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In 1999, evidence for time variability of the fine-structure constant based on observation of quasars was announced [9] but a much more precise study based on CH molecules did not find any variation. [10] [11] An upper bound of 10 −17 per year for the time variation, based on laboratory measurements, was published in 2008. [12]
Fluorescein is an organic compound and dye based on the xanthene tricyclic structural motif, formally belonging to triarylmethine dyes family. It is available as a dark orange/red powder slightly soluble in water and alcohol.
Fold change is a measure describing how much a quantity changes between an original and a subsequent measurement. It is defined as the ratio between the two quantities; for quantities A and B the fold change of B with respect to A is B/A. In other words, a change from 30 to 60 is defined as a fold-change of 2.
Time metrology or time and frequency metrology is the application of metrology for timekeeping, including frequency stability. [28] [29] Its main tasks are the realization of the second as the SI unit of measurement for time and the establishment of time standards and frequency standards as well as their dissemination. [30]
Molar concentration or molarity is most commonly expressed in units of moles of solute per litre of solution. [2] For use in broader applications, it is defined as amount of substance of solute per unit volume of solution, or per unit volume available to the species, represented by lowercase : [3]
Viscosity is a measure of a fluid's rate-dependent resistance to a change in shape or to movement of its neighboring portions relative to one another. [1] For liquids, it corresponds to the informal concept of thickness; for example, syrup has a higher viscosity than water. [2]
The standard liter per minute (SLM or SLPM) is a unit of (molar or) mass flow rate of a gas at standard conditions for temperature and pressure (STP), which is most commonly practiced in the United States, whereas European practice revolves around the normal litre per minute (NLPM). [1]
Air changes per hour, abbreviated ACPH or ACH, or air change rate is the number of times that the total air volume in a room or space is completely removed and replaced in an hour. If the air in the space is either uniform or perfectly mixed, air changes per hour is a measure of how many times the air within a defined space is replaced each hour.