Transitions between phyllotactic lattice states in curved geometries.

Phyllotaxis, the regular arrangement of leaves or other lateral organs in plants including pineapples, sunflowers and some cacti, has attracted scientific interest for centuries. More recently there has been interest in phyllotaxis within physical systems, especially for cylindrical geometry. In this letter, we expand from a cylindrical geometry and investigate transitions between phyllotactic states of soft vortex matter confined to a conical frustum. We show that the ground states of this system are consistent with previous results for cylindrical confinement and discuss the resulting defect structures at the transitions. We then eliminate these defects from the system by introducing a density gradient to create a configuration in a single state. The nature of the density gradient limits this approach to a small parameter range on the conical system. We therefore seek a new surface, the horn, for which a defect-free state can be maintained for a larger range of parameters.

Characterisation of pillared clays by contrast-matching small-angle neutron scattering.

The contrast-matching SANS technique has been utilised to determine inter-pillar distances (and surface texture) in montmorillonite and beidellite pillared smectite clays; they lie in the range 1.40-1.80 nm, reflecting different inter-pillar orderings.

The use of central venous cannulae in neuroanaesthesia. A survey of current practice in the UK.

A postal questionnaire was sent to all UK consultant members of the Neuroanaesthesia Society to ascertain whether there was any consensus on indications for use and route of insertion of central venous cannulae in elective neuroanaesthetic practice. Five brief clinical scenarios were presented. Of 179 respondents, 98% indicated that they would insert a central venous cannula into patients requiring excision of an acoustic neuroma in the sitting position, 76% for clipping of an intracranial aneurysm and 75% for resection of an arteriovenous malformation. The antecubital fossa was the preferred route of insertion for 43.5% of respondents with 36.5% preferring the internal jugular approach. The subclavian (17%) and femoral (3%) routes were unpopular first-choice approaches. A significant proportion of respondents (43.5%) do not routinely order a chest X-ray at any stage following pre-operative central venous cannulation. The indications for use and advantages and disadvantages of each route of insertion, with reference to neuro-anaesthetic practice, are discussed.

Decomposition of nitrous oxide on pillared clays.

Alumina-pillared smectites have been found to abate nitrous oxide in the presence of methane. The results indicate that the yield of the reaction (N20 --> N2 + (1/2)O2) increases when pillared clays are exchanged with transition metals, single-pass conversion rates of >70% being attainable. In particular, when double exchanged (calcium and subsequently copper) alumina pillared montmorillonite/beidellite is used as a catalyst, de-N2O activity reaches a maximum, which is maintained even after 4 h of work at a space velocity of 5.5 h(-1). A mechanism for the reaction is suggested, which implies that N2O is first adsorbed by the catalyst and then decomposes through two different paths: catalyst oxidation and catalyst reduction. Such a redox process explains the kinetic data.

Double-blind comparison of sevofluran vs propofol and succinylcholine for tracheal intubation in children.

We have studied intubating conditions in 64 healthy children, aged 3-10 yr, undergoing adenotonsillectomy, in a double-blind, randomized study. Intubation was performed 150 s after induction using either 8% sevoflurane in nitrous oxide and oxygen or propofol 3-4 mg kg-1 with succinylcholine 2 mg kg-1. An anaesthetist blinded to the technique performed intubation and scored intubating conditions using Krieg and Copenhagen Consensus Conference (CCC) scores. The trachea was intubated successfully at the first attempt in all patients under clinically acceptable conditions, although scores were significantly better with propofol and succinylcholine. The sevoflurane technique cost 3.62 +/- 0.55 Pounds to completion of tracheal intubation, significantly more (P < 0.001) than the cost of propofol-succinylcholine and isoflurane (2.04 +/- 0.54 Pounds) when based on actual amount of drug used. This cost increased to 4.38 +/- 0.05 Pounds when based on whole ampoules, which is significantly more than the cost of sevoflurane (P < 0.001).

Evaluation of the efficacy and safety of amethocaine gel applied topically before venous cannulation in adults.

We have assessed in a placebo-controlled, double-blind trial, the efficacy and safety of an amethocaine gel preparation for alleviating the pain of venous cannulation. Forty-two unpremedicated adult patients were allocated randomly to receive either amethocaine gel 1 g (4% w/w) or placebo gel 1 g applied to the dorsum of the hand for 40 min before venous cannulation. After removal of the gel, a 20-gauge cannula was inserted and the pain of cannulation assessed by a three-point rank score and a 100-mm visual analogue scale: 90% of patients who received amethocaine reported clinically acceptable topical anaesthesia. Both verbal rating scores and visual analogue scores for pain were significantly less with amethocaine. Slight erythema associated with amethocaine occurred in one patient and slight itching in two patients. No other adverse features were evident.

Preliminary study to assay plasma amethocaine concentrations after topical application of a new local anaesthetic cream containing amethocaine.

Plasma concentrations of amethocaine were measured after topical application of amethocaine cream 2 g (5% w/w) to the dorsum of the right hand of 10 adult volunteers. The cream was applied for 240 min and plasma was assayed for amethocaine and its metabolite p-n-butylaminobenzoic acid at 0, 30, 60, 90, 120 and 240 min in all 10 volunteers, and at 360 min in seven volunteers, by high pressure liquid chromatography. No amethocaine was detected in the plasma of seven volunteers. Plasma concentrations of amethocaine up to 0.20 mg litre-1 were observed in three volunteers. No significant side effects were seen and pain scores on insertion of a 16-gauge cannula were 0 in all subjects. We conclude that the absence of clinical toxicity in the 10 healthy volunteers was a reflection of slow absorption and tissue hydrolysis of amethocaine after topical dermal application.

An EXAFS, and preliminary X-ray crystallographic, investigation of an iron-containing product from the lichen Cladonia deformis.

An iron-containing product in the acetone extract from the lichen Cladonia deformis has been investigated using chemical, spectroscopic and X-ray crystallographic methods. Visible-near UV, EPR and IR spectra indicate that the iron is present as high-spin Fe(III) and coordinates in an oxygen-containing environment arising from graciliformin (or graciliformin-like) ligands. This has been confirmed by an XAS (X-ray absorption) study using synchrotron radiation. Comparison of the EXAFS and XANES results with those obtained from a model, tris(pent-2,4-dionato)Fe(III), and detailed fitting using the single-scattering, curved-wave formalism for the EXAFS strongly supports the presence of a Fe(III) coordinated to five oxygen atoms from the graciliformin.

The use of etomidate infusions during anaesthesia for cardiopulmonary bypass.

The effects of cardiopulmonary bypass and hypothermia were studied on the plasma concentration and metabolism of a continuous infusion of etomidate in six patients. Continuous etomidate infusions (20 micrograms/kg/minute) with analgesic cover may be a suitable anaesthetic for cardiac surgery. This rate of infusion provides adequate plasma concentrations, and it would appear unnecessary from the results to alter the rate of infusion during cardiopulmonary bypass and hypothermia.

Human visual acuity assessment through linear extrapolation to threshold of bar grating VERs.

Visual evoked responses (VERs) were obtained from seven normal eyes, using high contrast square-wave gratings of varying bar size on an 8 degrees or 24 degrees stimulus field. VER amplitude was plotted as a function of bar size. These plots, called square wave transfer functions (SWTFs), have one or more peaks when generated by a 24 degree field. In some individuals, the small bar size extreme of the function can be fitted well with a straight line for purposes of extrapolation to the visual acuity bar size. However, interindividual differences in the shape of the 24 degree field SWTF invalidates any a priori assumption of what bar sizes may be included in the extrapolation. Results from three subjects, using an 8 degree field, suggest that a more uniform single-peaked triangular SWTF with a peak near 5 min arc may be assumed for extrapolation purposes. The interindividual SWTF differences obtained with the 24 degree field were not random, the subjects falling into one of two groups on the basis of SWTF shape. This SWTF shape dichotomy may be correlated with the presence or absence of strabismus.