12,780 research outputs found
One-Dimensional Transition Metal-Benzene Sandwich Polymers: Possible Ideal Conductors for Spin Transport
We investigate the electronic and magnetic properties of the proposed
one-dimensional transition metal (TM=Sc, Ti, V, Cr, and Mn)-benzene (Bz)
sandwich polymers by means of density functional calculations.
[V(Bz)] is found to be a quasi-half-metallic ferromagnet and
half-metallic ferromagnetism is predicted for [Mn(Bz)]. Moreover, we
show that stretching the [TM(Bz)] polymers could have dramatic
effects on their electronic and magnetic properties. The elongated
[V(Bz)] displays half-metallic behavior, and [Mn(Bz)]
stretched to a certain degree becomes an antiferromagnetic insulator. The
possibilities to stabilize the ferromagnetic order in [V(Bz)] and
[Mn(Bz)] polymers at finite temperature are discussed. We suggest
that the hexagonal bundles composed by these polymers might display intrachain
ferromagnetic order at finite temperature by introducing interchain exchange
coupling
Electronic, Mechanical, and Piezoelectric Properties of ZnO Nanowires
Hexagonal [0001] nonpassivated ZnO nanowires are studied with density
functional calculations. The band gap and Young's modulus in nanowires which
are larger than those in bulk ZnO increase along with the decrease of the
radius of nanowires. We find ZnO nanowires have larger effective piezoelectric
constant than bulk ZnO due to their free boundary. In addition, the effective
piezoelectric constant in small ZnO nanowires doesn't depend monotonously on
the radius due to two competitive effects: elongation of the nanowires and
increase of the ratio of surface atoms
Co-projection-plane based 3-D padding for polyhedron projection for 360-degree video
The polyhedron projection for 360-degree video is becoming more and more
popular since it can lead to much less geometry distortion compared with the
equirectangular projection. However, in the polyhedron projection, we can
observe very obvious texture discontinuity in the area near the face boundary.
Such a texture discontinuity may lead to serious quality degradation when
motion compensation crosses the discontinuous face boundary. To solve this
problem, in this paper, we first propose to fill the corresponding neighboring
faces in the suitable positions as the extension of the current face to keep
approximated texture continuity. Then a co-projection-plane based 3-D padding
method is proposed to project the reference pixels in the neighboring face to
the current face to guarantee exact texture continuity. Under the proposed
scheme, the reference pixel is always projected to the same plane with the
current pixel when performing motion compensation so that the texture
discontinuity problem can be solved. The proposed scheme is implemented in the
reference software of High Efficiency Video Coding. Compared with the existing
method, the proposed algorithm can significantly improve the rate-distortion
performance. The experimental results obviously demonstrate that the texture
discontinuity in the face boundary can be well handled by the proposed
algorithm.Comment: 6 pages, 9 figure
The Role of Grain Boundaries under Long-Time Radiation
Materials containing a high proportion of grain boundaries offer significant
potential for the development of radiation-resistent structural materials.
However, a proper understanding of the connection between the radiation-induced
microstructural behaviour of grain boundary and its impact at long natural time
scales is still missing. In this letter, point defect absorption at interfaces
is summarised by a jump Robin-type condition at a coarse-grained level, wherein
the role of interface microstructure is effectively taken into account. Then a
concise formula linking the sink strength of a polycrystalline aggregate with
its grain size is introduced, and is well compared with experimental
observation. Based on the derived model, a coarse-grained formulation
incorporating the coupled evolution of grain boundaries and point defects is
proposed, so as to underpin the study of long-time morphological evolution of
grains induced by irradiation. Our simulation results suggest that the presence
of point defect sources within a grain further accelerates its shrinking
process, and radiation tends to trigger the extension of twin boundary
sections
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