Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/79822
Sun, 19 Nov 2017 10:11:10 GMT2017-11-19T10:11:10ZEstimation of the synaptic conductance in a McKean-model neuron
http://hdl.handle.net/2117/106463
Estimation of the synaptic conductance in a McKean-model neuron
Guillamon Grabolosa, Antoni; Prohens Sastre, Rafel; Teruel Aguilar, Antonio E.; Vich Llompart, Catalina
Estimating the synaptic conductances impinging on a single neuron directly from its membrane potential is one of the open problems to be solved in order to understand the flow of information in the brain. Despite the existence of some computational strategies that give circumstantial solutions ([1-3] for instance), they all present the inconvenience that the estimation can only be done in subthreshold activity regimes. The main constraint to provide strategies for the oscillatory regimes is related to the nonlinearity of the input-output curve and the difficulty to compute it. In experimental studies it is hard to obtain these strategies and, moreover, there are no theoretical indications of how to deal with this inverse non-linear problem. In this work, we aim at giving a first proof of concept to address the estimation of synaptic conductances when the neuron is spiking. For this purpose, we use a simplified model of neuronal activity, namely a piecewise linear version of the Fitzhugh-Nagumo model, the McKean model ([4], among others), which allows an exact knowledge of the nonlinear f-I curve by means of standard techniques of non-smooth dynamical systems. As a first step, we are able to infer a steady synaptic conductance from the cell's oscillatory activity. As shown in Figure ¿Figure1,1, the model shows the relative errors of the conductances of order C, where C is the membrane capacitance (C<<1), notably improving the errors obtained using filtering techniques on the membrane potential plus linear estimations, see numerical tests performed in [5].
Fri, 14 Jul 2017 12:07:45 GMThttp://hdl.handle.net/2117/1064632017-07-14T12:07:45ZGuillamon Grabolosa, AntoniProhens Sastre, RafelTeruel Aguilar, Antonio E.Vich Llompart, CatalinaEstimating the synaptic conductances impinging on a single neuron directly from its membrane potential is one of the open problems to be solved in order to understand the flow of information in the brain. Despite the existence of some computational strategies that give circumstantial solutions ([1-3] for instance), they all present the inconvenience that the estimation can only be done in subthreshold activity regimes. The main constraint to provide strategies for the oscillatory regimes is related to the nonlinearity of the input-output curve and the difficulty to compute it. In experimental studies it is hard to obtain these strategies and, moreover, there are no theoretical indications of how to deal with this inverse non-linear problem. In this work, we aim at giving a first proof of concept to address the estimation of synaptic conductances when the neuron is spiking. For this purpose, we use a simplified model of neuronal activity, namely a piecewise linear version of the Fitzhugh-Nagumo model, the McKean model ([4], among others), which allows an exact knowledge of the nonlinear f-I curve by means of standard techniques of non-smooth dynamical systems. As a first step, we are able to infer a steady synaptic conductance from the cell's oscillatory activity. As shown in Figure ¿Figure1,1, the model shows the relative errors of the conductances of order C, where C is the membrane capacitance (C<<1), notably improving the errors obtained using filtering techniques on the membrane potential plus linear estimations, see numerical tests performed in [5].Solar radiation pressure assisted transfers between Lissajous orbits of the Sun-Earth system
http://hdl.handle.net/2117/102382
Solar radiation pressure assisted transfers between Lissajous orbits of the Sun-Earth system
Stefania, Soldini; Gomez Muntané, Gerard; Masdemont Soler, Josep; Camilla, Colombo; Walker, Scott
This article investigates a propellant-free transfer between Lissa jous orbits in the Sun-Earth system modelled as a photo-gravitational circular restricted three body p roblem. The geometry of the phase space around the L 1 , 2 equilibrium points is exploited to change the amplitudes and phases of the initial Lissajous orbit using the associated hyperbolic invarian t manifolds. The desired Lissajous orbit is reached by cancelling out the instabilities by means o f solar radiation pressure manoeuvres. The acceleration required is controlled by the change in the spacecraft’s reflectivity and angle of incidence of the Sun-line direction. Changes in reflectivit y allow transfers along the x -axis, while re-orientations of the spacecraft move the equilibrium p oints, and the orbits around them, towards the x - y plane. For equilibrium points in the x - y plane, the in-plane centre manifold tends to a center × centre × focus equilibrium. The analytical solution is extended to this general case. An analysis in the magnitude of the manoeuvre required is pres ented for different Lissajous orbit amplitudes and reflectivity, along with a comment on harnessing solar radiation pressure devices
Mon, 13 Mar 2017 11:30:03 GMThttp://hdl.handle.net/2117/1023822017-03-13T11:30:03ZStefania, SoldiniGomez Muntané, GerardMasdemont Soler, JosepCamilla, ColomboWalker, ScottThis article investigates a propellant-free transfer between Lissa jous orbits in the Sun-Earth system modelled as a photo-gravitational circular restricted three body p roblem. The geometry of the phase space around the L 1 , 2 equilibrium points is exploited to change the amplitudes and phases of the initial Lissajous orbit using the associated hyperbolic invarian t manifolds. The desired Lissajous orbit is reached by cancelling out the instabilities by means o f solar radiation pressure manoeuvres. The acceleration required is controlled by the change in the spacecraft’s reflectivity and angle of incidence of the Sun-line direction. Changes in reflectivit y allow transfers along the x -axis, while re-orientations of the spacecraft move the equilibrium p oints, and the orbits around them, towards the x - y plane. For equilibrium points in the x - y plane, the in-plane centre manifold tends to a center × centre × focus equilibrium. The analytical solution is extended to this general case. An analysis in the magnitude of the manoeuvre required is pres ented for different Lissajous orbit amplitudes and reflectivity, along with a comment on harnessing solar radiation pressure devicesDynamics in the centre manifold around equilibrium points in periodically perturbed three-body problems
http://hdl.handle.net/2117/101316
Dynamics in the centre manifold around equilibrium points in periodically perturbed three-body problems
Le Bihan, Bastien; Masdemont Soler, Josep; Gomez Muntané, Gerard; Lizy-Destrez, Stephanie
A new application of the parameterization method is pre- sented to compute invariant manifolds about the equilib- rium points of Periodically Perturbed Three-Body Problems ( PPTBP ). These techniques are applied to obtain high-order semi-numerical approximations of the center manifolds abo ut the points L 1 , 2 of the Sun-perturbed Earth-Moon Quasi- Bicicular Problem ( QBCP ), which is a particular case of PPTBP . The quality of these approximations is compared with results obtained using equivalents of previous normal form procedures. Then, the parameterization is used to ini- tialize the computation of Poincaré maps, which allow to get a qualitative description of the periodically-perturb ed dynamics near the equilibrium points
Tue, 21 Feb 2017 12:51:32 GMThttp://hdl.handle.net/2117/1013162017-02-21T12:51:32ZLe Bihan, BastienMasdemont Soler, JosepGomez Muntané, GerardLizy-Destrez, StephanieA new application of the parameterization method is pre- sented to compute invariant manifolds about the equilib- rium points of Periodically Perturbed Three-Body Problems ( PPTBP ). These techniques are applied to obtain high-order semi-numerical approximations of the center manifolds abo ut the points L 1 , 2 of the Sun-perturbed Earth-Moon Quasi- Bicicular Problem ( QBCP ), which is a particular case of PPTBP . The quality of these approximations is compared with results obtained using equivalents of previous normal form procedures. Then, the parameterization is used to ini- tialize the computation of Poincaré maps, which allow to get a qualitative description of the periodically-perturb ed dynamics near the equilibrium pointsHAmsys 2014
http://hdl.handle.net/2117/85288
HAmsys 2014
Ollé Torner, Mercè; Barrabés Vera, Esther; Gomez Muntane, Gerard; Mondelo, Josep Maria
In this talk we give an explanation of transport in the
solar system based in dynamical systems theory. More concretely
we consider (as a first approximation) different bicircular problems
(i.e. Sun, Jupiter, a planet and an infinitesimal mass), we take
sl natural periodic orbits which are unstable and we study
their invariant manifolds as well as the existence
of possible heteroclinic connections. The role that these
particular trajectories
play in relation with transport from exterior planets
to the inner ones is discussed. Finally, some comments
concerning a more realistic model of the Solar System are given
and dynamical substitutes of invariant objects (from simpler models)
are obtained
Wed, 06 Apr 2016 10:35:29 GMThttp://hdl.handle.net/2117/852882016-04-06T10:35:29ZOllé Torner, MercèBarrabés Vera, EstherGomez Muntane, GerardMondelo, Josep MariaIn this talk we give an explanation of transport in the
solar system based in dynamical systems theory. More concretely
we consider (as a first approximation) different bicircular problems
(i.e. Sun, Jupiter, a planet and an infinitesimal mass), we take
sl natural periodic orbits which are unstable and we study
their invariant manifolds as well as the existence
of possible heteroclinic connections. The role that these
particular trajectories
play in relation with transport from exterior planets
to the inner ones is discussed. Finally, some comments
concerning a more realistic model of the Solar System are given
and dynamical substitutes of invariant objects (from simpler models)
are obtainedOn the rotational Cucker-Smale model: optimal formation configuration and adaptive gains design
http://hdl.handle.net/2117/85272
On the rotational Cucker-Smale model: optimal formation configuration and adaptive gains design
Paita, Fabrizio; Gómez Muntané, Gerard; Masdemont Soler, Josep
In the present paper we consider the attitude synchronization problem for a formation of spacecraft flying in free space. In particular, we consider the same control laws of [1] and we expand on the results presented there. First, we review the adaptive gains definition for one of the controls and we modify it in order to lighten the computational load (without compromising the performance). Secondly, given the limitations imposed by the formation dimension and configuration, we explore the parameters spaces for both controls in search for gains providing the best performances (in terms of synchronization time). Finally, following these analyses, we study the dependence of the synchronization time from the formation configuration, considered as a function of the latter dimension and of the graph structure
Wed, 06 Apr 2016 09:30:18 GMThttp://hdl.handle.net/2117/852722016-04-06T09:30:18ZPaita, FabrizioGómez Muntané, GerardMasdemont Soler, JosepIn the present paper we consider the attitude synchronization problem for a formation of spacecraft flying in free space. In particular, we consider the same control laws of [1] and we expand on the results presented there. First, we review the adaptive gains definition for one of the controls and we modify it in order to lighten the computational load (without compromising the performance). Secondly, given the limitations imposed by the formation dimension and configuration, we explore the parameters spaces for both controls in search for gains providing the best performances (in terms of synchronization time). Finally, following these analyses, we study the dependence of the synchronization time from the formation configuration, considered as a function of the latter dimension and of the graph structureNatural configurations for formation flying around triangular libration points for the elliptic and the bicircular problem in the earth-moon system
http://hdl.handle.net/2117/27848
Natural configurations for formation flying around triangular libration points for the elliptic and the bicircular problem in the earth-moon system
Salazar, Francisco; Winter, O. C.; Macau, E.E.N.; Masdemont Soler, Josep; Gómez Muntané, Gerard
The concept of Satellite Formation Flying (SFF) means to have two or more satellites in orbit such that their
relative positions remain constant or obeying a certain dynamical configuration along the trajectory. This concept
involves the control over the coordinated motion of a group of satellites, with the goal of maintaining a specific
geometric space configuration between the elements of the cluster. Assume a constellation of satellites is flying close
a given nominal trajectory around L
4
or L
5
in the Earth-Moon system, in such a way that, there is some freedom in
the selection of the geometry of the constellation. We are interested in avoiding large variations of the mutual
distances between spacecraft. In this case, previous studies about triangular libration points have determined the
existence of regions of zero and minimum relative radial acceleration with respect to the nominal trajectory that
prevent from the expansion or contraction of the constellation. Similarly, these studies have also shown the existence
of regions of maximum relative radial acceleration with respect to the nominal trajectory that produce a larger
expansion and contraction of the constellation. However, these studies only considered the gravitational force of the
Earth and the Moon using as approximation the Circular Restricted Three Body Problem (CRTBP). Although the
CRTBP model is a good approximation for the dynamics of spacecraft in the Earth-Moon system, the stability of
constellations flying around L4 and L5 is strongly a
ff
ected when the primary orbit eccentricity and perturbations
from the sun (gravity and light pressure) are considered. As consequence, the previous studies show that, using the
CRTBP model, the fuel consumption to maintain the geometry of the constellation computed by the residual
acceleration is practically zero. In this manner, the goal of this work is the study and analysis of the best regions to
place a constellation that is flying close a given nominal trajectory around L
4
or L
5
, involving a linear approximation
of the equations of motion relative to the periodic orbits around triangular libration points and taking into account the
Moon’s eccentricity and perturbations from the Sun. This model is not only more realistic for practical engineering
applications but permits to determine more accurately the fuel consumption to maintain the geometry of the
constellation
Fri, 08 May 2015 12:08:39 GMThttp://hdl.handle.net/2117/278482015-05-08T12:08:39ZSalazar, FranciscoWinter, O. C.Macau, E.E.N.Masdemont Soler, JosepGómez Muntané, GerardThe concept of Satellite Formation Flying (SFF) means to have two or more satellites in orbit such that their
relative positions remain constant or obeying a certain dynamical configuration along the trajectory. This concept
involves the control over the coordinated motion of a group of satellites, with the goal of maintaining a specific
geometric space configuration between the elements of the cluster. Assume a constellation of satellites is flying close
a given nominal trajectory around L
4
or L
5
in the Earth-Moon system, in such a way that, there is some freedom in
the selection of the geometry of the constellation. We are interested in avoiding large variations of the mutual
distances between spacecraft. In this case, previous studies about triangular libration points have determined the
existence of regions of zero and minimum relative radial acceleration with respect to the nominal trajectory that
prevent from the expansion or contraction of the constellation. Similarly, these studies have also shown the existence
of regions of maximum relative radial acceleration with respect to the nominal trajectory that produce a larger
expansion and contraction of the constellation. However, these studies only considered the gravitational force of the
Earth and the Moon using as approximation the Circular Restricted Three Body Problem (CRTBP). Although the
CRTBP model is a good approximation for the dynamics of spacecraft in the Earth-Moon system, the stability of
constellations flying around L4 and L5 is strongly a
ff
ected when the primary orbit eccentricity and perturbations
from the sun (gravity and light pressure) are considered. As consequence, the previous studies show that, using the
CRTBP model, the fuel consumption to maintain the geometry of the constellation computed by the residual
acceleration is practically zero. In this manner, the goal of this work is the study and analysis of the best regions to
place a constellation that is flying close a given nominal trajectory around L
4
or L
5
, involving a linear approximation
of the equations of motion relative to the periodic orbits around triangular libration points and taking into account the
Moon’s eccentricity and perturbations from the Sun. This model is not only more realistic for practical engineering
applications but permits to determine more accurately the fuel consumption to maintain the geometry of the
constellationConfinement of spacecraft swarms in J2-perturbed orbits about the earth
http://hdl.handle.net/2117/27845
Confinement of spacecraft swarms in J2-perturbed orbits about the earth
García-Taberner, Laura; Masdemont Soler, Josep
There have been studies of the reliability of a swarm
[3], based on nano-satellites, that give a study for the num-
ber of satellites that can be working as a period of time,
with good results for a 5-10 anys time step.
The strategies to control the swarm are based in three
main concepts. The first one studies the global movement
of the swarm as the ones that we can find in nature [5],
where each of the spacecraft has behavior depending on
the position and velocity of closest neighbors. The sec-
ond one are the strategies that include the provision of
collision-free orbits for long periods of time[1]. Finally
,
there is the strategy to keep the relative distance between
spacecraft [2].
The main contribution of this paper is the adapta-
tion of a methodology proposed for reconfigurations of
spacecraft [6] to swarms, taking into account that the
higher complexity of the problem needs some adjuste-
ments. These adjustements are based on the strategies of
swarms in nature (there are only reconfigurations based
on the neighbour states). The statement of the problem
is to calculate the cost to maintain the spacecraft of the
swarm for a year in a sphere of radius
R
for a year, avoid-
ing collisions and minimizing the fuel usage
Fri, 08 May 2015 11:40:27 GMThttp://hdl.handle.net/2117/278452015-05-08T11:40:27ZGarcía-Taberner, LauraMasdemont Soler, JosepThere have been studies of the reliability of a swarm
[3], based on nano-satellites, that give a study for the num-
ber of satellites that can be working as a period of time,
with good results for a 5-10 anys time step.
The strategies to control the swarm are based in three
main concepts. The first one studies the global movement
of the swarm as the ones that we can find in nature [5],
where each of the spacecraft has behavior depending on
the position and velocity of closest neighbors. The sec-
ond one are the strategies that include the provision of
collision-free orbits for long periods of time[1]. Finally
,
there is the strategy to keep the relative distance between
spacecraft [2].
The main contribution of this paper is the adapta-
tion of a methodology proposed for reconfigurations of
spacecraft [6] to swarms, taking into account that the
higher complexity of the problem needs some adjuste-
ments. These adjustements are based on the strategies of
swarms in nature (there are only reconfigurations based
on the neighbour states). The statement of the problem
is to calculate the cost to maintain the spacecraft of the
swarm for a year in a sphere of radius
R
for a year, avoid-
ing collisions and minimizing the fuel usageMixed dynamics in reversible maps with gure-8 homoclinic connections
http://hdl.handle.net/2117/27151
Mixed dynamics in reversible maps with gure-8 homoclinic connections
Delshams Valdés, Amadeu; Gonchenko, Sergey; Lázaro Ochoa, José Tomás
We study dynamics and bifurcations of two-dimensional reversible maps having non-transversal heteroclinic cycles containing symmetric saddle periodic points. We consider one-parameter families of rev
ersible maps unfolding generally the initial heteroclinic tangency and prove that there are infinitely sequences (cascades) of bifurcations of birth of asymptotically stable and unstable as well as elliptic periodic orbits.
Wed, 08 Apr 2015 09:40:14 GMThttp://hdl.handle.net/2117/271512015-04-08T09:40:14ZDelshams Valdés, AmadeuGonchenko, SergeyLázaro Ochoa, José TomásWe study dynamics and bifurcations of two-dimensional reversible maps having non-transversal heteroclinic cycles containing symmetric saddle periodic points. We consider one-parameter families of rev
ersible maps unfolding generally the initial heteroclinic tangency and prove that there are infinitely sequences (cascades) of bifurcations of birth of asymptotically stable and unstable as well as elliptic periodic orbits.