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  2. Crystallographic defect - Wikipedia

    en.wikipedia.org/wiki/Crystallographic_defect

    A twin boundary is a defect that introduces a plane of mirror symmetry in the ordering of a crystal. For example, in cubic close-packed crystals, the stacking sequence of a twin boundary would be ABCABCBACBA. On planes of single crystals, steps between atomically flat terraces can also be regarded as planar defects.

  3. Crystal twinning - Wikipedia

    en.wikipedia.org/wiki/Crystal_twinning

    The relationship is defined by a symmetry operation called a twin operation. [1] [2] The twin operation is not one of the normal symmetry operations of the untwinned crystal structure. For example, the twin operation may be reflection across a plane that is not a symmetry plane of the single crystal. [1] [2]

  4. Topological defect - Wikipedia

    en.wikipedia.org/wiki/Topological_defect

    The terminology of a topological defect vs. a topological soliton, or even just a plain "soliton", varies according to the field of academic study. Thus, the hypothesized but unobserved magnetic monopole is a physical example of the abstract mathematical setting of a monopole ; much like the Skyrmion, it owes its stability to belonging to a non ...

  5. Kirkendall effect - Wikipedia

    en.wikipedia.org/wiki/Kirkendall_effect

    The Kirkendall effect is the motion of the interface between two metals that occurs due to the difference in diffusion rates of the metal atoms. The effect can be observed, for example, by placing insoluble markers at the interface between a pure metal and an alloy containing that metal, and heating to a temperature where atomic diffusion is reasonable for the given timescale; the boundary ...

  6. Middle-range theory (archaeology) - Wikipedia

    en.wikipedia.org/wiki/Middle-range_theory...

    Theory building began to gain tract in the late 1970s in the time of New Archaeology and took several years to be a topic of critical interest. The concept is often misunderstood because of the multiplicity of the middle-range theory in another scholarly discipline – sociology. It is suggested in this approach that scientific knowledge ...

  7. Twin paradox - Wikipedia

    en.wikipedia.org/wiki/Twin_paradox

    In his famous paper on special relativity in 1905, Albert Einstein deduced that for two stationary and synchronous clocks that are placed at points A and B, if the clock at A is moved along the line AB and stops at B, the clock that moved from A would lag behind the clock at B. He stated that this result would also apply if the path from A to B ...

  8. Thomas J. Bouchard Jr. - Wikipedia

    en.wikipedia.org/wiki/Thomas_J._Bouchard_Jr.

    Thomas J. Bouchard Jr. (born October 3, 1937) is an American psychologist known for his behavioral genetics studies of twins raised apart. He is professor emeritus of psychology and director of the Minnesota Center for Twin and Adoption Research at the University of Minnesota.

  9. Twin Earth thought experiment - Wikipedia

    en.wikipedia.org/wiki/Twin_Earth_thought_experiment

    Twin Earth is a thought experiment proposed by philosopher Hilary Putnam in his papers "Meaning and Reference" (1973) and "The Meaning of 'Meaning '" (1975). It is meant to serve as an illustration of his argument for semantic externalism , or the view that the meanings of words are not purely psychological.