4,020 research outputs found
Reflection of Channel-Guided Solitons at Junctions in Two-Dimensional Nonlinear Schroedinger Equation
Solitons confined in channels are studied in the two-dimensional nonlinear
Schr\"odinger equation. We study the dynamics of two channel-guided solitons
near the junction where two channels are merged. The two solitons merge into
one soliton, when there is no phase shift. If a phase difference is given to
the two solitons, the Josephson oscillation is induced. The Josephson
oscillation is amplified near the junction. The two solitons are reflected when
the initial velocity is below a critical value.Comment: 3 pages, 2 figure
Solitons in combined linear and nonlinear lattice potentials
We study ordinary solitons and gap solitons (GSs) in the effectively
one-dimensional Gross-Pitaevskii equation, with a combination of linear and
nonlinear lattice potentials. The main points of the analysis are effects of
the (in)commensurability between the lattices, the development of analytical
methods, viz., the variational approximation (VA) for narrow ordinary solitons,
and various forms of the averaging method for broad solitons of both types, and
also the study of mobility of the solitons. Under the direct commensurability
(equal periods of the lattices, the family of ordinary solitons is similar to
its counterpart in the free space. The situation is different in the case of
the subharmonic commensurability, with L_{lin}=(1/2)L_{nonlin}, or
incommensurability. In those cases, there is an existence threshold for the
solitons, and the scaling relation between their amplitude and width is
different from that in the free space. GS families demonstrate a bistability,
unless the direct commensurability takes place. Specific scaling relations are
found for them too. Ordinary solitons can be readily set in motion by kicking.
GSs are mobile too, featuring inelastic collisions. The analytical
approximations are shown to be quite accurate, predicting correct scaling
relations for the soliton families in different cases. The stability of the
ordinary solitons is fully determined by the VK (Vakhitov-Kolokolov) criterion,
while the stability of GS families follows an inverted ("anti-VK") criterion,
which is explained by means of the averaging approximation.Comment: 9 pages, 6 figure
Nondegenerate Super-Anti-de Sitter Algebra and a Superstring Action
We construct an Anti-de Sitter(AdS) algebra in a nondegenerate superspace.
Based on this algebra we construct a covariant kappa-symmetric superstring
action, and we examine its dynamics: Although this action reduces to the usual
Green-Schwarz superstring action in flat limit, the auxiliary fermionic
coordinates of the nondegenerate superspace becomes dynamical in the AdS
background.Comment: Latex, 12 pages, explanations added, version to be published in Phys.
Rev.
Fluctuation Dissipation Relation for a Langevin Model with Multiplicative Noise
A random multiplicative process with additive noise is described by a
Langevin equation. We show that the fluctuation-dissipation relation is
satisfied in the Langevin model, if the noise strength is not so strong.Comment: 11 pages, 6 figures, other comment
Starting at the endophenotype: A role for alpha-CaMKII in schizophrenia?
Using an endophenotype-driven screen, a new study finds that α-calcium/calmodulin kinase II mutant mice exhibit a range of behavioral abnormalities related to schizophrenia. Perhaps most strikingly, this cluster of schizophrenia-related endophenotypes was associated with abnormal neurogenesis in the adult hippocampus, raising the possibility that disrupted adult neurogenesis lies at the core of this and other psychiatric disorders
Cascade Failure in a Phase Model of Power Grids
We propose a phase model to study cascade failure in power grids composed of
generators and loads. If the power demand is below a critical value, the model
system of power grids maintains the standard frequency by feedback control. On
the other hand, if the power demand exceeds the critical value, an electric
failure occurs via step out (loss of synchronization) or voltage collapse. The
two failures are incorporated as two removal rules of generator nodes and load
nodes. We perform direct numerical simulation of the phase model on a
scale-free network and compare the results with a mean-field approximation.Comment: 7 pages, 2 figure
Delocalization transition of a small number of particles in a box with periodic boundary conditions
We perform molecular dynamics simulation of a small number of particles in a
box with periodic boundary conditions from a view point of chaotic dynamical
systems. There is a transition at a critical energy E_c that each particle is
confined in each unit cell for E<E_c, and the chaotic diffusion occurs for
E>E_c. We find an anomalous behavior of the jump frequency above the critical
energy in a two-particle system, which is related with the infinitely
alternating stability change of the straight motion passing through a saddle
point. We find simultaneous jump motions just above the critical energy in a
four-particle system and sixteen-particle system, which is also related with
the motion passing through the saddle point.Comment: 9 pages, 10 figure
Quantum switches and quantum memories for matter-wave lattice solitons
We study the possibility of implementing a quantum switch and a quantum
memory for matter wave lattice solitons by making them interact with
"effective" potentials (barrier/well) corresponding to defects of the optical
lattice. In the case of interaction with an "effective" potential barrier, the
bright lattice soliton experiences an abrupt transition from complete
transmission to complete reflection (quantum switch) for a critical height of
the barrier. The trapping of the soliton in an "effective" potential well and
its release on demand, without loses, shows the feasibility of using the system
as a quantum memory. The inclusion of defects as a way of controlling the
interactions between two solitons is also reported
Relevance of pseudospin symmetry in proton-nucleus scattering
The manifestation of pseudospin-symmetry in proton-nucleus scattering is
discussed. Constraints on the pseudospin-symmetry violating scattering
amplitude are given which require as input cross section and polarization data,
but no measurements of the spin rotation function. Application of these
constraints to p-58Ni and p-208Pb scattering data in the laboratory energy
range of 200 MeV to 800 MeV, reveals a significant violation of the symmetry at
lower energies and a weak one at higher energies. Using a schematic model
within the Dirac phenomenology, the role of the Coulomb potential in
proton-nucleus scattering with regard to pseudospin symmetry is studied. Our
results indicate that the existence of pseudospin-symmetry in proton-nucleus
scattering is questionable in the whole energy region considered and that the
violation of this symmetry stems from the long range nature of the Coulomb
interaction.Comment: 22 pages including 9 figures, correction of 1 reference, revision of
abstract and major modification of chapter 4, Fig. 6, and Fig. 7; addition of
Fig. 8 and Fig.
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