Evolution Of Cavities Research Articles

A conserved peptide-binding pocket in HyNaC/ASIC ion channels

The only known peptide-gated ion channels-FaNaCs/WaNaCs and HyNaCs-belong to different clades of the DEG/ENaC family. FaNaCs are activated by the short neuropeptide FMRFamide, and HyNaCs by Hydra RFamides, which are not evolutionarily related to FMRFamide. The FMRFamide-binding site in FaNaCs was recently identified in a cleft atop the large extracellular domain. However, this cleft is not conserved in HyNaCs. Here, we combined molecular modeling and site-directed mutagenesis and identified a putative binding pocket for Hydra-RFamides in the extracellular domain of the heterotrimeric HyNaC2/3/5. This pocket localizes to only one of the three subunit interfaces, indicating that this trimeric ion channel binds a single peptide ligand. We engineered an unnatural amino acid at the putative binding pocket entrance, which allowed covalent tethering of Hydra RFamide to the channel, thereby trapping the channel in an open conformation. The identified pocket localizes to the same region as the acidic pocket of acid-sensing ion channels (ASICs), which binds peptide ligands. The pocket in HyNaCs is less acidic, and both electrostatic and hydrophobic interactions contribute to peptide binding. Collectively, our results reveal a conserved ligand-binding pocket in HyNaCs and ASICs and indicate independent evolution of peptide-binding cavities in the two subgroups of peptide-gated ion channels.

Microstructural evolution and deformation mechanisms of superplastic aluminium alloys: A review

Aluminium alloy is one of the earliest and most widely used superplastic materials. The objective of this work is to review the scientific advances in superplastic Al alloys. Particularly, the emphasis is placed on the microstructural evolution and deformation mechanisms of Al alloys during superplastic deformation. The evolution of grain structure, texture, secondary phase, and cavities during superplastic flow in typical superplastic Al alloys is discussed in detail. The quantitative evaluation of different deformation mechanisms based on the focus ion beam (FIB)-assisted surface study provides new insights into the superplasticity of Al alloys. The main features, such as grain boundary sliding, intragranular dislocation slip, and diffusion creep can be observed intuitively and analyzed quantitatively. This study provides some reference for the research of superplastic deformation mechanism and the development of superplastic Al alloys.

Computational comparison of passive control for cavitation suppression on cambered hydrofoils in sheet, cloud, and supercavitation regimes

Cavitation is a transient, highly complex phenomenon found in numerous applications and can have a significant impact on the characteristics as well as the performance of the hydrofoils. This study compares the evolution of transient cavitating flow over a NACA4412(base) (NACA stands for National Advisory Committee for Aeronautics) cambered hydrofoil and over the same hydrofoil modified with a pimple and a finite (circular) trailing edge. The assessment covers sheet, cloud, and supercavitation regimes at an 8° angle of attack and the Reynolds number of 1×106, with cavitation numbers ranging from 0.9 to 0.2. The study aims to comprehensively understand the role of the rectangular pimple in controlling cavitation and its impact on hydrodynamic performance across these regimes. Numerical simulations were performed using a realizable model and the Zwart–Gerber–Belamri (ZGB) cavitation model to resolve turbulence and cavitation effects. The accuracy of the present numerical predictions has been verified both quantitatively and qualitatively with available experimental results. The present analysis includes the time evolution of cavities, temporal variation in total cavity volume, time-averaged total cavity volume, distributions of vapor volume fractions along the chord length, and their hydrodynamic performance parameters. Results demonstrate that rectangular pimples have significant impacts in the different cavitation regimes. In the sheet cavitation regime (σ=0.9), the NACA4412(pimpled) hydrofoil exhibits minimal cavity length and transient volume changes as compared to the NACA4412(base) hydrofoil. In the cloud cavitation regimes (σ=0.5), cavity initiation occurs differently, starting from the pimpled location for the NACA4412(pimpled) hydrofoil, unlike the initiation just downstream of the nose in the case of base hydrofoil. In the supercavitation regimes (σ=0.2), the cavity length remains comparable, but the NACA4412(pimpled) hydrofoil exhibits larger cavity volume evolution in both cloud and supercavitation regimes (σ=0.5 and σ=0.2) after initial fluctuations. Furthermore, hydrodynamic performance for the NACA4412(pimpled) hydrofoil shows 41%, 36%, and 17% lower lift coefficients, and 46%, 27%, and 9% lower drag coefficients in sheet, cloud, and supercavitation, respectively.

Progressive hollow engineering induced raspberry-like magnetoelectric microspheres via synergistic etching-assembly strategy toward boosted microwave attenuation

Optimizing the electromagnetic (EM) properties of composites through elaborate tailoring of their microstructures has become an attractive research branch, but determining the correlations between morphology, composition, and performance remains challenging. Herein, a novel progressive hollow engineering strategy is proposed for the construction of hollow CuFe Prussian blue analog (CuFePBA, CF) precursors with asymptotic variations of cavities and PBA units based on a synergistic etching-assembly approach, subsequently combined with a polydopamine (PDA) coating and carbothermal process to acquire raspberry-like hollow Cu/Fe/Fe3C@NC (CFC) composites. The proposed approach addresses the drawbacks caused by organic ligand depletion or corrosive agent usage. We then present a systematic investigation of the mechanism by which the progressive hollow engineering-induced concurrent evolution of hollow cavities, phases, defects, and inhomogeneous interfaces contributes to the improvement of the dielectric properties of the CFC samples. An optimal reflection loss (RLmin) of − 65.17 dB at 3.29 mm was realized for the CFC-2 sample and the CFC-3 sample achieved an effective absorption bandwidth (EAB) of 4.4 GHz at an ultra-thin thickness of 1.29 mm. This work reveals the synergistic effects of compositional, interfacial, and defect variations on the EM wave attenuation properties of the composites, and will provide new design inspiration for novel absorbers with modulatable hollow architectures.

Suppression of helium migration in arc-melted and 3D-printed CoCrFeMnNi high entropy alloy

We compare the evolution and migration of helium cavities in 3D-printed and arc-melted CoCrFeMnNi high entropy alloys (HEAs), and 304 stainless steel (SS), using transmission electron microscopy (TEM). The materials are subjected to Ni and He sequential implantation as well as subsequent thermal annealing. After irradiation at room temperature, all samples initially display similar He cavity sizes. Annealing up to 673 K has a minimal impact on cavity size. However, annealing at 873 K leads to significant cavity growth. Both HEA materials exhibit larger average cavity sizes compared to 304 SS, while a higher proportion of small cavities is found in the 304 SS. This indicates that Ostwald Ripening is more prevalent in 304 SS, confirmed by in-situ thermal annealing in TEM. Depth distribution analysis reveals distinct cavity belts after annealing: from the narrowest in 3D printed HEA to the broadest belts in 304 SS. These results indicate that the He concentration at the peak of irradiation damage decreases in the same order. We suggest that the long-range migration of He atoms is limited in both the Cantor and 3D-printed Cantor HEAs, potentially due to the complex diffusion paths of the He atoms.

Evolution of the cavity structure of HDPE/UHMWPE blends during cold stretching

AbstractThe cavitation process of high‐performance HDPE/UHMWPE blends with a uniform dispersion of UHMWPE during cold stretching was investigated. It was observed that incorporating a small amount of UHMWPE into the HDPE matrix resin can serve as a nucleating agent, increasing the number of contact sites and accelerating the crystallization rate. This leads to the formation of thicker lamellar crystals and tethered molecules, ultimately enhancing the mechanical properties of the HDPE matrix. Furthermore, the relationship between the natural tensile ratio and strain‐hardening modulus was confirmed. Microstructural changes within the blends were also explored. As the drawing tangles in the middle, the cavities subsequently evolve by collapsing and merging to align parallel to the tensile direction, culminating in tensile damage forming a large crack in the final macroscopic form. As a result, the presence of more tethered molecules in the later stages of stretching inhibits further cavity growth.Highlights The HDPE/UHMWPE blends were prepared by solution blending and ultrasound‐assisted twin‐screw extrusion. The mechanisms underlying the formation and evolution of cavities in HDPE/UHMWPE blends, which lead to stress whitening during tensile damage, were examined by using DSC and SAXS/WAXD. The relationship between microstructure and mechanical properties was analyzed by cold‐drawing the molded blended sheets at room temperature.

Study on the ablative characteristics of steel target irradiated by nanosecond pulsed pseudo spark electron beams: Experiment and molecular dynamics simulation

A combination of simulation and experimentation is employed to explore the influence of the non-uniformity of energy distribution in nanosecond PSEB on the target ablation. Firstly, A spatiotemporally distributed heat source model is built using Monte Carlo computational method and an ablation phase transition model is established using molecular dynamics method. The results reveal the time evolution of multiple cavities in the sub-surface region, as well as the temperature and stress field distributions with electron beam irradiation. Phase explosion formation and lattice structure changes in the steel target during the ablation process is found for the first time. The PSEB modified AISI1045 steel samples is experimentally conducted. The characterization results show the changes in the crystal structure within AISI1045 steel, which is attributed to the formation of an amorphous layer resulting from grain refinement and structural defects, as well as the combined effects of thermal elastic stress waves, shock thermal stress waves and temperature gradient distribution. The experimentally obtained crystal phase changes are consistent with the simulation results, confirming the accuracy and validity of the modelling. The findings of this study provide a molecular-scale explanation for the formation of unique morphology and micro-structures during the PSEB ablated metal target.

Investigation of cavitation shedding mechanisms including reentrant jet and shock wave by Eulerian–Lagrangian multiscale simulation

Sheet-to-cloud cavitation in a Venturi pipe is investigated experimentally and numerically in this work. The multiscale vapor structures are simulated by Eulerian–Lagrangian multiscale modeling. The volume of fluid method with adaptive mesh refinement is employed to capture the macroscale cavity features, utilizing the large eddy simulation approach. The results of mesh sensitivity study demonstrate that second-order refinement is capable of capturing phase details and cavitation shedding behaviors. A comparison with experimental results reveals the mechanisms of different types of cavitation shedding induced by reentrant jet and shock wave. Taking microscale bubbles into account using the Lagrangian approach and achieving Eulerian–Lagrangian coupling, the multiscale cavitation features, including the morphological evolution of large cavities and characteristics of microbubbles, are accurately reproduced. The evolution features of microbubbles during pressure wave or condensation shock propagation are well recognized by different changing rates. The results indicate that shedding mechanisms in Venturi pipe cavitation can be categorized into three types: reentrant jet, condensation shock, and pressure wave. In the three conditions investigated in this work, shedding cycles are found to be mainly induced by the reentrant jet (σ = 1.03), reentrant jet, condensation shock, and pressure wave (σ = 0.64), and condensation shock (σ = 0.39), respectively, with a decrease in the cavitation number.

Control of nano-cavitation in semi-crystalline polymer nanocomposites during uniaxial tension: In situ synchrotron X-ray study

The cavitation behavior of polypropylene-silica (PP-silica) and high density polyethylene-silica (HDPE-silica) composites with varying silica content during uniaxial tension was investigated via in situ X-ray techniques. The introduction of silica was found to significantly influence the mechanical properties of the materials. Small-angle X-ray scattering (SAXS) was employed to determine the cavitation onset strain and to observe the evolution of cavity structures. Through model fitting, the size evolution of nanoscale cavities at the onset of cavitation was quantitatively characterized. Scanning electron microscopy (SEM) was utilized to examine the morphology before and after stretching, revealing that cavity structures primarily resulted from internal defects in the polymer matrix and interfacial debonding between silica and the polymer. The long axis of the nanoscale cavities at the onset of cavitation was perpendicular to the tensile direction, and further deformation led to the coalescence into micron-sized cavities with the long axis parallel to the tensile direction. Wide-angle X-ray scattering (WAXS) was used to characterize the microscale deformation process of crystals, showing that during stretching, the lamellae reoriented with the angle between their normal direction and the tensile direction gradually decreasing. Several sets of transition strains representing the plastic deformation were used to compare the microscale and macroscale deformation, elucidating the sequence and differentiation between crystal plastic deformation, cavitation, and yield in the two polymer materials. Intriguingly, both PP-silica and HDPE-silica composites exhibited optimal silica additions and initial structural parameters for regulating cavitation behavior. These findings offer significant guidance for the control of internal structures in porous separators in industrial production.

Investigating the performance of the modified two-component pressure approach in capturing column separation with large vapour cavities

This paper investigates the performance of the modified two-component pressure approach (proposed model), recently proposed by the authors, in capturing column separation with large vapour cavities. The proposed model calculates both the cavitating and waterhammer flow regions using a single set of equations that governs unsteady flow in open channels. Comparing the results with experimental data, and the results obtained from the discrete gas cavity model (counterpart model) reveals that: (1) the proposed model can accurately capture the evolution of large vapour cavities in pipe systems; (2) the model provides more accurate results compared to the counterpart model; (3) under some circumstances the counterpart provides inaccurate results as it fails to account for the energy loss in the cavitating flow zone while the proposed model was shown to resolve the issue. Finally, the results exhibit the superiority of the proposed model over the counterpart model and the conventional open-channel-based models.

Multi-GPU multi-resolution SPH framework towards massive hydrodynamics simulations and its applications in high-speed water entry

We propose a multi-phase, multi-resolution SPH method for fluid/solid interaction with multi-GPU implementation and dynamic load balancing following the movement of the refinement regions. The primary design goal of this framework is to maintain the efficiency of the single-resolution SPH model running on a single GPU. To this end, a multi-background mesh is introduced, and the domain is regarded as a nested multi-domain with different resolutions. Validation using both a δ-SPH and Riemann SPH model is shown, and applications to the simulation of the water entry of a projectile with a high Froude number are considered, with comparisons to experimental data from three challenging test cases, showing the proposed model's ability to correctly reproduce the free surface evolution on water entry, the motion of the projectile, and the formation and evolution of multiple cavities depending on entry angle and velocity. An analysis of the computational performance and resolutions achieved (up to 120 million particles) is also provided across several test cases.

Investigation of transient sheet/cloud cavitating flow dynamics from multiscale perspective

Sheet/cloud cavitation usually leads to a wide range of length scales in both turbulence and phase distribution from microbubbles to cavity advection. In the present work, the Eulerian–Lagrangian multiscale cavitation model with two-way coupling is utilized to simulate the cavitating flow around a (National Advisory Committee for Aeronautics) NACA66 hydrofoil at an incidence angle of 8° and a cavitation number of σ = 1.4. The model can simultaneously capture the large-scale cavities and the microscale bubbles. The cavitating flow features are in good agreement with the experimental observations containing not only the periodical formation, growth, detachment, and advection of large-scale cavities, but also thousands of microbubbles around the large-scale cavities. The results show that the overall evolution frequency in the flow is about 45 Hz. Meanwhile, the dynamic mode decomposition method is utilized to identify the large-scale coherent spatial and temporal features of the sheet/cloud cavitating flow, which indicates that complex vortices in various scales dominate the evolution of cavities in the corresponding scale, and the evolution frequency of large-scale vapor structure decreases with increasing the length scale of cavities. Under the effect of turbulence, the large-scale cavities break into microbubbles, causing the size and number of discrete bubbles to increase rapidly in the re-entrant jet and cloud shedding regions. Additionally, the bubble-size spectrum of the time-averaged distribution of a period in sheet/cloud cavitating flow has two size regimes. For larger bubbles, the bubble density is proportional to the bubble radius to the power of −10/3. The bubble size spectrum of smaller microbubbles exhibits a −4/3 power-law scaling.

Cavitation dynamics of the semi-sealed cylindrical shell during high-speed water entry

This paper experimentally investigates the vertical high-speed water entry of a semi-sealed cylindrical shell, which has one end sealed and one end opened. The unsteady water-entry cavitating flow characteristics of the shell are analyzed, and the evolution of cavities and jet impacts with different structures is studied. The results show that a nested multi-cavity is generated due to the self-jet phenomenon during water entry. The jet causes the diameter of the secondary cavity to be much larger than that of the primary cavity, and the morphology of the secondary cavity is more atomized. Due to the irregular motion of the jet, the primary cavity undergoes neck-shrinking phenomenon and is compressed, and the neck-shrinking position moves up as the secondary cavity grows. After secondary impact, a small jet appears at the bottom of the shell, which ejects out from the shell and increases the size of the bottom cavity, leading to the formation of quaternary cavity. Moreover, as the inner wall length increases, the time of the primary jet is advanced, while the depth of secondary cavity shortens. With the increase in the thickness, cavity shape becomes more similar to traditional supercavity, and the maximum diameter of the primary cavity increases.

Cavitation mechanism and effect on pump power-trip transient process of a pumped-storage unit

Backflow vortexes (BFV) and cavitation are the main sources of pressure fluctuations (PF) in pump-turbine (PT) transitions. However, their interaction mechanism and effect on the transitions of pumped-storage power systems remain unclear. In the present work, the guide vane closing process (GVCP) after the pump power-trip (PPT) of a pumped-storage power system was investigated adopting the one- and three-dimensional coupled two-phase cavitation flow simulation approaches and time-frequency combined signal processing approach. Based on the study findings, large-scale vapor cavities in the draft tube and flow-separated vortexes in the guide/stay vane blocked the PT flow passage. Further, their dynamic evolution induced instantaneous flow rate pulses and further caused pressure pulses, which are equivalent to the water hammer effects. Large amounts of BFV and vapor cavities were found on the impeller high-pressure (HP) side. The unsteady evolution of BFV and vapor cavities and their interactions induced complex-frequency PF near the maximum reverse discharge (Qmax_r) condition in the pump brake (PB) mode. Herein, the flow-separated vortexes were related to the low matching degree between the guide vane (GV) and stay vane. Overall, our findings can provide an important theoretical basis for avoiding the vibration of pumped-storage power systems.

The Evolution of Protostellar Outflow Cavities, Kinematics, and Angular Distribution of Momentum and Energy in Orion A: Evidence for Dynamical Cores

We present Atacama Large Millimeter/submillimeter Array observations of the ∼10,000 au environment surrounding 21 protostars in the Orion A molecular cloud tracing outflows. Our sample is composed of Class 0 to flat-spectrum protostars, spanning the full ∼1 Myr lifetime. We derive the angular distribution of outflow momentum and energy profiles and obtain the first two-dimensional instantaneous mass, momentum, and energy ejection rate maps using our new approach: the pixel flux-tracing technique. Our results indicate that by the end of the protostellar phase, outflows will remove ∼2–4 M ⊙ from the surrounding ∼1 M ⊙ low-mass core. These high values indicate that outflows remove a significant amount of gas from their parent cores and continuous core accretion from larger scales is needed to replenish core material for star formation. This poses serious challenges to the concept of cores as well-defined mass reservoirs, and hence to the simplified core-to-star conversion prescriptions. Furthermore, we show that cavity opening angles, and momentum and energy distributions all increase with protostar evolutionary stage. This is clear evidence that even garden-variety protostellar outflows: (a) effectively inject energy and momentum into their environments on 10,000 au scales, and (b) significantly disrupt their natal cores, ejecting a large fraction of the mass that would have otherwise fed the nascent star. Our results support the conclusion that protostellar outflows have a direct impact on how stars get their mass, and that the natal sites of individual low-mass star formation are far more dynamic than commonly accepted theoretical paradigms.

A spalling evolution model for time-varying mesh stiffness evaluation and service life prediction of gears

Spalling is one of the most common contact fatigue failure modes on gear face. Although there are some prediction models for spalling formation, few prediction models have previously addressed the evolution from initial defects to spalling cavities. In this paper, a damage-connectivity spalling model (DCSM) is proposed to describe the formation and evolution of multiple irregular spalling cavities on the tooth face deriving from the initial defects. Subsequently, a type of TVMS-based indicator is established to represent the evolutionary severity of irregular spalling cavities. Finally, a service life prediction method is developed based on the proposed indicators. The correctness of the proposed DCSM model is verified by comparison with the extant gear spalling experiments. The effects of working load, depth ratio and quantify ratio of initial defect groups on the service life are discussed, which contributes to the service life improvements of gear pairs in the design stage.

Shear-band cavitation determines the shape of the stress-strain curve of metallic glasses

Metallic glasses are known to have a remarkably robust yield strength, admitting Weibull moduli as high as for crystalline engineering alloys. However, their postyielding behavior is strongly varying, with large scatter in both flow stress levels and strains at failure. Using x-ray tomography, we reveal how a strain-dependent internal evolution of shear-band cavities underlies this unpredictable postyielding response. We demonstrate how macroscopic strain softening coincides with the first detection of internal shear-band cavitation. Cavity growth during plastic flow is found to follow a power law, which yields a fractal dimension and a roughness exponent in excellent agreement with self-similar surface properties obtained after fracture. These findings demonstrate how internal microcracking coexists with shear-band plasticity along the plastic part of a stress-strain curve, rationalizing the large variability of plastic flow behavior seen for metallic glasses.

The impact of gravity on the evolution of cavity in the cluster of stars

This paper investigates the evolution of cavities for the cluster of stars in the context of extended Gauss–Bonnet gravity. We assume a spherically symmetric geometry along with locally anisotropic fluid distribution. It is assumed that the proper radial distance among neighboring stellar components stays unchanged during purely areal evolution stage. We provide some analytical solutions by using general formulism in gravitation theory. The thick-shells cavities at one or both boundary surfaces are found to satisfy the Darmois conditions. Moreover, we also investigate the physical behavior of cavity models by considering the stellar , and . We conclude that the dark matter has a strong impact on the evolution of cavities in the cluster of stars.

Dynamic investigations on hydrogen–helium interaction around the vacancy in BCC iron from ab-initio calculations

Coexistence of hydrogen (H) and helium (He) under vacancy (V) supersaturation in the fusion environment alters the dynamic evolution of cavities and ultimately influences the swelling of structural materials. Herein, we investigate H–He interaction around a V as one prototype trapping site for H and He in body-centered cubic (BCC) iron (Fe) utilizing ab initio calculations from the thermal dynamics. First, we demonstrate the significantly stronger He–V interaction than H–V interaction by comparing the dynamic trapping and de-trapping of H with those of He. Furthermore, we confirm the repulsive H–He interaction around the V by examining their hopping around H–He–V complexes. The prior He in the V imposes weak influence on the dynamic trapping of H while enhances H de-trapping. Due to the prior He, more H atoms can be accommodated in the V resulting from larger H–H distances to attenuate repulsive H–H interaction. The dynamic trapping of He by the V is weakly influenced, even though the V is densely coated by the prior H. There exists a critical density of the prior H in the V, below which the prior H enhances He de-trapping. Above this critical density, He de-trapping is inhibited by the prior H. This work provides significant dynamic insights at the atomic scale toward a better understanding of the cavity nucleation and H isotopes/He retention in structural materials in the fusion environment.

Cavitation behavior of polypropylene/polyethylene multilayer films during uniaxial tensile deformation: In-situ synchrotron X-ray study

The cavitation of melt-coextruded multilayer films of alternated polypropylene (PP) and polyethylene (PE) during the uniaxial tensile deformation has been investigated. The initiation and evolution of cavities and the relationship between cavitation and plastic deformation have been studied via in-situ SAXS and WAXS techniques. The critical strain for the initiation of cavitation (εcav), crystal shear (εCSh), and yield (εyield) have been estimated from the in-situ experiments. The results show that the sequence of deformation is crystal shear, cavitation and yield, i.e. εCSh<εcav<εyield, indicating that crystal plastic deformation occurs before the cavitation and yield. Additionally, the layer numerosity and annealing temperature (Tanneal) have been discovered to not only modify the mechanical behavior but also regulate cavitation by changing the initial microstructure. The samples with less layer numerosity and high Tanneal improve the macroscopic mechanical strength, whereas the increase of layer numerosity can reduce the stress of cavitation onset (σcav) and retard the onset of cavitation onset (high εcav value). The current study is significant in elucidating the internal mechanism of stretch-induced cavitation behavior in multilayer films.