The transition to Earth-like torsional oscillations in magnetoconvection simulations

Evidence for torsional oscillations (TOs) operating within the Earth's fluid outer core has been found in the secular variation of the geomagnetic field. These waves arise via disturbances to the predominant (magnetostrophic) force balance believed to exist in the core. The coupling of the core and mantle allow TOs to affect the length-of-day of the Earth via angular momentum conservation. Encouraged by previous work, where we were able to observe TOs in geodynamo simulations, we perform 3-D magnetoconvection simulations in a spherical shell in order to reach more Earth-like parameter regimes that proved hitherto elusive. At large Ekman numbers we find that TOs can be present but are typically only a small fraction of the overall dynamics and are often driven by Reynolds forcing at various locations throughout the domain. However, as the Ekman number is reduced to more Earth-like values, TOs become more apparent and can make up the dominant portion of the short timescale flow. This coincides with a transition to regimes where excitation is found only at the tangent cylinder, is delivered by the Lorentz force and gives rise to a periodic Earth-like wave pattern, approximately operating on a 4 to 5 year timescale. The core travel times of our waves also become independent of rotation at low Ekman number with many converging to Earth-like values of around 4 years

Gastric residual volume in children: a study comparing efficiency of erythromycin and metoclopramide as prokinetic agents

Metoclopramide may be used to stimulate gastric emptying when anaesthetizing children for emergency operations. Unfortunately, metoclopramide is associated with extrapyramidal side effects. Erythromycin, a motilin receptor agonist, is a prokinetic agent but its use has been little investigated in children. This randomized double-blind study compared the effects of premedication with oral metoclopramide 0.15 mg kg(-1) or erythromycin 1 mg kg(-1) on gastric emptying in 80 children undergoing tonsillectomy. Pre-operative fluids, premedication and anaesthetic technique were standardized and gastric volume was measured with an orogastric tube. Post-operative nausea and vomiting was recorded. Metoclopramide and erythromycin produced similar gastric volumes (0.29 and 0.24 ml kg(-1)) and there was no difference in post-operative vomiting. In the erythromycin group there were more patients with negative aspirates (45.9%) than in the metoclopramide group (35.1%), but the difference was not statistically significant. These results indicate that erythromycin may be as effective as metoclopramide as a prokinetic agent