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  2. Real number - Wikipedia

    en.wikipedia.org/wiki/Real_number

    The set of rational numbers is not complete. For example, the sequence (1; 1.4; 1.41; 1.414; 1.4142; 1.41421; ...), where each term adds a digit of the decimal expansion of the positive square root of 2, is Cauchy but it does not converge to a rational number (in the real numbers, in contrast, it converges to the positive square root of 2).

  3. Parts-per notation - Wikipedia

    en.wikipedia.org/wiki/Parts-per_notation

    For example, the conversion factor between a mass fraction of 1 ppb and a mole fraction of 1 ppb is about 4.7 for the greenhouse gas CFC-11 in air (Molar mass of CFC-11 / Mean molar mass of air = 137.368 / 28.97 = 4.74). For volume fraction, the suffix "V" or "v" is sometimes appended to the parts-per notation (e.g. ppmV, ppbv, pptv).

  4. Roman numerals - Wikipedia

    en.wikipedia.org/wiki/Roman_numerals

    The base "Roman fraction" is S, indicating 1 ⁄ 2. The use of S (as in VIIS to indicate 7 1 ⁄ 2 ) is attested in some ancient inscriptions [ 45 ] and also in the now rare apothecaries' system (usually in the form SS ): [ 44 ] but while Roman numerals for whole numbers are essentially decimal , S does not correspond to 5 ⁄ 10 , as one might ...

  5. Darcy–Weisbach equation - Wikipedia

    en.wikipedia.org/wiki/Darcy–Weisbach_equation

    In fluid dynamics, the Darcy–Weisbach equation is an empirical equation that relates the head loss, or pressure loss, due to friction along a given length of pipe to the average velocity of the fluid flow for an incompressible fluid.

  6. Letter frequency - Wikipedia

    en.wikipedia.org/wiki/Letter_frequency

    The California Job Case was a compartmentalized box for printing in the 19th century, sizes corresponding to the commonality of letters. The frequency of letters in text has been studied for use in cryptanalysis, and frequency analysis in particular, dating back to the Arab mathematician al-Kindi (c. AD 801–873 ), who formally developed the method (the ciphers breakable by this technique go ...

  7. Renewable energy - Wikipedia

    en.wikipedia.org/wiki/Renewable_energy

    In October 2021, European Commissioner for Climate Action Frans Timmermans suggested "the best answer" to the 2021 global energy crisis is "to reduce our reliance on fossil fuels." [ 240 ] He said those blaming the European Green Deal were doing so "for perhaps ideological reasons or sometimes economic reasons in protecting their vested interests."

  8. Global surface temperature - Wikipedia

    en.wikipedia.org/wiki/Global_surface_temperature

    Projected global surface temperature changes relative to 1850–1900, based on CMIP6 multi-model mean changes. The IPCC Sixth Assessment Report defines global mean surface temperature (GMST) as the "estimated global average of near-surface air temperatures over land and sea ice, and sea surface temperature (SST) over ice-free ocean regions, with changes normally expressed as departures from a ...