Modelling ageing

Figure 14. ratios vs. model ages obtained by in situ ion mieroprobe dating of... 

Xenoliths from Siberian continental lithosphere, with Archean model ages, had b Li as low as +0.5 (Eouman et al. 2000). If these values accurately represent the Archean mantle, they suggest the potential for Li isotopic evolution in the Earth, from lighter compositions in the ancient mantle to what is seen in present-day MORE. In spite of the analytical challenges presented by ultramafic rocks, more data from these materials are crucial to an understanding of Li in the mantle, and in resolving questions about the appropriateness of the accepted MORE mantle range. 

The time, Tmodel, is a model age that assumes a single-state evolution of the sample once it was separated from the CHUR. On Figure 8.12a, the time Tmodei is the time, TA, for planet A and the time TB for planet B . 

If an internal isochron cannot be generated, a model age can be determined from the measured 207pb /206Pb of the sample and the assumed initial lead isotopic ratios. For studies of the early solar system, this initial lead composition is assumed to be that measured in troilite (FeS) from the Canyon Diablo meteorite. Troilite is a uranium-free mineral and its host meteorite formed very early in the history of the solar system. Because the U/Pb ratio of the solar system is low, the lead incorporated into the troilite should not have evolved significantly from the initial composition in the solar system. 

The U-Pb system has been a chronometer of choice for the Earth s age since the pioneering study of Clair Patterson in 1956, as discussed in Chapter 8. Virtually all U-Pb model ages of the Earth (reviewed by Allegre et al., 1995) are younger than the ages of chondritic and achondritic meteorites. The oldest Pb-Pb age, based on ancient terrestrial... 

Fedrizzi, B., Zapparoli, G., Finato, F., Tosi, E., Turri, A., Azzolini, M., and Versini, G. (2011). Model aging and oxidation effects on varietal, fermentative, and sulfur compounds in a dry botrytized red wine. J. Agric. Food Chem. 59,1804—1813. 

Cahen, L., P. Eberhardt, J. Geiss, F. G. Houtermans, J. Jedwab, and P. Signer On a correlation between the common lead model age and the trace element content of galenas. Geochim. cosmochim. Acta 14, 134 (1958). 

The W isotopic compositions of various terrestrial samples, chondrites, iron meteorites, basaltic achondrites, lunar samples, and Martian meteorites are expressed as deviations in parts per 104 from the value for the silicate earth (such as the W in a drill bit or chisel), which are the same as those of average solar system materials, represented by carbonaceous chondrites. These values are summarized in Fig. 8.9, from which it can be seen that early segregated metals such as the iron meteorites and metals from ordinary chondrites have only unradiogenic W because they formed early with low Hf/W. The time differences between metal objects segregated from parents with chondritic Hf/W are revealed by the differences in W isotopic compositions between each of the metal objects and chondrites. The Hf-W model ages of all these metals indicate that all of their parent bodies formed within a few million years, implying rapid accretion in the early history of the solar system. 

Some suggestions for additional work in the model aging study were made in Part I (I). In the search for a better textile consolidant, the following areas still need to be examined ... 

Figure 9. Lead isotope compositions for Early Bronze Age copper-based alloy artifacts from Troy II and artifacts from Kastri and Chalandriani on Cycladic island of Syros. The lead isotope fields indicated by broken lines are approximate. Model ages calculated in millions of years on the basis of Cummings and Richards (1975) model Jit are indicated for each grouping of lead isotope data. (Reproduced with permission from ref. 6. Copyright 1984 Basil Blackwell...

The score was derived and validated on patients in the acute phase of GBS who were unable to walk independently (van Koningsveld et al. 2007). The derivation set included 388 patients from randomized controlled trials and the outcome was inability to walk independently at six months. A simple score was developed from the coefficients in a regression model age, preceding diarrhea and GBS disability score at 2 weeks after entry. Scores range from 1 to 7, with three categories for age (<40, 41-60 and >60 years scoring 0, 0.5 and 1, respectively), 1 point for recent diarrhea and 1-5 points for disability score at 2 weeks. 

In recent years, poly(p-phenylene benzobisoxazole) (PBO) fibers have become prominent in high strength applications such as body armor, ropes and cables, and recreational equipment. However, degradation of PBO fiber mechanical properties following exposure to moisture has been documented by the manufacturer (7) and at least one failure of PBO-based body armor in the field has occurred (2). The objectives of this study were to compare changes in mechanical and chemical properties of yams extracted from PBO-based body armor that was penetrated by a bullet in the field approximately 6 months after being deployed, with PBO-based body armor panels of the same model aged in the laboratory under elevated temperature and moisture conditions. 

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