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Abstract While blood clot formation has been relatively well studied, little is known about the mechanisms underlying the subsequent structural and mechanical clot remodeling called contraction or retraction . Impairment of the clot contraction process is associated with both life-threatening bleeding and thrombotic conditions, such as ischemic stroke, venous thromboembolism, and others. Recently, blood clot contraction was observed to be hindered in patients with COVID-19. A three-dimensional multiscale computational model is developed and used to quantify biomechanical mechanisms of the kinetics of clot contraction driven by platelet-fibrin pulling interactions. These results provide important biological insights into contraction of platelet filopodia, the mechanically active thin protrusions of the plasma membrane, described previously as performing mostly a sensory function. The biomechanical mechanisms and modeling approach described can potentially apply to studying other systems in which cells are embedded in a filamentous network and exert forces on the extracellular matrix modulated by the substrate stiffness. 

The alignment of striated intensity structures in thin neutral hydrogen (H i) spectroscopic channels with Galactic magnetic fields has been observed. However, the origin and nature of these striations are still debatable. Some studies suggest that the striations result solely from real cold-density filaments without considering the role of turbulent velocity fields in shaping the channel’s intensity distribution. To determine the relative contribution of density and velocity in forming the striations in channel maps, we analyse synthetic observations of channel maps obtained from realistic magnetized multiphase H i simulations with thermal broadening included. We vary the thickness of the channel maps and apply the Velocity Decomposition Algorithm to separate the velocity and density contributions. In parallel, we analyse GALFA-H i observations and compare the results. Our analysis shows that the thin channels are dominated by velocity contribution, and velocity caustics mainly generate the H i striations. We show that velocity caustics can cause a correlation between unsharp-masked H i structures and far-infrared emission. We demonstrate that the linear H i fibers revealed by the Rolling Hough Transform (RHT) in thin velocity channels originate from velocity caustics. As the thickness of channel maps increases, the relative contribution of density fluctuations in channel maps increases and more RHT-detected fibers tend to be perpendicular to the magnetic field. Conversely, the alignment with the magnetic field is the most prominent in thin channels. We conclude that similar to the velocity channel gradients (VChGs) approach, RHT traces magnetic fields through the analysis of velocity caustics in thin channel maps.

 

Polarization of interstellar dust emission is a powerful probe of dust properties and magnetic field structure. Yet studies of external galaxies are hampered by foreground dust contribution. The study aims at separating the polarized signal from the Large Magellanic Cloud (LMC) from that of the Milky Way (MW) to construct a wide-field, spatially complete map of dust polarization using the Planck 353 GHz data. To estimate the foreground polarization direction, we used velocity gradients in H i spectral line data and assessed the performance of the output by comparing to starlight extinction polarization. We estimate the foreground intensity using the dust-to-gas correlation and the average intensity around the LMC and we assume the foreground polarization to be uniform and equal to the average of the MW around the galaxy to derive foreground I, Q, and U parameters. After foreground removal, the geometry of the plane-of-the-sky magnetic field tends to follow the structure of the atomic gas. This is notably the case along the molecular ridges extending south and south-east of the 30 Doradus star-forming complex and along the more diffuse southern arm extending towards the Small Magellanic Cloud. There is also an alignment between the magnetic field and the outer arm in the western part. The median polarization fraction in the LMC is slightly lower than that observed for the MW as well as the anticorrelation between the polarization angle dispersion function and the polarization fraction. Overall, polarization fraction distribution is similar to that observed in the MW.

 

Context. The role of large-scale magnetic fields in the evolution of star-forming regions remains elusive. Its investigation requires the observational characterization of well-constrained molecular clouds. The Monoceros OB 1 molecular cloud is a large complex containing several structures that have been shown to be engaged in an active interaction and to have a rich star formation history. However, the magnetic fields in this region have only been studied on small scales. Aims. We study the large-scale magnetic field structure and its interplay with the gas dynamics in the Monoceros OB 1 east molecular cloud. Methods. We combined observations of dust polarized emission from the Planck telescope and CO molecular line emission observations from the Taeduk Radio Astronomy Observatory 14-metre telescope. We calculated the strength of the plane-of-sky magnetic field using a modified Chandrasekhar-Fermi method and estimated the mass-over-flux ratios in different regions of the cloud. We used the comparison of the velocity and intensity gradients of the molecular line observations with the polarimetric observations to trace dynamically active regions. Results. The molecular complex shows an ordered large-scale plane-of-sky magnetic field structure. In the northern part, it is mostly orientated along the filamentary structures, while the southern part shows at least two regions with distinct magnetic field orientations. Our analysis reveals a shock region in the northern part right between two filamentary clouds that, in previous studies, were suggested to be involved in a collision. The magnetic properties of the north-main and north-eastern filaments suggest that these filaments once formed a single one, and that the magnetic field evolved together with the material and did not undergo major changes during the evolution of the cloud. In the southern part, we find that either the magnetic field guides the accretion of interstellar matter towards the cloud or it is dragged by the matter falling towards the main cloud. Conclusions. The large-scale magnetic field in the Monoceros OB 1 east molecular cloud is tightly connected to the global structure of the complex. In the northern part, it seems to serve a dynamically important role by possibly providing support against gravity in the direction perpendicular to the field and to the filament. In the southern part, it is probably the most influential factor governing the morphological structure by guiding possible gas inflow. A study of the whole Monoceros OB 1 molecular complex at large scales is necessary to form a global picture of the formation and evolution of the Monoceros OB 1 east cloud and the role of the magnetic field in this process.