28 research outputs found
Simulational study of anomalous tracer diffusion in hydrogels
In this article, we analyze different factors that affect the diffusion
behavior of small tracer particles (as they are used e.g.in fluorescence
correlation spectroscopy (FCS)) in the polymer network of a hydrogel and
perform simulations of various simplified models. We observe, that under
certain circumstances the attraction of a tracer particle to the polymer
network strands might cause subdiffusive behavior on intermediate time scales.
In theory, this behavior could be employed to examine the network structure and
swelling behavior of weakly crosslinked hydrogels with the help of FCS.Comment: 11 pages, 11 figure
Biological measurement beyond the quantum limit
Quantum noise places a fundamental limit on the per photon sensitivity
attainable in optical measurements. This limit is of particular importance in
biological measurements, where the optical power must be constrained to avoid
damage to the specimen. By using non-classically correlated light, we
demonstrated that the quantum limit can be surpassed in biological
measurements. Quantum enhanced microrheology was performed within yeast cells
by tracking naturally occurring lipid granules with sensitivity 2.4 dB beyond
the quantum noise limit. The viscoelastic properties of the cytoplasm could
thereby be determined with a 64% improved measurement rate. This demonstration
paves the way to apply quantum resources broadly in a biological context
The Localization Transition of the Two-Dimensional Lorentz Model
We investigate the dynamics of a single tracer particle performing Brownian
motion in a two-dimensional course of randomly distributed hard obstacles. At a
certain critical obstacle density, the motion of the tracer becomes anomalous
over many decades in time, which is rationalized in terms of an underlying
percolation transition of the void space. In the vicinity of this critical
density the dynamics follows the anomalous one up to a crossover time scale
where the motion becomes either diffusive or localized. We analyze the scaling
behavior of the time-dependent diffusion coefficient D(t) including corrections
to scaling. Away from the critical density, D(t) exhibits universal
hydrodynamic long-time tails both in the diffusive as well as in the localized
phase.Comment: 13 pages, 7 figures
Finding the Cell Center by a Balance of Dynein and Myosin Pulling and Microtubule Pushing: A Computational Study
By comparing computer modeling predictions with observations, we conclude that strong dynein and weaker myosin-generated forces pull the microtubules inward competing with microtubule plus-ends pushing the microtubule aster outward and that the balance of these forces positions the centrosome at the cell center