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At least 163 records · Page 9

An SDO/AIA-Observed Filament Eruption Triggered by a Lid-Removal Onset Mechanism

An eruption of a solar filament often presages the onset of a more general solar eruption, often leading to a solar flare and coronal mass ejection (CME). Among the mechanisms suggested for triggering eruptions are flux cancellation, flux emergence, tether‐cutting reconnection, and breakout reconnection. Here we present an example of a filament eruption due to a different trigger mechanism, which we call ``lid removal,'' whereby a magnetic structure overlying the filament is removed by a preceding adjacent eruption, rendering MHD unstable the magnetic system containing the filament and resulting in the subsequent eruption of the filament. This filament eruption occurred on 23 Jan 2013, and was well‐seen in SDO/AIA 193 Ang images. Prior to its eruption the filament was at an approximately constant height above the solar surface for approx. 4 hours, before smoothly lifting off. Evidence for the overlying "lid'' field was difficult to discern in 193 Ang images, but was apparent in hotter coronal images, such as SDO/AIA 335. Removal of the lid field was due to an eruption of that field visible in the hotter‐corona images. In this way, the lid‐removal filament‐eruption mechanism is similar to recent observations of connected or cascading eruptions originating from magnetically‐linked locations.

Sterling, Alphonse C.↗

An SDO/AIA-Observed Filament Eruption Triggered by a Lid-Removal Onset Mechanism

An eruption of a solar filament often presages the onset of a more general solar eruption, often leading to a solar flare and coronal mass ejection (CME). Among the mechanisms suggested for triggering eruptions are flux cancellation, flux emergence, tether-cutting reconnection, and breakout reconnection. Here we present an example of a filament eruption due to a different trigger mechanism, which we call "lid removal,'' whereby a magnetic structure overlying the filament is removed by a preceding adjacent eruption, rendering MHD unstable the magnetic system containing the filament and resulting in the subsequent eruption of the filament. This filament eruption occurred on 23 Jan 2013, and was well-seen in SDO/AIA 193 Ang images. Prior to its eruption the filament was at an approximately constant height above the solar surface for approx 4 hours, before smoothly lifting off. Evidence for the overlying "lid'' field was difficult to discern in 193 Ang images, but was apparent in hotter coronal images, such as SDO/AIA 335. Removal of the lid field was due to an eruption of that field visible in the hotter‐corona images. In this way, the lid‐removal filament‐eruption mechanism is similar to recent observations of connected or cascading eruptions originating from magnetically‐linked locations.

Sterling, Alphonse C.↗

Formation of Nano- and Micro-Scale Surface Features Induced by Long-Range Femtosecond Filament Laser Ablation

In this work, we study the characteristics of femtosecond-filament-laser–matter interactions and laser-induced periodic surface structures (LIPSS) at a beam-propagation distance up to 55 m. The quantification of the periodicity of filament-induced self-organized surface structures was accomplished by SEM and AFM measurements combined with the use of discrete two-dimensional fast Fourier transform (2D-FFT) analysis, at different filament propagation distances. The results show that the size of the nano-scale surface features increased with ongoing laser filament processing and, further, periodic ripples started to form in the ablation-spot center after irradiation with five spatially overlapping pulses. The effective number of irradiating filament pulses per spot area affected the developing surface texture, with the period of the low spatial frequency LIPSS reducing notably at a high pulse number. The high regularity of the filament-induced ripples was verified by the demonstration of the angle-of-incidence-dependent diffraction of sunlight. This work underlines the potential of long-range femtosecond filamentation for energy delivery at remote distances, with suppressed diffraction and long depth focus, which can be used in biomimetic laser surface engineering and remote-sensing applications.

36 MATERIALS SCIENCE↗

Deinococcus radiodurans RecA nucleoprotein filaments characterized at the single-molecule level with optical tweezers

Deinococcus radiodurans can survive extreme doses of ionizing radiation due to the very efficient DNA repair mechanisms that are able to cope even with hundreds of double-strand breaks. RecA, the critical protein of homologous recombination in bacteria, is one of the key components of the DNA-repair system. Repair of double-strand breaks requires RecA binding to DNA and assembly of the RecA nucleoprotein helical filaments. The Escherichia coli RecA protein (EcRecA) and its interactions with DNA have been extensively studied using various approaches including single-molecule techniques, while the D. radiodurans RecA (DrRecA) remains much less characterized. However, DrRecA shows some remarkable differences from E. coli homolog. Here we combine microfluidics and single-molecule DNA manipulation with optical tweezers to follow the binding of DrRecA to long double-stranded DNA molecules and probe the mechanical properties of DrRecA nucleoprotein filaments at physiological pH. Our data provide a direct comparison of DrRecA and EcRecA binding to double-stranded DNA under identical conditions. We report a significantly faster filaments assembly as well as lower values of persistence length and contour length for DrRecA nucleoprotein filaments compared to EcRecA. Our results support the existing model of DrRecA forming more frequent and less continuous filaments relative to those of EcRecA. - Highlights: • We investigate Deinococcus radiodurans RecA interactions with long double-stranded DNA at the single-molecule level. • At physiological pH D. radiodurans RecA forms nucleoprotein filaments significantly faster relative to Escherichia coli RecA. • D. radiodurans RecA-dsDNA nucleoprotein filaments are more flexible and slightly shorter compared to those of E. coli RecA.

60 APPLIED LIFE SCIENCES↗

Fast imaging of filaments in the X-point region of Alcator C-Mod

A rich variety of field-aligned fluctuations has been revealed using fast imaging of D α emission from Alcator C-Mod's lower X-point region. Field-aligned filamentary fluctuations are observed along the inner divertor leg, within the Private-Flux-Zone (PFZ), in the Scrape-Off Layer (SOL) outside the outer divertor leg, and, under some conditions, at or above the X-point. The locations and dynamics of the filaments in these regions are strikingly complex in C-Mod. Changes in the filaments’ generation appear to be ordered by plasma density and magnetic configuration. Filaments are not observed for plasmas with n/n Greenwald ≲ 0.12 nor are they observed in Upper Single Null configurations. In a Lower Single Null with 0.12 ≲ n/n Greenwald ≲ 0.45 and Bx∇B directed down, filaments typically move up the inner divertor leg toward the X-point. Reversing the field direction results in the appearance of filaments outside of the outer divertor leg. With the divertor targets “detached”, filaments inside the LCFS are seen. Lastly, these studies were motivated by observations of filaments in the X-point and PFZ regions in MAST, and comparisons with those observations are made.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Characterization of 3D printing filaments containing metal additives and their particulate emissions

Polylactic acid (PLA) filaments are widely used in fused filament fabrication (FFF) processes (3D printing). Filament additives such as metallic particles incorporated into PLA to modify functional and aesthetic features of print objects are becoming increasingly popular. However, the identities and concentrations of low percentage and trace metals in these filaments have not been well described in either the literature or product safety information included with the product. Here, we report the structures and concentrations of metals in selected Copperfill, Bronzefill and Steelfill filaments. We also report size-weighted number concentrations and size-weighted mass concentrations of particulate emissions as a function of print temperature for each filament. Particulate emissions were heterogenous in shape and size with airborne particles below 50 nm diameter dominating the size-weighted particle concentrations and larger particles (approximately 300 nm) dominating the mass weighted particle concentration. Results indicate that potential exposure to particles in the nano-size range increase when using print temperatures above 200o C. Because inhalation exposure to nanoparticles has been linked to adverse health outcomes, we suggest that using lower print temperatures for specific metal-fill filaments may reduce their operational hazard.

36 MATERIALS SCIENCE↗

High-Resolution Full-Field Structural Microscopy of the Voltage-Induced Filament Formation in VO 2 -Based Neuromorphic Devices

In order to make neuromorphic functions in memristive devices more efficient, information about the structural properties of filament formation at the micro- and mesoscopic scales is necessary. Despite extensive research on VO 2 , a key material due to its filament formation, local operando structural measurements remain challenging and often involve destructive specimen preparation and long rastering times, greatly limiting the scope of experimental studies. Utilizing dark-field X-ray microscopy (DFXM), a fullfield imaging modality, structural signatures of the filament formation process operando are revealed in VO 2 devices. DFXM experiments illustrate that rutile filaments contain isolated monoclinic clusters, indicating structural nonuniformity interior to the filament. The formation of the rutile phase beneath device electrodes was shown to precede filament development, followed by the formation of filament paths guided by nucleation sites within the device. Finally, a medium-term (<30 min) memory mechanism is observed in VO 2 , mediated by sites within the device gap that tend to switch at significantly lower voltages after electrical cycling, a tendency that persists through a brief thermal reset. High spatial resolution, large field-of-view, structure selectivity, and fast signal acquisition of DFXM provided insight into structural features of the filamentary channel and surrounding regions during voltage cycling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

PARTIAL ERUPTION OF A FILAMENT WITH TWISTING NON-UNIFORM FIELDS

The eruption of a filament in a kinklike fashion is often regarded as a signature of kink instability. However, the kink instability threshold for the filament’s magnetic structure is not widely understood. Using Hα observations from the New Vacuum Solar Telescope, we present a partial eruptive filament. During the eruption, the filament thread appeared to split from its middle and to break out in a kinklike fashion. In this period, the remaining filament material stayed below and erupted without the kinking motion later on. The coronal magnetic field lines associated with the filament are obtained from nonlinear force-free field extrapolations using the twelve-minute-cadence vector magnetograms of the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory. We studied the extrapolated field lines passing through the magnetic dips which are in good agreement with the observed filament. The field lines are non-uniformly twisted and appear to be composed of two twisted flux ropes winding around each other. One of them has a higher twist than the other, and the flux rope with the higher twist has its dips aligned with the kinking eruptive thread at the beginning of its eruption. Before the eruption, moreover, the flux rope with the higher twist was found to expand with an approximately constant field twist. In addition, the helicity flux maps deduced from the HMI magnetograms show that some helicity is injected into the overlying magnetic arcade, but no significant helicity is injected into the flux ropes. Accordingly, we suggest that the highly twisted flux rope became kink unstable when the instability threshold declined with the expansion of the flux rope.

79 ASTRONOMY AND ASTROPHYSICS↗

SPECTROSCOPIC STUDY OF STAR-FORMING GALAXIES IN FILAMENTS AND THE FIELD AT z ∼ 0.5: EVIDENCE FOR ENVIRONMENTAL DEPENDENCE OF ELECTRON DENSITY

We study the physical properties of a spectroscopic sample of 28 star-forming galaxies in a large filamentary structure in the COSMOS field at z ∼ 0.53, with spectroscopic data taken with the Keck/DEIMOS spectrograph, and compare them with a control sample of 30 field galaxies. We spectroscopically confirm the presence of a large galaxy filament (∼8 Mpc), along which five confirmed X-ray groups exist. We show that within the uncertainties, the ionization parameter, equivalent width (EW), EW versus specific star-formation rate (sSFR) relation, EW versus stellar mass relation, line-of-sight velocity dispersion, dynamical mass, and stellar-to-dynamical mass ratio are similar for filament and field star-forming galaxies. However, we show that, on average, filament star-forming galaxies are more metal enriched (∼0.1–0.15 dex), possibly owing to the inflow of the already-enriched intrafilamentary gas into filament galaxies. Moreover, we show that electron densities are significantly lower (a factor of ∼17) in filament star-forming systems compared to those in the field, possibly because of a longer star-formation timescale for filament star-forming galaxies. Our results highlight the potential pre-processing role of galaxy filaments and intermediate-density environments on the evolution of galaxies, which has been highly underestimated.

79 ASTRONOMY AND ASTROPHYSICS↗

THE FORMATION AND MAGNETIC STRUCTURES OF ACTIVE-REGION FILAMENTS OBSERVED BY NVST, SDO, AND HINODE

To better understand the properties of solar active-region filaments, we present a detailed study on the formation and magnetic structures of two active-region filaments in active region NOAA 11884 during a period of four days. It is found that the shearing motion of the opposite magnetic polarities and the rotation of the small sunspots with negative polarity play an important role in the formation of two active-region filaments. During the formation of these two active-region filaments, one foot of the filaments was rooted in a small sunspot with negative polarity. The small sunspot rotated not only around another small sunspot with negative polarity, but also around the center of its umbra. By analyzing the nonlinear force-free field extrapolation using the vector magnetic fields in the photosphere, twisted structures were found in the two active-region filaments prior to their eruptions. These results imply that the magnetic fields were dragged by the shearing motion between opposite magnetic polarities and became more horizontal. The sunspot rotation twisted the horizontal magnetic fields and finally formed the twisted active-region filaments.

79 ASTRONOMY AND ASTROPHYSICS↗

A 3D helical filament surrogate model for 3D tokamak equilibria

A novel approach for efficient representation of three-dimensional (3D) tokamak equilibria is investigated, where a set of helical current filaments occupying the plasma region are employed to resolve deviations from the two-dimensional (2D) axi-symmetric state. A discrete set of 3D filaments, located at rational surfaces for a given toroidal mode number n and following the 2D equilibrium field lines (thus forming closed current loops), are found to provide a surrogate model of 3D equilibria with reasonable accuracy. Specifically, application of the filament model to 3D perturbed equilibria, due to the resonant magnetic perturbation (RMP) in DIII-D and MAST-U discharges, reveals that (1) a single helical filament per rational surface is sufficient; (2) 21 such helical filaments are capable of representing the n = 2 3D response field in MAST-U with less than 10% relative error as compared to that computed by a full magnetohydrodynamic code; (3) optimizing currents (both amplitude and phase) flowing in 3D filaments with fixed geometry, the highest accuracy fitting is found to depend on the characteristics of the 3D equilibria such as the coil current phasing of the RMP coils in our case studies. Here, whis filament approach is also applicable for generating surrogate models of other type of 3D tokamak equilibria, including those during the initial phase of the plasma disruption.

MARS-F↗

GALAXY SPIN ALIGNMENT IN FILAMENTS AND SHEETS: OBSERVATIONAL EVIDENCE

The properties of galaxies are known to be affected by their environment. One important question is how their angular momentum reflects the surrounding cosmic web. We use the Sloan Digital Sky Survey to investigate the spin axes of spiral and elliptical galaxies relative to their surrounding filament/sheet orientations. To detect filaments, a marked point process with interactions (the {sup B}isous model{sup )} is used. Sheets are found by detecting 'flattened' filaments. The minor axes of ellipticals are found to be preferentially perpendicular to hosting filaments. A weak correlation is found with sheets. These findings are consistent with the notion that elliptical galaxies formed via mergers, which predominantly occurred along the filaments. The spin axis of spiral galaxies is found to align with the host filament, with no correlation between spiral spin and sheet normal. When examined as a function of distance from the filament axis, a much stronger correlation is found in the outer parts, suggesting that the alignment is driven by the laminar infall of gas from sheets to filaments. When compared with numerical simulations, our results suggest that the connection between dark matter halo and galaxy spin is not straightforward. Our results provide an important input to the understanding of how galaxies acquire their angular momentum.

79 ASTRONOMY AND ASTROPHYSICS↗

TWO MASS DISTRIBUTIONS IN THE L 1641 MOLECULAR CLOUDS: THE HERSCHEL CONNECTION OF DENSE CORES AND FILAMENTS IN ORION A

We present Herschel survey maps of the L 1641 molecular clouds in Orion A. We extracted both the filaments and dense cores in the region. We identified which of the dense sources are proto- or pre-stellar, and studied their association with the identified filaments. We find that although most (71%) of the pre-stellar sources are located on filaments there, is still a significant fraction of sources not associated with such structures. We find that these two populations (on and off the identified filaments) have distinctly different mass distributions. The mass distribution of the sources on the filaments is found to peak at 4 M {sub ☉} and drives the shape of the core mass function (CMF) at higher masses, which we fit with a power law of the form dN/dlogM∝M {sup –1.4±0.4}. The mass distribution of the sources off the filaments, on the other hand, peaks at 0.8 M {sub ☉} and leads to a flattening of the CMF at masses lower than ∼4 M {sub ☉}. We postulate that this difference between the mass distributions is due to the higher proportion of gas that is available in the filaments, rather than in the diffuse cloud.

79 ASTRONOMY AND ASTROPHYSICS↗

NONLINEAR FORCE-FREE FIELD EXTRAPOLATION OF A CORONAL MAGNETIC FLUX ROPE SUPPORTING A LARGE-SCALE SOLAR FILAMENT FROM A PHOTOSPHERIC VECTOR MAGNETOGRAM

Solar filaments are commonly thought to be supported in magnetic dips, in particular, in those of magnetic flux ropes (FRs). In this Letter, based on the observed photospheric vector magnetogram, we implement a nonlinear force-free field (NLFFF) extrapolation of a coronal magnetic FR that supports a large-scale intermediate filament between an active region and a weak polarity region. This result is a first, in the sense that current NLFFF extrapolations including the presence of FRs are limited to relatively small-scale filaments that are close to sunspots and along main polarity inversion lines (PILs) with strong transverse field and magnetic shear, and the existence of an FR is usually predictable. In contrast, the present filament lies along the weak-field region (photospheric field strength ≲ 100 G), where the PIL is very fragmented due to small parasitic polarities on both sides of the PIL and the transverse field has a low signal-to-noise ratio. Thus, extrapolating a large-scale FR in such a case represents a far more difficult challenge. We demonstrate that our CESE-MHD-NLFFF code is sufficient for the challenge. The numerically reproduced magnetic dips of the extrapolated FR match observations of the filament and its barbs very well, which strongly supports the FR-dip model for filaments. The filament is stably sustained because the FR is weakly twisted and strongly confined by the overlying closed arcades.

79 ASTRONOMY AND ASTROPHYSICS↗

A CIRCULAR-RIBBON SOLAR FLARE FOLLOWING AN ASYMMETRIC FILAMENT ERUPTION

The dynamic properties of flare ribbons and the often associated filament eruptions can provide crucial information on the flaring coronal magnetic field. This Letter analyzes the GOES-class X1.0 flare on 2014 March 29 (SOL2014-03-29T17:48), in which we found an asymmetric eruption of a sigmoidal filament and an ensuing circular flare ribbon. Initially both EUV images and a preflare nonlinear force-free field model show that the filament is embedded in magnetic fields with a fan-spine-like structure. In the first phase, which is defined by a weak but still increasing X-ray emission, the western portion of the sigmoidal filament arches upward and then remains quasi-static for about five minutes. The western fan-like and the outer spine-like fields display an ascending motion, and several associated ribbons begin to brighten. Also found is a bright EUV flow that streams down along the eastern fan-like field. In the second phase that includes the main peak of hard X-ray (HXR) emission, the filament erupts, leaving behind two major HXR sources formed around its central dip portion and a circular ribbon brightened sequentially. The expanding western fan-like field interacts intensively with the outer spine-like field, as clearly seen in running difference EUV images. We discuss these observations in favor of a scenario where the asymmetric eruption of the sigmoidal filament is initiated due to an MHD instability and further facilitated by reconnection at a quasi-null in corona; the latter is in turn enhanced by the filament eruption and subsequently produces the circular flare ribbon.

79 ASTRONOMY AND ASTROPHYSICS↗

Characterization of thin film deposits on tungsten filaments in catalytic chemical vapor deposition using 1,1-dimethylsilacyclobutane

Metal filament plays a key role in the technique of catalytic chemical vapor deposition (Cat-CVD) as it serves as a catalyst in dissociating the source gas to form reactive species. These reactive species initiate the gas-phase reaction chemistry and final thin film and nanostructure formation. At the same time, they also react with the metal itself, leading to the formation of metal alloys and other deposits. The deposits on the tungsten filaments when exposed to 1,1-dimethylsilacyclobutane (DMSCB), a single-source precursor for silicon carbide thin films, in the process of Cat-CVD were studied in this work. It has been demonstrated that a rich variety of deposits, including tungsten carbides (W{sub 2}C and WC), tungsten silicide (W{sub 5}Si{sub 3}), silicon carbide, amorphous carbon, and graphite, form on the W filament surfaces. The structural and morphological changes in the tungsten filaments depend strongly on the DMSCB pressure and filament temperature. At 1000 and 2000 °C, the formation of WC and W{sub 2}C dominates. In addition, a thin amorphous carbon layer has been found at 1500 °C with the 0.12 and 0.24 Torr of DMSCB and a lower temperature of 1200 °C with the 0.48 Torr of DMSCB. An increase in the DMSCB sample pressure gives rise to higher Si and C contents. As a result, the formation of SiC and W{sub 5}Si{sub 3} has been observed with the two high-pressure DMSCB samples (i.e., 0.24 and 0.48 Torr). The rich decomposition chemistry of DMSCB on the W surfaces is responsible for the extensive changes in the structure of the W filament, providing support for the close relationship between the gas-phase decomposition chemistry and the nature of alloy formation on the metal surface. The understanding of the structural changes obtained from this work will help guide the development of efficient methods to solve the filament aging problem in Cat-CVD and also to achieve a controllable deposition process.

36 MATERIALS SCIENCE↗

How Clonal Is Clonal? Genome Plasticity across Multicellular Segments of a “Candidatus Marithrix sp.” Filament from Sulfidic, Briny Seafloor Sediments in the Gulf of Mexico

“Candidatus Marithrix” is a recently described lineage within the group of large sulfur bacteria (Beggiatoaceae, Gammaproteobacteria). This genus of bacteria comprises vacuolated, attached-living filaments that inhabit the sediment surface around vent and seep sites in the marine environment. A single filament is ca. 100 µm in diameter, several millimeters long, and consists of hundreds of clonal cells, which are considered highly polyploid. Based on these characteristics, “Candidatus Marithrix” was used as a model organism for the assessment of genomic plasticity along segments of a single filament using next generation sequencing to possibly identify hotspots of microevolution. Using six consecutive segments of a single filament sampled from a mud volcano in the Gulf of Mexico, we recovered ca. 90% of the “Candidatus Marithrix” genome in each segment. There was a high level of genome conservation along the filament with average nucleotide identities between 99.98 and 100%. Different approaches to assemble all reads into a complete consensus genome could not fill the gaps. Each of the six segment datasets encoded merely a few hundred unique nucleotides and 5 or less unique genes—the residual content was redundant in all datasets. Besides the overall high genomic identity, we identified a similar number of single nucleotide polymorphisms (SNPs) between the clonal segments, which are comparable to numbers reported for other clonal organisms. An increase of SNPs with greater distance of filament segments was not observed. The polyploidy of the cells was apparent when analyzing the heterogeneity of reads within a segment. Here, a strong increase in single nucleotide variants, or “intrasegmental sequence heterogeneity” (ISH) events, was observed. These sites may represent hotspots for genome plasticity, and possibly microevolution, since two thirds of these variants were not co-localized across the genome copies of the multicellular filament.

59 BASIC BIOLOGICAL SCIENCES↗

Tracing Actin Filament Bundles in Three-Dimensional Electron Tomography Density Maps of Hair Cell Stereocilia

Cryo-electron tomography (cryo-ET) is a powerful method of visualizing the three-dimensional organization of supramolecular complexes, such as the cytoskeleton, in their native cell and tissue contexts. Due to its minimal electron dose and reconstruction artifacts arising from the missing wedge during data collection, cryo-ET typically results in noisy density maps that display anisotropic XY versus Z resolution. Molecular crowding further exacerbates the challenge of automatically detecting supramolecular complexes, such as the actin bundle in hair cell stereocilia. Stereocilia are pivotal to the mechanoelectrical transduction process in inner ear sensory epithelial hair cells. Given the complexity and dense arrangement of actin bundles, traditional approaches to filament detection and tracing have failed in these cases. In this study, we introduce BundleTrac, an effective method to trace hundreds of filaments in a bundle. A comparison between BundleTrac and manually tracing the actin filaments in a stereocilium showed that BundleTrac accurately built 326 of 330 filaments (98.8%), with an overall cross-distance of 1.3 voxels for the 330 filaments. BundleTrac is an effective semi-automatic modeling approach in which a seed point is provided for each filament and the rest of the filament is computationally identified. We also demonstrate the potential of a denoising method that uses a polynomial regression to address the resolution and high-noise anisotropic environment of the density map.

stereocilia↗