Repopulation time

Radiation treatment schemes that accelerate the dose delivery, i.e., attempt to deliver it in a shorter overall time, endeavor to compensate for any accelerated repopulation of the tumor that may be occurring. These schemes are often accompanied by increased morbidity. Ultimately abetter understanding of the molecular and cellular events involved may give rise to measures that will allow us to compensate for accelerated repopulation in tumors or to induce repopulation in normal tissues earlier in a course of therapy in order to minimize treatment related morbidity. 

It is of interest to note that the 225-ps bleach recovery transient observed in the transient absorption kinetics is significantly shorter than the 275-ps decays observed in the polarized emission and the bare nanoparticle absorption kinetics. Tltis difference, along with magnitude of this component at 660 and 700 nm, indicates that partial repopulation of the ground-state dye from the conduction-band electron occurs with this time constant. These dynamics are summarized in Scheme 1. From the difference of the bare nanoparticle and nanoparticle/dye conduction-band decays, it is possible to estimate the rates of conduction-band reverse electron transfer. These values (275 ps and 225 ps, respectively) give an estimate for the reverse electron-transfer time of about 1.2 ns. The ratio of the... 

As discussed in Section 8.3.1, the (100) split-dumbbell self-interstitial in the f.c.c. structure can exist with its axis along [100], [010], or [001], Under stress, certain of these orientation states are preferentially populated due to the tetragonality of the defect as a center of dilation. When the stress is suddenly released, the defects repopulate the available states until the populations in the three states become equal. Show that the relaxation time for this repopulation is... 

The action of a circularly polarised pulse leads to a repopulation of electrons and holes between states with a different angular momentum component in the direction of the pump pulse wave vector. The corresponding SIFE relaxation time describes the recovery of the symmetry of the initial angular momentum distribution. Again it is preferable that the probe response is dominated by intraband transitions or else inelastic scattering may obscure the relaxation of hot electron (hole) angular momentum. 

This is an up-conversion process (57). The C=N stretch and C-C stretch excitations are in fast equilibrium with C-H stretch excitations, but the C-H stretch decays with a 5 ps time constant. That explains the C=N stretch decay in 5 ps. The population oscillation in the C-C stretch data occurs as follows. First we see C-C stretch excitation pumped by the laser. This is actually a sign of combination band excitation (C=N + C-C stretch). Then the C-C stretch starts to be annihilated by the 5 ps up-conversion and C-H stretch decay process. C-H stretch decay produces C-H bending excitations, which subsequently repopulate the C-C stretch, causing the second rise in the C-C stretch transient (47). 

The occurrence of the electronic origin 11 in the time-delayed spectrum is not expected on first sight. However, its appearance is a consequence of a thermal repopulation of state II -according to a Boltzmann distribution which applies after a sufficiently long delay time (see Refs. [22,24]) - and of the relatively large transition probability of the II 0 transition. 

RRKM theory assumes reactants remain in equilibrium at all times. However, a small fraction of vibrational states of the reactant, the transition states, are depopulated by formation of product and, in the absence of collisions, become repopulated only by vibrational energy redistribution. 

In the case of vibrational responses the population relaxation times may be dominating the coherence decays. In addition, it can be essential to incorporate the multilevel nature of molecular vibrators into the response. The rate of repopulation of the ground state is seldom equal to the decay of the fundamental V = 1 state, so there can be bottlenecks in the ground state recovery. Following... 

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