1,105 research outputs found
The semi-discrete AKNS system: Conservation laws, reductions and continuum limits
In this paper, the semi-discrete Ablowitz-Kaup-Newell-Segur (AKNS) hierarchy
is shown in spirit composed by the Ablowitz-Ladik flows under certain
combinations. Furthermore, we derive its explicit Lax pairs and infinitely many
conservation laws, which are non-trivial in light of continuum limit.
Reductions of the semi-discrete AKNS hierarchy are investigated to include the
semi-discrete Korteweg-de Vries (KdV), the semi-discrete modified KdV, and the
semi-discrete nonlinear Schr\"odinger hierarchies as its special cases.
Finally, under the uniform continuum limit we introduce in the paper, the above
results of the semi-discrete AKNS hierarchy, including Lax pairs, infinitely
many conservation laws and reductions, recover their counterparts of the
continuous AKNS hierarchy
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
Five-dimensional generalized gravity with curvature-matter coupling
The generalized gravity with curvature-matter coupling in
five-dimensional (5D) spacetime can be established by assuming a
hypersurface-orthogonal spacelike Killing vector field of 5D spacetime, and it
can be reduced to the 4D formulism of FRW universe. This theory is quite
general and can give the corresponding results to the Einstein gravity,
gravity with both no-coupling and non-minimal coupling in 5D spacetime as
special cases, that is, we would give the some new results besides previous
ones given by Ref.\cite{60}. Furthermore, in order to get some insight into the
effects of this theory on the 4D spacetime, by considering a specific type of
models with and , we not
only discuss the constraints on the model parameters , , but also
illustrate the evolutionary trajectories of the scale factor , the
deceleration parameter and the scalar field , in
the reduced 4D spacetime. The research results show that this type of
gravity models given by us could explain the current accelerated expansion of
our universe without introducing dark energy.Comment: arXiv admin note: text overlap with arXiv:0912.4581,
arXiv:gr-qc/0411066 by other author
Nearby SNR: a possible common origin to multi-messenger anomalies in spectra, ratios and anisotropy of cosmic rays
The multi-messenger anomalies, including spectral hardening or excess for
nuclei, leptons, ratios of and B/C, and anisotropic reversal, were
observed in past years. AMS-02 experiment also revealed different spectral
break for positron and electron at 284 GeV and beyond TeV respectively. It is
natural to ask whether all those anomalies originate from one unified physical
scenario. In this work, the spatially-dependent propagation (SDP) with a nearby
SNR source is adopted to reproduce above mentioned anomalies. There possibly
exists dense molecular cloud(DMC) around SNRs and the secondary particles can
be produced by pp-collision or fragmentation between the accelerated primary
cosmic rays and DMC. As a result, the spectral hardening for primary, secondary
particles and ratios of and can be well reproduced. Due to the
energy loss at source age of 330 kyrs, the characteristic spectral break-off
for primary electron is at about 1 TeV hinted from the measurements. The
secondary positron and electron from charged pion take up energy from
their mother particles, so the positron spectrum has a cut-off at 250
GeV. Therefore, the different spectral break for positron and electron together
with other anomalies can be fulfilled in this unified physical scenario. More
interesting is that we also obtain the featured structures as spectral
break-off at 5 TV for secondary particles of Li, Be, B, which can be served to
verify our model. We hope that those tagged structures can be observed by the
new generation of space-borne experiment HERD in future.Comment: 16 pages, 12 figure
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