The Bumper Boats Effect: Effect of Inertia on Self Propelled Active Particles Systems

NASA Astrophysics Data System (ADS)

Dai, Chengyu; Bruss, Isaac; Glotzer, Sharon

Active matter has been well studied using the standard Brownian dynamics model, which assumes that the self-propelled particles have no inertia. However, many examples of active systems, such as sub-millimeter bacteria and colloids, have non-negligible inertia. Using particle-based Langevin Dynamics simulation with HOOMD-blue, we study the role of particle inertia on the collective emergent behavior of self-propelled particles. We find that inertia hinders motility-induced phase separation. This is because the effective speed of particles is reduced due to particle-particle collisions-\\x9Dmuch like bumper boats, which take time to reach terminal velocity after a crash. We are able to fully account for this effect by tracking a particle's average rather than terminal velocity, allowing us to extend the standard Brownian dynamics model to account for the effects of momentum. This study aims to inform experimental systems where the inertia of the active particles is non-negligible. We acknowledge the funding support from the Center for Bio-Inspired Energy Science (CBES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0000989.

Shear-banding and superdiffusivity in entangled polymer solutions

NASA Astrophysics Data System (ADS)

Shin, Seunghwan; Dorfman, Kevin D.; Cheng, Xiang

2017-12-01

Using high-resolution confocal rheometry, we study the shear profiles of well-entangled DNA solutions under large-amplitude oscillatory shear in a rectilinear planar shear cell. With increasing Weissenberg number (Wi), we observe successive transitions from normal Newtonian linear shear profiles to wall-slip dominant shear profiles and, finally, to shear-banding profiles at high Wi. To investigate the microscopic origin of the observed shear banding, we study the dynamics of micron-sized tracers embedded in DNA solutions. Surprisingly, tracer particles in the shear frame exhibit transient superdiffusivity and strong dynamic heterogeneity. The probability distribution functions of particle displacements follow a power-law scaling at large displacements, indicating a Lévy-walk-type motion, reminiscent of tracer dynamics in entangled wormlike micelle solutions and sheared colloidal glasses. We further characterize the length and time scales associated with the abnormal dynamics of tracer particles. We hypothesize that the unusual particle dynamics arise from localized shear-induced chain disentanglement.

Simulation of hydrodynamically interacting particles near a no-slip boundary

NASA Astrophysics Data System (ADS)

Swan, James W.; Brady, John F.

2007-11-01

The dynamics of spherical particles near a single plane wall are computed using an extension of the Stokesian dynamics method that includes long-range many-body and pairwise lubrication interactions between the spheres and the wall in Stokes flow. Extra care is taken to ensure that the mobility and resistance tensors are symmetric, positive, and definite—something which is ineluctable for particles in low-Reynolds-number flows. We discuss why two previous simulation methods for particles near a plane wall, one using multipole expansions and the other using the Rotne-Prager tensor, fail to produce symmetric resistance and mobility tensors. Additionally, we offer some insight on how the Stokesian dynamics paradigm might be extended to study the dynamics of particles in any confining geometry.

Modelling non-equilibrium secondary organic aerosol formation and evaporation with the aerosol dynamics, gas- and particle-phase chemistry kinetic multilayer model ADCHAM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roldin, P.; Eriksson, A. C.; Nordin, E. Z.

2014-08-11

We have developed the novel Aerosol Dynamics, gas- and particle- phase chemistry model for laboratory CHAMber studies (ADCHAM). The model combines the detailed gas phase Master Chemical Mechanism version 3.2, an aerosol dynamics and particle phase chemistry module (which considers acid catalysed oligomerization, heterogeneous oxidation reactions in the particle phase and non-ideal interactions between organic compounds, water and inorganic ions) and a kinetic multilayer module for diffusion limited transport of compounds between the gas phase, particle surface and particle bulk phase. In this article we describe and use ADCHAM to study: 1) the mass transfer limited uptake of ammonia (NH3)more » and formation of organic salts between ammonium (NH4+) and carboxylic acids (RCOOH), 2) the slow and almost particle size independent evaporation of α-pinene secondary organic aerosol (SOA) particles, and 3) the influence of chamber wall effects on the observed SOA formation in smog chambers.« less

Magnetic field induced dynamical chaos.

PubMed

Ray, Somrita; Baura, Alendu; Bag, Bidhan Chandra

2013-12-01

In this article, we have studied the dynamics of a particle having charge in the presence of a magnetic field. The motion of the particle is confined in the x-y plane under a two dimensional nonlinear potential. We have shown that constant magnetic field induced dynamical chaos is possible even for a force which is derived from a simple potential. For a given strength of the magnetic field, initial position, and velocity of the particle, the dynamics may be regular, but it may become chaotic when the field is time dependent. Chaotic dynamics is very often if the field is time dependent. Origin of chaos has been explored using the Hamiltonian function of the dynamics in terms of action and angle variables. Applicability of the present study has been discussed with a few examples.

Numerical simulations of the charged-particle flow dynamics for sources with a curved emission surface

NASA Astrophysics Data System (ADS)

Altsybeyev, V. V.

2016-12-01

The implementation of numerical methods for studying the dynamics of particle flows produced by pulsed sources is discussed. A particle tracking method with so-called gun iteration for simulations of beam dynamics is used. For the space charge limited emission problem, we suggest a Gauss law emission model for precise current-density calculation in the case of a curvilinear emitter. The results of numerical simulations of particle-flow formation for cylindrical bipolar diode and for diode with elliptical emitter are presented.

Dynamic analysis of geometrically non-linear three-dimensional beams under moving mass

NASA Astrophysics Data System (ADS)

Zupan, E.; Zupan, D.

2018-01-01

In this paper, we present a coupled dynamic analysis of a moving particle on a deformable three-dimensional frame. The presented numerical model is capable of considering arbitrary curved and twisted initial geometry of the beam and takes into account geometric non-linearity of the structure. Coupled with dynamic equations of the structure, the equations of moving particle are solved. The moving particle represents the dynamic load and varies the mass distribution of the structure and at the same time its path is adapting due to deformability of the structure. A coupled geometrically non-linear behaviour of beam and particle is studied. The equation of motion of the particle is added to the system of the beam dynamic equations and an additional unknown representing the coordinate of the curvilinear path of the particle is introduced. The specially designed finite-element formulation of the three-dimensional beam based on the weak form of consistency conditions is employed where only the boundary conditions are affected by the contact forces.

Rotational Brownian Dynamics simulations of clathrin cage formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ilie, Ioana M.; Briels, Wim J.; MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede

2014-08-14

The self-assembly of nearly rigid proteins into ordered aggregates is well suited for modeling by the patchy particle approach. Patchy particles are traditionally simulated using Monte Carlo methods, to study the phase diagram, while Brownian Dynamics simulations would reveal insights into the assembly dynamics. However, Brownian Dynamics of rotating anisotropic particles gives rise to a number of complications not encountered in translational Brownian Dynamics. We thoroughly test the Rotational Brownian Dynamics scheme proposed by Naess and Elsgaeter [Macromol. Theory Simul. 13, 419 (2004); Naess and Elsgaeter Macromol. Theory Simul. 14, 300 (2005)], confirming its validity. We then apply the algorithmmore » to simulate a patchy particle model of clathrin, a three-legged protein involved in vesicle production from lipid membranes during endocytosis. Using this algorithm we recover time scales for cage assembly comparable to those from experiments. We also briefly discuss the undulatory dynamics of the polyhedral cage.« less

Nanoparticle motion on the surface of drying droplets

NASA Astrophysics Data System (ADS)

Zhao, Mingfei; Yong, Xin

2018-03-01

Advances in solution-based printing and surface patterning techniques for additive manufacturing demand a clear understanding of particle dynamics in drying colloidal droplets and its relationship with deposit structure. Although the evaporation-driven deposition has been studied thoroughly for the particles dispersed in the bulk of the droplet, few investigations have focused on the particles strongly adsorbed to the droplet surface. We modeled the assembly and deposition of the surface-active particles in a drying sessile droplet with a pinned contact line by the multiphase lattice Boltzmann-Brownian dynamics method. The particle trajectory and its area density profile characterize the assembly dynamics and deposition pattern development during evaporation. While the bulk-dispersed particles continuously move to the contact line, forming the typical "coffee-ring" deposit, the interface-bound particles migrate first toward the apex and then to the contact line as the droplet dries out. To understand this unexpected behavior, we resolve the droplet velocity field both in the bulk and within the interfacial region. The simulation results agree well with the analytical solution for the Stokes flow inside an evaporating droplet. At different stages of evaporation, our study reveals that the competition between the tangential surface flow and the downward motion of the evaporating liquid-vapor interface governs the dynamics of the interface-bound particles. In particular, the interface displacement contributes to the particle motion toward the droplet apex in a short phase, while the outward advective flow prevails at the late stage of drying and carries the particles to the contact line. The final deposit of the surface-adsorbed particles exhibits a density enhancement at the center, in addition to a coffee ring. Despite its small influence on the final deposit in the present study, the distinct dynamics of surface-active particles due to the interfacial confinement could offer a new route to deposition control when combined with Marangoni effects.

Dynamics of many-body localization in the presence of particle loss

NASA Astrophysics Data System (ADS)

van Nieuwenburg, EPL; Yago Malo, J.; Daley, AJ; Fischer, MH

2018-01-01

At long times, residual couplings to the environment become relevant even in the most isolated experiments, a crucial difficulty for the study of fundamental aspects of many-body dynamics. A particular example is many-body localization in a cold-atom setting, where incoherent photon scattering introduces both dephasing and particle loss. Whereas dephasing has been studied in detail and is known to destroy localization already on the level of non-interacting particles, the effect of particle loss is less well understood. A difficulty arises due to the ‘non-local’ nature of the loss process, complicating standard numerical tools using matrix product decomposition. Utilizing symmetries of the Lindbladian dynamics, we investigate the particle loss on both the dynamics of observables, as well as the structure of the density matrix and the individual states. We find that particle loss in the presence of interactions leads to dissipation and a strong suppression of the (operator space) entanglement entropy. Our approach allows for the study of the interplay of dephasing and loss for pure and mixed initial states to long times, which is important for future experiments using controlled coupling of the environment.

Physical characteristics of cometary dust from dynamical studies - A review

NASA Technical Reports Server (NTRS)

Sekanina, Z.

1980-01-01

Progress made in the determination of the physical characteristics of cometary dust particles from studies of dust tail dynamics is reviewed. Applications of the combined dynamical photometric approach of Finson and Probstein (1968) to studies of cometary tails exhibiting continuous light intensity variations are discussed, with attention given to determinations of the particle-size-related distribution function of the solar radiation pressure exerted on the particles, the contribution of comets to the interplanetary dust, calculations of dust ejection rates and a Monte Carlo approach to the analysis of dust tails. Investigations of dust streamers and striae, which are believed to be related to comet outbursts entailing brief but sharp enhancements of dust production, are then reviewed, with particular attention given to observations of Comet West 1976 VI. Finally, the question of cometary particle type is addressed, and it is pointed out that the presence of submicron absorbing particles in the striae of Comet West is not incompatible with the presence of micron-size dielectric particles in the inner coma.

Detailed Studies on Flame Extinction by Inert Particles in Normal- and Micro-gravity

NASA Technical Reports Server (NTRS)

Andac, M. G.; Egolfopoulos, F. N.; Campbell, C. S.

2001-01-01

The combustion of dusty flows has been studied to lesser extent than pure gas phase flows and sprays. Particles can have a strong effect by modifying the dynamic response and detailed structure of flames through the dynamic, thermal, and chemical couplings between the two phases. A rigorous understanding of the dynamics and structure of two-phase flows can be attained in stagnation flow configurations, which have been used by others to study spray combustion as well as reacting dusty flows. In earlier studies on reacting dusty flows, the thermal coupling between the two phases as well as the effect of gravity on the flame response were not considered. However, in Ref. 6, the thermal coupling between chemically inert particles and the gas was addressed in premixed flames. The effects of gravity was also studied showing that it can substantially affect the profiles of the particle velocity, number density, mass flux, and temperature. The results showed a strong dynamic and thermal dependence of reacting dusty flows to particle number density. However, the work was only numerical and limited to twin-flames, stagnation, premixed flames. In Ref. 7 the effects of chemically inert particle clouds on the extinction of strained premixed and non-premixed flames were studied both experimentally and numerically at 1-g. It was shown and explained that large particles can cause more effective flame cooling compared to smaller particles. The effects of flame configuration and particle injection orientation were also addressed. The complexity of the coupling between the various parameters in such flows was demonstrated and it was shown that it was impossible to obtain a simple and still meaningful scaling that captured all the pertinent physics.

A centroid molecular dynamics study of liquid para-hydrogen and ortho-deuterium.

PubMed

Hone, Tyler D; Voth, Gregory A

2004-10-01

Centroid molecular dynamics (CMD) is applied to the study of collective and single-particle dynamics in liquid para-hydrogen at two state points and liquid ortho-deuterium at one state point. The CMD results are compared with the results of classical molecular dynamics, quantum mode coupling theory, a maximum entropy analytic continuation approach, pair-product forward- backward semiclassical dynamics, and available experimental results. The self-diffusion constants are in excellent agreement with the experimental measurements for all systems studied. Furthermore, it is shown that the method is able to adequately describe both the single-particle and collective dynamics of quantum liquids. (c) 2004 American Institute of Physics

Stochastic dynamics of coupled active particles in an overdamped limit

NASA Astrophysics Data System (ADS)

Ann, Minjung; Lee, Kong-Ju-Bock; Park, Pyeong Jun

2015-10-01

We introduce a model for Brownian dynamics of coupled active particles in an overdamped limit. Our system consists of several identical active particles and one passive particle. Each active particle is elastically coupled to the passive particle and there is no direct coupling among the active particles. We investigate the dynamics of the system with respect to the number of active particles, viscous friction, and coupling between the active and passive particles. For this purpose, we consider an intracellular transport process as an application of our model and perform a Brownian dynamics simulation using realistic parameters for processive molecular motors such as kinesin-1. We determine an adequate energy conversion function for molecular motors and study the dynamics of intracellular transport by multiple motors. The results show that the average velocity of the coupled system is not affected by the number of active motors and that the stall force increases linearly as the number of motors increases. Our results are consistent with well-known experimental observations. We also examine the effects of coupling between the motors and the cargo, as well as of the spatial distribution of the motors around the cargo. Our model might provide a physical explanation of the cooperation among active motors in the cellular transport processes.

Dynamic Simulation of Random Packing of Polydispersive Fine Particles

NASA Astrophysics Data System (ADS)

Ferraz, Carlos Handrey Araujo; Marques, Samuel Apolinário

2018-02-01

In this paper, we perform molecular dynamic (MD) simulations to study the two-dimensional packing process of both monosized and random size particles with radii ranging from 1.0 to 7.0 μm. The initial positions as well as the radii of five thousand fine particles were defined inside a rectangular box by using a random number generator. Both the translational and rotational movements of each particle were considered in the simulations. In order to deal with interacting fine particles, we take into account both the contact forces and the long-range dispersive forces. We account for normal and static/sliding tangential friction forces between particles and between particle and wall by means of a linear model approach, while the long-range dispersive forces are computed by using a Lennard-Jones-like potential. The packing processes were studied assuming different long-range interaction strengths. We carry out statistical calculations of the different quantities studied such as packing density, mean coordination number, kinetic energy, and radial distribution function as the system evolves over time. We find that the long-range dispersive forces can strongly influence the packing process dynamics as they might form large particle clusters, depending on the intensity of the long-range interaction strength.

Kinetics of the chiral phase transition in a linear σ model

NASA Astrophysics Data System (ADS)

Wesp, Christian; van Hees, Hendrik; Meistrenko, Alex; Greiner, Carsten

2018-02-01

We study the dynamics of the chiral phase transition in a linear quark-meson σ model using a novel approach based on semiclassical wave-particle duality. The quarks are treated as test particles in a Monte Carlo simulation of elastic collisions and the coupling to the σ meson, which is treated as a classical field, via a kinetic approach motivated by wave-particle duality. The exchange of energy and momentum between particles and fields is described in terms of appropriate Gaussian wave packets. It has been demonstrated that energy-momentum conservation and the principle of detailed balance are fulfilled, and that the dynamics leads to the correct equilibrium limit. First schematic studies of the dynamics of matter produced in heavy-ion collisions are presented.

Equivalence of Brownian dynamics and dynamic Monte Carlo simulations in multicomponent colloidal suspensions.

PubMed

Cuetos, Alejandro; Patti, Alessandro

2015-08-01

We propose a simple but powerful theoretical framework to quantitatively compare Brownian dynamics (BD) and dynamic Monte Carlo (DMC) simulations of multicomponent colloidal suspensions. By extending our previous study focusing on monodisperse systems of rodlike colloids, here we generalize the formalism described there to multicomponent colloidal mixtures and validate it by investigating the dynamics in isotropic and liquid crystalline phases containing spherical and rodlike particles. In order to investigate the dynamics of multicomponent colloidal systems by DMC simulations, it is key to determine the elementary time step of each species and establish a unique timescale. This is crucial to consistently study the dynamics of colloidal particles with different geometry. By analyzing the mean-square displacement, the orientation autocorrelation functions, and the self part of the van Hove correlation functions, we show that DMC simulation is a very convenient and reliable technique to describe the stochastic dynamics of any multicomponent colloidal system. Our theoretical formalism can be easily extended to any colloidal system containing size and/or shape polydisperse particles.

Structure and Dynamics of Bimodal Colloidal Dispersions in a Low-Molecular-Weight Polymer Solution

DOE PAGES

Zhang, Fan; Allen, Andrew J.; Levine, Lyle E.; ...

2017-02-24

We present an experimental study of the structural and dynamical properties of bimodal, micrometersized colloidal dispersions (size ratio ≈ 2) in an aqueous solution of low-molecular weight polymer (polyethylene glycol 2000) using synchrotron ultra-small angle X-ray scattering (USAXS) and USAXSbased X-ray photon correlation spectroscopy. We fixed the volume fraction of the large particles at 5 % and systematically increased the volume fraction of the small particles from 0 % to 5 % to evaluate its effect on the structure and dynamics. The bimodal dispersions were homogenous through the investigated parameter space. We found that the partial structure factors can bemore » satisfactorily retrieved for the bimodal colloidal dispersions using a Percus-Yevick hard sphere potential when the particle size distributions of the particles were taken into account. We also found that the partial structure factor between the large particles does not exhibit significant variation with increasing volume fraction of small particles, whereas the isothermal compressibility of the binary mixture was found to decrease with increasing volume fraction of small particles. The dynamics of single-component large particle dispersion obey the principles of de Gennes narrowing, where the wave vector dependence of the interparticle diffusion coefficient is inversely proportional to the interparticle structure factor. The dynamics of the bimodal dispersions demonstrate strong dependence on the fraction of small particles. As a result, we also made a comparison between the experimental effective dynamic viscosity of the bimodal dispersion with theoretical predictions, which suggest that the complex mutual interactions between large and small particles have a strong effect on the dynamic behaviors of bimodal dispersions.« less

Structure and Dynamics of Bimodal Colloidal Dispersions in a Low-Molecular-Weight Polymer Solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Fan; Allen, Andrew J.; Levine, Lyle E.

We present an experimental study of the structural and dynamical properties of bimodal, micrometersized colloidal dispersions (size ratio ≈ 2) in an aqueous solution of low-molecular weight polymer (polyethylene glycol 2000) using synchrotron ultra-small angle X-ray scattering (USAXS) and USAXSbased X-ray photon correlation spectroscopy. We fixed the volume fraction of the large particles at 5 % and systematically increased the volume fraction of the small particles from 0 % to 5 % to evaluate its effect on the structure and dynamics. The bimodal dispersions were homogenous through the investigated parameter space. We found that the partial structure factors can bemore » satisfactorily retrieved for the bimodal colloidal dispersions using a Percus-Yevick hard sphere potential when the particle size distributions of the particles were taken into account. We also found that the partial structure factor between the large particles does not exhibit significant variation with increasing volume fraction of small particles, whereas the isothermal compressibility of the binary mixture was found to decrease with increasing volume fraction of small particles. The dynamics of single-component large particle dispersion obey the principles of de Gennes narrowing, where the wave vector dependence of the interparticle diffusion coefficient is inversely proportional to the interparticle structure factor. The dynamics of the bimodal dispersions demonstrate strong dependence on the fraction of small particles. As a result, we also made a comparison between the experimental effective dynamic viscosity of the bimodal dispersion with theoretical predictions, which suggest that the complex mutual interactions between large and small particles have a strong effect on the dynamic behaviors of bimodal dispersions.« less

CFD modeling of particle dispersion and deposition coupled with particle dynamical models in a ventilated room

NASA Astrophysics Data System (ADS)

Xu, Guangping; Wang, Jiasong

2017-10-01

Two dynamical models, the traditional method of moments coupled model (MCM) and Taylor-series expansion method of moments coupled model (TECM) for particle dispersion distribution and gravitation deposition are developed in three-dimensional ventilated environments. The turbulent airflow field is modeled with the renormalization group (RNG) k-ε turbulence model. The particle number concentration distribution in a ventilated room is obtained by solving the population balance equation coupled with the airflow field. The coupled dynamical models are validated using experimental data. A good agreement between the numerical and experimental results can be achieved. Both models have a similar characteristic for the spatial distribution of particle concentration. Relative to the MCM model, the TECM model presents a more close result to the experimental data. The vortex structure existed in the air flow makes a relative large concentration difference at the center region and results in a spatial non-uniformity of concentration field. With larger inlet velocity, the mixing level of particles in the room is more uniform. In general, the new dynamical models coupled with computational fluid dynamics (CFD) in the current study provide a reasonable and accurate method for the temporal and spatial evolution of particles effected by the deposition and dispersion behaviors. In addition, two ventilation modes with different inlet velocities are proceeded to study the effect on the particle evolution. The results show that with the ceiling ventilation mode (CVM), the particles can be better mixed and the concentration level is also higher. On the contrast, with the side ceiling ventilation mode (SVM), the particle concentration has an obvious stratified distribution with a relative lower level and it makes a much better environment condition to the human exposure.

Structure and Dynamics of Interacting Nanoparticles in Semidilute Polymer Solutions

DOE PAGES

Pollng-Skutvik, Ryan; Mongcopa, Katrina Irene S.; Faraone, Antonio; ...

2016-08-17

We investigate the structure and dynamics of silica nanoparticles and polymer chains in semidilute solutions of high molecular weight polystyrene in 2-butanone to determine the effect of long-range interparticle interactions on the coupling between particle and polymer dynamics. Particles at concentrations of 1–10 wt % are well dispersed in the semidilute polymer solutions and exhibit long-range electrostatic repulsions between particles. Because the particles are comparably sized to the radius of gyration of the polymer, the particle dynamics is predicted to couple to that of the polymer. We verify that the polymer structure and dynamics are not significantly affected by themore » particles, indicating that the particle–polymer coupling does not change with increasing particle loading. We find that the coupling between the dynamics of comparably sized particles and polymer results in subdiffusive particle dynamics, as expected. Over the interparticle distance, however, the particle dynamics is hindered and not fully described by the relaxation of the surrounding polymer chains. Instead, the particle dynamics is inversely related to the structure factor, suggesting that physical particle–polymer coupling on short length scales and interparticle interactions on long length scales both present energetic barriers to particle motion that lead to subdiffusive dynamics and de Gennes narrowing, respectively.« less

Non-Extensive Statistical Analysis of Solar Wind Electric, Magnetic Fields and Solar Energetic Particle time series.

NASA Astrophysics Data System (ADS)

Pavlos, G. P.; Malandraki, O.; Khabarova, O.; Livadiotis, G.; Pavlos, E.; Karakatsanis, L. P.; Iliopoulos, A. C.; Parisis, K.

2017-12-01

In this work we study the non-extensivity of Solar Wind space plasma by using electric-magnetic field data obtained by in situ spacecraft observations at different dynamical states of solar wind system especially in interplanetary coronal mass ejections (ICMEs), Interplanetary shocks, magnetic islands, or near the Earth Bow shock. Especially, we study the energetic particle non extensive fractional acceleration mechanism producing kappa distributions as well as the intermittent turbulence mechanism producing multifractal structures related with the Tsallis q-entropy principle. We present some new and significant results concerning the dynamics of ICMEs observed in the near Earth at L1 solar wind environment, as well as its effect in Earth's magnetosphere as well as magnetic islands. In-situ measurements of energetic particles at L1 are analyzed, in response to major solar eruptive events at the Sun (intense flares, fast CMEs). The statistical characteristics are obtained and compared for the Solar Energetic Particles (SEPs) originating at the Sun, the energetic particle enhancements associated with local acceleration during the CME-driven shock passage over the spacecraft (Energetic Particle Enhancements, ESPs) as well as the energetic particle signatures observed during the passage of the ICME. The results are referred to Tsallis non-extensive statistics and in particular to the estimation of Tsallis q-triplet, (qstat, qsen, qrel) of electric-magnetic field and the kappa distributions of solar energetic particles time series of the ICME, magnetic islands, resulting from the solar eruptive activity or the internal Solar Wind dynamics. Our results reveal significant differences in statistical and dynamical features, indicating important variations of the magnetic field dynamics both in time and space domains during the shock event, in terms of rate of entropy production, relaxation dynamics and non-equilibrium meta-stable stationary states.

Experimental studies of tuned particle damper: Design and characterization

NASA Astrophysics Data System (ADS)

Zhang, Kai; Xi, Yanhui; Chen, Tianning; Ma, Zhihao

2018-01-01

To better suppress the structural vibration in the micro vibration and harsh environment, a new type of damper, tuned particle damper (TPD), was designed by combining the advantage of classical dynamic vibration absorber (DVA) and particle damper (PD). An equivalent theoretical model was established to describe the dynamic behavior of a cantilever system treated with TPD. By means of a series of sine sweep tests, the dynamic characteristic of TPD under different excitation intensity was explored and the damping performance of TPD was investigated by comparing with classical DVA and PD with the same mass ratio. Experimental results show that with the increasing of excitation intensity TPD shows two different dynamic characteristics successively, i.e., PD-like and DVA-like. TPD shows a wider suppression frequency band than classical DVA and better practicability than PD in the micro vibration environment. Moreover, to characterize the dynamic characteristic of TPD, a simple evaluation of the equivalent dynamic mass and equivalent dynamic damping of the cantilever system treated with TPD was performed by fitting the experimental data to the presented theoretical model. Finally, based on the rheology behaviors of damping particles reported by the previous research results, an approximate phase diagram which shows the motion states of damping particles in TPD was employed to analyze the dynamic characteristic of TPD and several motion states of damping particles in TPD were presented via a high-speed camera.

Collective Surfing of Chemically Active Particles

NASA Astrophysics Data System (ADS)

Masoud, Hassan; Shelley, Michael J.

2014-03-01

We study theoretically the collective dynamics of immotile particles bound to a 2D surface atop a 3D fluid layer. These particles are chemically active and produce a chemical concentration field that creates surface-tension gradients along the surface. The resultant Marangoni stresses create flows that carry the particles, possibly concentrating them. For a 3D diffusion-dominated concentration field and Stokesian fluid we show that the surface dynamics of active particle density can be determined using nonlocal 2D surface operators. Remarkably, we also show that for both deep or shallow fluid layers this surface dynamics reduces to the 2D Keller-Segel model for the collective chemotactic aggregation of slime mold colonies. Mathematical analysis has established that the Keller-Segel model can yield finite-time, finite-mass concentration singularities. We show that such singular behavior occurs in our finite-depth system, and study the associated 3D flow structures.

An experimental study on particle effects in liquid sheets

NASA Astrophysics Data System (ADS)

Sauret, Alban; Troger, Anthony; Jop, Pierre

2017-06-01

Many industrial processes, such as surface coating or liquid transport in tubes, involve liquid sheets or thin films of suspensions. In these situations, the thickness of the liquid film becomes comparable to the particle size, which leads to unexpected dynamics. In addition, the classical constitutive rheological law for suspensions cannot be applied as the continuum approximation is no longer valid. Here, we consider experimentally a transient particle-laden liquid sheet that expands radially. We characterize the influence of the particles on the shape of the liquid film and the atomization process. We highlight that the presence of particles modifies the thickness and stability of the liquid sheet. Our study suggests that the influence of particles through capillary effects can modify significantly the dynamics of processes that involve suspensions and particles confined in liquid films.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ballouz, Ronald-Louis; Richardson, Derek C.; Morishima, Ryuji

We study the B ring’s complex optical depth structure. The source of this structure may be the complex dynamics of the Keplerian shear and the self-gravity of the ring particles. The outcome of these dynamic effects depends sensitively on the collisional and physical properties of the particles. Two mechanisms can emerge that dominate the macroscopic physical structure of the ring: self-gravity wakes and viscous overstability. Here we study the interplay between these two mechanisms by using our recently developed particle collision method that allows us to better model the inter-particle contact physics. We find that for a constant ring surfacemore » density and particle internal density, particles with rough surfaces tend to produce axisymmetric ring features associated with the viscous overstability, while particles with smoother surfaces produce self-gravity wakes.« less

Nonlinear dynamics optimization with particle swarm and genetic algorithms for SPEAR3 emittance upgrade

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Xiaobiao; Safranek, James

2014-09-01

Nonlinear dynamics optimization is carried out for a low emittance upgrade lattice of SPEAR3 in order to improve its dynamic aperture and Touschek lifetime. Two multi-objective optimization algorithms, a genetic algorithm and a particle swarm algorithm, are used for this study. The performance of the two algorithms are compared. The result shows that the particle swarm algorithm converges significantly faster to similar or better solutions than the genetic algorithm and it does not require seeding of good solutions in the initial population. These advantages of the particle swarm algorithm may make it more suitable for many accelerator optimization applications.

Structure and Dynamics of Bimodal Colloidal Dispersions in a Low-Molecular-Weight Polymer Solution.

PubMed

Zhang, Fan; Allen, Andrew J; Levine, Lyle E; Tsai, De-Hao; Ilavsky, Jan

2017-03-21

We present an experimental study of the structural and dynamical properties of bimodal, micrometer-sized colloidal dispersions (size ratio ≈ 2) in an aqueous solution of low-molecular-weight polymer (polyethylene glycol 2000) using synchrotron ultra-small angle X-ray scattering (USAXS) and USAXS-based X-ray photon correlation spectroscopy. We fixed the volume fraction of the large particles at 5% and systematically increased the volume fraction of the small particles from 0 to 5% to evaluate their effects on the structure and dynamics. The bimodal dispersions were homogenous through the investigated parameter space. We found that the partial structure factors can be satisfactorily retrieved for the bimodal colloidal dispersions using a Percus-Yevick hard-sphere potential when the size distributions of the particles were taken into account. We also found that the partial structure factor between the large particles did not exhibit a significant variation with increasing volume fraction of the small particles, whereas the isothermal compressibility of the binary mixture was found to decrease with increasing volume fraction of the small particles. The dynamics of single-component large-particle dispersion obey the principles of de Gennes narrowing, where the wave vector dependence of the interparticle diffusion coefficient is inversely proportional to the interparticle structure factor. The dynamics of the bimodal dispersions demonstrate a strong dependence on the fraction of small particles. We also made a comparison between the experimental effective dynamic viscosity of the bimodal dispersion with the theoretical predictions, which suggest that the complex mutual interactions between the large and small particles have a strong effect on the dynamic behaviors of bimodal dispersions.

Nonlinear dynamics of resonant electrons interacting with coherent Langmuir waves

NASA Astrophysics Data System (ADS)

Tobita, Miwa; Omura, Yoshiharu

2018-03-01

We study the nonlinear dynamics of resonant particles interacting with coherent waves in space plasmas. Magnetospheric plasma waves such as whistler-mode chorus, electromagnetic ion cyclotron waves, and hiss emissions contain coherent wave structures with various discrete frequencies. Although these waves are electromagnetic, their interaction with resonant particles can be approximated by equations of motion for a charged particle in a one-dimensional electrostatic wave. The equations are expressed in the form of nonlinear pendulum equations. We perform test particle simulations of electrons in an electrostatic model with Langmuir waves and a non-oscillatory electric field. We solve equations of motion and study the dynamics of particles with different values of inhomogeneity factor S defined as a ratio of the non-oscillatory electric field intensity to the wave amplitude. The simulation results demonstrate deceleration/acceleration, thermalization, and trapping of particles through resonance with a single wave, two waves, and multiple waves. For two-wave and multiple-wave cases, we describe the wave-particle interaction as either coherent or incoherent based on the probability of nonlinear trapping.

Marangoni-driven chemotaxis, chemotactic collapse, and the Keller-Segel equation

NASA Astrophysics Data System (ADS)

Shelley, Michael; Masoud, Hassan

2013-11-01

Almost by definition, chemotaxis involves the biased motion of motile particles along gradients of a chemical concentration field. Perhaps the most famous model for collective chemotaxis in mathematical biology is the Keller-Segel model, conceived to describe collective aggregation of slime mold colonies in response to an intrinsically produced, and diffusing, chemo-attractant. Heavily studied, particularly in 2D where the system is ``super-critical'', it has been proved that the KS model can develop finite-time singularities - so-called chemotactic collapse - of delta-function type. Here, we study the collective dynamics of immotile particles bound to a 2D interface above a 3D fluid. These particles are chemically active and produce a diffusing field that creates surface-tension gradients along the surface. The resultant Marangoni stresses create flows that carry the particles, possibly concentrating them. Remarkably, we show that this system involving 3D diffusion and fluid dynamics, exactly yields the 2D Keller-Segel model for the surface-flow of active particles. We discuss the consequences of collapse on the 3D fluid dynamics, and generalizations of the fluid-dynamical model.

Fluidization of spherocylindrical particles

NASA Astrophysics Data System (ADS)

Mahajan, Vinay V.; Nijssen, Tim M. J.; Fitzgerald, Barry W.; Hofman, Jeroen; Kuipers, Hans; Padding, Johan T.

2017-06-01

Multiphase (gas-solid) flows are encountered in numerous industrial applications such as pharmaceutical, food, agricultural processing and energy generation. A coupled computational fluid dynamics (CFD) and discrete element method (DEM) approach is a popular way to study such flows at a particle scale. However, most of these studies deal with spherical particles while in reality, the particles are rarely spherical. The particle shape can have significant effect on hydrodynamics in a fluidized bed. Moreover, most studies in literature use inaccurate drag laws because accurate laws are not readily available. The drag force acting on a non-spherical particle can vary considerably with particle shape, orientation with the flow, Reynolds number and packing fraction. In this work, the CFD-DEM approach is extended to model a laboratory scale fluidized bed of spherocylinder (rod-like) particles. These rod-like particles can be classified as Geldart D particles and have an aspect ratio of 4. Experiments are performed to study the particle flow behavior in a quasi-2D fluidized bed. Numerically obtained results for pressure drop and bed height are compared with experiments. The capability of CFD-DEM approach to efficiently describe the global bed dynamics for fluidized bed of rod-like particles is demonstrated.

Dynamics and interactions of particles in a thermophoretic trap

NASA Astrophysics Data System (ADS)

Foster, Benjamin; Fung, Frankie; Fieweger, Connor; Usatyuk, Mykhaylo; Gaj, Anita; DeSalvo, B. J.; Chin, Cheng

2017-08-01

We investigate dynamics and interactions of particles levitated and trapped by the thermophoretic force in a vacuum cell. Our analysis is based on footage taken by orthogonal cameras that are able to capture the three dimensional trajectories of the particles. In contrast to spherical particles, which remain stationary at the center of the cell, here we report new qualitative features of the motion of particles with non-spherical geometry. Singly levitated particles exhibit steady spinning around their body axis and rotation around the symmetry axis of the cell. When two levitated particles approach each other, repulsive or attractive interactions between the particles are observed. Our levitation system offers a wonderful platform to study interaction between particles in a microgravity environment.

Dynamic of particle-laden liquid sheet

NASA Astrophysics Data System (ADS)

Sauret, Alban; Jop, Pierre; Troger, Anthony

2016-11-01

Many industrial processes, such as surface coating or liquid transport in tubes, involve liquid sheets or thin liquid films of suspensions. In these situations, the thickness of the liquid film becomes comparable to the particle size, which leads to unexpected dynamics. In addition, the classical constitutive rheological law cannot be applied as the continuum approximation is no longer valid. Here, we consider experimentally a transient free liquid sheet that expands radially. We characterize the influence of the particles on the shape of the liquid film as a function of time and the atomization process. We highlight that the presence of particles modifies the thickness and the stability of the liquid sheet. Our study suggests that the influence of particles through capillary effects can modify significantly the dynamics of processes that involve suspensions and particles confined in liquid films.

Reynolds-number-dependent dynamical transitions on hydrodynamic synchronization modes of externally driven colloids

NASA Astrophysics Data System (ADS)

Oyama, Norihiro; Teshigawara, Kosuke; Molina, John Jairo; Yamamoto, Ryoichi; Taniguchi, Takashi

2018-03-01

The collective dynamics of externally driven Np-colloidal systems (1 ≤Np≤4 ) in a confined viscous fluid have been investigated using three-dimensional direct numerical simulations with fully resolved hydrodynamics. The dynamical modes of collective particle motion are studied by changing the particle Reynolds number as determined by the strength of the external driving force and the confining wall distance. For a system with Np=3 , we found that at a critical Reynolds number a dynamical mode transition occurs from the doublet-singlet mode to the triplet mode, which has not been reported experimentally. The dynamical mode transition was analyzed in detail from the following two viewpoints: (1) spectrum analysis of the time evolution of a tagged particle velocity and (2) the relative acceleration of the doublet cluster with respect to the singlet particle. For a system with Np=4 , we found similar dynamical mode transitions from the doublet-singlet-singlet mode to the triplet-singlet mode and further to the quartet mode.

Reynolds-number-dependent dynamical transitions on hydrodynamic synchronization modes of externally driven colloids.

PubMed

Oyama, Norihiro; Teshigawara, Kosuke; Molina, John Jairo; Yamamoto, Ryoichi; Taniguchi, Takashi

2018-03-01

The collective dynamics of externally driven N_{p}-colloidal systems (1≤N_{p}≤4) in a confined viscous fluid have been investigated using three-dimensional direct numerical simulations with fully resolved hydrodynamics. The dynamical modes of collective particle motion are studied by changing the particle Reynolds number as determined by the strength of the external driving force and the confining wall distance. For a system with N_{p}=3, we found that at a critical Reynolds number a dynamical mode transition occurs from the doublet-singlet mode to the triplet mode, which has not been reported experimentally. The dynamical mode transition was analyzed in detail from the following two viewpoints: (1) spectrum analysis of the time evolution of a tagged particle velocity and (2) the relative acceleration of the doublet cluster with respect to the singlet particle. For a system with N_{p}=4, we found similar dynamical mode transitions from the doublet-singlet-singlet mode to the triplet-singlet mode and further to the quartet mode.

Lipid membrane-assisted condensation and assembly of amphiphilic Janus particles

DOE PAGES

Chambers, Mariah; Mallory, Stewart Anthony; Malone, Heather; ...

2016-01-01

Amphiphilic Janus particles self-assemble into complex metastructures, but little is known about how their assembly might be modified by weak interactions with a nearby biological membrane surface. Here, we report an integrated experimental and molecular dynamics simulation study to investigate the self-assembly of amphiphilic Janus particles on a lipid membrane. We created an experimental system in which Janus particles are allowed to self-assemble in the same medium where zwitterionic lipids form giant unilamellar vesicles (GUVs). Janus particles spontaneously concentrated on the inner leaflet of the GUVs. They exhibited biased orientation and heterogeneous rotational dynamics as revealed by single particle rotationalmore » tracking. The combined experimental and simulation results show that Janus particles concentrate on the lipid membranes due to weak particle–lipid attraction, whereas the biased orientation of particles is driven predominantly by inter-particle interactions. Furthermore, this study demonstrates the potential of using lipid membranes to influence the self-assembly of Janus particles.« less

DEM study of the size-induced segregation dynamics of a ternary-size granular mixture in the rolling-regime rotating drum

NASA Astrophysics Data System (ADS)

Yang, Shiliang; Zhang, Liangqi; Luo, Kun; Chew, Jia Wei

2017-12-01

Segregation induced by size, shape, or density difference of the granular material is inevitable in both natural and industrial processes; unfortunately, the underlying mechanism is still not fully understood. In view of the ubiquitous continuous particle size distributions, this study builds on the considerable knowledge gained so far from binary-size mixtures and extends it to a ternary-size mixture to understand the impact of the presence of a third particle size in the three-dimensional rotating drum operating in the rolling flow regime. The discrete element method is employed. The evolution of segregation, the active-passive interface, and the dynamical response of the particle-scale characteristics of the different particle types in the two regions are investigated. The results reveal that the medium particles are spatially sandwiched in between the large and small particles in both the radial and axial directions and therefore exhibit behaviors intermediate to the other two particle types. Compared to the binary-size mixture, the presence of the medium particles leads to (i) higher purity of small particles in the innermost of the radial core, causing a decrease of the translational velocity of small particles; (ii) decrease and increase of the collision forces exerted on, respectively, the large and small particles in both regions; and (iii) increase in the relative ratio of the active-passive exchange rates of small to large particles. The results obtained in the current study therefore provide valuable insights regarding the size-segregation dynamics of granular mixtures with constituents of different sizes.

Simulating coupled dynamics of a rigid-flexible multibody system and compressible fluid

NASA Astrophysics Data System (ADS)

Hu, Wei; Tian, Qiang; Hu, HaiYan

2018-04-01

As a subsequent work of previous studies of authors, a new parallel computation approach is proposed to simulate the coupled dynamics of a rigid-flexible multibody system and compressible fluid. In this approach, the smoothed particle hydrodynamics (SPH) method is used to model the compressible fluid, the natural coordinate formulation (NCF) and absolute nodal coordinate formulation (ANCF) are used to model the rigid and flexible bodies, respectively. In order to model the compressible fluid properly and efficiently via SPH method, three measures are taken as follows. The first is to use the Riemann solver to cope with the fluid compressibility, the second is to define virtual particles of SPH to model the dynamic interaction between the fluid and the multibody system, and the third is to impose the boundary conditions of periodical inflow and outflow to reduce the number of SPH particles involved in the computation process. Afterwards, a parallel computation strategy is proposed based on the graphics processing unit (GPU) to detect the neighboring SPH particles and to solve the dynamic equations of SPH particles in order to improve the computation efficiency. Meanwhile, the generalized-alpha algorithm is used to solve the dynamic equations of the multibody system. Finally, four case studies are given to validate the proposed parallel computation approach.

Multiscale Particle-Based Modeling of Flowing Platelets in Blood Plasma Using Dissipative Particle Dynamics and Coarse Grained Molecular Dynamics

PubMed Central

Zhang, Peng; Gao, Chao; Zhang, Na; Slepian, Marvin J.; Deng, Yuefan; Bluestein, Danny

2014-01-01

We developed a multiscale particle-based model of platelets, to study the transport dynamics of shear stresses between the surrounding fluid and the platelet membrane. This model facilitates a more accurate prediction of the activation potential of platelets by viscous shear stresses - one of the major mechanisms leading to thrombus formation in cardiovascular diseases and in prosthetic cardiovascular devices. The interface of the model couples coarse-grained molecular dynamics (CGMD) with dissipative particle dynamics (DPD). The CGMD handles individual platelets while the DPD models the macroscopic transport of blood plasma in vessels. A hybrid force field is formulated for establishing a functional interface between the platelet membrane and the surrounding fluid, in which the microstructural changes of platelets may respond to the extracellular viscous shear stresses transferred to them. The interaction between the two systems preserves dynamic properties of the flowing platelets, such as the flipping motion. Using this multiscale particle-based approach, we have further studied the effects of the platelet elastic modulus by comparing the action of the flow-induced shear stresses on rigid and deformable platelet models. The results indicate that neglecting the platelet deformability may overestimate the stress on the platelet membrane, which in turn may lead to erroneous predictions of the platelet activation under viscous shear flow conditions. This particle-based fluid-structure interaction multiscale model offers for the first time a computationally feasible approach for simulating deformable platelets interacting with viscous blood flow, aimed at predicting flow induced platelet activation by using a highly resolved mapping of the stress distribution on the platelet membrane under dynamic flow conditions. PMID:25530818

Chaos and nonlinear dynamics of single-particle orbits in a magnetotaillike magnetic field

NASA Technical Reports Server (NTRS)

Chen, J.; Palmadesso, P. J.

1986-01-01

The properties of charged-particle motion in Hamiltonian dynamics are studied in a magnetotaillike magnetic field configuration. It is shown by numerical integration of the equation of motion that the system is generally nonintegrable and that the particle motion can be classified into three distinct types of orbits: bounded integrable orbits, unbounded stochastic orbits, and unbounded transient orbits. It is also shown that different regions of the phase space exhibit qualitatively different responses to external influences. The concept of 'differential memory' in single-particle distributions is proposed. Physical implications for the dynamical properties of the magnetotail plasmas and the possible generation of non-Maxwellian features in the distribution functions are discussed.

Particle Interactions Mediated by Dynamical Networks: Assessment of Macroscopic Descriptions

NASA Astrophysics Data System (ADS)

Barré, J.; Carrillo, J. A.; Degond, P.; Peurichard, D.; Zatorska, E.

2018-02-01

We provide a numerical study of the macroscopic model of Barré et al. (Multiscale Model Simul, 2017, to appear) derived from an agent-based model for a system of particles interacting through a dynamical network of links. Assuming that the network remodeling process is very fast, the macroscopic model takes the form of a single aggregation-diffusion equation for the density of particles. The theoretical study of the macroscopic model gives precise criteria for the phase transitions of the steady states, and in the one-dimensional case, we show numerically that the stationary solutions of the microscopic model undergo the same phase transitions and bifurcation types as the macroscopic model. In the two-dimensional case, we show that the numerical simulations of the macroscopic model are in excellent agreement with the predicted theoretical values. This study provides a partial validation of the formal derivation of the macroscopic model from a microscopic formulation and shows that the former is a consistent approximation of an underlying particle dynamics, making it a powerful tool for the modeling of dynamical networks at a large scale.

Particle Interactions Mediated by Dynamical Networks: Assessment of Macroscopic Descriptions.

PubMed

Barré, J; Carrillo, J A; Degond, P; Peurichard, D; Zatorska, E

2018-01-01

We provide a numerical study of the macroscopic model of Barré et al. (Multiscale Model Simul, 2017, to appear) derived from an agent-based model for a system of particles interacting through a dynamical network of links. Assuming that the network remodeling process is very fast, the macroscopic model takes the form of a single aggregation-diffusion equation for the density of particles. The theoretical study of the macroscopic model gives precise criteria for the phase transitions of the steady states, and in the one-dimensional case, we show numerically that the stationary solutions of the microscopic model undergo the same phase transitions and bifurcation types as the macroscopic model. In the two-dimensional case, we show that the numerical simulations of the macroscopic model are in excellent agreement with the predicted theoretical values. This study provides a partial validation of the formal derivation of the macroscopic model from a microscopic formulation and shows that the former is a consistent approximation of an underlying particle dynamics, making it a powerful tool for the modeling of dynamical networks at a large scale.

Magnetotail particle dynamics and transport

NASA Technical Reports Server (NTRS)

Speiser, Theodore W.

1995-01-01

The main thrust of our research is to study the consequences of particle dynamics in the current sheet region of the magnetotail. The importance of understanding particle dynamics, in and near current sheets, cannot be over estimated, especially in light of NASA's recent interest in developing global circulation models to predict space weather. We have embarked on a long-term study to investigate the electrical resistance due to chaotic behavior, compare this resistance to inertial effects, and relate it to that resistance required in MHD modeling for reconnection to proceed. Using a single-particle model and observations, we have also found that a neutral line region can be remotely sensed. We plan to evaluate other cases of satellite observations near times of substorm onset to elucidate the relationship between the temporal development of a near-Earth neutral line and onset.

Transport properties and efficiency of elastically coupled particles in asymmetric periodic potentials

NASA Astrophysics Data System (ADS)

Igarashi, Akito; Tsukamoto, Shinji

2000-02-01

Biological molecular motors drive unidirectional transport and transduce chemical energy to mechanical work. In order to identify this energy conversion which is a common feature of molecular motors, many workers have studied various physical models, which consist of Brownian particles in spatially periodic potentials. Most of the models are, however, based on "single-particle" dynamics and too simple as models for biological motors, especially for actin-myosin motors, which cause muscle contraction. In this paper, particles coupled by elastic strings in an asymmetric periodic potential are considered as a model for the motors. We investigate the dynamics of the model and calculate the efficiency of energy conversion with the use of molecular dynamical method. In particular, we find that the velocity and efficiency of the elastically coupled particles where the natural length of the springs is incommensurable with the period of the periodic potential are larger than those of the corresponding single particle model.

A size-composition resolved aerosol model for simulating the dynamics of externally mixed particles: SCRAM (v 1.0)

NASA Astrophysics Data System (ADS)

Zhu, S.; Sartelet, K. N.; Seigneur, C.

2015-06-01

The Size-Composition Resolved Aerosol Model (SCRAM) for simulating the dynamics of externally mixed atmospheric particles is presented. This new model classifies aerosols by both composition and size, based on a comprehensive combination of all chemical species and their mass-fraction sections. All three main processes involved in aerosol dynamics (coagulation, condensation/evaporation and nucleation) are included. The model is first validated by comparison with a reference solution and with results of simulations using internally mixed particles. The degree of mixing of particles is investigated in a box model simulation using data representative of air pollution in Greater Paris. The relative influence on the mixing state of the different aerosol processes (condensation/evaporation, coagulation) and of the algorithm used to model condensation/evaporation (bulk equilibrium, dynamic) is studied.

Dynamic facilitation explains 'democratic' particle motion of metabasin transitions

NASA Astrophysics Data System (ADS)

Hedges, Lester O.; Garrahan, Juan P.

2008-08-01

Transitions between metabasins in supercooled liquids seem to occur through rapid collective particle rearrangements. These events have been called 'democratic' as they appear homogeneous over a significant number of particles. This could suggest that 'democratic' rearrangements are fundamentally distinct to those leading to dynamic heterogeneity. Here we show, however, that this apparent homogeneous particle motion can be explained solely in terms of dynamic facilitation, and is therefore intriniscally heterogeneous. We do so by studying metabasin transitions in facilitated spin models and constrained lattice gases. We find that metabasin transitions occur through a sequence of locally facilitated events taking place over a relatively short time frame. When observed on small enough spatial windows these events appear sudden and homogeneous. Our results indicate that metabasin transitions, while apparently homogeneous and 'democratic', are yet another manifestation of dynamical heterogeneity in glass formers.

Novel changes in discoidal high density lipoprotein morphology: a molecular dynamics study.

PubMed

Catte, Andrea; Patterson, James C; Jones, Martin K; Jerome, W Gray; Bashtovyy, Denys; Su, Zhengchang; Gu, Feifei; Chen, Jianguo; Aliste, Marcela P; Harvey, Stephen C; Li, Ling; Weinstein, Gilbert; Segrest, Jere P

2006-06-15

ApoA-I is a uniquely flexible lipid-scavenging protein capable of incorporating phospholipids into stable particles. Here we report molecular dynamics simulations on a series of progressively smaller discoidal high density lipoprotein particles produced by incremental removal of palmitoyloleoylphosphatidylcholine via four different pathways. The starting model contained 160 palmitoyloleoylphosphatidylcholines and a belt of two antiparallel amphipathic helical lipid-associating domains of apolipoprotein (apo) A-I. The results are particularly compelling. After a few nanoseconds of molecular dynamics simulation, independent of the starting particle and method of size reduction, all simulated double belts of the four lipidated apoA-I particles have helical domains that impressively approximate the x-ray crystal structure of lipid-free apoA-I, particularly between residues 88 and 186. These results provide atomic resolution models for two of the particles produced by in vitro reconstitution of nascent high density lipoprotein particles. These particles, measuring 95 angstroms and 78 angstroms by nondenaturing gradient gel electrophoresis, correspond in composition and in size/shape (by negative stain electron microscopy) to the simulated particles with molar ratios of 100:2 and 50:2, respectively. The lipids of the 100:2 particle family form minimal surfaces at their monolayer-monolayer interface, whereas the 50:2 particle family displays a lipid pocket capable of binding a dynamic range of phospholipid molecules.

Novel Changes in Discoidal High Density Lipoprotein Morphology: A Molecular Dynamics Study

PubMed Central

Catte, Andrea; Patterson, James C.; Jones, Martin K.; Jerome, W. Gray; Bashtovyy, Denys; Su, Zhengchang; Gu, Feifei; Chen, Jianguo; Aliste, Marcela P.; Harvey, Stephen C.; Li, Ling; Weinstein, Gilbert; Segrest, Jere P.

2006-01-01

ApoA-I is a uniquely flexible lipid-scavenging protein capable of incorporating phospholipids into stable particles. Here we report molecular dynamics simulations on a series of progressively smaller discoidal high density lipoprotein particles produced by incremental removal of palmitoyloleoylphosphatidylcholine via four different pathways. The starting model contained 160 palmitoyloleoylphosphatidylcholines and a belt of two antiparallel amphipathic helical lipid-associating domains of apolipoprotein (apo) A-I. The results are particularly compelling. After a few nanoseconds of molecular dynamics simulation, independent of the starting particle and method of size reduction, all simulated double belts of the four lipidated apoA-I particles have helical domains that impressively approximate the x-ray crystal structure of lipid-free apoA-I, particularly between residues 88 and 186. These results provide atomic resolution models for two of the particles produced by in vitro reconstitution of nascent high density lipoprotein particles. These particles, measuring 95 Å and 78 Å by nondenaturing gradient gel electrophoresis, correspond in composition and in size/shape (by negative stain electron microscopy) to the simulated particles with molar ratios of 100:2 and 50:2, respectively. The lipids of the 100:2 particle family form minimal surfaces at their monolayer-monolayer interface, whereas the 50:2 particle family displays a lipid pocket capable of binding a dynamic range of phospholipid molecules. PMID:16581834

Detailed Studies on the Structure and Dynamics of Reacting Dusty Flows at Normal and Microgravity

NASA Technical Reports Server (NTRS)

Andac, M. Gurhan; Cracchiola, Brad; Egolfopoulos, Fokion N.; Campbell, Charles S.

1999-01-01

Dusty reacting flows are of particular interest for a wide range of applications. Inert particles can alter the flammability and extinction limits of a combustible mixture. Reacting particles can release substantial amount of heat and can be used either for power generation or propulsion. Accumulation of combustible particles in air can result in explosions which, for example, can occur in grain elevators, during lumber milling and in mine galleries. Furthermore, inert particles are used as flow velocity markers in reacting flows, and their velocity is measured by non-intrusive laser diagnostic techniques. Despite their importance, dusty reacting flows have been less studied and understood compared to gas phase as well as sprays. The addition of solid particles in a flowing gas stream can lead to strong couplings between the two phases, which can be of dynamic, thermal, and chemical nature. The dynamic coupling between the two phases is caused by the inertia that causes the phases to move with different velocities. Furthermore, gravitational, thermophoretic, photophoretic, electrophoretic, diffusiophoretic, centrifugal, and magnetic forces can be exerted on the particles. In general, magnetic, electrophoretic, centrifugal, photophoretic, and diffusiophoretic can be neglected. On the other hand, thermophoretic forces, caused by steep temperature gradients, can be important. The gravitational forces are almost always present and can affect the dynamic response of large particles. Understanding and quantifying the chemical coupling between two phases is a challenging task. However, all reacting particles begin this process as inert particles, and they must be heated before they participate in the combustion process. Thus, one must first understand the interactions of inert particles in a combustion environment. The in-detail understanding of the dynamics and structure of dusty flows can be only advanced by considering simple flow geometries such as the opposed-jet, stagnation-type. In such configurations the imposed strain rate is well characterized, and the in-depth understanding of the details of the physico-chemical processes can be systematically obtained. A number of computational and experimental studies on spray and particle flows have been conducted in stagnation-type configurations. Numerically, the need for a hybrid Eulerian-Lagrangian approach has been identified by Continillo and Sirignano, and the use of such approach has allowed for the prediction of the phenomenon of droplet flow reversal. Gomez and Rosner have conducted a detailed study on the particle response in the opposed-jet configuration, and the particle thermophoretic diffusivities were determined experimentally. Sung, Law and co-workers have conducted numerical studies on the effect of strain rate and temperature gradients on the dynamics of inert particles, as a way of understanding potential errors in experimental LDV data that may arise from thermophoretic forces. This investigation is a combined experimental and numerical study on the details of reacting dusty flows. The specific tasks are: (1) Experimental determination of laminar flame speeds, and extinction strain rates of dusty flows at normal- and micro-gravity as functions of the particle type, particle initial diameter, particle initial number density, and gas phase chemical composition; (2) Detailed numerical simulation of the experiments. Results are compared with experiments and the adequacy of theoretical models is assessed; and (3) Provision of enhanced insight into the thermo-chemical coupling between the two phases.

Molecular dynamic simulation of weakly magnetized complex plasmas

NASA Astrophysics Data System (ADS)

Funk, Dylan; Konopka, Uwe; Thomas, Edward

2017-10-01

A complex plasma consists of the usual plasma components (electrons, ions and neutrals), as well as a heavier component made of solid, micrometer-sized particles. The particles are in general highly charged as a result of the interaction with the other plasma components. The static and dynamic properties of a complex plasma such as its crystal structure or wave properties are influenced by many forces acting on the individual particles such as the dust particle interaction (a screened Coulomb interaction), neutral (Epstein) drag, the particle inertia and various plasma drag or thermophoretic forces. To study the behavior of complex plasmas we setup an experiment accompanying molecular dynamic simulation. We will present the approach taken in our simulation and give an overview of experimental situations that we want to cover with our simulation such as the particle charge under microgravity condition as performed on the PK-4 space experiment, or to study the detailed influences of high magnetic fields. This work was supported by the US Dept. of Energy (DE-SC0016330), NSF (PHY-1613087) and JPL/NASA (JPL-RSA 1571699).

Dynamic self-assembly of charged colloidal strings and walls in simple fluid flows.

PubMed

Abe, Yu; Zhang, Bo; Gordillo, Leonardo; Karim, Alireza Mohammad; Francis, Lorraine F; Cheng, Xiang

2017-02-22

Colloidal particles can self-assemble into various ordered structures in fluid flows that have potential applications in biomedicine, materials synthesis and encryption. These dynamic processes are also of fundamental interest for probing the general principles of self-assembly under non-equilibrium conditions. Here, we report a simple microfluidic experiment, where charged colloidal particles self-assemble into flow-aligned 1D strings with regular particle spacing near a solid boundary. Using high-speed confocal microscopy, we systematically investigate the influence of flow rates, electrostatics and particle polydispersity on the observed string structures. By studying the detailed dynamics of stable flow-driven particle pairs, we quantitatively characterize interparticle interactions. Based on the results, we construct a simple model that explains the intriguing non-equilibrium self-assembly process. Our study shows that the colloidal strings arise from a delicate balance between attractive hydrodynamic coupling and repulsive electrostatic interaction between particles. Finally, we demonstrate that, with the assistance of transverse electric fields, a similar mechanism also leads to the formation of 2D colloidal walls.

Reactive multi-particle collision dynamics with reactive boundary conditions

NASA Astrophysics Data System (ADS)

Sayyidmousavi, Alireza; Rohlf, Katrin

2018-07-01

In the present study, an off-lattice particle-based method called the reactive multi-particle collision (RMPC) dynamics is extended to model reaction-diffusion systems with reactive boundary conditions in which the a priori diffusion coefficient of the particles needs to be maintained throughout the simulation. To this end, the authors have made use of the so-called bath particles whose purpose is only to ensure proper diffusion of the main particles in the system. In order to model partial adsorption by a reactive boundary in the RMPC, the probability of a particle being adsorbed, once it hits the boundary, is calculated by drawing an analogy between the RMPC and Brownian Dynamics. The main advantages of the RMPC compared to other molecular based methods are less computational cost as well as conservation of mass, energy and momentum in the collision and free streaming steps. The proposed approach is tested on three reaction-diffusion systems and very good agreement with the solutions to their corresponding partial differential equations is observed.

Effect of finite particle number sampling on baryon number fluctuations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steinheimer, Jan; Koch, Volker

The effects of finite particle number sampling on the net baryon number cumulants, extracted from fluid dynamical simulations, are studied. The commonly used finite particle number sampling procedure introduces an additional Poissonian (or multinomial if global baryon number conservation is enforced) contribution which increases the extracted moments of the baryon number distribution. If this procedure is applied to a fluctuating fluid dynamics framework, one severely overestimates the actual cumulants. We show that the sampling of so-called test particles suppresses the additional contribution to the moments by at least one power of the number of test particles. We demonstrate this methodmore » in a numerical fluid dynamics simulation that includes the effects of spinodal decomposition due to a first-order phase transition. Furthermore, in the limit where antibaryons can be ignored, we derive analytic formulas which capture exactly the effect of particle sampling on the baryon number cumulants. These formulas may be used to test the various numerical particle sampling algorithms.« less

A parallel direct-forcing fictitious domain method for simulating microswimmers

NASA Astrophysics Data System (ADS)

Gao, Tong; Lin, Zhaowu

2017-11-01

We present a 3D parallel direct-forcing fictitious domain method for simulating swimming micro-organisms at small Reynolds numbers. We treat the motile micro-swimmers as spherical rigid particles using the ``Squirmer'' model. The particle dynamics are solved on the moving Larangian meshes that overlay upon a fixed Eulerian mesh for solving the fluid motion, and the momentum exchange between the two phases is resolved by distributing pseudo body-forces over the particle interior regions which constrain the background fictitious fluids to follow the particle movement. While the solid and fluid subproblems are solved separately, no inner-iterations are required to enforce numerical convergence. We demonstrate the accuracy and robustness of the method by comparing our results with the existing analytical and numerical studies for various cases of single particle dynamics and particle-particle interactions. We also perform a series of numerical explorations to obtain statistical and rheological measurements to characterize the dynamics and structures of Squirmer suspensions. NSF DMS 1619960.

Effect of finite particle number sampling on baryon number fluctuations

DOE PAGES

Steinheimer, Jan; Koch, Volker

2017-09-28

The effects of finite particle number sampling on the net baryon number cumulants, extracted from fluid dynamical simulations, are studied. The commonly used finite particle number sampling procedure introduces an additional Poissonian (or multinomial if global baryon number conservation is enforced) contribution which increases the extracted moments of the baryon number distribution. If this procedure is applied to a fluctuating fluid dynamics framework, one severely overestimates the actual cumulants. We show that the sampling of so-called test particles suppresses the additional contribution to the moments by at least one power of the number of test particles. We demonstrate this methodmore » in a numerical fluid dynamics simulation that includes the effects of spinodal decomposition due to a first-order phase transition. Furthermore, in the limit where antibaryons can be ignored, we derive analytic formulas which capture exactly the effect of particle sampling on the baryon number cumulants. These formulas may be used to test the various numerical particle sampling algorithms.« less

Dynamic cross correlation studies of wave particle interactions in ULF phenomena

NASA Technical Reports Server (NTRS)

Mcpherron, R. L.

1979-01-01

Magnetic field observations made by satellites in the earth's magnetic field reveal a wide variety of ULF waves. These waves interact with the ambient particle populations in complex ways, causing modulation of the observed particle fluxes. This modulation is found to be a function of species, pitch angle, energy and time. The characteristics of this modulation provide information concerning the wave mode and interaction process. One important characteristic of wave-particle interactions is the phase of the particle flux modulation relative to the magnetic field variations. To display this phase as a function of time a dynamic cross spectrum program has been developed. The program produces contour maps in the frequency time plane of the cross correlation coefficient between any particle flux time series and the magnetic field vector. This program has been utilized in several studies of ULF wave-particle interactions at synchronous orbit.

Size-Dependent Particle Dynamics in Entangled Polymer Nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mangal, Rahul; Srivastava, Samanvaya; Narayanan, Suresh

Polymer-grafted nanoparticles with diameter d homogeneously dispersed in entangled polymer melts with varying random coil radius R0, but fixed entanglement mesh size ae, are used to study particle motions in entangled polymers. We focus on materials in the transition region between the continuum regime (d > R0), where the classical Stokes-Einstein (S-E) equation is known to describe polymer drag on particles, and the non-continuum regime (d < ae), in which several recent studies report faster diffusion of particles than expected from continuum S-E analysis, based on the bulk polymer viscosity. Specifically, we consider dynamics of particles with sizes d ≥more » ae in entangled polymers with varying molecular weight Mw in order to investigate how the transition from non-continuum to continuum dynamics occur. We take advantage of favorable enthalpic interactions between SiO2 nanoparticles tethered with PEO molecules and entangled PMMA host polymers to create model nanoparticle-polymer composites, in which spherical nanoparticles are uniformly dispersed in entangled polymers. Investigation of the particle dynamics via X-ray photon correlation spectroscopy measurements reveal a transition from fast to slow particle motion as the PMMA molecular weight is increased beyond the entanglement threshold, with a much weaker Mw dependence for Mw>Me than expected from S-E analysis based on bulk viscosity of entangled PMMA melts. We rationalize these observations using a simple force balance analysis around particles and find that nanoparticle motion in entangled melts can be described using a variant of the S-E analysis in which motion of particles is assumed to only disturb sub-chain entangled host segments with sizes comparable to the particle diameter.« less

Size-Dependent Particle Dynamics in Entangled Polymer Nanocomposites.

PubMed

Mangal, Rahul; Srivastava, Samanvaya; Narayanan, Suresh; Archer, Lynden A

2016-01-19

Polymer-grafted nanoparticles with diameter d homogeneously dispersed in entangled polymer melts with varying random coil radius R0, but fixed entanglement mesh size a(e), are used to study particle motions in entangled polymers. We focus on materials in the transition region between the continuum regime (d > R0), where the classical Stokes-Einstein (S-E) equation is known to describe polymer drag on particles, and the noncontinuum regime (d < a(e)), in which several recent studies report faster diffusion of particles than expected from continuum S-E analysis, based on the bulk polymer viscosity. Specifically, we consider dynamics of particles with sizes d ≥ a(e) in entangled polymers with varying molecular weight M(w) in order to investigate how the transition from noncontinuum to continuum dynamics occur. We take advantage of favorable enthalpic interactions between SiO2 nanoparticles tethered with PEO molecules and entangled PMMA host polymers to create model nanoparticle-polymer composites, in which spherical nanoparticles are uniformly dispersed in entangled polymers. Investigation of the particle dynamics via X-ray photon correlation spectroscopy measurements reveals a transition from fast to slow particle motion as the PMMA molecular weight is increased beyond the entanglement threshold, with a much weaker M(w) dependence for M(w) > M(e) than expected from S-E analysis based on bulk viscosity of entangled PMMA melts. We rationalize these observations using a simple force balance analysis around particles and find that nanoparticle motion in entangled melts can be described using a variant of the S-E analysis in which motion of particles is assumed to only disturb subchain entangled host segments with sizes comparable to the particle diameter.

Fluid and particle transport of a hairy structure

NASA Astrophysics Data System (ADS)

Lee, Hongki; Lahooti, Mohsen; Kim, Daegyoum; Jung, Seyeong

2017-11-01

Hairy appendages of animals are used to capture particles, sense surrounding flow, and generate propulsive force. Due to the small size of the hairy structures, their hydrodynamics have been studied mostly in very low Reynolds number. In this work, in a broad range of Reynolds number, O(1) - O(100), flow structure and inertial particle dynamics around an array of two-dimensional cylinders are investigated numerically by using an immersed boundary method. Given flow fields, Maxey-Riley equation is adopted to examine particle dynamics. Here, we discuss the effects of Reynolds number, density ratio of inertial particles and fluid, and distance between cylinders on particle behaviors around a moving structure. In addition, drift volume of inertial particles is correlated with the model parameters.

The van Hove distribution function for Brownian hard spheres: Dynamical test particle theory and computer simulations for bulk dynamics

NASA Astrophysics Data System (ADS)

Hopkins, Paul; Fortini, Andrea; Archer, Andrew J.; Schmidt, Matthias

2010-12-01

We describe a test particle approach based on dynamical density functional theory (DDFT) for studying the correlated time evolution of the particles that constitute a fluid. Our theory provides a means of calculating the van Hove distribution function by treating its self and distinct parts as the two components of a binary fluid mixture, with the "self " component having only one particle, the "distinct" component consisting of all the other particles, and using DDFT to calculate the time evolution of the density profiles for the two components. We apply this approach to a bulk fluid of Brownian hard spheres and compare to results for the van Hove function and the intermediate scattering function from Brownian dynamics computer simulations. We find good agreement at low and intermediate densities using the very simple Ramakrishnan-Yussouff [Phys. Rev. B 19, 2775 (1979)] approximation for the excess free energy functional. Since the DDFT is based on the equilibrium Helmholtz free energy functional, we can probe a free energy landscape that underlies the dynamics. Within the mean-field approximation we find that as the particle density increases, this landscape develops a minimum, while an exact treatment of a model confined situation shows that for an ergodic fluid this landscape should be monotonic. We discuss possible implications for slow, glassy, and arrested dynamics at high densities.

Snap-in of particles at curved liquid interfaces

NASA Astrophysics Data System (ADS)

Li, Chao; Moradiafrapoli, Momene; Marston, Jeremy

2016-11-01

The contact of particles with liquid interfaces constitutes the first stage in the formation of a particle-laden interface, the so-called "snap-in effect". Here, we report on an experimental study using high-speed video to directly visualize the snap-in process and the approach to the equilibrium state of a particle at a curved liquid interface (i.e. droplet surface). We image the evolution of the contact line, which is found to follow a power-law scaling in time, and the dynamic contact angle during the snap-in. Both hydrophilic and hydrophobic particles are explored and we match the lift-off stage of the particles with a simple force balance. We also explore some multi-particle experiments, eluding to the dynamics of particle-laden interface formation.

Dielectric resonator: cavity-enhanced optical manipulation in the near field

NASA Astrophysics Data System (ADS)

Reece, Peter J.; Wright, Ewan; Garcés-Chávez, Veneranda; Dholakia, Kishan

2006-08-01

In the following paper we explore the dynamics of single colloidal particles and particle aggregates in a counterpropagating cavity-enhanced evanescent wave optical trap. For this study we make use of Fabry-Perot like cavity modes generated in a prism-coupled resonant dielectric waveguide. The advantage of using this type of optical structure is that there is an enhancement in the electric field of the evanescent at the sample surface that may be used to achieve greater coupling to colloidal particles for the purposes of optical micromanipulation. We demonstrate an order of magnitude increase in the optical forces acting on micrometer sized colloidal particles using cavity enhanced evanescent waves, compared with evanescent wave produced by conventional prism-coupling techniques. The combination of the enhanced optical interaction and the wide area illumination provided by the prism coupler makes it an ideal geometry for studying the collective dynamics of many particles over a large area. We study the different type of ordering observed when particles of different sizes are accumulated at the centre of this novel optical trap. We find that for large particles sizes (greater than 2μm), colloid dynamics are primarily driven by thermodynamics, whilst for smaller particles, in the range of 200-600nm, particles ordering is dictated by optical-matter interactions. We suggest a qualitative model for the observed optically induced ordering occurs and discuss how these results tie in with existing demonstrations of twodimensional optical binding.

Capturing inertial particle transport in turbulent flows

NASA Astrophysics Data System (ADS)

Stott, Harry; Lawrie, Andrew; Szalai, Robert

2017-11-01

The natural world is replete with examples of particle advection; mankind is both a beneficiary from and sufferer of the consequences. As such, the study of inertial particle dynamics, both aerosol and bubble, is vitally important. In many interesting examples such as cloud microphysics, sedimentation, or sewage transport, many millions of particles are advected in a relatively small volume of fluid. It is impossible to model these processes computationally and simulate every particle. Instead, we advect the probability density field of particle positions allowing unbiased sampling of particle behaviour across the domain. Given a 3-dimensional space discretised into cubes, we construct a transport operator that encodes the flow of particles through the faces of the cubes. By assuming that the dynamics of the particles lie close to an inertial manifold, it is possible to preserve the majority of the inertial properties of the particles between the time steps. We demonstrate the practical use of this method in a pair of instances: the first is an analogue to cloud microphysics- the turbulent breakdown of Taylor Green vortices; the second example is the case of a turbulent jet which has application both in sewage pipe outflow and pesticide spray dynamics. EPSRC.

Single-Particle Quantum Dynamics in a Magnetic Lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Venturini, Marco

2001-02-01

We study the quantum dynamics of a spinless charged-particle propagating through a magnetic lattice in a transport line or storage ring. Starting from the Klein-Gordon equation and by applying the paraxial approximation, we derive a Schroedinger-like equation for the betatron motion. A suitable unitary transformation reduces the problem to that of a simple harmonic oscillator. As a result we are able to find an explicit expression for the particle wavefunction.

Effects of Turbulence on Settling Velocities of Synthetic and Natural Particles

NASA Astrophysics Data System (ADS)

Jacobs, C.; Jendrassak, M.; Gurka, R.; Hackett, E. E.

2014-12-01

For large-scale sediment transport predictions, an important parameter is the settling or terminal velocity of particles because it plays a key role in determining the concentration of sediment particles within the water column as well as the deposition rate of particles onto the seabed. The settling velocity of particles is influenced by the fluid dynamic environment as well as attributes of the particle, such as its size, shape, and density. This laboratory study examines the effects of turbulence, generated by an oscillating grid, on both synthetic and natural particles for a range of flow conditions. Because synthetic particles are spherical, they serve as a reference for the natural particles that are irregular in shape. Particle image velocimetry (PIV) and high-speed imaging systems were used simultaneously to study the interaction between the fluid mechanics and sediment particles' dynamics in a tank. The particles' dynamics were analyzed using a custom two-dimensional tracking algorithm used to obtain distributions of the particle's velocity and acceleration. Turbulence properties, such as root-mean-square turbulent velocity and vorticity, were calculated from the PIV data. Results are classified by Stokes number, which was based-on the integral scale deduced from the auto-correlation function of velocity. We find particles with large Stokes numbers are unaffected by the turbulence, while particles with small Stokes numbers primarily show an increase in settling velocity in comparison to stagnant flow. The results also show an inverse relationship between Stokes number and standard deviation of the settling velocity. This research enables a better understanding of the interdependence between particles and turbulent flow, which can be used to improve parameterizations in large-scale sediment transport models.

Structure and Entanglement Factors on Dynamics of Polymer-Grafted Nanoparticles

DOE PAGES

Liu, Siqi; Senses, Erkan; Jiao, Yang; ...

2016-04-15

Nanoparticles functionalized with long polymer chains at low graft density are interesting systems to study structure–dynamic relationships in polymer nanocomposites since they are shown to aggregate into strings in both solution and melts and also into spheres and branched aggregates in the presence of free polymer chains. Our work investigates structure and entanglement effects in composites of polystyrene-grafted iron oxide nanoparticles by measuring particle relaxations using X-ray photon correlation spectroscopy. And for particles within highly ordered strings and aggregated systems, they experience a dynamically heterogeneous environment displaying hyperdiffusive relaxation commonly observed in jammed soft glassy systems. Furthermore, particle dynamics ismore » diffusive for branched aggregated structures which could be caused by less penetration of long matrix chains into brushes. These results suggest that particle motion is dictated by the strong interactions of chains grafted at low density with the host matrix polymer.« less

Cultural-based particle swarm for dynamic optimisation problems

NASA Astrophysics Data System (ADS)

Daneshyari, Moayed; Yen, Gary G.

2012-07-01

Many practical optimisation problems are with the existence of uncertainties, among which a significant number belong to the dynamic optimisation problem (DOP) category in which the fitness function changes through time. In this study, we propose the cultural-based particle swarm optimisation (PSO) to solve DOP problems. A cultural framework is adopted incorporating the required information from the PSO into five sections of the belief space, namely situational, temporal, domain, normative and spatial knowledge. The stored information will be adopted to detect the changes in the environment and assists response to the change through a diversity-based repulsion among particles and migration among swarms in the population space, and also helps in selecting the leading particles in three different levels, personal, swarm and global levels. Comparison of the proposed heuristics over several difficult dynamic benchmark problems demonstrates the better or equal performance with respect to most of other selected state-of-the-art dynamic PSO heuristics.

Classical and quantum dynamics of a kicked relativistic particle in a box

NASA Astrophysics Data System (ADS)

Yusupov, J. R.; Otajanov, D. M.; Eshniyazov, V. E.; Matrasulov, D. U.

2018-03-01

We study classical and quantum dynamics of a kicked relativistic particle confined in a one dimensional box. It is found that in classical case for chaotic motion the average kinetic energy grows in time, while for mixed regime the growth is suppressed. However, in case of regular motion energy fluctuates around certain value. Quantum dynamics is treated by solving the time-dependent Dirac equation with delta-kicking potential, whose exact solution is obtained for single kicking period. In quantum case, depending on the values of the kicking parameters, the average kinetic energy can be quasi periodic, or fluctuating around some value. Particle transport is studied by considering spatio-temporal evolution of the Gaussian wave packet and by analyzing the trembling motion.

Emergence of Collective Motion in a Model of Interacting Brownian Particles.

PubMed

Dossetti, Victor; Sevilla, Francisco J

2015-07-31

By studying a system of Brownian particles that interact among themselves only through a local velocity-alignment force that does not affect their speed, we show that self-propulsion is not a necessary feature for the flocking transition to take place as long as underdamped particle dynamics can be guaranteed. Moreover, the system transits from stationary phases close to thermal equilibrium, with no net flux of particles, to far-from-equilibrium ones exhibiting collective motion, phase coexistence, long-range order, and giant number fluctuations, features typically associated with ordered phases of models where self-propelled particles with overdamped dynamics are considered.

Swinging motion of active deformable particles in Poiseuille flow

NASA Astrophysics Data System (ADS)

Tarama, Mitsusuke

2017-08-01

Dynamics of active deformable particles in an external Poiseuille flow is investigated. To make the analysis general, we employ time-evolution equations derived from symmetry considerations that take into account an elliptical shape deformation. First, we clarify the relation of our model to that of rigid active particles. Then, we study the dynamical modes that active deformable particles exhibit by changing the strength of the external flow. We emphasize the difference between the active particles that tend to self-propel parallel to the elliptical shape deformation and those self-propelling perpendicularly. In particular, a swinging motion around the centerline far from the channel walls is discussed in detail.

How Actuated Particles Effectively Capture Biomolecular Targets

PubMed Central

2017-01-01

Because of their high surface-to-volume ratio and adaptable surface functionalization, particles are widely used in bioanalytical methods to capture molecular targets. In this article, a comprehensive study is reported of the effectiveness of protein capture by actuated magnetic particles. Association rate constants are quantified in experiments as well as in Brownian dynamics simulations for different particle actuation configurations. The data reveal how the association rate depends on the particle velocity, particle density, and particle assembly characteristics. Interestingly, single particles appear to exhibit target depletion zones near their surface, caused by the high density of capture molecules. The depletion effects are even more limiting in cases with high particle densities. The depletion effects are overcome and protein capture rates are enhanced by applying dynamic particle actuation, resulting in an increase in the association rate constants by up to 2 orders of magnitude. PMID:28192952

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parab, Niranjan D.; Hudspeth, Matthew; Claus, Ben

Granular materials are widely used to resist impact and blast. Under these dynamic loadings, the constituent particles in the granular system fracture. To study the fracture mechanisms in brittle particles under dynamic compressive loading, a high speed X-ray phase contrast imaging setup was synchronized with a Kolsky bar apparatus. Controlled compressive loading was applied on two contacting particles using the Kolsky bar apparatus and fracture process was captured using the high speed X-ray imaging setup. Five different particles were investigated: soda-lime glass, polycrystalline silica (silicon dioxide), polycrystalline silicon, barium titanate glass, and yttrium stabilized zirconia. For both soda lime glassmore » and polycrystalline silica particles, one of the particles fragmented explosively, thus breaking into many small pieces. For Silicon and barium titanate glass particles, a finite number of cracks were observed in one of the particles causing it to fracture. For yttrium stabilized zirconia particles, a single meridonial crack developed in one of the particles, breaking it into two parts.« less

Dynamic self-organization of confined autophoretic particles

NASA Astrophysics Data System (ADS)

Medrano, Anthony; Michelin, Sébastien; Kanso, Eva

2016-11-01

We study the behavior of chemically-active Janus particles in microfluidic Hele-Shaw-type confinement. These micron-scale chemical motors, when immersed in a fuel-laden fluid, produce an ionic chemical field which leads to motility and consequently a local fluid flow. In unconfined settings, experimental and computational studies have shown these particles to spontaneously self-organize into crystal structures, and form into asters of two or more particles. Here, we show that geometric confinement alters both the chemical and hydrodynamic signature of the particles in such a way that their far-field effects can be modeled as source dipoles. Each particle moves according to its own self-propelled motion and in response to the chemical and hydrodynamic field created by other particles. Two interaction modes are observed: self-assembly into quasi-static crystals and into dynamically-evolving chains. We discuss the conditions that lead to these modes of interactions and the phase transitions between them for various Janus particle concentrations. The National GEM Consortium.

Ideal Particle Sizes for Inhaled Steroids Targeting Vocal Granulomas: Preliminary Study Using Computational Fluid Dynamics.

PubMed

Perkins, Elizabeth L; Basu, Saikat; Garcia, Guilherme J M; Buckmire, Robert A; Shah, Rupali N; Kimbell, Julia S

2018-03-01

Objectives Vocal fold granulomas are benign lesions of the larynx commonly caused by gastroesophageal reflux, intubation, and phonotrauma. Current medical therapy includes inhaled corticosteroids to target inflammation that leads to granuloma formation. Particle sizes of commonly prescribed inhalers range over 1 to 4 µm. The study objective was to use computational fluid dynamics to investigate deposition patterns over a range of particle sizes of inhaled corticosteroids targeting the larynx and vocal fold granulomas. Study Design Retrospective, case-specific computational study. Setting Tertiary academic center. Subjects/Methods A 3-dimensional anatomically realistic computational model of a normal adult airway from mouth to trachea was constructed from 3 computed tomography scans. Virtual granulomas of varying sizes and positions along the vocal fold were incorporated into the base model. Assuming steady-state, inspiratory, turbulent airflow at 30 L/min, computational fluid dynamics was used to simulate respiratory transport and deposition of inhaled corticosteroid particles ranging over 1 to 20 µm. Results Laryngeal deposition in the base model peaked for particle sizes 8 to 10 µm (2.8%-3.5%). Ideal sizes ranged over 6 to 10, 7 to 13, and 7 to 14 µm for small, medium, and large granuloma sizes, respectively. Glottic deposition was maximal at 10.8% for 9-µm-sized particles for the large posterior granuloma, 3 times the normal model (3.5%). Conclusion As the virtual granuloma size increased and the location became more posterior, glottic deposition and ideal particle size generally increased. This preliminary study suggests that inhalers with larger particle sizes, such as fluticasone propionate dry-powder inhaler, may improve laryngeal drug deposition. Most commercially available inhalers have smaller particles than suggested here.

Experimental studies of the effects of buffered particle dampers attached to a multi-degree-of-freedom system under dynamic loads

NASA Astrophysics Data System (ADS)

Lu, Zheng; Lu, Xilin; Lu, Wensheng; Masri, Sami F.

2012-04-01

This paper presents a systematic experimental investigation of the effects of buffered particle dampers attached to a multi-degree-of-freedom (mdof) system under different dynamic loads (free vibration, random excitation as well as real onsite earthquake excitations), and analytical/computational study of such a system. A series of shaking table tests of a three-storey steel frame with the buffered particle damper system are carried out to evaluate the performance and to verify the analysis method. It is shown that buffered particle dampers have good performance in reducing the response of structures under dynamic loads, especially under random excitation case. It can effectively control the fundamental mode of the mdof primary system; however, the control effect for higher modes is variable. It is also shown that, for a specific container geometry, a certain mass ratio leads to more efficient momentum transfer from the primary system to the particles with a better vibration attenuation effect, and that buffered particle dampers have better control effect than the conventional rigid ones. An analytical solution based on the discrete element method is also presented. Comparison between the experimental and computational results shows that reasonably accurate estimates of the response of a primary system can be obtained. Properly designed buffered particle dampers can effectively reduce the response of lightly damped mdof primary system with a small weight penalty, under different dynamic loads.

Quantum Tunneling and Chaos in Classical Scale Walkers

NASA Astrophysics Data System (ADS)

Su, Jenny; Dijksman, Joshua; Ward, Jeremy; Behringer, Robert

2014-03-01

We study the behavior of `walkers' small droplets bouncing on a fluid layer vibrated at amplitudes just below the onset of Faraday instability. It was shown recently that despite their macroscopic size, the droplet dynamics are stochastic in nature and reminiscent of the dual particle-wave dynamics in the realm of quantum mechanics (Couder PRL 2006). We use these walkers to study how chaos, which is macroscopically unpredictable, will manifest in a quantum setting. Pecora showed in 2011 that tunneling for particles that have a chaotic ground state is different from tunneling for particles with a regular ground state (PRE 2011). In the experiment we gather data that illustrates the particle trajectory and tunneling behavior as particles transition across the barrier in the double well system with both integrable and chaotic shapes.

Deposition and fine particle production during dynamic flow in a dry powder inhaler: a CFD approach.

PubMed

Milenkovic, J; Alexopoulos, A H; Kiparissides, C

2014-01-30

In this work the dynamic flow as well as the particle motion and deposition in a commercial dry powder inhaler, DPI (i.e., Turbuhaler) is described using computational fluid dynamics, CFD. The dynamic flow model presented here is an extension of a steady flow model previously described in Milenkovic et al. (2013). The model integrates CFD simulations for dynamic flow, an Eulerian-fluid/Lagrangian-particle description of particle motion as well as a particle/wall interaction model providing the sticking efficiency of particles colliding with the DPI walls. The dynamic flow is imposed by a time varying outlet pressure and the particle injections into the DPI are assumed to occur instantaneously and follow a prescribed particle size distribution, PSD. The total particle deposition and the production of fine particles in the DPI are determined for different peak inspiratory flow rates, PIFR, flow increase rates, FIR, and particle injection times. The simulation results for particle deposition are found to agree well with available experimental data for different values of PIFR and FIR. The predicted values of fine particle fraction are in agreement with available experimental results when the mean size of the injected PSD is taken to depend on the PIFR. Copyright © 2013 Elsevier B.V. All rights reserved.

Langmuir waveforms at interplanetary shocks: STEREO statistical analysis

NASA Astrophysics Data System (ADS)

Briand, C.

2016-12-01

Wave-particle interactions and particle acceleration are the two main processes allowing energy dissipation at non collisional shocks. Ion acceleration has been deeply studied for many years, also for their central role in the shock front reformation. Electron dynamics is also important in the shock dynamics through the instabilities they can generate which may impact the ion dynamics.Particle measurements can be efficiently completed by wave measurements to determine the characteristics of the electron beams and study the turbulence of the medium. Electric waveforms obtained from the S/WAVES instrument of the STEREO mission between 2007 to 2014 are analyzed. Thus, clear signature of Langmuir waves are observed on 41 interplanetary shocks. These data enable a statistical analysis and to deduce some characteristics of the electron dynamics on different shocks sources (SIR or ICME) and types (quasi-perpendicular or quasi-parallel). The conversion process between electrostatic to electromagnetic waves has also been tested in several cases.

Particle dynamics in the original Schwarzschild metric

NASA Astrophysics Data System (ADS)

Fimin, N. N.; Chechetkin, V. M.

2016-04-01

The properties of the original Schwarzschild metric for a point gravitating mass are considered. The laws of motion in the corresponding space-time are established, and the transition from the Schwarzschildmetric to the metric of a "dusty universe" are studied. The dynamics of a system of particles in thr post-Newtonian approximation are analyzed.

On safe configurations of a natural-artificial space tether system

NASA Astrophysics Data System (ADS)

Rodnikov, A. V.

2018-05-01

We study the dynamics of a particle moving under gravitation of precessing dynamically symmetric rigid body if the particle motion is restricted by two unilateral (flexible) constraints realized by two weightless unstretchable tethers with ends fixed at body poles, formed as the intersection of the body surface with the axis of its dynamical symmetry. The system under consideration is a simple model of an original natural-artificial space construction consisting of an asteroid and a space station tethered to each other via two cables. We note that the problem is integrable for the system safe configurations, i.e. for motions along the constraints common boundary (both tethers are tensed) if the body gravitational potential is invariant with respect to rotation about the axis of dynamical symmetry. We study these motions depicting phase portraits for possible values of system parameters. We also deduce conditions for the particle coming off the boundary of constraint(s) (if the tether(s) are slackened) and analyze these conditions, eliminating corresponding areas from phase portraits. We also formulate some statements, concerning the particle safety.

Particle tagging and its implications for stellar population dynamics

NASA Astrophysics Data System (ADS)

Le Bret, Theo; Pontzen, Andrew; Cooper, Andrew P.; Frenk, Carlos; Zolotov, Adi; Brooks, Alyson M.; Governato, Fabio; Parry, Owen H.

2017-07-01

We establish a controlled comparison between the properties of galactic stellar haloes obtained with hydrodynamical simulations and with 'particle tagging'. Tagging is a fast way to obtain stellar population dynamics: instead of tracking gas and star formation, it 'paints' stars directly on to a suitably defined subset of dark matter particles in a collisionless, dark-matter-only simulation. Our study shows that 'live' particle tagging schemes, where stellar masses are painted on to the dark matter particles dynamically throughout the simulation, can generate good fits to the hydrodynamical stellar density profiles of a central Milky Way-like galaxy and its most prominent substructure. Energy diffusion processes are crucial to reshaping the distribution of stars in infalling spheroidal systems and hence the final stellar halo. We conclude that the success of any particular tagging scheme hinges on this diffusion being taken into account, and discuss the role of different subgrid feedback prescriptions in driving this diffusion.

A boundary element method for particle and droplet electrohydrodynamics in the Quincke regime

NASA Astrophysics Data System (ADS)

Das, Debasish; Saintillan, David

2014-11-01

Quincke electrorotation is the spontaneous rotation of dielectric particles suspended in a dielectric liquid of higher conductivity when placed in a sufficiently strong electric field. This phenomenon of Quincke rotation has interesting implications for the rheology of these suspensions, whose effective viscosity can be controlled and reduced by application of an external field. While spherical harmonics can be used to solve the governing equations for a spherical particle, they cannot be used to study the dynamics of particles of more complex shapes or deformable particles or droplets. Here, we develop a novel boundary element formulation to model the dynamics of a dielectric particle under Quincke rotation based on the Taylor-Melcher leaky dielectric model, and compare the numerical results to theoretical predictions. We then employ this boundary element method to analyze the dynamics of a two-dimensional drop under Quincke rotation, where we allow the drop to deform under the electric field. Extensions to three-dimensions and to the electrohydrodynamic interactions of multiple droplets are also discussed.

Exploring dynamics in living cells by tracking single particles.

PubMed

Levi, Valeria; Gratton, Enrico

2007-01-01

In the last years, significant advances in microscopy techniques and the introduction of a novel technology to label living cells with genetically encoded fluorescent proteins revolutionized the field of Cell Biology. Our understanding on cell dynamics built from snapshots on fixed specimens has evolved thanks to our actual capability to monitor in real time the evolution of processes in living cells. Among these new tools, single particle tracking techniques were developed to observe and follow individual particles. Hence, we are starting to unravel the mechanisms driving the motion of a wide variety of cellular components ranging from organelles to protein molecules by following their way through the cell. In this review, we introduce the single particle tracking technology to new users. We briefly describe the instrumentation and explain some of the algorithms commonly used to locate and track particles. Also, we present some common tools used to analyze trajectories and illustrate with some examples the applications of single particle tracking to study dynamics in living cells.

Compensation Techniques in Accelerator Physics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sayed, Hisham Kamal

2011-05-01

Accelerator physics is one of the most diverse multidisciplinary fields of physics, wherein the dynamics of particle beams is studied. It takes more than the understanding of basic electromagnetic interactions to be able to predict the beam dynamics, and to be able to develop new techniques to produce, maintain, and deliver high quality beams for different applications. In this work, some basic theory regarding particle beam dynamics in accelerators will be presented. This basic theory, along with applying state of the art techniques in beam dynamics will be used in this dissertation to study and solve accelerator physics problems. Twomore » problems involving compensation are studied in the context of the MEIC (Medium Energy Electron Ion Collider) project at Jefferson Laboratory. Several chromaticity (the energy dependence of the particle tune) compensation methods are evaluated numerically and deployed in a figure eight ring designed for the electrons in the collider. Furthermore, transverse coupling optics have been developed to compensate the coupling introduced by the spin rotators in the MEIC electron ring design.« less

Molecular simulation investigation of the nanorheology of an entangled polymer melt

NASA Astrophysics Data System (ADS)

Karim, Mir; Khare, Rajesh; Indei, Tsutomu; Schieber, Jay

2014-03-01

Knowledge of the ``local rheology'' is important for viscoelastic systems that contain significant structural and dynamic heterogeneities, such as cellular and extra-cellular crowded environments. For homogeneous viscoelastic media, a study of probe particle motion provides information on the microstructural evolution of the medium in response to the probe particle motion. Over the last two decades, probe particle rheology has emerged as a leading experimental technique for capturing local rheology of complex fluids. In recent work [M. Karim, S. C. Kohale, T. Indei, J. D. Schieber, and R. Khare, Phys. Rev. E86, 051501 (2012)], we showed that this approach can be used in molecular dynamics (MD) simulations to study the nanoscale viscoelastic properties of an unentangled polymer melt; an important conclusion of that work was that medium and particle inertia play a crucial role in analysis of the particle rheology simulation data. MD simulations have a natural advantage that they enable study of deformation and dynamics over a small length scale around the moving probe particle. In this work, the approach is extended to compare the motion of a nanoscale probe in melts of entangled and unentangled chains. The simulations will be used to elucidate the differences between the local responses of these media to the probe particle motion. In particular, results will be presented for the differences in the resultant velocity and stress fields as well as any possible structural asymmetry developed around the moving probe particle in the entangled and unentangled cases.

Investigation of electric charge on inertial particle dynamics in turbulence

NASA Astrophysics Data System (ADS)

Lu, Jiang; Shaw, Raymond

2014-11-01

The behavior of electrically charged, inertial particles in homogeneous, isotropic turbulence is investigated. Both like-charged and oppositely-charged particle interactions are considered. Direct numerical simulations (DNS) of turbulence in a periodic box using the pseudospectral numerical method are performed, with Lagrangian tracking of the particles. We study effects of mutual electrostatic repulsion and attraction on the particle dynamics, as quantified by the radial distribution function (RDF) and the radial relative velocity. For the like-charged particle case, the Coulomb force leads to a short range repulsion behavior and an RDF reminiscent of that for a dilute gas. For the oppositely-charged particle case, the Coulomb force increases the RDF beyond that already occurring for neutral inertial particles. For both cases, the relative velocities are calculated as a function of particle separation distance and show distinct deviations from the expected scaling within the dissipation range. This research was supported by NASA Grant NNX113AF90G.

Simulations of Model Microswimmers with Fully Resolved Hydrodynamics

NASA Astrophysics Data System (ADS)

Oyama, Norihiro; Molina, John J.; Yamamoto, Ryoichi

2017-10-01

Swimming microorganisms, which include bacteria, algae, and spermatozoa, play a fundamental role in most biological processes. These swimmers are a special type of active particle, that continuously convert local energy into propulsive forces, thereby allowing them to move through their surrounding fluid medium. While the size, shape, and propulsion mechanism vary from one organism to the next, they share certain general characteristics: they exhibit force-free motion and they swim at a small Reynolds number. To study the dynamics of such systems, we use the squirmer model, which provides an ideal representation of swimmers as spheroidal particles that propel owing to a modified boundary condition at their surface. We have considered the single-particle and many-particle dynamics of swimmers in bulk and confined systems using the smoothed profile method, which allows us to efficiently solve the coupled particle-fluid problem. For the single-particle dynamics, we studied the diffusive behavior caused by the swimming of the particles. At short-time scales, the diffusion is caused by the hydrodynamic interactions, whereas at long-time scales, it is determined by the particle-particle collisions. Thus, the short-time diffusion will be the same for both swimmers and inert tracer particles. We then investigated the dynamics of confined microswimmers using cylindrical and parallel-plate confining walls. For the cylindrical confinement, we find evidence of an order/disorder phase transition which depends on the specific type of swimmers and the size of the cylinder. Under parallel-plane walls, some swimmers exhibit wavelike modes, which lead to traveling density waves that bounce back and forth between the walls. From an analysis of the bulk systems, we can show that this wavelike motion can be understood as a pseudoacoustic mode and is a consequence of the intrinsic swimming properties of the particles. The results presented here, together with the simulation method that we have developed, allow us to better understand the complex hydrodynamic interactions in microswimmer dispersions.

Motion-Blurred Particle Image Restoration for On-Line Wear Monitoring

PubMed Central

Peng, Yeping; Wu, Tonghai; Wang, Shuo; Kwok, Ngaiming; Peng, Zhongxiao

2015-01-01

On-line images of wear debris contain important information for real-time condition monitoring, and a dynamic imaging technique can eliminate particle overlaps commonly found in static images, for instance, acquired using ferrography. However, dynamic wear debris images captured in a running machine are unavoidably blurred because the particles in lubricant are in motion. Hence, it is difficult to acquire reliable images of wear debris with an adequate resolution for particle feature extraction. In order to obtain sharp wear particle images, an image processing approach is proposed. Blurred particles were firstly separated from the static background by utilizing a background subtraction method. Second, the point spread function was estimated using power cepstrum to determine the blur direction and length. Then, the Wiener filter algorithm was adopted to perform image restoration to improve the image quality. Finally, experiments were conducted with a large number of dynamic particle images to validate the effectiveness of the proposed method and the performance of the approach was also evaluated. This study provides a new practical approach to acquire clear images for on-line wear monitoring. PMID:25856328

Hybrid finite element and Brownian dynamics method for charged particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huber, Gary A., E-mail: ghuber@ucsd.edu; Miao, Yinglong; Zhou, Shenggao

2016-04-28

Diffusion is often the rate-determining step in many biological processes. Currently, the two main computational methods for studying diffusion are stochastic methods, such as Brownian dynamics, and continuum methods, such as the finite element method. A previous study introduced a new hybrid diffusion method that couples the strengths of each of these two methods, but was limited by the lack of interactions among the particles; the force on each particle had to be from an external field. This study further develops the method to allow charged particles. The method is derived for a general multidimensional system and is presented usingmore » a basic test case for a one-dimensional linear system with one charged species and a radially symmetric system with three charged species.« less

Dynamic simulations of many-body electrostatic self-assembly

NASA Astrophysics Data System (ADS)

Lindgren, Eric B.; Stamm, Benjamin; Maday, Yvon; Besley, Elena; Stace, A. J.

2018-03-01

Two experimental studies relating to electrostatic self-assembly have been the subject of dynamic computer simulations, where the consequences of changing the charge and the dielectric constant of the materials concerned have been explored. One series of calculations relates to experiments on the assembly of polymer particles that have been subjected to tribocharging and the simulations successfully reproduce many of the observed patterns of behaviour. A second study explores events observed following collisions between single particles and small clusters composed of charged particles derived from a metal oxide composite. As before, observations recorded during the course of the experiments are reproduced by the calculations. One study in particular reveals how particle polarizability can influence the assembly process. This article is part of the theme issue `Modern theoretical chemistry'.

A parametric study of the dynamic failure of energetic composites

NASA Astrophysics Data System (ADS)

Tanasoiu, Bogdan; Koslowski, Marisol

2017-09-01

Heating by frictional sliding of cracks is often considered to be one of the most important causes of localized melting and ignition in solid explosives. Furthermore, recent high speed X-ray phase contrast experiments on energetic composites under dynamic compression [Parab et al., Appl. Phys. Lett. 109(13) (2016)] show that most fracture events appear inside the particles. Initial cracks develop in regions where particles are close, and widespread fragmentation is observed in the interior of the particles as the stress waves propagate through the sample. However, most simulations have focused on interface debonding of energetic composites and, in general, do not include fracture of the particles explicitly. A phase field damage approach is used to model the dynamic response of a system of cyclotetramethylene-tetranitramine particles embedded in a Sylgard matrix. The simulations show several damage mechanisms observed in the experiments. The effects of the energy release rate and the initial crack distribution on the energy dissipation due to fracture are studied. The numerical results confirm that initial cracks play an important role in the evolution of damage, energy dissipation and consequently, the formation of hot-spots.

LAMMPS Implementation of Constant Energy Dissipative Particle Dynamics (DPD-E)

DTIC Science & Technology

2014-03-01

LAMMPS Implementation of Constant Energy Dissipative Particle Dynamics (DPD-E) by James P. Larentzos, John K. Brennan, Joshua D. Moore, and...MD 21005-5069 ARL-TR-6863 March 2014 LAMMPS Implementation of Constant Energy Dissipative Particle Dynamics (DPD-E) James P...13 September 2013 4. TITLE AND SUBTITLE LAMMPS Implementation of Constant Energy Dissipative Particle Dynamics (DPD-E) 5a. CONTRACT NUMBER 5b

A dynamic feedforward neural network based on gaussian particle swarm optimization and its application for predictive control.

PubMed

Han, Min; Fan, Jianchao; Wang, Jun

2011-09-01

A dynamic feedforward neural network (DFNN) is proposed for predictive control, whose adaptive parameters are adjusted by using Gaussian particle swarm optimization (GPSO) in the training process. Adaptive time-delay operators are added in the DFNN to improve its generalization for poorly known nonlinear dynamic systems with long time delays. Furthermore, GPSO adopts a chaotic map with Gaussian function to balance the exploration and exploitation capabilities of particles, which improves the computational efficiency without compromising the performance of the DFNN. The stability of the particle dynamics is analyzed, based on the robust stability theory, without any restrictive assumption. A stability condition for the GPSO+DFNN model is derived, which ensures a satisfactory global search and quick convergence, without the need for gradients. The particle velocity ranges could change adaptively during the optimization process. The results of a comparative study show that the performance of the proposed algorithm can compete with selected algorithms on benchmark problems. Additional simulation results demonstrate the effectiveness and accuracy of the proposed combination algorithm in identifying and controlling nonlinear systems with long time delays.

Dynamical stability of slip-stacking particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eldred, Jeffrey; Zwaska, Robert

2014-09-01

We study the stability of particles in slip-stacking configuration, used to nearly double proton beam intensity at Fermilab. We introduce universal area factors to calculate the available phase space area for any set of beam parameters without individual simulation. We find perturbative solutions for stable particle trajectories. We establish Booster beam quality requirements to achieve 97% slip-stacking efficiency. We show that slip-stacking dynamics directly correspond to the driven pendulum and to the system of two standing-wave traps moving with respect to each other.

Simultaneous measurements of bulk moduli and particle dynamics in a sheared colloidal glass

NASA Astrophysics Data System (ADS)

Massa, Michael V.; Eisenmann, Christoph; Kim, Chanjoong; Weitz, David A.

2007-03-01

We present a novel study of glassy colloidal systems, using a stress-controlled rheometer in conjunction with a confocal microscope. This experimental setup combines the measurement of bulk moduli, using conventional rheology, with the ability to track the motion of individual particles, through confocal microscopy techniques. We explore the response of the system to applied shear, by simultaneously monitoring the macroscopic relaxation and microscopic particle dynamics, under conditions from the quiescent glass to a shear-melted liquid.

Numerical Study of Particle Damping Mechanism in Piston Vibration System via Particle Dynamics Simulation

NASA Astrophysics Data System (ADS)

Bai, Xian-Ming; Shah, Binoy; Keer, Leon; Wang, Jane; Snurr, Randall

2008-03-01

Mechanical damping systems with granular particles as the damping media have promising applications in extreme temperature conditions. In particle-based damping systems, the mechanical energy is dissipated through the inelastic collision and friction of particles. In the past, many experiments have been performed to investigate the particle damping problems. However, the detailed energy dissipation mechanism is still unclear due to the complex collision and flow behavior of dense particles. In this work, we use 3-D particle dynamics simulation to investigate the damping mechanism of an oscillating cylinder piston immerged in millimeter-size steel particles. The time evolution of the energy dissipation through the friction and inelastic collision is accurately monitored during the damping process. The contribution from the particle-particle interaction and particle-wall interaction is also separated for investigation. The effects of moisture, surface roughness, and density of particles are carefully investigated in the simulation. The comparison between the numerical simulation and experiment is also performed. The simulation results can help us understand the particle damping mechanism and design the new generation of particle damping devices.

How half-coated janus particles enter cells.

PubMed

Gao, Yuan; Yu, Yan

2013-12-26

Janus particles possess functional asymmetry and directionality within a single entity and thus are predicted to enable many promising biomedical applications that are not offered by homogeneous particles. However, it remains elusive what role the Janus principle plays in Janus particle-cell interactions, particularly in cellular uptake. We studied how asymmetric distribution of ligands on half-coated Janus microparticles dictates the membrane dynamics during receptor-mediated particle uptake, and found key differences from those characteristic of homogeneous particles. Live-cell fluorescence imaging combined with single-particle level quantification of particle-cell membrane interactions shows that the asymmetric distribution of ligands leads to a three-step endocytic process: membrane cup formation on the ligand-coated hemisphere, stalling at the Janus interface, and rapid membrane protrusion on the ligand-absent hemisphere to complete the particle engulfment. The direct correlation between the spatial presentation of ligands on Janus particles and the temporal changes of membrane dynamics revealed in this work elucidates the potential of using the Janus principle to fine-tune particle-cell interactions.

Some astrophysical processes around magnetized black hole

NASA Astrophysics Data System (ADS)

Kološ, M.; Tursunov, A.; Stuchlík, Z.

2018-01-01

We study the dynamics of charged test particles in the vicinity of a black hole immersed into an asymptotically uniform external magnetic field. A real magnetic field around a black hole will be far away from to be completely regular and uniform, a uniform magnetic field is used as linear approximation. Ionized particle acceleration, charged particle oscillations and synchrotron radiation of moving charged particle have been studied.

On the deflagration-to-detonation transition (DDT) process with added energetic solid particles for pulse detonation engines (PDE)

NASA Astrophysics Data System (ADS)

Nguyen, V. B.; Li, J.; Chang, P.-H.; Phan, Q. T.; Teo, C. J.; Khoo, B. C.

2018-01-01

In this paper, numerical simulations are performed to study the dynamics of the deflagration-to-detonation transition (DDT) in pulse detonation engines (PDE) using energetic aluminum particles. The DDT process and detonation wave propagation toward the unburnt hydrogen/air mixture containing solid aluminum particles is numerically studied using the Eulerian-Lagrangian approach. A hybrid numerical methodology combined with appropriate sub-models is used to capture the gas dynamic characteristics, particle behavior, combustion characteristics, and two-way solid-particle-gas flow interactions. In our approach, the gas mixture is expressed in the Eulerian frame of reference, while the solid aluminum particles are tracked in the Lagrangian frame of reference. The implemented computer code is validated using published benchmark problems. The obtained results show that the aluminum particles not only shorten the DDT length but also reduce the DDT time. The improvement of DDT is primarily attributed to the heat released from surface chemical reactions on the aluminum particles. The temperatures associated with the DDT process are greater than the case of non-reacting particles added, with an accompanying rise in the pressure. For an appropriate range of particle volume fraction, particularly in this study, the higher volume fraction of the micro-aluminum particles added in the detonation chamber can lead to more heat energy released and more local instabilities in the combustion process (caused by the local high temperature), thereby resulting in a faster DDT process. In essence, the aluminum particles contribute to the DDT process of successfully transitioning to detonation waves for (failure) cases in which the fuel gas mixture can be either too lean or too rich. With a better understanding of the influence of added aluminum particles on the dynamics of the DDT and detonation process, we can apply it to modify the geometry of the detonation chamber (e.g., the length of the detonation tube) accordingly to improve the operational performance of the PDE.

Differential dynamic microscopy of bidisperse colloidal suspensions.

PubMed

Safari, Mohammad S; Poling-Skutvik, Ryan; Vekilov, Peter G; Conrad, Jacinta C

2017-01-01

Research tasks in microgravity include monitoring the dynamics of constituents of varying size and mobility in processes such as aggregation, phase separation, or self-assembly. We use differential dynamic microscopy, a method readily implemented with equipment available on the International Space Station, to simultaneously resolve the dynamics of particles of radius 50 nm and 1 μm in bidisperse aqueous suspensions. Whereas traditional dynamic light scattering fails to detect a signal from the larger particles at low concentrations, differential dynamic microscopy exhibits enhanced sensitivity in these conditions by accessing smaller wavevectors where scattering from the large particles is stronger. Interference patterns due to scattering from the large particles induce non-monotonic decay of the amplitude of the dynamic correlation function with the wavevector. We show that the position of the resulting minimum contains information on the vertical position of the particles. Together with the simple instrumental requirements, the enhanced sensitivity of differential dynamic microscopy makes it an appealing alternative to dynamic light scattering to characterize samples with complex dynamics.

Numerical studies from quantum to macroscopic scales of carbon nanoparticules in hydrogen plasma

NASA Astrophysics Data System (ADS)

Lombardi, Guillaume; Ngandjong, Alain; Mezei, Zsolt; Mougenot, Jonathan; Michau, Armelle; Hassouni, Khaled; Seydou, Mahamadou; Maurel, François

2016-09-01

Dusty plasmas take part in large scientific domains from Universe Science to nanomaterial synthesis processes. They are often generated by growth from molecular precursor. This growth leads to the formation of larger clusters which induce solid germs nucleation. Particle formed are described by an aerosol dynamic taking into account coagulation, molecular deposition and transport processes. These processes are controlled by the elementary particle. So there is a strong coupling between particle dynamics and plasma discharge equilibrium. This study is focused on the development of a multiscale physic and numeric model of hydrogen plasmas and carbon particles around three essential coupled axes to describe the various physical phenomena: (i) Macro/mesoscopic fluid modeling describing in an auto-coherent way, characteristics of the plasma, molecular clusters and aerosol behavior; (ii) the classic molecular dynamics offering a description to the scale molecular of the chains of chemical reactions and the phenomena of aggregation; (iii) the quantum chemistry to establish the activation barriers of the different processes driving the nanopoarticule formation.

Impact of dynamic distribution of floc particles on flocculation effect.

PubMed

Nan, Jun; He, Weipeng; Song, Xinin; Li, Guibai

2009-01-01

Polyaluminum chloride (PAC) was used as coagulant and suspended particles in kaolin water. Online instruments including turbidimeter and particle counter were used to monitor the flocculation process. An evaluation model for demonstrating the impact on the flocculation effect was established based on the multiple linear regression analysis method. The parameter of the index weight of channels quantitatively described how the variation of floc particle population in different size ranges cause the decrement of turbidity. The study showed that the floc particles in different size ranges contributed differently to the decrease of turbidity and that the index weight of channel could excellently indicate the impact degree of floc particles dynamic distribution on flocculation effect. Therefore, the parameter may significantly benefit the development of coagulation and sedimentation techniques as well as the optimal coagulant selection.

Near Wall Dynamics in Colloidal Suspensions Studied by Evansescent Wave Dynamic Light Scattering

NASA Astrophysics Data System (ADS)

Lang, Peter R.

2011-03-01

The dynamics of dispersed colloidal particles is slowed down, and becomes anisotropic in the ultimate vicinity of a flat wall due to the wall drag effect. Although theoretically predicted in the early 20th century, experimental verification of this effect for Brownian particles became possible only in the late 80s. Since then a variety of experimental investigations on near wall Brownian dynamics by evanescent wave dynamic light scattering (EWDLS) has been published. In this contribution the method of EWDLS will be briefly introduced, experiments at low and high colloid concentration for hard-sphere suspensions, and the theoretical prediction for measured initial slopes of correlation functions will be discussed. On increasing the particle concentration the influence of the wall drag effect is found to diminishes gradually, until it becomes negligible at volume fractions above ϕ 0.35. The effect that a wall exerts on the orientational dynamics was investigated for different kinds of colloids. Experiments, simulations and a virial expansion theory show that rotational dynamics is slowed down as well. However, the effect is prominent in EWDLS only if the particles' short axis is of the order of the evanescent wave penetration depth. The author acknowledges financial support from the EU through FP7, project Nanodirect (Grant 395 No. NMP4-SL-2008-213948).

Topological solitons in helical strings

NASA Astrophysics Data System (ADS)

Nisoli, Cristiano; Balatsky, Alexander V.

2015-06-01

The low-energy physics of (quasi)degenerate one-dimensional systems is typically understood as the particle-like dynamics of kinks between stable, ordered structures. Such dynamics, we show, becomes highly nontrivial when the ground states are topologically constrained: a dynamics of the domains rather than on the domains which the kinks separate. Motivated by recently reported observations of charged polymers physio-adsorbed on nanotubes, we study kinks between helical structures of a string wrapping around a cylinder. While their motion cannot be disentangled from domain dynamics, and energy and momentum is not concentrated in the solitons, the dynamics of the domains can be folded back into a particle-like description of the local excitations.

Merging for Particle-Mesh Complex Particle Kinetic Modeling of the Multiple Plasma Beams

NASA Technical Reports Server (NTRS)

Lipatov, Alexander S.

2011-01-01

We suggest a merging procedure for the Particle-Mesh Complex Particle Kinetic (PMCPK) method in case of inter-penetrating flow (multiple plasma beams). We examine the standard particle-in-cell (PIC) and the PMCPK methods in the case of particle acceleration by shock surfing for a wide range of the control numerical parameters. The plasma dynamics is described by a hybrid (particle-ion-fluid-electron) model. Note that one may need a mesh if modeling with the computation of an electromagnetic field. Our calculations use specified, time-independent electromagnetic fields for the shock, rather than self-consistently generated fields. While a particle-mesh method is a well-verified approach, the CPK method seems to be a good approach for multiscale modeling that includes multiple regions with various particle/fluid plasma behavior. However, the CPK method is still in need of a verification for studying the basic plasma phenomena: particle heating and acceleration by collisionless shocks, magnetic field reconnection, beam dynamics, etc.

Tracking single particle rotation: Probing dynamics in four dimensions

DOE PAGES

Anthony, Stephen Michael; Yu, Yan

2015-04-29

Direct visualization and tracking of small particles at high spatial and temporal resolution provides a powerful approach to probing complex dynamics and interactions in chemical and biological processes. Analysis of the rotational dynamics of particles adds a new dimension of information that is otherwise impossible to obtain with conventional 3-D particle tracking. In this review, we survey recent advances in single-particle rotational tracking, with highlights on the rotational tracking of optically anisotropic Janus particles. Furthermore, strengths and weaknesses of the various particle tracking methods, and their applications are discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Siqi; Senses, Erkan; Jiao, Yang

Nanoparticles functionalized with long polymer chains at low graft density are interesting systems to study structure–dynamic relationships in polymer nanocomposites since they are shown to aggregate into strings in both solution and melts and also into spheres and branched aggregates in the presence of free polymer chains. Our work investigates structure and entanglement effects in composites of polystyrene-grafted iron oxide nanoparticles by measuring particle relaxations using X-ray photon correlation spectroscopy. And for particles within highly ordered strings and aggregated systems, they experience a dynamically heterogeneous environment displaying hyperdiffusive relaxation commonly observed in jammed soft glassy systems. Furthermore, particle dynamics ismore » diffusive for branched aggregated structures which could be caused by less penetration of long matrix chains into brushes. These results suggest that particle motion is dictated by the strong interactions of chains grafted at low density with the host matrix polymer.« less

Dynamics and density distribution of strongly confined noninteracting nonaligning self-propelled particles in a nonconvex boundary

NASA Astrophysics Data System (ADS)

Fily, Yaouen; Baskaran, Aparna; Hagan, Michael F.

2015-01-01

We study the dynamics of nonaligning, noninteracting self-propelled particles confined to a box in two dimensions. In the strong confinement limit, when the persistence length of the active particles is much larger than the size of the box, particles stay on the boundary and align with the local boundary normal. It is then possible to derive the steady-state density on the boundary for arbitrary box shapes. In nonconvex boxes, the nonuniqueness of the boundary normal results in hysteretic dynamics and the density is nonlocal, i.e., it depends on the global geometry of the box. These findings establish a general connection between the geometry of a confining box and the behavior of an ideal active gas it confines, thus providing a powerful tool to understand and design such confinements.

Particle statistics and lossy dynamics of ultracold atoms in optical lattices

NASA Astrophysics Data System (ADS)

Yago Malo, J.; van Nieuwenburg, E. P. L.; Fischer, M. H.; Daley, A. J.

2018-05-01

Experimental control over ultracold quantum gases has made it possible to investigate low-dimensional systems of both bosonic and fermionic atoms. In closed one-dimensional systems there are many similarities in the dynamics of local quantities for spinless fermions and strongly interacting "hard-core" bosons, which on a lattice can be formalized via a Jordan-Wigner transformation. In this study, we analyze the similarities and differences for spinless fermions and hard-core bosons on a lattice in the presence of particle loss. The removal of a single fermion causes differences in local quantities compared with the bosonic case because of the different particle exchange symmetry in the two cases. We identify deterministic and probabilistic signatures of these dynamics in terms of local particle density, which could be measured in ongoing experiments with quantum gas microscopes.

Variational symplectic algorithm for guiding center dynamics in the inner magnetosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Jinxing; Pu Zuyin; Xie Lun

Charged particle dynamics in magnetosphere has temporal and spatial multiscale; therefore, numerical accuracy over a long integration time is required. A variational symplectic integrator (VSI) [H. Qin and X. Guan, Phys. Rev. Lett. 100, 035006 (2008) and H. Qin, X. Guan, and W. M. Tang, Phys. Plasmas 16, 042510 (2009)] for the guiding-center motion of charged particles in general magnetic field is applied to study the dynamics of charged particles in magnetosphere. Instead of discretizing the differential equations of the guiding-center motion, the action of the guiding-center motion is discretized and minimized to obtain the iteration rules for advancing themore » dynamics. The VSI conserves exactly a discrete Lagrangian symplectic structure and has better numerical properties over a long integration time, compared with standard integrators, such as the standard and adaptive fourth order Runge-Kutta (RK4) methods. Applying the VSI method to guiding-center dynamics in the inner magnetosphere, we can accurately calculate the particles'orbits for an arbitrary long simulating time with good conservation property. When a time-independent convection and corotation electric field is considered, the VSI method can give the accurate single particle orbit, while the RK4 method gives an incorrect orbit due to its intrinsic error accumulation over a long integrating time.« less

Improved Boron for Enhanced Combustion

DTIC Science & Technology

1990-06-01

elements scanned. - 11 - C. Particle Dynamics Ultrafine particles on the order of 0.01 to 0.1 micron diameter are known to exhibit dynamic behavior...very short relaxation times after perturbations [7]. Of the four major regimes of particle dynamic behavior, these ultrafine particles are classified in...modeling. Ultrafine particles up to approximately 0.1 micron in diameter tend to have unequilibrated surface energy [7,8,9,101. This is particularly

Study of thermal stability of disordered alloy AgxCu1-x nanoparticles by molecular dynamic simulations

NASA Astrophysics Data System (ADS)

Baidyshev, V. S.; Chepkasov, I. V.; Artemova, N. D.

2018-05-01

In this paper melting processes of particles of disordered AgCu alloy in the size range of D=3-5 nm were investigated. The simulation was carried out with molecular dynamics, using the embedded atom potential. It was defined that for nanoparticles of D=3 nm, the melting process is connected with the formation of the outer layer consisting of Ag atoms as well as with the further transition of the particle into an amorphous state. The increase of the particle size to D=5 nm did not show the processes of redistributing Ag atoms on the particle surface.

Steady-state and dynamic models for particle engulfment during solidification

NASA Astrophysics Data System (ADS)

Tao, Yutao; Yeckel, Andrew; Derby, Jeffrey J.

2016-06-01

Steady-state and dynamic models are developed to study the physical mechanisms that determine the pushing or engulfment of a solid particle at a moving solid-liquid interface. The mathematical model formulation rigorously accounts for energy and momentum conservation, while faithfully representing the interfacial phenomena affecting solidification phase change and particle motion. A numerical solution approach is developed using the Galerkin finite element method and elliptic mesh generation in an arbitrary Lagrangian-Eulerian implementation, thus allowing for a rigorous representation of forces and dynamics previously inaccessible by approaches using analytical approximations. We demonstrate that this model accurately computes the solidification interface shape while simultaneously resolving thin fluid layers around the particle that arise from premelting during particle engulfment. We reinterpret the significance of premelting via the definition an unambiguous critical velocity for engulfment from steady-state analysis and bifurcation theory. We also explore the complicated transient behaviors that underlie the steady states of this system and posit the significance of dynamical behavior on engulfment events for many systems. We critically examine the onset of engulfment by comparing our computational predictions to those obtained using the analytical model of Rempel and Worster [29]. We assert that, while the accurate calculation of van der Waals repulsive forces remains an open issue, the computational model developed here provides a clear benefit over prior models for computing particle drag forces and other phenomena needed for the faithful simulation of particle engulfment.

Particle-based simulations of self-motile suspensions

NASA Astrophysics Data System (ADS)

Hinz, Denis F.; Panchenko, Alexander; Kim, Tae-Yeon; Fried, Eliot

2015-11-01

A simple model for simulating flows of active suspensions is investigated. The approach is based on dissipative particle dynamics. While the model is potentially applicable to a wide range of self-propelled particle systems, the specific class of self-motile bacterial suspensions is considered as a modeling scenario. To mimic the rod-like geometry of a bacterium, two dissipative particle dynamics particles are connected by a stiff harmonic spring to form an aggregate dissipative particle dynamics molecule. Bacterial motility is modeled through a constant self-propulsion force applied along the axis of each such aggregate molecule. The model accounts for hydrodynamic interactions between self-propelled agents through the pairwise dissipative interactions conventional to dissipative particle dynamics. Numerical simulations are performed using a customized version of the open-source software package LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) software package. Detailed studies of the influence of agent concentration, pairwise dissipative interactions, and Stokes friction on the statistics of the system are provided. The simulations are used to explore the influence of hydrodynamic interactions in active suspensions. For high agent concentrations in combination with dominating pairwise dissipative forces, strongly correlated motion patterns and a fluid-like spectral distributions of kinetic energy are found. In contrast, systems dominated by Stokes friction exhibit weaker spatial correlations of the velocity field. These results indicate that hydrodynamic interactions may play an important role in the formation of spatially extended structures in active suspensions.

Self Diffusion in Nano Filled Polymer Melts: a Molecular Dynamics Simulation Study

NASA Astrophysics Data System (ADS)

Desai, Tapan; Keblinski, Pawel

2003-03-01

SELF DIFFUSION IN NANO FILLED POLYMER MELTS: A MOLECULAR DYNAMICS SIMULATION STUDY* T. G. Desai,P. Keblinski, Material Science and Engineering Department, Rensselaer Polytechnic Institute, Troy, NY. Using molecular dynamics simulations, we studied the dynamics of the polymeric systems containing immobile and analytically smooth spherical nanoparticles. Each chain consisted of N monomers connected by an anharmonic springs described by the finite extendible nonlinear elastic, FENE potential. The system comprises of 3nanoparticles and the rest by freely rotating but not overlapping chains. The longest chain studied has a Radius of gyration equal to particle size radius and comparable to inter-particle distance. There is no effect on the structural characteristics such as Radius of gyration or end to end distance due to the nanoparticles. Diffusion of polymeric chains is not affected by the presence of either attractive or repulsive nanoparticles. In all cases Rouse dynamics is observed for short chains with a crossover to reptation dynamics for longer chains.

Effect of particle-size dynamics on properties of dense spongy-particle systems: Approach towards equilibrium.

PubMed

Zakhari, Monica E A; Anderson, Patrick D; Hütter, Markus

2017-07-01

Open-porous deformable particles, often envisaged as sponges, are ubiquitous in biological and industrial systems (e.g., casein micelles in dairy products and microgels in cosmetics). The rich behavior of these suspensions is owing to the elasticity of the supporting network of the particle, and the viscosity of permeating solvent. Therefore, the rate-dependent size change of these particles depends on their structure, i.e., the permeability. This work aims at investigating the effect of the particle-size dynamics and the underlying particle structure, i.e., the particle permeability, on the transient and long-time behavior of suspensions of spongy particles in the absence of applied deformation, using the dynamic two-scale model developed by Hütter et al. [Farad. Discuss. 158, 407 (2012)1359-664010.1039/c2fd20025b]. In the high-density limit, the transient behavior is found to be accelerated by the particle-size dynamics, even at average size changes as small as 1%. The accelerated dynamics is evidenced by (i) the higher short-time diffusion coefficient as compared to elastic-particle systems and (ii) the accelerated formation of the stable fcc crystal structure. Furthermore, after long times, the particle-size dynamics of spongy particles is shown to result in lower stationary values of the energy and normal stresses as compared to elastic-particle systems. This dependence of the long-time behavior of these systems on the permeability, that essentially is a transport coefficient and hence must not affect the equilibrium properties, confirms that full equilibration has not been reached.

Effect of particle-size dynamics on properties of dense spongy-particle systems: Approach towards equilibrium

NASA Astrophysics Data System (ADS)

Zakhari, Monica E. A.; Anderson, Patrick D.; Hütter, Markus

2017-07-01

Open-porous deformable particles, often envisaged as sponges, are ubiquitous in biological and industrial systems (e.g., casein micelles in dairy products and microgels in cosmetics). The rich behavior of these suspensions is owing to the elasticity of the supporting network of the particle, and the viscosity of permeating solvent. Therefore, the rate-dependent size change of these particles depends on their structure, i.e., the permeability. This work aims at investigating the effect of the particle-size dynamics and the underlying particle structure, i.e., the particle permeability, on the transient and long-time behavior of suspensions of spongy particles in the absence of applied deformation, using the dynamic two-scale model developed by Hütter et al. [Farad. Discuss. 158, 407 (2012), 10.1039/c2fd20025b]. In the high-density limit, the transient behavior is found to be accelerated by the particle-size dynamics, even at average size changes as small as 1 % . The accelerated dynamics is evidenced by (i) the higher short-time diffusion coefficient as compared to elastic-particle systems and (ii) the accelerated formation of the stable fcc crystal structure. Furthermore, after long times, the particle-size dynamics of spongy particles is shown to result in lower stationary values of the energy and normal stresses as compared to elastic-particle systems. This dependence of the long-time behavior of these systems on the permeability, that essentially is a transport coefficient and hence must not affect the equilibrium properties, confirms that full equilibration has not been reached.

Grain scale observations of stick-slip dynamics in fluid saturated granular fault gouge

NASA Astrophysics Data System (ADS)

Johnson, P. A.; Dorostkar, O.; Guyer, R. A.; Marone, C.; Carmeliet, J.

2017-12-01

We are studying granular mechanics during slip. In the present work, we conduct coupled computational fluid dynamics (CFD) and discrete element method (DEM) simulations to study grain scale characteristics of slip instabilities in fluid saturated granular fault gouge. The granular sample is confined with constant normal load (10 MPa), and sheared with constant velocity (0.6 mm/s). This loading configuration is chosen to promote stick-slip dynamics, based on a phase-space study. Fluid is introduced in the beginning of stick phase and characteristics of slip events i.e. macroscopic friction coefficient, kinetic energy and layer thickness are monitored. At the grain scale, we monitor particle coordination number, fluid-particle interaction forces as well as particle and fluid kinetic energy. Our observations show that presence of fluids in a drained granular fault gouge stabilizes the layer in the stick phase and increases the recurrence time. In saturated model, we observe that average particle coordination number reaches higher values compared to dry granular gouge. Upon slip, we observe that a larger portion of the granular sample is mobilized in saturated gouge compared to dry system. We also observe that regions with high particle kinetic energy are correlated with zones of high fluid motion. Our observations highlight that spatiotemporal profile of fluid dynamic pressure affects the characteristics of slip instabilities, increasing macroscopic friction coefficient drop, kinetic energy release and granular layer compaction. We show that numerical simulations help characterize the micromechanics of fault mechanics.

On the origins of the universal dynamics of endogenous granules in mammalian cells.

PubMed

Vanapalli, Siva A; Li, Yixuan; Mugele, Frieder; Duits, Michel H G

2009-12-01

Endogenous granules (EGs) that consist of lipid droplets and mitochondria have been commonly used to assess intracellular mechanical properties via multiple particle tracking microrheology (MPTM). Despite their widespread use, the nature of interaction of EGs with the cytoskeletal network and the type of forces driving their dynamics--both of which are crucial for the interpretation of the results from MPTM technique--are yet to be resolved. In this report, we study the dynamics of endogenous granules in mammalian cells using particle tracking methods. We find that the ensemble dynamics of EGs is diffusive in three types of mammalian cells (endothelial cells, smooth muscle cells and fibroblasts), thereby suggesting an apparent universality in their dynamical behavior. Moreover, in a given cell, the amplitude of the mean-squared displacement for EGs is an order of magnitude larger than that of injected particles. This observation along with results from ATP depletion and temperature intervention studies suggests that cytoskeletal active forces drive the dynamics of EGs. To elucidate the dynamical origin of the diffusive-like nonthermal motion, we consider three active force generation mechanisms--molecular motor transport, actomyosin contractility and microtubule polymerization forces. We test these mechanisms using pharmacological interventions. Experimental evidence and model calculations suggest that EGs are intimately linked to microtubules and that microtubule polymerization forces drive their dynamics. Thus, endogenous granules could serve as non-invasive probes for microtubule network dynamics in mammalian cells.

New estimate of the micrometeoroids flux at the heliocentric distance of Mercury

NASA Astrophysics Data System (ADS)

Borin, Patrizia; Cremonese, Gabriele; Marzari, Francesco

This work shows preliminary results of a study of the orbital evolution of dust particles originating from the Main Belt in order to obtain a statistical analysis, then to provide an estimate of the flux of particles hitting the Mercury's surface. Meteoritic flux on Mercury really depends on the particle size, because meteoroids of different size follow different dynamical evolution. In this work we consider meteoritic sizes smaller than 1 cm that are particles with a dynamical evolution dominated by the Poynting-Robertson effect. The meteoroid impact mechanism seems to be an important source of neutral atoms contributing to the exosphere and, according to recent papers, mostly due to particles smaller than 1 cm. Unfortunately the dynamical studies and statistics of meteoroids smaller than 1 cm are based on quite old papers and always extrapolated from calculations made for the Earth. This is the reason why we are working on a dynamical model following small dust particles that may hit the surface of Mercury. Up to now we have taken into account only particles coming from the Main Belt. The main effects that determine the distribution of dust in the Solar System are the gravitational attractions of the Sun and planets, Poynting-Robertson drag, solar radiation pressure, solar wind pressure and the effects of different magnetic fields. In order to determine the meteoritic flux at the heliocentric distance of Mercury we utilize the dynamical evolution model of dust particles of Marzari and Vanzani (1994) that numerically solves a (N+1)+M body problem (Sun + N planets + M body with zero mass) with the high-precision integrator RA15 (Everhart 1985). The solar radiation pressure and Poynting-Robertson drag, together with the gravitational interactions of the planets, are taken as major perturbing forces affecting the orbital evolution of the dust particles. We have performed numerical simulations with different initial conditions for the dust particles, depending on the sources, with the aim of estimating to flux of dust on the surface of Mercury. In this work we will report the first interesting estimate of the flux of small particles, and their velocity distribution, hitting the surface of Mercury. We intend also to evaluate a possible asymmetry between the leading and trailing surface of Mercury in terms of impact frequency.

Electrode Slurry Particle Density Mapping Using X-ray Radiography

DOE PAGES

Higa, Kenneth; Zhao, Hui; Parkinson, Dilworth Y.; ...

2017-01-05

The internal structure of a porous electrode strongly influences battery performance. Understanding the dynamics of electrode slurry drying could aid in engineering electrodes with desired properties. For instance, one might monitor the dynamic, spatially-varying thickness near the edge of a slurry coating, as it should lead to non-uniform thickness of the dried film. This work examines the dynamic behavior of drying slurry drops consisting of SiO x and carbon black particles in a solution of carboxymethylcellulose and deionized water, as an experimental model of drying behavior near the edge of a slurry coating. An X-ray radiography-based procedure is developed tomore » calculate the evolving spatial distribution of active material particles from images of the drying slurry drops. To the authors’ knowledge, this study is the first to use radiography to investigate battery slurry drying, as well as the first to determine particle distributions from radiography images of drying suspensions. The dynamic results are consistent with tomography reconstructions of the static, fully-dried films. It is found that active material particles can rapidly become non-uniformly distributed within the drops. Heating can promote distribution uniformity, but seemingly must be applied very soon after slurry deposition. Higher slurry viscosity is found to strongly restrain particle redistribution.« less

Oppositely charged colloids out of equilibrium

NASA Astrophysics Data System (ADS)

Vissers, T.

2010-11-01

Colloids are particles with a size in the range of a few nanometers up to several micrometers. Similar to atomic and molecular systems, they can form gases, liquids, solids, gels and glasses. Colloids can be used as model systems because, unlike molecules, they are sufficiently large to be studied directly with light microscopy and move sufficiently slow to study their dynamics. In this thesis, we study binary systems of polymethylmethacrylate (PMMA) colloidal particles suspended in low-polar solvent mixtures. Since the ions can still partially dissociate, a surface charge builds up which causes electrostatic interactions between the colloids. By carefully tuning the conditions inside the suspension, we make two kinds of particles oppositely charged. To study our samples, we use Confocal Laser Scanning Microscopy (CLSM). The positively and negatively charged particles can be distinguished by a different fluorescent dye. Colloids constantly experience a random motion resulting from random kicks of surrounding solvent molecules. When the attractions between the oppositely charged particles are weak, the particles can attach and detach many times and explore a lot of possible configurations and the system can reach thermodynamic equilibrium. For example, colloidal ‘ionic’ crystals consisting of thousands to millions of particles can form under the right conditions. When the attractions are strong, the system can become kinetically trapped inside a gel-like state. We observe that when the interactions change again, crystals can even emerge again from this gel-like phase. By using local order parameters, we quantitatively study the crystallization of colloidal particles and identify growth defects inside the crystals. We also study the effect of gravity on the growth of ionic crystals by using a rotating stage. We find that sedimentation can completely inhibit crystal growth and plays an important role in crystallization from the gel-like state. The surface potential and charge are studied by electrophoresis. Here, the velocity of the particles is measured while they are moving in an electric field. Using our real-space CLSM setup, we find that for a single-component system, the charge on the particles decreases with increasing volume fraction. Apart from structures that oppositely charged particles form close to thermodynamic equilibrium, we also study pattern formation when the system is driven out of equilibrium by an electric field. When oppositely charged particles are driven in opposite directions, the collisions between them cause particle of the same kind to form lanes. By combining our CLSM experiments with Brownian dynamics computer simulations, we study the structure and the dynamics of the suspension on the single-particle level. We find that the number of particles in a lane increases continuously with the field strength. By studying the dynamics and fluctuations parallel and perpendicular to the electric field direction, we identify the key mechanism of lane-formation. We show that pattern formation can easily become more complicated when we introduce alternating current (AC) fields. In addition to the formation of lanes parallel to the field-axis, bands of like-charged particles can form perpendicular to it. When the particles are sufficiently mobile, the system can be remixed again by changing the frequency. When AC-fields with higher field strengths are used, we show that complex patterns, including rotating instabilities, can emerge. The results in this thesis yield fundamental insight in electrophoresis, crystallization and pattern formation when systems are driven out of equilibrium. The results on lane- and band-formation can be relevant for the design of electronic ink (e-ink), where electrically driven oppositely charged particles are used to change the image on a piece of electronic paper.

Rearrangements and Yielding in Concentrated Suspensions of Hard and Soft Colloids

NASA Astrophysics Data System (ADS)

Petekidis, Georgios; Carrier, Vincent; Vlassoppoulos, Dimitris; Pusey, Peter; Ballauff, Matthias

2004-03-01

The rheology and microscopic particle rearrangements of concentrated colloidal suspensions were studied by a combination of conventional rheology and Light Scattering under shear (LS Echo). In particular we studied the rheological response and the microscopic particle dynamics under shear near and above the glass transitions concentration. Measurements were done in model hard and soft sphere particles (sterically stabilized PMMA and PS-PNIPA microgels respectively) to assess the effect of inter-particle interactions. Creep and recovery measurements and dynamic strain sweeps showed that glasses of hard particles can tolerate surprisingly large strains, up to at least 15probes the extent of irreversible particle rearrangement under oscillatory shear, verified that within their cage particles move reversibly at least up to such a strain. Such a behavior was attributed to 'cage elasticity', the ability of a particle and its neighbors to retain their relative positions within the cage under quite large distortion [1]. The onset of irreversible rearrangements measured by LS echo decreased with decreasing frequency revealing an interplay between shear and Brownian forces. The effects of interparticle interactions were studied using soft thermoreversible migrogel particles where a glass state may be reached either increasing the particle concentration or decreasing the temperature. Here, although particle rearrangements appear to be reversible up to strains as high as 100sweep is observed at much lower strains. [1] G. Petekidis, D. Vlassopoulos and P.N. Pusey, Faraday Discuss., 123, 287 (2003)

Small Particle Driven Chain Disentanglements in Polymer Nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Senses, Erkan; Ansar, Siyam M.; Kitchens, Christopher L.

2017-04-01

Using neutron spin-echo spectroscopy, X-ray photon correlation spectroscopy and bulk rheology, we studied the effect of particle size on the single chain dynamics, particle mobility, and bulk viscosity in athermal polyethylene oxide-gold nanoparticle composites. The results reveal an ≈ 25 % increase in the reptation tube diameter with addition of nanoparticles smaller than the entanglement mesh size (≈ 5 nm), at a volume fraction of 20 %. The tube diameter remains unchanged in the composite with larger (20 nm) nanoparticles at the same loading. In both cases, the Rouse dynamics is insensitive to particle size. These results provide a directmore » experimental observation of particle size driven disentanglements that can cause non-Einstein-like viscosity trends often observed in polymer nanocomposites.« less

Tracking control of colloidal particles through non-homogeneous stationary flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Híjar, Humberto, E-mail: humberto.hijar@lasallistas.org.mx

2013-12-21

We consider the problem of controlling the trajectory of a single colloidal particle in a fluid with steady non-homogeneous flow. We use a Langevin equation to describe the dynamics of this particle, where the friction term is assumed to be given by the Faxén's Theorem for the force on a sphere immersed in a stationary flow. We use this description to propose an explicit control force field to be applied on the particle such that it will follow asymptotically any given desired trajectory, starting from an arbitrary initial condition. We show that the dynamics of the controlled particle can bemore » mapped into a set of stochastic harmonic oscillators and that the velocity gradient of the solvent induces an asymmetric coupling between them. We study the particular case of a Brownian particle controlled through a plane Couette flow and show explicitly that the velocity gradient of the solvent renders the dynamics non-stationary and non-reversible in time. We quantify this effect in terms of the correlation functions for the position of the controlled particle, which turn out to exhibit contributions depending exclusively on the non-equilibrium character of the state of the solvent. In order to test the validity of our model, we perform simulations of the controlled particle moving in a simple shear flow, using a hybrid method combining molecular dynamics and multi-particle collision dynamics. We confirm numerically that the proposed guiding force allows for controlling the trajectory of the micro-sized particle by obligating it to follow diverse specific trajectories in fluids with homogeneous shear rates of different strengths. In addition, we find that the non-equilibrium correlation functions in simulations exhibit the same qualitative behavior predicted by the model, thus revealing the presence of the asymmetric non-equilibrium coupling mechanism induced by the velocity gradient.« less

On the micromechanics of slip events in sheared, fluid-saturated fault gouge

NASA Astrophysics Data System (ADS)

Dorostkar, Omid; Guyer, Robert A.; Johnson, Paul A.; Marone, Chris; Carmeliet, Jan

2017-06-01

We used a three-dimensional discrete element method coupled with computational fluid dynamics to study the poromechanical properties of dry and fluid-saturated granular fault gouge. The granular layer was sheared under dry conditions to establish a steady state condition of stick-slip dynamic failure, and then fluid was introduced to study its effect on subsequent failure events. The fluid-saturated case showed increased stick-slip recurrence time and larger slip events compared to the dry case. Particle motion induces fluid flow with local pressure variation, which in turn leads to high particle kinetic energy during slip due to increased drag forces from fluid on particles. The presence of fluid during the stick phase of loading promotes a more stable configuration evidenced by higher particle coordination number. Our coupled fluid-particle simulations provide grain-scale information that improves understanding of slip instabilities and illuminates details of phenomenological, macroscale observations.

Hybrid dynamic radioactive particle tracking (RPT) calibration technique for multiphase flow systems

NASA Astrophysics Data System (ADS)

Khane, Vaibhav; Al-Dahhan, Muthanna H.

2017-04-01

The radioactive particle tracking (RPT) technique has been utilized to measure three-dimensional hydrodynamic parameters for multiphase flow systems. An analytical solution to the inverse problem of the RPT technique, i.e. finding the instantaneous tracer positions based upon instantaneous counts received in the detectors, is not possible. Therefore, a calibration to obtain a counts-distance map is needed. There are major shortcomings in the conventional RPT calibration method due to which it has limited applicability in practical applications. In this work, the design and development of a novel dynamic RPT calibration technique are carried out to overcome the shortcomings of the conventional RPT calibration method. The dynamic RPT calibration technique has been implemented around a test reactor with 1foot in diameter and 1 foot in height using Cobalt-60 as an isotopes tracer particle. Two sets of experiments have been carried out to test the capability of novel dynamic RPT calibration. In the first set of experiments, a manual calibration apparatus has been used to hold a tracer particle at known static locations. In the second set of experiments, the tracer particle was moved vertically downwards along a straight line path in a controlled manner. The obtained reconstruction results about the tracer particle position were compared with the actual known position and the reconstruction errors were estimated. The obtained results revealed that the dynamic RPT calibration technique is capable of identifying tracer particle positions with a reconstruction error between 1 to 5.9 mm for the conditions studied which could be improved depending on various factors outlined here.

3D structural fluctuation of IgG1 antibody revealed by individual particle electron tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xing; Zhang, Lei; Tong, Huimin

2015-05-05

Commonly used methods for determining protein structure, including X-ray crystallography and single-particle reconstruction, often provide a single and unique three-dimensional (3D) structure. However, in these methods, the protein dynamics and flexibility/fluctuation remain mostly unknown. Here, we utilized advances in electron tomography (ET) to study the antibody flexibility and fluctuation through structural determination of individual antibody particles rather than averaging multiple antibody particles together. Through individual-particle electron tomography (IPET) 3D reconstruction from negatively-stained ET images, we obtained 120 ab-initio 3D density maps at an intermediate resolution (~1–3 nm) from 120 individual IgG1 antibody particles. Using these maps as a constraint, wemore » derived 120 conformations of the antibody via structural flexible docking of the crystal structure to these maps by targeted molecular dynamics simulations. Statistical analysis of the various conformations disclosed the antibody 3D conformational flexibility through the distribution of its domain distances and orientations. This blueprint approach, if extended to other flexible proteins, may serve as a useful methodology towards understanding protein dynamics and functions.« less

Non-invasive studies of multiphase flow in process equipment. Positron emission particle tracking technique

NASA Astrophysics Data System (ADS)

Balakin, B. V.; Adamsen, T. C. H.; Chang, Y.-F.; Kosinski, P.; Hoffmann, A. C.

2017-01-01

Positron emission particle tracking (PEPT) is a novel experimental technique for non-invasive inspection of industrial fluid/particle flows. The method is based on the dynamic positioning of a positron-emitting, flowing object (particle) performed through the sensing of annihilation events and subsequent numerical treatment to determine the particle position. The present paper shows an integrated overview of PEPT studies which were carried out using a new PET scanner in the Bergen University Hospital to study multiphase flows in different geometric configurations.

Numerical study of impact erosion of multiple solid particle

NASA Astrophysics Data System (ADS)

Zheng, Chao; Liu, Yonghong; Chen, Cheng; Qin, Jie; Ji, Renjie; Cai, Baoping

2017-11-01

Material erosion caused by continuous particle impingement during hydraulic fracturing results in significant economic loss and increased production risks. The erosion process is complex and has not been clearly explained through physical experiments. To address this problem, a multiple particle model in a 3D configuration was proposed to investigate the dynamic erosion process. This approach can significantly reduce experiment costs. The numerical model considered material damping and elastic-plastic material behavior of target material. The effects of impact parameters on erosion characteristics, such as plastic deformation, contact time, and energy loss rate, were investigated. Based on comprehensive studies, the dynamic erosion mechanism and geometry evolution of eroded crater was obtained. These findings can provide a detailed erosion process of target material and insights into the material erosion caused by multiple particle impingement.

The transport of wear particles in the prosthetic hip joint: a computational fluid dynamics investigation.

PubMed

Hölzer, Andreas; Schröder, Christian; Woiczinski, Matthias; Sadoghi, Patrick; Müller, Peter E; Jansson, Volkmar

2012-02-02

The joint fluid mechanics and transport of wear particles in the prosthetic hip joint were analyzed for subluxation and flexion motion using computational fluid dynamics (CFD). The entire joint space including a moving capsule boundary was considered. It was found that particles suspended in the joint space are drawn into the joint gap between prosthesis cup and head during subluxation, which was also documented by Lundberg et al. (2007; Journal of Biomechanics 40, 1676-1685), however, wear particles remain in the joint gap. Wear particles leave the joint gap during flexion and can finally migrate to the proximal boundaries including the acetabular bone, where the particle deposition can cause osteolysis according to the established literature. Thus, the present study supports the theory of polyethylene wear particle induced osteolysis of the acetabular bone as a major factor in the loosening of hip prosthesis cups. Copyright © 2011 Elsevier Ltd. All rights reserved.

Ion size effects on the electrokinetics of spherical particles in salt-free concentrated suspensions

NASA Astrophysics Data System (ADS)

Roa, Rafael; Carrique, Felix; Ruiz-Reina, Emilio

2012-02-01

In this work we study the influence of the counterion size on the electrophoretic mobility and on the dynamic mobility of a suspended spherical particle in a salt-free concentrated colloidal suspension. Salt-free suspensions contain charged particles and the added counterions that counterbalance their surface charge. A spherical cell model approach is used to take into account particle-particle electro-hydrodynamic interactions in concentrated suspensions. The finite size of the counterions is considered including an entropic contribution, related with the excluded volume of the ions, in the free energy of the suspension, giving rise to a modified counterion concentration profile. We are interested in studying the linear response of the system to an electric field, thus we solve the different electrokinetic equations by using a linear perturbation scheme. We find that the ionic size effect is quite important for moderate to high particles charges at a given particle volume fraction. In addition for such particle surface charges, both the electrophoretic mobility and the dynamic mobility suffer more important changes the larger the particle volume fraction for each ion size. The latter effects are more relevant the larger the ionic size.

Dynamical turbulent flow on the Galton board with friction.

PubMed

Chepelianskii, A D; Shepelyansky, D L

2001-07-16

We study numerically and analytically the dynamics of charged particles on the Galton board, a regular lattice of disk scatters, in the presence of constant external force, magnetic field, and friction. It is shown that under certain conditions friction leads to the appearance of a strange chaotic attractor. In this regime the average velocity and direction of particle flow can be effectively affected by electric and magnetic fields. We discuss the applications of these results to the charge transport in antidot superlattices and the stream of suspended particles in a viscous flow through scatters.

Thermodynamic and Dynamic Aspects of Ice Nucleation

NASA Technical Reports Server (NTRS)

Barahona, Donifan

2018-01-01

It is known that ice nucleating particles (INP) immersed within supercooled droplets promote the formation of ice. Common theoretical models used to represent this process assume that the immersed particle lowers the work of ice nucleation without significantly affecting the dynamics of water in the vicinity of the particle. This is contrary to evidence showing that immersed surfaces significantly affect the viscosity and diffusivity of vicinal water. To study how this may affect ice formation this work introduces a model linking the ice nucleation rate to the modification of the dynamics and thermodynamics of vicinal water by immersed particles. It is shown that INP that significantly reduce the work of ice nucleation also pose strong limitations to the growth of the nascent ice germs. This leads to the onset of a new ice nucleation regime, called spinodal ice nucleation, where the dynamics of ice germ growth instead of the ice germ size determines the nucleation rate. Nucleation in this regime is characterized by an enhanced sensitivity to particle area and cooling rate. Comparison of the predicted ice nucleation rate against experimental measurements for a diverse set of species relevant to cloud formation suggests that spinodal ice nucleation may be common in nature.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Higa, Kenneth; Zhao, Hui; Parkinson, Dilworth Y.

The internal structure of a porous electrode strongly influences battery performance. Understanding the dynamics of electrode slurry drying could aid in engineering electrodes with desired properties. For instance, one might monitor the dynamic, spatially-varying thickness near the edge of a slurry coating, as it should lead to non-uniform thickness of the dried film. This work examines the dynamic behavior of drying slurry drops consisting of SiO x and carbon black particles in a solution of carboxymethylcellulose and deionized water, as an experimental model of drying behavior near the edge of a slurry coating. An X-ray radiography-based procedure is developed tomore » calculate the evolving spatial distribution of active material particles from images of the drying slurry drops. To the authors’ knowledge, this study is the first to use radiography to investigate battery slurry drying, as well as the first to determine particle distributions from radiography images of drying suspensions. The dynamic results are consistent with tomography reconstructions of the static, fully-dried films. It is found that active material particles can rapidly become non-uniformly distributed within the drops. Heating can promote distribution uniformity, but seemingly must be applied very soon after slurry deposition. Higher slurry viscosity is found to strongly restrain particle redistribution.« less

Dynamics of aspherical dust grains in a cometary atmosphere: I. axially symmetric grains in a spherically symmetric atmosphere

NASA Astrophysics Data System (ADS)

Ivanovski, S. L.; Zakharov, V. V.; Della Corte, V.; Crifo, J.-F.; Rotundi, A.; Fulle, M.

2017-01-01

In-situ measurements of individual dust grain parameters in the immediate vicinity of a cometary nucleus are being carried by the Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko. For the interpretations of these observational data, a model of dust grain motion as realistic as possible is requested. In particular, the results of the Stardust mission and analysis of samples of interplanetary dust have shown that these particles are highly aspherical, which should be taken into account in any credible model. The aim of the present work is to study the dynamics of ellipsoidal shape particles with various aspect ratios introduced in a spherically symmetric expanding gas flow and to reveal the possible differences in dynamics between spherical and aspherical particles. Their translational and rotational motion under influence of the gravity and of the aerodynamic force and torque is numerically integrated in a wide range of physical parameters values including those of comet 67P/Churyumov-Gerasimenko. The main distinctions of the dynamics of spherical and ellipsoidal particles are discussed. The aerodynamic characteristics of the ellipsoidal particles, and examples of their translational and rotational motion in the postulated gas flow are presented.

Modeling and Bio molecular Self-assembly via Molecular Dynamics and Dissipative Particle Dynamics

NASA Astrophysics Data System (ADS)

Rakesh, L.

2009-09-01

Surfactants like materials can be used to increase the solubility of poorly soluble drugs in water and to increase drug bioavailability. A typical case study will be demonstrated using DPD simulation to model the distribution of anti-inflammatory drug molecules. Computer simulation is a convenient approach to understand drug distribution and solubility concepts without much wastage and costly experiments in the laboratory. Often in molecular dynamics (MD) the atoms are represented explicitly and the equation of motion as described by Newtonian dynamics is integrated explicitly. MD has been used to study spontaneous formation of micelles by hydrophobic molecules with amphiphilic head groups in bulk water, as well as stability of pre-configured micelles and membranes. DPD is a state-of the- art mesoscale simulation, it is a more recent molecular dynamics technique, originally developed for simulating complex fluids but lately also applied to membrane dynamics, hemodynamic in biomedical applications. Such fluids pervade industrial research from paints to pharmaceuticals and from cosmetics to the controlled release of drugs. Dissipative particle dynamics (DPD) can provide structural and dynamic properties of fluids in equilibrium, under shear or confined to narrow cavities, at length- and time-scales beyond the scope of traditional atomistic molecular dynamics simulation methods. Mesoscopic particles are used to represent clusters of molecules. The interaction conserves mass and momentum and as a consequence the dynamics is consistent with Navier-Stokes equations. In addition to the conservative forces, stochastic drive and dissipation is introduced to represent internal degrees of freedom in the mesoscopic particles. In this research, an initial study is being conducted using the aqueous solubilization of the nonsteroidal, anti-inflammatory drug is studied theoretically in micellar solution of nonionic (dodecyl hexa(ethylene oxide), C12E6) surfactants possessing the hydrocarbon "tail" and their hydrophilic head groups. We find that, for the surfactants, the aqueous solubility of anti-inflammatory molecules increases linearly with increasing surfactant concentration. In particular, we observed a 10-fold increase in the solubility of anti-inflammatory drugs relative to that in the aqueous buffer upon the addition of 100 mM dodecyltrimethyl ammonium bromide -DTAB.

Dynamic properties of micro-particles in ultrasonic transportation using phase-controllable standing waves

NASA Astrophysics Data System (ADS)

Jia, Kun; Mei, Deqing; Meng, Jianxin; Yang, Keji

2014-10-01

Ultrasonic manipulation has become an attractive method for surface-sensitive objects in micro-technology. Related phenomena, such as radiation force, multiple scattering, and acoustic streaming, have been widely studied. However, in current studies, the behavior of micro-particles in potential force fields is always analyzed in a quasi-static manner. We developed a dynamic model of a dilute micro-particle in the commonly used two-dimensional ultrasonic manipulation system to provide a systemic and quantitative analysis of the transient properties of particle movement. In this model, the acoustic streaming and hydrodynamic forces, omitted in previous work, were both considered. The trajectory of a spherical silica particle with different initial conditions was derived by numerically solving the established nonlinear differential integral equation system, which was then validated experimentally. The envelope of the experimental data on the x-axis showed good agreement with the theoretical calculation, and the greater influence on the y-axis of the deviation between the actual sound field and the ideal distribution employed in our dynamic model could account for the differences in displacement in that direction. Finally, the influence of particle size on its movement and the effect of acoustic streaming on calculating the hydrodynamic forces for an isolated particle with motion relative to the fluid were analyzed theoretically. It was found that the ultrasonic manipulation system will translate from an under-damped system to an over-damped system with a decrease in particle size and the micro-scale acoustic streaming velocity was negligible when calculating the hydrodynamic forces on the particle in the ultrasonic manipulation system.

Effect of work of adhesion on deep bed filtration process

NASA Astrophysics Data System (ADS)

Przekop, Rafał; Jackiewicz, Anna; WoŻniak, Michał; Gradoń, Leon

2016-06-01

Collection of aerosol particles in the particular steps of the technology of their production, and purification of the air at the workplace and atmospheric environment, requires the efficient method of separation of particulate matter from the carrier gas. There are many papers published in last few years in which the deposition of particles on fibrous collectors is considered, Most of them assume that collisions between particle and collector surface is 100% effective. In this work we study the influence of particles and fiber properties on the deposition efficiency. For the purpose of this work the lattice-Boltzmann model describes fluid dynamics, while the solid particle motion is modeled by the Brownian dynamics. The interactions between particles and surface are modelled using energy balanced oscillatory model. The work of adhesion was estimated using Atomic Force Microscopy.

Effect of work of adhesion on deep bed filtration process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Przekop, Rafał; Jackiewicz, Anna; Gradoń, Leon

2016-06-08

Collection of aerosol particles in the particular steps of the technology of their production, and purification of the air at the workplace and atmospheric environment, requires the efficient method of separation of particulate matter from the carrier gas. There are many papers published in last few years in which the deposition of particles on fibrous collectors is considered, Most of them assume that collisions between particle and collector surface is 100% effective. In this work we study the influence of particles and fiber properties on the deposition efficiency. For the purpose of this work the lattice-Boltzmann model describes fluid dynamics,more » while the solid particle motion is modeled by the Brownian dynamics. The interactions between particles and surface are modelled using energy balanced oscillatory model. The work of adhesion was estimated using Atomic Force Microscopy.« less

Effects of the finite particle size in turbulent wall-bounded flows of dense suspensions

NASA Astrophysics Data System (ADS)

Costa, Pedro; Picano, Francesco; Brandt, Luca; Breugem, Wim-Paul

2018-05-01

We use interface-resolved simulations to study finite-size effects in turbulent channel flow of neutrally-buoyant spheres. Two cases with particle sizes differing by a factor of 2, at the same solid volume fraction of 20% and bulk Reynolds number are considered. These are complemented with two reference single-phase flows: the unladen case, and the flow of a Newtonian fluid with the effective suspension viscosity of the same mixture in the laminar regime. As recently highlighted in Costa et al. (PRL 117, 134501), a particle-wall layer is responsible for deviations of the statistics from what is observed in the continuum limit where the suspension is modeled as a Newtonian fluid with an effective viscosity. Here we investigate the fluid and particle dynamics in this layer and in the bulk. In the particle-wall layer, the near wall inhomogeneity has an influence on the suspension micro-structure over a distance proportional to the particle size. In this layer, particles have a significant (apparent) slip velocity that is reflected in the distribution of wall shear stresses. This is characterized by extreme events (both much higher and much lower than the mean). Based on these observations we provide a scaling for the particle-to-fluid apparent slip velocity as a function of the flow parameters. We also extend the flow scaling laws in to second-order Eulerian statistics in the homogeneous suspension region away from the wall. Finite-size effects in the bulk of the channel become important for larger particles, while negligible for lower-order statistics and smaller particles. Finally, we study the particle dynamics along the wall-normal direction. Our results suggest that 1-point dispersion is dominated by particle-turbulence (and not particle-particle) interactions, while differences in 2-point dispersion and collisional dynamics are consistent with a picture of shear-driven interactions.

An elementary singularity-free Rotational Brownian Dynamics algorithm for anisotropic particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ilie, Ioana M.; Briels, Wim J.; MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede

2015-03-21

Brownian Dynamics is the designated technique to simulate the collective dynamics of colloidal particles suspended in a solution, e.g., the self-assembly of patchy particles. Simulating the rotational dynamics of anisotropic particles by a first-order Langevin equation, however, gives rise to a number of complications, ranging from singularities when using a set of three rotational coordinates to subtle metric and drift corrections. Here, we derive and numerically validate a quaternion-based Rotational Brownian Dynamics algorithm that handles these complications in a simple and elegant way. The extension to hydrodynamic interactions is also discussed.

Modeling and simulation of dielectrophoretic collective dynamics in a suspension of polarizable particles under the action of a gradient AC electric field.

PubMed

Tada, Shigeru; Shen, Yan; Qiu, Zhiyong

2017-06-01

When a suspension of polarizable particles is subjected to a gradient AC electric field, the particles exhibit collective motion due to an interaction between the dipole induced in the particles and the spatial gradient of the electric field; this is known as dielectrophoresis. In the present study, the collective dynamics of suspended particles in a parallel-plate electric chamber was investigated by simulating numerically the trajectories of individual particles under the action of combined dielectrophoretic and dipole-dipole interparticle forces. The particles were transported by the dielectrophoretic forces toward the grounded electrodes. Before long, when the particles approached the site of the minimum field strength, attractive/repulsive interparticle forces became dominant and acted among the particles attempting to form a column-like cluster, having the particles distribution in concentric circles in its cross-section, in line with the centerline of the grounded electrodes. Our results also well reproduced the transient particle aggregation that was observed experimentally. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Radiation reaction effect on laser driven auto-resonant particle acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sagar, Vikram; Sengupta, Sudip; Kaw, P. K.

2015-12-15

The effects of radiation reaction force on laser driven auto-resonant particle acceleration scheme are studied using Landau-Lifshitz equation of motion. These studies are carried out for both linear and circularly polarized laser fields in the presence of static axial magnetic field. From the parametric study, a radiation reaction dominated region has been identified in which the particle dynamics is greatly effected by this force. In the radiation reaction dominated region, the two significant effects on particle dynamics are seen, viz., (1) saturation in energy gain by the initially resonant particle and (2) net energy gain by an initially non-resonant particlemore » which is caused due to resonance broadening. It has been further shown that with the relaxation of resonance condition and with optimum choice of parameters, this scheme may become competitive with the other present-day laser driven particle acceleration schemes. The quantum corrections to the Landau-Lifshitz equation of motion have also been taken into account. The difference in the energy gain estimates of the particle by the quantum corrected and classical Landau-Lifshitz equation is found to be insignificant for the present day as well as upcoming laser facilities.« less

A simple dynamic subgrid-scale model for LES of particle-laden turbulence

NASA Astrophysics Data System (ADS)

Park, George Ilhwan; Bassenne, Maxime; Urzay, Javier; Moin, Parviz

2017-04-01

In this study, a dynamic model for large-eddy simulations is proposed in order to describe the motion of small inertial particles in turbulent flows. The model is simple, involves no significant computational overhead, contains no adjustable parameters, and is flexible enough to be deployed in any type of flow solvers and grids, including unstructured setups. The approach is based on the use of elliptic differential filters to model the subgrid-scale velocity. The only model parameter, which is related to the nominal filter width, is determined dynamically by imposing consistency constraints on the estimated subgrid energetics. The performance of the model is tested in large-eddy simulations of homogeneous-isotropic turbulence laden with particles, where improved agreement with direct numerical simulation results is observed in the dispersed-phase statistics, including particle acceleration, local carrier-phase velocity, and preferential-concentration metrics.

Emergent dynamics of Cucker-Smale particles under the effects of random communication and incompressible fluids

NASA Astrophysics Data System (ADS)

Ha, Seung-Yeal; Xiao, Qinghua; Zhang, Xiongtao

2018-04-01

We study the dynamics of infinitely many Cucker-Smale (C-S) flocking particles under the interplay of random communication and incompressible fluids. For the dynamics of an ensemble of flocking particles, we use the kinetic Cucker-Smale-Fokker-Planck (CS-FP) equation with a degenerate diffusion, whereas for the fluid component, we use the incompressible Navier-Stokes (N-S) equations. These two subsystems are coupled via the drag force. For this coupled model, we present the global existence of weak and strong solutions in Rd (d = 2 , 3). Under the extra regularity assumptions of the initial data, the unique solvability of strong solutions is also established in R2. In a large coupling regime and periodic spatial domain T2 : =R2 /Z2, we show that the velocities of C-S particles and fluids are asymptotically aligned to two constant velocities which may be different.

The Relative Effectiveness of the Use of Static and Dynamic Mechanical Models in Teaching Elementary School Children the Theoretical Concept--The Particle Nature of Matter.

ERIC Educational Resources Information Center

Ziegler, Robert Edward

This study is concerned with determining the relative effectiveness of a static and dynamic theoretical model in teaching elementary school students to use the particle idea of matter when explaining certain physical phenomena. A clinical method of personal individual interview-testing, teaching, and retesting of a random sample population from…

Noise enhanced stability of a metastable state containing coupled Brownian particles

NASA Astrophysics Data System (ADS)

Singh, R. K.

2017-05-01

Dynamics of coupled Brownian particles with color correlated additive Gaussian colored noises in a metastable state is analyzed to study the phenomenon of noise enhanced stability. The lifetime of such a metastable state is found to depend on the noise correlations and initial conditions. Dynamics of the slow variable is analyzed using the method of adiabatic elimination in the weak color limit.

Diffusive real-time dynamics of a particle with Berry curvature

NASA Astrophysics Data System (ADS)

Misaki, Kou; Miyashita, Seiji; Nagaosa, Naoto

2018-02-01

We study theoretically the influence of Berry phase on the real-time dynamics of the single particle focusing on the diffusive dynamics, i.e., the time dependence of the distribution function. Our model can be applied to the real-time dynamics of intraband relaxation and diffusion of optically excited excitons, trions, or particle-hole pair. We found that the dynamics at the early stage is deeply influenced by the Berry curvature in real space (B ), momentum space (Ω ), and also the crossed space between these two (C ). For example, it is found that Ω induces the rotation of the wave packet and causes the time dependence of the mean square displacement of the particle to be linear in time t at the initial stage; it is qualitatively different from the t3 dependence in the absence of the Berry curvature. It is also found that Ω and C modify the characteristic time scale of the thermal equilibration of momentum distribution. Moreover, the dynamics under various combinations of B ,Ω , and C shows singular behaviors such as the critical slowing down or speeding up of the momentum equilibration and the reversals of the direction of rotations. The relevance of our model for time-resolved experiments in transition metal dichalcogenides is also discussed.

Dynamic behavior of microscale particles controlled by standing bulk acoustic waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greenhall, J.; Raeymaekers, B., E-mail: bart.raeymaekers@utah.edu; Guevara Vasquez, F.

2014-10-06

We analyze the dynamic behavior of a spherical microparticle submerged in a fluid medium, driven to the node of a standing bulk acoustic wave created by two opposing transducers. We derive the dynamics of the fluid-particle system taking into account the acoustic radiation force and the time-dependent and time-independent drag force acting on the particle. Using this dynamic model, we characterize the transient and steady-state behavior of the fluid-particle system as a function of the particle and fluid properties and the transducer operating parameters. The results show that the settling time and percent overshoot of the particle trajectory are dependentmore » on the ratio of the acoustic radiation force and time-independent damping force. In addition, we show that the particle oscillates around the node of the standing wave with an amplitude that depends on the ratio of the time-dependent drag forces and the particle inertia.« less

Fluorescence-correlation spectroscopy study of molecular transport within reversed-phase chromatographic particles compared to planar model surfaces.

PubMed

Cooper, Justin; Harris, Joel M

2014-12-02

Reversed-phase liquid chromatography (RPLC) is a widely used technique for molecular separations. Stationary-phase materials for RPLC generally consist of porous silica-gel particles functionalized with n-alkane ligands. Understanding motions of molecules within the interior of these particles is important for developing efficient chromatographic materials and separations. To characterize these dynamics, time-resolved spectroscopic methods (photobleach recovery, fluorescence correlation, single-molecule imaging) have been adapted to measure molecular diffusion rates, typically at n-alkane-modified planar silica surfaces, which serve as models of chromatographic interfaces. A question arising from these studies is how dynamics of molecules on a planar surface relate to motions of molecules within the interior of a porous chromatographic particle. In this paper, imaging-fluorescence-correlation spectroscopy is used to measure diffusion rates of a fluorescent probe molecule 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate (DiI) within authentic RPLC porous silica particles and compared with its diffusion at a planar C18-modified surface. The results show that surface diffusion on the planar C18 substrate is much faster than the diffusion rate of the probe molecule through a chromatographic particle. Surface diffusion within porous particles, however, is governed by molecular trajectories along the tortuous contours of the interior surface of the particles. By accounting for the greater surface area that a molecule must explore to diffuse macroscopic distances through the particle, the molecular-scale diffusion rates on the two surfaces can be compared, and they are virtually identical. These results provide support for the relevance of surface-diffusion measurements made on planar model surfaces to the dynamic behavior of molecules on the internal surfaces of porous chromatographic particles.

Particle Dynamics Simulation for Aeroengine Intake Design

DTIC Science & Technology

1999-09-10

Turbo Propulsores. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. ß Particle impingement angle p Fluid...2. March-April 1995. [4] Hamed, A., "Particle Dynamics of Inlet Flowfields with Swirling Vanes ". Journal of Aircraft ., Vol.19, Sep 1982, pp 707-712...DISTRIBUTION STATEMENT A Approved for Public Release Distribution Unlimited ISABE 99-7280 PARTICLE DYNAMICS SIMULATION FOR AEROENGINE INTAKE

Dynamics of the Wigner crystal of composite particles

NASA Astrophysics Data System (ADS)

Shi, Junren; Ji, Wencheng

2018-03-01

Conventional wisdom has long held that a composite particle behaves just like an ordinary Newtonian particle. In this paper, we derive the effective dynamics of a type-I Wigner crystal of composite particles directly from its microscopic wave function. It indicates that the composite particles are subjected to a Berry curvature in the momentum space as well as an emergent dissipationless viscosity. While the dissipationless viscosity is the Chern-Simons field counterpart for the Wigner crystal, the Berry curvature is a feature not presented in the conventional composite fermion theory. Hence, contrary to general belief, composite particles follow the more general Sundaram-Niu dynamics instead of the ordinary Newtonian one. We show that the presence of the Berry curvature is an inevitable feature for a dynamics conforming to the dipole picture of composite particles and Kohn's theorem. Based on the dynamics, we determine the dispersions of magnetophonon excitations numerically. We find an emergent magnetoroton mode which signifies the composite-particle nature of the Wigner crystal. It occurs at frequencies much lower than the magnetic cyclotron frequency and has a vanishing oscillator strength in the long-wavelength limit.

Digital stereo-holographic microscopy for studying three-dimensional particle dynamics

NASA Astrophysics Data System (ADS)

Byeon, Hyeokjun; Go, Taesik; Lee, Sang Joon

2018-06-01

A digital stereo-holographic microscopy (DsHM) with two viewing angles is proposed to measure 3D information of microscale particles. This approach includes two volumetric recordings and numerical reconstruction, and it involves the combination of separately reconstructed holograms. The 3D positional information of a particle was determined by searching the center of the overlapped reconstructed volume. After confirming the proposed technique using static spherical particles, the 3D information of moving particles suspended in a Hagen-Poiseiulle flow was successfully obtained. Moreover, the 3D information of nonspherical particles, including ellipsoidal particles and red blood cells, were measured using the proposed technique. In addition to 3D positional information, the orientation and shape of the test samples were obtained from the plane images by slicing the overlapped volume perpendicular to the directions of the image recordings. This DsHM technique will be useful in analyzing the 3D dynamic behavior of various nonspherical particles, which cannot be measured by conventional digital holographic microscopy.

Development and applications of single particle orientation and rotational tracking in dynamic systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Kuangcai

The goal of this study is to help with future data analysis and experiment designs in rotational dynamics research using DIC-based SPORT technique. Most of the current studies using DIC-based SPORT techniques are technical demonstrations. Understanding the mechanisms behind the observed rotational behaviors of the imaging probes should be the focus of the future SPORT studies. More efforts are still needed in the development of new imaging probes, particle tracking methods, instrumentations, and advanced data analysis methods to further extend the potential of DIC-based SPORT technique.

A Hamiltonian Model of Dissipative Wave-particle Interactions and the Negative-mass Effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

A. Zhmoginov

2011-02-07

The effect of radiation friction is included in the Hamiltonian treatment of wave-particle interactions with autoresonant phase-locking, yielding a generalized canonical approach to the problem of dissipative dynamics near a nonlinear resonance. As an example, the negativemass eff ect exhibited by a charged particle in a pump wave and a static magnetic field is studied in the presence of the friction force due to cyclotron radiation. Particles with negative parallel masses m! are shown to transfer their kinetic energy to the pump wave, thus amplifying it. Counterintuitively, such particles also undergo stable dynamics, decreasing their transverse energy monotonically due tomore » cyclotron cooling, whereas some of those with positive m! undergo cyclotron heating instead, extracting energy from the pump wave.« less

Molecular dynamics simulation of the coalescence and melting process of Au and Cu nano-clusters

NASA Astrophysics Data System (ADS)

Chen, Gang; Wang, Chuan Jie; Zhang, Peng

2018-03-01

Molecular dynamic (MD) method is used to study the coalescence and fusing process of Au and Cu nanoclusters. The results show that shear deformation, surface and interface diffusion play important role in different stages of all simulation procedure. In most cases, shear deformation produces the twin boundary or/and stacking fault in particles by particle rotation and slide. The angle between the {111} of Au and Cu particles decrease with increasing temperature, which promotes the formation of the stable interface. Furthermore, the coalescence point and melting temperature increase as cluster diameter increases. For the other cases, there are no particle rotation and slide phenomenon in the elevating temperature process because the stable interface can be formed by forming twin boundaries once two particles contact.

Non-Destructive Evaluation of Material System Using Highly Nonlinear Acoustic Waves

NASA Astrophysics Data System (ADS)

Khatri, Devvrath

A chain of granular particles is one of the most studied examples of highly nonlinear systems deriving its response from the nonlinear Hertzian contact interaction between particles. Interest in these systems derives from their tunable dynamic response, encompassing linear, weakly nonlinear, and strongly nonlinear regimes, controlled by varying the static and dynamic load applied. In chains with a very weak (or zero) static precompression, the system supports the formation and propagation of highly nonlinear solitary waves (HNSWs). The dual-nonlinear interaction between particles (i.e., a power-law type contact potential in compression, and zero strength in tension) combined with discreteness of the system, makes the granular system highly tunable. The propagation properties of these waves, such as traveling pulse width, wave speed, number of separated pulses (single or train of pulses), etc., can be controlled by modifying one or many of the parameters, like the particle's dimension, material properties, static and dynamic force amplitude, the type and duration of the initial excitation applied to the system, and/or the periodicity of the chain. The ability to control the wave properties in such chains has been proposed for several different practical engineering applications. The dynamic properties of these granular chains have been conventionally studied using discrete particle models (DPMs) which consider the particles in the chains as point masses connected by nonlinear Hertzian springs with the neighboring particles. Although, this is a good approximation under proper circumstances, it does not capture many features of the three dimensional elastic particles such as the elastic wave propagation within the particles, the local deformation of the particles in the vicinity of the contact point, the corresponding changes in the contact area, and the collective vibrations of the particles among others. This thesis focuses on the development of a finite element model (FEM) using the commercially available software Abaqus, which takes into account many of these characteristic features. The finite element model discretizes particles by considering them as three-dimensional deformable bodies of revolution and describes the nonlinear dynamic response of one-dimensional granular chains composed of particles with various geometries and orientations. We showed that particles' geometries and orientations provide additional design parameters for controlling the dynamic response of the system, compared to chains composed of spherical particles. We also showed that the tunable and compact nature of these waves can be used to tailor the properties of HNSWs for specific application, such as information carriers for actuation and sensing of mechanical properties and boundary effects of adjoining media in Non-Destructive Evaluation (NDE) and Structural Health Monitoring (SHM). Using experiments and numerics, we characterized interface dynamics between granular media and adjoining linear elastic media, and found that the coupling produced temporary localization of the incident waves at the boundaries between the two media and their decomposition into reflected waves. We monitored the formation of reflected solitary waves propagating back from the interface and found that their properties are sensitive to the geometric and material properties of the adjoining media. The work done in this research enhances our understanding of the basic physics and tunability of nonlinear granular media, and further establishes a theoretical and numerical foundation in the applications of HNSWs as information carriers.

Ordered and disordered dynamics in monolayers of rolling particles.

PubMed

Kim, Byungsoo; Putkaradze, Vakhtang

2010-12-10

We consider the ordered and disordered dynamics for monolayers of rolling self-interacting particles modeling water molecules. The rolling constraint represents a simplified model of a strong, but rapidly decaying bond with the surface. We show the existence and nonlinear stability of ordered lattice states, as well as disturbance propagation through and chaotic vibrations of these states. We study the dynamics of disordered gas states and show that there is a surprising and universal linear connection between distributions of angular and linear velocity, allowing definition of temperature.

Desorption to Delamination: Dynamics of Detachment in a Colloidal Thin Film

NASA Astrophysics Data System (ADS)

Varshney, Atul; Sharma, P.; Sane, A.; Ghosh, S.; Bhattacharya, S.

2010-10-01

Colloidal thin films of varying rigidity detaching from a substrate under an electric field induced stress are studied by video microscopy. For soft films, the process of detachment shows single-particle dynamics, analogous to desorption. For rigid films, a collective delamination spanning hundreds of particles occurs. A competition among the rigidity of the film, the interaction with the substrate, and the external stress leads to a correlation length over which the film delaminates at a critical stress. The phenomenon is described as a dynamical transition in a disordered elastic medium.

Particle Creation in Oscillating Cavities with Cubic and Cylindrical Geometry

NASA Astrophysics Data System (ADS)

Setare, M. R.; Dinani, H. T.

2008-04-01

In the present paper we study the creation of massless scalar particles from the quantum vacuum due to the dynamical Casimir effect by oscillating cavities with cubic and cylindrical geometry. To the first order of the amplitude we derive the expressions for the number of the created particles.

Detection of weak signals through nonlinear relaxation times for a Brownian particle in an electromagnetic field.

PubMed

Jiménez-Aquino, J I; Romero-Bastida, M

2011-07-01

The detection of weak signals through nonlinear relaxation times for a Brownian particle in an electromagnetic field is studied in the dynamical relaxation of the unstable state, characterized by a two-dimensional bistable potential. The detection process depends on a dimensionless quantity referred to as the receiver output, calculated as a function of the nonlinear relaxation time and being a characteristic time scale of our system. The latter characterizes the complete dynamical relaxation of the Brownian particle as it relaxes from the initial unstable state of the bistable potential to its corresponding steady state. The one-dimensional problem is also studied to complement the description.

Stochastic driven systems far from equilibrium

NASA Astrophysics Data System (ADS)

Kim, Kyung Hyuk

We study the dynamics and steady states of two systems far from equilibrium: a 1-D driven lattice gas and a driven Brownian particle with inertia. (1) We investigate the dynamical scaling behavior of a 1-D driven lattice gas model with two species of particles hopping in opposite directions. We confirm numerically that the dynamic exponent is equal to z = 1.5. We show analytically that a quasi-particle representation relates all phase points to a special phase line directly related to the single-species asymmetric simple exclusion process. Quasi-particle two-point correlations decay exponentially, and in such a manner that quasi-particles of opposite charge dynamically screen each other with a special balance. The balance encompasses all over the phase space. These results indicate that the model belongs to the Kardar-Parisi-Zhang (KPZ) universality class. (2) We investigate the non-equilibrium thermodynamics of a Brownian particle with inertia under feedback control of its inertia. We find such open systems can act as a molecular refrigerator due to an entropy pumping mechanism. We extend the fluctuation theorems to the refrigerator. The entropy pumping modifies both the Jarzynski equality and the fluctuation theorems. We discover that the entropy pumping has a dual role of work and heat. We also investigate the thermodynamics of the particle under a hydrodynamic interaction described by a Langevin equation with a multiplicative noise. The Stratonovich stochastic integration prescription involved in the definition of heat is shown to be the unique physical choice.

Cooperative particle motion in complex (dusty) plasmas

NASA Astrophysics Data System (ADS)

Zhdanov, Sergey; Morfill, Gregor

2014-05-01

Strongly coupled complex (dusty) plasmas give us a unique opportunity to go beyond the limits of continuous media and study various generic processes occurring in liquids or solids at the kinetic level. A particularly interesting and challenging topic is to study dynamic cooperativity at local and intermediate scales. As an important element of self-organization, cooperative particle motion is present in many physical, astrophysical and biological systems. As a rule, cooperative dynamics, bringing to life 'abnormal' effects like enhanced diffusion, self-dragging, or self-propelling of particles, hold aspects of 'strange' kinetics. The synergy effects are also important. Such kind of cooperative behavior was evidenced for string-like formations of colloidal rods, dynamics of mono- and di-vacancies in 2d colloidal crystals. Externally manipulated 'dust molecules' and self-assembled strings in driven 3d particle clusters were other noticeable examples. There is a certain advantage to experiment with complex plasmas merely because these systems are easy to manipulate in a controllable way. We report on the first direct observation of microparticle cooperative movements occurring under natural conditions in a 2d complex plasma.

Dusty Plasma Dynamics Near Surfaces in Space

NASA Technical Reports Server (NTRS)

Colwell, Joshua E.; Robertson, S.; Horanyi, M.; Nahra, Henry (Technical Monitor)

1998-01-01

The investigation 'Dusty Plasma Dynamics Near Surfaces in Space' is an experimental and theoretical study of the dynamics of dust particles on airless bodies in the solar system in the presence of a photoelectron sheath generated by solar ultraviolet light impinging on the surface. Solar UV illumination of natural and manmade surfaces in space produces photoelectrons which form a plasma sheath near the surface. Dust particles on the surface acquire a charge and may be transported by electric fields in the photoelectron sheath generated by inhomogeneities in the surface or the illumination (such as shadows). The sheath itself has a finite vertical extent leading to (at least) an electric field normal to the illuminated surface. If dust particles are launched from the surface by some other process, such as meteoroid impact, or spacecraft activity on the surface, these grains become charged and move under the influence of gravity and the electric field. This can give rise to suspension of the particles above the surface, loss from the parent body entirely (if accelerated beyond escape velocity), and a different distribution of dust ejecta from what would be expected with purely gravitational dynamics.

Indoor particle dynamics in a school office: determination of particle concentrations, deposition rates and penetration factors under naturally ventilated conditions.

PubMed

Cong, X C; Zhao, J J; Jing, Z; Wang, Q G; Ni, P F

2018-05-09

Recently, the problem of indoor particulate matter pollution has received much attention. An increasing number of epidemiological studies show that the concentration of atmospheric particulate matter has a significant effect on human health, even at very low concentrations. Most of these investigations have relied upon outdoor particle concentrations as surrogates of human exposures. However, considering that the concentration distribution of the indoor particulate matter is largely dependent on the extent to which these particles penetrate the building and on the degree of suspension in the indoor air, human exposures to particles of outdoor origin may not be equal to outdoor particle concentration levels. Therefore, it is critical to understand the relationship between the particle concentrations found outdoors and those found in indoor micro-environments. In this study, experiments were conducted using a naturally ventilated office located in Qingdao, China. The indoor and outdoor particle concentrations were measured at the same time using an optical counter with four size ranges. The particle size distribution ranged from 0.3 to 2.5 μm, and the experimental period was from April to September, 2016. Based on the experimental data, the dynamic and mass balance model based on time was used to estimate the penetration rate and deposition rate at air exchange rates of 0.03-0.25 h -1 . The values of the penetration rate and deposition velocity of indoor particles were determined to range from 0.45 to 0.82 h -1 and 1.71 to 2.82 m/h, respectively. In addition, the particulate pollution exposure in the indoor environment was analyzed to estimate the exposure hazard from indoor particulate matter pollution, which is important for human exposure to particles and associated health effects. The conclusions from this study can serve to provide a better understanding the dynamics and behaviors of airborne particle entering into buildings. And they will also highlight effective methods to reduce exposure to particles in office buildings.

Laboratory and Cloud Chamber Studies of Formation Processes and Properties of Atmospheric Ice Particles

NASA Astrophysics Data System (ADS)

Leisner, T.; Abdelmonem, A.; Benz, S.; Brinkmann, M.; Möhler, O.; Rzesanke, D.; Saathoff, H.; Schnaiter, M.; Wagner, R.

2009-04-01

The formation of ice in tropospheric clouds controls the evolution of precipitation and thereby influences climate and weather via a complex network of dynamical and microphysical processes. At higher altitudes, ice particles in cirrus clouds or contrails modify the radiative energy budget by direct interaction with the shortwave and longwave radiation. In order to improve the parameterisation of the complex microphysical and dynamical processes leading to and controlling the evolution of tropospheric ice, laboratory experiments are performed at the IMK Karlsruhe both on a single particle level and in the aerosol and cloud chamber AIDA. Single particle experiments in electrodynamic levitation lend themselves to the study of the interaction between cloud droplets and aerosol particles under extremely well characterized and static conditions in order to obtain microphysical parameters as freezing nucleation rates for homogeneous and heterogeneous ice formation. They also allow the observation of the freezing dynamics and of secondary ice formation and multiplication processes under controlled conditions and with very high spatial and temporal resolution. The inherent droplet charge in these experiments can be varied over a wide range in order to assess the influence of the electrical state of the cloud on its microphysics. In the AIDA chamber on the other hand, these processes are observable under the realistic dynamic conditions of an expanding and cooling cloud- parcel with interacting particles and are probed simultaneously by a comprehensive set of analytical instruments. By this means, microphysical processes can be studied in their complex interplay with dynamical processes as for example coagulation or particle evaporation and growth via the Bergeron - Findeisen process. Shortwave scattering and longwave absorption properties of the nucleating and growing ice crystals are probed by in situ polarised laser light scattering measurements and infrared extinction spectroscopy. In conjunction with ex situ single particle imaging and light scattering measurements the relation between the overall extinction and depolarization properties of the ice clouds and the morphological details of the constituent ice crystals are investigated. In our contribution we will concentrate on the parameterization of homogeneous and heterogeneous ice formation processes under various atmospheric conditions and on the optical properties of the ice crystals produced under these conditions. First attempts to parameterize the observations will be presented.

Dissipative gravitational bouncer on a vibrating surface

NASA Astrophysics Data System (ADS)

Espinoza Ortiz, J. S.; Lagos, R. E.

2017-12-01

We study the dynamical behavior of a particle flying under the influence of a gravitational field, with dissipation constant λ (Stokes-like), colliding successive times against a rigid surface vibrating harmonically with restitution coefficient α. We define re-scaled dimensionless dynamical variables, such as the relative particle velocity Ω with respect to the surface’s velocity; and the real parameter τ accounting for the temporal evolution of the system. At the particle-surface contact point and for the k‧th collision, we construct the mapping described by (τk ; Ω k ) in order to analyze the system’s nonlinear dynamical behavior. From the dynamical mapping, the fixed point trajectory is computed and its stability is analyzed. We find the dynamical behavior of the fixed point trajectory to be stable or unstable, depending on the values of the re-scaled vibrating surface amplitude Γ, the restitution coefficient α and the damping constant λ. Other important dynamical aspects such as the phase space volume and the one cycle vibrating surface (decomposed into absorbing and transmitting regions) are also discussed. Furthermore, the model rescues well known results in the limit λ = 0.

Dynamics of the one-dimensional Anderson insulator coupled to various bosonic baths

NASA Astrophysics Data System (ADS)

Bonča, Janez; Trugman, Stuart A.; Mierzejewski, Marcin

2018-05-01

We study a particle which propagates in a one-dimensional strong random potential and is coupled to a bosonic bath. We independently test various properties of bosons (hopping term, hard-core effects, and generic boson-boson interaction) and show that bosonic itineracy is the essential ingredient governing the dynamics of the particle. Coupling of the particle to itinerant phonons or hard-core bosons alike leads to delocalization of the particle by virtue of a subdiffusive (or diffusive) spread from the initially localized state. Delocalization remains in effect even when the boson frequency and the bandwidth of itinerant bosons remain an order of magnitude smaller than the magnitude of the random potential. When the particle is coupled to localized bosons, its spread remains logarithmic or even sublogarithmic. The latter result together with the survival probability shows that the particle remains localized despite being coupled to bosons.

LES of Laminar-to-Turbulent Particle-Fluid Dynamics in Human and Nonhuman Primate Airways: Applications to Aerosolized Drug Delivery Animal Testing

NASA Astrophysics Data System (ADS)

Geisler, Taylor; Padhy, Sourav; Shaqfeh, Eric; Iaccarino, Gianluca

2016-11-01

Both the human health benefit and risk from the inhalation of aerosolized medications is often predicted by extrapolating experimental data taken using nonhuman primates to human inhalation. In this study, we employ Large Eddy Simulation to simulate particle-fluid dynamics in realistic upper airway models of both humans and rhesus monkeys. We report laminar-to-turbulent flow transitions triggered by constrictions in the upper trachea and the persistence of unsteadiness into the low Reynolds number bifurcating lower airway. Micro-particle deposition fraction and locations are shown to depend significantly on particle size. In particular, particle filtration in the nasal airways is shown to approach unity for large aerosols (8 microns) or high-rate breathing. We validate the accuracy of LES mean flow predictions using MRV imaging results. Additionally, particle deposition fractions are validated against experiments in 3 model airways.

Dynamic Load Balancing Based on Constrained K-D Tree Decomposition for Parallel Particle Tracing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jiang; Guo, Hanqi; Yuan, Xiaoru

Particle tracing is a fundamental technique in flow field data visualization. In this work, we present a novel dynamic load balancing method for parallel particle tracing. Specifically, we employ a constrained k-d tree decomposition approach to dynamically redistribute tasks among processes. Each process is initially assigned a regularly partitioned block along with duplicated ghost layer under the memory limit. During particle tracing, the k-d tree decomposition is dynamically performed by constraining the cutting planes in the overlap range of duplicated data. This ensures that each process is reassigned particles as even as possible, and on the other hand the newmore » assigned particles for a process always locate in its block. Result shows good load balance and high efficiency of our method.« less

EFFECTS OF DYNAMICAL EVOLUTION OF GIANT PLANETS ON SURVIVAL OF TERRESTRIAL PLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsumura, Soko; Ida, Shigeru; Nagasawa, Makiko

2013-04-20

The orbital distributions of currently observed extrasolar giant planets allow marginally stable orbits for hypothetical, terrestrial planets. In this paper, we propose that many of these systems may not have additional planets on these ''stable'' orbits, since past dynamical instability among giant planets could have removed them. We numerically investigate the effects of early evolution of multiple giant planets on the orbital stability of the inner, sub-Neptune-like planets which are modeled as test particles, and determine their dynamically unstable region. Previous studies have shown that the majority of such test particles are ejected out of the system as a resultmore » of close encounters with giant planets. Here, we show that secular perturbations from giant planets can remove test particles at least down to 10 times smaller than their minimum pericenter distance. Our results indicate that, unless the dynamical instability among giant planets is either absent or quiet like planet-planet collisions, most test particles down to {approx}0.1 AU within the orbits of giant planets at a few AU may be gone. In fact, out of {approx}30% of survived test particles, about three quarters belong to the planet-planet collision cases. We find a good agreement between our numerical results and the secular theory, and present a semi-analytical formula which estimates the dynamically unstable region of the test particles just from the evolution of giant planets. Finally, our numerical results agree well with the observations, and also predict the existence of hot rocky planets in eccentric giant planet systems.« less

The Development and Comparison of Molecular Dynamics Simulation and Monte Carlo Simulation

NASA Astrophysics Data System (ADS)

Chen, Jundong

2018-03-01

Molecular dynamics is an integrated technology that combines physics, mathematics and chemistry. Molecular dynamics method is a computer simulation experimental method, which is a powerful tool for studying condensed matter system. This technique not only can get the trajectory of the atom, but can also observe the microscopic details of the atomic motion. By studying the numerical integration algorithm in molecular dynamics simulation, we can not only analyze the microstructure, the motion of particles and the image of macroscopic relationship between them and the material, but can also study the relationship between the interaction and the macroscopic properties more conveniently. The Monte Carlo Simulation, similar to the molecular dynamics, is a tool for studying the micro-molecular and particle nature. In this paper, the theoretical background of computer numerical simulation is introduced, and the specific methods of numerical integration are summarized, including Verlet method, Leap-frog method and Velocity Verlet method. At the same time, the method and principle of Monte Carlo Simulation are introduced. Finally, similarities and differences of Monte Carlo Simulation and the molecular dynamics simulation are discussed.

Aggregation of asbestos fibers in water: role of solution chemistry

NASA Astrophysics Data System (ADS)

Wu, L.; Ortiz, C. P.; Jerolmack, D. J.

2016-12-01

Aggregation kinetics and stability of colloidal particles have been extensively studied using bulk techniques such as dynamic light scattering; these techniques involve large ensembles of particles and interpretation of results is difficult when particles are non-spherical and poorly characterized, as is always the case with non-ideal natural hazardous materials such as asbestos fibers. These difficulties hinder greatly progress on fundamental understanding of whether the classic colloidal aggregation theories can be applied to natural materials and how the heterogeneity of particles (e.g., shape) affects the colloidal aggregation kinetics and structure. By using in-situ microscopy and particle tracking techniques, we were able to observe the particle-by-particle growth of aggregated formed by elongated particles (synthetic glass rods and natural asbestos fibers) and demonstrated the rod-shaped geometry induced novel structures and growth dynamics that challenge existing theory. In this study, we continue to use asbestos as model system of elongated colloidal contaminant, and investigate the effects of changing solution chemistry (e.g., ionic strength, pH, and natural organic matter (NOM)), on growth dynamics and aggregates structure. The results show that aggregate growth curves are self-similar with a characteristic timescale that increases with increasing pH. By varying ionic strength for fixed pH values, we determine that the ccc is sensitive to pH. Fractal dimension decreases slightly with increasing pH and decreasing ionic strength, indicating that stronger inter-particle repulsion create sparser aggregates; however, the magnitude of the solution chemistry effects is much smaller than that of colloid shape. In monovalent solutions, regardless of their concentration, HA drastically reduces the aggregation kinetics of asbestos fiber. This work may lead to enhanced prediction of the colloidal contaminants' mobility in the environment, bioavailability, and toxicity to organisms.

Dynamics of dissipative self-assembly of particles interacting through oscillatory forces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tagliazucchi, M.; Szleifer, I.

Dissipative self-assembly is the formation of ordered structures far from equilibrium, which continuously uptake energy and dissipate it into the environment. Due to its dynamical nature, dissipative self-assembly can lead to new phenomena and possibilities of self-organization that are unavailable to equilibrium systems. Understanding the dynamics of dissipative self-assembly is required in order to direct the assembly to structures of interest. In the present work, Brownian dynamics simulations and analytical theory were used to study the dynamics of self-assembly of a mixture of particles coated with weak acids and bases under continuous oscillations of the pH. The pH of themore » system modulates the charge of the particles and, therefore, the interparticle forces oscillate in time. This system produces a variety of self-assembled structures, including colloidal molecules, fibers and different types of crystalline lattices. The most important conclusions of our study are: (i) in the limit of fast oscillations, the whole dynamics (and not only those at the non-equilibrium steady state) of a system of particles interacting through time-oscillating interparticle forces can be described by an effective potential that is the time average of the time-dependent potential over one oscillation period; (ii) the oscillation period is critical to determine the order of the system. In some cases the order is favored by very fast oscillations while in others small oscillation frequencies increase the order. In the latter case, it is shown that slow oscillations remove kinetic traps and, thus, allow the system to evolve towards the most stable non-equilibrium steady state.« less

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids.

PubMed

Dahlberg, Jerry; Tkacik, Peter T; Mullany, Brigid; Fleischhauer, Eric; Shahinian, Hossein; Azimi, Farzad; Navare, Jayesh; Owen, Spencer; Bisel, Tucker; Martin, Tony; Sholar, Jodie; Keanini, Russell G

2017-12-04

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a standard fluid dynamic diagnostic, particle image velocimetry (PIV), to measure: i) velocities of individual particles (grains), extant on short, grain-collision time-scales, ii) velocities of systems of particles, on both short collision-time- and long, continuum-flow-time-scales, iii) collective hydrodynamic modes known to exist in dense molecular fluids, and iv) short- and long-time-scale velocity autocorrelation functions, central to understanding particle-scale dynamics in strongly interacting, dense fluid systems. The basic system is composed of an imaging system, light source, vibrational sensors, vibrational system with a known media, and PIV and analysis software. Required experimental measurements and an outline of the theoretical tools needed when using the analog technique to study molecular-scale hydrodynamic processes are highlighted. The proposed technique provides a relatively straightforward alternative to photonic and neutron beam scattering methods traditionally used in molecular hydrodynamic studies.

Computing fluid-particle interaction forces for nano-suspension droplet spreading: molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Zhou, Weizhou; Shi, Baiou; Webb, Edmund

2017-11-01

Recently, there are many experimental and theoretical studies to understand and control the dynamic spreading of nano-suspension droplets on solid surfaces. However, fundamental understanding of driving forces dictating the kinetics of nano-suspension wetting and spreading, especially capillary forces that manifest during the process, is lacking. Here, we present results from atomic scale simulations that were used to compute forces between suspended particles and advancing liquid fronts. The role of nano-particle size, particle loading, and interaction strength on forces computed from simulations will be discussed. Results demonstrate that increasing the particle size dramatically changes observed wetting behavior from depinning to pinning. From simulations on varying particle size, a relationship between computed forces and particle size is advanced and compared to existing expressions in the literature. High particle loading significantly slowed spreading kinetics, by introducing tortuous transport paths for liquid delivery to the advancing contact line. Lastly, we show how weakening the interaction between the particle and the underlying substrate can change a system from exhibiting pinning behavior to de-pinning.

Lozenge Tiling Dynamics and Convergence to the Hydrodynamic Equation

NASA Astrophysics Data System (ADS)

Laslier, Benoît; Toninelli, Fabio Lucio

2018-03-01

We study a reversible continuous-time Markov dynamics of a discrete (2 + 1)-dimensional interface. This can be alternatively viewed as a dynamics of lozenge tilings of the {L× L} torus, or as a conservative dynamics for a two-dimensional system of interlaced particles. The particle interlacement constraints imply that the equilibrium measures are far from being product Bernoulli: particle correlations decay like the inverse distance squared and interface height fluctuations behave on large scales like a massless Gaussian field. We consider a particular choice of the transition rates, originally proposed in Luby et al. (SIAM J Comput 31:167-192, 2001): in terms of interlaced particles, a particle jump of length n that preserves the interlacement constraints has rate 1/(2 n). This dynamics presents special features: the average mutual volume between two interface configurations decreases with time (Luby et al. 2001) and a certain one-dimensional projection of the dynamics is described by the heat equation (Wilson in Ann Appl Probab 14:274-325, 2004). In this work we prove a hydrodynamic limit: after a diffusive rescaling of time and space, the height function evolution tends as L\\to∞ to the solution of a non-linear parabolic PDE. The initial profile is assumed to be C 2 differentiable and to contain no "frozen region". The explicit form of the PDE was recently conjectured (Laslier and Toninelli in Ann Henri Poincaré Theor Math Phys 18:2007-2043, 2017) on the basis of local equilibrium considerations. In contrast with the hydrodynamic equation for the Langevin dynamics of the Ginzburg-Landau model (Funaki and Spohn in Commun Math Phys 85:1-36, 1997; Nishikawa in Commun Math Phys 127:205-227, 2003), here the mobility coefficient turns out to be a non-trivial function of the interface slope.

Path-integral formalism for stochastic resetting: Exactly solved examples and shortcuts to confinement

NASA Astrophysics Data System (ADS)

Roldán, Édgar; Gupta, Shamik

2017-08-01

We study the dynamics of overdamped Brownian particles diffusing in conservative force fields and undergoing stochastic resetting to a given location at a generic space-dependent rate of resetting. We present a systematic approach involving path integrals and elements of renewal theory that allows us to derive analytical expressions for a variety of statistics of the dynamics such as (i) the propagator prior to first reset, (ii) the distribution of the first-reset time, and (iii) the spatial distribution of the particle at long times. We apply our approach to several representative and hitherto unexplored examples of resetting dynamics. A particularly interesting example for which we find analytical expressions for the statistics of resetting is that of a Brownian particle trapped in a harmonic potential with a rate of resetting that depends on the instantaneous energy of the particle. We find that using energy-dependent resetting processes is more effective in achieving spatial confinement of Brownian particles on a faster time scale than performing quenches of parameters of the harmonic potential.

High hydrostatic pressure specifically affects molecular dynamics and shape of low-density lipoprotein particles

PubMed Central

Golub, M.; Lehofer, B.; Martinez, N.; Ollivier, J.; Kohlbrecher, J.; Prassl, R.; Peters, J.

2017-01-01

Lipid composition of human low-density lipoprotein (LDL) and its physicochemical characteristics are relevant for proper functioning of lipid transport in the blood circulation. To explore dynamical and structural features of LDL particles with either a normal or a triglyceride-rich lipid composition we combined coherent and incoherent neutron scattering methods. The investigations were carried out under high hydrostatic pressure (HHP), which is a versatile tool to study the physicochemical behavior of biomolecules in solution at a molecular level. Within both neutron techniques we applied HHP to probe the shape and degree of freedom of the possible motions (within the time windows of 15 and 100 ps) and consequently the flexibility of LDL particles. We found that HHP does not change the types of motion in LDL, but influences the portion of motions participating. Contrary to our assumption that lipoprotein particles, like membranes, are highly sensitive to pressure we determined that LDL copes surprisingly well with high pressure conditions, although the lipid composition, particularly the triglyceride content of the particles, impacts the molecular dynamics and shape arrangement of LDL under pressure. PMID:28382948

High hydrostatic pressure specifically affects molecular dynamics and shape of low-density lipoprotein particles

NASA Astrophysics Data System (ADS)

Golub, M.; Lehofer, B.; Martinez, N.; Ollivier, J.; Kohlbrecher, J.; Prassl, R.; Peters, J.

2017-04-01

Lipid composition of human low-density lipoprotein (LDL) and its physicochemical characteristics are relevant for proper functioning of lipid transport in the blood circulation. To explore dynamical and structural features of LDL particles with either a normal or a triglyceride-rich lipid composition we combined coherent and incoherent neutron scattering methods. The investigations were carried out under high hydrostatic pressure (HHP), which is a versatile tool to study the physicochemical behavior of biomolecules in solution at a molecular level. Within both neutron techniques we applied HHP to probe the shape and degree of freedom of the possible motions (within the time windows of 15 and 100 ps) and consequently the flexibility of LDL particles. We found that HHP does not change the types of motion in LDL, but influences the portion of motions participating. Contrary to our assumption that lipoprotein particles, like membranes, are highly sensitive to pressure we determined that LDL copes surprisingly well with high pressure conditions, although the lipid composition, particularly the triglyceride content of the particles, impacts the molecular dynamics and shape arrangement of LDL under pressure.

ReaDDy - A Software for Particle-Based Reaction-Diffusion Dynamics in Crowded Cellular Environments

PubMed Central

Schöneberg, Johannes; Noé, Frank

2013-01-01

We introduce the software package ReaDDy for simulation of detailed spatiotemporal mechanisms of dynamical processes in the cell, based on reaction-diffusion dynamics with particle resolution. In contrast to other particle-based reaction kinetics programs, ReaDDy supports particle interaction potentials. This permits effects such as space exclusion, molecular crowding and aggregation to be modeled. The biomolecules simulated can be represented as a sphere, or as a more complex geometry such as a domain structure or polymer chain. ReaDDy bridges the gap between small-scale but highly detailed molecular dynamics or Brownian dynamics simulations and large-scale but little-detailed reaction kinetics simulations. ReaDDy has a modular design that enables the exchange of the computing core by efficient platform-specific implementations or dynamical models that are different from Brownian dynamics. PMID:24040218

Activated dynamics in dense fluids of attractive nonspherical particles. II. Elasticity, barriers, relaxation, fragility, and self-diffusion

NASA Astrophysics Data System (ADS)

Tripathy, Mukta; Schweizer, Kenneth S.

2011-04-01

In paper II of this series we apply the center-of-mass version of Nonlinear Langevin Equation theory to study how short-range attractive interactions influence the elastic shear modulus, transient localization length, activated dynamics, and kinetic arrest of a variety of nonspherical particle dense fluids (and the spherical analog) as a function of volume fraction and attraction strength. The activation barrier (roughly the natural logarithm of the dimensionless relaxation time) is predicted to be a rich function of particle shape, volume fraction, and attraction strength, and the dynamic fragility varies significantly with particle shape. At fixed volume fraction, the barrier grows in a parabolic manner with inverse temperature nondimensionalized by an onset value, analogous to what has been established for thermal glass-forming liquids. Kinetic arrest boundaries lie at significantly higher volume fractions and attraction strengths relative to their dynamic crossover analogs, but their particle shape dependence remains the same. A limited universality of barrier heights is found based on the concept of an effective mean-square confining force. The mean hopping time and self-diffusion constant in the attractive glass region of the nonequilibrium phase diagram is predicted to vary nonmonotonically with attraction strength or inverse temperature, qualitatively consistent with recent computer simulations and colloid experiments.

An experimental study of the dynamics of saltation within a three-dimensional framework

NASA Astrophysics Data System (ADS)

O'Brien, Patrick; McKenna Neuman, Cheryl

2018-04-01

Our understanding of aeolian sand transport via saltation lacks an experimental determination of the particle borne kinetic energy partitioned into 3 dimensions relative to the mean flow direction. This in turn creates a disconnect between global wind erosion estimates and particle scale processes. The present study seeks to address this deficiency through an extended analysis of data obtained from a series of particle tracking velocimetry experiments conducted in a boundary layer wind tunnel under transport limited conditions. Particle image diameter, as it appeared within each camera frame, was extensively calibrated against that obtained by sieving, and the ballistic trajectories detected were disassembled into discrete particle image pairs whose distribution and dynamics were then examined in vertical profile with sub-millimeter resolution. The vertical profile of the wind aligned particle transport rate was found to follow a power relation within 10 mm of the bed surface. The exponent of this power function changes with increasing spanwise angle (θ) to produce a family of curves representing particle diffusion in 3 dimensions. Particle mass was found to increase with θ, and the distribution of the total particle kinetic energy was found to be very similar to that for the particle concentration. The spanwise component of the kinetic energy of a saltating particle peaks at θ = 45°, with the stream-aligned component an order of magnitude higher in value. Low energy, splashed particles near the bed account for a majority of the kinetic energy distributed throughout the particle cloud, regardless of their orientation.

High-resolution structure, interactions, and dynamics of self-assembled virus-like partilces

NASA Astrophysics Data System (ADS)

Raviv, Uri; Asor, R.; Ben-Shaul, O.; Oppenheim, A.; Schlicksup, L. C.; Seltzer, L.; Jarrold, M. F.; Zlotnick, A.

Using SAXS, in combination with Monte Carlo simulations, and our unique solution x-ray scattering data analysis program, we resolved at high spatial resolution, the manner by which wtSV40 packages its 5.2kb circular DNA about 20 histone octamers in the virus capsid (Figure 1). This structure, known as a mini-chromosome, is highly dynamic and could not be resolved by microscopy methods. Using time-resolved solution SAXS, stopped-flow, and flow-through setups the assembly process of VP1, the major caspid protein of the SV40 virus, with RNA or DNA to form virus-like particles (VLPs) was studied in msec temporal resolution. By mixing the nucleotides and the capsid protein, virus-like particles formed within 35 msec, in the case of RNA that formed T =1 particles, and within 15 seconds in the case of DNA that formed T =7 particles, similar to wt SV40. The structural changes leading to the particle formation were followed in detail. More recently, we have extended this work to study the assembly of HBV virus-like particles.

Microfluidic Examination of the "Hard" Biomolecular Corona Formed on Engineered Particles in Different Biological Milieu.

PubMed

Weiss, Alessia C G; Kempe, Kristian; Förster, Stephan; Caruso, Frank

2018-04-18

The formation of a biomolecular corona around engineered particles determines, in large part, their biological behavior in vitro and in vivo. To gain a fundamental understanding of how particle design and the biological milieu influence the formation of the "hard" biomolecular corona, we conduct a series of in vitro studies using microfluidics. This setup allows the generation of a dynamic incubation environment with precise control over the applied flow rate, stream orientation, and channel dimensions, thus allowing accurate control of the fluid flow and the shear applied to the proteins and particles. We used mesoporous silica particles, poly(2-methacryloyloxyethylphosphorylcholine) (PMPC)-coated silica hybrid particles, and PMPC replica particles (obtained by removal of the silica particle templates), representing high-, intermediate-, and low-fouling particle systems, respectively. The protein source used in the experiments was either human serum or human full blood. The effects of flow, particle surface properties, incubation medium, and incubation time on the formation of the biomolecular corona formation are examined. Our data show that protein adhesion on particles is enhanced after incubation in human blood compared to human serum and that dynamic incubation leads to a more complex corona. By varying the incubation time from 2 s to 15 min, we demonstrate that the "hard" biomolecular corona is kinetically subdivided into two phases comprising a tightly bound layer of proteins interacting directly with the particle surface and a loosely associated protein layer. Understanding the influence of particle design parameters and biological factors on the corona composition, as well as its dynamic assembly, may facilitate more accurate prediction of corona formation and therefore assist in the design of advanced drug delivery vehicles.

Spatial and temporal dynamics of suspended particle characteristics and composition in Navigation Pool 19 of the Upper Mississippi River

USGS Publications Warehouse

Milde, Amanda S.; Richardson, William B.; Strauss, Eric A.; Larson, James H.; Vallazza, Jon; Knights, Brent C.

2017-01-01

Suspended particles are an essential component of large rivers influencing channel geomorphology, biogeochemical cycling of nutrients, and food web resources. The Upper Mississippi River is a large floodplain river that exhibits pronounced spatiotemporal variation in environmental conditions and biota, providing an ideal environment for investigating dynamics of suspended particles in large river ecosystems. Here we investigated two questions: (i) How do suspended particle characteristics (e.g. size and morphology) vary temporally and spatially? and (ii) What environmental variables have the strongest association with particle characteristics? Water sampling was conducted in June, August, and September of 2013 and 2014 in Navigation Pool 19 of the Upper Mississippi River. A FlowCAM® (Flow Cytometer and Microscope) particle imaging system was used to enumerate and measure particles 53–300 μm in diameter for size and shape characteristics (e.g. volume, elongation, and symmetry). Suspended particle characteristics varied considerably over space and time and were strongly associated with discharge and concentrations of nitrate + nitrite (NO3−) and soluble reactive phosphorus. Particle characteristics in backwaters were distinct from those in other habitats for most of the study period, likely due to reduced hydrologic connectivity and higher biotic production in backwaters. During low discharge, phytoplankton and zooplankton made up relatively greater proportions of the observed particles. Concurrently during low discharge, concentrations of chlorophyll, volatile suspended solids, and total phosphorus were higher. Our results suggest that there are complex interactions among space, time, discharge, and other environmental variables (e.g. water nutrients), which drive suspended particle dynamics in large rivers.

Dynamic self-organization of side-propelling colloidal rods: experiments and simulations.

PubMed

Vutukuri, Hanumantha Rao; Preisler, Zdeněk; Besseling, Thijs H; van Blaaderen, Alfons; Dijkstra, Marjolein; Huck, Wilhelm T S

2016-12-06

In recent years, there is a growing interest in designing artificial analogues of living systems, fueled not only by potential applications as 'smart micro-machines', but also by the demand for simple models that can be used to study the behavior of their more complex natural counterparts. Here, we present a facile, internally driven, experimental system comprised of fluorescently labeled colloidal silica rods of which the self-propulsion is powered by the decomposition of H 2 O 2 catalyzed by a length-wise half Pt coating of the particles in order to study how shape anisotropy and swimming direction affect the collective behavior. We investigated the emerging structures and their time evolution for various particle concentrations in (quasi-)two dimensional systems for three aspect ratios of the rods on a single particle level using a combination of experiments and simulations. We found that the dynamic self-organization relied on a competition between self-propulsion and phoretic attractions induced by phoresis of the rods. We observed that the particle clustering behavior depends on the concentration as well as the aspect ratio of the rods. Our findings provide a more detailed understanding of dynamic self-organization of anisotropic particles and the role the propulsion direction plays in internally driven systems.

Turbulent complex (dusty) plasma

NASA Astrophysics Data System (ADS)

Zhdanov, Sergey; Schwabe, Mierk

2017-04-01

As a paradigm of complex system dynamics, solid particles immersed into a weakly ionized plasma, so called complex (dusty) plasmas, were (and continue to be) a subject of many detailed studies. Special types of dynamical activity have been registered, in particular, spontaneous pairing, entanglement and cooperative action of a great number of particles resulting in formation of vortices, self-propelling, tunneling, and turbulent movements. In the size domain of 1-10 mkm normally used in experiments with complex plasmas, the characteristic dynamic time-scale is of the order of 0.01-0.1 s, and these particles can be visualized individually in real time, providing an atomistic (kinetic) level of investigations. The low-R turbulent flow induced either by the instability in a complex plasma cloud or formed behind a projectile passing through the cloud is a typical scenario. Our simulations showed formation of a fully developed system of vortices and demonstrated that the velocity structure functions scale very close to the theoretical predictions. As an important element of self-organization, cooperative and turbulent particle motions are present in many physical, astrophysical, and biological systems. Therefore, experiments with turbulent wakes and turbulent complex plasma oscillations are a promising mean to observe and study in detail the anomalous transport on the level of individual particles.

Experimental investigation of clogging dynamics in homogeneous porous medium

NASA Astrophysics Data System (ADS)

Shen, Jikang; Ni, Rui

2017-03-01

A 3-D refractive-index matching Lagrangian particle tracking (3D-RIM-LPT) system was developed to study the filtration and the clogging process inside a homogeneous porous medium. A small subset of particles flowing through the porous medium was dyed and tracked. As this subset was randomly chosen, its dynamics is representative of all the rest. The statistics of particle locations, number, and velocity were obtained as functions of different volumetric concentrations. It is found that in our system the clogging time decays with the particle concentration following a power law relationship. As the concentration increases, there is a transition from depth filtration to cake filtration. At high concentration, more clogged pores lead to frequent flow redirections and more transverse migrations of particles. In addition, the velocity distribution in the transverse direction is symmetrical around zero, and it is slightly more intermittent than the random Gaussian curve due to particle-particle and particle-grain interactions. In contrast, as clogging develops, the longitudinal velocity of particles along the mean flow direction peaks near zero because of many trapped particles. But at the same time, the remaining open pores will experience larger pressure and, as a result, particles through those pores tend to have larger longitudinal velocities.

Transport in sheared stochastic magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vanden Eijnden, E.; Balescu, R.

1997-02-01

The transport of test particles in a stochastic magnetic field with a sheared component is studied. Two stages in the particle dynamics are distinguished depending on whether the collisional effects perpendicular to the main field are negligible or not. Whenever the perpendicular collisions are unimportant, the particles show a subdiffusive behavior which is slower in the presence of shear. The particle dynamics is then inhomogeneous and non-Markovian and no diffusion coefficient may be properly defined. When the perpendicular collision frequency is small, this subdiffusive stage may be very long. In the truly asymptotic stage, however, the perpendicular collisions must bemore » accounted for and the particle motion eventually becomes diffusive. Here again, however, the shear is shown to reduce the anomalous diffusion coefficient of the system. {copyright} {ital 1997 American Institute of Physics.}« less

REBOUND-ing Off Asteroids: An N-body Particle Model for Ejecta Dynamics on Small Bodies

NASA Astrophysics Data System (ADS)

Larson, Jennifer; Sarid, Gal

2017-10-01

Here we describe our numerical approach to model the evolution of ejecta clouds. Modeling with an N-body particle method enables us to study the micro-dynamics while varying the particle size distribution. A hydrodynamic approach loses many of the fine particle-particle interactions included in the N-body particle approach (Artemieva 2008).We use REBOUND, an N-body integration package (Rein et al. 2012) developed to model various dynamical systems (planetary orbits, ring systems, etc.) with high resolution calculations at a lower performance cost than other N-body integrators (Rein & Tamayo 2017). It offers both symplectic (WHFast) and non-symplectic (IAS15) methods (Rein & Spiegel 2014, Rein & Tamayo 2015). We primarily use the IAS15 integrator due to its robustness and accuracy with short interaction distances and non-conservative forces. We implemented a wrapper (developed in Python) to handle changes in time step and integrator at different stages of ejecta particle evolution.To set up the system, each particle is given a velocity away from the target body’s surface at a given angle within a defined ejecta cone. We study the ejecta cloud evolution beginning immediately after an impact rather than the actual impact itself. This model considers effects such as varying particle size distribution, radiation pressure, perturbations from a binary component, particle-particle collisions and non-axisymmetric gravity of the target body. Restrictions on the boundaries of the target body’s surface define the physical shape and help count the number of particles that land on the target body. Later, we will build the central body from individual particles to allow for a wider variety of target body shapes and topographies.With our particle modeling approach, individual particle trajectories are tracked and predicted on short, medium and long timescales. Our approach will be applied to modeling of the ejecta cloud produced during the Double Asteroid Redirection Test (DART) impact (Cheng et al. 2016, Schwartz et al. 2016). We will present some preliminary results of our applied model and possible applications to other asteroid impact events and Centaur ring formation mechanisms.

Dynamics and yielding of binary self-suspended nanoparticle fluids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agrawal, Akanksha; Yu, Hsiu-Yu; Srivastava, Samanvaya

Yielding and flow transitions in bi-disperse suspensions of particles are studied using a model system comprised of self-suspended spherical nanoparticles. An important feature of the materials is that the nanoparticles are uniformly dispersed in the absence of a solvent. Addition of larger particles to a suspension of smaller ones is found to soften the suspensions, and in the limit of large size disparities, completely fluidizes the material. We show that these behaviors coincide with a speeding-up of de-correlation dynamics of all particles in the suspensions and are accompanied by a reduction in the energy dissipated at the yielding transition. Wemore » discuss our findings in terms of ligand-mediated jamming and un-jamming of hairy particle suspensions.« less

STARPROBE: Scientific rationale

NASA Technical Reports Server (NTRS)

Underwood, J. H. (Editor); Randolph, J. E. (Editor)

1982-01-01

The scientific rationale and instrumentation problems in the areas of solar internal dynamics and relativity, solar plasma and particle dynamics, and solar atmosphere structure were studied. Current STARPROBE mission and system design concepts are summarized.

Dynamic localization and shear-induced hopping of particles: A way to understand the rheology of dense colloidal dispersions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Tianying; Zukoski, Charles F., E-mail: czukoski@illinois.edu

2014-09-01

For decades, attempts have been made to understand the formation of colloidal glasses and gels by linking suspension mechanics to particle properties where details of size, shape, and spatial dependencies of pair potentials present a bewildering array of variables that can be manipulated to achieve observed properties. Despite the range of variables that control suspension properties, one consistent observation is the remarkably similarity of flow properties observed as particle properties are varied. Understanding the underlying origins of the commonality in those behaviors (e.g., shear-thinning with increasing stress, diverging zero shear rate viscosity with increasing volume fraction, development of a dynamicmore » yield stress plateau with increases in volume faction or strength of attraction, development of two characteristic relaxation times probed in linear viscoelasticity, the creation of a rubbery plateau modulus at high strain frequencies, and shear-thickening) remains a challenge. Recently, naïve mode coupling and dynamic localization theories have been developed to capture collective behavior giving rise to formation of colloidal glasses and gels. This approach characterizes suspension mechanics of strongly interacting particles in terms of sluggish long-range particle diffusion modulated by varying particle interactions and volume fraction. These theories capture the scaling of the modulus with the volume fraction and strength of interparticle attraction, the frequency dependence of the moduli at the onset of the gel/glass transition, together with the divergence of the zero shear rate viscosity and cessation of diffusivity for hard sphere systems as close packing is approached. In this study, we explore the generality of the predictions of dynamic localization theory for systems of particles composed of bimodal particle size distributions experiencing weak interactions. We find that the mechanical properties of these suspensions are well captured within the framework of dynamic localization theory and that suspension mechanics can be understood in terms of a dynamical potential barrier, the magnitude of which governs the zero shear rate viscosity, and onset of a dynamic yield stress plateau as volume fraction or strength of interaction is raised.« less

Microscopic theory for dynamics in entangled polymer nanocomposites

NASA Astrophysics Data System (ADS)

Yamamoto, Umi

New microscopic theories for describing dynamics in polymer nanocomposites are developed and applied. The problem is addressed from two distinct perspectives and using two different theoretical approaches. The first half of this dissertation studies the long-time and intermediate-time dynamics of nanoparticles in entangled and unentangled polymer melts for dilute particle concentrations. Using a combination of mode-coupling, Brownian motion, and polymer physics ideas, the nanoparticle long-time diffusion coefficients is formulated in terms of multiple length-scales, packing microstructures, and spatially-resolved polymer density fluctuation dynamics. The key motional mechanism is described via the parallel relaxation of the force exerted on the particle controlled by collective polymer constraint-release and the particle self-motion. A sharp but smooth crossover from the hydrodynamic to the non-hydrodynamic regime is predicted based on the Stokes-Einstein violation ratio as a function of all the system variables. Quantitative predictions are made for the recovery of the Stokes-Einstein law, and the diffusivity in the crossover regime agrees surprisingly well with large-scale molecular dynamics simulations for all particle sizes and chain lengths studied. The approach is also extended to address intermediate-time anomalous transport of a single nanoparticle and two-particle relative diffusion. The second half of this dissertation focuses on developing a novel dynamical theory for a liquid of infinitely-thin rods in the presence of hard spherical obstacles, aiming at a technical and conceptual extension of the existing paradigm for entangled polymer dynamics. As a fundamental theoretical development, the two-component generalization of a first-principles dynamic meanfield approach is presented. The theory enforces inter-needle topological uncrossability and needlesphere impenetrability in a unified manner, leading to a generalized theory of entanglements that includes the sphere excluded volume effect. Coupled self-consistent equations for the generalized diffusion tensors are constructed, and the expressions for the transverse localization lengths and the long-time diffusion coefficients are derived. In the static sphere limit, we find the effective tube diameter is generally reduced as a function of a single confinement parameter that quantifies the number of particles penetrating into the pure-polymer tube. A preliminary extension to treat flexible chain melts has also been achieved, and shown to agree reasonably well with simulations. The anisotropic needle diffusion constants are rich functions of the length-scale ratios, needle concentration and particle volume fraction. We show that the steric blocking of the longitudinal motion causes a literal and simultaneous localization of the two diffusion channels, and entangled needles can diffuse via a modified reptation dynamics over a window of polymer concentration but the compression of the tube and the blocking of the reptation motion must be accounted for. Generalization to treat mobile spheres is also possible and fully formulated.

Statistics, distillation, and ordering emergence in a two-dimensional stochastic model of particles in counterflowing streams

NASA Astrophysics Data System (ADS)

Stock, Eduardo Velasco; da Silva, Roberto; Fernandes, H. A.

2017-07-01

In this paper, we propose a stochastic model which describes two species of particles moving in counterflow. The model generalizes the theoretical framework that describes the transport in random systems by taking into account two different scenarios: particles can work as mobile obstacles, whereas particles of one species move in the opposite direction to the particles of the other species, or particles of a given species work as fixed obstacles remaining in their places during the time evolution. We conduct a detailed study about the statistics concerning the crossing time of particles, as well as the effects of the lateral transitions on the time required to the system reaches a state of complete geographic separation of species. The spatial effects of jamming are also studied by looking into the deformation of the concentration of particles in the two-dimensional corridor. Finally, we observe in our study the formation of patterns of lanes which reach the steady state regardless of the initial conditions used for the evolution. A similar result is also observed in real experiments involving charged colloids motion and simulations of pedestrian dynamics based on Langevin equations, when periodic boundary conditions are considered (particles counterflow in a ring symmetry). The results obtained through Monte Carlo simulations and numerical integrations are in good agreement with each other. However, differently from previous studies, the dynamics considered in this work is not Newton-based, and therefore, even artificial situations of self-propelled objects should be studied in this first-principles modeling.

Multiscale simulations of patchy particle systems combining Molecular Dynamics, Path Sampling and Green's Function Reaction Dynamics

NASA Astrophysics Data System (ADS)

Bolhuis, Peter

Important reaction-diffusion processes, such as biochemical networks in living cells, or self-assembling soft matter, span many orders in length and time scales. In these systems, the reactants' spatial dynamics at mesoscopic length and time scales of microns and seconds is coupled to the reactions between the molecules at microscopic length and time scales of nanometers and milliseconds. This wide range of length and time scales makes these systems notoriously difficult to simulate. While mean-field rate equations cannot describe such processes, the mesoscopic Green's Function Reaction Dynamics (GFRD) method enables efficient simulation at the particle level provided the microscopic dynamics can be integrated out. Yet, many processes exhibit non-trivial microscopic dynamics that can qualitatively change the macroscopic behavior, calling for an atomistic, microscopic description. The recently developed multiscale Molecular Dynamics Green's Function Reaction Dynamics (MD-GFRD) approach combines GFRD for simulating the system at the mesocopic scale where particles are far apart, with microscopic Molecular (or Brownian) Dynamics, for simulating the system at the microscopic scale where reactants are in close proximity. The association and dissociation of particles are treated with rare event path sampling techniques. I will illustrate the efficiency of this method for patchy particle systems. Replacing the microscopic regime with a Markov State Model avoids the microscopic regime completely. The MSM is then pre-computed using advanced path-sampling techniques such as multistate transition interface sampling. I illustrate this approach on patchy particle systems that show multiple modes of binding. MD-GFRD is generic, and can be used to efficiently simulate reaction-diffusion systems at the particle level, including the orientational dynamics, opening up the possibility for large-scale simulations of e.g. protein signaling networks.

Wake-Driven Dynamics of Finite-Sized Buoyant Spheres in Turbulence

NASA Astrophysics Data System (ADS)

Mathai, Varghese; Prakash, Vivek N.; Brons, Jon; Sun, Chao; Lohse, Detlef

2015-09-01

Particles suspended in turbulent flows are affected by the turbulence and at the same time act back on the flow. The resulting coupling can give rise to rich variability in their dynamics. Here we report experimental results from an investigation of finite-sized buoyant spheres in turbulence. We find that even a marginal reduction in the particle's density from that of the fluid can result in strong modification of its dynamics. In contrast to classical spatial filtering arguments and predictions of particle models, we find that the particle acceleration variance increases with size. We trace this reversed trend back to the growing contribution from wake-induced forces, unaccounted for in current particle models in turbulence. Our findings highlight the need for improved multiphysics based models that account for particle wake effects for a faithful representation of buoyant-sphere dynamics in turbulence.

Dynamic particle refinement in SPH: application to free surface flow and non-cohesive soil simulations

NASA Astrophysics Data System (ADS)

Reyes López, Yaidel; Roose, Dirk; Recarey Morfa, Carlos

2013-05-01

In this paper, we present a dynamic refinement algorithm for the smoothed particle Hydrodynamics (SPH) method. An SPH particle is refined by replacing it with smaller daughter particles, which positions are calculated by using a square pattern centered at the position of the refined particle. We determine both the optimal separation and the smoothing distance of the new particles such that the error produced by the refinement in the gradient of the kernel is small and possible numerical instabilities are reduced. We implemented the dynamic refinement procedure into two different models: one for free surface flows, and one for post-failure flow of non-cohesive soil. The results obtained for the test problems indicate that using the dynamic refinement procedure provides a good trade-off between the accuracy and the cost of the simulations.

Energy Dissipation and Dynamics in Large Guide Field Turbulence Driven Reconnection at the Magnetopause

NASA Astrophysics Data System (ADS)

TenBarge, J. M.; Shay, M. A.; Sharma, P.; Juno, J.; Haggerty, C. C.; Drake, J. F.; Bhattacharjee, A.; Hakim, A.

2017-12-01

Turbulence and magnetic reconnection are the primary mechanisms responsible for the conversion of stored magnetic energy into particle energy in many space and astrophysical plasmas. The magnetospheric multiscale mission (MMS) has given us unprecedented access to high cadence particle and field data of turbulence and magnetic reconnection at earth's magnetopause. The observations include large guide field reconnection events generated within the turbulent magnetopause. Motivated by these observations, we present a study of large guide reconnection using the fully kinetic Eulerian Vlasov-Maxwell component of the Gkeyll simulation framework, and we also employ and compare with gyrokinetics to explore the asymptotically large guide field limit. In addition to studying the configuration space dynamics, we leverage the recently developed field-particle correlations to diagnose the dominant sources of dissipation and compare the results of the field-particle correlation to other energy dissipation measures.

GPU accelerated Discrete Element Method (DEM) molecular dynamics for conservative, faceted particle simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spellings, Matthew; Biointerfaces Institute, University of Michigan, 2800 Plymouth Rd., Ann Arbor, MI 48109; Marson, Ryan L.

Faceted shapes, such as polyhedra, are commonly found in systems of nanoscale, colloidal, and granular particles. Many interesting physical phenomena, like crystal nucleation and growth, vacancy motion, and glassy dynamics are challenging to model in these systems because they require detailed dynamical information at the individual particle level. Within the granular materials community the Discrete Element Method has been used extensively to model systems of anisotropic particles under gravity, with friction. We provide an implementation of this method intended for simulation of hard, faceted nanoparticles, with a conservative Weeks–Chandler–Andersen (WCA) interparticle potential, coupled to a thermodynamic ensemble. This method ismore » a natural extension of classical molecular dynamics and enables rigorous thermodynamic calculations for faceted particles.« less

Hysteretic dynamics of active particles in a periodic orienting field

PubMed Central

Romensky, Maksym; Scholz, Dimitri; Lobaskin, Vladimir

2015-01-01

Active motion of living organisms and artificial self-propelling particles has been an area of intense research at the interface of biology, chemistry and physics. Significant progress in understanding these phenomena has been related to the observation that dynamic self-organization in active systems has much in common with ordering in equilibrium condensed matter such as spontaneous magnetization in ferromagnets. The velocities of active particles may behave similar to magnetic dipoles and develop global alignment, although interactions between the individuals might be completely different. In this work, we show that the dynamics of active particles in external fields can also be described in a way that resembles equilibrium condensed matter. It follows simple general laws, which are independent of the microscopic details of the system. The dynamics is revealed through hysteresis of the mean velocity of active particles subjected to a periodic orienting field. The hysteresis is measured in computer simulations and experiments on unicellular organisms. We find that the ability of the particles to follow the field scales with the ratio of the field variation period to the particles' orientational relaxation time, which, in turn, is related to the particle self-propulsion power and the energy dissipation rate. The collective behaviour of the particles due to aligning interactions manifests itself at low frequencies via increased persistence of the swarm motion when compared with motion of an individual. By contrast, at high field frequencies, the active group fails to develop the alignment and tends to behave like a set of independent individuals even in the presence of interactions. We also report on asymptotic laws for the hysteretic dynamics of active particles, which resemble those in magnetic systems. The generality of the assumptions in the underlying model suggests that the observed laws might apply to a variety of dynamic phenomena from the motion of synthetic active particles to crowd or opinion dynamics. PMID:26040594

Three-dimensional structural dynamics and fluctuations of DNA-nanogold conjugates by individual-particle electron tomography

NASA Astrophysics Data System (ADS)

Zhang, Lei; Lei, Dongsheng; Smith, Jessica M.; Zhang, Meng; Tong, Huimin; Zhang, Xing; Lu, Zhuoyang; Liu, Jiankang; Alivisatos, A. Paul; Ren, Gang

2016-03-01

DNA base pairing has been used for many years to direct the arrangement of inorganic nanocrystals into small groupings and arrays with tailored optical and electrical properties. The control of DNA-mediated assembly depends crucially on a better understanding of three-dimensional structure of DNA-nanocrystal-hybridized building blocks. Existing techniques do not allow for structural determination of these flexible and heterogeneous samples. Here we report cryo-electron microscopy and negative-staining electron tomography approaches to image, and three-dimensionally reconstruct a single DNA-nanogold conjugate, an 84-bp double-stranded DNA with two 5-nm nanogold particles for potential substrates in plasmon-coupling experiments. By individual-particle electron tomography reconstruction, we obtain 14 density maps at ~2-nm resolution. Using these maps as constraints, we derive 14 conformations of dsDNA by molecular dynamics simulations. The conformational variation is consistent with that from liquid solution, suggesting that individual-particle electron tomography could be an expected approach to study DNA-assembling and flexible protein structure and dynamics.

Retention and Migration of Fine Organic Particles within an Agricultural Stream: Toenepi, Waikato, New Zealand

NASA Astrophysics Data System (ADS)

Drummond, J. D.; Davies-Colley, R.; Stott, R.; Sukias, J.; Nagels, J.; Sharp, A.; Packman, A. I.

2013-12-01

Fine organic particle dynamics are important to stream biogeochemistry, ecology, and transport of contaminant microbes. These particles migrate downstream through a series of deposition and resuspension events, which results in a wide range of residence times. This retention influences biogeochemical processing and in-stream stores of contaminant microbes that may mobilize during flood events and present a hazard to downstream uses such as water supplies and recreation. We are conducting studies to gain insights into organic particle dynamics in streams, with a campaign of experiments and modeling. The results should improve understanding of nutrient (C, N, P) spiraling and fine sediment movement in streams, and have particular application to microbial hazards. We directly measure microbial transport by including the indicator organism, E. coli, as a tracer, which is compared to a fluorescent inert particle tracer and conservative solute to gain insight on both microbial ecology and waterborne disease transmission. We developed a stochastic model to describe the transport and retention of fine suspended particles in rivers, including advective delivery of particles to the streambed, transport through porewaters, and reversible filtration within the streambed. Because fine particles are only episodically transported in streams, with intervening periods at rest in the bed, this transport process violates conventional advection-dispersion assumptions. Instead we adopt a stochastic mobile-immobile model formulation to describe fine particle transport. We apply this model to measurements of particle transport from multiple tracer experiments in an agricultural stream in the Waikato dairy region of New Zealand, and use the model to improve interpretation of baseflow particle dynamics. Our results show the importance of the benthic and hyporheic regions and in-stream vegetation as a reservoir for fine organic particles in streams.

ROCK1 and LIM kinase modulate retrovirus particle release and cell-cell transmission events.

PubMed

Wen, Xiaoyun; Ding, Lingmei; Wang, Jaang-Jiun; Qi, Mingli; Hammonds, Jason; Chu, Hin; Chen, Xuemin; Hunter, Eric; Spearman, Paul

2014-06-01

The assembly and release of retroviruses from the host cells require dynamic interactions between viral structural proteins and a variety of cellular factors. It has been long speculated that the actin cytoskeleton is involved in retrovirus production, and actin and actin-related proteins are enriched in HIV-1 virions. However, the specific role of actin in retrovirus assembly and release remains unknown. Here we identified LIM kinase 1 (LIMK1) as a cellular factor regulating HIV-1 and Mason-Pfizer monkey virus (M-PMV) particle release. Depletion of LIMK1 reduced not only particle output but also virus cell-cell transmission and was rescued by LIMK1 replenishment. Depletion of the upstream LIMK1 regulator ROCK1 inhibited particle release, as did a competitive peptide inhibitor of LIMK1 activity that prevented cofilin phosphorylation. Disruption of either ROCK1 or LIMK1 led to enhanced particle accumulation on the plasma membrane as revealed by total internal reflection fluorescence microscopy (TIRFM). Electron microscopy demonstrated a block to particle release, with clusters of fully mature particles on the surface of the cells. Our studies support a model in which ROCK1- and LIMK1-regulated phosphorylation of cofilin and subsequent local disruption of dynamic actin turnover play a role in retrovirus release from host cells and in cell-cell transmission events. Viruses often interact with the cellular cytoskeletal machinery in order to deliver their components to the site of assembly and budding. This study indicates that a key regulator of actin dynamics at the plasma membrane, LIM kinase, is important for the release of viral particles for HIV as well as for particle release by a distantly related retrovirus, Mason-Pfizer monkey virus. Moreover, disruption of LIM kinase greatly diminished the spread of HIV from cell to cell. These findings suggest that LIM kinase and its dynamic modulation of the actin cytoskeleton in the cell may be an important host factor for the production, release, and transmission of retroviruses. Copyright © 2014, American Society for Microbiology. All Rights Reserved.

Predictive accuracy of particle filtering in dynamic models supporting outbreak projections.

PubMed

Safarishahrbijari, Anahita; Teyhouee, Aydin; Waldner, Cheryl; Liu, Juxin; Osgood, Nathaniel D

2017-09-26

While a new generation of computational statistics algorithms and availability of data streams raises the potential for recurrently regrounding dynamic models with incoming observations, the effectiveness of such arrangements can be highly subject to specifics of the configuration (e.g., frequency of sampling and representation of behaviour change), and there has been little attempt to identify effective configurations. Combining dynamic models with particle filtering, we explored a solution focusing on creating quickly formulated models regrounded automatically and recurrently as new data becomes available. Given a latent underlying case count, we assumed that observed incident case counts followed a negative binomial distribution. In accordance with the condensation algorithm, each such observation led to updating of particle weights. We evaluated the effectiveness of various particle filtering configurations against each other and against an approach without particle filtering according to the accuracy of the model in predicting future prevalence, given data to a certain point and a norm-based discrepancy metric. We examined the effectiveness of particle filtering under varying times between observations, negative binomial dispersion parameters, and rates with which the contact rate could evolve. We observed that more frequent observations of empirical data yielded super-linearly improved accuracy in model predictions. We further found that for the data studied here, the most favourable assumptions to make regarding the parameters associated with the negative binomial distribution and changes in contact rate were robust across observation frequency and the observation point in the outbreak. Combining dynamic models with particle filtering can perform well in projecting future evolution of an outbreak. Most importantly, the remarkable improvements in predictive accuracy resulting from more frequent sampling suggest that investments to achieve efficient reporting mechanisms may be more than paid back by improved planning capacity. The robustness of the results on particle filter configuration in this case study suggests that it may be possible to formulate effective standard guidelines and regularized approaches for such techniques in particular epidemiological contexts. Most importantly, the work tentatively suggests potential for health decision makers to secure strong guidance when anticipating outbreak evolution for emerging infectious diseases by combining even very rough models with particle filtering method.

Dynamics of Small Inertia-Free Spheroidal Particles in a Turbulent Channel Flow

NASA Astrophysics Data System (ADS)

Challabotla, Niranjan Reddy; Zhao, Lihao; Andersson, Helge I.; Department of Energy; Process Engineering Team

2015-11-01

The study of small non-spherical particles suspended in turbulent fluid flows is of interest in view of the potential applications in industry and the environment. In the present work, we investigated the dynamics of inertia-free spheroidal particles suspended in fully-developed turbulent channel flow at Re τ = 180 by using the direct numerical simulations (DNS) for the Eulerian fluid phase coupled with the Lagrangian point-particle tracking. We considered inertia-free spheroidal particles with a wide range of aspect ratios from 0.01 to 50, i.e. from flat disks to long rods. Although the spheroids passively translate along with the fluid, the particle orientation and rotation strongly depend on the particle shape. The flattest disks were preferentially aligned with their symmetry axis normal to the wall, whereas the longest rods aligned parallel to the wall. Strong mean rotational spin was observed for spherical particles and this has been damped with increasing asphericity both for rod-like and disk-like spheroids. The anisotropic mean and fluctuating fluid vorticity resulted in particle spin anisotropies which exhibited a complex dependence on the particle asphericty. The Research Council of Norway, Notur and COST Action FP1005 are gratefully acknowledged.

Fast Particle Methods for Multiscale Phenomena Simulations

NASA Technical Reports Server (NTRS)

Koumoutsakos, P.; Wray, A.; Shariff, K.; Pohorille, Andrew

2000-01-01

We are developing particle methods oriented at improving computational modeling capabilities of multiscale physical phenomena in : (i) high Reynolds number unsteady vortical flows, (ii) particle laden and interfacial flows, (iii)molecular dynamics studies of nanoscale droplets and studies of the structure, functions, and evolution of the earliest living cell. The unifying computational approach involves particle methods implemented in parallel computer architectures. The inherent adaptivity, robustness and efficiency of particle methods makes them a multidisciplinary computational tool capable of bridging the gap of micro-scale and continuum flow simulations. Using efficient tree data structures, multipole expansion algorithms, and improved particle-grid interpolation, particle methods allow for simulations using millions of computational elements, making possible the resolution of a wide range of length and time scales of these important physical phenomena.The current challenges in these simulations are in : [i] the proper formulation of particle methods in the molecular and continuous level for the discretization of the governing equations [ii] the resolution of the wide range of time and length scales governing the phenomena under investigation. [iii] the minimization of numerical artifacts that may interfere with the physics of the systems under consideration. [iv] the parallelization of processes such as tree traversal and grid-particle interpolations We are conducting simulations using vortex methods, molecular dynamics and smooth particle hydrodynamics, exploiting their unifying concepts such as : the solution of the N-body problem in parallel computers, highly accurate particle-particle and grid-particle interpolations, parallel FFT's and the formulation of processes such as diffusion in the context of particle methods. This approach enables us to transcend among seemingly unrelated areas of research.

Electrokinetic motion of a spherical micro particle at an oil-water interface in microchannel.

PubMed

Wang, Chengfa; Li, Mengqi; Song, Yongxin; Pan, Xinxiang; Li, Dongqing

2018-03-01

The electrokinetic motion of a negatively charged spherical particle at an oil-water interface in a microchannel is numerically investigated and analyzed in this paper. A three-dimensional (3D) transient numerical model is developed to simulate the particle electrokinetic motion. The channel wall, the surface of the particle and the oil-water interface are all considered negatively charged. The effects of the direct current (DC) electric field, the zeta potentials of the particle-water interface and the oil-water interface, and the dynamic viscosity ratio of oil to water on the velocity of the particle are studied in this paper. In addition, the influences of the particle size are also discussed. The simulation results show that the micro-particle with a small value of negative zeta potential moves in the same direction of the external electric field. However, if the zeta potential value of the particle-water interface is large enough, the moving direction of the particle is opposite to that of the electric field. The velocity of the particle at the interface increases with the increase in the electric field strength and the particle size, but decreases with the increase in the dynamic viscosity ratio of oil to water, and the absolute value of the negative zeta potentials of both the particle-water interface and the oil-water interface. This work is the first numerical study of the electrokinetic motion of a charged particle at an oil-water interface in a microchannel. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Study of Nonlinear Dynamics of Intense Charged Particle Beams in the Paul Trap Simulator Experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hua

The Paul Trap Simulator Experiment (PTSX) is a compact laboratory device that simulates the nonlinear dynamics of intense charged particle beams propagating over a large distance in an alternating-gradient magnetic transport system. The radial quadrupole electric eld forces on the charged particles in the Paul Trap are analogous to the radial forces on the charged particles in the quadrupole magnetic transport system. The amplitude of oscillating voltage applied to the cylindrical electrodes in PTSX is equivalent to the quadrupole magnetic eld gradient in accelerators. The temporal periodicity in PTSX corresponds to the spatial periodicity in magnetic transport system. This thesismore » focuses on investigations of envelope instabilities and collective mode excitations, properties of high-intensity beams with significant space-charge effects, random noise-induced beam degradation and a laser-induced-fluorescence diagnostic. To better understand the nonlinear dynamics of the charged particle beams, it is critical to understand the collective processes of the charged particles. Charged particle beams support a variety of collective modes, among which the quadrupole mode and the dipole mode are of the greatest interest. We used quadrupole and dipole perturbations to excite the quadrupole and dipole mode respectively and study the effects of those collective modes on the charge bunch. The experimental and particle-in-cell (PIC) simulation results both show that when the frequency and the spatial structure of the external perturbation are matched with the corresponding collective mode, that mode will be excited to a large amplitude and resonates strongly with the external perturbation, usually causing expansion of the charge bunch and loss of particles. Machine imperfections are inevitable for accelerator systems, and we use random noise to simulate the effects of machine imperfection on the charged particle beams. The random noise can be Fourier decomposed into various frequency components and experimental results show that when the random noise has a large frequency component that matches a certain collective mode, the mode will also be excited and cause heating of the charge bunch. It is also noted that by rearranging the order of the random noise, the adverse effects of the random noise may be eliminated. As a non-destructive diagnostic method, a laser-induced- fluorescence (LIF) diagnostic is developed to study the transverse dynamics of the charged particle beams. The accompanying barium ion source and dye laser system are developed and tested.« less

Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) Study of Mass-Transfer Mechanisms in Riser Flow.

PubMed

Carlos Varas, Álvaro E; Peters, E A J F; Kuipers, J A M

2017-05-17

We report a computational fluid dynamics-discrete element method (CFD-DEM) simulation study on the interplay between mass transfer and a heterogeneous catalyzed chemical reaction in cocurrent gas-particle flows as encountered in risers. Slip velocity, axial gas dispersion, gas bypassing, and particle mixing phenomena have been evaluated under riser flow conditions to study the complex system behavior in detail. The most important factors are found to be directly related to particle cluster formation. Low air-to-solids flux ratios lead to more heterogeneous systems, where the cluster formation is more pronounced and mass transfer more influenced. Falling clusters can be partially circumvented by the gas phase, which therefore does not fully interact with the cluster particles, leading to poor gas-solid contact efficiencies. Cluster gas-solid contact efficiencies are quantified at several gas superficial velocities, reaction rates, and dilution factors in order to gain more insight regarding the influence of clustering phenomena on the performance of riser reactors.

Non-Markovian effects in the first-passage dynamics of obstructed tracer particle diffusion in one-dimensional systems

NASA Astrophysics Data System (ADS)

Forsling, Robin; Sanders, Lloyd P.; Ambjörnsson, Tobias; Lizana, Ludvig

2014-09-01

The standard setup for single-file diffusion is diffusing particles in one dimension which cannot overtake each other, where the dynamics of a tracer (tagged) particle is of main interest. In this article, we generalize this system and investigate first-passage properties of a tracer particle when flanked by identical crowder particles which may, besides diffuse, unbind (rebind) from (to) the one-dimensional lattice with rates koff (kon). The tracer particle is restricted to diffuse with rate kD on the lattice and the density of crowders is constant (on average). The unbinding rate koff is our key parameter and it allows us to systematically study the non-trivial transition between the completely Markovian case (koff ≫ kD) to the non-Markovian case (koff ≪ kD) governed by strong memory effects. This has relevance for several quasi one-dimensional systems. One example is gene regulation where regulatory proteins are searching for specific binding sites on a crowded DNA. We quantify the first-passage time distribution, f (t) (t is time), numerically using the Gillespie algorithm, and estimate f (t) analytically. In terms of koff (keeping kD fixed), we study the transition between the two known regimes: (i) when koff ≫ kD the particles may effectively pass each other and we recover the single particle result f (t) ˜ t-3/2, with a reduced diffusion constant; (ii) when koff ≪ kD unbinding is rare and we obtain the single-file result f (t) ˜ t-7/4. The intermediate region displays rich dynamics where both the characteristic f (t) - peak and the long-time power-law slope are sensitive to koff.

Influence of a depletion interaction on dynamical heterogeneity in a dense quasi-two-dimensional colloid liquid.

PubMed

Ho, Hau My; Cui, Bianxiao; Repel, Stephen; Lin, Binhua; Rice, Stuart A

2004-11-01

We report the results of digital video microscopy studies of the large particle displacements in a quasi-two-dimensional binary mixture of large (L) and small (S) colloid particles with diameter ratio sigma(L)/sigma(S)=4.65, as a function of the large and small colloid particle densities. As in the case of the one-component quasi-two-dimensional colloid system, the binary mixtures exhibit structural and dynamical heterogeneity. The distribution of large particle displacements over the time scale examined provides evidence for (at least) two different mechanisms of motion, one associated with particles in locally ordered regions and the other associated with particles in locally disordered regions. When rhoL*=Npisigma(L) (2)/4A< or =0.35, the addition of small colloid particles leads to a monotonic decrease in the large particle diffusion coefficient with increasing small particle volume fraction. When rhoL* > or =0.35 the addition of small colloid particles to a dense system of large colloid particles at first leads to an increase in the large particle diffusion coefficient, which is then followed by the expected decrease of the large particle diffusion coefficient with increasing small colloid particle volume fraction. The mode coupling theory of the ideal glass transition in three-dimensional systems makes a qualitative prediction that agrees with the initial increase in the large particle diffusion coefficient with increasing small particle density. Nevertheless, because the structural and dynamical heterogeneities of the quasi-two-dimensional colloid liquid occur within the field of equilibrium states, and the fluctuations generate locally ordered domains rather than just disordered regions of higher and lower density, it is suggested that mode coupling theory does not account for all classes of relevant fluctuations in a quasi-two-dimensional liquid. (c) 2004 American Institute of Physics.

Quantum walks of two interacting particles on percolation graphs

NASA Astrophysics Data System (ADS)

Siloi, Ilaria; Benedetti, Claudia; Piccinini, Enrico; Paris, Matteo G. A.; Bordone, Paolo

2017-10-01

We address the dynamics of two indistinguishable interacting particles moving on a dynamical percolation graph, i.e., a graph where the edges are independent random telegraph processes whose values jump between 0 and 1, thus mimicking percolation. The interplay between the particle interaction strength, initial state and the percolation rate determine different dynamical regimes for the walkers. We show that, whenever the walkers are initially localised within the interaction range, fast noise enhances the particle spread compared to the noiseless case.

Forced and natural convection in aggregate-laden nanofluids

NASA Astrophysics Data System (ADS)

Thajudeen, Thaseem; Hogan, Christopher J.

2011-12-01

A number of experimental and theoretical studies of convective heat transfer in nanofluids (liquid suspensions of nanoparticles, typically with features below 100 nm in size) reveal contrasting results; nanoparticles can either enhance or reduce the convective heat transfer coefficient. These disparate conclusions regarding the influence of nanoparticles on convective heat transfer may arise due to the aggregation of nanoparticles, which is often not considered in studies of nanofluids. Here, we examine theoretically forced and natural convective heat transfer of aggregate-laden nanofluids using Monte Carlo-based models to determine how the aggregate morphology influences the convective heat transfer coefficient. Specifically, in this study, it is first shown that standard heat transfer correlations should apply to nanofluids, and the main influence of the nanoparticles is to alter suspension thermal conductivity, dynamic viscosity, density, specific heat, and thermal expansion coefficient. Aggregated particles in suspension are modeled as quasi-fractal aggregates composed of individual primary particles described by the primary particle radius, number of primary particles, fractal (Hausdorff) dimension, pre-exponential factor, and degree of coalescence between primary particles. A sequential algorithm is used to computationally generate aggregates with prescribed morphological descriptors. Four types of aggregates are considered; spanning the range of aggregate morphologies observed in nanofluids. For each morphological type, the influences of aggregates on nanofluid dynamic viscosity and thermal conductivity are determined via first passage-based Brownian dynamics calculations. It is found that depending on both the material properties of the nanoparticles as well as the nanoparticle morphology, the addition of nanoparticles to a suspension can either increase or decrease both the forced and natural convective heat transfer coefficients, with both a 51% increase and a 32% decrease in the heat transfer coefficient achievable at particle volume fractions of 0.05. This study shows clearly that the influence of particle morphology needs to be accounted for in all studies of heat transfer in nanofluids.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pramanik, Souvik, E-mail: souvick.in@gmail.com; Ghosh, Subir, E-mail: subir_ghosh2@rediffmail.com; Pal, Probir, E-mail: probirkumarpal@rediffmail.com

In the present paper, dynamics of generalized charged particles are studied in the presence of external electromagnetic interactions. This particular extension of the free relativistic particle model lives in Non-Commutative κ-Minkowski space–time, compatible with Doubly Special Relativity, that is motivated to describe Quantum Gravity effects. Furthermore we have also considered the electromagnetic field to be dynamical and have derived the modified forms of Lienard–Wiechert like potentials for these extended charged particle models. In all the above cases we exploit the new and extended form of κ-Minkowski algebra where electromagnetic effects are incorporated in the lowest order, in the Dirac frameworkmore » of Hamiltonian constraint analysis.« less

Simulation of collisional transport processes and the stability of planetary rings

NASA Technical Reports Server (NTRS)

Brophy, Thomas G.; Esposito, Larry W.

1989-01-01

The utility of the phase-space fluid method for the study of planetary ring dynamics is presently demonstrated through the numerical solution of a model kinetic equation for a flattened Keplerian disk. Attention is given to ringlets composed of single-sized particles, as well as to ringlets composed of two different-sized particles; in the latter case, the ringlets evolve in such a way that the lighter particles are confined by the heavier ones. The results obtained indicate that some natural process may sharpen the optical depth profile of edges even without an external forcing mechanism, and that intermediate optical depths are dynamically preferred in some cases.

Brownian motion on random dynamical landscapes

NASA Astrophysics Data System (ADS)

Suñé Simon, Marc; Sancho, José María; Lindenberg, Katja

2016-03-01

We present a study of overdamped Brownian particles moving on a random landscape of dynamic and deformable obstacles (spatio-temporal disorder). The obstacles move randomly, assemble, and dissociate following their own dynamics. This landscape may account for a soft matter or liquid environment in which large obstacles, such as macromolecules and organelles in the cytoplasm of a living cell, or colloids or polymers in a liquid, move slowly leading to crowding effects. This representation also constitutes a novel approach to the macroscopic dynamics exhibited by active matter media. We present numerical results on the transport and diffusion properties of Brownian particles under this disorder biased by a constant external force. The landscape dynamics are characterized by a Gaussian spatio-temporal correlation, with fixed time and spatial scales, and controlled obstacle concentrations.

Modeling crystal growth from solution with molecular dynamics simulations: approaches to transition rate constants.

PubMed

Reilly, Anthony M; Briesen, Heiko

2012-01-21

The feasibility of using the molecular dynamics (MD) simulation technique to study crystal growth from solution quantitatively, as well as to obtain transition rate constants, has been studied. The dynamics of an interface between a solution of Lennard-Jones particles and the (100) face of an fcc lattice comprised of solute particles have been studied using MD simulations, showing that MD is, in principle, capable of following growth behavior over large supersaturation and temperature ranges. Using transition state theory, and a nearest-neighbor approximation growth and dissolution rate constants have been extracted from equilibrium MD simulations at a variety of temperatures. The temperature dependence of the rates agrees well with the expected transition state theory behavior. © 2012 American Institute of Physics

Brownian dynamics simulations of lipid bilayer membrane with hydrodynamic interactions in LAMMPS

NASA Astrophysics Data System (ADS)

Fu, Szu-Pei; Young, Yuan-Nan; Peng, Zhangli; Yuan, Hongyan

2016-11-01

Lipid bilayer membranes have been extensively studied by coarse-grained molecular dynamics simulations. Numerical efficiencies have been reported in the cases of aggressive coarse-graining, where several lipids are coarse-grained into a particle of size 4 6 nm so that there is only one particle in the thickness direction. Yuan et al. proposed a pair-potential between these one-particle-thick coarse-grained lipid particles to capture the mechanical properties of a lipid bilayer membrane (such as gel-fluid-gas phase transitions of lipids, diffusion, and bending rigidity). In this work we implement such interaction potential in LAMMPS to simulate large-scale lipid systems such as vesicles and red blood cells (RBCs). We also consider the effect of cytoskeleton on the lipid membrane dynamics as a model for red blood cell (RBC) dynamics, and incorporate coarse-grained water molecules to account for hydrodynamic interactions. The interaction between the coarse-grained water molecules (explicit solvent molecules) is modeled as a Lennard-Jones (L-J) potential. We focus on two sets of LAMMPS simulations: 1. Vesicle shape transitions with varying enclosed volume; 2. RBC shape transitions with different enclosed volume. This work is funded by NSF under Grant DMS-1222550.

Brownian dynamics simulations of lipid bilayer membrane with hydrodynamic interactions in LAMMPS

NASA Astrophysics Data System (ADS)

Fu, Szu-Pei; Young, Yuan-Nan; Peng, Zhangli; Yuan, Hongyan

Lipid bilayer membranes have been extensively studied by coarse-grained molecular dynamics simulations. Numerical efficiency has been reported in the cases of aggressive coarse-graining, where several lipids are coarse-grained into a particle of size 4 6 nm so that there is only one particle in the thickness direction. Yuan et al. proposed a pair-potential between these one-particle-thick coarse-grained lipid particles to capture the mechanical properties of a lipid bilayer membrane (such as gel-fluid-gas phase transitions of lipids, diffusion, and bending rigidity). In this work we implement such interaction potential in LAMMPS to simulate large-scale lipid systems such as vesicles and red blood cells (RBCs). We also consider the effect of cytoskeleton on the lipid membrane dynamics as a model for red blood cell (RBC) dynamics, and incorporate coarse-grained water molecules to account for hydrodynamic interactions. The interaction between the coarse-grained water molecules (explicit solvent molecules) is modeled as a Lennard-Jones (L-J) potential. We focus on two sets of LAMMPS simulations: 1. Vesicle shape transitions with varying enclosed volume; 2. RBC shape transitions with different enclosed volume.

Pseudochemotaxis in inhomogeneous active Brownian systems

NASA Astrophysics Data System (ADS)

Vuijk, Hidde D.; Sharma, Abhinav; Mondal, Debasish; Sommer, Jens-Uwe; Merlitz, Holger

2018-04-01

We study dynamical properties of confined, self-propelled Brownian particles in an inhomogeneous activity profile. Using Brownian dynamics simulations, we calculate the probability to reach a fixed target and the mean first passage time to the target of an active particle. We show that both these quantities are strongly influenced by the inhomogeneous activity. When the activity is distributed such that high-activity zone is located between the target and the starting location, the target finding probability is increased and the passage time is decreased in comparison to a uniformly active system. Moreover, for a continuously distributed profile, the activity gradient results in a drift of active particle up the gradient bearing resemblance to chemotaxis. Integrating out the orientational degrees of freedom, we derive an approximate Fokker-Planck equation and show that the theoretical predictions are in very good agreement with the Brownian dynamics simulations.

A study of the diffusion dynamics and concentration distribution of gold nanospheres (GNSs) without fluorescent labeling inside live cells using fluorescence single particle spectroscopy.

PubMed

Liu, Fangchao; Dong, Chaoqing; Ren, Jicun

2018-03-15

Colloidal gold nanospheres (GNSs) have become important nanomaterials in biomedical applications due to their special optical properties, good chemical stability, and biocompatibility. However, measuring the diffusion coefficients or concentration distribution of GNSs within live cells accurately without any extra fluorescent labeling in situ has still not been resolved. In this work, a single particle method is developed to study the concentration distribution of folic acid-modified GNSs (FA-GNSs) internalized via folate receptors, and investigates their diffusion dynamics within live cells using single particle fluorescence correlation spectroscopy (FCS). We optimized the experimental conditions and verified the feasibility of 30 nm GNSs without extra fluorescence labeling being used for single particle detection inside live cells. Then, the FCS characterization strategy was used to measure the concentration and diffusion coefficient distributions of GNSs inside live cells and the obtained results were basically in agreement with those obtained by TEM. The results demonstrate that our strategy is characterized as an in situ, nondestructive, rapid and dynamic method for the assay of live cells, and it may be widely used in the further design of GNP-based drug delivery and therapeutics.

The effect of shear flow on the rotational diffusivity of a single axisymmetric particle

NASA Astrophysics Data System (ADS)

Leahy, Brian; Koch, Donald; Cohen, Itai

2014-11-01

Colloidal suspensions of nonspherical particles abound in the world around us, from red blood cells in arteries to kaolinite discs in clay. Understanding the orientation dynamics of these particles is important for suspension rheology and particle self-assembly. However, even for the simplest case of dilute suspensions in simple shear flow, the orientation dynamics of Brownian nonspherical particles are poorly understood at large shear rates. Here, we analytically calculate the time-dependent orientation distributions of particles confined to the flow-gradient plane when the rotary diffusion is small but nonzero. For both startup and oscillatory shear flows, we find a coordinate change that maps the convection-diffusion equation to a simple diffusion equation with an enhanced diffusion constant, simplifying the orientation dynamics. For oscillatory shear, this enhanced diffusion drastically alters the quasi-steady orientation distributions. Our theory of the unsteady orientation dynamics provides an understanding of a nonspherical particle suspension's rheology for a large class of unsteady flows. For particles with aspect ratio 10 under oscillatory shear, the rotary diffusion and intrinsic viscosity vary with amplitude by a factor of ~ 40 and ~ 2 , respectively.

Dynamic acoustic field activated cell separation (DAFACS).

PubMed

Skotis, G D; Cumming, D R S; Roberts, J N; Riehle, M O; Bernassau, A L

2015-02-07

Advances in diagnostics, cell and stem cell technologies drive the development of application-specific tools for cell and particle separation. Acoustic micro-particle separation offers a promising avenue for high-throughput, label-free, high recovery, cell and particle separation and isolation in regenerative medicine. Here, we demonstrate a novel approach utilizing a dynamic acoustic field that is capable of separating an arbitrary size range of cells. We first demonstrate the method for the separation of particles with different diameters between 6 and 45 μm and secondly particles of different densities in a heterogeneous medium. The dynamic acoustic field is then used to separate dorsal root ganglion cells. The shearless, label-free and low damage characteristics make this method of manipulation particularly suited for biological applications. Advantages of using a dynamic acoustic field for the separation of cells include its inherent safety and biocompatibility, the possibility to operate over large distances (centimetres), high purity (ratio of particle population, up to 100%), and high efficiency (ratio of separated particles over total number of particles to separate, up to 100%).

Correlating contact line capillarity and dynamic contact angle hysteresis in surfactant-nanoparticle based complex fluids

NASA Astrophysics Data System (ADS)

Harikrishnan, A. R.; Dhar, Purbarun; Agnihotri, Prabhat K.; Gedupudi, Sateesh; Das, Sarit K.

2018-04-01

Dynamic wettability and contact angle hysteresis can be correlated to shed insight onto any solid-liquid interaction. Complex fluids are capable of altering the expected hysteresis and dynamic wetting behavior due to interfacial interactions. We report the effect of capillary number on the dynamic advancing and receding contact angles of surfactant-based nanocolloidal solutions on hydrophilic, near hydrophobic, and superhydrophobic surfaces by performing forced wetting and de-wetting experiments by employing the embedded needle method. A segregated study is performed to infer the contributing effects of the constituents and effects of particle morphology. The static contact angle hysteresis is found to be a function of particle and surfactant concentrations and greatly depends on the nature of the morphology of the particles. An order of estimate of line energy and a dynamic flow parameter called spreading factor and the transient variations of these parameters are explored which sheds light on the dynamics of contact line movement and response to perturbation of three-phase contact. The Cox-Voinov-Tanner law was found to hold for hydrophilic and a weak dependency on superhydrophobic surfaces with capillary number, and even for the complex fluids, with a varying degree of dependency for different fluids.

Shock Dynamics for particle-laden thin film

NASA Astrophysics Data System (ADS)

Wang, Li; Bertozzi, Andrea

2013-11-01

We study the shock dynamics for a recently proposed system of conservation laws (Murisic et al. [J. Fluid Mech. 2013]) describing gravity-driven thin film flow of a suspension of particles down an incline. When the particle concentration is above a critical value, singular shock solutions can occur. We analyze the Hugoniot topology associated with the Riemann problem for this system, describing in detail how the transition from a double shock to a singular shock happen. We also derive the singular shock speed based on a key observation that the particles pilling up at the maximum packing fraction near the contact line. These results are further applied to constant volume case to generate a rarefaction-singular shock solution. The particle/fluid front are shown to move linearly to the leading order with time to the one-third power as predicted by the Huppert solution for clear fluid.

Self ordering threshold and superradiant backscattering to slow a fast gas beam in a ring cavity with counter propagating pump

NASA Astrophysics Data System (ADS)

Maes, C.; Asbóth, J. K.; Ritsch, H.

2007-05-01

We study the dynamics of a fast gaseous beam in a high Q ring cavity counter propagating a strong pump laser with large detuning from any particle optical resonance. As spontaneous emission is strongly suppressed the particles can be treated as polarizable point masses forming a dynamic moving mirror. Above a threshold intensity the particles exhibit spatial periodic ordering enhancing collective coherent backscattering which decelerates the beam. Based on a linear stability analysis in their accelerated rest frame we derive analytic bounds for the intensity threshold of this selforganization as a function of particle number, average velocity, kinetic temperature, pump detuning and resonator linewidth. The analytical results agree well with time dependent simulations of the N-particle motion including field damping and spontaneous emission noise. Our results give conditions which may be easily evaluated for stopping and cooling a fast molecular beam.

Temperature effects on drift of suspended single-domain particles induced by the Magnus force

NASA Astrophysics Data System (ADS)

Denisov, S. I.; Lyutyy, T. V.; Reva, V. V.; Yermolenko, A. S.

2018-03-01

We study the temperature dependence of the drift velocity of single-domain ferromagnetic particles induced by the Magnus force in a dilute suspension. A set of stochastic equations describing the translational and rotational dynamics of particles is derived, and the particle drift velocity that depends on components of the average particle magnetization is introduced. The Fokker-Planck equation for the probability density of magnetization orientations is solved analytically in the limit of strong thermal fluctuations for both the planar rotor and general models. Using these solutions, we calculate the drift velocity and show that the out-of-plane fluctuations of magnetization, which are not accounted for in the planar rotor model, play an important role. In the general case of arbitrary fluctuations, we investigate the temperature dependence of the drift velocity by numerically simulating a set of effective stochastic differential equations for the magnetization dynamics.

Self ordering threshold and superradiant backscattering to slow a fast gas beam in a ring cavity with counter propagating pump.

PubMed

Maes, C; Asbóth, J K; Ritsch, H

2007-05-14

We study the dynamics of a fast gaseous beam in a high Q ring cavity counter propagating a strong pump laser with large detuning from any particle optical resonance. As spontaneous emission is strongly suppressed the particles can be treated as polarizable point masses forming a dynamic moving mirror. Above a threshold intensity the particles exhibit spatial periodic ordering enhancing collective coherent backscattering which decelerates the beam. Based on a linear stability analysis in their accelerated rest frame we derive analytic bounds for the intensity threshold of this selforganization as a function of particle number, average velocity, kinetic temperature, pump detuning and resonator linewidth. The analytical results agree well with time dependent simulations of the N-particle motion including field damping and spontaneous emission noise. Our results give conditions which may be easily evaluated for stopping and cooling a fast molecular beam.

Nonlinear stochastic exclusion financial dynamics modeling and time-dependent intrinsic detrended cross-correlation

NASA Astrophysics Data System (ADS)

Zhang, Wei; Wang, Jun

2017-09-01

In attempt to reproduce price dynamics of financial markets, a stochastic agent-based financial price model is proposed and investigated by stochastic exclusion process. The exclusion process, one of interacting particle systems, is usually thought of as modeling particle motion (with the conserved number of particles) in a continuous time Markov process. In this work, the process is utilized to imitate the trading interactions among the investing agents, in order to explain some stylized facts found in financial time series dynamics. To better understand the correlation behaviors of the proposed model, a new time-dependent intrinsic detrended cross-correlation (TDI-DCC) is introduced and performed, also, the autocorrelation analyses are applied in the empirical research. Furthermore, to verify the rationality of the financial price model, the actual return series are also considered to be comparatively studied with the simulation ones. The comparison results of return behaviors reveal that this financial price dynamics model can reproduce some correlation features of actual stock markets.

Optical properties of mineral dust aerosol including analysis of particle size, composition, and shape effects, and the impact of physical and chemical processing

NASA Astrophysics Data System (ADS)

Alexander, Jennifer Mary

Atmospheric mineral dust has a large impact on the earth's radiation balance and climate. The radiative effects of mineral dust depend on factors including, particle size, shape, and composition which can all be extremely complex. Mineral dust particles are typically irregular in shape and can include sharp edges, voids, and fine scale surface roughness. Particle shape can also depend on the type of mineral and can vary as a function of particle size. In addition, atmospheric mineral dust is a complex mixture of different minerals as well as other, possibly organic, components that have been mixed in while these particles are suspended in the atmosphere. Aerosol optical properties are investigated in this work, including studies of the effect of particle size, shape, and composition on the infrared (IR) extinction and visible scattering properties in order to achieve more accurate modeling methods. Studies of particle shape effects on dust optical properties for single component mineral samples of silicate clay and diatomaceous earth are carried out here first. Experimental measurements are modeled using T-matrix theory in a uniform spheroid approximation. Previous efforts to simulate the measured optical properties of silicate clay, using models that assumed particle shape was independent of particle size, have achieved only limited success. However, a model which accounts for a correlation between particle size and shape for the silicate clays offers a large improvement over earlier modeling approaches. Diatomaceous earth is also studied as an example of a single component mineral dust aerosol with extreme particle shapes. A particle shape distribution, determined by fitting the experimental IR extinction data, used as a basis for modeling the visible light scattering properties. While the visible simulations show only modestly good agreement with the scattering data, the fits are generally better than those obtained using more commonly invoked particle shape distributions. The next goal of this work is to investigate if modeling methods developed in the studies of single mineral components can be generalized to predict the optical properties of more authentic aerosol samples which are complex mixtures of different minerals. Samples of Saharan sand, Iowa loess, and Arizona road dust are used here as test cases. T-matrix based simulations of the authentic samples, using measured particle size distributions, empirical mineralogies, and a priori particle shape models for each mineral component are directly compared with the measured IR extinction spectra and visible scattering profiles. This modeling approach offers a significant improvement over more commonly applied models that ignore variations in particle shape with size or mineralogy and include only a moderate range of shape parameters. Mineral dust samples processed with organic acids and humic material are also studied in order to explore how the optical properties of dust can change after being aged in the atmosphere. Processed samples include quartz mixed with humic material, and calcite reacted with acetic and oxalic acid. Clear differences in the light scattering properties are observed for all three processed mineral dust samples when compared to the unprocessed mineral dust or organic salt products. These interactions result in both internal and external mixtures depending on the sample. In addition, the presence of these organic materials can alter the mineral dust particle shape. Overall, however, these results demonstrate the need to account for the effects of atmospheric aging of mineral dust on aerosol optical properties. Particle shape can also affect the aerodynamic properties of mineral dust aerosol. In order to account for these effects, the dynamic shape factor is used to give a measure of particle asphericity. Dynamic shape factors of quartz are measured by mass and mobility selecting particles and measuring their vacuum aerodynamic diameter. From this, dynamic shape factors in both the transition and vacuum regime can be derived. The measured dynamic shape factors of quartz agree quite well with the spheroidal shape distributions derived through studies of the optical properties.

Ball Rolling on a Turntable: Analog for Charged Particle Dynamics.

ERIC Educational Resources Information Center

Burns, Joseph A.

1981-01-01

Describes how a ball's motion duplicates that of a charged particle moving through a magnetic field and thereby allows students to visualize directly many aspects of charged particle dynamics otherwise not accessible to them. (Author/JN)

Influence of Dissipative Particle Dynamics parameters and wall models on planar micro-channel flows

NASA Astrophysics Data System (ADS)

Wang, Yuyi; She, Jiangwei; Zhou, Zhe-Wei; microflow Group Team

2017-11-01

Dissipative Particle Dynamics (DPD) is a very effective approach in simulating mesoscale hydrodynamics. The influence of solid boundaries and DPD parameters are typically very strong in DPD simulations. The present work studies a micro-channel Poisseuille flow. Taking the neutron scattering experiment and molecular dynamics simulation result as bench mark, the DPD results of density distribution and velocity profile are systematically studied. The influence of different levels of coarse-graining, the number densities of wall and fluid, conservative force coefficients, random and dissipative force coefficients, different wall model and reflective boundary conditions are discussed. Some mechanisms behind such influences are discussed and the artifacts in the simulation are identified with the bench mark. Chinese natural science foundation (A020405).

Particle swarm optimization with recombination and dynamic linkage discovery.

PubMed

Chen, Ying-Ping; Peng, Wen-Chih; Jian, Ming-Chung

2007-12-01

In this paper, we try to improve the performance of the particle swarm optimizer by incorporating the linkage concept, which is an essential mechanism in genetic algorithms, and design a new linkage identification technique called dynamic linkage discovery to address the linkage problem in real-parameter optimization problems. Dynamic linkage discovery is a costless and effective linkage recognition technique that adapts the linkage configuration by employing only the selection operator without extra judging criteria irrelevant to the objective function. Moreover, a recombination operator that utilizes the discovered linkage configuration to promote the cooperation of particle swarm optimizer and dynamic linkage discovery is accordingly developed. By integrating the particle swarm optimizer, dynamic linkage discovery, and recombination operator, we propose a new hybridization of optimization methodologies called particle swarm optimization with recombination and dynamic linkage discovery (PSO-RDL). In order to study the capability of PSO-RDL, numerical experiments were conducted on a set of benchmark functions as well as on an important real-world application. The benchmark functions used in this paper were proposed in the 2005 Institute of Electrical and Electronics Engineers Congress on Evolutionary Computation. The experimental results on the benchmark functions indicate that PSO-RDL can provide a level of performance comparable to that given by other advanced optimization techniques. In addition to the benchmark, PSO-RDL was also used to solve the economic dispatch (ED) problem for power systems, which is a real-world problem and highly constrained. The results indicate that PSO-RDL can successfully solve the ED problem for the three-unit power system and obtain the currently known best solution for the 40-unit system.

Dynamics of Aerosol Particles in Stationary, Isotropic Turbulence

NASA Technical Reports Server (NTRS)

Collins, Lance R.; Meng, Hui

2004-01-01

A detailed study of the dynamics of sub-Kolmogorov-size aerosol particles in stationary isotropic turbulence has been performed. The study combined direct numerical simulations (DNS; directed by Prof. Collins) and high-resolution experimental measurements (directed by Prof. Meng) under conditions of nearly perfect geometric and parametric overlap. The goal was to measure the accumulation of particles in low-vorticity regions of the flow that arises from the effect commonly referred to as preferential concentration. The grant technically was initiated on June 13, 2000; however, funding was not available until July 11, 2000. The grant was originally awarded to Penn State University (numerical simulations) and SUNY-Buffalo (experiments); however, Prof. Collins effort was moved to Cornell University on January 2002 when he joined that university. He completed the study there. A list of the specific tasks that were completed under this study is presented.

Flocking from a quantum analogy: spin-orbit coupling in an active fluid

NASA Astrophysics Data System (ADS)

Loewe, Benjamin; Souslov, Anton; Goldbart, Paul M.

2018-01-01

Systems composed of strongly interacting self-propelled particles can form a spontaneously flowing polar active fluid. The study of the connection between the microscopic dynamics of a single such particle and the macroscopic dynamics of the fluid can yield insights into experimentally realizable active flows, but this connection is well understood in only a few select cases. We introduce a model of self-propelled particles based on an analogy with the motion of electrons that have strong spin-orbit coupling. We find that, within our model, self-propelled particles are subject to an analog of the Heisenberg uncertainty principle that relates translational and rotational noise. Furthermore, by coarse-graining this microscopic model, we establish expressions for the coefficients of the Toner-Tu equations—the hydrodynamic equations that describe an active fluid composed of these ‘active spins.’ The connection between stochastic self-propelled particles and quantum particles with spin may help realize exotic phases of matter using active fluids via analogies with systems composed of strongly correlated electrons.

Continual model of magnetic dynamics for antiferromagnetic particles in analyzing size effects on Morin transition in hematite nanoparticles

NASA Astrophysics Data System (ADS)

Mishchenko, I.; Chuev, M.; Kubrin, S.; Lastovina, T.; Polyakov, V.; Soldatov, A.

2018-05-01

Alternative explanation to the effect of disappearance of the Morin transition on hematite nanoparticles with their size decreasing is proposed basing on an idea of the predominant role of the shape anisotropy for nanosize particles. Three types of the magnetic structure of hematite nanoparticles with various sizes are found by Mössbauer spectroscopy: coexistence of the well-pronounced antiferromagnetic and weakly ferromagnetic phases for particles with average diameters of about 55 nm, non-uniform distribution of the magnetization axes which concentrate on the vicinity of the basal plane (111) for prolonged particles with cross sections of about 20 nm, and uniform distribution of the easy axes in regard to the crystalline directions for 3-nm particles. Description of the temperature evolution of experimental data within novel model of the magnetic dynamics for antiferromagnetic particles which accounts the exchange, relativistic, and anisotropy interactions is provided, and the structural as well as energy characteristics of the studied systems are reconstructed.

A Bond-Fluctuation Model of Translational Dynamics of Chain-like Particles through Mucosal Scaffolds.

PubMed

Bajd, Franci; Serša, Igor

2018-06-05

Mucus scaffolds represent one of the most common barriers in targeted drug delivery and can remarkably reduce the outcome of pharmacological therapies. An efficient transport of drug particles through a mucus barrier is a precondition for an efficient drug delivery. Understanding the transport mechanism is particularly important for treatment of disorders such as cystic fibrosis. These are characterized by an onset of high-density mucus scaffolds imposing an increased steric filtering. In this study, we employed the bond-fluctuation model to analyze the effect of steric interactions on slowing the translational dynamics of compound chain-like particles traversing through scaffolds of different configurations (regular isotropic and anisotropic versus irregular random). The model, which accounts for both the geometry-imposed steric interaction as well as the intrachain steric interaction between the chain subunits, yields a transient subdiffusive motional pattern persists between the short-time and long-time Gaussian diffusion limits. The motion is analyzed in terms of a mean-squared displacement, diffusion coefficient, and radius of gyration. With higher levels of restriction or larger particles, the subdiffusive motional regime persists longer. The study also demonstrates that an important feature of the motion is also geometry-induced chain accommodation. The presented model is generic and could also be applied to studying the translational dynamics of other particles with more complex architecture such as dendrites or chain-decorated nanoparticles. Copyright © 2018 Biophysical Society. Published by Elsevier Inc. All rights reserved.

A unified gas-kinetic scheme for continuum and rarefied flows IV: Full Boltzmann and model equations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Chang, E-mail: cliuaa@ust.hk; Xu, Kun, E-mail: makxu@ust.hk; Sun, Quanhua, E-mail: qsun@imech.ac.cn

Fluid dynamic equations are valid in their respective modeling scales, such as the particle mean free path scale of the Boltzmann equation and the hydrodynamic scale of the Navier–Stokes (NS) equations. With a variation of the modeling scales, theoretically there should have a continuous spectrum of fluid dynamic equations. Even though the Boltzmann equation is claimed to be valid in all scales, many Boltzmann solvers, including direct simulation Monte Carlo method, require the cell resolution to the order of particle mean free path scale. Therefore, they are still single scale methods. In order to study multiscale flow evolution efficiently, themore » dynamics in the computational fluid has to be changed with the scales. A direct modeling of flow physics with a changeable scale may become an appropriate approach. The unified gas-kinetic scheme (UGKS) is a direct modeling method in the mesh size scale, and its underlying flow physics depends on the resolution of the cell size relative to the particle mean free path. The cell size of UGKS is not limited by the particle mean free path. With the variation of the ratio between the numerical cell size and local particle mean free path, the UGKS recovers the flow dynamics from the particle transport and collision in the kinetic scale to the wave propagation in the hydrodynamic scale. The previous UGKS is mostly constructed from the evolution solution of kinetic model equations. Even though the UGKS is very accurate and effective in the low transition and continuum flow regimes with the time step being much larger than the particle mean free time, it still has space to develop more accurate flow solver in the region, where the time step is comparable with the local particle mean free time. In such a scale, there is dynamic difference from the full Boltzmann collision term and the model equations. This work is about the further development of the UGKS with the implementation of the full Boltzmann collision term in the region where it is needed. The central ingredient of the UGKS is the coupled treatment of particle transport and collision in the flux evaluation across a cell interface, where a continuous flow dynamics from kinetic to hydrodynamic scales is modeled. The newly developed UGKS has the asymptotic preserving (AP) property of recovering the NS solutions in the continuum flow regime, and the full Boltzmann solution in the rarefied regime. In the mostly unexplored transition regime, the UGKS itself provides a valuable tool for the non-equilibrium flow study. The mathematical properties of the scheme, such as stability, accuracy, and the asymptotic preserving, will be analyzed in this paper as well.« less

A many-body dissipative particle dynamics study of forced water-oil displacement in capillary.

PubMed

Chen, Chen; Zhuang, Lin; Li, Xuefeng; Dong, Jinfeng; Lu, Juntao

2012-01-17

The forced water-oil displacement in capillary is a model that has important applications such as the groundwater remediation and the oil recovery. Whereas it is difficult for experimental studies to observe the displacement process in a capillary at nanoscale, the computational simulation is a unique approach in this regard. In the present work, the many-body dissipative particle dynamics (MDPD) method is employed to simulate the process of water-oil displacement in capillary with external force applied by a piston. As the property of all interfaces involved in this system can be manipulated independently, the dynamic displacement process is studied systematically under various conditions of distinct wettability of water in capillary and miscibility between water and oil as well as of different external forces. By analyzing the dependence of the starting force on the properties of water/capillary and water/oil interfaces, we find that there exist two different modes of the water-oil displacement. In the case of stronger water-oil interaction, the water particles cannot displace those oil particles sticking to the capillary wall, leaving a low oil recovery efficiency. To minimize the residual oil content in capillary, enhancing the wettability of water and reducing the external force will be beneficial. This simulation study provides microscopic insights into the water-oil displacement process in capillary and guiding information for relevant applications. © 2011 American Chemical Society

Beyond the dynamic density functional theory for steady currents: application to driven colloidal particles in a channel.

PubMed

Tarazona, P; Marini Bettolo Marconi, Umberto

2008-04-28

Motivated by recent studies on the dynamics of colloidal solutions in narrow channels, we consider the steady state properties of an assembly of noninteracting particles subject to the action of a traveling potential moving at a constant speed, while the solvent is modeled by a heat bath at rest in the laboratory frame. Here, since the description we propose takes into account the inertia of the colloidal particles, it is necessary to consider the evolution of both positions and momenta and study the governing equation for the one-particle phase-space distribution. First, we derive the asymptotic form of its solutions as an expansion in Hermite polynomials and their generic properties, such as the force and energy balance, and then we particularize our study to the case of an inverted parabolic potential barrier. We numerically obtain the steady state density and temperature profile and show that the expansion is rapidly convergent for large values of the friction constant and small drifting velocities. On the one hand, the present results confirm the previous studies based on the dynamic density functional theory (DDFT): On the other hand, when the friction constant is large, it display effects such as the presence of a wake behind the barrier and a strong inhomogeneity in the temperature field which are beyond the DDFT description.

Modeling of electrochemical flow capacitors using Stokesian dynamics

NASA Astrophysics Data System (ADS)

Karzar Jeddi, Mehdi; Luo, Haoxiang; Cummings, Peter; Hatzell, Kelsey

2017-11-01

Electrochemical flow capacitors (EFCs) are supercapacitors designed to store electrical energy in the form of electrical double layer (EDL) near the surface of porous carbon particles. During its operation, a slurry of activated carbon beads and smaller carbon black particles is pumped between two flat and parallel electrodes. In the charging phase, ions in the electrolyte diffuse to the EDL, and electrical charges percolate through the dynamic network of particles from the flat electrodes; during the discharging phase, the process is reversed with the ions released to the bulk fluid and electrical charges percolating back through the network. In these processes, the relative motion and contact of particle of different sizes affect not only the rheology of the slurry but also charge transfer of the percolation network. In this study, we use Stoekesian dynamics simulation to investigate the role of hydrodynamic interactions of packed carbon particles in the charging/discharging behaviors of EFCs. We derived mobility functions for polydisperse spheres near a no-slip wall. A code is implemented and validated, and a simple charging model has been incorporated to represent charge transfer. Theoretical formulation and results demonstration will be presented in this talk.

Microviscoelasticity of adhesive hard sphere dispersions: Tracer particle microrheology of aqueous Pluronic L64 solutions

NASA Astrophysics Data System (ADS)

Kloxin, Christopher J.; van Zanten, John H.

2009-10-01

DWS-based tracer particle microrheology is demonstrated to be a useful way to study the dynamics of aqueous Pluronic L64 solutions, which is viewed as a model adhesive hard sphere (AHS) system. The short-time dynamics of aqueous Pluronic L64 solutions indicate a purely hydrodynamic high frequency microviscosity as predicted by Batchelor for colloidal dispersions. The evolution of the micellar dynamics reveals a zero shear microviscosity in good agreement with steady shear viscosity measurements. As the temperature is increased, the dynamics become dominated by an apparent attractive intermicellar potential observed in microscopic creep measurements. While Pluronic L64 solutions have been reported to form a percolated micellar network, DWS-based microviscoelasticity measurements do not detect the previously observed G'˜G″˜ωΔ scaling expected for a static percolated network at low frequencies. This most likely owes to the fact that tracer particle microrheology is dominated by local Pluronic L64 micelle dynamics in the near sphere region and not the bulk mechanical properties as measured by traditional rheometry. The sensitivity of tracer particle microrheological measurements to the true dynamic nature of the percolated network in weak physical gels highlights the distinct differences between these micro- and macrorheology measurement techniques. Such discrepancies should be most evident in systems that are dominated by association processes such as those occurring in AHS solutions or polymer solutions approaching a phase boundary. Despite this, the AHS potential is qualitatively consistent with the results found here.

Microviscoelasticity of adhesive hard sphere dispersions: tracer particle microrheology of aqueous Pluronic L64 solutions.

PubMed

Kloxin, Christopher J; van Zanten, John H

2009-10-07

DWS-based tracer particle microrheology is demonstrated to be a useful way to study the dynamics of aqueous Pluronic L64 solutions, which is viewed as a model adhesive hard sphere (AHS) system. The short-time dynamics of aqueous Pluronic L64 solutions indicate a purely hydrodynamic high frequency microviscosity as predicted by Batchelor for colloidal dispersions. The evolution of the micellar dynamics reveals a zero shear microviscosity in good agreement with steady shear viscosity measurements. As the temperature is increased, the dynamics become dominated by an apparent attractive intermicellar potential observed in microscopic creep measurements. While Pluronic L64 solutions have been reported to form a percolated micellar network, DWS-based microviscoelasticity measurements do not detect the previously observed G(') approximately G(") approximately omega(Delta) scaling expected for a static percolated network at low frequencies. This most likely owes to the fact that tracer particle microrheology is dominated by local Pluronic L64 micelle dynamics in the near sphere region and not the bulk mechanical properties as measured by traditional rheometry. The sensitivity of tracer particle microrheological measurements to the true dynamic nature of the percolated network in weak physical gels highlights the distinct differences between these micro- and macrorheology measurement techniques. Such discrepancies should be most evident in systems that are dominated by association processes such as those occurring in AHS solutions or polymer solutions approaching a phase boundary. Despite this, the AHS potential is qualitatively consistent with the results found here.

Computational plasticity algorithm for particle dynamics simulations

NASA Astrophysics Data System (ADS)

Krabbenhoft, K.; Lyamin, A. V.; Vignes, C.

2018-01-01

The problem of particle dynamics simulation is interpreted in the framework of computational plasticity leading to an algorithm which is mathematically indistinguishable from the common implicit scheme widely used in the finite element analysis of elastoplastic boundary value problems. This algorithm provides somewhat of a unification of two particle methods, the discrete element method and the contact dynamics method, which usually are thought of as being quite disparate. In particular, it is shown that the former appears as the special case where the time stepping is explicit while the use of implicit time stepping leads to the kind of schemes usually labelled contact dynamics methods. The framing of particle dynamics simulation within computational plasticity paves the way for new approaches similar (or identical) to those frequently employed in nonlinear finite element analysis. These include mixed implicit-explicit time stepping, dynamic relaxation and domain decomposition schemes.

Explicit symplectic algorithms based on generating functions for relativistic charged particle dynamics in time-dependent electromagnetic field

NASA Astrophysics Data System (ADS)

Zhang, Ruili; Wang, Yulei; He, Yang; Xiao, Jianyuan; Liu, Jian; Qin, Hong; Tang, Yifa

2018-02-01

Relativistic dynamics of a charged particle in time-dependent electromagnetic fields has theoretical significance and a wide range of applications. The numerical simulation of relativistic dynamics is often multi-scale and requires accurate long-term numerical simulations. Therefore, explicit symplectic algorithms are much more preferable than non-symplectic methods and implicit symplectic algorithms. In this paper, we employ the proper time and express the Hamiltonian as the sum of exactly solvable terms and product-separable terms in space-time coordinates. Then, we give the explicit symplectic algorithms based on the generating functions of orders 2 and 3 for relativistic dynamics of a charged particle. The methodology is not new, which has been applied to non-relativistic dynamics of charged particles, but the algorithm for relativistic dynamics has much significance in practical simulations, such as the secular simulation of runaway electrons in tokamaks.

Single-Particle Tracking of Human Immunodeficiency Virus Type 1 Productive Entry into Human Primary Macrophages.

PubMed

Li, Qin; Li, Wei; Yin, Wen; Guo, Jia; Zhang, Zhi-Ping; Zeng, Dejun; Zhang, Xiaowei; Wu, Yuntao; Zhang, Xian-En; Cui, Zongqiang

2017-04-25

Macrophages are one of the major targets of human immunodeficiency virus (HIV-1), but the viral entry pathway remains poorly understood in these cells. Noninvasive virus labeling and single-virus tracking are effective tools for studying virus entry. Here, we constructed a quantum dot (QD)-encapsulated infectious HIV-1 particle to track viral entry at a single-particle level in live human primary macrophages. QDs were encapsulated in HIV-1 virions by incorporating viral accessory protein Vpr-conjugated QDs during virus assembly. With the HIV-1 particles encapsulating QDs, we monitored the early phase of viral infection in real time and observed that, during infection, HIV-1 was endocytosed in a clathrin-mediated manner; the particles were translocated into Rab5A-positive endosomes, and the core was released into the cytoplasm by viral envelope-mediated endosomal fusion. Drug inhibition assays verified that endosome fusion contributes to HIV-1 productive infection in primary macrophages. Additionally, we observed that a dynamic actin cytoskeleton is critical for HIV-1 entry and intracellular migration in primary macrophages. HIV-1 dynamics and infection could be blocked by multiple different actin inhibitors. Our study revealed a productive entry pathway in macrophages that requires both endosomal function and actin dynamics, which may assist in the development of inhibitors to block the HIV entry in macrophages.

Dynamics of solid nanoparticles near a liquid-liquid interface

NASA Astrophysics Data System (ADS)

Daher, Ali; Ammar, Amine; Hijazi, Abbas

2018-05-01

The liquid - liquid interface can be used as a suitable medium for generating some nanostructured films of metals, or inorganic materials such as semi conducting metals. This process can be controlled well if we study the dynamics of nanoparticles (NPs) at the liquid-liquid interface which is a new field of study, and is not understood well yet. The dynamics of NPs at liquid-liquid interfaces is investigated by solving the fluid-particle and particle-particle interactions. Our work is based on the Molecular Dynamics (MD) simulation in addition to Phase Field (PF) method. We modeled the liquid-liquid interface using the diffuse interface model, where the interface is considered to have a characteristic thickness. We have shown that the concentration gradient of one fluid in the other gives rise to a hydrodynamic force that drives the NPs to agglomerate at the interface. These obtained results may introduce new applications where certain interfaces can be considered to be suitable mediums for the synthesis of nanostructured materials. In addition, some liquid interfaces can play the role of effective filters for different species of biological NPs and solid state waste NPs, which will be very important in many industrial and biomedical domains.

3D Multispecies Nonlinear Perturbative Particle Simulation of Intense Nonneutral Particle Beams (Research supported by the Department of Energy and the Short Pulse Spallation Source Project and LANSCE Division of LANL.)

NASA Astrophysics Data System (ADS)

Qin, Hong; Davidson, Ronald C.; Lee, W. Wei-Li

1999-11-01

The Beam Equilibrium Stability and Transport (BEST) code, a 3D multispecies nonlinear perturbative particle simulation code, has been developed to study collective effects in intense charged particle beams described self-consistently by the Vlasov-Maxwell equations. A Darwin model is adopted for transverse electromagnetic effects. As a 3D multispecies perturbative particle simulation code, it provides several unique capabilities. Since the simulation particles are used to simulate only the perturbed distribution function and self-fields, the simulation noise is reduced significantly. The perturbative approach also enables the code to investigate different physics effects separately, as well as simultaneously. The code can be easily switched between linear and nonlinear operation, and used to study both linear stability properties and nonlinear beam dynamics. These features, combined with 3D and multispecies capabilities, provides an effective tool to investigate the electron-ion two-stream instability, periodically focused solutions in alternating focusing fields, and many other important problems in nonlinear beam dynamics and accelerator physics. Applications to the two-stream instability are presented.

An Improved Co-evolutionary Particle Swarm Optimization for Wireless Sensor Networks with Dynamic Deployment

PubMed Central

Wang, Xue; Wang, Sheng; Ma, Jun-Jie

2007-01-01

The effectiveness of wireless sensor networks (WSNs) depends on the coverage and target detection probability provided by dynamic deployment, which is usually supported by the virtual force (VF) algorithm. However, in the VF algorithm, the virtual force exerted by stationary sensor nodes will hinder the movement of mobile sensor nodes. Particle swarm optimization (PSO) is introduced as another dynamic deployment algorithm, but in this case the computation time required is the big bottleneck. This paper proposes a dynamic deployment algorithm which is named “virtual force directed co-evolutionary particle swarm optimization” (VFCPSO), since this algorithm combines the co-evolutionary particle swarm optimization (CPSO) with the VF algorithm, whereby the CPSO uses multiple swarms to optimize different components of the solution vectors for dynamic deployment cooperatively and the velocity of each particle is updated according to not only the historical local and global optimal solutions, but also the virtual forces of sensor nodes. Simulation results demonstrate that the proposed VFCPSO is competent for dynamic deployment in WSNs and has better performance with respect to computation time and effectiveness than the VF, PSO and VFPSO algorithms.

Peculiarities of structural transformations in metal nanoparticles at high speed collisions

NASA Astrophysics Data System (ADS)

Zolnikov, K. P.; Kryzhevich, D. S.; Korchuganov, A. V.

2018-01-01

A molecular dynamics simulation of nanosized particle collision under the electrical explosion of metal wires of different types was conducted. Interatomic interactions were described on the base of the embedded atom method. Used potentials allowed describing with high accuracy many mechanical and physical properties which are very important for the simulations of nanoparticle collisions with high velocities. The dynamics of the nanosized particle formation at the electric pulse explosion of metal wires of different types was studied. Features of particle collisions on the example of nanoscale particles of copper and nickel, whose velocities varied from 50 to 1500 m/s were investigated. The peculiarities of structural transformations in the colliding particles depending on the velocity of collision were determined. The intervals of collision velocities in which interaction between particles is elastic or leads to the formation of structural defects or melting were calculated. The analysis of the structure and distribution of chemical elements over the cross section of the particles which were synthesized under simultaneous explosions of different metal wires was carried out.

Classical dynamics on curved Snyder space

NASA Astrophysics Data System (ADS)

Ivetić, B.; Meljanac, S.; Mignemi, S.

2014-05-01

We study the classical dynamics of a particle in nonrelativistic Snyder-de Sitter space. We show that for spherically symmetric systems, parameterizing the solutions in terms of an auxiliary time variable, which is a function only of the physical time and of the energy and angular momentum of the particles, one can reduce the problem to the equivalent one in classical mechanics. We also discuss a relativistic extension of these results, and a generalization to the case in which the algebra is realized in flat space.

Three-dimensional ordering of cold ion beams in a storage ring: A molecular-dynamics simulation study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuri, Yosuke, E-mail: yuri.yosuke@jaea.go.jp

Three-dimensional (3D) ordering of a charged-particle beams circulating in a storage ring is systematically studied with a molecular-dynamics simulation code. An ion beam can exhibit a 3D ordered configuration at ultralow temperature as a result of powerful 3D laser cooling. Various unique characteristics of the ordered beams, different from those of crystalline beams, are revealed in detail, such as the single-particle motion in the transverse and longitudinal directions, and the dependence of the tune depression and the Coulomb coupling constant on the operating points.

Lunar particle shadows and boundary layer experiment: Plasma and energetic particles on the Apollo 15 and 16 subsatellites

NASA Technical Reports Server (NTRS)

Anderson, K. A.; Chase, L. M.; Lin, R. P.; Mccoy, J. E.; Mcguire, R. E.

1974-01-01

The lunar particle shadows and boundary layer experiments aboard the Apollo 15 and 16 subsatellites and scientific reduction and analysis of the data to date are discussed with emphasis on four major topics: solar particles; interplanetry particle phenomena; lunar interactions; and topology and dynamics of the magnetosphere at lunar orbit. The studies of solar and interplanetary particles concentrated on the low energy region which was essentially unexplored, and the studies of lunar interaction pointed up the transition from single particle to plasma characteristics. The analysis concentrated on the electron angular distributions as highly sensitive indicators of localized magnetization of the lunar surface. Magnetosphere experiments provided the first electric field measurements in the distant magnetotail, as well as comprehensive low energy particle measurements at lunar distance.

Applications of Density Functional Theory in Soft Condensed Matter

NASA Astrophysics Data System (ADS)

Löwen, Hartmut

Applications of classical density functional theory (DFT) to soft matter systems like colloids, liquid crystals and polymer solutions are discussed with a focus on the freezing transition and on nonequilibrium Brownian dynamics. First, after a brief reminder of equilibrium density functional theory, DFT is applied to the freezing transition of liquids into crystalline lattices. In particular, spherical particles with radially symmetric pair potentials will be treated (like hard spheres, the classical one-component plasma or Gaussian-core particles). Second, the DFT will be generalized towards Brownian dynamics in order to tackle nonequilibrium problems. After a general introduction to Brownian dynamics using the complementary Smoluchowski and Langevin pictures appropriate for the dynamics of colloidal suspensions, the dynamical density functional theory (DDFT) will be derived from the Smoluchowski equation. This will be done first for spherical particles (e.g. hard spheres or Gaussian-cores) without hydrodynamic interactions. Then we show how to incorporate hydrodynamic interactions between the colloidal particles into the DDFT framework and compare to Brownian dynamics computer simulations. Third orientational degrees of freedom (rod-like particles) will be considered as well. In the latter case, the stability of intermediate liquid crystalline phases (isotropic, nematic, smectic-A, plastic crystals etc) can be predicted. Finally, the corresponding dynamical extension of density functional theory towards orientational degrees of freedom is proposed and the collective behaviour of "active" (self-propelled) Brownian particles is briefly discussed.

Dynamics of Nanoparticles in Entangled Polymer Solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nath, Pooja; Mangal, Rahul; Kohle, Ferdinand

The mean square displacement < r 2 > of nanoparticle probes dispersed in simple isotropic liquids and in polymer solutions is interrogated using fluorescence correlation spectroscopy and single-particle tracking (SPT) experiments. Probe dynamics in different regimes of particle diameter (d), relative to characteristic polymer length scales, including the correlation length (ξ), the entanglement mesh size (a), and the radius of gyration (R g), are investigated. In simple fluids and for polymer solutions in which d >> R g, long-time particle dynamics obey random-walk statistics < r 2 >:t, with the bulk zero-shear viscosity of the polymer solution determining the frictionalmore » resistance to particle motion. In contrast, in polymer solutions with d < R g, polymer molecules in solution exert noncontinuum resistances to particle motion and nanoparticle probes appear to interact hydrodynamically only with a local fluid medium with effective drag comparable to that of a solution of polymer chain segments with sizes similar to those of the nanoparticle probes. Under these conditions, the nanoparticles exhibit orders of magnitude faster dynamics than those expected from continuum predictions based on the Stokes–Einstein relation. SPT measurements further show that when d > a, nanoparticle dynamics transition from diffusive to subdiffusive on long timescales, reminiscent of particle transport in a field with obstructions. This last finding is in stark contrast to the nanoparticle dynamics observed in entangled polymer melts, where X-ray photon correlation spectroscopy measurements reveal faster but hyperdiffusive dynamics. As a result, we analyze these results with the help of the hopping model for particle dynamics in polymers proposed by Cai et al. and, on that basis, discuss the physical origins of the local drag experienced by the nanoparticles in entangled polymer solutions.« less

Dynamics of Nanoparticles in Entangled Polymer Solutions

DOE PAGES

Nath, Pooja; Mangal, Rahul; Kohle, Ferdinand; ...

2017-12-01

The mean square displacement < r 2 > of nanoparticle probes dispersed in simple isotropic liquids and in polymer solutions is interrogated using fluorescence correlation spectroscopy and single-particle tracking (SPT) experiments. Probe dynamics in different regimes of particle diameter (d), relative to characteristic polymer length scales, including the correlation length (ξ), the entanglement mesh size (a), and the radius of gyration (R g), are investigated. In simple fluids and for polymer solutions in which d >> R g, long-time particle dynamics obey random-walk statistics < r 2 >:t, with the bulk zero-shear viscosity of the polymer solution determining the frictionalmore » resistance to particle motion. In contrast, in polymer solutions with d < R g, polymer molecules in solution exert noncontinuum resistances to particle motion and nanoparticle probes appear to interact hydrodynamically only with a local fluid medium with effective drag comparable to that of a solution of polymer chain segments with sizes similar to those of the nanoparticle probes. Under these conditions, the nanoparticles exhibit orders of magnitude faster dynamics than those expected from continuum predictions based on the Stokes–Einstein relation. SPT measurements further show that when d > a, nanoparticle dynamics transition from diffusive to subdiffusive on long timescales, reminiscent of particle transport in a field with obstructions. This last finding is in stark contrast to the nanoparticle dynamics observed in entangled polymer melts, where X-ray photon correlation spectroscopy measurements reveal faster but hyperdiffusive dynamics. As a result, we analyze these results with the help of the hopping model for particle dynamics in polymers proposed by Cai et al. and, on that basis, discuss the physical origins of the local drag experienced by the nanoparticles in entangled polymer solutions.« less

Explicit symplectic algorithms based on generating functions for charged particle dynamics.

PubMed

Zhang, Ruili; Qin, Hong; Tang, Yifa; Liu, Jian; He, Yang; Xiao, Jianyuan

2016-07-01

Dynamics of a charged particle in the canonical coordinates is a Hamiltonian system, and the well-known symplectic algorithm has been regarded as the de facto method for numerical integration of Hamiltonian systems due to its long-term accuracy and fidelity. For long-term simulations with high efficiency, explicit symplectic algorithms are desirable. However, it is generally believed that explicit symplectic algorithms are only available for sum-separable Hamiltonians, and this restriction limits the application of explicit symplectic algorithms to charged particle dynamics. To overcome this difficulty, we combine the familiar sum-split method and a generating function method to construct second- and third-order explicit symplectic algorithms for dynamics of charged particle. The generating function method is designed to generate explicit symplectic algorithms for product-separable Hamiltonian with form of H(x,p)=p_{i}f(x) or H(x,p)=x_{i}g(p). Applied to the simulations of charged particle dynamics, the explicit symplectic algorithms based on generating functions demonstrate superiorities in conservation and efficiency.

Explicit symplectic algorithms based on generating functions for charged particle dynamics

NASA Astrophysics Data System (ADS)

Zhang, Ruili; Qin, Hong; Tang, Yifa; Liu, Jian; He, Yang; Xiao, Jianyuan

2016-07-01

Dynamics of a charged particle in the canonical coordinates is a Hamiltonian system, and the well-known symplectic algorithm has been regarded as the de facto method for numerical integration of Hamiltonian systems due to its long-term accuracy and fidelity. For long-term simulations with high efficiency, explicit symplectic algorithms are desirable. However, it is generally believed that explicit symplectic algorithms are only available for sum-separable Hamiltonians, and this restriction limits the application of explicit symplectic algorithms to charged particle dynamics. To overcome this difficulty, we combine the familiar sum-split method and a generating function method to construct second- and third-order explicit symplectic algorithms for dynamics of charged particle. The generating function method is designed to generate explicit symplectic algorithms for product-separable Hamiltonian with form of H (x ,p ) =pif (x ) or H (x ,p ) =xig (p ) . Applied to the simulations of charged particle dynamics, the explicit symplectic algorithms based on generating functions demonstrate superiorities in conservation and efficiency.

Dynamic heterogeneities and non-Gaussian behavior in two-dimensional randomly confined colloidal fluids

NASA Astrophysics Data System (ADS)

Schnyder, Simon K.; Skinner, Thomas O. E.; Thorneywork, Alice L.; Aarts, Dirk G. A. L.; Horbach, Jürgen; Dullens, Roel P. A.

2017-03-01

A binary mixture of superparamagnetic colloidal particles is confined between glass plates such that the large particles become fixed and provide a two-dimensional disordered matrix for the still mobile small particles, which form a fluid. By varying fluid and matrix area fractions and tuning the interactions between the superparamagnetic particles via an external magnetic field, different regions of the state diagram are explored. The mobile particles exhibit delocalized dynamics at small matrix area fractions and localized motion at high matrix area fractions, and the localization transition is rounded by the soft interactions [T. O. E. Skinner et al., Phys. Rev. Lett. 111, 128301 (2013), 10.1103/PhysRevLett.111.128301]. Expanding on previous work, we find the dynamics of the tracers to be strongly heterogeneous and show that molecular dynamics simulations of an ideal gas confined in a fixed matrix exhibit similar behavior. The simulations show how these soft interactions make the dynamics more heterogeneous compared to the disordered Lorentz gas and lead to strong non-Gaussian fluctuations.

Software package for modeling spin-orbit motion in storage rings

NASA Astrophysics Data System (ADS)

Zyuzin, D. V.

2015-12-01

A software package providing a graphical user interface for computer experiments on the motion of charged particle beams in accelerators, as well as analysis of obtained data, is presented. The software package was tested in the framework of the international project on electric dipole moment measurement JEDI (Jülich Electric Dipole moment Investigations). The specific features of particle spin motion imply the requirement to use a cyclic accelerator (storage ring) consisting of electrostatic elements, which makes it possible to preserve horizontal polarization for a long time. Computer experiments study the dynamics of 106-109 particles in a beam during 109 turns in an accelerator (about 1012-1015 integration steps for the equations of motion). For designing an optimal accelerator structure, a large number of computer experiments on polarized beam dynamics are required. The numerical core of the package is COSY Infinity, a program for modeling spin-orbit dynamics.

Simulation of quantum dynamics with integrated photonics

NASA Astrophysics Data System (ADS)

Sansoni, Linda; Sciarrino, Fabio; Mataloni, Paolo; Crespi, Andrea; Ramponi, Roberta; Osellame, Roberto

2012-12-01

In recent years, quantum walks have been proposed as promising resources for the simulation of physical quantum systems. In fact it is widely adopted to simulate quantum dynamics. Up to now single particle quantum walks have been experimentally demonstrated by different approaches, while only few experiments involving many-particle quantum walks have been realized. Here we simulate the 2-particle dynamics on a discrete time quantum walk, built on an array of integrated waveguide beam splitters. The polarization independence of the quantum walk circuit allowed us to exploit the polarization entanglement to encode the symmetry of the two-photon wavefunction, thus the bunching-antibunching behavior of non interacting bosons and fermions has been simulated. We have also characterized the possible distinguishability and decoherence effects arising in such a structure. This study is necessary in view of the realization of a quantum simulator based on an integrated optical array built on a large number of beam splitters.

Davisson-Germer Prize in Atomic or Surface Physics: The COLTRIMS multi-particle imaging technique-new Insight into the World of Correlation

NASA Astrophysics Data System (ADS)

Schmidt-Bocking, Horst

2008-05-01

The correlated many-particle dynamics in Coulombic systems, which is one of the unsolved fundamental problems in AMO-physics, can now be experimentally approached with so far unprecedented completeness and precision. The recent development of the COLTRIMS technique (COLd Target Recoil Ion Momentum Spectroscopy) provides a coincident multi-fragment imaging technique for eV and sub-eV fragment detection. In its completeness it is as powerful as the bubble chamber in high energy physics. In recent benchmark experiments quasi snapshots (duration as short as an atto-sec) of the correlated dynamics between electrons and nuclei has been made for atomic and molecular objects. This new imaging technique has opened a powerful observation window into the hidden world of many-particle dynamics. Recent multiple-ionization studies will be presented and the observation of correlated electron pairs will be discussed.

Towards a self-consistent dynamical nuclear model

NASA Astrophysics Data System (ADS)

Roca-Maza, X.; Niu, Y. F.; Colò, G.; Bortignon, P. F.

2017-04-01

Density functional theory (DFT) is a powerful and accurate tool, exploited in nuclear physics to investigate the ground-state and some of the collective properties of nuclei along the whole nuclear chart. Models based on DFT are not, however, suitable for the description of single-particle dynamics in nuclei. Following the field theoretical approach by A Bohr and B R Mottelson to describe nuclear interactions between single-particle and vibrational degrees of freedom, we have taken important steps towards the building of a microscopic dynamic nuclear model. In connection with this, one important issue that needs to be better understood is the renormalization of the effective interaction in the particle-vibration approach. One possible way to renormalize the interaction is by the so-called subtraction method. In this contribution, we will implement the subtraction method in our model for the first time and study its consequences.

Microgels: Structure, Dynamics, and Possible Applications.

NASA Astrophysics Data System (ADS)

McKenna, John; Streletzky, Kiril

2007-03-01

We cross-linked Hydropxypropylcellulose (HPC) polymer chains to produce microgel nanoparticles and studied their structure and dynamics using Dynamic Light Scattering spectroscopy. The complex nature of the fluid and large size distribution of the particles renders typical characterization algorithm CONTIN ineffective and inconsistent. Instead, the particles spectra have been fit to a sum of stretched exponentials. Each term offers three parameters for analysis and represents a single mode. The results of this analysis show that the microgels undergo a transition to a fewer modes around 41C. The CONTIN size distribution analysis shows similar results, but these come with much less consistency and resolution. Our experiments prove that microgel particles shrink under volume phase transition. The shrinkage is reversible and depends on the amount of cross-linker, salt and polymer concentrations and rate of heating. Reversibility of microgel volume phase transition property might be particularly useful for a controlled drug delivery and release.

Diffusion and interactions of interstitials in hard-sphere interstitial solid solutions

NASA Astrophysics Data System (ADS)

van der Meer, Berend; Lathouwers, Emma; Smallenburg, Frank; Filion, Laura

2017-12-01

Using computer simulations, we study the dynamics and interactions of interstitial particles in hard-sphere interstitial solid solutions. We calculate the free-energy barriers associated with their diffusion for a range of size ratios and densities. By applying classical transition state theory to these free-energy barriers, we predict the diffusion coefficients, which we find to be in good agreement with diffusion coefficients as measured using event-driven molecular dynamics simulations. These results highlight that transition state theory can capture the interstitial dynamics in the hard-sphere model system. Additionally, we quantify the interactions between the interstitials. We find that, apart from excluded volume interactions, the interstitial-interstitial interactions are almost ideal in our system. Lastly, we show that the interstitial diffusivity can be inferred from the large-particle fluctuations alone, thus providing an empirical relationship between the large-particle fluctuations and the interstitial diffusivity.

Particle dynamics and deposition in true-scale pulmonary acinar models.

PubMed

Fishler, Rami; Hofemeier, Philipp; Etzion, Yael; Dubowski, Yael; Sznitman, Josué

2015-09-11

Particle transport phenomena in the deep alveolated airways of the lungs (i.e. pulmonary acinus) govern deposition outcomes following inhalation of hazardous or pharmaceutical aerosols. Yet, there is still a dearth of experimental tools for resolving acinar particle dynamics and validating numerical simulations. Here, we present a true-scale experimental model of acinar structures consisting of bifurcating alveolated ducts that capture breathing-like wall motion and ensuing respiratory acinar flows. We study experimentally captured trajectories of inhaled polydispersed smoke particles (0.2 to 1 μm in diameter), demonstrating how intrinsic particle motion, i.e. gravity and diffusion, is crucial in determining dispersion and deposition of aerosols through a streamline crossing mechanism, a phenomenon paramount during flow reversal and locally within alveolar cavities. A simple conceptual framework is constructed for predicting the fate of inhaled particles near an alveolus by identifying capture and escape zones and considering how streamline crossing may shift particles between them. In addition, we examine the effect of particle size on detailed deposition patterns of monodispersed microspheres between 0.1-2 μm. Our experiments underline local modifications in the deposition patterns due to gravity for particles ≥0.5 μm compared to smaller particles, and show good agreement with corresponding numerical simulations.

Particle dynamics and deposition in true-scale pulmonary acinar models

PubMed Central

Fishler, Rami; Hofemeier, Philipp; Etzion, Yael; Dubowski, Yael; Sznitman, Josué

2015-01-01

Particle transport phenomena in the deep alveolated airways of the lungs (i.e. pulmonary acinus) govern deposition outcomes following inhalation of hazardous or pharmaceutical aerosols. Yet, there is still a dearth of experimental tools for resolving acinar particle dynamics and validating numerical simulations. Here, we present a true-scale experimental model of acinar structures consisting of bifurcating alveolated ducts that capture breathing-like wall motion and ensuing respiratory acinar flows. We study experimentally captured trajectories of inhaled polydispersed smoke particles (0.2 to 1 μm in diameter), demonstrating how intrinsic particle motion, i.e. gravity and diffusion, is crucial in determining dispersion and deposition of aerosols through a streamline crossing mechanism, a phenomenon paramount during flow reversal and locally within alveolar cavities. A simple conceptual framework is constructed for predicting the fate of inhaled particles near an alveolus by identifying capture and escape zones and considering how streamline crossing may shift particles between them. In addition, we examine the effect of particle size on detailed deposition patterns of monodispersed microspheres between 0.1–2 μm. Our experiments underline local modifications in the deposition patterns due to gravity for particles ≥0.5 μm compared to smaller particles, and show good agreement with corresponding numerical simulations. PMID:26358580

Particle response to shock waves in solids: dynamic witness plate/PIV method for detonations

NASA Astrophysics Data System (ADS)

Murphy, Michael J.; Adrian, Ronald J.

2007-08-01

Studies using transparent, polymeric witness plates consisting of polydimethlysiloxane (PDMS) have been conducted to measure the output of exploding bridge wire (EBW) detonators and exploding foil initiators (EFI). Polymeric witness plates are utilized to alleviate particle response issues that arise in gaseous flow fields containing shock waves and to allow measurements of shock-induced material velocities to be made using particle image velocimetry (PIV). Quantitative comparisons of velocity profiles across the shock waves in air and in PDMS demonstrate the improved response achieved by the dynamic witness plate method. Schlieren photographs complement the analysis through direct visualization of detonator-induced shock waves in the witness plates.

Nonlinear dynamics of toroidal Alfvén eigenmodes in presence of tearing modes

NASA Astrophysics Data System (ADS)

Zhu, Jia; Ma, Zhiwei; Wang, Sheng; Zhang, Wei

2016-10-01

A new hybrid kinetic-MHD code CLT-K is developed to study nonlinear dynamics of n =1 toroidal Alfvén eigenmodes (TAEs) with the m/n =2/1 tearing mode. It is found that the n =1 TAE is first excited by isotropic energetic particles in the earlier stage and reaches the steady state due to wave-particle interaction. After the saturation of the n =1 TAE, the tearing mode intervenes and triggers the second growth of the mode. The modes goes into the second steady state due to multiple tearing mode-mode nonlinear coupling. Both wave-particle and wave-wave interactions are observed in our hybrid simulation.

3D dust clouds (Yukawa Balls) in strongly coupled dusty plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Melzer, A.; Passvogel, M.; Miksch, T.

2010-06-16

Three-dimensional finite systems of charged dust particles confined to concentric spherical shells in a dusty plasma, so-called 'Yukawa balls', have been studied with respect to their static and dynamic properties. Here, we review the charging of particles in a dusty plasma discharge by computer simulations and the respective particle arrangements. The normal mode spectrum of Yukawa balls is measured from the 3D thermal Brownian motion of the dust particles around their equilibrium positions.

Characterization of quantum vortex dynamics in superfluid helium

NASA Astrophysics Data System (ADS)

Meichle, David P.

Liquid helium obtains superfluid properties when cooled below the Lambda transition temperature of 2.17 K. A superfluid, which is a partial Bose Einstein condensate, has many exotic properties including free flow without friction, and ballistic instead of diffusive heat transport. A superfluid is also uniquely characterized by the presence of quantized vortices, dynamical line-like topological phase defects around which all circulation in the flow is constrained. Two vortices can undergo a violent process called reconnection when they approach, cross, and retract having exchanged tails. With a numerical examination of a local, linearized solution near reconnection we discovered a dynamically unstable stationary solution to the Gross-Pitaevskii equation, which was relaxed to a fully non-linear solution using imaginary time propagation. This investigation explored vortex reconnection in the context of the changing topology of the order parameter, a complex field governing the superfluid dynamics at zero temperature. The dynamics of the vortices can be studied experimentally by dispersing tracer particles into a superfluid flow and recording their motions with movie cameras. The pioneering work of Bewley et al. provided the first visualization technique using frozen gases to create tracer particles. Using this technique, we experimentally observed for the first time the excitation of helical traveling waves on a vortex core called Kelvin waves. Kelvin waves are thought to be a central mechanism for dissipation in this inviscid fluid, as they provide an efficient cascade mechanism for transferring energy from large to microscopic length scales. We examined the Kelvin waves in detail, and compared their dynamics in fully self-similar non-dimensional coordinates to theoretical predictions. Additionally, two experimental advances are presented. A newly invented technique for reliably dispersing robust, nanometer-scale fluorescent tracer particles directly into the superfluid is described. A detailed numerical investigation of the particle-vortex interactions provides novel calculations of the force trapping particles on vortices, and a scaling was found suggesting that smaller particles may remain bound to the vortices at much higher speeds than larger particles. Lastly, a new stereographic imaging system has been developed, allowing for the world-first three-dimensional reconstruction of individual particles and vortex filament trajectories. Preliminary data, including the first three-dimensional observation of a vortex reconnection are presented.

Real-time dynamics of high-velocity micro-particle impact

NASA Astrophysics Data System (ADS)

Veysset, David; Hsieh, Alex; Kooi, Steve; Maznev, Alex A.; Tang, Shengchang; Olsen, Bradley D.; Nelson, Keith A.

High-velocity micro-particle impact is important for many areas of science and technology, from space exploration to the development of novel drug delivery platforms. We present real-time observations of supersonic micro-particle impacts using multi-frame imaging. In an all optical laser-induced projectile impact test, a monolayer of micro-particles is placed on a transparent substrate coated with a laser absorbing polymer layer. Ablation of a laser-irradiated polymer region accelerates the micro-particles into free space with speeds up to 1.0 km/s. The particles are monitored during the impact on the target with an ultrahigh-speed multi-frame camera that can record up to 16 images with time resolution as short as 3 ns. In particular, we investigated the high-velocity impact deformation response of poly(urethane urea) (PUU) elastomers to further the fundamental understanding of the molecular influence on dynamical behaviors of PUUs. We show the dynamic-stiffening response of the PUUs and demonstrate the significance of segmental dynamics in the response. We also present movies capturing individual particle impact and penetration in gels, and discuss the observed dynamics. The results will provide an impetus for modeling high-velocity microscale impact responses and high strain rate deformation in polymers, gels, and other materials.

Analytical structure, dynamics, and coarse graining of a kinetic model of an active fluid

NASA Astrophysics Data System (ADS)

Gao, Tong; Betterton, Meredith D.; Jhang, An-Sheng; Shelley, Michael J.

2017-09-01

We analyze one of the simplest active suspensions with complex dynamics: a suspension of immotile "extensor" particles that exert active extensile dipolar stresses on the fluid in which they are immersed. This is relevant to several experimental systems, such as recently studied tripartite rods that create extensile flows by consuming a chemical fuel. We first describe the system through a Doi-Onsager kinetic theory based on microscopic modeling. This theory captures the active stresses produced by the particles that can drive hydrodynamic instabilities, as well as the steric interactions of rodlike particles that lead to nematic alignment. This active nematic system yields complex flows and disclination defect dynamics very similar to phenomenological Landau-deGennes Q -tensor theories for active nematic fluids, as well as by more complex Doi-Onsager theories for polar microtubule-motor-protein systems. We apply the quasiequilibrium Bingham closure, used to study suspensions of passive microscopic rods, to develop a nonstandard Q -tensor theory. We demonstrate through simulation that this B Q -tensor theory gives an excellent analytical and statistical accounting of the suspension's complex dynamics, at a far reduced computational cost. Finally, we apply the B Q -tensor model to study the dynamics of extensor suspensions in circular and biconcave domains. In circular domains, we reproduce previous results for systems with weak nematic alignment, but for strong alignment we find unusual dynamics with activity-controlled defect production and absorption at the boundaries of the domain. In biconcave domains, a Fredericks-like transition occurs as the width of the neck connecting the two disks is varied.

Dust grains in the coma of 67P/Churyumov-Gerasimenko - link with surface properties and cometary activity

NASA Astrophysics Data System (ADS)

Capria, M. T.; Ivanovski, S.; Zakharov, W.; Capaccioni, F.; Filacchione, G.; De Sanctis, M. C.; Rotundi, A.; Della Corte, V.; Longobardo, A.; Palomba, E.; Colangeli, L.; Bockelee-Morvan, D.; Erard, S.; Leyrat, C.

2016-11-01

The imaging spectrometer VIRTIS and the dust analyzer GIADA, onboard Rosetta, made an extensive observation of the dust particles in the coma of the comet 67P/Churyumov-Gerasimenko. From the analysis of GIADA data, two different kind of particles have been revealed, compact and fluffy with different compositions and dynamical properties. Compact particles are characterized by densities of about 10E3 kg/m3, while fluffy particles have an almost fractal nature, with densities less than 1 kg/m3. In this work we present the initial results of a model linking the dust flux distribution, as obtained from a theoretical thermal nucleus model, with a model describing the dynamics of aspherical grains in the coma. The results are discussed in the context of the latest observations from VIRTIS and GIADA instruments. The 2D nucleus thermal model, when applied to the real shape of the comet, provides the size distribution and physical properties of the emitted grains at different times and location on the surface. The thermal model can simulate grains of various size distribution, composition and physical properties. This information is used as an input for the dust dynamical model that follows the emitted particles in the coma. The main source of heating is the solar illumination. In the dust dynamical model, the grain trajectory of emitted particles remains in a plane perpendicular to the rotational axis and the direction of illumination is taken to be in the same plane (i.e. does not cause transversal forces). The dust particles are assumed to be isothermal convex bodies and temperature changes only induce modest changes in the aerodynamic force (twice higher temperature changes aerodynamic force less than 30%). This study reviews the theoretical values at which temperature difference starts to play a role on the dynamics. We discuss to what extent the particle's temperature affects the terminal velocities of the dust grains in the 67P coma in dependence on their mass and temperature constrained by the observations.

Dust grains in the coma of 67P/Churyumov-Gerasimenko - link with surface properties and cometary activity

NASA Astrophysics Data System (ADS)

Capria, Maria Teresa; Ivanovski, Stavro; Zakharov, Vladimir; Capaccioni, Fabrizio; Filacchione, Gianrico; De Sanctis, Maria Cristina; rotundi, alessandra; della corte, vincenzo; Longobardo, Andrea; Palomba, Ernesto; colangeli, luigi; Bockelee-Morvan, Dominique; Érard, Stéphane; Leyrat, Cedric; VIRTIS, GIADA

2016-10-01

The imaging spectrometer VIRTIS and the dust analyzer GIADA, onboard Rosetta, made an extensive observation of the dust particles in the coma of the comet 67P/Churyumov-Gerasimenko. From the analysis of GIADA data, two different kind of particles have been revealed, compact and fluffy with different compositions and dynamical properties. Compact particles are characterized by densities of about 103 kg/m3, while fluffy particles have an almost fractal nature, with densities less than 1 kg/m3.In this work we present the initial results of a model linking the dust flux distribution, as obtained from a theoretical thermal nucleus model, with a model describing the dynamics of aspherical grains in the coma. The results are discussed in the context of the latest observations from VIRTIS and GIADA instruments.The 2D nucleus thermal model, when applied to the real shape of the comet, provides the size distribution and physical properties of the emitted grains at different times and location on the surface. The thermal model can simulate grains of various size distribution, composition and physical properties. This information is used as an input for the dust dynamical model that follows the emitted particles in the coma. The main source of heating is the solar illumination. In the dust dynamical model, the grain trajectory of emitted particles remains in a plane perpendicular to the rotational axis and the direction of illumination is taken to be in the same plane (i.e. does not cause transversal forces). The dust particles are assumed to be isothermal convex bodies and temperature changes only induce modest changes in the aerodynamic force (twice higher temperature changes aerodynamic force less than ~30%). This study reviews the theoretical values at which temperature difference starts to play a role on the dynamics. We discuss to what extent the particle's temperature affects the terminal velocities of the dust grains in the 67P coma in dependence on their mass and temperature constrained by the observations.

Explaining electric conductivity using the particle-in-a-box model: quantum superposition is the key

NASA Astrophysics Data System (ADS)

Sivanesan, Umaseh; Tsang, Kin; Izmaylov, Artur F.

2017-12-01

Most of the textbooks explaining electric conductivity in the context of quantum mechanics provide either incomplete or semi-classical explanations that are not connected with the elementary concepts of quantum mechanics. We illustrate the conduction phenomena using the simplest model system in quantum dynamics, a particle in a box (PIB). To induce the particle dynamics, a linear potential tilting the bottom of the box is introduced, which is equivalent to imposing a constant electric field for a charged particle. Although the PIB model represents a closed system that cannot have a flow of electrons through the system, we consider the oscillatory dynamics of the particle probability density as the analogue of the electric current. Relating the amplitude and other parameters of the particle oscillatory dynamics with the gap between the ground and excited states of the PIB model allows us to demonstrate one of the most basic dependencies of electric conductivity on the valence-conduction band gap of the material.

Particle dynamics and pair production in tightly focused standing wave

NASA Astrophysics Data System (ADS)

Jirka, M.; Klimo, O.; Vranić, M.; Weber, S.; Korn, G.

2017-05-01

With the advent of 10 PW laser facilities, new regimes of laser-matter interaction are opening since effects of quantum electrodynamics, such as electron-positron pair production and cascade development, start to be important. The dynamics of light charged particles, such as electrons and positrons, is affected by the radiation reaction force. This effect can strongly influence the interaction of intense laser pulses with matter since it lowers the energy of emitting particles and transforms their energy to the gamma radiation. Consequently, electron-positron pairs can be generated via Breit-Wheeler process. To study this new regime of interaction, numerical simulations are required. With their help it is possible to predict and study quantum effects which may occur in future experiments at modern laser facilities. In this work we present results of electron interaction with an intense standing wave formed by two colliding laser pulses. Due to the necessity to achieve ultra intense laser field, the laser beam has to be focused to a μm-diameter spot. Since the paraxial approximation is not valid for tight focusing, the appropriate model describing the tightly focused laser beam has to be employed. In tightly focused laser beam the longitudinal component of the electromagnetic field becomes significant and together with the ponderomotive force they affect the dynamics of interacting electrons and also newly generated Breit-Wheeler electron-positron pairs. Using the Particle-In-Cell code we study electron dynamics, gamma radiation and pair production in such a configuration for linear polarization and different types of targets.

Electrohydrodynamics of a particle-covered drop

NASA Astrophysics Data System (ADS)

Ouriemi, Malika; Vlahovska, Petia

2014-11-01

We study the dynamics of a drop nearly-completely covered with a particle monolayer in a uniform DC electric field. The weakly conducting fluid system consists of a silicon oil drop suspended in castor oil. A broad range of particle sizes, conductivities, and shapes is explored. In weak electric fields, the presence of particles increases drop deformation compared to a particle-free drop and suppresses the electrohydrodynamic flow. Very good agreement is observed between the measured drop deformation and the small deformation theory derived for surfactant-laden drops (Nganguia et al., 2013). In stronger electric fields, where drops are expected to undergo Quincke rotation (Salipante and Vlahovska, 2010), the presence of the particles greatly decreases the threshold for rotation and the stationary tilted drop configuration observed for clean drop is replaced by a spinning drop with either a wobbling inclination or a very low inclination. These behaviors resemble the predicted response of rigid ellipsoids in uniform electric fields. At even stronger electric fields, the particles can form dynamic wings or the drop implodes. The similar behavior of particle-covered and surfactant-laden drops provides new insights into understanding stability of Pickering emulsions. Supported by NSF-CBET 1437545.

Large deviation function for a driven underdamped particle in a periodic potential

NASA Astrophysics Data System (ADS)

Fischer, Lukas P.; Pietzonka, Patrick; Seifert, Udo

2018-02-01

Employing large deviation theory, we explore current fluctuations of underdamped Brownian motion for the paradigmatic example of a single particle in a one-dimensional periodic potential. Two different approaches to the large deviation function of the particle current are presented. First, we derive an explicit expression for the large deviation functional of the empirical phase space density, which replaces the level 2.5 functional used for overdamped dynamics. Using this approach, we obtain several bounds on the large deviation function of the particle current. We compare these to bounds for overdamped dynamics that have recently been derived, motivated by the thermodynamic uncertainty relation. Second, we provide a method to calculate the large deviation function via the cumulant generating function. We use this method to assess the tightness of the bounds in a numerical case study for a cosine potential.

A Study of Particle Beam Spin Dynamics for High Precision Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fiedler, Andrew J.

In the search for physics beyond the Standard Model, high precision experiments to measure fundamental properties of particles are an important frontier. One group of such measurements involves magnetic dipole moment (MDM) values as well as searching for an electric dipole moment (EDM), both of which could provide insights about how particles interact with their environment at the quantum level and if there are undiscovered new particles. For these types of high precision experiments, minimizing statistical uncertainties in the measurements plays a critical role. \\\\ \\indent This work leverages computer simulations to quantify the effects of statistical uncertainty for experimentsmore » investigating spin dynamics. In it, analysis of beam properties and lattice design effects on the polarization of the beam is performed. As a case study, the beam lines that will provide polarized muon beams to the Fermilab Muon \\emph{g}-2 experiment are analyzed to determine the effects of correlations between the phase space variables and the overall polarization of the muon beam.« less

A multiscale modeling study of particle size effects on the tissue penetration efficacy of drug-delivery nanoparticles.

PubMed

Islam, Mohammad Aminul; Barua, Sutapa; Barua, Dipak

2017-11-25

Particle size is a key parameter for drug-delivery nanoparticle design. It is believed that the size of a nanoparticle may have important effects on its ability to overcome the transport barriers in biological tissues. Nonetheless, such effects remain poorly understood. Using a multiscale model, this work investigates particle size effects on the tissue distribution and penetration efficacy of drug-delivery nanoparticles. We have developed a multiscale spatiotemporal model of nanoparticle transport in biological tissues. The model implements a time-adaptive Brownian Dynamics algorithm that links microscale particle-cell interactions and adhesion dynamics to tissue-scale particle dispersion and penetration. The model accounts for the advection, diffusion, and cellular uptakes of particles. Using the model, we have analyzed how particle size affects the intra-tissue dispersion and penetration of drug delivery nanoparticles. We focused on two published experimental works that investigated particle size effects in in vitro and in vivo tissue conditions. By analyzing experimental data reported in these two studies, we show that particle size effects may appear pronounced in an in vitro cell-free tissue system, such as collagen matrix. In an in vivo tissue system, the effects of particle size could be relatively modest. We provide a detailed analysis on how particle-cell interactions may determine distribution and penetration of nanoparticles in a biological tissue. Our work suggests that the size of a nanoparticle may play a less significant role in its ability to overcome the intra-tissue transport barriers. We show that experiments involving cell-free tissue systems may yield misleading observations of particle size effects due to the absence of advective transport and particle-cell interactions.

The Mochi project: a field theory approach to plasma dynamics and self-organization

NASA Astrophysics Data System (ADS)

You, Setthivoine; von der Linden, Jens; Lavine, Eric Sander; Card, Alexander; Carroll, Evan

2016-10-01

The Mochi project is designed to study the interaction between plasma flows and magnetic fields from the point-of-view of canonical flux tubes. The Mochi Labjet experiment is being commissioned after achieving first plasma. Analytical and numerical tools are being developed to visualize canonical flux tubes. One analytical tool described here is a field theory approach to plasma dynamics and self-organization. A redefinition of the Lagrangian of a multi-particle system in fields reformulates the single-particle, kinetic, and fluid equations governing fluid and plasma dynamics as a single set of generalized Maxwell's equations and Ohm's law for canonical force-fields. The Lagrangian includes new terms representing the coupling between the motion of particle distributions, between distributions and electromagnetic fields, with relativistic contributions. The formulation shows that the concepts of self-organization and canonical helicity transport are applicable across single-particle, kinetic, and fluid regimes, at classical and relativistic scales. The theory gives the basis for comparing canonical helicity change to energy change in general systems. This work is supported by by US DOE Grant DE-SC0010340.

Three-dimensional structural dynamics and fluctuations of DNA-nanogold conjugates by individual-particle electron tomography

DOE PAGES

Zhang, Lei; Lei, Dongsheng; Smith, Jessica M.; ...

2016-03-30

DNA base pairing has been used for many years to direct the arrangement of inorganic nanocrystals into small groupings and arrays with tailored optical and electrical properties. The control of DNA-mediated assembly depends crucially on a better understanding of three-dimensional structure of DNA-nanocrystal-hybridized building blocks. Existing techniques do not allow for structural determination of these flexible and heterogeneous samples. Here we report cryo-electron microscopy and negative-staining electron tomography approaches to image, and three-dimensionally reconstruct a single DNA-nanogold conjugate, an 84-bp double-stranded DNA with two 5-nm nanogold particles for potential substrates in plasmon-coupling experiments. By individual-particle electron tomography reconstruction, we obtainmore » 14 density maps at ~ 2-nm resolution . Using these maps as constraints, we derive 14 conformations of dsDNA by molecular dynamics simulations. The conformational variation is consistent with that from liquid solution, suggesting that individual-particle electron tomography could be an expected approach to study DNA-assembling and flexible protein structure and dynamics.« less

Coffee-stain growth dynamics on dry and wet surfaces

NASA Astrophysics Data System (ADS)

Boulogne, François; Ingremeau, François; Stone, Howard A.

2017-02-01

The drying of a drop containing particles often results in the accumulation of the particles at the contact line. In this work, we investigate the drying of an aqueous colloidal drop surrounded by a hydrogel that is also evaporating. We combine theoretical and experimental studies to understand how the surrounding vapor concentration affects the particle deposit during the constant radius evaporation mode. In addition to the common case of evaporation on an otherwise dry surface, we show that in a configuration where liquid is evaporating from a flat surface around the drop, the singularity of the evaporative flux at the contact line is suppressed and the drop evaporation is homogeneous. For both conditions, we derive the velocity field and we establish the temporal evolution of the number of particles accumulated at the contact line. We predict the growth dynamics of the stain and the drying timescales. Thus, dry and wet conditions are compared with experimental results and we highlight that only the dynamics is modified by the evaporation conditions, not the final accumulation at the contact line.

Stochastic dynamics of intermittent pore-scale particle motion in three-dimensional porous media

NASA Astrophysics Data System (ADS)

Morales, V. L.; Dentz, M.; Willmann, M.; Holzner, M.

2017-12-01

A proper understanding of velocity dynamics is key for making transport predictions through porous media at any scale. We study the velocity evolution process from particle dynamics at the pore-scale with particular interest in preasymptotic (non-Fickian) behavior. Experimental measurements from 3-dimensional particle tracking velocimetry are used to obtain Lagrangian velocity statistics for three different types of media heterogeneity. Particle velocities are found to be intermittent in nature, log-normally distributed and non-stationary. We show that these velocity characteristics can be captured with a correlated Ornstein-Uhlenbeck process for a random walk in space that is parameterized from velocity distributions. Our simple model is rigorously tested for accurate reproduction of velocity variability in magnitude and frequency. We further show that it captures exceptionally well the preasymptotic mean and mean squared displacement in the ballistic and superdiffusive regimes, and can be extended to determine if and when Fickian behavior will be reached. Our approach reproduces both preasymptotic and asymptotic transport behavior with a single transport model, demonstrating correct description of the fundamental controls of anomalous transport.

Energy loss of α-particle moving in warm dense deuterium plasma: Role of local field corrections

NASA Astrophysics Data System (ADS)

Fu, Zhen-Guo; Wang, Zhigang; Zhang, Ping

2017-11-01

We theoretically study the energy loss of α-particles traveling in the warm dense plasma (WDP) of deuterium (D) with temperatures from 10 to 100 eV and electron number densities from 1023 to 1024 cm-3. Beyond the random phase approximation (RPA) model, the extended Mermin dielectric function (MDF) model including the static and dynamic local field corrections (LFC) is employed in the calculations. Compared with the static LFC, the dynamic LFC introduced in the extended MDF model gives rise to a more significant departure from the RPA result. For the plasma conditions focused in this work, the departure induced by dynamic LFC reaches almost ˜ 30 % , which may be detected in the inertial confinement fusion (ICF) related experiment. Moreover, we find that the effect of static e-e collision may be of importance (unimportance) for the WDP of D with a temperature of tens (hundreds) of eV. Our findings may be important for ICF ignition since the uncertainty induced by the correlation effects between plasma component particles is crucial for the prediction of α-particle heating in fusion plasmas.

Dynamics of metastable breathers in nonlinear chains in acoustic vacuum

NASA Astrophysics Data System (ADS)

Sen, Surajit; Mohan, T. R. Krishna

2009-03-01

The study of the dynamics of one-dimensional chains with both harmonic and nonlinear interactions, as in the Fermi-Pasta-Ulam and related problems, has played a central role in efforts to identify the broad consequences of nonlinearity in these systems. Nevertheless, little is known about the dynamical behavior of purely nonlinear chains where there is a complete absence of the harmonic term, and hence sound propagation is not admissible, i.e., under conditions of “acoustic vacuum.” Here we study the dynamics of highly localized excitations, or breathers, which are known to be initiated by the quasistatic stretching of the bonds between adjacent particles. We show via detailed particle-dynamics-based studies that many low-energy pulses also form in the vicinity of the perturbation, and the breathers that form are “fragile” in the sense that they can be easily delocalized by scattering events in the system. We show that the localized excitations eventually disperse, allowing the system to attain an equilibrium-like state that is realizable in acoustic vacuum. We conclude with a discussion of how the dynamics is affected by the presence of acoustic oscillations.

Anisotropy and probe-medium interactions in the microrheology of nematic fluids.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cordoba, Andres; Stieger, Tillmann; Mazza, Marco G.

2016-01-01

A theoretical formalism is presented to analyze and interpret microrheology experiments in anisotropic fluids with nematic order. The predictions of that approach are examined in the context of a simple coarse-grained molecular model which is simulated using nonequilibrium molecular dynamics calculations. The proposed formalism is used to study the effect of confinement, the type of anchoring at the probe-particle surface, and the strength of the nematic field on the rheological response functions obtained from probe-particle active microrheology. As expected, a stronger nematic field leads to increased anisotropy in the rheological response of the material. It is also found that themore » defect structures that arise around the probe particle, which are determined by the type of anchoring and the particle size, have a significant effect on the rheological response observed in microrheology simulations. Independent estimates of the bulk dynamic modulus of the model nematic fluid considered here are obtained from small-amplitude oscillatory shear simulations with Lees Edwards boundary conditions. The results of simulations indicate that the dynamic modulus extracted from particle-probe microrheology is different from that obtained in the absence of the particle, but that the differences decrease as the size of the defect also decreases. Importantly, the results of the nematic microrheology theory proposed here are in much closer agreement with simulations than those from earlier formalisms conceived for isotropic fluids. As such, it is anticipated that the theoretical framework advanced in this study could provide a useful tool for interpretation of microrheology experiments in systems such as liquid crystals and confined macromolecular solutions or gels.« less

Slip-stacking Dynamics for High-Power Proton Beams at Fermilab

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eldred, Jeffrey Scott

Slip-stacking is a particle accelerator configuration used to store two particle beams with different momenta in the same ring. The two beams are longitudinally focused by two radiofrequency (RF) cavities with a small frequency difference between them. Each beam is synchronized to one RF cavity and perturbed by the other RF cavity. Fermilab uses slip-stacking in the Recycler so as to double the power of the 120 GeV proton beam in the Main Injector. This dissertation investigates the dynamics of slip-stacking beams analytically, numerically and experimentally. In the analytic analysis, I find the general trajectory of stable slip-stacking particles andmore » identify the slip-stacking parametric resonances. In the numerical analysis, I characterize the stable phase-space area and model the particle losses. In particular, I evaluate the impact of upgrading the Fermilab Booster cycle-rate from 15 Hz to 20 Hz as part of the Proton Improvement Plan II (PIP-II). The experimental analysis is used to verify my approach to simulating slip-stacking loss. I design a study for measuring losses from the longitudinal single-particle dynamics of slip-stacking as a function of RF cavity voltage and RF frequency separation. I further propose the installation of a harmonic RF cavity and study the dynamics of this novel slip-stacking configuration. I show the harmonic RF cavity cancels out parametric resonances in slip-stacking, reduces emittance growth during slip-stacking, and dramatically enhances the stable phase-space area. The harmonic cavity is expected to reduce slip-stacking losses to far exceed PIP-II requirements. These results raise the possibility of extending slip-stacking beyond the PIP-II era.« less

The role of ice particles in the microphysics and dynamics of deep convective storms in various latitudes

NASA Astrophysics Data System (ADS)

Huang, Y. C.; Wang, P. K.

2017-12-01

The role of ice particles in the microphysics and dynamics of deep convective storms in various latitudes Yi-Chih Huang and Pao K. Wang Ice particles contribute to the microphysics and dynamics of severe storms in various regions of the world to a degree that is not commonly recognized. This study is motivated by the need to understand the role of ice particles plays in the development of severe storms so that their impact on various aspects of the storm behavior can be properly assessed. In this study, we perform numerical simulations of thunderstorms using a cloud resolving model WISCDYMM that includes parameterized microphysical processes to understand the role played by ice processes. We simulate thunderstorms occurred over various regions of the world including tropics, substropics and midlatitudes. We then perform statistical analysis of the simulated results to show the formation of various categories of hydrometeors to reveal the importance of ice processes. We will show that ice hydrometeors (cloud ice, snow, graupel/hail) account for 80% of the total hydrometeor mass for the High Plains storms but 50% for the subtropical storms. In addition, the melting of large ice particles (graupel and hail) is the major production process of rain in tropical storms although the ratio of ice-phase mass is responsible for only 40% of the total hydrometeor mass. Furthermore, hydrometeors have their own special microphysical processes in development and depletion over various latitudes. Microphysical structures depend on atmospheric dynamical and thermodynamical conditions which determine the partitioning of hydrometeors. This knowledge would benefit the microphysics parameterization in cloud models and cumulus parameterization in global circulation models.

Molecular Dynamic Studies of Particle Wake Potentials in Plasmas

NASA Astrophysics Data System (ADS)

Ellis, Ian; Graziani, Frank; Glosli, James; Strozzi, David; Surh, Michael; Richards, David; Decyk, Viktor; Mori, Warren

2010-11-01

Fast Ignition studies require a detailed understanding of electron scattering, stopping, and energy deposition in plasmas with variable values for the number of particles within a Debye sphere. Presently there is disagreement in the literature concerning the proper description of these processes. Developing and validating proper descriptions requires studying the processes using first-principle electrostatic simulations and possibly including magnetic fields. We are using the particle-particle particle-mesh (P^3M) code ddcMD to perform these simulations. As a starting point in our study, we examined the wake of a particle passing through a plasma. In this poster, we compare the wake observed in 3D ddcMD simulations with that predicted by Vlasov theory and those observed in the electrostatic PIC code BEPS where the cell size was reduced to .03λD.

Particles size distribution in diluted magnetic fluids

NASA Astrophysics Data System (ADS)

Yerin, Constantine V.

2017-06-01

Changes in particles and aggregates size distribution in diluted kerosene based magnetic fluids is studied by dynamic light scattering method. It has been found that immediately after dilution in magnetic fluids the system of aggregates with sizes ranging from 100 to 250-1000 nm is formed. In 50-100 h after dilution large aggregates are peptized and in the sample stationary particles and aggregates size distribution is fixed.

Mixing, segregation, and flow of granular materials

NASA Astrophysics Data System (ADS)

McCarthy, Joseph J.

1998-11-01

This dissertation addresses mixing, segregation, and flow of granular materials with the ultimate goal of providing fundamental understanding and tools for the rational design and optimization of mixing devices. In particular, the paradigm cases of a slowly rotated tumbler mixer and flow down an inclined plane are examined. Computational work, as well as supporting experiments, are used to probe both two and three dimensional systems. In the avalanching regime, the mixing and flow can be viewed either on a global-scale or a local-scale. On the global-scale, material is transported via avalanches whose gross motion can be well described by geometrical considerations. On the local-scale, the dynamics of the particle motion becomes important; particles follow complicated trajectories that are highly sensitive to differences in size/density/morphology. By decomposing the problem in this way, it is possible to study the implications of the geometry and dynamics separately and to add complexities in a controlled fashion. This methodology allows even seemingly difficult problems (i.e., mixing in non-convex geometries, and mixing of dissimilar particles) to be probed in a simple yet methodical way. In addition this technique provides predictions of optimal mixing conditions in an avalanching tumbler, a criterion for evaluating the effect of mixer shape, and mixing enhancement strategies for both two and three dimensional mixers. In the continuous regime, the flow can be divided into two regions: a rapid flow region of the cascading layer at the free surface, and a fixed bed region undergoing solid body rotation. A continuum-based description, in which averages are taken across the layer, generates quantitative predictions about the flow in the cascading layer and agrees well with experiment. Incorporating mixing through a diffusive flux (as well as constitutive expression for segregation) within the cascading layer allows for the determination of optimal mixing conditions. Segregation requires a detailed understanding of the interplay between the flow and the properties of the particles. A relatively mature simulation technique, particle dynamics (PD), aptly captures these effects and is eminently suited to mixing studies; particle properties can be varied on a particle-by-particle basis and detailed mixed structures are easily captured and visualized. However, PD is computationally intensive and is therefore of questionable general utility. By combining PD and geometrical insight-in essence, by focusing the particle dynamics simulation only where it is needed-a new hybrid method of simulation, which is much faster than a conventional particle dynamics method, can be achieved. This technique can yield more than an order of magnitude increase in computational speed while maintaining the versatility of a particle dynamics simulation. Alternatively, by utilizing PD to explore segregation mechanisms in simple flows-e.g., flow down an inclined plane-heuristic models and constitutive relations for segregation can be tested. Incorporating these segregation flux terms into a continuum description of the flow in a tumbler allows rapid Lagrangian simulation of the competition between mixing and segregation. For the case of density segregation, this produces good agreement between theory and experiment with essentially no adjustable parameters. In addition, an accurate quantitative prediction of the optimal mixing time is obtained.

The erosion performance of particle reinforced metal matrix composite coatings produced by co-deposition cold gas dynamic spraying

NASA Astrophysics Data System (ADS)

Peat, Tom; Galloway, Alexander; Toumpis, Athanasios; McNutt, Philip; Iqbal, Naveed

2017-02-01

This work reports on the erosion performance of three particle reinforced metal matrix composite coatings, co-deposited with an aluminium binder via cold-gas dynamic spraying. The deposition of ceramic particles is difficult to achieve with typical cold spray techniques due to the absence of particle deformation. This issue has been overcome in the present study by simultaneously spraying the reinforcing particles with a ductile metallic binder which has led to an increased level of ceramic/cermet particles deposited on the substrate with thick (>400 μm) coatings produced. The aim of this investigation was to evaluate the erosion performance of the co-deposited coatings within a slurry environment. The study also incorporated standard metallographic characterisation techniques to evaluate the distribution of reinforcing particles within the aluminium matrix. All coatings exhibited poorer erosion performance than the uncoated material, both in terms of volume loss and mass loss. The Al2O3 reinforced coating sustained the greatest amount of damage following exposure to the slurry and recorded the greatest volume loss (approx. 2.8 mm3) out of all of the examined coatings. Despite the poor erosion performance, the WC-CoCr reinforced coating demonstrated a considerable hardness increase over the as-received AA5083 (approx. 400%) and also exhibited the smallest free space length between adjacent particles. The findings of this study reveal that the removal of the AA5083 matrix by the impinging silicon carbide particles acts as the primary wear mechanism leading to the degradation of the coating. Analysis of the wear scar has demonstrated that the damage to the soft matrix alloy takes the form of ploughing and scoring which subsequently exposes carbide/oxide particles to the impinging slurry.

Numerical study of A+A-->0 and A+B-->0 reactions with inertia.

PubMed

Romero, A H; Lacasta, A M; Sancho, J M; Lindenberg, Katja

2007-11-07

Using numerical methods the authors study the annihilation reactions A+A-->0 and A+B-->0 in one and two dimensions in the presence of inertial contributions to the motion of the particles. The particles move freely following Langevin dynamics at a fixed temperature. The authors focus on the role of friction.

A Brownian dynamics study on ferrofluid colloidal dispersions using an iterative constraint method to satisfy Maxwell’s equations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dubina, Sean Hyun, E-mail: sdubin2@uic.edu; Wedgewood, Lewis Edward, E-mail: wedge@uic.edu

2016-07-15

Ferrofluids are often favored for their ability to be remotely positioned via external magnetic fields. The behavior of particles in ferromagnetic clusters under uniformly applied magnetic fields has been computationally simulated using the Brownian dynamics, Stokesian dynamics, and Monte Carlo methods. However, few methods have been established that effectively handle the basic principles of magnetic materials, namely, Maxwell’s equations. An iterative constraint method was developed to satisfy Maxwell’s equations when a uniform magnetic field is imposed on ferrofluids in a heterogeneous Brownian dynamics simulation that examines the impact of ferromagnetic clusters in a mesoscale particle collection. This was accomplished bymore » allowing a particulate system in a simple shear flow to advance by a time step under a uniformly applied magnetic field, then adjusting the ferroparticles via an iterative constraint method applied over sub-volume length scales until Maxwell’s equations were satisfied. The resultant ferrofluid model with constraints demonstrates that the magnetoviscosity contribution is not as substantial when compared to homogeneous simulations that assume the material’s magnetism is a direct response to the external magnetic field. This was detected across varying intensities of particle-particle interaction, Brownian motion, and shear flow. Ferroparticle aggregation was still extensively present but less so than typically observed.« less

Incomplete Thermalization from Trap-Induced Integrability Breaking: Lessons from Classical Hard Rods

NASA Astrophysics Data System (ADS)

Cao, Xiangyu; Bulchandani, Vir B.; Moore, Joel E.

2018-04-01

We study a one-dimensional gas of hard rods trapped in a harmonic potential, which breaks integrability of the hard-rod interaction in a nonuniform way. We explore the consequences of such broken integrability for the dynamics of a large number of particles and find three distinct regimes: initial, chaotic, and stationary. The initial regime is captured by an evolution equation for the phase-space distribution function. For any finite number of particles, this hydrodynamics breaks down and the dynamics becomes chaotic after a characteristic timescale determined by the interparticle distance and scattering length. The system fails to thermalize over the timescale studied (1 04 natural units), but the time-averaged ensemble is a stationary state of the hydrodynamic evolution. We close by discussing logical extensions of the results to similar systems of quantum particles.

Weekly variation of atmospheric particle micromorphology and chemistry in Brussels urban environment.

PubMed

Zaady, Eli; Carati, D; Brenig, L; Vanderstraeten, P; Lénelle, Y; Meurrens, A; Offer, Z Y

2010-10-01

The purpose of this study was to measure the impact of urban activities on airborne particle dynamics during weekend periods in Brussels urban area. Differences in the granulometry and micromorphology between particles sampled on working days and weekends were studied. We quantified the area, size, number, and the chemistry parameters of the airborne particles and compared between Saturday, Sunday, and Monday. We report and analyze data on airborne particles up to PM10, measured in the Brussels region from October 2002 to September 2003. Our investigation reveals detailed information regarding chemical composition of the airborne particles over the weekend period in the Brussels urban area. Furthermore, the majority of the airborne particles in the Brussels region may belong to sources geographically outside the (in situ) Brussels area.

A hybrid molecular dynamics study on the non-Newtonian rheological behaviors of shear thickening fluid.

PubMed

Chen, Kaihui; Wang, Yu; Xuan, Shouhu; Gong, Xinglong

2017-07-01

To investigate the microstructural evolution dependency on the apparent viscosity in shear-thickening fluids (STFs), a hybrid mesoscale model combined with stochastic rotation dynamics (SRD) and molecular dynamics (MD) is used. Muller-Plathe reverse perturbation method is adopted to analyze the viscosities of STFs in a two-dimensional model. The characteristic of microstructural evolution of the colloidal suspensions under different shear rate is studied. The effect of diameter of colloidal particles and the phase volume fraction on the shear thickening behavior is investigated. Under low shear rate, the two-atom structure is formed, because of the strong particle attractions in adjacent layers. At higher shear rate, the synergetic pair structure extends to layered structure along flow direction because of the increasing hydrodynamics action. As the shear rate rises continuously, the layered structure rotates and collides with other particles, then turned to be individual particles under extension or curve string structure under compression. Finally, at the highest shear rate, the strings curve more severely and get into two-dimensional cluster. The apparent viscosity of the system changes from shear-thinning behavior to the shear-thickening behavior. This work presents valuable information for further understanding the shear thickening mechanism. Copyright © 2017 Elsevier Inc. All rights reserved.

Self Assembled Particles

NASA Technical Reports Server (NTRS)

Palacci, Jeremie (Inventor); Pine, David J. (Inventor); Chaikin, Paul Michael (Inventor); Sacanna, Stefano (Inventor)

2017-01-01

A self-assembling structure using non-equilibrium driving forces leading to 'living crystals' and other maniputable particles with a complex dynamics. The dynamic self-assembly assembly results from a competition between self-propulsion of particles and an attractive interaction between the particles. As a result of non-equilibrium driving forces, the crystals form, grow, collide, anneal, repair themselves and spontaneously self-destruct, thereby enabling reconfiguration and assembly to achieve a desired property.

A CFD-Based Study of the Feasibility of Adapting an Erosion Burner Rig for Examining the Effect of CMAS Deposition Corrosion on Environmental Barrier Coatings

NASA Technical Reports Server (NTRS)

Miller, Robert A.; Kuczmarski, Maria A.

2015-01-01

Thermodynamic and computational fluid dynamics modeling has been conducted to examine the feasibility of adapting the NASA-Glenn erosion burner rigs for use in studies of corrosion of environmental barrier coatings by the deposition of molten CMAS. The effect of burner temperature, Mach number, particle preheat, duct heating, particle size, and particle phase (crystalline vs. glass) were analyzed. Detailed strategies for achieving complete melting of CMAS particles were developed, thereby greatly improving the probability of future successful experimental outcomes.

Experimental Study of Short-Time Brownian Motion

NASA Astrophysics Data System (ADS)

Mo, Jianyong; Simha, Akarsh; Riegler, David; Raizen, Mark

2015-03-01

We report our progress on the study of short-time Brownian motion of optically-trapped microspheres. In earlier work, we observed the instantaneous velocity of microspheres in gas and in liquid, verifying a prediction by Albert Einstein from 1907. We now report a more accurate test of the energy equipartition theorem for a particle in liquid. We also observe boundary effects on Brownian motion in liquid by setting a wall near the trapped particle, which changes the dynamics of the motion. We find that the velocity autocorrelation of the particle decreases faster as the particle gets closer to the wall.

Plastic fluctuations in empty crystals formed by cubic wireframe particles

NASA Astrophysics Data System (ADS)

McBride, John M.; Avendaño, Carlos

2018-05-01

We present a computer simulation study of the phase behavior of colloidal hard cubic frames, i.e., particles with nonconvex cubic wireframe geometry interacting purely by excluded volume. Despite the propensity of cubic wireframe particles to form cubic phases akin to their convex counterparts, these particles exhibit unusual plastic fluctuations in which a random and dynamic fraction of particles rotate around their lattice positions in the crystal lattice while the remainder of the particles remains fully ordered. We argue that this unexpected effect stems from the nonconvex geometry of the particles in which the faces of a particle can be penetrated by the vertices of the nearest neighbors even at high number densities.

Silverton Conference on Applications of the Zero Gravity Space Shuttle Environment to Problems in Fluid Dynamics

NASA Technical Reports Server (NTRS)

Eisner, M. (Editor)

1974-01-01

The possible utilization of the zero gravity resource for studies in a variety of fluid dynamics and fluid-dynamic related problems was investigated. A group of experiments are discussed and described in detail; these include experiments in the areas of geophysical fluid models, fluid dynamics, mass transfer processes, electrokinetic separation of large particles, and biophysical and physiological areas.

Modeling of the rough spherical nanoparticles manipulation on a substrate based on the AFM nanorobot

NASA Astrophysics Data System (ADS)

Zakeri, M.; Faraji, J.

2014-12-01

In this paper, dynamic behavior of the rough spherical micro/nanoparticles during pulling/pushing on the flat substrate has been investigated and analyzed. For this purpose, at first, two hexagonal roughness models (George and Cooper) were studied and then evaluations for adhesion force were determined for rough particle manipulation on flat substrate. These two models were then changed by using of the Rabinovich theory. Evaluations were determined for contact adhesion force between rough particle and flat substrate; depth of penetration evaluations were determined by the Johnson-Kendall-Roberts contact mechanic theory and the Schwartz method and according to Cooper and George roughness models. Then, the novel contact theory was used to determine a dynamic model for rough micro/nanoparticle manipulation on flat substrate. Finally, simulation of particle dynamic behavior was implemented during pushing of rough spherical gold particles with radii of 50, 150, 400, 600, and 1,000 nm. Results derived from simulations of particles with several rates of roughness on flat substrate indicated that compared to results for flat particles, inherent roughness on particles might reduce the rate of critical force needed for sliding and rolling given particles. Given a fixed radius for roughness value and increased roughness height, evaluations for sliding and rolling critical forces showed greater reduction. Alternately, the rate of critical force was shown to reduce relative to an increased roughness radius. With respect to both models, based on the George roughness model, the predicted rate of adhesion force was greater than that determined in the Cooper roughness model, and as a result, the predicted rate of critical force based on the George roughness model was closer to the critical force value of flat particle.

Augmenting regional and targeted delivery in the pulmonary acinus using magnetic particles

PubMed Central

Ostrovski, Yan; Hofemeier, Philipp; Sznitman, Josué

2016-01-01

Background It has been hypothesized that by coupling magnetic particles to inhaled therapeutics, the ability to target specific lung regions (eg, only acinar deposition), or even more so specific points in the lung (eg, tumor targeting), can be substantially improved. Although this method has been proven feasible in seminal in vivo studies, there is still a wide gap in our basic understanding of the transport phenomena of magnetic particles in the pulmonary acinar regions of the lungs, including particle dynamics and deposition characteristics. Methods Here, we present computational fluid dynamics-discrete element method simulations of magnetically loaded microdroplet carriers in an anatomically inspired, space-filling, multi-generation acinar airway tree. Breathing motion is modeled by kinematic sinusoidal displacements of the acinar walls, during which droplets are inhaled and exhaled. Particle dynamics are governed by viscous drag, gravity, and Brownian motion as well as the external magnetic force. In particular, we examined the roles of droplet diameter and volume fraction of magnetic material within the droplets under two different breathing maneuvers. Results and discussion Our results indicate that by using magnetic-loaded droplets, 100% of the particles that enter are deposited in the acinar region. This is consistent across all particle sizes investigated (ie, 0.5–3.0 µm). This is best achieved through a deep inhalation maneuver combined with a breath-hold. Particles are found to penetrate deep into the acinus and disperse well, while the required amount of magnetic material is maintained low (<2.5%). Although particles in the size range of ~90–500 nm typically show the lowest deposition fractions, our results suggest that this feature could be leveraged to augment targeted delivery. PMID:27547034

Simulations of electrically induced particle structuring on spherical drop surface

NASA Astrophysics Data System (ADS)

Hu, Yi; Vlahovska, Petia; Miksis, Michael

2016-11-01

Recent experiments (Ouriemi and Vlahovska, 2014) show intriguing surface patterns when a uniform electric field is applied to a droplet covered with colloidal particles. Depending on the particle properties and the electrical field intensity, particles organize into an equatorial belt, pole-to-pole chains, or dynamic vortices. Here we present a model to simulate the collective particle dynamics, which accounts for the electrohydrodynamic flow and particle dielectrophoresis due to the non-uniformity of local electrical field. In stronger electric fields, particles are expected to undergo Quincke rotation, inducing rotating clusters through inter-particle hydrodynamical interaction. We discuss how the field intensity influences the width, orientation and periodicity of the particle clusters. Our results provide insight into the various particle assembles discovered in the experiments.

Dynamics of particles in central Encke ringlet

NASA Astrophysics Data System (ADS)

Sun, K.-L.; Spahn, F.; Schmidt, J.

2012-09-01

The Encke gap is a 320 km wide division in the Saturn A ring centered at 133,581 km. There are at least 3 ringlets in Encke gap, and the central one shares the orbit with Pan [1]. Observations suggest that these ringlets are mainly composed of micronsized particles [2]. The lifetime of these particles are restricted, mechanisms must be at work to replenish these ringlets. The kinetic balance of dust production, dynamical evolution, and loss of dust has been investigated in [3]. In this work, we focus on the particle dynamics in the Encke gap. Our results show that in the central Encke ringlet: (1) The solar radiation pressure provides a minimum particle radius of 7μm; (2) The plasma drag force pushes particle outward in a rate of ˜ 1km/yr; (3) Particles are in a 'modified' horseshoe orbit which is the result of horseshoe orbit plus plasma drag, this orbit prevent particles to reach large co-rotational longitudes of Pan.

Modelling the contribution of biogenic volatile organic compounds to new particle formation in the Jülich plant atmosphere chamber

NASA Astrophysics Data System (ADS)

Roldin, P.; Liao, L.; Mogensen, D.; Dal Maso, M.; Rusanen, A.; Kerminen, V.-M.; Mentel, T. F.; Wildt, J.; Kleist, E.; Kiendler-Scharr, A.; Tillmann, R.; Ehn, M.; Kulmala, M.; Boy, M.

2015-09-01

We used the Aerosol Dynamics gas- and particle-phase chemistry model for laboratory CHAMber studies (ADCHAM) to simulate the contribution of BVOC plant emissions to the observed new particle formation during photooxidation experiments performed in the Jülich Plant-Atmosphere Chamber and to evaluate how well smog chamber experiments can mimic the atmospheric conditions during new particle formation events. ADCHAM couples the detailed gas-phase chemistry from Master Chemical Mechanism with a novel aerosol dynamics and particle phase chemistry module. Our model simulations reveal that the observed particle growth may have either been controlled by the formation rate of semi- and low-volatility organic compounds in the gas phase or by acid catalysed heterogeneous reactions between semi-volatility organic compounds in the particle surface layer (e.g. peroxyhemiacetal dimer formation). The contribution of extremely low-volatility organic gas-phase compounds to the particle formation and growth was suppressed because of their rapid and irreversible wall losses, which decreased their contribution to the nano-CN formation and growth compared to the atmospheric situation. The best agreement between the modelled and measured total particle number concentration (R2 > 0.95) was achieved if the nano-CN was formed by kinetic nucleation involving both sulphuric acid and organic compounds formed from OH oxidation of BVOCs.

Active Brownian Particles. From Individual to Collective Stochastic Dynamics

NASA Astrophysics Data System (ADS)

Romanczuk, P.; Bär, M.; Ebeling, W.; Lindner, B.; Schimansky-Geier, L.

2012-03-01

We review theoretical models of individual motility as well as collective dynamics and pattern formation of active particles. We focus on simple models of active dynamics with a particular emphasis on nonlinear and stochastic dynamics of such self-propelled entities in the framework of statistical mechanics. Examples of such active units in complex physico-chemical and biological systems are chemically powered nano-rods, localized patterns in reaction-diffusion system, motile cells or macroscopic animals. Based on the description of individual motion of point-like active particles by stochastic differential equations, we discuss different velocity-dependent friction functions, the impact of various types of fluctuations and calculate characteristic observables such as stationary velocity distributions or diffusion coefficients. Finally, we consider not only the free and confined individual active dynamics but also different types of interaction between active particles. The resulting collective dynamical behavior of large assemblies and aggregates of active units is discussed and an overview over some recent results on spatiotemporal pattern formation in such systems is given.

Study of static and dynamic magnetic properties of Fe nanoparticles composited with activated carbon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pal, Satyendra Prakash, E-mail: sppal85@gmail.com; Department of Physical Sciences, Indian Institute of Science Education and Research, Mohali, Knowledge city, Sector81, SAS Nagar, Manauli-140306, Punjab; Kaur, Guratinder

2016-05-23

Nanocomposite of Fe nanoparticles with activated carbon has been synthesized to alter the magnetic spin-spin interaction and hence study the dilution effect on the static and dynamic magnetic properties of the Fe nanoparticle system. Transmission electron microscopic (TEM) image shows the spherical Fe nanoparticles dispersed in carbon matrix with 13.8 nm particle size. Temperature dependent magnetization measurement does not show any blocking temperature at all, right up to the room temperature. Magnetic hysteresis curve, taken at 300 K, shows small value of the coercivity and this small hysteresis indicates the presence of an energy barrier and inherent magnetization dynamics. Langevinmore » function fitting of the hysteresis curve gives almost similar value of particle size as obtained from TEM analysis. Magnetic relaxation data, taken at a temperature of 100 K, were fitted with a combination of two exponentially decaying function. This diluted form of nanoparticle system, which has particles size in the superparamagnetic limit, behaves like a dilute ensemble of superspins with large value of the magnetic anisotropic barrier.« less

A study on independently using static and dynamic light scattering methods to determine the coagulation rate

NASA Astrophysics Data System (ADS)

Zhou, Hongwei; Xu, Shenghua; Mi, Li; Sun, Zhiwei; Qin, Yanming

2014-09-01

Absolute coagulation rate constants were determined by independently, instead of simultaneously, using static and dynamic light scattering with the requested optical factors calculated by T-matrix method. The aggregating suspensions of latex particles with diameters of 500, 700, and 900 nm, that are all beyond validity limit of the traditional Rayleigh-Debye-Gans approximation, were adopted. The results from independent static and dynamic light scattering measurements were compared with those by simultaneously using static and dynamic light scattering; and three of them show good consistency. We found, theoretically and experimentally, that for independent static light scattering measurements there are blind scattering angles at that the scattering measurements become impossible and the number of blind angles increases rapidly with particle size. For independent dynamic light scattering measurements, however, there is no such a blind angle at all. A possible explanation of the observed phenomena is also presented.

Mode coupling theory for nonequilibrium glassy dynamics of thermal self-propelled particles.

PubMed

Feng, Mengkai; Hou, Zhonghuai

2017-06-28

We present a mode coupling theory study for the relaxation and glassy dynamics of a system of strongly interacting self-propelled particles, wherein the self-propulsion force is described by Ornstein-Uhlenbeck colored noise and thermal noises are included. Our starting point is an effective Smoluchowski equation governing the distribution function of particle positions, from which we derive a memory function equation for the time dependence of density fluctuations in nonequilibrium steady states. With the basic assumption of the absence of macroscopic currents and standard mode coupling approximation, we can obtain expressions for the irreducible memory function and other relevant dynamic terms, wherein the nonequilibrium character of the active system is manifested through an averaged diffusion coefficient D[combining macron] and a nontrivial structural function S 2 (q) with q being the magnitude of wave vector q. D[combining macron] and S 2 (q) enter the frequency term and the vertex term for the memory function, and thus influence both the short time and the long time dynamics of the system. With these equations obtained, we study the glassy dynamics of this thermal self-propelled particle system by investigating the Debye-Waller factor f q and relaxation time τ α as functions of the persistence time τ p of self-propulsion, the single particle effective temperature T eff as well as the number density ρ. Consequently, we find the critical density ρ c for given τ p shifts to larger values with increasing magnitude of propulsion force or effective temperature, in good accordance with previously reported simulation work. In addition, the theory facilitates us to study the critical effective temperature T for fixed ρ as well as its dependence on τ p . We find that T increases with τ p and in the limit τ p → 0, it approaches the value for a simple passive Brownian system as expected. Our theory also well recovers the results for passive systems and can be easily extended to more complex systems such as active-passive mixtures.

Charged particle dynamics in the presence of non-Gaussian Lévy electrostatic fluctuations

DOE PAGES

Del-Castillo-Negrete, Diego B.; Moradi, Sara; Anderson, Johan

2016-09-01

Full orbit dynamics of charged particles in a 3-dimensional helical magnetic field in the presence of -stable Levy electrostatic fluctuations and linear friction modeling collisional Coulomb drag is studied via Monte Carlo numerical simulations. The Levy fluctuations are introduced to model the effect of non-local transport due to fractional diffusion in velocity space resulting from intermittent electrostatic turbulence. The probability distribution functions of energy, particle displacements, and Larmor radii are computed and showed to exhibit a transition from exponential decay, in the case of Gaussian fluctuations, to power law decay in the case of Levy fluctuations. The absolute value ofmore » the power law decay exponents are linearly proportional to the Levy index. Furthermore, the observed anomalous non-Gaussian statistics of the particles' Larmor radii (resulting from outlier transport events) indicate that, when electrostatic turbulent fluctuations exhibit non-Gaussian Levy statistics, gyro-averaging and guiding centre approximations might face limitations and full particle orbit effects should be taken into account.« less

Charged particle dynamics in the presence of non-Gaussian Lévy electrostatic fluctuations

NASA Astrophysics Data System (ADS)

Moradi, Sara; del-Castillo-Negrete, Diego; Anderson, Johan

2016-09-01

Full orbit dynamics of charged particles in a 3-dimensional helical magnetic field in the presence of α-stable Lévy electrostatic fluctuations and linear friction modeling collisional Coulomb drag is studied via Monte Carlo numerical simulations. The Lévy fluctuations are introduced to model the effect of non-local transport due to fractional diffusion in velocity space resulting from intermittent electrostatic turbulence. The probability distribution functions of energy, particle displacements, and Larmor radii are computed and showed to exhibit a transition from exponential decay, in the case of Gaussian fluctuations, to power law decay in the case of Lévy fluctuations. The absolute value of the power law decay exponents is linearly proportional to the Lévy index α. The observed anomalous non-Gaussian statistics of the particles' Larmor radii (resulting from outlier transport events) indicate that, when electrostatic turbulent fluctuations exhibit non-Gaussian Lévy statistics, gyro-averaging and guiding centre approximations might face limitations and full particle orbit effects should be taken into account.

Cold Active Motion: How Time-Independent Disorder Affects the Motion of Self-Propelled Agents

NASA Astrophysics Data System (ADS)

Peruani, Fernando; Aranson, Igor S.

2018-06-01

Assemblages of self-propelled particles, often termed active matter, exhibit collective behavior due to competition between neighbor alignment and noise-induced decoherence. However, very little is known of how the quenched (i.e., time-independent) disorder impacts active motion. Here we report on the effects of quenched disorder on the dynamics of self-propelled point particles. We identified three major types of quenched disorder relevant in the context of active matter: random torque, force, and stress. We demonstrate that even in the absence of external fluctuations ("cold active matter"), quenched disorder results in nontrivial dynamic phases not present in their "hot" counterpart. In particular, by analyzing when the equations of motion exhibit a Hamiltonian structure and when attractors may be present, we identify in which scenarios particle trapping, i.e., the asymptotic convergence of particle trajectories to bounded areas in space ("traps"), can and cannot occur. Our study provides new fundamental insights into active systems realized by self-propelled particles on natural and synthetic disordered substrates.

Design and Computational Fluid Dynamics Investigation of a Personal, High Flow Inhalable Sampler

PubMed Central

Anthony, T. Renée; Landázuri, Andrea C.; Van Dyke, Mike; Volckens, John

2016-01-01

The objective of this research was to develop an inlet to meet the inhalable sampling criterion at 10 l min−1 flow using the standard, 37-mm cassette. We designed a porous head for this cassette and evaluated its performance using computational fluid dynamics (CFD) modeling. Particle aspiration efficiency was simulated in a wind tunnel environment at 0.4 m s−1 freestream velocity for a facing-the-wind orientation, with sampler oriented at both 0° (horizontal) and 30° down angles. The porous high-flow sampler oriented 30° downward showed reasonable agreement with published mannequin wind tunnel studies and humanoid CFD investigations for solid particle aspiration into the mouth, whereas the horizontal orientation resulted in oversampling. Liquid particles were under-aspirated in all cases, however, with 41–84% lower aspiration efficiencies relative to solid particles. A sampler with a single central 15-mm pore at 10 l min−1 was also investigated and was found to match the porous sampler’s aspiration efficiency for solid particles; the single-pore sampler is expected to be more suitable for liquid particle use. PMID:20418278

Colloidal suspensions in external rotating electric field: experimental studies and prospective applications in physics, material science, and biomedicine

NASA Astrophysics Data System (ADS)

Yakovlev, Egor V.; Troshina, Anna V.; Korsakova, Sofia A.; Andronik, Mikhail; Rodionov, Ilya A.; Aliev, Ismail N.; Zaytsev, Kirill I.; Cherkasova, Olga P.; Tuchin, Valery V.; Yurchenko, Stanislav O.

2018-04-01

Colloidal suspensions and tunable self-assembly of colloidal particles attract a great interest in recent years. In this paper, we propose a new setup and technology for studies of self-assembly of colloidal particles, interection of which between themselves is tuned by external rotating electric fields. We reveal wide prospectives of electric field employment for tunable self-assembly, from suspensions of inorganic particles to ensembles of biological cells. These results make enable particle-resolved studies of various collective phenomena and fundamental processes in many-particle systems in equilibrium state and far from it, while the dynamics can be resolved at the level of individual particles using video microscopy. For the first time, we demonstrate that, apart from ability to prepare photonic crystalline films of inorganic silica particles, the tunable self-assembly provides a novel technological way for manipulation with ensembles of biological cells by control of interactions between them.

Hydrodynamic Capture of Particles by Micro-swimmers under Hele-Shaw Flows

NASA Astrophysics Data System (ADS)

Mishler, Grant; Tsang, Alan Cheng Hou; Pak, On Shun

2017-11-01

We explore a hydrodynamic capture mechanism of a driven particle by a micro-swimmer in confined microfluidic environments with an idealized model. The capture is mediated by the hydrodynamic interactions between the micro-swimmer, the driven particle, and the background flow. This capture mechanism relies on the existence of attractive stable equilibrium configurations between the driven particle and the micro-swimmer, which occurs when the background flow is larger than a certain critical threshold. Dynamics and stability of capture and non-capture events will be discussed. This study may have potential applications in the study of capture and delivery of therapeutic payloads by micro-swimmers as well as particle self-assembly under confinements.

Quantum and classical dissipation of charged particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ibarra-Sierra, V.G.; Anzaldo-Meneses, A.; Cardoso, J.L.

2013-08-15

A Hamiltonian approach is presented to study the two dimensional motion of damped electric charges in time dependent electromagnetic fields. The classical and the corresponding quantum mechanical problems are solved for particular cases using canonical transformations applied to Hamiltonians for a particle with variable mass. Green’s function is constructed and, from it, the motion of a Gaussian wave packet is studied in detail. -- Highlights: •Hamiltonian of a damped charged particle in time dependent electromagnetic fields. •Exact Green’s function of a charged particle in time dependent electromagnetic fields. •Time evolution of a Gaussian wave packet of a damped charged particle.more » •Classical and quantum dynamics of a damped electric charge.« less

Dynamics of a suspension of interacting yolk-shell particles

DOE PAGES

Sánchez Díaz, L. E.; Cortes-Morales, E. C.; Li, X.; ...

2014-12-01

In this work we study the self-diusion properties of a liquid of hollow spherical particles (shells) bearing a smaller solid sphere in their interior (yolks). We model this system using purely repulsive hard-body interactions between all (shell and yolk) particles, but assume the presence of a background ideal solvent such that all the particles execute free Brownian motion between collisions, characterized by short-time self-diusion coecients D0 s for the shells and D0 y for the yolks. Using a softened version of these interparticle potentials we perform Brownian dynamics simulations to determine the mean squared displacement and intermediate scattering function ofmore » the yolk-shell complex. These results can be understood in terms of a set of eective Langevin equations for the N interacting shell particles, pre-averaged over the yolks' degrees of freedom, from which an approximate self-consistent description of the simulated self-diusion properties can be derived. Here we compare the theoretical and simulated results between them, and with the results for the same system in the absence of yolks. We nd that the yolks, which have no eect on the shell-shell static structure, in uence the dynamic properties in a predictable manner, fully captured by the theory.« less

Dynamics of cosmological perturbations and reheating in the anamorphic universe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graef, L.L.; Ferreira, Elisa G.M.; Brandenberger, Robert

We discuss scalar-tensor realizations of the Anamorphic cosmological scenario recently proposed by Ijjas and Steinhardt [1]. Through an analysis of the dynamics of cosmological perturbations we obtain constraints on the parameters of the model. We also study gravitational Parker particle production in the contracting Anamorphic phase and we compute the fraction between the energy density of created particles at the end of the phase and the background energy density. We find that, as in the case of inflation, a new mechanism is required to reheat the universe.

A Dynamic Approach to Monitoring Particle Fallout in a Cleanroom Environment

NASA Technical Reports Server (NTRS)

Perry, Radford L., III

2010-01-01

This slide presentation discusses a mathematical model to monitor particle fallout in a cleanroom. "Cleanliness levels" do not lead to increases with regards to cleanroom type or time because the levels are not linear. Activity level, impacts the cleanroom class. The numerical method presented leads to a simple Class-hour formulation, that allows for dynamic monitoring of the particle using a standard air particle counter.

Smoothed-particle hydrodynamics and nonequilibrium molecular dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoover, W. G.; Hoover, C. G.

1993-08-01

Gingold, Lucy, and Monaghan invented a grid-free version of continuum mechanics ``smoothed-particle hydrodynamics,`` in 1977. It is a likely contributor to ``hybrid`` simulations combining atomistic and continuum simulations. We describe applications of this particle-based continuum technique from the closely-related standpoint of nonequilibrium molecular dynamics. We compare chaotic Lyapunov spectra for atomistic solids and fluids with those which characterize a two-dimensional smoothed-particle fluid system.

Beam Dynamics Simulation Platform and Studies of Beam Breakup in Dielectric Wakefield Structures

NASA Astrophysics Data System (ADS)

Schoessow, P.; Kanareykin, A.; Jing, C.; Kustov, A.; Altmark, A.; Gai, W.

2010-11-01

A particle-Green's function beam dynamics code (BBU-3000) to study beam breakup effects is incorporated into a parallel computing framework based on the Boinc software environment, and supports both task farming on a heterogeneous cluster and local grid computing. User access to the platform is through a web browser.

Detecting Interplanetary Dust Particles with Radars to Study the Dynamics at the Edge of the Space

NASA Technical Reports Server (NTRS)

Janches, Diego

2015-01-01

The Earth's mesosphere is the region of the atmosphere between approximately 60-120 km altitude, where the transition from hydrodynamic flow to molecular diffusion occurs. It is highly dynamic region where turbulence by wave braking is produced and energy is deposited from sources from both, below and above this altitude range. Because aircraft and nearly all balloons reach altitudes below approximately 50 km and orbital spacecrafts are well above approximately 400 km, the mesosphere has only been accessed through the use of sounding rockets or remote sensing techniques, and as a result, it is the most poorly understood part of the atmosphere. In addition, millions of Interplanetary Dust Particles (IDPs) enter the atmosphere. Within the mesosphere most of these IDPs melt or vaporize as a result of collisions with the air particles producing meteors that can be detected with radars. This provides a mean to study the dynamics of this region. In this lecture the basic principles of the utilization of meteor radars to study the dynamics of the mesosphere will be presented. A system overview of these systems will be provided as well as discuss the advantages/disadvantages of these systems, provide details of the data processing methodology and give a brief overview of the current status of the field as well as the vision for the next decade.

Phase separation and large deviations of lattice active matter

NASA Astrophysics Data System (ADS)

Whitelam, Stephen; Klymko, Katherine; Mandal, Dibyendu

2018-04-01

Off-lattice active Brownian particles form clusters and undergo phase separation even in the absence of attractions or velocity-alignment mechanisms. Arguments that explain this phenomenon appeal only to the ability of particles to move persistently in a direction that fluctuates, but existing lattice models of hard particles that account for this behavior do not exhibit phase separation. Here we present a lattice model of active matter that exhibits motility-induced phase separation in the absence of velocity alignment. Using direct and rare-event sampling of dynamical trajectories, we show that clustering and phase separation are accompanied by pronounced fluctuations of static and dynamic order parameters. This model provides a complement to off-lattice models for the study of motility-induced phase separation.

A comprehensive study of MPI parallelism in three-dimensional discrete element method (DEM) simulation of complex-shaped granular particles

NASA Astrophysics Data System (ADS)

Yan, Beichuan; Regueiro, Richard A.

2018-02-01

A three-dimensional (3D) DEM code for simulating complex-shaped granular particles is parallelized using message-passing interface (MPI). The concepts of link-block, ghost/border layer, and migration layer are put forward for design of the parallel algorithm, and theoretical scalability function of 3-D DEM scalability and memory usage is derived. Many performance-critical implementation details are managed optimally to achieve high performance and scalability, such as: minimizing communication overhead, maintaining dynamic load balance, handling particle migrations across block borders, transmitting C++ dynamic objects of particles between MPI processes efficiently, eliminating redundant contact information between adjacent MPI processes. The code executes on multiple US Department of Defense (DoD) supercomputers and tests up to 2048 compute nodes for simulating 10 million three-axis ellipsoidal particles. Performance analyses of the code including speedup, efficiency, scalability, and granularity across five orders of magnitude of simulation scale (number of particles) are provided, and they demonstrate high speedup and excellent scalability. It is also discovered that communication time is a decreasing function of the number of compute nodes in strong scaling measurements. The code's capability of simulating a large number of complex-shaped particles on modern supercomputers will be of value in both laboratory studies on micromechanical properties of granular materials and many realistic engineering applications involving granular materials.

Simulations of particle structuring driven by electric fields

NASA Astrophysics Data System (ADS)

Hu, Yi; Vlahovska, Petia; Miksis, Michael

2015-11-01

Recent experiments (Ouriemi and Vlahovska, 2014) show intriguing surface patterns when a uniform electric field is applied to a droplet covered with colloidal particles. Depending on the particle properties and the electric field intensity, particles organize into an equatorial belt, pole-to-pole chains, or dynamic vortices. Here we present 3D simulations of the collective particle dynamics, which account for electrohydrodynamic flow and dielectrophoresis of particles. In stronger electric fields, particles are expected to undergo Quincke rotation and impose disturbance to the ambient flow. Transition from ribbon-shaped belt to rotating clusters is observed in the presence of the rotation-induced hydrodynamical interactions. Our results provide insight into the various particle assembles discovered in the experiments.

Rheology of U-Shaped Granular Particles

NASA Astrophysics Data System (ADS)

Hill, Matthew; Franklin, Scott

We study the response of cylindrical samples of U-shaped granular particles (staples) to extensional loads. Samples elongate in discrete bursts (events) corresponding to particles rearranging and re-entangling. Previous research on samples of constant cross-sectional area found a Weibullian weakest-link theory could explain the distribution of yield points. We now vary the cross-sectional area, and find that the maximum yield pressure (force/area) is a function of particle number density and independent of area. The probability distribution function of important event characteristics -- the stress increase before an event and stress released during an event -- both fall of inversely with magnitude, reminiscent of avalanche dynamics. Fourier transforms of the fluctuating force (or stress) scales inversely with frequency, suggesting dry friction plays a role in the rearrangements. Finally, there is some evidence that dynamics are sensitive to the stiffness of the tensile testing machine, although an explanation for this behavior is unknown.

Brownian Dynamics of Colloidal Particles in Lyotropic Chromonic Liquid Crystals

NASA Astrophysics Data System (ADS)

Martinez, Angel; Collings, Peter J.; Yodh, Arjun G.

We employ video microscopy to study the Brownian dynamics of colloidal particles in the nematic phase of lyotropic chromonic liquid crystals (LCLCs). These LCLCs (in this case, DSCG) are water soluble, and their nematic phases are characterized by an unusually large elastic anisotropy. Our preliminary measurements of particle mean-square displacement for polystyrene colloidal particles (~5 micron-diameter) show diffusive and sub-diffusive behaviors moving parallel and perpendicular to the nematic director, respectively. In order to understand these motions, we are developing models that incorporate the relaxation of elastic distortions of the surrounding nematic field. Further experiments to confirm these preliminary results and to determine the origin of these deviations compared to simple diffusion theory are ongoing; our results will also be compared to previous diffusion experiments in nematic liquid crystals. We gratefully acknowledge financial support through NSF DMR12-05463, MRSEC DMR11-20901, and NASA NNX08AO0G.

Numerical simulations of particle orbits around 2060 Chiron

NASA Technical Reports Server (NTRS)

Stern, S. A.; Jackson, A. A.; Boice, D. C.

1994-01-01

Scattered light from orbiting or coorbiting dust is a primary signature by which Earth-based observers study the activity and atmosphere of the unusual outer solar system object 2060 Chiron. Therefore, it is important to understand the lifetime, dynamics, and loss rates of dust in its coma. We report here dynamical simulations of particles in Chiron's collisionless coma. The orbits of 17,920 dust particles were numerically integrated under the gravitational influence of Chiron, the Sun, and solar radiation pressure. These simulations show that particles ejected from Chiron are more likely to follow suborbital trajectories, or to escape altogether, than to enter quasistable orbits. Significant orbital lifetimes can only be achieved for very specific launch conditions. These results call into question models of a long-term, bound coma generated by discrete outbursts, and instead suggest that Chiron's coma state is closely coupled to the nearly instantaneous level of Chiron's surface activity.

Heterogeneous Nucleation of Trichloroethylene Ozonation Products in the Formation of New Fine Particles

NASA Astrophysics Data System (ADS)

Wang, Ning; Sun, Xiaomin; Chen, Jianmin; Li, Xiang

2017-02-01

Free radicals in atmosphere have played an important role in the atmospheric chemistry. The chloro-Criegee free radicals are produced easily in the decomposition of primary ozonide (POZ) of the trichloroethylene, and can react with O2, NO, NO2, SO2 and H2O subsequently. Then the inorganic salts, polar organic nitrogen and organic sulfur compounds, oxygen-containing heterocyclic intermediates and polyhydroxy compounds can be obtained. The heterogeneous nucleation of oxidation intermediates in the formation of fine particles is investigated using molecular dynamics simulation. The detailed nucleation processes are reported. According to molecular dynamics simulation, the nucleation with a diameter of 2 nm is formed in the Organic Compounds-(NH4)2SO4-H2O system. The spontaneous nucleation is an important process in the formation of fine particles in atmosphere. The model study gives a good example from volatile organic compounds to new fine particles.

Brownian Dynamics simulations of model colloids in channel geometries and external fields

NASA Astrophysics Data System (ADS)

Siems, Ullrich; Nielaba, Peter

2018-04-01

We review the results of Brownian Dynamics simulations of colloidal particles in external fields confined in channels. Super-paramagnetic Brownian particles are well suited two- dimensional model systems for a variety of problems on different length scales, ranging from pedestrian walking through a bottleneck to ions passing ion-channels in living cells. In such systems confinement into channels can have a great influence on the diffusion and transport properties. Especially we will discuss the crossover from single file diffusion in a narrow channel to the diffusion in the extended two-dimensional system. Therefore a new algorithm for computing the mean square displacement (MSD) on logarithmic time scales is presented. In a different study interacting colloidal particles were dragged over a washboard potential and are additionally confined in a two-dimensional micro-channel. In this system kink and anti-kink solitons determine the depinning process of the particles from the periodic potential.

Snakes on a plane: modeling flexible active nematics

NASA Astrophysics Data System (ADS)

Selinger, Robin

Active soft matter systems of self-propelled rod-shaped particles exhibit ordered phases and collective behavior that are remarkably different from their passive analogs. In nature, many self-propelled rod-shaped particles, such as gliding bacteria and kinesin-driven microtubules, are flexible and can bend. We model these ``living liquid crystals'' to explore their phase behavior, dynamics, and pattern formation. We model particles as short polymers via molecular dynamics with a Langevin thermostat and various types of activity, substrate, and environments. For self-propelled polar particles gliding on a solid substrate, we map out the phase diagram as a function of particle density and flexibility. We compare simulated defect structures to those observed in colonies of gliding myxobacteria; compare spooling behavior to that observed in microtubule gliding assays; and analyze emergence of nematic and polar order. Next we explore pattern formation of self-propelled polar particles under flexible encapsulation, and on substrates with non-uniform Gaussian curvature. Lastly, we impose an activity mechanism that mimics extensile shear, study flexible particles both on solid substrates and coupled to a lipid membrane, and discuss comparisons to relevant experiments. Work performed in collaboration with Michael Varga (Kent State) and Luca Giomi (Universiteit Leiden.) Work supported by NSF DMR-1409658.

Shape-dependent guidance of active Janus particles by chemically patterned surfaces

NASA Astrophysics Data System (ADS)

Uspal, W. E.; Popescu, M. N.; Tasinkevych, M.; Dietrich, S.

2018-01-01

Self-phoretic chemically active Janus particles move by inducing—via non-equilibrium chemical reactions occurring on their surfaces—changes in the chemical composition of the solution in which they are immersed. This process leads to gradients in chemical composition along the surface of the particle, as well as along any nearby boundaries, including solid walls. Chemical gradients along a wall can give rise to chemi-osmosis, i.e., the gradients drive surface flows which, in turn, drive flow in the volume of the solution. This bulk flow couples back to the particle, and thus contributes to its self-motility. Since chemi-osmosis strongly depends on the molecular interactions between the diffusing molecular species and the wall, the response flow induced and experienced by a particle encodes information about any chemical patterning of the wall. Here, we extend previous studies on self-phoresis of a sphere near a chemically patterned wall to the case of particles with rod-like, elongated shape. We focus our analysis on the new phenomenology potentially emerging from the coupling—which is inoperative for a spherical shape—of the elongated particle to the strain rate tensor of the chemi-osmotic flow. Via detailed numerical calculations, we show that the dynamics of a rod-like particle exhibits a novel ‘edge-following’ steady state: the particle translates along the edge of a chemical step at a steady distance from the step and with a steady orientation. Moreover, within a certain range of system parameters, the edge-following state co-exists with a ‘docking’ state (the particle stops at the step, oriented perpendicular to the step edge), i.e., a bistable dynamics occurs. These findings are rationalized as a consequence of the competition between the fluid vorticity and the rate of strain by using analytical theory based on the point-particle approximation which captures quasi-quantitatively the dynamics of the system.

Molecular dynamics simulation of highly charged proteins: Comparison of the particle-particle particle-mesh and reaction field methods for the calculation of electrostatic interactions

PubMed Central

Gargallo, Raimundo; Hünenberger, Philippe H.; Avilés, Francesc X.; Oliva, Baldomero

2003-01-01

Molecular dynamics (MD) simulations of the activation domain of porcine procarboxypeptidase B (ADBp) were performed to examine the effect of using the particle-particle particle-mesh (P3M) or the reaction field (RF) method for calculating electrostatic interactions in simulations of highly charged proteins. Several structural, thermodynamic, and dynamic observables were derived from the MD trajectories, including estimated entropies and solvation free energies and essential dynamics (ED). The P3M method leads to slightly higher atomic positional fluctuations and deviations from the crystallographic structure, along with somewhat lower values of the total energy and solvation free energy. However, the ED analysis of the system leads to nearly identical results for both simulations. Because of the strong similarity between the results, both methods appear well suited for the simulation of highly charged globular proteins in explicit solvent. However, the lower computational demand of the RF method in the present implementation represents a clear advantage over the P3M method. PMID:14500874

Kinematic Model of Transient Shape-Induced Anisotropy in Dense Granular Flow

NASA Astrophysics Data System (ADS)

Nadler, B.; Guillard, F.; Einav, I.

2018-05-01

Nonspherical particles are ubiquitous in nature and industry, yet previous theoretical models of granular media are mostly limited to systems of spherical particles. The problem is that in systems of nonspherical anisotropic particles, dynamic particle alignment critically affects their mechanical response. To study the tendency of such particles to align, we propose a simple kinematic model that relates the flow to the evolution of particle alignment with respect to each other. The validity of the proposed model is supported by comparison with particle-based simulations for various particle shapes ranging from elongated rice-like (prolate) to flattened lentil-like (oblate) particles. The model shows good agreement with the simulations for both steady-state and transient responses, and advances the development of comprehensive constitutive models for shape-anisotropic particles.

Modeling of conductive particle motion in viscous medium affected by an electric field considering particle-electrode interactions and microdischarge phenomenon

NASA Astrophysics Data System (ADS)

Eslami, Ghiyam; Esmaeilzadeh, Esmaeil; Pérez, Alberto T.

2016-10-01

Up and down motion of a spherical conductive particle in dielectric viscous fluid driven by a DC electric field between two parallel electrodes was investigated. A nonlinear differential equation, governing the particle dynamics, was derived, based on Newton's second law of mechanics, and solved numerically. All the pertaining dimensionless groups were extracted. In contrast to similar previous works, hydrodynamic interaction between the particle and the electrodes, as well as image electric forces, has been taken into account. Furthermore, the influence of the microdischarge produced between the electrodes and the approaching particle on the particle dynamics has been included in the model. The model results were compared with experimental data available in the literature, as well as with some additional experimental data obtained through the present study showing very good agreement. The results indicate that the wall hydrodynamic effect and the dielectric liquid ionic conductivity are very dominant factors determining the particle trajectory. A lower bound is derived for the charge transferred to the particle while rebounding from an electrode. It is found that the time and length scales of the post-microdischarge motion of the particle can be as small as microsecond and micrometer, respectively. The model is able to predict the so called settling/dwelling time phenomenon for the first time.

The ALTEA/ALTEINO projects: studying functional effects of microgravity and cosmic radiation

NASA Technical Reports Server (NTRS)

Narici, L.; Belli, F.; Bidoli, V.; Casolino, M.; De Pascale, M. P.; Di Fino, L.; Furano, G.; Modena, I.; Morselli, A.; Picozza, P.;

The ALTEA/ALTEINO projects: studying functional effects of microgravity and cosmic radiation.

PubMed

Narici, L; Belli, F; Bidoli, V; Casolino, M; De Pascale, M P; Di Fino, L; Furano, G; Modena, I; Morselli, A; Picozza, P; Reali, E; Rinaldi, A; Ruggieri, D; Sparvoli, R; Zaconte, V; Sannita, W G; Carozzo, S; Licoccia, S; Romagnoli, P; Traversa, E; Cotronei, V; Vazquez, M; Miller, J; Salnitskii, V P; Shevchenko, O I; Petrov, V P; Trukhanov, K A; Galper, A; Khodarovich, A; Korotkov, M G; Popov, A; Vavilov, N; Avdeev, S; Boezio, M; Bonvicini, W; Vacchi, A; Zampa, N; Mazzenga, G; Ricci, M; Spillantini, P; Castellini, G; Vittori, R; Carlson, P; Fuglesang, C; Schardt, D

2004-01-01

The ALTEA project investigates the risks of functional brain damage induced by particle radiation in space. A modular facility (the ALTEA facility) is being implemented and will be operated in the International Space Station (ISS) to record electrophysiological and behavioral descriptors of brain function and to monitor their time dynamics and correlation with particles and space environment. The focus of the program will be on abnormal visual perceptions (often reported as "light flashes" by astronauts) and the impact on retinal and brain visual structures of particle in microgravity conditions. The facility will be made available to the international scientific community for human neurophysiological, electrophysiological and psychophysics experiments, studies on particle fluxes, and dosimetry. A precursor of ALTEA (the 'Alteino' project) helps set the experimental baseline for the ALTEA experiments, while providing novel information on the radiation environment onboard the ISS and on the brain electrophysiology of the astronauts during orbital flights. Alteino was flown to the ISS on the Soyuz TM34 as part of mission Marco Polo. Controlled ground experiments using mice and accelerator beams complete the experimental strategy of ALTEA. We present here the status of progress of the ALTEA project and preliminary results of the Alteino study on brain dynamics, particle fluxes and abnormal visual perceptions. c2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

Opening and retraction of particulate soap films

NASA Astrophysics Data System (ADS)

Timounay, Yousra; Lorenceau, Elise; Rouyer, Florence

2015-07-01

We study for the first time the bursting dynamics of thin liquid films laden with hydrophobic micronic particles either with free or constrained edges. We highlight that the particles can arrange in bilayer or monolayer configurations and explore a range of particles coverage from zero to random close packing. When the particles bridge the two interfaces (monolayer configuration) of free-edge films, the hole opens intermittently. For the other cases, we observe constant retraction velocities, modeled by balancing liquid and particles inertia against surface tension as in Taylor-Culick theory. But, this approach is only valid up to a critical value of particles coverage due to the interplay between the interfaces and the friction between particles.

Dynamics of planetary rings

NASA Technical Reports Server (NTRS)

Araki, Suguru

1991-01-01

The modeling of the dynamics of particle collisions within planetary rings is discussed. Particles in the rings collide with one another because they have small random motions in addition to their orbital velocity. The orbital speed is roughly 10 km/s, while the random motions have an average speed of about a tenth of a millimeter per second. As a result, the particle collisions are very gentle. Numerical analysis and simulation of the ring dynamics, performed with the aid of a supercomputer, is outlined.

Particle based plasma simulation for an ion engine discharge chamber

NASA Astrophysics Data System (ADS)

Mahalingam, Sudhakar

Design of the next generation of ion engines can benefit from detailed computer simulations of the plasma in the discharge chamber. In this work a complete particle based approach has been taken to model the discharge chamber plasma. This is the first time that simplifying continuum assumptions on the particle motion have not been made in a discharge chamber model. Because of the long mean free paths of the particles in the discharge chamber continuum models are questionable. The PIC-MCC model developed in this work tracks following particles: neutrals, singly charged ions, doubly charged ions, secondary electrons, and primary electrons. The trajectories of these particles are determined using the Newton-Lorentz's equation of motion including the effects of magnetic and electric fields. Particle collisions are determined using an MCC statistical technique. A large number of collision processes and particle wall interactions are included in the model. The magnetic fields produced by the permanent magnets are determined using Maxwell's equations. The electric fields are determined using an approximate input electric field coupled with a dynamic determination of the electric fields caused by the charged particles. In this work inclusion of the dynamic electric field calculation is made possible by using an inflated plasma permittivity value in the Poisson solver. This allows dynamic electric field calculation with minimal computational requirements in terms of both computer memory and run time. In addition, a number of other numerical procedures such as parallel processing have been implemented to shorten the computational time. The primary results are those modeling the discharge chamber of NASA's NSTAR ion engine at its full operating power. Convergence of numerical results such as total number of particles inside the discharge chamber, average energy of the plasma particles, discharge current, beam current and beam efficiency are obtained. Steady state results for the particle number density distributions and particle loss rates to the walls are presented. Comparisons of numerical results with experimental measurements such as currents and the particle number density distributions are made. Results from a parametric study and from an alternative magnetic field design are also given.

Self-consistent Simulation of Microparticle and Ion Wakefield Configuration

NASA Astrophysics Data System (ADS)

Sanford, Dustin; Brooks, Beau; Ellis, Naoki; Matthews, Lorin; Hyde, Truell

2017-10-01

In a complex plasma, positively charged ions often have a directed flow with respect to the negatively charged dust grains. The resulting interaction between the dust and the flowing plasma creates an ion wakefield downstream from the dust particles, with the resulting positive space region modifying the interaction between the grains and contributing to the observed dynamics and equilibrium structure of the system. Here we present a proof of concept method that uses a molecular dynamics simulation to model the ion wakefield allowing the dynamics of the dust particles to be determined self-consistently. The trajectory of each ion is calculated including the forces from all other ions, which are treated as ``Yukawa particles'' and shielded from thermal electrons and the forces of the charged dust particles. Both the dust grain charge and the wakefield structure are also self-consistently determined for various particle configurations. The resultant wakefield potentials are then used to provide dynamic simulations of dust particle pairs. These results will be employed to analyze the formation and dynamics of field-aligned chains in CASPER's PK4 experiment onboard the International Space Station, allowing examination of extended dust chains without the masking force of gravity. This work was supported by the National Science Foundation under Grants PHY-1414523 and PHY-1740203.

The Million-Body Problem: Particle Simulations in Astrophysics

ScienceCinema

Rasio, Fred

2018-05-21

Computer simulations using particles play a key role in astrophysics. They are widely used to study problems across the entire range of astrophysical scales, from the dynamics of stars, gaseous nebulae, and galaxies, to the formation of the largest-scale structures in the universe. The 'particles' can be anything from elementary particles to macroscopic fluid elements, entire stars, or even entire galaxies. Using particle simulations as a common thread, this talk will present an overview of computational astrophysics research currently done in our theory group at Northwestern. Topics will include stellar collisions and the gravothermal catastrophe in dense star clusters.

Cementation of colloidal particles on electrodes in a galvanic microreactor.

PubMed

Jan, Linda; Punckt, Christian; Aksay, Ilhan A

2013-07-10

We have studied the processes leading to the cementation of colloidal particles during their autonomous assembly on corroding copper electrodes within a Cu-Au galvanic microreactor. We determined the onset of particle immobilization through particle tracking, monitored the dissolution of copper as well as the deposition of insoluble products of the corrosion reactions in situ, and showed that particle immobilization initiated after reaction products (RPs) began to deposit on the electrode substrate. We further demonstrated that the time and the extent of RP precipitation and thus the strength of the particle-substrate bond could be tuned by varying the amount of copper in the system and the microreactor pH. The ability to cement colloidal particles at locations undergoing corrosion illustrates that the studied colloidal assembly approach holds potential for applications in dynamic material property adaptation.

A review of our understanding of the aerosol-cloud interaction from the perspective of a bin resolved cloud scale modelling

NASA Astrophysics Data System (ADS)

Flossmann, Andrea I.; Wobrock, Wolfram

2010-09-01

This review compiles the main results obtained using a mesoscale cloud model with bin resolved cloud micophysics and aerosol particle scavenging, as developed by our group over the years and applied to the simulation of shallow and deep convective clouds. The main features of the model are reviewed in different dynamical frameworks covering parcel model dynamics, as well as 1.5D, 2D and 3D dynamics. The main findings are summarized to yield a digested presentation which completes the general understanding of cloud-aerosol interaction, as currently available from textbook knowledge. Furthermore, it should provide support for general cloud model development, as it will suggest potentially minor processes that might be neglected with respect to more important ones and can support development of parameterizations for air quality, chemical transport and climate models. Our work has shown that in order to analyse dedicated campaign results, the supersaturation field and the complex dynamics of the specific clouds needs to be reproduced. Only 3D dynamics represents the variation of the supersaturation over the entire cloud, the continuous nucleation and deactivation of hydrometeors, and the dependence upon initial particle size distribution and solubility. However, general statements on certain processes can be obtained also by simpler dynamics. In particular, we found: Nucleation incorporates about 90% of the initial aerosol particle mass inside the cloud drops. Collision and coalescence redistributes the scavenged aerosol particle mass in such a way that the particle mass follows the main water mass. Small drops are more polluted than larger ones, as pollutant mass mixing ratio decreases with drops size. Collision and coalescence mixes the chemical composition of the generated drops. Their complete evaporation will release processed particles that are mostly larger and more hygroscopic than the initial particles. An interstitial aerosol is left unactivated between the cloud drops which is reduced in number and almost devoid of large particles. Consequently, impaction scavenging can probably be neglected inside clouds. Below clouds, impaction scavenging contributes around 30% to the particle mass reaching the ground by a rainfall event. The exact amount depends on the precise case studied. Nucleation and impaction scavenging directly by the ice phase in mixed phase clouds seems to play a minor role with respect to the particle mass that enters the ice particles via freezing of the liquid phase.The aerosol scavenging efficiency generally follows rather closely the precipitation scavenging value. The nucleation scavenging efficiency is around 90% for the liquid phase clouds and impaction scavenging generally contributed to about 30% of the particle mass in the rain. Clouds are very efficient in pumping up the boundary layer aerosol which essentially determines the cloud properties. For a marine case studied the net pumping depleted about 70% of the aerosol from the section of the boundary layer considered. The larger particles (and thus 70% of the mass vented up) got activated inside the cloud. A weak net import through cloud top and the upwind side was found, as well as a larger net export at the downwind side. The outside cloud subsidence can add to the replenishment of the boundary layer and eventually cause a recycling of the particles into the cloud. The results of the parcel model studies seem to indicate that increasing particulate pollution and decreasing solubility suppresses rain formation. In individual and short time cloud simulations this behaviour was even confirmed in our 3D model studies. However, taking into account entire cloud fields over longer periods of time yields the strong spatial and temporal variability of the results with isolated regions of inverse correlation of the effects. Even though in general initially the expected behaviour was found, after several hours of simulation, the overall precipitation amounts of the more polluted cases caught up. This suggests that a changing pollution will affect the spatial and temporal pattern of precipitation, but will probably not reduce the overall long term precipitation amount which might be entirely governed by the moisture state of the atmosphere. Our results regarding mixed phase precipitation with respect to "all liquid" cases seem to confirm this idea, as with increasing modelling time the precipitation mass of both cases also become similar.

Cloud-In-Cell modeling of shocked particle-laden flows at a ``SPARSE'' cost

NASA Astrophysics Data System (ADS)

Taverniers, Soren; Jacobs, Gustaaf; Sen, Oishik; Udaykumar, H. S.

2017-11-01

A common tool for enabling process-scale simulations of shocked particle-laden flows is Eulerian-Lagrangian Particle-Source-In-Cell (PSIC) modeling where each particle is traced in its Lagrangian frame and treated as a mathematical point. Its dynamics are governed by Stokes drag corrected for high Reynolds and Mach numbers. The computational burden is often reduced further through a ``Cloud-In-Cell'' (CIC) approach which amalgamates groups of physical particles into computational ``macro-particles''. CIC does not account for subgrid particle fluctuations, leading to erroneous predictions of cloud dynamics. A Subgrid Particle-Averaged Reynolds-Stress Equivalent (SPARSE) model is proposed that incorporates subgrid interphase velocity and temperature perturbations. A bivariate Gaussian source distribution, whose covariance captures the cloud's deformation to first order, accounts for the particles' momentum and energy influence on the carrier gas. SPARSE is validated by conducting tests on the interaction of a particle cloud with the accelerated flow behind a shock. The cloud's average dynamics and its deformation over time predicted with SPARSE converge to their counterparts computed with reference PSIC models as the number of Gaussians is increased from 1 to 16. This work was supported by AFOSR Grant No. FA9550-16-1-0008.

Correlation between Surface Tension and Water Activity in New Particle Formation

NASA Astrophysics Data System (ADS)

Daskalakis, E.; Salameh, A.

2016-12-01

The impact of aerosol properties on cloud dynamics and the radiative balance of the atmosphere relies on the parametrizations of cloud droplet formation. Such parametrization is based on equilibrium thermodynamics proposed by Köhler in 1936. There is considerable debate in the literature on the importance of factors like the surface tension depression or the water activity decrease for the correct parametrization. To gain fundamental insight into New Particle Formation (NPF), or Cloud Condensation Nuclei (CCN) activation one has to study microscopic properties of aqueous droplets, involving surface and bulk dynamics. The surface tension of droplets can be associated with the effects from Organic Matter (OM), whereas the static dielectric constant of water reflects the structure and dynamics of ions within solutions and can present a measure of water activity. In this study we employ Molecular Dynamics Simulations on aquatic droplets that contain surface active OM (acetaldehyde, methylglyoxal) and salts. We give insight into the dynamics of aquatic droplets with radials of 3.6nm at a level of detail that is not accessible experimentally (J. Phys. Chem. C 2016, 120:11508). We propose that as the surface tension of an aquatic droplet is decreased in the presence of surface-active OM, the water activity is affected as well. This is due to the fact that the water dipoles are oriented based on the salt morphology within the droplet. We suggest that the surface tension depression can be accompanied by the water activity change. This can be associated with the possible effects of surface-active species in terms of salt morphology transitions within an aerosol at the NPF and early particle growth time scales. Based on this study, surface-active OM seems important in controlling (a) the salt morphology transitions within a nucleus during NPF and particle growth and (b) a correlation between surface activity and water activity of ionic aquatic droplets. The latter correlation could be a fundamental property to consider when assessing NPF and the Köhler theory.

Multiscale modeling of particle in suspension with smoothed dissipative particle dynamics

NASA Astrophysics Data System (ADS)

Bian, Xin; Litvinov, Sergey; Qian, Rui; Ellero, Marco; Adams, Nikolaus A.

2012-01-01

We apply smoothed dissipative particle dynamics (SDPD) [Español and Revenga, Phys. Rev. E 67, 026705 (2003)] to model solid particles in suspension. SDPD is a thermodynamically consistent version of smoothed particle hydrodynamics (SPH) and can be interpreted as a multiscale particle framework linking the macroscopic SPH to the mesoscopic dissipative particle dynamics (DPD) method. Rigid structures of arbitrary shape embedded in the fluid are modeled by frozen particles on which artificial velocities are assigned in order to satisfy exactly the no-slip boundary condition on the solid-liquid interface. The dynamics of the rigid structures is decoupled from the solvent by solving extra equations for the rigid body translational/angular velocities derived from the total drag/torque exerted by the surrounding liquid. The correct scaling of the SDPD thermal fluctuations with the fluid-particle size allows us to describe the behavior of the particle suspension on spatial scales ranging continuously from the diffusion-dominated regime typical of sub-micron-sized objects towards the non-Brownian regime characterizing macro-continuum flow conditions. Extensive tests of the method are performed for the case of two/three dimensional bulk particle-system both in Brownian/ non-Brownian environment showing numerical convergence and excellent agreement with analytical theories. Finally, to illustrate the ability of the model to couple with external boundary geometries, the effect of confinement on the diffusional properties of a single sphere within a micro-channel is considered, and the dependence of the diffusion coefficient on the wall-separation distance is evaluated and compared with available analytical results.

A 3-D model of tumor progression based on complex automata driven by particle dynamics.

PubMed

Wcisło, Rafał; Dzwinel, Witold; Yuen, David A; Dudek, Arkadiusz Z

2009-12-01

The dynamics of a growing tumor involving mechanical remodeling of healthy tissue and vasculature is neglected in most of the existing tumor models. This is due to the lack of efficient computational framework allowing for simulation of mechanical interactions. Meanwhile, just these interactions trigger critical changes in tumor growth dynamics and are responsible for its volumetric and directional progression. We describe here a novel 3-D model of tumor growth, which combines particle dynamics with cellular automata concept. The particles represent both tissue cells and fragments of the vascular network. They interact with their closest neighbors via semi-harmonic central forces simulating mechanical resistance of the cell walls. The particle dynamics is governed by both the Newtonian laws of motion and the cellular automata rules. These rules can represent cell life-cycle and other biological interactions involving smaller spatio-temporal scales. We show that our complex automata, particle based model can reproduce realistic 3-D dynamics of the entire system consisting of the tumor, normal tissue cells, blood vessels and blood flow. It can explain phenomena such as the inward cell motion in avascular tumor, stabilization of tumor growth by the external pressure, tumor vascularization due to the process of angiogenesis, trapping of healthy cells by invading tumor, and influence of external (boundary) conditions on the direction of tumor progression. We conclude that the particle model can serve as a general framework for designing advanced multiscale models of tumor dynamics and it is very competitive to the modeling approaches presented before.

Molecular Dynamics Simulations of Carbon Nanotubes in Water

NASA Technical Reports Server (NTRS)

Walther, J. H.; Jaffe, R.; Halicioglu, T.; Koumoutsakos, P.

2000-01-01

We study the hydrophobic/hydrophilic behavior of carbon nanotubes using molecular dynamics simulations. The energetics of the carbon-water interface are mainly dispersive but in the present study augmented with a carbon quadrupole term acting on the charge sites of the water. The simulations indicate that this contribution is negligible in terms of modifying the structural properties of water at the interface. Simulations of two carbon nanotubes in water display a wetting and drying of the interface between the nanotubes depending on their initial spacing. Thus, initial tube spacings of 7 and 8 A resulted in a drying of the interface whereas spacing of > 9 A remain wet during the course of the simulation. Finally, we present a novel particle-particle-particle-mesh algorithm for long range potentials which allows for general (curvilinear) meshes and "black-box" fast solvers by adopting an influence matrix technique.

Interaction of PLGA and trimethyl chitosan modified PLGA nanoparticles with mixed anionic/zwitterionic phospholipid bilayers studied using molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Novak, Brian; Astete, Carlos; Sabliov, Cristina; Moldovan, Dorel

2012-02-01

Poly(lactic-co-glycolic acid) (PLGA) is a biodegradable polymer. Nanoparticles of PLGA are commonly used for drug delivery applications. The interaction of the nanoparticles with the cell membrane may influence the rate of their uptake by cells. Both PLGA and cell membranes are negatively charged, so adding positively charged polymers such as trimethyl chitosan (TMC) which adheres to the PLGA particles improves their cellular uptake. The interaction of 3 nm PLGA and TMC-modified-PLGA nanoparticles with lipid bilayers composed of mixtures of phosphatidylcholine and phosphatidylserine lipids was studied using molecular dynamics simulations. The free energy profiles as function of nanoparticles position along the normal direction to the bilayers were calculated, the distribution of phosphatidylserine lipids as a function of distance of the particle from the bilayer was calculated, and the time scale for particle motion in the directions parallel to the bilayer surface was estimated.

Calculated high-pressure structural properties, lattice dynamics and quasi particle band structures of perovskite fluorides KZnF3, CsCaF3 and BaLiF3

NASA Astrophysics Data System (ADS)

Vaitheeswaran, G.; Kanchana, V.; Zhang, Xinxin; Ma, Yanming; Svane, A.; Christensen, N. E.

2016-08-01

A detailed study of the high-pressure structural properties, lattice dynamics and band structures of perovskite structured fluorides KZnF3, CsCaF3 and BaLiF3 has been carried out by means of density functional theory. The calculated structural properties including elastic constants and equation of state agree well with available experimental information. The phonon dispersion curves are in good agreement with available experimental inelastic neutron scattering data. The electronic structures of these fluorides have been calculated using the quasi particle self-consistent GW approximation. The GW calculations reveal that all the fluorides studied are wide band gap insulators, and the band gaps are significantly larger than those obtained by the standard local density approximation, thus emphasizing the importance of quasi particle corrections in perovskite fluorides.

Calculated high-pressure structural properties, lattice dynamics and quasi particle band structures of perovskite fluorides KZnF3, CsCaF3 and BaLiF3.

PubMed

Vaitheeswaran, G; Kanchana, V; Zhang, Xinxin; Ma, Yanming; Svane, A; Christensen, N E

2016-08-10

A detailed study of the high-pressure structural properties, lattice dynamics and band structures of perovskite structured fluorides KZnF3, CsCaF3 and BaLiF3 has been carried out by means of density functional theory. The calculated structural properties including elastic constants and equation of state agree well with available experimental information. The phonon dispersion curves are in good agreement with available experimental inelastic neutron scattering data. The electronic structures of these fluorides have been calculated using the quasi particle self-consistent [Formula: see text] approximation. The [Formula: see text] calculations reveal that all the fluorides studied are wide band gap insulators, and the band gaps are significantly larger than those obtained by the standard local density approximation, thus emphasizing the importance of quasi particle corrections in perovskite fluorides.

MRI Measurements and Granular Dynamics Simulation of Segregation of Granular Mixture

NASA Technical Reports Server (NTRS)

Nakagawa, M.; Moss, Jamie L.; Altobelli, Stephen A.

1999-01-01

A counter intuitive axial segregation phenomenon in a rotating horizontal cylinder has recently captured attention of many researchers in different disciplines. There is a growing consensus that the interplay between the particle dynamics and the evolution of the internal structure during the segregation process must be carefully investigated. Magnetic resonance imaging (MRI) has been used to non-invasively obtain much needed dynamic/static information such as velocity and concentration profiles, and it has proven to be capable of depicting the evolution of segregation processes. Segregation in a rotating cylinder involves two processes: the first is to transport small particles in the radial direction to form a radial core, and the second is to transform the radial core into axially segregated bands. Percolation and/or "stopping" have been proposed as mechanisms for the radial segregation. As to mechanisms for axial band formation, much less is known. The difference in the dynamic angle of repose has been proposed to segregate different components in the axial direction. Recently, Hill and Kakalios have reported that particles mix or demix depending upon the competition between diffusion and preferential drift whose order can be determined by the dynamic angle of repose through the adjustment of the rotation rate. We claim that the dynamic angle of repose could be one of the causes, however, it fails to offer reasonable explanations for certain aspects of the axial migration. For example, we always observe that the radial segregation precedes the axial segregation and small particles migrate in the radial direction to form an axially extended radial core. It then transforms into axially segregated bands. By definition, the effects of the dynamic angle of repose are restricted near the free surface where the flowing layer is present. However, during the process of transforming from the radially segregated core to axially segregated bands, small particles located in the deep core region, which is untouched by the flowing layer, also completely disappear. Usually, the dynamics angle of repose are uniquely defined for individual species to characterize particle properties, and the dynamic angle of repose thus defined provides little information for the dynamic angle of repose of the mixture since the concentration ratio and the internal packing structure do not remain the same during the segregation processes. Under microgravity environment, the dynamics angle of repose argument does not hold since there is simply no flowing layer to influence/determine the preferred directions of segregation. We have thus designed an experiment so that the effects of the dynamic angle of repose can be minimized by filling the cylinder almost completely full. Small particles still formed a radial core and also migrated to form axial bands. As ground based experiments we have designed and conducted both 2D and 3D segregation experiments. The 2D experiments are performed using a thin cylinder (the gap between two end caps is about 5 mm) filled with different combinations of particles. The 3D experiments are conducted with a long cylinder of its length and diameter of 27cm and 7cm, respectively. Results of 2D experiments indicate that different mechanisms govern particle motion in regions near and far from the axis of rotation. Results of 3D experiments indicate that a series of collapses of microstructures of particle packing (micro-collapses) may be responsible for the creation of voids for small particles to migrate through in the axial direction. We have successfully eliminated the dynamic angle of repose as a cause for segregation, however, by almost completely filling the cylinder with the particles, we have lost an opportunity to investigate a possibility of particle "mobility" being a cause for segregation which requires a flowing surface but not the difference in the angle of repose. This is currently being investigated.

Dynamics and structure of an aging binary colloidal glass

NASA Astrophysics Data System (ADS)

Lynch, Jennifer M.; Cianci, Gianguido C.; Weeks, Eric R.

2008-09-01

We study aging in a colloidal suspension consisting of micron-sized particles in a liquid. This system is made glassy by increasing the particle concentration. We observe samples composed of particles of two sizes, with a size ratio of 1:2.1 and a volume fraction ratio 1:6, using fast laser scanning confocal microscopy. This technique yields real-time, three-dimensional movies deep inside the colloidal glass. Specifically, we look at how the size, motion, and structural organization of the particles relate to the overall aging of the glass. Particles move in spatially heterogeneous cooperative groups. These mobile regions tend to be richer in small particles, and these small particles facilitate the motion of nearby particles of both sizes.

Analyses of turbulent flow fields and aerosol dynamics of diesel engine exhaust inside two dilution sampling tunnels using the CTAG model.

PubMed

Wang, Yan Jason; Yang, Bo; Lipsky, Eric M; Robinson, Allen L; Zhang, K Max

2013-01-15

Experimental results from laboratory emission testing have indicated that particulate emission measurements are sensitive to the dilution process of exhaust using fabricated dilution systems. In this paper, we first categorize the dilution parameters into two groups: (1) aerodynamics (e.g., mixing types, mixing enhancers, dilution ratios, residence time); and (2) mixture properties (e.g., temperature, relative humidity, particle size distributions of both raw exhaust and dilution gas). Then we employ the Comprehensive Turbulent Aerosol Dynamics and Gas Chemistry (CTAG) model to investigate the effects of those parameters on a set of particulate emission measurements comparing two dilution tunnels, i.e., a T-mixing lab dilution tunnel and a portable field dilution tunnel with a type of coaxial mixing. The turbulent flow fields and aerosol dynamics of particles are simulated inside two dilution tunnels. Particle size distributions under various dilution conditions predicted by CTAG are evaluated against the experimental data. It is found that in the area adjacent to the injection of exhaust, turbulence plays a crucial role in mixing the exhaust with the dilution air, and the strength of nucleation dominates the level of particle number concentrations. Further downstream, nucleation terminates and the growth of particles by condensation and coagulation continues. Sensitivity studies reveal that a potential unifying parameter for aerodynamics, i.e., the dilution rate of exhaust, plays an important role in new particle formation. The T-mixing lab tunnel tends to favor the nucleation due to a larger dilution rate of the exhaust than the coaxial mixing field tunnel. Our study indicates that numerical simulation tools can be potentially utilized to develop strategies to reduce the uncertainties associated with dilution samplings of emission sources.

Ultra-high-speed 3D astigmatic particle tracking velocimetry: application to particle-laden supersonic impinging jets

NASA Astrophysics Data System (ADS)

Buchmann, N. A.; Cierpka, C.; Kähler, C. J.; Soria, J.

2014-11-01

The paper demonstrates ultra-high-speed three-component, three-dimensional (3C3D) velocity measurements of micron-sized particles suspended in a supersonic impinging jet flow. Understanding the dynamics of individual particles in such flows is important for the design of particle impactors for drug delivery or cold gas dynamic spray processing. The underexpanded jet flow is produced via a converging nozzle, and micron-sized particles ( d p = 110 μm) are introduced into the gas flow. The supersonic jet impinges onto a flat surface, and the particle impact velocity and particle impact angle are studied for a range of flow conditions and impingement distances. The imaging system consists of an ultra-high-speed digital camera (Shimadzu HPV-1) capable of recording rates of up to 1 Mfps. Astigmatism particle tracking velocimetry (APTV) is used to measure the 3D particle position (Cierpka et al., Meas Sci Technol 21(045401):13, 2010) by coding the particle depth location in the 2D images by adding a cylindrical lens to the high-speed imaging system. Based on the reconstructed 3D particle positions, the particle trajectories are obtained via a higher-order tracking scheme that takes advantage of the high temporal resolution to increase robustness and accuracy of the measurement. It is shown that the particle velocity and impingement angle are affected by the gas flow in a manner depending on the nozzle pressure ratio and stand-off distance where higher pressure ratios and stand-off distances lead to higher impact velocities and larger impact angles.

Magnetically actuated and controlled colloidal sphere-pair swimmer

NASA Astrophysics Data System (ADS)

Ran, Sijie; Guez, Allon; Friedman, Gary

2016-12-01

Magnetically actuated swimming of microscopic objects has been attracting attention partly due to its promising applications in the bio-medical field and partly due to interesting physics of swimming in general. While colloidal particles that are free to move in fluid can be an attractive swimming system due it its simplicity and ability to assemble in situ, stability of their dynamics and the possibility of stable swimming behavior in periodically varying magnetic fields has not been considered. Dynamic behavior of two magnetically interacting colloidal particles subjected to rotating magnetic field of switching frequency is analyzed here and is shown to result in stable swimming without any stabilizing feedback. A new mechanism of swimming that relies only on rotations of the particles themselves and of the particle pair axis is found to dominate the swimming dynamics of the colloidal particle pair. Simulation results and analytical arguments demonstrate that this swimming strategy compares favorably to dragging the particles with an external magnetic force when colloidal particle sizes are reduced.

α - synuclein under the magnifying glass. Insights from atomistic and coarse-grain simulations

NASA Astrophysics Data System (ADS)

Ilie, Ioana M.; Nayar, Divya; den Otter, Wouter K.; van der Vegt, Nico F. A.; Briels, Wim J.; University of Twente Collaboration; University of Darmstadt Collaboration

Neurodegenerative diseases are linked to the accumulation of misfolded intrinsically disordered proteins in the brain. Here, we use both all-atom and coarse-grain simulations to explore the intricate dynamics and the aggregation of α-synuclein, the protein implicated in Parkinson's disease. We explore the free energy landscapes of α-synuclein by using Molecular Dynamics simulations and extract information on the structure of the protein as well as on its binding affinities. Next, to study the aggregation, we proceed with representing α-synuclein as a chain of deformable particles that can adapt their geometry, binding affinities and can rearrange into different disordered and ordered structures. We use Brownian Dynamics to simulate the translational and rotational motions of the particles, as well as their interaction properties. The simulations show valuable insight into the internal dynamics of α-synuclein and the formation of ordered and disordered aggregates. In addition, the study is extended to investigate the attachment and folding of a protein to a fiber.

Direct observation of individual particle armored bubble interaction, stability, and coalescence dynamics.

PubMed

Tan, Sin-Ying; Ata, Seher; Wanless, Erica J

2013-07-18

The interactions between two individual particle-stabilized bubbles were investigated, in the absence of surfactant, using a combination of coalescence rig and high-speed video camera. This combination allows the visualization of bubble coalescence dynamics which provide information on bubble stability. Experimental data suggested that bubble stability is enhanced by both the adsorption of particles at the interface as indicated by the long induction time and the increase in damping coefficient at high surface coverage. The interaction between an armored bubble and a bare bubble (asymmetric interaction) can be destabilized through the addition of a small amount of salt, which suggested that electrostatic interactions play a significant role in bubble stability. Interestingly, the DLVO theory cannot be used to describe the bubble stability in the case of a symmetric interaction as coalescence was inhibited at 0.1 M KCl in both the absence and presence of particles at the interfaces. Furthermore, bubbles can also be destabilized by increasing the particle hydrophobicity. This behavior is due to thinner liquid films between bubbles and an increase in film drainage rate. The fraction of particles detached from the bubble surface after film rupture was found to be very similar within the range of solution ionic strength, surface coverage, and particle hydrophobicity studied. This lack of dependence implies that the kinetic energy generated by the coalescing bubbles is larger than the attachment energy of the particles and dominates the detachment process. This study illuminates the stability behavior of individual particle-stabilized bubbles and has potential impact on processes which involve their interaction.

Coarsening dynamics of binary liquids with active rotation.

PubMed

Sabrina, Syeda; Spellings, Matthew; Glotzer, Sharon C; Bishop, Kyle J M

2015-11-21

Active matter comprised of many self-driven units can exhibit emergent collective behaviors such as pattern formation and phase separation in both biological (e.g., mussel beds) and synthetic (e.g., colloidal swimmers) systems. While these behaviors are increasingly well understood for ensembles of linearly self-propelled "particles", less is known about the collective behaviors of active rotating particles where energy input at the particle level gives rise to rotational particle motion. A recent simulation study revealed that active rotation can induce phase separation in mixtures of counter-rotating particles in 2D. In contrast to that of linearly self-propelled particles, the phase separation of counter-rotating fluids is accompanied by steady convective flows that originate at the fluid-fluid interface. Here, we investigate the influence of these flows on the coarsening dynamics of actively rotating binary liquids using a phenomenological, hydrodynamic model that combines a Cahn-Hilliard equation for the fluid composition with a Navier-Stokes equation for the fluid velocity. The effect of active rotation is introduced though an additional force within the Navier-Stokes equations that arises due to gradients in the concentrations of clockwise and counter-clockwise rotating particles. Depending on the strength of active rotation and that of frictional interactions with the stationary surroundings, we observe and explain new dynamical behaviors such as "active coarsening" via self-generated flows as well as the emergence of self-propelled "vortex doublets". We confirm that many of the qualitative behaviors identified by the continuum model can also be found in discrete, particle-based simulations of actively rotating liquids. Our results highlight further opportunities for achieving complex dissipative structures in active materials subject to distributed actuation.

Breakdown of dynamic balance of a particle in a quadrupole cell by laser-induced aerosol heating.

PubMed

Itoh, M; Lwamoto, T; Takahashi, K; Kuno, S

1992-08-20

The retention stability of an aerosol particle in a quadrupole cell exposed to horizontal irradiation with a CO(2) laser is investigated for several sizes of single spherical carbon particles. The stability of dynamic balance for the particle levitation is affected significantly by the irradiation and breaks down at a power higher than 10(5) W/m(2). The particle is pushed away along the beam line, and its trajectory is slightly upward owing to the laser-induced aerosol heating.

Self-assembly and speed distributions of active granular particles

NASA Astrophysics Data System (ADS)

Sánchez, R.; Díaz-Leyva, P.

2018-06-01

The relationship between the dynamics of self-propelled systems and the self-assembly of structured clusters are studied via the experimental speed distributions of submonolayers of self-propelled granular particles. A distribution developed for non-self-propelled granular particles describes the speed distributions remarkably well, despite some of the assumptions behind its original derivation not being applicable. This is explained in terms of clustering and dissipation being the key phenomena governing this regime.

Universal Scaling Laws in the Dynamics of a Homogeneous Unitary Bose Gas

NASA Astrophysics Data System (ADS)

Eigen, Christoph; Glidden, Jake A. P.; Lopes, Raphael; Navon, Nir; Hadzibabic, Zoran; Smith, Robert P.

2017-12-01

We study the dynamics of an initially degenerate homogeneous Bose gas after an interaction quench to the unitary regime at a magnetic Feshbach resonance. As the cloud decays and heats, it exhibits a crossover from degenerate- to thermal-gas behavior, both of which are characterized by universal scaling laws linking the particle-loss rate to the total atom number N . In the degenerate and thermal regimes, the per-particle loss rate is ∝N2 /3 and N26 /9, respectively. The crossover occurs at a universal kinetic energy per particle and at a universal time after the quench, in units of energy and time set by the gas density. By slowly sweeping the magnetic field away from the resonance and creating a mixture of atoms and molecules, we also map out the dynamics of correlations in the unitary gas, which display a universal temporal scaling with the gas density, and reach a steady state while the gas is still degenerate.

Software package for modeling spin–orbit motion in storage rings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zyuzin, D. V., E-mail: d.zyuzin@fz-juelich.de

2015-12-15

A software package providing a graphical user interface for computer experiments on the motion of charged particle beams in accelerators, as well as analysis of obtained data, is presented. The software package was tested in the framework of the international project on electric dipole moment measurement JEDI (Jülich Electric Dipole moment Investigations). The specific features of particle spin motion imply the requirement to use a cyclic accelerator (storage ring) consisting of electrostatic elements, which makes it possible to preserve horizontal polarization for a long time. Computer experiments study the dynamics of 10{sup 6}–10{sup 9} particles in a beam during 10{supmore » 9} turns in an accelerator (about 10{sup 12}–10{sup 15} integration steps for the equations of motion). For designing an optimal accelerator structure, a large number of computer experiments on polarized beam dynamics are required. The numerical core of the package is COSY Infinity, a program for modeling spin–orbit dynamics.« less

Equations of motion of test particles for solving the spin-dependent Boltzmann–Vlasov equation

DOE PAGES

Xia, Yin; Xu, Jun; Li, Bao-An; ...

2016-06-16

A consistent derivation of the equations of motion (EOMs) of test particles for solving the spin-dependent Boltzmann–Vlasov equation is presented. The resulting EOMs in phase space are similar to the canonical equations in Hamiltonian dynamics, and the EOM of spin is the same as that in the Heisenburg picture of quantum mechanics. Considering further the quantum nature of spin and choosing the direction of total angular momentum in heavy-ion reactions as a reference of measuring nucleon spin, the EOMs of spin-up and spin-down nucleons are given separately. The key elements affecting the spin dynamics in heavy-ion collisions are identified. Themore » resulting EOMs provide a solid foundation for using the test-particle approach in studying spin dynamics in heavy-ion collisions at intermediate energies. Future comparisons of model simulations with experimental data will help to constrain the poorly known in-medium nucleon spin–orbit coupling relevant for understanding properties of rare isotopes and their astrophysical impacts.« less

Universal Scaling Laws in the Dynamics of a Homogeneous Unitary Bose Gas.

PubMed

Eigen, Christoph; Glidden, Jake A P; Lopes, Raphael; Navon, Nir; Hadzibabic, Zoran; Smith, Robert P

2017-12-22

We study the dynamics of an initially degenerate homogeneous Bose gas after an interaction quench to the unitary regime at a magnetic Feshbach resonance. As the cloud decays and heats, it exhibits a crossover from degenerate- to thermal-gas behavior, both of which are characterized by universal scaling laws linking the particle-loss rate to the total atom number N. In the degenerate and thermal regimes, the per-particle loss rate is ∝N^{2/3} and N^{26/9}, respectively. The crossover occurs at a universal kinetic energy per particle and at a universal time after the quench, in units of energy and time set by the gas density. By slowly sweeping the magnetic field away from the resonance and creating a mixture of atoms and molecules, we also map out the dynamics of correlations in the unitary gas, which display a universal temporal scaling with the gas density, and reach a steady state while the gas is still degenerate.

Sliding states of a soft-colloid cluster crystal: Cluster versus single-particle hopping

NASA Astrophysics Data System (ADS)

Rossini, Mirko; Consonni, Lorenzo; Stenco, Andrea; Reatto, Luciano; Manini, Nicola

2018-05-01

We study a two-dimensional model for interacting colloidal particles which displays spontaneous clustering. Within this model we investigate the competition between the pinning to a periodic corrugation potential and a sideways constant pulling force which would promote a sliding state. For a few sample particle densities and amplitudes of the periodic corrugation potential we investigate the depinning from the statically pinned to the dynamically sliding regime. This sliding state exhibits the competition between a dynamics where entire clusters are pulled from a minimum to the next and a dynamics where single colloids or smaller groups leave a cluster and move across the corrugation energy barrier to join the next cluster downstream in the force direction. Both kinds of sliding states can occur either coherently across the entire sample or asynchronously: the two regimes result in different average mobilities. Finite temperature tends to destroy separate sliding regimes, generating a smoother dependence of the mobility on the driving force.

Iterants, Fermions and Majorana Operators

NASA Astrophysics Data System (ADS)

Kauffman, Louis H.

Beginning with an elementary, oscillatory discrete dynamical system associated with the square root of minus one, we study both the foundations of mathematics and physics. Position and momentum do not commute in our discrete physics. Their commutator is related to the diffusion constant for a Brownian process and to the Heisenberg commutator in quantum mechanics. We take John Wheeler's idea of It from Bit as an essential clue and we rework the structure of that bit to a logical particle that is its own anti-particle, a logical Marjorana particle. This is our key example of the amphibian nature of mathematics and the external world. We show how the dynamical system for the square root of minus one is essentially the dynamics of a distinction whose self-reference leads to both the fusion algebra and the operator algebra for the Majorana Fermion. In the course of this, we develop an iterant algebra that supports all of matrix algebra and we end the essay with a discussion of the Dirac equation based on these principles.

Restricted Euler dynamics along trajectories of small inertial particles in turbulence

NASA Astrophysics Data System (ADS)

Johnson, Perry; Meneveau, Charles

2016-11-01

The fate of small particles in turbulent flows depends strongly on the surrounding fluid's velocity gradient properties such as rotation and strain-rates. For non-inertial (fluid) particles, the Restricted Euler model provides a simple, low-dimensional dynamical system representation of Lagrangian evolution of velocity gradients in fluid turbulence, at least for short times. Here we derive a new restricted Euler dynamical system for the velocity gradient evolution of inertial particles such as solid particles in a gas or droplets and bubbles in turbulent liquid flows. The model is derived in the limit of small (sub Kolmogorov scale) particles and low Stokes number. The system exhibits interesting fixed points, stability and invariant properties. Comparisons with data from Direct Numerical Simulations show that the model predicts realistic trends such as the tendency of increased straining over rotation along heavy particle trajectories and, for light particles such as bubbles, the tendency of severely reduced self-stretching of strain-rate. Supported by a National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1232825 and by a Grant from The Gulf of Mexico Research Initiative.

Quantifying non-ergodic dynamics of force-free granular gases.

PubMed

Bodrova, Anna; Chechkin, Aleksei V; Cherstvy, Andrey G; Metzler, Ralf

2015-09-14

Brownian motion is ergodic in the Boltzmann-Khinchin sense that long time averages of physical observables such as the mean squared displacement provide the same information as the corresponding ensemble average, even at out-of-equilibrium conditions. This property is the fundamental prerequisite for single particle tracking and its analysis in simple liquids. We study analytically and by event-driven molecular dynamics simulations the dynamics of force-free cooling granular gases and reveal a violation of ergodicity in this Boltzmann-Khinchin sense as well as distinct ageing of the system. Such granular gases comprise materials such as dilute gases of stones, sand, various types of powders, or large molecules, and their mixtures are ubiquitous in Nature and technology, in particular in Space. We treat-depending on the physical-chemical properties of the inter-particle interaction upon their pair collisions-both a constant and a velocity-dependent (viscoelastic) restitution coefficient ε. Moreover we compare the granular gas dynamics with an effective single particle stochastic model based on an underdamped Langevin equation with time dependent diffusivity. We find that both models share the same behaviour of the ensemble mean squared displacement (MSD) and the velocity correlations in the limit of weak dissipation. Qualitatively, the reported non-ergodic behaviour is generic for granular gases with any realistic dependence of ε on the impact velocity of particles.

Correlation of microstructure with dynamic deformation behavior and penetration performance of tungsten heavy alloys fabricated by mechanical alloying

NASA Astrophysics Data System (ADS)

Kim, Dong-Kuk; Lee, Sunghak; Ryu, Ho Jin; Hyunghong, Soon; Noh, Joon-Woong

2000-10-01

In this study, tungsten heavy alloy specimens were fabricated by mechanical alloying (MA), and their dynamic torsional properties and penetration performance were investigated. Dynamic torsional tests were conducted on the specimens fabricated with different sintering temperatures after MA, and then the test data were compared with those of a conventionally processed specimen. Refinement of tungsten particles was obtained after MA, but contiguity was seriously increased, thereby leading to low ductility and impact energy. Specimens in which both particle size and contiguity were simultaneously reduced by MA and two-step sintering and those having higher matrix fraction by partial MA were successfully fabricated. The dynamic test results indicated that the formation of adiabatic shear bands was expected because of the plastic localization at the central area of the gage section. Upon highspeed impact testing of these specimens, self-sharpening was promoted by the adiabatic shear band formation, but their penetration performance did not improve since much of kinetic energy of the penetrators was consumed for the microcrack formation due to interfacial debonding and cleavage fracture of tungsten particles. In order to improve penetration performance as well as to achieve selfsharpening by applying MA, conditions of MA and sintering process should be established so that alloy densification, particle refinement, and contiguity reduction can be simultaneously achieved.

Local random configuration-tree theory for string repetition and facilitated dynamics of glass

NASA Astrophysics Data System (ADS)

Lam, Chi-Hang

2018-02-01

We derive a microscopic theory of glassy dynamics based on the transport of voids by micro-string motions, each of which involves particles arranged in a line hopping simultaneously displacing one another. Disorder is modeled by a random energy landscape quenched in the configuration space of distinguishable particles, but transient in the physical space as expected for glassy fluids. We study the evolution of local regions with m coupled voids. At a low temperature, energetically accessible local particle configurations can be organized into a random tree with nodes and edges denoting configurations and micro-string propagations respectively. Such trees defined in the configuration space naturally describe systems defined in two- or three-dimensional physical space. A micro-string propagation initiated by a void can facilitate similar motions by other voids via perturbing the random energy landscape, realizing path interactions between voids or equivalently string interactions. We obtain explicit expressions of the particle diffusion coefficient and a particle return probability. Under our approximation, as temperature decreases, random trees of energetically accessible configurations exhibit a sequence of percolation transitions in the configuration space, with local regions containing fewer coupled voids entering the non-percolating immobile phase first. Dynamics is dominated by coupled voids of an optimal group size, which increases as temperature decreases. Comparison with a distinguishable-particle lattice model (DPLM) of glass shows very good quantitative agreements using only two adjustable parameters related to typical energy fluctuations and the interaction range of the micro-strings.

Dynamic Light Scattering Study of Inhibition of Nucleation and Growth of Hydroxyapatite Crystals by Osteopontin

PubMed Central

de Bruyn, John R.; Goiko, Maria; Mozaffari, Maryam; Bator, Daniel; Dauphinee, Ron L.; Liao, Yinyin; Flemming, Roberta L.; Bramble, Michael S.; Hunter, Graeme K.; Goldberg, Harvey A.

2013-01-01

We study the effect of isoforms of osteopontin (OPN) on the nucleation and growth of crystals from a supersaturated solution of calcium and phosphate ions. Dynamic light scattering is used to monitor the size of the precipitating particles and to provide information about their concentration. At the ion concentrations studied, immediate precipitation was observed in control experiments with no osteopontin in the solution, and the size of the precipitating particles increased steadily with time. The precipitate was identified as hydroxyapatite by X-ray diffraction. Addition of native osteopontin (nOPN) extracted from rat bone caused a delay in the onset of precipitation and reduced the number of particles that formed, but the few particles that did form grew to a larger size than in the absence of the protein. Recombinant osteopontin (rOPN), which lacks phosphorylation, caused no delay in initial calcium phosphate precipitation but severely slowed crystal growth, suggesting that rOPN inhibits growth but not nucleation. rOPN treated with protein kinase CK2 to phosphorylate the molecule (p-rOPN) produced an effect similar to that of nOPN, but at higher protein concentrations and to a lesser extent. These results suggest that phosphorylations are critical to OPN’s ability to inhibit nucleation, whereas the growth of the hydroxyapatite crystals is effectively controlled by the highly acidic OPN polypeptide. This work also demonstrates that dynamic light scattering can be a powerful tool for delineating the mechanism of protein modulation of mineral formation. PMID:23457612

Magnetic drug targeting through a realistic model of human tracheobronchial airways using computational fluid and particle dynamics.

PubMed

Pourmehran, Oveis; Gorji, Tahereh B; Gorji-Bandpy, Mofid

2016-10-01

Magnetic drug targeting (MDT) is a local drug delivery system which aims to concentrate a pharmacological agent at its site of action in order to minimize undesired side effects due to systemic distribution in the organism. Using magnetic drug particles under the influence of an external magnetic field, the drug particles are navigated toward the target region. Herein, computational fluid dynamics was used to simulate the air flow and magnetic particle deposition in a realistic human airway geometry obtained by CT scan images. Using discrete phase modeling and one-way coupling of particle-fluid phases, a Lagrangian approach for particle tracking in the presence of an external non-uniform magnetic field was applied. Polystyrene (PMS40) particles were utilized as the magnetic drug carrier. A parametric study was conducted, and the influence of particle diameter, magnetic source position, magnetic field strength and inhalation condition on the particle transport pattern and deposition efficiency (DE) was reported. Overall, the results show considerable promise of MDT in deposition enhancement at the target region (i.e., left lung). However, the positive effect of increasing particle size on DE enhancement was evident at smaller magnetic field strengths (Mn [Formula: see text] 1.5 T), whereas, at higher applied magnetic field strengths, increasing particle size has a inverse effect on DE. This implies that for efficient MTD in the human respiratory system, an optimal combination of magnetic drug career characteristics and magnetic field strength has to be achieved.

Coagulation of particles in Saturn's rings - Measurements of the cohesive force of water frost

NASA Technical Reports Server (NTRS)

Hatzes, A. P.; Bridges, F.; Lin, D. N. C.; Sachtjen, S.

1991-01-01

Experimental data are presented on the sticking force of water ice particles which are indicative of the role that the cohesive properties of such particles could play in the dynamics of Saturn ring particles. Sticking forces are dependent on particle impact velocities; a 'Velcro' model is devised to describe the surface structure involved in sticking. The data indicate that below the critical impact velocity of about 0.03 cm/sec, particle cohesion always occurs. Due to the optical depth of micron-sized grains in the Saturn rings, particles are hypothesized to be coated with a layer of frost which will render cohesion an important ring-dynamics process.

LIDT-DD: A new self-consistent debris disc model that includes radiation pressure and couples dynamical and collisional evolution

NASA Astrophysics Data System (ADS)

Kral, Q.; Thébault, P.; Charnoz, S.

2013-10-01

Context. In most current debris disc models, the dynamical and the collisional evolutions are studied separately with N-body and statistical codes, respectively, because of stringent computational constraints. In particular, incorporating collisional effects (especially destructive collisions) into an N-body scheme has proven a very arduous task because of the exponential increase of particles it would imply. Aims: We present here LIDT-DD, the first code able to mix both approaches in a fully self-consistent way. Our aim is for it to be generic enough to be applied to any astrophysical case where we expect dynamics and collisions to be deeply interlocked with one another: planets in discs, violent massive breakups, destabilized planetesimal belts, bright exozodiacal discs, etc. Methods: The code takes its basic architecture from the LIDT3D algorithm for protoplanetary discs, but has been strongly modified and updated to handle the very constraining specificities of debris disc physics: high-velocity fragmenting collisions, radiation-pressure affected orbits, absence of gas that never relaxes initial conditions, etc. It has a 3D Lagrangian-Eulerian structure, where grains of a given size at a given location in a disc are grouped into super-particles or tracers whose orbits are evolved with an N-body code and whose mutual collisions are individually tracked and treated using a particle-in-a-box prescription designed to handle fragmenting impacts. To cope with the wide range of possible dynamics for same-sized particles at any given location in the disc, and in order not to lose important dynamical information, tracers are sorted and regrouped into dynamical families depending on their orbits. A complex reassignment routine that searches for redundant tracers in each family and reassignes them where they are needed, prevents the number of tracers from diverging. Results: The LIDT-DD code has been successfully tested on simplified cases for which robust results have been obtained in past studies: we retrieve the classical features of particle size distributions in unperturbed discs and the outer radial density profiles in ~r-1.5 outside narrow collisionally active rings as well as the depletion of small grains in dynamically cold discs. The potential of the new code is illustrated with the test case of the violent breakup of a massive planetesimal within a debris disc. Preliminary results show that we are able for the first time to quantify the timescale over which the signature of such massive break-ups can be detected. In addition to studying such violent transient events, the main potential future applications of the code are planet and disc interactions, and more generally, any configurations where dynamics and collisions are expected to be intricately connected.

Nonlinear saturation of wave packets excited by low-energy electron horseshoe distributions.

PubMed

Krafft, C; Volokitin, A

2013-05-01

Horseshoe distributions are shell-like particle distributions that can arise in space and laboratory plasmas when particle beams propagate into increasing magnetic fields. The present paper studies the stability and the dynamics of wave packets interacting resonantly with electrons presenting low-energy horseshoe or shell-type velocity distributions in a magnetized plasma. The linear instability growth rates are determined as a function of the ratio of the plasma to the cyclotron frequencies, of the velocity and the opening angle of the horseshoe, and of the relative thickness of the shell. The nonlinear stage of the instability is investigated numerically using a symplectic code based on a three-dimensional Hamiltonian model. Simulation results show that the dynamics of the system is mainly governed by wave-particle interactions at Landau and normal cyclotron resonances and that the high-order normal cyclotron resonances play an essential role. Specific features of the dynamics of particles interacting simultaneously with two or more waves at resonances of different natures and orders are discussed, showing that such complex processes determine the main characteristics of the wave spectrum's evolution. Simulations with wave packets presenting quasicontinuous spectra provide a full picture of the relaxation of the horseshoe distribution, revealing two main phases of the evolution: an initial stage of wave energy growth, characterized by a fast filling of the shell, and a second phase of slow damping of the wave energy, accompanied by final adjustments of the electron distribution. The influence of the density inhomogeneity along the horseshoe on the wave-particle dynamics is also discussed.

Quantum dynamics at finite temperature: Time-dependent quantum Monte Carlo study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Christov, Ivan P., E-mail: ivan.christov@phys.uni-sofia.bg

2016-08-15

In this work we investigate the ground state and the dissipative quantum dynamics of interacting charged particles in an external potential at finite temperature. The recently devised time-dependent quantum Monte Carlo (TDQMC) method allows a self-consistent treatment of the system of particles together with bath oscillators first for imaginary-time propagation of Schrödinger type of equations where both the system and the bath converge to their finite temperature ground state, and next for real time calculation where the dissipative dynamics is demonstrated. In that context the application of TDQMC appears as promising alternative to the path-integral related techniques where the realmore » time propagation can be a challenge.« less

Singularity and stability in a periodic system of particle accelerators

NASA Astrophysics Data System (ADS)

Cai, Yunhai

2018-05-01

We study the single-particle dynamics in a general and parametrized alternating-gradient cell with zero chromaticity using the Lie algebra method. To our surprise, the first-order perturbation of the sextupoles largely determines the dynamics away from the major resonances. The dynamic aperture can be estimated from the topology and geometry of the phase space. In the linearly normalized phase space, it is scaled according to A ¯ ∝ϕ √{L } , where ϕ is the bending angle and L the length of the cell. For the 2 degrees of freedom with equal betatron tunes, the analytical perturbation theory leads us to the invariant or quasi-invariant tori, which play an important role in determining the stable volume in the four-dimensional phase space.

Exploiting Conjugated Polyelectrolyte Photophysics toward Monitoring Real-Time Lipid Membrane-Surface Interaction Dynamics at the Single-Particle Level.

PubMed

Calver, Christina F; Liu, Hsiao-Wei; Cosa, Gonzalo

2015-11-03

Herein we report the real-time observation of the interaction dynamics between cationic liposomes flowing in solution and a surface-immobilized charged scaffolding formed by the deposition of conjugated polyanion poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene (MPS-PPV) onto 100-nm-diameter SiO2 nanoparticles (NPs). Contact of the freely floating liposomes with the polymer-coated surfaces led to the formation of supported lipid bilayers (SLBs). The interaction of the incoming liposomes with MPS-PPV adsorbed on individual SiO2 nanoparticles promoted the deaggregation of the polymer conformation and led to large emission intensity enhancements. Single-particle total internal reflection fluorescence microscopy studies exploited this phenomenon as a way to monitor the deformation dynamics of liposomes on surface-immobilized NPs. The MPS-PPV emission enhancement (up to 25-fold) reflected on the extent of membrane contact with the surface of the NP and was correlated with the size of the incoming liposome. The time required for the MPS-PPV emission to reach a maximum (ranging from 400 to 1000 ms) revealed the dynamics of membrane deformation and was also correlated with the liposome size. Cryo-TEM experiments complemented these results by yielding a structural view of the process. Immediately following the mixing of liposomes and NPs the majority of NPs had one or more adsorbed liposomes, yet the presence of a fully formed SLB was rare. Prolonged incubation of liposomes and NPs showed completely formed SLBs on all of the NPs, confirming that the liposomes eventually ruptured to form SLBs. We foresee that the single-particle studies we report herein may be readily extended to study membrane dynamics of other lipids including cellular membranes in live cell studies and to monitor the formation of polymer-cushioned SLBs.

Internal dynamics of semiflexible polymers with active noise

NASA Astrophysics Data System (ADS)

Eisenstecken, Thomas; Gompper, Gerhard; Winkler, Roland G.

2017-04-01

The intramolecular dynamics of flexible and semiflexible polymers in response to active noise is studied theoretically. The active noise may either originate from interactions of a passive polymer with a bath of active Brownian particles or the polymer itself is comprised of active Brownian particles. We describe the polymer by the continuous Gaussian semiflexible-polymer model, taking into account the finite polymer extensibility. Our analytical calculations predict a strong dependence of the polymer dynamics on the activity. In particular, active semiflexible polymers exhibit a crossover from a bending elasticity-dominated dynamics at weak activity to that of flexible polymers at strong activity. The end-to-end vector correlation function decays exponentially for times longer than the longest polymer relaxation time. Thereby, the polymer relaxation determines the decay of the correlation function for long and flexible polymers. For shorter and stiffer polymers, the relaxation behavior of individual active Brownian particles dominates the decay above a certain activity. The diffusive dynamics of a polymer is substantially enhanced by the activity. Three regimes can be identified in the mean square displacement for sufficiently strong activities: an activity-induced ballistic regime at short times, followed by a Rouse-type polymer-specific regime for any polymer stiffness, and free diffusion at long times, again determined by the activity.

Ultrafast transient absorption studies of hematite nanoparticles: the effect of particle shape on exciton dynamics.

PubMed

Fitzmorris, Bob C; Patete, Jonathan M; Smith, Jacqueline; Mascorro, Xiomara; Adams, Staci; Wong, Stanislaus S; Zhang, Jin Z

2013-10-01

Much progress has been made in using hematite (α-Fe2 O3 ) as a potentially practical and sustainable material for applications such as solar-energy conversion and photoelectrochemical (PEC) water splitting; however, recent studies have shown that the performance can be limited by a very short charge-carrier diffusion length or exciton lifetime. In this study, we performed ultrafast studies on hematite nanoparticles of different shapes to determine the possible influence of particle shape on the exciton dynamics. Nanorice, multifaceted spheroidal nanoparticles, faceted nanocubes, and faceted nanorhombohedra were synthesized and characterized by using SEM and XRD techniques. Their exciton dynamics were investigated by using femtosecond transient absorption (TA) spectroscopy. Although the TA spectral features differ for the four samples studied, their decay profiles are similar, which can be fitted with time constants of 1-3 ps, approximately 25 ps, and a slow nanosecond component extending beyond the experimental time window that was measured (2 ns). The results indicate that the overall exciton lifetime is weakly dependent on the shape of the hematite nanoparticles, even though the overall optical absorption and scattering are influenced by the particle shape. This study suggests that other strategies need to be developed to increase the exciton lifetime or to lengthen the exciton diffusion length in hematite nanostructures. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigating the settling dynamics of cohesive silt particles with particle-resolving simulations

NASA Astrophysics Data System (ADS)

Sun, Rui; Xiao, Heng; Sun, Honglei

2018-01-01

The settling of cohesive sediment is ubiquitous in aquatic environments, and the study of the settling process is important for both engineering and environmental reasons. In the settling process, the silt particles show behaviors that are different from non-cohesive particles due to the influence of inter-particle cohesive force. For instance, the flocs formed in the settling process of cohesive silt can loosen the packing, and thus the structural densities of cohesive silt beds are much smaller than that of non-cohesive sand beds. While there is a consensus that cohesive behaviors depend on the characteristics of sediment particles (e.g., Bond number, particle size distribution), little is known about the exact influence of these characteristics on the cohesive behaviors. In addition, since the cohesive behaviors of the silt are caused by the inter-particle cohesive forces, the motions of and the contacts among silt particles should be resolved to study these cohesive behaviors in the settling process. However, studies of the cohesive behaviors of silt particles in the settling process based on particle-resolving approach are still lacking. In the present work, three-dimensional settling process is investigated numerically by using CFD-DEM (Computational Fluid Dynamics-Discrete Element Method). The inter-particle collision force, the van der Waals force, and the fluid-particle interaction forces are considered. The numerical model is used to simulate the hindered settling process of silt based on the experimental setup in the literature. The results obtained in the simulations, including the structural densities of the beds, the characteristic lines, and the particle terminal velocity, are in good agreement with the experimental observations in the literature. To the authors' knowledge, this is the first time that the influences of non-dimensional Bond number and particle polydispersity on the structural densities of silt beds have been investigated separately. The results demonstrate that the cohesive behavior of silt in the settling process is attributed to both the cohesion among silt particles themselves and the particle polydispersity. To guide to the macro-scale modeling of cohesive silt sedimentation, the collision frequency functions obtained in the numerical simulations are also presented based on the micromechanics of particles. The results obtained by using CFD-DEM indicate that the binary collision theory over-estimated the particle collision frequency in the flocculation process at high solid volume fraction.

Granular Segregation Driven by Particle Interactions

NASA Astrophysics Data System (ADS)

Lozano, C.; Zuriguel, I.; Garcimartín, A.; Mullin, T.

2015-05-01

We report the results of an experimental study of particle-particle interactions in a horizontally shaken granular layer that undergoes a second order phase transition from a binary gas to a segregation liquid as the packing fraction C is increased. By focusing on the behavior of individual particles, the effect of C is studied on (1) the process of cluster formation, (2) cluster dynamics, and (3) cluster destruction. The outcomes indicate that the segregation is driven by two mechanisms: attraction between particles with the same properties and random motion with a characteristic length that is inversely proportional to C . All clusters investigated are found to be transient and the probability distribution functions of the separation times display a power law tail, indicating that the splitting probability decreases with time.

Structure and Transport Anomalies in Soft Colloids

NASA Astrophysics Data System (ADS)

Srivastava, Samanvaya; Archer, Lynden A.; Narayanan, Suresh

2013-04-01

Anomalous trends in nanoparticle correlation and motion are reported in soft nanoparticle suspensions using static and dynamic x-ray scattering measurements. Contrary to normal expectations, we find that particle-particle correlations decrease and particle dynamics become faster as volume fraction rises above a critical particle loading associated with overlap. Our observations bear many similarities to the cascade of structural and transport anomalies reported for complex, network forming molecular fluids such as water, and are argued to share similar physical origins.

Nonlinear dynamics of charged particles in the magnetotail

NASA Technical Reports Server (NTRS)

Chen, James

1992-01-01

An important region of the earth's magnetosphere is the nightside magnetotail, which is believed to play a significant role in energy storage and release associated with substorms. The magnetotail contains a current sheet which separates regions of oppositely directed magnetic field. Particle motion in the collisionless magnetotail has been a long-standing problem. Recent research from the dynamical point of view has yielded considerable new insights into the fundamental properties of orbits and of particle distribution functions. A new framework of understanding magnetospheric plasma properties is emerging. Some novel predictions based directly on nonlinear dynamics have proved to be robust and in apparent good agreement with observation. The earth's magnetotail may serve as a paradigm, one accessible by in situ observation, of a broad class of boundary regions with embedded current sheets. This article reviews the nonlinear dynamics of charged particles in the magnetotail configuration. The emphasis is on the relationships between the dynamics and physical observables. At the end of the introduction, sections containing basic material are indicated.

Modeling Oblique Impact Dynamics of Particle-Laden Nanodroplets

NASA Astrophysics Data System (ADS)

Yong, Xin; Qin, Shiyi

2016-11-01

A fundamental understanding of the impact dynamics of nanoscopic droplets laden with nanoparticles has important implications for materials printing and thin film processing. Using many-body dissipative particle dynamics (MDPD), we model nanometer sized suspension droplets imping on dry solid substrate with oblique angles, and compare their behavior with pure liquid droplets. Equilibrated floating droplets containing two types of nanoparticles, namely fully-wetted hydrophilic particles and surface-active Janus particles, impact onto the solid surface with varying initial velocities and impact angles. The velocity components in the normal and tangential directions to the substrate defines normal and tangential Reynolds and Weber numbers, which are used to classify impact regimes. Droplets with nanoparticles dispersed in the bulk and covering the droplet surface (resembling liquid marbles) exhibit quite different behavior in the course of impact. We also reveal the influences of substrate wettability and its interaction with nanoparticles on the impact dynamics. In addition, the vapor film beneath an impinging droplet shows no significant effect on the impact dynamics in our MDPD simulations.

Reaction-diffusion processes and metapopulation models on duplex networks

NASA Astrophysics Data System (ADS)

Xuan, Qi; Du, Fang; Yu, Li; Chen, Guanrong

2013-03-01

Reaction-diffusion processes, used to model various spatially distributed dynamics such as epidemics, have been studied mostly on regular lattices or complex networks with simplex links that are identical and invariant in transferring different kinds of particles. However, in many self-organized systems, different particles may have their own private channels to keep their purities. Such division of links often significantly influences the underlying reaction-diffusion dynamics and thus needs to be carefully investigated. This article studies a special reaction-diffusion process, named susceptible-infected-susceptible (SIS) dynamics, given by the reaction steps β→α and α+β→2β, on duplex networks where links are classified into two groups: α and β links used to transfer α and β particles, which, along with the corresponding nodes, consist of an α subnetwork and a β subnetwork, respectively. It is found that the critical point of particle density to sustain reaction activity is independent of the network topology if there is no correlation between the degree sequences of the two subnetworks, and this critical value is suppressed or extended if the two degree sequences are positively or negatively correlated, respectively. Based on the obtained results, it is predicted that epidemic spreading may be promoted on positive correlated traffic networks but may be suppressed on networks with modules composed of different types of diffusion links.

Large Scale Brownian Dynamics of Confined Suspensions of Rigid Particles

NASA Astrophysics Data System (ADS)

Donev, Aleksandar; Sprinkle, Brennan; Balboa, Florencio; Patankar, Neelesh

2017-11-01

We introduce new numerical methods for simulating the dynamics of passive and active Brownian colloidal suspensions of particles of arbitrary shape sedimented near a bottom wall. The methods also apply for periodic (bulk) suspensions. Our methods scale linearly in the number of particles, and enable previously unprecedented simulations of tens to hundreds of thousands of particles. We demonstrate the accuracy and efficiency of our methods on a suspension of boomerang-shaped colloids. We also model recent experiments on active dynamics of uniform suspensions of spherical microrollers. This work was supported in part by the National Science Foundation under award DMS-1418706, and by the U.S. Department of Energy under award DE-SC0008271.

Pressure calculation in hybrid particle-field simulations

NASA Astrophysics Data System (ADS)

Milano, Giuseppe; Kawakatsu, Toshihiro

2010-12-01

In the framework of a recently developed scheme for a hybrid particle-field simulation techniques where self-consistent field (SCF) theory and particle models (molecular dynamics) are combined [J. Chem. Phys. 130, 214106 (2009)], we developed a general formulation for the calculation of instantaneous pressure and stress tensor. The expressions have been derived from statistical mechanical definition of the pressure starting from the expression for the free energy functional in the SCF theory. An implementation of the derived formulation suitable for hybrid particle-field molecular dynamics-self-consistent field simulations is described. A series of test simulations on model systems are reported comparing the calculated pressure with those obtained from standard molecular dynamics simulations based on pair potentials.

Mixing and demixing of binary mixtures of polar chiral active particles.

PubMed

Ai, Bao-Quan; Shao, Zhi-Gang; Zhong, Wei-Rong

2018-05-17

We study a binary mixture of polar chiral (counterclockwise or clockwise) active particles in a two-dimensional box with periodic boundary conditions. Besides the excluded volume interactions between particles, the particles are also subjected to the polar velocity alignment. From the extensive Brownian dynamics simulations, it is found that the particle configuration (mixing or demixing) is determined by the competition between the chirality difference and the polar velocity alignment. When the chirality difference competes with the polar velocity alignment, the clockwise particles aggregate in one cluster and the counterclockwise particles aggregate in the other cluster; thus, the particles are demixed and can be separated. However, when the chirality difference or the polar velocity alignment is dominant, the particles are mixed. Our findings could be used for the experimental pursuit of the separation of binary mixtures of chiral active particles.

Dust emission modelling around a stockpile by using computational fluid dynamics and discrete element method

NASA Astrophysics Data System (ADS)

Derakhshani, S. M.; Schott, D. L.; Lodewijks, G.

2013-06-01

Dust emissions can have significant effects on the human health, environment and industry equipment. Understanding the dust generation process helps to select a suitable dust preventing approach and also is useful to evaluate the environmental impact of dust emission. To describe these processes, numerical methods such as Computational Fluid Dynamics (CFD) are widely used, however nowadays particle based methods like Discrete Element Method (DEM) allow researchers to model interaction between particles and fluid flow. In this study, air flow over a stockpile, dust emission, erosion and surface deformation of granular material in the form of stockpile are studied by using DEM and CFD as a coupled method. Two and three dimensional simulations are respectively developed for CFD and DEM methods to minimize CPU time. The standard κ-ɛ turbulence model is used in a fully developed turbulent flow. The continuous gas phase and the discrete particle phase link to each other through gas-particle void fractions and momentum transfer. In addition to stockpile deformation, dust dispersion is studied and finally the accuracy of stockpile deformation results obtained by CFD-DEM modelling will be validated by the agreement with the existing experimental data.

Characterization of deposition from nasal spray devices using a computational fluid dynamics model of the human nasal passages.

PubMed

Kimbell, Julia S; Segal, Rebecca A; Asgharian, Bahman; Wong, Brian A; Schroeter, Jeffry D; Southall, Jeremy P; Dickens, Colin J; Brace, Geoff; Miller, Frederick J

2007-01-01

Many studies suggest limited effectiveness of spray devices for nasal drug delivery due primarily to high deposition and clearance at the front of the nose. Here, nasal spray behavior was studied using experimental measurements and a computational fluid dynamics model of the human nasal passages constructed from magnetic resonance imaging scans of a healthy adult male. Eighteen commercially available nasal sprays were analyzed for spray characteristics using laser diffraction, high-speed video, and high-speed spark photography. Steadystate, inspiratory airflow (15 L/min) and particle transport were simulated under measured spray conditions. Simulated deposition efficiency and spray behavior were consistent with previous experimental studies, two of which used nasal replica molds based on this nasal geometry. Deposition fractions (numbers of deposited particles divided by the number released) of 20- and 50-microm particles exceeded 90% in the anterior part of the nose for most simulated conditions. Predicted particle penetration past the nasal valve improved when (1) the smaller of two particle sizes or the lower of two spray velocities was used, (2) the simulated nozzle was positioned 1.0 rather than 0.5 or 1.5 cm into the nostril, and (3) inspiratory airflow was present rather than absent. Simulations also predicted that delaying the appearance of normal inspiratory airflow more than 1 sec after the release of particles produced results equivalent to cases in which no inspiratory airflow was present. These predictions contribute to more effective design of drug delivery devices through a better understanding of the effects of nasal airflow and spray characteristics on particle transport in the nose.

Size-segregated urban aerosol characterization by electron microscopy and dynamic light scattering and influence of sample preparation

NASA Astrophysics Data System (ADS)

Marvanová, Soňa; Kulich, Pavel; Skoupý, Radim; Hubatka, František; Ciganek, Miroslav; Bendl, Jan; Hovorka, Jan; Machala, Miroslav

2018-04-01

Size-segregated particulate matter (PM) is frequently used in chemical and toxicological studies. Nevertheless, toxicological in vitro studies working with the whole particles often lack a proper evaluation of PM real size distribution and characterization of agglomeration under the experimental conditions. In this study, changes in particle size distributions during the PM sample manipulation and also semiquantitative elemental composition of single particles were evaluated. Coarse (1-10 μm), upper accumulation (0.5-1 μm), lower accumulation (0.17-0.5 μm), and ultrafine (<0.17 μm) PM fractions were collected by high volume cascade impactor in Prague city center. Particles were examined using electron microscopy and their elemental composition was determined by energy dispersive X-ray spectroscopy. Larger or smaller particles, not corresponding to the impaction cut points, were found in all fractions, as they occur in agglomerates and are impacted according to their aerodynamic diameter. Elemental composition of particles in size-segregated fractions varied significantly. Ns-soot occurred in all size fractions. Metallic nanospheres were found in accumulation fractions, but not in ultrafine fraction where ns-soot, carbonaceous particles, and inorganic salts were identified. Dynamic light scattering was used to measure particle size distribution in water and in cell culture media. PM suspension of lower accumulation fraction in water agglomerated after freezing/thawing the sample, and the agglomerates were disrupted by subsequent sonication. Ultrafine fraction did not agglomerate after freezing/thawing the sample. Both lower accumulation and ultrafine fractions were stable in cell culture media with fetal bovine serum, while high agglomeration occurred in media without fetal bovine serum as measured during 24 h.

Parallel Large-Scale Molecular Dynamics Simulation Opens New Perspective to Clarify the Effect of a Porous Structure on the Sintering Process of Ni/YSZ Multiparticles.

PubMed

Xu, Jingxiang; Higuchi, Yuji; Ozawa, Nobuki; Sato, Kazuhisa; Hashida, Toshiyuki; Kubo, Momoji

2017-09-20

Ni sintering in the Ni/YSZ porous anode of a solid oxide fuel cell changes the porous structure, leading to degradation. Preventing sintering and degradation during operation is a great challenge. Usually, a sintering molecular dynamics (MD) simulation model consisting of two particles on a substrate is used; however, the model cannot reflect the porous structure effect on sintering. In our previous study, a multi-nanoparticle sintering modeling method with tens of thousands of atoms revealed the effect of the particle framework and porosity on sintering. However, the method cannot reveal the effect of the particle size on sintering and the effect of sintering on the change in the porous structure. In the present study, we report a strategy to reveal them in the porous structure by using our multi-nanoparticle modeling method and a parallel large-scale multimillion-atom MD simulator. We used this method to investigate the effect of YSZ particle size and tortuosity on sintering and degradation in the Ni/YSZ anodes. Our parallel large-scale MD simulation showed that the sintering degree decreased as the YSZ particle size decreased. The gas fuel diffusion path, which reflects the overpotential, was blocked by pore coalescence during sintering. The degradation of gas diffusion performance increased as the YSZ particle size increased. Furthermore, the gas diffusion performance was quantified by a tortuosity parameter and an optimal YSZ particle size, which is equal to that of Ni, was found for good diffusion after sintering. These findings cannot be obtained by previous MD sintering studies with tens of thousands of atoms. The present parallel large-scale multimillion-atom MD simulation makes it possible to clarify the effects of the particle size and tortuosity on sintering and degradation.

Nano-scale measurement of biomolecules by optical microscopy and semiconductor nanoparticles

PubMed Central

Ichimura, Taro; Jin, Takashi; Fujita, Hideaki; Higuchi, Hideo; Watanabe, Tomonobu M.

2014-01-01

Over the past decade, great developments in optical microscopy have made this technology increasingly compatible with biological studies. Fluorescence microscopy has especially contributed to investigating the dynamic behaviors of live specimens and can now resolve objects with nanometer precision and resolution due to super-resolution imaging. Additionally, single particle tracking provides information on the dynamics of individual proteins at the nanometer scale both in vitro and in cells. Complementing advances in microscopy technologies has been the development of fluorescent probes. The quantum dot, a semi-conductor fluorescent nanoparticle, is particularly suitable for single particle tracking and super-resolution imaging. This article overviews the principles of single particle tracking and super resolution along with describing their application to the nanometer measurement/observation of biological systems when combined with quantum dot technologies. PMID:25120488

Static and dynamic light scattering by red blood cells: A numerical study.

PubMed

Mauer, Johannes; Peltomäki, Matti; Poblete, Simón; Gompper, Gerhard; Fedosov, Dmitry A

2017-01-01

Light scattering is a well-established experimental technique, which gains more and more popularity in the biological field because it offers the means for non-invasive imaging and detection. However, the interpretation of light-scattering signals remains challenging due to the complexity of most biological systems. Here, we investigate static and dynamic scattering properties of red blood cells (RBCs) using two mesoscopic hydrodynamics simulation methods-multi-particle collision dynamics and dissipative particle dynamics. Light scattering is studied for various membrane shear elasticities, bending rigidities, and RBC shapes (e.g., biconcave and stomatocyte). Simulation results from the two simulation methods show good agreement, and demonstrate that the static light scattering of a diffusing RBC is not very sensitive to the changes in membrane properties and moderate alterations in cell shapes. We also compute dynamic light scattering of a diffusing RBC, from which dynamic properties of RBCs such as diffusion coefficients can be accessed. In contrast to static light scattering, the dynamic measurements can be employed to differentiate between the biconcave and stomatocytic RBC shapes and generally allow the differentiation based on the membrane properties. Our simulation results can be used for better understanding of light scattering by RBCs and the development of new non-invasive methods for blood-flow monitoring.

Static and dynamic light scattering by red blood cells: A numerical study

PubMed Central

Mauer, Johannes; Peltomäki, Matti; Poblete, Simón; Gompper, Gerhard

2017-01-01

Light scattering is a well-established experimental technique, which gains more and more popularity in the biological field because it offers the means for non-invasive imaging and detection. However, the interpretation of light-scattering signals remains challenging due to the complexity of most biological systems. Here, we investigate static and dynamic scattering properties of red blood cells (RBCs) using two mesoscopic hydrodynamics simulation methods—multi-particle collision dynamics and dissipative particle dynamics. Light scattering is studied for various membrane shear elasticities, bending rigidities, and RBC shapes (e.g., biconcave and stomatocyte). Simulation results from the two simulation methods show good agreement, and demonstrate that the static light scattering of a diffusing RBC is not very sensitive to the changes in membrane properties and moderate alterations in cell shapes. We also compute dynamic light scattering of a diffusing RBC, from which dynamic properties of RBCs such as diffusion coefficients can be accessed. In contrast to static light scattering, the dynamic measurements can be employed to differentiate between the biconcave and stomatocytic RBC shapes and generally allow the differentiation based on the membrane properties. Our simulation results can be used for better understanding of light scattering by RBCs and the development of new non-invasive methods for blood-flow monitoring. PMID:28472125

Study on the thermal resistance in secondary particles chain of silica aerogel by molecular dynamics simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, M.; Department of Physics, University of Chinese Academy of Sciences, Beijing 100049; Qiu, L., E-mail: qiulin111@sina.com, E-mail: jzzhengxinghua@163.com

2014-09-07

In this article, molecular dynamics simulation was performed to study the heat transport in secondary particles chain of silica aerogel. The two adjacent particles as the basic heat transport unit were modelled to characterize the heat transfer through the calculation of thermal resistance and vibrational density of states (VDOS). The total thermal resistance of two contact particles was predicted by non-equilibrium molecular dynamics simulations (NEMD). The defects were formed by deleting atoms in the system randomly first and performing heating and quenching process afterwards to achieve the DLCA (diffusive limited cluster-cluster aggregation) process. This kind of treatment showed a verymore » reasonable prediction of thermal conductivity for the silica aerogels compared with the experimental values. The heat transport was great suppressed as the contact length increased or defect concentration increased. The constrain effect of heat transport was much significant when contact length fraction was in the small range (<0.5) or the defect concentration is in the high range (>0.5). Also, as the contact length increased, the role of joint thermal resistance played in the constraint of heat transport was increasing. However, the defect concentration did not affect the share of joint thermal resistance as the contact length did. VDOS of the system was calculated by numerical method to characterize the heat transport from atomic vibration view. The smaller contact length and greater defect concentration primarily affected the longitudinal acoustic modes, which ultimately influenced the heat transport between the adjacent particles.« less

Single-particle dynamics of the Anderson model: a local moment approach

NASA Astrophysics Data System (ADS)

Glossop, Matthew T.; Logan, David E.

2002-07-01

A non-perturbative local moment approach to single-particle dynamics of the general asymmetric Anderson impurity model is developed. The approach encompasses all energy scales and interaction strengths. It captures thereby strong coupling Kondo behaviour, including the resultant universal scaling behaviour of the single-particle spectrum; as well as the mixed valence and essentially perturbative empty orbital regimes. The underlying approach is physically transparent and innately simple, and as such is capable of practical extension to lattice-based models within the framework of dynamical mean-field theory.

Experiments on the enhancement of compressible mixing via streamwise vorticity. II - Vortex strength assessment and seed particle dynamics

NASA Technical Reports Server (NTRS)

Naughton, J. W.; Cattafesta, L. N.; Settles, G. S.

1993-01-01

The effect of streamwise vorticity on compressible axisymmetric mixing layers is examined using vortex strength assessment and seed particle dynamics analysis. Experimental results indicate that the particles faithfully represent the dynamics of the turbulent swirling flow. A comparison of the previously determined mixing layer growth rates with the present vortex strength data reveals that the increase of turbulent mixing up to 60 percent scales with the degree of swirl. The mixing enhancement appears to be independent of the compressibility level of the mixing layer.

Dynamic strength, particle deformation, and fracture within fluids with impact-activated microstructures

NASA Astrophysics Data System (ADS)

Petel, Oren E.; Ouellet, Simon

2017-07-01

The evolution of material strength within several dense particle suspensions impacted by a projectile is investigated and shown to be strongly dependent on the particle material in suspension. For stronger particles, such as silicon carbide, the shear strength of the fluid is shown to increase with the ballistic impact strength. For weaker particles, such as silica, the shear strength of the suspension is found to be independent of impact strength in this dynamic range of tests. A soft-capture technique is employed to collect ejecta samples of a silica-based shear thickening fluid, following a ballistic impact and penetration event. Ejecta samples that were collected from impacts at three different velocities are observed and compared to the benchmark particles using a Scanning Electron Microscope. The images show evidence of fractured and deformed silica particles recovered among the nominally 1 μm diameter monodisperse spheres. There is also evidence of particle fragments that appear to be the result of interparticle grinding. The trends observed in the shear strength estimates are interpreted with regards to the particle damage seen in the ejecta recovery experiments to develop a concept of the impact response of these fluids. The results suggest that particle slip through deformation is likely the dominant factor in limiting the transient impact strength of these fluids. Particularly, particle strength is important in the formation and collapse of dynamically jammed particle contact networks in the penetration process.

The effect of microscopic friction and size distributions on conditional probability distributions in soft particle packings

NASA Astrophysics Data System (ADS)

Saitoh, Kuniyasu; Magnanimo, Vanessa; Luding, Stefan

2017-10-01

Employing two-dimensional molecular dynamics (MD) simulations of soft particles, we study their non-affine responses to quasi-static isotropic compression where the effects of microscopic friction between the particles in contact and particle size distributions are examined. To quantify complicated restructuring of force-chain networks under isotropic compression, we introduce the conditional probability distributions (CPDs) of particle overlaps such that a master equation for distribution of overlaps in the soft particle packings can be constructed. From our MD simulations, we observe that the CPDs are well described by q-Gaussian distributions, where we find that the correlation for the evolution of particle overlaps is suppressed by microscopic friction, while it significantly increases with the increase of poly-dispersity.

Self focusing in a spatially modulated electrostatic field particle accelerator

NASA Astrophysics Data System (ADS)

Russman, F.; Marini, S.; Peter, E.; de Oliveira, G. I.; Rizzato, F. B.

2018-02-01

In the present analysis, we study the action of a three-dimensional (3D) modulated electrostatic wave over a charged particle. Meanwhile, the particle's velocity is smaller than the phase-velocity of the carrier, and the particle could be reflected by the potential or could pass through the potential with no significant change in the longitudinal velocity—and its dynamics could be described by a ponderomotive approximation. Otherwise, the particle is trapped by the potential and it is accelerated towards the speed of light, independently of the initial particle's phase—in this case, the ponderomotive approximation is no longer valid. During the acceleration process, numerical simulations show the particle is focused, simultaneously. These results suggest the accelerator proposed here is promising.

Role of quantum statistics in multi-particle decay dynamics

NASA Astrophysics Data System (ADS)

Marchewka, Avi; Granot, Er'el

2015-04-01

The role of quantum statistics in the decay dynamics of a multi-particle state, which is suddenly released from a confining potential, is investigated. For an initially confined double particle state, the exact dynamics is presented for both bosons and fermions. The time-evolution of the probability to measure two-particle is evaluated and some counterintuitive features are discussed. For instance, it is shown that although there is a higher chance of finding the two bosons (as oppose to fermions, and even distinguishable particles) at the initial trap region, there is a higher chance (higher than fermions) of finding them on two opposite sides of the trap as if the repulsion between bosons is higher than the repulsion between fermions. The results are demonstrated by numerical simulations and are calculated analytically in the short-time approximation. Furthermore, experimental validation is suggested.

Simulation of Particle Size Effect on Dynamic Properties and Fracture of PTFE-W-Al Composites

NASA Astrophysics Data System (ADS)

Herbold, E. B.; Cai, J.; Benson, D. J.; Nesterenko, V. F.

2007-12-01

Recent investigations of the dynamic compressive strength of cold isostatically pressed composites of polytetrafluoroethylene (PTFE), tungsten (W) and aluminum (Al) powders show significant differences depending on the size of metallic particles. The addition of W increases the density and changes the overall strength of the sample depending on the size of W particles. To investigate relatively large deformations, multi-material Eulerian and arbitrary Lagrangian-Eulerian methods, which have the ability to efficiently handle the formation of free surfaces, were used. The calculations indicate that the increased sample strength with fine metallic particles is due to the dynamic formation of force chains. This phenomenon occurs for samples with a higher porosity of the PTFE matrix compared to samples with larger particle size of W and a higher density PTFE matrix.

FCC-HCP coexistence in dense thermo-responsive microgel crystals

NASA Astrophysics Data System (ADS)

Karthickeyan, D.; Joshi, R. G.; Tata, B. V. R.

2017-06-01

Analogous to hard-sphere suspensions, monodisperse thermo-responsive poly (N-isopropyl acrylamide) (PNIPAM) microgel particles beyond a volume fraction (ϕ) of 0.5 freeze into face centered cubic (FCC)-hexagonal close packed (HCP) coexistence under as prepared conditions and into an FCC structure upon annealing. We report here FCC-HCP coexistence to be stable in dense PNIPAM microgel crystals (ϕ > 0.74) with particles in their deswollen state (referred to as osmotically compressed microgel crystals) and the FCC structure with particles in their swollen state by performing annealing studies with different cooling rates. The structure of PNIPAM microgel crystals is characterized using static light scattering technique and UV-Visible spectroscopy and dynamics by dynamic light scattering (DLS). DLS studies reveal that the particle motion is diffusive at short times in crystals with ϕ < 0.74 and sub-diffusive at short times in PNIPAM crystals with ϕ > 0.74. The observed sub-diffusive behavior at short times is due to the overlap (interpenetration) of the dangling polymer chains between the shells of neighbouring PNIPAM microgel particles. Overlap is found to disappear upon heating the crystals well above their melting temperature, Tm due to reduction in the particle size. Annealing studies confirm that the overlap of dangling polymer chains between the shells of neighbouring PNIPAM spheres is responsible for the stability of FCC-HCP coexistence observed in osmotically compressed PNIPAM microgel crystals. Results are discussed in the light of recent reports of stabilizing the HCP structure in hard sphere crystals by adding interacting polymer chains.

The dynamics of submicron-sized dust particles lost from Phobos

NASA Technical Reports Server (NTRS)

Horanyi, M.; Tatrallyay, M.; Juhasz, A.; Luhmann, J. G.

1991-01-01

The dynamics of submicron-sized dielectric particles lost from the Martian moon Phobos are studied in connection with the possible detection of dust by the Phobos 2 spacecraft. The motion of these small dust grains is influenced not only by gravity but also by solar radiation pressure and electromagnetic forces. The plasma environment of Mars is described by applying a hybrid gasdynamic-cometary model. Some of the submicron-sized grains ejected at speeds on the order of a few tens meters per second can stay in orbit around Mars for several months forming a nonuniform and time-dependent dust halo.

Universal shape characteristics for the mesoscopic star-shaped polymer via dissipative particle dynamics simulations

NASA Astrophysics Data System (ADS)

Kalyuzhnyi, O.; Ilnytskyi, J. M.; Holovatch, Yu; von Ferber, C.

2018-05-01

In this paper we study the shape characteristics of star-like polymers in various solvent quality using a mesoscopic level of modeling. The dissipative particle dynamics simulations are performed for the homogeneous and four different heterogeneous star polymers with the same molecular weight. We analyse the gyration radius and asphericity at the poor, good and θ-solvent regimes. Detailed explanation based on interplay between enthalpic and entropic contributions to the free energy and analyses on of the asphericity of individual branches are provided to explain the increase of the apsphericity in θ-solvent regime.

Exact dynamics of a one dimensional Bose gas in a periodic time-dependent harmonic trap

NASA Astrophysics Data System (ADS)

Scopa, Stefano; Unterberger, Jéremie; Karevski, Dragi

2018-05-01

We study the unitary dynamics of a 1D gas of hard-core bosons trapped into a harmonic potential which varies periodically in time with frequency . Such periodic systems can be classified into orbits of different monodromies corresponding to two different physical situations, namely the case in which the bosonic cloud remains stable during the time-evolution and the case where it turns out to be unstable. In the present work we derive in the large particle number limit exact results for the stroboscopic evolution of the energy and particle densities in both physical situations.

Thermodynamics of a time-dependent and dissipative oval billiard: A heat transfer and billiard approach.

PubMed

Leonel, Edson D; Galia, Marcus Vinícius Camillo; Barreiro, Luiz Antonio; Oliveira, Diego F M

2016-12-01

We study some statistical properties for the behavior of the average squared velocity-hence the temperature-for an ensemble of classical particles moving in a billiard whose boundary is time dependent. We assume the collisions of the particles with the boundary of the billiard are inelastic, leading the average squared velocity to reach a steady-state dynamics for large enough time. The description of the stationary state is made by using two different approaches: (i) heat transfer motivated by the Fourier law and (ii) billiard dynamics using either numerical simulations and theoretical description.

Emergent Vortex Patterns in Systems of Self-Propelled, Chiral Particles

NASA Astrophysics Data System (ADS)

Huber, Lorenz; Denk, Jonas; Reithmann, Emanuel; Frey, Erwin

Self-organization of FtsZ polymers is vital for Z-ring assembly during bacterial cell division, and has been studied using reconstituted in vitro model systems. Employing Brownian dynamics simulations and a Boltzmann approach, we model FtsZ polymers as active particles moving along chiral circular paths. With both theoretical approaches we find self-organization into vortex structures and characterize different states in parameter states. Our work demonstrates that these patterns are robust and are generic for active chiral matter. Moreover, we show that the dynamics at the onset of pattern formation is described by a generalized complex Ginzburg-Landau equation.

Controlling mixing and segregation in time periodic granular flows

NASA Astrophysics Data System (ADS)

Bhattacharya, Tathagata

Segregation is a major problem for many solids processing industries. Differences in particle size or density can lead to flow-induced segregation. In the present work, we employ the discrete element method (DEM)---one type of particle dynamics (PD) technique---to investigate the mixing and segregation of granular material in some prototypical solid handling devices, such as a rotating drum and chute. In DEM, one calculates the trajectories of individual particles based on Newton's laws of motion by employing suitable contact force models and a collision detection algorithm. Recently, it has been suggested that segregation in particle mixers can be thwarted if the particle flow is inverted at a rate above a critical forcing frequency. Further, it has been hypothesized that, for a rotating drum, the effectiveness of this technique can be linked to the probability distribution of the number of times a particle passes through the flowing layer per rotation of the drum. In the first portion of this work, various configurations of solid mixers are numerically and experimentally studied to investigate the conditions for improved mixing in light of these hypotheses. Besides rotating drums, many studies of granular flow have focused on gravity driven chute flows owing to its practical importance in granular transportation and to the fact that the relative simplicity of this type of flow allows for development and testing of new theories. In this part of the work, we observe the deposition behavior of both mono-sized and polydisperse dry granular materials in an inclined chute flow. The effects of different parameters such as chute angle, particle size, falling height and charge amount on the mass fraction distribution of granular materials after deposition are investigated. The simulation results obtained using DEM are compared with the experimental findings and a high degree of agreement is observed. Tuning of the underlying contact force parameters allows the achievement of realistic results and is used as a means of validating the model against available experimental data. The tuned model is then used to find the critical chute length for segregation based on the hypothesis that segregation can be thwarted if the particle flow is inverted at a rate above a critical forcing frequency. The critical frequency, fcrit, is inversely proportional to the characteristic time of segregation, ts. Mixing is observed instead of segregation when the chute length L < U avgts, where Uavg denotes the average stream-wise flow velocity of the particles. While segregation is often an undesired effect, sometimes separating the components of a particle mixture is the ultimate goal. Rate-based separation processes hold promise as both more environmentally benign as well as less energy intensive when compared to conventional particle separations technologies such as vibrating screens or flotation methods. This approach is based on differences in the kinetic properties of the components of a mixture, such as the velocity of migration or diffusivity. In this portion of the work, two examples of novel rate-based separation devices are demonstrated. The first example involves the study of the dynamics of gravity-driven particles through an array of obstacles. Both discrete element (DEM) simulations and experiments are used to augment the understanding of this device. Dissipative collisions (both between the particles themselves and with the obstacles) give rise to a diffusive motion of particles perpendicular to the flow direction and the differences in diffusion lengths are exploited to separate the particles. The second example employs DEM to analyze a ratchet mechanism where a current of particles can be produced in a direction perpendicular to the energy input. In this setup, a vibrating saw-toothed base is employed to induce different mobility for different types of particles. The effect of operating conditions and design parameters on the separation efficiency are discussed. Keywords: granular flow, particle, mixing, segregation, discrete element method, particle dynamics, tumbler, chute, periodic flow inversion, collisional flow, rate-based separation, ratchet, static separator, dissipative particle dynamics, non-spherical droplet.

Electrostatically confined nanoparticle interactions and dynamics.

PubMed

Eichmann, Shannon L; Anekal, Samartha G; Bevan, Michael A

2008-02-05

We report integrated evanescent wave and video microscopy measurements of three-dimensional trajectories of 50, 100, and 250 nm gold nanoparticles electrostatically confined between parallel planar glass surfaces separated by 350 and 600 nm silica colloid spacers. Equilibrium analyses of single and ensemble particle height distributions normal to the confining walls produce net electrostatic potentials in excellent agreement with theoretical predictions. Dynamic analyses indicate lateral particle diffusion coefficients approximately 30-50% smaller than expected from predictions including the effects of the equilibrium particle distribution within the gap and multibody hydrodynamic interactions with the confining walls. Consistent analyses of equilibrium and dynamic information in each measurement do not indicate any roles for particle heating or hydrodynamic slip at the particle or wall surfaces, which would both increase diffusivities. Instead, lower than expected diffusivities are speculated to arise from electroviscous effects enhanced by the relative extent (kappaa approximately 1-3) and overlap (kappah approximately 2-4) of electrostatic double layers on the particle and wall surfaces. These results demonstrate direct, quantitative measurements and a consistent interpretation of metal nanoparticle electrostatic interactions and dynamics in a confined geometry, which provides a basis for future similar measurements involving other colloidal forces and specific biomolecular interactions.

Path Sampling Methods for Enzymatic Quantum Particle Transfer Reactions

PubMed Central

Dzierlenga, M.W.; Varga, M.J.

2016-01-01

The mechanisms of enzymatic reactions are studied via a host of computational techniques. While previous methods have been used successfully, many fail to incorporate the full dynamical properties of enzymatic systems. This can lead to misleading results in cases where enzyme motion plays a significant role in the reaction coordinate, which is especially relevant in particle transfer reactions where nuclear tunneling may occur. In this chapter, we outline previous methods, as well as discuss newly developed dynamical methods to interrogate mechanisms of enzymatic particle transfer reactions. These new methods allow for the calculation of free energy barriers and kinetic isotope effects (KIEs) with the incorporation of quantum effects through centroid molecular dynamics (CMD) and the full complement of enzyme dynamics through transition path sampling (TPS). Recent work, summarized in this chapter, applied the method for calculation of free energy barriers to reaction in lactate dehydrogenase (LDH) and yeast alcohol dehydrogenase (YADH). It was found that tunneling plays an insignificant role in YADH but plays a more significant role in LDH, though not dominant over classical transfer. Additionally, we summarize the application of a TPS algorithm for the calculation of reaction rates in tandem with CMD to calculate the primary H/D KIE of YADH from first principles. It was found that the computationally obtained KIE is within the margin of error of experimentally determined KIEs, and corresponds to the KIE of particle transfer in the enzyme. These methods provide new ways to investigate enzyme mechanism with the inclusion of protein and quantum dynamics. PMID:27497161

Transfer Ionization Studies for Proton on He - new Inside into the World of Correlation

NASA Astrophysics Data System (ADS)

Schmidt-Böcking, Horst

2005-04-01

Correlated many-particle dynamics in Coulombic systems, which is one of the unsolved fundamental problems in AMO-physics, can now be experimentally approached with so far unprecedented completeness and precision. The recent development of the COLTRIMS technique (COLd Target Recoil Ion Momentum Spectroscopy) provides a coincident multi-fragment imaging technique for eV and sub-eV fragment detection. In its completeness it is as powerful as the bubble chamber in high energy physics. In recent benchmark experiments quasi snapshots (duration as short an atto-sec) of the correlated dynamics between electrons and nuclei has been made for atomic and molecular objects. This new imaging technique has opened a powerful observation window into the hidden world of many-particle dynamics. Recent transfer ionization studies will be presented and the direct observation of correlated electron pairs will be discussed.

Nearshore dynamics of artificial sand and oil agglomerates

USGS Publications Warehouse

Dalyander, P. Soupy; Plant, Nathaniel G.; Long, Joseph W.; McLaughlin, Molly R.

2015-01-01

Weathered oil can mix with sediment to form heavier-than-water sand and oil agglomerates (SOAs) that can cause beach re-oiling for years after a spill. Few studies have focused on the physical dynamics of SOAs. In this study, artificial SOAs (aSOAs) were created and deployed in the nearshore, and shear stress-based mobility formulations were assessed to predict SOA response. Prediction sensitivity to uncertainty in hydrodynamic conditions and shear stress parameterizations were explored. Critical stress estimates accounting for large particle exposure in a mixed bed gave the best predictions of mobility under shoaling and breaking waves. In the surf zone, the 10-cm aSOA was immobile and began to bury in the seafloor while smaller size classes dispersed alongshore. aSOAs up to 5 cm in diameter were frequently mobilized in the swash zone. The uncertainty in predicting aSOA dynamics reflects a broader uncertainty in applying mobility and transport formulations to cm-sized particles.

Cellular automaton model for molecular traffic jams

NASA Astrophysics Data System (ADS)

Belitsky, V.; Schütz, G. M.

2011-07-01

We consider the time evolution of an exactly solvable cellular automaton with random initial conditions both in the large-scale hydrodynamic limit and on the microscopic level. This model is a version of the totally asymmetric simple exclusion process with sublattice parallel update and thus may serve as a model for studying traffic jams in systems of self-driven particles. We study the emergence of shocks from the microscopic dynamics of the model. In particular, we introduce shock measures whose time evolution we can compute explicitly, both in the thermodynamic limit and for open boundaries where a boundary-induced phase transition driven by the motion of a shock occurs. The motion of the shock, which results from the collective dynamics of the exclusion particles, is a random walk with an internal degree of freedom that determines the jump direction. This type of hopping dynamics is reminiscent of some transport phenomena in biological systems.

A fast integrated mobility spectrometer for rapid measurement of sub-micrometer aerosol size distribution, Part I: Design and model evaluation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jian; Pikridas, Michael; Spielman, Steven R.

This study discusses, a fast integrated mobility spectrometer (FIMS) was previously developed to characterize submicron aerosol size distributions at a frequency of 1 Hz and with high size resolution and counting statistics. However, the dynamic size range of the FIMS was limited to one decade in particle electrical mobility. It was proposed that the FIMS dynamic size range can be greatly increased by using a spatially varying electric field. This electric field creates regions with drastically different field strengths in the separator, such that particles of a wide diameter range can be simultaneously classified and subsequently measured. A FIMS incorporatingmore » this spatially varying electric field is developed. This paper describes the theoretical frame work and numerical simulations of the FIMS with extended dynamic size range, including the spatially varying electric field, particle trajectories, activation of separated particles in the condenser, and the transfer function, transmission efficiency, and mobility resolution. The influences of the particle Brownian motion on FIMS transfer function and mobility resolution are examined. The simulation results indicate that the FIMS incorporating the spatially varying electric field is capable of measuring aerosol size distribution from 8 to 600 nm with high time resolution. As a result, the experimental characterization of the FIMS is presented in an accompanying paper.« less

A fast integrated mobility spectrometer for rapid measurement of sub-micrometer aerosol size distribution, Part I: Design and model evaluation

DOE PAGES

Wang, Jian; Pikridas, Michael; Spielman, Steven R.; ...

2017-06-01

This study discusses, a fast integrated mobility spectrometer (FIMS) was previously developed to characterize submicron aerosol size distributions at a frequency of 1 Hz and with high size resolution and counting statistics. However, the dynamic size range of the FIMS was limited to one decade in particle electrical mobility. It was proposed that the FIMS dynamic size range can be greatly increased by using a spatially varying electric field. This electric field creates regions with drastically different field strengths in the separator, such that particles of a wide diameter range can be simultaneously classified and subsequently measured. A FIMS incorporatingmore » this spatially varying electric field is developed. This paper describes the theoretical frame work and numerical simulations of the FIMS with extended dynamic size range, including the spatially varying electric field, particle trajectories, activation of separated particles in the condenser, and the transfer function, transmission efficiency, and mobility resolution. The influences of the particle Brownian motion on FIMS transfer function and mobility resolution are examined. The simulation results indicate that the FIMS incorporating the spatially varying electric field is capable of measuring aerosol size distribution from 8 to 600 nm with high time resolution. As a result, the experimental characterization of the FIMS is presented in an accompanying paper.« less

Comet Gas and Dust Dynamics Modeling

NASA Technical Reports Server (NTRS)

Von Allmen, Paul A.; Lee, Seungwon

2010-01-01

This software models the gas and dust dynamics of comet coma (the head region of a comet) in order to support the Microwave Instrument for Rosetta Orbiter (MIRO) project. MIRO will study the evolution of the comet 67P/Churyumov-Gerasimenko's coma system. The instrument will measure surface temperature, gas-production rates and relative abundances, and velocity and excitation temperatures of each species along with their spatial temporal variability. This software will use these measurements to improve the understanding of coma dynamics. The modeling tool solves the equation of motion of a dust particle, the energy balance equation of the dust particle, the continuity equation for the dust and gas flow, and the dust and gas mixture energy equation. By solving these equations numerically, the software calculates the temperature and velocity of gas and dust as a function of time for a given initial gas and dust production rate, and a dust characteristic parameter that measures the ability of a dust particle to adjust its velocity to the local gas velocity. The software is written in a modular manner, thereby allowing the addition of more dynamics equations as needed. All of the numerical algorithms are added in-house and no third-party libraries are used.

Nonlinear Bayesian filtering and learning: a neuronal dynamics for perception.

PubMed

Kutschireiter, Anna; Surace, Simone Carlo; Sprekeler, Henning; Pfister, Jean-Pascal

2017-08-18

The robust estimation of dynamical hidden features, such as the position of prey, based on sensory inputs is one of the hallmarks of perception. This dynamical estimation can be rigorously formulated by nonlinear Bayesian filtering theory. Recent experimental and behavioral studies have shown that animals' performance in many tasks is consistent with such a Bayesian statistical interpretation. However, it is presently unclear how a nonlinear Bayesian filter can be efficiently implemented in a network of neurons that satisfies some minimum constraints of biological plausibility. Here, we propose the Neural Particle Filter (NPF), a sampling-based nonlinear Bayesian filter, which does not rely on importance weights. We show that this filter can be interpreted as the neuronal dynamics of a recurrently connected rate-based neural network receiving feed-forward input from sensory neurons. Further, it captures properties of temporal and multi-sensory integration that are crucial for perception, and it allows for online parameter learning with a maximum likelihood approach. The NPF holds the promise to avoid the 'curse of dimensionality', and we demonstrate numerically its capability to outperform weighted particle filters in higher dimensions and when the number of particles is limited.

Differential dynamic microscopy to characterize Brownian motion and bacteria motility

NASA Astrophysics Data System (ADS)

Germain, David; Leocmach, Mathieu; Gibaud, Thomas

2016-03-01

We have developed a lab module for undergraduate students, which involves the process of quantifying the dynamics of a suspension of microscopic particles using Differential Dynamic Microscopy (DDM). DDM is a relatively new technique that constitutes an alternative method to more classical techniques such as dynamic light scattering (DLS) or video particle tracking (VPT). The technique consists of imaging a particle dispersion with a standard light microscope and a camera and analyzing the images using a digital Fourier transform to obtain the intermediate scattering function, an autocorrelation function that characterizes the dynamics of the dispersion. We first illustrate DDM in the textbook case of colloids under Brownian motion, where we measure the diffusion coefficient. Then we show that DDM is a pertinent tool to characterize biological systems such as motile bacteria.

Growth dynamics of carbon-metal particles and nanotubes synthesized by CO2 laser vaporization

NASA Astrophysics Data System (ADS)

Kokai, F.; Takahashi, K.; Yudasaka, M.; Iijima, S.

To study the growth of carbon-Co/Ni particles and single-wall carbon nanotubes (SWNTs) by 20 ms CO2 laser-pulse irradiation of a graphite-Co/Ni (1.2 at.%) target in an Ar gas atmosphere (600 Torr), we used emission imaging spectroscopy and shadowgraphy with a temporal resolution of 1.67 ms. Wavelength-selected emission images showed that C2 emission was strong in the region close to the target (within 2 cm), while for the same region the blackbody radiation from the large clusters or particles increased with increasing distance from the target. Shadowgraph images showed that the viscous flow of carbon and metal species formed a mushroom or a turbulent cloud spreading slowly into the Ar atmosphere, indicating that particles and SWNTs continued to grow as the ejected material cooled. In addition, emission imaging spectroscopy at 1200 °C showed that C2 and hot clusters and particles with higher emission intensities were distributed over much wider areas. We discuss the growth dynamics of the particles and SWNTs through the interaction of the ambient Ar with the carbon and metal species released from the target by the laser pulse.

Dynamics of colloidal particles in electrohydrodynamic convection of nematic liquid crystal.

PubMed

Takahashi, Kentaro; Kimura, Yasuyuki

2014-07-01

We have studied the dynamics of micrometer-sized colloidal particles in electrohydrodynamic convection of nematic liquid crystal. Above the onset voltage of electroconvection, the parallel array of convection rolls appears to be perpendicular to the nematic field at first. The particles are forced to rotate by convection flow and are trapped within a single roll in this voltage regime. A slow glide motion along the roll axis is also observed. The frequency of rotational motion and the glide velocity increase with the applied voltage. Under a much larger voltage where the roll axis temporally fluctuates, the particles occasionally hop to the neighbor rolls. In this voltage regime, the motion of the particles becomes two-dimensional. The motion perpendicular to the roll axis exhibits diffusion behavior at a long time period. The effective diffusion constant is 10(3)-10(4) times larger than the molecular one. The observed behavior is compared with the result obtained by a simple stochastic model for the transport of the particles in convection. The enhancement of diffusion can be quantitatively described well by the rotation frequency in a roll, the width of the roll, and the hopping probability to the neighbor rolls.

Simulation of nanopowder compaction in terms of granular dynamics

NASA Astrophysics Data System (ADS)

Boltachev, G. Sh.; Volkov, N. B.

2011-07-01

The uniaxial compaction of nanopowders is simulated using the granular dynamics in the 2D geometry. The initial arrangement of particles is represented by (i) a layer of particles executing Brownian motion (isotropic structures) and (ii) particles falling in the gravity field (anisotropic structures). The influence of size effects and the size of a model cell on the properties of the structures are studied. The compaction of the model cell is simulated with regard to Hertz elastic forces between particles, Cattaneo-Mindlin-Deresiewicz shear friction forces, and van der Waals-Hamaker dispersion forces of attraction. Computation is performed for monodisperse powders with particle sizes ranging from 10 to 400 nm and for "cohesionless" powder, in which attractive forces are absent. It is shown that taking into account dispersion forces makes it possible to simulate the size effect in the nanopowder compaction: the compressibility of the nanopowder drops as the particles get finer. The mean coordination number and the axial and lateral pressures in the powder systems are found, and the effect of the density and isotropy of the initial structure on the compressibility is analyzed. The applicability of well-known Rumpf's formula for the size effect is discussed.

A study of sedimentation and aggregation of volcanic particles based on experiments carried out with a vertical wind tunnel

NASA Astrophysics Data System (ADS)

Bagheri, G.; Bonadonna, C.; Manzella, I.; Pontelandolfo, P.; Haas, P.

2012-12-01

A complete understanding and parameterization of both particle sedimentation and particle aggregation require systematic and detailed laboratory investigations performed in controlled conditions. For this purpose, a dedicated 4-meter-high vertical wind tunnel has been designed and constructed at the University of Geneva in collaboration with the Groupe de compétence en mécanique des fluides et procédés énergétiques (CMEFE). Final design is a result of Computational Fluid Dynamics simulations combined with laboratory tests. With its diverging test section, the tunnel is designed to suspend particles of different shapes and sizes in order to study the aero-dynamical behavior of volcanic particles and their collision and aggregation. In current set-up, velocities between 5.0 to 27 ms-1 can be obtained, which correspond to typical volcanic particles with diameters between 10 to 40 mm. A combination of Particle Tracking Velocimetry (PTV) and statistical methods is used to derive particle terminal velocity. The method is validated using smooth spherical particles with known drag coefficient. More than 120 particles of different shapes (i.e. spherical, regular and volcanic) and compositions are 3D-scanned and almost 1 million images of their suspension in the test section of wind tunnel are recorded by a high speed camera and analyzed by a PTV code specially developed for the wind tunnel. Measured values of terminal velocity for tested particles are between 3.6 and 24.9 ms-1 which corresponds to Reynolds numbers between 8×103 and 1×105. In addition to the vertical wind tunnel, an apparatus with height varying between 0.5 and 3.5 m has been built to measure terminal velocity of micrometric particles in Reynolds number between 4 and 100. In these experiments, particles are released individually in the air at top of the apparatus and their terminal velocities are measured at the bottom of apparatus by a combination of high-speed camera imaging and PTV post-analyzing. Effects of shape, porosity and orientation of the particles on their terminal velocity are studied. Various shape factors are measured based on different methods, such as 3D-scanning, 2D-image processing, SEM image analysis, caliper measurements, pycnometer and buoyancy tests. Our preliminary experiments on non-smooth spherical particles and irregular particles reveal some interesting aspects. First, the effect of surface roughness and porosity is more important for spherical particles than for regular non-spherical and irregular particles. Second, results underline how, the aero-dynamical behavior of individual irregular particles is better characterized by a range of values of drag coefficients instead of a single value. Finally, since all the shape factors are calculated precisely for each individual particle, the resulted database can provide important information to benchmark and improve existing terminal-velocity models. Modifications of the wind tunnel, i.e. very low air speed (0.03-5.0 ms-1) for suspension of micrometric particles, and of the PTV code, i.e. multiple particle tracking and collision counting, have also been performed in combination to the installation of a particle charging device, a controlled humidifier and a high-power chiller (to reach values down to -20 °C) in order to investigate both wet and dry aggregation of volcanic particles.

Structure of bicomponent particles synthesized from colliding metal clusters

NASA Astrophysics Data System (ADS)

Kryzhevich, D. S.; Zolnikov, K. P.; Korchuganov, A. V.; Psakhie, S. G.

2017-12-01

Here, based on a molecular dynamics simulation with many-body interaction potentials, we consider several scenarios of the formation of bicomponent particles from colliding clusters in an electrical explosion of Cu and Ni wires. The data suggest that the structure of bicomponent particles depends largely on the explosion time of one wire with respect to the other and on the phase state of colliding clusters. Diagrams are presented demonstrating the dynamics of bicomponent particles with block structure synthesized from crystalline Ni and molten Cu clusters.

Dynamic Modeling of Yield and Particle Size Distribution in Continuous Bayer Precipitation

NASA Astrophysics Data System (ADS)

Stephenson, Jerry L.; Kapraun, Chris

Process engineers at Alcoa's Point Comfort refinery are using a dynamic model of the Bayer precipitation area to evaluate options in operating strategies. The dynamic model, a joint development effort between Point Comfort and the Alcoa Technical Center, predicts process yields, particle size distributions and occluded soda levels for various flowsheet configurations of the precipitation and classification circuit. In addition to rigorous heat, material and particle population balances, the model includes mechanistic kinetic expressions for particle growth and agglomeration and semi-empirical kinetics for nucleation and attrition. The kinetic parameters have been tuned to Point Comfort's operating data, with excellent matches between the model results and plant data. The model is written for the ACSL dynamic simulation program with specifically developed input/output graphical user interfaces to provide a user-friendly tool. Features such as a seed charge controller enhance the model's usefulness for evaluating operating conditions and process control approaches.

Simulation of Particle Size Effect on Dynamic Properties and Fracture of PTFE-W-Al Composites

NASA Astrophysics Data System (ADS)

Herbold, Eric; Cai, Jing; Benson, David; Nesterenko, Vitali

2007-06-01

Recent investigations of the dynamic compressive strength of cold isostatically pressed (CIP) composites of polytetrafluoroethylene (PTFE), tungsten and aluminum powders show significant differences depending on the size of metallic particles. PTFE and aluminum mixtures are known to be energetic under dynamic and thermal loading. The addition of tungsten increases density and overall strength of the sample. Multi-material Eulerian and arbitrary Lagrangian-Eulerian methods were used for the investigation due to the complexity of the microstructure, relatively large deformations and the ability to handle the formation of free surfaces in a natural manner. The calculations indicate that the observed dependence of sample strength on particle size is due to the formation of force chains under dynamic loading in samples with small particle sizes even at larger porosity in comparison with samples with large grain size and larger density.

Computing the non-Markovian coarse-grained interactions derived from the Mori-Zwanzig formalism in molecular systems: Application to polymer melts

NASA Astrophysics Data System (ADS)

Li, Zhen; Lee, Hee Sun; Darve, Eric; Karniadakis, George Em

2017-01-01

Memory effects are often introduced during coarse-graining of a complex dynamical system. In particular, a generalized Langevin equation (GLE) for the coarse-grained (CG) system arises in the context of Mori-Zwanzig formalism. Upon a pairwise decomposition, GLE can be reformulated into its pairwise version, i.e., non-Markovian dissipative particle dynamics (DPD). GLE models the dynamics of a single coarse particle, while DPD considers the dynamics of many interacting CG particles, with both CG systems governed by non-Markovian interactions. We compare two different methods for the practical implementation of the non-Markovian interactions in GLE and DPD systems. More specifically, a direct evaluation of the non-Markovian (NM) terms is performed in LE-NM and DPD-NM models, which requires the storage of historical information that significantly increases computational complexity. Alternatively, we use a few auxiliary variables in LE-AUX and DPD-AUX models to replace the non-Markovian dynamics with a Markovian dynamics in a higher dimensional space, leading to a much reduced memory footprint and computational cost. In our numerical benchmarks, the GLE and non-Markovian DPD models are constructed from molecular dynamics (MD) simulations of star-polymer melts. Results show that a Markovian dynamics with auxiliary variables successfully generates equivalent non-Markovian dynamics consistent with the reference MD system, while maintaining a tractable computational cost. Also, transient subdiffusion of the star-polymers observed in the MD system can be reproduced by the coarse-grained models. The non-interacting particle models, LE-NM/AUX, are computationally much cheaper than the interacting particle models, DPD-NM/AUX. However, the pairwise models with momentum conservation are more appropriate for correctly reproducing the long-time hydrodynamics characterised by an algebraic decay in the velocity autocorrelation function.

Micro-rheology and interparticle interactions in aerosols probed with optical tweezers

NASA Astrophysics Data System (ADS)

Reid, Jonathan P.; Power, Rory M.; Cai, Chen; Simpson, Stephen H.

2014-09-01

Using optical tweezers for micro-rheological investigations of a surrounding fluid has been routinely demonstrated. In this work, we will demonstrate that rheological measurements of the bulk and surface properties of aerosol particles can be made directly using optical tweezers, providing important insights into the phase behavior of materials in confined environments and the rate of molecular diffusion in viscous phases. The use of holographic optical tweezers to manipulate aerosol particles has become standard practice in recent years, providing an invaluable tool to investigate particle dynamics, including evaporation/ condensation kinetics, chemical aging and phase transformation. When combined with non-linear Raman spectroscopy, the size and refractive index of a particle can be determined with unprecedented accuracy <+/- 0.05%). Active control of the relative positions of pairs of particles can allow studies of the coalescence of particles, providing a unique opportunity to investigate the bulk and surface properties that govern the hydrodynamic relaxation in particle shape. In particular, we will show how the viscosity and surface tension of particles can be measured directly in the under-damped regime at low viscosity. In the over-damped regime, we will show that viscosity measurements can extend close to the glass transition, allowing measurements over an impressive dynamic range of 12 orders of magnitude in relaxation timescale and viscosity. Indeed, prior to the coalescence event, we will show how the Brownian trajectories of trapped particles can yield important and unique insights into the interactions of aerosol particles.

Real-time particle tracking for studying intracellular trafficking of pharmaceutical nanocarriers.

PubMed

Huang, Feiran; Watson, Erin; Dempsey, Christopher; Suh, Junghae

2013-01-01

Real-time particle tracking is a technique that combines fluorescence microscopy with object tracking and computing and can be used to extract quantitative transport parameters for small particles inside cells. Since the success of a nanocarrier can often be determined by how effectively it delivers cargo to the target organelle, understanding the complex intracellular transport of pharmaceutical nanocarriers is critical. Real-time particle tracking provides insight into the dynamics of the intracellular behavior of nanoparticles, which may lead to significant improvements in the design and development of novel delivery systems. Unfortunately, this technique is not often fully understood, limiting its implementation by researchers in the field of nanomedicine. In this chapter, one of the most complicated aspects of particle tracking, the mean square displacement (MSD) calculation, is explained in a simple manner designed for the novice particle tracker. Pseudo code for performing the MSD calculation in MATLAB is also provided. This chapter contains clear and comprehensive instructions for a series of basic procedures in the technique of particle tracking. Instructions for performing confocal microscopy of nanoparticle samples are provided, and two methods of determining particle trajectories that do not require commercial particle-tracking software are provided. Trajectory analysis and determination of the tracking resolution are also explained. By providing comprehensive instructions needed to perform particle-tracking experiments, this chapter will enable researchers to gain new insight into the intracellular dynamics of nanocarriers, potentially leading to the development of more effective and intelligent therapeutic delivery vectors.

Interaction of a supersonic particle with a three-dimensional complex plasma

NASA Astrophysics Data System (ADS)

Zaehringer, E.; Schwabe, M.; Zhdanov, S.; Mohr, D. P.; Knapek, C. A.; Huber, P.; Semenov, I. L.; Thomas, H. M.

2018-03-01

The influence of a supersonic projectile on a three-dimensional complex plasma is studied. Micron sized particles in a low-temperature plasma formed a large undisturbed system in the new "Zyflex" chamber during microgravity conditions. A supersonic probe particle excited a Mach cone with Mach number M ≈ 1.5-2 and double Mach cone structure in the large weakly damped particle cloud. The speed of sound is measured with different methods and particle charge estimations are compared to the calculations from standard theories. The high image resolution enables the study of Mach cones in microgravity on the single particle level of a three-dimensional complex plasma and gives insight to the dynamics. A heating of the microparticles is discovered behind the supersonic projectile but not in the flanks of the Mach cone.

Void initiation from interfacial debonding of spherical silicon particles inside a silicon-copper nanocomposite: a molecular dynamics study

NASA Astrophysics Data System (ADS)

Cui, Yi; Chen, Zengtao

2017-02-01

Silicon particles with diameters from 1.9 nm to 30 nm are embedded in a face-centered-cubic copper matrix to form nanocomposite specimens for simulation. The interfacial debonding of silicon particles from the copper matrix and the subsequent growth of nucleated voids are studied via molecular dynamics (MD). The MD results are examined from several different perspectives. The overall mechanical performance is monitored by the average stress-strain response and the accumulated porosity. The ‘relatively farthest-traveled’ atoms are identified to characterize the onset of interfacial debonding. The relative displacement field is plotted to illustrate both subsequent interfacial debonding and the growth of a nucleated void facilitated by a dislocation network. Our results indicate that the initiation of interfacial debonding is due to the accumulated surface stress if the matrix is initially dislocation-free. However, pre-existing dislocations can make a considerable difference. In either case, the dislocation emission also contributes to the subsequent debonding process. As for the size effect, the debonding of relatively larger particles causes a drop in the stress-strain curve. The volume fraction of second-phase particles is found to be more influential than the size of the simulation box on the onset of interfacial debonding. The volume fraction of second-phase particles also affects the shape of the nucleated void and, therefore, influences the stress response of the composite.

Effect of induced cohesion on stick-slip dynamics in weakly saturated, sheared granular fault gouge

DOE PAGES

Dorostkar, Omid; Guyer, Robert A.; Johnson, Paul Allan; ...

2018-02-28

We use three-dimensional discrete element calculations to study stick-slip dynamics in a weakly wet granular layer designed to simulate fault gouge. The granular gouge is constituted by 8000 spherical particles with a poly-disperse size distribution. At very low liquid content, liquids impose cohesive and viscous forces on particles. Our simulations show that by increasing the liquid content, friction increases and granular layer shows higher recurrence time between slip events. We also observe that slip events exhibit larger friction drop and layer compaction in wet system compared to dry. We demonstrate that a small volume of liquid induces cohesive forces betweenmore » wet particles that are responsible for an increase in coordination number leading to a more stable arrangement of particles. This stabilization is evidenced with two orders of magnitude lower particle kinetic energy in wet system during stick phase. Similar to previous experimental studies, we observe enhanced frictional strength for wet granular layers. In experiments, the physicochemical processes are believed to be the main reason for such behavior, we show however, that at low confining stresses the hydromechanical effects of induced cohesion are sufficient for observed behavior. Our simulations illuminate the role of particle interactions and demonstrate the conditions under which induced cohesion plays a significant role in fault zone processes, including slip initiation, weakening, and failure.« less

Effect of induced cohesion on stick-slip dynamics in weakly saturated, sheared granular fault gouge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dorostkar, Omid; Guyer, Robert A.; Johnson, Paul Allan

We use three-dimensional discrete element calculations to study stick-slip dynamics in a weakly wet granular layer designed to simulate fault gouge. The granular gouge is constituted by 8000 spherical particles with a poly-disperse size distribution. At very low liquid content, liquids impose cohesive and viscous forces on particles. Our simulations show that by increasing the liquid content, friction increases and granular layer shows higher recurrence time between slip events. We also observe that slip events exhibit larger friction drop and layer compaction in wet system compared to dry. We demonstrate that a small volume of liquid induces cohesive forces betweenmore » wet particles that are responsible for an increase in coordination number leading to a more stable arrangement of particles. This stabilization is evidenced with two orders of magnitude lower particle kinetic energy in wet system during stick phase. Similar to previous experimental studies, we observe enhanced frictional strength for wet granular layers. In experiments, the physicochemical processes are believed to be the main reason for such behavior, we show however, that at low confining stresses the hydromechanical effects of induced cohesion are sufficient for observed behavior. Our simulations illuminate the role of particle interactions and demonstrate the conditions under which induced cohesion plays a significant role in fault zone processes, including slip initiation, weakening, and failure.« less

Cohesion-Induced Stabilization in Stick-Slip Dynamics of Weakly Wet, Sheared Granular Fault Gouge

NASA Astrophysics Data System (ADS)

Dorostkar, Omid; Guyer, Robert A.; Johnson, Paul A.; Marone, Chris; Carmeliet, Jan

2018-03-01

We use three-dimensional discrete element calculations to study stick-slip dynamics in a weakly wet granular layer designed to simulate fault gouge. The granular gouge is constituted by 8,000 spherical particles with a polydisperse size distribution. At very low liquid content, liquids impose cohesive and viscous forces on particles. Our simulations show that by increasing the liquid content, friction increases and granular layer shows higher recurrence time between slip events. We also observe that slip events exhibit larger friction drop and layer compaction in wet system compared to dry. We demonstrate that a small volume of liquid induces cohesive forces between wet particles that are responsible for an increase in coordination number leading to a more stable arrangement of particles. This stabilization is evidenced with 2 orders of magnitude lower particle kinetic energy in wet system during stick phase. Similar to previous experimental studies, we observe enhanced frictional strength for wet granular layers. In experiments, the physicochemical processes are believed to be the main reason for such behavior; we show, however, that at low confining stresses, the hydromechanical effects of induced cohesion are sufficient for observed behavior. Our simulations illuminate the role of particle interactions and demonstrate the conditions under which induced cohesion plays a significant role in fault zone processes, including slip initiation, weakening, and failure.

Dynamical density functional theory for arbitrary-shape colloidal fluids including inertia and hydrodynamic interactions

NASA Astrophysics Data System (ADS)

Duran-Olivencia, Miguel A.; Goddard, Ben; Kalliadasis, Serafim

2015-11-01

Over the last few decades the classical density-functional theory (DFT) and its dynamic extensions (DDFTs) have become a remarkably powerful tool in the study of colloidal fluids. Recently there has been extensive research to generalise all previous DDFTs finally yielding a general DDFT equation (for spherical particles) which takes into account both inertia and hydrodynamic interactions (HI) which strongly influence non-equilibrium properties. The present work will be devoted to a further generalisation of such a framework to systems of anisotropic particles. To this end, the kinetic equation for the Brownian particle distribution function is derived starting from the Liouville equation and making use of Zwanzig's projection-operator techniques. By averaging over all but one particle, a DDFT equation is finally obtained with some similarities to that for spherical colloids. However, there is now an inevitable translational-rotational coupling which affects the diffusivity of asymmetric particles. Lastly, in the overdamped (high friction) limit the theory is notably simplified leading to a DDFT equation which agrees with previous derivations. We acknowledge financial support from European Research Council via Advanced Grant No. 247031.

Emergence of chaos in a spatially confined reactive system

NASA Astrophysics Data System (ADS)

Voorsluijs, Valérie; De Decker, Yannick

2016-11-01

In spatially restricted media, interactions between particles and local fluctuations of density can lead to important deviations of the dynamics from the unconfined, deterministic picture. In this context, we investigated how molecular crowding can affect the emergence of chaos in small reactive systems. We developed to this end an amended version of the Willamowski-Rössler model, where we account for the impenetrability of the reactive species. We analyzed the deterministic kinetics of this model and studied it with spatially-extended stochastic simulations in which the mobility of particles is included explicitly. We show that homogeneous fluctuations can lead to a destruction of chaos through a fluctuation-induced collision between chaotic trajectories and absorbing states. However, an interplay between the size of the system and the mobility of particles can counterbalance this effect so that chaos can indeed be found when particles diffuse slowly. This unexpected effect can be traced back to the emergence of spatial correlations which strongly affect the dynamics. The mobility of particles effectively acts as a new bifurcation parameter, enabling the system to switch from stationary states to absorbing states, oscillations or chaos.

Self-Healing Nanocomposite Hydrogel with Well-Controlled Dynamic Mechanics

NASA Astrophysics Data System (ADS)

Li, Qiaochu; Mishra, Sumeet; Chen, Pangkuan; Tracy, Joseph; Holten-Andersen, Niels

Network dynamics is a crucial factor that determines the macroscopic self-healing rate and efficiency in polymeric hydrogel materials, yet its controllability is seldom studied in most reported self-healing hydrogel systems. Inspired by mussel's adhesion chemistry, we developed a novel approach to assemble inorganic nanoparticles and catechol-decorated PEG polymer into a hydrogel network. When utilized as reversible polymer-particle crosslinks, catechol-metal coordination bonds yield a unique gel network with dynamic mechanics controlled directly by interfacial crosslink structure. Taking advantage of this structure-property relationship at polymer-particle interfaces, we next designed a hierarchically structured hybrid gel with two distinct relaxation timescales. By tuning the relative contribution of the two hierarchical relaxation modes, we are able to finely control the gel's dynamic mechanical behavior from a viscoelastic fluid to a stiff solid, yet preserving its fast self-healing property without the need for external stimuli.

The effects of particle shape, size, and interaction on colloidal glasses and gels

NASA Astrophysics Data System (ADS)

Kramb, Ryan C.

Using multiple step seeded emulsion polymerization reactions, colloid particles of tunable shape are synthesized from polystyrene. In all, four particle shapes are studied referred to as spheres (S), heteronuclear dicolloids (hDC), symmetric homonuclear dicolloids (sDC), and tricolloids (TC). Two size ranges of particles are studied with approximate diameters in the range of 200-300nm and 1.1-1.3mum. The solvent ionic strength is varied from 10 -3M to 1M resulting in particle interaction potentials that range from repulsive to attractive. The effect of anisotropic shape is found to increase the glass transition volume fraction (φg) in good agreement with activated naive Mode Coupling Theory (nMCT) calculations. Differences in φg and the linear elastic modulus (G0') due to particle shape can be understood in terms of the Random Close Packed volume fraction (φRCP ) for each shape; φRCP- φg is a constant. In addition, a reentrant phase diagram is found for S and sDC particles with a maximum in the fluid state volume fraction found at weakly attractive interaction potential, in agreement well with theoretical calculations. Nonlinear rheology and yielding behavior of repulsive and attractive spheres and anisotropic particles are examined and understood in terms of barriers constraining motion. The barriers are due to interparticle bonds or cages constraining translational or rotational motion. Yield stress has similar volume fraction dependence as G 0' and a similar framework is used to understand differences due to particle shape and interaction. For larger particles, the effects of shape and interaction are studied with respect to dynamic yielding and shear thickening. The dynamic yield stress is found to increase with volume fraction while the stress at thickening is constant. The intersection of these indicates a possible jamming point below φRCP.

Nucleation and growth of Y2O3 nanoparticles in a RF-ICTP reactor: a discrete sectional study based on CFD simulation supported with experiments

NASA Astrophysics Data System (ADS)

Dhamale, G. D.; Tak, A. K.; Mathe, V. L.; Ghorui, S.

2018-06-01

Synthesis of yttria (Y2O3) nanoparticles in an atmospheric pressure radiofrequency inductively coupled thermal plasma (RF-ICTP) reactor has been investigated using the discrete-sectional (DS) model of particle nucleation and growth with argon as the plasma gas. Thermal and fluid dynamic information necessary for the investigation have been extracted through rigorous computational fluid dynamic (CFD) study of the system with coupled electromagnetic equations under the extended field approach. The theoretical framework has been benchmarked against published data first, and then applied to investigate the nucleation and growth process of yttrium oxide nanoparticles in the plasma reactor using the discrete-sectional (DS) model. While a variety of nucleation and growth mechanisms are suggested in literature, the study finds that the theory of homogeneous nucleation fits well with the features observed experimentally. Significant influences of the feed rate and quench rate on the distribution of particles sizes are observed. Theoretically obtained size distribution of the particles agrees well with that observed in the experiment. Different thermo-fluid dynamic environments with varied quench rates, encountered by the propagating vapor front inside the reactor under different operating conditions are found to be primarily responsible for variations in the width of the size distribution.

Crystalline structures of particles interacting through the harmonic-repulsive pair potential

NASA Astrophysics Data System (ADS)

Levashov, V. A.

2017-09-01

The behavior of identical particles interacting through the harmonic-repulsive pair potential has been studied in 3D using molecular dynamics simulations at a number of different densities. We found that at many densities, as the temperature of the systems decreases, the particles crystallize into complex structures whose formation has not been anticipated in previous studies on the harmonic-repulsive pair potential. In particular, at certain densities, crystallization into the structure I a 3 ¯ d (space group #230) with 16 particles in the unit cell occupying Wyckoff special positions (16b) was observed. This crystal structure has not been observed previously in experiments or in computer simulations of single component atomic or soft matter systems. At another density, we observed a liquid which is rather stable against crystallization. Yet, we observed crystallization of this liquid into the monoclinic C2/c (space group #15) structure with 32 particles in the unit cell occupying four different non-special Wyckoff (8f) sites. In this structure particles located at different Wyckoff sites have different energies. From the perspective of the local atomic environment, the organization of particles in this structure resembles the structure of some columnar quasicrystals. At a different value of the density, we did not observe crystallization at all despite rather long molecular dynamics runs. At two other densities, we observed the formation of the β S n distorted diamond structures instead of the expected diamond structure. Possibly, we also observed the formation of the R 3 ¯ c hexagonal lattice with 24 particles per unit cell occupying non-equivalent positions.

Anti-Brownian ELectrokinetic (ABEL) Trapping of Single High Density Lipoprotein (HDL) Particles

NASA Astrophysics Data System (ADS)

Bockenhauer, Samuel; Furstenberg, Alexandre; Wang, Quan; Devree, Brian; Jie Yao, Xiao; Bokoch, Michael; Kobilka, Brian; Sunahara, Roger; Moerner, W. E.

2010-03-01

The ABEL trap is a novel device for trapping single biomolecules in solution for extended observation. The trap estimates the position of a fluorescently-labeled object as small as ˜10 nm in solution and then applies a feedback electrokinetic drift every 20 us to trap the object by canceling its Brownian motion. We use the ABEL trap to study HDL particles at the single-copy level. HDL particles, essential in regulation of ``good'' cholesterol in humans, comprise a small (˜10 nm) lipid bilayer disc bounded by a belt of apolipoproteins. By engineering HDL particles with single fluorescent donor/acceptor probes and varying lipid compositions, we are working to study lipid diffusion on small length scales. We also use HDL particles as hosts for single transmembrane receptors, which should enable study of receptor conformational dynamics on long timescales.

Composition, morphology, and growth of clusters in a gas of particles with random interactions

NASA Astrophysics Data System (ADS)

Azizi, Itay; Rabin, Yitzhak

2018-03-01

We use Langevin dynamics simulations to study the growth kinetics and the steady-state properties of condensed clusters in a dilute two-dimensional system of particles that are all different (APD) in the sense that each particle is characterized by a randomly chosen interaction parameter. The growth exponents, the transition temperatures, and the steady-state properties of the clusters and of the surrounding gas phase are obtained and compared with those of one-component systems. We investigate the fractionation phenomenon, i.e., how particles of different identities are distributed between the coexisting mother (gas) and daughter (clusters) phases. We study the local organization of particles inside clusters, according to their identity—neighbourhood identity ordering (NIO)—and compare the results with those of previous studies of NIO in dense APD systems.

Molecular Dynamics Studies of Overbased Detergents on a Water Surface.

PubMed

Bodnarchuk, M S; Dini, D; Heyes, D M; Breakspear, A; Chahine, S

2017-07-25

Molecular dynamics (MD) simulations are reported of model overbased detergent nanoparticles on a model water surface which mimic their behavior on a Langmuir trough or large water droplet in engine oil. The simulations predict that the structure of the nanoparticle on a water surface is different to when it is immersed in a bulk hydrophobic solvent. The surfactant tails are partly directed out of the water, while the carbonate core maximizes its extent of contact with the water. Umbrella sampling calculations of the potential of mean force between two particles showed that they are associated with varying degrees with a maximum binding free energy of ca. 10 k B T for the salicylate stabilized particle, ca. 8 k B T for a sulfurized alkyl phenate stabilized particle, and ca. 5 k B T for a sulfonate stabilized particle. The differences in the strength of attraction depend on the proximity of nearest approach and the energy penalty associated with the disruption of the hydration shell of water molecules around the calcium carbonate core when the two particles approach. This is greatest for the sulfonate particle, which partially loses the surfactant ions to the solution, and least for the salicylate, which forms the weakest water "cage". The particles are separated by a water hydration layer, even at the point of closest approach.

A MD simulation and analysis for aggregation behaviors of nanoscale zero-valent iron particles in water via MS.

PubMed

Zhao, Ying; Liu, Dongmei; Tang, Huan; Lu, Jing; Cui, Fuyi

2014-01-01

With the development of nanotechnology, more nanomaterials will enter into water environment system. Studying the existing form of nanomaterials in water environment will help people benefit from the correct use of them and to reduce the harm to human caused by them for some nanomaterials can bring polluting effect. Aggregation is a main behavior for nanoparticle in water environment. NZVI are used widely in many fields resulting in more NZVI in water environment. Molecular dynamics simulations and Materials Studio software are used to investigate the microaggregation behaviors of NZVI particles. Two scenes are involved: (1) particle size of NZVI in each simulation system is the same, but initial distance of two NZVI particles is different; (2) initial distance of two NZVI particles in each simulation system is the same, but particle size of NZVI is different. Atomistic trajectory, NP activity, total energy, and adsorption of H2O are analyzed with MS. The method provides new quantitative insight into the structure, energy, and dynamics of the aggregation behaviors of NZVI particles in water. It is necessary to understand microchange of NPs in water because it can provide theoretical research that is used to reduce polluting effect of NPs on water environment.

A MD Simulation and Analysis for Aggregation Behaviors of Nanoscale Zero-Valent Iron Particles in Water via MS

PubMed Central

Liu, Dongmei; Tang, Huan; Lu, Jing; Cui, Fuyi

2014-01-01

With the development of nanotechnology, more nanomaterials will enter into water environment system. Studying the existing form of nanomaterials in water environment will help people benefit from the correct use of them and to reduce the harm to human caused by them for some nanomaterials can bring polluting effect. Aggregation is a main behavior for nanoparticle in water environment. NZVI are used widely in many fields resulting in more NZVI in water environment. Molecular dynamics simulations and Materials Studio software are used to investigate the microaggregation behaviors of NZVI particles. Two scenes are involved: (1) particle size of NZVI in each simulation system is the same, but initial distance of two NZVI particles is different; (2) initial distance of two NZVI particles in each simulation system is the same, but particle size of NZVI is different. Atomistic trajectory, NP activity, total energy, and adsorption of H2O are analyzed with MS. The method provides new quantitative insight into the structure, energy, and dynamics of the aggregation behaviors of NZVI particles in water. It is necessary to understand microchange of NPs in water because it can provide theoretical research that is used to reduce polluting effect of NPs on water environment. PMID:25250388

Flocking dynamics with voter-like interactions

NASA Astrophysics Data System (ADS)

Baglietto, Gabriel; Vazquez, Federico

2018-03-01

We study the collective motion of a large set of self-propelled particles subject to voter-like interactions. Each particle moves on a 2D space at a constant speed in a direction that is randomly assigned initially. Then, at every step of the dynamics, each particle adopts the direction of motion of a randomly chosen neighboring particle. We investigate the time evolution of the global alignment of particles measured by the order parameter φ, until complete order \\varphi=1.0 is reached (polar consensus). We find that φ increases as t 1/2 for short times and approaches 1.0 exponentially fast for longer times. Also, the mean time to consensus τ varies non-monotonically with the density of particles ρ, reaching a minimum at some intermediate density ρmin . At ρmin , the mean consensus time scales with the system size N as τmin ∼ N0.765 , and thus the consensus is faster than in the case of all-to-all interactions (large ρ) where τ=2N . We show that the fast consensus, also observed at intermediate and high densities, is a consequence of the segregation of the system into clusters of equally-oriented particles which breaks the balance of transitions between directional states in well mixed systems.

Effects of temperature and particles concentration on the dynamic viscosity of MgO-MWCNT/ethylene glycol hybrid nanofluid: Experimental study

NASA Astrophysics Data System (ADS)

Soltani, Omid; Akbari, Mohammad

2016-10-01

In this paper, the effects of temperature and particles concentration on the dynamic viscosity of MgO-MWCNT/ethylene glycol hybrid nanofluid is examined. The experiments carried out in the solid volume fraction range of 0 to 1.0% under the temperature ranging from 30 °C to 60 °C. The results showed that the hybrid nanofluid behaves as a Newtonian fluid for all solid volume fractions and temperatures considered. The measurements also indicated that the dynamic viscosity increases with increasing the solid volume fraction and decreases with the temperature rising. The relative viscosity revealed that when the solid volume fraction enhances from 0.1 to 1%, the dynamic viscosity increases up to 168%. Finally, using experimental data, in order to predict the dynamic viscosity of MgO-MWCNT/ethylene glycol hybrid nanofluids, a new correlation has been suggested. The comparisons between the correlation outputs and experimental results showed that the suggested correlation has an acceptable accuracy.

Involvement of the Rac1-IRSp53-Wave2-Arp2/3 Signaling Pathway in HIV-1 Gag Particle Release in CD4 T Cells.

PubMed

Thomas, Audrey; Mariani-Floderer, Charlotte; López-Huertas, Maria Rosa; Gros, Nathalie; Hamard-Péron, Elise; Favard, Cyril; Ohlmann, Theophile; Alcamí, José; Muriaux, Delphine

2015-08-01

During HIV-1 assembly, the Gag viral proteins are targeted and assemble at the inner leaflet of the cell plasma membrane. This process could modulate the cortical actin cytoskeleton, located underneath the plasma membrane, since actin dynamics are able to promote localized membrane reorganization. In addition, activated small Rho GTPases are known for regulating actin dynamics and membrane remodeling. Therefore, the modulation of such Rho GTPase activity and of F-actin by the Gag protein during virus particle formation was considered. Here, we studied the implication of the main Rac1, Cdc42, and RhoA small GTPases, and some of their effectors, in this process. The effect of small interfering RNA (siRNA)-mediated Rho GTPases and silencing of their effectors on Gag localization, Gag membrane attachment, and virus-like particle production was analyzed by immunofluorescence coupled to confocal microscopy, membrane flotation assays, and immunoblot assays, respectively. In parallel, the effect of Gag expression on the Rac1 activation level was monitored by G-LISA, and the intracellular F-actin content in T cells was monitored by flow cytometry and fluorescence microscopy. Our results revealed the involvement of activated Rac1 and of the IRSp53-Wave2-Arp2/3 signaling pathway in HIV-1 Gag membrane localization and particle release in T cells as well as a role for actin branching and polymerization, and this was solely dependent on the Gag viral protein. In conclusion, our results highlight a new role for the Rac1-IRSp53-Wave2-Arp2/3 signaling pathway in the late steps of HIV-1 replication in CD4 T lymphocytes. During HIV-1 assembly, the Gag proteins are targeted and assembled at the inner leaflet of the host cell plasma membrane. Gag interacts with specific membrane phospholipids that can also modulate the regulation of cortical actin cytoskeleton dynamics. Actin dynamics can promote localized membrane reorganization and thus can be involved in facilitating Gag assembly and particle formation. Activated small Rho GTPases and effectors are regulators of actin dynamics and membrane remodeling. We thus studied the effects of the Rac1, Cdc42, and RhoA GTPases and their specific effectors on HIV-1 Gag membrane localization and viral particle release in T cells. Our results show that activated Rac1 and the IRSp53-Wave2-Arp2/3 signaling pathway are involved in Gag plasma membrane localization and viral particle production. This work uncovers a role for cortical actin through the activation of Rac1 and the IRSp53/Wave2 signaling pathway in HIV-1 particle formation in CD4 T lymphocytes. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

Involvement of the Rac1-IRSp53-Wave2-Arp2/3 Signaling Pathway in HIV-1 Gag Particle Release in CD4 T Cells

PubMed Central

Thomas, Audrey; Mariani-Floderer, Charlotte; López-Huertas, Maria Rosa; Gros, Nathalie; Hamard-Péron, Elise; Favard, Cyril; Ohlmann, Theophile; Alcamí, José

2015-01-01

ABSTRACT During HIV-1 assembly, the Gag viral proteins are targeted and assemble at the inner leaflet of the cell plasma membrane. This process could modulate the cortical actin cytoskeleton, located underneath the plasma membrane, since actin dynamics are able to promote localized membrane reorganization. In addition, activated small Rho GTPases are known for regulating actin dynamics and membrane remodeling. Therefore, the modulation of such Rho GTPase activity and of F-actin by the Gag protein during virus particle formation was considered. Here, we studied the implication of the main Rac1, Cdc42, and RhoA small GTPases, and some of their effectors, in this process. The effect of small interfering RNA (siRNA)-mediated Rho GTPases and silencing of their effectors on Gag localization, Gag membrane attachment, and virus-like particle production was analyzed by immunofluorescence coupled to confocal microscopy, membrane flotation assays, and immunoblot assays, respectively. In parallel, the effect of Gag expression on the Rac1 activation level was monitored by G-LISA, and the intracellular F-actin content in T cells was monitored by flow cytometry and fluorescence microscopy. Our results revealed the involvement of activated Rac1 and of the IRSp53-Wave2-Arp2/3 signaling pathway in HIV-1 Gag membrane localization and particle release in T cells as well as a role for actin branching and polymerization, and this was solely dependent on the Gag viral protein. In conclusion, our results highlight a new role for the Rac1-IRSp53-Wave2-Arp2/3 signaling pathway in the late steps of HIV-1 replication in CD4 T lymphocytes. IMPORTANCE During HIV-1 assembly, the Gag proteins are targeted and assembled at the inner leaflet of the host cell plasma membrane. Gag interacts with specific membrane phospholipids that can also modulate the regulation of cortical actin cytoskeleton dynamics. Actin dynamics can promote localized membrane reorganization and thus can be involved in facilitating Gag assembly and particle formation. Activated small Rho GTPases and effectors are regulators of actin dynamics and membrane remodeling. We thus studied the effects of the Rac1, Cdc42, and RhoA GTPases and their specific effectors on HIV-1 Gag membrane localization and viral particle release in T cells. Our results show that activated Rac1 and the IRSp53-Wave2-Arp2/3 signaling pathway are involved in Gag plasma membrane localization and viral particle production. This work uncovers a role for cortical actin through the activation of Rac1 and the IRSp53/Wave2 signaling pathway in HIV-1 particle formation in CD4 T lymphocytes. PMID:26018170

Spatial correlation of the dynamic propensity of a glass-forming liquid

NASA Astrophysics Data System (ADS)

Razul, M. Shajahan G.; Matharoo, Gurpreet S.; Poole, Peter H.

2011-06-01

We present computer simulation results on the dynamic propensity (as defined by Widmer-Cooper et al 2004 Phys. Rev. Lett. 93 135701) in a Kob-Andersen binary Lennard-Jones liquid system consisting of 8788 particles. We compute the spatial correlation function for the dynamic propensity as a function of both the reduced temperature T, and the time scale on which the particle displacements are measured. For T <= 0.6, we find that non-zero correlations occur at the largest length scale accessible in our system. We also show that a cluster-size analysis of particles with extremal values of the dynamic propensity, as well as 3D visualizations, reveal spatially correlated regions that approach the size of our system as T decreases, consistently with the behavior of the spatial correlation function. Next, we define and examine the 'coordination propensity', the isoconfigurational average of the coordination number of the minority B particles around the majority A particles. We show that a significant correlation exists between the spatial fluctuations of the dynamic and coordination propensities. In addition, we find non-zero correlations of the coordination propensity occurring at the largest length scale accessible in our system for all T in the range 0.466 < T < 1.0. We discuss the implications of these results for understanding the length scales of dynamical heterogeneity in glass-forming liquids.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cherkaduvasala, V.; Murphy, D.W.; Ban, H.

Popcorn ash particles are fragments of sintered coal fly ash masses that resemble popcorn in low apparent density. They can travel with the flow in the furnace and settle on key places such as catalyst surfaces. Computational fluid dynamics (CFD) models are often used in the design process to prevent the carryover and settling of these particles on catalysts. Particle size, density, and drag coefficient are the most important aerodynamic parameters needed in CFD modeling of particle flow. The objective of this study was to experimentally determine particle size, shape, apparent density, and drag characteristics for popcorn ash particles frommore » a coal-fired power plant. Particle size and shape were characterized by digital photography in three orthogonal directions and by computer image analysis. Particle apparent density was determined by volume and mass measurements. Particle terminal velocities in three directions were measured in water and each particle was also weighed in air and in water. The experimental data were analyzed and models were developed for equivalent sphere and equivalent ellipsoid with apparent density and drag coefficient distributions. The method developed in this study can be used to characterize the aerodynamic properties of popcorn-like particles.« less

Photo-ionization and modification of nanoparticles on transparent substrates by ultrashort laser pulses

NASA Astrophysics Data System (ADS)

Gruzdev, Vitaly; Komolov, Vladimir; Li, Hao; Yu, Qingsong; Przhibel'skii, Sergey; Smirnov, Dmitry

2011-02-01

The objective of this combined experimental and theoretical research is to study the dynamics and mechanisms of nanoparticle interaction with ultrashort laser pulses and related modifications of substrate surface. For the experimental effort, metal (gold), dielectric (SiO2) and dielectric with metal coating (about 30 nm thick) spherical nanoparticles deposited on glass substrate are utilized. Size of the particles varies from 20 to 200 nm. Density of the particles varies from low (mean inter-particle distance 100 nm) to high (mean inter-particle distance less than 1 nm). The nanoparticle assemblies and the corresponding empty substrate surfaces are irradiated with single 130-fs laser pulses at wavelength 775 nm and different levels of laser fluence. Large diameter of laser spot (0.5-2 mm) provides gradient variations of laser intensity over the spot and allows observing different laser-nanoparticle interactions. The interactions vary from total removal of the nanoparticles in the center of laser spot to gentle modification of their size and shape and totally non-destructive interaction. The removed particles frequently form specific sub-micrometer-size pits on the substrate surface at their locations. The experimental effort is supported by simulations of the nanoparticle interactions with high-intensity ultrashort laser pulse. The simulation employs specific modification of the molecular dynamics approach applied to model the processes of non-thermal particle ablation following laser-induced electron emission. This technique delivers various characteristics of the ablation plume from a single nanoparticle including energy and speed distribution of emitted ions, variations of particle size and overall dynamics of its ablation. The considered geometry includes single isolated particle as well a single particle on a flat substrate that corresponds to the experimental conditions. The simulations confirm existence of the different regimes of laser-nanoparticle interactions depending on laser intensity and wavelength. In particular, implantation of ions departing from the nanoparticles towards the substrate is predicted.

Electrokinetic and hydrodynamic properties of charged-particles systems. From small electrolyte ions to large colloids

NASA Astrophysics Data System (ADS)

Nägele, G.; Heinen, M.; Banchio, A. J.; Contreras-Aburto, C.

2013-11-01

Dynamic processes in dispersions of charged spherical particles are of importance both in fundamental science, and in technical and bio-medical applications. There exists a large variety of charged-particles systems, ranging from nanometer-sized electrolyte ions to micron-sized charge-stabilized colloids. We review recent advances in theoretical methods for the calculation of linear transport coefficients in concentrated particulate systems, with the focus on hydrodynamic interactions and electrokinetic effects. Considered transport properties are the dispersion viscosity, self- and collective diffusion coefficients, sedimentation coefficients, and electrophoretic mobilities and conductivities of ionic particle species in an external electric field. Advances by our group are also discussed, including a novel mode-coupling-theory method for conduction-diffusion and viscoelastic properties of strong electrolyte solutions. Furthermore, results are presented for dispersions of solvent-permeable particles, and particles with non-zero hydrodynamic surface slip. The concentration-dependent swelling of ionic microgels is discussed, as well as a far-reaching dynamic scaling behavior relating colloidal long- to short-time dynamics.

Interactive Computer Simulation and Animation for Improving Student Learning of Particle Kinetics

ERIC Educational Resources Information Center

Fang, N.; Guo, Y.

2016-01-01

Computer simulation and animation (CSA) has been receiving growing attention and wide application in engineering education in recent years. A new interactive CSA module was developed in the present study to improve student learning of particle kinetics in an undergraduate engineering dynamics course. The unique feature of this CSA module is that…

Activated Random Walkers: Facts, Conjectures and Challenges

NASA Astrophysics Data System (ADS)

Dickman, Ronald; Rolla, Leonardo T.; Sidoravicius, Vladas

2010-02-01

We study a particle system with hopping (random walk) dynamics on the integer lattice ℤ d . The particles can exist in two states, active or inactive (sleeping); only the former can hop. The dynamics conserves the number of particles; there is no limit on the number of particles at a given site. Isolated active particles fall asleep at rate λ>0, and then remain asleep until joined by another particle at the same site. The state in which all particles are inactive is absorbing. Whether activity continues at long times depends on the relation between the particle density ζ and the sleeping rate λ. We discuss the general case, and then, for the one-dimensional totally asymmetric case, study the phase transition between an active phase (for sufficiently large particle densities and/or small λ) and an absorbing one. We also present arguments regarding the asymptotic mean hopping velocity in the active phase, the rate of fixation in the absorbing phase, and survival of the infinite system at criticality. Using mean-field theory and Monte Carlo simulation, we locate the phase boundary. The phase transition appears to be continuous in both the symmetric and asymmetric versions of the process, but the critical behavior is very different. The former case is characterized by simple integer or rational values for critical exponents ( β=1, for example), and the phase diagram is in accord with the prediction of mean-field theory. We present evidence that the symmetric version belongs to the universality class of conserved stochastic sandpiles, also known as conserved directed percolation. Simulations also reveal an interesting transient phenomenon of damped oscillations in the activity density.

On the role of adhesion in single-file dynamics

NASA Astrophysics Data System (ADS)

Fouad, Ahmed M.; Noel, John A.

2017-08-01

For a one-dimensional interacting system of Brownian particles with hard-core interactions (a single-file model), we study the effect of adhesion on both the collective diffusion (diffusion of the entire system with respect to its center of mass) and the tracer diffusion (diffusion of the individual tagged particles). For the case with no adhesion, all properties of these particle systems that are independent of particle labeling (symmetric in all particle coordinates and velocities) are identical to those of non-interacting particles (Lebowitz and Percus, 1967). We clarify this last fact twice. First, we derive our analytical predictions that show that the probability-density functions of single-file (ρsf) and ordinary (ρord) diffusion are identical, ρsf =ρord, predicting a nonanomalous (ordinary) behavior for the collective single-file diffusion, where the average second moment with respect to the center of mass, < x(t) 2 > , is calculated from ρ for both diffusion processes. Second, for single-file diffusion, we show, both analytically and through large-scale simulations, that < x(t) 2 > grows linearly with time, confirming the nonanomalous behavior. This nonanomalous collective behavior comes in contrast to the well-known anomalous sub-diffusion behavior of the individual tagged particles (Harris, 1965). We introduce adhesion to single-file dynamics as a second inter-particle interaction rule and, interestingly, we show that adding adhesion does reduce the magnitudes of both < x(t) 2 > and the mean square displacement per particle Δx2; but the diffusion behavior remains intact independent of adhesion in both cases. Moreover, we study the dependence of both the collective diffusion constant D and the tracer diffusion constant DT on the adhesion coefficient α.

A coarse grained protein model with internal degrees of freedom. Application to α-synuclein aggregation

NASA Astrophysics Data System (ADS)

Ilie, Ioana M.; den Otter, Wouter K.; Briels, Wim J.

2016-02-01

Particles in simulations are traditionally endowed with fixed interactions. While this is appropriate for particles representing atoms or molecules, objects with significant internal dynamics—like sequences of amino acids or even an entire protein—are poorly modelled by invariable particles. We develop a highly coarse grained polymorph patchy particle with the ultimate aim of simulating proteins as chains of particles at the secondary structure level. Conformational changes, e.g., a transition between disordered and β-sheet states, are accommodated by internal coordinates that determine the shape and interaction characteristics of the particles. The internal coordinates, as well as the particle positions and orientations, are propagated by Brownian Dynamics in response to their local environment. As an example of the potential offered by polymorph particles, we model the amyloidogenic intrinsically disordered protein α-synuclein, involved in Parkinson's disease, as a single particle with two internal states. The simulations yield oligomers of particles in the disordered state and fibrils of particles in the "misfolded" cross-β-sheet state. The aggregation dynamics is complex, as aggregates can form by a direct nucleation-and-growth mechanism and by two-step-nucleation through conversions between the two cluster types. The aggregation dynamics is complex, with fibrils formed by direct nucleation-and-growth, by two-step-nucleation through the conversion of an oligomer and by auto-catalysis of this conversion.

Radiation induced rotation of interplanetary dust particles - A feasibility study for a space experiment

NASA Technical Reports Server (NTRS)

Ratcliff, K. F.; Misconi, N. Y.; Paddack, S. J.

1980-01-01

Irregular interplanetary dust particles may acquire a considerable spin rate due to two non-statistical dynamical mechanisms induced by solar radiation. These arise from variations in surface albedo discussed by Radzievskii (1954) and from irregularities in surface geometry discussed by Paddack (1969). An experiment is reported which will lead to an evaluation in space of the effectiveness of these two spin mechanisms. The technique of optical levitation in an argon laser beam provides a stable trap for particles 10-60 microns in diameter. The objective is to design an optical trap for dielectric particles in vacuum to study these rotation mechanisms in the gravity-free environment of a Spacelab experiment.

Propagation and deposition of non-circular finite release particle-laden currents

NASA Astrophysics Data System (ADS)

Zgheib, Nadim; Bonometti, Thomas; Balachandar, S.

2015-08-01

The dynamics of non-axisymmetric turbidity currents is considered here for a range of Reynolds numbers of O (104) when based on the initial height of the release. The study comprises a series of experiments and highly resolved simulations for which a finite volume of particle-laden solution is released into fresh water. A mixture of water and polystyrene particles of mean diameter d ˜ p = 300 μ m and mixture density ρ ˜ c = 1012 kg / m 3 is initially confined in a hollow cylinder at the centre of a large tank filled with fresh water. Cylinders with two different cross-sectional shapes, but equal cross-sectional areas, are examined: a circle and a rounded rectangle in which the sharp corners are smoothened. The time evolution of the front is recorded as well as the spatial distribution of the thickness of the final deposit via the use of a laser triangulation technique. The dynamics of the front and final deposits are significantly influenced by the initial geometry, displaying substantial azimuthal variation especially for the rectangular case where the current extends farther and deposits more particles along the initial minor axis of the rectangular cross section. Several parameters are varied to assess the dependence on the settling velocity, initial height aspect ratio, and volume fraction. Even though resuspension is not taken into account in our simulations, good agreement with experiments indicates that it does not play an important role in the front dynamics, in terms of velocity and extent of the current. However, wall shear stress measurements show that incipient motion of particles and particle transport along the bed are likely to occur in the body of the current and should be accounted to properly capture the final deposition profile of particles.

Performance impact of dynamic surface coatings on polymeric insulator-based dielectrophoretic particle separators.

PubMed

Davalos, Rafael V; McGraw, Gregory J; Wallow, Thomas I; Morales, Alfredo M; Krafcik, Karen L; Fintschenko, Yolanda; Cummings, Eric B; Simmons, Blake A

2008-02-01

Efficient and robust particle separation and enrichment techniques are critical for a diverse range of lab-on-a-chip analytical devices including pathogen detection, sample preparation, high-throughput particle sorting, and biomedical diagnostics. Previously, using insulator-based dielectrophoresis (iDEP) in microfluidic glass devices, we demonstrated simultaneous particle separation and concentration of various biological organisms, polymer microbeads, and viruses. As an alternative to glass, we evaluate the performance of similar iDEP structures produced in polymer-based microfluidic devices. There are numerous processing and operational advantages that motivate our transition to polymers such as the availability of numerous innate chemical compositions for tailoring performance, mechanical robustness, economy of scale, and ease of thermoforming and mass manufacturing. The polymer chips we have evaluated are fabricated through an injection molding process of the commercially available cyclic olefin copolymer Zeonor 1060R. This publication is the first to demonstrate insulator-based dielectrophoretic biological particle differentiation in a polymeric device injection molded from a silicon master. The results demonstrate that the polymer devices achieve the same performance metrics as glass devices. We also demonstrate an effective means of enhancing performance of these microsystems in terms of system power demand through the use of a dynamic surface coating. We demonstrate that the commercially available nonionic block copolymer surfactant, Pluronic F127, has a strong interaction with the cyclic olefin copolymer at very low concentrations, positively impacting performance by decreasing the electric field necessary to achieve particle trapping by an order of magnitude. The presence of this dynamic surface coating, therefore, lowers the power required to operate such devices and minimizes Joule heating. The results of this study demonstrate that iDEP polymeric microfluidic devices with surfactant coatings provide an affordable engineering strategy for selective particle enrichment and sorting.

Experimental Studies of the Brownian Diffusion of Boomerang Colloidal Particle in a Confined Geometry

NASA Astrophysics Data System (ADS)

Chakrabarty, Ayan; Wang, Feng; Joshi, Bhuwan; Wei, Qi-Huo

2011-03-01

Recent studies shows that the boomerang shaped molecules can form various kinds of liquid crystalline phases. One debated topic related to boomerang molecules is the existence of biaxial nematic liquid crystalline phase. Developing and optical microscopic studies of colloidal systems of boomerang particles would allow us to gain better understanding of orientation ordering and dynamics at ``single molecule'' level. Here we report the fabrication and experimental studies of the Brownian motion of individual boomerang colloidal particles confined between two glass plates. We used dark-field optical microscopy to directly visualize the Brownian motion of the single colloidal particles in a quasi two dimensional geometry. An EMCCD was used to capture the motion in real time. An indigenously developed imaging processing algorithm based on MatLab program was used to precisely track the position and orientation of the particles with sub-pixel accuracy. The experimental finding of the Brownian diffusion of a single boomerang colloidal particle will be discussed.

Dynamic fracture behavior of single and contacting Poly(methyl methacrylate) particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parab, Niranjan D.; Guo, Zherui; Hudspeth, Matthew C.

Fracture behaviors of single, two, and multiple contacting spherical Poly (methyl methacrylate) (PMMA) particles were recorded using high speed synchrotron X-ray phase contrast imaging. A miniaturized Kolsky bar setup was used to apply dynamic compressive loading on the PMMA particles. In both single and two particle experiments, cracking initiated near the center of the particles and propagated towards the contacts. The crack bifurcated near the contact points for single particle experiments, thus forming conical fragments. The crack bifurcation and subsequent conical fragment formation was observed only at the particle-particle contact for two particle experiments. The particles were observed to fracturemore » in hemispherical fragments normal to the contact plane in the multiparticle experiments. The observed failure mechanisms strongly suggest that the maximum tensile stress near the center of the particle is the critical parameter governing fracture of the particles. Moreover, the compressive stress under the contact areas led to the bifurcation and subsequent conical fragment formation.« less

Dynamic fracture behavior of single and contacting Poly(methyl methacrylate) particles

DOE PAGES

Parab, Niranjan D.; Guo, Zherui; Hudspeth, Matthew C.; ...

2017-09-19

Fracture behaviors of single, two, and multiple contacting spherical Poly (methyl methacrylate) (PMMA) particles were recorded using high speed synchrotron X-ray phase contrast imaging. A miniaturized Kolsky bar setup was used to apply dynamic compressive loading on the PMMA particles. In both single and two particle experiments, cracking initiated near the center of the particles and propagated towards the contacts. The crack bifurcated near the contact points for single particle experiments, thus forming conical fragments. The crack bifurcation and subsequent conical fragment formation was observed only at the particle-particle contact for two particle experiments. The particles were observed to fracturemore » in hemispherical fragments normal to the contact plane in the multiparticle experiments. The observed failure mechanisms strongly suggest that the maximum tensile stress near the center of the particle is the critical parameter governing fracture of the particles. Moreover, the compressive stress under the contact areas led to the bifurcation and subsequent conical fragment formation.« less

Long-time self-diffusion of charged spherical colloidal particles in parallel planar layers.

PubMed

Contreras-Aburto, Claudio; Báez, César A; Méndez-Alcaraz, José M; Castañeda-Priego, Ramón

2014-06-28

The long-time self-diffusion coefficient, D(L), of charged spherical colloidal particles in parallel planar layers is studied by means of Brownian dynamics computer simulations and mode-coupling theory. All particles (regardless which layer they are located on) interact with each other via the screened Coulomb potential and there is no particle transfer between layers. As a result of the geometrical constraint on particle positions, the simulation results show that D(L) is strongly controlled by the separation between layers. On the basis of the so-called contraction of the description formalism [C. Contreras-Aburto, J. M. Méndez-Alcaraz, and R. Castañeda-Priego, J. Chem. Phys. 132, 174111 (2010)], the effective potential between particles in a layer (the so-called observed layer) is obtained from integrating out the degrees of freedom of particles in the remaining layers. We have shown in a previous work that the effective potential performs well in describing the static structure of the observed layer (loc. cit.). In this work, we find that the D(L) values determined from the simulations of the observed layer, where the particles interact via the effective potential, do not agree with the exact values of D(L). Our findings confirm that even when an effective potential can perform well in describing the static properties, there is no guarantee that it will correctly describe the dynamic properties of colloidal systems.

Effect of polarization and focusing on laser pulse driven auto-resonant particle acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sagar, Vikram; Sengupta, Sudip; Kaw, Predhiman

2014-04-15

The effect of laser polarization and focusing is theoretically studied on the final energy gain of a particle in the Auto-resonant acceleration scheme using a finite duration laser pulse with Gaussian shaped temporal envelope. The exact expressions for dynamical variables viz. position, momentum, and energy are obtained by analytically solving the relativistic equation of motion describing particle dynamics in the combined field of an elliptically polarized finite duration pulse and homogeneous static axial magnetic field. From the solutions, it is shown that for a given set of laser parameters viz. intensity and pulse length along with static magnetic field, themore » energy gain by a positively charged particle is maximum for a right circularly polarized laser pulse. Further, a new scheme is proposed for particle acceleration by subjecting it to the combined field of a focused finite duration laser pulse and static axial magnetic field. In this scheme, the particle is initially accelerated by the focused laser field, which drives the non-resonant particle to second stage of acceleration by cyclotron Auto-resonance. The new scheme is found to be efficient over two individual schemes, i.e., auto-resonant acceleration and direct acceleration by focused laser field, as significant particle acceleration can be achieved at one order lesser values of static axial magnetic field and laser intensity.« less

Modeling Evaporation and Particle Assembly in Colloidal Droplets.

PubMed

Zhao, Mingfei; Yong, Xin

2017-06-13

Evaporation-induced assembly of nanoparticles in a drying droplet is of great importance in many engineering applications, including printing, coating, and thin film processing. The investigation of particle dynamics in evaporating droplets can provide fundamental hydrodynamic insight for revealing the processing-structure relationship in the particle self-organization induced by solvent evaporation. We develop a free-energy-based multiphase lattice Boltzmann method coupled with Brownian dynamics to simulate evaporating colloidal droplets on solid substrates with specified wetting properties. The influence of interface-bound nanoparticles on the surface tension and evaporation of a flat liquid-vapor interface is first quantified. The results indicate that the particles at the interface reduce surface tension and enhance evaporation flux. For evaporating particle-covered droplets on substrates with different wetting properties, we characterize the increase of evaporate rate via measuring droplet volume. We find that droplet evaporation is determined by the number density and circumferential distribution of interfacial particles. We further correlate particle dynamics and assembly to the evaporation-induced convection in the bulk and on the surface of droplet. Finally, we observe distinct final deposits from evaporating colloidal droplets with bulk-dispersed and interface-bound particles. In addition, the deposit pattern is also influenced by the equilibrium contact angle of droplet.

Particle size effect on strength, failure, and shock behavior in polytetrafluoroethylene-Al-W granular composite materials

NASA Astrophysics Data System (ADS)

Herbold, E. B.; Nesterenko, V. F.; Benson, D. J.; Cai, J.; Vecchio, K. S.; Jiang, F.; Addiss, J. W.; Walley, S. M.; Proud, W. G.

2008-11-01

The variation of metallic particle size and sample porosity significantly alters the dynamic mechanical properties of high density granular composite materials processed using a cold isostatically pressed mixture of polytetrafluoroethylene (PTFE), aluminum (Al), and tungsten (W) powders. Quasistatic and dynamic experiments are performed with identical constituent mass fractions with variations in the size of the W particles and pressing conditions. The relatively weak polymer matrix allows the strength and fracture modes of this material to be governed by the granular type behavior of agglomerated metal particles. A higher ultimate compressive strength was observed in relatively high porosity samples with small W particles compared to those with coarse W particles in all experiments. Mesoscale granular force chains of the metallic particles explain this unusual phenomenon as observed in hydrocode simulations of a drop-weight test. Macrocracks forming below the critical failure strain for the matrix and unusual behavior due to a competition between densification and fracture in dynamic tests of porous samples were also observed. Numerical modeling of shock loading of this granular composite material demonstrated that the internal energy, specifically thermal energy, of the soft PTFE matrix can be tailored by the W particle size distribution.

Nonequilibrium quantum field dynamics from the two-particle-irreducible effective action

NASA Astrophysics Data System (ADS)

Laurie, Nathan S.

The two-particle-irreducible effective action offers a powerful approach to the study of quantum field dynamics far from equilibrium. Recent and upcoming heavy ion collision experiments motivate the study of such nonequilibrium dynamics in an expanding space-time background. For the O(N) model I derive exact, causal evolution equations for the statistical and spectral functions in a longitudinally expanding system. It is followed by an investigation into how the expansion affects the prospect of the system reaching equilibrium. Results are obtained in 1+1 dimensions at next-to- leading order in loop- and 1/N-expansions of the 2PI effective action. I focus on the evolution of the statistical function from highly nonequilibrium initial conditions, presenting a detailed analysis of early, intermediate and late-time dynamics. It is found that dynamics at very early times is attracted by a nonthermal fixed point of the mean field equations, after which interactions attempt to drive the system to equilibrium. The competition between the interactions and the expansion is eventually won by the expansion, with so-called freeze-out emerging naturally in this description. In order to investigate the convergence of the 2PI-1/N expansion in the 0(N) model, I compare results obtained numerically in 1+1 dimensions at leading, next- to-leading and next-to-next-to-leading order in 1/N. Convergence with increasing N, and also with decreasing coupling are discussed. A comparison is also made in the classical statistical field theory limit, where exact numerical results are available. I focus on early-time dynamics and quasi-particle properties far from equilibrium and observe rapid effective convergence already for moderate values of 1/N or the coupling strength.

Granular segregation driven by particle interactions.

PubMed

Lozano, C; Zuriguel, I; Garcimartín, A; Mullin, T

2015-05-01

We report the results of an experimental study of particle-particle interactions in a horizontally shaken granular layer that undergoes a second order phase transition from a binary gas to a segregation liquid as the packing fraction C is increased. By focusing on the behavior of individual particles, the effect of C is studied on (1) the process of cluster formation, (2) cluster dynamics, and (3) cluster destruction. The outcomes indicate that the segregation is driven by two mechanisms: attraction between particles with the same properties and random motion with a characteristic length that is inversely proportional to C. All clusters investigated are found to be transient and the probability distribution functions of the separation times display a power law tail, indicating that the splitting probability decreases with time.