•A new multiphase Incompressible Smoothed Particle Hydrodynamics (ISPH) method is developed for simulation of coalescence.•The film drainage model is used to drain out particles of the surrounding ...fluid from the region between the droplets’ interfaces.•The head-on and head-off coalescence, and electro-coalescence of suspended droplets are simulated with the proposed method.
In this paper, a numerical algorithm is introduced for simulation of droplet coalescence and electro-coalescence within the framework of the Smoothed Particle Hydrodynamics (SPH) method. The algorithm is developed based on the film drainage model which is used for simulation of coalescence in mesh-dependent methods. The film drainage model allows the SPH particles which are entrapped between two colliding droplets to be discharged. The algorithm is validated with available numerical and experimental results. Then, the algorithm is employed to model two-dimensional coalescence problems for wide ranges of Weber number (0 < We < 30) and impact parameter (0 < β < 0.8). Moreover, the method is extended for the simulation of the electro-coalescence of 2D stationary droplets. Employing the leaky dielectric model, it is observed that both prolate and oblate deformed pair of droplets approach each-other, leading to the permanent coalescence.
W UMa type binaries have two defining characteristics. These are (i) the effective temperatures of both components are very similar, and (ii) the secondary (currently less massive) component is ...overluminous for its current mass. We consider the latter to be an indication of its mass before the mass transfer event. For these stars, we define a mass difference (δM) between the mass determined from its luminosity and the present mass determined from fitting the binary orbit. We compare the observed values of the mass difference to stellar models with mass-loss. The range of initial secondary masses that we find for observed W UMa type binaries is 1.3-2.6 M. We discover that the A- and the W-subtype contact binaries have different ranges of initial secondary masses. Binary systems with an initial mass higher than 1.8 ± 0.1 M become A-subtype while systems with initial masses lower than this become W-subtype. Only 6 per cent of systems violate this behaviour. We also obtain the initial masses of the primaries using the following constraint for the reciprocal of the initial mass ratio: 0 < 1/q
i < 1. The range of initial masses we find for the primaries is 0.2-1.5 M, except for two systems. Finally in comparing our models to observed systems, we find evidence that the mass transfer process is not conservative. We find that only 34 per cent of the mass from the secondary is transferred to the primary. The remainder is lost from the system.
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► Knowledge on the Mn–Na2WO4/SiO2 was summarized and critically reviewed. ► Stability of the catalyst is proven, which is important because many catalysts deactivate. ► Variations of ...the content were studied, but, variations of the support are missing in literature.
Mn–Na2WO4/SiO2 is one of the very few catalysts for the oxidative coupling of methane, whose stability over extended times on stream has been reported by different research groups. The high stability turned Mn–Na2WO4/SiO2 into an object of research, despite the rather complex composition and structure. The nature of the active site or the active phase is unclear, in spite of the research on this catalytic system. This manuscript tries to critically summarize the literature on this system and to discuss the available information about the relationship of structure and activity.
Summary
Aims: To identify the relevance and impact of walking speed (WS) over a short distance on activities of daily living (ADLs) in patients with multiple sclerosis (MS).
Methods: An ...internet‐administered survey of MS patients in four countries was distributed to 605 individuals in 2010. Participants had MS for > 5 years and must have reported difficulty walking as a result of MS. The impact of MS on walking and the effects of WS on ADLs were assessed based upon responses (scored on a scale of 1–10) to five questions and categorised post hoc as: high (8–10), moderate (4–7) or low (1–3) impact/importance.
Results: Of the participants who completed the survey (n = 112), 60% were female patients, 63% were aged ≥ 45 years, and 55% had relapsing‐remitting MS. Approximately, half of participants reported a high impact of MS on their general walking ability (46%) and their ability to increase WS over a short distance (55%). Up to 53% of participants reported avoiding ADLs because of concerns about WS; within this cohort, older male patients and patients with secondary‐progressive MS were highly represented.
Discussion: These results, which highlight the importance of WS to patients with MS and emphasise the impact of WS on health‐related quality of life and ADLs, underscore the importance of clinical measures of WS, such as the timed 25‐foot walk, in assessing walking in MS patients.
Conclusion: Walking speed over a short distance has a significant impact on ADLs for patients with MS.
We have presented a multiphase incompressible smoothed particle hydrodynamics method with an improved interface treatment procedure. To demonstrate the effectiveness of the interface treatment which ...can handle multiphase flow problems with high density and viscosity ratios, we have modeled several challenging two phase flow problems; namely, single vortex flow, square droplet deformation, droplet deformation in shear flow, and finally the Newtonian bubble rising in viscous and viscoelastic liquids. The proposed interface treatment includes the usage of (i) different smoothing functions (in this work, cubic spline kernel function for discretizing equations associated with the calculation of the surface tension force while the quintic spline for the discretization of governing equations and the relevant boundary conditions), and (ii) a new discretization scheme for calculating the pressure gradient. It is shown that with the application of the improved interface treatment, it becomes possible to model multiphase flow problems with the density and viscosity ratios up to 1000 and 100 respectively while using standard projection method. The utilization of cubic spline for the continuum surface force model significantly improves the quality of the calculated interface, thereby eliminating the interphase particle penetrations, and in turn leading to the calculation of more accurate velocity and pressure fields.
Practically, every processing technology deals with complex multi-phase flows and predicting the fluid flow behavior is crucial for these processes. Current study discusses the application of a ...mesh-less numerical methodology, i.e. Incompressible Smoothed Particle Hydrodynamics (ISPH) to investigate the behavior of different multi-phase flow systems. This work is presented in a coherent way with increasing test problem difficulties and their concerned physical complexities. A wide range of problems including Laplace’s law, bubble rising, bubble suspension under an external electric field are considered for a code validation purpose, while the numerical results manifest very good accordance with the experimental and theoretical data. Finally, we show the effectiveness of using an external electric field for controlling a complex problem such as Couette flow for a range of electrical permittivity and electrical conductivity ratios. It is noted that the Electrohydrodynamics (EHD) effect on a suspended droplet in Couette flow case is simulated for the first time using the SPH method.
Context.
NGC 4993 is the shell galaxy host of the GRB170817A short gamma-ray burst and the GW170817 gravitational-wave event produced during a binary-neutron-star coalescence.
Aims.
The galaxy shows ...signs, including the stellar shells, that it has recently accreted a smaller, late-type galaxy. The accreted galaxy might be the original host of the binary neutron star.
Methods.
We measured the positions of the stellar shells of NGC 4993 in an HST/ACS archival image and use the shell positions to constrain the time of the galactic merger.
Results.
According to the analytical model of the evolution of the shell structure in the expected gravitational potential of NGC 4993, the galactic merger happened at least 200 Myr ago, with a probable time roughly around 400 Myr, and the estimates higher than 600 Myr being improbable. This constitutes the lower limit on the age of the binary neutron star, because the host galaxy was probably quenched even before the galactic merger, and the merger has likely shut down the star formation in the accreted galaxy. We roughly estimate the probability that the binary neutron star originates in the accreted galaxy to be around 30%.
A smoothed particle hydrodynamics (SPH) solution to the Rayleigh–Taylor instability (RTI) problem in an incompressible viscous two-phase immiscible fluid with surface tension is presented. The ...present model is validated by solving Laplace’s law, and square bubble deformation without surface tension whereby it is shown that the implemented SPH discretization does not produce any artificial surface tension. To further validate the numerical model for the RTI problem, results are quantitatively compared with analytical solutions in a linear regime. It is found that the SPH method slightly overestimates the border of instability. The long time evolution of simulations is presented for investigating changes in the topology of rising bubbles and falling spike in RTI, and the computed Froude numbers are compared with previous works. It is shown that the numerical algorithm used in this work is capable of capturing the interface evolution and growth rate in RTI accurately.
A two-dimensional incompressible smoothed particle hydrodynamics scheme is presented for simulation of rigid bodies moving through Newtonian fluids. The scheme relies on combined usage of the ...rigidity constraints and the viscous penalty method to simulate rigid body motion. Different viscosity ratios and interpolation schemes are tested by simulating a rigid disc descending in quiescent medium. A viscosity ratio of 100 coupled with weighted harmonic averaging scheme has been found to provide satisfactory results. The performance of the resulting scheme is systematically tested for cases with linear motion, rotational motion and their combination. The test cases include sedimentation of a single and a pair of circular discs, sedimentation of an elliptic disc and migration and rotation of a circular disc in linear shear flow. Comparison with previous results at various Reynolds numbers indicates that the proposed method captures the motion of rigid bodies driven by flow or external body forces accurately.
•An ISPH scheme for the motion of rigid bodies in Newtonian fluids is presented.•The scheme relies on combined use of rigidity constraints and viscous penalty.•A viscosity ratio of 100 and weighted harmonic averaging was found satisfactory.•The proposed scheme is easy to implement and circumvents explicit boundary conditions.•The scheme is successfully tested for linear and rotational motion.
Casual observation reveals a striking phenomenon of Preferential Trade Agreements (PTAs): while Customs Unions (CUs) are only intra-regional, Free Trade Agreements (FTAs) are inter and ...intra-regional. Using a farsighted dynamic model, we endogenize the equilibrium path of PTAs among two close countries and one far country. Rising transport costs mitigate the cost of discrimination faced by the far country as a CU non-member and diminish the value of preferential access as a CU member. Thus, sufficiently large transport costs imply that an FTA is the only type of PTA that can induce the far country's participation in PTA formation. Unlike CU formation, FTA formation can induce participation because FTAs provide a flexibility benefit: an FTA member can form further PTAs with non-members but a CU member must do so jointly with all existing members. Hence, in equilibrium, CUs are intra-regional while FTAs are intra- and inter-regional.
•Dynamic farsighted model of preferential trade agreement formation•Endogenous choice between Free Trade Agreements (FTAs) and Customs Unions (CUs)•Market size and geographic asymmetries drive equilibrium formation of agreements•Explain why CUs are only intra-regional while FTAs are inter and intra-regional•Various extensions assess the robustness of our key findings
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