4,245 research outputs found
A cycling state that can lead to glassy dynamics in intracellular transport
Power-law dwell times have been observed for molecular motors in living
cells, but the origins of these trapped states are not known. We introduce a
minimal model of motors moving on a two-dimensional network of filaments, and
simulations of its dynamics exhibit statistics comparable to those observed
experimentally. Analysis of the model trajectories, as well as experimental
particle tracking data, reveals a state in which motors cycle unproductively at
junctions of three or more filaments. We formulate a master equation for these
junction dynamics and show that the time required to escape from this
vortex-like state can account for the power-law dwell times. We identify trends
in the dynamics with the motor valency for further experimental validation. We
demonstrate that these trends exist in individual trajectories of myosin II on
an actin network. We discuss how cells could regulate intracellular transport
and, in turn, biological function, by controlling their cytoskeletal network
structures locally
Mass, Light and Colour of the Cosmic Web in the Supercluster SCL2243-0935 (z=0.447)
Context: In 2.2m MPG-ESO/WFI data we discovered several mass peaks through
weak lensing, forming a possible supercluster at redshift 0.45. Through
multi-colour wide-field imaging with CFHT/Megaprime and INT/WFC we identify
early-type galaxies and trace the supercluster network with them. Through
EMMI/NTT multi-object spectroscopy we verify the initial shear-selected cluster
candidates. Using weak lensing we obtain mass estimates for the supercluster
centre and the filaments.
Results: We identified the centre of the SCL2243-0935 supercluster, MACS
J2243-0935, which was found independently by Ebeling et al. (2010). 13 more
clusters or overdensities are embedded in a filamentary network, half of them
are already spectroscopically confirmed. Three (5-15) Mpc filaments are
detected, and we estimate the global size of SCL2243 to 45x15x50 Mpc, making it
one of the largest superclusters known at intermediate redshifts. Weak lensing
yields r_200=(2.06+/-0.13) Mpc and M_200=(1.54+/-0.29)x10^15 M_sun for MACS
J2243 with M/L=428+/-82, very similar to results from size-richness cluster
scaling relations. Integrating the weak lensing surface mass density over the
supercluster network (defined by increased i-band luminosity or g-i colours),
we find (1.53+/-1.01)x10^15 M_sun and M/L=305+/-201 for the three main
filaments, consistant with theoretical predictions. The filaments' projected
surface mass density is 0.007-0.012, corresponding to 10-100 times the critical
density. The greatly varying density of the cosmic web is also reflected in the
mean colour of galaxies. Conclusions: SCL2243 is significantly larger and much
more richly structured than other known superclusters such as A901/902 or
MS0302 studied with weak lensing before. It is a text-book supercluster with
little contamination along the line of sight, making it a perfect sandbox for
testing new techniques probing the cosmic web.Comment: 26 pages, 16 figures, accepted for publication Astronomy and
Astrophysics. Minor corrections implemented as requested by the refere
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