15,752 research outputs found
Continuum percolation theory of epimorphic regeneration
A biophysical model of epimorphic regeneration based on a continuum
percolation process of fully penetrable disks in two dimensions is proposed.
All cells within a randomly chosen disk of the regenerating organism are
assumed to receive a signal in the form of a circular wave as a result of the
action/reconfiguration of neoblasts and neoblast-derived mesenchymal cells in
the blastema. These signals trigger the growth of the organism, whose cells
read, on a faster time scale, the electric polarization state responsible for
their differentiation and the resulting morphology. In the long time limit, the
process leads to a morphological attractor that depends on experimentally
accessible control parameters governing the blockage of cellular gap junctions
and, therefore, the connectivity of the multicellular ensemble. When this
connectivity is weakened, positional information is degraded leading to more
symmetrical structures. This general theory is applied to the specifics of
planaria regeneration. Computations and asymptotic analyses made with the model
show that it correctly describes a significant subset of the most prominent
experimental observations, notably anterior-posterior polarization (and its
loss) or the formation of four-headed planaria.Comment: This author wish to retract the paper arXiv:1705.06720 because it
began as part of a collaboration that later fell apart and it was published
without the consent from the collaborators. Furthermore, the collaborators
have managed to provide a better solution to this proble
PWM Control of a Buck Converter with an Amorphous Core Coil
Pulse-width modulation is widely used to control electronic converters. One of the most topologies used for high DC voltage/low DC voltage conversion is the Buck converter. It is obtained as a second order system with a LC filter between the switching subsystem and the load. The use of a coil with an amorphous magnetic material core instead of air core lets design converters with smaller size. If high switching frequencies are used for obtaining high quality voltage output, the value of the auto inductance L is reduced throughout the time. Then, robust controllers are needed if the accuracy of the converter response must not be affected by auto inductance and load variations. This paper presents a robust controller for a Buck converter based on a state space feedback control system combined with an additional virtual space variable which minimizes the effects of the inductance and load variations when a not-toohigh switching frequency is applied. The system exhibits a null steady-state average error response for the entire range of parameter variations. Simulation results are presented
Using the Own Flexibility of a Climbing Robot as a Double Force Sensor
Force sensors are used when interaction tasks are carried out by robots in general, and by climbing robots in particular. If the mechanics and electronics systems are contained inside the own robot, the robot becomes portable without external control. Commercial force sensors cannot be used due to limited space and weight. By selecting the links material with appropriate stiffness and placing strain gauges on the structure, the own robot flexibility can be used such as force sensor. Thus, forces applied on the robot tip can be measured without additional external devices. Only gauges and small internal electronic converters are necessary. This paper illustrates the proposed algorithm to achieve these measurements. Additionally, experimental results are presented
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