Synchronization of periodic self-oscillations by common noise

We consider the effect of external noise on the stability properties of self-oscillations. A stochastic equation for the phase is derived at the limit of weak noise (in the appropriate sense). The stationary probability-density distribution is used for an analytic calculation of the Lyapunov exponent. We show that the exponent is always negative for the small noise level, which corresponds to synchronization of self-oscillations.     

Development of Josephson Traveling-Wave Parametric Amplifier Based on Aluminum SIS Junctions

Physics of the Solid State - Prototypes of the design of Josephson traveling-wave parametric amplifier based on aluminum superconductor–insulator–superconductor junctions in the form of...     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

Nonlinear resonance between a soliton and Josephson plasma waves: experiment and theory

Resonant interaction of a soliton (Josephson fluxon) with its self-generated Josephson plasma waves is studied experimentally, numerically, and analytically. An externally applied magnetic field H forms a cos-like potential relief for the soliton in the annular junction. Soliton motion under the influence of the bias current leads to an emission of plasma waves, which gives rise to a resonance at a certain soliton velocity. This resonance on the current–voltage characteristics shows a clear backbending accompanied by a negative differential resistance. Our analysis quantitatively explains the observed effect.     

Soret-driven convection of binary mixture in a horizontal porous layer in the presence of a heat or concentration source

Soret-driven convection of a binary mixture in a shallow porous layer is analyzed. The analysis focuses on the behavior of the system in the presence of a concentration or heat source. In the long-wavelength limit, regimes are found in which the flow regions near the source and at the periphery are separated by narrow annular transition regions. It is also shown that the outward concentration flux from the source is dominated by convection, whereas heat can be transferred from the source both by convection and by diffusion. Multistability between these two regimes is possible.     

Aerodynamics and heat transfer in cyclones with particle-laden gas flow

Experiments were performed on a 204 mm diameter water-cooled cyclone to measure the pressure drop and heat transfer in different sections of the cyclone. Hot gas at 250°C entered the cyclone with and without suspended particles. Heat transfer and pressure drop in solids-free gas flow were compared with those measured for particle-laden gas flow of different solids.     

Combinatorial sputtering in planetary type systems for alloy libraries with perpendicular gradients of layer thickness and composition realised by a timing approach

We present a combinatorial sputtering technique to fabricate alloy thin films with orthogonal gradients of thickness and stoichiometry in a planetary type sputtering system. Using this approach we prepared a library of planar Nb Josephson junctions with a magnetic compound layer made from Si and Fe on one wafer. The independent investigation of thickness and composition changes of the Fe \(_x\) Si \(_{1-x}\) layer allows the identification of transition regions where the phase difference of the superconducting order parameter across the barrier changes from 0 to \(\pi \) . A mapping technique which allows to identify the different coupling regimes depending on material properties might facilitate the fabrication of \(\pi \) junctions with tailored critical current, damping and normal resistance parameters for applications.     

Uncertainty principle for control of ensembles of oscillators driven by common noise

We discuss control techniques for noisy self-sustained oscillators with a focus on reliability, stability of the response to noisy driving, and oscillation coherence understood in the sense of constancy of oscillation frequency. For any kind of linear feedback control — single and recursive delay feedback, linear frequency filter, etc. — the phase diffusion constant, quantifying coherence, and the Lyapunov exponent, quantifying reliability, can be efficiently controlled but their ratio remains constant. Thus, an “uncertainty principle” can be formulated: the loss of reliability occurs when coherence is enhanced and, vice versa, coherence is weakened when reliability is enhanced. Treatment of this principle for ensembles of oscillators synchronized by common noise or global coupling reveals a substantial difference between the cases of slightly non-identical oscillators and identical ones with intrinsic noise.     

0-pi Josephson tunnel junctions with ferromagnetic barrier

We fabricated high quality Nb/Al2O3/Ni(0.6)Cu(0.4)/Nb superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions. Using a ferromagnetic layer with a steplike thickness, we obtain a 0-pi junction, with equal lengths and critical currents of 0 and pi parts. The ground state of our 330 microm (1.3lambda(J)) long junction corresponds to a spontaneous vortex of supercurrent pinned at the 0-pi step and carrying approximately 6.7% of the magnetic flux quantum Phi(0). The dependence of the critical current on the applied magnetic field shows a clear minimum in the vicinity of zero field.     

Effective long-time phase dynamics of limit-cycle oscillators driven by weak colored noise

An effective white-noise Langevin equation is derived that describes long-time phase dynamics of a limit-cycle oscillator driven by weak stationary colored noise. Effective drift and diffusion coefficients are given in terms of the phase sensitivity of the oscillator and the correlation function of the noise, and are explicitly calculated for oscillators with sinusoidal phase sensitivity functions driven by two typical colored Gaussian processes. The results are verified by numerical simulations using several types of stochastic or chaotic noise. The drift and diffusion coefficients of oscillators driven by chaotic noise exhibit anomalous dependence on the oscillator frequency, reflecting the peculiar power spectrum of the chaotic noise.