18,830 research outputs found
Spin chain sigma models with fermions
The complete one-loop planar dilatation operator of N=4 supersymmetric
Yang-Mills is isomorphic to the hamiltonian of an integrable PSU(2,2|4) quantum
spin chain. We construct the non-linear sigma models describing the continuum
limit of the SU(1|3) and SU(2|3) sectors of the complete N=4 chain. We
explicitely identify the spin chain sigma model with the one for a superstring
moving in AdS_5xS^5 with large angular momentum along the five-sphere.Comment: 16 pages. Latex. v2: Misprints corrected and references adde
Sustained plankton blooms under open chaotic flows
We consider a predator-prey model of planktonic population dynamics, of
excitable character, living in an open and chaotic fluid flow, i.e., a state of
fluid motion in which fluid trajectories are unbounded but a chaotic region
exists that is restricted to a localized area. Despite that excitability is a
transient phenomenon and that fluid trajectories are continuously leaving the
system, there is a regime of parameters where the excitation remains
permanently in the system, given rise to a persistent plankton bloom. This
regime is reached when the time scales associated to fluid stirring become
slower than the ones associated to biological growth.Comment: 14 pages, 3 figure
Non-Unitarity vs sterile neutrinos at DUNE
Neutrino masses are one of the most promising open windows to physics beyond
the Standard Model (SM). Several extensions of the SM which accommodate
neutrino masses require the addition of right-handed neutrinos to its particle
content. These extra fermions will either be kinematically accessible (sterile
neutrinos) or not (deviations from Unitarity of the PMNS matrix) but at some
point they will impact neutrino oscillation searches. We explore the
differences and similitudes between the two cases and compare their present
bounds with the expected sensitivities of DUNE. We conclude that Non-Unitarity
(NU) effects are too constrained to impact present or near future neutrino
oscillation facilities but that sterile neutrinos can play an important role at
long baseline experiments.Comment: Talk and poster presented at NuPhys2016 (London, 12-14 December
2016). 8 pages, LaTeX, 4 eps figures. Based on arXiv:1609.0863
Consciosusness in Cognitive Architectures. A Principled Analysis of RCS, Soar and ACT-R
This report analyses the aplicability of the principles of consciousness developed in the ASys project to three of the most relevant cognitive architectures. This is done in relation to their aplicability to build integrated control systems and studying their support for general mechanisms of real-time consciousness.\ud
To analyse these architectures the ASys Framework is employed. This is a conceptual framework based on an extension for cognitive autonomous systems of the General Systems Theory (GST).\ud
A general qualitative evaluation criteria for cognitive architectures is established based upon: a) requirements for a cognitive architecture, b) the theoretical framework based on the GST and c) core design principles for integrated cognitive conscious control systems
Spatial Patterns in Chemically and Biologically Reacting Flows
We present here a number of processes, inspired by concepts in Nonlinear
Dynamics such as chaotic advection and excitability, that can be useful to
understand generic behaviors in chemical or biological systems in fluid flows.
Emphasis is put on the description of observed plankton patchiness in the sea.
The linearly decaying tracer, and excitable kinetics in a chaotic flow are
mainly the models described. Finally, some warnings are given about the
difficulties in modeling discrete individuals (such as planktonic organisms) in
terms of continuous concentration fields.Comment: 41 pages, 10 figures; To appear in the Proceedings of the 2001 ISSAOS
School on 'Chaos in Geophysical Flows
Spatial patterns of competing random walkers
We review recent results obtained from simple individual-based models of
biological competition in which birth and death rates of an organism depend on
the presence of other competing organisms close to it. In addition the
individuals perform random walks of different types (Gaussian diffusion and
L\'{e}vy flights). We focus on how competition and random motions affect each
other, from which spatial instabilities and extinctions arise. Under suitable
conditions, competitive interactions lead to clustering of individuals and
periodic pattern formation. Random motion has a homogenizing effect and then
delays this clustering instability. When individuals from species differing in
their random walk characteristics are allowed to compete together, the ones
with a tendency to form narrower clusters get a competitive advantage over the
others. Mean-field deterministic equations are analyzed and compared with the
outcome of the individual-based simulations.Comment: 38 pages, including 6 figure
Species clustering in competitive Lotka-Volterra models
We study the properties of Lotka-Volterra competitive models in which the
intensity of the interaction among species depends on their position along an
abstract niche space through a competition kernel. We show analytically and
numerically that the properties of these models change dramatically when the
Fourier transform of this kernel is not positive definite, due to a pattern
forming instability. We estimate properties of the species distributions, such
as the steady number of species and their spacings, for different types of
kernels.Comment: 4 pages, 3 figure
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