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Sample records for active brownian particle

  1. Active Brownian particles with velocity-alignment and active fluctuations

    NASA Astrophysics Data System (ADS)

    Großmann, R.; Schimansky-Geier, L.; Romanczuk, P.

    2012-07-01

    We consider a model of active Brownian particles (ABPs) with velocity alignment in two spatial dimensions with passive and active fluctuations. Here, active fluctuations refers to purely non-equilibrium stochastic forces correlated with the heading of an individual active particle. In the simplest case studied here, they are assumed to be independent stochastic forces parallel (speed noise) and perpendicular (angular noise) to the velocity of the particle. On the other hand, passive fluctuations are defined by a noise vector independent of the direction of motion of a particle, and may account, for example, for thermal fluctuations. We derive a macroscopic description of the ABP gas with velocity-alignment interaction. Here, we start from the individual-based description in terms of stochastic differential equations (Langevin equations) and derive equations of motion for the coarse-grained kinetic variables (density, velocity and temperature) via a moment expansion of the corresponding probability density function. We focus here on the different impact of active and passive fluctuations on onset of collective motion and show how active fluctuations in the active Brownian dynamics can change the phase-transition behaviour of the system. In particular, we show that active angular fluctuations lead to an earlier breakdown of collective motion and to the emergence of a new bistable regime in the mean-field case.

  2. Active Brownian particles escaping a channel in single file.

    PubMed

    Locatelli, Emanuele; Baldovin, Fulvio; Orlandini, Enzo; Pierno, Matteo

    2015-02-01

    Active particles may happen to be confined in channels so narrow that they cannot overtake each other (single-file conditions). This interesting situation reveals nontrivial physical features as a consequence of the strong interparticle correlations developed in collective rearrangements. We consider a minimal two-dimensional model for active Brownian particles with the aim of studying the modifications introduced by activity with respect to the classical (passive) single-file picture. Depending on whether their motion is dominated by translational or rotational diffusion, we find that active Brownian particles in single file may arrange into clusters that are continuously merging and splitting (active clusters) or merely reproduce passive-motion paradigms, respectively. We show that activity conveys to self-propelled particles a strategic advantage for trespassing narrow channels against external biases (e.g., the gravitational field).

  3. Entropic Ratchet transport of interacting active Brownian particles

    SciTech Connect

    Ai, Bao-Quan; He, Ya-Feng; Zhong, Wei-Rong

    2014-11-21

    Directed transport of interacting active (self-propelled) Brownian particles is numerically investigated in confined geometries (entropic barriers). The self-propelled velocity can break thermodynamical equilibrium and induce the directed transport. It is found that the interaction between active particles can greatly affect the ratchet transport. For attractive particles, on increasing the interaction strength, the average velocity first decreases to its minima, then increases, and finally decreases to zero. For repulsive particles, when the interaction is very weak, there exists a critical interaction at which the average velocity is minimal, nearly tends to zero, however, for the strong interaction, the average velocity is independent of the interaction.

  4. Additivity, density fluctuations, and nonequilibrium thermodynamics for active Brownian particles

    NASA Astrophysics Data System (ADS)

    Chakraborti, Subhadip; Mishra, Shradha; Pradhan, Punyabrata

    2016-05-01

    Using an additivity property, we study particle-number fluctuations in a system of interacting self-propelled particles, called active Brownian particles (ABPs), which consists of repulsive disks with random self-propulsion velocities. From a fluctuation-response relation, a direct consequence of additivity, we formulate a thermodynamic theory which captures the previously observed features of nonequilibrium phase transition in the ABPs from a homogeneous fluid phase to an inhomogeneous phase of coexisting gas and liquid. We substantiate the predictions of additivity by analytically calculating the subsystem particle-number distributions in the homogeneous fluid phase away from criticality where analytically obtained distributions are compatible with simulations in the ABPs.

  5. Continuum Theory of Phase Separation Kinetics for Active Brownian Particles

    NASA Astrophysics Data System (ADS)

    Stenhammar, Joakim; Tiribocchi, Adriano; Allen, Rosalind J.; Marenduzzo, Davide; Cates, Michael E.

    2013-10-01

    Active Brownian particles (ABPs), when subject to purely repulsive interactions, are known to undergo activity-induced phase separation broadly resembling an equilibrium (attraction-induced) gas-liquid coexistence. Here we present an accurate continuum theory for the dynamics of phase-separating ABPs, derived by direct coarse graining, capturing leading-order density gradient terms alongside an effective bulk free energy. Such gradient terms do not obey detailed balance; yet we find coarsening dynamics closely resembling that of equilibrium phase separation. Our continuum theory is numerically compared to large-scale direct simulations of ABPs and accurately accounts for domain growth kinetics, domain topologies, and coexistence densities.

  6. Propagating interfaces in mixtures of active and passive Brownian particles

    NASA Astrophysics Data System (ADS)

    Wysocki, Adam; Winkler, Roland G.; Gompper, Gerhard

    2016-12-01

    The emergent collective dynamics in phase-separated mixtures of isometric active and passive Brownian particles is studied numerically in two-dimensions. A novel steady-state of well-defined propagating interfaces is observed, where the interface between the dense and the dilute phase propagates and the bulk of both phases is (nearly) at rest. Two kind of interfaces, advancing and receding, are formed by spontaneous symmetry breaking, induced by an instability of a planar interface due to the formation of localized vortices. The propagation arises due to flux imbalance at the interface, resembling the growth behavior of rough surfaces far from equilibrium. Above a threshold, the interface velocity decreases linearly with increasing fraction of active particles.

  7. Brownian aggregation rate of colloid particles with several active sites

    SciTech Connect

    Nekrasov, Vyacheslav M.; Yurkin, Maxim A.; Chernyshev, Andrei V.; Polshchitsin, Alexey A.; Yakovleva, Galina E.; Maltsev, Valeri P.

    2014-08-14

    We theoretically analyze the aggregation kinetics of colloid particles with several active sites. Such particles (so-called “patchy particles”) are well known as chemically anisotropic reactants, but the corresponding rate constant of their aggregation has not yet been established in a convenient analytical form. Using kinematic approximation for the diffusion problem, we derived an analytical formula for the diffusion-controlled reaction rate constant between two colloid particles (or clusters) with several small active sites under the following assumptions: the relative translational motion is Brownian diffusion, and the isotropic stochastic reorientation of each particle is Markovian and arbitrarily correlated. This formula was shown to produce accurate results in comparison with more sophisticated approaches. Also, to account for the case of a low number of active sites per particle we used Monte Carlo stochastic algorithm based on Gillespie method. Simulations showed that such discrete model is required when this number is less than 10. Finally, we applied the developed approach to the simulation of immunoagglutination, assuming that the formed clusters have fractal structure.

  8. Intermediate scattering function of an anisotropic active Brownian particle

    NASA Astrophysics Data System (ADS)

    Kurzthaler, Christina; Leitmann, Sebastian; Franosch, Thomas

    2016-10-01

    Various challenges are faced when animalcules such as bacteria, protozoa, algae, or sperms move autonomously in aqueous media at low Reynolds number. These active agents are subject to strong stochastic fluctuations, that compete with the directed motion. So far most studies consider the lowest order moments of the displacements only, while more general spatio-temporal information on the stochastic motion is provided in scattering experiments. Here we derive analytically exact expressions for the directly measurable intermediate scattering function for a mesoscopic model of a single, anisotropic active Brownian particle in three dimensions. The mean-square displacement and the non-Gaussian parameter of the stochastic process are obtained as derivatives of the intermediate scattering function. These display different temporal regimes dominated by effective diffusion and directed motion due to the interplay of translational and rotational diffusion which is rationalized within the theory. The most prominent feature of the intermediate scattering function is an oscillatory behavior at intermediate wavenumbers reflecting the persistent swimming motion, whereas at small length scales bare translational and at large length scales an enhanced effective diffusion emerges. We anticipate that our characterization of the motion of active agents will serve as a reference for more realistic models and experimental observations.

  9. Relation between cooperative molecular motors and active Brownian particles

    NASA Astrophysics Data System (ADS)

    Touya, Clément; Schwalger, Tilo; Lindner, Benjamin

    2011-05-01

    Active Brownian particles (ABPs), obeying a nonlinear Langevin equation with speed-dependent drift and noise amplitude, are well-known models used to describe self-propelled motion in biology. In this paper we study a model describing the stochastic dynamics of a group of coupled molecular motors (CMMs). Using two independent numerical methods, one based on the stationary velocity distribution of the motors and the other one on the local increments (also known as the Kramers-Moyal coefficients) of the velocity, we establish a connection between the CMM and the ABP models. The parameters extracted for the ABP via the two methods show good agreement for both symmetric and asymmetric cases and are independent of N, the number of motors, provided that N is not too small. This indicates that one can indeed describe the CMM problem with a simpler ABP model. However, the power spectrum of velocity fluctuations in the CMM model reveals a peak at a finite frequency, a peak which is absent in the velocity spectrum of the ABP model. This implies richer dynamic features of the CMM model which cannot be captured by an ABP model.

  10. Active Brownian particles and run-and-tumble particles separate inside a maze

    NASA Astrophysics Data System (ADS)

    Khatami, Maryam; Wolff, Katrin; Pohl, Oliver; Ejtehadi, Mohammad Reza; Stark, Holger

    2016-11-01

    A diverse range of natural and artificial self-propelled particles are known and are used nowadays. Among them, active Brownian particles (ABPs) and run-and-tumble particles (RTPs) are two important classes. We numerically study non-interacting ABPs and RTPs strongly confined to different maze geometries in two dimensions. We demonstrate that by means of geometrical confinement alone, ABPs are separable from RTPs. By investigating Matryoshka-like mazes with nested shells, we show that a circular maze has the best filtration efficiency. Results on the mean first-passage time reveal that ABPs escape faster from the center of the maze, while RTPs reach the center from the rim more easily. According to our simulations and a rate theory, which we developed, ABPs in steady state accumulate in the outermost region of the Matryoshka-like mazes, while RTPs occupy all locations within the maze with nearly equal probability. These results suggest a novel technique for separating different types of self-propelled particles by designing appropriate confining geometries without using chemical or biological agents.

  11. Active Brownian particles and run-and-tumble particles separate inside a maze

    PubMed Central

    Khatami, Maryam; Wolff, Katrin; Pohl, Oliver; Ejtehadi, Mohammad Reza; Stark, Holger

    2016-01-01

    A diverse range of natural and artificial self-propelled particles are known and are used nowadays. Among them, active Brownian particles (ABPs) and run-and-tumble particles (RTPs) are two important classes. We numerically study non-interacting ABPs and RTPs strongly confined to different maze geometries in two dimensions. We demonstrate that by means of geometrical confinement alone, ABPs are separable from RTPs. By investigating Matryoshka-like mazes with nested shells, we show that a circular maze has the best filtration efficiency. Results on the mean first-passage time reveal that ABPs escape faster from the center of the maze, while RTPs reach the center from the rim more easily. According to our simulations and a rate theory, which we developed, ABPs in steady state accumulate in the outermost region of the Matryoshka-like mazes, while RTPs occupy all locations within the maze with nearly equal probability. These results suggest a novel technique for separating different types of self-propelled particles by designing appropriate confining geometries without using chemical or biological agents. PMID:27876867

  12. Active Brownian particles at interfaces: An effective equilibrium approach

    NASA Astrophysics Data System (ADS)

    Wittmann, René; Brader, Joseph M.

    2016-06-01

    A simple theoretical approach is used to investigate active colloids at the free interface and near repulsive substrates. We employ dynamical density functional theory to determine the steady-state density profiles in an effective equilibrium system (Farage T. F. F. et al., Phys. Rev. E, 91 (2015) 042310). In addition to the known accumulation at surfaces, we predict wetting and drying transitions at a flat repulsive wall and capillary condensation and evaporation in a slit pore. These new phenomena are closely related to the motility-induced phase separation (MIPS) in the bulk.

  13. Population variability in the Active Brownian Particle model of Daphnia motions

    NASA Astrophysics Data System (ADS)

    Moss, Frank; Erdmann, Udo; Schimansky-Geier, Lutz; Ordmann, Anke

    2004-03-01

    Three characteristic motions of foraging biological agents are predicted by the Active Brownian Particle model [1]. These are random motions about the minimum of a central attracting potential, a bifurcation to bidirectional circular motions about the axis of symmetry of the potential, and a transition to vortex motion. All three can be observed in swarms of the zooplankton Daphnia swimming in light fields. Here we focus on the bidirectional circular motions in 2-D space [1]. The mean radii, as well as other characteristics of the paths, are determined by three strength parameters appropriate to individual Daphnia: energy uptake from the medium, metabolistic drain, and dissipation due to movement. It is shown that individual variability can be represented by distributions of these strength parameters. Conditions for which the experimental data are best described by the model are discussed. [1] U. Erdmann, W. Ebeling and V. S. Anishchenko, Excitation of rotational modes in two-dimensional systems of driven Brownian particles. Phys. Rev. E 65, 061106 (2002)

  14. When are active Brownian particles and run-and-tumble particles equivalent? Consequences for motility-induced phase separation

    NASA Astrophysics Data System (ADS)

    Cates, M. E.; Tailleur, J.

    2013-01-01

    Active Brownian particles (ABPs, such as self-phoretic colloids) swim at fixed speed v along a body-axis u that rotates by slow angular diffusion. Run-and-tumble particles (RTPs, such as motile bacteria) swim with constant u until a random tumble event suddenly decorrelates the orientation. We show that when the motility parameters depend on density ρ but not on u, the coarse-grained fluctuating hydrodynamics of interacting ABPs and RTPs can be mapped onto each other and are thus strictly equivalent. In both cases, a steeply enough decreasing v(ρ) causes phase separation in dimensions d = 2,3, even when no attractive forces act between the particles. This points to a generic role for motility-induced phase separation in active matter. However, we show that the ABP/RTP equivalence does not automatically extend to the more general case of u-dependent motilities.

  15. Ratcheted electrophoresis of Brownian particles

    NASA Astrophysics Data System (ADS)

    Kowalik, Mikołaj; Bishop, Kyle J. M.

    2016-05-01

    The realization of nanoscale machines requires efficient methods by which to rectify unbiased perturbations to perform useful functions in the presence of significant thermal noise. The performance of such Brownian motors often depends sensitively on their operating conditions—in particular, on the relative rates of diffusive and deterministic motions. In this letter, we present a type of Brownian motor that uses contact charge electrophoresis of a colloidal particle within a ratcheted channel to achieve directed transport or perform useful work against an applied load. We analyze the stochastic dynamics of this model ratchet to show that it functions under any operating condition—even in the limit of strong thermal noise and in contrast to existing ratchets. The theoretical results presented here suggest that ratcheted electrophoresis could provide a basis for electrochemically powered, nanoscale machines capable of transport and actuation of nanoscale components.

  16. Swimming path statistics of an active Brownian particle with time-dependent self-propulsion

    NASA Astrophysics Data System (ADS)

    Babel, S.; ten Hagen, B.; Löwen, H.

    2014-02-01

    Typically, in the description of active Brownian particles, a constant effective propulsion force is assumed, which is then subjected to fluctuations in orientation and translation, leading to a persistent random walk with an enlarged long-time diffusion coefficient. Here, we generalize previous results for the swimming path statistics to a time-dependent, and thus in many situations more realistic, propulsion which is a prescribed input. We analytically calculate both the noise-free and the noise-averaged trajectories for time-periodic propulsion under the action of an additional torque. In the deterministic case, such an oscillatory microswimmer moves on closed paths that can be much more complicated than the commonly observed straight lines and circles. When exposed to random fluctuations, the mean trajectories turn out to be self-similar curves which bear the characteristics of their noise-free counterparts. Furthermore, we consider a propulsion force which scales in time t as ∝tα (with α = 0,1,2, …) and analyze the resulting superdiffusive behavior. Our predictions are verifiable for diffusiophoretic artificial microswimmers with prescribed propulsion protocols.

  17. Active Brownian rods

    NASA Astrophysics Data System (ADS)

    Peruani, Fernando

    2016-11-01

    Bacteria, chemically-driven rods, and motility assays are examples of active (i.e. self-propelled) Brownian rods (ABR). The physics of ABR, despite their ubiquity in experimental systems, remains still poorly understood. Here, we review the large-scale properties of collections of ABR moving in a dissipative medium. We address the problem by presenting three different models, of decreasing complexity, which we refer to as model I, II, and III, respectively. Comparing model I, II, and III, we disentangle the role of activity and interactions. In particular, we learn that in two dimensions by ignoring steric or volume exclusion effects, large-scale nematic order seems to be possible, while steric interactions prevent the formation of orientational order at large scales. The macroscopic behavior of ABR results from the interplay between active stresses and local alignment. ABR exhibit, depending on where we locate ourselves in parameter space, a zoology of macroscopic patterns that ranges from polar and nematic bands to dynamic aggregates.

  18. Fluctuation relations for a driven Brownian particle.

    PubMed

    Imparato, A; Peliti, L

    2006-08-01

    We consider a driven Brownian particle, subject to both conservative and nonconservative applied forces, whose probability evolves according to the Kramers equation. We derive a general fluctuation relation, expressing the ratio of the probability of a given Brownian path in phase space with that of the time-reversed path, in terms of the entropy flux to the heat reservoir. This fluctuation relation implies those of Seifert, Jarzynski, and Gallavotti-Cohen in different special cases.

  19. Fluctuation relations for a driven Brownian particle

    NASA Astrophysics Data System (ADS)

    Imparato, A.; Peliti, L.

    2006-08-01

    We consider a driven Brownian particle, subject to both conservative and nonconservative applied forces, whose probability evolves according to the Kramers equation. We derive a general fluctuation relation, expressing the ratio of the probability of a given Brownian path in phase space with that of the time-reversed path, in terms of the entropy flux to the heat reservoir. This fluctuation relation implies those of Seifert, Jarzynski, and Gallavotti-Cohen in different special cases.

  20. Dynamical mean-field theory and weakly non-linear analysis for the phase separation of active Brownian particles

    SciTech Connect

    Speck, Thomas; Menzel, Andreas M.; Bialké, Julian; Löwen, Hartmut

    2015-06-14

    Recently, we have derived an effective Cahn-Hilliard equation for the phase separation dynamics of active Brownian particles by performing a weakly non-linear analysis of the effective hydrodynamic equations for density and polarization [Speck et al., Phys. Rev. Lett. 112, 218304 (2014)]. Here, we develop and explore this strategy in more detail and show explicitly how to get to such a large-scale, mean-field description starting from the microscopic dynamics. The effective free energy emerging from this approach has the form of a conventional Ginzburg-Landau function. On the coarsest scale, our results thus agree with the mapping of active phase separation onto that of passive fluids with attractive interactions through a global effective free energy (motility-induced phase transition). Particular attention is paid to the square-gradient term necessary for the phase separation kinetics. We finally discuss results from numerical simulations corroborating the analytical results.

  1. Hydrodynamically enforced entropic trapping of Brownian particles

    NASA Astrophysics Data System (ADS)

    Martens, Steffen; Schmid, Gerhard; Straube, Arthur; Schimansky-Geier, Lutz; Hänggi, Peter

    2014-03-01

    In small systems on length scales spatial confinement causes entropic forces that in turn implies spectacular consequences for the control for mass and charge transport. In view of its importance, recent efforts in theory triggered activities which allow for an approximate description that involves a reduction of dimensionality; thus making detailed predictions tractable. Up to present days, the focus was on the role of conservative forces and its interplay with confinement. Within the presented work, we overcome this limitation and succeeded in considering also non-conservative forces that derive from a vector potential [S. Martens et al., PRL 110, 010601 (2013)]. A relevant application is the fluid flow across microfluidic structures where a solute of Brownian particles is subject to both, an external bias and a pressure-driven flow. Then a new phenomenon emerges; namely, the intriguing finding of identically vanishing average particle flow which is accompanied by a colossal suppression of diffusion. This entropy-induced phenomenon, which we termed hydrodynamically enforced entropic trapping, offers the unique opportunity to separate particles of the same size in a tunable manner [S. Martens et al., Eur. Phys. ST 222, 2453-2463 (2013)].

  2. Simulation of the active Brownian motion of a microswimmer

    NASA Astrophysics Data System (ADS)

    Volpe, Giorgio; Gigan, Sylvain; Volpe, Giovanni

    2014-07-01

    Unlike passive Brownian particles, active Brownian particles, also known as microswimmers, propel themselves with directed motion and thus drive themselves out of equilibrium. Understanding their motion can provide insight into out-of-equilibrium phenomena associated with biological examples such as bacteria, as well as with artificial microswimmers. We discuss how to mathematically model their motion using a set of stochastic differential equations and how to numerically simulate it using the corresponding set of finite difference equations both in homogenous and complex environments. In particular, we show how active Brownian particles do not follow the Maxwell-Boltzmann distribution—a clear signature of their out-of-equilibrium nature—and how, unlike passive Brownian particles, microswimmers can be funneled, trapped, and sorted.

  3. Effective diffusivity in active Brownian suspensions

    NASA Astrophysics Data System (ADS)

    Burkholder, Eric; Brady, John

    2016-11-01

    We study the single-particle diffusion of a Brownian probe of size R in a suspension comprised of a Newtonian solvent and a dilute dispersion of active Brownian particles (ABPs) with size a, characteristic swim velocity U0, and a reorientation time τR. These ABPs, or "swimmers," have a run length l =U0τR , and a mechanical activity ksTs =ζaU02τR / 6 , where ζa is the Stokes drag coefficient of a swimmer. When the swimmers are inactive, collisions between the probe and the swimmers sterically hinder the probe's diffusive motion. When the activity of the swimmers is greater than the Boltzmann energy, ksTs >kB T , rather than being sterically hindered, the probe diffusivity is actually greater than its Stokes-Einstein-Sutherland diffusivity due to the mechanical energy imparted to the probe upon collisions with the swimmers. The active contribution to the effective diffusivity is a non-monotonic function of the swimmers' run length compared to the contact length between the probe and a swimmer: l / (R + a) . Comparisons are made to previous theoretical and experimental investigations of the hydrodynamic diffusion of a colloidal particle in a dilute suspension of swimming bacteria. NSF Grant No. CBET 1437570.

  4. Ellipsoidal Brownian self-driven particles in a magnetic field

    NASA Astrophysics Data System (ADS)

    Fan, Wai-Tong Louis; Pak, On Shun; Sandoval, Mario

    2017-03-01

    We study the two-dimensional Brownian dynamics of an ellipsoidal paramagnetic microswimmer moving at a low Reynolds number and subject to a magnetic field. Its corresponding mean-square displacement, showing the effect of a particles's shape, activity, and magnetic field on the microswimmer's diffusion, is analytically obtained. Comparison between analytical and computational results shows good agreement. In addition, the effect of self-propulsion on the transition time from anisotropic to isotropic diffusion of the ellipse is investigated.

  5. Smoluchowski diffusion equation for active Brownian swimmers

    NASA Astrophysics Data System (ADS)

    Sevilla, Francisco J.; Sandoval, Mario

    2015-05-01

    We study the free diffusion in two dimensions of active Brownian swimmers subject to passive fluctuations on the translational motion and to active fluctuations on the rotational one. The Smoluchowski equation is derived from a Langevin-like model of active swimmers and analytically solved in the long-time regime for arbitrary values of the Péclet number; this allows us to analyze the out-of-equilibrium evolution of the positions distribution of active particles at all time regimes. Explicit expressions for the mean-square displacement and for the kurtosis of the probability distribution function are presented and the effects of persistence discussed. We show through Brownian dynamics simulations that our prescription for the mean-square displacement gives the exact time dependence at all times. The departure of the probability distribution from a Gaussian, measured by the kurtosis, is also analyzed both analytically and computationally. We find that for the inverse of Péclet numbers ≲0.1 , the distance from Gaussian increases as ˜t-2 at short times, while it diminishes as ˜t-1 in the asymptotic limit.

  6. Engineered Swift Equilibration of a Brownian particle

    PubMed Central

    Martínez, Ignacio A.; Petrosyan, Artyom; Guéry-Odelin, David; Trizac, Emmanuel; Ciliberto, Sergio

    2016-01-01

    A fundamental and intrinsic property of any device or natural system is its relaxation time relax, which is the time it takes to return to equilibrium after the sudden change of a control parameter [1]. Reducing τrelax, is frequently necessary, and is often obtained by a complex feedback process. To overcome the limitations of such an approach, alternative methods based on driving have been recently demonstrated [2, 3], for isolated quantum and classical systems [4–9]. Their extension to open systems in contact with a thermostat is a stumbling block for applications. Here, we design a protocol, named Engineered Swift Equilibration (ESE), that shortcuts time-consuming relaxations, and we apply it to a Brownian particle trapped in an optical potential whose properties can be controlled in time. We implement the process experimentally, showing that it allows the system to reach equilibrium times faster than the natural equilibration rate. We also estimate the increase of the dissipated energy needed to get such a time reduction. The method paves the way for applications in micro and nano devices, where the reduction of operation time represents as substantial a challenge as miniaturization [10]. PMID:27610190

  7. Engineered swift equilibration of a Brownian particle

    NASA Astrophysics Data System (ADS)

    Martínez, Ignacio A.; Petrosyan, Artyom; Guéry-Odelin, David; Trizac, Emmanuel; Ciliberto, Sergio

    2016-09-01

    A fundamental and intrinsic property of any device or natural system is its relaxation time τrelax, which is the time it takes to return to equilibrium after the sudden change of a control parameter. Reducing τrelax is frequently necessary, and is often obtained by a complex feedback process. To overcome the limitations of such an approach, alternative methods based on suitable driving protocols have been recently demonstrated, for isolated quantum and classical systems. Their extension to open systems in contact with a thermostat is a stumbling block for applications. Here, we design a protocol, named Engineered Swift Equilibration (ESE), that shortcuts time-consuming relaxations, and we apply it to a Brownian particle trapped in an optical potential whose properties can be controlled in time. We implement the process experimentally, showing that it allows the system to reach equilibrium 100 times faster than the natural equilibration rate. We also estimate the increase of the dissipated energy needed to get such a time reduction. The method paves the way for applications in micro- and nano-devices, where the reduction of operation time represents as substantial a challenge as miniaturization.

  8. Relaxation of Brownian particles in a gravitational field

    NASA Astrophysics Data System (ADS)

    Saka, Halil; Bengtson, Roger D.; Reichl, Linda E.

    2009-03-01

    We describe an upper level undergraduate experiment on the time-dependent behavior of a suspension of Brownian particles under gravitational attraction. We employed the Fokker-Planck equation in the strong friction limit and measured the time-evolution of the probability distribution for 1.0μm diameter latex Brownian particles in water at room temperature and pressure. The experiment provides evidence of the atomic nature of water.

  9. Brownian dynamics of charged particles in a constant magnetic field

    SciTech Connect

    Hou, L. J.; Piel, A.; Miskovic, Z. L.; Shukla, P. K.

    2009-05-15

    Numerical algorithms are proposed for simulating the Brownian dynamics of charged particles in an external magnetic field, taking into account the Brownian motion of charged particles, damping effect, and the effect of magnetic field self-consistently. Performance of these algorithms is tested in terms of their accuracy and long-time stability by using a three-dimensional Brownian oscillator model with constant magnetic field. Step-by-step recipes for implementing these algorithms are given in detail. It is expected that these algorithms can be directly used to study particle dynamics in various dispersed systems in the presence of a magnetic field, including polymer solutions, colloidal suspensions, and, particularly, complex (dusty) plasmas. The proposed algorithms can also be used as thermostat in the usual molecular dynamics simulation in the presence of magnetic field.

  10. Pressure and phase equilibria in interacting active brownian spheres.

    PubMed

    Solon, Alexandre P; Stenhammar, Joakim; Wittkowski, Raphael; Kardar, Mehran; Kafri, Yariv; Cates, Michael E; Tailleur, Julien

    2015-05-15

    We derive a microscopic expression for the mechanical pressure P in a system of spherical active Brownian particles at density ρ. Our exact result relates P, defined as the force per unit area on a bounding wall, to bulk correlation functions evaluated far away from the wall. It shows that (i) P(ρ) is a state function, independent of the particle-wall interaction; (ii) interactions contribute two terms to P, one encoding the slow-down that drives motility-induced phase separation, and the other a direct contribution well known for passive systems; and (iii) P is equal in coexisting phases. We discuss the consequences of these results for the motility-induced phase separation of active Brownian particles and show that the densities at coexistence do not satisfy a Maxwell construction on P.

  11. Brownian motion in granular gases of viscoelastic particles

    SciTech Connect

    Bodrova, A. S. Brilliantov, N. V.; Loskutov, A. Yu.

    2009-12-15

    A theory is developed of Brownian motion in granular gases (systems of many macroscopic particles undergoing inelastic collisions), where the energy loss in inelastic collisions is determined by a restitution coefficient {epsilon}. Whereas previous studies used a simplified model with {epsilon} = const, the present analysis takes into account the dependence of the restitution coefficient on relative impact velocity. The granular temperature and the Brownian diffusion coefficient are calculated for a granular gas in the homogeneous cooling state and a gas driven by a thermostat force, and their variation with grain mass and size and the restitution coefficient is analyzed. Both equipartition principle and fluctuation-dissipation relations are found to break down. One manifestation of this behavior is a new phenomenon of 'relative heating' of Brownian particles at the expense of cooling of the ambient granular gas.

  12. Brownian motion of a particle with arbitrary shape

    NASA Astrophysics Data System (ADS)

    Wajnryb, Eligiusz; Cichocki, Bogdan; Ekiel-Jezewska, Maria L.

    2015-11-01

    We consider a single Brownian particle of an arbitrary shape, in general non-axisymmetric. Starting from the Smoluchowski equation we develop a new formalism, which allows to determine the particle rotational and translational motion in a much simpler way as this which is based on the Euler angles and Wigner functions. Our approach makes use of the rotational matrix and irreducible tensors. The essential result of our presentation is that using our new formalism, we derive simple explicit analytical expressions for the cross-correlations of the Brownian translational and rotational displacements. The role of the particle mobility center is determined and discussed. No such formulas have been known yet - instead, numerical Brownian simulations have been extensively used. We compare our analytical results with low Reynolds number experiment and numerical simulations performed at the time scales comparable with the characteristic time of the rotational Brownian diffusion. E.W. and M.L.E.-J. are supported by the Polish National Science Centre under Grant No. 2012/05/B/ST8/ 03010.

  13. Stochastically gated local and occupation times of a Brownian particle

    NASA Astrophysics Data System (ADS)

    Bressloff, Paul C.

    2017-01-01

    We generalize the Feynman-Kac formula to analyze the local and occupation times of a Brownian particle moving in a stochastically gated one-dimensional domain. (i) The gated local time is defined as the amount of time spent by the particle in the neighborhood of a point in space where there is some target that only receives resources from (or detects) the particle when the gate is open; the target does not interfere with the motion of the Brownian particle. (ii) The gated occupation time is defined as the amount of time spent by the particle in the positive half of the real line, given that it can only cross the origin when a gate placed at the origin is open; in the closed state the particle is reflected. In both scenarios, the gate randomly switches between the open and closed states according to a two-state Markov process. We derive a stochastic, backward Fokker-Planck equation (FPE) for the moment-generating function of the two types of gated Brownian functional, given a particular realization of the stochastic gate, and analyze the resulting stochastic FPE using a moments method recently developed for diffusion processes in randomly switching environments. In particular, we obtain dynamical equations for the moment-generating function, averaged with respect to realizations of the stochastic gate.

  14. Exact master equation for a noncommutative Brownian particle

    SciTech Connect

    Costa Dias, Nuno Nuno Prata, Joao

    2009-01-15

    We derive the Hu-Paz-Zhang master equation for a Brownian particle linearly coupled to a bath of harmonic oscillators on the plane with spatial noncommutativity. The results obtained are exact to all orders in the noncommutative parameter. As a by-product we derive some miscellaneous results such as the equilibrium Wigner distribution for the reservoir of noncommutative oscillators, the weak coupling limit of the master equation and a set of sufficient conditions for strict purity decrease of the Brownian particle. Finally, we consider a high-temperature Ohmic model and obtain an estimate for the time scale of the transition from noncommutative to ordinary quantum mechanics. This scale is considerably smaller than the decoherence scale.

  15. Work fluctuations for a Brownian particle between two thermostats

    NASA Astrophysics Data System (ADS)

    Visco, Paolo

    2006-06-01

    We explicitly determine the large deviation function of the energy flow of a Brownian particle coupled to two heat baths at different temperatures. This toy model, initially introduced by Derrida and Brunet (2005, Einstein aujourd'hui (Les Ulis: EDP Sciences)), not only allows us to sort out the influence of initial conditions on large deviation functions but also allows us to pinpoint various restrictions bearing upon the range of validity of the Fluctuation Relation.

  16. Brownian motion: Absolute negative particle mobility

    NASA Astrophysics Data System (ADS)

    Ros, Alexandra; Eichhorn, Ralf; Regtmeier, Jan; Duong, Thanh Tu; Reimann, Peter; Anselmetti, Dario

    2005-08-01

    Noise effects in technological applications, far from being a nuisance, can be exploited with advantage - for example, unavoidable thermal fluctuations have found application in the transport and sorting of colloidal particles and biomolecules. Here we use a microfluidic system to demonstrate a paradoxical migration mechanism in which particles always move in a direction opposite to the net acting force (`absolute negative mobility') as a result of an interplay between thermal noise, a periodic and symmetric microstructure, and a biased alternating-current electric field. This counterintuitive phenomenon could be used for bioanalytical purposes, for example in the separation and fractionation of colloids, biological molecules and cells.

  17. Effective diffusion of confined active Brownian swimmers

    NASA Astrophysics Data System (ADS)

    Sandoval, Mario; Dagdug, Leonardo

    2014-11-01

    We find theoretically the effect of confinement and thermal fluctuations, on the diffusivity of a spherical active swimmer moving inside a two-dimensional narrow cavity of general shape. The explicit formulas for the effective diffusion coefficient of a swimmer moving inside two particular cavities are presented. We also compare our analytical results with Brownian Dynamics simulations and we obtain excellent agreement. L.D. thanks Consejo Nacional de Ciencia y Tecnologia (CONACyT) Mexico, for partial support by Grant No. 176452. M. S. thanks CONACyT and Programa de Mejoramiento de Profesorado (PROMEP) for partially funding this work under Grant No. 103.5/13/6732.

  18. Communication: Memory effects and active Brownian diffusion

    NASA Astrophysics Data System (ADS)

    Ghosh, Pulak K.; Li, Yunyun; Marchegiani, Giampiero; Marchesoni, Fabio

    2015-12-01

    A self-propelled artificial microswimmer is often modeled as a ballistic Brownian particle moving with constant speed aligned along one of its axis, but changing direction due to random collisions with the environment. Similarly to thermal noise, its angular randomization is described as a memoryless stochastic process. Here, we speculate that finite-time correlations in the orientational dynamics can affect the swimmer's diffusivity. To this purpose, we propose and solve two alternative models. In the first one, we simply assume that the environmental fluctuations governing the swimmer's propulsion are exponentially correlated in time, whereas in the second one, we account for possible damped fluctuations of the propulsion velocity around the swimmer's axis. The corresponding swimmer's diffusion constants are predicted to get, respectively, enhanced or suppressed upon increasing the model memory time. Possible consequences of this effect on the interpretation of the experimental data are discussed.

  19. Communication: Memory effects and active Brownian diffusion.

    PubMed

    Ghosh, Pulak K; Li, Yunyun; Marchegiani, Giampiero; Marchesoni, Fabio

    2015-12-07

    A self-propelled artificial microswimmer is often modeled as a ballistic Brownian particle moving with constant speed aligned along one of its axis, but changing direction due to random collisions with the environment. Similarly to thermal noise, its angular randomization is described as a memoryless stochastic process. Here, we speculate that finite-time correlations in the orientational dynamics can affect the swimmer's diffusivity. To this purpose, we propose and solve two alternative models. In the first one, we simply assume that the environmental fluctuations governing the swimmer's propulsion are exponentially correlated in time, whereas in the second one, we account for possible damped fluctuations of the propulsion velocity around the swimmer's axis. The corresponding swimmer's diffusion constants are predicted to get, respectively, enhanced or suppressed upon increasing the model memory time. Possible consequences of this effect on the interpretation of the experimental data are discussed.

  20. Communication: Memory effects and active Brownian diffusion

    SciTech Connect

    Ghosh, Pulak K.; Li, Yunyun; Marchegiani, Giampiero; Marchesoni, Fabio

    2015-12-07

    A self-propelled artificial microswimmer is often modeled as a ballistic Brownian particle moving with constant speed aligned along one of its axis, but changing direction due to random collisions with the environment. Similarly to thermal noise, its angular randomization is described as a memoryless stochastic process. Here, we speculate that finite-time correlations in the orientational dynamics can affect the swimmer’s diffusivity. To this purpose, we propose and solve two alternative models. In the first one, we simply assume that the environmental fluctuations governing the swimmer’s propulsion are exponentially correlated in time, whereas in the second one, we account for possible damped fluctuations of the propulsion velocity around the swimmer’s axis. The corresponding swimmer’s diffusion constants are predicted to get, respectively, enhanced or suppressed upon increasing the model memory time. Possible consequences of this effect on the interpretation of the experimental data are discussed.

  1. Singular perturbation theory for predicting extravasation of Brownian particles

    PubMed Central

    Shah, Preyas; Fitzgibbon, Sean; Narsimhan, Vivek; Shaqfeh, Eric S. G.

    2013-01-01

    Motivated by recent studies on tumor treatments using the drug delivery of nanoparticles, we provide a singular perturbation theory and perform Brownian dynamics simulations to quantify the extravasation rate of Brownian particles in a shear flow over a circular pore with a lumped mass transfer resistance. The analytic theory we present is an expansion in the limit of a vanishing Péclet number (P), which is the ratio of convective fluxes to diffusive fluxes on the length scale of the pore. We state the concentration of particles near the pore and the extravasation rate (Sherwood number) to O(P1/2). This model improves upon previous studies because the results are valid for all values of the particle mass transfer coefficient across the pore, as modeled by the Damköhler number (κ), which is the ratio of the reaction rate to the diffusive mass transfer rate at the boundary. Previous studies focused on the adsorption-dominated regime (i.e., κ → ∞). Specifically, our work provides a theoretical basis and an interpolation-based approximate method for calculating the Sherwood number (a measure of the extravasation rate) for the case of finite resistance [κ ~ O(1)] at small Péclet numbers, which are physiologically important in the extravasation of nanoparticles. We compare the predictions of our theory and an approximate method to Brownian dynamics simulations with reflection–reaction boundary conditions as modeled by κ. They are found to agree well at small P and for the κ ≪ 1 and κ ≫ 1 asymptotic limits representing the diffusion-dominated and adsorption-dominated regimes, respectively. Although this model neglects the finite size effects of the particles, it provides an important first step toward understanding the physics of extravasation in the tumor vasculature. PMID:24563548

  2. Asymmetric exclusion process in a system of interacting Brownian particles.

    PubMed

    Eduardo de Oliveira Rodrigues, José; Dickman, Ronald

    2010-06-01

    We study a continuous-space version of the totally asymmetric simple exclusion process (TASEP), consisting of interacting Brownian particles subject to a driving force in a periodic array of potential wells. Particles are inserted into the leftmost well at rate α, hop to the right at unit rate, and are removed at the rightmost well at rate β. Our study is motivated by recent experiments on colloidal particles in a periodic potential generated by an optical tweezers array. Particles spend most of the time near potential minima, approximating the situation on the lattice; a short-range repulsive interaction prevents two particles from occupying the same potential well. A constant driving force, representing Stokes drag on particles suspended in a moving fluid, leads to biased motion. Our results for the density profile and current, obtained via numerical integration of the Langevin equation and dynamic Monte Carlo simulations, indicate that the continuous-space model exhibits phase transitions analogous to those observed in the lattice TASEP. The correspondence is not exact, however, due to the lack of particle-hole symmetry in our model.

  3. Normal and anomalous diffusion of Brownian particles on disordered potentials

    NASA Astrophysics Data System (ADS)

    Salgado-García, R.

    2016-07-01

    In this work we study the transition from normal to anomalous diffusion of Brownian particles on disordered potentials. The potential model consists of a series of "potential hills" (defined on a unit cell of constant length) whose heights are chosen randomly from a given distribution. We calculate the exact expression for the diffusion coefficient in the case of uncorrelated potentials for arbitrary distributions. We show that when the potential heights have a Gaussian distribution (with zero mean and a finite variance) the diffusion of the particles is always normal. In contrast, when the distribution of the potential heights is exponentially distributed the diffusion coefficient vanishes when the system is placed below a critical temperature. We calculate analytically the diffusion exponent for the anomalous (subdiffusive) phase by using the so-called "random trap model". Our predictions are tested by means of Langevin simulations obtaining good agreement within the accuracy of our numerical calculations.

  4. Displacements Of Brownian Particles In Terms Of Marian Von Smoluchowski's Heuristic Model

    ERIC Educational Resources Information Center

    Klein, Hermann; Woermann, Dietrich

    2005-01-01

    Albert Einstein's theory of the Brownian motion, Marian von Smoluchowski's heuristic model, and Perrin's experimental results helped to bring the concept of molecules from a state of being a useful hypothesis in chemistry to objects existing in reality. Central to the theory of Brownian motion is the relation between mean particle displacement and…

  5. Diffusion in different models of active Brownian motion

    NASA Astrophysics Data System (ADS)

    Lindner, B.; Nicola, E. M.

    2008-04-01

    Active Brownian particles (ABP) have served as phenomenological models of self-propelled motion in biology. We study the effective diffusion coefficient of two one-dimensional ABP models (simplified depot model and Rayleigh-Helmholtz model) differing in their nonlinear friction functions. Depending on the choice of the friction function the diffusion coefficient does or does not attain a minimum as a function of noise intensity. We furthermore discuss the case of an additional bias breaking the left-right symmetry of the system. We show that this bias induces a drift and that it generally reduces the diffusion coefficient. For a finite range of values of the bias, both models can exhibit a maximum in the diffusion coefficient vs. noise intensity.

  6. Dual-frequency magnetic particle imaging of the Brownian particle contribution

    NASA Astrophysics Data System (ADS)

    Viereck, Thilo; Kuhlmann, Christian; Draack, Sebastian; Schilling, Meinhard; Ludwig, Frank

    2017-04-01

    Magnetic particle imaging (MPI) is an emerging medical imaging modality based on the non-linear response of magnetic nanoparticles to an exciting magnetic field. MPI has been recognized as a fast imaging technique with high spatial resolution in the mm range. For some applications of MPI, especially in the field of functional imaging, the determination of the particle mobility (Brownian rotation) is of great interest, as it enables binding detection in MPI. It also enables quantitative imaging in the presence of Brownian-dominated particles, which is otherwise implausible. Discrimination of different particle responses in MPI is possible via the joint reconstruction approach. In this contribution, we propose a dual-frequency acquisition scheme to enhance sensitivity and contrast in the detection of different particle mobilities compared to a standard single-frequency MPI protocol. The method takes advantage of the fact, that the magnetization response of the tracer is strongly frequency-dependent, i.e. for low excitation frequencies a stronger Brownian contribution is observed.

  7. First passage time of multiple Brownian particles on networks with applications

    NASA Astrophysics Data System (ADS)

    Wang, Shao-Ping; Pei, Wen-Jiang

    2008-07-01

    In this article, we study some theoretical and technological problems with relation to multiple Brownian particles on networks. We are especially interested in the behavior of the first arriving Brownian particle when all the Brownian particles start out from the source s simultaneously and head to the destination h randomly. We analyze the first passage time (FPT) Y(z) and the mean first passage time (MFPT) of multiple Brownian particles on complex networks. Equations of Y(z) and are obtained. On a variety of commonly encountered networks, we observe first passage properties of multiple Brownian particles from different aspects. We find that drops substantially when particle number z increases at the first stage, and converges to d, the distance between the source and the destination when z→∞. The distribution of FPT Prob{Y(z)=t},t=0,1,2,… is also analyzed in these networks. The distribution curve peaks up towards t=d when z increases. Consequently, if particle number z is set appropriately large, the first arriving Brownian particle will go along the shortest or near shortest paths between the source and the destination with high probability. Simulations confirm our analysis. Based on theoretical studies, we also investigate some practical problems using multiple Brownian particles, such as communication on P2P networks, optimal routing in small world networks, phenomenon of asymmetry in scale-free networks, information spreading in social networks, pervasion of viruses on the Internet, and so on. Our analytic and experimental results on multiple Brownian particles provide useful evidence for further understanding and properly tackling these problems.

  8. Digital holography for observing aerosol particles undergoing Brownian motion in microgravity conditions

    NASA Astrophysics Data System (ADS)

    Prodi, F.; Santachiara, G.; Travaini, S.; Belosi, F.; Vedernikov, A.; Dubois, F.; Queeckers, P.; Legros, J. C.

    2006-11-01

    Brownian diffusion of aerosol particles was studied in microgravity conditions using a digital holographic velocimeter. Based on digital image processing, the observed volume, recorded on a charge-coupled device (CCD) camera, is reconstructed slice by slice in order to achieve a full focused volume. Three dimensional coordinates of the particles are retrieved by such procedures and particle trajectories are reconstructed by analysing the sequence of the particle position. We deduced that the displacement of particles in microgravity, due to Brownian motion, follows a Gaussian distribution, like at 1 g. Particle sizes obtained from SEM measurements were in good agreement with those calculated from the three dimensional trajectories provided by the holographic microscope.

  9. A generalized Brownian motion model for turbulent relative particle dispersion

    NASA Astrophysics Data System (ADS)

    Shivamoggi, B. K.

    2016-08-01

    There is speculation that the difficulty in obtaining an extended range with Richardson-Obukhov scaling in both laboratory experiments and numerical simulations is due to the finiteness of the flow Reynolds number Re in these situations. In this paper, a generalized Brownian motion model has been applied to describe the relative particle dispersion problem in more realistic turbulent flows and to shed some light on this issue. The fluctuating pressure forces acting on a fluid particle are taken to be a colored noise and follow a stationary process and are described by the Uhlenbeck-Ornstein model while it appears plausible to take their correlation time to have a power-law dependence on Re, thus introducing a bridge between the Lagrangian quantities and the Eulerian parameters for this problem. This ansatz is in qualitative agreement with the possibility of a connection speculated earlier by Corrsin [26] between the white-noise representation for the fluctuating pressure forces and the large-Re assumption in the Kolmogorov [4] theory for the 3D fully developed turbulence (FDT) as well as a similar argument of Monin and Yaglom [23] and a similar result of Sawford [13] and Borgas and Sawford [24]. It also provides an insight into the result that the Richardson-Obukhov scaling holds only in the infinite-Re limit and disappears otherwise. This ansatz further provides a determination of the Richardson-Obukhov constant g as a function of Re, with an asymptotic constant value in the infinite-Re limit. It is shown to lead to full agreement, in the small-Re limit as well, with the Batchelor-Townsend [27] scaling for the rate of change of the mean square interparticle separation in 3D FDT, hence validating its soundness further.

  10. Study of Submicron Particle Size Distribution by Laser Doppler Measurement of Brownian Motion.

    DTIC Science & Technology

    1987-01-30

    BROWNIAN MOTION .............. -- e-ee..... 6-1 6.1 Thermal Characteristics of the Particles ........ 6-2 6.2 Thermophoresis of the Particles oo-ee...for particles such as soot particles which have a high absorptivity. 6.2 Thermophoresis of the Particles When a particle with non-zero absorptivity is...illuminated by a laser beam, thermophoresis occurs because a temperature gradient is set up so that the illuminated side of the particle has a higher

  11. Irreversible shear-activated aggregation in non-Brownian suspensions.

    PubMed

    Guery, J; Bertrand, E; Rouzeau, C; Levitz, P; Weitz, D A; Bibette, J

    2006-05-19

    We have studied the effect of shear on the stability of suspensions made of non-Brownian solid particles. We demonstrate the existence of an irreversible transition where the solid particles aggregate at remarkably low volume fractions (phi approximately 0.1). This shear-induced aggregation is dramatic and exhibits a very sudden change in the viscosity, which increases sharply after a shear-dependent induction time. We show that this induction time is related exponentially to the shear rate, reflecting the importance of the hydrodynamic forces in reducing the repulsive energy barrier that prevents the particles from aggregating.

  12. Nonequilibrium statistical mechanics of the heat bath for two Brownian particles.

    PubMed

    De Bacco, Caterina; Baldovin, Fulvio; Orlandini, Enzo; Sekimoto, Ken

    2014-05-09

    We propose a new look at the heat bath for two Brownian particles, in which the heat bath as a "system" is both perturbed and sensed by the Brownian particles. Nonlocal thermal fluctuations give rise to bath-mediated static forces between the particles. Based on the general sum rule of the linear response theory, we derive an explicit relation linking these forces to the friction kernel describing the particles' dynamics. The relation is analytically confirmed in the case of two solvable models and could be experimentally challenged. Our results point out that the inclusion of the environment as a part of the whole system is important for micron- or nanoscale physics.

  13. Stochastic electrodynamics with particle structure Part I: Zero-point induced Brownian behavior

    NASA Astrophysics Data System (ADS)

    Rueda, A.

    1993-02-01

    If ordinary views on particle structure are introduced in a simple classical particle model in replacement of the point particles of standard use in stochastic electrodynamics, it can be shown that an internal Zitterbewegung induced by the zero-point field background gives rise to a Brownian movement for the whole particle with a diffusion constant of the form D = ħ/2mD , where mD is a modeldependent mass. Since the days of Madeleung and Fuhr brownian behaviour has often been associated with quantization. We discuss this from the viewpoint of stochastic electrodynamics.

  14. Financial Brownian Particle in the Layered Order-Book Fluid and Fluctuation-Dissipation Relations

    NASA Astrophysics Data System (ADS)

    Yura, Yoshihiro; Takayasu, Hideki; Sornette, Didier; Takayasu, Misako

    2014-03-01

    We introduce a novel description of the dynamics of the order book of financial markets as that of an effective colloidal Brownian particle embedded in fluid particles. The analysis of comprehensive market data enables us to identify all motions of the fluid particles. Correlations between the motions of the Brownian particle and its surrounding fluid particles reflect specific layering interactions; in the inner layer the correlation is strong and with short memory, while in the outer layer it is weaker and with long memory. By interpreting and estimating the contribution from the outer layer as a drag resistance, we demonstrate the validity of the fluctuation-dissipation relation in this nonmaterial Brownian motion process.

  15. Derivation of diffusion coefficient of a Brownian particle in tilted periodic potential from the coordinate moments

    NASA Astrophysics Data System (ADS)

    Zhang, Yunxin

    2009-07-01

    In this research, diffusion of an overdamped Brownian particle in the tilted periodic potential is investigated. Using the one-dimensional hopping model, the formulations of the mean velocity V and effective diffusion coefficient D of the Brownian particle have been obtained [B. Derrida, J. Stat. Phys. 31 (1983) 433]. Based on the relation between the effective diffusion coefficient and the moments of the mean first passage time, the formulation of effective diffusion coefficient D of the Brownian particle also has been obtained [P. Reimann, et al., Phys. Rev. E 65 (2002) 031104]. In this research, we'll give another analytical expression of the effective diffusion coefficient D from the moments of the particle's coordinate.

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

    SciTech Connect

    Ilie, Ioana M.; Briels, Wim J.; Otter, Wouter K. den

    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.

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

    PubMed

    Ilie, Ioana M; Briels, Wim J; den Otter, Wouter K

    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.

  18. Statistical Properties of Thermal Noise Driving the Brownian Particles in Fluids

    NASA Astrophysics Data System (ADS)

    Tóthová, Jana; Lisý, Vladimír

    2016-02-01

    In several recent works high-resolution interferometric detection allowed to study the Brownian motion of optically trapped microparticles in air and fluids. The observed positional fluctuations of the particles are well described by the generalized Langevin equation with the Boussinesq-Basset "history force" instead of the Stokes friction, which is valid only for the steady motion. Recently, also the time correlation function of the thermal random force Fth driving the Brownian particles through collisions with the surrounding molecules has been measured. In the present contribution we propose a method to describe the statistical properties of Fth in incompressible fluids. Our calculations show that the time decay of the correlator is significantly slower than that found in the literature. It is also shown how the "color" of the thermal noise can be determined from the measured positions of the Brownian particles.

  19. Brownian motion of a charged test particle in vacuum between two conducting plates

    NASA Astrophysics Data System (ADS)

    Yu, Hongwei; Chen, Jun

    2004-12-01

    The Brownian motion of a charged test particle caused by quantum electromagnetic vacuum fluctuations between two perfectly conducting plates is examined and the mean squared fluctuations in the velocity and position of the test particle are calculated. Our results show that the Brownian motion in the direction normal to the plates is reinforced in comparison to that in the single plate case. The effective temperature associated with this normal Brownian motion could be three times as large as that in the single plate case. However, the negative dispersions for the velocity and position in the longitudinal directions, which could be interpreted as reducing the quantum uncertainties of the particle, acquire positive corrections due to the presence of the second plate, and are thus weakened.

  20. Dynamic light scattering arising from flowing Brownian particles: analytical model in optical coherence tomography conditions.

    PubMed

    Popov, Ivan; Weatherbee, Andrew S; Vitkin, I Alex

    2014-12-01

    The statistical model of scattered by flowing Brownian particles coherent radiation is suggested. The model includes the random Doppler shifts caused by particle Brownian motion and the speckle fluctuations caused primarily by the flow motion of particles. Analytical expressions are obtained for the correlation function, power spectrum, and spectral width of scattered radiation in the imaging geometry typically used in optical coherence tomography (OCT). It is shown that the spectral density has the Voigt shape, a well-known spectral profile from atomic and molecular spectroscopy. The approach enables the choice of the experimental regimes for the measurement of Brownian particle motion parameters even in the presence of flow. These regimes are characterized by the dominant contribution of Brownian motion in the spectral width of the flow-caused Doppler shift component. Further, the new formalism suggests that prior attempts to extract transverse flow velocity are only valid at near-perpendicular geometry. The impact of the small scattering volume contributing to the OCT signal is also discussed.

  1. Experimental Study of Brownian Dynamics of Bent-core Colloidal Particles

    NASA Astrophysics Data System (ADS)

    Fan, Chun-Zhen; Joshi, Bhuwan; Huang, Ji-Ping; Wei, Qi-Huo

    2009-03-01

    Bent-core or banana-shaped molecules exhibit a variety of intriguing liquid crystalline mesophases including nematics and smectic phases. We try to develop suspensions of bent-core shaped colloidal particles to mimic the bent-core liquid crystals. This report will focus on the fabrication of bent-core colloidal particle suspension, and optical microscopic studies of the Brownian dynamics of individual bent-core colloidal particles. The bent-core colloidal particles confined between two glass substrates are observed through dark-field optical microscopy, and their orientation and position are obtained through imaging processing. Results on the translational and rotational Brownian dynamics of these type of particles will be reported.

  2. Mean distance of two Brownian particles trapped in a suspended droplet and its dependence on the Debye length

    NASA Astrophysics Data System (ADS)

    Goto, Kosuke; Sakata, Shinya; Moritani, Kousuke; Inui, Norio

    2017-01-01

    The Brownian motion of two particles confined near the bottom of a suspended droplet was considered in order to examine the electrical double-layer interaction between them. The mean distance between the particles was expressed as a function of the Debye screening length. We report the application of Brownian particle trajectories for the experimental determination of the Debye screening length between gold particles trapped within a water droplet. This was computed through a comparison of the mean distance measured by observing the Brownian motion with its theoretical value.

  3. Large-displacement statistics of the rightmost particle of the one-dimensional branching Brownian motion.

    PubMed

    Derrida, Bernard; Meerson, Baruch; Sasorov, Pavel V

    2016-04-01

    Consider a one-dimensional branching Brownian motion and rescale the coordinate and time so that the rates of branching and diffusion are both equal to 1. If X_{1}(t) is the position of the rightmost particle of the branching Brownian motion at time t, the empirical velocity c of this rightmost particle is defined as c=X_{1}(t)/t. Using the Fisher-Kolmogorov-Petrovsky-Piscounov equation, we evaluate the probability distribution P(c,t) of this empirical velocity c in the long-time t limit for c>2. It is already known that, for a single seed particle, P(c,t)∼exp[-(c^{2}/4-1)t] up to a prefactor that can depend on c and t. Here we show how to determine this prefactor. The result can be easily generalized to the case of multiple seed particles and to branching random walks associated with other traveling-wave equations.

  4. Dynamics of non-Brownian rodlike particles in a nonuniform elongational flow

    NASA Astrophysics Data System (ADS)

    Cloitre, M.; Mongruel, A.

    1999-04-01

    This paper deals with the orientation of non-Brownian rodlike particles in a nonuniform elongational flow at low-Reynolds number. Experimentally, an elongational flow is created by introducing a small circular orifice into a cylindrical channel. The flow field is studied using a tracer anemometry technique. On the axis of symmetry, the deformation field is that of a pure elongation with a nonuniform elongation rate. It is well described by the analytical solution obtained for an infinite contraction ratio. This flow is used to study the dynamics of non-Brownian rodlike particles subject to nonuniform elongation. The orientation dynamics of a particle depends on the history of the deformation that it has experienced. The effects of small perturbations existing in the vicinity of the orifice are greatly amplified downstream. Consequently, particle motion does not exhibit the symmetry with respect to the orifice which is expected at low-Reynolds number.

  5. Large-displacement statistics of the rightmost particle of the one-dimensional branching Brownian motion

    NASA Astrophysics Data System (ADS)

    Derrida, Bernard; Meerson, Baruch; Sasorov, Pavel V.

    2016-04-01

    Consider a one-dimensional branching Brownian motion and rescale the coordinate and time so that the rates of branching and diffusion are both equal to 1. If X1(t ) is the position of the rightmost particle of the branching Brownian motion at time t , the empirical velocity c of this rightmost particle is defined as c =X1(t ) /t . Using the Fisher-Kolmogorov-Petrovsky-Piscounov equation, we evaluate the probability distribution P (c ,t ) of this empirical velocity c in the long-time t limit for c >2 . It is already known that, for a single seed particle, P (c ,t ) ˜exp[-(c2/4 -1 ) t ] up to a prefactor that can depend on c and t . Here we show how to determine this prefactor. The result can be easily generalized to the case of multiple seed particles and to branching random walks associated with other traveling-wave equations.

  6. Research on bimodal particle extinction coefficient during Brownian coagulation and condensation for the entire particle size regime

    NASA Astrophysics Data System (ADS)

    Tang, Hong; Lin, Jian-Zhong

    2011-12-01

    The extinction coefficient of atmospheric aerosol particles influences the earth's radiation balance directly or indirectly, and it can be determined by the scattering and absorption characteristics of aerosol particles. The problem of estimating the change of extinction coefficient due to time evolution of bimodal particle size distribution is studied, and two improved methods for calculating the Brownian coagulation coefficient and the condensation growth rate are proposed, respectively. Through the improved method based on Otto kernel, the Brownian coagulation coefficient can be expressed simply in powers of particle volume for the entire particle size regime based on the fitted polynomials of the mean enhancement function. Meanwhile, the improved method based on Fuchs-Sutugin kernel is developed to obtain the condensation growth rate for the entire particle size regime. And then, the change of the overall extinction coefficient of bimodal distributions undergoing Brownian coagulation and condensation can be estimated comprehensively for the entire particle size regime. Simulation experiments indicate that the extinction coefficients obtained with the improved methods coincide fairly well with the true values, which provide a simple, reliable, and general method to estimate the change of extinction coefficient for the entire particle size regime during the bimodal particle dynamic processes.

  7. Coarse-graining Brownian motion: from particles to a discrete diffusion equation.

    PubMed

    de la Torre, J A; Español, Pep

    2011-09-21

    We study the process of coarse-graining in a simple model of diffusion of Brownian particles. At a detailed level of description, the system is governed by a Brownian dynamics of non-interacting particles. The coarse-level is described by discrete concentration variables defined in terms of Delaunay cells. These coarse variables obey a stochastic differential equation that can be understood as a discrete version of a diffusion equation. We study different models for the two basic building blocks of this equation which are the free energy function and the diffusion matrix. The free energy function is shown to be non-additive due to the overlapping of cells in the Delaunay construction. The diffusion matrix is state dependent in principle, but for near-equilibrium situations it is shown that it may be safely evaluated at the equilibrium value of the concentration field.

  8. Two-dimensional transport model of coupled Brownian particles driven by biharmonic forces and constant forces

    NASA Astrophysics Data System (ADS)

    Wu, Weixia; Meng, Tao

    2017-01-01

    A directed transport model of coupled Brownian particles in a two-dimensional potential is established. In this model, the system of Brownian particles is driven by biharmonic forces and constant forces. By numerical simulation, the cooperative transport behaviours of the system are investigated. The results show that the average velocity of the system is significantly independent of the frequencies and intensities of the harmonic forces, the barrier height of the ratchet potential, coupling strength and noise intensity. The average velocity increases monotonically with increasing the intensities of the harmonic forces, and can reach some maximum values when the two frequencies are equal. In addition, the average velocity presents stochastic resonance and generalized resonance for noise intensity, coupling strength and the barrier height of the ratchet potential. Moreover, when a constant force is exerted on the ratchet potential direction, it will promote the directed transport of the system. But, when on the non-ratchet potential direction, the transport will not be affected.

  9. Application of GPU processing for Brownian particle simulation

    NASA Astrophysics Data System (ADS)

    Cheng, Way Lee; Sheharyar, Ali; Sadr, Reza; Bouhali, Othmane

    2015-01-01

    Reports on the anomalous thermal-fluid properties of nanofluids (dilute suspension of nano-particles in a base fluid) have been the subject of attention for 15 years. The underlying physics that govern nanofluid behavior, however, is not fully understood and is a subject of much dispute. The interactions between the suspended particles and the base fluid have been cited as a major contributor to the improvement in heat transfer reported in the literature. Numerical simulations are instrumental in studying the behavior of nanofluids. However, such simulations can be computationally intensive due to the small dimensions and complexity of these problems. In this study, a simplified computational approach for isothermal nanofluid simulations was applied, and simulations were conducted using both conventional CPU and parallel GPU implementations. The GPU implementations significantly improved the computational performance, in terms of the simulation time, by a factor of 1000-2500. The results of this investigation show that, as the computational load increases, the simulation efficiency approaches a constant. At a very high computational load, the amount of improvement may even decrease due to limited system memory.

  10. Lock-and-key dimerization in dense Brownian systems of hard annular sector particles

    NASA Astrophysics Data System (ADS)

    Hodson, Wade D.; Mason, Thomas G.

    2016-08-01

    We develop a translational-rotational cage model that describes the behavior of dense two-dimensional (2D) Brownian systems of hard annular sector particles (ASPs), resembling C shapes. At high particle densities, pairs of ASPs can form mutually interdigitating lock-and-key dimers. This cage model considers either one or two mobile central ASPs which can translate and rotate within a static cage of surrounding ASPs that mimics the system's average local structure and density. By comparing with recent measurements made on dispersions of microscale lithographic ASPs [P. Y. Wang and T. G. Mason, J. Am. Chem. Soc. 137, 15308 (2015), 10.1021/jacs.5b10549], we show that mobile two-particle predictions of the probability of dimerization Pdimer, equilibrium constant K , and 2D osmotic pressure Π2 D as a function of the particle area fraction ϕA correspond closely to these experiments. By contrast, predictions based on only a single mobile particle do not agree well with either the two-particle predictions or the experimental data. Thus, we show that collective entropy can play an essential role in the behavior of dense Brownian systems composed of nontrivial hard shapes, such as ASPs.

  11. The stochastic thermodynamics of a rotating Brownian particle in a gradient flow

    PubMed Central

    Lan, Yueheng; Aurell, Erik

    2015-01-01

    We compute the entropy production engendered in the environment from a single Brownian particle which moves in a gradient flow, and show that it corresponds in expectation to classical near-equilibrium entropy production in the surrounding fluid with specific mesoscopic transport coefficients. With temperature gradient, extra terms are found which result from the nonlinear interaction between the particle and the non-equilibrated environment. The calculations are based on the fluctuation relations which relate entropy production to the probabilities of stochastic paths and carried out in a multi-time formalism. PMID:26194015

  12. Local characterization of hindered Brownian motion by using digital video microscopy and 3D particle tracking

    SciTech Connect

    Dettmer, Simon L.; Keyser, Ulrich F.; Pagliara, Stefano

    2014-02-15

    In this article we present methods for measuring hindered Brownian motion in the confinement of complex 3D geometries using digital video microscopy. Here we discuss essential features of automated 3D particle tracking as well as diffusion data analysis. By introducing local mean squared displacement-vs-time curves, we are able to simultaneously measure the spatial dependence of diffusion coefficients, tracking accuracies and drift velocities. Such local measurements allow a more detailed and appropriate description of strongly heterogeneous systems as opposed to global measurements. Finite size effects of the tracking region on measuring mean squared displacements are also discussed. The use of these methods was crucial for the measurement of the diffusive behavior of spherical polystyrene particles (505 nm diameter) in a microfluidic chip. The particles explored an array of parallel channels with different cross sections as well as the bulk reservoirs. For this experiment we present the measurement of local tracking accuracies in all three axial directions as well as the diffusivity parallel to the channel axis while we observed no significant flow but purely Brownian motion. Finally, the presented algorithm is suitable also for tracking of fluorescently labeled particles and particles driven by an external force, e.g., electrokinetic or dielectrophoretic forces.

  13. Brownian Motion.

    ERIC Educational Resources Information Center

    Lavenda, Bernard H.

    1985-01-01

    Explains the phenomenon of Brownian motion, which serves as a mathematical model for random processes. Topics addressed include kinetic theory, Einstein's theory, particle displacement, and others. Points out that observations of the random course of a particle suspended in fluid led to the first accurate measurement of atomic mass. (DH)

  14. Stochastic heating of a single Brownian particle by charge fluctuations in a radio-frequency produced plasma sheath.

    PubMed

    Schmidt, Christian; Piel, Alexander

    2015-10-01

    The Brownian motion of a single particle in the plasma sheath is studied to separate the effect of stochastic heating by charge fluctuations from heating by collective effects. By measuring the particle velocities in the ballistic regime and by carefully determining the particle mass from the Epstein drag it is shown that for a pressure of 10 Pa, which is typical of many experiments, the proper kinetic temperature of the Brownian particle remains close to the gas temperature and rises only slightly with particle size. This weak effect is confirmed by a detailed model for charging and charge fluctuations in the sheath. A substantial temperature rise is found for decreasing pressure, which approximately shows the expected scaling with p(-2). The system under study is an example for non-equilibrium Brownian motion under the influence of white noise without corresponding dissipation.

  15. Pseudo-random number generation for Brownian Dynamics and Dissipative Particle Dynamics simulations on GPU devices

    SciTech Connect

    Phillips, Carolyn L.; Anderson, Joshua A.; Glotzer, Sharon C.

    2011-08-10

    Highlights: {yields} Molecular Dynamics codes implemented on GPUs have achieved two-order of magnitude computational accelerations. {yields} Brownian Dynamics and Dissipative Particle Dynamics simulations require a large number of random numbers per time step. {yields} We introduce a method for generating small batches of pseudorandom numbers distributed over many threads of calculations. {yields} With this method, Dissipative Particle Dynamics is implemented on a GPU device without requiring thread-to-thread communication. - Abstract: Brownian Dynamics (BD), also known as Langevin Dynamics, and Dissipative Particle Dynamics (DPD) are implicit solvent methods commonly used in models of soft matter and biomolecular systems. The interaction of the numerous solvent particles with larger particles is coarse-grained as a Langevin thermostat is applied to individual particles or to particle pairs. The Langevin thermostat requires a pseudo-random number generator (PRNG) to generate the stochastic force applied to each particle or pair of neighboring particles during each time step in the integration of Newton's equations of motion. In a Single-Instruction-Multiple-Thread (SIMT) GPU parallel computing environment, small batches of random numbers must be generated over thousands of threads and millions of kernel calls. In this communication we introduce a one-PRNG-per-kernel-call-per-thread scheme, in which a micro-stream of pseudorandom numbers is generated in each thread and kernel call. These high quality, statistically robust micro-streams require no global memory for state storage, are more computationally efficient than other PRNG schemes in memory-bound kernels, and uniquely enable the DPD simulation method without requiring communication between threads.

  16. The Measurement and Analysis of Brownian Particle Fall Rates in a New Regime of Dense Gases.

    NASA Astrophysics Data System (ADS)

    Fedele, Paul David

    Millikan's law of fall is an empirical relationship describing the dependence of the fall rate of submicron particles in gases in terms of the particle radius and the gas density. It had been long thought that the physics of slip, embodied in the law, gave a complete description of the phenomenon. During measurements of the velocity autocorrelation function for a single Brownian particle at different gas densities, we have discovered that for sufficiently small particles the fall rate increases with increasing density, in contrast to the prediction of Millikan's law. Vertical displacements during a 10 sec interval of a single oil drop have been measured as a function of nitrogen gas density in the range of one to 22 atm at room temperature by retaining the particle for up to 15 hours. Altogether 24 particles in the radius range of 0.1 to 0.4 (mu)m have been analyzed. The density dependence of the average fall rate undergoes a smooth transition from the Millikan behavior in the large size limit to the newly observed behavior in the small size limit. No anomalies are seen, however, in the density dependence of the rms displacement. In attempts to explain the observations we have examined a model based on the fact that Brownian fluctuation increases with decreasing particle size at a given gas density that the contributions of the vorticity field about such a Brownian particle on the fluctuation increases with density and that gravity sustains the entire system of the host gas and the test particle in a steady non-equilibrium state. The modified Langevin equation with gravity has been numerically solved under varying conditions. The fluctuating force is modeled by means of a series of randomly applied impulsive velocities of the test particle. The results are that while there is no sufficient physics in the model to generate any asymmetry in the fluctuation, the model has a mechanism to preserve any asymmetry given to the system for a long time and to produce

  17. Single potassium niobate nano/microsized particles as local mechano-optical Brownian probes

    NASA Astrophysics Data System (ADS)

    Mor, Flavio M.; Sienkiewicz, Andrzej; Magrez, Arnaud; Forró, László; Jeney, Sylvia

    2016-03-01

    Perovskite alkaline niobates, due to their strong nonlinear optical properties, including birefringence and the capability to produce second-harmonic generation (SHG) signals, attract a lot of attention as potential candidates for applications as local nano/microsized mechano-optical probes. Here, we report on an implementation of photonic force microscopy (PFM) to explore the Brownian motion and optical trappability of monocrystalline potassium niobate (KNbO3) nano/microsized particles having sizes within the range of 50 to 750 nm. In particular, we exploit the anisotropic translational diffusive regime of the Brownian motion to quantify thermal fluctuations and optical forces of singly-trapped KNbO3 particles within the optical trapping volume of a PFM microscope. We also show that, under near-infrared (NIR) excitation of the highly focused laser beam of the PFM microscope, a single optically-trapped KNbO3 particle reveals a strong SHG signal manifested by a narrow peak (λem = 532 nm) at half the excitation wavelength (λex = 1064 nm). Moreover, we demonstrate that the thus induced SHG emission can be used as a local light source that is capable of optically exciting molecules of an organic dye, Rose Bengal (RB), which adhere to the particle surface, through the mechanism of luminescence energy transfer (LET).Perovskite alkaline niobates, due to their strong nonlinear optical properties, including birefringence and the capability to produce second-harmonic generation (SHG) signals, attract a lot of attention as potential candidates for applications as local nano/microsized mechano-optical probes. Here, we report on an implementation of photonic force microscopy (PFM) to explore the Brownian motion and optical trappability of monocrystalline potassium niobate (KNbO3) nano/microsized particles having sizes within the range of 50 to 750 nm. In particular, we exploit the anisotropic translational diffusive regime of the Brownian motion to quantify thermal

  18. Brownian motion

    NASA Astrophysics Data System (ADS)

    Lavenda, B. H.

    1985-02-01

    Brownian motion, the doubly random motion of small particles suspended in a liquid due to molecular collisions, and its implications and applications in the history of modern science are discussed. Topics examined include probabilistic phenomena, the kinetic theory of gases, Einstein's atomic theory of Brownian motion, particle displacement, diffusion measurements, the determination of the mass of the atom and of Avogadro's number, the statistical mechanics of thermodynamics, nonequilibrium systems, Langevin's equation of motion, time-reversed evolution, mathematical analogies, and applications in economics and radio navigation. Diagrams and drawings are provided.

  19. Memory effects for a trapped Brownian particle in viscoelastic shear flows

    NASA Astrophysics Data System (ADS)

    Mankin, Romi; Laas, Katrin; Lumi, Neeme

    2013-10-01

    The long-time limit behavior of the positional distribution for an underdamped Brownian particle in a fluctuating harmonic potential well, which is simultaneously exposed to an oscillatory viscoelastic shear flow is investigated using the generalized Langevin equation with a power-law-type memory kernel. The influence of a fluctuating environment is modeled by a multiplicative white noise (fluctuations of the stiffness of the trapping potential) and by an additive internal fractional Gaussian noise. The exact expressions of the second-order moments of the fluctuating position for the Brownian particle in the shear plane have been calculated. Also, shear-induced cross correlation between particle fluctuations along orthogonal directions as well as the angular momentum are found. It is shown that interplay of shear flow, memory, and multiplicative noise can generate a variety of cooperation effects, such as energetic instability, multiresonance versus the shear frequency, and memory-induced anomalous diffusion in the direction of the shear flow. Particularly, two different critical memory exponents have been found, which mark dynamical transitions from a stationary regime to a subdiffusive (or superdiffusive) regime of the system. Similarities and differences between the behaviors of the models with oscillatory and nonoscillatory shear flow are also discussed.

  20. Estimating the viscoelastic moduli of complex fluids from observation of Brownian motion of a particle confined to a harmonic trap.

    PubMed

    Felderhof, B U

    2011-05-28

    A procedure is proposed to estimate the viscoelastic properties of a complex fluid from the behavior of the velocity autocorrelation function of a suspended Brownian particle, trapped in a harmonic potential. The procedure is tested for a model complex fluid with a given frequency-dependent shear viscosity. The analysis shows that the procedure can provide a rather accurate prediction of the viscoelastic properties of the fluid on the basis of experimental data on the velocity autocorrelation function of the trapped Brownian particle in a limited range of time.

  1. Accurate method for the Brownian dynamics simulation of spherical particles with hard-body interactions

    NASA Astrophysics Data System (ADS)

    Barenbrug, Theo M. A. O. M.; Peters, E. A. J. F. (Frank); Schieber, Jay D.

    2002-11-01

    In Brownian Dynamics simulations, the diffusive motion of the particles is simulated by adding random displacements, proportional to the square root of the chosen time step. When computing average quantities, these Brownian contributions usually average out, and the overall simulation error becomes proportional to the time step. A special situation arises if the particles undergo hard-body interactions that instantaneously change their properties, as in absorption or association processes, chemical reactions, etc. The common "naı̈ve simulation method" accounts for these interactions by checking for hard-body overlaps after every time step. Due to the simplification of the diffusive motion, a substantial part of the actual hard-body interactions is not detected by this method, resulting in an overall simulation error proportional to the square root of the time step. In this paper we take the hard-body interactions during the time step interval into account, using the relative positions of the particles at the beginning and at the end of the time step, as provided by the naı̈ve method, and the analytical solution for the diffusion of a point particle around an absorbing sphere. Öttinger used a similar approach for the one-dimensional case [Stochastic Processes in Polymeric Fluids (Springer, Berlin, 1996), p. 270]. We applied the "corrected simulation method" to the case of a simple, second-order chemical reaction. The results agree with recent theoretical predictions [K. Hyojoon and Joe S. Kook, Phys. Rev. E 61, 3426 (2000)]. The obtained simulation error is proportional to the time step, instead of its square root. The new method needs substantially less simulation time to obtain the same accuracy. Finally, we briefly discuss a straightforward way to extend the method for simulations of systems with additional (deterministic) forces.

  2. Brownian particle-kinetics in a superparamagnetic ferrofluid subjected to static magnetic-field

    NASA Astrophysics Data System (ADS)

    Trisnanto, Suko Bagus; Kitamoto, Yoshitaka

    2017-01-01

    The stochastic Brownian particle-kinetics in a superparamagnetic ferrofluid at room temperature is of significance in nullifying total magnetization vectors of the suspended particles. Correspondingly, the apparent magnetization response observed under static magnetic field shows no hysteresis loop, but being linear at a given finite field-difference. Owing to this superparamagnetism, we propose a differential magnetometry to analyze the static field-induced particle-kinetics and further to identify the effective field-strength in reorienting particle-moments toward the applied field direction. A polydispersive ferrofluid containing iron-oxide nanoparticles, in practice, is subjected to a very-low oscillatory-field, immediately after applying the static-field. For a given frequency, we confirm a decreasing ac susceptibility as dc field-strength increases, which suggests a statistically less fluctuating magnetization-vectors. Via numerical integration of ac susceptibility recorded, we furthermore estimate the nonlinear quasi-static magnetization at various measurement frequencies. The resulting nonlinearity is attributable to the contributing relaxation dynamics of the particles. More importantly, the difference between dc and ac susceptibilities is found to be field-strength and frequency-dependent. Its value is further maximized at an effective field-strength, from which we identified the coexisting energy-barriers.

  3. Shear-induced reaction-limited aggregation kinetics of brownian particles at arbitrary concentrations.

    PubMed

    Zaccone, Alessio; Gentili, Daniele; Wu, Hua; Morbidelli, Massimo

    2010-04-07

    The aggregation of interacting brownian particles in sheared concentrated suspensions is an important issue in colloid and soft matter science per se. Also, it serves as a model to understand biochemical reactions occurring in vivo where both crowding and shear play an important role. We present an effective medium approach within the Smoluchowski equation with shear which allows one to calculate the encounter kinetics through a potential barrier under shear at arbitrary colloid concentrations. Experiments on a model colloidal system in simple shear flow support the validity of the model in the concentration range considered. By generalizing Kramers' rate theory to the presence of shear and collective hydrodynamics, our model explains the significant increase in the shear-induced reaction-limited aggregation kinetics upon increasing the colloid concentration.

  4. On the description of Brownian particles in confinement on a non-Cartesian coordinates basis.

    PubMed

    Dagdug, Leonardo; García-Chung, Angel A; Chacón-Acosta, Guillermo

    2016-08-21

    We developed a theoretical framework to study the diffusion of Brownian point-like particles in bounded geometries in two and three dimensions. We use the Frenet-Serret moving frame as the coordinate system. For narrow tubes and channels, we use an effective one-dimensional description reducing the diffusion equation to a Fick-Jacobs-like equation. From this last equation, we can calculate the effective diffusion coefficient applying Neumann boundary conditions. On one hand, for channels with a straight axis our theoretical approximation for the effective coefficient does coincide with the reported in the literature [D. Reguera and J. M. Rubí, Phys. Rev. E 64, 061106 (2001) and P. Kalinay and J. K. Percus, ibid. 74, 041203 (2006)]. On the other hand, for tubes with a straight axis and circular cross-section our analytical expression does not coincide with the reported by Rubí and Reguera and by Kalinay and Percus, although it is practically identical.

  5. On the description of Brownian particles in confinement on a non-Cartesian coordinates basis

    NASA Astrophysics Data System (ADS)

    Dagdug, Leonardo; García-Chung, Angel A.; Chacón-Acosta, Guillermo

    2016-08-01

    We developed a theoretical framework to study the diffusion of Brownian point-like particles in bounded geometries in two and three dimensions. We use the Frenet-Serret moving frame as the coordinate system. For narrow tubes and channels, we use an effective one-dimensional description reducing the diffusion equation to a Fick-Jacobs-like equation. From this last equation, we can calculate the effective diffusion coefficient applying Neumann boundary conditions. On one hand, for channels with a straight axis our theoretical approximation for the effective coefficient does coincide with the reported in the literature [D. Reguera and J. M. Rubí, Phys. Rev. E 64, 061106 (2001) and P. Kalinay and J. K. Percus, ibid. 74, 041203 (2006)]. On the other hand, for tubes with a straight axis and circular cross-section our analytical expression does not coincide with the reported by Rubí and Reguera and by Kalinay and Percus, although it is practically identical.

  6. Hydrodynamically enforced entropic current of Brownian particles with a transverse gravitational force

    NASA Astrophysics Data System (ADS)

    Li, Feng-guo; Ai, Bao-quan

    2014-04-01

    Transport of overdamped Brownian particles in a periodic hydrodynamical channel is investigated in the presence of an asymmetric unbiased force, a transverse gravitational force, and a pressure-driven flow. With the help of the generalized Fick-Jacobs approach, we obtain an analytical expression for the directed current and the generalized potential of mean force. It is found that, when the transverse gravitational force is larger than a certain value, the current is suppressed. Moreover, when the temporal asymmetry parameter of the unbiased force is negative, the current is always negative. However, when the temporal asymmetry parameter is positive, the transverse gravitational force and the pressure drop not only determine the direction of the current but also affect its amplitude. In particular, the competition between the asymmetric unbiased force and the pressure drop can result in multiple current reversals.

  7. 3D tracking the Brownian motion of colloidal particles using digital holographic microscopy and joint reconstruction.

    PubMed

    Verrier, Nicolas; Fournier, Corinne; Fournel, Thierry

    2015-06-01

    In-line digital holography is a valuable tool for sizing, locating, and tracking micro- or nano-objects in a volume. When a parametric imaging model is available, inverse problem approaches provide a straightforward estimate of the object parameters by fitting data with the model, thereby allowing accurate reconstruction. As recently proposed and demonstrated, combining pixel super-resolution techniques with inverse problem approaches improves the estimation of particle size and 3D position. Here, we demonstrate the accurate tracking of colloidal particles in Brownian motion. Particle size and 3D position are jointly optimized from video holograms acquired with a digital holographic microscopy setup based on a low-end microscope objective (×20, NA 0.5). Exploiting information redundancy makes it possible to characterize particles with a standard deviation of 15 nm in size and a theoretical resolution of 2×2×5  nm3 for position under additive white Gaussian noise assumption.

  8. Generation of microswimmers from passive Brownian particles in a spherically aberrated optical trap.

    PubMed

    Mondal, Argha; Roy, Basudev; Banerjee, Ayan

    2015-03-23

    We induce spontaneous motion that is both directed and complex in micron-sized asymmetric Brownian particles in a spherically aberrated optical trap to generate microswimmers. The aberrated optical trap is prepared in a slightly modified optical tweezers configuration where we use a refractive index mismatched cover slip leading to the formation of an annular intensity distribution near the trap focal plane. Asymmetric scattering from a micro-particle trapped in this annular trap gives rise to a net tangential force on the particle causing it to revolve spontaneously in the intensity ring. The rate of revolution can be controlled from sub-Hz to a few Hz by changing the intensity of the trapping light. Theoretical simulations performed using finite-difference time-domain method verify the experimental observations. We also experimentally demonstrate simultaneous spin and revolution of a micro-swimmer which shows that complex motion can be achieved by designing a suitable shape of a micro-swimmer in the optical potential.

  9. Experimental study of the stochastic heating of a single Brownian particle by charge fluctuations

    NASA Astrophysics Data System (ADS)

    Schmidt, Christian; Piel, Alexander

    2016-08-01

    The Brownian motion of a micro-particle, which is suspended in the sheath of a radio-frequency discharge, is studied by high-speed video microscopy. In this environment, stochastic heating by charge fluctuations is expected, which should lead to an anisotropic kinetic temperature of the particle with a preferential heating in the direction of the mean electric field in the sheath. The stochastic heating should become more effective at low gas pressures where cooling by the neutral gas becomes ineffective. Our refined experiments confirm the anisotropic heating and the temperature rise for diminishing pressure. Particle-in-cell simulations have guided us in modifying the gap width of the discharge and to specify the dependence of the plasma density on gas pressure as n i ∝ p 1 / 2 . Since the stochastic heating rate also depends on the life-time of charge fluctuations, a temperature scaling T kin ∝ p 3 / 2 results, which is in agreement with the experimental data. The experimental procedure to eliminate other spurious heating mechanisms is described in detail.

  10. Dependence of crystallization of Brownian particles by sedimentation on the force direction

    NASA Astrophysics Data System (ADS)

    Sato, Masahide; Yusuf Hakim Widianto, Muhammad; Kanatsu, Youhei

    2015-11-01

    The formation of a large close-packed colloidal crystal with the fcc structure was observed during the sedimentation of colloidal particles in an inverted pyramidal pit [S. Matsuo et al., Appl. Phys. Lett. 82, 4285 (2003)]. Carrying out Brownian dynamics simulations, we confirmed that large grains with the fcc structure are formed when the apex angle of the inverted pyramidal container is suitable and the force direction is parallel to the the center axis [Y. Kanatsu and M. Sato, J. Phys. Soc. Jpn. 84, 044601 (2015)]. To form a high-quality colloidal crystal without defects, it is important to investigate in detail how the quality of a colloidal crystal is affected by the force direction and container shape. In this paper, we focus on the effect of the force direction on crystal quality and investigate how the ratio of the number of the hcp structured particles, Nhcp, to that of fcc structured particles, Nfcc, is affected by the force direction. In our simulation, the ratio of Nfcc to Nhcp is hardly changed when the force direction deviates from the central axis: Nfcc is much larger than Nhcp irrespective of the force direction. Thus, our results show that the crystal structure is insensitive to the force direction in forming a colloidal crystal by sedimentation in an inverted pyramidal container.

  11. Diffusion of active chiral particles

    NASA Astrophysics Data System (ADS)

    Sevilla, Francisco J.

    2016-12-01

    The diffusion of chiral active Brownian particles in three-dimensional space is studied analytically, by consideration of the corresponding Fokker-Planck equation for the probability density of finding a particle at position x and moving along the direction v ̂ at time t , and numerically, by the use of Langevin dynamics simulations. The analysis is focused on the marginal probability density of finding a particle at a given location and at a given time (independently of its direction of motion), which is found from an infinite hierarchy of differential-recurrence relations for the coefficients that appear in the multipole expansion of the probability distribution, which contains the whole kinematic information. This approach allows the explicit calculation of the time dependence of the mean-squared displacement and the time dependence of the kurtosis of the marginal probability distribution, quantities from which the effective diffusion coefficient and the "shape" of the positions distribution are examined. Oscillations between two characteristic values were found in the time evolution of the kurtosis, namely, between the value that corresponds to a Gaussian and the one that corresponds to a distribution of spherical shell shape. In the case of an ensemble of particles, each one rotating around a uniformly distributed random axis, evidence is found of the so-called effect "anomalous, yet Brownian, diffusion," for which particles follow a non-Gaussian distribution for the positions yet the mean-squared displacement is a linear function of time.

  12. Brownian Emitters

    NASA Astrophysics Data System (ADS)

    Tsekov, Roumen

    2016-06-01

    A Brownian harmonic oscillator, which dissipates energy either by friction or via emission of electromagnetic radiation, is considered. This Brownian emitter is driven by the surrounding thermo-quantum fluctuations, which are theoretically described by the fluctuation-dissipation theorem. It is shown how the Abraham-Lorentz force leads to dependence of the half-width on the peak frequency of the oscillator amplitude spectral density. It is found that for the case of a charged particle moving in vacuum at zero temperature, its root-mean-square velocity fluctuation is a universal constant, equal to roughly 1/18 of the speed of light. The relevant Fokker-Planck and Smoluchowski equations are also derived.

  13. Dependence of the Apex Angle of an Inverted Pyramidal-Shaped Container on Crystallization of Brownian Particles

    NASA Astrophysics Data System (ADS)

    Kanatsu, Youhei; Sato, Masahide

    2015-11-01

    Large grains of a close-packed colloidal crystal have been experimentally shown to form in an inverted pyramidal pit by sedimentation [S. Matsuo et al., http://dx.doi.org/10.1063/1.1583138, Appl. Phys. Lett. 82, 4285 (2003)]. Keeping this experiment in mind, we study the crystallization of Brownian particles. We carry out Brownian dynamics simulations in an inverted pyramidal-shaped container. The Brownian particles settle out toward the apex of the container by a uniform external force. If the apex angle is suitable, large grains with the face-centered cubic (fcc) structure are formed [Y. Kanatsu and M. Sato, http://dx.doi.org/10.7566/JPSJ.84.044601, J. Phys. Soc. Jpn. 84, 044601 (2015)]. When the apex angle deviates from a suitable value, the number of hexagonal close-packed (hcp) structured particles, Nhcp, increases with increasing angle deviation. The formation of the hcp structure is induced by disordered particles remaining in the center region of the container.

  14. Avalanche-like fluidization of a non-Brownian particle gel

    NASA Astrophysics Data System (ADS)

    Kurokawa, Aika; Vidal, Valérie; Kurita, Kei; Divoux, Thibaut; Manneville, Sébastien

    We report on the fluidization dynamics of an attractive gel composed of non-Brownian particles made of fused silica colloids. Extensive rheology coupled to ultrasonic velocimetry allows us to characterize the global stress response together with the local dynamics of the gel during shear startup experiments. In practice, after being rejuvenated by a preshear, the gel is left to age during a time tw before being submitted to a constant shear rate γ˙. We investigate in detail the effects of both tw and γ˙ on the fluidization dynamics and build a detailed state diagram of the gel response to shear startup flows. The gel may either display transient shear banding towards complete fluidization, or steady-state shear banding. In the former case, we unravel that the progressive fluidization occurs by successive steps that appear as peaks on the global stress relaxation signal. Flow imaging reveals that the shear band grows up to complete fluidization of the material by sudden avalanche-like events which are distributed heterogeneously along the vorticity direction and correlated to large peaks in the slip velocity at the moving wall. PRC CNRS/JSPS RheoVolc, IUF & ERC Grant Agreement No. 258803.

  15. I. Statistical mechanics of bubbly liquids. II. Behavior of sheared suspensions of non-Brownian particles

    NASA Astrophysics Data System (ADS)

    Yurkovetsky, Yevgeny

    I. The dynamics of bubbles at high Reynolds numbers is studied from the viewpoint of statistical mechanics. Individual bubbles are treated as dipoles in potential flow. A virtual mass matrix of the system of bubbles is introduced, which depends on the instantaneous positions of the bubbles, and is used to calculate the energy of the bubbly flow as a quadratic form of the bubbles' velocities. The energy is shown to be the system's Hamiltonian and is used to construct a canonical ensemble partition function, which explicitly includes the total impulse of the suspension along with its energy. The Hamiltonian is decomposed into an effective potential due to the bubbles' collective motion and a kinetic term due to the random motion about the mean. An effective bubble temperature-a measure of the relative importance of the bubbles' relative to collective motion-is derived with the help of the impulse-dependent partition function. Two effective potentials are shown to operate: one, due to the mean motion of the bubbles, dominates at low bubble temperatures where it leads to their grouping in flat clusters normal to the direction of the collective motion, while the other, temperature invariant, is due to the bubbles' position-dependent virtual mass and results in their mutual repulsion. Numerical evidence is presented for the existence of the effective potentials, the condensed and dispersed phases and a phase transition. II. Suspensions of non-Brownian particles in simple shear flow of a Newtonian solvent in the range of particle phase concentration, φ, from 0.05 to 0.52, are studied numerically by Stokesian Dynamics. The simulations are a function of φ and the dimensionless shear rate, γ*, which measures the relative importance of the shear and short-ranged interparticle forces. The pair-distribution functions, shear viscosity, normal stress differences, suspension pressure, long-time self-diffusion coefficients, and mean square of the particle velocity fluctuations

  16. Avalanche-like fluidization of a non-Brownian particle gel.

    PubMed

    Kurokawa, Aika; Vidal, Valérie; Kurita, Kei; Divoux, Thibaut; Manneville, Sébastien

    2015-12-14

    We report on the fluidization dynamics of an attractive gel composed of non-Brownian particles made of fused silica colloids. Extensive rheology coupled to ultrasonic velocimetry allows us to characterize the global stress response together with the local dynamics of the gel during shear startup experiments. In practice, after being rejuvenated by a preshear, the gel is left to age for a time tw before being subjected to a constant shear rate [small gamma, Greek, dot above]. We investigate in detail the effects of both tw and [small gamma, Greek, dot above] on the fluidization dynamics and build a detailed state diagram of the gel response to shear startup flows. The gel may display either transient shear banding towards complete fluidization or steady-state shear banding. In the former case, we unravel that the progressive fluidization occurs by successive steps that appear as peaks on the global stress relaxation signal. Flow imaging reveals that the shear band grows until complete fluidization of the material by sudden avalanche-like events which are distributed heterogeneously along the vorticity direction and correlated to large peaks in the slip velocity at the moving wall. These features are robust over a wide range of tw and [small gamma, Greek, dot above] values, although the very details of the fluidization scenario vary with [small gamma, Greek, dot above]. Finally, the critical shear rate [small gamma, Greek, dot above]* that separates steady-state shear-banding from steady-state homogeneous flow depends on the width of the shear cell and exhibits a nonlinear dependence with tw. Our work brings about valuable experimental data on transient flows of attractive dispersions, highlighting the subtle interplay between shear, wall slip and aging whose modeling constitutes a major challenge that has not been met yet.

  17. Stochastic thermodynamics with a Brownian particle in an optical trap (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Martinez, Ignacio A.; Roldán, Édgar; Dinis, Luis; Mestres, Pau; Parrondo, Juan M. R.; Rica, Raúl A.

    2015-08-01

    Stochastic thermodynamics [1,2] is a recently developed framework to deal with the thermodynamics at the microscope, where thermal fluctuations strongly influence their behaviour. Typical such systems are colloids and biomolecules or cells. These thermal fluctuations do not only lead to Brownian motion, but to a continuous and unavoidable heat exchange between the suspending medium and the particles, leading to a very interesting phenomenology. In order to explore such phenomenology and to test theoretical results obtained from stochastic thermodynamics, we developed an "experimental simulator" of thermodynamic devices in the microscale with an optically trapped bead that is subject to an external noise that mimics a controllable thermal bath. The noise is applied by means of electric fields acting on the charge of the trapped particle. In this talk, I will present some of the results we obtained with this simulator, demonstrating excellent control over the effective temperature of the system and a control parameter. This allows us to perform a variety of equilibrium and non-equilibrium thermodynamic processes [3-5]. In particular, we were able to realize microadiabatic processes, where no heat is exchanged on average between the particle and the medium [6]. This achievement allowed us to implement a Carnot microengine as a concatenation of isothermal and adiabatic processes [7], whose theoretical study is playing a key role in the foundations of stochastic thermodynamics. References [1] K Sekimoto; Lecture Notes in Physics (Springer, Berlin, 2010), Vol. 799. [2] U Seifert; Rep. Prog. Phys. 75 (2012) 126001 [3] IA Martínez, E Roldan, JMR Parrondo, D Petrov; Phys. Rev. E 87 (2013) 032159 [4] É Roldán, IA Martínez, L Dinis, RA Rica; Appl. Phys. Lett. 104 (2014) 234103 [5] P Mestres, IA Martinez, A Ortiz-Ambriz, RA Rica, E Roldan; Phys. Rev. E 90 (2014) 032116 [6] IA Martínez, E Roldan, L Dinis, D Petrov, RA Rica; Phys. Rev. Lett. (2015) In press [7] IA Martinez

  18. The van Hove distribution function for brownian hard spheres: dynamical test particle theory and computer simulations for bulk dynamics.

    PubMed

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

    2010-12-14

    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.

  19. Active Particles in Complex and Crowded Environments

    NASA Astrophysics Data System (ADS)

    Bechinger, Clemens; Di Leonardo, Roberto; Löwen, Hartmut; Reichhardt, Charles; Volpe, Giorgio; Volpe, Giovanni

    2016-10-01

    Differently from passive Brownian particles, active particles, also known as self-propelled Brownian particles or microswimmers and nanoswimmers, are capable of taking up energy from their environment and converting it into directed motion. Because of this constant flow of energy, their behavior can be explained and understood only within the framework of nonequilibrium physics. In the biological realm, many cells perform directed motion, for example, as a way to browse for nutrients or to avoid toxins. Inspired by these motile microorganisms, researchers have been developing artificial particles that feature similar swimming behaviors based on different mechanisms. These man-made micromachines and nanomachines hold a great potential as autonomous agents for health care, sustainability, and security applications. With a focus on the basic physical features of the interactions of self-propelled Brownian particles with a crowded and complex environment, this comprehensive review will provide a guided tour through its basic principles, the development of artificial self-propelling microparticles and nanoparticles, and their application to the study of nonequilibrium phenomena, as well as the open challenges that the field is currently facing.

  20. Size-Resolved Ultrafine Particle Deposition and Brownian Coagulation from Gasoline Vehicle Exhaust in an Environmental Test Chamber.

    PubMed

    Zhao, Yu; Wang, Fang; Zhao, Jianing

    2015-10-20

    Size-resolved deposition rates and Brownian coagulation of particles between 20 and 900 nm (mobility diameter) were estimated in a well-mixed environmental chamber from a gasoline vehicle exhaust with a total peak particle concentration of 10(5)-10(6) particles/cm(3) at 12.24-25.22 °C. A deposition theory with modified friction velocity and coagulation model was also employed to predict particle concentration decay. Initially during particle decay, approximately 85% or more of the particles had diameters of <100 nm. Particle deposition rates with standard deviations were highly dependent on particle size ranges, and varied from 0.012 ± 0.003 to 0.48 ± 0.02 h(-1). In the experiment, the friction velocity obtained was in the range 1.5-2.5 cm/s. The most explainable fractal dimension and Hamaker constant in coagulation model were 2.5-3 and 20 kT, respectively, and the contribution from coagulation dominated the total particle decay during the first 1 h of decay. It is considered that the modified friction velocity and best fitted fractal dimension and Hamaker constants could be further used to analyze gasoline vehicle exhaust particle dynamics and assess human exposure to vehicle particle pollutants in urban areas, tunnels, and underground parking lots.

  1. Brownian vortexes

    NASA Astrophysics Data System (ADS)

    Sun, Bo; Lin, Jiayi; Darby, Ellis; Grosberg, Alexander Y.; Grier, David G.

    2009-07-01

    Mechanical equilibrium at zero temperature does not necessarily imply thermodynamic equilibrium at finite temperature for a particle confined by a static but nonconservative force field. Instead, the diffusing particle can enter into a steady state characterized by toroidal circulation in the probability flux, which we call a Brownian vortex. The circulatory bias in the particle’s thermally driven trajectory is not simply a deterministic response to the solenoidal component of the force but rather reflects interplay between advection and diffusion in which thermal fluctuations extract work from the nonconservative force field. As an example of this previously unrecognized class of stochastic heat engines, we consider a colloidal sphere diffusing in a conventional optical tweezer. We demonstrate both theoretically and experimentally that nonconservative optical forces bias the particle’s fluctuations into toroidal vortexes whose circulation can reverse direction with temperature or laser power.

  2. Instability of a uniformly collapsing cloud of classical and quantum self-gravitating Brownian particles

    NASA Astrophysics Data System (ADS)

    Chavanis, Pierre-Henri

    2011-03-01

    We study the growth of perturbations in a uniformly collapsing cloud of self-gravitating Brownian particles. This problem shares analogies with the formation of large-scale structures in a universe experiencing a “big-crunch” or with the formation of stars in a molecular cloud experiencing gravitational collapse. Starting from the barotropic Smoluchowski-Poisson system, we derive a new equation describing the evolution of the density contrast in the comoving (collapsing) frame. This equation can serve as a prototype to study the process of self-organization in complex media with structureless initial conditions. We solve this equation analytically in the linear regime and compare the results with those obtained by using the “Jeans swindle” in a static medium. The stability criteria, as well as the laws for the time evolution of the perturbations, differ. The Jeans criterion is expressed in terms of a critical wavelength λJ while our criterion is expressed in terms of a critical polytropic index γ4/3. In a static background, the system is stable for λ<λJ and unstable for λ>λJ. In a collapsing cloud, the system is stable for γ>γ4/3 and unstable for γ<γ4/3. If γ=γ4/3, it is stable for λ<λJ and unstable for λ>λJ. We also study the fragmentation process in the nonlinear regime. We determine the growth of the skewness, the long-wavelength tail of the power spectrum and find a self-similar solution to the nonlinear equations valid for large times. Finally, we consider dissipative self-gravitating Bose-Einstein condensates with short-range interactions and show that, in a strong friction limit, the dissipative Gross-Pitaevskii-Poisson system is equivalent to the quantum barotropic Smoluchowski-Poisson system. This yields new types of nonlinear mean-field Fokker-Planck equations, including quantum effects.

  3. Backward transformation of the colored-noise Fokker-Planck equation for shear-induced diffusion processes of non-Brownian particles

    NASA Astrophysics Data System (ADS)

    Lukassen, Laura; Oberlack, Martin

    2014-11-01

    As described in literature, non-Brownian particles in shear flow show a diffusive behavior due to hydrodynamic interactions. This shear-induced diffusion differs from the well-known Brownian diffusion, as there is no separation of time scales. That means that the configuration of non-Brownian particles changes on the same time scale as the hydrodynamic velocity. This fact impedes the derivation of a Fokker-Planck equation describing non-Brownian particles in pure position space. In this context, we derived a new Fokker-Planck approach in coupled position-velocity space to assure the validity of the Markov process assumption which is violated in pure position space formulation (Lukassen, Oberlack, Phys. Rev. E 89, 2014). Here, we present a further validation of our new Fokker-Planck approach that allows us to establish a relation to a modified purely position space Fokker-Planck equation. This backward transformation exhibits additional correction terms when compared to other position space Fokker-Planck equations in that context known from literature. Our extended approach shall enable a better stochastic description of non-Brownian particle flows. The work of L. Lukassen is supported by the ``Excellence Initiative'' of the German Federal and State Governments and the Graduate School of Computational Engineering at TU Darmstadt.

  4. Segregation and phase inversion of strongly and weakly fluctuating Brownian particle mixtures and a chain of such particle mixtures in spherical containers

    NASA Astrophysics Data System (ADS)

    Awazu, Akinori

    2014-10-01

    We investigate the segregation pattern formation of strongly and weakly fluctuating Brownian particle mixtures confined in a three-dimensional spherical container. We consider systems where the particle motion is restricted by the harmonic external trapping potential and the container edge wall. In such systems, two segregation patterns are observed. When the container radius is sufficiently large, more weakly fluctuating particles accumulate near the center of the container than strongly fluctuating particles. On the other hand, the distributions of the strongly and weakly fluctuating particles are inverted when the container radius is small. With no external trapping potentials, we find similar segregation and phase inversion if the particles construct a chain (heterofluctuating polymer) and are confined in a three-dimensional spherical container. We could apply these phenomena in the study of biopolymer behavior, such as chromosomes in the cell nucleus.

  5. Virial theorem and dynamical evolution of self-gravitating Brownian particles in an unbounded domain. I. Overdamped models

    NASA Astrophysics Data System (ADS)

    Chavanis, Pierre-Henri; Sire, Clément

    2006-06-01

    We derive the virial theorem appropriate to the generalized Smoluchowski-Poisson (GSP) system describing self-gravitating Brownian particles in an overdamped limit. We extend previous works by considering the case of an unbounded domain and an arbitrary equation of state. We use the virial theorem to study the diffusion (evaporation) of an isothermal Brownian gas above the critical temperature Tc in dimension d=2 and show how the effective diffusion coefficient and the Einstein relation are modified by self-gravity. We also study the collapse at T=Tc and show that the central density increases logarithmically with time instead of exponentially in a bounded domain. Finally, for d>2 , we show that the evaporation of the system is essentially a pure diffusion slightly slowed down by self-gravity. We also study the linear dynamical stability of stationary solutions of the GSP system representing isolated clusters of particles and investigate the influence of the equation of state and of the dimension of space on the dynamical stability of the system.

  6. Aging underdamped scaled Brownian motion: Ensemble- and time-averaged particle displacements, nonergodicity, and the failure of the overdamping approximation.

    PubMed

    Safdari, Hadiseh; Cherstvy, Andrey G; Chechkin, Aleksei V; Bodrova, Anna; Metzler, Ralf

    2017-01-01

    We investigate both analytically and by computer simulations the ensemble- and time-averaged, nonergodic, and aging properties of massive particles diffusing in a medium with a time dependent diffusivity. We call this stochastic diffusion process the (aging) underdamped scaled Brownian motion (UDSBM). We demonstrate how the mean squared displacement (MSD) and the time-averaged MSD of UDSBM are affected by the inertial term in the Langevin equation, both at short, intermediate, and even long diffusion times. In particular, we quantify the ballistic regime for the MSD and the time-averaged MSD as well as the spread of individual time-averaged MSD trajectories. One of the main effects we observe is that, both for the MSD and the time-averaged MSD, for superdiffusive UDSBM the ballistic regime is much shorter than for ordinary Brownian motion. In contrast, for subdiffusive UDSBM, the ballistic region extends to much longer diffusion times. Therefore, particular care needs to be taken under what conditions the overdamped limit indeed provides a correct description, even in the long time limit. We also analyze to what extent ergodicity in the Boltzmann-Khinchin sense in this nonstationary system is broken, both for subdiffusive and superdiffusive UDSBM. Finally, the limiting case of ultraslow UDSBM is considered, with a mixed logarithmic and power-law dependence of the ensemble- and time-averaged MSDs of the particles. In the limit of strong aging, remarkably, the ordinary UDSBM and the ultraslow UDSBM behave similarly in the short time ballistic limit. The approaches developed here open ways for considering other stochastic processes under physically important conditions when a finite particle mass and aging in the system cannot be neglected.

  7. Aging underdamped scaled Brownian motion: Ensemble- and time-averaged particle displacements, nonergodicity, and the failure of the overdamping approximation

    NASA Astrophysics Data System (ADS)

    Safdari, Hadiseh; Cherstvy, Andrey G.; Chechkin, Aleksei V.; Bodrova, Anna; Metzler, Ralf

    2017-01-01

    We investigate both analytically and by computer simulations the ensemble- and time-averaged, nonergodic, and aging properties of massive particles diffusing in a medium with a time dependent diffusivity. We call this stochastic diffusion process the (aging) underdamped scaled Brownian motion (UDSBM). We demonstrate how the mean squared displacement (MSD) and the time-averaged MSD of UDSBM are affected by the inertial term in the Langevin equation, both at short, intermediate, and even long diffusion times. In particular, we quantify the ballistic regime for the MSD and the time-averaged MSD as well as the spread of individual time-averaged MSD trajectories. One of the main effects we observe is that, both for the MSD and the time-averaged MSD, for superdiffusive UDSBM the ballistic regime is much shorter than for ordinary Brownian motion. In contrast, for subdiffusive UDSBM, the ballistic region extends to much longer diffusion times. Therefore, particular care needs to be taken under what conditions the overdamped limit indeed provides a correct description, even in the long time limit. We also analyze to what extent ergodicity in the Boltzmann-Khinchin sense in this nonstationary system is broken, both for subdiffusive and superdiffusive UDSBM. Finally, the limiting case of ultraslow UDSBM is considered, with a mixed logarithmic and power-law dependence of the ensemble- and time-averaged MSDs of the particles. In the limit of strong aging, remarkably, the ordinary UDSBM and the ultraslow UDSBM behave similarly in the short time ballistic limit. The approaches developed here open ways for considering other stochastic processes under physically important conditions when a finite particle mass and aging in the system cannot be neglected.

  8. A particle-in-mesh method for Brownian Dynamics simulation of many-particle systems with hydrodynamics interactions in a confined geometry

    NASA Astrophysics Data System (ADS)

    Zhao, Xujun; Hernandez-Ortiz, Juan; Karpeyev, Dmitry; de Pablo, Juan; Smith, Barry

    In this work, we present an efficient parallel particle-in-mesh method for Brownian Dynamics simulations of many-particle systems confined in micro- and nano-fluidic devices. A general geometry Ewald-like method (GGEM) combined with finite element method is used to account for the hydrodynamic interaction. A fast parallel Krylov-type iterative solver with hybrid preconditioning techniques is developed for solving the large sparse systems of equations arising from finite element discretization of the Stokes equations. In addition, the current computer code is developed based on PETSc, a scalable library of numerical algorithms developed at Argonne, SLEPc - Scalable Library for Eigenvalue Problem Computations, and libMesh, a finite element library for numerical solution of PDEs built on top of PETSc, which allows for direct simulation of large scale systems with arbitrary confined geometries. This scheme is applied to Brownian dynamics simulations of flowing confined polymer solutions and colloidal dispersions in micro-fluid channels. The effects of hydrodynamics interactions and geometric confinement on the migration phenomena are illustrated.

  9. Escape rate of active particles in the effective equilibrium approach

    NASA Astrophysics Data System (ADS)

    Sharma, A.; Wittmann, R.; Brader, J. M.

    2017-01-01

    The escape rate of a Brownian particle over a potential barrier is accurately described by the Kramers theory. A quantitative theory explicitly taking the activity of Brownian particles into account has been lacking due to the inherently out-of-equilibrium nature of these particles. Using an effective equilibrium approach [Farage et al., Phys. Rev. E 91, 042310 (2015), 10.1103/PhysRevE.91.042310] we study the escape rate of active particles over a potential barrier and compare our analytical results with data from direct numerical simulation of the colored noise Langevin equation. The effective equilibrium approach generates an effective potential that, when used as input to Kramers rate theory, provides results in excellent agreement with the simulation data.

  10. Brownian dynamics simulation of substrate motion near active site of enzyme entrapped inside reverse micelle.

    PubMed

    Ermakova, Elena A; Zakhartchenko, Nataliya L; Zuev, Yuri F

    2010-08-01

    Brownian dynamics simulation has been applied to analyze the influence of the electrostatic field of a reverse micelle on the enzyme-substrate complex formation inside a micelle. The probability that the enzyme-substrate complex will form from serine protease (trypsin) and the specific hydrophilic cationic substrate Nalpha-benzoyl-L: -arginine ethyl ester has been studied within the framework of the encounter complex formation theory. It has been shown that surfactant charge, dipole moments created by charged surfactant molecules and counterions, and permittivity of the inner core of reverse micelles can all be used as regulatory parameters to alter the substrate orientation near the active site of the enzyme and to change the probability that the enzyme-substrate complex will form.

  11. Colored-noise Fokker-Planck equation for the shear-induced self-diffusion process of non-Brownian particles.

    PubMed

    Lukassen, Laura J; Oberlack, Martin

    2014-05-01

    In the literature, it is pointed out that non-Brownian particles tend to show shear-induced diffusive behavior due to hydrodynamic interactions. Several authors indicate a long correlation time of the particle velocities in comparison to Brownian particle velocities modeled by a white noise. This work deals with the derivation of a Fokker-Planck equation both in position and velocity space which describes the process of shear-induced self-diffusion, whereas, so far, this problem has been described by Fokker-Planck equations restricted to position space. The long velocity correlation times actually would necessitate large time-step sizes in the mathematical description of the problem in order to capture the diffusive regime. In fact, time steps of specific lengths pose problems to the derivation of the corresponding Fokker-Planck equation because the whole particle configuration changes during long time-step sizes. On the other hand, small time-step sizes, i.e., in the range of the velocity correlation time, violate the Markov property of the position variable. In this work we regard the problem of shear-induced self-diffusion with respect to the Markov property and reformulate the problem with respect to small time-step sizes. In this derivation, we regard the nondimensionalized Langevin equation and develop a new compact form which allows us to analyze the Langevin equation for all time scales of interest for both Brownian and non-Brownian particles starting from a single equation. This shows that the Fokker-Planck equation in position space should be extended to a colored-noise Fokker-Planck equation in both position and colored-noise velocity space, which we will derive.

  12. Colored-noise Fokker-Planck equation for the shear-induced self-diffusion process of non-Brownian particles

    NASA Astrophysics Data System (ADS)

    Lukassen, Laura J.; Oberlack, Martin

    2014-05-01

    In the literature, it is pointed out that non-Brownian particles tend to show shear-induced diffusive behavior due to hydrodynamic interactions. Several authors indicate a long correlation time of the particle velocities in comparison to Brownian particle velocities modeled by a white noise. This work deals with the derivation of a Fokker-Planck equation both in position and velocity space which describes the process of shear-induced self-diffusion, whereas, so far, this problem has been described by Fokker-Planck equations restricted to position space. The long velocity correlation times actually would necessitate large time-step sizes in the mathematical description of the problem in order to capture the diffusive regime. In fact, time steps of specific lengths pose problems to the derivation of the corresponding Fokker-Planck equation because the whole particle configuration changes during long time-step sizes. On the other hand, small time-step sizes, i.e., in the range of the velocity correlation time, violate the Markov property of the position variable. In this work we regard the problem of shear-induced self-diffusion with respect to the Markov property and reformulate the problem with respect to small time-step sizes. In this derivation, we regard the nondimensionalized Langevin equation and develop a new compact form which allows us to analyze the Langevin equation for all time scales of interest for both Brownian and non-Brownian particles starting from a single equation. This shows that the Fokker-Planck equation in position space should be extended to a colored-noise Fokker-Planck equation in both position and colored-noise velocity space, which we will derive.

  13. Exact analytical solution of the collapse of self-gravitating Brownian particles and bacterial populations at zero temperature

    NASA Astrophysics Data System (ADS)

    Chavanis, Pierre-Henri; Sire, Clément

    2011-03-01

    We provide an exact analytical solution of the collapse dynamics of self-gravitating Brownian particles and bacterial populations at zero temperature. These systems are described by the Smoluchowski-Poisson system or Keller-Segel model in which the diffusion term is neglected. As a result, the dynamics is purely deterministic. A cold system undergoes a gravitational collapse, leading to a finite-time singularity: The central density increases and becomes infinite in a finite time tcoll. The evolution continues in the postcollapse regime. A Dirac peak emerges, grows, and finally captures all the mass in a finite time tend, while the central density excluding the Dirac peak progressively decreases. Close to the collapse time, the pre- and postcollapse evolutions are self-similar. Interestingly, if one starts from a parabolic density profile, one obtains an exact analytical solution that describes the whole collapse dynamics, from the initial time to the end, and accounts for non-self-similar corrections that were neglected in previous works. Our results have possible application in different areas including astrophysics, chemotaxis, colloids, and nanoscience.

  14. Constructive role of Brownian motion: Brownian motors and Stochastic Resonance

    NASA Astrophysics Data System (ADS)

    Hänggi, Peter

    2005-03-01

    Noise is usually thought of as the enemy of order rather as a constructive influence. For the phenomena of Stochastic Resonance [1] and Brownian motors [2], however, stochastic noise can play a beneficial role in enhancing detection and/or facilitating directed transmission of information in absence of biasing forces. Brownian motion assisted Stochastic Resonance finds useful applications in physical, technological, biological and biomedical contexts [1,3]. The basic principles that underpin Stochastic Resonance are elucidated and novel applications for nonlinear classical and quantum systems will be addressed. The presence of non-equilibrium disturbances enables to rectify Brownian motion so that quantum and classical objects can be directed around on a priori designed routes in biological and physical systems (Brownian motors). In doing so, the energy from the haphazard motion of (quantum) Brownian particles is extracted to perform useful work against an external load. This very concept together with first experimental realizations are discussed [2,4,5]. [1] L. Gammaitoni, P. Hä'nggi, P. Jung and F. Marchesoni, Stochastic Resonance, Rev. Mod. Phys. 70, 223 (1998).[2] R. D. Astumian and P. Hä'nggi, Brownian motors, Physics Today 55 (11), 33 (2002).[3] P. Hä'nggi, Stochastic Resonace in Physics and Biology, ChemPhysChem 3, 285 (2002).[4] H. Linke, editor, Special Issue on Brownian Motors, Applied Physics A 75, No. 2 (2002).[5] P. Hä'nggi, F. Marchesoni, F. Nori, Brownian motors, Ann. Physik (Leipzig) 14, xxx (2004); cond-mat/0410033.

  15. From Mechanical Motion to Brownian Motion, Thermodynamics and Particle Transport Theory

    ERIC Educational Resources Information Center

    Bringuier, E.

    2008-01-01

    The motion of a particle in a medium is dealt with either as a problem of mechanics or as a transport process in non-equilibrium statistical physics. The two kinds of approach are often unrelated as they are taught in different textbooks. The aim of this paper is to highlight the link between the mechanical and statistical treatments of particle…

  16. Meandering Brownian Donkeys

    NASA Astrophysics Data System (ADS)

    Eichhorn, R.; Reimann, P.

    2004-04-01

    We consider a Brownian particle whose motion is confined to a ``meandering'' pathway and which is driven away from thermal equilibrium by an alternating external force. This system exhibits absolute negative mobility, i.e. when an external static force is applied the particle moves in the direction opposite to that force. We reveal the physical mechanism behind this ``donkey-like'' behavior, and derive analytical approximations that are in excellent agreement with numerical results.

  17. Brownian motion studies of viscoelastic colloidal gels by rotational single particle tracking

    DOE PAGES

    Liang, Mengning; Harder, Ross; Robinson, Ian K.

    2014-04-14

    Colloidal gels have unique properties due to a complex microstructure which forms into an extended network. Although the bulk properties of colloidal gels have been studied, there has been difficulty correlating those properties with individual colloidal dynamics on the microscale due to the very high viscosity and elasticity of the material. We utilize rotational X-ray tracking (RXT) to investigate the rotational motion of component crystalline colloidal particles in a colloidal gel of alumina and decanoic acid. Our investigation has determined that the high elasticity of the bulk is echoed by a high elasticity experienced by individual colloidal particles themselves butmore » also finds an unexpected high degree of rotational diffusion, indicating a large degree of freedom in the rotational motion of individual colloids even within a tightly bound system.« less

  18. Brownian motion studies of viscoelastic colloidal gels by rotational single particle tracking

    PubMed Central

    Liang, Mengning; Harder, Ross; Robinson, Ian K.

    2014-01-01

    Colloidal gels have unique properties due to a complex microstructure which forms into an extended network. Although the bulk properties of colloidal gels have been studied, there has been difficulty correlating those properties with individual colloidal dynamics on the microscale due to the very high viscosity and elasticity of the material. We utilize rotational X-ray tracking (RXT) to investigate the rotational motion of component crystalline colloidal particles in a colloidal gel of alumina and decanoic acid. Our investigation has determined that the high elasticity of the bulk is echoed by a high elasticity experienced by individual colloidal particles themselves but also finds an unexpected high degree of rotational diffusion, indicating a large degree of freedom in the rotational motion of individual colloids even within a tightly bound system. PMID:25075336

  19. A correlation for the collector efficiency of Brownian particles in clean-bed filtration in sphere packings by a Lattice-Boltzmann method.

    PubMed

    Long, Wei; Hilpert, Markus

    2009-06-15

    In this paper, we develop a new correlation for the clean-bed filter coefficient (lambda0) for Brownian particles, for which diffusion is the main deposition mechanism. The correlation is based on numerical Lattice-Boltzmann (LB) simulations in random packings of spheres of uniform diameter. We use LB methods to solve the Navier-Stokes equation for flow and then the advection-diffusion equation for particle transport. We determine a correlation for an "equivalent" single-collector diffusion efficiency, etaD, so that we can compare our predictions to "true" single-collector correlations stemming from unit-cell modeling approaches. We compared our new correlation to experiments on the filtration of latex particles. For small particle diameters, 50 nm < dp < 300 nm, when gravity and interception are negligible, our correlation for etaD predicts measurements better than unit-cell correlations, which overestimate etaD. The good agreement suggests that the representation of three-dimensional transport pathways in porous media plays an important role when modeling transport and deposition of Brownian particles. To model larger particles, for which gravity and interception are important too, we build a correlation for the overall single-collector efficiency eta0 by adding corresponding etaG and nI terms from unit-cell correlations to our etaD model. The resulting correlation predicts experiments with latex particles of dp > 300 nm well.

  20. Effects of non-Gaussian Brownian motion on direct force optical tweezers measurements of the electrostatic forces between pairs of colloidal particles.

    PubMed

    Raudsepp, Allan; A K Williams, Martin; B Hall, Simon

    2016-07-01

    Measurements of the electrostatic force with separation between a fixed and an optically trapped colloidal particle are examined with experiment, simulation and analytical calculation. Non-Gaussian Brownian motion is observed in the position of the optically trapped particle when particles are close and traps weak. As a consequence of this motion, a simple least squares parameterization of direct force measurements, in which force is inferred from the displacement of an optically trapped particle as separation is gradually decreased, contains forces generated by the rectification of thermal fluctuations in addition to those originating directly from the electrostatic interaction between the particles. Thus, when particles are close and traps weak, simply fitting the measured direct force measurement to DLVO theory extracts parameters with modified meanings when compared to the original formulation. In such cases, however, physically meaningful DLVO parameters can be recovered by comparing the measured non-Gaussian statistics to those predicted by solutions to Smoluchowski's equation for diffusion in a potential.

  1. Thon rings from amorphous ice and implications of beam-induced Brownian motion in single particle electron cryo-microscopy.

    PubMed

    McMullan, G; Vinothkumar, K R; Henderson, R

    2015-11-01

    We have recorded dose-fractionated electron cryo-microscope images of thin films of pure flash-frozen amorphous ice and pre-irradiated amorphous carbon on a Falcon II direct electron detector using 300 keV electrons. We observe Thon rings [1] in both the power spectrum of the summed frames and the sum of power spectra from the individual frames. The Thon rings from amorphous carbon images are always more visible in the power spectrum of the summed frames whereas those of amorphous ice are more visible in the sum of power spectra from the individual frames. This difference indicates that while pre-irradiated carbon behaves like a solid during the exposure, amorphous ice behaves like a fluid with the individual water molecules undergoing beam-induced motion. Using the measured variation in the power spectra amplitude with number of electrons per image we deduce that water molecules are randomly displaced by a mean squared distance of ∼1.1 Å(2) for every incident 300 keV e(-)/Å(2). The induced motion leads to an optimal exposure with 300 keV electrons of 4.0 e(-)/Å(2) per image with which to observe Thon rings centred around the strong 3.7 Å scattering peak from amorphous ice. The beam-induced movement of the water molecules generates pseudo-Brownian motion of embedded macromolecules. The resulting blurring of single particle images contributes an additional term, on top of that from radiation damage, to the minimum achievable B-factor for macromolecular structure determination.

  2. Confined Brownian ratchets

    NASA Astrophysics Data System (ADS)

    Malgaretti, Paolo; Pagonabarraga, Ignacio; Rubi, J. Miguel

    2013-05-01

    We analyze the dynamics of Brownian ratchets in a confined environment. The motion of the particles is described by a Fick-Jakobs kinetic equation in which the presence of boundaries is modeled by means of an entropic potential. The cases of a flashing ratchet, a two-state model, and a ratchet under the influence of a temperature gradient are analyzed in detail. We show the emergence of a strong cooperativity between the inherent rectification of the ratchet mechanism and the entropic bias of the fluctuations caused by spatial confinement. Net particle transport may take place in situations where none of those mechanisms leads to rectification when acting individually. The combined rectification mechanisms may lead to bidirectional transport and to new routes to segregation phenomena. Confined Brownian ratchets could be used to control transport in mesostructures and to engineer new and more efficient devices for transport at the nanoscale.

  3. 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.

  4. Interplay between optical, viscous, and elastic forces on an optically trapped Brownian particle immersed in a viscoelastic fluid

    NASA Astrophysics Data System (ADS)

    Domínguez-García, P.; Forró, László; Jeney, Sylvia

    2016-10-01

    We provide a detailed study of the interplay between the different interactions which appear in the Brownian motion of a micronsized sphere immersed in a viscoelastic fluid measured with optical trapping interferometry. To explore a wide range of viscous, elastic, and optical forces, we analyze two different viscoelastic solutions at various concentrations, which provide a dynamic polymeric structure surrounding the Brownian sphere. Our experiments show that, depending on the fluid, optical forces, even if small, slightly modify the complex modulus at low frequencies. Based on our findings, we propose an alternative methodology to calibrate this kind of experimental set-up when non-Newtonian fluids are used. Understanding the influence of the optical potential is essential for a correct interpretation of the mechanical properties obtained by optically-trapped probe-based studies of biomaterials and living matter.

  5. Microscopic derivation of open quantum Brownian motion

    NASA Astrophysics Data System (ADS)

    Petruccione, Francesco; Sinayskiy, Ilya; UKZN Team

    2015-03-01

    Recently a model of open quantum Brownian motion (OQBM) [M. Bauer, D. Bernard, A. Tilloy, Phys. Rev. A 88 (2013) 062340] was introduced as a scaling limit of Open Quantum Walks (OQWs) [S. Attal, F. Petruccione, C. Sabot, I. Sinayskiy, J. Stat. Phys. 147 (20120 832]. OQBM is a new type of quantum Brownian motion where the dynamics of the Brownian particle not only depends on the interactions with a thermal environment, but also depends on the state of the internal degrees of freedom of the Brownian particle. Here, we present the microscopic derivation of the OQBM for a Brownian particle with two internal degrees of freedom. Examples of the dynamics for initial Gaussian and non-Gaussian distributions are presented. This work is based upon research supported by the South African Research Chair Initiative of the Department of Science and Technology and National Research Foundation.

  6. Phase Transitions in Brownian Pumps

    NASA Astrophysics Data System (ADS)

    Dierl, Marcel; Dieterich, Wolfgang; Einax, Mario; Maass, Philipp

    2014-04-01

    We study stochastic particle transport between two reservoirs along a channel, where the particles are pumped against a bias by a traveling wave potential. It is shown that phase transitions of period-averaged densities or currents occur inside the channel when exclusion interactions between the particles are taken into account. These transitions reflect those known for the asymmetric simple exclusion process. We argue that their occurrence is a generic feature of Brownian motors operating in open systems.

  7. First-passage-time statistics of a Brownian particle driven by an arbitrary unidimensional potential with a superimposed exponential time-dependent drift

    NASA Astrophysics Data System (ADS)

    Urdapilleta, Eugenio

    2015-12-01

    In one-dimensional systems, the dynamics of a Brownian particle are governed by the force derived from a potential as well as by diffusion properties. In this work, we obtain the first-passage-time statistics of a Brownian particle driven by an arbitrary potential with an exponential temporally decaying superimposed field up to a prescribed threshold. The general system analyzed here describes the sub-threshold signal integration of integrate-and-fire neuron models, of any kind, supplemented by an adaptation-like current, whereas the first-passage-time corresponds to the declaration of a spike. Following our previous studies, we base our analysis on the backward Fokker-Planck equation and study the survival probability and the first-passage-time density function in the space of the initial condition. By proposing a series solution we obtain a system of recurrence equations, which given the specific structure of the exponential time-dependent drift, easily admit a simpler Laplace representation. Naturally, the present general derivation agrees with the explicit solution we found previously for the Wiener process in (2012 J. Phys. A: Math. Theor. 45 185001). However, to demonstrate the generality of the approach, we further explicitly evaluate the first-passage-time statistics of the underlying Ornstein-Uhlenbeck process. To test the validity of the series solution, we extensively compare theoretical expressions with the data obtained from numerical simulations in different regimes. As shown, agreement is precise whenever the series is truncated at an appropriate order. Beyond the fact that both the Wiener and Ornstein-Uhlenbeck processes have a direct interpretation in the context of neuronal models, given their ubiquity in different fields, our present results will be of interest in other settings where an additive state-independent temporal relaxation process is being developed as the particle diffuses.

  8. Relativistic Brownian motion

    NASA Astrophysics Data System (ADS)

    Dunkel, Jörn; Hänggi, Peter

    2009-02-01

    Over the past one hundred years, Brownian motion theory has contributed substantially to our understanding of various microscopic phenomena. Originally proposed as a phenomenological paradigm for atomistic matter interactions, the theory has since evolved into a broad and vivid research area, with an ever increasing number of applications in biology, chemistry, finance, and physics. The mathematical description of stochastic processes has led to new approaches in other fields, culminating in the path integral formulation of modern quantum theory. Stimulated by experimental progress in high energy physics and astrophysics, the unification of relativistic and stochastic concepts has re-attracted considerable interest during the past decade. Focusing on the framework of special relativity, we review, here, recent progress in the phenomenological description of relativistic diffusion processes. After a brief historical overview, we will summarize basic concepts from the Langevin theory of nonrelativistic Brownian motions and discuss relevant aspects of relativistic equilibrium thermostatistics. The introductory parts are followed by a detailed discussion of relativistic Langevin equations in phase space. We address the choice of time parameters, discretization rules, relativistic fluctuation-dissipation theorems, and Lorentz transformations of stochastic differential equations. The general theory is illustrated through analytical and numerical results for the diffusion of free relativistic Brownian particles. Subsequently, we discuss how Langevin-type equations can be obtained as approximations to microscopic models. The final part of the article is dedicated to relativistic diffusion processes in Minkowski spacetime. Since the velocities of relativistic particles are bounded by the speed of light, nontrivial relativistic Markov processes in spacetime do not exist; i.e., relativistic generalizations of the nonrelativistic diffusion equation and its Gaussian solutions

  9. Synaptic fusion pore structure and AMPA receptor activation according to Brownian simulation of glutamate diffusion.

    PubMed

    Ventriglia, Francesco; Maio, Vito Di

    2003-03-01

    The rising phase of fast, AMPA-mediated Excitatory Post Synaptic Currents (EPSCs) has a primary role in the computational ability of neurons. The structure and radial expansion velocity of the fusion pore between the vesicle and the presynaptic membrane could be important factors in determining the time course of the EPSC. We have used a Brownian simulation model for glutamate neurotransmitter diffusion to test two hypotheses on the fusion pore structure, namely, the proteinaceous pore and the purely lipidic pore. Three more hypotheses on the radial expansion velocity were also tested. The rising phases of the EPSC, computed under various conditions, were compared with experimental data from the literature. Our present results show that a proteinaceous fusion pore should produce a more marked foot at the beginning of the rising phase of the EPSC. They also confirm the hypothesis that the structure of the fusion pore and its radial expansion velocity play significant roles in shaping the fast EPSC time course.

  10. Thermophoretically modified aerosol brownian coagulation.

    PubMed

    Arias-Zugasti, Manuel; Rosner, Daniel E

    2011-08-01

    A theory of aerosol coagulation rates resulting from continuum-regime brownian coagulation in the presence of size-dependent particle thermophoresis is developed and explored here. We are motivated by a wide variety of applications in which particle brownian coagulation occurs in a nonisothermal gas where differential thermophoretic drift contributes to, but does not dominate, the encounter frequency between suspended spherical particles (e.g., mist droplets) of different sizes. We employ a Smoluchowski-like population-balance to demonstrate the relative roles of brownian diffusion and thermophoresis in shaping the short and long time (asymptotic or "coagulation-aged") mist-droplet size distribution (DSD) function. To carry out these combined-mechanism DSD-evolution calculations we developed a rational "coupled" coagulation rate constant (allowing for simultaneous brownian diffusion and relative thermophoretic drift) rather than simply adding the relevant individual coagulation "kernels." Dimensionless criteria are provided to facilitate precluding other coagulation mechanisms not considered here (such as simultaneous sedimentation or Marangoni-flow-induced mist-droplet phoresis) and potential complications not included in the present model [as finite-rate coalescence, initial departures from the continuum (Stokes drag-) limit, and even dense (nonideal) vapor effects].

  11. Thermophoretically modified aerosol Brownian coagulation

    NASA Astrophysics Data System (ADS)

    Arias-Zugasti, Manuel; Rosner, Daniel E.

    2011-08-01

    A theory of aerosol coagulation rates resulting from continuum-regime Brownian coagulation in the presence of size-dependent particle thermophoresis is developed and explored here. We are motivated by a wide variety of applications in which particle Brownian coagulation occurs in a nonisothermal gas where differential thermophoretic drift contributes to, but does not dominate, the encounter frequency between suspended spherical particles (e.g., mist droplets) of different sizes. We employ a Smoluchowski-like population-balance to demonstrate the relative roles of Brownian diffusion and thermophoresis in shaping the short and long time (asymptotic or “coagulation-aged”) mist-droplet size distribution (DSD) function. To carry out these combined-mechanism DSD-evolution calculations we developed a rational “coupled” coagulation rate constant (allowing for simultaneous Brownian diffusion and relative thermophoretic drift) rather than simply adding the relevant individual coagulation “kernels.” Dimensionless criteria are provided to facilitate precluding other coagulation mechanisms not considered here (such as simultaneous sedimentation or Marangoni-flow-induced mist-droplet phoresis) and potential complications not included in the present model [as finite-rate coalescence, initial departures from the continuum (Stokes drag-) limit, and even dense (nonideal) vapor effects].

  12. Exact Green's functions for a Brownian particle reversibly binding to a fixed target in a finite, two-dimensional, circular domain

    NASA Astrophysics Data System (ADS)

    Kalay, Ziya

    2012-06-01

    Despite the apparent need to study reversible reactions between molecules confined to a two-dimensional space such as the cell membrane, exact Green’s functions for this case have not been reported. Here we present exact analytical Green’s functions for a Brownian particle reversibly reacting with a fixed reaction center in a finite two-dimensional circular region with reflecting or absorbing boundaries, considering either a spherically symmetric initial distribution or a particle that is initially bound. We show that Green’s function can be used to predict the effect of measurement uncertainties on the outcome of single-particle/molecule-tracking experiments in which molecular interactions are investigated. Hence, we bridge the gap between previously known solutions in one dimension (Agmon 1984 J. Chem. Phys. 81 2811) and three dimensions (Kim and Shin 1999 Phys. Rev. Lett. 82 1578), and provide an example of how the knowledge of Green’s function can be used to predict experimentally accessible quantities.

  13. Perturbative theory for Brownian vortexes

    NASA Astrophysics Data System (ADS)

    Moyses, Henrique W.; Bauer, Ross O.; Grosberg, Alexander Y.; Grier, David G.

    2015-06-01

    Brownian vortexes are stochastic machines that use static nonconservative force fields to bias random thermal fluctuations into steadily circulating currents. The archetype for this class of systems is a colloidal sphere in an optical tweezer. Trapped near the focus of a strongly converging beam of light, the particle is displaced by random thermal kicks into the nonconservative part of the optical force field arising from radiation pressure, which then biases its diffusion. Assuming the particle remains localized within the trap, its time-averaged trajectory traces out a toroidal vortex. Unlike trivial Brownian vortexes, such as the biased Brownian pendulum, which circulate preferentially in the direction of the bias, the general Brownian vortex can change direction and even topology in response to temperature changes. Here we introduce a theory based on a perturbative expansion of the Fokker-Planck equation for weak nonconservative driving. The first-order solution takes the form of a modified Boltzmann relation and accounts for the rich phenomenology observed in experiments on micrometer-scale colloidal spheres in optical tweezers.

  14. Perturbative theory for Brownian vortexes.

    PubMed

    Moyses, Henrique W; Bauer, Ross O; Grosberg, Alexander Y; Grier, David G

    2015-06-01

    Brownian vortexes are stochastic machines that use static nonconservative force fields to bias random thermal fluctuations into steadily circulating currents. The archetype for this class of systems is a colloidal sphere in an optical tweezer. Trapped near the focus of a strongly converging beam of light, the particle is displaced by random thermal kicks into the nonconservative part of the optical force field arising from radiation pressure, which then biases its diffusion. Assuming the particle remains localized within the trap, its time-averaged trajectory traces out a toroidal vortex. Unlike trivial Brownian vortexes, such as the biased Brownian pendulum, which circulate preferentially in the direction of the bias, the general Brownian vortex can change direction and even topology in response to temperature changes. Here we introduce a theory based on a perturbative expansion of the Fokker-Planck equation for weak nonconservative driving. The first-order solution takes the form of a modified Boltzmann relation and accounts for the rich phenomenology observed in experiments on micrometer-scale colloidal spheres in optical tweezers.

  15. Brownian Ratchets

    NASA Astrophysics Data System (ADS)

    Cubero, David; Renzoni, Ferruccio

    2016-01-01

    Part I. Historical Overview and Early Developments: 1. Limitations imposed by the second law of thermodynamics; 2. Fundamental models of ratchet devices; 3. General relevance of the concept of ratchet; Part II. Theoretical Foundations: 4. Classical ratchets; 5. Quantum ratchets; 6. Energetics and characterization; Part III. Experimental Realizations of Ratchet Devices: 7. Ratchets for colloidal particles; 8. Cold atom ratchets; 9. Solid state ratchets; 10. Bio-inspired molecular motors; Appendix A. Stochastic processes techniques; Appendix B. Symmetries in a 1D overdamped system; Appendix C. Floquet theory; References; Index.

  16. Apparent viscosity and particle pressure of a concentrated suspension of non-Brownian hard spheres near the jamming transition.

    PubMed

    Mills, P; Snabre, P

    2009-11-01

    We consider the steady shear flow of a homogeneous and dense assembly of hard spheres suspended in a Newtonian viscous fluid. In a first part, a mean-field approach based on geometric arguments is used to determine the viscous dissipation in a dense isotropic suspension of smooth hard spheres and the hydrodynamic contribution to the suspension viscosity. In a second part, we consider the coexistence of transient solid clusters coupled to regions with free flowing particles near the jamming transition. The fraction of particles in transient clusters is derived through the Landau-Ginzburg concepts for first-order phase transition with an order parameter corresponding to the proportion of "solid" contacts. A state equation for the fraction of particle-accessible volume is introduced to derive the average normal stresses and a constitutive law that relates the total shear stress to the shear rate. The analytical expression of the average normal stresses well accounts for numerical or experimental evaluation of the particle pressure and non-equilibrium osmotic pressure in a dense sheared suspension. Both the friction level between particles and the suspension dilatancy are shown to determine the singularity of the apparent shear viscosity and the flow stability near the jamming transition. The model further predicts a Newtonian behavior for a concentrated suspension of neutrally buoyant particles and no shear thinning behavior in relation with the shear liquefaction of transient solid clusters.

  17. Brownian dynamics without Green's functions

    SciTech Connect

    Delong, Steven; Donev, Aleksandar; Usabiaga, Florencio Balboa; Delgado-Buscalioni, Rafael; Griffith, Boyce E.

    2014-04-07

    We develop a Fluctuating Immersed Boundary (FIB) method for performing Brownian dynamics simulations of confined particle suspensions. Unlike traditional methods which employ analytical Green's functions for Stokes flow in the confined geometry, the FIB method uses a fluctuating finite-volume Stokes solver to generate the action of the response functions “on the fly.” Importantly, we demonstrate that both the deterministic terms necessary to capture the hydrodynamic interactions among the suspended particles, as well as the stochastic terms necessary to generate the hydrodynamically correlated Brownian motion, can be generated by solving the steady Stokes equations numerically only once per time step. This is accomplished by including a stochastic contribution to the stress tensor in the fluid equations consistent with fluctuating hydrodynamics. We develop novel temporal integrators that account for the multiplicative nature of the noise in the equations of Brownian dynamics and the strong dependence of the mobility on the configuration for confined systems. Notably, we propose a random finite difference approach to approximating the stochastic drift proportional to the divergence of the configuration-dependent mobility matrix. Through comparisons with analytical and existing computational results, we numerically demonstrate the ability of the FIB method to accurately capture both the static (equilibrium) and dynamic properties of interacting particles in flow.

  18. Broadband boundary effects on Brownian motion

    NASA Astrophysics Data System (ADS)

    Mo, Jianyong; Simha, Akarsh; Raizen, Mark G.

    2015-12-01

    Brownian motion of particles in confined fluids is important for many applications, yet the effects of the boundary over a wide range of time scales are still not well understood. We report high-bandwidth, comprehensive measurements of Brownian motion of an optically trapped micrometer-sized silica sphere in water near an approximately flat wall. At short distances we observe anisotropic Brownian motion with respect to the wall. We find that surface confinement not only occurs in the long time scale diffusive regime but also in the short time scale ballistic regime, and the velocity autocorrelation function of the Brownian particle decays faster than that of a particle in bulk fluid. Furthermore, at low frequencies the thermal force loses its color due to the reflected flow from the no-slip boundary. The power spectrum of the thermal force on the particle near a no-slip boundary becomes flat at low frequencies. This detailed understanding of boundary effects on Brownian motion opens a door to developing a 3D microscope using particles as remote sensors.

  19. Diffusion of passive particles in active suspensions

    NASA Astrophysics Data System (ADS)

    Mussler, Matthias; Rafai, Salima; John, Thomas; Peyla, Philippe; Wagner, Christian

    2013-11-01

    We study how an active suspension consisting of a definite volume fraction of the microswimmer Chlamydomonas Reinhardtii modifies the Brownian movement of small to medium size microspheres. We present measurements and simulations of trajectories of microspheres with a diameter of 20 μm in suspensions of Chlamydomonas Reinhardtii, a so called ``puller,'' and show that the mean squared displacement of such trajectories consist of parabolic and a linear part. The linear part is due to the hydrodynamic noise of the microswimmers while the parabolic part is a consequence of directed motion events that occur randomly, when a microsphere is transported by a microswimmer on a timescale that is in higher order of magnitude than the Brownian like hydrodynamic interaction. In addition, we theoretically describe this effect with a dimensional analysis that takes the force dipole model used to describe ``puller'' like Chlamydomonas Reinhardtii into account.

  20. Anomalous Brownian refrigerator

    NASA Astrophysics Data System (ADS)

    Rana, Shubhashis; Pal, P. S.; Saha, Arnab; Jayannavar, A. M.

    2016-02-01

    We present a detailed study of a Brownian particle driven by Carnot-type refrigerating protocol operating between two thermal baths. Both the underdamped as well as the overdamped limits are investigated. The particle is in a harmonic potential with time-periodic strength that drives the system cyclically between the baths. Each cycle consists of two isothermal steps at different temperatures and two adiabatic steps connecting them. Besides working as a stochastic refrigerator, it is shown analytically that in the quasistatic regime the system can also act as stochastic heater, depending on the bath temperatures. Interestingly, in non-quasistatic regime, our system can even work as a stochastic heat engine for certain range of cycle time and bath temperatures. We show that the operation of this engine is not reliable. The fluctuations of stochastic efficiency/coefficient of performance (COP) dominate their mean values. Their distributions show power law tails, however the exponents are not universal. Our study reveals that microscopic machines are not the microscopic equivalent of the macroscopic machines that we come across in our daily life. We find that there is no one to one correspondence between the performance of our system under engine protocol and its reverse.

  1. Hydrodynamically enforced entropic Brownian pump

    NASA Astrophysics Data System (ADS)

    Ai, Bao-quan; He, Ya-feng; Li, Feng-guo; Zhong, Wei-rong

    2013-04-01

    Transport of overdamped Brownian particles in a finite hydrodynamical channel is investigated in the presence of the ac driving force and the pressure-driven flow. The system is bounded by two particle reservoirs. With the help of the Fick-Jacobs method, we obtain the directed current of Brownian particles and the pumping capacity of the system. The directed transport is determined by the competitions among the asymmetry of the channel, the ac driving force, the pressure-driven flow, and the concentration difference. Their interplays can exhibit the peculiar properties. Remarkably, the particles can be pumped through the channel from the lower concentration reservoir to the higher concentration one, or from the lower pressure side to the higher pressure one. In addition, due to the existence of the pressure drop, ac driving force still plays the significant role on directed transport even in a completely symmetric channel. Our results could be implemented in constrained structures with narrow channels or pores where the particles are suspended in a solvent.

  2. The Fluctuation-Dissipation Theorem of Colloidal Particle's energy on 2D Periodic Substrates: A Monte Carlo Study of thermal noise-like fluctuation and diffusion like Brownian motion

    NASA Astrophysics Data System (ADS)

    Najafi, Amin

    2014-05-01

    Using the Monte Carlo simulations, we have calculated mean-square fluctuations in statistical mechanics, such as those for colloids energy configuration are set on square 2D periodic substrates interacting via a long range screened Coulomb potential on any specific and fixed substrate. Random fluctuations with small deviations from the state of thermodynamic equilibrium arise from the granular structure of them and appear as thermal diffusion with Gaussian distribution structure as well. The variations are showing linear form of the Fluctuation-Dissipation Theorem on the energy of particles constitutive a canonical ensemble with continuous diffusion process of colloidal particle systems. The noise-like variation of the energy per particle and the order parameter versus the Brownian displacement of sum of large number of random steps of particles at low temperatures phase are presenting a markovian process on colloidal particles configuration, too.

  3. Active particles on curved surfaces

    NASA Astrophysics Data System (ADS)

    Fily, Yaouen; Baskaran, Aparna; Hagan, Michael

    Active systems have proved to be very sensitive to the geometry of their environment. This is often achieved by spending significant time at the boundary, probing its shape by gliding along it. I will discuss coarse graining the microscopic dynamics of self-propelled particles on a general curved surface to predict the way the density profile on the surface depends on its geometry. Beyond confined active particles, this formalism is a natural starting point to study objects that cannot leave the boundary at all, such as cells crawling on a curved substrate, animals running on uneven ground, or active colloids trapped at an interface.

  4. Brownian Carnot engine

    PubMed Central

    Dinis, L.; Petrov, D.; Parrondo, J. M. R.; Rica, R. A.

    2016-01-01

    The Carnot cycle imposes a fundamental upper limit to the efficiency of a macroscopic motor operating between two thermal baths1. However, this bound needs to be reinterpreted at microscopic scales, where molecular bio-motors2 and some artificial micro-engines3–5 operate. As described by stochastic thermodynamics6,7, energy transfers in microscopic systems are random and thermal fluctuations induce transient decreases of entropy, allowing for possible violations of the Carnot limit8. Here we report an experimental realization of a Carnot engine with a single optically trapped Brownian particle as the working substance. We present an exhaustive study of the energetics of the engine and analyse the fluctuations of the finite-time efficiency, showing that the Carnot bound can be surpassed for a small number of non-equilibrium cycles. As its macroscopic counterpart, the energetics of our Carnot device exhibits basic properties that one would expect to observe in any microscopic energy transducer operating with baths at different temperatures9–11. Our results characterize the sources of irreversibility in the engine and the statistical properties of the efficiency—an insight that could inspire new strategies in the design of efficient nano-motors. PMID:27330541

  5. Brownian Carnot engine.

    PubMed

    Martínez, I A; Roldán, É; Dinis, L; Petrov, D; Parrondo, J M R; Rica, R A

    2016-01-01

    The Carnot cycle imposes a fundamental upper limit to the efficiency of a macroscopic motor operating between two thermal baths1. However, this bound needs to be reinterpreted at microscopic scales, where molecular bio-motors2 and some artificial micro-engines3-5 operate. As described by stochastic thermodynamics6,7, energy transfers in microscopic systems are random and thermal fluctuations induce transient decreases of entropy, allowing for possible violations of the Carnot limit8. Here we report an experimental realization of a Carnot engine with a single optically trapped Brownian particle as the working substance. We present an exhaustive study of the energetics of the engine and analyse the fluctuations of the finite-time efficiency, showing that the Carnot bound can be surpassed for a small number of non-equilibrium cycles. As its macroscopic counterpart, the energetics of our Carnot device exhibits basic properties that one would expect to observe in any microscopic energy transducer operating with baths at different temperatures9-11. Our results characterize the sources of irreversibility in the engine and the statistical properties of the efficiency-an insight that could inspire new strategies in the design of efficient nano-motors.

  6. Brownian Carnot engine

    NASA Astrophysics Data System (ADS)

    Martínez, I. A.; Roldán, É.; Dinis, L.; Petrov, D.; Parrondo, J. M. R.; Rica, R. A.

    2016-01-01

    The Carnot cycle imposes a fundamental upper limit to the efficiency of a macroscopic motor operating between two thermal baths. However, this bound needs to be reinterpreted at microscopic scales, where molecular bio-motors and some artificial micro-engines operate. As described by stochastic thermodynamics, energy transfers in microscopic systems are random and thermal fluctuations induce transient decreases of entropy, allowing for possible violations of the Carnot limit. Here we report an experimental realization of a Carnot engine with a single optically trapped Brownian particle as the working substance. We present an exhaustive study of the energetics of the engine and analyse the fluctuations of the finite-time efficiency, showing that the Carnot bound can be surpassed for a small number of non-equilibrium cycles. As its macroscopic counterpart, the energetics of our Carnot device exhibits basic properties that one would expect to observe in any microscopic energy transducer operating with baths at different temperatures. Our results characterize the sources of irreversibility in the engine and the statistical properties of the efficiency--an insight that could inspire new strategies in the design of efficient nano-motors.

  7. O'Connell's process as a vicious Brownian motion

    SciTech Connect

    Katori, Makoto

    2011-12-15

    Vicious Brownian motion is a diffusion scaling limit of Fisher's vicious walk model, which is a system of Brownian particles in one dimension such that if two motions meet they kill each other. We consider the vicious Brownian motions conditioned never to collide with each other and call it noncolliding Brownian motion. This conditional diffusion process is equivalent to the eigenvalue process of the Hermitian-matrix-valued Brownian motion studied by Dyson [J. Math. Phys. 3, 1191 (1962)]. Recently, O'Connell [Ann. Probab. (to be published)] introduced a generalization of the noncolliding Brownian motion by using the eigenfunctions (the Whittaker functions) of the quantum Toda lattice in order to analyze a directed polymer model in 1 + 1 dimensions. We consider a system of one-dimensional Brownian motions with a long-ranged killing term as a generalization of the vicious Brownian motion and construct the O'Connell process as a conditional process of the killing Brownian motions to survive forever.

  8. The Brownian mean field model

    NASA Astrophysics Data System (ADS)

    Chavanis, Pierre-Henri

    2014-05-01

    We discuss the dynamics and thermodynamics of the Brownian mean field (BMF) model which is a system of N Brownian particles moving on a circle and interacting via a cosine potential. It can be viewed as the canonical version of the Hamiltonian mean field (HMF) model. The BMF model displays a second order phase transition from a homogeneous phase to an inhomogeneous phase below a critical temperature T c = 1 / 2. We first complete the description of this model in the mean field approximation valid for N → +∞. In the strong friction limit, the evolution of the density towards the mean field Boltzmann distribution is governed by the mean field Smoluchowski equation. For T < T c , this equation describes a process of self-organization from a non-magnetized (homogeneous) phase to a magnetized (inhomogeneous) phase. We obtain an analytical expression for the temporal evolution of the magnetization close to T c . Then, we take fluctuations (finite N effects) into account. The evolution of the density is governed by the stochastic Smoluchowski equation. From this equation, we derive a stochastic equation for the magnetization and study its properties both in the homogenous and inhomogeneous phase. We show that the fluctuations diverge at the critical point so that the mean field approximation ceases to be valid. Actually, the limits N → +∞ and T → T c do not commute. The validity of the mean field approximation requires N( T - T c ) → +∞ so that N must be larger and larger as T approaches T c . We show that the direction of the magnetization changes rapidly close to T c while its amplitude takes a long time to relax. We also indicate that, for systems with long-range interactions, the lifetime of metastable states scales as e N except close to a critical point. The BMF model shares many analogies with other systems of Brownian particles with long-range interactions such as self-gravitating Brownian particles, the Keller-Segel model describing the chemotaxis

  9. Superdiffusive trajectories in Brownian motion.

    PubMed

    Duplat, Jérôme; Kheifets, Simon; Li, Tongcang; Raizen, Mark G; Villermaux, Emmanuel

    2013-02-01

    The Brownian motion of a microscopic particle in a fluid is one of the cornerstones of statistical physics and the paradigm of a random process. One of the most powerful tools to quantify it was provided by Langevin, who explicitly accounted for a short-time correlated "thermal" force. The Langevin picture predicts ballistic motion, ~t(2) at short-time scales, and diffusive motion ~t at long-time scales, where x is the displacement of the particle during time t, and the average is taken over the thermal distribution of initial conditions. The Langevin equation also predicts a superdiffusive regime, where ~t(3), under the condition that the initial velocity is fixed rather than distributed thermally. We analyze the motion of an optically trapped particle in air and indeed find t(3) dispersion. This observation is a direct proof of the existence of the random, rapidly varying force imagined by Langevin.

  10. Particle fallout/activity sensor

    NASA Technical Reports Server (NTRS)

    Curtis, Ihlefeld M. (Inventor); Youngquist, Robert C. (Inventor); Moerk, John S. (Inventor); Rose, Kenneth A., III (Inventor)

    1995-01-01

    A particle fallout/activity sensor measures relative amounts of dust or other particles which collect on a mirror in an area to be monitored. The sensor includes a sensor module and a data acquisition module, both of which can be operated independently of one another or in combination with one another. The sensor module includes a housing containing the mirror, an LED assembly for illuminating the mirror and an optical detector assembly for detecting light scattered off of the mirror by dust or other particles collected thereon. A microprocessor controls operation of the sensor module's components and displays results of a measurement on an LCD display mounted on the housing. A push button switch is also mounted on the housing which permits manual initiation of a measurement. The housing is constructed of light absorbing material, such as black delrin, which minimizes detection of light by the optical detector assembly other than that scattered by dust or particles on the mirror. The data acquisition module can be connected to the sensor module and includes its own microprocessor, a timekeeper and other digital circuitry for causing the sensor module to make a measurement periodically and send the measurement data to the data acquisition module for display and storage in memory for later retrieval and transfer to a separate computer. The time tagged measurement data can also be used to determine the relative level of activity in the monitored area since this level is directly related to the amount of dust or particle fallout in the area.

  11. Onsager coefficients of a Brownian Carnot cycle

    NASA Astrophysics Data System (ADS)

    Izumida, Y.; Okuda, K.

    2010-10-01

    We study a Brownian Carnot cycle introduced by Schmiedl and Seifert [Europhys. Lett. 81, 20003 (2008)] from a viewpoint of the linear irreversible thermodynamics. By considering the entropy production rate of this cycle, we can determine thermodynamic forces and fluxes of the cycle and calculate the Onsager coefficients for general protocols, that is, arbitrary schedules to change the potential confining the Brownian particle. We show that these Onsager coefficients contain the information of the protocol shape and they satisfy the tight-coupling condition irrespective of whatever protocol shape we choose. These properties may give an explanation why the Curzon-Ahlborn efficiency often appears in the finite-time heat engines.

  12. Generalized formulation of Brownian Vortexes

    NASA Astrophysics Data System (ADS)

    Moyses, Henrique; Bauer, Ross; Grier, David

    2013-03-01

    Brownian vortexes are stochastic noise driven machines that arise from the motion of particles subjected to static non conservative force fields. This motion is characterized by a toroidal circulation in the probability flux whose direction can be tuned by changing the temperature of the system. A discrete minimal model for Brownian Vortexes were described by previous work done by B.Sun, D.G.Grier and A.Y.Grosberg. Here we theoretically look for a continuous model in the form of a generalization of the equilibrium Boltzmann relation for the probability density in the case where the driven forces have a non conservative solenoidal component. This generalized relation features the temperature induced probability flux reversal. We further extend our theory to time dependent force fields and study the possibility of stochastic resonance in the characteristic frequency of circulation of the driven particle. This model is experimentally applied to investigate the motion of colloidal spheres in an optical trap whose intensity is oscillatory in time.

  13. Rotational Brownian dynamics simulations of clathrin cage formation.

    PubMed

    Ilie, Ioana M; den Otter, Wouter K; Briels, Wim J

    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 algorithm 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.

  14. Rotational Brownian Dynamics simulations of clathrin cage formation

    SciTech Connect

    Ilie, Ioana M.; Briels, Wim J.; Otter, Wouter K. den

    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 algorithm 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.

  15. Brownian motion of graphene.

    PubMed

    Maragó, Onofrio M; Bonaccorso, Francesco; Saija, Rosalba; Privitera, Giulia; Gucciardi, Pietro G; Iatì, Maria Antonia; Calogero, Giuseppe; Jones, Philip H; Borghese, Ferdinando; Denti, Paolo; Nicolosi, Valeria; Ferrari, Andrea C

    2010-12-28

    Brownian motion is a manifestation of the fluctuation-dissipation theorem of statistical mechanics. It regulates systems in physics, biology, chemistry, and finance. We use graphene as prototype material to unravel the consequences of the fluctuation-dissipation theorem in two dimensions, by studying the Brownian motion of optically trapped graphene flakes. These orient orthogonal to the light polarization, due to the optical constants anisotropy. We explain the flake dynamics in the optical trap and measure force and torque constants from the correlation functions of the tracking signals, as well as comparing experiments with a full electromagnetic theory of optical trapping. The understanding of optical trapping of two-dimensional nanostructures gained through our Brownian motion analysis paves the way to light-controlled manipulation and all-optical sorting of biological membranes and anisotropic macromolecules.

  16. Langevin theory of anomalous Brownian motion made simple

    NASA Astrophysics Data System (ADS)

    Tóthová, Jana; Vasziová, Gabriela; Glod, Lukáš; Lisý, Vladimír

    2011-05-01

    During the century from the publication of the work by Einstein (1905 Ann. Phys. 17 549) Brownian motion has become an important paradigm in many fields of modern science. An essential impulse for the development of Brownian motion theory was given by the work of Langevin (1908 C. R. Acad. Sci., Paris 146 530), in which he proposed an 'infinitely more simple' description of Brownian motion than that by Einstein. The original Langevin approach has however strong limitations, which were rigorously stated after the creation of the hydrodynamic theory of Brownian motion (1945). Hydrodynamic Brownian motion is a special case of 'anomalous Brownian motion', now intensively studied both theoretically and in experiments. We show how some general properties of anomalous Brownian motion can be easily derived using an effective method that allows one to convert the stochastic generalized Langevin equation into a deterministic Volterra-type integro-differential equation for the mean square displacement of the particle. Within the Gibbs statistics, the method is applicable to linear equations of motion with any kind of memory during the evolution of the system. We apply it to memoryless Brownian motion in a harmonic potential well and to Brownian motion in fluids, taking into account the effects of hydrodynamic memory. Exploring the mathematical analogy between Brownian motion and electric circuits, which are at nanoscales also described by the generalized Langevin equation, we calculate the fluctuations of charge and current in RLC circuits that are in contact with the thermal bath. Due to the simplicity of our approach it could be incorporated into graduate courses of statistical physics. Once the method is established, it allows bringing to the attention of students and effectively solving a number of attractive problems related to Brownian motion.

  17. Movement of particles using sequentially activated dielectrophoretic particle trapping

    DOEpatents

    Miles, Robin R.

    2004-02-03

    Manipulation of DNA and cells/spores using dielectrophoretic (DEP) forces to perform sample preparation protocols for polymerized chain reaction (PCR) based assays for various applications. This is accomplished by movement of particles using sequentially activated dielectrophoretic particle trapping. DEP forces induce a dipole in particles, and these particles can be trapped in non-uniform fields. The particles can be trapped in the high field strength region of one set of electrodes. By switching off this field and switching on an adjacent electrodes, particles can be moved down a channel with little or no flow.

  18. 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.

  19. Ising model for a Brownian donkey

    NASA Astrophysics Data System (ADS)

    Cleuren, B.; Van den Broeck, C.

    2001-04-01

    We introduce a thermal engine consisting of N interacting Brownian particles moving in a periodic potential, featuring an alternation of hot and cold symmetric peaks. A discretized Ising-like version is solved analytically. In response to an external force, absolute negative mobility is observed for N >= 4. For N → ∞ a nonequilibrium phase transition takes place with a spontaneous symmetry breaking entailing the appearance of a current in the absence of an external force.

  20. Quantum Brownian motion with inhomogeneous damping and diffusion

    NASA Astrophysics Data System (ADS)

    Massignan, Pietro; Lampo, Aniello; Wehr, Jan; Lewenstein, Maciej

    2015-03-01

    We analyze the microscopic model of quantum Brownian motion, describing a Brownian particle interacting with a bosonic bath through a coupling which is linear in the creation and annihilation operators of the bath, but may be a nonlinear function of the position of the particle. Physically, this corresponds to a configuration in which damping and diffusion are spatially inhomogeneous. We derive systematically the quantum master equation for the Brownian particle in the Born-Markov approximation and we discuss the appearance of additional terms, for various polynomials forms of the coupling. We discuss the cases of linear and quadratic coupling in great detail and we derive, using Wigner function techniques, the stationary solutions of the master equation for a Brownian particle in a harmonic trapping potential. We predict quite generally Gaussian stationary states, and we compute the aspect ratio and the spread of the distributions. In particular, we find that these solutions may be squeezed (superlocalized) with respect to the position of the Brownian particle. We analyze various restrictions to the validity of our theory posed by non-Markovian effects and by the Heisenberg principle. We further study the dynamical stability of the system, by applying a Gaussian approximation to the time-dependent Wigner function, and we compute the decoherence rates of coherent quantum superpositions in position space. Finally, we propose a possible experimental realization of the physics discussed here, by considering an impurity particle embedded in a degenerate quantum gas.

  1. Three-dimensional tracking of Brownian motion of a particle trapped in optical tweezers with a pair of orthogonal tracking beams and the determination of the associated optical force constants.

    PubMed

    Wei, Ming-Tzo; Chiou, Arthur

    2005-07-25

    We report the first experimental results on quantitative mapping of three-dimensional optical force field on a silica micro-particle and on a Chinese hamster ovary cell trapped in optical tweezers by using a pair of orthogonal laser beams in conjunction with two quadrant photo-diodes to track the particle's (or the cell's) trajectory, analyze its Brownian motion, and calculate the optical force constants in a three-dimensional parabolic potential model. For optical tweezers with a 60x objective lens (NA = 0.85), a trapping beam wavelength lambda = 532nm, and a trapping optical power of 75mW, the optical force constants along the axial and the transverse directions (of the trapping beam) were measured to be approximately 1.1x10-8N/m and 1.3x10-7N/m, respectively, for a silica particle (diameter = 2.58microm), and 3.1x10-8 N/m and 2.3x10-7 N/m, respectively, for a Chinese hamster ovary cell (diameter ~ 10 microm to 15microm). The set of force constants (Kx, Ky, and Kz ) completely defines the optical force field E(x, y, z) = [Kx x2 + Ky y2 + Kz z2]/2 (in the parabolic potential approximation) on the trapped particle. Practical advantages and limitations of using a pair of orthogonal tracking beams are discussed.

  2. Two-dimensional Brownian vortices

    NASA Astrophysics Data System (ADS)

    Chavanis, Pierre-Henri

    2008-12-01

    We introduce a stochastic model of 2D Brownian vortices associated with the canonical ensemble. The point vortices evolve through their usual mutual advection but they experience in addition a random velocity and a systematic drift generated by the system as a whole. The statistical equilibrium state of this stochastic model is the Gibbs canonical distribution. We consider a single species system and a system made of two types of vortices with positive and negative circulations. At positive temperatures, like-sign vortices repel each other (“plasma” case) and at negative temperatures, like-sign vortices attract each other (“gravity” case). We derive the stochastic equation satisfied by the exact vorticity field and the Fokker-Planck equation satisfied by the N-body distribution function. We present the BBGKY-like hierarchy of equations satisfied by the reduced distribution functions and close the hierarchy by considering an expansion of the solutions in powers of 1/N, where N is the number of vortices, in a proper thermodynamic limit. For spatially inhomogeneous systems, we derive the kinetic equations satisfied by the smooth vorticity field in a mean field approximation valid for N→+∞. For spatially homogeneous systems, we study the two-body correlation function, in a Debye-Hückel approximation valid at the order O(1/N). The results of this paper can also apply to other systems of random walkers with long-range interactions such as self-gravitating Brownian particles and bacterial populations experiencing chemotaxis. Furthermore, for positive temperatures, our study provides a kinetic derivation, from microscopic stochastic processes, of the Debye-Hückel model of electrolytes.

  3. Optimal tuning of a confined Brownian information engine.

    PubMed

    Park, Jong-Min; Lee, Jae Sung; Noh, Jae Dong

    2016-03-01

    A Brownian information engine is a device extracting mechanical work from a single heat bath by exploiting the information on the state of a Brownian particle immersed in the bath. As for engines, it is important to find the optimal operating condition that yields the maximum extracted work or power. The optimal condition for a Brownian information engine with a finite cycle time τ has been rarely studied because of the difficulty in finding the nonequilibrium steady state. In this study, we introduce a model for the Brownian information engine and develop an analytic formalism for its steady-state distribution for any τ. We find that the extracted work per engine cycle is maximum when τ approaches infinity, while the power is maximum when τ approaches zero.

  4. Ratchet transport powered by chiral active particles

    PubMed Central

    Ai, Bao-quan

    2016-01-01

    We numerically investigate the ratchet transport of mixtures of active and passive particles in a transversal asymmetric channel. A big passive particle is immersed in a ‘sea’ of active particles. Due to the chirality of active particles, the longitudinal directed transport is induced by the transversal asymmetry. For the active particles, the chirality completely determines the direction of the ratchet transport, the counterclockwise and clockwise particles move to the opposite directions and can be separated. However, for the passive particle, the transport behavior becomes complicated, the direction is determined by competitions among the chirality, the self-propulsion speed, and the packing fraction. Interestingly, within certain parameters, the passive particle moves to the left, while active particles move to the right. In addition, there exist optimal parameters (the chirality, the height of the barrier, the self-propulsion speed and the packing fraction) at which the rectified efficiency takes its maximal value. Our findings could be used for the experimental pursuit of the ratchet transport powered by chiral active particles. PMID:26795952

  5. Active Teaching of Diffusion through History of Science, Computer Animation and Role Playing

    ERIC Educational Resources Information Center

    Krajsek, Simona Strgulc; Vilhar, Barbara

    2010-01-01

    We developed and tested a lesson plan for active teaching of diffusion in secondary schools (grades 10-13), which stimulates understanding of the thermal (Brownian) motion of particles as the principle underlying diffusion. During the lesson, students actively explore the Brownian motion through microscope observations of irregularly moving small…

  6. Brownian Ratchets: Transport Controlled by Thermal Noise

    NASA Astrophysics Data System (ADS)

    Kula, J.; Czernik, T.; Łuczka, J.

    1998-02-01

    We analyze directed transport of overdamped Brownian particles in a 1D spatially periodic potential that are subjected to both zero-mean thermal equilibrium Nyquist noise and zero-mean exponentially correlated dichotomous fluctuations. We show that particles can reverse the direction of average motion upon a variation of noise parameters if two fundamental symmetries, namely, the reflection symmetry of the spatial periodic structure, and the statistical symmetry of dichotomous fluctuations, are broken. There is a critical thermal noise intensity Dc, or equivalently a critical temperature Tc, at which the mean velocity of particles is zero. Below Tc and above Tc particles move in opposite directions. At fixed temperature, there is a region of noise parameters in which particles of different linear size are transported in opposite directions.

  7. Dynamical and thermodynamical control of open quantum Brownian motion

    NASA Astrophysics Data System (ADS)

    Petruccione, Francesco; Sinayskiy, Ilya

    Open quantum Brownian motion was introduced as a new type of quantum Brownian motion for Brownian particles with internal quantum degrees of freedom. Recently, an example of the microscopic derivation of open quantum Brownian motion has been presented [I. Sinayskiy and F. Petruccione, Phys. Scr. T165, 014017 (2015)]. The microscopic derivation allows to relate the dynamical properties of open Quantum Brownian motion and the thermodynamical properties of the environment. In the present work, we study the possibility of control of the external degrees of freedom of the ''walker'' (position) by manipulating the internal one, e.g. spin, polarization, occupation numbers. In the particular example of the known microscopic derivation the connection between dynamics of the ''walker'' and thermodynamical parameters of the system is established. For the system of open Brownian walkers coupled to the same environment controllable creation of quantum correlations is investigated. This work is based upon research supported by the South African Research Chair Initiative of the Department of Science and Technology and National Research Foundation.

  8. Brownian Heat Engines -- from Leidenfrost Droplets to Nanowire Thermoelectrics

    NASA Astrophysics Data System (ADS)

    Linke, Heiner

    2007-03-01

    A Brownian heat engine is a system that rectifies the flow of Brownian particles to transform local temperature variations into directed motion (work). In the context of electronics, this is the principle of thermoelectric energy conversion. For a long time it was thought that Brownian heat engines (and thermoelectric devices) are inherently irreversible and would therefore necessarily fall short of the Carnot limit for the energy conversion efficiency. I will introduce the concept of a Brownian heat engine, and will discuss how quantum energy-filtering can in fact be used to design a Carnot efficient, Brownian heat engine [1]. I will then present two experimental systems. The first, heat-propelled Leidenfrost droplets [2], is not really `Brownian' but nevertheless a very entertaining and illustrative ratchet heat engine. The second is our experimental effort to demonstrate a near-Carnot efficient thermal-to-electric energy converter [3] based on a quantum dot embedded into a heterostructure nanowire [4]. The physics behind this novel thermoelectric system, and the status of experiments will be discussed. [1] T. E. Humphrey, R. Newbury, R. P. Taylor, H. Linke, Phys. Rev. Lett. 89, 116801 (2002). [2] H. Linke et al., Phys. Rev. Lett. 96, 154502 (2006). [3] M. O'Dwyer, T. E. Humphrey, H. Linke, Nanotechnology 17, S338 (2006). [4] M. T. Bj"ork et al., Nano Letters 2, 87 (2002).

  9. Theory of Brownian motion in a Jeffreys fluid

    SciTech Connect

    Raikher, Yu. L.; Rusakov, V. V.

    2010-11-15

    We have constructed a kinetic theory of Brownian motion in a rheologically complex medium-a Jeffreys fluid that is characterized by a combination of two viscosity mechanisms: ordinary and delayed. This model is shown to be much better suited for the interpretation of experiments on the microrheology of viscoelastic media than the standard Maxwell model. In particular, no oscillations of the mean-square particle displacement arise in a Jeffreys fluid, which is a nonremovable artifact of the theory of Brownian motion in a Maxwell fluid. The developed approach can to be used also consider the diffusion of particles in other complex fluids whose rheology is described by phenomenological schemes.

  10. Entropy production of a Brownian ellipsoid in the overdamped limit.

    PubMed

    Marino, Raffaele; Eichhorn, Ralf; Aurell, Erik

    2016-01-01

    We analyze the translational and rotational motion of an ellipsoidal Brownian particle from the viewpoint of stochastic thermodynamics. The particle's Brownian motion is driven by external forces and torques and takes place in an heterogeneous thermal environment where friction coefficients and (local) temperature depend on space and time. Our analysis of the particle's stochastic thermodynamics is based on the entropy production associated with single particle trajectories. It is motivated by the recent discovery that the overdamped limit of vanishing inertia effects (as compared to viscous fricion) produces a so-called "anomalous" contribution to the entropy production, which has no counterpart in the overdamped approximation, when inertia effects are simply discarded. Here we show that rotational Brownian motion in the overdamped limit generates an additional contribution to the "anomalous" entropy. We calculate its specific form by performing a systematic singular perturbation analysis for the generating function of the entropy production. As a side result, we also obtain the (well-known) equations of motion in the overdamped limit. We furthermore investigate the effects of particle shape and give explicit expressions of the "anomalous entropy" for prolate and oblate spheroids and for near-spherical Brownian particles.

  11. An active particle in a complex fluid

    NASA Astrophysics Data System (ADS)

    Datt, Charu; Natale, Giovanniantonio; Hatzikiriakos, Savvas G.; Elfring, Gwynn J.

    2016-11-01

    Active particles are self-driven units capable of converting stored or ambient free-energy into systematic movement. We discuss here the case when such particles move through non-Newtonian fluids. Neglecting inertial forces, we employ the reciprocal theorem to calculate the propulsion velocity of a single swimmer in a weakly non-Newtonian fluid with background flow. We also derive a general expression for the velocity of an active particle modelled as a squirmer in a second-order fluid. We then discuss how active colloids are affected by the medium rheology, namely viscoelasticity and shear-thinning.

  12. Effect of interfaces on the nearby Brownian motion

    NASA Astrophysics Data System (ADS)

    Huang, Kai; Szlufarska, Izabela

    2015-10-01

    Near-boundary Brownian motion is a classic hydrodynamic problem of great importance in a variety of fields, from biophysics to micro-/nanofluidics. However, owing to challenges in experimental measurements of near-boundary dynamics, the effect of interfaces on Brownian motion has remained elusive. Here we report a computational study of this effect using μs-long large-scale molecular dynamics simulations and our newly developed Green-Kubo relation for friction at the liquid-solid interface. Our computer experiment unambiguously reveals that the t-3/2 long-time decay of the velocity autocorrelation function of a Brownian particle in bulk liquid is replaced by a t-5/2 decay near a boundary. We discover a general breakdown of traditional no-slip boundary condition at short time scales and we show that this breakdown has a profound impact on the near-boundary Brownian motion. Our results demonstrate the potential of Brownian-particle-based micro-/nanosonar to probe the local wettability of liquid-solid interfaces.

  13. Effect of interfaces on the nearby Brownian motion

    PubMed Central

    Huang, Kai; Szlufarska, Izabela

    2015-01-01

    Near-boundary Brownian motion is a classic hydrodynamic problem of great importance in a variety of fields, from biophysics to micro-/nanofluidics. However, owing to challenges in experimental measurements of near-boundary dynamics, the effect of interfaces on Brownian motion has remained elusive. Here we report a computational study of this effect using μs-long large-scale molecular dynamics simulations and our newly developed Green–Kubo relation for friction at the liquid–solid interface. Our computer experiment unambiguously reveals that the t−3/2 long-time decay of the velocity autocorrelation function of a Brownian particle in bulk liquid is replaced by a t−5/2 decay near a boundary. We discover a general breakdown of traditional no-slip boundary condition at short time scales and we show that this breakdown has a profound impact on the near-boundary Brownian motion. Our results demonstrate the potential of Brownian-particle-based micro-/nanosonar to probe the local wettability of liquid–solid interfaces. PMID:26438034

  14. Estimating the contribution of Brownian and Néel relaxation in a magnetic fluid through dynamic magnetic susceptibility measurements

    NASA Astrophysics Data System (ADS)

    Maldonado-Camargo, L.; Torres-Díaz, I.; Chiu-Lam, A.; Hernández, M.; Rinaldi, C.

    2016-08-01

    We demonstrate how dynamic magnetic susceptibility measurements (DMS) can be used to estimate the relative contributions of Brownian and Néel relaxation to the dynamic magnetic response of a magnetic fluid, a suspension of magnetic nanoparticles. The method applies to suspensions with particles that respond through Brownian or Néel relaxation and for which the characteristic Brownian and Néel relaxation times are widely separated. First, we illustrate this using magnetic fluids consisting of mixtures of particles that relax solely by the Brownian or Néel mechanisms. Then, it is shown how the same approach can be applied to estimate the relative contributions of Brownian and Néel relaxation in a suspension consisting of particles obtained from a single synthesis and whose size distribution straddles the transition from Néel to Brownian relaxation.

  15. Relativistic Brownian motion on a graphene chip

    NASA Astrophysics Data System (ADS)

    Pototsky, A.; Marchesoni, F.; Kusmartsev, F. V.; Hänggi, P.; Savel'ev, S. E.

    2012-10-01

    Relativistic Brownian motion can be inexpensively demonstrated on a graphene chip. The interplay of stochastic and relativistic dynamics, governing the transport of charge carrier in graphene, induces noise-controlled effects such as (i) a stochastic effective mass, detectable as a suppression of the particle mobility with increasing the temperature; (ii) transverse harmonic mixing, whereby electron transport can be controlled by two orthogonal, commensurate ac drives; (iii) a transverse ratchet effect, measurable as a net current orthogonal to an ac drive on an asymmetric substrate, and (iv) chaotic stochastic resonance. Such properties can be of practical applications in the emerging graphene technology.

  16. Velocity distribution in active particles systems

    PubMed Central

    Marconi, Umberto Marini Bettolo; Gnan, Nicoletta; Paoluzzi, Matteo; Maggi, Claudio; Di Leonardo, Roberto

    2016-01-01

    We derive an analytic expression for the distribution of velocities of multiple interacting active particles which we test by numerical simulations. In clear contrast with equilibrium we find that the velocities are coupled to positions. Our model shows that, even for two particles only, the individual velocities display a variance depending on the interparticle separation and the emergence of correlations between the velocities of the particles. When considering systems composed of many particles we find an analytic expression connecting the overall velocity variance to density, at the mean-field level, and to the pair distribution function valid in the limit of small noise correlation times. Finally we discuss the intriguing analogies and main differences between our effective free energy functional and the theoretical scenario proposed so far for phase-separating active particles. PMID:27001289

  17. Discontinuous shear thickening in Brownian suspensions by dynamic simulation

    PubMed Central

    Mari, Romain; Seto, Ryohei; Morris, Jeffrey F.; Denn, Morton M.

    2015-01-01

    Dynamic particle-scale numerical simulations are used to show that the shear thickening observed in dense colloidal, or Brownian, suspensions is of a similar nature to that observed in noncolloidal suspensions, i.e., a stress-induced transition from a flow of lubricated near-contacting particles to a flow of a frictionally contacting network of particles. Abrupt (or discontinuous) shear thickening is found to be a geometric rather than hydrodynamic phenomenon; it stems from the strong sensitivity of the jamming volume fraction to the nature of contact forces between suspended particles. The thickening obtained in a colloidal suspension of purely hard frictional spheres is qualitatively similar to experimental observations. However, the agreement cannot be made quantitative with only hydrodynamics, frictional contacts, and Brownian forces. Therefore, the role of a short-range repulsive potential mimicking the stabilization of actual suspensions on the thickening is studied. The effects of Brownian and repulsive forces on the onset stress can be combined in an additive manner. The simulations including Brownian and stabilizing forces show excellent agreement with experimental data for the viscosity η and the second normal stress difference N2. PMID:26621744

  18. Brownian gyrator: a minimal heat engine on the nanoscale.

    PubMed

    Filliger, Roger; Reimann, Peter

    2007-12-07

    A Brownian particle moving in the vicinity of a generic potential minimum under the influence of dissipation and thermal noise from two different heat baths is shown to act as a minimal heat engine, generating a systematic torque onto the physical object at the origin of the potential and an opposite torque onto the medium generating the dissipation.

  19. Thermodynamic laws and equipartition theorem in relativistic Brownian motion.

    PubMed

    Koide, T; Kodama, T

    2011-06-01

    We extend the stochastic energetics to a relativistic system. The thermodynamic laws and equipartition theorem are discussed for a relativistic Brownian particle and the first and the second law of thermodynamics in this formalism are derived. The relation between the relativistic equipartition relation and the rate of heat transfer is discussed in the relativistic case together with the nature of the noise term.

  20. Discontinuous shear thickening in Brownian suspensions by dynamic simulation.

    PubMed

    Mari, Romain; Seto, Ryohei; Morris, Jeffrey F; Denn, Morton M

    2015-12-15

    Dynamic particle-scale numerical simulations are used to show that the shear thickening observed in dense colloidal, or Brownian, suspensions is of a similar nature to that observed in noncolloidal suspensions, i.e., a stress-induced transition from a flow of lubricated near-contacting particles to a flow of a frictionally contacting network of particles. Abrupt (or discontinuous) shear thickening is found to be a geometric rather than hydrodynamic phenomenon; it stems from the strong sensitivity of the jamming volume fraction to the nature of contact forces between suspended particles. The thickening obtained in a colloidal suspension of purely hard frictional spheres is qualitatively similar to experimental observations. However, the agreement cannot be made quantitative with only hydrodynamics, frictional contacts, and Brownian forces. Therefore, the role of a short-range repulsive potential mimicking the stabilization of actual suspensions on the thickening is studied. The effects of Brownian and repulsive forces on the onset stress can be combined in an additive manner. The simulations including Brownian and stabilizing forces show excellent agreement with experimental data for the viscosity η and the second normal stress difference N2.

  1. Brownian transport controlled by dichotomic and thermal fluctuations

    NASA Astrophysics Data System (ADS)

    Kula, J.; Kostur, M.; Łuczka, J.

    1998-09-01

    We study transport of Brownian particles in spatially periodic structures, driven by both thermal equilibrium fluctuations and dichotomic noise of zero mean values. Introducing specific scaling, we show that the dimensionless Newton-Langevin type equation governing the motion of Brownian particles is very well approximated by the overdamped dynamics; inertial effects can be neglected because for generic systems dimensionless mass is many orders less than a dimensionless friction coefficient. An exact probability current, proportional to the mean drift velocity of particles, is obtained for a piecewise linear spatially periodic potential. We analyze in detail properties of the macroscopic averaged motion of particles. In dependence on statistics of both sources of fluctuations, the directed transport of particles exhibits such distinctive non-monotonic behavior as: bell-shaped dependence (there exists optimal statistics of fluctuations maximizing velocity) and reversal in the direction of macroscopic motion (there exists critical statistics at which the drift velocity is zero).

  2. Relating Brownian motion to diffusion with superparamagnetic colloids

    NASA Astrophysics Data System (ADS)

    Darras, A.; Fiscina, J.; Vandewalle, N.; Lumay, G.

    2017-04-01

    An original experiment is introduced that allows students to relate the Brownian motion of a set of superparamagnetic colloidal particles to their macroscopic diffusion. An external and constant magnetic field is first applied to the colloidal suspension so that the particles self-organize into chains. When the magnetic field is removed, the particles then freely diffuse from their positions in the chain, starting from the same coordinate on the axis perpendicular to the initial chain. This configuration thus enables an observer to study the one dimensional diffusion process, while also observing the underlying Brownian motion of the microscopic particles. Moreover, by studying the evolution of the particle distribution, a measurement of the diffusion coefficient can be obtained. In addition, by repeating this measurement with fluids of various viscosities, the Stokes-Einstein relation may be illustrated.

  3. Brownian motion with adhesion: harmonic oscillator with fluctuating mass.

    PubMed

    Gitterman, M; Klyatskin, V I

    2010-05-01

    In contrast to the cases usually studied of a harmonic oscillator subject to a random force (Brownian motion) or having random frequency or random damping, we consider a random mass which corresponds to an oscillator for which the particles of the surrounding medium adhere to it for some (random) time after the collision, thereby changing the oscillator mass. This model, which describes Brownian motion with adhesion, can be useful for the analysis of chemical and biological solutions as well as nanotechnological devices. We consider dichotomous noise and its limiting case, white noise.

  4. Collective surfing of chemically active particles.

    PubMed

    Masoud, Hassan; Shelley, Michael J

    2014-03-28

    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.

  5. Quantum Brownian motion model for the stock market

    NASA Astrophysics Data System (ADS)

    Meng, Xiangyi; Zhang, Jian-Wei; Guo, Hong

    2016-06-01

    It is believed by the majority today that the efficient market hypothesis is imperfect because of market irrationality. Using the physical concepts and mathematical structures of quantum mechanics, we construct an econophysical framework for the stock market, based on which we analogously map massive numbers of single stocks into a reservoir consisting of many quantum harmonic oscillators and their stock index into a typical quantum open system-a quantum Brownian particle. In particular, the irrationality of stock transactions is quantitatively considered as the Planck constant within Heisenberg's uncertainty relationship of quantum mechanics in an analogous manner. We analyze real stock data of Shanghai Stock Exchange of China and investigate fat-tail phenomena and non-Markovian behaviors of the stock index with the assistance of the quantum Brownian motion model, thereby interpreting and studying the limitations of the classical Brownian motion model for the efficient market hypothesis from a new perspective of quantum open system dynamics.

  6. A Brownian dynamics algorithm for colloids in curved manifolds.

    PubMed

    Castro-Villarreal, Pavel; Villada-Balbuena, Alejandro; Méndez-Alcaraz, José Miguel; Castañeda-Priego, Ramón; Estrada-Jiménez, Sendic

    2014-06-07

    The many-particle Langevin equation, written in local coordinates, is used to derive a Brownian dynamics simulation algorithm to study the dynamics of colloids moving on curved manifolds. The predictions of the resulting algorithm for the particular case of free particles diffusing along a circle and on a sphere are tested against analytical results, as well as with simulation data obtained by means of the standard Brownian dynamics algorithm developed by Ermak and McCammon [J. Chem. Phys. 69, 1352 (1978)] using explicitly a confining external field. The latter method allows constraining the particles to move in regions very tightly, emulating the diffusion on the manifold. Additionally, the proposed algorithm is applied to strong correlated systems, namely, paramagnetic colloids along a circle and soft colloids on a sphere, to illustrate its applicability to systems made up of interacting particles.

  7. Antibacterial activity of nanosilver ions and particles.

    PubMed

    Sotiriou, Georgios A; Pratsinis, Sotiris E

    2010-07-15

    The antibacterial activity of nanosilver against Gram negative Escherichia coli bacteria is investigated by immobilizing nanosilver on nanostructured silica particles and closely controlling Ag content and size. These Ag/SiO(2) nanoparticles were characterized by S/TEM, EDX spectroscopy, X-ray diffraction the exposed Ag surface area was measured qualitatively by O(2) chemisorption. Furthermore, the fraction of dissolved nanosilver was determined by measuring the released (leached) Ag(+) ion concentration in aqueous suspensions of such Ag/SiO(2) particles. The antibacterial effect of Ag(+) ions was distinguished from that of nanosilver particles by monitoring the growth of E. coli populations in the presence and absence of Ag/SiO(2) particles. The antibacterial activity of nanosilver was dominated by Ag(+) ions when fine Ag nanoparticles (less than about 10 nm in average diameter) were employed that release high concentrations of Ag(+) ions. In contrast, when relatively larger Ag nanoparticles were used, the concentration of the released Ag(+) ions was lower. Then the antibacterial activity of the released Ag(+) ions and nanosilver particles was comparable.

  8. Response of Brownian Fluctuations to External Forces

    NASA Astrophysics Data System (ADS)

    Laub, Jeffrey William

    Millikan's law of particle fall is an empirical result which shows the dependence of particle fall rate in a gas on particle radius and host gas density. The size of submicron particles in gases has long been determined by Millikan's law. The dominant factor is Stokes' law with a correction added to account for the physics of slip. However, it was recently shown by Kim and Fedele that Brownian fluctuations affect the fall rate while showing no anomalies in the density dependence of the rms displacement. The effect was an enhancement of the fall rate of small particles as the density of the host gas is increased. This enhancement showed a size dependence in the form of a smooth transition from the one of decreasing fall rate with increasing density for large particles (~0.4 μm radius) to another of increasing fall rate with increasing gas density for small particles ( ~0.15mum radius). The magnitude of the anomaly is determined by how the rms Brownian velocity compares with its fall rate. In an effort to understand the effect of Brownian fluctuations coupling with gravity, a new experiment has been carried out where an AC field was applied to force particles to fluctuate more in the vertical direction on one hand and where a constant DC field was applied to change the effective force of gravity on the other. These fields were applied to a charged oil drop in the 0.2 to 0.3 μm radius range falling in a nitrogen environment. Displacements over a 4 second time interval were repeatedly measured in both the vertical and horizontal directions. The original experimental apparatus was used with some modifications. The modifications included computer automation of particle control and data taking to allow for longer use of the same particle, up to 120 hours, and to facilitate application of the additional fields. The objective was to make large particles appear to be smaller via forced oscillations and make them fall faster or slower via the DC bias to effect the change in

  9. Reconfiguring active particles by electrostatic imbalance

    NASA Astrophysics Data System (ADS)

    Yan, Jing; Han, Ming; Zhang, Jie; Xu, Cong; Luijten, Erik; Granick, Steve

    2016-10-01

    Active materials represent a new class of condensed matter in which motile elements may collectively form dynamic, global structures out of equilibrium. Here, we present a general strategy to reconfigure active particles into various collective states by introducing imbalanced interactions. We demonstrate the concept with computer simulations of self-propelled colloidal spheres, and experimentally validate it in a two-dimensional (2D) system of metal-dielectric Janus colloids subjected to perpendicular a.c. electric fields. The mismatched, frequency-dependent dielectric responses of the two hemispheres of the colloids allow simultaneous control of particle motility and colloidal interactions. We realized swarms, chains, clusters and isotropic gases from the same precursor particle by changing the electric-field frequency. Large-scale polar waves, vortices and jammed domains are also observed, with the persistent time-dependent evolution of their collective structure evoking that of classical materials. This strategy of asymmetry-driven active self-organization should generalize rationally to other active 2D and three-dimensional (3D) materials.

  10. Temperature (de)activated patchy colloidal particles.

    PubMed

    de Las Heras, Daniel; da Gama, Margarida M Telo

    2016-06-22

    We present a new model of patchy particles in which the interaction sites can be activated or deactivated by varying the temperature of the system. We study the thermodynamics of the system by means of Wertheim's first order perturbation theory, and use Flory-Stockmayer theory of polymerization to analyse the percolation threshold. We find a very rich phase behaviour including lower critical points and reentrant percolation.

  11. Brownian dynamics simulations of amelogenin microribbons formation

    NASA Astrophysics Data System (ADS)

    Li, Wei; Perez Lopez, Anthony; Liu, Ya; Chakrabarti, Amit; Gunton, James

    2011-03-01

    Recent advances in chemical particle synthesis have emphasized the fundamental role of surface colloidal heterogeneities and their detailed chemical composition, which is particularly significant for an important subclass of colloidal systems, namely, proteins. Recently, the process of self-assembly of amelogenin monomers with a hydrophobic/hydrophilic bipolar nature into ordered ribbon structures has been studied experimentally. In this work, we study this dynamical process by means of a Brownian dynamic simulation of a simple model which represents the bipolar character of the globular amelogenin molecule and the hydrophilic C-terminal tail. We monitor the kinetics of self-assembly through a study of the structure factor. We also calculate the phase diagram of the model using Gibbs ensemble Monte Carlo simulation and thermodynamic perturbation theory. This work is supported by grants from the NSF and Mathers Foundation.

  12. Weighted-ensemble Brownian dynamics simulations for protein association reactions.

    PubMed Central

    Huber, G A; Kim, S

    1996-01-01

    A new method, weighted-ensemble Brownian dynamics, is proposed for the simulation of protein-association reactions and other events whose frequencies of outcomes are constricted by free energy barriers. The method features a weighted ensemble of trajectories in configuration space with energy levels dictating the proper correspondence between "particles" and probability. Instead of waiting a very long time for an unlikely event to occur, the probability packets are split, and small packets of probability are allowed to diffuse almost immediately into regions of configuration space that are less likely to be sampled. The method has been applied to the Northrup and Erickson (1992) model of docking-type diffusion-limited reactions and yields reaction rate constants in agreement with those obtained by direct Brownian simulation, but at a fraction of the CPU time (10(-4) to 10(-3), depending on the model). Because the method is essentially a variant of standard Brownian dynamics algorithms, it is anticipated that weighted-ensemble Brownian dynamics, in conjunction with biophysical force models, can be applied to a large class of association reactions of interest to the biophysics community. Images FIGURE 4 PMID:8770190

  13. p-adic Brownian motion

    NASA Astrophysics Data System (ADS)

    Zelenov, E. I.

    2016-12-01

    We define p-adic Brownian motion (Wiener process) and study its properties. We construct a presentation of the trajectories of this process by their series expansions with respect to van der Put's basis and show that they are nowhere differentiable functions satisfying the p-adic Lipschitz condition of order 1. We define the p-adic Wiener measure on the space of continuous functions and study its properties.

  14. Collective dynamics of soft active particles

    NASA Astrophysics Data System (ADS)

    van Drongelen, Ruben; Pal, Anshuman; Goodrich, Carl P.; Idema, Timon

    2015-03-01

    We present a model of soft active particles that leads to a rich array of collective behavior found also in dense biological swarms of bacteria and other unicellular organisms. Our model uses only local interactions, such as Vicsek-type nearest-neighbor alignment, short-range repulsion, and a local boundary term. Changing the relative strength of these interactions leads to migrating swarms, rotating swarms, and jammed swarms, as well as swarms that exhibit run-and-tumble motion, alternating between migration and either rotating or jammed states. Interestingly, although a migrating swarm moves slower than an individual particle, the diffusion constant can be up to three orders of magnitude larger, suggesting that collective motion can be highly advantageous, for example, when searching for food.

  15. Stokesian spherical swimmers and active particles

    NASA Astrophysics Data System (ADS)

    Felderhof, B. U.

    2015-04-01

    The net steady state flow pattern of a distorting sphere is studied in the framework of the bilinear theory of swimming at low Reynolds number. It is argued that the starting point of a theory of interacting active particles should be based on such a calculation, since any arbitrarily chosen steady state flow pattern is not necessarily the result of a swimming motion. Furthermore, it is stressed that as a rule the phase of stroke is relevant in hydrodynamic interactions, so that the net flow pattern must be used with caution.

  16. Pricing European option under the time-changed mixed Brownian-fractional Brownian model

    NASA Astrophysics Data System (ADS)

    Guo, Zhidong; Yuan, Hongjun

    2014-07-01

    This paper deals with the problem of discrete time option pricing by a mixed Brownian-fractional subdiffusive Black-Scholes model. Under the assumption that the price of the underlying stock follows a time-changed mixed Brownian-fractional Brownian motion, we derive a pricing formula for the European call option in a discrete time setting.

  17. Brownian motion of helical flagella.

    PubMed

    Hoshikawa, H; Saito, N

    1979-07-01

    We develops a theory of the Brownian motion of a rigid helical object such as bacterial flagella. The statistical properties of the random forces acting on the helical object are discussed and the coefficients of the correlations of the random forces are determined. The averages , and are also calculated where z and theta are the position along and angle around the helix axis respectively. Although the theory is limited to short time interval, direct comparison with experiment is possible by using the recently developed cinematography technique.

  18. Anomalous Brownian motion and viscoelasticity of the ear's mechanoelectrical transducer

    NASA Astrophysics Data System (ADS)

    Andor-Ardó, Daniel; Kozlov, Andrei; Hudspeth, A. J.

    2009-03-01

    The Brownian motion of a particle in a complex environment is known to display anomalous power-law scaling in which the mean squared displacement is proportional to a fractional power of time. Using laser interferometry and analytical methods of microrheology, we examine nanometer-scale thermal motions of hair bundles in the internal ear and show that these cellular organelles undergo fractional Brownian motion. This anomalous scaling is caused by viscoelasticity of the gating springs, elements that transmit energy in a sound to the mechanosensitive ion channels. These results demonstrate a connection between rheology and auditory physiology, and indicate that statistical properties of the thermal noise in the ear can be determined by dynamics of a small number of key molecules.

  19. A parity breaking Ising chain Hamiltonian as a Brownian motor

    NASA Astrophysics Data System (ADS)

    Cornu, F.; Hilhorst, H. J.

    2014-10-01

    We consider the translationally invariant but parity (left-right symmetry) breaking Ising chain Hamiltonian {\\cal H} =-{U_2}\\sumk sksk+1 - {U_3}\\sumk sksk+1sk+3 and let this system evolve by Kawasaki spin exchange dynamics. Monte Carlo simulations show that perturbations forcing this system off equilibrium make it act as a Brownian molecular motor which, in the lattice gas interpretation, transports particles along the chain. We determine the particle current under various different circumstances, in particular as a function of the ratio {U_3}/{U_2} and of the conserved magnetization M=\\sum_ksk . The symmetry of the U3 term in the Hamiltonian is discussed.

  20. Biased Brownian motion in extremely corrugated tubes

    NASA Astrophysics Data System (ADS)

    Martens, S.; Schmid, G.; Schimansky-Geier, L.; Hänggi, P.

    2011-12-01

    Biased Brownian motion of point-size particles in a three-dimensional tube with varying cross-section is investigated. In the fashion of our recent work, Martens et al. [Phys. Rev. E 83, 051135 (2011)] we employ an asymptotic analysis to the stationary probability density in a geometric parameter of the tube geometry. We demonstrate that the leading order term is equivalent to the Fick-Jacobs approximation. Expression for the higher order corrections to the probability density is derived. Using this expansion orders, we obtain that in the diffusion dominated regime the average particle current equals the zeroth order Fick-Jacobs result corrected by a factor including the corrugation of the tube geometry. In particular, we demonstrate that this estimate is more accurate for extremely corrugated geometries compared with the common applied method using a spatially-dependent diffusion coefficient D(x, f) which substitutes the constant diffusion coefficient in the common Fick-Jacobs equation. The analytic findings are corroborated with the finite element calculation of a sinusoidal-shaped tube.

  1. Fokker-Planck equation for Boltzmann-type and active particles: transfer probability approach.

    PubMed

    Trigger, S A

    2003-04-01

    A Fokker-Planck equation with velocity-dependent coefficients is considered for various isotropic systems on the basis of probability transition (PT) approach. This method provides a self-consistent and universal description of friction and diffusion for Brownian particles. Renormalization of the friction coefficient is shown to occur for two-dimensional and three-dimensional cases, due to the tensorial character of diffusion. The specific forms of PT are calculated for Boltzmann-type and absorption-type collisions (the latter are typical in dusty plasmas and some other systems). The validity of the Einstein's relation for Boltzmann-type collisions is analyzed for the velocity-dependent friction and diffusion coefficients. For Boltzmann-type collisions in the region of very high grain velocity as well as it is always for non-Boltzmann collisions, such as, absorption collisions, the Einstein relation is violated, although some other relations (determined by the structure of PT) can exist. The generalized friction force is investigated in dusty plasmas in the framework of the PT approach. The relation among this force, the negative collecting friction force, and scattering and collecting drag forces is established. The concept of probability transition is used to describe motion of active particles in an ambient medium. On basis of the physical arguments, the PT for a simple model of the active particle is constructed and the coefficients of the relevant Fokker-Planck equation are found. The stationary solution of this equation is typical for the simplest self-organized molecular machines.

  2. Optically active biological particle distinguishing apparatus

    DOEpatents

    Salzman, Gary C.; Kupperman, Robert H.

    1989-01-01

    The disclosure is directed to organic particle sorting and identification. High frequency pulses of circularly polarized light, alternating between left and right, intersect a fast moving stream of organic particles. Circular intensity differential scattering and linear intensity differential scattering are monitored to uniquely identify a variety of organic particles.

  3. Revision of the DELFIC Particle Activity Module

    SciTech Connect

    Hooper, David A; Jodoin, Vincent J

    2010-09-01

    The Defense Land Fallout Interpretive Code (DELFIC) was originally released in 1968 as a tool for modeling fallout patterns and for predicting exposure rates. Despite the continual advancement of knowledge of fission yields, decay behavior of fission products, and biological dosimetry, the decay data and logic of DELFIC have remained mostly unchanged since inception. Additionally, previous code revisions caused a loss of conservation of radioactive nuclides. In this report, a new revision of the decay database and the Particle Activity Module is introduced and explained. The database upgrades discussed are replacement of the fission yields with ENDF/B-VII data as formatted in the Oak Ridge Isotope Generation (ORIGEN) code, revised decay constants, revised exposure rate multipliers, revised decay modes and branching ratios, and revised boiling point data. Included decay logic upgrades represent a correction of a flaw in the treatment of the fission yields, extension of the logic to include more complex decay modes, conservation of nuclides (including stable nuclides) at all times, and conversion of key variables to double precision for nuclide conservation. Finally, recommended future work is discussed with an emphasis on completion of the overall radiation physics upgrade, particularly for dosimetry, induced activity, decay of the actinides, and fractionation.

  4. Dynamics of two interacting active Janus particles

    NASA Astrophysics Data System (ADS)

    Bayati, Parvin; Najafi, Ali

    2016-04-01

    Starting from a microscopic model for a spherically symmetric active Janus particle, we study the interactions between two such active motors. The ambient fluid mediates a long range hydrodynamic interaction between two motors. This interaction has both direct and indirect hydrodynamic contributions. The direct contribution is due to the propagation of fluid flow that originated from a moving motor and affects the motion of the other motor. The indirect contribution emerges from the re-distribution of the ionic concentrations in the presence of both motors. Electric force exerted on the fluid from this ionic solution enhances the flow pattern and subsequently changes the motion of both motors. By formulating a perturbation method for very far separated motors, we derive analytic results for the translation and rotational dynamics of the motors. We show that the overall interaction at the leading order modifies the translational and rotational speeds of motors which scale as O (" separators=" [ 1 / D ] 3 ) and O (" separators=" [ 1 / D ] 4 ) with their separation, respectively. Our findings open up the way for studying the collective dynamics of synthetic micro-motors.

  5. A multiscale guide to Brownian motion

    NASA Astrophysics Data System (ADS)

    Grebenkov, Denis S.; Belyaev, Dmitry; Jones, Peter W.

    2016-01-01

    We revise the Lévy construction of Brownian motion as a simple though rigorous approach to operate with various Gaussian processes. A Brownian path is explicitly constructed as a linear combination of wavelet-based ‘geometrical features’ at multiple length scales with random weights. Such a wavelet representation gives a closed formula mapping of the unit interval onto the functional space of Brownian paths. This formula elucidates many classical results about Brownian motion (e.g., non-differentiability of its path), providing an intuitive feeling for non-mathematicians. The illustrative character of the wavelet representation, along with the simple structure of the underlying probability space, is different from the usual presentation of most classical textbooks. Similar concepts are discussed for the Brownian bridge, fractional Brownian motion, the Ornstein-Uhlenbeck process, Gaussian free fields, and fractional Gaussian fields. Wavelet representations and dyadic decompositions form the basis of many highly efficient numerical methods to simulate Gaussian processes and fields, including Brownian motion and other diffusive processes in confining domains.

  6. Fractional Brownian motions: memory, diffusion velocity, and correlation functions

    NASA Astrophysics Data System (ADS)

    Fuliński, A.

    2017-02-01

    Fractional Brownian motions (FBMs) have been observed recently in the measured trajectories of individual molecules or small particles in the cytoplasm of living cells and in other dense composite systems, among others. Various types of FBMs differ in a number of ways, including the strength, range and type of damping of the memory encoded in their definitions, but share several basic characteristics: distributions, non-ergodic properties, and scaling of the second moment, which makes it difficult to determine which type of Brownian motion (fractional or normal) the measured trajectory belongs to. Here, we show, by introducing FBMs with regulated range and strength of memory, that it is the structure of memory which determines their physical properties, including mean velocity of diffusion; therefore, the course and kinetics of several processes (including coagulation and some chemical reactions). We also show that autocorrelation functions possess characteristic features which enable identification of an observed FBM, and of the type of memory governing its trajectory. In memoriam Marian Smoluchowski, on the 100th anniversary of the publication of his seminal papers on Brownian motion and diffusion-limited kinetics.

  7. Non-conservative optical forces and Brownian vortexes

    NASA Astrophysics Data System (ADS)

    Sun, Bo

    Optical manipulation using optical tweezers has been widely adopted in physics, chemical engineering and biology. While most applications and fundamental studies of optical trapping have focused on optical forces resulting from intensity gradients, we have also explored the role of radiation pressure, which is directed by phase gradients in beams of light. Interestingly, radiation pressure turns out to be a non-conservative force and drives trapped objects out of thermodynamic equilibrium with their surrounding media. We have demonstrated the resulting nonequilibrium effects experimentally by tracking the thermally driven motions of optically trapped colloidal spheres using holographic video microscopy. Rather than undergoing equilibrium thermal fluctuations, as has been assumed for more than a quarter century, a sphere in an optical tweezer enters into a stochastic steady-state characterized by closed loops in its probability current density. These toroidal vortexes constitute a bias in the particle's otherwise random thermal fluctuations arising at least indirectly from a solenoidal component in the optical force. This surprising effect is a particular manifestation of a more general class of noise-driven machines that we call Brownian vortexes. This previously unrecognized class of stochastic heat engines operates on qualitatively different principles from such extensively studied nonequilibrium systems as thermal ratchets and Brownian motors. Among its interesting properties, a Brownian vortex can reverse its direction with changes in temperature or equivalent control parameters.

  8. Charged particles and cluster ions produced during cooking activities.

    PubMed

    Stabile, L; Jayaratne, E R; Buonanno, G; Morawska, L

    2014-11-01

    Previous studies showed that a significant number of the particles present in indoor air are generated by cooking activities, and measured particle concentrations and exposures have been used to estimate the related human dose. The dose evaluation can be affected by the particle charge level which is usually not considered in particle deposition models. To this purpose, in this paper we show, for the very first time, the electric charge of particles generated during cooking activities and thus extending the interest on particle charging characterization to indoor micro-environments, so far essentially focused on outdoors. Particle number, together with positive and negative cluster ion concentrations, was monitored using a condensation particle counter and two air ion counters, respectively, during different cooking events. Positively-charged particle distribution fractions during gas combustion, bacon grilling, and eggplant grilling events were measured by two Scanning Mobility Particle Sizer spectrometers, used with and without a neutralizer. Finally, a Tandem Differential Mobility Analyzer was used to measure the charge specific particle distributions of bacon and eggplant grilling experiments, selecting particles of 30, 50, 80 and 100 nm in mobility diameter. The total fraction of positively-charged particles was 4.0%, 7.9%, and 5.6% for gas combustion, bacon grilling, and eggplant grilling events, respectively, then lower than other typical outdoor combustion-generated particles.

  9. Brownian ratchets in physics and biology

    NASA Astrophysics Data System (ADS)

    Bier, Martin

    1997-06-01

    Thirty years ago Feynman et al. presented a paradox in the Lectures on Physics: an imagined device could let Brownian motion do work by allowing it in one direction and blocking it in the opposite direction. In the chapter Feynman et al. eventually show that such ratcheting can only be achieved if there is, in compliance with the basic conservation laws, some energy input from an external source. Now that technology is going into ever smaller dimensions, ratcheting Brownian motion seems to be a real possibility in nanotechnological applications. Furthermore, Brownian motion plays an essential role in the action of motor proteins (individual molecules that convert chemical energy into motion).

  10. Transport of active ellipsoidal particles in ratchet potentials

    SciTech Connect

    Ai, Bao-Quan Wu, Jian-Chun

    2014-03-07

    Rectified transport of active ellipsoidal particles is numerically investigated in a two-dimensional asymmetric potential. The out-of-equilibrium condition for the active particle is an intrinsic property, which can break thermodynamical equilibrium and induce the directed transport. It is found that the perfect sphere particle can facilitate the rectification, while the needlelike particle destroys the directed transport. There exist optimized values of the parameters (the self-propelled velocity, the torque acting on the body) at which the average velocity takes its maximal value. For the ellipsoidal particle with not large asymmetric parameter, the average velocity decreases with increasing the rotational diffusion rate, while for the needlelike particle (very large asymmetric parameter), the average velocity is a peaked function of the rotational diffusion rate. By introducing a finite load, particles with different shapes (or different self-propelled velocities) will move to the opposite directions, which is able to separate particles of different shapes (or different self-propelled velocities)

  11. Lagrangian turbulence and the Brownian motion paradox

    NASA Astrophysics Data System (ADS)

    Viecelli, J. A.

    1991-11-01

    The unique properties of three-dimensional hydrodynamic turbulence depend on the nature of the long-range time correlations as well as the spatial correlations. Although Kolmogorov's second similarity hypothesis predicts a power-law spatial scaling exponent for the Eulerian velocity fluctuations in agreement with experiments, it also leads, via the Lagrangian velocity time structure function relationship, to particle dispersion predictions that are inconsistent with enhanced diffusion. Recently, a new computational technique has been developed which can generate random power-law correlated fields in any number of dimensions with unlimited scale range. This new method is used to explore the consequences of a proposed set of assumptions about the nature of the time correlations and their relationship to the spatial correlations. In particular, the Brownian motion paradox is examined and it is shown that it can be resolved if the time domain constraint part of Kolmogorov's second hypothesis is relaxed and replaced with an assumption of space-time isotropy. The proposed modification preserves the observed one-dimensional k-5/3 spatial energy spectrum, allows for enhanced diffusion consistent with Richardson's law, is consistent with Taylor's frozen turbulence assumption under the appropriate conditions, and yields an ω-5/3 frequency spectrum for the velocity fluctuations in a frame at rest with respect to the turbulence.

  12. Frequency dispersion of electrokinetically activated Janus particles

    NASA Astrophysics Data System (ADS)

    Boymelgreen, Alicia; Balli, Tov; Yossifon, Gilad; Miloh, Touvia

    2015-11-01

    We examine the influence of the applied frequency of the electric field on the induced-charge electroosmotic flow around a metallo-dielectric Janus particle. Previously, we have used three dimensional-two component micro-particle-image-velocimetry (3D-2C μ PIV) around a stagnant particle, to illustrate the presence of a number of competing effects including dielectrophoresis and electrohydrodynamic flow which distort both the strength and shape of the frequency dispersion predicted for pure induced-charge effects. Here, we extend this work by examining the frequency dispersion of mobile Janus particles of different sizes (3 - 15 μm in diameter) at different electrolyte concentrations. In all cases, towards the DC limit, and in the frequency domain where previously EHD flow was shown to dominate, the velocity of a mobile particle decays to zero. At the same time significant variations in the frequency dispersion, including its shape and the value for maximum velocity are recorded as a function of both electrolyte concentration and particle size. This work is of both fundamental and practical importance and may be used to further refine non-linear electrokinetic theory and optimize the application of Janus particles as carriers in lab-on-a-chip analysis systems.

  13. Fractional Brownian motion and motion governed by the fractional Langevin equation in confined geometries.

    PubMed

    Jeon, Jae-Hyung; Metzler, Ralf

    2010-02-01

    Motivated by subdiffusive motion of biomolecules observed in living cells, we study the stochastic properties of a non-Brownian particle whose motion is governed by either fractional Brownian motion or the fractional Langevin equation and restricted to a finite domain. We investigate by analytic calculations and simulations how time-averaged observables (e.g., the time-averaged mean-squared displacement and displacement correlation) are affected by spatial confinement and dimensionality. In particular, we study the degree of weak ergodicity breaking and scatter between different single trajectories for this confined motion in the subdiffusive domain. The general trend is that deviations from ergodicity are decreased with decreasing size of the movement volume and with increasing dimensionality. We define the displacement correlation function and find that this quantity shows distinct features for fractional Brownian motion, fractional Langevin equation, and continuous time subdiffusion, such that it appears an efficient measure to distinguish these different processes based on single-particle trajectory data.

  14. The Asymmetric Exclusion Process and Brownian Excursions

    NASA Astrophysics Data System (ADS)

    Derrida, B.; Enaud, C.; Lebowitz, J. L.

    2004-04-01

    We consider the totally asymmetric exclusion process (TASEP) in one dimension in its maximal current phase. We show, by an exact calculation, that the non-Gaussian part of the fluctuations of density can be described in terms of the statistical properties of a Brownian excursion. Numerical simulations indicate that the description in terms of a Brownian excursion remains valid for more general one dimensional driven systems in their maximal current phase.

  15. Human behavioral regularity, fractional Brownian motion, and exotic phase transition

    NASA Astrophysics Data System (ADS)

    Li, Xiaohui; Yang, Guang; An, Kenan; Huang, Jiping

    2016-08-01

    The mix of competition and cooperation (C&C) is ubiquitous in human society, which, however, remains poorly explored due to the lack of a fundamental method. Here, by developing a Janus game for treating C&C between two sides (suppliers and consumers), we show, for the first time, experimental and simulation evidences for human behavioral regularity. This property is proved to be characterized by fractional Brownian motion associated with an exotic transition between periodic and nonperiodic phases. Furthermore, the periodic phase echoes with business cycles, which are well-known in reality but still far from being well understood. Our results imply that the Janus game could be a fundamental method for studying C&C among humans in society, and it provides guidance for predicting human behavioral activity from the perspective of fractional Brownian motion.

  16. On asymptotic behavior of work distributions for driven Brownian motion

    NASA Astrophysics Data System (ADS)

    Holubec, Viktor; Lips, Dominik; Ryabov, Artem; Chvosta, Petr; Maass, Philipp

    2015-12-01

    We propose a simple conjecture for the functional form of the asymptotic behavior of work distributions for driven overdamped Brownian motion of a particle in confining potentials. This conjecture is motivated by the fact that these functional forms are independent of the velocity of the driving for all potentials and protocols, where explicit analytical solutions for the work distributions have been derived in the literature. To test the conjecture, we use Brownian dynamics simulations and a recent theory developed by Engel and Nickelsen (EN theory), which is based on the contraction principle of large deviation theory. Our tests suggest that the conjecture is valid for potentials with a confinement equal to or weaker than the parabolic one, both for equilibrium and for nonequilibrium distributions of the initial particle position. For potentials with stronger confinement, the conjecture fails and gives a good approximate description only for fast driving. In addition we obtain a new analytical solution for the asymptotic behavior of the work distribution for the V-potential by application of the EN theory, and we extend this theory to nonequilibrated initial particle positions.

  17. Nonlinear Behavior of Magnetic Fluid in Brownian Relaxation

    SciTech Connect

    Yoshida, Takashi; Ogawa, Koutaro; Bhuiya, Anwarul K.; Enpuku, Keiji

    2010-12-02

    This study investigated the nonlinear behavior of magnetic fluids under high excitation fields due to nonlinear Brownian relaxation. As a direct indication of nonlinear behavior, we characterized the higher harmonics of the magnetization signal generated by the magnetic fluid. The amplitudes of the fundamental to the ninth harmonic of the magnetization signal were measured as a function of the external field. The experimental results were compared with numerical simulations based on the Fokker-Planck equation, which describes nonlinear Brownian relaxation. To allow a quantitative comparison, we estimated the size distribution and size dependence of the magnetic moment in the sample. In the present magnetic fluid, composed of agglomerates of Fe{sub 3}O{sub 4} particles, the magnetic moment was estimated to be roughly proportional to the diameter of the particles, in contrast to the case of single-domain particles. When the size distribution and the size dependence of the magnetic moment were taken into account, there was good quantitative agreement between the experiment and simulation.

  18. The Effect of Brownian Motion on the Trajectory of Diffusiophoretic Locomotors near a Solid Boundary

    NASA Astrophysics Data System (ADS)

    Mozaffari, Ali; Sharifi-Mood, Nima; Koplik, Joel; Maldarelli, Charles

    2015-11-01

    Diffusiophoretically self-propelled locomotors are a class of active colloids in which a particle autonomously swims through the liquid as a result of an unbalanced interaction with solute molecules asymmetrically distributed around the colloid. This solute distribution is maintained by a reaction which produces the solute on one catalytically active side of the Janus motor colloid. For the simplest case of diffusiophoretic self-propulsion near a planar infinite wall with zero solute flux, and repulsive solute-colloid interactions, hydrodynamic solutions for deterministic Stokes flow have shown that that for large catalytically active areas pointed away from the wall, and for distances less than the particle radius, the particles can skim at a constant distance along the surface without rotation, or can become stationary. To examine the effect of thermal fluctuations on the stability of these regimes for small motor sizes, Brownian dynamics simulations including the hydrodynamic interaction with the wall are undertaken, and we identify critical Peclet numbers above which the skimming and stationary regimes are stable. Below these values, less predictable behavior is found in which the colloid can be repelled from or intersect with the wall.

  19. Brownian Ratchets in Biophysics: from Diffusing Phospholipids to Polymerizing Actin Filaments

    NASA Astrophysics Data System (ADS)

    van Oudenaarden, Alexander

    2000-03-01

    In the 'Feynman Lectures on Physics' Feynman introduces a mechanical ratchet and pawl subjected to thermal fluctuations to demonstrate the impossibility to violate the second law of thermodynamics. Since this introduction the Brownian ratchet has evolved from Gedanken experiments to real experiments in the interdisciplinary sciences such as biophysics and biochemistry. In this symposium I will present two experiments in which the concept Brownian ratchet is of key importance. The first experiment addresses a so-called geometrical Brownian ratchet [1]. This ratchet consists of a two-dimensional microfabricated periodic array of asymmetric diffusion barriers. As an experimental realization of a two-dimensional fluid of Brownian particles, a bilayer of phospholipid molecules is used. I will demonstrate that the geometrical Brownian ratchet can be used as a molecular sieve to separate mixtures of membrane molecules without the need to extract them from the membrane. In the second experiment I explore the spontaneous symmetry breaking of polymerizing actin networks [2]. Small submicron size beads coated uniformly with a protein that catalyzes actin polymerization, are initially surrounded by a symmetrical cloud of actin filaments. This symmetry can be broken spontaneously after which the beads undergo directional motion with constant velocity. I will present a simple stochastic theory, in which each filament is modeled as an elastic Brownian ratchet that qualitatively reproduces the experimental results. The presence of the bead couples the dynamics of different filaments which results in a complex collective system of interacting Brownian ratchets that exhibits an emergent symmetry breaking behavior. [1] A. van Oudenaarden and S. G. Boxer, Science 285, 1046 (1999). [2] A. van Oudenaarden and J. A. Theriot, Nature Cell Biology 1, 493 (1999).

  20. 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

  1. The International Particle Physics Outreach Group (ippog):. Aims and Activities

    NASA Astrophysics Data System (ADS)

    Barney, David

    2012-08-01

    The International Particle Physics Outreach Group, IPPOG, is a network of particle physics communication and education experts. IPPOG's principle aim is to maximize the impact of education and outreach efforts related to particle physics through information exchange and the sharing of expertise. IPPOG has initiated several major European and Worldwide activities, such as the "International Particle Physics Masterclasses" where each year thousands of high school students in more than 20 countries come to one of about 120 nearby universities or research centres for a day in order to unravel the mysteries of particle physics. IPPOG has also initiated a global database of education and outreach materials, aimed at supporting other particle physicists and education professionals. The aims and activities of IPPOG will be described, as well as plans to include more countries & laboratories in the network.

  2. A Brownian-ratchet DNA pump with applications to single-nucleotide polymorphism genotyping

    NASA Astrophysics Data System (ADS)

    Bader, J. S.; Deem, M. W.; Hammond, R. W.; Henck, S. A.; Simpson, J. W.; Rothberg, J. M.

    2002-08-01

    We have fabricated a micron-scale device capable of transporting DNA oligomers using Brownian ratchets. The ratchet potential is generated by applying a voltage difference to interdigitated electrodes. Cycling between the charged state and a discharged, free-diffusion state rectifies the Brownian motion of charged particles. The observed macroscopic transport properties agree with the transport rate predicted from microscopic parameters including the DNA diffusivity, the dimensions of the ratchet potential, and the cycling time. Applications to human genetics, primarily genotyping of single-nucleotide polymorphisms (SNPs), are discussed.

  3. Convective self-propulsion of chemically active particles

    NASA Astrophysics Data System (ADS)

    Shklyaev, Oleg; Shum, Henry; Balazs, Anna

    2016-11-01

    A mechanism of particle self-propulsion activated by transduction of chemical energy into convective motion of fluid that drags microscale particles is proposed. The convection is generated by an active spherical particle located on the bottom of a microchannel and coated with a catalyst that decomposes reagent dissolved in the solution into less dense products and gives rise to a buoyancy force. The symmetry of the flow generated around the active particle can be broken if a passive spherical particle, which does not produce the flow, is present in the vicinity of the first one. The generated flow drags the passive particle toward the active one along the bottom wall until they form a dimer. The resulting asymmetric fluid flow, which is generated by only one of the particles, imposes a different drag on the different sides on the dimer. The net force causes the dimer to translate along the bottom wall. By varying numbers of active and passive particles, as well as their positions within a group, one can control the structure of the generated convective flow and, therefore, design clusters with different mobile properties. The proposed mechanism can be harnessed to transport cargo in microchannels.

  4. Probing Brownian relaxation in water-glycerol mixtures using magnetic hyperthermia

    NASA Astrophysics Data System (ADS)

    Nemala, Humeshkar; Milgie, Michael; Wadehra, Anshu; Thakur, Jagdish; Naik, Vaman; Naik, Ratna

    2013-03-01

    Generation of heat by magnetic nanoparticles in the presence of an external oscillating magnetic field is known as magnetic hyperthermia (MHT). This heat is generated by two mechanisms: the Neel relaxation and Brownian relaxation. While the internal spin relaxation of the nanoparticles known as Neel relaxation is largely dependent on the magnetic properties of the nanoparticles, the physical motion of the particle or the Brownian relaxation is largely dependent on the viscous properties of the carrier liquid. The MHT properties of dextran coated iron oxide nanoparticles have been investigated at a frequency of 400KHz. To understand the influence of Brownian relaxation on heating, we probe the MHT properties of these ferrofluids in water-glycerol mixtures of varying viscosities. The heat generation is quantified using the specific absorption rate (SAR) and its maximum at a particular temperature is discussed with reference to the viscosity.

  5. Monotone and boolean unitary Brownian motions

    NASA Astrophysics Data System (ADS)

    Hamdi, Tarek

    2015-06-01

    The additive monotone (respectively boolean) unitary Brownian motion is a non-commutative stochastic process with monotone (respectively boolean) independent and stationary increments which are distributed according to the arcsine law (respectively Bernoulli law). We introduce the monotone and boolean unitary Brownian motions and derive a closed formula for their associated moments. This provides a description of their spectral measures. We prove that, in the monotone case, the multiplicative analog of the arcsine distribution is absolutely continuous with respect to the Haar measure on the unit circle, whereas in the boolean case the multiplicative analog of the Bernoulli distribution is discrete. Finally, we use quantum stochastic calculus to provide a realization of these processes as the stochastic exponential of the correspending additive Brownian motions.

  6. Particle Growth Processes in Screening Smokes.

    DTIC Science & Technology

    1981-03-26

    These are axial and radial convection, Brownian coagulation, Brownian diffusion, and thermophoresis . Evolution of the aerosol in the heated jet... thermophoresis . As in the isothermal process affecting the particle size distribution, coagulation is the dominant rate process affecting the particle size

  7. Thermal diffusion by Brownian-motion-induced fluid stress.

    PubMed

    Kreft, Jennifer; Chen, Yeng-Long

    2007-08-01

    The Ludwig-Soret effect, the migration of a species due to a temperature gradient, has been extensively studied without a complete picture of its cause emerging. Here we investigate the dynamics of DNA and spherical particles subjected to a thermal gradient using a combination of Brownian dynamics and the lattice Boltzmann method. We observe that the DNA molecules will migrate to colder regions of the channel, an observation also made in experiments. In fact, the thermal diffusion coefficient found agrees quantitatively with the experimentally measured value. We also observe that the thermal diffusion coefficient decreases as the radius of the studied spherical particles increases. Furthermore, we observe that the thermal-fluctuation-fluid-momentum-flux coupling induces a gradient in the stress which leads to thermal migration in both systems.

  8. Electric-field-induced rotation of Brownian metal nanowires.

    PubMed

    Arcenegui, Juan J; García-Sánchez, Pablo; Morgan, Hywel; Ramos, Antonio

    2013-09-01

    We describe the physical mechanism responsible for the rotation of Brownian metal nanowires suspended in an electrolyte exposed to a rotating electric field. The electric field interacts with the induced charge in the electrical double layer at the metal-electrolyte interface, causing rotation due to the torque on the induced dipole and to the induced-charge electro-osmotic flow around the particle. Experiments demonstrate that the primary driving mechanism is the former of these two. Our analysis contrasts with previous work describing the electrical manipulation of metallic particles with electric fields, which neglected the electrical double layer. Theoretical values for the rotation speed are calculated and good agreement with experiments is found.

  9. Mean-squared-displacement statistical test for fractional Brownian motion

    NASA Astrophysics Data System (ADS)

    Sikora, Grzegorz; Burnecki, Krzysztof; Wyłomańska, Agnieszka

    2017-03-01

    Anomalous diffusion in crowded fluids, e.g., in cytoplasm of living cells, is a frequent phenomenon. A common tool by which the anomalous diffusion of a single particle can be classified is the time-averaged mean square displacement (TAMSD). A classical mechanism leading to the anomalous diffusion is the fractional Brownian motion (FBM). A validation of such process for single-particle tracking data is of great interest for experimentalists. In this paper we propose a rigorous statistical test for FBM based on TAMSD. To this end we analyze the distribution of the TAMSD statistic, which is given by the generalized chi-squared distribution. Next, we study the power of the test by means of Monte Carlo simulations. We show that the test is very sensitive for changes of the Hurst parameter. Moreover, it can easily distinguish between two models of subdiffusion: FBM and continuous-time random walk.

  10. Activation volumes of enzymes adsorbed on silica particles.

    PubMed

    Schuabb, Vitor; Czeslik, Claus

    2014-12-30

    The immobilization of enzymes on carrier particles is useful in many biotechnological processes. In this way, enzymes can be separated from the reaction solution by filtering and can be reused in several cycles. On the other hand, there is a series of examples of free enzymes in solution that can be activated by the application of pressure. Thus, a potential loss of enzymatic activity upon immobilization on carrier particles might be compensated by pressure. In this study, we have determined the activation volumes of two enzymes, α-chymotrypsin (α-CT) and horseradish peroxidase (HRP), when they are adsorbed on silica particles and free in solution. The experiments have been carried out using fluorescence assays under pressures up to 2000 bar. In all cases, activation volumes were found to depend on the applied pressure, suggesting different compressions of the enzyme-substrate complex and the transition state. The volume profiles of free and adsorbed HRP are similar. For α-CT, larger activation volumes are found in the adsorbed state. However, up to about 500 bar, the enzymatic reaction of α-CT, which is adsorbed on silica particles, is characterized by a negative activation volume. This observation suggests that application of pressure might indeed be useful to enhance the activity of enzymes on carrier particles.

  11. Particle dynamics in an active medium

    SciTech Connect

    Schaechter, L.

    1997-03-01

    When a point-charge moves in an active medium it can gain energy at the expense of that stored in the medium. The maximum gradient is evaluated and its relation to the energy stored in the medium is established. The dynamics of a distribution of electrons was also examined and it is reported here. {copyright} {ital 1997 American Institute of Physics.}

  12. Self-organized vortices of circling self-propelled particles and curved active flagella

    NASA Astrophysics Data System (ADS)

    Yang, Yingzi; Qiu, Feng; Gompper, Gerhard

    2014-01-01

    Self-propelled pointlike particles move along circular trajectories when their translocation velocity is constant and the angular velocity related to their orientation vector is also constant. We investigate the collective behavior of ensembles of such circle swimmers by Brownian dynamics simulations. If the particles interact via a "velocity-trajectory coordination" rule within neighboring particles, a self-organized vortex pattern emerges. This vortex pattern is characterized by its particle-density correlation function Gρ, the density correlation function Gc of trajectory centers, and an order parameter S representing the degree of the aggregation of the particles. Here we systematically vary the system parameters, such as the particle density and the interaction range, in order to reveal the transition of the system from a light-vortex-dominated to heavy-vortex-dominated state, where vortices contain mainly a single and many self-propelled particles, respectively. We also study a semidilute solution of curved, sinusoidal-beating flagella, as an example of circling self-propelled particles with explicit propulsion mechanism and excluded-volume interactions. Our simulation results are compared with previous experimental results for the vortices in sea-urchin sperm solutions near a wall. The properties of the vortices in simulations and experiments are found to agree quantitatively.

  13. Strongly Accelerated Margination of Active Particles in Blood Flow

    PubMed Central

    Gekle, Stephan

    2016-01-01

    Synthetic nanoparticles and other stiff objects injected into a blood vessel filled with red blood cells are known to marginate toward the vessel walls. By means of hydrodynamic lattice-Boltzmann simulations, we show that active particles can strongly accelerate their margination by moving against the flow direction: particles located initially in the channel center migrate much faster to their final position near the wall than in the nonactive case. We explain our findings by an enhanced rate of collisions between the stiff particles and the deformable red blood cells. Our results imply that a significantly faster margination can be achieved either technically by the application of an external magnetic field (if the particles are magnetic) or biologically by self-propulsion (if the particles are, e.g., swimming bacteria). PMID:26789773

  14. Undergraduate Labs for Biological Physics: Brownian Motion and Optical Trapping

    NASA Astrophysics Data System (ADS)

    Chu, Kelvin; Laughney, A.; Williams, J.

    2006-12-01

    We describe a set of case-study driven labs for an upper-division biological physics course. These labs are motivated by case-studies and consist of inquiry-driven investigations of Brownian motion and optical-trapping experiments. Each lab incorporates two innovative educational techniques to drive the process and application aspects of scientific learning. Case studies are used to encourage students to think independently and apply the scientific method to a novel lab situation. Student input from this case study is then used to decide how to best do the measurement, guide the project and ultimately evaluate the success of the program. Where appropriate, visualization and simulation using VPython is used. Direct visualization of Brownian motion allows students to directly calculate Avogadro's number or the Boltzmann constant. Following case-study driven discussion, students use video microscopy to measure the motion of latex spheres in different viscosity fluids arrive at a good approximation of NA or kB. Optical trapping (laser tweezer) experiments allow students to investigate the consequences of 100-pN forces on small particles. The case study consists of a discussion of the Boltzmann distribution and equipartition theorem followed by a consideration of the shape of the potential. Students can then use video capture to measure the distribution of bead positions to determine the shape and depth of the trap. This work supported by NSF DUE-0536773.

  15. Nonlinear Filtering with Fractional Brownian Motion

    SciTech Connect

    Amirdjanova, A.

    2002-12-19

    Our objective is to study a nonlinear filtering problem for the observation process perturbed by a Fractional Brownian Motion (FBM) with Hurst index 1/2

  16. Brownian dynamics simulation of electrostatically interacting proteins

    NASA Astrophysics Data System (ADS)

    Ermakova, E.; Krushelnitsky, A. G.; Fedotov, V. D.

    Brownian dynamics simulation software has been developed to study the dynamics of proteins as a whole in solution. The proteins were modelled as spheres with point dipoles embedded in the centre of sphere. A set of Brownian dynamics simulations at different values of the dipole moments, protein concentration and translational diffusion coefficient was performed to investigate the influence of interprotein electrostatic interactions on dynamic protein behaviour in solution. It was shown that these interactions led to the slowing down of protein rotation and a complex non-exponential shape of the rotational correlation function. Analysis of the correlation functions was performed within the frame of the model of electrostatic interprotein interactions advanced earlier on the basis of NMR and dielectric spectroscopy data. This model assumes that, due to electrostatic interactions, protein Brownian rotation becomes anisotropic. The lifetime of this anisotropy is controlled mainly by translational diffusion of proteins. Thus, the correlation function can be decomposed into two components corresponding to anisotropic Brownian rotation and an isotropic motion of an external electric field vector produced by the surrounding proteins.

  17. Myosin V is a biological Brownian machine

    PubMed Central

    Fujita, Keisuke; Iwaki, Mitsuhiro

    2014-01-01

    Myosin V is a vesicle transporter that unidirectionally walks along cytoskeletal actin filaments by converting the chemical energy of ATP into mechanical work. Recently, it was found that myosin V force generation is a composition of two processes: a lever-arm swing, which involves a conformational change in the myosin molecule, and a Brownian search-and-catch, which involves a diffusive “search” by the motor domain that is followed by an asymmetric “catch” in the forward actin target such that Brownian motion is rectified. Here we developed a system that combines optical tweezers with DNA nano-material to show that the Brownian search-and-catch mechanism is the energetically dominant process at near stall force, providing 13 kBT of work compared to just 3 kBT by the lever-arm swing. Our result significantly reconsiders the lever-arm swinging model, which assumes the swing dominantly produces work (>10 kBT), and sheds light on the Brownian search-and-catch as a driving process. PMID:27493501

  18. Optofluidics incorporating actively controlled micro- and nano-particles

    PubMed Central

    Kayani, Aminuddin A.; Khoshmanesh, Khashayar; Ward, Stephanie A.; Mitchell, Arnan; Kalantar-zadeh, Kourosh

    2012-01-01

    The advent of optofluidic systems incorporating suspended particles has resulted in the emergence of novel applications. Such systems operate based on the fact that suspended particles can be manipulated using well-appointed active forces, and their motions, locations and local concentrations can be controlled. These forces can be exerted on both individual and clusters of particles. Having the capability to manipulate suspended particles gives users the ability for tuning the physical and, to some extent, the chemical properties of the suspension media, which addresses the needs of various advanced optofluidic systems. Additionally, the incorporation of particles results in the realization of novel optofluidic solutions used for creating optical components and sensing platforms. In this review, we present different types of active forces that are used for particle manipulations and the resulting optofluidic systems incorporating them. These systems include optical components, optofluidic detection and analysis platforms, plasmonics and Raman systems, thermal and energy related systems, and platforms specifically incorporating biological particles. We conclude the review with a discussion of future perspectives, which are expected to further advance this rapidly growing field. PMID:23864925

  19. Brownian motors and stochastic resonance.

    PubMed

    Mateos, José L; Alatriste, Fernando R

    2011-12-01

    We study the transport properties for a walker on a ratchet potential. The walker consists of two particles coupled by a bistable potential that allow the interchange of the order of the particles while moving through a one-dimensional asymmetric periodic ratchet potential. We consider the stochastic dynamics of the walker on a ratchet with an external periodic forcing, in the overdamped case. The coupling of the two particles corresponds to a single effective particle, describing the internal degree of freedom, in a bistable potential. This double-well potential is subjected to both a periodic forcing and noise and therefore is able to provide a realization of the phenomenon of stochastic resonance. The main result is that there is an optimal amount of noise where the amplitude of the periodic response of the system is maximum, a signal of stochastic resonance, and that precisely for this optimal noise, the average velocity of the walker is maximal, implying a strong link between stochastic resonance and the ratchet effect.

  20. ELECTROSTATIC CHARGE ON NANO-PARTICLES ACTIVATES CNS MACROPHAGES (MICROGLIA).

    EPA Science Inventory

    Nanometer size particles carry free radical activity on their surface and can produce oxidative stress (OS)-mediated damage upon impact to target cells. The initiating event of phage cell activation (i.e., the oxidative burst) is unknown, although many proximal events have been i...

  1. Mixed Brownian alignment and Néel rotations in superparamagnetic iron oxide nanoparticle suspensions driven by an ac field

    PubMed Central

    Shah, Saqlain A.; Reeves, Daniel B.; Ferguson, R. Matthew; Weaver, John B.

    2015-01-01

    Superparamagnetic iron oxide nanoparticles with highly nonlinear magnetic behavior are attractive for biomedical applications like magnetic particle imaging and magnetic fluid hyperthermia. Such particles display interesting magnetic properties in alternating magnetic fields and here we document experiments that show differences between the magnetization dynamics of certain particles in frozen and melted states. This effect goes beyond the small temperature difference (ΔT ~ 20 °C) and we show the dynamics to be a mixture of Brownian alignment of the particles and Néel rotation of their moments occurring in liquid particle suspensions. These phenomena can be modeled in a stochastic differential equation approach by postulating log-normal distributions and partial Brownian alignment of an effective anisotropy axis. We emphasize that precise particle-specific characterization through experiments and nonlinear simulations is necessary to predict dynamics in solution and optimize their behavior for emerging biomedical applications including magnetic particle imaging. PMID:26504371

  2. Brownian diffusion of a partially wetted colloid

    NASA Astrophysics Data System (ADS)

    Boniello, Giuseppe; Blanc, Christophe; Fedorenko, Denys; Medfai, Mayssa; Mbarek, Nadia Ben; in, Martin; Gross, Michel; Stocco, Antonio; Nobili, Maurizio

    2015-09-01

    The dynamics of colloidal particles at interfaces between two fluids plays a central role in microrheology, encapsulation, emulsification, biofilm formation, water remediation and the interface-driven assembly of materials. Common intuition corroborated by hydrodynamic theories suggests that such dynamics is governed by a viscous force lower than that observed in the more viscous fluid. Here, we show experimentally that a particle straddling an air/water interface feels a large viscous drag that is unexpectedly larger than that measured in the bulk. We suggest that such a result arises from thermally activated fluctuations of the interface at the solid/air/liquid triple line and their coupling to the particle drag through the fluctuation-dissipation theorem. Our findings should inform approaches for improved control of the kinetically driven assembly of anisotropic particles with a large triple-line-length/particle-size ratio, and help to understand the formation and structure of such arrested materials.

  3. Discontinuous fluidization transition in dense suspensions of actively deforming particles

    NASA Astrophysics Data System (ADS)

    Tjhung, Elsen; Berthier, Ludovic

    Collective dynamics of self-propelled particles at high density have been shown to display a glass-like transition with a critical slowing down of 2 to 4 orders of magnitude. In this talk, we propose a new mechanism of injecting energy or activity via volume fluctuations. We show that the behaviour of actively deforming particles is strikingly different from that of self-propelled particles. In particular, we find a discontinuous non-equilibrium phase transition from a flowing state to an arrested state. Our minimal model might also explain the collective dynamics in epithelial tissues. In particular, without needing self-propulsion or cell-cell adhesion, volume fluctuations of individual cells alone might be sufficient to give rise to an active fluidization and collective dynamics in densely packed tissues.

  4. Suppression of a Brownian noise in a hole-type sensor due to induced-charge electro-osmosis

    NASA Astrophysics Data System (ADS)

    Sugioka, Hideyuki

    2016-03-01

    Noise reduction is essential for a single molecular sensor. Thus, we propose a novel noise reduction mechanism using a hydrodynamic force due to induced-charge electro-osmosis (ICEO) in a hole-type sensor and numerically examine the performance. By the boundary element method that considers both a Brownian motion and an ICEO flow of a polarizable particle, we find that the Brownian noise in a current signal is suppressed significantly in a converging channel because of the ICEO flow around the particle in the presence of an electric field. Further, we propose a simple model that explains a numerically obtained threshold voltage of the suppression of the Brownian noise due to ICEO. We believe that our findings contribute greatly to developments of a single molecular sensor.

  5. Kinetics of small particle activation in supersaturated vapors

    SciTech Connect

    McGraw, R.; Wang, J.

    2010-08-29

    We examine the nucleated (with barrier) activation of perfectly wetting (zero contact angle) particles ranging from bulk size down to one nanometer. Thermodynamic properties of the particles, coated with liquid layers of varying thickness and surrounded by vapor, are analyzed. Nano-size particles are predicted to activate at relative humidity below the Kelvin curve on crossing a nucleation barrier, located at a critical liquid layer thickness such that the total particle size (core + liquid layer) equals the Kelvin radius (Fig. 1). This barrier vanishes precisely as the critical layer thickness approaches the thin layer limit and the Kelvin radius equals the radius of the particle itself. These considerations are similar to those included in Fletcher's theory (Fletcher, 1958) however the present analysis differs in several important respects. Firstly, where Fletcher used the classical prefactor-exponent form for the nucleation rate, requiring separate estimation of the kinetic prefactor, we solve a diffusion-drift equation that is equivalent to including the full Becker-Doering (BD) multi-state kinetics of condensation/evaporation along the growth coordinate. We also determine the mean first passage time (MFPT) for barrier crossing (Wedekind et al., 2007), which is shown to provide a generalization of BD nucleation kinetics especially useful for barrier heights that are considerably lower than those typically encountered in homogeneous vapor-liquid nucleation, and make explicit comparisons between the MFPT and BD kinetic models. Barrier heights for heterogeneous nucleation are computed by a thermo-dynamic area construction introduced recently to model deliquescence and efflorescence of small particles (McGraw and Lewis, 2009). In addition to providing a graphical representation of the activation process that offers new insights, the area construction provides a molecular approach that avoids explicit use of the interfacial tension. Typical barrier profiles for

  6. Diffusion in crowded biological environments: applications of Brownian dynamics

    PubMed Central

    2011-01-01

    Biochemical reactions in living systems occur in complex, heterogeneous media with total concentrations of macromolecules in the range of 50 - 400 mgml. Molecular species occupy a significant fraction of the immersing medium, up to 40% of volume. Such complex and volume-occupied environments are generally termed 'crowded' and/or 'confined'. In crowded conditions non-specific interactions between macromolecules may hinder diffusion - a major process determining metabolism, transport, and signaling. Also, the crowded media can alter, both qualitatively and quantitatively, the reactions in vivo in comparison with their in vitro counterparts. This review focuses on recent developments in particle-based Brownian dynamics algorithms, their applications to model diffusive transport in crowded systems, and their abilities to reproduce and predict the behavior of macromolecules under in vivo conditions. PMID:21595998

  7. Submicrometre particle filtration with a dc activated plasma textile

    NASA Astrophysics Data System (ADS)

    Rasipuram, S. C.; Wu, M.; Kuznetsov, I. A.; Kuznetsov, A. V.; Levine, J. F.; Jasper, W. J.; Saveliev, A. V.

    2014-01-01

    Plasma textiles are novel fabrics incorporating the advantages of cold plasma and low-cost non-woven or woven textile fabrics. In plasma textiles, electrodes are integrated into the fabric, and a corona discharge is activated within and on the surface of the fabric by applying high voltages above 10 kV between the electrodes. When the plasma textile is activated, submicrometre particles approaching the textile are charged by the deposition of ions and electrons produced by the corona, and then collected by the textile material. A stable plasma discharge was experimentally verified on the surface of the textile that was locally smooth but not rigid. A filtration efficiency close to 100% was observed in experiments conducted on salt particles with diameters ranging from 50 to 300 nm. Unlike conventional fibrous filters, the plasma textile provided uniform filtration in this range, without exhibiting a maximum particle penetration size.

  8. Functionally charged nanosize particles differentially activate BV2 microglia.

    EPA Science Inventory

    The effect of particle surface charge on the biological activation of immortalized mouse microglia (BV2) was examined. Nanosize (860-950 nm) spherical polystyrene microparticles (SPM) were coated with carboxyl (COOH-) or dimethyl amino (CH3)2-N- groups to give a net negative or p...

  9. New analytical TEMOM solutions for a class of collision kernels in the theory of Brownian coagulation

    NASA Astrophysics Data System (ADS)

    He, Qing; Shchekin, Alexander K.; Xie, Ming-Liang

    2015-06-01

    New analytical solutions in the theory of the Brownian coagulation with a wide class of collision kernels have been found with using the Taylor-series expansion method of moments (TEMOM). It has been shown at different power exponents in the collision kernels from this class and at arbitrary initial conditions that the relative rates of changing zeroth and second moments of the particle volume distribution have the same long time behavior with power exponent -1, while the dimensionless particle moment related to the geometric standard deviation tends to the constant value which equals 2. The power exponent in the collision kernel in the class studied affects the time of approaching the self-preserving distribution, the smaller the value of the index, the longer time. It has also been shown that constant collision kernel gives for the moments in the Brownian coagulation the results which are very close to that in the continuum regime.

  10. Relativistic Brownian motion: from a microscopic binary collision model to the Langevin equation.

    PubMed

    Dunkel, Jörn; Hänggi, Peter

    2006-11-01

    The Langevin equation (LE) for the one-dimensional relativistic Brownian motion is derived from a microscopic collision model. The model assumes that a heavy pointlike Brownian particle interacts with the lighter heat bath particles via elastic hard-core collisions. First, the commonly known, nonrelativistic LE is deduced from this model, by taking into account the nonrelativistic conservation laws for momentum and kinetic energy. Subsequently, this procedure is generalized to the relativistic case. There, it is found that the relativistic stochastic force is still delta correlated (white noise) but no longer corresponds to a Gaussian white noise process. Explicit results for the friction and momentum-space diffusion coefficients are presented and discussed.

  11. Quantum dynamical framework for Brownian heat engines

    NASA Astrophysics Data System (ADS)

    Agarwal, G. S.; Chaturvedi, S.

    2013-07-01

    We present a self-contained formalism modeled after the Brownian motion of a quantum harmonic oscillator for describing the performance of microscopic Brownian heat engines such as Carnot, Stirling, and Otto engines. Our theory, besides reproducing the standard thermodynamics results in the steady state, enables us to study the role dissipation plays in determining the efficiency of Brownian heat engines under actual laboratory conditions. In particular, we analyze in detail the dynamics associated with decoupling a system in equilibrium with one bath and recoupling it to another bath and obtain exact analytical results, which are shown to have significant ramifications on the efficiencies of engines involving such a step. We also develop a simple yet powerful technique for computing corrections to the steady state results arising from finite operation time and use it to arrive at the thermodynamic complementarity relations for various operating conditions and also to compute the efficiencies of the three engines cited above at maximum power. Some of the methods and exactly solvable models presented here are interesting in their own right and could find useful applications in other contexts as well.

  12. Intrinsic and extrinsic measurement for Brownian motion

    NASA Astrophysics Data System (ADS)

    Castro-Villarreal, Pavel

    2014-05-01

    Based upon the Smoluchowski equation on curved manifolds, three physical observables are considered for Brownian displacement, namely geodesic displacement s, Euclidean displacement δR, and projected displacement δR⊥. The Weingarten-Gauss equations are used to calculate the mean-square Euclidean displacements in the short-time regime. Our findings show that from an extrinsic point of view the geometry of the space affects the Brownian motion in such a way that the particle’s diffusion is decelerated, contrasting with the intrinsic point of view where dynamics is controlled by the sign of the Gaussian curvature (Castro-Villarreal, 2010 J. Stat. Mech. P08006). Furthermore, it is possible to give exact formulas for <δR> and <δR2> on spheres and minimal surfaces, which are valid for all values of time. In the latter case, surprisingly, Brownian motion corresponds to the usual diffusion in flat geometries, albeit minimal surfaces have non-zero Gaussian curvature. Finally, the two-dimensional case is emphasized due to its close relation to surface self-diffusion in fluid membranes.

  13. Dynamics of Brownian motors in deformable medium

    NASA Astrophysics Data System (ADS)

    Woulaché, Rosalie Laure; Kepnang Pebeu, Fabrice Maxime; Kofané, Timoléon C.

    2016-10-01

    The directed transport in a one-dimensional overdamped, Brownian motor subjected to a travelling wave potential with variable shape and exposed to an external bias is studied numerically. We focus our attention on the class of Remoissenet-Peyrard parametrized on-site potentials with slight modification, whose shape can be varied as a function of a parameter s, recovering the sine-Gordon shape as the special case. We demonstrate that in the presence of the travelling wave potential the observed dynamical properties of the Brownian motor which crucially depends on the travelling wave speed, the intensity of the noise and the external load is significantly influenced also by the geometry of the system. In particular, we notice that systems with sharp wells and broad barriers favour the transport under the influence of an applied load. The efficiency of transport of Brownian motors in deformable systems remains equal to 1 (in the absence of an applied load) up to a critical value of the travelling wave speed greater than that of the pure sine-Gordon shape.

  14. Identification of Ice Nucleation Active Sites on Silicate Dust Particles

    NASA Astrophysics Data System (ADS)

    Zolles, Tobias; Burkart, Julia; Häusler, Thomas; Pummer, Bernhard; Hitzenberger, Regina; Grothe, Hinrich

    2015-04-01

    Mineral dusts originating from Earth's crust are known to be important atmospheric ice nuclei. In agreement with earlier studies, feldspar was found as the most active of the tested natural mineral dusts [1-3]. Nevertheless, among those structures K-feldspar showed by far the highest ice nucleation activity. In this study, the reasons for its activity and the difference in the activity of the different feldspars were investigated in closer details. Conclusions are drawn from scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, and oil-immersion freezing experiments. We give a potential explanation of the increased ice nucleation activity of K-feldspar. The ice nucleating sites are very much dependent on the alkali ion present by altering the water structure and the feldspar surface. The higher activity of K-feldspar can be attributed to the presence of potassium ions on the surface and surface bilayer. The alkali-ions have different hydration shells and thus an influence on the ice nucleation activity of feldspar. Chaotropic behavior of Calcium and Sodium ions are lowering the ice nucleation potential of the other feldspars, while kosmotropic Potassium has a neutral or even positive effect. Furthermore we investigated the influence of milling onto the ice nucleation of quartz particles. The ice nucleation activity can be increased by mechanical milling, by introducing more molecular, nucleation active defects to the particle surface. This effect is larger than expected by plane surface increase. [1] Atkinson et al. The Importance of Feldspar for Ice Nucleation by Mineral Dust in Mixed-Phase Clouds. Nature 2013, 498, 355-358. [2] Yakobi-Hancock et al.. Feldspar Minerals as Efficient Deposition Ice Nuclei. Atmos. Chem. Phys. 2013, 13, 11175-11185. [3] Zolles et al. Identification of Ice Nucleation Active Sites on Feldspar Dust Particles. J. Phys. Chem. A 2015 accepted.

  15. Guiding catalytically active particles with chemically patterned surfaces

    NASA Astrophysics Data System (ADS)

    Uspal, William; Popescu, Mihail; Dietrich, Siegfried; Tasinkevych, Mykola

    Catalytically active Janus particles in solution create gradients in the chemical composition of the solution along their surfaces, as well as along any nearby container walls. The former leads to self-phoresis, while the latter gives rise to chemi-osmosis, providing an additional contribution to self-motility. Chemi-osmosis strongly depends on the molecular interactions between the diffusing chemical species and the wall. We show analytically, using an approximate ``point-particle'' approach, that by chemically patterning a planar substrate (e.g., by adsorbing two different materials) one can direct the motion of Janus particles: the induced chemi-osmotic flows can cause particles to either ``dock'' at a chemical step between the two materials, or to follow a chemical stripe. These theoretical predictions are confirmed by full numerical calculations. Generically, docking occurs for particles which tend to move away from their catalytic caps, while stripe-following occurs in the opposite case. Our analysis reveals the physical mechanisms governing this behavior.

  16. Mechanisms of particle-induced activation of alveolar macrophages.

    PubMed

    Gercken, G; Berg, I; Dörger, M; Schlüter, T

    1996-11-01

    Bovine alveolar macrophages were exposed in vitro to quartz dusts, metal-containing dusts or silica particles coated with a single metal oxide. The release of reactive oxygen intermediates (ROI) was measured in short-term incubations (90 min). The secretion of both ROI was markedly enhanced by silica particles coated with vanadium oxide and lowered by copper oxide-coated particles. The particle-induced ROI release was significantly decreased by the inhibition of protein kinase C (PKC) as well as phospholipase A2, suggesting the involvement of both enzymes in the NADPH oxidase activation. Quartz dusts induced a transient increase of free cytosolic calcium ion concentration, slight intracellular acidification, and depolarization of the plasma membrane. In the presence of EGTA or verapamil the rise of [Ca2+]i was diminished, suggesting an influx of extracellular calcium ions. The PKC inhibitor GF 109203X did not inhibit the quartz-induced calcium rise, while both the cytosolic acidification and depolarization were prevented. BSA-coating of the quartz particles abolished the calcium influx as well as the decrease of pHi, and possibly hyperpolarized the plasma membrane.

  17. Performance of Brownian-motion-generated universal portfolios

    NASA Astrophysics Data System (ADS)

    Tan, Choon Peng; Pang, Sook Theng

    2014-06-01

    Investment in a market of m stocks is considered. Generating a universal portfolio using m independent Brownian motions is demonstrated. The asymptotic behaviour of a Brownian-motion-generated universal portfolio is described. The empirical performance of such portfolios on some selected three-stock data sets is analysed. Investment wealth can be increased by varying the drift coefficients or parameters of the Brownian motions.

  18. Ice Nucleation Activity of Various Agricultural Soil Dust Aerosol Particles

    NASA Astrophysics Data System (ADS)

    Schiebel, Thea; Höhler, Kristina; Funk, Roger; Hill, Thomas C. J.; Levin, Ezra J. T.; Nadolny, Jens; Steinke, Isabelle; Suski, Kaitlyn J.; Ullrich, Romy; Wagner, Robert; Weber, Ines; DeMott, Paul J.; Möhler, Ottmar

    2016-04-01

    Recent investigations at the cloud simulation chamber AIDA (Aerosol Interactions and Dynamics in the Atmosphere) suggest that agricultural soil dust has an ice nucleation ability that is enhanced up to a factor of 10 compared to desert dust, especially at temperatures above -26 °C (Steinke et al., in preparation for submission). This enhancement might be caused by the contribution of very ice-active biological particles. In addition, soil dust aerosol particles often contain a considerably higher amount of organic matter compared to desert dust particles. To test agricultural soil dust as a source of ice nucleating particles, especially for ice formation in warm clouds, we conducted a series of laboratory measurements with different soil dust samples to extend the existing AIDA dataset. The AIDA has a volume of 84 m3 and operates under atmospherically relevant conditions over wide ranges of temperature, pressure and humidity. By controlled adiabatic expansions, the ascent of an air parcel in the troposphere can be simulated. As a supplement to the AIDA facility, we use the INKA (Ice Nucleation Instrument of the KArlsruhe Institute of Technology) continuous flow diffusion chamber based on the design by Rogers (1988) to expose the sampled aerosol particles to a continuously increasing saturation ratio by keeping the aerosol temperature constant. For our experiments, soil dust was dry dispersed into the AIDA vessel. First, fast saturation ratio scans at different temperatures were performed with INKA, sampling soil dust aerosol particles directly from the AIDA vessel. Then, we conducted the AIDA expansion experiment starting at a preset temperature. The combination of these two different methods provides a robust data set on the temperature-dependent ice activity of various agriculture soil dust aerosol particles with a special focus on relatively high temperatures. In addition, to extend the data set, we investigated the role of biological and organic matter in more

  19. Phase Segregation of Passive Advective Particles in an Active Medium

    NASA Astrophysics Data System (ADS)

    Das, Amit; Polley, Anirban; Rao, Madan

    2016-02-01

    Localized contractile configurations or asters spontaneously appear and disappear as emergent structures in the collective stochastic dynamics of active polar actomyosin filaments. Passive particles which (un)bind to the active filaments get advected into the asters, forming transient clusters. We study the phase segregation of such passive advective scalars in a medium of dynamic asters, as a function of the aster density and the ratio of the rates of aster remodeling to particle diffusion. The dynamics of coarsening shows a violation of Porod behavior; the growing domains have diffuse interfaces and low interfacial tension. The phase-segregated steady state shows strong macroscopic fluctuations characterized by multiscaling and intermittency, signifying rapid reorganization of macroscopic structures. We expect these unique nonequilibrium features to manifest in the actin-dependent molecular clustering at the cell surface.

  20. Therapeutic activity of modified U1 core spliceosomal particles

    PubMed Central

    Rogalska, Malgorzata Ewa; Tajnik, Mojca; Licastro, Danilo; Bussani, Erica; Camparini, Luca; Mattioli, Chiara; Pagani, Franco

    2016-01-01

    Modified U1 snRNAs bound to intronic sequences downstream of the 5′ splice site correct exon skipping caused by different types of mutations. Here we evaluate the therapeutic activity and structural requirements of these exon-specific U1 snRNA (ExSpeU1) particles. In a severe spinal muscular atrophy, mouse model, ExSpeU1, introduced by germline transgenesis, increases SMN2 exon 7 inclusion, SMN protein production and extends life span. In vitro, RNA mutant analysis and silencing experiments show that while U1A protein is dispensable, the 70K and stem loop IV elements mediate most of the splicing rescue activity through improvement of exon and intron definition. Our findings indicate that precise engineering of the U1 core spliceosomal RNA particle has therapeutic potential in pathologies associated with exon-skipping mutations. PMID:27041075

  1. Materials for Active Engagement in Nuclear and Particle Physics Courses

    NASA Astrophysics Data System (ADS)

    Loats, Jeff; Schwarz, Cindy; Krane, Ken

    2013-04-01

    Physics education researchers have developed a rich variety of research-based instructional strategies that now permeate many introductory courses. Carrying these active-engagement techniques to upper-division courses requires effort and is bolstered by experience. Instructors interested in these methods thus face a large investment of time to start from scratch. This NSF-TUES grant, aims to develop, test and disseminate active-engagement materials for nuclear and particle physics topics. We will present examples of these materials, including: a) Conceptual discussion questions for use with Peer Instruction; b) warm-up questions for use with Just in Time Teaching, c) ``Back of the Envelope'' estimation questions and small-group case studies that will incorporate use of nuclear and particle databases, as well as d) conceptual exam questions.

  2. Paul Langevin's 1908 paper ``On the Theory of Brownian Motion'' [``Sur la théorie du mouvement brownien,'' C. R. Acad. Sci. (Paris) 146, 530-533 (1908)

    NASA Astrophysics Data System (ADS)

    Lemons, Don S.; Gythiel, Anthony

    1997-11-01

    We present a translation of Paul Langevin's landmark paper. In it Langevin successfully applied Newtonian dynamics to a Brownian particle and so invented an analytical approach to random processes which has remained useful to this day.

  3. Measurements of meteor smoke particles during the ECOMA-2006 campaign: 1. Particle detection by active photoionization

    NASA Astrophysics Data System (ADS)

    Rapp, Markus; Strelnikova, Irina

    2009-03-01

    We present a new design of an in situ detector for the study of meteor smoke particles (MSPs) in the middle atmosphere. This detector combines a classical Faraday cup with a xenon-flashlamp for the active photoionization/photodetachment of MSPs and the subsequent detection of corresponding photoelectrons. This instrument was successfully launched in September 2006 from the Andøya Rocket Range in Northern Norway. A comparison of photocurrents measured during this rocket flight and measurements performed in the laboratory proves that observed signatures are truly due to photoelectrons. In addition, the observed altitude cut-off at 60 km (i.e., no signals were observed below this altitude) is fully understood in terms of the mean free path of the photoelectrons in the ambient atmosphere. This interpretation is also proven by a corresponding laboratory experiment. Consideration of all conceivable species which can be ionized by the photons of the xenon-flashlamp demonstrates that only MSPs can quantitatively explain the measured currents below an altitude of 90 km. Above this altitude, measured photocurrents are most likely due to photoionization of nitric oxide. In conclusion, our results demonstrate that the active photoionization and subsequent detection of photoelectrons provides a promising new tool for the study of MSPs in the middle atmosphere. Importantly, this new technique does not rely on the a priori charge of the particles, neither is the accessible particle size range severely limited by aerodynamical effects. Based on the analysis described in this study, the geophysical interpretation of our measurements is presented in the companion paper by Strelnikova, I., et al. [2008. Measurements of meteor smoke particles during the ECOMA-2006 campaign: 2. results. Journal of Atmospheric and Solar-Terrestrial Physics, this issue, doi:10.1016/j.jastp.2008.07.011].

  4. Two Time Distribution in Brownian Directed Percolation

    NASA Astrophysics Data System (ADS)

    Johansson, Kurt

    2017-04-01

    In the zero temperature Brownian semi-discrete directed polymer we study the joint distribution of two last-passage times at positions ordered in the time-like direction. This is the situation when we have the slow de-correlation phenomenon. We compute the limiting joint distribution function in a scaling limit. This limiting distribution is given by an expansion in determinants that is not a Fredholm expansion. A somewhat similar looking formula was derived non-rigorously in a related model by Dotsenko.

  5. A Brownian model for recurrent earthquakes

    USGS Publications Warehouse

    Matthews, M.V.; Ellsworth, W.L.; Reasenberg, P.A.

    2002-01-01

    We construct a probability model for rupture times on a recurrent earthquake source. Adding Brownian perturbations to steady tectonic loading produces a stochastic load-state process. Rupture is assumed to occur when this process reaches a critical-failure threshold. An earthquake relaxes the load state to a characteristic ground level and begins a new failure cycle. The load-state process is a Brownian relaxation oscillator. Intervals between events have a Brownian passage-time distribution that may serve as a temporal model for time-dependent, long-term seismic forecasting. This distribution has the following noteworthy properties: (1) the probability of immediate rerupture is zero; (2) the hazard rate increases steadily from zero at t = 0 to a finite maximum near the mean recurrence time and then decreases asymptotically to a quasi-stationary level, in which the conditional probability of an event becomes time independent; and (3) the quasi-stationary failure rate is greater than, equal to, or less than the mean failure rate because the coefficient of variation is less than, equal to, or greater than 1/???2 ??? 0.707. In addition, the model provides expressions for the hazard rate and probability of rupture on faults for which only a bound can be placed on the time of the last rupture. The Brownian relaxation oscillator provides a connection between observable event times and a formal state variable that reflects the macromechanics of stress and strain accumulation. Analysis of this process reveals that the quasi-stationary distance to failure has a gamma distribution, and residual life has a related exponential distribution. It also enables calculation of "interaction" effects due to external perturbations to the state, such as stress-transfer effects from earthquakes outside the target source. The influence of interaction effects on recurrence times is transient and strongly dependent on when in the loading cycle step pertubations occur. Transient effects may

  6. Quantum Darwinism in Quantum Brownian Motion

    NASA Astrophysics Data System (ADS)

    Blume-Kohout, Robin; Zurek, Wojciech H.

    2008-12-01

    Quantum Darwinism—the redundant encoding of information about a decohering system in its environment—was proposed to reconcile the quantum nature of our Universe with apparent classicality. We report the first study of the dynamics of quantum Darwinism in a realistic model of decoherence, quantum Brownian motion. Prepared in a highly squeezed state—a macroscopic superposition—the system leaves records whose redundancy increases rapidly with initial delocalization. Redundancy appears rapidly (on the decoherence time scale) and persists for a long time.

  7. Quantum Darwinism in quantum Brownian motion.

    PubMed

    Blume-Kohout, Robin; Zurek, Wojciech H

    2008-12-12

    Quantum Darwinism--the redundant encoding of information about a decohering system in its environment--was proposed to reconcile the quantum nature of our Universe with apparent classicality. We report the first study of the dynamics of quantum Darwinism in a realistic model of decoherence, quantum Brownian motion. Prepared in a highly squeezed state--a macroscopic superposition--the system leaves records whose redundancy increases rapidly with initial delocalization. Redundancy appears rapidly (on the decoherence time scale) and persists for a long time.

  8. Stochastic Energetics of a Brownian Motor and Refrigerator Driven by Nonuniform Temperature

    NASA Astrophysics Data System (ADS)

    Benjamin, Ronald

    2014-02-01

    The energetics of a Brownian heat engine and heat pump driven by position dependent temperature, known as the Büttiker-Landauer heat engine and heat pump, is investigated by numerical simulations of the inertial Langevin equation. We identify parameter values for optimal performance of the heat engine and heat pump. Our results qualitatively differ from approaches based on the overdamped model. The behavior of the heat engine and heat pump, in the linear response regime is examined under finite time conditions and we find that the efficiency is lower than that of an endoreversible engine working under the same condition. Finally, we investigate the role of different potential and temperature profiles to enhance the efficiency of the system. Our simulations show that optimizing the potential and temperature profile leads only to a marginal enhancement of the system performance due to the large entropy production via the Brownian particle's kinetic energy.

  9. Brownian motor with competing spatial and temporal asymmetry of potential energy.

    PubMed

    Rozenbaum, V M; Korochkova, T Ye; Chernova, A A; Dekhtyar, M L

    2011-05-01

    A Brownian motor is considered which operates due to asymmetric dichotomic fluctuations of the spatially periodic asymmetric potential energy. As shown, the motion direction and stopping points of this motor are dictated by the competition between the spatial and temporal asymmetry of the potential energy (or solely by temporal asymmetry in the case that the potential energy sign fluctuates). For an asymmetric sawtooth potential, the Brownian-particle average velocity is calculated numerically as a function of certain parameters of the model, whereas the low-frequency and low-energy approximations allow the corresponding analytical relationships to be derived for an arbitrarily shaped potential profile. It is shown that temporal asymmetry is not necessary for stopping point occurrence provided that the potential profile fluctuates not only in amplitude but in shape as well. This inference is illustrated by photoinduced fluctuations of the potential energy for a number of substituted arylpyrene molecules on a substrate with symmetrically distributed charge density.

  10. Fluctuating Hydrodynamics Approach for the Simulation of Nanoparticle Brownian Motion in a Newtonian Fluid.

    PubMed

    Uma, B; Ayyaswamy, P S; Radhakrishnan, R; Eckmann, D M

    2012-06-01

    The Brownian motion of a nanoparticle in an incompressible Newtonian fluid (quiescent or fully developed Poiseuille flow) has been investigated with an arbitrary Lagrangian-Eulerian based finite element method. Results for the motion in a compressible fluid medium are estimated. Thermal fluctuations from the fluid are implemented using a fluctuating hydrodynamics approach. The instantaneous flow around the particle and the particle motion are fully resolved. Carriers of two different sizes with three different densities have been investigated (nearly neutrally buoyant). The numerical results show that (a) the calculated temperature of the nearly neutrally buoyant Brownian particle in a quiescent fluid satisfies the equipartition theorem; (b) the translational and rotational decay of the velocity autocorrelation functions result in algebraic tails, over long time; (c) the translational and rotational mean square displacements of the particle obeys Stokes-Einstein and Stokes-Einstein-Debye relations, respectively. Larger the particle, longer the time taken to attain this limit; and (d) the parallel and perpendicular diffusivities of the particle closer to the wall are consistent with the analytical results, where available.

  11. Langevin Theory of Anomalous Brownian Motion Made Simple

    ERIC Educational Resources Information Center

    Tothova, Jana; Vasziova, Gabriela; Glod, Lukas; Lisy, Vladimir

    2011-01-01

    During the century from the publication of the work by Einstein (1905 "Ann. Phys." 17 549) Brownian motion has become an important paradigm in many fields of modern science. An essential impulse for the development of Brownian motion theory was given by the work of Langevin (1908 "C. R. Acad. Sci.", Paris 146 530), in which he proposed an…

  12. Crystallization and melting of bacteria colonies and Brownian bugs.

    PubMed

    Ramos, Francisco; López, Cristóbal; Hernández-García, Emilio; Muñoz, Miguel A

    2008-02-01

    Motivated by the existence of remarkably ordered cluster arrays of bacteria colonies growing in Petri dishes and related problems, we study the spontaneous emergence of clustering and patterns in a simple nonequilibrium system: the individual-based interacting Brownian bug model. We map this discrete model into a continuous Langevin equation which is the starting point for our extensive numerical analyses. For the two-dimensional case we report on the spontaneous generation of localized clusters of activity as well as a melting-freezing transition from a disordered or isotropic phase to an ordered one characterized by hexagonal patterns. We study in detail the analogies and differences with the well-established Kosterlitz-Thouless-Halperin-Nelson-Young theory of equilibrium melting, as well as with another competing theory. For that, we study translational and orientational correlations and perform a careful defect analysis. We find a nonstandard one-stage, defect-mediated transition whose nature is only partially elucidated.

  13. Emergent ultra-long-range interactions between active particles in hybrid active-inactive systems

    NASA Astrophysics Data System (ADS)

    Steimel, Joshua P.; Aragones, Juan L.; Hu, Helen; Qureshi, Naser

    2016-04-01

    Particle-particle interactions determine the state of a system. Control over the range of such interactions as well as their magnitude has been an active area of research for decades due to the fundamental challenges it poses in science and technology. Very recently, effective interactions between active particles have gathered much attention as they can lead to out-of-equilibrium cooperative states such as flocking. Inspired by nature, where active living cells coexist with lifeless objects and structures, here we study the effective interactions that appear in systems composed of active and passive mixtures of colloids. Our systems are 2D colloidal monolayers composed primarily of passive (inactive) colloids, and a very small fraction of active (spinning) ferromagnetic colloids. We find an emergent ultra-long-range attractive interaction induced by the activity of the spinning particles and mediated by the elasticity of the passive medium. Interestingly, the appearance of such interaction depends on the spinning protocol and has a minimum actuation timescale below which no attraction is observed. Overall, these results clearly show that, in the presence of elastic components, active particles can interact across very long distances without any chemical modification of the environment. Such a mechanism might potentially be important for some biological systems and can be harnessed for newer developments in synthetic active soft materials.

  14. Survival of Near-Critical Branching Brownian Motion

    NASA Astrophysics Data System (ADS)

    Berestycki, Julien; Berestycki, Nathanaël; Schweinsberg, Jason

    2011-06-01

    Consider a system of particles performing branching Brownian motion with negative drift μ= sqrt{2 - \\varepsilon} and killed upon hitting zero. Initially there is one particle at x>0. Kesten (Stoch. Process. Appl. 7:9-47, 1978) showed that the process survives with positive probability if and only if ɛ>0. Here we are interested in the asymptotics as ɛ→0 of the survival probability Q μ ( x). It is proved that if L=π/sqrt{\\varepsilon} then for all x∈ℝ, lim ɛ→0 Q μ ( L+ x)= θ( x)∈(0,1) exists and is a traveling wave solution of the Fisher-KPP equation. Furthermore, we obtain sharp asymptotics of the survival probability when x< L and L- x→∞. The proofs rely on probabilistic methods developed by the authors in (Berestycki et al. in arXiv: 1001.2337, 2010). This completes earlier work by Harris, Harris and Kyprianou (Ann. Inst. Henri Poincaré Probab. Stat. 42:125-145, 2006) and confirms predictions made by Derrida and Simon (Europhys. Lett. 78:60006, 2007), which were obtained using nonrigorous PDE methods.

  15. Transport properties of elastically coupled fractional Brownian motors

    NASA Astrophysics Data System (ADS)

    Lv, Wangyong; Wang, Huiqi; Lin, Lifeng; Wang, Fei; Zhong, Suchuan

    2015-11-01

    Under the background of anomalous diffusion, which is characterized by the sub-linear or super-linear mean-square displacement in time, we proposed the coupled fractional Brownian motors, in which the asymmetrical periodic potential as ratchet is coupled mutually with elastic springs, and the driving source is the external harmonic force and internal thermal fluctuations. The transport mechanism of coupled particles in the overdamped limit is investigated as the function of the temperature of baths, coupling constant and natural length of the spring, the amplitude and frequency of driving force, and the asymmetry of ratchet potential by numerical stimulations. The results indicate that the damping force involving the information of historical velocity leads to the nonlocal memory property and blocks the traditional dissipative motion behaviors, and it even plays a cooperative role of driving force in drift motion of the coupled particles. Thus, we observe various non-monotonic resonance-like behaviors of collective directed transport in the mediums with different diffusion exponents.

  16. A simple microviscometric approach based on Brownian motion tracking

    NASA Astrophysics Data System (ADS)

    Hnyluchová, Zuzana; Bjalončíková, Petra; Karas, Pavel; Mravec, Filip; Halasová, Tereza; Pekař, Miloslav; Kubala, Lukáš; Víteček, Jan

    2015-02-01

    Viscosity—an integral property of a liquid—is traditionally determined by mechanical instruments. The most pronounced disadvantage of such an approach is the requirement of a large sample volume, which poses a serious obstacle, particularly in biology and biophysics when working with limited samples. Scaling down the required volume by means of microviscometry based on tracking the Brownian motion of particles can provide a reasonable alternative. In this paper, we report a simple microviscometric approach which can be conducted with common laboratory equipment. The core of this approach consists in a freely available standalone script to process particle trajectory data based on a Newtonian model. In our study, this setup allowed the sample to be scaled down to 10 μl. The utility of the approach was demonstrated using model solutions of glycerine, hyaluronate, and mouse blood plasma. Therefore, this microviscometric approach based on a newly developed freely available script can be suggested for determination of the viscosity of small biological samples (e.g., body fluids).

  17. Extreme-value statistics of fractional Brownian motion bridges

    NASA Astrophysics Data System (ADS)

    Delorme, Mathieu; Wiese, Kay Jörg

    2016-11-01

    Fractional Brownian motion is a self-affine, non-Markovian, and translationally invariant generalization of Brownian motion, depending on the Hurst exponent H . Here we investigate fractional Brownian motion where both the starting and the end point are zero, commonly referred to as bridge processes. Observables are the time t+ the process is positive, the maximum m it achieves, and the time tmax when this maximum is taken. Using a perturbative expansion around Brownian motion (H =1/2 ), we give the first-order result for the probability distribution of these three variables and the joint distribution of m and tmax. Our analytical results are tested and found to be in excellent agreement, with extensive numerical simulations for both H >1/2 and H <1/2 . This precision is achieved by sampling processes with a free end point and then converting each realization to a bridge process, in generalization to what is usually done for Brownian motion.

  18. Emergence of collective dynamical chirality for achiral active particles.

    PubMed

    Jiang, Huijun; Ding, Huai; Pu, Mingfeng; Hou, Zhonghuai

    2017-01-25

    Emergence of collective dynamical chirality (CDC) at mesoscopic scales plays a key role in many formation processes of chiral structures in nature, which may also provide possible routines for people to fabricate complex chiral architectures. So far, most of the reported CDCs have been found in systems of active objects with individual structure chirality or/and dynamical chirality, and whether CDC can arise from simple and achiral units is still an attractive mystery. Here, we report a spontaneous formation of CDC in a system of both dynamically and structurally achiral particles motivated by active motion of cells adhered onto a substrate. Active motion, confinement and hydrodynamic interaction are found to be the three key factors. Detailed analysis shows that the system can support abundant collective dynamical behaviors, including rotating droplets, rotating bubbles, CDC oscillations, arrays of collective rotations, and interesting transitions such as chirality transition, structure transition and state reentrance.

  19. Mucosal and systemic adjuvant activity of alphavirus replicon particles

    NASA Astrophysics Data System (ADS)

    Thompson, Joseph M.; Whitmore, Alan C.; Konopka, Jennifer L.; Collier, Martha L.; Richmond, Erin M. B.; Davis, Nancy L.; Staats, Herman F.; Johnston, Robert E.

    2006-03-01

    Vaccination represents the most effective control measure in the fight against infectious diseases. Local mucosal immune responses are critical for protection from, and resolution of, infection by numerous mucosal pathogens. Antigen processing across mucosal surfaces is the natural route by which mucosal immunity is generated, as peripheral antigen delivery typically fails to induce mucosal immune responses. However, we demonstrate in this article that mucosal immune responses are evident at multiple mucosal surfaces after parenteral delivery of Venezuelan equine encephalitis virus replicon particles (VRP). Moreover, coinoculation of null VRP (not expressing any transgene) with inactivated influenza virions, or ovalbumin, resulted in a significant increase in antigen-specific systemic IgG and fecal IgA antibodies, compared with antigen alone. Pretreatment of VRP with UV light largely abrogated this adjuvant effect. These results demonstrate that alphavirus replicon particles possess intrinsic systemic and mucosal adjuvant activity and suggest that VRP RNA replication is the trigger for this activity. We feel that these observations and the continued experimentation they stimulate will ultimately define the specific components of an alternative pathway for the induction of mucosal immunity, and if the activity is evident in humans, will enable new possibilities for safe and inexpensive subunit and inactivated vaccines. vaccine vector | Venezuelan equine encephalitis virus | viral immunology | RNA virus

  20. Dependence of Brownian and Néel relaxation times on magnetic field strength

    SciTech Connect

    Deissler, Robert J. Wu, Yong; Martens, Michael A.

    2014-01-15

    Purpose: In magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS) the relaxation time of the magnetization in response to externally applied magnetic fields is determined by the Brownian and Néel relaxation mechanisms. Here the authors investigate the dependence of the relaxation times on the magnetic field strength and the implications for MPI and MPS. Methods: The Fokker–Planck equation with Brownian relaxation and the Fokker–Planck equation with Néel relaxation are solved numerically for a time-varying externally applied magnetic field, including a step-function, a sinusoidally varying, and a linearly ramped magnetic field. For magnetic fields that are applied as a step function, an eigenvalue approach is used to directly calculate both the Brownian and Néel relaxation times for a range of magnetic field strengths. For Néel relaxation, the eigenvalue calculations are compared to Brown's high-barrier approximation formula. Results: The relaxation times due to the Brownian or Néel mechanisms depend on the magnitude of the applied magnetic field. In particular, the Néel relaxation time is sensitive to the magnetic field strength, and varies by many orders of magnitude for nanoparticle properties and magnetic field strengths relevant for MPI and MPS. Therefore, the well-known zero-field relaxation times underestimate the actual relaxation times and, in particular, can underestimate the Néel relaxation time by many orders of magnitude. When only Néel relaxation is present—if the particles are embedded in a solid for instance—the authors found that there can be a strong magnetization response to a sinusoidal driving field, even if the period is much less than the zero-field relaxation time. For a ferrofluid in which both Brownian and Néel relaxation are present, only one relaxation mechanism may dominate depending on the magnetic field strength, the driving frequency (or ramp time), and the phase of the magnetization relative to the

  1. Interrelationships between cellulase activity and cellulose particle morphology

    SciTech Connect

    Olsen, Johan P.; Donohoe, Bryon S.; Borch, Kim; Resch, Michael G.

    2016-06-11

    It is well documented that the enzymatic hydrolysis of cellulose follows a reaction pattern where an initial phase of relatively high activity is followed by a gradual slow-down over the entire course of the reaction. This phenomenon is not readily explained by conventional factors like substrate depletion, product inhibition or enzyme instability. It has been suggested that the underlying reason for the loss of enzyme activity is connected to the heterogeneous structure of cellulose, but so far attempts to establish quantitative measures of such a correlation remain speculative. Here, we have carried out an extensive microscopy study of Avicel particles during extended hydrolysis with Hypocrea jecorina cellobiohydrolase 1 (CBH1) and endoglucanase 1 and 3 (EG1 and EG3) alone and in mixtures. We have used differential interference contrast microscopy and transmission electron microscopy to observe and quantify structural features at um and nm resolution, respectively. We implemented a semi-automatic image analysis protocol, which allowed us to analyze almost 3000 individual micrographs comprising a total of more than 300,000 particles. From this analysis we estimated the temporal development of the accessible surface area throughout the reaction. We found that the number of particles and their size as well as the surface roughness contributed to surface area, and that within the investigated degree of conversion (<30 %) this measure correlated linearly with the rate of reaction. Lastly, based on this observation we argue that cellulose structure, specifically surface area and roughness, plays a major role in the ubiquitous rate loss observed for cellulases.

  2. Ice nucleation active particles are efficiently removed by precipitating clouds.

    PubMed

    Stopelli, Emiliano; Conen, Franz; Morris, Cindy E; Herrmann, Erik; Bukowiecki, Nicolas; Alewell, Christine

    2015-11-10

    Ice nucleation in cold clouds is a decisive step in the formation of rain and snow. Observations and modelling suggest that variations in the concentrations of ice nucleating particles (INPs) affect timing, location and amount of precipitation. A quantitative description of the abundance and variability of INPs is crucial to assess and predict their influence on precipitation. Here we used the hydrological indicator δ(18)O to derive the fraction of water vapour lost from precipitating clouds and correlated it with the abundance of INPs in freshly fallen snow. Results show that the number of INPs active at temperatures ≥ -10 °C (INPs-10) halves for every 10% of vapour lost through precipitation. Particles of similar size (>0.5 μm) halve in number for only every 20% of vapour lost, suggesting effective microphysical processing of INPs during precipitation. We show that INPs active at moderate supercooling are rapidly depleted by precipitating clouds, limiting their impact on subsequent rainfall development in time and space.

  3. Ice nucleation active particles are efficiently removed by precipitating clouds

    PubMed Central

    Stopelli, Emiliano; Conen, Franz; Morris, Cindy E.; Herrmann, Erik; Bukowiecki, Nicolas; Alewell, Christine

    2015-01-01

    Ice nucleation in cold clouds is a decisive step in the formation of rain and snow. Observations and modelling suggest that variations in the concentrations of ice nucleating particles (INPs) affect timing, location and amount of precipitation. A quantitative description of the abundance and variability of INPs is crucial to assess and predict their influence on precipitation. Here we used the hydrological indicator δ18O to derive the fraction of water vapour lost from precipitating clouds and correlated it with the abundance of INPs in freshly fallen snow. Results show that the number of INPs active at temperatures ≥ −10 °C (INPs−10) halves for every 10% of vapour lost through precipitation. Particles of similar size (>0.5 μm) halve in number for only every 20% of vapour lost, suggesting effective microphysical processing of INPs during precipitation. We show that INPs active at moderate supercooling are rapidly depleted by precipitating clouds, limiting their impact on subsequent rainfall development in time and space. PMID:26553559

  4. Directed transport of active particles over asymmetric energy barriers.

    PubMed

    Koumakis, N; Maggi, C; Di Leonardo, R

    2014-08-21

    We theoretically and numerically investigate the transport of active colloids to target regions, delimited by asymmetric energy barriers. We show that it is possible to introduce a generalized effective temperature that is related to the local variance of particle velocities. The stationary probability distributions can be derived from a simple diffusion equation in the presence of an inhomogeneous effective temperature resulting from the action of external force fields. In particular, transition rates over asymmetric energy barriers can be unbalanced by having different effective temperatures over the two slopes of the barrier. By varying the type of active noise, we find that equal values of diffusivity and persistence time may produce strongly varied effective temperatures and thus stationary distributions.

  5. A bound particle coupled to two thermostats

    NASA Astrophysics Data System (ADS)

    Fogedby, Hans C.; Imparato, Alberto

    2011-05-01

    We consider a harmonically bound Brownian particle coupled to two distinct heat reservoirs at different temperatures. We show that the presence of a harmonic trap does not change the large deviation function from the case of a free Brownian particle discussed by Derrida and Brunet and Visco. Likewise, the Gallavotti-Cohen fluctuation theorem related to the entropy production at the heat sources remains in force. We support the analytical results with numerical simulations.

  6. Molecular Motors: Power Strokes Outperform Brownian Ratchets.

    PubMed

    Wagoner, Jason A; Dill, Ken A

    2016-07-07

    Molecular motors convert chemical energy (typically from ATP hydrolysis) to directed motion and mechanical work. Their actions are often described in terms of "Power Stroke" (PS) and "Brownian Ratchet" (BR) mechanisms. Here, we use a transition-state model and stochastic thermodynamics to describe a range of mechanisms ranging from PS to BR. We incorporate this model into Hill's diagrammatic method to develop a comprehensive model of motor processivity that is simple but sufficiently general to capture the full range of behavior observed for molecular motors. We demonstrate that, under all conditions, PS motors are faster, more powerful, and more efficient at constant velocity than BR motors. We show that these differences are very large for simple motors but become inconsequential for complex motors with additional kinetic barrier steps.

  7. Power functional theory for Brownian dynamics.

    PubMed

    Schmidt, Matthias; Brader, Joseph M

    2013-06-07

    Classical density functional theory (DFT) provides an exact variational framework for determining the equilibrium properties of inhomogeneous fluids. We report a generalization of DFT to treat the non-equilibrium dynamics of classical many-body systems subject to Brownian dynamics. Our approach is based upon a dynamical functional consisting of reversible free energy changes and irreversible power dissipation. Minimization of this "free power" functional with respect to the microscopic one-body current yields a closed equation of motion. In the equilibrium limit the theory recovers the standard variational principle of DFT. The adiabatic dynamical density functional theory is obtained when approximating the power dissipation functional by that of an ideal gas. Approximations to the excess (over ideal) power dissipation yield numerically tractable equations of motion beyond the adiabatic approximation, opening the door to the systematic study of systems far from equilibrium.

  8. Parallel Molecular Distributed Detection With Brownian Motion.

    PubMed

    Rogers, Uri; Koh, Min-Sung

    2016-12-01

    This paper explores the in vivo distributed detection of an undesired biological agent's (BAs) biomarkers by a group of biological sized nanomachines in an aqueous medium under drift. The term distributed, indicates that the system information relative to the BAs presence is dispersed across the collection of nanomachines, where each nanomachine possesses limited communication, computation, and movement capabilities. Using Brownian motion with drift, a probabilistic detection and optimal data fusion framework, coined molecular distributed detection, will be introduced that combines theory from both molecular communication and distributed detection. Using the optimal data fusion framework as a guide, simulation indicates that a sub-optimal fusion method exists, allowing for a significant reduction in implementation complexity while retaining BA detection accuracy.

  9. Parallel Molecular Distributed Detection with Brownian Motion.

    PubMed

    Rogers, Uri; Koh, Min-Sung

    2016-12-05

    This paper explores the in vivo distributed detection of an undesired biological agent's (BAs) biomarkers by a group of biological sized nanomachines in an aqueous medium under drift. The term distributed, indicates that the system information relative to the BAs presence is dispersed across the collection of nanomachines, where each nanomachine possesses limited communication, computation, and movement capabilities. Using Brownian motion with drift, a probabilistic detection and optimal data fusion framework, coined molecular distributed detection, will be introduced that combines theory from both molecular communication and distributed detection. Using the optimal data fusion framework as a guide, simulation indicates that a suboptimal fusion method exists, allowing for a significant reduction in implementation complexity while retaining BA detection accuracy.

  10. Stochastic interactions of two Brownian hard spheres in the presence of depletants.

    PubMed

    Karzar-Jeddi, Mehdi; Tuinier, Remco; Taniguchi, Takashi; Fan, Tai-Hsi

    2014-06-07

    A quantitative analysis is presented for the stochastic interactions of a pair of Brownian hard spheres in non-adsorbing polymer solutions. The hard spheres are hypothetically trapped by optical tweezers and allowed for random motion near the trapped positions. The investigation focuses on the long-time correlated Brownian motion. The mobility tensor altered by the polymer depletion effect is computed by the boundary integral method, and the corresponding random displacement is determined by the fluctuation-dissipation theorem. From our computations it follows that the presence of depletion layers around the hard spheres has a significant effect on the hydrodynamic interactions and particle dynamics as compared to pure solvent and uniform polymer solution cases. The probability distribution functions of random walks of the two interacting hard spheres that are trapped clearly shift due to the polymer depletion effect. The results show that the reduction of the viscosity in the depletion layers around the spheres and the entropic force due to the overlapping of depletion zones have a significant influence on the correlated Brownian interactions.

  11. Stochastic interactions of two Brownian hard spheres in the presence of depletants

    SciTech Connect

    Karzar-Jeddi, Mehdi; Fan, Tai-Hsi; Tuinier, Remco; Taniguchi, Takashi

    2014-06-07

    A quantitative analysis is presented for the stochastic interactions of a pair of Brownian hard spheres in non-adsorbing polymer solutions. The hard spheres are hypothetically trapped by optical tweezers and allowed for random motion near the trapped positions. The investigation focuses on the long-time correlated Brownian motion. The mobility tensor altered by the polymer depletion effect is computed by the boundary integral method, and the corresponding random displacement is determined by the fluctuation-dissipation theorem. From our computations it follows that the presence of depletion layers around the hard spheres has a significant effect on the hydrodynamic interactions and particle dynamics as compared to pure solvent and uniform polymer solution cases. The probability distribution functions of random walks of the two interacting hard spheres that are trapped clearly shift due to the polymer depletion effect. The results show that the reduction of the viscosity in the depletion layers around the spheres and the entropic force due to the overlapping of depletion zones have a significant influence on the correlated Brownian interactions.

  12. A quantitative immunosensing technique based on the measurement of nanobeads' Brownian motion.

    PubMed

    Fan, Yu-Jui; Sheen, Horn-Jiunn; Hsu, Chia-Jui; Liu, Cheng-Pang; Lin, Shiming; Wu, Kuang-Chong

    2009-12-15

    A novel bio-sensing technique based on the measurement of nanobeads' Brownian motion using a micro-particle tracking velocimetry (micro-PTV) has been successfully developed to detect antigen-antibody interactions. The rapid interaction between antigens (C-reactive proteins, CRPs) and nanobeads with conjugated antibodies (anti-CRPs) has enabled real-time detection of CRPs to be easily carried out. During the binding process of CRPs to nanobeads, the mean value of the beads' diameters increases so that the Brownian velocity decreases with the increase of time. Moreover, higher CRP concentration leads to a lower Brownian velocity of the nanobeads in the equilibrium state. From the results, the limit of detection 0.1microg/ml was observed and could be further improved by using smaller nanobeads. Moreover, based on kinetic analysis, the average dissociation constant K(D)=(6.48+/-1.43)x10(-7) found by this technique for anti-CRP was shown to be in close agreement with the literature values obtained by dual-polarization interferometry (DPI) and indirect competition enzyme-linked immunosorbent assay (ELISA). This simple sensing method can further be used to detect other bio-molecules and viruses.

  13. Non-Equilibrium Thermodynamic Analysis on the Performance of AN Irreversible Thermally Driven Brownian Motor

    NASA Astrophysics Data System (ADS)

    Gao, Tianfu; Chen, Jincan

    Based on the general model of thermally-driven Brownian motors, an equivalent cycle system is established and the Onsager coefficients and efficiency at the maximum power output of the system are analytically calculated from non-equilibrium thermodynamics. It is found that the Onsager reciprocity relation holds and the Onsager coefficients are affected by the main irreversibilities existing in practical systems. Only when the heat leak and the kinetic energy change of the particle in the system are negligible, can the determinant of the Onsager matrix vanish. It is also found that in the frame of non-equilibrium thermodynamics, the power output and efficiency of an irreversible Brownian motor can be expressed to be the same form as those of an irreversible Carnot heat engine, so the results obtained here are of general significance. Moreover, these results are used to analyze the performance characteristics of a class of thermally-driven Brownian motors so that some important conclusions in literature may be directly derived from the present paper.

  14. Charged particle detectors with active detector surface for partial energy deposition of the charged particles and related methods

    DOEpatents

    Gerts, David W; Bean, Robert S; Metcalf, Richard R

    2013-02-19

    A radiation detector is disclosed. The radiation detector comprises an active detector surface configured to generate charge carriers in response to charged particles associated with incident radiation. The active detector surface is further configured with a sufficient thickness for a partial energy deposition of the charged particles to occur and permit the charged particles to pass through the active detector surface. The radiation detector further comprises a plurality of voltage leads coupled to the active detector surface. The plurality of voltage leads is configured to couple to a voltage source to generate a voltage drop across the active detector surface and to separate the charge carriers into a plurality of electrons and holes for detection. The active detector surface may comprise one or more graphene layers. Timing data between active detector surfaces may be used to determine energy of the incident radiation. Other apparatuses and methods are disclosed herein.

  15. Kramers escape of a self-propelled particle

    NASA Astrophysics Data System (ADS)

    Geiseler, Alexander; Hänggi, Peter; Schmid, Gerhard

    2016-08-01

    We investigate the escape rate of an overdamped, self-propelled spherical Brownian particle on a surface from a metastable potential well. Within a modeling in terms of a 1D constant speed of the particle's active dynamics we consider the associated rate using both numerical and analytical approaches. Regarding the properties of the stationary state in the potential well, two major timescales exist, each governing the translational and the rotational dynamics of the particle, respectively. The particle radius is identified to present the essential quantity in charge of regulating the ratio between those timescales. For very small and very large particle radii, approximate analytic expressions for the particle's escape rate can be derived, which, within their respective range of validity, compare favorably with the precise escape numerics of the underlying full two-dimensional Fokker-Planck description.

  16. Small intestinal transit of spherical particles in the active rat

    SciTech Connect

    Beall, P.T.; Sutton, S.C.; LeRoy-Wayne, S.

    1986-03-05

    Reproducible measurements of small intestine transit for spherical particles of 0.5 ..mu.. to 1 mm diameter, have been accomplished in the conscious rat. A short cannula of polyethylene is surgically implanted into the duodenum and exists through the abdominal wall. After recovery, a bolus of saline containing colored or isotopically labeled particulate material and an internal standard of NaCr/sup 51/O/sub 4/ is introduced with a modified pipette tip that snugly fills the cannula to prevent back flow. The rats eat and drink during the transit period and are maintained on a reversed light cycle so that transit is measured during their physically active period. Glass microspheres of 1mm, 500 ..mu.., and 50 ..mu.. were followed at 30 min, 1 hr, and 2 hr intervals by opening the intestine and photographing 1 cm segments along its length. Polymer beads of 500 ..mu.., 125 ..mu.., and 70 ..mu.. were labeled with /sup 125/I and located by freezing the exteriorized intestine and counting 1 cm segments in a gamma counter. Movement of the fluid bolus as detected by NaCr/sup 51/O/sub 4/ was reproducible with the fluid front moving through 59%, 73%, and 81% of the length at 30 min, 1 hr, and 2 hr. One millimeter to 125 ..mu.. glass and polymer beads moved with the fluid bolus. Evidence for separation of the fluid phase and particles under approx. 100 ..mu.. is accumulating. It is hypothesized that small particles under a critical size may become lodged in the mucus lining of the intestinal wall.

  17. Inhibition of catalase activity in vitro by diesel exhaust particles

    SciTech Connect

    Mori, Yoki; Murakami, Sumika; Sagae, Toshiyuki

    1996-02-09

    The effect of diesel exhaust particles (DEP) on the activity of catalase, an intracellular anti-oxidant, was investigated because H{sub 2}O{sub 2} is a cytotoxic oxidant, and catalase released from alveolar cells is an important antioxidant in the epithelial lining fluid in the lung. DEP inhibited the activity of bovine liver catalase dose-dependently, to 25-30% of its original value. The inhibition of catalase by DEP was observed only in the presence of anions such as Cl{sup {minus}}, Br{sup {minus}}, or thiocyanate. Other anions, such as CH{sub 3}COO{sup {minus}} or SO{sub 4}{sup {minus}}, and cations such as K{sup +}, Na{sup +}, Mg{sup 2+}, or Fe{sup 2+}, did not affect the activity of catalase, even in the presence of DEP extract. Catalase from guinea pig alveolar cells and catalase from red blood cells were also inhibited by DEP extracts, as was catalase from bovine liver. These results suggest that DEP taken up in the lung and located on alveolar spaces might cause cell injury by inhibiting the activity of catalase in epithelial lining fluid, enhancing the toxicity of H{sub 2}O{sub 2} generated from cells in addition to that of O{sub 2}{sup {minus}} generated by the chemical reaction of DEP with oxygen. 10 refs., 6 figs.

  18. Inhibition of catalase activity in vitro by diesel exhaust particles.

    PubMed

    Mori, Y; Murakami, S; Sagae, T; Hayashi, H; Sakata, M; Sagai, M; Kumagai, Y

    1996-02-09

    The effect of diesel exhaust particles (DEP) on the activity of catalase, an intracellular antioxidant, was investigated because H2O2 is a cytotoxic oxidant, and catalase released from alveolar cells is an important antioxidant in the epithelial lining fluid in the lung. DEP inhibited the activity of bovine liver catalase dose-dependently, to 25-30% of its original value. The inhibition of catalase by DEP was observed only in the presence of anions such as Cl-,Br-, or thiocyanate. Other anions, such as CH3COO- or SO4-, and cations such as K+, Na+, Mg2+, or Fe2+, did not affect the activity of catalase, even in the presence of DEP extract. Catalase from guinea pig alveolar cells and catalase from red blood cells were also inhibited by DEP extracts, as was catalase from bovine liver. These results suggest that DEP taken up in the lung and located on alveolar spaces might cause cell injury by inhibiting the activity of catalase in epithelial lining fluid, enhancing the toxicity of H2O2 generated from cells in addition to that of O2- generated by the chemical reaction of DEP with oxygen.

  19. Performance Estimation for Two-Dimensional Brownian Rotary Ratchet Systems

    NASA Astrophysics Data System (ADS)

    Tutu, Hiroki; Horita, Takehiko; Ouchi, Katsuya

    2015-04-01

    Within the context of the Brownian ratchet model, a molecular rotary system that can perform unidirectional rotations induced by linearly polarized ac fields and produce positive work under loads was studied. The model is based on the Langevin equation for a particle in a two-dimensional (2D) three-tooth ratchet potential of threefold symmetry. The performance of the system is characterized by the coercive torque, i.e., the strength of the load competing with the torque induced by the ac driving field, and the energy efficiency in force conversion from the driving field to the torque. We propose a master equation for coarse-grained states, which takes into account the boundary motion between states, and develop a kinetic description to estimate the mean angular momentum (MAM) and powers relevant to the energy balance equation. The framework of analysis incorporates several 2D characteristics and is applicable to a wide class of models of smooth 2D ratchet potential. We confirm that the obtained expressions for MAM, power, and efficiency of the model can enable us to predict qualitative behaviors. We also discuss the usefulness of the torque/power relationship for experimental analyses, and propose a characteristic for 2D ratchet systems.

  20. Controlling enantiomeric populations in fluctuating Brownian monolayers of chiral colloids.

    PubMed

    Rossi, L; Mason, T G

    2015-03-28

    An ideal parallelogram platelet, although achiral in 3D, has an identifiable chirality when confined in a 2D monolayer. We lithographically fabricate microscale parallelogram platelets, disperse them in an aqueous surfactant solution, and allow them to settle towards a lower glass wall. To reduce the thermal-gravitational height, we add polystyrene nanospheres as a depletion agent to create a depletion attraction between the parallelograms and the wall. Surprisingly, by increasing the volume fraction of the depletion agent, we show that a nearly enantiopure monolayer can be created. We explain this by developing a model of 2D monolayer formation based on anisotropic facial attractions; one face of a platelet is more strongly attracted to the wall than the other as a consequence of an anisotropy introduced by the lithographic process. We study enantiopure Brownian systems of parallelograms as a function of particle area fraction and show that oblique chiral crystals form at high densities. By mixing parallelogram platelets printed in opposite senses, we also dictate the chiral ratio in the monolayer over the entire possible range. This approach is not limited to parallelograms and provides a means for tuning the chiral ratio in fluctuating 2D monolayers composed of a wide variety of chiral shapes.

  1. Surface activity of solid particles with extremely rough surfaces.

    PubMed

    Nonomura, Yoshimune; Komura, Shigeyuki

    2008-01-15

    The solid particles are adsorbed at liquid-liquid interfaces and form self-assembled structures when the particles have suitable wettability to both liquids. Here, we show theoretically how the extreme roughness on the particle surface affects their adsorption properties. In our previous work, we discussed the adsorption behavior of the solid particles with microstructured surfaces using the so-called Wenzel model [Y. Nonomura et al., J. Phys. Chem. B 110 (2006) 13124]. In the present study, the wettability and the adsorbed position of the particles with extremely rough surfaces are studied based on the Cassie-Baxter model. We predict that the adsorbed position and the interfacial energy depend on the interfacial tensions between the solid and liquid phases, the radius of the particle, and the fraction of the particle surface area that is in contact with the external liquid phase. Interestingly, the initial state of the system governs whether the particle is adsorbed at the interface or not. The shape of the particle is also an important factor which governs the adsorbed position. The disk-shaped particle and the spherical particle which is partially covered with the extremely rough surface, i.e. Janus particle, are adsorbed at the liquid-liquid interface in an oriented state. We should consider not only the interfacial tensions, but also the surface structure and the particle shape to control the adsorption behavior of the particle.

  2. Self-Consistent Simulation of the Brownian Stage of Dust Growth

    NASA Technical Reports Server (NTRS)

    Kempf, S.; Pfalzner, S.; Henning, Th.

    1996-01-01

    It is a widely accepted view that in proto-planetary accretion disks the collision and following sticking of dust particles embedded in the gas eventually leads to the formation of planetesimals (coagulation). For the smallest dust grains, Brownian motion is assumed to be the dominant source of their relative velocities leading to collisions between these dust grains. As the dust grains grow they eventually couple to the turbulent motion of the gas which then drives the coagulation much more efficiently. Many numerical coagulation simulations have been carried out to calculate the fractal dimension of the aggregates, which determines the duration of the ineffective Brownian stage of growth. Predominantly on-lattice and off-lattice methods were used. However, both methods require simplification of the astrophysical conditions. The aggregates found by those methods had a fractal dimension of approximately 2 which is equivalent to a constant, mass-independent friction time. If this value were valid for the conditions in an accretion disk, this would mean that the coagulation process would finally 'freeze out' and the growth of a planetesimal would be impossible within the lifetime of an accretion disk. In order to investigate whether this fractal dimension is model independent, we simulate self-consistently the Brownian stage of the coagulation by an N-particle code. This method has the advantage that no further assumptions about homogeneity of the dust have to be made. In our model, the dust grains are considered as aggregates built up of spheres. The equation of motion of the dust grains is based on the probability density for the diffusive transport within the gas atmosphere. Because of the very low number density of the dust grains, only 2-body-collisions have to be considered. As the Brownian stage of growth is very inefficient, the system is to be simulated over long periods of time. In order to find close particle pairs of the system which are most likely to

  3. Particle-Cell Contact Enhances Antibacterial Activity of Silver Nanoparticles

    PubMed Central

    Bondarenko, Olesja; Ivask, Angela; Käkinen, Aleksandr; Kurvet, Imbi; Kahru, Anne

    2013-01-01

    Background It is generally accepted that antibacterial properties of Ag nanoparticles (AgNPs) are dictated by their dissolved fraction. However, dissolution-based concept alone does not fully explain the toxic potency of nanoparticulate silver compared to silver ions. Methodology/Principal Findings Herein, we demonstrated that the direct contact between bacterial cell and AgNPs' surface enhanced the toxicity of nanosilver. More specifically, cell-NP contact increased the cellular uptake of particle-associated Ag ions – the single and ultimate cause of toxicity. To prove that, we evaluated the toxicity of three different AgNPs (uncoated, PVP-coated and protein-coated) to six bacterial strains: Gram-negative Escherichia coli, Pseudomonas fluorescens, P. putida and P. aeruginosa and Gram-positive Bacillus subtilis and Staphylococcus aureus. While the toxicity of AgNO3 to these bacteria varied only slightly (the 4-h EC50 ranged from 0.3 to 1.2 mg Ag/l), the 4-h EC50 values of protein-coated AgNPs for various bacterial strains differed remarkably, from 0.35 to 46 mg Ag/l. By systematically comparing the intracellular and extracellular free Ag+ liberated from AgNPs, we demonstrated that not only extracellular dissolution in the bacterial test environment but also additional dissolution taking place at the particle-cell interface played an essential role in antibacterial action of AgNPs. The role of the NP-cell contact in dictating the antibacterial activity of Ag-NPs was additionally proven by the following observations: (i) separation of bacterial cells from AgNPs by particle-impermeable membrane (cut-off 20 kDa, ∼4 nm) significantly reduced the toxicity of AgNPs and (ii) P. aeruginosa cells which tended to attach onto AgNPs, exhibited the highest sensitivity to all forms of nanoparticulate Ag. Conclusions/Significance Our findings provide new insights into the mode of antibacterial action of nanosilver and explain some discrepancies in this field, showing that

  4. Composite generalized Langevin equation for Brownian motion in different hydrodynamic and adhesion regimes.

    PubMed

    Yu, Hsiu-Yu; Eckmann, David M; Ayyaswamy, Portonovo S; Radhakrishnan, Ravi

    2015-05-01

    We present a composite generalized Langevin equation as a unified framework for bridging the hydrodynamic, Brownian, and adhesive spring forces associated with a nanoparticle at different positions from a wall, namely, a bulklike regime, a near-wall regime, and a lubrication regime. The particle velocity autocorrelation function dictates the dynamical interplay between the aforementioned forces, and our proposed methodology successfully captures the well-known hydrodynamic long-time tail with context-dependent scaling exponents and oscillatory behavior due to the binding interaction. Employing the reactive flux formalism, we analyze the effect of hydrodynamic variables on the particle trajectory and characterize the transient kinetics of a particle crossing a predefined milestone. The results suggest that both wall-hydrodynamic interactions and adhesion strength impact the particle kinetics.

  5. Emergent smectic order in simple active particle models

    NASA Astrophysics Data System (ADS)

    Romanczuk, Pawel; Chaté, Hugues; Chen, Leiming; Ngo, Sandrine; Toner, John

    2016-06-01

    Novel ‘smectic-P’ behavior, in which self-propelled particles form rows and move on average along them, occurs generically within the orientationally ordered phase of simple models that we simulate. Both apolar (head-tail symmetric) and polar (head-tail asymmetric) models with aligning and repulsive interactions exhibit slow algebraic decay of smectic order with system size up to some finite length scale, after which faster decay occurs. In the apolar case, this scale is that of an undulation instability of the rows. In the polar case, this instability is absent, but traveling fluctuations disrupt the rows in large systems and motion and smectic order may spontaneously globally rotate. These observations agree with a new hydrodynamic theory which we present here. Variants of our models also exhibit active smectic ‘A’ and ‘C’ order, with motion orthogonal and oblique to the layers respectively.

  6. Interrelationships between cellulase activity and cellulose particle morphology

    DOE PAGES

    Olsen, Johan P.; Donohoe, Bryon S.; Borch, Kim; ...

    2016-06-11

    It is well documented that the enzymatic hydrolysis of cellulose follows a reaction pattern where an initial phase of relatively high activity is followed by a gradual slow-down over the entire course of the reaction. This phenomenon is not readily explained by conventional factors like substrate depletion, product inhibition or enzyme instability. It has been suggested that the underlying reason for the loss of enzyme activity is connected to the heterogeneous structure of cellulose, but so far attempts to establish quantitative measures of such a correlation remain speculative. Here, we have carried out an extensive microscopy study of Avicel particlesmore » during extended hydrolysis with Hypocrea jecorina cellobiohydrolase 1 (CBH1) and endoglucanase 1 and 3 (EG1 and EG3) alone and in mixtures. We have used differential interference contrast microscopy and transmission electron microscopy to observe and quantify structural features at um and nm resolution, respectively. We implemented a semi-automatic image analysis protocol, which allowed us to analyze almost 3000 individual micrographs comprising a total of more than 300,000 particles. From this analysis we estimated the temporal development of the accessible surface area throughout the reaction. We found that the number of particles and their size as well as the surface roughness contributed to surface area, and that within the investigated degree of conversion (<30 %) this measure correlated linearly with the rate of reaction. Lastly, based on this observation we argue that cellulose structure, specifically surface area and roughness, plays a major role in the ubiquitous rate loss observed for cellulases.« less

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

    NASA Astrophysics Data System (ADS)

    Dubina, Sean Hyun; Wedgewood, Lewis Edward

    2016-07-01

    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 by 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.

  8. Hygroscopicity of aerosol particles and CCN activity of nearly hydrophobic particles in the urban atmosphere over Japan during summer

    NASA Astrophysics Data System (ADS)

    Ogawa, Shuhei; Setoguchi, Yoshitaka; Kawana, Kaori; Nakayama, Tomoki; Ikeda, Yuka; Sawada, Yuuki; Matsumi, Yutaka; Mochida, Michihiro

    2016-06-01

    We investigated the hygroscopicity of 150 nm particles and the number-size distributions and the cloud condensation nuclei (CCN) activity of nearly hydrophobic particles in aerosols over Nagoya, Japan, during summer. We analyzed the correlations between the number concentrations of particles in specific hygroscopic growth factor (g) ranges and the mass concentrations of chemical components. This analysis suggests the association of nearly hydrophobic particles with hydrocarbon-like organic aerosol, elemental carbon and semivolatile oxygenated organic aerosol (SV-OOA), that of less hygroscopic particles with SV-OOA and nitrate and that of more hygroscopic particles with low-volatile oxygenated organic aerosol (LV-OOA) and sulfate. The hygroscopicity parameter (κ) of organics was derived based on the g distributions and chemical composition of 150 nm particles. The κ of the organics correlated positively with the fraction of the total organic mass spectral signal at m/z 44 and the volume fraction of the LV-OOA to the organics, indicating that organics with highly oxygenated structures including carboxylic acid groups contribute to the water uptake. The number-size distributions of the nearly hydrophobic particles with g around 1.0 and 1.1 correlated with the mass concentrations of chemical components. The results show that the chemical composition of the particles with g around 1.0 was different between the Aitken mode and the accumulation mode size ranges. An analysis for a parameter Fmax of the curves fitted to the CCN efficiency spectra of the particles with g around 1.0 suggests that the coating by organics associated with SV-OOA elevated the CCN activity of these particles.

  9. Brownian motion of massive black hole binaries and the final parsec problem

    NASA Astrophysics Data System (ADS)

    Bortolas, E.; Gualandris, A.; Dotti, M.; Spera, M.; Mapelli, M.

    2016-09-01

    Massive black hole binaries (BHBs) are expected to be one of the most powerful sources of gravitational waves in the frequency range of the pulsar timing array and of forthcoming space-borne detectors. They are believed to form in the final stages of galaxy mergers, and then harden by slingshot ejections of passing stars. However, evolution via the slingshot mechanism may be ineffective if the reservoir of interacting stars is not readily replenished, and the binary shrinking may come to a halt at roughly a parsec separation. Recent simulations suggest that the departure from spherical symmetry, naturally produced in merger remnants, leads to efficient loss cone refilling, preventing the binary from stalling. However, current N-body simulations able to accurately follow the evolution of BHBs are limited to very modest particle numbers. Brownian motion may artificially enhance the loss cone refilling rate in low-N simulations, where the binary encounters a larger population of stars due its random motion. Here we study the significance of Brownian motion of BHBs in merger remnants in the context of the final parsec problem. We simulate mergers with various particle numbers (from 8k to 1M) and with several density profiles. Moreover, we compare simulations where the BHB is fixed at the centre of the merger remnant with simulations where the BHB is free to random walk. We find that Brownian motion does not significantly affect the evolution of BHBs in simulations with particle numbers in excess of one million, and that the hardening measured in merger simulations is due to collisionless loss cone refilling.

  10. Continuum Level Results from Particle Simulations of Active Suspensions

    NASA Astrophysics Data System (ADS)

    Delmotte, Blaise; Climent, Eric; Plouraboue, Franck; Keaveny, Eric

    2014-11-01

    Accurately simulating active suspensions on the lab scale is a technical challenge. It requires considering large numbers of interacting swimmers with well described hydrodynamics in order to obtain representative and reliable statistics of suspension properties. We have developed a computationally scalable model based on an extension of the Force Coupling Method (FCM) to active particles. This tool can handle the many-body hydrodynamic interactions between O (105) swimmers while also accounting for finite-size effects, steady or time-dependent strokes, or variable swimmer aspect ratio. Results from our simulations of steady-stroke microswimmer suspensions coincide with those given by continuum models, but, in certain cases, we observe collective dynamics that these models do not predict. We provide robust statistics of resulting distributions and accurately characterize the growth rates of these instabilities. In addition, we explore the effect of the time-dependent stroke on the suspension properties, comparing with those from the steady-stroke simulations. Authors acknowledge the ANR project Motimo for funding and the Calmip computing centre for technical support.

  11. Underdamped scaled Brownian motion: (non-)existence of the overdamped limit in anomalous diffusion

    PubMed Central

    Bodrova, Anna S.; Chechkin, Aleksei V.; Cherstvy, Andrey G.; Safdari, Hadiseh; Sokolov, Igor M.; Metzler, Ralf

    2016-01-01

    It is quite generally assumed that the overdamped Langevin equation provides a quantitative description of the dynamics of a classical Brownian particle in the long time limit. We establish and investigate a paradigm anomalous diffusion process governed by an underdamped Langevin equation with an explicit time dependence of the system temperature and thus the diffusion and damping coefficients. We show that for this underdamped scaled Brownian motion (UDSBM) the overdamped limit fails to describe the long time behaviour of the system and may practically even not exist at all for a certain range of the parameter values. Thus persistent inertial effects play a non-negligible role even at significantly long times. From this study a general questions on the applicability of the overdamped limit to describe the long time motion of an anomalously diffusing particle arises, with profound consequences for the relevance of overdamped anomalous diffusion models. We elucidate our results in view of analytical and simulations results for the anomalous diffusion of particles in free cooling granular gases. PMID:27462008

  12. Comparisons of characteristic timescales and approximate models for Brownian magnetic nanoparticle rotations

    SciTech Connect

    Reeves, Daniel B. Weaver, John B.

    2015-06-21

    Magnetic nanoparticles are promising tools for a host of therapeutic and diagnostic medical applications. The dynamics of rotating magnetic nanoparticles in applied magnetic fields depend strongly on the type and strength of the field applied. There are two possible rotation mechanisms and the decision for the dominant mechanism is often made by comparing the equilibrium relaxation times. This is a problem when particles are driven with high-amplitude fields because they are not necessarily at equilibrium at all. Instead, it is more appropriate to consider the “characteristic timescales” that arise in various applied fields. Approximate forms for the characteristic time of Brownian particle rotations do exist and we show agreement between several analytical and phenomenological-fit models to simulated data from a stochastic Langevin equation approach. We also compare several approximate models with solutions of the Fokker-Planck equation to determine their range of validity for general fields and relaxation times. The effective field model is an excellent approximation, while the linear response solution is only useful for very low fields and frequencies for realistic Brownian particle rotations.

  13. Comparisons of characteristic timescales and approximate models for Brownian magnetic nanoparticle rotations

    PubMed Central

    Reeves, Daniel B.; Weaver, John B.

    2015-01-01

    Magnetic nanoparticles are promising tools for a host of therapeutic and diagnostic medical applications. The dynamics of rotating magnetic nanoparticles in applied magnetic fields depend strongly on the type and strength of the field applied. There are two possible rotation mechanisms and the decision for the dominant mechanism is often made by comparing the equilibrium relaxation times. This is a problem when particles are driven with high-amplitude fields because they are not necessarily at equilibrium at all. Instead, it is more appropriate to consider the “characteristic timescales” that arise in various applied fields. Approximate forms for the characteristic time of Brownian particle rotations do exist and we show agreement between several analytical and phenomenological-fit models to simulated data from a stochastic Langevin equation approach. We also compare several approximate models with solutions of the Fokker-Planck equation to determine their range of validity for general fields and relaxation times. The effective field model is an excellent approximation, while the linear response solution is only useful for very low fields and frequencies for realistic Brownian particle rotations. PMID:26130846

  14. The moment method for boundary layer problems in Brownian motion theory

    SciTech Connect

    Widder, M.E.; Titulaer, U.M. )

    1989-08-01

    The authors apply Grad's moment method, with Hermite moments and Marshak-type boundary conditions, to several boundary layer problems for the Klein-Kramers equation, the kinetic equation for noninteracting Brownian particles, and study its convergence properties as the number of moments is increased. The errors in various quantities of physical interest decrease asymptotically as inverse powers of this number; the exponent is roughly three times as large as in an earlier variational method, based on an expansion in the exact boundary layer eigenfunctions. For the case of a fully absorbing wall (the Milne problem) they obtain full agreement with the recent exact solution of Marshall and Watson; the relevant slip coefficient, the Milne length, is reproduced with an accuracy better than 10{sup {minus}6}. They also consider partially absorbing walls, with specular or diffuse reflection of nonabsorbed particles. In the latter case they allow for a temperature difference between the wall and the medium in which the particles move. There is no a priori reason why their method should work only for Brownian dynamics; one may hope to extend it to a broad class of linear transport equations. As a first test, they looked at the Milne problem for the BGK equation. In spite of the completely different analytic structure of the boundary layer eigenfunctions, the agreement with the exact solution is almost as good as for the Klein-Kramers equation.

  15. Cost and Precision of Brownian Clocks

    NASA Astrophysics Data System (ADS)

    Barato, Andre C.; Seifert, Udo

    2016-10-01

    Brownian clocks are biomolecular networks that can count time. A paradigmatic example are proteins that go through a cycle, thus regulating some oscillatory behavior in a living system. Typically, such a cycle requires free energy often provided by ATP hydrolysis. We investigate the relation between the precision of such a clock and its thermodynamic costs. For clocks driven by a constant thermodynamic force, a given precision requires a minimal cost that diverges as the uncertainty of the clock vanishes. In marked contrast, we show that a clock driven by a periodic variation of an external protocol can achieve arbitrary precision at arbitrarily low cost. This result constitutes a fundamental difference between processes driven by a fixed thermodynamic force and those driven periodically. As a main technical tool, we map a periodically driven system with a deterministic protocol to one subject to an external protocol that changes in stochastic time intervals, which simplifies calculations significantly. In the nonequilibrium steady state of the resulting bipartite Markov process, the uncertainty of the clock can be deduced from the calculable dispersion of a corresponding current.

  16. Brownian dynamics simulation of DNA condensation.

    PubMed Central

    Sottas, P E; Larquet, E; Stasiak, A; Dubochet, J

    1999-01-01

    DNA condensation observed in vitro with the addition of polyvalent counterions is due to intermolecular attractive forces. We introduce a quantitative model of these forces in a Brownian dynamics simulation in addition to a standard mean-field Poisson-Boltzmann repulsion. The comparison of a theoretical value of the effective diameter calculated from the second virial coefficient in cylindrical geometry with some experimental results allows a quantitative evaluation of the one-parameter attractive potential. We show afterward that with a sufficient concentration of divalent salt (typically approximately 20 mM MgCl(2)), supercoiled DNA adopts a collapsed form where opposing segments of interwound regions present zones of lateral contact. However, under the same conditions the same plasmid without torsional stress does not collapse. The condensed molecules present coexisting open and collapsed plectonemic regions. Furthermore, simulations show that circular DNA in 50% methanol solutions with 20 mM MgCl(2) aggregates without the requirement of torsional energy. This confirms known experimental results. Finally, a simulated DNA molecule confined in a box of variable size also presents some local collapsed zones in 20 mM MgCl(2) above a critical concentration of the DNA. Conformational entropy reduction obtained either by supercoiling or by confinement seems thus to play a crucial role in all forms of condensation of DNA. PMID:10512808

  17. Microstructure from simulated Brownian suspension flows at large shear rate

    NASA Astrophysics Data System (ADS)

    Morris, Jeffrey F.; Katyal, Bhavana

    2002-06-01

    Pair microstructure of concentrated Brownian suspensions in simple-shear flow is studied by sampling of configurations from dynamic simulations by the Stokesian Dynamics technique. Simulated motions are three dimensional with periodic boundary conditions to mimic an infinitely extended suspension. Hydrodynamic interactions through Newtonian fluid and Brownian motion are the only physical influences upon the motion of the monodisperse hard-sphere particles. The dimensionless parameters characterizing the suspension are the particle volume fraction and Péclet number, defined, respectively, as φ=(4π/3)na3 with n the number density and a the sphere radius, and Pe=6πηγ˙a3/kT with η the fluid viscosity, γ˙ the shear rate, and kT the thermal energy. The majority of the results reported are from simulations at Pe=1000; results of simulations at Pe=1, 25, and 100 are also reported for φ=0.3 and φ=0.45. The pair structure is characterized by the pair distribution function, g(r)=P1|1(r)/n, where P1|1(r) is the conditional probability of finding a pair at a separation vector r. The structure under strong shearing exhibits an accumulation of pair probability at contact, and angular distortion (from spherical symmetry at Pe=0), with both effects increasing with Pe. Flow simulations were performed at Pe=1000 for eight volume fractions in the range 0.2⩽φ⩽0.585. For φ=0.2-0.3, the pair structure at contact, g(|r|=2)≡g(2), is found to exhibit a single region of strong correlation, g(2)≫1, at points around the axis of compression, with a particle-deficient wake in the extensional zones. A qualitative change in microstructure is observed between φ=0.3 and φ=0.37. For φ⩾0.37, the maximum g(2) lies at points in the shear plane nearly on the x axis of the bulk simple shear flow Ux=γ˙y, while at smaller φ, the maximum g(2) lies near the compressional axis; long-range string ordering is not observed. For φ=0.3 and φ=0.45, g(2)˜Pe0.7 for 1⩽Pe⩽1000, a

  18. Titanium particles that have undergone phagocytosis by macrophages lose the ability to activate other macrophages.

    PubMed

    Xing, Zhiqing; Schwab, Luciana P; Alley, Carie F; Hasty, Karen A; Smith, Richard A

    2008-04-01

    Titanium particles derived from the wear of the orthopaedic implant surfaces can activate macrophages to secrete cytokines and stimulate osteoclastic bone resorption, causing osteolysis around orthopaedic implants. However, what happens to the titanium particles after being phagocytosed by macrophages is not known. We prepared titanium particles (as received, clean, and LPS-coated), and exposed them to macrophages in culture. Free particles were washed away after 24 h and the intracellular particles were kept in culture for additional 48 h until being harvested by lysing the cells. Particles that had been cell treated or noncell treated were examined by scanning electronic microscopy to analyze the shape, size, and concentration of the particles. The cell treated and noncell treated particles were exposed to macrophages in culture with a particle to cell ratio of 300:1. After 18 h, the levels of TNF-alpha in culture medium and the viability of the cells were examined. Clean particles did not stimulate TNF-alpha secretion by macrophages, while LPS-coated particles dramatically increased that response. Phagocytosis by macrophages did not change the shape and size of the particles, but depleted the ability of the particles to stimulate TNF-alpha secretion by macrophages. This indicates that macrophages are capable of rendering titanium particles inactive without degrading the particles, possibly by altering the surface chemistry of the particles.

  19. Large Deviations for the Branching Brownian Motion in Presence of Selection or Coalescence

    NASA Astrophysics Data System (ADS)

    Derrida, Bernard; Shi, Zhan

    2016-06-01

    The large deviation function has been known for a long time in the literature for the displacement of the rightmost particle in a branching random walk (BRW), or in a branching Brownian motion (BBM). More recently a number of generalizations of the BBM and of the BRW have been considered where selection or coalescence mechanisms tend to limit the exponential growth of the number of particles. Here we try to estimate the large deviation function of the position of the rightmost particle for several such generalizations: the L-BBM, the N-BBM, and the coalescing branching random walk (CBRW) which is closely related to the noisy FKPP equation. Our approach allows us to obtain only upper bounds on these large deviation functions. One noticeable feature of our results is their non analytic dependence on the parameters (such as the coalescence rate in the CBRW).

  20. Transport coefficients for a confined Brownian ratchet operating between two heat reservoirs

    NASA Astrophysics Data System (ADS)

    Ryabov, A.; Holubec, V.; Yaghoubi, M. H.; Varga, M.; Foulaadvand, M. E.; Chvosta, P.

    2016-09-01

    We discuss two-dimensional diffusion of a Brownian particle confined to a periodic asymmetric channel with soft walls modeled by a parabolic potential. In the channel, the particle experiences different thermal noise intensities, or temperatures, in the transversal and longitudinal directions. The model is inspired by the famous Feynman’s ratchet and pawl. Although the standard Fick-Jacobs approximation predicts correctly the effective diffusion coefficient, it fails to capture the ratchet effect. Deriving a correction, which breaks the local detailed balance with the transversal noise source, we obtain a correct mean velocity of the particle and a stationary probability density in the potential unit cell. The derived results are exact for small channel width. Yet, we check by exact numerical calculation that they qualitatively describe the ratchet effect observed for an arbitrary width of the channel.

  1. Quantum harmonic Brownian motion in a general environment: A modified phase-space approach

    SciTech Connect

    Yeh, L. |

    1993-06-23

    After extensive investigations over three decades, the linear-coupling model and its equivalents have become the standard microscopic models for quantum harmonic Brownian motion, in which a harmonically bound Brownian particle is coupled to a quantum dissipative heat bath of general type modeled by infinitely many harmonic oscillators. The dynamics of these models have been studied by many authors using the quantum Langevin equation, the path-integral approach, quasi-probability distribution functions (e.g., the Wigner function), etc. However, the quantum Langevin equation is only applicable to some special problems, while other approaches all involve complicated calculations due to the inevitable reduction (i.e., contraction) operation for ignoring/eliminating the degrees of freedom of the heat bath. In this dissertation, the author proposes an improved methodology via a modified phase-space approach which employs the characteristic function (the symplectic Fourier transform of the Wigner function) as the representative of the density operator. This representative is claimed to be the most natural one for performing the reduction, not only because of its simplicity but also because of its manifestation of geometric meaning. Accordingly, it is particularly convenient for studying the time evolution of the Brownian particle with an arbitrary initial state. The power of this characteristic function is illuminated through a detailed study of several physically interesting problems, including the environment-induced damping of quantum interference, the exact quantum Fokker-Planck equations, and the relaxation of non-factorizable initial states. All derivations and calculations axe shown to be much simplified in comparison with other approaches. In addition to dynamical problems, a novel derivation of the fluctuation-dissipation theorem which is valid for all quantum linear systems is presented.

  2. (Bio)hybrid materials based on optically active particles

    NASA Astrophysics Data System (ADS)

    Reitzig, Manuela; Härtling, Thomas; Opitz, Jörg

    2014-03-01

    In this contribution we provide an overview of current investigations on optically active particles (nanodiamonds, upconversion phospors) for biohybrid and sensing applications. Due to their outstanding properties nanodiamonds gain attention in various application elds such as microelectronics, optical monitoring, medicine, and biotechnology. Beyond the typical diamond properties such as high thermal conductivity and extreme hardness, the carbon surface and its various functional groups enable diverse chemical and biological surface functionalization. At Fraunhofer IKTS-MD we develop a customization of material surfaces via integration of chemically modi ed nanodiamonds at variable surfaces, e.g bone implants and pipelines. For the rst purpose, nanodiamonds are covalently modi ed at their surface with amino or phosphate functionalities that are known to increase adhesion to bone or titanium alloys. The second type of surface is approached via mechanical implementation into coatings. Besides nanodiamonds, we also investigate the properties of upconversion phosphors. In our contribution we show how upconversion phosphors are used to verify sterilization processes via a change of optical properties due to sterilizing electron beam exposure.

  3. Activating Molecules, Ions, and Solid Particles with Acoustic Cavitation

    PubMed Central

    Pflieger, Rachel; Chave, Tony; Virot, Matthieu; Nikitenko, Sergey I.

    2014-01-01

    The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophotoluminescence dominates in diluted solutions, and collisional excitation contributes at higher uranium concentration. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble, but then diffuse into the liquid phase and react with solution precursors to form a variety of products. For instance, the sonochemical reduction of Pt(IV) in pure water provides an innovative synthetic route for monodispersed nanoparticles of metallic platinum without any templates or capping agents. Many studies reveal the advantages of ultrasound to activate the divided solids. In general, the mechanical effects of ultrasound strongly contribute in heterogeneous systems in addition to chemical effects. In particular, the sonolysis of PuO2 powder in pure water yields stable colloids of plutonium due to both effects. PMID:24747272

  4. Activating molecules, ions, and solid particles with acoustic cavitation.

    PubMed

    Pflieger, Rachel; Chave, Tony; Virot, Matthieu; Nikitenko, Sergey I

    2014-04-11

    The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophotoluminescence dominates in diluted solutions, and collisional excitation contributes at higher uranium concentration. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble, but then diffuse into the liquid phase and react with solution precursors to form a variety of products. For instance, the sonochemical reduction of Pt(IV) in pure water provides an innovative synthetic route for monodispersed nanoparticles of metallic platinum without any templates or capping agents. Many studies reveal the advantages of ultrasound to activate the divided solids. In general, the mechanical effects of ultrasound strongly contribute in heterogeneous systems in addition to chemical effects. In particular, the sonolysis of PuO2 powder in pure water yields stable colloids of plutonium due to both effects.

  5. Shape and Displacement Fluctuations in Soft Vesicles Filled by Active Particles

    PubMed Central

    Paoluzzi, Matteo; Di Leonardo, Roberto; Marchetti, M. Cristina; Angelani, Luca

    2016-01-01

    We investigate numerically the dynamics of shape and displacement fluctuations of two-dimensional flexible vesicles filled with active particles. At low concentration most of the active particles accumulate at the boundary of the vesicle where positive particle number fluctuations are amplified by trapping, leading to the formation of pinched spots of high density, curvature and pressure. At high concentration the active particles cover the vesicle boundary almost uniformly, resulting in fairly homogeneous pressure and curvature, and nearly circular vesicle shape. The change between polarized and spherical shapes is driven by the number of active particles. The center-of-mass of the vesicle performs a persistent random walk with a long time diffusivity that is strongly enhanced for elongated active particles due to orientational correlations in their direction of propulsive motion. In our model shape-shifting induces directional sensing and the cell spontaneously migrate along the polarization direction. PMID:27678166

  6. Instantaneous ballistic velocity of suspended Brownian nanocrystals measured by upconversion nanothermometry

    NASA Astrophysics Data System (ADS)

    Brites, Carlos D. S.; Xie, Xiaoji; Debasu, Mengistie L.; Qin, Xian; Chen, Runfeng; Huang, Wei; Rocha, João; Liu, Xiaogang; Carlos, Luís D.

    2016-10-01

    Brownian motion is one of the most fascinating phenomena in nature. Its conceptual implications have a profound impact in almost every field of science and even economics, from dissipative processes in thermodynamic systems, gene therapy in biomedical research, artificial motors and galaxy formation to the behaviour of stock prices. However, despite extensive experimental investigations, the basic microscopic knowledge of prototypical systems such as colloidal particles in a fluid is still far from being complete. This is particularly the case for the measurement of the particles' instantaneous velocities, elusive due to the rapid random movements on extremely short timescales. Here, we report the measurement of the instantaneous ballistic velocity of Brownian nanocrystals suspended in both aqueous and organic solvents. To achieve this, we develop a technique based on upconversion nanothermometry. We find that the population of excited electronic states in NaYF4:Yb/Er nanocrystals at thermal equilibrium can be used for temperature mapping of the nanofluid with great thermal sensitivity (1.15% K-1 at 296 K) and a high spatial resolution (<1 μm). A distinct correlation between the heat flux in the nanofluid and the temporal evolution of Er3+ emission allows us to measure the instantaneous velocity of nanocrystals with different sizes and shapes.

  7. Robustness of multidimensional Brownian ratchets as directed transport mechanisms

    NASA Astrophysics Data System (ADS)

    González-Candela, Ernesto; Romero-Rochín, Víctor; Del Río, Fernando

    2011-08-01

    Brownian ratchets have recently been considered as models to describe the ability of certain systems to locate very specific states in multidimensional configuration spaces. This directional process has particularly been proposed as an alternative explanation for the protein folding problem, in which the polypeptide is driven toward the native state by a multidimensional Brownian ratchet. Recognizing the relevance of robustness in biological systems, in this work we analyze such a property of Brownian ratchets by pushing to the limits all the properties considered essential to produce directed transport. Based on the results presented here, we can state that Brownian ratchets are able to deliver current and locate funnel structures under a wide range of conditions. As a result, they represent a simple model that solves the Levinthal's paradox with great robustness and flexibility and without requiring any ad hoc biased transition probability. The behavior of Brownian ratchets shown in this article considerably enhances the plausibility of the model for at least part of the structural mechanism behind protein folding process.

  8. Elasticity-induced force reversal between active spinning particles in dense passive media

    NASA Astrophysics Data System (ADS)

    Aragones, J. L.; Steimel, J. P.; Alexander-Katz, A.

    2016-04-01

    The self-organization of active particles is governed by their dynamic effective interactions. Such interactions are controlled by the medium in which such active agents reside. Here we study the interactions between active agents in a dense non-active medium. Our system consists of actuated, spinning, active particles embedded in a dense monolayer of passive, or non-active, particles. We demonstrate that the presence of the passive monolayer alters markedly the properties of the system and results in a reversal of the forces between active spinning particles from repulsive to attractive. The origin of such reversal is due to the coupling between the active stresses and elasticity of the system. This discovery provides a mechanism for the interaction between active agents in complex and structured media, opening up opportunities to tune the interaction range and directionality via the mechanical properties of the medium.

  9. Elasticity-induced force reversal between active spinning particles in dense passive media

    PubMed Central

    Aragones, J. L.; Steimel, J. P.; Alexander-Katz, A.

    2016-01-01

    The self-organization of active particles is governed by their dynamic effective interactions. Such interactions are controlled by the medium in which such active agents reside. Here we study the interactions between active agents in a dense non-active medium. Our system consists of actuated, spinning, active particles embedded in a dense monolayer of passive, or non-active, particles. We demonstrate that the presence of the passive monolayer alters markedly the properties of the system and results in a reversal of the forces between active spinning particles from repulsive to attractive. The origin of such reversal is due to the coupling between the active stresses and elasticity of the system. This discovery provides a mechanism for the interaction between active agents in complex and structured media, opening up opportunities to tune the interaction range and directionality via the mechanical properties of the medium. PMID:27112961

  10. Brownian Motion and the Temperament of Living Cells

    NASA Astrophysics Data System (ADS)

    Tsekov, Roumen; Lensen, Marga C.

    2013-07-01

    The migration of living cells usually obeys the laws of Brownian motion. While the latter is due to the thermal motion of the surrounding matter, the locomotion of cells is generally associated with their vitality. We study what drives cell migration and how to model memory effects in the Brownian motion of cells. The concept of temperament is introduced as an effective biophysical parameter driving the motion of living biological entities in analogy with the physical parameter of temperature, which dictates the movement of lifeless physical objects. The locomemory of cells is also studied via the generalized Langevin equation. We explore the possibility of describing cell locomemory via the Brownian self-similarity concept. An heuristic expression for the diffusion coefficient of cells on structured surfaces is derived.

  11. Near-field optically driven Brownian motors (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Wu, Shao-Hua; Huang, Ningfeng; Jaquay, Eric; Povinelli, Michelle L.

    2016-09-01

    Brownian ratchets are of fundamental interest in fields from statistical physics to molecular motors. The realization of Brownian ratchets in engineered systems opens up the potential to harness thermal energy for directed motion, with applications in transport and sorting of nanoparticles. Implementations based on optical traps provide a high degree of tunability along with precise spatiotemporal control. Near-field optical methods provide particular flexibility and ease of on-chip integration with other microfluidic components. Here, we demonstrate the first all-optical, near-field Brownian ratchet. Our approach uses an asymmetrically patterned photonic crystal and yields an ultra-stable trap stiffness of 253.6 pN/nm-W, 100x greater than conventional optical tweezers. By modulating the laser power, optical ratcheting with transport speed of 1 micron/s can be achieved, allowing a variety of dynamical lab-on-a-chip applications. The resulting transport speed matches well with the theoretical prediction.

  12. Effect of external periodic regulations on Brownian motor

    NASA Astrophysics Data System (ADS)

    Yu, Lilong; Chen, Ruyin; Nie, Linru

    2015-01-01

    Effect of external periodic regulations on a symmetric Brownian motor performing between two temperature sources was investigated. By means of numerical calculations, we found that: (i) The regulations can control magnitude and direction of the motor's current to a large degree. As one of the motor's compartments is regulated, the motor's current can be both inversed and maximized, dependent on amplitude and frequency of the periodic driving force. If two periodic driving forces with identical amplitudes and frequencies are employed to regulate respectively two compartments of the Brownian motor, the current's magnitude and direction will make periodic oscillations with phase difference between them. In addition, the external periodic regulation can also change direction of thermal rectifier of the system as a switch. (ii) Optimal regulating parameters of the external periodic forces can enhance pronouncedly conversion efficiency of energy of the Brownian motor.

  13. "Active" drops as phantom models for living cells: a mesoscopic particle-based approach.

    PubMed

    Dallavalle, Marco; Lugli, Francesca; Rapino, Stefania; Zerbetto, Francesco

    2016-04-21

    Drops and biological cells share some morphological features and visco-elastic properties. The modelling of drops by mesoscopic non-atomistic models has been carried out to a high degree of success in recent years. We extend such treatment and discuss a simple, drop-like model to describe the interactions of the outer layer of cells with the surfaces of materials. Cells are treated as active mechanical objects that are able to generate adhesion forces. They appear with their true size and are made of "parcels of fluids" or beads. The beads are described by (very) few quantities/parameters related to fundamental chemical forces such as hydrophilicity and lipophilicity that represent an average of the properties of a patch of material or an area of the cell(s) surface. The investigation of adhesion dynamics, motion of individual cells, and the collective behavior of clusters of cells on materials is possible. In the simulations, the drops become active soft matter objects and different from regular droplets they do not fuse when in contact, their trajectories are not Brownian, and they can be forced "to secrete" molecules, to name some of the properties targeted by the modeling. The behavior that emerges from the simulations allows ascribing some cell properties to their mechanics, which are related to their biological features.

  14. Stochastic description of quantum Brownian dynamics

    NASA Astrophysics Data System (ADS)

    Yan, Yun-An; Shao, Jiushu

    2016-08-01

    Classical Brownian motion has well been investigated since the pioneering work of Einstein, which inspired mathematicians to lay the theoretical foundation of stochastic processes. A stochastic formulation for quantum dynamics of dissipative systems described by the system-plus-bath model has been developed and found many applications in chemical dynamics, spectroscopy, quantum transport, and other fields. This article provides a tutorial review of the stochastic formulation for quantum dissipative dynamics. The key idea is to decouple the interaction between the system and the bath by virtue of the Hubbard-Stratonovich transformation or Itô calculus so that the system and the bath are not directly entangled during evolution, rather they are correlated due to the complex white noises introduced. The influence of the bath on the system is thereby defined by an induced stochastic field, which leads to the stochastic Liouville equation for the system. The exact reduced density matrix can be calculated as the stochastic average in the presence of bath-induced fields. In general, the plain implementation of the stochastic formulation is only useful for short-time dynamics, but not efficient for long-time dynamics as the statistical errors go very fast. For linear and other specific systems, the stochastic Liouville equation is a good starting point to derive the master equation. For general systems with decomposable bath-induced processes, the hierarchical approach in the form of a set of deterministic equations of motion is derived based on the stochastic formulation and provides an effective means for simulating the dissipative dynamics. A combination of the stochastic simulation and the hierarchical approach is suggested to solve the zero-temperature dynamics of the spin-boson model. This scheme correctly describes the coherent-incoherent transition (Toulouse limit) at moderate dissipation and predicts a rate dynamics in the overdamped regime. Challenging problems

  15. Brownian motion of solitons in a Bose-Einstein condensate.

    PubMed

    Aycock, Lauren M; Hurst, Hilary M; Efimkin, Dmitry K; Genkina, Dina; Lu, Hsin-I; Galitski, Victor M; Spielman, I B

    2017-03-07

    We observed and controlled the Brownian motion of solitons. We launched solitonic excitations in highly elongated [Formula: see text] Bose-Einstein condensates (BECs) and showed that a dilute background of impurity atoms in a different internal state dramatically affects the soliton. With no impurities and in one dimension (1D), these solitons would have an infinite lifetime, a consequence of integrability. In our experiment, the added impurities scatter off the much larger soliton, contributing to its Brownian motion and decreasing its lifetime. We describe the soliton's diffusive behavior using a quasi-1D scattering theory of impurity atoms interacting with a soliton, giving diffusion coefficients consistent with experiment.

  16. On the use of reverse Brownian motion to accelerate hybrid simulations

    NASA Astrophysics Data System (ADS)

    Bakarji, Joseph; Tartakovsky, Daniel M.

    2017-04-01

    Multiscale and multiphysics simulations are two rapidly developing fields of scientific computing. Efficient coupling of continuum (deterministic or stochastic) constitutive solvers with their discrete (stochastic, particle-based) counterparts is a common challenge in both kinds of simulations. We focus on interfacial, tightly coupled simulations of diffusion that combine continuum and particle-based solvers. The latter employs the reverse Brownian motion (rBm), a Monte Carlo approach that allows one to enforce inhomogeneous Dirichlet, Neumann, or Robin boundary conditions and is trivially parallelizable. We discuss numerical approaches for improving the accuracy of rBm in the presence of inhomogeneous Neumann boundary conditions and alternative strategies for coupling the rBm solver with its continuum counterpart. Numerical experiments are used to investigate the convergence, stability, and computational efficiency of the proposed hybrid algorithm.

  17. Non-Markovian Brownian motion in a magnetic field and time-dependent force fields

    NASA Astrophysics Data System (ADS)

    Hidalgo-Gonzalez, J. C.; Jiménez-Aquino, J. I.; Romero-Bastida, M.

    2016-11-01

    This work focuses on the derivation of the velocity and phase-space generalized Fokker-Planck equations for a Brownian charged particle embedded in a memory thermal bath and under the action of force fields: a constant magnetic field and arbitrary time-dependent force fields. To achieve the aforementioned goal we use a Gaussian but non-Markovian generalized Langevin equation with an arbitrary friction memory kernel. In a similar way, the generalized diffusion equation in the zero inertia limit is also derived. Additionally we show, in the absence of the time-dependent external forces, that, if the fluctuation-dissipation relation of the second kind is valid, then the generalized Langevin dynamics associated with the charged particle reaches a stationary state in the large-time limit. The consistency of our theoretical results is also verified when they are compared with those derived in the absence of the force fields and in the Markovian case.

  18. Clusters in sedimentation equilibrium for an experimental hard-sphere-plus-dipolar Brownian colloidal system

    PubMed Central

    Newman, Hugh D.; Yethiraj, Anand

    2015-01-01

    In this work, we use structure and dynamics in sedimentation equilibrium, in the presence of gravity, to examine, via confocal microscopy, a Brownian colloidal system in the presence of an external electric field. The zero field equation of state (EOS) is hard sphere without any re-scaling of particle size, and the hydrodynamic corrections to the long-time self-diffusion coefficient are quantitatively consistent with the expected value for hard spheres. Care is taken to ensure that both the dimensionless gravitational energy, which is equivalent to a Peclet number Peg, and dipolar strength Λ are of order unity. In the presence of an external electric field, anisotropic chain-chain clusters form; this cluster formation manifests itself with the appearance of a plateau in the diffusion coefficient when the dimensionless dipolar strength Λ ~ 1. The structure and dynamics of this chain-chain cluster state is examined for a monodisperse system for two particle sizes. PMID:26323363

  19. Generalized Scaling and the Master Variable for Brownian Magnetic Nanoparticle Dynamics.

    PubMed

    Reeves, Daniel B; Shi, Yipeng; Weaver, John B

    2016-01-01

    Understanding the dynamics of magnetic particles can help to advance several biomedical nanotechnologies. Previously, scaling relationships have been used in magnetic spectroscopy of nanoparticle Brownian motion (MSB) to measure biologically relevant properties (e.g., temperature, viscosity, bound state) surrounding nanoparticles in vivo. Those scaling relationships can be generalized with the introduction of a master variable found from non-dimensionalizing the dynamical Langevin equation. The variable encapsulates the dynamical variables of the surroundings and additionally includes the particles' size distribution and moment and the applied field's amplitude and frequency. From an applied perspective, the master variable allows tuning to an optimal MSB biosensing sensitivity range by manipulating both frequency and field amplitude. Calculation of magnetization harmonics in an oscillating applied field is also possible with an approximate closed-form solution in terms of the master variable and a single free parameter.

  20. Chains, Rings, and Dendrites of Active Colloidal Polymers

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Granick, Steve

    2015-03-01

    In order to better understand active polymeric matter, colloidal polymers are imaged, in situ in real time, obtaining not only temporal and spatial information about each ``monomer'' in these living polymers but also about the time-dependent and orientation-dependent correlations between them. Our reversible colloidal polymer system is assembled from self-propelled monomeric Janus particles with dynamic ``plug and play'' self-assembly and programmed direction-specific interactions between the particles. Enabling this, AC voltage induces dipoles on the monomeric Janus particles that link them into chains while also generating active phoretic motility. Unique features of this system relative to conventional Brownian polymers are emphasized.

  1. Emerging activity in bilayered dispersions with wake-mediated interactions

    NASA Astrophysics Data System (ADS)

    Bartnick, Jörg; Kaiser, Andreas; Löwen, Hartmut; Ivlev, Alexei V.

    2016-06-01

    In a bilayered system of particles with wake-mediated interactions, the action-reaction symmetry for the effective forces between particles of different layers is broken. Under quite general conditions we show that, if the interaction nonreciprocity exceeds a certain threshold, this creates an active dispersion of self-propelled clusters of Brownian particles. The emerging activity promotes unusual melting scenarios and an enormous diffusivity in the dense fluid. Our results are obtained by computer simulation and analytical theory and can be verified in experiments with colloidal dispersions and complex plasmas.

  2. LARGE PARTICLES IN ACTIVE ASTEROID P/2010 A2

    SciTech Connect

    Jewitt, David; Ishiguro, Masateru; Agarwal, Jessica

    2013-02-10

    The previously unknown asteroid P/2010 A2 rose to prominence in 2010 by forming a transient, comet-like tail consisting of ejected dust. The observed dust production was interpreted as the result of either a hypervelocity impact with a smaller body or a rotational disruption. We have re-observed this object, finding that large particles remain a full orbital period after the initial outburst. In the intervening years, particles smaller than {approx}3 mm in radius have been dispersed by radiation pressure, leaving only larger particles in the trail. Since the total mass is dominated by the largest particles, the radiation pressure filtering allows us to obtain a more reliable estimate of the debris mass than was previously possible. We find that the mass contained in the debris is {approx}5 Multiplication-Sign 10{sup 8} kg (assumed density 3000 kg m{sup -3}), the ratio of the total debris mass to the nucleus mass is {approx}0.1, and that events like P/2010 A2 contribute <3% to the Zodiacal dust production rate. Physical properties of the nucleus and debris are also determined.

  3. Spontaneous pulsing states in an active particle system

    NASA Astrophysics Data System (ADS)

    Klein, Sarah; Appert-Rolland, Cécile; Evans, Martin R.

    2016-09-01

    We study a two-lane two-species exclusion process inspired by Lin et al (2011 J. Stat. Mech. P09027) that exhibits a non-equilibrium pulsing phase. Particles move on two parallel one-dimensional tracks, with one open and one reflecting boundary. The particle type defines the hopping direction. When only particles hopping towards the open end are allowed to change lane, the system exhibits a phase transition from a low density phase to a pulsing phase depending on the ratio between particle injection and type-changing rate. This phase transition can be observed in the stochastic model as well as in a mean-field description. In the low density phase, the density profile can be predicted analytically. The pulsing phase is characterised by a fast filling of the system and—once filled—by a slowly backwards moving front separating a decreasing dense region and an expanding low density region. The hopping of the front on the discrete lattice is found to create density oscillations, both, in time and space. By means of a stability analysis we can predict the structure of the dense region during the emptying process, characterised by exponentially damped perturbations, both at the open end and near the moving front.

  4. Cloud droplet activation through oxidation of organic aerosol influenced by temperature and particle phase state

    NASA Astrophysics Data System (ADS)

    Slade, Jonathan H.; Shiraiwa, Manabu; Arangio, Andrea; Su, Hang; Pöschl, Ulrich; Wang, Jian; Knopf, Daniel A.

    2017-02-01

    Chemical aging of organic aerosol (OA) through multiphase oxidation reactions can alter their cloud condensation nuclei (CCN) activity and hygroscopicity. However, the oxidation kinetics and OA reactivity depend strongly on the particle phase state, potentially influencing the hydrophobic-to-hydrophilic conversion rate of carbonaceous aerosol. Here, amorphous Suwannee River fulvic acid (SRFA) aerosol particles, a surrogate humic-like substance (HULIS) that contributes substantially to global OA mass, are oxidized by OH radicals at different temperatures and phase states. When oxidized at low temperature in a glassy solid state, the hygroscopicity of SRFA particles increased by almost a factor of two, whereas oxidation of liquid-like SRFA particles at higher temperatures did not affect CCN activity. Low-temperature oxidation appears to promote the formation of highly-oxygenated particle-bound fragmentation products with lower molar mass and greater CCN activity, underscoring the importance of chemical aging in the free troposphere and its influence on the CCN activity of OA.

  5. High Fc Density Particles Result in Binary Complement Activation but Tunable Macrophage Phagocytosis

    NASA Astrophysics Data System (ADS)

    Sulchek, Todd; Pacheco, Patricia; White, David

    2014-03-01

    Macrophage phagocytosis and complement system activation represent two key components of the immune system and both can be activated through the presentation of multiple Fc domains of IgG antibodies. We have created functionalized micro- and nanoparticles with various densities of Fc domains to understand the modulation of the immune system for eventual use as a novel immunomodulation platform. Phagocytosis assays were carried out by adding functionalized particles to macrophage cells and quantitatively determined using fluorescent microscopy and flow cytometry. Complement system activation by the functionalized particles in human serum was quantified with an enzyme immunoassay. Our phagocytosis assay revealed a strong dependence on particle size and Fc density. For small particles, as the Fc density increased, the number of particles phagocytosed also increased. Large particles were phagocytosed at significantly lower levels and showed no dependency on Fc density. Complement was successfully activated at levels comparable to positive controls for small particles at high Fc densities. However at low Fc densities, there is a significant decrease in complement activation. This result suggests a binary response for complement system activation with a threshold density for successful activation. Therefore, varying the Fc density on micro/nanoparticles resulted in a tunable response in macrophage phagocytosis while a more binary response for complement activation.

  6. Controlling the motion and placement of micrometer-sized metal particles using patterned polymer brush surfaces.

    PubMed

    Dunderdale, Gary J; Howse, Jonathan R; Fairclough, J Patrick A

    2011-10-04

    In this paper, we show that silicon surfaces patterned with poly(methacrylic acid) brushes are able to control the Brownian motion of 2-3 μm iron particles, which sediment onto the surface in aqueous solution and experience differences in repulsive force depending upon their position. Differences in repulsion lead to different gravitational potential energies across the surface, which gives bias to the Brownian motion taking place. Three regimes have been identified depending upon the brush height: (i) no control of Brownian motion when the brush height is small, (ii) Brownian motion that is influenced by the polymer brush when the brush 17 height is intermediate, (iii) Brownian motion that is confined by polymer brush barriers when the brush height is greatest. The height of brush found necessary to significantly influence iron particle motion was small at 39 nm or 2% of the particle diameter.

  7. The influence of human physical activity and contaminated clothing type on particle resuspension.

    PubMed

    McDonagh, A; Byrne, M A

    2014-01-01

    A study was conducted to experimentally quantify the influence of three variables on the level of resuspension of hazardous aerosol particles from clothing. Variables investigated include physical activity level (two levels, low and high), surface type (four different clothing material types), and time i.e. the rate at which particles resuspend. A mixture of three monodisperse tracer-labelled powders, with median diameters of 3, 5, and 10 microns, was used to "contaminate" the samples, and the resuspended particles were analysed in real-time using an Aerodynamic Particle Sizer (APS), and also by Neutron Activation Analysis (NAA). The overall finding was that physical activity resulted in up to 67% of the contamination deposited on clothing being resuspended back into the air. A detailed examination of the influence of physical activity level on resuspension, from NAA, revealed that the average resuspended fraction (RF) of particles at low physical activity was 28 ± 8%, and at high physical activity was 30 ± 7%, while the APS data revealed a tenfold increase in the cumulative mass of airborne particles during high physical activity in comparison to that during low physical activity. The results also suggest that it is not the contaminated clothing's fibre type which influences particle resuspension, but the material's weave pattern (and hence the material's surface texture). Investigation of the time variation in resuspended particle concentrations indicated that the data were separable into two distinct regimes: the first (occurring within the first 1.5 min) having a high, positive rate of change of airborne particle concentration relative to the second regime. The second regime revealed a slower rate of change of particle concentration and remained relatively unchanged for the remainder of each resuspension event.

  8. Binding, stability, and antioxidant activity of quercetin with soy protein isolate particles.

    PubMed

    Wang, Yufang; Wang, Xiaoyong

    2015-12-01

    This work is to study the potential of particles fabricated from soy protein isolate (SPI) as a protective carrier for quercetin. When the concentration of SPI particles increases from 0 to 0.35 g/L, quercetin gives a gradually increased fluorescence intensity and fluorescence anisotropy. The addition of quercetin can highly quench the intrinsic fluorescence of SPI particles. These results are explained in terms of the binding of quercetin to the hydrophobic pockets of SPI particles mainly through the hydrophobic force together with the hydrogen bonding. The small difference in the binding constants at 25 and 40 °C suggests the structural stability of SPI particles. The relative changes in values of Gibbs energy, enthalpy, and entropy indicate that the binding of quercetin with SPI particles is spontaneous and hydrophobic interaction is the major force. Furthermore, SPI particles are superior to native SPI for improving the stability and radical scavenging activity of quercetin.

  9. Brownian dynamics simulations of electrostatic adsorption and ordering of charged colloidal nanoparticles

    NASA Astrophysics Data System (ADS)

    Luna-Singh, Jennifer; Barrera, Enrique; Varshney, Vikas; Kelley, John; Vaia, Richard

    2014-03-01

    Self-limiting assembly of nanoparticle (NP) and biomacromolecular arrays promises to revolutionize compliant device fabrication by enabling print-on-demand. Presently, quantitative understanding of the relationship between the array order, nanoparticle size, surface characteristics, and process conditions remain elusive. Previous simulations have shown that tuning particle and surface potentials, screening lengths, and particle concentrations can lead to ordering. However, identifying the experimental conditions to observe these in-plane order-disorder and order-order transitions for NPs remains a challenge. Here in, the absorption of electrostatically stabilized NPs with increasing ratio of particle-particle repulsion to particle-surface attraction via Brownian dynamics simulations is discussed. The orientation correlation function follows the KTHNY theory of phase transition as particle and surface potentials are tuned. Detailed Voronoi analysis reveals movement and defect annihilation during the final stages of adsorption. Identifying the transition between liquid, hexatic, and crystalline NP arrays will provide experimental conditions necessary to create high resolution patterns and smaller devices.

  10. Inertial and bias effects in the rotational Brownian motion of rodlike molecules in a uniaxial potential

    NASA Astrophysics Data System (ADS)

    Kalmykov, Yuri P.; Titov, Sergey V.; Coffey, William T.

    2011-01-01

    Inertial effects in the rotational Brownian motion in space of a rigid dipolar rotator (needle) in a uniaxial potential biased by an external field giving rise to asymmetry are treated via the infinite hierarchy of differential-recurrence relations for the statistical moments (orientational correlation functions) obtained by averaging the Euler-Langevin equation over its realizations in phase space. The solutions of this infinite hierarchy for the dipole correlation function and its characteristic times are obtained using matrix continued fractions showing that the model simultaneously predicts both slow overbarrier (or interwell) relaxation at low frequencies accompanied by intermediate frequency Debye relaxation due to fast near-degenerate motion in the wells of the potential (intrawell relaxation) as well as the high frequency resonance (Poley) absorption due to librations of the dipole moments. It is further shown that the escape rate of a Brownian particle from a potential well as extended to the Kramers turnover problem via the depopulation factor yields a close approximation to the longest (overbarrier) relaxation time of the system. For zero and small values of the bias field parameter h, both the dipole moment correlation time and the longest relaxation time have Arrhenius behavior (exponential increase with increasing barrier height). While at values of h in excess of a critical value however far less than that required to achieve nucleation, the Arrhenius behavior of the correlation time disappears.

  11. Brownian motors in the microscale domain: Enhancement of efficiency by noise

    NASA Astrophysics Data System (ADS)

    Spiechowicz, J.; Hänggi, P.; Łuczka, J.

    2014-09-01

    We study a noisy drive mechanism for efficiency enhancement of Brownian motors operating on the microscale domain. It was proven [J. Spiechowicz et al., J. Stat. Mech. (2013) P02044, 10.1088/1742-5468/2013/02/P02044] that biased noise η (t) can induce normal and anomalous transport processes similar to those generated by a static force F acting on inertial Brownian particles in a reflection-symmetric periodic structure in the presence of symmetric unbiased time-periodic driving. Here, we show that within selected parameter regimes, noise η (t) of the mean value <η(t)>=F can be significantly more effective than the deterministic force F: the motor can move much faster, its velocity fluctuations are much smaller, and the motor efficiency increases several times. These features hold true in both normal and absolute negative mobility regimes. We demonstrate this with detailed simulations by resource to generalized white Poissonian noise. Our theoretical results can be tested and corroborated experimentally by use of a setup that consists of a resistively and capacitively shunted Josephson junction. The suggested strategy to replace F by η (t) may provide a new operating principle in which micro- and nanomotors could be powered by biased noise.

  12. Cellular motions and thermal fluctuations: the Brownian ratchet.

    PubMed Central

    Peskin, C S; Odell, G M; Oster, G F

    1993-01-01

    We present here a model for how chemical reactions generate protrusive forces by rectifying Brownian motion. This sort of energy transduction drives a number of intracellular processes, including filopodial protrusion, propulsion of the bacterium Listeria, and protein translocation. Images FIGURE 1 FIGURE 2 FIGURE 3 PMID:8369439

  13. Brownian Movement and Avogadro's Number: A Laboratory Experiment.

    ERIC Educational Resources Information Center

    Kruglak, Haym

    1988-01-01

    Reports an experimental procedure for studying Einstein's theory of Brownian movement using commercially available latex microspheres and a video camera. Describes how students can monitor sphere motions and determine Avogadro's number. Uses a black and white video camera, microscope, and TV. (ML)

  14. Brownian Motion of a Torsion Pendulum Damped by Internal Friction.

    NASA Astrophysics Data System (ADS)

    Gonzalez, Gabriela Ines

    1995-01-01

    Brownian motion is a well known limit to precision experiments, and it is also going to be a limiting factor in the sensitivity of interferometric gravitational wave detectors. The power spectral density of Brownian motion depends dramatically on the strength and frequency dependence of the energy dissipation in the system of interest. We present here the measurement of Brownian motion of a simple oscillator, a torsion pendulum, where the energy losses are due to internal friction in the suspension fiber. We calculate from these measurements the power spectrum S _theta(f) of the Brownian motion, as well as other statistical functions defined in irreversible thermodynamics, such as the autocorrelation function and conditional probability distributions. We also present a measurement of internal friction as a function of frequency. With this and the physical parameters describing the pendulum, we use the fluctuation -dissipation theorem to calculate S_theta(f). . We then compare the prediction and measurement of S_theta(f), and show excellent agreement over a decade in frequency around the pendulum frequency. The spectrum S_theta(f) is not flat below resonance, and in fact follows a S_theta(f)~1/f law.

  15. Non-cooperative Brownian donkeys: A solvable 1D model

    NASA Astrophysics Data System (ADS)

    Jiménez de Cisneros, B.; Reimann, P.; Parrondo, J. M. R.

    2003-12-01

    A paradigmatic 1D model for Brownian motion in a spatially symmetric, periodic system is tackled analytically. Upon application of an external static force F the system's response is an average current which is positive for F < 0 and negative for F > 0 (absolute negative mobility). Under suitable conditions, the system approaches 100% efficiency when working against the external force F.

  16. Brownian dynamics determine universality of charge transport in ionic liquids

    SciTech Connect

    Sangoro, Joshua R; Iacob, Ciprian; Mierzwa, Michal; Paluch, Marian; Kremer, Friedrich

    2012-01-01

    Broadband dielectric spectroscopy is employed to investigate charge transport in a variety of glass-forming ionic liquids over wide frequency, temperature and pressure ranges. Using a combination of Einstein, Einstein-Smoluchowski, and Langevin relations, the observed universal scaling of charge transport in ionic liquids is traced back to the dominant role of Brownian dynamics.

  17. Ultrasound-assisted Micro-emulsion Synthesis of a Highly Active Nano-particle Catalyst

    DTIC Science & Technology

    2010-03-01

    Ultrasound-assisted Micro -emulsion Synthesis of a Highly Active Nano -particle Catalyst by Rongzhong Jiang and Charles Rong ARL-TR-5114...ARL-TR-5114 March 2010 Ultrasound-assisted Micro -emulsion Synthesis of a Highly Active Nano -particle Catalyst Rongzhong Jiang and...TYPE DRI 3. DATES COVERED (From - To) 2009 to 2010 4. TITLE AND SUBTITLE Ultrasound-assisted Micro -emulsion Synthesis of a Highly Active Nano

  18. Critical phenomena in active matter

    NASA Astrophysics Data System (ADS)

    Paoluzzi, Matteo; Marchetti, M. Cristina; Claudio Maggi Collaboration; Umberto Marini Bettolo Marconi Collaboration; Nicoletta Gnan Collaboration

    A collection of active agents can organize in phases with structural properties remarkably similar to those of ordinary materials, such as active gases, liquids and glasses. These phases are formed, however, out of equilibrium, where the machinery of equilibrium statistical mechanics cannot be applied. It has recently been shown that models of particles with Gaussian colored noise can capture some of the nonequilibrium behavior of active Brownian particles, including motility-induced phase separation. By using the Unified Gaussian Colored Noise Approximation (UCNA) it has been possible to obtain an equilibrium-like probability distribution function and an effective free energy for active Brownian particles. Here we employ UCNA to examine the effect of colored noise on mean-field order-disorder transitions. Starting with a φ4 Landau model that undergoes a second-order phase transition as a function of a tuning parameter, we calculate the shift in transition due to colored noise as a function of the noise amplitude and correlation time τ. We find that the transition line exhibits reentrance as a function of τ. The mean-field theoretical predictions are compared with Molecular Dynamics simulations of active Lennard-Jones particles. We acknowledge support from NSF-DMR-1305184.

  19. Robust Biased Brownian Dynamics for Rate Constant Calculation

    PubMed Central

    Zou, Gang; Skeel, Robert D.

    2003-01-01

    A reaction probability is required to calculate the rate constant of a diffusion-dominated reaction. Due to the complicated geometry and potentially high dimension of the reaction probability problem, it is usually solved by a Brownian dynamics simulation, also known as a random walk or path integral method, instead of solving the equivalent partial differential equation by a discretization method. Building on earlier work, this article completes the development of a robust importance sampling algorithm for Brownian dynamics—i.e., biased Brownian dynamics with weight control—to overcome the high energy and entropy barriers in biomolecular association reactions. The biased Brownian dynamics steers sampling by a bias force, and the weight control algorithm controls sampling by a target weight. This algorithm is optimal if the bias force and the target weight are constructed from the solution of the reaction probability problem. In reality, an approximate reaction probability has to be used to construct the bias force and the target weight. Thus, the performance of the algorithm depends on the quality of the approximation. Given here is a method to calculate a good approximation, which is based on the selection of a reaction coordinate and the variational formulation of the reaction probability problem. The numerically approximated reaction probability is shown by computer experiments to give a factor-of-two speedup over the use of a purely heuristic approximation. Also, the fully developed method is compared to unbiased Brownian dynamics. The tests for human superoxide dismutase, Escherichia coli superoxide dismutase, and antisweetener antibody NC6.8, show speedups of 17, 35, and 39, respectively. The test for reactions between two model proteins with orientations shows speedups of 2578 for one set of configurations and 3341 for another set of configurations. PMID:14507681

  20. Activity of an enzyme immobilized on superparamagnetic particles in a rotational magnetic field

    SciTech Connect

    Mizuki, Toru; Watanabe, Noriyuki; Nagaoka, Yutaka; Fukushima, Tadamasa; Morimoto, Hisao; Usami, Ron; Maekawa, Toru

    2010-03-19

    We immobilize {alpha}-amylase extracted from Bacillus Iicheniformis on the surfaces of superparamagnetic particles and investigate the effect of a rotational magnetic field on the enzyme's activity. We find that the activity of the enzyme molecules immobilized on superparamagnetic particles increases in the rotational magnetic field and reaches maximum at a certain frequency. We clarify the effect of the cluster structures formed by the superparamagnetic particles on the activity. Enzyme reactions are enhanced even in a tiny volume of solution using the present method, which is very important for the development of efficient micro reactors and micro total analysis systems ({mu}-TAS).

  1. Electrostatic Channeling in P. falciparum DHFR-TS: Brownian Dynamics and Smoluchowski Modeling

    PubMed Central

    Metzger, Vincent T.; Eun, Changsun; Kekenes-Huskey, Peter M.; Huber, Gary; McCammon, J. Andrew

    2014-01-01

    We perform Brownian dynamics simulations and Smoluchowski continuum modeling of the bifunctional Plasmodium falciparum dihydrofolate reductase-thymidylate synthase (P. falciparum DHFR-TS) with the objective of understanding the electrostatic channeling of dihydrofolate generated at the TS active site to the DHFR active site. The results of Brownian dynamics simulations and Smoluchowski continuum modeling suggest that compared to Leishmania major DHFR-TS, P. falciparum DHFR-TS has a lower but significant electrostatic-mediated channeling efficiency (∼15–25%) at physiological pH (7.0) and ionic strength (150 mM). We also find that removing the electric charges from key basic residues located between the DHFR and TS active sites significantly reduces the channeling efficiency of P. falciparum DHFR-TS. Although several protozoan DHFR-TS enzymes are known to have similar tertiary and quaternary structure, subtle differences in structure, active-site geometry, and charge distribution appear to influence both electrostatic-mediated and proximity-based substrate channeling. PMID:25418308

  2. Activation of respiratory epithelial cells by wood smoke particles persists beyond immediate exposure.

    EPA Science Inventory

    The biological effect of particles on epithelial cells involves, in part, oxidant generation and a cascade of reactions culminating in inflammatory mediator release. Whether there is an immediate short-lived activation or continued persistent response of the cells to the particle...

  3. Alpha-particle activity of apollo 11 samples.

    PubMed

    Richardson, K A; McCkay, D S; Greenwood, W R; Foss, T H

    1970-01-30

    Nine polishled thin sectionis have been exposed to nulclear track plates, three have been counted by alplia-particle spectrometry, and one has been examined by electron mocroprobe. Interpretation of the results is in a preliminary stage. Alpha track distribiutioni in the autoradiograph of a breccia forms a network that appears related to the rims of accretionary lapilli comiiposinig the breccia. Thorium in a coarse-grained crystalline rock is concenitrated in micron-sized, zirconium-rich crystals. Alplia count rates agree with what would be predicted from previously reported thorium and uranium contents of the same rocks, suggesting secular equilibriunm for the thorium and uranium decay series.

  4. Study and Analyze Energetic Particle and Magnetic Activity Data.

    DTIC Science & Technology

    1982-06-01

    and Vette, 1976) 111-1. The diameter distribution of etch pits of protons 95 111-2. Etch pit diameter ( D ) as a function of proton energy (E). 96 The...parameter on each curve represents etch time. 111-3. Etch pit diameter ( D ) as a function of bulk material 97 removed from one surface (Vgt) 111-4...curvature of plates d = plate separation (R1 - R2) Thus, the energy of particles passing through the exit aperture is directly proportional to the

  5. Nonisothermal Brownian motion: Thermophoresis as the macroscopic manifestation of thermally biased molecular motion.

    PubMed

    Brenner, Howard

    2005-12-01

    A quiescent single-component gravity-free gas subject to a small steady uniform temperature gradient T, despite being at rest, is shown to experience a drift velocity UD=-D* gradient ln T, where D* is the gas's nonisothermal self-diffusion coefficient. D* is identified as being the gas's thermometric diffusivity alpha. The latter differs from the gas's isothermal isotopic self-diffusion coefficient D, albeit only slightly. Two independent derivations are given of this drift velocity formula, one kinematical and the other dynamical, both derivations being strictly macroscopic in nature. Within modest experimental and theoretical uncertainties, this virtual drift velocity UD=-alpha gradient ln T is shown to be constitutively and phenomenologically indistinguishable from the well-known experimental and theoretical formulas for the thermophoretic velocity U of a macroscopic (i.e., non-Brownian) non-heat-conducting particle moving under the influence of a uniform temperature gradient through an otherwise quiescent single-component rarefied gas continuum at small Knudsen numbers. Coupled with the size independence of the particle's thermophoretic velocity, the empirically observed equality, U=UD, leads naturally to the hypothesis that these two velocities, the former real and the latter virtual, are, in fact, simply manifestations of the same underlying molecular phenomenon, namely the gas's Brownian movement, albeit biased by the temperature gradient. This purely hydrodynamic continuum-mechanical equality is confirmed by theoretical calculations effected at the kinetic-molecular level on the basis of an existing solution of the Boltzmann equation for a quasi-Lorentzian gas, modulo small uncertainties pertaining to the choice of collision model. Explicitly, this asymptotically valid molecular model allows the virtual drift velocity UD of the light gas and the thermophoretic velocity U of the massive, effectively non-Brownian, particle, now regarded as the tracer particle

  6. Boundaries can steer active Janus spheres

    PubMed Central

    Das, Sambeeta; Garg, Astha; Campbell, Andrew I.; Howse, Jonathan; Sen, Ayusman; Velegol, Darrell; Golestanian, Ramin; Ebbens, Stephen J.

    2015-01-01

    The advent of autonomous self-propulsion has instigated research towards making colloidal machines that can deliver mechanical work in the form of transport, and other functions such as sensing and cleaning. While much progress has been made in the last 10 years on various mechanisms to generate self-propulsion, the ability to steer self-propelled colloidal devices has so far been much more limited. A critical barrier in increasing the impact of such motors is in directing their motion against the Brownian rotation, which randomizes particle orientations. In this context, here we report directed motion of a specific class of catalytic motors when moving in close proximity to solid surfaces. This is achieved through active quenching of their Brownian rotation by constraining it in a rotational well, caused not by equilibrium, but by hydrodynamic effects. We demonstrate how combining these geometric constraints can be utilized to steer these active colloids along arbitrary trajectories. PMID:26627125

  7. Impact of pectin esterification on the antimicrobial activity of nisin-loaded pectin particles.

    PubMed

    Krivorotova, Tatjana; Staneviciene, Ramune; Luksa, Juliana; Serviene, Elena; Sereikaite, Jolanta

    2017-01-01

    The relationship between pectin structure and the antimicrobial activity of nisin-loaded pectin particles was examined. The antimicrobial activity of five different nisin-loaded pectin particles, i.e., nisin-loaded high methoxyl pectin, low methoxyl pectin, pectic acid, dodecyl pectin with 5.4 and 25% degree of substitution were tested in the pH range of 4.0-7.0 by agar-diffusion assay and agar plate count methods. It was found that the degree of esterification of carboxyl group of galacturonic acid in pectin molecule is important for the antimicrobial activity of nisin-loaded pectin particles. Nisin-loaded particles prepared using pectic acid or the pectin with low degree of esterification exhibit higher antimicrobial activity than nisin-loaded high methoxyl pectin particles. Pectins with free carboxyl groups or of low degree of esterification are the most suitable for particles preparation. Moreover, nisin-loaded pectin particles were active at close to neutral or neutral pH values. Therefore, they could be effectively applied for food preservation. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 33:245-251, 2017.

  8. Physicochemical characteristics and occupational exposure to coarse, fine and ultrafine particles during building refurbishment activities

    NASA Astrophysics Data System (ADS)

    Azarmi, Farhad; Kumar, Prashant; Mulheron, Mike; Colaux, Julien L.; Jeynes, Chris; Adhami, Siavash; Watts, John F.

    2015-08-01

    Understanding of the emissions of coarse (PM10 ≤10 μm), fine (PM2.5 ≤2.5 μm) and ultrafine particles (UFP <100 nm) from refurbishment activities and their dispersion into the nearby environment is of primary importance for developing efficient risk assessment and management strategies in the construction and demolition industry. This study investigates the release, occupational exposure and physicochemical properties of particulate matter, including UFPs, from over 20 different refurbishment activities occurring at an operational building site. Particles were measured in the 5-10,000-nm-size range using a fast response differential mobility spectrometer and a GRIMM particle spectrometer for 55 h over 8 days. The UFPs were found to account for >90 % of the total particle number concentrations and <10 % of the total mass concentrations released during the recorded activities. The highest UFP concentrations were 4860, 740, 650 and 500 times above the background value during wall-chasing, drilling, cementing and general demolition activities, respectively. Scanning electron microscopy, X-ray photoelectron spectroscopy and ion beam analysis were used to identify physicochemical characteristics of particles and attribute them to probable sources considering the size and the nature of the particles. The results confirm that refurbishment activities produce significant levels (both number and mass) of airborne particles, indicating a need to develop appropriate regulations for the control of occupational exposure of operatives undertaking building refurbishment.

  9. Pattern formation for active particles on optically created ordered and disordered substrates (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Reichhardt, Charles M.; Ray, Dipanjan; Reichhardt, Cynthia J.

    2015-08-01

    There has been tremendous growth in the field of active matter, where the individual particles that comprise the system are self-driven. Examples of this class of system include biological systems such as swimming bacteria and crawling cells. More recently, non-biological swimmers have been created using colloidal Janus particles that undergo chemical reactions on one side to produce self-propulsion. These active matter systems exhibit a wide variety of behaviors that are absent in systems undergoing purely thermal fluctuations, such as transitions from uniform liquids to clusters or living crystals, pushing objects around, ratchet effects, and phase separation in mixtures of active and passive particles. Here we examine the collective effects of active matter disks in the presence of static or dynamic substrates. For colloids, such substrates could be created optically in the form of periodic, random, or quasiperiodic patterns. For thermal particles, increasing the temperature generally increases the diffusion or mobility of the particles when they move over a random or periodic substrates. We find that when the particles are active, increasing the activity can increase the mobility for smaller run lengths but decrease the mobility at large run lengths. Additionally we find that at large run lengths on a structured substrate, a variety of novel active crystalline states can form such as stripes, squares and triangular patterns.

  10. Activity-assisted self-assembly of colloidal particles

    NASA Astrophysics Data System (ADS)

    Mallory, S. A.; Cacciuto, A.

    2016-08-01

    We outline a basic strategy of how self-propulsion can be used to improve the yield of a typical colloidal self-assembly process. The success of this approach is predicated on the thoughtful design of the colloidal building block as well as how self-propulsion is endowed to the particle. As long as a set of criteria are satisfied, it is possible to significantly increase the rate of self-assembly, and greatly expand the window in parameter space where self-assembly can occur. In addition, we show that by tuning the relative on-off time of the self-propelling force it is possible to modulate the effective speed of the colloids allowing for further optimization of the self-assembly process.

  11. Identification of Ice Nucleation Active Sites on Feldspar Dust Particles

    PubMed Central

    2015-01-01

    Mineral dusts originating from Earth’s crust are known to be important atmospheric ice nuclei. In agreement with earlier studies, feldspar was found as the most active of the tested natural mineral dusts. Here we investigated in closer detail the reasons for its activity and the difference in the activity of the different feldspars. Conclusions are drawn from scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, and oil-immersion freezing experiments. K-feldspar showed by far the highest ice nucleation activity. Finally, we give a potential explanation of this effect, finding alkali-metal ions having different hydration shells and thus an influence on the ice nucleation activity of feldspar surfaces. PMID:25584435

  12. Active Particles with Soft and Curved Walls: Equation of State, Ratchets, and Instabilities.

    PubMed

    Nikola, Nikolai; Solon, Alexandre P; Kafri, Yariv; Kardar, Mehran; Tailleur, Julien; Voituriez, Raphaël

    2016-08-26

    We study, from first principles, the pressure exerted by an active fluid of spherical particles on general boundaries in two dimensions. We show that, despite the nonuniform pressure along curved walls, an equation of state is recovered upon a proper spatial averaging. This holds even in the presence of pairwise interactions between particles or when asymmetric walls induce ratchet currents, which are accompanied by spontaneous shear stresses on the walls. For flexible obstacles, the pressure inhomogeneities lead to a modulational instability as well as to the spontaneous motion of short semiflexible filaments. Finally, we relate the force exerted on objects immersed in active baths to the particle flux they generate around them.

  13. Generalized Scaling and the Master Variable for Brownian Magnetic Nanoparticle Dynamics

    PubMed Central

    Reeves, Daniel B.; Shi, Yipeng; Weaver, John B.

    2016-01-01

    Understanding the dynamics of magnetic particles can help to advance several biomedical nanotechnologies. Previously, scaling relationships have been used in magnetic spectroscopy of nanoparticle Brownian motion (MSB) to measure biologically relevant properties (e.g., temperature, viscosity, bound state) surrounding nanoparticles in vivo. Those scaling relationships can be generalized with the introduction of a master variable found from non-dimensionalizing the dynamical Langevin equation. The variable encapsulates the dynamical variables of the surroundings and additionally includes the particles’ size distribution and moment and the applied field’s amplitude and frequency. From an applied perspective, the master variable allows tuning to an optimal MSB biosensing sensitivity range by manipulating both frequency and field amplitude. Calculation of magnetization harmonics in an oscillating applied field is also possible with an approximate closed-form solution in terms of the master variable and a single free parameter. PMID:26959493

  14. System and method for collisional activation of charged particles

    DOEpatents

    Ibrahim, Yehia M; Belov, Mikhail E; Prior, David C

    2013-09-24

    A collision cell is disclosed that provides ion activation in various selective modes. Ion activation is performed inside selected segments of a segmented quadrupole that provides maximum optimum capture and collection of fragmentation products. The invention provides collisional cooling of precursor ions as well as product fragments and further allows effective transmission of ions through a high pressure interface into a coupled mass analysis instrument.

  15. Filterable redox cycling activity: a comparison between diesel exhaust particles and secondary organic aerosol constituents.

    PubMed

    McWhinney, Robert D; Badali, Kaitlin; Liggio, John; Li, Shao-Meng; Abbatt, Jonathan P D

    2013-04-02

    The redox activity of diesel exhaust particles (DEP) collected from a light-duty diesel passenger car engine was examined using the dithiothreitol (DTT) assay. DEP was highly redox-active, causing DTT to decay at a rate of 23-61 pmol min(-1) μg(-1) of particle used in the assay, which was an order of magnitude higher than ambient coarse and fine particulate matter (PM) collected from downtown Toronto. Only 2-11% of the redox activity was in the water-soluble portion, while the remainder occurred at the black carbon surface. This is in contrast to redox-active secondary organic aerosol constituents, in which upward of 90% of the activity occurs in the water-soluble fraction. The redox activity of DEP is not extractable by moderately polar (methanol) and nonpolar (dichloromethane) organic solvents, and is hypothesized to arise from redox-active moieties contiguous with the black carbon portion of the particles. These measurements illustrate that "Filterable Redox Cycling Activity" may therefore be useful to distinguish black carbon-based oxidative capacity from water-soluble organic-based activity. The difference in chemical environment leading to redox activity highlights the need to further examine the relationship between activity in the DTT assay and toxicology measurements across particles of different origins and composition.

  16. Electrode including porous particles with embedded active material for use in a secondary electrochemical cell

    DOEpatents

    Vissers, Donald R.; Nelson, Paul A.; Kaun, Thomas D.; Tomczuk, Zygmunt

    1978-04-25

    Particles of carbonaceous matrices containing embedded electrode active material are prepared for vibratory loading within a porous electrically conductive substrate. In preparing the particles, active materials such as metal chalcogenides, solid alloys of alkali or alkaline earth metals along with other metals and their oxides in powdered or particulate form are blended with a thermosetting resin and particles of a volatile to form a paste mixture. The paste is heated to a temperature at which the volatile transforms into vapor to impart porosity at about the same time as the resin begins to cure into a rigid, solid structure. The solid structure is then comminuted into porous, carbonaceous particles with the embedded active material.

  17. Thermally activated repolarization of antiferromagnetic particles: Monte Carlo dynamics

    NASA Astrophysics Data System (ADS)

    Soloviev, S. V.; Popkov, A. F.; Knizhnik, A. A.; Iskandarova, I. M.

    2017-02-01

    Based on the equation of motion of an antiferromagnetic moment, taking into account a random field of thermal fluctuations, we propose a Monte Carlo (MC) scheme for the numerical simulation of the evolutionary dynamics of an antiferromagnetic particle, corresponding to the Langevin dynamics in the Kramers theory for the two-well potential. Conditions for the selection of the sphere of fluctuations of random deviations of the antiferromagnetic vector at an MC time step are found. A good agreement with the theory of Kramers thermal relaxation is demonstrated for varying temperatures and heights of energy barrier over a wide range of integration time steps in an overdamped regime. Based on the developed scheme, we performed illustrative calculations of the temperature drift of the exchange bias under the fast annealing of a ferromagnet-antiferromagnet structure, taking into account the random variation of anisotropy directions in antiferromagnetic grains and their sizes. The proposed approach offers promise for modeling magnetic sensors and spintronic memory devices containing heterostructures with antiferromagnetic layers.

  18. Investigating Primary Marine Aerosol Properties: CCN Activity of Sea Salt and Mixed Inorganic–Organic Particles

    PubMed Central

    2012-01-01

    Sea spray particles ejected as a result of bubbles bursting from artificial seawater containing salt and organic matter in a stainless steel tank were sampled for size distribution, morphology, and cloud condensation nucleus (CCN) activity. Bubbles were generated either by aeration through a diffuser or by water jet impingement on the seawater surface. Three objectives were addressed in this study. First, CCN activities of NaCl and two types of artificial sea salt containing only inorganic components were measured to establish a baseline for further measurements of mixed organic–inorganic particles. Second, the effect of varying bubble residence time in the bulk seawater solution on particle size and CCN activity was investigated and was found to be insignificant for the organic compounds studied. Finally, CCN activities of particles produced from jet impingement were compared with those produced from diffuser aeration. Analyses indicate a considerable amount of organic enrichment in the jet-produced particles relative to the bulk seawater composition when sodium laurate, an organic surfactant, is present in the seawater. In this case, the production of a thick foam layer during impingement may explain the difference in activation and supports hypotheses that particle production from the two methods of generating bubbles is not equal. PMID:22809370

  19. Investigating primary marine aerosol properties: CCN activity of sea salt and mixed particles

    NASA Astrophysics Data System (ADS)

    King, S. M.; Butcher, A. C.; Rosenoern, T.; Coz, E.; Lieke, K. I.; de Leeuw, G.; Nilsson, E. D.; Bilde, M.

    2012-04-01

    Sea salt particles ejected as a result of bubbles bursting from artificial seawater in a closed stainless steel tank were sampled for size distribution, morphology, and cloud condensation nucleus (CCN) activity. The two-component artificial seawater consisted of salt, either NaCl or sea salt, and one organic compound in deionized water. Several organic molecules representative of oceanic organic matter were investigated. Bubbles were generated either by aeration through a porous diffuser or by water jet impingement on the surface of the artificial seawater. The effect of bubble lifetime, which was controlled by varying the depth of the diffuser in the water column, on particle size and CCN activity was investigated and was found to be insignificant for the organic compounds studied. The CCN activities of particles produced from diffuser-generated bubbles were generally governed by the high hygroscopicity of salt, such that activation was indistinguishable from that of salt, except in the case of very low mass ratio of salt to organic matter in the seawater solution. There was, however, a considerable decrease in CCN activity for particles produced from jet impingement on seawater that had a salinity of 10‰ and contained 0.45 mM of sodium laurate, an organic surfactant. The production of a thick foam layer from impingement may explain the difference in activation and supports hypotheses that particle production from the two methods of generating bubbles is not similar. Accurate conclusions from observed CCN activities of particles from artificial seawater containing organic matter require knowledge of the CCN activity of the inorganic component, especially as a small amount of the inorganic can heavily influence activation. Therefore, the CCN activity of both artificial sea salt and NaCl were measured and compared. Part of the discrepancy observed between the CCN activities of the two salts may be due to morphological differences, which were investigated using

  20. Fractional Brownian Motion:. Theory and Application to DNA Walk

    NASA Astrophysics Data System (ADS)

    Lim, S. C.; Muniandy, S. V.

    2001-09-01

    This paper briefly reviews the theory of fractional Brownian motion (FBM) and its generalization to multifractional Brownian motion (MBM). FBM and MBM are applied to a biological system namely the DNA sequence. By considering a DNA sequence as a fractal random walk, it is possible to model the noncoding sequence of human retinoblastoma DNA as a discrete version of FBM. The average scaling exponent or Hurst exponent of the DNA walk is estimated to be H = 0.60 ± 0.05 using the monofractal R/S analysis. This implies that the mean square fluctuation of DNA walk belongs to anomalous superdiffusion type. We also show that the DNA landscape is not monofractal, instead one has multifractal DNA landscape. The empirical estimates of the Hurst exponent falls approximately within the range H ~ 0.62 - 0.72. We propose two multifractal models, namely the MBM and multiscale FBM to describe the existence of different Hurst exponents in DNA walk.

  1. On a nonstandard Brownian motion and its maximal function

    NASA Astrophysics Data System (ADS)

    Andrade, Bernardo B. de

    2015-07-01

    This article uses Radically Elementary Probability Theory (REPT) to prove results about the Wiener walk (the radically elementary Brownian motion) without the technical apparatus required by stochastic integration. The techniques used replace measure-theoretic tools by discrete probability and the rigorous use of infinitesimals. Specifically, REPT is applied to the results in Palacios (The American Statistician, 2008) to calculate certain expectations related to the Wiener walk and its maximal function. Because Palacios uses mostly combinatorics and no measure theory his results carry over through REPT with minimal changes. The paper also presents a construction of the Wiener walk which is intended to mimic the construction of Brownian motion from "continuous" white noise. A brief review of the nonstandard model on which REPT is based is given in the Appendix in order to minimize the need for previous exposure to the subject.

  2. Hidden Symmetries, Instabilities, and Current Suppression in Brownian Ratchets

    NASA Astrophysics Data System (ADS)

    Cubero, David; Renzoni, Ferruccio

    2016-01-01

    The operation of Brownian motors is usually described in terms of out-of-equilibrium and symmetry-breaking settings, with the relevant spatiotemporal symmetries identified from the analysis of the equations of motion for the system at hand. When the appropriate conditions are satisfied, symmetry-related trajectories with opposite current are thought to balance each other, yielding suppression of transport. The direction of the current can be precisely controlled around these symmetry points by finely tuning the driving parameters. Here we demonstrate, by studying a prototypical Brownian ratchet system, the existence of hidden symmetries, which escape identification by the standard symmetry analysis, and which require different theoretical tools for their revelation. Furthermore, we show that system instabilities may lead to spontaneous symmetry breaking with unexpected generation of directed transport.

  3. Brownian motion of a circle swimmer in a harmonic trap

    NASA Astrophysics Data System (ADS)

    Jahanshahi, Soudeh; Löwen, Hartmut; ten Hagen, Borge

    2017-02-01

    We study the dynamics of a Brownian circle swimmer with a time-dependent self-propulsion velocity in an external temporally varying harmonic potential. For several situations, the noise-free swimming paths, the noise-averaged mean trajectories, and the mean-square displacements are calculated analytically or by computer simulation. Based on our results, we discuss optimal swimming strategies in order to explore a maximum spatial range around the trap center. In particular, we find a resonance situation for the maximum escape distance as a function of the various frequencies in the system. Moreover, the influence of the Brownian noise is analyzed by comparing noise-free trajectories at zero temperature with the corresponding noise-averaged trajectories at finite temperature. The latter reveal various complex self-similar spiral or rosette-like patterns. Our predictions can be tested in experiments on artificial and biological microswimmers under dynamical external confinement.

  4. Convex hull of a Brownian motion in confinement.

    PubMed

    Chupeau, Marie; Bénichou, Olivier; Majumdar, Satya N

    2015-05-01

    We study the effect of confinement on the mean perimeter of the convex hull of a planar Brownian motion, defined as the minimum convex polygon enclosing the trajectory. We use a minimal model where an infinite reflecting wall confines the walk to one side. We show that the mean perimeter displays a surprising minimum with respect to the starting distance to the wall and exhibits a nonanalyticity for small distances. In addition, the mean span of the trajectory in a fixed direction θ∈]0,π/2[, which can be shown to yield the mean perimeter by integration over θ, presents these same two characteristics. This is in striking contrast to the one-dimensional case, where the mean span is an increasing analytical function. The nonmonotonicity in the two-dimensional case originates from the competition between two antagonistic effects due to the presence of the wall: reduction of the space accessible to the Brownian motion and effective repulsion.

  5. Convex hull of a Brownian motion in confinement

    NASA Astrophysics Data System (ADS)

    Chupeau, Marie; Bénichou, Olivier; Majumdar, Satya N.

    2015-05-01

    We study the effect of confinement on the mean perimeter of the convex hull of a planar Brownian motion, defined as the minimum convex polygon enclosing the trajectory. We use a minimal model where an infinite reflecting wall confines the walk to one side. We show that the mean perimeter displays a surprising minimum with respect to the starting distance to the wall and exhibits a nonanalyticity for small distances. In addition, the mean span of the trajectory in a fixed direction θ ∈]0 ,π /2 [ , which can be shown to yield the mean perimeter by integration over θ , presents these same two characteristics. This is in striking contrast to the one-dimensional case, where the mean span is an increasing analytical function. The nonmonotonicity in the two-dimensional case originates from the competition between two antagonistic effects due to the presence of the wall: reduction of the space accessible to the Brownian motion and effective repulsion.

  6. Brownian motion of a circle swimmer in a harmonic trap.

    PubMed

    Jahanshahi, Soudeh; Löwen, Hartmut; Ten Hagen, Borge

    2017-02-01

    We study the dynamics of a Brownian circle swimmer with a time-dependent self-propulsion velocity in an external temporally varying harmonic potential. For several situations, the noise-free swimming paths, the noise-averaged mean trajectories, and the mean-square displacements are calculated analytically or by computer simulation. Based on our results, we discuss optimal swimming strategies in order to explore a maximum spatial range around the trap center. In particular, we find a resonance situation for the maximum escape distance as a function of the various frequencies in the system. Moreover, the influence of the Brownian noise is analyzed by comparing noise-free trajectories at zero temperature with the corresponding noise-averaged trajectories at finite temperature. The latter reveal various complex self-similar spiral or rosette-like patterns. Our predictions can be tested in experiments on artificial and biological microswimmers under dynamical external confinement.

  7. How superdiffusion gets arrested: ecological encounters explain shift from Lévy to Brownian movement.

    PubMed

    de Jager, Monique; Bartumeus, Frederic; Kölzsch, Andrea; Weissing, Franz J; Hengeveld, Geerten M; Nolet, Bart A; Herman, Peter M J; van de Koppel, Johan

    2014-01-07

    Ecological theory uses Brownian motion as a default template for describing ecological movement, despite limited mechanistic underpinning. The generality of Brownian motion has recently been challenged by empirical studies that highlight alternative movement patterns of animals, especially when foraging in resource-poor environments. Yet, empirical studies reveal animals moving in a Brownian fashion when resources are abundant. We demonstrate that Einstein's original theory of collision-induced Brownian motion in physics provides a parsimonious, mechanistic explanation for these observations. Here, Brownian motion results from frequent encounters between organisms in dense environments. In density-controlled experiments, movement patterns of mussels shifted from Lévy towards Brownian motion with increasing density. When the analysis was restricted to moves not truncated by encounters, this shift did not occur. Using a theoretical argument, we explain that any movement pattern approximates Brownian motion at high-resource densities, provided that movement is interrupted upon encounters. Hence, the observed shift to Brownian motion does not indicate a density-dependent change in movement strategy but rather results from frequent collisions. Our results emphasize the need for a more mechanistic use of Brownian motion in ecology, highlighting that especially in rich environments, Brownian motion emerges from ecological interactions, rather than being a default movement pattern.

  8. Application of Brownian motion theory to the analysis of membrane channel ionic trajectories calculated by molecular dynamics.

    PubMed Central

    Jakobsson, E; Chiu, S W

    1988-01-01

    This paper shows how Brownian motion theory can be used to analyze features of individual ion trajectories in channels as calculated by molecular dynamics, and that its use permits more precise determinations of diffusion coefficients than would otherwise be possible. We also show how a consideration of trajectories of single particles can distinguish between effects due to the magnitude of the diffusion coefficient and effects due to barriers and wells in the potential profile, effects which can not be distinguished by consideration of average fluxes. PMID:2465032

  9. Intranasal exposure to amorphous nanosilica particles could activate intrinsic coagulation cascade and platelets in mice

    PubMed Central

    2013-01-01

    Background Nanomaterials with particle sizes <100 nm have been already applied in various applications such as cosmetics, medicines, and foods. Therefore, ensuring the safety of nanomaterials is becoming increasingly important. Here we examined the localization and biological responses of intranasally administered amorphous nanosilica particles in mice, focusing on the coagulation system. Methods We used nanosilica particles with diameters of 30, 70, or 100 nm (nSP30, nSP70, or nSP100 respectively), and conventional microscale silica particles with diameters of 300 or 1000 nm (mSP300 or mSP1000, respectively). BALB/c mice were intranasally exposed to nSP30, nSP70, nSP100, mSP300, or mSP1000 at concentrations of 500 μg/mouse for 7 days. After 24 hours of last administration, we performed the in vivo transmission electron microscopy analysis, hematological examination and coagulation tests. Results In vivo transmission electron microscopy analysis showed that nanosilica particles with a diameter <100 nm were absorbed through the nasal cavity and were distributed into liver and brain. Hematological examination and coagulation tests showed that platelet counts decreased and that the activated partial thromboplastin time was prolonged in nSP30 or nSP70-treated groups of mice, indicating that nanosilica particles might have activated a coagulation cascade. In addition, in in vitro activation tests of human plasma, nanosilica particles had greater potential than did conventional microscale silica particles to activate coagulation factor XII. In nanosilica-particle-treated groups, the levels of soluble CD40 ligand, and von Willebrand factor which are involved in stimulating platelets tended to slightly increase with decreasing particle size. Conclusions These results suggest that intranasally administered nanosilica particles with diameters of 30 and 70 nm could induce abnormal activation of the coagulation system through the activation of an intrinsic coagulation cascade

  10. Effect of particle surface area on ice active site densities retrieved from droplet freezing spectra

    NASA Astrophysics Data System (ADS)

    Beydoun, Hassan; Polen, Michael; Sullivan, Ryan C.

    2016-10-01

    Heterogeneous ice nucleation remains one of the outstanding problems in cloud physics and atmospheric science. Experimental challenges in properly simulating particle-induced freezing processes under atmospherically relevant conditions have largely contributed to the absence of a well-established parameterization of immersion freezing properties. Here, we formulate an ice active, surface-site-based stochastic model of heterogeneous freezing with the unique feature of invoking a continuum assumption on the ice nucleating activity (contact angle) of an aerosol particle's surface that requires no assumptions about the size or number of active sites. The result is a particle-specific property g that defines a distribution of local ice nucleation rates. Upon integration, this yields a full freezing probability function for an ice nucleating particle. Current cold plate droplet freezing measurements provide a valuable and inexpensive resource for studying the freezing properties of many atmospheric aerosol systems. We apply our g framework to explain the observed dependence of the freezing temperature of droplets in a cold plate on the concentration of the particle species investigated. Normalizing to the total particle mass or surface area present to derive the commonly used ice nuclei active surface (INAS) density (ns) often cannot account for the effects of particle concentration, yet concentration is typically varied to span a wider measurable freezing temperature range. A method based on determining what is denoted an ice nucleating species' specific critical surface area is presented and explains the concentration dependence as a result of increasing the variability in ice nucleating active sites between droplets. By applying this method to experimental droplet freezing data from four different systems, we demonstrate its ability to interpret immersion freezing temperature spectra of droplets containing variable particle concentrations. It is shown that general

  11. Analysis of a Brownian heat engine with ecological criteria

    NASA Astrophysics Data System (ADS)

    Açıkkalp, Emin

    2016-12-01

    The purpose of this study is to investigate the Brownian heat engine with thermo-ecological function ( ECF) and ecological coefficient of performance ( ECOP). Potential and kinetic heat flows are taken into account. Different parameters are considered in the analyses. Beside the thermo-ecological function and ecological coefficient of performance, the basic thermodynamics parameters involving power output and efficiency are investigated. Results are presented numerically and the optimum points of the system are determined.

  12. Free Energies and Fluctuations for the Unitary Brownian Motion

    NASA Astrophysics Data System (ADS)

    Dahlqvist, Antoine

    2016-12-01

    We show that the Laplace transforms of traces of words in independent unitary Brownian motions converge towards an analytic function on a non trivial disc. These results allow one to study the asymptotic behavior of Wilson loops under the unitary Yang-Mills measure on the plane with a potential. The limiting objects obtained are shown to be characterized by equations analogue to Schwinger-Dyson's ones, named here after Makeenko and Migdal.

  13. Algorithms for Brownian first-passage-time estimation.

    PubMed

    Adib, Artur B

    2009-09-01

    A class of algorithms in discrete space and continuous time for Brownian first-passage-time estimation is considered. A simple algorithm is derived that yields exact mean first-passage times (MFPTs) for linear potentials in one dimension, regardless of the lattice spacing. When applied to nonlinear potentials and/or higher spatial dimensions, numerical evidence suggests that this algorithm yields MFPT estimates that either outperform or rival Langevin-based (discrete time and continuous space) estimates.

  14. Variation of CCN activity during new particle formation events in the North China Plain

    NASA Astrophysics Data System (ADS)

    Ma, Nan; Zhao, Chunsheng; Tao, Jiangchuan; Wu, Zhijun; Kecorius, Simonas; Wang, Zhibin; Größ, Johannes; Liu, Hongjian; Bian, Yuxuan; Kuang, Ye; Teich, Monique; Spindler, Gerald; Müller, Konrad; van Pinxteren, Dominik; Herrmann, Hartmut; Hu, Min; Wiedensohler, Alfred

    2016-07-01

    The aim of this investigation was to obtain a better understanding of the variability of the cloud condensation nuclei (CCN) activity during new particle formation (NPF) events in an anthropogenically polluted atmosphere of the North China Plain (NCP). We investigated the size-resolved activation ratio as well as particle number size distribution, hygroscopicity, and volatility during a 4-week intensive field experiment in summertime at a regional atmospheric observatory in Xianghe. Interestingly, based on a case study, two types of NPF events were found, in which the newly formed particles exhibited either a higher or a lower hygroscopicity. Therefore, the CCN activity of newly formed particles in different NPF events was largely different, indicating that a simple parameterization of particle CCN activity during NPF events over the NCP might lead to poor estimates of CCN number concentration (NCCN). For a more accurate estimation of the potential NCCN during NPF events, the variation of CCN activity has to be taken into account. Considering that a fixed activation ratio curve or critical diameter are usually used to calculate NCCN, the influence of the variation of particle CCN activity on the calculation of NCCN during NPF events was evaluated based on the two parameterizations. It was found that NCCN might be underestimated by up to 30 % if a single activation ratio curve (representative of the region and season) were to be used in the calculation; and might be underestimated by up to 50 % if a fixed critical diameter (representative of the region and season) were used. Therefore, we suggest not using a fixed critical diameter in the prediction of NCCN in NPF. If real-time CCN activity data are not available, using a proper fixed activation ratio curve can be an alternative but compromised choice.

  15. Non-Brownian dynamics and strategy of amoeboid cell locomotion

    NASA Astrophysics Data System (ADS)

    Nishimura, Shin I.; Ueda, Masahiro; Sasai, Masaki

    2012-04-01

    Amoeboid cells such as Dictyostelium discoideum and Madin-Darby canine kidney cells show the non-Brownian dynamics of migration characterized by the superdiffusive increase of mean-squared displacement. In order to elucidate the physical mechanism of this non-Brownian dynamics, a computational model is developed which highlights a group of inhibitory molecules for actin polymerization. Based on this model, we propose a hypothesis that inhibitory molecules are sent backward in the moving cell to accumulate at the rear of cell. The accumulated inhibitory molecules at the rear further promote cell locomotion to form a slow positive feedback loop of the whole-cell scale. The persistent straightforward migration is stabilized with this feedback mechanism, but the fluctuation in the distribution of inhibitory molecules and the cell shape deformation concurrently interrupt the persistent motion to turn the cell into a new direction. A sequence of switching behaviors between persistent motions and random turns gives rise to the superdiffusive migration in the absence of the external guidance signal. In the complex environment with obstacles, this combined process of persistent motions and random turns drives the simulated amoebae to solve the maze problem in a highly efficient way, which suggests the biological advantage for cells to bear the non-Brownian dynamics.

  16. Amoeba-inspired nanoarchitectonic computing implemented using electrical Brownian ratchets.

    PubMed

    Aono, M; Kasai, S; Kim, S-J; Wakabayashi, M; Miwa, H; Naruse, M

    2015-06-12

    In this study, we extracted the essential spatiotemporal dynamics that allow an amoeboid organism to solve a computationally demanding problem and adapt to its environment, thereby proposing a nature-inspired nanoarchitectonic computing system, which we implemented using a network of nanowire devices called 'electrical Brownian ratchets (EBRs)'. By utilizing the fluctuations generated from thermal energy in nanowire devices, we used our system to solve the satisfiability problem, which is a highly complex combinatorial problem related to a wide variety of practical applications. We evaluated the dependency of the solution search speed on its exploration parameter, which characterizes the fluctuation intensity of EBRs, using a simulation model of our system called 'AmoebaSAT-Brownian'. We found that AmoebaSAT-Brownian enhanced the solution searching speed dramatically when we imposed some constraints on the fluctuations in its time series and it outperformed a well-known stochastic local search method. These results suggest a new computing paradigm, which may allow high-speed problem solving to be implemented by interacting nanoscale devices with low power consumption.

  17. Semicircular Canals Circumvent Brownian Motion Overload of Mechanoreceptor Hair Cells

    PubMed Central

    Muller, Mees; Heeck, Kier

    2016-01-01

    Vertebrate semicircular canals (SCC) first appeared in the vertebrates (i.e. ancestral fish) over 600 million years ago. In SCC the principal mechanoreceptors are hair cells, which as compared to cochlear hair cells are distinctly longer (70 vs. 7 μm), 10 times more compliant to bending (44 vs. 500 nN/m), and have a 100-fold higher tip displacement threshold (< 10 μm vs. <400 nm). We have developed biomechanical models of vertebrate hair cells where the bundle is approximated as a stiff, cylindrical elastic rod subject to friction and thermal agitation. Our models suggest that the above differences aid SCC hair cells in circumventing the masking effects of Brownian motion noise of about 70 nm, and thereby permit transduction of very low frequency (<10 Hz) signals. We observe that very low frequency mechanoreception requires increased stimulus amplitude, and argue that this is adaptive to circumvent Brownian motion overload at the hair bundles. We suggest that the selective advantage of detecting such low frequency stimuli may have favoured the evolution of large guiding structures such as semicircular canals and otoliths to overcome Brownian Motion noise at the level of the mechanoreceptors of the SCC. PMID:27448330

  18. Radiative transfer theory for active remote sensing of a layer of nonspherical particles

    NASA Technical Reports Server (NTRS)

    Tsang, L.; Kong, J. A.; Shin, R. T.

    1984-01-01

    The radiative transfer theory is applied to calculate the scattering by a layer of randomly positioned and oriented nonspherical particles. The scattering amplitude functions of each individual particle are calculated with Waterman's T matrix method, which utilizes vector spherical wave functions for expansion of incident, scattered, and surface fields. The orientation of the particles is described by a probability density function of the Eulerian angles of rotation. A rotation matrix is used to relate the T matrix of the principal frame to that of the natural frame of the particle. The extinction matrix and phase matrix of the radiative transfer equations are expressed in terms of the T matrix elements. The extinction matrix for nonspherical particles is generally nondiagonal. There are only two attenuation rates in a specified direction of propagation. The radiative transfer equations are solved by an iterative method to first order in albedo. Numerical results are illustrated as functions of incidence angle and frequency with applications to active remote sensing.

  19. Effect of the mechanical activation on size reduction of crystalline acetaminophen drug particles

    PubMed Central

    Biazar, Esmaeil; Beitollahi, Ali; Rezayat, S Mehdi; Forati, Tahmineh; Asefnejad, Azadeh; Rahimi, Mehdi; Zeinali, Reza; Ardeshir, Mahmoud; Hatamjafari, Farhad; Sahebalzamani, Ali; Heidari, Majid

    2009-01-01

    The decrease in particle size may offer new properties to drugs. In this study, we investigated the size reduction influence of the acetaminophen (C8H9O2N) particles by mechanical activation using a dry ball mill. The activated samples with the average size of 1 μm were then investigated in different time periods with the infrared (IR), inductively coupled plasma (ICP), atomic force microscopy (AFM), and X-ray diffraction (XRD) methods. The results of the IR and XRD images showed no change in the drug structure after the mechanical activation of all samples. With the peak height at full width at half maximum from XRD and the Scherrer equation, the size of the activated crystallite samples illustrated that the AFM images were in sound agreement with the Scherrer equation. According to the peaks of the AFM images, the average size of the particles in 30 hours of activation was 24 nm with a normal particle distribution. The ICP analysis demonstrated the presence of tungsten carbide particle impurities after activation from the powder sample impacting with the ball and jar. The greatest reduction in size was after milling for 30 hours. PMID:20054432

  20. Facilitation of polymer looping and giant polymer diffusivity in crowded solutions of active particles

    NASA Astrophysics Data System (ADS)

    Shin, Jaeoh; Cherstvy, Andrey G.; Kim, Won Kyu; Metzler, Ralf

    2015-11-01

    We study the dynamics of polymer chains in a bath of self-propelled particles (SPP) by extensive Langevin dynamics simulations in a two-dimensional model system. Specifically, we analyse the polymer looping properties versus the SPP activity and investigate how the presence of the active particles alters the chain conformational statistics. We find that SPPs tend to extend flexible polymer chains, while they rather compactify stiffer semiflexible polymers, in agreement with previous results. Here we show that higher activities of SPPs yield a higher effective temperature of the bath and thus facilitate the looping kinetics of a passive polymer chain. We explicitly compute the looping probability and looping time in a wide range of the model parameters. We also analyse the motion of a monomeric tracer particle and the polymer’s centre of mass in the presence of the active particles in terms of the time averaged mean squared displacement, revealing a giant diffusivity enhancement for the polymer chain via SPP pooling. Our results are applicable to rationalising the dimensions and looping kinetics of biopolymers at constantly fluctuating and often actively driven conditions inside biological cells or in suspensions of active colloidal particles or bacteria cells.

  1. Accurate and efficient calculation of excitation energies with the active-space particle-particle random phase approximation

    DOE PAGES

    Zhang, Du; Yang, Weitao

    2016-10-13

    An efficient method for calculating excitation energies based on the particle-particle random phase approximation (ppRPA) is presented. Neglecting the contributions from the high-lying virtual states and the low-lying core states leads to the significantly smaller active-space ppRPA matrix while keeping the error to within 0.05 eV from the corresponding full ppRPA excitation energies. The resulting computational cost is significantly reduced and becomes less than the construction of the non-local Fock exchange potential matrix in the self-consistent-field (SCF) procedure. With only a modest number of active orbitals, the original ppRPA singlet-triplet (ST) gaps as well as the low-lying single and doublemore » excitation energies can be accurately reproduced at much reduced computational costs, up to 100 times faster than the iterative Davidson diagonalization of the original full ppRPA matrix. For high-lying Rydberg excitations where the Davidson algorithm fails, the computational savings of active-space ppRPA with respect to the direct diagonalization is even more dramatic. The virtues of the underlying full ppRPA combined with the significantly lower computational cost of the active-space approach will significantly expand the applicability of the ppRPA method to calculate excitation energies at a cost of O(K^{4}), with a prefactor much smaller than a single SCF Hartree-Fock (HF)/hybrid functional calculation, thus opening up new possibilities for the quantum mechanical study of excited state electronic structure of large systems.« less

  2. Accurate and efficient calculation of excitation energies with the active-space particle-particle random phase approximation

    SciTech Connect

    Zhang, Du; Yang, Weitao

    2016-10-13

    An efficient method for calculating excitation energies based on the particle-particle random phase approximation (ppRPA) is presented. Neglecting the contributions from the high-lying virtual states and the low-lying core states leads to the significantly smaller active-space ppRPA matrix while keeping the error to within 0.05 eV from the corresponding full ppRPA excitation energies. The resulting computational cost is significantly reduced and becomes less than the construction of the non-local Fock exchange potential matrix in the self-consistent-field (SCF) procedure. With only a modest number of active orbitals, the original ppRPA singlet-triplet (ST) gaps as well as the low-lying single and double excitation energies can be accurately reproduced at much reduced computational costs, up to 100 times faster than the iterative Davidson diagonalization of the original full ppRPA matrix. For high-lying Rydberg excitations where the Davidson algorithm fails, the computational savings of active-space ppRPA with respect to the direct diagonalization is even more dramatic. The virtues of the underlying full ppRPA combined with the significantly lower computational cost of the active-space approach will significantly expand the applicability of the ppRPA method to calculate excitation energies at a cost of O(K^{4}), with a prefactor much smaller than a single SCF Hartree-Fock (HF)/hybrid functional calculation, thus opening up new possibilities for the quantum mechanical study of excited state electronic structure of large systems.

  3. Accurate and efficient calculation of excitation energies with the active-space particle-particle random phase approximation

    NASA Astrophysics Data System (ADS)

    Zhang, Du; Yang, Weitao

    2016-10-01

    An efficient method for calculating excitation energies based on the particle-particle random phase approximation (ppRPA) is presented. Neglecting the contributions from the high-lying virtual states and the low-lying core states leads to the significantly smaller active-space ppRPA matrix while keeping the error to within 0.05 eV from the corresponding full ppRPA excitation energies. The resulting computational cost is significantly reduced and becomes less than the construction of the non-local Fock exchange potential matrix in the self-consistent-field (SCF) procedure. With only a modest number of active orbitals, the original ppRPA singlet-triplet (ST) gaps as well as the low-lying single and double excitation energies can be accurately reproduced at much reduced computational costs, up to 100 times faster than the iterative Davidson diagonalization of the original full ppRPA matrix. For high-lying Rydberg excitations where the Davidson algorithm fails, the computational savings of active-space ppRPA with respect to the direct diagonalization is even more dramatic. The virtues of the underlying full ppRPA combined with the significantly lower computational cost of the active-space approach will significantly expand the applicability of the ppRPA method to calculate excitation energies at a cost of O(K4), with a prefactor much smaller than a single SCF Hartree-Fock (HF)/hybrid functional calculation, thus opening up new possibilities for the quantum mechanical study of excited state electronic structure of large systems.

  4. Controlling active self-assembly through broken particle-shape symmetry.

    PubMed

    Wensink, H H; Kantsler, V; Goldstein, R E; Dunkel, J

    2014-01-01

    Many structural properties of conventional passive materials are known to arise from the symmetries of their microscopic constituents. By contrast, it is largely unclear how the interplay between particle shape and self-propulsion controls the meso- and macroscale behavior of active matter. Here we use large-scale simulations of homo- and heterogeneous self-propelled particle systems to identify generic effects of broken particle-shape symmetry on collective motion. We find that even small violations of fore-aft symmetry lead to fundamentally different collective behaviors, which may facilitate demixing of differently shaped species as well as the spontaneous formation of stable microrotors. These results suggest that variation of particle shape yields robust physical mechanisms to control self-assembly of active matter, with possibly profound implications for biology and materials design.

  5. The mechanics of active matter: Broken-symmetry hydrodynamics of motile particles and granular layers

    NASA Astrophysics Data System (ADS)

    Ramaswamy, Sriram; Simha, R. Aditi

    2006-09-01

    This articles reviews briefly our recent theoretical results on order, fluctuations and flow in collections of self-driven particles, in suspension or on a solid surface. The theoretical approach we have developed applies not only to collections of organisms such as schools of fish or collectively swimming bacteria, but also to motor-microtubule extracts with ATP and, most surprisingly, to agitated monolayers of orientable granular particles. We contrast the behaviour of these active systems with that of thermal equilibrium systems with the same symmetry. As an illustration of the role of activity we show that active smectics in three dimensions show true long-range order, unlike their thermal equilibrium counterparts.

  6. Properties of Spent Active Coke Particles Analysed via Comminution in Spouted Bed

    PubMed Central

    Buczek, Bronislaw

    2013-01-01

    Samples of active coke, fresh and spent after cleaning flue gases from communal waste incinerators, were investigated. The outer layers of both coke particles were separately removed by comminution in a spouted bed. The samples of both active cokes were analysed by means of densities, mercury porosimetry, and adsorption technique. Remaining cores were examined to determine the degree of consumption of coke by the sorption of hazardous emissions (SO2, HCl, and heavy metals) through its bed. Differences in contamination levels within the porous structure of the particles were estimated. The study demonstrated the effectiveness of commercial active coke in the cleaning of flue gases. PMID:24459454

  7. Statistical Mechanics of Colloidal Particles in Non-Conservative Force Fields

    NASA Astrophysics Data System (ADS)

    Wakil Moyses, Henrique

    Systems that are in mechanical equilibrium but are driven away from thermodynamic equilibrium present directed motion when in a thermal bath. This thesis explores this motion when systems are out of thermodynamic equilibrium due to the presence of non-conservative force fields. The first system we explored are Brownian vortexes. These are stochastic machines that use static non-conservative force fields to bias random thermal fluctuations into steadily circulating currents. The archetype for this class of systems is a colloidal sphere in an optical tweezer. Trapped near the focus of a strongly converging beam of light, the particle is displaced by random thermal kicks into the nonconservative part of the optical force field arising from radiation pressure, which then biases its diffusion. Assuming the particle remains localized within the trap, its time-averaged trajectory traces out a toroidal vortex. Unlike trivial Brownian vortexes, such as the biased Brownian pendulum, which circulate preferentially in the direction of the bias, the general Brownian vortex can change direction and even topology in response to temperature changes. In this thesis we introduce a theory based on a perturbative expansion of the Fokker-Planck equation for weak non-conservative driving. We show that the first-order solution takes the form of a modified Boltzmann relation and accounts for the rich phenomenology observed in experiments on micrometer-scale colloidal spheres in optical tweezers. Another system we explore are colloidal Janus particles composed of an optically absorbing and transparent faces. When illuminated by a defocused optical tweezer these particles swim vigorously, without requiring any chemical fuel. Most surprisingly, these optically activated colloidal swimmers circulate back and forth through the beam of light, tracing out regular sinuous patterns. In this thesis we propose a model for this class of light-activated swimmers in which a combination of radiation

  8. Particle properties in granular activated carbon filter during drinking water treatment.

    PubMed

    Lin, Tao; Chen, Wei; Wang, Leilei

    2010-01-01

    The elemental composition and bacteria attached in particles were investigated during granular activated carbon (GAC) filtration. The experimental results showed that trapped influent particles could form new, larger particles on GAC surface. The sloughing of individuals off GAC surface caused an increase in effluent particles in the size range from 5 to 25 tm. The selectivity for element removal in GAC filters caused an increasing proportion of metallic elements in the effluent particles. The distribution of molar ratio indicated a complicated composition for large particles, involving organic and inorganic substances. The organic proportion accounted for 40% of total carbon attached to the particles. Compared with dissolved carbon, there was potential for the formation of trihalomethanes by organic carbon attached to particles, especially for those with size larger than 10 im. The pure carbon energy spectrum was found only in the GAC effluent and the size distribution of carbon fines was mainly above 10 microm. The larger carbon fines provided more space for bacterial colonization and stronger protection for attached bacteria against disinfection. The residual attached bacteria after chorine disinfection was increased to 10(2)-l0(3) CFU/mL within 24 hours at 25 degrees C.

  9. Emergent ultra–long-range interactions between active particles in hybrid active–inactive systems

    PubMed Central

    Steimel, Joshua P.; Aragones, Juan L.; Hu, Helen; Qureshi, Naser; Alexander-Katz, Alfredo

    2016-01-01

    Particle–particle interactions determine the state of a system. Control over the range of such interactions as well as their magnitude has been an active area of research for decades due to the fundamental challenges it poses in science and technology. Very recently, effective interactions between active particles have gathered much attention as they can lead to out-of-equilibrium cooperative states such as flocking. Inspired by nature, where active living cells coexist with lifeless objects and structures, here we study the effective interactions that appear in systems composed of active and passive mixtures of colloids. Our systems are 2D colloidal monolayers composed primarily of passive (inactive) colloids, and a very small fraction of active (spinning) ferromagnetic colloids. We find an emergent ultra–long-range attractive interaction induced by the activity of the spinning particles and mediated by the elasticity of the passive medium. Interestingly, the appearance of such interaction depends on the spinning protocol and has a minimum actuation timescale below which no attraction is observed. Overall, these results clearly show that, in the presence of elastic components, active particles can interact across very long distances without any chemical modification of the environment. Such a mechanism might potentially be important for some biological systems and can be harnessed for newer developments in synthetic active soft materials. PMID:27071096

  10. Particle size tailoring of ursolic acid nanosuspensions for improved anticancer activity by controlled antisolvent precipitation.

    PubMed

    Wang, Yancai; Song, Ju; Chow, Shing Fung; Chow, Albert H L; Zheng, Ying

    2015-10-15

    The present study was aimed at tailoring the particle size of ursolic acid (UA) nanosuspension for improved anticancer activity. UA nanosuspensions were prepared by antisolvent precipitation using a four-stream multi-inlet vortex mixer (MIVM) under defined conditions of varying solvent composition, drug feeding concentration or stream flow rate. The resulting products were characterized for particle size and polydispersity. Two of the UA nanosuspensions with mean particle sizes of 100 and 300 nm were further assessed for their in-vitro activity against MCF-7 breast cancer cells using fluorescence microscopy with 4',6-diamidino-2-phenylindole (DAPI) staining, as well as flow cytometry with propidium (PI) staining and with double staining by fluorescein isothiocyanate. It was revealed that the solvent composition, drug feeding concentration and stream flow rate were critical parameters for particle size control of the UA nanosuspensions generated with the MIVM. Specifically, decreasing the UA feeding concentration or increasing the stream flow rate or ethanol content resulted in a reduction of particle size. Excellent reproducibility for nanosuspension production was demonstrated for the 100 and 300 nm UA preparations with a deviation of not more than 5% in particle size from the mean value of three independent batches. Fluorescence microscopy and flow cytometry revealed that these two different sized UA nanosuspensions, particularly the 300 nm sample, exhibited a higher anti-proliferation activity against the MCF-7 cells and afforded a larger population of these cells in both early and late apoptotic phases. In conclusion, MIVM is a robust and pragmatic tool for tailoring the particle size of the UA nanosuspension. Particle size appears to be a critical determinant of the anticancer activity of the UA nanoparticles.

  11. Pre-activation of ice nucleating particles by the pore condensation and freezing mechanism

    NASA Astrophysics Data System (ADS)

    Wagner, R.; Kiselev, A.; Möhler, O.; Saathoff, H.; Steinke, I.

    2015-10-01

    In spite of the resurgence in ice nucleation research a comparatively small number of studies deal with the phenomenon of pre-activation in heterogeneous ice nucleation. Already fifty years ago, it was shown that various mineral dust and volcanic ash particles can be pre-activated to become nuclei for ice crystal formation even at temperatures as high as 270-271 K. Pre-activation was achieved under ice subsaturated conditions without any preceding macroscopic ice growth by just temporarily cooling the particles to temperatures below 228 K. A two-step mechanism involving capillary condensation of supercooled water and subsequent homogeneous freezing was proposed to account for the particles' enhanced ice nucleation ability at high temperatures. This work reinvestigates the efficiency of the proposed pre-activation mechanism in temperature-cycling experiments performed in a large cloud chamber with suspended particles. We find the efficiency to be highest for the clay mineral illite as well as for highly porous materials like zeolite and diatomaceous earth, whereas most aerosols generated from desert dust surface samples did not reveal a measurable pre-activation ability. The pre-activation efficiency is linked to particle pores in a certain size range. As estimated by model calculations, only pores with diameters between about 5 and 8 nm contribute to pre-activation under ice subsaturated conditions. In contrast to the early study, pre-activation is only observed for temperatures below 260 K. Above that threshold, the particles' improved ice nucleation ability disappears due to the melting of ice in the pores.

  12. Pre-activation of ice-nucleating particles by the pore condensation and freezing mechanism

    NASA Astrophysics Data System (ADS)

    Wagner, Robert; Kiselev, Alexei; Möhler, Ottmar; Saathoff, Harald; Steinke, Isabelle

    2016-02-01

    In spite of the resurgence in ice nucleation research a comparatively small number of studies deal with the phenomenon of pre-activation in heterogeneous ice nucleation. Fifty years ago, it was shown that various mineral dust and volcanic ash particles can be pre-activated to become nuclei for ice crystal formation even at temperatures as high as 270-271 K. Pre-activation was achieved under ice-subsaturated conditions without any preceding macroscopic ice growth by just temporarily cooling the particles to temperatures below 228 K. A two-step mechanism involving capillary condensation of supercooled water and subsequent homogeneous freezing was proposed to account for the particles' enhanced ice nucleation ability at high temperatures. This work reinvestigates the efficiency of the proposed pre-activation mechanism in temperature-cycling experiments performed in a large cloud chamber with suspended particles. We find the efficiency to be highest for the clay mineral illite as well as for highly porous materials like zeolite and diatomaceous earth, whereas most aerosols generated from desert dust surface samples did not reveal a measurable pre-activation ability. The pre-activation efficiency is linked to particle pores in a certain size range. As estimated by model calculations, only pores with diameters between about 5 and 8 nm contribute to pre-activation under ice-subsaturated conditions. This range is set by a combination of requirements from the negative Kelvin effect for condensation and a critical size of ice embryos for ice nucleation and melting. In contrast to the early study, pre-activation is only observed for temperatures below 260 K. Above that threshold, the particles' improved ice nucleation ability disappears due to the melting of ice in the pores.

  13. Cloud condensation nuclei and ice nucleation activity of hydrophobic and hydrophilic soot particles.

    PubMed

    Koehler, Kirsten A; DeMott, Paul J; Kreidenweis, Sonia M; Popovicheva, Olga B; Petters, Markus D; Carrico, Christian M; Kireeva, Elena D; Khokhlova, Tatiana D; Shonija, Natalia K

    2009-09-28

    Cloud condensation nuclei (CCN) activity and ice nucleation behavior (for temperaturesparticle sub-types even within a narrow size cut. The heterogeneity could have resulted from both chemical and sizing differences, the latter attributable in part to particle non-sphericity. Neither GTS nor TS, hydrophobic particles distinguished only by the lower porosity and polarity of the GTS surface, showed CCN activity at or below water supersaturations required for wettable, insoluble particles (the Kelvin limit). TC1 soot particles, despite classification as hydrophilic, did not show CCN activity at or below the Kelvin limit. We attribute this result to the microporosity of this soot. In contrast, oxidized, non-porous, and hydrophilic TOS particles exhibited CCN activation at very near the Kelvin limit, with a small percentage of these particles CCN-active even at lower supersaturations. Due to containing a range of surface coverage of organic and inorganic hydrophilic and hygroscopic compounds, up to approximately 35% of hygroscopic AEC particles were active as CCN, with a small percentage of these particles CCN-active at lower supersaturations. In ice nucleation experiments below -40 degrees C, AEC particles nucleated ice near the expected condition for homogeneous freezing of water from aqueous solutions. In

  14. A CMOS Active Pixel Sensor for Charged Particle Detection

    SciTech Connect

    Matis, Howard S.; Bieser, Fred; Kleinfelder, Stuart; Rai, Gulshan; Retiere, Fabrice; Ritter, Hans George; Singh, Kunal; Wurzel, Samuel E.; Wieman, Howard; Yamamoto, Eugene

    2002-12-02

    Active Pixel Sensor (APS) technology has shown promise for next-generation vertex detectors. This paper discusses the design and testing of two generations of APS chips. Both are arrays of 128 by 128 pixels, each 20 by 20 {micro}m. Each array is divided into sub-arrays in which different sensor structures (4 in the first version and 16 in the second) and/or readout circuits are employed. Measurements of several of these structures under Fe{sup 55} exposure are reported. The sensors have also been irradiated by 55 MeV protons to test for radiation damage. The radiation increased the noise and reduced the signal. The noise can be explained by shot noise from the increased leakage current and the reduction in signal is due to charge being trapped in the epi layer. Nevertheless, the radiation effect is small for the expected exposures at RHIC and RHIC II. Finally, we describe our concept for mechanically supporting a thin silicon wafer in an actual detector.

  15. Detection of Brownian Torque in a Magnetically-Driven Rotating Microsystem

    NASA Astrophysics Data System (ADS)

    Romodina, Maria N.; Lyubin, Evgeny V.; Fedyanin, Andrey A.

    2016-02-01

    Thermal fluctuations significantly affect the behavior of microscale systems rotating in shear flow, such as microvortexes, microbubbles, rotating micromotors, microactuators and other elements of lab-on-a-chip devices. The influence of Brownian torque on the motion of individual magnetic microparticles in a rotating magnetic field is experimentally determined using optical tweezers. Rotational Brownian motion induces the flattening of the breakdown transition between the synchronous and asynchronous modes of microparticle rotation. The experimental findings regarding microparticle rotation in the presence of Brownian torque are compared with the results of numerical Brownian dynamics simulations.

  16. Cloud droplet activation through oxidation of organic aerosol influenced by temperature and particle phase state

    DOE PAGES

    Slade, Jonathan H.; Shiraiwa, Manabu; Arangio, Andrea; ...

    2017-01-27

    Chemical aging of organic aerosol (OA) through multiphase oxidation reactions can alter their cloud condensation nuclei (CCN) activity and hygroscopicity. However, the oxidation kinetics and OA reactivity depend strongly on the particle phase state, potentially influencing the hydrophobic-to-hydrophilic conversion rate of carbonaceous aerosol. Here, amorphous Suwannee River fulvic acid (SRFA) aerosol particles, a surrogate humic-like substance (HULIS) that contributes substantially to global OA mass, are oxidized by OH radicals at different temperatures and phase states. When oxidized at low temperature in a glassy solid state, the hygroscopicity of SRFA particles increased by almost a factor of two, whereas oxidation ofmore » liquid-like SRFA particles at higher temperatures did not affect CCN activity. Low-temperature oxidation appears to promote the formation of highly-oxygenated particle-bound fragmentation products with lower molar mass and greater CCN activity, underscoring the importance of chemical aging in the free troposphere and its influence on the CCN activity of OA.« less

  17. Hydrodynamic interactions of two nearly touching Brownian spheres in a stiff potential: Effect of fluid inertia

    SciTech Connect

    Radiom, Milad Ducker, William; Robbins, Brian; Paul, Mark

    2015-02-15

    The hydrodynamic interaction of two closely spaced micron-scale spheres undergoing Brownian motion was measured as a function of their separation. Each sphere was attached to the distal end of a different atomic force microscopy cantilever, placing each sphere in a stiff one-dimensional potential (0.08 Nm{sup −1}) with a high frequency of thermal oscillations (resonance at 4 kHz). As a result, the sphere’s inertial and restoring forces were significant when compared to the force due to viscous drag. We explored interparticle gap regions where there was overlap between the two Stokes layers surrounding each sphere. Our experimental measurements are the first of their kind in this parameter regime. The high frequency of oscillation of the spheres means that an analysis of the fluid dynamics would include the effects of fluid inertia, as described by the unsteady Stokes equation. However, we find that, for interparticle separations less than twice the thickness of the wake of the unsteady viscous boundary layer (the Stokes layer), the hydrodynamic interaction between the Brownian particles is well-approximated by analytical expressions that neglect the inertia of the fluid. This is because elevated frictional forces at narrow gaps dominate fluid inertial effects. The significance is that interparticle collisions and concentrated suspensions at this condition can be modeled without the need to incorporate fluid inertia. We suggest a way to predict when fluid inertial effects can be ignored by including the gap-width dependence into the frequency number. We also show that low frequency number analysis can be used to determine the microrheology of mixtures at interfaces.

  18. Motion of chromosomal loci and the mean-squared displacement of a fractional Brownian motion in the presence of static and dynamic errors

    NASA Astrophysics Data System (ADS)

    Backlund, Mikael P.; Moerner, W. E.

    2015-03-01

    Mean-squared displacement (MSD) analysis is one of the most prevalent tools employed in the application of single-particle tracking to biological systems. In camera-based tracking, the effects of "static error" due to photon fluctuations and "dynamic error" due to motion blur on the MSD have been well-characterized for the case of pure Brownian motion, producing a known constant offset to the straight-line MSD. However, particles tracked in cellular environments often do not undergo pure Brownian motion, but instead can for instance exhibit anomalous diffusion wherein the MSD curve obeys a power law with respect to time, MSD=2D*τα, where D* is an effective diffusion coefficient and 0 < α <= 1. There are a number of models that can explain anomalous diffusive behavior in different subcellular contexts. Of these models, fractional Brownian motion (FBM) has been shown to accurately describe the motion of labeled particles such as mRNA and chromosomal loci as they traverse the cytoplasm or nucleoplasm (i.e. crowded viscoelastic environments). Despite the importance of FBM in biological tracking, there has yet to be a complete treatment of the MSD in the presence of static and dynamic errors analogous to the special case of pure Brownian motion. We here present a closed-form, analytical expression of the FBM MSD in the presence of both types of error. We have previously demonstrated its value in live-cell data by applying it to the study of chromosomal locus motion in budding yeast cells. Here we focus on validations in simulated data.

  19. Characterization of airborne particles generated from metal active gas welding process.

    PubMed

    Guerreiro, C; Gomes, J F; Carvalho, P; Santos, T J G; Miranda, R M; Albuquerque, P

    2014-05-01

    This study is focused on the characterization of particles emitted in the metal active gas welding of carbon steel using mixture of Ar + CO2, and intends to analyze which are the main process parameters that influence the emission itself. It was found that the amount of emitted particles (measured by particle number and alveolar deposited surface area) are clearly dependent on the distance to the welding front and also on the main welding parameters, namely the current intensity and heat input in the welding process. The emission of airborne fine particles seems to increase with the current intensity as fume-formation rate does. When comparing the tested gas mixtures, higher emissions are observed for more oxidant mixtures, that is, mixtures with higher CO2 content, which result in higher arc stability. These mixtures originate higher concentrations of fine particles (as measured by number of particles by cm(3) of air) and higher values of alveolar deposited surface area of particles, thus resulting in a more severe worker's exposure.

  20. Dynamics and Emergent Structures in Active Fluids

    NASA Astrophysics Data System (ADS)

    Baskaran, Aparna

    2014-03-01

    In this talk, we consider an active fluid of colloidal sized particles, with the primary manifestation of activity being a self-replenishing velocity along one body axis of the particle. This is a minimal model for varied systems such as bacterial colonies, cytoskeletal filament motility assays vibrated granular particles and self propelled diffusophoretic colloids, depending on the nature of interaction among the particles. Using microscopic Brownian dynamics simulations, coarse-graining using the tools of non-equilibrium statistical mechanics and analysis of macroscopic hydrodynamic theories, we characterize emergent structures seen in these systems, which are determined by the symmetry of the interactions among the active units, such as propagating density waves, dense stationary bands, asters and phase separated isotropic clusters. We identify a universal mechanism, termed ``self-regulation,'' as the underlying physics that leads to these structures in diverse systems. Support from NSF through DMR-1149266 and DMR-0820492.

  1. Mechanisms of Increased Particle and VOC Emissions during DPF Active Regeneration and Practical Emissions Considering Regeneration.

    PubMed

    Yamada, Hiroyuki; Inomata, Satoshi; Tanimoto, Hiroshi

    2017-03-07

    Mechanisms involved in increased particle and volatile organic compound (VOC) emissions during active and parked active regenerations of a diesel particulate filter (DPF) were investigated using heavy-duty trucks equipped with both a urea selective catalytic reduction system and a DPF (SCR + DPF) and a DPF-only. Particle emissions increased in the later part of the regeneration period but the mechanisms were different above and below 23 nm. Particles above 23 nm were emitted due to the lower filtering efficiency of the DPF because of the decreasing amount of soot trapped during regeneration. Small particles below 23 nm were thought to be mainly sulfuric acid particles produced from SO2 trapped by the catalyst, being released and oxidized during regeneration. Contrary to the particle emissions, VOCs increased in the earlier part of the regeneration period. The mean molecular weights of the VOCs increased gradually as the regeneration proceeded. To evaluate "practical emissions" in which increased emissions during the regeneration were considered, a Regeneration Correction Factor (RCF), which is the average emission during one cycle of regeneration/emission in normal operation, was adopted. The RCFs of PM and VOCs were 1.1-1.5, and those of PNs were as high as 3-140, although they were estimated from a limited number of observations.

  2. Rapid quantification of dimethyl methylphosphonate from activated carbon particles by static headspace gas chromatography mass spectrometry.

    PubMed

    Mitchell, Brendan L; Billingsley, Brit G; Logue, Brian A

    2013-06-07

    Activated carbon (AC) particles are utilized as an adsorbent for binding hazardous vapors in protective equipment. The binding affinity and utilization of these AC particles should be known to ensure effective and efficient use. Therefore, a simple and effective method was developed for the quantification of the chemical warfare agent simulant, dimethyl methylphosphonate (DMMP), from AC particles. Static headspace gas chromatography mass-spectrometry with internal standard, DMMP-d6, was used to perform the analysis. The method produced a linear dynamic range of 2.48-620g DMMP/kg carbon and a detection limit of 1.24g DMMP/kg carbon. Furthermore, the method produced a coefficient of variation of less than 16% for all intra- and inter-assay analyses. The method provided a simple and effective procedure for quantifying DMMP from AC particles and was applied to the analysis of a DMMP-exposed AC protective respirator filter.

  3. The effect of phase partitioning of semivolatile compounds on the measured CCN activity of aerosol particles

    NASA Astrophysics Data System (ADS)

    Romakkaniemi, S.; Jaatinen, A.; Laaksonen, A.; Nenes, A.; Raatikainen, T.

    2013-09-01

    The effect of inorganic semivolatile aerosol compounds on the CCN activity of aerosol particles was studied by using a computational model for a DMT-CCN counter, a cloud parcel model for condensation kinetics and experiments to quantify the modelled results. Concentrations of water vapour and semivolatiles as well as aerosol trajectories in the CCN column were calculated by a computational fluid dynamics model. These trajectories and vapour concentrations were then used as an input for the cloud parcel model to simulate mass transfer kinetics of water and semivolatiles between aerosol particles and the gas phase. Two different questions were studied: (1) how big fraction of semivolatiles is evaporated from particles before activation in the CCN counter? (2) How much the CCN activity can be increased due to condensation of semivolatiles prior to the maximum water supersaturation in the case of high semivolatile concentration in the gas phase? The results show that, to increase the CCN activity of aerosol particles, a very high gas phase concentration (as compared to typical ambient conditions) is needed. We used nitric acid as a test compound. A concentration of several ppb or higher is needed for measurable effect. In the case of particle evaporation, we used ammonium nitrate as a test compound and found that it partially evaporates before maximum supersaturation is reached in the CCN counter, thus causing an underestimation of CCN activity. The effect of evaporation is clearly visible in all supersaturations, leading to an underestimation of the critical dry diameter by 10 to 15 nanometres in the case of ammonium nitrate particles in different supersaturations. This result was also confirmed by measurements in supersaturations between 0.1 and 0.7%.

  4. Fractional activation of accumulation-mode particles in warm continental stratiform clouds

    SciTech Connect

    Gillani, N.V.; Daum, P.H.; Schwartz, S.E.; Leaitch, W.R.; Strapp, J.W.; Isaac, G.A.

    1991-07-01

    The degree of activation of accumulation-mode particles (AMP) in clouds has been studied using continuous (1 second average) aircraft measurements of the number concentrations of cloud droplets (N{sub cd}, 2 to 35 {mu}m diameter) and of unactivated AMP (N{sub amp}, 0.17 to 2.07 {mu}m diameter) in cloud interstitial air. The magnitude and spatial variation of the activated fraction (F) of all measured particles (defined as F {triple_bond} N{sub cd}/N{sub tot}, where N{sub tot} = N{sub cd} + N{sub amp}) are investigated, based on measurements made during ten aircraft flights in non-precipitating warm continental stratiform clouds near Syracuse NY in the fall of 1984. Based on instantaneous observations throughout the clouds, the spatial distribution of F was found to be quite nonuniform. In general, F was low in cloud edges and where total particle loading was high and/or cloud convective activity was low. In the interior of clouds, the value of F exceeded 0.9 for 36% of the data, but was below 0.6 for 28%. Factors influencing F the most were the total particle loading (N{sub tot}) and the thermal stability of the cloud layer. The dependence of F on N{sub tot} in cloud interior was characterized by two distinct regimes. For N{sub tot} < 600 cm{sup {minus}3}, F was generally close to unity and relatively insensitive to N{sub tot}. For N{sub tot} > 800 cm{sup {minus}3}, F tended to decrease with increasing N{sub tot}. This decrease was greatest in a stable stratus deck embedded in a warm moist airmass. The results suggest that, in warm continental stratiform clouds, the process of particle activation becomes nonlinear and self-limiting at high particle loading. The degree of this nonlinearity depends on cloud convective activity (thermal instability).

  5. Fractional activation of accumulation-mode particles in warm continental stratiform clouds

    SciTech Connect

    Gillani, N.V. Associates, Inc., St. Louis, MO ); Daum, P.H.; Schwartz, S.E. ); Leaitch, W.R.; Strapp, J.W.; Isaac, G.A. . Cloud Physics Research Div.)

    1991-07-01

    The degree of activation of accumulation-mode particles (AMP) in clouds has been studied using continuous (1 second average) aircraft measurements of the number concentrations of cloud droplets (N[sub cd], 2 to 35 [mu]m diameter) and of unactivated AMP (N[sub amp], 0.17 to 2.07 [mu]m diameter) in cloud interstitial air. The magnitude and spatial variation of the activated fraction (F) of all measured particles (defined as F [triple bond] N[sub cd]/N[sub tot], where N[sub tot] = N[sub cd] + N[sub amp]) are investigated, based on measurements made during ten aircraft flights in non-precipitating warm continental stratiform clouds near Syracuse NY in the fall of 1984. Based on instantaneous observations throughout the clouds, the spatial distribution of F was found to be quite nonuniform. In general, F was low in cloud edges and where total particle loading was high and/or cloud convective activity was low. In the interior of clouds, the value of F exceeded 0.9 for 36% of the data, but was below 0.6 for 28%. Factors influencing F the most were the total particle loading (N[sub tot]) and the thermal stability of the cloud layer. The dependence of F on N[sub tot] in cloud interior was characterized by two distinct regimes. For N[sub tot] < 600 cm[sup [minus]3], F was generally close to unity and relatively insensitive to N[sub tot]. For N[sub tot] > 800 cm[sup [minus]3], F tended to decrease with increasing N[sub tot]. This decrease was greatest in a stable stratus deck embedded in a warm moist airmass. The results suggest that, in warm continental stratiform clouds, the process of particle activation becomes nonlinear and self-limiting at high particle loading. The degree of this nonlinearity depends on cloud convective activity (thermal instability).

  6. Membrane ruffles capture C3bi-opsonized particles in activated macrophages.

    PubMed

    Patel, Prerna C; Harrison, Rene E

    2008-11-01

    A widespread belief in phagocyte biology is that FcgammaR-mediated phagocytosis utilizes membrane pseudopods, whereas Mac-1-mediated phagocytosis does not involve elaborate plasma membrane extensions. Here we report that dynamic membrane ruffles in activated macrophages promote binding of C3bi-opsonized particles. We identify these ruffles as components of the macropinocytosis machinery in both PMA- and LPS-stimulated macrophages. C3bi-particle capture is facilitated by enrichment of high-affinity Mac-1 and the integrin-regulating protein talin in membrane ruffles. Membrane ruffle formation and C3bi-particle binding are cytoskeleton dependent events, having a strong requirement for F-actin and microtubules (MTs). MT disruption blunts ruffle formation and PMA- and LPS-induced up-regulation of surface Mac-1 expression. Furthermore, the MT motor, kinesin participates in ruffle formation implicating a requirement for intracellular membrane delivery to active membrane regions during Mac-1-mediated phagocytosis. We observed colocalization of Rab11-positive vesicles with CLIP-170, a MT plus-end binding protein, at sites of particle adherence using TIRF imaging. Rab11 has been implicated in recycling endosome dynamics and mutant Rab11 expression inhibits both membrane ruffle formation and C3bi-sRBC adherence to macrophages. Collectively these findings represent a novel membrane ruffle "capture" mechanism for C3bi-particle binding during Mac-1-mediated phagocytosis. Importantly, this work also demonstrates a strong functional link between integrin activation, macropinocytosis and phagocytosis in macrophages.

  7. Bioinspired synthesis of polydopamine/Ag nanocomposite particles with antibacterial activities.

    PubMed

    Wu, Chengjiao; Zhang, Guoxing; Xia, Tian; Li, Zhenni; Zhao, Kai; Deng, Ziwei; Guo, Dingzong; Peng, Bo

    2015-10-01

    Mussel-inspired chemistry (polydopamine) offers great opportunities to develop inexpensive and efficient process for many types of materials with complex shapes and functions in a mild and friendly environment. This paper describes a facile, yet green approach to synthesize polydopamine/silver (PDA/Ag) nanocomposite particles with a combination use of polydopamine chemistry and electroless metallization of Ag. In this approach, monodisperse spherical polydopamine particles are first synthesized by the oxidation and self-polymerization of dopamine (monomer) in an alkaline water-ethanol solution at room temperature, which are served as the active templates for secondary reactions due to the abundant catechol and amine groups on the surface. Subsequently, the silver precursor-[Ag(NH3)2](+) ions introduced are easily absorbed onto the surface of the PDA particles, and are immediately in situ reduced to metallic Ag nanoparticles with the help of these active catechol and amine groups. During the preparation, no additional reductants, toxic reagents and intricate instruments are needed. These as-synthesized PDA/Ag nanocomposite particles are ideal candidates for antibacterial application because they do not show significant cytotoxicity against HEK293T human embryonic kidney cells in the in vitro cytotoxicity assay, whereas demonstrate enhanced antibacterial abilities against Escherichia coli (Gram-negative bacteria) and Staphylococcus aureus (Gram-positive bacteria) in the antibacterial assays. Owing to their excellent cytocompatibilities and antibacterial activities, these PDA/Ag nanocomposite particles can be considered as the promising antibacterial materials for future biomedical applications.

  8. A phenomenological particle-based platelet model for simulating filopodia formation during early activation.

    PubMed

    Pothapragada, Seetha; Zhang, Peng; Sheriff, Jawaad; Livelli, Mark; Slepian, Marvin J; Deng, Yuefan; Bluestein, Danny

    2015-03-01

    We developed a phenomenological three-dimensional platelet model to characterize the filopodia formation observed during early stage platelet activation. Departing from continuum mechanics based approaches, this coarse-grained molecular dynamics (CGMD) particle-based model can deform to emulate the complex shape change and filopodia formation that platelets undergo during activation. The platelet peripheral zone is modeled with a two-layer homogeneous elastic structure represented by spring-connected particles. The structural zone is represented by a cytoskeletal assembly comprising of a filamentous core and filament bundles supporting the platelet's discoid shape, also modeled by spring-connected particles. The interior organelle zone is modeled by homogeneous cytoplasm particles that facilitate the platelet deformation. Nonbonded interactions among the discrete particles of the membrane, the cytoskeletal assembly, and the cytoplasm are described using the Lennard-Jones potential with empirical constants. By exploring the parameter space of this CGMD model, we have successfully simulated the dynamics of varied filopodia formations. Comparative analyses of length and thickness of filopodia show that our numerical simulations are in agreement with experimental measurements of flow-induced activated platelets. Copyright © 2015 John Wiley & Sons, Ltd.

  9. Random functions via Dyson Brownian Motion: progress and problems

    NASA Astrophysics Data System (ADS)

    Wang, Gaoyuan; Battefeld, Thorsten

    2016-09-01

    We develope a computationally efficient extension of the Dyson Brownian Motion (DBM) algorithm to generate random function in C2 locally. We further explain that random functions generated via DBM show an unstable growth as the traversed distance increases. This feature restricts the use of such functions considerably if they are to be used to model globally defined ones. The latter is the case if one uses random functions to model landscapes in string theory. We provide a concrete example, based on a simple axionic potential often used in cosmology, to highlight this problem and also offer an ad hoc modification of DBM that suppresses this growth to some degree.

  10. Random functions via Dyson Brownian Motion: progress and problems

    SciTech Connect

    Wang, Gaoyuan; Battefeld, Thorsten

    2016-09-05

    We develope a computationally efficient extension of the Dyson Brownian Motion (DBM) algorithm to generate random function in C{sup 2} locally. We further explain that random functions generated via DBM show an unstable growth as the traversed distance increases. This feature restricts the use of such functions considerably if they are to be used to model globally defined ones. The latter is the case if one uses random functions to model landscapes in string theory. We provide a concrete example, based on a simple axionic potential often used in cosmology, to highlight this problem and also offer an ad hoc modification of DBM that suppresses this growth to some degree.

  11. Non-Markovian quantum Brownian motion of a harmonic oscillator

    SciTech Connect

    Tang, J.

    1994-02-01

    We apply the density-matrix method to the study of quantum Brownian motion of a harmonic oscillator coupled to a heat bath, a system investigated previously by Caldeira and Leggett using a different method. Unlike the earlier work, in our derivation of the master equation the non-Markovian terms are maintained. Although the same model of interaction is used, discrepancy is found between their results and our equation in the Markovian limit. We also point out that the particular interaction model used by both works cannot lead to the phenomenological generalized Langevin theory of Kubo.

  12. Active one-particle microrheology of an unentangled polymer melt studied by molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Kuhnhold, A.; Paul, W.

    2015-04-01

    We present molecular dynamics simulations for active one-particle microrheology of an unentangled polymer melt. The tracer particle is forced to oscillate by an oscillating harmonic potential, which models an experiment using optical tweezers. The amplitude and phase shift of this oscillation are related to the complex shear modulus of the polymer melt. In the linear response regime at low frequencies, the active microrheology gives the same result as the passive microrheology, where the thermal motion of a tracer particle is related to the complex modulus. We expand the analysis to include full hydrodynamic effects instead of stationary Stokes friction only, and show that different approaches suggested in the literature lead to completely different results, and that none of them improves on the description using the stationary Stokes friction.

  13. Rotation of Magnetization Derived from Brownian Relaxation in Magnetic Fluids of Different Viscosity Evaluated by Dynamic Hysteresis Measurements over a Wide Frequency Range.

    PubMed

    Ota, Satoshi; Kitaguchi, Ryoichi; Takeda, Ryoji; Yamada, Tsutomu; Takemura, Yasushi

    2016-09-10

    The dependence of magnetic relaxation on particle parameters, such as the size and anisotropy, has been conventionally discussed. In addition, the influences of external conditions, such as the intensity and frequency of the applied field, the surrounding viscosity, and the temperature on the magnetic relaxation have been researched. According to one of the basic theories regarding magnetic relaxation, the faster type of relaxation dominates the process. However, in this study, we reveal that Brownian and Néel relaxations coexist and that Brownian relaxation can occur after Néel relaxation despite having a longer relaxation time. To understand the mechanisms of Brownian rotation, alternating current (AC) hysteresis loops were measured in magnetic fluids of different viscosities. These loops conveyed the amplitude and phase delay of the magnetization. In addition, the intrinsic loss power (ILP) was calculated using the area of the AC hysteresis loops. The ILP also showed the magnetization response regarding the magnetic relaxation over a wide frequency range. To develop biomedical applications of magnetic nanoparticles, such as hyperthermia and magnetic particle imaging, it is necessary to understand the mechanisms of magnetic relaxation.

  14. Rotation of Magnetization Derived from Brownian Relaxation in Magnetic Fluids of Different Viscosity Evaluated by Dynamic Hysteresis Measurements over a Wide Frequency Range

    PubMed Central

    Ota, Satoshi; Kitaguchi, Ryoichi; Takeda, Ryoji; Yamada, Tsutomu; Takemura, Yasushi

    2016-01-01

    The dependence of magnetic relaxation on particle parameters, such as the size and anisotropy, has been conventionally discussed. In addition, the influences of external conditions, such as the intensity and frequency of the applied field, the surrounding viscosity, and the temperature on the magnetic relaxation have been researched. According to one of the basic theories regarding magnetic relaxation, the faster type of relaxation dominates the process. However, in this study, we reveal that Brownian and Néel relaxations coexist and that Brownian relaxation can occur after Néel relaxation despite having a longer relaxation time. To understand the mechanisms of Brownian rotation, alternating current (AC) hysteresis loops were measured in magnetic fluids of different viscosities. These loops conveyed the amplitude and phase delay of the magnetization. In addition, the intrinsic loss power (ILP) was calculated using the area of the AC hysteresis loops. The ILP also showed the magnetization response regarding the magnetic relaxation over a wide frequency range. To develop biomedical applications of magnetic nanoparticles, such as hyperthermia and magnetic particle imaging, it is necessary to understand the mechanisms of magnetic relaxation. PMID:28335297

  15. Hygroscopic growth and droplet activation of soot particles: uncoated, succinic or sulfuric acid coated

    NASA Astrophysics Data System (ADS)

    Henning, S.; Ziese, M.; Kiselev, A.; Saathoff, H.; Möhler, O.; Mentel, T. F.; Buchholz, A.; Spindler, C.; Michaud, V.; Monier, M.; Sellegri, K.; Stratmann, F.

    2012-05-01

    The hygroscopic growth and droplet activation of uncoated soot particles and such coated with succinic acid and sulfuric acid were investigated during the IN-11 campaign at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) facility. A GFG-1000 soot generator applying either nitrogen or argon as carrier gas and a miniCAST soot generator were utilized to generate soot particles. Different organic carbon (OC) to black carbon (BC) ratios were adjusted for the CAST-soot by varying the fuel to air ratio. The hygroscopic growth was investigated by means of the mobile Leipzig Aerosol Cloud Interaction Simulator (LACIS-mobile) and two different Hygroscopicity Tandem Differential Mobility Analyzers (HTDMA, VHTDMA). Two Cloud Condensation Nucleus Counter (CCNC) were applied to measure the activation of the particles. For the untreated soot particles neither hygroscopic growth nor activation was observed at a supersaturation of 1%, with exception of a partial activation of GFG-soot generated with argon as carrier gas. Coatings of succinic acid lead to a detectable hygroscopic growth of GFG-soot and enhanced the activated fraction of GFG- (carrier gas: argon) and CAST-soot, whereas no hygroscopic growth of the coated CAST-soot was found. Sulfuric acid coatings led to an OC-content dependent hygroscopic growth of CAST-soot. Such a dependence was not observed for activation measurements. Coating with sulfuric acid decreased the amount of Polycyclic Aromatic Hydrocarbons (PAH), which were detected by AMS-measurements in the CAST-soot, and increased the amount of substances with lower molecular weight than the initial PAHs. We assume that these reaction products increased the hygroscopicity of the coated particles in addition to the coating substance itself.

  16. Hygroscopic growth and droplet activation of soot particles: uncoated, succinic or sulfuric acid coated

    NASA Astrophysics Data System (ADS)

    Henning, S.; Ziese, M.; Kiselev, A.; Saathoff, H.; Möhler, O.; Mentel, T. F.; Buchholz, A.; Spindler, C.; Michaud, V.; Monier, M.; Sellegri, K.; Stratmann, F.

    2011-10-01

    The hygroscopic growth and droplet activation of uncoated soot particles and such coated with succinic acid and sulfuric acid were investigated during the IN-11 campaign at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) facility. A GFG-1000 soot generator applying nitrogen, respectively argon as carrier gas and a miniCAST soot generator were utilized to generate soot particles. Different organic carbon (OC) to black carbon (BC) ratios were adjusted for the CAST-soot by varying the fuel to air ratio. The hygroscopic growth was investigated by means of the mobile Leipzig Aerosol Cloud Interaction Simulator (LACIS-mobile) and two different Hygroscopicity Tandem Differential Mobility Analyzers (HTDMA, VHTDMA). Two Cloud Condensation Nucleus Counter (CCNC) were applied to measure the activation of the particles. For the untreated soot particles neither hygroscopic growth nor activation was observed, with exception of a partial activation of GFG-soot generated with argon as carrier gas. Coatings of succinic acid lead to a detectable hygroscopic growth of GFG-soot and enhanced the activated fraction of GFG- (carrier gas: argon) and CAST-soot, whereas no hygroscopic growth of the coated CAST-soot was found. Sulfuric acid coatings lead to an OC-content dependent hygroscopic growth of CAST-soot. Such a dependence was not observed for activation measurements. Coating with sulfuric acid decreased the amount of Polycyclic Aromatic Hydrocarbons (PAH), which were detected by AMS-measurements in the CAST-soot, and increased the amount of substances with lower molecular weight than the initial PAHs. We assume, that these reaction products increased the hygroscopicity of the coated particles in addition to the coating substance itself.

  17. NANOMETER DIESEL EXHAUST PARTICLES ARE NEUROTOXIC TO DOPAMINERGIC NEURONS THROUGH MICROGLIAL ACTIVATION.

    EPA Science Inventory

    NANOMETER DIESEL EXHAUST PARTICLES ARE NEUROTOXIC TO DOPAMINERGIC NEURONS THROUGH MICROGLIAL ACTIVATION. M.L. Block1,2, X. Wu1, P. Zhong1, G. Li1, T. Wang1, J.S. Hong1 & B.Veronesi.2
    1The Laboratory of Pharmacology and Chemistry, NIEHS, RTP, NC and 2 National Health and Envi...

  18. Functionally Charged Polystyrene Particles Activate Immortalized Mouse Microglia (BV2): Cellular and Genomic Response

    EPA Science Inventory

    The effect of particle surface charge on the biological activation of immortalized mouse microglia (BV2) was examined. Same size (~850-950 nm) spherical polystyrene microparticles (SPM) with net negative (carboxyl, COOH-) or positive (dimethyl amino, CH3)2

  19. Activation of immune complement by fly ash particles from coal combustion. [Dogs

    SciTech Connect

    Hill, J.O.; Rothenberg, S.J.; Kanapilly, G.M.; Hanson, R.L.; Scott, B.R.

    1982-06-01

    The interaction of immune complement with fly ash particles from coal combustion was studied in vitro. Fly ash from different coal combustors was incubated for 1 hr with pooled normal dog serum at 37/sup 0/C. The serum supernatants were assayed for complement by a 505 hemolytic (CH/sub 50/) endpoint method. Ash produced by burning one type of coal activated complement with up to 70% of the complement activated at 10 mg ash/ml serum. This activation was concentration dependent and a linear dose-response curve was obtained. Heat treatment and surface area measurements, as well as immunofluorescence studies, suggest that the active component(s) is volatile or heat labile, found on the surface of the particles, and removed by saline or water extraction.

  20. Coarse-grained picture of Brownian motion in water: Role of size and interaction distance range on the nature of randomness.

    PubMed

    Hanasaki, Itsuo; Nagura, Ryo; Kawano, Satoyuki

    2015-03-14

    The Brownian motion of a particle in a fluid is often described by the linear Langevin equation, in which it is assumed that the mass of the particle is sufficiently large compared to the surrounding fluid molecules. This assumption leads to a diffusion coefficient that is independent of the particle mass. The Stokes-Einstein equation indicates that the diffusion coefficient depends solely on the particle size, but the concept of size can be ambiguous when close to the molecular scale. We first examine the Brownian motion of simple model particles based on short-range interactions in water by the molecular dynamics method and show that the diffusion coefficient can vary with mass when this mass is comparable to that of the solvent molecules, and that this effect is evident when the solute particle size is sufficiently small. We then examine the properties of a water molecule considered as a solute in the bulk solvent consisting of the remainder of the water. A comparison with simple solute models is used to clarify the role of force fields. The long-range Coulomb interaction between water molecules is found to lead to a Gaussian force distribution in spite of a mass ratio and nominal size ratio of unity, such that solutes with short-range interactions exhibit non-Gaussian force distribution. Thus, the range of the interaction distance determines the effective size even if it does not represent the volume excluded by the repulsive force field.

  1. Active Curved Polymers Form Vortex Patterns on Membranes

    NASA Astrophysics Data System (ADS)

    Denk, Jonas; Huber, Lorenz; Reithmann, Emanuel; Frey, Erwin

    2016-04-01

    Recent in vitro experiments with FtsZ polymers show self-organization into different dynamic patterns, including structures reminiscent of the bacterial Z ring. We model FtsZ polymers as active particles moving along chiral, circular paths by Brownian dynamics simulations and a Boltzmann approach. Our two conceptually different methods point to a generic phase behavior. At intermediate particle densities, we find self-organization into vortex structures including closed rings. Moreover, we show that the dynamics at the onset of pattern formation is described by a generalized complex Ginzburg-Landau equation.

  2. A Simplified Treatment of Brownian Motion and Stochastic Differential Equations Arising in Financial Mathematics

    ERIC Educational Resources Information Center

    Parlar, Mahmut

    2004-01-01

    Brownian motion is an important stochastic process used in modelling the random evolution of stock prices. In their 1973 seminal paper--which led to the awarding of the 1997 Nobel prize in Economic Sciences--Fischer Black and Myron Scholes assumed that the random stock price process is described (i.e., generated) by Brownian motion. Despite its…

  3. Redox activity and chemical interactions of metal oxide nano- and micro-particles with dithiothreitol (DTT).

    PubMed

    Nicolas, Johny; Jaafar, Malek; Sepetdjian, Elizabeth; Saad, Walid; Sioutas, Constantinos; Shihadeh, Alan; Saliba, Najat A

    2015-11-01

    The wide application and production of nanotechnology have increased the interest in studying the toxicity of nano- and micro-sized particles escaping into air from various aspects of the production process. Metal oxides (MOs) are one particular class of particles that exist abundantly in ambient PM. Studies show an emphasis on biological mechanisms by which inhalation exposure to MOs leads to disease. However, different biological assays provide different redox activity rankings making it difficult to assess the contributions of various MOs to measures of aggregate toxicity in multi-pollutant systems such as ambient PM. Therefore, research to evaluate the chemical interaction between these particles and molecules that are relevant to cellular redox activity can help in establishing indicators of reactivity. In particular, this study assesses the redox activity of six MOs mainly emitted from anthropogenic industrial activities using the dithiothreitol (DTT) assay. DTT is commonly used in acellular assays due to its analogous structure to cellular glutathione. The structural and chemical behaviors between active MOs and DTT were elucidated using FTIR, NMR, and BET methods. The results indicate that the health risk (redox activity) associated with MOs is mainly a function of their surface reactivity demonstrated by the ability of the oxidized (S-H) bond in DTT to form a stable bond with the MO surface.

  4. Droplet activation of wet particles: development of the Wet CCN approach

    NASA Astrophysics Data System (ADS)

    Nakao, S.; Suda, S. R.; Camp, M.; Petters, M. D.; Kreidenweis, S. M.

    2014-01-01

    Relationships between critical supersaturation required for activation and particle dry diameter have been the primary means for experimentally characterizing cloud condensation nuclei (CCN) activity; however, use of the dry diameter inherently limits the application to cases where the dry diameter can be used to accurately estimate solute volume. This study challenges the requirement and proposes a new experimental approach, Wet CCN, for studying CCN activity without the need for a drying step. The new approach directly measures Köhler curves under sub-saturated conditions. The experimental setup consists of a humidity-controlled differential mobility analyzer and a CCN counter; wet diameter equilibrated at known relative humidity is used to characterize CCN activity instead of the dry diameter. The experimental approach was validated against ammonium sulfate, glucose and non-spherical ammonium oxalate monohydrate. Further, the approach was applied to a mixture of non-spherical iodine oxide particles. The Wet CCN approach successfully determined the hygroscopicity of non-spherical particles by collapsing them into spherical, deliquesced droplets. We further show that the Wet CCN approach offers unique insights to the physical and chemical impacts of the aqueous phase on CCN activity; a potential application is to investigate the impact of evaporation/co-condensation of water-soluble semi-volatile species on CCN activity.

  5. Droplet activation of wet particles: development of the Wet CCN approach

    NASA Astrophysics Data System (ADS)

    Nakao, S.; Suda, S. R.; Camp, M.; Petters, M. D.; Kreidenweis, S. M.

    2014-07-01

    Relationships between critical supersaturation required for activation and particle dry diameter have been the primary means for experimentally characterizing cloud condensation nuclei (CCN) activity; however, use of the dry diameter inherently limits the application to cases where the dry diameter can be used to accurately estimate solute volume. This study challenges the requirement and proposes a new experimental approach, Wet CCN, for studying CCN activity without the need for a drying step. The new approach directly measures the subsaturated portion of the Köhler curves. The experimental setup consists of a humidity-controlled differential mobility analyzer and a CCN counter; wet diameter equilibrated at known relative humidity is used to characterize CCN activity instead of the dry diameter. The experimental approach was validated against ammonium sulfate, glucose, and nonspherical ammonium oxalate monohydrate. Further, the approach was applied to a mixture of nonspherical iodine oxide particles. The Wet CCN approach successfully determined the hygroscopicity of nonspherical particles by collapsing them into spherical, deliquesced droplets. We further show that the Wet CCN approach offers unique insights into the physical and chemical impacts of the aqueous phase on CCN activity; a potential application is to investigate the impact of evaporation/co-condensation of water-soluble semivolatile species on CCN activity.

  6. Particle transport in asymmetrically modulated pores

    NASA Astrophysics Data System (ADS)

    Mathwig, Klaus; Müller, Frank; Gösele, Ulrich

    2011-03-01

    Brownian motion plays an important role in the separation of small particles and molecules, but generally leads to undirected motion or intermixing by diffusion. Matthias and Müller (2003 Nature 424 53-7) reported on the experimental realization of a drift ratchet, a microfluidic particle transport mechanism that utilizes random fluctuations instead, i.e. a Brownian motor. Here, we offer a new interpretation of this previously published work on the drift ratchet. New experiments, which allow us to distinguish between particles of different sizes, as well as a re-examination of the original work, lead to the conclusion that the measured particle transport does not result from a ratchet effect. We demonstrate that the transport is caused by convection instead. While our result challenges one specific type of experiment, we do not assess the feasibility of a drift ratchet in principle. Instead, we identify the experimental conditions that need to be fulfilled for the successful separation of particles.

  7. CNT based thermal Brownian motor to pump water in nanodevices

    NASA Astrophysics Data System (ADS)

    Oyarzua, Elton; Zambrano, Harvey; Walther, J. H.

    2016-11-01

    Brownian molecular motors are nanoscale machines that exploit thermal fluctuations for directional motion by employing mechanisms such as the Feynman-Smoluchowski ratchet. In this study, using Non Equilibrium Molecular Dynamics, we propose a novel thermal Brownian motor for pumping water through Carbon Nanotubes (CNTs). To achieve this we impose a thermal gradient along the axis of a CNT filled with water and impose, in addition, a spatial asymmetry by fixing specific zones on the CNT in order to modify the vibrational modes of the CNT. We find that the temperature gradient and imposed spatial asymmetry drive the water flow in a preferential direction. We systematically modified the magnitude of the applied thermal gradient and the axial position of the fixed points. The analysis involves measurement of the vibrational modes in the CNTs using a Fast Fourier Transform (FFT) algorithm. We observed water flow in CNTs of 0.94, 1.4 and 2.0 nm in diameter, reaching a maximum velocity of 5 m/s for a thermal gradient of 3.3 K/nm. The proposed thermal motor is capable of delivering a continuous flow throughout a CNT, providing a useful tool for driving liquids in nanofluidic devices by exploiting thermal gradients. We aknowledge partial support from Fondecyt project 11130559.

  8. Relaxation dynamics near nonequilibrium stationary states in Brownian ratchets

    NASA Astrophysics Data System (ADS)

    Woo, Hyung-June

    2009-02-01

    A comprehensive study of the static and dynamical properties of a representative stochastic model of Brownian ratchet effects for molecular motors is reported. The model describes Brownian motions on two periodic potentials under static and time-dependent forces, where there are two distinct locations of chemical reactions coupling the levels with reversible rates within a period. Complete stationary properties have been obtained analytically for arbitrary potentials under external force. Dynamical relaxation properties near nonequilibrium stationary states were examined by considering the response function of velocity upon time-dependent external force, expressed in terms of the conditional probability density of the model. The latter is fully calculated using a systematic numerical method using matrix diagonalization, which is easily generalized to more complicated models for studying both static and dynamical properties. The behavior of the time-dependent response examined for model potentials suggests that the characteristic relaxation time near stationary states generally decreases linearly with respect to increasing velocity as one goes away from equilibrium via an increase in chemical potential of fuel species, a prediction testable in single molecule experiments.

  9. Amoeba-inspired nanoarchitectonic computing implemented using electrical Brownian ratchets

    NASA Astrophysics Data System (ADS)

    Aono, M.; Kasai, S.; Kim, S.-J.; Wakabayashi, M.; Miwa, H.; Naruse, M.

    2015-06-01

    In this study, we extracted the essential spatiotemporal dynamics that allow an amoeboid organism to solve a computationally demanding problem and adapt to its environment, thereby proposing a nature-inspired nanoarchitectonic computing system, which we implemented using a network of nanowire devices called ‘electrical Brownian ratchets (EBRs)’. By utilizing the fluctuations generated from thermal energy in nanowire devices, we used our system to solve the satisfiability problem, which is a highly complex combinatorial problem related to a wide variety of practical applications. We evaluated the dependency of the solution search speed on its exploration parameter, which characterizes the fluctuation intensity of EBRs, using a simulation model of our system called ‘AmoebaSAT-Brownian’. We found that AmoebaSAT-Brownian enhanced the solution searching speed dramatically when we imposed some constraints on the fluctuations in its time series and it outperformed a well-known stochastic local search method. These results suggest a new computing paradigm, which may allow high-speed problem solving to be implemented by interacting nanoscale devices with low power consumption.

  10. Average hydrodynamic correction for the Brownian dynamics calculation of flocculation rates in concentrated dispersions

    NASA Astrophysics Data System (ADS)

    Urbina-Villalba, German; García-Sucre, Máximo; Toro-Mendoza, Jhoan

    2003-12-01

    In order to account for the hydrodynamic interaction (HI) between suspended particles in an average way, Honig et al. [J. Colloid Interface Sci. 36, 97 (1971)] and more recently Heyes [Mol. Phys. 87, 287 (1996)] proposed different analytical forms for the diffusion constant. While the formalism of Honig et al. strictly applies to a binary collision, the one from Heyes accounts for the dependence of the diffusion constant on the local concentration of particles. However, the analytical expression of the latter approach is more complex and depends on the particular characteristics of each system. Here we report a combined methodology, which incorporates the formula of Honig et al. at very short distances and a simple local volume-fraction correction at longer separations. As will be shown, the flocculation behavior calculated from Brownian dynamics simulations employing the present technique, is found to be similar to that of Batchelor’s tensor [J. Fluid. Mech. 74, 1 (1976); 119, 379 (1982)]. However, it corrects the anomalous coalescence found in concentrated systems as a result of the overestimation of many-body HI.

  11. Exact path-integral evaluation of the heat distribution function of a trapped Brownian oscillator

    NASA Astrophysics Data System (ADS)

    Chatterjee, Debarati; Cherayil, Binny J.

    2010-11-01

    Using path integrals, we derive an exact expression—valid at all times t —for the distribution P(Q,t) of the heat fluctuations Q of a Brownian particle trapped in a stationary harmonic well. We find that P(Q,t) can be expressed in terms of a modified Bessel function of zeroth order that in the limit t→∞ exactly recovers the heat distribution function obtained recently by Imparato [Phys. Rev. E 76, 050101(R) (2007)]10.1103/PhysRevE.76.050101 from the approximate solution to a Fokker-Planck equation. This long-time result is in very good agreement with experimental measurements carried out by the same group on the heat effects produced by single micron-sized polystyrene beads in a stationary optical trap. An earlier exact calculation of the heat distribution function of a trapped particle moving at a constant speed v was carried out by van Zon and Cohen [Phys. Rev. E 69, 056121 (2004)]10.1103/PhysRevE.69.056121; however, this calculation does not provide an expression for P(Q,t) itself, but only its Fourier transform (which cannot be analytically inverted), nor can it be used to obtain P(Q,t) for the case v=0 .

  12. Transport of Brownian spheroidal nanoparticles in near-wall vascular flows for cancer therapy

    NASA Astrophysics Data System (ADS)

    Lin, Tiras Y.; Shah, Preyas N.; Smith, Bryan R.; Shaqfeh, Eric S. G.

    2016-11-01

    The microenvironment local to a tumor is characterized by a leaky vasculature induced by angiogenesis from tumor growth. Small pores form in the blood vessel walls, and these pores provide a pathway for cancer-ameliorating nanoparticle drug carriers. Using both simulations and microfluidics experiments, we investigate the extravasation of nanoparticles through pores. Using Brownian dynamics simulations, we evolve the stochastic equations for both point particles and finite-size spheroids of varying aspect ratio. We investigate the effect of wall shear flow and pore suction flow (Sampson flow) on the extravasation process. We consider pores of two types: physiologically relevant short pores with a length equal to the particle size and long pores which are relevant to diffusion through membranes. Additionally, we perform microfluidics experiments in which the extravasation rates of various nanoparticles tagged with fluorescent dye through pores are measured. In particular, using fluorometry we measure the flux of nanoparticles across a track-etched membrane, which separates two chambers. Our preliminary results indicate that the flux measured from experiment agrees reasonably with the simulations done with long pores, and we discuss the effect of pore length on extravasation. T.Y.L. is supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

  13. Particle Size Distribution Data From Existing Boreholes at the Immobilized Low-Activity Waste Site

    SciTech Connect

    Valenta, Michelle M.; Martin, Maria B.; Moreno, Jorge R.; Ferri, Rosalie M.; Horton, Duane G.; Reidel, Stephen P.

    2000-09-25

    This report provides particle size distribution data for samples near the Immobilized Low-Activity Waste (ILAW) Site that were archived in the Hanford Geotechnical Sample Library. Seventy-nine sediment samples were analyzed from four boreholes. Samples were collected from every ten feet in the boreholes. Eightly percent of the samples were classified as slightly gravelly sand. Fifteen percent were classified as gravelly sand, gravelly silty sand, or sandy gravels. These data indicate that the particle size of the sediment is consistent across the ILAW site and is dominated by sand in the upper part of the Hanford formation with more gravel rich units in the lower part.

  14. Redox activity of urban quasi-ultrafine particles from primary and secondary sources

    NASA Astrophysics Data System (ADS)

    Verma, Vishal; Ning, Zhi; Cho, Arthur K.; Schauer, James J.; Shafer, Martin M.; Sioutas, Constantinos

    2009-12-01

    To characterize the redox activity profiles of atmospheric aerosols from primary (traffic) and secondary photochemical sources, ambient quasi-ultrafine particles were collected near downtown Los Angeles in two different time periods - morning (6:00-9:00 PDT) and afternoon (11:00-14:00 PDT) in the summer of 2008. Detailed chemical analysis of the collected samples, including water-soluble elements, inorganic ions, organic species and water soluble organic carbon (WSOC) was conducted and redox activity of the samples was measured by two different assays: the dithiothreitol (DTT) and the macrophage reactive oxygen species (ROS) assays. Tracers of secondary photochemical reactions, such as sulfate and organic acids were higher (2.1 ± 0.6 times for sulfate, and up to 3 times for the organic acids) in the afternoon period. WSOC was also elevated by 2.5 ± 0.9 times in the afternoon period due to photo-oxidation of primary particles during atmospheric aging. Redox activity measured by the DTT assay was considerably higher for the samples collected during the afternoon; on the other hand, diurnal trends in the ROS-based activity were not consistent between the morning and afternoon periods. A linear regression between redox activity and various PM chemical constituents showed that the DTT assay was highly correlated with WSOC ( R2 = 0.80), while ROS activity was associated mostly with water soluble transition metals (Vanadium, Nickel and Cadmium; R2 > 0.70). The DTT and ROS assays, which are based on the generation of different oxidizing species by chemical PM constituents, provide important information for elucidating the health risks related to PM exposure from different sources. Thus, both primary and secondary particles possess high redox activity; however, photochemical transformations of primary emissions with atmospheric aging enhance the toxicological potency of primary particles in terms of generating oxidative stress and leading to subsequent damage in cells.

  15. Transport of finite size particles in confined narrow channels: Diffusion, coherence, and particle separation

    NASA Astrophysics Data System (ADS)

    Ai, Bao-Quan; Wu, Jian-Chun

    2013-07-01

    Transport of the finite size spherical Brownian particles is investigated in confined narrow channels with varying cross-section width. Applying the Fick-Jacobs approximation, we obtain the expressions of the particle current, the effective diffusion coefficient, and the coherence level of Brownian transport (the Péclet number). For the case of the biased constant force, the dependencies of the nonlinear mobility, the effective diffusion coefficient, and the Péclet number on the particle size exhibit striking behaviors. The Péclet number decreases with increasing the radius of the particle which shows that the big sizes of the particles reduce the coherence level of Brownian transport. There exists an optimized value of the radius at which the effective diffusion coefficient is maximal. For the case of the asymmetric unbiased force, due to the competition between the spatial asymmetry and the temporal asymmetry, the transport directions of the particles depend very sensitively on the size of the particle. Particles larger than a given threshold radius move to the left, whereas particles smaller than that move to the right. Therefore, one can separate particles of different radii and make them move towards opposite directions.

  16. Children exposure assessment to ultrafine particles and black carbon: The role of transport and cooking activities

    NASA Astrophysics Data System (ADS)

    Buonanno, G.; Stabile, L.; Morawska, L.; Russi, A.

    2013-11-01

    An accurate evaluation of the airborne particle dose-response relationship requires detailed measurements of the actual particle concentration levels that people are exposed to, in every microenvironment in which they reside. The aim of this work was to perform an exposure assessment of children in relation to two different aerosol species: ultrafine particles (UFPs) and black carbon (BC). To this purpose, personal exposure measurements, in terms of UFP and BC concentrations, were performed on 103 children aged 8-11 years (10.1 ± 1.1 years) using hand-held particle counters and aethalometers. Simultaneously, a time-activity diary and a portable GPS were used to determine the children's daily time-activity pattern and estimate their inhaled dose of UFPs and BC. The median concentration to which the study population was exposed was found to be comparable to the high levels typically detected in urban traffic microenvironments, in terms of both particle number (2.2 × 104 part. cm-3) and BC (3.8 μg m-3) concentrations. Daily inhaled doses were also found to be relatively high and were equal to 3.35 × 1011 part. day-1 and 3.92 × 101 μg day-1 for UFPs and BC, respectively. Cooking and using transportation were recognized as the main activities contributing to overall daily exposure, when normalized according to their corresponding time contribution for UFPs and BC, respectively. Therefore, UFPs and BC could represent tracers of children exposure to particulate pollution from indoor cooking activities and transportation microenvironments, respectively.

  17. Impacts of new particle formation on aerosol cloud condensation nuclei (CCN) activity in Shanghai: case study

    NASA Astrophysics Data System (ADS)

    Leng, C.; Zhang, Q.; Zhang, D.; Zhang, H.; Xu, C.; Li, X.; Kong, L.; Tao, J.; Cheng, T.; Zhang, R.; Chen, J.; Qiao, L.; Lou, S.; Wang, H.; Chen, C.

    2014-07-01

    New particle formation (NPF) events and their impacts on cloud condensation nuclei (CCN) were investigated using continuous measurements collected in urban Shanghai from 1 to 30 April 2012. During the campaign, NPF occurred in 8 out of the 30 days and enhanced CCN number concentration (NCCN) by a actor of 1.2-1.8, depending on supersaturation (SS). The NPF event on 3 April 2012 was chosen as an example to investigate the NPF influence on CCN activity. In this NPF event, secondary aerosols were produced continuously and increased PM2.5 mass concentration at a~rate of 4.33 μg cm-3 h-1, and the growth rate (GR) and formation rate (FR) were on average 5 nm h-1 and 0.36 cm-3 s-1, respectively. The newly formed particles grew quickly from nucleation mode (10-20 nm) into CCN size range. NCCN increased rapidly at SS of 0.4-1.0% but weakly at SS of 0.2%. Correspondingly, aerosol CCN activities (fractions of activated aerosol particles in total aerosols, NCCN / NCN) were significantly enhanced from 0.24-0.60 to 0.30-0.91 at SS of 0.2-1.0% due to the NPF. On the basis of the κ-Köhler theory, aerosol size distributions and chemical composition measured simultaneously were used to predict NCCN. There was a good agreement between the predicted and measured NCCN (R2 = 0.96, Npredicted / Nmeasured = 1.04). This study reveals that NPF exerts large impacts on aerosol particle abundance and size spectra, thus significantly promotes NCCN and aerosol CCN activity in this urban environment. The GR of NPF is the key factor controlling the newly formed particles to become CCN at all SS levels, whereas the FR is an effective factor only under high SS (e.g. 1.0%) conditions.

  18. Immobilization of inorganic pyrophosphatase on nanodiamond particles retaining its high enzymatic activity.

    PubMed

    Rodina, Elena V; Valueva, Anastasiya V; Yakovlev, Ruslan Yu; Vorobyeva, Nataliya N; Kulakova, Inna I; Lisichkin, Georgy V; Leonidov, Nikolay B

    2015-12-21

    Nanodiamond (ND) particles are popular platforms for the immobilization of molecular species. In the present research, enzyme Escherichia coli inorganic pyrophosphatase (PPase) was immobilized on detonation ND through covalent or noncovalent bonding and its enzymatic activity was characterized. Factors affecting adsorption of PPase such as ND size and surface chemistry were studied. The obtained material is a submicron size association of ND particles and protein molecules in approximately equal amounts. Both covalently and noncovalently immobilized PPase retains a significant enzymatic activity (up to 95% of its soluble form) as well as thermostability. The obtained hybrid material has a very high enzyme loading capacity (∼1 mg mg(-1)) and may be considered as a promising delivery system of biologically active proteinaceous substances, particularly in the treatment of diseases such as calcium pyrophosphate crystal deposition disease and related pathologies. They can also be used as recoverable heterogeneous catalysts in the traditional uses of PPase.

  19. Collective dynamics of chemically active particles trapped at a fluid interface.

    PubMed

    Domínguez, Alvaro; Malgaretti, P; Popescu, M N; Dietrich, S

    2016-10-12

    Chemically active colloids generate changes in the chemical composition of their surrounding solution and thereby induce flows in the ambient fluid which affect their dynamical evolution. Here we study the many-body dynamics of a monolayer of spherically symmetric active particles trapped at a fluid-fluid interface. To this end we consider a model for the large-scale spatial distribution of particles which incorporates the direct pair interaction (including also the capillary interaction which is caused specifically by the interfacial trapping) as well as the effect of hydrodynamic interactions (including the Marangoni flow induced by the response of the interface to the chemical activity). The values of the relevant physical parameters for typical experimental realizations of such systems are estimated and various scenarios, which are predicted by our approach for the dynamics of the monolayer, are discussed. In particular, we show that the chemically-induced Marangoni flow can prevent the clustering instability driven by the capillary attraction.

  20. Surface activity of Janus particles adsorbed at fluid-fluid interfaces: Theoretical and experimental aspects.

    PubMed

    Fernandez-Rodriguez, Miguel Angel; Rodriguez-Valverde, Miguel Angel; Cabrerizo-Vilchez, Miguel Angel; Hidalgo-Alvarez, Roque

    2016-07-01

    Since de Gennes coined in 1992 the term Janus particle (JP), there has been a continued effort to develop this field. The purpose of this review is to present the most relevant theoretical and experimental results obtained so far on the surface activity of amphiphilic JPs at fluid interfaces. The surface activity of JPs at fluid-fluid interfaces can be experimentally determined using two different methods: the classical Langmuir balance or the pendant drop tensiometry. The second method requires much less amount of sample than the first one, but it has also some experimental limitations. In all cases collected here the JPs exhibited a higher surface or interfacial activity than the corresponding homogeneous particles. This reveals the significant advantage of JPs for the stabilization of emulsions and foams.

  1. Effects of mineral tourmaline particles on the photocatalytic activity of TiO2 thin films.

    PubMed

    Meng, Junping; Liang, Jinsheng; Ou, Xiuqin; Ding, Yan; Liang, Guangchuan

    2008-03-01

    Titania composite thin films (T/TiO2) containing tourmaline particles were prepared by a sol-gel method, using alkoxide solutions as precursor. The tourmaline particles and thin films were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and so on. The effects of tourmaline on the photocatalytic activity of TiO2 were measured with methyl orange as an objective photodegradation substance. The results showed that the photocatalytic degradation of methyl orange conformed to the first-order kinetic equation and the composite thin films had better photocatalytic activity due to the cooperation of polarity and the far infrared emission of tourmaline. The T/TiO2 thin films including 0.5 wt% tourmaline exhibited better photocatalytic activity when heat-treated at 250 degrees C for 3 h, than pure TiO2 thin films under the ultraviolet irradiation.

  2. Apparatus having reduced background for measuring radiation activity in aerosol particles

    DOEpatents

    Rodgers, John C.; McFarland, Andrew R.; Oritz, Carlos A.; Marlow, William H.

    1992-01-01

    Apparatus having reduced background for measuring radiation activity in aerosol particles. A continuous air monitoring sampler is described for use in detecting the presence of alpha-emitting aerosol particles. An inlet fractionating screen has been demonstrated to remove about 95% of freshly formed radon progeny from the aerosol sample, and approximately 33% of partially aged progeny. Addition of an electrical condenser and a modified dichotomous virtual impactor are expected to produce considerable improvement in these numbers, the goal being to enrich the transuranic (TRU) fraction of the aerosols. This offers the possibility of improving the signal-to-noise ratio for the detected alpha-particle energy spectrum in the region of interest for detecting TRU materials associated with aerosols, thereby enhancing the performance of background-compensation algorithms for improving the quality of alarm signals intended to warn personnel of potentially harmful quantities of TRU materials in the ambient air.

  3. Pre-activation of aerosol particles by ice preserved in pores

    NASA Astrophysics Data System (ADS)

    Marcolli, Claudia

    2017-02-01

    Pre-activation denotes the capability of particles or materials to nucleate ice at lower relative humidities or higher temperatures compared to their intrinsic ice nucleation efficiency after having experienced an ice nucleation event or low temperature before. This review presumes that ice preserved in pores is responsible for pre-activation and analyses pre-activation under this presumption. Idealized trajectories of air parcels are used to discuss the pore characteristics needed for ice to persist in pores and to induce macroscopic ice growth out of the pores. The pore width needed to keep pores filled with water decreases with decreasing relative humidity as described by the inverse Kelvin equation. Thus, narrow pores remain filled with ice well below ice saturation. However, the smaller the pore width, the larger the melting and freezing point depressions within the pores. Therefore, pre-activation due to pore ice is constrained by the melting of ice in narrow pores and the sublimation of ice from wide pores imposing restrictions on the temperature and relative humidity range of pre-activation for cylindrical pores. Ice is better protected in ink-bottle-shaped pores with a narrow opening leading to a large cavity. However, whether pre-activation is efficient also depends on the capability of ice to grow macroscopically, i.e. out of the pore. A strong effect of pre-activation is expected for swelling pores, because at low relative humidity (RH) their openings narrow and protect the ice within them against sublimation. At high relative humidities, they open up and the ice can grow to macroscopic size and form an ice crystal. Similarly, ice protected in pockets is perfectly sheltered against sublimation but needs the dissolution of the surrounding matrix to be effective. Pores partially filled with condensable material may also show pre-activation. In this case, complete filling occurs at lower RH than for empty pores and freezing shifts to lower temperatures.Pre-activation

  4. IMPACT OF SIPHONING ACTIVITY AND NATURALLY SUSPENDED PARTICLE LOAD ON MUSSEL KILL by PSEUDOMONAS FLUORESCENS

    SciTech Connect

    Daniel Molloy

    2003-08-04

    Under this USDOE-NETL contract, the bacterium Pseudomonas fluorescens is being developed as a biocontrol agent for zebra mussels. The specific purpose of the contract is to identify biotic and abiotic factors that affect mussel kill. Ingestion of these bacteria by zebra mussels is required to achieve kill, and tests evaluating factors that relate to mussel feeding are contained in this report. Specifically the impact of the following two factors were investigated: (1) Mussel siphoning behavior--In nature, zebra mussels typically have their two shells spread apart and their inhalant siphon tube extended from between their shells for taking food particles into their mantle cavities (Fig. 1). Our tests indicated that there is a direct correlation between mussel siphoning activity and mussel mortality achieved by a bacterial treatment. Therefore, to encourage mussel feeding on bacteria, future pipe treatments within power plants should be carried out using procedures which minimize disturbance to mussel siphoning. 2. Naturally suspended particle loads--Since bacterial cells are lethal only if ingested by mussels, waters containing very high levels of naturally suspended particles might reduce the mortality that can be achieved by a bacterial treatment. If true, this inhibition might occur as a result of particle exclusion, i.e., there could be reduced ingestion of bacterial cells since they represent a reduced percentage of all particles ingested. Our tests indicated that a range of particle concentrations that might naturally exist in a turbid river did not inhibit mussel kill by the bacterial cells, but that an artificially high load of natural particles was capable of causing a reduction in kill. To be conservative, therefore, future pipe treatments should be timed to occur when intake waters have relatively low quantities of naturally suspended particulate matter.

  5. Cloud condensation nucleus activity of secondary organic aerosol particles mixed with sulfate

    NASA Astrophysics Data System (ADS)

    King, Stephanie M.; Rosenoern, Thomas; Shilling, John E.; Chen, Qi; Martin, Scot T.

    2007-12-01

    The cloud condensation nucleus (CCN) activity of organic-sulfate particles was investigated using a steady-state environmental chamber. The organic component consisted of secondary organic aerosol (SOA) generated in the dark from 24 +/- 2 ppb α-pinene for conditions of 300 +/- 5 ppb ozone, 40 +/- 2% relative humidity, and 25 +/- 1°C, with the organic mass loading in the chamber ranging from 23 to 37 μg m-3. CCN analysis was performed for 80- to 150-nm particles having variable organic-sulfate volume fractions, which were estimated from the diameter of the organic-sulfate particle relative to that of the seed as well as independently from mass spectra. Critical supersaturation, which increased for greater SOA volume fraction and smaller particle diameter, was well predicted by a Köhler model having two components, one for ammonium sulfate and another for SOA. The entire data set could be successfully modeled by a single suite of effective chemical parameters for SOA. The results suggest that the effects of limited organic solubility in mixed SOA-sulfate particles may be reliably omitted in the treatment of cloud droplet formation.

  6. Optimal run-and-tumble–based transportation of a Janus particle with active steering

    PubMed Central

    Mano, Tomoyuki; Iwasawa, Junichiro; Sano, Masaki

    2017-01-01

    Although making artificial micrometric swimmers has been made possible by using various propulsion mechanisms, guiding their motion in the presence of thermal fluctuations still remains a great challenge. Such a task is essential in biological systems, which present a number of intriguing solutions that are robust against noisy environmental conditions as well as variability in individual genetic makeup. Using synthetic Janus particles driven by an electric field, we present a feedback-based particle-guiding method quite analogous to the “run-and-tumbling” behavior of Escherichia coli but with a deterministic steering in the tumbling phase: the particle is set to the run state when its orientation vector aligns with the target, whereas the transition to the “steering” state is triggered when it exceeds a tolerance angle α. The active and deterministic reorientation of the particle is achieved by a characteristic rotational motion that can be switched on and off by modulating the ac frequency of the electric field, which is reported in this work. Relying on numerical simulations and analytical results, we show that this feedback algorithm can be optimized by tuning the tolerance angle α. The optimal resetting angle depends on signal to noise ratio in the steering state, and it is shown in the experiment. The proposed method is simple and robust for targeting, despite variability in self-propelling speeds and angular velocities of individual particles. PMID:28292904

  7. Optimal run-and-tumble-based transportation of a Janus particle with active steering.

    PubMed

    Mano, Tomoyuki; Delfau, Jean-Baptiste; Iwasawa, Junichiro; Sano, Masaki

    2017-03-14

    Although making artificial micrometric swimmers has been made possible by using various propulsion mechanisms, guiding their motion in the presence of thermal fluctuations still remains a great challenge. Such a task is essential in biological systems, which present a number of intriguing solutions that are robust against noisy environmental conditions as well as variability in individual genetic makeup. Using synthetic Janus particles driven by an electric field, we present a feedback-based particle-guiding method quite analogous to the "run-and-tumbling" behavior of Escherichia coli but with a deterministic steering in the tumbling phase: the particle is set to the run state when its orientation vector aligns with the target, whereas the transition to the "steering" state is triggered when it exceeds a tolerance angle [Formula: see text] The active and deterministic reorientation of the particle is achieved by a characteristic rotational motion that can be switched on and off by modulating the ac frequency of the electric field, which is reported in this work. Relying on numerical simulations and analytical results, we show that this feedback algorithm can be optimized by tuning the tolerance angle [Formula: see text] The optimal resetting angle depends on signal to noise ratio in the steering state, and it is shown in the experiment. The proposed method is simple and robust for targeting, despite variability in self-propelling speeds and angular velocities of individual particles.

  8. Understanding the Role of Water in Modifying Particle Mixing States for CCN Activity

    NASA Astrophysics Data System (ADS)

    Vu, D. N.; Gao, S.; Pierce, J. R.; Asa-Awuku, A. A.

    2014-12-01

    CCN data sets from ambient and chamber studies, which consist of complex heterogeneous mixtures of organic and inorganic aerosol mixtures, may not show a single activation curve but instead can exhibit multiple activations not associated with doubly charged particles. It has been suggested that these activation curves may be representative of multiple externally mixed compounds, whereas single activation curves are representative of single component or multicomponent internally mixed aerosols. To characterize and modify mixing states, a new laminar flow tube apparatus was developed to control the extent of mixing of organic and inorganic fractions under different environmental conditions such as relative humidity. Data sets yielding multiple activation curves have been recreated by mixing multiple inorganic and organic compounds. Preliminary results suggest that aerosol water is a significant factor; under dry conditions, the aerosols remained externally mixed while humid conditions facilitated internal mixing. For example, ammonium sulfate (inorganic) and succinic acid (organic) when dry, maintained an external mixture and multiple activation curves were observed to be constant. Under humid conditions, external mixing was initially observed; however, the aerosol water promoted internal mixing and the activation curves were observed to converge into a single curve. The data agrees well with Köhler Theory and single parameter (kappa) theory thermodynamic predictions of droplet activation. Data sets are also compared with a diffusion based coagulation particle model to predict mixing behavior. The method of analysis and the effect of mixing states of multiple components on the supersaturated hygroscopic properties of aerosols are presented.

  9. Soot Aerosol Particles as Cloud Condensation Nuclei: from Ice Nucleation Activity to Ice Crystal Morphology

    NASA Astrophysics Data System (ADS)

    Pirim, Claire; Ikhenazene, Raouf; Ortega, Isamel Kenneth; Carpentier, Yvain; Focsa, Cristian; Chazallon, Bertrand; Ouf, François-Xavier

    2016-04-01

    Emissions of solid-state particles (soot) from engine exhausts due to incomplete fuel combustion is considered to influence ice and liquid water cloud droplet activation [1]. The activity of these aerosols would originate from their ability to be important centers of ice-particle nucleation, as they would promote ice formation above water homogeneous freezing point. Soot particles are reported to be generally worse ice nuclei than mineral dust because they activate nucleation at higher ice-supersaturations for deposition nucleation and at lower temperatures for immersion freezing than ratios usually expected for homogeneous nucleation [2]. In fact, there are still numerous opened questions as to whether and how soot's physico-chemical properties (structure, morphology and chemical composition) can influence their nucleation ability. Therefore, systematic investigations of soot aerosol nucleation activity via one specific nucleation mode, here deposition nucleation, combined with thorough structural and compositional analyzes are needed in order to establish any association between the particles' activity and their physico-chemical properties. In addition, since the morphology of the ice crystals can influence their radiative properties [3], we investigated their morphology as they grow over both soot and pristine substrates at different temperatures and humidity ratios. In the present work, Combustion Aerosol STandart soot samples were produced from propane using various experimental conditions. Their nucleation activity was studied in deposition mode (from water vapor), and monitored using a temperature-controlled reactor in which the sample's relative humidity is precisely measured with a cryo-hygrometer. Formation of water/ice onto the particles is followed both optically and spectroscopically, using a microscope coupled to a Raman spectrometer. Vibrational signatures of hydroxyls (O-H) emerge when the particle becomes hydrated and are used to characterize ice

  10. Ice nucleation active particles in continental air samples over Mainz, Germany

    NASA Astrophysics Data System (ADS)

    Pummer, Bernhard G.; Pöschl, Ulrich; Fröhlich-Nowoisky, Janine

    2016-04-01

    Aerosol particles are of central importance for atmospheric chemistry and physics, climate and public health. Some of these particles possess ice nucleation activity (INA), which is highly relevant for cloud formation and precipitation. In 2010, air filter samples were collected with a high-volume filter sampler separating fine and coarse particles (aerodynamic cut-off diameter 3 μm) in Mainz, Germany. In this study, the INA of the atmospheric particles deposited on these filters was determined. Therefore,they were extracted with ultrapure water, which was then measured in a droplet freezing assay, as described in Fröhlich-Nowoisky et al. (2015). The determined concentration of ice nucleators (INs) was between 0.3 and 2per m³ at 266 K, and between5 and 75 per m³ at 260 K. The INs were further characterized by different treatments, like heating (308 K, 371 K), filtration (0.1 μm, 300 kDa), and digestion with papain (10 mg/ml). We further investigated, which atmospheric conditions (e.g. weather) and distinguished events (e.g. dust storms, volcanic eruptions, and pollen peaks) influenced the number and nature of these INs. Fröhlich-Nowoisky, J., Hill, T. C. J., Pummer, B. G., Yordanova, P., Franc, G. D., and Pöschl, U.: Ice nucleation activity in the widespread soil fungus Mortierella alpina, Biogeosci., 12, 1057-1071, doi:10.5194/bg-12-1057-2015, 2015.

  11. Catalytic activity in individual cracking catalyst particles imaged throughout different life stages by selective staining.

    PubMed

    Buurmans, Inge L C; Ruiz-Martínez, Javier; Knowles, William V; van der Beek, David; Bergwerff, Jaap A; Vogt, Eelco T C; Weckhuysen, Bert M

    2011-09-18

    Fluid catalytic cracking (FCC) is the major conversion process used in oil refineries to produce valuable hydrocarbons from crude oil fractions. Because the demand for oil-based products is ever increasing, research has been ongoing to improve the performance of FCC catalyst particles, which are complex mixtures of zeolite and binder materials. Unfortunately, there is limited insight into the distribution and activity of individual zeolitic domains at different life stages. Here we introduce a staining method to visualize the structure of zeolite particulates and other FCC components. Brønsted acidity maps have been constructed at the single particle level from fluorescence microscopy images. By applying a statistical methodology to a series of catalysts deactivated via industrial protocols, a correlation is established between Brønsted acidity and cracking activity. The generally applicable method has clear potential for catalyst diagnostics, as it determines intra- and interparticle Brønsted acidity distributions for industrial FCC materials.

  12. Catalytic activity in individual cracking catalyst particles imaged throughout different life stages by selective staining

    NASA Astrophysics Data System (ADS)

    Buurmans, Inge L. C.; Ruiz-Martínez, Javier; Knowles, William V.; van der Beek, David; Bergwerff, Jaap A.; Vogt, Eelco T. C.; Weckhuysen, Bert M.

    2011-11-01

    Fluid catalytic cracking (FCC) is the major conversion process used in oil refineries to produce valuable hydrocarbons from crude oil fractions. Because the demand for oil-based products is ever increasing, research has been ongoing to improve the performance of FCC catalyst particles, which are complex mixtures of zeolite and binder materials. Unfortunately, there is limited insight into the distribution and activity of individual zeolitic domains at different life stages. Here we introduce a staining method to visualize the structure of zeolite particulates and other FCC components. Brønsted acidity maps have been constructed at the single particle level from fluorescence microscopy images. By applying a statistical methodology to a series of catalysts deactivated via industrial protocols, a correlation is established between Brønsted acidity and cracking activity. The generally applicable method has clear potential for catalyst diagnostics, as it determines intra- and interparticle Brønsted acidity distributions for industrial FCC materials.

  13. Toluene vapor capture by activated carbon particles in a dual gas-solid cyclone system.

    PubMed

    Lim, Yun Hui; Ngo, Khanh Quoc; Park, Young Koo; Jo, Young Min

    2012-08-01

    Capturing of odorous compounds such as toluene vapor by a particulate-activated carbon adsorbent was investigated in a gas-solid cyclone, which is one type of mobile beds. The test cyclone was early modified with the post cyclone (PoC) and a spiral flow guide to the vortex finder. The proposed process may contribute to the reduction of gases and dust from industrial exhausts, especially when dealing with a low concentration of odorous elements and a large volume ofdust flow. In this device, the toluene capturing efficiency at a 400 ppm concentration rose up to 77.4% when using activated carbon (AC) particles with a median size of 27.03 microm. A maximum 96% of AC particles could be collected for reuse depending on the size and flow rate. The AC regenerated via thermal treatment showed an adsorption potential up to 66.7% throughout repeated tests.

  14. Epidermal growth factor receptor activation by diesel particles is mediated by tyrosine phosphatase inhibition

    SciTech Connect

    Tal, Tamara L.; Bromberg, Philip A.; Kim, Yumee; Samet, James M.

    2008-12-15

    Exposure to particulate matter (PM) is associated with increased cardiopulmonary morbidity and mortality. Diesel exhaust particles (DEP) are a major component of ambient PM and may contribute to PM-induced pulmonary inflammation. Proinflammatory signaling is mediated by phosphorylation-dependent signaling pathways whose activation is opposed by the activity of protein tyrosine phosphatases (PTPases) which thereby function to maintain signaling quiescence. PTPases contain an invariant catalytic cysteine that is susceptible to electrophilic attack. DEP contain electrophilic oxy-organic compounds that may contribute to the oxidant effects of PM. Therefore, we hypothesized that exposure to DEP impairs PTPase activity allowing for unopposed basal kinase activity. Here we report that exposure to 30 {mu}g/cm{sup 2} DEP for 4 h induces differential activation of signaling in primary cultures of human airway epithelial cells (HAEC), a primary target cell in PM inhalation. In-gel kinase activity assay of HAEC exposed to DEPs of low (L-DEP), intermediate (I-DEP) or high (H-DEP) organic content showed differential activation of intracellular kinases. Exposure to these DEP also induced varying levels of phosphorylation of the receptor tyrosine kinase EGFR in a manner that requires EGFR kinase activity but does not involve receptor dimerization. We demonstrate that treatment with DEP results in an impairment of total and EGFR-directed PTPase activity in HAEC with a potency that is independent of the organic content of these particles. These data show that DEP-induced EGFR phosphorylation in HAEC is the result of a loss of PTPase activities which normally function to dephosphorylate EGFR in opposition to baseline EGFR kinase activity.

  15. Mechanism of self-propulsion in 3D-printed active granular particles

    NASA Astrophysics Data System (ADS)

    Koumakis, N.; Gnoli, A.; Maggi, C.; Puglisi, A.; Di Leonardo, R.

    2016-11-01

    Active granular particles can harness unbiased mechanical vibrations in the environment to generate directed motion. We provide a theoretical framework that connects the geometrical shape of a three dimensional object to its self-propulsion characteristics over a vertically vibrated plate. We find that a maximally efficient propulsion is achieved for structures having tilted flexible legs forming a characteristic angle with the vertical. Our predictions are verified by experimental observations on a class of 3D printed structures with smoothly varying geometrical features.

  16. Chalk-Ex: Transport of Optically Active Particles from the Surface Mixed Layer

    DTIC Science & Technology

    2005-05-02

    dissolution , aggregation, and grazing- related "repackaging" into fecal pellets). Approach The focus of the Chalk-Ex project was a sequence of...experiment in which the production term of optically-active particles could be defined, significantly reducing the uncertainty of the net loss rates of...suspended calcite algorithm. The NASA project paid for the 26 T of chalk and some of the ship time for the November 2001 experiments. A DURIP Grant to J

  17. Observation of non-Markovian micromechanical Brownian motion

    PubMed Central

    Gröblacher, S.; Trubarov, A.; Prigge, N.; Cole, G. D.; Aspelmeyer, M.; Eisert, J.

    2015-01-01

    All physical systems are to some extent open and interacting with their environment. This insight, basic as it may seem, gives rise to the necessity of protecting quantum systems from decoherence in quantum technologies and is at the heart of the emergence of classical properties in quantum physics. The precise decoherence mechanisms, however, are often unknown for a given system. In this work, we make use of an opto-mechanical resonator to obtain key information about spectral densities of its condensed-matter heat bath. In sharp contrast to what is commonly assumed in high-temperature quantum Brownian motion describing the dynamics of the mechanical degree of freedom, based on a statistical analysis of the emitted light, it is shown that this spectral density is highly non-Ohmic, reflected by non-Markovian dynamics, which we quantify. We conclude by elaborating on further applications of opto-mechanical systems in open system identification. PMID:26216619

  18. Brownian ratchets: How stronger thermal noise can reduce diffusion

    NASA Astrophysics Data System (ADS)

    Spiechowicz, Jakub; Kostur, Marcin; Łuczka, Jerzy

    2017-02-01

    We study diffusion properties of an inertial Brownian motor moving on a ratchet substrate, i.e., a periodic structure with broken reflection symmetry. The motor is driven by an unbiased time-periodic symmetric force that takes the system out of thermal equilibrium. For selected parameter sets, the system is in a non-chaotic regime in which we can identify a non-monotonic dependence of the diffusion coefficient on temperature: for low temperature, it initially increases as the temperature grows, passes through its local maximum, next starts to diminish reaching its local minimum, and finally it monotonically increases in accordance with the Einstein linear relation. Particularly interesting is the temperature interval in which diffusion is suppressed by the thermal noise, and we explain this effect in terms of transition rates of a three-state stochastic model.

  19. Brownian dynamics simulation of fission yeast mitotic spindle formation

    NASA Astrophysics Data System (ADS)

    Edelmaier, Christopher

    2014-03-01

    The mitotic spindle segregates chromosomes during mitosis. The dynamics that establish bipolar spindle formation are not well understood. We have developed a computational model of fission-yeast mitotic spindle formation using Brownian dynamics and kinetic Monte Carlo methods. Our model includes rigid, dynamic microtubules, a spherical nuclear envelope, spindle pole bodies anchored in the nuclear envelope, and crosslinkers and crosslinking motor proteins. Crosslinkers and crosslinking motor proteins attach and detach in a grand canonical ensemble, and exert forces and torques on the attached microtubules. We have modeled increased affinity for crosslinking motor attachment to antiparallel microtubule pairs, and stabilization of microtubules in the interpolar bundle. We study parameters controlling the stability of the interpolar bundle and assembly of a bipolar spindle from initially adjacent spindle-pole bodies.

  20. Analytical studies of spectrum broadcast structures in quantum Brownian motion

    NASA Astrophysics Data System (ADS)

    Tuziemski, J.; Korbicz, J. K.

    2016-11-01

    Spectrum broadcast structures are a new and fresh concept in the quantum-to-classical transition, introduced recently in the context of decoherence and the appearance of objective features in quantum mechanics. These are specific quantum state structures, responsible for the objectivization of the decohered state of a system. Recently, they have been demonstrated by means of the well-known quantum Brownian motion model of the recoilless limit (infinitely massive central system), as the principal interest lies in information transfer from the system to the environment. However, a final analysis relied on numerics. Here, after a presentation of the main concepts, we perform analytical studies of the model, showing the timescales and the efficiency of the spectrum broadcast structure formation. We consider a somewhat simplified environment, being random with a uniform distribution of frequencies.

  1. Non-Markovian expansion in quantum Brownian motion

    NASA Astrophysics Data System (ADS)

    Fraga, Eduardo S.; Krein, Gastão; Palhares, Letícia F.

    2014-01-01

    We consider the non-Markovian Langevin evolution of a dissipative dynamical system in quantum mechanics in the path integral formalism. After discussing the role of the frequency cutoff for the interaction of the system with the heat bath and the kernel and noise correlator that follow from the most common choices, we derive an analytic expansion for the exact non-Markovian dissipation kernel and the corresponding colored noise in the general case that is consistent with the fluctuation-dissipation theorem and incorporates systematically non-local corrections. We illustrate the modifications to results obtained using the traditional (Markovian) Langevin approach in the case of the exponential kernel and analyze the case of the non-Markovian Brownian motion. We present detailed results for the free and the quadratic cases, which can be compared to exact solutions to test the convergence of the method, and discuss potentials of a general nonlinear form.

  2. Temporal Correlations of the Running Maximum of a Brownian Trajectory

    NASA Astrophysics Data System (ADS)

    Bénichou, Olivier; Krapivsky, P. L.; Mejía-Monasterio, Carlos; Oshanin, Gleb

    2016-08-01

    We study the correlations between the maxima m and M of a Brownian motion (BM) on the time intervals [0 ,t1] and [0 ,t2], with t2>t1. We determine the exact forms of the distribution functions P (m ,M ) and P (G =M -m ), and calculate the moments E {(M-m ) k} and the cross-moments E {mlMk} with arbitrary integers l and k . We show that correlations between m and M decay as √{t1/t2 } when t2/t1→∞ , revealing strong memory effects in the statistics of the BM maxima. We also compute the Pearson correlation coefficient ρ (m ,M ) and the power spectrum of Mt, and we discuss a possibility of extracting the ensemble-averaged diffusion coefficient in single-trajectory experiments using a single realization of the maximum process.

  3. Brownian dynamics simulation of sickle hemoglobin bundle formation

    NASA Astrophysics Data System (ADS)

    Liu, Ya; Gunton, James; Chakrabarti, Amit

    2010-03-01

    The physical properties of biopolymer fibers, such as their stability and degree of aggregation, are implicated in many diseases, including sickle cell anemia. The natural chirality of protofilaments plays a crucial role in the formation of sickle hemoglobin fiber which leads to the permanent blockage of microvessels. We use Brownian dynamics to investigate the kinetics of fiber aggregation. The geometrical helical structure and chirality of the filaments are modeled by anisotropic patch-like interactions. We present the kinetics of fiber formation and study the possibility of a finite critical fiber bundle size. We compare our results with various experimental and theoretical results. This work is supported by grants from the NSF and the G. Harold and Leila Y. Mathers Foundation.

  4. Micro rectennas: Brownian ratchets for thermal-energy harvesting

    SciTech Connect

    Pan, Y.; Powell, C. V.; Balocco, C.; Song, A. M.

    2014-12-22

    We experimentally demonstrated the operation of a rectenna for harvesting thermal (blackbody) radiation and converting it into dc electric power. The device integrates an ultrafast rectifier, the self-switching nanodiode, with a wideband log-periodic spiral microantenna. The radiation from the thermal source drives the rectenna out of thermal equilibrium, permitting the rectification of the excess thermal fluctuations from the antenna. The power conversion efficiency increases with the source temperatures up to 0.02% at 973 K. The low efficiency is attributed mainly to the impedance mismatch between antenna and rectifier, and partially to the large field of view of the antenna. Our device not only opens a potential solution for harvesting thermal energy but also provides a platform for experimenting with Brownian ratchets.

  5. Momentum conserving Brownian dynamics propagator for complex soft matter fluids

    SciTech Connect

    Padding, J. T.; Briels, W. J.

    2014-12-28

    We present a Galilean invariant, momentum conserving first order Brownian dynamics scheme for coarse-grained simulations of highly frictional soft matter systems. Friction forces are taken to be with respect to moving background material. The motion of the background material is described by locally averaged velocities in the neighborhood of the dissolved coarse coordinates. The velocity variables are updated by a momentum conserving scheme. The properties of the stochastic updates are derived through the Chapman-Kolmogorov and Fokker-Planck equations for the evolution of the probability distribution of coarse-grained position and velocity variables, by requiring the equilibrium distribution to be a stationary solution. We test our new scheme on concentrated star polymer solutions and find that the transverse current and velocity time auto-correlation functions behave as expected from hydrodynamics. In particular, the velocity auto-correlation functions display a long time tail in complete agreement with hydrodynamics.

  6. Controlling local order of athermal self-propelled particles

    NASA Astrophysics Data System (ADS)

    Dougan, Niamh; Crowther, Peter; Royall, C. Patrick; Turci, Francesco

    2016-12-01

    We consider a model of self-propelled dynamics for athermal active particles, where the non-equilibrium active forces are modelled by a Ornstein-Uhlenbeck process. In the limit of no-driving force, the model reduces to the passive, Brownian dynamics of an atomistic glass forming fluid, the Wahnström binary mixture. The Wahnström mixture is known to show strong correlations between the emergence of slow dynamics and the formation of locally favoured structures based on icosahedra. Here, we study how the non-equilibrium driving affects the local structure of the system, and find that it strongly promotes icosahedral order. The states rich in local icosahedral order correspond to configurations of very low potential energy, suggesting that the non-equilibrium dynamics in the self propelled model can be effectively exploited to explore the potential energy surface of the binary mixture and have access to states that are difficult to attain using passive dynamics.

  7. Platelet Activation by Low Concentrations of Intact Oxidized LDL Particles Involves the PAF Receptor

    PubMed Central

    Chen, Rui; Chen, Xi; Salomon, Robert G.; McIntyre, Thomas M.

    2008-01-01

    Objective Mitochondrial depolarization aids platelet activation. Oxidized LDL (oxLDL) contains the medium length oxidatively truncated phospholipid hexadecyl azelaoyl-lysoPAF (HAz-LPAF) that disrupts mitochondrial function in nucleated cells, so oxLDL may augment platelet activation. Methods and Results Flow cytometry showed intact oxLDL particles synergized with sub-threshold amounts of soluble agonists to increase intracellular Ca++, and initiate platelet aggregation and surface expression of activated gpIIb/IIIa and P-selectin. oxLDL also induced aggregation and increased intracellular Ca++ in FURA2-labeled cells by itself at low, although not higher, concentrations. HAz-LPAF, alone and in combination with sub-stimulatory amounts of thrombin, rapidly increased cytoplasmic Ca++ and initiated aggregation. HAz-LPAF depolarized mitochondria in intact platelets, but this required concentrations beyond those that directly activated platelets. An unexpectedly large series of chemically pure truncated phospholipids generated by oxidative fragmentation of arachidonoyl-, docosahexaneoyl-, or linoleoyl alkyl phospholipids were platelet agonists. The PAF receptor, thought to effectively recognize only phospholipids with very short sn-2 residues, was essential for platelet activation because PAF receptor agonists blocked signaling by all these medium length phospholipids and oxLDL. Conclusions Intact oxLDL particles activate platelets through the PAF receptor, and the PAF receptor responds to a far wider range of oxidized phospholipids in oxLDL than anticipated. PMID:19112165

  8. Effect of time-activity adjustment on exposure assessment for traffic-related ultrafine particles.

    PubMed

    Lane, Kevin J; Levy, Jonathan I; Scammell, Madeleine Kangsen; Patton, Allison P; Durant, John L; Mwamburi, Mkaya; Zamore, Wig; Brugge, Doug

    2015-01-01

    Exposures to ultrafine particles (<100 nm, estimated as particle number concentration, PNC) differ from ambient concentrations because of the spatial and temporal variability of both PNC and people. Our goal was to evaluate the influence of time-activity adjustment on exposure assignment and associations with blood biomarkers for a near-highway population. A regression model based on mobile monitoring and spatial and temporal variables was used to generate hourly ambient residential PNC for a full year for a subset of participants (n=140) in the Community Assessment of Freeway Exposure and Health study. We modified the ambient estimates for each hour using personal estimates of hourly time spent in five micro-environments (inside home, outside home, at work, commuting, other) as well as particle infiltration. Time-activity adjusted (TAA)-PNC values differed from residential ambient annual average (RAA)-PNC, with lower exposures predicted for participants who spent more time away from home. Employment status and distance to highway had a differential effect on TAA-PNC. We found associations of RAA-PNC with high sensitivity C-reactive protein and Interleukin-6, although exposure-response functions were non-monotonic. TAA-PNC associations had larger effect estimates and linear exposure-response functions. Our findings suggest that time-activity adjustment improves exposure assessment for air pollutants that vary greatly in space and time.

  9. Effect of time-activity adjustment on exposure assessment for traffic-related ultrafine particles

    PubMed Central

    Lane, Kevin J; Levy, Jonathan I; Scammell, Madeleine Kangsen; Patton, Allison P; Durant, John L; Mwamburi, Mkaya; Zamore, Wig; Brugge, Doug

    2015-01-01

    Exposures to ultrafine particles (<100 nm, estimated as particle number concentration, PNC) differ from ambient concentrations because of the spatial and temporal variability of both PNC and people. Our goal was to evaluate the influence of time-activity adjustment on exposure assignment and associations with blood biomarkers for a near-highway population. A regression model based on mobile monitoring and spatial and temporal variables was used to generate hourly ambient residential PNC for a full year for a subset of participants (n=140) in the Community Assessment of Freeway Exposure and Health study. We modified the ambient estimates for each hour using personal estimates of hourly time spent in five micro-environments (inside home, outside home, at work, commuting, other) as well as particle infiltration. Time-activity adjusted (TAA)-PNC values differed from residential ambient annual average (RAA)-PNC, with lower exposures predicted for participants who spent more time away from home. Employment status and distance to highway had a differential effect on TAA-PNC. We found associations of RAA-PNC with high sensitivity C-reactive protein and Interleukin-6, although exposure-response functions were non-monotonic. TAA-PNC associations had larger effect estimates and linear exposure-response functions. Our findings suggest that time-activity adjustment improves exposure assessment for air pollutants that vary greatly in space and time. PMID:25827314

  10. Alpha spectrometric characterization of process-related particle size distributions from active particle sampling at the Los Alamos National Laboratory uranium foundry

    SciTech Connect

    Plionis, Alexander A; Peterson, Dominic S; Tandon, Lav; Lamont, Stephen P

    2009-01-01

    Uranium particles within the respirable size range pose a significant hazard to the health and safety of workers. Significant differences in the deposition and incorporation patterns of aerosols within the respirable range can be identified and integrated into sophisticated health physics models. Data characterizing the uranium particle size distribution resulting from specific foundry-related processes are needed. Using personal air sampling cascade impactors, particles collected from several foundry processes were sorted by activity median aerodynamic diameter onto various Marple substrates. After an initial gravimetric assessment of each impactor stage, the substrates were analyzed by alpha spectrometry to determine the uranium content of each stage. Alpha spectrometry provides rapid nondestructive isotopic data that can distinguish process uranium from natural sources and the degree of uranium contribution to the total accumulated particle load. In addition, the particle size bins utilized by the impactors provide adequate resolution to determine if a process particle size distribution is: lognormal, bimodal, or trimodal. Data on process uranium particle size values and distributions facilitate the development of more sophisticated and accurate models for internal dosimetry, resulting in an improved understanding of foundry worker health and safety.

  11. A unified framework for non-Brownian suspension flows and soft amorphous solids

    PubMed Central

    Lerner, Edan; Düring, Gustavo; Wyart, Matthieu

    2012-01-01

    While the rheology of non-Brownian suspensions in the dilute regime is well understood, their behavior in the dense limit remains mystifying. As the packing fraction of particles increases, particle motion becomes more collective, leading to a growing length scale and scaling properties in the rheology as the material approaches the jamming transition. There is no accepted microscopic description of this phenomenon. However, in recent years it has been understood that the elasticity of simple amorphous solids is governed by a critical point, the unjamming transition where the pressure vanishes, and where elastic properties display scaling and a diverging length scale. The correspondence between these two transitions is at present unclear. Here we show that for a simple model of dense flow, which we argue captures the essential physics near the jamming threshold, a formal analogy can be made between the rheology of the flow and the elasticity of simple networks. This analogy leads to a new conceptual framework to relate microscopic structure to rheology. It enables us to define and compute numerically normal modes and a density of states. We find striking similarities between the density of states in flow, and that of amorphous solids near unjamming: both display a plateau above some frequency scale ω∗ ∼ |zc - z|, where z is the coordination of the network of particle in contact, zc = 2D where D is the spatial dimension. However, a spectacular difference appears: the density of states in flow displays a single mode at another frequency scale ωmin ≪ ω∗ governing the divergence of the viscosity. PMID:22392976

  12. Engineering of radiation of optically active molecules with chiral nano-meta-particles

    NASA Astrophysics Data System (ADS)

    Klimov, V. V.; Guzatov, D. V.; Ducloy, M.

    2012-02-01

    The radiation of an optically active (chiral) molecule placed near a chiral nanosphere is investigated. The optimal conditions for engineering of radiation of optically active (chiral) molecules with the help of chiral nanoparticles are derived. It is shown that for this purpose, the substance of the chiral particle must have both ɛ and μ negative (double negative material (DNG)) or negative μ and positive ɛ (μ negative material (MNG)). Our results pave the way to an effective engineering of radiation of "left" and "right" molecules and to creating pure optical devices for separation of drugs enantiomers.

  13. Spatial ordering and abnormal optical activity of DNA liquid-crystalline dispersion particles

    NASA Astrophysics Data System (ADS)

    Semenov, S. V.; Yevdokimov, Yu. M.

    2016-12-01

    In our work, we investigate physicochemical and optical properties of double-strand DNA dispersions. The study of these properties is of biological interest, because it allows one to describe the characteristics of certain classes of chromosomes and DNA containing viruses. The package pattern of DNA molecules in the dispersions particles (DP) is examined. The consideration of the DNA liquid-crystalline DP optical activity based on the theory of electromagnetic wave absorption by large molecular aggregates has been performed. The investigation is also focused on various effects induced by the interaction between biological active compounds and DNA in the content of liquid-crystalline DP.

  14. Particle exhaust of helium plasmas with actively cooled outboard pump limiter on Tore Supra

    SciTech Connect

    Uckan, T.; Mioduszewski, P.K.; Loarer, T.; Chatelier, M.; Guilhem, D.; Lutz, T.; Nygren, R.E.; Mahdavi, M.A.

    1995-08-01

    The superconducting tokamak Tore Supra was designed for long-pulse (30-s) high input power operation. Here observations on the particle-handling characteristics of the actively cooled modular outboard pump limiter (OPL) are presented for helium discharges. The important experimental result was that a modest pumping speed (1 m{sup 3}/s) of the OPL turbomolecular pump (TMP) provided background helium exhaust. This result came about due to a well-conditioned vessel wall with helium discharges that caused no wall outgasing. The particle accountability in these helium discharges was excellent, and the well-conditioned wall did not play a significant role in the particle balance. The helium density control, 25% density drop with OPL exhaust efficiency of {approximately}1%, was possible with TMP although this may not be the case with reactive gases such as deuterium. The observed quadratic increase of the OPL neutral pressure with helium density was consistent with an improvement of the particle control with increasing plasma density.

  15. Euphorbia characias latex: micromorphology of rubber particles and rubber transferase activity.

    PubMed

    Spanò, Delia; Pintus, Francesca; Esposito, Francesca; Loche, Danilo; Floris, Giovanni; Medda, Rosaria

    2015-02-01

    We have recently characterized a natural rubber in the latex of Euphorbia characias. Following that study, we here investigated the rubber particles and rubber transferase in that Mediterranean shrub. Rubber particles, observed by scanning electron microscopy, are spherical in shape with diameter ranging from 0.02 to 1.2 μm. Washed rubber particles exhibit rubber transferase activity with a rate of radiolabeled [(14)C]IPP incorporation of 4.5 pmol min(-1)mg(-1). Denaturing electrophoresis profile of washed rubber particles reveals a single protein band of 37 kDa that is recognized in western blot analysis by antibodies raised against the synthetic peptide whose sequence, DVVIRTSGETRLSNF, is included in one of the five regions conserved among cis-prenyl chain elongation enzymes. The cDNA nucleotide sequence of E. characias rubber transferase (GenBank JX564541) and the deduced amino acid sequence appear to be highly homologous to the sequence of several plant cis-prenyltransferases.

  16. Particle size reduction effectively enhances the cholesterol-lowering activities of carrot insoluble fiber and cellulose.

    PubMed

    Chou, Sze-Yuan; Chien, Po-Jung; Chau, Chi-Fai

    2008-11-26

    This study investigated and compared the effects of particle size reduction on the cholesterol-lowering activities of carrot insoluble fiber-rich fraction (IFF) and plant cellulose. Our results demonstrated that micronization treatment effectively pulverized the particle sizes of these insoluble fibers to different microsizes. Feeding the micronized insoluble fibers, particularly the micronized carrot IFF, significantly (p < 0.05) improved their abilities in lowering the concentrations of serum triglyceride (18.6-20.0%), serum total cholesterol (15.5-19.5%), and liver lipids (16.7-20.3%) to different extents by means of enhancing (p < 0.05) the excretion of lipids (124-131%), cholesterol (120-135%), and bile acids (130-141%) in feces. These results suggested that particle size was one of the crucial factors in affecting the characteristics and physiological functions of insoluble fibers. Therefore, particle size reduction by micronization might offer the industry an opportunity to improve the physiological functions of insoluble fibers, particularly the carrot IFF, in health food applications.

  17. Flowable conducting particle networks in redox-active electrolytes for grid energy storage

    DOE PAGES

    Hatzell, K. B.; Boota, M.; Kumbur, E. C.; ...

    2015-01-09

    This paper reports a new hybrid approach toward achieving high volumetric energy and power densities in an electrochemical flow capacitor for grid energy storage. The electrochemical flow capacitor suffers from high self-discharge and low energy density because charge storage is limited to the available surface area (electric double layer charge storage). Here, we examine two carbon materials as conducting particles in a flow battery electrolyte containing the VO2+/VO2+ redox couple. Highly porous activated carbon spheres (CSs) and multi-walled carbon nanotubes (MWCNTs) are investigated as conducting particle networks that facilitate both faradaic and electric double layer charge storage. Charge storage contributionsmore » (electric double layer and faradaic) are distinguished for flow-electrodes composed of MWCNTs and activated CSs. A MWCNT flow-electrode based in a redox-active electrolyte containing the VO2+/VO2+ redox couple demonstrates 18% less self-discharge, 10 X more energy density, and 20 X greater power densities (at 20 mV s-1) than one based on a non-redox active electrolyte. Additionally, a MWCNT redox-active flow electrode demonstrates 80% capacitance retention, and >95% coulombic efficiency over 100 cycles, indicating the feasibility of utilizing conducting networks with redox chemistries for grid energy storage.« less

  18. Flowable conducting particle networks in redox-active electrolytes for grid energy storage

    SciTech Connect

    Hatzell, K. B.; Boota, M.; Kumbur, E. C.; Gogotsi, Yury G.

    2015-01-09

    This paper reports a new hybrid approach toward achieving high volumetric energy and power densities in an electrochemical flow capacitor for grid energy storage. The electrochemical flow capacitor suffers from high self-discharge and low energy density because charge storage is limited to the available surface area (electric double layer charge storage). Here, we examine two carbon materials as conducting particles in a flow battery electrolyte containing the VO2+/VO2+ redox couple. Highly porous activated carbon spheres (CSs) and multi-walled carbon nanotubes (MWCNTs) are investigated as conducting particle networks that facilitate both faradaic and electric double layer charge storage. Charge storage contributions (electric double layer and faradaic) are distinguished for flow-electrodes composed of MWCNTs and activated CSs. A MWCNT flow-electrode based in a redox-active electrolyte containing the VO2+/VO2+ redox couple demonstrates 18% less self-discharge, 10 X more energy density, and 20 X greater power densities (at 20 mV s-1) than one based on a non-redox active electrolyte. Additionally, a MWCNT redox-active flow electrode demonstrates 80% capacitance retention, and >95% coulombic efficiency over 100 cycles, indicating the feasibility of utilizing conducting networks with redox chemistries for grid energy storage.

  19. Size effect of se-enriched green tea particles on in vitro antioxidant and antitumor activities.

    PubMed

    Li, Huajia; Li, Feng; Yang, Fangmei; Fang, Yong; Xin, Zhihong; Zhao, Liyan; Hu, Qiuhui

    2008-06-25

    The antioxidant and antitumor activities (in vitro) of superfine regular and Se-enriched green tea particles with different sizes (3.52 microm and 220 nm) were investigated in this paper. The vitamin C and tea polyphenol contents of green tea in different sizes were significantly different, and amino acid and chlorophyll just changed a little. The antioxidant activity of green tea particles was evaluated by DPPH radical scavenging and linoleic acid peroxidation inhibition methods, and the antitumor activity was evaluated by antiproliferation assay on HepG2, A549, and MGC803 cells. The results indicated that enrichment of selenium endowed green tea with higher antioxidant activity and antitumor activity on HepG2 and A549 cells but not on MGC803 cells. The DPPH radical scavenging rates of regular and Se-enriched green tea of 220 nm (67.87% and 69.49%, respectively) were significantly greater than that of 3.52 microm, but the inhibition of linoleic acid peroxidation for green tea of 220 nm was lower. The inhibitory rates of green tea of 220 nm on HepG2, A549, and MGC803 cells achieved 77.35%, 80.76%, and 87.54% for regular green tea, and 82.51%, 88.09%, and 74.48% for Se-enriched green tea at the dose of 100 microg mL (-1), values that were all significantly higher compared to that of 3.52 microm.

  20. Depletion forces induce visco-elasto-capillary thinning of non-Brownian suspensions

    NASA Astrophysics Data System (ADS)

    Harich, R.; Deblais, A.; Colin, A.; Kellay, H.

    2016-06-01

    Droplet pinch-off, which occurs when a drop of liquid detaches from a capillary, can be strongly modified in the presence of complex fluids such as polymer solutions and suspensions giving rise to long and slender filaments that thin slowly in time. While for polymers, the molecular conformations of the molecules in the filament are responsible for such a behavior, in suspensions the mechanisms at play remain to be deciphered. Here we show, experimentally, that while liquid bridges of non-Brownian suspensions of moderate concentrations have a thinning behavior very close to that of the solvent, the addition of short-chain polymers inducing depletion attractions between the particles in the suspension changes the thinning dynamics and gives rise to exponential thinning in time. The characteristic time of this dynamics increases with polymer concentration and therefore the intensity of the depletion forces at play. The tunability of this dynamics may be important for injket and 3D printing applications where short rupture times are sought for or in other situations where drop formation has to be minimized or inhibited.