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Large gas bubbles can reach the surface of pools of mud and lava where they burst, often through the formation and expansion of circular holes. Bursting bubbles release volatiles and generate spatter, and hence play a key role in volcanic degassing and volcanic edifice construction. Here, we study the ascent and rupture of bubbles using a combination of field observations at Pâclele Mici (Romania), laboratory experiments with mud from the Imperial Valley (California, USA), numerical simulations and theoretical models. Numerical simulations predict that bubbles ascend through the mud as elliptical caps that develop a dimple at the apex as they impinge on the free surface. We documented the rupture of bubbles in nature and under laboratory conditions using high-speed video. The bursting of mud bubbles starts with the nucleation of multiple holes, which form at a near-constant rate and in quick succession. The quasi-circular holes rapidly grow and coalesce, and the sheet evolves towards a filamentous structure that finally falls back into the mud pool, sometimes breaking up into droplets. The rate of expansion of holes in the sheet can be explained by a generalization of the Taylor-Culick theory, which is shown to hold independent of the fluid rheology.

Two-dimensional (2D) computational fluid dynamics (CFD) simulations of water-based microencapsulated phase change material suspension (MPCMS) on the flow boiling in a gas–liquid–solid flow system was performed with volume of fluid (VOF) method and discrete particle model (DPM). The Lagrangian particles were linked to the Eulerian phases through the interchange terms such as the drag force in the respective momentum equations. Influences of particle properties including mass fraction and core phase transition temperature, fluid properties including liquid surface tension force and viscosity, detachment time and rise velocity of gas bubbles and particle entrainment in the gas–liquid–solid flow under ambient conditions were numerically investigated. The effects of particles on bubble nucleation, growth and rupture during boiling were studied by visualization. The results show that MPCM can enhance the boiling heat transfer ability of the base liquid. The maximum heat transfer enhancement rate of MPCMS (28 °C) is 4.8%, the maximum heat transfer enhancement rate of MPCMS (90 °C) is 5.1%, the maximum heat transfer enhancement rate of MPCMS (110 °C) can reach 6.7%. MPCM can promote the formation of new bubbles and the rupture of large bubbles, reduce the departure diameter of bubbles, and enhance the boiling heat transfer capacity of the base liquid. The MPCM with core phase change temperature higher than the boiling temperature of base fluid has the best enhancement effect. Through the combination of numerical simulation methods such as VOF and DPM, the complex phase transition heat transfer process of gas-liquid-solid particle coupling of latent thermal functional thermal fluid can be accurately simulated. The work lays a foundation for further explorations on the gas–liquid–solid flows and possible industry applications. [ABSTRACT FROM AUTHOR]

In the present paper, the influence of liquid flow above the needle on a periodic or chaotic nature of the bubble departures process was numerically investigated. During the numerical simulations bubbles departing from the needle was considered. The perturbations of liquid flow were simulated based on the results of experimental investigations described in the paper [1]. The numerical model contains a bubble growth process and a liquid penetration into a needle process. In order to identify the influence of liquid flow above the needle on a periodic or chaotic nature of bubble departures process, the methods data analysis: wavelet decomposition and FFT were used. It can be inferred that the bubble departure process can be regulated by altering the hydrodynamic conditions above the needle, as variations in the liquid velocity in this area affect the gas supply system's conditions. Moreover, the results of numerical investigations were compared with the results of experimental investigation which are described in the paper [2]. It can be considered that, described in this paper, the numerical model can be used to study the interaction between the bubbles and the needle system for supplying gas during the bubble departures from two needles, because the interaction between the bubbles is related to disturbances in the liquid flow above the needle. [ABSTRACT FROM AUTHOR]

Suspension of solid particles at interfaces is a common phenomenon, pivotal in natural, and industrial contexts. This study focuses on gas marbles which are single soap‐like air bubbles in air environment stabilized by colloidal particles. A unique stabilization method employing edible cinnamon particles is introduced. Unlike previous studies using spherical particles, the irregularly‐shaped micrometer‐sized cinnamon particles demonstrate remarkable long‐term stability through jamming and interlocking at the air‐liquid interface. Comprehensive characterization via optical and scanning electron microscopy, and contact angle experiments, elucidates the stabilization mechanism. These gas marbles exhibit exceptional resilience against drying, heating, freezing, and mechanical stress. They can be fabricated with various edible liquids offering extensive customization possibilities. This breakthrough introduces a promising method for creating stable gas marbles with edible particles, offering versatility for various fields and applications. The application scope includes surface catalysis and shock/vibration sensors, and also molecular gastronomy. [ABSTRACT FROM AUTHOR]

The study analyzes the unique behavior of two-phase flows when incorporating nanofluids containing aluminum trioxide (Al2O3) and copper (Cu) nanoparticles in a vertical channel. The main goal is to investigate the behavior of airnanofluid mixtures in this setting, with potential implications for industrial and exploration applications. Research in this area could provide valuable insights into the dynamics of these flows and their impact on heat transfer, fluid dynamics, and material science. This study includes an analysis of upwelling dynamics, the effect of fluid characteristics on bubble growth, and the system's thermal efficiency. Using numerical and quantitative visualization techniques, we seek to understand the behavior of these particles at the interface between the liquid and gas phases by integrating Al2O3 and Cu nanoparticles into the VOF approach. Because of their superior thermal conductivity, copper nanoparticles have a higher volumetric density and provide more efficient heat transfer, leading to quick and efficient thermal dissipation. Smaller nanoparticles offer an increased surface area-to-volume ratio, which improves heat transfer capabilities and ensures uniform heat dissipation throughout the material. Consequently, copper nanoparticles emerge as the preferred choice for applications necessitating high thermal transfer and optimal performance. These results significantly impact the design of more efficient heat exchangers and optimize recovery techniques by elucidating the interactions between these nanoparticles and the surrounding fluids. Furthermore, the selection of smaller copper nanoparticles further amplifies thermal transfer, maximizing performance across diverse applications. [ABSTRACT FROM AUTHOR]

As a simple and safe alternative intervention, percutaneous balloon compression (PBC) has been gradually adopted by a growing number of neurosurgeons to treat trigeminal neuralgia. A pear-shaped opacity observed fluoroscopically, which indicates full suffusion of Meckel's cave conducting sufficient pressure against Gasserian ganglion, is believed to be the key to its success. Sometimes, a bitten pear may appear due to bubbles in the balloon but is usually ignored. This study aims to investigate the effects of the bubbles on postoperative outcomes. Patient data were obtained from the consecutive cases undergoing PBCs in our department between 2019 and 2021. Among them, pain and numbness were used to assess the efficacy of PBC based on Barrow Neurology Institute (BNI) scoring system. It was defined as an effective outcome if the postoperative pain intensity grade was lower than II. And those with numbness grade > II were regarded as numb incidence. We eventually recruited 59 cases, including 42 in full pear and 17 in bitten pear groups with follow-up time up to 44 months. The early effective rates were 95.2% and 82.4%, respectively (p > 0.05), which turned to 88.1% and 52.9% during the last follow-up period (p < 0.01). This result indicated that the bitten pear gave rise to a significantly higher recurrence. In terms of numbness, there was no significant difference. Gas does not yield enough pressure as liquid, and cannot exert enough pressure to the semilunar ganglion. Therefore, air evacuation should not be ignored before injection. [ABSTRACT FROM AUTHOR]

The porosity of freshwater ice and sea ice is one of the main parameters that determine their strength. The strength of ice varies over a wide range of values, and the differences in the intensity of the mechanisms of ice porosity formation in different water areas can be one of the possible reasons for these variations. The water mass contains gases in two forms: gases dissolved in the water mass, as well as gas bubbles that are formed when wind waves break up, and bubbles that float up from the seabed. This article presents the results of an analysis of the role of each of these forms in the formation of gas inclusions (pores) in the crystal structure of ice. The results showed that the main source of gas pores in ice crystals is the gas bubbles coming to the surface from the bottom, formed during the decomposition of bottom sediments or during gas leaks from near-bottom oil and gas fields. The possibility of gas bubbles occurring and rising to the ice–water boundary depends on the presence of bottom sources of the gases, the intensity of dissolution of the bubbles and the depth of the water area. Therefore, the variation in the porosity and the strength of ice over the space of the water areas can be associated with the changes in their depths, and the presence and location of the natural gas sources. [ABSTRACT FROM AUTHOR]

Mass transfer of bubbles is important in microalgae cultivation. In this study, aiming to improve the microalgae culturing efficiency, computational fluid dynamics (CFD) was adopted to study the influence of the aeration manners on mass transfer of bubbles within ascending columns in multi‐column airlift photobioreactor (PBR) and the hydrodynamic conditions within the PBR under different aeration manners. In addition, the bubble generation time, the detachment diameter, and the average volumetric mass transfer coefficient of bubbles in ascending columns were analyzed. Furthermore, the experimental results were compared with the simulation results obtained from microalgae cultivation. The results showed that the whole aeration manner yields the lowest mixing strength and mass transfer efficiency of bubbles at an aeration rate of 0.2 vvm. Conversely, both the mixing strength of the liquid and mass transfer coefficient of bubbles were enhanced under the half and alternate aeration manners. However, the results demonstrated that the distribution of the flow field was not uniform under the half aeration manner and there were obvious high‐speed and low‐speed zones. In contrast, the flow field distribution in the PBR was more uniform under the alternate aeration manner, which was suitable for microalgae cultivation at high concentration. This study effectively enhanced the mixing strength and CO2 transfer rate in the PBR. [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.)

The available experimental data focusing on the differences between bubble and drop breakages are still scarce in the literature. This work conducts the experiments of single bubble and single drop breakages in agitated turbulent flows. The effects of fluid particle size and agitation speed on daughter fragment number, breakage time, breakage probability, breakage frequency, and daughter size distribution (DSD) are analyzed. The breakage frequencies of bubble and drop show the monotonic and non‐monotonic variation trends with increasing fluid particle size, respectively. The variations of bubble and drop DSDs exhibit opposite trends, the probability of equal‐sized breakage of bubble increases while that of drop decreases when agitation speed or fluid particle size increases. These different trends cannot be predicted by most of the existing models simultaneously. The processes of elongation and internal flow redistribution during deformation may be the important factors causing these differences. [ABSTRACT FROM AUTHOR]

ObjectiveThis paper studies the damage modes of targets simultaneously subjected to multiple damage elements by analyzing the damage characteristics of a cylindrical shell structure subject to a double underwater explosion (UNDEX). MethodsFirst, a finite element model of the cylindrical shell is established, then the arbitrary Lagrangian−Eulerian (ALE) method is used to investigate its damage characteristics when subject to UNDEX with single or dual explosion sources, and the damage effects are evaluated in terms of the structural fracture area, maximum vertical displacement and extent of plastic strain area, and the 500 kg TNT charge is calculated and analyzed. ResultsThe results show that when the standoff distance of dual explosion source is 1 m, the damage to the outer cylindrical shell is more serious when the standoff distance of dual explosion sources is equal to that of the single explosion source, but the damage to the inner cylindrical shell is less than that of the single explosion source. At the same time, with the increase in standoff distance of the two TNT charges, especially when the standoff distance is greater than 3 m, the damage effects on the cylindrical shell structure become weaker. ConclusionsBy calculating the damage to a cylindrical shell structure by UNDEX under different initial parameters, the general rules of damage to cylindrical shell structures by single and dual explosion sources are given, which can provide references for enhancing the power of underwater weapons.

The study analyzes the unique behavior of two-phase flows when incorporating nanofluids containing aluminum trioxide (Al2O3) and copper (Cu) nanoparticles in a vertical channel. The main goal is to investigate the behavior of air-nanofluid mixtures in this setting, with potential implications for industrial and exploration applications. Research in this area could provide valuable insights into the dynamics of these flows and their impact on heat transfer, fluid dynamics, and material science. This study includes an analysis of upwelling dynamics, the effect of fluid characteristics on bubble growth, and the system's thermal efficiency. Using numerical and quantitative visualization techniques, we seek to understand the behavior of these particles at the interface between the liquid and gas phases by integrating Al2O3 and Cu nanoparticles into the VOF approach. Because of their superior thermal conductivity, copper nanoparticles have a higher volumetric density and provide more efficient heat transfer, leading to quick and efficient thermal dissipation. Smaller nanoparticles offer an increased surface area-to-volume ratio, which improves heat transfer capabilities and ensures uniform heat dissipation throughout the material. Consequently, copper nanoparticles emerge as the preferred choice for applications necessitating high thermal transfer and optimal performance. These results significantly impact the design of more efficient heat exchangers and optimize recovery techniques by elucidating the interactions between these nanoparticles and the surrounding fluids. Furthermore, the selection of smaller copper nanoparticles further amplifies thermal transfer, maximizing performance across diverse applications.

The study of the attachment process between particles and bubbles in a turbulent environment is essential for understanding the microscopic process of flotation. The interaction force model between particles and bubbles is developed based on the API (Application Programming Interface) secondary development module of EDEM. The model establishes a three-dimensional discrete element method (DEM) to simulate the interaction process between particles and bubbles. Isotropic turbulence is generated by constructing regular grids in the Fluent software. The turbulent environment is then incorporated into the EDEM software using the computational fluid dynamics discrete element (CFD-DEM). The simulation consists of regular particles with sizes ranging from 0.10 to 0.30 mm and densities of 1500, 2000 and 2500 kg/m3. Additionally, the irregular particles with sphericity values ranging from 0.746 to 0.854 are included. Bubble sizes are set at 1.00, 1.20, 1.60, and 2.00 mm. To study the attachment process between particles and bubbles, the distance between the grid and the bubble in the turbulent environment are set as 1.00, 1.50, 2.00, and 3.00 mm. The results demonstrate the existence of a critical detachment flow rate (the minimum turbulent flow velocity where particles and bubbles cannot achieve a stable attachment state) for both regular and irregular particles adhering to bubbles in a turbulent environment. It is found that the particles with larger density and diameter exhibit a smaller critical detachment flow velocity when adhering to bubbles, indicating that particles with larger diameter and density have difficulty in achieving stable attachment with bubbles. As the bubble diameter increases, the critical detachment flow velocity required for stable particle-bubble attachment decreases, making it more difficult for particles to achieve stable attachment. At the same flow velocity, a smaller distance between the bubbles and the grid results in a higher turbulent flow intensity, leading to a smaller critical detachment flow velocity for stable particle-bubble attachment, suggesting that an increase in turbulent intensity is detrimental to the stable attachment of particles and bubbles. Furthermore, the particles with lower sphericity also exhibit a smaller critical detachment flow velocity for stable attachment to bubbles, indicating that the particles with lower sphericity have difficulty in achieving stable attachment with bubbles.

Previous studies on epoxy foams were subjected to the specific property, and improvements in thermal insulation or dielectric property were usually accompanied by the sacrifice of mechanical strength or thermal stability. The current research reported a high‐performance epoxy foam by the pre‐curing process using E‐51/DDS and expandable microsphere (EMP) as polymer matrix and physical blowing agent, respectively. The effect of EMP loading on the structure & property of epoxy foam was reported. The mean diameter of E‐51/EMP foam was in the range of 19–21 μm. The compression property of E‐51/EMP foam was fit for the power‐law model and its integrity was well maintained during compressive test. Compared with bulky epoxy, a significant decrease of thermal conductivity of 62.93% was observed in 10 wt% EMP‐filled epoxy foam. E‐51/EMP foam showed superior thermal stabilities, with a T5% of over 300°C. The dielectric constant was decreased by 54.5% from 4.92 in bulky epoxy to 2.24 in E‐51/EMP foam (10 wt% EMP). Notably, there was a percolation phenomenon of EMP (6 wt%) regarding on the structure & property of E‐51/EMP foam. This study provides lightweight, robust, high‐temperature‐resistant, and low‐dielectric‐constant epoxy foams with the wide application prospects in buoyant, electronic packaging, and energy‐saving industries. [ABSTRACT FROM AUTHOR]

The rich interaction of multiple bubbles with multiple vortical structures makes the study of bubbly turbulent flows quite challenging. An idealisation of this problem would be the interaction between a single bubble and an elliptic vortex ring, the latter of which can be considered a representative vortical structure. The elliptic vortex ring is characterised by its initial aspect ratio A R 0 , defined as the ratio of the semi-minor to semi-major axes of the ellipse, with A R 0 = 1 corresponding to a circular vortex ring. In the first part, we focus on the interaction between the elliptic vortex ring ( A R 0 = 0.6 ) and a bubble, where we explore the effects of the capture angle ( θ C ) on the different quantities relevant to the ring as well as the bubble, using simultaneous side and top-view high-speed visualisations; θ C is defined as the angle subtended by the bubble with the instantaneous major axis of the elliptic vortex ring at bubble capture. We study the effect of θ C on the reduction in the ring's convection speed Δ U ∗ and the number of daughter bubbles N b , computed at a later stage of the interaction. For this part of the study, the Weber number W e = ρ U 0 2 D b / σ , defined as the ratio of the ring's inertial effects to surface tension effects, is fixed at W e = 11 . We find that bubble capture at lower capture angles ( θ C ≈ 0 ∘ ) corresponding to the high-curvature part of the elliptic vortex ring is found to be more probable compared to that at higher capture angles ( θ C ≈ 90 ∘ ). Further, a lower capture angle ( θ C ≈ 0 ∘ ) leads to a larger number of daughter bubbles N b and a slightly higher reduction in ring speed Δ U ∗ . In the second part, we study the effect of A R 0 by contrasting the elliptic ring ( A R 0 = 0.6 ) with a circular ring ( A R 0 = 1 ) over a range of Weber numbers, in which the parameters of interest are the ring's speed and the number of daughter bubbles. We observe that the elliptic vortex ring produces fewer daughter bubbles than the circular ring, with the difference increasing at larger ring strengths corresponding to higher Weber numbers. At higher We, the elliptic ring deviates from the N b ∝ W e 0.42 scaling, which holds for the circular ring. The current study thus helps to gain a better insight into the complex problem of bubbly turbulent flows. [ABSTRACT FROM AUTHOR]

The tribological property and corrosion of a steel ball sliding against anodic oxide film (AOF) on Al-Li alloy lubricated by an ionic liquid (imidazolium hexafluorophosphate, LP108) are investigated without and with electric field. Upon sliding, no bubbles are observed without electric field (0 V) and with electric field at 1 V, while bubbles are produced continually with electric field at applied voltages of 5 V and 10 V. Higher voltage produces more bubbles. It is found that bubbles accelerate the worn-out of the AOF in sliding and corrosion of the steel ball after sliding. In the absence of bubbles, friction coefficient lower than 0.1 and long wear lifetime suggest that LP108 is a good lubricant at both 0 V and 1 V. In the presence of bubbles, however, AOF is rapidly worn out, i.e., 3.3±0.2 min at 5 V and 1.6±0.3 min at 10 V. Because the bubbles are produced continually at 5 V and 10 V, there is a rapid transition of the lubricating regime from a flooded state (boundary lubrication regime) to a bubble-dominated state (dry sliding regime). By turning off the electric field after one-minute sliding (no more newly born bubbles), the effective lubrication by LP108 can be preserved. Once the tribo-test is ended, the collapse of the bubbles occurs rapidly and hence the corrosion of the steel ball is greatly accelerated when compared to that in the absence of bubbles. In addition to bubble collapse, the bubbles are responsible for the accelerated corrosion of the steel ball because they are the reactive species of electrochemical decomposition of LP108 by synergistic action of electric field and friction, which is supported by experimental evidence. In other words, neither sliding friction without electric field nor electric field without sliding friction up to 10 V produces bubbles. A friction-activated mechanism is proposed to explain the synergistic action of electric field and friction. In short, sliding friction produces wear of the steel ball and this initiates friction activation of the worn surface of the steel ball. Consequently, the generation of bubbles occurs. [ABSTRACT FROM AUTHOR]

Blasting and shaped charges are the main forms of underwater weapons, and their near-field underwater explosions (UNDEX) can severely damage structures. Therefore, it is of great importance to study underwater explosive load characteristics of different forms of charges. The full physical process of a typical underwater explosion of a sphere/column blasting charge and a shaped charge was simulated using the Eulerian method. The loading characteristics of the underwater blast shock wave and bubble, as well as the projectile, were studied. The results show that the shock wave loads of spherical, cylindrical, and polygonal charges propagate outward in spherical, ellipsoidal–spherical and ellipsoidal–spherical wavefronts, respectively. When the shock wave reaches 16 times the distance-to-diameter ratio, its surface is approximately spherical. In addition, in the shaped charge underwater explosion, the shaped charge liner cover absorbs 30°–90© of the shock wave energy and some of the bubble energy to form a high-speed shaped penetrator. Spherical, ellipsoidal, and ellipsoidal bubbles are generated by underwater explosions of spherical, cylindrical, and shaped charges, respectively. The obtained results provide a reference for evaluating the power of underwater weapons. [ABSTRACT FROM AUTHOR]

[Display omitted] The droplet/bubble adhesion characteristics depend on the length of the droplet/bubble three-phase contact line. Since the deformation caused by the liquid–gas interfacial tension on the soft substrate, referred as to the wetting ridge, retards contact line spreading and retraction, we conjecture that the droplet/bubble adhesion characteristics depend also on the substrate softness. Soft substrates with various shear moduli are prepared and characterized by the spreading and receding dynamics of water droplets and underwater bubbles. Snap-in and normal adhesion forces of droplets/bubbles on such soft substrates are directly measured along with the visualized droplet/bubble shape profiles. The droplet/bubble snap-in force, which corresponds to the short-time spreading dynamics, decreases with a decrease in the substrate shear modulus because of the retarded contact line spreading. The droplet maximal adhesion force on a soft substrate can be counterintuitively either smaller or larger than its counterpart on the rigid substrate depending on different dwelling times, i.e., the droplet/bubble-substrate contact time before droplet/bubble-substrate separation. The former is attributed to the retarded contact line spreading, whereas the latter is attributed to the retarded contact line retraction. The substrate softness- and dwelling time-dependent droplet/bubble adhesion reported in this study will benefit various applications related to soft substrates. [ABSTRACT FROM AUTHOR]

A new extended bubble dynamical equation has been recently proposed by the authors Jin-Ze Liu, Wen-Shan Duan et al. Based on this equation, the dependence of the mass loss of a solid boundary material on the bubble parameters, such as the initial bubble radius, the distance from the center of the bubble to a solid boundary, and the intensity of external disturbances, is given in this paper. Our results can explain why there is mass loss when there are bubbles close to a solid boundary. Based on our results, it is also possible to estimate the mass loss of a solid boundary material due to bubble collapse. [ABSTRACT FROM AUTHOR]

We consider two models of interacting DNA molecules: First is (four parametric) bubble coalescence model in interacting DNAs (shortly: BCI-DNA). Second is (three parametric) bubble coalescence model in a condensed DNA molecules (shortly BCC-DNA). To study bubble coalescence thermodynamics of BCI-DNA and BCC-DNA models we use methods of statistical physics. Namely, we define Hamiltonian of each model and give their translation-invariant Gibbs measures (TIGMs). For the first model, we find parameters such that corresponding Hamiltonian has up to three TIGMs (three phases of system) biologically meaning existence of three states: "No bubble coalescence", "Dominated soft zone", "Bubble coalescence". For the second model, we show that for any (admissible) parameters, this model has unique TIGM. This is a state where "No bubble coalescence" phase dominates. [ABSTRACT FROM AUTHOR]

Details of calculation of the critical Reynolds number that separates two different types of agglomeration of bubbles in a viscous fluid are given. [ABSTRACT FROM AUTHOR]

Understanding the collision between kerosene droplets and coal particles in the bubble trailing vortex region is crucial for enhancing slurry conditioning. We found the area of the bubble trailing vortex region increased as the bubble size increased via the Fluent 6.3.26 software. A kerosene droplet velocity range of 0.074–0.106 m/s and a coal particle velocity range of 0.062–0.104 m/s were obtained if a bubble had a diameter of 0.3 mm. We employed a high‐speed motion acquisition system and observed the collision process, which was divided into two stages: Compression and Rebound. The critical motion distance increased as the kerosene droplet size increased, and sufficient kerosene droplet motion distance and enough kinetic energy normally resulted in a rebound phenomenon. The attenuation energy was almost positively linear to the initial energy, and the energy attenuation coefficient of the collision process was fitted to 0.626. Our results can provide valuable insight into mineral separation. [ABSTRACT FROM AUTHOR]

In this study, a nonlinear theoretical model has been proposed to describe the effect of compressibility on two-dimensional ablative Rayleigh–Taylor instability. The model is based on the Layzer's potential flow model with the vorticity generation inside the bubble. The analytic expression of curvature and asymptotic velocity of the tip of the bubble are obtained, and the growth of the bubble tip is described by a second-order nonlinear differential equation. It is observed that growth and asymptotic velocity are affected by the compression or decompression of both the fluids, together with the unperturbed static pressure at the interface of two fluids and adiabatic indices of both fluids. The obtained results are compared with the earlier linear and nonlinear results. [ABSTRACT FROM AUTHOR]

We provide a unified framework with demand for housing over the life cycle and financial frictions to analyze the existence and macroeconomic effects of rational housing bubbles. We distinguish a housing price bubble, defined as the difference between the housing market price and its fundamental value, from a housing demand bubble, which corresponds to a situation where a pure speculative housing demand exists. In an overlapping generation exchange economy, we show that no housing price bubble occurs. However, a housing demand bubble may occur, generating a boom in housing prices and a drop in the interest rate, when households face a binding borrowing constraint. The multiplicity of steady states and endogenous fluctuations can occur when credit market imperfections are moderate. These fluctuations involve transitions between equilibria with and without a housing demand bubble that generate large fluctuations in housing prices consistent with observed patterns. We finally extend the basic framework to a production economy and we show that a housing demand bubble increases housing prices, which can still be characterized by large fluctuations. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology 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.)

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office 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.)

In recent years, the research of bubbles, partially circular structures in the interstellar medium, consisting of dust and gas, has received the considerable attention. The analysis of the structure and evolution of bubbles provides insight into the conditions under which stars and planets form in the interstellar medium. Dust bubbles are inextricably linked with star formation regions and are powerful tools for studying the interaction of young stellar objects with their environment at various stages of evolution. The main goal of this article is to study the region of the N126 dust bubble, search for and identify young stellar objects. Identification of young stellar objects by their fluxes at infrared wavelengths is relatively recent, and identification criteria are still at the stage of improvement. Therefore, in this article, the criteria for identifying young stellar objects were used according to the works of Koenig X.P. (2012), Koenig X.P. & Leisawitz D.V. (2014) and Fischer W.J. (2016), which are based on analysis of WISE observational data in the near- and mid-infrared bands W1 (3.4 μm), W2 (4.6 μm), W3 (12 μm), and W4 (22 μm). The data from the 2MASS and AllWISE catalogs with reliable non-zero fluxes of infrared radiation sources were used in that work. For the researched dust bubble, young stellar objects of class 0 (protostars) and class I were not detected. 4 objects of class II, 1 object of the class of transition disks and 48 objects of class III were identified. Energy distributions in the spectra for class II objects were constructed, which also confirmed their evolutionary status. For all identified YSOs, color diagrams were constructed showing the locations of the found objects with their corresponding areas of evolution. Maps of the distribution of YSOs in space are analyzed, which indicate possible signs of an initiated star formation process in the N126 dust bubble. [ABSTRACT FROM AUTHOR]

Due to its excellent performance, polyurethane rubber is often used as a protective baffle for the automatic passing neutral section sensor to protect the sensor from the impact of silt and stones, while the high-speed train is operating. However, this paper conducts case analysis of abnormal cracking of the sensor baffle used in high-speed trains. In fact, this kind of problem has happened several times, and the previous solution method was to replace the failed baffle. But such kind of method mainly treats the faults instead the root cause analysis, so it still brings the safety issue to the normal operation of the train. In order to avoid such potential accidents, this paper adopted a variety of material analysis methods to detect the properties of materials and analyzed the damaged area in detail by combining macroscopic and microscopic methods. Finally, the root cause of the failure was further confirmed by confirmatory experiment. Based on the above comprehensive analysis, a reasonable solution is proposed to avoid the recurrence of the accidents and provide an important basis for solving the complicated polyurethane rubber failure problem quickly, correctly and effectively. [ABSTRACT FROM AUTHOR]

To improve the capability of nanosecond lasers to process structures with a high aspect ratio, a new method of nanosecond laser processing in closed flowing water was proposed in this paper. The microgrooves on a stainless steel 304 surface were processed by the new method, and the influence of processing parameters on the microgrooves was studied. The comparative experiments of laser processing in still water and overflowing water were also carried out, and the unusual phenomenon of laser processing in different flowing water was discovered by a high-speed camera. The results showed that the flowing velocity played a crucial role in underwater laser processing, and that high flowing velocity could timely remove bubbles in closed flowing water, thus obtaining higher processing efficiency. As the depth of the groove increased, the bubbles firstly affected the processing of the sidewall, causing a circular transition between the sidewall and bottom surface. The reflection of the laser beam by the bubble could cause secondary processing on the sidewall, resulting in a decrease in the taper angle. Based on the above research, the microgroove with a width of 0.5 mm, aspect ratio of 3, and taper angle of 87.57° was successfully processed by a nanosecond laser in closed flowing water. Compared to conventional nanosecond laser processing, laser processing in closed flowing water was more advantageous in processing microgrooves with a small taper angle and high aspect ratio. [ABSTRACT FROM AUTHOR]

We study investors' trading behaviours during bubbles on the Vietnam stock market. Vietnam offers a great setting due to its high susceptibility to bubbles and large heterogeneity among various groups of investors. We document evidence of trading explosions during two bubbles identified in our sample period, followed by reversions in the aftermath. Financial sectors make a significant contribution to this phenomenon in both episodes. We also find that foreign and sophisticated investors increase their holdings when the bubbles form and start selling well before the bursts, suggesting their superior ability to local individuals in timing the market. [ABSTRACT FROM AUTHOR]

The Japan Atomic Energy Agency (JAEA) is developing an evaluation method for a two-phase flow in the reactor core using simulation codes based on the volume of fluid (VOF) method. However, it is impossible to simulate boiling on the heating surface in large-scale domains, such as fuel assemblies, using this simulation method because simulating boiling based on the VOF method requires fine meshes to resolve the initiation of boiling. Therefore, the JAEA started developing a simplified boiling model (SBM) for the two-phase flow simulation in fuel assemblies. In the SBM, the motion and growth equations of a bubble are solved to obtain their diameter and time length at the detachment, the size scale of which is within/around the calculation grid size of the numerical simulation. This information is given as the vapor injection flow rate for the boundary condition on the heating surface. JUPITER calculates the bubble behavior with a scale of more than several millimeters. Using the developed SBM, this study simulates convection boiling on a vertical heating surface. A comparison between the simulation and experimental results showed good reproducibility of the heat flux and velocity dependency on the passage period of the bubble.

Large gas bubbles can reach the surface of pools of mud and lava where they burst, often through the formation and expansion of circular holes. Bursting bubbles release volatiles and generate spatter, and hence play a key role in volcanic degassing and volcanic edifice construction. Here, we study the ascent and rupture of bubbles using a combination of field observations at Pâclele Mici (Romania), laboratory experiments with mud from the Imperial Valley (California, USA), numerical simulations and theoretical models. Numerical simulations predict that bubbles ascend through the mud as elliptical caps that develop a dimple at the apex as they impinge on the free surface. We documented the rupture of bubbles in nature and under laboratory conditions using high-speed video. The bursting of mud bubbles starts with the nucleation of multiple holes, which form at a near-constant rate and in quick succession. The quasi-circular holes rapidly grow and coalesce, and the sheet evolves towards a filamentous structure that finally falls back into the mud pool, sometimes breaking up into droplets. The rate of expansion of holes in the sheet can be explained by a generalization of the Taylor–Culick theory, which is shown to hold independent of the fluid rheology.

Cavitation erosion is one of the most severe problems encountered in hydraulic turbomachinery. When testing the materials, the engineers usually rely on standardized procedures. The most common one being the vibratory ASTM G-32 test, which offers two possibilities of performing the test – the direct, where the specimen is attached to the ultrasonic device and the indirect, where the specimen is stationary and exposed to the ultrasonic horn, positioned just 0.5 mm from it. The erosion rates from the two are significantly different and a question may be asked if they are at all comparable and further on are they comparable to the “real-life” hydrodynamic cavitation which occurs in turbomachinery.In this study we performed erosion tests on a stationary specimen where the gap between the specimen and the horn was varied from 0.3 to 4 mm. In addition, we used high speed visualization to observe the cavitation in the gap.We observed that the cavitation erosion rate strongly depends on the gap. From visualization we see that the cavitation dynamics significantly changes in a small gap, leading to a large, but 2-dimensional cavitation bubbles which collapse very slowly, compared to the small spherical ones in a larger gap.We investigated the probability of shock wave occurrence and derived a very simple model, which gives accurate qualitative predictions of experimental data.Finally, the study puts into question the validity of ASTM G32 test – the most common approach used in engineering today.

Gas–liquid flow in the dissolved air flotation (DAF) tank was studied through computational fluid dynamics through the realizable k-ε model and the population balance model (PBM) to predict the gas content of different flotation mediums (air, carbon dioxide, and chlorine) at different heights of the separation zone in the DAF tank. Simultaneously, a particular focus was placed on studying the effects of bubble aggregation and breakage on gas content. The results indicated that there were virtually no bubbles present in the region below 0.1 m of the separation zone. The gas content in the separation zone could meet the needs for gas content in the DAF tank when all these three gases were adopted as flotation medium. The introduction of models for bubble aggregation and breakage resulted in lower gas content at the bottom of the separation zone and higher gas content at the top, aligning more closely with experimental data. Due to the structural similarity and similar physicochemical characteristics of carbon dioxide and water molecules, the impact of bubble aggregation and breakage on the gas content is minimal. HIGHLIGHTS Considering the aggregation and breakage of bubbles during simulation.; Introducing the population balance model to consider non-uniform-sized bubbles.; Study the hydraulic characteristics of the separation zone when adopting air, carbon dioxide, and chlorine gas as flotation medium.;

In order to evaluate the insulation of two-phase immersion cooling in the HV power electronic package, the insulation degradation of the dielectric interface induced by bubbles is investigated. In this paper, a test strategy with 50 Hz unipolar DC and AC combined voltage for partial discharge (PD) at boiling interface of AIN ceramic is proposed. The insulation threshold of an AIN ceramic surface is acquired in several dielectric environments, such as air, FC-72 liquid (FC-72, a Fluorinert™ from 3M™), FC-72 vapor, and boiling state of FC-72. This reveals the deterioration of boiling on the insulation of the surface immersed in the dielectric refrigerant. To investigate the mechanism of the PD feature at the boiling interface, the PD patterns of the unrestricted bubble and the accumulated bubble are acquired and contrastively analyzed. Combined with the feature of the back discharge and the bubble behavior, the charged vapor-ceramic interface is relatively stable due to the accumulated vapor layer. This stability of the charged vapor-ceramic interface is broken if the bubble is unrestricted. Besides, it is discovered that the vapor-liquid interface inside the bubble may be another charged interface, which can also trigger a back discharge.

Dough extensional properties obtained from 14 wheat flours hydrated at 50% (/flour weight) were assessed by the empirical test of Alveograph, a bubble inflation test, and by the rheometric test of uniaxial compression in lubricated conditions (LSF) at large deformations. In baking industry, comparison between flours is based on several parameters (n ≥ 5) defined from the alveogram, which is the time variations of pressure inside dough. In this study, the alveogram is converted into a stress-strain curve (σ = f(εb)). Then, from this curve, the extensional behavior coefficient of the flours, assessed by the consistency k0, is fitted between 0 ≤ εb ≤ 1.5, assuming ε b ˙ = 0.25 s−1 (R2 = 0.99 ± 0.01 for 14 flours). The flow index (n = 0.36) and strain hardening index (SHI = 1.73) are kept constant. The model is validated by comparing the stress values calculated from the alveogram to those measured in LSF for wheat flour doughs hydrated at 50% (R2 = 0.91) at εb = 1 and 0.25.10−2 < ε b ˙ < 2.5 s−1. Therefore, the Alveograph, which allows classifying flours according to several dough stretching properties, also provides access to the model of dough extensional behavior. Determining dough extensional properties for alveograph test and validating by comparison with resutls obtained by LSF [ABSTRACT FROM AUTHOR]

The aerosol released during a severe reactor accident may be retained in the liquid pool. During the venting stage of the suppression pool, bubbles generated in the pool will rise to the free surface and burst to generate droplets. The airflow re-entrains aerosols from the liquid to the air via droplets. Accurate evaluation of droplet entrainment needs to acquire the diameter and number of droplets generated by a bubble, so studying the various behaviors that affect the above parameters is necessary. In this paper, high-speed photography is used to visualize the phenomenon of a single bubble burst to generate film droplets in deionized water and TiO 2 suspensions at different phase temperatures. Image processing is used to obtain the bubble film opening rate, the bubble burst position, the bubble lifetime, and the diameter and number of film droplets. The results show that the film thickness decays with time in a power law with a parameter of 2/3, and the newly defined film thickness also decays with time in a power law after considering the bubble radius and physical parameters. This rule is applicable in different liquid temperatures and solutes. Besides, the film thickness increases with liquid temperature and aerosol concentration; the bubble lifetime obeys the Weibull distribution, with the average bubble lifetime of deionized water varies non-monotonically with the liquid temperature, the average lifetime increase with aerosol concentration and liquid temperature in aerosol suspension; The average droplet diameter decreases with bubble lifetime in a power law with a parameter of 5/16, the droplet diameter distribution can be calculated by the gamma distribution of the normalized droplet diameter and the bubble lifetime, and in good agreement with the experimental data, the droplet entrainment factor can also be calculated from the critical droplet diameter and bubble lifetime, which decreases with bubble lifetime. [Display omitted] • Bubble lifetime obeys Weibull distribution. • Film thickness decays exponentially with time and is affected by Marangoni effect. • Film droplet diameter decreases with bubble lifetime following a 5/16 power law. • Gamma and Weibull distribution can describe film droplet diameter distribution. • The entrainment of film droplets from a single bubble burst is 0.04–0.18. [ABSTRACT FROM AUTHOR]

Three‐dimensional (3D) printing is an emerging technique that has shown promising success in engineering human tissues in recent years. Further development of vat‐photopolymerization printing modalities has significantly enhanced the complexity level for 3D printing of various functional structures and components. Similarly, the development of microfluidic chip systems is an emerging research sector with promising medical applications. This work demonstrates the coupling of a digital light processing (DLP) printing procedure with a microfluidic chip system to produce size‐tunable, 3D‐printable porosities with narrow pore size distributions within a gelatin methacryloyl (GelMA) hydrogel matrix. It is found that the generation of size‐tunable gas bubbles trapped within an aqueous GelMA hydrogel‐precursor can be controlled with high precision. Furthermore, the porosities are printed in two‐dimensional (2D) as well as in 3D using the DLP printer. In addition, the cytocompatibility of the printed porous scaffolds is investigated using fibroblasts, where high cell viabilities as well as cell proliferation, spreading, and migration are confirmed. It is anticipated that the strategy is widely applicable in a range of application areas such as tissue engineering and regenerative medicine, among others. [ABSTRACT FROM AUTHOR]

Stock bubbles are characterized by unpredictable price surges and subsequent declines, causing significant losses for investors. This study investigates the effectiveness of the Generalized Sup Augmented Dickey–Fuller (GSADF) test in identifying mild explosive patterns and speculative bubbles within individual S&P 500 stocks, as compared to the Sup Augmented Dickey–Fuller (SADF) test. Utilizing real-time monitoring data, this research examines unit roots, stationarity, and the ability to detect multiple structural breaks. The GSADF test consistently outperforms the SADF test in rejecting the null hypothesis, demonstrating greater sensitivity and efficacy in recognizing stock bubbles. Monte Carlo simulations address size distortions in the GSADF test, enhancing accuracy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]