Circular Filaments Research Articles

Fe XII STALKS AND THE ORIGIN OF THE AXIAL FIELD IN FILAMENT CHANNELS

Employing Fe XII images and line-of-sight magnetograms, we deduce the direction of the axial field in high-latitude filament channels from the orientation of the adjacent stalklike structures. Throughout the rising phase of the current solar cycle 24, filament channels poleward of latitude 30° overwhelmingly obeyed the hemispheric chirality rule, being dextral (sinistral) in the northern (southern) hemisphere, corresponding to negative (positive) helicity. During the deep minimum of 2007-2009, the orientation of the Fe XII stalks was often difficult to determine, but no obvious violations of the rule were found. Although the hemispheric trend was still present during the maximum and early declining phase of cycle 23 (2000-2003), several high-latitude exceptions were identified at that time. From the observation that dextral (sinistral) filament channels form through the decay of active regions whose Fe XII features show a counterclockwise (clockwise) whorl, we conclude that the axial field direction is determined by the intrinsic helicity of the active regions. In contrast, generation of the axial field component by the photospheric differential rotation is difficult to reconcile with the observed chirality of polar crown and circular filament channels, and with the presence of filament channels along the equator. The main role of differential rotation in filament channel formation is to expedite the cancellation of flux and thus the removal of the transverse field component. We propose further that, rather than being ejected into the heliosphere, the axial field is eventually resubmerged by flux cancellation as the adjacent unipolar regions become increasingly mixed.

Microwave guiding in air along single femtosecond laser filament

Microwave guiding along single plasma filament generated through the propagation of femtosecond (fs) laser pulses in air has been demonstrated over a distance of about 6.5 cm, corresponding to a microwave signal intensity enhancement of more than 3-fold over free space propagation. The current propagation distance along the fs laser filament is in agreement with the calculations and limited by the relatively high resistance of the single plasma filament. Using a single fs laser filament to channel microwave radiation considerably alleviate requirements to the power of fs laser pulses compared to the case of the circular filaments waveguide. In addition, it can be used as a simple and non-intrusive method to obtain the basic parameters of laser-generated plasma filament.

Vortex rings: history and state of the art

In the present paper, we describe the fascinating 150-year history of vortex dynamics, which started from the classical work by H. Helmholtz (1858). This work contains not only the general theorems on vortex motion, but also a special section devoted to axisymmetric circular vortex filaments and, in particular, to vortex rings. The aim of our investigation is both to clarify some purely mathematical questions connected with the Dyson model for coaxial vortex rings with a small circular cross-section in an ideal incompressible fluid and to provide a historical overview of the achievements in experimental, analytical, and numerical studies of the interaction of vortex rings. The model is illustrated by several examples of the motion of vortex rings. Finally, we present a complete classification of the interactions of two coaxial vortex rings in an ideal fluid.

Impact of a Plasma Disruption on the Magnetic Field Variations and Heat Deposition in the TF Conductor of JT-60SA

During a plasma disruption a complex map of magnetic field variation is generated along the JT-60SA TF conductor. The current variations associated with a symmetric plasma disruption are modeled in JT-60SA, on the basis of a circuit approach. The main components of the circuit model are: the poloidal field coils, the plasma represented by circular filaments, the vacuum vessel, and the stabilizing plates. The disruption induces currents in all elements of the circuit model which produce a variation of the field map. At the location of the TF coil, this field change can be assessed and used for ac losses and stability calculations on the TF conductor. An analysis of the map will allow estimating the field change time constants and investigating which points the JT-60SA TF conductor experience the most severe field variations. Based on a recent multi-constant AC losses model for the JT-60SA TF conductor, an analytical model of stability is presented to describe the temperature increase in the cable after a plasma disruption, taking into account the heat transfer to helium during the power losses deposition. A discussion will be introduced about a possible influence of the synchronous parallel field variations, which may saturate the strand filaments and increase the heat losses dissipation.

An analytical model of a ferrite-cored inductor used as an eddy current probe

An analytical model of an axisymmetric eddy current ferrite-cored probe above a multi-layered conducting half-space has been developed using a procedure in which the domain of the problem is truncated radially. This means that solutions can be expressed in the form of generalized Fourier-Bessel series. The expansion coefficients are found by matching the field across the interfaces between the subregions of the problem. Initially, the magnetic vector potential of a simple circular current filament is expanded in a series form. The solution is then modified to accommodate an infinitely long coaxial ferrite core, and the principle of superposition is invoked to derive a coil field from the filament field in the presence of the core. Next, we consider a semi-infinite core and then one of finite length. Finally, the effects of a multi-layered conductor are included. Numerical predictions of probe impedance have been compared with experimental data showing excellent agreement.

Numerical analysis of guiding a microwave radiation using a set of plasma filaments: dielectric waveguide concept

A proposed model for a circular bunch of plasma filaments used as a virtual waveguide for microwave radiation is presented. The virtual circular guiding system is shown to support guided modes of electromagnetic radiation in the millimetre and sub-millimetre wavelength range. Transmission is due to total internal reflection of the wave on the less dense plasma cladding. The energy loss of microwave radiation propagating in such a virtual waveguide is calculated. Optimum spatial configurations of circular plasma filament waveguides are proposed. Plasma filament waveguides are shown to enhance microwave transmission relative to free space propagation of microwave radiation over limited distances.

Magnetic Force Between Inclined Circular Filaments Placed in Any Desired Position

This paper presents new general formulas for calculating the magnetic force between inclined circular filaments placed in any desired position. We use two approaches to calculate the magnetic force, one based on Biot-Savart law and another based on the mutual inductance between these coils. All mathematical procedures are completely described to define coil positions that lead to relatively easy method for calculating the magnetic force between inclined circular filaments in any desired position. Two formulas obtained by the simple integration of different expressions in terms of complete elliptic integrals of the first and second kind give the same numerical results. The presented methods are understandable, numerically suitable and easy applicable for engineers and physicists. We validated the new formulas through a series of examples, which are presented here.

Mutual Inductance Calculation Between Circular Filaments Arbitrarily Positioned in Space: Alternative to Grover's Formula

In this paper, we present the full derivation of a new formula for calculating the mutual inductance between inclined circular filaments arbitrarily positioned with respect to each other. Although such a formula was already proposed by Grover more than 50 years ago, the formula presented here is slightly more general and simpler to use, i.e., it involves only a sequential evaluation of expressions and the numerical resolution of a simple numerical integration. We derived the new formula using the method of vector potential, as opposed to Grover's approach, which was based on the Neumann formula. We validated the new formula through a series of examples, which are presented here. Finally, we present the relationship between the two general formulas (i.e., Grover's and our new one) explicitly (Example 12).

Analysis of a concentric coplanar capacitive sensor for nondestructive evaluation of multi-layered dielectric structures

A concentric coplanar capacitive sensor is analyzed for the quantitative characterization of material properties for multi-layered dielectrics. The sensor output signal, transcapacitance CT, is related to the thickness and dielectric constant of each layer of the material under test. Electrostatic Green's functions due to point charges over different dielectric structures are derived utilizing the Hankel transform given the cylindrical symmetry of the proposed sensor. Numerical implementations based on the Green's functions are presented. The sensor electrodes are divided into a number of circular filaments, and the sensor surface charge distribution is then calculated using the method of moments (MoM). From the sensor surface charge, CT is calculated. Numerical calculations on sensor optimization are conducted and show that normalized CT as a function of sensor configuration is determined solely by its own relative dimensions, regardless of the overall dimensions of the sensor. In addition, calculations indicate how the sensor can be optimized for sensitivity to changes in core permittivity of a three-layer test-piece such as an aircraft radome. Benchmark experiment results are provided for one, two-, and three-layer test-pieces and very good agreement with calculated CT is observed. The sensor is also applied to water ingression measurements in a sandwich structure resembling the aircraft radome, in which the water-injected area can be successfully detected from the sensor output signal.

Tubulin binding protein, CacyBP/SIP, induces actin polymerization and may link actin and tubulin cytoskeletons

CacyBP/SIP, originally identified as a S100A6 target, was shown to interact with some other S100 proteins as well as with Siah-1, Skp1, tubulin and ERK1/2 kinases (reviewed in Schneider and Filipek, Amino Acids, 2010). Here, we show that CacyBP/SIP interacts and co-localizes with actin in NB2a cells. Using a zero-length cross-linker we found that both proteins bound directly to each other. Co-sedimentation assays revealed that CacyBP/SIP induced G-actin polymerization and formation of unique circular actin filament bundles. The N-terminal fragment of CacyBP/SIP (residues 1–179) had similar effect on actin polymerization as the entire CacyBP/SIP protein, while the C-terminal one (residues 178–229) had not. To check the influence of CacyBP/SIP on cell morphology as well as on cell adhesion and migration, a stable NIH 3T3 cell line with an increased level of CacyBP/SIP was generated. We found that the adhesion and migration rates of the modified cells were changed in comparison with the control ones. Interestingly, the co-sedimentation and proximity ligation assays indicated that CacyBP/SIP could simultaneously interact with tubulin and actin, suggesting that CacyBP/SIP might link actin and tubulin cytoskeletons.

Equilibrium charge density on a thin curved wire

We address the electrostatic problem of a thin, curved, and cylindrical conductor (a conducting filament) and show that the corresponding linear charge density slowly tends to uniformity as the inverse of the logarithm of a characteristic parameter, which is the ratio of the diameter to the smaller of the length and minimum radius of curvature of the filament. An alternative derivation of this result based on energy minimization is given. These results follow from a general asymptotic analysis of the electric field components and potential near a charged filament in the limit of vanishing diameter. It is found that the divergent parts of the radial and azimuthal electric field components are determined by the local charge density, while the axial component is determined by the local dipole density. For a straight filament our results reduce to those known for conducting needles. For curved filaments, the configuration of charges and fields is no longer azimuthally symmetric, and there is an additional length scale arising from the finite radius of curvature of the filament. The basic uniformity result survives the added complications, which include an azimuthal variation in the surface charge density of the filament. As with the variations in linear charge density along the filament, the azimuthal variations vanish with the characteristic parameter, only more rapidly. These findings allow us to derive an asymptotic formula for the capacitance of a curved filament that generalizes a result first obtained by Maxwell. The examples of a straight filament with uniform and linearly varying charge densities and a circular filament with a uniform charge distribution are treated analytically and found to agree with the general analysis. Numerical calculations illustrating the slow convergence of linear charge distribution to uniformity for an elliptical filament are presented. An interactive computer program implementing and animating the numerical calculations is available.

Coaxial axisymmetric vortex rings: 150 years after Helmholtz

This article addresses the fascinating 150 years history of the classical Helmholtz paper that laid the foundation of the vortex dynamics. Among general theorems on vortex motion, this memoir contains the special section on circular vortex filaments and axisymmetric vortex rings, in particular. The objective of this article is both to clarify some purely mathematical questions connected with the Dyson model of coaxial vortex rings in inviscid incompressible fluid and to provide a historical overview of achievements in experimental, analytical, and numerical studies of vortex rings interactions. The model is illustrated by several examples both of regular and chaotic motion of several vortex rings in an unbounded fluid.

A Crescent-Shaped ALIX Dimer Targets ESCRT-III CHMP4 Filaments

ALIX recruits ESCRT-III CHMP4 and is involved in membrane remodeling during endosomal receptor sorting, budding of some enveloped viruses, and cytokinesis. We show that ALIX dimerizes via the middle domain (ALIX(-V)) in solution. Structural modeling based on small angle X-ray scattering (SAXS) data reveals an elongated crescent-shaped conformation for dimeric ALIX lacking the proline-rich domain (ALIX(BRO1-V)). Mutations at the dimerization interface prevent dimerization and induce an open elongated monomeric conformation of ALIX(-V) as determined by SAXS modeling. ALIX dimerizes in vivo and dimeric ALIX colocalizes with CHMP4B upon coexpression. We show further that ALIX dimerization affects HIV-1 budding. C-terminally truncated activated CHMP4B retaining the ALIX binding site forms linear, circular, and helical filaments in vitro, which can be bridged by ALIX. Our data suggest that dimeric ALIX represents the active form that interacts with ESCRT-III CHMP4 polymers and functions as a scaffolding protein during membrane remodeling processes.

Concentration profiles in drying cylindrical filaments

We analyze theoretically the drying of cylindrical filaments. For modelling the mass transfer on the gas side of the liquid-gas interface of the shrinking circular cylindrical filament, we apply the model of Abramzon and Sirignano, which was originally developed for spherical geometry. As a consequence of mass transfer at constant Sherwood number, we obtain a d2-law for the shrinkage of the cylinder as in the case of the spherical geometry, which expresses that the cross-sectional area of the cylinder shrinks at a constant rate with time. For this situation, the diffusion equation for the liquid phase mixture components becomes separable upon transformation into similarity coordinates and is solved analytically to obtain the concentration profiles inside the filament as functions of time. The dependency of the profiles on the radial coordinate is determined by a series of Kummer’s functions. Applying this result, we study the evolution of the concentration profiles in the liquid phase with time as dependent on a parameter given as the ratio of rate of shrinkage of the cross-sectional area of the cylinder to liquid-phase diffusion coefficient, which was identified as relevant for the shape of the concentration profiles formed in the liquid during the drying process. As an example, we present computed results for the constant evaporation rate regime in the dry-spinning process of a polyvinyl-alcohol (PVA)-water system. Comparison of our analytical results with full numerical solutions of the diffusion equation from the literature, achieved with concentration-dependent diffusion coefficient, reveals very good agreement.

Three-dimensional spiral waves in an excitable reaction system: Initiation and dynamics of scroll rings and scroll ring pairs

We report experimental results on spiral and scroll waves in the 1,4-cyclohexanedione Belousov-Zhabotinsky reaction. The propagating concentration waves are detected by two-dimensional photometry and optical tomography. Wave pulses can disappear in front-to-front and front-to-back collisions. This anomaly causes the nucleation of vortices from collisions of three nonrotating waves. In three-dimensional systems, these vortices are scroll rings that rotate around initially circular filaments. Depending on reactant concentrations, the filaments shrink or expand indicating positive and negative filament tensions, respectively. Shrinkage results in vortex annihilation. Expansion is accompanied by filament buckling and bending, which is interpreted as developing Winfree turbulence. We also describe the initiation of scroll ring pairs in four-wave collisions. The two filaments are stacked on top of each other and their motion suggests filament repulsion.

Negative filament tension of scroll rings in an excitable system

Scroll rings are three-dimensional spiral waves of excitation that rotate around circular filaments. In a modified Belousov-Zhabotinsky reaction, these filaments expand, buckle, and build up gradients in rotation phase. The instability is caused by negative filament tension (-4.3x10;{-4}cm;{2}s) . Initial deformations are strongest in the direction normal to the filament's osculating plane, and their growth rates decrease rapidly with increasing wave number.

Novel Compensated Moment Detection Coil

We constructed a coil system providing a homogeneity of the sixth order and a compensation of the second order to measure the magnetic dipole moment. The coil system consists of six circular filaments connected in series; two of them are connected with the other four in opposition. This coil system is highly insensitive to external magnetic disturbances, even if they are inhomogeneous, whereas its sensitivity inside the coil is constant over a large part of its volume. In this paper, we report our optimization calculation for the system, calculation of the performance, and measurement results. We measured the influence of a magnet and of an iron plate close to the coil on the magnetic dipole moment for the coil system and also for a pair of Helmholtz coils and compared the results with the calculated values. By reason of the principle of inversion, the coil system can also be used as a field-generating coil, where the decay of the field strength outside the system is much more rapid than for noncompensated systems.

Liquid crystal formation of RecA–DNA filamentous complexes

Spontaneous optical birefringence of RecA-bound linear and closed circular single-stranded DNA filaments, as well as RecA self-assembled polymer, was observed in aqueous buffer solutions, which demonstrates the formation of lyotropic liquid crystalline phases.

A wide-beam X-ray source suitable for diffraction enhanced imaging applications

Research in diffraction-enhanced imaging (DEI), using a synchrotron source with an X-ray flux of 1.4×10 12 ph/mm 2/s, has shown strong potential in obtaining high-resolution images as compared to conventional radiographs. This research investigates the feasibility of developing a large area circular X-ray source with fluxes comparable to a synchrotron source. The source should be capable of integration into a compact system with peak powers not to exceed 200 kW to be feasible for use in a major medical facility, industrial complex or screening facility (such as cargo or airport). A computational study of a circular concentric filament wide-beam area X-ray source has been investigated in this research. The design features are based on generating electrons from three concentric circular filaments to provide an area electron flux, with a 60 kV accelerating potential and a beam current of up to 3 A. The X-ray target is a grounded stationary oxygen-free copper target with a layer of molybdenum. This target feature differs from standard rotating X-ray targets in conventional X-ray systems. Studies of electron trajectories and their distribution on the target were conducted using the SIMION 3D code. Heat loading and thermal management were studied using heat transfer modules from the coupled FEMLAB multi-physics and MATLAB codes. The Monte Carlo code MCNP 5 was used to obtain the X-ray flux and energy distribution for aluminum and beryllium windows. This computational study shows that this target configuration generates X-rays with photon flux comparable to synchrotron source and sufficient for DEI applications. The maximum target temperature rise is 1357 K after 70 s when cooling the back of the target to liquid nitrogen temperature using cold finger contact, and 325 K for an invaded target, in which liquid nitrogen circulates inside the target.

Writhing and coiling of closed filaments

The kinematics of writhing and coiling of circular filaments is here analysed by new equations that govern the evolution of curves generated by epicycloids and hypocycloids. We show how efficiency of coil formation and compaction depend on writhing rates, relative bending, torsion and mean twist energy. We demonstrate that for coiling formation hypocycloid evolution achieves higher writhing rates, but in terms of deformation energy, the epicycloid evolution is much more effective. We also show how the occurrence and multiple appearance of inflexional configurations determine coil formation. Compaction and packing rate are also briefly examined. These results are fundamental and provide useful information for physical applications and for modelling natural phenomena, including relaxation of magnetic fields in the solar corona, magnetic dynamos in astrophysical flows, tertiary folding of macromolecules in chemical-physics, and DNA packing in cell biology.