Cyclohexane C6H12 (m.p. 279.8 °K) undergoes an isothermal transition at 186 °K. The so-called phase I is stable between 279.8 and 186°K, phase II below 186°K. Starting from a single crystal I grown by a zone melting technique at 187 °K, suitable single crystals II were obtained through a careful control of the phase transformation and annealing at 185 °K for two days. X-ray diffraction data have been collected at 195 and 115 °K by the low-temperature precession technique. At 115 °K, crystal data are: monoclinic cell, a= 11.23 (2), b = 6.44 (2), c= 8.20 (2) A, fl= 108.83 (17) °, Z= 4; space group Cc or C2/c (the analysis confirmed the centrosymmetric group). The crystal and molecular structures were refined to an R index of 0.061 ; the 'chair'-shaped molecule departs slightly but significantly from Dan symmetry. The rigid-body model is a good approximation for the thermal motion. At 195 °K, crystal data for the plastic phase I are: cubic cell, a = 8.61 (2)/~, Z= 4, space group Fm3m. Using the molecular shape previously found, two types of orientational disorder have been investigated: isotropic reorientations of the molecules about their centre of gravity (Pauling-Fowler model) and step reorientations between 24 equivalent positions (Frenkel model). In this case, the packing was found by a Monte-Carlo method coupled with a rigidgroup least-squares refinement. The Frenkel model gives a better agreement with experiment. A tentative interpretation of the transformation is given. The same general procedure can probably be applied to other plastic crystals.
The molecular packing of benzene 1I has been redetermined by a Monte Carlo technique using data of Piermarini and co-workers, and then group-refined. The Hamilton tests show a significant improvement of the agreement between observed and calculated structure factors.
A versatile apparatus for X-ray structural investigation down to 90°K has been devised. A quasilaminar flow of cold nitrogen keeps the crystal free from frost; no other protection is necessary, even with a fiat cassette. This technique is especially suitable for routine growth, orientation and maintenance of single crystals obtained from organic substances which are liquid at room temperature. Standard Weissenberg and Buerger goniometers require only a few modifications, which are described.
We present qualitative experimental evidence that the "Wiimprovisation" process of using Nintendo Wiimotes as virtual instruments linked to a musical sound system within the framework of Group Music Therapy sessions can provide effective psychodynamic mediation for patients. We designed and implemented specific modalities for movement-based sound control and tested our tool in two clinical settings with children (age 7 to 12) suffering from behavioral disorders. Our preliminary results show immediate acceptance of, long term motivation for and meaningful expression through our system by patients. Future work will focus on assessing the therapeutic potential of our platform's personalization features in a controlled experiment.
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