2,793 research outputs found
Shrinking Point Bifurcations of Resonance Tongues for Piecewise-Smooth, Continuous Maps
Resonance tongues are mode-locking regions of parameter space in which stable
periodic solutions occur; they commonly occur, for example, near Neimark-Sacker
bifurcations. For piecewise-smooth, continuous maps these tongues typically
have a distinctive lens-chain (or sausage) shape in two-parameter bifurcation
diagrams. We give a symbolic description of a class of "rotational" periodic
solutions that display lens-chain structures for a general -dimensional map.
We then unfold the codimension-two, shrinking point bifurcation, where the
tongues have zero width. A number of codimension-one bifurcation curves emanate
from shrinking points and we determine those that form tongue boundaries.Comment: 27 pages, 6 figure
Quantitative Characterization of α-Synuclein Aggregation in Living Cells through Automated Microfluidics Feedback Control
Aggregation of α-synuclein and formation of inclusions are hallmarks of Parkinson's disease (PD). Aggregate formation is affected by cellular environment, but it has been studied almost exclusively in cell-free systems. We quantitatively analyzed α-synuclein inclusion formation and clearance in a yeast cell model of PD expressing either wild-type (WT) α-synuclein or the disease-associated A53T mutant from the galactose (Gal)-inducible promoter. A computer-controlled microfluidics device regulated α-synuclein in cells by means of closed-loop feedback control. We demonstrated that inclusion formation is strictly concentration dependent and that the aggregation threshold of the A53T mutant is about half of the WT α-synuclein (56%). We chemically modulated the proteasomal and autophagic pathways and demonstrated that autophagy is the main determinant of A53T α-synuclein inclusions’ clearance. In addition to proposing a technology to overcome current limitations in dynamically regulating protein expression levels, our results contribute to the biology of PD and have relevance for therapeutic applications
Smoothing tautologies, hidden dynamics, and sigmoid asymptotics for piecewise smooth systems
Switches in real systems take many forms, such as impacts, electronic relays,
mitosis, and the implementation of decisions or control strategies. To
understand what is lost, and what can be retained, when we model a switch as an
instantaneous event, requires a consideration of so-called hidden terms. These
are asymptotically vanishing outside the switch, but can be encoded in the form
of nonlinear switching terms. A general expression for the switch can be
developed in the form of a series of sigmoid functions. We review the key steps
in extending the Filippov's method of sliding modes to such systems. We show
how even slight nonlinear effects can hugely alter the behaviour of an
electronic control circuit, and lead to `hidden' attractors inside the
switching surface.Comment: 12 page
Bifurcation Phenomena in Two-Dimensional Piecewise Smooth Discontinuous Maps
In recent years the theory of border collision bifurcations has been
developed for piecewise smooth maps that are continuous across the border, and
has been successfully applied to explain nonsmooth bifurcation phenomena in
physical systems. However, many switching dynamical systems have been found to
yield two-dimensional piecewise smooth maps that are discontinuous across the
border. The theory for understanding the bifurcation phenomena in such systems
is not available yet. In this paper we present the first approach to the
problem of analysing and classifying the bifurcation phenomena in
two-dimensional discontinuous maps, based on a piecewise linear approximation
in the neighborhood of the border. We explain the bifurcations occurring in the
static VAR compensator used in electrical power systems, using the theory
developed in this paper. This theory may be applied similarly to other systems
that yield two-dimensional discontinuous maps
Coexisting patterns of population oscillations: the degenerate Neimark Sacker bifurcation as a generic mechanism
We investigate a population dynamics model that exhibits a Neimark Sacker
bifurcation with a period that is naturally close to 4. Beyond the bifurcation,
the period becomes soon locked at 4 due to a strong resonance, and a second
attractor of period 2 emerges, which coexists with the first attractor over a
considerable parameter range. A linear stability analysis and a numerical
investigation of the second attractor reveal that the bifurcations producing
the second attractor occur naturally in this type of system.Comment: 8 pages, 3 figure
Design and validation of a virtual player for studying interpersonal coordination in the mirror game
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.The mirror game has been recently proposed as
a simple, yet powerful paradigm for studying interpersonal
interactions. It has been suggested that a virtual partner able
to play the game with human subjects can be an effective tool
to affect the underlying neural processes needed to establish the
necessary connections between the players, and also to provide
new clinical interventions for rehabilitation of patients suffering
from social disorders. Inspired by the motor processes of the
central nervous system (CNS) and the musculoskeletal system in
the human body, in this paper we develop a novel interactive
cognitive architecture based on nonlinear control theory to drive
a virtual player (VP) to play the mirror game with a human
player (HP) in different configurations. Specifically, we consider
two cases: the former where the VP acts as leader and the latter
where it acts as follower. The crucial problem is to design a
feedback control architecture capable of imitating and following
or leading a human player in a joint action task. Movement of
the end-effector of the VP is modeled by means of a feedback
controlled Haken-Kelso-Bunz (HKB) oscillator, which is coupled
with the observed motion of the HP measured in real time.
To this aim, two types of control algorithms (adaptive control
and optimal control) are used and implemented on the HKB
model so that the VP can generate a human-like motion while
satisfying certain kinematic constraints. A proof of convergence
of the control algorithms is presented in the paper together
with an extensive numerical and experimental validation of their
effectiveness. A comparison with other existing designs is also
discussed, showing the flexibility and the advantages of our
control-based approach.This work was funded by the European Project AlterEgo
FP7 ICT 2.9 - Cognitive Sciences and Robotics, Grant Number
600610
Simultaneous Border-Collision and Period-Doubling Bifurcations
We unfold the codimension-two simultaneous occurrence of a border-collision
bifurcation and a period-doubling bifurcation for a general piecewise-smooth,
continuous map. We find that, with sufficient non-degeneracy conditions, a
locus of period-doubling bifurcations emanates non-tangentially from a locus of
border-collision bifurcations. The corresponding period-doubled solution
undergoes a border-collision bifurcation along a curve emanating from the
codimension-two point and tangent to the period-doubling locus here. In the
case that the map is one-dimensional local dynamics are completely classified;
in particular, we give conditions that ensure chaos.Comment: 22 pages; 5 figure
Activity of bacterial seed endophytes of landrace durum wheat for control of Fusarium foot rot
Five bacterial endophytic isolates obtained from durum wheat seeds (Iandrace "Timilia reste nere") and identified as belonging to Pantoea (isolates A1, F7, F15 and GI) and Paenibacillus (isolate B) genera on the basis of 16S rDNA gene sequences, were assayed in vitro and in vivo for their ability to inhibit Fusarium culmorum growth and the disease (Fusarium foot rot) it causes in durum wheat. All isolates significantly reduced in vitro growth of F. culmorum in comparison with the control. After 120 hours of incubation, isolates B and GI showed the greatest mycelial growth inhibition, i.e., respectively, 76 and 74%. When durum wheat "Simeto" seeds were treated with bacterial isolates singly or in combinations and then inoculated with F. culmorum, all treatments with endophytes showed increased, but not statistically significant, seed germination. Except for isolate Al, all bacterial isolates stimulated vegetative parameters of durum wheat seedlings. Mixture of isolates F7 + F15 was the most effective in improving shoot height (+94%), root length (+47%) and vigour index (+81%). Mixture of isolates A1 + B reduced Fusarium foot rot incidence (-21%) and severity (-30%), and isolate A1 reduced incidence (-15%) and severity (-16%) of the disease. These results indicate potential of bacterial seed endophytes, identified in this study, for control of Fusarium foot rot and suggest that bacterial seed endophytes may provide a new biocontrol agent for an environmentally sustainable durum wheat disease management programme
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