Non-helical models of DNA structure the top of this article, or there could be an equal number of right-handed and left-handed twists, as in the Rodley structure below. The abbreviation "TN", to be used to refer to any DNA structure whose strands are topologically non-linked, has been proposed. The double-helix model of DNA structure was first published in the journal "Nature" by James D. Watson and Francis Crick in 1953 with further details in 1954.) Their work was based upon the crucial X-ray diffraction image of DNA - labeled as "Photo 51" - from Rosalind Franklin in 1952, followed by her more highly clarified DNA
James Watson determined that their results were inconclusive and could not specifically identify the newly labeled molecules as DNA. Watson never developed a constructive interaction with Kalckar, but he did accompany Kalckar to a meeting in Italy, where Watson saw Maurice Wilkins talk about his X-ray diffraction data for DNA. Watson was now certain that DNA had a definite molecular structure that could be elucidated. In 1951, the chemist Linus Pauling in California published his model of the amino acid alpha helix, a result that grew out of Pauling's efforts in X-ray crystallography and molecular model building. After obtaining some results from