Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOrder, intermittency and pressure fluctuations in a system of proliferating rods
187
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Non-motile elongated bacteria confined in two-dimensional open micro-channels can exhibit collective motion and form dense monolayers with nematic order if the cells proliferate, i.e., grow and divide. Using soft molecular dynamics simulations of a system of rods interacting through short range mechanical forces, we study the effects of the cell growth rate, the cell aspect ratio and of the sliding friction on nematic ordering and on pressure fluctuations in confined environments. Our results indicate that rods with aspect ratio >3.0 reach quasi-perfect nematic states at low sliding friction. At higher frictions, the global nematic order parameter shows intermittent fluctuations due to sudden losses of order and the time intervals between these bursts are power-law distributed. The pressure transverse to the channel axis can vary abruptly in time and shows hysteresis due to lateral crowding effects. The longitudinal pressure field is on average correlated to nematic order, but it is locally very heterogeneous and its distribution follows an inverse power-law, in sharp contrast with non-active granular systems. We discuss some implications of these findings for tissue growth.
rate research
Read More
This paper has been temporarily withdrawn by the authors. We have recently found that noise in the experiments is at the origin of the supposed back-and-forth motion which is discussed in the first version of the paper. As a consequence, figs 4 and 5 as well as their discussion are incorrect. Figure 1 and the general trend of fig. 2 are still valid. At this time, we are uncertain whether or not the short time behavior of cI, shown in fig. 3, is affected by measurement noise. We are working on a new version of the paper, using new techniques that allow us to correct for the experimental noise.
We report phase separation and liquid-crystal ordering induced by scalar activity in a system of Soft Repulsive Spherocylinders (SRS) of aspect ratio $L/D = 5 $. Activity was introduced by increasing the temperature of half of the SRS (labeled textit{`hot}) while maintaining the temperature of the other half constant at a lower value (labeled textit{`cold}). The difference between the two temperatures scaled by the lower temperature provides a measure of the activity. Starting from different equilibrium initial phases, we find that activity leads to segregation of the hot and cold particles. Activity also drives the cold particles through a phase transition to a more ordered state and the hot particles to a state of less order compared to the initial equilibrium state. The cold components of a homogeneous isotropic (I) structure acquire nematic (N) and, at higher activity, crystalline (K) order. Similarly, the cold zone of a nematic initial state undergoes smectic (Sm) and crystal ordering above a critical value of activity while the hot component turns isotropic. We find that the hot particles occupy a larger volume and exert an extra kinetic pressure, confining, compressing and provoking an ordering transition of the cold-particle domains.
In biological tissues, it is now well-understood that mechanical cues are a powerful mechanism for pattern regulation. While much work has focused on interactions between cells and external substrates, recent experiments suggest that cell polarization and motility might be governed by the internal shear stiffness of nearby tissue, deemed plithotaxis. Meanwhile, other work has demonstrated that there is a direct relationship between cell shapes and tissue shear modulus in confluent tissues. Joining these two ideas, we develop a hydrodynamic model that couples cell shape, and therefore tissue stiffness, to cell motility and polarization. Using linear stability analysis and numerical simulations, we find that tissue behavior can be tuned between largely homogeneous states and patterned states such as asters, controlled by a composite morphotaxis parameter that encapsulates the nature of the coupling between shape and polarization. The control parameter is in principle experimentally accessible, and depends both on whether a cell tends to move in the direction of lower or higher shear modulus, and whether sinks or sources of polarization tend to fluidize the system.
A liquid meniscus, a bending rod (also called elastica) and a simple pendulum are all described by the same non-dimensional equation. The oscillatory regime of the pendulum corresponds to buckling rods and pendant drops, and the high-velocity regime corresponds to spherical drops, puddles and multiple rod loopings. We study this analogy in a didactic way and discuss how, despite this common governing equation, the three systems are not completely equivalent. We also consider the cylindrical deformations of an inextensible, flexible membrane containing a liquid, which in some sense interpolates between the meniscus and rod conformations.
Collective systems across length scales display order in their spatiotemporal patterns. These patterns contain information that correlates with their orders and reflects the system dynamics. Here we show the collective patterns and behaviors of up to 250 micro-rafts spinning at the air-water interface and demonstrate the link between order and information in the collective motion. These micro-rafts display a rich variety of collective behaviors that resemble thermodynamic equilibrium phases such as gases, hexatics, and crystals. Moreover, owing to the unique coupling of magnetic and fluidic forces, a number of collective properties and functions emerge as the micro-rafts interact with magnetic potential and nonmagnetic floating objects. Our findings are relevant for analyzing collective systems in nature and for designing collective robotic systems.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
