75.6 μm and surface roughness Ra < 0.35 μm. The machining quality is high and the variation observed in the experiments is consistent with the simulation results, the validity and correctness of the simulations are verified. Thus, the vertical flow mode proposed in this paper is appropriate, can be used for other complex structures in ECM. [ABSTRACT FROM AUTHOR]

The scanning trajectory method of laser cladding has a great influence on the quality of the clad layer. Herein, the effects of single spiral and double spiral trajectories on the clad morphology, temperature gradient and solidification rate of the Fe-based powder clad at different solidification positions during the injection of the cladding powder on a 45 steel elongated slender shaft when cladding with a high power diode laser (HPDL) are investigated. A three-dimensional (3-D) mathematical model was developed. The temperature variation curves of the substrate and the molten coating were obtained by the birth-death cell technique. The influence of the output parameters on the coating quality was analysed and discussed. In order to verify the reliability of the model, experimental tests were carried out to verify the surface quality and tissue morphology of the molten coating under the two scanning methods. The results show that the agreement between the theoretical calculation results and the experimental results is good. In addition, both scanning methods generate pores at the coating laps. The above conclusions are further confirmed by the dimensional change analysis. For this reason, this paper serves as a good guideline for the melting and cladding process of slender shafts. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to examine whether there is a bubble in the Turkish housing market during the period of 2006–2018. In conjunction with the irrational bubble theory, this study applies the Pitros and Arayici (Int J Hous Mark Anal 9(2):190-221, 2016. 10.1108/IJHMA-01-2015-0002) bubble algorithmic model. The empirical results reveal that the Turkish housing market was in a bubble during 2013–2017 period, the peak/last year of the bubble is the year 2017 and that the bubble-bust occurred in 2018. The foremost contribution of this study is that it is the first to document a historical housing bubble episode for Turkey using the premises of irrational bubble theory and the first to apply an algorithmic approach to assess the bubble risk for the period of 2006 and 2018. As to the implications, this documented model may be used as a tool to enhance policymakers' knowledge toward the early identification of housing bubbles. [ABSTRACT FROM AUTHOR]

We develop a present-value model where the fundamental and non-fundamental components switch between distinct regimes. The non-fundamental component is specified as a periodically collapsing bubble of Balke and Wohar [Balke, N. S., & Wohar, M. E. (2009). Market fundamentals versus rational bubbles in stock prices: A Bayesian perspective. Journal of Applied Econometrics, 24(1), 35–75. https://doi.org/10.1002/jae.1025]. The fundamental component is constructed as in van Binsbergen and Koijen [van Binsbergen, J. H., & Koijen, R. S. J. (2010). Predictive regressions: A present-value approach. The Journal of Finance, 65(4), 1439–1471. https://doi.org/10.1111/j.1540-6261.2010.01575.x], by treating the expectations of market fundamentals as latent variables. Unlike existing methods, e.g. [Zhu, X. (2015). Tug-of-war: Time-varying predictability of stock returns and dividend growth. Review of Finance, 19(6), 2317–2358. https://doi.org/10.1093/rof/rfu047; Choi, K. H., Kim, C., & Park, C. (2017). Regime shifts in price-dividend ratios and expected stock returns: A present-value approach. Journal of Money, Credit and Banking, 49(2–3), 417–441. https://doi.org/10.1111/jmcb.12384; Chan, J. C., & Santi, C. (2021). Speculative bubbles in present-value models: A Bayesian Markov-switching state space approach. Journal of Economic Dynamics and Control, 127, 1–26], ours requires no unnecessary approximations, accommodates flexible forms of regime-switching, and the resulting present-value formula is internally consistent. [ABSTRACT FROM AUTHOR]

The rapid growth in defence expenditure in China raises the concern that investments in the defence sector crowd out investments in social sectors, i.e., the 'guns for butter' argument. This article resorts to the bubble testing method to study the trade-off between defence and utilities sectors in the Chinese capital market. Based upon the generalized sup Augmented Dickey-Fuller (GSADF) test, this paper captures and date stampings explosive behaviors in defence and utilities industries using stock indexes. Empirical results reveal bubbles for defence and utilities sectors in similar time periods, thus indicating that the factors driving explosive movements are alike for both sectors. However, bubbles in a certain sector do not necessarily crowd out investments in the other sector. Through testing bubbles in the ratio of stock indexes of two sectors, we find that the explosive episodes vanish. The results indicate that the crowding-out effect between defence and utilities sectors does not exist in the Chinese capital market. Increases in the military expenditure in China are necessary to safeguard the national security because of frequent geopolitical conflicts and terrorism. However, the defence to utilities ratio is increasing rapidly, implying the possibility that excessive growth in military expenditure may generate the 'guns for butter' problem, which can be detrimental to economic growth. [ABSTRACT FROM AUTHOR]

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Microbubbles were applied to remove phosphorus (P) and improve environmental water conditions on the surface of the benthic sediment in a eutrophic lake. Microbubble flotation (MF) was used to remove P in a laboratory-scale experiment device from the benthic sediment and overlying water field samples. The results of P tracing observation for MF treatment, which were identified based on the mass balance, showed P accumulated at a higher concentration in the floated scum than in the deposited sludge. Furthermore, while the amount of soluble P separated was insignificant, the removal efficiency of soluble P in the floated scum was higher than total P. As an additional effect, P release was suppressed by the injection of microbubbles, which reduced anaerobicization and improved environmental conditions in the overlying water of the lake. We also confirmed that the sludge that settled after flotation separation caused capping, which restrained P release by forming a layer on the surface of the sediment. The direct P flotation separation, provision of oxygen by injected microbubbles, and capping effect of re-deposited sludge are advantages associated with MF, and our results show that field application studies are warranted. HIGHLIGHTS MF can be applied to reduce P in the benthic sediment and overlying water of a lake.; Soluble P was removed more easily than T-P.; MF accumulated P at a higher concentration in the floated scum than in the deposited sludge.; MF reduced anaerobicization and improved environmental conditions in the overlying water.; While MF is not efficient at T-P removal, the process does effectively separate soluble P.;

To analyze the effect of flow characteristics on electrochemical water softening, characteristics of flow fields in the vicinity of vertical plate electrodes in a bench-scale electrolysis cell for electrochemical water softening were visualized using particle image velocimetry technology, and the hardness drop values under different process conditions were measured. Properly increasing the current density or reducing the electrode spacing can increase the average flow velocity in the electrode gap. Excessive current density will cause bubble accumulation, form a bubble vortex, interfere with the orderly flow of surrounding liquid and reduce mass transfer efficiency. When the electrode spacing is 120 mm, the highest water softening efficiency measured at the current density of 60 A/m2 is 16.56%. When the current density is 50 A/m2, the highest average speed measured at the electrode spacing of 60 mm is 0.00169 m/s, but the highest water softening efficiency measured at the electrode spacing of 90 mm is 23.3%.The circulation efficiency in the electrode gap of a semi-closed structure is lower than that of a free convection structure. The behavior of bubbles is the key to flow and mass transfer. It is important to consider its influence on bubble behavior when optimizing electrochemical parameters. HIGHLIGHTS Effect of flow characteristics between vertical plate electrodes on water softening efficiency.; The main flow patterns of mass transfer between vertical plate electrodes.; Effect of bubble behavior on flow patterns between vertical plate electrodes.; Optimization of flow mass transfer efficiency by current density, electrode spacing and electrode position.; Trend of velocity distribution between vertical plate electrodes.;

This article contributes to research into price dynamics on the real estate market. It proposes a simplified index-based speculative frame method for measuring above-average increases and decreases in real estate prices and monitoring market performance. The theoretical part of the article reviews the literature on the implications of real estate market stability on the economy, monitoring market development, and standard methods for analyzing the housing market with special emphasis on index-based methods. The experimental part of the article presents the results of a study analyzing more than 100,000 transactions on the Warsaw housing market between 2004 and 2015, a period characterized by a considerable increase in house prices. The price dynamics of apartments on the Warsaw real estate market was determined with the use of a time variable. The turning point in the market trend was identified. This article contributes to research into price dynamics on the real estate market.

[Display omitted] • The terminal velocities of single bubbles were affected by reducing the pitch in the fiber bundles. • Bubbles in the cap-bubble regime took remarkably deformed shapes. • The developed correlation predicted the terminal velocities of single bubbles in the fiber bundles. The shapes and terminal velocities of single bubbles in the surface tension force and the inertial force dominant regime were measured in a vertical bundle consisting of fluorinated ethylene propylene fibers of 2 mm diameter. Three kinds of fiber arrangements were tested with the fiber pitches L p of 18, 12, and 6 mm. The terminal velocities in the bundles were larger than those in the absence of a fiber bundle and increased with decreasing L p. The bubble shapes were significantly deformed by fibers, which would be the cause of the velocity increase, i.e., a reduction in the form drag. The terminal velocities in the bundles were well predicted by the combination of the drag correlation in the absence of a fiber bundle and the multiplier for bubbles in fiber bundles. [ABSTRACT FROM AUTHOR]

• Three types of carbonation produced distinct sensory attributes and stimulation. • Small abundant bubbles increased salivary flow, substance P levels, and heart rate. • Water carbonation acts similarly to capsaicin-induced stimulation of vanilloid channels. This study explores the impact of various types of carbonation on sensory stimulation in the mouth, salivary secretion and the neurotransmitter substance P (SP), as well as body responses such as heart rate (HR) and Galvanic Skin Response (GSR). Three types of carbonation (one made using a soda machine, another carbonated with a gasifier, and the last commercial sparkling water) were used to produce different bubbles resulting in distinct sensory characteristics assessed by a trained panel. The impact of carbonation was measured by recording changes in salivary flow rate, SP levels, salivary secretory immunoglobulin A (SIgA), HR, and GSR in fifteen healthy participants. The results showed that the bubble type only affected the sensory perception of carbonation. Regardless of bubble type, carbonation increased salivary flow rate and SP values, SigA and HR. These characteristics are being sought to improve treatments for dysphagia or dry mouth. Therefore, these findings highlight the potential therapeutic application of carbonation in these situations. [ABSTRACT FROM AUTHOR]

Foamed cereal foods are a significant part of our daily diet. Colloidal and interfacial science principles provide insights on how to devise novel aerated cereal foods that may also address environmental and human health needs in our diets and for optimizing the sensory and nutritional quality of foamed cereal products. We review recent literature where colloidal science principles have been employed to understand relations between the creation of bubbles in food materials, bubble growth and interactions, and how this history governs the microstructure and the mechanical properties of foamed cereal products that are critical to the appearance and quality of a range of food products such as bread, cakes, snack foods, and breakfast cereals. Product density and its frequently measured corresponding quality equivalent, specific volume, are key considerations of both the visual appeal and the eating quality of foamed cereal products. [Display omitted] [ABSTRACT FROM AUTHOR]

The mechanism of particle detachment induced by air-water interface collision has been controversial. This study utilizes high-speed dynamic camera to assess how particle hydrophobicity and bubble size affect the dynamics of detachment at the air-water interface. We discovered that only particles with hydrophobicity ranging from 22° to 41° and a diameter of 1 mm successfully detach. Particles with a contact angle below 22° struggle to adhere, whereas those above 41° are difficult to detach. The detachment probability increases with the Eo number of the bubble, primarily for two reasons: bubbles with larger Eo numbers possess greater kinetic energy, and the higher collision angle with the interface leads to an increased relative velocity. Additionally, A portion of bubble kinetic energy deformed the air-water interface, reducing energy for particle detachment. This research offers valuable insights for precisely controlling the detachment process in coarse particle flotation systems. [Display omitted] • Collision-induced detachment is highly sensitive to particle hydrophobicity. • The magnitude of kinetic energy affects the probability of particle detachment. • Larger Eo number bubbles increase their impact angle with the interface. • Larger Eo number bubbles reduce detachment energy due to deformation. [ABSTRACT FROM AUTHOR]

• Si-rich precipitates result in the differences of hardness in Ti 3 SiC 2. • Xe generates Si frenkel pairs while he enhances their recombination. • Strip-like Si clusters are formed by emitting dislocation loops in TiC. Ti 3 SiC 2 is recognized as a promising candidate material for nuclear energy applications; however, the microstructural defects resulting from complex irradiation processes remain elusive. This study investigates the microstructural evolution of Ti 3 SiC 2 under sequential Xe-He-H ions irradiation at room temperature, followed by annealing at 900 °C, employing both experimental and first-principles computational approaches. A reverse phase transformation occurred following He irradiation, indicating that He facilitates the remote migration and recombination of Si vacancies through the formation of He-Si pairs during annealing. Post-annealing, the Xe-irradiated sample exhibited a widespread distribution of small Xe bubbles, whereas larger bubbles were prevalent at peak damage regions in the samples subjected to Xe+He and Xe+He+ H irradiation. Concurrently, Si-rich precipitates with distinct distribution patterns were observed in samples irradiated with Xe, Xe+He, and Xe+He+ H ions, significantly affecting the hardness. First-principles calculations reveal that the distinct damage profiles are primarily attributed to the dynamic behaviors of Si interstitials. The Ti-Si bonds are relatively weak and easily broken, leading to abundant Si interstitials in Xe ion irradiation, and He enhances Si diffusion. Conversely, H enhances Si segregation by preventing He from capturing Si interstitials. Within the TiC grains, He promotes Si migration, causing an approximately 700-fold increase in Si diffusivity at 900 °C. The Si segregation leads to the nucleation of 〈110〉 dislocation loops, culminating in the formation of distinctive strip-like Si clusters. This study elucidates the formation mechanism of Si segregation within Ti 3 SiC 2 , providing valuable insights for the design of irradiation-resistant materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Fig. The mechanism model diagram of the effect of surface roughness on hydrophobicity of magnesite and bubble-particle adhesion: a, smooth magnesite particles; b, rough magnesite particles. [Display omitted] • Rough magnesite particles have better floatability. • Induction time decreases as surface roughness of magnesite particles increases. • Wrap angle increases with the increase of surface roughness of magnesite particles. • The adhesion efficiency of rough magnesite particles is higher. Flotation is a technique for separating and purifying minerals based on the differences in their surface physicochemical properties (mainly wettability). The surface roughness of mineral particles will significantly affect their hydrophobicity and adhesion to bubbles, thereby affecting the floatability. In this study, −0.074 + 0.045 mm magnesite particles with different surface roughness were obtained via ultrasonic pretreatment for different time, and the surface roughness of magnesite particles was characterized by BET method and atomic force microscopy (AFM) method. To investigate the influence mechanism of surface roughness of magnesite particles on bubble-particle adhesion, flotation experiments, XPS analysis, NaOL adsorption capacity test, contact angle test, induction time test, bubble coverage wrap angle test and adhesion efficiency test of particle were carried out. The results indicated that rough magnesite particles exposed more Mg2+ on their surface, which can adsorb more NaOL, resulting in stronger hydrophobicity and better floatability of magnesite particles. Increasing the surface roughness of magnesite particles can enhance the adhesion between magnesite particle and bubble, shorten the bubble-particle induction time, increase the bubble coverage wrap angle of magnesite particles, and improve the adhesion efficiency of magnesite particle when slipping on the surface of bubble. [ABSTRACT FROM AUTHOR]

• Combined damage effects of shock wave and bubble on a concrete gravity dam are studied. • The shock wave causes a first attack, inducing tensile cracks in the vulnerable part of the dam. • The bubble pulse generates a secondary attack, facilitating the development of the tensile crack. • The bubble jet and bubble collapse, united with the upstream reservoir water, accelerate the failure of the cracked dam, forming a breach in the dam's upper part. • The shock wave is the key trigger for dam failure, while the bubble accelerates the process of failure. The underwater explosion bubble accounts for half of the total explosive energy and has been found to induce serious structural damage to ship structures. However, the existing research has commonly ignored the damage effect of an underwater explosion bubble on a concrete gravity dam. The current study aims to narrow this gap through high-fidelity numerical simulations and scale model tests. A fully-coupled numerical model is established first and is validated by small-scale centrifugal model tests. The bubble dynamics of underwater explosions near the perpendicular dam structure have been explored. The main focus is then on the sequential damage effects of the underwater explosion shock wave, bubble pulse, bubble jet, and bubble collapse on a concrete gravity dam. It is found that the shock wave causes a first attack, inducing tensile cracks in the vulnerable part of the dam. Subsequently, the bubble pulse generates a secondary attack, facilitating the penetration of the tensile crack throughout the entire dam structure. Additionally, the bubble jet driving the high-speed fluid flow and the bubble collapse causing the uplifted free water surface, united with the upstream reservoir water with huge hydrostatic pressure, largely accelerate the fracture of the dam, then facilitate the fractured dam to fall downstream leaving a breach with certain widths in the dam's upper part, and finally speed up the discharge of the upstream reservoir water through the breach. It also finds that the underwater explosion bubble can generate no new cracks in the gravity dam, even in the pre-damaged area as long as there are no obvious pre-cracks by the shock wave. That is, the shock wave is the key trigger for dam failure, without which the dam failure will not happen, while the bubble, united with the upstream reservoir water, accelerates the process of dam failure. [ABSTRACT FROM AUTHOR]

Bitcoin market crashes bring huge economic losses and weaken the global financial system. Thus, predicting Bitcoin market crashes is very important for investors. However, due to the high volatility of Bitcoin prices, accurate prediction of crash events is difficult. This study proposes three components within a hybrid prediction approach to improve Bitcoin market crash prediction for better investment decision-making. First, we offer a hybrid prediction approach that combines various machine learning models with knowledge modeling of bubble phenomenon through the Generalized Supremum Augmented Dickey-Fuller (GSADF) test. Second, we employed the Synthetic Minority Oversampling Technique to address the loss of predictive power due to the severe imbalance between crash and no-crash periods in real-world data. Each machine learning model was trained using an effective oversampling strategy to determine the best predictive performance. Finally, SHapley Additive exPlanations interpretation of outcomes from the predictive model provides practical information for establishing efficient investment strategies. As a result, our crash prediction model based on four long-term bubble cycle information captured via the GSADF test showed significantly improved predictive performance. In particular, the precision-recall area under the curve performance of our prediction model after 7 and 14 days increased by 9.9% and 6.2% compared to original models, which proves that it is effective for mid-to long-term prediction. In addition, factors such as increased interest rates and the continuation of the bubble greatly increased the probability of future crashes in the Bitcoin market. We found that bubble phenomena lasting longer than 14 days significantly increase the probability of a crash. • Hybrid prediction for better Bitcoin crash event forecast and decision-making. • Machine learning models are combined with a multiple bubble detection model. • SMOTE is applied to balance imbalanced real-world data with skewed class distribution. • Interpretation of the outcomes using SHAP proposes efficient investment strategies. [ABSTRACT FROM AUTHOR]