12,307 research outputs found
Universal quantized spin-Hall conductance fluctuation in graphene
We report a theoretical investigation of quantized spin-Hall conductance
fluctuation of graphene devices in the diffusive regime. Two graphene models
that exhibit quantized spin-Hall effect (QSHE) are analyzed. Model-I is with
unitary symmetry under an external magnetic field but with zero
spin-orbit interaction, . Model-II is with symplectic symmetry where
B=0 but . Extensive numerical calculations indicate that the two
models have exactly the same universal QSHE conductance fluctuation value
regardless of the symmetry. Qualitatively different from the
conventional charge and spin universal conductance distributions, in the
presence of edge states the spin-Hall conductance shows an one-sided log-normal
distribution rather than a Gaussian distribution. Our results strongly suggest
that the quantized spin-Hall conductance fluctuation belongs to a new
universality class
Generation of spiral bevel gears with conjugate tooth surfaces and tooth contact analysis
A new method for generation of spiral bevel gears is proposed. The main features of this method are as follows: (1) the gear tooth surfaces are conjugated and can transform rotation with zero transmission errors; (2) the tooth bearing contact is localized; (3) the center of the instantaneous contact ellipse moves in a plane that has a fixed orientation; (4) the contact normal performs in the process of meshing a parallel motion; (5) the motion of the contact ellipse provides improved conditions of lubrication; and (6) the gears can be manufactured by use of Gleason's equipment
Empirical study on clique-degree distribution of networks
The community structure and motif-modular-network hierarchy are of great
importance for understanding the relationship between structures and functions.
In this paper, we investigate the distribution of clique-degree, which is an
extension of degree and can be used to measure the density of cliques in
networks. The empirical studies indicate the extensive existence of power-law
clique-degree distributions in various real networks, and the power-law
exponent decreases with the increasing of clique size.Comment: 9 figures, 4 page
Kondo effect in carbon nanotube quantum dots with spin-orbit coupling
Motivated by recent experimental observation of spin-orbit coupling in carbon
nanotube quantum dots [F. Kuemmeth \textsl{et al.}, Nature (London) {\bf 452},
448 (2008)], we investigate in detail its influence on the Kondo effect. The
spin-orbit coupling intrinsically lifts out the fourfold degeneracy of a single
electron in the dot, thereby breaking the SU(4) symmetry and splitting the
Kondo resonance even at zero magnetic field. When the field is applied, the
Kondo resonance further splits and exhibits fine multipeak structures resulting
from the interplay of spin-orbit coupling and Zeeman effect. A microscopic
cotunneling process for each peak can be uniquely identified. Finally, a purely
orbital Kondo effect in the two-electron regime is also obtained.Comment: published version, 5 pages, 4 figure
Soliton solutions of the improved quark mass density-dependent model at finite temperature
The improved quark mass density-dependent model (IQMDD) based on soliton bag
model is studied at finite temperature. Appling the finite temperature field
theory, the effective potential of the IQMDD model and the bag constant
have been calculated at different temperatures. It is shown that there is a
critical temperature . We also calculate the
soliton solutions of the IQMDD model at finite tmperature. It turns out that
when , there is a bag constant and the soliton solutions are
stable. However, when the bag constant and there is no
soliton solution, therefore, the confinement of quarks are removed quickly.Comment: 10 pages, 9 figures; Version to appear in Physical Review
New application of decomposition of U(1) gauge potential:Aharonov-Bohm effect and Anderson-Higgs mechanism
In this paper we study the Aharonov-Bohm (A-B) effect and Anderson-Higgs
mechanism in Ginzburg-Landau model of superconductors from the perspective of
the decomposition of U(1) gauge potential. By the Helmholtz theorem, we derive
exactly the expression of the transverse gauge potential in A-B
experiment, which is gauge-invariant and physical. For the case of a bulk
superconductor, we find that the gradient of the total phase field
provides the longitudinal component , which reflects the
Anderson-Higgs mechanism. For the case of a superconductor ring, the gradient
of the longitudinal phase field provides the longitudinal component
, while the transverse phase field produces
new physical effects such as the flux quantization inside a superconducting
ring.Comment: 6 pages, no figures, final version to appear in Modern Physics
Letters
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