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Now showing items 1 - 16 of 197579

  • Time-dependent geoid anomalies at subduction zones due to the seismic cycle

    Cambiotti, G.   Sabadini, R.   Yuen, D. A.  

    We model the geoid anomalies excited during a megathrust earthquake cycle at subduction zones, including the interseismic phase and the contribution from the infinite series of previous earthquakes, within the frame of self-gravitating, spherically symmetric, compressible, viscoelastic Earth models. The fault cuts the whole 50 km lithosphere, dips 20 degrees, and the slip amplitude, together with the length of the fault, are chosen in order to simulate an M-w =3D 9.0 earthquake, while the viscosity of the 170 km thick asthenosphere ranges from 10(17) to 10(20) Pa s. On the basis of a new analysis from the Correspondence Principle, we show that the geoid anomaly is characterized by a periodic anomaly due to the elastic and viscous contribution from past earthquakes and to the back-slip of the interseismic phase, and by a smaller static contribution from the steady-state response to the previous infinite earthquake cycles. For asthenospheric viscosities from 10(17)-10(18) to 10(19)-10(20) Pa s, the characteristic relaxation times of the Earth model change from shorter to longer timescales compared to the 400 yr earthquake recurrence time, which dampen the geoid anomaly for the higher asthenospheric viscosities, since the slower relaxation cannot contribute its whole strength within the interseismic cycle. The geoid anomaly pattern is characterized by a global, time-dependent positive upwarping of the geoid topography, involving the whole hanging wall and partially the footwall compared to the sharper elastic contribution, attaining, for a moment magnitude M-w =3D 9.0, amplitudes as high as 6.6 cm for the lowermost asthenospheric viscosities during the viscoelastic response compared to the elastic maximum of 3.8 cm. The geoid anomaly vanishes due to the back-slip of the interseismic phase, leading to its disappearance at the end of the cycle before the next earthquake. Our results are of importance for understanding the post-seismic and interseismic geoid patterns at subduction zones.
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  • eNOS Deficiency Predisposes Podocytes to Injury in Diabetes

    Yuen, D. A.   Stead, B. E.   Zhang, Y.   White, K. E.   Kabir, M. G.   Thai, K.   Advani, S. L.   Connelly, K. A.   Takano, T.   Zhu, L.   Cox, A. J.   Kelly, D. J.   Gibson, I. W.   Takahashi, T.   Harris, R. C.   Advani, A.  

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  • Multiscale brittle-ductile coupling and genesis of slow earthquakes RID F-9560-2011

    Regenauer-Lieb, K.   Yuen, D. A.  

    We present the first attempt to explain slow earthquakes as cascading thermal-mechanical instabilities. To attain this goal we investigate brittle-ductile coupled thermal-mechanical simulation on vastly different time scales. The largest scale model consists of a cross section of a randomly perturbed elasto-visco-plastic continental lithosphere on the order of 100 x 100 km scale with no other initial structures. The smallest scale model investigates a km-scale subsection of the large model and has a local resolution of 40 x 40 m. The model is subject to a constant extension velocity applied on either side. We assume a free top surface and with a zero tangential stress along the other boundaries. Extension is driven by velocity boundary conditions of 1 cm/a applied on either side of the model. This is the simplest boundary condition, and makes it an ideal starting point for understanding the behavior of a natural system with multiscale brittle-ductile coupling. Localization feedback is observed as faulting in the brittle upper crust and ductile shearing in an elasto-viscoplastic lower crust. In this process brittle faulting may rupture at seismogenic rates, e.g., at 10(2)-10(3) ms(-1), whereas viscous shear zones propagate at much slower rates, up to 3 x 10(-9) ms(-1). This sharp contrast in the strain rates leads to complex short-time-scale interactions at the brittle-ductile transition. We exploit the multiscale capabilities from our new simulations for understanding the underlying thermo-mechanics, spanning vastly different, time- and length-scales.
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  • Recombinant N-Terminal Slit2 Inhibits TGF-?-Induced Fibroblast Activation and Renal Fibrosis

    Yuen, D. A.   Huang, Y.-W.   Liu, G.-Y.   Patel, S.   Fang, F.   Zhou, J.   Thai, K.   Sidiqi, A.   Szeto, S. G.   Chan, L.   Lu, M.   He, X.   John, R.   Gilbert, R. E.   Scholey, J. W.   Robinson, L. A.  

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  • Spin transition-induced anomalies in the lower mantle:implications for mid-mantle partial layering

    Shahnas, M. H.   Pysklywec, R. N.   Justo, J. F.   Yuen, D. A.  

    Recent advances in high pressure mineral physics reveal that the thermoelastic properties of the lower mantle may significantly change as a consequence of the spin transition in ferric iron in the major lower mantle minerals, ferropericlase (Fp) and perovskite (Pv). The spin transition in iron introduces anomalies in the thermoelastic properties, like the bulk modulus, which influences the mixing and the style of mantle convection and the thermal history of the planet. Employing high resolution axi-symmetric spherical models, we explore the influence of the spin transition-induced anomalies in density and viscosity on mantle dynamics. Model results reveal that both a viscosity increase in the lower regions of the mantle and a negative spin transition-induced density anomaly can slow sinking slabs they approach mid-mantle depths; however, more profoundly, the density anomaly may halt slabs at mid-mantle depths for tens of millions of years, and up to similar to 200 Myr before they finally penetrate to the lower depths. This phenomenon is consistent with the nature of sinking slabs inferred from high resolution tomographic images which show slab stagnations at mid-mantle depths (from 1200 to around 1600 km).
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  • A hybrid radial basis function-pseudospectral method for thermal convection in a 3-D spherical shell

    Wright, G. B.   Flyer, N.   Yuen, D. A.  

    A novel hybrid spectral method that combines radial basis function (RBF) and Chebyshev pseudospectral methods in a "2 + 1" approach is presented for numerically simulating thermal convection in a 3-D spherical shell. This is the first study to apply RBFs to a full 3-D physical model in spherical geometry. In addition to being spectrally accurate, RBFs are not defined in terms of any surface-based coordinate system such as spherical coordinates. As a result, when used in the lateral directions, as in this study, they completely circumvent the pole issue with the further advantage that nodes can be "scattered" over the surface of a sphere. In the radial direction, Chebyshev polynomials are used, which are also spectrally accurate and provide the necessary clustering near the boundaries to resolve boundary layers. Applications of this new hybrid methodology are given to the problem of convection in the Earth's mantle, which is modeled by a Boussinesq fluid at infinite Prandtl number. To see whether this numerical technique warrants further investigation, the study limits itself to an isoviscous mantle. Benchmark comparisons are presented with other currently used mantle convection codes for Rayleigh number (Ra) 7 x 10(3) and 10(5). Results from a Ra = 10(6) simulation are also given. The algorithmic simplicity of the code (mostly due to RBFs) allows it to be written in less than 400 lines of MATLAB and run on a single workstation. We find that our method is very competitive with those currently used in the literature.
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  • The dynamical impact of electronic thermal conductivity on deep mantle convection of exosolar planets

    van den Berg, A. P.   Yuen, D. A.   Beebe, G. L.   Christiansen, M. D.  

    We have modelled the time-dependent dynamics of exosolar planets within the framework of a two-dimensional Cartesian model and the extended-Boussinesq approximation. The mass of the super-Earth models considered is 8 times the Earth's mass and the thickness of the mantle is 4700 km, based on a constant density approximation and a similar core mass fraction as in the Earth. The effects of depth-dependent properties have been considered for the thermal expansion coefficient, the viscosity and thermal conductivity. The viscosity and thermal conductivity are also temperature-dependent. The thermal conductivity has contributions from phonons, photons and electrons. The last dependence comes from the band-gap nature of the material under high pressure and increases exponentially with temperature and kicks in at temperatures above 5000 K. The thermal expansivity decreases by a factor of 20 across the mantle because of the high pressures, greater than 1 TPa in the deep mantle. We have varied the temperatures at the core-mantle boundary between 6000 and 10,000 K. Accordingly the Rayleigh number based on the surface values varies between 3.5 x 10(7) and 7 x 10(7) in the different models investigated. Three phase transitions have been considered: the spinel to perovskite, the post-perovskite transition and the post-perovskite decomposition in the deep lower mantle. We have considered an Arrhenius type of temperature dependence in the viscosity and have extended the viscosity contrast due to temperature to over one million. The parameter values put us well over into the stagnant lid regime. Our numerical results show that because of the multiple phase transitions and strongly depth-dependent properties, particularly the thermal expansitivity, initially most of the planetary interior is strongly super-adiabatic in spite of a high surface Rayleigh number, because of the presence of partially layered and penetrative convective flows throughout the mantle, very much unlike convection in the Earth's mantle. But with the passage of time, after several billion years, the temperature profiles become adiabatic. The notable influence of electronic thermal conductivity is to heat up the bottom boundary layer quasi-periodically, giving rise to strong coherent upwellingss, which can punch their way to the upper mantle and break up the layered convective pattern. (C) 2009 Elsevier B.V. All rights reserved.
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  • Is the long-wavelength geoid sensitive to the presence of postperovskite above the core-mantle boundary?

    Tosi, N.   Cadek, O.   Martinec, Z.   Yuen, D. A.   Kaufmann, G.  

    The analysis of seismic data represents today the primary tool in the search for the presence of postperovskite in the lowermost mantle (D ''). This work aims at testing whether the inversion of gravitational data can also contribute to the detection of postperovskite in D ''. We assume that the transition from perovskite to postperovskite is accompanied by a reduction in viscosity and test the effects of such viscosity change on the prediction of the dynamic geoid with a numerical model of subducted lithosphere. Our results show that the long-wavelength component of the geoid is very sensitive to the presence of postperovskite areas in D '', especially if their viscosity is significantly lower than the viscosity of the surrounding perovskite and if these areas are located close to density anomalies, i.e. subducted slabs. Citation: Tosi, N., O. Cadek, Z. Martinec, D. A. Yuen, and G. Kaufmann (2009), Is the long-wavelength geoid sensitive to the presence of postperovskite above the core-mantle boundary?, Geophys. Res. Lett., 36, L05303, doi: 10.1029/2008GL036902.
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  • Hard turbulent thermal convection and thermal evolution of the mantle

    Yuen, D. A.   Hansen, U.   Zhao, W.   Vincent, A. P.   Malevsky, A. V.  

    This article summarizes the results of hard turbulent convection obtained in laboratory experiments and numerical simulations. Its applications to mantle convection are illustrated by two-dimensional numerical solutions to (1) Newtonian, (2) non-Newtonian convection and (3) Newtonian convection with multiple phase transitions. In Newtonian mantle convection the transition from soft to hard turbulence is marked by the appearance of disconnected plumes. Spectral analysis of the time series of the Nusselt number reveals the presence of a spectral scaling subrange for hard turbulence but not for soft turbulence. In hard turbulence there is correspondence between the spectra in frequency and wavenumber domains. The slope of the seismic wave spectra measured from seismology suggests that the mantle convection today is strongly time-dependent. The transition to hard-turbulence takes place at much lower Nusselt numbers for non-Newtonian than for Newtonian rheology
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  • Geophysical inferences of thermal-chemical structures in the lower mantle

    Yuen, D. A.   Cadek, O.   Chopelas, A.   Matyska, C.  

    Lateral variations of the temperature field in the lower mantle have been reconstructed using new results in mineral physics and seismic tomographic data. We show that, with the application of high-pressure experimental values of thermal expansivity and of sound velocities, the slow seismic anomalies in the lower mantle under the Pacific and Africa can be converted into realistically looking plume structures with large dimensions of 0(10(3) km). The outer fringes of the plumes have an excess temperature of around 400 K. In the core of the plumes are found tongue-like structures with extremely high thermal anomalies. These values can exceed 1200 K and are too high to be explained on the basis of thermal anomalies alone. We suggest that these major plumes in the deep mantle may be driven by both thermal and chemical buoyancies or that enhanced conductive heat-transfer may be important there.
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  • Non-equilibrium effects of core-cooling and time-dependent internal heating on mantle flush events

    Yuen, D. A.   Balachandar, S.   Steinbach, V. C.   Honda, S.   Reuteler, D. M.   Smedsmo, J. J.   Lauer, G. S.  

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  • The fate of the slabs interacting with a density/viscosity hill in the mid-mantle RID E-8377-2010 RID A-2846-2008

    Morra, G.   Yuen, D. A.   Boschi, L.   Chatelain, P.   Koumoutsakos, P.   Tackley, P. J.  

    In the last two decades it has been proposed several times that a non-monotonic profile might fit the average lower mantle radial viscosity. Most proposed profiles consist in a more or less broad viscosity hill in the middle of the mantle, at a depth roughly between 1200 km and 2000 km. Also many tomographic models display strong signals of the presence of "fast" material lying at mid mantle depths and a recent spectral analysis of seismic tomography shows a very clear transition for degree up to around 16 at a less than 1500 km depth. Finally latest works, both theoretical and experimental, on the high-to-low-spin transition for periclase, have suggested that the high-spin to low-spin transition of Fe++ might lie at the heart of all these observations. To verify the dynamical compatibility between possible mantle profile and observed tomographic images and compare them with possible mineral physics scenarios, such as the spin transition, we employ here a recently developed Fast Multipole-accelerated Boundary Element Method (FMM-BEM), a numerical approach for solving the viscous momentum equation in a global spherical setting, for simulating the interaction of an individual slab with a mid mantle smooth discontinuity in density and viscosity. We have focused on the complexities induced to the behaviour of average and very large plates O (2000-10,000 km), characteristic of the Farallon, Tethys and Pacific plate subducting during the Cenozoic, demonstrating that the a mid mantle density and/or viscosity discontinuity produces a strong alteration of the sinking velocity and an intricate set of slab morphologies. We also employ the Kula-Farallon plate system subducting at 60 Ma as a paradigmatic case, which reveals the best high resolution tomography models and clearly suggests an interaction with a strong and/or denser layer in the mantle. Our 38 models show that a plate might or might not penetrate into the lowest mantle and might stall in the mid lower mantle for long periods, depending on the radial profiles of density and viscosity, within a realistic range (viscosity 1, 10 or 100 times more viscous of the rest of the mantle, and a change of differential density in the range -2% to 2%), of a transitional layer of 200 km or 500 km. We conclude that a layer with high viscosity or negative density would naturally trigger the observed geodynamic snapshot. We finally propose a scenario in which the long time accumulation of depleted slabs in the mid mantle would give rise to a partially chemically stratified mantle, starting from the less prominent high-spin to low-spin contribution on the basis of mantle density and rheology. (C) 2010 Elsevier B.V. All rights reserved.
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  • Mid-mantle heterogeneities and iron spin transition in the lower mantle:Implications for mid-mantle slab stagnation

    Shahnas, M. H.   Yuen, D. A.   Pysklywec, R. N.  

    Recent high pressure experimental results reveal that the elastic and transport properties of mantle materials are impacted by the electronic spin transition in iron under lower mantle pressure and temperature conditions. The electronic transition in ferropericlase (Fp), the second major constituent mineral of the lower mantle material, is associated with a smooth increase in density starting from the mid-mantle depth to the core-mantle boundary (CMB). The transition also yields softening in the elastic moduli and an increase in the thermal expansivity over the transition zone in the lower mantle. Although there is not yet robust experimental evidence for spin-transition induced density change in the perovskite (Pv) phase (the major constituent mineral in the lower mantle), the spin transition in the octahedral (B) site in Al-free perovskite causes a bulk modulus hardening (increase in the bulk modulus) in the mineral. We have incorporated these physical processes into high resolution 3D-spherical control volume models for mantle convection. A series of numerical experiments explore how the electronic spin transition in iron modifies the mantle flow, and in particular the fate of sinking cold slabs. Such mid mantle stagnations are prevalent globally in seismic tomographic inversions, but previous explanations for their existence are not satisfactory. Employing density anomalies from the iron spin transition in ferropericlase and density anomaly models for perovskite, we study the influence of the spin transition in the minerals of the lower mantle on mantle flow. Our model results reveal that while the spin transition induced property variations in ferropericlase enhance mixing in the lower depths of the mantle, the density anomaly arising from the hardening in the bulk modulus of Al-free perovskite can be effective in slowing the descent of slabs and may cause stagnation at mid-mantle levels. A viscosity hill in the lower mantle may further enhance the stagnation effect. Cold descending slabs can stall in the mid mantle for tens of million years or even longer before penetrating to the lower mantle. (C) 2016 Elsevier B.V. All rights reserved.
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  • Nocturnal Hemodialysis Is Associated with Restoration of Early-Outgrowth Endothelial Progenitor-Like Cell Function

    Yuen, D. A.   Kuliszewski, M. A.   Liao, C.   Rudenko, D.   Leong-Poi, H.   Chan, C. T.  

    Background and objectives Angiogenesis is a key response to tissue ischemia that may be impaired by uremia. Although early-outgrowth endothelial progenitor-like cells promote angiogenesis in the setting of normal renal function, cells from uremic patients are dysfunctional. When compared with conventional hemodialysis, it was hypothesized that nocturnal hemodialysis would improve the in vivo angiogenic activity of these cells in a well described model of ischemic vascular disease. Design, setting, participants, and measurements Early-outgrowth endothelial progenitor-like cells were cultured from healthy controls (n = 5) and age- and gender-matched conventional hemodialysis (12 h/wk, n = 10) and nocturnal hemodialysis (30 to 50 h/wk, a = 9) patients. Cells (5 x 105) or saline were injected into the ischemic hincilimb of athymic nude rats I day after left common iliac artery ligation. Results Although conventional dialysis cell injection had no effect versus saline, nocturnal hemodialysis and healthy control cell injection significantly improved ischemic hindlimb perfusion and capillary density. Nocturnal hemodialysis cell injection was also associated with significant increases in endogenous angiopoietin 1 expression in the ischemic hindlimb compared with saline and conventional dialysis cell injection. Conclusions In contrast to a conventional dialytic regimen, nocturnal hemodialysis is associated with a significantly improved ability of early-outgrowth endothelial progenitor-like cells to promote angiogenesis and thus restore perfusion in a model of ischemic vascular disease. Clin J Am Soc Nephrol 6: 1345-1353, 2011. doi: 10.2215/CJN.10911210
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  • Role of Magnetic Resonance Elastography as a Noninvasive Measurement Tool of Fibrosis in a Renal Allograft:A Case Report

    Kim, J. K.   Yuen, D. A.   Leung, G.   Jothy, S.   Zaltzman, J.   Prasad, G. V. Ramesh   Prabhudesai, V.   Mnatzakanian, G.   Kirpalani, A.  

    A major reason for poor long-term kidney transplant outcomes is the development of chronic allograft injury, characterized by interstitial fibrosis and tubular atrophy. Currently, an invasive biopsy that samples only <1% of the kidney is the gold standard for detecting kidney allograft fibrosis. We report the use of magnetic resonance elastography (MRE) to quantify tissue stiffness as a noninvasive and whole-kidney measurement tool of allograft fibrosis in a kidney transplant patient at 2 time points. The MRE whole-kidney stiffness values reflected the changes in fibrosis of the kidney allograft as assessed by histologic examination. To our knowledge, this technique is the first observation of change over time in MRE-derived whole-kidney stiffness in an allograft that is consistent with changes in histology-derived fibrosis scores in a single patient.
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  • Stationary points in activation energy for heat dissipated with a power law temperature-dependent viscoelastoplastic rheology

    So, B. -D.   Yuen, D. A.  

    We report that there exist a local maximum and minimum in the activation energy Ea describing mechanical heat dissipation of olivine for a given initial temperature and amount of deformation. The stationary point for the minimum dissipation is similar to 200 kJ/mol lower than that for the maximum. For larger activation energy than the stationary point for maximum dissipation, plastic deformation is sharply weakened and the temperature rise disappears altogether. Higher values of the initial temperature produce a larger local maximum for activation energy. The amount of heat dissipation increases with Ea in a nonlinear manner. Our results have direct ramifications on shear zone, which is governed by the amount of mechanical heat dissipation. We have observed them over a wide range of temperature and deformation boundary conditions. Our two-dimensional model study can provide valuable insight to enable greater predictive capability for the development of geodynamic shear zone in planetary-scale plate tectonics.
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