54 research outputs found
Boundary induced phase transition with stochastic entrance and exit
We study an open-chain totally asymmetric exclusion process (TASEP) with
stochastic gates present at the two boundaries. The gating dynamics has been
modeled keeping the physical system of ion-channel gating in mind. These gates
can randomly switch between an open state and a closed state. In the open
state, the gates are highly permeable such that any particle arriving at the
gate immediately passes through. In the closed state, a particle gets trapped
at the gate and cannot pass through until the gate switches open again. We
calculate the phase-diagram of the system and find important and non-trivial
differences with the phase-diagram of a regular open-chain TASEP. In
particular, depending on switching rates of the two gates, the system may or
may not admit a maximal current phase. Our analytic calculation within
mean-field theory captures the main qualitative features of our Monte Carlo
simulation results. We also perform a refined mean-field calculation where the
correlations at the boundaries are taken into account. This theory shows
significantly better quantitative agreement with our simulation results
Thermodynamic behaviour of two-dimensional vesicles revisited
We study pressurised self-avoiding ring polymers in two dimensions using
Monte Carlo simulations, scaling arguments and Flory-type theories, through
models which generalise the model of Leibler, Singh and Fisher [Phys. Rev.
Lett. Vol. 59, 1989 (1987)]. We demonstrate the existence of a thermodynamic
phase transition at a non-zero scaled pressure , where , with the number of monomers and the pressure
, keeping constant, in a class of such models.
This transition is driven by bond energetics and can be either continuous or
discontinuous. It can be interpreted as a shape transition in which the ring
polymer takes the shape, above the critical pressure, of a regular N-gon whose
sides scale smoothly with pressure, while staying unfaceted below this critical
pressure. In the general case, we argue that the transition is replaced by a
sharp crossover. The area, however, scales with for all positive in
all such models, consistent with earlier scaling theories.Comment: 6 pages, 4 figures, EPL forma
Recommended from our members
Integrative analysis of the inter-tumoral heterogeneity of triple-negative breast cancer.
Triple-negative breast cancers (TNBC) lack estrogen and progesterone receptors and HER2 amplification, and are resistant to therapies that target these receptors. Tumors from TNBC patients are heterogeneous based on genetic variations, tumor histology, and clinical outcomes. We used high throughput genomic data for TNBC patients (n = 137) from TCGA to characterize inter-tumor heterogeneity. Similarity network fusion (SNF)-based integrative clustering combining gene expression, miRNA expression, and copy number variation, revealed three distinct patient clusters. Integrating multiple types of data resulted in more distinct clusters than analyses with a single datatype. Whereas most TNBCs are classified by PAM50 as basal subtype, one of the clusters was enriched in the non-basal PAM50 subtypes, exhibited more aggressive clinical features and had a distinctive signature of oncogenic mutations, miRNAs and expressed genes. Our analyses provide a new classification scheme for TNBC based on multiple omics datasets and provide insight into molecular features that underlie TNBC heterogeneity
Dynein catch bond as a mediator of codependent bidirectional cellular transport
Intracellular bidirectional transport of cargo on microtubule filaments is
achieved by the collective action of oppositely directed dynein and kinesin
motors. Experiments have found that in certain cases, inhibiting the activity
of one type of motor results in an overall decline in the motility of the
cellular cargo in both directions. This counter-intuitive observation, referred
to as {\em paradox of codependence} is inconsistent with the existing paradigm
of a mechanistic tug-of-war between oppositely directed motors. Unlike kinesin,
dynein motors exhibit catchbonding, wherein the unbinding rates of these motors
decrease with increasing force on them. Incorporating this catchbonding
behavior of dynein in a theoretical model, we show that the functional
divergence of the two motors species manifests itself as an internal regulatory
mechanism, and leads to codependent transport behaviour in biologically
relevant regimes. Using analytical methods and stochastic simulations, we
analyse the processivity characteristics and probability distribution of run
times and pause times of transported cellular cargoes. We show that
catchbonding can drastically alter the transport characteristics and also
provide a plausible resolution of the paradox of codependence.Comment: 14 pages, 13 figure
Non-monotonic behavior of timescales of passage in heterogeneous media: Dependence on the nature of barriers
Usually time of passage across a region may be expected to increase with the
number of barriers along the path. Can this intuition fail depending on the
special nature of the barrier? We study experimentally the transport of a
robotic bug which navigates through a spatially patterned array of obstacles.
Depending on the nature of the obstacles we call them either entropic or
energetic barriers. For energetic barriers we find that the timescales of first
passage vary non-monotonically with the number of barriers, while for entropic
barriers first passage times increase monotonically. We perform an exact
analytic calculation to derive closed form solutions for the mean first passage
time for different theoretical models of diffusion. Our analytic results
capture this counter-intuitive non-monotonic behaviour for energetic barriers.
We also show non-monotonic effective diffusivity in the case of energetic
barriers. Finally, using numerical simulations, we show this non-monotonic
behaviour for energetic barriers continues to hold true for super-diffusive
transport. These results may be relevant for timescales of intra-cellular
biological processes
Asymptotic behaviour of convex and column-convex lattice polygons with fixed area and varying perimeter
We study the inflated phase of two dimensional lattice polygons, both convex
and column-convex, with fixed area A and variable perimeter, when a weight
\mu^t \exp[- Jb] is associated to a polygon with perimeter t and b bends. The
mean perimeter is calculated as a function of the fugacity \mu and the bending
rigidity J. In the limit \mu -> 0, the mean perimeter has the asymptotic
behaviour \avg{t}/4 \sqrt{A} \simeq 1 - K(J)/(\ln \mu)^2 + O (\mu/ \ln \mu) .
The constant K(J) is found to be the same for both types of polygons,
suggesting that self-avoiding polygons should also exhibit the same asymptotic
behaviour.Comment: 10 pages, 3 figure
- …