Aging rate definition

It must be emphasized that a component whose lifetime is exponentially distributed cannot be improved by maintenance. For an improvement would imply a reduction of its failure rate. In the present model it is ensured that the unavailability is equal to zero after every functional test. This is achieved by determining in the first place whether it is still capable of functioning or has failed. In the latter case the component is either repaired or replaced. If it is still capable of functioning it is as good as new because components with a constant failure rate do not age by definition. If it has to be repaired, as good as new is a hypothesis usually corroborated in plants with a good safety culture. 

Insulation systems were first classified according to the material used, and permissible temperatures were established based on the thermal aging characteristics of these materials. For example. Class B insulation was defined as inorganic materials such as mica and glass with organic binders 130°C was the allowable maximum operating temperature. The present definition of insulation system Class B stipulates that the system be proven. . by experience or accepted tests. .. to have adequate life expectancy at its rated temperature, such life expectancy to equal or... 

In the absence of aging (deactivation) of the catalyst, a phenomenological definition of catalysis would be enhancement of chemical reactions or a change of their rate under the influence of substances — catalysts — which several times enter into transient chemical interactions with reaction participants and then, after each cycle of transient interactions, regenerate their chemical identity [1]. 

An accurate evaluation of kxa is complicated by the heterogeneous nature and poor definition of contaminant/soil systems. Some success has been achieved in modeling mass transfer from a separate contaminant phase. During degradation these nonaqueous phase liquids (NAPLs) often dissolve under conditions where phase equilibrium is not achieved and dissolution is proportional to k a. Experimental determinations and correlations for k-p depend on interfacial area of the NAPL and liquid velocity at the interface (Geller Hunt, 1993). For adsorbed contaminants, kxa varies with soil composition and structure, concentration and age of contamination, and therefore with time. For example, slurry reactor tests indicate that the rate of naphthalene mass transfer decreases with time, with media size, and with aging of the tar prior to testing (Luthy et al., 1994). 

Studies for carcinogenicity in rats and mice should last at least 24 months. This rule avoids problems of acceptance at the international health authorities. There are other aspects which can influence the duration of a carcinogenicity study, e.g. survival rate. In case survival after a certain time of treatment is below 25 % health authorities should be informed with the request to sacrifice the remaining animals. In other cases survival will be higher than 75 % after 24 months of treatment. With this result, it can be considered to prolong the exposure period. The duration (and therefore the age of the animals) of a carcinogenicity study has a definite influence on the tumor incidence in the animals. The interpretation of the results with regard to tumor incidences has to be corrected for the age of the test animals. 

The OXVASC study showed that the annual incidence of stroke in the UK in the first few years of this century, including subarachnoid hemorrhage, was 2.3/1000 and the incidence of TIA was 0.5/1000 (Rothwell et al. 2005), with about a quarter of events occurring in those under the age of 65 and about a half in those above the age of 75 (Fig. 1.1). The incidence of cerebrovascular events in OXVASC was similar to that of acute coronary vascular events in the same population during the same period (Fig. 1.2), with a similar age distribution (Rothwell et al 2005). Incidence rates, however, measure first-ever-in-a-lifetime definite events only and exclude possible, recurrent and suspected events, so do not represent the true burden of a condition. This is especially true for TIA, where a significant proportion of cases referred to a TIA service have alternative, non-vascular... 

The inhibited esterase can also undergo aging, e.g. via net loss of the R-group to yield the negatively charged phos-phonyl adduct on the active site serine of the enzyme. Aging is characterized by a first-order rate constant, fcj, and the operational definition of this reaction is the time-dependent... 

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