A smoothed particle hydrodynamics and coarse‐grained molecular dynamics hybrid technique for modelling elastic particles and breakable capsules under various flow conditions

In this work, a hybrid numerical approach, which combines elements of SPH and coarse‐grained molecular dynamics, is used to investigate the effect of various flow conditions to deformable and breakable shell‐structures such as capsules, vesicles or biological cells. Copyright © 2014 John Wiley & Sons, Ltd.     

Analysis of volume‐to‐surface ratio effects on methane oxidative coupling using microkinetic modeling

The effect of the volume‐to‐surface (V/S) ratio on the catalytic performance of a La–Sr/CaO catalyst in a fixed bed reactor under oxidative coupling of methane (OCM) conditions is investigated by adjusting the amount of diluent in the catalyst bed. It was observed experimentally that the catalyst activity, C₂ selectivity, and C₂H₄/C₂H₆ ratio are all favored at high V/S ratios. The total void volume, available in the intraparticle and the interstitial phase, was considered. A comprehensive OCM microkinetic model, explicitly distinguishing between these two phases, allowed accounting for the observed dependence of catalytic performance on V/S ratio. The major experimentally implemented variation in interstitial volume available for reaction, provoked also changes in radical concentration profiles in intraparticle phase. Given the high reaction rates occurring at this location, the experimentally observed effects with varying the V/S ratio, are attributed to concentration and, hence, reaction rate changes occurring mainly in the intraparticle phase. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2603–2611, 2018     

Estimation of multiple accelerated motions using chirp-Fourier transform and clustering.

Motion estimation in the spatiotemporal domain has been extensively studied and many methodologies have been proposed, which, however, cannot handle both time-varying and multiple motions. Extending previously published ideas, we present an efficient method for estimating multiple, linearly time-varying motions. It is shown that the estimation of accelerated motions is equivalent to the parameter estimation of superpositioned chirp signals. From this viewpoint, one can exploit established signal processing tools such as the chirp-Fourier transform. It is shown that accelerated motion results in energy concentration along planes in the 4-D space: spatial frequencies-temporal frequency-chirp rate. Using fuzzy c-planes clustering, we estimate the plane/motion parameters. The effectiveness of our method is verified on both synthetic as well as real sequences and its advantages are highlighted.     

Estimation of multiple, time-varying motions using time-frequency representations and moving-objects segmentation.

We extend existing spatiotemporal approaches to handle time-varying motions estimation of multiple objects. It is shown that multiple, time-varying motions estimation is equivalent to the instantaneous frequency estimation of superpositioned FM sinusoids. Therefore, we apply established signal processing tools, such as time-frequency representations to show that for each time instant, the energy is concentrated along planes in the 3-D space: spatial frequencies-instantaneous frequency. Using fuzzy C-planes, we estimate indirectly the instantaneous velocities. Furthermore, adapting existing approaches to our problem, we attain the identification of the moving objects. The experimental results verify the effectiveness of our methodology.     

Estimation of Multiple Accelerated Motions Using Chirp-Fourier Transform and Clustering

Motion estimation in the spatiotemporal domain has been extensively studied and many methodologies have been proposed, which, however, cannot handle both time-varying and multiple motions. Extending previously published ideas, we present an efficient method for estimating multiple, linearly time-varying motions. It is shown that the estimation of accelerated motions is equivalent to the parameter estimation of superpositioned chirp signals. From this viewpoint, one can exploit established signal processing tools such as the chirp-Fourier transform. It is shown that accelerated motion results in energy concentration along planes in the 4-D space: spatial frequencies-temporal frequency-chirp rate. Using fuzzy c-planes clustering, we estimate the plane/motion parameters. The effectiveness of our method is verified on both synthetic as well as real sequences and its advantages are highlighted     

Influence of water model and nanotube rigidity on the density of water in carbon nanotubes

The density of water calculated through molecular dynamic simulations using different water models and rigid/flexible carbon nanotubes is studied. A previous equation, determined in an earlier work in order to correlate density and nanotube diameter, is tested against these new data. It is demonstrated that this equation provides a reasonable approximation for all the configurations investigated. It is also confirmed that the use of flexible nanotube models does not bring any significant improvement and the average carbon dislocation is small compared to the size of the water molecules. Comparison between SPC/E and TIP3P models, furthermore, shows that the first model leads to polygonal water structures, which are not evident in the other case.     

Modelling of a photocatalytic reactor with a fixed bed of supported catalyst

This work intends to develop a mathematical model of a fixed bed reactor and tests this model with experimental data. For this reason, we introduce some specific knowledge about light absorption from the catalyst, about the hydrodynamic interpretation of the reactor and the kinetic behaviour of photocatalytic reactions. Afterwards, we summarise this information and set up a complex mathematical model. We use this model in order to identify the kinetic constants of some reactions. We also formulate some simplified models to be used in particular circumstances and we compare the results of the complex model and the simplified models. Moreover, we compare experimental data of conversion and the results estimated with our model.     

On the use of the BLYP functional for the DFT calculation of graphite–hydrogen systems

This letter focuses on a possible pitfall that can occur in the DFT calculation of graphite–hydrogen interactions under tokamaks conditions. Calculations based on the BLYP functional, in fact, result in a stable –C₂H₃ group that other functionals (OLYP, XLYP, PBE and BP) do not confirm.     

Mathematical Modeling of Homopolymerization on Supported Metallocene Catalysts

Summary: In this paper, a mathematical model describing olefin polymerization with metallocene catalysts is presented. It is an improvement of a previous model, the “particle growth model” (PGM) proposed by, among others, one of the authors of the present work and derives from the so‐called “multigrane model” (MGM). The main differences between this work and others is a more sophisticated approach to fragmentation with respect to the MGM. Additionally, there is a more specific modeling for the unfragmented core with respect to the PGM. The numerical results obtained by the model are compared with experimental data. The results of this work allow to extend the PGM to catalysts with lower activity. The importance of those catalysts depends on the fact that high activity catalysts could bring, in some cases, too poor polymer morphology.

Geometrical representation of the micro‐ and macroparticle.