1,808 research outputs found
Polytypism and Unexpected Strong Interlayer Coupling of two-Dimensional Layered ReS2
The anisotropic two-dimensional (2D) van der Waals (vdW) layered materials,
with both scientific interest and potential application, have one more
dimension to tune the properties than the isotropic 2D materials. The
interlayer vdW coupling determines the properties of 2D multi-layer materials
by varying stacking orders. As an important representative anisotropic 2D
materials, multilayer rhenium disulfide (ReS2) was expected to be random
stacking and lack of interlayer coupling. Here, we demonstrate two stable
stacking orders (aa and a-b) of N layer (NL, N>1) ReS2 from ultralow-frequency
and high-frequency Raman spectroscopy, photoluminescence spectroscopy and
first-principles density functional theory calculation. Two interlayer shear
modes are observed in aa-stacked NL-ReS2 while only one interlayer shear mode
appears in a-b-stacked NL-ReS2, suggesting anisotropic-like and isotropic-like
stacking orders in aa- and a-b-stacked NL-ReS2, respectively. The frequency of
the interlayer shear and breathing modes reveals unexpected strong interlayer
coupling in aa- and a-b-NL-ReS2, the force constants of which are 55-90% to
those of multilayer MoS2. The observation of strong interlayer coupling and
polytypism in multi-layer ReS2 stimulate future studies on the structure,
electronic and optical properties of other 2D anisotropic materials
Kerr-Sen Black Hole as Accelerator for Spinning Particles
It has been proved that arbitrarily high-energy collision between two
particles can occur near the horizon of an extremal Kerr black hole as long as
the energy and angular momentum of one particle satisfies a critical
relation, which is called the BSW mechanism. Previous researchers mainly
concentrate on geodesic motion of particles. In this paper, we will take
spinning particle which won't move along a timelike geodesic into our
consideration, hence, another parameter describing the particle's spin
angular momentum was introduced. By employing the Mathisson-Papapetrou-Dixon
equation describing the movement of spinning particle, we will explore whether
a Kerr-Sen black hole which is slightly different from Kerr black hole can be
used to accelerate a spinning particle to arbitrarily high energy. We found
that when one of the two colliding particles satisfies a critical relation
between the energy and the total angular momentum , or has a critical
spinning angular momentum , a divergence of the center-of-mass energy
will be obtained.Comment: Latex,17 pages,1 figure,minor revision,accepted by PR
Involvement of polyphosphate kinase in virulence and stress tolerance of uropathogenic Proteus mirabilis
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