Expected lifetimes

For fluorescent compounds and for times in die range of a tenth of a nanosecond to a hundred microseconds, two very successftd teclmiques have been used. One is die phase-shift teclmique. In this method the fluorescence is excited by light whose intensity is modulated sinusoidally at a frequency / chosen so its period is not too different from die expected lifetime. The fluorescent light is then also modulated at the same frequency but with a time delay. If the fluorescence decays exponentially, its phase is shifted by an angle A([) which is related to the mean life, i, of the excited state. The relationship is... 

Because of limited commercial experience with anode coatings in membrane cells, commercial lifetimes have yet to be defined. Expected lifetime is 5—8 years. In some cases as of this writing (ca 1995), 10-years performance has already been achieved. Actual lifetime is dictated by the membrane replacement schedule, cell design, the level of oxygen in the chlorine gas, and by the current density at which the anode is operated. 

Details of the function and service conditions of the component part are ascertained, this including the expected lifetime and maximum service temperature. 

Economic factors include (a) the capital cost of the control technology (b) the operating and maintenance costs of the technology and (c) the expected lifetime and salvage value of the equipment. 

Documentation requirements - Create quality policy, quality manual, procedures, and document control and distribution function. Retain records for the expected lifetime of the device or a minimum of 2 years... 

Antioxidants are species that accept the reactive byproducts of oxidation reactions. They are typically hindered amines or phenols that accept radicals, inactivating them and preventing further effects of oxidation. The level of antioxidant used in a polymeric item depends on the expected lifetime of the final part, the environment in which the part will be used, and the susceptibility of the polymer to oxidation. Figure 9.7 shows two common antioxidants used in polyolefins. 

In general, the longer the sweep time the better the sensitivity since the filter time constant parameter can be set longer with consequent improvement in signal-to-noise ratio. In practice, however, sweep times are usually set in accordance with the expected lifetime of the radical species, the stability of the instrument, and the patience of the operator. Decay of the radical or drift of the spectrometer during a scan is clearly undesirable. The sweep time is most commonly set in the range 4-10 min. 

How long will it last An answer to this question is wanted by both suppliers and users, but it is usually a very difficult question to answer for polymer products. This is because the expected lifetime is often in tens of years, the service conditions may be complex and there is a scarcity of definitive data. 

Two of the fundamental hurdles in assessing the service life of a product are definition of the service conditions - uncertainty and variation - and establishing the time scales for expected lifetime. 

When expected lifetimes are usually in years and may be in tens of years, the time scale to prove the life of the product by conducting trials under service conditions is often prohibitive. Satisfactory accelerated testing is neither cheap nor easy nor even always valid. 

Simulating service conditions avoids all the risks of using real service, and offers the possibility of moderate acceleration by simulating the worst conditions possible. The name implies that all factors present are considered, for example mechanical stress and the environment. However, the time scales will still be long and in many cases it is difficult, if not impossible, to simulate real conditions accurately. Clearly, simulated service trials are most attractive where the expected lifetimes are relatively modest and the conditions to be simulated are not too complicated. 

There are a number of intrinsic problems with accelerated tests used to assess lifetime. Firstly, the general problems in assessing service life mentioned in Section 1.2 apply. Regardless of how you go about making assessments, service conditions are not constant and, with long expected lifetimes, either the degree of extrapolation is very large or even accelerated tests need considerable time scales. 

Since one of the main goals of reference material production is to provide a stable reference material, tests for stability begin early in the production process. Ideally, these should be conducted over the expected lifetime of the reference material prior to its distribution however, these tests can be conducted concurrently if required. 

The petroleum industry requires very large, capital-intensive process equipment. Expected lifetimes of process equipment are measured in decades. This limits economic incentives to make capital-intensive process modifications to reduce wastes generation. Reductions in waste generation can be accomplished by process modifications ... 

Satisfactory performance of the fireproofing material over its expected lifetime depends on the user s and the applier s knowledge of materials and application techniques and on continuing inspection by qualified personnel. Specifically, once a fireproofing system has been chosen, it is imperative that personnel involved in each phase of the project be familiar with the relevant aspects of the manufacturer s requirements and specifications. 

Whether exposure of humans to a substance has been associated with adverse toxicological effects occurring as a result of repeated daily exposure for a part of the expected lifetime or for the major part of the lifetime. 

Age 25-55 years expected whole-body career dose females vs. males Adverse effects expected lifetime exposure... 

Application of the collected thermodynamic data to model the oxidative alteration pathway of U02 under repositoiy conditions by using the PHREEQC code (Parkhurst Appelo 1999) is given in Fig. 1 la and b. Once the thermodynamic framework is set for the geochemical evolution of the repositoiy system, we have to take into consideration that for many of the processes involved, there will be some kinetic constraints. This is illustrated by Table 2, where a comparison of the expected lifetime for some of the phases expected in the repositoiy system is made. 

A 13-W fluorescent light that fits in a standard screw-in socket provides the same light as the 60-W bulb it replaces. The expected lifetime of the fluorescent lamp is 10 000 h, whereas that of the incandescent bulb is 750 h. The fluorescent light is more expensive than the incandescent bulb but saves a great deal of electricity and money over its lifetime. 

Pom and 269110 both decay by the emission of high-energy a particles (Ea =11.6 and 11.1 MeV, respectively). Calculate the expected lifetime of these nuclei using the one-body theory of a decay. The observed half-lives are 45.1 s and 170 jjls, respectively. Comment on any difference between the observed and calculated half-lives. 

The evaluation should also examine the ease of calibration and self-docu-mentation of both the computer system and associated measurement and control instrumentation, along with the availability of replacement parts and service support for the expected lifetime of the system application. 

For simple materials such as zinc or CaC03, research has shown stoichiometry between deposited sulfur and the base material (30). Thus in equivalent molar units, the deposition rate of sulfur is equal to the removal rate of the base material. At present environmental conditions in the U.S., these rates are low in terms of expected lifetimes of consumer-oriented components. There are some exceptions, such as galvanized fence wire, for which S02 deposition rates may be 2-3 times higher than on large flat surfaces (31). For CaC03, dissolution in (normal) rain can be an important mode of material loss and acts to remove the more soluble CaS0A, creating conditions more receptive to additional S02 deposition (32). 

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