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  2. Reference materials for stable isotope analysis - Wikipedia

    en.wikipedia.org/wiki/Reference_materials_for...

    The δ values and absolute isotope ratios of common reference materials are summarized in Table 1 and described in more detail below. Alternative values for the absolute isotopic ratios of reference materials, differing only modestly from those in Table 1, are presented in Table 2.5 of Sharp (2007) [1] (a text freely available online), as well as Table 1 of the 1993 IAEA report on isotopic ...

  3. Sharp series - Wikipedia

    en.wikipedia.org/wiki/Sharp_series

    The sharp series limit is the same as the diffuse series limit. In the late 1800s these two were termed supplementary series. In 1896 Arthur Schuster stated his law: "If we subtract the frequency of the fundamental vibration from the convergence frequency of the principal series, we obtain the convergence frequency of the supplementary series". [5]

  4. Cheat sheet - Wikipedia

    en.wikipedia.org/wiki/Cheat_sheet

    Cheat sheets were historically used by students without an instructor or teacher's knowledge to cheat on a test or exam. [1] In the context of higher education or vocational training, where rote memorization is not as important, students may be permitted (or even encouraged) to develop and consult their cheat sheets during exams.

  5. Hypodermic needle - Wikipedia

    en.wikipedia.org/wiki/Hypodermic_needle

    The hypodermic needle reduces contamination for two reasons: First, its surface is extremely smooth, which prevents airborne pathogens from becoming trapped between irregularities on the needle's surface, which would subsequently be transferred into the media (e.g. agar) as contaminants; second, the needle's surface is extremely sharp, which ...

  6. Block (periodic table) - Wikipedia

    en.wikipedia.org/wiki/Block_(periodic_table)

    The s-block, with the s standing for "sharp" and azimuthal quantum number 0, is on the left side of the conventional periodic table and is composed of elements from the first two columns plus one element in the rightmost column, the nonmetals hydrogen and helium and the alkali metals (in group 1) and alkaline earth metals (group 2).

  7. List of chemistry mnemonics - Wikipedia

    en.wikipedia.org/wiki/List_of_chemistry_mnemonics

    A mnemonic is a memory aid used to improve long-term memory and make the process of consolidation easier. Many chemistry aspects, rules, names of compounds, sequences of elements, their reactivity, etc., can be easily and efficiently memorized with the help of mnemonics.

  8. Multiple choice - Wikipedia

    en.wikipedia.org/wiki/Multiple_choice

    A well written multiple-choice question avoids obviously wrong or implausible distractors (such as the non-Indian city of Detroit being included in the third example), so that the question makes sense when read with each of the distractors as well as with the correct answer. A more difficult and well-written multiple choice question is as follows:

  9. List of unsolved problems in chemistry - Wikipedia

    en.wikipedia.org/wiki/List_of_unsolved_problems...

    [13] Protein folding problem : Is it possible to predict the secondary, tertiary and quaternary structure of a polypeptide sequence based solely on the sequence and environmental information? Inverse protein-folding problem: Is it possible to design a polypeptide sequence which will adopt a given structure under certain environmental conditions?