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
Multiple unit This is not so easy for a multiple unit, since individual cars can be attached or detached only in a maintenance facility. This also allows a loco-hauled train to be flexible in terms of number of cars. Cars can be removed or added one by one, but on multiple units two or more units have to be coupled. This is not so flexible. The passenger environment of a multiple unit is often noticeably noisier than that of a locomotive-hauled train, due to the presence of underfloor machinery. The same applies to vibration. This is a particular problem with DMUs. Separating