1,888 research outputs found
The hierarchical fragmentation of filaments and the role of sub-filaments
Recent observations have revealed the presence of small fibres or
sub-filaments within larger filaments. We present a numerical fragmentation
study of fibrous filaments investigating the link between cores and
sub-filaments using hydrodynamical simulations performed with the moving-mesh
code Arepo. Our study suggests that cores form in two environments: (i) as
isolated cores, or small chains of cores, on a single sub-filament, or (ii) as
an ensemble of cores located at the junction of sub-filaments. We term these
isolated and hub cores respectively. We show that these core populations are
statistically different from each other. Hub cores have a greater mean mass
than isolated cores, and the mass distribution of hub cores is significantly
wider than isolated cores. This fragmentation is reminiscent of parsec-scale
hub-filament systems, showing that the combination of turbulence and gravity
leads to similar fragmentation signatures on multiple scales, even within
filaments. Moreover, the fact that fragmentation proceeds through sub-filaments
suggests that there exists no characteristic fragmentation length-scale between
cores. This is in opposition to earlier theoretical works studying fibre-less
filaments which suggest a strong tendency towards the formation of
quasi-periodically spaced cores, but in better agreement with observations. We
also show tentative signs that global collapse of filaments preferentially form
cores at both filament ends, which are more massive and dense than other cores.Comment: Accepted in MNRAS. 13 pages and 13 figures, 8 page appendix and 7
figure
Expression of a catalytically inactive mutant form of glutathione peroxidase 4 (Gpx4) confers a dominant-negative effect in male fertility.
The selenoenzyme Gpx4 is essential for early embryogenesis and cell viability for its unique function to prevent phospholipid oxidation. Recently, the cytosolic form of Gpx4 was identified as an upstream regulator of a novel form of non-apoptotic cell death, called ferroptosis, whereas the mitochondrial isoform of Gpx4 (mGpx4) was previously shown to be crucial for male fertility. Here, we generated and analyzed mice with targeted mutation of the active site selenocysteine (Sec) of Gpx4 (Gpx4_U46S). Mice homozygous for Gpx4_U46S died at the same embryonic stage (E7.5) as Gpx4-/- embryos as expected. Surprisingly, male mice heterozygous for Gpx4_U46S presented subfertility. Subfertility was manifested in a reduced number of litters from heterozygous breedings and an impairment of spermatozoa to fertilize oocytes in vitro. Morphologically, sperm isolated from heterozygous Gpx4_U46S mice revealed many structural abnormalities particularly in the spermatozoan midpiece due to improper oxidation and polymerization of sperm capsular proteins and malformation of the mitochondrial capsule surrounding and stabilizing sperm mitochondria. These findings are reminiscent of sperm isolated from selenium-deprived rodents or from mice specifically lacking mGpx4. Due to a strongly facilitated incorporation of Ser in the polypeptide chain as compared to Sec at the UGA codon, expression of the catalytically inactive Gpx4_U46S was found to be strongly increased. Since the stability of the mitochondrial capsule of mature spermatozoa depends on the moonlighting function of Gpx4 both as an enzyme oxidizing capsular protein thiols and being a structural protein, tightly controlled expression of functional Gpx4 emerges being key for full male fertility
Surface acoustic waves induced micropatterning of cells in gelatin methacryloyl (GelMA) hydrogels
Acoustic force patterning is an emerging technology that provides a platform to control the spatial location of cells in a rapid, accurate, yet contactless manner. However, very few studies have been reported on the usage of acoustic force patterning for the rapid arrangement of biological objects, such as cells, in a three-dimensional (3D) environment. In this study, we report on a bio-acoustic force patterning technique, which uses surface acoustic waves (SAWs) for the rapid arrangement of cells within an extracellular matrix-based hydrogel such as gelatin methacryloyl (GelMA). A proof-of-principle was achieved through both simulations and experiments based on the in-house fabricated piezoelectric SAW transducers, which enabled us to explore the effects of various parameters on the performance of the built construct. The SAWs were applied in a fashion that generated standing SAWs (SSAWs) on the substrate, the energy of which subsequently was transferred into the gel, creating a rapid, and contactless alignment of the cells (<10 s, based on the experimental conditions). Following ultraviolet radiation induced photo-crosslinking of the cell encapsulated GelMA pre-polymer solution, the patterned cardiac cells readily spread after alignment in the GelMA hydrogel and demonstrated beating activity in 5–7 days. The described acoustic force assembly method can be utilized not only to control the spatial distribution of the cells inside a 3D construct, but can also preserve the viability and functionality of the patterned cells (e.g. beating rates of cardiac cells). This platform can be potentially employed in a diverse range of applications, whether it is for tissue engineering, in vitro cell studies, or creating 3D biomimetic tissue structures
Unravelling the structure of magnetised molecular clouds with SILCC-Zoom: sheets, filaments and fragmentation
To what extent magnetic fields affect how molecular clouds (MCs) fragment and
create dense structures is an open question. We present a numerical study of
cloud fragmentation using the SILCC-Zoom simulations. These simulations follow
the self-consistent formation of MCs in a few hundred parsec sized region of a
stratified galactic disc; and include magnetic fields, self-gravity,
supernova-driven turbulence, as well as a non-equilibrium chemical network. To
discern the role of magnetic fields in the evolution of MCs, we study seven
simulated clouds, five with magnetic fields, and two without, with a maximum
resolution of 0.1 parsec. Using a dendrogram we identify hierarchical
structures which form within the clouds. Overall, the magnetised clouds have
more mass in a diffuse envelope with a number density between 1-100 cm.
We find that six out of seven clouds are sheet-like on the largest scales, as
also found in recent observations, and with filamentary structures embedded
within, consistent with the bubble-driven MC formation mechanism. Hydrodynamic
simulations tend to produce more sheet-like structures also on smaller scales,
while the presence of magnetic fields promotes filament formation. Analysing
cloud energetics, we find that magnetic fields are dynamically important for
less dense, mostly but not exclusively atomic structures (typically up to ~cm), while the denser, potentially star-forming structures
are energetically dominated by self-gravity and turbulence. In addition, we
compute the magnetic surface term and demonstrate that it is generally
confining, and some atomic structures are even magnetically held together. In
general, magnetic fields delay the cloud evolution and fragmentation by
1 Myr.Comment: 21 pages, 13 figures, accepted for publication in MNRA
Magnetic fields in star-forming systems (II): examining dust polarization, the Zeeman effect, and the Faraday rotation measure as magnetic field tracers
The degree to which the formation and evolution of clouds and filaments in
the interstellar medium is regulated by magnetic fields remains an open
question. Yet the fundamental properties of the fields (strength and 3D
morphology) are not readily observable. We investigate the potential for
recovering magnetic field information from dust polarization, the Zeeman
effect, and the Faraday rotation measure () in a SILCC-Zoom
magnetohydrodynamic (MHD) filament simulation. The object is analyzed at the
onset of star formation, and it is characterized by a line-mass of about M/L
out to a radius of pc and a kinked 3D
magnetic field morphology. We generate synthetic observations via POLARIS
radiative transfer (RT) post-processing, and compare with an analytical model
of helical or kinked field morphology to help interpreting the inferred
observational signatures. We show that the tracer signals originate close to
the filament spine. We find regions along the filament where the
angular-dependency with the line-of-sight (LOS) is the dominant factor and dust
polarization may trace the underlying kinked magnetic field morphology. We also
find that reversals in the recovered magnetic field direction are not
unambiguously associated to any particular morphology. Other physical
parameters, such as density or temperature, are relevant and sometimes dominant
compared to the magnetic field structure in modulating the observed signal. We
demonstrate that the Zeeman effect and the recover the line-of-sight
magnetic field strength to within a factor 2.1 - 3.4. We conclude that the
magnetic field morphology may not be unambiguously determined in low-mass
systems by observations of dust polarization, Zeeman effect, or , whereas
the field strengths can be reliably recovered.Comment: 22 pages, 17 figures, 3 table
Impact of magnetic fields on ram pressure stripping in disk galaxies
(abridged) Ram pressure can remove significant amounts of gas from galaxies
in clusters, and thus has a large impact on the evolution of cluster galaxies.
Recent observations have shown that key properties of ram pressure stripped
tails of galaxies are in conflict with predictions by simulations. To increase
the realism of existing simulations, we simulated for the first time a disk
galaxy exposed to a uniformly magnetized wind including radiative cooling and
self-gravity of the gas. We find that B-fields have a strong effect on the
morphology of the gas in the tail of the galaxy. While in the pure hydro case
the tail is very clumpy, the MHD case shows very filamentary structures in the
tail. The filaments can be strongly supported by magnetic pressure and, when
this is the case, the B-field vectors tend to be aligned with the filaments.
The ram pressure stripping may lead to the formation of magnetized density
tails that appear as bifurcated in the plane of the sky and resemble the double
tails observed in ESO 137-001 and ESO 137-002. Such tails can be formed under a
variety of situations, both for the disks oriented face-on with respect to the
ICM wind and for the tilted ones. While this bifurcation is due to the generic
tendency for the B-fields to produce very filamentary tail morphology, the tail
properties are further shaped by the combination of the B-field orientation and
the sliding of the field past the disk surface exposed to the wind. Magnetic
draping does not strongly change the rate of gas stripping. For a face-on
galaxy, the field tends to reduce the amount of stripping compared to the pure
hydro case, and is associated with the formation of a magnetic draping layer on
the side of the galaxy exposed to the ICM wind. For significantly tilted disks,
the stripping rate may be enhanced by the ``scraping'' of the disk surface by
the B-fields sliding past the ISM/ICM interface.Comment: ApJ in press. arXiv admin note: text overlap with arXiv:0909.3097 by
other author
Soft X-ray absorption excess in gamma-ray burst afterglow spectra: Absorption by turbulent ISM
This is the accepted manuscript version of the following article: M. Tanga, P. Schady, A. Gatto, J. Greiner, M. G. H. Krause, R. Diehl, S. Savaglio, and S. Walch, ‘Soft X-ray absorption excess in gamma-ray burst afterglow spectra: Absorption by turbulent ISM’ Astronomy & Astrophysics, Vol 595, November 2016, A24. The final, published version is available online at doi: http://dx.doi.org/10.1051/0004-6361/201527961 Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.Two-thirds of long duration gamma-ray bursts (GRBs) show soft X-ray absorption in excess of the Milky Way. The column densities of metals inferred from UV and optical spectra differ from those derived from soft X-ray spectra, at times by an order of magnitude, with the latter being higher. The origin of the soft X-ray absorption excess observed in GRB X-ray afterglow spectra remains a heavily debated issue, which has resulted in numerous investigations on the effect of hot material both internal and external to the GRB host galaxy on our X-ray afterglow observations. Nevertheless, all models proposed so far have either only been able to account for a subset of our observations (i.e. at z > 2), or they have required fairly extreme conditions to be present within the absorbing material. In this paper, we investigate the absorption of the GRB afterglow by a collisionally ionised and turbulent interstellar medium (ISM). We find that a dense (3 per cubic centimeters) collisionally ionised ISM could produce UV/optical and soft X-ray absorbing column densities that differ by a factor of 10, however the UV/optical and soft X-ray absorbing column densities for such sightlines and are 2-3 orders of magnitude lower in comparison to the GRB afterglow spectra. For those GRBs with a larger soft X-ray excess of up to an order of magnitude, the contribution in absorption from a turbulent ISM as considered here would ease the required conditions of additional absorbing components, such as the GRB circumburst medium and intergalactic medium.Peer reviewedFinal Accepted Versio
Spatio-Temporal Variability of Suspended Particulate Matter in a High-Arctic Estuary (Adventfjorden, Svalbard) Using Sentinel-2 Time-Series
Arctic coasts, which feature land-ocean transport of freshwater, sediments, and other terrestrial material, are impacted by climate change, including increased temperatures, melting glaciers, changes in precipitation and runoff. These trends are assumed to affect productivity in fjordic estuaries. However, the spatial extent and temporal variation of the freshwater-driven darkening of fjords remain unresolved. The present study illustrates the spatio-temporal variability of suspended particulate matter (SPM) in the Adventfjorden estuary, Svalbard, using in-situ field campaigns and ocean colour remote sensing (OCRS) via high-resolution Sentinel-2 imagery. To compute SPM concentration (CSPMsat), a semi-analytical algorithm was regionally calibrated using local in-situ data, which improved the accuracy of satellite-derived SPM concentration by ~20% (MRD). Analysis of SPM concentration for two consecutive years (2019, 2020) revealed strong seasonality of SPM in Adventfjorden. Highest estimated SPM concentrations and river plume extent (% of fjord with CSPMsat > 30 mg L−1) occurred during June, July, and August. Concurrently, we observed a strong relationship between river plume extent and average air temperature over the 24 h prior to the observation (R2 = 0.69). Considering predicted changes to environmental conditions in the Arctic region, this study highlights the importance of the rapidly changing environmental parameters and the significance of remote sensing in analysing fluxes in light attenuating particles, especially in the coastal Arctic Ocean.publishedVersio
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