306 citations
Counting papers with at most 25 authors, so collaboration author lists do not stand in for the people here.
- Universidade do PortoPT174 papers
- University of CoimbraPT98 papers
- University of MinhoPT81 papers
- University of LisbonPT24 papers
- Centre National de la Recherche ScientifiqueFR22 papers
- Instituto Superior TécnicoPT22 papers
- UCLouvainBE13 papers
- Universidade Federal da BahiaBR13 papers
- Centro de Análise Matemática Geometria e Sistemas DinâmicosPT10 papers
- Pontifícia Universidade Católica do Rio de JaneiroBR10 papers
- Universidad de La LagunaES9 papers
- Universidade Federal do Rio de JaneiroBR9 papers
25 papers · 1 filter
Shades of Hyperbolicity for Hamiltonians
M. Bessa, J. Rocha, M. J. Torres
We prove that a C2 Hamiltonian system H in M is globally hyperbolic if any of the following statements holds: H is robustly topologically stable; H is stably shadowable; H is stabl…
On periodic points of free inverse monoid endomorphisms
Emanuele Rodaro, Pedro V. Silva
It is proved that the periodic point submonoid of a free inverse monoid endomorphism is always finitely generated. Using Chomsky's hierarchy of languages, we prove that the fixed p…
Bounding the gap between a free group (outer) automorphism and its inverse
Manuel Ladra, Pedro V. Silva, Enric Ventura
For any finitely generated group , two complexity functions and are defined to measure the maximal possible gap between the norm of an automorphism (respectively out…
Hom-Lie algebroids
Camille Laurent-Gengoux, Joana Teles
We define hom-Lie algebroids, a definition that may seem cumbersome at first, but which is justified, first, by a one-to-one corespondence with hom-Gerstenhaber algebras, a notion…
A -linear analogue of the plane wave expansion
Luís Daniel Abreu, Óscar Ciaurri, Juan Luis Varona
We obtain a -linear analogue of Gegenbauer's expansion of the plane wave. It is expanded in terms of the little -Gegenbauer polynomials and the \textit{third} Jackson -Bes…
Fixed points of endomorphisms of graph groups
Emanuele Rodaro, Pedro V. Silva, Mihalis Sykiotis
It is shown, for a given graph group , that the fixed point subgroup Fix is finitely generated for every endomorphism of if and only if is a free product of fre…
Pointed homotopy and pointed lax homotopy of 2-crossed module maps
Bjorn Gohla, Joao Faria Martins
We address the (pointed) homotopy theory of 2-crossed modules (of groups), which are known to faithfully represent Gray 3-groupoids, with a single object, and also connected homoto…
Einstein manifolds with skew torsion
Ilka Agricola, Ana Cristina Ferreira
This paper is devoted to the first systematic investigation of manifolds that are Einstein for a connection with skew symmetric torsion. We derive the Einstein equation from a vari…
Extreme value statistics for dynamical systems with noise
Davide Faranda, Jorge Milhazes Freitas, Valerio Lucarini +2
We study the distribution of maxima (Extreme Value Statistics) for sequences of observables computed along orbits generated by random transformations. The underlying, deterministic…
Laws of rare events for deterministic and random dynamical systems
Hale Aytaç, Jorge Milhazes Freitas, Sandro Vaienti
The object of this paper is twofold. From one side we study the dichotomy, in terms of the Extremal Index of the possible Extreme Value Laws, when the rare events are centred aroun…
Nijenhuis and Compatible Tensors on Lie and Courant algebroids
Paulo Antunes, Joana M. Nunes da Costa
We show that well known structures on Lie algebroids can be viewed as Nijenhuis tensors or pairs of compatible tensors on Courant algebroids. We study compatibility and construct h…
Subalgebras of FA-presentable algebras
Alan J. Cain, Nik Ruškuc
Automatic presentations, also called FA-presentations, were introduced to extend finite model theory to infinite structures whilst retaining the solubility of fundamental decision…
The problem of a self-gravitating scalar field with positive cosmological constant
Joao L. Costa, Artur Alho, Jose Natario
We study the Einstein-scalar field system with positive cosmological constant and spherically symmetric characteristic initial data given on a truncated null cone. We prove well-po…
Studying conformally flat spacetimes with an elastic stress energy tensor using 1+3 formalism
I. Brito, M. P. Machado Ramos
Conformally flat spacetimes with an elastic stress energy tensor given by a diagonal trace-free anisotropic pressure tensor are investigated using 1+3 formalism. We show how the nu…
Finite Gröbner--Shirshov bases for Plactic algebras and biautomatic structures for Plactic monoids
Alan J. Cain, Robert D. Gray, António Malheiro
This paper shows that every Plactic algebra of finite rank admits a finite Gröbner--Shirshov basis. The result is proved by using the combinatorial properties of Young tableaux to…
Anomalous fluctuations for a perturbed Hamiltonian system with exponential interactions
Cedric Bernardin, P. Gonçalves
A one-dimensional Hamiltonian system with exponential interactions perturbed by a conservative noise is considered. It is proved that energy superdiffuses and upper and lower bound…
The compound Poisson limit ruling periodic extreme behaviour of non-uniformly hyperbolic dynamics
Ana Cristina Moreira Freitas, Jorge Milhazes Freitas, Mike Todd
We prove that the distributional limit of the normalised number of returns to small neighbourhoods of periodic points of non-uniformly hyperbolic dynamical systems is compound Pois…
Application of Neural Networks to the study of stellar model solutions
F. J. G. Pinheiro, T. Simas, J. Fernandes +1
Artificial neural networks (ANN) have different applications in Astronomy, including data reduction and data mining. In this work we propose the use ANNs in the identification of s…
Finitely presented monoids with linear Dehn function need not have regular cross-sections
Alan J. Cain, Victor Maltcev
This paper shows that a finitely presented monoid with linear Dehn function need not have a regular cross-section, strengthening the previously-known result that such a monoid need…
On the asymmetric zero-range in the rarefaction fan
Patricia Gonçalves
We consider the one-dimensional asymmetric zero-range process starting from a step decreasing profile. In the hydrodynamic limit this initial condition leads to the rarefaction fan…
Markov semigroups, monoids, and groups
Alan J. Cain, Victor Maltcev
A group is Markov if it admits a prefix-closed regular language of unique representatives with respect to some generating set, and strongly Markov if it admits such a language of u…
An Inverse Problem for Localization Operators
Luis Daniel Abreu, Monika Doerfler
A classical result of time-frequency analysis, obtained by I. Daubechies in 1988, states that the eigenfunctions of a time-frequency localization operator with circular localizatio…
Global Dynamics for Symmetric Planar Maps
B. Alarcon, S. B. S. D. Castro, I. S. Labouriau
We consider sufficient conditions to determine the global dynamics for equivariant maps of the plane with a unique fixed point which is also hyperbolic. When the map is equivariant…
Context-free rewriting systems and word-hyperbolic structures with uniqueness
Alan J. Cain, Victor Maltcev
This paper proves that any monoid presented by a confluent context-free monadic rewriting system is word-hyperbolic. This result then applied to answer a question asked by Duncan &…