Coalescence Of Filaments Research Articles

Investigation on the Coalescence of Filaments in Fused Filament Fabrication Process for Amorphous Polyether Ketone Ketone for Varying Nozzle Diameters and Chamber Temperatures.

The use of Fused Filament Fabrication (FFF) of high-performance polymers is becoming increasingly prevalent, leading to the exploration of new applications. The use of such materials in critical cases for aerospace applications necessitates the verification of industry standards, particularly with regard to the requirements for part porosity. The authors investigate the effect of nozzle diameter and cooling temperature printing parameters on the porosity of the part by using existing modelling methods based on the sintering of cylinders and spheres and comparing the results to microscope snapshots of sections of parts. The models are able to be used as limits for predicting the longitudinal neck growth of the part. The authors show through experiments that the value of the cooling temperature of the deposited filament has a minimal effect on the outcome, while nozzle diameter has a strong impact on the resulting porosity. The modelling results show that there is a significant impact of both the nozzle diameter and cooling temperature on the porosity of the part. This implies that further refinement of the models is needed for the resulting parts to be applied in critical structures.

Cluster Formation in a Filamentary Cloud: The Case of the Stellar Cluster NGC 2316

We present a multiwavelength analysis of the star cluster NGC 2316 and its surroundings. We estimated the physical parameters of the NGC 2316 cluster, including its shape (elongated), size (R cluster = 0.4 pc), distance (1.3 ± 0.3 kpc), and minimum reddening (A V = 1.55 mag). We discovered two massive stars (B2.0V-B1.5V, age ∼12 Myr) embedded (A V = 4 mag) within this cluster. The cluster region still forms young stars even though the most massive star was born ∼12 Myr ago. We also found evidence of positive feedback from these massive stars. We identified a cold gas/dust lane extending westward from the cluster. The western end of the dust lane seems to favor low-mass star formation, whereas the cluster end favors bit massive star formation, which seems to have started earlier than the western end. We found an elongated molecular cloud in this region, characterized by numerous filamentary structures. The morphology of the filaments, along with position–velocity maps, velocity dispersion maps, channel maps, etc., indicate a coalescence of filaments and a potential longitudinal flow of matter toward the cluster through the western end of the gas/dust lane. This entire region seems to be a Hub-filamentary system (HFS), in which the NGC 2316 cluster is probably the hub and the dark lane is the main filamentary structure. Being the gravity well of this HFS, star formation started first in the NGC 2316 region and went on to the other filamentary nodes.

Filament coalescence and hub structure in Mon R2

There is growing evidence of the role of hub-filament systems (HFS) in the formation of stars from low to high masses. As of today, however, the detailed structures of these systems are still not well described. Here we study the Mon R2 star-forming region, which has a rich network of filaments joining in a star cluster forming hub, and aim to understand the hub structure and to examine the mass fraction residing in the hub and in the filaments, which is a key factor that influences massive star formation. We conducted a multi-scale, multi-component analysis of the Herschel column density maps (resolution of 18.2′′ or ~0.07 pc at 830 pc) of the region using a newly developed algorithm getsf to identify the structural components, namely, extended cloud, filaments, and sources. We find that cascades of lower column density filaments coalesce to form higher-density filaments eventually merging inside the hub (0.8 pc radius). As opposed to the previous view of the hub as a massive clump with ~1 pc radius, we find it to be a network of short high-density filaments. We analyse the orientations and mass per unit length (M∕L) of the filaments as a function of distance from the hub centre. The filaments are radially aligned towards the centre of the hub. The total mass reservoir in the Mon R2 HFS (5 pc × 5 pc) is split between filaments (54%), an extended cloud (37%), and sources (9%). The M∕L of filaments increases from ~10 M⊙ pc−1 at 1.5 pc from the hub to ~100 M⊙ pc−1 at its centre, while the number of filaments per annulus of 0.2 pc width decreases from 20 to two in the same range. The observed radial column density structure of the HFS (filament component only) displays a power-law dependence of NH2 ∝ r−2.17 up to a radius of ~2.5 pc from the central hub, resembling a global collapse of the HFS. We present a scenario where the HFS can be supported by magnetic fields which interact, merge, and reorganise themselves as the filaments coalesce. We plotted the plane-of-the-sky magnetic field line geometry using archival Planck data to support our scenario. In the new view of the hub as a network of high-density filaments, we suggest that only the stars located in the network can benefit from the longitudinal flows of gas to become massive, which may explain the reason for the formation of many low-mass stars in cluster centres. We show the correlation of massive stars in the region to the intertwined network-like hub, based on which we updated the implications of the filaments to clusters (F2C) model for massive star formation.

Additive manufacturing of short carbon fiber-reinforced polyamide composites by fused filament fabrication: Formulation, manufacturing and characterization

Short carbon fiber-reinforced Polyamide 12 composite materials were prepared and used as filaments for additive manufacturing (AM) of structures using the Fused Filament Fabrication (FFF) method. The effect of carbon fibers concentration and type, infill pattern and environmental temperatures on mechanical properties of the printed test samples were investigated. The measured tensile modulus of the printed composite ranged from 1.4 to 8.8 GPa, an increase of up to 6.3 times the value of the neat printed polymer. The tensile strength ranged from 40 to 90 MPa, for an increase of up to 2.15 times. Optimization of the environmental temperature for improved coalescence of filaments led to a fair increase in values of the tensile modulus and strength, with an improvement up to 1.5 and 2 times, respectively, for the printed samples with pattern orthogonal to the loading directions. Microstructure characterizations were performed for mechanical results interpretations, with the help of a specialized homogenization model. The combination of FFF and carbon fiber-reinforced composite shows high promises for applications in the transportation industry.

When do cosmic peaks, filaments or walls merge? A theory of critical events in a multi-scale landscape.

Abstract The merging rate of cosmic structures is computed, relying on the Ansatz that they can be predicted in the initial linear density field from the coalescence of critical points with increasing smoothing scale, used here as a proxy for cosmic time. Beyond the mergers of peaks with saddle points (a proxy for halo mergers), we consider the coalescence and nucleation of all sets of critical points, including wall-saddle to filament-saddle and wall-saddle to minima (a proxy for filament and void mergers respectively), as they impact the geometry of galactic infall, and in particular filament disconnection. Analytical predictions of the one-point statistics are validated against multiscale measurements in 2D and 3D realisations of Gaussian random fields (the corresponding code being available upon request) and compared qualitatively to cosmological N-body simulations at early times (z ≥ 10) and large scales (≥ 5Mpc/h). The rate of filament coalescence is compared to the merger rate of haloes and the two-point clustering of these events is computed, along with their cross-correlations with critical points. These correlations are qualitatively consistent with the preservation of the connectivity of dark matter haloes, and the impact of the large scale structures on assembly bias. The destruction rate of haloes and voids as a function of mass and redshift is quantified down to z = 0 for a ΛCDM cosmology. The one-point statistics in higher dimensions are also presented, together with consistency relations between critical point and critical event counts.

Nonlinear dynamics of the ion Weibel-filamentation instability: An analytical model for the evolution of the plasma and spectral properties

We present a predictive model of the nonlinear phase of the Weibel instability induced by two symmetric, counter-streaming ion beams in the non-relativistic regime. This self-consistent model combines the quasilinear kinetic theory of Davidson et al. [Phys. Fluids 15, 317 (1972)] with a simple description of current filament coalescence. It allows us to follow the evolution of the ion parameters up to a stage close to complete isotropization, and is thus of prime interest to understand the dynamics of collisionless shock formation. Its predictions are supported by 2-D and 3-D particle-in-cell simulations of the ion Weibel instability. The derived approximate analytical solutions reveal the various dependencies of the ion relaxation to isotropy. In particular, it is found that the influence of the electron screening can affect the results of simulations using an unphysical electron mass.

Spatial Uniformity of Atmospheric Pressure Discharges: A Simulation Study

AbstractSpatial uniformity is important in most applications of dielectric barrier discharges operating at atmospheric pressure. However, such uniformity is not easily achieved. Under many conditions, a filamentary structure usually develops. In this paper, we employ a two‐dimensional self‐consistent fluid model to explore the influence of several factors on the evolution of spatial structure of dielectric barrier discharges. In particular, we contrast the behavior of discharges in pure helium and He‐N2 gas mixture, which represent the reduction in breakdown voltage of gas during the evolvement of uniform glow discharge plasma. The transformation from filamentary to uniform mode of discharge plasma is analyzed by the phenomenon of coalescence of filaments and we investigate the effect of several external discharge parameters, such as driving frequency and effect of overvoltage, and the dielectric constant of the barrier material for the uniform and filamentary discharge plasmas. This simulation study is useful to describe the spatio‐temporal profiles of electron density in different phases of the filamentary, uniform Townsend and glow discharge regimes under various constraints. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

SIZE DISTRIBUTION OF AMYLOID FIBRILS. MATHEMATICAL MODELS AND EXPERIMENTAL DATA

More than twenty types of proteins can adopt misfolded conformations, which can co-aggregate into amyloid fibrils, and are related to pathologies such as Alzheimer's disease. This article surveys mathematical models for aggregation chain reactions, and discuss the ability to use them to understand amyloid distributions. Numerous reactions have been proposed to play a role in their aggregation kinetics, though the relative importance of each reaction in vivo is unclear: these include activation steps, with nucleation compared to initiation, disaggregation steps, with depolymerization compared to fragmentation, and additional processes such as filament coalescence or secondary nucleation. We have statistically analysed the shape of the size distribution of prion fibrils, with the specific example of truncated data due to the experimental technique (electron microscopy). A model of polymerization and depolymerization succeeds in explaining this distribution. It is a very plausible scheme though, as evidenced in the review of other mathematical models, other types of reactions could also give rise to the same type of distributions.

Plasma waveguide array induced by filament interaction

We demonstrate that interference-assisted coalescence of two noncollinearly overlapped filaments creates a wavelength-scale periodic plasma density modulation to guide the input pulses equivalently as a photonic crystal plasma waveguide. The periodic self-channeling is evidenced by the direct observation of the filament coalescence, which reveals wavelength-scale spatial widths and periodicity dependent on the crossing angles and intensity ratios between the incident filaments.

Global Simulation for Laser-Driven MeV Electrons in Fast Ignition

A comprehensive examination of the interaction of a picosecond-long ignition pulse on high-density (40 times critical density) pellets using a two-dimensional particle-in-cell model is described. The global geometry consists of a 50 mum diameter pellet surrounded by a corona which is isolated by a vacuum region from the boundary. For cone-attached targets, as much as 67% of the incident laser energy is absorbed with 12% sent forward as fast electrons in a 23 degrees cone. The current filaments are driven by the Weibel instability of the forward-going fast electron flux and its return current with the ions playing an important role of neutralizing the space charge. No global current filament coalescence has been observed. The electron distribution function obeys a power law, which begins at E approximately 0.2 MeV and falls off as E-(2-3).

Filamentation patterns in Kerr media vs. beam shape robustness, nonlinear saturation and polarization states

The filamentation of optical beams in focusing Kerr media is investigated. First, the creation of filamentary structures is shown to strongly depend on the radial distribution of the incident beam in the diffraction plane. With a cubic nonlinearity, broadening an input beam from Gaussian to super-Gaussian (SG) shapes relaxes the self-focusing (SF) attractor and triggers the formation of independent filaments. Analytical criteria for the mutual coalescence of filaments in the context of collapsing and saturating nonlinearities are proposed. Second, the influence of the polarization state on the filamentation instability is investigated. Rigorous conditions for the SF of beams with different polarizations are derived, which prove that the power threshold for collapse noticeably increases for circularly-polarized beams. The growth rate for modulational instability decreases accordingly and the minimal separation distance for coalescence becomes larger, which slows down the production of uncorrelated filaments. Implications of these results in atmospheric propagation are finally discussed.

Strong Proton Acceleration during Successive Coalescence of Filament Currents in Relativistic Electron Beam System

We investigate the relaxation process of relativistic electron beam in a plasma, using a two-dimensional fully relativistic electromagnetic particle-in-cell code. The relaxation mechanism of the electron beam with return current is related to the electromagnetic filamentation instability. This instability produces many small current filaments whose size is of order of the electron skin depth. These generated current filaments rapidly merge and the electron pinching occurs in each filament. After that, these filaments merge further. There are two types of coalescence processes. One is the coalescence of almost same size filaments, the other is the coalescence of the different size filaments. We find that during successive coalescence, the strong proton acceleration occurs due to electric field perpendicular to local magnetic field.

Ion acceleration, magnetic field line reconnection, and multiple current filament coalescence of a relativistic electron beam in a plasma

Results are presented from analytical theory and from two-dimensional particle-in-cell simulations of the relaxation of a relativistic electron beam in a plasma. When the electron beam enters the plasma, it generates a return current which is carried by the plasma electrons. In a collisionless plasma, the relaxation mechanism is related to the onset of an electromagnetic filamentation instability, which leads to the generation of a quasistatic magnetic field associated with many small-scale current filaments. Each filament consists of a direct and of a return electric current which repel each other. This produces a strong electric field which accelerates the ions in the radial direction. In the long time evolution, the successive coalescence of the small-scale current filaments is seen. This process is accompanied by the reconnection of the magnetic field lines, by the formation of current sheets, and by strong ion acceleration inside these sheets.

Filamentous fabrics in low-temperature mineral assemblages: are they fossil biomarkers? Implications for the search for a subsurface fossil record on the early Earth and Mars

The subsurface has been recognized as a possible habitat for microbial life on Mars. An analogous fossil record of subsurface life is nearly missing on Earth. Here we present evidence of the widespread occurrence of such a record: tubular filamentous structures with typical core diameters of 1– 2 μm were found as inclusions in minerals deposited from low- T (<100°C) aqueous fluids in subsurface environments at >140 localities worldwide. Filaments are frequently organized in composite structures with architectures similar to microbial mats. Filaments thickly encrusted by minerals exhibit gravity-oriented structures of macroscopic dimensions that are similar to stalactites. Environments of formation are sites of low- T water circulation in macroporous rocks such as volcanics, oxidized ores, limestone solution cavities and cavernous macrofossils. The age of occurrence ranges from Precambrian to Subrecent. We interpret the filamentous structures as permineralized and encrusted microbial filaments based on the following arguments: tubular construction of filaments with constant core diameters typical of microbes ( 1.5±1.1 μm ), coalescence of filaments to form mat-like structures, gravity draping of micron-thin filaments indicating an originally flexible consistency, and restriction to low- T mineral assemblages. These filamentous structures formed in subsurface environments are similar in size, morphology and construction to fossilized microbes observed in modern terrestrial and marine thermal springs. This newly recognized fossil record of subterranean microbial life opens up new perspectives in the study of the paleobiology of the terrestrial subsurface and in the exploration for fossil life on Mars. Potential host rocks on Mars include major nonsedimentary units such as volcanics and impactites.

The deformation and break-up of thermotropic co-polyester droplets in a molten polypropylene matrix subjecting to oscillatory simple shear and entry flow

In this paper, we report experimental optical observations on the deformation, possible breakup and coalescence of molten thermotropic liquid crystalline polymers (TLCPs) embedded in a molten polypropylene matrix. Both simple oscillatory shear and extensional flow deformations are considered. In the case of oscillatory simple shear, different regimes of deformation and filament formation are observed. In one case, stable filaments form by an accumulated strain effect. In the second case, extended unstable filaments are formed mainly by filament coalescence. It is found that the coalescence of droplets occurs by droplets migrating towards each other. The low pressure produced behind the droplets during flow was thought to be the driving force for the droplets alignment and migration. Experiments on droplets deformation and relaxation in extensional entry flow experiments are also presented, and from the data presented in the paper it is possible to establish general conditions for the formation and survival of TLCP filaments in a thermoplastics matrix, which is a necessary condition for the manufacture of in situ self reinforced thermoplastic products.

Dynamics of hot filaments in a tokamak plasma

The reaction of an equilibrium tokamak plasma to a sudden localized deposition of heat is investigated by means of numerical simulations of the time-dependent equations of resistive magnetohydrodynamics (MHD) in two spatial dimensions, in order to obtain a better understanding of the structure and dynamics of the hot plasma filaments that are observed in recent tokamak experiments. Simulation results show that the fast heating generates MHD waves and creates a localised hot filament. Pressure perturbations are carried away from the heated area by slow waves, even when the heating is applied on the Alfvén time scale. When a temperature-dependent resistivity is considered, a current peak is formed at the place of the temperature peak, and the order of magnitude of the current is given by the condition that ηJz is constant. Next to the wave dynamics, the simulations show another type of hot filament dynamics caused by j×B forces. These forces drive filaments to the centre of the plasma at a nearly constant velocity, which decreases for smaller resistivities. Two filaments can merge under the influence of this current–current interaction. This process happens on a very long time scale. For realistic tokamak resistivities, the coalescence of filaments may take place on time scales of the order of the experimentally reported lifetime of filaments, and may thus be the mechanism that determines the lifetime of the filamentation process.

4364916 Process for the production of stabilized acrylic fibers which are particularly suited for thermal conversion to carbon fibers

An improved process for the relatively rapid thermal stabilization of a multifilamentary acrylic fibrous material in the substantial absence of filament coalescence is provided. The fibrous material is initially contacted with a solution of hydroxylamine (as described), and subsequently with a solution of ammonium permanganate, calcium permanganate, magnesium permanganate, or mixtures thereof (as described). The resulting fibrous material which possesses a chemically altered structure is heated in an oxygen-containing atmosphere until a thermally stabilized acrylic fibrous material is formed which is capable of undergoing carbonization and is non-burning when subjected to an ordinary match flame.