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Biomedical subjects

K Ø Rasmussen

Publications and source records attributed to K Ø Rasmussen.

3 recordsLinked to original sources

Hysteresis and metastability in the quenched turbulent dynamics of the complex Ginzburg-Landau equation.

We consider the quenched dynamics of the two-dimensional complex Ginzburg-Landau equation in its turbulent regime. We initialize the system in a frustrated state and observe how frustration affects the evolution towards the turbulent state. This process is performed for parameter values where, for random initial conditions, the system evolves into the turbulent state. We observe that the glassiness of the initial condition can inhibit the occurrence of the absolute instability close to the critical point for that instability in parameter space. Sufficiently far from the critical point, the turbulent state will develop, but only after spending considerable time in a transient metastable state of fixed vortex density. The parameter distance from the critical point is found to scale as an exponential of a power of the lifetime of the metastable state, and with a power exponent depending on the "depth" of the original quench. The limiting regimes of shallow and deep quench are identified by their respective values of the exponent, and the distinct mechanisms leading to the relaxation to turbulence in each case are highlighted.

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Three-dimensional elastic compatibility and varieties of twins in martensites.

We model a cubic-to-tetragonal martensitic transition by a Ginzburg-Landau free energy in the symmetric strain tensor. We show in three dimensions (3D) that solving the St. Venant compatibility relations for strain, treated as independent field equations, generates three anisotropic long-range potentials between the two order parameter components. These potentials encode 3D discrete symmetries, express the energetics of lattice integrity, and determine 3D textures. Simulation predictions include twins with temperature-varying orientation, helical twins, competing metastable states, and compatibility-induced elastic frustration. Our approach also applies to improper ferroelastics.

Journal Article↗

Twisted localized modes.

In a number of recent papers the so-called twisted localized mode of the discrete nonlinear Schrödinger equation has been proposed. Herein, we study the existence and stability properties of such modes. We analyze the persistence of quasiperiodic modes and study the domains of existence and numerical stability of the exact form of such solutions. We identify the bifurcations through which they lose their stability and follow the behavior of the intrinsic localized modes and their eigenmodes even in the unstable regime.

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