Mass in special relativity (including the kinetic energy of the gas) only when it is measured in the center of momentum frame. Just as is the case for single particles, the calculated "rest mass" of such a container of gas does not change when it is in motion, although its "relativistic mass" does change. The container may even be subjected to a force which gives it an overall velocity, or else (equivalently) it may be viewed from an inertial frame in which it has an overall velocity (that is, technically, a frame in which its center of mass has a velocity). In this case,
Enzyme multiplied immunoassay technique is a branch of the U.S. Department of Health and Human Services). The setting of reasonable cutoff limits help reduce false positive results that occur from assay limitations. Because of the social and legal consequences, a positive test result must be confirmed by an alternative method, usually Gas Chromatography/Mass spectrometry. As an example the SAMHSA cutoffs for cannabinoids are 50 ng/ml for the immunoassay and 15 ng/ml as confirmed by GC/MS. Immunoassays that do not conform with SAMHSA, featuring a cutoff of 20 ng/ml, have been shown to produce false positives from passive inhalation of marijuana smoke. Enzyme multiplied immunoassay