233 research outputs found
A Liquid Assay for Screening Fungal Virulence Factors
It is difficult to develop drugs against fungal infections due to the fact that both fungi and their hosts are eukaryotic. Using a model host-pathogen system, factors involved in the infection can be identified and studied. By using these two genetic model organisms and this assay in high-throughput screens of genetic knockouts, fungal virulence factors can be identified. We are developing a liquid culture assay for studying the effects of co-culturing Caenorhabditis elegans with Saccharomyces cerevisiae mutants. From the results of all the experiments, we concluded that there are other factors that can cause the death of the C. elegans in liquid assay which are not S. cerevisiae related
Forcing anomalous scaling on demographic fluctuations
We discuss the conditions under which a population of anomalously diffusing
individuals can be characterized by demographic fluctuations that are
anomalously scaling themselves. Two examples are provided in the case of
individuals migrating by Gaussian diffusion, and by a sequence of L\'evy
flights.Comment: 5 pages 2 figure
Particle Dispersion on Rapidly Folding Random Hetero-Polymers
We investigate the dynamics of a particle moving randomly along a disordered
hetero-polymer subjected to rapid conformational changes which induce
superdiffusive motion in chemical coordinates. We study the antagonistic
interplay between the enhanced diffusion and the quenched disorder. The
dispersion speed exhibits universal behavior independent of the folding
statistics. On the other hand it is strongly affected by the structure of the
disordered potential. The results may serve as a reference point for a number
of translocation phenomena observed in biological cells, such as protein
dynamics on DNA strands.Comment: 4 pages, 4 figure
Levy Flights in Inhomogeneous Media
We investigate the impact of external periodic potentials on superdiffusive
random walks known as Levy flights and show that even strongly superdiffusive
transport is substantially affected by the external field. Unlike ordinary
random walks, Levy flights are surprisingly sensitive to the shape of the
potential while their asymptotic behavior ceases to depend on the Levy index
. Our analysis is based on a novel generalization of the Fokker-Planck
equation suitable for systems in thermal equilibrium. Thus, the results
presented are applicable to the large class of situations in which
superdiffusion is caused by topological complexity, such as diffusion on folded
polymers and scale-free networks.Comment: 4 pages, 4 figure
Spatial clustering of interacting bugs: Levy flights versus Gaussian jumps
A biological competition model where the individuals of the same species
perform a two-dimensional Markovian continuous-time random walk and undergo
reproduction and death is studied. The competition is introduced through the
assumption that the reproduction rate depends on the crowding in the
neighborhood. The spatial dynamics corresponds either to normal diffusion
characterized by Gaussian jumps or to superdiffusion characterized by L\'evy
flights. It is observed that in both cases periodic patterns occur for
appropriate parameters of the model, indicating that the general macroscopic
collective behavior of the system is more strongly influenced by the
competition for the resources than by the type of spatial dynamics. However,
some differences arise that are discussed.Comment: This version incorporates in the text the correction published as an
Erratum in Europhysics Letters (EPL) 95, 69902 (2011) [doi:
10.1209/0295-5075/95/69902
The fractional Keller-Segel model
The Keller-Segel model is a system of partial differential equations
modelling chemotactic aggregation in cellular systems. This model has blowing
up solutions for large enough initial conditions in dimensions d >= 2, but all
the solutions are regular in one dimension; a mathematical fact that crucially
affects the patterns that can form in the biological system. One of the
strongest assumptions of the Keller-Segel model is the diffusive character of
the cellular motion, known to be false in many situations. We extend this model
to such situations in which the cellular dispersal is better modelled by a
fractional operator. We analyze this fractional Keller-Segel model and find
that all solutions are again globally bounded in time in one dimension. This
fact shows the robustness of the main biological conclusions obtained from the
Keller-Segel model
Enhancing Rip Current/ Beach Safety Awareness Among Teenagers
Rip current awareness is a serious issue considering the average 100 fatalities annually and 23,000 lifeguard rescues. This report prepared for the National Oceanic and Atmospheric Administration\u27s Rip Current Task Force, recommends powerful and cost-effective ways to promote rip current awareness to teenagers. Top recommendations include: creating an internet chat bot which provides weather forecasts, implementing classroom enhancement including programs and partnerships, and placing public service announcements. These recommendations can educate teenagers about rip currents and help save lives
Fractional Diffusion Equation for a Power-Law-Truncated Levy Process
Truncated Levy flights are stochastic processes which display a crossover
from a heavy-tailed Levy behavior to a faster decaying probability distribution
function (pdf). Putting less weight on long flights overcomes the divergence of
the Levy distribution second moment. We introduce a fractional generalization
of the diffusion equation, whose solution defines a process in which a Levy
flight of exponent alpha is truncated by a power-law of exponent 5 - alpha. A
closed form for the characteristic function of the process is derived. The pdf
of the displacement slowly converges to a Gaussian in its central part showing
however a power law far tail. Possible applications are discussed
Sheared bioconvection in a horizontal tube
The recent interest in using microorganisms for biofuels is motivation enough
to study bioconvection and cell dispersion in tubes subject to imposed flow. To
optimize light and nutrient uptake, many microorganisms swim in directions
biased by environmental cues (e.g. phototaxis in algae and chemotaxis in
bacteria). Such taxes inevitably lead to accumulations of cells, which, as many
microorganisms have a density different to the fluid, can induce hydrodynamic
instabilites. The large-scale fluid flow and spectacular patterns that arise
are termed bioconvection. However, the extent to which bioconvection is
affected or suppressed by an imposed fluid flow, and how bioconvection
influences the mean flow profile and cell transport are open questions. This
experimental study is the first to address these issues by quantifying the
patterns due to suspensions of the gravitactic and gyrotactic green
biflagellate alga Chlamydomonas in horizontal tubes subject to an imposed flow.
With no flow, the dependence of the dominant pattern wavelength at pattern
onset on cell concentration is established for three different tube diameters.
For small imposed flows, the vertical plumes of cells are observed merely to
bow in the direction of flow. For sufficiently high flow rates, the plumes
progressively fragment into piecewise linear diagonal plumes, unexpectedly
inclined at constant angles and translating at fixed speeds. The pattern
wavelength generally grows with flow rate, with transitions at critical rates
that depend on concentration. Even at high imposed flow rates, bioconvection is
not wholly suppressed and perturbs the flow field.Comment: 19 pages, 9 figures, published version available at
http://iopscience.iop.org/1478-3975/7/4/04600
Modeling the Searching Behavior of Social Monkeys
We discuss various features of the trajectories of spider monkeys looking for
food in a tropical forest, as observed recently in an extensive {\it in situ}
study. Some of the features observed can be interpreted as the result of social
interactions. In addition, a simple model of deterministic walk in a random
environment reproduces the observed angular correlations between successive
steps, and in some cases, the emergence of L\'evy distributions for the length
of the steps.Comment: 7 pages, 3 figure
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