27,251 research outputs found
Self-organized critical behavior: the evolution of frozen spin networks model in quantum gravity
In quantum gravity, we study the evolution of a two-dimensional planar open
frozen spin network, in which the color (i.e. the twice spin of an edge)
labeling edge changes but the underlying graph remains fixed. The mainly
considered evolution rule, the random edge model, is depending on choosing an
edge randomly and changing the color of it by an even integer. Since the change
of color generally violate the gauge invariance conditions imposed on the
system, detailed propagation rule is needed and it can be defined in many ways.
Here, we provided one new propagation rule, in which the involved even integer
is not a constant one as in previous works, but changeable with certain
probability. In random edge model, we do find the evolution of the system under
the propagation rule exhibits power-law behavior, which is suggestive of the
self-organized criticality (SOC), and it is the first time to verify the SOC
behavior in such evolution model for the frozen spin network. Furthermore, the
increase of the average color of the spin network in time can show the nature
of inflation for the universe.Comment: 5 pages, 5 figure
Eddy current generation enhancement using ferrite for electromagnetic acoustic transduction
Eddy currents are generated in an electrically conducting surface as a step in electromagnetic acoustic transduction (EAT). In eddy current testing, wire coils are often wound onto a ferrite core to increase the generated eddy current. With EAT, increased coil inductance is unacceptable as it leads to a reduction in the amplitude of a given frequency of eddy current from a limited voltage source, particularly where the current arises from capacitor discharge. The authors present a method for EAT where ferrite is used to increase the eddy current amplitude without significantly increasing coil inductance or changing the frequency content of the eddy current
Collins Fragmentation and the Single Transverse Spin Asymmetry
We study the Collins mechanism for the single transverse spin asymmetry in
the collinear factorization approach. The correspondent twist-three
fragmentation function is identified. We show that the Collins function
calculated in this approach is universal. We further examine its contribution
to the single transverse spin asymmetry of semi-inclusive hadron production in
deep inelastic scattering and demonstrate that the transverse momentum
dependent and twist-three collinear approaches are consistent in the
intermediate transverse momentum region where both apply.Comment: 10 pages, 2 figure
Effects of interorbital hopping on orbital fluctuations and metal-insulator transitions: Extended linearized dynamical mean-field theory
We study the effects of interorbital hopping on orbital fluctuations and
Mott-Hubbard metal-insulator transition (MIT) in the two-orbital Hubbard model
within the extended linearized dynamical mean-field theory. By mapping the
model onto an effective model with different bandwidths through the canonical
transformation, we find that at half-filling, the increases of the interorbital
Coulomb interaction and the Hund's coupling drive the MIT, and
the critical for MIT increases with the lift of the inter-orbital
hopping integral . Meanwhile at quarter filling and in the strong
correlation regime, the system without exhibits MIT with the
decreasing of , and favors the orbital liquid ground state. However, the
system transits from metal to insulator with the increasing of t,
accompanied with the rising of the orbital order parameter. These results show
the important role of the interorbital hopping in the orbital fluctuation and
orbital ordering.Comment: 7 pages, 6 figure
Transverse single spin asymmetry in the Drell-Yan process
We revisit the transverse single spin asymmetry in the angular distribution
of a Drell-Yan dilepton pair. We study this asymmetry by using twist-3
collinear factorization, and we obtain the same result both in covariant gauge
and in the light-cone gauge. Moreover, we have checked the electromagnetic
gauge invariance of our calculation. Our final expression for the asymmetry
differs from all the previous results given in the literature. The overall sign
of this asymmetry is as important as the sign of the Sivers asymmetry in
Drell-Yan.Comment: 9 page
Searching for Effects of Spatial Noncommutativity via Chern-Simons' Processes
The possibility of testing spatial noncommutativity in the case of both
position-position and momentum-momentum noncommuting via a Chern-Simons'
process is explored. A Chern-Simons process can be realized by an interaction
of a charged particle in special crossed electric and magnetic fields, in which
the Chern-Simons term leads to non-trivial dynamics in the limit of vanishing
kinetic energy. Spatial noncommutativity leads to the spectrum of the orbital
angular momentum possessing fractional values. Furthermore, in both limits of
vanishing kinetic energy and subsequent vanishing magnetic field, the
Chern-Simons term leads to this system having non-trivial dynamics again, and
the dominant value of the lowest orbital angular momentum being ,
which is a clear signal of spatial noncommutativity. An experimental
verification of this prediction by a Stern-Gerlach-type experiment is
suggested.Comment: 18 page
First-principles investigation of dynamical properties of molecular devices under a steplike pulse
We report a computationally tractable approach to first principles
investigation of time-dependent current of molecular devices under a step-like
pulse. For molecular devices, all the resonant states below Fermi level
contribute to the time-dependent current. Hence calculation beyond wideband
limit must be carried out for a quantitative analysis of transient dynamics of
molecules devices. Based on the exact non-equilibrium Green's function (NEGF)
formalism of calculating the transient current in Ref.\onlinecite{Maciejko}, we
develop two approximate schemes going beyond the wideband limit, they are all
suitable for first principles calculation using the NEGF combined with density
functional theory. Benchmark test has been done by comparing with the exact
solution of a single level quantum dot system. Good agreement has been reached
for two approximate schemes. As an application, we calculate the transient
current using the first approximated formula with opposite voltage
in two molecular structures: Al--Al and Al--Al. As illustrated in these examples, our formalism can be easily
implemented for real molecular devices. Importantly, our new formula has
captured the essential physics of dynamical properties of molecular devices and
gives the correct steady state current at and .Comment: 15 pages, 8 figure
Vibrating Superconducting Island in a Josephson Junction
We consider a combined nanomechanical-supercondcuting device that allows the
Cooper pair tunneling to interfere with the mechanical motion of the middle
superconducting island. Coupling of mechanical oscillations of a
superconducting island between two superconducting leads to the electronic
tunneling generate a supercurrent which is modulated by the oscillatory motion
of the island. This coupling produces alternating finite and vanishing
supercurrent as function of the superconducting phases. Current peaks are
sensitive to the superconducting phase shifts relative to each other. The
proposed device may be used to study the nanoelectromechanical coupling in case
of superconducting electronics.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
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