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  2. Chinese siege weapons - Wikipedia

    en.wikipedia.org/wiki/Chinese_siege_weapons

    [20] Joseph Needham on the range of the triple-bow crossbow: This range seems credible only with difficulty, yet strangely enough there is a confirmation of it from a Persian source, namely the historian 'Alā'al-Dīn al-Juwainī, who wrote of what happened when one of the almost impregnable castles of the Assassins was taken by Hulagu Khan.

  3. Argon–argon dating - Wikipedia

    en.wikipedia.org/wiki/Argonargon_dating

    Argonargon (or 40 Ar/ 39 Ar) dating is a radiometric dating method invented to supersede potassium–argon (K/Ar) dating in accuracy. The older method required splitting samples into two for separate potassium and argon measurements, while the newer method requires only one rock fragment or mineral grain and uses a single measurement of argon isotopes.

  4. Argon - Wikipedia

    en.wikipedia.org/wiki/Argon

    Ar contamination. Most of the argon in Earth's atmosphere was produced by electron capture of long-lived 40 K (40 K + e − → 40 Ar + ν) present in natural potassium within Earth. The 39 Ar activity in the atmosphere is maintained by cosmogenic production through the knockout reaction 40 Ar (n,2n) 39 Ar and similar reactions. The half-life of 39

  5. List of UN numbers 1001 to 1100 - Wikipedia

    en.wikipedia.org/wiki/List_of_UN_numbers_1001_to...

    n.o.s. = not otherwise specified meaning a collective entry to which substances, mixtures, solutions or articles may be assigned if a) they are not mentioned by name in 3.2 Dangerous Goods List AND b) they exhibit chemical, physical and/or dangerous properties corresponding to the Class, classification code, packing group and the name and description of the n.o.s. entry [2]

  6. K–Ar dating - Wikipedia

    en.wikipedia.org/wiki/K–Ar_dating

    The ArAr dating method was developed to measure the presence of extraneous argon. Great care is needed to avoid contamination of samples by absorption of non-radiogenic 40 Ar from the atmosphere. The equation may be corrected by subtracting from the 40 Ar measured value of the amount present in the air where 40 Ar is 295.5 times more ...

  7. Shielding gas - Wikipedia

    en.wikipedia.org/wiki/Shielding_gas

    C-25 (75% argon/25% CO 2) is commonly used by hobbyists and in small-scale production. Limited to short circuit and globular transfer welding. Common for short-circuit gas metal arc welding of low carbon steel. C-20 (80% argon/20% CO 2) is used for short-circuiting and spray transfer of carbon steel.

  8. Noble gas compound - Wikipedia

    en.wikipedia.org/wiki/Noble_gas_compound

    Solid argon-hydrogen clathrate (Ar(H 2) 2) has the same crystal structure as the MgZn 2 Laves phase. It forms at pressures between 4.3 and 220 GPa, though Raman measurements suggest that the H 2 molecules in Ar(H 2) 2 dissociate above 175 GPa. A similar Kr(H 2) 4 solid forms at pressures above 5 GPa. It has a face-centered cubic structure where ...

  9. Industrial gas - Wikipedia

    en.wikipedia.org/wiki/Industrial_gas

    The term “industrial gases” [32] is sometimes narrowly defined as just the major gases sold, which are: nitrogen, oxygen, carbon dioxide, argon, hydrogen, acetylene and helium. [33] Many names are given to gases outside of this main list by the different industrial gas companies, but generally the gases fall into the categories "specialty ...

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