Motion Of Filament Research Articles

Motion of current filaments in avalanching PIN diodes

The motion of current filaments in avalanching PIN diodes has been investigated in this paper by 2D transient numerical simulations. The simulation results show that the filament can move along the length of the PIN diode back and forth when the self-heating effect is considered. The voltage waveform varies periodically due to the motion of the filament. The filament motion is driven by the temperature gradient in the filament due to the negative temperature dependence of the impact ionization rates. Contrary to the traditional understanding that current filamentation is a potential cause of thermal destruction, it is shown in this paper that the thermally-driven motion of current filaments leads to the homogenization of temperature in the diode and is expected to have a positive influence on the failure threshold of the PIN diode.

Stability of solitons on vortex filaments

Abstract A vortex filament is a filament on which fluid vorticity is concentrated. This concept is particularly important in superfluidity and turbulence. This Letter focuses on the vortex filament equation (VFE), which is a model for the motion of a vortex filament in an incompressible and inviscid fluid. The VFE soliton solutions are considered and their spectral stability is proven by developing a straightforward method to solve the corresponding eigenvalue problem. A similar analysis is performed on the planar vortex filament equation. We discuss the applicability of the methods introduced in this Letter to other physically relevant curve equations and other types of solutions.

Tracking Actomyosin at Fluorescence Check Points

Emerging concepts for on-chip biotechnologies aim to replace microfluidic flow by active, molecular-motor driven transport of cytoskeletal filaments, including applications in bio-simulation, biocomputation, diagnostics, and drug screening. Many of these applications require reliable detection, with minimal data acquisition, of filaments at many, local checkpoints in a device consisting of a potentially complex network of channels that guide filament motion. Here we develop such a detection system using actomyosin motility. Detection points consist of pairs of gold lines running perpendicular to nanochannels that guide motion of fluorescent actin filaments. Fluorescence interference contrast (FLIC) is used to locally enhance the signal at the gold lines. A cross-correlation method is used to suppress errors, allowing reliable detection of single or multiple filaments. Optimal device design parameters are discussed. The results open for automatic read-out of filament count and velocity in high-throughput motility assays, helping establish the viability of active, motor-driven on-chip applications.

Spatiotemporal Domains in Active Actin Gels

Using a standard actin filament gliding assay, rhodamine-phalloidin labeled actin filaments were visualized moving over a myosin-II coated surface by fluorescence microscopy and filament tracks were analyzed by computer. When micromolar amounts of non-fluorescent phalloidin-stabilised actin were added, filament motion became aligned into a common direction (Butt et al., 2010, J Biol Chem285:4964-4974). Experiments conducted at low filament densities show that, on average, there is a small angular deflection that tends to align the paths of individual colliding filaments. Path alignment is independent of relative track directionality and increases with collision incident angle. Filament elastic deformation during collision events indicates the collision bending energy is ∼20kBT. As increasing amounts of bulk actin are added, individual filament paths become straighter and start to move in a common direction. Spatial correlation analysis shows that increased alignment is due to incremental recruitment of filament tracks into one orientation rather than fusion of seed domains to larger ones. Experiments performed over a wide range of actin filament concentrations and HMM surface densities, show that ordering of filament motion peaks over a range of conditions and decreases at extreme values. This finding differs from theoretical prediction of a critical phase transition (Kraikivski et al., 2006, Phys Rev. Lett.96:258103). Loss of order at high bulk actin concentration might be explained if there is increased filament exchange between bulk, disordered, actin and surface bound material. Loss of order at high myosin surface densities might arise from increased probability of motor attachment that would reduce ability of actin to change its path following a collision. Although our results are broadly compatible with generation of long-range order from mechanics of individual actin filament interactions; other phenomena become important at high protein concentrations.

Physical Effects Controlling Flock Formation in Systems of Self-Propelled Rods

Collective motion occurs in a wide range of biological settings, including flocks of birds, swimming bacteria, and cytoskeletal filaments. Motivated by swimming microorganisms and filament motion in a motility assay, we study a simple model of self-propelled rods using Brownian dynamics simulations and analytic theory. A flock is a group of neighboring rods that move collectively. Because the physical interactions between the rods are purely repulsive, the formation of flocks requires nonequilibrium driving. We characterize the physical interactions controlling flock stability, internal flock structure, and the distribution of flock sizes. Quantifying the dynamic phases of the flocking system through measurement of correlation functions, order parameters, and stress tensor gives insight into the origin of flocking in a simplified model system.

The Affect of Omecamtiv Mecarbilon the Phosphoate Dissociation and Motile Properties of the Recombinant Human β-Cardiac Heavymeromyosin

Omecamtiv mecarbil (OM), a small-molecule increases cardiac contractility by directly activating cardiac myosin by accelerating phosphate (Pi) release (Malik et al., 2011). Here we analyzed the affect of OM on the mechanochemical cycle and motility of human β-cardiac heavymeromyosin expressed in a adenoviral/C2C12 muscle cell based system, and purified porcine ventricular myosin (PV-HMM). Double-mixing stopped-flow fluorescence and phosphate binding protein (MDCC-PBP) were used to determine the maximum rate (kmax) of phosphate release. Rates of 30s−1 and 35s−1 were obtained for human and porcine cardiac HMM respectively. Addition of 20 µM OM resulted in a 2-fold increase in the maximal rate of actin activated Pi release to kmax = 70 s−1 (AM-ADP-Pi _> AM-ADP + Pi) for both human and porcine cardiac HMM. The unloaded actin filament velocity measured in the in vitro motility assay was 0.76 ± 0.37 µm/sec for human β-cardiac HMM and 0.97 ± 0.23 µm/sec for PV-HMM. OM has two effects on the motor activity: 1) The actin filament velocity was significantly slower (∼ 16 -fold at saturation); 2) the filament motion became more persistent with long periods of uninterrupted movement. This suggests that OM recruits more crossbridges to participate in the movement of the actin filaments resulting in higher forces per filament, which overcomes the pinning defects that invariably trap actin filaments in normal motility assays. The increase in attached crossbridges/filament also slows the filament velocity. The motility data are consistent with the kinetic analysis indicating that OM accelerates Pi release without dramatically enhancing the rate of the ATPase hydrolysis. This produces a higher duty ratio in which the motor spends more of the ATPase cycle in tight binding states. Supported by AHA-BGIA to EF and AHA-GI to DAW.

The ATP Hydrolysis Cycle and the Corresponding Motion of RecA Filament on Single-Stranded DNA

RecA is involved in DNA repair mechanism in bacteria by catalyzing homologous strand exchange reaction. RecA forms a filament on a single-stranded DNA made at the double-strand breaks. RecA adopts either a stretched (active) structure with ATP as a cofactor, or a compressed (inactive) structure with ADP. At the filament end, a monomer is allowed to dissociate after ATP hydrolysis and to rebind. We developed a single-molecule fluorescence assay to investigate how the ATP hydrolysis is coupled with the dynamics of the RecA filament. We dissected the intermediate steps of ATP hydrolysis and discovered that a monomer at the filament end dissociated upon the hydrolysis of ATP and not after the release of Pi. Interconversion of the structure between stretched- and compressed forms was achieved via cooperative structural change of a group of neighboring monomers. Owing to this cooperativity, an internal RecA monomer continuously consumes and rapidly refreshes ATP molecule without changing its stretched conformation. Based on our observation, we suggest a model of ATP hydrolysis cycle of the RecA in the filament.

Dephosphorylated Cardiac Myosin-Binding Protein C (cMyBP-C) Activates Native Cardiac Thin Filaments within the C-Zone of Native Cardiac Thick Filaments

cMyBP-C is a potent modulator of actomyosin motion generation within two distinct ∼350nm regions (C-zones) flanking the myosin thick filament bare zone. cMyBP-C's modulatory capacity is tunable by phosphorylation of 4 serines within the cMyBP-C motif. To determine cMyBP-C's phosphorylation-dependent impact on calcium activation of fully regulated actin thin filaments (i.e. containing troponin and tropomyosin), we observed rhodamine-phalloidin labeled native thin filament shards (∼250nm) moving over native thick filaments isolated from mouse ventricular tissue (Previs et al., 2012). For these experiments, the state of cMyBP-C phosphorylation in native thick filaments was either ∼64% on each of the 4 serines upon isolation (wild-type) or reduced to ∼22% by lambda-phosphatase treatment. Native thin filament movement was observed by TIRF microscopy at 25mM KCl, 100µM ATP, 20°C. At pCa 5, thin filaments landed on wild-type thick filaments and moved for 402±21nm at an initial fast velocity of 2.2±0.1µm/s before slowing abruptly to 0.9±0.1µm/s for 311±19nm within the C-zone. Similar trajectories were observed on phosphatase-treated thick filaments (fast velocity: 2.0±0.1 µm/s, 392±16nm; slow velocity: 0.8±0.1µm/s, 347±15nm within the C-zone). At pCa 7, little to no thin filament motion was observed on wild-type thick filaments but surprisingly, on phosphatase-treated thick filaments, a single slow phase of velocity (0.6±0.1µm/s) with a run length (397±137nm) similar to the C-zone length was observed. We conclude that cMyBP C plays two mechanistic roles within the thick filament C-zone in vivo: 1) allowing for cMyBP-C phosphorylation-dependent activation of the thin filaments at resting calcium levels; 2) providing an internal load that governs the speed of thin filaments once the muscle is calcium activated.

A numerical study of vortex filament motion around an ellipse by a conformal mapping technique

The paper presents a numerical study of the vortex motion around an ellipse using the conformal mapping of the circle exterior on the ellipse exterior. The vortex motion velocity and the stream function were obtained taking into account Routh’s correction. The trajectories of the vortex filament motion were constructed by integrating the vortex velocity differential equation and according to the condition of the stream function equality to a constant magnitude.

Origins of Rolling, Twisting, and Non-radial Propagation of Eruptive Solar Events

We demonstrate that major asymmetries in erupting filaments and CMEs, namely major twists and non-radial motions are typically related to the larger-scale ambient environment around eruptive events. Our analysis of prominence eruptions observed by the STEREO, SDO and SOHO spacecraft shows that prominence spines retain, during the initial phases, the thin ribbon-like topology they had prior to the eruption. This topology allows bending, rolling, and twisting during the early phase of the eruption, but not before. The combined ascent and initial bending of the filament ribbon is non-radial in the same general direction as for the enveloping CME. However, the non-radial motion of the filament is greater than that of the CME. In considering the global magnetic environment around CMEs, as approximated by the Potential Field Source Surface (PFSS) model, we find that the non-radial propagation of both erupting filaments and associated CMEs is correlated with the presence of nearby coronal holes, which deflect the erupting plasma and embedded fields. In addition, CME and filament motions respectively are guided towards weaker field regions, namely null points existing at different heights in the overlying configuration. Due to the presence of the coronal hole, the large-scale forces acting on the CME may be asymmetric. We find that the CME propagates usually non-radially in the direction of least resistance, which is always away from the coronal hole. We demonstrate these results using both low and high latitude examples.

Exact solution for the self-induced motion of a vortex filament in the arc-length representation of the local induction approximation

We review two formulations of the fully nonlinear local induction equation approximating the self-induced motion of the vortex filament (in the local induction approximation), corresponding to the Cartesian and arc-length coordinate systems. The arc-length representation put forth by Umeki [Theor. Comput. Fluid Dyn. 24, 383 (2010)] results in a type of 1+1 derivative nonlinear Schrödinger (NLS) equation describing the motion of such a vortex filament. We obtain exact stationary solutions to this derivative NLS equation; such exact solutions are a rarity. These solutions are periodic in space and we determine the nonlinear dependence of the period on the amplitude.

Autonomous Motility of Active Filaments due to Spontaneous Flow-Symmetry Breaking

We simulate the nonlocal Stokesian hydrodynamics of an elastic filament which is active due a permanent distribution of stresslets along its contour. A bending instability of an initially straight filament spontaneously breaks flow symmetry and leads to autonomous filament motion which, depending on conformational symmetry, can be translational or rotational. At high ratios of activity to elasticity, the linear instability develops into nonlinear fluctuating states with large amplitude deformations. The dynamics of these states can be qualitatively understood as a superposition of translational and rotational motion associated with filament conformational modes of opposite symmetry. Our results can be tested in molecular-motor filament mixtures, synthetic chains of autocatalytic particles, or other linearly connected systems where chemical energy is converted to mechanical energy in a fluid environment.

Quasi‐Classical Approximation in Vortex Filament Dynamics. Integrable Systems, Gradient Catastrophe, and Flutter

Quasi‐classical approximation in the intrinsic description of the vortex filament dynamics is discussed. Within this approximation, the governing equations are given by elliptic system of quasi‐linear partial differential equations of the first order. Dispersionless Da Rios system and dispersionless Hirota equation are among them. They describe motion of vortex filament with slow‐varying curvature and torsion without or with axial flow. Gradient catastrophe for governing equations is studied. It is shown that geometrically this catastrophe manifests as a fast oscillation of a filament curve around the rectifying plane which resembles the flutter of airfoils. Analytically, it is the elliptic umbilic singularity in the terminology of the catastrophe theory. It is demonstrated that its double scaling regularization is governed by the Painlevé I equation.

On the stability of self-similar solutions of 1D cubic Schrödinger equations

In this paper we will study the stability properties of self-similar solutions of $$1$$ D cubic NLS equations with time-dependent coefficients of the form 0.1 $$\begin{aligned} \displaystyle { iu_t+u_{xx}+\frac{u}{2} \left(|u|^2-\frac{A}{t}\right)=0, \quad A\in \mathbb{R }. } \end{aligned}$$ The study of the stability of these self-similar solutions is related, through the Hasimoto transformation, to the stability of some singular vortex dynamics in the setting of the Localized Induction Equation (LIE), an equation modeling the self-induced motion of vortex filaments in ideal fluids and superfluids. We follow the approach used by Banica and Vega that is based on the so-called pseudo-conformal transformation, which reduces the problem to the construction of modified wave operators for solutions of the equation $$\begin{aligned} iv_t+ v_{xx} +\frac{v}{2t}(|v|^2-A)=0. \end{aligned}$$ As a by-product of our results we prove that Eq. (0.1) is well-posed in appropriate function spaces when the initial datum is given by $$u(0,x)= z_0 \mathrm p.v \frac{1}{x}$$ for some values of $$z_0\in \mathbb{C }\setminus \{ 0\}$$ , and $$A$$ is adequately chosen. This is in deep contrast with the case when the initial datum is the Dirac-delta distribution.

Stationary Vortex Loops Induced by Filament Interaction and Local Pinning in a Chemical Reaction-Diffusion System

Scroll rings are three-dimensional excitation waves rotating around one-dimensional filament loops. In experiments with the Belousov-Zhabotinsky reaction we show that the collapse of these loops can be stopped by local pinning to only two unexcitable heterogeneities. The resulting vortices rotate around stationary but curved filaments. The absence of filament motion can be explained by repulsive interaction that counteracts the expected curvature-induced motion. The shape and key dependencies of the stationary filaments are well described by a curvature-flow model with additive interaction velocities that rapidly decrease with filament distance.

THE PROPER MOTION OF THE CENTRAL COMPACT OBJECT RX J0822–4300 IN THE SUPERNOVA REMNANT PUPPIS A

Using the High Resolution Camera (HRC) aboard the Chandra X-ray Observatory, we have re-examined the proper motion of the central compact object RX J0822-4300 in the supernova remnant Puppis A. New data from 2010 August, combined with three archival data sets from as early as 1999 December, provide a baseline of 3886 days (more than 10 1/2 years) to perform the measurement. Correlating the four positions of RX J0822-4300 measured in each data set implies a projected proper motion of mu 71 \pm 12 masy. For a distance of 2 kpc this proper motion is equivalent to a recoil velocity of 672 \pm 115 km/s. The position angle is found to be 244 \pm 11 degrees. Both the magnitude and direction of the proper motion are in agreement with RX J0822-4300 originating near the optical expansion center of the supernova remnant. For a displacement of 371 \pm 31 arcsec between its birth place and today's position we deduce an age of (5.2 \pm 1.0) 10^3 yrs for RX J0822-4300. The age inferred from the neutron star proper motion and filament motions can be considered as two independent measurements of the same quantity. They average to 4450 \pm 750 yrs for the age of the supernova remnant Puppis A.

Observational evidence of unwinding and chirality changing in penumbral filaments by Hinode

AbstractIn this paper, we study twisting motions of the penumbral filaments of active region NOAA 10930. At first, they made unwinding motions. After unwinding, the filaments are found to twist again and developed the opposite chirality in them. These observational results indicate that penumbral filaments are more inclined to be the twisted magnetic flux tubes in nature.

Fully nonlinear local induction equation describing the motion of a vortex filament in superfluid 4He

AbstractWe obtain the fully nonlinear local induction equation describing the motion of a vortex filament in superfluid 4He. As the relevant friction parameters are small, we linearize terms involving such parameters, while keeping the remaining nonlinearities, which accurately describe the curvature of the vortex filament, intact. The resulting equation is a type of nonlinear Schrödinger equation, and, under an appropriate change of variables, this equation is shown to have a first integral. This is in direct analogy with the simpler equation studied previously in the literature; indeed, in the limit where the superfluid parameters are taken to zero, we recover the results of Van Gorder. While this first integral is mathematically interesting, it is not particularly useful for computing solutions to the nonlinear partial differential equation which governs the vortex filament. As such, we introduce a new change of dependent variable, which results in a nonlinear four-dimensional system that can be numerically integrated. Integrating this system, we recover solutions to the fully nonlinear local induction equation describing the motion of a vortex filament in superfluid 4He. We find that the qualitative features of the solutions depend not only on the superfluid friction parameters, but also strongly on the initial conditions taken, the curvature and the normal fluid velocity.

Generation, annihilation, dynamics and self-organized patterns of filaments in dielectric barrier discharge plasmas

Dielectric barrier discharges (DBDs) operating in a glow regime exhibit a variety of complex self-organized static or dynamical structures of filaments. Using a fluid model combined with fast camera diagnostics, we propose a clear physical description and explanation of the mechanisms responsible for the generation, annihilation, motion and self-organization of discharge filaments in DBDs in a glow regime. We show that low current “side discharges” generated during the same half-cycle in the vicinity of an isolated filament beyond the inhibition zone associated with charge spreading along the dielectric surface play an essential role in the triggering of these mechanisms.

WAVES AS THE SOURCE OF APPARENT TWISTING MOTIONS IN SUNSPOT PENUMBRAE

The motion of dark striations across bright filaments in a sunspot penumbra has become an important new diagnostic of convective gas flows in penumbral filaments. The nature of these striations has, however, remained unclear. Here we present an analysis of small scale motions in penumbral filaments in both simulations and observations. The simulations, when viewed from above, show fine structure with dark lanes running outwards from the dark core of the penumbral filaments. The dark lanes either occur preferentially on one side or alternate between both sides of the filament. We identify this fine structure with transverse (kink) oscillations of the filament, corresponding to a sideways swaying of the filament. These oscillations have periods in the range of 5-7 min and propagate outward and downward along the filament. Similar features are found in observed G-band intensity time series of penumbral filaments in a sunspot located near disk center obtained by the Broadband Filter Imager (BFI) on board {\it Hinode}. We also find that some filaments show dark striations moving to both sides of the filaments. Based on the agreement between simulations and observations we conclude that the motions of these striations are caused by transverse oscillations of the underlying bright filaments.