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1
Moraczewska, Joanna. "Filamenty cienkie i mikrofilamenty – funkcjonalne kompleksy aktyny z tropomiozyną." Kosmos 67, no. 1 (July 10, 2018): 31–41. http://dx.doi.org/10.36921/kos.2018_2366.
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Aktyna jest uniwersalnym białkiem o strukturze dobrze zachowanej w toku ewolucji. W komórkach aktyna istnieje w równowadze pomiędzy formą monomeryczną i filamentową. Pomimo zachowanej w toku ewolucji struktury, aktyna pełni zdumiewająco wiele różnorodnych funkcji. Jest to możliwe dzięki zdolności aktyny do oddziaływania z wieloma białkami, wśród których znajdują się motory miozynowe oraz białka regulujące dynamiczną polimeryzację i depolimeryzację aktyny. Nadrzędnymi regulatorami filamentów aktynowych są tropomiozyny, rodzina superhelikalnych białek, które polimeryzują wzdłuż filamentowej aktyny, dzięki czemu stabilizują filamenty zapobiegając ich depolimeryzacji oraz kontrolują dostęp i aktywność białek wiążących aktynę. Tropomiozyny działają jako „stróże” filamentu, którzy kontrolują oddziaływania aktyny, co prowadzi do segregacji białek wiążących aktynę do swoistych przedziałów komórkowych gdzie białka te realizują określone funkcje komórkowe. W artykule zostały omówione zależne od tropomiozyny mechanizmy regulacji oddziaływań aktyny z niektórymi miozynami oraz z Arp2/3 i kofiliną – białkami, które inicjują rozgałęzianie, polimeryzację i depolimeryzację filamentów aktynowych.
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Alina, D., I. Ristorcelli, L. Montier, and M. Juvela. "Statistics on the relative orientation between magnetic fields and filaments hosting Planck Galactic Cold Clumps." Proceedings of the International Astronomical Union 14, A30 (August 2018): 104. http://dx.doi.org/10.1017/s1743921319003594.
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AbstractWe present a statistical analysis of the relative orientation between the plane-of-sky magnetic field and the filaments associated with the Galactic Cold Clumps. We separated polarization parameters components of the filaments and their background using thin optical medium assumption, the filaments were detected using the Rolling Hough Transform algorithm and we separated the clump and the filament contributions in our maps. We found that in high column density environments the magnetic fields inside the filaments and in the background are less likely to be aligned with each other. This suggests a decoupling between the inner and background magnetic fields at some stage of filaments’ evolution. A preferential alignment between the filaments and their inferred magnetic fields is observed in the whole selection if the clumps’ contribution is subtracted. Interestingly, a bimodal distribution of relative orientation is observed between the filamentary structures of the clumps and the filaments’ magnetic field. Similar results are seen in a subsample of nearby filaments. The relative orientation clearly shows a transition from parallel to no preferential and perpendicular alignment depending on the volume densities of both clumps and filaments. Our results confirm a strong interplay between the magnetic field and filamentary structures during their formation and evolutionary process.
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Hoemann, Elena, Stefan Heigl, and Andreas Burkert. "Merging filaments I: a race against collapse." Monthly Notices of the Royal Astronomical Society 507, no. 3 (June 14, 2021): 3486–94. http://dx.doi.org/10.1093/mnras/stab1698.
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ABSTRACT The interstellar medium is characterized by an intricate filamentary network that exhibits complex structures. These show a variety of different shapes (e.g. junctions, rings, etc.) deviating strongly from the usually assumed cylindrical shape. A possible formation mechanism are filament mergers that we analyse in this study. Indeed, the proximity of filaments in networks suggests mergers to be rather likely. As the merger has to be faster than the end dominated collapse of the filament along its major axis, we expect three possible results: (a) The filaments collapse before a merger can happen, (b) the merged filamentary complex shows already signs of cores at the edges, or (c) the filaments merge into a structure which is not end-dominated. We develop an analytic formula for the merging and core-formation time-scale at the edge and validate our model via hydrodynamical simulations with the adaptive-mesh-refinement-code ramses. This allows us to predict the outcome of a filament merger, given different initial conditions which are the initial distance and the respective line-masses of each filament as well as their relative velocities.
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Arzoumanian, D., Ph André, V. Könyves, P. Palmeirim, A. Roy, N. Schneider, M. Benedettini, et al. "Characterizing the properties of nearby molecular filaments observed with Herschel." Astronomy & Astrophysics 621 (January 2019): A42. http://dx.doi.org/10.1051/0004-6361/201832725.
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Context. Molecular filaments have received special attention recently thanks to new observational results on their properties. In particular, our early analysis of filament properties from Herschel imaging data in three nearby molecular clouds revealed a narrow distribution of median inner widths centered at a characteristic value of about 0.1 pc. Aims. Here, we extend and complement our initial study with a detailed analysis of the filamentary structures identified with Herschel in eight nearby molecular clouds (at distances <500 pc). Our main goal is to establish statistical distributions of median properties averaged along the filament crests and to compare the results with our earlier work based on a smaller number of filaments. Aims. We use the column density (NH2) maps derived from Herschel data and the DisPerSE algorithm to trace a network of individual filaments in each cloud. We analyze the density structure along and across the main filament axes in detail. We build synthetic maps of filamentary clouds to assess the completeness limit of our extracted filament sample and validate our measurements of the filament properties. These tests also help us to select the best choice of parameters to be used for tracing filaments with DisPerSE and fitting their radial column density profiles. Methods. Our analysis yields an extended sample of 1310 filamentary structures and a selected sample of 599 filaments with aspect ratios larger than 3 and column density contrasts larger than 0.3. We show that our selected sample of filaments is more than 95% complete for column density contrasts larger than 1, with only ~ 5% spurious detections. On average, more than 15% of the total gas mass in the clouds, and more than 80% of the dense gas mass (at NH2 > 7 × 1021 cm−2), is found to be in the form of filaments. Analysis of the radial column density profiles of the 599 filaments in the selected sample indicates a narrow distribution of crest-averaged inner widths, with a median value of 0.10 pc and an interquartile range of 0.07 pc. In contrast, the extracted filaments span wide ranges in length, central column density, column density contrast, and mass per unit length. The characteristic filament width is well resolved by Herschel observations, and a median value of ~0.1 pc is consistently found using three distinct estimates based on (1) a direct measurement of the width at half power after background subtraction, as well as (2) Gaussian and (3) Plummer fits. The existence of a characteristic filament width is further supported by the presence of a tight correlation between mass per unit length and central column density for the observed filaments. Results. Our detailed analysis of a large filament sample confirms our earlier result that nearby molecular filaments share a common mean inner width of ~0.1 pc, with typical variations along and on either side of the filament crests of about ± 0.06 pc around the mean value. This observational result sets strong constraints on possible models for the formation and evolution of filaments in molecular clouds. It also provides important hints on the initial conditions of star formation.
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Goldsmith, K. J. A., and J. M. Pittard. "The isothermal evolution of a shock-filament interaction." Monthly Notices of the Royal Astronomical Society 491, no. 4 (December 4, 2019): 4783–801. http://dx.doi.org/10.1093/mnras/stz3320.
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ABSTRACT Studies of filamentary structures that are prevalent throughout the interstellar medium are of great significance to a number of astrophysical fields. Here, we present 3D hydrodynamic simulations of shock-filament interactions where the equation of state has been softened to become almost isothermal. We investigate the effect of such an isothermal regime on the interaction (where both the shock and filament are isothermal), and we examine how the nature of the interaction changes when the orientation of the filament, the shock Mach number, and the filament density contrast are varied. We find that only sideways-oriented filaments with a density contrast of 102 form a three-rolled structure, dissimilar to the results of a previous study. Moreover, the angle of orientation of the filament plays a large role in the evolution of the filament morphology: the greater the angle of orientation, the longer and less turbulent the wake. Turbulent stripping of filament material leading to fragmentation of the core occurs in most filaments; however, filaments orientated at an angle of 85° to the shock front do not fragment and are longer lived. In addition, values of the drag time are influenced by the filament length, with longer filaments being accelerated faster than shorter ones. Furthermore, filaments in an isothermal regime exhibit faster acceleration than those struck by an adiabatic shock. Finally, we find that the drag and mixing times of the filament increase as the angle of orientation of the filament is increased.
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Буланин, В. В., В. К. Гусев, Г. С. Курскиев, В. Б. Минаев, М. И. Патров, А. В. Петров, Ю. В. Петров, et al. "Влияние низкочастотных магнитогидродинамических мод на развитие филаментов в токамаке Глобус-М." Письма в журнал технической физики 45, no. 19 (2019): 21. http://dx.doi.org/10.21883/pjtf.2019.19.48312.17933.
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Experimental data indicating the influence of the magnetohydrodynamic tearing mode in the Globus-M spherical tokamak on the appearance of filamentary structures (filaments) are presented. The filaments were detected by the Doppler backscattering method. Filament groups localized in the toroidal direction were detected, the appearance of which turned out to be synchronized with the spreading of the tearing mode. The possible causes of the influence of low-frequency MHD oscillations on the occurrence of groups of filamentary perturbations are considered.
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Muru, Moorits Mihkel, and Elmo Tempel. "Assessing the reliability of the Bisous filament finder." Astronomy & Astrophysics 649 (May 2021): A108. http://dx.doi.org/10.1051/0004-6361/202039169.
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Context. Recent years have given rise to numerous methods of detecting the cosmic web elements in the large-scale structure of the Universe. All of these methods describe more or less the same features, but each with its nuance. The Bisous filament finder is a stochastic tool for identifying the spines of filaments using galaxy positions. Aims. This work provides an analysis of how the galaxy number density of the input data affects the filaments detected with the Bisous model and gives estimates of the reliability of the method itself to assess the robustness of the results. Methods. We applied the Bisous filament finder to MultiDark-Galaxies data, using various magnitude cuts from the catalogue to study the effects of different galaxy number densities on the results and different parameters of the model. We compared the structures by the fraction of galaxies in filaments and the volume filled by filaments, and we analysed the similarities between the results from different cuts based on the overlap between detected filamentary structures. The filament finder was also applied to the exact same data 200 times with the same parameters to study the stochasticity of the results and the correlation between different runs was calculated. Results. Multiple samples show that galaxies in filaments have preferentially higher luminosity. We found that when a galaxy is in a filament there is a 97% chance that the same galaxy would be in a filament with even more complete input data and about 85% of filaments are persistent when detecting the filamentary network with higher-density input data. Lower galaxy number density inputs mean the Bisous model finds fewer filaments, but the filaments found are persistent even if we use more complete input data for the detection. We calculated the correlation coefficient between 200 Bisous runs on the exact same input, which is 0.98. Conclusions. This study confirms that increased number density of galaxies is important to obtain a more complete picture of the cosmic web. To overcome the limitation of the spectroscopic surveys, we will develop the Bisous model further to apply this tool to combined spectroscopic and narrow-band photometric redshift surveys, such as the J-PAS.
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Xia, Qianli, Mark C. Neyrinck, Yan-Chuan Cai, and Miguel A. Aragón-Calvo. "Intergalactic filaments spin." Monthly Notices of the Royal Astronomical Society 506, no. 1 (July 13, 2021): 1059–72. http://dx.doi.org/10.1093/mnras/stab1713.
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ABSTRACT Matter in the Universe is arranged in a cosmic web, with a filament of matter typically connecting each neighbouring galaxy pair, separated by tens of millions of light-years. A quadrupolar pattern of the spin field around filaments is known to influence the spins of galaxies and haloes near them, but it remains unknown whether filaments themselves spin. Here, we measure dark matter velocities around filaments in cosmological simulations, finding that matter generally rotates around them, much faster than around a randomly located axis. It also exhibits some coherence along the filament. The net rotational component is comparable to, and often dominant over, the known quadrupolar flow. The evidence of net rotations revises previous emphasis on a quadrupolar spin field around filaments. The full picture of rotation in the cosmic web is more complicated and multiscale than a network of spinning filamentary rods, but we argue that filament rotation is substantial enough to be an essential part of the picture. It is likely that the longest coherently rotating objects in the Universe are filaments. Also, we speculate that this rotation could provide a mechanism to generate or amplify intergalactic magnetic fields in filaments.
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Uehara, Kenta, Masato Tsuboi, Yoshimi Kitamura, Ryosuke Miyawaki, and Atsushi Miyazaki. "ALMA view of the Galactic Center 50km/s molecular cloud." Proceedings of the International Astronomical Union 11, S322 (July 2016): 162–63. http://dx.doi.org/10.1017/s1743921316011984.
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AbstractWe have observed the Galactic Center 50km/s molecular cloud (50MC) with ALMA to search for filamentary structures. In the CS J=2-1 emission line channel maps, we succeeded in identifying 27 molecular cloud filaments using the DisPerSE algorithm. This is the first attempt of filament-finding in the Galactic Center Region. These molecular cloud filaments strongly suggest that the molecular cloud filaments are also ubiquitous in the molecular clouds of the Galactic Center Region.
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Rędowicz, Maria Jolanta. "Modyfikacje potranslacyjne aktyny." Kosmos 67, no. 1 (July 10, 2018): 43–55. http://dx.doi.org/10.36921/kos.2018_2367.
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Aktyna, komponent cytoszkieletu komórek eukariotycznych, to jedno z białek najistotniejszych dla funkcjonowania organizmów i najlepiej zachowanych w toku ewolucji. Ta globularna cząsteczka o masie cząsteczkowej około 42,3 kDa występuje zarówno w formie monomerycznej, jak i spolimeryzowanej (filamenty), a zdolność do dynamicznej reorganizacji aktyny jest niezbędna dla życia komórki. Przejście pomiędzy obiema formami jest możliwe dzięki precyzyjnej w czasie i przestrzeni, dynamicznej regulacji organizacji aktyny przez szereg białek wiążących się zarówno z monomerami, jak i filamentami aktyny. Istotnym czynnikiem wpływającym na stopień spolimeryzowania aktyny są także liczne modyfikacje potranslacyjne tego białka. Niniejszy artykuł przeglądowy jest poświęcony omówieniu tego obszernego i wciąż mało poznanego zagadnienia, a w szczególności opisowi jakim modyfikacjom ulega aktyna i w jaki sposób modyfikacje te wpływają na strukturę i funkcje tego wyjątkowego białka.
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Kuchner, Ulrike, Alfonso Aragón-Salamanca, Frazer R. Pearce, Meghan E. Gray, Agustín Rost, Chunliang Mu, Charlotte Welker, et al. "Mapping and characterization of cosmic filaments in galaxy cluster outskirts: strategies and forecasts for observations from simulations." Monthly Notices of the Royal Astronomical Society 494, no. 4 (April 23, 2020): 5473–91. http://dx.doi.org/10.1093/mnras/staa1083.
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ABSTRACT Upcoming wide-field surveys are well suited to studying the growth of galaxy clusters by tracing galaxy and gas accretion along cosmic filaments. We use hydrodynamic simulations of volumes surrounding 324 clusters from The ThreeHundred project to develop a framework for identifying and characterizing these filamentary structures and associating galaxies with them. We define three-dimensional reference filament networks reaching 5R200 based on the underlying gas distribution and quantify their recovery using mock galaxy samples mimicking observations such as those of the WEAVE Wide-Field Cluster Survey. Since massive galaxies trace filaments, they are best recovered by mass-weighting galaxies or imposing a bright limit (e.g. >L*) on their selection. We measure the transverse gas density profile of filaments, derive a characteristic filament radius of ≃ 0.7–1 h−1Mpc, and use this to assign galaxies to filaments. For different filament extraction methods, we find that at R > R200, ∼15–$20{{\ \rm per\ cent}}$ of galaxies with M* > 3 × 109M⊙ are in filaments, increasing to $\sim 60{{\ \rm per\ cent}}$ for galaxies more massive than the Milky Way. The fraction of galaxies in filaments is independent of cluster mass and dynamical state and is a function of cluster-centric distance, increasing from ∼13 per cent at 5R200 to ∼21 per cent at 1.5R200. As a bridge to the design of observational studies, we measure the purity and completeness of different filament galaxy selection strategies. Encouragingly, the overall three-dimensional filament networks and ∼67 per cent of the galaxies associated with them are recovered from two-dimensional galaxy positions.
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Ossenkopf-Okada, V., and R. Stepanov. "Measuring the filamentary structure of interstellar clouds through wavelets." Astronomy & Astrophysics 621 (December 19, 2018): A5. http://dx.doi.org/10.1051/0004-6361/201731596.
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Context. The ubiquitous presence of filamentary structures in the interstellar medium asks for an unbiased characterization of their properties including a stability analysis. Aims. We propose a novel technique to measure the spectrum of filaments in any two-dimensional data set. By comparing the power in isotropic and anisotropic structures we can measure the relative importance of spherical and cylindrical collapse modes. Methods. Using anisotropic wavelets we can quantify and distinguish local and global anisotropies and measure the size distribution of filaments. The wavelet analysis does not require any assumptions on the alignment or shape of filaments in the maps, but directly measures their typical spatial dimensions. In a rigorous test program, we calibrate the scale dependence of the method and test the angular and spatial sensitivity. We apply the method to molecular line maps from magneto-hydrodynamic (MHD) simulations and observed column-density maps from Herschel observations. Results. When applying the anisotropic wavelet analysis to the MHD data, we find that the observed filament sizes depend on the combination of magnetic-field-dominated density–velocity correlations and radiative transfer effects. This can be exploited by observing tracers with different optical depth to measure the transition from a globally ordered large-scale structure to small-scale filaments with entangled field lines. The unbiased view to Herschel column-density maps does not confirm a universal characteristic filament width. The map of the Polaris Flare shows an almost scale-free filamentary spectrum up to the size of the dominating filament of about 0.4 pc. For the Aquila molecular cloud the range of filament widths is limited to 0.05–0.2 pc. The filaments in Polaris show no preferential direction in contrast to the global alignment that we trace in Aquila. Conclusions. By comparing the power in isotropic and anisotropic structures we can measure the relative importance of spherical and cylindrical collapse modes and their spatial distribution.
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Lee, K. H., and S. I. Hong. "Interfacial and twin boundary structures of nanostructured Cu–Ag filamentary composites." Journal of Materials Research 18, no. 9 (September 2003): 2194–202. http://dx.doi.org/10.1557/jmr.2003.0306.
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A high-resolution transmission electron microscope was used to study the interfacial and twin boundary structure of nanostructured Cu–Ag filamentary composites. Copper matrix and silver filaments have the orientation relationship {111}Cu∥{111}Ag and 〈111〉Cu∥〈111〉Ag. In some regions, twin bands propagated through the silver filaments with some boundary steps at the matrix/filament interface, and the silver filament appeared to be kinked in the twin band in the same direction as the twinning shear. This suggests that twins propagated after the formation of silver filament, and twin bands were deformation twins. At the matrix/filament interface, misfit interface dislocations were introduced periodically to relieve the misfit strain. The distance between interfacial misfit dislocations along the matrix/filament interface in the longitudinal section was measured to be 1.88 nm, which is in good agreement with that (1.81 nm) calculated based on lattice misfit. In Cu–Ag nanocomposites, the spacing between Moire fringes was found to be quite close to that between interfacial misfit dislocations.
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Chen, Yen-Chi, Shirley Ho, Jonathan Blazek, Siyu He, Rachel Mandelbaum, Peter Melchior, and Sukhdeep Singh. "Detecting galaxy–filament alignments in the Sloan Digital Sky Survey III." Monthly Notices of the Royal Astronomical Society 485, no. 2 (February 26, 2019): 2492–504. http://dx.doi.org/10.1093/mnras/stz539.
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Abstract Previous studies have shown the filamentary structures in the cosmic web influence the alignments of nearby galaxies. We study this effect in the LOWZ sample of the Sloan Digital Sky Survey using the ‘Cosmic Web Reconstruction' filament catalogue. We find that LOWZ galaxies exhibit a small but statistically significant alignment in the direction parallel to the orientation of nearby filaments. This effect is detectable even in the absence of nearby galaxy clusters, which suggests it is an effect from the matter distribution in the filament. A non-parametric regression model suggests that the alignment effect with filaments extends over separations of 30–40 Mpc. We find that galaxies that are bright and early-forming align more strongly with the directions of nearby filaments than those that are faint and late-forming; however, trends with stellar mass are less statistically significant, within the narrow range of stellar mass of this sample.
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Hacar, Alvaro, Mario Tafalla, Jan Forbrich, and Josefa Grossschedl. "ALMA observations of the Orion Integral Filament: evidence for fibers in a massive cloud." Proceedings of the International Astronomical Union 14, S345 (August 2018): 51–55. http://dx.doi.org/10.1017/s1743921319002102.
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AbstractThe connection between low- and high-mass filaments is a matter of strong debate. In order to bridge these two filamentary regimes, we have investigated the internal structure of the Integral Filament in Orion using ALMA observations of the N2H+ (1-0) emission line in Band 3 in combination with previous single-dish data. Our ALMA mosaics, the largest of its kind carried out so-far in local clouds, reveal the presence of multiple sonic-like fibers inside this massive filament. In combination with the identification of fibers in regions such as Taurus, Musca, and Perseus, the first unambiguous detection of fibers in Orion highlights the importance of these gas substructures as the fundamental building blocks of both low- and high-mass filaments.
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Gong, Y., G. X. Li, R. Q. Mao, C. Henkel, K. M. Menten, M. Fang, M. Wang, and J. X. Sun. "The Serpens filament at the onset of slightly supercritical collapse." Astronomy & Astrophysics 620 (November 28, 2018): A62. http://dx.doi.org/10.1051/0004-6361/201833583.
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The Serpens filament, as one of the nearest infrared dark clouds, is regarded as a pristine filament at a very early evolutionary stage of star formation. In order to study its molecular content and dynamical state, we mapped this filament in seven species: C18O, HCO+, HNC, HCN, N2H+, CS, and CH3OH. Among them, HCO+, HNC, HCN, and CS show self-absorption, while C18O is most sensitive to the filamentary structure. A kinematic analysis demonstrates that this filament forms a velocity-coherent (trans)sonic structure, a large part of which is one of the most quiescent regions in the Serpens cloud. Widespread C18O depletion is found throughout the Serpens filament. Based on the Herschel dust-derived H2 column density map, the line mass of the filament is 36–41 M⊙ pc−1, and its full width at half maximum is 0.17 ± 0.01 pc, while its length is ≈1.6 pc. The inner radial column density profile of this filament can be well fitted with a Plummer profile with an exponent of 2.2 ± 0.1, a scale radius of 0.018 ± 0.003 pc, and a central density of (4.0 ± 0.8) × 104 cm−3. The Serpens filament appears to be slightly supercritical. The widespread blue-skewed HNC and CS line profiles and HCN hyperfine line anomalies across this filament indicate radial infall in parts of the Serpens filament. C18O velocity gradients also indicate accretion flows along the filament. The velocity and density structures suggest that such accretion flows are likely due to a longitudinal collapse parallel to the filament’s long axis. Both the radial infall rate (~72 M⊙ Myr−1, inferred from HNC and CS blue-skewed profiles) and the longitudinal accretion rate (~10 M⊙ Myr−1, inferred from C18O velocity gradients) along the Serpens filament are lower than all previously reported values in other filaments. This indicates that the Serpens filament lies at an early evolutionary stage when collapse has just begun, or that thermal and nonthermal support are effective in providing support against gravity.
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Pereyra, Luis A., Mario A. Sgró, Manuel E. Merchán, Federico A. Stasyszyn, and Dante J. Paz. "Detection and analysis of cluster–cluster filaments." Monthly Notices of the Royal Astronomical Society 499, no. 4 (October 10, 2020): 4876–86. http://dx.doi.org/10.1093/mnras/staa3112.
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ABSTRACT In this work, we identify and analyse the properties of cluster–cluster filaments within a cosmological simulation assuming that they are structures connecting maxima of the density field defined by dark matter haloes with masses $M \, \ge 10^{14}\, h^{-1} \, \mathrm{M_{\odot }}$. To extract these filaments we develop an identification algorithm based on two standard tools: the Minimal Spanning Tree and the friends-of-friends algorithm. Focusing our analysis on the densest dark matter filaments, we found that the radial density profile, at scales around $1\, h^{-1} \, \mathrm{Mpc}$, approximately follow a power-law function with index −2. Without making any assumption about the velocity field, our algorithm finds that the saddle point arises as a natural characteristic of the filamentary structure. In addition, its location along the filament depends on the masses of the haloes at the filament ends. We also found that the infall velocities follow a cross-pattern near the saddle point, being perpendicular to the filament spine when approaching from low-density regions, and parallel away from the saddle point towards the ends of the filament. Following theoretical prescriptions, we estimate the linear density from the transverse velocity dispersion, finding a good correspondence with the measured mass per unit length of our filaments. Our results can be applied to observational samples of filaments in order to link the saddle point location and the mass per unit length with measurements obtained from observations such as cluster masses and the velocity dispersion of galaxies.
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Chen, Che-Yu, Lee G. Mundy, Eve C. Ostriker, Shaye Storm, and Arnab Dhabal. "Self-gravitating filament formation from shocked flows: velocity gradients across filaments." Monthly Notices of the Royal Astronomical Society 494, no. 3 (April 10, 2020): 3675–85. http://dx.doi.org/10.1093/mnras/staa960.
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ABSTRACT In typical environments of star-forming clouds, converging supersonic turbulence generates shock-compressed regions, and can create strongly magnetized sheet-like layers. Numerical magnetohydrodynamic simulations show that within these post-shock layers, dense filaments and embedded self-gravitating cores form via gathering material along the magnetic field lines. As a result of the preferred-direction mass collection, a velocity gradient perpendicular to the filament major axis is a common feature seen in simulations. We show that this prediction is in good agreement with recent observations from the CARMA Large Area Star Formation Survey (CLASSy), from which we identified several filaments with prominent velocity gradients perpendicular to their major axes. Highlighting a filament from the north-west part of Serpens South, we provide both qualitative and quantitative comparisons between simulation results and observational data. In particular, we show that the dimensionless ratio Cv ≡ Δvh2/(GM/L), where Δvh is half of the observed perpendicular velocity difference across a filament, and M/L is the filament’s mass per unit length, can distinguish between filaments formed purely due to turbulent compression and those formed due to gravity-induced accretion. We conclude that the perpendicular velocity gradient observed in the Serpens South north-west filament can be caused by gravity-induced anisotropic accretion of material from a flattened layer. Using synthetic observations of our simulated filaments, we also propose that a density-selection effect may explain observed subfilaments (one filament breaking into two components in velocity space) as reported in recent observations.
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Hong, Sun Ig. "Effect of Nb content on the strength of Cu–Nb filamentary microcomposites." Journal of Materials Research 15, no. 9 (September 2000): 1889–93. http://dx.doi.org/10.1557/jmr.2000.0274.
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The yield strength of Cu–Nb filamentary microcomposites was predicted as a function of Nb content by modifying the barrier strengthening model. To predict the variation of the yield strength with Nb content, the interfilamentary spacing was calculated as a function of Nb content on the basis of the assumption that Nb filaments are distributed regularly along the sides of triangular unit cells. The yield stress can be described as the sum of the substructural strengthening component and the filament boundary strengthening term. The good agreement between the prediction and the experimental data suggests that the strength increase in Cu–Nb filamentary microcomposites with increasing Nb content results mostly from increasing the volume fraction of Nb filaments, which act as barriers to plastic flow.
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Fard, Mohammad Ansari, Sina Taamoli, and Shant Baghram. "Cosmological filaments in the light of excursion set of saddle points." Monthly Notices of the Royal Astronomical Society 489, no. 1 (August 9, 2019): 900–909. http://dx.doi.org/10.1093/mnras/stz2210.
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ABSTRACT The universe in large scales is structured as a network known as cosmic web. Filaments are one of the structural components of this web, which can be introduced as a novel probe to study the formation and evolution of structures and as a probe to study the cosmological models and to address the missing baryon problem. The aim of this work is to introduce an analytical framework to study the statistics of filaments such as number density of them and also to obtain the length-mass relation. For this objective, we model filaments as collapsed objects which have an extension in one direction, accordingly we use the ellipsoidal collapse to study the evolution of an over-dense region via gravitational instability. We find that the non-linear density of filaments in the epoch of formation is almost mass independent and is in order of ∼30. By introducing filament’s extended condition, we find a fitting function for length-mass relation. For the statistics of filaments, we propose a novel framework named excursion set of saddle points. In this approach, we count the saddle points of the density field Hessian matrix, and relate it to the count of filaments. In addition, we addressed the filament in filament problem with up-crossing approximation.
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Sundin, L., G. E. Nilsson, M. Block, and C. O. Lofman. "Control of gill filament blood flow by serotonin in the rainbow trout, Oncorhynchus mykiss." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 268, no. 5 (May 1, 1995): R1224—R1229. http://dx.doi.org/10.1152/ajpregu.1995.268.5.r1224.
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The effects of exogenously applied serotonin [5-hydroxytryptamine (5-HT)] on the distal arterial vasculature of gill filaments were observed using an epi-illumination microscope equipped with a water-immersion objective and connected to a video camera. In addition, ventral aortic flow (Q) and celiac artery pressure (PCA) were measured. Intra-arterial injection of serotonin (100 nmol/kg) completely stopped the blood flow in the distal part of the filaments and caused a rapid decrease of PCA. Repeatedly, the flow reduction was found to coincide with a constriction of the distal portion of the efferent filamental vasculature. Because there was no concomitant reduction in Q, it is concluded that a redistribution of blood to more proximal parts of the filaments occurred. After treatment with the serotonergic receptor antagonist methysergide, the vasoconstrictor effect of serotonin on the filamental vasculature was eliminated, while a decrease in PCA was still observed. The results demonstrate a specific site(s) for the serotonergic vasoconstriction in the distal portion of the filament.
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Pratt, Zachary L., Bingming Chen, Charles J. Czuprynski, Amy C. L. Wong, and Charles W. Kaspar. "Characterization of Osmotically Induced Filaments of Salmonella enterica." Applied and Environmental Microbiology 78, no. 18 (July 13, 2012): 6704–13. http://dx.doi.org/10.1128/aem.01784-12.
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ABSTRACTSalmonella entericaforms aseptate filaments with multiple nucleoids when cultured in hyperosmotic conditions. These osmotic-induced filaments are viable and form single colonies on agar plates even though they contain multiple genomes and have the potential to divide into multiple daughter cells. Introducing filaments that are formed during osmotic stress into culture conditions without additional humectants results in the formation of septa and their division into individual cells, which could present challenges to retrospective analyses of infectious dose and risk assessments. We sought to characterize the underlying mechanisms of osmotic-induced filament formation. The concentration of proteins and chromosomal DNA in filaments and control cells was similar when standardized by biomass. Furthermore, penicillin-binding proteins in the membrane of salmonellae were activein vitro. The activity of penicillin-binding protein 2 was greater in filaments than in control cells, suggesting that it may have a role in osmotic-induced filament formation. Filaments contained more ATP than did control cells in standardized cell suspensions, though the levels of two F0F1-ATP synthase subunits were reduced. Furthermore, filaments could septate and divide within 8 h in 0.2× Luria-Bertani broth at 23°C, while nonfilamentous control cells did not replicate. Based upon the ability of filaments to septate and divide in this diluted broth, a method was developed to enumerate by plate count the number of individual, viable cells within a population of filaments. This method could aid in retrospective analyses of infectious dose of filamented salmonellae.
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Treviño-Morales, S. P., A. Fuente, Á. Sánchez-Monge, J. Kainulainen, P. Didelon, S. Suri, N. Schneider, et al. "Dynamics of cluster-forming hub-filament systems." Astronomy & Astrophysics 629 (September 2019): A81. http://dx.doi.org/10.1051/0004-6361/201935260.
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Context. High-mass stars and star clusters commonly form within hub-filament systems. Monoceros R2 (hereafter Mon R2), at a distance of 830 pc, harbors one of the closest of these systems, making it an excellent target for case studies. Aims. We investigate the morphology, stability and dynamical properties of the Mon R2 hub-filament system. Methods. We employed observations of the 13CO and C18O 1 →0 and 2 →1 lines obtained with the IRAM-30 m telescope. We also used H2 column density maps derived from Herschel dust emission observations. Results. We identified the filamentary network in Mon R2 with the DisPerSE algorithm and characterized the individual filaments as either main (converging into the hub) or secondary (converging to a main filament). The main filaments have line masses of 30–100 M⊙ pc−1 and show signs of fragmentation, while the secondary filaments have line masses of 12–60 M⊙ pc−1 and show fragmentation only sporadically. In the context of Ostriker’s hydrostatic filament model, the main filaments are thermally supercritical. If non-thermal motions are included, most of them are transcritical. Most of the secondary filaments are roughly transcritical regardless of whether non-thermal motions are included or not. From the morphology and kinematics of the main filaments, we estimate a mass accretion rate of 10−4–10−3 M⊙ yr−1 into the central hub. The secondary filaments accrete into the main filaments at a rate of 0.1–0.4 × 10−4 M⊙ yr−1. The main filaments extend into the central hub. Their velocity gradients increase toward the hub, suggesting acceleration of the gas. We estimate that with the observed infall velocity, the mass-doubling time of the hub is ~2.5 Myr, ten times longer than the free-fall time, suggesting a dynamically old region. These timescales are comparable with the chemical age of the HII region. Inside the hub, the main filaments show a ring- or a spiral-like morphology that exhibits rotation and infall motions. One possible explanation for the morphology is that gas is falling into the central cluster following a spiral-like pattern.
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Arzoumanian, Doris, Philippe André, and François Boulanger. "Properties of interstellar filaments as derived from Herschel, Planck, and molecular line observations." Proceedings of the International Astronomical Union 11, S315 (August 2015): 53–60. http://dx.doi.org/10.1017/s1743921316007250.
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AbstractRecent Herschel and Planck observations of submillimeter dust emission revealed the omnipresence of filamentary structures in the interstellar medium (ISM). The ubiquity of filaments in quiescent clouds as well as in star-forming regions indicates that the formation of filamentary structures is a natural product of the physics at play in the magnetized turbulent cold ISM. An analysis of more than 270 filaments observed with Herschel in 8 regions of the Gould Belt, shows that interstellar filaments are characterized by a narrow distribution of central width sharply peaked at ~0.1 pc, while they span a wide column density range. Molecular line observations of a sample of these filaments show evidence of an increase in the velocity dispersion of dense filaments with column density, suggesting an evolution in mass per unit length due to accretion of surrounding material onto these star-forming filaments. The analyses of Planck dust polarization observations show that both the mean magnetic field and its fluctuations along the filaments are different from those of their surrounding clouds. This points to a coupling between the matter and the $\vec{B}$-field in the filament formation process. These observational results, derived from dust and gas tracers in total and polarized intensity, set strong constraints on our understanding of the formation and evolution of filaments in the ISM. They provide important clues on the initial conditions of the star formation process along interstellar filaments.
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Kuutma, Teet, Anup Poudel, Maret Einasto, Pekka Heinämäki, Heidi Lietzen, Antti Tamm, and Elmo Tempel. "Properties of brightest group galaxies in cosmic web filaments." Astronomy & Astrophysics 639 (July 2020): A71. http://dx.doi.org/10.1051/0004-6361/201937282.
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Context. The cosmic web, a complex network of galaxy groups and clusters connected by filaments, is a dynamical environment in which galaxies form and evolve. However, the impact of cosmic filaments on the properties of galaxies is difficult to study because of the much more influential local (galaxy-group scale) environment. Aims. The aim of this paper is to investigate the dependence of intrinsic galaxy properties on distance to the nearest cosmic web filament, using a sample of galaxies for which the local environment is easily assessable. Methods. Our study is based on a volume-limited galaxy sample with Mr ≤ −19 mag, drawn from the SDSS DR12. We chose brightest group galaxies (BGGs) in groups with two to six members as our probes of the impact of filamentary environment because their local environment can be determined more accurately. We use the Bisous marked point process method to detect cosmic-web filaments with radii of 0.5−1.0 Mpc and measure the perpendicular filament spine distance (Dfil) for the BGGs. We limit our study to Dfil values up to 4 Mpc. We use the luminosity density field as a tracer of the local environment. To achieve uniformity of the sample and to reduce potential biases we only consider filaments longer than 5 Mpc. Our final sample contains 1427 BGGs. Results. We note slight deviations between the galaxy populations inside and outside the filament radius in terms of stellar mass, colour, the 4000 Å break, specific star formation rates, and morphologies. However, all these differences remain below 95% confidence and are negligible compared to the effects arising from local environment density. Conclusions. Within a 4 Mpc radius of the filament axes, the effect of filaments on BGGs is marginal. The local environment is the main factor in determining BGG properties.
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Fily, Yaouen, Priya Subramanian, Tobias M. Schneider, Raghunath Chelakkot, and Arvind Gopinath. "Buckling instabilities and spatio-temporal dynamics of active elastic filaments." Journal of The Royal Society Interface 17, no. 165 (April 2020): 20190794. http://dx.doi.org/10.1098/rsif.2019.0794.
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Biological filaments driven by molecular motors tend to experience tangential propulsive forces also known as active follower forces. When such a filament encounters an obstacle, it deforms, which reorients its follower forces and alters its entire motion. If the filament pushes a cargo, the friction on the cargo can be enough to deform the filament, thus affecting the transport properties of the cargo. Motivated by cytoskeletal filament motility assays, we study the dynamic buckling instabilities of a two-dimensional slender elastic filament driven through a dissipative medium by tangential propulsive forces in the presence of obstacles or cargo. We observe two distinct instabilities. When the filament’s head is pinned or experiences significant translational but little rotational drag from its cargo, it buckles into a steadily rotating coiled state. When it is clamped or experiences both significant translational and rotational drag from its cargo, it buckles into a periodically beating, overall translating state. Using minimal analytically tractable models, linear stability theory and fully nonlinear computations, we study the onset of each buckling instability, characterize each buckled state, and map out the phase diagram of the system. Finally, we use particle-based Brownian dynamics simulations to show our main results are robust to moderate noise and steric repulsion. Overall, our results provide a unified framework to understand the dynamics of tangentially propelled filaments and filament-cargo assemblies.
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Suri, Sümeyye, Álvaro Sánchez-Monge, Peter Schilke, Seamus D. Clarke, Rowan J. Smith, Volker Ossenkopf-Okada, Ralf Klessen, et al. "The CARMA-NRO Orion Survey." Astronomy & Astrophysics 623 (March 2019): A142. http://dx.doi.org/10.1051/0004-6361/201834049.
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Context. We present an initial overview of the filamentary structure in the Orion A molecular cloud utilizing a high angular and velocity resolution C18O(1–0) emission map that was recently produced as part of the CARMA-NRO Orion Survey. Aims. The main goal of this study is to build a credible method to study varying widths of filaments which has previously been linked to star formation in molecular clouds. Due to the diverse star forming activities taking place throughout its ~20 pc length, together with its proximity of 388 pc, the Orion A molecular cloud provides an excellent laboratory for such an experiment to be carried out with high resolution and high sensitivity. Methods. Using the widely-known structure identification algorithm, DisPerSE, on a three-dimensional (PPV) C18O cube, we identify 625 relatively short (the longest being 1.74 pc) filaments over the entire cloud. We studied the distribution of filament widths using FilChaP, a python package that we have developed and made publicly available. Results. We find that the filaments identified in a two square-degree PPV cube do not overlap spatially, except for the complex OMC-4 region that shows distinct velocity components along the line of sight. The filament widths vary between 0.02 and 0.3 pc depending on the amount of substructure that a filament possesses. The more substructure a filament has, the larger is its width. We also find that despite this variation, the filament width shows no anticorrelation with the central column density which is in agreement with previous Herschel observations.
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Xia, Qianli, Naomi Robertson, Catherine Heymans, Alexandra Amon, Marika Asgari, Yan-Chuan Cai, Thomas Erben, et al. "A gravitational lensing detection of filamentary structures connecting luminous red galaxies." Astronomy & Astrophysics 633 (January 2020): A89. http://dx.doi.org/10.1051/0004-6361/201936678.
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We present a weak lensing detection of filamentary structures in the cosmic web, combining data from the Kilo-Degree Survey, the Red Cluster Sequence Lensing Survey, and the Canada-France-Hawaii Telescope Lensing Survey. The line connecting luminous red galaxies with a separation of 3 − 5 h−1 Mpc was chosen as a proxy for the location of filaments. We measured the average weak lensing shear around ∼11 000 candidate filaments selected in this way from the Sloan Digital Sky Survey. After nulling the shear induced by the dark matter haloes around each galaxy, we reported a 3.4σ detection of an anisotropic shear signal from the matter that connects them. Adopting a filament density profile, motivated from N-body simulations, the average density at the centre of these filamentary structures was found to be 15 ± 4 times the critical density.
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André, Ph, D. Arzoumanian, V. Könyves, Y. Shimajiri, and P. Palmeirim. "The role of molecular filaments in the origin of the prestellar core mass function and stellar initial mass function." Astronomy & Astrophysics 629 (August 26, 2019): L4. http://dx.doi.org/10.1051/0004-6361/201935915.
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Context. The origin of the stellar initial mass function (IMF) is one of the most debated issues in astrophysics. Aims. Here we explore the possible link between the quasi-universal filamentary structure of star-forming molecular clouds and the origin of the IMF. Methods. Based on our recent comprehensive study of filament properties from Herschel Gould Belt survey observations, we derive, for the first time, a good estimate of the filament mass function (FMF) and filament line mass function (FLMF) in nearby molecular clouds. We use the observed FLMF to propose a simple toy model for the origin of the prestellar core mass function (CMF), relying on gravitational fragmentation of thermally supercritical but virialized filaments. Results. We find that the FMF and the FLMF have very similar shapes and are both consistent with a Salpeter-like power-law function (dN/dlog Mline ∝ Mline−1.5±0.1) in the regime of thermally supercritical filaments (Mline > 16 M⊙ pc−1). This is a remarkable result since, in contrast, the mass distribution of molecular clouds and clumps is known to be significantly shallower than the Salpeter power-law IMF, with dN/dlog Mcl ∝ Mcl−0.7. Conclusions. Since the vast majority of prestellar cores appear to form in thermally transcritical or supercritical filaments, we suggest that the prestellar CMF and by extension the stellar IMF are at least partly inherited from the FLMF through gravitational fragmentation of individual filaments.
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KEVLAHAN, N. K. R., and M. FARGE. "Vorticity filaments in two-dimensional turbulence: creation, stability and effect." Journal of Fluid Mechanics 346 (September 10, 1997): 49–76. http://dx.doi.org/10.1017/s0022112097006113.
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Vorticity filaments are characteristic structures of two-dimensional turbulence. The formation, persistence and effect of vorticity filaments are examined using a high-resolution direct numerical simulation (DNS) of the merging of two positive Gaussian vortices pushed together by a weaker negative vortex. Many intense spiral vorticity filaments are created during this interaction and it is shown using a wavelet packet decomposition that, as has been suggested, the coherent vortex stabilizes the filaments. This result is confirmed by a linear stability analysis at the edge of the vortex and by a calculation of the straining induced by the spiral structure of the filament in the vortex core. The time-averaged energy spectra for simulations using hyper-viscosity and Newtonian viscosity have slopes of −3 and −4 respectively. Apart from a much higher effective Reynolds number (which accounts for the difference in energy spectra), the hyper-viscous simulation has the same dynamics as the Newtonian viscosity simulation. A wavelet packet decomposition of the hyper-viscous simulation reveals that after the merger the energy spectra of the filamentary and coherent parts of the vorticity field have slopes of −2 and −6 respectively. An asymptotic analysis and DNS for weak external strain shows that a circular filament at a distance R from the vortex centre always reduces the deformation of a Lamb's (Gaussian) vortex in the region r[ges ]R. In the region r<R the deformation is also reduced provided the filament is intense and is in the vortex core, otherwise the filament may slightly increase the deformation. The results presented here should be useful for modelling the coherent and incoherent parts of two-dimensional turbulent flows.
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Ren, Zhiyuan, Lei Zhu, Hui Shi, Nannan Yue, Di Li, Qizhou Zhang, Diego Mardones, et al. "Convergent filaments contracting towards an intermediate-mass pre-stellar core." Monthly Notices of the Royal Astronomical Society 505, no. 4 (May 28, 2021): 5183–91. http://dx.doi.org/10.1093/mnras/stab1509.
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ABSTRACT Filamentary structures are closely associated with star-forming cores, but their detailed physical connections are still not clear. We studied the dense gas in OMC-3 MMS-7 region in the Orion A molecular cloud using the molecular lines observed with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Submillimeter Array (SMA). The ALMA N2H+ (1–0) emission has revealed three dense filaments intersected at the centre, coincident with the central core MMS-7, which has a mass of 3.6 M⊙. The filaments and cores are embedded in a parental clump with a total mass of 29 M⊙. The N2H+ velocity field exhibits a noticeable increasing trend along the filaments towards the central core MMS-7 with a scale of v − vlsr ≃ 1.5 km s−1 over a spatial range of ∼20 arcsec (8 × 103 au), corresponding to a gradient of $40\, {\rm km\, s^{-1}}\, {\rm pc}^{-1}$. This feature is most likely to indicate an infall motion towards the centre. The derived infall rate (8 × 10−5 M⊙ yr−1) and time-scale (3.6 × 105 yr) are much lower than that for a spherical free-fall collapse and more consistent with the contraction of the filament structures. The filaments also exhibit a possible fragmentation. But this does not seem to largely interrupt the gas structure or its contraction towards the centre. Thus, MMS-7 provides an example of filamentary inward motion directly towards a pre-stellar core. The filament contraction could be less intense but more steady than global spherical collapse, and may help generate an intermediate-mass or even high-mass star.
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Chira, R. A., J. Kainulainen, J. C. Ibáñez-Mejía, Th Henning, and M. M. Mac Low. "On the fragmentation of filaments in a molecular cloud simulation." Astronomy & Astrophysics 610 (February 2018): A62. http://dx.doi.org/10.1051/0004-6361/201731836.
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Context. The fragmentation of filaments in molecular clouds has attracted a lot of attention recently as there seems to be a close relation between the evolution of filaments and star formation. The study of the fragmentation process has been motivated by simple analytical models. However, only a few comprehensive studies have analysed the evolution of filaments using numerical simulations where the filaments form self-consistently as part of large-scale molecular cloud evolution. Aim. We address the early evolution of parsec-scale filaments that form within individual clouds. In particular, we focus on three questions: How do the line masses of filaments evolve? How and when do the filaments fragment? How does the fragmentation relate to the line masses of the filaments? Methods. We examine three simulated molecular clouds formed in kiloparsec-scale numerical simulations performed with the FLASH adaptive mesh refinement magnetohydrodynamic code. The simulations model a self-gravitating, magnetised, stratified, supernova-driven interstellar medium, including photoelectric heating and radiative cooling. We follow the evolution of the clouds for 6 Myr from the time self-gravity starts to act. We identify filaments using the DisPerSe algorithm, and compare the results to other filament-finding algorithms. We determine the properties of the identified filaments and compare them with the predictions of analytic filament stability models. Results. The average line masses of the identified filaments, as well as the fraction of mass in filamentary structures, increases fairly continuously after the onset of self-gravity. The filaments show fragmentation starting relatively early: the first fragments appear when the line masses lie well below the critical line mass of Ostriker’s isolated hydrostatic equilibrium solution (~16 M⊙ pc−1), commonly used as a fragmentation criterion. The average line masses of filaments identified in three-dimensional volume density cubes increases far more quickly than those identified in two-dimensional column density maps. Conclusions. Our results suggest that hydrostatic or dynamic compression from the surrounding cloud has a significant impact on the early dynamical evolution of filaments. A simple model of an isolated, isothermal cylinder may not provide a good approach for fragmentation analysis. Caution must be exercised in interpreting distributions of properties of filaments identified in column density maps, especially in the case of low-mass filaments. Comparing or combining results from studies that use different filament finding techniques is strongly discouraged.
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Roy, A., Ph André, D. Arzoumanian, M. A. Miville-Deschênes, V. Könyves, N. Schneider, S. Pezzuto, P. Palmeirim, and J. M. Kirk. "How the power spectrum of dust continuum images may hide the presence of a characteristic filament width." Astronomy & Astrophysics 626 (June 2019): A76. http://dx.doi.org/10.1051/0004-6361/201832869.
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Context. Herschel observations of interstellar clouds support a paradigm for star formation in which molecular filaments play a central role. One of the foundations of this paradigm is the finding, based on detailed studies of the transverse column density profiles observed with Herschel, that nearby molecular filaments share a common inner width of ∼0.1 pc. The existence of a characteristic filament width has been recently questioned, however, on the grounds that it seems inconsistent with the scale-free nature of the power spectrum of interstellar cloud images. Aims. In an effort to clarify the origin of this apparent discrepancy, we examined the power spectra of the Herschel/SPIRE 250 μm images of the Polaris, Aquila, and Taurus–L1495 clouds in detail and performed a number of simple numerical experiments by injecting synthetic filaments in both the Herschel images and synthetic background images. Methods. We constructed several populations of synthetic filaments of 0.1 pc width with realistic area filling factors (Afil) and distributions of column density contrasts (δc). After adding synthetic filaments to the original Herschel images, we recomputed the image power spectra and compared the results with the original, essentially scale-free power spectra. We used the χ2variance of the residuals between the best power-law fit and the output power spectrum in each simulation as a diagnostic of the presence (or absence) of a significant departure from a scale-free power spectrum. Results. We find that χ2variance depends primarily on the combined parameter δ22 Afil. According to our numerical experiments, a significant departure from a scale-free behavior and thus the presence of a characteristic filament width become detectable in the power spectrum when δ22 Afil ⪆ 0.1 for synthetic filaments with Gaussian profiles and δ22 Afil ⪆ 0.4 for synthetic filaments with Plummer-like density profiles. Analysis of the real Herschel 250 μm data suggests that δ22 Afil is ∼0.01 in the case of the Polaris cloud and ∼0.016 in the Aquila cloud, significantly below the fiducial detection limit of δ22 Afil ∼ 0.1 in both cases. In both clouds, the observed filament contrasts and area filling factors are such that the filamentary structure contributes only ∼1/5 of the power in the image power spectrum at angular frequencies where an effect of the characteristic filament width is expected. Conclusions. We conclude that the essentially scale-free power spectra of Herschel images remain consistent with the existence of a characteristic filament width ∼0.1 pc and do not invalidate the conclusions drawn from studies of the filament profiles.
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Russell, H. R., B. R. McNamara, A. C. Fabian, P. E. J. Nulsen, F. Combes, A. C. Edge, M. Madar, V. Olivares, P. Salomé, and A. N. Vantyghem. "Driving massive molecular gas flows in central cluster galaxies with AGN feedback." Monthly Notices of the Royal Astronomical Society 490, no. 3 (September 30, 2019): 3025–45. http://dx.doi.org/10.1093/mnras/stz2719.
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Abstract We present an analysis of new and archival ALMA observations of molecular gas in 12 central cluster galaxies. We examine emerging trends in molecular filament morphology and gas velocities to understand their origins. Molecular gas masses in these systems span $10^9 {--}10^{11} {\rm \, M_{\odot }}$, far more than most gas-rich galaxies. ALMA images reveal a distribution of morphologies from filamentary to disc-dominated structures. Circumnuclear discs on kiloparsec scales appear rare. In most systems, half to nearly all of the molecular gas lies in filamentary structures with masses of a few $\times 10^{8{\text{--}}10}{\rm \, M_{\odot }}$ that extend radially several to several tens of kpc. In nearly all cases the molecular gas velocities lie far below stellar velocity dispersions, indicating youth, transience, or both. Filament bulk velocities lie far below the galaxy’s escape and free-fall speeds indicating they are bound and being decelerated. Most extended molecular filaments surround or lie beneath radio bubbles inflated by the central active galactic nuclei (AGNs). Smooth velocity gradients found along the filaments are consistent with gas flowing along streamlines surrounding these bubbles. Evidence suggests most of the molecular clouds formed from low entropy X-ray gas that became thermally unstable and cooled when lifted by the buoyant bubbles. Uplifted gas will stall and fall back to the galaxy in a circulating flow. The distribution in morphologies from filament to disc-dominated sources therefore implies slowly evolving molecular structures driven by the episodic activity of the AGNs.
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Kumar, M. S. N., P. Palmeirim, D. Arzoumanian, and S. I. Inutsuka. "Unifying low- and high-mass star formation through density-amplified hubs of filaments." Astronomy & Astrophysics 642 (October 2020): A87. http://dx.doi.org/10.1051/0004-6361/202038232.
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Context. Star formation takes place in giant molecular clouds, resulting in mass-segregated young stellar clusters composed of Sun-like stars, brown dwarfs, and massive O-type(50–100 M⊙) stars. Aims. We aim to identify candidate hub-filament systems (HFSs) in the Milky Way and examine their role in the formation of the highest mass stars and star clusters. Methods. The Herschel survey HiGAL has catalogued about 105 clumps. Of these, approximately 35 000 targets are detected at the 3σ level in a minimum of four bands. Using the DisPerSE algorithm we detect filamentary skeletons on 10′ × 10′ cut-outs of the SPIRE 250 μm images (18′′ beam width) of the targets. Any filament with a total length of at least 55′′ (3 × 18′′) and at least 18′′ inside the clump was considered to form a junction at the clump. A hub is defined as a junction of three or more filaments. Column density maps were masked by the filament skeletons and averaged for HFS and non-HFS samples to compute the radial profile along the filaments into the clumps. Results. Approximately 3700 (11%) are candidate HFSs, of which about 2150 (60%) are pre-stellar and 1400 (40%) are proto-stellar. The filaments constituting the HFSs have a mean length of ~10–20 pc, a mass of ~5 × 104 M⊙, and line masses (M∕L) of ~2 × 103 M⊙ pc−1. All clumps with L > 104 L⊙ and L > 105 L⊙ at distances within 2 and 5 kpc respectively are located in the hubs of HFSs. The column densities of hubs are found to be enhanced by a factor of approximately two (pre-stellar sources) up to about ten (proto-stellar sources). Conclusions. All high-mass stars preferentially form in the density-enhanced hubs of HFSs. This amplification can drive the observed longitudinal flows along filaments providing further mass accretion. Radiation pressure and feedback can escape into the inter-filamentary voids. We propose a “filaments to clusters” unified paradigm for star formation, with the following salient features: (a) low-intermediate-mass stars form slowly (106 yr) in the filaments and massive stars form quickly (105 yr) in the hub, (b) the initial mass function is the sum of stars continuously created in the HFS with all massive stars formed in the hub, (c) feedback dissipation and mass segregation arise naturally due to HFS properties, and explain the (d) age spreads within bound clusters and the formation of isolated OB associations.
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Orkisz, Jan H., Nicolas Peretto, Jérôme Pety, Maryvonne Gerin, François Levrier, Emeric Bron, Sébastien Bardeau, et al. "A dynamically young, gravitationally stable network of filaments in Orion B." Astronomy & Astrophysics 624 (April 2019): A113. http://dx.doi.org/10.1051/0004-6361/201833410.
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Context. Filaments are a key step on the path that leads from molecular clouds to star formation. However, their characteristics, for instance their width, are heavily debated and the exact processes that lead to their formation and fragmentation into dense cores still remain to be fully understood. Aims. We aim at characterising the mass, kinematics, and stability against gravitational collapse of a statistically significant sample of filaments in the Orion B molecular cloud, which is renown for its very low star formation efficiency. Methods. We characterised the gas column densities and kinematics over a field of 1.9 deg2, using C18O (J = 1−0) data from the IRAM 30 m large programme ORION-B at angular and spectral resolutions of 23.5″ and 49.5 kHz, respectively. Using two different Hessian-based filters, we extracted and compared two filamentary networks, each containing over 100 filaments. Results. Independent of the extraction method, the filament networks have consistent characteristics. The filaments have widths of ~0.12 ± 0.04 pc and show a wide range of linear (~1−100 M⊙ pc−1) and volume densities (~2 × 103−2 × 105 cm−3). Compared to previous studies, the filament population is dominated by low-density, thermally sub-critical structures, suggesting that most of the identified filaments are not collapsing to form stars. In fact, only ~1% of the Orion B cloud mass covered by our observations can be found in super-critical, star-forming filaments, explaining the low star formation efficiency of the region. The velocity profiles observed across the filaments show quiescence in the centre and coherency in the plane of the sky, even though these profiles are mostly supersonic. Conclusions. The filaments in Orion B apparently belong to a continuum which contains a few elements comparable to already studied star-forming filaments, for example in the IC 5146, Aquila or Taurus regions, as well as many lower density, gravitationally unbound structures. This comprehensive study of the Orion B filaments shows that the mass fraction in super-critical filaments is a key factor in determining star formation efficiency.
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Schisano, Eugenio, S. Molinari, D. Elia, M. Benedettini, L. Olmi, S. Pezzuto, A. Traficante, et al. "The Hi-GAL catalogue of dusty filamentary structures in the Galactic plane." Monthly Notices of the Royal Astronomical Society 492, no. 4 (December 10, 2019): 5420–56. http://dx.doi.org/10.1093/mnras/stz3466.
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ABSTRACT The recent data collected by Herschel have confirmed that interstellar structures with a filamentary shape are ubiquitously present in the Milky Way. Filaments are thought to be formed by several physical mechanisms acting from large Galactic scales down to subparsec fractions of molecular clouds, and they might represent a possible link between star formation and the large-scale structure of the Galaxy. In order to study this potential link, a statistically significant sample of filaments spread throughout the Galaxy is required. In this work, we present the first catalogue of 32 059 candidate filaments automatically identified in the Herschel Infrared Galactic plane Survey (Hi-GAL) of the entire Galactic plane. For these objects, we determined morphological (length la and geometrical shape) and physical (average column density $N_{\rm H_{2}}$ and average temperature T) properties. We identified filaments with a wide range of properties: 2 ≤ la ≤ 100 arcmin, $10^{20} \le N_{\rm H_{2}} \le 10^{23}$ cm−2 and 10 ≤ T ≤ 35 K. We discuss their association with the Hi-GAL compact sources, finding that the most tenuous (and stable) structures do not host any major condensation. We also assign a distance to ∼18 400 filaments, for which we determine mass, physical size, stability conditions and Galactic distribution. When compared with the spiral arms structure, we find no significant difference between the physical properties of on-arm and inter-arm filaments. We compare our sample with previous studies, finding that our Hi-GAL filament catalogue represents a significant extension in terms of Galactic coverage and sensitivity. This catalogue represents a unique and important tool for future studies devoted to understanding the filament life-cycle.
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Bonne, L., N. Schneider, S. Bontemps, S. D. Clarke, A. Gusdorf, A. Lehmann, M. Steinke, et al. "Dense gas formation in the Musca filament due to the dissipation of a supersonic converging flow." Astronomy & Astrophysics 641 (September 2020): A17. http://dx.doi.org/10.1051/0004-6361/201937104.
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Observations with the Herschel Space Telescope have established that most star forming gas is organised in filaments, a finding that is supported by numerical simulations of the supersonic interstellar medium (ISM) where dense filamentary structures are ubiquitous. We aim to understand the formation of these dense structures by performing observations covering the 12CO(4→3), 12CO(3→2), and various CO(2–1) isotopologue lines of the Musca filament, using the APEX telescope. The observed CO intensities and line ratios cannot be explained by PDR (photodissociation region) emission because of the low ambient far-UV field that is strongly constrained by the non-detections of the [C II] line at 158 μm and the [O I] line at 63 μm, observed with the upGREAT receiver on SOFIA, as well as a weak [C I] 609 μm line detected with APEX. We propose that the observations are consistent with a scenario in which shock excitation gives rise to warm and dense gas close to the highest column density regions in the Musca filament. Using shock models, we find that the CO observations can be consistent with excitation by J-type low-velocity shocks. A qualitative comparison of the observed CO spectra with synthetic observations of dynamic filament formation simulations shows a good agreement with the signature of a filament accretion shock that forms a cold and dense filament from a converging flow. The Musca filament is thus found to be dense molecular post-shock gas. Filament accretion shocks that dissipate the supersonic kinetic energy of converging flows in the ISM may thus play a prominent role in the evolution of cold and dense filamentary structures.
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Lombardo, Andrew T., Shane R. Nelson, Guy G. Kennedy, Kathleen M. Trybus, Sam Walcott, and David M. Warshaw. "Myosin Va transport of liposomes in three-dimensional actin networks is modulated by actin filament density, position, and polarity." Proceedings of the National Academy of Sciences 116, no. 17 (April 9, 2019): 8326–35. http://dx.doi.org/10.1073/pnas.1901176116.
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The cell’s dense 3D actin filament network presents numerous challenges to vesicular transport by teams of myosin Va (MyoVa) molecular motors. These teams must navigate their cargo through diverse actin structures ranging from Arp2/3-branched lamellipodial networks to the dense, unbranched cortical networks. To define how actin filament network organization affects MyoVa cargo transport, we created two different 3D actin networks in vitro. One network was comprised of randomly oriented, unbranched actin filaments; the other was comprised of Arp2/3-branched actin filaments, which effectively polarized the network by aligning the actin filament plus-ends. Within both networks, we defined each actin filament’s 3D spatial position using superresolution stochastic optical reconstruction microscopy (STORM) and its polarity by observing the movement of single fluorescent reporter MyoVa. We then characterized the 3D trajectories of fluorescent, 350-nm fluid-like liposomes transported by MyoVa teams (∼10 motors) moving within each of the two networks. Compared with the unbranched network, we observed more liposomes with directed and fewer with stationary motion on the Arp2/3-branched network. This suggests that the modes of liposome transport by MyoVa motors are influenced by changes in the local actin filament polarity alignment within the network. This mechanism was supported by an in silico 3D model that provides a broader platform to understand how cellular regulation of the actin cytoskeletal architecture may fine tune MyoVa-based intracellular cargo transport.
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Saajasto, Mika, Jorma Harju, Mika Juvela, Liu Tie, Qizhou Zhang, Sheng-Yuan Liu, Naomi Hirano, et al. "Cloud G074.11+00.11: a stellar cluster in formation." Astronomy & Astrophysics 630 (September 23, 2019): A69. http://dx.doi.org/10.1051/0004-6361/201834991.
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Context. We present molecular line and dust continuum observations of a Planck-detected cold cloud, G074.11+00.11. The cloud consists of a system of curved filaments and a central star-forming clump. The clump is associated with several infrared sources and H2O maser emission. Aims. We aim to determine the mass distribution and gas dynamics within the clump to investigate if the filamentary structure seen around the clump repeats itself on a smaller scale, and to estimate the fractions of mass contained in dense cores and filaments. The velocity distribution of pristine dense gas can be used to investigate the global dynamical state of the clump, the role of filamentary inflows, filament fragmentation, and core accretion. Methods. We used molecular line and continuum observations from single dish observatories and interferometric facilities to study the kinematics of the region. Results. The molecular line observations show that the central clump may have formed as a result of a large-scale filament collision. The central clump contains three compact cores. Assuming a distance of 2.3 kpc, based on Gaia observations and a three-dimensional extinction method of background stars, the mass of the central clump exceeds 700 M⊙, which is roughly ~25% of the total mass of the cloud. Our virial analysis suggests that the central clump and all identified substructures are collapsing. We find no evidence for small-scale filaments associated with the cores. Conclusions. Our observations indicate that the clump is fragmented into three cores with masses in the range [10, 50] M⊙ and that all three are collapsing. The presence of an H2O maser emission suggests active star formation. However, the CO lines show only weak signs of outflows. We suggest that the region is young and any processes leading to star formation have just recently begun.
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Mudry, Ryan E., Cynthia N. Perry, Meredith Richards, Velia M. Fowler, and Carol C. Gregorio. "The interaction of tropomodulin with tropomyosin stabilizes thin filaments in cardiac myocytes." Journal of Cell Biology 162, no. 6 (September 15, 2003): 1057–68. http://dx.doi.org/10.1083/jcb.200305031.
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Actin (thin) filament length regulation and stability are essential for striated muscle function. To determine the role of the actin filament pointed end capping protein, tropomodulin1 (Tmod1), with tropomyosin, we generated monoclonal antibodies (mAb17 and mAb8) against Tmod1 that specifically disrupted its interaction with tropomyosin in vitro. Microinjection of mAb17 or mAb8 into chick cardiac myocytes caused a dramatic loss of the thin filaments, as revealed by immunofluorescence deconvolution microscopy. Real-time imaging of live myocytes expressing green fluorescent protein–α-tropomyosin and microinjected with mAb17 revealed that the thin filaments depolymerized from their pointed ends. In a thin filament reconstitution assay, stabilization of the filaments before the addition of mAb17 prevented the loss of thin filaments. These studies indicate that the interaction of Tmod1 with tropomyosin is critical for thin filament stability. These data, together with previous studies, indicate that Tmod1 is a multifunctional protein: its actin filament capping activity prevents thin filament elongation, whereas its interaction with tropomyosin prevents thin filament depolymerization.
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Cohen, Shenhav, Bo Zhai, Steven P. Gygi, and Alfred L. Goldberg. "Ubiquitylation by Trim32 causes coupled loss of desmin, Z-bands, and thin filaments in muscle atrophy." Journal of Cell Biology 198, no. 4 (August 20, 2012): 575–89. http://dx.doi.org/10.1083/jcb.201110067.
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During muscle atrophy, myofibrillar proteins are degraded in an ordered process in which MuRF1 catalyzes ubiquitylation of thick filament components (Cohen et al. 2009. J. Cell Biol. http://dx.doi.org/10.1083/jcb.200901052). Here, we show that another ubiquitin ligase, Trim32, ubiquitylates thin filament (actin, tropomyosin, troponins) and Z-band (α-actinin) components and promotes their degradation. Down-regulation of Trim32 during fasting reduced fiber atrophy and the rapid loss of thin filaments. Desmin filaments were proposed to maintain the integrity of thin filaments. Accordingly, we find that the rapid destruction of thin filament proteins upon fasting was accompanied by increased phosphorylation of desmin filaments, which promoted desmin ubiquitylation by Trim32 and degradation. Reducing Trim32 levels prevented the loss of both desmin and thin filament proteins. Furthermore, overexpression of an inhibitor of desmin polymerization induced disassembly of desmin filaments and destruction of thin filament components. Thus, during fasting, desmin phosphorylation increases and enhances Trim32-mediated degradation of the desmin cytoskeleton, which appears to facilitate the breakdown of Z-bands and thin filaments.
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Virga, Epifanio G. "Dissipative shocks behind bacteria gliding." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, no. 2029 (November 28, 2014): 20130360. http://dx.doi.org/10.1098/rsta.2013.0360.
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Gliding is a means of locomotion on rigid substrates used by a number of bacteria, including myxobacteria and cyanobacteria. One of the hypotheses advanced to explain this motility mechanism hinges on the role played by the slime filaments continuously extruded from gliding bacteria. This paper solves, in full, a non-linear mechanical theory that treats as dissipative shocks both the point where the extruded slime filament comes into contact with the substrate, called the filament’s foot , and the pore on the bacterium outer surface from where the filament is ejected. I prove that kinematic compatibility for shock propagation requires that the bacterium uniform gliding velocity (relative to the substrate) and the slime ejecting velocity (relative to the bacterium) must be equal, a coincidence that seems to have already been observed.
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Çolakoğlu, Gülsen, and Anthony Brown. "Intermediate filaments exchange subunits along their length and elongate by end-to-end annealing." Journal of Cell Biology 185, no. 5 (May 25, 2009): 769–77. http://dx.doi.org/10.1083/jcb.200809166.
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Actin filaments and microtubules lengthen and shorten by addition and loss of subunits at their ends, but it is not known whether this is also true for intermediate filaments. In fact, several studies suggest that in vivo, intermediate filaments may lengthen by end-to-end annealing and that addition and loss of subunits is not confined to the filament ends. To test these hypotheses, we investigated the assembly dynamics of neurofilament and vimentin intermediate filament proteins in cultured cells using cell fusion, photobleaching, and photoactivation strategies in combination with conventional and photoactivatable fluorescent fusion proteins. We show that neurofilaments and vimentin filaments lengthen by end-to-end annealing of assembled filaments. We also show that neurofilaments and vimentin filaments incorporate subunits along their length by intercalation into the filament wall with no preferential addition of subunits to the filament ends, a process which we term intercalary subunit exchange.
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Tilney, L. G., D. J. DeRosier, A. Weber, and M. S. Tilney. "How Listeria exploits host cell actin to form its own cytoskeleton. II. Nucleation, actin filament polarity, filament assembly, and evidence for a pointed end capper." Journal of Cell Biology 118, no. 1 (July 1, 1992): 83–93. http://dx.doi.org/10.1083/jcb.118.1.83.
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After Listeria, a bacterium, is phagocytosed by a macrophage, it dissolves the phagosomal membrane and enters the cytoplasm. The Listeria than nucleates actin filaments from its surface. These newly assembled actin filaments show unidirectional polarity with their barbed ends associated with the surface of the Listeria. Using actin concentrations below the pointed end critical concentration we find that filament elongation must be occurring by monomers adding to the barbed ends, the ends associated with the Listerial surface. If Listeria with tails are incubated in G actin under polymerizing conditions, the Listeria is translocated away from its preformed tail by the elongation of filaments attached to the Listeria. This experiment and others tell us that in vivo filament assembly must be tightly coupled to filament capping and cross-bridging so that if one process outstrips another, chaos ensues. We also show that the actin filaments in the tail are capped on their pointed ends which inhibits further elongation and/or disassembly in vitro. From these results we suggest a simple picture of how Listeria competes effectively for host cell actin. When Listeria secretes a nucleator, the host's actin subunits polymerize into a filament. Host cell machinery terminate the assembly leaving a short filament. Listeria overcomes the host control by nucleating new filaments and thus many short filaments assemble. The newest filaments push existing ones into a growing tail. Thus the competition is between nucleation of filaments caused by Listeria and the filament terminators produced by the host.
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Ijpma, Gijs, Ahmed M. Al-Jumaily, Simeon P. Cairns, and Gary C. Sieck. "Myosin filament polymerization and depolymerization in a model of partial length adaptation in airway smooth muscle." Journal of Applied Physiology 111, no. 3 (September 2011): 735–42. http://dx.doi.org/10.1152/japplphysiol.00114.2011.
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Length adaptation in airway smooth muscle (ASM) is attributed to reorganization of the cytoskeleton, and in particular the contractile elements. However, a constantly changing lung volume with tidal breathing (hence changing ASM length) is likely to restrict full adaptation of ASM for force generation. There is likely to be continuous length adaptation of ASM between states of incomplete or partial length adaption. We propose a new model that assimilates findings on myosin filament polymerization/depolymerization, partial length adaptation, isometric force, and shortening velocity to describe this continuous length adaptation process. In this model, the ASM adapts to an optimal force-generating capacity in a repeating cycle of events. Initially the myosin filament, shortened by prior length changes, associates with two longer actin filaments. The actin filaments are located adjacent to the myosin filaments, such that all myosin heads overlap with actin to permit maximal cross-bridge cycling. Since in this model the actin filaments are usually longer than myosin filaments, the excess length of the actin filament is located randomly with respect to the myosin filament. Once activated, the myosin filament elongates by polymerization along the actin filaments, with the growth limited by the overlap of the actin filaments. During relaxation, the myosin filaments dissociate from the actin filaments, and then the cycle repeats. This process causes a gradual adaptation of force and instantaneous adaptation of shortening velocity. Good agreement is found between model simulations and the experimental data depicting the relationship between force development, myosin filament density, or shortening velocity and length.
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Priestley, F. D., and A. P. Whitworth. "Synthetic line and continuum observations of simulated turbulent clouds: the apparent widths of filaments." Monthly Notices of the Royal Astronomical Society 499, no. 3 (October 9, 2020): 3728–37. http://dx.doi.org/10.1093/mnras/staa3111.
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ABSTRACT Filamentary structures are ubiquitous in observations of real molecular clouds and also in simulations of turbulent, self-gravitating gas. However, making comparisons between observations and simulations is complicated by the difficulty of estimating volume densities observationally. Here, we have post-processed hydrodynamical simulations of a turbulent isothermal molecular cloud, using a full time-dependent chemical network. We have then run radiative transfer models to obtain synthetic line and continuum intensities that can be compared directly with those observed. We find that filaments have a characteristic width of ${\sim }0.1 \, {\rm pc}$, both on maps of their true surface density and on maps of their $850\, {\rm \mu m}$ dust continuum emission in agreement with previous work. On maps of line emission from CO isotopologues, the apparent widths of filaments are typically several times larger because the line intensities are poorly correlated with the surface density. On maps of line emission from dense gas tracers such as N2H+ and HCN, the apparent widths of filaments are ${\la}0.1\, {\rm pc}$. Thus, current observations of molecular-line emission are compatible with the universal $0.1 \, {\rm pc}$ filament width inferred from Herschel observations, provided proper account is taken of abundance, optical depth, and excitation considerations. We find evidence for ${\sim}0.4 \, {\rm km \, s^{-1}}$ radial velocity differences across filaments. These radial velocity differences might be a useful indicator of the mechanism by which a filament has formed or is forming, for example the turbulent cloud scenario modelled here, as against other mechanisms such as cloud–cloud collisions.
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Guan, Chengyu, Jun Zou, Qingchang Chen, Mingming Shi, and Bobo Yang. "Effect of Different Bonding Materials on Flip-Chip LED Filament Properties." Applied Sciences 10, no. 1 (December 19, 2019): 47. http://dx.doi.org/10.3390/app10010047.
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This article researches the effect of Sn-based solder alloys on flip-chip light-emitting diode LED (FC-LED) filament properties. SEM images, shearing force, steady-state voltage, blue light luminous flux, and junction temperature were examined to demonstrate the difference between two types of FC-LED filaments welded with two solders. The microstructure surface of Sn90Sb10 filament solder joints was smoother and had fewer voids and cracks compared with that of SAC0307 filament solder joints, which indicates that the Sn90Sb10 filaments had a higher shearing force than the SAC0307 filaments; moreover, the average shearing force was beyond 200 gf (standard shearing force). The steady-state voltage and junction temperature of the Sn90Sb10 solder-welded FC-LED filament were lower, and the Sn90Sb10 filament had a relatively higher blue light luminous flux. If high reliability of the solder joints and better photoelectric properties of the filaments are required, this Sn90Sb10 solder is the best bonding material for FC-LED filament welding.
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Schepers, Anna V., Charlotta Lorenz, Peter Nietmann, Andreas Janshoff, Stefan Klumpp, and Sarah Köster. "Multiscale mechanics and temporal evolution of vimentin intermediate filament networks." Proceedings of the National Academy of Sciences 118, no. 27 (June 29, 2021): e2102026118. http://dx.doi.org/10.1073/pnas.2102026118.
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The cytoskeleton, an intricate network of protein filaments, motor proteins, and cross-linkers, largely determines the mechanical properties of cells. Among the three filamentous components, F-actin, microtubules, and intermediate filaments (IFs), the IF network is by far the most extensible and resilient to stress. We present a multiscale approach to disentangle the three main contributions to vimentin IF network mechanics—single-filament mechanics, filament length, and interactions between filaments—including their temporal evolution. Combining particle tracking, quadruple optical trapping, and computational modeling, we derive quantitative information on the strength and kinetics of filament interactions. Specifically, we find that hydrophobic contributions to network mechanics enter mostly via filament-elongation kinetics, whereas electrostatics have a direct influence on filament–filament interactions.
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Cesar, F., J.-O. Bovin, L. R. Wallenberg, G. Karlsson, L. K. L. Falk, and T. Oku. "Synthesis and characterization of carbon filaments grown from Pd3P colloids." Journal of Materials Research 15, no. 9 (September 2000): 1857–59. http://dx.doi.org/10.1557/jmr.2000.0267.
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Amorphous carbon filaments were synthesized by catalytic pyrolysis of propene over Pd3P colloids. The channel close to the center of the filaments usually contained particles, which were analyzed by analytical electron microscopy to be palladium. The palladium particles could be found anywhere along the filament. The carbon filaments were of two types and of different diameters, about 8–15 nm and about 40–80 nm. The thinner type of filament shows a channel diameter of about 5 nm. The type of filament produced depends on the reaction conditions. Increased reaction time results in a large number of filaments, whereas an increased propene gas flow results in more of the thicker type of filaments.