17,706 research outputs found
New approach to the origin of the tektite in China
The tektites in China are distributed on the north part of Australia - Southeastern Asia strewfield of tektite: Leizhou Peninsula of Guangdong Province and Hainan Island, and located exactly at the boundary between Zanjiang Formation and Beihai Formation. A new hypothesis is suggested: During the end of Lower Pleistocene, a comet of special components from the outer part of the Solar System approached the Earth, and then it was captured by the Earth, when it came approximately to the Roche's limet. It was crushed into countless fragments, detritus and dusts, which rotated around the Earth, probably far above the Earth's atmosphere, as a cloud ring. Under the action of crushing energy they could be in the situation of liquid-melt drop in the almost vacuum circumstances and the flow and bubble structure were formed. During their rotation the climate became anomalous and the violet Fe-Si concentration were formed on the surface of sediments. After a rather short time of rotation the unstable ring was broken and the fragments impacted on the hard ground instantaneously
Diverse anisotropy of phonon transport in two-dimensional IV-VI compounds: A comparative study
New classes two-dimensional (2D) materials beyond graphene, including layered
and non-layered, and their heterostructures, are currently attracting
increasing interest due to their promising applications in nanoelectronics,
optoelectronics and clean energy, where thermal transport property is one of
the fundamental physical parameters. In this paper, we systematically
investigated the phonon transport properties of 2D orthorhombic group IV-VI
compounds of , , and by solving the Boltzmann transport
equation (BTE) based on first-principles calculations. Despite the similar
puckered (hinge-like) structure along the armchair direction as phosphorene,
the four monolayer compounds possess diverse anisotropic properties in many
aspects, such as phonon group velocity, Young's modulus and lattice thermal
conductivity (), etc. Especially, the along the zigzag and
armchair directions of monolayer shows the strongest anisotropy while
monolayer and shows an almost isotropy in phonon transport. The
origin of the diverse anisotropy is fully studied and the underlying mechanism
is discussed in detail. With limited size, the could be effectively
lowered, and the anisotropy could be effectively modulated by nanostructuring,
which would extend the applications in nanoscale thermoelectrics and thermal
management. Our study offers fundamental understanding of the anisotropic
phonon transport properties of 2D materials, and would be of significance for
further study, modulation and aplications in emerging technologies.Comment: 14 pages, 8 figures, 2 table
Intramolecular Torque, an Indicator of the Internal Rotation Direction of Rotor Molecules and Similar Systems
Torque is ubiquitous in many molecular systems, including collisions,
chemical reactions, vibrations, electronic excitations and especially rotor
molecules. We present a straightforward theoretical method based on forces
acting on atoms and obtained from atomistic quantum mechanics calculations, to
quickly and qualitatively determine whether a molecule or sub-unit thereof has
a tendency to rotation and, if so, around which axis and in which sense:
clockwise or counterclockwise. The method also indicates which atoms, if any,
are predominant in causing the rotation. Our computational approach can in
general efficiently provide insights into the rotational ability of many
molecules and help to theoretically screen or modify them in advance of
experiments or before analyzing their rotational behavior in more detail with
more extensive computations guided by the results from the torque approach. As
an example, we demonstrate the effectiveness of the approach using a specific
light-driven molecular rotary motor which was successfully synthesized and
analyzed in prior experiments and simulations.Comment: 11 pages, 4 figures, 1 SI fil
Reversal of Thermal Rectification in Quantum Systems
We study thermal transport in anisotropic Heisenberg spin chains using the
quantum master equation. It is found that thermal rectification changes sign
when the external homogeneous magnetic field is varied. This reversal also
occurs when the magnetic field becomes inhomogeneous. Moreover, we can tune the
reversal of rectification by temperatures of the heat baths, the anisotropy and
size of the spin chains.Comment: 4 pages, 7 figure
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