Lifetime parameter

Another group of important battery characteristics are the lifetime parameters. For primary batteries and charged storage batteries, a factor of paramount importance is the rate of self-discharge. Self-discharge may be the result of processes occurring at one of the electrodes (e.g., corrosion of zinc in batteries with zinc anodes or the decomposition of higher metal oxides in batteries with oxide cathodes), or it... 

For both organic dyes and QDs, bioconjugation often leads to a decrease in fluorescence quantum yield and thus typically also in emission lifetime. Parameters that can affect label fluorescence are the chemical nature and the length of the spacer and, at least for organic dyes, the type of neighboring biomolecules like oligonucleotides or amino acids in the bioconjugated form. 

Although satisfactory criteria for deciding whether data are better analyzed by distributions or multiexponential sums have yet to established, several methods for determining distributions have been developed. For pulse fluorometry, James and Ware(n) have introduced an exponential series method. Here, data are first analyzed as a sum of up to four exponential terms with variable lifetimes and preexponential weights. This analysis serves to establish estimates for the range of the preexponential and lifetime parameters used in the next step. Next, a probe function is developed with fixed lifetime values and equal preexponential factors. An iterative Marquardt(18) least-squares analysis is undertaken with the lifetimes remaining fixed and the preexponential constrained to remain positive. When the preexponential... 

For a given frequency w and choice of lifetime parameter, solve frequency-dependent complex CPKS equations to obtain I/-coefficients due to the applied electric field. 

Influence of filler content on the positron lifetime parameters... 

The application of vb-DMASP to MIPs was continued in subsequent works [64, 65], In these investigations, time-resolved fluorescence spectroscopy was applied to study bulk fluorescent MIP. The imprinted polymer fluorescence quenching with increasing concentrations of aqueous cAMP was determined from the fluorescence lifetime parameters. Two components in the fluorescence decays were identified and assigned to two different types of cavities present in the polymer matrix. One was accessible and open to binding, whereas the other was inaccessible, being buried inside the bulk polymer. The fluorescence lifetime decreased due to the increase in the concentration of the initial target analyte. However, the accessible... 

Photoluminescence analysis has the advantages that (a) it can he highly selective because the absorption, emission, and lifetime parameters must match (b) it is highly sensitive (c) it is often nondestructive (d) it is inexpensive to perform and (e) it often does not require the separation of complex mixtures. 

Figure 9.2 Annealing temperature dependence of positron lifetime parameters for the a-Si H films (a) t3 and I3 (b) t2. (Suzuki et al., 1997)...

One of the main factors which needs to be considered in PAL analysis of polymers, is the affect which prolonged exposure to the positron source has on the lifetime parameters. It has been found that on prolonged exposure to a positron source, the o-Ps lifetimes are largely unchanged, but that there are significant variations in the o-Ps intensities for some polymers. Examples of these effects for a wide variety of polymers can be found polypropylene (PP), polyethylene (PE) [71], polystyrene [72], polycarbonates [73] poly(a-olefins) [49], poly(vinlyacetate) [74], poly(methyl methacrylate) [74] and a number of copolymers [75]. 

Clearly in any polymer studies the possibility of positronium chemistry influencing the lifetime parameters needs to be considered. Once again the in-... 

The value Am = 0 is associated with a maximum or a minimum, depending on whether r is long or short. The location of the maxima is simplified if 1 IT2 in each site is small compared to 8m = 8, the chemical shift in radians sec-1. The collapse of the two peaks depends on r the lifetime parameter and no correction for overlapping tails of the peaks is necessary. The observed separation 8ioe is then given by... 

Although a Trp residue does not belong necessarily to the domain where the interaction between the protein and the ligand occurs, measuring fluorescence lifetime parameters of this particular Trp residue can monitor effects of these interactions. 

Thus after a period of tf the intensity has dropped to 37% of h, that is 63% of the molecules return to the ground state before tf. In many cases the above expression needs to be modified into more complex expressions. First of all it is assumed that the instrument yields an infinite (or very) short light pulse at time zero. In cases where tf is small Ig must be replaced by a function, which describes the lamp profile of the instrument. Also, more than one lifetime parameter is often needed to describe the decay profile, which is l(t) must be expressed as a sum of exponentials. Finally the concept of anisotropy should be mentioned. Anisotropy is based on selectively exciting molecules with their absorption transition moments aligned parallel to the electric vector of polarized light. By looking at the polarization of the emission the orientation of the fluorophore can be measured. The anisotropy of the system is defined as (Equation 6) (Rendell, 1987 Lakowicz, 2006) ... 

Region IV occurs in the temperature range above T v where the knee in (vft> appears. Here the calculated (vh) and ah remain constant or may even show a decrease. From the continuous expansion of Vf we expect that the true hole size increases further. This different behavior shows that above T v the o-Ps lifetime parameters do not adequately mirror the fluctuating free volume via snapshots, and owing to this, PALS fails. We have attributed this effect to structural motions where the relaxation time decreases with increasing temperature, becoming comparable to and then decreasing below the mean o-Ps lifetime. 

Dlubek, G., Eichler, S., Hiibner, Ch., and NageL Ch., Reasons for the deviation of Iff and x from the expected lifetime parameters of positronium annihilation in polymers, Nucl. Instrum. Methods Phys. Res. B, 149, 501-513 (1999a). 

Table 2 Fluorescence lifetime parameters of (S,S)-NPX-PYR and related systems. Data from [114]...

Fluorescence lifetime parameters and steady-state anisotropy for TPPS porphyrin (alone) and in vesicles at different TPPS/CD 3 molar ratios ... 

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