Showing papers on "Critical radius published in 2019"
TL;DR: In this article, the fugacity is introduced into the model to increase the calculation accuracy of nucleation rate and the latent heat of condensation plays a dominant role in the change of the droplet growth rate of the binary mixture.
95 citations
TL;DR: The mechanisms of flame instability in ammonia/oxygen mixture were analyzed, and the stabilize effect of flame stretch in ammonia /oxygen have been observed.
67 citations
TL;DR: In this article, the authors investigated the explosion processes of H2/CO/air mixtures with diluents with a confined vessel and obtained explosion pressure and maximum rate of pressure rise with increasing equivalence ratios.
50 citations
TL;DR: A microscopic model of a frictional interface that includes asperity-level disorder, elastic interaction between local slip events, and inertia is introduced, and it is found that after slip, the density of asperities at a local distance to yielding xσ presents a pseudogap P(xσ)∼( xσ)θ, where θ is a nonuniversal exponent that depends on the statistics of the disorder.
Abstract: Sliding at a quasi-statically loaded frictional interface can occur via macroscopic slip events, which nucleate locally before propagating as rupture fronts very similar to fracture. We introduce a microscopic model of a frictional interface that includes asperity-level disorder, elastic interaction between local slip events, and inertia. For a perfectly flat and homogeneously loaded interface, we find that slip is nucleated by avalanches of asperity detachments of extension larger than a critical radius A c governed by a Griffith criterion. We find that after slip, the density of asperities at a local distance to yielding x σ presents a pseudogap P ( x σ ) ∼ ( x σ ) θ , where θ is a nonuniversal exponent that depends on the statistics of the disorder. This result makes a link between friction and the plasticity of amorphous materials where a pseudogap is also present. For friction, we find that a consequence is that stick–slip is an extremely slowly decaying finite-size effect, while the slip nucleation radius A c diverges as a θ-dependent power law of the system size. We discuss how these predictions can be tested experimentally.
25 citations
TL;DR: In this paper, the effects of flame instability on 2-methylfuran (MF) outwardly propagating laminar flames have been investigated experimentally and theoretically at the initial pressures of 1-4 bar, temperatures of 363-423 K and equivalence ratios of 0.7-1.4.
24 citations
TL;DR: In this article, the authors simulated the coalescence-induced self-propelled jumping of binary unequal-sized droplets on superhydrophobic surfaces and all energy terms were studied.
Abstract: The coalescence-induced self-propelled droplet jumping on superhydrophobic surfaces has a large number of potential applications such as enhancement of condensation heat transfer, self-cleaning, and anti-icing, which becomes a current hotspot. At present, most of the research studies focus on the self-propelled jumping of two identical droplets; however, the jumping induced by unequal-sized droplets is much closer to actuality. In this paper, the coalescence-induced self-propelled jumping of binary unequal-sized droplets is simulated and all energy terms are studied. The normalized liquid bridge width induced by unequal-sized droplets is a function of the square root of the normalized time, and the maximum jumping velocity is a function of the radius ratio as well. The maximum jumping velocity descends with the decrease in the radius ratio and contact angle, and the critical radius ratio shows an upward trend with the decrease in the contact angle. Furthermore, all energy terms decline with the decrease in the radius ratio. The effective energy conversion rate of binary equal-sized jumping is very low, less than 3% in our results. This rate of binary unequal-sized jumping further reduces due to the existence of asymmetric flow. This work helps for a better understanding of the characteristics of coalescence-induced self-propelled droplet jumping.
21 citations
TL;DR: In this paper, numerical modeling of particle formation of TBTPP (5, 10, 15, 20-tetrakis (3, 5-bis (trifluoromethyl) phenyl) porphyrin) through Rapid Expansion of supercritical fluid (RESS) is investigated.
19 citations
TL;DR: This study is the first of its kind showing the crucial role of the membrane host in retarding the reaction kinetics which allowed successful probing of temporal variation of monomer concentration during nucleation and growth using a radiotracer.
Abstract: Size controlled synthesis of nanoparticles in a structured media, such as a membrane, has not yet been achieved successfully in comparison to that in solution due to the lack of mechanistic investigations on the nucleation and growth of nanoparticles in these media. Slower diffusion of precursor and monomer species inside these structured media complicates the nanoparticle formation mechanism. We herein report a novel experimental approach to reveal the mechanism of nucleation and growth during the synthesis of silver nanoparticles in a Nafion-117 membrane using radiolabeling and small angle X-ray scattering (SAXS). The study has been conducted under the conditions of continuous supply of precursor (silver citrate). Repetitive “LaMer type” nucleations have been found to occur in the membrane leading to the formation of polydispersed spherical nanoparticles as evident from time resolved small angle X-ray scattering. These repetitive nucleations have been shown to be responsible for continuous birth of new seeds, which grow to larger particles, mainly by random coagulation introducing non-uniformity in the growth profile of nanoparticles. The additional nucleation events have been successfully ceased by careful tuning of reaction temperature and precursor concentration, thereby eliminating the nanoparticle growth by random coagulation. This has led to the formation of silver nanoparticles with improved morphology and size distributions, which has been manifested in remarkable improvement in the optical quality of the silver nanoparticles. The present study is the first of its kind showing the crucial role of the membrane host in retarding the reaction kinetics which allowed successful probing of temporal variation of monomer concentration during nucleation and growth using a radiotracer. This was hitherto difficult to probe in solution due to its ultrafast kinetics. Additionally, using the experimental monomer concentrations during nucleation, the free energy of activation (ΔGcrit) and the critical radius (rcrit) for nucleation have been estimated and found to be 73 kJ mol−1 and 6.6 A, respectively. The present work validates the well known theoretical model by La Mer for the synthesis of nanoparticles in a membrane under continuous precursor supply.
19 citations
TL;DR: In this paper, the effects of Cr additions on the morphologies οf γ′(L12 ordered) precipitates are studied in three Ni-Al-Cr alloys utilizing atom-probe tomography (APT) and first-principles calculations.
19 citations
TL;DR: In this paper, the authors examined mixtures of circularly moving and passive disks as a function of density and active orbit radius, and showed that for low or intermediate densities and small orbit radii, the system can organize into a reversible partially phase separated labyrinth state in which there are no collisions between disks, with the degree of phase separation increasing as the orbit radius increases.
Abstract: We numerically examine mixtures of circularly moving and passive disks as a function of density and active orbit radius. For low or intermediate densities and/or small orbit radii, the system can organize into a reversible partially phase separated labyrinth state in which there are no collisions between disks, with the degree of phase separation increasing as the orbit radius increases. As a function of orbit radius, we find a divergence in the number of cycles required to reach a collision-free steady state at a critical radius, while above this radius, the system remains in a fluctuating liquid state. For high densities, the system can organize into a fully phase separated state that is mostly reversible, but collisions at the boundaries between the phases lead to a net transport of disks along the boundary edges in a direction determined by the chirality of the active disk orbits. We map the dynamic phases as a function of density and orbit radii and discuss the results in terms of the reversible-irreversible transition found in other periodically driven non-thermal systems. We also consider mixtures of circularly driven disks and ac driven disks where the ac drive is either in or out of phase with the circular motion and find a rich variety of pattern forming and reentrant disordered phases.
17 citations
TL;DR: In this article, the effect of reactive elements on the precipitation of oxide particles, especially focusing upon the appropriate amount of the oxide composing elements, by addition of the large amounts of Y2O3 and reactive elements.
Abstract: The reactive elements (Ti, Al and Zr) have been widely used for the improvement of the strength or the oxide resistance of ODS steels. In the present work, we studied the effect of the reactive elements on the precipitation of oxide particles, especially focusing upon the appropriate amount of the oxide composing elements, by addition of the large amounts of Y2O3 and reactive elements. The mechanically alloyed powders are annealed in a wide temperature range from 773 to 1423 K and then analysed by various analysis methods (small-angle X-ray scattering and X-ray diffraction by synchrotron radiation X-ray, scanning transmission electron microscope combined with energy dispersion X-ray spectroscopy, high-resolution transmission microscopy and 3D-atom probe). Ti, Al and Zr enhanced the growth of oxide particles, opposite to the many studies of Ti- and Zr-added ODS steels, as a result of the addition of Y2O3 and these elements ten times larger than those for usual use. The nucleation and growth of oxide particles are discussed by simulating the critical radius of nucleation and the growth based on the LSW theory. Y4Zr3O12 is stable and easy to precipitate even at lower annealing temperature. All reactive elements enhance the growth of oxide particles because of their big molar volume as compared to that of Y2O3.
TL;DR: This work considers the process of chemical erosion of a porous medium infiltrated by a reactive fluid in a thin-front limit, in which the width of the reactive front is negligible with respect to the diffusive length, and shows that in the radial geometry the advancing front becomes unstable only if the flow rate in the system is sufficiently high.
Abstract: We consider the process of chemical erosion of a porous medium infiltrated by a reactive fluid in a thin-front limit, in which the width of the reactive front is negligible with respect to the diffusive length. We show that in the radial geometry the advancing front becomes unstable only if the flow rate in the system is sufficiently high. The existence of such a stable region in parameter space is in contrast to the Saffman-Taylor instability in radial geometry, where for a given flow rate the front always eventually becomes unstable, after reaching a certain critical radius. We also examine the similarities between the reactive-infiltration instability and the similar instability in the heat transfer, which is driving the formation of star-like patterns on frozen lakes.
TL;DR: Parameters of hydrate nucleation such as rates of nucleation and crystal growth, critical radius of the nucleus, and theoretical induction time for carbon dioxide and methane were considered and an attempt was made to define the induction time from a theoretical perspective and derive a relevant equation from the existing models.
Abstract: Research in the field of hydrate formation requires more focus upon its modelling to enable the researchers to predict and assess the hydrate formation and its characteristics. The main focus of the study was to analyze the deviations induced in various parameters related to hydrate nucleation caused by the choice of different measuring correlations or methods of their sub-components. To serve this purpose under a range of operational conditions, parameters of hydrate nucleation such as rates of nucleation and crystal growth, critical radius of the nucleus, and theoretical induction time for carbon dioxide and methane were considered in this study. From these measurements, we have quantitatively compared the ease of hydrate formation in CO₂ and CH₄ systems in terms of nucleation while analyzing how various correlations for intermediate parameters were affecting the final output. Values of these parameters were produced under the considered bracket of operational conditions and distributed among six cases using both general and guest-gas specific correlations for gas dissolution and fugacity and their combinations. The isotherms and isobars produced from some of the cases differed from each other considerably. The rate of nucleation in one case showed an exponential deviation with a value over 1 × 1028 at 5 MPa, while the rest showed values as multiples of 10⁶. These deviations explain how sensitive hydrate formation is to processing variables and their respective correlations, highlighting the importance of understanding the applicability of semi-empirical correlations. An attempt was made to define the induction time from a theoretical perspective and derive a relevant equation from the existing models. This equation was validated and analyzed within these six cases from the experimental observations.
08 Apr 2019
TL;DR: It is shown, through computer simulations and nucleation kinetics, that SOS may heterogeneously nucleate on SSS surfaces and this may point to strategies to enhance the nucleation of one of the three major triglycerides present in cocoa butter and the one that crystallizes first from the melt for better control of the chocolate tempering process.
Abstract: The following work investigates the heterogeneous nucleation of 2-oleodistearin (SOS) triglycerides on surfaces formed by crystals of tristearin triglyceride (SSS). This work shows, through computer simulations and nucleation kinetics, that SOS may heterogeneously nucleate on SSS surfaces. Atomic-scale molecular dynamics showed that SOS molecules exhibited an affinity to a simulated SSS surface. Nucleation kinetics using differential scanning calorimetry showed that the inclusion of minor amounts of SSS (from 1 to 4%) in an SOS melt resulted in an increase in the isothermal nucleation rate of crystallizing SOS. Using a model based on the Fisher-Turnbull approach, estimates of the surface free energy, activation free energy, and the critical radius were calculated from the nucleation rates. The estimated parameters demonstrate the heterogeneous nucleation of SOS on SSS surfaces: reduced surface free energies, activation free energies, and critical radii with the inclusion of SSS in an SOS melt. This may point to strategies to enhance the nucleation of one of the three major triglycerides present in cocoa butter and the one that crystallizes first from the melt for better control of the chocolate tempering process.
TL;DR: In this paper, the structural origin of hydration repulsive force is investigated, which is reasonably attributed to the effects of surface roughness of solute on hydrophobic interactions.
TL;DR: It is found that there exists a critical radius dependent on the contact angle, the domain size, and the interface width, below which the drop will eventually disappear, which can be very large when the surface becomes very hydrophilic.
Abstract: Phase-field theory is widely used to model multiphase flow. The fact that a drop can shrink or grow spontaneously due to the redistribution of interface and bulk energies to minimize the system energy may produce ill effects on the simulation. In this Rapid Communication, the spontaneous behavior of a drop on a partially wetting surface is investigated. It is found that there exists a critical radius dependent on the contact angle, the domain size, and the interface width, below which the drop will eventually disappear. In particular, the critical radius can be very large when the surface becomes very hydrophilic. The theoretical prediction of the critical radius is verified numerically by simulating a drop on a surface with various contact angles, the domain sizes, and the interface widths.
TL;DR: In this article, the incorporation of different size of nanoparticles in polymer matrix plays a dominating role in determining the overall structural, microstructural and electrical properties of fabricated composites.
Abstract: The incorporation of different size of nanoparticles in polymer matrix plays a dominating role in determining the overall structural, microstructural and electrical properties of the fabricated composites. In this paper, an investigation was done in order to establish the effect of incorporating different size of zinc ferrite (ZF) nanoparticles in poly(vinylidene fluoride) (PVDF) matrix. The incorporated spherical ZF nanoparticle induced nucleation of electroactive phases in PVDF matrix by means of electrostatic interaction between the surface charge of the filler and the dipoles of PVDF. The fraction of nucleated electroactive phases is strongly dependent on the size of the nanoparticles. There is a critical size of the nanoparticle, below which the nucleation efficiency of the filler diminishes as it may be swelled by the polymer macromolecules. On the other hand, if the filler size is too large, there is a possibility of formation of mixed conformation of polar and nonpolar phase. Further, this behaviour was correlated with the electrical response of composite where nanoparticle with the critical radius incorporated PVDF composite, exhibited maximum dielectric and ferroelectric property. Finally, a number of participating dipoles of polymer chain interact with ZF nanoparticle of different size were calculated by a model analysis and were represented schematically.
TL;DR: Lamstaes et al. as mentioned in this paper showed that the critical width of the square channels is much smaller than the critical radius of the cylindrical ones, due to the fluid leakage at the corners.
Abstract: A bubble in a vertical cylindrical capillary can get stuck due to the drainage of its lubrication film, according to the prediction originally made by Bretherton. When stuck, the profile of the lubrication film around the bubble is measured using an optical interference method. Our experimental results verified the theoretical prediction of the time-dependent minimum thickness hmin ∼ t−4/5 [C. Lamstaes and J. Eggers, “Arrested bubble ‘rise’ in a narrow tube,” J. Stat. Phys. 167, 656–682 (2017)]. The bubble is stuck in a cylindrical capillary if the critical radius is proportional to the capillary length. We show that this result can be extended to square capillaries, where bubbles will get stuck in square capillaries below a critical width. For the same capillary length, the critical width of the square capillaries is much smaller than the critical radius of the cylindrical ones, due to the fluid leakage at the corners. As the square channels are also commonly used in microfluidic devices, our results provide helpful insights into the different features of the motion of bubbles resulting from the shape of channels.A bubble in a vertical cylindrical capillary can get stuck due to the drainage of its lubrication film, according to the prediction originally made by Bretherton. When stuck, the profile of the lubrication film around the bubble is measured using an optical interference method. Our experimental results verified the theoretical prediction of the time-dependent minimum thickness hmin ∼ t−4/5 [C. Lamstaes and J. Eggers, “Arrested bubble ‘rise’ in a narrow tube,” J. Stat. Phys. 167, 656–682 (2017)]. The bubble is stuck in a cylindrical capillary if the critical radius is proportional to the capillary length. We show that this result can be extended to square capillaries, where bubbles will get stuck in square capillaries below a critical width. For the same capillary length, the critical width of the square capillaries is much smaller than the critical radius of the cylindrical ones, due to the fluid leakage at the corners. As the square channels are also commonly used in microfluidic devices, our results pro...
TL;DR: In this paper, the formation of micropits on large terraces of the Si(111) surface with the application of focused-ion-beam (Ga+) technology has been investigated by in situ ultrahigh-vacuum reflection electron microscopy upon thermal annealing of the substrate in the range of 1200-1400°C.
Abstract: The transformation of micropits on large terraces of the Si(111) surface containing no vicinal atomic steps has been investigated by in situ ultrahigh-vacuum reflection electron microscopy upon thermal annealing of the substrate in the range of 1200–1400°C. A procedure for the formation of micropits on large terraces of the Si(111) surface with the application of focused-ion-beam (Ga+) technology has been proposed. It has been found that the micropit decay kinetics varies upon reaching the critical radius Rcrit, which is caused by the activation of nucleation of two-dimensional vacancy islands on the micropit bottom. A theoretical model describing variations in the lateral sizes of the micropit both before and after reaching Rcrit has been proposed. Based on analysis of the found temperature dependence of the nucleation frequencies of two-dimensional vacancy pits on the micropit bottom, the effective energy of nucleation of a vacancy island has been determined to be 4.1 ± 0.1 eV.
TL;DR: In this article, the dynamics of interfacial evolution of a particle in the binary alloy melt affected by anisotropic surface tension is studied by means of the multiple variable expansion method.
TL;DR: In this paper, the critical energy required for homogeneous nucleation in a superheated liquid, and the related critical radius of the nucleated vapour bubble, are obtained, the former by the direct application of the first law of thermodynamics, the latter by considering that the bubble formation implies the overcoming of a barrier of the free enthalpy potential.
Abstract: Two equations for the calculation of the critical energy required for homogeneous nucleation in a superheated liquid, and the related critical radius of the nucleated vapour bubble, are obtained, the former by the direct application of the first law of thermodynamics, the latter by considering that the bubble formation implies the overcoming of a barrier of the free enthalpy potential. Compared with the currently used relationships, the present equations, still allowing for reversible processes only, lead to thermodynamic energy thresholds of the bubble chambers employed in dark matter searches that are closer to the experimental values.
TL;DR: By altering key system parameters such as the number of particles per lipid and the periodicity, this work describes scenarios in which pores of any initial size can seal or even remain stable, showing a fundamental difference in the behaviour of lipid membranes from polymer films.
Abstract: We investigate with computer simulations the critical radius of pores in a lipid bilayer membrane. Ilton et al. (Ilton et al. 2016 Phys. Rev. Lett. 117, 257801 (doi:10.1103/PhysRevLett.117.257801))...
TL;DR: In this article, a gas-liquid phase transition was found based on the particle dynamics on a radius-R circle in which the coordinate appears as the angle-variable of the 1D XY -model.
Abstract: A gas-liquid type of phase transition is found based on the particle dynamics on a radius-R circle in which the coordinate appears as the angle-variable of the 1D XY -model. Due to the specific appearance of a compact-space radius (volume) in the present interpretation of the XY -model, the ground state develops a minimum at some critical radius, leading to the multi-valued Gibbs energy similar to systems with first-order phase transition.
TL;DR: In this paper, the authors studied a flocking model in which the interaction between agents is described by a general local nonlinear function depending on the distance between agents and established sufficient conditions and necessary conditions for flocking with large population.
Abstract: This paper studies a flocking model in which the interaction between agents is described by a general local nonlinear function depending on the distance between agents. The existing analysis provided sufficient conditions for flocking under an assumption imposed on the system’s closed-loop states; however this assumption is hard to verify. To avoid this kind of assumption the authors introduce some new methods including large deviations theory and estimation of spectral radius of random geometric graphs. For uniformly and independently distributed initial states, the authors establish sufficient conditions and necessary conditions for flocking with large population. The results reveal that under some conditions, the critical interaction radius for flocking is almost the same as the critical radius for connectivity of the initial neighbor graph.
TL;DR: In this paper, the peculiarities of the nucleation of CuCl nanoparticles at the heating stage in sodium-aluminum-borosilicate glass are studied by the method of exciton-thermal analysis.
Abstract: The peculiarities of the nucleation of CuCl nanoparticles at the heating stage in sodium-aluminum-borosilicate glass are studied by the method of exciton-thermal analysis. It is found that the concentration of CuCl particles in this process reaches its maximum. The concentration of CuCl particles increases as the heating time increases, while the average radius decreases. The numerical simulation shows that heating leads to the development of the maximum number of new phase nuclei due to the rapid growth of the critical radius. From a certain moment of heating, the dissolution of previously formed nuclei is observed. The CuCl phase concentration and the average radius of the particles’ radial distribution under heating for more than 5 min tend to the equilibrium value for the corresponding nucleation temperature.
TL;DR: In this article, the authors studied the internal structure of a geometric object with a nontrivial topology, the wormhole, and they showed that the galactic black hole recently discovered by astronomers and astrophysicists as part of the Event Horizon Telescope project with the radius about 1016 cm and the mass of about 1043 g can be a wormhole almost neutralized in charge with parameters close to critical.
Abstract: Using the new exact solution of Einstein and Maxwell equations in the general relativity theory, they studied the internal structure of a geometric object with a nontrivial topology, the wormhole. They showed that the galactic black hole recently discovered by astronomers and astrophysicists as the part of the Event Horizon Telescope project with the radius about 1016 cm and the mass of about 1043 g can be a wormhole almost neutralized in charge with parameters close to critical—megamaximon, the radius of its neck curvature is equal to the so-called critical radius coinciding with half of the gravitational radius.
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TL;DR: In this paper, it was shown that diffraction can be treated kinematically when the bending radius is small compared to the critical radius given by the ratio of the Bragg-case extinction length for the actual reflection to the Darwin width of this reflection.
Abstract: The use of strongly bent crystals in spectrometers for pulses of a hard x-ray free-electron laser is explored theoretically. Diffraction is calculated in both dynamical and kinematical theories. It is shown that diffraction can be treated kinematically when the bending radius is small compared to the critical radius given by the ratio of the Bragg-case extinction length for the actual reflection to the Darwin width of this reflection. As a result, the spectral resolution is limited by the crystal thickness, rather than the extinction length, and can become better than the resolution of a planar dynamically diffracting crystal. As an example, we demonstrate that spectra of the 12 keV pulses can be resolved in 440 reflection from a 20 micron thick diamond crystal bent to a radius of 10 cm.
07 May 2019
TL;DR: In this paper, the stability issue of ferroelectric domain in lead meta niobate (PbNb2O6) single crystal for its manipulation using electric field at nano-scale control on the geometrical dimensions of domain is reported, which is highly desirable for both applications and fundamental study.
Abstract: Ferroelectrics have received intense attention due to its great application potential in RAM devices and new types of sensors. The stability issue of ferroelectric domain in lead meta niobate (PbNb2O6) single crystal for its manipulation using electric field at nano scale control on the geometrical dimensions of domain is reported, which is highly desirable for both applications and fundamental study. The analytical parameters like critical radius of nucleation of domain (rc), domain wall energy (α), critical energy of nucleation (ωc), geometrical dimensions of domain for this peculiar ferroelectric crystal are calculated and condition of back-switching on removal of applied electric field is discussed.Ferroelectrics have received intense attention due to its great application potential in RAM devices and new types of sensors. The stability issue of ferroelectric domain in lead meta niobate (PbNb2O6) single crystal for its manipulation using electric field at nano scale control on the geometrical dimensions of domain is reported, which is highly desirable for both applications and fundamental study. The analytical parameters like critical radius of nucleation of domain (rc), domain wall energy (α), critical energy of nucleation (ωc), geometrical dimensions of domain for this peculiar ferroelectric crystal are calculated and condition of back-switching on removal of applied electric field is discussed.