8,646 research outputs found
Modelling fungal colonies and communities:challenges and opportunities
This contribution, based on a Special Interest Group session held during IMC9, focuses on physiological based models of filamentous fungal colony growth and interactions. Fungi are known to be an important component of ecosystems, in terms of colony dynamics and interactions within and between trophic levels. We outline some of the essential components necessary to develop a fungal ecology: a mechanistic model of fungal colony growth and interactions, where observed behaviour can be linked to underlying function; a model of how fungi can cooperate at larger scales; and novel techniques for both exploring quantitatively the scales at which fungi operate; and addressing the computational challenges arising from this highly detailed quantification. We also propose a novel application area for fungi which may provide alternate routes for supporting scientific study of colony behaviour. This synthesis offers new potential to explore fungal community dynamics and the impact on ecosystem functioning
From a thin film model for passive suspensions towards the description of osmotic biofilm spreading
Biofilms are ubiquitous macro-colonies of bacteria that develop at various
interfaces (solid-liquid, solid-gas or liquid-gas). The formation of biofilms
starts with the attachment of individual bacteria to an interface, where they
proliferate and produce a slimy polymeric matrix - two processes that result in
colony growth and spreading. Recent experiments on the growth of biofilms on
agar substrates under air have shown that for certain bacterial strains, the
production of the extracellular matrix and the resulting osmotic influx of
nutrient-rich water from the agar into the biofilm are more crucial for the
spreading behaviour of a biofilm than the motility of individual bacteria. We
present a model which describes the biofilm evolution and the advancing biofilm
edge for this spreading mechanism. The model is based on a gradient dynamics
formulation for thin films of biologically passive liquid mixtures and
suspensions, supplemented by bioactive processes which play a decisive role in
the osmotic spreading of biofilms. It explicitly includes the wetting
properties of the biofilm on the agar substrate via a disjoining pressure and
can therefore give insight into the interplay between passive surface forces
and bioactive growth processes
Meso-scale turbulence in living fluids
Turbulence is ubiquitous, from oceanic currents to small-scale biological and
quantum systems. Self-sustained turbulent motion in microbial suspensions
presents an intriguing example of collective dynamical behavior amongst the
simplest forms of life, and is important for fluid mixing and molecular
transport on the microscale. The mathematical characterization of turbulence
phenomena in active non-equilibrium fluids proves even more difficult than for
conventional liquids or gases. It is not known which features of turbulent
phases in living matter are universal or system-specific, or which
generalizations of the Navier-Stokes equations are able to describe them
adequately. Here, we combine experiments, particle simulations, and continuum
theory to identify the statistical properties of self-sustained meso-scale
turbulence in active systems. To study how dimensionality and boundary
conditions affect collective bacterial dynamics, we measured energy spectra and
structure functions in dense Bacillus subtilis suspensions in quasi-2D and 3D
geometries. Our experimental results for the bacterial flow statistics agree
well with predictions from a minimal model for self-propelled rods, suggesting
that at high concentrations the collective motion of the bacteria is dominated
by short-range interactions. To provide a basis for future theoretical studies,
we propose a minimal continuum model for incompressible bacterial flow. A
detailed numerical analysis of the 2D case shows that this theory can reproduce
many of the experimentally observed features of self-sustained active
turbulence.Comment: accepted PNAS version, 6 pages, click doi for Supplementary
Informatio
How bacterial cells and colonies move on solid substrates
Many bacteria rely on active cell appendages, such as type IV pili, to move
over substrates and interact with neighboring cells. Here, we study the motion
of individual cells and bacterial colonies, mediated by the collective
interactions of multiple pili. It was shown experimentally that the substrate
motility of Neisseria gonorrhoeae cells can be described as a persistent random
walk with a persistence length that exceeds the mean pili length. Moreover, the
persistence length increases for a higher number of pili per cell. With the
help of a simple, tractable stochastic model, we test whether a tug-of-war
without directional memory can explain the persistent motion of single
Neisseria gonorrhoeae cells. While the persistent motion of single cells indeed
emerges naturally in the model, a tug-of-war alone is not capable of explaining
the motility of microcolonies, which becomes weaker with increasing colony
size. We suggest sliding friction between the microcolonies and the substrate
as the missing ingredient. While such friction almost does not affect the
general mechanism of single cell motility, it has a strong effect on colony
motility. We validate the theoretical predictions by using a three-dimensional
computational model that includes explicit details of the pili dynamics, force
generation and geometry of cells.Comment: 25 pages, 17 figure
GPU accelerated Nature Inspired Methods for Modelling Large Scale Bi-Directional Pedestrian Movement
Pedestrian movement, although ubiquitous and well-studied, is still not that
well understood due to the complicating nature of the embedded social dynamics.
Interest among researchers in simulating pedestrian movement and interactions
has grown significantly in part due to increased computational and
visualization capabilities afforded by high power computing. Different
approaches have been adopted to simulate pedestrian movement under various
circumstances and interactions. In the present work, bi-directional crowd
movement is simulated where an equal numbers of individuals try to reach the
opposite sides of an environment. Two movement methods are considered. First a
Least Effort Model (LEM) is investigated where agents try to take an optimal
path with as minimal changes from their intended path as possible. Following
this, a modified form of Ant Colony Optimization (ACO) is proposed, where
individuals are guided by a goal of reaching the other side in a least effort
mode as well as a pheromone trail left by predecessors. The basic idea is to
increase agent interaction, thereby more closely reflecting a real world
scenario. The methodology utilizes Graphics Processing Units (GPUs) for general
purpose computing using the CUDA platform. Because of the inherent parallel
properties associated with pedestrian movement such as proximate interactions
of individuals on a 2D grid, GPUs are well suited. The main feature of the
implementation undertaken here is that the parallelism is data driven. The data
driven implementation leads to a speedup up to 18x compared to its sequential
counterpart running on a single threaded CPU. The numbers of pedestrians
considered in the model ranged from 2K to 100K representing numbers typical of
mass gathering events. A detailed discussion addresses implementation
challenges faced and averted
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