Calendar aging

It is well known that the radiocarbon age does not correspond to the real calendar age of an organism, since Equation (16.2) is based on assumptions that are true only to a first approximation namely, the hypothesis of a constant value of 14/f0 over time in the past. [ 10] An accurate calibration curve[ll,12] has thus to be used to convert the tRC value of a measured sample into its true age. For a complete discussion on this topic, the already cited literature on radiocarbon dating can be considered for reference. In contrast, the focus of this chapter is on how to measure the radiocarbon age tRC, i.e. how to measure uR(t). Assuming, as explained above, 14/f0 and t in Equation (16.2) are known, it is indeed clear that a measurement of 14/ (f) allows us to determine the radiocarbon age. 

It is important to remember that sometimes, in spite of the excellent performances of an AMS measurement, the final uncertainty on the true calendar age of a sample is a function of the behaviour of the calibration curve in that time interval a small error on the radiocarbon age does not necessarily correspond to a small, or a unique, calendar span on the BC/AD axis. 

Physiologic Having to do with the functions of the body. When used in the phrase "physiologic age," it refers to an age assigned by general health, as opposed to calendar age. 

The skeletal age, which is not necessarily identical with the calendar age of the individual, has an important impact on the fluorine uptake, because osteoporosis is a process that fundamentally influences the bone structure. The disease pattern becomes visible in material loss within both the trabecular and the compact bone structure. Furthermore, the mineral density even in a healthy individual is not uniform in compact bone, but is a function of bone stress at this skeletal position and is increased at the point where muscles and tendons are fixed. 

Calibration of Radiocarbon Measurement To Yield the Calendar Age. It was previously thought that if the half-life of 14C was accurately known, then a simple exponential decay equation could be applied to learn the age of archaeological organic materials. The measurement would be subject only to errors in measurement of the ratio of the radiocarbon in the sample, A, to the equivalent quantity in modern carbon, A0. However, it is now known that A0 has been far from constant in the past few thousand... 

This conventional age t is converted to a calendar date by calibration curves that were obtained by very precise measurement of the A/A0 values of tree-ring wood of exactly known calendar age (11-13). 

However, once such processes cease, the amount of radiocarbon decreases by decay as measured by the isotope s half-life. Thus, a radiocarbon date is based on the measurement of the residual contained in the sample. However, for a radiocarbon age of a sample to be equivalent to its real or calendar age, certain fundamental parameters and assumptions must... 

The ability of the radiocarbon method to provide accurate and precise determinations of the actual or calendar age of organic samples is obviously a function of the degree to which each sample fulfills the set of basic conditions on which the validity of the method itself rests. These basic assumptions can be summarized as follows ... 

However, the issue of the correct half-life for radiocarbon has lost a considerable amount of its significance because of the discovery and documentation of the long- and short-term secular variation effects. The existence of dendrochronologically documented relationships between radiocarbon age and calendar age fortunately enables researchers to circumvent completely the problem of the real half-life. This will also hold true even for radiocarbon determinations on Pleistocene age materials where the use of the 5730 value increases values at, for example, 35,000 years... 

Foraminifera from the sediments of the Cariaco Trench (Fig. 7.6) (Hughen et al, 2004). Since the sediments of this anoxic basin are varved, the age filter applied to most sediment cores by bioturbation is not an issue. Calendar ages of the varves in the sediments of this basin were determined by matching the percent reflectance (a measure of the color of the sediments) with 5 0 variations in the ice of a Greenland ice core (described later in Fig. 7.19). Since the latter record is precisely dated back to 40 000 years by actual counting of annual ice layers, and the two records are undeniably correlated, it was possible to determine an accurate calendar age for the Cariaco Trench sediment core by using variations in the percent reflectance record. The results in Fig. 7.6 indicate offsets of up to 5 ky between C age and calendar age at about 30 ky BP and an abrupt shift at 40 calendar kiloyears (cal. ky) BP in which 7000 C years elapsed in only 2000 y. The results have been explained as variations in the source function and the ventilation of the deep sea and are now used to correct C dates back to more than 40 cal. ky BP. 

A C activity versus calendar age of sediments from the Cariaco Trench. The carbon-14 dates illustrated by the dots were determined on the shells of planktonic Foraminifera preserved in the sediments. Calendar ages were determined by correlating sediment reflectance measurements from the cores with 5 0 changes in the GISP2 ice core from Greenland (see Fig. 7.19). 

The shaded region represents an estimate of the error due to calendar age uncertainty. The solid line spanning the calendar age 10-12 ky BP is from tree rings and the open squares are from paired Th and C ages on corals. Redrawn from Hughen et al. (2004). 

The first five Heinrich events have been dated at calendar ages of 12, 16.5, 23, 29 and 40 ly BP. They coincide with cold intervals in between some of the D/0 cycles. It is somewhat counterintuitive that armadas of icebergs would appear during cold intervals however, the... 

At the three laboratories, samples were cleaned and treated following standard procednres to remove contaminants. The cloth samples were then combusted to gas and their radiocarbon content was measured in an Accelerator Mass Spectrometer. The almost identical AMS measurements at the three laboratories provided a calendar age range of ad 1260-1390 with at least 95% confidence (Fig. 5.17). The results from the three control samples agree with previous radiocarbon measurements and/or historical dates. The AMS dating provides conclusive evidence that the linen of the Shroud of Turin is medieval. 

Fig. 5.42 (a) Deviation of radiocarbon age from true calendar age (based on dendrochronology) (b) detailed variation and error range of age calibration for the period following the Younger Dryas stadial (after Roberts 1998 based on OxCal calibration). See Box 6.5 for discussion of the Younger Dryas. 

Effective age models implicitly assume that maintenance actions do not affect the failuie rate expression proper, but lead to a shift in time. There exists thus for the component under study an intrinsic failure density, which corresponds to a situation in which no maintenance action is ever performed on the component. When the effect of maintenance is accounted for, the calendar age is replaced, as mentioned before, by the effective age, i.e. an equivalent operating time of the component time giving allowance to the level of rejuvenation obtained via maintenance. The actual failuie density of the component is hence modified according to the changes in the effective age value. 

Batteries will also degrade even if they are not being used. This is known as calendar aging. 

Figure 6.24 gives a quantified example of calendar aging and cycle aging for a C-Li(Co,Ni,Al)02 element. For the example of calendar aging, the... 

Figure 6.24. Degradation of capacity due to calendar aging and cycle aging for C-Li(Co,Niyll)02 (C-NCA) elements...

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