Models of social networks based on social distance attachment

We propose a class of models of social network formation based on a mathematical abstraction of the concept of social distance. Social distance attachment is represented by the tendency of peers to establish acquaintances via a decreasing function of the relative distance in a representative social space. We derive analytical results (corroborated by extensive numerical simulations), showing that the model reproduces the main statistical characteristics of real social networks: large clustering coefficient, positive degree correlations, and the emergence of a hierarchy of communities. The model is confronted with the social network formed by people that shares confidential information using the Pretty Good Privacy (PGP) encryption algorithm, the so-called web of trust of PGP.

Estudios de los restos vegetales de diversas muestras procedentes del abrigo de Son Gallard- Son Marroig: el resultado de los analisis de fitolitos.

[spa] Los fitólitos son microrestos síliceos que reproducen el tejido celular de las plantas. Su identificación y cuantificación en un yacimiento arqueológico permiten obtener información sobre el tipo de plantas utilizadas en un contexto determinado así como su distribución. Fueron realizados análisis de fitolitos en diversos niveles correspondientes a diferentes períodos cronológicos del abrigo de Son Gallard-Son Marroig. Los resultados obtenidos señalan una deposición de carácter «antrópico» de materia vegetal en dos de los niveles analizados (TB3 y UE5), aunque sin una selección aparente del tipo de plantas depositadas. Por otro lado las muestras analizadas de la Covacha Este parecen indicar que se trata del suelo de hábitat del abrigo sin una deposición intencionada de materia vegetal, mas allá de la derivada por el uso continuado del abrigo. [eng] Phytoliths are silica microremains that reproduce the cellular tissue of plants. The identification and quantification of phytoliths in archaeological sediments, allows for a better understanding of the utilised plants in a pecific area as well as the distribution of the plants used. Phytolith analyses were performed on different levels from different periods in Son Gallard-Son Marroig rockshelter. The results obtained show an «anthropological» deposition of plants in two of the studied levels (TB3 and UE5), without apparent selection of plants. On the other hand, the samples analyzed from the Covacha Este seem to indicate the presence of vegetal remains product of the continued use of the soils with no intentional deposition.