High‐order long‐time approximation of ( N  + 1)‐level systems with near‐resonance control

Author(s):  
Ru Geng ◽  
Jian Zu

2009 ◽  
Vol 642 ◽  
pp. 235-277 ◽  
Author(s):  
M. NITSCHE ◽  
P. D. WEIDMAN ◽  
R. GRIMSHAW ◽  
M. GHRIST ◽  
B. FORNBERG

Over two decades ago, some numerical studies and laboratory experiments identified the phenomenon of leapfrogging internal solitary waves located on separated pycnoclines. We revisit this problem to explore the behaviour of the near resonance phenomenon. We have developed a numerical code to follow the long-time inviscid evolution of isolated mode-two disturbances on two separated pycnoclines in a three-layer stratified fluid bounded by rigid horizontal top and bottom walls. We study the dependence of the solution on input system parameters, namely the three fluid densities and the two interface thicknesses, for fixed initial conditions describing isolated mode-two disturbances on each pycnocline. For most parameter values, the initial disturbances separate immediately and evolve into solitary waves, each with a distinct speed. However, in a narrow region of parameter space, the waves pair up and oscillate for some time in leapfrog fashion with a nearly equal average speed. The motion is only quasi-periodic, as each wave loses energy into its respective dispersive tail, which causes the spatial oscillation magnitude and period to increase until the waves eventually separate. We record the separation time, oscillation period and magnitude, and the final amplitudes and celerity of the separated waves as a function of the input parameters, and give evidence that no perfect periodic solutions occur. A simple asymptotic model is developed to aid in interpretation of the numerical results.











1970 ◽  
Vol 48 (5) ◽  
pp. 616-629 ◽  
Author(s):  
V. F. Sears

The calculation of slow neutron scattering cross sections for simple classical liquids by means of Mori's continued fraction representation was discussed in a previous article on the basis of the long-time approximation. In the present work it is shown that by going beyond the long-time approximation one can eliminate certain difficulties that arose in the previous work. This new approach yields results equivalent to those found by Kadanoff and Martin, and others, from linear response theory. Numerical calculations are made for liquid argon and compared with available experimental data.



2012 ◽  
Vol 241-244 ◽  
pp. 20-37 ◽  
Author(s):  
Daniel Baffet ◽  
Jacobo Bielak ◽  
Dan Givoli ◽  
Thomas Hagstrom ◽  
Daniel Rabinovich


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