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Vertically neutral collapse of a pulsating bubble occurs when the boundaries above or below the bubble balance the buoyancy effect over a pulsation. In this study, the vertically neutral collapse of a bubble near a vertical rigid wall below the free surface is investigated. The boundary integral method (BIM) is employed to model the bubble dynamics with an open-domain free surface. Moreover, this method is validated against several buoyant bubble experiments. Bubble dynamics in such conditions are associated with three dimensionless parameters: the bubble-free surface distance $\\gamma _{{f}}$, bubble–wall distance $\\gamma _{{w}}$ and buoyancy parameter $\\delta$. We derive the Kelvin impulse of a spherical bubble and the algebraic relationship for vertically neutral collapse, which proves to be accurate for predicting vertically neutral collapse when the bubble is relatively far from the boundaries. Four patterns of the vertically neutral collapse of the bubble for different $\\gamma _{{w}}$ and $\\gamma _{{f}}$ are identified: (i) formally downward jet; (ii) annular collapse; (iii) horizontal jet; and (iv) weak jet. Despite the downward jet shape, the ‘formally downward jet’ is in the vertically neutral collapse state in terms of the profile of toroidal bubbles and the orientation of local high-pressure zones around the bubble at jet impact. A bulge with a high curvature above the bubble in the ‘annular collapse’ pattern is formed during bubble collapse under two local high-pressure zones at the left and right extremities of the bubble. The ‘horizontal jet’ pattern has the greatest potential to attack the wall, and the power laws of the moment of the jet impact, jet velocity and bubble displacement with respect to the theoretical Kelvin impulse are discussed. In particular, we quantitatively illustrate the role of the free surface on bubble migration towards the wall through the variational power-law exponents of the bubble displacement with respect to $\\gamma _{{w}}$.

High-speed water entry is a transient hydrodynamic process that is accompanied by strongly compressible flow, free surface splash, cavity evolution and other nonlinear hydrodynamic phenomena. To address these problems, a novel fluid–structure interaction (FSI) scheme based on the immersed boundary method is proposed which is suitable for strongly compressible multiphase flows. In this scheme, considering the multiphase interfaces at the immersed boundary, an improved immersed boundary method for effectively suppressing the non-physical force oscillation is proposed. Additionally, a quaternion-based six degrees of freedom motion system is used to describe rigid body motion, and the multiphase flow Eulerian finite element method is applied as the fluid solver. Using analytical solutions, experimental data and literature data, the accuracy and robustness of the FSI scheme are validated. Finally, the high-speed water entry of the slender body with different noses is investigated, and the hydrodynamic loads including the axial and normal drag forces and the bending moment are extensively discussed. The hydrodynamic load and motion trajectory are determined by the nose configuration. The tail slamming phenomenon is the primary focus, and it is revealed that its formation is primarily related to the pitch moment formed at the stage of crossing the free surface. Tail slamming also causes violent impact loads, especially bending moments, which may cause slender projectiles to break off. Finally, to combine the features of the flat and hemispherical noses, the water entry of the projectile with a truncated hemispherical nose is simulated and discussed.

A novel theoretical model for bubble dynamics is established that simultaneously accounts for the liquid compressibility, phase transition, oscillation, migration, ambient flow field, etc. The bubble dynamics equations are presented in a unified and concise mathematical form, with clear physical meanings and extensibility. The bubble oscillation equation can be simplified to the Keller–Miksis equation by neglecting the effects of phase transition and bubble migration. The present theoretical model effectively captures the experimental results for bubbles generated in free fields, near free surfaces, adjacent to rigid walls, and in the vicinity of other bubbles. Based on the present theory, we explore the effect of the bubble content by changing the vapour proportion inside the cavitation bubble for an initial high-pressure bubble. It is found that the energy loss of the bubble shows a consistent increase with increasing Mach number and initial vapour proportion. However, the radiated pressure peak by the bubble at the collapse stage increases with decreasing Mach number and increasing vapour proportion. The energy analyses of the bubble reveal that the presence of vapour inside the bubble not only directly contributes to the energy loss of the bubble through phase transition but also intensifies the bubble collapse, which leads to greater radiation of energy into the surrounding flow field due to the fluid compressibility.

The evolution of the water-entry cavity affects the impact load and the motion of the body. This paper adopts the Eulerian finite element method for multiphase flow for simulations of the high-speed water-entry process. The accuracy and convergence of the numerical method are verified by comparing it with the experimental data and the results of the transient cavity dynamics theory. Based on the results, the representative characteristics of the cavity are discussed from the perspective of the cavity cross-section. It is found that the asymmetry of the cavity expansion and contraction durations is related to the motion of the free surface and the closure of the cavity. The uplift of the free surface suppresses cavity expansion, while the jet generated from free surface closure accelerates cavity contraction. The duration of the contraction of the cavity near the free surface is shorter than the expansion duration due to the change in the velocity distribution caused by the free surface motion. The necking phenomenon during deep closure leads to an increase in the internal pressure of the cavity, prolonging cavity contraction near the deep closure area. This work provides new insights into the cavity dynamics in high-speed water entry.

In this work ice breaking caused by a pair of interacting collapsing bubbles was studied by an experimental approach. The bubbles were generated by an underwater electric discharge simultaneously, positioned either horizontally or vertically below a floating ice plate and observed via high-speed photography. The bubble-induced shock waves, which turn out to be crucial to the fracturing of the ice, were visualized using a shadowgraph method and also measured using pressure transduces. Unique bubble behaviour was observed, including bubble coalescence, bubble splitting, inclined counter-jets and asymmetric toroidal bubble collapse. Bubble dynamic properties, such as jet speed, jet energy and bubble centre displacement, were measured. Shock wave emission and ice breaking capability of the two bubbles were investigated over a range of inter-bubble and bubble–boundary distances. Regions where the damaging potential of the bubble pair are strengthened or weakened were summarized and possible reasons for the variation in the ice breaking capability were analysed based on bubble morphology, jet characteristics and shock wave pressure. The findings may contribute to more efficient ice breaking and also inspire new ways to manipulate cavitation bubble damage.

The jetting behaviour and migratory characteristics of a laser-induced cavitation bubble in a rectangular channel are investigated both experimentally and numerically, for various combinations of the geometric and physical parameters of the system. High-speed photography is used to visualize the temporal development of the bubble shape, the formation of liquid jets during bubble collapse, and the bubble displacement in contact with the sidewalls of the channel during two oscillation cycles of the bubble. The bubble profiles, pressure contours and velocity vectors ambient to the bubble are obtained through numerical simulation results by using an Eulerian finite element method with a compressible liquid impact model. The jetting behaviour of the bubble varies between single jet formation and the formation of three liquid jets directed towards each wall of the channel. The numerical calculations indicate that the liquid jets directed towards the sidewalls of the channel reach maximum velocities of 100 m s−1 while the peak velocity of the liquid jet directed towards the channel endwall is about 55 m s−1. A small bubble generated close to a sidewall of the channel develops only a single inclined jet during collapse. Such jets can reach velocities of up to 110 m s−1. A bubble displacement in contact with the sidewalls of the channels of 350 μm was observed during the first two oscillation cycles for a bubble with a maximum diameter slightly smaller than the height of the channel. The results of our investigations are compared to previous results obtained in similar configurations.

Rapid evolutionary radiations are among the most challenging phylogenetic problems, wherein different types of data (e.g., morphology and molecular) or genetic markers (e.g., nuclear and organelle) often yield inconsistent results. The tribe Arundinarieae, that is, the temperate bamboos, is a clade of tetraploid originated 22 Ma and subsequently radiated in East Asia. Previous studies of Arundinarieae have found conflicting relationships and/or low support. Here, we obtain nuclear markers from ddRAD data for 213 Arundinarieae taxa and parallel sampling of chloroplast genomes from genome skimming for 147 taxa. We first assess the feasibility of using ddRAD-seq data for phylogenetic estimates of paleopolyploid and rapidly radiated lineages, optimize clustering thresholds, and analysis workflow for orthology identification. Reference based ddRAD data assembly approaches perform well and yield strongly supported relationships that are generally concordant with morphology-based taxonomy. We recover five major lineages, two of which are notable (the pachymorph and leptomorph lineages), in that they correspond with distinct rhizome morphologies. By contrast, the phylogeny from chloroplast genomes differed significantly. Based on multiple lines of evidence, the ddRAD tree is favored as the best species tree estimation for temperate bamboos. Using a time-calibrated ddRAD tree, we find that Arundinarieae diversified rapidly around the mid-Miocene corresponding with intensification of the East Asian monsoon and the evolution of key innovations including the leptomorph rhizomes. Our results provide a highly resolved phylogeny of Arundinarieae, shed new light on the radiation and reticulate evolutionary history of this tribe, and provide an empirical example for the study of recalcitrant plant radiations.

Sepsis is a dynamic state that progresses at variable rates and has life-threatening consequences. Staging patients along the sepsis timeline requires a thorough knowledge of the evolution of cellular and molecular events at the tissue level. Here, we investigated the kidney, an organ central to the pathophysiology of sepsis. Single-cell RNA-sequencing in a murine endotoxemia model revealed the involvement of various cell populations to be temporally organized and highly orchestrated. Endothelial and stromal cells were the first responders. At later time points, epithelial cells upregulated immune-related pathways while concomitantly downregulating physiological functions such as solute homeostasis. Sixteen hours after endotoxin, there was global cell–cell communication failure and organ shutdown. Despite this apparent organ paralysis, upstream regulatory analysis showed significant activity in pathways involved in healing and recovery. This rigorous spatial and temporal definition of murine endotoxemia will uncover precise biomarkers and targets that can help stage and treat human sepsis.

To understand the potential genetic basis of highland adaptation of fungal pathogenicity, we present here the ~116 Mb de novo assembled high-quality genome of Ophiocordyceps sinensis endemic to the Qinghai-Tibetan Plateau. Compared with other plain-dwelling fungi, we find about 3.4-fold inflation of the O . sinensis genome due to a rapid amplification of long terminal repeat retrotransposons that occurred ~38 million years ago in concert with the uplift of the plateau. We also observe massive removal of thousands of genes related to the transport process and energy metabolism. O . sinensis displays considerable lineage-specific expansion of gene families functionally enriched in the adaptability of low-temperature of cold tolerance, fungal pathogenicity and specialized host infection. We detect signals of positive selection for genes involved in peroxidase and hypoxia to enable its highland adaptation. Resequencing and analyzing 31 whole genomes of O . sinensis , representing nearly all of its geographic range, exhibits latitude-based population divergence and nature selection for population inhabitation towards higher altitudes on the Qinghai-Tibetan Plateau.

ObjectiveTo increase the in vivo stability of bioactive proteins via optimized loading methods.Resultsβ-Glucosidase (β-Glu), as a model protein, was immobilized on magnetic nanoparticles(denoted as MNP-β-Glu) by chemical coupling methods and was further modified by poly(ethylene glycol) (PEG) molecules (denoted as MNP-β-Glu-PEG) to increase its stability. The physicochemical properties of the as-prepared nanohybrids, including the particle size, zeta potential, and enzyme activity, were well characterized. The proper MNP/β-Glu feed ratio was important for optimizing the particle size. Analysis of enzyme activity showed that the stability of immobilized β-Glu compared with free β-Glu was lower in deionized water and higher in blood serum at 37 °C. MNP-β-Glu-PEG retained 77.9% of the initial activity within 30 days at 4 °C, whereas the free enzyme retained only 58.2%. Pharmacokinetic studies of Sprague–Dawley (SD) rats showed that the MNP-β-Glu-PEG group retained a higher enzyme activity in vivo (41.46% after 50 min) than the MNP-β-Glu group (0.03% after 50 min) and the β-Glu group (0.37% after 50 min). Moreover, in contrast to the MNP-β-Glu group, the enzyme activity was not fully synchronous with the decrease in the Fe concentration in the MNP-β-Glu-PEG group.ConclusionsAll findings indicated that the method of immobilization on magnetic nanoparticles and PEG modification is promising for the application of bioactive proteins in vivo.