Propagator, excitation

For a three-photon and a two-photon process we have shown that vibrational wavepacket propagation excited by an ultrashort laser pulse can be used to drive a molecule to a nuclear configuration where the desired product formation by a second probe pulse is favored (Tannor-Kosloff-Rice scheme). In both cases the relative fragmentation and ionization yield of Na2 was controlled as a function of pump-probe delay. By varying the delay between pump and probe pulses very slowly and therefore controlling the phase relation between the two pulses, additional interference effects could be detected. 

The strong electron-phonon interaction inherent in this description leads to a coupled electronic-vibration2J. (polaron-like) excitation propagating through the crystal. If initiation occurs at random and the chain propagating excitations move out from the initiation site in both directions with a velocity v for an initiation density of p per unit chain length, the conversion rate at time t is ... 

In a typical design, the acoustic wave propagates to any components mechanically coupled with the piezo actuator. This uncontrolled propagation excites vibrations of spurious resonances in the propagation paths. In air and vacuum, the influence from the spurious resonances is often negligible since their Q factors are lower than that of the cantilever resonance. In liquid, the Q factor of the cantilever drops to less than 10, which is often lower than that for a spurious resonance. Hence, the amplitude and phase versus frequency curves obtained in liquid are heavily distorted because of the influence of the spurious resonances. 

Membrane polarization The sustained (and approximately constant) transmembrane potential of a cell at rest that arises due to different intracellular and extracellular ionic concentrations. Propagation Excitation of one region of tissue as a result of an action potential in an adjacent region. Stimulation Change in the transmembrane potential at a site due to an influence from another site. The term is used most frequently when current is applied through wires from an artificial current source. 

Actually, the motion of the curves is not completely independent. A propagating excitation front is followed in excitable media by the recovery tail. When the distance between the waves moving in the same direction is shorter than the length of such a tail the waves interact. Such recovery effects become important for spiral waves when their rotation period is comparable to the characteristic refractory time of the medium. This happens when spiral waves are no longer sparse, i.e. the conditions of weakly excitable media are... 

Generally, the width of the excitation zone is of the same order of magnitude as the width of the recovery tail. Therefore, when a spiral ceases to be sparse with an increase in the excitability of the medium its pitch is no longer large as compared to width of the propagating excitation pulse. It means also that the width of the wave s tip becomes comparable with the radius of the core of the spiral wave. Obviously, in this situation the kinematical description, developed above for the weakly excitable media and picturing the entire wave as a single curve with a free end, is not applicable. 

The critical curvature kd for the breakup of a solitary propagating excitation wave is higher (cf. Figure 10) than the critical curvature kc which sets at the tip of the free rigidly rotating spiral wave. Therefore, for instance, the radius Rq of the core of the free spiral is larger than the minimal radius R ... 

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