Jamming transition in a driven lattice gas

We study a two-lane driven lattice gas model with oppositely directed particles moving on two periodic lanes with correlated lane switching processes, so that particles can switch lanes with finite probability only when oppositely directed particles meet on the same lane. This system exhibits an unique behavior, wherein a phase transition is observed between a homogeneous absorbing phase, characterized by complete segregation of oppositely directed particles between the two lanes, and a jammed phase where each species of particles occupy both the lanes, along with formation of large cluster. This transition is accompanied by a finite drop of current in the lattice, emergence of cluster comprising of both species of particles, and is determined by the interplay of the relative rates of translation of particles on the same lane and their lane switching rates. These findings may have interesting implications for understanding the phenomenon of jamming in microtubule filaments observed in context of axonal transport.Comment: 6 pages, 7 fi

Mechanical stability of bipolar spindle assembly

Assembly and stability of mitotic spindle is governed by the interplay of various intra-cellular forces, e.g. the forces generated by motor proteins by sliding overlapping anti-parallel microtubules (MTs) polymerized from the opposite centrosomes, the interaction of kinetochores with MTs, and the interaction of MTs with the chromosomes arms. We study the mechanical behavior and stability of spindle assembly within the framework of a minimal model which includes all these effects. For this model, we derive a closed--form analytical expression for the force acting between the centrosomes as a function of their separation distance and we show that an effective potential can be associated with the interactions at play. We obtain the stability diagram of spindle formation in terms of parameters characterizing the strength of motor sliding, repulsive forces generated by polymerizing MTs, and the forces arising out of interaction of MTs with kinetochores. The stability diagram helps in quantifying the relative effects of the different interactions and elucidates the role of motor proteins in formation and inhibition of spindle structures during mitotic cell division. We also predict a regime of bistability for certain parameter range, wherein the spindle structure can be stable for two different finite separation distances between centrosomes. This occurrence of bistability also suggests mechanical versatility of such self-assembled spindle structures.Comment: 7 pages, 6 figures, under review in EP

Collective transport of weakly interacting molecular motors with Langmuir kinetics

Filament based intracellular transport involves the collective action of molecular motor proteins. Experimental evidences suggest that microtubule (MT) filament bound motor proteins such as {\it kinesins} weakly interact among themselves during transport and with the surrounding cellular environment. Motivated by these observations we study a driven lattice gas model for collective unidirectional transport of molecular motors on open filament, which incorporates the short-range interactions between the motors on filaments and couples the transport process on filament with surrounding cellular environment through adsorption-desorption Langmuir (LK) kinetics of the motors. We analyse this model within the framework of a Mean Field (MF) theory in the limit of {\it weak} interactions between the motors. We point to the mapping of this model with the non-conserved version of Katz-Lebowitz-Spohn (KLS) model. The system exhibits rich phase behavior with variety of inhomogeneous phases including localized shocks in the bulk of the filament. We obtain the steady state density and current profiles and analyse their variation as function of the strength of interaction. We compare these MF results with Monte Carlo simulations and find that the MF analysis shows reasonably good agreement as long as the motors are weakly interacting. We also construct the non-equilibrium MF phase diagram.Comment: 4 figure

Indication of transverse radial flow in high-multiplicity proton-proton collisions at the Large Hadron Collider

We analyze the measured spectra of $\pi^\pm$, $K^\pm$, $p$($\bar p$) in $pp$ collisions at $\sqrt {s}$ = 0.9, 2.76 and 7 TeV, in the light of blast-wave model to extract the transverse radial flow velocity and kinetic temperature at freeze-out for the system formed in $pp$ collisions. The dependency of the blast-wave parameters on average charged particle multiplicity of event sample or the `centrality' of collisions has been studied and compared with results of similar analysis in nucleus-nucleus ($AA$) and proton-nucleus ($pA$) collisions. We analyze the spectra of $K_{s}^0$, $\Lambda$($\bar \Lambda$) and $\Xi^-$ also to see the dependence of blast-wave description on the species of produced particles. Within the framework of the blast-wave model, the study reveals indication of collective behavior for high-multiplicity events in $pp$ collisions at LHC. Strong transverse radial flow in high multiplicity $pp$ collisions and its comparison with that in $pA$ and $AA$ collisions match with predictions from a very recent theoretical work [Shuryak and Zahed 2013 arXiv:1301.4470] that addresses the conditions for applicability of hydrodynamics in $pp$ and $pA$ collisions.Comment: 14 pages 8 figure