Time-varying laboratory tests

Since weather varies from day to day, year to year, and place to place, no precise correlation exists between artificial laboratory weathering and natural outdoor weathering. However, standard laboratory test conditions produce results with acceptable reproducibility and in general agreement with data obtained from long-time outdoor exposures. 

V. Laboratory. Timing of laboratory analysis may be crucial, as elimination rates of commonly used sedative and amnestic drugs vary and some may be extremely short. Immediate collection of toxicology specimens is important to avoid loss of evidence. For a service that deals in assaults or sexual abuse, it is important to confer in advance with the laboratory, so that it is clearly understood what type of testing will be performed the laboratory can then develop a testing strategy (what tests to use, the sequence of tests and confirmations, and level of sensitivity and specificity). Such a service should ideally be part of a law enforcement agency. 

The UV energy in sunlight varies in wavelength distribution and intensity with the time of day and year as well as latitude and elevation of exposure. The presence of water also depends on the region, time of year, etc. Therefore, predicting natural weather resistance from laboratory tests can be difficult. 

Available methods can only compare different materials on the basis of their corrosion resistance. Their actual behavior cannot be determined because the service conditions cannot be simulated in laboratory tests. For example, service temperature tends to vary with time. Laboratory tests are carried out at a constant temperature. Hence, the effect of thermal gradients is not considered in laboratory tests. 

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