38,322 research outputs found
Differential quadrature method for space-fractional diffusion equations on 2D irregular domains
In mathematical physics, the space-fractional diffusion equations are of
particular interest in the studies of physical phenomena modelled by L\'{e}vy
processes, which are sometimes called super-diffusion equations. In this
article, we develop the differential quadrature (DQ) methods for solving the 2D
space-fractional diffusion equations on irregular domains. The methods in
presence reduce the original equation into a set of ordinary differential
equations (ODEs) by introducing valid DQ formulations to fractional directional
derivatives based on the functional values at scattered nodal points on problem
domain. The required weighted coefficients are calculated by using radial basis
functions (RBFs) as trial functions, and the resultant ODEs are discretized by
the Crank-Nicolson scheme. The main advantages of our methods lie in their
flexibility and applicability to arbitrary domains. A series of illustrated
examples are finally provided to support these points.Comment: 25 pages, 25 figures, 7 table
First-principles Calculations of Engineered Surface Spin Structures
The engineered spin structures recently built and measured in scanning
tunneling microscope experiments are calculated using density functional
theory. By determining the precise local structure around the surface
impurities, we find the Mn atoms can form molecular structures with the binding
surface, behaving like surface molecular magnets. The spin structures are
confirmed to be antiferromagnetic, and the exchange couplings are calculated
within 8% of the experimental values simply by collinear-spin GGA+U
calculations. We can also explain why the exchange couplings significantly
change with different impurity binding sites from the determined local
structure. The bond polarity is studied by calculating the atomic charges with
and without the Mn adatoms
Coexistence and competition of multiple charge-density-wave orders in rare-earth tri-telluride RTe3
The occurrences of collective quantum states, such as superconductivity (SC)
and charge- or spin-densitywaves (CDWs or SDWs), are among the most fascinating
phenomena in solids. To date much effort has been made to explore the interplay
between different orders, yet little is known about the relationship of
multiple orders of the same type. Here we report optical spectroscopy study on
CDWs in the rare-earth tri-telluride compounds RTe3 (R = rare earth elements).
Besides the prior reported two CDW orders, the study reveals unexpectedly the
presence of a third CDW order in the series which evolves systematically with
the size of R element. With increased chemical pressure, the first and third
CDW orders are both substantially suppressed and compete with the second one by
depleting the low energy spectral weight. A complete phase diagram for the
multiple CDW orders in this series is established.Comment: 7 pages, 4 figures, 1 tabl
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