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  2. Ramanujan's sum - Wikipedia

    en.wikipedia.org/wiki/Ramanujan's_sum

    Let =. Then ζ q is a root of the equation x q − 1 = 0.Each of its powers, ,, …,, = = is also a root. Therefore, since there are q of them, they are all of the roots. The numbers where 1 ≤ n ≤ q are called the q-th roots of unity.

  3. Klinkenberg correction - Wikipedia

    en.wikipedia.org/wiki/Klinkenberg_correction

    A more accurate correction factor can be obtained using Knudsen correction. When using nitrogen gas for core plug measurements, the Klinkenberg correction is usually necessary due to the so-called Klinkenberg gas slippage effect. This takes place when the pore space approaches the mean free path of the gas

  4. Nomogram - Wikipedia

    en.wikipedia.org/wiki/Nomogram

    Being proportional to the harmonic mean of A and B, this formula has several applications. For example, it is the parallel-resistance formula in electronics, and the thin-lens equation in optics. In the example, the red line demonstrates that parallel resistors of 56 and 42 ohms have a combined resistance of 24 ohms.

  5. Normal moveout - Wikipedia

    en.wikipedia.org/wiki/Normal_moveout

    Seismic data is sorted by common midpoint and then corrected for normal moveout. In reflection seismology, normal moveout (NMO) describes the effect that the distance between a seismic source and a receiver (the offset) has on the arrival time of a reflection in the form of an increase of time with offset. [1]

  6. Corner reflector - Wikipedia

    en.wikipedia.org/wiki/Corner_reflector

    This causes them to show a strong "return" on radar screens. A simple corner reflector consists of three conducting sheet metal or screen surfaces at 90° angles to each other, attached to one another at the edges, forming a "corner". These reflect radio waves coming from in front of them back parallel to the incoming beam.

  7. Total internal reflection - Wikipedia

    en.wikipedia.org/wiki/Total_internal_reflection

    Fig. 1: Underwater plants in a fish tank, and their inverted images (top) formed by total internal reflection in the water–air surface. In physics, total internal reflection (TIR) is the phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected back into ...

  8. Frustum - Wikipedia

    en.wikipedia.org/wiki/Frustum

    The Egyptians knew the correct formula for the volume of such a truncated square pyramid, but no proof of this equation is given in the Moscow papyrus. The volume of a conical or pyramidal frustum is the volume of the solid before slicing its "apex" off, minus the volume of this "apex":

  9. Pellin–Broca prism - Wikipedia

    en.wikipedia.org/wiki/Pellin–Broca_prism

    A Pellin–Broca prism is a type of constant-deviation dispersive prism similar to an Abbe prism. The prism is named for its inventors, the French instrument maker Ph. Pellin and professor of physiological optics André Broca .