La Universidad de las Islas Baleares ante la Ley de Reforma universitaria

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Stability of three-dimensional relativistic jets: implications for jet collimation

The stable propagation of jets in FRII sources is remarkable if one takes into account that large-scale jets are subjected to potentially highly disruptive three-dimensional (3D) Kelvin-Helmholtz instabilities. Numerical simulations can address this problem and help clarify the causes of this remarkable stability. Following previous studies of the stability of relativistic flows in two dimensions (2D), it is our aim to test and extend the conclusions of such works to three dimensions. We present numerical simulations for the study of the stability properties of 3D, sheared, relativistic flows. This work uses a fully parallelized code Ratpenat that solves equations of relativistic hydrodynamics in 3D. The results of the present simulations confirm those in 2D. We conclude that the growth of resonant modes in sheared relativistic flows could be important in explaining the long-term collimation of extragalactic jets.Comment: Accepted for publication in A&

Tevelev degrees and Hurwitz moduli spaces

We interpret the degrees which arise in Tevelev's study of scatteringamplitudes in terms of moduli spaces of Hurwitz covers. Via excess intersectiontheory, the boundary geometry of the Hurwitz moduli space yields a simplerecursion for the Tevelev degrees (together with their natural two parametergeneralization). We find exact solutions which specialize to Tevelev's formulain his cases and connect to the projective geometry of lines and Castelnuovo'sclassical count of linear series in other cases. For almost all values, thecalculation of the two parameter generalization of the Tevelev degree is new. Arelated count of refined Dyck paths is solved along the way.<br

New special cases of the quadratic assignment problem with diagonally structured coefficient matrices

We consider new polynomially solvable cases of the well-known Quadratic Assignment Problem involving coefficient matrices with a special diagonal structure. By combining the new special cases with polynomially solvable special cases known in the literature we obtain a new and larger class of polynomially solvable special cases of the QAP where one of the two coefficient matrices involved is a Robinson matrix with an additional structural property: this matrix can be represented as a conic combination of cut matrices in a certain normal form. The other matrix is a conic combination of a monotone anti-Monge matrix and a down-benevolent Toeplitz matrix. We consider the recognition problem for the special class of Robinson matrices mentioned above and show that it can be solved in polynomial time

Vigilance by Sentinels in a group of baboons (Papio hamadryas hamadryas) in a zoo setting

Vigilance by sentinels is an anti-predator strategy by which certain group members keep watch from strategic positions, while the group is involved in other activities. Many anti-predatory behavior patterns observed in natural habitats are also deployed similarly when provoked by human presence. This work is part of a study conducted with a group of hamadryas baboons (Papio h. hamadryas) in semi-freedom in a 15-hectare zoo complex with extensive human pressure. The animals make incursions into an adjoining high-risk area to access food resources, making use of vigilance with sentinels and other risk minimization strategies. Results reveal that human presence provokes similar reactions to natural predatory pressure, forcing them to select strategies to minimize the factors involved in risk perception, such as the degree of visibility of the surroundings, minimizing the length of the incursion and behavioral restrictions

Geografía de la deuda pública española. Algunas consideraciones espaciales desde la perspectiva política

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La función de la cosmovisión del moro en el <i>Poema de Alfonso Onceno</i>

Existe en el Poema de Alfonso Onceno una intencionalidad manifiesta de exaltar la figura del rey, mostrando su poder para pacificar las revueltas internas de Castilla y para poder hacerle la guerra al infiel: el moro. El trabajo que nos ocupa tiende a evidenciar de qué manera el autor del Poema de Alfonso Onceno realiza una construcción de la cosmovisión del moro como enemigo externo en vistas de exaltar las virtudes de un rey hasta convertirlo en “espejo y escudo de la cristiandad”, permitiéndole a través de éste procedimiento, juzgar con la misma vara a todo aquél que impida a Alfonso XI luchar contra el enemigo de la fe verdadera.Facultad de Humanidades y Ciencias de la Educació