Lifetime estimations

Amorphous silicon modules experience a conversion efficiency loss of about 10 percent when initially exposed to sunlight, but then stabilize at the reduced figure. The mechanism for this reduction is being actively investigated, but is still not well understood. Individual modules made with other PV materials do not exliibit such loss of conversion efficiency, but combinations of modules in arrays do exhibit systematic reductions in power output over their lifetimes. Estimated at about 1 percent per year on average, based on data to date, these reductions are most likely associated with deteriorating electrical connections and non-module electrical components. 

Estimates of the lifetime COl are needed for temporal and international comparisons and for assessment of the efficiency of prevention strategies. During the first years of HIV/AIDS treatment, direct lifetime costs were only estimated by simple projections based on retrospective data. Later, specific statistical tools were adopted to estimate life expectancy and lifetime costs. The results of lifetime estimates are very sensitive to imputed assumptions. Table 4 demonstrates some studies in this field. 

Holtgrave and Pinkerton (1997) also estimated the lifetime costs after the diffusion of new combination therapies. Having discounted the costs of care, their lifetime estimates ranged from US 71,143 to US 424,763. The ranges reflect different levels of access to care. 

In a study on the thermal and UV ageing of two commercial polyfoxymethy-lene) (POM) samples, one of which was a copolymer (see related study discussed later under Section 4.3, thermogravimetric analysis (TGA)), used in car interior applications, involving both DSC and TGA, isothermal OIT measurements were made at several different temperatures [8]. One conclusion from this study was that "extrapolation of the OIT data from high temperatures (molten state) to ambient temperatures in the solid state does not reflect effective antioxidant performance at room temperature", and thus measurements close to the melting point are not appropriate for reliable lifetime estimations. 

In Fig. 3.5A a comparison between time-gated detection and TCSPC is shown. The time-gated detection system was based on four 2 ns wide gates. The first gate opened about 0.5 ns after the peak of the excitation pulse from a pulsed diode laser. The TCSPC trace was recorded using 1024 channels of 34.5 ps width. The specimen consisted of a piece of fluorescent plastic with a lifetime of about 3.8 ns. In order to compare the results, approximately 1700-1800 counts were recorded in both experiments. The lifetimes obtained with TG and TCSPC amounted to 3.85 0.2 ns and 3.80 0.2 ns respectively, see Fig. 3.5B. Both techniques yield comparable lifetime estimations and statistical errors. 

In some simple cases an additive approach can be successful. The service life is divided into stages, for example moderate exposure for one year, severe exposure for one month and low exposure for five years. The predicted degradation effects for the three periods can be summed and the condition of the product at the end, and hence residual lifetime, estimated. If it is assumed that degradation is proportional to the time of exposure and that the damage from different exposure conditions can be cumulatively added then the so called Miner s rule could be used ... 

Tropospheric lifetime estimated to be 0.5-3 days by De Bruyn et al. (1992, 1995) based on measurements of uptake by water surfaces see also George et al. (1994a,b). 

Calculational estimates of the lifetimes of the trimethylene diradical " based on microcanonical variational unimolecular rate theory and direct dynamics simulations have been reported. The lifetimes derived from theory, 91 and 118 fs, are comparable to the experimental estimate, 120 20 fs. Similar lifetime estimates from theory for tetramethylene are comparable, or slightly below, the experimental value. ... 

Ling CC, Michaels HB, Epp ER, Peterson EC (1978) Oxygen diffusion into mammalian cells following ultrahigh dose rate irradiation and lifetime estimates of oxygen-sensitive species. Radiat Res 76 522-532... 

It is difficult to assess the effect of non-coordinated heteroatoms on emission efficiency because of the lack of quantum yield information. One compound, [Ru(bpym)3]2+ shows an interesting anomaly. Hunziker and Ludi reported an emission quantum yield of 0.0915) in aqueous solution while Rillema et al.27 reported 0.011 in propylenecarbonate. The radiative lifetimes estimated from the data of these two reports are very different... 

Making some assumptions on the chemical filiation between some organo-sulfur compounds, it was possible to establish the mathematical variation law for the concentration ratio of the various detected species and consequently to deduce the depletion rate constant of these compounds. From the measurements at the "Pointe de Penmarc h" in September 1983, the DMS lifetime estimations obtained are reported in Table I. This method for determining chemical lifetimes can only be applied for local and intensive sources. The most critical point concerns the chemical relation between the various sulfur compounds which should be verified in order to validate these estimations. However, the other assumptions do not seem to have a significant influence on the lifetime estimation within an order of magnitude. 

Kumar et al., 2005). In turn the Judd-Ofelt parameters were calculated and the radiative lifetime estimated from eqs. (14)—(18). It is noteworthy that Judd-Ofelt parameters reproduce the observed spectra well. Photophysical data are listed in table 19 along with the emission cross section and the lifetime of the Er(4Ii3/2) level. The emission spectra were obtained by exci-... 

Air tropospheric lifetime of 0.5 d for gas phase reaction with OH radicals wet deposition lifetime estimated to be 2.8 d in the atmosphere by rainfall (Gautier et al. 2003)... 

Fourthly, the starting point for lifetime estimations is often laboratorygenerated kinetic data for reaction of the compound of interest with OH radicals. The bimolecular rate constants measured in laboratory kinetic experiments need to be converted into a pseudo first order rate constant for loss of the compound, k . In principal this conversion is simple, i.e., the bimolecular rate constant merely has to be multiplied by the OH concentration ([OH]). In practice there are difficulties associated with the choice of an appropriate value of [OH], At present we cannot measure the global OH concentration field directly. The OH radical concentration varies widely with location, season, and meteorological conditions. To account for such variations requires use of sophisticated 3D computer models of the atmosphere. 

A generic scheme for the atmospheric oxidation of a C2 haloalkane is given in Fig. 6. Values in parentheses are order of magnitude lifetime estimates. Reaction with OH radicals gives a halogenated alkyl radical which reacts with O2 to give the corresponding peroxy radical (RO2). As discussed in previous sections, peroxy radicals can react with three important trace species in the atmosphere NO, NO2, and HO2 radicals. 

We may estimate the lifetime of a surface monolayer by assuming that each primary ion will knock out one atom in the monolayer. Estimate the lifetime of surface monolayer bombarded by primary ion beam densities of 10 nA cm-2 and 0.1 nA cm-2, respectively. Why should the primary ion dose be even less than that based on the lifetime estimation ... 

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