Filament Density Research Articles

Shortened tethering filaments stabilize presynaptic vesicles in support of elevated release probability during LTP in rat hippocampus

Long-term potentiation (LTP) is a cellular mechanism of learning and memory that results in a sustained increase in the probability of vesicular release of neurotransmitter. However, previous work in hippocampal area CA1 of the adult rat revealed that the total number of vesicles per synapse decreases following LTP, seemingly inconsistent with the elevated release probability. Here, electron-microscopic tomography (EMT) was used to assess whether changes in vesicle density or structure of vesicle tethering filaments at the active zone might explain the enhanced release probability following LTP. The spatial relationship of vesicles to the active zone varies with functional status. Tightly docked vesicles contact the presynaptic membrane, have partially formed SNARE complexes, and are primed for release of neurotransmitter upon the next action potential. Loosely docked vesicles are located within 8 nm of the presynaptic membrane where SNARE complexes begin to form. Nondocked vesicles comprise recycling and reserve pools. Vesicles are tethered to the active zone via filaments composed of molecules engaged in docking and release processes. The density of tightly docked vesicles was increased 2 h following LTP compared to control stimulation, whereas the densities of loosely docked or nondocked vesicles congregating within 45 nm above the active zones were unchanged. The tethering filaments on all vesicles were shorter and their attachment sites shifted closer to the active zone. These findings suggest that tethering filaments stabilize more vesicles in the primed state. Such changes would facilitate the long-lasting increase in release probability following LTP.

Effect of fibre cross-sectional shape on bending behaviour of yarns and fabrics; part I

To study the effect of fibre cross-sectional shapes on the bending behaviour of continuous multifilament polyethylene terephthalate (PET) yarns and corresponding fabrics, a circular cross-sectional shape has been taken as reference shape. To mimic the natural fibres in different ways, the cross-sectional shape is an important parameter in this regard. Different cross-sectional shapes like circular, trilobal, rectangular, plus, double flange dumble shape, octagonal, hexalobal, square and trilobal plus or Y-shape were selected for the study. The linear density of single filament and yarn were kept constant (i.e. 76/48/0) in all cross-sectional shapes. The area of cross section was approximately constant for all shapes. The theoretical bending rigidity was calculated for all cross-sectional shapes about its neutral axis. The experimental BR ratio concerning reference circular cross section of fibre was compared with the theoretical BR ratio. It is assumed that individual filament is free to bend in fibre assembly having zero twists. All yarns were converted to fabric having constant areal density. The yarn bending behaviour is compared with fabric bending behaviour to study the effect of cross-sectional shapes on bending behaviour.

Factors affecting properties of Ti-6Al-4V alloy additive manufactured by metal fused filament fabrication

This paper aims to break the current material-process-property tradeoffs in metal fused filament fabrication (MF3) to effectively fabricate Ti-6Al-4V alloy specimens beyond 90% relative density without any post-processing with consistent mechanical properties and microstructure, which are critical for aerospace and medical applications. Existing knowledge gaps in MF3 3D printing fail to address how properties scale from the filament processing stage to green part printing to sintering and what contributing factors cause significant deviation in mechanical properties in samples having the same sintered densities. To tackle these gaps, this work holistically investigates four key aspects specifically for MF3 of Ti-6Al-4V to address a) influence of filament extrusion conditions on filament density variance and diameter control, b) use of the design of experiments to identify factors influencing MF3 3D printed green sample density and dimensions, c) identifying sintering time and temperature conditions that yield densities beyond 90% and mechanical properties close to literature and d) powder attributes (size and interstitial concentrations) and its effect on sintered density and mechanical properties for MF3 samples.

A Modified Actin (Gly65Val Substitution) Expressed in Cotton Disrupts Polymerization of Actin Filaments Leading to the Phenotype of Ligon Lintless-1 (Li1) Mutant.

Dynamic remodeling of the actin cytoskeleton plays a central role in the elongation of cotton fibers, which are the most important natural fibers in the global textile industry. Here, a high-resolution mapping approach combined with comparative sequencing and a transgenic method revealed that a G65V substitution in the cotton actin Gh_D04G0865 (GhACT17D in the wild-type) is responsible for the Gossypium hirsutum Ligon lintless-1 (Li1) mutant (GhACT17DM). In the mutant GhACT17DM from Li1 plant, Gly65 is substituted with valine on the lip of the nucleotide-binding domain of GhACT17D, which probably affects the polymerization of F-actin. Over-expression of GhACT17DM, but not GhACT17D, driven by either a CaMV35 promoter or a fiber-specific promoter in cotton produced a Li1-like phenotype. Compared with the wild-type control, actin filaments in Li1 fibers showed higher growth and shrinkage rates, decreased filament skewness and parallelness, and increased filament density. Taken together, our results indicate that the incorporation of GhACT17DM during actin polymerization disrupts the establishment and dynamics of the actin cytoskeleton, resulting in defective fiber elongation and the overall dwarf and twisted phenotype of the Li1 mutant.

Dust polarized emission observations of NGC 6334

Context.Molecular filaments and hubs have received special attention recently thanks to new studies showing their key role in star formation. While the (column) density and velocity structures of both filaments and hubs have been carefully studied, their magnetic field (B-field) properties have yet to be characterized. Consequently, the role of B-fields in the formation and evolution of hub-filament systems is not well constrained.Aims.We aim to understand the role of the B-field and its interplay with turbulence and gravity in the dynamical evolution of the NGC 6334 filament network that harbours cluster-forming hubs and high-mass star formation.Methods.We present new observations of the dust polarized emission at 850μm toward the 2 pc × 10 pc map of NGC 6334 at a spatial resolution of 0.09 pc obtained with theJames Clerk MaxwellTelescope (JCMT) as part of the B-field In STar-forming Region Observations (BISTRO) survey. We study the distribution and dispersion of the polarized intensity (PI), the polarization fraction (PF), and the plane-of-the-sky B-field angle (χB_POS) toward the whole region, along the 10 pc-long ridge and along the sub-filaments connected to the ridge and the hubs. We derived the power spectra of the intensity andχBPOSalong the ridge crest and compared them with the results obtained from simulated filaments.Results.The observations span ~3 orders of magnitude in StokesIandPIand ~2 orders of magnitude inPF(from ~0.2 to ~ 20%). A large scatter inPIandPFis observed for a given value ofI. Our analyses show a complex B-field structure when observed over the whole region (~ 10 pc); however, at smaller scales (~1 pc),χBPOSvaries coherently along the crests of the filament network. The observed power spectrum ofχBPOScan be well represented with a power law function with a slope of − 1.33 ± 0.23, which is ~20% shallower than that ofI. We find that this result is compatible with the properties of simulated filaments and may indicate the physical processes at play in the formation and evolution of star-forming filaments. Along the sub-filaments,χBPOSrotates frombeing mostly perpendicular or randomly oriented with respect to the crests to mostly parallel as the sub-filaments merge with the ridge and hubs. This variation of the B-field structure along the sub-filaments may be tracing local velocity flows of infalling matter in the ridge and hubs. Our analysis also suggests a variation in the energy balance along the crests of these sub-filaments, from magnetically critical or supercritical at their far ends to magnetically subcritical near the ridge and hubs. We also detect an increase inPFtoward the high-column density (NH2≳ 1023 cm−2) star cluster-forming hubs. These latter largePFvalues may be explained by the increase in grain alignment efficiency due to stellar radiation from the newborn stars, combined with an ordered B-field structure.Conclusions.These observational results reveal for the first time the characteristics of the small-scale (down to ~ 0.1 pc) B-field structure of a 10 pc-long hub-filament system. Our analyses show variations in the polarization properties along the sub-filaments that may be tracing the evolution of their physical properties during their interaction with the ridge and hubs. We also detect an impact of feedback from young high-mass stars on the local B-field structure and the polarization properties, which could put constraints on possible models for dust grain alignment and provide important hints as to the interplay between the star formation activity and interstellar B-fields.

Parameters Evaluation in 3D Spare Parts Printing

Future trends in maritime technology include the application of additive technology in spare parts management. Nowadays, 3D printing has become an integral technology in many fields. Maritime industry is one of the fields where 3D printing has become a focus of research. To prepare Electro-technical Officers (ETOs) for the future, it is necessary to investigate parameters which help with deciding whether to use additive technology or to order a spare part. This paper aims to research parameters influencing spare parts printing as a job carried out by ETOs aboard ships. Conclusions about the filament density and quality of the printed parts are derived and presented. Suggestions for future work and possible applications are given.

Estructura de la comunidad de céspedes algales en interacciones con corales masivos en arrecifes del Parque Nacional Natural Tayrona, Caribe colombiano

ecidos y en interacción directa con corales masivos, y se relacionó su complejidad estructural con la capacidad de retención de sedimentos. Para ello, se determinó la composición taxonómica y se cuantificaron la altura del dosel, la cobertura y densidad de filamentos y la biomasa algal de los céspedes que crecían sobre colonias vivas de cuatro especies de corales. Los resultados mostraron que existen diferencias estructurales importantes entre arrecifes y tipo de sustrato. En el arrecife de Granate (10-16 m), los céspedes forman tapetes discontinuos entre algas costrosas, y están constituidos por algas calcáreas articuladas, pequeñas corticadas y juveniles de algas frondosas, principalmente del género Dictyota. Durante el afloramiento costero este género crece profusamente formando transitoriamente tapetes densos que luego se desprenden. Por el contrario, en el arrecife de Nenguange (4-6 m), los céspedes son perennes, forman tapetes muy bajos, tupidos y densos con escasas algas costrosas, y están dominados por algas filamentosas y pequeñas corticadas. Se sugiere que la presencia de territorios de damiselas del género Stegastes ayuda a controlar la complejidad estructural de los céspedes, y que la propagación vegetativa es el mecanismo de crecimiento más frecuente. Además, se encontró que los céspedes morfológicamente más complejos retienen mayor cantidad de sedimentos (limos-arcillas). Este material particulado les sirve de soporte; pueden avanzar lateralmente y ahogar el tejido coralino adyacente. Esta investigación provee los primeros datos cuantitativos de la estructura y cantidad de sedimentos retenidos por céspedes algales que crecen sobre corales arrecifales de Colombia.

Deciphering the dynamics of lamellipodium in a fish keratocytes model

Motile cells depend on an intricate network of feedback loops that are essential in driving cell movement. Integrin-based focal adhesions (FAs) along with actin are the two key factors that mediate such motile behaviour. Together, they generate excitable dynamics that are essential for forming protrusions at the leading edge of the cell and, in certain cases, traveling waves along the membrane. A partial differential equation (PDE) model of a self-organizing lamellipodium in crawling keratocytes has been previously developed to understand how the three spatiotemporal patterns of activity observed in such cells, namely, stalling, waving and smooth motility, are produced. The model consisted of three key variables: the density of barbed actin filaments, newly formed FAs called nascent adhesions (NAs) and VASP, an anti-capping protein that gets sequestered by NAs during maturation. Using parameter sweeping techniques, the distinct regimes of behaviour associated with the three activity patterns were identified. In this study, we convert the PDE model into an ordinary differential equation (ODE) model to examine its excitability properties and determine all the patterns of activity exhibited by this system. Our results reveal that there are two additional regimes not previously identified, including bistability and oscillatory-like type IV excitability (generated by three steady states and their manifolds, rather than limit cycles). These regimes are also present in the PDE model. Applying slow-fast analysis on the ODE model shows that it exhibits a canard explosion through a folded-saddle and that rough motility seen in keratocytes is likely due to noise-dependent motility governed by dynamics near the interface of bistability and type IV excitability. The two parameter bifurcation suggests that the increase in the proportion of rough motion is due to a shift in activity towards the bistable and type IV excitable regimes induced by a decrease in NA maturation rate. Our results thus provide important insight into how microscopic mechanical effects are integrated to produce the observed modes of motility.

Adaptive ordering and filament polymerization of cell cytoskeleton by tunable nanoarrays

Matrix adaptation reconstructs the architecture of cell, and has important implication in proper biological functioning. However, how the network of cytoskeleton filament undergoes reconstruction, reordering, and surface adaptation, requires a systematic investigation. Here, we show that surface sensing and adaptation occur correspondingly with related reorganization of cytoskeleton filaments (actin, tubulin, and vimentin). The microstructure of filament network is built by adaptive change of chemical polymerization on cytoskeleton filaments. The transition of cellular morphology, from spheroidal architecture on nanoarray to extending structure with stress fibers on flat surface, involves spatial reorganization and polymerization modulation of filaments. The dimension of filaments (diameter, orientation, and density) are changed accordingly to spatiotemporal distribution of cytoskeleton network. In addition, our findings elucidate how cell can tune their architecture at nanoscale by matrix adaptation, and provide a novel information on interplay between cytoskeleton and pathophysiology.

Impact of filament denier on functional performance of microfiber in situ bags

In situ bags made from microfiber fabrics have a greater surface area and filtration efficiency that retains the fine particles and reduce the variation in the results. Also, it is more durable than that made from traditional fabrics. This work aimed to study the effect of filament denier on the performance of in situ bags. Two polyester microfilaments with 0.4 and 0.7 deniers were used in manufacturing of four fabrics. Physical and mechanical properties of manufactured fabrics were measured before and after incubation to show the efficiency of the manufactured samples. In vitro trail was conducted to estimate ruminal degradability after 24 and 48 hours for three feedstuffs using three cannulated rams as replicates. The mechanical properties of manufactured in situ bags were significantly affected with both denier per filament and weft densities. According to the statistical analysis of radar chart, sample 2 remarked the highest value which achieved the acceptable ruminal dry matter disappearance compared with Ankom bags in different incubation times.

Effect of ultrasonic-vibration drawing process on Bi-2212 round wires

Bi2Sr2CaCu2O8+δ (Bi-2212)/Ag round wires were fabricated by imposing ultrasonic-vibration drawing (UVD) technique during both the single-filament and multi-filament cold-drawing processes. The frequency of ultrasonic-vibration was set fixed at 20 kHz and different output power density levels had been altered by varied amplitudes. The influence of ultrasonic-vibration on the deformation process of Ag metal sheath, filament density, Ag/superconductor ratio, wire dimension, drawing force reduction, and the superconducting properties of final wires has been systematically studied. Softening effect of ultrasonic-vibration on the Ag metal can be deduced with the decreasing drawing flow stress and drawing force under certain amplitude. It was found that powder densification could be promoted and higher filament volume fraction as well as high wire diameter uniformity had been reached with the introduction of UVD process, leading to the enhancement of Jc and JE after proper heat treatment. Such technique could be considered in fabrication of Bi-2212 long wires as well as other superconducting materials.

The Nature of the Young Supernova Remnant S8 in the Dwarf Galaxy IC 1613

Abstract We present subarcsecond optical images and low- to moderate-resolution spectra of the compact, X-ray, and optically bright supernova remnant known as S8 in the nearby dwarf galaxy IC 1613. Deep Hα images of the remnant show a sharply defined crescent-shaped nebula, while narrow passband images reveal a coincident and unexpectedly bright continuum nebulosity exhibiting a size and morphology like that seen for the remnant’s line emissions. Low-dispersion spectra covering 3600–9000 Å show numerous low-ionization line emissions such as [O i] and [Fe ii], along with higher-ionization emission lines including He ii and optical coronal lines [Fe vii], [Fe x], [Fe xi], and [Fe xiv]. This suggests the presence of a wide range of shock velocities from ∼50 to over 350 km s−1, corresponding to preshock densities of ∼1–30 cm−3. Higher-resolution spectra indicate an expansion velocity around 180 km s−1 with an ∼45 km s−1 wide central cavity. The Hα emission spans rest-frame velocities of +120 to −240 km s−1, and we estimate a total nebula mass of 119 ± 34 M ⊙. We conclude that S8 is a relatively young supernova remnant (≃2700–4400 yr) exhibiting properties remarkably like those seen in the young LMC remnant N49, including age, physical size, shock velocities, filament densities, optical line strengths, X-ray and optical luminosities, and coronal line and continuum emissions.

Kinetic Monte Carlo analysis of data retention in Al:HfO2-based resistive random access memories

Kinetic Monte Carlo resistive random access memory simulations are used to understand different retention experiments performed at several temperatures. The physics behind resistive switching allows to explain experimental results, in particular the degradation of the conductive filaments with temperature. It is observed that competing mechanisms control resistive switching in this type of experiments and the thermal dependencies involved are key to explain the measurements. Besides, the simulation approach allows to analyze the existence of percolation paths in the device dielectric and the conductive filament density and compactness. Finally, the key physical mechanisms are detected and some clues related to the retention performance and possible technology improvements are unveiled.

Electromechanical Assessment and Induced Temperature Measurement of Carbon Fiber Tows under Tensile Condition

The paper presents an investigation and analysis of the electromechanical and thermal characteristics of the carbon fiber alone as single tow and embedded in host materials such as polymer e.g., acrylonitrile butadiene styrene (ABS) using 3D printing. While carbon fibers can partially reinforce the structure, they can act as sensors to monitor the structural health of the host material. The piezo-resistive behavior was examined without any pretreatment of the carbon fiber under tensile test in both cases. Special focus on the filaments clamping types and their effects was observed. An auxetic behavior was exhibited; otherwise, the free part shows elastic and yielding ranges with break point at high resistance. An induced temperature of the carbon fiber was measured during the tensile test to show low variation. The carbon fiber can provide strength contribution to the host material depending on the percentage of filling the material in 3D printing. The relative variation of the electrical resistance increases by 400% while embedded in the host material, but decreases as the tows filament density increases from 1 to 12 K.

A continuum model for the growth of dendritic actin networks

Polymerization of dendritic actin networks underlies important mechanical processes in cell biology such as the protrusion of lamellipodia, propulsion of growth cones in dendrites of neurons, intracellular transport of organelles and pathogens, among others. The forces required for these mechanical functions have been deduced from mechano-chemical models of actin polymerization; most models are focused on single growing filaments, and only a few address polymerization of filament networks through simulations. Here, we propose a continuum model of surface growth and filament nucleation to describe polymerization of dendritic actin networks. The model describes growth and elasticity in terms of macroscopic stresses, strains and filament density rather than focusing on individual filaments. The microscopic processes underlying polymerization are subsumed into kinetic laws characterizing the change of filament density and the propagation of growing surfaces. This continuum model can predict the evolution of actin networks in disparate experiments. A key conclusion of the analysis is that existing laws relating force to polymerization speed of single filaments cannot predict the response of growing networks. Therefore, a new kinetic law, consistent with the dissipation inequality, is proposed to capture the evolution of dendritic actin networks under different loading conditions. This model may be extended to other settings involving a more complex interplay between mechanical stresses and polymerization kinetics, such as the growth of networks of microtubules, collagen filaments, intermediate filaments and carbon nanotubes.

Filament conductivity enhancement through nonlinear beam interaction.

Laser filament applications relying on filament plasma conductivity are limited by their low electron densities and corresponding short lifetimes. Filament plasma formation, an intensity-dependent process, is limited by the clamping of the filament core intensity. Consequently, increasing initial beam energy results in the breakup of the beam into multiple filaments rather than the enhancement of the electron density and conductivity of an individual filament. However, we demonstrate here the augmentation of the filament plasma density up to three times the typical value through the energy exchange between two co-propagating femtosecond beams with total powers between 1.7 and 2.2 Pfil.

Laminin-coated multifilament entubulation, combined with Schwann cells and glial cell line-derived neurotrophic factor, promotes unidirectional axonal regeneration in a rat model of thoracic spinal cord hemisection.

Biomaterial bridging provides physical substrates to guide axonal growth across the lesion. To achieve efficient directional guidance, combinatory strategies using permissive matrix, cells and trophic factors are necessary. In the present study, we evaluated permissive effect of poly (acrylonitrile-co-vinyl chloride) guidance channels filled by different densities of laminin-precoated unidirectional polypropylene filaments combined with Schwann cells, and glial cell line-derived neurotrophic factor for axonal regeneration through a T10 hemisected spinal cord gap in adult rats. We found that channels with filaments significantly reduced the lesion cavity, astrocytic gliosis, and inflammatory responses at the graft-host boundaries. The laminin coated low density filament provided the most favorable directional guidance for axonal regeneration which was enhanced by co-grafting of Schwann cells and glial cell line-derived neurotrophic factor. These results demonstrate that the combinatorial strategy of filament-filled guiding scaffold, adhesive molecular laminin, Schwann cells, and glial cell line-derived neurotrophic factor, provides optimal topographical cues in stimulating directional axonal regeneration following spinal cord injury. This study was approved by Indiana University Institutional Animal Care and Use Committees (IACUC #:11011) on October 29, 2015.

The Power Spectra of Polarized, Dusty Filaments

Abstract We develop an analytic model for the power spectra of polarized filamentary structures as a way to study the Galactic polarization foreground to the cosmic microwave background. Our approach is akin to the cosmological halo-model framework, and reproduces the main features of the Planck 353 GHz power spectra. We model the foreground as randomly oriented, three-dimensional, spheroidal filaments, accounting for their projection onto the sky. The main tunable parameters are the distribution of filament sizes, the physical aspect ratio of filaments, and the dispersion of the filament axis around the local magnetic field direction. The abundance and properties of filaments as a function of size determine the slopes of the foreground power spectra, as we show via scaling arguments. The filament aspect ratio determines the ratio of B-mode power to E-mode power, and specifically reproduces the Planck-observed dust ratio of one-half when the short axis is roughly one-fourth the length of the long axis. Filament misalignment to the local magnetic field determines the TE cross-correlation, and to reproduce Planck measurements we need a (three-dimensional) misalignment angle with an rms dispersion of about 50°. These parameters are not sensitive to the particular filament density profile. By artificially skewing the distribution of the misalignment angle, this model can reproduce the Planck-observed (and parity-violating) TB correlation. The skewing of the misalignment angle necessary to explain TB will cause a yet-unobserved, positive EB dust correlation, a possible target for future experiments.

Scattering of ion cyclotron range of frequency waves by filaments and ELMs

The scattering of ion cyclotron range of frequency (ICRF) waves by filaments and ELMs has been comprehensively studied via modeling. The influence of filaments on the propagation of ICRF waves is studied by building a 2D COMSOL model which solves the wave equation. It is benchmarked against the Mie scattering theoretical model. Cases either with perfect matching layer boundary condition or with poloidal periodic boundary condition are considered. Parameter scans, including the filament density, the filament radius, the number of filaments as well as the distance between filaments, are performed. Then, the influence of ELMs on the propagation of ICRF waves in realistic geometry is studied by importing density distributions calculated by 3D non-linear MHD code JOREK into the 3D antenna code RAPLICASOL. The evolution of density and wave fields during an ELM is analyzed for cases with a low and high scrape-off layer density, respectively. Both the COMSOL simulation and the realistic simulation with JOREK and RAPLICASOL show that the wave fields and Poynting flux can be significantly and globally modified by the ELM filaments. Due to the mutual influence of many density filaments, radially elongated and poloidally distributed stripe structures of the wave fields develop, leading to poloidally inhomogeneous wave fields. Furthermore, the influence of ELMs on the antenna power and antenna coupling resistance is investigated with experimental results in ASDEX Upgrade.

Similarity of angular distribution for THz radiation emitted by laser filament plasma channels of different lengths.

The influence of plasma channel length on an angular terahertz (THz) radiation distribution is experimentally studied for the channel formed under filamentation of an ultrashort laser pulse. It is shown that the angular distribution of the THz emission depends only on laser intensity in the filament and plasma density of the plasma channel and does not depend on the plasma channel length. A qualitative explanation of the THz emission screening by the filament plasma channel is proposed.