5 research outputs found
The Holocene volcanism at El Hierro: insights from petrology and geochemistry
The Holocene volcanism at El Hierro consists of basaltic monogenetic
volcanic fields associated with o the three rift systems present in this island. In
this work we report preliminary petrological and geochemical data of Holocene
lava flows belonging to the WNW-striking rift. Sampling was focused in three
zones: Orchilla, Verodal-Sabinosa, and Tanganasoga. Petrography of the studied
lavas shows that they are homogeneous. All samples are porphyritic with
macrocrysts of clinopyroxene and olivine immersed in a groundmass formed
by microcrysts of plagioclase, Fe-Ti oxides and clinopyroxene. Clinopyroxenes
are diopsides, olivines have forsterite contents ranging from 74 to 84 % and
anorthite in plagioclase varies from 66 to 76% (labradorite). Whole-rock
geochemical results evidence that all magmas are basic in composition, ranging
from picrobasalts to phonotephrites. Major, trace elements and isotope support
fractional crystallization as the main process of magma evolution. However,
petrography and chemistry of clinopyroxene cores agree with a xenocrystic
nature of some of them. We suggest that these clinopyroxene cores crystallized
from a genetically related magma and subsequently were entrapped or
cannibalized by the basic rising magmas.Published35-382V. Struttura e sistema di alimentazione dei vulcaniN/A or not JC
Distributed Dynamic Spectrum Access in Multichannel Random Access Networks with Selfish Users
Dynamic spectrum allocation schemes enable users to share spectrum resources by exploiting the variations in spectrum demand over time and space. Performing dynamic spectrum allocation centrally can be prohibitively complex. Therefore distributed schemes in which users can access the available channels independently may be preferable to centralized allocation. However, in distributed dynamic spectrum access, the lack of central coordination makes it difficult to utilize the system resources efficiently. Furthermore, if some or all of the users decide to deviate selfishly from the commonly agreed access procedure, this may have a decisive effect on system performance. In this paper we investigate the effect of incomplete information and selfish behavior on system performance in wireless access systems. We extend previous work by studying a distributed multichannel wireless random access system. Using a game-theoretic approach, we analyze the behavior of users in the selfish system and derive the transmission strategies at the Nash equilibrium. Our results show that lack of information leads to substantial degredation in performance of cooperative systems. We also show that there is a large incentive for selfish behavior in such cooperative systems. Selfish behavior of all users, however, causes further performance degradation, particularly in high load settings.QC 20111208. © 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111207</p