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Sample records for pyrochlore structure type

  1. The pressure-induced structural response of rare earth hafnate and stannate pyrochlore from 0.1-50 GPa

    Science.gov (United States)

    Turner, K. M.; Rittman, D.; Heymach, R.; Turner, M.; Tracy, C.; Mao, W. L.; Ewing, R. C.

    2017-12-01

    Complex oxides with the pyrochlore (A2B2O7) and defect-fluorite ((A,B)4O7) structure-types undergo structural transformations under high-pressure. These compounds are under consideration for applications including as a proposed waste-form for actinides generated in the nuclear fuel cycle. High-pressure transformations in rare earth hafnates (A2Hf2O7, A=Sm, Eu, Gd, Dy, Y, Yb) and stannates (A2Sn2O7, A=Nd, Gd, Er) were investigated to 50 GPa by in situ Raman spectroscopy and synchrotron x-ray diffraction (XRD). Rare-earth hafnates form the pyrochlore structure for A=La-Tb and the defect-fluorite structure for A=Dy-Lu. Lanthanide stannates form the pyrochlore structure. Raman spectra revealed that at ambient pressure all compositions have pyrochlore-type short-range order. Stannate compositions show a larger degree of pyrochlore-type short-range ordering relative to hafnates. In situ high-pressure synchrotron XRD showed that rare earth hafnates and stannates underwent a pressure-induced phase transition to a cotunnite-like (Pnma) structure that begins between 18-25 GPa in hafnates and between 30-33 GPa in stannates. The phase transition is not complete at 50 GPa, and upon decompression, XRD indicates that all compositions transform to defect-fluorite with an amorphous component. In situ Raman spectroscopy showed that disordering in stannates and hafnates occurs gradually upon compression. Pyrochlore-structured hafnates retain short-range order to a higher pressure (30 GPa vs. <10 GPa) than defect-fluorite-structured hafnates. Hafnates and stannates decompressed from 50 GPa show Raman spectra consistent with weberite-type structures, also reported in irradiated stannates. The second-order Birch-Murnaghan equation of state fit gives a bulk modulus of 250 GPa for hafnate compositions with the pyrochlore structure, and 400 GPa for hafnate compositions with the defect-fluorite structure. Stannates have a lower bulk modulus relative to hafnates (between 80-150 GPa

  2. Pyrochlore-type catalysts for the reforming of hydrocarbon fuels

    Science.gov (United States)

    Berry, David A [Morgantown, WV; Shekhawat, Dushyant [Morgantown, WV; Haynes, Daniel [Morgantown, WV; Smith, Mark [Morgantown, WV; Spivey, James J [Baton Rouge, LA

    2012-03-13

    A method of catalytically reforming a reactant gas mixture using a pyrochlore catalyst material comprised of one or more pyrochlores having the composition A.sub.2-w-xA'.sub.wA''.sub.xB.sub.2-y-zB'.sub.yB''.sub.zO.sub.7-.DELTA.. Distribution of catalytically active metals throughout the structure at the B site creates an active and well dispersed metal locked into place in the crystal structure. This greatly reduces the metal sintering that typically occurs on supported catalysts used in reforming reactions, and reduces deactivation by sulfur and carbon. Further, oxygen mobility may also be enhanced by elemental exchange of promoters at sites in the pyrochlore. The pyrochlore catalyst material may be utilized in catalytic reforming reactions for the conversion of hydrocarbon fuels into synthesis gas (H.sub.2+CO) for fuel cells, among other uses.

  3. Incorporation of uranium in pyrochlore oxides and pressure-induced phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, F.X., E-mail: zhangfx@umich.edu [Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109 (United States); Lang, M.; Tracy, C.; Ewing, R.C. [Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109 (United States); Gregg, D.J.; Lumpkin, G.R. [Institute of Materials Engineering, ANSTO, Locked Bag 2001, Kirrawee DC 2232, NSW (Australia)

    2014-11-15

    Uranium-doped gadolinium zirconates with pyrochlore structure were studied at ambient and high-pressure conditions up to 40 GPa. The bonding environment of uranium in the structure was determined by x-ray photoelectron and Raman spectroscopies and x-ray diffraction. The uranium valence for samples prepared in air is mainly U{sup 6+}, but U{sup 4+} is present in pyrochlores fabricated in an argon atmosphere. Rietveld refinement of the XRD pattern suggests that uranium ions in pyrochlores are on the 16d site in 6-fold coordination with oxygen. At pressures greater than 22 GPa, the pyrochlore structure transformed to a cotunnite-type phase. The cotunnite high-pressure phase transformed to a defect fluorite structure on the release of pressure. - Graphical abstract: In U-bearing pyrochlore, U ions mainly occupy the 16d site and replace the smaller Zr{sup 4+}, part of the oxygen will occupy the 8b site, which is empty to most pyrochlores. At pressure of 22 GPa, the pyrochlore lattice is not stable and transforms to a cotunnite-type structure. The high-pressure structure is not stable and transform to a fluorite or back to the pyrochlore structure when pressure is released. - Highlights: • We found that U ions mainly occupy the smaller cation site in U-bearing pyrochlore. • Pyrochlore structure is not stable at pressure of more than 20 GPa. • The quenched sample has a pyrochlore or a disordered fluorite structure.

  4. Structural and photoluminescence properties of stannate based displaced pyrochlore-type red phosphors: Ca(3-x)Sn₃Nb₂O₁₄:xEu³⁺.

    Science.gov (United States)

    Sreena, T S; Prabhakar Rao, P; Francis, T Linda; Raj, Athira K V; Babu, Parvathi S

    2015-05-14

    New stannate based displaced pyrochlore-type red phosphors, Ca(3-x)Sn3Nb2O14:xEu(3+), were prepared via a conventional solid state method. The influence of partial occupancy of Sn in both A and B sites of the pyrochlore-type oxides on the photoluminescence properties was studied using powder X-ray diffraction, FT-Raman, transmission electron microscopy, scanning electron microscopy with energy dispersive spectrometry, UV-visible absorption spectroscopy, and photoluminescence excitation and emission spectra with lifetime measurements. The structural analysis establishes that these oxides belong to a cubic displaced pyrochlore type structure with a space group Fd3̄m. These phosphors exhibit strong absorptions at near UV and blue wavelength regions and emit intense multiband emissions due to Eu(3+ 5)D0-(7)F(0, 1, 2) transitions. The absence of characteristic MD transition splitting points out that local cation disorder exists in this type of displaced pyrochlores, reducing the D(3d) inversion symmetry, which is not evidenced by such disorder in the X-ray diffraction analysis. The unusual forbidden intense sharp (5)D0-(7)F0 transition indicates single site occupancy of Eu(3+) with a narrower range of bonding environment, preventing the cluster formation. This is supported by the stable (5)D0 lifetime with Eu(3+) concentration. The Judd-Ofelt intensity parameter assessment corroborates these results. The CIE color coordinates of these phosphors were found to be (0.60, 0.40), which are close to the NTSC standard values (0.67, 0.33) for a potential red phosphor.

  5. Investigation into the magnetic properties of pyrochlore-type rare-earth hafnates

    Energy Technology Data Exchange (ETDEWEB)

    Chun, Jung Hwan; Kremer, Reinhard K.; Lin, Chengtian [MPI for Solid State Research, Stuttgart (Germany)

    2015-07-01

    Cubic rare-earths transition metal pyrochlores with composition R{sub 2}TM{sub 2}O{sub 7} have attracted broad attention because of their unusual magnetic ground state properties related to geometrical frustration of the pyrochlores lattice. So far, the investigation focused mainly on 3d and 4d transition metal systems. The magnetic properties of rare-earths 5d TM pyrochlores are comparatively less well studied. Here we report on the single-crystal growth and the magnetic properties of some rare-earth hafnates (R =Nd, Gd, Dy; TM = Hf) of composition R{sub 2}Hf{sub 2}O{sub 7}. Nd{sub 2}Hf{sub 2}O{sub 7} and Gd{sub 2}Hf{sub 2}O{sub 7} crystallize with the cubic pyrochlores structure whereas diverging reports on the structure of Dy{sub 2}Hf{sub 2}O{sub 7} are available in literature. Crystals of R{sub 2}Hf{sub 2}O{sub 7} have been grown and their structural and magnetic properties have been investigated. Our investigations confirm Nd{sub 2}Hf{sub 2}O{sub 7} and Gd{sub 2}Hf{sub 2}O{sub 7} to crystallize in the cubic pyrochlores structure. Antiferromagnetic ordering below ∝0.5 K has been observed by magnetic susceptibility and heat capacity measurements for both compounds.

  6. Analysis of coordination polyhedra symmetry in pyrochlore and zirconolite structures

    International Nuclear Information System (INIS)

    Troole, A.Y.; Stefanovsky, S.V.

    1999-01-01

    Zirconolite and pyrochlore are considered as promising host phases for high level waste (HLW). However, correct information on substitution mechanisms, forms of dopants incorporation in their structures and distortions in coordination polyhedra is presently unavailable. To clarify these points the authors use the electron paramagnetic resonance (EPR). Pyrochlore and three of zirconolite polytypes: zirconolite-2M, zirconolite-3T, and zirconolite-3O are considered. Pyrochlore is the parent structure for zirconolite since any zirconolite variety is produced by means of distortion of the initial pyrochlore structure. Space groups of pyrochlore and basic polymorphous zirconolite varieties found from XRD and TEM data, as well as interatomic distances and angles, were taken from reference data. This allows the determination of the most probable sites for impurities, substitution mechanisms, and local symmetry of coordination polyhedra (initial). Ions chosen for EPR were Gd(III) as an analog of trivalent rare earth and actinide elements which are also occurred in HLW and Fe(III) as a typical corrosion product which occurs in all HLW. For Gd(III) a strong ligand field approximation is suggested, theoretical computation using perturbation theory in this approximation has been carried out. All the non-diagonal members plus magnetic field were chosen as perturbation and formulate for transition frequencies, estimations of fine structure and g-factors parameters in the given approximation have been obtained

  7. Pyrochlore type semiconducting ceramic oxides in Ca-Ce-Ti-M-O system (M = Nb or Ta)-Structure, microstructure and electrical properties

    International Nuclear Information System (INIS)

    Deepa, M.; Prabhakar Rao, P.; Radhakrishnan, A.N.; Sibi, K.S.; Koshy, Peter

    2009-01-01

    A new series of pyrochlore type ceramic semiconducting oxides in Ca-Ce-Ti-M-O (M = Nb or Ta) system has been synthesized by the conventional ceramic route. The electrical conductivity measurements show that these oxides exhibit semiconducting behavior and the conductivity increases with the Ce content in the compound. Activation energy of the current carriers is in the range of 0.5-1.6 eV. The electrical conductivity in these oxides is due to the presence of Ce 3+ , which remains in the reduced state without being oxidized to Ce 4+ by structural stabilization. The photoluminescence and X-ray photoelectron spectroscopy analysis corroborate the presence of Ce in the 3+ state. Impedance spectral analysis is carried out to evaluate the transport properties and indicates that the conduction in these compounds is mainly due to electronic contribution. The X-ray powder diffraction and Raman spectroscopy analysis establishes that these oxides belong to a cubic pyrochlore type structure.

  8. Pyrochlore type semiconducting ceramic oxides in Ca-Ce-Ti-M-O system (M = Nb or Ta)-Structure, microstructure and electrical properties

    Energy Technology Data Exchange (ETDEWEB)

    Deepa, M. [Materials and Minerals Division, National Institute for Interdisciplinary Science and Technology (NIIST), Trivandrum 695019 (India); Prabhakar Rao, P., E-mail: padala_rao@yahoo.com [Materials and Minerals Division, National Institute for Interdisciplinary Science and Technology (NIIST), Trivandrum 695019 (India); Radhakrishnan, A.N.; Sibi, K.S.; Koshy, Peter [Materials and Minerals Division, National Institute for Interdisciplinary Science and Technology (NIIST), Trivandrum 695019 (India)

    2009-07-01

    A new series of pyrochlore type ceramic semiconducting oxides in Ca-Ce-Ti-M-O (M = Nb or Ta) system has been synthesized by the conventional ceramic route. The electrical conductivity measurements show that these oxides exhibit semiconducting behavior and the conductivity increases with the Ce content in the compound. Activation energy of the current carriers is in the range of 0.5-1.6 eV. The electrical conductivity in these oxides is due to the presence of Ce{sup 3+}, which remains in the reduced state without being oxidized to Ce{sup 4+} by structural stabilization. The photoluminescence and X-ray photoelectron spectroscopy analysis corroborate the presence of Ce in the 3+ state. Impedance spectral analysis is carried out to evaluate the transport properties and indicates that the conduction in these compounds is mainly due to electronic contribution. The X-ray powder diffraction and Raman spectroscopy analysis establishes that these oxides belong to a cubic pyrochlore type structure.

  9. Electronic Structure of the Pyrochlore-Type Ru Oxides through the Metal--Insulator Transition

    International Nuclear Information System (INIS)

    Okamoto, J.; Fujimori, S.I.; Okane, T.; Fujimori, A.; Abbate, M.; Yoshii, S.; Sato, M.

    2003-01-01

    The electronic structures of the pyrochlore-type Ru oxides Sm 2-x Ca x Ru 2 O 7 and Sm 2-x Bi x Ru 2 O 7 , which show metal-insulator transition with increasing Ca or Bi concentration, have been studied by ultraviolet photoemission spectroscopy. Spectral changes near the Fermi level are different but reflect the tendency of their transport properties in both systems. The Sm 2-x Ca x Ru 2 O 7 system shows an energy shift, which is expected from the increase of hole in the Ru 4d t 2g band and the Sm 2 - x Bi x Ru 2 O 7 system shows spectral weight transfer within the Ru 4d t 2g band, which is expected to be observed in bandwidth-control Mott-Hubbard system. (author)

  10. The fluorite-pyrochlore transformation of Ho2-yNdyZr2O7

    International Nuclear Information System (INIS)

    Clements, Richard; Hester, James R.; Kennedy, Brendan J.; Ling, Chris D.; Stampfl, Anton P.J.

    2011-01-01

    Twelve members of the Ho 2-y Nd y Zr 2 O 7 series, prepared using conventional solid state methods, have been characterised by neutron powder diffraction. Ho 2 Zr 2 O 7 has a defect fluorite structure whereas Nd 2 Zr 2 O 7 is found to adopt the ordered pyrochlore structure with the composition induced fluorite-pyrochlore transformation occurring near y=1. Rietveld analysis on the neutron data for all the compositions reveals an increase in lattice parameter as a function of y across the entire series, with a small discontinuity associated with the transformation. The neutron profile results suggest that domains of pyrochlore-type initially begin to form before crystallising into a separate phase, and therefore that anion and cation ordering processes are distinct. There is a strong correlation between the extent of disorder in the anion sublattice and the x-parameter of 48f oxygen. These results point the way to a better understanding of the stability observed in pyrochlore structures. - Graphical abstract: Neutron diffraction profiles for Nd 2-y Ho y Zr 2 O 7 type oxides reveal details of the transformation from the ordered pyrochlore structure (y=0) to the disordered fluorite structure (y=2). Highlights: → Structures of twelve members of the Ho 2-y Nd y Zr 2 O 7 series studied using neutron powder diffraction. → Domains of pyrochlore-type materials form at low doping levels. → Higher doping stabilises the pyrochlore. → Anion and cation ordering processes are distinct.

  11. Synthesis, crystal structure, and magnetic properties of pyrochlore-type Eu{sub 2}Ta{sub 2}(O,N){sub 7+δ}

    Energy Technology Data Exchange (ETDEWEB)

    Anke, Bjoern; Hund, Sophie; Lorent, Christian; Lerch, Martin [Institut fuer Chemie, Technische Universitaet Berlin (Germany); Janka, Oliver; Block, Theresa; Poettgen, Rainer [Institut fuer Anorganische und Analytische Chemie, Universitaet Muenster (Germany)

    2017-12-13

    Pyrochlore-type Eu{sub 2}Ta{sub 2}(O,N){sub 7+δ} phases were prepared by reaction of ammonia with an amorphous europium tantalum oxide precursor. {sup 151}Eu Moessbauer and EPR spectroscopy as well as magnetic susceptibility measurements point to the presence of exclusively Eu{sup 3+}. For phase-pure samples (X-ray powder diffraction), the nitrogen content varies between 1.0 and 1.8 wt %, leading to compositions in the range Eu{sub 2}Ta{sub 2}O{sub 7.1}N{sub 0.6} - Eu{sub 2}Ta{sub 2}O{sub 6.5}N{sub 1.0}. Pyrochlore-type phases are structurally derived from the fluorite type with 1/8 of the anions missing, resulting in an ideal composition A{sub 2}B{sub 2}X{sub 7}. In Eu{sub 2}Ta{sub 2}(O,N){sub 7+δ} the excess anions partly occupy these vacancies. The prepared phases are colorless with a direct optical bandgap of 4.3 eV and they show the typical Van Vleck paramagnetic behavior known for trivalent Eu atoms. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  12. Investigation of annealed and metamict pyrochlore minerals by x-ray absorption spectroscopy

    International Nuclear Information System (INIS)

    Greegor, R.B.; Lytle, F.W.; Ewing, R.C.; Chakoumakos, B.C.; Lumpkin, G.R.

    1984-01-01

    Materials of the pyrochlore structure type exhibit a variety of interesting properties including phases capable of acting as hosts for actinides in radioactive wastes. Studies of curium doped gadolinium titanate phases (Gd 2 Ti 2 O 7 ) have been made which showed that the radiation damage ingrowth followed an exponential relationship. For the study reported here a series of synthetic pyrochlores were produced having the titanate phase with the general formula (RE) 2 Ti 2 O 7 , RE = Er, Y 2 , Gd 2 , Dy, La. Additionally a set of metamict (radiation damaged) pyrochlores was examined in both a natural and post temperature annealed state. Experiments were conducted on these samples using the Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) techniques. In summary, these studies show that in pyrochlore structure types the Ti-O cage undergoes changes due to radiation damage. The individual Ti-O bonds become more disordered which leads to a loss of short and long range order and, ultimately, to expansion of the bulk material. 2 refs., 2 figs

  13. Structural properties of the geometrically frustrated pyrochlore Tb2Ti2O7

    International Nuclear Information System (INIS)

    Han, Sang-Wook; Gardner, Jason S.; Booth, Corwin H.

    2004-01-01

    Although materials that exhibit nearest-neighbor-only antiferromagnetic interactions and geometrical frustration theoretically should not magnetically order in the absence of disorder, few such systems have been observed experimentally. One such system appears to be the pyrochlore Tb 2 Ti 2 O 7 . However, previous structural studies indicated that Tb 2 Ti 2 O 7 is an imperfect pyrochlore. To clarify the situation, we performed neutron powder diffraction (NPD) and x-ray absorption fine structure (XAFS) measurements on samples that were prepared identically to those that show no magnetic order. The NPD measurements show that the long-range structure of Tb 2 Ti 2 O 7 is well ordered with no structural transitions between 4.5 and 600 K. In particular, mean-squared displacements (u 2 's) for each site follow a Debye model with no offsets. No evidence for Tb/Ti site interchange was observed within an upper limit of 2%. Likewise, no excess or deficiency in the oxygen stoichiometry was observed, within an upper limit of 2% of the nominal pyrochlore value. Tb L III and Ti K-edge XAFS measurements from 20-300 K similarly indicate a well-ordered local structure. Other aspects of the structure are considered. We conclude that Tb 2 Ti 2 O 7 has, within experimental error, an ideal, disorder-free pyrochlore lattice, thereby allowing the system to remain in a dynamic, frustrated spin state to the lowest observed temperatures

  14. Ion-Exchange Reaction Of A-Site In A2Ta2O6 Pyrochlore Crystal Structure

    Directory of Open Access Journals (Sweden)

    Matsunami M.

    2015-06-01

    Full Text Available Na+ or K+ ion rechargeable battery is started to garner attention recently in Place of Li+ ion cell. It is important that A+ site ion can move in and out the positive-electrode materials. When K2Ta2O6 powder had a pyrochlore structure was only dipped into NaOH aqueous solution at room temperature, Na2Ta2O6 was obtained. K2Ta2O6 was fabricated from a tantalum sheet by a hydrothermal synthesize with KOH aqueous solution. When Na2Ta2O6 was dipped into KOH aqueous solution, K2Ta2O6 was obtained again. If KTaO3 had a perovskite structure was dipped, Ion-exchange was not observed by XRD. Because a lattice constant of pyrochlore structure of K-Ta-O system is bigger than perovskite, K+ or Na+ ion could shinny through and exchange between Ta5+ and O2− ion site in a pyrochlore structure. K+ or Na+ ion exchange of A2Ta2O6 pyrochlore had reversibility. Therefore, A2Ta2O6 had a pyrochlore structure can be expected such as Na+ ion rechargeable battery element.

  15. Structural properties of the geometrically frustrated pyrochlore Tb2Ti2O7

    Energy Technology Data Exchange (ETDEWEB)

    Han, Sang-Wook; Gardner, Jason S.; Booth, Corwin H.

    2004-06-14

    Although materials that exhibit nearest-neighbor-only antiferromagnetic interactions and geometrical frustration theoretically should not magnetically order in the absence of disorder, few such systems have been observed experimentally. One such system appears to be the pyrochlore Tb{sub 2}Ti{sub 2}O{sub 7}. However, previous structural studies indicated that Tb{sub 2}Ti{sub 2}O{sub 7} is an imperfect pyrochlore. To clarify the situation, we performed neutron powder diffraction (NPD) and x-ray absorption fine structure (XAFS) measurements on samples that were prepared identically to those that show no magnetic order. The NPD measurements show that the long-range structure of Tb{sub 2}Ti{sub 2}O{sub 7} is well ordered with no structural transitions between 4.5 and 600 K. In particular, mean-squared displacements (u{sup 2}'s) for each site follow a Debye model with no offsets. No evidence for Tb/Ti site interchange was observed within an upper limit of 2%. Likewise, no excess or deficiency in the oxygen stoichiometry was observed, within an upper limit of 2% of the nominal pyrochlore value. Tb L{sub III} and Ti K-edge XAFS measurements from 20-300 K similarly indicate a well-ordered local structure. Other aspects of the structure are considered. We conclude that Tb{sub 2}Ti{sub 2}O{sub 7} has, within experimental error, an ideal, disorder-free pyrochlore lattice, thereby allowing the system to remain in a dynamic, frustrated spin state to the lowest observed temperatures.

  16. New Type of Quantum Criticality in the Pyrochlore Iridates

    Directory of Open Access Journals (Sweden)

    Lucile Savary

    2014-11-01

    Full Text Available Magnetic fluctuations and electrons couple in intriguing ways in the vicinity of zero-temperature phase transitions—quantum critical points—in conducting materials. Quantum criticality is implicated in non-Fermi liquid behavior of diverse materials and in the formation of unconventional superconductors. Here, we uncover an entirely new type of quantum critical point describing the onset of antiferromagnetism in a nodal semimetal engendered by the combination of strong spin-orbit coupling and electron correlations, and which is predicted to occur in the iridium oxide pyrochlores. We formulate and solve a field theory for this quantum critical point by renormalization group techniques and show that electrons and antiferromagnetic fluctuations are strongly coupled and that both these excitations are modified in an essential way. This quantum critical point has many novel features, including strong emergent spatial anisotropy, a vital role for Coulomb interactions, and highly unconventional critical exponents. Our theory motivates and informs experiments on pyrochlore iridates and constitutes a singular realistic example of a nontrivial quantum critical point with gapless fermions in three dimensions.

  17. Thermal annealing of natural, radiation-damaged pyrochlore

    Energy Technology Data Exchange (ETDEWEB)

    Zietlow, Peter; Mihailova, Boriana [Hamburg Univ. (Germany). Dept. of Earth Sciences; Beirau, Tobias [Hamburg Univ. (Germany). Dept. of Earth Sciences; Stanford Univ., CA (United States). Dept. of Geological Sciences; and others

    2017-03-01

    Radiation damage in minerals is caused by the α-decay of incorporated radionuclides, such as U and Th and their decay products. The effect of thermal annealing (400-1000 K) on radiation-damaged pyrochlores has been investigated by Raman scattering, X-ray powder diffraction (XRD), and combined differential scanning calorimetry/thermogravimetry (DSC/TG). The analysis of three natural radiation-damaged pyrochlore samples from Miass/Russia [6.4 wt% Th, 23.1.10{sup 18} α-decay events per gram (dpg)], Panda Hill/Tanzania (1.6 wt% Th, 1.6.10{sup 18} dpg), and Blue River/Canada (10.5 wt% U, 115.4.10{sup 18} dpg), are compared with a crystalline reference pyrochlore from Schelingen (Germany). The type of structural recovery depends on the initial degree of radiation damage (Panda Hill 28%, Blue River 85% and Miass 100% according to XRD), as the recrystallization temperature increases with increasing degree of amorphization. Raman spectra indicate reordering on the local scale during annealing-induced recrystallization. As Raman modes around 800 cm{sup -1} are sensitive to radiation damage (M. T. Vandenborre, E. Husson, Comparison of the force field in various pyrochlore families. I. The A{sub 2}B{sub 2}O{sub 7} oxides. J. Solid State Chem. 1983, 50, 362, S. Moll, G. Sattonnay, L. Thome, J. Jagielski, C. Decorse, P. Simon, I. Monnet, W. J. Weber, Irradiation damage in Gd{sub 2}Ti{sub 2}O{sub 7} single crystals: Ballistic versus ionization processes. Phys. Rev. 2011, 84, 64115.), the degree of local order was deduced from the ratio of the integrated intensities of the sum of the Raman bands between 605 and 680 cm{sup -1} divided by the sum of the integrated intensities of the bands between 810 and 860 cm{sup -1}. The most radiation damaged pyrochlore (Miass) shows an abrupt recovery of both, its short- (Raman) and long-range order (X-ray) between 800 and 850 K, while the weakly damaged pyrochlore (Panda Hill) begins to recover at considerably lower temperatures (near 500 K

  18. Structural response of titanate pyrochlores to swift heavy ion irradiation

    International Nuclear Information System (INIS)

    Shamblin, Jacob; Tracy, Cameron L.; Ewing, Rodney C.; Zhang, Fuxiang; Li, Weixing; Trautmann, Christina; Lang, Maik

    2016-01-01

    The structure, size, and morphology of ion tracks resulting from irradiation of five different pyrochlore compositions (A 2 Ti 2 O 7 , A = Yb, Er, Y, Gd, Sm) with 2.2 GeV 197 Au ions were investigated by means of synchrotron X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Radiation-induced amorphization occurred in all five materials analyzed following an exponential rate as a function of ion fluence. XRD patterns showed a general trend of increasing susceptibility of amorphization with increasing ratio of A- to B-site cation ionic radii (r A /r B ) with the exception of Y 2 Ti 2 O 7 and Sm 2 Ti 2 O 7 . This indicates that the track size does not necessarily increase with r A /r B , in contrast with results from previous swift heavy ion studies on Gd 2 Zr 2-x Ti x O 7 pyrochlore materials. For Y 2 Ti 2 O 7 , this effect is attributed to the significantly lower electron density of this material relative to the lanthanide-bearing pyrochlores, thus lowering the electronic energy loss (dE/dx) of the high-energy ions in this composition. An energy loss normalization procedure was performed which reveals an initial increase of amorphous track size with r A /r B that saturates above a cation radius ratio larger than Gd 2 Ti 2 O 7 . This is in agreement with previous low-energy ion irradiation experiments and first principles calculations of the disordering energy of titanate pyrochlores indicating that the same trends in disordering energy apply to radiation damage induced in both the nuclear and electronic energy loss regimes. HRTEM images indicate that single ion tracks in Yb 2 Ti 2 O 7 and Er 2 Ti 2 O 7 , which have small A-site cations and low r A /r B , exhibit a core-shell structure with a small amorphous core surrounded by a larger disordered shell. In contrast, single tracks in Gd 2 Ti 2 O 7 and Sm 2 Ti 2 O 7 , have a larger amorphous core with minimal disordered shells.

  19. Structures and solid solution mechanisms of pyrochlore phases in the systems Bi2O3-ZnO-(Nb, Ta)2O5

    International Nuclear Information System (INIS)

    Tan, K.B.; Khaw, C.C.; Lee, C.K.; Zainal, Z.; Miles, G.C.

    2010-01-01

    Research highlights: → Combined XRD and ND Rietveld structural refinement of pyrochlores. → Structures and solid solution mechanisms of Bi-pyrochlores. → Bi and Zn displaced off-centre to different 96g A-site positions. → Summary of composition-structure-property of Bi-pyrochlores. - Abstract: The crystal structures of two pyrochlore phases have been determined by Rietveld refinement of combined X-ray and neutron powder diffraction data. These are stoichiometric, Bi 1.5 ZnTa 1.5 O 7 and non-stoichiometric Bi 1.56 Zn 0.92 Nb 1.44 O 6.86 . In both structures, Zn is distributed over A- and B-sites; Bi and Zn are displaced off-centre, to different 96g A-site positions; of the three sets of oxygen positions, O(1) are full, O(2) contain vacancies and O(3) contain a small number of oxygen, again in both cases. Comparisons between these structures, those of related Sb analogues and literature reports are made.

  20. Structural disorder and transport in ternary oxides with the pyrochlore structure. Final report; FINAL

    International Nuclear Information System (INIS)

    Tuller, Harry L.

    2001-01-01

    This research program has focused on the structure-electrical property relations in families of pyrochlore compounds which exhibit, on the one hand, controlled levels of structural disorder and on the other, controlled levels of ionic and electronic conductivities. Models have been developed to evaluate the often complex defect chemistry of these systems. Much progress has been made in extracting key thermodynamic and kinetic data. From a technological standpoint, novel solid electrolytes and compatible mixed conducting electrodes have been identified and the concept of the single phase monolithic fuel cell design has been demonstrated and patented. Related work on lanthanum gallate-based perovskites has shown even more promising results for use of such materials in the monolithic fuel cell structures. Recent work on the Bi(sub 3)Zn(sub 2)Sb(sub 3)O(sub 14) Pyrochlore, a phase found at grain boundaries in varistors, was also completed. This material was found to be a mixed ionic-electronic conductor with interesting implications for grain boundary equilibration kinetics in SnO-base varistor materials. Three of the most recent projects are summarized in this paper. The results of work on the perovskites are reported in recent publications

  1. High-Performance Pyrochlore-Type Yttrium Ruthenate Electrocatalyst for Oxygen Evolution Reaction in Acidic Media

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jaemin [Department; Shih, Pei-Chieh [Department; Tsao, Kai-Chieh [Department; Pan, Yung-Tin [Department; Yin, Xi [Department; Sun, Cheng-Jun [X-ray; Yang, Hong [Department

    2017-08-17

    Development of acid-stable electrocatalysts with low overpotential for oxygen evolution reaction (OER) is a major challenge for the production of hydrogen directly from water. We report in this paper a pyrochlore yttrium ruthenate (Y2Ru2O7-δ) electrocatalyst that has significantly enhanced performance towards OER in acid media over the best-known catalysts, with an onset overpotential of 190 mV and high stability in 0.1-M perchloric acid solution. X-ray absorption near-edge structure (XANES) indicates Y2Ru2O7-δ electrocatalyst had a low valence state that favors the high OER activity. Density functional theory (DFT) calculation shows this pyrochlore has lower band center energy for the overlap between Ru 4d and O 2p orbitals and therefore more stable Ru-O bond than RuO2, highlighting the effect of yttrium on the enhancement in stability. The Y2Ru2O7-δ pyrochlore is also free of expensive iridium metal, thus a cost-effective candidate for practical applications.

  2. Adiabatic cooling processes in frustrated magnetic systems with pyrochlore structure

    Science.gov (United States)

    Jurčišinová, E.; Jurčišin, M.

    2017-11-01

    We investigate in detail the process of adiabatic cooling in the framework of the exactly solvable antiferromagnetic spin-1/2 Ising model in the presence of the external magnetic field on an approximate lattice with pyrochlore structure. The behavior of the entropy of the model is studied and exact values of the residual entropies of all ground states are found. The temperature variation of the system under adiabatic (de)magnetization is investigated and the central role of the macroscopically degenerated ground states in cooling processes is explicitly demonstrated. It is shown that the model parameter space of the studied geometrically frustrated system is divided into five disjunct regions with qualitatively different processes of the adiabatic cooling. The effectiveness of the adiabatic (de)magnetization cooling in the studied model is compared to the corresponding processes in paramagnetic salts. It is shown that the processes of the adiabatic cooling in the antiferromagnetic frustrated systems are much more effective especially in nonzero external magnetic fields. It means that the frustrated magnetic materials with pyrochlore structure can be considered as very promising refrigerants mainly in the situations with nonzero final values of the magnetic field.

  3. Pyrochlore as nuclear waste form. Actinide uptake and chemical stability

    International Nuclear Information System (INIS)

    Finkeldei, Sarah Charlotte

    2015-01-01

    Radioactive waste is generated by many different technical and scientific applications. For the past decades, different waste disposal strategies have been considered. Several questions on the waste disposal strategy remain unanswered, particularly regarding the long-term radiotoxicity of minor actinides (Am, Cm, Np), plutonium and uranium. These radionuclides mainly arise from high level nuclear waste (HLW), specific waste streams or dismantled nuclear weapons. Although many countries have opted for the direct disposal of spent fuel, from a scientific and technical point of view it is imperative to pursue alternative waste management strategies. Apart from the vitrification, especially for trivalent actinides and Pu, crystalline ceramic waste forms are considered. In contrast to glasses, crystalline waste forms, which are chemically and physically highly stable, allow the retention of radionuclides on well-defined lattice positions within the crystal structure. Besides polyphase ceramics such as SYNROC, single phase ceramics are considered as tailor made host phases to embed a specific radionuclide or a specific group. Among oxidic single phase ceramics pyrochlores are known to have a high potential for this application. This work examines ZrO 2 based pyrochlores as potential nuclear waste forms, which are known to show a high aqueous stability and a high tolerance towards radiation damage. This work contributes to (1) understand the phase stability field of pyrochlore and consequences of non-stoichiometry which leads to pyrochlores with mixed cationic sites. Mixed cationic occupancies are likely to occur in actinide-bearing pyrochlores. (2) The structural uptake of radionuclides themselves was studied. (3) The chemical stability and the effect of phase transition from pyrochlore to defect fluorite were probed. This phase transition is important, as it is the result of radiation damage in ZrO 2 based pyrochlores. ZrO 2 - Nd 2 O 3 pellets with pyrochlore and defect

  4. Characterization, Microstructure, and Dielectric properties of cubic pyrochlore structural ceramics

    KAUST Repository

    Li, Yangyang

    2013-05-01

    The (BMN) bulk materials were sintered at 1050°C, 1100°C, 1150°C, 1200°C by the conventional ceramic process, and their microstructure and dielectric properties were investigated by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Transmission electron microscopy (TEM) (including the X-ray energy dispersive spectrometry EDS and high resolution transmission electron microscopy HRTEM) and dielectric impedance analyzer. We systematically investigated the structure, dielectric properties and voltage tunable property of the ceramics prepared at different sintering temperatures. The XRD patterns demonstrated that the synthesized BMN solid solutions had cubic phase pyrochlore-type structure when sintered at 1050°C or higher, and the lattice parameter (a) of the unit cell in BMN solid solution was calculated to be about 10.56Å. The vibrational peaks observed in the Raman spectra of BMN solid solutions also confirmed the cubic phase pyrochlore-type structure of the synthesized BMN. According to the Scanning Electron Microscope (SEM) images, the grain size increased with increasing sintering temperature. Additionally, it was shown that the densities of the BMN ceramic tablets vary with sintering temperature. The calculated theoretical density for the BMN ceramic tablets sintered at different temperatures is about 6.7521 . The density of the respective measured tablets is usually amounting more than 91% and 5 approaching a maximum value of 96.5% for sintering temperature of 1150°C. The microstructure was investigated by using Scanning Transmission Electron Microscope (STEM), X-ray diffraction (XRD). Combined with the results obtained from the STEM and XRD, the impact of sintering temperature on the macroscopic and microscopic structure was discussed. The relative dielectric constant ( ) and dielectric loss ( ) of the BMN solid solutions were measured to be 161-200 and (at room temperature and 100Hz-1MHz), respectively. The BMN solid

  5. Properties and recrystallization of radiation damaged pyrochlore and titanite

    Energy Technology Data Exchange (ETDEWEB)

    Zietlow, Peter

    2016-11-02

    Radiation damage in minerals is caused by the alpha-decay of incorporated radionuclides, such as U and Th and their decay products. The effect of thermal annealing (400-1400 K) on radiation-damaged pyrochlores has been investigated by Raman scattering, X-ray powder diffraction (XRD), and combined differential scanning calorimetry/thermogravimetry (DSC/TG) (Zietlow et al., in print). The analysis of three natural radiation-damaged pyrochlore samples from Miass/Russia (6.4 wt% Th, 23.1.10{sup 18} a-decay events per gram (dpg)), Zlatoust/Russia (6.3 wt% Th, 23.1.10{sup 18} dpg), Panda Hill/Tanzania (1.6 wt% Th, 1.6.10{sup 18} dpg), and Blue River/Canada (10.5 wt% U, 115.4.10{sup 18} dpg), are compared with a crystalline reference pyrochlore from Schelingen (Germany). The type of structural recovery depends on the initial degree of radiation damage (Panda Hill 28 %, Blue River 85 %, Zlatoust and Miass 100 % according to XRD), as the recrystallization temperature increases with increasing degree of amorphization. Raman spectra indicate reordering on the local scale during annealing-induced recrystallization. As Raman modes around 800 cm{sup -1} are sensitive to radiation damage (Vandenborre and Husson 1983, Moll et al. 2011), the degree of local order was deduced from the ratio of the integrated intensities of the sum of the Raman bands between 605 and 680 cm{sup -1} devided by the sum of the integrated intensities of the bands between 810 and 860 cm{sup -1}. The most radiation damaged pyrochlores (Miass and Zlatoust) show an abrupt recovery of both, its short- (Raman) and long-range order (X-ray) between 800 and 850 K. The volume decrease upon recrystallization in Zlatoust pyrochlore was large enough to crack the sample repeatedly. In contrast, the weakly damaged pyrochlore (Panda Hill) begins to recover at considerably lower temperatures (near 500 K), extending over a temperature range of ca. 300 K, up to 800 K (Raman). The pyrochlore from Blue River shows in its

  6. Atomic-scale microstructures, Raman spectra and dielectric properties of cubic pyrochlore-typed Bi1.5MgNb1.5O7 dielectric ceramics

    KAUST Repository

    Li, Yangyang

    2014-07-01

    Single-phase cubic pyrochlore-typed Bi1.5MgNb 1.5O7 (BMN) dielectric ceramics were synthesized at temperatures of 1050-1200 °C by solid-state reaction method. Their atomic-scale microstructures and dielectric properties were investigated. X-ray diffraction patterns revealed that the BMN ceramics had an average cubic pyrochlore structure, whereas the Raman spectra indicated that they had an essentially cubic symmetry with small local deviations at the A and O\\' sites of the cubic pyrochlore structure. This was confirmed by selected electron area diffraction (SAED) patterns, where the reflections of {442} (not allowed in the cubic pyrochlore with Fd3̄m symmetry) were clearly observed. SEM and TEM images revealed that the average grain size was increased with the sintering temperature, and an un-homogeneous grain growth was observed at high temperatures. HRTEM images and SAED patterns revealed the single-crystalline nature of the BMN ceramic grains. Energy dispersive spectroscopy (EDS) elemental mapping studies indicated that the compositional distributions of Bi, Mg, Nb and O elements in the ceramic grains were homogenous, and no elemental precipitation was observed at the grain boundary. Quantitative EDS data on ceramic grains revealed the expected cationic stoichiometry based on the initial composition of Bi1.5MgNb1.5O7. Dielectric constants of all the BMN samples exhibited almost frequency independent characteristic in the frequency range of 102-106 Hz, and the highest value was 195 for the BMN ceramics sintered at sintered at 1150 °C with the highest bulk density. The dielectric losses were stable and less than 0.002 in the frequency range of 102-105 Hz. The high dielectric constants of the present BMN samples can be ascribed to the local atomic deviations at the A and O\\' sites from the ideal atomic positions of the pyrochlore structure, which affect the different polarization mechanisms in the BMN ceramics, and which in turn enhance the dielectric

  7. Atomic-scale microstructures, Raman spectra and dielectric properties of cubic pyrochlore-typed Bi1.5MgNb1.5O7 dielectric ceramics

    KAUST Repository

    Li, Yangyang; Zhu, Xinhua; Al-Kassab, Talaat

    2014-01-01

    Single-phase cubic pyrochlore-typed Bi1.5MgNb 1.5O7 (BMN) dielectric ceramics were synthesized at temperatures of 1050-1200 °C by solid-state reaction method. Their atomic-scale microstructures and dielectric properties were investigated. X-ray diffraction patterns revealed that the BMN ceramics had an average cubic pyrochlore structure, whereas the Raman spectra indicated that they had an essentially cubic symmetry with small local deviations at the A and O' sites of the cubic pyrochlore structure. This was confirmed by selected electron area diffraction (SAED) patterns, where the reflections of {442} (not allowed in the cubic pyrochlore with Fd3̄m symmetry) were clearly observed. SEM and TEM images revealed that the average grain size was increased with the sintering temperature, and an un-homogeneous grain growth was observed at high temperatures. HRTEM images and SAED patterns revealed the single-crystalline nature of the BMN ceramic grains. Energy dispersive spectroscopy (EDS) elemental mapping studies indicated that the compositional distributions of Bi, Mg, Nb and O elements in the ceramic grains were homogenous, and no elemental precipitation was observed at the grain boundary. Quantitative EDS data on ceramic grains revealed the expected cationic stoichiometry based on the initial composition of Bi1.5MgNb1.5O7. Dielectric constants of all the BMN samples exhibited almost frequency independent characteristic in the frequency range of 102-106 Hz, and the highest value was 195 for the BMN ceramics sintered at sintered at 1150 °C with the highest bulk density. The dielectric losses were stable and less than 0.002 in the frequency range of 102-105 Hz. The high dielectric constants of the present BMN samples can be ascribed to the local atomic deviations at the A and O' sites from the ideal atomic positions of the pyrochlore structure, which affect the different polarization mechanisms in the BMN ceramics, and which in turn enhance the dielectric constants of

  8. Pyrochlore as nuclear waste form. Actinide uptake and chemical stability

    Energy Technology Data Exchange (ETDEWEB)

    Finkeldei, Sarah Charlotte

    2015-07-01

    Radioactive waste is generated by many different technical and scientific applications. For the past decades, different waste disposal strategies have been considered. Several questions on the waste disposal strategy remain unanswered, particularly regarding the long-term radiotoxicity of minor actinides (Am, Cm, Np), plutonium and uranium. These radionuclides mainly arise from high level nuclear waste (HLW), specific waste streams or dismantled nuclear weapons. Although many countries have opted for the direct disposal of spent fuel, from a scientific and technical point of view it is imperative to pursue alternative waste management strategies. Apart from the vitrification, especially for trivalent actinides and Pu, crystalline ceramic waste forms are considered. In contrast to glasses, crystalline waste forms, which are chemically and physically highly stable, allow the retention of radionuclides on well-defined lattice positions within the crystal structure. Besides polyphase ceramics such as SYNROC, single phase ceramics are considered as tailor made host phases to embed a specific radionuclide or a specific group. Among oxidic single phase ceramics pyrochlores are known to have a high potential for this application. This work examines ZrO{sub 2} based pyrochlores as potential nuclear waste forms, which are known to show a high aqueous stability and a high tolerance towards radiation damage. This work contributes to (1) understand the phase stability field of pyrochlore and consequences of non-stoichiometry which leads to pyrochlores with mixed cationic sites. Mixed cationic occupancies are likely to occur in actinide-bearing pyrochlores. (2) The structural uptake of radionuclides themselves was studied. (3) The chemical stability and the effect of phase transition from pyrochlore to defect fluorite were probed. This phase transition is important, as it is the result of radiation damage in ZrO{sub 2} based pyrochlores. ZrO{sub 2} - Nd{sub 2}O{sub 3} pellets

  9. Ion irradiation of rare-earth- and yttrium-titanate-pyrochlores

    International Nuclear Information System (INIS)

    Wang, S.X.; Wang, L.M.; Ewing, R.C.; Govindan Kutty, K.V.

    2000-01-01

    Pyrochlore, A 1-2 B 2 O 6 (O,OH,F) 0-1 , is an actinide-bearing phase in Synroc, a polyphase ceramic proposed for the immobilization of high level nuclear waste. Structural damage due to alpha-decay events can significantly affect the chemical and physical stability of the nuclear waste form. Pyrochlore can effectively incorporate a variety of actinides into its structure. Four titanate pyrochlores were synthesized with compositions of Gd 2 Ti 2 O 7 , Sm 2 Ti 2 O 7 , Eu 2 Ti 2 O 7 and Y 2 Ti 2 O 2 . These samples were irradiated with 1 MeV Kr + in order to simulate alpha-decay damage and were observed by in situ electron microscopy. Irradiations were conducted from 25 K to 1023 K. At room temperature, Gd-, Sm- and Eu-pyrochlores amorphized at a dose of ∼2x10 14 ions/cm 2 (∼0.5 dpa) and Y-pyrochlore amorphized at 4x10 14 ions/cm 2 (∼0.8 dpa). The amorphization dose became higher at elevated temperatures with different rates of increase for each composition. The critical temperatures for amorphization are ∼1100 K for Gd-, Sm-, Eu-pyrochlore and ∼780 K for Y-pyrochlore. The rare-earth-pyrochlores are more susceptible to amorphization and have higher critical temperatures than Y-pyrochlore. The difference in amorphization dose and critical temperature is attributed to the different cascade sizes caused by the different cation masses of the target. Based on a model of cascade quenching, the larger cascade is related to a lower amorphization dose and higher critical temperature. The irradiated materials were studied by electron diffraction and high-resolution electron microscopy. All the pyrochlores transformed to a fluorite substructure prior to the completion of amorphization of the observed regions. This transformation was caused by the disordering between cations and between oxygen and oxygen vacancies. The concurrence of cation disordering with amorphization suggests the partial recrystallization of the displacement cascades. Isolated cascade damage

  10. Single crystal growth and structure refinements of CsMxTe2-xO6 (M = Al, Ga, Ge, In) pyrochlores

    International Nuclear Information System (INIS)

    Siritanon, Theeranun; Sleight, A.W.; Subramanian, M.A.

    2011-01-01

    Graphical abstract: Single crystals of CsM x Te 2-x O 6 pyrochlores with M = Al, Ga, Ge, and In have been grown and structure refinements indicate deviations from ideal stoichiometry presumably related to mixed valency of tellurium. Highlights: → Single crystals of CsM x Te 2-x O 6 pyrochlores with M = Al, Ga, Ge, and In have been grown. → Structure refinements from single crystal X-ray diffraction data confirm e structure. → Deviations from ideal stoichiometry suggest mixed valency of tellurium and hence conductivity. -- Abstract: Single crystals of CsM x Te 2-x O 6 pyrochlores with M = Al, Ga, Ge, and In have been grown from a TeO 2 flux. Structure refinements from single crystal X-ray diffraction data are reported. These results are used to discuss deviations from ideal stoichiometry that result in electronic conductivity presumably related to mixed valency of tellurium.

  11. Evolution of pyrochlore composition in a carbonatite complex of the Eastern European platform

    International Nuclear Information System (INIS)

    Nechelyastnov, G.N.; Pozharitskaya, L.K.

    1986-01-01

    X-ray microanalysis is used to study 29 pyrochlore group mineral samples of the East European platform carbonatite complex. Pyrochlore sequential evolution: frm high in tantalum and uranium, passing uranium poor in tantalum to low in tantalum and uranium and also an increased content of iron, manganese, magnesium and lead, is shown. Calcium, niobium, tantalum non-homogeneous distribution in pyrochlore grains is detected. Peculiarities of pyrochlore group mineral composition reflect the effect of specific geologic-structural position of the East European platform carbonatites high depth of formation and intensive development of deformations) on general evolution for pyrochlore of carbonatite complexes and related to it pyrochlore specific nature, in particular, high uranium and low niobium contents

  12. Atomic disorder in Gd{sub 2}Zr{sub 2}O{sub 7} pyrochlore

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, F. X. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao, Hebei 066004 (China); Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, Michigan 48109 (United States); Lang, M. [Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996 (United States); Ewing, R. C. [Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305 (United States)

    2015-05-11

    Gd{sub 2}Zr{sub 2}O{sub 7} pyrochlore with different degrees of cation disorder were synthesized by isothermal annealing at various temperatures (1100–1550 °C), and the related changes in the structure were investigated by ambient and high pressure x-ray diffraction (XRD) measurements. Unit cell parameters increase almost linearly with increasing treatment temperature. The degree of cation order in pyrochlore also increases with the increase of temperature, but saturates at ∼60%. The compressibility of the pyrochlore structures decreases when the degree of cation order increases. High pressure XRD measurements also indicate that the phase stability of Gd{sub 2}Zr{sub 2}O{sub 7} is not very sensitive to the degree of atomic disorder in the pyrochlore structure.

  13. Dielectric properties and microstructural characterization of cubic pyrochlored bismuth magnesium niobates

    KAUST Repository

    Zhang, Yuan

    2013-08-06

    Cubic bismuth pyrochlores in the Bi2O3 Bi 2O3-MgO-Nb2O5 Nb2O 5 system have been investigated as promising dielectric materials due to their high dielectric constant and low dielectric loss. Here, we report on the dielectric properties and microstructures of cubic pyrochlored Bi 1.5 MgNb 1.5 O 7 Bi1.5MgNb1.5O7 (BMN) ceramic samples synthesized via solid-state reactions. The dielectric constant (measured at 1 MHz) was measured to be ∼ 120 ∼120 at room temperature, and the dielectric loss was as low as 0.001. X-ray diffraction patterns demonstrated that the BMN samples had a cubic pyrochlored structure, which was also confirmed by selected area electron diffraction (SAED) patterns. Raman spectrum revealed more than six vibrational models predicted for the ideal pyrochlore structure, indicating additional atomic displacements of the A and O′ O\\' sites from the ideal atomic positions in the BMN samples. Structural modulations of the pyrochlore structure along the [110] and [121] directions were observed in SAED patterns and high-resolution transmission electron microscopy (HR-TEM) images. In addition, HR-TEM images also revealed that the grain boundaries (GBs) in the BMN samples were much clean, and no segregation or impure phase was observed forming at GBs. The high dielectric constants in the BMN samples were ascribed to the long-range ordered pyrochlore structures since the electric dipoles formed at the superstructural direction could be enhanced. The low dielectric loss was attributed to the existence of noncontaminated GBs in the BMN ceramics. © 2013 Springer-Verlag Berlin Heidelberg.

  14. Frustration under pressure: Exotic magnetism in new pyrochlore oxides

    Directory of Open Access Journals (Sweden)

    C. R. Wiebe

    2015-04-01

    Full Text Available Pyrochlore structures, of chemical formula A2B2O7 (A and B are typically trivalent and tetravalent ions, respectively, have been the focus of much activity in the condensed matter community due to the ease of substitution of rare earth and transition metal ions upon the two interpenetrating corner-shared tetrahedral lattices. Over the last few decades, superconductivity, spin liquid states, spin ice states, glassy states in the absence of chemical disorder, and metal-insulator transitions have all been discovered in these materials. Geometric frustration plays a role in the relevant physics of all of these phenomena. In the search for new pyrochlore materials, it is the RA/RB cation radius ratio which determines the stability of the lattice over the defect fluorite structure in the lower limit. Under ambient pressure, the pyrochlores are stable for 1.36 ≤ RA/RB ≤ 1.71. However, using high pressure synthesis techniques (1-10 GPa of pressure, metastable pyrochlores exist up to RA/RB = 2.30. Many of these compounds are stable on a timescale of years after synthesis, and provide a means to greatly enhance exchange, and thus test theories of quantum magnetism and search for new phenomena. Within this article, we review new pyrochlore compounds synthesized via high pressure techniques and show how the ground states are extremely sensitive to chemical pressure.

  15. Synthesis, crystal structure and luminescent properties of a new pyrochlore type tungstate CsGa0.333W1.667O6

    Science.gov (United States)

    Zhao, Dan; Zhao, Ji; Fan, Yun-Chang; Ma, Zhao; Zhang, Rui-Juan; Liu, Bao-Zhong

    2018-06-01

    High temperature solution reaction leads to a new tungstate compound CsGa0.333W1.667O6, whose structure was determined by single-crystal X-ray diffraction analysis. The results show that it crystallizes in pyrochlore structure with cubic space group Fd-3m and a = 10.2529 (13) Å. In this structure, Ga and W atoms are in a statistical disorder manner. The self-activated luminescent properties CsGa0.333W1.667O6 were studied. Under the excitation of 323 nm, the emission spectrum exhibits a blue emission centered at 466 nm with the chromaticity coordinates (0.1838, 0.1814).

  16. Structures and solid solution mechanisms of pyrochlore phases in the systems Bi{sub 2}O{sub 3}-ZnO-(Nb, Ta){sub 2}O{sub 5}

    Energy Technology Data Exchange (ETDEWEB)

    Tan, K.B., E-mail: tankb@science.upm.edu.m [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor (Malaysia); Khaw, C.C. [Department of Engineering, Universiti Tunku Abdul Rahman, 53300 Setapak, Kuala Lumpur (Malaysia); Lee, C.K. [Academic Science Malaysia, 902-4 Jalan Tun Ismail, 50480 Kuala Lumpur (Malaysia); Zainal, Z. [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor (Malaysia); Miles, G.C. [Department of Engineering Materials, The University of Sheffield, Mappin Street, Sheffield, S1 3JD (United Kingdom)

    2010-10-22

    Research highlights: {yields} Combined XRD and ND Rietveld structural refinement of pyrochlores. {yields} Structures and solid solution mechanisms of Bi-pyrochlores. {yields} Bi and Zn displaced off-centre to different 96g A-site positions. {yields} Summary of composition-structure-property of Bi-pyrochlores. - Abstract: The crystal structures of two pyrochlore phases have been determined by Rietveld refinement of combined X-ray and neutron powder diffraction data. These are stoichiometric, Bi{sub 1.5} ZnTa{sub 1.5}O{sub 7} and non-stoichiometric Bi{sub 1.56}Zn{sub 0.92}Nb{sub 1.44}O{sub 6.86}. In both structures, Zn is distributed over A- and B-sites; Bi and Zn are displaced off-centre, to different 96g A-site positions; of the three sets of oxygen positions, O(1) are full, O(2) contain vacancies and O(3) contain a small number of oxygen, again in both cases. Comparisons between these structures, those of related Sb analogues and literature reports are made.

  17. Investigation of structural and electrical properties of vanadium substituted disordered pyrochlore-type Ho{sub 2−x}V{sub x}Zr{sub 2}O{sub 7} nanostructure

    Energy Technology Data Exchange (ETDEWEB)

    Karamat, Nazia, E-mail: naziakaramatgoraya@yahoo.com [Institute of Chemical Sciences, Bahauddin Zakariya University, Multan (Pakistan); Ashiq, Muhammad Naeem, E-mail: naeemashiqqau@yahoo.com [Institute of Chemical Sciences, Bahauddin Zakariya University, Multan (Pakistan); Najam-ul-Haq, Muhammad [Institute of Chemical Sciences, Bahauddin Zakariya University, Multan (Pakistan); Ali, Irshad; Iqbal, M. Asif; Irfan, Muhammad [Department of Physics, Bahauddin Zakariya University, Multan (Pakistan); Abbas, Yasir; Athar, Muhammad [Institute of Chemical Sciences, Bahauddin Zakariya University, Multan (Pakistan)

    2014-04-01

    Graphical abstract: - Highlights: • Normal microemulsion method has been used for the synthesis of zirconates nanomaterials. • Structure shifted towards highly disordered pyrochlore state with substitution. • The electrical resistivity increase with the vanadium content. • The dielectric constant show resonance behavior. • The synthesized materials are suitable for microwave devices. - Abstract: Disordered pyrochlore system with composition Ho{sub 2−x}V{sub x}Zr{sub 2}O{sub 7} (where x = 0, 0.25, 0.50, 0.75 and 1) has been synthesized by the normal microemulsion route to examine the effect of vanadium substitution on structural and electrical properties. The prepared compounds are characterized by several techniques including X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, energy dispersive X-ray fluorescence (ED-XRF), energy dispersive spectra (EDS), scanning electron microscopy (SEM), temperature dependent electrical and frequency dependent dielectric measurements. The XRD analysis confirms the formation of disordered pyrochlore phase with crystallite size 7–30 nm while a second phase is also observed in the highly substituted materials. The increase in resistivity is attributed to the removal of low energy pathway due to cation disordering. The dielectric constant decreases due to lowering of dipole moment with substitution and its resonance behavior shifted toward higher frequencies. The electrical and dielectric measurements suggest that materials are suitable for high frequency electronic devices, such as oscillators, resonators and frequency filters.

  18. Lanthanide stannate pyrochlores (Ln2Sn2O7; Ln  =  Nd, Gd, Er) at high pressure

    Science.gov (United States)

    Turner, Katlyn M.; Tracy, Cameron L.; Mao, Wendy L.; Ewing, Rodney C.

    2017-12-01

    Lanthanide stannate pyrochlores (Ln2Sn2O7; Ln  =  Nd, Gd, and Er) were investigated in situ to 50 GPa in order to determine their structural response to compression and compare their response to that of lanthanide titanate, zirconate, and hafnate pyrochlores. The cation radius ratio of A3+/B4+ in pyrochlore oxides (A2B2O7) is thought to be the dominant feature that influences their response on compression. The ionic radius of Sn4+ is intermediate to that of Ti4+, Zr4+, and Hf4+, but the 〈Sn-O〉 bond in stannate pyrochlore is more covalent than the 〈B-O〉 bonds in titanates, zirconate, and hafnates. In stannates, based on in situ Raman spectroscopy, pyrochlore cation and anion sublattices begin to disorder with the onset of compression, first measured at 0.3 GPa. The extent of sublattice disorder versus pressure is greater in stannates with a smaller Ln3+ cation. Stannate pyrochlores (Fd-3m) begin a sluggish transformation to an orthorhombic, cotunnite-like structure at ~28 GPa similar transitions have been observed in titanate, zirconate, and hafnate pyrochlores at varying pressures (18-40 GPa) with cation radius ratio. The extent of the phase transition versus pressure varies directly with the size of the Ln3+ cation. Post-decompression from ~50 GPa, Er2Sn2O7 and Gd2Sn2O7 adopt a pyrochlore structure, rather than the multi-scale defect-fluorite  +  weberite-type structure adopted by Nd2Sn2O7 that is characteristic of titanate, zirconate, and hafnate pyrochlores under similar conditions. Like pyrochlore titanates, zirconates, and hafnates, the bulk modulus, B 0, of stannates varies linearly and inversely with cation radius ratio from 1 1 1 GPa (Nd2Sn2O7) to 251 GPa (Er2Sn2O7). The trends of bulk moduli in stannates in this study are in excellent agreement with previous experimental studies on stannates and suggest that the size of the Ln3+ cation is the primary determining factor of B 0. Additionally, when normalized to r A

  19. Experimental Insights into Ground-State Selection of Quantum XY Pyrochlores

    Science.gov (United States)

    Hallas, Alannah M.; Gaudet, Jonathan; Gaulin, Bruce D.

    2018-03-01

    Extensive experimental investigations of the magnetic structures and excitations in the XY pyrochlores have been carried out over the past decade. Three families of XY pyrochlores have emerged: Yb2B2O7, Er2B2O7, and, most recently, [Formula: see text]Co2F7. In each case, the magnetic cation (either Yb, Er, or Co) exhibits XY anisotropy within the local pyrochlore coordinates, a consequence of crystal field effects. Materials in these families display rich phase behavior and are candidates for exotic ground states, such as quantum spin ice, and exotic ground-state selection via order-by-disorder mechanisms. In this review, we present an experimental summary of the ground-state properties of the XY pyrochlores, including evidence that they are strongly influenced by phase competition. We empirically demonstrate the signatures for phase competition in a frustrated magnet: multiple heat capacity anomalies, suppressed TN or TC, sample- and pressure-dependent ground states, and unconventional spin dynamics.

  20. Lanthanide stannate pyrochlores (Ln2Sn2O7; Ln = Nd, Gd, Er) at high pressure.

    Science.gov (United States)

    Turner, Katlyn M; Tracy, Cameron L; Mao, Wendy L; Ewing, Rodney C

    2017-11-09

    Lanthanide stannate pyrochlores (Ln2Sn2O7; Ln=Nd, Gd, and Er) were investigated in situ to 50 GPa in order to determine their structural response to compression and compare it to that of lanthanide titanate, zirconate, and hafnate pyrochlores. The cation radius ratio of A3+/B4+ in pyrochlore oxides (A2B2O7) is thought to be the dominant property that influences their compression response. The ionic radius of Sn4+ is intermediate to that of Ti4+, Zr4+, and Hf4+, but the bond in stannate pyrochlore is more covalent than the bonds in titanates, zirconate, and hafnates. In stannates, the pyrochlore cation and anion sublattices begin to disorder at 0.3 GPa. The extent of sublattice disorder vs. pressure is greater in stannates with a smaller Ln3+ cation. Stannate pyrochlores (Fd-3m) begin a sluggish transformation to a cotunnite-like structure (Pnma) at ~28 GPa; similar transitions have been observed in titanate, zirconate, and hafnate pyrochlore at varying pressures with cation radius ratio. The extent of the phase transition vs. pressure varies directly with the size of the Ln3+ cation. Post-decompression from ~50 GPa, Er2Sn2O7 and Gd2Sn2O7 adopt a pyrochlore structure, rather than the multiscale defect-fluorite + weberite structure adopted by Nd2Sn2O7 that is characteristic of titanate, zirconate, and hafnate pyrochlore treated to similar conditions. Like pyrochlore titanates, zirconates, and hafnates, the bulk modulus, B0, of stannates varies linearly and inversely with cation radius ratio. The trends of bulk moduli in stannates in this study are in excellent agreement with previous experimental studies on stannates, and suggest that the size of the Ln3+ cation is a primary determining factor of B0. Additionally, when normalized to rA/rB, the bulk moduli of stannates are comparable to those of zirconates and hafnates, which vary from titanates. Our results suggest that the cation radius ratio strongly influences the bulk moduli of stannates as well as

  1. Processing glass-pyrochlore composites for nuclear waste encapsulation

    International Nuclear Information System (INIS)

    Pace, S.; Cannillo, V.; Wu, J.; Boccaccini, D.N.; Seglem, S.; Boccaccini, A.R.

    2005-01-01

    Glass matrix composites have been developed as alternative materials to immobilize nuclear solid waste, in particular actinides. These composites are made of soda borosilicate glass matrix, into which particles of lanthanum zirconate pyrochlore are encapsulated in concentrations of 30 vol.%. The fabrication process involves powder mixing followed by hot-pressing. At the relatively low processing temperature used (620 deg. C), the pyrochlore crystalline structure of the zirconate, which is relevant for containment of radioactive nuclei, remains unaltered. The microstructure of the composites exhibits a homogeneous distribution of isolated pyrochlore particles in the glass matrix and strong bonding at the matrix-particle interfaces. Hot-pressing was found to lead to high densification (95% th.d.) of the composite. The materials are characterized by relatively high elastic modulus, flexural strength, hardness and fracture toughness. A numerical approach using a microstructure-based finite element solver was used in order to investigate the mechanical properties of the composites

  2. Isomorphic Structural Transition in the β-Pyrochlore Oxide Superconductor KOs2O6

    Science.gov (United States)

    Yamaura, Jun-ichi; Takigawa, Masashi; Yamamuro, Osamu; Hiroi, Zenji

    2010-04-01

    A phase transition observed at Tp = 7.65 K in the β-pyrochlore oxide superconductor KOs2O6 is studied by means of heat capacity, 39K-NMR, and X-ray diffraction measurements using high-quality single crystals. We find evidence of an isomorphic structural transition at Tp without the off-center freezing of the K ion even below Tp. It is possibly related to the rattling motion of the K ion in an oversized atomic cage.

  3. Transmission electron microscopic study of pyrochlore to defect-fluorite transition in rare-earth pyrohafnates

    Energy Technology Data Exchange (ETDEWEB)

    Karthik, Chinnathambi, E-mail: Karthikchinnathambi@boisestate.edu [Department of Materials Science and Engineering, Boise State University, 1910 University drive, Boise, ID 83725 (United States); Center for Advanced Energy Studies, 995 University Blvd, Idaho Falls, ID 83415 (United States); Anderson, Thomas J. [Department of Materials Science and Engineering, Boise State University, 1910 University drive, Boise, ID 83725 (United States); Gout, Delphine [Oak Ridge National Lab, Neutron Scattering Science Division, Oak Ridge, TN (United States); Ubic, Rick [Department of Materials Science and Engineering, Boise State University, 1910 University drive, Boise, ID 83725 (United States); Center for Advanced Energy Studies, 995 University Blvd, Idaho Falls, ID 83415 (United States)

    2012-10-15

    A structural transition in rare earth pyrohafnates, Ln{sub 2}Hf{sub 2}O{sub 7} (Ln=Y, La, Pr, Nd, Tb, Dy, Yb and Lu), has been identified. Neutron diffraction showed that the structure transforms from well-ordered pyrochloric to fully fluoritic through the lanthanide series from La to Lu with a corresponding increase in the position parameter x of the 48f (Fd3{sup Macron }m) oxygen site from 0.330 to 0.375. As evidenced by the selected area electron diffraction, La{sub 2}Hf{sub 2}O{sub 7}, Pr{sub 2}Hf{sub 2}O{sub 7} and Nd{sub 2}Hf{sub 2}O{sub 7} exhibited a well-ordered pyrocholoric structure with the presence of intense superlattice spots, which became weak and diffuse (in Dy{sub 2}Hf{sub 2}O{sub 7} and Tb{sub 2}Hf{sub 2}O{sub 7}) before disappearing completely as the series progressed towards the Lu end. High resolution electron microscopic studies showed the breakdown of the pyrochlore ordering in the form of antiphase domains resulting in diffused smoke-like superlattice spots in the case of Dy{sub 2}Hf{sub 2}O{sub 7} and Tb{sub 2}Hf{sub 2}O{sub 7}. - Graphical abstract: Transmission electron microscopic studies showed the ordered pyrochlore to defect fluorite transition in rare-earth pyrohafnates to occur via the formation of anti-phase domains to start with. Highlights: Black-Right-Pointing-Pointer Pyrochlore to fluorite structural transition in rare earth pyrohafnates. Black-Right-Pointing-Pointer La{sub 2}Hf{sub 2}O{sub 7}, Pr{sub 2}Hf{sub 2}O{sub 7} and Nd{sub 2}Hf{sub 2}O{sub 7} showed well ordered pyrochlore structure. Black-Right-Pointing-Pointer Short range ordering in Dy{sub 2}Hf{sub 2}O{sub 7} and Tb{sub 2}Hf{sub 2}O{sub 7}. Black-Right-Pointing-Pointer Break down of pyrochlore ordering due to antiphase boundaries. Black-Right-Pointing-Pointer Rest of the series showed fluoritic structure.

  4. XPS studies of ceramics with pyrochlore structure for radioactive wastes disposal

    International Nuclear Information System (INIS)

    Teterin, Yu.A.; Vukchevich, L.; Ivanov, K.E.; Utkin, I.O; Teterin, A. Yu.; Maslakov, K.I.; Yudintseva, T.S.; Yudintsev, S.V.; Stefanovsky, S.V.; Lapina, M.I. . E-mail address of corresponding author: vukas@rc.pmf.cg.ac.yu; Vukchevich, L.)

    2005-01-01

    X-ray photoelectron spectroscopy (XPS) study of ceramics CaThSn 2 O 7 and CaThZr 2 O 7 with pyrochlore structure used as matrixes for the disposal of long lived high level radioactive wastes was done. On the basis of the XPS parameters of the core and outer electrons in the binding energy range 0 - 1000 eV the oxidation states of the included metals were determined, quantitative elemental and ionic analysis was carried out and a conclusion on the monophaseness of the studied samples was drawn. The obtained data agree with the X-ray diffraction and scanning electron microscopy results. (author)

  5. Energetics of stepwise disordering transformation in pyrochlores, RE2Ti2O7 (RE = Y, Gd and Dy)

    International Nuclear Information System (INIS)

    Hayun, Shmuel; Tran, Tien B.; Lian, Jie; Fuentes, Antonio F.; Navrotsky, Alexandra

    2012-01-01

    Graphical abstract: The transformation from disordered to more order state in the pyrochlore system go through multiple energetics steps; the cation sublattice rearrangement is control by the diffusion of the cations while the anion sublattice display an irreversible transformation from a disordered to a higher-ordered state via diffusionless transformation. - Abstract: The capacity to incorporate actinide cations makes pyrochlore titanates first-choice phases in titanate-based waste form ceramics. Despite broad interest in the pyrochlore order–disorder transformation due to the cumulative effects of 238 U, 235 U and 232 Th radioactive decay and their daughter products, only limited thermodynamic data, mainly based on simulations of ion-beam irradiation experiments, have been reported. In this work, for the first time, heavily disordered pyrochlores, RE 2 Ti 2 O 7 (RE = Y, Gd and Dy), from mechanical milling of their constituent oxides, were thermochemically investigated. Two types of thermal events were identified using high-temperature differential scanning calorimetry and correlated to the structural disorder in the cation and anion sublattices. Moreover, the excess formation energy measured by oxide melt solution calorimetry shows that the smaller the ionic radius of the RE, the easier it is to remove damage domains.

  6. Soft modes in the easy plane pyrochlore antiferromagnet

    International Nuclear Information System (INIS)

    Champion, J D M; Holdsworth, P C W

    2004-01-01

    Thermal fluctuations lift the high ground state degeneracy of the classical nearest neighbour pyrochlore antiferromagnet, with easy plane anisotropy, giving a first-order phase transition to a long range ordered state. We show, from spin wave analysis and numerical simulation, that even below this transition a continuous manifold of states, of dimension N 2/3 , exist (N is the number of degrees of freedom). As the temperature goes to zero a further 'order by disorder' selection is made from this manifold. The pyrochlore antiferromagnet Er 2 Ti 2 O 7 is believed to have an easy plane anisotropy and is reported to have the same magnetic structure. This is perhaps surprising, given that the dipole interaction lifts the degeneracy of the classical model in favour of a different structure. We interpret our results in the light of these facts

  7. Multifunctional Sm2-xDyxZr2O7 pyrochlore system: potential ionic conductors and photocatalysts

    International Nuclear Information System (INIS)

    Grover, V.; Sayed, Farheen N.; Bhattacharyya, K.; Jain, D.; Pillai, C.G.S.; Tyagi, A.K.; Arya, A.

    2010-01-01

    Full text: Pyrochlores have garnered considerable interest over the years because of a range of potentially useful properties such as fast-ion (mainly anion) conductivity, electrical conductivity, catalysis, luminescence etc. In present work a series of Sm 2-x Dy x Zr 2 O 7 compounds (0.0 ≤ x ≤ 2.0) were synthesized by gel combustion and characterized by Powder XRD and Raman spectroscopic studies. XRD studies revealed the system to be single-phasic throughout with the retention of pyrochlore phase till 40 mol% of Dy 3+ beyond which, an order-disorder phase transition occurred resulting in a defect fluorite structure. Surprisingly, Raman studies showed the retention of pyrochlore type ordering till the other end member, i.e. Dy 2 Zr 2 O 7 . This is the first study, which reports the retention of a weak pyrochlore type superstructure in Dy 2 Zr 2 O 7 system. Ionic conductivity measurements were performed on these samples, which showed that the activation Energy (E a ) increases with increase in Dy 3+ mol% owing to the decreased mobility with increasing degree of disorder. The representative nquist Plots are given for Sm 2 Zr 2 O 7 . These materials have a definite band gap absorbing mainly in the UV region which makes them good candidates for photocatalysed dye degradation studies. Potential of some of these compositions as photocatalysts was also explored and they were found to efficiently catalyse the degradation of Xylenol Orange with t 1/2 decreasing from pure Sm 2 Zr 2 O 7 to pure Dy 2 Zr 2 O 7

  8. Yttrium bismuth titanate pyrochlore mixed oxides for photocatalytic hydrogen production

    Energy Technology Data Exchange (ETDEWEB)

    Merka, Oliver

    2012-10-18

    In this work, the sol-gel synthesis of new non-stoichiometric pyrochlore titanates and their application in photocatalytic hydrogen production is reported. Visible light response is achieved by introducing bismuth on the A site or by doping the B site by transition metal cations featuring partially filled d orbitals. This work clearly focusses on atomic scale structural changes induced by the systematical introduction of non-stoichiometry in pyrochlore mixed oxides and the resulting influence on the activity in photocatalytic hydrogen production. The materials were characterized in detail regarding their optical properties and their atomic structure. The pyrochlore structure tolerates tremendous stoichiometry variations. The non-stoichiometry in A{sub 2}O{sub 3} rich compositions is compensated by distortions in the cationic sub-lattice for the smaller Y{sup 3+} cation and by evolution of a secondary phase for the larger Bi{sup 3+} cation on the A site. For TiO{sub 2} rich compositions, the non-stoichiometry leads to a special vacancy formation in the A and optionally O' sites. It is shown that pyrochlore mixed oxides in the yttrium bismuth titanate system represent very active and promising materials for photocatalytic hydrogen production, if precisely and carefully tuned. Whereas Y{sub 2}Ti{sub 2}O{sub 7} yields stable hydrogen production rates over time, the bismuth richer compounds of YBiTi{sub 2}O{sub 7} and Bi{sub 2}Ti{sub 2}O{sub 7} are found to be not stable under irradiation. This drawback is overcome by applying a special co-catalyst system consisting of a precious metal core and a Cr{sub 2}O{sub 3} shell on the photocatalysts.

  9. Weyl magnons in breathing pyrochlore antiferromagnets

    Science.gov (United States)

    Li, Fei-Ye; Li, Yao-Dong; Kim, Yong Baek; Balents, Leon; Yu, Yue; Chen, Gang

    2016-01-01

    Frustrated quantum magnets not only provide exotic ground states and unusual magnetic structures, but also support unconventional excitations in many cases. Using a physically relevant spin model for a breathing pyrochlore lattice, we discuss the presence of topological linear band crossings of magnons in antiferromagnets. These are the analogues of Weyl fermions in electronic systems, which we dub Weyl magnons. The bulk Weyl magnon implies the presence of chiral magnon surface states forming arcs at finite energy. We argue that such antiferromagnets present a unique example, in which Weyl points can be manipulated in situ in the laboratory by applied fields. We discuss their appearance specifically in the breathing pyrochlore lattice, and give some general discussion of conditions to find Weyl magnons, and how they may be probed experimentally. Our work may inspire a re-examination of the magnetic excitations in many magnetically ordered systems. PMID:27650053

  10. Odd-parity magnetoresistance in pyrochlore iridate thin films with broken time-reversal symmetry

    Science.gov (United States)

    Fujita, T. C.; Kozuka, Y.; Uchida, M.; Tsukazaki, A.; Arima, T.; Kawasaki, M.

    2015-01-01

    A new class of materials termed topological insulators have been intensively investigated due to their unique Dirac surface state carrying dissipationless edge spin currents. Recently, it has been theoretically proposed that the three dimensional analogue of this type of band structure, the Weyl Semimetal phase, is materialized in pyrochlore oxides with strong spin-orbit coupling, accompanied by all-in-all-out spin ordering. Here, we report on the fabrication and magnetotransport of Eu2Ir2O7 single crystalline thin films. We reveal that one of the two degenerate all-in-all-out domain structures, which are connected by time-reversal operation, can be selectively formed by the polarity of the cooling magnetic field. Once formed, the domain is robust against an oppositely polarised magnetic field, as evidenced by an unusual odd field dependent term in the magnetoresistance and an anomalous term in the Hall resistance. Our findings pave the way for exploring the predicted novel quantum transport phenomenon at the surfaces/interfaces or magnetic domain walls of pyrochlore iridates. PMID:25959576

  11. Electrical transport properties of manganese containing pyrochlore type semiconducting oxides using impedance analyses

    International Nuclear Information System (INIS)

    Sumi, S.; Prabhakar Rao, P.; Mahesh, S.K.; Koshy, Peter

    2012-01-01

    Graphical abstract: DC conductivity variation of CaCe 1−x Mn x SnNbO 7−δ (x = 0, 0.2, 0.4 and 0.6) with inverse of temperature. Variation of conductivity with Mn concentration at 600 °C is shown in the inset. Display Omitted Highlights: ► We have observed that the structural ordering as well as grain size increase with Mn substitution. ► Impedance analysis proved that a correlated barrier hopping type conduction mechanism is involved in the materials. ► Activation energy as well as electrical conductivity increases with increase in Mn substitution. ► Localization of electrons associated with Mn 2+ and structural ordering are the key factors for the increased activation energy with Mn substitution. ► All the materials showed good NTC thermistor properties. -- Abstract: A new series of manganese containing pyrochlore type semiconducting oxides CaCe 1−x Mn x SnNbO 7−δ (x = 0, 0.2, 0.4 and 0.6) have been synthesized to study the effect of Mn substitution on the structure, microstructure and electrical properties of these samples. X-ray diffraction and scanning electron microscopy studies revealed an increase of structural ordering and grain size respectively with increase of Mn substitution. Rietveld analysis and Raman spectroscopy were also employed to corroborate the XRD results. The bulk resistance measurements with temperature exhibit negative temperature coefficient behavior. The impedance analysis of the samples revealed a non-Debye type relaxation existed in the materials. The ac conductivity variation with temperature and frequency indicates a correlated barrier hopping type conduction mechanism in these materials. The barrier height and the intersite separation for hopping influence the electrical conductivity of these samples and are found to be a function of localization of electrons associated with the Mn 2+ ions and the unit cell volume respectively. The Mn substitution increases both electrical conductivity and activation energy

  12. Exchange interactions in two-state systems: rare earth pyrochlores

    Science.gov (United States)

    Curnoe, S. H.

    2018-06-01

    The general form of the nearest neighbour exchange interaction for rare earth pyrochlores is derived based on symmetry. Generally, the rare earth angular momentum degeneracy is lifted by the crystal electric field (CEF) into singlets and doublets. When the CEF ground state is a doublet that is well-separated from the first excited state the CEF ground state doublet can be treated as a pseudo-spin of some kind. The general form of the nearest neighbour exchange interaction for pseudo-spins on the pyrochlore lattice is derived for three different types of pseudo-spins. The methodology presented in this paper can be applied to other two-state spin systems with a high space group symmetry.

  13. Density Functional Theory Study of Leaching Performance of Different Acids on Pyrochlore (100) Surface

    Science.gov (United States)

    Yang, Xiuli; Fang, Qing; Ouyang, Hui

    2018-06-01

    Pyrochlore leaching using hydrofluoric, sulfuric, and hydrochloric acids has been studied via experimental methods for years, but the interactions between niobium atoms on the pyrochlore surface and different acids have not been investigated. In this work, first-principles calculations based on density functional theory were used to elucidate the leaching performance of these three acids from the viewpoint of geometrical and electronic structures. The calculation results indicate that sulfate, chloride, and fluoride anions influence the geometric structure of pyrochlore (100) to different extents, decreasing in the order: sulfate, fluoride, chloride. Orbitals of O1 and O2 atoms of sulfate hybridized with those of surface niobium atom. Fluorine orbitals hybridized with those of surface niobium atoms. However, no obvious overlap exists between any orbitals of chlorine and surface niobium, revealing that chlorine does not interact chemically with surface niobium atoms.

  14. Structural, magnetic, and electronic transport properties of pyrochlore iridate Pr2Ir2O7

    Science.gov (United States)

    Kumar, Harish; Chaurasia, Rachna; Kumari, Pratibha; Paramanik, A. K.

    2018-04-01

    We have studied the structural, magnetic, and electronic transport properties of pyrochlore iridate Pr2Ir2O7. Structural investigation has been done using x-ray powder diffraction and Rietveld analysis. Pr2Ir2O7 crystallize in cubic crystallographic phase with Fd-3m space group. Temperature dependent magnetization data does not show magnetic bifurcation down to 2 K. Electrical resistivity data of Pr2Ir2O7 exhibits metallic behavior throughout temperature range. Below 50 K, a small rise in resistivity data of Pr2Ir2O7 is observed down to 12 K.

  15. Crystal chemistry of pyrochlore from the Mesozoic Panda Hill carbonatite deposit, western Tanzania

    Science.gov (United States)

    Boniface, Nelson

    2017-02-01

    The Mesozoic Panda Hill carbonatite deposit in western Tanzania hosts pyrochlore, an ore and source of niobium. This study was conducted to establish the contents of radioactive elements (uranium and thorium) in pyrochlore along with the concentration of niobium in the ore. The pyrochlore is mainly hosted in sövite and is structurally controlled by NW-SE (SW dipping) or NE-SW (NW dipping) magmatic flow bands with dip angles of between 60° and 90°. Higher concentrations of pyrochlore are associated with magnetite, apatite and/or phlogopite rich flow bands. Electron microprobe analyses on single crystals of pyrochlore yield very low UO2 concentrations that range between 0 and 0.09 wt% (equivalent to 0 atoms per formula unit: a.p.f.u.) and ThO2 between 0.55 and 1.05 wt% (equivalent to 0.1 a.p.f.u.). The analyses reveal high concentrations of Nb2O5 (ranging between 57.13 and 65.50 wt%, equivalent to a.p.f.u. ranging between 1.33 and 1.43) and therefore the Panda Hill Nb-oxide is classified as pyrochlore sensu stricto. These data point to a non radioactive pyrochlore and a deposit rich in Nb at Panda Hill. The Panda Hill pyrochlore has low concentrations of REEs as displayed by La2O3 that range between 0.10 and 0.49 wt% (equivalent to a.p.f.u. ranging between 0 and 0.01) and Ce2O3 ranging between 0.86 and 1.80 wt% (equivalent to a.p.f.u. ranging between 0.02 and 0.03), Pr2O3 concentrations range between 0 and 0.23 wt% (equivalent to 0 a.p.f.u.), and Y2O3 is 0 wt% (equivalent to 0 a.p.f.u.). The abundance of the REEs in pyroclore at the Panda Hill Carbonatite deposit is of no economic significance.

  16. A spin-frustrated cobalt(II) carbonate pyrochlore network.

    Science.gov (United States)

    Zheng, Yanzhen; Ellern, Arkady; Kögerler, Paul

    2011-11-01

    The crystal structure of the cobalt(II) carbonate-based compound cobalt(II) dicarbonate trisodium chloride, Co(CO(3))(2)Na(3)Cl, grown from a water-ethanol mixture, exhibits a three-dimensional network of corner-sharing {Co(4)(μ(3)-CO(3))(4)} tetrahedral building blocks, in which the Co(II) centres define a pyrochlore lattice and reside in a slightly distorted octahedral Co(O-CO(2))(6) environment. The space outside the hexagonal framework defined by these interlinked groups is occupied by Na(+) and Cl(-) ions. Antiferromagnetic coupling between adjacent Co(II) centres, mediated by carbonate bridges, results in geometric spin frustration which is typical for pyrochlore networks. The Co and Cl atoms reside on the special position 3, one Na atom on position 2 and a carbonate C atom on position 3.

  17. Theoretical and experimental investigations of frustrated pyrochlore magnets

    International Nuclear Information System (INIS)

    Champion, John Dickon Mathison

    2001-01-01

    This thesis describes the investigation of frustrated magnetic systems based on the pyrochlore lattice of corner-sharing tetrahedra. Monte Carlo simulations and analytical calculations have been performed on a pyrochlore ferromagnet with local (111) easy-axis anisotropy related to the problem of 'spin ice'. The anisotropy-temperature-magnetic field phase diagram was determined. It contained a tricritical point as well as features related to some real ferroelectrics. A pyrochlore antiferromagnet with local (111) easy-plane anisotropy was studied by Monte Carlo simulation. A general expression for its degenerate ground states was discovered and normal- modes out of the ground states were calculated. Both systems are frustrated yet have a long-range ordered state at low temperature. The degeneracy lifting observed is discussed as well as the reasons for its presence. The rare-earth titanate series Ln 2 Ti 2 O 7 (Ln = rare earth), crystallizes in the Fd3-barm space group, with the magnetic ions situated on the 16c sites which constitute the pyrochlore lattice. Crystal-field effects are known to play a significant role in the frustration observed in these compounds. Powder neutron diffraction was performed on gadolinium and erbium titanate. Both systems are frustrated antiferromagnets yet show long-range magnetic order at ∼ 1 K and ∼ 1.2 K respectively. The magnetic structures of both these compounds have been determined by powder neutron diffraction techniques and related to other theoretical results as well as the theoretical results of the author. Further neutron scattering experiments on the 'spin ice' materials Ho 2 Ti 2 O 7 and Dy 2 Ti 2 O 7 are also described. (author)

  18. Steam Reforming of CH4 Using Ni- Substituted Pyrochlore Catalysts

    Science.gov (United States)

    Haynes, Daniel J.

    The steam reforming of methane (SMR) continues to remain an important industrial reaction for large-scale production of H2 as well as synthesis gas mixtures which can be used for the production of useful chemicals (e.g. methanol). Although SMR is a rather mature technology, traditional nickel based catalysts used industrially are subjected to severe temperatures and reaction conditions, which lead to irreversible activity loss through sintering, support collapse, and carbon formation. Pyrochlore-based mixed oxide have been identified as refractory materials that can be modified through the substitution of catalytic metals and other promoting species into the structure to mitigate these issues causing deactivation. For this study, a lanthanum zirconate pyrochlore catalyst was substituted with Ni to determine whether the oxide structure could effectively stabilize the activity of the catalytic metal during the SMR. The effect of different variables including calcination temperature, a comparison of a substituted versus supported Ni pyrochlore catalyst, Ni weight loading, and Sr promotion have been evaluated to determine the location of the Ni in the structure, and their effect on catalytic behavior. It was revealed that the effect of calcination temperature on a 6wt% Ni substituted pyrochlore produced by the Pechini method demonstrated very little Ni was soluble in the pyrochlore lattice. It was further revealed that by XRD, TEM, and atom probe tomography that, despite the metal loading, Ni exsolves from the structure upon crystallization of the pyrochlore at 700°C, and forms NiO at the surface and grain boundaries. An additional separate La2ZrNiO6 perovskite phase also began to form at higher temperatures (>800°C). Increasing calcination temperature was found to lead to slight sintering of the NiO at the surface, which made the NiO more reducible. Meanwhile decreasing the Ni weight loading was found to produce a lower reduction temperature due to the presence of

  19. Thermodynamic stability of actinide pyrochlore minerals in deep geologic repository environments

    International Nuclear Information System (INIS)

    Wang, YIFENG; Xu, HUIFANG

    2000-01-01

    Crystalline phases of pyrochlore (e.g., CaPuTi 2 O 7 , CaUTi 2 O 7 ) have been proposed as a durable ceramic waste form for disposal of high level radioactive wastes including surplus weapons-usable plutonium. In this paper, the authors use a linear free energy relationship to predict the Gibbs free energies of formation of pyrochlore phases (CaMTi 2 O 7 ). The Pu-pyrochlore phase is predicted to be stable with respect to PuO 2 , CaTiO 3 , and TiO 2 at room temperatures. Pu-pyrochlore is expected to be stable in a geologic repository where silica and carbonate components are absent or limited. The authors suggest that a repository in a salt formation be an ideal environment for disposal of high level, pyrochlore-based ceramic wastes. In such environment, adding CaO as a backfill will make pyrochlore minerals thermodynamically stable and therefore effectively prevent actinide release from these mineral phases

  20. Re-examination of the crystal structure of the β-pyrochlore oxide superconductor KOs 2O 6 by X-ray and convergent-beam electron diffraction analyses

    Science.gov (United States)

    Yamaura, Jun-Ichi; Hiroi, Zenji; Tsuda, Kenji; Izawa, Koichi; Ohishi, Yasuo; Tsutsui, Satoshi

    2009-01-01

    The crystal structure of the β-pyrochlore oxide superconductor KOs 2O 6 is re-examined. A single-crystal X-ray diffraction (XRD) analysis at room temperature first revealed that the compound crystallizes in a cubic structure with the centrosymmetric space group Fd3¯m, as in conventional pyrochlore oxides. Later, however, Schuck et al. claimed a different non-centrosymmetric F4¯3m structure based on their single-crystal XRD analysis. To unambiguously determine the true crystal structure of KOs 2O 6, we carried out high-resolution synchrotron powder X-ray and convergent-beam electron diffraction measurements at room temperature. The space group was determined with high reliability to be centrosymmetric Fd3¯m, not F4¯3m. This confirms the importance of the K atom location in a high-symmetry site, which causes unusually large rattling of the K atom.

  1. Stability of the Weyl-semimetal phase on the pyrochlore lattice

    Science.gov (United States)

    Berke, Christoph; Michetti, Paolo; Timm, Carsten

    2018-04-01

    Motivated by the proposal of a Weyl-semimetal phase in pyrochlore iridates, we consider a Hubbard-type model on the pyrochlore lattice. To shed light on the question as to why such a state has not been observed experimentally, its robustness is analyzed. On the one hand, we study the possible phases when the system is doped. Magnetic frustration favors several phases with magnetic and charge order that do not occur at half filling, including additional Weyl-semimetal states close to quarter filling. On the other hand, we search for density waves that break translational symmetry and destroy the Weyl-semimetal phase close to half filling. The uniform Weyl semimetal is found to be stable, which we attribute to the low density of states close to the Fermi energy.

  2. The XPS study of pyrochlore matrixes for the radioactive waste disposal

    Directory of Open Access Journals (Sweden)

    Teterin Anton Yu.

    2010-01-01

    Full Text Available Two pyrochlore ceramic samples were studied in this work. The X-ray diffraction and the scanning electron microscopy showed that the ceramics with the calculated composition CaThSn2O7 was formed by the dominating pyrochlore phase with the traces of thorianite and hematite, while the CaThZr2O7 ceramics - by the dominating pyrochlore phase with the minor admixtures of thorianite and perovskite. The real compositions of pyrochlore phases determined by the scaning electron microscopy are Ca0.88Th0.92Sn2O6.72 and Ca0.84Th0.80Zr2O6.44. On the basis of the X-ray photoelectron spectral parameters of the outer and core electrons in the binding energy range of 0-1250 eV it was found that tin, zirconium and thorium in pyrochlore are at least 93%-94% tetravalent. Sn-O and Zr-O interatomic distances in BO6-octahedrons in the pyrochlore were found to be 0.210 nm and 0.220 nm, respectively, and these octahedrons are possible to be tetragonaly distorted.

  3. Experimental hydrothermal alteration of crystalline and radiation-damaged pyrochlore

    International Nuclear Information System (INIS)

    Geisler, T.; Seydoux-Guillaume, A.-M.; Poeml, P.; Golla-Schindler, U.; Berndt, J.; Wirth, R.; Pollok, K.; Janssen, A.; Putnis, A.

    2005-01-01

    We have performed hydrothermal experiments with a crystalline microlite and a heavily self-irradiation-damaged (i.e., X-ray amorphous) betafite in a solution containing 1 mol/l HCl and 1 mol/l CaCl 2 at 175 deg. C for 14 days. The well-crystalline microlite grains were partly (∼5-10 μm rim) replaced by a Ca and Na-poorer, defect pyrochlore phase with a larger unit-cell and a sharp chemical gradient at the interface (on a nm scale) to the unreacted core. The amorphous betafite grains (up to ∼2 mm in diameter), on the other hand, were completely transformed into an intergrowth of different crystalline phases (polycrystalline anatase and rutile, a yet unidentified Nb-Ta oxide, and a Y-REE phase), showing complex non-equilibrium structures. Our experimental observations bear a remarkable resemblance to those made on natural samples. They indicate that the processes of the fluid-pyrochlore interaction are influenced by self-irradiation structural damage and that thermodynamic equilibrium models can hardly be applied to adequately describe such systems

  4. Thermal annealing of natural, radiation-damaged pyrochlore

    Energy Technology Data Exchange (ETDEWEB)

    Zietlow, Peter; Beirau, Tobias; Mihailova, Boriana; Groat, Lee A.; Chudy, Thomas; Shelyug, Anna; Navrotsky, Alexandra; Ewing, Rodney C.; Schlüter, Jochen; Škoda, Radek; Bismayer, Ulrich

    2017-01-01

    Abstract

    Radiation damage in minerals is caused by the α-decay of incorporated radionuclides, such as U and Th and their decay products. The effect of thermal annealing (400–1000 K) on radiation-damaged pyrochlores has been investigated by Raman scattering, X-ray powder diffraction (XRD), and combined differential scanning calorimetry/thermogravimetry (DSC/TG). The analysis of three natural radiation-damaged pyrochlore samples from Miass/Russia [6.4 wt% Th, 23.1·10

  5. Weyl magnons in pyrochlore antiferromagnets with an all-in-all-out order

    Science.gov (United States)

    Jian, Shao-Kai; Nie, Wenxing

    2018-03-01

    We investigate topological magnon band crossings of pyrochlore antiferromagnets with all-in-all-out (AIAO) magnetic order. By general symmetry analysis and spin-wave theory, we show that pyrochlore materials with AIAO orders can host Weyl magnons under external magnetic fields or uniaxial strains. Under a small magnetic field, the magnon bands of the pyrochlore with AIAO background can feature two opposite-charged Weyl points, which is the minimal number of Weyl points realizable in quantum materials, and has not been experimentally observed so far. We further show that breathing pyrochlores with AIAO orders can exhibit Weyl magnons upon uniaxial strains. These findings apply to any pyrochlore material supporting AIAO orders, irrespective of the forms of interactions. Specifically, we show that the Weyl magnons are robust against direct (positive) Dzyaloshinskii-Moriya interactions. Because of the ubiquitous AIAO orders in pyrochlore magnets including R2Ir2O7 , and experimentally achievable external strain and magnetic field, our predictions provide a promising arena to witness the Weyl magnons in quantum magnets.

  6. Emergence of magnetic order in ultra-thin pyrochlore iridate films

    Science.gov (United States)

    Cheema, Suraj; Serrao, Claudy; Mundy, Julia; Patankar, Shreyas; Birgeneau, Robert; Orenstein, Joseph; Salahuddin, Sayeef; Ramesh, Ramamoorthy

    We report on thickness-dependent magnetotransport in (111) - oriented Pb2Ir2O7-x (Pb227) epitaxial thin films. For thicknesses greater than 4 nm, the magnetoresistance (MR) of metallic Pb227 is positive, linear and non-saturated up to 14 T. Meanwhile at 4 nm, the conduction turns nonmetallic and the MR becomes negative and asymmetric upon field-cooling; such traits are reminiscent of all-in-all-out (AIAO) magnetic order in the insulating pyrochlore iridates. Hysteretic low-field MR dips and trained-untrained resistivity bifurcations suggest the presence of magnetic conducting domain walls within the chiral AIAO spin structure. Beyond just AIAO order, angular-dependent MR indicates a magnetic phase space hosting 2-in-2-out (2I2O) spin ice order. Such anomalous magnetotransport calls for re-evaluation of the pyrochlore iridate phase diagram, as epitaxially strained Pb227 exhibits traits reminiscent of both the insulating magnetic and metallic spin-liquid members. Furthermore, these results open avenues for realizing topological phase predictions in (111) - oriented pyrochlore slabs of kagome-triangular iridate heterostructures. This work is supported by the Office of Basic Energy Sciences of the US Department of Energy under Contract No. DE-AC02-05CH11231.

  7. Heavy ion irradiation effects of brannerite-type ceramics

    International Nuclear Information System (INIS)

    Lian, J.; Wang, L.M.; Lumpkin, G.R.; Ewing, R.C.

    2002-01-01

    Brannerite, UTi 2 O 6 , occurs in polyphase Ti-based, crystalline ceramics that are under development for plutonium immobilization. In order to investigate radiation effects caused by α-decay events of Pu, a 1 MeV Kr + irradiation on UTi 2 O 6 , ThTi 2 O 6 , CeTi 2 O 6 and a more complex material, composed of Ca-containing brannerite and pyrochlore, was performed over a temperature range of 25-1020 K. The ion irradiation-induced crystalline-to-amorphous transformation was observed in all brannerite samples. The critical amorphization temperatures of the different brannerite compositions are: 970 K, UTi 2 O 6 ; 990 K, ThTi 2 O 6 ; 1020 K, CeTi 2 O 6 . The systematic increase in radiation resistance from Ce-, Th- to U-brannerite is related to the difference of mean atomic mass of A-site cation in the structure. As compared with the pyrochlore structure-type, brannerite phases are more susceptible to ion irradiation-induced amorphization. The effects of structure and chemical compositions on radiation resistance of brannerite-type and pyrochlore-type ceramics are discussed

  8. Synthesis by two methods and crystal structure determination of a new pyrochlore-related compound Sm{sub 2}FeTaO{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Torres-Martinez, Leticia M., E-mail: lettorresg@yahoo.com [Departamento de Ecomateriales y Energia, Facultad de Ingenieria Civil, Universidad Autonoma de Nuevo Leon, Cd. Universitaria, San Nicolas de los Garza, Nuevo Leon 66450 (Mexico); Ruiz-Gomez, Miguel A. [Departamento de Ecomateriales y Energia, Facultad de Ingenieria Civil, Universidad Autonoma de Nuevo Leon, Cd. Universitaria, San Nicolas de los Garza, Nuevo Leon 66450 (Mexico); Facultad de Ciencias Quimicas, Universidad Autonoma de San Luis Potosi, Av. Manuel Nava 6, San Luis Potosi, S.L.P. 78290 (Mexico); Figueroa-Torres, M.Z.; Juarez-Ramirez, Isaias [Departamento de Ecomateriales y Energia, Facultad de Ingenieria Civil, Universidad Autonoma de Nuevo Leon, Cd. Universitaria, San Nicolas de los Garza, Nuevo Leon 66450 (Mexico); Moctezuma, Edgar [Facultad de Ciencias Quimicas, Universidad Autonoma de San Luis Potosi, Av. Manuel Nava 6, San Luis Potosi, S.L.P. 78290 (Mexico); and others

    2012-04-16

    Graphical abstract: The monoclinic (space group C2/c) structure of a new compound, Sm{sub 2}FeTaO{sub 7} shows an alternating Sm-O and Fe/Ta-O layers. In the Fe/Ta-O layer, Fe/Ta1 and Fe/Ta3 cations are coordinated by six oxygen atoms, forming irregular octahedral interconnected into a hexagonal tungsten bronze (HTB) type network. The HTB layer is a fundamental framework in the pyrohlore-related structure. Highlights: Black-Right-Pointing-Pointer Pyrochlore-related compound Sm{sub 2}FeTaO{sub 7} prepared by solid state reaction and sol-gel. Black-Right-Pointing-Pointer Sm{sub 2}FeTaO{sub 7} crystallizes with a monoclinic crystal structure and space group C2/c. Black-Right-Pointing-Pointer The compound is synthesized by sol-gel at lower temperature and time than solid state. Black-Right-Pointing-Pointer Surface area of sol-gel Sm{sub 2}FeTaO{sub 7} is 10 times higher than that prepared by solid state. - Abstract: This paper reports on the synthesis of a new pyrochlore-related compound Sm{sub 2}FeTaO{sub 7} by both solid state reaction and sol-gel synthesis routes. Structural features were determined by X-ray powder diffraction and Rietveld refinement and were corroborated using Transmission Electron Microscopy (TEM). The results revealed that Sm{sub 2}FeTaO{sub 7} crystallized in the monoclinic system with space group C2/c and the following cell parameters: a = 13.1307(5) Angstrom-Sign , b = 7.5854(3) Angstrom-Sign , c = 11.6425(4) Angstrom-Sign and {beta} = 100.971(2) Degree-Sign . The monoclinic structure of Sm{sub 2}FeTaO{sub 7} showed an arrangement of alternating Sm-O and Fe/Ta-O layers and two types of irregular octahedra of Fe/Ta-O, which are interconnected into a hexagonal tungsten bronze (HTB)-type network. On the other hand, Sm{sub 2}FeTaO{sub 7} prepared by sol-gel was obtained with lower particle sizes than the solid state produced compound. The difference in particle size causes a difference of one order of magnitude in the specific surface area. In

  9. Tunable Magnon Weyl Points in Ferromagnetic Pyrochlores.

    Science.gov (United States)

    Mook, Alexander; Henk, Jürgen; Mertig, Ingrid

    2016-10-07

    The dispersion relations of magnons in ferromagnetic pyrochlores with Dzyaloshinskii-Moriya interaction are shown to possess Weyl points, i. e., pairs of topologically nontrivial crossings of two magnon branches with opposite topological charge. As a consequence of their topological nature, their projections onto a surface are connected by magnon arcs, thereby resembling closely Fermi arcs of electronic Weyl semimetals. On top of this, the positions of the Weyl points in reciprocal space can be tuned widely by an external magnetic field: rotated within the surface plane, the Weyl points and magnon arcs are rotated as well; tilting the magnetic field out of plane shifts the Weyl points toward the center Γ[over ¯] of the surface Brillouin zone. The theory is valid for the class of ferromagnetic pyrochlores, i. e., three-dimensional extensions of topological magnon insulators on kagome lattices. In this Letter, we focus on the (111) surface, identify candidates of established ferromagnetic pyrochlores which apply to the considered spin model, and suggest experiments for the detection of the topological features.

  10. Order and disorder in the local and long-range structure of the spin-glass pyrochlore, Tb{sub 2}Mo{sub 2}O{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Yu; Huq, Ashfia; Booth, Corwin H.; Ehlers, Georg; Greedan, John E.; Gardner, Jason S.

    2011-02-11

    To understand the origin of the spin-glass state in molybdate pyrochlores, the structure of Tb{sub 2}Mo{sub 2}O{sub 7} is investigated using two techniques: the long-range lattice structure was measured using neutron powder diffraction (NPD), and local structure information was obtained from the extended x-ray absorption fine structure (EXAFS) technique. While the long-range structure appears generally well ordered, enhanced mean-squared site displacements on the O(1) site and the lack of temperature dependence of the strongly anisotropic displacement parameters for both the Mo and O(1) sites indicate some disorder exists. Likewise, the local structure measurements indicate some Mo-Mo and Tb-O(1) nearest-neighbor disorder exists, similar to that found in the related spin-glass pyrochlore, Y{sub 2}Mo{sub 2}O{sub 7}. Although the freezing temperature in Tb{sub 2}Mo{sub 2}O{sub 7}, 25 K, is slightly higher than in Y{sub 2}Mo{sub 2}O{sub 7}, 22 K, the degree of local pair distance disorder is actually less in Tb{sub 2}Mo{sub 2}O{sub 7}. This apparent contradiction is considered in light of the interactions involved in the freezing process.

  11. Strain engineered pyrochlore at high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Rittman, Dylan R.; Turner, Katlyn M.; Park, Sulgiye; Fuentes, Antonio F.; Park, Changyong; Ewing, Rodney C.; Mao, Wendy L.

    2017-05-22

    Strain engineering is a promising method for next-generation materials processing techniques. Here, we use mechanical milling and annealing followed by compression in diamond anvil cell to tailor the intrinsic and extrinsic strain in pyrochlore, Dy2Ti2O7 and Dy2Zr2O7. Raman spectroscopy, X-ray pair distribution function analysis, and X-ray diffraction were used to characterize atomic order over short-, medium-, and long-range spatial scales, respectively, under ambient conditions. Raman spectroscopy and X-ray diffraction were further employed to interrogate the material in situ at high pressure. High-pressure behavior is found to depend on the species and concentration of defects in the sample at ambient conditions. Overall, we show that defects can be engineered to lower the phase transformation onset pressure by ~50% in the ordered pyrochlore Dy2Zr2O7, and lower the phase transformation completion pressure by ~20% in the disordered pyrochlore Dy2Zr2O7. These improvements are achieved without significantly sacrificing mechanical integrity, as characterized by bulk modulus.

  12. A novel high-temperature commensurate superstructure in a natural bariopyrochlore: A structural study by means of a multiphase crystal structure refinement

    International Nuclear Information System (INIS)

    Bindi, L.; Petricek, V.; Withers, R.L.; Zoppi, M.; Bonazzi, P.

    2006-01-01

    Additional X-ray diffraction effects yielding an eightfold commensurate superstructure [a=20.974(5)A] of the ideal pyrochlore structure were observed after annealing at 873K of a thallium-doped bariopyrochlore single crystal. Electron diffraction indicated the coexistence of two cubic phases, the pyrochlore structure and a new F-centred, cubic phase. The superstructure was solved and refined in the space group F4-bar 3m. The two phases were combined together and refined as independently diffracting to R=0.0628. The resulting unit-cell content is (A,-bar ) 20 Nb 16 Ti 2 O 53 (Z=8), with A=Ba, Tl, Ce, Th. For some atomic positions of the superstructure, third- and fourth-order anharmonic ADP's were used to account for the specific density shape having a continuous character as typical for ionic conductors. There are three distinct clusters in the superstructure, leading to a new structure type no longer strictly of pyrochlore-structure type

  13. Large-scale calculation of ferromagnetic spin systems on the pyrochlore lattice

    Energy Technology Data Exchange (ETDEWEB)

    Soldatov, Konstantin, E-mail: soldatov_ks@students.dvfu.ru [School of Natural Sciences, Far Eastern Federal University, Vladivostok (Russian Federation); Nefedev, Konstantin, E-mail: nefedev.kv@dvfu.ru [School of Natural Sciences, Far Eastern Federal University, Vladivostok (Russian Federation); Institute of Applied Mathematics, Far Eastern Branch, Russian Academy of Science, Vladivostok (Russian Federation); Komura, Yukihiro [CIJ-solutions, Chuo-ku, Tokyo 103-0023 (Japan); Okabe, Yutaka, E-mail: okabe@phys.se.tmu.ac.jp [Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 (Japan)

    2017-02-19

    We perform the high-performance computation of the ferromagnetic Ising model on the pyrochlore lattice. We determine the critical temperature accurately based on the finite-size scaling of the Binder ratio. Comparing with the data on the simple cubic lattice, we argue the universal finite-size scaling. We also calculate the classical XY model and the classical Heisenberg model on the pyrochlore lattice. - Highlights: • Calculations of the ferromagnetic models on the pyrochlore lattice were performed. • Precise critical temperatures were determined using Binder ratio finite-size scaling. • The universal finite-size scaling was argued.

  14. Aspects of reduction clorination of pyrochlore concentrates

    International Nuclear Information System (INIS)

    Gameiro, D.H.; Brocchi, E.A.

    1985-01-01

    Reduction chlorination experiments were carried out with two different Brazilian pyrochlore concentrates in order to evaluate the effects of some variables on the extent of niobium pentoxide gaseification as well as to compare the behavior of concentrate under the same chlorination conditions. The pyrochlore concentrates from Araxa (MG) and Catalao (GO), Brazil, were submitted to X ray diffraction and X ray fluorescence analysis for determining their chemical compositions. Kinetic curves were obtained with the main variables being temperature and percentage of reducing agent. Analysis of the condensed material in terms of Nb 2 O 5 indicated that chlorination can be used to produce niobium pentoxide. (Author) [pt

  15. Ceramic Single Phase High-Level Nuclear Waste Forms: Hollandite, Perovskite, and Pyrochlore

    Science.gov (United States)

    Vetter, M.; Wang, J.

    2017-12-01

    The lack of viable options for the safe, reliable, and long-term storage of nuclear waste is one of the primary roadblocks of nuclear energy's sustainable future. The method being researched is the incorporation and immobilization of harmful radionuclides (Cs, Sr, Actinides, and Lanthanides) into the structure of glasses and ceramics. Borosilicate glasses are the main waste form that is accepted and used by today's nuclear industry, but they aren't the most efficient in terms of waste loading, and durability is still not fully understood. Synroc-phase ceramics (i.e. hollandite, perovskite, pyrochlore, zirconolite) have many attractive qualities that glass waste forms do not: high waste loading, moderate thermal expansion and conductivity, high chemical durability, and high radiation stability. The only downside to ceramics is that they are more complex to process than glass. New compositions can be discovered by using an Artificial Neural Network (ANN) to have more options to optimize the composition, loading for performance by analyzing the non-linear relationships between ionic radii, electronegativity, channel size, and a mineral's ability to incorporate radionuclides into its structure. Cesium can be incorporated into hollandite's A-site, while pyrochlore and perovskite can incorporate actinides and lanthanides into their A-site. The ANN is used to predict new compositions based on hollandite's channel size, as well as the A-O bond distances of pyrochlore and perovskite, and determine which ions can be incorporated. These new compositions will provide more options for more experiments to potentially improve chemical and thermodynamic properties, as well as increased waste loading capabilities.

  16. Hydrothermal synthesis of electrode materials pyrochlore tungsten trioxide film

    Science.gov (United States)

    Guo, Jingdong; Li, Yingjeng James; Stanley Whittingham, M.

    Hydrothermal synthesis methods have been successfully used to prepare new transition-metal oxides for cathodes in electrochemical devices such as lithium batteries and electrochromic windows. The tungsten oxides were the first studied, but the method has been extended to the oxides of molybdenum, vanadium and manganese. Sodium tungsten oxide films with the pyrochlore structure have been prepared on gold/alumina and indium-doped tin oxide substrates. These films reversibly and rapidly intercalate lithium and hydrogen ions.

  17. Combined experimental–theoretical study of the optoelectronic properties of non-stoichiometric pyrochlore bismuth titanate

    KAUST Repository

    Noureldine, Dalal; Lardhi, Sheikha F.; Ziani, Ahmed; Harb, Moussab; Cavallo, Luigi; Takanabe, Kazuhiro

    2015-01-01

    A combination of experimental and computational methods was applied to investigate the crystal structure and optoelectronic properties of the non-stoichiometric pyrochlore Bi2−xTi2O7−1.5x. The detailed experimental protocol for both powder and thin

  18. Structural order parameter in the pyrochlore superconductor Cd sub 2 Re sub 2 O sub 7

    CERN Document Server

    Sergienko, I A

    2003-01-01

    It is shown that both structural phase transitions in Cd sub 2 Re sub 2 O sub 7 , which occur at T sub s sub 1 = 200 K and T sub s sub 2 = 120 K, are due to an instability of the Re tetrahedral network with respect to the same doubly degenerate long-wavelength phonon mode. The primary structural order parameter transforms according to the irreducible representation E sub u of the point group O sub h. We argue that the transition at T sub s sub 1 may be of the second order, in accordance with experimental data. We obtain the phase diagram in the space of phenomenological parameters and propose a thermodynamic path that Cd sub 2 Re sub 2 O sub 7 follows upon cooling. Coupling of the itinerant electronic system and localized spin states in pyrochlores and spinels to atomic displacements are discussed. (author)

  19. Superconducting and Structural Transitions in the β-Pyrochlore Oxide KOs2O6 under High Pressure

    Science.gov (United States)

    Ogusu, Hiroki; Takeshita, Nao; Izawa, Koichi; Yamaura, Jun-ichi; Ohishi, Yasuo; Tsutsui, Satoshi; Okamoto, Yoshihiko; Hiroi, Zenji

    2010-11-01

    Rattling-induced superconductivity in the β-pyrochlore oxide KOs2O6 is investigated under high pressure up to 5 GPa. Resistivity measurements in a high-quality single crystal reveal a gradual decrease in the superconducting transition temperature Tc from 9.7 K at 1.0 GPa to 6.5 K at 3.5 GPa, followed by a sudden drop to 3.3 K at 3.6 GPa. Powder X-ray diffraction experiments show a structural transition from cubic to monoclinic or triclinic at a similar pressure. The sudden drop in Tc is ascribed to this structural transition, by which an enhancement in Tc due to a strong electron-rattler interaction present in the low-pressure cubic phase is abrogated as the rattling of the K ion is completely suppressed or weakened in the high-pressure phase of reduced symmetry. In addition, we find two anomalies in the temperature dependence of resistivity in the low-pressure phase, which may be due to subtle changes in rattling vibration.

  20. George E. Valley, Jr. Prize Talk: Quantum Frustrated Magnetism and its Expression in the Ground State Selection of Pyrochlore Magnets

    Science.gov (United States)

    Ross, Kate

    In the search for novel quantum states of matter, such as highly entangled Quantum Spin Liquids, ``geometrically frustrated'' magnetic lattices are essential for suppressing conventional magnetic order. In three dimensions, the pyrochlore lattice is the canonical frustrated geometry. Magnetic materials with pyrochlore structures have the potential to realize unusual phases such as ``quantum spin ice'', which is predicted to host emergent magnetic monopoles, electrons, and photons as its fundamental excitations. Even in pyrochlores that form long range ordered phases, this often occurs through unusual routes such as ``order by disorder'', in which the fluctuation spectrum dictates the preferred ordered state. The rare earth-based pyrochlore series R2Ti2O7 provides a fascinating variety of magnetic ground states. I will introduce the general anisotropic interaction Hamiltonian that has been successfully used to describe several materials in this series. Using inelastic neutron scattering, the relevant anisotropic interaction strengths can be extracted quantitatively. I will discuss this approach, and its application to two rare earth pyrochlore materials, Er2Ti2O7 and Yb2Ti<2O7, whose ground state properties have long been enigmatic. From these studies, ErTi2O7 and Yb2Ti2O7 have been suggested to be realizations of "quantum order by disorder" and "quantum spin ice", respectively. This research was supported by NSERC of Canada and the National Science Foundation.

  1. Synthesis and characterization of bismuth zinc niobate pyrochlore nanopowders

    Directory of Open Access Journals (Sweden)

    Sonia Maria Zanetti

    2007-09-01

    Full Text Available Bismuth zinc niobate pyrochlores Bi1.5ZnNb1.5O7 (alpha-BZN, and Bi2(Zn1/3Nb2/32O 7 (beta-BZN have been synthesized by chemical method based on the polymeric precursors. The pyrochlore phase was investigated by differential scanning calorimetry, infrared spectroscopy, and X ray diffraction. Powder and sintered pellets morphology was examined by scanning electron microscopy. The study of alpha-BZN phase formation reveals that, at 500 °C, the pyrochlore phase was already present while a single-phased nanopowder was obtained after calcination at 700 °C. The crystallization mechanism of the beta-BZN is quite different, occurring through the crystallization of alpha-BZN and BiNbO4 intermediary phases. Both compositions yielded soft agglomerated powders. alpha-BZN pellets, sintered at 800 °C for 2 hours, presented a relative density of 97.3% while those of beta-BZN, sintered at 900 °C for 2 hours, reached only 91.8%. Dielectric constant and dielectric loss, measured at 1 MHz, were 150 and 4 x/10-4 for a-BZN, and 97 and 8 x 10-4 for beta-BZN.

  2. Two-magnon scattering in the 5d all-in-all-out pyrochlore magnet Cd2Os2O7.

    Science.gov (United States)

    Nguyen, Thi Minh Hien; Sandilands, Luke J; Sohn, C H; Kim, C H; Wysocki, Aleksander L; Yang, In-Sang; Moon, S J; Ko, Jae-Hyeon; Yamaura, J; Hiroi, Z; Noh, Tae Won

    2017-08-15

    5d pyrochlore oxides with all-in-all-out magnetic order are prime candidates for realizing strongly correlated, topological phases of matter. Despite significant effort, a full understanding of all-in-all-out magnetism remains elusive as the associated magnetic excitations have proven difficult to access with conventional techniques. Here we report a Raman spectroscopy study of spin dynamics in the all-in-all-out magnetic state of the 5d pyrochlore Cd 2 Os 2 O 7 . Through a comparison between the two-magnon scattering and spin-wave theory, we confirm the large single ion anisotropy in this material and show that the Dzyaloshinskii-Moriya and exchange interactions play a significant role in the spin-wave dispersions. The Raman data also reveal complex spin-charge-lattice coupling and indicate that the metal-insulator transition in Cd 2 Os 2 O 7 is Lifshitz-type. Our work establishes Raman scattering as a simple and powerful method for exploring the spin dynamics in 5d pyrochlore magnets.Pyrochlore 5d transition metal oxides are expected to have interesting forms of magnetic order but are hard to study with conventional probes. Here the authors show that Raman scattering can be used to measure magnetic excitations in Cd 2 Os 2 O 7 and that it exhibits complex spin-charge-lattice coupling.

  3. Compositional Evolution of Pyrochlore-Group Minerals in Carbonatites of the Belaya Zima Pluton, Eastern Sayan

    Science.gov (United States)

    Khromova, E. A.; Doroshkevich, A. G.; Sharygin, V. V.; Izbrodin, L. A.

    2017-12-01

    Pyrochlore-group minerals are the main concentrators of niobium in carbonatites of the Belaya Zima alkaline pluton. Fluorcalciopyrochlore, kenopyrochlore and hydropyrochlore were identified in chemical composition. Their main characteristics are given: compositional variation, morphology, and zoning. During evolution from early calcite to late ankerite carbonatites, the UO2, TiO2, REE, and Y contents gradually increased. All carbonatite types are suggested to contain initial fluorcalciopyrochlore. However, in calcite-dolomite and ankerite carbonatites, it is partially or completely hydrated due to hydrothermal processes at the late stage of the pluton. This hydration resulted in the appearance of kenopyrochlore and hydropyrochlore due to removal of Ca, Na and F, and input of Ba, H2O, K, Si, Fe, and probably U and REE. At the last stage of the pluton, this hydrated pyrochlore was replaced by Fe-bearing columbite.

  4. Preparation, structural characterization, and enhanced electrical conductivity of pyrochlore-type (Sm{sub 1-x}Eu{sub x}){sub 2}Zr{sub 2}O{sub 7} ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Xia, X.L. [Institute for Advanced Ceramics, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin (China); Institute of Oceanography Instruments, Shandong Academy of Science, Chinese National Engineering Research Center for Marine Monitoring Equipment, Qingdao (China); Liu, Z.G.; Ouyang, J.H. [Institute for Advanced Ceramics, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin (China); Zheng, Y. [Institute of Oceanography Instruments, Shandong Academy of Science, Chinese National Engineering Research Center for Marine Monitoring Equipment, Qingdao (China)

    2012-08-15

    (Sm{sub 1-x}Eu{sub x}){sub 2}Zr{sub 2}O{sub 7} (0 {<=} x {<=} 1.0) samples are prepared by solid state reaction method using Sm{sub 2}O{sub 3}, Eu{sub 2}O{sub 3}, and ZrO{sub 2} as starting materials. The phase composition and microstructure of (Sm{sub 1-x}Eu{sub x}){sub 2}Zr{sub 2}O{sub 7} ceramics are investigated by X-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM) coupled with selected area electron diffraction and Raman spectroscopy. XRD and TEM show that all the samples exhibit a single pyrochlore-type structure. HRTEM observation indicates that the whole grain interior of Sm{sub 2}Zr{sub 2}O{sub 7} ceramic is a perfect crystal free of any dislocation. Raman spectroscopy reveals that the degree of structural disorder of (Sm{sub 1-x}Eu{sub x}){sub 2}Zr{sub 2}O{sub 7} ceramics increases gradually with increasing Eu content. The electrical conductivity of (Sm{sub 1-x}Eu{sub x}){sub 2}Zr{sub 2}O{sub 7} ceramics is investigated by impedance spectroscopy in the air and hydrogen atmospheres, respectively. The electrical conductivity of (Sm{sub 1-x}Eu{sub x}){sub 2}Zr{sub 2}O{sub 7} ceramics increases with increasing Eu content at identical temperature levels. Both the activation energy E{sub g} and the pre-exponential factor {sigma}{sub 0g} for the grain conductivity gradually increase with increasing Eu content. As the ionic conductivity shows no obvious change in both air and hydrogen atmospheres, the conduction of (Sm{sub 1-x}Eu{sub x}){sub 2}Zr{sub 2}O{sub 7} is purely ionic with negligible electronic conduction. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  5. Preparation and characterization of bismuth ruthenate pyrochlore via solid state reaction and sol-gel methods

    Directory of Open Access Journals (Sweden)

    Mayuree Sansernnivet

    2010-01-01

    Full Text Available Bismuth ruthenate pyrochlores, potential cathode materials for intermediate temperature solid oxide fuel cells(ITSOFCs, were prepared via solid-state and sol-gel method. Effects of the preparation routes and conditions on the phase and microstructures of the materials were investigated in this study using XRD and SEM. The study showed that the preparation method and the adding sequence of the starting meterials have a significant effect on the crystal phase and the particle size obtained. Sol-gel synthesis could yield a material with only pyrochlore structure, i.e. Bi2Ru2O7, while the solid state method yielded powder with a small amount of the secondary RuO2 phase. The sol-gel synthesis resulted in materialswith a finer particle size (~0.3-1.0 μm compared to powder synthesized via the solid state reaction method.

  6. Synthesis and electrical properties of the pyrochlore-type Gd2-yLayZr2O7 solid solution

    Directory of Open Access Journals (Sweden)

    León, C.

    2008-06-01

    Full Text Available Different compositions in the pyrochlore-type Gd2-yLayZr2O7 solid solution (0 ≤ y ≤ 1 were prepared at room-temperature by mechanically milling stoichiometric mixtures of the corresponding oxides. Irrespective of their lanthanum content, as-prepared powder samples consist of single-phase anion deficient fluorite materials, although long-range ordering of cations and anion vacancies characteristic of pyrochlores was observed in all cases after firing the samples at 1500°C. Interestingly, activation energy for oxygen migration in the series decreases as La-content increases, from 1.13 eV for Gd2Zr2O7 to 0.81 eV for GdLaZr2O7, whereas ionic conductivity was found to be almost La-content independent, at least for y ≤ 0.8 at T = 500°C and y ≤ 0.4 at T = 800°C. These results are explained in terms of weaker ion-ion interactions in better ordered structures (i.e., as La-content increases and highlight the importance of structural ordering/disordering in determining the dynamics of mobile oxygen ions.Partiendo de mezclas estequiométricas de los óxidos correspondientes, se prepararon por molienda mecánica y a temperatura ambiente diferentes composiciones en la solución sólida Gd2-yLayZr2O7 (0 ≤ y ≤ 1 con estructura de tipo pirocloro y conductora de iones oxígeno. Independientemente del contenido de lantano, los polvos extraídos del molino presentaron difractogramas similares al de una fluorita no estequiométrica aunque en todos los casos, el tratamiento térmico a 1500°C indujo la aparición del ordenamiento de largo alcance de cationes y vacancias aniónicas característico de pirocloros. La energía de activación para el proceso de migración de iones oxígeno en la serie disminuye a medida que se incrementa el contenido de lantano, desde 1.13 eV de Gd2Zr2O7 hasta 0.81 eV de GdLaZr2O7, mientras que la conductividad resultó ser prácticamente independiente del mismo hasta y ≤ 0.8 para T = 500°C e y ≤ 0.4 para T = 800

  7. Disorder-induced transition from grain boundary to bulk dominated ionic diffusion in pyrochlores

    International Nuclear Information System (INIS)

    Perriot, Romain; Dholabhai, Pratik P.; Uberuaga, Blas P.

    2017-01-01

    In this paper, we use molecular dynamics simulations to investigate the role of grain boundaries (GBs) on ionic diffusion in pyrochlores, as a function of the GB type, chemistry of the compound, and level of cation disorder. We observe that the presence of GBs promotes oxygen transport in ordered and low-disordered systems, as the GBs are found to have a higher concentration of mobile carriers with higher mobilities than in the bulk. Thus, in ordered samples, the ionic diffusion is 2D, localized along the grain boundary. When cation disorder is introduced, bulk carriers begin to contribute to the overall diffusion, while the GB contribution is only slightly enhanced. In highly disordered samples, the diffusive behavior at the GBs is bulk-like, and the two contributions (bulk vs. GB) can no longer be distinguished. There is thus a transition from 2D/GB dominated oxygen diffusivity to 3D/bulk dominated diffusivity versus disorder in pyrochlores. Finally, these results provide new insights into the possibility of using internal interfaces to enhance ionic conductivity in nanostructured complex oxides.

  8. Order-disorder phase transformations in quaternary pyrochlore oxide system: Investigated by X-ray diffraction, transmission electron microscopy and Raman spectroscopic techniques

    International Nuclear Information System (INIS)

    Radhakrishnan, A.N.; Prabhakar Rao, P.; Sibi, K.S.; Deepa, M.; Koshy, Peter

    2009-01-01

    Order-disorder transformations in a quaternary pyrochlore oxide system, Ca-Y-Zr-Ta-O, were studied by powder X-ray diffraction (XRD) method, transmission electron microscope (TEM) and FT-NIR Raman spectroscopic techniques. The solid solutions in different ratios, 4:1, 2:1, 1:1, 1:2, 1:4, 1:6, of CaTaO 3.5 and YZrO 3.5 were prepared by the conventional high temperature ceramic route. The XRD results and Rietveld analysis revealed that the crystal structure changed from an ordered pyrochlore structure to a disordered defect fluorite structure as the ratios of the solid solutions of CaTaO 3.5 and YZrO 3.5 were changed from 4:1 to 1:4. This structural transformation in the present system is attributed to the lowering of the average cation radius ratio, r A /r B as a result of progressive and simultaneous substitution of larger cation Ca 2+ for Y 3+ at A sites and smaller cation Ta 5+ for Zr 4+ at B sites. Raman spectroscopy and TEM analysis corroborated the XRD results. - Graphical abstract: Selected area electron diffraction (SAED) patterns showed highly ordered diffraction maxima with characteristic superlattice weak diffraction spots of the pyrochlore structure for (a) Ca 0.6 7Y 1.33 Zr 1.33 Ta 0.33 O 7 (C2YZT2) and bright diffraction maxima arranged in a ring pattern of the fluorite structure for (b) Ca 0.29 7Y 1.71 Zr 1.71 Ta 0.29 O 7 (CY6Z6T).

  9. Radiation damage effects in pyrochlore and zirconolite ceramic matrices for the immobilization of actinide-rich wastes

    International Nuclear Information System (INIS)

    Lumpkin, G.R.; Begg, B.D.; Smith, K.L.

    2000-01-01

    Actinide-doping experiments using short-lived 238 Pu and 244 Cm have demonstrated that pyrochlore and zirconolite become fully amorphous at a dose of 0.2-0.5 x 10 16 α/mg at ambient temperature and exhibit bulk swelling of 5-7%. Detailed studies of natural samples have included determination of the critical amorphization dose, long-term annealing rate, microstructural changes as a function of dose, and the thermal histories of the host rocks. Together, the laboratory based work and studies of natural samples indicate that the critical amorphization dose will increase by about a factor of 2-4 for samples stored at temperatures of 100-200 deg. C for up to 10 million years. These studies of alpha-decay damage have been complemented by heavy ion irradiation studies over the last ten years. Most of the irradiation work has concerned the critical amorphization dose as a function of temperature in thin films; however, some work has been carried out on bulk samples. The irradiation work indicates that most pyrochlore and zirconolite compositions will have similar critical amorphization doses at low temperatures (e.g., below 300-400 deg. C). Pyrochlore with Zr as the major B-site cation transform to a defect fluorite structure with increasing ion irradiation dose, but do not become amorphous. (authors)

  10. Speciation of uranium in La{sub 2}Zr{sub 2}O{sub 7} pyrochlore by TRPLS

    Energy Technology Data Exchange (ETDEWEB)

    Mohapatra, M.; Rajeswari, B.; Hon, N. S.; Kadam, R. M., E-mail: rmkadam@barc.gov.in; Natarajan, V. [Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400085 (India)

    2015-06-24

    We discuss the speciation of uranium in lanthanum zirconate (La{sub 2}Zr{sub 2}O{sub 7} =LZO) pyrochlore ceramic prepared via a gel-combustion route. Uranium concentration in the pyrochlore was optimized to 2 mol%. XRD and SEM experiments were carried out to assess the phase and homogeneity of the prepared samples. Time resolved photoluminescence (TRPLS) investigations were carried out for understanding the species stabilized in the pyrochlore host. It was observed that, uranium exists as uranate ion (UO{sub 6}{sup 6−}) in the zirconate host where it replaces the ‘Zr’ ions at its regular site with surrounding defect centers created for charge compensation.

  11. The effect of B-site substitution on structural transformation and ionic conductivity in Ho2(ZryTi1−y)2O7

    International Nuclear Information System (INIS)

    Shafique, Muhammad; Kennedy, Brenden J.; Iqbal, Yaseen; Ubic, Rick

    2016-01-01

    Compounds in the pyrochlore system Ho 2 (Zr y Ti 1−y ) 2 O 7 exhibit an order-disorder transition from pyrochlore to a defect-fluorite type structure. Compositions in this system were prepared via mechanical milling, followed by a two-step sintering process. Structural characterization was carried out via Rietveld refinements using neutron powder diffraction data, supported by X-ray diffraction to determine the phase and location of the pyrochlore-fluorite transformation. Unit-cell parameters were determined for the whole series using Rietveld refinements as well as the Nelson–Riley function. The neutron refinement results confirmed that the cation disorder was independent of the anion Frenkel disorder. The relation between the x-parameter in the oxygen 48f position and anion Frenkel disorder was found to be linear for the pyrochlore structure. The ionic conductivity studies were undertaken via AC impedance analysis to determine the electronic behaviour and its relation to the structural change in the temperature range 300°C–700 °C. The trends in ionic conductivity and activation energy were explained structurally via neutron powder diffraction and X-ray diffraction data. The pyrochlore-fluorite boundary composition (at y = 0.5) exhibited the lowest activation energy and highest ionic conductivity. - Highlights: • Ho 2 (Zr y Ti 1-y ) 2 O 7 structure changed from ordered pyrochlore to defect-fluorite at y = 0.6. • Ho 2 (Zr 0.5 Ti 0.5 ) 2 O 7 exhibited high ionic conductivity and low activation energy. • Doping improved stability in ionic conductivity behaviour at lower temperature.

  12. Interface formation and defect structures in epitaxial La2Zr2O7 thin films on (111) Si

    International Nuclear Information System (INIS)

    Seo, J.W.; Fompeyrine, J.; Guiller, A.; Norga, G.; Marchiori, C.; Siegwart, H.; Locquet, J.-P.

    2003-01-01

    We have studied the growth of epitaxial La 2 Zr 2 O 7 thin films on (111) Si. Although the interface structure can be strongly affected by the Si oxidation during the deposition process, epitaxial growth of La 2 Zr 2 O 7 was obtained. A detailed study by means of transmission electron microscopy reveals two types of structures (pyrochlore and fluorite) with the same average chemical composition but strong differences in reactivity and interface formation. The structural complexity of the ordered pyrochlore structure seems to prevent excess oxygen diffusion and interfacial SiO 2 formation

  13. Anisotropic vortex pinning in the β-pyrochlore oxide superconductor KOs 2O 6

    Science.gov (United States)

    Ishii, Y.; Yamaura, J.; Okamoto, Y.; Maeda, A.; Hiroi, Z.

    2011-11-01

    Vortex pinning in the β-pyrochlore oxide superconductor KOs2O6 with Tc = 9.6 K is investigated by measuring magnetic torque. A large anisotropy of magnetic torque is observed in the superconducting state below Tp = 7.6 K, where a first-order structural transition takes place, in spite of the inherent isotropic nature of the structural and electronic properties. Magnetic torque is enhanced at external magnetic fields parallel to the [1 1 1] and [0 0 1] directions. Moreover, a pronounced peak effect is also observed in the magnetic field dependence of the torque in these two directions. We consider that the observed anisotropy is related to a microstructure associated with the structural transition.

  14. An unusual hybrid fluoride featuring a [V7F27]6- chain motif based on a pyrochlore-like building unit

    International Nuclear Information System (INIS)

    Aldous, David W.; Slawin, Alexandra M.Z.; Lightfoot, Philip

    2008-01-01

    A new hybrid vanadium (III) fluoride [C 4 H 12 N 2 ] 3 [V 7 F 27 ] has been synthesised solvothermally. The crystal structure (trigonal, R3-bar c; a=17.367(2) A, c=19.604(2) A) reveals an unusual and novel chain motif consisting of pyrochlore-like heptameric units of corner-sharing octahedra, which are further linked into linear chains of alternating triple and single octahedral groups. The chains are separated by hydrogen-bonded piperazinium moieties. Magnetic susceptibility data show moderate antiferromagnetic interactions but no long-range order above 2 K, consistent with pronounced one-dimensional character, as well as frustration arising within the triangular units of magnetic ions in the chains. - Graphical abstract: A unique chain-structure vanadium(III) fluoride [C 4 H 12 N 2 ] 3 [V 7 F 27 ], based on a pyrochlore-like building unit, has been prepared solvothermally. Despite antiferromagnetic interactions, no long-range magnetic order occurs above 2 K, suggesting possible frustration

  15. X-ray diffraction study of the Y{sub 2}Ti{sub 2}O{sub 7} pyrochlore disordering sequence under irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Soulié, Aurélien, E-mail: aurelien.soulie@cea.fr [CEA, DEN, Service de Recherches de Métallurgie Physique, Université Paris-Saclay, F-91191 Gif sur Yvette (France); CEA, DEN, Service de Recherches de Métallurgie Appliqué, Université Paris-Saclay, F-91191 Gif sur Yvette (France); Menut, Denis [CEA, DEN, Service de Recherches de Métallurgie Appliqué, Université Paris-Saclay, F-91191 Gif sur Yvette (France); Crocombette, Jean-Paul [CEA, DEN, Service de Recherches de Métallurgie Physique, Université Paris-Saclay, F-91191 Gif sur Yvette (France); Chartier, Alain [CEA, DEN, Service de la Corrosion et du Comportement des Matériaux dans leur Environnement, Laboratoire de Modélisation, de Thermodynamique et de Thermochimie, Université Paris-Saclay, F-91191 Gif sur Yvette (France); Sellami, Neila [Univ. Paris Sud, ICMMO-SP2M, Bât. 410, F-91405 Orsay (France); Sattonnay, Gaël [Univ. Paris-Sud, CSNSM, CNRS, IN2P3, Bât. 108, F-91405 Orsay (France); Monnet, Isabelle [CIMAP, CEA, CNRS, Université de Caen, BP 5133, F-14070 Caen Cedex 5 (France); and others

    2016-11-15

    The disordering sequence of Y{sub 2}Ti{sub 2}O{sub 7} pyrochlore, a nano-oxide phase that strengthens ODS steels under irradiation is studied in the experimental and modeling framework. XRD analysis has been performed considering both swift heavy ion and low energy/low mass ion irradiations. The simulation within molecular dynamics of Frenkel pair accumulation proves able to reproduce the variation of the amorphization fluence with temperature. XRD patterns calculated from the simulations reproduce well the patterns observed experimentally in the literature. Both experiments and calculations point to a first transition from pyrochlore to fluorite before an eventual amorphization. For swift heavy ion irradiations with 93 MeV Xe ions, tracks of direct impact amorphization are visible by HRTEM. Advanced refinement shows that one third of the pyrochlore impacted by an ion transforms into fluorite, while two third are directly amorphized. - Highlights: • A comparison between swift heavy ion and low energy/low mass ion irradiation of Y{sub 2}Ti{sub 2}O{sub 7} pyrochlore is performed. • Simulations of the irradiation with Molecular dynamics reproduce the amorphization dose at low energy/mass ion irradiation. • Advanced refinement of X-ray diffraction patterns gives the evolution of phase fractions in pyrochlore under irradiation. • The disordering sequence a transition from pyrochlore to defect fluorite before an eventual amorphization.

  16. Low temperature spin dynamics and high pressure effects in frustrated pyrochlores

    Science.gov (United States)

    Mirebeau, Isabelle

    2008-03-01

    Frustrated pyrochlores R2M2O7, where R^3+ is a rare earth and M^4+ a transition or sp metal ion, show a large variety of exotic magnetic states due to the geometrical frustration of the pyrochlore lattice, consisting of corner sharing tetrahedra for both R and M ions. Neutron scattering allows one to measure their magnetic ground state as well as the spin fluctuations, in a microscopic way. An applied pressure may change the subtle energy balance between magnetic interactions, inducing new magnetic states. In this talk, I will review recent neutron results on Terbium pyrochlores, investigated by high pressure neutron diffraction and inelastic neutron scattering. Tb2M2O7 pyrochlores show respectively a spin liquid state for M=Ti [1], an ordered spin ice state for M= Sn [2], and a spin glass state with chemical order for M=Mo [3]. In Tb2Ti2O7 spin liquid, where only Tb^3+ ions are magnetic, an applied pressure induces long range antiferromagnetic order due to a small distortion of the lattice and magneto elastic coupling [4]. In Tb2Sn2O7, the substitution of Ti^4+ by the bigger Sn^4+ ion expands the lattice, inducing a long range ordered ferromagnetic state, with the local structure of a spin ice [2] and unconventional spin fluctuations [2,5]. The local ground state and excited crystal field states of the Tb^3+ ion were recently investigated by inelastic neutron scattering in both compounds [6]. Tb2Mo2O7, where Mo^4+ ions are also magnetic, shows an even more rich behaviour, due to the complex interaction between frustrated Tb and Mo lattices, having respectively localized and itinerant magnetism. In Tb2Mo2O7 spin glass, the lattice expansion induced by Tb/La substitution yields an ordered ferromagnetic state, which transforms back to spin glass under applied pressure [7]. New data about the spin fluctuations in these compounds, as measured by inelastic neutron scattering, will be presented. The talk will be dedicated to the memory of Igor Goncharenko, a renowned

  17. Low-temperature specific heat of the β-pyrochlore oxide superconductors under high pressure

    Science.gov (United States)

    Isono, T.; Iguchi, D.; Machida, Y.; Izawa, K.; Salce, B.; Flouquet, J.; Ogusu, H.; Yamaura, J.; Hiroi, Z.

    2011-01-01

    We report the results of the low-temperature specific heat measurements of the single crystalline β-pyrochlore oxide superconductors AOs 2O 6 (A=K, Rb, and Cs) under high pressure up to 13 GPa. We find that superconducting transition temperature ( Tc) monotonically increases for CsOs 2O 6 and RbOs 2O 6, while the one for KOs 2O 6 decreases by applying the pressure. With further increasing the pressure, Tc is suddenly suppressed at the same lattice volume for all compounds, concomitant with the first-order structural phase transition.

  18. Static magnetic susceptibility, crystal field and exchange interactions in rare earth titanate pyrochlores.

    Science.gov (United States)

    Malkin, B Z; Lummen, T T A; van Loosdrecht, P H M; Dhalenne, G; Zakirov, A R

    2010-07-14

    The experimental temperature dependence (T = 2-300 K) of single crystal bulk and site susceptibilities of rare earth titanate pyrochlores R(2)Ti(2)O(7) (R = Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) is analyzed in the framework of crystal field theory and a mean field approximation. Analytical expressions for the site and bulk susceptibilities of the pyrochlore lattice are derived taking into account long range dipole-dipole interactions and anisotropic exchange interactions between the nearest neighbor rare earth ions. The sets of crystal field parameters and anisotropic exchange coupling constants have been determined and their variations along the lanthanide series are discussed.

  19. Structural vs. intrinsic carriers: contrasting effects of cation chemistry and disorder on ionic conductivity in pyrochlores

    International Nuclear Information System (INIS)

    Perriot, Romain; Uberuaga, Blas P.

    2015-01-01

    We use molecular dynamics simulations to investigate the role of cation disorder on oxygen diffusion in Gd 2 Zr 2 O 7 (GZO) and Gd 2 Ti 2 O 7 (GTO) pyrochlores, a class of complex oxides which contain a structural vacancy relative to the basic fluorite structure. The introduction of disorder has distinct effects depending on the chemistry of the material, increasing the mobility of structural carriers by up to four orders of magnitude in GZO. In contrast, in GTO, there is no mobility at zero or low disorder on the ns timescale, but higher disorder liberates the otherwise immobile carriers, allowing diffusion with rates comparable to GZO for the fully disordered material. Here, we show that the cation disorder enhances the diffusivity by both increasing the concentration of mobile structural carriers and their individual mobility. The disorder also influences the diffusion in materials containing intrinsic carriers, such as additional vacancies VO or oxygen interstitials OI. And while in ordered GZO and GTO the contribution of the intrinsic carriers dominates the overall diffusion of oxygen, OI in GZO contributes along with structural carriers, and the total diffusion rate can be calculated by assuming simple additive contributions from the two sources. Although the disorder in the materials with intrinsic defects usually enhances the diffusivity as in the defect-free case, in low concentrations, cation antisites AB or BA, where A = Gd and B = Zr or Ti, can act as traps for fast intrinsic defects. The trapping results in a lowering of the diffusivity, and causes a non-monotonic behavior of the diffusivity with disorder. Conversely, in the case of slow intrinsic defects, the main effect of the disorder is to liberate the structural carriers, resulting in an increase of the diffusivity regardless of the defect trapping.

  20. The atomic structure of protons and hydrides in Sm1.92Ca0.08Sn2O7-δ pyrochlore from DFT calculations and FTIR spectroscopy

    DEFF Research Database (Denmark)

    Bork, Nicolai Christian; Eurenius, K. E. J.; Rossmeisl, Jan

    2012-01-01

    A combined density functional theory and Fourier transform infrared spectroscopy study of the structure and specific site preference of protons and hydrides in the pyrochlore Sm1.92Ca0.08Sn2O7-δ is presented. Two protonic sites of particular high stability are identified, both located on O(1......) oxygen atoms closely associated with a Ca dopant. Further, the unexpected presence of Ho hydride defects in undoped, oxygen deficient Sm2Sn2O7 is reported. Finally, the stretching frequencies and relative intensities for these and other sites are calculated. The main features of the Fourier transform...

  1. High-pressure resistivity measurements on the β-pyrochlore oxide KOs2O6

    Science.gov (United States)

    Ogusu, Hiroki; Takeshita, Nao; Yamaura, Jun-Ichi; Okamoto, Yoshihiko; Hiroi, Zenji

    2010-12-01

    High-pressure resistivity measurements are performed on a high-quality single crystal of the β-pyrochlore oxide KOs2O6 in the pressure range of 1.0 to 5.0 GPa. The superconducting transition temperature T increases slightly from 9.6 K at ambient pressure to 9.8 K at 1.0 GPa, decreases gradually with increasing pressure, and suddenly drops from 6.5 K to 3.2 K across P=3.6GPa. The drop of T at P is likely to be related to a change in the rattling vibration associated with a symmetry-breaking structural transition.

  2. Use of linear free energy relationship to predict Gibbs free energies of formation of pyrochlore phases (CaMTi2O7)

    International Nuclear Information System (INIS)

    Xu, H.; Wang, Y.

    1999-01-01

    In this letter, a linear free energy relationship is used to predict the Gibbs free energies of formation of crystalline phases of pyrochlore and zirconolite families with stoichiometry of MCaTi 2 O 7 (or, CaMTi 2 O 7 ,) from the known thermodynamic properties of aqueous tetravalent cations (M 4+ ). The linear free energy relationship for tetravalent cations is expressed as ΔG f,M v X 0 =a M v X ΔG n,M 4+ 0 +b M v X +β M v X r M 4+ , where the coefficients a M v X , b M v X , and β M v X characterize a particular structural family of M v X, r M 4+ is the ionic radius of M 4+ cation, ΔG f,M v X 0 is the standard Gibbs free energy of formation of M v X, and ΔG n,M 4+ 0 is the standard non-solvation energy of cation M 4+ . The coefficients for the structural family of zirconolite with the stoichiometry of M 4+ CaTi 2 O 7 are estimated to be: a M v X =0.5717, b M v X =-4284.67 (kJ/mol), and β M v X =27.2 (kJ/mol nm). The coefficients for the structural family of pyrochlore with the stoichiometry of M 4+ CaTi 2 O 7 are estimated to be: a M v X =0.5717, b M v X =-4174.25 (kJ/mol), and β M v X =13.4 (kJ/mol nm). Using the linear free energy relationship, the Gibbs free energies of formation of various zirconolite and pyrochlore phases are calculated. (orig.)

  3. Structural determination of new solid solutions [Y2-x Mx ][Sn2-x Mx ]O7-3x/2 (M = Mg or Zn by Rietveld method

    Directory of Open Access Journals (Sweden)

    Mohamed Douma

    2010-12-01

    Full Text Available New [Y2-x Mx][Sn2-x Mx]O7-3x/2 (0 ≤x≤ 0.30 for M = Mg and 0 ≤x≤ 0.36 for M = Zn solid solutions with the pyrochlore structure were synthesized via high-temperature solid-state reaction method. Powder X-ray diffraction (PXRD patterns and Fourier transform infrared (FT-IR spectra showed that these materials are new non-stoichiometric solid solutions with the pyrochlore type structure. The structural parameters for the solids obtained were successfully determined by Rietveld refinement based on the analysis of the PXRD diagrams. Lattice parameter (a of these solid solutions decreases when x increases in both series. All samples obtained have the pyrochlore structure Fd-3m, no. 227 (origin at center -3m with M2+ (M = Mg2+ or Zn2+ cations in Y3+ and Sn4+ sites, thus creating vacancies in the anionic sublattice.

  4. Structural, hyperfine and Raman properties of RE2FeSbO7 compounds

    International Nuclear Information System (INIS)

    Berndt, G.; Silva, K.L.; Ivashita, F.F.; Paesano, A.; Blanco, M.C.; Miner, E.V.P.; Carbonio, R.E.; Dantas, S.M.; Ayala, A.P.; Isnard, O.

    2015-01-01

    Highlights: • We prepared monophasic RE 2 FeSbO 7 pyrochlores. • RE 2 FeSbO 7 compounds were characterized regarding crystallographic, vibrational and hyperfine properties. • We find out that a site disorder takes place for the RE’s of larger ionic radii. • Lattice parameters, Raman bands and quadrupole splittings were shown to depend correlatedly on the RE ionic radius. - Abstract: Pyrochlores of the RE 2 FeSbO 7 type were synthesized by ball-milling followed by annealing in free atmosphere at high temperatures. The samples prepared were characterized by X-ray diffraction, Raman spectroscopy and 57 Fe Mössbauer spectroscopy, at room temperature. The results showed that RE 2 FeSbO 7 compounds have a cubic structure, i.e., Fd-3m (#227) space group, and that a site disorder takes place for the RE’s of larger ionic radii. Lattice parameters, Raman bands and quadrupole splittings were shown to depend correlatedly on the RE ionic radius. This behavior is discussed in terms of the pyrochlore crystallographic structure

  5. Synthesis, magnetic properties and Moessbauer spectroscopy for the pyrochlore family Bi{sub 2}BB Prime O{sub 7} with B=Cr and Fe and B Prime =Nb, Ta and Sb

    Energy Technology Data Exchange (ETDEWEB)

    Blanco, Maria C. [INFIQC (CONICET), Dpto. de Fisicoquimica, Fac. de Ciencias Quimicas, U.N.C., Cordoba (X5000HUA) (Argentina); Franco, Diego G. [INFIQC (CONICET), Dpto. de Fisicoquimica, Fac. de Ciencias Quimicas, U.N.C., Cordoba (X5000HUA) (Argentina); Centro Atomico Bariloche - CNEA, Av. E. Bustillo 9500, S.C. de Bariloche (8500), R.N. (Argentina); Jalit, Yamile; Pannunzio Miner, Elisa V. [INFIQC (CONICET), Dpto. de Fisicoquimica, Fac. de Ciencias Quimicas, U.N.C., Cordoba (X5000HUA) (Argentina); Berndt, Graciele; Paesano, Andrea [Departamento de Fisica, Universidade Estadual de Maringa, Parana (Brazil); Nieva, Gladys [Centro Atomico Bariloche - CNEA, Av. E. Bustillo 9500, S.C. de Bariloche (8500), R.N. (Argentina); Carbonio, Raul E., E-mail: carbonio@mail.fcq.unc.edu.ar [INFIQC (CONICET), Dpto. de Fisicoquimica, Fac. de Ciencias Quimicas, U.N.C., Cordoba (X5000HUA) (Argentina)

    2012-08-15

    The samples Bi{sub 2}BB Prime O{sub 7}, with B=Cr and Fe and B Prime =Nb, Ta and Sb were prepared by solid state method. The crystallographic structure was investigated on the basis of X-ray powder diffraction data. Rietveld refinements show that the crystal structure is cubic, space group Fd-3m. The Bi{sup 3+} cation on the eight-coordinate pyrochlore A-site shows displacive disorder, as a consequence of its lone pair electron configuration. There is also a considerable A-site disorder shown by Rietveld Analysis and confirmed in the case of the iron containing samples with Moessbauer spectroscopy. The magnetic measurements show paramagnetic behavior at all temperatures for the Cr oxides. The Fe pyrochlores show antiferromagnetic order around 10 K.

  6. Many-Body Theory of Pyrochlore Iridates and Related Materials

    Science.gov (United States)

    Wang, Runzhi

    perform combined density functional plus dynamical mean-field calculations in Lu2Ir2O7, Y2Ir2O 7, Eu2Ir2O7, with spin-orbit coupling included and both single-site and cluster approximations appiled. A broad range of Weyl metal is predicted as the intervening phase in the metal-insulator transition. By comparing to experiments, we find that the single-site approximation fails to predict the gap values and substantial difference between the Y and Eu-compound, demonstrating the inadequacy of this approximation and indicating the key role played by the intersite effects. Finally, we provide a more accurate description of the vicinity of the metal-insulator and topological transitions implied by density functional plus cluster dynamical mean-field calculations of pyrochlore iridates. We find definitive evidence of the Weyl semimetal phase, the electronic structure of which can be approximately described as ``Weyl rings" with an extremely flat dispersion of one of the Weyl bands. This Weyl semimetal phase is further investigated by the k • p analysis fitting to the numerical results. We find that this unusual structure leads to interesting behavior in the optical conductivity including a Hall effect in the interband component, and to an enhanced susceptibility.

  7. Study on the chemical treatment processes of the uranium pyrochlore of Araxa

    International Nuclear Information System (INIS)

    Batista, H.F.; Fernandes, M.D.

    Several processes are presented for the chemical treatment, in laboratory scale, of the uranium pyrochlore concentrates found in Araxa (Minas Gerais, Brazil), aiming to the extraction of uranium, thorium and rare earths, besides the recovery of niobium pentoxide [pt

  8. High-pressure synthesis and characterizations of the R2Pt2O7 pyrochlores.

    Science.gov (United States)

    Cai, Yunqi; Cui, Qi; Cheng, Jinguang; Dun, Zhiling; Zhou, Haidong; Ma, Jie; Cruz, C. Dela; Yan, Jiaqiang; Li, Xiang; Zhou, Jianshi

    Pyrochlore R2B2O7 where R3 + stands for rear-earth ion and B4 + for a nonmagnetic cation such as Sn4 +or Ti4 +consist of an important family of geometrically frustrated magnets, which have been the focus of extensive investigations over last decades. To further enlarge the R2B2O7, we have chosen to stabilize the Pt-based cubic pyrochlores under HPHT conditions for two reasons: (1) Pt4 + is in a low-spin state which ionic radius is located in between Ti4 + (0.605\\x85) and Sn4 + (0.69\\x85), and (2) Pt4 + has a spatially much more extended 5d orbitals and thus enhanced Pt 5d-O 2p hybridizations that might modify the local anisotropic exchange interactions. Such an effect has never been taken into account in the previous studies. In this work, we will present the detailed characterizations on the pyrochlores R2Pt2O7 obtained under HPHT conditions. This work is supported by the National Science Foundation of China (Grant Nos.11304371, 11574377), part of the work was supported by the CEM, and NSF MRSEC, under Grant DMR-1420451, and Grant No. NSF-DMR-1350002.

  9. Phase transition and water incorporation into Eu2Sn2O7 pyrochlore at high pressure

    Science.gov (United States)

    Zhang, F. X.; Lang, M.; Ewing, R. C.

    2016-04-01

    Structural changes of europium stannate pyrochlore, Eu2Sn2O7, have been investigated at high pressures with in situ Raman spectroscopy, photoluminescence (PL), and synchrotron X-ray diffraction (XRD) techniques. The XRD measurements suggest that a pressure-induced phase transition starts at 34.4 GPa. The PL spectrum from Eu3+ cations also suggests a phase transition above 36 GPa. XRD analysis shows that the unit cell of the cubic phase deviates from the equation of state at pressures above 23.8 GPa. This is due to the incorporation of water from the pressure medium in the structure at high pressures, which is confirmed by optical spectroscopy measurements.

  10. A spin-liquid with pinch-line singularities on the pyrochlore lattice.

    Science.gov (United States)

    Benton, Owen; Jaubert, L D C; Yan, Han; Shannon, Nic

    2016-05-26

    The mathematics of gauge theories lies behind many of the most profound advances in physics in the past 200 years, from Maxwell's theory of electromagnetism to Einstein's theory of general relativity. More recently it has become clear that gauge theories also emerge in condensed matter, a prime example being the spin-ice materials which host an emergent electromagnetic gauge field. In spin-ice, the underlying gauge structure is revealed by the presence of pinch-point singularities in neutron-scattering measurements. Here we report the discovery of a spin-liquid where the low-temperature physics is naturally described by the fluctuations of a tensor field with a continuous gauge freedom. This gauge structure underpins an unusual form of spin correlations, giving rise to pinch-line singularities: line-like analogues of the pinch points observed in spin-ice. Remarkably, these features may already have been observed in the pyrochlore material Tb2Ti2O7.

  11. Irradiation-induced amorphization of Cd2Nb2O7 pyrochlore

    International Nuclear Information System (INIS)

    Meldrum, A.; White, C. W.; Keppens, V.; Boatner, L. A.; Ewing, R. C.

    2001-01-01

    Several investigations have recently been undertaken in order to achieve a more complete understanding of the radiation-damage mechanisms in A 2 B 2 O 7 pyrochlore-structure compounds. The present work represents the first systematic study of the irradiation-induced amorphization of a pyrochlore with A- and B-site cation valences of +2 and +5, respectively. Relatively large single crystals of Cd 2 Nb 2 O 7 were grown for these experiments. In situ ion-irradiation experiments were carried out in a transmission electron microscope in conjunction with ex situ Rutherford backscattering measurements of ion-irradiated Cd 2 Nb 2 O 7 single crystals. Cd 2 Nb 2 O 7 can be amorphized in situ by Ne or Xe ions at temperatures up to 480 and 620 K, respectively. At room temperature, the amorphization fluence was 36 times higher for 280 keV Ne + than for 1200 keV Xe 2+ , corresponding to a displacement dose that was higher by a factor of 3. Disordering of Cd and Nb over the available cation sites occurs at intermediate ion doses prior to amorphization. The temperature dependence of the amorphization dose is modeled, and the results are compared to those of a previous model. The bulk-sample Rutherford backscattering spectroscopy (RBS) results were generally consistent with the in situ TEM measurements. Effects of crystallographic orientation and ion charge state had relatively little effect on the damage accumulation in bulk crystals. The RBS data are consistent with a defect-accumulation, cascade-overlap model of amorphization of Cd 2 Nb 2 O 7 , as are the in situ TEM observations

  12. Novel rattling of K atoms in aluminium-doped defect pyrochlore tungstate

    International Nuclear Information System (INIS)

    Shoko, Elvis; Kearley, Gordon J; Peterson, Vanessa K; Thorogood, Gordon J; Mutka, Hannu; Koza, Michael M; Yamaura, Jun-ichi; Hiroi, Zenji

    2014-01-01

    Rattling dynamics have been identified as fundamental to superconductivity in defect pyrochlore osmates and aluminium vanadium intermetallics, as well as low thermal conductivity in clathrates and filled skutterudites. Combining inelastic neutron scattering (INS) measurements and ab initio molecular dynamics (MD) simulations, we use a new approach to investigate rattling in the Al-doped defect pyrochlore tungstates: AAl 0.33 W 1.67 O 6 (A = K, Rb, Cs). We find that although all the alkali metals rattle, the rattling of the K atoms is unique, not only among the tungstates but also among the analogous defect osmates, KOs 2 O 6 and RbOs 2 O 6 . Detailed analysis of the MD trajectories reveals that two unique features set the K dynamics apart from the rest, namely, (1) quasi one-dimensional local diffusion within a cage, and (2) vibration at a range of frequencies. The local diffusion is driven by strongly anharmonic local potentials around the K atoms exhibiting a double-well structure in the direction of maximum displacement, which is also the direction of local diffusion. On the other hand, vibration at a range of frequencies is a consequence of the strong anisotropy in the local potentials around the K atoms as revealed by directional magnitude spectra. We present evidence to show that it is the smaller size rather than the smaller mass of the K rattler which leads to the unusual dynamics. Finally, we suggest that the occurrence of local diffusion and vibration at a range of frequencies in the dynamics of a single rattler, as found here for the K atoms, may open new possibilities for phonon engineering in thermoelectric materials. (paper)

  13. Tm-doped TiO2 and Tm2Ti2O7 pyrochlore nanoparticles: enhancing the photocatalytic activity of rutile with a pyrochlore phase.

    Science.gov (United States)

    De Los Santos, Desiré M; Navas, Javier; Aguilar, Teresa; Sánchez-Coronilla, Antonio; Fernández-Lorenzo, Concha; Alcántara, Rodrigo; Piñero, Jose Carlos; Blanco, Ginesa; Martín-Calleja, Joaquín

    2015-01-01

    Tm-doped TiO2 nanoparticles were synthesized using a water-controlled hydrolysis reaction. Analysis was performed in order to determine the influence of the dopant concentration and annealing temperature on the phase, crystallinity, and electronic and optical properties of the resulting material. Various characterization techniques were utilized such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and UV-vis spectroscopy. For the samples annealed at 773 and 973 K, anatase phase TiO2 was obtained, predominantly internally doped with Tm(3+). ICP-AES showed that a doping concentration of up to 5.8 atom % was obtained without reducing the crystallinity of the samples. The presence of Tm(3+) was confirmed by X-ray photoelectron spectroscopy and UV-vis spectroscopy: the incorporation of Tm(3+) was confirmed by the generation of new absorption bands that could be assigned to Tm(3+) transitions. Furthermore, when the samples were annealed at 1173 K, a pyrochlore phase (Tm2Ti2O7) mixed with TiO2 was obtained with a predominant rutile phase. The photodegradation of methylene blue showed that this pyrochlore phase enhanced the photocatalytic activity of the rutile phase.

  14. Phase Competition in the Palmer-Chalker X Y Pyrochlore Er2Pt2O7

    Science.gov (United States)

    Hallas, A. M.; Gaudet, J.; Butch, N. P.; Xu, Guangyong; Tachibana, M.; Wiebe, C. R.; Luke, G. M.; Gaulin, B. D.

    2017-11-01

    We report neutron scattering measurements on Er2Pt2O7 , a new addition to the X Y family of frustrated pyrochlore magnets. Symmetry analysis of our elastic scattering data shows that Er2Pt2O7 orders into the k =0 , Γ7 magnetic structure (the Palmer-Chalker state), at TN=0.38 K . This contrasts with its sister X Y pyrochlore antiferromagnets Er2Ti2O7 and Er2Ge2O7 , both of which order into Γ5 magnetic structures at much higher temperatures, TN=1.2 and 1.4 K, respectively. In this temperature range, the magnetic heat capacity of Er2Pt2O7 contains a broad anomaly centered at T*=1.5 K . Our inelastic neutron scattering measurements reveal that this broad heat capacity anomaly sets the temperature scale for strong short-range spin fluctuations. Below TN=0.38 K , Er2Pt2O7 displays a gapped spin-wave spectrum with an intense, flat band of excitations at lower energy and a weak, diffusive band of excitations at higher energy. The flat band is well described by classical spin-wave calculations, but these calculations also predict sharp dispersive branches at higher energy, a striking discrepancy with the experimental data. This, in concert with the strong suppression of TN, is attributable to enhanced quantum fluctuations due to phase competition between the Γ7 and Γ5 states that border each other within a classically predicted phase diagram.

  15. Raman effect in ferroelectric Cd2Nb2O7 and in other crystals with pyrochlorine-type structure

    International Nuclear Information System (INIS)

    Pisarev, R.V.; Sinij, I.G.; Kuz'minov, E.G.; Myl'nikova, I.E.

    1976-01-01

    Vibrational structure of cadmium and lead pyroniobates and a number of other crystals with a pyrochlore structure has been investigated by Raman scattering. The scattering has been studied using a double monochromator, HeNe laser, and a photons counter. In the Raman spectrum of cadmium and lead pyroniobates three frequency band1 can be distinguished. In the spectrum of rhombohedral lead pyroniobate the band structure in resolved much better than in the spectrum of cubic cadmium pyroniobate. The spectrum of lead pyroniobate crystals doped with magnesium and zinc ions has a medium (in the sense of complexity) structure, because big lead ions deteriorate the pyrochlore structure but doping of lead pyroniobate with Mg 2+ and Zn 2+ ions improves it. More than six bands in the Raman spectrum is associated with the presence of impurities in cubic cadmium pyroniobate that deteriorate its cubic structure. The decrease of temperature leads to a big change of the Cd 2 Nb 2 O 7 spectrum. However, the spectrum of Pb 2 Nb 2 O 7 -Zn cubic crystal measured ar temperatures below 100 deg K remais unchanged. The chages of the Cd 2 Nb 2 O 7 spectrum are associated with phase transitions at 200 and 85 K and also with ferroelectric transition at 185 K

  16. Phonon Dynamics and Multipolar Isomorphic Transition in β-Pyrochlore KOs2O6

    Science.gov (United States)

    Hattori, Kazumasa

    2011-02-01

    We investigate with a microscopic model anharmonic K-cation oscillation observed by neutron experiments in β-pyrochlore superconductor KOs2O6, which also shows a mysterious first-order structural transition at Tp = 7.5 K. We have identified a set of microscopic model parameters that successfully reproduce the observed tem perature dependence and the superconducting transition temperature. Considering changes in the parameters at Tp, we can explain puzzling experimental results about electron--phonon coupling and neutron data. Our analysis demonstrates that the first-order transition is multipolar transition driven by the octupolar component of K-cation oscillations. The octupole moment does not change the symmetry and is characteristic to noncentrosymmetric K-cation potential.

  17. Heat capacity and magnetic properties of fluoride CsFe{sup 2+}Fe{sup 3+}F{sub 6} with defect pyrochlore structure

    Energy Technology Data Exchange (ETDEWEB)

    Gorev, M.V., E-mail: gorev@iph.krasn.ru [Kirensky Institute of Physics, Russian Academy of Sciences, Siberian Branch, 660036 Krasnoyarsk (Russian Federation); Institute of Engineering Physics and Radio Electronics, Siberian State University, 660074 Krasnoyarsk (Russian Federation); Flerov, I.N. [Kirensky Institute of Physics, Russian Academy of Sciences, Siberian Branch, 660036 Krasnoyarsk (Russian Federation); Institute of Engineering Physics and Radio Electronics, Siberian State University, 660074 Krasnoyarsk (Russian Federation); Tressaud, A. [Institut de Chimie de la Matière Condensée, ICMCB-CNRS, Université Bordeaux, 33608 Pessac Cedex (France); Bogdanov, E.V. [Kirensky Institute of Physics, Russian Academy of Sciences, Siberian Branch, 660036 Krasnoyarsk (Russian Federation); Astafijev Krasnoyarsk State Pedagogical University, 660049 Krasnoyarsk (Russian Federation); Kartashev, A.V. [Kirensky Institute of Physics, Russian Academy of Sciences, Siberian Branch, 660036 Krasnoyarsk (Russian Federation); Krasnoyarsk State Agrarian University, 660049 Krasnoyarsk (Russian Federation); Bayukov, O.A. [Kirensky Institute of Physics, Russian Academy of Sciences, Siberian Branch, 660036 Krasnoyarsk (Russian Federation); Eremin, E.V. [Kirensky Institute of Physics, Russian Academy of Sciences, Siberian Branch, 660036 Krasnoyarsk (Russian Federation); Institute of Engineering Physics and Radio Electronics, Siberian State University, 660074 Krasnoyarsk (Russian Federation); Krylov, A.S. [Kirensky Institute of Physics, Russian Academy of Sciences, Siberian Branch, 660036 Krasnoyarsk (Russian Federation)

    2016-05-15

    Heat capacity, Mössbauer and Raman spectra as well as magnetic properties of fluoride CsFe{sub 2}F{sub 6} with defect pyrochlore structure were studied. In addition to recently found above room temperature three successive structural transformations Pnma-Imma-I4{sub 1}amd-Fd-3m, phase transition of antiferromagnetic nature with the 13.7 K Neel temperature and a broad heat capacity anomaly with a maximum at about 30 K were observed. The room temperature symmetry Pnma is unchanged at least down to 7 K. Simple model of indirect bond used to estimate the exchange interactions and to propose a magnetic structure model. - Graphical abstract: The ordered arrangement of Fe{sup 2+} and Fe{sup 3+} ions in high-spin states as well as antiferromagnetic phase transition followed by significant magnetic frustrations were found in pyrocholore-related CsFe{sup 2+}Fe{sup 3+}F{sub 6}. A magnetic structure was proposed using a simple model of indirect bonds. - Highlights: • The Pnma structure in pyrocholore CsFe{sub 2}F{sub 6} is stable down to helium temperature. • Mössbauer spectra confirmed the ordering of Fe{sup 2+} and Fe{sup 3+} ions. • Antiferromagnetic transformation and significant magnetic frustrations are found. • Experimental magnetic entropy agrees with entropy for Fe ions in high-spin state. • Superexchange interactions were calculated and a magnetic structure was proposed.

  18. High throughput synthesis and characterization of the PbnNb2O5+n (0.5 < n < 4.1) system on a single chip

    International Nuclear Information System (INIS)

    Mirsaneh, Mehdi; Hayden, Brian E.; Miao Shu; Pokorny, Jan; Perini, Steve; Furman, Eugene; Lanagan, Michael T.; Ubic, Rick; Reaney, Ian M.

    2011-01-01

    Most high throughput studies focus on assessing the effect of composition within a single known fundamental structure type, such as perovskite. Here we demonstrate how high throughput synthesis and screening can be used to establish structure-property relations in the PbO-Nb 2 O 5 system, for which eight distinct fundamental structure types are known to exist. PbNb 4 O 11 , PbNb 2 O 6 and pyrochlore could be easily distinguished by X-ray diffraction (XRD). However, XRD was insensitive to distortions of the pyrochlore structure and instead Raman spectroscopy was utilized to determine changes in symmetry from cubic to rhombohedral as the PbO concentration increased. High throughput screening of the capacitance revealed permittivity (ε r ) maxima in the PbNb 4 O 11 (ε r = 700) and cubic pyrochlore phases (ε r = 450). The ε r of PbNb 4 O 11 has not to date been reported but the value for cubic pyrochlore is higher than that reported for bulk ceramics (ε r = 270). Initial high electric field studies also revealed exceptionally high tunability (four times that reported for bismuth zinc niobate-based pyrochlores) of the capacitance in the pyrochlore phase.

  19. Crystal structures of orthorhombic, hexagonal, and cubic compounds of the Sm(x)Yb(2−x)TiO5 series

    International Nuclear Information System (INIS)

    Aughterson, Robert D.; Lumpkin, Gregory R.; Reyes, Massey de los; Sharma, Neeraj; Ling, Christopher D.; Gault, Baptiste; Smith, Katherine L.; Avdeev, Maxim; Cairney, Julie M.

    2014-01-01

    A series of single phase compounds with nominal stoichiometry Sm (x) Yb (2−x) TiO 5 (x=2, 1.4, 1, 0.6, and 0) have been successfully fabricated to generate a range of crystal structures covering the most common polymorphs previously discovered in the Ln 2 TiO 5 series (Ln=lanthanides and yttrium). Four of the five samples have not been previously fabricated in bulk, single phase form so their crystal structures are refined and detailed using powder synchrotron and single crystal x-ray diffraction, neutron diffraction and transmission electron microscopy. Based on the phase information from diffraction data, there are four crystal structure types in this series; orthorhombic Pnma, hexagonal P6 3 /mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. The cubic materials show modulated structures with variation between long and short range ordering and the variety of diffraction techniques were used to describe these complex crystal structure types. - Graphical abstract: A high resolution image of the compound Sm 0.6 Yb 1.4 TiO 5 showing contrast from lattice fringes and the corresponding fast Fourier transform (FFT) of the HREM image with pyrochlore related diffraction spots marked “P” and fluorite marked “F”. The crystal is oriented down the [1 1 0] zone axis based on the Fd-3m structure. The ideal crystal structure (no vacancies) of the cubic, pyrochlore-like (Sm 0.6 Yb 1.4 TiO 5 ). - Highlights: • First fabrication of bulk single-phase material with stoichiometry Sm 2 TiO 5 . • Systematic study of crystal structure types within Ln 2 TiO 5 series (Ln=lanthanides). • A novel technique using IFFT of HREM images to study cubic structures

  20. Effect of excess Mg and Excess Nb incorporation into the B-site of pyrochlore in the Pb-Mg-Nb-O system

    Directory of Open Access Journals (Sweden)

    Mergen, A.

    2002-12-01

    Full Text Available In the Pb-Mg-Nb-O system, excess Mg and excess Nb incorporation into the B-site of PMN pyrochlore were investigated along the compositons of Pb1.83Mg0.29+xNb1.71-xO6.39-1.5x where x=0.1, 0.2, 0.3, 0.4, 0.522 and Pb1.83Mg0.29-xNb1.71+xO6.39+1.5x where x=0.1, 0.2, 0.29 respectively. Excess Mg incorporation led to the formation of perovskite and excess Nb resulted in formation of Pb2Nb2O7 monoclinic pyrochlore. The densities of the PMN pyrochlore-PMN perovskite mixtures decreased with an increase in Mg concentration. The relative permittivity of the mixtures increased with decreasing pyrochlore content. The effect of pyrochlore on the permittivity follows the Weiner’s mixture rule up to a pyrochlore content of 50 vol%.

    Se investigó la incorporación en lugares B de pirocloro PMN de un exceso de Mg y un exceso de Nb. En el sistema Pb-Mg-Nb-O2 las composiciones analizadas fueron Pb1.83Mg0.29+xNb1.71-xO6.39-1.5x donde x=0.1, 0.2, 0.3, 0.4, 0.522 y en Pb1.83Mg0.29-xNb1.71+xO6.39+1.5x donde x= 0.1, 0.2,0.29. El exceso de Mg condujo a la formación de perovskita y el exceso de Nb resultó en la formación del pirocloro monolínico, Pb2Nb2O7. La densidad de la mezcla de PMN pirocloro-perovskita dismunuye con el aumento de la concentración de Mg. La permitividad dieléctrica de las mezclas aumenta con la disminución del contenido de pirocloro. El efecto del pirocloro sobre la permitividad sigue la regla de mezclas de Weiner hasta conenidos de pirocloro del 50%.

  1. Electrical conductivities and chemical stabilities of mixed conducting pyrochlores for SOFC applications

    DEFF Research Database (Denmark)

    Holtappels, P.; Poulsen, F.W.; Mogensen, Mogens Bjerg

    2000-01-01

    Pyrochlores with praseodymium as the A-site cation and zirconium, tin, cerium and manganese cations on the B-site were prepared in air and their electrical conductivities were investigated as a function of oxygen partial pressure and temperature. Pure Pr2Zr2O7+/-delta as well as samples modified...

  2. Intricate disorder in defect fluorite/pyrochlore: a concord of chemistry and crystallography

    Czech Academy of Sciences Publication Activity Database

    Simeone, D.; Thorogood, G.J.; Huo, D.; Luneville, L.; Baldinozzi, G.; Petříček, Václav; Porcher, F.; Ribis, J.; Mazerolles, L.; Largeau, L.; Berar, J.F.; Surble, S.

    2017-01-01

    Roč. 7, Jun (2017), 1-7, č. článku 3727. ISSN 2045-2322 Institutional support: RVO:68378271 Keywords : disorder * atomic scale * metallic allys * oxides * fluorite/pyrochlore Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 4.259, year: 2016

  3. Forging Fast Ion Conducting Nanochannels with Swift Heavy Ions: The Correlated Role of Local Electronic and Atomic Structure

    Energy Technology Data Exchange (ETDEWEB)

    Sachan, Ritesh [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Material Science and Technology Division; Cooper, Valentino R. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Material Science and Technology Division; Liu, Bin [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Materials Science and Engineering; Aidhy, Dilpuneet S. [Univ. of Wyoming, Laramie, WY (United States). Dept. of Mechanical Engineering; Voas, Brian K. [Iowa State Univ., Ames, IA (United States). Dept. of Materials Science and Engineering; Lang, Maik [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Nuclear Engineering; Ou, Xin [Chinese Academy of Sciences (CAS), Shanghai (China). State Key Lab. of Functional Material for Informatics; Trautmann, Christina [GSI Helmholtz Centre for Heavy Ion Research, Darmstadt (Germany); Technical Univ. of Darmstadt (Germany). Dept. of Materials Science; Zhang, Yanwen [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Material Science and Technology Division; Univ. of Tennessee, Knoxville, TN (United States). Dept. of Materials Science and Engineering; Chisholm, Matthew F. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Material Science and Technology Division; Weber, William J. [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Materials Science and Engineering; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Material Science and Technology Division

    2016-12-19

    Atomically disordered oxides have attracted significant attention in recent years due to the possibility of enhanced ionic conductivity. However, the correlation between atomic disorder, corresponding electronic structure, and the resulting oxygen diffusivity is not well understood. The disordered variants of the ordered pyrochlore structure in gadolinium titanate (Gd2Ti2O7) are seen as a particularly interesting prospect due to intrinsic presence of a vacant oxygen site in the unit atomic structure, which could provide a channel for fast oxygen conduction. In this paper, we provide insights into the subangstrom scale on the disordering-induced variations in the local atomic environment and its effect on the electronic structure in high-energy ion irradiation-induced disordered nanochannels, which can be utilized as pathways for fast oxygen ion transport. With the help of an atomic plane-by-plane-resolved analyses, the work shows how the presence of various types of TiOx polyhedral that exist in the amorphous and disordered crystalline phase modify the electronic structures relative to the ordered pyrochlore phase in Gd2Ti2O7. Finally, the correlated molecular dynamics simulations on the disordered structures show a remarkable enhancement in oxygen diffusivity as compared with ordered pyrochlore lattice and make that a suitable candidate for applications requiring fast oxygen conduction.

  4. Topological Magnon Bands and Unconventional Superconductivity in Pyrochlore Iridate Thin Films

    Science.gov (United States)

    Laurell, Pontus; Fiete, Gregory A.

    2017-04-01

    We theoretically study the magnetic properties of pyrochlore iridate bilayer and trilayer thin films grown along the [111] direction using a strong coupling approach. We find the ground state magnetic configurations on a mean field level and carry out a spin-wave analysis about them. In the trilayer case the ground state is found to be the all-in-all-out (AIAO) state, whereas the bilayer has a deformed AIAO state. For all parameters of the spin-orbit coupled Hamiltonian we study, the lowest magnon band in the trilayer case has a nonzero Chern number. In the bilayer case we also find a parameter range with nonzero Chern numbers. We calculate the magnon Hall response for both geometries, finding a striking sign change as a function of temperature. Using a slave-boson mean-field theory we study the doping of the trilayer system and discover an unconventional time-reversal symmetry broken d +i d superconducting state. Our study complements prior work in the weak coupling limit and suggests that the [111] grown thin film pyrochlore iridates are a promising candidate for topological properties and unconventional orders.

  5. Topological Magnon Bands and Unconventional Superconductivity in Pyrochlore Iridate Thin Films.

    Science.gov (United States)

    Laurell, Pontus; Fiete, Gregory A

    2017-04-28

    We theoretically study the magnetic properties of pyrochlore iridate bilayer and trilayer thin films grown along the [111] direction using a strong coupling approach. We find the ground state magnetic configurations on a mean field level and carry out a spin-wave analysis about them. In the trilayer case the ground state is found to be the all-in-all-out (AIAO) state, whereas the bilayer has a deformed AIAO state. For all parameters of the spin-orbit coupled Hamiltonian we study, the lowest magnon band in the trilayer case has a nonzero Chern number. In the bilayer case we also find a parameter range with nonzero Chern numbers. We calculate the magnon Hall response for both geometries, finding a striking sign change as a function of temperature. Using a slave-boson mean-field theory we study the doping of the trilayer system and discover an unconventional time-reversal symmetry broken d+id superconducting state. Our study complements prior work in the weak coupling limit and suggests that the [111] grown thin film pyrochlore iridates are a promising candidate for topological properties and unconventional orders.

  6. High-pressure synthesis and characterization of the effective pseudospin S =1 /2 XY pyrochlores R2P t2O7 (R =Er ,Yb )

    Science.gov (United States)

    Cai, Y. Q.; Cui, Q.; Li, X.; Dun, Z. L.; Ma, J.; dela Cruz, C.; Jiao, Y. Y.; Liao, J.; Sun, P. J.; Li, Y. Q.; Zhou, J. S.; Goodenough, J. B.; Zhou, H. D.; Cheng, J.-G.

    2016-01-01

    We report on the high-pressure syntheses and detailed characterizations of two effective pseudospin S =1 /2 XY pyrochlores E r2P t2O7 and Y b2P t2O7 via x-ray/neutron powder diffraction, dc and ac magnetic susceptibility, and specific-heat measurements down to 70 mK. We found that both compounds undergo long-range magnetic transitions at TN ,C≈0.3 K , which are ascribed to an antiferromagnetic- and ferromagnetic-type order for E r2P t2O7 and Y b2P t2O7 , respectively, based on the field dependence of their transition temperatures as well as the systematic comparisons with other similar pyrochlores R2B2O7 (R =Er ,Yb ;B =Sn ,Ti ,Ge ). The observed TN of E r2P t2O7 is much lower than that expected from the relationship of TN versus the ionic radius of B4 + derived from the series of E r2B2O7 , while the TC of Y b2P t2O7 is the highest among the series of ferromagnetic compounds Y b2B2O7 (B =Sn ,Pt ,Ti ). Given the monotonic variation of the lattice constant as a function of the B -cation size across these two series of R2B2O7 (R =Er ,Yb ), the observed anomalous values of TN ,C in the Pt-based XY pyrochlores imply that another important factor beyond the nearest-neighbor R -R distance is playing a role. In light of the anisotropic exchange interactions Jex={Jz z,J±,J±±,Jz ± } for the S =1 /2 XY pyrochlores, we have rationalized these observations by considering a weakened (enhanced) antiferromagnetic planar J± (ferromagnetic Ising-like Jz z) due to strong Pt 5 d -O 2 p hybridization within the plane perpendicular to the local [111] direction.

  7. Synthesis and structural characterization of Ce-doped bismuth titanate

    International Nuclear Information System (INIS)

    Pavlovic, Nikolina; Srdic, Vladimir V.

    2009-01-01

    Ce-modified bismuth titanate nanopowders Bi 4-x Ce x Ti 3 O 12 (x ≤ 1) have been synthesized using a coprecipitation method. DTA/TG, FTIR, XRD, SEM/EDS and BET methods were used in order to investigate the effect of Ce-substitution on the structure, morphology and sinterability of the obtained powders. The phase structure investigation revealed that after calcinations at 600 deg. C powder without Ce addition exhibited pure bismuth titanate phase; however, powders with Ce (x = 0.25, 0.5 and 0.75) had bismuth titanate pyrochlore phase as the second phase. The strongest effect of Ce addition on the structure was noted for the powder with the highest amount of Ce (x = 1) having a cubic pyrochlore structure. The presence of pure pyrochlore phase was explained by its stabilization due to the incorporation of cerium ions in titanate structure. Ce-modified bismuth titanate ceramic had a density over 95% of theoretical density and the fracture in transgranular manner most probably due to preferable distribution of Ce in boundary region

  8. Static magnetic susceptibility, crystal field and exchange interactions in rare earth titanate pyrochlores

    NARCIS (Netherlands)

    Malkin, B. Z.; Lummen, T. T. A.; van Loosdrecht, P. H. M.; Dhalenne, G.; Zakirov, A. R.

    2010-01-01

    The experimental temperature dependence (T = 2-300 K) of single crystal bulk and site susceptibilities of rare earth titanate pyrochlores R2Ti2O7 (R = Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) is analyzed in the framework of crystal field theory and a mean field approximation. Analytical expressions for the

  9. Spin-1/2 Heisenberg antiferromagnet on the pyrochlore lattice: An exact diagonalization study

    Science.gov (United States)

    Chandra, V. Ravi; Sahoo, Jyotisman

    2018-04-01

    We present exact diagonalization calculations for the spin-1/2 nearest-neighbor antiferromagnet on the pyrochlore lattice. We study a section of the lattice in the [111] direction and analyze the Hamiltonian of the breathing pyrochlore system with two coupling constants J1 and J2 for tetrahedra of different orientations and investigate the evolution of the system from the limit of disconnected tetrahedra (J2=0 ) to a correlated state at J1=J2 . We evaluate the low-energy spectrum, two and four spin correlations, and spin chirality correlations for a system size of up to 36 sites. The model shows a fast decay of spin correlations and we confirm the presence of several singlet excitations below the lowest magnetic excitation. We find chirality correlations near J1=J2 to be small at the length scales available at this system size. Evaluation of dimer-dimer correlations and analysis of the nature of the entanglement of the tetrahedral unit shows that the triplet sector of the tetrahedron contributes significantly to the ground-state entanglement at J1=J2 .

  10. Room temperature aerobic oxidation of amines by a nanocrystalline ruthenium oxide pyrochlore nafion composite catalyst.

    Science.gov (United States)

    Venkatesan, Shanmuganathan; Kumar, Annamalai Senthil; Lee, Jyh-Fu; Chan, Ting-Shan; Zen, Jyh-Myng

    2012-05-14

    The aerobic oxidation of primary amines to their respective nitriles has been carried out at room temperature using a highly reusable nanocrystalline ruthenium oxide pyrochlore Nafion composite catalyst (see figure). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Conductivity and hydration trends in disordered fluorite and pyrochlore oxides: A study on lanthanum cerate–zirconate based compounds

    DEFF Research Database (Denmark)

    Besikiotis, Vasileios; Ricote, Sandrine; Jensen, Molly Hjorth

    2012-01-01

    In the present contribution we discuss the influence of order/disorder on the concentration and mobility of ionic charge carriers in undoped and acceptor (calcium) doped fluorite and pyrochlore structured lanthanum cerate–zirconate solid solutions: (La1−yCay)2(Ce1−xZrx)2O7−δ (y=0, 0.02, 0.10; x=0...... enthalpy becomes more exothermic with higher cerium content, i.e. with more disordered materials. The proton conductivity decreases upon acceptor substitution of La3+ with Ca2+ which is attributed to trapping of the charge carriers by the effectively negative acceptor....

  12. Potassium Disorder in the Defect Pyrochlore KSbTeO6: A Neutron Diffraction Study

    Directory of Open Access Journals (Sweden)

    José Antonio Alonso

    2017-01-01

    Full Text Available KSbTeO6 defect pyrochlore has been prepared from K2C2O4, Sb2O3, and 15% excess TeO2 by solid-state reaction at 850 °C. Direct methods implemented in the software EXPO2013 allowed establishing the basic structural framework. This was followed by a combined Rietveld refinement from X-ray powder diffraction (XRD and neutron powder diffraction (NPD data, which unveiled additional structural features. KSbTeO6 is cubic, a = 10.1226(7 Å, space group F d 3 ¯ m , Z = 8 and it is made of a mainly covalent framework of corner-sharing (Sb,TeO6 octahedra, with weakly bonded K+ ions located within large cages. The large K-O distances, 3.05(3–3.07(3 Å, and quite large anisotropic atomic displacement parameters account for the easiness of K+ exchange for other cations of technological importance.

  13. Crystal-field study of magnetization and specific heat properties of frustrated pyrochlore Pr2Zr2O7

    International Nuclear Information System (INIS)

    Alam, J.; Jana, Y.M.; Biswas, A. Ali

    2016-01-01

    The experimental results of temperature dependent dc magnetic susceptibility, field dependent isothermal magnetization, magnetic specific heat and entropy of the pyrochlore Pr 2 Zr 2 O 7 are simulated and analyzed using appropriate D 3d crystal-field (CF) and anisotropic molecular field tensors at Pr-sites in the self-consistent mean-field approach involving four magnetically non-equivalent rare-earth spins on the tetrahedral unit of the pyrochlore structure. CF level pattern and wave-functions of the ground 3 H 4 multiplet of the Pr 3+ ions are obtained considering intermediate coupling between different Russell-Saunders terms of the 4f 2 electronic configurations of Pr-ion and J-mixing effects. CF analysis shows that the CF ground-state of the Pr 3+ ion in Pr 2 Zr 2 O 7 is a well-isolated doublet, with significant admixtures of terms coming from |M J =±4〉 and |M J =±1〉, and the Pr-spins are effectively Ising-like along the local <111> axes. Magnetic specific heat in zero-field is simulated by considering a temperature dependence of the exchange splitting of the ground doublet. - Highlights: • Full CF diagonalization using intermediate coupling and J-mixing. • Pr-spins are Ising-like along local [111] axis. • Magnetic specific heat is due to temperature dependence exchange splitting of ground CF doublet.

  14. Combined experimental–theoretical study of the optoelectronic properties of non-stoichiometric pyrochlore bismuth titanate

    KAUST Repository

    Noureldine, Dalal

    2015-10-27

    A combination of experimental and computational methods was applied to investigate the crystal structure and optoelectronic properties of the non-stoichiometric pyrochlore Bi2−xTi2O7−1.5x. The detailed experimental protocol for both powder and thin-film material synthesis revealed that a non-stoichiometric Bi2−xTi2O7−1.5x structure with an x value of ∼0.25 is the primary product, consistent with the thermodynamic stability of the defect-containing structure computed using density functional theory (DFT). The approach of density functional perturbation theory (DFPT) was used along with the standard GGA PBE functional and the screened Coulomb hybrid HSE06 functional, including spin–orbit coupling, to investigate the electronic structure, the effective electron and hole masses, the dielectric constant, and the absorption coefficient. The calculated values for these properties are in excellent agreement with the measured values, corroborating the overall analysis. This study indicates potential applications of bismuth titanate as a wide-bandgap material, e.g., as a substitute for TiO2 in dye-sensitized solar cells and UV-light-driven photocatalysis.

  15. Quantum phase transitions and anomalous Hall effect in a pyrochlore Kondo lattice

    Science.gov (United States)

    Grefe, Sarah; Ding, Wenxin; Si, Qimiao

    The metallic variant of the pyrochlore iridates Pr2Ir2O7 has shown characteristics of a possible chiral spin liquid state [PRL 96 087204 (2006), PRL 98, 057203 (2007), Nature 463, 210 (2010)] and quantum criticality [Nat. Mater. 13, 356 (2014)]. An important question surrounding the significant anomalous Hall response observed in Pr2Ir2O7 is the nature of the f-electron local moments, including their Kondo coupling with the conduction d-electrons. The heavy effective mass and related thermodynamic characteristics indicate the involvement of the Kondo effect in this system's electronic properties. In this work, we study the effects of Kondo coupling on candidate time-reversal-symmetry-breaking spin liquid states on the pyrochlore lattice. Representing the f-moments as slave fermions Kondo-coupled to conduction electrons, we study the competition between Kondo-singlet formation and chiral spin correlations and determine the zero-temperature phase diagram. We derive an effective chiral interaction between the local moments and the conduction electrons and calculate the anomalous Hall response across the quantum phase transition from the Kondo destroyed phase to the Kondo screened phase. We discuss our results' implications for Pr2Ir2O7 and related frustrated Kondo-lattice systems.

  16. C60 and U ion irradiation of Gd2TixZr2-xO7 pyrochlore

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Jiaming; Toulemonde, Marcel; Lang, Maik; Costantini, Jean Marc; Della-Negra, Serge; Ewing, Rodney C.

    2015-08-01

    Gd2TixZr2-xO7 (x = 0 to 2) pyrochlore was irradiated by 30 MeV C60 clusters, which provide an extremely high ionizing energy density. Here, high-resolution transmission electron microscopy revealed a complex ion-track structure in Gd2Ti2O7 and Gd2TiZrO7, consisting of an amorphous core and a shell of a disordered, defect-fluorite structure.

  17. Study of the nearly constant dielectric loss regime in ionic conductors with pyrochlore-like structure; Estudio del regimen de perdidas dielectricas constantes en conductores ionicos con estructura de tipo pirocloro

    Energy Technology Data Exchange (ETDEWEB)

    Diaz-Guillen, M. r.; Fuentes, A. F.; Diaz-Guillen, J. a.; Santamaria, J.; Leon, C.

    2012-07-01

    We report on ac conductivity measurement of oxide ion conductors with composition Gd{sub 2}(ZryTi{sub 1}-y){sub 2}O{sub 7} and a pyrochlore type structure, at temperatures between -20 and 250 degree centigrade and in the frequency range from 1 Hz to 3 MHz by using impedance spectroscopy. Results show that a crossover from a power law dependence to a linear frequency dependence (or nearly constant loss behavior) in the ac conductivity can be clearly observed in a wide temperature range. This crossover is found to be thermally activated, and its activation energy ENCL to be much lower than the activation energy Edc for the dc conductivity. We also found that the values of ENCL are almost independent of composition, and therefore of the concentration of mobile oxygen vacancies, unlike those of Edc. Moreover, for each composition, the values of E{sub N}CL=0.67{+-}0.04 eV are very similar to those estimated for the energy barrier for the ions to leave their cages, E{sub {alpha}}=0.69{+-}0.05 eV. These results support that the nearly constant loss behavior, ubiquitous in ionic conductors, is originated from caged ion dynamics. (Author) 33 refs.

  18. Atomic-scale microstructural characterization and dielectric properties of crystalline cubic pyrochlore Bi1.5MgNb1.5O7 nanoparticles synthesized by sol-gel method

    KAUST Repository

    Zhang, Yuan; Zhu, Xinhua; Zhou, Shunhua; Zhu, Jianmin; Liu, Zhiguo; Al-Kassab, Talaat

    2013-01-01

    Here, we report the atomic-scale microstructural characterization and dielectric properties of crystalline cubic pyrochlore Bi1.5MgNb 1.5O7 (BMN) nanoparticles with mean size of 70 nm, which were synthesized by sol-gel method. The crystallinity, phase formation, morphology, and surface microstructure of the BMN nanoparticles were characterized by X-ray diffraction (XRD), Raman spectra, transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM), respectively. The phase evolution of the BMN nanoparticles investigated by XRD patterns showed that uniform cubic pyrochlore BMN nanoparticles were obtained after calcination at temperature of 800 C, and their structural information was revealed by Raman spectrum. TEM images demonstrated that the BMN nanoparticles had a spherical morphology with an average particle size of 70 nm, and their crystalline nature was revealed by HRTEM images. In addition, HRTEM images also demonstrate a terrace-ledge-kink (TLK) surface structure at the edges of rough BMN nanoparticles, where the terrace was on the (100) plane, and the ledge on the (001) plane. The formation of such a TLK surface structure can be well explained by a theory of periodic bond chains. Due to the surface structural reconstruction in the BMN nanoparticles, the formation of a tetragonal structure in a rough BMN nanoparticle was also revealed by HRTEM image. The BMN nanoparticles exhibited dielectric constants of 50 at 100 kHz and 30 at 1 MHz, and the dielectric loss of 0.19 at 1 MHz. © 2013 Springer Science+Business Media Dordrecht.

  19. Atomic-scale microstructural characterization and dielectric properties of crystalline cubic pyrochlore Bi1.5MgNb1.5O7 nanoparticles synthesized by sol-gel method

    KAUST Repository

    Zhang, Yuan

    2013-12-24

    Here, we report the atomic-scale microstructural characterization and dielectric properties of crystalline cubic pyrochlore Bi1.5MgNb 1.5O7 (BMN) nanoparticles with mean size of 70 nm, which were synthesized by sol-gel method. The crystallinity, phase formation, morphology, and surface microstructure of the BMN nanoparticles were characterized by X-ray diffraction (XRD), Raman spectra, transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM), respectively. The phase evolution of the BMN nanoparticles investigated by XRD patterns showed that uniform cubic pyrochlore BMN nanoparticles were obtained after calcination at temperature of 800 C, and their structural information was revealed by Raman spectrum. TEM images demonstrated that the BMN nanoparticles had a spherical morphology with an average particle size of 70 nm, and their crystalline nature was revealed by HRTEM images. In addition, HRTEM images also demonstrate a terrace-ledge-kink (TLK) surface structure at the edges of rough BMN nanoparticles, where the terrace was on the (100) plane, and the ledge on the (001) plane. The formation of such a TLK surface structure can be well explained by a theory of periodic bond chains. Due to the surface structural reconstruction in the BMN nanoparticles, the formation of a tetragonal structure in a rough BMN nanoparticle was also revealed by HRTEM image. The BMN nanoparticles exhibited dielectric constants of 50 at 100 kHz and 30 at 1 MHz, and the dielectric loss of 0.19 at 1 MHz. © 2013 Springer Science+Business Media Dordrecht.

  20. Direct Measurement of Surface Dissolution Rates in Potential Nuclear Waste Forms: The Example of Pyrochlore.

    Science.gov (United States)

    Fischer, Cornelius; Finkeldei, Sarah; Brandt, Felix; Bosbach, Dirk; Luttge, Andreas

    2015-08-19

    The long-term stability of ceramic materials that are considered as potential nuclear waste forms is governed by heterogeneous surface reactivity. Thus, instead of a mean rate, the identification of one or more dominant contributors to the overall dissolution rate is the key to predict the stability of waste forms quantitatively. Direct surface measurements by vertical scanning interferometry (VSI) and their analysis via material flux maps and resulting dissolution rate spectra provide data about dominant rate contributors and their variability over time. Using pyrochlore (Nd2Zr2O7) pellet dissolution under acidic conditions as an example, we demonstrate the identification and quantification of dissolution rate contributors, based on VSI data and rate spectrum analysis. Heterogeneous surface alteration of pyrochlore varies by a factor of about 5 and additional material loss by chemo-mechanical grain pull-out within the uppermost grain layer. We identified four different rate contributors that are responsible for the observed dissolution rate range of single grains. Our new concept offers the opportunity to increase our mechanistic understanding and to predict quantitatively the alteration of ceramic waste forms.

  1. High-pressure effects on the superconductivity of β-pyrochlore oxides AOs2O6

    International Nuclear Information System (INIS)

    Muramatsu, Takaki; Takeshita, Nao; Terakura, Chikeko; Takagi, Hidenori; Tokura, Yoshinori; Yonezawa, Shigeki; Muraoka, Yuji; Hiroi, Zenji

    2006-01-01

    High-pressure effects on the superconducting transitions of β-pyrochlore oxide superconductors AOs 2 O 6 (A=Cs, Rb, K) are studied by measuring resistivity under high pressures up to 16 GPa. The superconducting transition temperature T c first increases with increasing pressure in all the compounds and then exhibits a broad maximum at 7.6 K (6 GPa), 8.2 K (2 GPa) and 10 K (0.6 GPa) for A=Cs, Rb and K, respectively. Finally, the superconductivity is suppressed completely at a critical pressure near 7 and 6 GPa for A=Rb and K and probably above 10 GPa for A=Cs. Characteristic changes in the temperature dependence of resistivity of RbOs 2 O 6 under high pressure. The residual resistivity largely increases with pressure above 4 GPa and, as a result, resistivity indicates small temperature dependence down to 4.2 K at 7 GPa and application of further pressure up to 10 GPa indicates that temperature dependence of resistivity decrease below 100 K. This characteristic behavior in the β-pyrochlore oxides may originate from the nesting of nearly octahedron shape of Fermi surface

  2. Diffraction and spectroscopic study of pyrochlores Bi{sub 2−x}Fe{sub 1+x}SbO{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Qingdi; Blanchard, Peter E.R. [School of Chemistry, The University of Sydney, Sydney, NSW 2006 (Australia); Kennedy, Brendan J., E-mail: kennedyb@chem.usyd.edu.au [School of Chemistry, The University of Sydney, Sydney, NSW 2006 (Australia); Ling, Chris D.; Liu, Samuel [School of Chemistry, The University of Sydney, Sydney, NSW 2006 (Australia); Avdeev, Max [Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales 2234 (Australia); Aitken, Jade B. [Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria 3168 (Australia); Institute of Materials Structure Science, KEK, Tsukuba, Ibaraki 305-0801 (Japan); School of Chemistry, The University of Sydney, Sydney, NSW 2006 (Australia); Tadich, Anton; Brand, Helen E.A. [Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria 3168 (Australia)

    2014-03-15

    Highlights: • Fe rich pyrochlores of the type Bi{sub 2−x}Fe{sub 1+x}SbO{sub 7} were prepared by solid state methods. • Structures determined using a combination of neutron and synchrotron X-ray diffraction. • Fe partially occupies the 8-coordinate site. • Dispacive disorder of the Bi cations observed as a consequence of the 6s{sup 2} electrons. • Non-Vegard behaviour seen at low Fe contents due to disorder. -- Abstract: The structural and electronic properties of the series Bi{sub 2−x}Fe{sub 1+x}SbO{sub 7} (0 ⩽ x ⩽ 0.6) were investigated using a combination of diffraction and spectroscopy. Synchrotron and neutron diffraction analysis show that Fe{sup 3+} cations substitute for Bi{sup 3+} onto the A site with increasing x, which was further confirmed by analysis of the Fe K/L-edge X-ray absorption near-edge spectra. The diffraction analysis indicated the presence of displacive disorder along the A{sub 2}O chains, likely the result of the Bi{sup 3+} 6s{sup 2} lone pair, as well as non-Vegard-like behaviour of the lattice parameters in the Fe-poor region. Fe K-edge extended X-ray absorption fine-structure analysis of Bi{sub 2}FeSbO{sub 7} confirmed the displacive disorder of the Bi{sup 3+} cations as well as Sb{sup 5+} and Fe{sup 3+} disorder on the B site.

  3. High-pressure behavior of A 2 B 2 O 7 pyrochlore (A=Eu, Dy; B=Ti, Zr)

    Energy Technology Data Exchange (ETDEWEB)

    Rittman, Dylan R.; Turner, Katlyn M.; Park, Sulgiye; Fuentes, Antonio F.; Yan, Jinyuan; Ewing, Rodney C.; Mao, Wendy L.

    2017-01-28

    In situ high-pressure X-ray diffraction and Raman spectroscopy were used to determine the influence of composition on the high-pressure behavior of A2B2O7 pyrochlore (A=Eu, Dy; B=Ti, Zr) up to ~50GPa. Based on X-ray diffraction results, all compositions transformed to the high-pressure cotunnite structure. The B-site cation species had a larger effect on the transition pressure than the A-site cation species, with the onset of the phase transformation occurring at ~41 GPa for B=Ti and ~16 GPa B=Zr. However, the A-site cation affected the kinetics of the phase transformation, with the transformation for compositions with the smaller ionic radii, i.e., A=Dy, proceeding faster than those with a larger ionic radii, i.e., A=Eu. These results were consistent with previous work in which the radius-ratio of the A- and B-site cations determined the energetics of disordering, and compositions with more similarly sized A- and B-site cations had a lower defect formation energy. Raman spectra revealed differences in the degree of short-range order of the different compositions. Due to the large phase fraction of cotunnite at high pressure for B=Zr compositions, Raman modes for cotunnite could be observed, with more modes recorded for A=Eu than A=Dy. These additional modes are attributed to increased short-to-medium range ordering in the initially pyrochlore structured Eu2Zr2O7 as compared with the initially defect-fluorite structured Dy2Zr2O7.

  4. A new triclinic modification of the pyrochlore-type KOs2O6 superconductor

    International Nuclear Information System (INIS)

    Katrych, S.; Gu, Q.F.; Bukowski, Z.; Zhigadlo, N.D.; Krauss, G.; Karpinski, J.

    2009-01-01

    A new modification of KOs 2 O 6 , the representative of a new structural type (Pearson symbol aP18, a=5.5668(1) A, b=6.4519(2) A, c=7.2356(2) A, α=65.377(3) o , β=70.572(3) o , γ=75.613(2) o space group P-1, no. 2 was synthesized employing high pressure technique. Its structure was determined by single-crystal X-ray diffraction. The structure can be described as two OsO 6 octahedral chains relating to each other through inversion and forming big voids with K atoms inside. Quantum chemical calculations were performed on the novel compound and structurally related cubic compound. High-pressure X-ray study showed that cubic KOs 2 O 6 phase was stable up to 32.5(2) GPa at room temperature. - Graphical abstract: A new modification of KOs 2 O 6 , the representative of a new structural type (Pearson symbol aP18, a=5.5668(1) A, b=6.4519(2) A, c=7.2356(2) A, α=65.377(3) o , β=70.572(3) o , γ=75.613(2) o space group P-1, no. 2 was synthesized employing high pressure technique. The structure can be described as two OsO 6 octahedral chains relating to each other through inversion and forming big voids with K atoms inside

  5. Induced quadrupolar singlet ground state of praseodymium in a modulated pyrochlore

    Science.gov (United States)

    van Duijn, J.; Kim, K. H.; Hur, N.; Ruiz-Bustos, R.; Adroja, D. T.; Bridges, F.; Daoud-Aladine, A.; Fernandez-Alonso, F.; Wen, J. J.; Kearney, V.; Huang, Q. Z.; Cheong, S.-W.; Perring, T. G.; Broholm, C.

    2017-09-01

    The complex structure and magnetism of Pr2 -xBixRu2O7 was investigated by neutron scattering and extended x-ray absorption fine structure. Pr has an approximate doublet ground state and the first excited state is a singlet. While the B -site (Ru) is well ordered throughout, this is not the case for the A -site (Pr/Bi). A broadened distribution for the Pr-O2 bond length at low temperature indicates the Pr environment varies from site to site even for x =0 . The environment about the Bi site is highly disordered ostensibly due to the 6 s lone pairs on Bi3 +. Correspondingly, we find that the non-Kramers doublet ground-state degeneracy, otherwise anticipated for Pr in the pyrochlore structure, is lifted so as to produce a quadrupolar singlet ground state with a spatially varying energy gap. For x =0 , below TN, the Ru sublattice orders antiferromagnetically, with propagation vector k =(0 ,0 ,0 ) as for Y2Ru2O7 . No ordering associated with the Pr sublattice is observed down to 100 mK. The low-energy magnetic response of Pr2 -xBixRu2O7 features a broad spectrum of magnetic excitations associated with inhomogeneous splitting of the Pr quasidoublet ground state. For x =0 (x =0.97 ), the spectrum is temperature dependent (independent). It appears disorder associated with Bi alloying enhances the inhomogeneous Pr crystal-field level splitting so that intersite interactions become irrelevant for x =0.97 . The structural complexity for the A -site may be reflected in the hysteretic uniform magnetization of B -site ruthenium in the Néel phase.

  6. PDF analysis on re-crystallized structure from amorphous BiT

    Energy Technology Data Exchange (ETDEWEB)

    Yoneda, Yasuhiro [Japan Atomic Energy Research Institute, Synchrotron Radiation Research Center, Kouto 1-1-1, Mikazuki-cho, Sayo-gun, Hyogo 679-5148 (Japan)]. E-mail: yoneda@spring8.or.jp; Kohara, Shinji [Synchrotron Radiation Research Laboratory, Japan Synchrotron Radiation, Research Institute, Kouto 1-1-1, Mikazuki-cho, Sayo-gun, Hyogo 679-5198 (Japan); Hamazaki, Shin' ichi [Department of Electronics, Iwaki Meisei University, Iino 5-5-1, Chuohdai, Fukushima 970-8551 (Japan); Takashige, Masaaki [Department of Electronics, Iwaki Meisei University, Iino 5-5-1, Chuohdai, Fukushima 970-8551 (Japan); Mizuki, Jun' ichiro [Japan Atomic Energy Research Institute, Synchrotron Radiation Research Center, Kouto 1-1-1, Mikazuki-cho, Sayo-gun, Hyogo 679-5148 (Japan)

    2005-08-15

    A glass sample of composition Bi{sub 4}Ti{sub 3}O{sub 12} was prepared by rapid quenching. The as-quenched sample was confirmed to be amorphous by synchrotron X-ray measurements. The crystallization process of the amorphous sample was also investigated by high-energy X-ray diffraction and by atomic pair distribution function analysis. The perovskite layer in the crystal Bi{sub 4}Ti{sub 3}O{sub 12} is transformed to a pyrochlore structure in the amorphous sample. The amorphous sample first crystallized to a metastable phase by acquiring long-range ordering of the pyrochlore structure at T {sub cryst1}, and then secondary crystallized into a reverted Bi{sub 4}Ti{sub 3}O{sub 12} structure at T {sub cryst2}.

  7. Multilayer Thermal Barrier Coating (TBC) Architectures Utilizing Rare Earth Doped YSZ and Rare Earth Pyrochlores

    Science.gov (United States)

    Schmitt, Michael P.; Rai, Amarendra K.; Bhattacharya, Rabi; Zhu, Dongming; Wolfe, Douglas E.

    2014-01-01

    To allow for increased gas turbine efficiencies, new insulating thermal barrier coatings (TBCs) must be developed to protect the underlying metallic components from higher operating temperatures. This work focused on using rare earth doped (Yb and Gd) yttria stabilized zirconia (t' Low-k) and Gd2Zr2O7 pyrochlores (GZO) combined with novel nanolayered and thick layered microstructures to enable operation beyond the 1200 C stability limit of current 7 wt% yttria stabilized zirconia (7YSZ) coatings. It was observed that the layered system can reduce the thermal conductivity by approximately 45 percent with respect to YSZ after 20 hr of testing at 1316 C. The erosion rate of GZO is shown to be an order to magnitude higher than YSZ and t' Low-k, but this can be reduced by almost 57 percent when utilizing a nanolayered structure. Lastly, the thermal instability of the layered system is investigated and thought is given to optimization of layer thickness.

  8. Effect of Ion Irradiation in Cadmium Niobate Pyrochlores

    International Nuclear Information System (INIS)

    Jiang, Weilin; Weber, William J.; Thevuthasan, Suntharampillai; Boatner, Lynn A.

    2003-01-01

    Irradiation experiments have been performed for cadmium niobate pyrochlore (CdNb2O) single crystals at both 150 and 300 K using 1.0 MeV Au ions over fluences ranging from 0.01 to 0.10 ions/nm. In-situ 3.0 MeV He Rutherford backscattering spectrometry along the -axial channeling direction (RBS/C) has been applied to study the damage states ranging from small defect concentrations to a fully amorphous state. Results show that the crystal can be readily amorphized under the irradiation conditions. Room-temperature recovery of the defects produced at 150 K has been observed, while the defects produced at 300 K are thermally stable at room temperature. Results also indicate that the RBS/C analysis used in this study induced negligible damage in the near-surface regime. In addition, irradiation at and below room temperature using He and C3 ions leads to surface exfoliation at the corresponding damage peaks

  9. Rattling motion in β-pyrochlore compounds explored by the millimeter-wave conductivity measurement

    International Nuclear Information System (INIS)

    Maeda, Atsutaka; Oba, Kentaro; Imai, Yoshinori; Yamaura, Jun-ichi; Hiroi, Zenji

    2010-01-01

    Complex conductivity is investigated at 19 GHz and 44 GHz in the normal state in β-pyrochlore materials, AOs 2 O 6 (A = Cs, Rb and K). In Cs material, large enhancement of the quasiparticle (QP) scattering time, τ, is observed at low temperatures, whereas there is no such enhancement in Rb and K materials. This indicates that rattling motion is absent in Cs material, whether in K and Rb materials it plays the role as a scatterer for QPs. In Rb materials, we find charge excitation possibly originated from the rattling motion.

  10. Effects of sintering temperature on the pyrochlore phase in PZT nanotubes and their transformation to the perovskite phase by coating with PbO multilayers.

    Science.gov (United States)

    Han, Jin Kyu; Choi, Yong Chan; Jeon, Do Hyen; Lee, Min Ku; Bu, Sang Don

    2014-11-01

    We report the phase evolution of Pb(Zr0.52Ti0.48)O3 nanotubes (PZT-NTs), from the pyrochlore to perovskite phase, with an outer diameter of about 420 nm and a wall thickness of about 10 nm. The PZT-NTs were fabricated in pores of porous anodic alumina membrane (PAM) using a spin coating of PZT sol-gel solution and subsequent annealing at 500-700 degrees C in oxygen gas. The pyrochlore phase was found to be formed at 500 degrees C, and also found not to be transformed into the perovskite phase, even though annealing was performed at higher temperatures to 700 degrees C. Elementary distribution analysis of PZT-NTs embedded in PAM reveal that Pb diffusion from nanotubes into pore walls of PAM is one of the main reasons. By employing firstly an additional PbO coating on the pyrochlore nanotubes and then subsequent annealing at 700 degrees C, we have successfully achieved an almost pure perovskite phase in nanotubes. These results suggest that PbO acts as a Pb-compensation agent in the Pb- deficient PZT-NTs. Moreover, our method can be used in the synthesis of all metal-oxide materials, including volatile elements.

  11. Synthesis and characterization of Bi{sub 1.56}Sb{sub 1.48}Co{sub 0.96}O{sub 7} pyrochlore sun-light-responsive photocatalyst

    Energy Technology Data Exchange (ETDEWEB)

    Naceur, Benhadria, E-mail: nacer1974@yahoo.fr [Laboratory of Inorganic Materials Chemistry and Application, Department of Materials Engineering, University of Science and Technology of Oran (USTO M.B), BP 1505, El M’naouar, 31000 Oran (Algeria); Abdelkader, Elaziouti, E-mail: elaziouti_a@yahoo.com [Laboratory of Inorganic Materials Chemistry and Application, Department of Materials Engineering, University of Science and Technology of Oran (USTO M.B), BP 1505, El M’naouar, 31000 Oran (Algeria); Dr Moulay Tahar University, Saida (Algeria); Nadjia, Laouedj, E-mail: nlaouedj@yahoo.fr [Laboratory of Inorganic Materials Chemistry and Application, Department of Materials Engineering, University of Science and Technology of Oran (USTO M.B), BP 1505, El M’naouar, 31000 Oran (Algeria); Dr Moulay Tahar University, Saida (Algeria); Sellami, Mayouf, E-mail: Mourad7dz@yahoo.fr [Laboratory of Inorganic Materials Chemistry and Application, Department of Materials Engineering, University of Science and Technology of Oran (USTO M.B), BP 1505, El M’naouar, 31000 Oran (Algeria); Noureddine, Bettahar, E-mail: nbettahar2001@yahoo.fr [Laboratory of Inorganic Materials Chemistry and Application, Department of Materials Engineering, University of Science and Technology of Oran (USTO M.B), BP 1505, El M’naouar, 31000 Oran (Algeria)

    2016-02-15

    Graphical abstract: Heterogeneous photo Fenton process with dye sensitized mechanism of RhB by Bi{sub 1.56}Sb{sub 1.48}Co{sub 0.96}O{sub 7} compound. - Highlights: • Bi{sub 1.56}Sb{sub 1.48}Co{sub 0.96}O{sub 7} (BSCO) catalyst was synthesized by improved solid state reaction method. • BSCO/H{sub 2}O{sub 2}/UVA and BSCO/H{sub 2}O{sub 2}/SL catalyst systems exhibit excellent photocatalytic activities for rhodamine B. • The photocatalytic degradation was preceded via heterogeneous photo Fenton mechanism process. • ·OH radicals are the main reactive species for the degradation of RhB. - Abstract: Novel nanostructure pyrochlore Bi{sub 1.56}Sb{sub 1.48}Co{sub 0.96}O{sub 7} was successfully synthesized via solid state reaction method in air. The as-synthesized photocatalyst was characterized by X-ray diffraction, Scanning electron microscopy and UV–vis diffuse reflectance spectroscopy techniques. The results showed that the BSCO was crystallized with the pyrochlore-type structure, cubic crystal system and space group Fd3m. The average particle size and band gap for BSCO were D = 76.29 nm and E{sub g} = 1.50 eV respectively. Under the optimum conditions for discoloration of the dye: initial concentration of 20 mg L{sup −1} RhB, pH 7, 25 °C, 0.5 mL H{sub 2}O{sub 2} and BSCO/dye mass ration of 1 g L{sup −1}, 97.77 and 90.16% of RhB were removed with BSCO/H{sub 2}O{sub 2} photocatalytic system within 60 min of irradiation time under UVA- and SL irradiations respectively. Pseudo-second-order kinetic model gave the best fit, with highest correlation coefficients (R{sup 2} ≥ 0.99). On the base of these results, the mechanism of the enhancement of the discoloration efficiency was discussed. .

  12. Geometrical frustration in the ferromagnetic pyrochlore Ho2Ti2O7

    DEFF Research Database (Denmark)

    Harris, M.J.; Bramwell, S.T.; McMorrow, D.F.

    1997-01-01

    We report a detailed study of the pyrochlore Ho2Ti2O7, in which the magnetic ions (Ho3+) are ferromagnetically coupled with J similar to 1 K. We show that the presence of local Ising anisotropy leads to a geometrically frustrated ground state, preventing long-range magnetic order down to at least 0...

  13. A new triclinic modification of the pyrochlore-type KOs 2O 6 superconductor

    Science.gov (United States)

    Katrych, S.; Gu, Q. F.; Bukowski, Z.; Zhigadlo, N. D.; Krauss, G.; Karpinski, J.

    2009-03-01

    A new modification of KOs 2O 6, the representative of a new structural type (Pearson symbol a P18, a=5.5668(1) Å, b=6.4519(2) Å, c=7.2356(2) Å, α=65.377(3)°, β=70.572(3)°, γ=75.613(2)° space group P-1, no. 2 was synthesized employing high pressure technique. Its structure was determined by single-crystal X-ray diffraction. The structure can be described as two OsO 6 octahedral chains relating to each other through inversion and forming big voids with K atoms inside. Quantum chemical calculations were performed on the novel compound and structurally related cubic compound. High-pressure X-ray study showed that cubic KOs 2O 6 phase was stable up to 32.5(2) GPa at room temperature.

  14. Key insights on the structural characterization of textured Er2O3–ZrO2 nano-oxides prepared by a surfactant-free solvothermal route

    International Nuclear Information System (INIS)

    Julián-López, Beatriz; Luz, Verónica de la; Gonell, Francisco; Cordoncillo, Eloisa; López-Haro, Miguel; Calvino, Jose J.; Escribano, Purificación

    2012-01-01

    Highlights: ► Structural resolution of fluorite vs. pyrochlore in small nanocrystals. ► Simple template-free solvothermal synthesis of Er 2 O 3 –ZrO 2 nanooxides. ► Good control over size, morphology and surface properties (280 m 2 g −1 ). - Abstract: Zirconia-mixed oxides can exhibit cubic fluorite and pyrochlore structure. Their discrimination is not easy in nanooxides with a crystal size close to that of a few unit cells. In this work, high resolution transmission electron microscopy (HRTEM) has been employed to provide key insights on the structural characterization of a nanometric and porous mixed Er 2 O 3 –ZrO 2 oxide. The material was prepared by a simple template-free solvothermal route that provided nanocrystalline powders at low temperature (170 °C) with spherical morphology, and high surface area (∼280 m 2 g −1 ). The porosity was mainly originated from the assembling of organic complexing agents used in the synthesis to limit the crystal growth and to control hydrolysis and condensation reaction rates. The samples were characterized by thermal analysis, X-ray diffraction, scanning electron microscopy and N 2 adsorption measurements. A detailed study by HRTEM was conducted on microtomed samples. It was observed that the material was made of nanocrystals packed into spherical agglomerates. HRTEM simulations indicated that it is not possible to identify the pyrochlore phase in nanoparticles with diameter below 2 nm. In our samples, the analysis of the HRTEM lattice images by means of fast Fourier transform (FFT) techniques revealed well defined spots that can be assigned to different planes of a cubic fluorite-type phase, even in the raw material. Raman spectroscopy was also a powerful technique to elucidate the crystalline phase of the materials with the smallest nanoparticles. HREM and Raman results evidenced that the material is constituted, irrespective of the temperature of the final calcination step, by an ensemble of randomly

  15. Spin freezing in the geometrically frustrated pyrochlore antiferromagnet Tb2Mo2O7

    DEFF Research Database (Denmark)

    Gaulin, B.D.; Reimers, J.N.; Mason, T.E.

    1992-01-01

    The magnetic metal ions in the cubic pyrochlore Tb2Mo2O7 form an infinite three-dimensional network of corner-sharing tetrahedra with a very high potential for frustration in the presence of antiferromagnetism. We have performed neutron scattering measurements which show short-range spatial...... correlations that develop continuously with decreasing temperature, while the characteristic time scale for the fluctuating moments decreases dramatically below T(f) is similar to 25 K. Therefore, this pure material, which possesses frustration that is purely geometrical in origin, displays a spin-glass state...

  16. Key insights on the structural characterization of textured Er{sub 2}O{sub 3}-ZrO{sub 2} nano-oxides prepared by a surfactant-free solvothermal route

    Energy Technology Data Exchange (ETDEWEB)

    Julian-Lopez, Beatriz, E-mail: julian@qio.uji.es [Departamento de Quimica Inorganica y Organica, Universitat Jaume I, Avda. Vicente Sos Baynat s/n, 12071 Castellon (Spain); Luz, Veronica de la; Gonell, Francisco; Cordoncillo, Eloisa [Departamento de Quimica Inorganica y Organica, Universitat Jaume I, Avda. Vicente Sos Baynat s/n, 12071 Castellon (Spain); Lopez-Haro, Miguel; Calvino, Jose J. [Departamento de Ciencia de los Materiales e Ingenieria Metalurgica y Quimica Inorganica, Facultad de Ciencias, Universidad de Cadiz, Campus Rio San Pedro, Puerto Real, 11510 Cadiz (Spain); Escribano, Purificacion [Departamento de Quimica Inorganica y Organica, Universitat Jaume I, Avda. Vicente Sos Baynat s/n, 12071 Castellon (Spain)

    2012-04-05

    Highlights: Black-Right-Pointing-Pointer Structural resolution of fluorite vs. pyrochlore in small nanocrystals. Black-Right-Pointing-Pointer Simple template-free solvothermal synthesis of Er{sub 2}O{sub 3}-ZrO{sub 2} nanooxides. Black-Right-Pointing-Pointer Good control over size, morphology and surface properties (280 m{sup 2} g{sup -1}). - Abstract: Zirconia-mixed oxides can exhibit cubic fluorite and pyrochlore structure. Their discrimination is not easy in nanooxides with a crystal size close to that of a few unit cells. In this work, high resolution transmission electron microscopy (HRTEM) has been employed to provide key insights on the structural characterization of a nanometric and porous mixed Er{sub 2}O{sub 3}-ZrO{sub 2} oxide. The material was prepared by a simple template-free solvothermal route that provided nanocrystalline powders at low temperature (170 Degree-Sign C) with spherical morphology, and high surface area ({approx}280 m{sup 2} g{sup -1}). The porosity was mainly originated from the assembling of organic complexing agents used in the synthesis to limit the crystal growth and to control hydrolysis and condensation reaction rates. The samples were characterized by thermal analysis, X-ray diffraction, scanning electron microscopy and N{sub 2} adsorption measurements. A detailed study by HRTEM was conducted on microtomed samples. It was observed that the material was made of nanocrystals packed into spherical agglomerates. HRTEM simulations indicated that it is not possible to identify the pyrochlore phase in nanoparticles with diameter below 2 nm. In our samples, the analysis of the HRTEM lattice images by means of fast Fourier transform (FFT) techniques revealed well defined spots that can be assigned to different planes of a cubic fluorite-type phase, even in the raw material. Raman spectroscopy was also a powerful technique to elucidate the crystalline phase of the materials with the smallest nanoparticles. HREM and Raman results evidenced

  17. Cluster-Glass Phase in Pyrochlore X Y Antiferromagnets with Quenched Disorder

    Science.gov (United States)

    Andrade, Eric C.; Hoyos, José A.; Rachel, Stephan; Vojta, Matthias

    2018-03-01

    We study the impact of quenched disorder (random exchange couplings or site dilution) on easy-plane pyrochlore antiferromagnets. In the clean system, order by disorder selects a magnetically ordered state from a classically degenerate manifold. In the presence of randomness, however, different orders can be chosen locally depending on details of the disorder configuration. Using a combination of analytical considerations and classical Monte Carlo simulations, we argue that any long-range-ordered magnetic state is destroyed beyond a critical level of randomness where the system breaks into magnetic domains due to random exchange anisotropies, becoming, therefore, a glass of spin clusters, in accordance with the available experimental data. These random anisotropies originate from off-diagonal exchange couplings in the microscopic Hamiltonian, establishing their relevance to other magnets with strong spin-orbit coupling.

  18. Emergent Topological Phenomena in Thin Films of Pyrochlore Iridates

    Science.gov (United States)

    Yang, Bohm-Jung; Nagaosa, Naoto

    2014-06-01

    Because of the recent development of thin film and artificial superstructure growth techniques, it is possible to control the dimensionality of the system, smoothly between two and three dimensions. In this Letter we unveil the dimensional crossover of emergent topological phenomena in correlated topological materials. In particular, by focusing on the thin film of pyrochlore iridate antiferromagnets grown along the [111] direction, we demonstrate that the thin film can have a giant anomalous Hall conductance, proportional to the thickness of the film, even though there is no Hall effect in 3D bulk material. Moreover, in the case of ultrathin films, a quantized anomalous Hall conductance can be observed, despite the fact that the system is an antiferromagnet. In addition, we uncover the emergence of a new topological phase, the nontrivial topological properties of which are hidden in the bulk insulator and manifest only in thin films. This shows that the thin film of correlated topological materials is a new platform to search for unexplored novel topological phenomena.

  19. Superconductivity mediated by anharmonic phonons: application to β-pyrochlore oxides

    Science.gov (United States)

    Hattori, Kazumasa; Tsunetsugu, Hirokazu

    2010-03-01

    We investigate three dimensional anharmonic phonons under tetrahedral symmetry and superconductivity mediated by these phonons. Three dimensional anharmonic phonon spectra are calculated directly by solving Schr"odinger equation and the superconducting transition temperature is determined by using the theory of strong coupling superconductivity assuming an isotropic gap function. With increasing the third order anharmonicity b of the tetrahedral potential, we find a crossover in the energy spectrum to a quantum tunneling regime. We obtain strongly enhanced transition temperatures around the crossover point. The first order transition observed in KOs2O6 is discussed in terms of the first excited state energy δ, and the coupling constant λ in the strong coupling theory of superconductivity. Our results suggest that the decrease of λ and increase of δ below the first order transition temperature. We point out that the change in the oscillation amplitude and characterizes this isomorphic transition. The chemical trends of the superconducting transition temperature, λ, and δ in the β-pyrochlore compounds are also discussed.

  20. Isotope effect on superconductivity and Raman phonons of Pyrochlore Cd2Re2O7

    Science.gov (United States)

    Razavi, F. S.; Hajialamdari, M.; Reedyk, M.; Kremer, R. K.

    2018-06-01

    Cd2Re2O7 is the only α-Pyrochlore exhibiting superconductivity with a transition temperature (Tc) of ∼ 1 K. In this study, we present the effect of oxygen isotope (18O) as well as combined 18O and cadmium isotope (116Cd) substitution on the superconductivity and Raman scattering spectrum of Cd2Re2O7. The change of Tc and the energy gap Δ(T) are reported using various techniques including point contact spectroscopy. The shift in Raman phonon frequencies upon isotope substitution will be compared with measurement of the isotope effect on the superconducting transition temperature.

  1. Cooper-pair formation by anharmonic rattling modes in the β-pyrochlore superconductor KOs2O6

    Science.gov (United States)

    Chang, Jun; Eremin, Ilya; Thalmeier, Peter

    2009-05-01

    We study the influence of anharmonic rattling phonons in the β-pyrochlore superconductor KOs2O6 using the strong-coupling Eliashberg approach. In particular, by analyzing the specific heat data, we find that the rattling phonon frequency changes discontinuously at the critical temperature of the first-order phase transition. Solving the strong-coupling Eliashberg equations with effective temperature-dependent α2F(ω), we investigate the consequence of this first-order phase transition for the anomalous temperature dependence of the superconducting gap. We discuss our results in the context of the recent experimental data.

  2. All-in-all-out magnetic domain size in pyrochlore iridate thin films as probed by local magnetotransport

    Energy Technology Data Exchange (ETDEWEB)

    Fujita, T. C.; Uchida, M., E-mail: uchida@ap.t.u-tokyo.ac.jp; Kozuka, Y.; Ogawa, S. [Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo 113-8656 (Japan); Tsukazaki, A. [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); PRESTO, Japan Science and Technology Agency (JST), Tokyo 102-0075 (Japan); Arima, T. [Department of Advanced Materials Science, University of Tokyo, Kashiwa 277-8561 (Japan); RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198 (Japan); Kawasaki, M. [Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo 113-8656 (Japan); RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198 (Japan)

    2016-01-11

    Pyrochlore iridates have attracted growing attention because of a theoretical prediction of a possible topological semimetal phase originating from all-in-all-out spin ordering. Related to the topological band structure, recent findings of the magnetic domain wall conduction have stimulated investigations of magnetic domain distribution in this system. Here, we investigate the size of magnetic domains in Eu{sub 2}Ir{sub 2}O{sub 7} single crystalline thin films by magnetoresistance (MR) using microscale Hall bars. Two distinct magnetic domains of the all-in-all-out spin structure are known to exhibit linear MR but with opposite signs, which enables us to estimate the ratio of the two domains in the patterned channel. The linear MR for 80 × 60 μm{sup 2} channel is nearly zero after zero-field cooling, suggesting random distribution of domains smaller than the channel size. In contrast, the wide distribution of the value of the linear MR is detected in 2 × 2 μm{sup 2} channel, reflecting the detectable domain size depending on each cooling-cycle. Compared to simulation results, we estimate the average size of a single all-in-all-out magnetic domain as 1–2 μm.

  3. A novel high-temperature commensurate superstructure in a natural bariopyrochlore: A structural study by means of a multiphase crystal structure refinement

    Czech Academy of Sciences Publication Activity Database

    Bindi, L.; Petříček, Václav; Withers, R. L.; Zoppi, M.; Bonazzi, P.

    2006-01-01

    Roč. 179, - (2006), s. 716-725 ISSN 0022-4596 R&D Projects: GA ČR(CZ) GA202/03/0430 Institutional research plan: CEZ:AV0Z10100521 Keywords : pyrochlore * superstructure * X-ray data * multiphase structure refinement * TEM study Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.107, year: 2006

  4. Steering Charge Kinetics of Tin Niobate Photocatalysts: Key Roles of Phase Structure and Electronic Structure.

    Science.gov (United States)

    Huang, Shushu; Wang, Chunyan; Sun, Hao; Wang, Xiaojing; Su, Yiguo

    2018-05-23

    Tin niobate photocatalysts with the phase structures of froodite (SnNb 2 O 6 ) and pyrochlore (Sn 2 Nb 2 O 7 ) were obtained by a facile solvothermal method in order to explore the impact of phase structure and electronic structure on the charge kinetics and photocatalytic performance. By employing tin niobate as a model compound, the effects of phase structure over electronic structure, photocatalytic activity toward methyl orange solution and hydrogen evolution were systematically investigated. It is found that the variation of phase structure from SnNb 2 O 6 to Sn 2 Nb 2 O 7 accompanied with modulation of particle size and band edge potentials that has great consequences on photocatalytic performance. In combination with the electrochemical impedance spectroscopy (EIS), transient photocurrent responses, transient absorption spectroscopy (TAS), and the analysis of the charge-carrier dynamics suggested that variation of electronic structure has great impacts on the charge separation and transfer rate of tin niobate photocatalysts and the subsequent photocatalytic performance. Moreover, the results of the X-ray photoelectron spectroscopy (XPS) indicated that the existent of Sn 4+ species in Sn 2 Nb 2 O 7 could result in a decrease in photocatalytic activity. Photocatalytic test demonstrated that the SnNb 2 O 6 (froodite) catalyst possesses a higher photocatalytic activity toward MO degradation and H 2 evolution compared with the sample of Sn 2 Nb 2 O 7 (pyrochlore). On the basis of spin resonance measurement and trapping experiment, it is expected that photogenerated holes, O 2 -• , and OH • active species dominate the photodegradation of methyl orange.

  5. Atomic scale simulations of pyrochlore oxides with a tight-binding variable-charge model: implications for radiation tolerance

    International Nuclear Information System (INIS)

    Sattonnay, G; Tétot, R

    2014-01-01

    Atomistic simulations with new interatomic potentials derived from a tight-binding variable-charge model were performed in order to investigate the lattice properties and the defect formation energies in Gd 2 Ti 2 O 7 and Gd 2 Zr 2 O 7 pyrochlores. The main objective was to determine the role played by the defect stability on the radiation tolerance of these compounds. Calculations show that the titanate has a more covalent character than the zirconate. Moreover, the properties of oxygen Frenkel pairs, cation antisite defects and cation Frenkel pairs were studied. In Gd 2 Ti 2 O 7 the cation antisite defect and the Ti-Frenkel pair are not stable: they evolve towards more stable defect configurations during the atomic relaxation process. This phenomenon is driven by a decrease of the Ti coordination number down to five which leads to a local atomic reorganization and strong structural distortions around the defects. These kinds of atomic rearrangements are not observed around defects in Gd 2 Zr 2 O 7 . Therefore, the defect stability in A 2 B 2 O 7 depends on the ability of B atoms to accommodate high coordination number (higher than six seems impossible for Ti). The accumulation of structural distortions around Ti-defects due to this phenomenon could drive the Gd 2 Ti 2 O 7 amorphization induced by irradiation. (paper)

  6. Quantum Spin Ice under a [111] Magnetic Field: From Pyrochlore to Kagome.

    Science.gov (United States)

    Bojesen, Troels Arnfred; Onoda, Shigeki

    2017-12-01

    Quantum spin ice, modeled for magnetic rare-earth pyrochlores, has attracted great interest for hosting a U(1) quantum spin liquid, which involves spin-ice monopoles as gapped deconfined spinons, as well as gapless excitations analogous to photons. However, the global phase diagram under a [111] magnetic field remains open. Here we uncover by means of unbiased quantum Monte Carlo simulations that a supersolid of monopoles, showing both a superfluidity and a partial ionization, intervenes the kagome spin ice and a fully ionized monopole insulator, in contrast to classical spin ice where a direct discontinuous phase transition takes place. We also show that on cooling, kagome spin ice evolves towards a valence-bond solid similar to what appears in the associated kagome lattice model [S. V. Isakov et al., Phys. Rev. Lett. 97, 147202 (2006)PRLTAO0031-900710.1103/PhysRevLett.97.147202]. Possible relevance to experiments is discussed.

  7. First-principles study of strong correlation effects in pyrochlore iridates

    Energy Technology Data Exchange (ETDEWEB)

    Shinaoka, Hiroshi [Department of Physics, Saitama University (Japan); Hoshino, Shintaro [Department of Basic Science, The University of Tokyo (Japan); Troyer, Matthias [Theoretische Physik, ETH Zuerich (Switzerland); Werner, Philipp [Department of Physics, University of Fribourg (Switzerland)

    2016-07-01

    The pyrochlore iridates A{sub 2}Ir{sub 2}O{sub 7} (A=Pr, Nd, Y, etc.) are an ideal system to study fascinating phenomena induced by strong electron correlations and spin-orbit coupling. In this talk, we study strong correlation effects in the prototype compound Y{sub 2}Ir{sub 2}O{sub 7} using the local density approximation and dynamical mean-field theory (LDA+DMFT). We map out the phase diagram in the space of temperature, onsite Coulomb repulsion U, and filling. Consistent with experiments, we find that an all-in/all-out ordered insulating phase is stable for realistic values of U. We reveal the importance of the hybridization between j{sub eff} = 1/2 and j{sub eff} = 3/2 states under the Coulomb interaction and trigonal crystal field. We demonstrate a substantial band narrowing in the paramagnetic metallic phase and non-Fermi liquid behavior in the electron/hole doped system originating from long-lived quasi-spin moments induced by nearly flat bands. We further compare our results with recent experimental results of Eu{sub 2}Ir{sub 2}O{sub 7} under hydrostatic pressure.

  8. Catalytic Oxidation of Soot on a Novel Active Ca-Co Dually-Doped Lanthanum Tin Pyrochlore Oxide

    Directory of Open Access Journals (Sweden)

    Lijie Ai

    2018-04-01

    Full Text Available A novel active Ca-Co dually-doping pyrochlore oxide La2−xCaxSn2−yCoyO7 catalyst was synthesized by the sol-gel method for catalytic oxidation of soot particulates. The microstructure, atomic valence, reduction, and adsorption performance were investigated by X-ray powder diffraction (XRD, scanning electron microscope (SEM, Fourier-transform infrared spectroscopy (FT-IR, X-ray photoelectron spectroscopy (XPS, H2-TPR (temperature-programmed reduction, and in situ diffuse reflection infrared Fourier transformed (DRIFTS techniques. Temperature programmed oxidation (TPO tests were performed with the mixture of soot-catalyst under tight contact conditions to evaluate the catalytic activity for soot combustion. Synergetic effect between Ca and Co improved the structure and redox properties of the solids, increased the surface oxygen vacancies, and provided a suitable electropositivity for oxide, directly resulting in the decreased ignition temperature for catalyzed soot oxidation as low as 317 °C. The presence of NO in O2 further promoted soot oxidation over the catalysts with the ignition temperature decreased to about 300 °C. The DRIFTS results reveal that decomposition of less stable surface nitrites may account for NO2 formation in the ignition period of soot combustion, which thus participate in the auxiliary combustion process.

  9. Nanostructured KTaTeO6 and Ag-doped KTaTeO6 Defect Pyrochlores: Promising Photocatalysts for Dye Degradation and Water Splitting

    Science.gov (United States)

    Venkataswamy, Perala; Sudhakar Reddy, CH.; Gundeboina, Ravi; Sadanandam, Gullapelli; Veldurthi, Naveen Kumar; Vithal, M.

    2018-03-01

    In this study, the nanostructured parent KTaTeO6 (KTTO) and Ag-doped KTaTeO6 (ATTO) catalysts with defect pyrochlore structure were prepared by solid-state and ion-exchange methods, respectively. The synthesized materials were characterized by various techniques to determine their chemical composition, morphology and microstructural features. The XRD studies show that both KTTO and ATTO have cubic structure (space group Fd3m) with high crystallinity. The doping of Ag altered the BET surface area of parent KTTO. The nano nature of the samples was studied by TEM images. A considerable red-shift in the absorption edge is observed for ATTO compared to KTTO. Incorporation of Ag+ in the KTTO lattice is clearly identified from EDX, elemental mapping and XPS results. Degradation of methyl violet and solar water splitting reactions were used to access the photocatalytic activity of KTTO and ATTO. The results obtained suggest that compared to KTTO, the ATTO showed higher photocatalytic activity in both cases. The favourable properties such as high surface area, more surface hydroxyl groups, stronger light absorption in visible region and narrower band gap energy were supposed to be the reasons for the high activity observed in ATTO.

  10. Sudden Disappearance of the First-Order Transition in β-Pyrochlore KOs2O6 under Low Pressure

    Science.gov (United States)

    Umeo, Kazunori; Kubo, Hirokazu; Yamaura, Jun-ichi; Hiroi, Zenji; Takabatake, Toshiro

    2009-12-01

    We report the first observation of the pressure effect on the first-order transition at Tp = 7.5 K in the β-pyrochlore oxide superconductor KOs2O6 by specific-heat measurement. The peak in the specific heat at Tp disappeared at a low pressure of 0.02 GPa. With increasing pressure up to 0.02 GPa, the coefficient of the T5 dependence of the specific heat increases by 30%. This finding implies that low-energy excitations of phonons are enhanced by the suppression of the first-order transition. However, the specific-heat jump at Tc is unchanged with pressure up to 1 GPa, indicating that the strong coupling superconductivity is rather robust under pressure.

  11. Absence of magnetic long-range order in Y2CrSbO7 : Bond-disorder-induced magnetic frustration in a ferromagnetic pyrochlore

    Science.gov (United States)

    Shen, L.; Greaves, C.; Riyat, R.; Hansen, T. C.; Blackburn, E.

    2017-09-01

    The consequences of random nonmagnetic-ion dilution for the pyrochlore family Y2(M 1 -xN x)2O7 (M = magnetic ion, N = nonmagnetic ion) have been investigated. As a first step, we experimentally examine the magnetic properties of Y2CrSbO7 (x =0.5 ), in which the magnetic sites (Cr3 +) are percolative. Although the effective Cr-Cr spin exchange is ferromagnetic, as evidenced by a positive Curie-Weiss temperature, ΘCW ≃19.5 K , our high-resolution neutron powder diffraction measurements detect no sign of magnetic long-range order down to 2 K. In order to understand our observations, we construct a lattice model to numerically study the bond disorder introduced by the ionic size mismatch between M and N , which reveals that the bond disorder percolates at xb ≃0.23 , explaining the absence of magnetic long-range order. This model could be applied to a series of frustrated magnets with a pyrochlore sublattice, for example, the spinel compound Zn (Cr1 -xGax )2O4 , wherein a Néel to spin glass phase transition occurs between x =0.2 and 0.25 [Lee et al., Phys. Rev. B 77, 014405 (2008), 10.1103/PhysRevB.77.014405]. Our study stresses the non-negligible role of bond disorder on magnetic frustration, even in ferromagnets.

  12. Phase evolution and microwave dielectric properties of A5M5O17-type ceramics

    Directory of Open Access Journals (Sweden)

    Ali Murad

    2017-07-01

    Full Text Available A number of A5M5O17 (A = Na, Ca, Sr, La, Nd, Sm, Gd, Dy, Yb; B = Ti, Nb, Ta type compounds were prepared by a solid-state sintering route and characterized in terms of structure, microstructure and microwave dielectric properties. The compatibility of rare earths with mixed niobate/tantalate and titanate phases was investigated. The larger ionic radii mismatch resulted in the formation of pyrochlore and/or mixed phases while in other cases, pure A5M5O17 phase was formed. The samples exhibited relative permittivity in the range of 35 to 82, quality factor (Q × fo = 897 GHz to 11946 GHz and temperature coefficient of resonance frequency (τf = -120 ppm/°C to 318 ppm/°C.

  13. First-principles calculation of structural and energetic properties for A2Ti2O7 (A = Lu, Er, Y, Gd, Sm, Nd, La)

    International Nuclear Information System (INIS)

    Zhang, Z.L.; Xiao, H.Y.; Zu, Xiaotao T.; Gao, Fei; Weber, William J.

    2009-01-01

    A first-principles method has been employed to investigate the structural and energetic properties for A2Ti2O7 (A = Lu, Er, Y, Gd, Sm, Nd, La), including the formation energies of the cation antisite-pair, the anion Frenkel pair that defines anion-disorder, and the coupled cation antisite-pair/anion-Frenkel. It is proposed that the interaction may have more significant influence on the radiation resistance behavior of titanate pyrochlores, although the interactions are relatively much stronger than the interactions. It is found that the defect formation energies are not simple functions of the A-site cation radii. The formation energy of the cation antisite-pair increases continuously as the A-site cation varies from Lu to Gd, and then decreases continuously with the variation of the A-site cation from Gd to La, in excellent agreement with the radiation-resistance trend of the titanate pyrochlores. The band gaps in these pyrochlores were also measured, and the band gap widths changed continuously with cation radius.

  14. Observation of magnetic polarons in the magnetoresistive pyrochlore Lu2V2O7

    International Nuclear Information System (INIS)

    Storchak, Vyacheslav G; Brewer, Jess H; Eshchenko, Dmitry G; Mengyan, Patrick W; Zhou Haidong; Wiebe, Christopher R

    2013-01-01

    Materials that exhibit colossal magnetoresistance (CMR) have attracted much attention due to their potential technological applications. One particularly interesting model for the magnetoresistance of low-carrier-density ferromagnets involves mediation by magnetic polarons (MP)—electrons localized in nanoscale ferromagnetic ‘droplets’ by their exchange interaction. However, MP have not previously been directly detected and their size has been difficult to determine from macroscopic measurements. In order to provide this crucial information, we have carried out muon spin rotation measurements on the magnetoresistive semiconductor Lu 2 V 2 O 7 in the temperature range from 2 to 300 K and in magnetic fields up to 7 T. Magnetic polarons with characteristic radius R ≈ 0.4 nm are detected below about 100 K, where Lu 2 V 2 O 7 exhibits CMR; at higher temperature, where the magnetoresistance vanishes, these MP also disappear. This observation confirms the MP-mediated model of CMR and reveals the microscopic size of the MP in magnetoresistive pyrochlores. (paper)

  15. Response of Gd 2 Ti 2 O 7 and La 2 Ti 2 O 7 to swift-heavy ion irradiation and annealing

    Energy Technology Data Exchange (ETDEWEB)

    Park, Sulgiye; Lang, Maik; Tracy, Cameron L.; Zhang, Jiaming; Zhang, Fuxiang; Trautmann, Christina; Rodriguez, Matias D.; Kluth, Patrick; Ewing, Rodney C.

    2015-07-01

    Swift heavy ion (2 GeV 181Ta) irradiation-induced amorphization and temperature-induced recrystallization of cubic pyrochlore Gd2Ti2O7 (Fd3¯m) are compared with the response of a compositionally-similar material with a monoclinic-layered perovskite-type structure, La2Ti2O7 (P21). The averaged electronic energy loss, dE/dx, was 37 keV/nm and 35 keV/nm in Gd2Ti2O7 and La2Ti2O7, respectively. Systematic analysis of the structural modifications was completed using transmission electron microscopy, synchrotron X-ray diffraction, Raman spectroscopy, and small-angle X-ray scattering. Increasing ion-induced amorphization with increasing ion fluence was evident in the X-ray diffraction patterns of both compositions by a reduction in the intensity of the diffraction maxima concurrent with the growth in intensity of a broad diffuse scattering halo. Transmission electron microscopy analysis showed complete amorphization within ion tracks (diameter: ~10 nm) for the perovskite-type material; whereas a concentric, core–shell morphology was evident in the ion tracks of the pyrochlore, with an outer shell of disordered yet still crystalline material with the fluorite structure surrounding an amorphous track core (diameter: ~9 nm). The radiation response of both titanate oxides with the same stoichiometry can be understood in terms of differences in their structures and compositions. While the radiation damage susceptibility of pyrochlore A2B2O7 materials decreases as a function of the cation radius ratio rA/rB, the current study correlates this behavior with the stability field of monoclinic structures, where rLa/rTi > rGd/rTi. Isochronal annealing experiments of the irradiated materials showed complete recrystallization of La2Ti2O7 at 775 °C and of Gd2Ti2O7 at 850 °C. The annealing behavior is discussed in terms of enhanced damage recovery in La2Ti2O7, compared to the pyrochlore compounds Gd2Ti2O7. The difference in the recrystallization behavior may be related to structural

  16. Thermo-selective Tm(x)Ti(1-x)O(2-x/2) nanoparticles: from Tm-doped anatase TiO2 to a rutile/pyrochlore Tm2Ti2O7 mixture. An experimental and theoretical study with a photocatalytic application.

    Science.gov (United States)

    Navas, Javier; Sánchez-Coronilla, Antonio; Aguilar, Teresa; De los Santos, Desireé M; Hernández, Norge C; Alcántara, Rodrigo; Fernández-Lorenzo, Concha; Martín-Calleja, Joaquín

    2014-11-07

    This is an experimental and theoretical study of thulium doped TiO2 nanoparticles. From an experimental perspective, a method was used to synthesize thulium-doped TiO2 nanoparticles in which Tm(3+) replaces Ti(4+) in the lattice, which to our knowledge has neither been reported nor studied theoretically so far. Different proportions of anatase and rutile phases were obtained at different annealing temperatures, and XRD and Raman spectroscopy also revealed the presence of a pyrochlore phase (Tm2Ti2O7) at 1173 K. Thus, the structure of the Tm-doped nanoparticles was thermally-controlled. Furthermore, XPS showed the presence of Tm(3+) in the samples synthesized, which produces oxygen vacancies to maintain the local neutrality in the lattice. The presence of Tm(3+) in the samples led to changes in the UV-Vis absorption spectra, so they showed photoluminescence properties and new states in the band gap, which produce a new lower energy electronic transition than the main TiO2 one. Periodic DFT calculations were performed to understand the experimentally produced structures. The production of oxygen vacancies was analysed and the changes generated in the structure were fully detailed. The DOS and PDOS analyses confirmed the experimental results obtained using UV-Vis spectroscopy, and showed that the new electronic states in the band gap are due to interactions of the f state of Tm and the p state of O. Likewise, the charge study and the ELF analysis indicate that when Tm is introduced into the TiO2 structure, the Ti-O bond around the oxygen vacancy is strengthened. Finally, an example of a photocatalytic application was developed to show the high efficiency of the samples due to the heterojunction in the interfaces of the phases in the samples, which improved the charge separation and the good charge carrier mobility due to the presence of the pyrochlore phase, as was also shown theoretically.

  17. Fundamental aspects of Am and Cm in zirconia-based materials. Investigations using X-ray diffraction and Raman spectroscopy

    International Nuclear Information System (INIS)

    Raison, P.E.; Haire, R.G.; Assefa, Z.

    2002-01-01

    We have investigated incorporation of americium and curium in selected zirconia-based materials. Fundamental aspects were explored via X-ray diffraction and Raman spectroscopy. First explored was the pseudo ternary system, AmO 2 -ZrO 2 -Y 2 O 3 . It was found that stable, cubic solid solutions (Am x Zr 1-x Y y )O 2-2/y can be obtained for selected compositions. The cell parameters of the cubic phases were established as being linear with the AmO 2 content. For the Cm 2 O 3 -ZrO 2 system, it was determined that diphasic materials are produced, except for two compositions: 25 mol% and 50 mol% of CmO 1.5 . For these compositions a single-phase cubic fluorite type solid solution (a=5.21A±0.01) and a pyrochlore oxide Cm 2 Zr 2 O 7 (a=10.63A±0.02) are formed, respectively. The stability of pyrochlore oxides is also being investigated as a function of self-irradiation, using shorter-lived isotopes, one being the californium pyrochlore 249 Cf 2 Zr 2 O 7 . We obtained evidence that after six months of storage the pyrochlore oxide is undergoing structural change. Additional studies are in progress. (author)

  18. Dielectric and magnetic properties, and electronic structure of multiferroic perovskite PbFe.sub.0.5./sub.Ta.sub.0.5./sub.O.sub.3./sub. and incipient ferroelectric pyrochlore Pb.sub.2./sub.Fe.sub.0.34./sub.Ta.sub.1.84./sub.O.sub.7.11./sub. single crystals and ceramics

    Czech Academy of Sciences Publication Activity Database

    Kania, A.; Miga, S.; Talik, E.; Gruszka, I.; Szubka, M.; Savinov, Maxim; Prokleška, J.; Kamba, Stanislav

    2016-01-01

    Roč. 36, č. 14 (2016), s. 3369-3381 ISSN 0955-2219 R&D Projects: GA ČR GA15-08389S Institutional support: RVO:68378271 Keywords : lead iron tantalate * perovskite multiferroic * pyrochlore * incipient ferroelectric * X-ray photoelectron spectroscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.411, year: 2016

  19. Structural study and electrical properties of Zr-doped Nd2Sn2O7 ...

    Indian Academy of Sciences (India)

    applications as neutron absorbers and radioactive waste forms for final disposal. [2,3]. The cubic pyrochlore structure, space group Fd3m, has eight molecules of the general formula A2B2O6O in the unit cell. The anion array consists of three independent sites O(1), O(2) and O(3), occupying the locations 48f, 8a and 8b.

  20. First-principles study on cubic pyrochlore iridates Y2Ir2O7 and Pr2Ir2O7

    International Nuclear Information System (INIS)

    Ishii, Fumiyuki; Mizuta, Yo Pierre; Kato, Takehiro; Ozaki, Taisuke; Weng Hongming; Onoda, Shigeki

    2015-01-01

    Fully relativistic first-principles electronic structure calculations based on a noncollinear local spin density approximation (LSDA) are performed for pyrochlore iridates Y 2 Ir 2 O 7 and Pr 2 Ir 2 O 7 . The all-in, all-out antiferromagnetic (AF) order is stablized by the on-site Coulomb repulsion U > U c in the LSDA+U scheme, with U c ∼ 1.1 eV and 1.3 eV for Y 2 Ir 2 O 7 and Pr 2 Ir 2 O 7 , respectively. AF semimetals with and without Weyl points and then a topologically trivial AF insulator successively appear with further increasing U. For U = 1.3 eV, Y 2 Ir 2 O 7 is a topologically trivial narrow-gap AF insulator having an ordered local magnetic moment ∼0.5μ B /Ir, while Pr 2 Ir 2 O 7 is barely a paramagnetic semimetal with electron and hole concentrations of 0.016/Ir, in overall agreements with experiments. With decreasing oxygen position parameter x describing the trigonal compression of IrO 6 octahedra, Pr 2 Ir 2 O 7 is driven through a non-Fermi-liquid semimetal having only an isolated Fermi point of Γ 8 + , showing a quadratic band touching, to a Z 2 topological insulator. (author)

  1. Investigations of the magnetic properties in the pyrochlore Ho{sub 2}Ti{sub 2}O{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Schoenemann, Rico; Herrmannsdoerfer, Thomas; Green, Elizabeth Lauren; Wang, Zhaosheng; Wosnitza, Joachim [Dresden High Magnetic Field Laboratory, Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany); Skrotzki, Richard [Dresden High Magnetic Field Laboratory, Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany); Department of Chemistry and Food Chemistry, TU Dresden, Dresden (Germany); Kaneko, Hiroshi; Suzuki, Haruhiko [Faculty of Mathematics and Physics, Kanazawa University, Kanazawa (Japan)

    2013-07-01

    Pyrochlore compounds such as R{sub 2}Ti{sub 2}O{sub 7} (where R is Ho or Dy) have an highly degenerate ground state where the R{sup 3+} moments obey the ''ice rules''. This provides access to study extraordinary physical phenomena, like the formation of magnetic monopoles. Recent publications evidence monopoles which can be probed using high frequency (adiabatic) susceptibility measurements. We performed ac susceptibility measurements on a single-crystal Ho{sub 2}Ti{sub 2}O{sub 7} sample at low temperatures down to 30 mK and magnetic fields up to 14 T. Based on isothermal frequency sweeps we were able to determine spin relaxation rates. Both the real and imaginary parts of the temperature-dependent magnetic susceptibility measurements show the spins freezing below 1 K and provide insight into the magnetic-monopole density.

  2. Photoluminescence properties of ‘red’ emitting La{sub 2}Zr{sub 2}O{sub 7}:Eu pyrochlore ceramics for potential phosphor application

    Energy Technology Data Exchange (ETDEWEB)

    Mohapatra, M., E-mail: manojm@barc.gov.in; Rajeswari, B.; Hon, N.S.; Kadam, R.M.; Natarajan, V.

    2015-10-15

    Lanthanum zirconate (La{sub 2}Zr{sub 2}O{sub 7}=LZO) pyrochlores doped with varying concentrations of Eu were synthesized using a low temperature gel-combustion synthesis route and characterized using X-ray diffraction, scanning electron microscopic and photoluminescence techniques. The final annealing temperature of the system could be brought down to 700 °C to produce a single phase compound. In addition, the optimum activator ion concentration for maximum luminescence yield was evaluated for the system. The site occupancy for the Eu ions was also investigated which suggested that at 500 °C, the ions were on the surface of the LZO host and later diffused into the lattice and replaced the La{sup 3+} ions on annealing at 700 °C 5 h. However, due to difference in the ionic radii, the doped RE ions were of the inversion center forming a D{sub 2d} symmetry around them. For the first time the radiative properties and the commercial utility of the LZO system have been investigated. These parameters were used to get an idea about the M–L bond covalency in the system. The radiative properties suggested the system can be used as a potential ‘red’ emitting phosphor. - Highlights: • Synthesis of lanthanum zirconate pyrochlores doped with Eu using gel-combustion route. • Optimization of dopant ion concentration and annealing temperature and evaluation of its local site symmetry. • Evaluation of various photo-physical properties for the Eu-LZO system to investigate the M–L bond covalency. • Investigation of the commercial utility of the system by calculating the color coordinates. • Comparison of the emission properties with commercial sample.

  3. Pseudo-Goldstone Magnons in the Frustrated S=3/2 Heisenberg Helimagnet ZnCr_{2}Se_{4} with a Pyrochlore Magnetic Sublattice

    Directory of Open Access Journals (Sweden)

    Y. V. Tymoshenko

    2017-11-01

    Full Text Available Low-energy spin excitations in any long-range ordered magnetic system in the absence of magnetocrystalline anisotropy are gapless Goldstone modes emanating from the ordering wave vectors. In helimagnets, these modes hybridize into the so-called helimagnon excitations. Here we employ neutron spectroscopy supported by theoretical calculations to investigate the magnetic excitation spectrum of the isotropic Heisenberg helimagnet ZnCr_{2}Se_{4} with a cubic spinel structure, in which spin-3/2 magnetic Cr^{3+} ions are arranged in a geometrically frustrated pyrochlore sublattice. Apart from the conventional Goldstone mode emanating from the (0 0 q_{h} ordering vector, low-energy magnetic excitations in the single-domain proper-screw spiral phase show soft helimagnon modes with a small energy gap of ∼0.17  meV, emerging from two orthogonal wave vectors (q_{h} 0 0 and (0 q_{h} 0 where no magnetic Bragg peaks are present. We term them pseudo-Goldstone magnons, as they appear gapless within linear spin-wave theory and only acquire a finite gap due to higher-order quantum-fluctuation corrections. Our results are likely universal for a broad class of symmetric helimagnets, opening up a new way of studying weak magnon-magnon interactions with accessible spectroscopic methods.

  4. Structural, photoluminescence and radioluminescence properties of Eu{sup 3+} doped La{sub 2}Hf{sub 2}O{sub 7} nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Wahid, Kareem; Pokhrel, Madhab; Mao, Yuanbing, E-mail: yuanbing.mao@utrgv.edu

    2017-01-15

    This study presents the structural, optical, and radioluminescent characterization of newly synthesized europium-doped lanthanum hafnate (La{sub 2}Hf{sub 2}O{sub 7}:xmol%Eu{sup 3+}, x=0 to 35) nanoparticles (NPs) for use as phosphors and scintillation materials. Samples prepared through a combined co-precipitation and molten salt synthetic process were found to crystalize in the pyrochlore phase, a radiation tolerant structure related to the fluorite structure. These samples exhibit red luminescence under ultraviolet and X-ray excitation. Under these excitations, the optical intensity and quantum yield of the La{sub 2}Hf{sub 2}O{sub 7}:xmol%Eu{sup 3+} NPs depend on the Eu{sup 3+} concentration and are maximized at 5%. It is proposed that there is a trade-off between the quenching due to defect states/cross-relaxation and dopant concentration. An optimal dopant concentration allows the La{sub 2}Hf{sub 2}O{sub 7}:5 mol%Eu{sup 3+} NPs to show the best luminescent properties of all the samples. - Graphical abstract: Incident X-ray and UV photons interact with La{sub 2}Hf{sub 2}O{sub 7}: xmol%Eu{sup 3+}(x=1–35) nanoparticles (NPs) to yield strong red luminescence centered at 612 nm. Colored spheres inside NP diagram represent pyrochlore coordination environment of La{sub 2}Hf{sub 2}O{sub 7}:xmol%Eu{sup 3+}. Blue, red, yellow, green and black spheres represent hafnium(IV) atoms, lanthanum(III)/europium(III) atoms, oxygen atoms at 48f site, oxygen atoms at 8b site and oxygen vacancies, respectively. - Highlights: • La{sub 2}Hf{sub 2}O{sub 7}:xmol%Eu{sup 3+} (x=0–35) nanoparticles with weakly-ordered pyrochlore structures were synthesized. • Optically and X-ray excited emission spectra showed strong luminescence centered at 612 nm. • Photoluminescence quantum yield increases with doping concentration up to 5% and decreases at higher concentrations.

  5. Spin correlations in the pyrochlore slab compounds Ba2Sn2Ga10-7pZnCr7pO22

    International Nuclear Information System (INIS)

    Bonnet, P; Payen, C; Mutka, H; Danot, M; Fabritchnyi, P; Stewart, J R; Mellergaard, A; Ritter, C

    2004-01-01

    The low-temperature properties of a diluted antiferromagnetic pyrochlore slab of S = 3/2 spins are investigated through a study of the frustrated oxides Ba 2 Sn 2 Ga 10-7p ZnCr 7p O 22 (p>0.85). Powder neutron diffraction and 119 Sn Moessbauer absorption show no evidence of long-range magnetic order above 1.5 K. As in SrCr 9q Ga 12-9q O 19 , diffuse magnetic scattering, indicative of short range spin-spin correlations, is observed at low temperature. The dependence of the low-temperature sub-Curie bulk susceptibility to weak site depletion is the inverse of that observed in SrCr 9q Ga 12-9q O 19

  6. Mechanism of mechanochemical synthesis of complex oxides and the peculiarities of their nano-structurization determining sintering

    Directory of Open Access Journals (Sweden)

    Zyryanov V.V.

    2005-01-01

    Full Text Available A mechanism of superfast mechanosynthesis reaction for oxide systems is proposed on the base of a dynamics study. The threshold effect and linear dependence of the chemical response on the effective temperature of the reaction zone are established. Major factors are determined: molecular mass of reagents, enthalpy and difference of reagents in Mohs’s hardness, which also influence the composition of the primary product. Primary acts are characterized by a superfast roller mechanism of mass transfer with the formation of a transient dynamic state (D*. Secondary acts slowly approximate the composition of the product to the composition of the starting mixture by diffusion mass transfer in a deformation mixing regime with a contribution of a rotation (roller mechanism. The list of structure types for complex oxides derived by mechanosynthesis includes perovskites, fluorites, pyrochlors, sheelites, and some other ones. Powders of crystal products display multilevel structurization. In all studied complex oxides strong disordering of the “anti-glass” type was observed. The mechanism of sintering was studied in BaTiO3 powders of different origin and in metastable complex oxides derived by mechanosynthesis. The major contribution in shrinkage belongs to rearrangements of crystalline particles as a whole. Structure transformations accompany, as a rule, sintering of inhomogeneous powders derived by mechanosynthesis.

  7. Comparison of the Supercooled Spin Liquid States in the Pyrochlore Magnets Dy2Ti2O7 and Ho2Ti2O7

    Science.gov (United States)

    Eyal, Anna; Eyvazov, Azar B.; Dusad, Ritika; Munsie, Timothy J. S.; Luke, Graeme M.; Davis, J. C. Séamus

    Despite a well-ordered crystal structure and strong magnetic interactions between the Dy or Ho ions, no long-range magnetic order has been detected in the pyrochlore titanates Ho2Ti2O7 and Dy2Ti2O7. The low temperature state in these materials is governed by spin-ice rules. These constrain the Ising like spins in the materials, yet does not result in a global broken symmetry state. To explore the actual magnetic phases, we simultaneously measure the time- and frequency-dependent magnetization dynamics of Dy2Ti2O7 and Ho2Ti2O7 using toroidal, boundary-free magnetization transport techniques. We demonstrate a distinctive behavior of the magnetic susceptibility of both compounds, that is indistinguishable in form from the permittivity of supercooled dipolar liquids. Moreover, we show that the microscopic magnetic relaxation times for both materials increase along a super-Arrhenius trajectory also characteristic of supercooled glass-forming liquids. Both materials therefore exhibit characteristics of a supercooled spin liquid. Strongly-correlated dynamics of loops of spins is suggested as a possible mechanism which could account for these findings. Potential connections to many-body spin localization will also be discussed.

  8. Preparation, optical, and photocatalytic studies of defect pyrochlores: KCr{sub 0.33}W{sub 1.67}O{sub 6} and A{sub x}Cr{sub 0.33}W{sub 1.67}O{sub 6}{center_dot}nH{sub 2}O

    Energy Technology Data Exchange (ETDEWEB)

    Ravi, G.; Veldurthi, Naveen Kumar [Osmania University, Department of Chemistry (India); Prasad, Muvva D. [University of Hyderabad, School of Chemistry (India); Muniratnam, N. R. [Centre for Materials Electronics Technology (C-MET) (India); Prasad, G. [Osmania University, Department of Physics (India); Vithal, M., E-mail: mugavithal@gmail.com [Osmania University, Department of Chemistry (India)

    2013-09-15

    Nano sized defect pyrochlores of compositions KCr{sub 0.33}W{sub 1.67}O{sub 6} and A{sub x}Cr{sub 0.33}W{sub 1.67}O{sub 6}{center_dot}nH{sub 2}O (A = Sn, Ag, Bi, Sm, Eu, and Gd) have been synthesized by sol-gel and ion exchange methods, respectively. These oxides were characterized by thermogravimetric analysis, powder X-ray diffraction, energy dispersive spectra, transmission electron microscopy, UV-Vis diffuse reflectance spectra, Raman spectra, and Fourier transform infrared spectra. Spontaneous exchange of K{sup +} with A ion is accompanied by insertion of water also into the lattice. KCr{sub 0.33}W{sub 1.67}O{sub 6} and A{sub x}Cr{sub 0.33}W{sub 1.67}O{sub 6}{center_dot}nH{sub 2}O crystallize in cubic lattice and isomorphous with KSbWO{sub 6}. The optical properties of Cr{sup 3+} were investigated. Substitution of K{sup +} by A ion leads to a shift of absorption onset to longer wavelengths marginally. The Raman spectra of all the samples are characteristic of defect pyrochlore system. The photocatalytic degradation of methylene blue aqueous solution was investigated using these oxides. The results obtained were fitted with the Langmuir-Hinshelwood model to study the degradation kinetics. Both Sn{sup 2+} and Bi{sup 3+}-doped KCr{sub 0.33}W{sub 1.67}O{sub 6} exhibit higher photoactivity in the degradation of methylene blue. The structure/composition of the photocatalyst remains the same even after fourth cycle of photodegradation.

  9. Monazite-type ceramics for conditioning of minor actinides. Structural characterization and properties

    International Nuclear Information System (INIS)

    Babelot, Carole

    2013-01-01

    damage created by the recoils accompanying alpha-decay can be simulated on ceramic matrices. Preliminary experiments are realized by means of ion bombardment. Kr 2+ ions are implanted in La-monazite-type pellets, and the effects on the LaPO 4 structure resulting from the Raman spectroscopy are poor. On a laboratory scale, the promising characteristics of the monazite mineral are found again in the synthetic phosphate. In particular, the doping of actinide surrogates is successful and the corrosion tests under repository conditions show a good resistance of the samples. The results achieved in this work confirm that among other favorable ceramics (e.g. pyrochlore) the ''monazite-route'' has to be further pursued regarding the research on the conditioning of MA.

  10. Anomalous pressure dependence of the superconducting transition temperature in the β-Pyrochlore KOs2O6

    Science.gov (United States)

    Miyoshi, Kiyotaka; Takaichi, Yuta; Takeuchi, Jun

    2009-03-01

    DC magnetic measurements have been performed for β-pyrochlore superconductor KOs2O6 (Tc = 9.6 K) under pressure for the precise determination of the pressure dependence of Tc, using a miniature diamond anvil cell combined with a commercial SQUID magnetometer. It is found that the critical temperature Tc shows a maximum of ~10 K at P=0.5 GPa. The maximum of Tc is higher than that for CsOs2O6 and RbOs2O6, in both of which Tc is known to increase and saturate at Tcm = 8.8 K by the application of pressure, suggesting the enhanced superconductivity due to the rattling of K ions in an oversized cage of Os-O network. For the further application of pressure, Tc decreases linearly but the decreasing rate appears to be suddenly changed at P~2 GPa and Tc~8 K. The sharp bend of the Tc — P line probably corresponds to the transition concerning to the rattling motion which occurs at Tp=7.5 K at ambient pressure, suggesting the positive pressure dependence of Tp.

  11. Quantum Magnetism Applied to the Iron-Pnictides and Rare Earth Pyrochlores

    Science.gov (United States)

    Applegate, Ryan

    This dissertation presents computational studies of two families of magnetic materials of significant current interest. The iron pnictides are new high temperature superconductors with interesting parent compound antiferromagnetism. The rare earth pyrochlore material Yb2Ti2O7 is a candidate quantum spin ice. The magnetic and structural phases of individual iron pnictides have both many common features and material specific differences. In an attempt to unify these behaviors as instances of a larger theoretical picture, we use Monte Carlo simulations of a two-dimensional Hamiltonian with coupled Heisenberg-spin and Ising-orbital degrees of freedom. We introduce spin-space and single-ion anisotropies and study the finite temperature transitions in our model. We develop a phase diagram and propose that the interplay of spin and orbital physics in the presence of anisotropy could explain how material details affect the transitions of the pnictide materials. Nuclear magnetic resonance (NMR) can study magnetic materials via the hyperfine interaction and the coupling between the nuclear moment and the field produced by the samples local moment environment. Recent measurements suggest that Zn doped BaFe2As2 may have quantum fluctuations about the striped phase that produce a distribution of fields at As nuclear sites. The non-magnetic ion Zn replaces Fe and can be treated as an impurity which can be studied by a zero-temperature Ising Series expansion method. We propose a Heisenberg-like J1a-J 1b-J2 model which has small ferromagnetic exchanges along the b axis and strong antiferromagnetic exchanges along the a axis. In our impurity model we find that the magnetic moments are everywhere reduced by quantum fluctuations, except on the nearest neighbor site in the AFM direction. We suggest that the presented impurity model may provide an explanation for the experimental measurements. Based on a recently proposed quantum spin ice model, we use numerical linked cluster (NLC

  12. Roentgenological structural types of the unaltered breast

    International Nuclear Information System (INIS)

    Kolganova, I.P.; Zal'tsman, I.N.

    1981-01-01

    The authors present a roentgenoanatomical analysis of normal breast specimens and mammograms of 324 healthy women aged 31 to 60. Four roentgenological structural types of the unaltered breast have been singled out: linear-reticular, lamellar-cellular, large focal, and a single polygonal shadow. These structural types were detected in age groups from 31 to 40, from 41 to 50, and from 51 to 60 with various frequency. Each type corresponds to a certain morphological and functional state of the breast. The frequency of the 2nd and 4th types decreases and of the 1st type increases with advancing age [ru

  13. Roentgenological structural types of the unaltered breast

    Energy Technology Data Exchange (ETDEWEB)

    Kolganova, I P; Zal' tsman, I N [Akademiya Meditsinskikh Nauk RSFSR, Moscow. Pervyj Moskovskij Meditsinskij Inst.

    1981-11-01

    The authors present a roentgenoanatomical analysis of normal breast specimens and mammograms of 324 healthy women aged 31 to 60. Four roentgenological structural types of the unaltered breast have been singled out: linear-reticular, lamellar-cellular, large focal, and a single polygonal shadow. These structural types were detected in age groups from 31 to 40, from 41 to 50, and from 51 to 60 with various frequency. Each type corresponds to a certain morphological and functional state of the breast. The frequency of the 2nd and 4th types decreases and of the 1st type increases with advancing age.

  14. Radiation effects in uranium-niobium titanates

    International Nuclear Information System (INIS)

    Lian, J.; Wang, S.X.; Wang, L.M.; Ewing, R.C.

    2000-01-01

    Pyrochlore is an important actinide host phase proposed for the immobilization of high level nuclear wastes and excess weapon plutonium.[1] Synthetic pyrochlore has a great variety of chemical compositions due to the possibility of extensive substitutions in the pyrochlore structure.[2] During the synthesis of pyrochlore, additional complex titanate phases may form in small quantities. The response of these phases to radiation damage must be evaluated because volume expansion of minor phases may cause micro-fracturing. In this work, two complex uranium-niobium titanates, U 3 NbO 9.8 (U-rich titanate) and Nb 3 UO 10 (Nb-rich titanate) were synthesized by the alkoxide/nitrate route at 1300 deg. C under an argon atmosphere. The phase composition and structure were analyzed by EDS, BSE, XRD, EMPA and TEM techniques. An 800 KeVKr 2+ irradiation was performed using the IVEM-Tandem Facility at Argonne National Laboratory in a temperature range from 30 K to 973 K. The radiation effects were observed by in situ TEM

  15. Weakly nonlocal symplectic structures, Whitham method and weakly nonlocal symplectic structures of hydrodynamic type

    International Nuclear Information System (INIS)

    Maltsev, A Ya

    2005-01-01

    We consider the special type of field-theoretical symplectic structures called weakly nonlocal. The structures of this type are, in particular, very common for integrable systems such as KdV or NLS. We introduce here the special class of weakly nonlocal symplectic structures which we call weakly nonlocal symplectic structures of hydrodynamic type. We investigate then the connection of such structures with the Whitham averaging method and propose the procedure of 'averaging' the weakly nonlocal symplectic structures. The averaging procedure gives the weakly nonlocal symplectic structure of hydrodynamic type for the corresponding Whitham system. The procedure also gives 'action variables' corresponding to the wave numbers of m-phase solutions of the initial system which give the additional conservation laws for the Whitham system

  16. Self-assembled, rare earth tantalate pyrochlore nanoparticles for superior flux pinning in YBa2Cu3O7-δ films

    International Nuclear Information System (INIS)

    Harrington, S A; Durrell, J H; Wimbush, S C; Kursumovic, A; MacManus-Driscoll, J L; Maiorov, B; Wang, H; Lee, J H

    2009-01-01

    Addition of pyrochlore rare earth tantalate phases, RE 3 TaO 7 (RTO, where RE = rare earth, Er, Gd and Yb) to YBa 2 Cu 3 O 7-δ (YBCO) is shown to vastly improve pinning, without being detrimental to the superconducting transition temperature. The closely lattice matched to RTO phase provides a lower interfacial energy with YBCO than BaZrO 3 (BZO) and produces very fine (∼5 nm) particles with high linearity in their self-assembly along c. Critical current densities of 0.86, 0.38 MA cm -2 at 1 and 3 T (for fields) parallel to the c axis were recorded at 77 K in 0.5-1.0 μm thick films and a transition temperature of 92 K was observed even in the highest level doped sample (8 mol%). (rapid communication)

  17. Nuclear resonance scattering study of iridates, iridium and antimony based pyrochlores

    International Nuclear Information System (INIS)

    Alexeev, P.

    2017-04-01

    This thesis shows the first synchrotron-based Moessbauer spectroscopy studies on iridium containing compounds and first vibrational spectroscopy on Sb containing compounds carried out at the P01 beamline of PETRA III. In this context, two types of X-ray monochromators have been developed: a monochromator for 73 keV photons with medium energy resolution, and a high-resolution backscattering monochromator based on a sapphire crystal. The monochromator for 73 keV X-rays is the key instrument for hyperfine spectroscopy on Iridium compounds, while the sapphire backscattering monochromator is purposed to vibrational spectroscopy on any Moessbauer resonances with the transition energies in the 20-50 keV range. Additionally, the signal detection for nuclear resonance scattering experiments at the beamline was significantly improved during this work, inspired by the high energies and low lifetimes of the employed resonances. The first synchrotron-based hyperfine spectroscopy on Iridium-containing compounds was demonstrated by NRS on 73 keV resonance in "1"9"3Ir. The results can be interpreted by dynamical theory of nuclear resonance scattering. In this work, special emphasis is set onto the electronic and magnetic properties of Ir nuclei in IrO_2 and in Ruddlesden-Popper (RP) phases of strontium iridates Sr_n_+_1Ir_nO_3_n_+_1 (n=0,1). These systems are well-suited for studies with X-ray scattering techniques, since the scattered signal contains vast information about the widely tunable crystallographic and electronic structure of these systems; furthermore, studies with X-rays are less limited by absorption from iridium as it is the case for neutron scattering experiments. The hyperfine parameters in IrO_2, SrIrO_3 and Sr_2IrO_4 have been measured via Nuclear Forward Scattering for the first time. Using the dynamical theory of NRS, the temperature and magnetic field dependence of the electric field gradient and magnetic hyperfine field on Ir nucleus have been determined for

  18. Nuclear resonance scattering study of iridates, iridium and antimony based pyrochlores

    Energy Technology Data Exchange (ETDEWEB)

    Alexeev, P.

    2017-04-15

    This thesis shows the first synchrotron-based Moessbauer spectroscopy studies on iridium containing compounds and first vibrational spectroscopy on Sb containing compounds carried out at the P01 beamline of PETRA III. In this context, two types of X-ray monochromators have been developed: a monochromator for 73 keV photons with medium energy resolution, and a high-resolution backscattering monochromator based on a sapphire crystal. The monochromator for 73 keV X-rays is the key instrument for hyperfine spectroscopy on Iridium compounds, while the sapphire backscattering monochromator is purposed to vibrational spectroscopy on any Moessbauer resonances with the transition energies in the 20-50 keV range. Additionally, the signal detection for nuclear resonance scattering experiments at the beamline was significantly improved during this work, inspired by the high energies and low lifetimes of the employed resonances. The first synchrotron-based hyperfine spectroscopy on Iridium-containing compounds was demonstrated by NRS on 73 keV resonance in {sup 193}Ir. The results can be interpreted by dynamical theory of nuclear resonance scattering. In this work, special emphasis is set onto the electronic and magnetic properties of Ir nuclei in IrO{sub 2} and in Ruddlesden-Popper (RP) phases of strontium iridates Sr{sub n+1}Ir{sub n}O{sub 3n+1} (n=0,1). These systems are well-suited for studies with X-ray scattering techniques, since the scattered signal contains vast information about the widely tunable crystallographic and electronic structure of these systems; furthermore, studies with X-rays are less limited by absorption from iridium as it is the case for neutron scattering experiments. The hyperfine parameters in IrO{sub 2}, SrIrO{sub 3} and Sr{sub 2}IrO{sub 4} have been measured via Nuclear Forward Scattering for the first time. Using the dynamical theory of NRS, the temperature and magnetic field dependence of the electric field gradient and magnetic hyperfine field

  19. Interspecies radioimmunoassay for the major structural proteins of primate type-D retroviruses

    International Nuclear Information System (INIS)

    Colcher, D.; Teramoto, Y.A.; Schlom, J.

    1977-01-01

    A competition radioimmunoassay has been developed in which type-D retroviruses from three primate species compete. The assay utilizes the major structural protein (36,000 daltons) of the endogenous squirrel monkey retrovirus and antisera directed against the major structural protein (27,000 daltons) of the Mason-Pfizer monkey virus isolated from rhesus monkeys. Purified preparations of both viruses grown in heterologous cells, as well as extracts of heterologous cells infected with squirrel monkey retrovirus or Mason-Pfizer monkey virus, compete completely in the assay. Addition of an endogenous virus of the langur monkey also results in complete blocking. No blocking in the assay is observed with type-C baboon viruses, woolly monkey virus, and gibbon virus. Various other type-C and type-B viruses also showed no reactivity. An interspecies assay has thus been developed that recognizes the type-D retroviruses from both Old World monkey (rhesus and langur) and New World monkey (squirrel) species

  20. Monazite-type ceramics for conditioning of minor actinides. Structural characterization and properties

    Energy Technology Data Exchange (ETDEWEB)

    Babelot, Carole

    2013-07-01

    essential parameter is their resistance to radiation. The damage created by the recoils accompanying alpha-decay can be simulated on ceramic matrices. Preliminary experiments are realized by means of ion bombardment. Kr{sup 2+} ions are implanted in La-monazite-type pellets, and the effects on the LaPO{sub 4} structure resulting from the Raman spectroscopy are poor. On a laboratory scale, the promising characteristics of the monazite mineral are found again in the synthetic phosphate. In particular, the doping of actinide surrogates is successful and the corrosion tests under repository conditions show a good resistance of the samples. The results achieved in this work confirm that among other favorable ceramics (e.g. pyrochlore) the ''monazite-route'' has to be further pursued regarding the research on the conditioning of MA.

  1. Liandratite from Karkonosze pegmatites, Sudetes, Southwestern Poland

    Science.gov (United States)

    Matyszczak, Witold

    2018-06-01

    The chemical composition of liandratite, U6+(Nb,Ta)2O8, was determined from material collected in Niobium, Yttrium, Fluorine type (NYF) pegmatites of the Karkonosze intrusion (Sudetes, SW Poland). Liandratite occurs mainly as rims, up to 40 µm thick, and fracture infillings in fergusonite-(Y) and other Nb-Ta-Ti minerals. Its formation was related to the fluid-driven alteration of primary minerals by three potential mechanisms: (i) direct replacement of a primary mineral by liandratite; (ii) breakdown of the primary mineral to liandratite and a product with the composition of minerals of the pyrochlore group; (iii) multistage alteration, which involved: removal of A-site cations (mostly Y + REE with the exception of U4+) and formation of phases with the composition of pyrochlore group minerals; then crystallization of U-, Bi-, Pb-rich pyrochlores and their replacement by liandratite. The chemical compositions of liandratite formed by the breakdown of different primary minerals are also different, mainly in their U, Ti and Nb contents. Excess Ti, relative to the U6+Nb2O8 end-member, is incorporated into the structure together with additional U. The Ti content of liandratite, and partially through this the U content, are dependent on the nature of the precursor mineral.

  2. Coexistence of Cluster Structure and Mean-field-type Structure in Medium-weight Nuclei

    International Nuclear Information System (INIS)

    Taniguchi, Yasutaka; Horiuchi, Hisashi; Kimura, Masaaki

    2006-01-01

    We have studied the coexistence of cluster structure and mean-field-type structure in 20Ne and 40Ca using Antisymmetrized Molecular Dynamics (AMD) + Generator Coordinate Method (GCM). By energy variation with new constraint for clustering, we calculate cluster structure wave function. Superposing cluster structure wave functions and mean-field-type structure wave function, we found that 8Be-12C, α-36Ar and 12C-28Si cluster structure are important components of K π = 0 3 + band of 20Ne, that of normal deformed band of 40Ca and that of super deformed band of 40Ca, respectively

  3. A 2 TiO 5 (A = Dy, Gd, Er, Yb) at High Pressure

    Energy Technology Data Exchange (ETDEWEB)

    Park, Sulgiye [Department of Geological Science, Stanford University, Stanford, California 94305, United States; Rittman, Dylan R. [Department of Geological Science, Stanford University, Stanford, California 94305, United States; Tracy, Cameron L. [Department of Geological Science, Stanford University, Stanford, California 94305, United States; Chapman, Karena W. [X-ray Science Division, Advanced Photon; Zhang, Fuxiang [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States; Park, Changyong [HPCAT, Carnegie Institution of Washington, Argonne, Illinois 60439, United States; Tkachev, Sergey N. [Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, United States; O’Quinn, Eric [Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States; Shamblin, Jacob [Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States; Lang, Maik [Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States; Mao, Wendy L. [Department of Geological Science, Stanford University, Stanford, California 94305, United States; Stanford; amp, Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States; Ewing, Rodney C. [Department of Geological Science, Stanford University, Stanford, California 94305, United States

    2018-02-07

    The structural evolution of lanthanide A2TiO5 (A = Dy, Gd, Yb, and Er) at high pressure is investigated using synchrotron X-ray diffraction. The effects of A-site cation size and of the initial structure are systematically examined by varying the composition of the isostructural lanthanide titanates, and the structure of dysprosium titanate polymorphs (orthorhombic, hexagonal and cubic), respectively. All samples undergo irreversible high pressure phase transformations, but with different onset pressures depending on the initial structure. While individual phase exhibits different phase transformation histories, all samples commonly experience a sluggish transformation to a defect cotunnite-like (Pnma) phase for a certain pressure range. Orthorhombic Dy2TiO5 and Gd2TiO5 form P21am at pressures below 9 GPa and Pnma above 13 GPa. Pyrochlore-type Dy2TiO5 and Er2TiO5 as well as defect-fluorite-type Yb2TiO5 form Pnma at ~ 21 GPa, followed by Im-3m. Hexagonal Dy2TiO5 forms Pnma directly, although a small amount of remnants of hexagonal Dy2TiO5 is observed even at the highest pressure (~ 55 GPa) reached, indicating a kinetic limitations in the hexagonal Dy2TiO5 phase transformations at high pressure. Decompression of these materials leads to different metastable phases. Most interestingly, a high pressure cubic X-type phase (Im-3m) is confirmed using highresolution transmission electron microscopy on recovered pyrochlore-type Er2TiO5. The kinetic constraints on this metastable phase yield a mixture of both the X-type phase and amorphous domains upon pressure release. This is the first observation of an X-type phase for an A2BO5 composition at high pressure.

  4. The Gd14Ag51 structure type and its relation to some complex amalgam structures

    International Nuclear Information System (INIS)

    Tambornino, Frank; Sappl, Jonathan; Hoch, Constantin

    2015-01-01

    Highlights: • The Gd 14 Ag 51 structure type has been revisited on the basis of single crystal diffraction data. • Symmetry analysis from electron density and TEM shows the space group P6/m to be true. • Gd 14 Ag 51 shows good metallic behaviour. • Structure relations to alkali, alkaline-earth and rare-earth metal amalgams can be established. • Complexity values for the RE 14 Ag 51 structure family were calculated. - Abstract: A plethora of binary and ternary intermetallic compounds has been assigned to the Gd 14 Ag 51 structure type, crystallising in the hexagonal system (space group P6/m, a = 1264.30(18) pm, c = 933.58(11) pm for Gd 14 Ag 51 ). Starting in the late 1960s, much work has been invested in the structural elucidation of these crystal structures. However, reliable single crystal data are scarce, and most structure type assignments have been performed merely on the basis of powder data. We have redetermined four representatives of the binary RE 14 Ag 51 structure type (RE = Y, Ce, Gd, Tb) with modern high-precision single crystal X-ray methods. The assignment of the Gd 14 Ag 51 structure type to space group P6/m was additionally verified by careful analysis of high resolution transmission electron micrographs. We emphasise the close relation of the Gd 14 Ag 51 structure type to the structures of some recently described amalgams of similar composition focussing on disorder phenomena and structural complexity. Furthermore, we provide detailed information on synthesis as well as electrical and magnetic properties for Gd 14 Ag 51 , the parent compound of this structure family

  5. AgLnSb/sub 2/O/sub 7/ compounds with weberite structure

    Energy Technology Data Exchange (ETDEWEB)

    Lopatin, S S; Aver' yanova, L N; Belyaev, I N; Zvyagintsev, B I; Dyatlov, Eh V [Rostovskij-na-Donu Gosudarstvennyj Univ. (USSR)

    1982-11-01

    The interaction between AgSbO/sub 3/ and LnSbO/sub 4/ in the solid phase at 1100-1150 deg C has been investigated. AgLnSb/sub 2/O/sub 7/ compounds with weberite crystal structure are formed in Ln=La, Pr, Nd, Sm cases but in Ln=Eu, Cd, Dy, Er cases the formation of termary oxides of the indicated composition has not been observed. Inasmuch as compounds of the general formula A/sub 2/B/sub 2/O/sub 7/ with average cation radii Rsub(B) >0.60 A and 1.65 <= Rsub(A)/Rsub(B) <= 2.20 can crystallize in weberite, pyrochlore and laminated perovskite-like structurer, conditions of the existence of the above mentioned structures depending on A and B dimensions and electronegativity are discussed.

  6. Quasiparticle Breakdown and Spin Hamiltonian of the Frustrated Quantum Pyrochlore Yb_{2}Ti_{2}O_{7} in a Magnetic Field.

    Science.gov (United States)

    Thompson, J D; McClarty, P A; Prabhakaran, D; Cabrera, I; Guidi, T; Coldea, R

    2017-08-04

    The frustrated pyrochlore magnet Yb_{2}Ti_{2}O_{7} has the remarkable property that it orders magnetically but has no propagating magnons over wide regions of the Brillouin zone. Here we use inelastic neutron scattering to follow how the spectrum evolves in cubic-axis magnetic fields. At high fields we observe, in addition to dispersive magnons, a two-magnon continuum, which grows in intensity upon reducing the field and overlaps with the one-magnon states at intermediate fields leading to strong renormalization of the dispersion relations, and magnon decays. Using heat capacity measurements we find that the low- and high-field regions are smoothly connected with no sharp phase transition, with the spin gap increasing monotonically in field. Through fits to an extensive data set of dispersion relations combined with magnetization measurements, we reevaluate the spin Hamiltonian, finding dominant quantum exchange terms, which we propose are responsible for the anomalously strong fluctuations and quasiparticle breakdown effects observed at low fields.

  7. Quasiparticle Breakdown and Spin Hamiltonian of the Frustrated Quantum Pyrochlore Yb2 Ti2 O7 in a Magnetic Field

    Science.gov (United States)

    Thompson, J. D.; McClarty, P. A.; Prabhakaran, D.; Cabrera, I.; Guidi, T.; Coldea, R.

    2017-08-01

    The frustrated pyrochlore magnet Yb2 Ti2 O7 has the remarkable property that it orders magnetically but has no propagating magnons over wide regions of the Brillouin zone. Here we use inelastic neutron scattering to follow how the spectrum evolves in cubic-axis magnetic fields. At high fields we observe, in addition to dispersive magnons, a two-magnon continuum, which grows in intensity upon reducing the field and overlaps with the one-magnon states at intermediate fields leading to strong renormalization of the dispersion relations, and magnon decays. Using heat capacity measurements we find that the low- and high-field regions are smoothly connected with no sharp phase transition, with the spin gap increasing monotonically in field. Through fits to an extensive data set of dispersion relations combined with magnetization measurements, we reevaluate the spin Hamiltonian, finding dominant quantum exchange terms, which we propose are responsible for the anomalously strong fluctuations and quasiparticle breakdown effects observed at low fields.

  8. Ceramic materials on perovskite-type structure for electronic applications

    International Nuclear Information System (INIS)

    Surowiak, Z.

    2003-01-01

    Ceramic materials exhibiting the perovskite-type structure constitute among others, resource base for many fields of widely understood electronics (i.e., piezoelectronics, accustoelectronics, optoelectronics, computer science, tele- and radioelectronics etc.). Most often they are used for fabrication of different type sensors (detectors), transducers, ferroelectric memories, limiters of the electronic current intensity, etc., and hence they are numbered among so-called intelligent materials. Prototype structure of this group of materials is the structure of the mineral called perovskite (CaTiO 3 ). By means of right choice of the chemical composition of ABO 3 and deforming the regular perovskite structure (m3m) more than 5000 different chemical compounds and solid solutions exhibiting the perovskite-type structure have been fabricated. The concept of perovskite functional ceramics among often things ferroelectric ceramics, pyroelectric ceramics, piezoelectric ceramics, electrostrictive ceramics, posistor ceramics, superconductive ceramics and ferromagnetic ceramics. New possibilities of application of the perovskite-type ceramics are opened by nanotechnology. (author)

  9. Signatures of a gearwheel quantum spin liquid in a spin-1/2 pyrochlore molybdate Heisenberg antiferromagnet

    Science.gov (United States)

    Iqbal, Yasir; Müller, Tobias; Riedl, Kira; Reuther, Johannes; Rachel, Stephan; Valentí, Roser; Gingras, Michel J. P.; Thomale, Ronny; Jeschke, Harald O.

    2017-12-01

    We theoretically investigate the low-temperature phase of the recently synthesized Lu2Mo2O5N2 material, an extraordinarily rare realization of a S =1 /2 three-dimensional pyrochlore Heisenberg antiferromagnet in which Mo5 + are the S =1 /2 magnetic species. Despite a Curie-Weiss temperature (ΘCW) of -121 (1 ) K, experiments have found no signature of magnetic ordering or spin freezing down to T*≈0.5 K. Using density functional theory, we find that the compound is well described by a Heisenberg model with exchange parameters up to third nearest neighbors. The analysis of this model via the pseudofermion functional renormalization group method reveals paramagnetic behavior down to a temperature of at least T =| ΘCW|/100 , in agreement with the experimental findings hinting at a possible three-dimensional quantum spin liquid. The spin susceptibility profile in reciprocal space shows momentum-dependent features forming a "gearwheel" pattern, characterizing what may be viewed as a molten version of a chiral noncoplanar incommensurate spiral order under the action of quantum fluctuations. Our calculated reciprocal space susceptibility maps provide benchmarks for future neutron scattering experiments on single crystals of Lu2Mo2O5N2 .

  10. Structural and evolutionary relationships of "AT-less" type I polyketide synthase ketosynthases.

    Science.gov (United States)

    Lohman, Jeremy R; Ma, Ming; Osipiuk, Jerzy; Nocek, Boguslaw; Kim, Youngchang; Chang, Changsoo; Cuff, Marianne; Mack, Jamey; Bigelow, Lance; Li, Hui; Endres, Michael; Babnigg, Gyorgy; Joachimiak, Andrzej; Phillips, George N; Shen, Ben

    2015-10-13

    Acyltransferase (AT)-less type I polyketide synthases (PKSs) break the type I PKS paradigm. They lack the integrated AT domains within their modules and instead use a discrete AT that acts in trans, whereas a type I PKS module minimally contains AT, acyl carrier protein (ACP), and ketosynthase (KS) domains. Structures of canonical type I PKS KS-AT didomains reveal structured linkers that connect the two domains. AT-less type I PKS KSs have remnants of these linkers, which have been hypothesized to be AT docking domains. Natural products produced by AT-less type I PKSs are very complex because of an increased representation of unique modifying domains. AT-less type I PKS KSs possess substrate specificity and fall into phylogenetic clades that correlate with their substrates, whereas canonical type I PKS KSs are monophyletic. We have solved crystal structures of seven AT-less type I PKS KS domains that represent various sequence clusters, revealing insight into the large structural and subtle amino acid residue differences that lead to unique active site topologies and substrate specificities. One set of structures represents a larger group of KS domains from both canonical and AT-less type I PKSs that accept amino acid-containing substrates. One structure has a partial AT-domain, revealing the structural consequences of a type I PKS KS evolving into an AT-less type I PKS KS. These structures highlight the structural diversity within the AT-less type I PKS KS family, and most important, provide a unique opportunity to study the molecular evolution of substrate specificity within the type I PKSs.

  11. Structural and evolutionary relationships of "AT-less" type I polyketide synthase ketosynthases

    Energy Technology Data Exchange (ETDEWEB)

    Lohman, Jeremy; Ma, Ming; Osipiuk, Jerzy; Nocek, Boguslaw; Kim, Youngchang; Chang, Changsoo; Cuff, Marianne E.; Mack, Jamey; Bigelow, Lance; Li, Hui; Endres, Michael; Babnigg, Gyorgy; Joachimiak, Andrzej; Phillips, George N.; Shen, B G

    2015-10-13

    Acyltransferase (AT)-less type I polyketide synthases (PKSs) break the type I PKS paradigm. They lack the integrated AT domains within their modules and instead use a discrete AT that acts in trans, whereas a type I PKS module minimally contains AT, acyl carrier protein (ACP), and ketosynthase (KS) domains. Structures of canonical type I PKS KS-AT didomains reveal structured linkers that connect the two domains. AT-less type I PKS KSs have remnants of these linkers, which have been hypothesized to be AT docking domains. Natural products produced by AT-less type I PKSs are very complex because of an increased representation of unique modifying domains. AT-less type I PKS KSs possess substrate specificity and fall into phylogenetic clades that correlate with their substrates, whereas canonical type I PKS KSs are monophyletic. We have solved crystal structures of seven AT-less type I PKS KS domains that represent various sequence clusters, revealing insight into the large structural and subtle amino acid residue differences that lead to unique active site topologies and substrate specificities. One set of structures represents a larger group of KS domains from both canonical and AT-less type I PKSs that accept amino acid-containing substrates. One structure has a partial AT-domain, revealing the structural consequences of a type I PKS KS evolving into an AT-less type I PKS KS. These structures highlight the structural diversity within the AT-less type I PKS KS family, and most important, provide a unique opportunity to study the molecular evolution of substrate specificity within the type I PKSs.

  12. Synthesis, characterization and luminescence study of Eu3+ doped Y2Sn2O7 nano-particles

    International Nuclear Information System (INIS)

    Nigam, Sandeep; Sudarsan, V.; Vatsa, R.K.

    2011-01-01

    In recent years, advanced materials derived from Pyrochlore-type oxides (A 2 B 2 O 7 ), have been of extensive scientific and technological interest. Chemical substitution of A or B sites of pyrochlore oxide by rare earth ions is a widely used approach to prepare thermally stable, lanthanide ion doped luminescent materials. The present study deals with the synthesis and characterization of Eu 3+ doped Y 2 Sn 2 O 7 : nanoparticles prepared by the hydrolysis of Y 3+ , Sn 4+ , and Eu 3+ in ethylene glycol medium followed by heating at 700 deg C for 4 hours. As prepared samples are amorphous in nature and 700 deg C heated sample showed well crystalline pyrochlore structure in XRD studies. Average particle size is calculated from the width of the X-ray diffraction peaks and found to t be around 5 nm. Luminescence measurements were carried out for as prepared and 700 deg C heated samples. The undoped as prepared sample showed a broad emission peak around 420 nm after excitation at 285 nm. While for 700 deg C undoped heated sample, the peak maxima was shifted to 435 nm. The emission spectrum for doped as prepared samples is characterized by both host emission around 420 nm along with the characteristic Eu 3+ emission peaks in the visible region. However, very poor Eu 3+ emission from heated sample was observed

  13. Unusual spin frozen state in a frustrated pyrochlore system NaCaCo{sub 2}F{sub 7} as observed by NMR

    Energy Technology Data Exchange (ETDEWEB)

    Sarkar, R.; Brueckner, F.; Klauss, H.H. [IFP, TU Dresden (Germany); Krizan, J.W.; Cava, R.J. [Department of Chemistry, Princeton University, Princeton, NJ (United States)

    2016-07-01

    We present {sup 23}Na -and {sup 19}F NMR results on the magnetically frustrated pyrochlore NaCaCo{sub 2}F{sub 7} with a frustration index of f = θ{sub CW}/T{sub f} ∝ 56. Recent neutron scattering experiments proposed XY like antiferromagnetic spin clusters at low energies in NaCaCo{sub 2}F{sub 7}. {sup 23}Na NMR -spectra reveal the presence of two magnetically non equivalent Na sites in conjunction with the local Co{sup 2+} spin structure. Below 3.6 K both the {sup 23}Na -and {sup 19}F spectra broaden due to the formation of static spin correlations. A huge reduction of the {sup 19}F -and {sup 23}Na NMR signal intensity hints at a quasi-static field distribution in NaCaCo{sub 2}F{sub 7} in this regime. The {sup 19}F spin-lattice relaxation rate {sup 19}(1/T{sub 1}) exhibits a peak at around 2.9 K, at the same temperature range where ac and dc susceptibility data show a broad maximum. The character of the spin fluctuation appears to be isotropic. The overall temperature dependence of {sup 19}(1/T{sub 1}) can be described by the BPP theory considering a fluctuating hyperfine field with an autocorrelation function. The correlation time of the autocorrelation function exhibits an activation behavior further indicating the spin-frozen state. While the present NMR studies suggest the spin frozen state at low temperatures, μSR investigations however reveal the presence of so called persistent spin dynamics down to 20 mK implying an exotic ground state in NaCaCo{sub 2}F{sub 7}.

  14. An Owen-type value for games with two-level communication structures

    NARCIS (Netherlands)

    van den Brink, René; Khmelnitskaya, Anna Borisovna; van der Laan, Gerard

    We introduce an Owen-type value for games with two-level communication structure, which is a structure where the players are partitioned into a coalition structure such that there exists restricted communication between as well as within the a priori unions of the coalition structure. Both types of

  15. Synthesis, structural and luminescence properties of Bi3+ co-doped Y2Sn2O7:Tb nanoparticles

    International Nuclear Information System (INIS)

    Nigam, S.; Sudarsan, V.; Vatsa, R.K.

    2010-01-01

    Full text: In recent years, advanced materials derived from Pyrochlore-type oxides (A 2 B 2 O 7 ) have been of extensive scientific and technological interest. Chemical substitution of A or B sites of pyrochlore oxide by rare earth ions is a widely used approach to prepare thermally stable, lanthanide ion doped luminescent materials. Due to the higher symmetry around the A and B sites in the lattice lanthanide ions like Eu 3+ and Tb 3+ when incorporated at the A or B sites give very poor luminescence. This problem can be avoided by incorporating other ions like Bi 3+ in the lattice so that the lattice gets distorted and luminescent intensity from the lanthanide ions increases. The present study deals with the synthesis and characterization of Bi 3+ co-doped Y 2 Sn 2 O 7 :Tb nanoparticles. For the preparation of Tb 3+ and Bi 3+ doped Y 2 Sn 2 O 7 nano-materials, Sn metal, Bi(NO 3 ) 3 , Tb 4 O 7 , Y 2 CO 3 , were used as starting materials. The solution containing Y 3+ , Sn 4+ ,and Bi 3+ -Tb 3+ in ethylene glycol medium was slowly heated up to 120 deg C and then subjected to urea hydrolysis. The obtained precipitate after washing was heated to 700 deg C. As prepared samples are amorphous in nature and 700 deg C heated sample showed well crystalline pyrochlore structure as revealed by the XRD studies. Average particles size is calculated from the width of the X-ray diffraction peaks and found to be ∼ 5 nm. TEM images of the nanoparticles obtained at 700 deg C shows very fine spherical particles having a diameter in the range of 2-5 nm. Luminescence measurements were carried out for as prepared and 700 deg C heated samples of 2.5%Tb doped Y 2 Sn 2 O 7 nanoparticles. Green emission characteristic 5 D 4 7 F 5 transition of Tb 3+ has been observed from as prepared sample but on heating to 700 deg C the emission characteristic of Tb 3+ ions got completely removed . However, there is a significant improvement in Tb 3+ emission from 2.5% Bi 3+ co-doped Y 2 Sn 2 O 7 :Tb 3

  16. The Gd{sub 14}Ag{sub 51} structure type and its relation to some complex amalgam structures

    Energy Technology Data Exchange (ETDEWEB)

    Tambornino, Frank; Sappl, Jonathan; Hoch, Constantin, E-mail: constantin.hoch@cup.uni-muenchen.de

    2015-01-05

    Highlights: • The Gd{sub 14}Ag{sub 51} structure type has been revisited on the basis of single crystal diffraction data. • Symmetry analysis from electron density and TEM shows the space group P6/m to be true. • Gd{sub 14}Ag{sub 51} shows good metallic behaviour. • Structure relations to alkali, alkaline-earth and rare-earth metal amalgams can be established. • Complexity values for the RE{sub 14}Ag{sub 51} structure family were calculated. - Abstract: A plethora of binary and ternary intermetallic compounds has been assigned to the Gd{sub 14}Ag{sub 51} structure type, crystallising in the hexagonal system (space group P6/m, a = 1264.30(18) pm, c = 933.58(11) pm for Gd{sub 14}Ag{sub 51}). Starting in the late 1960s, much work has been invested in the structural elucidation of these crystal structures. However, reliable single crystal data are scarce, and most structure type assignments have been performed merely on the basis of powder data. We have redetermined four representatives of the binary RE{sub 14}Ag{sub 51} structure type (RE = Y, Ce, Gd, Tb) with modern high-precision single crystal X-ray methods. The assignment of the Gd{sub 14}Ag{sub 51} structure type to space group P6/m was additionally verified by careful analysis of high resolution transmission electron micrographs. We emphasise the close relation of the Gd{sub 14}Ag{sub 51} structure type to the structures of some recently described amalgams of similar composition focussing on disorder phenomena and structural complexity. Furthermore, we provide detailed information on synthesis as well as electrical and magnetic properties for Gd{sub 14}Ag{sub 51}, the parent compound of this structure family.

  17. Stochastic Fatigue Analysis of Jacket Type Offshore Structures

    DEFF Research Database (Denmark)

    Sigurdsson, Gudfinnur

    In this paper, a stochastic reliability assessment for jacket type offshore structures subjected to wave loads in deep water environments is outlined. In the reliability assessment, structural and loading uncertainties are taken into account by means of some stochastic variables. To estimate stat...... statistical measures of structural stress variations the modal spectral analysis method is applied....

  18. Orange-red emitting Gd2Zr2O7:Sm3+: Structure-property correlation, optical properties and defect spectroscopy

    Science.gov (United States)

    Gupta, Santosh K.; Reghukumar, C.; Sudarshan, K.; Ghosh, P. S.; Pathak, Nimai; Kadam, R. M.

    2018-05-01

    Local structure analysis of dopant ion, understanding host to dopant energy transfer dynamics and defects characterization in a doped material which plays an important role in the designing a highly efficient opto-electronic material. In this connection a new Sm3+ doped Gd2Zr2O7 pyrochlore material was synthesized using gel-combustion technique and was characterized systematically using X-ray diffraction (XRD), time resolved photoluminescence spectroscopy (TRPLS), positron annihilation lifetime spectroscopy (PALS) and density functional theory (DFT) based ab-initio calculation. Based on DFT site selective energetics calculation and luminescence decay measurement, it was observed that the Sm3+ was distributed at both Gd3+ and Zr4+ site with higher Sm3+ fraction at the Gd3+ site. PALS was used to probe the presence of defects in the phosphor. In this work intense orange-red emission is realized through manipulating the energy transfer from host defect emission (oxygen vacancies) to Sm3+ which allows color emission from green in undoped to orange-red in doped samples. Effect of dopant concentration and annealing temperature was probed using TRPLS and PALS. These all information is highly important for researcher looking to achieve pyrochlore based phosphor materials with high quantum yield.

  19. Review and Perspectives of Aurivillius Structures as a Lead-Free Piezoelectric System

    Directory of Open Access Journals (Sweden)

    Alberto Moure

    2018-01-01

    Full Text Available According to the EU-Directives 2002/95/EC, 2002/96/EC, lead-based piezoceramics must be substituted in the future with more environmentally friendly alternatives, only when a reliable alternative is found. This is why an increasing interest has grown in the research community to find lead free piezoelectric materials that fulfil the requirements for this substitution. Different families of compounds have been shown to be possible candidates for this use, such as bismuth and niobates based perovskites, pyrochlores, etc. However, a material with piezoelectric coefficients similar to those of PZT (lead zirconate titanate, Pb[ZrxTi1-x]O3 has not been yet found. Besides, each of these families has its specific characteristics in terms of remnant polarization, coercive field or application temperature. Thus, the choice of each material should be made according to the specific needs of the application. In this sense, Aurivillius-type structure materials (also known as Bismuth Layered Structure Ferroelectrics, BLSF can take advantage of their specific properties for uses as Lead Free Piezoelectric systems. Some of them have a high Curie temperature, which make them good candidates to be used as high temperature piezoelectrics; high coercive fields, which facilitates their use as actuators; or a high switching fatigue resistance, which can be useful for future applications as Ferroelectric Random Access Memories (FERAM.

  20. Subaortic (Type 6 Muscular Band—Innocent Bystander or Pathologic Structure?

    Directory of Open Access Journals (Sweden)

    J Ker

    2010-08-01

    Full Text Available Intraventricular tendons are structures that was identified more than a hundred years ago. It has been suggested that they represent intracavitary radiations of the bundle of His and that they may be an isolated finding or be associated with structural cardiac abnormalities. Loukas et al divided these structures into five categories and recently a sixth type have been added. Various physiological disturbances have been observed due to the sixth type of tendon, such as ST segment elevation and right bundle branch block. It has been noted that this peculiar structure appears too thick to be called a tendon, thus the term band. This retrospective analysis analyzed the incidence of the thick, subaortic (type 6 muscular band in a cardiovascular clinic.

  1. Structural and evolutionary relationships of “AT-less” type I polyketide synthase ketosynthases

    Science.gov (United States)

    Lohman, Jeremy R.; Ma, Ming; Osipiuk, Jerzy; Nocek, Boguslaw; Kim, Youngchang; Chang, Changsoo; Cuff, Marianne; Mack, Jamey; Bigelow, Lance; Li, Hui; Endres, Michael; Babnigg, Gyorgy; Joachimiak, Andrzej; Phillips, George N.; Shen, Ben

    2015-01-01

    Acyltransferase (AT)-less type I polyketide synthases (PKSs) break the type I PKS paradigm. They lack the integrated AT domains within their modules and instead use a discrete AT that acts in trans, whereas a type I PKS module minimally contains AT, acyl carrier protein (ACP), and ketosynthase (KS) domains. Structures of canonical type I PKS KS-AT didomains reveal structured linkers that connect the two domains. AT-less type I PKS KSs have remnants of these linkers, which have been hypothesized to be AT docking domains. Natural products produced by AT-less type I PKSs are very complex because of an increased representation of unique modifying domains. AT-less type I PKS KSs possess substrate specificity and fall into phylogenetic clades that correlate with their substrates, whereas canonical type I PKS KSs are monophyletic. We have solved crystal structures of seven AT-less type I PKS KS domains that represent various sequence clusters, revealing insight into the large structural and subtle amino acid residue differences that lead to unique active site topologies and substrate specificities. One set of structures represents a larger group of KS domains from both canonical and AT-less type I PKSs that accept amino acid-containing substrates. One structure has a partial AT-domain, revealing the structural consequences of a type I PKS KS evolving into an AT-less type I PKS KS. These structures highlight the structural diversity within the AT-less type I PKS KS family, and most important, provide a unique opportunity to study the molecular evolution of substrate specificity within the type I PKSs. PMID:26420866

  2. Development, characteristics and comparative structural analysis of tensegrity type cable domes

    Directory of Open Access Journals (Sweden)

    Nenadović Aleksandra

    2010-01-01

    Full Text Available Tensegrity type cable domes are three-dimensional structural configurations, prestressed inside the perimeter compression ring, in which the continuous tension throughout the roof structure is made by continuous tension cables and discontinuous compression struts. These kinds of structures can be formed like spatially triangulated networks or like networks nontriangulated in space. This paper examines some effects of network geometry on the behaviour and structural efficiency of tensegrity type cable domes. In this paper the roof cover is considered non-interactive with the supporting structure, unlike rigidly clad tensegrity type cable domes. Since the main bearing elements of tensegrity type cable domes are prestressed cables, they show non-linear load deformation and rely upon geometric stiffness. A geometrically non-linear analysis of non-triangulated and triangulated structures for different load conditions was conducted employing a computer program based on the perturbation theory. The incrementally-iterative procedure, with an approximation of the stiffness matrix by combining the elastic and geometric stiffness matrix, allows detection of structural instabilities.

  3. Crystal structure of the second fibronectin type III (FN3) domain from human collagen α1 type XX.

    Science.gov (United States)

    Zhao, Jingfeng; Ren, Jixia; Wang, Nan; Cheng, Zhong; Yang, Runmei; Lin, Gen; Guo, Yi; Cai, Dayong; Xie, Yong; Zhao, Xiaohong

    2017-12-01

    Collagen α1 type XX, which contains fibronectin type III (FN3) repeats involving six FN3 domains (referred to as the FN#1-FN#6 domains), is an unusual member of the fibril-associated collagens with interrupted triple helices (FACIT) subfamily of collagens. The results of standard protein BLAST suggest that the FN3 repeats might contribute to collagen α1 type XX acting as a cytokine receptor. To date, solution NMR structures of the FN#3, FN#4 and FN#6 domains have been determined. To obtain further structural evidence to understand the relationship between the structure and function of the FN3 repeats from collagen α1 type XX, the crystal structure of the FN#2 domain from human collagen α1 type XX (residues Pro386-Pro466; referred to as FN2-HCXX) was solved at 2.5 Å resolution. The crystal structure of FN2-HCXX shows an immunoglobulin-like fold containing a β-sandwich structure, which is formed by a three-stranded β-sheet (β1, β2 and β5) packed onto a four-stranded β-sheet (β3, β4, β6 and β7). Two consensus domains, tencon and fibcon, are structural analogues of FN2-HCXX. Fn8, an FN3 domain from human oncofoetal fibronectin, is the closest structural analogue of FN2-HCXX derived from a naturally occurring sequence. Based solely on the structural similarity of FN2-HCXX to other FN3 domains, the detailed functions of FN2-HCXX and the FN3 repeats in collagen α1 type XX cannot be identified.

  4. Synthesis and characterization of pyrochlore-type yttrium titanate ...

    Indian Academy of Sciences (India)

    2Key Laboratory of Radioactive Geology and Exploration Technology Fundamental Science for National Defense, ... soft-chemistry technique viz. citric acid sol–gel method (CAM). ... waste (in particular, actinides) (Ewing et al 2004; Pace et al.

  5. In-situ high temperature irradiation setup for temperature dependent structural studies of materials under swift heavy ion irradiation

    International Nuclear Information System (INIS)

    Kulriya, P.K.; Kumari, Renu; Kumar, Rajesh; Grover, V.; Shukla, R.; Tyagi, A.K.; Avasthi, D.K.

    2015-01-01

    An in-situ high temperature (1000 K) setup is designed and installed in the materials science beam line of superconducting linear accelerator at the Inter-University Accelerator Centre (IUAC) for temperature dependent ion irradiation studies on the materials exposed with swift heavy ion (SHI) irradiation. The Gd 2 Ti 2 O 7 pyrochlore is irradiated using 120 MeV Au ion at 1000 K using the high temperature irradiation facility and characterized by ex-situ X-ray diffraction (XRD). Another set of Gd 2 Ti 2 O 7 samples are irradiated with the same ion beam parameter at 300 K and simultaneously characterized using in-situ XRD available in same beam line. The XRD studies along with the Raman spectroscopic investigations reveal that the structural modification induced by the ion irradiation is strongly dependent on the temperature of the sample. The Gd 2 Ti 2 O 7 is readily amorphized at an ion fluence 6 × 10 12 ions/cm 2 on irradiation at 300 K, whereas it is transformed to a radiation-resistant anion-deficient fluorite structure on high temperature irradiation, that amorphized at ion fluence higher than 1 × 10 13 ions/cm 2 . The temperature dependent ion irradiation studies showed that the ion fluence required to cause amorphization at 1000 K irradiation is significantly higher than that required at room temperature irradiation. In addition to testing the efficiency of the in-situ high temperature irradiation facility, the present study establishes that the radiation stability of the pyrochlore is enhanced at higher temperatures

  6. The XPS study of the structure of uranium-containing ceramics

    Directory of Open Access Journals (Sweden)

    Teterin Anton Yu.

    2010-01-01

    Full Text Available The samples of the (Ca0.5GdU0.5Zr2O7 and (Ca0.5GdU0.5(ZrTiO7 ceramics with the fluorite and pyrochlore structures used as matrixes for the long-lived high-level radioactive waste disposal were studied with the X-ray photoelectron spectroscopy method. On the basis of the X-ray photoelectron spectroscopy parameters of the outer and core electrons from the binding energy range of 0-1250 eV the oxidation states of the included metal ions were determined, the quantitative elemental and ionic analysis was done, and the orderliness (monophaseness was evaluated. The obtained data agree with the X-ray diffraction and the scanning electron microscopy results.

  7. A Review of Influence of Various Types of Structural Bracing to the Structural Performance of Buildings

    Science.gov (United States)

    Razak, S. M.; Kong, T. C.; Zainol, N. Z.; Adnan, A.; Azimi, M.

    2018-03-01

    Excessive lateral drift can contribute significantly towards crack formation, leading to structural damage. The structural damage will in turn reduce the capacity of the structure and weaken it from the intended design capacity. Generally, lateral drift is more pronounced in higher and longer structure, such as high rise buildings and bridges. A typical method employed to control lateral drift is structural bracing, which works by increasing stiffness and stability of structure. This paper reviews the influence of various types of structural bracing to structural performance of buildings. The history of structural bracing is visited and the differences between numerous structural bracing in term of suitability to different types of buildings and loading, mechanisms, technical details, advantages and limitations, and the overall effect on the structural behaviour and performance are dissected. Proper and efficient structural bracing is pertinent for each high rise building as this will lead towards safer, sustainable and more economical buildings, which are cheaper to maintain throughout the life of the buildings in the future.

  8. Bismuth zinc vanadate, BiZn2VO6: New crystal structure type and electronic structure

    International Nuclear Information System (INIS)

    Eliziario Nunes, Sayonara; Wang, Chun-Hai; So, Karwei; Evans, John S.O.; Evans, Ivana Radosavljević

    2015-01-01

    We report a combined experimental and computational study of the crystal structure and electronic properties of bismuth zinc vanadate, BiZn 2 VO 6 , known for its visible light photocatalytic activity. The crystal structure has been solved from laboratory powder X-ray diffraction data using the repeated minimisations from random starting values method. BiZn 2 VO 6 adopts a new structure type, based on the following building blocks: corner- and edge-sharing ZnO 4 tetrahedra, ZnO 6 octahedra and VO 4 tetrahedra, and Bi 2 O 12 dimers. It is the only known member of the BiM 2 AO 6 (M=Pb, Ca, Cd, Mn, Zn, Mg, Cu; A=V, P, As) family which does not appear to be structurally closely related to others. The electronic structure of BiZn 2 VO 6 , calculated by DFT methods, shows that it is an indirect gap semiconductor with a calculated band gap of 1.6 eV, which compares favourably to the experimentally measured value of 2.4 eV. - Graphical abstract: The crystal structure of BiZn 2 VO 6 , a new structure type in the BiM 2 AO 6 (M=Mg, Ca, Cd, Cu, Pb, Mn, Zn; A=V, P, As) family. - Highlights: • Structure solution from PXRD data by repeated minimisations from random starting values. • New structure type in the BiM 2 AO 6 (M=Pb, Ca, Cd, Mn, Zn, Mg, Cu; A=V, P, As) family. • Electronic structure calculation

  9. Luminescence studies on Sb3+ co-doped Y2Sn2O7: Tb nanoparticles

    International Nuclear Information System (INIS)

    Nigam, Sandeep; Sudarsan, V.; Vatsa, R.K.

    2008-01-01

    Pyrochlore-type oxides (A 2 B 2 O 7 ) have emerged as important host matrices for lanthanide doped luminescent materials due to their good thermal stability. Due to the higher symmetry around the A and B cations in the lattice lanthanide ions like Eu 3+ and Tb 3+ when incorporated at the A or B sites give very poor luminescence. One way to circumvent this problem is to incorporate ions like Sb 3+ or Bi 3+ in the lattice so that the lattice get distorted and luminescent intensity from the lanthanide ions increases. The present study deals with the synthesis and characterisation of Sb 3+ co-doped Y 2 Sn 2 O 7 :Tb nanoparticles prepared by the hydrolysis of Y 3+ , Sn 4+ , Tb 3+ and Sb 3+ in ethylene glycol medium followed by heating at 700 deg C for 4 hours. From XRD studies it is confirmed that as prepared sample is amorphous and heat treatment at 700 deg C results in the formation of highly crystalline Y 2 Sn 2 O 7 phase having pyrochlore structure

  10. Structural assessments of plate type support system for APR1400 reactor

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Anh Tung; Namgung, Ihn, E-mail: inamgung@kings.ac.kr

    2017-04-01

    Highlights: • This paper investigates plate-type support structure for the reactor vessel of the APR 1400. • The tall column supports of APR1400 reactor challenges in seismic and severe accident events. • A plate-type support of reactor vessel was proposed and evaluated based on ASME code. • The plate-type support was assessed to show its higher rigidity than column-type. - Abstract: This paper investigates an alternative form of support structure for the reactor vessel of the APR 1400. The current reactor vessel adopts a four-column support arrangement locating on the cold legs of the vessel. Although having been successfully designed, the tall column structure challenges in seismic events. In addition, for the mitigation of severe accident consequences, the columns inhibit ex-vessel coolant flow, hence the elimination of the support columns proposes extra safety advantages. A plate-type support was proposed and evaluated for the adequacy of meeting the structural stiffness by Finite Element Analysis (FEA) approach. ASME Boiler and Pressure Vessel Code was used to verify the design. The results, which cover thermal and static structural analysis, show stresses are within allowable limits in accordance with the design code. Even the heat conduction area is increased for the plate-type of support system, the results showed that the thermal stresses are within allowable limits. A comparison of natural frequencies and mode shapes for column support and plate-type support were presented as well which showed higher fundamental frequencies for the plate-type support system resulting in greater rigidity of the support system. From the outcome of this research, the plate-type support is proven to be an alternative to current APR column type support design.

  11. Colloidal alloys with preassembled clusters and spheres.

    Science.gov (United States)

    Ducrot, Étienne; He, Mingxin; Yi, Gi-Ra; Pine, David J

    2017-06-01

    Self-assembly is a powerful approach for constructing colloidal crystals, where spheres, rods or faceted particles can build up a myriad of structures. Nevertheless, many complex or low-coordination architectures, such as diamond, pyrochlore and other sought-after lattices, have eluded self-assembly. Here we introduce a new design principle based on preassembled components of the desired superstructure and programmed nearest-neighbour DNA-mediated interactions, which allows the formation of otherwise unattainable structures. We demonstrate the approach using preassembled colloidal tetrahedra and spheres, obtaining a class of colloidal superstructures, including cubic and tetragonal colloidal crystals, with no known atomic analogues, as well as percolating low-coordination diamond and pyrochlore sublattices never assembled before.

  12. Prediction of compounds with electric and magnetic ordering

    Energy Technology Data Exchange (ETDEWEB)

    Nikiforov, L G [Rybinskij Aviatsionnyj Tekhnologicheskij Inst. (USSR)

    1979-03-01

    The possibility of polymorphic transformations from the structure of the pyrochlore type into that of the perovskite type for nine lead-containing compounds has been forecast. Some of them (PbTaO/sub 3/, Pb/sub 2/NiTaO/sub 6/, Pb/sub 2/MnTaO/sub 6/, Pb/sub 2/SmTaO/sub 6/) are expected to have, in addition to common for all lead-containing perovskites ferro-or antiferro-electric properties, specific magnetic properties. The periods of elementary cells of new perovskites are forecast. The possibility of considerable reduction of the number of errors when searching thermodynamical parameters of transformation has been shown.

  13. Computer simulations applied in materials

    International Nuclear Information System (INIS)

    2003-01-01

    This workshop takes stock of the simulation methods applied to nuclear materials and discusses the conditions in which these methods can predict physical results when no experimental data are available. The main topic concerns the radiation effects in oxides and includes also the behaviour of fission products in ceramics, the diffusion and segregation phenomena and the thermodynamical properties under irradiation. This document brings together a report of the previous 2002 workshop and the transparencies of 12 presentations among the 15 given at the workshop: accommodation of uranium and plutonium in pyrochlores; radiation effects in La 2 Zr 2 O 7 pyrochlores; first principle calculations of defects formation energies in the Y 2 (Ti,Sn,Zr) 2 O 7 pyrochlore system; an approximate approach to predicting radiation tolerant materials; molecular dynamics study of the structural effects of displacement cascades in UO 2 ; composition defect maps for A 3+ B 3+ O 3 perovskites; NMR characterization of radiation damaged materials: using simulation to interpret the data; local structure in damaged zircon: a first principle study; simulation studies on SiC; insertion and diffusion of He in 3C-SiC; a review of helium in silica; self-trapped holes in amorphous silicon dioxide: their short-range structure revealed from electron spin resonance and optical measurements and opportunities for inferring intermediate range structure by theoretical modelling. (J.S.)

  14. Crystal structure of a copper-transporting PIB-type ATPase

    DEFF Research Database (Denmark)

    Gourdon, Pontus Emanuel; Liu, Xiang-Yu; Skjørringe, Tina

    2011-01-01

    Heavy-metal homeostasis and detoxification is crucial for cell viability. P-type ATPases of the class IB (PIB) are essential in these processes, actively extruding heavy metals from the cytoplasm of cells. Here we present the structure of a PIB-ATPase, a Legionella pneumophila CopA Cu(+)-ATPase, ......Heavy-metal homeostasis and detoxification is crucial for cell viability. P-type ATPases of the class IB (PIB) are essential in these processes, actively extruding heavy metals from the cytoplasm of cells. Here we present the structure of a PIB-ATPase, a Legionella pneumophila CopA Cu...

  15. Photovoltaic properties of ZnO nanorods/p-type Si heterojunction structures

    Directory of Open Access Journals (Sweden)

    Rafal Pietruszka

    2014-02-01

    Full Text Available Selected properties of photovoltaic (PV structures based on n-type zinc oxide nanorods grown by a low temperature hydrothermal method on p-type silicon substrates (100 are investigated. PV structures were covered with thin films of Al doped ZnO grown by atomic layer deposition acting as transparent electrodes. The investigated PV structures differ in terms of the shapes and densities of their nanorods. The best response is observed for the structure containing closely-spaced nanorods, which show light conversion efficiency of 3.6%.

  16. Self-assembly of three-dimensional open structures using patchy colloidal particles.

    Science.gov (United States)

    Rocklin, D Zeb; Mao, Xiaoming

    2014-10-14

    Open structures can display a number of unusual properties, including a negative Poisson's ratio, negative thermal expansion, and holographic elasticity, and have many interesting applications in engineering. However, it is a grand challenge to self-assemble open structures at the colloidal scale, where short-range interactions and low coordination number can leave them mechanically unstable. In this paper we discuss the self-assembly of three-dimensional open structures using triblock Janus particles, which have two large attractive patches that can form multiple bonds, separated by a band with purely hard-sphere repulsion. Such surface patterning leads to open structures that are stabilized by orientational entropy (in an order-by-disorder effect) and selected over close-packed structures by vibrational entropy. For different patch sizes the particles can form into either tetrahedral or octahedral structural motifs which then compose open lattices, including the pyrochlore, the hexagonal tetrastack and the perovskite lattices. Using an analytic theory, we examine the phase diagrams of these possible open and close-packed structures for triblock Janus particles and characterize the mechanical properties of these structures. Our theory leads to rational designs of particles for the self-assembly of three-dimensional colloidal structures that are possible using current experimental techniques.

  17. UNDERSTANDING THE STRUCTURE OF THE HOT INTERSTELLAR MEDIUM IN NORMAL EARLY-TYPE GALAXIES.

    Science.gov (United States)

    Traynor, Liam; Kim, Dong-Woo; Chandra Galaxy Atlas

    2018-01-01

    The hot interstellar medium (ISM) of early-type galaxies (ETG's) provides crucial insight into the understanding of their formation and evolution. Mechanisms such as type Ia supernovae heating, AGN feedback, deepening potential depth through dark matter assembly and ramp-pressure stripping are known to affect the structure of the ISM. By using temperature maps and radial temperature profiles of the hot ISM from ~70 ETG's with archival Chandra data, it is possible to classify the galaxy's ISM into common structural types. This is extended by using 3D fitting of the radial temperature profile in order to provide models that further constrain the structural types. Five structural types are present, negative (temperature decreases with radii), positive (temperature increases with radii), hybrid-dip (temperature decreases at small radii and increases at large radii), hybrid-bump (inverse of hybrid-dip) and quasi-isothermal (temperature is constant at all radii). This work will be continued by 1) determining which mechanisms are present in which galaxies and 2) analysing the model parameters between galaxies within each structural type to determine whether each type can be described by a single set of model parameters, indicating that the same physical processes are responsible for creating that structural type.

  18. Nanoscopic characterization of Pr2Zr2O7 at Zr sites

    International Nuclear Information System (INIS)

    Martinez, J.A.; Caracoche, M.C.; Rodriguez, A.M.; Rivas, P.C.; Bondioli, F.; Manfredini, T.; Ferrari, A.M.

    2005-01-01

    By using Perturbed Angular Correlation Spectroscopy, a suitable technique to explore internal fields at nanoscopic scale, the electric field gradients at Zr 4+ sites in the Pr 2 Zr 2 O 7 compound have been determined as a function of temperature. Three nonequivalent nanoconfigurations are present, which have been interpreted with the aid of point charge model calculations. Two of them correspond to pyrochlore - oxygen defective and perfect structures -, and the third one to the pyrochlore-related defect fluorite structure. The most abundant interaction is a disordered and fluctuating electric field gradient, which describes the oxygen defective pyrochlore. As temperature increases, its gradual and reversible transformation towards the perfect form is observed. Below 750 C the oxygen vacancies movement, which exhibits an activation energy of 0.14 eV, is assumed to be due to vacancies jumping among 48f equivalent sites. At higher temperatures the movement is interpreted as the fast diffusion of oxygen vacancies involving 48f and 8b sites, thus giving place to anionic disorder. The activation energy for this movement has been determined to be of 0.85 eV. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. X-ray structure of a soluble Rieske-type ferredoxin from Mus musculus

    International Nuclear Information System (INIS)

    Levin, Elena J.; Elsen, Nathaniel L.; Seder, Kory D.; McCoy, Jason G.; Fox, Brian G.; Phillips Jr, George N.

    2008-01-01

    The X-ray crystal structure of a soluble Rieske ferredoxin from M. musculus was solved at 2.07 Å resolution, revealing an iron–sulfur cluster-binding domain with similar architecture to the Rieske-type domains of bacterial aromatic dioxygenases. The ferredoxin was also shown to be capable of accepting electrons from both eukaryotic and prokaryotic oxidoreductases. The 2.07 Å resolution X-ray crystal structure of a soluble Rieske-type ferredoxin from Mus musculus encoded by the gene Mm.266515 is reported. Although they are present as covalent domains in eukaryotic membrane oxidase complexes, soluble Rieske-type ferredoxins have not previously been observed in eukaryotes. The overall structure of the mouse Rieske-type ferredoxin is typical of this class of iron–sulfur proteins and consists of a larger partial β-barrel domain and a smaller domain containing Cys57, His59, Cys80 and His83 that binds the [2Fe–2S] cluster. The S atoms of the cluster are hydrogen-bonded by six backbone amide N atoms in a pattern typical of membrane-bound high-potential eukaryotic respiratory Rieske ferredoxins. However, phylogenetic analysis suggested that the mouse Rieske-type ferredoxin was more closely related to bacterial Rieske-type ferredoxins. Correspondingly, the structure revealed an extended loop most similar to that seen in Rieske-type ferredoxin subunits of bacterial aromatic dioxygenases, including the positioning of an aromatic side chain (Tyr85) between this loop and the [2Fe–2S] cluster. The mouse Rieske-type ferredoxin was shown to be capable of accepting electrons from both eukaryotic and prokaryotic oxidoreductases, although it was unable to serve as an electron donor for a bacterial monooxygenase complex. The human homolog of mouse Rieske-type ferredoxin was also cloned and purified. It behaved identically to mouse Rieske-type ferredoxin in all biochemical characterizations but did not crystallize. Based on its high sequence identity, the structure of the

  20. PROVIDING SERVICEABILITY OF STRUCTURAL BEARING TYPES FOR ROADWAY BRIDGES

    Directory of Open Access Journals (Sweden)

    R. I. Polyuga

    2010-03-01

    Full Text Available In the article the description of structural bearing types for roadway bridges and their classification is given. Special attention is paid to effective bearings with elastomeric materials – rubber, pot, spherical ones. Characteristic defects of structural bearings and demands of serviceability are noticed.

  1. Cryo-EM structures of two bovine adenovirus type 3 intermediates

    International Nuclear Information System (INIS)

    Cheng, Lingpeng; Huang, Xiaoxing; Li, Xiaomin; Xiong, Wei; Sun, Wei; Yang, Chongwen; Zhang, Kai; Wang, Ying; Liu, Hongrong; Huang, Xiaojun; Ji, Gang; Sun, Fei; Zheng, Congyi; Zhu, Ping

    2014-01-01

    Adenoviruses (Ads) infect hosts from all vertebrate species and have been investigated as vaccine vectors. We report here near-atomic structures of two bovine Ad type 3 (BAd3) intermediates obtained by cryo-electron microscopy. A comparison between the two intermediate structures reveals that the differences are localized in the fivefold vertex region, while their facet structures are identical. The overall facet structure of BAd3 exhibits a similar structure to human Ads; however, BAd3 protein IX has a unique conformation. Mass spectrometry and cryo-electron tomography analyses indicate that one intermediate structure represents the stage during DNA encapsidation, whilst the other intermediate structure represents a later stage. These results also suggest that cleavage of precursor protein VI occurs during, rather than after, the DNA encapsidation process. Overall, our results provide insights into the mechanism of Ad assembly, and allow the first structural comparison between human and nonhuman Ads at backbone level. - Highlights: • First structure of bovine adenovirus type 3. • Some channels are located at the vertex of intermediate during DNA encapsidation. • Protein IX exhibits a unique conformation of trimeric coiled–coiled structure. • Cleavage of precursor protein VI occurs during the DNA encapsidation process

  2. Cryo-EM structures of two bovine adenovirus type 3 intermediates

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Lingpeng; Huang, Xiaoxing; Li, Xiaomin [National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101 (China); Xiong, Wei [State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Luo-jia-shan, Wuhan, Hubei 430072 (China); Sun, Wei; Yang, Chongwen; Zhang, Kai; Wang, Ying [National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101 (China); Liu, Hongrong [College of Physics and Information Science, Hunan Normal University, Changsha, Hunan 410081 (China); Huang, Xiaojun; Ji, Gang; Sun, Fei [National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101 (China); Zheng, Congyi, E-mail: cctcc202@whu.edu.cn [State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Luo-jia-shan, Wuhan, Hubei 430072 (China); Zhu, Ping, E-mail: zhup@ibp.ac.cn [National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101 (China)

    2014-02-15

    Adenoviruses (Ads) infect hosts from all vertebrate species and have been investigated as vaccine vectors. We report here near-atomic structures of two bovine Ad type 3 (BAd3) intermediates obtained by cryo-electron microscopy. A comparison between the two intermediate structures reveals that the differences are localized in the fivefold vertex region, while their facet structures are identical. The overall facet structure of BAd3 exhibits a similar structure to human Ads; however, BAd3 protein IX has a unique conformation. Mass spectrometry and cryo-electron tomography analyses indicate that one intermediate structure represents the stage during DNA encapsidation, whilst the other intermediate structure represents a later stage. These results also suggest that cleavage of precursor protein VI occurs during, rather than after, the DNA encapsidation process. Overall, our results provide insights into the mechanism of Ad assembly, and allow the first structural comparison between human and nonhuman Ads at backbone level. - Highlights: • First structure of bovine adenovirus type 3. • Some channels are located at the vertex of intermediate during DNA encapsidation. • Protein IX exhibits a unique conformation of trimeric coiled–coiled structure. • Cleavage of precursor protein VI occurs during the DNA encapsidation process.

  3. Relationship Structures and Semantic Type Assignments of the UMLS Enriched Semantic Network

    Science.gov (United States)

    Zhang, Li; Halper, Michael; Perl, Yehoshua; Geller, James; Cimino, James J.

    2005-01-01

    Objective: The Enriched Semantic Network (ESN) was introduced as an extension of the Unified Medical Language System (UMLS) Semantic Network (SN). Its multiple subsumption configuration and concomitant multiple inheritance make the ESN's relationship structures and semantic type assignments different from those of the SN. A technique for deriving the relationship structures of the ESN's semantic types and an automated technique for deriving the ESN's semantic type assignments from those of the SN are presented. Design: The technique to derive the ESN's relationship structures finds all newly inherited relationships in the ESN. All such relationships are audited for semantic validity, and the blocking mechanism is used to block invalid relationships. The mapping technique to derive the ESN's semantic type assignments uses current SN semantic type assignments and preserves nonredundant categorizations, while preventing new redundant categorizations. Results: Among the 426 newly inherited relationships, 326 are deemed valid. Seven blockings are applied to avoid inheritance of the 100 invalid relationships. Sixteen semantic types have different relationship structures in the ESN as compared to those in the SN. The mapping of semantic type assignments from the SN to the ESN avoids the generation of 26,950 redundant categorizations. The resulting ESN contains 138 semantic types, 149 IS-A links, 7,303 relationships, and 1,013,876 semantic type assignments. Conclusion: The ESN's multiple inheritance provides more complete relationship structures than in the SN. The ESN's semantic type assignments avoid the existing redundant categorizations appearing in the SN and prevent new ones that might arise due to multiple parents. Compared to the SN, the ESN provides a more accurate unifying semantic abstraction of the UMLS Metathesaurus. PMID:16049233

  4. Structure of a fibronectin type III-like module from Clostridium thermocellum

    International Nuclear Information System (INIS)

    Alahuhta, Markus; Xu, Qi; Brunecky, Roman; Adney, William S.; Ding, Shi-You; Himmel, Michael E.; Lunin, Vladimir V.

    2010-01-01

    The 1.6 Å resolution structure of a fibronectin type III-like module from Clostridium thermocellum with two molecules in the asymmetric unit is reported. The 1.6 Å resolution structure of a fibronectin type III-like module from Clostridium thermocellum with two molecules in the asymmetric unit is reported. The crystals used for data collection belonged to space group P2 1 2 1 2 1 , with unit-cell parameters a = 35.43, b = 45.73, c = 107.72 Å, and the structure was refined to an R factor of 0.166. Structural comparisons found over 800 similar structures in the Protein Data Bank. The broad range of different proteins or protein domains with high structural similarity makes it especially demanding to classify these proteins. Previous studies of fibronectin type III-like modules have indicated that they might function as ligand-binding modules, as a compact form of peptide linkers or spacers between other domains, as cellulose-disrupting modules or as proteins that help large enzyme complexes remain soluble

  5. Diversity, assembly and regulation of archaeal type IV pili-like and non-type-IV pili-like surface structures.

    Science.gov (United States)

    Lassak, Kerstin; Ghosh, Abhrajyoti; Albers, Sonja-Verena

    2012-01-01

    Archaea have evolved fascinating surface structures allowing rapid adaptation to changing environments. The archaeal surface appendages display such diverse biological roles as motility, adhesion, biofilm formation, exchange of genetic material and species-specific interactions and, in turn, increase fitness of the cells. Intriguingly, despite sharing the same functions with their bacterial counterparts, the assembly mechanism of many archaeal surface structures is rather related to assembly of bacterial type IV pili. This review summarizes our state-of-the-art knowledge about unique structural and biochemical properties of archaeal surface appendages with a particular focus on archaeal type IV pili-like structures. The latter comprise not only widely distributed archaella (formerly known as archaeal flagella), but also different highly specialized archaeal pili, which are often restricted to certain species. Recent findings regarding assembly mechanisms, structural aspects and physiological roles of these type IV pili-like structures will be discussed in detail. Recently, first regulatory proteins involved in transition from both planktonic to sessile lifestyle and in assembly of archaella were identified. To conclude, we provide novel insights into regulatory mechanisms underlying the assembly of archaeal surface structures. Copyright © 2012. Published by Elsevier Masson SAS.

  6. The influence of crystal structure on ion-irradiation tolerance in the Sm{sub (x)}Yb{sub (2-x)}TiO{sub 5} series

    Energy Technology Data Exchange (ETDEWEB)

    Aughterson, R.D., E-mail: roa@ansto.gov.au [Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234 (Australia); Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia); Lumpkin, G.R.; Reyes, M. de los [Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234 (Australia); Gault, B. [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Baldo, P.; Ryan, E. [Materials Science Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Whittle, K.R. [Centre for Materials and Structures, School of Engineering, The University of Liverpool, Liverpool L69 3GH UK (United Kingdom); Smith, K.L. [Government International and External Relations, Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234 (Australia); Cairney, J.M. [Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia)

    2016-04-01

    This ion-irradiation study covers the four major crystal structure types in the Ln{sub 2}TiO{sub 5} series (Ln = lanthanide), namely orthorhombic Pnma, hexagonal P6{sub 3}/mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. This is the first systematic examination of the complete Ln{sub 2}TiO{sub 5} crystal system and the first reported examination of the hexagonal structure. A series of samples, based on the stoichiometry Sm{sub (x)}Yb{sub (2-x)}TiO{sub 5} (where x = 2, 1.4, 1, 0.6, and 0) have been irradiated using 1 MeV Kr{sup 2+} ions and characterised in-situ using a transmission electron microscope. Two quantities are used to define ion-irradiation tolerance: critical dose of amorphisation (D{sub c}), which is the irradiating ion dose required for a crystalline to amorphous transition, and the critical temperature (T{sub c}), above which the sample cannot be rendered amorphous by ion irradiation. The structure type plus elements of bonding are correlated to ion-irradiation tolerance. The cubic phases, Yb{sub 2}TiO{sub 5} and Sm{sub 0.6}Yb{sub 1.4}TiO{sub 5}, were found to be the most radiation tolerant, with T{sub c} values of 479 and 697 K respectively. The improved radiation tolerance with a change in symmetry to cubic is consistent with previous studies of similar compounds.

  7. High-pressure U3O8 with the fluorite-type structure

    International Nuclear Information System (INIS)

    Zhang, F.X.; Lang, M.; Wang, J.W.; Li, W.X.; Sun, K.; Prakapenka, V.; Ewing, R.C.

    2014-01-01

    A new high-pressure phase of U 3 O 8 , which has a fluorite-type structure, forms at pressures greater than ∼8.1 GPa that was confirmed by in situ x-ray diffraction (XRD) measurements. The fluorite-type U 3 O 8 is stable at pressures at least up to ∼40 GPa and temperatures to 1700 K, and quenchable to ambient conditions. Based on the XRD analysis, there is a huge volume collapse (>20%) for U 3 O 8 during the phase transition and the quenched high-pressure phase is 28% denser than the initial orthorhombic phase at ambient conditions. The high-pressure phase has a very low compressibility comparing with the starting orthorhombic phase. - Graphical abstract: α-U 3 O 8 is in a layered structure with orthorhombic symmetry, at high pressures, it transformed to a fluorite-type cubic structure. There are a lot of defects in the cubic structure, and it is a new kind of hyperstoichiometric uranium oxide, which is stable at ambient conditions. - Highlights: • A new fluorite-type high-pressure phase was found in hyperstoichometric UO 2 +x (x∼0.8). • The new high-pressure structure is quenchable to ambient conditions. • Pressure driven phase transition in orthorhombic U 3 O 8 was first found

  8. Changes in the internal structure of the human crystalline lens with diabetes mellitus type 1 and type 2

    NARCIS (Netherlands)

    Wiemer, N.G.M.; Dubbelman, M.; Hermans, E.A.; Ringens, P.J.; Polak, B.C.P.

    2008-01-01

    Purpose: To investigate the effect of diabetes mellitus (DM) type 1 and type 2 on the internal structure of the lens. Design: Observational cross-sectional study. Participants and Controls: One hundred seven patients with DM type 1, 106 patients with DM type 2, and 75 healthy control subjects.

  9. Co-linear spin configurations in corundum-type structures

    International Nuclear Information System (INIS)

    Bertaut, F.

    1961-01-01

    The colinear magnetic configurations possible in corundum-type structures (α-Fe 2 O 3 ; Cr 2 O 3 ) are solutions of a matrices problem. Their regions of stability are bounded by inequality relationships between exchange integrals. (author) [fr

  10. Soil structure interactions of eastern U.S. type earthquakes

    International Nuclear Information System (INIS)

    Chang Chen; Serhan, S.

    1991-01-01

    Two types of earthquakes have occurred in the eastern US in the past. One of them was the infrequent major events such as the 1811-1812 New Madrid Earthquakes, or the 1886 Charleston Earthquake. The other type was the frequent shallow earthquakes with high frequency, short duration and high accelerations. Two eastern US nuclear power plants, V.C Summer and Perry, went through extensive licensing effort to obtain fuel load licenses after this type of earthquake was recorded on sites and exceeded the design bases beyond 10 hertz region. This paper discusses the soil-structure interactions of the latter type of earthquakes

  11. Type III radio bursts in a flaming structure

    International Nuclear Information System (INIS)

    Karlicky, M.; Tlamicha, A.

    1977-01-01

    An interpretation is presented of the burst of 3.7.1974. The slowly drifting, fine structure in this type III burst is evidence of the existence of very fast, spatially extensive processes in the corona. The concept is presented of a rapidly varying, magnetohydrodynamically unstable, flaming structure of the magnetic field and, using this model, the intensities were computed of the magnetic field at certain altitudes and at two moments differing by 1.4 s. (author)

  12. Computer simulations applied in materials

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2003-07-01

    This workshop takes stock of the simulation methods applied to nuclear materials and discusses the conditions in which these methods can predict physical results when no experimental data are available. The main topic concerns the radiation effects in oxides and includes also the behaviour of fission products in ceramics, the diffusion and segregation phenomena and the thermodynamical properties under irradiation. This document brings together a report of the previous 2002 workshop and the transparencies of 12 presentations among the 15 given at the workshop: accommodation of uranium and plutonium in pyrochlores; radiation effects in La{sub 2}Zr{sub 2}O{sub 7} pyrochlores; first principle calculations of defects formation energies in the Y{sub 2}(Ti,Sn,Zr){sub 2}O{sub 7} pyrochlore system; an approximate approach to predicting radiation tolerant materials; molecular dynamics study of the structural effects of displacement cascades in UO{sub 2}; composition defect maps for A{sup 3+}B{sup 3+}O{sub 3} perovskites; NMR characterization of radiation damaged materials: using simulation to interpret the data; local structure in damaged zircon: a first principle study; simulation studies on SiC; insertion and diffusion of He in 3C-SiC; a review of helium in silica; self-trapped holes in amorphous silicon dioxide: their short-range structure revealed from electron spin resonance and optical measurements and opportunities for inferring intermediate range structure by theoretical modelling. (J.S.)

  13. Crystal structure of clathrates of Hofmann dma-type

    International Nuclear Information System (INIS)

    NIshikiori, Sh.; Ivamoto, T.

    1999-01-01

    Seven new clathrates Cd(DMA) 2 Ni(CN) 4 ·xG (x=1, G=aniline, 2,3-xylidine, 2,4-xylidine, 2,5-xylidine, 2,6-xylidine, 3,5-xylidine, and x=2, G=2,4,6-trimethylaniline) of Hofmann type are synthesized by amine substitution for dimethylamine (DMA). On the base of x-ray diffraction data it is shown that geometry of guest molecule in cage-like hollow determines the structure of the host and crystal structure of clathrates. Two-dimension metallocomplex of the host of studied clathrates is characterized by elastic folded structure appearing as a result of angular deformation of bond between Cd atoms and host cyanide bridge. Guest molecule orientation is fixed by hydrogen bond. Structural elasticity of the host complex directs to differences in crystal structure of clathrates formed and to considerable variety of incorporated guests [ru

  14. Structures and Corresponding Functions of Five Types of Picornaviral 2A Proteins

    Directory of Open Access Journals (Sweden)

    Xiaoyao Yang

    2017-07-01

    Full Text Available Among the few non-structural proteins encoded by the picornaviral genome, the 2A protein is particularly special, irrespective of structure or function. During the evolution of the Picornaviridae family, the 2A protein has been highly non-conserved. We believe that the 2A protein in this family can be classified into at least five distinct types according to previous studies. These five types are (A chymotrypsin-like 2A, (B Parechovirus-like 2A, (C hepatitis-A-virus-like 2A, (D Aphthovirus-like 2A, and (E 2A sequence of the genus Cardiovirus. We carried out a phylogenetic analysis and found that there was almost no homology between each type. Subsequently, we aligned the sequences within each type and found that the functional motifs in each type are highly conserved. These different motifs perform different functions. Therefore, in this review, we introduce the structures and functions of these five types of 2As separately. Based on the structures and functions, we provide suggestions to combat picornaviruses. The complexity and diversity of the 2A protein has caused great difficulties in functional and antiviral research. In this review, researchers can find useful information on the 2A protein and thus conduct improved antiviral research.

  15. Evaluation of soil-structure interaction for structures subjected to earthquake loading with different types of foundation

    Directory of Open Access Journals (Sweden)

    Elwi Mohammed

    2018-01-01

    Full Text Available However though the structures are supported on soil, most of the designers do not consider the soil structure interaction and its subsequent effect on structure during an earthquake. Different soil properties can affect seismic waves as they pass through a soil layer. When a structure is subjected to an earthquake excitation, it interacts the foundation and soil, and thus changes the motion of the ground. It means that the movement of the whole ground structure system is influenced by type of soil as well as by the type of structure. Tall buildings are supposed to be of engineered construction in sense that they might have been analyzed and designed to meet the provision of relevant codes of practice and building bye-laws. IS 1893: 2002 “Criteria for Earthquake Resistant Design of Structures” gives response spectrum for different types of soil such as hard, medium and soft. An attempt has been made in this paper to study the effect of Soil-structure interaction on multi storeyed buildings with various foundation systems. Also to study the response of buildings subjected to seismic forces with Rigid and Flexible foundations. Multi storeyed buildings with fixed and flexible support subjected to seismic forces were analyzed under different soil conditions like hard, medium and soft. The buildings were analyzed by Response spectrum method using software SAP2000. The response of building frames such as Lateral deflection, Story drift, Base shear, Axial force and Column moment values for all building frames were presented in this paper.

  16. Structural damage detection-oriented multi-type sensor placement with multi-objective optimization

    Science.gov (United States)

    Lin, Jian-Fu; Xu, You-Lin; Law, Siu-Seong

    2018-05-01

    A structural damage detection-oriented multi-type sensor placement method with multi-objective optimization is developed in this study. The multi-type response covariance sensitivity-based damage detection method is first introduced. Two objective functions for optimal sensor placement are then introduced in terms of the response covariance sensitivity and the response independence. The multi-objective optimization problem is formed by using the two objective functions, and the non-dominated sorting genetic algorithm (NSGA)-II is adopted to find the solution for the optimal multi-type sensor placement to achieve the best structural damage detection. The proposed method is finally applied to a nine-bay three-dimensional frame structure. Numerical results show that the optimal multi-type sensor placement determined by the proposed method can avoid redundant sensors and provide satisfactory results for structural damage detection. The restriction on the number of each type of sensors in the optimization can reduce the searching space in the optimization to make the proposed method more effective. Moreover, how to select a most optimal sensor placement from the Pareto solutions via the utility function and the knee point method is demonstrated in the case study.

  17. Mixed oxides forming in CdO-OsO2 and PbO-OsO2 systems

    International Nuclear Information System (INIS)

    Shaplygin, I.S.; Lazarev, V.B.

    1978-01-01

    The formation of mixed oxides in systems CdO-OsO 2 and PbO-OsO 2 was studied by derivatography, X-ray phase analysis, and IR spectroscopy. It was established that in the system CdO-OsO 2 cubic phases of Cdsub(2)Ossub(2)Osub(6.7) and Cdsub(2)Ossub(2)Osub(7.2) with a pyrochlor-type structure, as well as new compounds with the structure of rhombic perovskite CdOsO 3 and Cd(Cdsub(0.5)Ossub(0.5))Osub(3) containing osmium in the formal degree of oxidation +4 and +6, respectively, are formed. The thermal stability of the compounds obtained was studied and their electrical properties determined

  18. The Cryoelectron Microscopy Structure of the Type 1 Chaperone-Usher Pilus Rod.

    Science.gov (United States)

    Hospenthal, Manuela K; Zyla, Dawid; Costa, Tiago R D; Redzej, Adam; Giese, Christoph; Lillington, James; Glockshuber, Rudi; Waksman, Gabriel

    2017-12-05

    Adhesive chaperone-usher pili are long, supramolecular protein fibers displayed on the surface of many bacterial pathogens. The type 1 and P pili of uropathogenic Escherichia coli (UPEC) play important roles during urinary tract colonization, mediating attachment to the bladder and kidney, respectively. The biomechanical properties of the helical pilus rods allow them to reversibly uncoil in response to flow-induced forces, allowing UPEC to retain a foothold in the unique and hostile environment of the urinary tract. Here we provide the 4.2-Å resolution cryo-EM structure of the type 1 pilus rod, which together with the previous P pilus rod structure rationalizes the remarkable "spring-like" properties of chaperone-usher pili. The cryo-EM structure of the type 1 pilus rod differs in its helical parameters from the structure determined previously by a hybrid approach. We provide evidence that these structural differences originate from different quaternary structures of pili assembled in vivo and in vitro. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

  19. Structure of V-type ATPase from Clostridium fervidus by electron microscopy

    NARCIS (Netherlands)

    Boekema, EJ; Ubbink-Kok, T; Lolkema, JS; Brisson, A; Konings, WN

    F-type and V-type ATPases couple synthesis or hydrolysis of ATP to the translocation of H+ or Na+ across biological membranes and have similarities in structure and mechanism. In both types of enzymes three main parts can be distinguished: headpiece, membrane-bound piece and stalk region. We report

  20. Bismuth zinc vanadate, BiZn{sub 2}VO{sub 6}: New crystal structure type and electronic structure

    Energy Technology Data Exchange (ETDEWEB)

    Eliziario Nunes, Sayonara [Department of Chemistry, Durham University, South Road, Durham DH1 3LE (United Kingdom); Department of Materials Engineering, Federal University of São Carlos, 13565-905 São Carlos, SP (Brazil); Wang, Chun-Hai; So, Karwei; Evans, John S.O. [Department of Chemistry, Durham University, South Road, Durham DH1 3LE (United Kingdom); Evans, Ivana Radosavljević, E-mail: ivana.radosavljevic@durham.ac.uk [Department of Chemistry, Durham University, South Road, Durham DH1 3LE (United Kingdom)

    2015-02-15

    We report a combined experimental and computational study of the crystal structure and electronic properties of bismuth zinc vanadate, BiZn{sub 2}VO{sub 6}, known for its visible light photocatalytic activity. The crystal structure has been solved from laboratory powder X-ray diffraction data using the repeated minimisations from random starting values method. BiZn{sub 2}VO{sub 6} adopts a new structure type, based on the following building blocks: corner- and edge-sharing ZnO{sub 4} tetrahedra, ZnO{sub 6} octahedra and VO{sub 4} tetrahedra, and Bi{sub 2}O{sub 12} dimers. It is the only known member of the BiM{sub 2}AO{sub 6} (M=Pb, Ca, Cd, Mn, Zn, Mg, Cu; A=V, P, As) family which does not appear to be structurally closely related to others. The electronic structure of BiZn{sub 2}VO{sub 6}, calculated by DFT methods, shows that it is an indirect gap semiconductor with a calculated band gap of 1.6 eV, which compares favourably to the experimentally measured value of 2.4 eV. - Graphical abstract: The crystal structure of BiZn{sub 2}VO{sub 6}, a new structure type in the BiM{sub 2}AO{sub 6} (M=Mg, Ca, Cd, Cu, Pb, Mn, Zn; A=V, P, As) family. - Highlights: • Structure solution from PXRD data by repeated minimisations from random starting values. • New structure type in the BiM{sub 2}AO{sub 6} (M=Pb, Ca, Cd, Mn, Zn, Mg, Cu; A=V, P, As) family. • Electronic structure calculation.

  1. Chemical synthesis and characterization of nano-sized rare-earth ...

    Indian Academy of Sciences (India)

    2

    pyrochlore samples indicated a single phase crystalline material with a cubic ... vary with the size and the surface area of the particles.6 Thus, a method to ..... From qualitative band-model consideration of the type discussed by Goodenough.

  2. Post accelerator of the IH type structure

    International Nuclear Information System (INIS)

    Chen Ming

    2002-01-01

    The principle, structure, adjustment of the gap voltage, beam dynamic, RF system and the bunchers of the post-accelerator with Interdigital-H type structure, which was developed by the author and Technical University Munich in four years, is described. The energy of ions with mass of three was increased from 340 keV to 1.74 MeV, when resonant frequency of 84.2 MHz and input RF power of 3 kW. The effective shunt impedance reached to 408 MΩ/m. The commissioning was succeeded with H 3 + ion beams. The output energy of H 3 + ion beams reached the design value. The two harmonic double drift buncher used by the IH structure bunches the beam to the bunches with the width of 360 ps. Then the acceptance of the IH structure is increased to 240 degree. Its shunt impedance is three times higher than former single gap bunchers used by TUM and the length of the buncher system is one fifth of former one only because the use of λ/4 coaxial cavities with double gaps

  3. Extraordinary electronic properties in uncommon structure types

    Science.gov (United States)

    Ali, Mazhar Nawaz

    In this thesis I present the results of explorations into several uncommon structure types. In Chapter 1 I go through the underlying idea of how we search for new compounds with exotic properties in solid state chemistry. The ideas of exploring uncommon structure types, building up from the simple to the complex, using chemical intuition and thinking by analogy are discussed. Also, the history and basic concepts of superconductivity, Dirac semimetals, and magnetoresistance are briefly reviewed. In chapter 2, the 1s-InTaS2 structural family is introduced along with the discovery of a new member of the family, Ag0:79VS2; the synthesis, structure, and physical properties of two different polymorphs of the material are detailed. Also in this chapter, we report the observation of superconductivity in another 1s structure, PbTaSe2. This material is especially interesting due to it being very heavy (resulting in very strong spin orbit coulping (SOC)), layered, and noncentrosymmetric. Electronic structure calculations reveal the presence of a bulk 3D Dirac cone (very similar to graphene) that is gapped by SOC originating from the hexagonal Pb layer. In Chapter 3 we show the re-investigation of the crystal structure of the 3D Dirac semimetal, Cd3As2. It is found to be centrosymmetric, rather than noncentrosymmetric, and as such all bands are spin degenerate and there is a 4-fold degenerate bulk Dirac point at the Fermi level, making Cd3As2 a 3D electronic analog to graphene. Also, for the first time, scanning tunneling microscopy experiments identify a 2x2 surface reconstruction in what we identify as the (112) cleavage plane of single crystals; needle crystals grow with a [110] long axis direction. Lastly, in chapter 4 we report the discovery of "titanic" (sadly dubbed ⪉rge, nonsaturating" by Nature editors and given the acronym XMR) magnetoresistance (MR) in the non-magnetic, noncentrosymmetric, layered transition metal dichalcogenide WTe2; over 13 million% at 0.53 K in

  4. Effect of cerium additive and secondary phase analysis on Ag0.5Bi0 ...

    Indian Academy of Sciences (India)

    Technical University of Madrid (UPM), Madrid 28012, Spain. MS received 27 ... XRD analysis showed the presence of pyrochlore structure and secondary phase when more .... The present work reports the effect of incorporation of cerium in ...

  5. Atomic Structure of Type VI Contractile Sheath from Pseudomonas aeruginosa.

    Science.gov (United States)

    Salih, Osman; He, Shaoda; Planamente, Sara; Stach, Lasse; MacDonald, James T; Manoli, Eleni; Scheres, Sjors H W; Filloux, Alain; Freemont, Paul S

    2018-02-06

    Pseudomonas aeruginosa has three type VI secretion systems (T6SSs), H1-, H2-, and H3-T6SS, each belonging to a distinct group. The two T6SS components, TssB/VipA and TssC/VipB, assemble to form tubules that conserve structural/functional homology with tail sheaths of contractile bacteriophages and pyocins. Here, we used cryoelectron microscopy to solve the structure of the H1-T6SS P. aeruginosa TssB1C1 sheath at 3.3 Å resolution. Our structure allowed us to resolve some features of the T6SS sheath that were not resolved in the Vibrio cholerae VipAB and Francisella tularensis IglAB structures. Comparison with sheath structures from other contractile machines, including T4 phage and R-type pyocins, provides a better understanding of how these systems have conserved similar functions/mechanisms despite evolution. We used the P. aeruginosa R2 pyocin as a structural template to build an atomic model of the TssB1C1 sheath in its extended conformation, allowing us to propose a coiled-spring-like mechanism for T6SS sheath contraction. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

  6. The indentification of Jueluotage V-type structure in Xinjiang and its orderness

    International Nuclear Information System (INIS)

    Fang Maolong; Sun Wenpeng; Cai Wenbo; Xu Daoyi

    2005-01-01

    Based on the interpretation of satellite image and field checking in Jueluotage area, Xinjiang, it is thought that the sublatitudinal arc fault zones have been formed since Mesozoic through the evolution of the NWW-trending and NEE-trending faults occurring in pre-Mesozoic time. These three sets of faults comprise the Jueluotage 'V-type structure' formed by the NW-trending structural stress field and drastically activated since Neocene. The Jueluotage V-type structure is expressed in time as an ordered process, and in space as an ordered arrangement and an ordered evolution direction, and characterizes the Information Ordered Series (IOS) of the evolution process of fault structure. (authors)

  7. Structural inheritance in cast 30KhGNM-type steel

    International Nuclear Information System (INIS)

    Sadovskij, V.D.; Bershtejn, L.I.; Mel'nikova, A.A.; Polyakova, A.M.; Schastlivtsev, V.M.

    1980-01-01

    Structural inheritance in the cast 30KhGNM-type steel depending on the heating rate and the temperature of preliminary tempering is investigated. When eating the cast steel with a beinite structure at the rate of 1-150 deg/min, the restoration of austenite grain and the following recrystallization due to the phase cold work, are observed. Slow heating from room temperature or preliminary tempering hinder grain restoration during heating. A non-monotonous effect of tempering temperature on the structural inheritance is established which can be connected with the kinetics of decomposition of residual austenite in steel

  8. Filamentary structures of the cosmic web and the nonlinear Schroedinger type equation

    International Nuclear Information System (INIS)

    Tigrak, E; Weygaert, R van de; Jones, B J T

    2011-01-01

    We show that the filamentary type structures of the cosmic web can be modeled as solitonic waves by solving the reaction diffusion system which is the hydrodynamical analogous of the nonlinear Schroedinger type equation. We find the analytical solution of this system by applying the Hirota direct method which produces the dissipative soliton solutions to formulate the dynamical evolution of the nonlinear structure formation.

  9. Seismic verification methods for structures and equipment of VVER-type and RBMK-type NPPs (summary of experiences)

    International Nuclear Information System (INIS)

    Masopust, R.

    2003-01-01

    The main verification methods for structures and equipment of already existing VVER-type and RBMK-type NPPs are briefly described. The following aspects are discussed: fundamental seismic safety assessment principles for VVER/RBMK-type NPPs (seismic safety assessment procedure, typical work plan for seismic safety assessment of existing NPPs, SMA (HCLPF) calculations, modified GIP (GIP-VVER) procedure, similarity of VVER/RBMK equipment to that included in the SQUG databases and seismic interactions

  10. Reverse engineering of wörner type drilling machine structure.

    Science.gov (United States)

    Wibowo, A.; Belly, I.; llhamsyah, R.; Indrawanto; Yuwana, Y.

    2018-03-01

    A product design needs to be modified based on the conditions of production facilities and existing resource capabilities without reducing the functional aspects of the product itself. This paper describes the reverse engineering process of the main structure of the wörner type drilling machine to obtain a machine structure design that can be made by resources with limited ability by using simple processes. Some structural, functional and the work mechanism analyzes have been performed to understand the function and role of each basic components. The process of dismantling of the drilling machine and measuring each of the basic components was performed to obtain sets of the geometry and size data of each component. The geometric model of each structure components and the machine assembly were built to facilitate the simulation process and machine performance analysis that refers to ISO standard of drilling machine. The tolerance stackup analysis also performed to determine the type and value of geometrical and dimensional tolerances, which could affect the ease of the components to be manufactured and assembled

  11. New types of organizational structures of accounting departments and their development

    OpenAIRE

    Шигун, Марія Михайлівна

    2015-01-01

    Development directions of new types of organizational structures of accounting departments, emergence of which has been caused by present-day conditions of keeping economics relationships, have been researched, as well as peculiarity of complex hierarchical and adaptive structures has been disclosed.

  12. Cofiring behavior and interfacial structure of NiCuZn ferrite/PMN ferroelectrics composites for multilayer LC filters

    International Nuclear Information System (INIS)

    Miao Chunlin; Zhou Ji; Cui Xuemin; Wang Xiaohui; Yue Zhenxing; Li Longtu

    2006-01-01

    The cofiring behavior, interfacial structure and cofiring migration between NiCuZn ferrite and lead magnesium niobate (PMN)-based relaxor ferroelectric materials were investigated via thermomechanical analyzer (TMA), X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Mismatched sintering shrinkage between NiCuZn ferrite and PMN was modified by adding an appropriate amount of sintering aids, Bi 2 O 3 , into NiCuZn ferrite. Pyrochlore phase appeared in the mixture of NiCuZn ferrite and PMN, which is detrimental to the final electric properties of LC filters. EDS results indicated that the interdiffusion at the heterogeneous interfaces in the composites, such as Fe, Pb, Zn, existed which can strengthen combinations between ferrite layers and ferroelectrics layers

  13. A Low Cost Structurally Optimized Design for Diverse Filter Types

    Science.gov (United States)

    Kazmi, Majida; Aziz, Arshad; Akhtar, Pervez; Ikram, Nassar

    2016-01-01

    A wide range of image processing applications deploys two dimensional (2D)-filters for performing diversified tasks such as image enhancement, edge detection, noise suppression, multi scale decomposition and compression etc. All of these tasks require multiple type of 2D-filters simultaneously to acquire the desired results. The resource hungry conventional approach is not a viable option for implementing these computationally intensive 2D-filters especially in a resource constraint environment. Thus it calls for optimized solutions. Mostly the optimization of these filters are based on exploiting structural properties. A common shortcoming of all previously reported optimized approaches is their restricted applicability only for a specific filter type. These narrow scoped solutions completely disregard the versatility attribute of advanced image processing applications and in turn offset their effectiveness while implementing a complete application. This paper presents an efficient framework which exploits the structural properties of 2D-filters for effectually reducing its computational cost along with an added advantage of versatility for supporting diverse filter types. A composite symmetric filter structure is introduced which exploits the identities of quadrant and circular T-symmetries in two distinct filter regions simultaneously. These T-symmetries effectually reduce the number of filter coefficients and consequently its multipliers count. The proposed framework at the same time empowers this composite filter structure with additional capabilities of realizing all of its Ψ-symmetry based subtypes and also its special asymmetric filters case. The two-fold optimized framework thus reduces filter computational cost up to 75% as compared to the conventional approach as well as its versatility attribute not only supports diverse filter types but also offers further cost reduction via resource sharing for sequential implementation of diversified image

  14. Robust structural optimization using Gauss-type quadrature formula

    International Nuclear Information System (INIS)

    Lee, Sang Hoon; Seo, Ki Seog; Chen, Shikui; Chen, Wei

    2009-01-01

    In robust design, the mean and variance of design performance are frequently used to measure the design performance and its robustness under uncertainties. In this paper, we present the Gauss-type quadrature formula as a rigorous method for mean and variance estimation involving arbitrary input distributions and further extend its use to robust design optimization. One dimensional Gauss-type quadrature formula are constructed from the input probability distributions and utilized in the construction of multidimensional quadrature formula such as the Tensor Product Quadrature (TPQ) formula and the Univariate Dimension Reduction (UDR) method. To improve the efficiency of using it for robust design optimization, a semi-analytic design sensitivity analysis with respect to the statistical moments is proposed. The proposed approach is applied to a simple bench mark problems and robust topology optimization of structures considering various types of uncertainty.

  15. Robust structural optimization using Gauss-type quadrature formula

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sang Hoon; Seo, Ki Seog [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Chen, Shikui; Chen, Wei [Northwestern University, Illinois (United States)

    2009-07-01

    In robust design, the mean and variance of design performance are frequently used to measure the design performance and its robustness under uncertainties. In this paper, we present the Gauss-type quadrature formula as a rigorous method for mean and variance estimation involving arbitrary input distributions and further extend its use to robust design optimization. One dimensional Gauss-type quadrature formula are constructed from the input probability distributions and utilized in the construction of multidimensional quadrature formula such as the Tensor Product Quadrature (TPQ) formula and the Univariate Dimension Reduction (UDR) method. To improve the efficiency of using it for robust design optimization, a semi-analytic design sensitivity analysis with respect to the statistical moments is proposed. The proposed approach is applied to a simple bench mark problems and robust topology optimization of structures considering various types of uncertainty.

  16. Robust Structural Optimization Using Gauss-type Quadrature Formula

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sang Hoon; Seo, Ki Seog; Chen, Shikui; Chen, Wei [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2009-08-15

    In robust design, the mean and variance of design performance are frequently used to measure the design performance and its robustness under uncertainties. In this paper, we present the Gauss-type quadrature formula as a rigorous method for mean and variance estimation involving arbitrary input distributions and further extend its use to robust design optimization. One dimensional Gauss-type quadrature formula are constructed from the input probability distributions and utilized in the construction of multidimensional quadrature formula such as the tensor product quadrature (TPQ) formula and the univariate dimension reduction (UDR) method. To improve the efficiency of using it for robust design optimization, a semi-analytic design sensitivity analysis with respect to the statistical moments is proposed. The proposed approach is applied to a simple bench mark problems and robust topology optimization of structures considering various types of uncertainty.

  17. Robust Structural Optimization Using Gauss-type Quadrature Formula

    International Nuclear Information System (INIS)

    Lee, Sang Hoon; Seo, Ki Seog; Chen, Shikui; Chen, Wei

    2009-01-01

    In robust design, the mean and variance of design performance are frequently used to measure the design performance and its robustness under uncertainties. In this paper, we present the Gauss-type quadrature formula as a rigorous method for mean and variance estimation involving arbitrary input distributions and further extend its use to robust design optimization. One dimensional Gauss-type quadrature formula are constructed from the input probability distributions and utilized in the construction of multidimensional quadrature formula such as the tensor product quadrature (TPQ) formula and the univariate dimension reduction (UDR) method. To improve the efficiency of using it for robust design optimization, a semi-analytic design sensitivity analysis with respect to the statistical moments is proposed. The proposed approach is applied to a simple bench mark problems and robust topology optimization of structures considering various types of uncertainty

  18. Crystal chemistry of six-coordinated silicon: A key to understanding the earth's deep interior

    International Nuclear Information System (INIS)

    Finger, L.W.; Hazen, R.M.

    1991-01-01

    A survey of high-pressure silicates reveals 12 distinct high-density structural topologies with octahedral Si. Seven of these structure types - stishovite, perovskite, ilmenite, hollandite, calcium ferrite, pyrochlore and K 2 NiF 4 type - contain only six-corrdinated silicon. Other high-pressure silicates, including those with the garnet, pyroxene, wadeite, anhydrous phase B and phase B structures, contain both tetrahedral and octahedral Si. Five systematic trends among these dozen structures suggest the existence of other, as yet unobserved, possible mantle Si phases. The criteria are: (1) Structures like rutile, hollandite and calcium ferrite formed from edge-sharing chains of silicon octahedra; (2) germanates synthesized at room pressure with octahedral Ge; (3) isomorphs of room-pressure oxides with 3+ or 4+ transition-metal cations; (4) high-pressure magnesium silicates related to room-pressure aluminates by the substitution 2Al→Mg+Si; and (5) the homologous structures in system Mg-Si-O-H that includes phase B and anhydrous phase B. Each of these criteria can be used to predict other potential octahedral Si phases. Of special interest are predicted structure types that fulfill more than one criterion: Diaspore-type (MgSi)O 2 (OH) 2 , aerugite-type Mg 10 Si 3 O 16 , sphene-type CaSi 2 O 5 , benitoite-type BaSi 4 O 9 , gibbsite-type MgSi(OH) 6 and pseudobrookite-type Fe 2 SiO 5 . (orig.)

  19. A novel isomorphic phase transition in β-pyrochlore oxide KOs2O6: a study using high resolution neutron powder diffraction

    Science.gov (United States)

    Sasai, Kenzo; Kofu, Maiko; Ibberson, Richard M.; Hirota, Kazuma; Yamaura, Jun-ichi; Hiroi, Zenji; Yamamuro, Osamu

    2010-01-01

    We have carried out adiabatic calorimetric and neutron powder diffraction experiments on the β-pyrochlore oxide KOs2O6, which has a superconducting transition at Tc = 9.6 K and another novel transition at Tp = 7.6 K. A characteristic feature of this compound is that the K ions exhibit rattling vibrations in the cages formed by O atoms even at very low temperatures. The temperature and entropy of the Tp transition is in good agreement with previous data measured using a heat relaxation method, indicating that the present sample is of high purity and the transition entropy, 0.296 J K-1 mol-1, does not depend on the calorimetric method used. The neutron powder diffraction data show no peak splitting nor extra peaks over the temperature range between 2 and 295 K, suggesting that the Tp transition is a rather unusual isomorphic transition. Rietveld analysis revealed an anomalous expansion of the lattice and a deformation of the O atom cage below 7.6 K. In the low-temperature phase, the distribution of scattering density corresponding to the K ions becomes broader whilst maintaining its maximum at the cage center. Based on these findings, we suggest that the Tp transition is due to the expansion of the cage volume and cooperative condensation of the K ions into the ground state of the rattling motion.

  20. Crystal structure of calcioburbankite and the characteristic features of the burbankite structure type

    International Nuclear Information System (INIS)

    Belovitskaya, Yu.V.; Pekov, I.V.; Gobechiya, E.R.; Kabalov, Yu.K.; Subbotin, V.V.

    2001-01-01

    The crystal structure of calcioburbankite (Na,Ca) 3 (Ca,RE,Sr,Ba) 3 (CO 3 ) 5 found in carbonatites from Vuoriyarvi (North Kareliya) was solved by the Rietveld method. The experimental data were collected on an ADP-2 diffractometer (λCuK α radiation; Ni filter; 16.00 deg. 1 + α 2 ) reflections was 455). All the calculations were performed within the sp. gr. P6 3 mc; a = 10.4974(1) A, c = 6.4309(1) A, V = 613.72(1) A 3 ; R wp = 2.49%. The structure was refined with the use of the anisotropic thermal parameters for the (Na,Ca) and (Sr,Ba,Ce) cations. The comparison of the crystal structures of all of the known hexagonal representatives of the burbankite family demonstrates that the burbankite structure type (sp. gr. P6 3 mc) is stable, irrespectively of the occupancy of the ten-vertex polyhedra predominantly with Ca, Sr, or Ba cations and the occupancies of the positions in the eight-vertex polyhedra

  1. Subband structure comparison between n- and p- type double delta-doped Ga As quantum wells

    International Nuclear Information System (INIS)

    Rodriguez V, I.; Gaggero S, L.M.

    2004-01-01

    We compute the electron level structure (n-type) and the hole subband structure (p-type) of double -doped GaAs (DDD) quantum wells, considering exchange effects. The Thomas-Fermi (TF), and Thomas-Fermi-Dirac (TFD) approximations have been applied in order to describe the bending of the conduction and valence band, respectively. The electron and the hole subband structure study indicates that exchange effects are more important in p-type DDD quantum wells than in n-type DDD Also our results agree with the experimental data available. (Author) 33 refs., 2 tabs., 5 figs

  2. An Integrated Structural Strength Analysis Method for Spar Type Floating Wind Turbine

    Institute of Scientific and Technical Information of China (English)

    胡志强; 刘毅; 王晋

    2016-01-01

    An integrated structural strength analysis method for a Spar type floating wind turbine is proposed in this paper, and technical issues related to turbine structure modeling and stress combination are also addressed. The NREL-5MW “Hywind” Spar type wind turbine is adopted as study object. Time-domain dynamic coupled simulations are performed by a fully-coupled aero-hydro-servo-elastic tool, FAST, on the purpose of obtaining the dynamic characteristics of the floating wind turbine, and determining parameters for design load cases of finite element calculation. Then design load cases are identified, and finite element analyses are performed for these design load cases. The structural stresses due to wave-induced loads and wind-induced loads are calculated, and then combined to assess the structural strength of the floating wind turbine. The feasibility of the proposed structural strength analysis method for floating wind turbines is then validated.

  3. A Study of the Types of Organizational Structure in Venezuelan University Institutes

    Directory of Open Access Journals (Sweden)

    Rafael Antonio Pertuz Belloso

    2013-12-01

    Full Text Available This study aimed at identifying the type of organizational structure of Venezuelan university institutes. It is a field investigation of a descriptive nature with a non-experimental transactional field design. We worked with a population sample consisting of a director, assistant directors, academic assistant directors and eighty-eight teachers from technological institutes in Cabimas and Maracaibo in Venezuela. A survey, in the form of a questionnaire, was used as the data collection technique, which included 24 items, validated by 5 experts, with Cronbach Alpha reliability of 0.93. The data analysis technique utilized was the percentage frequency distribution. The results indicated the coexistence of bureaucratic structural typologies; departmental and simple. An implementation of a structural migration strategy to the implementation of a matrix-type structure is recommended.

  4. High temperature phase transition of Tm2Ti2O7

    International Nuclear Information System (INIS)

    Shlyakhtina, A.V.; Shcherbakova, L.G.; Knot'ko, A.V.; Larina, L.L.; Borichev, S.A.

    2004-01-01

    A high temperature phase transition type order-disorder is investigated in Tm 2 Ti 2 O 7 at t>1600 Deg C. It is shown that this transformation is irreversible. Ion conductivity of synthesized at 1670 Deg C nanocrystalline Tm 2 Ti 2 O 7 constitutes 2x10 -3 S/cm at 740 Deg C and remains constant after heat treatment at 860 Deg C for 240 h in the air. It is revealed that the conductivity of specimens (grain size of 20-30 nm) on the basis of Tm 2 Ti 2 O 7 high temperature modification with a structure of disordered pyrochlore is independent of grain size [ru

  5. Crystal structures of type IIIH NAD-dependent D-3-phosphoglycerate dehydrogenase from two thermophiles

    International Nuclear Information System (INIS)

    Kumar, S.M.; Pampa, K.J.; Manjula, M.; Hemantha Kumar, G.; Kunishima, Naoki; Lokanath, N.K.

    2014-01-01

    Highlights: • Determined the crystal structures of PGDH from two thermophiles. • Monomer is composed of nucleotide binding domain and substrate binding domain. • Crystal structures of type III H PGDH. - Abstract: In the L-Serine biosynthesis, D-3-phosphoglycerate dehydrogenase (PGDH) catalyzes the inter-conversion of D-3-phosphoglycerate to phosphohydroxypyruvate. PGDH belongs to 2-hydroxyacid dehydrogenases family. We have determined the crystal structures of PGDH from Sulfolobus tokodaii (StPGDH) and Pyrococcus horikoshii (PhPGDH) using X-ray diffraction to resolution of 1.77 Å and 1.95 Å, respectively. The PGDH protomer from both species exhibits identical structures, consisting of substrate binding domain and nucleotide binding domain. The residues and water molecules interacting with the NAD are identified. The catalytic triad residues Glu-His-Arg are highly conserved. The residues involved in the dimer interface and the structural features responsible for thermostability are evaluated. Overall, structures of PGDHs with two domains and histidine at the active site are categorized as type III H and such PGDHs structures having this type are reported for the first time

  6. Left ventricular structure and function in black normotensive type 2 ...

    African Journals Online (AJOL)

    Keywords: Black normotensive patients, left ventricular function, type 2 DM. Résumé ... sickle cell disease and structural heart disease were excluded ... Pulmonary venous flow (PVF) velocity ... had abnormal ECG pattern compared with 30%.

  7. Association of igneous phophate and uranium

    International Nuclear Information System (INIS)

    Loureiro, F.E.V.L.

    1980-10-01

    Data from Catalao permit some brief comments about the association of igneous phosphate and uranium, and on the possible economic importance of this type of mineralization in spite of the low grades of metals observed. Chemical and mineralogical analyses of carbonatites, phosphate ore and different phosphate concentrates, reveal the existence of important low-grade reserves of Th, Nb, Zr, U and La, and possibly of other metals such as V and Cu. Uranium is enriched 1.6 and 1.2 times, respectively, in the residual muds and flotation wastes produced at the processing plant of Goiasfertil operating in the area. The uranium is associated with two types of minerals, the first one comprised primarily of phosphates of the gorceixite group and secondarily of apatite and dahllite. THe second association is with pyrochlore, or rather barium-pyrochlore. Further investigations of similar occurences may define more clearly and specifically the various factors controlling the observed enrichment in heavy elements. (Author) [pt

  8. Electronic structures near surfaces of perovskite type oxides

    International Nuclear Information System (INIS)

    Hara, Toru

    2005-01-01

    This work is intended to draw attention to the origin of the electronic structures near surfaces of perovskite type oxides. Deep states were observed by ultraviolet photoelectron spectroscopic measurements. The film thickness dependent electronic structures near surfaces of (Ba 0.5 Sr 0.5 )TiO 3 thin films were observed. As for the 117-308 nm thick (Ba 0.5 Sr 0.5 )TiO 3 films, deep states were lying at 0.20, 0.55, and 0.85 eV below the quasi-fermi level, respectively. However, as for the 40 nm thick (Ba 0.5 Sr 0.5 )TiO 3 film, the states were overlapped. The A-site doping affected electronic structures near surfaces of SrTiO 3 single crystals. No evolution of deep states in non-doped SrTiO 3 single crystal was observed. However, the evolution of deep states in La-doped SrTiO 3 single crystal was observed

  9. Temperature dependent XAFS studies of local atomic structure of the perovskite-type zirconates

    International Nuclear Information System (INIS)

    Vedrinskii, R. V.; Lemeshko, M. P.; Novakovich, A. A.; Nazarenko, E. S.; Nassif, V.; Proux, O.; Joly, Y.

    2006-01-01

    Temperature dependent preedge and extended x-ray absorption fine structure measurements at the Zr K edge for the perovskite-type zirconates PbZr 0.515 Ti 0.485 O 3 (PZT), PbZrO 3 (PZ), and BaZrO 3 are performed. To carry out a more accurate study of the weak reconstruction of the local atomic structure we employed a combination of two techniques: (i) analysis of the preedge fine structure, and (ii) analysis of the Fourier transform of the difference between χ(k) functions obtained at different temperatures. A detailed investigation of local atomic structure in the cubic phase for all the crystals is also performed. It is shown that neither the displacive nor the order-disorder model can describe correctly the changes of local atomic structure during phase transitions in PZ and PZT. A spherical model describing the local atomic structure of perovskite-type crystals suffering structural phase transitions is proposed

  10. The research of structural features of astralens - nanodimensional carbon particles of fulleroid type

    International Nuclear Information System (INIS)

    Ponomarev, A.N.; Nikitin, V.A.; Rybalko, V.V.

    2006-01-01

    The article is focused on the research of structural features of astralens - nanodimensional carbonic particles of fulleroid type. Astralens are perspective nanomodificators of properties of materials of different types. The potentials os astralens as modificators depend on their characteristic structural features, and in the first place, on the distribution of nanoparticles by sizes. The typical dimensions of astralens are determined to be within the range of 15-75 nm [ru

  11. In and out of the cation pumps: P-type ATPase structure revisited

    DEFF Research Database (Denmark)

    Bublitz, Maike; Poulsen, Hanne; Morth, Jens Preben

    2010-01-01

    Active transport across membranes is a crucial requirement for life. P-type ATPases build up electrochemical gradients at the expense of ATP by forming and splitting a covalent phosphoenzyme intermediate, coupled to conformational changes in the transmembrane section where the ions are translocated....... The marked increment during the last three years in the number of crystal structures of P-type ATPases has greatly improved our understanding of the similarities and differences of pumps with different ion specificities, since the structures of the Ca2+-ATPase, the Na+,K+-ATPase and the H+-ATPase can now...

  12. Dowel-type fastener connections in timber structures subjected to short-term loading

    DEFF Research Database (Denmark)

    Lauritzen Jensen, J.

    Design of dowel-type fastener connections in framed timber structures usually involves a two-step analysis: determination of the distribution of the sectional forces, and design of the eccentrically loaded connections. This report presents an integrated model for design of framed timber structures...

  13. Structural and Thermal Safety Analysis Report for the Type B Radioactive Waste Transport Package

    Energy Technology Data Exchange (ETDEWEB)

    Kim, D. H.; Seo, K. S.; Lee, J. C.; Bang, K. S

    2007-09-15

    We carried out structural safety evaluation for the type B radioactive waste transport package. Requirements for type B packages according to the related regulations such as IAEA Safety Standard Series No. TS-R-1, Korea Most Act. 2001-23 and US 10 CFR Part 71 were evaluated. General requirements for packages such as those for a lifting attachment, a tie-down attachment and pressure condition were considered. For the type B radioactive waste transport package, the structural, thermal and containment analyses were carried out under the normal transport conditions. Also the safety analysis were conducted under the accidental transport conditions. The 9 m drop test, 1 m puncture test, fire test and water immersion test under the accidental transport conditions were consecutively done. The type B radioactive waste transport packages were maintained the structural and thermal integrities.

  14. Theoretical study of disorder in Ti-substituted La2Zr2O7

    International Nuclear Information System (INIS)

    Chartier, Alain; Meis, Constantin; Weber, William J.; Corrales, L. Rene

    2002-01-01

    Pyrochlores have the striking feature that their radiation resistance is highly dependent on their composition. In this work, the propensity of a pyrochlore to transform to a cation-disordered structure and the influence of titanium ions is ascertained from the mechanisms of defect formation. A detailed study of defect formation and migration activation energies in Ti-substituted La 2 Zr 2 O 7 is carried out by modern theoretical computational methods that include the use of a classical interatomic potential with a modified shell model to capture the effects of local charge transfer. The results show that La 2 Zr 2 O 7 has a tendency towards cation disorder, whereas, substitution of Zr with Ti makes this tendency energetically less favorable

  15. Structural and functional salivary disorders in type 2 diabetic patients.

    Science.gov (United States)

    Carda, Carmen; Mosquera-Lloreda, Nezly; Salom, Lucas; Gomez de Ferraris, Maria Elsa; Peydró, Amando

    2006-07-01

    Diabetes mellitus type 2 is the most common metabolic disorder and it causes an important morbimortality. The structural modifications in the parotid gland (sialosis) had already been described in these patients and could result in variations in the salivary composition, as well as an increase in periodontal and dental pathology. To compare the biochemical findings in the saliva and to correlate these biochemical disturbances with the morphologic findings previously described. Clinical information were gathered about 33 patients, 17 had type 2 diabetes. Samples of whole saliva were obtained for biochemical analysis and serum samples to determine metabolic control. In the diabetics saliva we found urea and total proteins increased and reduced levels of microalbumina. Salivary glucose was only augmented in patients with poor metabolic control. Clinical symptoms of xerostomia were present in 76,4% and dental and periodontal disease in 100%. The parotid gland was characterised by the presence of small acini, lipid intracytoplasmic droplets, as well as adipose stroma infiltration. The acinar cytoqueratins expression was heterogeneous and very positive in the hyperplasic ducts. These biochemical disorders in the saliva of the type 2 diabetic patients would be related with the structural changes previously observed in parotid glands.

  16. The Types of Argument Structure Used by Hillary Clinton in the CNN Democratic Presidential Debate

    Directory of Open Access Journals (Sweden)

    Anggie Angeline

    2009-01-01

    Full Text Available This qualitative research was conducted to examine the types of argument structure by Hillary Clinton in part one of the CNN Democratic Presidential Debate since Hillary, who had a great deal of experiences in political parties, was supposed to be able to construct convincing arguments that had good argument structures. The theories used to analyze were Bierman and Assali’s (1996, King’s (n.d. and Stanlick’s (2003. The findings showed that there were five types of argument structure used: serial, linked, convergent, divergent, and hybrid argument structures. The linked argument structure was the argument structure used the most frequently in Hillary’s utterances in the debate, while the divergent was the least one. Thus, it could be concluded that Hillary’s speech in the Presidential Debate was quite interesting since she could combine all the five types of argument structure, though the frequency of using them was not the same and it seems that linked argument structure was the most effective strategy for her in arguing about the politic, economy, and social issues.

  17. Structure of a Kunitz-type potato cathepsin D inhibitor

    Czech Academy of Sciences Publication Activity Database

    Guo, J.; Erskine, P. T.; Coker, A. R.; Wood, S. P.; Cooper, J. B.; Mareš, Michael; Baudyš, Miroslav

    2015-01-01

    Roč. 192, č. 3 (2015), s. 554-560 ISSN 1047-8477 R&D Projects: GA ČR GA15-18929S; GA MŠk LO1302 Institutional support: RVO:61388963 Keywords : potato cathepsin D inhibitor * Kunitz-type protease inhibitor * protein X-ray structure * reactive-site loop * docking Subject RIV: CE - Biochemistry Impact factor: 2.570, year: 2015

  18. Determination of a new structure type in the Sc–Fe–Ge–Sn system

    International Nuclear Information System (INIS)

    Brgoch, Jakoah; Ran, Sheng; Thimmaiah, Srinivasa; Canfield, Paul C.; Miller, Gordon J.

    2013-01-01

    Highlights: ► A new structure type with the composition Sc 4 Fe 5 Ge 6.10(3) Sn 1.47(2) . ► Crystallizes in the space group Immm (No. 71, oI144). ► Sample obtained using a reactive Sn flux. ► Electronic structure calculations indicate polar intermetallic bonding network. - Abstract: A new structure type has been discovered in the system Sc–Fe–Ge–Sn by employing Sn as a flux medium. According to single crystal X-ray diffraction, the new structure has a composition of Sc 4 Fe 5 Ge 6.10(3) Sn 1.47(2) and crystallizes in the space group Immm (No. 71, oI144) with lattice parameters of a = 5.230(1) Å, b = 13.467(3) Å, and c = 30.003(6) Å. The structure is composed of square anti-prismatic clusters that are condensed into zig-zag chains along the [0 1 0] direction. These chains are further condensed through a split Sn/Ge position, forming a three-dimensional network. Magnetization measurements indicate an antiferromagnetic phase transition near 240 K. Electronic structure calculations identified the most favorable bonding network in this new system. Using crystal orbital Hamilton population (COHP) curves and their integrated values (ICOHP), a polar intermetallic bonding network involving Sc–Ge as well as Fe–Sn and Fe–Ge contacts can be assigned to this new structure type.

  19. Quantification of age-related changes in the structure model type and trabecular thickness of human tibial cancellous

    DEFF Research Database (Denmark)

    Ding, Ming; Hvid, I

    2000-01-01

    Structure model type and trabecular thickness are important characteristics in describing cancellous bone architecture. It has been qualitatively observed that a radical change of trabeculae from plate-like to rod-like occurs in aging, bone remodeling, and osteoporosis. Thickness of trabeculae has...... traditionally been measured using model-based histomorphometric methods on two-dimensional (2-D) sections. However, no quantitative study has been published based on three-dimensional (3-D) methods on the age-related changes in structure model type and trabecular thickness for human peripheral (tibial......, structure model type and trabecular thickness were quantified by means of novel 3-D methods. Structure model type was assessed by calculating the structure model index (SMI). The SMI was quantified based on a differential analysis of the triangulated bone surface of a structure. This technique allows...

  20. Cerium intermetallics with TiNiSi-type structure

    Energy Technology Data Exchange (ETDEWEB)

    Janka, Oliver; Niehaus, Oliver; Poettgen, Rainer [Muenster Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie; Chevalier, Bernard [Bordeaux Univ. CNRS (UPR 9048), Pessac (France). Inst. de Chimie de la Matiere Condensee de Bordeaux (ICMCB)

    2016-08-01

    Intermetallic compounds with the equiatomic composition CeTX that crystallize with the orthorhombic TiNiSi-type structure can be synthesized with electron-rich transition metals (T) and X = Zn, Al, Ga, Si, Ge, Sn, As, Sb, and Bi. The present review focusses on the crystal chemistry and chemical bonding of these CeTX phases and on their physical properties, {sup 119}Sn and {sup 121}Sb Moessbauer spectra, high-pressure effects, hydrogenation reactions and the formation of solid solutions in order to elucidate structure-property relationships. This paper is the final one of a series of four reviews on equiatomic intermetallic cerium compounds [Part I: Z. Naturforsch. 2015, 70b, 289; Part II: Z. Naturforsch. 2015, 70b, 695; Part III: Z. Naturforsch. 2016, 71b, 165].

  1. UV laser micromachining of piezoelectric ceramic using a pulsed Nd:YAG laser

    International Nuclear Information System (INIS)

    Zeng, D.W.; Xie, C.S.; Li, K.; Chan, H.L.W.; Choy, C.L.; Yung, K.C.

    2004-01-01

    UV laser (λ=355 nm) ablation of piezoelectric lead zirconate titanate (PZT) ceramics in air has been investigated under different laser parameters. It has been found that there is a critical pulse number (N=750). When the pulse number is smaller than the critical value, the ablation rate decreases with increasing pulse number. Beyond the critical value, the ablation rate becomes constant. The ablation rate and concentrations of O, Zr and Ti on the ablated surface increase with the laser fluence, while the Pb concentration decreases due to the selective evaporation of PbO. The loss of the Pb results in the formation of a metastable pyrochlore phase. ZrO 2 was detected by XPS in the ablated zone. Also, the concentrations of the pyrochlore phase and ZrO 2 increase with increasing laser fluence. These results clearly indicate that the chemical composition and phase structure in the ablated zone strongly depend on the laser fluence. The piezoelectric properties of the cut PZT ceramic samples completely disappear due to the loss of the Pb and the existence of the pyrochlore phase. After these samples were annealed at 1150 C for 1 h in a PbO-controlled atmosphere, their phase structure and piezoelectric properties were recovered again. Finally, 1-3 and concentric-ring 2-2 PZT/epoxy composites were fabricated by UV laser micromachining and their thickness modes were measured by impedance spectrum analysis and a d 33 meter. Both composites show high piezoelectric properties. (orig.)

  2. Frequency Modulation and Absorption Improvement of THz Micro-bolometer with Micro-bridge Structure by Spiral-Type Antennas.

    Science.gov (United States)

    Gou, Jun; Niu, Qingchen; Liang, Kai; Wang, Jun; Jiang, Yadong

    2018-03-05

    Antenna-coupled micro-bridge structure is proven to be a good solution to extend infrared micro-bolometer technology for THz application. Spiral-type antennas are proposed in 25 μm × 25 μm micro-bridge structure with a single separate linear antenna, two separate linear antennas, or two connected linear antennas on the bridge legs, in addition to traditional spiral-type antenna on the support layer. The effects of structural parameters of each antenna on THz absorption of micro-bridge structure are discussed for optimized absorption of 2.52 THz wave radiated by far infrared CO 2 lasers. The design of spiral-type antenna with two separate linear antennas for wide absorption peak and spiral-type antenna with two connected linear antennas for relatively stable absorption are good candidates for high absorption at low absorption frequency with a rotation angle of 360*n (n = 1.6). Spiral-type antenna with extended legs also provides a highly integrated micro-bridge structure with fast response and a highly compatible, process-simplified way to realize the structure. This research demonstrates the design of several spiral-type antenna-coupled micro-bridge structures and provides preferred schemes for potential device applications in room temperature sensing and real-time imaging.

  3. Lanthanide ions doped Y2Sn2O7 nano-particles: low temperature synthesis and photoluminescence study

    International Nuclear Information System (INIS)

    Nigam, Sandeep; Sudarsan, V.; Vatsa, R.K.

    2008-01-01

    During the past decade, pyrochlore-type oxides (A 2 B 2 O 7 ) have emerged as important host matrices for lanthanide doped luminescent materials due to their higher thermal stability. Up to now, conventional solid-state reaction is the most commonly used synthetic method for preparation, of rare-earth pyrochlore oxides. This synthesis route employs a solid-state reaction of metal-oxide with appropriate rare-earth oxides at high temperature (>1200 deg C) for a long time (several days). However, in present work, Y 2 Sn 2 O 7 nanoparticles co-doped with lanthanide ions Tb 3+ and Ce 3+ were prepared based on the urea hydrolysis of Y 3+ , Sn 4+ , and Ln 3+ in ethylene glycol medium at 150 deg C followed by heating at 500, 700 and 900 deg C

  4. Interference enhanced thermoelectricity in quinoid type structures

    Energy Technology Data Exchange (ETDEWEB)

    Strange, M., E-mail: strange@chem.ku.dk; Solomon, G. C. [Nano-Science Center and Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø (Denmark); Seldenthuis, J. S.; Verzijl, C. J. O.; Thijssen, J. M. [Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ Delft (Netherlands)

    2015-02-28

    Quantum interference (QI) effects in molecular junctions may be used to obtain large thermoelectric responses. We study the electrical conductance G and the thermoelectric response of a series of molecules featuring a quinoid core using density functional theory, as well as a semi-empirical interacting model Hamiltonian describing the π-system of the molecule which we treat in the GW approximation. Molecules with a quinoid type structure are shown to have two distinct destructive QI features close to the frontier orbital energies. These manifest themselves as two dips in the transmission, that remain separated, even when either electron donating or withdrawing side groups are added. We find that the position of the dips in the transmission and the frontier molecular levels can be chemically controlled by varying the electron donating or withdrawing character of the side groups as well as the conjugation length inside the molecule. This feature results in a very high thermoelectric power factor S{sup 2}G and figure of merit ZT, where S is the Seebeck coefficient, making quinoid type molecules potential candidates for efficient thermoelectric devices.

  5. Determination of a new structure type in the Sc-Fe-Ge-Sn system

    Energy Technology Data Exchange (ETDEWEB)

    Brgoch, Jakoah [Department of Chemistry, Iowa State University, Ames, IA 50011 (United States); Ran, Sheng [Ames Laboratory, US Department of Energy, Ames, IA 50011 (United States); Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States); Thimmaiah, Srinivasa [Department of Chemistry, Iowa State University, Ames, IA 50011 (United States); Ames Laboratory, US Department of Energy, Ames, IA 50011 (United States); Canfield, Paul C. [Ames Laboratory, US Department of Energy, Ames, IA 50011 (United States); Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States); Miller, Gordon J., E-mail: gmiller@iastate.edu [Department of Chemistry, Iowa State University, Ames, IA 50011 (United States); Ames Laboratory, US Department of Energy, Ames, IA 50011 (United States)

    2013-01-05

    Highlights: Black-Right-Pointing-Pointer A new structure type with the composition Sc{sub 4}Fe{sub 5}Ge{sub 6.10(3)}Sn{sub 1.47(2)}. Black-Right-Pointing-Pointer Crystallizes in the space group Immm (No. 71, oI144). Black-Right-Pointing-Pointer Sample obtained using a reactive Sn flux. Black-Right-Pointing-Pointer Electronic structure calculations indicate polar intermetallic bonding network. - Abstract: A new structure type has been discovered in the system Sc-Fe-Ge-Sn by employing Sn as a flux medium. According to single crystal X-ray diffraction, the new structure has a composition of Sc{sub 4}Fe{sub 5}Ge{sub 6.10(3)}Sn{sub 1.47(2)} and crystallizes in the space group Immm (No. 71, oI144) with lattice parameters of a = 5.230(1) A, b = 13.467(3) A, and c = 30.003(6) A. The structure is composed of square anti-prismatic clusters that are condensed into zig-zag chains along the [0 1 0] direction. These chains are further condensed through a split Sn/Ge position, forming a three-dimensional network. Magnetization measurements indicate an antiferromagnetic phase transition near 240 K. Electronic structure calculations identified the most favorable bonding network in this new system. Using crystal orbital Hamilton population (COHP) curves and their integrated values (ICOHP), a polar intermetallic bonding network involving Sc-Ge as well as Fe-Sn and Fe-Ge contacts can be assigned to this new structure type.

  6. In and out of the cation pumps: P-type ATPase structure revisited

    DEFF Research Database (Denmark)

    Bublitz, Maike; Poulsen, Hanne; Morth, Jens Preben

    2010-01-01

    . The marked increment during the last three years in the number of crystal structures of P-type ATPases has greatly improved our understanding of the similarities and differences of pumps with different ion specificities, since the structures of the Ca2+-ATPase, the Na+,K+-ATPase and the H+-ATPase can now......Active transport across membranes is a crucial requirement for life. P-type ATPases build up electrochemical gradients at the expense of ATP by forming and splitting a covalent phosphoenzyme intermediate, coupled to conformational changes in the transmembrane section where the ions are translocated...... be compared directly. Mechanisms for ion gating, charge neutralization and backflow prevention are starting to emerge from comparative structural analysis; and in combination with functional studies of mutated pumps this provides a framework for speculating on how the ions are bound and released as well...

  7. Structural studies on a non-toxic homologue of type II RIPs from ...

    Indian Academy of Sciences (India)

    Structural studies on a non-toxic homologue of type II RIPs from bitter gourd: Molecular basis of non-toxicity, conformational selection and glycan structure. MS accepted http://www.ias.ac.in/jbiosci. THYAGESHWAR CHANDRAN, ALOK SHARMA and M VIJAYAN. J. Biosci. 40(5), October 2015, 929–941, © Indian Academy of ...

  8. Crystal structure of a novel cysteinless plant Kunitz-type protease inhibitor

    International Nuclear Information System (INIS)

    Hansen, Daiane; Macedo-Ribeiro, Sandra; Verissimo, Paula; Yoo Im, Sonia; Sampaio, Misako Uemura; Oliva, Maria Luiza Vilela

    2007-01-01

    Bauhinia bauhinioides Cruzipain Inhibitor (BbCI) is a cysteine protease inhibitor highly homologous to plant Kunitz-type inhibitors. However, in contrast to classical Kunitz family inhibitors it lacks cysteine residues and therefore disulfide bridges. BbCI is also distinct in the ability to inactivate enzymes belonging to two different classes, cysteine and serine proteases. Besides inhibiting the cysteine protease cruzipain, BbCI also inhibits cathepsin L and the serine proteases HNE (human neutrophil elastase) and PPE (porcine pancreatic elastase). Monoclinic crystals of the recombinant inhibitor that diffract to 1.7 A resolution were obtained using hanging drop method by vapor diffusion at 18 o C. The refined structure shows the conservative β-trefoil fold features of the Kunitz inhibitors. In BbCI, one of the two characteristic S-S bonds is replaced by the water-mediated interaction between Tyr125 and Gly132. In this work we explore the structural differences between Kunitz-type inhibitors and analyze the essential interactions that maintain the protein structural stability preserving its biological function

  9. Foot Type Biomechanics Part 2: are structure and anthropometrics related to function?

    Science.gov (United States)

    Mootanah, Rajshree; Song, Jinsup; Lenhoff, Mark W; Hafer, Jocelyn F; Backus, Sherry I; Gagnon, David; Deland, Jonathan T; Hillstrom, Howard J

    2013-03-01

    Many foot pathologies are associated with specific foot types. If foot structure and function are related, measurement of either could assist with differential diagnosis of pedal pathologies. Biomechanical measures of foot structure and function are related in asymptomatic healthy individuals. Sixty-one healthy subjects' left feet were stratified into cavus (n=12), rectus (n=27) and planus (n=22) foot types. Foot structure was assessed by malleolar valgus index, arch height index, and arch height flexibility. Anthropometrics (height and weight), age, and walking speed were measured. Foot function was assessed by center of pressure excursion index, peak plantar pressure, maximum force, and gait pattern parameters. Foot structure and anthropometric variables were entered into stepwise linear regression models to identify predictors of function. Measures of foot structure and anthropometrics explained 10-37% of the model variance (adjusted R(2)) for gait pattern parameters. When walking speed was included, the adjusted R(2) increased to 45-77% but foot structure was no longer a factor. Foot structure and anthropometrics predicted 7-47% of the model variance for plantar pressure and 16-64% for maximum force parameters. All multivariate models were significant (pFoot structure and function are related in asymptomatic healthy individuals. The structural parameters employed are basic measurements that do not require ionizing radiation and could be used in a clinical setting. Further research is needed to identify additional predictive parameters (plantar soft tissue characteristics, skeletal alignment, and neuromuscular control) and to include individuals with pathology. Copyright © 2012. Published by Elsevier B.V.

  10. Of the crystal chemistry of Ruddlesden-Porter type structures in high Tc ceramic superconductors

    International Nuclear Information System (INIS)

    Dwivedi, A.; Cormack, A.N.

    1990-01-01

    This paper reports on atomistic computer simulation employed to examine the energetics and crystal chemistry of some Ruddlesden-Popper type oxide superconductors. Similar structural patterns have been noticed in the superconducting oxides. The formation of Ruddlesden-Popper type layers (alternating slabs of rocksalt and perovskite structures) is similar in many respects to that seen in the system Sr-Ti-O. However, there are some significant differences, for example, the rocksalt and perovskite blocks in the new superconducting compounds are not necessarily electrically neutral unlike in the Sr-Ti-O system and this may well lead to significant differences in their structural chemistry

  11. Type I Clathrates as Novel Silicon Anodes: An Electrochemical and Structural Investigation

    OpenAIRE

    Li, Ying; Raghavan, Rahul; Wagner, Nicholas A.; Davidowski, Stephen K.; Baggetto, Lo?c; Zhao, Ran; Cheng, Qian; Yarger, Jeffery L.; Veith, Gabriel M.; Ellis?Terrell, Carol; Miller, Michael A.; Chan, Kwai S.; Chan, Candace K.

    2015-01-01

    Silicon clathrates contain cage?like structures that can encapsulate various guest atoms or molecules. An electrochemical evaluation of type I silicon clathrates based on Ba8Al y Si46?y as the anode material for lithium?ion batteries is presented here. Postcycling characterization with nuclear magnetic resonance and X?ray diffraction shows no discernible structural or volume changes even after electrochemical insertion of 44 Li (?1 Li/Si) into the clathrate structure. The observed properties ...

  12. Radioheliograph observations of a pulsating structure associated with a moving type IV burst

    International Nuclear Information System (INIS)

    Pick, M.; Trottet, G.

    1978-01-01

    Observations of a pulsating structure with the Mark II Nancay Radioheliograph are reported. These fluctuations are found to occur early in the development of a moving type IV burst. It is confirmed that the source of these fluctuations is of small extent and that it is embedded in the moving type IV continuum, plausibly at the top of an expanding arch. The observations suggest that the pulsating structure consists of recurrent enhanced pulses (mean recurrency time 1.7 s) followed by trains of periodic pulses (mean periodicity 0.37 s). The intensity of the mean enhanced pulses has a damping time of about 5 s. It is shown that previous interpretation of the pulsating structure by Rosenberg (1970) cannot account for the present observations. (Auth.)

  13. Effect of Different Structure Type Traffic On Railway Line Capacity

    Directory of Open Access Journals (Sweden)

    Gleba Radosław

    2017-04-01

    Full Text Available The article points to methods of analyzing railway traffic conditions based on two parameters: capacity and delay of trains. The impact of the differentiated railway type structure on the capacity of the railway line was presented. Particular attention has been paid to the assessment of commonly used simplifications in analyzes.

  14. Crystallization of sol-gel derived lead zirconate titanate thin films in argon and oxygen atmospheres

    International Nuclear Information System (INIS)

    Bursill, L.A.

    1994-01-01

    Electron diffraction and high-resolution electron microscopic techniques are applied to reveal the mechanisms of crystallization of 75 nm thin films of ferroelectric lead-zirconate-titanate (PZT). Sol-gel methods, followed by pyrolysis at 350 deg C, were used to provide a common starting point after which a variety of rapid-thermal annealing (RTA) experiments in the temperature range 400-700 deg C were made in argon, oxygen and nitrogen/hydrogen atmospheres. The results are interpreted in terms of the crystal chemical analysis, which points out that partial pressure of oxygen and heating rate are important experimental parameters which must be controlled if ferroelectric perovskite-type Pb 2 ZrTiO 6 , rather than pyrochlore-type Pb 2 ZrTiO 6+x , where O < X < 1 or -1 < X < O, is to be obtained after the RTA step. Thus significant improvements in the crystallization of perovskite-type PZT were clearly demonstrated by using argon atmospheres for the RTA step. The results have significance for the production of high-quality ferroelectric thin films, with improved switching and fatigue characteristics, since even small amounts of the pyrochlore phase prove detrimental for these properties. 18 refs., 1 tab., 10 figs

  15. Cryo-EM studies of the structure and dynamics of vacuolar-type ATPases

    Science.gov (United States)

    Mazhab-Jafari, Mohammad T.; Rubinstein, John L.

    2016-01-01

    Electron cryomicroscopy (cryo-EM) has significantly advanced our understanding of molecular structure in biology. Recent innovations in both hardware and software have made cryo-EM a viable alternative for targets that are not amenable to x-ray crystallography or nuclear magnetic resonance (NMR) spectroscopy. Cryo-EM has even become the method of choice in some situations where x-ray crystallography and NMR spectroscopy are possible but where cryo-EM can determine structures at higher resolution or with less time or effort. Rotary adenosine triphosphatases (ATPases) are crucial to the maintenance of cellular homeostasis. These enzymes couple the synthesis or hydrolysis of adenosine triphosphate to the use or production of a transmembrane electrochemical ion gradient, respectively. However, the membrane-embedded nature and conformational heterogeneity of intact rotary ATPases have prevented their high-resolution structural analysis to date. Recent application of cryo-EM methods to the different types of rotary ATPase has led to sudden advances in understanding the structure and function of these enzymes, revealing significant conformational heterogeneity and characteristic transmembrane α helices that are highly tilted with respect to the membrane. In this Review, we will discuss what has been learned recently about rotary ATPase structure and function, with a particular focus on the vacuolar-type ATPases. PMID:27532044

  16. Growth of equilibrium structures built from a large number of distinct component types.

    Science.gov (United States)

    Hedges, Lester O; Mannige, Ranjan V; Whitelam, Stephen

    2014-09-14

    We use simple analytic arguments and lattice-based computer simulations to study the growth of structures made from a large number of distinct component types. Components possess 'designed' interactions, chosen to stabilize an equilibrium target structure in which each component type has a defined spatial position, as well as 'undesigned' interactions that allow components to bind in a compositionally-disordered way. We find that high-fidelity growth of the equilibrium target structure can happen in the presence of substantial attractive undesigned interactions, as long as the energy scale of the set of designed interactions is chosen appropriately. This observation may help explain why equilibrium DNA 'brick' structures self-assemble even if undesigned interactions are not suppressed [Ke et al. Science, 338, 1177, (2012)]. We also find that high-fidelity growth of the target structure is most probable when designed interactions are drawn from a distribution that is as narrow as possible. We use this result to suggest how to choose complementary DNA sequences in order to maximize the fidelity of multicomponent self-assembly mediated by DNA. We also comment on the prospect of growing macroscopic structures in this manner.

  17. Impact of type 2 diabetes and duration of type 2 diabetes on cardiac structure and function

    DEFF Research Database (Denmark)

    Jørgensen, Peter G; Jensen, Magnus T; Mogelvang, Rasmus

    2016-01-01

    BACKGROUND: Contemporary treatment of type 2 diabetes (T2D) has improved patient outcome and may also have affected myocardial structure and function. We aimed to describe the effect of T2D and T2D duration on cardiac structure and function in a large outpatient population. METHODS: We performed...... comprehensive echocardiography on a representative sample of 1004 persons including a representative sample of 770 patients with T2D without known heart disease and 234 age- and sex-matched controls. RESULTS: T2D was associated with increased left ventricular (LV) wall thicknesses and decreased LV internal...... dysfunction persisted after multivariable adjustment (P=0.013). CONCLUSIONS: In patients with T2D, LV structural and functional alterations persist and are accentuated with increasing diabetes duration despite reductions in overall risk of cardiovascular disease in this patient population....

  18. Relaxation path of metastable nanoclusters in oxide dispersion strengthened materials

    Energy Technology Data Exchange (ETDEWEB)

    Ribis, J., E-mail: joel.ribis@cea.fr [DEN-Service de Recherches Métallurgiques Appliquées, CEA, Université Paris-Saclay, F-91191, Gif-sur-Yvette (France); Thual, M.A. [LLB, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191, Gif-sur-Yvette (France); Guilbert, T.; Carlan, Y. de [DEN-Service de Recherches Métallurgiques Appliquées, CEA, Université Paris-Saclay, F-91191, Gif-sur-Yvette (France); Legris, A. [UMET, CNRS/UMR 8207, Bât. C6, Univ. Lille 1, 59655 Villeneuve d’Ascq (France)

    2017-02-15

    ODS steels are a promising class of structural materials for sodium cooled fast reactor application. The ultra-high density of the strengthening nanoclusters dispersed within the ferritic matrix is responsible of the excellent creep properties of the alloy. Fine characterization of the nanoclusters has been conducted on a Fe-14Cr-0.3Ti-0.3Y{sub 2}O{sub 3} ODS material using High Resolution and Energy Filtered Transmission Electron Microscopy. The nanoclusters exhibit a cubic symmetry possibly identified as f.c.c and display a non-equilibrium YTiCrO chemical composition thought to be stabilized by a vacancy supersaturation. These nanoclusters undergo relaxation towards the Y{sub 2}Ti{sub 2}O{sub 7}-like state as they grow. A Cr shell is observed around the relaxed nano-oxides, this size-dependent shell may form after the release of Cr by the particles. The relaxation energy barrier appears to be higher for the smaller particles probably owing to a volume/surface ratio effect in reason to the full coherency of the nanoclusters. - Highlights: • The nanoclusters display a f.c.c. cubic symmetry and a non-equilibrium YTiCrO chemical composition. • During thermal annealing the coherent nanocluster transform into semi-coherent pyrochlore particles. • A Cr ring is observed around the relaxed pyrochlore type particles.

  19. Atlas of fine structures of dynamic spectra of solar type IV-dm and some type II radio bursts

    International Nuclear Information System (INIS)

    Slottje, C.

    1982-01-01

    The author presents an atlas of spectral fine structures of solar radio bursts of types IV and II around 1 m wavelength, as obtained with a multichannel spectrograph at Dwingeloo. The structures form largely a collection of observations of these events during late 1968 through 1974, thus covering almost entirely the declining branch of solar cycle 20. The spectrograph has an extra enhanced contrast output with properties quite different from those of the commonly used swept frequency spectrographs. The corresponding instrumental characteristics and effects are discussed. A classification of fine structures and an analysis of their statistical properties and of those of the pertinent radio events are also given. (Auth.)

  20. Biophysical investigation of type A PutAs reveals a conserved core oligomeric structure

    Energy Technology Data Exchange (ETDEWEB)

    Korasick, David A. [Department of Biochemistry, University of Missouri, Columbia MO USA; Singh, Harkewal [Department of Chemistry, University of Missouri, Columbia MO USA; Pemberton, Travis A. [Department of Chemistry, University of Missouri, Columbia MO USA; Luo, Min [Department of Chemistry, University of Missouri, Columbia MO USA; Dhatwalia, Richa [Department of Chemistry, University of Missouri, Columbia MO USA; Tanner, John J. [Department of Biochemistry, University of Missouri, Columbia MO USA; Department of Chemistry, University of Missouri, Columbia MO USA

    2017-08-01

    Many enzymes form homooligomers, yet the functional significance of self-association is seldom obvious. Herein, we examine the connection between oligomerization and catalytic function for proline utilization A (PutA) enzymes. PutAs are bifunctional enzymes that catalyze both reactions of proline catabolism. Type A PutAs are the smallest members of the family, possessing a minimal domain architecture consisting of N-terminal proline dehydrogenase and C-terminal l-glutamate-γ-semialdehyde dehydrogenase modules. Type A PutAs form domain-swapped dimers, and in one case (Bradyrhizobium japonicum PutA), two of the dimers assemble into a ring-shaped tetramer. Whereas the dimer has a clear role in substrate channeling, the functional significance of the tetramer is unknown. To address this question, we performed structural studies of four-type A PutAs from two clades of the PutA tree. The crystal structure of Bdellovibrio bacteriovorus PutA covalently inactivated by N-propargylglycine revealed a fold and substrate-channeling tunnel similar to other PutAs. Small-angle X-ray scattering (SAXS) and analytical ultracentrifugation indicated that Bdellovibrio PutA is dimeric in solution, in contrast to the prediction from crystal packing of a stable tetrameric assembly. SAXS studies of two other type A PutAs from separate clades also suggested that the dimer predominates in solution. To assess whether the tetramer of B. japonicum PutA is necessary for catalytic function, a hot spot disruption mutant that cleanly produces dimeric protein was generated. The dimeric variant exhibited kinetic parameters similar to the wild-type enzyme. These results implicate the domain-swapped dimer as the core structural and functional unit of type A PutAs.

  1. Structure and organization of heteromeric AMPA-type glutamate receptors.

    Science.gov (United States)

    Herguedas, Beatriz; García-Nafría, Javier; Cais, Ondrej; Fernández-Leiro, Rafael; Krieger, James; Ho, Hinze; Greger, Ingo H

    2016-04-29

    AMPA-type glutamate receptors (AMPARs), which are central mediators of rapid neurotransmission and synaptic plasticity, predominantly exist as heteromers of the subunits GluA1 to GluA4. Here we report the first AMPAR heteromer structures, which deviate substantially from existing GluA2 homomer structures. Crystal structures of the GluA2/3 and GluA2/4 N-terminal domains reveal a novel compact conformation with an alternating arrangement of the four subunits around a central axis. This organization is confirmed by cysteine cross-linking in full-length receptors, and it permitted us to determine the structure of an intact GluA2/3 receptor by cryogenic electron microscopy. Two models in the ligand-free state, at resolutions of 8.25 and 10.3 angstroms, exhibit substantial vertical compression and close associations between domain layers, reminiscent of N-methyl-D-aspartate receptors. Model 1 resembles a resting state and model 2 a desensitized state, thus providing snapshots of gating transitions in the nominal absence of ligand. Our data reveal organizational features of heteromeric AMPARs and provide a framework to decipher AMPAR architecture and signaling. Copyright © 2016, American Association for the Advancement of Science.

  2. UNIFIED CONTROL STRUCTURE OF MULTI-TYPE INTERIOR PERMANENT MAGNET MOTOR

    Directory of Open Access Journals (Sweden)

    M. NORHISAM

    2015-03-01

    Full Text Available This paper presents the control strategy structure to extract the speed torque characteristic for the newly designed three phase Multi Type Interior Permanent Magnet Motor. The proposed structure with the driving circuits exhibit the performance of torque characteristics of the stepper motor and brushless motor with independent coil winding per phase especially used as an in-wheel motor in agricultural applications. Brushless Direct Current motors exhibit characteristics of generating high torque at high speed while the Permanent Magnet Stepper motors has characteristic of generating high torque at low speed. The typical characteristics of the above two are integrated in the proposed structure with a complex control structure that handle the switching complexity and speed control in real time. Thus, a specially designed driving system is essential to drive and control this special motor. The evaluation of the motor mechanical characteristics when applying load torque is also presented. The result determines the practical torque range applicable for each motor configuration and as combined machine.

  3. Types of architectural structures and the use of smart materials

    Science.gov (United States)

    Tavşan, Cengiz; Sipahi, Serkan

    2017-07-01

    about smart materials; the second discusses the types and characteristics of smart materials over the tables detailing their utilization and functions in the structures included in the set of examples. The final section of the study, on the other hand, elaborates on the findings, discussing them with reference to the types of structures.

  4. Numerical analysis and comparison of three types of herringbone frame structure for highway subgrade slopes protection

    Science.gov (United States)

    Nie, Yihua; Tang, Saiqian; Xu, Yang; Mao, Kunli

    2018-04-01

    In order to obtain mechanical response distribution of herringbone frame structure for highway subgrade slopes protection and select the best structure type, 3D numerical models of three types herringbone frame structure were established and analyzed in finite element software ANSYS. Indoor physical model of soil slope protected by herringbone frame structure was built and mechanical response of the frame structure was measured by loading tests. Numerical results indicate slope foot is the stress most disadvantageous location. Comparative analysis shows that structure composed of mortar rubble base layer and precast concrete blocks paving layer is the best one for resisting deformation and structure with cement mortar base layer and precast concrete blocks paving layer is the best one for being of low stress.

  5. Relationship between the structural stability with the types and land uses in southeastern Spain

    International Nuclear Information System (INIS)

    Marin Sanleandro, P.; Sanchez Navarro, A.; Delgado Iniesta, M. J.; Fernandez-Delgado Juarez, M.

    2009-01-01

    Structural stability is one of the most important physical properties and is proposed as an indicator of quality. The aim of this study is to see the possible relationship between this property with soil types and uses of them. In this paper we have selected the Mazarron area based on their environmental characteristics and has taken forty-one topsoil samples, after analysis and study of the relationship between its structural stability with soil types and uses of same, we find a closer relationship in the case of uses that type, so that the natural soil as the percentage of stable aggregates close to 75%, while in soils anthropized this value reaches 44 %. (Author) 6 refs

  6. Structure and Composition of Protein Bodies from Wild-Type and High-Lysine Barley Endosperm

    DEFF Research Database (Denmark)

    Ingversen, J.

    1975-01-01

    Protein bodies were isolated from 13 and 28 day old endosperms of barley mutant 1508 and its wild type, Bomi barley. The fine structure of the isolated protein bodies was determined by electron microscopy, and the proteins present in the preparations characterized by amino-acid analysis and SDS......-polyacrylamidegel electrophoresis. Sections through pellets of isolated protein bodies from both the mutant and the wild type revealed protein body structures corresponding with those observed in sections through the intact starchy endosperms. The majority of the wild-type protein bodies was homogeneous spheres accompanied...... that the wild-type protein bodies contained large amounts of prolamines (the storage protein group which is soluble in 55 % isopropanol) and some glutelins (the storage proteins soluble in dilute alkali), whereas the mutant protein bodies have glutelin as the major component and little prolamines...

  7. Structure-activity relationships of lanostane-type triterpenoids from Ganoderma lingzhi as α-glucosidase inhibitors.

    Science.gov (United States)

    Fatmawati, Sri; Kondo, Ryuichiro; Shimizu, Kuniyoshi

    2013-11-01

    A series of lanostane-type triterpenoids, identified as ganoderma alcohols and ganoderma acids, were isolated from the fruiting body of Ganoderma lingzhi. Some of these compounds were confirmed as active inhibitors of the in vitro human recombinant aldose reductase. This paper aims to explain the structural requirement for α-glucosidase inhibition. Our structure-activity studies of ganoderma alcohols showed that the OH substituent at C-3 and the double-bond moiety at C-24 and C-25 are necessary to increase α-glucosidase inhibitory activity. The structure-activity relationships of ganoderma acids revealed that the OH substituent at C-11 is an important feature and that the carboxylic group in the side chain is essential for the recognition of α-glucosidase inhibitory activity. Moreover, the double-bond moiety at C-20 and C-22 in the side chain and the OH substituent at C-3 of ganoderma acids improve α-glucosidase inhibitory activity. These results provide an approach with which to consider the structural requirements of lanostane-type triterpenoids from G. lingzhi. An understanding of these requirements is considered necessary in order to improve a new type of α-glucosidase inhibitor. Copyright © 2013 Elsevier Ltd. All rights reserved.

  8. Fourier transform infrared microspectroscopic analysis of the effects of cereal type and variety within a type of grain on structural makeup in relation to rumen degradation kinetics.

    Science.gov (United States)

    Walker, Amanda M; Yu, Peiqiang; Christensen, Colleen R; Christensen, David A; McKinnon, John J

    2009-08-12

    The objectives of this study were to use Fourier transform infrared microspectroscopy (FTIRM) to determine structural makeup (features) of cereal grain endosperm tissue and to reveal and identify differences in protein and carbohydrate structural makeup between different cereal types (corn vs barley) and between different varieties within a grain (barley CDC Bold, CDC Dolly, Harrington, and Valier). Another objective was to investigate how these structural features relate to rumen degradation kinetics. The items assessed included (1) structural differences in protein amide I to nonstructural carbohydrate (NSC, starch) intensity and ratio within cellular dimensions; (2) molecular structural differences in the secondary structure profile of protein, alpha-helix, beta-sheet, and their ratio; (3) structural differences in NSC to amide I ratio profile. From the results, it was observed that (1) comparison between grain types [corn (cv. Pioneer 39P78) vs barley (cv. Harrington)] showed significant differences in structural makeup in terms of NSC, amide I to NSC ratio, and rumen degradation kinetics (degradation ratio, effective degradability of dry matter, protein and NSC) (P makeup in terms of amide I, NSC, amide I to NSC ratio, alpha-helix and beta-sheet protein structures, and rumen degradation kinetics (effective degradability of dry matter, protein, and NSC) (P makeup differences between cereal types and between different varieties within a type of grain could be revealed. These structural makeup differences were related to the rate and extent of rumen degradation.

  9. Oxygen potentials of transuranium oxides

    International Nuclear Information System (INIS)

    Haruyoshi Otobe; Mituso Akabori; Arai Yasuo; Kazuo Minato

    2008-01-01

    The oxygen potentials of pyrochlore-type Pu 2 Zr 2 O 7+y , fluorite-type (Pu 0.5 Zr 0.5 )O 2-x and AmO 2-x have been measured by the electromotive force (EMF) method with a zirconia solid-electrolyte. The oxygen potentials of these oxides were reviewed. The phase relations, microstructure, equilibrium state of these oxides were discussed, referring to the isothermal curve of the oxygen potentials. (authors)

  10. Structural, electronic and magnetic properties of chevron-type graphene, BN and BC{sub 2}N nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Guerra, T.; Azevedo, S. [Departamento de Física/CCEN, Universidade Federal da Paraíba, Caixa Postal 5008, 58051-900 João Pessoa, PB (Brazil); Kaschny, J.R. [Instituto Federal da Bahia-Campus Vitória da Conquista, Caixa Postal 3150, 45075-265 Vitória da Conquista, BA (Brazil)

    2017-04-15

    Graphene nanoribbons are predicted to be essential components in future nanoelectronics. The size, edge type, arrangement of atoms and width of nanoribbons drastically change their properties. Boronnitrogencarbon nanoribbons properties are not fully understood so far. In the present contribution it was investigated the structural, electronic and magnetic properties of chevron-type carbon, boron nitride and BC{sub 2}N nanoribbons, using first-principles calculations. The results indicate that the structural stability is closely related to the discrepancies in the bond lengths, which can induce structural deformations and stress. Such nanoribbons present a wide range of electronic behaviors, depending on their composition and particularities of the atomic arrangement. A net magnetic moment is found for structures that present carbon atoms at the nanoribbon borders. Nevertheless, the calculated magnetic moment depends on the peculiarities of the symmetric arrangement of atoms and imbalance of carbon atoms between different sublattices. It was found that all structures which have a significant energy gap do not present magnetic moment, and vice-versa. Such result indicates the strong correlation between the electronic and magnetic properties of the chevron-type nanoribbons. - Highlights: • Small discrepancies between distinct bond lengths can influence the formation energy of the BC{sub 2}N nanoribbons. • The electronic behavior of the BC{sub 2}N chevron-type nanoribbons depends on the atomic arrangement and structural symmetries. • There is a strong correlation between the electronic and magnetic properties for the BC{sub 2}N structures.

  11. Shock modon: a new type of coherent structure in rotating shallow water.

    Science.gov (United States)

    Lahaye, Noé; Zeitlin, Vladimir

    2012-01-27

    We show that a new type of coherent structure, a shock modon, exists in a rotating shallow water model at large Rossby numbers. It is a combination of an asymmetric vortex dipole with a stationary hydraulic jump. The structure is long living, despite the energy dissipation by the hydraulic jump, and moving along a circular path. Collisions of shock modons can be elastic, or lead to formation of shock tripoles.

  12. Analysis of waves in the plasma guided by a periodical vane-type slow wave structure

    International Nuclear Information System (INIS)

    Wu, T.J.; Kou, C.S.

    2005-01-01

    In this study, the dispersion relation has been derived to characterize the propagation of the waves in the plasma guided by a periodical vane-type slow wave structure. The plasma is confined by a quartz plate. Results indicate that there are two different waves in this structure. One is the plasma mode that originates from the plasma surface wave propagating along the interface between the plasma and the quartz plate, and the other is the guide mode that originally travels along the vane-type slow wave structure. In contrast to its original slow wave characteristics, the guide mode becomes a fast wave in the low-frequency portion of the passband, and there exists a cut-off frequency for the guide mode. The vane-type guiding structure has been shown to limit the upper frequency of the passband of the plasma mode, compared with that of the plasma surface wave. In addition, the passband of the plasma mode increases with the plasma density while it becomes narrower for the guide mode. The influences of the parameters of the guiding structure and plasma density on the propagation of waves are also presented

  13. Structural Health Monitoring for a Z-Type Special Vehicle

    Directory of Open Access Journals (Sweden)

    Chaolin Yuan

    2017-06-01

    Full Text Available Nowadays there exist various kinds of special vehicles designed for some purposes, which are different from regular vehicles in overall dimension and design. In that case, accidents such as overturning will lead to large economical loss and casualties. There are still no technical specifications to follow to ensure the safe operation and driving of these special vehicles. Owing to the poor efficiency of regular maintenance, it is more feasible and effective to apply real-time monitoring during the operation and driving process. In this paper, the fiber Bragg grating (FBG sensors are used to monitor the safety of a z-type special vehicle. Based on the structural features and force distribution, a reasonable structural health monitoring (SHM scheme is presented. Comparing the monitoring results with the finite element simulation results guarantees the accuracy and reliability of the monitoring results. Large amounts of data are collected during the operation and driving progress to evaluate the structural safety condition and provide reference for SHM systems developed for other special vehicles.

  14. Brain structural changes and their correlation with vascular disease in type 2 diabetes mellitus patients: a voxel-based morphometric study

    OpenAIRE

    Wang, Chunxia; Fu, Kailiang; Liu, Huaijun; Xing, Fei; Zhang, Songyun

    2014-01-01

    Voxel-based morphometry has been used in the study of alterations in brain structure in type 1 diabetes mellitus patients. These changes are associated with clinical indices. The age at onset, pathogenesis, and treatment of type 1 diabetes mellitus are different from those for type 2 diabetes mellitus. Thus, type 1 and type 2 diabetes mellitus may have different impacts on brain structure. Only a few studies of the alterations in brain structure in type 2 diabetes mellitus patients using voxe...

  15. Ultrasonic measurement of β-type pyrochlore oxide KOs2O6

    Science.gov (United States)

    Kamiya, Ryosuke; Yoshizawa, Masahito; Nakanishi, Yoshiki; Nakamura, Mitsuteru; Yamaura, Jun-ichi; Hiroi, Zenji

    2010-01-01

    We have measured the temperature dependence of the elastic constants of KOs2O6 single crystal. The longitudinal elastic constant 1/3(C11 + 2C12 + 4C44) and the transverse one 1/3(C11 - C12 + C44), which are obtained by the corresponding sound velocities propagating along direction, show a remarkable elastic softening toward low temperatures. No elastic anomaly was observed at the superconducting transition temperature. On the other hand, an anomaly was found at TP = 7.5 K. These results suggests that the irreducible representation of T2 in Td point group play an important role for the phase transition at Tp.

  16. Life Comparative Analysis of Energy Consumption and CO2 Emissions of Different Building Structural Frame Types

    Science.gov (United States)

    Kim, Sangyong; Moon, Joon-Ho; Shin, Yoonseok; Kim, Gwang-Hee; Seo, Deok-Seok

    2013-01-01

    The objective of this research is to quantitatively measure and compare the environmental load and construction cost of different structural frame types. Construction cost also accounts for the costs of CO2 emissions of input materials. The choice of structural frame type is a major consideration in construction, as this element represents about 33% of total building construction costs. In this research, four constructed buildings were analyzed, with these having either reinforced concrete (RC) or steel (S) structures. An input-output framework analysis was used to measure energy consumption and CO2 emissions of input materials for each structural frame type. In addition, the CO2 emissions cost was measured using the trading price of CO2 emissions on the International Commodity Exchange. This research revealed that both energy consumption and CO2 emissions were, on average, 26% lower with the RC structure than with the S structure, and the construction costs (including the CO2 emissions cost) of the RC structure were about 9.8% lower, compared to the S structure. This research provides insights through which the construction industry will be able to respond to the carbon market, which is expected to continue to grow in the future. PMID:24227998

  17. Life Comparative Analysis of Energy Consumption and CO2 Emissions of Different Building Structural Frame Types

    Directory of Open Access Journals (Sweden)

    Sangyong Kim

    2013-01-01

    Full Text Available The objective of this research is to quantitatively measure and compare the environmental load and construction cost of different structural frame types. Construction cost also accounts for the costs of CO2 emissions of input materials. The choice of structural frame type is a major consideration in construction, as this element represents about 33% of total building construction costs. In this research, four constructed buildings were analyzed, with these having either reinforced concrete (RC or steel (S structures. An input-output framework analysis was used to measure energy consumption and CO2 emissions of input materials for each structural frame type. In addition, the CO2 emissions cost was measured using the trading price of CO2 emissions on the International Commodity Exchange. This research revealed that both energy consumption and CO2 emissions were, on average, 26% lower with the RC structure than with the S structure, and the construction costs (including the CO2 emissions cost of the RC structure were about 9.8% lower, compared to the S structure. This research provides insights through which the construction industry will be able to respond to the carbon market, which is expected to continue to grow in the future.

  18. Equipment and building structures ageing management for WWER type NPPs

    International Nuclear Information System (INIS)

    Mayboroda, O.

    2001-01-01

    This report presents the working group 'Equipment and building structures ageing management for WWER type NPPs' activities. The analysis of experience in ageing management, recommendations for regulatory guidelines on ageing management, investigation of case studies, definition suitable communication channels among regulators for ageing related data are given. Analyses of water chemistry, inspection data (safety margins criteria), plugging criteria, volume and time of ECT implementation in all WWER countries are presented. The results of Working group activity show that it is advisable to concentrate efforts on: set up the permanent communication channel among regulators, collection of regulatory criteria for WWER type NPP key components based on understanding of ageing mechanisms and data collection

  19. Observation of Current Structures at Type-III ELM Onset on EAST

    DEFF Research Database (Denmark)

    Yan, Ning; Naulin, Volker; Xu, G.

    structure. To verify the current characteristic of this structure, a mono-polar current filaments model was involved, which can reproduce same pattern commendably. Thus, current transport may dominant in transitional stage and plays an important role in the nonlinear development phase of ELM exhaustive......In far scrape-o layer (SOL), alternating negative and positive burst structures in ion saturation current were detected at the onset of each type-III edge localized mode (ELM) on EAST. Different from the fast streaming phenomenon reported previously, one subsequent positive burst structure appears...... every time in the early phase of ELM. It seems like a quick transitional stage between edge localized mode (MHD) phase and transport phase during the ELM. A pronounced sinusoidal pattern has been observed on the radial magnetic induction signal by Langmuir - magnetic probe, corresponding with almost...

  20. Tangshen Formula Attenuates Colonic Structure Remodeling in Type 2 Diabetic Rats

    DEFF Research Database (Denmark)

    Chen, Pengmin; Zhao, Jingbo; Zhang, Haojun

    2017-01-01

    Aim. This study investigated the effect and mechanism of the Chinese herbal medicine Tangshen Formula (TSF) on GI structure remodeling in the rat model of diabetes. Methods. Type 2 diabetic rats were used. Wet weight per unit length, layer thicknesses, levels of collagens I and III, nuclear factor...

  1. Untitled

    Indian Academy of Sciences (India)

    Materials Science Research Centre, Indian Institute of Technology, Madras 600 036,. India. MS received 10 May 1980. Abstract. Complete series of solid solutions exist in the mixed oxide pyrochlore system, Erº (Vºl. Feºf) vs W:O, with the crystal structure changing from cubic to rhombohedral at x = 0.25. The compounds are ...

  2. Nonlinear dynamic systems identification using recurrent interval type-2 TSK fuzzy neural network - A novel structure.

    Science.gov (United States)

    El-Nagar, Ahmad M

    2018-01-01

    In this study, a novel structure of a recurrent interval type-2 Takagi-Sugeno-Kang (TSK) fuzzy neural network (FNN) is introduced for nonlinear dynamic and time-varying systems identification. It combines the type-2 fuzzy sets (T2FSs) and a recurrent FNN to avoid the data uncertainties. The fuzzy firing strengths in the proposed structure are returned to the network input as internal variables. The interval type-2 fuzzy sets (IT2FSs) is used to describe the antecedent part for each rule while the consequent part is a TSK-type, which is a linear function of the internal variables and the external inputs with interval weights. All the type-2 fuzzy rules for the proposed RIT2TSKFNN are learned on-line based on structure and parameter learning, which are performed using the type-2 fuzzy clustering. The antecedent and consequent parameters of the proposed RIT2TSKFNN are updated based on the Lyapunov function to achieve network stability. The obtained results indicate that our proposed network has a small root mean square error (RMSE) and a small integral of square error (ISE) with a small number of rules and a small computation time compared with other type-2 FNNs. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

  3. Microbial mat ecosystems: Structure types, functional diversity, and biotechnological application

    Directory of Open Access Journals (Sweden)

    Cristina M. Prieto-Barajas

    2018-01-01

    Full Text Available Microbial mats are horizontally stratified microbial communities, exhibiting a structure defined by physiochemical gradients, which models microbial diversity, physiological activities, and their dynamics as a whole system. These ecosystems are commonly associated with aquatic habitats, including hot springs, hypersaline ponds, and intertidal coastal zones and oligotrophic environments, all of them harbour phototrophic mats and other environments such as acidic hot springs or acid mine drainage harbour non-photosynthetic mats. This review analyses the complex structure, diversity, and interactions between the microorganisms that form the framework of different types of microbial mats located around the globe. Furthermore, the many tools that allow studying microbial mats in depth and their potential biotechnological applications are discussed.

  4. Structural barriers to coping with Type 1 Diabetes Mellitus in Ghana ...

    African Journals Online (AJOL)

    Structural barriers to coping with Type 1 Diabetes Mellitus in Ghana: Experiences of diabetic youth and their families. ... Methods: Qualitative study conducted with families with a child with T1DM, receiving care in the greater Accra area. Total of 17 individuals ... Social support networks need to be explored and strengthened.

  5. Type IIA orientifolds on SU(2)-structure manifolds

    Energy Technology Data Exchange (ETDEWEB)

    Danckaert, Thomas

    2010-11-15

    We investigate the possible supersymmetry-preserving orientifold projections of type IIA string theory on a six-dimensional background with SU(2)-structure. We find two categories of projections which preserve half of the low-energy supersymmetry, reducing the effective theory from an N=4 supergravity theory, to an N=2 supergravity. For these two cases, we impose the projection on the low-energy spectrum and reduce the effective N=4 supergravity action accordingly. We can identify the resulting gauged N=2 supergravity theory and bring the action into canonical form. We compute the scalar moduli spaces and characterize the gauged symmetries in terms of the geometry of these moduli spaces. Due to their origin in N=4 supergravity, which is a highly constrained theory, the moduli spaces are of a very simple form. We find that, for suitable background manifolds, isometries in all scalar sectors can become gauged. The obtained gaugings share many features with those of N=2 supergravities obtained previously from other G-structure compactifications. (orig.)

  6. Structure of the atmosphere of late-type stars

    International Nuclear Information System (INIS)

    Straume, Ya.I.

    1976-01-01

    A method of calculation of model atmospheres of late-type stars is described. The model atmospheres have been constructed for effective temperature Tsub(e)=2500, 3000, 3500, 4000, 4500 and 5785 K at solar chemical composition and surface gravities log g = 0.0, 1.0, 2.0, 3.0, 4.0 and 5.0 based on LTE and a plane-parallel horizontally homogeneous structure. Opacity due to H, H - and H 2 - was taken into account. The equation of state includes 10 metals and H 2 , H 2 - and H 2 + molecules. The results are compared with those published elsewhere. A satisfactory agreement is obtained for Tsub(e) > 3000 K

  7. The thermodynamic and structural properties of metallocenes-type random ethylene copolymers

    International Nuclear Information System (INIS)

    Simanke, Adriane G.; Mauler, Raquel S.; Galland, Griselda B.; Alamo, Rufina G.

    2001-01-01

    The properties of a series of random ethylene copolymers prepared with the metallocenes catalytic system rac-Et[Ind] 2 ZrCl 2 /MAO were studied for a large variety of comonomer types. These include the classical 1-alkene type with length up to 10 carbons and those of the cyclic type such as cyclopentadiene and dicyclopentadiene. Under rapid crystallization, the melting temperatures of the newly synthesized copolymers followed the relation of model random copolymers indicating a behavior that conforms to that predicted by Flory's phase equilibrium theory. The molar entropy of fusion is not significantly altered by the comonomer type including the dicyclopentadiene type. All types of comonomers studied showed, for a fixed comonomer content, the same change in properties during annealing, except the ethylene 1-butenes. These latter copolymers and the hydrogenated poly butadiene showed a faster rate of change in thermal properties. This is consistent with a higher molecular diffusion for the butene comonomer than for the rest of comonomers analyzed. The properties of the inter lamellar region were also studied as a function of comonomer type and content following the variation of the amorphous halo extracted from the WAXS diffractograms. The observed systematic decrease in the peak scattering angle with increasing comonomer content indicates a variation of the intermolecular liquid structure. (author)

  8. EXAFS and XANES analysis of plutonium and cerium edges from titanate ceramics for fissile materials disposal

    International Nuclear Information System (INIS)

    Fortner, J. A.; Kropf, A. J.; Bakel, A. J.; Hash, M. C.; Aase, S. B.; Buck, E. C.; Chamerlain, D. B.

    1999-01-01

    We report x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectra from the plutonium L III edge and XANES from the cerium L II edge in prototype titanate ceramic hosts. The titanate ceramics studied are based upon the hafnium-pyrochlore and zirconolite mineral structures and will serve as an immobilization host for surplus fissile materials, containing as much as 10 weight % fissile plutonium and 20 weight % (natural or depleted) uranium. Three ceramic formulations were studied: one employed cerium as a ''surrogate'' element, replacing both plutonium and uranium in the ceramic matrix, another formulation contained plutonium in a ''baseline'' ceramic formulation, and a third contained plutonium in a formulation representing a high-impurity plutonium stream. The cerium XANES from the surrogate ceramic clearly indicates a mixed III-IV oxidation state for the cerium. In contrast, XANES analysis of the two plutonium-bearing ceramics shows that the plutonium is present almost entirely as Pu(IV) and occupies the calcium site in the zirconolite and pyrochlore phases. The plutonium EXAFS real-space structure shows a strong second-shell peak, clearly distinct from that of PuO 2 , with remarkably little difference in the plutonium crystal chemistry indicated between the baseline and high-impurity formulations

  9. Structure- and oil type-based efficacy of emulsion adjuvants.

    Science.gov (United States)

    Jansen, Theo; Hofmans, Marij P M; Theelen, Marc J G; Manders, Frans; Schijns, Virgil E J C

    2006-06-29

    Oil-based emulsions are well-known immunopotentiators for inactivated, "killed" vaccines. We addressed the relationship between emulsion structure and levels of in vivo antibody formation to inactivated New Castle Disease virus (NDV) and Infectious Bronchitis virus (IBV) as antigens in 3-week-old chickens. The use of a polymeric emulsifier allowed for direct comparison of three types of emulsions, water-in-oil (W/O), oil-in-water (O/W) and W/O-in-water (W/O/W), while maintaining an identical content of components for each vehicle. They were prepared with either non-metabolizable, mineral oil or metabolizable, Miglyol 840. In addition, we assessed the inherent release capacity of each emulsion variant in vitro. Remarkably, we noted that W/O-type emulsions induced the best immune responses, while they released no antigen during 3 weeks. In general, mineral oil vaccines showed superior efficacy compared to Miglyol 840-based vaccines.

  10. Universal properties of type IIB and F-theory flux compactifications at large complex structure

    International Nuclear Information System (INIS)

    Marsh, M.C. David; Sousa, Kepa

    2016-01-01

    We consider flux compactifications of type IIB string theory and F-theory in which the respective superpotentials at large complex structure are dominated by cubic or quartic terms in the complex structure moduli. In this limit, the low-energy effective theory exhibits universal properties that are insensitive to the details of the compactification manifold or the flux configuration. Focussing on the complex structure and axio-dilaton sector, we show that there are no vacua in this region and the spectrum of the Hessian matrix is highly peaked and consists only of three distinct eigenvalues (0, 2m 3/2 2 and 8m 3/2 2 ), independently of the number of moduli. We briefly comment on how the inclusion of Kähler moduli affect these findings. Our results generalise those of Brodie & Marsh http://dx.doi.org/10.1007/JHEP01(2016)037, in which these universal properties were found in a subspace of the large complex structure limit of type IIB compactifications.

  11. S K Paranjpe

    Indian Academy of Sciences (India)

    Home; Journals; Pramana – Journal of Physics. S K Paranjpe. Articles written in Pramana – Journal of Physics. Volume 63 Issue 2 August 2004 pp 189-197 Contributed Papers : Neutron diffraction. Structural study and electrical properties of Zr-doped Nd2Sn2O7 pyrochlore compounds · Y D Kolekar S B Kulkarni Keka ...

  12. Actinides compounds for the transmutation: scientific contributions of american and japanese collaborations; Composes d'actinides pour la transmutation: apports scientifiques de collaborations americaines et japonaises

    Energy Technology Data Exchange (ETDEWEB)

    Raison, Ph.; Albiot, T

    2000-07-01

    This paper deals with the minor actinides transmutation and the scientific contribution of the ORNL and the JAERI. It presents researches on the Am-Zr-Y-O system in the framework of the heterogeneous reprocessing, the curium and pyrochlore structures, with the ORNL contribution and phase diagrams, data of Thermodynamics, actinides nitrides, with the JAERI. (A.L.B.)

  13. Actinides compounds for the transmutation: scientific contributions of american and japanese collaborations

    International Nuclear Information System (INIS)

    Raison, Ph.; Albiot, T.

    2000-01-01

    This paper deals with the minor actinides transmutation and the scientific contribution of the ORNL and the JAERI. It presents researches on the Am-Zr-Y-O system in the framework of the heterogeneous reprocessing, the curium and pyrochlore structures, with the ORNL contribution and phase diagrams, data of Thermodynamics, actinides nitrides, with the JAERI. (A.L.B.)

  14. Fine structure near the starting frequency of solar type III radio bursts

    Energy Technology Data Exchange (ETDEWEB)

    Benz, A.O.; Zlobec, P.; Jaeggi, M.

    1982-06-01

    We have systematically analyzed the period in time and frequency adjacent to the beginning of type III bursts digitally recorded at Bleien during the second half of 1980. A surprisingly high percentage (10%, possibly more than 20%) of the type III bursts show fine structure in the form of narrow-banded spikes of 0.05 s and less duration, which form clusters of relatively large bandwidth. These spikes are not totally polarized (contrary to claims in the literature) and they are uniformly distributed over the disk. Individual spikes often show highly variable polarization, which may even change sense. The average degree of polarization of the clouds has a wider distribution than that of the associated type III bursts, but generally the same sign. Spikes are considerably different from type I bursts.

  15. Levels of Urinary Trypsin Inhibitor and Structure of Its Chondroitin Sulphate Moiety in Type 1 and Type 2 Diabetes

    Science.gov (United States)

    Ucciferri, Nadia; Idini, Michela; De Muro, Pierina

    2018-01-01

    Background Diabetes mellitus is a global health problem representing the fifth leading cause of mortality and a major risk factor for cardiovascular diseases. In the last years, we reported an association among urinary trypsin inhibitor (UTI), a small proteoglycan that plays pleiotropic roles in many inflammatory processes, and both type 1 and 2 diabetes and developed a method for its direct quantitation and structural characterization. Methods Urine from 39 patients affected by type 1 diabetes, 32 patients with type 2 diabetes, and 52 controls were analysed. UTI was separated from the main glycosaminoglycans physiologically present in urine by anion exchange chromatography, treated for chondroitin sulphate (CS) chain complete depolymerisation, and analysed for both UTI content and CS structure. UTI identification was performed by nano-LC-MS/MS analysis. Results We evidenced increased UTI levels, as well as reduced sulphation of its CS moiety in association with diabetes, regardless of both age and medium-term glycaemic control. Furthermore, no association between UTI and albumin excretion rate was found. Conclusions Evidences suggest that UTI levels are not directly correlated with renal function or, otherwise, that they may increase before the onset of renal impairment in diabetes, representing a potential marker for the underlying inflammatory condition. PMID:29541644

  16. Pool Structures: A New Type of Interaction Zones of Lithospheric Plate Flows

    Science.gov (United States)

    Garetskyi, R. G.; Leonov, M. G.

    2018-02-01

    Study of tectono-geodynamic clusters of the continental lithosphere (the Sloboda cluster of the East European Platform and the Pamir cluster of Central Asia) permitted identification of pool structures, which are a specific type of zone of intraplate interaction of rock masses.

  17. Crystallization of sol-gel derived lead zirconate titanate thin films in argon and oxygen atmospheres

    Energy Technology Data Exchange (ETDEWEB)

    Bursill, L A [Melbourne Univ., Parkville, VIC (Australia). School of Physics; Brooks, K G [Ecole Polytechnique Federale, Lausanne (Switzerland)

    1994-12-31

    Electron diffraction and high-resolution electron microscopic techniques are applied to reveal the mechanisms of crystallization of 75 nm thin films of ferroelectric lead-zirconate-titanate (PZT). Sol-gel methods, followed by pyrolysis at 350 deg C, were used to provide a common starting point after which a variety of rapid-thermal annealing (RTA) experiments in the temperature range 400-700 deg C were made in argon, oxygen and nitrogen/hydrogen atmospheres. The results are interpreted in terms of the crystal chemical analysis, which points out that partial pressure of oxygen and heating rate are important experimental parameters which must be controlled if ferroelectric perovskite-type Pb{sub 2}ZrTiO{sub 6}, rather than pyrochlore-type Pb{sub 2}ZrTiO{sub 6+x}, where O < X < 1 or -1 < X < O, is to be obtained after the RTA step. Thus significant improvements in the crystallization of perovskite-type PZT were clearly demonstrated by using argon atmospheres for the RTA step. The results have significance for the production of high-quality ferroelectric thin films, with improved switching and fatigue characteristics, since even small amounts of the pyrochlore phase prove detrimental for these properties. 18 refs., 1 tab., 10 figs.

  18. Synthesis, crystal structure, and magnetic properties of novel 2D kagome materials RE{sub 3}Sb{sub 3}Mg{sub 2}O{sub 14} (RE = La, Pr, Sm, Eu, Tb, Ho): Comparison to RE{sub 3}Sb{sub 3}Zn{sub 2}O{sub 14} family

    Energy Technology Data Exchange (ETDEWEB)

    Sanders, M.B.; Baroudi, K.M.; Krizan, J.W.; Mukadam, O.A.; Cava, R.J. [Department of Chemistry, Princeton University, Princeton, NJ (United States)

    2016-10-15

    The crystal structures and magnetic properties of RE{sub 3}Sb{sub 3}Mg{sub 2}O{sub 14} (RE = La, Pr, Sm, Eu, Tb, Ho) with a perfect kagome lattice are presented and compared to RE{sub 3}Sb{sub 3}Zn{sub 2}O{sub 14}. Rietveld structure refinements were performed using X-ray diffraction data, indicating that the layered compounds are fully structurally ordered. The compounds crystallize in a rhombohedral supercell of the cubic pyrochlore structure, in the space group R-3m. Magnetic susceptibility measurements show no signs of magnetic ordering above 2 K. The RE{sub 3}Sb{sub 3}Mg{sub 2}O{sub 14} family is similar to that of RE{sub 3}Sb{sub 3}Zn{sub 2}O{sub 14}; however, the series reported here features a fully ordered distribution of cations in both the nonmagnetic antimony and magnetic rare earth kagome lattices. Unlike the offsite disorder that Zn{sup 2+} experiences in RE{sub 3}Sb{sub 3}Zn{sub 2}O{sub 14}, the magnesium sites in RE{sub 3}Sb{sub 3}Mg{sub 2}O{sub 14} are completely ordered. Here we compare the magnetic properties in both series of kagome compounds to determine how significant Zn{sup 2+}'s positional ordering is within this structure type. The compounds reported here appear to be relatively defect-free and are therefore model systems for investigating magnetic frustration on an ideal 2D rare earth kagome lattice. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  19. PREDICTING APHASIA TYPE FROM BRAIN DAMAGE MEASURED WITH STRUCTURAL MRI

    Science.gov (United States)

    Yourganov, Grigori; Smith, Kimberly G.; Fridriksson, Julius; Rorden, Chris

    2015-01-01

    Chronic aphasia is a common consequence of a left-hemisphere stroke. Since the early insights by Broca and Wernicke, studying the relationship between the loci of cortical damage and patterns of language impairment has been one of the concerns of aphasiology. We utilized multivariate classification in a cross-validation framework to predict the type of chronic aphasia from the spatial pattern of brain damage. Our sample consisted of 98 patients with five types of aphasia (Broca’s, Wernicke’s, global, conduction, and anomic), classified based on scores on the Western Aphasia Battery. Binary lesion maps were obtained from structural MRI scans (obtained at least 6 months poststroke, and within 2 days of behavioural assessment); after spatial normalization, the lesions were parcellated into a disjoint set of brain areas. The proportion of damage to the brain areas was used to classify patients’ aphasia type. To create this parcellation, we relied on five brain atlases; our classifier (support vector machine) could differentiate between different kinds of aphasia using any of the five parcellations. In our sample, the best classification accuracy was obtained when using a novel parcellation that combined two previously published brain atlases, with the first atlas providing the segmentation of grey matter, and the second atlas used to segment the white matter. For each aphasia type, we computed the relative importance of different brain areas for distinguishing it from other aphasia types; our findings were consistent with previously published reports of lesion locations implicated in different types of aphasia. Overall, our results revealed that automated multivariate classification could distinguish between aphasia types based on damage to atlas-defined brain areas. PMID:26465238

  20. Predicting aphasia type from brain damage measured with structural MRI.

    Science.gov (United States)

    Yourganov, Grigori; Smith, Kimberly G; Fridriksson, Julius; Rorden, Chris

    2015-12-01

    Chronic aphasia is a common consequence of a left-hemisphere stroke. Since the early insights by Broca and Wernicke, studying the relationship between the loci of cortical damage and patterns of language impairment has been one of the concerns of aphasiology. We utilized multivariate classification in a cross-validation framework to predict the type of chronic aphasia from the spatial pattern of brain damage. Our sample consisted of 98 patients with five types of aphasia (Broca's, Wernicke's, global, conduction, and anomic), classified based on scores on the Western Aphasia Battery (WAB). Binary lesion maps were obtained from structural MRI scans (obtained at least 6 months poststroke, and within 2 days of behavioural assessment); after spatial normalization, the lesions were parcellated into a disjoint set of brain areas. The proportion of damage to the brain areas was used to classify patients' aphasia type. To create this parcellation, we relied on five brain atlases; our classifier (support vector machine - SVM) could differentiate between different kinds of aphasia using any of the five parcellations. In our sample, the best classification accuracy was obtained when using a novel parcellation that combined two previously published brain atlases, with the first atlas providing the segmentation of grey matter, and the second atlas used to segment the white matter. For each aphasia type, we computed the relative importance of different brain areas for distinguishing it from other aphasia types; our findings were consistent with previously published reports of lesion locations implicated in different types of aphasia. Overall, our results revealed that automated multivariate classification could distinguish between aphasia types based on damage to atlas-defined brain areas. Copyright © 2015 Elsevier Ltd. All rights reserved.

  1. Earthquake-proof support structures for the recycling pump in FBR type reactors

    International Nuclear Information System (INIS)

    Nakagawa, Masaki; Shigeta, Masayuki.

    1984-01-01

    Purpose: To improve the earthquake proofness of the recycling pump for use in FBR type reactors upon earthquake by reducing the vibration response of the pump. Constitution: The outer casing of a recycle pump suspended into liquid sodium is extended to the portion that penetrates a reactor core support structures. Support structures surrounding the outer side of the recycling pump are disposed with a gap not restraining the free thermal deformations of the recycling pump to the inside of the partition wall structures and the portion of the recycling pump penetrating the reator core support structures, to integrate the support structures with the reactor core support structures. Accordingly, there are no interferences between the recycling pump and the support structures with respect to the thermal deformations that change gradually with time. Upon vibrating under the rapidly changing external forces of earthquakes, however, the pressure resulted to the liquid in the gap due to the vibrations of the recycling pump is transmitted with no escape to the support structures, the recycling pump and the support structures integrally resist the vibrations thereby enabling to reduce the vibrations in the recycling pumps. (Horiuchi, T.)

  2. Comparative study on the effects of type 1 and type 2 diabetes on structural changes and hormonal output of the adrenal cortex in male Wistar rats

    Directory of Open Access Journals (Sweden)

    Elahi-Moghaddam Zohreh

    2013-01-01

    Full Text Available Abstract Introduction Diabetes is one of the most common endocrine disorders characterized by hyperglycemia due to defects in insulin secretion, insulin function, or both. Causing dysfunction in the body general metabolism, diabetes-induced chronic hyperglycemia leads to alterations in those endocrine glands involved in regulating the body metabolism. In this line, the present study has been conducted to investigate the effects of type 1 and type 2 diabetes on the structural changes and hormonal output of the adrenal cortex in male Wistar rat. Methods Eighteen male Wistar rats were divided into three groups including control, experimental type 1 diabetes (subcutaneous injection of 135 mg/kg alloxan and experimental type 2 diabetes (8 weeks treatment with drinking water containing 10% fructose. Two months after the induction of both types of diabetes, the level of blood biochemical factors (glucose, insulin, cortisol, triglycerides, cholesterol, LDL, and HDL were measured. Structural changes of the adrenal cortex were then evaluated, using stereological techniques. Results Serum biochemical analysis showed significant difference in the levels of glucose, triglycerides, insulin and cortisol in experimental groups, compared to the control. The results of structural alterations were also indicative of increase in adrenal cortex volume in both types of diabetes. Conclusion Probably through increasing HPA axis activity, type1 diabetes-induced hyperglycemia leads to adrenal hypertrophy and increase the hormonal output of adrenal gland.

  3. Crystal structure of alluaudite-type Na4Co(MoO4)3.

    Science.gov (United States)

    Nasri, Rawia; Fakhar Bourguiba, Noura; Zid, Mohamed Faouzi; Driss, Ahmed

    2014-09-01

    The title compound, tetra-sodium cobalt(II) tris-[molyb-date(IV)], was prepared by solid-state reactions. The structure is isotypic with Na3In2(AsO4)3 and Na3In2(PO4)3. The main structural feature is the presence of infinite chains of edge-sharing X 2O10 (X = Co/Na) dimers, which are linked by MoO4 tetra-hedra, forming a three-dimensional framework enclosing two types of hexa-gonal tunnels in which Na(+) cations reside. In this alluaudite structure, Co and Na atoms are located at the same general site with occupancies of 0.503 (5) and 0.497 (6), respectively. The other three Na and one of the two Mo atoms lie on special positions (site symmetries 2, -1, 2 and 2, respectively). The structure is compared with similar structures and other members of alluaudite family.

  4. Design study of an IHX support structure for a POOL-TYPE Sodium-cooled fast reactor

    International Nuclear Information System (INIS)

    Park, Chang Gyu; Kim, Jong Bum; Lee, Jae Han

    2009-01-01

    The IHX (Intermediate Heat eXchanger) for a pool-type SFR (Sodium-cooled Fast Reactor) system transfers heat from the primary high temperature sodium to the intermediate cold temperature sodium. The upper structure of the IHX is a coaxial structure designed to form a flow path for both the secondary high temperature and low temperature sodium. The coaxial structure of the IHX consists of a central downcomer and riser for the incoming and outgoing intermediate sodium, respectively. The IHX of a pool-type SFR is supported at the upper surface of the reactor head with an IHX support structure that connects the IHX riser cylinder to the reactor head. The reactor head is generally maintained at the low temperature regime, but the riser cylinder is exposed in the elevated temperature region. The resultant complicated temperature distribution of the co-axial structure including the IHX support structure may induce a severe thermal stress distribution. In this study, the structural feasibility of the current upper support structure concept is investigated through a preliminary stress analysis and an alternative design concept to accommodate the IHTS (Intermediate Heat Transport System) piping expansion loads and severe thermal stress is proposed. Through the structural analysis it is found that the alternative design concept is effective in reducing the thermal stress and acquiring structural integrity

  5. Tuning structure in epitaxial Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–PbTiO{sub 3} thin films by using miscut substrates

    Energy Technology Data Exchange (ETDEWEB)

    Mietschke, M., E-mail: m.mietschke@ifw-dresden.de [IFW Dresden, P.O. Box 270116, D-01171 Dresden (Germany); Dresden University of Technology, Faculty of Mechanical Science and Engineering, D-01062 Dresden (Germany); Oswald, S.; Fähler, S. [IFW Dresden, P.O. Box 270116, D-01171 Dresden (Germany); Schultz, L. [IFW Dresden, P.O. Box 270116, D-01171 Dresden (Germany); Dresden University of Technology, Faculty of Mechanical Science and Engineering, D-01062 Dresden (Germany); Hühne, R. [IFW Dresden, P.O. Box 270116, D-01171 Dresden (Germany)

    2015-08-31

    Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–PbTiO{sub 3} (PMN–PT) is one of the most promising ferroelectric material for actuator, dielectric and electrocaloric applications. However, oriented and phase pure thin films are essential to use the outstanding properties of these compounds. In this work it is demonstrated that the use of miscut substrates influences the growth mechanism leading to a significantly broader deposition window to achieve the required film quality. Therefore, epitaxial 0.68Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–0.32PbTiO{sub 3} films were grown by pulsed laser deposition on (001)-oriented single crystalline SrTiO{sub 3} (STO) substrates with a miscut angle between 0 and 15° towards the [100] direction using a conducting La{sub 0.7}Sr{sub 0.3}CoO{sub 3} buffer layer. The influence of the vicinal angle on the PMN–PT structure was studied by high resolution X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. A nearly pure perovskite phase growth with a cube-on-cube epitaxial relationship was obtained on all miscut STO substrates, whereas a significant volume fraction of the pyrochlore phase was present on the standard substrate. Reciprocal space measurements revealed a peak split of the perovskite reflections indicating structural variants of PMN–PT with different c/a ratios. An additional tilting of the PMN–PT planes with respect to the buffer layer was observed on some samples, which might be explained with the incorporation of dislocations according to the Nagai model. Polarization loops were measured in a temperature range between room temperature and 150 °C showing a sharp drop of the remanent polarization above 65 °C on vicinal substrates. - Highlights: • Epitaxial growth of pure perovskite Pb (Mg{sub 1}/{sub 3}Nb{sub 2}/{sub 3})O{sub 3}–PbTiO{sub 3} on miscut SrTiO{sub 3}. • Significant broadening of the deposition window for pyrochlore-free films. • Dependence of the structural parameters

  6. Investigation of fluid-structure interaction with various types of junction coupling

    Science.gov (United States)

    Ahmadi, A.; Keramat, A.

    2010-10-01

    In this study of water hammer with fluid-structure interaction (FSI) the main aim was the investigation of junction coupling effects. Junction coupling effects were studied in various types of discrete points, such as pumps, valves and branches. The emphasis was placed on an unrestrained pump and branch in the system, and the associated relations were derived for modelling them. Proposed relations were considered as boundary conditions for the numerical modelling which was implemented using the finite element method for the structural equations and the method of characteristics for the hydraulic equations. The results can be used by engineers in finding where junction coupling is significant.

  7. New tetragonal derivatives of cubic NaZn13-type structure: RNi6Si6 compounds, crystal structure and magnetic ordering (R=Y, La, Ce, Sm, Gd–Yb)

    International Nuclear Information System (INIS)

    Pani, M.; Manfrinetti, P.; Provino, A.; Yuan, Fang; Mozharivskyj, Y.; Morozkin, A.V.; Knotko, A.V.; Garshev, A.V.; Yapaskurt, V.O.; Isnard, O.

    2014-01-01

    Novel RNi 6 Si 6 compounds adopt the new CeNi 6 Si 6 -type structure for R=La–Ce (tP52, space group P4/nbm N 125-1) and new YNi 6 Si 6 -type structure for R=Y, Sm, Gd–Yb (tP52, space group P4 ¯ b2N 117) that are tetragonal derivative of NaZn 13 -type structure, like LaCo 9 Si 4 -type. The CeNi 6 Si 6 , GdNi 6 Si 6 , TbNi 6 Si 6 , DyNi 6 Si 6 and HoNi 6 Si 6 compounds are Curie–Weiss paramagnets down to ∼30 K, and do not order magnetically down to 5 K. However, the inverse paramagnetic susceptibility of LaNi 6 Si 6 does not follow Curie–Weiss law. The DyNi 6 Si 6 shows ferromagnetic-like saturation behaviour at 5 K in applied fields of 50 kOe, giving rise to a magnetic moment value of 6.5 μ B /f.u. in 50 kOe. The powder neutron diffraction study in zero applied filed indicates square modulated the c-collinear antiferromagnetic ordering of TbNi 6 Si 6 with K=[±1/4, ±1/4, 0] wave vector below ∼10 K. - Graphical abstract: Novel (La, Ce)Ni 6 Si 6 compounds adopt the new CeNi 6 Si 6 -type structure and (Y, Sm, Gd–Yb) adopt the new YNi 6 Si 6 -type structure that are tetragonal derivative of NaZn 13 -type structure, like LaCo 9 Si 4 -type. The CeNi 6 Si 6 , GdNi 6 Si 6 , TbNi 6 Si 6 , DyNi 6 Si 6 and HoNi 6 Si 6 compounds are Curie–Weiss paramagnets down to ∼30 K, and do not order magnetically down to 4.2 K. The powder neutron diffraction study in zero applied filed indicates square modulated the c-collinear antiferromagnetic ordering of TbNi 6 Si 6 with K=[±1/4, ±1/4, 0] wave vector below ∼10 K. Display Omitted - Highlights: • The new (La, Ce)Ni 6 Si 6 compounds adopt the new CeNi 6 Si 6 -type structure. • The new (Y, Sm, Gd–Yb)Ni 6 Si 6 compounds adopt the new YNi 6 Si 6 -type structure. • TbNi 6 Si 6 has square modulated c-collinear antiferromagnetic ordering below ∼10 K

  8. Electronic structure and p-type doping of ZnSnN2

    Science.gov (United States)

    Wang, Tianshi; Janotti, Anderson; Ni, Chaoying

    ZnSnN2 is a promising solar-cell absorber material composed of earth abundant elements. Little is known about doping, defects, and how the valence and conduction bands in this material align with the bands in other semiconductors. Using density functional theory with the the Heyd-Scuseria-Ernzerhof hybrid functional (HSE06), we investigate the electronic structure of ZnSnN2, its band alignment to other semiconductors, such as GaN and ZnO, the possibility of p-type doping, and the possible causes of the observed unintentional n-type conductivity. We find that the position of the valence-band maximum of ZnSnN2 is 0.55 eV higher than that of GaN, yet the conduction-band minimum is close to that in ZnO. As possible p-type dopants, we explore Li, Na, and K substituting on the Zn site. Finally, we discuss the cause of unintentional n-type conductivity by analyzing the position of the conduction-band minimum with respect to that of GaN and ZnO.

  9. Structural characterization of CFA/III and Longus type IVb pili from enterotoxigenic Escherichia coli.

    Science.gov (United States)

    Kolappan, Subramaniapillai; Roos, Justin; Yuen, Alex S W; Pierce, Owen M; Craig, Lisa

    2012-05-01

    The type IV pili are helical filaments found on many Gram-negative pathogenic bacteria, with multiple diverse roles in pathogenesis, including microcolony formation, adhesion, and twitching motility. Many pathogenic enterotoxigenic Escherichia coli (ETEC) isolates express one of two type IV pili belonging to the type IVb subclass: CFA/III or Longus. Here we show a direct correlation between CFA/III expression and ETEC aggregation, suggesting that these pili, like the Vibrio cholerae toxin-coregulated pili (TCP), mediate microcolony formation. We report a 1.26-Å resolution crystal structure of CofA, the major pilin subunit from CFA/III. CofA is very similar in structure to V. cholerae TcpA but possesses a 10-amino-acid insertion that replaces part of the α2-helix with an irregular loop containing a 3(10)-helix. Homology modeling suggests a very similar structure for the Longus LngA pilin. A model for the CFA/III pilus filament was generated using the TCP electron microscopy reconstruction as a template. The unique 3(10)-helix insert fits perfectly within the gap between CofA globular domains. This insert, together with differences in surface-exposed residues, produces a filament that is smoother and more negatively charged than TCP. To explore the specificity of the type IV pilus assembly apparatus, CofA was expressed heterologously in V. cholerae by replacing the tcpA gene with that of cofA within the tcp operon. Although CofA was synthesized and processed by V. cholerae, no CFA/III filaments were detected, suggesting that the components of the type IVb pilus assembly system are highly specific to their pilin substrates.

  10. Peculiarities of crystalline structure and mechanism of disordering of anion sublattice in superionic conductors of LaF3 structural type

    International Nuclear Information System (INIS)

    Krivorotov, V.F.; Fridman, A.A.

    2005-01-01

    On the basis of the analysis of LaF 3 type lattice structure the physical process of disordering of tysonit type ionic crystals is considered in the region of superionic phase transitions. The correlation of cell movement of disordering sublattice ions with parameter dynamics of Raman scattering spectrum of these crystals is observed. The anomaly behaviour of Raman scattering frequencies and intensities of lines 370, 392 sm -1 (LaF 3 ) and 304, 376, 404 sm -1 (PrF 3 ) in three intervals: 160-180, 260-290, and 440-480 K is obtained. Two more high temperature ones are connected with anion sublattice disordering process in the region of phase transitions. Excessive scattering in the region 160-180 K is described by the change of oscillation state of fluoride ions in small displacements in splitted site positions with several potential minimums. It is shown in the framework of splitted sites model that the possibility of thermoactivational formation of interstitials which are comparable with the size of mobile ions is due to the peculiarities of the structure of tysonit type ionic crystals. (author)

  11. Effects of Structured Versus Usual Care on Renal Endpoint in Type 2 Diabetes: The SURE Study

    Science.gov (United States)

    Chan, Juliana C.; So, Wing-Yee; Yeung, Chun-Yip; Ko, Gary T.; Lau, Ip-Tim; Tsang, Man-Wo; Lau, Kam-Piu; Siu, Sing-Chung; Li, June K.; Yeung, Vincent T.; Leung, Wilson Y.; Tong, Peter C.

    2009-01-01

    OBJECTIVE Multifaceted care has been shown to reduce mortality and complications in type 2 diabetes. We hypothesized that structured care would reduce renal complications in type 2 diabetes. RESEARCH DESIGN AND METHODS A total of 205 Chinese type 2 diabetic patients from nine public hospitals who had plasma creatinine levels of 150–350 μmol/l were randomly assigned to receive structured care (n = 104) or usual care (n = 101) for 2 years. The structured care group was managed according to a prespecified protocol with the following treatment goals: blood pressure triglyceride 500 μmol/l or dialysis). RESULTS Of these 205 patients (mean ± SD age 65 ± 7.2 years; disease duration 14 ± 7.9 years), the structured care group achieved better control than the usual care group (diastolic blood pressure 68 ± 12 vs. 71 ± 12 mmHg, respectively, P = 0.02; A1C 7.3 ± 1.3 vs. 8.0 ± 1.6%, P structured care (23.1%, n = 24) and usual care (23.8%, n = 24; NS) groups had similar end points, but more patients in the structured care group attained ≥3 treatment goals (61%, n = 63, vs. 28%, n = 28; P < 0.001). Patients who attained ≥3 treatment targets (n = 91) had reduced risk of the primary end point (14 vs. 34; relative risk 0.43 [95% CI 0.21–0.86] compared with that of those who attained ≤2 targets (n = 114). CONCLUSIONS Attainment of multiple treatment targets reduced the renal end point and death in type 2 diabetes. In addition to protocol, audits and feedback are needed to improve outcomes. PMID:19460913

  12. Effect of annealing temperature on the structural, photoluminescence and magnetic properties of sol-gel derived Magnetoplumbite-type (M-type) hexagonal strontium ferrite

    International Nuclear Information System (INIS)

    Teh, Geok Bee; Wong, Yat Choy; Tilley, Richard D.

    2011-01-01

    Magnetoplumbite-type (M-type) hexagonal strontium ferrite particles were synthesized via sol-gel technique employing ethylene glycol as the gel precursor at two different calcination temperatures (800 and 1000 deg. C). Structural properties were systematically investigated via X-ray diffraction (XRD), field emission scanning electron microscopy, high resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA), photoluminescence spectrophotometry and superconducting quantum interference device magnetometer. XRD results showed that the sample synthesized at 1000 deg. C was of single-phase with a space group of P6 3 /mmc and lattice cell parameter values of a=5.882 A and c=23.048 A. EDS confirmed the composition of strontium ferrite calcined at 1000 deg. C being mainly of M-type SrFe 12 O 19 with HRTEM micrographs confirming the ferrites exhibiting M-type long range ordering along the c-axis of the crystal structure. The photoluminescence (PL) property of strontium ferrite was examined at excitation wavelengths of 260 and 270 nm with significant PL emission peaks centered at 350 nm being detected. Strontium ferrite annealed at higher temperature (1000 deg. C) was found to have grown into larger particle size, having higher content of oxygen vacancies and exhibited 83-85% more intense PL. Both the as-prepared strontium ferrites exhibited significant oxygen vacancies defect structures, which were verified via TGA. Higher calcination temperature turned strontium ferrite into a softer ferrite. - Highlights: → High annealing temperature produced M-type ferrite with higher oxygen vacancies. → Photoluminescence intensity is proportional to the existence of oxygen vacancies. → XRD data showed cell contraction well suited to the change of oxygen vacancies. → Shift in hysteresis loop due to defect-induced exchange bias was observed.

  13. Effect of annealing temperature on the structural, photoluminescence and magnetic properties of sol-gel derived Magnetoplumbite-type (M-type) hexagonal strontium ferrite

    Energy Technology Data Exchange (ETDEWEB)

    Teh, Geok Bee, E-mail: sharonteh2009@gmail.com [Division of Bioscience and Chemistry, School of Arts and Science, Tunku Abdul Rahman College, Jalan Genting Kelang, 53300 Kuala Lumpur (Malaysia); Wong, Yat Choy [Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, PO Box 218, Hawthorn, Victoria 3122 (Australia); Tilley, Richard D. [School of Chemical and Physical Sciences, MacDiarmid Institute of Advanced Materials and Nanotechnology, Victoria University of Wellington, PO Box 600, Wellington (New Zealand)

    2011-09-15

    Magnetoplumbite-type (M-type) hexagonal strontium ferrite particles were synthesized via sol-gel technique employing ethylene glycol as the gel precursor at two different calcination temperatures (800 and 1000 deg. C). Structural properties were systematically investigated via X-ray diffraction (XRD), field emission scanning electron microscopy, high resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA), photoluminescence spectrophotometry and superconducting quantum interference device magnetometer. XRD results showed that the sample synthesized at 1000 deg. C was of single-phase with a space group of P6{sub 3}/mmc and lattice cell parameter values of a=5.882 A and c=23.048 A. EDS confirmed the composition of strontium ferrite calcined at 1000 deg. C being mainly of M-type SrFe{sub 12}O{sub 19} with HRTEM micrographs confirming the ferrites exhibiting M-type long range ordering along the c-axis of the crystal structure. The photoluminescence (PL) property of strontium ferrite was examined at excitation wavelengths of 260 and 270 nm with significant PL emission peaks centered at 350 nm being detected. Strontium ferrite annealed at higher temperature (1000 deg. C) was found to have grown into larger particle size, having higher content of oxygen vacancies and exhibited 83-85% more intense PL. Both the as-prepared strontium ferrites exhibited significant oxygen vacancies defect structures, which were verified via TGA. Higher calcination temperature turned strontium ferrite into a softer ferrite. - Highlights: > High annealing temperature produced M-type ferrite with higher oxygen vacancies. > Photoluminescence intensity is proportional to the existence of oxygen vacancies. > XRD data showed cell contraction well suited to the change of oxygen vacancies. > Shift in hysteresis loop due to defect-induced exchange bias was observed.

  14. Influence of Boundary Conditions on the Simulation of a Diamond-Type Lattice Structure: A Preliminary Study

    Directory of Open Access Journals (Sweden)

    Patrick Terriault

    2017-01-01

    Full Text Available Emergent additive manufacturing processes allow the use of metallic porous structures in various industrial applications. Because these structures comprise a large number of ordered unit cells, their design using conventional modeling approaches, such as finite elements, becomes a real challenge. A homogenization technique, in which the lattice structure is simulated as a fully dense volume having equivalent material properties, can then be employed. To determine these equivalent material properties, numerical simulations can be performed on a single unit cell of the lattice structure. However, a critical aspect to consider is the boundary conditions applied to the external faces of the unit cell. In the literature, different types of boundary conditions are used, but a comparative study is definitely lacking. In this publication, a diamond-type unit cell is studied in compression by applying different boundary conditions. If the porous structure’s boundaries are free to deform, then the periodic boundary condition is found to be the most representative, but constraint equations must be introduced in the model. If, instead, the porous structure is inserted in a rigid enclosure, it is then better to use frictionless boundary conditions. These preliminary results remain to be validated for other types of unit cells loaded beyond the yield limit of the material.

  15. Impact of model structure and parameterization on Penman-Monteith type evaporation models

    KAUST Repository

    Ershadi, A.

    2015-04-12

    The impact of model structure and parameterization on the estimation of evaporation is investigated across a range of Penman-Monteith type models. To examine the role of model structure on flux retrievals, three different retrieval schemes are compared. The schemes include a traditional single-source Penman-Monteith model (Monteith, 1965), a two-layer model based on Shuttleworth and Wallace (1985) and a three-source model based on Mu et al. (2011). To assess the impact of parameterization choice on model performance, a number of commonly used formulations for aerodynamic and surface resistances were substituted into the different formulations. Model response to these changes was evaluated against data from twenty globally distributed FLUXNET towers, representing a cross-section of biomes that include grassland, cropland, shrubland, evergreen needleleaf forest and deciduous broadleaf forest. Scenarios based on 14 different combinations of model structure and parameterization were ranked based on their mean value of Nash-Sutcliffe Efficiency. Results illustrated considerable variability in model performance both within and between biome types. Indeed, no single model consistently outperformed any other when considered across all biomes. For instance, in grassland and shrubland sites, the single-source Penman-Monteith model performed the best. In croplands it was the three-source Mu model, while for evergreen needleleaf and deciduous broadleaf forests, the Shuttleworth-Wallace model rated highest. Interestingly, these top ranked scenarios all shared the simple lookup-table based surface resistance parameterization of Mu et al. (2011), while a more complex Jarvis multiplicative method for surface resistance produced lower ranked simulations. The highly ranked scenarios mostly employed a version of the Thom (1975) formulation for aerodynamic resistance that incorporated dynamic values of roughness parameters. This was true for all cases except over deciduous broadleaf

  16. Safety classification of systems, structures, and components for pool-type research reactors

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Tae Ryong [KEPCO International Nuclear Graduate School, Ulsan (Korea, Republic of)

    2016-08-15

    Structures, systems, and components (SSCs) important to safety of nuclear facilities shall be designed, fabricated, erected, and tested to quality standards commensurate with the importance of the safety functions. Although SSC classification guidelines for nuclear power plants have been well established and applied, those for research reactors have been only recently established by the International Atomic Energy Agency (IAEA). Korea has operated a pool-type research reactor (the High Flux Advanced Neutron Application Reactor) and has recently exported another pool-type reactor (Jordan Research and Training Reactor), which is being built in Jordan. Korea also has a plan to build one more pool-type reactor, the Kijang Research Reactor, in Kijang, Busan. The safety classification of SSCs for pool-type research reactors is proposed in this paper based on the IAEA methodology. The proposal recommends that the SSCs of pool-type research reactors be categorized and classified on basis of their safety functions and safety significance. Because the SSCs in pool-type research reactors are not the pressure-retaining components, codes and standards for design of the SSCs following the safety classification can be selected in a graded approach.

  17. Structure of comorbid psychopathological disorders in patients with type 2nd diabetes mellitus

    Directory of Open Access Journals (Sweden)

    V. V. Chugunov

    2017-04-01

    Full Text Available Aim: to identify and explore the structure of comorbid psychopathological disorders in patients with type 2nd diabetes mellitus (DM. Materials and methods: 543 patients with type 2nd DM were included into the study. The average age of patients was (56.2 ± 0.65 years. The patients were divided into three groups according to the severity of DM. The first clinical group (CG-1 included 57 patients with type 2nd DM of mild severity, who was treated in outpatient department; the average age in the group was (51.8 ± 1.28 years. The second clinical group (CG-2 made up of 312 patients with type 2nd DM, moderate severity, they were in inpatient department; the median age of the group was (55.1 ± 1.12 years. The third clinical group (CG-3 included 174 patients with type 2nd DM, severe degrees of severity, they undergone inpatient treatment too; average age in the group was (61.8 ± 0.85 years. Research methods: clinical-anamnesis, clinical- psychopathological, statistical. Research results. The study established the incidence of non-psychotic mental disorders of varying severity in patients with type 2nd DM at the level of 94.11 %, among them, for 91.16 % – of psychogenic origin. Proportional correlation between the severity of type 2nd DM and the absence of comorbid psychopathological manifestations was detected (rs = -0.3416, p < 0.01. It is revealed that the dominant psychopathological syndromes among all patients with type 2nd DM were psychoorganic (62.43 %, dyssomnia (60.86 %, asthenic (55.58 % and anxiety (43.05 % syndromes. Structure of the dominant psychopathological syndromes was established depending on severity of type 2nd DM: in CG-1 dominated dyssomnia (36.84 %, anxiety (31.58 %, psychoorganic (21.05 % syndromes; in CG-2 – psychoorganic (65.38 %, asthenic (40.38 %, dyssomnia (38.46 %, anxiety (37, and 82 % syndromes; in CG-3 – dyssomnia (97.70 %, asthenic (89.08 %, organic mental (70.69 %, anxious 48.28 % syndromes. Significant

  18. Equivalent linearization method for limit cycle flutter analysis of plate-type structure in axial flow

    International Nuclear Information System (INIS)

    Lu Li; Yang Yiren

    2009-01-01

    The responses and limit cycle flutter of a plate-type structure with cubic stiffness in viscous flow were studied. The continuous system was dispersed by utilizing Galerkin Method. The equivalent linearization concept was performed to predict the ranges of limit cycle flutter velocities. The coupled map of flutter amplitude-equivalent linear stiffness-critical velocity was used to analyze the stability of limit cycle flutter. The theoretical results agree well with the results of numerical integration, which indicates that the equivalent linearization concept is available to the analysis of limit cycle flutter of plate-type structure. (authors)

  19. Complex structure of type VI peptidoglycan muramidase effector and a cognate immunity protein

    International Nuclear Information System (INIS)

    Wang, Tianyu; Ding, Jinjing; Zhang, Ying; Wang, Da-Cheng; Liu, Wei

    2013-01-01

    The structure of the Tse3–Tsi3 complex associated with the bacterial type VI secretion system of P. aeruginosa has been solved and refined at 1.9 Å resolution. The structural basis of the recognition of the muramidase effector and its inactivation by its cognate immunity protein is revealed. The type VI secretion system (T6SS) is a bacterial protein-export machine that is capable of delivering virulence effectors between Gram-negative bacteria. The T6SS of Pseudomonas aeruginosa transports two lytic enzymes, Tse1 and Tse3, to degrade cell-wall peptidoglycan in the periplasm of rival bacteria that are competing for niches via amidase and muramidase activities, respectively. Two cognate immunity proteins, Tsi1 and Tsi3, are produced by the bacterium to inactivate the two antibacterial effectors, thereby protecting its siblings from self-intoxication. Recently, Tse1–Tsi1 has been structurally characterized. Here, the structure of the Tse3–Tsi3 complex is reported at 1.9 Å resolution. The results reveal that Tse3 contains a C-terminal catalytic domain that adopts a soluble lytic transglycosylase (SLT) fold in which three calcium-binding sites were surprisingly observed close to the catalytic Glu residue. The electrostatic properties of the substrate-binding groove are also distinctive from those of known structures with a similar fold. All of these features imply that a unique catalytic mechanism is utilized by Tse3 in cleaving glycosidic bonds. Tsi3 comprises a single domain showing a β-sandwich architecture that is reminiscent of the immunoglobulin fold. Three loops of Tsi3 insert deeply into the groove of Tse3 and completely occlude its active site, which forms the structural basis of Tse3 inactivation. This work is the first crystallographic report describing the three-dimensional structure of the Tse3–Tsi3 effector–immunity pair

  20. Complex structure of type VI peptidoglycan muramidase effector and a cognate immunity protein

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Tianyu [Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Ding, Jinjing; Zhang, Ying; Wang, Da-Cheng, E-mail: dcwang@ibp.ac.cn [Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101 (China); Liu, Wei, E-mail: dcwang@ibp.ac.cn [The Third Military Medical University, Chongqing 400038 (China); Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101 (China)

    2013-10-01

    The structure of the Tse3–Tsi3 complex associated with the bacterial type VI secretion system of P. aeruginosa has been solved and refined at 1.9 Å resolution. The structural basis of the recognition of the muramidase effector and its inactivation by its cognate immunity protein is revealed. The type VI secretion system (T6SS) is a bacterial protein-export machine that is capable of delivering virulence effectors between Gram-negative bacteria. The T6SS of Pseudomonas aeruginosa transports two lytic enzymes, Tse1 and Tse3, to degrade cell-wall peptidoglycan in the periplasm of rival bacteria that are competing for niches via amidase and muramidase activities, respectively. Two cognate immunity proteins, Tsi1 and Tsi3, are produced by the bacterium to inactivate the two antibacterial effectors, thereby protecting its siblings from self-intoxication. Recently, Tse1–Tsi1 has been structurally characterized. Here, the structure of the Tse3–Tsi3 complex is reported at 1.9 Å resolution. The results reveal that Tse3 contains a C-terminal catalytic domain that adopts a soluble lytic transglycosylase (SLT) fold in which three calcium-binding sites were surprisingly observed close to the catalytic Glu residue. The electrostatic properties of the substrate-binding groove are also distinctive from those of known structures with a similar fold. All of these features imply that a unique catalytic mechanism is utilized by Tse3 in cleaving glycosidic bonds. Tsi3 comprises a single domain showing a β-sandwich architecture that is reminiscent of the immunoglobulin fold. Three loops of Tsi3 insert deeply into the groove of Tse3 and completely occlude its active site, which forms the structural basis of Tse3 inactivation. This work is the first crystallographic report describing the three-dimensional structure of the Tse3–Tsi3 effector–immunity pair.

  1. New orthorhombic derivative of CaCu{sub 5}-type structure: RNi{sub 4}Si compounds (R=Y, La, Ce, Sm, Gd–Ho), crystal structure and some magnetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Morozkin, A.V., E-mail: morozkin@general.chem.msu.ru [Department of Chemistry, Moscow State University, Leninskie Gory, House 1, Building 3, GSP-2, Moscow 119992 (Russian Federation); Knotko, A.V. [Department of Chemistry, Moscow State University, Leninskie Gory, House 1, Building 3, GSP-2, Moscow 119992 (Russian Federation); Yapaskurt, V.O. [Department of Petrology, Geological Faculty, Moscow State University, Leninskie Gory, Moscow 119992 (Russian Federation); Yuan, Fang; Mozharivskyj, Y. [Department of Chemistry and Chemical Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1 (Canada); Nirmala, R. [Indian Institute of Technology Madras, Chennai 600036 (India)

    2013-12-15

    The crystal structure of new YNi{sub 4}Si-type RNi{sub 4}Si (R=Y, La, Ce, Sm, Gd–Ho) compounds has been established using powder X-ray diffraction. The YNi{sub 4}Si structure is a new structure type, which is orthorhombic derivative of CaCu{sub 5}-type structure (space group Cmmm N 65, oC12). GdNi{sub 4}Si and DyNi{sub 4}Si compounds order ferromagnetically at 25 and 19 K, respectively whereas YNi{sub 4}Si shows antiferromagnetic nature. At 15 K, DyNi{sub 4}Si shows second antiferromagnetic-like transition. The magnetic moment of GdNi{sub 4}Si at 5 K in 50 kOe field is ∼7.2 μ{sub B}/f.u. suggesting a completely ordered ferromagnetic state. The magnetocaloric effect of GdNi{sub 4}Si is calculated in terms of isothermal magnetic entropy change and it reaches the maximum value of −12.8 J/kg K for a field change of 50 kOe near T{sub C} ∼25 K. - Graphical abstract: The RNi{sub 4}Si (R=Y, La, Ce, Sm, Gd–Ho) compounds crystallize in new YNi{sub 4}Si-type structure which is orthorhombic derivative of the basic CaCu{sub 5}-type structure. GdNi{sub 4}Si and DyNi{sub 4}Si compounds show the ferromagnetic-like ordering, whereas.YNi{sub 4}Si has the antiferromagnetic nature. The GdNi{sub 4}Si demonstrates the big magnetocaloric effect near temperature of ferromagnetic ordering. The relationship between initial CaCu{sub 5}-type DyNi{sub 5} and YNi{sub 4}Si-type DyNi{sub 4}Si lattices.

  2. Predicting temperate forest stand types using only structural profiles from discrete return airborne lidar

    Science.gov (United States)

    Fedrigo, Melissa; Newnham, Glenn J.; Coops, Nicholas C.; Culvenor, Darius S.; Bolton, Douglas K.; Nitschke, Craig R.

    2018-02-01

    Light detection and ranging (lidar) data have been increasingly used for forest classification due to its ability to penetrate the forest canopy and provide detail about the structure of the lower strata. In this study we demonstrate forest classification approaches using airborne lidar data as inputs to random forest and linear unmixing classification algorithms. Our results demonstrated that both random forest and linear unmixing models identified a distribution of rainforest and eucalypt stands that was comparable to existing ecological vegetation class (EVC) maps based primarily on manual interpretation of high resolution aerial imagery. Rainforest stands were also identified in the region that have not previously been identified in the EVC maps. The transition between stand types was better characterised by the random forest modelling approach. In contrast, the linear unmixing model placed greater emphasis on field plots selected as endmembers which may not have captured the variability in stand structure within a single stand type. The random forest model had the highest overall accuracy (84%) and Cohen's kappa coefficient (0.62). However, the classification accuracy was only marginally better than linear unmixing. The random forest model was applied to a region in the Central Highlands of south-eastern Australia to produce maps of stand type probability, including areas of transition (the 'ecotone') between rainforest and eucalypt forest. The resulting map provided a detailed delineation of forest classes, which specifically recognised the coalescing of stand types at the landscape scale. This represents a key step towards mapping the structural and spatial complexity of these ecosystems, which is important for both their management and conservation.

  3. Localized and collectivized behaviour of d-electrons in complicated titanium, vanadium and niobium oxides

    International Nuclear Information System (INIS)

    Bazuev, G.V.; Shvejkin, G.P.

    1980-01-01

    On the basis of investigation of electric and magnetic properties of oxide compounds of transition metals made are the conclusions on the degree of localization and delocalization of d-electrons in them. Generalized are the investigation results of complicated titanium, vanadium, niobium oxide compounds in low degrees of oxidation with rare earth and alkaline earth elements belonging to the two structural types: perovskite and pyrochlore. Presented are the results of investigations of perovskite-like solid solutions and of variable-content phases containing cations of transition metals in two different oxidation degrees: oxide niobium bronzes of two-valent europium and titanium bronzes of rare-earth elements, as well as Lnsub(1-x)Msub(x)Vsub(1-x)sup(3+)Vsub(x)sup(4+)Osub(3), where M is an alkaline earth element

  4. Progress report - Physical and Environmental Sciences - Physics Division, 1996 January 1 to December 31

    International Nuclear Information System (INIS)

    Powell, B.M.

    1997-04-01

    This document is the last Progress Report for the Neutron and Condensed Matter Science Branch, at Chalk River Labs of Atomic Energy of Canada Limited. The materials science program continued to include measurements of stress as a major component, but the determination of phase diagrams for specific alloys was also a prominent activity. Studies were made of two types of unusual magnetic materials. The magnetic properties of several oxide pyrochlore were investigated and spin waves were measured in the magnetic semiconductor, chalcopyrite. The crystal structures of the deuterated anti fluorite were determined and the reorientation of the ammonium ion was refined in detail. Differential scanning calorimetry measurements were used to investigate whether spontaneous phase separation into chiral domains occurs for mixtures of DPPC of opposite chirality. A new Neutron Velocity Selector was commissioned

  5. Progress report - Physical and Environmental Sciences - Physics Division, 1996 January 1 to December 31

    Energy Technology Data Exchange (ETDEWEB)

    Powell, B.M. (ed.)

    1997-04-01

    This document is the last Progress Report for the Neutron and Condensed Matter Science Branch, at Chalk River Labs of Atomic Energy of Canada Limited. The materials science program continued to include measurements of stress as a major component, but the determination of phase diagrams for specific alloys was also a prominent activity. Studies were made of two types of unusual magnetic materials. The magnetic properties of several oxide pyrochlore were investigated and spin waves were measured in the magnetic semiconductor, chalcopyrite. The crystal structures of the deuterated anti fluorite were determined and the reorientation of the ammonium ion was refined in detail. Differential scanning calorimetry measurements were used to investigate whether spontaneous phase separation into chiral domains occurs for mixtures of DPPC of opposite chirality. A new Neutron Velocity Selector was commissioned.

  6. Structural and bioinformatic characterization of an Acinetobacter baumannii type II carrier protein

    International Nuclear Information System (INIS)

    Allen, C. Leigh; Gulick, Andrew M.

    2014-01-01

    The high-resolution crystal structure of a free-standing carrier protein from Acinetobacter baumannii that belongs to a larger NRPS-containing operon, encoded by the ABBFA-003406–ABBFA-003399 genes of A. baumannii strain AB307-0294, that has been implicated in A. baumannii motility, quorum sensing and biofilm formation, is presented. Microorganisms produce a variety of natural products via secondary metabolic biosynthetic pathways. Two of these types of synthetic systems, the nonribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs), use large modular enzymes containing multiple catalytic domains in a single protein. These multidomain enzymes use an integrated carrier protein domain to transport the growing, covalently bound natural product to the neighboring catalytic domains for each step in the synthesis. Interestingly, some PKS and NRPS clusters contain free-standing domains that interact intermolecularly with other proteins. Being expressed outside the architecture of a multi-domain protein, these so-called type II proteins present challenges to understand the precise role they play. Additional structures of individual and multi-domain components of the NRPS enzymes will therefore provide a better understanding of the features that govern the domain interactions in these interesting enzyme systems. The high-resolution crystal structure of a free-standing carrier protein from Acinetobacter baumannii that belongs to a larger NRPS-containing operon, encoded by the ABBFA-003406–ABBFA-003399 genes of A. baumannii strain AB307-0294, that has been implicated in A. baumannii motility, quorum sensing and biofilm formation, is presented here. Comparison with the closest structural homologs of other carrier proteins identifies the requirements for a conserved glycine residue and additional important sequence and structural requirements within the regions that interact with partner proteins

  7. Structural and bioinformatic characterization of an Acinetobacter baumannii type II carrier protein

    Energy Technology Data Exchange (ETDEWEB)

    Allen, C. Leigh; Gulick, Andrew M., E-mail: gulick@hwi.buffalo.edu [University at Buffalo, Buffalo, NY 14203 (United States)

    2014-06-01

    The high-resolution crystal structure of a free-standing carrier protein from Acinetobacter baumannii that belongs to a larger NRPS-containing operon, encoded by the ABBFA-003406–ABBFA-003399 genes of A. baumannii strain AB307-0294, that has been implicated in A. baumannii motility, quorum sensing and biofilm formation, is presented. Microorganisms produce a variety of natural products via secondary metabolic biosynthetic pathways. Two of these types of synthetic systems, the nonribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs), use large modular enzymes containing multiple catalytic domains in a single protein. These multidomain enzymes use an integrated carrier protein domain to transport the growing, covalently bound natural product to the neighboring catalytic domains for each step in the synthesis. Interestingly, some PKS and NRPS clusters contain free-standing domains that interact intermolecularly with other proteins. Being expressed outside the architecture of a multi-domain protein, these so-called type II proteins present challenges to understand the precise role they play. Additional structures of individual and multi-domain components of the NRPS enzymes will therefore provide a better understanding of the features that govern the domain interactions in these interesting enzyme systems. The high-resolution crystal structure of a free-standing carrier protein from Acinetobacter baumannii that belongs to a larger NRPS-containing operon, encoded by the ABBFA-003406–ABBFA-003399 genes of A. baumannii strain AB307-0294, that has been implicated in A. baumannii motility, quorum sensing and biofilm formation, is presented here. Comparison with the closest structural homologs of other carrier proteins identifies the requirements for a conserved glycine residue and additional important sequence and structural requirements within the regions that interact with partner proteins.

  8. Crystal Structure of the Receptor-Binding Domain of Botulinum Neurotoxin Type HA, Also Known as Type FA or H.

    Science.gov (United States)

    Yao, Guorui; Lam, Kwok-Ho; Perry, Kay; Weisemann, Jasmin; Rummel, Andreas; Jin, Rongsheng

    2017-03-08

    Botulinum neurotoxins (BoNTs), which have been exploited as cosmetics and muscle-disorder treatment medicines for decades, are well known for their extreme neurotoxicity to humans. They pose a potential bioterrorism threat because they cause botulism, a flaccid muscular paralysis-associated disease that requires immediate antitoxin treatment and intensive care over a long period of time. In addition to the existing seven established BoNT serotypes (BoNT/A-G), a new mosaic toxin type termed BoNT/HA (aka type FA or H) was reported recently. Sequence analyses indicate that the receptor-binding domain (H C ) of BoNT/HA is ~84% identical to that of BoNT/A1. However, BoNT/HA responds differently to some potent BoNT/A-neutralizing antibodies (e.g., CR2) that target the H C . Therefore, it raises a serious concern as to whether BoNT/HA poses a new threat to our biosecurity. In this study, we report the first high-resolution crystal structure of BoNT/HA-H C at 1.8 Å. Sequence and structure analyses reveal that BoNT/HA and BoNT/A1 are different regarding their binding to cell-surface receptors including both polysialoganglioside (PSG) and synaptic vesicle glycoprotein 2 (SV2). Furthermore, the new structure also provides explanations for the ~540-fold decreased affinity of antibody CR2 towards BoNT/HA compared to BoNT/A1. Taken together, these new findings advance our understanding of the structure and function of this newly identified toxin at the molecular level, and pave the way for the future development of more effective countermeasures.

  9. Crystal Structure of the Receptor-Binding Domain of Botulinum Neurotoxin Type HA, Also Known as Type FA or H

    Directory of Open Access Journals (Sweden)

    Guorui Yao

    2017-03-01

    Full Text Available Botulinum neurotoxins (BoNTs, which have been exploited as cosmetics and muscle-disorder treatment medicines for decades, are well known for their extreme neurotoxicity to humans. They pose a potential bioterrorism threat because they cause botulism, a flaccid muscular paralysis-associated disease that requires immediate antitoxin treatment and intensive care over a long period of time. In addition to the existing seven established BoNT serotypes (BoNT/A–G, a new mosaic toxin type termed BoNT/HA (aka type FA or H was reported recently. Sequence analyses indicate that the receptor-binding domain (HC of BoNT/HA is ~84% identical to that of BoNT/A1. However, BoNT/HA responds differently to some potent BoNT/A-neutralizing antibodies (e.g., CR2 that target the HC. Therefore, it raises a serious concern as to whether BoNT/HA poses a new threat to our biosecurity. In this study, we report the first high-resolution crystal structure of BoNT/HA-HC at 1.8 Å. Sequence and structure analyses reveal that BoNT/HA and BoNT/A1 are different regarding their binding to cell-surface receptors including both polysialoganglioside (PSG and synaptic vesicle glycoprotein 2 (SV2. Furthermore, the new structure also provides explanations for the ~540-fold decreased affinity of antibody CR2 towards BoNT/HA compared to BoNT/A1. Taken together, these new findings advance our understanding of the structure and function of this newly identified toxin at the molecular level, and pave the way for the future development of more effective countermeasures.

  10. Crystal Structure of the Receptor-Binding Domain of Botulinum Neurotoxin Type HA, Also Known as Type FA or H

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Guorui; Lam, Kwok-ho; Perry, Kay; Weisemann, Jasmin; Rummel, Andreas; Jin, Rongsheng (Cornell); (Dusseldorf); (UCI)

    2017-03-01

    Botulinum neurotoxins (BoNTs), which have been exploited as cosmetics and muscle-disorder treatment medicines for decades, are well known for their extreme neurotoxicity to humans. They pose a potential bioterrorism threat because they cause botulism, a flaccid muscular paralysis-associated disease that requires immediate antitoxin treatment and intensive care over a long period of time. In addition to the existing seven established BoNT serotypes (BoNT/A–G), a new mosaic toxin type termed BoNT/HA (aka type FA or H) was reported recently. Sequence analyses indicate that the receptor-binding domain (HC) of BoNT/HA is ~84% identical to that of BoNT/A1. However, BoNT/HA responds differently to some potent BoNT/A-neutralizing antibodies (e.g., CR2) that target the HC. Therefore, it raises a serious concern as to whether BoNT/HA poses a new threat to our biosecurity. In this study, we report the first high-resolution crystal structure of BoNT/HA-HC at 1.8 Å. Sequence and structure analyses reveal that BoNT/HA and BoNT/A1 are different regarding their binding to cell-surface receptors including both polysialoganglioside (PSG) and synaptic vesicle glycoprotein 2 (SV2). Furthermore, the new structure also provides explanations for the ~540-fold decreased affinity of antibody CR2 towards BoNT/HA compared to BoNT/A1. Taken together, these new findings advance our understanding of the structure and function of this newly identified toxin at the molecular level, and pave the way for the future development of more effective countermeasures

  11. Structure of the ent-Copalyl Diphosphate Synthase PtmT2 from Streptomyces platensis CB00739, a Bacterial Type II Diterpene Synthase.

    Science.gov (United States)

    Rudolf, Jeffrey D; Dong, Liao-Bin; Cao, Hongnan; Hatzos-Skintges, Catherine; Osipiuk, Jerzy; Endres, Michael; Chang, Chin-Yuan; Ma, Ming; Babnigg, Gyorgy; Joachimiak, Andrzej; Phillips, George N; Shen, Ben

    2016-08-31

    Terpenoids are the largest and most structurally diverse family of natural products found in nature, yet their presence in bacteria is underappreciated. The carbon skeletons of terpenoids are generated through carbocation-dependent cyclization cascades catalyzed by terpene synthases (TSs). Type I and type II TSs initiate cyclization via diphosphate ionization and protonation, respectively, and protein structures of both types are known. Most plant diterpene synthases (DTSs) possess three α-helical domains (αβγ), which are thought to have arisen from the fusion of discrete, ancestral bacterial type I TSs (α) and type II TSs (βγ). Type II DTSs of bacterial origin, of which there are no structurally characterized members, are a missing piece in the structural evolution of TSs. Here, we report the first crystal structure of a type II DTS from bacteria. PtmT2 from Streptomyces platensis CB00739 was verified as an ent-copalyl diphosphate synthase involved in the biosynthesis of platensimycin and platencin. The crystal structure of PtmT2 was solved at a resolution of 1.80 Å, and docking studies suggest the catalytically active conformation of geranylgeranyl diphosphate (GGPP). Site-directed mutagenesis confirmed residues involved in binding the diphosphate moiety of GGPP and identified DxxxxE as a potential Mg(2+)-binding motif for type II DTSs of bacterial origin. Finally, both the shape and physicochemical properties of the active sites are responsible for determining specific catalytic outcomes of TSs. The structure of PtmT2 fundamentally advances the knowledge of bacterial TSs, their mechanisms, and their role in the evolution of TSs.

  12. The use of impression management tactics in structured interviews: a function of question type?

    Science.gov (United States)

    Ellis, Aleksander P J; West, Bradley J; Ryan, Ann Marie; DeShon, Richard P

    2002-12-01

    This study investigated impression management tactic use during structured interviews containing both experience-based and situational questions. Specifically, the authors examined whether applicants' use of impression management tactics depended on question type. Results from 119 structured interviews indicated that almost all of the applicants used some form of impression management. Significantly more assertive than defensive impression management tactics were used, and among assertive tactics, applicants tended to use self-promotion rather than ingratiation. However, different question types prompted the use of different impression management tactics. Ingratiation tactics were used significantly more when applicants answered situational questions, whereas self-promotion tactics were used significantly more when applicants answered experience-based questions. Furthermore, the use of self-promotion and ingratiation tactics was positively related to interviewer evaluations.

  13. Function and Evolutionary Origin of Unicellular Camera-Type Eye Structure

    KAUST Repository

    Hayakawa, Shiho

    2015-03-03

    The ocelloid is an extraordinary eyespot organelle found only in the dinoflagellate family Warnowiaceae. It contains retina- and lens-like structures called the retinal body and the hyalosome. The ocelloid has been an evolutionary enigma because of its remarkable resemblance to the multicellular camera-type eye. To determine if the ocelloid is functionally photoreceptive, we investigated the warnowiid dinoflagellate Erythropsidinium. Here, we show that the morphology of the retinal body changed depending on different illumination conditions and the hyalosome manifests the refractile nature. Identifying a rhodopsin gene fragment in Erythropsidinium ESTs that is expressed in the retinal body by in situ hybridization, we also show that ocelloids are actually light sensitive photoreceptors. The rhodopsin gene identified is most closely related to bacterial rhodopsins. Taken together, we suggest that the ocelloid is an intracellular camera-type eye, which might be originated from endosymbiotic origin. © 2015 Hayakawa et al.

  14. Function and Evolutionary Origin of Unicellular Camera-Type Eye Structure

    KAUST Repository

    Hayakawa, Shiho; Takaku, Yasuharu; Hwang, Jung Shan; Horiguchi, Takeo; Suga, Hiroshi; Gehring, Walter; Ikeo, Kazuho; Gojobori, Takashi

    2015-01-01

    The ocelloid is an extraordinary eyespot organelle found only in the dinoflagellate family Warnowiaceae. It contains retina- and lens-like structures called the retinal body and the hyalosome. The ocelloid has been an evolutionary enigma because of its remarkable resemblance to the multicellular camera-type eye. To determine if the ocelloid is functionally photoreceptive, we investigated the warnowiid dinoflagellate Erythropsidinium. Here, we show that the morphology of the retinal body changed depending on different illumination conditions and the hyalosome manifests the refractile nature. Identifying a rhodopsin gene fragment in Erythropsidinium ESTs that is expressed in the retinal body by in situ hybridization, we also show that ocelloids are actually light sensitive photoreceptors. The rhodopsin gene identified is most closely related to bacterial rhodopsins. Taken together, we suggest that the ocelloid is an intracellular camera-type eye, which might be originated from endosymbiotic origin. © 2015 Hayakawa et al.

  15. Structure and properties of alloys of A15 type compounds with carbon

    International Nuclear Information System (INIS)

    Savitskij, E.M.; Efimov, Yu.V.; Myasnikova, E.A.

    1983-01-01

    Microstructure and some properties of the alloys on the base of the phases of A15 type in the V-Si-C, Nb-Si-C, Nb-Sn-C, Nb-Al-C, Nb-Ga-C, V-Ga-C ternary systems are investigated. It is established that in the niobium-rich corners of the A-B-C ternary systems the new ternary conpounds do not form, as a rule, bUt the wide ranges of threephase equilibrium A-A 3 B-C exist. New ternary phases with A15 type structure stabilized with carbon are established only in the Nb-Si-C and V-Al-C systems. Alloying with carbon results in sharp refining of structural components of stable and metastable alloys, promotes transition of the alloys into amorphous state at super fast cooling of the melts as well as increases stability of metastable state of the alloys against tempering. After super fast quenching and tempering Tsub(c) of the ternary alloys close to the A15 phases exceed Tsub(c) of equilibrium samples

  16. DG-FEM solution for nonlinear wave-structure interaction using Boussinesq-type equations

    DEFF Research Database (Denmark)

    Engsig-Karup, Allan Peter; Hesthaven, Jan; Bingham, Harry B.

    2008-01-01

    equations in complex and curvilinear geometries which amends the application range of previous numerical models that have been based on structured Cartesian grids. The Boussinesq method provides the basis for the accurate description of fully nonlinear and dispersive water waves in both shallow and deep...... waters within the breaking limit. To demonstrate the current applicability of the model both linear and mildly nonlinear test cases are considered in two horizontal dimensions where the water waves interact with bottom-mounted fully reflecting structures. It is established that, by simple symmetry...... considerations combined with a mirror principle, it is possible to impose weak slip boundary conditions for both structured and general curvilinear wall boundaries while maintaining the accuracy of the scheme. As is standard for current high-order Boussinesq-type models, arbitrary waves can be generated...

  17. Analysis of Side-Wall Structure of Grown-in Twin-Type Octahedral Defects in Czochralski Silicon

    Science.gov (United States)

    Ueki, Takemi; Itsumi, Manabu; Takeda, Tadao

    1998-04-01

    We analyzed the side-wall structure of grown-in octahedral defects in Czochralski silicon standard wafers for large-scale integrated circuits. There are two types of twin octahedral defects: an overlapping type and an adjacent type. In the twin octahedral defects of the overlapping type, a hole is formed in the connection part. The side-wall layer in the hole part is formed continually and is the same thickness as the side-wall layers of both octahedrons. In the twin octahedral defects of the adjacent type, a partition layer is formed in the connection part. Our electron energy-loss spectroscopy analyses identified that the side-wall layer includes SiO2.

  18. Electronic structure and chemical bonding in LaIrSi-type intermetallics

    Energy Technology Data Exchange (ETDEWEB)

    Matar, Samir F. [Bordeaux Univ., Pessac (France). CNRS; Poettgen, Rainer [Muenster Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie; Nakhl, Michel [Univ. Libanaise, Fanar (Lebanon). Ecole Doctorale Sciences et Technologies

    2017-05-01

    The cubic LaIrSi type has 23 representatives in aluminides, gallides, silicides, germanides, phosphides, and arsenides, all with a valence electron count of 16 or 17. The striking structural motif is a three-dimensional network of the transition metal (T) and p element (X) atoms with TX{sub 3/3} respectively XT{sub 3/3} coordination. Alkaline earth or rare earth atoms fill cavities within the polyanionic [TX]{sup δ-} networks. The present work presents a detailed theoretical study of chemical bonding in LaIrSi-type representatives, exemplarily for CaPtSi, BaIrP, BaAuGa, LaIrSi, CeRhSi, and CeIrSi. DFT-GGA-based electronic structure calculations show weakly metallic compounds with itinerant small magnitude DOSs at E{sub F} except for CeRhSi whose large Ce DOS at E{sub F} leads to a finite magnetization on Ce (0.73 μ{sub B}) and induced small moments of opposite sign on Rh and Si in a ferromagnetic ground state. The chemical bonding analyses show dominant bonding within the [TX]{sup δ-} polyanionic networks. Charge transfer magnitudes were found in accordance with the course of the electronegativites of the chemical constituents.

  19. Split Fermi Surfaces of the Spin-Orbit-Coupled Metal Cd2Re2O7 Probed by de Haas-van Alphen Effect

    Science.gov (United States)

    Matsubayashi, Yasuhito; Sugii, Kaori; Hirose, Hishiro T.; Hirai, Daigorou; Sugiura, Shiori; Terashima, Taichi; Uji, Shinya; Hiroi, Zenji

    2018-05-01

    The superconducting pyrochlore oxide Cd2Re2O7 shows a structural transition with inversion symmetry breaking (ISB) at Ts1 = 200 K. A recent theory [https://doi.org/10.1103/PhysRevLett.115.026401" xlink:type="simple">L. Fu, Phys. Rev. Lett. 115, 026401 (2015)] suggests that the origin is an electronic instability that leads to a multipolar order in the spin-orbit-coupled metal. To observe the Fermi surface of the low-temperature phase of Cd2Re2O7, we perform de Haas-van Alphen effect measurements by means of magnetic torque. In reference to a calculated band structure, the spin-split Fermi surfaces with large cyclotron masses of 5-9m0 are revealed. The splitting is suggested to be due to an antisymmetric spin-orbit coupling induced by ISB, the strength of which is estimated to be approximately 67 K, which is rather smaller than those of typical non-centrosymmetric metals.

  20. Population structure of Lactobacillus helveticus isolates from naturally fermented dairy products based on multilocus sequence typing.

    Science.gov (United States)

    Sun, Zhihong; Liu, Wenjun; Song, Yuqin; Xu, Haiyan; Yu, Jie; Bilige, Menghe; Zhang, Heping; Chen, Yongfu

    2015-05-01

    Lactobacillus helveticus is an economically important lactic acid bacterium used in industrial dairy fermentation. In the present study, the population structure of 245 isolates of L. helveticus from different naturally fermented dairy products in China and Mongolia were investigated using an multilocus sequence typing scheme with 11 housekeeping genes. A total of 108 sequence types were detected, which formed 8 clonal complexes and 27 singletons. Results from Structure, SplitsTree, and ClonalFrame software analyses demonstrated the presence of 3 subpopulations in the L. helveticus isolates used in our study, namely koumiss, kurut-tarag, and panmictic lineages. Most L. helveticus isolates from particular ecological origins had specific population structures. Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

  1. Structure and fluid evolution of Yili basin and their relation to sandstone type uranium mineralization

    International Nuclear Information System (INIS)

    Wang Juntang; Wang Chengwei; Feng Shirong

    2008-01-01

    Based on the summary of strata and structure distribution of Yili basin, the relation of structure and fluid evolution to sandstone type ur alum mineraliation are analyzed. It is found that uranium mineralization in Yili basin experienced ore hosting space forming, pre-alteration of hosting space, hosting space alteration and uranium formation stages. (authors)

  2. Impact of model structure and parameterization on Penman-Monteith type evaporation models

    KAUST Repository

    Ershadi, A.; McCabe, Matthew; Evans, J.P.; Wood, E.F.

    2015-01-01

    Overall, the results illustrate the sensitivity of Penman-Monteith type models to model structure, parameterization choice and biome type. A particular challenge in flux estimation relates to developing robust and broadly applicable model formulations. With many choices available for use, providing guidance on the most appropriate scheme to employ is required to advance approaches for routine global scale flux estimates, undertake hydrometeorological assessments or develop hydrological forecasting tools, amongst many other applications. In such cases, a multi-model ensemble or biome-specific tiled evaporation product may be an appropriate solution, given the inherent variability in model and parameterization choice that is observed within single product estimates.

  3. Structural Characterization and Oligomerization of the TssL Protein, a Component Shared by Bacterial Type VI and Type IVb Secretion Systems*

    Science.gov (United States)

    Durand, Eric; Zoued, Abdelrahim; Spinelli, Silvia; Watson, Paul J. H.; Aschtgen, Marie-Stéphanie; Journet, Laure; Cambillau, Christian; Cascales, Eric

    2012-01-01

    The Type VI secretion system (T6SS) is a macromolecular system distributed in Gram-negative bacteria, responsible for the secretion of effector proteins into target cells. The T6SS has a broad versatility as it can target both eukaryotic and prokaryotic cells. It is therefore involved in host pathogenesis or killing neighboring bacterial cells to colonize a new niche. At the architecture level, the T6SS core apparatus is composed of 13 proteins, which assemble in two subcomplexes. One of these subcomplexes, composed of subunits that share structural similarities with bacteriophage tail and baseplate components, is anchored to the cell envelope by the membrane subcomplex. This latter is constituted of at least three proteins, TssL, TssM, and TssJ. The crystal structure of the TssJ outer membrane lipoprotein and its interaction with the inner membrane TssM protein have been recently reported. TssL and TssM share sequence homology and characteristics with two components of the Type IVb secretion system (T4bSS), IcmH/DotU and IcmF, respectively. In this study, we report the crystal structure of the cytoplasmic domain of the TssL inner membrane protein from the enteroaggregative Escherichia coli Sci-1 T6SS. It folds as a hook-like structure composed of two three-helix bundles. Two TssL molecules associate to form a functional complex. Although the TssL trans-membrane segment is the main determinant of self-interaction, contacts between the cytoplasmic domains are required for TssL function. Based on sequence homology and secondary structure prediction, we propose that the TssL structure is the prototype for the members of the TssL and IcmH/DotU families. PMID:22371492

  4. Europium-Doped Lanthanum Hafnate Nanoparticles: Structure, Photoluminescence, and Radioluminescence

    Science.gov (United States)

    Wahid, Kareem; Pokhrel, Madhab; Mao, Yuanbing

    Due to their novel physical properties, nanostructured phosphors are of interest for radiation-based imaging and therapeutics. Herein, the structural and luminescent properties of europium-doped lanthanum hafnate (La2Hf2O7:xmol%Eu3+, x = 0 - 35) nanoparticles are investigated for use as scintillators. X-ray diffraction, Raman spectroscopy, and scanning electron microscopy confirm samples prepared through a combined co-precipitation and low-temperature molten salt synthetic process homogenously form spherical nanocrystals of 36 nm in the ordered pyrochlore phase. Ultraviolet and X-ray excitation of these samples induce strong red emissions in the 580 - 590 and 612 - 630 nm range corresponding to the 5D0->7 F1 magnetic dipole and 5D0->7 F2 electric dipole transitions of Eu3+. Optical response and quantum yield are optimized at 5% Eu3+; a proposed trade-off between quenching mechanisms (defect-states/cross-relaxation) and dopant concentration is discussed. Owing to their high density, large effective atomic number, and bright luminescence, these La2Hf2O7:xmol%Eu3+ nanoparticles warrant further investigation for scintillator applications. The authors thank the support from the Defense Threat Reduction Agency of the U.S. Department of Defense (award #HDTRA1- 10-1-0114).

  5. Predicting beta-turns and their types using predicted backbone dihedral angles and secondary structures.

    Science.gov (United States)

    Kountouris, Petros; Hirst, Jonathan D

    2010-07-31

    Beta-turns are secondary structure elements usually classified as coil. Their prediction is important, because of their role in protein folding and their frequent occurrence in protein chains. We have developed a novel method that predicts beta-turns and their types using information from multiple sequence alignments, predicted secondary structures and, for the first time, predicted dihedral angles. Our method uses support vector machines, a supervised classification technique, and is trained and tested on three established datasets of 426, 547 and 823 protein chains. We achieve a Matthews correlation coefficient of up to 0.49, when predicting the location of beta-turns, the highest reported value to date. Moreover, the additional dihedral information improves the prediction of beta-turn types I, II, IV, VIII and "non-specific", achieving correlation coefficients up to 0.39, 0.33, 0.27, 0.14 and 0.38, respectively. Our results are more accurate than other methods. We have created an accurate predictor of beta-turns and their types. Our method, called DEBT, is available online at http://comp.chem.nottingham.ac.uk/debt/.

  6. Equilibrium vortex structures of type-II/1 superconducting films with washboard pinning landscapes

    Science.gov (United States)

    Wei, C. A.; Xu, X. B.; Xu, X. N.; Wang, Z. H.; Gu, M.

    2018-05-01

    We numerically study the equilibrium vortex structures of type-II/1 superconducting films with a periodic quasi-one-dimensional corrugated substrate. We show as a function of substrate period and pinning strength that, the vortex system displays a variety of vortex phases including arrays consisted of vortex clumps with different morphologies, ordered vortex stripes parallel and perpendicular to pinning troughs, and ordered one-dimensional vortex chains. Our simulations are helpful in understanding the structural modulations for extensive systems with both competing interactions and competing periodicities.

  7. Development of an Acoustic Levitation Linear Transportation System Based on a Ring-Type Structure.

    Science.gov (United States)

    Thomas, Gilles P L; Andrade, Marco A B; Adamowski, Julio Cezar; Silva, Emilio Carlos Nelli

    2017-05-01

    A linear acoustic levitation transportation system based on a ring-type vibrator is presented. The system is composed by two 21-kHz Langevin transducers connected to a ring-shaped structure formed by two semicircular sections and two flat plates. In this system, a flexural standing wave is generated along the ring structure, producing an acoustic standing wave between the vibrating ring and a plane reflector located at a distance of approximately a half wavelength from the ring. The acoustic standing wave in air has a series of pressure nodes, where small particles can be levitated and transported. The ring-type transportation system was designed and analyzed by using the finite element method. Additionally, a prototype was built and the acoustic levitation and transport of a small polystyrene particle was demonstrated.

  8. Analysis of the Shear Behavior of Stubby Y-Type Perfobond Rib Shear Connectors for a Composite Frame Structure.

    Science.gov (United States)

    Kim, Sang-Hyo; Kim, Kun-Soo; Lee, Do-Hoon; Park, Jun-Seung; Han, Oneil

    2017-11-22

    Shear connectors are used in steel beam-concrete slabs of composite frame and bridge structures to transfer shear force according to design loads. The existing Y-type perfobond rib shear connectors are designed for girder slabs of composite bridges. Therefore, the rib and transverse rebars of the conventional Y-type perfobond rib shear connectors are extremely large for the composite frames of building structures. Thus, this paper proposes stubby Y-type perfobond rib shear connectors, redefining the existing connectors, for composite frames of building structures; these were used to perform push-out tests. These shear connectors have relatively small ribs compared to the conventional Y-type perfobond rib shear connectors. To confirm the shear resistance of these stubby shear connectors, we performed an experiment by using transverse rebars D13 and D16. The results indicate that these shear connectors have suitable shear strength and ductility for application in composite frame structures. The shear strengths obtained using D13 and D16 were not significantly different. However, the ductility of the shear connectors with D16 was 45.1% higher than that of the shear connectors with D13.

  9. Electronic structure of p type Delta doped systems

    International Nuclear Information System (INIS)

    Gaggero S, L.M.; Perez A, R.

    1998-01-01

    We summarize of the results obtained for the electronic structure of quantum wells that consist in an atomic layer doped with impurities of p type. The calculations are made within the frame worth of the wrapper function approach to independent bands and with potentials of Hartree. We study the cases reported experimentally (Be in GaAs and B in Si). We present the levels of energy, the wave functions and the rate of the electronic population between the different subbands, as well as the dependence of these magnitudes with the density of impurities in the layer. The participation of the bans of heavy holes is analysed, light and split-off band in the total electronic population. The effect of the temperature is discussed and we give a possible qualitative explanation of the experimental optical properties. (Author)

  10. Enhancement of structural and magnetic properties of M-type hexaferrite permanent magnet based on synthesis temperature

    Science.gov (United States)

    Anjum, Safia; Sehar, Fatima; Mustafa, Zeeshan; Awan, M. S.

    2018-01-01

    The main purpose of this research work is to develop the single domain magnetic particles of M-type barium hexaferrite (BaFe12O19) using oxide precursors employing conventional powder metallurgy technique. The phase formation and magnetic performance of the powders and magnets will be optimized by adjusting calcination and sintering temperatures. The synthesis of M-type barium hexaferrite was carried out in two sections. A series of four samples have been prepared by initial wet mixed powders calcined at different temperatures, i.e., 750, 850, 950 and 1050 °C. On the basis of structural analysis, the sample calcined at 950 °C has been selected and further divided into four parts to sintered them at 1100, 1150, 1200 and 1250 °C. The structural measurements depict the confirmation of M-type barium hexaferrite structure. SEM micrographs show the hexagonal-shaped grains. The abrupt decrease in coercivity for the sample sintered at 1250 °C has been seen which may be due to high sintering temperature, at which the particles have multi-domain properties.

  11. Genomic structure and evolution of the mating type locus in the green seaweed Ulva partita.

    Science.gov (United States)

    Yamazaki, Tomokazu; Ichihara, Kensuke; Suzuki, Ryogo; Oshima, Kenshiro; Miyamura, Shinichi; Kuwano, Kazuyoshi; Toyoda, Atsushi; Suzuki, Yutaka; Sugano, Sumio; Hattori, Masahira; Kawano, Shigeyuki

    2017-09-15

    The evolution of sex chromosomes and mating loci in organisms with UV systems of sex/mating type determination in haploid phases via genes on UV chromosomes is not well understood. We report the structure of the mating type (MT) locus and its evolutionary history in the green seaweed Ulva partita, which is a multicellular organism with an isomorphic haploid-diploid life cycle and mating type determination in the haploid phase. Comprehensive comparison of a total of 12.0 and 16.6 Gb of genomic next-generation sequencing data for mt - and mt + strains identified highly rearranged MT loci of 1.0 and 1.5 Mb in size and containing 46 and 67 genes, respectively, including 23 gametologs. Molecular evolutionary analyses suggested that the MT loci diverged over a prolonged period in the individual mating types after their establishment in an ancestor. A gene encoding an RWP-RK domain-containing protein was found in the mt - MT locus but was not an ortholog of the chlorophycean mating type determination gene MID. Taken together, our results suggest that the genomic structure and its evolutionary history in the U. partita MT locus are similar to those on other UV chromosomes and that the MT locus genes are quite different from those of Chlorophyceae.

  12. New transition metal oxide fluorides with ReO{sub 3}-type structure

    Energy Technology Data Exchange (ETDEWEB)

    Nakhal, Suliman; Lerch, Martin [Technische Universitaet Berlin (Germany). Inst. fuer Chemie

    2016-08-01

    The new niobium oxide fluorides MNbO{sub 2}F{sub 4} [M = (Cr, Fe)], CrNb{sub 2}O{sub 4}F{sub 5}, and Fe{sub 2}Nb{sub 3}O{sub 6}F{sub 9} were prepared by treatment of chromium or iron nitrate with Nb-containing hydrofluoric acid solutions. Crystal structures were investigated by means of X-ray powder diffraction. All new compounds can be structurally refined in the cubic ReO{sub 3}-type. The iron niobium oxide fluorides are reddish orange, and chromium containing phases exhibit a light green color. The niobium atoms are in the highest formal oxidation state.

  13. Structure and Function of p97 and Pex1/6 Type II AAA+ Complexes.

    Science.gov (United States)

    Saffert, Paul; Enenkel, Cordula; Wendler, Petra

    2017-01-01

    Protein complexes of the Type II AAA+ (ATPases associated with diverse cellular activities) family are typically hexamers of 80-150 kDa protomers that harbor two AAA+ ATPase domains. They form double ring assemblies flanked by associated domains, which can be N-terminal, intercalated or C-terminal to the ATPase domains. Most prominent members of this family include NSF (N-ethyl-maleimide sensitive factor), p97/VCP (valosin-containing protein), the Pex1/Pex6 complex and Hsp104 in eukaryotes and ClpB in bacteria. Tremendous efforts have been undertaken to understand the conformational dynamics of protein remodeling type II AAA+ complexes. A uniform mode of action has not been derived from these works. This review focuses on p97/VCP and the Pex1/6 complex, which both structurally remodel ubiquitinated substrate proteins. P97/VCP plays a role in many processes, including ER- associated protein degradation, and the Pex1/Pex6 complex dislocates and recycles the transport receptor Pex5 from the peroxisomal membrane during peroxisomal protein import. We give an introduction into existing knowledge about the biochemical and cellular activities of the complexes before discussing structural information. We particularly emphasize recent electron microscopy structures of the two AAA+ complexes and summarize their structural differences.

  14. Development of a Cloud Computing-Based Pier Type Port Structure Stability Evaluation Platform Using Fiber Bragg Grating Sensors.

    Science.gov (United States)

    Jo, Byung Wan; Jo, Jun Ho; Khan, Rana Muhammad Asad; Kim, Jung Hoon; Lee, Yun Sung

    2018-05-23

    Structure Health Monitoring is a topic of great interest in port structures due to the ageing of structures and the limitations of evaluating structures. This paper presents a cloud computing-based stability evaluation platform for a pier type port structure using Fiber Bragg Grating (FBG) sensors in a system consisting of a FBG strain sensor, FBG displacement gauge, FBG angle meter, gateway, and cloud computing-based web server. The sensors were installed on core components of the structure and measurements were taken to evaluate the structures. The measurement values were transmitted to the web server via the gateway to analyze and visualize them. All data were analyzed and visualized in the web server to evaluate the structure based on the safety evaluation index (SEI). The stability evaluation platform for pier type port structures involves the efficient monitoring of the structures which can be carried out easily anytime and anywhere by converging new technologies such as cloud computing and FBG sensors. In addition, the platform has been successfully implemented at “Maryang Harbor” situated in Maryang-Meyon of Korea to test its durability.

  15. Nanoscale Structure of Type I Collagen Fibrils: Quantitative Measurement of D-spacing

    Science.gov (United States)

    Erickson, Blake; Fang, Ming; Wallace, Joseph M.; Orr, Bradford G.; Les, Clifford M.; Holl, Mark M. Banaszak

    2012-01-01

    This paper details a quantitative method to measure the D-periodic spacing of Type I collagen fibrils using Atomic Force Microscopy coupled with analysis using a 2D Fast Fourier Transform approach. Instrument calibration, data sampling and data analysis are all discussed and comparisons of the data to the complementary methods of electron microscopy and X-ray scattering are made. Examples of the application of this new approach to the analysis of Type I collagen morphology in disease models of estrogen depletion and Osteogenesis Imperfecta are provided. We demonstrate that it is the D-spacing distribution, not the D-spacing mean, that showed statistically significant differences in estrogen depletion associated with early stage Osteoporosis and Osteogenesis Imperfecta. The ability to quantitatively characterize nanoscale morphological features of Type I collagen fibrils will provide important structural information regarding Type I collagen in many research areas, including tissue aging and disease, tissue engineering, and gene knock out studies. Furthermore, we also envision potential clinical applications including evaluation of tissue collagen integrity under the impact of diseases or drug treatments. PMID:23027700

  16. Novel barium triel/tetrelides with the Pu3Pd5 structure type

    International Nuclear Information System (INIS)

    Duerr, Ines; Schwarz, Michael; Wendorff, Marco; Roehr, Caroline

    2010-01-01

    A series of ternary barium triel(M III )/tetrel(M IV )-ides Ba 3 M x III M 5-x IV (M III =Ga,In;M IV =Si,Ge,Sn;x=0-0.7) has been prepared from melts of the elements. They all crystallize with the Pu 3 Pd 5 type structure (orthorhombic, space group Cmcm) exhibiting isolated M 5 clusters of slightly distorted nido shape (square pyramids). For the silicides, where the binary border compound Ba 3 Si 5 does not exist, the Pu 3 Pd 5 type is stabilized by substituting 0.7 Si atoms per formula unit against Ga (Ba 3 Ga 0.7 Si 4.3 :a=1024.82(1),b=856.58(1),c=1024.18(1) pm, R1=0.0220) or by a very small substitution of In (Ba 3 In 0.1 Si 4.9 :a=1017.8(2),b=852.5(2),c=1020.1(3) pm, R1=0.0406). A comparable situation is found for the corresponding germanides, where 0.7 atoms of In (Ba 3 In 0.7 Ge 4.3 :a=1051.3(2),b=864.05(14),c=1054.7(3) pm, R1=0.0248) or Ga (Ba 3 Ga x Ge 5-x :a=1035.1(1),b=861.5(1),c=1036.8(1) pm, R1=0.0148) are necessary to stabilize a Ge-rich compound of this structure type. For the stannides, the situation is somewhat different, because the binary phase Ba 3 Sn 5 itself forms the Pu 3 Pd 5 type. In this case, the structure type remains stable up to a Ga content of 0.5 Ga/f.u. (Ba 3 Ga 0.5 Sn 4.5 :a=1100.41(14),b=896.19(11),c=1111.82(14) pm, R1=0.0169) and also with a substantial In content (Ba 3 In x Sn 5-x :x∼0.9(1);a=1110.5(2),b=900.0(2),c=1120.7(2) pm, R1=0.0262). As the five-atom nido cluster requires only 24 valence electrons per formula unit according to Zintl and Wade, an excess of electrons would be assumed for the binary tetrelides such as Ba 3 Sn 5 (26 v.e./f.u.) that even the maximal amount of triel substitution 0.7 M III /f.u. attained in the title compounds cannot sufficiently compensate for. An assessment of the geometric influence of varied valence electron counts however, coupled with a detailed analysis of the calculated electron densities and the partial densities of states in the energy region above the pseudo band gap at 24 v

  17. Design of medium band gap Ag-Bi-Nb-O and Ag-Bi-Ta-O semiconductors for driving direct water splitting with visible light.

    Science.gov (United States)

    Wang, Limin; Cao, Bingfei; Kang, Wei; Hybertsen, Mark; Maeda, Kazuhiko; Domen, Kazunari; Khalifah, Peter G

    2013-08-19

    Two new metal oxide semiconductors belonging to the Ag-Bi-M-O (M = Nb, Ta) chemical systems have been synthesized as candidate compounds for driving overall water splitting with visible light on the basis of cosubstitution of Ag and Bi on the A-site position of known Ca2M2O7 pyrochlores. The low-valence band edge energies of typical oxide semiconductors prevents direct water splitting in compounds with band gaps below 3.0 eV, a limitation which these compounds are designed to overcome through the incorporation of low-lying Ag 4d(10) and Bi 6s(2) states into compounds of nominal composition "AgBiM2O7". It was found that the "AgBiTa2O7" pyrochlores are in fact a solid solution with an approximate range of Ag(x)Bi(5/6)Ta2O(6.25+x/2) with 0.5 semiconductors with the onset of strong direct absorption at 2.72 and 2.96 eV, respectively. Electronic structure calculations for an ordered AgBiNb2O7 structure show that the band gap reduction and the elevation of the valence band primarily result from hybridized Ag d(10)-O 2p orbitals that lie at higher energy than the normal O 2p states in typical pyrochlore oxides. While the minimum energy gap is direct in the band structure, the lowest energy dipole allowed optical transitions start about 0.2 eV higher in energy than the minimum energy transition and involve different bands. This suggests that the minimum electronic band gap in these materials is slightly smaller than the onset energy for strong absorption in the optical measurements. The elevated valence band energies of the niobate and tantalate compounds are experimentally confirmed by the ability of these compounds to reduce 2 H(+) to H2 gas when illuminated after functionalization with a Pt cocatalyst.

  18. The spectra of type IIB flux compactifications at large complex structure

    International Nuclear Information System (INIS)

    Brodie, Callum; Marsh, M.C. David

    2016-01-01

    We compute the spectra of the Hessian matrix, H, and the matrix M that governs the critical point equation of the low-energy effective supergravity, as a function of the complex structure and axio-dilaton moduli space in type IIB flux compactifications at large complex structure. We find both spectra analytically in an h − 1,2 +3 real-dimensional subspace of the moduli space, and show that they exhibit a universal structure with highly degenerate eigenvalues, independently of the choice of flux, the details of the compactification geometry, and the number of complex structure moduli. In this subspace, the spectrum of the Hessian matrix contains no tachyons, but there are also no critical points. We show numerically that the spectra of H and M remain highly peaked over a large fraction of the sampled moduli space of explicit Calabi-Yau compactifications with 2 to 5 complex structure moduli. In these models, the scale of the supersymmetric contribution to the scalar masses is strongly linearly correlated with the value of the superpotential over almost the entire moduli space, with particularly strong correlations arising for g s <1. We contrast these results with the expectations from the much-used continuous flux approximation, and comment on the applicability of Random Matrix Theory to the statistical modelling of the string theory landscape.

  19. On the equilibrium configuration of the Kittel type domain structure with Bloch walls, l80deg

    International Nuclear Information System (INIS)

    Gavrila, H.

    1975-01-01

    Using a phenomenologic method for appreciating different components of the free energy, the equilibrium configuration of the Kittel-type domain structure with Bloch walls is obtained. By improving the known methods, more accurate magnetostatic energy calculations are reported. In order to determine the equilibrium structure, the total free energy is minimized with respect to two system parameters: the Bloch wall width and the structure half-period. (author)

  20. Magmatic evolution and controls on rare metal-enrichment of the Strange Lake A-type peralkaline granitic pluton, Québec-Labrador

    Science.gov (United States)

    Siegel, Karin; Vasyukova, Olga V.; Williams-Jones, Anthony E.

    2018-05-01

    Although it is well known that A-type granites are enriched in the rare earth elements (REE) and other high field strength elements (HFSE), the magmatic processes that concentrate these elements are still poorly understood. The 1.24 Ga Strange Lake pluton in northern Québec-Labrador provides an extraordinary example of hyper-enrichment in the REE, Zr, and Nb in a peralkaline A-type granite. The pluton consists of two hypersolvus granite units (southern and northern) and a transsolvus granite, all of which contain perthitic alkali feldspar as the earliest major mineral; the transsolvus granite also contains separate albite and microcline crystals. Arfvedsonite, a sodic amphibole, occurs exclusively as phenocrysts in the transsolvus granite, whereas in the hypersolvus granite it is present as a late, interstitial phase. The primary HFSE minerals are zircon, monazite-(Ce), gagarinite-(Ce) and the pyrochlore group minerals. Magma evolution was monitored by the alumina content in the bulk rock, which decreases from the southern to the northern hypersolvus granite and is lowest in the transsolvus granite. Alkalinity indices and bulk Si, Fe, Rb, REE, Zr, Nb concentrations show the opposite trend. Alkali feldspar compositions mirror the trend shown by the bulk rock, i.e., decreasing Al contents are accompanied by increasing Si, Fe3+, REE, Zr and Nb contents. The major driving forces for the evolution of the hypersolvus magma prior to emplacement were the early separation of a fluoride melt from the silicate melt and the crystallization of alkali feldspar and HFSE-rich phases (zircon, monazite-(Ce), pyrochlore group). An alkali feldspar-rich crystal-mush containing LREE-fluoride melt droplets was emplaced as the least evolved southern hypersolvus granite. Massive fractionation of alkali feldspar led to a sharp increase in ƒH2O and F- activity in the magma chamber that triggered the crystallization of arfvedsonite and was followed by emplacement of the northern hypersolvus

  1. Heterotic and type II orientifold compactifications on SU(3) structure manifolds

    International Nuclear Information System (INIS)

    Benmachiche, I.

    2006-07-01

    We study the four-dimensional N=1 effective theories of generic SU(3) structure compactifications in the presence of background fluxes. For heterotic and type IIA/B orientifold theories, the N=1 characteristic data are determined by a Kaluza-Klein reduction of the fermionic actions. The Kaehler potentials, superpotentials and the D-terms are entirely encoded by geometrical data of the internal manifold. The background flux and the intrinsic torsion of the SU(3) structure manifold, gives rise to contributions to the four-dimensional F-terms. The corresponding superpotentials generalize the Gukov-Vafa-Witten superpotential. For the heterotic compactification, the four-dimensional fermionic supersymmetry variations, as well as the conditions on supersymmetric vacua, are determined. The Yukawa couplings of the theory turn out to be similar to their Calabi-Yau counterparts. (Orig.)

  2. Severity of clinical presentation in youth with type 1 diabetes is associated with differences in brain structure.

    Science.gov (United States)

    Siller, Alejandro F; Lugar, Heather; Rutlin, Jerrel; Koller, Jonathan M; Semenkovich, Katherine; White, Neil H; Arbelaez, Ana Maria; Shimony, Joshua; Hershey, Tamara

    2017-12-01

    Differences in cognition and brain structure have been found in youth with type 1 diabetes compared with controls, even after relatively short disease duration. To determine whether severity of clinical presentation contributes to these differences, we obtained structural magnetic resonance imaging (MRI) scans in youth ages 7-17 who were either newly diagnosed with type 1 diabetes (presentation was measured by the presence of diabetic ketoacidosis (DKA) and degree of hyperglycemia exposure [hemoglobin A1c (HbA1c)] at diagnosis. MRI were obtained using T1-weighted, T2-weighted, and diffusion-weighted sequences. Within the group with type 1 diabetes, 12 subjects presented in DKA and 34 did not. After controlling for age, sex, and multiple comparisons, the type 1 diabetes group had lower volume in the left temporal-parietal-occipital cortex compared with controls. Within the type 1 diabetes group, DKA at presentation was associated with lower radial, axial, and mean diffusivity (MD) throughout major white matter tracts and higher HbA1c was associated with lower hippocampal, thalamic, and cerebellar white matter volumes, lower right posterior parietal cortical thickness, and greater right occipital cortical thickness. These data suggest that severity of clinical presentation is an important factor in predicting brain structural differences in youth with type 1 diabetes approximately 3 months after diagnosis. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  3. Production of fine structures in type III solar radio bursts due to turbulent density profiles

    International Nuclear Information System (INIS)

    Loi, Shyeh Tjing; Cairns, Iver H.; Li, Bo

    2014-01-01

    Magnetic reconnection events in the corona release energetic electron beams along open field lines, and the beams generate radio emission at multiples of the electron plasma frequency f p to produce type III solar radio bursts. Type III bursts often exhibit irregularities in the form of flux modulations with frequency and/or local temporal advances and delays, and a type IIIb burst represents the extreme case where a type III burst is fragmented into a chain of narrowband features called striae. Remote and in situ spacecraft measurements have shown that density turbulence is ubiquitous in the corona and solar wind, and often exhibits a Kolmogorov power spectrum. In this work, we numerically investigate the effects of one-dimensional macroscopic density turbulence (along the beam direction) on the behavior of type III bursts, and find that this turbulence produces stria-like fine structures in the dynamic spectra of both f p and 2 f p radiation. Spectral and temporal fine structures in the predicted type III emission are produced by variations in the scattering path lengths and group speeds of radio emission, and in the locations and sizes of emitting volumes. Moderate turbulence levels yield flux enhancements with much broader half-power bandwidths in f p than 2 f p emission, possibly explaining the often observed type IIIb-III harmonic pairs as being where intensifications in 2 f p radiation are not resolved observationally. Larger turbulence levels producing trough-peak regions in the plasma density profile may lead to broader, resolvable intensifications in 2 f p radiation, which may account for the type IIIb-IIIb pairs that are sometimes observed.

  4. Structural trends in off stoichiometric chalcopyrite type compound semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Stephan, Christiane

    2011-03-15

    Energy supply is one of the most controversial topics that are currently discussed in our global community. Most of the energy delivered to the customer today has its origin in fossil and nuclear power plants. Indefinable risks and the radioactive waste repository problem of the latter as well as the global scarcity of fossil resources cause the renewable energies to grow more and more important for achieving sustainability. The main renewable energy sources are wind power, hydroelectric power and solar energy. On the photovoltaic (PV) market different materials are competing as part of different kinds of technologies, with the largest contribution still coming from wafer based crystalline silicon solar cells (95 %). Until now thin film solar cells only contribute a small portion to the whole PV market, but large capacities are under construction. Thin film photovoltaic shows a number of advantages in comparison to wafer based crystalline silicon PV. Among these material usage and production cost reduction are two prominent examples. The type of PV materials, which are analyzed in this work, are high potential compounds that are widely used as absorber layer in thin film solar cells. These are compound semiconductors of the type CuB{sup III}C{sup VI}{sub 2} (B{sup III} = In, Ga and C{sup VI} = Se, S). Several years of research have already gone into understanding the efficiency limiting factors for solar cell devices fabricated from this compound. Most of the studies concerning electronic defects are done by spectroscopic methods mostly performed using thin films from different kinds of synthesis, without any real knowledge regarding the structural origin of these defects. This work shows a systematic fundamental structural study of intrinsic point defects that are present within the material at various compositions in CuB{sup III}C{sup VI}{sub 2} compound semiconductors. The study is done on reference powder samples with well determined chemical composition and

  5. Structural trends in off stoichiometric chalcopyrite type compound semiconductors

    International Nuclear Information System (INIS)

    Stephan, Christiane

    2011-01-01

    Energy supply is one of the most controversial topics that are currently discussed in our global community. Most of the energy delivered to the customer today has its origin in fossil and nuclear power plants. Indefinable risks and the radioactive waste repository problem of the latter as well as the global scarcity of fossil resources cause the renewable energies to grow more and more important for achieving sustainability. The main renewable energy sources are wind power, hydroelectric power and solar energy. On the photovoltaic (PV) market different materials are competing as part of different kinds of technologies, with the largest contribution still coming from wafer based crystalline silicon solar cells (95 %). Until now thin film solar cells only contribute a small portion to the whole PV market, but large capacities are under construction. Thin film photovoltaic shows a number of advantages in comparison to wafer based crystalline silicon PV. Among these material usage and production cost reduction are two prominent examples. The type of PV materials, which are analyzed in this work, are high potential compounds that are widely used as absorber layer in thin film solar cells. These are compound semiconductors of the type CuB III C VI 2 (B III = In, Ga and C VI = Se, S). Several years of research have already gone into understanding the efficiency limiting factors for solar cell devices fabricated from this compound. Most of the studies concerning electronic defects are done by spectroscopic methods mostly performed using thin films from different kinds of synthesis, without any real knowledge regarding the structural origin of these defects. This work shows a systematic fundamental structural study of intrinsic point defects that are present within the material at various compositions in CuB III C VI 2 compound semiconductors. The study is done on reference powder samples with well determined chemical composition and using advanced diffraction techniques

  6. Synthesis, crystal structure and charge-distribution validation of β-Na4Cu(MoO43 adopting the alluadite structure-type

    Directory of Open Access Journals (Sweden)

    Wassim Dridi

    2016-08-01

    Full Text Available Single crystals of a new variety of tetrasodium copper(II tris[molybdate(VI], Na4Cu(MoO43, have been synthesized by solid-state reactions and characterized by single-crystal X-ray diffraction. This alluaudite structure-type is characterized by the presence of infinite layers of composition (Cu/Na2Mo3O14 parallel to the (100 plane, which are linked by MoO4 tetrahedra, forming a three-dimensional framework containing two types of hexagonal channels in which Na+ cations reside. The Cu2+ and Na2+ cations are located at the same general site with occupancies of 0.5. All atoms are on general positions except for one Mo, two Na (site symmetry 2 and another Na (site symmetry -1 atom. One O atom is split into two separate positions with occupancies of 0.5. The title compound is isotypic with Na5Sc(MoO44 and Na3In2As3O12. The structure model is supported by bond-valence-sum (BVS and charge-distribution CHARDI methods. β-Na4Cu(MoO43 is compared and discussed with the K4Cu(MoO43 and α-Na4Cu(MoO43 structures.

  7. Structural Analysis of the Pantograph Type IVTM in PGSFR

    International Nuclear Information System (INIS)

    Kim, S. H.; Koo, G. H.

    2014-01-01

    The pantograph type IVTM (In.Vessel Transfer Machine) in PGSFR handle fuel assemblies inside the reactor core, which has six kinds of movements and transfers the new and spent core assemblies between the fuel transfer port and the reactor core. In the IVTM, the main tube supports the pantograph arm and the slot in which the movement of the pantograph arm is possible. The gripper mechanism is mounted to the gripper guide structure and the vertical movement of the gripper is possible by using the screw driver shaft. In this study, we performed the primary stress analysis by considering the IVTM 3D configuration. Also, the thermal stress analysis was carried out and the mode characteristics of the structure by the natural frequency analysis were analyzed. The IVTM is supported by the rotating plug, which has the maximum arm length of 1.125 m. When the fuel assemblies are inserted and withdrawn from the reactor core, the refueling design load of 24.5 kN is considered at the gripper. The primary stress analysis is carried out by considering the above design load and a dead weight. Fig. 2 shows the stress intensity distribution due to the refueling design load and the dead weight. As shown in this figure, the maximum stress intensity is 40.6 MPa. Also, from the Fig. 3, we can see that the maximum stress occurs at the rotation pin joint of the pantograph arm link. The maximum dIsplacement is 4mm, which occurs at the lowest end of the pantograph arm. The structural analyses are carried out to evaluate the structural integrity of the IVTM. The primary stress analysis for the refueling design load, the thermal stress analysis and the natural frequency analysis are performed, and the stresses and dIsplacements are evaluated

  8. Topological honeycomb magnon Hall effect: A calculation of thermal Hall conductivity of magnetic spin excitations

    Energy Technology Data Exchange (ETDEWEB)

    Owerre, S. A., E-mail: solomon@aims.ac.za [African Institute for Mathematical Sciences, 6 Melrose Road, Muizenberg, Cape Town 7945, South Africa and Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo, Ontario N2L 2Y5 (Canada)

    2016-07-28

    Quite recently, the magnon Hall effect of spin excitations has been observed experimentally on the kagome and pyrochlore lattices. The thermal Hall conductivity κ{sup xy} changes sign as a function of magnetic field or temperature on the kagome lattice, and κ{sup xy} changes sign upon reversing the sign of the magnetic field on the pyrochlore lattice. Motivated by these recent exciting experimental observations, we theoretically propose a simple realization of the magnon Hall effect in a two-band model on the honeycomb lattice. The magnon Hall effect of spin excitations arises in the usual way via the breaking of inversion symmetry of the lattice, however, by a next-nearest-neighbour Dzyaloshinsky-Moriya interaction. We find that κ{sup xy} has a fixed sign for all parameter regimes considered. These results are in contrast to the Lieb, kagome, and pyrochlore lattices. We further show that the low-temperature dependence on the magnon Hall conductivity follows a T{sup 2} law, as opposed to the kagome and pyrochlore lattices. These results suggest an experimental procedure to measure thermal Hall conductivity within a class of 2D honeycomb quantum magnets and ultracold atoms trapped in a honeycomb optical lattice.

  9. Ternary and quaternary solid solutions in rare earth alloy phases with the CaCu5-type structure

    International Nuclear Information System (INIS)

    Malani, G.K.; Raman, A.; Mohanty, R.C.

    1992-01-01

    Crystal structural data were analyzed in seleced CaCu 5 -type ternary and quaternary solid solutions to assess the crystal chemical characteristics and stability features of the CaCu 5 -type structure in rare earth containing alloy phases. LaNi 5 was found to dissolve 100 mol% LaCu 5 , 100 mol% ErNi 5 , about 50 mol% LaIr 5 , 40 mol% 'LaMn 5 ', 20 mol% 'LaFe 5 ', and 25 mol% ErRh 5 . In contrast, LaCo 5 did not dissolve any Mn or any of the other elements other than Al - it dissolved about 20 mol% 'LaAl 5 '. LaCu 5 behaves similar to LaNi 5 in solid solutions. From the lack of solubility of any other element in LaFe 5 , LaCo 5 , LaRh 5 , and LaIr 5 and their great instability, these are inferred to be borderline cases in the realm of the CaCu 5 -type structure. In the CaCu 5 and related crystal structures, Ir is compatible with Ni, but not with Co or Rh, and Rh is not compatible with either Ni or Ir. (orig.) [de

  10. Structure, Raman spectra and defect chemistry modelling of conductive pyrochlore oxides

    DEFF Research Database (Denmark)

    Poulsen, F.W.; Glerup, M.; Holtappels, P.

    2000-01-01

    -O(x) and V-O on the O site, interstitial oxygens O-i", and delocalised electrons and electron holes. Four mass action law expressions govern such a model. The defect model can rationalise why home-valent doping, i.e. substitution of Zr(4+) by Ce(4+), can lead to an increase in ionic conductivity...

  11. X-ray diffuse scattering effects from Coulomb-type defects in multilayered structures

    International Nuclear Information System (INIS)

    Olikhovskii, S.I.; Molodkin, V.B.; Skakunova, E.S.; Kislovskii, E.N.; Fodchuk, I.M.

    2009-01-01

    The theoretical X-ray diffraction model starting from Takagi-Taupin equation has been developed for the description of coherent and diffuse components of the rocking curve (RC) measured from the multilayered crystal structure with randomly distributed Coulomb-type defects in all the layers and substrate. The model describes both diffuse scattering (DS) intensity distribution and influence of DS on attenuation and angular redistribution of the coherent X-ray scattering intensity. By analyzing the total measured RC with using the proposed diffraction model, the chemical compositions, strains, and characteristics of dislocation loops in layers and substrate of the multilayered structure with InGaAsN/GaAs single quantum well have been determined. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  12. A structure development in electron-irradiated type Ia diamond

    International Nuclear Information System (INIS)

    Novikov, N.V.; Ositinskaya, T.D.; Tkach, V.N.

    1998-01-01

    A type Ia diamond crystal with nitrogen impurity in different forms was irradiated by 3.5 MeV electrons with increasing doses 5 centre dot 10 16 , 2 centre dot 10 17 , 4 centre dot 10 17 , 2 centre dot 10 18 e/cm 2 and investigated before and after each dose by positron annihilation, EPR, and optical spectroscopy. After irradiation with the highest dose, the effect of development of a visible defective structure of the crystal is revealed. A description of this effect and data of EPR and IR-measurements depending on irradiation doses are presented. First results of cathodoluminescence (CL) studies in the form CL-topograms and CL-spectra for difference zones of the crystal are also given

  13. Croatian banking sector research: relationship between ownership structure, concentration, owners’ type and bank performance

    Directory of Open Access Journals (Sweden)

    Igor Tomičić

    2012-12-01

    Full Text Available Banks are important financial intermediaries of any national economy, and corporate governance has an important role in banking sector; especially due to processes of the globalization and the internationalization, and also because of the sensitivity of the activities between the interest groups. The objective of this paper is to examine the relationship between ownership structure, concentration, owners’ type and bank performance. The authors made a research of banks' ownership structure using publicly available data. Using statistical tools authors discovered relationships between bank ownership structure and bank performance indicators (average asset, total asset, average equity, profit (loss before taxes, profit (loss after taxes, ROAA, ROAE. Further they discuss the relationships between ownership structure and a number of consequences for the bank performance. The authors discovered significant correlation between bank ownership structure and performance indicators variables that are described in the paper.

  14. An efficient algorithm for planar drawing of RNA structures with pseudoknots of any type.

    Science.gov (United States)

    Byun, Yanga; Han, Kyungsook

    2016-06-01

    An RNA pseudoknot is a tertiary structural element in which bases of a loop pair with complementary bases are outside the loop. A drawing of RNA secondary structures is a tree, but a drawing of RNA pseudoknots is a graph that has an inner cycle within a pseudoknot and possibly outer cycles formed between the pseudoknot and other structural elements. Visualizing a large-scale RNA structure with pseudoknots as a planar drawing is challenging because a planar drawing of an RNA structure requires both pseudoknots and an entire structure enclosing the pseudoknots to be embedded into a plane without overlapping or crossing. This paper presents an efficient heuristic algorithm for visualizing a pseudoknotted RNA structure as a planar drawing. The algorithm consists of several parts for finding crossing stems and page mapping the stems, for the layout of stem-loops and pseudoknots, and for overlap detection between structural elements and resolving it. Unlike previous algorithms, our algorithm generates a planar drawing for a large RNA structure with pseudoknots of any type and provides a bracket view of the structure. It generates a compact and aesthetic structure graph for a large pseudoknotted RNA structure in O([Formula: see text]) time, where n is the number of stems of the RNA structure.

  15. Fixed-structure Control of LTI Systems with Polytopic-type Uncertainty: Application to Inverter-interfaced Microgrids

    OpenAIRE

    Sad Abadi, Mahdieh Sadat

    2016-01-01

    This thesis focuses on the development of robust control solutions for linear time-invariant interconnected systems affected by polytopic-type uncertainty. The main issues involved in the control of such systems, e.g. sensor and actuator placement, control configuration selection, and robust fixed-structure control design are included. The problem of fixed-structure control is intrinsically nonconvex and hence computationally intractable. Nevertheless, the problem has attracted considerab...

  16. Performance of the mesh-type liquid cadmium cathode structure for the electrodeposition of uranium from the molten salt

    International Nuclear Information System (INIS)

    Paek, S.; Kim, S.H.; Lee, H.; Ahn, D.H.; Yoon, D.S.

    2010-01-01

    A mesh-type liquid cadmium cathode (LCC) structure has been devised to improve the performance of the electro-winning process for the recovery of actinides in a molten chloride system. For the verification of its performance, electrodeposition experiments of uranium from the molten LiCl-KCl-UCl 3 salt were conducted at 773 K for different current densities using the mesh-type LCC structure. Uranium was successfully collected over 5 wt. % in the LCC without growing uranium dendrites. The mesh-type LCC structure prevented the uncontrolled growth of uranium dendrites into the electrolyte phase above the cadmium surface and caused the LCC deposit to accumulate at the higher in the cadmium phase over uranium solubility in cadmium. After cooling the LCC crucible, its solid deposits were identified as an intermetallic compound UCd 11 by EPMA and XRD analysis. The cathode potential profiles from the electrochemical experiments and the chemical structure of the LCC deposits showed that it could be applied practically to recover the actinides above their solubility in cadmium. (orig.)

  17. Phase transformations during HLnTiO{sub 4} (Ln=La, Nd) thermolysis and photocatalytic activity of obtained compounds

    Energy Technology Data Exchange (ETDEWEB)

    Silyukov, Oleg I., E-mail: olegsilyukov@yandex.ru; Abdulaeva, Liliia D.; Burovikhina, Alena A.; Rodionov, Ivan A.; Zvereva, Irina A.

    2015-03-15

    Layered HLnTiO{sub 4} (Ln=La, Nd) compounds belonging to Ruddlesden–Popper phases were found to form partially hydrated compounds Ln{sub 2}Ti{sub 2}O{sub 7}·xH{sub 2}O during thermal dehydration as well as defect oxides Ln{sub 2}□Ti{sub 2}O{sub 7} as final products. Further heating of metastable defect Ln{sub 2}□Ti{sub 2}O{sub 7} substances leads to the formation of pyrochlore-type oxides Ln{sub 2}Ti{sub 2}O{sub 7} {sub (p)}, with subsequent transformation under higher temperatures to stable layered 110-type perovskites Ln{sub 2}Ti{sub 2}O{sub 7}. The occurring structure transformations lead to an increase of photocatalytic activity in the order of HLnTiO{sub 4}pyrochlor-type oxides Ln{sub 2}Ti{sub 2}O{sub 7} {sub (p)}, with subsequent transformation to layered 110-type perovskites Ln{sub 2}Ti{sub 2}O{sub 7}. Structure transformations lead to an increase of photocatalytic activity in the order of HLnTiO{sub 4}structure changes during thermolysis.

  18. Regional factors rather than forest type drive the community structure of soil living oribatid mites (Acari, Oribatida).

    Science.gov (United States)

    Erdmann, Georgia; Scheu, Stefan; Maraun, Mark

    2012-06-01

    Most European forests are managed by humans. However, the manner and intensity of management vary. While the effect of forest management on above-ground communities has been investigated in detail, effects on the below-ground fauna remain poorly understood. Oribatid mites are abundant microarthropods in forest soil and important decomposers in terrestrial ecosystems. Here, we investigated the effect of four forest types (i.e., managed coniferous forests; 30 and 70 years old managed beech forests; natural beech forests) on the density, diversity and community structure of oribatid mites (Acari). The study was replicated at three regions in Germany: the Swabian Alb, the Hainich and the Schorfheide. To relate changes in oribatid mite community structure to environmental factors, litter mass, pH, C and N content of litter, fine roots and C content of soil were measured. Density of oribatid mites was highest in the coniferous forests and decreased in the order 30 years old, 70 years old, and natural beech forests. Mass of the litter layer and density of oribatid mites were strongly correlated indicating that the litter layer is an important factor regulating oribatid mite densities. Diversity of oribatid mites was little affected by forest type indicating that they harbor similar numbers of niches. Species composition differed between the forest types, suggesting different types of niches. The community structure of oribatid mites differed more strongly between the three regions than between the forest types indicating that regional factors are more important than effects associated with forest type.

  19. The Differential-Algebraic Analysis of Symplectic and Lax Structures Related with New Riemann-Type Hydrodynamic Systems

    Science.gov (United States)

    Prykarpatsky, Yarema A.; Artemovych, Orest D.; Pavlov, Maxim V.; Prykarpatski, Anatolij K.

    2013-06-01

    A differential-algebraic approach to studying the Lax-type integrability of the generalized Riemann-type hydrodynamic hierarchy, proposed recently by O. D. Artemovych, M. V. Pavlov, Z. Popowicz and A. K. Prykarpatski, is developed. In addition to the Lax-type representation, found before by Z. Popowicz, a closely related representation is constructed in exact form by means of a new differential-functional technique. The bi-Hamiltonian integrability and compatible Poisson structures of the generalized Riemann type hierarchy are analyzed by means of the symplectic and gradient-holonomic methods. An application of the devised differential-algebraic approach to other Riemann and Vakhnenko type hydrodynamic systems is presented.

  20. Paired structures, imprecision types and two-level knowledge representation by means of opposites

    DEFF Research Database (Denmark)

    Rodríguez, J. Tinguaro; Franco de los Ríos, Camilo; Gómez, Daniel

    2016-01-01

    Opposition-based models are a current hot-topic in knowledge representation. The point of this paper is to suggest that opposition can be in fact introduced at two different levels, those of the predicates of interest being represented (as short/tall) and of the logical references (true/false) used...... to evaluate the verification of the former. We study this issue by means of the consideration of different paired structures at each level. We also pay attention at how different types of fuzziness may be introduced in these paired structures to model imprecision and lack of knowledge. As a consequence, we...

  1. Topology of Large-Scale Structure by Galaxy Type: Hydrodynamic Simulations

    Science.gov (United States)

    Gott, J. Richard, III; Cen, Renyue; Ostriker, Jeremiah P.

    1996-07-01

    The topology of large-scale structure is studied as a function of galaxy type using the genus statistic. In hydrodynamical cosmological cold dark matter simulations, galaxies form on caustic surfaces (Zeldovich pancakes) and then slowly drain onto filaments and clusters. The earliest forming galaxies in the simulations (defined as "ellipticals") are thus seen at the present epoch preferentially in clusters (tending toward a meatball topology), while the latest forming galaxies (defined as "spirals") are seen currently in a spongelike topology. The topology is measured by the genus (number of "doughnut" holes minus number of isolated regions) of the smoothed density-contour surfaces. The measured genus curve for all galaxies as a function of density obeys approximately the theoretical curve expected for random- phase initial conditions, but the early-forming elliptical galaxies show a shift toward a meatball topology relative to the late-forming spirals. Simulations using standard biasing schemes fail to show such an effect. Large observational samples separated by galaxy type could be used to test for this effect.

  2. Sintering Characteristics of Multilayered Thermal Barrier Coatings Under Thermal Gradient and Isothermal High Temperature Annealing Conditions

    Science.gov (United States)

    Rai, Amarendra K.; Schmitt, Michael P.; Bhattacharya, Rabi; Zhu, Dongming; Wolfe, Douglas E.

    2014-01-01

    Pyrochlore oxides have most of the relevant attributes for use as next generation thermal barrier coatings such as phase stability, low sintering kinetics and low thermal conductivity. One of the issues with the pyrochlore oxides is their lower toughness and therefore higher erosion rate compared to the current state-of-the-art TBC material, yttria (6 to 8 wt%) stabilized zirconia (YSZ). In this work, sintering characteristics were investigated for novel multilayered coating consisted of alternating layers of pyrochlore oxide viz Gd2Zr2O7 and t' low k (rare earth oxide doped YSZ). Thermal gradient and isothermal high temperature (1316 C) annealing conditions were used to investigate sintering and cracking in these coatings. The results are then compared with that of relevant monolayered coatings and a baseline YSZ coating.

  3. Lexicographical structuring: the number and types of fields, data distribution, searching and data presentation

    DEFF Research Database (Denmark)

    Bergenholtz, Henning; Pedersen, Heidi Agerbo

    2015-01-01

    This contribution will not describe the structure in existing dictionaries. Instead, it will focus on the decisions that lexicographers make when they draw up the concept for and carry out the production of one or more new dictionaries, or when they consider making changes in the data presentation...... in an existing dictionary. This part of the lexicographical work is what we call structuring, which encompasses a number of various lexicographical decisions. One of these is choosing the fields that a database should contain. Typically, for some of these field types, it will be easy to distribute data......, but for other fields it will require long considerations as there are several distribution options with different outcomes of varying usefulness. A second type of lexicographical decision to be made by the lexicographer is the predefined searching, which involves in what order searches are to be made...

  4. Structural Pre-sizing of a Coaxial Double-tube Type Hot Gas Duct

    Energy Technology Data Exchange (ETDEWEB)

    Song, Kee Nam; Kim, Y-W [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2008-10-15

    The nuclear hydrogen system being researched at KAERI is planning to produce hydrogen in the order of 950 .deg. C by using nuclear energy and a thermo-chemical process, and helium gas is tentatively considered as the choice for the coolant. A hot gas duct (HGD) is a key component connecting the reactor pressure vessel and the intermediate heat exchanger (IHX) for the nuclear hydrogen system. The HGD is a unique component exclusively found in an HTR-module concept where a nuclear core and IHX are placed separately into two pressure vessels, which require a connecting duct between them. A coaxial double-tube type cross vessel is considered for the HGD structure of the nuclear hydrogen system because of its successive extensive experience. In this study, a structural pre-sizing for the primary HGD was carried out. These activities include a predecision on the geometric dimensions, a pre-evaluation on the strength, and a pre-selection on the material of the coaxial double-tube type cross vessel components. A predecision on the geometric dimensions was undertaken based on various engineering concepts, such as a constant flow velocity (CFV) model, a constant flow rate (CFR) model, a constant hydraulic head (CHH) model, and finally a heat balanced (HB) model. For the CFV model, CFR model, and CHH model, the HGD structure might be insensitive to a flow induced vibration (FIV) in the case where there are no pressure differences between the hot and cold helium regions. Also we compared the geometric dimensions from the various models.

  5. A study on structural changes in protein by time-division type Laue method

    International Nuclear Information System (INIS)

    Morimoto, Hideki

    1995-01-01

    In order to know the physiological roles of proteins, it is important to investigate the intermediate states of their structural changes. The sizes of proteins are generally several tens angstrom(A). Considering the resolution, only x-ray crystal analysis can be used in practice for the investigation of the mechanism of protein structural changes, though NMR is applicable only for small-sized proteins. However, x-ray analysis is not so suitable for analysis of their intermediate states. Thus, the author paid attention to the time-division type Laue method for the study of hemoglobin (Hb). Laser-flash induces to release carbonmonooxide (CO) from carboxyhemoglobin (Hb(CO) 4 ). Therefore, if an appropriate length of x-ray pulse (∼100 picosec) is available, the processes in the period from cleavage of the bond between a ligand (O 2 , CO or NO) and Hb to recombination of them might be monitored. Using DNA recombination and chemical modification techniques, recombinant Hb, of which T structure is stable was produced. An investigation on the conditions which allow to release CO from the Hb is undertaken using a single crystal of this Hb. The experimental systems applicable to time-division type Laue method are some protein molecules participating in chemical reactions inducible by light absorption, the electron-transfer system excited by light and so on. (M.N.)

  6. A study on structural changes in protein by time-division type Laue method

    Energy Technology Data Exchange (ETDEWEB)

    Morimoto, Hideki [Osaka Univ., Toyonaka (Japan). Faculty of Engineering Science

    1995-11-01

    In order to know the physiological roles of proteins, it is important to investigate the intermediate states of their structural changes. The sizes of proteins are generally several tens angstrom(A). Considering the resolution, only x-ray crystal analysis can be used in practice for the investigation of the mechanism of protein structural changes, though NMR is applicable only for small-sized proteins. However, x-ray analysis is not so suitable for analysis of their intermediate states. Thus, the author paid attention to the time-division type Laue method for the study of hemoglobin (Hb). Laser-flash induces to release carbonmonooxide (CO) from carboxyhemoglobin (Hb(CO){sub 4}). Therefore, if an appropriate length of x-ray pulse ({approx}100 picosec) is available, the processes in the period from cleavage of the bond between a ligand (O{sub 2}, CO or NO) and Hb to recombination of them might be monitored. Using DNA recombination and chemical modification techniques, recombinant Hb, of which T structure is stable was produced. An investigation on the conditions which allow to release CO from the Hb is undertaken using a single crystal of this Hb. The experimental systems applicable to time-division type Laue method are some protein molecules participating in chemical reactions inducible by light absorption, the electron-transfer system excited by light and so on. (M.N.)

  7. Finite Element Analysis of Doorframe Structure of Single Oblique Pole Type in Container Crane

    Science.gov (United States)

    Cheng, X. F.; Wu, F. Q.; Tang, G.; Hu, X.

    2017-07-01

    Compared with the composite type, the single oblique pole type has more advantages, such as simple structure, thrift steel and high safe overhead clearance. The finite element model of the single oblique pole type is established in nodes by ANSYS, and more details are considered when the model is simplified, such as the section of Girder and Boom, torque in Girder and Boom occurred by Machinery house and Trolley, density according to the way of simplification etc. The stress and deformation of ten observation points are compared and analyzed, when the trolley is in nine dangerous positions. Based on the result of analysis, six dangerous points are selected to provide reference for the detection and evaluation of container crane.

  8. CTAB-Assisted Hydrothermal Synthesis of Bi2Sn2O7 Photocatalyst and Its Highly Efficient Degradation of Organic Dye under Visible-Light Irradiation

    Directory of Open Access Journals (Sweden)

    Weicheng Xu

    2013-01-01

    Full Text Available Pyrochlore-type Bi2Sn2O7 (BSO nanoparticles have been prepared by a hydrothermal method assisted with a cationic surfactant cetyltrimethylammonium bromide (CTAB. These BSO products were characterized by powder X-ray diffraction (XRD, infrared spectroscopy (IR, scanning electron microscopy (SEM, transmission electron microscopy (TEM, Brunauer-Emmett-Teller (BET, and UV-visible diffuse reflectance spectroscopy (DRS. The results indicated that CTAB alters the surface parameters and the morphology and enhances the photoinduced charge separation rate of BSO. The photocatalytic degradation test using rhodamine B as a model pollutant showed that the photocatalytic activity of the BSO assisted with CTAB was two times that of the reference BSO. Close investigation revealed that the size, the band gap, the structure, and the existence of impurity level played an important role in the photocatalytic activities.

  9. Fabrication and spectroscopic properties of nanocrystalline La{sub 2}Hf{sub 2}O{sub 7}:Pr

    Energy Technology Data Exchange (ETDEWEB)

    Trojan-Piegza, J., E-mail: jtp@eto.wchuwr.p [Faculty of Chemistry, Wroclaw University, 14 F. Joliot-Curie Street, 50383 Wroclaw (Poland); Zych, E.; Kosinska, M. [Faculty of Chemistry, Wroclaw University, 14 F. Joliot-Curie Street, 50383 Wroclaw (Poland)

    2010-03-15

    La{sub 2}Hf{sub 2}O{sub 7} nanopowders doped with different Pr concentrations (0.05-10 mol.%) were synthesized by the Pechini method. XRD measurements confirmed the single crystalline phase formed already at 800 {sup o}C and the structure was cubic pyrochlore. Luminescence excitation and emission as well as radioluminescence spectra were recorded for the materials. Both optical and X-ray excitation of La{sub 2}Hf{sub 2}O{sub 7}:Pr produced a red emission resulting from the 4f-4f transitions of Pr{sup 3+} ions. Luminescence of materials synthesized at low temperatures was characterized by broadband glass-type emissions, while heat treatment at 1400 {sup o}C led to spectra showing the typical for crystalline hosts narrow and intense 4f-4f transitions of Pr{sup 3+}.

  10. Phase transition in metastable perovskite Pb(AlNb)0,5O3

    International Nuclear Information System (INIS)

    Zhabko, T.E.; Olekhnovich, N.M.; Shilin, A.D.

    1987-01-01

    Dielectric properties of metastable perovskite Pb(AlNb) 0.5 O 3 and X-ray temperature investigations of both perovskite and pyrochlore modifications of the given compound are studied. Samples with the perovskite structure are prepared from the pyrochlorephase at 4-5 GPa pressure and 1170-1270 K. Ferroelectric phase transition is shown to occur in the metastable perovskite phase Pb(AlNb) 0.5 O 3 at 170 K

  11. Galaxy clusters, type Ia supernovae and the fine structure constant

    Energy Technology Data Exchange (ETDEWEB)

    Holanda, R.F.L. [Departamento de Física, Universidade Estadual da Paraíba, street Baraúnas, Campina Grande, PB, 58429-500 (Brazil); Busti, V.C. [Departamento de Física Matemática, Instituto de Física, Universidade de São Paulo, CP 66318, São Paulo, SP, CEP 05508-090 Brazil (Brazil); Colaço, L.R. [Departamento de Física, Universidade Federal de Campina Grande, street Aprígio Veloso, Campina Grande, PB, 58429-900 (Brazil); Alcaniz, J.S. [Observatório Nacional, Street José Cristino, Rio de Janeiro, RJ, 20921-400 (Brazil); Landau, S.J., E-mail: holanda@uepb.edu.br, E-mail: viniciusbusti@gmail.com, E-mail: colacolrc@gmail.com, E-mail: alcaniz@on.br, E-mail: slandau@df.uba.ar [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Viamonte, Buenos Aires, 1053 Argentina (Argentina)

    2016-08-01

    As is well known, measurements of the Sunyaev-Zeldovich effect can be combined with observations of the X-ray surface brightness of galaxy clusters to estimate the angular diameter distance to these structures. In this paper, we show that this technique depends on the fine structure constant, α. Therefore, if α is a time-dependent quantity, e.g., α = α{sub 0}φ( z ), where φ is a function of redshift, we argue that current data do not provide the real angular diameter distance, D {sub A}( z ), to the cluster, but instead D {sub A}{sup data}( z ) = φ( z ){sup 2} D {sub A}( z ). We use this result to derive constraints on a possible variation of α for a class of dilaton runaway models considering a sample of 25 measurements of D {sub A}{sup data}( z ) in redshift range 0.023 < z < 0.784 and estimates of D {sub A}( z ) from current type Ia supernovae observations. We find no significant indication of variation of α with the present data.

  12. White Matter Structural Differences in Young Children With Type 1 Diabetes: A Diffusion Tensor Imaging Study

    Science.gov (United States)

    Aye, Tandy; Barnea-Goraly, Naama; Ambler, Christian; Hoang, Sherry; Schleifer, Kristin; Park, Yaena; Drobny, Jessica; Wilson, Darrell M.; Reiss, Allan L.; Buckingham, Bruce A.

    2012-01-01

    OBJECTIVE To detect clinical correlates of cognitive abilities and white matter (WM) microstructural changes using diffusion tensor imaging (DTI) in young children with type 1 diabetes. RESEARCH DESIGN AND METHODS Children, ages 3 to <10 years, with type 1 diabetes (n = 22) and age- and sex-matched healthy control subjects (n = 14) completed neurocognitive testing and DTI scans. RESULTS Compared with healthy controls, children with type 1 diabetes had lower axial diffusivity (AD) values (P = 0.046) in the temporal and parietal lobe regions. There were no significant differences between groups in fractional anisotropy and radial diffusivity (RD). Within the diabetes group, there was a significant, positive correlation between time-weighted HbA1c and RD (P = 0.028). A higher, time-weighted HbA1c value was significantly correlated with lower overall intellectual functioning measured by the full-scale intelligence quotient (P = 0.03). CONCLUSIONS Children with type 1 diabetes had significantly different WM structure (as measured by AD) when compared with controls. In addition, WM structural differences (as measured by RD) were significantly correlated with their HbA1c values. Additional studies are needed to determine if WM microstructural differences in young children with type 1 diabetes predict future neurocognitive outcome. PMID:22966090

  13. New tetragonal derivatives of cubic NaZn{sub 13}-type structure: RNi{sub 6}Si{sub 6} compounds, crystal structure and magnetic ordering (R=Y, La, Ce, Sm, Gd–Yb)

    Energy Technology Data Exchange (ETDEWEB)

    Pani, M.; Manfrinetti, P.; Provino, A. [INFM and Dipartimento di Chimica e Chimica Industriale, Universita‘ di Genova, Via Dodecaneso 31, 16146 Genova (Italy); Yuan, Fang; Mozharivskyj, Y. [Department of Chemistry and Chemical Biology, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4M1 (Canada); Morozkin, A.V., E-mail: morozkin@general.chem.msu.ru [Department of Chemistry, Moscow State University, Leninskie Gory, House 1, Building 3, GSP-2, Moscow 119992 (Russian Federation); Knotko, A.V.; Garshev, A.V. [Department of Chemistry, Moscow State University, Leninskie Gory, House 1, Building 3, GSP-2, Moscow 119992 (Russian Federation); Yapaskurt, V.O. [Department of Petrology, Geological Faculty, Moscow State University, Leninskie Gory, Moscow 119992 (Russian Federation); Isnard, O. [Université Grenoble Alpes, Inst NEEL, BP166, F-38042 Grenoble (France); CNRS, Institut NEEL, 25 rue des martyrs, F-38042 Grenoble (France)

    2014-02-15

    Novel RNi{sub 6}Si{sub 6} compounds adopt the new CeNi{sub 6}Si{sub 6}-type structure for R=La–Ce (tP52, space group P4/nbm N 125-1) and new YNi{sub 6}Si{sub 6}-type structure for R=Y, Sm, Gd–Yb (tP52, space group P4{sup ¯}b2N 117) that are tetragonal derivative of NaZn{sub 13}-type structure, like LaCo{sub 9}Si{sub 4}-type. The CeNi{sub 6}Si{sub 6}, GdNi{sub 6}Si{sub 6}, TbNi{sub 6}Si{sub 6}, DyNi{sub 6}Si{sub 6} and HoNi{sub 6}Si{sub 6} compounds are Curie–Weiss paramagnets down to ∼30 K, and do not order magnetically down to 5 K. However, the inverse paramagnetic susceptibility of LaNi{sub 6}Si{sub 6} does not follow Curie–Weiss law. The DyNi{sub 6}Si{sub 6} shows ferromagnetic-like saturation behaviour at 5 K in applied fields of 50 kOe, giving rise to a magnetic moment value of 6.5 μ{sub B}/f.u. in 50 kOe. The powder neutron diffraction study in zero applied filed indicates square modulated the c-collinear antiferromagnetic ordering of TbNi{sub 6}Si{sub 6} with K=[±1/4, ±1/4, 0] wave vector below ∼10 K. - Graphical abstract: Novel (La, Ce)Ni{sub 6}Si{sub 6} compounds adopt the new CeNi{sub 6}Si{sub 6}-type structure and (Y, Sm, Gd–Yb) adopt the new YNi{sub 6}Si{sub 6}-type structure that are tetragonal derivative of NaZn{sub 13}-type structure, like LaCo{sub 9}Si{sub 4}-type. The CeNi{sub 6}Si{sub 6}, GdNi{sub 6}Si{sub 6}, TbNi{sub 6}Si{sub 6}, DyNi{sub 6}Si{sub 6} and HoNi{sub 6}Si{sub 6} compounds are Curie–Weiss paramagnets down to ∼30 K, and do not order magnetically down to 4.2 K. The powder neutron diffraction study in zero applied filed indicates square modulated the c-collinear antiferromagnetic ordering of TbNi{sub 6}Si{sub 6} with K=[±1/4, ±1/4, 0] wave vector below ∼10 K. Display Omitted - Highlights: • The new (La, Ce)Ni{sub 6}Si{sub 6} compounds adopt the new CeNi{sub 6}Si{sub 6}-type structure. • The new (Y, Sm, Gd–Yb)Ni{sub 6}Si{sub 6} compounds adopt the new YNi{sub 6}Si{sub 6}-type structure. • TbNi{sub 6}Si

  14. Comparative study of hydroelastic responses of semisubmersible type and pontoon type very large floating structure in waves; Tachushiki semisabugata to pontoon gata choogata futai no harochu dansei oto no hikaku

    Energy Technology Data Exchange (ETDEWEB)

    Ma, N; Hirayama, T; Sato, N [Yokohama National University, Yokohama (Japan). Faculty of Engineering

    1997-12-31

    A semisubmersible very large floating structure is compared with an equivalent pontoon type in vertical displacement and longitudinal bending moment in waves. The theoretical calculation is based on the mode synthesis method, and fluid force is analyzed by the three-dimensional singularity method for the symmetric structure, in which the effects of elastic deformation are taken into account. The semisubmersible and pontoon types are not much different from each other in eigenfrequency and mode shape in the dry mode. In the wet mode, on the other hand, the pontoon type is characterized by the synthetic mode in which torsional and bending modes overlap each other, each mode having a similar eigenfrequency. These types are different in elastic response, the pontoon type having several tens times higher coefficient of attenuation than the semisubmersible type. The pontoon type is generally lower in response, but its torsional mode is excited in transverse waves, making it higher than the semisubmersible type at near eigenfrequency of this mode. 15 refs., 17 figs., 2 tabs.

  15. Comparative study of hydroelastic responses of semisubmersible type and pontoon type very large floating structure in waves; Tachushiki semisabugata to pontoon gata choogata futai no harochu dansei oto no hikaku

    Energy Technology Data Exchange (ETDEWEB)

    Ma, N.; Hirayama, T.; Sato, N. [Yokohama National University, Yokohama (Japan). Faculty of Engineering

    1996-12-31

    A semisubmersible very large floating structure is compared with an equivalent pontoon type in vertical displacement and longitudinal bending moment in waves. The theoretical calculation is based on the mode synthesis method, and fluid force is analyzed by the three-dimensional singularity method for the symmetric structure, in which the effects of elastic deformation are taken into account. The semisubmersible and pontoon types are not much different from each other in eigenfrequency and mode shape in the dry mode. In the wet mode, on the other hand, the pontoon type is characterized by the synthetic mode in which torsional and bending modes overlap each other, each mode having a similar eigenfrequency. These types are different in elastic response, the pontoon type having several tens times higher coefficient of attenuation than the semisubmersible type. The pontoon type is generally lower in response, but its torsional mode is excited in transverse waves, making it higher than the semisubmersible type at near eigenfrequency of this mode. 15 refs., 17 figs., 2 tabs.

  16. Some properties of tetravalent actinide phosphates of M1M42(PO4)3 type and peculiarities of their structure

    International Nuclear Information System (INIS)

    Burnaeva, A.A.; Volkov, Yu.F.; Kryukova, A.I.; Skiba, O.V.; Spiryakov, V.I.; Korshunov, I.A.; Samojlova, T.K.

    1987-01-01

    Generalizing analysis of data on crystallographic and IR spectral properties of double phosphates of actinide and alkali elements of M (1) M 2 (4) (PO 4 ) 3 type is conducted. It is shown, that Li - , Na - , K - , Rb - , CsTh 2 (PO 4 ) 3 , Li - , Na - , KU 2 (PO 4 ) 3 , NaNp 2 (PO 4 ) 3 compounds crystallize in a monoclinic type structure and form an isostructural phosphate series. It is ascertained, that in rubidium-uranium, uranium-cesium systems double salt formation is not observed. Plutonium-sodium phosphate has a rhombic-type structure, which points out to the existence of a morphotropic transition in NaM 2 4 (PO 4 ) 3 phosphate series at the Np-Pu boundary. Some regularities of structure and effect of M 1 and M 4 nature on the double phosphate structure are revealed

  17. Heat transfer performance of multi-layer insulation structure under roof-slab of pool-type LMFBR

    International Nuclear Information System (INIS)

    Kinoshita, I.; Yoshida, K.; Uotani, M.; Fukada, T.

    1988-01-01

    At the normal operation of the pool-type LMFBR, the free surface of liquid sodium at about 500 0 C is present below the roof-slab, separated by a space of the argon cover gas. The temperature of the roof-slab has to be maintained low and uniform in the horizontal direction for sufficient strength of the structure. Therefore, thermal insulation structures must be installed on the lower surface of the roof-slab. In addition to the installation of thermal insulator, forced cooling of the roof-slab is required for assured structural integrity of the roof-slab. The capacity of cooling equipment can be reduced by installation of structures with high thermal insulating performance. The objective of this study is to evaluate the thermal insulation characteristics of multi-layer type insulator installed below the roof-slab by analytically and experimentally. The analytical study is intended to evaluate the effect of number, distance and emissivity of layers on the heat transfer performances. This is treated as the one-dimensional heat transfer with natural convection, conduction and thermal radiation. In the experiments, we have evaluated effects of gap distances between adjacent thermal insulators placed below the roof-slab on the thermal insulation performances

  18. Three NiAs-Ni 2In Type Structures in the Mn-Sn System

    Science.gov (United States)

    Elding-Pontén, Margareta; Stenberg, Lars; Larsson, Ann-Kristin; Lidin, Sven; Ståhl, Kenny

    1997-03-01

    TheB8-type structure field of the Mn-Sn system has been investigated. Two high temperature phases (HTP1 and HTP2) and one low temperature phase (Mn3Sn2) were found. They all crystallize with the NiAs structure type with part of the trigonal bipyramidal interstices filled by manganese atoms in an ordered manner. The ordering as well as the manganese content is different for the three phases, giving rise to three different orthorhombic superstructures. Mn3Sn2seems to have the lowest manganese content, since the corresponding basal unit cell is smaller than for HTP1-2. Structural models of the phases are based on selected area electron diffraction, X-ray powder diffraction, and preliminary single crystal X-ray measurements. The ideal cell parameters found are (a=7ahex,b=3ahex,c=chex), (a=5ahex,b=3ahex,c=chex), and (a=2ahex,b=3ahex,c=chex) for HTP1, HTP2, and Mn3Sn2, respectively. The crystal structure of Mn3Sn2has been refined by means of the Rietveld method from X-ray powder diffraction data. Mn3Sn2is orthorhombic,Pnma,a=7.5547(2),b=5.4994(2),c=8.5842(2) Å,Z=4. (Pbnmin the setting above.) The compound is isostructural with Ni3Sn2andγ‧-Co3Sn2(H. Fjellvåg and A. Kjekshus,Acta Chem. Scand.A40, 23-30 (1986)). FinalRp=8.97%,Rwp=11.44%, GOF=2.86, andRBragg=4.11% using 43 parameters and 5701 observations and 330 Bragg reflections.

  19. Wildfires alter rodent community structure across four vegetation types in southern California, USA

    Science.gov (United States)

    Brehme, Cheryl S.; Clark, Denise R.; Rochester, Carlton J.; Fisher, Robert N.

    2011-01-01

    We surveyed burned and unburned plots across four habitat reserves in San Diego County, California, USA, in 2005 and 2006, to assess the effects of the 2003 wildfires on the community structure and relative abundance of rodent species. The reserves each contained multiple vegetation types (coastal sage scrub, chaparral, woodland, and grassland) and spanned from 250 m to 1078 m in elevation. Multivariate analyses revealed a more simplified rodent community structure in all burned habitats in comparison to unburned habitats. Reduction in shrub and tree cover was highly predictive of changes in post-fire rodent community structure in the burned coastal sage scrub and chaparral habitats. Reduction in cover was not predictive for the less substantially burned woodlands and grasslands, for which we hypothesized that interspecific competition played a greater role in post-fire community structure. Across vegetation types, generalists and open habitat specialists typically increased in relative abundance, whereas closed habitat specialists decreased. We documented significant increases in relative abundance of the deer mouse (Peromyscus maniculatus Wagner) and Dulzura kangaroo rat (Dipodomys simulans Merriam). In contrast, we found significant decreases in relative abundance for the California mouse (Peromyscus californicus Gambel), San Diego pocket mouse (Chaetodipus fallax Merriam), desert woodrat (Neotoma lepida Thomas), and brush mouse (Peromyscus boylii Baird). Currently, our research program involves assessment of whether habitat conservation plans (HCPs) in southern California provide long-term protection to HCP covered species, as well as preserve ecosystem function. The scenario of increased wildfires needs to be incorporated into this assessment. We discuss our results in relation to management and conservation planning under a future scenario of larger and more frequent wildfires in southern California.

  20. Heat resistant/radiation resistant cable and incore structure test device for FBR type reactor

    International Nuclear Information System (INIS)

    Tanimoto, Hajime; Shiono, Takeo; Sato, Yoshimi; Ito, Kazumi; Sudo, Shigeaki; Saito, Shin-ichi; Mitsui, Hisayasu.

    1995-01-01

    A heat resistant/radiation resistant coaxial cable of the present invention comprises an insulation layer, an outer conductor and a protection cover in this order on an inner conductor, in which the insulation layer comprises thermoplastic polyimide. In the same manner, a heat resistant/radiation resistant power cable has an insulation layer comprising thermoplastic polyimide on a conductor, and is provided with a protection cover comprising braid of alamide fibers at the outer circumference of the insulation layer. An incore structure test device for an FBR type reactor comprises the heat resistant/radiation resistant coaxial cable and/or the power cable. The thermoplastic polyimide can be extrusion molded, and has excellent radiation resistant by the extrusion, as well as has high dielectric withstand voltage, good flexibility and electric characteristics at high temperature. The incore structure test device for the FBR type reactor of the present invention comprising such a cable has excellent reliability and durability. (T.M.)

  1. Structural Characterization of Lignin in Wild-Type versus COMT Down-Regulated Switchgrass

    Energy Technology Data Exchange (ETDEWEB)

    Samuel, Reichel [School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA (United States); BioEnergy Science Center, Oak Ridge, TN (United States); Pu, Yunqiao, E-mail: yunqiao.pu@ipst.gatech.edu [BioEnergy Science Center, Oak Ridge, TN (United States); Institute of Paper Science and Technology, Georgia Institute of Technology, Atlanta, GA (United States); Jiang, Nan [School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA (United States); BioEnergy Science Center, Oak Ridge, TN (United States); Fu, Chunxiang [Forage Improvement Division, The Samuel Roberts Noble Foundation, Ardmore, OK (United States); Wang, Zeng-Yu [BioEnergy Science Center, Oak Ridge, TN (United States); Forage Improvement Division, The Samuel Roberts Noble Foundation, Ardmore, OK (United States); Ragauskas, Arthur, E-mail: yunqiao.pu@ipst.gatech.edu [School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA (United States); BioEnergy Science Center, Oak Ridge, TN (United States)

    2014-01-20

    This study examined the chemical structural characteristics of cellulolytic enzyme lignin isolated from switchgrass focusing on comparisons between wild-type control and caffeic acid 3-O-methyltransferase (COMT) down-regulated transgenic line. Nuclear magnetic resonance techniques including {sup 13}C, {sup 31}P, and two-dimensional {sup 13}C-{sup 1}H heteronuclear single quantum coherence as well as gel permeation chromatography were employed. Compared to the wild-type, the COMT down-regulated transgenic switchgrass lignin demonstrated a decrease in syringyl (S):guaiacyl (G) ratio and p-coumarate:ferulate ratio, an increase in relative abundance of phenylcoumaran unit, and a comparable content of total free phenolic OH groups along with formation of benzodioxane unit. In addition, COMT down-regulation had no significant effects on the lignin molecular weights during its biosynthesis process.

  2. Mechanical adaptability of the Bouligand-type structure in natural dermal armour

    Science.gov (United States)

    Zimmermann, Elizabeth A.; Gludovatz, Bernd; Schaible, Eric; Dave, Neil K. N.; Yang, Wen; Meyers, Marc A.; Ritchie, Robert O.

    2013-10-01

    Arapaima gigas, a fresh water fish found in the Amazon Basin, resist predation by piranhas through the strength and toughness of their scales, which act as natural dermal armour. Arapaima scales consist of a hard, mineralized outer shell surrounding a more ductile core. This core region is composed of aligned mineralized collagen fibrils arranged in distinct lamellae. Here we show how the Bouligand-type (twisted plywood) arrangement of collagen fibril lamellae has a key role in developing their unique protective properties, by using in situ synchrotron small-angle X-ray scattering during mechanical tensile tests to observe deformation mechanisms in the fibrils. Specifically, the Bouligand-type structure allows the lamellae to reorient in response to the loading environment; remarkably, most lamellae reorient towards the tensile axis and deform in tension through stretching/sliding mechanisms, whereas other lamellae sympathetically rotate away from the tensile axis and compress, thereby enhancing the scale’s ductility and toughness to prevent fracture.

  3. Relationships between NDVI, canopy structure, and photosynthesis in three California vegetation types

    International Nuclear Information System (INIS)

    Gamon, J.A.; Field, C.B.; Goulden, M.L.; Griffin, K.L.; Hartley, A.E.; Joel, G.; Penuelas, J.; Valentini, R.

    1995-01-01

    In a range of plant species from three Californian vegetation types, we examined the widely used ''normalized difference vegetation index'' (NDVI) and ''simple ratio'' (SR) as indicators of canopy structure, light absorption, and photosynthetic activity. These indices, which are derived from canopy reflectance in the red and near-infrared wavebands, highlighted phenological differences between evergreen and deciduous canopies. They were poor indicators of total canopy biomass due to the varying abundance of non-green standing biomass in these vegetation types. However, in sparse canopies (leaf area index (LAI) apprxeq 0-2), NDVI was a sensitive indicator of canopy structure and chemical content (green biomass, green leaf area index, chlorophyll content, and foliar nitrogen content). At higher canopy green LAI values ( gt 2; typical of dense shrubs and trees), NDVI was relatively insensitive to changes in canopy structure. Compared to SR, NDVI was better correlated with indicators of canopy structure and chemical content, but was equivalent to the logarithm of SR. In agreement with theoretical expectations, both NDVI and SR exhibited near-linear correlations with fractional PAR intercepted by green leaves over a wide range of canopy densities. Maximum daily photosynthetic rates were positively correlated with NDVI and SR in annual grassland and semideciduous shrubs where canopy development and photosynthetic activity were in synchrony. The indices were also correlated with peak springtime canopy photosynthetic rates in evergreens. However, over most of the year, these indices were poor predictors of photosynthetic performance in evergreen species due to seasonal reductions in photosynthetic radiation-use efficiency that occurred without substantial declines in canopy greenness. Our results support the use of these vegetation indices as remote indicators of PAR absorption, and thus potential photosynthetic activity, even in

  4. Multi-Cohort Stand Structural Classification: Ground- and LiDAR-based Approaches for Boreal Mixedwood and Black Spruce Forest Types of Northeastern Ontario

    Science.gov (United States)

    Kuttner, Benjamin George

    Natural fire return intervals are relatively long in eastern Canadian boreal forests and often allow for the development of stands with multiple, successive cohorts of trees. Multi-cohort forest management (MCM) provides a strategy to maintain such multi-cohort stands that focuses on three broad phases of increasingly complex, post-fire stand development, termed "cohorts", and recommends different silvicultural approaches be applied to emulate different cohort types. Previous research on structural cohort typing has relied upon primarily subjective classification methods; in this thesis, I develop more comprehensive and objective methods for three common boreal mixedwood and black spruce forest types in northeastern Ontario. Additionally, I examine relationships between cohort types and stand age, productivity, and disturbance history and the utility of airborne LiDAR to retrieve ground-based classifications and to extend structural cohort typing from plot- to stand-levels. In both mixedwood and black spruce forest types, stand age and age-related deadwood features varied systematically with cohort classes in support of an age-based interpretation of increasing cohort complexity. However, correlations of stand age with cohort classes were surprisingly weak. Differences in site productivity had a significant effect on the accrual of increasingly complex multi-cohort stand structure in both forest types, especially in black spruce stands. The effects of past harvesting in predictive models of class membership were only significant when considered in isolation of age. As an age-emulation strategy, the three cohort model appeared to be poorly suited to black spruce forests where the accrual of structural complexity appeared to be more a function of site productivity than age. Airborne LiDAR data appear to be particularly useful in recovering plot-based cohort types and extending them to the stand-level. The main gradients of structural variability detected using Li

  5. [Soil microbial community structure of two types of forests in the mid-subtropics of China].

    Science.gov (United States)

    Han, Shi-zhong; Gao, Ren; Li, Ai-ping; Ma, Hong-liang; Yin, Yun-feng; Si, You-tao; Chen, Shi-dong; Zheng, Qun-rui

    2015-07-01

    Soil microbial community structures were analyzed by biomarker method of phospholipid fatty acid (PLFA) for a natural forest dominated by Castanopsis fabri (CF) and an adjacent plantation of Cunninghamia lanceolata (CL) in the mid-subtropics of China. The results showed that the amounts of total PLFAs, bacterial PLFAs, fungal PLFAs, gram-positive bacterial PLFAs and gramnegative bacterial PLFAs in the 0-10 cm soil layer were higher than in the 10-20 cm soil layer, and each type of PLFAs in CF were higher than in CL. In either soil layer of the two forest types, the contents of bacterial PLFAs were significantly higher than those of fungal PLFAs. In the two forests, the contents of bacterial PLFAs accounted for 44%-52% of total PLFAs, while the contents of fungal PLFAs just accounted for 6%-8%, indicating the bacteria were dominant in the soils of the two vegetation types. Principal component analysis showed that the influence of vegetation types was greater than soil depth on the microbial community structures. Correlation analysis showed that gram-negative bacterial PLFAs, gram-positive bacterial PLFAs and bacterial PLFAs were significantly negatively correlated with pH, positively with water content, and the PLFAs of main soil microorganism groups were significantly positively correlated with soil total nitrogen, organic carbon, C/N and ammonium.

  6. Stellar Photometric Structures of the Host Galaxies of Nearby Type 1 Active Galactic Nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Minjin [Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of); Ho, Luis C. [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China); Peng, Chien Y. [Giant Magellan Telescope Corporation, 251 S. Lake Ave., Suite 300, Pasadena, CA 91101 (United States); Barth, Aaron J. [Department of Physics and Astronomy, University of California at Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697-4575 (United States); Im, Myungshin, E-mail: mkim@kasi.re.kr, E-mail: lho.pku@gmail.com, E-mail: peng@gmto.org, E-mail: barth@uci.edu, E-mail: mim@astro.snu.ac.kr [Department of Physics and Astronomy, Frontier Physics Research Division (FPRD), Seoul National University, Seoul (Korea, Republic of)

    2017-10-01

    We present detailed image analysis of rest-frame optical images of 235 low-redshift ( z ≲ 0.35) Type 1 active galactic nuclei (AGNs) observed with the Hubble Space Telescope . The high-resolution images enable us to perform rigorous two-dimensional image modeling to decouple the luminous central point source from the host galaxy, which, when warranted, is further decomposed into its principal structural components (bulge, bar, and disk). In many cases, care must be taken to account for structural complexities such as spiral arms, tidal features, and overlapping or interacting companion galaxies. We employ Fourier modes to characterize the degree of asymmetry of the light distribution of the stars as a quantitative measure of morphological distortion due to interactions or mergers. We examine the dependence of the physical parameters of the host galaxies on the properties of the AGNs, namely, radio-loudness and the width of the broad emission lines. In accordance with previous studies, narrow-line (H β FWHM ≤ 2000 km s{sup −1}) Type 1 AGNs, in contrast to their broad-line (H β FWHM > 2000 km s{sup −1}) counterparts, are preferentially hosted in later-type, lower-luminosity galaxies, which have a higher incidence of pseudo-bulges, are more frequently barred, and are less morphologically disturbed. This suggests that narrow-line Type 1 AGNs experienced a more quiescent evolutionary history driven primarily by internal secular evolution instead of external dynamical perturbations. The fraction of AGN hosts showing merger signatures is larger for more luminous sources. Radio-loud AGNs generally preferentially live in earlier-type (bulge-dominated), more massive hosts, although a minority of them appear to contain a significant disk component. We do not find convincing evidence for enhanced merger signatures in the radio-loud population.

  7. The structure of Serratia marcescens Lip, a membrane-bound component of the type VI secretion system

    International Nuclear Information System (INIS)

    Rao, Vincenzo A.; Shepherd, Sharon M.; English, Grant; Coulthurst, Sarah J.; Hunter, William N.

    2011-01-01

    The high-resolution crystal structure of S. marcescens Lip reveals a new member of the transthyretin family of proteins. Lip, a core component of the type VI secretion apparatus, is localized to the outer membrane and is positioned to interact with other proteins forming this complex system. Lip is a membrane-bound lipoprotein and a core component of the type VI secretion system found in Gram-negative bacteria. The structure of a Lip construct (residues 29–176) from Serratia marcescens (SmLip) has been determined at 1.92 Å resolution. Experimental phases were derived using a single-wavelength anomalous dispersion approach on a sample cocrystallized with iodide. The membrane localization of the native protein was confirmed. The structure is that of the globular domain lacking only the lipoprotein signal peptide and the lipidated N-terminus of the mature protein. The protein fold is dominated by an eight-stranded β-sandwich and identifies SmLip as a new member of the transthyretin family of proteins. Transthyretin and the only other member of the family fold, 5-hydroxyisourate hydrolase, form homotetramers important for their function. The asymmetric unit of SmLip is a tetramer with 222 symmetry, but the assembly is distinct from that previously noted for the transthyretin protein family. However, structural comparisons and bacterial two-hybrid data suggest that the SmLip tetramer is not relevant to its role as a core component of the type VI secretion system, but rather reflects a propensity for SmLip to participate in protein–protein interactions. A relatively low level of sequence conservation amongst Lip homologues is noted and is restricted to parts of the structure that might be involved in interactions with physiological partners

  8. The structure of Serratia marcescens Lip, a membrane-bound component of the type VI secretion system

    Energy Technology Data Exchange (ETDEWEB)

    Rao, Vincenzo A.; Shepherd, Sharon M.; English, Grant; Coulthurst, Sarah J.; Hunter, William N., E-mail: w.n.hunter@dundee.ac.uk [College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland (United Kingdom)

    2011-12-01

    The high-resolution crystal structure of S. marcescens Lip reveals a new member of the transthyretin family of proteins. Lip, a core component of the type VI secretion apparatus, is localized to the outer membrane and is positioned to interact with other proteins forming this complex system. Lip is a membrane-bound lipoprotein and a core component of the type VI secretion system found in Gram-negative bacteria. The structure of a Lip construct (residues 29–176) from Serratia marcescens (SmLip) has been determined at 1.92 Å resolution. Experimental phases were derived using a single-wavelength anomalous dispersion approach on a sample cocrystallized with iodide. The membrane localization of the native protein was confirmed. The structure is that of the globular domain lacking only the lipoprotein signal peptide and the lipidated N-terminus of the mature protein. The protein fold is dominated by an eight-stranded β-sandwich and identifies SmLip as a new member of the transthyretin family of proteins. Transthyretin and the only other member of the family fold, 5-hydroxyisourate hydrolase, form homotetramers important for their function. The asymmetric unit of SmLip is a tetramer with 222 symmetry, but the assembly is distinct from that previously noted for the transthyretin protein family. However, structural comparisons and bacterial two-hybrid data suggest that the SmLip tetramer is not relevant to its role as a core component of the type VI secretion system, but rather reflects a propensity for SmLip to participate in protein–protein interactions. A relatively low level of sequence conservation amongst Lip homologues is noted and is restricted to parts of the structure that might be involved in interactions with physiological partners.

  9. On the existence of europium aluminum oxynitrides with a magnetoplumbite or beta-alumina type structure

    NARCIS (Netherlands)

    Hintzen, H.T.J.M.; Hanssen, R.; Jansen, S.R.; Metselaar, R.

    1999-01-01

    In the literature confusion exists concerning the structure type, the valence of europium, and the amount of nitrogen incorporation of the compound europium aluminum oxynitride. By using X-ray diffraction and luminescence measurements, we show that europium aluminum oxynitride has the

  10. Deposition of highly (111)-oriented PZT thin films by using metal organic chemical deposition

    CERN Document Server

    Bu, K H; Choi, D K; Seong, W K; Kim, J D

    1999-01-01

    Lead zirconate titanate (PZT) thin films have been grown on Pt/Ta/SiNx/Si substrates by using metal organic chemical vapor deposition with Pb(C sub 2 H sub 5) sub 4 , Zr(O-t-C sub 4 H sub 9) sub 4 , and Ti(O-i-C sub 3 H sub 7) sub 4 as source materials and O sub 2 as an oxidizing gas. The Zr fraction in the thin films was controlled by varying the flow rate of the Zr source material. The crystal structure and the electrical properties were investigated as functions of the composition. X-ray diffraction analysis showed that at a certain range of Zr fraction, highly (111)-oriented PZT thin films with no pyrochlore phases were deposited. On the other hand, at low Zr fractions, there were peaks from Pb-oxide phases. At high Zr fractions, peaks from pyrochlore phase were seen. The films also showed good electrical properties, such as a high dielectric constant of more than 1200 and a low coercive voltage of 1.35 V.

  11. A new type of intelligent wireless sensing network for health monitoring of large-size structures

    Science.gov (United States)

    Lei, Ying; Liu, Ch.; Wu, D. T.; Tang, Y. L.; Wang, J. X.; Wu, L. J.; Jiang, X. D.

    2009-07-01

    In recent years, some innovative wireless sensing systems have been proposed. However, more exploration and research on wireless sensing systems are required before wireless systems can substitute for the traditional wire-based systems. In this paper, a new type of intelligent wireless sensing network is proposed for the heath monitoring of large-size structures. Hardware design of the new wireless sensing units is first studied. The wireless sensing unit mainly consists of functional modules of: sensing interface, signal conditioning, signal digitization, computational core, wireless communication and battery management. Then, software architecture of the unit is introduced. The sensing network has a two-level cluster-tree architecture with Zigbee communication protocol. Important issues such as power saving and fault tolerance are considered in the designs of the new wireless sensing units and sensing network. Each cluster head in the network is characterized by its computational capabilities that can be used to implement the computational methodologies of structural health monitoring; making the wireless sensing units and sensing network have "intelligent" characteristics. Primary tests on the measurement data collected by the wireless system are performed. The distributed computational capacity of the intelligent sensing network is also demonstrated. It is shown that the new type of intelligent wireless sensing network provides an efficient tool for structural health monitoring of large-size structures.

  12. Purification, crystal structure determination and functional characterization of type III antifreeze proteins from the European eelpout Zoarces viviparus

    DEFF Research Database (Denmark)

    Wilkens, Casper; Poulsen, Jens-Christian Navarro; Ramløv, Hans

    2014-01-01

    Antifreeze proteins (AFPs) are essential components of many organisms adaptation to cold temperatures. Fish type III AFPs are divided into two groups, SP isoforms being much less active than QAE1 isoforms. Two type III AFPs from Zoarces viviparus, a QAE1 (ZvAFP13) and an SP (ZvAFP6) isoform......, are here characterized and their crystal structures determined. We conclude that the higher activity of the QAE1 isoforms cannot be attributed to single residues, but rather a combination of structural effects. Furthermore both ZvAFP6 and ZvAFP13 crystal structures have water molecules around T18...... equivalent to the tetrahedral-like waters previously identified in a neutron crystal structure. Interestingly, ZvAFP6 forms dimers in the crystal, with a significant dimer interface. The presence of ZvAFP6 dimers was confirmed in solution by native electrophoresis and gel filtration. To our knowledge...

  13. Structural studies of P-type ATPase–ligand complexes using an X-ray free-electron laser

    Directory of Open Access Journals (Sweden)

    Maike Bublitz

    2015-07-01

    Full Text Available Membrane proteins are key players in biological systems, mediating signalling events and the specific transport of e.g. ions and metabolites. Consequently, membrane proteins are targeted by a large number of currently approved drugs. Understanding their functions and molecular mechanisms is greatly dependent on structural information, not least on complexes with functionally or medically important ligands. Structure determination, however, is hampered by the difficulty of obtaining well diffracting, macroscopic crystals. Here, the feasibility of X-ray free-electron-laser-based serial femtosecond crystallography (SFX for the structure determination of membrane protein–ligand complexes using microcrystals of various native-source and recombinant P-type ATPase complexes is demonstrated. The data reveal the binding sites of a variety of ligands, including lipids and inhibitors such as the hallmark P-type ATPase inhibitor orthovanadate. By analyzing the resolution dependence of ligand densities and overall model qualities, SFX data quality metrics as well as suitable refinement procedures are discussed. Even at relatively low resolution and multiplicity, the identification of ligands can be demonstrated. This makes SFX a useful tool for ligand screening and thus for unravelling the molecular mechanisms of biologically active proteins.

  14. The cartilage-derived, C-type lectin (CLECSF1): structure of the gene and chromosomal location.

    Science.gov (United States)

    Neame, P J; Tapp, H; Grimm, D R

    1999-09-03

    Cartilage is a tissue that is primarily extracellular matrix, the bulk of which consists of proteoglycan aggregates constrained within a collagen framework. Candidate components that organize the extracellular assembly of the matrix consist of collagens, proteoglycans and multimeric glycoproteins. We describe the human gene structure of a potential organizing factor, a cartilage-derived member of the C-type lectin superfamily (CLECSF1; C-type lectin superfamily) related to the serum protein, tetranectin. We show by Northern analysis that this protein is restricted to cartilage and locate the gene on chromosome 16q23. We have characterized 10.9 kb of sequence upstream of the first exon. Similarly to human tetranectin, there are three exons. The residues that are conserved between CLECSF1 and tetranectin suggest that the cartilage-derived protein forms a trimeric structure similar to that of tetranectin, with three N-terminal alpha-helical domains aggregating through hydrophobic faces. The globular, C-terminal domain that has been shown to bind carbohydrate in some members of the family and plasminogen in tetranectin, is likely to have a similar overall structure to that of tetranectin.

  15. Structural studies of P-type ATPase–ligand complexes using an X-ray free-electron laser

    Energy Technology Data Exchange (ETDEWEB)

    Bublitz, Maike; Nass, Karol; Drachmann, Nikolaj D.; Markvardsen, Anders J.; Gutmann, Matthias J.; Barends, Thomas R. M.; Mattle, Daniel; Shoeman, Robert L.; Doak, R. Bruce; Boutet, Sébastien; Messerschmidt, Marc; Seibert, Marvin M.; Williams, Garth J.; Foucar, Lutz; Reinhard, Linda; Sitsel, Oleg; Gregersen, Jonas L.; Clausen, Johannes D.; Boesen, Thomas; Gotfryd, Kamil; Wang, Kai-Tuo; Olesen, Claus; Møller, Jesper V.; Nissen, Poul; Schlichting, Ilme

    2015-06-11

    Membrane proteins are key players in biological systems, mediating signalling events and the specific transport ofe.g.ions and metabolites. Consequently, membrane proteins are targeted by a large number of currently approved drugs. Understanding their functions and molecular mechanisms is greatly dependent on structural information, not least on complexes with functionally or medically important ligands. Structure determination, however, is hampered by the difficulty of obtaining well diffracting, macroscopic crystals. Here, the feasibility of X-ray free-electron-laser-based serial femtosecond crystallography (SFX) for the structure determination of membrane protein–ligand complexes using microcrystals of various native-source and recombinant P-type ATPase complexes is demonstrated. The data reveal the binding sites of a variety of ligands, including lipids and inhibitors such as the hallmark P-type ATPase inhibitor orthovanadate. By analyzing the resolution dependence of ligand densities and overall model qualities, SFX data quality metrics as well as suitable refinement procedures are discussed. Even at relatively low resolution and multiplicity, the identification of ligands can be demonstrated. This makes SFX a useful tool for ligand screening and thus for unravelling the molecular mechanisms of biologically active proteins.

  16. Fluid-Structure Interaction of a Reed Type Valve Subjected to Piston Displacement

    OpenAIRE

    Estruch, Olga; Lehmkuhl, Oriol; Rigola, Joaquim; Pérez-Segarra, Carles David

    2014-01-01

    In the field of reciprocating compressors, the developing of reed type valves is a challenging task. The understanding of the fluid flow behaviour through the valve reed is essential to improve the valve design. Hence, this work attempts the dynamic simulation of this fluid-structure interaction (FSI) problem, taking into account valve movement due to piston displacement. In this work attends the in-house implemented CFD&HT and moving mesh coupled code TermoFluids [1]. The CFD&HT solver consi...

  17. Structural and magnetic Properties of TbZn-substituted calcium barium M-type nano-structured hexa-ferrites

    Energy Technology Data Exchange (ETDEWEB)

    Khan, Hasan M. [Department of Physics, Bahauddin Zakariya University, Multan 60800 (Pakistan); Department of Electronics, University of York, York YO10 5DD (United Kingdom); Islam, M.U., E-mail: dr.misbahulislam@bzu.edu.pk [Department of Physics, Bahauddin Zakariya University, Multan 60800 (Pakistan); Xu, Yongbing [Department of Electronics, University of York, York YO10 5DD (United Kingdom); Nanjing–York International Centre of Spintronics and Nano-Engineering, Nanjing University, Nanjing 210093 (China); Asif Iqbal, M. [Department of Physics, Bahauddin Zakariya University, Multan 60800 (Pakistan); National University of Science and Technology, College of E and ME, Islamabad (Pakistan); Ali, Irshad [Department of Physics, Bahauddin Zakariya University, Multan 60800 (Pakistan)

    2014-03-15

    Highlights: • Tb–Zn substituted Ca{sub 0.5}Ba{sub 0.5}Fe{sub 12}O{sub 19} samples exhibit single magnetoplumbite phase. • Lattice parameters a and c have increasing values. • Coercivity can be tuned at lower substitution level • Crystallites size was found in the range 18–25 nm by TEM and by Scherrer formula. • These hexa-ferrites are suitable for microwave devices and magnetic recording media. -- Abstract: Effect of TbZn substitution on the structural and magnetic properties of Ca{sub 0.5}Ba{sub 0.5−x}Tb{sub x}Zn{sub y}Fe{sub 12−y}O{sub 19}, (x = 0.00–0.10; y = 0.00–1.00) ferrites prepared by sol–gel auto combustion is reported. The synthesized samples were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Vibrating Sample magnetometery. The X-ray diffraction analysis confirmed single phase M-type hexa-ferrite structure. The lattice parameters were found to increase as TbZn contents increases, which is attributed to the ionic sizes of the implicated cations. The TbZn seems to be completely soluble in the lattice. The results of scanning electron microscopy and transmission electron microscopy shows that the grain size decreases with increase of TbZn substitution. The coercivity values (1277–2025 Oe) of all samples lies in the range of M-type hexa-ferrite and indicate that an increase of anisotropy was achieved by substitution of TbZn, while the size of nanoparticles was drastically reduced between 18 and 25 nm. The increased anisotropy and fine particle size are useful for many applications, such as improving signal noise ratio of recording devices.

  18. Rare-earth organic frameworks involving three types of architecture tuned by the lanthanide contraction effect: hydrothermal syntheses, structures and luminescence.

    Science.gov (United States)

    Deng, Zhao-Peng; Kang, Wei; Huo, Li-Hua; Zhao, Hui; Gao, Shan

    2010-07-21

    The first example of rare-earth organic frameworks with 3-aminopyrazine-2-carboxylic acid (Hapca) was synthesized under hydrothermal conditions and characterized by elemental analysis, IR, PL, TG, powder and single-crystal X-ray diffraction. These ten complexes exhibit three different structure types with decreasing lanthanide radii: [La(apca)(3)](n) () for type I, {[Ln(apca)(ox)(H(2)O)(2)].H(2)O}(n) (Ln = Pr (2), Nd (3), ox = oxalate) for type II, and [Ln(2)(apca)(4)(OH)(2)(H(2)O)(2)](n) (Ln = Sm (4), Eu (5), Gd (6), Tb (7), Dy (8), Er (9), Y (10)) for type III. The structure of type I consists of 1D "snowflake" chains along a-axis, which are further interconnected by hydrogen bonds to produce a 3D sra net topology containing infinite (-C-O-La-)(n) rod-shaped SBU. Type II has 2D Ln-apca-ox 4(4)-net, in which a planar udud water tetramers (H(2)O)(4) are formed by coordinated and free water molecules. Type III also comprises of 2D 4(4)-layer network constructed from Ln-apca-OH. The structure diversity is mainly caused by the variation of coordinated ligand and lanthanide contraction effect. Remarkably, the oxalate in type II was in situ synthesized from 3-aminopyrazine-2-carboxylic acid through an oxidation-hydrolysis reaction. The luminescent investigations reveal that complex exhibits strong blue emission and complex exhibits characteristic luminescence of Eu(3+).

  19. Fluid Flow through Porous Sandstone with Overprinting and Intersecting Geological Structures of Various Types

    Science.gov (United States)

    Zhou, X.; Karimi-Fard, M.; Durlofsky, L.; Aydin, A.

    2010-12-01

    Impact of a wide variety of structural heterogeneities on fluid flow in an aeolian sandstone in the Valley of Fire State Park (NV), such as (1) dilatant fractures (joints), (2) shear fractures (faults), and (3) contraction/compaction structures (compaction bands), are considered. Each type of these structures has its own geometry, spacing, distribution, connectivity, and hydraulic properties, which either enhance or impede subsurface fluid flow. Permeability of these structures may, on average, be a few orders of magnitude higher or lower than those of the corresponding matrix rocks. In recent years, the influence of a single type of these heterogeneities on fluid flow has been studied individually, such as joints, compaction bands or faults. However, as different types of geological structures are commonly present together in the same rock volume, their combined effect requires a more detailed assessment. In this study, fluid flow simulations are performed using a special finite-volume discretization technique that was developed by Karimi-Fard et al. (2004; 2006). Using this approach, thin features such as fractures and compaction bands are represented as linear elements in unstructured 2D models and as planar elements in 3D models, which significantly reduces the total number of cells and simplifies grid generation. The cell geometric information and the cell-to-cell transmissibility obtained from this discretization technique are input to Stanford’s General Purpose Research Simulator (GPRS) for fluid flow simulation. To account for the effects of the various geological structures on subsurface flow, we perform permeability upscaling over regions corresponding to large-scale simulation grid blocks in order to obtain equivalent permeability components in two principal directions. We will focus on the following problems: (1) compaction bands of multisets; (2) compartmentalization of compaction bands of high-angle, low-angle and horizontal; (3) joints overprinting

  20. Effects of different types of moderate severity disturbance on forest structural complexity and ecosystem functioning: A story of ice and fire

    Science.gov (United States)

    Fahey, R. T.; Atkins, J.; Gough, C. M.; Hardiman, B. S.; Haber, L.; Stuart-Haentjens, E.; David, O.; Campbell, J. L.; Rustad, L.; Duffy, M.

    2017-12-01

    Disturbances that alter the structure and function of forest ecosystems occur along a continuum of severity. In contrast to the extremes of the disturbance gradient (i.e., stand-replacing disturbance and small gap formation), moderate severity disturbances are poorly understood, even though they make up the majority of the gradient and their spatial extent (and likely overall importance to regional disturbance regimes) often exceeds that of more severe disturbances. Moderate severity disturbances originate from a variety of causes, such as fires, ice storms, or pest and pathogen outbreaks, and each of these could reshape structure and function in different ways. Observational data from a limited number of sites shows that moderate disturbance can increase ecosystem complexity, but the generality of this effect has not been tested across a broad range of disturbance types and severities. Here, we utilize data from a set of five case studies of experimental or natural moderate disturbance to assess the effects of different types and severities of disturbance on forest canopy structural complexity (CSC) and the relationship of canopy structure with ecosystem functioning. Using pre- and post-disturbance measures of CSC derived from aerial and terrestrial LiDAR, UAV imagery, and Landsat data we quantified changes in CSC following an experimental ice storm, a low-severity surface fire, Beech Bark Disease and Hemlock Wooly Adelgid outbreaks, and experimental accelerated succession. Our initial findings indicate that different disturbance types have highly variable effects on CSC, and also that progressive increases in disturbance severity alter CSC differently among disturbance types. Differential effects of variable disturbance types on CSC has implications for the carbon cycle, as forest structure is strongly linked with both growth-limiting resource (e.g., nutrients and light) acquisition and net primary productivity. Understanding how different types and severities of

  1. Four types of interference competition and their impacts on the ecology and evolution of size-structured populations and communities

    DEFF Research Database (Denmark)

    Zhang, Lai; Andersen, Ken Haste; Dieckmann, Ulf

    2015-01-01

    We investigate how four types of interference competition - which alternatively affect foraging, metabolism, survival, and reproduction - impact the ecology and evolution of size-structured populations. Even though all four types of interference competition reduce population biomass, interference...

  2. Lattice dynamical investigation of the Raman and infrared wave numbers and heat capacity properties of the pyrochlores R2Zr2O7 (R = La, Nd, Sm, Eu)

    Science.gov (United States)

    Nandi, S.; Jana, Y. M.; Gupta, H. C.

    2018-04-01

    A short-range electrostatic forcefield model has been applied for the first time to investigate the Raman and infrared wave numbers in pyrochlore zirconates R2Zr2O7 (R3+ = La, Nd, Sm, Eu). The calculations of phonons involve five stretching and four bending force constants in the Wilson GF matrix method. The calculated phonon wave numbers are in reasonable agreement with the observed spectra in infrared and Raman excitation zones for all of these isomorphous compounds. The contributions of force constants to each mode show a similar trend of variation for all of these compounds. Furthermore, to validate the established forcefield model, we calculated the standard thermodynamic functions, e.g., molar heat capacity, entropy and enthalpy, and compared the results with the previous experimental data for each compound. Using the derived wave numbers for the acoustic and optical modes, the total phonon contribution to the heat capacity was calculated for all these zirconate compounds. The Schottky heat capacity contributions were also calculated for the magnetic compounds, Nd2Zr2O7, Sm2Zr2O7 and Eu2Zr2O7, taking account of crystal-field level schemes of the lanthanide ions. The derived total heat capacity and the integrated values of molar entropy and molar enthalpy showed satisfactory correlations at low temperatures with the experimental results available in the literature for these compounds. At higher temperatures, the discrepancies may be caused by the anharmonic effects of vibrations, phonon dispersion, distribution of phonon density of states, etc.

  3. Type Classes for Lightweight Substructural Types

    Directory of Open Access Journals (Sweden)

    Edward Gan

    2015-02-01

    Full Text Available Linear and substructural types are powerful tools, but adding them to standard functional programming languages often means introducing extra annotations and typing machinery. We propose a lightweight substructural type system design that recasts the structural rules of weakening and contraction as type classes; we demonstrate this design in a prototype language, Clamp. Clamp supports polymorphic substructural types as well as an expressive system of mutable references. At the same time, it adds little additional overhead to a standard Damas-Hindley-Milner type system enriched with type classes. We have established type safety for the core model and implemented a type checker with type inference in Haskell.

  4. FINEMET type alloy without Si: Structural and magnetic properties

    International Nuclear Information System (INIS)

    Muraca, D.; Cremaschi, V.; Moya, J.; Sirkin, H.

    2008-01-01

    Magnetic and structural properties of a Finemet type alloy (Fe 73.5 Ge 15.5 Nb 3 B 7 Cu 1 ) without Si and high Ge content were studied. Amorphous material was obtained by the melt spinning technique and was heat treated at different temperatures for 1 h under high vacuum to induce the nanocrystallization of the sample. The softest magnetic properties were obtained between 673 and 873 K. The role of Ge on the ferromagnetic paramagnetic transition of the as-quenched alloys and its influence on the crystallization process were studied using a calorimetric technique. Moessbauer spectroscopy was employed in the nanocrystallized alloy annealed at 823 K to obtain the composition of the nanocrystals and the amorphous phase fraction. Using this data and magnetic measurements of the as-quenched alloy, the magnetic contribution of nanocrystals to the alloy annealed at 823 K was estimated via a linear model

  5. Deriving and Analyzing Analytical Structures of a Class of Typical Interval Type-2 TS Fuzzy Controllers.

    Science.gov (United States)

    Zhou, Haibo; Ying, Hao

    2017-09-01

    A conventional controller's explicit input-output mathematical relationship, also known as its analytical structure, is always available for analysis and design of a control system. In contrast, virtually all type-2 (T2) fuzzy controllers are treated as black-box controllers in the literature in that their analytical structures are unknown, which inhibits precise and comprehensive understanding and analysis. In this regard, a long-standing fundamental issue remains unresolved: how a T2 fuzzy set's footprint of uncertainty, a key element differentiating a T2 controller from a type-1 (T1) controller, affects a controller's analytical structure. In this paper, we describe an innovative technique for deriving analytical structures of a class of typical interval T2 (IT2) TS fuzzy controllers. This technique makes it possible to analyze the analytical structures of the controllers to reveal the role of footprints of uncertainty in shaping the structures. Specifically, we have mathematically proven that under certain conditions, the larger the footprints, the more the IT2 controllers resemble linear or piecewise linear controllers. When the footprints are at their maximum, the IT2 controllers actually become linear or piecewise linear controllers. That is to say the smaller the footprints, the more nonlinear the controllers. The most nonlinear IT2 controllers are attained at zero footprints, at which point they become T1 controllers. This finding implies that sometimes if strong nonlinearity is most important and desired, one should consider using a smaller footprint or even just a T1 fuzzy controller. This paper exemplifies the importance and value of the analytical structure approach for comprehensive analysis of T2 fuzzy controllers.

  6. Emergence of a few distinct structures from a single formal structure type during high-throughput screening for stable compounds: The case of RbCuS and RbCuSe

    Science.gov (United States)

    Trimarchi, Giancarlo; Zhang, Xiuwen; DeVries Vermeer, Michael J.; Cantwell, Jacqueline; Poeppelmeier, Kenneth R.; Zunger, Alex

    2015-10-01

    Theoretical sorting of stable and synthesizable "missing compounds" from those that are unstable is a crucial step in the discovery of previously unknown functional materials. This active research area often involves high-throughput (HT) examination of the total energy of a given compound in a list of candidate formal structure types (FSTs), searching for those with the lowest energy within that list. While it is well appreciated that local relaxation methods based on a fixed list of structure types can lead to inaccurate geometries, this approach is widely used in HT studies because it produces answers faster than global optimization methods (that vary lattice vectors and atomic positions without local restrictions). We find, however, a different failure mode of the HT protocol: specific cry