New atom probe approaches to studying segregation in nanocrystalline materials.

Atom probe is a technique that is highly suited to the study of nanocrystalline materials. It can provide accurate atomic-scale information about the composition of grain boundaries in three dimensions. In this paper we have analysed the microstructure of a nanocrystalline super-duplex stainless steel prepared by high pressure torsion (HPT). Not all of the grain boundaries in this alloy display obvious segregation, making visualisation of the microstructure challenging. In addition, the grain boundaries present in the atom probe data acquired from this alloy have complex shapes that are curved at the scale of the dataset and the interfacial excess varies considerably over the boundaries, making the accurate characterisation of the distribution of solute challenging using existing analysis techniques. In this paper we present two new data treatment methods that allow the visualisation of boundaries with little or no segregation, the delineation of boundaries for further analysis and the quantitative analysis of Gibbsian interfacial excess at boundaries, including the capability of excess mapping.

Influence of Aging and Environment on Nanoparticle Chemistry - Implication to Confinement Effects in Nanoceria.

The oxidation state switching of cerium in cerium oxide nanoparticles is studied in detail. The influence of synthesis medium, aging time and local environment on the oxidation state switching, between +3 and + 4, is analyzed by tracking the absorption edge using UV-Visible spectroscopy. It is observed that by tuning the local environment, the chemistry of the nanoparticles could be altered. These time dependent, environmentally induced changes likely contribute to inconsistencies in the literature regarding quantum-confinement effects for ceria nanoparticles. The results in this article indicate that there is a need to carry out comprehensive analysis of nanoparticles while considering the influence of synthesis and processing conditions, aging time and local environment.

Vanadium doped tin dioxide as a novel sulfur dioxide sensor.

Considering the short-term exposure limit of SO2 to be 5 ppm, we first time report that semiconductor sensors based on vanadium doped SnO2 can be used for SO2 leak detection because of their good sensitivity towards SO2 at concentrations down to 5 ppm. Such sensors are quite selective in presence of other gases like carbon monoxide, methane and butane. The high sensitivity of vanadium doped tin dioxide towards SO2 may be understood by considering the oxidation of sulfur dioxide to sulfur trioxide on SnO2 surface through redox cycles of vanadium-sulfur-oxygen adsorbed species.

Postoperative pain after lumbar disc surgery: a comparison between parenteral ketorolac and narcotics.

OBJECTIVE: Lumbar discectomy is a common elective surgical procedure but many patients still experience postoperative back pain which may delay hospital discharge. We therefore evaluated the efficacy of a parenteral non-steroidal antiinflammatory agent, ketorolac, for the management of post-surgical pain. METHODS: Fifty three patients undergoing lumbar discectomy at a Medical School affiliated Veterans Administration hospital were randomly assigned to receive either: 1) 30 mg intramuscular ketorolac upon surgical closure and every 6 hours for 36 hours and narcotic analgesics as needed (PRN); or 2) only narcotic analgesics as needed. A blinded observer recorded the average, minimum and maximum postoperative pain intensity using a Numeric Pain Intensity Scale; total postoperative narcotic consumption, complications, length of hospitalization (from surgery to discharge) and outcome at 6 weeks. RESULTS: The patients who received ketorolac reported significantly lower average (p < 0.001), minimum (p < 0.001), and maximum (p < 0.001) pain scores than patients receiving only narcotic analgesics. Cumulative narcotic doses (standardized to parenteral morphine) were significantly lower in the ketorolac group (p < 0.001). There was no significant difference between groups in the frequency of side effects, and no complication specifically associated with ketorolac use was observed. Mean length of hospitalization was significantly shorter (p = 0.05) in patients receiving ketorolac than in patients receiving only narcotics. Six weeks after surgery 5 (19.2%) patients who received only narcotics were troubled by persistent back pain. By contrast, all patients who received ketorolac were free of back pain at follow-up (p = 0.03). CONCLUSIONS: These results suggest that ketorolac, when used with PRN narcotics, is more effective than PRN narcotics alone for postoperative pain following lumbar disc surgery. In addition, this strategy also may contribute to early discharge from hospital after lumbar disc surgery.

Complications during anterior surgery of the lumbar spine: an anatomically based study and review.

Procedures involving anterior surgical decompression and fusion are being performed with increasing frequency for the treatment of a variety of pathological processes of the spine including trauma, deformity, infection, degenerative disease, failed-back syndrome, discogenic pain, metastases, and primary spinal neoplasms. Because these operations involve anatomy that is often unfamiliar to many neurological and orthopedic surgeons, a significant proportion of the associated complications are not related to the actual decompressive or fusion procedure but instead to the actual exposure itself. To understand the nature of these injuries, a detailed anatomical study and dissection was undertaken in six cadaveric specimens. Critical structures at risk in the abdomen and retroperitoneum were identified, and their anatomical relationships were categorized and photographed. These structures included the psoas muscle, kidneys, ureters, diaphragm and crura, esophageal hiatus, thoracic duct, greater splanchnic nerves, phrenic nerves, sympathetic chains, medial arcuate ligament, superior and inferior hypogastric plexus, segmental and radicular vertebral vessels, aorta, vena cava, median sacral artery, common iliac vessels, iliolumbar veins, lumbosacral plexus, and presacral hypogastric plexus. Based on these dissections and an extensive review of the literature, the authors provide a detailed anatomically based discussion of the complications associated with anterior lumbar surgery.

Intraoperative monitoring of spinal cord function using motor evoked potentials via transcutaneous epidural electrode during anterior cervical spinal surgery.

Because false-positive results are not infrequent when monitoring somatosensory evoked potentials during surgery, monitoring of motor evoked potentials (MEPs) has been proposed and successfully used during the removal of spinal cord tumors. However, this often requires direct visual placement of an epidural electrode after a laminectomy. We evaluated the use of MEPs, recorded via a transcutaneously placed epidural electrode, to monitor motor pathway functional integrity during surgery on the anterior cervical spine. Sixteen patients underwent anterior cervical vertebral decompression and fusion for cervical myelopathy and/or radiculopathy. Before surgery, an epidural monitoring electrode was placed transcutaneously at the midthoracic level and was used to record MEPs after transcranial cortical electrical stimulation. Electrode placement was successful in all patients but one, and satisfactory baseline spinal MEPs were obtained except for one patient who had cerebral palsy with significant motor dysfunction. Patients showed no significant changes in spinal MEPs during surgery, and all had baseline or better motor function postoperatively. None had complications from epidural electrode placement or electrical stimulation. We conclude that motor pathways can be monitored safely during anterior cervical spinal surgery using spinal MEPs recorded via a transcutaneously placed epidural electrode, that MEP preservation during surgery correlates with good postoperative motor function, and that cerebral palsy patients may possess too few functional motor fibers to allow MEP recording.