Multiple Coalescence Research Articles

Multiple nanodroplets coalescence in the coupling of electric field and swirl centrifugal field: A molecular dynamics study

Multiple nanodroplets coalescence in the coupling of electric field and swirl centrifugal field: A molecular dynamics study

Multiple cracking, crack coalescence and fatigue lifetime – Model and experiments on an austenitic steel and on a nickel base alloy

In many metals and alloys, low-cycle fatigue (LCF) and thermomechanical fatigue (TMF) generate a large number of surface microcracks. Using the replica technique, we document their growth and coalescence in the austenitic steel 1.4550 and the nickel base alloy Inconel 100. A model based on elastic–plastic fracture mechanics is developed, which considers the growth and coalescence of many coplanar semi-elliptical surface cracks. The results of the model are consistent with the experiments. An important conclusion is that the fatigue lifetime predicted by the multi-crack model is not substantially shorter than that predicted by a corresponding model assuming only a single semi-circular surface crack. This means that lifetime assessment can still be based on single-crack data, if one considers a factor 2 to include scatter and multiple-crack effects.

Thermodynamically consistent phase field model for liquid-gas phase transition with soluble surfactant

Despite the enormous potential in facilitating natural development and migration of interfaces during multiphase simulation, the phase-field method remains restricted to low-density ratios, owing to inherent thermodynamic inconsistency, especially for multiphase flow systems with surfactants. The present paper first constructs a liquid-vapor phase transition phase-field model with soluble surfactants using the second law of thermodynamics as the original model. Then, a simplified liquid-vapor phase transition model with soluble surfactants that satisfies thermodynamic consistency is proposed to simulate pool boiling at higher-density ratio. A novel numerical algorithm for the simplified model that satisfies semi-discrete thermodynamic consistency is also developed. Compared with the original model, the thermodynamically consistent characteristics of the simplified numerical model proposed in this paper can significantly reduce the spurious velocity on the interface of a static droplet and thus enable the numerical model to simulate liquid-vapor transition at higher liquid/vapor density ratios. Vapor-liquid coexistence, Laplace's law, and multiple bubble coalescence are used to validate the accuracies and effectiveness of the mathematical model and numerical algorithm. The liquid/vapor density ratio can reach 6776:1 under saturation temperature 0.3Tc (Tc is the critical temperature). The approach is then used to model pool boiling at a low saturation temperature (0.5Tc) with and without soluble surfactants, significantly lower than reported in comparable literature. The results demonstrate that surfactants significantly influence the dynamics of bubbles, and a critical concentration can be identified. In addition, soluble surfactants can also suppress coalescence between adjacent bubbles and prevent the formation of larger bubbles during pool boiling.

Multiple Flux Rope Dynamics: MMS Observations and Reconstruction Results

A series of six ion-scale magnetic flux ropes (FR1–6) and a thin current sheet, encountered by Magnetospheric Multiscale spacecraft in the magnetosheath side of the dayside magnetopause boundary layer, are studied for multiple flux rope dynamics in terms of energy conversion and two-dimensional geometry structure. The thin current sheet is identified in between FR1 and FR2. The energy exchange between electromagnetic fields and plasmas is dynamic in FR1–5 and also surrounding the flux ropes, while a low-energy conversion rate is seen in FR6. Different energy conversions exist in the flux ropes: energy dynamo is predominant in FR1 and FR5, while energy dissipation is dominated in FR2–4. Both the energy dynamo and dissipation primarily result from j ∥ E ∥. Strong dissipation, surrounded by an energy dynamo, happens at the thin current sheet and is accompanied by ion agyrotropic behavior. From the reconstructed magnetic field maps, the estimated aspect ratios of the six flux ropes are 0.78, 0.16, 0.66, 0.11, 0.40, and 0.46 in order, and the thickness of the thin current sheet is ∼63 km (∼1.8 ion inertial length). Evidently, the magnetic field map shows that FR4 is a coalescing flux rope where a pronounced dissipation is present. The overall finding agrees with the previous simulation studies of multiple island coalescence.

Multi-crack propagation analysis of double-side welded rib-to-deck joint in orthotropic steel decks

Rib-to-deck welded joints are among the most susceptible to fatigue in orthotropic bridge decks (OSDs). Prior research has primarily examined the stress intensity factor (SIF) and propagation morphology of a solitary fracture at these joints, allocating limited attention to the investigation of the propagation of multiple cracks. This paper presents a methodology for simulating and computing the weld toe magnification factor and the SIF of semi-elliptical surface cracks in innovative double-sided welded rib-to-deck (DWRTD) joints. The intention was to simplify the calculation of the SIF for this fatigue detail. The SIF obtained from the calculation model in combination with a multiple crack coalescence approach resulted in a series of fatigue life prediction models of multiple co-planar semi-elliptical cracks. Compared with the results of fatigue tests on the DWRTD joints, the calculated fatigue life and propagation morphology of multiple cracks from the model showed good agreement. Finally, the parameters were analysed to investigate the effects of crack number, bridge deck thickness, residual stress, and penetration rate. Compared to a single crack, multiple cracks reduced the service life of the bridge deck by approximately 30%. When the bridge deck thickness increases from 12 mm to 20 mm, the nominal stress amplitude near the weld ∆σ decreases by 2.2 times, resulting in a 7-fold increase in crack propagation time. Compared to penetration rate and residual stress, ∆σ is the most crucial factor affecting fatigue propagation life. Therefore, it is suggested to increase the thickness of the bridge deck during design.

Numerical study of multiple hydraulic fractures propagation in poroelastic media based on energy decomposition phase field methods

This paper proposes a novel phase-filed model for simulating hydraulic fracturing in poroelastic media under complex stress conditions. The main theoretical contribution lies in the fact that a generalized strain energy density decomposition is incorporated to hydraulic fracturing phase field model, which unifies hydrostatic-deviatoric and spectral decompositions and predicts material failure through classical Mohr-Coulomb failure criterion. Based on Biot’s poroelastic theory, an indicator function is used to distinguish between fluid flow in fractures and in pores. The fully coupled equations are solved by combining staggered schemes with Newton-Raphson methods. The proposed model is validated by comparing laboratory experimental results with numerical results. In order to demonstrate the influence of introducing hydrostatic-deviatoric and spectral energy decompositions, we simulated propagation of multiple hydraulic fractures and coalescence of hydraulic fractures with natural fractures. Finally, the effects of stress ratios (σx/σy) on multiple hydraulic fractures are analysed. It is found that when the stress ratio is 2, a more complex hydraulic fracture network is formed in the porous media.

Highly malignant endometrial stromal sarcoma in a cat

An 11-year-old female Persian cat underwent ovariohysterectomy due to dilation of the uterine cavity with irregular thickening of the wall. Macroscopically, the middle and distal regions of the left uterine horn were swollen and the uterine wall was irregularly thickened due to the development of multiple coalescent, variably sized nodules. Microscopically, the nodules had originated in the endometrium and were composed of round to polygonal neoplastic cells arranged in dense sheets or ill-defined fascicles. The neoplastic cells had locally invaded the myometrium and reached the subserosa, with lymphovascular invasion. Immunohistochemically, the neoplastic cell population was partially positive for CD10, an established marker of endometrial stromal sarcoma (ESS) in humans, with focal and diffuse nuclear immunopositivity for oestrogen and progesterone receptors and immunonegativity for desmin and α-smooth muscle actin. Based on these findings, the uterine tumour was diagnosed as ESS and was considered to correspond morphologically to high-grade ESS in humans.

An efficient adaptive multi-mesh phase-field method for simulating rock fractures

Phase-field models have significant advantages in rock fractures, such as simulating multiple crack initiation, propagation and coalescence without requiring fracture criteria. However, the high computational cost is a notable drawback. For this reason, this paper proposes a simple, efficient and robust Adaptive Multi-Mesh phase-field method (AMM) for modelling crack propagation. The main concept of the AMM method is to adopt a coarser adaptive mesh and C0 elements for the displacement field in order to reduce computational cost, while employing a finer adaptive mesh and C1 elements for the damage field to accurately capture in-rock crack paths. The results show that the AMM method is capable of reducing the number of displacement elements by 58.2–72% and the computational time by 43.8–53% compared to the Adaptive Mesh phase-field method (AM), and by 92.4–96.4% and 95.9–98.8%, respectively, compared to the Uniform Refinement mesh method (UR). Additionally, this paper also proposes a simple and practical mesh Refinement Combination Strategy, RCS, and an efficient Local variable transfer method, LEI, which requires only the Exchange of Integration point positions. The proposed RCS makes it possible to perform variable transfer between two independent adaptive meshes without searching the topological relations, thus dramatically decreasing the implementation difficulty and computational time. The proposed LEI method achieves variable transfer simply by exchanging integration point positions, thereby ensuring simplicity and numerical stability.

Bamboozled! Resolving deep evolutionary nodes within the phylogeny of bamboo corals (Octocorallia: Scleralcyonacea: Keratoisididae)

Keratoisididae is a globally distributed, and exclusively deep-sea, family of octocorals that contains species and genera that are polyphyletic. An alphanumeric system, based on a three-gene-region phylogeny, is widely used to describe the biodiversity within this family. That phylogeny identified 12 major groups although it did not have enough signal to explore the relationships among groups. Using increased phylogenomic resolution generated from Ultraconserved Elements and exons (i.e. conserved elements), we aim to resolve deeper nodes within the family and investigate the relationships among those predefined groups. In total, 109 libraries of conserved elements were generated from individuals representing both the genetic and morphological diversity of our keratoisidids. In addition, the conserved element data of 12 individuals from previous studies were included. Our taxon sampling included 11 of the 12 keratoisidid groups. We present two phylogenies, constructed from a 75% (231 loci) and 50% (1729 loci) taxon occupancy matrix respectively, using both Maximum Likelihood and Multiple Species Coalescence methods. These trees were congruent at deep nodes. As expected, S1 keratoisidids were recovered as a well-supported sister clade to the rest of the bamboo corals. S1 corals do not share the same mitochondrial gene arrangement found in other members of Keratoisididae. All other bamboo corals were recovered within two major clades. Clade I comprises individuals assigned to alphanumeric groups B1, C1, D1&D2, F1, H1, I4, and J3 while Clade II contains representatives from A1, I1, and M1. By combining genomics with already published morphological data, we provide evidence that group H1 is not monophyletic, and that the division between other groups – D1 and D2, and A1 and M1 – needs to be reconsidered. Overall, there is a lack of robust morphological markers within Keratoisididae, but subtle characters such as sclerite microstructure and ornamentation seem to be shared within groups and warrant further investigation as taxonomically diagnostic characters.

Characterizing bubble dynamics in combustion and atomization of alcohol/PODE4 and alcohol/n-undecane binary droplets

This work explores bubble dynamics in the combustion and atomization of binary droplets, with special attentions on the effects of bubble dynamics on the combustion and atomization characteristics. A typical renewable synthetic fuel polyoxymethylene dimethyl ether 4 (PODE4) and a typical kerosene component n-undecane are used as the weakly volatile components, while C1-C5n-alcohols are used as the highly volatile components in order to change the boiling point difference of components in the binary droplets. Nucleation capability of alcohol/PODE4 binary droplets is found to be higher than that of alcohol/n-undecane binary droplets. Alcohol/PODE4 binary droplets with higher boiling point differences (ΔTbp s) tend to have multiple nucleation sites and undergo multiple bubble growth and coalescence, while most of the rest binary droplets tend to have limited nucleation sites and undergo single bubble growth. The bubble evolution velocity decreases with the decreasing ΔTbp, while the bubble growth in alcohol/PODE4 binary droplets are generally slower. Bubble breakup mainly results in ejection and micro-explosion in this work, which are associated with small and big bubble breakup, respectively. Five atomization modes with different bubble evolution, bubble breakup and droplet atomization processes are concluded. The combustion and atomization characteristics of most of the investigated binary droplets are remarkably influenced by the bubble dynamics. The binary droplets with higher ΔTbp s are susceptible to strong atomization modes and consequently tend to have shorter normalized droplet lifetimes and larger atomization indices. Alcohol/PODE4 binary droplets have generally greater atomization indices than alcohol/n-undecane binary droplets.

Probabilistic investigation into brittle fracture of functionally graded materials using phase-field method

Modelling fracture using numerical techniques based on discrete modelling is complex as it requires tracking of progressing discontinuities in field parameters. Phase-field method for fracture is based on the variational framework and represents discontinuous crack surfaces by a damage variable that diffuses onto the crack surface. This approach offers the advantage of modelling crack where multiple crack nucleation, branching and coalescence can be determined without prior knowledge of the crack path. In this work, a probabilistic approach is used to predict the crack growth response in functionally graded material media when the mechanical properties and geometric parameters are random independent variables. Numerical implementation based on the standard phase-field method is employed in a finite element framework to model crack growth in functionally graded brittle materials. Peak failure loads are estimated within acceptable limits due to dispersion in system properties. Benchmark problems are solved to demonstrate the applicability of this technique. The proposed approach is advantageous as no further intensive computations are needed after the initial evaluation of probabilistic measures for predicting dispersion in fracture propagation when material and geometric properties exhibit scatter.

The phylogenetic structure and coalescent species delimitation of an endemic trapdoor spider genus, Stasimopus (Araneae, Mygalomorphae, Stasimopidae) in the Karoo region of South Africa

The Karoo region of South Africa is a unique and sensitive ecosystem which is facing pressure for development due to economic incentives such as mining, farming and shale gas exploration. The species diversity of many taxa in the area is largely unknown. A phylogenetic analysis of the cork-lid trapdoor spider genus, Stasimopus (Stasimopidae) was undertaken in order to gain insight into the relationships between the species that may be present in the area. The species within Stasimopus are challenging to identify and define using traditional morphological methods due to a high degree of morphological conservatism within the genus. For this reason, multiple coalescent based species delimitation methods were used to attempt to determine the species present for Stasimopus in the region which was tested against the morphological identifications and genetic clades (based on CO1, 16S and EF-1ɣ). We tested single-locus methods Automatic Barcode Gap Discovery (ABGD), Bayesian implementation of Poisson Tree Processes (bPTP) and General Mixed Yule- Coalescent (GMYC), as well as multi-locus Brownie. The phylogenetic analysis of Stasimopus in the Karoo showed that there is a high degree of genetic diversity within the genus. The species delimitation results proved unfruitful for the genus, as they appear to delimit population structure rather than species for most methods. Alternative methods should be investigated to aid in the identification of the species in order truly understand the species diversity of the genus.

New Aspects of Energy Conversion in Magnetic Island Dynamics: Particle-in-cell Simulation of Multiple Island Coalescence and MMS Observations

Coalescence of multiple magnetic islands is recognized as an effective process to energize particles during magnetic reconnection, while its energy conversion process still remains unclear. Here, a two-dimensional fully kinetic simulation of multiple island coalescence with a small reconnection guide field is studied. In the analysis of energy conversion within a magnetic island, the dot product of is a useful quantity to compare with j · E = w 2, since the average work done by the Lorentz force on the circulating particles is negligible in the island and . A bipolar pattern of w 1 is found at a secondary island when the electrons are in circular motion inside the island. Significant energy dynamo (w 3 < 0) resulting from j ∥ E ∥ is found at the secondary island, which has not been reported before, where the parallel electric field E ∥ is highly correlated with w 3. Moreover, significant energy dissipation (w 3 > 0) due to is seen in the merging region between two coalescing islands. Both types of energy conversions are accompanied by enhancements in j ∥ and the parallel electron temperature T e∥. Three ion-scale magnetic islands (FR1, FR2, and FR3) observed by the Magnetospheric Multiscale spacecraft are compared favorably with the simulated signatures of energy dynamo and dissipation of an evolving secondary island. In particular, FR1 displayed a similar energy dynamo signature as that simulated in an early stage of the secondary island. FR2 and FR3 showed a dominant energy conversion similar to that obtained in a later stage of the secondary island.

Limits of multiplicative inhomogeneous random graphs and Lévy trees: The continuum graphs

Motivated by limits of critical inhomogeneous random graphs, we construct a family of measured metric spaces that we call continuous multiplicative graphs, that are expected to be the universal limit of graphs related to the multiplicative coalescent (the Erdős–Rényi random graph, more generally the so-called rank-one inhomogeneous random graphs of various types, and the configuration model). At the discrete level, the construction relies on a new point of view on (discrete) inhomogeneous random graphs that involves an embedding into a Galton–Watson forest. The new representation allows us to demonstrate that a process that was already present in the pioneering work of Aldous [Ann. Probab. 25 (1997) 812–854] and Aldous and Limic [Electron. J. Probab. 3 (1998) 1–59] about the multiplicative coalescent actually also essentially encodes the limiting metric. The discrete embedding of random graphs into a Galton–Watson forest is paralleled by an embedding of the encoding process into a Lévy process which is crucial in proving the very existence of the local time functionals on which the metric is based; it also yields a transparent approach to compactness and fractal dimensions of the continuous objects. In a companion paper, we show that the continuous multiplicative graphs are indeed the scaling limit of inhomogeneous random graphs.

Coalescence dynamics of platinum group metal nanoparticles revealed by liquid-phase transmission electron microscopy

SummaryCoalescence, one of the major pathways observed in the growth of nanoparticles, affects the structural diversity of the synthesized nanoparticles in terms of sizes, shapes, and grain boundaries. As coalescence events occur transiently during the growth of nanoparticles and are associated with the interaction between nanoparticles, mechanistic understanding is challenging. The ideal platform to study coalescence events may require real-time tracking of nanoparticle growth trajectories with quantitative analysis for coalescence events. Herein, we track nanoparticle growth trajectories using liquid-cell transmission electron microscopy (LTEM) to investigate the role of coalescence in nanoparticle formation and their morphologies. By evaluating multiple coalescence events for different platinum group metals, we reveal that the surface energy and ligand binding energy determines the rate of the reshaping process and the resulting final morphology of coalesced nanoparticles. The coalescence mechanism, based on direct LTEM observation explains the structures of noble metal nanoparticles that emerge in colloidal synthesis.

A smoothed particle hydrodynamics approach for phase field modeling of brittle fracture

Fracture is a very challenging and complicated problem with various applications in engineering and physics. Although it has been extensively studied within the context of mesh-based numerical techniques, such as the finite element method (FEM), the research activity within the Smoothed Particle Hydrodynamics (SPH) community remains scarce. SPH is a particle-based numerical method used to discretize equations of continuum media. Its meshfree nature makes it ideal to simulate fracture scenarios that involve extreme deformations. However, to model fracture, SPH researchers have mostly relied on ad-hoc empirical local damage models, cohesive zone approaches, or pseudo-spring models, which come with a set of drawbacks and limitations. On the other hand, phase field models of brittle fracture have recently gained popularity in academic circles and provide significant improvements compared to previous approaches. These improvements include the derivation from fundamental fracture theories, the introduction of non-locality, and the ability to model multiple crack initiation, propagation, branching, and coalescence, in situations where no prior knowledge of the crack paths is available. Nevertheless, phase field for fracture has not been studied within SPH. In this proof-of-concept paper we develop and implement a phase field model of brittle fracture within the context of SPH. Comprehensive mathematical and implementation details are provided, and several challenging numerical examples are computed and illustrate the proposed method’s ability to accurately and efficiently simulate complex fracture scenarios.

Debonding failure analysis of FRP-plated RC beams via an inter-element cohesive fracture approach

Debonding mechanisms in the externally reinforced structural elements have been widely studied by the scientific community since they lead to premature failure in concrete structures. Different numerical models, based on simplified strength approaches, have been proposed in the literature to simulate such debonding phenomena, but often are unable to accurately predict the development of diffuse crack patterns which are typical for reinforced concrete (RC) structures. In this context, the present work aims to propose a cohesive modeling technique, based on a diffuse interface fracture approach, to in-depth investigate the plate-end and mid-span debonding failures in FRP-strengthened RC structural elements. This model, already presented by some of the authors, is used in combination with bond-slip elements, to simulate the stress transfer between the rebars and the surrounding concrete, and with additional cohesive elements along the adhesive/concrete (AC) and adhesive/plate (AP) material interfaces. Numerical simulations have been performed by using the present fracture approach for predicting the load-carrying capacity and the related failure modes of real-scale retrofitted RC elements. The reliability and the effectiveness of the proposed fracture approach have been demonstrated through suitable comparisons with available experimental results. In particular, this model results to be an innovative and versatile numerical tool able to analyze the debonding mechanisms in FRP-strengthened RC elements as well as to provide more accurate crack patterns, including multiple crack branching and coalescence, than commonly used existing models.

Dynamic processes of hybrid nanostructured Au particles/nanobubbles in a quasi-2D system by in-situ liquid cell TEM

Recently hybrid structure of hydrogen nanobubble (HNB) and gold nanoparticles (GNP) have attracted a great deal of interest in many potential applications including ultrasound contrast agent, cancer therapy and drug delivery. For the first time, here we reported interaction of high energy electron beam with sodium citrate catalyzes a highly stable hybrid super structure (HNB ∈ Au) where sub-nanometer sized GNPs are decorated on the HNB surface. The formation mechanism of HNB ∈ Au has been in-depth studied in this work. This electron radiation technique is the easiest method for the large-scale production of environmentally benign sub-nanometer sized GNP and HNB at room temperature. We have successfully demonstrated the HNB can serve as a substrate or a template for attracting Au nano-clusters onto its surface by in-situ transmission electron microscopy in liquid environment. The kinetics of multiple coalescence process of merging ultra-small GNP and HNB has been analyzed with Mehl-Avrami-Kolmogorov (JMAK) scheme. It suggests that the growth modes for HNB and GNP in the formation process of HNB ∈ Au are 2D and 3D, respectively. Here we have also calculated the momentum transferred to the GNP from the incident electrons and surrounding liquid molecules. It indicates that the incident electrons can trigger the GNP sliding on HNB surface at relatively high dose rate.

Hot tensile behavior of a low-alloyed ultrahigh strength steel: fracture mechanism and physically-based constitutive model

The hot tensile behavior of a low-alloyed ultra-high strength (LUHS) steel is studied by performing the isothermal tensile tests under different tensile processing parameters (strain rates and tensile temperatures). The effects of tensile processing parameters on the hot tensile behaviors and fracture characteristics are comprehensively discussed by analyzing the hot tensile data and microstructure observation. For reproducing the hot tensile behaviors, the dislocation density based constitutive model is constructed and further improved by considering plastic damage. It is found that the hot tensile curves always show the high stress under low tensile temperatures or high strain rates. The ductile fracture characterized by dimples is the dominant fracture type. Meanwhile, the elongation to fracture roughly follows a decreasing trend under low strain rates or high tensile temperatures, and the variation of the reduction in cross-sectional area is opposite to that of elongation to fracture. This is because that the multiple coalescence of microvoids easily takes place with the progress of necking under low strain rates or high tensile temperatures. The relatively narrow error band (controlled in ±5.518 MPa), low mean absolute relative error (equals to 2.695%) and high correlation coefficient (higher than 0.998) indicate that the improved dislocation density based constitutive model is preferred for reconstructing the hot tensile behaviors of the studied steel.

Binarity in Prosodic Morphology and Elsewhere

This paper explores the role of binarity in prosodic morphology by proposing that all representations are maximally binary branching, as stated in (1).(1) Binarity Hypothesis: All representations are maximally binary branching.Our evidence comes from examining patterns in which fission (Integrity violations) and fusion (Uniformity violations) of segments satisfies morphological and phonological constraints: multiple reduplication, haplology, coalescence, and breaking. Where there appears to be 1:3 or a 3:1 mapping between input and output segments, we propose that this must arise from two separate 1:2 or 2:1 mappings (perhaps at a stem and word level). We illustrate that a number of seemingly complex patterns of multiple reduplication in Salish, Wakashan and Uto-Aztecan languages follow naturally from the Binarity Hypothesis.