In this work, the generic mechanism of the occasionally proportional feedback (OPF) technique in controlling chaos has been explored extensively. Except for stabilizing the unstable states that are embedded in the chaotic attractors, the OPF method is also found to generate a great number of new states during the control processes. The forms and characteristics of these new states have been addressed. Moreover, we clarify the roles of the parameters in the OPF method and this clarification leads to a practical and systematic approach in adjusting the parameters for control. To demonstrate the validity, an analogous electronic circuit of the resistively shunted Josephson junction oscillator is employed in addition to a numerical illustration of the logistic mapping.
The origin of photogenerated terahertz radiation pulse emitted from current-biased superconducting YBa 2 Cu 3 O 7Ϫ␦ thin films excited by femtosecond optical laser pulses is delineated. By investigating the performance of the transient terahertz radiation generated under different operating parameters, pulse reshaping in the measured terahertz electric field caused by the kinetic inductance of the superconducting charge carriers is identified. After recovering the original wave forms of the emitted terahertz pulses, the transient supercurrent density directly correlated to the optically excited quasiparticle dynamics is obtained. A fast decreasing component of about 1.0 ps and a slower recovery process with a value of 2.5 ps are unambiguously delineated in the optically induced supercurrent modulation. The radiation mechanism of the transient terahertz pulse related to nonequilibrium superconductivity is discussed.
AbslneL Inelastic neutron scattering experimenls in KzSeO,, CySeO, and KzCIQ are reported. ?be lowest CI-& phonon branches along the a*-axis in their plmm phase have teen characterized for the three mmpounds. lle mulls are mmpared with recent lattice dynamical simulations using rigid-ion models. Potassium chroma=, that simulations suggested to be incommensurate at low temperatures, evidences no s t~~l~r a l phase transition down to 12 K, but ik lowest Cz phonon branch exhibits a significative softening and decreases more than XI% as the temperature is lowered from MO K to 36 K . ? r e snflening mechanism m this "pound and in polassium selenate is related to an increase of the effective interaction between an amustic and an o p t i d branch.Previous inelastic neutron scattering investigations in A,BX, materials have focused on the temperature behaviour of the soft-mode branch and the characterization of phason and amplitudon branches in the INC phase [2, 16201. Here we report inelastic neutron scattering measurements of the low frequency C,-C, modes (same notation for irreducible representations as in [2]) of K,SeO,, Cs,SeO, and K,CrO, in the Phom phase. The main purpose of the study has
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