Neighboring Filaments Research Articles

Investigation of the impact behavior for composite materials reinforced by glass fibers

In this present work, a non-straight Shear-lag model has been created to anticipate the pressure centralization of a customary hexagonal cell containing a two-bundled fiber. This work is concretized by the advancement of a hypothetical plan of the micromechanical redistribution of the anxieties produced by the transverse burst along the strands in a unidirectional composite as an element of the number and the air of the messed up and flawless filaments. The scientific improvements utilized are introduced to legitimize the state of the conveyance of the worries around the messed up fiber and the adjoining filaments. The limit and coherence conditions are considered by this model to evaluate the exchange pace of the strands, imperatives through the lattice between the fiber broken and the neighboring filaments unblemished.

Toroidal Vortex Filament Knots and Links: Existence, Stability and Dynamics

Using the Klein--Majda--Damodaran model of nearly parallel vortex filaments, we construct vortex knots and links on a torus involving periodic boundary conditions and analyze their stability. For a special class of vortex knots---toroidal knots---we give a full characterization of both their energetic and dynamical stabilities. In addition to providing explicit expressions for the relevant waveforms, we derive explicit formulas for their stability boundaries. These include simple links and different realizations of a trefoil knot. It is shown that a ring of more than 7 filaments can potentially be stablized by giving it a slight twist and connecting neighboring filaments on a torus. In addition to rings, (helical) filament lattice configurations are also considered and are found to be dynamically stable for all rotation frequencies and also energetically stable for sufficiently fast rotations. Numerical simulations are used to compare the Klein--Majda--Damodaran model with the full three-dimensional (3D) Gross--Pitaevskii equations as well as to confirm the analytical theory. Potential differences between the quasi-one-dimensional and the fully 3D description are also discussed.

Online Packaging Method of Filament Cathode for Intelligent Manufacturing

It is challenging to automatically package spiral shaped filament cathodes that are widely used in worldwide microwave ovens. The difficulties include a fast packaging speed of over one parts per second and the dexterity required to handle tangling and embedding between spiral filaments’ multiple circles. In order to convert conventional labor intensive packaging lines of filament cathodes into automatic ones, an online fast automatic packaging method is reported. The method converts the fast incoming sequential flow of filament spirals into a batch of twenty-parallel queues with two stopping levers. The proposed method using two levers to release only the front twenty filaments at a time, one from each queue to fill one complete row of the plastic packaging tray. In this way, it speeds up packaging speed twenty times over conventional sequential packaging method. The inner diameter of the queue tube matches the outer diameter of the filament. It is this dimeter matching to eliminate the embedding problem occurred between neighboring filaments. The proposed method uses vibrating brush to decouple tangled filaments. Large number of validating experiments indicate that the proposed method could automatically package 200 filaments spirals within 2 minutes, with positional accuracy of over 97%. Thus, the proposed packaging method could meet the manufacturing requirement of filament cathodes, releasing four labors out of every production line at every work-shift. Further, this method also simultaneously improves the surface quality of the filaments by eliminating scratch caused by their sharp fresh-cutting cross sections.

DNA-Assembled Multilayer Sliding Nanosystems.

DNA nanotechnology allows for the realization of complex nanoarchitectures in which the spatial arrangements of different constituents and most functions can be enabled by DNA. When optically active components are integrated in such systems, the resulting nanoarchitectures not only provide great insights into the self-assembly of nanoscale elements in a systematic way but also impart tailored optical functionality to DNA origami. In this Letter, we demonstrate DNA-assembled multilayer nanosystems, which can carry out coordinated and reversible sliding motion powered by DNA fuels. Gold nanoparticles cross-link DNA origami filaments to define the configurations of the multilayer nanoarchitectures as well as to mediate relative sliding between the neighboring origami filaments. Meanwhile, the gold nanoparticles serve as optical probes to dynamically interact with the fluorophores tethered on the filaments, rendering in situ detection of the stepwise sliding processes possible. This work seeds the basis to implement DNA-assembled complex optical nanoarchitectures with programmability and addressability, advancing the field with new momentum.

Experimental and theoretical investigation of heat transfer in platform bed during polymer extrusion based additive manufacturing

Heat transfer plays a key role in polymer extrusion based additive manufacturing (AM) processes. Measurement and modeling of how temperature distribution on the platform bed changes with time during the dispensing of a polymer filament is of particular interest, as it determines the effectiveness of merging with neighboring filaments, and therefore, the properties of the built part. This paper reports infrared thermography based measurement of temperature field on the platform bed as a function of time during filament dispense and comparison with an analytical model based on moving heat source theory. Measurements identify two key heat transfer processes that influence temperature distribution on the bed. Data show that diffusion of thermal energy deposited on the bed with the filament and heat transfer from the hot nozzle tip both influence the temperature distribution on the bed. The relative contributions of these two sources of temperature rise on the bed are measured for different values of key process parameters. Measurement of temperature rise due to diffusion of thermal energy deposited on the bed is found to be in excellent agreement with an analytical model based on moving heat source theory. Evolution of the temperature field after completion of rastering of a line is measured. These data play a critical role in determining how effectively a filament merges with neighboring filaments. By identifying the key heat transfer processes that determine the temperature field on the platform bed, this work contributes towards thermal optimization of polymer-based additive manufacturing.

Kinetics of fiber impregnation by a binder. Gradient generalization of Navier–Stokes–Darcy equations

A model of polymer composition material that is composed of a unidirectional fiber and binder has been considered. The space between two neighboring filaments of fibers is considered as a capillary along which the binder propagates during impregnation. In order to describe the flow process, a gradient generalization of the Navier–Stokes equation has been suggested. A corrected model of the flow of binder in the capillary-porous space of a unidirectional fiber material is developed on its basis. In particular cases, the found solution coincides with the Navier–Stokes–Darcy equations and conventional Navier–Stokes equation. The model that has been developed allows the refinement of the nonclassical effect of the existence of two boundary layers that appear during flow and may prevent it.

Structure and Stability of Filamentary Clouds Supported by Lateral Magnetic Field

AbstractWe have constructed two types of analytical models for an isothermal filamentary cloud supported mainly by magnetic tension. The first one describes an isolated cloud while the second considers filamentary clouds spaced periodically. The filamentary clouds are assumed to be highly flattened in both the models. The former is proved to be the asymptotic limit of the latter in which each filamentary cloud is much thinner than the distance to the neighboring filaments. These models show that the mass to flux ratio is crucial for the magnetohydrodynamical equilibrium. The upper bound for the line density, i.e., the mass per unit length, is proportional to the magnetic flux. The mass to flux ratio is slightly larger than the critical value, ($2 \pi \sqrt{G}$)−1, in the first model and lower in the second model. The first model is unstable against fragmentation and the wavelength of the fastest growing mode is several times longer than the cloud diameter. The second model is likely to be unstable only when the mass to flux ratio is supercritical.

STRUCTURE AND STABILITY OF FILAMENTARY CLOUDS SUPPORTED BY A LATERAL MAGNETIC FIELD

We have constructed two types of analytical models for an isothermal filamentary cloud supported mainly by magnetic tension. The first one describes an isolated cloud while the second considers filamentary clouds spaced periodically. Both the models assume that the filamentary clouds are highly flattened. The former is proved to be the asymptotic limit of the latter in which each filamentary cloud is much thinner than the distance to the neighboring filaments. We show that these models reproduce main features of the 2D equilibrium model of Tomisaka (2014) for filamentary cloud threaded by perpendicular magnetic field. It is also shown that the critical mass to flux ratio is $ M /\Phi = (2 \pi \sqrt{G}) ^{-1} $, where $ M $, $ \Phi $ and $ G $ denote the cloud mass, the total magnetic flux of the cloud, and the gravitational constant, respectively. This upper bound coincides with that for an axisymmetric cloud supported by poloidal magnetic fields. We applied the variational principle for studying the Jeans instability of the first model. Our model cloud is unstable against fragmentation as well as the filamentary clouds threaded by longitudinal magnetic field. The fastest growing mode has a wavelength several times longer than the cloud diameter. The second model describes quasi-static evolution of filamentary molecular cloud by ambipolar diffusion.

Myosin lever arm directs collective motion on cellular actin network

The molecular motor myosin teams up to drive muscle contraction, membrane traffic, and cell division in biological cells. Myosin function in cells emerges from the interaction of multiple motors tethered to a scaffold, with surrounding actin filaments organized into 3D networks. Despite the importance of myosin function, the influence of intermotor interactions on collective motion remains poorly understood. In this study, we used precisely engineered myosin assemblies to examine emergence in collective myosin movement. We report that tethering multiple myosin VI motors, but not myosin V motors, modifies their movement trajectories on keratocyte actin networks. Single myosin V and VI dimers display similar skewed trajectories, albeit in opposite directions, when traversing the keratocyte actin network. In contrast, tethering myosin VI motors, but not myosin V motors, progressively straightens the trajectories with increasing myosin number. Trajectory shape of multimotor scaffolds positively correlates with the stiffness of the myosin lever arm. Swapping the flexible myosin VI lever arm for the relatively rigid myosin V lever increases trajectory skewness, and vice versa. A simplified model of coupled motor movement demonstrates that the differences in flexural rigidity of the two myosin lever arms is sufficient to account for the differences in observed behavior of groups of myosin V and VI motors. In accordance with this model trajectory, shapes for scaffolds containing both myosin V and VI are dominated by the myosin with a stiffer lever arm. Our findings suggest that structural features unique to each myosin type may confer selective advantages in cellular functions.

Microscopic Origin of the Non-Newtonian Viscosity of Semiflexible Polymer Solutions in the Semidilute Regime.

One of the great goals in polymer physics is to relate the various macroscopic features of polymeric fluids with the microscopic behavior of single chains. Here, we directly visualize the conformational dynamics of individual semiflexible polymers in a semidilute solution above the overlap concentration under shear. We observe that the tumbling dynamics are significantly slowed down, in marked contrast to the case of a dilute solution, due to steric interactions with neighboring filaments. The observed macroscopic shear thinning effect can be rationalized by a simple model based on the single filament dynamics.

Modulating Contraction by Binding of MyBP-C to Actin

Myosin-binding protein C (MyBP-C) is a ∼130 kDa protein of the thick filaments of vertebrate skeletal and cardiac muscle. It consists of a linear array of ten or eleven globular, 10-kDa domains from the immunoglobulin (Ig) and fibronectin type III families, and an additional, MyBP-C-specific motif. The cardiac isoform, cMyBP-C, plays a key role in modulating cardiac function, and mutations in MyBP-C cause heart disease. Despite its discovery 40 years ago, the mechanism of MyBP-C function remains poorly understood. In vitro studies suggest that it could modulate contraction by binding to thin filaments, but there has been no evidence for this in situ. We used electron tomography of exceptionally well-preserved skeletal muscle to study the 3D organization of MyBP-C in the intact sarcomere. The tomogram shows that MyBP-C projects perpendicular to the thick filament surface and reaches neighboring thin filaments. This thick-thin filament bridge suggests a possible physical basis for modulating filament sliding and thus contraction. In vitro, binding to actin has been shown to occur via MyBP-C's N-terminal end. To understand the structural basis of this binding, we used negative stain electron microscopy and 3D reconstruction to study F-actin decorated with bacterially expressed N-terminal cMyBP-C fragments. Clear decoration was obtained under a variety of salt conditions. 3D reconstructions showed MyBP-C density starting over subdomain 1 of actin and extending tangentially towards actin's pointed end. Molecular fitting with an atomic structure of a MyBP-C Ig domain suggested that most of the N-terminal domains may be well ordered on actin. The location of binding was such that it appeared to overlap the relaxed (low Ca2+) position of tropomyosin but not the activated position. This suggests that MyBP-C might help determine the state of thin filament activity by modulating tropomyosin position on actin.

Exploring Bundle Selectivity of Myosin X Forced Dimer Constructs in vivo

Cells organize their contents and regulate cell shape and mechanics through molecular motors functioning on cytoskeletal filaments. Myosin X, an actin-based motor that concentrates at the distal tips of filopodia of mammalian cells, selects the fascin-actin bundle at the filopodial core for motility. While poorly processive on single actin filaments, it takes processive runs on actin bundled by fascin. Recently we showed that the post-IQ region is the main contributor to myosin X's selectivity. This region contains a charged single alpha-helix (SAH), which may impart unique mechanical or affinity properties to the motor. The structural character of this region was perturbed by insertion of a free swivel (GSGGSG flexible linker) after the SAH domain. The post-SAH swivel mutant showed no preference for bundled actin for motility in vitro, thus providing support to a selectivity model where the search space of the forward head for the next binding site is constrained to neighboring filaments in a bundle. Here we investigate if interrupting the “selectivity module” also has the described effect in live cells.We overexpressed in the U2OS cell line three fluorescently tagged forms of myosin X: the GCN4 forced dimer used in in vivo experiments, the post-SAH swivel mutant of GCN4 dimer and the wild type with a native dimerization domain. GCN4 forced dimer performs in the cell in the same manner as full- length myosin X. Introducing a free swivel in the SAH domain region affects the selective nature of myosin X in the natural cytoskeleton environment of the cell interior as co-localization of GFP labeled protein with filopodial tips does not occur for the Swivel mutant.

Supplementary studies on Henneguya doneci Schulman, 1962 (Myxozoa: Myxosporea) infecting the gill filaments of Carassius auratus gibelio (Bloch) in China: histologic, ultrastructural, and molecular data

Henneguya doneci Schulman, 1962 was collected from the gill filaments of Carassius auratus gibelio (Bloch) in Hubei Province, China. The plasmodia located on the surface of the gill arches deformed the neighboring gill filaments. The size of the plasmodia ranged from 0.6 to 4.5 mm in diameter in different months. The myxospores in the plasmodia measured 10.1 (9.2-11.5) μm long × 8.0 (7.5-8.5) μm wide × 7.5 (7-8) μm thick, with two equal capsules at 4.7 (4-5.5) μm long × 3.3 (2.5-4) μm wide, and two caudal processes 32.7 (24-38.5) μm long, respectively. Polar filaments were coiled 5-6 turns. Ultrastructural observation of the plasmodia showing the capsulogenesis of H. doneci is described briefly. The external tubule initially invaginated into the polar capsule. The rudimentary polar filaments were observed to undergo a series of considerable modification, finally developing into mature polar filaments. Molecular analysis demonstrated that although the myxosporean species were collected from different tissues of hosts in various geographic locations, they clustered with the Cyprinidae-infecting myxosporean species in the phylogenetic tree.

Theory of crosslinked bundles of helical filaments: Intrinsic torques in self-limiting biopolymer assemblies

Inspired by the complex influence of the globular crosslinking proteins on the formation of biofilament bundles in living organisms, we study and analyze a theoretical model for the structure and thermodynamics of bundles of helical filaments assembled in the presence of crosslinking molecules. The helical structure of filaments, a universal feature of biopolymers such as filamentous actin, is shown to generically frustrate the geometry of crosslinking between the "grooves" of two neighboring filaments. We develop a coarse-grained model to investigate the interplay between the geometry of binding and mechanics of both linker and filament distortion, and we show that crosslinking in parallel bundles of helical filaments generates intrinsic torques, of the type that tend to wind the bundle superhelically about its central axis. Crosslinking mediates a non-linear competition between the preference for bundle twist and the size-dependent mechanical cost of filament bending, which in turn gives rise to feedback between the global twist of self-assembled bundles and their lateral size. Finally, we demonstrate that above a critical density of bound crosslinkers, twisted bundles form with a thermodynamically preferred radius that, in turn, increases with a further increase in crosslinking bonds. We identify the stiffness of crosslinking bonds as a key parameter governing the sensitivity of bundle structure and assembly to the availability and affinity of crosslinkers.

A myomesin mutation associated with hypertrophic cardiomyopathy deteriorates dimerisation properties

Myomesin plays an important structural and functional role in the M-band of striated muscles. The C-terminal domain 13 of myomesin dimerises and forms antiparallel strands which cross-link neighboring Myosin filaments and titin in the M-line of the sarcomeres. These interactions stabilise the contractile apparatus during striated muscle contraction. Since myomesin is an important component of the M-band we screened the myomesin gene for genetic variants in patients with hypertrophic cardiomyopathy (HCM). We identified the missense mutation V1490I in domain 12 of myomesin in a family with inherited HCM. Analytical ultracentrifugation experiments, circular dichroism spectra, and surface plasmon resonance spectroscopy of myomesin fragments were carried out to investigate the effects of the mutation V1490I on structure and function of myomesin domains 11–13 and 12–13. Both the wild type and mutated myomesin domains My11–13 revealed similar secondary structures and formed stable dimers. Mutated myomesin domains My11–13 and My12–13 dimers revealed a reduced thermal stability and a significantly decreased dimerisation affinity, showing disturbed functional properties of V1490I mutated myomesin. However, monomeric myomesin domains My11–12, i.e. without dimerisation domain 13 showed no difference in thermal stability between wild type and V1490I mutated myomesin. In conclusion, the V1490I mutation associated with HCM lead to myomesin proteins with abnormal functional properties which affect dimerisation properties of myomesin domain 13. These effects may contribute to the pathogenesis of HCM.

Phosphorylation-Mediated Conformational Changes in the Mouse Neurofilament Architecture: Insight from a Neurofilament Brush Model

Neurofilaments (NFs) are important cytoskeletal filaments that consist of long flexible C-terminal tails that are abundant with charges. The tails attain additional negative charges through serine phosphorylation of Lys-Ser-Pro (KSP) repeat motifs that are particularly found in neurofilament heavy (NF-H) and neurofilament medium (NF-M) proteins. These side-arm protrusions mediate the interaction between neighboring filaments and maintain axonal diameter. However, the precise role of NF proteins and their phosphorylation in regulating interfilament distances and axonal diameter still remains unclear. In this regard, a recent gene replacement study revealed that the phosphorylation of mouse NF-M KSP repeats does not affect axonal cytoarchitecture, challenging the conventional viewpoint on the role of NF phosphorylation. To better understand the effect of phosphorylation, particularly NF-M phosphorylation, we applied a computational method to reveal phosphorylation-mediated conformational changes in mouse NF architecture. We employed a three-dimensional sequence-based coarse-grained NF brush model to perform Monte Carlo simulations of mouse NF by using the sequence and stoichiometry of mouse NF proteins. Our result shows that the phosphorylation of mouse NF-M does not change the radial extension of NF-M side arms under a salt-free condition and in ionic solution, highlighting a structural factor that supports the notion that NF-M KSP phosphorylation has no effect on the axonal diameter of mouse. On the other hand, significant phosphorylation-mediated conformational changes were found in NF-H side arms under the salt-free condition, while the changes in ionic solution are not significant. However, NF-H side arms are found at the periphery of mouse NF architecture, implying a role in linking neighboring filaments.

The Stepping Pattern of Myosin X Is Adapted for Processive Motility on Bundled Actin

Myosin X is a molecular motor that is adapted to select bundled actin filaments over single actin filaments for processive motility. Its unique form of motility suggests that myosin X's stepping mechanism takes advantage of the arrangement of actin filaments and the additional target binding sites found within a bundle. Here we use fluorescence imaging with one-nanometer accuracy to show that myosin X takes steps of ∼18 nm along a fascin-actin bundle. This step-size is well short of the 36-nm step-size observed in myosin V and myosin VI that corresponds to the actin pseudohelical repeat distance. Myosin X is able to walk along bundles with this step-size if it straddles two actin filaments, but would be quickly forced to spiral into the constrained interior of the bundle if it were to use only a single actin filament. We also demonstrate that myosin X takes many sideways steps as it walks along a bundle, suggesting that it can switch actin filament pairs within the bundle as it walks. Sideways steps to the left or the right occur on bundles with equal frequency, suggesting a degree of lateral flexibility such that the motor's working stroke does not bias it to the left or to the right. On single actin filaments, we find a broad mixture of 10–20-nm steps, which again falls short of the 36-nm actin repeat. Moreover, the motor leans to the right as it walks along single filaments, which may require myosin X to adopt strained configurations. As a control, we also tracked myosin V stepping along actin filaments and fascin-actin bundles. We find that myosin V follows a narrower path on both structures, walking primarily along one surface of an actin filament and following a single filament within a bundle while occasionally switching to neighboring filaments. Together, these results delineate some of the structural features of the motor and the track that allow myosin X to recognize actin filament bundles.

Interference pattern generation and simulation in the single beam of a white light continuum

We demonstrate the interference phenomenon in the White Light Continuum (WLC) generated by a single femtosecond laser beam. Different kinds of spatial interference patterns of the WLC generation under various conditions were investigated. The spatial patterns were attributed to interference between the filaments in the WLC generated by the fundamental laser beam yielding the diffraction effect from spatial confinement. Simulations of different patterns were performed. By comparing the results of simulation with those of experiments, the distances of several micrometers between the neighboring filaments can be derived, which agree with the literature values from direct measurements.

Fine control of terahertz radiation from filamentation by molecular lensing in air

We demonstrate a method to control remotely the terahertz (THz) source in air based on the bifilamentation of femtosecond laser pulses. By fine tuning the time delay between the two pulses, a significant modulation of the THz intensity from bifilamentation is observed. The phenomenon is attributed to the molecule quantum lensing effect around the air molecule revival time, which changes the separation between the two neighboring plasma producing filaments.

A Structured Domain is Responsible for Bundle Selection of Myosin X

Cells organize their contents and regulate cell shape and mechanics through molecular motors functioning on cytoskeletal filaments. Presented with many apparently similar tracks within the cortex, how myosins identify the few actin filaments that lead to their correct cellular destinations is largely unknown. Myosin X, an actin-based motor that concentrates at the distal tips of filopodia, selects the fascin-actin bundle at the filopodial core for motility. While poorly processive on single actin filaments, it takes processive runs on actin bundled by fascin. Such a bundle is the precise structure to which myosin X localizes in vivo. Using single molecule optical trapping experiments we determined the step size to be 17 nm, half of the 36 nm pseudo-helical actin repeat essential for motors to be processive on single actin filaments. This suggested that straddling two filaments within a bundle stimulates this motor's processivity. Using combinatorial chimeric constructs of myosin V and myosin X, we show that the post-IQ region, not the short lever arm (three IQ repeats) or the motor domain, is the main contributor to myosin X's selectivity. This region contains two structures of interest: a charged single alpha-helix (SAH), which may impart unique mechanical or affinity properties to the motor, and a coiled-coil dimerization motif. The structural character of this region was perturbed by insertion of free swivels either before or after the SAH domain. The post-SAH swivel mutant showed no preference for bundled actin for motility, thus providing support to a selectivity model where the search-space of the forward head for the next binding site is constrained to neighboring filaments in a bundle. This result provides insight into the ability of nature to fine-tune myosin motors to serve their specific functions in the cell.