A nuclear magnetic resonance study of molecular disorder in the solid state of some medium ring hydrocarbons

Since the discovery of nuclear magnetic resonance in bulk matter in 1945, n.m.r studies of molecular motion in solids have provided a powerful insight into the details of molecular reorientation processes that occur in solids. By studying the variation of the n.m.r. parameters as a function of temperature it is usually possible to obtain information regarding such phenomena as solid-solid phase transitions, including the anomalous behaviour of heat capacity associated with order-disorder and co-operative processes, rotational disorder and self-diffusion. In suitable cases it is possible to estimate the origin and magnitude of the potential barriers of the crystalline field which hinder the various reorientation processes. The cycloalkane ring series (CH₂)[sub]n from cyclopropane n =3 to cyclohexane n=6 have all previously been studied in the solid state by n.m.r. The results indicate that considerable molecular mobility occurs in the solid state o these substances and that in general the solid-solid phase transitions detected by hear capacity measurements are associated with the onset of molecular reorientation and in some cases self-diffusion. The current interest in the molecular configuration of the medium ring hydrocarbons, and the extensive study by Finke et al. (1956) of the low temperature thermal properties of cycloheptane n=7, and cyclooctane n=8, showing three and two solid-solid phase transitions respectively, prompted an n.m.r. study of cycloheptane and cyclooctane. The results of this investigation together with those of a related seven membered ring hydrocarbon 1, 3, 5 cycloheptatriene C₇H₈ are presented in this thesis, and show that extensive molecular motion exists well below the melting points of all three substances, and information is given regarding the form of the motion in the various crystalline phases

Segmentation of Cortical Surface and Interior Brain Structures Using Active Surface / Active Volume Templates

Advanced applications such as neurosurgical planning and simulation require both surface and interior anatomical information in order to be truly effective. We are developing a segmentation scheme based on collections of active surface templates embedded within an active volume. This composite system encodes high-level anatomical knowledge of both cortical surface and interior brain structures in a self-assembling model of a reference, or atlas brain. Following initialization of the surface templates in the test brain volume, the cortical surface templates deform to achieve a segmentation of the surface of the brain. The displacements of the cortical surface templates cause an increase in the potential elastic energy of the active volume, and a subsequent minimization of this elastic energy is used to define a volumetric warp between the reference brain and the test data. This warp is used to deform the active surface models of the deep structures in the brain to their approximate fina..