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Brisbane, Australia

While P.T.,University of Tasmania | Forbes L.K.,University of Tasmania | Crozier S.,TheUniversity of Queensland
IEEE Transactions on Biomedical Engineering | Year: 2011

Heating caused by gradient coils is a considerable concern in the operation of MRI scanners. Hot spots can occur in regions where the gradient coil windings are closely spaced. These problem areas are particularly common in the design of gradient coils with asymmetrically located target regions. In this paper, an extension of an existing coil design method is described, to enable the design of asymmetric gradient coils with reduced hot spot temperatures. An improved model is presented for predicting steady-state spatial temperature distributions for gradient coils. A great amount of flexibility is afforded by this model to consider a wide range of geometries and system material properties. A feature of the temperature distribution related to the temperature gradient is used in a relaxed fixed point iteration routine for successively altering coil windings to have a lower hot spot temperature. Results show that significant reductions in peak temperature are possible at little or no cost to coil performance when compared to minimum power coils of equivalent field error. © 2011 IEEE. Source

Roberts A.E.,TheUniversity of Queensland | Schenk G.,TheUniversity of Queensland | Gahan L.R.,TheUniversity of Queensland
European Journal of Inorganic Chemistry | Year: 2015

Purple acid phosphatases (PAPs) are the only dinuclear metallohydrolases for which the necessity for a heterovalent active site (FeIII-MII; M = Fe, Zn or Mn) for catalysis has been established. A major goal for the synthesis of PAP biomimetics is to design a ligand in which the two coordination sites exhibit discrimination between the trivalent and divalent metal ions. With this goal in mind the ligand 2-{[bis(2-methoxyethyl)amino]methyl}-6-{[(2-hydroxybenzyl)(2-pyridylmethyl)amino]methyl}-4-methylphenol (BMMHPH2), with two distinct coordination sites, N2O2 (α) and NO3 (β), has been prepared. Although not exactly mimicking the active site of PAP, the ligand facilitated the formation of the complex [FeIIIZnII(BMMHP)(CH3COO)2](BPh4), which exhibited regioselectivity in the two metal binding sites. The phosphoesterase-like activity of the complex in 50:50 acetonitrile/water was investigated by using the substrate bis(2,4-dinitrophenyl) phosphate (BDNPP) yielding kinetically relevant pKa values of 6.89, 7.37 and 9.00, a KM of 10.8±2.1 mM and a kcat of 3.20±0.38×10-3 s-1 (at pH = 7.5). Attempts to prepare a diiron analogue resulted in a centrosymmetric dimer, [FeIII2(BMMHPH)2(μ-OH)2](BPh4)2, with one six-coordinate FeIII atom in each of the α-sites, connected by two μ-hydroxido groups. In this Fe(μ-OH)2Fe diamond core the FeIII ions are weakly antiferromagnetically coupled, with J = -1.76±0.03 cm-1. The β-sites were vacant. Attempts to replace the ZnII ion with MgII resulted in the formation of a centrosymmetric trimer, i.e. [FeIII2MgII(BMMHPH)2(CH3COO)2(CH3O)2](BPh4)2. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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