Distributions of diffusion measures from a local mean-square displacement analysis

The paper presents a performance analysis of global-local mean square error criterion of stochastic linearization for some nonlinear oscillators. This criterion of stochastic linearization for nonlinear oscillators bases on dual conception to the local mean square error criterion (LOMSEC). The algorithm is generally built to multi degree of freedom (MDOF) nonlinear oscillators. Then, the performance analysis is carried out for two applications which comprise a rolling ship oscillation and two degree of freedom one. The improvement on accuracy of the proposed criterion has been shown in comparison with the conventional Gaussian equivalent linearization (GEL).

Download Full-text

Effect of Terminal Groups on Thermomechanical and Dielectric Properties of Silica–Epoxy Composite Modified by Hyperbranched Polyester

Polymers ◽

10.3390/polym13152451 ◽

2021 ◽

Vol 13 (15) ◽

pp. 2451

Author(s):

Jianwen Zhang ◽

Dongwei Wang ◽

Lujia Wang ◽

Wanwan Zuo ◽

Lijun Zhou ◽

...

Keyword(s):

Dielectric Constant ◽

Dielectric Properties ◽

Binding Energy ◽

Epoxy Resin ◽

Volume Fraction ◽

Epoxy Composite ◽

Mean Square Displacement ◽

Mean Square ◽

Hyperbranched Polyester ◽

Free Volume Fraction

To study the effect of hyperbranched polyester with different kinds of terminal groups on the thermomechanical and dielectric properties of silica–epoxy resin composite, a molecular dynamics simulation method was utilized. Pure epoxy resin and four groups of silica–epoxy resin composites were established, where the silica surface was hydrogenated, grafted with silane coupling agents, and grafted with hyperbranched polyester with terminal carboxyl and terminal hydroxyl, respectively. Then the thermal conductivity, glass transition temperature, elastic modulus, dielectric constant, free volume fraction, mean square displacement, hydrogen bonds, and binding energy of the five models were calculated. The results showed that the hyperbranched polyester significantly improved the thermomechanical and dielectric properties of the silica–epoxy composites compared with other surface treatments, and the terminal groups had an obvious effect on the enhancement effect. Among them, epoxy composite modified by the hyperbranched polyester with terminal carboxy exhibited the best thermomechanical properties and lowest dielectric constant. Our analysis of the microstructure found that the two systems grafted with hyperbranched polyester had a smaller free volume fraction (FFV) and mean square displacement (MSD), and the larger number of hydrogen bonds and greater binding energy, indicating that weaker strength of molecular segments motion and stronger interfacial bonding between silica and epoxy resin matrix were the reasons for the enhancement of the thermomechanical and dielectric properties.

Download Full-text

Reconstruction of Diffusion Coefficients and Power Exponents from Single Lagrangian Trajectories

Fluids ◽

10.3390/fluids6030111 ◽

2021 ◽

Vol 6 (3) ◽

pp. 111

Author(s):

Leonid M. Ivanov ◽

Collins A. Collins ◽

Tetyana Margolina

Keyword(s):

Black Sea ◽

Diffusion Coefficients ◽

Current System ◽

Mean Square Displacement ◽

California Current ◽

The Black Sea ◽

Mean Square ◽

California Current System ◽

The Mean ◽

Non Gaussian

Using discrete wavelets, a novel technique is developed to estimate turbulent diffusion coefficients and power exponents from single Lagrangian particle trajectories. The technique differs from the classical approach (Davis (1991)’s technique) because averaging over a statistical ensemble of the mean square displacement (<X2>) is replaced by averaging along a single Lagrangian trajectory X(t) = {X(t), Y(t)}. Metzler et al. (2014) have demonstrated that for an ergodic (for example, normal diffusion) flow, the mean square displacement is <X2> = limT→∞τX2(T,s), where τX2 (T, s) = 1/(T − s) ∫0T−s(X(t+Δt) − X(t))2 dt, T and s are observational and lag times but for weak non-ergodic (such as super-diffusion and sub-diffusion) flows <X2> = limT→∞≪τX2(T,s)≫, where ≪…≫ is some additional averaging. Numerical calculations for surface drifters in the Black Sea and isobaric RAFOS floats deployed at mid depths in the California Current system demonstrated that the reconstructed diffusion coefficients were smaller than those calculated by Davis (1991)’s technique. This difference is caused by the choice of the Lagrangian mean. The technique proposed here is applied to the analysis of Lagrangian motions in the Black Sea (horizontal diffusion coefficients varied from 105 to 106 cm2/s) and for the sub-diffusion of two RAFOS floats in the California Current system where power exponents varied from 0.65 to 0.72. RAFOS float motions were found to be strongly non-ergodic and non-Gaussian.

Download Full-text

Tentative Peptide‒Lipid Bilayer Models Elucidating Molecular Behaviors and Interactions Driving Passive Cellular Uptake of Collagen-Derived Small Peptides

Molecules ◽

10.3390/molecules26030710 ◽

2021 ◽

Vol 26 (3) ◽

pp. 710

Author(s):

Pathomwat Wongrattanakamon ◽

Wipawadee Yooin ◽

Busaban Sirithunyalug ◽

Piyarat Nimmanpipug ◽

Supat Jiranusornkul

Keyword(s):

Lipid Bilayer ◽

Lipid Bilayers ◽

Mean Square Displacement ◽

Dynamics Simulation ◽

Coordinate Frame ◽

Mean Square ◽

Binding Modes ◽

Small Peptides ◽

Collagen Peptides ◽

Electron Density Profiles

Collagen contains hydroxyproline (Hyp), which is a unique amino acid. Three collagen-derived small peptides (Gly-Pro-Hyp, Pro-Hyp, and Gly-Hyp) interacting across a lipid bilayer (POPC model membrane) for cellular uptakes of these collagen-derived small peptides were studied using accelerated molecular dynamics simulation. The ligands were investigated for their binding modes, hydrogen bonds in each coordinate frame, and mean square displacement (MSD) in the Z direction. The lipid bilayers were evaluated for mass and electron density profiles of the lipid molecules, surface area of the head groups, and root mean square deviation (RMSD). The simulation results show that hydrogen bonding between the small collagen peptides and plasma membrane plays a significant role in their internalization. The translocation of the small collagen peptides across the cell membranes was shown. Pro-Hyp laterally condensed the membrane, resulting in an increase in the bilayer thickness and rigidity. Perception regarding molecular behaviors of collagen-derived peptides within the cell membrane, including their interactions, provides the novel design of specific bioactive collagen peptides for their applications.

Download Full-text

Molecular Dynamics Study of Microscopic Mechanism of Diffusion in Li2SiO3 System

Zeitschrift für Naturforschung A ◽

10.1515/zna-1991-0710 ◽

1991 ◽

Vol 46 (7) ◽

pp. 616-620 ◽

Cited By ~ 9

Author(s):

Junko Habasaki

Keyword(s):

Molecular Dynamics ◽

Coordination Number ◽

Md Simulation ◽

Mean Square Displacement ◽

Mean Square ◽

Lithium Ions ◽

Microscopic Mechanism ◽

Trapping Model ◽

The Mean

MD simulation has been performed to learn the microscopic mechanism of diffusion of ions in the Li2SiO3 system. The motion of lithium ions can be explained by the trapping model, where lithium is trapped in the polyhedron and moves with fluctuation of the coordination number. The mean square displacement of lithium was found to correlate well with the net changes in coordination number.

Download Full-text