Phase transitions in the adsorption system Li/Mo(112)

Journals published by the American Physical Society can be found at http://journals.aps.org/Experimental studies of the phase transitions in the adsorption system Li/Mo(112) are presented. This system is a model system for highly anisotropic interactions. From measurements of the half-widths of the low-energy electron diffraction spot profiles a phase diagram is derived for the whole submonolayer region of coverage in the temperature range 100-500 K. The commensurate low-coverage phases below theta=0.6 form chains normal to the troughs of the substrate. The commensurate p(4X1) phase, which is completed at a coverage, theta, of 0.25 monolayers (ML), seems to he truly long range ordered, whereas the p(2x1) phase at theta=0.5 still contains domain boundaries even at the lowest temperature of 100 K. Both undergo temperature driven order-disorder phase transitions. In contrast, the incommensurate phases existing in the coverage range theta=0.66-0.90 form chains along the troughs, which are only weakly coupled normal to the troughs of the substrate. These phases exhibit two coverage-driven phase transitions from rectangular to oblique units cells and back at critical coverages of 0.66 and 0.85, respectively, and represent floating solids. As a function of temperature, they undergo a two-dimensional melting transition. Close to the critical coverages, the melting temperatures show a sharp drop below the temperature range accessible in our experiments. Both functional dependences of the angular deviation from 90 degrees and of the melting temperature on coverage are in good agreement with a phenomenological theoretical model, assuming an instability of the shear modulus of the adsorbate unit cell at the critical coverages

Laser-induced thermal-desorption of CO ON NI(111) - determination of pre-exponential factor and heat of desorption

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Evaluation of a Navigated 3D Ultrasound Integration for Brain Tumor Surgery: First Results of an Ongoing Prospective Study

The aim of the study was to assess the quality, accuracy and benefit of navigated 2D and 3D ultrasound for intra-axial tumor surgery in a prospective study. Patients intended for gross total resection were consecutively enrolled. Intraoperatively, a 2D and 3D iUS-based resection was performed. During surgery, the image quality, clinical benefit and navigation accuracy were recorded based on a standardized protocol using Likert’s scales. A total of 16 consecutive patients were included. Mean ratings of image quality in 2D iUS were significantly higher than in 3D iUS (p 0.46). The benefit was rated 2.2 in 2D iUS and 2.6 in 3D iUS (p = 0.08). The benefit remained stable in 2D, while there was a slight decrease in the benefit in 3D after complete tumor resection (p = 0.09). The accuracy was similar in both (mean 2.2 p = 0.88). Seven patients had a small tumor remnant in intraoperative MRT (mean 0.98 cm3) that was not appreciated with iUS. Crucially, 3D iUS allows for an accurate intraoperative update of imaging with slightly lower image quality than 2D iUS. Our preliminary data suggest that the benefit and accuracy of 2D and 3D iUS navigation do not undergo significant variations during tumor resection