No abstract

Methanol−water mixtures are known to be microscopically inhomogeneous and show nonideal properties at ambient conditions and also at higher temperatures and pressures. To understand the nonideality of methanol−water mixtures, the behaviors of local compositions were studied through evaluating the local mole fractions by the well-known activity coefficient equation, Wilson equation, and by molecular dynamics (MD) simulation at three conditions: 25 °C−0.1 MPa, 300 °C−25 MPa, and 350 °C−25 MPa. The Wilson parameters were redetermined to generate the reference values for the comparison in this study. The deviation of local mole fraction from bulk mole fraction was selected as an indicator for local composition. The deviations by the Wilson equation were positive in all compositions, and its magnitude for water was much larger than that for methanol, which is principally independent of temperature and pressure and was completely supported by the results by MD simulation. The MD simulation provided the dependence of the local mole fraction deviation on the intermolecular distance and indicated that the immediate neighbor in the Wilson local mole fraction approximately corresponds to the distance range from first valley to second peak in the radial distribution function. In addition, the general trends of local mole fraction by MD simulation are similar at ambient and high temperature and pressure conditions, suggesting the applicability of the Wilson equation for methanol−water mixture to high temperature and pressure conditions in terms of representing the local mole fraction.

We experienced a rare case with conus medullaris syndrome caused by an intraspinal cystic mass derived from compressed vertebra. A 68 year old man suffered an L1 compressed fracture from falling. Two months later, he experienced severe lumbago after lifting something heavy. Then, he felt numbness in his buttocks and thighs after a few days, and this symptom became aggravated before he was finally referred to our center. On admission, he was also suffering intermittent claudication and had difficulty urinating. Plain radiographs showed a vertebral collapse at the L1 spine. MRI represented a large cystic lesion antero medial in the spinal canal strongly compressing the spinal cord at that level, of which the intensity was identical with that of fluid. A Myelogram showed the complete obstruction of contrast medium adjacent to the collapsed body of L1. The patient underwent laminectomy at the L1 level and microscopic resection of the cyst. The cyst wall had a surface covered with smooth and whitish tissue, but it didn't adhere to the dura. The fluid in the cyst was serous and yellowish. The cyst was reduced in size, followed by Th11 L3 transpedicular fixation combined with transpedicular focal bone and HA granule grafts at the L1 vertebra. The postoperative course was uneventful and the patient's neurological impairment soon disappeared completely. In this case, the sudden vertical load caused a comminuted burst of the L1 vertebral body. We suspect that the fluid inside the vertebral body extended posterior and formed a large intraspinal cystic mass, resulting in conus medullaris syndrome.