Simulation of the resistive state of superconducting films in a magnetic field on the basis of the nonstationary ginzburg-landau equation

By numerical simulation of the temporal two-dimensional Ginzburg-Landau equation, we study the resistive state in superconducting bridges with dimensions ξ ≪ d ≪ λ. It is found that the basis of the resistive state here is, as for d ≫ λ, the vortical structures (vortices) whose motion defines the resistive state. It is shown that the motion of vortices is stochastic in a certain range of currents and magnetic fields. We give a classification of possible dynamic and stochastic modes and examine the transitions from the current flow mode, which is observed for large magnetic fields and small transport currents, to the mode of fast phase slippage. The symmetry breaking effect of the resistive state, which results in cross tension with a quadrupole structure, has been detected. Institute of Physics of Microstructures, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenü, Radiofizika, Vol. 40, Nos. 1–2, pp. 213–231, January–February, 1997.     

Ergodic properties of certain surjective cellular automata

We consider one-dimensional cellular automata, i.e. the mapsT:P P (P is a finite set with more than one element) which are given by (Tx) _i =F(x _i+l , ...,x _i+r ),x=(x _i )P for some integerslr and a mappingFP ^r–l+1P. We prove that ifF is right- (left-) permutative (in Hedlund's terminology) and 0l<r (resp.l<r0), then the natural extension of the dynamical system (P , , ,T) is a Bernoulli automorphism ( stands for the (1/p, ..., 1/p)-Bernoulli measure on the full shiftP ). Ifr<0 orl>0 andT is surjective, then the natural extension of the system (P , , ,T) is aK-automorphism. We also prove that the shift ²-action on a two-dimensional subshift of finite type canonically associated with the cellular automatonT is mixing, ifF is both right and left permutative. These results answer some questions raised in [SR].     

MFM probe control of magnetic vortex chirality in elliptical Co nanoparticles

Magnetic force microscopy (MFM) methods were applied to investigate the peculiarities of magnetization distribution in elliptical 400×600×27 nm Co particles. Reversible transitions between the uniform and vortex states under inhomogeneous magnetic field of MFM probe were observed. Possibility to control the chirality of a magnetic vortex in these particles by MFM probe manipulation was shown.