Self-organization Of Filaments Research Articles

Manipulation of rotation for triangular plasma photonic crystals in dielectric barrier discharge

Rotation manipulation in the fields of metamaterials and metasurfaces has led to a variety of striking properties. Here, we propose an efficient scheme for realizing rotation-controllable plasma metamaterials in dielectric barrier discharge. Rotating triangular plasma photonic crystals (RTPPCs) are obtained by self-organization of filaments in simply ambient air. Independent control of the angular velocity and the lattice constant of RTPPCs is realized. A phenomenological reaction–diffusion model with two coupled layers is established to reveal the underlying mechanism of RTPPCs. Moreover, the changes in the bandgaps with angular reorientation of RTPPCs are demonstrated by using microwave diagnosis. Experimental observations and numerical simulations are in good agreement. Our method provides an additional degree of freedom to tailor plasma metamaterials, which may find potential applications, such as integrated optical components, wireless communications, precision radiolocation, time-resolved imaging, and sensing.

Numerical study of self-organized filaments affected by flow field in dielectric barrier discharges

Static and dynamic self-organized patterns are observed in dielectric barrier discharge by numerical simulation. The static pattern is characterized by regularly distributed standing discharge channels/filaments, and its morphology is significantly dependent on discharge parameters such as electrode size and voltage. The interaction between the filaments proves to be electrostatic repulsive force. The introduction of the external flow field breaks the stability of the pattern which finally results in the formation of a quasi-static pattern with a displaced filament or dynamic pattern with directional moving filaments. The thrust from the flow should be responsible for the motion of the filaments, which may also be described from the microscopic view that the neutral background atoms transfer the momentum to species by the collision. Moreover, the filaments may also exhibit particle-like behaviors, such as collision, vanishment, and generation under the effect of flow.

Efficient Dynamic Mesh Refinement Technique for Simulation of HPM Breakdown-Induced Plasma Pattern Formation

Numerical simulation of the complex plasma dynamics associated with high power, high-frequency microwave breakdown at high pressures, leading to the formation of filamentary plasma structures such as self-organized plasma arrays, is a computationally challenging problem. The widely used 2-D electromagnetic (EM)–plasma fluid model, which accurately captures the experimental observations, requires a runtime of several days to months to simulate standard problems due to stringent numerical requirements in terms of cell size and time step. This article presents a self-aware mesh refinement (MR) algorithm that uses a coarse mesh and a fine mesh that dynamically expand based on the plasma profile topology to resolve the sharp gradients in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -fields and plasma density in the breakdown region. The dynamic MR (DMR) technique is explained in detail, and its performance has been evaluated using a standard benchmark microwave breakdown problem. We observe a speedup of 8 (of the order of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$O(r^{3})$ </tex-math></inline-formula> , when the refinement factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$r$ </tex-math></inline-formula> ) is 2) compared with a traditional single uniform fine-mesh-based simulation. The technique is scalable and performs better when the problem size increases. We also present a comprehensive spatio-temporal visual analysis to explain the complex physics of high-power microwave (HPM) breakdown, leading to self-organized plasma filaments as an application of the DMR technique.

Reconfigurable plasma photonic crystals from triangular lattice to square lattice in dielectric barrier discharge

We demonstrate a flexible experimental method to realize fast reconfiguration of plasma photonic crystals by self-organization of filaments in dielectric barrier discharge (DBD). The symmetry and lattice constant of plasma photonic crystals can both be dynamically tuned by simply changing the applied voltage. The reconfiguration from a triangular lattice to a square lattice is realized and the triangular lattices with different lattice constants are also obtained. A phenomenological reaction-diffusion model of two interacting layers is established to simulate the formation of different plasma structures. Experimental observations and numerical simulation are in good agreement. Moreover, the band diagrams of different plasma photonic crystals have been studied by use of finite element method. It is shown that the positions and sizes of the band gaps change significantly when the configurations of plasma photonic crystals have been changed. Such plasma structures can be used as potential tunable metamaterials, which may find wide applications in the manipulation of microwaves and terahertz waves.

Autonomous mesoscale positioning emerging from myelin filament self-organization and Marangoni flows

Out-of-equilibrium molecular systems hold great promise as dynamic, reconfigurable matter that executes complex tasks autonomously. However, translating molecular scale dynamics into spatiotemporally controlled phenomena emerging at mesoscopic scale remains a challenge—especially if one aims at a design where the system itself maintains gradients that are required to establish spatial differentiation. Here, we demonstrate how surface tension gradients, facilitated by a linear amphiphile molecule, generate Marangoni flows that coordinate the positioning of amphiphile source and drain droplets floating at air-water interfaces. Importantly, at the same time, this amphiphile leads, via buckling instabilities in lamellar systems of said amphiphile, to the assembly of millimeter long filaments that grow from the source droplets and get absorbed at the drain droplets. Thereby, the Marangoni flows and filament organization together sustain the autonomous positioning of interconnected droplet-filament networks at the mesoscale. Our concepts provide potential for the development of non-equilibrium matter with spatiotemporal programmability.

Atmospheric pressure self-organized filaments in dielectric barrier discharge excited by a modulated sinusoidal voltage

Excited by a modulated sinusoidal voltage, self-organized filaments are generated in a parallel plate dielectric barrier discharge with a flowing mixture of argon and nitrogen at atmospheric pressure. With increasing off time of the modulated voltage, a single filament transits into a pair of filaments. Then, the self-organized filaments undergo a scenario from triangle, quadrilateral, pentagon, hexagon, and finally, to a ring composed of rotating filaments. During the transition process, the discharge current always presents a single pulse per half voltage cycle, whose amplitude increases for both positive and negative discharges. However, discharge current symmetry deteriorates. Moreover, with increasing off time, the inception voltage increases for the positive discharge, while it decreases for the negative discharge. For the hexagonal arranged filaments, temporal evolutions are implemented for the positive and negative discharges. The results reveal that the initiation in one current pulse seems to propagate opposite to the gas flow direction in the positive discharge, while advances along it in the negative discharge. By optical emission spectroscopy, the electron temperature and electron density are investigated via Boltzmann plotting and a line ratio from 738 nm to 750 nm, respectively. With increasing off time, both of them increase for the positive discharge, while they decrease for the negative discharge. What is more, both electron temperature and electron density increase as the inception voltage increases.

Numerical evidence of spontaneous division of dissipative solitons in a planar gas discharge–semiconductor system

This work deals with the formation of patterns of spatially localized solitary objects in a planar semiconductor gas-discharge system with a high Ohmic electrode. These objects, known as dissipative solitons, are generated in this system in the form of self-organized current filaments, which develop from the homogeneous stationary state by the Turing bifurcation. The numerical model reveals, for the first time, evidence of spontaneous division of the current filaments in this system, similar to that observed in the experiment, in the physically relevant parameter regime.

Multiscale Modeling of Clathrin-Mediated Endocytosis

Endocytosis is the process of uptake of cargo and fluid from the extracellular space to inside the cell; defects in endo- cytosis contribute to a wide spectrum of diseases including cancer, neurodegeneration, and heart disease. Clathrin- mediated endocytosis (CME) is an archetypal example of a membrane deformation process where multiple variables such as pre-existing membrane curvature, membrane bending due to the protein machinery, membrane tension regulation, and actin-mediated forces govern the progression of vesiculation. My group has been working for the past few years on deciphering the biophysical determinants of CME using multiscale modeling. We recently showed that membrane tension is a dynamic quantity that evolves over the progression of CME to modulate the energy barrier associated with vesiculation. Specifically, we identified that membrane tension governs CME through a snapthrough instability [1]. <br/> We then explored two ways by which the energy barrier associated with this instability can be overcome. First, we explored the role of actin cytoskeleton in force generation during CME. Our results show that a minimal branched actin network is sufficient to create sustained internalization of an endocytic pit against membrane tension. Furthermore, actin filament self-organization and bending, which arise from the spatial distribution of actin-coat attachment around the curved endocytic pit, allow the actin network to adapt to the changing load [2]. Second, we removed the restrictions of axisymmetric pit formation and showed that lower modes of symmetry naturally reduce the energy barrier associated with the constriction of a neck during CME [3]. Thus, we show that mechanical models of membrane bending and cytoskeletal organization can provide insight into the complex workings of CME.

Actin dynamics and competition for myosin monomer govern the sequential amplification of myosin filaments.

Cellular mechanisms governing non-muscle myosin 2 (NM2) filament assembly are largely unknown. Using EGFP-NM2A knock-in fibroblasts and multiple super-resolution imaging modalities, we characterized and quantified the sequential amplification of NM2 filaments within lamella, wherein filaments emanating from single nucleation events continuously partition, forming filament clusters that populate large-scale actomyosin structures deeper in the cell. Individual partitioning events coincide spatially and temporally with the movements of diverging actin fibers, suppression of which inhibits partitioning. These and other data indicate that NM2A filaments are partitioned by the dynamic movements of actin fibers to which they are bound. Finally, we showed that partition frequency and filament growth rate in the lamella depend on MLCK, and that MLCK is competing with centrally-active ROCK for a limiting pool of monomer with which to drive lamellar filament assembly. Together, our results provide new insights into the mechanism and spatio-temporal regulation of NM2 filament assembly in cells.

Two Levels of Myosin-IIA Dynamics in Cells: Turnover of Filaments and Self-Organization of Filament Stacks

Dynamics and self-organization of myosin-II filaments in non-muscle cells are poorly understood. Here, using structured illumination microscopy (SIM), we visualized with high resolution bipolar myosin-II filaments in REF52 fibroblasts by marking myosin-II light chain (MLC), or myosin-IIA heavy chain (MHC-IIA). The filaments demonstrated a uniform length of 300 nm and formed characteristic periodic striations along actin filament bundles, such as ventral stress-fibers, or transverse arcs in spreading cells. Myosin IIA striations were alternating with domains of variable length enriched by actin cross-linking protein alpha-actinin. Free barbed ends of actin filaments (visualized by incorporation of labeled G-actin) were localized between myosin-II striations, while pointed ends of actin filaments (visualized by labeling tropomodulin-3) were enriched in the regions corresponding to myosin-II striations. The most striking feature of the myosin-IIA filament organization was in registry alignment of the myosin-IIA filaments with subsequent formation of several microns long filament “stacks” that apparently formed bridges between parallel stress-fibers or arcs. FRAP experiments were performed in SIM showed that the recovery time for both GFP-MLC and GFP-MHC-IIA in tens of seconds and did not depend on actin filament turnover. However, the process of self-organization of the individual filaments into stacks required much longer time (tens of minutes) and depended on both myosin II contractility and actin filament dynamics. Our observations reveal basic modes of such self-organization. A physical model considering myosin filaments as active force-dipoles embedded in a elastic medium shows that myosin filaments bound to neighboring actin bundles can interact mechanically through deformations of the intervening disordered cytoskeletal network leading to the observed stacking (registry) of these myosin filaments. Thus, myosin-IIA filament stacks are novel cytoskeletal elements that could maintain integrity and drive self-organization of the actin cytoskeleton.

Investigation on the spectrum of complex self-organized plasma photonic crystal

A complex plasma photonic crystal (PPC) was obtained by self-organization of filaments in air dielectric barrier discharge using two planar water electrodes. The PPC structure consists of many square sublattices, and each sublattice is composed of large spots, two kinds of small spots and lines, corresponding to thick plasma columns, two kinds of thin plasma columns, and plasma slices, respectively. By using the optical emission spectrum method, the electron densities and molecular vibration temperatures at different positions of the PPC were studied. The electron densities were compared by comparing the broadenings of Ar I (2P2-->1S5) spectrum line, and the molecular vibration temperatures were calculated by the spectrum line of nitrogen band of second positive system (C3Πu-->B3Πg) . It was found that the electron densities and molecular vibration temperatures at different positions are both different, showing that the plasma states at different positions are different. The descending order of the electron density is: thin plasma columns around the thick plasma columns, thick plasma columns, plasma slices, and thin plasma columns at junction of plasma slices. The descending order of the molecular vibration temperature is: thin plasma columns at junction of plasma slices, plasma slices, thick plasma columns, and thin plasma columns around the thick plasma columns, which is opposite to that of the electron density. So, the electron densities and the molecular vibration temperatures in different positions of the PPC show the opposite changing trend. As the refractive index of plasma is dependent upon the electron density, the thick plasma columns, two kinds of thin plasma columns and plasma slices in this PPC have different refractive indexes. Together with the surrounding area where no discharges occur, in which the refractive index is also different from the discharging areas, the complex PPC can be seen as a self-organized periodic structure with five different refractive indexes. The PPC has the advantages of being obtained easily, having structural diversity, and being analyzed simply, which may lead to wide applications in many scientific and technical areas.

Three dimensional simulations of pattern formation during high-pressure, freely localized microwave breakdown in air

Recent experiments have demonstrated that a freely localized 100 GHz microwave discharge can propagate towards the microwave source with high speed, forming a complex pattern of self-organized filaments. We present three-dimensional simulations of the formation and propagation of such patterns that reveal more information on their nature and interaction with the electromagnetic waves. The developed three-dimensional Maxwell-plasma solver permits the study of different forms of incident field polarization. Results for linear and circular polarization of the wave are presented and comparisons with recent experiments show a good overall agreement. The three dimensional simulations provide a quantitative analysis of the parameters controlling the time and length scales of the strongly non-linear plasma dynamics and could be useful for potential microwave plasma applications such as aerodynamic flow and combustion control.

Self-organization of single filaments and diffusive plasmas during a single pulse in dielectric-barrier discharges

Self-organization of filaments in dielectric-barrier discharges (DBDs) probably has many origins. However, the dominant cause is proposed to be the accumulation of charge on the surfaces of the bounding dielectrics that reinforces successive discharge pulses to occur at the same locations. A secondary cause is the electrostatic repulsion of individual plasma filaments. Self-organization typically develops over many discharge pulses. In this paper, we discuss the results of a computational investigation of plasma filaments in overvoltage DBDs that, under select conditions, display self-organized patterns (SOPs) of plasma density during a single discharge pulse. (Overvoltage refers to the rapid application of a voltage in excess of the quasi-dc breakdown voltage.) The origin of the SOPs is a synergistic relationship between the speed of the surface-ionization waves that propagate along each dielectric and the rate at which avalanche occurs across the gap. For our test conditions, SOPs were not observed at lower voltages and gradually formed at higher voltages. The same conditions that result in SOPs, i.e. the application of an overvoltage, also produce more diffuse discharges. A transition from a single narrow filament to a more diffuse structure was observed as overvoltage was approached. The sensitivity of SOPs to the orientation and permittivity of the bounding dielectrics is discussed.

Optimizing Factors on High Concentration of Ozone Production with Dielectric Barrier Discharge

The gap distance, electrode material, voltage and gas flow velocity were optimized with gas pressure variation of dielectric barrier discharge (DBD) for producing high concentration of ozone. There exists an optimum gas pressure at which the highest ozone concentration is produced with other parameters being fixed. This optimum gas pressure value changes accordingly as the other parameters changed. As the discharge continues at the optimum pressure, the ozone concentration could increase or decrease slowly. This aging effect has different characteristics with the metal electrode material and the impurity level of the oxygen gas used for ozone generation. The aging effect is supposed to be related with the catalytic effect of metal oxide, which is generated in the discharge zone. The change in the characteristic of optimum pressure by the other parameters, indicate that the ozone concentration is deeply related with the filament self-organization characteristics of DBD. At the final optimized condition, the ozone concentration was higher than 22.5 wt.%.

Simulation of Self-Organized Pattern in Atmospheric Pressure Barrier Discharge Driven by Pulse-Modulated RF Voltage

In this paper, a spontaneous self-organized pattern in atmospheric pressure barrier discharge driven by pulse-modulated radio frequency (rf) power is reported with the help of a self-consistent 2-D fluid model. Under the action of pulse-modulated rf voltage with proper duty cycle, the filaments come into being, and at last four stable discharge channels are observed. The formation of self-organized filaments can be sequentially divided into three stages: preionization stage, discharge self-adjusting stage, and pattern formation stage. In the preionization stage, it exhibits homogeneous characteristics; in the discharge self-adjusting stage, discharge instability is magnified, and four filaments turn up; in the pattern formation stage, discharge channels are fixed at the same locations permanently. In addition, we widen the electrode plate and find out that the number of the self-organized discharge channels increases, while the adjacent channel distance is almost a constant as the width of the plane increases.

Self-Organization Pattern of Microgap Atmospheric Barrier Discharge

Symmetric self-organized discharge filaments have been observed in the 140- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $\mu\hbox{m}$</tex></formula> -microgap dielectric barrier discharge between two parallel glass plates. Images of the discharge in microseconds were obtained using an intensified charge-coupled device (ICCD) camera. The diameters of these self-organizing filaments, the distance between the filaments, and the approximate speed of the moving filaments were obtained using the ICCD images.

Self-Organization and Migration of Dielectric Barrier Discharge Filaments in Argon Gas Flow

Observations of atmospheric-pressure dielectric barrier discharge are conducted through a water-filled electrode in atmospheric-pressure argon gas flow. Quasi-symmetric self-organized discharge filaments were observed. The streamers moved with the gas flow, and the migration velocity increased with increasing gas velocity.

Time-Resolved Observation of Self-Organized Filaments Formed in a Helium-Dielectric Barrier Discharge

Self-organization phenomenon in a helium dielectric barrier discharge generated by a piezoelectric transformer (PT) has been investigated. Time-resolved images taken by an intensified charge-coupled device camera reveals the temporal behavior of the microdischarge filaments that coincide with the homogeneous discharge in a cycle of the secondary voltage of the PT. We have succeeded in optically observing the traces of the accumulated charges on the dielectric surface as dark spots remained after the extinction of the microdischarge filaments.

Development of Self-Organized Filaments in a Microgap Atmospheric Barrier Discharge on Bismuth Silicon Oxide Dielectrics

In this paper, we present subsequent images of self-organized filaments in a microgap atmospheric barrier discharge with and without bismuth silicon oxide (BSO) dielectrics. The images were obtained using an intensified charge-coupled device digital camera. Different developments of the discharge were observed in the region occupied by the filaments in the case of BSO and glass dielectrics. The charge distribution on the dielectric surface played an important role in the development of the self-organized patterns.

Self-organization of keratin intermediate filaments into cross-linked networks

Keratins, the largest subgroup of intermediate filament (IF) proteins, form a network of 10-nm filaments built from type I/II heterodimers in epithelial cells. A major function of keratin IFs is to protect epithelial cells from mechanical stress. Like filamentous actin, keratin IFs must be cross-linked in vitro to achieve the high level of mechanical resilience characteristic of live cells. Keratins 5 and 14 (K5 and K14), the main pairing occurring in the basal progenitor layer of epidermis and related epithelia, can readily self-organize into large filament bundles in vitro and in vivo. Here, we show that filament self-organization is mediated by multivalent interactions involving distinct regions in K5 and K14 proteins. Self-organization is determined independently of polymerization into 10-nm filaments, but involves specific type I–type II keratin complementarity. We propose that self-organization is a key determinant of the structural support function of keratin IFs in vivo.