Magmatic focusing to mid-ocean ridges: the role of grain size variability and non-Newtonian viscosity

Melting beneath mid-ocean ridges occurs over a region that is much broader than the zone of magmatic emplacement to form the oceanic crust. Magma is focused into this zone by lateral transport. This focusing has typically been explained by dynamic pressure gradients associated with corner flow, or by a sub-lithospheric channel sloping upward toward the ridge axis. Here we discuss a novel mechanism for magmatic focusing: lateral transport driven by gradients in compaction pressure within the asthenosphere. These gradients arise from the co-variation of melting rate and compaction viscosity. The compaction viscosity, in previous models, was given as a function of melt fraction and temperature. In contrast, we show that the viscosity variations relevant to melt focusing arise from grain-size variability and non-Newtonian creep. The asthenospheric distribution of melt fraction predicted by our models provides an improved ex- planation of the electrical resistivity structure beneath one location on the East Pacific Rise. More generally, although grain size and non-Newtonian viscosity are properties of the solid phase, we find that in the context of mid-ocean ridges, their effect on melt transport is more profound than their effect on the mantle corner-flow.Comment: 20 pages, 4 figures, 1 tabl

Too Big to Manage: US Megabanks’ Competition by Innovation and the Microfoundations of Financialization

Disagreements over the systemic implications—the future—of financialization can be traced in part to the absence of sustained attention to the role of banking firms in driving this secular shift forward. That is, the financialization literature lacks an adequate microfoundation. Accounting for the drivers of financialization processes solely at the macro level overlooks the problems of how these processes came about and whether they are sustainable. This paper addresses this explanatory gap, arguing that a key independent microeconomic driver of increasing financialization did exist: the incessant efforts by money-centre banks in the USA to break out of Depression-era restrictions on their size, activities, and markets. These banks’ growth strategies in turbulent times led to an institutional (meso) shift—the rise of a megabank-centred shadow banking system—that now shapes global financial architecture even while operating in ways that are unsustainable. In short, too-big-to-manage megabanks are at the heart of the fragility and instability of the economy today

BLITZ: Wireless Link Quality Estimation in the Dark

Abstract. We present BLITZ, a novel link quality estimator that relies on physical-layer synchronization errors to estimate the expected packet delivery ratio of wireless links. In contrast to all existing link quality estimators which estimate the packet delivery based on statistics from packets that are successfully decoded, our technique works even when packets at the receiver are not correctly received, i.e., when the synchronization fails. The core idea of BLITZ is to exploit informa-tion from chip errors in the received preamble of any transmitted direct sequence spread spectrum signals such as IEEE 802.15.4. Using extensive measurements over cable, wireless static and wireless mobile scenarios, we show that our pro-posed estimator outperforms existing estimators in terms of both accuracy and speed. Across diverse environmental conditions and the full range of possible link qualities, BLITZ provides packet delivery ratio estimates with an absolute error below six percent within just a few milliseconds.

Modeling liquid transport in the Earth's mantle as two-phase flow: effect of an enforced positive porosity on liquid flow and mass conservation

Fluid and melt transport in the solid mantle can be modeled as a two-phase flow in which the liquid flow is resisted by the compaction of the viscously deforming solid mantle. Given the wide impact of liquid transport on the geodynamical and geochemical evolution of the Earth, the so-called “compaction equations” are increasingly being incorporated into geodynamical modeling studies. When implementing these equations, it is common to use a regularization technique to handle the porosity singularity in the dry mantle. Moreover, it is also common to enforce a positive porosity (liquid fraction) to avoid unphysical negative values of porosity. However, the effects of this “capped” porosity on the liquid flow and mass conservation have not been quantitatively evaluated. Here, we investigate these effects using a series of 1- and 2-dimensional numerical models implemented using the commercial finite-element package COMSOL Multiphysics®. The results of benchmarking experiments against a semi-analytical solution for 1- and 2-D solitary waves illustrate the successful implementation of the compaction equations. We show that the solutions are accurate when the element size is smaller than half of the compaction length. Furthermore, in time-evolving experiments where the solid is stationary (immobile), we show that the mass balance errors are similarly low for both the capped and uncapped (i.e., allowing negative porosity) experiments. When Couette flow, convective flow, or subduction corner flow of the solid mantle is assumed, the capped porosity leads to overestimations of the mass of liquid in the model domain and the mass flux of liquid across the model boundaries, resulting in intrinsic errors in mass conservation even if a high mesh resolution is used. Despite the errors in mass balance, however, the distributions of the positive porosity and peaks (largest positive liquid fractions) in both the uncapped and capped experiments are similar. Hence, the capping of porosity in the compaction equations can be reasonably used to assess the main pathways and first-order distribution of fluids and melts in the mantle.</p

Geochronologically constrained life cycles of telescoped porphyry-epithermal systems at the La Arena district, Northern Peru

La Arena and Alizar are porphyry-type Cu-Au-(Mo) deposits with associated Calaorco and Vanessa high-sulfidation epithermal mineralizations, respectively. In this study, we conducted multiple conventional geochronologic analyses on samples from La Arena district, with the objective to obtain precise a temporal relationship among porphyry emplacement, hydrothermal alterations, cooling, exhumation history and preservation, together with published age data for the district. A precursor quartz–diorite pluton and a late–mineral andesite porphyry bracketed the mineralization in the La Arena and Alizar porphyry deposits. Zircon U-Pb dating of these intrusive rocks display markedly concordant ages, with emplacement beginning and ending at 26.50 ± 0.23 to 25.36 ± 0.07 Ma at La Arena, and at 26.47 ± 0.08 to 25.30 ± 0.07 Ma at Alizar. 40Ar/39Ar chronologic data for hydrothermal biotite from the potassic zone ranges from 25.97 ± 0.16 to 25.73 ± 0.16 Ma in the Alizar, and hypogene alunite from the advanced argillic alteration yield an age of 25.66 ± 0.15 Ma in the Vanessa. The weighted mean apatite (U–Th)/He ages of the porphyry intrusions of the La Arena and Alizar range from 24.26 ± 0.56 to 23.42 ± 0.37 Ma. These geochronologic data reveal that the porphyry systems were emplaced intermittently for at least 1.2 m.y. during the late Oligocene (26.5 – 25.3 Ma). The porphyry intrusions would have been uplifted from its depth of formation at ~ 2 km suggested by telescoped and a short time period (0.07 m.y.; 40Ar/39Ar ages) between porphyries and associated high-sulfidation epithermal events. The cooling history from zircon crystallization at 800 ◦C to thermal collapse at 75 ◦C (apatite helium close temperature) lasted ~ 2.5 m.y. in the ore-systems. The thermal collapse occurred coeval with the Inca IV orogeny (~24 Ma), period of rapid uplift and exhumation in northern Peru (0.24 km/m.y.; (U-Th)/He age-elevation spectrum). If exhumation continued at the rate of 0.24 km/m.y. unroof of the ore-deposits lasted 5 m.y. (24–19 Ma). Since their exposure at ~ 19 Ma, these ore deposits were subjected to weathering and oxidation during 2.12 m.y. It is thus estimated that approximately 500-m thickness of materials have been removed from the Alizar and La Arena during uplift and erosion, including a large volume of ore. Subsequent volcanic activity occurred during the Quechua I orogeny (~17 Ma) at ca. 16.88 Ma, leading to burial and partially preservation of these ore deposits

AFM study of morphology and mechanical properties of a chimeric 2 spider silk and bone sialoprotein protein for bone regeneration

Atomic force microscopy (AFM) was used to assess a new chimeric protein consisting of a fusion protein of the consensus repeat for Nephila clavipes spider dragline protein and bone sialoprotein (6merþBSP). The elastic modulus of this protein in film form was assessed through force curves, and film surface roughness was also determined. The results showed a significant difference among the elastic modulus of the chimeric silk protein, 6merþBSP, and control films consisting of only the silk component (6mer). The behavior of the 6merþBSP and 6mer proteins in aqueous solution in the presence of calcium (Ca) ions was also assessed to determine interactions between the inorganic and organic components related to bone interactions, anchoring, and biomaterial network formation. The results demonstrated the formation of protein networks in the presence of Ca2þ ions, characteristics that may be important in the context of controlling materials assembly and properties related to bone formation with this new chimeric silk-BSP protein.Silvia Games thanks the Foundation for Science and Technology (FCT) for supporting her Ph.D. grant, SFRH/BD/28603/2006. This work was carried out under the scope of the European NoE EXPERTISSUES (NMP3-CT-2004-500283), the Chimera project (PTDC/EBB-EBI/109093/2008) funded by the FCT agency, the NIH (P41 EB002520) Tissue Engineering Resource Center, and the NIH (EB003210 and DE017207)

Research on information systems failures and successes: Status update and future directions

The final publication is available at Springer via http://dx.doi.org/10.1007/s10796-014-9500-yInformation systems success and failure are among the most prominent streams in IS research. Explanations of why some IS fulfill their expectations, whereas others fail, are complex and multi-factorial. Despite the efforts to understand the underlying factors, the IS failure rate remains stubbornly high. A Panel session was held at the IFIP Working Group 8.6 conference in Bangalore in 2013 which forms the subject of this Special Issue. Its aim was to reflect on the need for new perspectives and research directions, to provide insights and further guidance for managers on factors enabling IS success and avoiding IS failure. Several key issues emerged, such as the need to study problems from multiple perspectives, to move beyond narrow considerations of the IT artifact, and to venture into underexplored organizational contexts, such as the public sector. © 2014 Springer Science+Business Media New York