20,265 research outputs found
Spatial weak-light solitons in an electro-magnetically induced nonlinear waveguide
We show that a weak probe light beam can form spatial solitons in an
electro-magnetically induced transparency (EIT) medium composed of four-level
atoms and a coupling light field. We find that the coupling light beam can
induce a highly controllable nonlinear waveguide and exert very strong effects
on the dynamical behavior of the solitons. Hence, in the EIT medium, it is not
only possible to produce spatial solitons at very low light intensities but
also simultaneously control these solitons by using the coupling-light-induced
nonlinear waveguide.Comment: 5 pages, 5 figures. Phys. Rev. Lett. 90, 183901 (2003
A Simple Method of Calculating Commutators in Hamilton System with Mathematica Software
As a powerful tool in scientific computation, Mathematica offers us algebraic
computation, but it does not provide functions to directly calculate
commutators in quantum mechanics. Different from present software packets to
deal with noncommutative algebra, such as NCAlgebra and NCComAlgebra, one
simple method of calculating the commutator in quantum mechanics is put forward
and is demonstrated by an example calculating SO(4) dynamical symmetry in 3
dimensions Coulomb potential. This method does not need to develop software
packets but rather to directly write program in Mathematica. It is based on the
connection between commutator in quantum mechanics and Poisson bracket in
classical mechanics to perform calculations. Both the length and the running
time of this example are very short, which demonstrates that this method is
simple and effective in scientific research. Moreover, this method is used to
calculate any commutator in Hamilton system in principle. In the end some
deficiencies and applications are discussed.Comment: 8 pages, Latex, no figure
A second-order and nonuniform time-stepping maximum-principle preserving scheme for time-fractional Allen-Cahn equations
In this work, we present a second-order nonuniform time-stepping scheme for
the time-fractional Allen-Cahn equation. We show that the proposed scheme
preserves the discrete maximum principle, and by using the convolution
structure of consistency error, we present sharp maximum-norm error estimates
which reflect the temporal regularity. As our analysis is built on nonuniform
time steps, we may resolve the intrinsic initial singularity by using the
graded meshes. Moreover, we propose an adaptive time-stepping strategy for
large time simulations. Numerical experiments are presented to show the
effectiveness of the proposed scheme. This seems to be the first second-order
maximum principle preserving scheme for the time-fractional Allen-Cahn
equation.Comment: 22pages, 22 figures, 2 table
Competition between phase coherence and correlation in a mixture of Bose-Einstein condensates
Two-species hard-core bosons trapped in a three-dimensional isotropic
harmonic potential are studied with the path-integral quantum Monte Carlo
simulation. The double condensates show two distinct structures depending on
how the external potentials are set. Contrary to the mean-field results, we
find that the heavier particles form an outer shell under an identical external
potential whereas the lighter particles form an outer shell under the equal
energy spacing condition. Phase separations in both the spatial and energy
spaces are observed. We provide physical interpretations of these phase
separations and suggest future experiment to confirm these findings.Comment: 4 pages, 4 figures, submitted to Physical Review Letter
A Global Algorithm for Training Multilayer Neural Networks
We present a global algorithm for training multilayer neural networks in this
Letter. The algorithm is focused on controlling the local fields of neurons
induced by the input of samples by random adaptations of the synaptic weights.
Unlike the backpropagation algorithm, the networks may have discrete-state
weights, and may apply either differentiable or nondifferentiable neural
transfer functions. A two-layer network is trained as an example to separate a
linearly inseparable set of samples into two categories, and its powerful
generalization capacity is emphasized. The extension to more general cases is
straightforward
Condensate-profile asymmetry of a boson mixture in a disk-shaped harmonic trap
A mixture of two types of hard-sphere bosons in a disk-shaped harmonic trap
is studied through path-integral quantum Monte Carlo simulation at low
temperature. We find that the system can undergo a phase transition to break
the spatial symmetry of the model Hamiltonian when some of the model parameters
are varied. The nature of such a phase transition is analyzed through the
particle distributions and angular correlation functions. Comparisons are made
between our calculations and the available mean-field results on similar
models. Possible future experiments are suggested to verify our findings.Comment: 4 pages, 4 figure
Traffic flow and efficient routing on scale-free networks: A survey
Recently, motivated by the pioneer works in revealing the small-world effect
and scale-free property of various real-life networks, many scientists devote
themselves to studying complex networks. In this paper, we give a brief review
on the studies of traffic flow and efficient routing on scale-free networks,
including the traffic dynamics based on global routing protocol, Traffic
dynamics based on local routing protocol, and the critical phenomena and
scaling behaviors of real and artificial traffic. Finally, perspectives and
some interesting problems are proposed.Comment: A brief review on recent progress of network traffi
Integrated Facility Location and Production Scheduling in Multi-Generation Energy Systems
In this paper, we investigate the energy system design problems with the
multi-generation technologies, i.e., simultaneous generation of multiple types
of energy. We propose a long-term planning model which integrates macro-level
strategic decisions such as facility location and multi-generation technology
investment, and micro-level operational decisions such as production planning
and energy transportation. Our results illustrate the economic value of
multi-generation technologies in lieu of the spatio-temporal demand uncertainty
for energy. In particular, we show that the multi-generation technologies can
reduce demand uncertainty by risk pooling both within and across different
facilities
Variational study of the one dimensional t-J model
We find the Gutzwiller projected Fermi sea wave function(GWF) has the correct
phase structure to describe the kink nature of the doped holes in the ground
state of the one dimensional model. We find the failure of the GWF for
general value of and electron density can be attributed to the
residual charge correlation in the ground state. We find such residual charge
correlation is well described by a XXZ-type effective Hamiltonian. Based on
these observations, a Pfaffian-type variational wave function is proposed and
is found to reproduce correctly the global phase diagram and corresponding
correlation functions of the one dimensional model, including the
Luther-Emery phase in the low electron density and large region.Comment: 8 pages, 8 figure
Spin Charge Recombination in Projected Wave Functions
We find spin charge recombination is a generic feature of projected wave
functions. We find this effect is responsible for a series of differences
between mean field theory prediction and the result from projected wave
functions. We also find spin charge recombination plays an important role in
determining the dissipation of supercurrent, the quasiparticle properties and
the hole - hole correlation.Comment: 13 pages,7 figure
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