Microscopic Motion Research Articles

Probing density waves in fluidized granular media with diffusing-wave spectroscopy.

Density waves are characteristic for fluidized beds and affect measurements on liquidlike dynamics in fluidized granular media. Here the intensity autocorrelation function as obtainable with diffusing-wave spectroscopy is derived in the presence of density waves. The predictions by the derived form of the intensity autocorrelation function match experimental observations from a gas-fluidized bed. The model suggests separability of the contribution from density waves from the contribution by microscopic scatterer displacement to the decay of correlation and thus paves the way for characterizing microscopic particle motions using diffusing-wave spectroscopy as well as heterogeneities in fluidized granular media.

Does intravoxel incoherent motion (IVIM) introduce a new biomarker in MRI?

Introduction Intravoxel Incoherent Motion (IVIM) imaging is a method that provides quantitative assessment all of the microscopic translational motions that could contribute to the signal acquired with diffusion weighted imaging (DWI) in MRI. The fundamental idea was that the molecular motion of water is randomly oriented in the capillary network at ultralow b values of diffusion imaging, mimicking a random walk. Diffusion parameters derived from IVIM model – perfusion F, true-ADC (D slow ), pseudo-ADC (D fast ) – have roused the researcher’s interest. Purpose The aim of this study is to quantify the IVIM model diffusion parameters in patients with brain lesions compared to the normal appearing symmetric regions of the brain. Materials and methods Patients underwent DWI on a 3T MRI system using an 8-channel sense head coil. DWI was performed with axial single-shot spin echo planar imaging (EPI) sequence with 10b values (0, 10, 15, 50, 80, 100, 200, 400, 700, 1000 s/mm 2 ). The IVIM model diffusion parameters of D slow , D fast and F were calculated using a biexponential curve fitting model based on Levenberg–Marquardt algorithm applied in an in-house platform in Matlab. The statistical analysis between contra lateral regions was based on Student’s t tests. Results Perfusion fraction F measured in brain damage regions showed significantly increased values compared to normal appearing symmetric regions. Parameters D slow and D fast had no statistical significance. Conclusion The F parameter may consist a new sensitive biomarker for providing additional information to conventional diffusion parameters and predicting preliminary brain damage.

A numerical study on magnetostrictive phenomena in magnetorheological elastomers

Herein, we present an investigation on magnetostrictive phenomena in magnetorheological elastomers. By using a continuum approach, constitutive as well as geometric properties on the microscale are taken into account in order to predict the effective behavior of these composites by means of a computational homogenization. Thus, the magnetic and mechanical fields are resolved explicitly without the simplifying assumption of dipoles. In the present work, a modeling strategy which accounts for elastic constituents and a nonlinear magnetization behavior of the particles is pursued. In order to provide a better understanding of fundamental deformation mechanisms, idealized lattices as well as compact and wavy chains are considered within a first study. Our results confirm assumptions stated in the literature according to which macroscopic magnetostriction can be ascribed to microscopic particle movements that result in an improved microstructure. The simulations that are performed for the subsequent investigations on random microstructures with different particle-volume fractions are evaluated statistically to ensure validity of our findings. They reveal anisotropic as well as isotropic macroscopic behavior for structured and unstructured particle distributions, respectively. In view of the macroscopic magnetostriction, all the results presented in this contribution are in good agreement with current experimental and theoretical findings.

Phase-field-crystal study on the reaction mechanisms of opposite sign edge dislocations appearing in the deformation processes of asymmetric tilt sub-grain boundary system

With phase-field-crystal method, the microscopic movement processes of asymmetric tilt sub-grain boundary system under applied stresses at high temperature are investigated. Reactions of opposite sign edge dislocations (OSEDs) gliding on the same and different slip planes are observed during the deformation processes. The reaction mechanisms of OSEDs are explored from the microstructure and energy perspectives. The simulation results show that OSEDs gliding on different slip planes can either annihilate or react into new perpendicular OSEDs. If the internal stress caused by the extra half-planes of edge dislocations in the region between different slip planes is in direction opposite to the applied stress, the free energy density (FED) curve has an obvious peak structure during the approaching process of dislocations. When FED achieves its maximum, new perpendicular OSEDs are generated. On the contrary, if the internal and applied stresses have the same direction, the FED curve changes gently without forming obvious peak structure. OSEDs annihilate.

Analysis of frequency domain dielectric response of pressboard insulation impregnated with different insulating liquids

This study investigates the influence of moisture, temperature and diverse oil properties on the frequency domain response of pressboard insulation samples, which are impregnated with four different insulating liquids including two commercially available natural esters, one synthetic ester and mineral oil. Measurements are performed over a wide frequency range from 0.1 mHz to 1 kHz at variable moisture contents and temperatures (35, 55 and 75°C). It has been found that dielectric response is extremely sensitive to moisture content regardless of the type of impregnated liquid. Furthermore, dielectric response behaviour of ester impregnated pressboard insulation is qualitatively resembles to that of mineral oil impregnated pressboard which contains two distinct relaxation processes including Quasi-DC (q-dc) conduction features at low frequencies, and loss peak behaviour at mid frequency range. This paper proposes that the loss peak arises due to cooperative microscopic motion in water cellulose mixed phase dipole clusters together with the microscopic level interfacial polarization occurring at the interface of oil filled cavities. It is also discussed the q-dc process in pressboard insulation due to the charge transport between water and oil cavity based charge clusters through a percolation network of water molecules and hydroxyl groups along the cellulose fiber wall. In order to provide better understanding on charge transport and polarization phenomena in oil impregnated pressboard insulation, this paper also proposes an equivalent circuit, which is mainly derived based on Dissado- Hill (DH) cluster framework theory. Furthermore, this study has used activation energy to characterize the temperature dependent dielectric response of pressboard impregnated in mineral oil, natural esters and synthetic esters.

Toward Improved Understanding of the Physical Meaning of Entropy in Classical Thermodynamics

The year 2015 marked the 150th anniversary of “entropy” as a concept in classical thermodynamics. Despite its central role in the mathematical formulation of the Second Law and most of classical thermodynamics, its physical meaning continues to be elusive and confusing. This is especially true when we seek a reconstruction of the classical thermodynamics of a system from the statistical behavior of its constituent microscopic particles or vice versa. This paper sketches the classical definition by Clausius and offers a modified mathematical definition that is intended to improve its conceptual meaning. In the modified version, the differential of specific entropy appears as a non-dimensional energy term that captures the invigoration or reduction of microscopic motion upon addition or withdrawal of heat from the system. It is also argued that heat transfer is a better model process to illustrate entropy; the canonical heat engines and refrigerators often used to illustrate this concept are not very relevant to new areas of thermodynamics (e.g., thermodynamics of biological systems). It is emphasized that entropy changes, as invoked in the Second Law, are necessarily related to the non-equilibrium interactions of two or more systems that might have initially been in thermal equilibrium but at different temperatures. The overall direction of entropy increase indicates the direction of naturally occurring heat transfer processes in an isolated system that consists of internally interacting (non-isolated) sub systems. We discuss the implication of the proposed modification on statements of the Second Law, interpretation of entropy in statistical thermodynamics, and the Third Law.

Microscopic Chain Motion in Polymer Nanocomposites with Dynamically Asymmetric Interphases.

Dynamics of the interphase region between matrix and bound polymers on nanoparticles is important to understand the macroscopic rheological properties of nanocomposites. Here, we present neutron scattering investigations on nanocomposites with dynamically asymmetric interphases formed by a high-glass transition temperature polymer, poly(methyl methacrylate), adsorbed on nanoparticles and a low-glass transition temperature miscible matrix, poly(ethylene oxide). By taking advantage of selective isotope labeling of the chains, we studied the role of interfacial polymer on segmental and collective dynamics of the matrix chains from subnanoseconds to 100 nanoseconds. Our results show that the Rouse relaxation remains unchanged in a weakly attractive composite system while the dynamics significantly slows down in a strongly attractive composite. More importantly, the chains disentangle with a remarkable increase of the reptation tube size when the bound polymer is vitreous. The glassy and rubbery states of the bound polymer as temperature changes underpin the macroscopic stiffening of nanocomposites.

Predicting vehicular emissions in high spatial resolution using pervasively measured transportation data and microscopic emissions model

Air pollution related to traffic emissions pose an especially significant problem in cities; this is due to its adverse impact on human health and well-being. Previous studies which have aimed to quantify emissions from the transportation sector have been limited by either simulated or coarsely resolved traffic volume data. Emissions inventories form the basis of urban pollution models, therefore in this study, Global Positioning System (GPS) trajectory data from a taxi fleet of over 15,000 vehicles were analyzed with the aim of predicting air pollution emissions for Singapore. This novel approach enabled the quantification of instantaneous drive cycle parameters in high spatio-temporal resolution, which provided the basis for a microscopic emissions model. Carbon dioxide (CO2), nitrogen oxides (NOx), volatile organic compounds (VOCs) and particulate matter (PM) emissions were thus estimated. Highly localized areas of elevated emissions levels were identified, with a spatio-temporal precision not possible with previously used methods for estimating emissions. Relatively higher emissions areas were mainly concentrated in a few districts that were the Singapore Downtown Core area, to the north of the central urban region and to the east of it. Daily emissions quantified for the total motor vehicle population of Singapore were found to be comparable to another emissions dataset. Results demonstrated that high-resolution spatio-temporal vehicle traces detected using GPS in large taxi fleets could be used to infer highly localized areas of elevated acceleration and air pollution emissions in cities, and may become a complement to traditional emission estimates, especially in emerging cities and countries where reliable fine-grained urban air quality data is not easily available. This is the first study of its kind to investigate measured microscopic vehicle movement in tandem with microscopic emissions modeling for a substantial study domain.

Simulation by using the lattice Boltzmann method of microscopic particle motion induced by artificial cilia

In this paper, we present the results obtained from the simulation of particle motion induced by the fluid flow driven by an array of beating artificial cilia inside a micro-channel. A worm-like-chain model is used to simulate the elastic cilia, and the lattice Boltzmann equation is used to compute the fluid flow. We employ a harmonic force at the extreme tip of each cilium to actuate it. Our simulation methods are first validated by applying them to the motion of a single cilium and a freely falling sphere. After validation, we simulate the fluid flow generated by an array of beating cilia and find that a maximum flow rate is achieved at an optimum sperm number. Next, we simulate the motion of a neutrally buoyant spherical particle at this optimum sperm number by tracking the particle motion with a smoothed profile method. We address the effect of the following parameters on the particle velocity: the gap between cilia and particle, the particle size, the cilia density, and the presence of an array of intermediate particles.

Phase-field model-based simulation of two-phase fluid motion on partially wetted and textured solid surface

The applicability of a numerical method is preliminarily examined to determine its suitability for simulations of microscopic immiscible liquid-liquid motion on solid walls, which is used for evaluating fluidic devices with heterogeneously wettable and textured surfaces. The method adopts a conservation-modified Allen-Cahn equation for calculations of diffuse-interface advection and formation based on a phase-field model, and a lattice-Boltzmann method is employed as numerical scheme for solving the two-phase fluid-dynamics equations. The simulations demonstrate the ability of the method to successfully capture the shape and motion of a droplet, not only on flat and grooved surfaces in a stagnant liquid under an external force, but also in a liquid flow inside a rectangular microchannel.

Microscopic Movement of Slow-Diffusing Nanoparticles in Cylindrical Nanopores Studied with Three-Dimensional Tracking.

To study slow mass transport in confined environments, we developed a three-dimensional (3D) single-particle localization technique to track their microscopic movements in cylindrical nanopores. Under two model conditions, particles are retained much longer inside the pores: (1) increased solvent viscosity, which slows down the particle throughout the whole pore, and (2) increased pore wall affinity, which slows down the particle only at the wall. In viscous solvents, the particle steps decrease proportionally to the increment of the viscosity, leading to macroscopically slow diffusion. As a contrast, the particles in sticky pores are microscopically active by showing limited reduction of step sizes. A restricted diffusion mode, possibly caused by the heterogeneous environment in sticky pores, is the main reason for macroscopically slow diffusion. This study shows that it is possible to differentiate slow diffusion in confined environments caused by different mechanisms.

Researchers watch biomolecules fold

As biomolecules such as DNA and proteins fold, they follow certain paths that take them from a disordered state to a folded one. These so-called folding transition paths are extremely brief, so researchers have not been able to analyze them directly by purely experimental methods. Michael T. Woodside of the University of Alberta and coworkers have now observed and measured biomolecular folding transition paths for the first time by direct experiment alone (Science 2016, DOI: 10.1126/science.aad0637). They used optical tweezers and force spectroscopy to observe the microscopic diffusive motions of a DNA hairpin and a prion protein dimer as they wiggled their way along folding paths. Optical tweezers use radiation pressure from a laser beam to grab hold of and move molecules, and force spectroscopy measures the molecular forces and displacements that result from those manipulations. The technique could help researchers classify different types of folding transition paths and uncover

High temperature breakdown of the Stokes-Einstein relation in a computer simulated Cu-Zr melt.

Transport properties and the Stokes-Einstein (SE) relation in liquid Cu8Zr3 are studied by molecular dynamics simulation with a modified embedded atom potential. The critical temperature Tc of mode coupling theory (MCT) is derived as 930 K from the self-diffusion coefficient D and viscosity η. The SE relation breaks down around TSE = 1900 K, which is far above Tc. At temperatures below TSE, the product of D and η fluctuates around a constant value, similar to the prediction of MCT near Tc. The influence of the microscopic atomic motion on macroscopic properties is investigated by analyzing the time dependent liquid structure and the self-hole filling process. The self-holes for the two components are preferentially filled by atoms of the same component. The self-hole filling dynamics explains the different breakdown behaviors of the SE relation in Zr-rich liquid CuZr2 compared to Cu-rich Cu8Zr3. At TSE, a kink is found in the temperature dependence of both partial and total coordination numbers for the three atomic pair combinations and of the typical time of self-hole filling. This indicates a strong correlation between liquid structure, atomic dynamics, and the breakdown of SE relation. The previously suggested usefulness of the parameter d(D1/D2)/dT to predict TSE is confirmed. Additionally we propose a viscosity criterion to predict TSE in the absence of diffusion data.

Identification of defect distribution at ferroelectric domain walls from evolution of nonlinear dielectric response during the aging process

Motion of ferroelectric domain walls greatly contributes to the macroscopic dielectric and piezoelectric response of ferroelectric materials. The domain wall motion through the ferroelectric material is however hindered by pinning on crystal defects which substantially reduces these contributions. Here, using thermodynamic models based on the Landau-Ginzburg-Devonshire theory, we find a relation between microscopic reversible motion of non-ferroelastic 180-degree domain walls interacting with a periodic array of pinning centers and the nonlinear macroscopic permittivity. We show, that the reversible motion of domain walls can be split into two basic modes. First, the bending of a domain wall between pinning centers, and, second, the uniform movement of domain wall plane. We show that their respective contributions may change when the distribution of pinning centers is rearranged during the material aging. We demonstrate that it is possible to indicate which mechanism of the domain wall motion is affected during material aging. This allows to judge whether the defects only homogeneously accumulate at domain walls or prefer to align in certain directions inside the domain wall plane. We suggest that this information can be obtained using simple macroscopic dielectric measurements and a proper analysis of the nonlinear response. Our results may therefore serve as a simple and useful tool to obtain details on domain wall pinning in an aging process.

Monocular microsaccades are visual-task related.

During visual fixation, we constantly move our eyes. These microscopic eye movements are composed of tremor, drift, and microsaccades. Early studies concluded that microsaccades, like larger saccades, are binocular and conjugate, as expected from Hering's law of equal innervation. Here, we document the existence of monocular microsaccades during both fixation and a discrimination task, reporting the location of the gap in a foveal, low-contrast letter C. Monocular microsaccades differ in frequency, amplitude, and peak velocity from binocular microsaccades. Our analyses show that these differences are robust to different velocity and duration criteria that have been used previously to identify microsaccades. Also, the frequency of monocular microsaccades differs systematically according to the task: monocular microsaccades occur more frequently during fixation than discrimination, the opposite of their binocular equivalents. However, during discrimination, monocular microsaccades occur more often around the discrimination threshold, particularly for each subject's dominant eye and in case of successful discrimination. We suggest that monocular microsaccades play a functional role in the production of fine corrections of eye position and vergence during demanding visual tasks.

Retrospective correction of involuntary microscopic head movement using highly accelerated fat image navigators (3D FatNavs) at 7T

PurposeThe goal of the present study was to use a three‐dimensional (3D) gradient echo volume in combination with a fat‐selective excitation as a 3D motion navigator (3D FatNav) for retrospective correction of microscopic head motion during high‐resolution 3D structural scans of extended duration. The fat excitation leads to a 3D image that is itself sparse, allowing high parallel imaging acceleration factors – with the additional advantage of a minimal disturbance of the water signal used for the host sequence.MethodsA 3D FatNav was inserted into two structural protocols: an inversion‐prepared gradient echo at 0.33 × 0.33 × 1.00 mm resolution and a turbo spin echo at 600 μm isotropic resolution.ResultsMotion estimation was possible with high precision, allowing retrospective motion correction to yield clear improvements in image quality, especially in the conspicuity of very small blood vessels.ConclusionThe highly accelerated 3D FatNav allowed motion correction with noticeable improvements in image quality, even for head motion which was small compared with the voxel dimensions of the host sequence. Magn Reson Med 75:1030–1039, 2016. © 2015 Wiley Periodicals, Inc.

Tracks to a Medical Diagnosis: Expertise Differences in Visual Problem Solving

SummaryThis study focuses on the visual problem‐solving process of clinical pathologists. Its aim is to find expertise‐related differences in the temporal arrangement of this process, with a special focus on the orientation phase. A theoretical model of the visual diagnostic process of medical specialists is extended with general problem‐solving theory. Participants were 13 experts, 12 intermediates, and 13 novices, who all diagnosed seven microscopic images. Their microscope movements and thinking aloud were recorded. To study temporal arrangement of the process, we applied a time‐grid to the data. The results reflected several aspects of general problem‐solving theory. Experts and intermediates showed a more extensive orientation phase and more refined schemata than novices. Intermediates also showed a control phase at the end of the diagnostic process. Novices showed a uniform process. These phases were reflected in microscope navigation and thinking aloud, which justifies the extension of the theoretical model.Copyright © 2016 John Wiley & Sons, Ltd.

Contraction limits of the proton-neutron symplectic model

The algebraic approach to nuclear structure physics allows a certain microscopic collective motion algebra to be also interpreted on macroscopic level which is achieved in the limit of large representation quantum numbers. Such limits are referred to as macroscopic or hydrodynamic limits and show how a given microscopic discrete system starts to behave like a continuous fluid. In the present paper, two contraction limits of the recently introduced fully microscopic proton-neutron symplectic model (PNSM) with the Sp(12; R) dynamical symmetry algebra are considered. As a result, two simplified macroscopic models of nuclear collective motion are obtained in simple geometrical terms. The first one is the U(6)-phonon model with the semi-direct product structure [HW(21)]U(6), which is shown to be actually an alternative formulation of the original proton-neutron symplectic model in the familiar IBM-terms. The second model which appears in double contraction limit is the two-rotor model with the ROTp(3) ⊗ ROTn(3) ⊃ ROT(3) algebraic structure. The latter, in contrast to the original two-rotor model, is not restricted to the case of two coupled axial rotors. In this way, the second contraction limit of the PNSM, provides the phenomenological two-rotor model with a simple microscopic foundation.

微細テクスチャ表面上での液滴挙動に関する拡散界面モデル数値シミュレーション

The applicability of a numerical method is preliminarily examined to determine its suitability for simulations of microscopic immiscible liquid-liquid motion on solid walls with textured surfaces, which is used for evaluating flexible large-area fluidic devices and a novel screen printing process. In the method, a conservation-modified Allen-Cahn equation is adopted for calculations of diffuse-interface advection and formation based on a phase-field model, and a lattice-Boltzmann method is employed as numerical scheme for solving the two-phase fluid-dynamics equations. The simulations demonstrate the ability of the method to successfully capture the shape and motion of a droplet, not only in a liquid flow inside a rectangular micro channel with linearly grooved wall, but also on wettable parallel-wall structured surface under capillary force.

Impact Analysis of Ecodriving Behaviour Using Suitable Simulation Platform (ICT-EMISSIONS Project)

Eco-driving is a way to drive that allow to use less fuel. To be eco-driver you need to follow a set of simple rules such as: upshifting to avoid engine speeds over 2500rpm, keep steady vehicle speed, anticipating traffic, accelerating and decelerating smoothly, and avoiding long idles.The promotion of an energy-efficient driving style is a measure that can have an important impact on fuel consumption.The eco-driving behaviour varies the attitude in setting speed and distance to the preceding vehicles. Speed and distance are parameters that influence, at the macroscopic level, the speed and density of traffic. To assess measure's impact at road network level we need to simulate, first the microscopic level movement of vehicles and then scale up in a suitable way the result to the macroscopic level.A suitable software platform has been developed using and enhancing the models adopted in the existing commercial tools in order to simulate traffic with drivers having different behaviour such as eco driver. The results shows that different behaviour, which imply different law for interaction between vehicle, can have different impact on emission when not a single vehicle is considered but the traffic on a real road network. Results show that Eco drive has more impact in free and normal traffic condition, but could be not useful when traffic condition is congested.