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  2. Metric system - Wikipedia

    en.wikipedia.org/wiki/Metric_system

    In the SI system and generally in older metric systems, multiples and fractions of a unit can be described via a prefix on a unit name that implies a decimal (base-10), multiplicative factor. The only exceptions are for the SI-accepted units of time (minute and hour) and angle (degree, arcminute, arcsecond) which, based on ancient convention ...

  3. Isotopes of lead - Wikipedia

    en.wikipedia.org/wiki/Isotopes_of_lead

    Lead (82 Pb) has four observationally stable isotopes: 204 Pb, 206 Pb, 207 Pb, 208 Pb. Lead-204 is entirely a primordial nuclide and is not a radiogenic nuclide.The three isotopes lead-206, lead-207, and lead-208 represent the ends of three decay chains: the uranium series (or radium series), the actinium series, and the thorium series, respectively; a fourth decay chain, the neptunium series ...

  4. History of the metre - Wikipedia

    en.wikipedia.org/wiki/History_of_the_metre

    Proposals for decimal measurement systems from scientists and mathematicians also lead to proposals to base units on reproducible natural phenomena, such as the motion of a pendulum or a fraction of a meridian. [8]: 85 Galileo discovered gravitational acceleration explaining the fall of bodies at the surface of the Earth. [9]

  5. Latin letters used in mathematics, science, and engineering

    en.wikipedia.org/wiki/Latin_letters_used_in...

    the digit "14" in hexadecimal and other positional numeral systems with a radix of 15 or greater; an exponent in decimal numbers. For example, 1.2E3 is 1.2×10 3 or 1200; the set of edges in a graph or matroid; the unit prefix exa (10 18) [10] energy in physics [10] electric field denoted or

  6. Perovskite solar cell - Wikipedia

    en.wikipedia.org/wiki/Perovskite_solar_cell

    Crystal structure of CH 3 NH 3 PbX 3 perovskites (X=I, Br and/or Cl). The methylammonium cation (CH 3 NH 3 +) is surrounded by PbX 6 octahedra. [13]The name "perovskite solar cell" is derived from the ABX 3 crystal structure of the absorber materials, referred to as perovskite structure, where A and B are cations and X is an anion.