14 research outputs found
Fragmentation of a Circular Disc by Impact on a Frictionless Plate
The break-up of a two-dimensional circular disc by normal and oblique impact
on a hard frictionless plate is investigated by molecular dynamics simulations.
The disc is composed of numerous unbreakable randomly shaped convex polygons
connected together by simple elastic beams that break when bent or stretched
beyond a certain limit. It is found that for both normal and oblique impacts
the crack patterns are the same and depend solely on the normal component of
the impact velocity. Analysing the pattern of breakage, amount of damage,
fragment masses and velocities, we show the existence of a critical velocity
which separates two regimes of the impact process: below the critical point
only a damage cone is formed at the impact site (damage), cleaving of the
particle occurs at the critical point, while above the critical velocity the
disc breaks into several pieces (fragmentation). In the limit of very high
impact velocities the disc suffers complete disintegration (shattering) into
many small fragments. In agreement with experimental results, fragment masses
are found to follow the Gates-Gaudin-Schuhmann distribution (power law) with an
exponent independent of the velocity and angle of impact. The velocity
distribution of fragments exhibit an interesting anomalous scaling behavior
when changing the impact velocity and the size of the disc.Comment: submitted to J. Phys: Condensed Matter special issue on Granular
Medi
Fragmentation processes in impact of spheres
We study the brittle fragmentation of spheres by using a three-dimensional
Discrete Element Model. Large scale computer simulations are performed with a
model that consists of agglomerates of many particles, interconnected by
beam-truss elements. We focus on the detailed development of the fragmentation
process and study several fragmentation mechanisms. The evolution of meridional
cracks is studied in detail. These cracks are found to initiate in the inside
of the specimen with quasi-periodic angular distribution. The fragments that
are formed when these cracks penetrate the specimen surface give a broad peak
in the fragment mass distribution for large fragments that can be fitted by a
two-parameter Weibull distribution. This mechanism can only be observed in 3D
models or experiments. The results prove to be independent of the degree of
disorder in the model. Our results significantly improve the understanding of
the fragmentation process for impact fracture since besides reproducing the
experimental observations of fragment shapes, impact energy dependence and mass
distribution, we also have full access to the failure conditions and evolution
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The E3-Ubiquitin Ligase TRIM50 Interacts with HDAC6 and p62, and Promotes the Sequestration and Clearance of Ubiquitinated Proteins into the Aggresome.
In this study we report that, in response to proteasome inhibition, the E3-Ubiquitin ligase TRIM50 localizes to and promotes the recruitment and aggregation of polyubiquitinated proteins to the aggresome. Using Hdac6-deficient mouse embryo fibroblasts (MEF) we show that this localization is mediated by the histone deacetylase 6, HDAC6. Whereas Trim50-deficient MEFs allow pinpointing that the TRIM50 ubiquitin-ligase regulates the clearance of polyubiquitinated proteins localized to the aggresome. Finally we demonstrate that TRIM50 colocalizes, interacts with and increases the level of p62, a multifunctional adaptor protein implicated in various cellular processes including the autophagy clearance of polyubiquitinated protein aggregates. We speculate that when the proteasome activity is impaired, TRIM50 fails to drive its substrates to the proteasome-mediated degradation, and promotes their storage in the aggresome for successive clearance