The intermediate filament protein, nestin, is a widely employed marker of multipotent neural stem cells (NSCs). Recent in vitro studies have implicated nestin in a number of cellular processes, but ...there is no data yet on its in vivo function. Here, we report the construction and functional characterization of Nestin knockout mice. We found that these mice show embryonic lethality, with neuroepithelium of the developing neural tube exhibiting significantly fewer NSCs and much higher levels of apoptosis. Consistent with this in vivo observation, NSC cultures derived from knockout embryos show dramatically reduced self‐renewal ability that is associated with elevated apoptosis but no overt defects in cell proliferation or differentiation. Unexpectedly, nestin deficiency has no detectable effect on the integrity of the cytoskeleton. Furthermore, the knockout of Vimentin, which abolishes nestin's ability to polymerize into intermediate filaments in NSCs, does not lead to any apoptotic phenotype. These data demonstrate that nestin is important for the proper survival and self‐renewal of NSCs, and that this function is surprisingly uncoupled from nestin's structural involvement in the cytoskeleton. STEM CELLS 2010;28:2162–2171
Nestin is an intermediate filament protein expressed in dividing cells during the early stages of development in the CNS, PNS and in myogenic and other tissues. Upon differentiation, nestin becomes ...downregulated and is replaced by tissue-specific intermediate filament proteins. Interestingly, nestin expression is reinduced in the adult during pathological situations, such as the formation of the glial scar after CNS injury and during regeneration of injured muscle tissue. Although it is utilised as a marker of proliferating and migrating cells very little is known about its functions or regulation. In depth studies on the distribution and expression of nestin in mitotically active cells indicate a complex role in regulation of the assembly and disassembly of intermediate filaments which together with other structural proteins, participate in remodeling of the cell. The role of nestin in dynamic cells, particularly structural organisation of the cell, appears strictly regulated by phosphorylation, especially its integration into heterogeneous intermediate filaments together with vimentin or alpha-internexin.
Abstract
Studying solar filament dynamical evolutions is an important approach to reveal the driving mechanism of solar eruptions, which seriously impact on the Sun–Earth system and could cause ...disastrous space weather. To better understand the evolution process of solar filaments, here we investigate an active-region filament by employing observations from the New Vacuum Solar Telescope (NVST), Solar Dynamics Observatory, and Interface Region Imaging Spectrograph. The high-resolution NVST H
α
images show that the northern footpoint of the filament gradually moved northward. Near the northern footpoint, there is an arch filament system (AFS). Between adjacent footpoints of the filament and the AFS, transient brightening, underlying magnetic cancellation, and bidirectional flows were detected, which jointly imply that it could be the magnetic reconnection between the filament and the AFS that changes the connection of filament threads and drives its footpoint to move northward. In addition, during the footpoint evolution, the filament with highly twisted structure underwent several untwisting motions. Meanwhile, transient brightenings were also observed and appeared as bright knots around several positions where filament threads might braid with each other. And some bright blobs were also detected to propagate outward from the brightening region. These observations suggest that magnetic reconnection might be responsible for the untwisting motion. This work exposes us to a dynamical scenario of the filament evolution driven by magnetic reconnection, which will promote our understanding of the formation and eruption of the filaments.
Fused Filament Fabricated parts exhibit mechanical anisotropy induced by the filament extrusion pattern and possibly due to the intrinsic nature of feedstock material. Consequently, an optimized ...filament deposition strategy is desirable for improving the part’s functionality. The present work optimizes the in-plane filament paths of Fused Filament Fabricated parts to strengthen component load-bearing capacity, with a particular focus on obtaining production-ready design solutions through a direct imposition of the manufacturing constraints. To perform an effective in-plane filament path optimization, the present contribution also addresses, among several other aspects, the following: (i) the development and implementation of a new material model that incorporates the transverse stiffness loss in the absence of inter-filament fusion, and (ii) a comparative study between a two-step gradient-based minimization and a global metaheuristic minimization. The results indicate that the new material model yields more realistic filament patterns compared to the assumption of neglecting the transverse stiffness loss at low filament densities. Further, the comparison of optimization approaches suggests the preference for the two-step gradient-based approach due to its better efficiency, flexibility, and compatibility with the proposed material model.
•Optimization of filament paths in Fused Filament Fabricated structures.•Optimized filament designs are readily printable.•A new anisotropic material model involving a realistic filament spacing role.•Application and comparison of gradient-based and evolutionary algorithms.
Abstract
Solar filament eruptions often show complex and dramatic geometric deformation that is highly relevant to the underlying physical mechanism triggering the eruptions. It is well known that ...the writhe of filament axes is a key parameter characterizing its global geometric deformation, but a quantitative investigation of the development of writhe during its eruption is still lacking. Here we introduce the Writhe Application Toolkit, which can be used to characterize accurately the topology of filament axes. This characterization is achieved based on the reconstruction and writhe number computation of three-dimensional paths of the filament axes from dual-perspective observations. We apply this toolkit to four dextral filaments located in the northern hemisphere with a counterclockwise (CCW) rotation during their eruptions. Initially, all these filaments possess a small writhe number (≤0.20) indicating a weak helical deformation of the axes. As the CCW rotation kicks in, their writhe numbers begin to decrease and reach large negative values. Combined with the extended Călugăreanu theorem, the absolute value of twist is deduced to decrease during the rotation. Such a quantitative analysis strongly indicates a consequence of the conversion of twist into writhe for the studied events.
ABSTRACT To better understand the properties of solar active-region filaments, we present a detailed study on the formation and magnetic structures of two active-region filaments in active region ...NOAA 11884 during a period of four days. It is found that the shearing motion of the opposite magnetic polarities and the rotation of the small sunspots with negative polarity play an important role in the formation of two active-region filaments. During the formation of these two active-region filaments, one foot of the filaments was rooted in a small sunspot with negative polarity. The small sunspot rotated not only around another small sunspot with negative polarity, but also around the center of its umbra. By analyzing the nonlinear force-free field extrapolation using the vector magnetic fields in the photosphere, twisted structures were found in the two active-region filaments prior to their eruptions. These results imply that the magnetic fields were dragged by the shearing motion between opposite magnetic polarities and became more horizontal. The sunspot rotation twisted the horizontal magnetic fields and finally formed the twisted active-region filaments.
Abstract
In this paper, we present a multiwavelength analysis to mass draining and oscillations in a large quiescent filament prior to its successful eruption on 2015 April 28. The eruption of a ...smaller filament that was parallel and in close, ∼350″ proximity was observed to induce longitudinal oscillations and enhance mass draining within the filament of interest. The longitudinal oscillation with an amplitude of ∼25 Mm and ∼23 km s
−1
underwent no damping during its observable cycle. Subsequently the slightly enhanced draining may have excited a eruption behind the limb, leading to a feedback that further enhanced the draining and induced simultaneous oscillations within the filament of interest. We find significant damping for these simultaneous oscillations, where the transverse oscillations proceeded with the amplitudes of ∼15 Mm and ∼14 km s
−1
, while the longitudinal oscillations involved a larger displacement and velocity amplitude (∼57 Mm, ∼43 km s
−1
). The second grouping of oscillations lasted for ∼2 cycles and had a similar period of ∼2 hr. From this, the curvature radius and transverse magnetic field strength of the magnetic dips supporting the filaments can be estimated to be ∼355 Mm and ≥34 G. The mass draining within the filament of interest lasted for ∼14 hr. The apparent velocity grew from ∼35 to ∼85 km s
−1
, with the transition being coincident with the occurrence of the oscillations. We conclude that two filament eruptions are sympathetic, i.e., the eruption of the quiescent filament was triggered by the eruption of the nearby smaller filament.
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•Extrusion optimization of PP and GRPP filaments for 3D printing.•3D printing vs. compression molding benchmark with the same raw material.•Optimal 3D printing conditions for PP and ...GRPP.•3D printing deposition orientation with minimum mechanical performance impact.•Reinforcing role of glass fibers is maintained with 3D printing.
This paper addresses the potential of polypropylene (PP) as a candidate for fused deposition modeling (FDM)-based 3D printing technique. The entire filament production chain is evaluated, starting with the PP pellets, filament production by extrusion and test samples printing. This strategy enables a true comparison between parts printed with parts manufactured by compression molding, using the same grade of raw material. Printed samples were mechanically characterized and the influence of filament orientation, layer thickness, infill degree and material was assessed. Regarding the latter, two grades of PP were evaluated: a glass-fiber reinforced and a neat, non-reinforced, one. The results showed the potential of the FDM to compete with conventional techniques, especially for the production of small series of parts/components; also, it was showed that this technique allows the production of parts with adequate mechanical performance and, therefore, does not need to be restricted to the production of mockups and prototypes.
Lamin A is a nuclear intermediate filament protein critical for nuclear architecture and mechanics and mutated in a wide range of human diseases. Yet little is known about the molecular architecture ...of lamins and mechanisms of their assembly. Here we use SILAC cross-linking mass spectrometry to determine interactions within lamin dimers and between dimers in higher-order polymers. We find evidence for a compression mechanism where coiled coils in the lamin A rod can slide onto each other to contract rod length, likely driven by a wide range of electrostatic interactions with the flexible linkers between coiled coils. Similar interactions occur with unstructured regions flanking the rod domain during oligomeric assembly. Mutations linked to human disease block these interactions, suggesting that this spring-like contraction can explain in part the dynamic mechanical stretch and flexibility properties of the lamin polymer and other intermediate filament networks.
The filaments rupture and recovery in oxide-type memristors have been theoretically studied. The model is based on the kinetics of oxygen vacancies and includes Joule heating of the oxide medium, ...which enhances the diffusion and drift of oxygen vacancies in an external electric field. The current-voltage characteristic of the model structure was obtained. Comparison with experimental results allowed for the determination of the constants used in the modeling. The peculiarity of the current-voltage characteristic observed in experimental works is explained.
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•An analytical model for switching a filament-type memristor cell is proposed.•The model allows one to theoretically determine the critical voltage at which switching occurs.•The model describes both I-V characteristics containing the feature and those not containing it.•Experimental current-voltage characteristics of reverse switching have been reconstructed.
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