Surface Conductivity of the Ytterbium-Doped Topological Kondo-Insulator SmB6

Doklady Physics - The temperature dependence of the conductivity of the topological Kondo-insulator (TKI) Sm1 – xYbxB6 is investigated in the temperature range 2 < T < 300 K for...     

Comparative hemodynamics in an aorta with bicuspid and trileaflet valves

Bicuspid aortic valve (BAV) is a congenital heart defect that has been associated with serious aortopathies, such as aortic stenosis, aortic regurgitation, infective endocarditis, aortic dissection, calcific aortic valve and dilatation of ascending aorta. There are two main hypotheses to explain the increase prevalence of aortopathies in patients with BAV: the genetic and the hemodynamic. In this study, we seek to investigate the possible role of hemodynamic factors as causes of BAV-associated aortopathy. We employ the curvilinear immersed boundary method coupled with an efficient thin-shell finite-element formulation for tissues to carry out fluid–structure interaction simulations of a healthy trileaflet aortic valve (TAV) and a BAV placed in the same anatomic aorta. The computed results reveal major differences between the TAV and BAV flow patterns. These include: the dynamics of the aortic valve vortex ring formation and break up; the large-scale flow patterns in the ascending aorta; the shear stress magnitude, directions, and dynamics on the heart valve surfaces. The computed results are in qualitative agreement with in vivo magnetic resonance imaging data and suggest that the linkages between BAV aortopathy and hemodynamics deserve further investigation.     

Magnetic Properties of the Topological Kondo Insulator SmB6: Localized Magnetic Moments and Pauli Paramagnetism

JETP Letters - The magnetic properties of the topological Kondo insulator SmB6 are studied in the temperature range T < 10 K in an applied magnetic field up to 5 T. The analysis of the...     

Anomalous spin relaxation and quantum criticality in Mn1 − x Fe x Si solid solutions

We report results of the high frequency (60 GHz) electron spin resonance (ESR) study of the quantum critical metallic system Mn_{1 ? x} Fe _x Si. The ESR is observed for the first time in the concentration range 0 < x < 0.24 at temperatures up to 50 K. The application of the original experimental technique allowed carrying out line shape analysis and finding full set of spectroscopic parameters, including oscillating magnetization, line width and g factor. The strongest effect of iron doping consists in influence on the ESR line width and spin relaxation is marked by both violation of the classical Korringa-type relaxation and scaling behavior. Additionally, the non-Fermi-liquid effects in the temperature dependence of the ESR line width, which may be quantitatively described in the theory of Wölfle and Abrahams, are observed at quantum critical points x* ～ 0.11 and x _c ～ 0.24.     

A hybrid immersed boundary and material point method for simulating 3D fluid–structure interaction problems

A numerical method is developed for solving the 3D, unsteady, incompressible Navier–Stokes equations in curvilinear coordinates containing immersed boundaries (IBs) of arbitrary geometrical complexity moving and deforming under forces acting on the body. Since simulations of flow in complex geometries with deformable surfaces require special treatment, the present approach combines a hybrid immersed boundary method (HIBM) for handling complex moving boundaries and a material point method (MPM) for resolving structural stresses and movement. This combined HIBM & MPM approach is presented as an effective approach for solving fluid–structure interaction (FSI) problems. In the HIBM, a curvilinear grid is defined and the variable values at grid points adjacent to a boundary are forced or interpolated to satisfy the boundary conditions. The MPM is used for solving the equations of solid structure and communicates with the fluid through appropriate interface‐boundary conditions. The governing flow equations are discretized on a non‐staggered grid layout using second‐order accurate finite‐difference formulas. The discrete equations are integrated in time via a second‐order accurate dual time stepping, artificial compressibility scheme. Unstructured, triangular meshes are employed to discretize the complex surface of the IBs. The nodes of the surface mesh constitute a set of Lagrangian control points used for tracking the motion of the flexible body. The equations of the solid body are integrated in time via the MPM. At every instant in time, the influence of the body on the flow is accounted for by applying boundary conditions at stationary curvilinear grid nodes located in the exterior but in the immediate vicinity of the body by reconstructing the solution along the local normal to the body surface. The influence of the fluid on the body is defined through pressure and shear stresses acting on the surface of the body. The HIBM & MPM approach is validated for FSI problems by solving for a falling rigid and flexible sphere in a fluid‐filled channel. The behavior of a capsule in a shear flow was also examined. Agreement with the published results is excellent. Copyright © 2007 John Wiley & Sons, Ltd.     

Electron Paramagnetic Resonance in HoxLu1−xB12 Dodecaborides

JETP Letters - The iron based superconductor FeSe0.5Te0.5 has been studied applying Mössbauer spectroscopy and ab initio density functional theory calculations of hyperfine parameters of iron...