9,173 research outputs found
Morphological analysis of Yarrowia lipolytica under stress conditions through image processing
Yarrowia lipolytica is an aerobic microrganism capable to produce important metabolites, has
an intense secretory activity which drives efforts to be employed in industry (as a biocatalyst),
in molecular biology and genetics studies. Dimorphism is refeered to fungi ability to growth
in two distinct forms, usually as single oval cells os as a filament and to be reversible between
each one. The cell shape is controlled by environmental factors and has been seeked by some
authors [1,2,3].
Y. lipolytica has been considered an adequate model for dimorphism studies in yeasts since it
has an efficient system for transformation and is easy to distinct between its morphological
forms, on opposite to S. cerevisiae that do not produce true filaments and exhibits pseudohyphae
growth under nitrogen limited conditions. Y. lipolytica has an hyphae diameter
corresponding 60 to 100% of its single cell stage [4,5]. It is believed that Y. lipolytica
dimorphism is related to defense mechanism from adverse conditions.
The aim of this work resides on investigate morphological changes in Y. lipolytica under
thermal and oxidative stress conditions. Yarrowia lipolytica (IMUFRJ 50682) was cultivated
in YPD medium (glucose 2%, peptone 0.64%, yeast extract 1%) at 29oC and 160 rpm.
Thermal stress experiments were carried employing a temperature shift (37oC / 1 h.). For
oxidative ones, an addition of H2O2 was used to reach final concentration of 10mM. Both
stress conditions were applied at exponential growth phase. Morphology was observed in a
optic microscope (Axiolab, Zeiss) and cell characteristics were determined employing image
processing analysis (Matlab v. 6.1, The Mathworks Inc.) and comparisons were carried on to
a control system.
A net increase around 22% on hyphae formation was detected as well as a significant
increment in its length in relation to control system, when both thermal and oxidative stress
was applied. The results herein obtained drives to consider a possible relationship between
dimorphism and a cell response mechanism to stress conditions.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação para a Ciência e a Tecnologia (FCT); CAPES
On fermionic tilde conjugation rules and thermal bosonization. Hot and cold thermofields
A generalization of Ojima tilde conjugation rules is suggested, which reveals
the coherent state properties of thermal vacuum state and is useful for the
thermofield bosonization. The notion of hot and cold thermofields is introduced
to distinguish different thermofield representations giving the correct normal
form of thermofield solution for finite temperature Thirring model with correct
renormalization and anticommutation properties.Comment: 13 page
Driven interfaces in disordered media: determination of universality classes from experimental data
While there have been important theoretical advances in understanding the
universality classes of interfaces moving in porous media, the developed tools
cannot be directly applied to experiments. Here we introduce a method that can
identify the universality class from snapshots of the interface profile. We
test the method on discrete models whose universality class is well known, and
use it to identify the universality class of interfaces obtained in experiments
on fluid flow in porous media.Comment: 4 pages, 5 figure
Topological mass mechanism and exact fields mapping
We present a class of mappings between models with topological mass mechanism
and purely topological models in arbitrary dimensions. These mappings are
established by directly mapping the fields of one model in terms of the fields
of the other model in closed expressions. These expressions provide the
mappings of their actions as well as the mappings of their propagators. For a
general class of models in which the topological model becomes the BF model the
mappings present arbitrary functions which otherwise are absent for
Chern-Simons like actions. This work generalizes the results of [1] for
arbitrary dimensions.Comment: 11 page
Stochastic Feedback and the Regulation of Biological Rhythms
We propose a general approach to the question of how biological rhythms
spontaneously self-regulate, based on the concept of ``stochastic feedback''.
We illustrate this approach by considering the neuroautonomic regulation of the
heart rate. The model generates complex dynamics and successfully accounts for
key characteristics of cardiac variability, including the power spectrum,
the functional form and scaling of the distribution of variations, and
correlations in the Fourier phases. Our results suggest that in healthy systems
the control mechanisms operate to drive the system away from extreme values
while not allowing it to settle down to a constant output.Comment: 15 pages, latex2e using rotate and epsf, with 4 ps figures. Submitted
to PR
Cascade Failure in a Phase Model of Power Grids
We propose a phase model to study cascade failure in power grids composed of
generators and loads. If the power demand is below a critical value, the model
system of power grids maintains the standard frequency by feedback control. On
the other hand, if the power demand exceeds the critical value, an electric
failure occurs via step out (loss of synchronization) or voltage collapse. The
two failures are incorporated as two removal rules of generator nodes and load
nodes. We perform direct numerical simulation of the phase model on a
scale-free network and compare the results with a mean-field approximation.Comment: 7 pages, 2 figure
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