arXiv subjects

Biplab Bhattacherjee

Publications and source records attributed to Biplab Bhattacherjee.

5 recordsLinked to original sources

arXiv2025

Emergence of chiral multi-armed spirals in an open system of migrating cells under continuous cell supply

Chirality organize living and active matter systems into striking collective states, yet the principles that govern chiral ordering in open systems, where elements are continuously added or removed, remain unclear. A mutant strain of Dictyostelium discoideum deficient in chemotaxis (KI cells) forms centimeter-scale, clockwise multi-armed spirals. Each arm is a traveling band produced by short-range alignment interactions and guided by a polar-ordered rotating core that encircles the cell source. A subtle clockwise bias in the single-cell migration is amplified by collective ordering into tissue-scale chirality. To uncover the minimal ingredients, we developed an open chiral Vicsek model and identified intrinsic chirality and continuous cell supply as the key factors. Our study establishes a general route by which weak microscopic chirality and sustained material flux generate macroscopic chiral order, offering new insight into chiral patterning in multicellular behaviors.

cond-mat.soft↗

arXiv2019

Re-entrant phase separation in nematically aligning active polar particles

We present a numerical study of the phase behavior of repulsively interacting active polar particles that align their active velocities nematically. The amplitude of the active velocity, and the noise in its orientational alignment control the active nature of the system. At high values of orientational noise, the structural fluid undergoes a continuous nematic-isotropic transition in active orientation. This transition is well separated from an active phase separation, characterized by the formation of high density hexatic clusters, observed at lower noise strengths. With increasing activity, the system undergoes a re-entrant fluid-phase separation-fluid transition. The phase coexistence at low activity can be understood in terms of motility induced phase separation. In contrast, the re-melting of hexatic clusters, and the collective motion at low orientational noise are dominated by flocking behavior. At high activity, sliding and jamming of polar sub-clusters, formation of grain boundaries, lane formation, and subsequent fragmentation of the polar patches mediate remelting.

cond-mat.soft↗

arXiv2019

Band structure in collective motion with quenched range of interaction

A variant of the well known Vicsek model of the collective motion of a group of agents has been studied where the range of interactions are spatially quenched and non-overlapping. To define such interactions, the underlying two dimensional space is discretized and is divided into the primitive cells of an imaginary square lattice. At any arbitrary time instant, all agents within one cell mutually interact with one another. Therefore, when an agent crosses the boundary of a cell, and moves to a neighboring cell, only then its influence is spread to the adjacent cell. Tuning the strength of the scalar noise $η$ it has been observed that the system makes a discontinuous transition from a random diffusive phase to an ordered phase through a critical noise strength $η_c$ where directed bands with high agent densities appear. Unlike the original Vicsek model here a host of different types of bands has been observed with different angles of orientation and different wrapping numbers. More interestingly, two mutually crossed independent sets of simultaneously moving bands are also observed. A prescription for the detailed characterization of different types of bands have been formulated.

cond-mat.stat-mech↗

arXiv2013

Cyclic and Coherent States in Flocks with Topological Distance

A simple model of the two dimensional collective motion of a group of mobile agents have been studied. Like birds, these agents travel in open free space where each of them interacts with the first $n$ neighbors determined by the topological distance with a free boundary condition. Using the same prescription for interactions used in the Vicsek model with scalar noise it has been observed that the flock, in absence of the noise, arrives at a number of interesting stationary states. In the `single sink state' the entire flock maintains perfect cohesion and coherence. In the `cyclic state' every agent executes a uniform circular motion, and the entire flock executes a pulsating dynamics i.e., expands and contracts periodically between a minimum and a maximum size of the flock. When refreshing rate of the interaction zone is the fastest, the entire flock gets fragmented into smaller clusters of different sizes. On introduction of scalar noise a crossover is observed when the agents cross over from a ballistic motion to a diffusive motion. Expectedly the crossover time is dependent on the strength of the noise $η$ and diverges as $η\to 0$. In simpler version the translational degrees of freedom of the agents are suppressed but their angular motion are retained. Here agents are the spins, placed at the sites of a square lattice with periodic boundary condition. Every spin interacts with its $n$ = 2, 3 or 4 nearest neighbors. In the stationary state the entire spin pattern moves as a whole when interactions are anisotropic with $n$ = 2 and 3; but it is completely frozen when the interaction is isotropic with $n=4$. These spin configurations have vortex-antivortex pairs whose density increases as the noise $η$ increases and follows an excellent finite-size scaling analysis.

physics.bio-ph↗

arXiv2013

Information sharing and sorting in a community

We present the results of detailed numerical study of a model for the sharing and sorting of informations in a community consisting of a large number of agents. The information gathering takes place in a sequence of mutual bipartite interactions where randomly selected pairs of agents communicate with each other to enhance their knowledge and sort out the common information. Though our model is less restricted compared to the well established naming game, yet the numerical results strongly indicate that the whole set of exponents characterizing this model are different from those of the naming game and they assume non-trivial values. Finally it appears that in analogy to the emergence of clusters in the phenomenon of percolation, one can define clusters of agents here having the same information. We have studied in detail the growth of the largest cluster in this article and performed its finite-size scaling analysis.

physics.soc-ph↗