On the Robustness of NK-Kauffman Networks Against Changes in their Connections and Boolean Functions

NK-Kauffman networks {\cal L}^N_K are a subset of the Boolean functions on N Boolean variables to themselves, \Lambda_N = {\xi: \IZ_2^N \to \IZ_2^N}. To each NK-Kauffman network it is possible to assign a unique Boolean function on N variables through the function \Psi: {\cal L}^N_K \to \Lambda_N. The probability {\cal P}_K that \Psi (f) = \Psi (f'), when f' is obtained through f by a change of one of its K-Boolean functions (b_K: \IZ_2^K \to \IZ_2), and/or connections; is calculated. The leading term of the asymptotic expansion of {\cal P}_K, for N \gg 1, turns out to depend on: the probability to extract the tautology and contradiction Boolean functions, and in the average value of the distribution of probability of the Boolean functions; the other terms decay as {\cal O} (1 / N). In order to accomplish this, a classification of the Boolean functions in terms of what I have called their irreducible degree of connectivity is established. The mathematical findings are discussed in the biological context where, \Psi is used to model the genotype-phenotype map.Comment: 17 pages, 1 figure, Accepted in Journal of Mathematical Physic

Understanding responses to political conflict: interactive effects of the need for closure and salient conflict schemas.

Two studies examined the relationship between the need for cognitive closure and preferences for conflict-resolution strategies in two different samples of elite political actors. While research suggests that the high need for closure should be associated with competitiveness, we argue that this relationship should be strongest among political actors with a hostile “conflict schema,” or representation of what a conflict is and how it should be dealt with. We provide evidence for this hypothesis using archival survey data on American foreign policy officials’ attitudes toward international conflict at the height of the Cold War (Study 1) and our own data on the relationship between the need for closure and conflict-strategy preferences among samples of activists from two political parties in Poland – a centrist party with a reputation for cooperativeness and an extremist party with a reputation for confrontation (Study 2). The broader implications of these findings are discussed

Explicit Spectral Decimation for a Class of Self--Similar Fractals

The method of spectral decimation is applied to an infinite collection of self--similar fractals. The sets considered belong to the class of nested fractals, and are thus very symmetric. An explicit construction is given to obtain formulas for the eigenvalues of the Laplace operator acting on these fractals

The relationship between the need for closure and support for military action against Iraq: moderating effects of national attachment.

A variety of studies suggest that a high need for closure—that is,a desire for knowledge that is clear, stable, and unambiguous as opposed to confusing or uncertain—may be associated with greater hostility toward relevant outgroups. Using international attitudes as the context, the authors examine the hypothesis that the relationship between the need for closure and support for military action against Iraq may be moderated by identification with the national ingroup. Specifically, it is expected that this relationship will be moderated by nationalism (i.e., an aggressive form of identification based on a desire for national dominance)but not patriotism (i.e., a more neutral love of one’s country). The data provided a clear pattern of support for this hypothesis and additional analyses indicated that a high need for closure reduced variability about the use of force among the highly nationalistic but not the highly patrioti

Need for closure and coercion in inter-group conflicts: experimental evidence for the mitigating effect of accessible conflict schemas

Three experimental studies demonstrate that momentarily-accessible conflict-schemas moderate the relationship between need for closure and conflict-strategy preferences, with the relationship between a high need for closure and increased competitiveness reduced to non-significance when a cooperative conflict schema is made salient but strengthened when a hostile one is activated. Study 1 manipulated the accessibility of competitive versus cooperative conflict schemas using different descriptions of a contemporary political conflict, while Studies 2 and 3 manipulated conflict-schema accessibility using primes embedded in an ostensibly-unrelated lexical decision task. Together, the present studies provide a strong pattern of experimental support for the moderating effect of conflict-schema accessibility suggested by earlier correlational studies. The implications for conflict reduction are discussed

Neutron star mergers and rare core-collapse supernovae as sources of r-process enrichment in simulated galaxies

We use cosmological, magnetohydrodynamical simulations of Milky Way-mass galaxies from the Auriga project to study their enrichment with rapid neutron capture (r-process) elements. We implement a variety of enrichment models from both binary neutron star mergers and rare core-collapse supernovae. We focus on the abundances of (extremely) metal-poor stars, most of which were formed during the first ~Gyr of the Universe in external galaxies and later accreted onto the main galaxy. We find that the majority of metal-poor stars are r-process enriched in all our enrichment models. Neutron star merger models result in a median r-process abundance ratio which increases with metallicity, whereas the median trend in rare core-collapse supernova models is approximately flat. The scatter in r-process abundance increases for models with longer delay times or lower rates of r-process producing events. Our results are nearly perfectly converged, in part due to the mixing of gas between mesh cells in the simulations. Additionally, different Milky Way-mass galaxies show only small variation in their respective r-process abundance ratios. Current (sparse and potentially biased) observations of metal-poor stars in the Milky Way seem to prefer rare core-collapse supernovae over neutron star mergers as the dominant source of r-process elements at low metallicity, but we discuss possible caveats to our models. Dwarf galaxies which experience a single r-process event early in their history show highly enhanced r-process abundances at low metallicity, which is seen both in observations and in our simulations. We also find that the elements produced in a single event are mixed with ~10^8 Msun of gas relatively quickly, distributing the r-process elements over a large region.Comment: Accepted for publication in MNRAS. Revised version: added Figure 13 (on mixing of iron and r-process elements) and an Appendix (on iron and magnesium abundances) and updated the r-process yields (Tables 1 and 2 and normalization of abundances

Finite-temperature properties of frustrated classical spins coupled to the lattice

We present extensive Monte Carlo simulations for a classical antiferromagnetic Heisenberg model with both nearest ($J_1$) and next-nearest ($J_2$) exchange couplings on the square lattice coupled to the lattice degrees of freedom. The Ising-like phase transition, that appears for $J_2/J_1>1/2$ in the pure spin model, is strengthened by the spin-lattice coupling, and is accompanied by a lattice deformation from a tetragonal symmetry to an orthorhombic one. Evidences that the universality class of the transition does not change with the inclusion of the spin-lattice coupling are reported. Implications for ${\rm Li_2VOSiO_4}$, the prototype for a layered $J_1{-}J_2$ model in the collinear regime, are also discussed.Comment: 6 pages and 8 figure

La nueva gobernanza de la zona euro: hoja de ruta a corto, medio y largo plazo

Este trabajo examina la compleja gestión del grave momento económico-financiero en la zona euro (ZE) distinguiendo tres dimensiones: (1) la superación de los problemas urgentes de la deuda pública soberana; (2) la implementación de una serie de nuevas medidas pensadas para evitar futuras crisis; y (3) el posible inicio de una reforma más profunda que desemboque en una unión económica y monetaria que de verdad merezca ese nombre. Casi dos años después de que se iniciara en los países de la zona euro (ZE) una segunda fase de la crisis económica y financiera –afectando primero a Grecia y su endeudamiento insostenible, luego al resto de países periféricos con problemas de financiación y finalmente a todos los demás–, el horizonte sigue sin despejarse. El desafío más apremiante pasa por encontrar una solución definitiva al problema griego y sus dos derivadas más importantes: (1) la necesidad de recapitalizar el sector financiero en caso de que se acuerde una quita sustancial su deuda; y (2) la potenciación de la capacidad e instrumentos del actual fondo de estabilidad para que pueda evitar el contagio y ayudar a otros países con dificultades de liquidez pero no de solvencia. El segundo paso consiste en empezar a aplicar un importante paquete legislativo recientemente aprobado por las instituciones europeas y que pretende, a través de seis nuevas normas y la reforma de la regulación financiera, que una situación como la actual no se vuelva a repetir. Como tercer elemento de la gestión de la crisis, se abre camino de forma cada vez más nítida la idea de una nueva y ambiciosa reforma de los tratados para avanzar hacia una auténtica unión fiscal de, al menos, los 17 miembros de la ZE. Ninguno de los tres planos –a corto, medio y largo plazo– se libran de una gran incertidumbre. Nada garantiza que la insolvencia griega explosione de manera desordenada y pueda desembocar en una nueva recesión europea e incluso mundial. Tampoco hay certeza de que el paquete de medidas regulatorias sea realmente eficaz para evitar crisis futuras. Y a nadie escapa las enormes complejidades que supone un nuevo proceso “constituyente” a la luz de la ardua experiencia que desembocó en el Tratado de Lisboa

Un renovado pacto de estabilidad (¿sin crecimiento?) para la UE

El Consejo Europeo de diciembre de 2011 ha lanzado un mensaje de apoyo al euro y al avance en la integración fiscal, pero deja grandes incertidumbres económicas y políticas que impiden vislumbrar el fin de la crisis. El resultado de la reunión del Consejo Europeo celebrada en Bruselas el 8-9 de diciembre de 2011 resulta moderadamente positivo. Por un lado, se percibe la voluntad clara de que el euro y la actual eurozona sobrevivan. Parece así demostrado que el proyecto europeo continúa disfrutando de unas fuertes dinámicas políticas de fondo que, pese a las graves dificultades económicas, le impulsan a seguir adelante con nuevas cesiones de soberanía que de hecho van a obligar a los Estados miembros menos europeístas –como el Reino Unido– a repensar su propia pertenencia a la UE. Sin embargo, los líderes europeos han vuelto a limitarse a llegar al mínimo acuerdo posible para mantener viva la moneda única –al menos por un tiempo– dejando que sean los mercados quienes juzguen si para superar la crisis de la deuda soberana es suficiente con reforzar la estabilidad presupuestaria y, además, delegando en el BCE la interlocución con los mismos a través de una implícita autorización para que sea más activista. Desde el punto de vista económico hay enormes dudas de que la receta de austeridad sea suficiente para generar crecimiento y desde el punto de vista político se abren grandes interrogantes sobre la línea acordada de avanzar a través de un tratado intergubernamental que no incluirá a los 27

El rescate a Grecia y el futuro de la zona euro

Ante el riesgo de que Grecia suspenda el pago de su deuda, la UE acordó el 11 de febrero una respuesta política que, además de esbozar un rescate financiero si fuera preciso, puede contribuir al reforzamiento de la gobernanza económica europea. Grecia ha incumplido sistemáticamente durante los últimos años sus obligaciones de política fiscal como miembro de la zona euro incurriendo en déficit presupuestarios tan elevados que, a comienzos de 2010, no es inverosímil una hipótesis de suspensión de pagos de su deuda. Algunos Estados miembros de la UE, movidos por el peligro real que ese escenario pudiera representar a los bancos privados acreedores –sobre todo alemanes y franceses–, por el riesgo más o menos remoto de un contagio a otras economías más importantes, o por un indeterminado sentido de solidaridad, han impulsado una operación de rescate financiero para ayudar a Atenas y salvaguardar a la zona euro. La iniciativa fue finalmente asumida por los 27, la Comisión y el Banco Central Europeo con ocasión del Consejo Europeo extraordinario celebrado el 11 de febrero. Más allá de las especificidades del caso griego, el episodio podría tener efectos importantes para fortalecer la coordinación real de las políticas económicas nacionales de la UE, en general, y de la eurozona, en particular