X-Ray photoelectron spectroscopy has been used to study a series of iron oxides. It has been shown that iron metal has a different ionisation energy from a number of iron(ll1) oxides. Small perturbations to the energy of the iron(ll1) 2p electrons can be attributed to changes in crystal structure. Multiplet splitting and shake-up in the iron oxides contributes to iron 2p peak widths. The chemisorption of water has a marked effect upon the observed peak profiles ; the oxygen 1 s peaks due to oxide, hydroxyl, and adsorbed water have been characterised.ing Board, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire G L13 9PB A NUMBER of compounds containing iron and oxygen have been examined by X-ray photoelectron (X.1i.e.) spectroscopy. The inaterials were chosen to reflect the change in electronic environment of atoms on going from simple binary oxides t o ternary oxides incorporating various alkali metal atoms.The difficulties of surface contamination due to chemisorption, particularly of water, experienced in an earlier study of chromium-oxygen systems were again evident. ,&o, the resulting spectra were highly complex due to multiplet splitting effects which are characteristic of such iron compounds. EXPERIMEKTALMaterials and Reagents.-Lithium ferrite was prepared i n its face-centred cubic phase modification by the reaction of AiialaR lithium carbonate with Specpure Grade a-Fe,O,. The reaction mixture (having a Li,CO, : Fe,O, molar ratio of 1.03 : 1 rather than 1 : 1 t o compensate for vaporisation of Li,O during the reaction) was ground intimately, compressed into pellet form, and fired in a platinum crucible a t 900 K for 48 h in a stream of dry oxygen-free argon.The powder S-ray diffraction pattern for the reaction product was in excellent agreement with that given by Anderson and Schieber and analyses for lithium and iron showed deviations within only 1% from the required 1 : 1 atomic ratio.Sodium ferrite was prepared in its hexagonal a-phase modificatioii by the reaction of an intimate mixture of NaOH : Fe,O, in 2 : 1 molar ratio. The reactants were heated to 620 K (above the m.p. of KaOH) in a platinum crucible under a stream of dry oxygen-free argon. 2SaOH + Fe,03 _t BNaFeO, + H20The poudcr X-ray diffraction pattern given by the orange-brown reaction product was in excellent agreement with that published by Thkry and Collongues for a-NaFeO 2.The orthorhombic F-phase of sodium ferrite and facecentred cubic potassium ferrite were each prepared by the reaction of the corresponding alkali metal carbonate with Fe,O,. I n both cases the reaction mixture, in pellet form, was fired i n ; I nickel crucible at 1175 K for 48 h in a stream of dry oxygen-free argon. The product of each reaction gave a pon-tler X-ray diffraction pattern in excellent agreement with data in the literature [Watanabe and Fukase (for P-NaFeO,) and Barth (for KFeO,)].Wiistite, ' FeO ', was prepared by the reaction of Fe,O,

X-Ray photoelectron spectroscopy has been used to study a series of chromium-oxygen compounds. It has been shown that the ionisation energy of the chromium 2p electrons is dependent primarily on the oxidation state of the chromium metal ion, but that small perturbations may be attributed to changes in crystal structure and hence the Madelung potential. Multiplet splitting in chromium(iii) compounds contributes to peak widths, and the chemisorption of water and oxygen has a marked effect on the observed peak profiles. In addition such chemisorption apparently contributes to the build up of surface charge, thereby complicating the precise determination of binding energies.WE report here a study in which X-ray photoelectron spectroscopy l y 2 has been used to monitor tlie behaviour of chromium and oxygen atoms in a series of chromium conipounds. Several studies of chromium compounds have appeared in the For example, Hendrickson et aL3 have reported values of the binding energy of the chromium 3p shell in a wide range of compounds including some oxides and several complexes. In an attempt to resolve tlie two expected oxygen lines in dichromate (vr) compounds, Brundle and Robin4 investigated the spectrum of sodium dicliromate(v~) but reported only a single peak. The very

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Use of simulation-based training is fast becoming a vital source of experiential learning in medical education. Although simulation is a common tool for undergraduate and graduate medical education curricula, the utilization of simulation in continuing medical education (CME) is still an area of growth. As more CME programs turn to simulation to address their training needs, it is important to highlight concepts of simulation technology that can help to optimize learning outcomes. This article discusses the role of fidelity in medical simulation. It provides support from a cross section of simulation training domains for determining the appropriate levels of fidelity, and it offers guidelines for creating an optimal balance of skill practice and realism for efficient training outcomes. After defining fidelity, 3 dimensions of fidelity, drawn from the human factors literature, are discussed in terms of their relevance to medical simulation. From this, research-based guidelines are provided to inform CME providers regarding the use of simulation in CME training.