The reorientational motion of benzene in the neat liquid and in a polystyrene/benzene solution was investigated by NMR relaxation as well as MD simulation methods. The temperature-dependent 13 C dipolar spin-lattice relaxation rates and cross correlation rates between the dipolar relaxation mechanism and the relaxation by chemical-shift anisotropy were measured. From the NMR measurements and MD simulation results, the rotational diffusion constants for rotations about the C 6 axis and perpendicular to it were evaluated, and it was found that the values of the former were larger than those of the latter. The rotational anisotropy, which is the ratio of these values, decreases for the NMR data from 2.3 to 1.2 when increasing the temperature from 280 to 323 K. The activation energy for reorientation about the main symmetry axis was 3.4 kJ mol -1 and about axes perpendicular to that 13.3 kJ mol -1 . The temperature effect was less pronounced for the MD results; the anisotropy changed from 1.9 to 1.3 between 280 and 360 K. The reorientational correlation functions showed a significant non-Debye behavior and were fitted with a Kohlrausch-Williams-Watts function. Furthermore, from the MD simulations the temperature dependence of the density and the translational diffusion coefficient were also determined. The NMR data for benzene rotational motions in a polystyrene matrix could not be explained by a simple rotational diffusion model. From the data, it was concluded that the rotations about the C 6 axis were much faster than about axes perpendicular to the C 6 axis. This finding is in accordance to a previous MD study by Mu ¨ller-Plathe.

No abstract

No abstract

No abstract

In patients scheduled for the resection of perisylvian brain tumours, knowledge of the cortical topography of language functions is crucial in order to avoid neurological deficits. We investigated the applicability of statistical parametric mapping (SPM) without stereotactic normalisation for individual preoperative language function brain mapping using positron emission tomography (PET). Seven right-handed adult patients with left-sided brain tumours (six frontal and one temporal) underwent 12 oxygen-15 labelled water PET scans during overt verb generation and rest. Individual activation maps were calculated for P<0.005 and P<0.001 without anatomical normalisation and overlaid onto the individuals' magnetic resonance images for preoperative planning. Activations corresponding to Broca's and Wernicke's areas were found in five and six cases, respectively, for P<0.005 and in three and six cases, respectively, for P<0.001. One patient with a glioma located in the classical Broca's area without aphasic symptoms presented an activation of the adjacent inferior frontal cortex and of a right-sided area homologous to Broca's area. Four additional patients with left frontal tumours also presented activations of the right-sided Broca's homologue; two of these showed aphasic symptoms and two only a weak or no activation of Broca's area. Other frequently observed activations included bilaterally the superior temporal gyri, prefrontal cortices, anterior insulae, motor areas and the cerebellum. The middle and inferior temporal gyri were activated predominantly on the left. An SPM group analysis ( P<0.05, corrected) in patients with left frontal tumours confirmed the activation pattern shown by the individual analyses. We conclude that SPM analyses without stereotactic normalisation offer a promising alternative for analysing individual preoperative language function brain mapping studies. The observed right frontal activations agree with proposed reorganisation processes, but they may also reflect an unspecific recruitment of the right-sided Broca's homologue in the effort to perform the task.

No abstract

The reorientational motion of toluene in neat liquid was examined by using 13 C nuclear magnetic relaxation. The temperature-dependent dipolar spin-lattice relaxation rates and cross-correlation rates between the dipolar and the chemical-shift anisotropy relaxation mechanisms were measured for different 13 C nuclei in the molecule over a temperature range of 253 to 318 K. Assuming the molecular frame to show an anisotropic rotational motion, we found three different rotational diffusion constants about the molecular rotation axes. Reorientation velocities about the C 2 axis and the axis perpendicular to the molecular plane were of comparable magnitude, but change their ratio in the temperature range investigated in this study. The reorientation about the axis in the molecular plane and perpendicular to the C 2 axis was found to be approximately 2 to 3 times slower. The rotational diffusion constants were fitted to an Arrhenius equation, and activation energies from 3.5 to 9.1 kJ mol -1 were found. Furthermore, correlation times for the reorientation of different 13 C-1 H bonds, spinlattice relaxation rates for the chemical-shift anisotropy and spin-rotation mechanisms were also derived for the different 13 C nuclei.

This paper gives an overview of the experiments on-board the International Space Station (ISS) performed so far by the CETSOL team. Al-7 wt% Si alloys with and without grain refiners were solidified in microgravity. Detailed grain structure analysis showed columnar growth in case of non-refined alloy, but the existence of a columnar to equiaxed transition (CET) in refined alloy. One main result is a sharp CET when increasing the solidification velocity and a progressive CET for lowering the temperature gradient. Applying a front tracking model this behavior was confirmed numerically for sharp CET. Using a CAFE model both segregation and grain structures were numerically modeled and show a fair agreement with the experimental findings.