3,509 research outputs found
Ediacaran Obduction of a Fore-Arc Ophiolite in SW Iberia: A Turning Point in the Evolving Geodynamic Setting of Peri- Gondwana
The Calzadilla Ophiolite is an ensemble of mafic and ultramafic rocks that represents the
transition between lower crust and upper mantle of a Cadomian (peri-Gondwanan) fore arc. Mapping and
structural analysis of the ophiolite demonstrates that it was obducted in latest Ediacaran times, because the
Ediacaran-Early Cambrian sedimentary series (Malcocinado Formation) discordantly covers it. The ophiolite
and emplacement-related structures are affected by Variscan deformation (Devonian-Carboniferous),
which includes SW verging overturned folds (D1) and thrusts (D2), upright folds (D3), extensional faults (D4),
and later faults (D5). These phases of deformation are explained in the context of Variscan tectonics as the
result of the progressive collision between Gondwana and Laurussia. Qualitative unstraining of Variscan
deformation reveals the primary geometry of Ediacaran-Cambrian structures and uncovers the generation of
east verging thrusts as responsible for the primary obduction of the Calzadilla Ophiolite. Restoration of
planar and linear structures associated with this event indicates an Ediacaran, east directed obduction of the
ophiolite, that is, emplacement of the Cadomian fore arc onto inner sections of the northern margin of
Gondwana. According to regional data, the obduction separates two extension-dominated stages in the
tectonic evolution of the African margin of northern Gondwana preserved in southern Europe. Preobduction
extension brought about the onset and widening of fore-arc and back-arc basins in the external part
of the continent, while postobduction extension facilitated the formation of extensional migmatitic domes,
an oceanward migration of back-arc spreading centers across peri-Gondwana, and the eventual opening
of a major basin such as the Rheic Ocean
Activación alcalina de cenizas volantes. Relación entre el desarrollo mecánico resistente y la composición química de la ceniza
Alkali-activated fly ash is the primary component of a new generation of high-strength, durable binders with excellent mechanical properties and durability (on occasion bettering traditional Portland cement performance). Moreover, development of these cements may contribute to mitigating CO2 emissions, since the base material is an industrial by-product. The present study was conducted to determine the effect of the composition of the initial materials (SiO2/Al2O3 and Na2O/Al2O3 ratios) on the mechanical properties, nature and composition of the reaction products. The results obtained indicate that there is no linear relationship between these ratios and mechanical strength, but rather a series of optimal values above and below which strength declines. In the specific case of the ratios studied in the present paper, these values were: SiO2/Al2O3= 4.0 and Na2O/Al2O3= 1.0 (molar ratios).Las cenizas volantes activadas alcalinamente constituyen la base de una nueva generación de cementos con muy interesantes propiedades mecánicas, adherentes y durables (a veces incluso mejores que las de los cementos Portland tradicionales). Adicionalmente el desarrollo de estos cementos podría contribuir a mitigar las emisiones de CO2 a la atmósfera, ya que el material base de los mismos puede estar formado por subproductos industriales. En la presente investigación se realizó un estudio para determinar la influencia de la composición de los materiales iniciales (ratios SiO2/Al2O3 y Na2O/Al2O3) en las propiedades mecánicas y en la naturaleza y composición de los productos de reacción. Los resultados obtenidos indican que no existe una relación lineal de dichas ratios con las resistencias mecánicas, sino que existen unos valores óptimos, por encima y debajo de los cuales las resistencias mecánicas disminuyen. En el caso concreto de las ratios estudiadas en el presente trabajo estos valores serian: SiO2/Al2O3= 4,0 y Na2O/Al2O3= 1,0 (relaciones molares
An AER handshake-less modular infrastructure PCB with x8 2.5Gbps LVDS serial links
Nowadays spike-based brain processing emulation is
taking off. Several EU and others worldwide projects are
demonstrating this, like SpiNNaker, BrainScaleS, FACETS, or
NeuroGrid. The larger the brain process emulation on silicon is,
the higher the communication performance of the hosting
platforms has to be. Many times the bottleneck of these system
implementations is not on the performance inside a chip or a
board, but in the communication between boards. This paper
describes a novel modular Address-Event-Representation (AER)
FPGA-based (Spartan6) infrastructure PCB (the AER-Node
board) with 2.5Gbps LVDS high speed serial links over SATA
cables that offers a peak performance of 32-bit 62.5Meps (Mega
events per second) on board-to-board communications. The
board allows back compatibility with parallel AER devices
supporting up to x2 28-bit parallel data with asynchronous
handshake. These boards also allow modular expansion
functionality through several daughter boards. The paper is
focused on describing in detail the LVDS serial interface and
presenting its performance.Ministerio de Ciencia e Innovación TEC2009-10639-C04-02/01Ministerio de Economía y Competitividad TEC2012-37868-C04-02/01Junta de Andalucía TIC-6091Ministerio de Economía y Competitividad PRI-PIMCHI-2011-076
Sharp values for the constants in the polynomial Bohnenblust-Hille inequality
In this paper we prove that the complex polynomial Bohnenblust-Hille constant
for -homogeneous polynomials in is exactly
. We also give the exact value of the real polynomial
Bohnenblust-Hille constant for -homogeneous polynomials in .
Finally, we provide lower estimates for the real polynomial Bohnenblust-Hille
constant for polynomials in of higher degrees.Comment: 16 page
Hydration of clinker phases in alkaline conditions
This research is focused on the individual behaviour of calcium silicates (C3S and C2S) and tricalcium aluminate (C3A) when hydrated with water, but in the presence of 4 wt% Na2SO4. Two- and 28‑day mechanical strength of pastes were determined and the reaction products were identified by means of XRD, SEM/EDX and 29Si and 27 Al MAS NMR. Analysis of C3A revealed that hydration was favoured in the presence of Na2SO4. This salt governed hydration kinetics while providing the alkalinity required to induce the joint precipitation of carbonated and calcium sulfoaluminate hydrate reaction product, both observed to contribute to the mechanical strength of the resulting material.
In both silicates (C3S and C2S), the findings showed that the presence of Na2SO4 stimulated mechanical strength development. The synergy among all chemical reactions taking place during the hydration of these calcium silicates favoured a substantial rise in the alkalinity of the pastes formed. In addition, the anion SO42- induced the precipitation of cementitious gels with a high percentage of Q2 units, which leads to a significant increase in the mechanical strength of the materials at 28 day
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