Showing papers by "Brendan J. Kennedy published in 2002"
TL;DR: If the potential opportunities of the Cu-NSAIDs are to be completely realized, a mechanistic understanding and delineation of their in vivo and in vitro pharmacological activity is fundamental, along with further characterization of their pharmacokinetic/pharmacodynamic disposition.
482 citations
TL;DR: In this paper, it has been shown that the crystal structure of the orthorhombic in space group Pnma, at room temperature, changes by a continuous transition to a structure in Imma at about 685 K, then by a discontinuous transformation to tetragonal $I4/mcm$ at about 825 K, and finally, continuously, to cubic at near 950 K.
Abstract: The crystal structure of ${\mathrm{SrRuO}}_{3}$ at high temperatures has been studied at fine temperature intervals using high-resolution synchrotron diffraction. It has been shown that ${\mathrm{SrRuO}}_{3},$ orthorhombic in space group Pnma, at room temperature, changes by a continuous transition to a structure in Imma at about 685 K, then by a discontinuous transformation to tetragonal $I4/mcm$ at about 825 K, and finally, continuously, to cubic at near 950 K.
88 citations
TL;DR: In this article, it was shown that for the model proposed by Ranjan et al., the correct space group of the high-temperature monoclinic phase should be Ω(Cc).
Abstract: Ranjan et al. [Phys. Rev. B 65, 060102(R) (2002)] have recently presented results of a powder neutron-diffraction study of the high-temperature monoclinic ${(F}_{M}^{\mathrm{HT}})$ to low-temperature monoclinic ${(F}_{M}^{\mathrm{LT}})$ phase transition in $\mathrm{Pb}({\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{Zr}}_{x}){\mathrm{O}}_{3}$ discovered by Ragini et al. [Phys. Rev. B 64, 054101 (2001)]. They attribute the presence of superlattice reflections in the diffraction data to tilting of oxygen octahedra and propose a monoclinic space group $\mathrm{Pc}$ for the ${F}_{M}^{\mathrm{LT}}$ phase. It is shown that for the model proposed by Ranjan et al., the correct space group of the ${F}_{M}^{\mathrm{LT}}$ phase should be $\mathrm{Cc}.$ This has also been corroborated by a group-theoretical approach to the problem. A different set of refined structural parameters for the $\mathrm{Cc}$ space group obtained from the Rietveld analysis of the powder neutron-diffraction data of Ranjan et al. is also presented.
79 citations
TL;DR: This is the first study that has enabled the determination of the localization of the biotransformation products of Cr(VI) carcinogens in a target lung cell.
Abstract: The uptake of carcinogenic and mutagenic Cr compounds and the intracellular distribution of their biotransformation products in V79 Chinese hamster lung cells were studied by synchrotron-radiation-induced X-ray emission (SRIXE). SRIXE analysis was performed on whole cells that had been treated with either Cr(III) or Cr(V) 1,10-phenanthroline complexes, or Cr(VI). The high spatial resolution (0.3 µm) and elemental sensitivity (~10–15 g Cr/cell) of the technique provided detailed maps of Cr and other cellular elements in thin sections prepared from Cr(VI)-treated cells. The Cr carcinogen concentrated in P-rich regions corresponding to the nucleus, as well as other areas of the cell that are likely to correspond to organelles. This is the first study that has enabled the determination of the localization of the biotransformation products of Cr(VI) carcinogens in a target lung cell. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00775-002-0343-5.
53 citations
TL;DR: In this paper, a powder neutron diffraction study of the high-temperature monoclinic phase transition in the perovskite system was conducted and the most plausible space group of the phase transition was shown to be Pc.
Abstract: Results of a powder neutron diffraction study of the high-temperature monoclinic ${(F}_{M}^{\mathrm{HT}})$ to a low-temperature monoclinic ${(F}_{M}^{\mathrm{LT}})$ phase transition in $\mathrm{Pb}({\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{Zr}}_{x}){\mathrm{O}}_{3}$ discovered recently by Ragini et al. are presented for $x=0.520.$ The powder neutron diffraction pattern of the ${F}_{M}^{\mathrm{LT}}$ phase contains superlattice reflections which have all odd hkl $(h\ensuremath{
e}k\ensuremath{
e}l)$ Miller indices with respect to a doubled elementary perovskite cell, characteristic of antiphase tilting of oxygen octahed\ifmmode \acute{r}\else \'{r}\fi{}a. In analogy to other perovskite systems, the appearance of these superlattice reflections is attributed to an instability at the R point of the cubic Brillouin zone. We show that the most plausible space group of the ${F}_{M}^{\mathrm{LT}}$ phase is Pc. Results of Rietveld refinement for this space group are presented to show that the oxygen octahedra indeed undergo antiphase rotations about [001] direction.
46 citations
TL;DR: In this article, the crystal structure of the TiF3 between 20 and 450 K with emphasis on the cubic to rhombohedral structural phase transition near 370 K was examined and a remarkable difference in the thermal expansion coefficients in the two phases was observed.
38 citations
TL;DR: The structure of the SrBi 2 Ta 2 O 9 between room temperature and 1100°C has been studied using high resolution powder neutron diffraction methods as mentioned in this paper, which is consistent with a group theoretical analysis.
Abstract: The structure of SrBi 2 Ta 2 O 9 between room temperature and 1100°C has been studied using high resolution powder neutron diffraction methods. At room temperature the structure is orthorhombic (space group A 2 1 am ) and this undergoes an apparently continuous transition to a paraelectric orthorhombic phase in space group Amam near 300°C in addition to a transition above 500°C to a tetragonal structure in space group I 4/ mmm . This sequence of transitions is consistent with a group theoretical analysis. The low temperature ferroelectric phase is characterised by both rotations of the TaO 6 and displacement of the Ta atoms from the center of these octahedra, the paralectric phase contains a single tilt of the TaO 6 octahedra while there are no rotations of the TaO 6 octahedra in the high temperature tetragonal structure.
32 citations
TL;DR: In this paper, the authors used powder diffraction to determine the structure of the layered ferroelectric oxide BaBi 2 Nb 2 O 9 (BBN) above and below its Curie temperature.
Abstract: Synchrotron powder diffraction methods have been used to determine the structure of the layered ferroelectric oxide BaBi 2 Nb 2 O 9 (BBN) above and below its Curie temperature. Although BBN is found to be tetragonal above and below the ferroelectric-paraelectric transition, there is clear evidence for a structural phase transition. The low-temperature ferroelectric structure is found to be well described in space group I4mm, while the high-temperature structure is in the more common I4/mmm space group. The identification of the low-temperature tetragonal structure resolves a long-standing question as to the origin of ferroelectric behavior in BBN and related oxides.
32 citations
TL;DR: In this paper, the preparation and structural properties of the series of oxides Ca 1− x Sr x AlO 4 are described using a combination of synchrotron and neutron powder diffraction methods, it is found that the single-phase solid solutions exist only over a very limited range, x and x>0.85.
30 citations
TL;DR: In this paper, the structure of Sr0.75Ca0.25TiO3 has been studied using powder neutron diffraction and the Rietveld method in the temperature range 24-300 K.
Abstract: The structure of Sr0.75Ca0.25TiO3 has been studied using powder neutron diffraction and the Rietveld method in the temperature range 24–300 K. It is shown that new superlattice reflections characteristic of an antiferroelectric phase appear around T=185 K. The unit cell parameters change discontinuously around 185 K indicating first order nature of the antiferroelectric phase transition. Rietveld analysis of the diffraction data confirms the Pbcm space group proposed by Ranjan et al. [Phys. Rev. Lett. 84, 3726 (2000)] for the antiferroelectric phase. The most likely space group for the paraelectric phase of Sr0.75Ca0.25TiO3 is proposed to be Ibmm. The antiparallel arrangement of dipoles in the antiferroelectric phase is shown to be of very novel type mimicking long period modulated phases predicted by axial next nearest neighbor interaction type models.
20 citations
TL;DR: In this article, the authors found no evidence for any phase transitions in BaPbO3 up to 760°C, with the structure remaining in Pnma from room temperature to 660°C.
Abstract: High-resolution X-ray powder diffraction studies have shown BaPbO3 to transform from an orthorhombic Imma structure at room temperature, through an intermediate I4/mcm phase, to a cubic Pm3–mstructure above 500°C. The Imma to I4/mcm transition is first order and the I4/mcm–Pm3–m transition for BaPbO3 is tricritical in nature. We find no evidence for any phase transitions in SrPbO3 up to 760°C, the structure remaining in Pnma from room temperature to 760°C.
TL;DR: In this article, the structural changes of rare earth aluminates La1-xPrxAlO3 over a wide range of temperatures were examined using neutron powder diffraction.
Abstract: Neutron powder diffraction has been used to examine the structural changes of the rare-earth aluminates La1-xPrxAlO3 over a wide range of temperatures. At room temperature the aluminates adopt the rhombohedral perovskite structure in space group R\(\)c. In all cases heating the sample results in a transition to cubic, the transition temperature increasing linearly with Pr content. The rhombohedral structure is characterised by rotation of the oxygen atom octahedra about the threefold axis. The maximum rotation angle also increases linearly with Pr content.
TL;DR: In this article, powder diffraction methods have been used to establish the structures of four known polymorphs of bis(glycinato)copper(II) using Rietveld analysis of powder data.
Abstract: Powder diffraction methods have been used to establish the structures of four known polymorphs of bis(glycinato)copper(II). The two cis-modifications are orthorhombic, and the two trans-complexes are monoclinic. Refinements of the structures, including the location of the hydrogen/deuterium atoms have been achieved utilizing Rietveld analysis of powder data. The cis-monohydrate complex crystallizes in the space group P212121 with lattice parameters a 10.8053(3), b 5.2101(1), and c 13.4983(4) A. Upon dehydration, contraction along the a- and c-axes and elongation of the b-axis is observed. The anhydrous cis-complex also crystallizes in the space group P212121 with lattice parameters a 10.0673(7), b 5.3152(4), and c 13.212(1) A. The trans-hydrated complex crystallizes in the space group I2/a with lattice parameters a 14.8218(3), b 5.2321(1), and c 9.6408(2) A, and β 87.243(1)°. Dehydration of the complex affords the anhydrous modification which crystallizes in the space group P21/c with lattice parameters a 7.0831(6), b 5.1459(4), and c 9.4431(9) A, and β 107.506(4)°. In all four modifications a network of hydrogen bonds stabilizes the complex. This study illustrates the current capabilities of powder diffraction techniques.
TL;DR: In this article, a simple solubility model is presented to explain the phase separation of mixed metal aluminates, and the structures of these hydrogarnets have been refined from neutron or synchrotron powder X-ray diffraction (XRD) data.
TL;DR: In this article, a high-resolution synchrotron diffraction study of the temperature dependence of the structures of the two layered Bi oxides PbBi2Ta2O9 (PBT) and Pb Bi2Nb2O 9 (PBN) is reported.
Abstract: A high-resolution synchrotron diffraction study of the temperature dependence of the structures of the two layered Bi oxides PbBi2Ta2O9 (PBT) and PbBi2Nb2O9 (PBN) is reported. The transition from the low-temperature orthorhombic ferroelectric structure to the high-temperature tetragonal paraelectric structure in PBN involves an intermediate orthorhombic paraelectric phase. We conclude that this has the same Amam structure as observed in SrBi2Ta2O9 and its Bi-rich analogue. Identifying the sequence of phase transitions in PBT is more challenging since above 200 °C the structure is metrically tetragonal within the resolution of the synchrotron diffraction measurements. By contrast, neutron diffraction measurements suggest that PBT remains orthorhombic to above the Curie temperature ≈430°C. The possible identity of the intermediate space group is discussed.
TL;DR: In this article, the application of synchrotron radiation to the analysis of archaeological human dentition has been discussed, and the results of the analysis are discussed. But, they do not reveal the full extent of the effects of fluoride on the enamel defects.
TL;DR: In this article, the metal particle size and distribution on the carbon support, the surface composition and the oxidation states of the metal particles, the metal-metal and metal support interactions are important parameters to define the activity of the catalyst.
Abstract: 11% Pt/C, 10% Pt + 1% Os/C, 9% Pt + 2% Os/C, 8% Pt + 3% Os/C, 7% Pt + 4% Os/C, 6% Pt + 5% Os/C and 5% Pt + 6% Os/C catalysts have been prepared for methanol oxidation reaction. Transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction and cyclic voltammetry have been used to understand the nature of the species present in these catalysts. 7% Pt + 4% Os/C was the most active catalyst, while 8% Pt + 3% Os/C was the least active one. It is found that the metal particle size and distribution on the carbon support, the surface composition and the oxidation states of the metal particles, the metal-metal and metal support interactions are important parameters to define the activity of the catalyst.
TL;DR: The influence of Rh doping on the structure of Sr 2 RuO 4 has been investigated using neutron powder diffraction methods as discussed by the authors, showing that regardless of Rh content the MO 6 polyhedra are not regular octahedra but are elongated along the c direction.
TL;DR: In this article, high-resolution synchrotron X-ray diffraction methods have been used to study the crystal structure of Sr 0.5 Ba0.5 HfO 3 (SBH) and demonstrated the coexistence of the orthorhombic ( Imma) and tetragonal ( I 4/mcm ) phases in SBH.