6,196 research outputs found
Coexistence of Antiferromagnetism and Superconductivity in Electron-doped High-Tc Superconductors
We present magnetotransport evidence for antiferromagnetism in films of the
electron-doped cuprates PrCeCuO. Our results show clear
signature of static antiferromagnetism up to optimal doping x=0.15, with a
quantum phase transition close to x=0.16, and a coexistence of static
antiferromagnetism and superconductivity for 0.12x0.15
Multigrid elliptic equation solver with adaptive mesh refinement
In this paper we describe in detail the computational algorithm used by our
parallel multigrid elliptic equation solver with adaptive mesh refinement. Our
code uses truncation error estimates to adaptively refine the grid as part of
the solution process. The presentation includes a discussion of the orders of
accuracy that we use for prolongation and restriction operators to ensure
second order accurate results and to minimize computational work. Code tests
are presented that confirm the overall second order accuracy and demonstrate
the savings in computational resources provided by adaptive mesh refinement.Comment: 12 pages, 9 figures, Modified in response to reviewer suggestions,
added figure, added references. Accepted for publication in J. Comp. Phy
Application of complement component 4d immunohistochemistry to ABO-compatible and ABO-incompatible liver transplantation.
Antibody-mediated rejection (AMR) is difficult to diagnose after ABO-compatible or ABO-identical (ABO-C) liver transplantation. To determine whether complement component 4d (C4d) immunostaining would be useful for diagnosing AMR, we compared the results of C4d immunohistochemistry for allograft biopsy samples with assays for anti-donor antibodies performed at the time of biopsy. One hundred fourteen patients with ABO-C grafts and 29 patients with ABO-incompatible (ABO-I) grafts were included. Linear C4d endothelial staining (identifiable with a 4× objective lens) or staining seen in 50% or more of the portal tracts was considered positive. Five of the 114 patients (4%) with ABO-C grafts and 15 of the 29 patients (52%) with ABO-I grafts showed C4d positivity. In the ABO-C cases, C4d positivity in late biopsy samples (≥30 days after transplantation) was associated with stage 2 or higher fibrosis (METAVIR score; P = 0.01) and with the presence of donor-specific anti-human leukocyte antigen DR antibodies (HLA-DR DSAs) with a mean fluorescence intensity > 5000 according to the Luminex single-antigen bead assay (P = 0.04). Conversely, the presence of HLA-DR DSAs was associated with the presence of stage 2 or higher fibrosis, acute cellular rejection, and C4d positivity. During the 2-year follow-up, neither C4d positivity nor HLA-DR DSAs were related to graft loss. Among ABO-I patients, C4d positivity was not associated with allograft dysfunction or fibrosis. Only 3 of the 15 C4d-positive patients (20%) showed periportal hemorrhagic edema, which could be a histological sign of AMR in ABO-I grafts, and they were the only cases associated with elevations in anti-donor A/B antibody titers. In conclusion, C4d endothelial positivity among ABO-C patients is an uncommon event that could be associated with chronic graft damage with or without clinical AMR. C4d positivity is common among ABO-I patients and may not be associated with allograft dysfunction if alloantibody titers are not elevated
Paramagnetic anisotropic magnetoresistance in thin films of SrRuO3
SrRuO3 is an itinerant ferromagnet and in its thin film form when grown on
miscut SrTiO3 it has Tc of ~ 150 K and strong uniaxial anisotropy. We measured
both the Hall effect and the magnetoresistance (MR) of the films as a function
of the angle between the applied field and the normal to the films at
temperatures above Tc. We extracted the extraordinary Hall effect that is
proportional to the perpendicular component of the magnetization and thus the
MR for each angle of the applied field could be correlated with the magnitude
and orientation of the induced magnetization. We successfully fit the MR data
with a second order magnetization expansion, which indicates large anisotropic
MR in the paramagnetic state. The extremum values of resistivity are not
obtained for currents parallel or perpendicular to the magnetization, probably
due to the crystal symmetry.Comment: 3 pages, 3 figure
AZEuS: An Adaptive Zone Eulerian Scheme for Computational MHD
A new adaptive mesh refinement (AMR) version of the ZEUS-3D astrophysical
magnetohydrodynamical (MHD) fluid code, AZEuS, is described. The AMR module in
AZEuS has been completely adapted to the staggered mesh that characterises the
ZEUS family of codes, on which scalar quantities are zone-centred and vector
components are face-centred. In addition, for applications using static grids,
it is necessary to use higher-order interpolations for prolongation to minimise
the errors caused by waves crossing from a grid of one resolution to another.
Finally, solutions to test problems in 1-, 2-, and 3-dimensions in both
Cartesian and spherical coordinates are presented.Comment: 52 pages, 17 figures; Accepted for publication in ApJ
Unconventional Planar Hall Effect in Exchange-Coupled Topological Insulator-Ferromagnetic Insulator Heterostructures
The Dirac electrons occupying the surface states (SSs) of topological
insulators (TIs) have been predicted to exhibit many exciting magneto-transport
phenomena. Here we report on the first experimental observation of an
unconventional planar Hall effect (PHE) and an electrically gate-tunable
hysteretic planar magnetoresistance (PMR) in EuS/TI heterostructures, in which
EuS is a ferromagnetic insulator (FMI) with an in-plane magnetization. In such
exchange-coupled FMI/TI heterostructures, we find a significant (suppressed)
PHE when the in-plane magnetic field is parallel (perpendicular) to the
electric current. This behavior differs from previous observations of the PHE
in ferromagnets and semiconductors. Furthermore, as the thickness of the 3D TI
films is reduced into the 2D limit, in which the Dirac SSs develop a
hybridization gap, we find a suppression of the PHE around the charge neutral
point indicating the vital role of Dirac SSs in this phenomenon. To explain our
findings, we outline a symmetry argument that excludes linear-Hall mechanisms
and suggest two possible non-linear Hall mechanisms that can account for all
the essential qualitative features in our observations.Comment: 17 pages, 4 figures, accepted by Phys. Rev.
Divergence-Free Adaptive Mesh Refinement for Magnetohydrodynamics
In this paper we present a full-fledged scheme for the second order accurate,
divergence-free evolution of vector fields on an adaptive mesh refinement (AMR)
hierarchy. We focus here on adaptive mesh MHD. The scheme is based on making a
significant advance in the divergence-free reconstruction of vector fields. In
that sense, it complements the earlier work of Balsara and Spicer (1999) where
we discussed the divergence-free time-update of vector fields which satisfy
Stoke's law type evolution equations. Our advance in divergence-free
reconstruction of vector fields is such that it reduces to the total variation
diminishing (TVD) property for one-dimensional evolution and yet goes beyond it
in multiple dimensions. Divergence-free restriction is also discussed. An
electric field correction strategy is presented for use on AMR meshes. The
electric field correction strategy helps preserve the divergence-free evolution
of the magnetic field even when the time steps are sub-cycled on refined
meshes. The above-mentioned innovations have been implemented in Balsara's
RIEMANN framework for parallel, self-adaptive computational astrophysics which
supports both non-relativistic and relativistic MHD. Several rigorous, three
dimensional AMR-MHD test problems with strong discontinuities have been run
with the RIEMANN framework showing that the strategy works very well.Comment: J.C.P., figures of reduced qualit
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