Nyquist frequency signal, whereas "Nyquist frequency" is a property of a discrete-time system. When the function domain is time, sample rates are usually expressed in samples per second, and the unit of Nyquist frequency is cycles per second (hertz). When the function domain is distance, as in an image sampling system, the sample rate might be dots per inch and the corresponding Nyquist frequency would be in cycles/inch. Referring again to Figure 1, undersampling of the sinusoid at 0.6 f is what allows there to be a lower-frequency "alias", which is a different function that produces the same set of samples. That
Mole (unit) of "exactly" 12 g. However, on 16 November 2018, after a meeting of scientists from more than 60 countries at the General Conference on Weights and Measures in Versailles, France, organised by the International Bureau of Weights and Measures (BIPM), all SI Units will be defined as constants. This means that any SI Unit, including the mole, will not be defined using physical objects but rather they will be defined by constants that are, in their nature, exact. Such changes will officially come into effect on 20 May 2019. For example, one mole of hydrogen atoms, will be defined as