Modeling the gravitational clustering in hierarchical scenarios of structure formation

[spa] En la tesis se presenta un método semianalítico para describir el crecimiento de objetos virializados en el escenario de inestabilidad gravitatoria. Se ha desarrollado el formalismo del sistema confluente de trayectorias, que permite seguir la evolución por filtrado de picos en un campo aleatorio gaussiano de perturbaciones de densidad. Este formalismo es aplicado para deducir la función de masas en el modelo de picos. Después de determinar el filtro (gaussiano) y las relaciones M(R) y SC(T) consistentes con la dinamica de colapso real, se ha encontrado una función de masas, corregida del efecto de nubes encajadas, muy próxima a la de Press y Schechter que ajusta bien los resultados de simulaciones a N-cuerpos. El formalismo del sistema confluente también permite calcular otras cantidades importantes relacionadas con la evolución de objetos virializados, con la ventaja de proporcionar una distinción práctica entre procesos de acreción y fusión. Esto conduce a una definición natural de los sucesos que indican la formación y destrucción de un objeto dado y, por lo tanto, a mejores estimaciones de los ritmos y tiempos típicos de crecimiento. En particular, se han deducido expresiones para los ritmos instantáneos de fusión, captura y formación, el ritmo de acreción de masa, la edad típica y el tiempo de supervivencia

Decentralized trust in the inter-domain routing infrastructure

Inter-domain routing security is of critical importance to the Internet since it prevents unwanted traffic redirections. The current system is based on a Public Key Infrastructure (PKI), a centralized repository of digital certificates. However, the inherent centralization of such design creates tensions between its participants and hinders its deployment. In addition, some technical drawbacks of PKIs delay widespread adoption. In this paper we present IPchain, a blockchain to store the allocations and delegations of IP addresses. IPchain leverages blockchains' properties to decentralize trust among its participants, with the final goal of providing flexible trust models that adapt better to the ever-changing geopolitical landscape. Moreover, we argue that Proof of Stake is a suitable consensus algorithm for IPchain due to the unique incentive structure of this use-case, and that blockchains offer relevant technical advantages when compared to existing systems, such as simplified management. In order to show its feasibility and suitability, we have implemented and evaluated IPchain's performance and scalability storing around 350k IP prefixes in a 2.5 GB chain.Peer ReviewedPostprint (published version

The Confluent System Formalism: I.The Mass Function of Objects in the Peak Model

This is the first paper of a series of two devoted to develop a practical method to describe the growth history of bound virialized objects in the gravitational instability scenario without resorting to $N$-body simulations. Here we present the basic tool of this method, ``the confluent system formalism'', which allows us to follow the filtering evolution of peaks in a random Gaussian field of density fluctuations. This is applied to derive the theoretical mass function of objects within the peak model framework. Along the process followed for the derivation of this function, we prove that the Gaussian window is the only one consistent with the peak model ansatz. We also give a well justified derivation of the density of peaks with density contrast upcrossing a given threshold in infinitesimal ranges of scale and correct this scale function for the cloud-in-cloud effect. Finally, we characterize the form of the mass vs. scale and the critical overdensity vs. collapse time relations which are physically consistent with the peak model in an Einstein-de Sitter universe with density field endowed with different power spectra. The result is a fully justified semianalytical mass function which is close to the Press \& Schechter (1974) one giving good fits to $N$-body simulations. But the interest of the confluent system formalism is not merely formal. It allows us to distinguish between accretion and merger events, which is essential for the detailed modelling of the clustering process experienced by objects.Comment: 24 pages, uuencoded compressed postscript file including 4 figures (164 kb). To be published in ApJ, 1st November issu