114,260 research outputs found
Probabilistic models of individual and collective animal behavior
Recent developments in automated tracking allow uninterrupted,
high-resolution recording of animal trajectories, sometimes coupled with the
identification of stereotyped changes of body pose or other behaviors of
interest. Analysis and interpretation of such data represents a challenge: the
timing of animal behaviors may be stochastic and modulated by kinematic
variables, by the interaction with the environment or with the conspecifics
within the animal group, and dependent on internal cognitive or behavioral
state of the individual. Existing models for collective motion typically fail
to incorporate the discrete, stochastic, and internal-state-dependent aspects
of behavior, while models focusing on individual animal behavior typically
ignore the spatial aspects of the problem. Here we propose a probabilistic
modeling framework to address this gap. Each animal can switch stochastically
between different behavioral states, with each state resulting in a possibly
different law of motion through space. Switching rates for behavioral
transitions can depend in a very general way, which we seek to identify from
data, on the effects of the environment as well as the interaction between the
animals. We represent the switching dynamics as a Generalized Linear Model and
show that: (i) forward simulation of multiple interacting animals is possible
using a variant of the Gillespie's Stochastic Simulation Algorithm; (ii)
formulated properly, the maximum likelihood inference of switching rate
functions is tractably solvable by gradient descent; (iii) model selection can
be used to identify factors that modulate behavioral state switching and to
appropriately adjust model complexity to data. To illustrate our framework, we
apply it to two synthetic models of animal motion and to real zebrafish
tracking data.Comment: 26 pages, 11 figure
Switching of magnetic domains reveals evidence for spatially inhomogeneous superconductivity
The interplay of magnetic and charge fluctuations can lead to quantum phases
with exceptional electronic properties. A case in point is magnetically-driven
superconductivity, where magnetic correlations fundamentally affect the
underlying symmetry and generate new physical properties. The superconducting
wave-function in most known magnetic superconductors does not break
translational symmetry. However, it has been predicted that modulated triplet
p-wave superconductivity occurs in singlet d-wave superconductors with
spin-density wave (SDW) order. Here we report evidence for the presence of a
spatially inhomogeneous p-wave Cooper pair-density wave (PDW) in CeCoIn5. We
show that the SDW domains can be switched completely by a tiny change of the
magnetic field direction, which is naturally explained by the presence of
triplet superconductivity. Further, the Q-phase emerges in a common
magneto-superconducting quantum critical point. The Q-phase of CeCoIn5 thus
represents an example where spatially modulated superconductivity is associated
with SDW order
Optimal Active Control of a Wave Energy Converter
Abstract-This paper investigates optimal active control schemes applied to a point absorber wave energy converter within a receding horizon fashion. A variational formulation of the power maximization problem is adapted to solve the optimal control problem. The optimal control method is shown to be of a bang-bang type for a power take-off mechanism that incorporates both linear dampers and active control elements. We also consider a direct transcription of the optimal control problem as a general nonlinear program. A variation of the projected gradient optimization scheme is formulated and shown to be feasible and computationally inexpensive compared to a standard NLP solver. Since the system model is bilinear and the cost function is non-convex quadratic, the resulting optimization problem is not a convex quadratic program. Results will be compared with an optimal command latching method to demonstrate the improvement in absorbed power. Time domain simulations are generated under irregular sea conditions
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