Persistence of Covalent Bonding in Liquid Silicon Probed by Inelastic X-ray Scattering

Metallic liquid silicon at 1787K is investigated using x-ray Compton scattering. An excellent agreement is found between the measurements and the corresponding Car-Parrinello molecular dynamics simulations. Our results show persistence of covalent bonding in liquid silicon and provide support for the occurrence of theoretically predicted liquid-liquid phase transition in supercooled liquid states. The population of covalent bond pairs in liquid silicon is estimated to be 17% via a maximally-localized Wannier function analysis. Compton scattering is shown to be a sensitive probe of bonding effects in the liquid state.Comment: 5pages, 3 postscript figure

Evoked Spinal Cord Potentials Monitored at Thoracoabdominal Region after Trans-intercostal Stimulation

To investigate the feasibility of a novel recording method for trans-intercostal evoked spinal cord potentials (Tic-ESCPs) and the properties of the waveforms, the potentials were recorded and analyzed in an animal model. In two beagle dogs, Tic-ESCPs were recorded at the left twelfth intercostal to fourth lumbar nerves following stimulation at the left eleventh intercostal nerve, either with or without the use of a muscle relaxant. The amplitude and latency of the Tic-ESCP waves were then measured and compared with those of conventional transcranial spinal motor evoked potentials (MEPs). Tic-ESCPs could be obtained at any nerve, with or without the use of a muscle relaxant. The Tic-ESCP waveform was clear and simple, consisting of a small positive (P1) wave and a subsequent large negative (N1) wave. As the site of recording moved farther from the stimulation site, the N1 amplitudes were reduced and the P1 latency was prolonged. Under muscle relaxation, the N1 amplitudes were reduced, and the P1 latencies were shorter. As compared with MEPs, Tic-ESCPs could be evoked by a weaker stimulus, the N1 amplitude was smaller, and the P1 latency was shorter. Tic-ESCP recording was feasible either with or without the use of a muscle relaxant. The Tic-ESCPs showed simple and clear waveforms with smaller stimulations. Therefore, Tic-ESCPs may be useful for intraoperative spinal cord monitoring

Echo-guided Identification of Key Lumbar Arteries Supplying the Spinal Cord in a Canine Model

The aim of this study was to anatomically verify echo-guided identification of key lumbar arteries supplying blood to the spinal cord and to examine whether changes in nerve root motion could be used for detecting malperfusion following aortic cross-clamping. In two beagle dogs, nerve root motion was monitored through the intervertebral disc using transesophageal echocardiography. Communications between each lumbar artery and the spinal vasculature were assessed by echogenic signals in the spinal cord following saline injection into each lumbar artery. Nerve root motion immediately disappeared after clamping the aorta and recovered as soon as it was declamped. These changes were induced specifically by clamping the aorta at the first lumbar level. The changes were instantaneous and may be beneficial because of minimal ischemic insult of the spinal cord. In dog #1, the result of the saline injection test was anatomically verified with the presence of a spinal branch. However, in dog #2 echogenic signals appeared in the muscles as well as in the spinal artery. A morphological study showed no spinal branch of the lumbar artery but only an indistinct artery in the intervertebral foramen. These findings probably account for those cases in humans where there is unsuccessful visualization of the Adamkiewicz artery by angiography. Consequently, the above two assessments identified the key artery. Cessation of nerve root motion following segmental clamping of the aorta and echogenic signals in the spinal cord following saline injection into a lumbar artery may represent the key artery with respect to hemodynamics and perfusion, respectively

Phase-contrast microtomography using an X-ray interferometer having a 40-μ\mum analyzer

Phase-contrast X-ray tomographic experiment using a triple Laue-case (LLL) interferometer having a 40-$\mu$m lamella which was fabricated to improve spatial resolution, was carried out using undulator X-rays at SPring-8, Japan. Three-dimensional images mapping the refractive index were measured for various animal tissues. Comparing the images with those obtained in previous experiments using conventional LLL interferometers having a 1-mm lamella, improvement in the spatial resolution was demonstrated in that histological structures, such as hepatic lobules in liver and tubules in kidney, were revealed