Quenching rate INDEX

Thus, E is defined as the product of the energy transfer rate constant, ku and the fluorescence lifetime, xDA, of the donor experiencing quenching by the acceptor. The other quantities in Eq. (12.1) are the DA separation, rDA the DA overlap integral, / the refractive index of the transfer medium, n the orientation factor, k2 the normalized (to unit area) donor emission spectrum, (2) the acceptor extinction coefficient, eA(k) and the unperturbed donor quantum yield, QD. 

Luminescence lifetime depends upon radiative and nomadiative decay rates. In nanoscale systems, there are many factors that may affect the luminescence lifetime. Usually the luminescence lifetime of lanthanide ions in nanociystals is shortened because of the increase in nomadiative relaxation rate due to surface defects or quenching centers. On the other hand, a longer radiative lifetime of lanthanide states (such as 5Do of Eu3+) in nanocrystals can be observed due to (1) the non-solid medium surrounding the nanoparticles that changes the effective index of refraction thus modifies the radiative lifetime (Meltzer et al., 1999 Schniepp and Sandoghdar, 2002) (2) size-dependent spontaneous emission rate increases up to 3 folds (Schniepp and Sandoghdar, 2002) (3) an increased lattice constant which reduces the odd crystal field component (Schmechel et al., 2001). 

Gastric membrane vesicle preparations enriched with H /K -ATPase have also been used to examine PPIs. The inhibition of hydrogen ion transport by PPIs is measured by use of the initial rate of acridine orange quenching as an index of acidification. However, steady-state acidification, as measured by aminopy-rine accumulation, is inhibited with greater potency and this is consistent with the accumulation of PPIs in the intravesicular acidic space (38). 

Frequently, the reactant M itself acts as a quencher of its excited molecules M, M + M —> 2M. It is difficult to determine self-quenching accurately from the dependence of the quantum yield on the concentration cM, because the absorbance by M increases as its concentration is raised. However, the effect is readily measured by time-resolved methods. Replacing the index q by M in Equation 3.39 and replacing t° by l/ obs(cM 0) one obtains Equation 3.40. The observed decay rate constant of the excited molecule M, k(thfcM) =1/rM, increases linearly with the concentration of M. The slope kM is the rate constant of self-quenching and the intercept kobfcM > 0) is the decay rate constant of M at infinite dilution.229... 

Isotactic PP has extremely good flow properties at a wide range of flow rates, and therefore good processing behavior. The melt flow index typically ranges from 0.5 to 50 g/10 min. Films, which can be produced by both blown and cast methods, can be oriented to provide improved optical characteristics and better strength. Because of the rapid crystallization of PP, blown films must be produced by either water quench or mandrel quench processes, unlike PE, which is cooled by air. 

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