Invariant trajectory defined

If the basis sequence creates a nonvanishing effective field this is only possible if n X0) is oriented parallel (or antiparallel) to the direction of Bf During the basis sequence, the time evolution of the components n jKt), n y t), and n j t) of the invariant trajectory can be expressed with the help of the coefficients a it) defined in Eq. (90) as... 

Effective autorelaxation rates of the invariant trajectory of an uncoupled spin i during a basis sequence can be defined as... 

An obvious map to consider is that which takes the state (x(t), y(t) into the state (x(t + r), y(t + t)), where r is the period of the forcing function. If we define xn = x(n t) and y = y(nr), the sequence of points for n = 0,1,2,... functions in this so-called stroboscopic phase plane vis-a-vis periodic solutions much as the trajectories function in the ordinary phase plane vis-a-vis the steady states (Fig. 29). Thus if (x , y ) = (x +1, y +j) and this is not true for any submultiple of r, then we have a solution of period t. A sequence of points that converges on a fixed point shows that the periodic solution represented by the fixed point is stable and conversely. Thus the stability of the periodic responses corresponds to that of the stroboscopic map. A quasi-periodic solution gives a sequence of points that drift around a closed curve known as an invariant circle. The points of the sequence are often joined by a smooth curve to give them more substance, but it must always be remembered that we are dealing with point maps. 

The first interesting phenomenon we observe is the breaking of the smooth invariant circle picture when the node-periodic points on the circle become foci [Figs. 8(a) and 8(b)]. The basic structure of the trajectories remains the same, but the object we are now studying is no longer a well-defined circle ... 

By Noether s theorem, invariance of the Lagrangian under an infinitesimal time displacement implies conservation of energy. This is consistent with the direct proof of energy conservation given above, when L and by implication H have no explicit time dependence. Define a continuous time displacement by the transformation t = t + oi(t ) whereat/(,) = a(t ) = 0. subject to a —0. Time intervals on the original and displaced trajectories are related by dt = (1 + a )dt or dt = (1 — a )dt. The transformed Lagrangian is... 

However, the effect of a small perturbation in action-action-angle type flows is quite different. The two-parameter family of invariant cycles coalesce into invariant tori that are connected by resonant sheets defined by the u(h,l2) = 0 condition. The consequence of this is that contrary to action-angle-angle flows in this case a trajectory can cover the whole phase space and no transport barriers exist. Thus, in this type of flows global uniform mixing can be achieved for arbitrarily small perturbations. This type of resonance induced dispersion has been demonstrated numerically in a low-Reynolds number Couette flow between two rotating spheres by Cartwright et al. 

The above theorem is related to the map on the center manifold. Reconstructing the behavior of trajectories of the original map (11.6.2) is relatively simple. Here, if L < 0, then the fixed point is stable when /i < 0. When /i > 0 it becomes a saddle-focus with an m-dimensional stable manifold (defined by T = 0) and with a two-dimensional unstable manifold which consists of a part of the plane y = 0 bounded by the stable invariant curve C,... 

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