Magnetic domain structure in hexagonal crystals

The domains structure of cobalt, gadolinium and terbium have been investigated; single crystals of gadolinium and terbium, were obtained in which the oxide content was considerably reduced by a solid state electrolysis technique. The Bitter technique has been used for most of the observations with a modified colloid, but a dry colloid technique has been used at temperatures below 240 K or higher than room temperature. Two different pieces of apparatus were designed for use at high or low temperatures. In the case of cobalt single crystals the results obtained at room, temperature are similar to those obtained previously. The pattern at 77 K was as expected from the anisotropy data. The lengths of daggers of reverse magnetization and the widths of their bases were found to be in direct proportion (for simple and complex daggers). The variation of the exchange constant A with temperature was also determined. It was not possible to observe a closure domain structure, however this did not rule out the possibility of a partial structure being present on the basal plane, though the variation of dam in width with temperature agrees best with that of Kittel model. The domain, structure of gadolinium was much easier to analyse than that of cobalt. At 274 K patterns on planes containing the c-axis shoved parallel l80 walls, with the development of partial closure structures at the surface near the basal plane and at the oxide inclusions. Basal plane patterns indicate that the l80 vails are not plane and give more detailed information about the mixed nature of the basal structure. The change in domain structure has been studied as the temperature is reduced to 77 K and under the influence of magnetic fields up to l400 Oe. Unexpected results were obtained when the normal field produced by a permanent magnet was applied to the basal plane. Such arrangements produced the well known honeycomb structure which was observed on other materials after an applied field of few K.Oe. was applied parallel or perpendicular to the c-axis. This was believed to be the result of a closure structure with magnetisation laid freely in basal plane. The non-uniformity of' the lines of force produced by such magnet will re-orient the direction of the magnetic moment within the closure region. The domain structure in a cube shaped terbium single crystal was observed at 210 K and different possibilities for the internal configuration were given. Agreement between experimental observation and the proposed model which consists of plate type domains magnetized along the b(_1) and b(_2) axis but not along the third axis b(_3)-axis, which is perpendicular to one surface. The equilibrium, width was measured and compared with the calculated one and they were in. good agreement. The structure at lower temperatures was studied. However as in gadolinium it is still not clear whether the pattern observed at low temperature represents a true domain structure

Body mass index and complications following major gastrointestinal surgery: A prospective, international cohort study and meta-analysis

Aim Previous studies reported conflicting evidence on the effects of obesity on outcomes after gastrointestinal surgery. The aims of this study were to explore the relationship of obesity with major postoperative complications in an international cohort and to present a metaanalysis of all available prospective data. Methods This prospective, multicentre study included adults undergoing both elective and emergency gastrointestinal resection, reversal of stoma or formation of stoma. The primary end-point was 30-day major complications (Clavien–Dindo Grades III–V). A systematic search was undertaken for studies assessing the relationship between obesity and major complications after gastrointestinal surgery. Individual patient meta-analysis was used to analyse pooled results. Results This study included 2519 patients across 127 centres, of whom 560 (22.2%) were obese. Unadjusted major complication rates were lower in obese vs normal weight patients (13.0% vs 16.2%, respectively), but this did not reach statistical significance (P = 0.863) on multivariate analysis for patients having surgery for either malignant or benign conditions. Individual patient meta-analysis demonstrated that obese patients undergoing surgery formalignancy were at increased risk of major complications (OR 2.10, 95% CI 1.49–2.96, P < 0.001), whereas obese patients undergoing surgery for benign indications were at decreased risk (OR 0.59, 95% CI 0.46–0.75, P < 0.001) compared to normal weight patients. Conclusions In our international data, obesity was not found to be associated with major complications following gastrointestinal surgery. Meta-analysis of available prospective data made a novel finding of obesity being associated with different outcomes depending on whether patients were undergoing surgery for benign or malignant disease