11,168 research outputs found
Perturbative analysis of generally nonlocal spatial optical solitons
In analogy to a perturbed harmonic oscillator, we calculate the fundamental
and some other higher order soliton solutions of the nonlocal nonlinear
Schroedinger equation (NNLSE) in the second approximation in the generally
nonlocal case. Comparing with numerical simulations we show that soliton
solutions in the 2nd approximation can describe the generally nonlocal soliton
states of the NNLSE more exactly than that in the zeroth approximation. We show
that for the nonlocal case of an exponential-decay type nonlocal response the
Gaussian-function-like soliton solutions can't describe the nonlocal soliton
states exactly even in the strongly nonlocal case. The properties of such
nonlocal solitons are investigated. In the strongly nonlocal limit, the
soliton's power and phase constant are both in inverse proportion to the 4th
power of its beam width for the nonlocal case of a Gaussian function type
nonlocal response, and are both in inverse proportion to the 3th power of its
beam width for the nonlocal case of an exponential-decay type nonlocal
response.Comment: 13 pages, 16 figures, accepted by Phys. Rev.
Resonance tongues and patterns in periodically forced reaction-diffusion systems
Various resonant and near-resonant patterns form in a light-sensitive
Belousov-Zhabotinsky (BZ) reaction in response to a spatially-homogeneous
time-periodic perturbation with light. The regions (tongues) in the forcing
frequency and forcing amplitude parameter plane where resonant patterns form
are identified through analysis of the temporal response of the patterns.
Resonant and near-resonant responses are distinguished. The unforced BZ
reaction shows both spatially-uniform oscillations and rotating spiral waves,
while the forced system shows patterns such as standing-wave labyrinths and
rotating spiral waves. The patterns depend on the amplitude and frequency of
the perturbation, and also on whether the system responds to the forcing near
the uniform oscillation frequency or the spiral wave frequency. Numerical
simulations of a forced FitzHugh-Nagumo reaction-diffusion model show both
resonant and near-resonant patterns similar to the BZ chemical system
Seed vigor, aging, and osmopriming affect anion and sugar leakage during imbition of maize (Zea mays L.) caryopses
Conductivity was significantly increased by aging and decreased by osmopriming of maize (Zea mays L.) caryopses. Chloride, phosphate, and sulfate were the main anions that leaked out of maize seeds; their leakage was closely related to conductivity, increased by aging, and decreased by osmopriming. The anion leakage of isolated embryos correlated closely to seed vigor and was more sensitive to aging and priming than that of the whole seed. Anion leakage may be a more sensitive measure for seed vigor than bulk conductivity readings. Aging did not increase the sugar leakage of whole seeds but significantly increased the sugar leakage of isolated embryos. Sugar leakage was not closely related to total soluble sugar content of seeds. While priming decreased seed conductivity, the decreased anion and sugar leakage of the primed seeds was mainly caused by the washing effect during priming. The total anions or sugars left in the polyethylene glycol (PEG) solution after priming and in the conductivity solution of the primed seeds was almost the same as in the conductivity solution of the unprimed seeds alone
Dirac Particles in Twisted Tubes
We consider the dynamics of a relativistic Dirac particle constrained to move
in the interior of a twisted tube by confining boundary conditions, in the
approximation that the curvature of the tube is small and slowly varying. In
contrast with the nonrelativistic theory, which predicts that a particle's spin
does not change as the particle propagates along the tube, we find that the
angular momentum eigenstates of a relativistic spin-1/2 particle may behave
nontrivially. For example, a particle with its angular momentum initially
polarized in the direction of propagation may acquire a nonzero component of
angular momentum in the opposite direction on turning through 2 \pi radians.
Also, the usual nonrelativistic effective potential acquires an additional
factor in the relativistic theory.Comment: 16 pages, 3 EPS figures, REVTeX using BoxedEPS package; email to
[email protected]
Dynamics of Turing patterns under spatio-temporal forcing
We study, both theoretically and experimentally, the dynamical response of
Turing patterns to a spatio-temporal forcing in the form of a travelling wave
modulation of a control parameter. We show that from strictly spatial
resonance, it is possible to induce new, generic dynamical behaviors, including
temporally-modulated travelling waves and localized travelling soliton-like
solutions. The latter make contact with the soliton solutions of P. Coullet
Phys. Rev. Lett. {\bf 56}, 724 (1986) and provide a general framework which
includes them. The stability diagram for the different propagating modes in the
Lengyel-Epstein model is determined numerically. Direct observations of the
predicted solutions in experiments carried out with light modulations in the
photosensitive CDIMA reaction are also reported.Comment: 6 pages, 5 figure
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