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A model is developed for the coalescence of unequal-sized amorphous primary particles commonly found in aerosol aggregates.Computational efficiency is achieved by deriving an analytical expression for the surface geometry of the c...
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A model is developed for the coalescence of unequal-sized amorphous primary particles commonly found in aerosol aggregates.Computational efficiency is achieved by deriving an analytical expression for the surface geometry of the coalescing particles and subsequently decoupling surface evolution from the fluid dynamic equations.Calculated shrinkage lengths and surface areas are in good agreement with results reported from finite element calculations for all particle size ratios considered.Results indicate that above a size ratio of 4,the normalized coalescence rate is independent of size ratio.Applying these results to the coalescence of SiO_2 particles indicates that rates are primarily dependent on the diameter of the smaller particle,although coalescence times do not scale linearly with either particle size ratio or total particle mass.Comparison with the widely used exponential model of Koch and Friedlander suggests that rates of surface area decrease are under-predicted by the Koch and Friedlander model.Modified values of the decay constant for both equal sized and heterogeneously sized particles are therefore proposed,with the value decreasing with increasing size ratio of the coalescing pair.
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The genealogical structure of neutral populations in which reproductive success is highly-skewed has been the subject of many recent studies. Here we derive a coalescent dual process for a related class of continuous-time Moran mo...
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The genealogical structure of neutral populations in which reproductive success is highly-skewed has been the subject of many recent studies. Here we derive a coalescent dual process for a related class of continuous-time Moran models with viability selection. In these models, individuals can give birth to multiple offspring whose survival depends on both the parental genotype and the brood size. This extends the dual process construction for a multi-type Moran model with genic selection described in . We show that in the limit of infinite population size the non-neutral Moran models converge to a Markov jump process which we call the I> -Fleming-Viot process with viability selection and we derive a coalescent dual for this process directly from the generator and as a limit from the Moran models. The dual is a branching-coalescing process similar to the Ancestral Selection Graph which follows the typed ancestry of genes backwards in time with real and virtual lineages. As an application, the transition functions of the non-neutral Moran and I> -coalescent models are expressed as mixtures of the transition functions of the dual process.
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We consider two population models subject to the evolutionary forces of selection and mutation, the Moran model and the A-Wright-Fisher model. In such models the block counting process traces back the number of potential ancestors...
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We consider two population models subject to the evolutionary forces of selection and mutation, the Moran model and the A-Wright-Fisher model. In such models the block counting process traces back the number of potential ancestors of a sample of the population at present. Under some conditions the block counting process is positive recurrent and its stationary distribution is described via a linear system of equations. In this work, we first characterise the measures A leading to a geometric stationary distribution, the Bolthausen-Sznitman model being the most prominent example having this feature. Next, we solve the linear system of equations corresponding to the Moran model. For the A-Wright-Fisher model we show that the probability generating function associated to the stationary distribution of the block counting process satisfies an integro differential equation. We solve the latter for the Kingman model and the star-shaped model. (C) 2019 Elsevier Inc. All rights reserved.
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We investigate through numerical simulations the effect of selection on two summary statistics for nucleotide variation in a sample of two genes from a population of N asexually reproducing haploid individuals. One is the mean tim...
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We investigate through numerical simulations the effect of selection on two summary statistics for nucleotide variation in a sample of two genes from a population of N asexually reproducing haploid individuals. One is the mean time since two individuals had their most recent common ancestor (<(T)over bar(s)>), and the other is the mean number of nucleotide differences between two genes in the sample (<(d)over bar(s)>). In the case of diminishing epistasis, in which the deleterious effect of a new mutation is attenuated, we find that the scale of <(d)over bar(s)> with the population size depends on the mutation rate, leading then to the onset of a sharp threshold phenomenon as N becomes large. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 10]
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Emulsification is a common process in the production in many non-solid foods. These food-emulsions often have high disperse phase volume fractions and slow emulsifier dynamics, giving rise to substantial coalescence during emulsif...
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Emulsification is a common process in the production in many non-solid foods. These food-emulsions often have high disperse phase volume fractions and slow emulsifier dynamics, giving rise to substantial coalescence during emulsification. Optimal design and operation of food-emulsification requires experimental methods to study how emulsification in general and coalescence in particular progresses under different conditions. Methods for coalescence quantification during emulsification has been suggested in literature but they are rarely used in food-emulsification research. This contribution offers a critical review of the different methods that have been suggested with special emphasis on their applicability to technical food-emulsification. The methods are critically compared in terms of design limitations, degree of quantification and applicability. A state-of-the-art in the form of two methods is identified and guidelines for their application are suggested. (C) 2016 Elsevier Ltd. All rights reserved.
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We consider the genealogy of a sample of individuals taken from a spatially structured population when the variance of the offspring distribution is relatively large. The space is structured into discrete sites of a graph G. If th...
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We consider the genealogy of a sample of individuals taken from a spatially structured population when the variance of the offspring distribution is relatively large. The space is structured into discrete sites of a graph G. If the population size at each site is large, spatial coalescents with multiple mergers, so called spatial Lambda-coalescents, for which ancestral lines migrate in space and coalesce according to some Lambda-coalescent mechanism, are shown to be appropriate approximations to the genealogy of a sample of individuals. We then consider as the graph G the two dimensional torus with side length 2L + 1 and show that as L tends to infinity, and time is rescaled appropriately, the partition structure of spatial Lambda-coalescents of individuals sampled far enough apart converges to the partition structure of a non-spatial Kingman coalescent. From a biological point of view this means that in certain circumstances both the spatial structure as well as larger variances of the underlying offspring distribution are harder to detect from the sample. However, supplemental simulations show that for moderately large L the different structure is still evident
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In the churn-turbulent bubbly flow regime with highly nonuniform bubble size distributions, bubble breakage and coalescence are important processes because they govern the bubble size distribution and consequently directly affect ...
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In the churn-turbulent bubbly flow regime with highly nonuniform bubble size distributions, bubble breakage and coalescence are important processes because they govern the bubble size distribution and consequently directly affect the interfacial mass, momentum, and heat transfer fluxes through the renewal bubble surfaces. At present, accurate prediction of bubble size distributions of dispersed gas–liquid flows by use of the population balance (PB) equation is a difficult task. The modeling of bubble breakup and coalescence rates is very complex and is based on the knowledge of collision and breakup frequencies, breakage daughter size distributions, and probability of coalescence. In this work, we focus on the coalescence phenomenon. The coalescence models are still on an empirical level and the mechanisms are not fully understood. This motivates the analysis of the suitability of the coalescence closures for the prediction of experimental data obtained from coalescence dominated gas–liquid flows. For this task, a cross-sectional averaged combined multifluid-PB model is adopted. Based on different theories for the coalescence efficiency, the simulation results show a similar trend in the prediction of the experimental data. Good prediction of the Sauter mean diameter is achieved although the shape of the bubble size distribution is not completely reproduced. The second aim of this work is to review the PB framework. Here, focus is placed on the coalescence term and the combined multifluid-PB model based on kinetic theory approach.
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Phylogenetic estimation under the multispecies coalescent model (MSCM) assumes all incongruence among loci is caused by incomplete lineage sorting. Therefore, applying the MSCM to datasets that contain incongruence that is caused ...
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Phylogenetic estimation under the multispecies coalescent model (MSCM) assumes all incongruence among loci is caused by incomplete lineage sorting. Therefore, applying the MSCM to datasets that contain incongruence that is caused by other processes, such as gene flow, can lead to biased phylogeny estimates. To identify possible bias when using the MSCM, we present P2C2M.SNAPP. P2C2M.SNAPP is an R package that identifies model violations using posterior predictive simulation. P2C2M.SNAPP uses the posterior distribution of species trees output by the software package SNAPP to simulate posterior predictive datasets under the MSCM, and then uses summary statistics to compare either the empirical data or the posterior distribution to the posterior predictive distribution to identify model violations. In simulation testing, P2C2M.SNAPP correctly classified up to 83% of datasets (depending on the summary statistic used) as to whether or not they violated the MSCM model. P2C2M.SNAPP represents a user-friendly way for researchers to perform posterior predictive model checks when using the popular SNAPP phylogenetic estimation program. It is freely available as an R package, along with additional program details and tutorials.
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We study experimentally and theoretically new aspects of condensation, growth and coalescence of droplets on a substrate. We address in particular the dynamics of a 'marked' droplet which undergoes coalescences with neighbouring d...
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We study experimentally and theoretically new aspects of condensation, growth and coalescence of droplets on a substrate. We address in particular the dynamics of a 'marked' droplet which undergoes coalescences with neighbouring droplets. We find that the number of coalescences of the droplet grows as log t (t is time) and that the traveled distance increases as [R(t)], the average radius of the droplets at time t. The fraction of the surface which was never covered by any droplet (an important quantity for applications, such as drug spreading or surface decontamination), decays as t(-theta), showing that completion occurs only slowly. Heuristic arguments, accurate numerical simulations on simplified models (which neglect polydispersity) and an exact solution reported elsewhere [A. Bray, B. Derrida and C. Godreche, Europhys. Lett. 27 (1994) 175] strongly support these findings, and show that this power law decay is a generic feature, common to many different situations. Finally, the contour of the ensemble of 'dry' sites appears fractal with dimension d(f) similar or equal to 1.22, an experimental result not reproduced by the simplified models. [References: 21]
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The influence of shear loading on damage development in Gurson-based modelshas long been neglected resulting in inadequate fracture strain predictionsat low triaxiality where shear effects become significant. The plastic limit-loa...
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The influence of shear loading on damage development in Gurson-based modelshas long been neglected resulting in inadequate fracture strain predictionsat low triaxiality where shear effects become significant. The plastic limit-load fracture criterion used in advanced Gurson models neglects the influenceof shear loading and overestimates the fracture strain and porosity at lowtriaxiality. In this paper, we extend the recently proposed shear damage model ofXue [1] to provide a stronger physical foundation by removing the simplifyingassumptions. Then we directly modify the plastic limit-load fracture criterionby coupling with the extended shear damage model to account for shearweakening and failure of the intervoid ligament in void coalescence. We applythe modified plastic limit-load criterion to predict the necking of sheet tensilespecimens and find very good agreement with the available experimental results.
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