Through the 'Scope: The Year in Micromounting

The Fifteenth Technical Session of the Rochester Mineralogical Symposium was held on 24 April 1998. Altogether eighteen abstracts were accepted and presented during the platform session moderated by Dr. Carl A. Francis. Submitted abstracts were reviewed by a committee consisting of Dr. Steven C. Chamberlain, Syracuse University; Dr. Carl A. Francis, Harvard University; Dr. Robert I. Gait, Royal Ontario Museum; Dr. William Kelly, New York State Geological Survey; Dr. Robert J. King, Tewksbury, Great Britain; and Dr. George W. Robinson, Michigan Technological University. The accepted abstracts follow.     

Clonidine for major vascular surgery in hypertensive patients: a double-blind, controlled, randomized study

The utility of clonidine for hypertensive patients presenting for major vascular procedures remains debatable. Twenty-one hypertensive patients presenting for aortic surgery were given clonidine (n = 11) or placebo (n = 10) in a double-blind, randomized manner. Clonidine was administered 6 micrograms/kg per os 120 min before induction of anesthesia and 3 micrograms/kg intravenously (i.v.) over 60 min from aortic declamping to skin closure. Anesthesia was induced with alfentanil 20 micrograms/kg, midazolam, and atracurium and maintained with nitrous oxide 70%, an alfentanil infusion (0.25 microgram.kg-1. min-1), and isoflurane. Anesthetic requirements, circulatory variables, interventions, and isoproterenol dose-response curves (pre- and postoperatively) were determined. Plasma concentrations of clonidine, alfentanil, and vasoactive hormones were measured. When the clonidine group was compared with the placebo group, (a) isoflurane, alfentanil, and midazolam requirements were reduced by 38%, 42%, and 41%, respectively (P = 0.04, 0.03, 0.0002, respectively); (b) supplemental circulatory and anesthetic adjustments were reduced by 51% (P = 0.0006); (c) interventions with vasopressors were not significantly increased (placebo: two; clonidine: five); (d) systolic and mean arterial pressures and heart rate were reduced; (e) increases in norepinephrine, epinephrine, and plasma renin activity were suppressed, whereas vasopressin surge was attenuated; and (f) chronotropic response to isoproterenol was unaffected. Clonidine was effective in reducing anesthetic requirements and in improving circulatory stability in hypertensive patients presenting for major vascular procedures.     

Study of the lithium insertion–deinsertion mechanism in nanocrystalline γ-Fe2O3 electrodes by means of electrochemical impedance spectroscopy

Lithium intercalation hosts are a key point to the energy density of the largely used LiCoO₂ (even if of high cost and toxicity) as well as of manganese oxides which have been investigated most extensively. Iron oxides are attractive electrode materials for low-voltage rechargeable lithium batteries from both cost and environmental standpoints. However, search for iron oxides of conventional crystalline structures and micrometer particle sizes as lithium intercalation cathodes, has been greeted with disappointing results. Here we report on the synthesis, characterizations, electrochemical study and electrochemical impedance spectroscopy (EIS) of a nanocrystalline γ-Fe₂O₃ that simultaneously exhibits high lithium insertion capacity and good capacity retention upon cycling. These properties reveal thermodynamics of the nanocrystalline material inherently different from those of its microcrystalline counterpart. Moreover, EIS showed that the intercalation process of the lithium ion occurs according to two processes involving first the reduction of the surface Fe³⁺ with concomitant charge neutralization by Li⁺ ions onto the surface defects of the nanoparticle followed by the reduction of the core Fe³⁺ with insertion of the Li⁺ deeper in the particle.