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We investigate in detail the nonlinear and chaotic dynamics of the Colpitts oscillator. We show that we can control the dynamics of the oscillator by either inductors, capacitors or resistors in the emitter or collector network. We find the bifurcation diagram and the Lyapunov exponent of the oscillator and investigate them. We also find bifurcation diagram in 2D space when two parameters from the mentioned parameters are variables. The 2D diagram shows the nonlinear behaviour of the system more clearly.

We theoretically investigate the tunneling time, including group delay and dwell time, through silicene barrier in the presence of extrinsic Rashba spin-orbit interaction (RSOI). It is found that the group delay and dwell time depend on the spin state of electron and have an oscillatory behavior with respect to on-site potential difference between A and B sublattices ( Δ z ) and barrier width. Furthermore similar to graphene the group delay time for normal incident angle is independent of spin state of electron, while unlike the graphene, the superluminal tunneling or Hartman effect can be observed even at the normal incidence. Moreover, the difference of the dwell time between spin-up and spin-down can be efficiently tuned by the ( Δ z ) and extrinsic RSOI strength.

We study an array of coupled Josephson junction of superconductor/insulator/superconductor type (SIS junction) as a model for high temperature superconductors with layered structure. In the current-voltage characteristics of this system there is a breakpoint region in which a net electric charge appear on superconducting layers, S-layers, of junctions which motivate us to study the charge dynamics in this region. In this paper first of all we show a current voltage characteristics (CVC) of Intrinsic Josephson Junctions (IJJs) with N=3 Junctions, then we show the breakpoint region in that CVC, then we try to investigate the chaos in this region. We will see that at the end of the breakpoint region, behavior of the system is chaotic and Lyapunov exponent become positive. We also study the route by which the system become chaotic and will see this route is bifurcation. Next goal of this paper is to show the self similarity in the bifurcation diagram of the system and detailed analysis of bifurcation diagram.

By applying a voltage to a Josephson junction, the charge in superconducting layers (S-layers) will oscillate. Wavelength of the charge oscillations in S-layers is related to external current in junction, by increasing the external current, the wavelength will decrease which cause in some currents the wavelength be incommensurate with width of junction, so the CVC shows Fiske like steps. External current throwing along junction has some components, resistive, capacitive and superconducting current, beside these currents there is a current in lateral direction of junction, (x direction). On the other hand, the emitted electromagnetic wave power in THz region is related to AC component of electric field in junction, which itself is related to charge density in S-layers, which is related to currents in the system. So we expect that features of variation of current components reflect the features of emitted THz power form junction. Here we study in detail the superconductive current in a long Josephson junction (JJ), the current voltage characteristics (CVC) of junction and emitted THz power from the system. Then we compare the results. Comparing the results we see that there is a good qualitative coincidence in features of emitted THz power and supercurrent in junction.

We theoretically study the spin-dependent group delay time through ferromagnetic bilayer graphene superlattice in the absence and presence of the bandgap. It is found that the group delay time depends on the spin degree of freedom and exhibits an oscillatory behavior with respect to the Fermi energy and barrier width. Furthermore, in the absence of the bandgap, the superluminal or Hartman effect exists only for the normal angle of incidence. Moreover, when bandgap value is large enough [Formula: see text], the Hartman effect can be observed for all angles of incidence. These results are contrary to the observed behavior for monolayer graphene superlattice.

Cathodic disbonding of the epoxy coatings on the mild steel was evaluated in 3.5% NaCl solution, where benzimidazole, benzothiazole and benzotriazole were used as additives in the coatings. Also, the electrochemical behavior of coatings delaminating in NaCl solution from a small artificial defect and the bare mild steel samples in the 3.5% NaCl solution containing the azole compounds was evaluated by electrochemical impedance spectroscopy at cathodic polarization condition. Results showed that the azole compounds were not immobilized in the coating as they could leach out and act as cathodic inhibitor at defect site and disbonding front.

We look for chaos in an intrinsically coupled system of Josephson junctions. This study has direct applications for the high-Tc resonators which require coherence amongst the junctions.

Chaotic features of systems of coupled Josephson junctions are studied. Manifestation of chaos in the temporal dependence of the electric charge, related to a parametric resonance, is demonstrated through the calculation of the maximal Lyapunov exponent, phase-charge and charge-charge Lissajous diagrams and correlation functions. The number of junctions in the stack strongly influences the fine structure in the current voltage characteristics and a strong proximity effect results from the nonperiodic boundary conditions. The observed resonance-related chaos exhibits intermittency over a range of conditions and parameters. General features of the system are analyzed by means of a linearized equation and the criteria for a breakpoint region with no chaos are obtained. Such criteria could clarify recent experimental observations of variations in the power output from intrinsic Josephson junctions in high temperature superconductors., Comment: 13 pages, 16 figures

The current-voltage characteristics (CVC) of capacitively coupled Josephson junctions are numerically calculated. The methods of branch structure simulation in the CVC and charge dynamics of the coupled Josephson junctions are described in detail. We discuss the features of the parametric resonance and its manifestation in the CVC and in the charge-charge diagrams.

We demonstrate a manifestation of the charge traveling wave along the c-axis (TW) in current voltage characteristics of coupled Josephson junctions in high-$T_c$ superconductors. The branches related to the TW with different wavelengths are found for the stacks with different number of Josephson junctions at different values of system's parameters. Transitions between the TW branches and the outermost branch are observed. Time dependence of the electric charge in the superconducting layers and charge-charge correlation functions for TW and outermost branches show different behavior with bias current. We propose an experimental testing of the TW by microwave irradiation., Comment: Supplement : http://theor.jinr.ru/~hamdipur/lambda0.avi

Charge formations on superconducting layers and creation of the longitudinal plasma wave in the stack of intrinsic Josephson junctions change crucially the superconducting current through the stack. Investigation of the correlations of superconducting currents in neighboring Josephson junctions and the charge correlations in neighboring superconducting layers allows us to predict the additional features in the current-voltage characteristics. The charge autocorrelation functions clearly demonstrate the difference between harmonic and chaotic behavior in the breakpoint region. Use of the correlation functions gives us a powerful method for the analysis of the current-voltage characteristics of coupled Josephson junctions.

Dynamics of stacked intrinsic Josephson junctions (IJJ) in the high-Tc superconductors is theoretically investigated. We calculate the current-voltage characteristics (CVC) of IJJ and study the breakpoint region on the outermost branch of the CVC for the stacks with 9 IJJ. A method for investigation of the fine structure in CVC of IJJ based on the recording the "phase-charge" diagrams is suggested. It is demonstrated that this method reflects the main features of the breakpoint region., Comment: Dubna-Nano2010 conference : http://theor.jinr.ru/~nano10/ will be published online in Journal of Physics: Conference series