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Sample records for fluorite baf2 structure

  1. Phonons in mixed superionic fluorites (BaF2)1–(LaF3)

    Indian Academy of Sciences (India)

    M M Sinha

    2002-11-01

    In recent years, the fluorite-structured solid solutions with the general formula, (MF2)1–(RF3) (M = Ca, Sr, Ba, Pb and R is a rare-earth element or Y), have been the subject of numerous experimental studies focussed on their superionic properties. The overall cubic crystal symmetry (space group 3) is conserved up to ≤ max, where max 0.4–0.5 depending on M and R. The zone centre phonons and phonon dispersion along three symmetry directions of the mixed superionic compound (BaF2)1–(LaF3) have been investigated by applying de Launey angular force model for ≤ max. The calculated results are compared and explained with available experimental results.

  2. Platinum nitride with fluorite structure

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Rong; Zhang, Xiao-Feng

    2005-01-31

    The mechanical stability of platinum nitride has been studied using first-principles calculations. By calculating the single-crystal elastic constants, we show that platinum nitride can be stabilized in the fluorite structure, in which the nitrogen atoms occupy all the tetrahedral interstitial sites of the metal lattice. The stability is attributed to the pseudogap effect from analysis of the electronic structure.

  3. The effects of Tb3+ doping concentration on luminescence properties and crystal structure of BaF2 phosphor

    Indian Academy of Sciences (India)

    Zhenxing Du; Quansheng Liu; Tianjiang Hou; Yue Song; Xiyan Zhang; Yanyu Cui

    2015-06-01

    This paper is aimed at explaining the effects of Tb3+ concentration on structure and luminescence properties and clarifying the concentration quenching mechanism of Tb3+. The lattice of BaF2 decreases with the increase of Tb3+ ions concentration. The emission spectrum of BaF2:Tb3+ consists of blue emission band and green emission band and corresponds to the transition of 5D3 $\\to$ 7F ( =0, 1, 2, 4, 5, 6) and 5D4 $\\to$ 7F ( =2, 3, 4, 5, 6) of Tb3+. The optimum concentration of Tb3+ is 4 mol%, and the concentration quenching mechanism of Tb3+ can be interpreted by the dipole–quadrupole (d–q) interaction.

  4. Optical properties of Cr3+ in fluorite-structure hosts and in MgF*2

    Science.gov (United States)

    Payne, Stephen A.; Chase, L. L.; Krupke, William F.

    1987-03-01

    We have examined the optical properties of Cr3+ in MgF2 and in the fluorite-structure hosts: CdF2, CaF2, SrF2, and BaF2. The properties of Cr3+ in MgF2 are similar to those observed for other fluoride crystals that have octahedral substitutional metal sites. Interestingly, Cr3+ is also found to be sixfold coordinated in the fluorite hosts, despite the fact that the metal sites of these crystal lattices are eightfold coordinated. The smaller ionic radius of Cr3+ compared to, say, Ca2+, undoubtedly results in considerable relaxation at the metal site. However, the crystal field stabilization energy present in the 4A2(d3) ground state also provides for the energetic preference of sixfold vs eightfold coordination. The similarity of the observed absorption spectra of Cr3+ in MgF2 and in fluorite give evidence that the ground state is octahedrally coordinated in all of these hosts. The reduction of this electronic stabilization energy in the 4T2(d3) excited state is considered to produce a configurational shift relative to the ground state. This shift may be the reason why Cr3+ luminesces effectively in MgF2 whereas it is largely quenched in the fluorite-structure materials.

  5. Configurational Model for Conductivity of Stabilized Fluorite Structure Oxides

    DEFF Research Database (Denmark)

    Poulsen, Finn Willy

    1981-01-01

    The formalism developed here furnishes means by which ionic configurations, solid solution limits, and conductivity mechanisms in doped fluorite structures can be described. The present model differs markedly from previous models but reproduces qualitatively reality. The analysis reported...

  6. Size of oxide vacancies in fluorite and perovskite structured oxides

    DEFF Research Database (Denmark)

    Chatzichristodoulou, Christodoulos; Norby, Poul; Hendriksen, Peter Vang

    2015-01-01

    An analysis of the effective radii of vacancies and the stoichiometric expansion coefficient is performed on metal oxides with fluorite and perovskite structures. Using the hard sphere model with Shannon ion radii we find that the effective radius of the oxide vacancy in fluorites increases...... with increasing ion radius of the host cation and that it is significantly smaller than the radius of the oxide ion in all cases, from 37% smaller for HfO2 to 13 % smaller for ThO2. The perovskite structured LaGaO3 doped with Sr or Mg or both is analyzed in some detail. The results show that the effective radius...... of an oxide vacancy in doped LaGaO3 is only about 6 % smaller than the oxide ion. In spite of this the stoichiometric expansion coefficient (a kind of chemical expansion coefficient) of the similar perovskite, LaCrO3, is significantly smaller than the stoichiometric expansion coefficient of the fluorite...

  7. Giant Mechanocaloric Effects in Fluorite-Structured Superionic Materials

    Science.gov (United States)

    Cazorla, Claudio; Errandonea, Daniel

    2016-05-01

    Mechanocaloric materials experience a change in temperature when a mechanical stress is adiabatically applied on them. Thus far, only ferroelectrics and superelastic metallic alloys have been considered as potential mechanocaloric compounds to be exploited in solid-state cooling applications. Here we show that giant mechanocaloric effects occur in hitherto overlooked fast ion conductors (FIC), a class of multicomponent materials in which above a critical temperature, Ts, a constituent ionic species undergoes a sudden increase in mobility. Using first-principles and molecular dynamics simulations, we found that the superionic transition in fluorite-structured FIC, which is characterised by a large entropy increase of the order of 100 J/K*Kg, can be externally tuned with hydrostatic, biaxial or uniaxial stresses. In particular, Ts can be reduced several hundreds of degrees through the application of moderate tensile stresses due to the concomitant drop in the formation energy of Frenkel pair defects. We predict that the adiabatic temperature change in CaF2 and PbF2, two archetypal fluorite-structured FIC, close to their critical points are of the order of 100 and 10 K, respectively. This work advocates that FIC constitute a new family of mechanocaloric materials showing great promise for prospective solid-state refrigeration applications.

  8. Molecular Dynamics Simulations for Melting Temperatures of SrF2and BaF2

    Institute of Scientific and Technical Information of China (English)

    Xiao-yu Huang; Xin-lu Cheng; Chao-lei Fan; Qiong Chen; Xiao-li Yuan

    2009-01-01

    The shell-model molecular dynamics method was applied to simulate the melting temper-atures of SrF2 and BaF2 at elevated temperatures and high pressures. The same method was used to calculate the equations of state for SrF2 and BaF2 over the pressure range of 0.1 MPa-3 GPa and 0.1 MPa-7 GPa. Compared with previous results for equations of state, the maximum errors are 0.3% and 2.2%, respectively. Considering the pre-melting in the fluorite-type crystals, we made the necessary corrections for the simulated melting temper-atures of SrF2 and BaF2. Consequently, the melting temperatures of SrF2 and BaF2 were obtained for high pressures. The melting temperatures of SrF2 and BaF2 that were obtained by the simulation are in good agreement with available experimental data.

  9. Vibrational spectra of (BaF2)n (n=1-6) clusters

    Science.gov (United States)

    Pandey, Ratnesh K.; Waters, Kevin; Nigam, Sandeep; Pandey, Ravindra; Pandey, Avinash C.

    2016-05-01

    The vibrational properties of alkaline-earth metal fluoride clusters (BaF2)n (n=1-6) are investigated in the framework of density functional theory. The calculated Raman and Infrared (IR) spectra reveals shift in Raman and IR peak position towards lower frequency region with the increase in the cluster size. Further the calculated spectra have been compared with the experimental vibrational spectra of bulk BaF2 crystal. Even though the smaller size cluster lacks translational symmetry, the structural and vibrational characteristic of (BaF2)5-6 are nearer to bulk counterpart.

  10. Importance of surface structure on dissolution of fluorite

    DEFF Research Database (Denmark)

    Godinho, Jose; Piazolo, Sandra; Balic Zunic, Tonci

    2014-01-01

    Dissolution rates are usually calculated as a function of surface area, which is assumed to remain constant ignoring the changes occurring on the surface during dissolution. Here we present a study of how topography of natural fluorite surfaces with different orientation changes during up to 3200 h...... of dissolution. Results are analyzed in terms of changes in surface area, surface reactivity and dissolution rates. All surfaces studied present fast changes in topography during the initial 200 h of dissolution. The controlling factors that cause the development of topography are the stability of the step edges...... forming the initial surface and its inclination to the closest stable planes, which are specific for each surface orientation. During an initial dissolution regime dissolution rates decrease significantly, even though the total surface area increases. During a second dissolution regime, some surfaces...

  11. Fast ion conductivity in strained defect-fluorite structure created by ion tracks in Gd2Ti2O7

    Science.gov (United States)

    Aidhy, Dilpuneet S.; Sachan, Ritesh; Zarkadoula, Eva; Pakarinen, Olli; Chisholm, Matthew F.; Zhang, Yanwen; Weber, William J.

    2015-11-01

    The structure and ion-conducting properties of the defect-fluorite ring structure formed around amorphous ion-tracks by swift heavy ion irradiation of Gd2Ti2O7 pyrochlore are investigated. High angle annular dark field imaging complemented with ion-track molecular dynamics simulations show that the atoms in the ring structure are disordered, and have relatively larger cation-cation interspacing than in the bulk pyrochlore, illustrating the presence of tensile strain in the ring region. Density functional theory calculations show that the non-equilibrium defect-fluorite structure can be stabilized by tensile strain. The pyrochlore to defect-fluorite structure transformation in the ring region is predicted to be induced by recrystallization during a melt-quench process and stabilized by tensile strain. Static pair-potential calculations show that planar tensile strain lowers oxygen vacancy migration barriers in pyrochlores, in agreement with recent studies on fluorite and perovskite materials. In view of these results, it is suggested that strain engineering could be simultaneously used to stabilize the defect-fluorite structure and gain control over its high ion-conducting properties.

  12. Special quasirandom structure modeling of fluorite-structured oxide solid solutions with aliovalent cation substitutions

    Science.gov (United States)

    Wolff-Goodrich, Silas; Hanken, Benjamin E.; Solomon, Jonathan M.; Asta, Mark

    2015-07-01

    The accuracy of the special quasirandom structure (SQS) approach for modeling the structure and energetics of fluorite-structured oxide solid solutions with aliovalent cation substitutions is assessed in an ionic-pair potential study of urania and ceria based systems mixed with trivalent rare-earth ions. Mixing enthalpies for SQS supercells containing 96 and 324 lattice sites were calculated using ionic pair potentials for U0.5La0.5O1.75, U0.5Y0.5O1.75, Ce0.5La0.5O1.75, Ce0.5Y0.5O1.75, and Ce0.5Gd0.5O1.75, which all have stoichiometries of pyrochlores. The SQS results were compared to benchmark values for random substitutional disorder obtained using large supercell models. The calculations show significant improvement of the mixing enthalpy for the larger 324 site SQS, which is attributed to a better description of the structural distortions, as characterized by the radial distribution functions in relaxed systems.

  13. Radioactive contamination of BaF2 crystal scintillator

    CERN Document Server

    Polischuk, O G; Bernabei, R; Cappella, F; Caracciolo, V; Cerulli, R; Di Marco, A; Danevich, F A; Incicchitti, A; Poda, D V; Tretyak, V I

    2013-01-01

    Barium fluoride (BaF$_2$) crystal scintillators are promising detectors to search for double beta decay processes in $^{130}$Ba ($Q_{2{\\beta}}$ = 2619(3) keV) and $^{132}$Ba ($Q_{2{\\beta}}$ = 844(1) keV). The $^{130}$Ba isotope is of particular interest because of the indications on 2${\\beta}$ decay found in two geochemical experiments. The radioactive contamination of BaF$_2$ scintillation crystal with mass of 1.714 kg was measured over 113.4 hours in a low-background DAMA/R&D set-up deep underground (3600 m w.e.) at the Gran Sasso National Laboratories of INFN (LNGS, Italy). The half-life of $^{212}$Po (present in the crystal scintillator due to contamination by radium) was estimated as $T_{1/2}$ = 298.8 $\\pm$ 0.8(stat.) $\\pm$ 1.4(syst.) ns by analysis of the events pulse profiles.

  14. BaF2 TIME DIFFERENTIAL PERTURBED ANGULAR DISTRIBUTION SPECTROMETER

    Institute of Scientific and Technical Information of China (English)

    朱升云; 勾振辉; 等

    1994-01-01

    A BaF2 time differential perturbed angular distribution spectrometer has been established at the HI-13 tandem accelerator in CIAE.The time resolution of the spectrometer is 195ps and the nonlinearity is less than 2%.The spectrometer works very stably and no time drift is found over a period of experimental runs.This spectrometer has been successfully used in the g-factor measurement of 43Sc(19/2-,3.1232MeV).

  15. Intervalence Charge Transfer Luminescence: Interplay between anomalous and 5d-4f emissions in Yb-doped fluorite-type crystals

    CERN Document Server

    Barandiaran, Zoila

    2014-01-01

    We report the existence of intervalence charge transfer (IVCT) luminescence in Yb-doped fluorites associated with Yb2+-Yb3+ mixed valence pairs. We show that the very broad band, anomalous emission of Yb2+-doped CaF2 and SrF2, usually associated with impurity-trapped excitons, is, rather, an IVCT luminescence associated with Yb2+-Yb3+ mixed valence pairs. It is very efficiently excited by a two-photon upconversion mechanism. The IVCT vertical transition leaves the pair moieties very far from their equilibrium structures; this explains the unexpectedly large band width of the emission band and its low peak energy, because the large reorganization energies are substracted from the normal emission. The ab initio IVCT energy diagrams explain the different luminescent properties of Yb-doped CaF2, SrF2, BaF2, and SrCl2: the presence of IVCT luminescence in Yb-doped CaF2 and SrF2; its coexistence with regular 5d-4f emission in SrF2; its absence in BaF2 and SrCl2; the quenching of all emissions in BaF2; and the prese...

  16. Surface modelling on heavy atom crystalline compounds: HfO{sub 2} and UO{sub 2} fluorite structures

    Energy Technology Data Exchange (ETDEWEB)

    Evarestov, Robert [Department of Quantum Chemistry, St. Petersburg State University, 26 Universitetsky Prospect, Peterhof, St. Petersburg 198504 (Russian Federation)], E-mail: re1973@re1973.spb.edu; Bandura, Andrei; Blokhin, Eugeny [Department of Quantum Chemistry, St. Petersburg State University, 26 Universitetsky Prospect, Peterhof, St. Petersburg 198504 (Russian Federation)

    2009-01-15

    The study of the bulk and surface properties of cubic (fluorite structure) HfO{sub 2} and UO{sub 2} was performed using the hybrid Hartree-Fock density functional theory linear combination of atomic orbitals simulations via the CRYSTAL06 computer code. The Stuttgart small-core pseudopotentials and corresponding basis sets were used for the core-valence interactions. The influence of relativistic effects on the structure and properties of the systems was studied. It was found that surface properties of Mott-Hubbard dielectric UO{sub 2} differ from those found for other metal oxides with the closed-shell configuration of d-electrons.

  17. Solid oxide fuel cell composite cathodes based on perovskite and fluorite structures

    Science.gov (United States)

    Sadykov, Vladislav; Mezentseva, Natalia; Usoltsev, Vladimir; Sadovskaya, Ekaterina; Ishchenko, Arkady; Pavlova, Svetlana; Bespalko, Yulia; Kharlamova, Tamara; Zevak, Ekaterina; Salanov, Aleksei; Krieger, Tamara; Belyaev, Vladimir; Bobrenok, Oleg; Uvarov, Nikolai; Okhlupin, Yury; Smorygo, Oleg; Smirnova, Alevtina; Singh, Prabhakar; Vlasov, Aleksandr; Korobeynikov, Mikhail; Bryazgin, Aleksandr; Kalinin, Peter; Arzhannikov, Andrei

    This work presents the results related to the functionally graded fluorite (F)-perovskite (P) nanocomposite cathodes for IT SOFC. Nanocrystalline fluorites (GDC, ScCeSZ) and perovskites (LSrMn, LSrFNi) were synthesized by Pechini method. Nanocomposites were prepared by the ultrasonic dispersion of F and P powders in isopropanol with addition of polyvinyl butyral. Different techniques for deposition and sintering of functionally graded cathode materials were applied including traditional approaches as well as original methods, such as radiation-thermal sintering under electron beam or microwave radiation. Morphology, microstructure and elemental composition of nanocomposites was characterized by XRD and HRTEM/SEM with EDX. Even for dense composites, the sizes of perovskite and fluorite domains remain in the nanorange providing developed P-F interfaces. Oxygen isotope heteroexchange and conductivity/weight relaxation studies demonstrated that these interfaces provide a path for fast oxygen diffusion. The redistribution of the elements between P and F phases in nanocomposites occurs without formation of insulating zirconate phases. Button-size fuel cells with nanocomposite functionally graded cathodes, thin YSZ layers and anode Ni/YSZ cermet (either bulk or supported on Ni-Al foam substrates) were manufactured. For optimized composition and functionally graded design of P-F nanocomposite cathodes, a stable performance in the intermediate temperature range with maximum power density up to 0.5 W cm -2 at 700 °C in wet H 2/air feeds was demonstrated.

  18. The new readout electronics for the BaF2-calorimeter TAPS

    NARCIS (Netherlands)

    Drexler, P; Thoring, U; Bonn, W; van der Duin, HAP; Holzmann, R; van der Kruk, G; Krusche, B; Lohner, H; Metag, [No Value; Nijboer, TW; Novotny, R; Potapov, A; Salz, C; Schadmand, S; Steinacher, M; Thiel, M; Vorenholt, H

    2003-01-01

    A highly compact and fast VME based readout board for BaF2 scintillation detectors has been designed, developed, and finally tested in an in-beam experiment. Adapted to the excellent properties of BaF2, the unit allows to digitize time, energy, and pulse-shape information of four detector channels i

  19. The new readout electronics for the BaF2-calorimeter TAPS

    NARCIS (Netherlands)

    Drexler, P; Thoring, U; Bonn, W; van der Duin, HAP; Holzmann, R; van der Kruk, G; Krusche, B; Lohner, H; Metag, [No Value; Nijboer, TW; Novotny, R; Potapov, A; Salz, C; Schadmand, S; Steinacher, M; Thiel, M; Vorenholt, H

    A highly compact and fast VME based readout board for BaF2 scintillation detectors has been designed, developed, and finally tested in an in-beam experiment. Adapted to the excellent properties of BaF2, the unit allows to digitize time, energy, and pulse-shape information of four detector channels

  20. Factors controlling the oxide ion conductivity of fluorite and perovskite structured oxides

    DEFF Research Database (Denmark)

    Mogensen, Mogens Bjerg; Lybye, D.; Bonanos, N.

    2004-01-01

    for the oxide ion movement, (2) free lattice volume, and (3) average metal-oxide bond energy have been proposed as predictors of high oxide ion conductivity. We discuss how these parameters all depend on ionic radii, and therefore, some of these may be redundant. Furthermore, we explore the interrelations among...... such parameters for fluorite and perovskite oxides by considering their sensitivities to the individual ionic radii. Based on experimental data available in the literature, it is argued that lattice distortion (lattice stress and deviation from cubic symmetry) due to ion radii mismatch determines the ionic...

  1. Solid State Structure-Reactivity Studies on Bixbyites, Fluorites and Perovskites Belonging to the Vanadate, Titanate and Cerate Families

    Science.gov (United States)

    Shafi, Shahid P.

    This thesis primarily focuses on the systematic understanding of structure-reactivity relationships in two representative systems: bixbyite and related structures as well as indium doped CeO2. Topotactic reaction routes have gained significant attention over the past two decades due to their potential to access kinetically controlled metastable materials. This has contributed substantially to the understanding of solid state reaction pathways and provided first insights into mechanisms. Contrary to the widely used ex-situ methods, in-situ techniques including powder x-ray diffraction and thermogravimetric-differential thermal analysis have been employed extensively throughout this work in order to follow the reaction pathways in real time. Detailed analysis of the AVO3 (A = In, Sc) bixbyite reactivity under oxidative conditions has been carried out and a variety of novel metastable oxygen defect phases have been identified and characterized. The novel metastable materials have oxygen deficient fluorite structures and consequently are potential ion conductors. Structural aspects of the topotactic vs. reconstructive transformations are illustrated with this model system. The structure-reactivity study of AVO3 phases was extended to AVO3 perovskite family. Based on the research methodologies and results from AVO3 bixbyite reactivity studies a generalized mechanistic oxidation pathway has been established with a non-vanadium phase, ScTiO3 bixbyite. However, there is stark contrast in terms of structural stability and features beyond this stability limit during AVO3 and ScTiO3 bixbyite reaction pathways. A series of complex reaction sequences including phase separation and phase transitions were identified during the investigation of ScTiO3 reactivity. The two-step formation pathway for the fluorite-type oxide ion conductor Ce1-xInxO2-delta (0 ≤ x ≤ 0.3) is being reported. The formation of the BaCe1-xInxO 3-delta perovskites and the subsequent CO2-capture reaction

  2. Luminescence and scintillation properties of BaF2sbnd Ce transparent ceramic

    Science.gov (United States)

    Luo, Junming; Sahi, Sunil; Groza, Michael; Wang, Zhiqiang; Ma, Lun; Chen, Wei; Burger, Arnold; Kenarangui, Rasool; Sham, Tsun-Kong; Selim, Farida A.

    2016-08-01

    Cerium doped Barium Fluoride (BaF2sbnd Ce) transparent ceramic was fabricated and its luminescence and scintillation properties were studied. The photoluminescence shows the emission peaks at 310 nm and 323 nm and is related to the 5d-4f transitions in Ce3+ ion. Photo peak at 511 keV and 1274 keV were obtained with BaF2sbnd Ce transparent ceramic for Na-22 radioisotopes. Energy resolution of 13.5% at 662 keV is calculated for the BaF2sbnd Ce transparent ceramic. Light yield of 5100 photons/MeV was recorded for BaF2sbnd Ce(0.2%) ceramic and is comparable to its single crystal counterpart. Scintillation decay time measurements shows fast component of 58 ns and a relatively slow component of 434 ns under 662 keV gamma excitation. The slower component in BaF2sbnd Ce(0.2%) ceramic is about 200 ns faster than the STE emission in BaF2 host and is associated with the dipole-dipole energy transfer from the host matrix to Ce3+ luminescence center.

  3. Fluorite and mixed-metal Kagome-related topologies in metal-organic framework compounds: synthesis, structure, and properties.

    Science.gov (United States)

    Mahata, Partha; Raghunathan, Rajamani; Banerjee, Debamalya; Sen, Diptiman; Ramasesha, S; Bhat, S V; Natarajan, S

    2009-06-01

    Two new three-dimensional metal-organic frameworks (MOFs) [Mn(2)(mu(3)-OH)(H(2)O)(2)(BTC)] x 2 H(2)O, I, and [NaMn(BTC)], II (BTC = 1,2,4-benzenetricarboxylate = trimellitate) were synthesized and their structures determined by single-crystal X-ray diffraction (XRD). In I, the Mn(4) cluster, [Mn(4)(mu(3)-OH)(2)(H(2)O)(4)O(12)], is connected with eight trimellitate anions and each trimellitate anion connects to four different Mn(4) clusters, resulting in a fluorite-like structure. In II, the Mn(2)O(8) dimer is connected with two Na(+) ions through carboxylate oxygen to form mixed-metal distorted Kagome-related two-dimensional -M-O-M- layers, which are pillared by the trimellitate anions forming the three-dimensional structure. The extra-framework water molecules in I are reversibly adsorbed and are also corroborated by powder XRD studies. The formation of octameric water clusters involving free and coordinated water molecules appears to be new. Interesting magnetic behavior has been observed for both compounds. Electron spin resonance (ESR) studies indicate a broadening of the signal below the ordering temperature and appear to support the findings of the magnetic studies.

  4. Luminescent and kinetic properties of the polystyrene composites based on BaF2 nanoparticles

    Science.gov (United States)

    Demkiv, T. M.; Halyatkin, O. O.; Vistovskyy, V. V.; Gektin, A. V.; Voloshinovskii, A. S.

    2016-02-01

    Luminescence-kinetic properties of polystyrene composites based on BaF2 nanoparticles were studied. The electron emission from the nanoparticles due to the photoelectric effect is the main luminescence excitation mechanism in the case of polystyrene composites loaded with small BaF2 nanoparticles (~20 nm). Scintillation pulse of polystyrene composites possesses only fast decay component with the time constant τ~2 ns, and its emission intensity considerably exceeds the one for pure polystyrene scintillator upon the X-ray excitations.

  5. X-RAY AND GAMMA-RAY LUMINESCENCE OF CE-3+ DOPED BAF2 CRYSTALS

    NARCIS (Netherlands)

    DORENBOS, P; VISSER, R; VANEIJK, CWE; HOLLANDER, RW; DENHARTOG, HW

    1991-01-01

    The scintillation properties of BaF2 doped with 0.002 to 10 mol% Ce3+ have been studied by means of X-ray and gamma ray excitation. The luminescence intensity increases with the Ce concentration until a maximum is reached for 0.2 mol% doped crystals. The light yield is then about 60% more intense th

  6. X-RAY AND GAMMA-RAY LUMINESCENCE OF CE-3+ DOPED BAF2 CRYSTALS

    NARCIS (Netherlands)

    DORENBOS, P; VISSER, R; VANEIJK, CWE; HOLLANDER, RW; DENHARTOG, HW

    1991-01-01

    The scintillation properties of BaF2 doped with 0.002 to 10 mol% Ce3+ have been studied by means of X-ray and gamma ray excitation. The luminescence intensity increases with the Ce concentration until a maximum is reached for 0.2 mol% doped crystals. The light yield is then about 60% more intense

  7. Response of MEDEA BaF 2 detectors to 20-280 MeV photons

    Science.gov (United States)

    Bellia, G.; Alba, R.; Coniglione, R.; Del Zoppo, A.; Finocchiaro, P.; Maiolino, C.; Migneco, E.; Piattelli, P.; Sapienza, P.; Frascaria, N.; Lhenry, I.; Roynette, J. C.; Suomijärvi, T.; Alamanos, N.; Auger, F.; Gillibert, A.; Pierroutsakou, D.; Sida, J. L.; Silveira Gomes, P. R.

    1993-05-01

    The response function of MEDEA BaF 2 crystals to high energy photons, up to 280 MeV, has been studied using monochromatic γ-rays from the in flight annihilation of positron beams. The experimental response functions are compared to the results of Monte Carlo simulations based on the EGS3 code and parametrized over the whole investigated energy range.

  8. In-Situ Conductivity Measurement of BaF2 under High Pressure and High Temperature

    Institute of Scientific and Technical Information of China (English)

    HAO Ai-Min; LI Xiao-Dong; LIU Jing; GAO Chun-Xiao; LI Ming; HE Chun-Yuan; HUANG Xiao-Wei; ZHANG Dong-Mei; YU Cui-Ling; ZOU Guang-Tian; LI Yan-Chun

    2006-01-01

    @@ We perform the in-situ conductivity measurement on BaF2 at high pressure using a microcircuit fabricated on a diamond anvil cell. The results show that BaF2 initially exhibits the electrical property of an insulator at pressure below 25 Gpa, it transforms to a wide energy gap semiconductor at pressure from 25 to 30 Gpa, and the conductivity increases gradually with increasing pressure from 30 Gpa. However, the metallization predicted by theoretical calculation at 30-33 Gpa cannot be observed. In addition, we measure the temperature dependence of the conductivity at several pressures and obtain the relationship between the energy gap and pressure. Based on the experimental data, it is predicted that BaF2 would transform to a metal at about 87 Gpa and ambient temperature. The conductivity of BaF2 reaches the order of 10-3Ω-1 cm-1 at 37 Gpa and 2400 K, the superionic conduction is not observed during the experiments, indicating the application of pressure elevates greatly the transition temperature of the superionic conduction.

  9. Clock distribution for BaF2 readout electronics at CSNS-WNS

    Science.gov (United States)

    He, Bing; Cao, Ping; Zhang, De-Liang; Wang, Qi; Zhang, Ya-Xi; Qi, Xin-Cheng; An, Qi

    2017-01-01

    A BaF2 (Barium Fluoride) detector array is designed to precisely measure the (n, γ) cross section at the CSNS-WNS (white neutron source at China Spallation Neutron Source). It is a 4π solid angle-shaped detector array consisting of 92 BaF2 crystal elements. To discriminate signals from the BaF2 detector, a pulse shape discrimination method is used, supported by a waveform digitization technique. There are 92 channels for digitizing. The precision and synchronization of clock distribution restricts the performance of waveform digitizing. In this paper, a clock prototype for the BaF2 readout electronics at CSNS-WNS is introduced. It is based on the PXIe platform and has a twin-stage tree topology. In the first stage, clock is synchronously distributed from the tree root to each PXIe crate through a coaxial cable over a long distance, while in the second stage, the clock is further distributed to each electronic module through a PXIe dedicated differential star bus. With the help of this topology, each tree node can fan out up to 20 clocks with 3U size. Test results show the clock jitter is less than 20 ps, which meets the requirements of the BaF2 readout electronics. Besides, this clock system has the advantages of high density, simplicity, scalability and cost saving, so it can be useful for other clock distribution applications. Supported by National Research and Development plan (2016 YFA0401602) NSAF (U1530111) and National Natural Science Foundation of China (11005107)

  10. Investigating the Electronic Structure of Fluorite Oxides: Comparsion of EELS and First Principles Calculations

    Energy Technology Data Exchange (ETDEWEB)

    Aguiar, J; Asta, M; Gronbech-Jensen, N; Perlov, A; Milman, V; Gao, S; Pickard, C; Browning, N

    2009-06-05

    Energy loss spectra from a variety of cubic oxides are compared with ab-initio calculations based on the density functional plane wave method (CASTEP). In order to obtain agreement between experimental and theoretical spectra, unique material specific considerations were taken into account. The spectra were calculated using various approximations to describe core-hole effects and electronic correlations. All the calculations are based on the local spin density approximation to show qualitative agreement with the sensitive oxygen K-edge spectra in ceria, zirconia, and urania. Comparison of experimental and theoretical results let us characterize the main electronic interactions responsible for both the electronic structure and the resulting EEL spectra of the compounds in question.

  11. Water orientation and hydrogen-bond structure at the fluorite/water interface

    CERN Document Server

    Khatib, Rémi; Bonn, Mischa; Perez-Haro, María-José; Gaigeot, Marie-Pierre; Sulpizi1, Marialore

    2016-01-01

    Water in contact with mineral interfaces is important for a variety of different processes. Here, we present a combined theoretical-experimental study which provides a quantitative, molecular-level understanding of the ubiquitous and important flourite-water interface. Our results show that, at low pH, the surface is positively charged, causing a substantial degree of water ordering. The surface charge originates primarily from the dissolution of fluoride ions, rather than from adsorption of protons to the surface. At high pH we observe the presence of Ca-OH species pointing into the water. These OH groups interact remarkably weakly with the surrounding water, and are responsible for the free OH signature in the SFG spectrum, which can be explained from local electronic structure effects. The quantification of the surface termination, near-surface ion distribution and water arrangement is enabled by a combination of advanced phase-resolved Vibrational Sum Frequency Generation spectra of flourite-water interfa...

  12. A BaF2 crystal array for high energy -ray measurements

    Indian Academy of Sciences (India)

    A Ray; S R Banerjee; P Das

    2001-07-01

    We shall discuss about the scientific motivation and construction of a 7 × 7 BaF2 crystal array at Variable Energy Cyclotron Centre, Calcutta. This detector would be used to measure high energy -ray photons from GDR decay and proton–neutron bremsstrahlung reactions at the present 88'' cyclotron and upcoming superconducting cyclotron at VECC, Calcutta. This detector can also be used to measure photons from quark–gluon plasma at the relativistic heavy ion collider (RHIC) in USA.

  13. Clock Distributing for BaF2 Readout Electronics at CSNS-WNS

    CERN Document Server

    He, Bing; De-Liang-Zhang,; Wang, Qi; Zhang, Ya-Xi; Qi, Xin-Cheng; Qi-An,

    2016-01-01

    aF2 (Barium Fluoride) detector array is designed for the measurement of (n,{\\gamma}) cross section precisely at CSNS-WNS (white neutron source at China Spallation Neutron Source). It is a 4{\\pi}solid angle-shaped detector array consisting of 92 BaF2 crystal elements. To discriminate signals from BaF2 detector, pulse shape discrimination methodology is used, which is supported by waveform digitization technique. There are total 92 channels for digitizing. The precision and synchronization of clock distribution restricts the performance of waveform digitizing. In this paper, the clock prototype for BaF2 readout electronics at CSNS-WNS is introduced. It is based on PXIe platform and has a twin-stage tree topology. In the first stage, clock is distributed from the tree root to each PXIe crate synchronously through coaxial cable over long distance, while in the second stage, clock is further distributed to each electronic module through PXIe dedicated differential star bus. With the help of this topology, each tre...

  14. Evaluation Software for BaF2 Detector Array Electronics at CSNS-WNS

    Science.gov (United States)

    Zhang, Yaxi; Cao, Ping; Wang, Qi; Zhang, Deliang; He, Bing; Qi, Xincheng; An, Qi

    2017-06-01

    The “in programming barium fluoride (BaF2) detector array” is one of the experiment facilities at China Spallation Neutron Source-White Neutron Sources, which is designed for the measurement of neutron capture cross section with high accuracy. It consists of 92 crystal elements with completely 4π solid-angle coverage, which needs 92 analog channels and 92 digitization channels for data acquisition. Accordingly, the readout electronics is comprised with four distributed readout PXIe crates, containing 46 field digitization modules (FDMs). Each FDM supports two valid channels for signal digitizing. In this paper, evaluation software is designed for evaluating the performance of BaF2 readout electronics. It focuses on evaluating the performance of data transmission, waveform digitizing, and working status monitoring. Test results show that the evaluation software can correctly acquire and assemble data from the BaF2 readout system and evaluate the analog digital converter (ADC) performance under ADC test mode. FDMs in the readout system can also be monitored and controlled by this software in real time.

  15. Hardness of CaF2 and BaF2 solid lubricants at 25 to 670 deg C

    Science.gov (United States)

    Deadmore, Daniel L.; Sliney, Harold E.

    1987-01-01

    Plastic deformation is a prominent factor in determining the lubricating value of solid lubricants. Little information is available and its direct measurement is difficult so hardness, which is an indirect measure of this property was determined for fluoride solid lubricant compositions. The Vickers hardness of BaF2 and CaF2 single crystals was measured up to 670 C in a vacuum. The orientation of the BaF2 was near the (013) plane and the CaF2 was about 16 degrees from the degrees from the (1'11) plane. The BaF2 has a hardness of 83 kg/sq mm at the 25 C and 9 at the 600 C. The CaF2 is 170 at 25 C and 13 at 670 C. The decrease in hardness in the temperature range of 25 to 100 C is very rapid and amounts to 40% for both materials. Melts of BaF2 and CaF2 were made in a platinum crucible in ambient air with compositions of 50 to 100 wt% BaF2. The Vickers hardness of these polycrystalline binary compositions at 25 C increased with increasing CaF2 reaching a maximum of 150 kn/sq mm near the eutectic. The polycrystalline CaF2 was 14% softer than that of the single crystal surface and BsF2 was 30% harder than the single crystal surface. It is estimated that the brittle to ductile transition temperature for CaF2 and BaF2 is less than 100 C for the conditions present in the hardness tester.

  16. Proposal of Readout Electronics for CSNS-WNS BaF2 Detector

    CERN Document Server

    Zhang, Deliang; Wang, Qi; He, Bing; Zhang, Yaxi; Qi, Xincheng; Yu, Tao; An, Qi

    2016-01-01

    BaF2 (Barium fluoride) detector is one of the experiment facilities at the under construction CSNS-WNS (White Neutron Source at China Spallation Neutron Source). It is designed for precisely measuring (n,gamma) cross section with total 92 crystal elements and completely 4 pi steradian coverage. In this proposal for readout electronics, waveform digitizing technique with 1GSps sampling rate and 12-bit resolution is adopted to precisely capture the detector signal. To solve the problem of massive data readout and processing, the readout electronics system is designed into a distributed architecture with 4 PXIe crates. The digitized detector's signal is concentrated to PXIe crate controller through PCIe bus on backplane and transmitted to data acquisition system over Gigabit Ethernet in parallel. Besides, clock and trigger can be fanned out synchronously to each electronic channel over a high-precision distributing network. Test results showed that the prototype of the readout electronics system achieved good pe...

  17. Electronic structures of (Pb sub 2 Cu)Sr sub 2 Eu sub x Ce sub n sub - sub x Cu sub 2 O sub 2 sub n sub + sub 6 (n=2, 3): Effect of fluorite blocks between adjacent CuO sub 2 layers

    CERN Document Server

    Arai, M

    2003-01-01

    The electronic structures of (Pb sub 2 Cu)Sr sub 2 Eu sub x Ce sub n sub - sub x Cu sub 2 O sub 2 sub n sub + sub 6 (n = 2, 3) compounds which have fluorite blocks between two adjacent CuO sub 2 layers have been studied by using ab-initio method. It is found that the anisotropy is enhanced by inserting the fluorite blocks. The Fermi velocity perpendicular to the CuO sub 2 layers decreases as the thickness of fluorite blocks increases. The Eu substitution is found to affect both the atomic positions and electronic structures. The distance between apical oxygen and copper becomes shorter by the Eu substitution. The energy bands derived from oxygens in the fluorite blocks approach Fermi energy as the content of Eu substitution increases. (author)

  18. Investigation of rare nuclear decays with BaF$_2$ crystal scintillator contaminated by radium

    CERN Document Server

    Belli, P; Cappella, F; Caracciolo, V; Cerulli, R; Danevich, F A; Di Marco, A; Incicchitti, A; Poda, D V; Polischuk, O G; Tretyak, V I

    2014-01-01

    The radioactive contamination of a BaF$_2$ scintillation crystal with mass of 1.714 kg was measured over 101 hours in the low-background DAMA/R&D set-up deep underground (3600 m w.e.) at the Gran Sasso National Laboratories of INFN (LNGS, Italy). The half-life of $^{212}$Po (present in the crystal scintillator due to contamination by radium) was measured as $T_{1/2}(^{212}$Po) = 298.8$\\pm$0.8(stat.)$\\pm$1.4(syst.) ns by analysis of the events' pulse profiles. The $^{222}$Rn nuclide is known as 100% decaying via emission of $\\alpha$ particle with $T_{1/2}$ = 3.82 d; however, its $\\beta$ decay is also energetically allowed with $Q_\\beta = 24\\pm21$ keV. Search for decay chains of events with specific pulse shapes characteristic for $\\alpha$ or for $\\beta/\\gamma$ signals and with known energies and time differences allowed us to set, for the first time, the limit on the branching ratio of $^{222}$Rn relatively to $\\beta$ decay as $B_\\beta 8.0$ y). Half-life limits of $^{212}$Pb, $^{222}$Rn and $^{226}$Ra rel...

  19. A 4p BaF2 detector for (n,g) cross section measurements at a spallation neutron source

    CERN Document Server

    Heil, M; Fowler, M M; Haight, R C; Käppeler, F; Rundberg, R S; Seabury, E H; Ullmann, J L; Wilhelmy, J B; Wisshak, K

    2013-01-01

    The quest for improved neutron capture cross sections for advanced reactor concepts, transmutation of radioactive wastes as well as for astrophysical scenarios of neutron capture nucleosynthesis has motivated new experimental efforts based on modern techniques. Recent measurements in the keV region have shown that a 4p BaF2 detector represents an accurate and versatile instrument for such studies. The present work deals with the potential of such a 4p BaF2 detector in combination with spallation neutron sources, which offer large neutron fluxes over a wide energy range. Detailed Monte Carlo simulations with the GEANT package have been performed to investigate the critical backgrounds at a spallation facility, to optimize the detector design, and to discuss alternative solutions.

  20. Numerical modeling of radiative heat transfer in Bridgman solidification of semi-transparent BaF 2 crystals

    Science.gov (United States)

    Stelian, C.

    2007-08-01

    The radiative heat transfer during Bridgman solidification of semi-transparent barium fluoride (BaF 2) crystals is numerically investigated by using the commercial software FIDAP. This code uses the P-1 approximation for the participating media modeling. The thermal field and the solid-liquid interface shape are computed for an opaque melt-crystal sample, a semi-transparent grey sample and a semi-transparent non-grey sample. The transient numerical analysis of the latent heat influence on the interface deflection shows a significant effect on the interface shape. In the case of an opaque sample, this effect is huge because of the small thermal conductivity of the BaF 2 melt. The interface curvature is drastically reduced when the latent heat is taken into account, and the growth front, which has a convex shape, becomes flat when the growth rate increases. The latent heat effect is reduced in the case of the participating BaF 2 sample because the effective thermal conductivity of the melt is augmented by the internal radiative heat transfer. The internal radiative effect is small at low solidified fractions but becomes significant when the crystal length increases, leading to a more curved interface. When the growth rates are greater than a critical value, the interface becomes concave and a destabilization of the growth process can occur. These results are in agreement with previous experimental measurements of the interface curvature and analytical investigations of the factors affecting the interface deflection.

  1. Synthesis, crystal structures and magnetic properties of fluorite-related compounds Ce3MO7 (M = Nb, Ta)

    Science.gov (United States)

    Inabayashi, Masaki; Doi, Yoshihiro; Wakeshima, Makoto; Hinatsu, Yukio

    2017-10-01

    Ternary oxides Ce3NbO7 and Ce3TaO7 were successfully synthesized by the solid state reaction under flowing hydrogen atmosphere. The structures were determined by the powder X-ray diffraction. Both the compounds were crystallized in the orthorhombic space groups Pnma (for Ce3NbO7) and Cmcm (for Ce3TaO7). Both the structures have similar features: two kinds of infinite chains formed by corner-sharing NbO6 (TaO6) octahedra and edge-sharing Ce(1)O8 cubes, the slabs consisting of alternate chains, and 7-coordinated Ce(2) ions existing between the slabs. In the structure of Ce3NbO7, the NbO6 octahedra running along the a-axis are titled towards the 0 0 1 direction, while in the Ce3TaO7 structure, the TaO6 octahedra running along the c-axis are titled towards the 0 1 0 direction. Magnetic susceptibility measurements for Ce3NbO7 and Ce3TaO7 show that both compounds are paramagnetic down to 1.8 K, and confirm that the Ce ion is in the trivalent state. From specific heat (Cp) measurements, a rapid increase of Cp/T has been observed below 3 K for both the compounds, indicating the onset of magnetic ordering between Ce3+ ions at further lower temperatures.

  2. Structures and stabilities of trivalent and tetravalent rare earth ions in sevenfold and eightfold coordination in fluorite-related complex oxides

    Energy Technology Data Exchange (ETDEWEB)

    Morss, L.R.

    1991-12-31

    This paper reports the preparation and characterization of a series of oxides containing 3+ or 4+ lanthanide (M = Ce, Pr, or Tb) ions, with different ionic sizes and varying M{sup 4+}/M{sup 3+} reduction potentials, in nearly cubic coordination. The objective of the study was to demonstrate how oxidation-reduction characteristics and ionic size trends explain the properties of these oxides and to compare the oxidation-reduction stability of M{sup 3+} and M{sup 4+} lanthanide ions in high (CN 7 or 8) coordination in fluorite-related oxides versus low (CN 6) coordination in perovskite oxides. Efficient preparative methods are reported, as well as powder diffraction and thermogravimetric measurements for oxides CaMTi{sub 2}O{sub 7-x} and CaMZr{sub 2}O{sub 7-x}. These oxides were characterized by X-ray powder diffraction and by thermogravimetric analysis. CaCeTi{sub 2}O{sub 7} is a pyrochlore, a = 10.142(4) {Angstrom}, with Ce{sup 4+} much more easily reducible than in the perovskite BaCeO{sub 3}. By contrast, a preparation with the stoichiometry ``CaPbTi{sub 2}O{sub 7-x}`` is a two-phase mixture-of perovskite CaTiCo{sub 3} and a presumably Pr{sup 3+}-rich pyrochlore Pr{sub 2}Ti{sub 2}O{sub 7}(?). CaTbTi{sub 2}O{sub 7-x} appears to be a Tb{sup 3+} pyrochlore, a = 10.149(2) {Angstrom}. CaCeZr{sub 2}O{sub 7} is a pyrochlore, a = 10.524(1) {Angstrom}. A preparation of ``CaPbZr{sub 2}O{sub 7-x}`` also appeared to yield a two-phase mixture, perovskite CaZrO{sub 3} and pyrochlore Pr{sub 2}Zr{sub 2}O{sub 7}. In this paper, the structures, f-element ion sites, and M(4)-M(3) stability trends in the CaMTi{sub 2}O{sub 7-x} and CaMZr{sub 2}O{sub 7-x} oxides are compared with the structural and stability trends in the perovskites BaMO{sub 3} which have M{sup 4+} ions in sixfold (tilted octahedra) coordination.

  3. Structures and stabilities of trivalent and tetravalent rare earth ions in sevenfold and eightfold coordination in fluorite-related complex oxides

    Energy Technology Data Exchange (ETDEWEB)

    Morss, L.R.

    1991-01-01

    This paper reports the preparation and characterization of a series of oxides containing 3+ or 4+ lanthanide (M = Ce, Pr, or Tb) ions, with different ionic sizes and varying M{sup 4+}/M{sup 3+} reduction potentials, in nearly cubic coordination. The objective of the study was to demonstrate how oxidation-reduction characteristics and ionic size trends explain the properties of these oxides and to compare the oxidation-reduction stability of M{sup 3+} and M{sup 4+} lanthanide ions in high (CN 7 or 8) coordination in fluorite-related oxides versus low (CN 6) coordination in perovskite oxides. Efficient preparative methods are reported, as well as powder diffraction and thermogravimetric measurements for oxides CaMTi{sub 2}O{sub 7-x} and CaMZr{sub 2}O{sub 7-x}. These oxides were characterized by X-ray powder diffraction and by thermogravimetric analysis. CaCeTi{sub 2}O{sub 7} is a pyrochlore, a = 10.142(4) {Angstrom}, with Ce{sup 4+} much more easily reducible than in the perovskite BaCeO{sub 3}. By contrast, a preparation with the stoichiometry CaPbTi{sub 2}O{sub 7-x}'' is a two-phase mixture-of perovskite CaTiCo{sub 3} and a presumably Pr{sup 3+}-rich pyrochlore Pr{sub 2}Ti{sub 2}O{sub 7}( ). CaTbTi{sub 2}O{sub 7-x} appears to be a Tb{sup 3+} pyrochlore, a = 10.149(2) {Angstrom}. CaCeZr{sub 2}O{sub 7} is a pyrochlore, a = 10.524(1) {Angstrom}. A preparation of CaPbZr{sub 2}O{sub 7-x}'' also appeared to yield a two-phase mixture, perovskite CaZrO{sub 3} and pyrochlore Pr{sub 2}Zr{sub 2}O{sub 7}. In this paper, the structures, f-element ion sites, and M(4)-M(3) stability trends in the CaMTi{sub 2}O{sub 7-x} and CaMZr{sub 2}O{sub 7-x} oxides are compared with the structural and stability trends in the perovskites BaMO{sub 3} which have M{sup 4+} ions in sixfold (tilted octahedra) coordination.

  4. Response of BaF 2 detectors to photons of 3-50 MeV energy

    Science.gov (United States)

    Matulewicz, T.; Grosse, E.; Emling, H.; Freifelder, R.; Grein, H.; Henning, W.; Herrmann, N.; Holzmann, R.; Kulessa, R.; Simon, R. S.; Wollersheim, H. J.; Schoch, B.; Vogt, J.; Wilhelm, M.; Kratz, J. V.; Schmidt, R.; Janssens, R. V. F.

    1990-04-01

    BaF 2 detectors of 20 cm length (10 radiation lengths) and hexagonal cross section (diameter 5.2 cm) were tested using monochromatic photons from the tagged-photon facility at the electron accelerator MAMIA at Mainz. The experimental spectra the deposited energy for a single detector and for an array of seven modules compare very well with the predictions of Monte Carlo shower simulations using the code GEANT3. At high photon energies a significant improvement (more than a factor 2) of the energy resolution is observed for the summed energy spectra as compared to the resolution of one single module.

  5. Scintillation light simulation in big-sized BaF$_{2}$ and pure CsI crystals

    CERN Document Server

    Usubov, Zafar

    2016-01-01

    We have investigated scintillation light distribution in BaF$_{2}$ and pure CsI crystals with dimensions 3x3x20 cm$^{3}$ using the Geant4 toolkit. The diffuse wrapping material is selected as coating for the crystals. The simulated cosmic muons and 105 MeV electrons are used as beam particles. The optical attenuation along the crystals is explored with the simulation data. We have demonstrated the impact of the crystal surface finish on the light distribution at the crystal end, optical photon arrival time, incidence angle distributions, and optical attenuation for the studied crystals.

  6. System design for precise digitization and readout of the CSNS-WNS BaF2 spectrometer

    Science.gov (United States)

    Zhang, De-Liang; Cao, Ping; Wang, Qi; He, Bing; Zhang, Ya-Xi; Qi, Xin-Cheng; Yu, Tao; An, Qi

    2017-02-01

    The BaF2 (barium fluoride) spectrometer is one of the experiment facilities at the CSNS-WNS (White Neutron Source at China Spallation Neutron Source), currently under construction. It is designed to precisely measure the (n, γ) cross section, with 92 crystal elements and complete 4π steradian coverage. In order to improve the precision of measurement, in this paper, a new precise digitization and readout method is proposed. Waveform digitizing with 1 GSps sampling rate and 12-bit resolution is used to precisely capture the detector signal. To solve the problem of massive data readout and processing, the readout electronics is designed as a distributed architecture with 4 PXIe crates. The digitized signal is concentrated to the PXIe crate controller through a PCIe bus on the backplane and transmitted to the data acquisition system over gigabit Ethernet in parallel. Besides, the clock and trigger can be fanned out synchronously to every electronic channel over a high-precision distribution network. Test results show that the prototype of the readout electronics can achieve good performance and meet the requirements of the CSNS-WNS BaF2 spectrometer. Supported by National Research and Development plan (2016YFA0401602) and NSAF (U1530111)

  7. Enhanced 2.0 microm emission and gain coefficient of transparent glass ceramic containing BaF2: Ho3+,Tm3+ nanocrystals.

    Science.gov (United States)

    Zhang, W J; Zhang, Q Y; Chen, Q J; Qian, Q; Yang, Z M; Qiu, J R; Huang, P; Wang, Y S

    2009-11-09

    Transparent glass ceramic containing BaF(2):Ho(3+),Tm(3+) nanocrystals has been prepared by melt quenching and subsequent thermal treatment. The precipitation of BaF(2) nanocrystals was confirmed by X-ray diffraction and high-resolution transmission electron microscopy. Intense 2.0 microm fluorescence originating from Ho(3+): (5)I(7) --> (5)I(8) transition was achieved upon excitation with 808 nm laser diode. A large ratio of forward Tm(3+) --> Ho(3+) energy transfer constant to that of backward process indicated high efficient energy transfer from Tm(3+)((3)F(4)) to Ho(3+)((5)I(7)), benefited from the reduced ionic distances of Tm(3+)-Tm(3+) and Tm(3+)-Ho(3+) pairs and low phonon energy environment with the incorporation of rare-earth ions into the precipitated BaF(2) nanocrystals. The results indicate that glass ceramic is a promising candidate material for 2.0 microm laser.

  8. Defect-induced wetting on BaF 2(111) and CaF 2(111) at ambient conditions

    Science.gov (United States)

    Cardellach, M.; Verdaguer, A.; Fraxedas, J.

    2011-12-01

    The interaction of water with freshly cleaved (111) surfaces of isostructural BaF2 and CaF2 single crystals at ambient conditions (room temperature and under controlled humidity) has been studied using scanning force microscopy in different operation modes and optical microscopy. Such surfaces exhibit contrasting behaviors for both materials: while on BaF2(111) two-dimensional water layers are formed after accumulation at step edges, CaF2(111) does not promote the formation of such layers. We attribute such opposed behavior to lattice match (mismatch) between hexagonal water ice and the hexagonal (111) surfaces of BaF2(CaF2). Optical microscope images reveal that this behavior also determines the way the surfaces become wetted at a macroscopic level.

  9. A Unique TAS Setup for high multiplicity events at VECC, Kolkata using BaF2 detectors

    Directory of Open Access Journals (Sweden)

    Mukherjee G.

    2014-03-01

    Full Text Available A granular total absorption spectrometer (TAS has been developed at the Variable Energy Cyclotron Centre, Kolkata, India using 50 elements of BaF2 detectors and covering 4π. The advantage with such a granular setup is that one can get sum spectrum with the condition of different multiplicity hits in an event. It has been shown that one can get clean sum-peaks devoid of individual peaks with the choice of two or higher fold of multiplicity. The large granularity makes it a unique TAS setup particularly for the high multiplicity events. The set up has been tested using different radioactive sources with one, two or multiple γ rays in cascade. The set up is ready to be used online.

  10. Test of the statistical model in Mo96 with the BaF2γ calorimeter DANCE array

    Science.gov (United States)

    Sheets, S. A.; Agvaanluvsan, U.; Becker, J. A.; Bečvář, F.; Bredeweg, T. A.; Haight, R. C.; Jandel, M.; Krtička, M.; Mitchell, G. E.; O'Donnell, J. M.; Parker, W.; Reifarth, R.; Rundberg, R. S.; Sharapov, E. I.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Wu, C. Y.

    2009-02-01

    The γ-ray cascades following the Mo95(n,γ)Mo96 reaction were studied with the γ calorimeter DANCE (Detector for Advanced Neutron Capture Experiments) consisting of 160 BaF2 scintillation detectors at the Los Alamos Neutron Science Center. The γ-ray energy spectra for different multiplicities were measured for s- and p-wave resonances below 2 keV. The shapes of these spectra were found to be in very good agreement with simulations using the DICEBOX statistical model code. The relevant model parameters used for the level density and photon strength functions were identical with those that provided the best fit of the data from a recent measurement of the thermal Mo95(n,γ)Mo96 reaction with the two-step-cascade method. The reported results strongly suggest that the extreme statistical model works very well in the mass region near A=100.

  11. Spectroscopic properties of Pr3+ and Er3+ ions in lead-free borate glasses modified by BaF2

    Science.gov (United States)

    Pisarska, Joanna; Pisarski, Wojciech A.; Dorosz, Dominik; Dorosz, Jan

    2015-09-01

    Lead-free oxyfluoride borate glasses singly doped with Pr3+ and Er3+ were prepared and next investigated using absorption and luminescence spectroscopy. In the studied glass system, barium oxide was substituted by BaF2. Two luminescence bands of Pr3+ located at visible spectral region are observed, which correspond to 3P0-3H4 (blue) and 1D2-3H4 (reddish orange) transitions, respectively. The luminescence bands due to 1D2-3H4 transition of Pr3+ are shifted to shorter wavelengths, when BaO was substituted by BaF2. Near-infrared luminescence spectra of Er3+ ions in lead-free borate glasses modified by BaF2 correspond to 4I13/2-4I15/2 transition. Their spectral linewidths increase with increasing BaF2 concentration. The changes in measured lifetimes of rare earth ions are well correlated with the bonding parameters calculated from the optical absorption spectra.

  12. Variable helium diffusion characteristics in fluorite

    Science.gov (United States)

    Wolff, R.; Dunkl, I.; Kempe, U.; Stockli, D.; Wiedenbeck, M.; von Eynatten, H.

    2016-09-01

    Precise analysis of the diffusion characteristics of helium in fluorite is crucial for establishing the new fluorite (U-Th-Sm)/He thermochronometer (FHe), which potentially provides a powerful tool for dating ore deposits unsuitable for the application of conventional geochronometers. Incremental helium outgassing experiments performed on fluorites derived from a spectrum of geological environments suggest a thermally activated volume diffusion mechanism. The diffusion behaviour is highly variable and the parameters range between log D0/a2 = 0.30 ± 0.27-7.27 ± 0.46 s-1 and Ea = 96 ± 3.5-182 ± 3.8 kJ/mol. Despite the fact that the CaF2 content of natural fluorites in most cases exceeds 99 weight percent, the closure temperature (Tc) of the fluorite (U-Th-Sm)/He thermochronometer as calculated from these diffusion parameters varies between 46 ± 14 °C and 169 ± 9 °C, considering a 125 μm fragment size. Here we establish that minor substitutions of calcium by rare earth elements and yttrium (REE + Y) and related charge compensation by sodium, fluorine, oxygen and/or vacancies in the fluorite crystal lattice have a significant impact on the diffusivity of helium in the mineral. With increasing REE + Y concentrations F vacancies are reduced and key diffusion pathways are narrowed. Consequently, a higher closure temperature is to be expected. An empirical case study confirms this variability: two fluorite samples from the same deposit (Horni Krupka, Czech Republic) with ca. 170 °C and ca. 43 °C Tc yield highly different (U-Th-Sm)/He ages of 290 ± 10 Ma and 79 ± 10 Ma, respectively. Accordingly, the fluorite sample with the high Tc could have quantitatively retained helium since the formation of the fluorite-bearing ores in the Permian, despite subsequent Mesozoic burial and associated regional hydrothermal heating. In contrast, the fluorite with the low Tc yields a Late Cretaceous age close to the apatite fission track (AFT) and apatite (U-Th)/He ages (AHe

  13. Control estructural de las mineralizaciones de fluorita del batolito Cerro Áspero, Sierras Pampeanas de Córdoba Structural control of vein-type fluorite deposits of Cerro Áspero batholith, Sierras Pampeanas of Córdoba

    Directory of Open Access Journals (Sweden)

    Jorge E Coniglio

    2010-12-01

    , NE, EW, and NW strike-slip regional fault zones, with thicknesses generally less than 3 metres. They can be continued up to 200 m deep below surface. The geometry and distributions of the veins were tectonically controlled by divergent shear zones, probably linked with the opening of the south Atlantic ocean. In the study area, this regional situation established a dextral simple shear system related to NNE lineaments, that is characterized by N70ºE striking extensional structures, less than 1 km long, and NE and NW striking shear systems, more than 4 km long. These shear systems show typical patterns of transcurrent faults such as stepovers, offsets, bends and horsetail splay. Four successive mineralizing stages were recognized on the basis of textural and structural analyses of the veins. The emplacement of these mineralizing stages were controlled by a discontinuous activity of dextral couple, with the minimum paleostress (σ3 always oriented toward NNW. The fact that some of the fluorite stages are absent in several veins in the investigated areas, confirm that the mineralized structures had different times of opening and sealing, and thus the depositional sequence established could be used as an effective prospection criteria. The main ore bodies are related to extensional zones (releasing bends and extensional structures, which registered the whole mineralizing sequence.

  14. Ion conductivity in cubically-stabilized fluorite-like structured Er5CeMoO12.5 and Yb5MMoO12.5 (M = Ce, Zr) solid solutions

    Science.gov (United States)

    Schildhammer, Daniel; Fuhrmann, Gerda; Petschnig, Lucas; Kogler, Michaela; Penner, Simon; Weinberger, Nikolaus; Schottenberger, Herwig; Huppertz, Hubert

    2016-12-01

    For the first time, the usually rhombohedral R 3 bar (no. 148) defect fluorite structured rare earth molybdenum oxides RE6MoO12 (RE = Er, Yb) could be stabilized in the cubic defect fluorite structure Fm 3 bar m (no. 225) through partial substitution of Er3+ and Yb3+ by M4+ cations with M4+ = Ce for Er6MoO12 and M4+ = Ce, Zr for Yb6MoO12. The solution combustion (SC) method and the classical solid state reaction are the synthetic approaches that were used (ambient atmosphere and temperatures of 1250 °C). The obtained oxide powders were characterized by energy dispersive X-ray (EDX) analysis, powder X-ray diffraction (PXRD), IR, and UV-Vis spectroscopy. The PXRD-data were used for Rietveld refinements. Electrochemical impedance spectroscopy (EIS) was conducted to identify oxygen vacancies in the cubic structure type, revealing oxygen ion conductivity starting at 500 °C. Additionally, the influence on ion conductivity by the cation substitutions are discussed. Calculation of the contributing activation energies for the bulk (best value for Yb5CeMoO12.5 is 119.8 kJmol-1), and the grain boundary (e.g. Er5CeMoO12.5: 152.1 kJmol-1) analyzed by means of the Arrhenius plot, shows similarities to the conventional stabilization of zirconia with yttrium (8-YSZ) (110 kJ mol-1 and 110-163 kJmol-1 respectively). The best-calculated conductivity values σ = 1.03 × 10-4 Scm-1 obtained for Er5CeMoO12.5 at 1000 °C are comparable to the values published for 8-YSZ with σ = 3.94 × 10-5 Scm-1 at similar temperatures. These promising preliminary results underline the potential of the title compounds for application in solid oxide fuel cells (SOFCs).

  15. Complex Refractive Index Measurements for BaF2 and CaF2 via Single-Angle Infrared Reflectance Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kelly-Gorham, Molly Rose K.; De Vetter, Brent M.; Brauer, Carolyn S.; Cannon, Bret D.; Burton, Sarah D.; Bliss, Mary; Johnson, Timothy J.; Myers, Tanya L.

    2017-10-01

    We have re-investigated the optical constants n and k for the homologous series of inorganic salts barium fluoride (BaF2) and calcium fluoride (CaF2) using a single-angle near-normal incidence reflectance device in combination with a calibrated Fourier transform infrared (FTIR) spectrometer. Our results are in good qualitative agreement with most previous works. However, certain features of the previously published data near the reststrahlen band exhibit distinct differences in spectral characteristics. Notably, our measurements of BaF2 do not include a spectral feature in the ~250 cm-1 reststrahlen band that was previously published. Additionally, CaF2 exhibits a distinct wavelength shift relative to the model derived from previously published data. We confirmed our results with recently published works that use significantly more modern instrumentation and data reduction techniques

  16. Ultralow threshold green lasing and optical bistability in ZBNA (ZrF4-BaF2-NaF-AlF3) microspheres

    Science.gov (United States)

    Wu, Yuqiang; Ward, Jonathan M.; Nic Chormaic, Síle

    2010-02-01

    Upconversion lasing and fluorescence from active microspheres fabricated from a novel fluorozirconate, Er3+ doped glass, ZBNA (ZrF4-BaF2-NaF-AlF3), when pumped at 978 nm via a tapered optical fiber is demonstrated. An ultralow, green lasing threshold of ˜3 μW for 550 nm emissions is measured. This is one order of magnitude lower than that previously reported for ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) microspheres. Optical bistability effects in ZBNA microspheres are reported and the bistable mechanism is discussed and attributed to shifts of the whispering gallery modes due to thermal expansion of the sphere, where heating is achieved by optical pumping around 978 nm. The effect of the bistability on the upconversion lasing is examined and we report multiple bistability loops within the microspheres.

  17. Simultaneous measurement of (n, γ) and (n, fission) cross sections with the DANCE 4π BaF 2 array

    Science.gov (United States)

    Bredeweg, T. A.; Fowler, M. M.; Becker, J. A.; Bond, E. M.; Chadwick, M. B.; Clement, R. R. C.; Esch, E.-I.; Ethvignot, T.; Granier, T.; Jandel, M.; Macri, R. A.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Wu, C. Y.

    2007-08-01

    We have recently begun a program of high precision measurements of the key production and destruction reactions of important radiochemical diagnostic isotopes, including several isotopes of uranium, plutonium and americium. The detector for advanced neutron capture experiments (DANCE), a 4π BaF2 array located at the Los Alamos Neutron Science Center, will be used to measure the neutron capture cross sections for most of the isotopes of interest. However, neutron capture measurements on many of the actinides are complicated by the presence of prompt γ-rays arising from low energy neutron-induced fission, which competes with neutron capture to varying degrees. Previous measurements of 235U using the DANCE array have shown that we can partially resolve capture from fission events based on total γ-ray calorimetry (i.e. total γ-ray energy versus γ-ray multiplicity). The addition of a dedicated fission-tagging detector to the DANCE array has greatly improved our ability to separate these two competing processes. In addition to higher quality neutron capture data, the addition of a fission-tagging detector offers a means to determine the capture-to-fission ratio (σγ/σf) in a single measurement, which should reduce the effect of systematic uncertainties. We are currently using a dual parallel-plate avalanche counter (PPAC) with the target material electro-deposited directly on the center cathode foil. This design provides a high efficiency for detecting fission fragments and allows loading of pre-assembled target/detector assemblies into the neutron beam line at DANCE. Results from tests of the fission-tag detector, as well as preliminary results from measurements on 235U and 252Cf that utilized the fission-tag detector will be presented.

  18. Optical characterization of Tm3+ doped Bi2O3-GeO2-Ga2O3 glasses in absence and presence of BaF2

    Science.gov (United States)

    Han, Kexuan; Zhang, Peng; Wang, Shunbin; Guo, Yanyan; Zhou, Dechun; Yu, Fengxia

    2016-08-01

    In this paper, Two new Bi2O3-GeO2-Ga2O3 glasses (one presence of BaF2) doped with 1mol% Tm2O3 were prepared by melt-quenching technique. Differential thermal analysis (DTA), the absorption, Raman, IR spectra and fluorescence spectra were measured. The Judd-Ofelt intensity parameters, emission cross section, absorption cross section, and gain coefficient of Tm3+ ions were comparatively investigated. After the BaF2 introduced, the glass showed a better thermal stability, lower phonon energy and weaker OH- absorption coefficient, meanwhile, a larger ~1.8 μm emission cross section σem (7.56 × 10-21 cm2) and a longer fluorescence lifetime τmea (2.25 ms) corresponding to the Tm3+: 4F3 → 3H6 transition were obtained, which is due to the addition of fluoride in glass could reduce the quenching rate of hydroxyls and raise the cross-relaxation (3H6 + 3H4 → 3F4 + 3F4) rate. Our results suggest that the Tm3+ doped Bi2O3-GeO2-Ga2O3 glass with BaF2 might be potential to the application in efficient ~1.8 μm lasers system.

  19. Luminescence properties of dual valence Eu doped nano-crystalline BaF2 embedded glass-ceramics and observation of Eu2+ → Eu3+ energy transfer.

    Science.gov (United States)

    Biswas, Kaushik; Sontakke, Atul D; Sen, R; Annapurna, K

    2012-03-01

    Europium doped glass-ceramics containing BaF(2) nano-crystals have been prepared by using the controlled crystallization of melt-quenched glasses. X-ray diffraction and transmission electron microscopy have confirmed the presence of cubic BaF(2) nano-crystalline phase in glass matrix in the ceramized samples. Incorporation of rare earth ions into the formed crystalline phase having low phonon energy of 346 cm(-1) has been demonstrated from the emission spectra of Eu(3+) ions showing the transitions from upper excitation states (5)D(J) (J = 1, 2, and 3) to ground states for the glass-ceramics samples. The presence of divalent europium ions in glass and glass-ceramics samples is confirmed from the dominant blue emission corresponding to its 5d-4f transition under an excitation of 300 nm. Increase in the reduction of trivalent europium (Eu(3+)) ions to divalent (Eu(2+)) with the extent of ceramization is explained by charge compensation model based on substitution defect mechanisms. Further, the phenomenon of energy transfer from Eu(2+) to Eu(3+) ion by radiative trapping or re-absorption is evidenced which increases with the degree of ceramization. For the first time, the reduction of Eu(3+) to Eu(2+) under normal air atmospheric condition has been observed in a BaF(2) containing oxyfluoride glass-ceramics system.

  20. Spectroscopic properties and mechanism of Tm3+/Er3+/Yb3+co-doped oxyfluorogermanate glass ceramics containing BaF2 nanocrystals

    Science.gov (United States)

    Hu, Yue-Bo; Qiu, Jian-Bei; Zhou, Da-Cheng; Song, Zhi-Guo; Yang, Zheng-Wen; Wang, Rong-Fei; Jiao, Qing; Zhou, Da-Li

    2014-02-01

    Transparent Tm3+/Er3+/Yb3+ co-doped oxyfluorogermanate glass ceramics containing BaF2 nanocrystals are prepared. Under excitation of a 980-nm laser diode (LD), compared with the glass before heat treatment, the Tm3+/Er3+/Yb3+co-doped oxyfluorogermanate glass ceramics can emit intense blue, green and red up-conversion luminescence and Stark-split peaks; X-ray diffraction (XRD) and transmission electron microscope (TEM) results show that BaF2 nanocrystals with an average diameter of 20 nm are precipitated from the glass matrix. Stark splitting of the up-conversion luminescence peaks in the glass ceramics indicates that Tm3+, Er3+ and (or) Yb3+ ions are incorporated into the BaF2 nanocrystals. The up-conversion luminescence intensities of Tm3+, Er3+ and the splitting degree of luminescence peaks in the glass ceramics increase significantly with the increase of heat treat temperature and heat treat time extension. In addition, the possible energy transfer process between rare earth ions and the up-conversion luminescence mechanism are also proposed.

  1. Ho3+/Yb3+ co-doped TeO2-BaF2-Y2O3 glasses for ∼1.2 μm laser applications

    Science.gov (United States)

    Wang, Shunbin; Li, Chengzhi; Yao, Chuanfei; Jia, Shijie; Jia, Zhixu; Qin, Guanshi; Qin, Weiping

    2017-02-01

    Intense ∼1.2 μm fluorescence is observed in Ho3+/Yb3+ co-doped TeO2-BaF2-Y2O3 glasses under 915 nm laser diode excitation. The 1.2 μm emission can be ascribed to the transition 5I6→5I8 of Ho3+. With the introducing of BaF2, the content of OH in the glasses drops markedly, and the 1.2 μm emission intensity increases gradually as increasing the concentration percentage of BaF2. Furthermore, microstructured fibers based on the TeO2-BaF2-Y2O3 glasses are fabricated by using a rod-in-tube method, and a relative positive gain of ∼9.42 dB at 1175.3 nm is obtained in a 5 cm long fiber.

  2. Reaction kinetics of fluorite in flow systems and surface chemistry

    Institute of Scientific and Technical Information of China (English)

    张荣华; 胡书敏

    1996-01-01

    The kinetic experiments of fluorite in water-HCl solution in an open-flow system at the temperatures ≤100℃ reveal that the variation of flow rate (U) can change the reaction rate orders from 0 to 2 or higher. In the far from equilibrium systems, the dissolution rates of fluorite in aqueous solutions have a zero order.The reaction rates are controlled by pH values of input solutions. In fact, the reaction rates are related to the concentrations of the active sites occupied by H+ on fluorite surface [SOH]. X-ray photospectroscopy observations on fluorite surface before and after reaction indicate that surface chemical processes control the reaction rates: Cl- cations attach on and enter into surface of fluorite besides H+ when fluorites react with HCl solutions, which affect the reaction rates.

  3. Optical properties of a new Bi38Mo7O78 semiconductor with fluorite-type δ-Bi2O3 structure

    Science.gov (United States)

    Wang, Zuoshan; Bi, Shala; Wan, Yingpeng; Huang, Pengjie; Zheng, Min

    2017-03-01

    Bi3+-containing inorganic materials usually show rich optical and electronic properties due to the hybridization between 6s and 6p electronic components together with the lone pair in Bi3+ ions. In this work, a new semiconductor of bismuth molybdate Bi38Mo7O78 (19Bi2O3·7MoO3) was synthesized by the sol-gel film coating and the following heat process. The samples developed into nanoparticles with average size of 40 nm. The phase formation was verified via the XRD Rietveld structural refinement. Orthorhombic Bi38Mo7O78 can be regarded to be derived from the cubic δ-phase Bi2O3 structure. The microstructure was investigated by SEM, EDX, TEM, BET and XPS measurements. The UV-vis absorption spectra showed that the band gap of Bi38Mo7O78 (2.38 eV) was greatly narrowed in comparison with Bi2O3 (2.6 eV). This enhances the efficient absorption of visible light. Meanwhile, the conduction band of is wider and shows more dispersion, which greatly benefits the mobility of the light-induced charges taking part in the photocatalytic reactions. Bi38Mo7O78 nanoparticles possess efficient activities on the photodegradation of methylene blue (MB) solutions under the excitation of visible-light. The photocatalysis activities and mechanisms were discussed on the crystal structure characteristics and the measurements such as photoluminescence, exciton lifetime and XPS results.

  4. Spectroscopy of laser properties of Nd(3+)-doped CaF2, SrF2, and BaF2

    Science.gov (United States)

    Payne, Stephen A.; Caird, John A.; Chase, L. L.; Smith, L. K.; Nielsen, N. D.; Krupke, William F.

    1990-03-01

    The optical properties of Nd(3+) in CaF2, SrF2, and BaF2 were investigated in order to determine if these materials are useful as laser-pumped amplifier media. The CaF2:Nd crystal was found to not be useful because the impurities tend to cluster at very low concentration, leading to the formation of nonluminescent centers. On the other hand, the Nd(3+) centers in BaF2 exhibit unacceptably low transition strengths. SrF2:Nd appears to have adequate absorption strength, and, in addition, to have a remarkably long emission lifetime of 1280 microns. A maximum doping of 0.20 atomic percent Nd(3+) can be tolerated in SrF2 without the occurrence of detrimental clustering. The peak emission cross section of SrF2:Nd is 1.7 x 10(exp -20) sq cm at 1036.5 nm. Direct measurement of the gain spectrum of SrF2:Nd(3+) reveals the presence of the F-4(sub 3/2) yields G-2(sub 9/2) excited state absorption lines, although the impact on the emission cross section is minor.

  5. Low-frequency inelastic light scattering in a ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) glass

    Science.gov (United States)

    Adichtchev, S. V.; Malinovsky, V. K.; Ignatieva, L. N.; Merkulov, E. B.; Surovtsev, N. V.

    2014-05-01

    Low-frequency (down to 30 GHz) inelastic light scattering is studied in a multicomponent glass ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) in a wide temperature range. The contributions of the THz vibrational spectrum (boson peak) and of the fast relaxation are extracted and analyzed. It is shown that the fast relaxation spectrum is described by a distribution of relaxation times leading to a power-law να dependence in the frequency range 30-300 GHz. Temperature dependence of α(T) is well described by the Gilroy-Phillips model, while the integrated intensity of the fast relaxation increases significantly with the temperature. This feature distinguishes the fast relaxation in ZBLAN from the case of most single-component glasses. Thermodynamic and kinetic fragility indexes are significantly different for the ZBLAN glass. The correlations between the boson peak intensity, elastic moduli, and fragility index, found earlier for single-component glasses, are fulfilled for the thermodynamic fragility index of ZBLAN. In contrast, the correlation between the fast relaxation intensity at Tg and the fragility holds better for the kinetic fragility index of ZBLAN. We propose that thermodynamic and kinetic fragilities reflect different aspects of glassy dynamics in the case of glass formers with the complex chemical composition and structure topology: the former correlates with the elastic properties and the boson peak, the latter with the relaxation.

  6. Selective Flotation of Calcite from Fluorite: A Novel Reagent Schedule

    Directory of Open Access Journals (Sweden)

    Zhiyong Gao

    2016-10-01

    Full Text Available Fluorite is an important strategic mineral. In general, fluorite ores will contain a certain amount of calcite gangue mineral. Thus, they need to be separated from each other. For an economic separation, a reverse flotation process is used to float calcite gangue from fluorite. However, little information on the separation is available. In this study, a novel reagent schedule using citric acid (CA as the depressant, sodium fluoride (NaF as the regulator and sulfoleic acid (SOA as the collector, was developed to separate calcite from fluorite. The results demonstrated a high selectivity for the flotation of calcite from fluorite using this new reagent schedule. The best selective separation for a single mineral and mixed binary minerals was obtained when 200 mg/L of NaF, 50 mg/L of CA, and 6 mg/L of SOA were used at pH 9. In addition, a batch flotation experiment was carried out using a run-of-mine feed material. Selective separation was achieved with 85.18% calcite removal while only 11.2% of fluorite was lost. An attempt was made to understand the effect of the new reagent schedule on the flotation of calcite. The results from both microflotation and bench scale flotation demonstrated a great potential for industrial application using this novel reagent schedule to upgrade fluorite ore.

  7. Geochemistry and microfabrics of syndiagenetic strata-bound fluorite from Eschwege, Germany - Implications for fluorite formation and remobilization in Zechstein carbonates from the Lower Saxony Basin

    Science.gov (United States)

    Duschl, Florian; Wischhöfer, Philipp; Vollbrecht, Axel

    2017-04-01

    Core samples of Stassfurt carbonate rocks (Zechstein, Ca2) from various locations in the Lower Saxony Basin (LSB) often contain fluorite which occurs as pore filling cement, replacement fluorite, or as fault-related fracture mineralizations. Recent studies on fluorite geochemistry and fluid migration in the LSB suggest a sedimentary rather than a hydrothermal fluorite source for some of these deep-seated (> 2500 mbs) accumulations. Outcrop samples from lens-shaped and stratiform fluorite occurrences within oolithic limestone (Ca2) near Eschwege, Germany, give insight into syndiagenetic fluorite formation in Zechstein carbonates. They serve as a shallow-burial analogue for remobilized fluorite within deeply buried carbonate rocks of the LSB. Samples were studied using petrographic microscopy, hot-cathodoluminescence microscopy, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Five different fluorite types were identified: a first generation (I) is represented by a dark brownish to violet fluorite that replaced ooids during early diagenesis. As pressure increased during burial the replacement fluorite recrystallized forming white aggregates of parallel bar-shaped fluorite crystals (type II), type (III) consists of white fluorite grains with rectangular and mostly polygonal grain boundaries; type (IV) is a colorless to blueish pore-filling fluorite, and type (V) is a colorless fracture-hosted fluorite. In-situ LA-ICP-MS analyses of respective fluorite types revealed relatively low REE concentrations in general with Tb/Ca vs. Tb/La signatures that are typical for sediment-hosted fluorite. The REE distribution patterns reflect the processes of recrystallization and remobilization. Though stylolitization affected both host rock and replacement fluorite, only little fluorite remobilization did occur due to pressure solution. Geochemical analyses prove that fluorite formation was controlled by precipitation from a sedimentary parental fluid

  8. Fluid Evolution During Mineralization of Atashkuh Fluorite-Barite (±Sulfide Deposit, South of Delijan

    Directory of Open Access Journals (Sweden)

    Seyed Javad Moghaddasi

    2016-07-01

    Full Text Available Introduction More than 30 fluorite occurrences with approximately 1.35 million tons of reserves have been recognized in Iran (Ghorbani, 2013. The Atashkuh fluorite-barite (±sulfide deposit is one of four occurrences located south of the city of Delijan in Markazi province, about 80 km SE of Arak city. The Atashkuh deposit occurs between the central Iran structural zone on the north and the Sanandaj-Sirjan structural zone on the south. The geology of the area is dominated by folded and faulted Jurassic carbonates and shales (Thiele et al., 1968. The lower Jurassic shale and calcareous sandstone of the Shemshak Formation and the Middle to Upper Jurassic dolomite of the Badamu Formation are the main host rocks for the fluorite veins. In this study, 40 samples from fluorite veins and host rocks were collected, from which 25 thin sections and 8 doubly-polished thin sections were prepared. Micro-thermometric studies were conducted on primary fluid inclusions using the Linkam THM600 heating-freezing stage. In addition, 10 samples were analyzed by XRD. Results Fluid inclusion data indicate that the Atashkuh fluorite-barite (±sulfides veins were deposited as a result of mixing a primary multi-component Na-K(-Mg-Ca high-salinity brine (SH type inclusions with less saline calcium-rich connate water (LVHH type inclusions and pressure reduction of ore bearing fluids. Fluid inclusions containing halite in high-salinity brine, and hydrohalite in connate water show suggest a high-salinity brine and connate water before mixing. The main mineralization stage was followed by circulation of low temperature meteoric water, responsible for the late stage mineralization. The micro-thermometry results suggest that the main fluorite mineralization occurred at 250 °C and 150 Mpa pressure. Dolomitization and silicification are the main alteration types associated with the Atashkuh mineralization. The occurrence of chlorite, talc, illite and dolomitized host rock all

  9. 10BaF2∶NaF, Na3AlF6/TiO2 composite as a novel visible-light-driven photocatalyst based on upconversion emission

    Institute of Scientific and Technical Information of China (English)

    Liu En-Zhou; Fan Jun; Hu Xiao-Yun; Hou Wen-Qian; Dai Hong-Zhe

    2012-01-01

    A rare-earth free upconversion luminescent material,10BaF2∶NaF,Na3AlF6,is synthesized by a hydrothermal method.The study of fluorescent spectrum indicates that it can convert visible light (550 nm-610 nm) into ultraviolet light (290 nm-350 nm),and two emission peaks at 304 nm and 324 nm are observed under the excitation of 583 nm at room temperature.Subsequently,10BaF2∶NaF,Na3AlF6/TiO2 composite photocatalyst is prepared and its catalyticactivity is evaluated by the photocatalytic reduction of CO2 under visible light irradiation (λ > 515 nm).The resultsshow that 10BaF2∶NaF,Na3AlF6/TiO2 is a more effective photocatalyst for CO2 reduction than pure TiO2,their corresponding methanol yields are 179 and 0 μmol/g-cat under the same conditions.Additionally,the mechanism of photocatalytic reduction of CO2 on 10BaF2∶NaF,Na3A1F6/TiO2 is proposed.

  10. Investigation of thermally induced anion disorder in fluorites using neutron scattering techniques

    DEFF Research Database (Denmark)

    Hutchings, M T; Clausen, Kurt Nørgaard; Dickens, M H

    1984-01-01

    Some materials with the fluorite structures show a pronounced specific heat anomaly well below their melting temperature. This anomaly is a consequence of lattice disorder and is associated with the onset of fast-ion conduction. This paper presents the results of a series of experiments in which ...... anion Frenkel interstitials, anion vacancies and relaxed anions has been developed which satisfactorily accounts for the distribution of intensity....

  11. TL response of a natural fluorite

    CERN Document Server

    Balogun, F A; Ogundare, F O; Fasasi, M K; Hussein, L A

    1999-01-01

    A batch of a naturally occurring fluorite (CaF sub 2) from the Middle Benue Valley region of Nigeria has been studied in some detail for its thermoluminescence (TL) properties. TL glow peaks are observed at 119, 144 and 224 deg. C at a heating rate of 10 deg. C s sup - sup 1. The TL response is observed to increase with increasing dose, as expected, over the dose range examined. Variations are observed in the decay curves of the various glow peaks with storage at room temperature. While the lower temperature peaks are observed to decay, enhancement of the TL signal is observed for the 224 deg. C glow peak when stored for four weeks. A low-level radioactivity measurement showed no evidence of self-irradiation from naturally occurring radionuclides. UV exposure was suppressed by storage in a black sealed container to exclude sunlight contribution to the observed TL response. A scheme involving the formation of large defect complexes, from smaller ones, during storage, as possible route leading to loss of signal...

  12. Enhanced processability of ZrF4-BaF2-LaF3-AlF3-NaF glass in microgravity

    Science.gov (United States)

    Torres, Anthony; Ganley, Jeff; Maji, Arup; Tucker, Dennis; Starodubov, Dmitry

    2013-06-01

    Fluorozirconate glasses, such as ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), have the potential for optical transmission from 0.3 μm in the UV to 7 μm in the IR region. However, crystallites formed during the fiber drawing process prevent this glass from achieving its desired transmission range. The temperature at which the glass can be drawn into a fiber is known as the working range, defined as (Tx - Tg), bounded by the glass transition temperature (Tg) and the crystallization temperature (Tx). In contrast to silica glasses, the working temperature range for ZBLAN glass is extremely narrow. Multiple ZBLAN samples were subject to a heating and quenching test apparatus on the parabolic aircraft, under a controlled 0-g and hyper-g environment and compared with 1-g ground tests. The microgravity duration on board Zero-G Corporation parabolic aircraft is approximately 20 seconds and the hyper-g intervals are approximately 56 seconds. Optical microscopy examination elucidates crystal growth in ZBLAN is suppressed when processed in a microgravity environment. The crystallization temperature, Tx, at which crystals form increased, therefore, significantly broadening the working temperature range for ZBLAN.

  13. The reasons for the color green fluorite Mehmandooye cover using UV spectroscopy and XRF results

    Science.gov (United States)

    Pirzadeh, Sara; Zahiri, Reza

    2016-04-01

    Fluorite mineral or fluorine with chemical formula CaF2 is most important mineralfluor in nature. This mineral crystallization to colors yellow, green, pink, blue, purple, colorless and sometimes black andin cubic system crystallized.assemi transparent and glass with polished.fluoritethe purity include 48/9% fluoreand 51/9% calcium. How the creation colors in minerals different greatly indebted to Kurt Nassau research from Bell Labs, Murray Hill, New Jersey.almostall the mechanisms that cause color in minerals, are the result of the interaction of light waves with the electrons The main factors affecting the color generation include the following: 1)the presence of a constructive element inherent (essential ingredient mineral composition) 2)The presence of a minor impurities (such a element as involved in latticesolid solution) 3) appearancedefects in the crystal structure 4) There are some physical boundaries with distances very small and delicate, like blades out of the solution (which may be the play of colors or Chatvyansy) 5) Mixing mechanical impurities dispersed in a host mineral Based on the results of the analysis, XRF and UV spectrum and also based on the results of ICP, because the color green fluorite examined, the focus color (F_center) and also the presence of some elementsintermediate (such as Y (yttrium). [1] Bill, H., Calas, G. Color centres associated rare earth ions and the origin of coloration in natural fluorites// PhysChem Min, (1978), v 3, pp. 117-131.

  14. The quasi-binary phase diagram BaF2-BaBr2 and its relation to the x-ray storage phosphor BaFBr : Eu2+

    Science.gov (United States)

    Kolb, R.; Schlapp, M.; Hesse, S.; Schmechel, R.; von Seggern, H.; Fasel, C.; Riedel, R.; Ehrenberg, H.; Fuess, H.

    2002-08-01

    In order to understand the formation and stoichiometry of the x-ray storage phosphor BaFBr : Eu2+, the phase diagram of the quasi-binary BaF2-BaBr2 system has been investigated. The phase diagram was obtained by means of differential thermal analysis and temperature controlled x-ray diffraction experiments. The resulting phase diagram indicates that BaFBr forms a compound with no detectable solid solubility for neither BaF2 nor BaBr2. Experiments to obtain non-stoichiometric BaFBr via the synthesis route using BaF2 and NH4Br as proposed in the literature could not be verified. It will be shown that the type of colour centre created during x-ray irradiation is related to the non-stoichiometry of the starting compositions before sintering. A surplus of either barium fluoride or barium bromide during sintering allows the controlled formation of F(Br-)- and F(F-)-centres, respectively.

  15. Fluorite transition metal hydride induced destabilization of the MgH2 system in MgH2/TMH2 multilayers ( TM=Sc , Ti, V, Cr, Y, Zr, Nb, La, Hf)

    Science.gov (United States)

    Tao, S. X.; Notten, P. H. L.; van Santen, R. A.; Jansen, A. P. J.

    2010-09-01

    The structural changes in MgH2 induced by contact with fluorite transition metal hydrides ( TMH2 , TM=Sc , Ti, V, Cr, Y, Zr, Nb, La, Hf) have been studied using density-functional theory calculations. Models of MgH2(rutile)/TiH2(fluorite) and MgH2(fluorite)/TiH2(fluorite) multilayers with different Mg:TM ratios have been designed. With a fixed thickness of the TMH2 layer, structure transformation of MgH2 from rutile to fluorite occurs with a decrease in thickness of the MgH2 layer. The hydrogen desorption energy from the fluorite MgH2 layer in the multilayers is significantly lower than that of the bulk rutile MgH2 . The structural deformation of the MgH2 layer due to the strain induced by TMH2 is found to be responsible for the destabilization of the Mg-H bond: the more structural deformation, the more destabilization of the Mg-H. Our results provide an important insight for the development of new hydrogen-storage materials with desirable thermodynamic properties.

  16. Fluid inclusion and cathodoluminescence studies on fluorite from the Kerio valley, Kenya

    Science.gov (United States)

    Ogola, J. S.; Behr, H. J.; van den Kerkhof, A. M.

    1994-04-01

    The Kerio valley lies between the Elgeyo escarpment and the Tugen hills which mark the western margin of the Kenya rift valley. The main fluorite deposits are located in the southern part of the valley at Kimwarer, Choff and Kamnaon. Three types of inclusion fillings were identified: Liquid+Vapour, Liquid+Daughter Minerals and Liquid. The L+V type is dominant. Inclusions occur as clusters, trails along the crystal growth zones and as isolated ones. Low salinities, apparently lower than the 5% wt. NaCl equivalent, were established. Homogenization temperatures suggest that fluorite mineralization took place at different stages and at temperatures between 120 and 180 °C. Isolated readings above 180°C may be referring to the original inclusions in limestone. These measurements and the absence of CO 2 in the inclusions, as well as the occurrence of vugs and crustifications with fluorite, suggest that mineralization took place at relatively shallow depths. Emission spectrum lines representing Eu 2+, Dy 3+, Tb 3+ and Sm 3+ in fluorite were identified. Sm 3+ was detected only in the pinkish luminescence of veined fluorite, whereas the pinkish zone in banded fluorite contains Tb 3+. Eu 2+ which gives the strongest emission lines in the blue part of the visible spectrum, apparently is responsible for the strong blue cathodoluminescence (CL) in fluorite. The dominance of Eu 2+ peaks further points to the fact that fluorite mineralization in the Kerio valley took place in an environment that was enriched in Lanthanide Rare Earth Elements (LREE). The presence of rare earths and radioactive elements in fluorite points towards their enrichment in the environment of fluorite mineralization. A juvenile origin of mineral forming solutions is proposed. Two generations of fluorite were established: allotriomorphic fluorite, forming the matrix, and the idiomorphic variety, occurring either in barite or in druzes in early fluorite. Barite in turn forms idiomorphic crystals in

  17. Influence of ions on two-dimensional and three-dimensional atomic force microscopy at fluorite-water interfaces

    Science.gov (United States)

    Miyazawa, K.; Watkins, M.; Shluger, A. L.; Fukuma, T.

    2017-06-01

    Recent advancement in liquid-environment atomic force microscopy (AFM) has enabled us to visualize three-dimensional (3D) hydration structures as well as two-dimensional (2D) surface structures with subnanometer-scale resolution at solid-water interfaces. However, the influence of ions present in solution on the 2D- and 3D-AFM measurements has not been well understood. In this study, we perform atomic-scale 2D- and 3D-AFM measurements at fluorite-water interfaces in pure water and a supersaturated solution of fluorite. The images obtained in these two environments are compared to understand the influence of the ions in solution on these measurements. In the 2D images, we found clear difference in the nanoscale structures but no significant difference in the atomic-scale contrasts. However, the 3D force images show clear difference in the subnanometer-scale contrasts. The force contrasts measured in pure water largely agree with those expected from the molecular dynamics simulation and the solvent tip approximation model. In the supersaturated solution, an additional force peak is observed over the negatively charged fluorine ion site. This location suggests that the observed force peak may originate from cations adsorbed on the fluorite surface. These results demonstrate that the ions can significantly alter the subnanometer-scale force contrasts in the 3D-AFM images.

  18. [Assessment of Soil Fluorine Pollution in Jinhua Fluorite Ore Areas].

    Science.gov (United States)

    Ye, Qun-feng; Zhou, Xiao-ling

    2015-07-01

    The contents of. soil total fluorine (TF) and water-soluble fluorine (WF) were measured in fluorite ore areas located in Jinhua City. The single factor index, geoaccumulation index and health risk assessment were used to evaluate fluorine pollution in soil in four fluorite ore areas and one non-ore area, respectively. The results showed that the TF contents in soils were 28. 36-56 052. 39 mg.kg-1 with an arithmetic mean value of 8 325.90 mg.kg-1, a geometric mean of 1 555. 94 mg.kg-1, and a median of 812. 98 mg.kg-1. The variation coefficient of TF was 172. 07% . The soil WF contents ranged from 0. 83 to 74. 63 mg.kg-1 with an arithmetic mean value of 16. 94 mg.kg-1, a geometric mean of 10. 59 mg.kg-1, and a median of 10. 17 mg.kg-1. The variation coefficient of WF was 100. 10%. The soil TF and WF contents were far higher than the national average level of the local fluorine epidemic occurrence area. The fluoride pollution in soil was significantly affected by human factors. Soil fluorine pollution in Yangjia, Lengshuikeng and Huajie fluorite ore areas was the most serious, followed by Daren fluorite ore area, and in non-ore area there was almost no fluorine pollution. Oral ingestion of soils was the main exposure route. Sensitivity analysis of model parameters showed that children's weight exerted the largest influence over hazard quotient. Furthermore, a significant positive correlation was found among the three kinds of evaluation methods.

  19. Near infrared ultrafast pump-probe spectroscopy with ZrF4-BaF2-LaF3-AlF3-NaF fiber supercontinuum

    Science.gov (United States)

    Fischbach, Stefan; Gorbach, Andrey V.; Di Nuzzo, Daniele; Da Como, Enrico

    2015-07-01

    We report on the performance of a setup designed for femtosecond pump-probe spectroscopy in the near infrared (NIR) spectral region. We generate a supercontinuum (SC) probe by coupling 140 fs light pulses at 1550 nm into a ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber. The combined high nonlinearity and transparency of the ZBLAN fluoride glass allows us to obtain a SC probe from 1 to 2.6 μm. The NIR pulses are used to demonstrate a proof of principle experiment probing the relaxation of photo induced excitations in a conjugated polymer:fullerene blend film. The results show the possibility to perform fibre based NIR SC femtosecond spectroscopy at >100 KHz repetition rate and using lasers with pulse energy just above 300 nJ.

  20. Symmetry-Guided Synthesis of Highly Porous Metal-Organic Frameworks with Fluorite Topology

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, MW; Chen, YP; Bosch, M; Gentle, T; Wang, KC; Feng, DW; Wang, ZYU; Zhou, HC

    2013-11-11

    Two stable, non-interpenetrated MOFs, PCN-521 and PCN-523, were synthesized by a symmetry-guided strategy. Augmentation of the 4-connected nodes in the fluorite structure with a rigid tetrahedral ligand and substitution of the 8-connected nodes by the Zr/Hf clusters yielded MOFs with large octahedral interstitial cavities. They are the first examples of Zr/Hf MOFs with tetrahedral linkers. PCN-521 has the largest BET surface area (3411 m(2) g(-1)), pore size (20.5 x 20.5 x 37.4 angstrom) and void volume (78.5%) of MOFs formed from tetrahedral ligands. This work not only demonstrates a successful implementation of rational design of MOFs with desired topology, but also provides a systematic way of constructing non-interpenetrated MOFs with high porosity.

  1. Round Top Mountain rhyolite (Texas, USA), a massive, unique Y-bearing-fluorite-hosted heavy rare earth element (HREE) deposit

    Institute of Scientific and Technical Information of China (English)

    PINGITORE Nicholas; CLAGUE Juan; GORSKI Daniel

    2014-01-01

    Round Top Mountain in Hudspeth County, west Texas, USA is a surface-exposed rhyolite intrusion enriched in Y and heavy rare earth elements (HREEs), as well as Nb, Ta, Be, Li, F, Sn, Rb, Th, and U. The massive tonnage, estimated at well over 1 billion tons, of the deposit makes it a target for recovery of valuable yttrium and HREEs (YHREEs), and possibly other scarce ele-ments. Because of the extremely fine grain size of the mineralized rhyolite matrix, it has not been clear which minerals host the YHREEs and in what proportions. REE-bearing minerals reported in the deposit included bastnäsite-Ce, Y-bearing fluorite, xeno-time-Y, zircon, aeschynite-Ce, a Ca-Th-Pb fluoride, and possibly ancylite-La and cerianite-Ce. Extended X-ray absorption fine struc-ture (EXAFS) indicated that virtually all of the yttrium, a proxy for the HREEs, resided in a coordination in the fluorite-type crystal structure, rather than those in the structures of bastnäsite-Ce and xenotime-Y. The YREE grade of the Round Top deposit was just over 0.05%, with 72%of this consisting of YHREEs. This grade was in the range of the South China ionic clay deposits that supply essentially all of the world’s YHREEs. Because the host Y-bearing fluorite is soluble in dilute sulfuric acid at room temperature, a heap leaching of the deposit appeared feasible, aided by the fact that 90%-95%of the rock consists of unreactive and insoluble feld-spars and quartz. The absence of overburden, remarkable consistency of mineralization grade throughout the massive rhyolite, prox-imity (a few km) to a US interstate highway, major rail systems and gas and electricity, temperate climate, and stable political location in the world’s largest economy all enhanced the potential economic appeal of Round Top.

  2. Fluorite equilibria in thermal springs of the Snake River Basin, Idaho

    Science.gov (United States)

    Roberson, C.E.; Schoen, Robert

    1973-01-01

    Some thermal water sources of the Snake River basin, Idaho, are near saturation with respect to fluorite. That mineral was identified by X-ray diffraction in precipitates induced in three water samples by adding sodium fluoride. The derived solubility product (KS0) for zero ionic strength was close to that calculated from Latimer's thermodynamic data (10-9.7 7). The relative ease of precipitation of fluorite from these water samples indicates that equilibrium with respect to fluorite may occur in some ground-water systems.

  3. Damage evolution of ion irradiated defected-fluorite La 2 Zr 2 O 7 epitaxial thin films

    Energy Technology Data Exchange (ETDEWEB)

    Kaspar, Tiffany C.; Gigax, Jonathan G.; Shao, Lin; Bowden, Mark E.; Varga, Tamas; Shutthanandan, Vaithiyalingam; Spurgeon, Steven R.; Yan, Pengfei; Wang, Chongmin; Ramuhalli, Pradeep; Henager, Charles H.

    2017-05-01

    Pyrochlore-structure oxides, A2B2O7, may exhibit remarkable radiation tolerance due to the ease with which they can accommodate disorder by transitioning to a defected fluorite structure. The mechanism of defect formation was explored by evaluating the radiation damage behavior of high quality epitaxial La2Zr2O7 thin films with the defected fluorite structure, irradiated with 1 MeV Zr+ at doses up to 10 displacements per atom (dpa). The level of film damage was evaluated as a function of dose by Rutherford backscattering spectrometry in the channeling geometry (RBS/c) and scanning transmission electron microscopy (STEM). At lower doses, the surface of the La2Zr2O7 film amorphized, and the amorphous fraction as a function of dose fit well to a stimulated amorphization model. As the dose increased, the surface amorphization slowed, and amorphization appeared at the interface. Even at a dose of 10 dpa, the core of the film remained crystalline, despite the prediction of amorphization from the model. To inform future ab initio simulations of La2Zr2O7, the bandgap of a thick La2Zr2O7 film was measured to be indirect at 4.96 eV, with a direct transition at 5.60 eV.

  4. DANCE (Detector for Advanced Neutron Capture Experiments) is a 4π array of BaF2 crystals installed at LANSCE, Lujan Center. Neutron capture measurements on ^157Gd and ^89Y nuclei were conducted using this facility.

    Science.gov (United States)

    Chyzh, A.; Mitchell, G.; Vieira, D.; Bredeweg, T.; Ullmann, J.; Jandel, M.; Couture, A.; Keksis, A.; Rundberg, R.; Wilhelmy, J.; O'Donnell, J.; Baramsai, B.; Haight, R.; Wouters, J.; Krticka, M.; Parker, W.; Becker, J.; Agvaanlusan, U.

    2009-10-01

    DANCE (Detector for Advanced Neutron Capture Experiments) is a 4π array of BaF2 crystals installed at LANSCE, Lujan Center. Neutron capture measurements on ^157Gd and ^89Y nuclei were conducted using this facility. The absolute cross sections of the ^89Y(n,γ) reaction was measured for the first time ever in the neutron energy range of 10 eV -- 10 keV and improvements were made in the 10 -- 300 keV range. The error bars were significantly reduced and number of cross section points was increased since the past ^89Y(n,γ) experiments. The ^157Gd(n,γ) cross section was determined at En = 20 eV -- 300 keV by normalizing the experimental DANCE data to a well known resonance taken from the ENDF/B-VII library. Computer simulations of the ^157Gd(n,γ) cascades and DANCE pulse height function were made using DICEBOX and GEANT4 codes and simulated Esum and Eγ spectra are compared to the experimental DANCE data. Values of spin and photon strength function (PSF) of the ^157Gd(n,γ) resonances are provided in the range of En = 2 -- 300 eV using spin dependence upon a γ-ray multiplicity.

  5. Enhanced ultraviolet upconversion luminescence of Tm and Yb codoped ZrF4-BaF2-LaF3-AlF3-NaF glass.

    Science.gov (United States)

    He, Chunfeng; Zhao, Dan; Qin, Guanshi; Zheng, Kezhi; Qin, Weiping

    2011-11-01

    Ultraviolet (UV) upconversion (UC) luminescence properties of Tm3+ ions sensitized by Yb3+ ions in ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) glass were studied in detail. Under the excitation from a 980 nm continuous wave (CW) diode laser, red, blue, and even UV emissions were observed in the fluorozirconate glass. Several fluorescence bands appeared in the UC emission spectrum from 292.8 nm to 805.8 nm. The UC emission peaks at 291 nm, 347 nm, 363 nm, 454 nm, 475 nm, 647 nm, 687 nm, and 804 nm correspond to the transitions of 1I6 --> 3H6, 1I6 --> 3F4, 1D2 --> 3H6, 1D2 --> 3F4, 1G4 --> 3H6, 1G4 --> 3F4, 3F3 --> 3H6, and 3H4 --> 3H6, respectively. Experimental results of intensity dependence of the up-converted fluorescence on the pump power indicate a five-photon excitation scheme of 1I6 energy level.

  6. Modified Ceria-Zirconia Fluorite-Like Catalysts for the Combustion of Methane

    Institute of Scientific and Technical Information of China (English)

    Tatiana Kuznetsova; Vladislav Sadykov; Lubsan Batuev; Ella Moroz; Elena Burgina; Vladimir Rogov; Vladimir Kriventsov; Dmitrii Kochubey

    2006-01-01

    For dispersed ceria-zirconia-based solid solutions prepared via the polymerized complex method and annealed at 700 ℃, effects of bulk doping by Ca, Mn, Co, Bi or Nb cations and surface modification by Mn and Pt on their structural features, surface/bulk oxygen reactivity and catalytic activity in methane combustion are considered. With up to 20 mol% doping, a structural type of homogeneous solid solutions of anion-deficient fluorite with disordered anion vacancies is formed. Doping by transition metal cations or Pt increases the mobility and reactivity of the surface/bulk oxygen. A broad variation in specific rates of methane combustion for the studied systems was observed, suggesting structural sensitivity of this reaction. In general, there is no universal relationship between the oxygen mobility, the reactivity and the catalytic activity in methane combustion, which is explained by the factor of specific methane activation on surface active sites. For the Pt-promoted samples, Pt efficiency in methane activation depends on the Pt-support interaction, and the most favorable ones being mixed Pt/MnOx and Pt/NbOx clusters on the surface of the supports that exhibit high lattice oxygen mobilities.

  7. PREPARATION OF BaF2 POWDERS BY HYDROTHERMAL METHOD%水热法制备BaF2粉体材料

    Institute of Scientific and Technical Information of China (English)

    李红; 赵星

    2012-01-01

    以销酸钡和氟化铵为原料,以柠檬酸为络合剂,采用水热法合成了BaF2粉体。用扫描电子显微镜(SEM)和X射线衍射仪(XRD)对产物的形貌和结构进行了表征,结果表明反应温度及pH值对产物的形状和尺寸有很大影响,可以通过改变温度和pH值调控产物的形貌。%BaF2 powders were synthesized by hydrothermal methods. For this preparation, Ba(NO3)2 and NH4F as the starting materials and citric acid served as chelator. The morphology and the structure was characterized by scanning electron microscopy (SEM) and X-ray diffraction. The results show that the temperature and pH value of the reaction have significant effects on the particle size and shape. The morphology could be controlled synthesized by the temperature and pH value.

  8. Microstructural characterization of the stabilized fluorite phases formed in the Ca 1- yLa yU 2O 6+ x (0 ≤ y ≤ 0.8) system

    Science.gov (United States)

    Gómez-Rebollo, E.; Herrero, P.; Rojas, R. M.

    1997-06-01

    The thermal behaviour and stability of the fluorite structure in the Ca 1- yLa yU 2O 6+ x (0 ≤ y ≤ 0.8) system during ageing have been studied by thermal analysis and X-ray powder diffraction. When the amount of La 3+ incorporated into the Ca 1- yLa yU 2O 6+ x structure is ≥ 0.6 the complete stabilization of the fluorite phase is achieved. This phase remains stable over the temperature range from room temperature-1400°C even after being submitted to long term give time. For lower amounts of La 3+ a mixture of cubic fluorite and calcium lanthanum diuranate solid solution is obtained on annealing. The microstructural characterization carried out by electron diffraction and high resolution transmission electron microscopy reveals short range order for the high temperature quenched materials. Annealing of the oxides leads to the formation of ordered nanodomains embedded within the fluorite matrix, but no ordered single phase is isolated. A hexagonal cell of a H = 3.8 and c H = 18.8 Å has been deduced for the domains.

  9. Microstructural characterization of the stabilized fluorite phases formed in the Ca{sub 1-y}La{sub y}U{sub 2}O{sub 6+x} (0{<=}y{<=}0.8) system.

    Energy Technology Data Exchange (ETDEWEB)

    Gomez-Rebollo, E. [CSIC, Madrid (Spain). Inst. de Ciencia de Mater.; Herrero, P. [CSIC, Madrid (Spain). Inst. de Ciencia de Mater.; Rojas, R.M. [CSIC, Madrid (Spain). Inst. de Ciencia de Mater.

    1997-06-01

    The thermal behaviour and stability of the fluorite structure in the Ca{sub 1-y}La{sub y}U{sub 2}O{sub 6+x} (0{<=}y{<=}0.8) system during ageing have been studied by thermal analysis and X-ray powder diffraction. When the amount of La{sup 3+} incorporated into the Ca{sub 1-y}La{sub y}U{sub 2}O{sub 6+x} structure is {>=}0.6 the complete stabilization of the fluorite phase is achieved. This phase remains stable over the temperature range from room temperature-1400 C even after being submitted to long term give time. For lower amounts of La{sup 3+} a mixture of cubic fluorite and calcium lanthanum diuranate solid solution is obtained on annealing. The microstructural characterization carried out by electron diffraction and high resolution transmission electron microscopy reveals short range order for the high temperature quenched materials. Annealing of the oxides leads to the formation of ordered nanodomains embedded within the fluorite matrix, but no ordered single phase is isolated. A hexagonal cell of a{sub H}=3.8 and c{sub H}=18.8 A has been deduced for the domains. (orig.).

  10. Fluorescence reabsorption analysis on laser cooling of Tm^3+ doped ZrF4-BaF2-LaF3-AlF3-NaF-PbF2 glass%Tm^3+掺杂ZrF4-BaF2-LaF3-AlF3-NaF-PbF2玻璃激光制冷中荧光再吸收效应的理论分析

    Institute of Scientific and Technical Information of China (English)

    贾佑华; 钟标; 印建平

    2011-01-01

    Laser cooling of solid material has become a new developing research area in recent years.Tm3+ doped ZrF4-BaF2-LaF3-AlF3-NaF-PbF2 glass is one of the hot materials in this field.Compared with Yb3+,Tm3+ has better cooling potential.Up to date,one of the main factors restricting the cooling effect is fluorescent reabsorption.In this paper,firstly,using several spectral parameters of Tm3+,the reabsorption effect is calculated by stochastic model which is a semianalytical approach to this problem.The average number of absorption events is obtained.Afterwards,the effect of fluorescence trapping due to total internal reflection is analyzed.The results show that the quantum efficiency will be lowed by 0.5%—1% due to reabsorption,that the redshift of the mean fluorescence wavelength is in the range of 2—10 nm,and that the cooling efficiency and the cooling power decrease.Finally,after discussion,we find that the use of a small size and a long thin geometry will benefit to the fluorescence emission and cooling effect.%固体材料的激光制冷是近年来发展起来的一个新的研究领域.掺Tm3+的ZrF4-BaF2-LaF3-AlF3-NaF-PbF2(ZBLANP)玻璃材料是激光冷却的典型材料之一.与另一种制冷掺杂离子Yb3+相比,Tm3+具有更好的制冷潜力.目前制约材料制冷的一个主要机理就是荧光再吸收.首先根据Tm3+:ZBLANP的光谱参数,利用半经典的随机行走模型得到了不同情况下的平均荧光再吸收次数,随后分析了荧光光子界面出射的全反射效应,并对所得结果进行了修正.计算结果表明,荧光再吸收会导致量子效率降低0.5%—1%,出射荧光波长红移达到2—10nm,激光制冷的效率和功率降低.为了有利于荧光出射和净制冷的实现,宜采用小体积细长棒的制冷元.

  11. 一种带葡萄柚空气孔的高双折射ZrF4-BaF2-LaF3-AlF3-NaF光子准晶光纤%Highly birefringent ZrF4-BaF2-LaF3-AlF3-NaF photonic quasi-crystal fib er with twin grap efruits holes

    Institute of Scientific and Technical Information of China (English)

    苏伟; 娄淑琴; 邹辉; 韩博琳

    2014-01-01

    A novel design of highly birefringent photonic quasi-crystal fiber based on ZrF4-BaF2-LaF3-AlF3-NaF glass with twin grapefruit air holes near the core and twofold symmetry is proposed. The basic unit is composed of one square and its neighboring regular triangle. Using the finite element method, the birefringence and confinement loss are investigated simultaneously by changing the pitch of air holes and sizes of air holes. Numerical results show that the fiber maintains single mode operation in a wide wavelength range from 1.8 µm to 2.2 µm, and the birefringence is on the order of 10-2, two orders of magnitude larger than that of the conventional polarization-maintaining fibers, which is largest (around 2 µm) ever reported to our knowledge and the same order of magnitude as that obtained by fiber using elliptic air holes But this designed fiber is easy to fabricate compared with the fibers using elliptic air holes.%提出了一种具有二重对称性的ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN)氟化物玻璃基的光子准晶光纤。光纤结构是以ZBLAN氟化物玻璃为背景材料,外包层由圆形空气孔以正方形与正三角形分布组成的基本单元构成,在芯区两侧引入两个对称的葡萄柚空气孔,以增加光纤的双折射。应用全矢量有限元法,研究了光纤的双折射和限制损耗特性与结构参数的关系。通过优化光纤结构参数,在1800-2200 nm的波长范围内获得了具有单模传输特性的高双折射光纤,其模式双折射高达10-2,比普通保偏光纤高出两个数量级,与目前报道的采用椭圆空气孔微结构光纤获得的高双折射具有同样的量级。但与具有椭圆空气孔微结构光纤相比,提出的光纤结构更易于制作。研究结果为开辟2µm波段光器件的研究做出了有益的探索。

  12. REE Geochemistry of Fluorite from the Maoniuping REE Deposit, Sichuan Province, China: Implications for the Source of Ore-forming Fluids

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Fluorite is one of the main gangue minerals in the Maoniuping REE deposit, Sichuan Province, China. Fluorite with different colors occurs not only within various orebodies, but also in wallrocks of the orefield. Based on REE geochemistry, fluorite in the orefieid can be classified as the LREE-rich, LREE-flat and LREE-depleted types. The three types of fluorite formed at different stages from the same hydrothermal fluid source, with the LREE-rich fluorite forming at the relatively early stage, the LREE-flat fluorite in the middle, and the LREE-depleted fluorite at the latest stage. Various lines of evidence demonstrate that the variation of the REE contents of fluorite shows no relation to the color. The mineralization of the Maoniuping REE deposit is associated spatially and temporally with carbonatite-syenite magmatism and the ore-forming fluids are mainly derived from carbonatite and syenite melts.

  13. Fluid Origin of the Stratabound Fluorite and Celestite Deposits in Coahuila, Mexico.

    Science.gov (United States)

    Tritlla, J.; Gonzalez-Partida, E.; Banks, D.; Levresse, G.; Baca-Gasca, S.; Rodriguez-Santos, A.

    2004-12-01

    The Mesozoic units that outcrop north of Coahuila State in northern Mexico host numerous celestite, celestite-fluorite and fluorite deposits, mainly enclosed in the Cretaceous limestone units. Celestite and celestite-fluorite deposits are lens-shaped bodies, up to 2 m thick and a total length exceeding 500 meters, intercalated within the carbonates of the Cupido Formation (Aptian) or equivalents. Celestite-free fluorite bodies, mainly enclosed in the Aurora Formation (Albian-Cenomanian), appear as sub-concordant lenses with abundant evidences of hydraulic fracturing, usually near low-angle fractures. The celestite brine halogen composition on a Cl/Br vs Na/Br molar ratio plot on the trend defined by the evaporation of seawater, while in a ppm Cl vs Cl/Br plot away from the seawater evaporation line but parallel to it, indicating that the solution was mainly modified by dilution. The fluids involved in the genesis of the La Encantada fluorite deposit probably are evolved seawater that undergone some degree of evaporation. Mixing of fluids is clearly delineated by both microthemometric and halogen data, where salinities calculated are too low for the halogen ratios found, indicating a mixing with a low-salinity end-member. Hydrocarbon-bearing fluid inclusions repeatedly show the presence of solid bitumen trapped along with heavy oils, indicative of thermal degradation. Both, mixing and thermal degradation of hydrocarbon-rich fluids along with hydraulic fracture of the host rock points to an "in situ" organic matter maturation, due to the mixing of a saline, oxidant, sulphate and CaCl2-rich "bittern", which probably transported fluorite, with an organic-matter rich fluid present in the cretaceous carbonates. It is noteworthy that these previous results suggest that both celestite and fluorite-dominated deposits formed from brines from similar origin, showing the same halogen systematics. Strontium enrichment can be explained by leaching of Sr from the carbonate series

  14. THE COUPLING RELATIONSHIP BETWEEN FLUORITE MINE AND ORGANIC REEF-BANK OIL POOL OF ORDOVICIAN CARBONATES AND METALLOGENIC MODEL OF FLUORITE MINE IN TARIM BASIN%塔里木盆地奥陶系萤石矿和礁滩相油藏耦合关系与成矿模式

    Institute of Scientific and Technical Information of China (English)

    周刚; 郑荣才; 罗平; 张兴阳; 刘伟; 宋金民; 饶红娟

    2011-01-01

    metallogenic fluids were the unconformity and faults. Reef-bank and regional structure had playing an important controlling role in the aspects of layer,facies and position over the fluorite mine or oil pool.%塔里木盆地巴楚-柯坪野外露头区和塔中井区奥陶系萤石矿体呈串珠状或沿裂缝呈条带状分布,通过露头岩心、钻井岩心、普通薄片、电子探针、X衍射、阴极发光、流体包裹体和微量元素、稳定同位素分析等方法,对萤石矿及其围岩和油藏进行详细研究,探讨萤石矿和礁滩相油藏耦合关系与成矿模式.萤石矿体富集在礁、滩相灰岩为基岩的与断层相关的部分岩溶洞穴中,和萤石一起共生的矿物还有方解石、重晶石、硬石膏、石英及黑色沥青,萤石中含丰富的液态、气态烃包裹体、固态沥青包裹体和柱条状石膏子晶;萤石的K/Rb和Sr/Ba比值远小于正常海水值,富铕及轻稀土元素而贫重稀土元素,其礁滩相围岩碳、氧同位素具越靠近萤石脉体δ13C和δ18O值负偏移越明显特征,萤石相对其围岩具有更高的87Sr/86 Sr比值.研究表明塔里木盆地奥陶系萤石矿属于“被动型”密西西比层控矿床,成矿机理为礁滩型“油气藏”转化为“矿捕”作用,具先成藏后成矿、多期成藏多期成矿特点,成矿流体具有盆地油田卤水和深循环大气淡水双重特征的后期低温热液成因性质,成矿物质来源于下寒武统下部黑色硅质岩及磷块岩,不整合面和断层是热液流体及成矿流体运移通道,生物礁滩和区域断层对萤石矿或油藏具有极其重要的“层、相、位”控制作用.

  15. Study of genesis in Qahr-Abad fluorite deposit using fluid inclusion, southeast of Saqqez, the Kurdistan province

    Directory of Open Access Journals (Sweden)

    Mehrdad Barati

    2017-07-01

    Full Text Available Introduction The Qahr-abad fluorite deposit is located in the area of 36°10′ 3′′ N and 46°34′ 21′′E within the Sanandaj-Sirjan district east of the Kurdistan province , Iran and it is located ~57 km southeast of the city of Saqqez (Kholghi Khasraghi, 1999. This deposit is developed as scatter lenses, veins, and veinlets (stockwork structure within carbonate rocks of Elika formation and controlled by the regional NW–SE trending Zagross thrust nappe system. Fault trends in this area are perpendicular to fault trends in the Zagros zone. The fault dips are nearly vertical and mineralization has occurred in the brecciation fault zone (Talaii, 2010. The rough geological instruction of the deposit has indicated that it is similar to worldwide Epithermal deposits. The mineralization occurs as replacement (type I/ open-space (type II vein fillings and bodies within Mesozoic lime stones (mostly Upper Triassic and Lower Jurassic members of the Elika Formation, where they crop out to form horst structures. The mineralization is typically associated with post Pliocene disjunctive faults, which in part appear to have served as channel ways for the fluorite forming fluids that are representative of the geological setting of the mineralized area. Fluorite occurs in several color variations such as green, violet, blue, white or colorless, and is accompanied by quartz, barite and calcite (Moslehi, 2013. Materials and methods The minerals sampled for the fluid inclusion study include fluorite from mineralization stages. Samples covered all ore types. Micro thermometry analyses for 23 samples were performed after careful microscopic observation of 35 sections and 30 doubly polished sections. Micro thermometry was undertaken using a Linkam THS600 heating-freezing stage, with a measurable temperature range of between −196 and +600 °C (precision of freezing data and homogenization temperature of ±0.2 °C. Micro thermometry was undertaken in the

  16. Chemical ordering in substituted fluorite oxides: a computational investigation of Ho2Zr2O7 and RE2Th2O7 (RE=Ho, Y, Gd, Nd, La)

    Science.gov (United States)

    Solomon, Jonathan M.; Shamblin, Jacob; Lang, Maik; Navrotsky, Alexandra; Asta, Mark

    2016-12-01

    Fluorite-structured oxides find widespread use for applications spanning nuclear energy and waste containment, energy conversion, and sensing. In such applications the host tetravalent cation is often partially substituted by trivalent cations, with an associated formation of charge-compensating oxygen vacancies. The stability and properties of such materials are known to be influenced strongly by chemical ordering of the cations and vacancies, and the nature of such ordering and associated energetics are thus of considerable interest. Here we employ density-functional theory (DFT) calculations to study the structure and energetics of cation and oxygen-vacancy ordering in Ho2Zr2O7. In a recent neutron total scattering study, solid solutions in this system were reported to feature local chemical ordering based on the fluorite-derivative weberite structure. The calculations show a preferred chemical ordering qualitatively consistent with these findings, and yield values for the ordering energy of 9.5 kJ/mol-cation. Similar DFT calculations are applied to additional RE2Th2O7 fluorite compounds, spanning a range of values for the ratio of the tetravalent and trivalent (RE) cation radii. The results demonstrate that weberite-type order becomes destabilized with increasing values of this size ratio, consistent with an increasing energetic preference for the tetravalent cations to have higher oxygen coordination.

  17. The luminescence properties of rare-earth ions in natural fluorite

    Science.gov (United States)

    Czaja, M.; Bodył-Gajowska, S.; Lisiecki, R.; Meijerink, A.; Mazurak, Z.

    2012-09-01

    For the first time, the luminescence properties of Pr3+, Nd3+ and Tm3+ and Yb3+ ions in fluorite crystal have been obtained by steady-state measurements. In addition, the luminescence spectra of Ce3+, Sm2+, Sm3+, Dy3+, Er3+ and Yb3+ were measured. It was pointed out that λexc. = 415 nm is most suitable for measuring the Ho3+ emission beside the Er3+. The emission of trivalent holmium and erbium ions was measured independently using time-resolved measurements and tentative assignment of luminescence lines to C 3v and C 4v symmetry sites was proposed. Besides for natural fluorite crystal, the transitions between Stark energy levels of lanthanide ions were presented.

  18. Flotation of high-grade fluorite in a short column under negative bias regime

    OpenAIRE

    2006-01-01

    RESTRITO This paper presents flotation results carried out on fluorite ore using a relatively short column, operated under negative bias regime and without wash water. The term short column is used from a kinetic point of view from which collection zone comes out to be around 8 m tall (the relation height/diameter appears valid for industrial size columns). Negative bias was achieved making tailing flow smaller than feed flow. Hence, part of the water is carried up within bubbles wakes. No...

  19. Flocculation of fine fluorite particles with Corynebacterium xerosis and commercial long chain polymers

    Directory of Open Access Journals (Sweden)

    Rigo Lisandra N.

    2002-01-01

    Full Text Available This work aimed to study, comparatively, the flocculation of fluorite particles with Corynebacterium xerosis cells and three commercial long chain polymers. Best flocculation results were obtained with cells of C. xerosis and with an anionic polyacrylamide. Both were effective in solids removal and water clarification, although flocculation with C. xerosis cells requires a higher dosage of reagent per mass unit of processed ore.

  20. Fluorite's precipitation in KOH solutions in view of removing fluorides from wastewaters

    OpenAIRE

    Taraves, Raquel; Garcia, Daniel; Moutte, Jacques; Cameirão, Ana; Févotte, Gilles; Amaraggi, David; Morel, Bertrand

    2011-01-01

    International audience; The process under study aims at removing dissolved fluorides from effluent waters through the addition of calcium and the precipitation of fluorite in a fluidized bed. In the concept developed at COMURHEX, the effluent is a highly concentrated KOH solution and the calcium is provided as a suspension of portlandite with calcite as an impurity. COMURHEX's target is to achieve an efficient defluorination of KOH solutions prior to recycling and to control the growth of the...

  1. Coagulation of fines in fluorite froth flotation; Coagulacion de finos en la flotacion de la fluorita

    Energy Technology Data Exchange (ETDEWEB)

    Sarquis, P. E.; Gonzalez, M.; Moyano, A.; Bazan, V.

    2011-07-01

    Fluorite, a valuable mineral in the metallurgical industry, can be found together with silicates, carbonates and oxides in ore deposits. Commercial concentrates with more than 95 % of CaF{sub 2} are obtained processing the mineral in flotation plants and using oleic acid as fluorite collector. Depressor reagents such as sodium silicate, tannin and sodium carbonate are commonly employed to allow the oleic acid selective performance. These reagents cause a dispersant effect separating the solid-liquid solution on tailing plants. Fine particles in the recovered water enter the circuit and affect the flotation efficiency. The effect of coagulant ions was studied as a method to clarify the returned water. The problem of the presence of these ions is related to its reactions with the collector by the formation of compounds and possibly on the selectivity. Variable quantities of Al{sup 3}+, Fe{sup 3}+ and Ca{sup 2}+ ions were added to the flotation to evaluate its effect on the fluorite recovery, in the selectivity and in solids content in recirculation water. Results show that some ions fail to improve water quality and are detrimental to flotation. On the contrary, some ions contribute to reduce fine content in suspension. Therefore, although there is a recovery reduction, such effect can be counteracted increasing the collector consumption a little. (Author) 21 refs.

  2. Selective Separation of Fluorite, Barite and Calcite with Valonea Extract and Sodium Fluosilicate as Depressants

    Directory of Open Access Journals (Sweden)

    Zijie Ren

    2017-02-01

    Full Text Available Fluorite, barite and calcite are important industry minerals. However, they often co-exist, presenting difficulty in selectively separating them due to their similar surface properties. In this study, valonea extract and sodium fluosilicate were used as depressants to selectively separate them by flotation, with sodium oleate as the collector. The single mineral flotation results showed that valonea extract displayed the strongest depression on calcite, while sodium fluosilicate displayed the strongest depression on barite. These two depressants allowed selective separation of the three minerals through sequential flotation. The flotation of mixed minerals showed that 94% of the calcite was successfully depressed by the valonea extract, and 95% recovery of the fluorite was achieved in the subsequent flotation with sodium fluosilicate depressing barite. The different depressant–mineral interactions were investigated via electro-kinetic studies and molecular dynamics (MD simulations using the Materials Studio 6.0 program. The valonea extract exhibited the strongest adsorption on the calcite surface, and sodium fluosilicate exhibited the strongest adsorption on the barite surface, which prevented oleate species from reacting with Ca2+ or Ba2+ surface sites. This study provides useful guidance for how to process fluorite, barite and calcite resources.

  3. Uranium exploration in the vicinity of abandoned fluorite mines, in northern Thailand, using cellulose nitrate films

    Energy Technology Data Exchange (ETDEWEB)

    Wattananikorn, K.; Asnachinda, P.; Lamphunphong, S. (Chiangmai Univ. (Thailand))

    1990-01-01

    Ground radon measurements using LR-115 type 2 as detectors were carried out covering an area of approx. 3.5 km{sup 2} in the vicinity of abandoned fluorite mines in northern Thailand. Each detector was enclosed in a PVC tube buried at a constant depth at each measuring station. Nine anomalies of {alpha}-track values were found covering an area of approx. 12000 m{sup 2}. Most of the anomalies were related closely to quartz veins, fluorite veins and faults. Three out of these nine anomalies showed corresponding distinct {gamma}-ray activities. The maximum {alpha}-track anomaly occurred at station P18, having a track density of 58685 t/cm{sup 2}.d. A small uranium-bearing quartz vein, about 10 cm wide and 2 m long, was subsequently discovered outcropping close to the station. The vein consists of quartz, fluorite and a secondary uranium mineral, torbernite. The maximum uranium content in the ore samples was found to be as much as 14%. (author).

  4. A kinetic study of the replacement of calcite marble by fluorite

    Science.gov (United States)

    Trindade Pedrosa, Elisabete; Boeck, Lena; Putnis, Christine V.; Putnis, Andrew

    2016-04-01

    Replacement reactions are relevant in any situation that involves the reequilibration between a solid and an aqueous fluid phase and are commonly controlled by an interface-coupled dissolution-precipitation mechanism (Putnis and Putnis, 2007). These reactions control many large-scale Earth processes whenever aqueous fluids are available, such as during metamorphism, metasomatism, and weathering. An important consequence of coupled dissolution-precipitation is the generation of porosity in the product phase that then allows the infiltration of the fluid within the mineral being replaced. Understanding the mechanism and kinetics of the replacement of carbonates by fluorite has application in earth sciences and engineering. Fluorite (CaF2) occurs in all kinds of rocks (igneous, sedimentary, and metamorphic) and its origin is commonly associated with hydrothermal fluids. Moreover, calcium carbonate has been suggested as a successful seed material for the sequestration of fluoride from contaminated waters (Waghmare and Arfin, 2015). The aim of the present work is to investigate aspects of the replacement of calcium carbonate by fluorite to better understand the mechanism and kinetics of this reaction. Small cubes (˜ 3 × 3 × 3 mm) of Carrara marble (CaCO3 > 99 %) were cut and reacted with a 4 M ammonium fluoride (NH4F) solution for different times (1 to 48 hours) and temperatures (60, 80, 100, and 140 ° C). The microstructure of the product phases was analysed using SEM. The kinetics of replacement was monitored from the Rietveld analysis of X-ray powder diffraction patterns of the products as a function of temperature and reaction time. After reaction, all samples preserved their size and external morphology (a pseudomorphic replacement) and the product phase (fluorite) was highly porous. The activation energy Ea (kJ/mol) of the replacement reaction was empirically determined by both model-fitting and model-free methods. The isoconversional method yielded an

  5. Lead-barium fluoroborate glass ceramics doped with Nd3+ or Er3+

    Science.gov (United States)

    Petrova, O. B.; Sevostjanova, T. S.; Anurova, M. O.; Khomyakov, A. V.

    2016-02-01

    Lead-barium fluoroborate glasses in the PbF2-BaF2-B2O3, PbF2-BaO-B2O3, and PbO- BaF2-B2O3 systems doped with rare-earth ions (Nd3+ or Er3+) are synthesized and studied. It is shown that, based on these glasses, it is possible to produce transparent glass ceramics with fluoride crystalline phases, including ceramics with one crystalline phase of the fluorite structure. The spectral and luminescent properties of the doped glasses, glass ceramics, and polycrystalline complex fluorides containing Pb, Ba, and rare ions are studied.

  6. Evaluation in situ of genotoxicity and stress in South American common toad Rhinella arenarum in environments related to fluorite mine.

    Science.gov (United States)

    Pollo, Favio E; Grenat, Pablo R; Salinas, Zulma A; Otero, Manuel A; Salas, Nancy E; Martino, Adolfo L

    2017-06-20

    Little attention has been paid to the impact of wastewater generated by mining activities on fluoride. In this study, we evaluated the hematology responses of common South American toad Rhinella arenarum inhabiting natural and artificial environments associated with a fluorite mine from central Argentina. We analyzed three sampling stations associated with the fluorite mine: (I) Los Cerros Negros stream (CN), which runs on granitic rock with a high fluorite content; (II) Los Vallecitos stream (LV), which runs on metamorphic rock with low fluorite content; and (III) artificial decantation ponds (DP) containing sediments produced by fluorite flotation process. We calculated frequencies of micronuclei, erythrocyte nuclear abnormalities, mitosis, and immature erythrocytes. In addition, we performed a differential leukocyte count and determined neutrophils/lymphocyte ratio as a stress response estimator. We found high micronucleus (MN) and erythrocyte nuclear abnormality (ENA) frequencies in DP and CN but low frequencies in LV. The neutrophil/lymphocyte ratio was different among sites, with a significant increase in individuals from DP. Values registered in DP could be caused by exposure to mixture of compounds registered in dams that hold wastewater, while high values registered in CN stream might be due to natural concentrations of fluoride. Our results suggest that blood is an effective and non-destructive sensitive indicator for monitoring genotoxic agents in freshwater ecosystems.

  7. Coontail fluorite rhythmites of southern Illinois: evidence for episodic basin dewatering

    Energy Technology Data Exchange (ETDEWEB)

    Cowan, C.A.; Kelly, W.C.; Wilkinson, B.H.

    1985-01-01

    Stratiform coontail ore of the Cave-in-Rock fluorite district, southern Illinois, display conspicuous, rhythmic banded textures similar to those reported in many MVT deposits throughout the world (e.g., east Tennessee, USA; Silesian-Cracow Region, Poland; and northern Baffin Island, Canada). Banding is expressed by the rhythmic alteration of two types of layers: detrital layers of fluorite mottled with particulate gangue dolomite and quartz, and layers of clear, crystalline fluorspar. Both are now composed principally of fluorite but differ in color, fabric and outline. In the past, this rhythmic banding has generally been attributed to fine-scale replacement of a primary host rock stratification or to cyclic replacement of host carbonates by a fluid of oscillating chemistry. Detailed megascopic and microscopic studies of these ores and their carbonate host real that ore bands were not derived by fine-scale in situ limestone replacement. Detrital bands contain hydraulically transported, sorted and graded, allochthonous debris derived by dissolution and disaggregation of host limestone and overlying shale. The banded fabric thus represents a cyclic interplay of chemical and hydraulic processes active during hydrothermal ore mineralization. Coontail ore bodies evidently formed in a hydrothermal spelean system, whose laterally sinuous trace reflects localization of hydrothermal activity where feeder faults intersected relatively impermeable roof-rock shales. The banded nature of these ores testifies to the ability of Mississippi Valley-type hydrothermal solutions to both create and fill their own open spaces. Moreover, the rhythmic nature of coontail ores suggests a prolonged and pulsating mineralization best explained by episodic dewatering of the Illinois Basin.

  8. The Research Status of Fluorite Color%萤石颜色研究现状

    Institute of Scientific and Technical Information of China (English)

    郑惠; 李葆华; 罗英; 祝秀

    2015-01-01

    Fluoritehas a variety of colors, in addition to red which is rarely seen, other colors are very common. The color difference is caused by different genetic types, through the study on the color factors of fluorite, this pa⁃per discovered the fluorite color formation mechanism. The main causes of the color include the mixing of the im⁃purities, crystal defects and the mixing of organic matters.%萤石颜色多样,除红色少见外,其他颜色都很常见。不同成因类型造成的萤石颜色不同,本文通过对萤石致色因素的研究,揭示了萤石颜色的形成机理,其颜色形成的原因主要有杂质元素的混入、晶体缺陷以及有机质的混入。

  9. The Improvement Effect of Dispersant in Fluorite Flotation: Determination by the Analysis of XRD and FESEM-EDX

    Directory of Open Access Journals (Sweden)

    Y. J. Li

    2015-01-01

    Full Text Available Different dispersants were added in the dispersion process to improve the efficiency of fluorite flotation. The types and dosage of dispersant on the improvement of fluorite flotation were investigated; when the sodium polyacrylate (SPA was used as the dispersant and its addition is 0.5%, the concentrate grade of CaF2 increased from 90% to 98% and the fluorite recovery increased from 81% to 85%. Methods of X-ray powder diffraction (XRD, field emission scanning electron microscopy (FESEM, and Energy dispersive X-ray spectrometer (EDX were used to characterize the sample. According to the analysis of results, the optimal sample consisted of CaF2 and very little CaCO3 in the size range of 0–5 μm. It could be concluded that the mechanism of improvement for the concentrate grade and recovery of CaF2 was attributed to the change of potential energy barrier which caused the separation of particles with different charge. All results indicate that SPA has a great potential to be an efficient and cost-effective dispersant for the improvement of fluorite flotation.

  10. Autoradiography of geological fluorite samples for determination of uranium and thorium distribution using nuclear track methodology

    Energy Technology Data Exchange (ETDEWEB)

    Pi, T.; Sole, J. [Instituto de Geologia, UNAM, Cd. Universitaria, Coyoacan, 04510 Mexico DF (Mexico); Golzarri, J.I; Rickards, J.; Espinosa, G. [IFUNAM, AP 20-364, 01000 Mexico DF (Mexico)]. e-mail: espinosa@fisica.unam.mx

    2007-07-01

    In this paper we present the uranium and thorium distribution analysis of several samples of the 'La Azul' an epithermal fluorspar deposit in southern Mexico, using nuclear track methodology (NTM), in the alpha-autoradiography mode, by placing the mineral sample in contact with a polycarbonate detector. This constitutes a non-destructive analysis, with sufficient sensitivity to provide valuable information about textural and para genetic characteristics of the geological samples. The selected nuclear track detector was CR-39 (Landauer). The region of interest of the geological samples was polished and put in contact with the detector material surface for 45 days in a vacuum chamber (10-3 torr). After this period of time, the detectors were chemically etched, revealing the auto radiograph of the radioactive material. The results show a clear distribution of bands of uranium and thorium in the fluorite samples. This is valuable information for the genetic or geochronological studies of the ore deposits. (Author)

  11. Fluid-melt Inclusions in Fluorite of the Huanggangliang Skarn Iron-Tin Deposit and Their Significance to Mineralization

    Institute of Scientific and Technical Information of China (English)

    王莉娟; 王京彬; 王玉往; 毛骞

    2001-01-01

    For the first time, fluid-melt inclusions are found in fluorite of the Huanggangliang skarn iron-tin deposit (HSID). The fluorite was formed in the main stage of mineralization, named the hydro-skarnization stage. The inclusions contain various components such as Fe, Mg and Cr from deep sources. The melts of primary inclusions are mainly Ca- and F-rich and those of secondary inclusions tend to become Si-rich. During this evolution process, the melts and iron daughter minerals decreased and even vanished. These facts reveal that the evolution of the primary mineralizing fluids and the differentiation of the fluids and melts are the main factors leading to the deposition of Fe, Sn and other elements. This discovery confirms the magmatic genesis of the HSID and has filled in the gaps in the research of magmatogenic skarn deposits and furnished new methods for such research. Furthermore, it has enlarged the scope of the research on fluid inclusions.

  12. The x-ray reflection efficiencies of planes (III) in germanium silicon and fluorite analyzing crystals. Experimental data

    Energy Technology Data Exchange (ETDEWEB)

    Bermudez Polonio, J.

    1964-07-01

    Integrated and peak reflection efficiency curves relative to a LiF crystal are presented. K{sub {alpha}} fluorescent radiations between (22) Ti and (41) Nb were used for both germanium and silicon crystals: the interval was extended to CaK{sub {alpha}} radiation in the short wavelength region with the fluorite crystal. Reflection efficiency curves show sharp declines in the region around the K absorption edges of germanium and calcium. For CuK{sub {alpha}} radiation, the experimental reflection efficiencies at the peak for germanium, silicon and fluorite crystals are 52, 38.5 and 17 percent, whereas the integrated reflection efficiencies are 65.5, 38 and 14 percent respectively. The data were obtained from untreated crystals, using a standard Norelco non-focussing X-ray spectrometer. Experimental procedures are presented. Some considerations about the (222) missing reflections are made. (Author) 12 refs.

  13. Structures and ionic conductivities in two fluorite type families: Pb{sub 5}Bi{sub 17}X{sub 5}O{sub 43} and Pb{sub 5}Bi{sub 18}X{sub 4}O{sub 42} (X = P, V and As)

    Energy Technology Data Exchange (ETDEWEB)

    Giraud, S.; Obbade, S.; Wignacourt, J.P. [Ecole Nationale Superieure de Chimie de Lille, Lab. de Cristallochimie et Physicochimie du Solide, CNRS UMR 8012, 59 - Villeneuve d' Ascq (France); Giraud, S. [University of Texas, Texas Materials Institute and Dept. of Chemical Engineering, Austin, TX (United States); Suard, E.; Steinfink, H. [Institut Laue-Langevin - ILL, 38 - Grenoble (France)

    2003-02-01

    The phases Pb{sub 5}Bi{sub 17}P{sub 5}O{sub 43} and Pb{sub 5}Bi{sub 18}P{sub 4}O{sub 42} are among many recent new oxy-phosphates discovered in the ternary system PbO-Bi{sub 2}O{sub 3}-P{sub 2}O{sub 5}. The syntheses of the vanadates and arsenates led to isostructural compounds. Both series display a distorted 3 x 3 x 3 superstructure of the tetragonal {delta}-Bi{sub 2}O{sub 3} polymorph. These types of phases display interesting anion conductivities and measurements were performed from 300 deg. C to 800 deg. C on the phosphates, arsenates and vanadates of the two families. The Pb{sub 5}Bi{sub 18}X{sub 4}O{sub 42} phases have higher conductivity values than those of Pb{sub 5}Bi{sub 17}X{sub 5}O{sub 43}. Of the three homologues the vanadates always have the highest conductivities, i.e., at 800 deg. C: 1.6 x 10{sup -2} Siemens.cm{sup -1} for Pb{sub 5}Bi{sub 18}V{sub 4}O{sub 42} and 1.6 x 10{sup -3} Siemens.cm{sup -1} for Pb{sub 5}Bi{sub 17}V{sub 5}O{sub 43}. An increase of the volume of the unit cell due to the increasing radius of the pentavalent cations from P, As to V, 0.34 Angstrom, 0.47 Angstrom, 0.59 Angstrom respectively, helps the anion migration through the structure. (authors)

  14. Stable isotope variations in the Quaternary epithermal calcite-fluorite deposit at Monte delle Fate near Cerveteri (Latium, central Italy)

    Science.gov (United States)

    Masi, U.; O'Neil, J.R.

    1980-01-01

    Carbon, oxygen and hydrogen isotope variations have been measured in samples from the epithermal fluorite vein deposit at Monte delle Fate, Latium. The ranges in ?? 13C and ??18O of calcite are -1.3 to 3.4 and 9.5 to 17.3, respectively. ??D values of water extracted from fluid inclusions are -49 to -39 for calcite and -41 to -34 for fluorite. Fluid inclusion filling temperatures (225??-240??C) and salinites (3.75) are nearly the same for both fluorite and sparry calcite. An elongated form of calcite, of minor abundance, precipitated at lower temperatures. The data indicate that (1) the CO2 involved in the mineralization was provided by the local marine limestones, (2) the waters were meteoric in origin and underwent an 18O shift of ??? 10 permil by exchange with marine country rocks, and (3) all geochemical features can be explained by the action of two hydrothermal fluids. Hot brines recently discovered in the Cesano geothermal area, 30 km to the east, have temperatures and some chemical characteristics similar to the hydrothermal fluids at Monte delle Fate. ?? 1980 Springer-Verlag.

  15. Fluoride removal by calcite: evidence for fluorite precipitation and surface adsorption.

    Science.gov (United States)

    Turner, Brett D; Binning, Philip; Stipp, S L S

    2005-12-15

    Fluoride contamination of groundwater, both anthropogenic and natural, is a major problem worldwide. In this study, fluoride removal by crushed limestone (99% pure calcite) was investigated by batch studies and surface-sensitive techniques from solutions with fluoride concentrations from 150 micromol/L (3 mg/L) to 110 mM (approximately 2100 mg/L). Surface-sensitive techniques, including atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) as well as zeta potential measurements, confirm that, in addition to precipitation reactions, adsorption of fluoride also occurs. Results indicate that fluoride adsorption occurs immediately over the entire calcite surface with fluorite precipitating at step edges and kinks, where dissolved Ca2+ concentration is highest. The PHREEQ geochemical model was applied to the observed data and indicates that existing models, especially at low fluoride concentrations and high pH (>7.5) are not equipped to describe this complex system, largely because the PHREEQ model includes only precipitation reactions, whereas a combination of adsorption and precipitation parameters are required.

  16. Prediction of giant mechanocaloric effects in fluorite-structured superionic materials

    OpenAIRE

    Cazorla, Claudio; Errandonea, Daniel

    2016-01-01

    Mechanocaloric materials experience a change in temperature when a mechanical stress is adiabatically applied on them. Thus far, only ferroelectrics and superelastic metallic alloys have been considered as potential mechanocaloric compounds to be exploited in solid-state cooling applications. Here we show that giant mechanocaloric effects occur in hitherto overlooked fast ion conductors (FIC), a class of multicomponent materials in which above a critical temperature, Ts, a constituent ionic s...

  17. Nanometric solid solutions of the fluorite and perovskite type crystal structures: Synthesis and properties

    Directory of Open Access Journals (Sweden)

    Snežana Bošković

    2012-09-01

    Full Text Available In this paper a short review of our results on the synthesis of nanosized CeO2, CaMnO3 and BaCeO3 solid solutions are presented. The nanopowders were prepared by two innovative methods: self propagating room temperature synthesis (SPRT and modified glycine/nitrate procedure (MGNP. Different types of solid solutions with rare earth dopants in concentrations ranging from 0–0.25 mol% were synthesized. The reactions forming solid solutions were studied. In addition, the characteristics of prepared nanopowders, phenomena during sintering and the properties of sintered samples are discussed.

  18. High-throughput continuous hydrothermal flow synthesis of Zn-Ce oxides: unprecedented solubility of Zn in the nanoparticle fluorite lattice.

    Science.gov (United States)

    Kellici, Suela; Gong, Kenan; Lin, Tian; Brown, Sonal; Clark, Robin J H; Vickers, Martin; Cockcroft, Jeremy K; Middelkoop, Vesna; Barnes, Paul; Perkins, James M; Tighe, Christopher J; Darr, Jawwad A

    2010-09-28

    High-throughput continuous hydrothermal flow synthesis has been used as a rapid and efficient synthetic route to produce a range of crystalline nanopowders in the Ce-Zn oxide binary system. High-resolution powder X-ray diffraction data were obtained for both as-prepared and heat-treated (850 degrees C for 10 h in air) samples using the new robotic beamline I11, located at Diamond Light Source. The influence of the sample composition on the crystal structure and on the optical and physical properties was studied. All the nanomaterials were characterized using Raman spectroscopy, UV-visible spectrophotometry, Brunauer-Emmett-Teller surface area and elemental analysis (via energy-dispersive X-ray spectroscopy). Initially, for 'as-prepared' Ce(1-x)Zn(x)O(y), a phase-pure cerium oxide (fluorite) structure was obtained for nominal values of x=0.1 and 0.2. Biphasic mixtures were obtained for nominal values of x in the range of 0.3-0.9 (inclusive). High-resolution transmission electron microscopy images revealed that the phase-pure nano-CeO(2) (x=0) consisted of ca 3.7 nm well-defined nanoparticles. The nanomaterials produced herein generally had high surface areas (greater than 150 m(2) g(-1)) and possessed combinations of particle properties (e.g. bandgap, crystallinity, size, etc.) that were unobtainable or difficult to achieve by other more conventional synthetic methods.

  19. Structural analysis of Bi{sub 3}TiNbO{sub 9} prepared by mechanical activation

    Energy Technology Data Exchange (ETDEWEB)

    Lara, Patricio; Serafini, Daniel; Romero, Rodrigo [Depto. de Fisica, Universidad de Santiago de Chile, Santiago (Chile); Avila, Ricardo E [Departamento de Materiales Nucleates, CCHEN, Cas. 188-D, Santiago (Chile); Cabrera, A L [Facultad de Fisica, Pontificia Universidad Catolica de Chile, Santiago (Chile)], E-mail: ravila@cchen.cl

    2008-11-01

    The synthesis by high energy mechanical activation and structural characterization of the phases of Bi{sub 3}TiNbO{sub 9} are described. A fluorite-like metastable phase was identified upon heating the activated powders in the temperature range of 593 to 823 K, followed by formation of the stable Aurivillius phase above 873 K. The crystallization temperature of the fluorite phase increases with milling time. From Rietveld analysis of X-ray diffraction patterns, the fluorite cell parameter is shown to decrease, while rutile TiO{sub 2} increases with milling time.

  20. U-Th/He ages of fluorite mineralizations of the Tangua alkaline intrusion; Idades U-Th/He das mineralizacoes de fluorita da intrusao alcalina de Tangua

    Energy Technology Data Exchange (ETDEWEB)

    Geraldes, M.C.; Vargas, T., E-mail: geraldes@uerj.br, E-mail: vargas@uerj.br [Universidade do Estado do Rio de Janeiro (UERJ), RJ (Brazil). Faculdade de Geologia; Evans, N., E-mail: Noreen.Evans@csiro.au [CSIRO and Curtin University for Technology, Western Australia (Australia); Nummer, A.R., E-mail: nummer@ufrrj.br [Universidade Federal Rural do Rio de Janeiro (DEGEOC/IA/UFRRJ), RJ (Brazil)

    2015-07-01

    The Tangua massif is part of a group of alkaline complexes that occurs in an extensive zone of faults and E-W lineaments and includes the Brazilian Southeastern Rift. This work presents U-He ages of the fluorite mineralization. The Tangua alkaline massif is emplaced in coarse-grained biotite gneiss (Oriental Domain, central portion of the Ribeira belt). Cataclastic gneiss with intense weathering are restricted to the intrusion contacts. The alkaline body is comprised of pulaskites and umptekites, nephelinesyenites, foiaites, and pseudoleucite foiaites and is cut by phonolite dykes, trachytes and alkaline lamprophyres. In the locality of Barbosao, veins of fluorite occur, accompanied by silica and pyrite within trachyte dykes. These veins are parallel to the gneiss foliation (N 50 - 70 E) with an average thickness of 30 cm and the fluorite contains limonite and manganese oxides inclusions. The U-He ages range from <2Ma to 73Ma. The older age is coherent with 80-65 ma range of K-Ar ages reported in the literature. The veins of fluorite crosscut the lithologies associated with shear zones, and are important to economic exploration in the region. The petrographic and U-Th/He sating studies indicate the fluorite formation coeval to alkaline intrusion and meteoric water fluid circulation recently. (author)

  1. A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS.

    Science.gov (United States)

    Suturin, S M; Fedorov, V V; Korovin, A M; Valkovskiy, G A; Konnikov, S G; Tabuchi, M; Sokolov, N S

    2013-08-01

    In this work epitaxial growth of cobalt on CaF2(111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright 〈111〉 streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles.

  2. Synthesis of Fluorite (CaF2 Crystal from Gypsum Waste of Phosphoric Acid Factory in Silica Gel

    Directory of Open Access Journals (Sweden)

    Mohammad Misbah Khunur

    2012-06-01

    Full Text Available This paper report the synthesis and characterization of fluorite single crystal prepared from gypsum waste of phosphoric acid production in silica gel. Instead of its high calcium, gypsum was used to recycle the waste which was massively produces in the phosphoric acid production. The gypsum waste, the raw material of CaCl2 supernatant, was dissolved in concentrated HCl and then precipitated as calcium oxalate (CaC2O4 by addition of ammonium oxalate. The CaCl2 was obtained by dissolving the CaC2O4 with HCl 3M. The crystals were grown at room temperature in silica gel and characterized by AAS, FTIR and powder XRD. The optimum crystal growth condition, which is pH of gel, CaCl2 concentration and growth time, were investigated. The result shows that at optimum condition of pH 5.80, CaCl2 concentrations of 1.2 M, and growth time of 144 hours, colorless crystals with the longest size of 3 mm, were obtained (72.57%. Characterization of the synthesized crystal by AAS indicates that the obtained crystal has high purity. Meanwhile, analysis by FTIR spectra shows a Ca–F peak at 775 cm-1, and powder-XRD analysis confirms that the obtained crystal was fluorite (CaF2. © 2012 BCREC UNDIP. All rights reservedReceived: 11st April 2012; Revised: 4th June 2012; Accepted: 13rd June 2012[How to Cite: M.M. Khunur, A. Risdianto, S. Mutrofin, Y.P. Prananto. (2012. Synthesis of Fluorite (CaF2 Crystal from Gypsum Waste of Phosphoric Acid Factory in Silica Gel. Bulletin of Chemical Reaction Engineering & Catalysis, 7 (1: 71-77.  doi:10.9767/bcrec.7.1.3171.71-77 ][How to Link / DOI: http://dx.doi.org/10.9767/bcrec.7.1.3171.71-77 ] | View in 

  3. States of the Schottky defect in uranium dioxide and other fluorite type crystals: Molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Kovalenko, M.A., E-mail: akm_max@mail.ru; Kupryazhkin, A. Ya, E-mail: a.ya.kupryazhkin@urfu.ru

    2015-10-05

    Highlights: • We derived the degree of vacancy association in Schottky defects from temperature. • At high temperatures cation vacancy forms complexes with anion vacancies. • Point defects model in the presence of complexes was considered. • The presence of anion vacancies around cation vacancy lowers its migration energy. • The formation of nanovoids at high cation vacancy concentrations was shown. - Abstract: Mass transfer processes in fluorite-type systems are determined by the diffusion of cations via vacancies from Schottky defects. To predict diffusion coefficients of cations and other parameters based on it the Lidiard and Matzke approximation of the point defects model, namely the assumption of isolated vacancies, is widely used. States of the Schottky defect were studied with the high-speed molecular dynamics method in a wide temperature range, with six different interaction potentials. Schottky vacancies were dynamically detected during the simulation. It is shown that contrary to the Lidiard and Matzke model, the Schottky cation vacancy is always associated with anion vacancies. The degree of the Schottky defect association depends on the temperature, at high temperatures near the cation vacancy two or more anion vacancies are located. It is shown that the calculated formation energy of Schottky defects in the form of the trivacancy (5.8–7.4) eV for all potentials are close to the experimental value (6–7) eV, in contrast to the formation energy of Schottky defects in the form of isolated vacancies that exceeds 10 eV. Point defects model of the simulated system in the presence of an artificially created Schottky defect was constructed and compared with calculation results. According to our study the point defects model is applicable only at low temperatures less than half of the melting temperature. It is shown that the presence of anion vacancies near the cation vacancy reduces the migration energy of cations. However, for systems with

  4. Optical and Electronic Analysis of the Two Fluorite-Related Phases in the Ga-In-Sn-O System

    Science.gov (United States)

    Dolgonos, Alex

    Optical transparency and electrical conductivity, traditionally mutually-exclusive materials properties, are both critical for the performance of electrode materials in applications such as flat-panel displays and organic photovoltaics (OPVs). Owing to their wide band gaps which are amenable to degenerate doping, transparent conducting oxides (TCOs) are widely utilized for organic optoelectronic applications. The two fluorite-related phases in the Ga-In-Sn-O (GITO) pseudo-ternary system---Ga,Sn co-substituted bixbyite 2O3 and the so-called "T-phase" Ga3--xIn5+xSn2O 16---have the potential to overcome the issues associated with Sn-doped 2O3 (ITO) by reducing the indium content, utilizing compositions that are more stable in acidic conditions, and offering work function levels that are in better alignment with adjacent layers in organic optoelectronic devices. In this work, the composition and processing effects on the optical and electronic properties of the bixbyite phase and the T-phase in the GITO system were determined. Electronic properties were analyzed by conductivity and Seebeck coefficient measurements, and the combination of these two properties revealed carrier characteristics for these two phases. The optical band gaps of the phases were determined from absorption data by methods developed in this work, which account for the band-altering effects of doping in TCOs. The optical characterization methods were experimentally confirmed through a combination of diffuse-reflectance and photoluminescence measurements of un-doped and Sn-doped In2O3. The bixbyite phase's conductivity, Seebeck coefficient, and optical band gap are dominated by the concentration of Sn-on-In substitution defects, as expected. Remarkably, Ga substition was found to have a negligible effect on the electronic properties. A conductivity of 3000 S/cm was achieved in bulk specimens containing a relatively small Sn content of 1 atomic percent and 4.5 atomic percent Ga. Ga behaves as an

  5. Fluid evolution and mineralogy of Mn-Fe-barite-fluorite mineralizations at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in Germany

    Science.gov (United States)

    Majzlan, Juraj; Brey-Funke, Maria; Malz, Alexander; Donndorf, Stefan; Milovský, Rastislav

    2016-02-01

    Numerous small deposits and occurrences of Mn-Fe-fluorite-barite mineralization have developed at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in central Germany. The studied mineralizations comprise the assemblages siderite+ankerite-calcite-fluorite-barite and hematite-Mn oxides-calcite-barite, with the precipitation sequence in that order within each assemblage. A structural geological analysis places the origin of the barite veins between the Middle Jurassic and Early Cretaceous. Primary fluid inclusions contain water vapour and an aqueous phase with NaCl and CaCl2 as the main solutes, with salinities mostly between 24-27 mass. % CaCl2 eq. Th measurements range between 85 °C and 160 °C in barite, between 139 °C and 163 °C in siderite, and between 80 °C and 130 °C in fluorite and calcite. Stable isotopes (S, O) point to the evaporitic source of sulphur in the observed mineralizations. The S,C,O isotopic compositions suggest that barite and calcite could not have precipitated from the same fluid. The isotopic composition of the fluid that precipitated barite is close to the sea water in the entire Permo-Mesozoic time span whereas calcite is isotopically distinctly heavier, as if the fluids were affected by evaporation. The fluid evolution in the siliciclastic/volcanic Rotliegend sediments (as determined by a number of earlier petrological and geochemical studies) can be correlated with the deposition sequence of the ore minerals. In particular, the bleaching of the sediments by reduced Rotliegend fluids (basinal brines) could be the event that mobilized Fe and Mn. These elements were deposited as siderite+ankerite within the Zechstein carbonate rocks and as hematite+Mn oxides within the oxidizing environment of the Permian volcanic and volcanoclastic rocks. A Middle-Jurassic illitization event delivered Ca, Na, Ba, and Pb from the feldspars into the basinal brines. Of these elements, Ba was deposited as massive barite

  6. Fluid evolution and mineralogy of Mn-Fe-barite-fluorite mineralizations at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in Germany

    Directory of Open Access Journals (Sweden)

    Majzlan Juraj

    2016-02-01

    Full Text Available Numerous small deposits and occurrences of Mn-Fe-fluorite-barite mineralization have developed at the contact of the Thuringian Basin, Thüringer Wald and Thüringer Schiefergebirge in central Germany. The studied mineralizations comprise the assemblages siderite+ankerite-calcite-fluorite-barite and hematite-Mn oxides-calcite-barite, with the precipitation sequence in that order within each assemblage. A structural geological analysis places the origin of the barite veins between the Middle Jurassic and Early Cretaceous. Primary fluid inclusions contain water vapour and an aqueous phase with NaCl and CaCl2 as the main solutes, with salinities mostly between 24–27 mass. % CaCl2 eq. Th measurements range between 85 °C and 160 °C in barite, between 139 °C and 163 °C in siderite, and between 80 °C and 130 °C in fluorite and calcite. Stable isotopes (S, O point to the evaporitic source of sulphur in the observed mineralizations. The S,C,O isotopic compositions suggest that barite and calcite could not have precipitated from the same fluid. The isotopic composition of the fluid that precipitated barite is close to the sea water in the entire Permo–Mesozoic time span whereas calcite is isotopically distinctly heavier, as if the fluids were affected by evaporation. The fluid evolution in the siliciclastic/volcanic Rotliegend sediments (as determined by a number of earlier petrological and geochemical studies can be correlated with the deposition sequence of the ore minerals. In particular, the bleaching of the sediments by reduced Rotliegend fluids (basinal brines could be the event that mobilized Fe and Mn. These elements were deposited as siderite+ankerite within the Zechstein carbonate rocks and as hematite+Mn oxides within the oxidizing environment of the Permian volcanic and volcanoclastic rocks. A Middle-Jurassic illitization event delivered Ca, Na, Ba, and Pb from the feldspars into the basinal brines. Of these elements, Ba was

  7. Accelerator-based analytical technique in the evaluation of some Nigeria's natural minerals: Fluorite, tourmaline and topaz

    Energy Technology Data Exchange (ETDEWEB)

    Olabanji, S.O. [Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Legnaro (LNL), viale dell' Universita 2, 35020 Legnaro, Padova (Italy)]. E-mail: skayode2002@yahoo.co.uk; Ige, O.A. [Natural History Museum, Obafemi Awolowo University, Ile-Ife (Nigeria); Mazzoli, C. [Dipartimento di Mineralogia e Petrologia, Universita di Padova, 35100 Padova (Italy); Ceccato, D. [Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Legnaro (LNL), viale dell' Universita 2, 35020 Legnaro, Padova (Italy); Dipartimento di Fisica, Universita di Padova, via Marzolo 8, 35100 Padova (Italy); Akintunde, J.A. [CERD, Obafemi Awolowo University, Ile-Ife (Nigeria); De Poli, M. [Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Legnaro (LNL), viale dell' Universita 2, 35020 Legnaro, Padova (Italy); Moschini, G. [Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Legnaro (LNL), viale dell' Universita 2, 35020 Legnaro, Padova (Italy); Dipartimento di Fisica, Universita di Padova, via Marzolo 8, 35100 Padova (Italy)

    2005-10-15

    For the first time, the complementary accelerator-based analytical technique of PIXE and electron microprobe analysis (EMPA) were employed for the characterization of some Nigeria's natural minerals namely fluorite, tourmaline and topaz. These minerals occur in different areas in Nigeria. The minerals are mainly used as gemstones and for other scientific and technological applications and therefore are very important. There is need to characterize them to know the quality of these gemstones and update the geochemical data on them geared towards useful applications. PIXE analysis was carried out using the 1.8 MeV collimated proton beam from the 2.5 MV AN 2000 Van de Graaff accelerator at INFN, LNL, Legnaro, Padova, Italy. The novel results which show many elements at different concentrations in these minerals are presented and discussed.

  8. Estimate of radiation doses to workers in underground mines of coal and fluorite in the Brazilian state of Santa Catarina and considerations on the optimisation of radiation protection

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Carlos Eduardo Lima dos; Vignol, Maria Lidia; Conceicao, Rommulo Vieira [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Inst. de Geociencias], e-mail: carlos.lima@ufrgs.br; Xavier, Ana Maria; Gouvea, Vandir; Macacini, Jose Flavio [Comissao Nacional de Energia Nuclear (CNEN/RJ), Rio de Janeiro, RJ (Brazil)], e-mail: axavier@cnen.gov.br

    2009-07-01

    The inhalation of radon present in underground mines can imply in the deposition of its descendants in the lungs, which may cause harm to the lungs tissues and induce cancer. Concentrations of radon in the environment of underground mines above 1000 - 1500 Bq/m{sup 3} are internationally considered to require protective measures for the miners. The objectives of the present work were to determine the concentrations of radon in air, as well as the resulting doses due to the presence of this radionuclide in three underground mines of fluorite and three underground mines of coal in the State of Santa Catarina. The concentration of radon was measured employing two types of detectors of nuclear tracks (SSNTD), the LEXAN and the CR-39. This detection method consisted in counting, with the help of a microscope, tracks resulting from the interaction of alpha particles with the film, due to the penetration of Rn-222 in the interior of the detector chamber and its decaying process. The average dose to the workers of the coal mines was estimated as 0.7 mSv/a, value inferior to the limit of 1 mSv/a established by the Brazilian Nuclear Energy Commission (CNEN) for members of the public. On the other hand, the fluorite mines showed much higher concentrations of radon and superior to 1000 Bq/m{sup 3}. The inefficiency of the ventilation system and the liberation of radon during the various explosions may have contributed to the high concentrations of radon in these mines since the concentration of radium in the rocks (normal and weathered granites) and in the minerals (green and purple fluorides) that compose the mining environment are not high. The modification of the ventilation system of one of the fluorite mines was sufficient to reduce the radon concentration to levels of the order of 500 Bq/m{sup 3}. The weathered granite contributes more significantly to the increase of the concentration of Rn-222 in the air than the other rocks here studied, i.e. normal granite as well as

  9. Structure and Properties of Some Layered U2O5 Phases: A Density Functional Theory Study

    OpenAIRE

    Molinari, Marco; Brincat, Nicholas A.; Allen, Geoffrey C.; Parker, Stephen C.

    2017-01-01

    U2O5 is the boundary composition between the fluorite and the layered structures of the UO2→3 system and the least studied oxide in the group. δ-U2O5 is the only layered structure proposed so far experimentally, although evidence of fluorite-based phases has also been reported. Our DFT work explores possible structures of U2O5 stoichiometry by starting from existing M2O5 structures (where M is an actinide or transition metal) and replacing the M ions with uranium ions. For all structures, we ...

  10. Direct reading spectrochemical determination of aluminium, iron and silicon in fluorite; Determinacion espectroquimica de lectura directa de aluminio, hierro y silicio en fluorita

    Energy Technology Data Exchange (ETDEWEB)

    Roca, M.

    1966-07-01

    A quantitative spectrochemical method for the determination of Al, Fe and Si in fluorite has been worked out. The sample was supported in a graphite electrode with crater of 5 mm. in diameter, 2,5 mm deep, and burned by a d.c. are in a direct reading spectrometer. The excitation of samples has been studied without dilution as well as using graphite powder as diluent in the ratios 1:1, 1:4, and 1:9; the latter factor was chosen. Ag, Ca, Co, Cr, Mo and Sn were tested as internal standards. It has not been found any significant inter element effect. It is necessary to use natural fluorite as base material for the standards. (Author) 5 refs.

  11. Effects of firing schedule on solubility limits and transport properties of ZrO2–TiO2–Y2O3 fluorites

    DEFF Research Database (Denmark)

    Fagg, D.P.; Frade, J.R.; Mogensen, Mogens Bjerg

    2007-01-01

    The low Y/high Zr edge of the cubic defect fluorite solid solution in the system ZrO2–TiO2–Y2O3 in air is reassessed, as it is these compositions which have been suggested to offer the highest levels of mixed conductivity. Vegard's law is obeyed for values of x which lie within the cubic defect...... fluorite phase in Zr1−x−yYyTixO2−δ for values of y=0.2 and 0.25. Measured lattice parameters show good agreement with those calculated from the Kim relation. Deviation from Vegard's law places the limit of the solid solution at x=0.18 and 0.20 for values of y=0.2 and 0.25, respectively, at 1500 °C...

  12. Fluid Inclusion Studies and Geochemistry of Rare Earth Elements of Hydrothermal Fluorites from P?hrenk, Kir?ehir, Central Turkey

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Fluorite mineralization occurs along fractures and cracks of Middle Eocene and Pliocene limestones and marls in the north and northeast of the P?hrenk region (?i?ekdagi, Kirsehir). Tb/Ca ( Tb/La and Y/Ho ratios were obtained from REE contents of fluorites which have revealed that mineralization is of hydrothermal type. Negative Ce anomalies and positive Eu anomalies reflect that hydrothermal solutions once had high oxygen fugacity. Fluid inclusion studies indicate that homogenization temperatures of mineralization varied between 90oC and 200oC, and hydrothermal solutions are composed of NaCl + KCl + MgCl2 + H2O. In addition, salinity measurements show that hydrothermal solutions were mixed with meteoric or rock formation water. Geologic setting, REE geochemistry and fluid inclusion studies suggest that mineralization was deposited from a solution generated by mixing of magmatic and meteoric water under epithermal conditions.

  13. Quantification of fluorite mass-content in powdered ores using a Laser-Induced Breakdown Spectroscopy method based on the detection of minor elements and CaF molecular bands

    Energy Technology Data Exchange (ETDEWEB)

    Álvarez, C.; Pisonero, J., E-mail: pisonerojorge@uniovi.es; Bordel, N., E-mail: bordel@uniovi.es

    2014-10-01

    Laser Induced Breakdown Spectroscopy (LIBS) is investigated as a fast and robust method to determine the fluorite (CaF{sub 2}) mass-content of powdered ore samples. Calibrating samples covering a wide CaF{sub 2} concentration range (from 2.3 to 97.6%) are employed. LIBS operating conditions are optimized for the analysis of elemental emission lines and molecular bands, respectively. In particular, LIBS emission intensities from different CaF molecular bands are evaluated to calibrate the fluorite concentration as an alternative to the use of atomic fluorine F I emission lines. Furthermore, the determination of LIBS emission signals from minor elements (e.g. Si I and Mg I) is studied to further improve the accuracy and precision of pure fluorite sample analyses (e.g. [CaF{sub 2}] > 75%). The proposed LIBS method avoids the tedious dissolution processes that are required by other analytical methods employed in mining industry for the quantitative analysis of fluorite. - Highlights: • Fluorite ore mass-content is determined using a LIBS system. • F I emission line at 685.60 nm is used to calibrate the fluorite mass-content. • CaF emission bands are used to quantify samples with low CaF2 concentrations. • Minor elements are used to quantify samples with high CaF2 concentrations.

  14. Test Research on Beneficiation of Calcite Type Fluorite Ore in Hu'nan%湖南某方解石型萤石选矿试验研究

    Institute of Scientific and Technical Information of China (English)

    胡瑞彪; 吉红; 陈典助; 荆正强

    2013-01-01

    The CaF 2 grade of calcite type fluorite ore from Hu'nan is reaching up to 56 .72%,regard as high-grades fluorite ore .According to the mineralogical characteristic of the ore ,the fluorite was studied,Using sodium carbonate as pH adjusting agent ,sodium silicate and starch as depressant ,so-dium oleate as collector , closed -circuit test were carried out in the condition that the roughing grinding fineness was -0 .074 mm 65%.The grade and recovery of the fluorite concentrate were 97.16%and 80.38%respectively,and the content of SiO2 and CaCO3 meet the national standards . The results showed that concentrate were obtained by swept one rougher -five cleaners-one scav-enging and coarse concentrate regrinding closed -circuit process .%湖南某方解石型萤石矿原矿含CaF256.72%,属高品位萤石矿。结合该矿石的工艺矿物学特性,采用碳酸钠为pH调整剂、水玻璃+淀粉为抑制剂、油酸钠为捕收剂进行浮选试验研究。闭路试验在粗选磨矿细度-0.074 mm占65%的情况下,通过一粗五精一扫-粗精矿再磨的工艺流程,可以获得品位97.16%、回收率80.38%的萤石精矿,且萤石精矿中含SiO21.20%、CaCO30.65%,达到国家萤石粉F97C的质量标准。

  15. Formation and properties of silicon/fluorite heterostructures. Final report, June 1, 1994--May 31, 1997

    Energy Technology Data Exchange (ETDEWEB)

    Olmstead, M.A.

    1997-10-01

    Our primary goal during the previous support periods was to determine the interrelationship among the structure of the CaF{sub 2}/Si interface, the growth kinetics, the structure and morphology of the overlying film, and the intrinsic dielectric properties of the interface itself. The experiments were designed (i) to determine the CaF{sub 2} overlayer structure and morphology as a function of kinetic conditions [Den93a, Den93b, Won93, Den95, Hes95], (ii) to develop and test models explaining the observed structures [Den95, Hes95], (iii) to investigate the stability of the interface structure [Les97] and (iv) to determine and interpret the photoelectron kinetic energy distributions as a function of the emitting atom location [Rot93, Rot94, Rot96]. As summarized below, we were successful in accomplishing these experiments and in largely fulfilling our original goal.

  16. Bubble Formation and Lattice Parameter Changes Resulting from He Irradiation of Defect-Fluorite Gd2Zr2O7

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, Caitlin A.; Patel, Maulik K.; Aguiar, Jeffery A.; Zhang, Yanwen; Crespillo, Miguel L.; Wen, Juan; Xue, Haizhou; Wang, Yongqiang; Weber, William J.

    2016-08-15

    Pyrochlores have long been considered as potential candidates for advanced ceramic waste-forms for the immobilization of radioactive waste nuclides. This work provides evidence that Gd2Zr2O7, often considered the most radiation tolerant pyrochlore, could be susceptible to radiation damage in the form of bubble nucleation at the highest He doses expected over geological time. Ion irradiations were utilized to experimentally simulate the radiation damage and He accumulation produced by ..alpha..-decay. Samples were pre-damaged using 7 MeV Au3+ to induce the pyrochlore to defect-fluorite phase transformation, which would occur due to ..alpha..-recoil damage within several hundred years of storage in a Gd2Zr2O7 waste-form. These samples were then implanted to various He concentrations in order to study the long-term effects of He accumulation. Helium bubbles 1-3 nm in diameter were observed in TEM at a concentration of 4.6 at.% He. Some bubbles remained isolated, while others formed chains 10-30 nm in length parallel to the surface. GIXRD measurements showed lattice swelling after irradiating pristine Gd2Zr2O7 with 7 MeV Au3+ to a fluence of 2.2 x 1015 Au/cm2. An increase in lattice swelling was also measured after 2.2 x 1015 Au/cm2 + 2 x 1015 He/cm2 and 2.2 x 1015 Au/cm2 + 2 x 1016 He/cm2. A decrease in lattice swelling was measured after irradiation with 2.2 x 1015 Au/cm2 + 2 x 1017 He/cm2, the fluence where bubbles and bubble chains were observed in TEM. Bubble chains are thought to form in order to reduce lattice strain normal to the surface, which is produced by the Au and He irradiation damage.

  17. Mineral chemistry of monazite-(Nd, xenotime-(Y, apatite, fluorite and zircon hosting in lamprophyre dyke in Abu Rusheid area, South Eastern Desert, Egypt

    Directory of Open Access Journals (Sweden)

    Mohamed A. Ali

    2012-06-01

    Full Text Available The studied mineralized lamprophyre dyke in Abu Rusheid area is trending NNW-SSE, and occurs withinAbu Rusheid mineralized shear zone, measuring 0.2 - 1.0 m in width and 0.5 - 1.0 km in length. It was emplacedparallel with the Abu Rusheid shear zone. The dyke is mainly composed of plagioclases, amphiboles, mica (musco-vite and biotite, relics of pyroxenes with K-feldspars and quartz derived from surrounding country rocks asphenocrysts embedded in fine-grained groundmass. The lamprophyre dyke hosts REE-minerals monazite-(Nd,xenotime-(Y, and REE-bearing minerals apatite, fluorite, zircon-(Hf, rutile with inclusions of xenotime and ironoxides. The emplacement of lamprophyre dyke caused heating in the mineralized shear zone of Abu Rusheid area.The lamprophyre dyke was subsequently affected by hydrothermal alterations (e.g. chlorite-carbonate, muscovitization,fluoritization.The REE were remobilized from the mineralized shear zones by hydrothermal solutionsand re-precipitatedas REE-minerals xenotime-(Y and monazite-(Nd around flourapatite, fluorite, zircon andrutile. The solid solutions between monazite-(Nd and xenotime-(Y were formed as a product precipitation fromhydrothermal solutions. Also, the apatite mineral in the lamprophyre dyke was subjected to the heating duringthe emplacement, which lead to its alteration and breakdown with concominant precipitation of xenotime-(Yand monazite-(Nd. The chemistry of monazite-(Nd and xenotime-(Y obtained by scanning electron microscopy(SEM, and electron probe microanalysis (EPMA, showed that these minerals are enriched in U and Th. Themonazite-(Nd associated with fluorapatite in the studied dyke is poor in Th (0.02 ≤ Th ≤ 0.81 wt%, but usuallyrich in U (0.92 ≤ U ≤ 2.91 wt%, which indicates that monazite formed as a result of flourapatite metasomatism.

  18. Spectroscopic and computer modelling studies of mixed-cation superionic fluorites

    CSIR Research Space (South Africa)

    Netshisaulu, TT

    2005-10-19

    Full Text Available -heating furnace with beryllium windows. 2.2. Experimental procedure EXAFS measurements around the Cd-K edge (26.716 keV) and the Pb-L3 edge (13.036 keV) were carried out using the Science and Engineering Research Council?s SynchrotronRadiation Source... solutions such as RbBiF4,werealso observed by Catlow and co-workers [1]. Table 3 gives the structural parameters (radial distances and 2sigma 2)determined from the first peaks of the FTs for both Cd-K and Pb-L3 edges in CdF2(xPbF2).Inspection of the table...

  19. Intervalence charge transfer luminescence: Interplay between anomalous and 5d − 4f emissions in Yb-doped fluorite-type crystals

    Energy Technology Data Exchange (ETDEWEB)

    Barandiarán, Zoila, E-mail: zoila.barandiaran@uam.es; Seijo, Luis [Departamento de Química, Universidad Autónoma de Madrid, 28049 Madrid (Spain); Instituto Universitario de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, 28049 Madrid (Spain)

    2014-12-21

    In this paper, we report the existence of intervalence charge transfer (IVCT) luminescence in Yb-doped fluorite-type crystals associated with Yb{sup 2+}–Yb{sup 3+} mixed valence pairs. By means of embedded cluster, wave function theory ab initio calculations, we show that the widely studied, very broad band, anomalous emission of Yb{sup 2+}-doped CaF{sub 2} and SrF{sub 2}, usually associated with impurity-trapped excitons, is, rather, an IVCT luminescence associated with Yb{sup 2+}–Yb{sup 3+} mixed valence pairs. The IVCT luminescence is very efficiently excited by a two-photon upconversion mechanism where each photon provokes the same strong 4f{sup 14}–1A{sub 1g}→ 4f{sup 13}({sup 2}F{sub 7/2})5de{sub g}–1T{sub 1u} absorption in the Yb{sup 2+} part of the pair: the first one, from the pair ground state; the second one, from an excited state of the pair whose Yb{sup 3+} moiety is in the higher 4f{sup 13}({sup 2}F{sub 5/2}) multiplet. The Yb{sup 2+}–Yb{sup 3+} → Yb{sup 3+}–Yb{sup 2+} IVCT emission consists of an Yb{sup 2+} 5de{sub g} → Yb{sup 3+} 4f{sub 7/2} charge transfer accompanied by a 4f{sub 7/2} → 4f{sub 5/2} deexcitation within the Yb{sup 2+} 4f{sup 13} subshell: [{sup 2}F{sub 5/2}5de{sub g},{sup 2}F{sub 7/2}] → [{sup 2}F{sub 7/2},4f{sup 14}]. The IVCT vertical transition leaves the oxidized and reduced moieties of the pair after electron transfer very far from their equilibrium structures; this explains the unexpectedly large band width of the emission band and its low peak energy, because the large reorganization energies are subtracted from the normal emission. The IVCT energy diagrams resulting from the quantum mechanical calculations explain the different luminescent properties of Yb-doped CaF{sub 2}, SrF{sub 2}, BaF{sub 2}, and SrCl{sub 2}: the presence of IVCT luminescence in Yb-doped CaF{sub 2} and SrF{sub 2}; its coexistence with regular 5d-4f emission in SrF{sub 2}; its absence in BaF{sub 2} and SrCl{sub 2}; the quenching of

  20. Modèles d'arrangements anioniques locaux dans les solutions solides à structure fluorine stabilisée par dopage Na 0.5- xY 0.5+ xF 2+2 x

    Science.gov (United States)

    Pontonnier, L.; Patrat, G.; Aléonard, S.

    1990-07-01

    Electron, X-ray, and neutron diffuse scattering measurements have been performed on single crystals of the Na 0.5- xY 0.5+ xF 2+2 x solid-solutions having a doped stabilized fluorite structure. The localization and the shape of the diffuse scattering agree with a description of the local structure using a tridimensional arrangement of microdomains. A model of the fluorine local order agreeing with the refinements of the average structure is proposed. It assumes that all the interstitial atoms are trapped in thermally stable [NaY 3F 12] 2- clusters diluted in a fluorite matrix. The high inelastic contribution to the diffuse scattering indicates that the fluorine sublattice of the fluorite structure is strongly affected by anharmonic vibrations.

  1. Sr2(Nd, Ce)2MCu2O9, M=Al, Co, Ga. A new layered copper oxide structure type

    NARCIS (Netherlands)

    Cava, R.J.; Zandbergen, H.W.; Krajewski, J.J.; Peck Jr., W.F.; Hessen, B.; Dover, R.B. Van; Cheong, S.-W.

    1992-01-01

    A new layered copper oxide structure type is reported based on the ordered interleaving of AlO4, CoO4 or GaO4 tetrahedra between the apices of copper oxide pyramids, and an (Nd, Ce)2O2 fluorite layer between the bases of the pyramids. Despite the structural similarities to the recently reported Sr2(

  2. New cubic structure compounds as actinide host phases

    Energy Technology Data Exchange (ETDEWEB)

    Stefanovsky, S V [SIA Radon, 7th Rostovskii lane 2/14, Moscow 119121 (Russian Federation); Yudintsev, S V; Livshits, T S, E-mail: profstef@mtu-net.ru [Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry RAS, Staromonetny lane 35, Moscow 119017 (Russian Federation)

    2010-03-15

    Various compounds with fluorite (cubic zirconia) and fluorite-derived (pyrochlore, zirconolite) structures are considered as promising actinide host phases at immobilization of actinide-bearing nuclear wastes. Recently some new cubic compounds - stannate and stannate-zirconate pyrochlores, murataite and related phases, and actinide-bearing garnet structure compounds were proposed as perspective matrices for complex actinide wastes. Zirconate pyrochlore (ideally Gd{sub 2}Zr{sub 2}O{sub 7}) has excellent radiation resistance and high chemical durability but requires high temperatures (at least 1500 deg. C) to be produced by hot-pressing from sol-gel derived precursor. Partial Sn{sup 4+} substitution for Zr{sup 4+} reduces production temperature and the compounds REE{sub 2}ZrSnO{sub 7} may be hot-pressed or cold pressed and sintered at {approx}1400 deg. C. Pyrochlore, A{sub 2}B{sub 2}O{sub 7-x} (two-fold elementary fluorite unit cell), and murataite, A{sub 3}B{sub 6}C{sub 2}O{sub 20-y} (three-fold fluorite unit cell), are end-members of the polysomatic series consisting of the phases whose structures are built from alternating pyrochlore and murataite blocks (nano-sized modules) with seven- (2C/3C/2C), five- (2C/3C), eight- (3C/2C/3C) and three-fold (3C - murataite) fluorite unit cells. Actinide content in this series reduces in the row: 2C (pyrochlore) > 7C > 5C > 8C > 3C (murataite). Due to congruent melting murataite-based ceramics may be produced by melting and the firstly segregated phase at melt crystallization is that with the highest fraction of the pyrochlore modules in its structure. The melts containing up to 10 wt. % AnO{sub 2} (An = Th, U, Np, Pu) or REE/An fraction of HLW form at crystallization zoned grains composed sequentially of the 5C {yields} 8C {yields} 3C phases with the highest actinide concentration in the core and the lowest - in the rim of the grains. Radiation resistance of the 'murataite' is comparable to titanate pyrochlores. One

  3. Beneficiation Study on a Low Grade Fluorite Ore%某低品位萤石矿选矿工艺研究

    Institute of Scientific and Technical Information of China (English)

    程建国; 廖乾; 周韫; 李淮湘; 解振朝

    2014-01-01

    某低品位萤石矿含CaF2为25.20%,在磨矿细度-0.075 mm含量70%的条件下,采用碳酸钠为pH调整剂、常规水玻璃和酸化水玻璃为抑制剂、油酸为捕收剂,经过一次粗选—粗精矿一次精选脱泥—五次精选,可获得产率为15.93%、CaF2品位98.27%、回收率为62.37%的高品质酸级萤石精矿产品1;中矿集中处理,经过三次精选,可以获得产率为6.20%、CaF2品位82.73%、回收率为20.44%的冶金级萤石精矿产品2,萤石总回收率达到82.81%。精选添加酸化水玻璃,有助于提升萤石精矿的品级。%A low grade fluorite ore of which the CaF 2 grade was 25.20%, flotation tests were con-ducted under the condition of grinding fineness -0 .075 mm 70%, using sodium carbonate as pH adjusting agent , sodium silicate and acidified sodium silicate as depressant and oleic acid as collec-tor .After a roughing and a cleaning flotation , the rough concentrate was deslimed and moved to an-other five cleaning flotation .A high quality concentrate assaying 98.27%CaF2 was obtained with a yield of 15.93%and recovery of 62.37%.The middling products of flowsheet were handled together by three cleaning flotation and another concentrate product was obtained with assaying 82 .81%CaF2 ,the quality of which reached to metallurgical level .The yield was 6.20% and recovery rate was 20 .44%.This fluorite concentrate was upgraded by using acidified sodium silicate .

  4. Preparation and properties of CeTe/sub 2/O/sub 6/ and ThTe/sub 2/O/sub 6/, compounds with a new superstructure of the fluorite type

    Energy Technology Data Exchange (ETDEWEB)

    Botto, I.L.; Baran, E.J. (La Plata Univ. Nacional (Argentina). Facultad de Ciencias Exactas)

    1982-01-01

    It is demonstrated that in the systems MO/sub 2//TeO/sub 2/ (with M = Ce, Th), treated in air and at 600 /sup 0/C, only phases of composition MTe/sub 2/O/sub 6/ are formed. They pertains to the cubic crystal system and constitutes a new type of fluorite-superstructure. Different aspects of its crystal chemistry are commented and also the infrared spectra are recorded and briefly discussed.

  5. Neutron Shielding Design for 4π BaF2 Detector Facility

    Institute of Scientific and Technical Information of China (English)

    HUANG; Xing; ZHANG; Qi-wei; HE; Guo-zhu; CHENG; Pin-jing; TANG; Hong-qing; ZHOU; Zu-ying

    2013-01-01

    Neutrons within energy range of 5 to 300 keV can be produced by pulsed proton beam striking thick lithium target,based on the HI-13 tandem accelerator.Neutron shielding is necessary when the Gamma-ray Total Absorption Facility(GTAF)is applied to measured(n,γ)reaction cross sections

  6. ENERGY-TRANSFER PROCESSES INVOLVING DIFFERENT LUMINESCENCE-CENTERS IN BAF2CE

    NARCIS (Netherlands)

    VISSER, R; DORENBOS, P; VANEIJK, CWE; MEIJERINK, A; BLASSE, G; DENHARTOG, HW

    1993-01-01

    The luminescence of cerium-doped barium fluoride crystals has been investigated as a function of wavelength and time. For excitation uv light, x-rays and gamma rays were used. The well known cross luminescence (CL) near 200 nm and self-trapped exciton luminescence (STE) near 300 nm, which are due to

  7. GEANT simulations of neutron capture experiments with a 4p BaF2 detector

    CERN Document Server

    Heil, M; Kaeppeler, F; Wisshak, K; Voss, F; Ullmann, J L; Haight, R C; Seabury, E H; Wilhelmy, J B; Rundberg, R S; Fowler, M M

    2004-01-01

    The goal of this research project is to give quantitative information useful for the design of a g-ray detector to investigate neutron capture (n, g) reactions on radioactive nuclei at the Manuel Lujan Jr. Neutron Scattering Center (MLNSC) moderated neutron source at LANSCE. Data for neutron energies from thermal up to approximately 500 keV are desired. The radioactive nuclei can have half-lives as short as a few months. With the sample sizes foreseen, typically 1 mg, the radioactive decay rate can exceed tens of Curies (Ci).

  8. X-ray luminescence of BaF 2:Ce 3+ powders

    OpenAIRE

    BATYGOV S. KH.; MAYAKOVA M.N.; S. V. Kuznetsov; FEDOROV P.P.

    2014-01-01

    We studied the mechanism for the formation of ceriumactivated barium fluoride scintillation ceramics and especially X-ray luminescence of its powdered precursors, prepared by coprecipitation of barium and cerium fluorides from aqueous solutions. We have found that the Ce 3+ luminescence, which is typical for cerium (III)-containing ceramics and single crystals, was not observed for such polycrystalline precursors, and the intensity of barium fluoride’s own luminescence decreases with increasi...

  9. 某难选萤石矿低温浮选试验研究%A flotation experimental research on a hard-selected fluorite in Inner Mongolia at low temperature

    Institute of Scientific and Technical Information of China (English)

    张凌燕; 洪礼; 王芳; 杨香风; 冷阳

    2009-01-01

    Fluorite mine in Inner Mongolia is a kind of fine-grained fluorite mine with quartz. By the research on the fluorite ore character and mineral processing tests, a best technology are determined, which consist of one weak alkaline roughing and seven weak acidic cleanings、roughing and cleaning Ⅰtailings discarded as a final tailing, and middlings sent back together to cleaning Ⅰ. By adding collector YSB-2 to cleaning Ⅲ at low temperature, the flotation result which is similar with at room temperature can be obtained. And the high-quality close circle fluorite concentrate can be obtained with CaF2 of 98.34%, recovery of 87.42% at 15℃, and the second-grade fluorite concentrate can also be obtained with CaF2 of 97.70% at 5℃.%内蒙古某萤石矿属石英型细粒嵌布萤石,在研究内蒙古某萤石原矿性质与特征的基础上,通过系统的选矿试验研究,确定了"一粗七精",在碱性条件下(pH=9.0)粗选,在弱酸性条件下(pH= 6.0)精选,粗选和精选Ⅰ排尾,中矿集中返回到精选Ⅰ的工艺流程.在低温下,通过在精Ⅲ补加捕收剂,可获得与常温下接近的浮选指标.15℃闭路浮选可获得含CaF2品位β=98.34%、回收率ε=87.42%的优质萤石精矿,在5℃开路浮选也能得到CaF2品位β=97.70%的二级萤石精矿.

  10. Investigation of material property influenced stoichiometric deviations as evidenced during UV laser-assisted atom probe tomography in fluorite oxides

    Energy Technology Data Exchange (ETDEWEB)

    Valderrama, Billy; Henderson, Hunter B. [Department of Materials Science and Engineering, University of Florida, 100 Rhines Hall, Gainesville, FL 32611 (United States); Yablinsky, Clarissa A. [Department of Nuclear Engineering, University of Wisconsin-Madison, 921 ERB, 1500 Engineering Drive, Madison, WI 53706 (United States); Gan, Jian [Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415 (United States); Allen, Todd R. [Department of Nuclear Engineering, University of Wisconsin-Madison, 921 ERB, 1500 Engineering Drive, Madison, WI 53706 (United States); Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415 (United States); Manuel, Michele V., E-mail: mmanuel@mse.ufl.edu [Department of Materials Science and Engineering, University of Florida, 100 Rhines Hall, Gainesville, FL 32611 (United States)

    2015-09-15

    Oxide materials are used in numerous applications such as thermal barrier coatings, nuclear fuels, and electrical conductors and sensors, all applications where nanometer-scale stoichiometric changes can affect functional properties. Atom probe tomography can be used to characterize the precise chemical distribution of individual species and spatially quantify the oxygen to metal ratio at the nanometer scale. However, atom probe analysis of oxides can be accompanied by measurement artifacts caused by laser-material interactions. In this investigation, two technologically relevant oxide materials with the same crystal structure and an anion to cation ratio of 2.00, pure cerium oxide (CeO{sub 2}) and uranium oxide (UO{sub 2}) are studied. It was determined that electronic structure, optical properties, heat transfer properties, and oxide stability strongly affect their evaporation behavior, thus altering their measured stoichiometry, with thermal conductance and thermodynamic stability being strong factors.

  11. The Li–Si–(O)–N system revisited: Structural characterization of Li{sub 21}Si{sub 3}N{sub 11} and Li{sub 7}SiN{sub 3}O

    Energy Technology Data Exchange (ETDEWEB)

    Casas-Cabanas, M. [CIC energiGUNE, Parque Tecnológico de Álava, Albert Einstein 48, ED.CIC, 01510 Miñano (Spain); Santner, H. [Institut de Ciència de Materials de Barcelona (CSIC) Campus UAB, 08193 Bellaterra, Catalonia (Spain); Palacín, M.R., E-mail: rosa.palacin@icmab.es [Institut de Ciència de Materials de Barcelona (CSIC) Campus UAB, 08193 Bellaterra, Catalonia (Spain)

    2014-05-01

    A systematic study of the Li–Si–(O)–N system is presented. The synthetic conditions to prepare Li{sub 2}SiN{sub 2}, Li{sub 5}SiN{sub 3}, Li{sub 18}Si{sub 3}N{sub 10}, Li{sub 21}Si{sub 3}N{sub 11} and Li{sub 7}SiN{sub 3}O are described and the structure of the last two compounds has been solved for the first time. While Li{sub 21}Si{sub 3}N{sub 11} crystallizes as a superstructure of the anti-fluorite structure with Li and Si ordering, Li{sub 7}SiN{sub 3}O exhibits the anti-fluorite structure with both anion and cation disorder. - Graphical abstract: A systematic study of the Li–Si–(O)–N system is presented. Li{sub 21}Si{sub 3}N{sub 11} crystallizes as a superstructure of the anti-fluorite structure with Li and Si ordering, Li{sub 7}SiN{sub 3}O exhibits the anti-fluorite structure with both anion and cation disorder. - Highlights: • Li{sub 2}SiN{sub 2}, Li{sub 5}SiN{sub 3}, Li{sub 18}Si{sub 3}N{sub 10}, Li{sub 21}Si{sub 3}N{sub 11} and Li{sub 7}SiN{sub 3}O are prepared. • The structures of Li{sub 21}Si{sub 3}N{sub 11} and Li{sub 7}SiN{sub 3}O are presented. • Li{sub 21}Si{sub 3}N{sub 11} exhibits an anti-fluorite superstructure with Li and Si ordering.

  12. Elastic stability and electronic structure of pyrite type PtN2: Ahard semiconductor

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Rong; Zhan, Qian; Zhang, Xiao-Feng

    2006-08-29

    The elastic properties and electronic structure of PtN2 withthe pyrite structure (PtN2(C2)) were studied with first-principlescalculations. The crystal structure is demonstrated to be elasticallystable with a lower energy than the metastable fluorite structureproposed before. The calculated shear modulus of 214 GPa suggests thatPtN2(C2) is harder than some well known hard materials such as TiN andSiC. The high elastic moduli are attributed to a stacking ofcorner-shared PtN6 octahedra bonded by strong N-N covalent bonding. Incontrast to the metallic fluorite-type phase, PtN2(C2) is semiconductingwith an indirect band gap.

  13. Changes and ore-forming significance of calcium and fluoride in Gannan Xintang fluorite mining area%赣南新塘萤石矿区地下水元素钙氟变化及其成矿意义

    Institute of Scientific and Technical Information of China (English)

    杨明生; 常凤琴; 赖劲虎

    2012-01-01

    Gannan is one of the most important areas of high quality fluorite in China. The systematic analysis on the calcium and fluorine ions of groundwater in Xintang fluorite mining area can not only reveal the properties of the mine itself,but also be important for the exploring of new mine areas. Our study results indicated that the ion contents of calcium and fluorine had obviously different spatial distribution. The a-bundance of calcium and fluorine in the groundwater of deposits and around was much higher,compared to that in the underground water 2 kilometers away from the deposit. The former's figure was almost ten times the latter"s. The analysis also showed that the contents of calcium have a higher correlation with that of fluorine in the groundwater. The paper revealed that the fluorite was mineralized by calcium and fluorine produced in the process that hydrothermal circulation incessantly leached the wall crack. Hence fluorite mineralization was determined by calcium and fluorine,and was closely related with the groundwater activity in this area as well. We finally reached the conclusion that the abnormal changes of calcium and fluorine could be used as an important indicator for exploring orgs.%对新塘脉状矿床及其附近地下水的钙、氟元素进行了系统检测,发现钙、氟含量存在明显的空间分布差异.采矿矿床及其附近地下水的钙、氟含量偏高,而2 km远的地下水钙、氟含量低且接近流域平均值,两处平均含量相差近10倍.钙、氟的相关性分析显示,水体中钙、氟含量具有很好的相关性,揭示该区萤石矿成矿受沉积物钙氟控制,并与地下水运动密切相关,通过热液循环不断淋滤溶蚀围岩获取钙氟形成萤石矿.由此,矿区的钙氟异常变化可以作为找矿的重要指标.

  14. Solution chemistry behavior of sodium silicate in flotation of fluorite and scheelite%萤石-白钨矿浮选分离体系中硅酸钠的溶液化学行为

    Institute of Scientific and Technical Information of China (English)

    孙伟; 唐鸿鹄; 陈臣

    2013-01-01

    Complex solution system can be difficult to deal with by conventional solution chemistry calculation. In order to avoid this problem and investigate the influence of sodium silicate on the flotation of scheelite from fluorite, Newton-Raphson method was applied to solution chemistry calculation. And a new kind of species distribution diagram was drawn in terms of changing the total concentration of sodium silicate rather than the activity of silicate or hydrogen ion. According to the study of single-mineral flotation tests, electrokinetic measurements and species distribution diagrams, the selective surface precipitation of calcium silicate on the fluorite was identified to be the major depression mechanism of fluorite in the flotation of separating scheelite from fluorite using sodium silicate as the modifier and sodium oleate as the collector. X-ray photoelectron spectroscopic (XPS) analyses also provided strong evidence for this conclusion. The results show that the selective depression of scheelite flotation from fluorite can be achieved under conditions of moderate depression. The evaluated surface precipitation concentrations are in good agreement with the results of flotation experiments and XPS analysis results. This study also confirms that solution chemistry calculation with Newton-Raphson method has practical value in the interpretation and prediction of mineral flotation.%针对传统溶液化学计算法难以处理复杂溶液体系的问题,采用 Newton-Raphson 数值计算法对复杂溶液体系进行溶液化学计算,利用硅酸钠添加总浓度代替活度绘制新型组分浓度图,研究硅酸钠在萤石白钨矿浮选分离中的作用机理。通过进行纯矿物浮选实验、Zeta电位测试,结合组分浓度图,初步确定硅酸钠在油酸钠浮选分离萤石白钨矿中的主要抑制机理是在萤石表面选择性地生成了硅酸钙沉淀,相关的XPS分析结果进一步证实了这一结论。结

  15. X-ray excited optical luminescence studies on the system Ba (, =F, Cl, Br, I)

    Indian Academy of Sciences (India)

    K Govinda Rajan; A Jestin Lenus

    2005-08-01

    The present paper reports the experimental observations on the x-ray excited optical luminescence (XEOL) along with the afterglow and colour center features found for the barium salts, represented by the formula, Ba, where and are the halides. The system thus consists of four dihalides (BaF2, . . . ,BaI2) and six mixed halides (BaFCl,. . . ,BaBrI). To start with, it was found that on two of the binary halides of barium, BaClI and BaBrI, no literature exists, and so these were prepared for the first time and their crystal structures were determined. An x-ray generator of 3-kW rating was next coupled to a spectrometer via a high throughput fiberoptic sensor for recording the luminescence spectra under x-irradiation. Also presented in this paper are the observations on the Ba compounds in which about 0.1 mole% of Eu2+ was doped, in order to study the efficiency between the prompt luminescence and the photostimulated luminescence in these compounds. The crystal structure varies from fluorite (BaF2), to matlockite (BaF) and finally to orthorhombic (BaCl2, . . .,BaBrI) for these compounds. Hence searching for systematics and empirical relations in the observed XEOL behaviour of these compounds is still a challenging problem.

  16. He isotopes constraints to the origin of hydrothermal fluids: application to the fluorite mineralizations of Asturias (N Spain); Contribucion de los isotopos de He al origen de los fluidos hidrotermales: aplicacion al estudio de las mineralizaciones de fluorita de Asturias (N de Espana) (Author) 24 refs.

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez, V.; Martin-Crespo, T.; Vindel, E.; Corbella, M.; Cardellach, E.

    2010-07-01

    Helium isotopes have been measured in fluorite and sulphides in order to obtain conclusive means of assessing the involvement of mantle and crustally derived volatiles in F-Ba deposits from Asturias (N of Spain). Fluorite mineralizations are hosted in Mesozoic (Permotriassic) and Paleozoic age rocks. Mineralization is composed of fluorite, barite, calcite, dolomite, quartz and sulphides, and shares the characteristics of most Mississippi Valley Type (MVT) deposits associated with rifting events related to the opening of the Atlantic Ocean. The 3{sup H}e/4{sup H}e values of the Asturias ore fluids ({<=} 0,1 Ra) indicate a crustal fluid source and exclude the involvement of a mantle helium component. These values are consistent with the acceptance of the existing basinal model for MVT genesis and sedimentary brines migration, with the lack of igneous activity in the area contemporary with the mineralization, and also consistent with similar helium isotope data recorded in other fluorite deposits in Europe. (Author) 24 refs.

  17. Generalized adsorption isotherms for molecular and dissociative adsorption of a polar molecular species on two polar surface geometries: Perovskite (100) (Pm-3m) and fluorite (111) (Fm-3m)

    Science.gov (United States)

    Danielson, Thomas; Hin, Celine; Savara, Aditya

    2016-08-01

    Lattice based kinetic Monte Carlo simulations have been used to determine a functional form for the second order adsorption isotherms on two commonly investigated crystal surfaces: the (111) fluorite surface and the (100) perovskite surface which has the same geometric symmetry as the NaCl (100) surface. The functional form is generalized to be applicable to all values of the equilibrium constant by a shift along the pressure axis. Functions have been determined for estimating the pressure at which a desired coverage would be achieved and, conversely, for estimating the coverage at a certain pressure. The generalized form has been calculated by investigating the surface adsorbate coverage across a range of thermodynamic equilibrium constants that span the range 10-26 to 1013. The equations have been shown to be general for any value of the adsorption equilibrium constant.

  18. 湖南魏家隐伏型钨-萤石矿床控矿因素及成矿规律分析%Ore controlling factors and metallogenic regularity of concealed tungsten-fluorite deposits in Weijia of Hunan

    Institute of Scientific and Technical Information of China (English)

    2015-01-01

    魏家钨矿区位于南岭成矿带中段,为2010年国土资源大调查中新发现的矿产地。通过近年的工程控制,在钨矿体内新发现了萤石矿。本文在对矿床地质特征进行了进一步研究基础上,对矿床的控矿因素及成矿规律进行了总结分析,认为本矿区矿床类型为矽卡岩型钨、萤石矿床,矿体的空间展布主要受矿区内隐伏型层间破碎带和层间破碎带内充填的花岗斑岩脉共同控制。%Weijia tungsten mining area,a newly discovered mineral site in"The Grand Survey of Land and Re-sources of 2010",is located in the middle part of Nanling metallogenic belt.In recent years,fluorite ores were discovered in tungsten orebodies by ore-controlling projects.Based on further study on geological char-acteristics of the deposits,this paper summarizes and analyzes the ore-controlling factors and the metallogen-ic regularity of the deposits,and it shows that the deposits in this area are skarn-type tungsten-fluorite de-posits and the spatial distribution of the orebodies are primarily controlled by concealed interlayer fracture zone and granite porphyry veins filled with in the interlayer fracture zone.

  19. Defect structure of yttria-stabilized zirconia and its influence on the ionic conductivity at elevated temperatures

    DEFF Research Database (Denmark)

    Goff, J.P.; Hayes, W.; Hull, S.

    1999-01-01

    of neutron and x-ray diffraction data, including both Bragg and coherent diffuse scattering components, has identified three principal types of defects within the fluorite lattice. At low yttria concentrations (x... relatively few oxygen vacancies, causing the lattice to undergo a slight tetragonal distortion of the type observed in the tetragonal phase of (ZrO2)(1-x)(Y2O3)(x) at x anion sites in the (111) fluorite...... directions, with a cation located between them and extensive relaxations of the surrounding nearest-neighbor cations and anions. As the yttria content increases, these (111) vacancy Fairs pack together in (112) directions to form aggregates, whose short-range defect structure resembles the long-range crystal...

  20. Near-edge x-ray absorption fine-structure study of ion-beam-induced phase transformation in Gd2(Ti1-yZry)2O7

    Science.gov (United States)

    Nachimuthu, P.; Thevuthasan, S.; Shutthanandan, V.; Adams, E. M.; Weber, W. J.; Begg, B. D.; Shuh, D. K.; Lindle, D. W.; Gullikson, E. M.; Perera, R. C. C.

    2005-02-01

    The structural and electronic properties of Gd2(Ti1-yZry)2O7 (y =0-1) pyrochlores following a 2.0-MeV Au2+ ion-beam irradiation (˜5.0×1014Au2+/cm2) have been investigated by Ti2p and O1s near-edge x-ray absorption fine structure (NEXAFS). The irradiation of Gd2(Ti1-yZry)2O7 leads to the phase transformation from the ordered pyrochlore structure (Fd3m) to the defect fluorite structure (Fm3m) regardless of Zr concentration. Irradiated Gd2(Ti1-yZry)2O7 with y ⩽0.5 are amorphous, although significant short-range order is present. Contrasting to this behavior, compositions with y ⩾0.75 retain crystallinity in the defect fluorite structure following irradiation. The local structures of Zr4+ in the irradiated Gd2(Ti1-yZry)2O7 with y ⩾0.75 determined by NEXAFS are the same as in the cubic fluorite-structured yttria-stabilized zirconia (Y -ZrO2), thereby providing conclusive evidence for the phase transformation. The TiO6 octahedra present in Gd2(Ti1-yZry)2O7 are completely modified by ion-beam irradiation to TiOx polyhedra, and the Ti coordination is increased to eight with longer Ti -O bond distances. The similarity between cation sites and the degree of disorder in Gd2Zr2O7 facilitate the rearrangement and relaxation of Gd, Zr, and O ions/defects. This inhibits amorphization during the ion-beam-induced phase transition to the radiation-resistant defect fluorite structure, which is in contrast to the ordered Gd2Ti2O7.

  1. Synthesis of the Nanotublar Cubic Fluorite CeO2%纳米管状结构立方萤石型CeO2的合成

    Institute of Scientific and Technical Information of China (English)

    杨儒; 郭亮

    2004-01-01

    低温水热条件下,Ce4+离子经尿素水解均匀沉淀,在十八胺分子模板导向下形成了多层有序排列的纳米管状结构的立方萤石型CeO2,采用粉末X射线衍射(PXRD)、透射电镜(TEM)、高分辨透射电镜(HRTEM)以及选区电子衍射(SEAD)等手段对产物进行了表征.结果表明,该结构是由单根外、内径分别为10~20 nm、5~6 am左右的纳米管有序排列形成的纳米管束构成,且产物具有结晶性良好的立方萤石型CeO2晶体结构.在管束的生长过程中,反应体系首先形成单根纳米管,继而管与管之间又相互缔合生长成多层有序排列的纳米管束.控制尿素的水解,获得了不同pH值下的反应产物,发现反应体系pH值在5~6之间时产物为立方萤石型CeO2、6~8时为立方萤石型CeO2与六方型Ce(OH)CO3的混合物、大于8则为六方型Ce(OH)CO3.%Under hydrothermal condition,nitrate cerium(IV) was used as a cerium source,octadecylamine (C18H37NH2)as the molecular template and urea as a precipitating agent, and the hierarchically well-aligned nanotublar bunches of the cubic fluorite ceria were successfully synthesized.The materials have been characterized by Powder X-ray diffraction (PXRD),transmission electron microscopy (TEM),high-resolution transmission electron microscopy (HRTEM)and the selected area electron diffraction (SAED).The products exhibited the hierarchically well-aligned nanotublar bunch which was composed of single nanotube with outer and inner diameter 10~20 and 5~6 nm. The growth process of nanotublar hunches was monitored.Firstly, the separated nanotube appeared in the reaction system. Subsequently, the separated nanotubes integrated into the hierarchically well-aligned nanotublar bunch each other. In addition, the products have different crystalline phase and composition ad increasing the final pH value of reaction system; And when the final pH values of reaction system were at 5~6,6~8 and >8 respectively, the

  2. Crystal structure of the Fe-member of usovite

    Directory of Open Access Journals (Sweden)

    Matthias Weil

    2015-06-01

    Full Text Available Crystals of the title compound, with the idealized composition Ba2CaFeAl2F14, dibarium calcium iron(II dialuminium tetradecafluoride, were obtained serendipitously by reacting a mixture of the binary fluorides BaF2, CaF2 and AlF3 in a leaky steel reactor. The compound crystallizes in the usovite structure type (Ba2CaMgAl2F14, with Fe2+ cations replacing the Mg2+ cations. The principal building units are distorted [CaF8] square-antiprisms (point group symmetry 2, [FeF6] octahedra (point group symmetry -1 and [AlF6] octahedra that are condensed into undulating 2∞[CaFeAl2F14]4− layers parallel (100. The Ba2+ cations separate the layers and exhibit a coordination number of 12. Two crystal structure models with a different treatment of the disordered Fe site [mixed Fe/Ca occupation, model (I, versus underoccupation of Fe, model (II], are discussed, leading to different refined formulae Ba2Ca1.310 (15Fe0.690 (15Al2F14 [model (I] and Ba2CaFe0.90 (1Al2F14 [model (II].

  3. Interplay of structural, optical and magnetic properties in Gd doped CeO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Soni, S.; Dalela, S., E-mail: sdphysics@rediffmail.com [Department of Pure & Applied Physics, University of Kota, Kota-324007, Rajasthan (India); Kumar, Sudish [Department of Physics, Mohan Lal Sukhadia University, Udaipur, Rajasthan (India); Meena, R. S. [National Physical Laboratory, Pusa, New-Delhi (India); Vats, V. S. [Department of Physics, Govt. College, Dhaliara (India)

    2015-06-24

    In this research wok systematic investigation on the synthesis, characterization, optical and magnetic properties of Ce{sub 1-x}Gd{sub x}O{sub 2} (where x=0.02, 0.04, 0.06, and 0.10) synthesized using the Solid-state method. Structural, Optical and Magnetic properties of the samples were investigated by X-ray diffraction (XRD), UV-VIS-NIR spectroscopy and VSM. Fluorite structure is confirmed from the XRD measurement on Gd doped CeO{sub 2} samples. Magnetic studies showed that the Gd doped polycrystalline samples display room temperature ferromagnetism and the ferromagnetic ordering strengthens with the Gd concentration.

  4. The modulated structure of Co3Al4Si2: incommensurability and Co-Co interactions in search of filled octadecets.

    Science.gov (United States)

    Fredrickson, Rie T; Fredrickson, Daniel C

    2013-03-18

    Incommensurate modulations are increasingly being recognized as a common phenomenon in solid-state compounds ranging from inorganic materials to molecular crystals. The origins of such modulations are often mysterious, but appear to be as diverse as the compounds in which they arise. In this Article, we describe the crystal structure and bonding of Co3Al4Si2, the δ phase of the Co-Si-Al system, whose modulated structure can be traced to a central concept of inorganic chemistry: the 18 electron rule. The structure is monoclinic, conforming to the 3 + 1D superspace group C/2m(0β0)s0. The basis of the crystal structure is a rod packing of columns of the fluorite (CaF2) type, a theme that is shared by the recently determined structure of Fe8Al(17.4)Si(7.6). The columns are arranged into sheets, within which the fluorite structure's primitive cubic network of Si/Al atoms continues uninterrupted from column to column. Between the sheets, layers of interstitial Si/Al atoms occur, some of which are arranged with a periodicity incommensurate with that of the fluorite-type columns. Strong modulations in the interstitial layers result. Electronic structure calculations, using a DFT-calibrated Hückel model on a commensurate approximate structure, reveal that the complex pattern of atoms within these interstitial layers serves to distribute Si/Al atoms around the Co atoms in order to reach 18 electron counts (filled octadecets). Central to this bonding scheme is the covalent sharing of electron pairs between Co atoms. The shared electron pairs occupy orbitals that are isolobal to classical Co-Co σ and π bonds, but whose stability is tied to multicenter character involving bridging Si/Al atoms. Through these features, Co3Al4Si2 expands the structural and electronic manifestations of the 18 electron rule in solid-state inorganic compounds.

  5. 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

  6. The Crystal Structure of Thorium and Zirconium Dihydrides by X-ray and Neutron Diffraction

    Science.gov (United States)

    Rundle, R.E.; Shull, C.G.; Wollan, E.O.

    1951-04-20

    Thorium forms a tetragonal lower hydride of composition ThH{sub 2}. The hydrides ThH{sub 2}, ThD{sub 2}, and ZrD{sub 2} have been studied by neutron diffraction in order that hydrogen positions could be determined. The hydrides are isomorphous, and have a deformed fluorite structure. Metal-hydrogen distances in thorium hydride are unusually large, as in UH{sub 3}. Thorium and zirconium scattering amplitudes and a revised scattering amplitude for deuterium are reported.

  7. Epitaxial crystals of Bi2Pt2O7 pyrochlore through the transformation of δ–Bi2O3 fluorite

    Directory of Open Access Journals (Sweden)

    Araceli Gutiérrez–Llorente

    2015-03-01

    Full Text Available Bi2Pt2O7 pyrochlore is thought to be one of the most promising oxide catalysts for application in fuel cell technology. Unfortunately, direct film growth of Bi2Pt2O7 has not yet been achieved, owing to the difficulty of oxidizing platinum metal in the precursor material to Pt4+. In this work, in order to induce oxidation of the platinum, we annealed pulsed laser deposited films consisting of epitaxial δ–Bi2O3 and co-deposited, comparatively disordered platinum. We present synchrotron x-ray diffraction results that show the nonuniform annealed films contain the first epitaxial crystals of Bi2Pt2O7. We also visualized the pyrochlore structure by scanning transmission electron microscopy, and observed ordered cation vacancies in the epitaxial crystals formed in a bismuth-rich film but not in those formed in a platinum-rich film. The similarity between the δ–Bi2O3 and Bi2Pt2O7 structures appears to facilitate the pyrochlore formation. These results provide the only route to date for the formation of epitaxial Bi2Pt2O7.

  8. Low temperature synthesis of fluorite-type Ce-based oxides of composition Ln₂Ce₂O₇ (Ln = Pr, Nd and Eu): photodegradation and Luminescence studies

    Indian Academy of Sciences (India)

    M MALATHI; K SREENU; GUNDEBOINA RAVI; P VIJAYA KUMAR; CH SUDHAKAR REDDY; RAVINDER GUJE; RADHA VELCHURI; M VITHAL

    2017-08-01

    In this work, we have studied the structural behavior of Fluortie-type (F-type) Ce-based oxides of compositions Ln₂Ce₂O₇ (Ln = Pr, Nd and Eu). F-type oxides can be considered as multi-functional materials due to the deficiency of anions. Pr₂Ce₂O₇ (PCO), Nd₂Ce₂O₇ (NCO) and Eu₂Ce₂O₇ (ECO) were prepared by ethylene glycol-assisted sol–gel method. The structural investigation of these oxides was carried out by Powder XRD and Rietveld refinement. All the materials were found to crystallize in the cubic lattice with space group $Fm\\bar{3}m$. Raman spectra of these materials are reliable with their XRD data. The morphology and bandgap energy of all the samples were obtained from SEM and KM plot, respectively. The visible light photocatalytic performance of these oxides was examined against the degradation of methylene blue under ambient conditions. The photoluminescence property of the rare earth ionswas also studied, and the color coordinates were calculated using CIE 1931 chromaticity.

  9. Determination of enrichment processes and the concentrations of radon in underground mines of fluorite and coal in Santa Catarina state: criteria for evaluation of radiological risks; Determinacao dos processos de enriquecimento e das concentracoes de Radonio em minas subterraneas de fluorita e carvao do estado de Santa Catarina: criterios para avaliacao dos riscos radiologicos

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Carlos Eduardo Lima dos

    2008-07-01

    The inhalation of radon present in underground mines can imply in the deposition of its descendent in the lungs, which may cause harm to the lungs tissues and induce cancer. Concentration of radon not greater than 500 Bq/m3 in the environment of underground mines is considered to be acceptable internationally and concentrations above 1500 Bq/m3 require protective measures for the miners. The objectives of this research work are to determine the enrichment processes and the concentrations of radon in air, as well as the resulting doses due to the presence of this radionuclide in three underground mines of fluorite and three underground mines of coal in the State of Santa Catarina. The concentration of radon was measured employing two types of detectors of nuclear tracks (SSNTD), the LEXAN and the CR-39. This detection method consists in counting, with the help of a microscope, tracks resulting from the interaction of alpha particles with the film, due to the penetration of Rn-222 in the interior of the detector chamber and its decaying process. Contents of radium in collected samples of rocks, minerals and underground water were determined and compared with the corresponding radon concentration found in the underground air. It was observed that the coal mines showed low concentrations of radon, which can be explained by the low concentration of radium in rocks (sandstones and siltites in the footwall and hang wall) and in the coal that composes the mining environment or, yet still, due to the good ventilation system. The average dose to the workers of the coal mines was estimated as 0.7 mSv/a, value inferior to the limit of 1 mSv/a established by the Brazilian Nuclear Energy Commission (CNEN) for members of the public, and corresponding to a risk of fatal cancer after 50 years of work under this condition of 0.2%. On the other hand, the fluorite mines showed much higher concentrations of radon and superior to 1000 Bq/m3. The inefficiency of the ventilation system

  10. Determination of enrichment processes and radon concentration in underground mines of fluorite and coal in Santa Catarina state: criteria for radiation risk assessment; Determinacao dos processos de enriquecimento e das concentracoes de radonio em minas subterraneas de fluorita e carvao do estado de Santa Catarina: criterios para avaliacao dos riscos radiologicos

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Carlos Eduardo Lima dos

    2008-07-01

    The inhalation of radon present in underground mines can imply in the deposition of its descendants in the lungs, which may cause harm to the lungs tissues and induce cancer. Concentration of radon not greater than 500 Bq/m{sup 3} in the environment of underground mines is considered to be acceptable internationally and concentrations above 1500 Bq/m{sup 3} require protective measures for the miners. The objectives of this research work are to determine the enrichment processes and the concentrations of radon in air, as well as the resulting doses due to the presence of this radionuclide in three underground mines of fluorite and three underground mines of coal in the State of Santa Catarina. The concentration of radon was measured employing two types of detectors of nuclear tracks (SSNTD), the LEXAN and the CR-39. This detection method consists in counting, with the help of a microscope, tracks resulting from the interaction of alpha particles with the film, due to the penetration of Rn-222 in the interior of the detector chamber and its decaying process. Contents of radium in collected samples of rocks, minerals and underground water were determined and compared with the corresponding radon concentration found in the underground air. It was observed that the coal mines showed low concentrations of radon, which can be explained by the low concentration of radium in rocks (sandstones and siltites in the foot wall and hang wall) and in the coal that composes the mining environment or, yet still, due to the good ventilation system. The average dose to the workers of the coal mines was estimated as 0.7 mSv/a, value inferior to the limit of 1 mSv/a established by the Brazilian Nuclear Energy Commission (CNEN) for members of the public, and corresponding to a risk of fatal cancer after 50 years of work under this condition of 0.2%. On the other hand, the fluorite mines showed much higher concentrations of radon and superior to 1000 Bq/m{sup 3}. The inefficiency of the

  11. Characterizing the relationship between hyperstoichiometry, defect structure and local corrosion kinetics of uranium dioxide

    Energy Technology Data Exchange (ETDEWEB)

    He Heming; Qin, Z. [Department of Chemistry, University of Western Ontario, 1151 Richmond Street, London, Ontario, N6A 5B7 (Canada); Shoesmith, D.W., E-mail: dwshoesm@uwo.c [Department of Chemistry, University of Western Ontario, 1151 Richmond Street, London, Ontario, N6A 5B7 (Canada)

    2010-12-15

    The ability of the UO{sub 2} fluorite structure to accommodate large amounts of interstitial oxygen in various lattice sites leads to the formation of hyper-stoichiometric phases. The defect structures occurring in hyper-stoichiometric UO{sub 2+x} over the range 0.02 {<=} x {<=} 0.1 have been characterized by SEM/EDX and Raman analyses. The results demonstrate that as the nominal stoichiometry increases from 2.002 to 2.1, the diversity of defective structures existing on the UO{sub 2+} surface also increases. Scanning electrochemical microscopy (SECM) measurements combined with a theoretical model were used to determine the rate constant for the reduction of the redox mediator ferrocene methanol, acting as a cathodic oxidant to corrode the four UO{sub 2+x} specimens. The rate constant was found to vary with location on the surface. Stoichiometric locations, with a well defined fluorite structure, exhibited very low corrosion rates. Higher rates were observed at more non-stoichiometric locations with the highest rates being obtained on locations exhibiting tetragonal distortions as their composition approached UO{sub 2.33}. The distribution of rates increases with the degree of nominal non-stoichiometry as the diversity of microstructures existing on the UO{sub 2+x} surface increases.

  12. Hydrothermally synthesized barium fluoride nanocubes for thermoluminescence dosimetry

    Science.gov (United States)

    Bhadane, Mahesh S.; Dahiwale, S. S.; Bhoraskar, V. N.; Dhole, S. D.

    2016-05-01

    In this work, we report a hydrothermally synthesized Dy doped BaF2 (BaF2:Dy) nanocubes and its Thermoluminescence studies. The synthesized BaF2:Dy samples was found to posses FCC structure and having average size ~ 60-70 nm, as revealed through X-Ray Diffraction. Cubical morphology having size ~90 nm was observed from TEM analysis. The 60Co γ- ray irradiated BaF2:Dy TL dosimetric experiments shows a pre-dominant single glow peak at 153 °C, indicating a single level trap present as a metastable state. Furthermore, BaF2:Dy nanophosphor shows a sharp linear response from 10 Gy to 3 kGy, thus it can be applicable as a gamma dosimeter.

  13. Site distortions created by the stereoactive lone pair of Tin(II) in highly symmetric structures

    Science.gov (United States)

    Dénès, Georges; Madamba, M. Cecilia; Merazig, Hocine; Muntasar, Abdualhafed; Zhu, Zhimeng

    2016-10-01

    Several fluoride compounds containing divalent tin that have a fluorite (CaF2-type) unit cell have been prepared and studied. Some are stoichiometric compounds while others are solid solutions. The cubic symmetry of the unit-cell (no lattice distortion and no superstructure) and the unique metal ion site of the fluorite structure make it that tin and the other metal have to be disordered on the normal metal site of the fluorite unit-cell. However, that site has the m3m-Oh point symmetry, and the metal ion is located in the center of a cube having fluoride ions in all its corners. Therefore, the same coordination should apply to tin. However, tin(II) possesses a non-bonding pair of electrons called a "lone pair", and in order for tin(II) to have a cubic symmetry, its lone pair has to be located on the unhybridized 5s orbital, that is spherical and thus does not distort the coordination. In such a case, the lone pair is said to be "non-stereoactive". This would make tin present in the form of the Sn2+ stannous ion, and therefore Sn-F bonding must be ionic. However, tin(II) fluorides are known to be always covalent with a hybridized lone pair on tin, which has therefore a reduced coordination number and therefore a highly distorted polyhedron of coordination. Such a hybridized lone pair is said to be "stereoactive". Tin-119 Mössbauer spectroscopy was used to probe the bonding type and it showed that bonding is covalent, the lone pair is hybridized and the tin coordination is dramatically distorted. A model based on a double disorder was made that accounts for the apparent contradiction between the crystallographic and the Mössbauer results.

  14. Structural characterization of mixed uranium-plutonium co-precipitates and oxides synthesized by oxalic co-conversion route

    Energy Technology Data Exchange (ETDEWEB)

    Arab-Chapelet, B.; De Bruycker, F.; Picart, S.; Leturcq, G.; Grandjean, S. [Laboratoire de Chimie des Actinides, CEA Valrho, bat 399, BP17171, 30207 Bagnols sur Ceze cedex (France)

    2008-07-01

    In this study, mixed uranium(IV)-plutonium(III) oxalate co-precipitates with Pu/(U+Pu) molar ratio equal to 29 and 45% were synthesized and characterized by X-ray powder diffraction (XRD) and Scanning Electron Microscopy (SEM). The thermal conversion step of these co-precipitates into oxide was carried out under argon flow up to 700 deg. C leading to mixed oxides. The structural investigation on these oxides indicates the formation of (U,Pu)O{sub 2} fluorite-type solid solution characterized by a very homogeneous distribution of plutonium and uranium, a controlled oxygen stoichiometry and well-defined morphology of particles. (authors)

  15. Percolating hierarchical defect structures drive phase transformation in Ce1−xGdxO2−x/2: a total scattering study

    Directory of Open Access Journals (Sweden)

    Marco Scavini

    2015-09-01

    Full Text Available A new hierarchical approach is presented for elucidating the structural disorder in Ce1−xGdxO2−x/2 solid solutions on different scale lengths. The primary goal of this investigation is to shed light on the relations between the short-range and the average structure of these materials via an analysis of disorder on the mesocopic scale. Real-space (pair distribution function and reciprocal-space (Rietveld refinement and microstructure probing analysis of X-ray powder diffraction data and electron spin resonance (ESR investigations were carried out following this approach. On the local scale, Gd- and Ce-rich droplets (i.e. small regions a few ångströms wide form, exhibiting either a distorted fluorite (CeO2 or a C-type (Gd2O3 structure in the whole compositional range. These droplets can then form C-type nanodomains which, for Gd concentrations xGd ≤ 0.25, are embedded in the fluorite matrix. At the site percolation threshold pC for a cubic lattice (xGd = pC ≃ 0.311, C-type nanodomains percolate inside each crystallite and a structural phase transformation is observed. When this occurs, the peak-to-peak ESR line width ΔHpp shows a step-like behaviour, which can be associated with the increase in Gd–Gd dipolar interactions. A general crystallographic rationale is presented to explain the fluorite-to-C-type phase transformation. The approach shown here could be adopted more generally in the analysis of disorder in other highly doped materials.

  16. Raman micro-spectroscopy of UOX and MOX spent nuclear fuel characterization and oxidation resistance of the high burn-up structure

    Science.gov (United States)

    Jegou, C.; Gennisson, M.; Peuget, S.; Desgranges, L.; Guimbretière, G.; Magnin, M.; Talip, Z.; Simon, P.

    2015-03-01

    Raman micro-spectroscopy was applied to study the structure and oxidation resistance of UO2 (burnup 60 GWd/tHM) and MOX (burnup 47 GWd/tHM) irradiated fuels. The Raman technique, adapted to working under extreme conditions, enabled structural information to be obtained at the cubic micrometer scale in various zones of interest within irradiated fuel (central and zones like the Rim for UOX60, and the plutonium-enriched agglomerates for MOX47 characterized by a high burn-up structure), and the study of their oxidation resistance. As regards the structural information after irradiation, the spectra obtained make up a set of data consistent with the systematic presence of the T2g band characteristic of the fluorite structure, and of a triplet band located between 500 and 700 cm-1. The existence of this triplet can be attributed to the presence of defects originating in changes to the fuel chemistry occurring in the reactor (presence of fission products) and to the accumulation of irradiation damage. As concerns the oxidation resistance of the different zones of interest, Raman spectroscopy results confirmed the good stability of the restructured zones (plutonium-enriched agglomerates and Rim) rich in fission products compared to the non-restructured UO2 grains. A greater structural stability was noticed in the case of high plutonium content agglomerates, as this element favors the maintenance of the fluorite structure.

  17. Crystal structure of {alpha} Triple-Prime -(Zn{sub 1-x}Cd{sub x}){sub 3}As{sub 2} (x = 0.26)

    Energy Technology Data Exchange (ETDEWEB)

    Volodina, G. F., E-mail: volodinagal@rambler.ru [Academy of Sciences of Moldova, Institute of Applied Physics (Moldova, Republic of); Zakhvalinskii, V. S. [Belgorod State University (Russian Federation); Kravtsov, V. Kh. [Academy of Sciences of Moldova, Institute of Applied Physics (Moldova, Republic of)

    2013-07-15

    Single crystals of the {alpha} Triple-Prime -phase of (Zn{sub 1-x}Cd{sub x}){sub 3}As{sub 2} solid solution (x = 0.26) have been prepared and investigated by X-ray diffraction analysis. The tetragonal unit-cell parameters are found to be a = b = 8.5377(2) A, c = 24.0666(9) A, sp. gr. I4{sub 1}/amd, Z = 16. Zn and Cd atoms in the crystal statistically occupy three symmetrically independent positions in the mirror planes and are tetrahedrally coordinated by arsenic atoms. (Zn,Cd) tetrahedra share edges to form a three-dimensional structure framework. The {alpha} Triple-Prime -phase is geometrically related to the fluorite structure. The character of arrangement of tetrahedral vacancies in fluorite-like unit cells is revealed. Chains of tetrahedral vacancies form microchannels oriented parallel the a and b axes, which pierce the three-dimensional structure framework at different levels along the c axis. The structure of {alpha} Double-Prime -Cd{sub 3}As{sub 2} crystals is found to be similar to that of {alpha} Triple-Prime -(Zn{sub 0.74}Cd{sub 0.26}){sub 3}As{sub 2}.

  18. Structural, electronic, elastic and superconducting properties of noble metal nitrides MN{sub 2} (M = Ru, Rh, Pd)

    Energy Technology Data Exchange (ETDEWEB)

    Puvaneswari, S. [Department of Physics, E.M.G. Yadava Women' s College, Madurai, Tamilnadu 625 014 (India); Rajeswarapalanichamy, R., E-mail: rrpcaspd2003@gmail.com [Department of Physics, N.M.S.S. Vellaichamy Nadar College, Madurai, Tamilnadu 625019 (India); Sudha Priyanga, G. [Department of Physics, N.M.S.S. Vellaichamy Nadar College, Madurai, Tamilnadu 625019 (India)

    2015-02-01

    The structural stability, electronic structure, elastic and superconducting properties of noble metal nitrides MN{sub 2} (M = Ru, Rh, Pd) are investigated in tetragonal (P4/mbm), fluorite (Fm3m), orthorhombic (Pnnm), pyrite (Pa-3) and hexagonal (P6/mmm) phases using first principles calculations. The calculated lattice parameters are in good agreement with other theoretical results. Among the considered structures, RhN{sub 2} and PdN{sub 2} are found to be most stable in tetragonal structure, whereas RuN{sub 2} is stable in fluorite structure. A sequence of structural phase transition is predicted under high pressure in these metal nitrides. The electronic structure reveals that these nitrides are metallic. These metal nitrides are found to be covalent, ionic and metallic in the stable phase. The observations show that these metal nitrides are mechanically stable at ambient condition. The superconducting transition temperatures for RuN{sub 2}, RhN{sub 2} and PdN{sub 2} are found to be 1.65 K, 5.01 K and 8.7 K respectively. - Highlights: • Electronic, structural and elastic properties of RuN{sub 2}, RhN{sub 2} and PdN{sub 2} are studied. • A pressure induced structural phase transition is predicted. • Electronic structure reveals that these materials exhibit metallic behavior. • High bulk modulus indicates that RuN{sub 2}, RhN{sub 2} and PdN{sub 2} are superhard materials. • Superconducting temperature values are reported.

  19. Phonon spectrum, electron spin-lattice relaxation and spin-phonon coupling of Cu2+ ions in BaF2 crystal

    Science.gov (United States)

    Hoffmann, Stanislaw K.; Lijewski, Stefan

    2015-03-01

    Electron spin-lattice relaxation rate is determined by electron spin echo method in temperature range 4-60 K. The Raman relaxation processes dominate and its theory is outlined in a form suitable for calculations of relaxation rate using real phonon spectrum. A few approximations have been considered: when phonon spectrum and Debye temperature are not available; when Debye temperature is available but phonon spectrum is not; and when spin-phonon coupling is known. All these approximations use the Debye model of phonons and give a non-satisfactory description the temperature dependence of the relaxation rate. A perfect description of experimental results is obtained when real phonon spectrum is considered. The value of the spin-phonon coupling parameter was determined as G = = 1362cm-1 . This value is discussed by a comparison with G-values published for various ions and crystals.

  20. Crystal structures of a pentavalent bismuthate, SrBi2O6 and a lead bismuth oxide (Pb1/3Bi2/3O1.4

    Directory of Open Access Journals (Sweden)

    Nobuhiro Kumada

    2014-06-01

    Full Text Available The crystal structures of a pentavalent bismuthate, SrBi2O6 with the PbSb2O6-type structure and a lead bismuth oxide, (Pb1/3Bi2/3O1.4 with the fluorite-type structure were refined by using neutron diffraction data. The final R-factors were Rwp = 4.49, Rp = 3.46, RI = 4.50 and RF = 1.70% for SrBi2O6 and Rwp = 5.04, Rp = 3.93, RI = 5.47 and RF = 4.26% for (Pb1/3Bi2/3O1.4. SrBi2O6 prepared from NaBiO3·1.4H2O is the first example of the bismuthate with the PbSb2O6-type structure. The fluorite-type lead bismuth oxide, (Pb1/3Bi2/3O1.4 was obtained by heating the PbSb2O6-type lead bismuthate, PbBi2O5.9·H2O which was prepared also from NaBiO3·1.4H2O.

  1. Highly stable, mesoporous mixed lanthanum-cerium oxides with tailored structure and reducibility

    Energy Technology Data Exchange (ETDEWEB)

    Liang, Shuang; Broitman, Esteban; Wang, Yanan; Cao, Anmin; Veser, Goetz

    2011-05-01

    Pure and mixed lanthanum and cerium oxides were synthesized via a reverse microemulsion-templated route. This approach yields highly homogeneous and phase-stable mixed oxides with high surface areas across the entire range of La:Ce ratios from pure lanthana to pure ceria. Surprisingly, all mixed oxides show the fluorite crystal structure of ceria, even for lanthanum contents as high as 90%. Varying the La:Ce ratio not only allows tailoring of the oxide morphology (lattice parameter, pore structure, particle size, and surface area), but also results in a fine-tuning of the reducibility of the oxide which can be explained by the creation of oxygen vacancies in the ceria lattice upon La addition. Such finely controlled syntheses, which enable the formation of stable, homogeneous mixed oxides across the entire composition range, open the path towards functional tailoring of oxide materials, such as rational catalyst design via fine-tuning of redox activity.

  2. Structure and mechanical properties of swift heavy ion irradiated tungsten-bearing delta-phase oxides Y{sub 6}W{sub 1}O{sub 12} and Yb{sub 6}W{sub 1}O{sub 12}

    Energy Technology Data Exchange (ETDEWEB)

    Tang, M., E-mail: mtang@lanl.gov [Materials Science and Technology Division, Mail-Stop G755, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Wynn, T.A. [Materials Physics and Application Division, Mail-Stop K771, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Patel, M.K.; Won, J. [Materials Science and Technology Division, Mail-Stop G755, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Monnet, I. [CIMAP, CEA-CNRS-ENSICAEN-Universite de Caen Normandie, Bd Henri Becquerel, BP 5133, F-14070, Caen Cedex 5 (France); Pivin, J.C. [Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse, CNRS-IN2P3-Universite Paris Sud, UMR 8609, Bat. 108, 91405 Orsay (France); Mara, N.A. [Materials Physics and Application Division, Mail-Stop K771, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Sickafus, K.E. [Materials Science and Technology Division, Mail-Stop G755, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2012-06-15

    We report on the relationship between structure and mechanical properties of complex oxides whose structures are derivatives of fluorite, following irradiation with swift heavy ion (92 MeV Xe) which approximately simulates fission product irradiation, where the electronic energy loss dominates. The two compounds of interest in this paper are Y{sub 6}W{sub 1}O{sub 12} and Yb{sub 6}W{sub 1}O{sub 12}. These compounds possess an ordered, fluorite derivative crystal structure known as the delta ({delta}) phase, a rhombohedral structure belonging to space group R3{sup Macron}. Structural changes induced by irradiation were examined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD investigations indicated an irradiation-induced amorphization in these compounds. This result is consistent with our previous study on Y{sub 6}W{sub 1}O{sub 12} under displacive radiation environment in which the nuclear energy loss is dominant. High resolution TEM also revealed that individual ion tracks was amorphized. The mechanical properties of both irradiated compounds, were determined by cross-sectional nano-indentation measurements as a function of ion penetration depth. The decreases in Young's modulus, E, and hardness, H (both by about 40% at the irradiated surface) suggest amorphization beyond simple defect accumulation occurs under this irradiation condition.

  3. 酸化水玻璃在墨西哥某高钙型萤石矿选矿试验中的作用%The Effect of Acidized Water Glass on Beneficiation Test of Mexico High Calcium Type Fluorite Ore

    Institute of Scientific and Technical Information of China (English)

    周文波; 程杰; 冯齐; 宋少先

    2013-01-01

      采用酸化水玻璃作为墨西哥高钙型萤石矿浮选抑制剂,结果表明,浮选使用酸化水玻璃有利于尾矿矿浆中微细粒沉降,得到澄清回水,同时获得比现有方案更好的分选指标和更快的浮选速度,并能降低药剂消耗。%The flotation of Mexico high calcium type fluorite ore using acidized water glass (AWG) as depressant has been studied. The experimental results showed that the flotation with AWG could considerably improve the sedimentation of fine particles in tailing slurry and thus produce clean recycled water, furthermore, the new scheme achieved a better separation indexes and higher flotation rate than the actual scheme, and allowed a great saving on reagent cost.

  4. Fluorite Ce0.8Sm0.2O2δ porous layer coating to enhance the oxygen permeation behavior of a BaCo0.7Fe0.2Nb0.1O3δ mixed conductor

    Institute of Scientific and Technical Information of China (English)

    Tai-he Wang; Wei-jia Song; Rong Li; Qiang Zhen

    2016-01-01

    Fluorite Ce0.8Sm0.2O2-δ (SDC) nanopowder with a crystallite size of 15 nm was synthesized by a co-precipitation method. An SDC porous layer was coated onto a BaCo0.7Fe0.2Nb0.1O3-d (BCFN) mixed conductor to improve its oxygen transport behavior. The results show that the SDC-coated BCFN membrane exhibits a remarkably higher oxygen permeation flux (JO2) than the uncoated BCFN in the partial oxidation of coke oven gas (COG). The maximumJO2 value of the SDC-coated BCFN is 18.28 mL·min-1·cm-2 under a COG/air flux of 177 mL·min-1/353 mL·min-1 at 875°C when the thickness of the BCFN membrane is 1 mm; thisJO2 value is 23% higher than that of the uncoated BCFN membrane. This enhancement is likely because of the higher oxygen ionic conductivity of SDC, which supplies oxygen va-cancies and accelerates oxygen exchange on the membrane/coating layer/gas three-phase boundary.

  5. Fluorite Ce0.8Sm0.2O2- δ porous layer coating to enhance the oxygen permeation behavior of a BaCo0.7Fe0.2Nb0.1O3- δ mixed conductor

    Science.gov (United States)

    Wang, Tai-he; Song, Wei-jia; Li, Rong; Zhen, Qiang

    2016-06-01

    Fluorite Ce0.8Sm0.2O2- δ (SDC) nanopowder with a crystallite size of 15 nm was synthesized by a co-precipitation method. An SDC porous layer was coated onto a BaCo0.7Fe0.2Nb0.1O3- δ (BCFN) mixed conductor to improve its oxygen transport behavior. The results show that the SDC-coated BCFN membrane exhibits a remarkably higher oxygen permeation flux ({J_{{O_2}}}) than the uncoated BCFN in the partial oxidation of coke oven gas (COG). The maximum {J_{{O_2}}} value of the SDC-coated BCFN is 18.28 mL·min-1·cm-2 under a COG/air flux of 177 mL·min-1/353 mL·min-1 at 875°C when the thickness of the BCFN membrane is 1 mm; this {J_{{O_2}}} value is 23% higher than that of the uncoated BCFN membrane. This enhancement is likely because of the higher oxygen ionic conductivity of SDC, which supplies oxygen vacancies and accelerates oxygen exchange on the membrane/coating layer/gas three-phase boundary.

  6. 广西资源县某萤石矿矿山地质灾害危险性评估及防治对策%Geology disaster risk assessment and Prevention countermeasures about a fluorite ore mine in Ziyuan county of Guangxi province

    Institute of Scientific and Technical Information of China (English)

    蒋剑; 郑剑锋; 陈雪源

    2015-01-01

    Taking a fluorite mine in Ziyuan county of Guangxi as an example, with emphasis on the analysis of the mine geological disaster risk evaluation thoughts and basic methods, and the effective prevention and control coun-termeasures are put forward. In understanding mine basic situation and find out the mine geological environment background, on the basis of On the basis of comprehensive mining area topography and the characteristics of engi-neering activities of situation assessment and forecast of mine geology hazard assessment, and put forward the corre-sponding countermeasures.%以广西资源县某萤石矿山为例,重点介绍矿山地质灾害危险性评估的分析思路及基本方法,并提出有效的防控对策。在了解矿山基本情况和查明矿山地质环境背景的基础上,综合采矿场地形及工程活动特征,对矿山地质灾害进行现状评估和预测评估,并提出了相应的防治对策。

  7. Chemical expansion affected oxygen vacancy stability in different oxide structures from first principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Aidhy, Dilpuneet S.; Liu, Bin; Zhang, Yanwen; Weber, William J.

    2015-03-01

    We study the chemical expansion for neutral and charged oxygen vacancies in fluorite, rocksalt, perovskite and pyrochlores materials using first principles calculations. We show that the neutral oxygen vacancy leads to lattice expansion whereas the charged vacancy leads to lattice contraction. In addition, we show that there is a window of strain within which an oxygen vacancy is stable; beyond that range, the vacancy can become unstable. Using CeO2|ZrO2 interface structure as an example, we show that the concentration of oxygen vacancies can be manipulated via strain, and the vacancies can be preferentially stabilized. These results could serve as guiding principles in predicting oxygen vacancy stability in strained systems and in the design of vacancy stabilized materials.

  8. 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.

  9. Effects of Technical Conditions on Structure, Morphology and Crystalline Size of Nanocrystalline Nd-Doped Ceria Powders

    Institute of Scientific and Technical Information of China (English)

    Gao Yong; Wang Lingling; Liu Huangqing

    2004-01-01

    Nanocrystalline solid solution CeO2-Nd2O3 powders were prepared by low temperature combustion process.Special attention was paid to the influence of the glycine/metal ratio and calcination temperature on the powders phase structure, morphology and particle size.TG-DSC curves and XRD peaks of different glycine/metal ratio show that smaller particle size can be obtained with a slightly fuel-deficient ratio.XRD results indicate that the as-prepared powders are crystallized in a single fluorite structure.The crystalline size ranges from 9 to 24 nm, which increases with the increase of calcination temperature.The lower SEM images were characterized by the spongy and form-like microstructure of the powders.Organic agent may be gradually eliminated by high temperature calcination process.

  10. Jubilite: A 4-,8-connected Cubic Structural Pattern in Space Group Pm3

    Directory of Open Access Journals (Sweden)

    Eduardo A. Castro

    2005-05-01

    Full Text Available Abstract: In the course of investigating structural modifications of the 3-,4-connected net known as the Pt3O4 structure-type (waserite, a novel 4-,8-connected structure-type was discovered. This lattice is generated by replacing the 3-connected trigonal planar vertices of the Pt3O4 structure-type with 4-connected tetrahedral vertices, to achieve a structure which possesses a generic empirical formula of JK6L8. In such a topological modification, the four 3-fold axes of the parent cubic, Pm3n, Pt3O4 structure-type are retained. Thus the 4-connected tetrahedral vertices are oriented so as to preserve cubic symmetry in the resulting Pm3, JK6L8 (jubilite lattice. The unit cell contains a single 8-connected cubecentered vertex, six 4-connected distorted square planar vertices and eight 4-connected distorted tetrahedral vertices. It is a Wellsean structure with a Wells point symbol given by (4166484(42826(43838 and a Schläfli symbol of (53/4, 4.2667. This latter index reveals a decrease in the lattice’s polygonality and concomitant increase in the connectivity through the transformation from waserite to jubilite. The topology of the parent waserite lattice (Pt3O4 corresponds to that of the Catalan structures with the Wells point symbol (843(834, which has the Schläfli symbol (8, 3.4285. Finally, it can be seen that a sequence of structure-types starting with waserite (Pt3O4 and moving to jubilite (JK6L8 and finally to fluorite (CaF2 represents a continuous crystallographic structural transformation in which the symmetry and topology undergo concomitant changes from one structure-type (waserite to the other structure-types. The topology of the fluorite lattice, represented by the Wells point symbol (424(462, and the Schläfli symbol (4, 51/3, indicates a discontinuous topological transformation from the intermediate jubilite lattice; like the discontinuous topological transformation from Pt3O4 to JK6L8; in which the

  11. Determination of the structure of the cubic phase in high-ZrO{sub 2}Y{sub 2}O{sub 2}-ZrO{sub 2} alloys by CBED

    Energy Technology Data Exchange (ETDEWEB)

    McClellan, K.J.; Xiao, S.Q.; Lagerlof, K.P.D.; Heuer, A.H. [Case Western Reserve Univ., Cleveland, OH (United States)

    1993-06-20

    Convergent beam electron diffraction (CBED) was used to determine the space group of 9.9 and 18 mol% Y{sub 2}O{sub 3}-stabilized cubic ZrO{sub 2} (Y-CSZ) single crystals. The result (P43m space group) is different from the known tetragonal structure (P4{sub 2}/nmc space group) present in lower solute (3.2 mol% Y{sub 2}O{sub 3}) alloys, and the cubic structure (space group Fm3m) traditionally assumed for cubic ZrO{sub 2}. The oxygen sublattice of the cubic structure is distorted from Fm3m, relative to the cation sublattice, by displacements along the <111> directions. Computer simulations of the CBED patterns agree with experiment and suggest an anion displacement of {approximately}0.3 {Angstrom} from the (1/4,1/4,1/4) positions of the ideal fluorite structure.

  12. The effect of Gd doping on the atomic and electronic structure of HfO2 thin films.

    Science.gov (United States)

    Ketsman, Ihor; Sokolov, Andrei; Belashchenko, Kirill; Dowben, Peter; Losovyj, Yaroslav; Tang, Jinke; Wang, Zhenjun

    2008-03-01

    HfO2 is a promising oxide for many applications, including high-k gate dielectric for CMOS devices. In addition, Gd-doped HfO2 could lead to a dilute magnetic semiconductor and provide an efficient neutron detection medium due to huge neutron absorption cross section of Gd. Gd-doped HfO2 films deposited on both p-type and n-type silicon by PLD retain monoclinic phase at small doping levels, but can be stabilized in fluorite phase by increased doping [1]. At small doping levels, photoemission measurements indicate n-type character of the films as a result of overcompensation with oxygen vacancies. Depending on a doping level, the films form heterojunctions with good rectifying properties on n- or p-type silicon. Preliminary results show the potential ability of the formed diode structures to detect neutrons. [1] Ya.B.Losovyj, I.Ketsman et al.,APL, 91, 132908, (2007)

  13. Studies on Structural and Morphological Properties of Multidoped Ceria Ce0.8Nd0.0025Sm0.0025Gd0.005Dy0.095Y0.095O2-δ (x=0.2 as Solid Solutions

    Directory of Open Access Journals (Sweden)

    Marija Stojmenović

    2016-01-01

    Full Text Available The nanopowdery solid solutions of multidoped ceria Ce0.8Nd0.0025Sm0.0025Gd0.005Dy0.095Y0.095O2-δ (x=0.2 with the fluorite type crystal structure of CeO2 were synthesized for the first time. Two synthesis procedures were applied: the modified glycine-nitrate procedure (MGNP method and room temperature self-propagating reaction (SPRT method. All nanopowders were characterized by XRPD analysis, Raman spectroscopy, low temperature nitrogen physisorption, TEM, and SEM methods. According to the XRPD and Raman spectroscopy results, single phase solid solutions of fluorite structure were evidenced regardless of the number of dopants and synthesis procedure. Both XRPD and TEM were analyses evidenced nanometer particle dimensions. The SPRT method results in obtaining sample with higher specific surface area, smaller crystallite and particles sizes, and the same values of the lattice parameter in comparison to pure CeO2. Raman spectroscopy was confirmed to the oxygen vacancies introduced into the ceria lattice when Ce4+ ions were replaced with cations (dopants of lower valence state (3+, which may indicate the potential improvement of ionic conductivity. Additionally, the presence of oxygen vacancies in the lattice ceria, as well as very developed grain boundaries, gives a new possibility for potential application of obtained nanopowders in the area of room temperature ferromagnetism as spintronics.

  14. Studies on Structural and Morphological Properties of Multidoped Ceria Ce 0.8 Nd 0.0025 Sm 0.0025 Gd 0.005 Dy 0.095 Y 0.095 O 2 - δ ( x = 0.2 ) as Solid Solutions

    KAUST Repository

    Stojmenović, Marija

    2016-04-17

    The nanopowdery solid solutions of multidoped ceria Ce0.8Nd0.0025Sm0.0025Gd0.005Dy0.095Y0.095 () with the fluorite type crystal structure of CeO2 were synthesized for the first time. Two synthesis procedures were applied: the modified glycine-nitrate procedure (MGNP method) and room temperature self-propagating reaction (SPRT method). All nanopowders were characterized by XRPD analysis, Raman spectroscopy, low temperature nitrogen physisorption, TEM, and SEM methods. According to the XRPD and Raman spectroscopy results, single phase solid solutions of fluorite structure were evidenced regardless of the number of dopants and synthesis procedure. Both XRPD and TEM were analyses evidenced nanometer particle dimensions. The SPRT method results in obtaining sample with higher specific surface area, smaller crystallite and particles sizes, and the same values of the lattice parameter in comparison to pure CeO2. Raman spectroscopy was confirmed to the oxygen vacancies introduced into the ceria lattice when Ce4+ ions were replaced with cations (dopants) of lower valence state (3+), which may indicate the potential improvement of ionic conductivity. Additionally, the presence of oxygen vacancies in the lattice ceria, as well as very developed grain boundaries, gives a new possibility for potential application of obtained nanopowders in the area of room temperature ferromagnetism as spintronics.

  15. Nano-crystals of cerium–hafnium binary oxide: Their size-dependent structure

    Energy Technology Data Exchange (ETDEWEB)

    Raitano, Joan M. [Department of Applied Physics and Applied Mathematics, Materials Science and Engineering Program, Columbia University, New York, NY 10027 (United States); Khalid, Syed [National Synchrotron Light Source, Brookhaven National Laboratory, Upton, NY 11973 (United States); Marinkovic, Nebojsa [Chemical Engineering Department, Columbia University, 500 W 120th St, Mudd 801, New York, NY 10027 (United States); Chan, Siu-Wai, E-mail: sc174@columbia.edu [Department of Applied Physics and Applied Mathematics, Materials Science and Engineering Program, Columbia University, New York, NY 10027 (United States)

    2015-09-25

    Highlights: • (1 − x)CeO{sub 2}–xHfO{sub 2} was precipitated (0 < x < 1) and calcined in air. • For x ⩽ 0.14, crystallites ⩽140 nm in size exhibit only the fluorite structure. • This low hafnia solubility is attributable to no auto-reduction (Ce{sup 3+} = 0). • The low solubility is also due to the high temperature required for homogenization. • Coarsening is lessened as Hf{sup 4+} ions slow cation diffusion in these crystallites. - Abstract: Cerium oxide (CeO{sub 2}, “ceria”) and hafnium oxide (HfO{sub 2}, “hafnia”) were aqueously co-precipitated and subsequently calcined to allow for homogenization. The size of the (1−x)CeO{sub 2}–xHfO{sub 2} crystallites, determined by the Scherrer equation, varied from 140 nm for x = 0 to 15 nm for x = 0.73. For x ⩽ 0.14, only cubic structures are visible in X-ray diffractograms, and the lattice parameters are consistent with the values expected for structurally cubic solid solutions of hafnia in ceria. At x = 0.26, tetragonal and monoclinic phases nucleated with the former not being observed in the bulk phase diagram for ceria–hafnia. Therefore, the solubility limit of the cubic structure is between x = 0.14 and x = 0.26 for 40–61 nm crystallites, the sizes of these respective compositions. More specifically, for the 40 nm crystallites of x = 0.26 (1 − x)CeO{sub 2}–xHfO{sub 2}, 15% of the hafnia remains in a structurally cubic solid solution with ceria based on the observed cubic lattice parameter. The compositional domain for the cubic fluorite structure in this study is narrower than other nanostructured (1 − x)CeO{sub 2}–xHfO{sub 2} studies, especially studies with crystallite sizes less than 10 nm, but wider than observed in the bulk and helps to expand the size regime over which the relationship between crystallite size and phase stability is known. The extent of this cubic-structure domain is mainly attributable to the intermediate crystallite size and the roughly zero Ce{sup 3

  16. New Tl-based copper oxide containing double-MO 2-unit fluorite block: (Tl, Cu) Sr 2 (R, Ce) 3Cu 2O 11 (R: rare earth element)

    Science.gov (United States)

    Wada, Takahiro; Hamada, Kazuyuki; Ichinose, Ataru; Kaneko, Tetsuyuki; Yamauchi, H.; Tanaka, Shoji

    1991-05-01

    New Tl-based copper oxides. (Tl, Cu)Sr 2(R, Ce) 3Cu 2O 11 (R: rare earth element) (Tl-based “1232”), have been synthesized. These compounds have tetragonal unit cells with lattice constants approximately equal to a=3.8 Å and c=17.3 Å. A Rietveld analysis using X-ray powder diffraction data shows that the crystal structure of (Tl {4}/{5}Cu {1}/{5})Sr 2(Ho {1}/{3}Ce {2}/{3}) 3Cu 2O 11 consists of a double-MO 2-unit flouride block, i.e. [(Ho, Ce)O 2] 2 and a Tl-based “1212” block, i.e. (Tl, Cu)Sr 2(Ho, Ce)Cu 2O 7. The temperature dependences of the electrical resistivity for all of these compounds are semiconductive. However, these compounds are considered to be candidates for parent materials for new high- Tc superconductors.

  17. Theoretical study of the structural stability for fcc-CHx phases using density functional theory

    Directory of Open Access Journals (Sweden)

    M Dadsetani

    2011-09-01

    Full Text Available  Recently, a new carbon modification, namly n-diamond, have been reported, whose structure is still a matter of debate. It is important to note that the synthesis of n-diamond was carried out in the presence of hydrogen or methan. In this work we evaluate the structural stability of five fcc-CHx phases by means of first-principle calculation. The total energy is obtained as a function of the isotropic, tetragonal and rhombohedral deformations for the bulk structures. First, we analyze the C2H (cuprite, CH (zincblende, CH (rocksalt and CH2 (fluorite structures.It is found that the four systems show a minimum in the total energy for the isotropic and rhombohedral deformations, but are unstable against tetragonal deformation. In the second part, we explore the structural stability of CH2 in the pyrite structure. We find that CH2 (pyrite with the hydrogen atoms defined by the internal parameter u=0.35 and a lattice parameter of 3.766 Å is elastically stable, providing a possible explanation for the experimental observation of fcc-carbon in materials prepared in the presence of hydrogen or methan. In final, we calculate density of states, band structure and EELS spectrum of CH2 (pyrite and compare them with n-diamond.

  18. On the Sr1−xBaxFeO2F Oxyfluoride Perovskites: Structure and Magnetism from Neutron Diffraction and Mössbauer Spectroscopy

    Directory of Open Access Journals (Sweden)

    Crisanto A. García-Ramos

    2016-11-01

    Full Text Available Four oxyfluorides of the title series (x = 0.00, 0.25, 0.50, 0.75 have been stabilized by topotactic treatment of perovskite precursors Sr1−xBaxFeO3−δ prepared by soft-chemistry procedures, yielding reactive materials that can easily incorporate a substantial amount of F atoms at moderate temperatures, thus avoiding the stabilization of competitive SrF2 and BaF2 parasitic phases. XRD and Neutron Powder Diffraction (NPD measurements assess the phase purity and yield distinct features concerning the unit cell parameters’ variation, the Sr and Ba distribution, the stoichiometry of the anionic sublattice and the anisotropic displacement factors for O and F atoms. The four oxyfluorides are confirmed to be cubic in all of the compositional range, the unit cell parameters displaying Vergard’s law. All of the samples are magnetically ordered above room temperature; the magnetic structure is always G-type antiferromagnetic, as shown from NPD data. The ordered magnetic moments are substantially high, around 3.5 μB, even at room temperature (RT. Temperature-dependent Mössbauer data allow identifying Fe3+ in all of the samples, thus confirming the Sr1−xBaxFeO2F stoichiometry. The fit of the magnetic hyperfine field vs. temperature curve yields magnetic ordering TN temperatures between 740 K (x = 0.00 and 683 K (x = 0.75. These temperatures are substantially higher than those reported before for some of the samples, assessing for stronger Fe-Fe superexchange interactions for these specimens prepared by fluorination of citrate precursors in mild conditions.

  19. The structure and petrography of alkaline rocks of the Mada Younger Granite complex, Nigeria

    Science.gov (United States)

    Abaa, S. I.

    The structural aspects of the Mada Younger Granite complex differ from those described from other ring complexes in the province. Ring-dykes and cauldron subsidence structures are not observed and the extrusive rhyolites do not appear to be related to a volcanic cauldron. The minor remnants of the extrusive rocks were domes over small vents since there are no clear indications of any unified volcanic structure. Volcanic eruptions may have taken place from dispersed vents probably including pipes and fissures. Linear intrusive structures have been observed and there is no concentric arrangement of rock units. The biotite granites appear more as sheet structures dipping gently to the south. Petrographically, the extrusive rocks are rhyolites, the comenditic ignimbrite being distinctly peralkaline with aegirine and arfvedsonite. The granite cupolas may be classified as 'A'-type and have been affected by pervasive potash metasomatism which caused recrystallization with microline and finely twinned clear euhedral albite, together with mica compositions between annite towards lithian siderophyllite. This process also introduced minerals like fluorite, cassiterite, columbite and thorite which make the Mada complex a possible source for economic minerals.

  20. Heterogeneous structure of the lithosphere of the Taimyr Peninsula

    Science.gov (United States)

    Litvinova, Tamara; Petrova, Alevtina

    2016-04-01

    Magnetic anomalies of the lower crust is well manifested in the satellite measurements and their reductions for the heights H = 100 and 400 km. Currently, however, a great interest is the area of negative magnetic anomalies, allocated to the same heights. They are confined to a special permeable zones of the crust and lithosphere, having increased geothermal activity and are associated with a variety of minerals. In digital magnetic anomalies and gravity anomalies circumpolar map of the Arctic Ocean (Total) was built geomagnetic and density sections along latitudinal and longitudinal cross sections of negative magnetic anomalies (n = 100 km). In the Taimyr Peninsula they capture the largest Fadyukudinsko Kotuiskaya-ring structure. In the north-central Siberia Fadyukudinsko Kotuiskaya ring structure is the "hub" articulation largest geoblocks (Anabar, Kureisko-Tunguska and North Kara). It is manifested in the gravity and magnetic field is also a ring structure. With Fadyukudinsko Kotui-ring structure formation associated injectors and high-carbonate metasomatic rocks tectonites controlling uranium and thorium-uranium-fluorite-barite-rare earth mineralization (VF Proskurnin, et al. 2010). It hypabyssal front of the hot spots. Fadyukudinsko-Kotuiskaya structure is defined posletrappovoe place in the north of the Eurasian plate, responding to a hot spot or a spot lower mantle plumes Triassic [Kravchenko SM, Hain VE 1996 Sazonov AM, Zvyagin EA, Leontiev SI et al., 2010]. Latitude and longitude revealed Profile permeable zones of low magnetic properties and density, confined to a weakened layer in the middle crust. Negative satellite magnetic anomalies (n = 100 km) at depths of 20 - 25-30 km weakly magnetic lens revealed a low density. The upper crust they overlap and dense magnetic rocks. At the bottom of the crust, these lenses are underlain by layers of dense and magnetic structures.

  1. Oxide-ion and proton conducting electrolyte materials for clean energy applications: structural and mechanistic features.

    Science.gov (United States)

    Malavasi, Lorenzo; Fisher, Craig A J; Islam, M Saiful

    2010-11-01

    This critical review presents an overview of the various classes of oxide materials exhibiting fast oxide-ion or proton conductivity for use as solid electrolytes in clean energy applications such as solid oxide fuel cells. Emphasis is placed on the relationship between structural and mechanistic features of the crystalline materials and their ion conduction properties. After describing well-established classes such as fluorite- and perovskite-based oxides, new materials and structure-types are presented. These include a variety of molybdate, gallate, apatite silicate/germanate and niobate systems, many of which contain flexible structural networks, and exhibit different defect properties and transport mechanisms to the conventional materials. It is concluded that the rich chemistry of these important systems provides diverse possibilities for developing superior ionic conductors for use as solid electrolytes in fuel cells and related applications. In most cases, a greater atomic-level understanding of the structures, defects and conduction mechanisms is achieved through a combination of experimental and computational techniques (217 references).

  2. Crystalline structure of ceria particles controlled by the oxygen partial pressure and STI CMP performances.

    Science.gov (United States)

    Kim, Ye-Hwan; Kim, Sang-Kyun; Kim, Namsoo; Park, Jea-Gun; Paik, Ungyu

    2008-09-01

    The effect of the crystalline structures of nano-sized ceria particles on shallow trench isolation (STI) chemical mechanical planarization (CMP) performance was investigated. The ceria particles were synthesized via a solid-state displacement reaction method, and their crystalline structure was controlled by regulating the oxygen partial pressure at the reaction site on the precursor. The crystalline structures of ceria particles were analyzed by the high-resolution TEM nano-beam diffraction pattern. In a calcination process with a high oxygen concentration, the synthesized ceria particles had a cubic fluorite structure (CeO(2)), because of the decarbonation of the cerium precursor. However, a low oxygen concentration results in a hexagonal phase cerium oxide (Ce(2)O(3)) rather than the cubic phase due to the insufficient oxidation of Ce(3+) to Ce(4+). In the STI CMP evaluation, the ceria slurry prepared with the cubic CeO(2) shows enhanced performances of the oxide-to-nitride removal selectivity.

  3. Theoretical investigation of structural, energetic and electronic properties of titanate pyrochlores

    Science.gov (United States)

    Xiao, H. Y.; Wang, L. M.; Zu, X. T.; Lian, Jie; Ewing, Rodney C.

    2007-08-01

    Ab initio total energy calculations using the plane-wave pseudopotential method based on density functional theory were carried out to investigate the structural, energetic and electronic properties of A2Ti2O7 (A = La, Gd and Yb) pyrochlores. It turned out that the formation energies of antisite defects are not linearly dependent on the ratio of the cation radii, and, for the three compositions, the cation antisite formation energy is largest for Gd2Ti2O7 pyrochlore. It was indicated that Gd2Ti2O7 compound is the least likely to form defect fluorite structure, which gives rise to the least resistance to radiation-induced amorphization. DOS analysis showed that stronger interaction exists in the Gd2Ti2O7 compound, and its electronic structure is very different from that of La2Ti2O7 and Yb2Ti2O7. Our calculations suggested that the electronic structure of the A cation and bond type should be taken into account when explaining the response behavior of A2Ti2O7 (A = La, Gd, Yb) pyrochlores to ion irradiation-induced amorphization.

  4. Investigation of Chemical Durability Mechanisms and Structure of Fluoride Glasses.

    Science.gov (United States)

    1988-03-01

    Eq. ( 1) normalized leach rates. The addition of Na and Al to form the 16. ZBLAN glass (Fig. 2(C ) increases the corrosion rate of all of the XV Ag...34) The series of glasses studied in Ref. 14 exhibits an order of hydration rate with respect to composition ( ZBLAN > ZBLAL > ZBL > ZBLA) which is the...with respect to composition is ZBLALPb> ZBLAN >ZBLAL>ZBL>ZBLA I where the compositions (in mol %) of these glasses are: ZBL- 62.0 ZrF 4 , 33.0 BaF 2

  5. Préparation et caractérisation d'oxynitrures Ln2W(O, N) 6- x à structure fluorine déficitaire

    Science.gov (United States)

    Marchand, R.; Antoine, P.; Laurent, Y.

    1993-11-01

    L'action de l'ammoniac sur les tungstates de lanthanides Ln2 WO 6 à 800°C permet de préparer une nouvelle famille d'oxynitrures à structure fluorine déficitaire, de formule Ln2W(O, N) 6- x ( Ln = Nd → Yb, Y). Leur composition générale de type A4X6.6 est intermédiaire entre la stoechiométrie de la fluorine CaF 2( A4X8) et celle de la bixbyite Mn 2O 3( A4X6) qui en dérive. La maille cristalline est cubique avec un paramètre, fonction de la taille du lanthanide, compris entre 5,16 et 5,39 Å. L'étude cristallochimique démontre que les atomes de lanthanide et de tungstène occupent une même position cristallographique. New oxynitrides corresponding to the general formulation Ln2 W(O,N) 6- x ( Ln = Nd → Yb, Y) have been prepared by reaction at 800°C between ammonia and Ln2 WO 6 tungstates, and characterized as defect fluorite type compounds. Their general composition A4X6.6 is intermediate between the Ca F 2( A4X8) fluorite and Mn 2O 3( A4X6) bixbyite stoichiometries. The parameter of the cubic unit cell, comprised between 5.16 and 5.39 Å, depends on the size of the lanthanide. Ln and W atoms occupy a same crystallographic position.

  6. An anti CuO2-type metal hydride square net structure in Ln2M2As2H(x) (Ln=La or Sm, M=Ti, V, Cr, or Mn).

    Science.gov (United States)

    Mizoguchi, Hiroshi; Park, SangWon; Hiraka, Haruhiro; Ikeda, Kazutaka; Otomo, Toshiya; Hosono, Hideo

    2015-03-02

    Using a high pressure technique and the strong donating nature of H(-), a new series of tetragonal La2Fe2Se2O3-type layered mixed-anion arsenides, Ln2M2As2H(x), was synthesized (Ln=La or Sm, M=Ti, V, Cr, or Mn; x≈3). In these compounds, an unusual M2H square net, which has anti CuO2 square net structures accompanying two As(3-) ions, is sandwiched by (LaH)2 fluorite layers. Notably, strong metal-metal bonding with a distance of 2.80 Å was confirmed in La2Ti2As2H2.3, which has metallic properties. In fact, these compounds are situated near the boundary between salt-like ionic hydrides and transition-metal hydrides with metallic characters.

  7. Structure reconstruction of TiO2-based multi-wall nanotubes: first-principles calculations.

    Science.gov (United States)

    Bandura, A V; Evarestov, R A; Lukyanov, S I

    2014-07-28

    A new method of theoretical modelling of polyhedral single-walled nanotubes based on the consolidation of walls in the rolled-up multi-walled nanotubes is proposed. Molecular mechanics and ab initio quantum mechanics methods are applied to investigate the merging of walls in nanotubes constructed from the different phases of titania. The combination of two methods allows us to simulate the structures which are difficult to find only by ab initio calculations. For nanotube folding we have used (1) the 3-plane fluorite TiO2 layer; (2) the anatase (101) 6-plane layer; (3) the rutile (110) 6-plane layer; and (4) the 6-plane layer with lepidocrocite morphology. The symmetry of the resulting single-walled nanotubes is significantly lower than the symmetry of initial coaxial cylindrical double- or triple-walled nanotubes. These merged nanotubes acquire higher stability in comparison with the initial multi-walled nanotubes. The wall thickness of the merged nanotubes exceeds 1 nm and approaches the corresponding parameter of the experimental patterns. The present investigation demonstrates that the merged nanotubes can integrate the two different crystalline phases in one and the same wall structure.

  8. Impact of lanthanum on the modification of HfO2 films structure

    Institute of Scientific and Technical Information of China (English)

    T. P. Smirnova; L.V. Yakovkina; V.O. Borisov

    2015-01-01

    LaxHf1–xOy thin films with various concentrations of La, homogeneous and nonhomogeneous distributions of elements throughout the films thickness was purposefully grown by CVD. The composition of the films and their chemical structures were characterized throughout the films thickness by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectrometry (EDXA). A full picture of the film crystallinity was provided by the combination of grazing incidence X-ray diffraction (GIXRD) synchrotron radiation (SR) and high resolution transmission electron microscopy (HR TEM). It was shown that La acted as “molar volume modulator” and stabilized the nonequilibrium atT≤1300 °C cubic phases. The samples with La content in range of 7 at.%fluorite-type (Fm-3m) structure. The pyrochlore phase formation was observed at ~18 at.% La content. The correlation between the La-doped content and the films microstructure was revealed.

  9. New measurements of (n,γ) and (n,fission) cross sections and capture-to-fission ratios for ^233,235U and ^239Pu using the DANCE 4π BaF2 array

    Science.gov (United States)

    Bredeweg, T. A.; Jandel, M.; Fowler, M. M.; Bond, E. M.; Haight, R. C.; Keksis, A. L.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.; Becker, J. A.; Parker, W. E.; Wu, C. Y.; Baker, J. D.; McGrath, C. A.

    2009-10-01

    Accurate neutron nuclear data are important to many issues in stockpile stewardship, nuclear reactor design and re-certification, nuclear non-proliferation and nuclear forensics. Of particular interest are the production and destruction reactions for all of the major and most of the minor actinides. The competition between capture and fission in many of the actinides presents both an obstacle and an opportunity for large γ detector arrays such as DANCE. Additional instrumentation is required to deconvolve the two contributions to the total observed γ-ray spectrum. However, conducting a simultaneous measurement can simplify background treatment and other sources of systematic uncertainty. An outline of the current experimental program will be presented along with results from neutron capture measurements on ^233,235U and ^239Pu.

  10. Measurement of the Np237(n,γ) cross section from 20 meV to 500 keV with a high efficiency, highly segmented 4π BaF2 detector

    Science.gov (United States)

    Esch, E.-I.; Reifarth, R.; Bond, E. M.; Bredeweg, T. A.; Couture, A.; Glover, S. E.; Greife, U.; Haight, R. C.; Hatarik, A. M.; Hatarik, R.; Jandel, M.; Kawano, T.; Mertz, A.; O'Donnell, J. M.; Rundberg, R. S.; Schwantes, J. M.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Wouters, J. M.

    2008-03-01

    The Np237(n,γ)Np238 cross section has been measured in the neutron energy range from 20 meV to 500 keV using the DANCE array at the Los Alamos National Laboratory. This new facility allows experiments with submilligram samples and is therefore well suited to investigate isotopes with half-lives as low as a few hundred days. In this benchmark measurement, only 0.42 mg of Np237 was sufficient to determine differential cross sections relative to the well-known resonance at 0.5 eV. The thermal cross section was measured to σ2200m/s=177±5 barn, σkT=25.3meV=167±4 barn and the resonance integral to RI=693±6 barn.

  11. 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.

  12. Influence of synthesis conditions on the crystal structure of the powder formed in the ZrO2 - Ce2O3/CeO2 system.

    Science.gov (United States)

    Popov, V. V.; Menushenkov, A. P.; Khubbutdinov, R. M.; Svetogorov, R. D.; Zubavichus, Ya V.; Sharapov, A. S.; Kurilkin, V. V.

    2016-09-01

    Influence of synthesis conditions (type of atmosphere, reduction and oxidation, annealing temperature) on the chemical composition and structure of the compounds formed in the “ZrO2 - Ce2O3 / CeO2” system has been investigated by X-ray absorption fine structure (XAFS) spectroscopy combined with X-ray diffraction (XRD) and thermogravimetric analysis (TGA). It is revealed that isothermal annealing of precursor at temperatures less than 1000 °C in air leads to formation of Ce0.5Zr0.5O2 powders with cubic fluorite-type structure (Fm-3m). Further increase of annealing temperatures above 1000 °C causes decomposition of formed crystal structure into two phases: cubic and tetragonal. Annealing in reduction hydrogen atmosphere causes formation of Ce4 + 2xCe3 + 2-2xZr2O7 + x compounds with intermediate valency of cerium, where value of x depends on the reducing conditions and treatment parameters of precursor. Annealing in vacuum at 1400 °C strongly reduces the content of Ce4+ in a powder samples and leads to formation of pyrochlore structure (space group Fd-3m) with practically Ce3+ valence state.

  13. Crystal Structure-Ionic Conductivity Relationships in Doped Ceria Systems

    DEFF Research Database (Denmark)

    Omar, Shobit; Wachsman, Eric D.; Jones, Jacob L.;

    2009-01-01

    In the past, it has been suggested that the maximum ionic conductivity is achieved in ceria, when doped with an acceptor cation that causes minimum distortion in the cubic fluorite crystal lattice. In the present work, this hypothesis is tested by measuring both the ionic conductivity and elastic...

  14. Stabilization flyuorytopodibnoyi structure in oxide vacuum condensate

    Directory of Open Access Journals (Sweden)

    О.М. Заславський

    2006-01-01

    Full Text Available  The influence of the oxide-stabilizer content, M'-cation radius and film deposition temperature on the stabilization of the fluorite-like solid solutions in the zirconium and hafnium oxides-based vacuum condensates, obtained by Laser-evaporating method, was investigated. The optimum parameters of the coatication of the isotropic thermostable coverings was determined. This results were explained by using of the high-speed condensation in vacuum theory.

  15. Investigation on synthesis, structure, morphology, spectroscopic and electrochemical studies of praseodymium-doped ceria nanoparticles by combustion method

    Energy Technology Data Exchange (ETDEWEB)

    Esther Jeyanthi, C., E-mail: esther.jeyanthi@yahoo.com [Research and Development Centre, Bharathiar University, Coimbatore 641046 (India); Department of Physics, Panimalar Engineering College, Chennai 600123, TN (India); Siddheswaran, R. [New Technologies Research Centre, University of West Bohemia in Pilsen, Plzeň 30614 (Czech Republic); Kumar, Pushpendra [Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan (China); Karl Chinnu, M. [Department of Applied Physics, Tunghai University, Taichung City, 40740, Taiwan (China); Rajarajan, K. [Department of Physics, Rajeswari Vedachalam Govt. Arts College, Chengalpet 603001, TN (India); Jayavel, R. [Centre for Nanoscience and Technology, Anna University, Chennai 600025 (India)

    2015-02-01

    The investigation deals with the synthesis and characterization of praseodymium doped ceria (PDC) nanoparticles by citrate nitrate auto-combustion method. The as prepared PDC powders were calcined at 700 °C, and then dense cylindrical electrolyte bodies were fabricated by uni-axial compression followed by sintering at 1200 °C. The PDC nanocrystals and compacts were subjected to characterization studies such as X-ray diffraction, scanning and transmission electron microscopy, elemental analysis, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and electrochemical analyses. The crystal structure of PDC was found to be a cubic fluorite system by X-ray diffraction analysis (XRD). The surface morphologies and the grain distributions of the calcined nanoparticles and sintered bodies were studied by scanning electron microscopy (SEM). The grain size of the sintered material was found to be in the range from 100 nm to 500 nm. Transmission electron microscopic (TEM) images revealed the presence of polyhedral, sphere-like shape of the nanoparticles with a size range 10–25 nm. The symmetric stretching mode of the Ce–O was obtained at 555 cm{sup −1} in the FTIR spectrum. The Raman active mode for the PDC was obtained at 457 cm{sup −1}. The presence of oxygen vacancies was confirmed from the weaker absorption band observed at 560 cm{sup −1} in the Raman spectrum. The change in current density with increasing sweep scan potential was studied by cyclic voltammetry (CV) analysis. The specific capacitance range of the PDC was calculated as 20–72.4 Fg{sup −1}. - Highlights: • Praseodymium doped Ceria was synthesized by citrate nitrate auto-combustion method. • XRD revealed that they crystallize as single-phase cubic fluorite structure. • FTIR and RAMAN studies were carried to analyze the existence of functional groups. • The morphology of the particles and compacts were analyzed by SEM and TEM. • Cyclic voltammetry (CV) for the

  16. Leucas aspera mediated multifunctional CeO2 nanoparticles: Structural, photoluminescent, photocatalytic and antibacterial properties.

    Science.gov (United States)

    Malleshappa, J; Nagabhushana, H; Sharma, S C; Vidya, Y S; Anantharaju, K S; Prashantha, S C; Daruka Prasad, B; Raja Naika, H; Lingaraju, K; Surendra, B S

    2015-01-01

    Spherical shaped cerium dioxide (CeO2) nanoparticles (NPs) were synthesized via bio mediated route using Leucas aspera (LA) leaf extract. The NPs were characterized by PXRD, SEM, UV-Visible techniques. Photoluminescence (PL), photocatalysis and antibacterial properties of NPs were studied. PXRD patterns and Rietveld analysis confirm cubic fluorite structure with space group Fm-3m. SEM results evident that morphology of the NPs was greatly influenced by the concentration of LA leaf extract in the reaction mixture. The band gap energy of the NPs was found to be in the range of 2.98-3.4 eV. The photocatalytic activity of NPs was evaluated by decolorization of Rhodamine-B (RhB) under UVA and Sun light irradiation. CeO2 NPs show intense blue emission with CIE coordinates (0.14, 0.22) and average color coordinated temperature value ∼148,953 K. Therefore the present NPs quite useful for cool LEDs. The superior photocatalytic activity was observed for CeO2 NPs with 20 ml LA under both UVA and Sunlight irradiation. The enhanced photocatalytic activity and photoluminescent properties were attributed to defect induced band gap engineered CeO2 NPs. Further, CeO2 with 20 ml LA exhibit significant antibacterial activity against Escherichia coli (EC) and Staphylococcus aureus (SA). These findings show great promise of CeO2 NPs as multifunctional material for various applications.

  17. Conductivity and structure of sub-micrometric SrTiO3-YSZ composites

    DEFF Research Database (Denmark)

    Ruiz Trejo, Enrique; Thydén, Karl Tor Sune; Bonanos, Nikolaos;

    2016-01-01

    Sub-micrometric composites of SrTiO3-YSZ (1:1 volume) and samples of SrTiO3 were prepared by high temperature consolidation of precursors obtained by precipitation with NaOH. The structure development and morphology of the precursors were studied by XRD and SEM. The perovskite and fluorite phases...... in the composites are clearly formed at 600°C with no signs of reaction up to 1100°C; the nominally pure SrTiO3 can be formed at temperatures as low as 400°C. Composites with sub-micrometric grain sizes can be prepared successfully without reaction between the components, although a change in the cell parameter...... of the SrTiO3 is attributed to the presence of Na. The consolidated composites were studied by impedance spectroscopy between 200 and 400°C and at a fixed temperature of 600°C with a scan in the partial pressure of oxygen. The composites did not exhibit high levels of ionic conductivity in the grain...

  18. Charge Distribution and Local Structure and Speciation in the UO2+x and PuO2+x Binary Oxides for x <= 0.25

    Energy Technology Data Exchange (ETDEWEB)

    Conradson, Steven D.; Begg, Bruce D.; Clark, David L.; Den Auwer, Christophe J.; Ding, Mei; Dorhout, Peter K.; Espinosa-Faller, Francisco J.; Gordon, Pamela L.; Haire, Richard G.; Hess, Nancy J.; Hess, Ryan F.; Keogh, D. Webster; Lander, Gerard H.; Manara, Dario; Morales, Luis A.; Neu, Mary P.; Paviet-Hartmann, Patricia; Rebizant, Jean; Rondinella, Vincenzo V.; Runde, Wolfgang; Tait, C DREW.; Veirs, D. Kirk; Villella, Phillip M.; Wastin, Franck

    2005-02-01

    The local structure and chemical speciation of the mixed valence, fluorite-based oxides UO2+x (0.00pxp0.20) and PuO2+x/PuO2+x*y(OH)2y * zH2O have been determined by U/Pu LIII XAFS spectroscopy. The U spectra indicate (1) that the O atoms are incorporated as oxo groups at short (1.75A ? ) U?O distances consistent with U(VI) concomitant with a large range of U displacements that reduce the apparent number of U neighbors and (2) that the UO2 fraction remains intact implying that these O defects interact to form clusters and give the heterogeneous structure consistent with the diffraction patterns. The PuO2+x system, which does not show a separate phase at its x ? 0:25 endpoint, also displays (1) oxo groups at longer 1.9A ? distances consistent with Pu(V+d), (2) a multisite Pu?O distribution even when x is close to zero indicative of the formation of stable species with H2O and its hydrolysis products with O2*, and (3) a highly disordered, spectroscopically invisible Pu?Pu component. The structure and bonding in AnO2+x are therefore more complicated than have previously been assumed and show both similarities but also distinct differences among the different elements.

  19. The influence of crystal structure on ion-irradiation tolerance in the Sm(x)Yb(2-x)TiO5 series

    Energy Technology Data Exchange (ETDEWEB)

    Aughterson, R. D.; Lumpkin, G. R.; de los Reyes, M.; Gault, B.; Baldo, P.; Ryan, E.; Whittle, K. R.; Smith, K. L.; Cairney, J. M.

    2016-04-01

    his ion-irradiation study covers the four major crystal structure types in the Ln(2)TiO(5) series (Ln = lanthanide), namely orthorhombic Pnma, hexagonal P63/mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. This is the first systematic examination of the complete Ln(2)TiO(5) crystal system and the first reported examination of the hexagonal structure. A series of samples, based on the stoichiometry Sm(x)Yb(2-x)TiO5 (where x = 2, 1.4, 1, 0.6, and 0) have been irradiated using 1 MeV Kr2+ ions and characterised in-situ using a transmission electron microscope. Two quantities are used to define ion-irradiation tolerance: critical dose of amorphisation (D-c), which is the irradiating ion dose required for a crystalline to amorphous transition, and the critical temperature (T-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, Yb2TiO5 and Sm0.6Yb1.4TiO5, were found to be the most radiation tolerant, with Tc 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.

  20. Synthesis, crystal structure and magnetic properties of new indium rhenium and scandium rhenium oxides, In 6ReO 12 and Sc 6ReO 12

    Science.gov (United States)

    Mikhailova, D.; Ehrenberg, H.; Fuess, H.

    2006-12-01

    The new complex indium rhenium and scandium rhenium oxides, In 6ReO 12 and Sc 6ReO 12, have been synthesized as single phases in sealed silica tubes and by high-pressure high-temperature syntheses, and their crystal structures have been determined by single crystal X-ray diffraction.The compounds crystallize in a rhombohedral structure related to the distorted fluorite structure like Ln 6ReO 12 for some rare earth elements, S. G.: R-3, Z=3, aH= 9.248(2) Å, cH=8.720(2) Å for Sc 6ReO 12 and aH=9.492(1) Å, cH=8.933(1) Å for In 6ReO 12. A maximum in magnetization is observed for Sc 6ReO 12 at T( Mmax)=1.89(2) K, whereas ferromagnetic ordering is found for In 6ReO 12 by a pronounced increase in the temperature dependence of magnetization at TC=7.5(5) K. The magnetic moment per rhenium ion in In 6ReO 12 and Sc 6ReO 12 is 0.84(1) and 0.65(1) μB, respectively, derived from the paramagnetic regions.

  1. Improved sinterability and conductivity enhancement of 10-mol% calcium-doped ceria using different fuel-aided combustion reactions and its structural characterisation

    Energy Technology Data Exchange (ETDEWEB)

    Ong, P.S., E-mail: pohshing@gmail.com [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Tan, Y.P., E-mail: yptan@science.upm.edu.my [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Putra Laboratory for Catalysis Science and Technology, Department Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Taufiq-Yap, Y.H., E-mail: yap@science.upm.edu.my [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Putra Laboratory for Catalysis Science and Technology, Department Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Zainal, Z., E-mail: zulkar@science.upm.edu.my [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia); Putra Laboratory for Catalysis Science and Technology, Department Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor (Malaysia)

    2014-07-01

    Highlights: • The analysis of the combustion parameters for different fuel-aided combustion syntheses of Ce{sub 0.9}Ca{sub 0.1}O{sub 1.9} is investigated. • The influence of fuel and its direct correlation with calculated thermochemistry is studied. • A complex reaction equation based on stoichiometric mole of fuels to propellant chemistry concept is created. • The influence of fuel utilised on the combustion process and on physiochemical properties is examined. • Ce{sub 0.9}Ca{sub 0.1}O{sub 1.9} ceramic from citric acid-aided combustion synthesis showed the highest conductivity (σ{sub 800°c} = 0.017 S cm{sup −1}). - Abstract: Cubic fluorite structure of ceria doped with 10-mol% calcium, Ce{sub 0.9}Ca{sub 0.1}O{sub 1.9}, was prepared using fuel-aided combustion techniques, utilising glycine, urea and citric acid as fuels along with metal nitrates as the oxidiser. The influence of fuel utilised on the combustion process and on physiochemical properties was thoroughly studied. The results of X-ray diffraction showed that all powders calcined at 400 °C were of single phase with cubic fluorite structure. Conductivity optimisation was achieved via ceramic sintering at various temperatures within 1000–1200 °C. The results showed that Ce{sub 0.9}Ca{sub 0.1}O{sub 1.9} ceramic prepared using citric acid-aided combustion synthesis had higher ionic conductivity, σ{sub 800°c} = 0.017 S cm{sup −1}, and lower activation energy, E{sub a} = 0.84 eV, compared to Ce{sub 0.9}Ca{sub 0.1}O{sub 1.9} ceramics prepared using glycine and urea. The scanning electron microscopy (SEM) results showed that pellets sintered at 1200 °C were dense, and the relative densities of these pellets were over 95%, determined using the Archimedes method.

  2. Structure properties and sintering densification of Gd2Zr2O7 nanoparticles prepared via different acid combustion methods

    Institute of Scientific and Technical Information of China (English)

    马雷; 马伟民; 孙旭东; 刘佳男; 纪连永; 宋晗

    2015-01-01

    Gadolinium zirconate (Gd2Zr2O7) nanocrystals were prepared via two different combustion methods:citric acid combus-tion (CAC) and stearic acid combustion (SAC). The effects of the different preparation methods on the phase composition, micro-topography, and sintering densification of the resulting Gd2Zr2O7 nanopowders were investigated by thermal-gravimetric and differ-ential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and transmission elec-tron microscopy (TEM) techniques. The results indicated that both methods could produce Gd2Zr2O7 nanopowders with an excellent defective fluorite structure. The reaction time was reduced by the SAC method, compared with the CAC method. The nanopowders synthesized by the two methods were different in grain size distribution. The resulting nanoparticle diameter was about 50 nm for CAC and 10 nm for SAC. After vacuum sintering, the sintered bodies also had a different relative density of about 93%and 98%, respectively. Thus the preparation of Gd2Zr2O7 nanopowders by SAC was the first choice to achieve the desired sintering densifi-cation.

  3. Structural cladding /clad structures:

    DEFF Research Database (Denmark)

    Beim, Anne

    2013-01-01

    tendencies, which can be traced in the use of materials, the structural features and the construction details of building systems in selected architectural works. With a particular focus at heavy constructions made of solid wood and masonry, and light weight constructions made of wooden frame structures...... do we see limitations of tectonic maneuver; how does the performative logic challenge the heavy building constructions....

  4. Multi-scale simulation of structural heterogeneity of swift-heavy ion tracks in complex oxides

    Science.gov (United States)

    Wang, Jianwei; Lang, Maik; Ewing, Rodney C.; Becker, Udo

    2013-04-01

    Tracks formed by swift-heavy ion irradiation, 2.2 GeV Au, of isometric Gd2Ti2O7 pyrochlore and orthorhombic Gd2TiO5 were modeled using the thermal-spike model combined with a molecular-dynamics simulation. The thermal-spike model was used to calculate the energy dissipation over time and space. Using the time, space, and energy profile generated from the thermal-spike model, the molecular-dynamics simulations were performed to model the atomic-scale evolution of the tracks. The advantage of the combination of these two methods, which uses the output from the continuum model as an input for the atomistic model, is that it provides a means of simulating the coupling of the electronic and atomic subsystems and provides simultaneously atomic-scale detail of the track structure and morphology. The simulated internal structure of the track consists of an amorphous core and a shell of disordered, but still periodic, domains. For Gd2Ti2O7, the shell region has a disordered pyrochlore with a defect fluorite structure and is relatively thick and heterogeneous with different degrees of disordering. For Gd2TiO5, the disordered region is relatively small as compared with Gd2Ti2O7. In the simulation, ‘facets’, which are surfaces with definite crystallographic orientations, are apparent around the amorphous core and more evident in Gd2TiO5 along [010] than [001], suggesting an orientational dependence of the radiation response. These results show that track formation is controlled by the coupling of several complex processes, involving different degrees of amorphization, disordering, and dynamic annealing. Each of the processes depends on the mass and energy of the energetic ion, the properties of the material, and its crystallographic orientation with respect to the incident ion beam.

  5. Retarded ionic motion in flourites

    NARCIS (Netherlands)

    Schoonman, J.

    1980-01-01

    Metals halides with the fluorite structure attain conductivity values typical of ionic melts far below their melting points, and also go through a second-order transition. Conductivity data for the fluorites are reviewed, and it is shown that the anion vacancies have a large and unique mobility valu

  6. Cation disorder and structural studies on Bi4−NdTi3O12 (0.0 ≤ ≤ 2.0)

    Indian Academy of Sciences (India)

    S N Achary; S J Patwe; P S R Krishna; A B Shinde; A K Tyagi

    2008-11-01

    Here we report the results of combined powder X-ray and neutron diffraction studies of Bi4−NdTi3O12 (0.0 ≤ ≤ 2.0) compositions. The parent Bi4Ti3O12 has an orthorhombic lattice (space group: B2cb) with unit cell parameters = 5.4432(5) Å, = 5.4099(5) Å and = 32.821(2) Å, and = 966.5(1) Å3. This orthorhombic lattice is retained in all the studied compositions. The unit cell parameters gradually decrease with Nd 3+ ion concentration with a discontinuity at = 0.75. Orthorhombicity of the lattice decreases with increase in Nd3+ content in the lattice. The orthorhombic unit cell parameters for a representative Bi2Nd2Ti3O12 composition are: = 5.3834(9), = 5.3846(9) and = 32.784(1) Å. The observed orthorhombic distortion at = 2.0 is very small and thus the crystal structure apparently has a pseudo-tetragonal lattice. In addition, Nd3+ preferentially substitutes in the perovskite slab of the Aurivillius structure. The fraction of Nd3+ in the fluorite slab increases with increase in Nd3+ contents.

  7. Structural characterization of nanosized CeO(2)-SiO(2), CeO(2)-TiO(2), and CeO(2)-ZrO(2) catalysts by XRD, Raman, and HREM techniques.

    Science.gov (United States)

    Reddy, Benjaram M; Khan, Ataullah; Lakshmanan, Pandian; Aouine, Mimoun; Loridant, Stéphane; Volta, Jean-Claude

    2005-03-03

    Structural characteristics of nanosized ceria-silica, ceria-titania, and ceria-zirconia mixed oxide catalysts have been investigated using X-ray diffraction (XRD), Raman spectroscopy, BET surface area, thermogravimetry, and high-resolution transmission electron microscopy (HREM). The effect of support oxides on the crystal modification of ceria cubic lattice was mainly focused. The investigated oxides were obtained by soft chemical routes with ultrahighly dilute solutions and were subjected to thermal treatments from 773 to 1073 K. The XRD results suggest that the CeO(2)-SiO(2) sample primarily consists of nanocrystalline CeO(2) on the amorphous SiO(2) surface. Both crystalline CeO(2) and TiO(2) anatase phases were noted in the case of CeO(2)-TiO(2) sample. Formation of cubic Ce(0.75)Zr(0.25)O(2) and Ce(0.6)Zr(0.4)O(2) (at 1073 K) were observed in the case of the CeO(2)-ZrO(2) sample. Raman measurements disclose the fluorite structure of ceria and the presence of oxygen vacancies/Ce(3+). The HREM results reveal well-dispersed CeO(2) nanocrystals over the amorphous SiO(2) matrix in the cases of CeO(2)-SiO(2), isolated CeO(2), and TiO(2) (anatase) nanocrystals, some overlapping regions in the case of CeO(2)-TiO(2), and nanosized CeO(2) and Ce-Zr oxides in the case of CeO(2)-ZrO(2) sample. The exact structural features of these crystals as determined by digital diffraction analysis of HREM experimental images reveal that the CeO(2) is mainly in cubic fluorite geometry. The oxygen storage capacity (OSC) as determined by thermogravimetry reveals that the OSC of the mixed oxide systems is more than that of pure CeO(2) and is system dependent.

  8. In Situ Diffraction from Levitated Solids Under Extreme Conditions-Structure and Thermal Expansion in the Eu 2 O 3 -ZrO 2 System

    Energy Technology Data Exchange (ETDEWEB)

    Maram, Pardha S. [Peter A. Rock Thermochemistry Laboratory and Neat ORU, University of California, Davis, One Shields Avenue 4415 Chemistry Annex Davis California 95616; Ushakov, Sergey V. [Peter A. Rock Thermochemistry Laboratory and Neat ORU, University of California, Davis, One Shields Avenue 4415 Chemistry Annex Davis California 95616; Weber, Richard J. K. [Materials Development, Inc., 3090 Daniels Court Arlington Heights Illinois 60004; X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue Lemont Illinois 60439; Benmore, Chris J. [X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue Lemont Illinois 60439; Navrotsky, Alexandra [Peter A. Rock Thermochemistry Laboratory and Neat ORU, University of California, Davis, One Shields Avenue 4415 Chemistry Annex Davis California 95616; Raveau, B.

    2014-12-31

    The accurate determination of structure and thermal expansion of refractory materials at temperatures above 1500 degrees C is challenging. Here, for the first time, we demonstrate the ability to reliably refine the structure and thermal expansion coefficient of oxides at temperatures to 2200 degrees C using in situ synchrotron diffraction coupled with aerodynamic levitation. Solid solutions in the Eu2O3-ZrO2 binary system were investigated, including the high-temperature order-disorder transformation in Eu2Zr2O7. The disordered fluorite phase is found to be stable above 1900 degrees C, and a reversible phase transition to the pyrochlore phase is noticed during cooling. Site occupancies in Eu2Zr2O7 show a gradual increase in disorder on both cation and anion sublattices with increasing temperature. The thermal expansion coefficients of all cubic solid solutions are relatively similar, falling in the range 8.6-12.0x10(-6)C(-1). These studies open new vistas for in situ exploration of complex structural changes in high-temperature materials.

  9. Hydrothermal synthesis and crystal structure analysis of two new cadmium bismuthates, CdBi2O6 and Cd0.37Bi0.63O1.79

    Directory of Open Access Journals (Sweden)

    N. Kumada

    2015-09-01

    Full Text Available Two new cadmium bismuthates, CdBi2O6 and Cd0.37Bi0.63O1.79, were prepared by hydrothermal reaction using NaBiO3·nH2O as one of the starting compounds. The crystal structures of these compounds were refined by using synchrotron X-ray powder diffraction data. The former bismuthate has a MnSb2O6-type structure with a hexagonal cell (space group: P321; the cell parameters were a = 9.3641(7 and c = 4.9523(3 Å, and the final R-factors were Rwp = 4.59% and Rp = 3.04%. The latter bismuthate has a fluorite-type structure with a cubic cell (space group: Fm3¯m of a = 5.4110(4 Å, and the final R-factors were Rwp = 4.79% and Rp = 3.57%. These new bismuthates exhibit no photocatalytic activity under visible light.

  10. Is Geometric Frustration-Induced Disorder a Recipe for High Ionic Conductivity?

    Science.gov (United States)

    Düvel, Andre; Heitjans, Paul; Fedorov, Pavel; Scholz, Gudrun; Cibin, Giannantonio; Chadwick, Alan V; Pickup, David M; Ramos, Silvia; Sayle, Lewis W L; Sayle, Emma K L; Sayle, Thi X T; Sayle, Dean C

    2017-04-26

    Ionic conductivity is ubiquitous to many industrially important applications such as fuel cells, batteries, sensors, and catalysis. Tunable conductivity in these systems is therefore key to their commercial viability. Here, we show that geometric frustration can be exploited as a vehicle for conductivity tuning. In particular, we imposed geometric frustration upon a prototypical system, CaF2, by ball milling it with BaF2, to create nanostructured Ba1-xCaxF2 solid solutions and increased its ionic conductivity by over 5 orders of magnitude. By mirroring each experiment with MD simulation, including "simulating synthesis", we reveal that geometric frustration confers, on a system at ambient temperature, structural and dynamical attributes that are typically associated with heating a material above its superionic transition temperature. These include structural disorder, excess volume, pseudovacancy arrays, and collective transport mechanisms; we show that the excess volume correlates with ionic conductivity for the Ba1-xCaxF2 system. We also present evidence that geometric frustration-induced conductivity is a general phenomenon, which may help explain the high ionic conductivity in doped fluorite-structured oxides such as ceria and zirconia, with application for solid oxide fuel cells. A review on geometric frustration [ Nature 2015 , 521 , 303 ] remarks that classical crystallography is inadequate to describe systems with correlated disorder, but that correlated disorder has clear crystallographic signatures. Here, we identify two possible crystallographic signatures of geometric frustration: excess volume and correlated "snake-like" ionic transport; the latter infers correlated disorder. In particular, as one ion in the chain moves, all the other (correlated) ions in the chain move simultaneously. Critically, our simulations reveal snake-like chains, over 40 Å in length, which indicates long-range correlation in our disordered systems. Similarly, collective

  11. Structural cladding /clad structures

    DEFF Research Database (Denmark)

    Beim, Anne

    2012-01-01

    of materials, the structural features and the construction details of building systems in selected architectural works. With a particular focus at heavy constructions made of solid wood and masonry, and light weight constructions made of wooden frame structures and steel profiles, it is the intention......, to ask for more restrictive building codes. As an example, in Denmark there are series of increasing demands in the current building legislations that are focused at enhancing the energy performance of buildings, which consequently foster rigid insulation standards and ask for improvement of air...... with at a global or national level. How to bring the knowledge, material evidence and cultural dimension, which exist in traditional building practices into play with present day hardcore technocratic demands in the construction industry and in building construction, seem be With point of departure...

  12. Structural cladding /clad structures

    DEFF Research Database (Denmark)

    Beim, Anne

    2012-01-01

    to analyze, compare, and discuss how these various construction solutions point out strategies for development based on fundamentally different mindsets. The research questions address the following issues: How to learn from traditional construction principles: When do we see limitations of tectonic maneuver...... in the challenges previously described this paper forms a ‘tectonic enquiry’ into contemporary building practice by looking at specific performative tendencies, which can be traced in the structural features and the construction details of selected building systems and architectural works. With a particular focus...... at heavy constructions made of solid wood and masonry, and light weight constructions made of wooden frame structures and steel profiles, it is the intention to analyze, compare, and discuss how these various construction solu-tions point out strategies for development based on fundamentally different...

  13. Effect of the loading content of CuO on the activity and structure of CuO/Ce-Mn-O catalysts for CO oxidation

    Institute of Scientific and Technical Information of China (English)

    赵福真; 龚渺; 张广营; 李金林

    2015-01-01

    A urea-nitrate combustion method was used to prepare Ce-Mn-O material, which was applied as the support for a series of CuO/Ce-Mn-O catalysts. The structure of the catalysts was characterized with N2 adsorption/desorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic activity of the catalysts for the oxidation of CO was evaluated on a conventional fixed-bed quartz reactor. XRD results showed that the synergetic effect between manganese and cerium led to a little higher electron density of Ce3+ in the mixed oxides. When the CuO content was lower than 5 wt.%, Cu species were well dispersed onto the Ce-Mn-O support or/and they formed a solid solution with CeO2 (inside the fluorite lattice). At higher CuO content (CuO>5 wt.%), large CuO particles were observed. There was strong interaction among ceria, man-ganese and copper oxide because of the doping of Mn. This interplay changed the reducibility and the valence states of the compo-nents, leading to the improved activity of the CuO/Ce-Mn-O catalysts.

  14. Nd3+-substituted (Zr1-xCex)O2 (0.0 ≤ x ≤ 1.0) system: Synthesis, structural and thermophysical investigations

    Science.gov (United States)

    Nandi, Chiranjit; Grover, V.; Sahu, M.; Krishnan, K.; Guleria, A.; Kaity, Santu; Prakash, Amrit; Tyagi, A. K.

    2016-10-01

    In order to mimic co-loading of Pu and Am in zirconia, Nd0.20[Zr1-xCex]0.80O1.90 (0.0 ≤ x ≤ 1.0) system was synthesized and thoroughly characterized by X-ray diffraction (XRD) and Raman spectroscopy. The entire system was found to be single-phasic fluorite-type and most interesting result is stabilization of multi-phasic ceria-zirconia system in a single-phasic system by substituting Nd3+. Raman spectroscopy revealed entirely different nature of defects prevalent in the solid solutions possessing F-type structure across the composition range. The heat capacity of representative compositions was measured by heat flux-type differential scanning calorimeter. Specific heat capacity of the solid solutions was found to increase with decreasing CeO2 content. Different thermodynamic functions such as enthalpy increment, entropy and Gibbs energy functions were determined using heat capacity values. The lattice thermal expansion (298-1273 K) behaviour of the few selected compositions revealed a gradual increase in thermal expansion coefficient with increasing CeO2 content.

  15. HfO_2and ZrO2 : Comparison of Structures and Thermodynamic and Electronic Properties Based on Ab Initio Calculations and Experiment

    Science.gov (United States)

    Demkov, Alexander A.; Navrotsky, Alexandra

    2001-03-01

    The International Technology Roadmap for Semiconductors (ITRS) predicts that the strategy of scaling complementary metal-oxide-semiconductor (CMOS) devices will come to an abrupt end around the year 2012. The main reason for this will be the unacceptably high leakage current through the silicon dioxide gate with a thickness below 20 ÅFinding a gate insulator alternative to SiO2 has proven to be far from trivial. Hafnium and zirconium dioxides and silicates have been recently considered as gate dielectrics with intermediate dielectric constants. Hafnia and ziconia are important ceramic materials as well, and their phase relations are rather well studied. There is also interest in hafnia as a constituent of ceramic waste forms for plutonium, based on its refractory nature and high neutron absorption cross section. We use a combination of the ab-initio calculations and calorimetry to investigate thermodynamic and electronic properties of hafnia and zirconia. We describe the cubic to tetragonal phase transition in the fluorite structure by computing the total energy surface for zone-edge distortions correct to fourth order in the soft-mode displacement with the strain coupling renormalization included. We compare the two materials using some simple chemical concepts.

  16. Electronic structures, hole-doping, and superconductivity of the s = 1, 2, 3, and 4 members of the (Cu,Mo)-12s2 homologous series of superconductive copper oxides.

    Science.gov (United States)

    Grigoraviciute, Inga; Karppinen, Maarit; Chan, Ting-Shan; Liu, Ru-Shi; Chen, Jin-Ming; Chmaissem, Omar; Yamauchi, Hisao

    2010-01-20

    We demonstrate that the T(c) value of superconductive copper oxides does not depend on the distance between two adjacent CuO(2) planes as long as the hole-doping level and the immediate (crystal) chemical surroundings of the planes are kept the same. Experimental evidence is accomplished for the homologous series of (Cu,Mo)-12s2, the member phases of which differ from each other by the number (s) of cation layers in the fluorite-structured (Ce,Y)-[O(2)-(Ce,Y)](s-1) block between the CuO(2) planes. X-ray absorption near-edge structure spectroscopy is employed as a probe for the hole states of these phases. The s = 1 member appears to be more strongly doped with holes than other phases of the series and accordingly to possess the highest T(c) value of 87 K. For s > or = 2, unexpectedly, both the CuO(2) plane hole concentration and the value of T(c) (approximately 55 K) remain constant, being independent of s.

  17. Distribution Structures

    NARCIS (Netherlands)

    Friedrich, H.; Tavasszy, L.A.; Davydenko, I.

    2013-01-01

    Distribution structures are important elements of the freight transportation system. Goods are routed via warehouses on their way from production to consumption. This chapter discusses drivers behind these structures, logistics decisions connected to distribution structures on the micro level, and

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

    Science.gov (United States)

    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 Gd2Ti2O7 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 Gd2Ti2O7 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 Gd2Ti2O7 is readily amorphized at an ion fluence 6 × 1012 ions/cm2 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 × 1013 ions/cm2. 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.

  19. Influence of grain growth on the structural properties of the nanocrystalline Gd2Ti2O7

    Science.gov (United States)

    Kulriya, P. K.; Yao, Tiankai; Scott, Spencer Michael; Nanda, Sonal; Lian, Jie

    2017-04-01

    The microstructural evolution and grain growth kinetics of the nanocrystalline Gd2Ti2O7 drastically affect its properties and functionalities as thermal barrier coatings and nuclear waste forms for actinide incorporation. Here, we report the synthesis of the dense nano-sized Gd2Ti2O7 by high energy ball milling (HEBM), and spark plasma sintering (SPS), and also investigated the isothermally annealing induced grain coarsening and structural properties variations. As-prepared nano powder (D∼60 nm) by HEBM exhibited an amorphous nature, which was consolidated to a dense single phase crystalline pyrochlore nano-ceramic (D∼120 ± 10 nm) by SPS sintering at 1200 °C. Isothermal annealing was performed at different temperatures (1300 °C - 1500 °C) with holding time varying from 0.5 to 8 h, and the pyrochlore phase is stable with no indication of a transformation into a defect fluorite structure. A rapid initial grain growth was observed which increased with temperature and annealing durations due to the large driving force of the curvature-driven grain coarsening of the nano-ceramics, and grain growth saturates at longer durations. The calculated value of the time constant and activation energy for the nanocrystalline Gd2Ti2O7 were 0.52 ± 0.02 and 240 ± 20 kJ/mol (∼2.48 eV), respectively. The enhanced grain growth kinetics with a lower value of activation energy can be explained by the effect of fast diffusion across the grain boundaries for dense nanoceramics.

  20. Scintillation characteristics of nonstoichiometric phases formed in MF sub 2 -GdF sub 3 -CeF sub 3 system Part II. (M=Ba), scintillation of Ba sub 1 sub - sub x Ce sub x F sub 2 sub + sub x (0.1<=x<=0.45) fluorite type crystals

    CERN Document Server

    Kobayashi, M; Sobolev, B P; Zhmurova, Z I; Krivandina, E A

    1999-01-01

    Among three different Ce-concentrations (10, 27 and 45 mol%) which we tested, the 27 mol% sample showed by far the best radiation hardness and the maximum fast component fraction in the luminescence. For this Ce-concentration, the scintillation intensity was about 30% of that in pure BaF sub 2 (within a 1 mu s gate) and comparable to that in CeF sub 3. The decay constant of scintillation was about 38 ns. The melting curve of the Ba sub 1 sub - sub x Ce sub x F sub 2 sub + sub x solid solutions has a maximum at approximately 27 mol% CeF sub 3. The congruent character of the melt with this composition, which should be related with specific structural defects configuration in anionic sublattice, could be the reason for the excellent radiation hardness observed in the Ba sub 0 sub . sub 7 sub 3 Ce sub 0 sub . sub 2 sub 7 F sub 2 sub . sub 2 sub 7 crystal.

  1. Atomic-Scale Study of Mineral Luminescent Materials and Their Microstructures

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    @@The aim of this thesis is to study the luminescence of fluorite: Eu3+ fluorite, Eu2+ and wollastonite: Ce3+, Tba+,to discuss crystal structures and defects using solid atomic images with high resolution transmission electron microscope,and to deal with the luminescent effect of mineral microscopic structure.In general, because of Eu3+ belongs to electric dipole transition, it is forbidden to free ion. But in fluorite, Eu3+system, Eu3+ is located at the nonsymmetrical center, and theparity selection rules are broken.

  2. Effects of Eu3+ concentration on structural, optical and vibrational properties of multifunctional Ce(1-x)Eu(x)O2-delta) nanoparticles synthesized by thermolysis of 2,4-pentanedione complexes.

    Science.gov (United States)

    Kremenovic, A; Bozanic, D K; Welsch, A M; Jancar, B; Nikolic, A S; Boskovic, M; Colomban, Ph; Fabian, Martin; Antic, B

    2012-12-01

    The 5-10 nm Ce(1-x)Eu(x)O(2-delta) (0 < or = x < or = 0.30) nanoparticles with fluorite structure were synthesized by thermal decomposition of Eu- and Ce-2,4-pentanedione complexes mixtures. X-ray line broadening analysis of mixed samples Ce(1-x)Eu(x)O(2-delta) (0.05 < or = x < or = 0.30) showed that the crystallite size was lower and root mean square strain higher than in pure ceria. However, within mixed samples Ce(1-x)Eu(x)O(2-delta) (0.05 < or = x < or = 0.30) crystallite size and root mean square strain were independent of Eu3+ concentration. Raman spectroscopy results indicated that europium ions yield disorder by breaking the phonon propagation and therefore making the non-centre Brillouin zone modes Raman active. The absorption bands in the spectra of mixed oxides were blue-shifted in comparison to pure CeO(2-delta) nanopowder. The samples show red emission typical for Eu ions. The biggest photoluminescent intensity was observed for the highest Eu3+ concentration (x = 0.30) and further enhanced with the increase in crystallinity.

  3. STRUCTURAL GEOLOGY

    Institute of Scientific and Technical Information of China (English)

    2014-01-01

    <正>20140014Deng Lin(College of Resources and Environment,Southwest Petroleum University,Chengdu 610500,China)Structural Geometry and Structural Kinematics of the Jiulongshan Structure in the North Longmenshan Mountains(Acta Geologica Sichuan,ISSN1006-0995,CN51-1273/P,33(1),2013,p.1-2,11,1illus.,9refs.)Key words:plate geometry,structural analysis,Longmenshan Fault Zone

  4. 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.

  5. Unusual Physical and Chemical Properties of Ni in Ce1-xNixO2-y Oxides: Structural Characterization and Catalytic Activity for the Water Gas Shift Reaction

    Energy Technology Data Exchange (ETDEWEB)

    Barrio, L.; Kubacka, A; Zhou, G; Estrella, M; Martinez-Arias, A; Hanson, J; Fernandez-Garcia, M; Rodriguez, J

    2010-01-01

    The structural and electronic properties of Ce{sub 1-x}Ni{sub x}O{sub 2-y} nanosystems prepared by a reverse microemulsion method were characterized with synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and density functional calculations. The Ce{sub 1-x}Ni{sub x}O{sub 2-y} systems adopt a lattice with a fluorite-type structure with an acute local order where Ni displays a strongly distorted (oxygen) nearest-neighbor coordination and the presence of Ni atoms as first cation distances, pointing to the existence of Ni-O-Ni entities embedded into the ceria lattice. A Ni {leftrightarrow} Ce exchange within the CeO{sub 2} leads to a charge redistribution and the appearance of O vacancies. The Ni-O bonds in Ce{sub 1-x}Ni{sub x}O{sub 2-y} are more difficult to reduce than the bonds in pure NiO. The specific structural configuration of Ni inside the mixed-metal oxide leads to a unique catalyst with a high activity for the water gas shift (CO + H{sub 2}O {yields} H{sub 2} + CO{sub 2}) reaction and a simultaneous reduction of the methanation activity of nickel. Characterization results indicate that small particles of metallic Ni at the interface position of a ceria network may be the key for high WGS activity and that the formate-carbonate route is operative for the production of hydrogen.

  6. Unusual Physical and Chemical Properties of Ni in Ce1-xNixO2-y Oxides: Structural Characterization and Catalytic Activity for the Water Gas Shift Reaction

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez, J.A.; Barrio, L.; Kubacka, A.; Zhou, G.; Estrella, M.; Mart& #305; nez-Arias, A.; Hanson, J.C.; Fernandez-Garc& #305; a, M.

    2010-07-29

    The structural and electronic properties of Ce{sub 1-x}Ni{sub x}O{sub 2-y} nanosystems prepared by a reverse microemulsion method were characterized with synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and density functional calculations. The Ce{sub 1-x}Ni{sub x}O{sub 2-y} systems adopt a lattice with a fluorite-type structure with an acute local order where Ni displays a strongly distorted (oxygen) nearest-neighbor coordination and the presence of Ni atoms as first cation distances, pointing to the existence of Ni-O-Ni entities embedded into the ceria lattice. A Ni {leftrightarrow} Ce exchange within the CeO{sub 2} leads to a charge redistribution and the appearance of O vacancies. The Ni?O bonds in Ce{sub 1-x}Ni{sub x}O{sub 2-y} are more difficult to reduce than the bonds in pure NiO. The specific structural configuration of Ni inside the mixed-metal oxide leads to a unique catalyst with a high activity for the water gas shift (CO + H{sub 2}O {yields} H{sub 2} + CO{sub 2}) reaction and a simultaneous reduction of the methanation activity of nickel. Characterization results indicate that small particles of metallic Ni at the interface position of a ceria network may be the key for high WGS activity and that the formate?carbonate route is operative for the production of hydrogen.

  7. Sentence Structure

    CERN Document Server

    Fabb, Nigel

    2012-01-01

    Sentence Structure:introduces the evidence for sentence structure and reveals its purposeis based on a problem-solving approach to languageteaches the reader how to identify word classes, such as noun, preposition and demonstrativeuses simple tree structures to analyse sentencescontains numerous exercises to encourage practical skills of sentence analysisincludes a database and exercises that compare the structure of English with other languages.The second edition of Sentence Structure has been revised and updated throughout and includes new material on tense, aspect, modality and the verb phr

  8. Structural, morphological, and electrical properties of doped ceria as a solid electrolyte for intermediate-temperature solid oxide fuel cells

    KAUST Repository

    Stojmenović, M.

    2015-03-11

    The solid solutions of CeO2 with one or more rare-earth oxides among Yb2O3, Sm2O3, and Gd2O3 are synthesized by either modified glycine nitrate procedure (MGNP) or self-propagating reaction at room temperature (SPRT). The overall mole fraction of rare-earth oxide dopants was x = 0.2. The characterization was committed by XRPD, TEM, BET, and Raman Spectroscopy methods. According to XRPD and Raman spectroscopy, the obtained products presented the single-phase solid solutions with basic fluorite-type CeO2 structure, regardless on the number and the concentration of dopants. Both XRPD and TEM analysis evidenced the nanometer particle dimensions. The defect model was applied to calculate lattice parameters of single-, co-, and multi-doped solids. The sintering of the sample nanopowders was performed at 1550 °C, in air atmosphere. The sintered samples were characterized by XRPD, SEM, and complex impedance methods. The sintering did not affect the concentration ratios of the constituents. The highest conductivity at 700 °C amounting to 2.14 × 10−2 and 1.92 × 10−2 Ω−1 cm−1 was measured for the sample Ce0.8Sm0.08Gd0.12O2−δ, synthesized by SPRT and MGNP methods, respectively. The corresponding activation energies of conductivity, measured in the temperature range 500–700 °C, amounted to 0.24 and 0.23 eV.

  9. Coilgun structures

    Science.gov (United States)

    Andrews, J. A.

    1993-01-01

    Recent research into the optimal design of 'coilgun' structures has indicated that structural requirements are strong functions of launcher classification as well as acceleration mode. Attention is presently given to both closed-form and numerical analytical techniques for coaxial DC accelerator (DCA) structural-design calculations. The DCA is a multistage pulsed-induction launcher that makes extensive use of composite materials technology; measured plastic deformations of the armature after a high energy experiment are compared to FEM analysis predictions.

  10. A wet-chemical approach to perovskite and fluorite-type nanoceramics: synthesis and processing

    NARCIS (Netherlands)

    Veldhuis, Sjoerd Antonius

    2015-01-01

    In thesis the low-temperature, wet-chemical approach to various functional inorganic oxide materials is described. The main focus of this research is to control the material’s synthesis from liquid precursor to metal oxide powder or thin film; while understanding its formation mechanism. In addition

  11. Thermally stimulated depolarization currents in the natural fluorite; Correntes de despolarizacao termicamente estimuladas na fluorita natural

    Energy Technology Data Exchange (ETDEWEB)

    Valerio, Mario Ernesto Giroldo

    1986-12-31

    The present work deals with natural calcium fluoride from Criciuma, Santa Catarina. Thermally Stimulated Depolarization Currents (TSDC) can be used to determine the properties of dipole defects present in this crystal. The TSDC spectrum of this material shows three bands in the temperature range of 80 to 450 K. The first one, at 130 K, is due the dipoles formed by a trivalent impurity and an interstitial fluorine ion in the next nearest position of an impurity ion (nn R{sub s}{sup 3+} -F{sub i}{sup -}). The second one, at 102 k, is due to the presence of small aggregates of dipoles (like a dimer). The last band, at 360 k is due to the formation of Large Clusters. The continuous distribution model gave the best fit for these bands with mean activation energies of 0.41 eV, 0.595 eV and 1.02 eV for the first, second and third band respectively. Thermal treatments can modify the number of dipoles, dimers and clusters present in the crystal. The variation in the areas under each band can be used to measure this effect. In this work we used thermal treatments between 15 minutes and 10 hours and temperatures between 200 deg C and 500 deg C. For thermal treatments at 300 deg C, the dipoles and dimers are created and the clusters are destroyed as the time of thermal treatment increases. At 400 deg C the clusters are created and the dipoles and dimers and 350 deg C for the clusters. (author) 60 refs., 41 figs., 1 tab.

  12. Transmission of visible light through mortars using fluorite as a fine aggregate

    Directory of Open Access Journals (Sweden)

    Ary Alain Hoyos Montilla

    2015-01-01

    Full Text Available En este artículo se presentan los resultados de la evaluación de las propiedades ópticas, en el intervalo de luz visible, en morteros de cemento Pórtland blanco y gris a partir de ocho variables controlables: tamaño del agregado, tipo de cemento, relación agua-cemento, tipo de agregado, relación cemento-agregado, espesor del mortero, porcentaje de aire incluido y porcentaje de fibra óptica. Se definió la modelación matemática que permitió identificar el comportamiento de un haz de luz a medida que atraviesa los morteros. Se midieron tres propiedades: reflexión, absorción y transmitancia. Se utilizó un espectrofotómetro y dos fuentes de luz. De las ocho variables controlables el espesor, el tamaño del agregado y el tipo de cemento son las de mayor incidencia sobre la transmitancia.

  13. A wet-chemical approach to perovskite and fluorite-type nanoceramics: synthesis and processing

    NARCIS (Netherlands)

    Veldhuis, Sjoerd

    2015-01-01

    In thesis the low-temperature, wet-chemical approach to various functional inorganic oxide materials is described. The main focus of this research is to control the material’s synthesis from liquid precursor to metal oxide powder or thin film; while understanding its formation mechanism. In

  14. Control of crystal structure, morphology and optical properties of ceria films by post deposition annealing treatments

    Energy Technology Data Exchange (ETDEWEB)

    Eltayeb, Asmaa, E-mail: asmaa.eltayeb2@mail.dcu.ie [School of Electronic Engineering, National Centre for Plasma Science and Technology, Dublin City University, Glasnevin, Dublin 9 (Ireland); Vijayaraghavan, Rajani K. [School of Electronic Engineering, National Centre for Plasma Science and Technology, Dublin City University, Glasnevin, Dublin 9 (Ireland); McCoy, Anthony P. [School of Physical Sciences, Dublin City University, Glasnevin, Dublin 9 (Ireland); Cullen, Joseph [School of Physical Sciences, National Centre for Plasma Science and Technology, Dublin City University, Glasnevin, Dublin 9 (Ireland); Daniels, Stephen [School of Electronic Engineering, National Centre for Plasma Science and Technology, Dublin City University, Glasnevin, Dublin 9 (Ireland); McGlynn, Enda [School of Physical Sciences, National Centre for Plasma Science and Technology, Dublin City University, Glasnevin, Dublin 9 (Ireland)

    2016-03-31

    In this paper, the effects of post-deposition annealing temperature and atmosphere on the properties of pulsed DC magnetron sputtered ceria (CeO{sub 2}) thin films, including crystalline structure, grain size and shape and optical properties were investigated. Experimental results, obtained from X-ray diffraction (XRD), showed that the prepared films crystallised predominantly in the CeO{sub 2} cubic fluorite structure, although evidence of Ce{sub 2}O{sub 3} was also seen and this was quantified by a Rietveld refinement. The anneal temperature and oxygen content of the Ar/O{sub 2} annealing atmosphere both played important roles on the size and shape of the nanocrystals as determined by atomic force microscopy (AFM). The average grain size (determined by an AFM) as well as the out of plane coherence length (obtained from XRD) varied with increasing oxygen flow rate (OFR) in the annealing chamber. In addition, the shape of the grains seen in the AFM studies transformed from circular to triangular as the OFR was raised from 20 sccm to 30 sccm during an 800 °C thermal anneal. X-ray photoelectron spectroscopy was used to measure near-surface oxidation states of the thin-films with varying OFR in the annealing chamber. The bandgap energies were estimated from the ultra-violet and visible absorption spectra and low-temperature photoluminescence. An extracted bandgap value of 3.04 eV was determined for as-deposited CeO{sub 2} films and this value increased with increasing annealing temperatures. However, no difference was observed in bandgap energies with variation of annealing atmosphere. - Highlights: • Deposition of ceria thin films by pulsed DC magnetron sputtering • Effect of annealing temperature and gas ambient on film crystalline structure • Evidence for control of the film roughness and grain size and shape is achieved. • Investigation of the effect of post-deposition annealing on the film stoichiometry • Films showed blue shifts in bandgap energies

  15. Structural, mechanical and thermodynamic properties of AuIn{sub 2} crystal under pressure: A first-principles density functional theory calculation

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Ching-Feng [Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Cheng, Hsien-Chie, E-mail: hccheng@fcu.edu.tw [Department of Aerospace and Systems Engineering, Feng Chia University, Taichung 40724, Taiwan (China); Chen, Wen-Hwa, E-mail: whchen@pme.nthu.edu.tw [Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

    2015-01-15

    Highlights: • The mechanical and thermodynamic properties of AuIn{sub 2} are reported for the first time. • The calculated lattice constants and elastic properties of AuIn{sub 2} are consistent with the literature data. • The results reveal that AuIn{sub 2} demonstrates low elastic anisotropy, low hardness and high ductility. • It is worth to note that the anisotropic AuIn{sub 2} tends to become elastically isotropic as hydrostatic pressure increases. - Abstract: The structural, mechanical and thermodynamic properties of cubic AuIn{sub 2} crystal in the cubic fluorite structure, and also their temperature, hydrostatic pressure and direction dependences are investigated using first-principles calculations based on density functional theory (DFT) within the generalized gradient approximation (GGA). The optimized lattice constants of AuIn{sub 2} single crystal are first evaluated, by which its hydrostatic pressure-dependent elastic constants are also derived. Then, the hydrostatic pressure-dependent mechanical characteristics of the single crystal, including ductile/brittle behavior and elastic anisotropy, are explored according to the characterized angular character of atomic bonding, Zener anisotropy factor and directional Young’s modulus. Moreover, the polycrystalline elastic properties of AuIn{sub 2}, such as bulk modulus, shear modulus and Young’s modulus, and its ductile/brittle and microhardness characteristics are assessed versus hydrostatic pressure. Finally, the temperature-dependent Debye temperature and heat capacity of AuIn{sub 2} single crystal are investigated by quasi-harmonic Debye modeling. The present results reveal that AuIn{sub 2} crystal demonstrates low elastic anisotropy, low hardness and high ductility. Furthermore, its heat capacity strictly follows the Debye T{sup 3}-law at temperatures below the Debye temperature, and reaches the Dulong–Petit limit at temperatures far above the Debye temperature.

  16. Protein Structure

    Science.gov (United States)

    Asmus, Elaine Garbarino

    2007-01-01

    Individual students model specific amino acids and then, through dehydration synthesis, a class of students models a protein. The students clearly learn amino acid structure, primary, secondary, tertiary, and quaternary structure in proteins and the nature of the bonds maintaining a protein's shape. This activity is fun, concrete, inexpensive and…

  17. Tau structures

    Directory of Open Access Journals (Sweden)

    Jesus Avila

    2016-11-01

    Full Text Available Tau is a microtubule-associated protein that plays an important role in axonal stabilization, neuronal development, and neuronal polarity. In this review, we focus on the primary, secondary, tertiary and quaternary tau structures. We describe the structure of tau from its specific residues until its conformation in dimers, oligomers and larger polymers in physiological and pathological situations.

  18. Organisational Structure

    Science.gov (United States)

    National Centre for Vocational Education Research (NCVER), 2006

    2006-01-01

    An understanding of organisational structure can provide guidance for organisations that want to change and innovate. Many writers agree that this understanding allows organisations to shape how their work is done to ultimately achieve their business goals--and that too often structure is given little consideration in business strategy and…

  19. Vcsel structure

    DEFF Research Database (Denmark)

    2015-01-01

    The invention relates to a VCSEL structure based on a novel grating reflector. The grating reflector comprises a grating layer with a contiguous core grating region having a grating structure, wherein an index of refraction of high-index sections of the grating structure is at least 2.......5, and wherein an index of refraction of low-index sections of the grating structure is less than 2. The core grating region defines a projection in a direction normal to the grating layer. The grating reflector further comprises a cap layer abutting the grating layer, and an index of refraction of the cap layer...... the projection of the core grating region, the grating layer is also abutted by a second low-index layer and/or by air, an index of refraction of the second low-index layer or air being less than 2. The VCSEL structure furthermore comprises a first reflector and an active region for providing a cavity...

  20. Structure and properties of the Mn doped CeO{sub 2} thin film grown on LaAlO{sub 3} (0 0 1) via a modified sol–gel spin-coating technique

    Energy Technology Data Exchange (ETDEWEB)

    Mahmoud, Waleed E., E-mail: w_e_mahmoud@yahoo.com [King Abdulaziz University, Faculty of Science, Department of Physics, Jeddah (Saudi Arabia); Suez Canal University, Faculty of Science, Department of Physics, Ismailia (Egypt); Al-Ghamdi, A.A. [King Abdulaziz University, Faculty of Science, Department of Physics, Jeddah (Saudi Arabia); Al-Agel, F.A. [Hail University, College of Science, Department of Physics, Hail (Saudi Arabia); Al-Arfaj, E. [Umm Alqura University, Department of Physics, Makkah (Saudi Arabia); Qaseem University, Physics Department, Qaseem (Saudi Arabia); Shokr, F.S. [King Abdulaziz University, Faculty of Science & Arts, Department of Physics, Rabigh (Saudi Arabia); Al-Gahtany, S.A. [King Abdulaziz University, Faculty of Science for Girls, Department of Physics, Jeddah (Saudi Arabia); Alshahrie, Ahmed [King Abdulaziz University, Faculty of Science, Department of Physics, Jeddah (Saudi Arabia); Hafez, M. [King Abdulaziz University, Faculty of Science, Department of Physics, Jeddah (Saudi Arabia); Suez Canal University, Faculty of Science, Department of Physics, Ismailia (Egypt); Bronstein, L.M. [King Abdulaziz University, Faculty of Science, Department of Physics, Jeddah (Saudi Arabia); Indiana University, Department of Chemistry, Bloomington, IN 47405 (United States); Beall, Gary W. [King Abdulaziz University, Faculty of Science, Department of Physics, Jeddah (Saudi Arabia); Texas State University-San Marcos, Department of Chemistry and Biochemistry, 601 University Dr., San Marcos, TX 78666 (United States)

    2015-08-15

    Highlights: • Mn doped CeO{sub 2} was grown on LaAlO{sub 3} (0 0 1) via sol–gel technique. • The concentration of the Mn ions was varied from 1 to 13 at.%. • The incorporation of 7 at.% of Mn ions was found to provide formation of exceptionally smooth films. • This amount demonstrated the highest saturation magnetization of 1.75 μ{sub B}/Mn and coercive field of 487 Gauss. - Abstract: Here we report Mn doped cerium oxide films prepared on the LaAlO{sub 3} (0 0 1) substrate via an ethylene glycol modified sol–gel spin coating technique and evaluation of their properties as diluted magnetic semiconductors. Cerium oxide was selected because of its high dielectric constant and fluorite cubic structure, matching the silicon and lanthanum aluminate based electronic devices. The concentration of the Mn ions was varied from 1 to 13 at.% and the influence of this concentration on the structure, surface morphology, optical and magnetic properties of these films was studied using scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy, ellipsometric spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and magnetic measurements. The incorporation of 7 at.% of Mn ions was found to provide formation of exceptionally smooth films, demonstrating the highest saturation magnetization of 1.75 μ{sub B}/Mn and the coercive field of 487 Gauss. These properties are assigned to the conversion of Ce{sup 4+} to Ce{sup 3+} upon incorporation of Mn ions into the CeO{sub 2} structure and the oxidation of Mn{sup 2+} to Mn{sup 4+}, creating two oxygen vacancies to preserve the cubic structure of cerium oxide and promoting ferromagnetism.

  1. Structural Behaviour of Reciprocal Structures

    DEFF Research Database (Denmark)

    Parigi, Dario; Kirkegaard, Poul Henning

    2013-01-01

    The present paper focuses on the comparison of several two-dimensional and three-dimensional reciprocal configurations. The goal of such comparison is to analyse the structural behaviour when changing the geometric parameters used to describe the geometry of reciprocal structures....

  2. Influence of nano-structural feature on electrolytic properties in Y2O3 doped CeO2 system

    Directory of Open Access Journals (Sweden)

    Toshiyuki Mori, John Drennan, Yarong Wang, Graeme Auchterlonie, Ji-Guang Li and Anya Yago

    2003-01-01

    Full Text Available Doped ceria (CeO2 compounds are fluorite type oxides which show oxide ionic conductivity higher than yttria stabilized zirconia, in oxidizing atmosphere. As a consequence of this, considerable interest has been shown in application of these materials for 'low temperature operation (500–650 °C' of solid oxide fuel cells (SOFCs. In this study, YxCe1−xO2−δ (x=0.05, 0.1, 0.15, 0.2 and 0.25 fine powders were prepared using a carbonate co-precipitation method. The relationship between electrolytic properties and nano-structural features in the sintered bodies was examined. The micro-structures of Y0.05Ce0.95O1.975, Y0.15Ce0.85O1.925 and Y0.25Ce0.75O1.875 as representative three specimens have been investigated in more detail with transmission electron microscopy (TEM. The big diffuse scattering was observed in the background of electron diffraction pattern recorded from Y0.15Ce0.85O1.925 and Y0.25Ce0.75O1.875 sintered bodies. This means that the coherent micro-domain with ordered structure is in the micro-structure. While Y0.25Ce0.75O1.875 sintered body with low conductivity and high activation energy has big micro-domains, the micro-domain size in Y0.15Ce0.85O1.925 with high conductivity and low activation energy was much smaller than that of Y0.25Ce0.75O1.875. TEM observation gives us message that the size of coherent micro-domain with ordered structure would closely relate to the electrolytic properties such as conductivity and activation energy in the specimens. It was concluded that a control of micro-domain size in nano-scale in Y2O3 doped CeO2 system was a key for development of high quality solid electrolyte in fuel cell application.

  3. Structured light in structured media

    Science.gov (United States)

    Zeng, Jinwei

    The objective of this dissertation is to investigate fundamental optical phenomena at the interface between two emerging fields of modern optics - structured light and micro/nano-structured optical materials. Until recently, these fields were developing in parallel yet independently. A majority of researchers in the field of metamaterials and photonic crystals considered "simple" linearly or circularly polarized light or Gaussian beam propagation in "structured" materials with properties not found in nature. However, in addition to conventional polarization states, light beams can be radially or azimuthally polarized and carry orbital angular momentum (OAM). A fascinating example of a beam carrying OAM is the optical vortex---a donut-shaped beam with a helical phase front. Similarly, the structured light community largely focused on complex light propagation in rather simple homogeneous, isotropic, transparent media. In this dissertation, we explore fundamentals and applications of light-matter interactions that involve both complex light and complex media. The central question that we aim to tackle is: How may the synergy of these two fields lead to a breakthrough in modern photonics? Structured materials, including metamaterials and photonic bandgap structures, realize unprecedented control over light propagation and design flexibility. They can enable new optical properties and functionalities, including new regimes of wave guiding, negative index of refraction, magnetism at optical frequencies, and subwavelength imaging to name a few. We demonstrate how nearly unlimited possibilities in engineering the properties of structured media can be used for generation and manipulation of structured light. Also, we show how the unique properties of structured light could be used for characterization of structured media.

  4. The Crystal Structure of Lanthanide Zirconates

    Science.gov (United States)

    Clements, Richard; Kennedy, Brendan; Ling, Christopher; Stampfl, Anton P. J.

    2010-03-01

    The lanthanide zirconates of composition Ln2Zr2O7 (Ln = La-Gd) are of interest for use in inert matrix fuels and nuclear wasteforms. The series undergoes a pyrochlore to fluorite phase transition as a function of the Ln atomic radii. The phase transition has been attributed to disordering of both the cation and the anion [1]. We have undertaken a synthesis of the lanthanide zirconate series Ln2Zr2O7 (Ln = La-Gd), Ln0.2Zr0.8O1.9 (Ln = Tb-Yb) and NdxHo2-xZr2O7 (0ANSTO's new high resolution powder diffractometer Echidna, in order to obtain accurate data on atomic displacement parameters and O 48f position across the series. These results will be presented, along with details of the analysis and synthetic techniques used.

  5. Hydraulic Structures

    Data.gov (United States)

    Department of Homeland Security — This table is required whenever hydraulic structures are shown in the flood profile. It is also required if levees are shown on the FIRM, channels containing the...

  6. Hydraulic structures

    CERN Document Server

    Chen, Sheng-Hong

    2015-01-01

    This book discusses in detail the planning, design, construction and management of hydraulic structures, covering dams, spillways, tunnels, cut slopes, sluices, water intake and measuring works, ship locks and lifts, as well as fish ways. Particular attention is paid to considerations concerning the environment, hydrology, geology and materials etc. in the planning and design of hydraulic projects. It also considers the type selection, profile configuration, stress/stability calibration and engineering countermeasures, flood releasing arrangements and scouring protection, operation and maintenance etc. for a variety of specific hydraulic structures. The book is primarily intended for engineers, undergraduate and graduate students in the field of civil and hydraulic engineering who are faced with the challenges of extending our understanding of hydraulic structures ranging from traditional to groundbreaking, as well as designing, constructing and managing safe, durable hydraulic structures that are economical ...

  7. Nuclear Structure

    Science.gov (United States)

    Gargano, Angela

    2003-04-01

    An account of recent studies in the field of theoretical nuclear structure is reported. These studies concern essentially research activities performed under the Italian project "Fisica Teorica del Nucleo e dei Sistemi a Molti Corpi". Special attention is addressed to results obtained during the last two years as regards the development of new many-body techniques as well as the interpretation of new experimental aspects of nuclear structure.

  8. Foundation Structure

    OpenAIRE

    Schakenda, Bruno; Nielsen, Søren Andreas; Ibsen, Lars Bo

    2009-01-01

    Method of installing a bucket foundation structure comprising one, two, three or more skirts, into soils in a controlled manner. The method comprises two stages: a first stage being a design phase and the second stage being an installation phase. In the first stage, design parameters are determined relating to the loads on the finished foundation structure; soil profile on the location; allowable installation tolerances, which parameters are used to estimate the minimum diameter and length of...

  9. Local structure and ionic conductivity in the Zr{sub 2}Y{sub 2}O{sub 7}-Y{sub 3}NbO{sub 7} system

    Energy Technology Data Exchange (ETDEWEB)

    Norberg, Stefan T; Ahmed, Istaq; Hull, Stephen [The ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX (United Kingdom); Marrocchelli, Dario; Madden, Paul A [School of Chemistry, Edinburgh University, The King' s Building, West Mains Road, Edinburgh EH9 3JJ (United Kingdom)], E-mail: stn@chalmers.se

    2009-05-27

    The Zr{sub 0.5-0.5x}Y{sub 0.5+0.25x}Nb{sub 0.25x}O{sub 1.75} solid solution possesses an anion-deficient fluorite structure across the entire 0{<=}x{<=}1 range. The relationship between the disorder within the crystalline lattice and the preferred anion diffusion mechanism has been studied as a function of x, using impedance spectroscopy measurements of the ionic conductivity ({sigma}), powder neutron diffraction studies, including analysis of the 'total' scattering to probe the nature of the short-range correlations between ions using reverse Monte Carlo (RMC) modelling, and molecular dynamics (MD) simulations using potentials derived with a strong ab initio basis. The highest total ionic conductivity ({sigma} = 2.66 x 10{sup -2} {omega}{sup -1} cm{sup -1} at 1473 K) is measured for the Zr{sub 2}Y{sub 2}O{sub 7} (x = 0) end member, with a decrease in {sigma} with increasing x, whilst the neutron diffraction studies show an increase in lattice disorder with x. This apparent contradiction can be understood by considering the local structural distortions around the various cation species, as determined from the RMC modelling and MD simulations. The addition of Nb{sup 5+} and its stronger Coulomb interaction generates a more disordered local structure and enhances the mobility of some anions. However, the influence of these pentavalent cations is outweighed by the effect of the additional Y{sup 3+} cations introduced as x increases, which effectively trap many anions and reduce the overall concentration of the mobile O{sup 2-} species.

  10. Ni-doped (CeO{sub 2−δ})–YSZ mesoarchitectured with nanocrystalline framework: the effect of thermal treatment on structure, surface chemistry and catalytic properties in the partial oxidation of methane (CPOM)

    Energy Technology Data Exchange (ETDEWEB)

    Somacescu, Simona, E-mail: ssimona@icf.ro [Romanian Academy, “Ilie Murgulescu” Institute of Physical Chemistry (Romania); Florea, Mihaela [University of Bucharest, Department of Organic Chemistry, Biochemistry and Catalysis, Faculty of Chemistry (Romania); Osiceanu, Petre; Calderon-Moreno, Jose Maria [Romanian Academy, “Ilie Murgulescu” Institute of Physical Chemistry (Romania); Ghica, Corneliu [National Institute of Materials Physics (Romania); Serra, Jose Manuel [Universidad Politécnica de Valencia - Consejo Superior de Investigaciones Científicas, Instituto de Tecnología Química (Spain)

    2015-11-15

    Ni-doped (CeO{sub 2−δ})–YSZ (5 mol% Ni oxide, 10 mol% ceria) mesoarchitectures (MA) with nanocrystalline framework have been synthesized by an original, facile and cheap approach based on Triton X100 nonionic surfactant as template and water as solvent at a strong basic pH value. Following the hydrothermal treatment under autogenous pressure (∼18 bars), Ni, Ce, Y, and Zr were well ordered as MA with nanocrystalline framework, assuring thermal stability. A comprehensive investigation of structure, texture, morphology, and surface chemistry was performed by means of a variety of complementary techniques (X-Ray Diffraction, XRD; Raman Spectroscopy, RS; Brunauer—Emmett—Teller, BET; Temperature—Programmed Reduction, TPR; Transmission Electron Microscopy, TEM and DF-STEM; X-ray Photoelectron Spectroscopy, XPS; Catalytic activity and selectivity). N{sub 2} sorption measurements highlighted that the mesoporous structure is formed at 600 °C and remains stable at 800 °C. At 900 °C, the MA collapses, favoring the formation of macropores. The XRD and Raman Spectroscopy of all samples showed the presence of a pure, single phase with fluorite-type structure. At 900 °C, an increased tetragonal distortion of the cubic lattice was observed. The surface chemistry probed by XPS exhibits a mixture of oxidation states (Ce{sup 3+} + Ce{sup 4+}) with high percentage of Ce{sup 3+} valence state ∼35 % and (Ni{sup 3+} and Ni{sup 2+}) oxidation states induced by the thermal treatment. These nanoparticles assembled into MA show high stability and selectivity over time in catalytic partial oxidation of methane (CPOM). These promising performances suggest an interesting prospect for introduction as anode within IT-SOFC assemblies.Graphical Abstract.

  11. Tension Structure

    Science.gov (United States)

    1978-01-01

    The fabric structure pictured is the Campus Center of La Verne College, La Verne, California. Unlike the facilities shown on the preceding pages, it is not air-supported. It is a "tension structure," its multi-coned fabric membrane supported by a network of cables attached to steel columns which function like circus tent poles. The spider-web in the accompanying photo is a computer graph of the tension pattern. The designers, Geiger-Berger Associates PC, of New York City, conducted lengthy computer analysis to determine the the best placement of columns and cables. The firm also served as structural engineering consultant on the Pontiac Silverdome and a number of other large fabric structures. Built by Birdair Structures, Inc., Buffalo, New York, the La Verne Campus Center was the first permanent facility in the United States enclosed by the space-spinoff fabric made of Owens-Corning Beta fiber glass coated with Du Pont Teflon TFE. The flexible design permits rearrangement of the interior to accommodate athletic events, student activities, theatrical productions and other recreational programs. Use of fabric covering reduced building cost 30 percent below conventional construction.

  12. Adenovirus structure.

    Science.gov (United States)

    Rux, John J; Burnett, Roger M

    2004-12-01

    Structural studies continue to play an essential role as the focus of adenovirus research shifts in emphasis from basic biology to adenovirus-based vector technologies. A crucial step in developing novel therapeutics for gene replacement, cancer, and vaccines is often to modify the virion. Such engineered changes are designed to retarget the virus, or to reduce the immunological responses to infection. These efforts are far more effective when they are based on detailed structural knowledge. This minireview provides a brief summary of the wealth of information that has been obtained from the combined application of X-ray crystallography and electron microscopy. This knowledge now includes a good working model for the architectural organization of the virion, and atomic resolution molecular structures for all the major capsid proteins, hexon, penton, and fiber. We highlight new developments, which include the structure of the penton base and the discovery that adenovirus has several relatives. We sketch how the structural information can be used to engineer novel virions and conclude with the prospects for future progress.

  13. Effect of fluxes on structure and luminescence properties of Y3Al5O12:Ce3+ phosphors

    Institute of Scientific and Technical Information of China (English)

    XU Shiqing; SUN Liuzheng; ZHANG Ying; JU Haidong; ZHAO Shilong; DENG Degang; WANG Huanping; WANG Baoling

    2009-01-01

    Ce3+-activated yttrium aluminum garnet (YAG) was prepared by the solid-state reaction, in which H3BO3, LiF, NaF, KF and BaF2 were used as the fluxes. The effect of fluxes on optical properties of phosphors was studied in detail, especially the fluxes of alkali fluorides, which could enhance the emission intensity and change the wavelength of emission peaks. Among these YAG:Ce phosphors, the phosphor sintered with H3BO3 and NaF exhibited the strongest emission. The emission peaks of phosphors prepared with fluxes from LiF to KF were shifted to long wavelength. The effect of NaF concentration on the emission intensity of YAG:Ce was also investigated. The value of emis-sion intensity reached the maximum when the concentration of NaF was 0.5%.

  14. Data Structures

    DEFF Research Database (Denmark)

    Davoodi, Pooya

    weight in a query path; (3) the range diameter problem: given a point set in the plane, find two points that are farthest away in a query rectangle. These and similar problems arise in various applications including document retrieval, genome sequence analysis, OLAP data cubes, network flows, shape......-fitting, and clustering. The three mentioned problems are considered for either static inputs or dynamic inputs. In the static setting, we investigate the space-efficiency of data structures, which is an important aspect in massive data algorithmics. We provide lower bounds on the trade-off between the query time......-dimensional range minimum queries. In the dynamic setting, we present data structures for the path minima problem that support optimal query time for various types of update operations. One of the results presents a comparison-based data structure which answers path minima queries in sub-logarithmic time...

  15. Effect of Mg doping and sintering temperature on structural and morphological properties of samarium-doped ceria for IT-SOFC electrolyte

    Science.gov (United States)

    Ahmad, Syed Ismail; Mohammed, Tasneem; Bahafi, Amal; Suresh, Madireddy Buchi

    2017-06-01

    Samples of Sm and Mg co-doped ceria electrolyte of Ce1- x Sm x- y Mg y O2- δ ( x = 0.2; y = 0.00, 0.05, 0.1, 0.15, and 0.175) were synthesized by sol-gel process. The prepared samples were sintered at 1100 and 1400 °C for 4 h. The bulk densities were measured by Archimedes method. XRD measurements indicate that the synthesized samples were in single-phase cubic fluorite structure (space group Fm3m). The cell parameters decrease with the concentration of Mg, and 2 θ values slightly shift towards right. The particle sizes obtained were between 7.14 and 17.44 nm. The sintered sample achieved 95% of theoretical density. FTIR spectra of samples sintered at 1400 °C indicates weak interactions between 3550-3400 cm-1 and 1600-1300 cm-1 are attributed to O-H stretching modes and strong bonds 850-450 cm-1 are assigned to characteristic Ce-O vibrations. The surface morphology and chemical composition were analyzed by SEM and EDS, SEM micrographs show spherical faceted grains, and the samples were crack free, dense material with some pores on surface which are inconsistent with density results. The average grain size obtained was 0.5 μm. Particle size obtained by TEM was in agreement with that obtained by XRD. The high-density ceria co-doped ceramic can be used as electrolyte in SOFC.

  16. Fireplace structure

    Energy Technology Data Exchange (ETDEWEB)

    Faehling, F.L.; Billmeyer, T.F.; Peterson, S.O.

    1984-09-18

    A fireplace having one or more conduits for directing outside combustion air into the firebox with a movable member adjacent a conduit outlet for normally closing said conduit and having either open or closed positions dependent upon the existence of a pressure difference across said member. A pressure difference caused by a fire in the firebox results in a higher pressure on the side of the member opposite the firebox to cause the member to move to open position. Operating structure is provided for positively closing the member and with the operating structure being operable from the front of the fireplace.

  17. Lightweight Structures.

    Science.gov (United States)

    Shaver and Co., Michigan City, IN.

    One of the newest and most promising developments in architecture has been the use of lightweight structures for encapsulating space. Using this new technology, builders can enclose large and small areas at a fraction of the cost of conventional construction and at the same time provide interior space that is totally flexible. This brochure shows…

  18. Structural parsing

    NARCIS (Netherlands)

    Hoede, C.; Zhang, Lei

    2000-01-01

    Parsing is an essential part of natural language processing. In this paper, structural parsing, which is based on the theory of knowledge graphs, is introduced. Under consideration of the semantic and syntactic features of natural language, both semantic and syntactic word graphs are formed. Grammar

  19. Coastal Structures

    DEFF Research Database (Denmark)

    Oumeraci, H.; Burcharth, H. F.; Rouck, J. De;

    1995-01-01

    The paper attempts to present an overview of five research projects supported by the Commission of the European Communities, Directorate General XII, under the MAST 2- Programme (Marine Sciences and Technology), with the overall objective of contributing to the development of improved rational me...... methods for the design of coastal structures....

  20. Organizational structure

    NARCIS (Netherlands)

    Hendriks, P.H.J.

    2011-01-01

    For many decades, organization scientists have paid considerable attention to the link between knowledge and organization structure. An early contributor to these discussions was Max Weber (1922), who elaborated his concepts of professional bureaucracy. History shows a multitude of other description

  1. STRUCTURAL GEOLOGY

    Institute of Scientific and Technical Information of China (English)

    2013-01-01

    <正>20130642 Bai Daoyuan (Hunan Institute of Geology Survey , Mineral Exploration and Development of Hunan Province , Changsha 410011 , China); Jia Baohua Potential Genesis of the Trending Changes of Jinning Period and Caledonian Structural Lineamens in Middle-Southern Hunan Province (Journal of Geomechanics , ISSN1006-6616 ,

  2. European structuralism

    OpenAIRE

    Willems, Klaas

    2014-01-01

    European structuralism is a paradigm for the study of language developed by prominent European linguists during the inter-war period and the first decades after World War II that radically rejected the prevailing atomism of 19th century (particularly neo-grammarian) linguistics and language psychology.

  3. Nuclear structure

    CERN Document Server

    Nazarewicz, W

    1999-01-01

    Current developments in nuclear structure are discussed from a theoretical perspective. The studies of the nuclear many-body system provide us with invaluable information about the nature of the nuclear interaction, nucleonic correlations at various energy-distance scales, and the modes of the nucleonic matter.

  4. Structure/property relationships of the thermoelectric oxyselenides (Bi1-xAxCuOSe) (A=Ba and Ca)

    Science.gov (United States)

    Wong-Ng, Winnie; Yan, Yonggao; Kaduk, James A.; Tang, Xin F.

    2017-10-01

    The crystal structures, solid solution limit, and powder X-ray reference diffraction patterns for two 'natural superlattice' series Bi1-xBaxCuOSe (x = 0.05, 0.075, 0.1, 0.2, and 0.3), and Bi1-xCaxCuOSe (x = 0, 0.05, 0.075, 0.1, 0.2 and 0.3) have been determined. The structure/property relationships of these thermoelectric materials are summarized. As the ionic radius of Ba2+ is greater than that of Bi3+, the unit cell volume, V, of Bi1-xBaxCuOSe increases progressively from x = 0 to x = 0.2 (from 137.868 (5) Å3 to 141.194 (10) Å3, respectively). However, even though the ionic radius of Ca2+ is smaller than that of Bi3+, the unit cell volumes, V, of Bi1-xCaxCuOSe also show an increasing trend as a function of x (137.868 (5) Å3 to 139.295 (12) Å3 from x = 0 to 0.3, respectively) due to the relatively large increase in c parameter. The structure of Bi1-xAxCuOSe (A = Ba and Ca) can be considered as built from [Bi2(1-x)A2xO2]2(1-x)+ layers normal to the c-axis alternating with fluorite-like [Cu2Se2]2(1-x)- layers in the c-direction. The substitutions of Ba and Ca on the Bi site of Bi1-xAxCuOSe lead to the weakening of the 'bonding' between the [Bi2(1-x)A2xO2]2(1-x)+ and the [Cu2Se2]2(1-x)- layers (a decrease of Columbic force), resulting in an increase of the c-axis parameter and V. Powder X-ray diffraction patterns of Bi1-xAxCuOSe were submitted for inclusion in the Powder Diffraction File (PDF).

  5. Data Structures

    DEFF Research Database (Denmark)

    Davoodi, Pooya

    We study data structures for variants of range query problems. In particular, we consider (1) the range minimum problem: given a multidimensional array, find the position of the minimum element in a query rectangle; (2) the path minima problem: given a weighted tree, find the edge with minimum...... weight in a query path; (3) the range diameter problem: given a point set in the plane, find two points that are farthest away in a query rectangle. These and similar problems arise in various applications including document retrieval, genome sequence analysis, OLAP data cubes, network flows, shape......-fitting, and clustering. The three mentioned problems are considered for either static inputs or dynamic inputs. In the static setting, we investigate the space-efficiency of data structures, which is an important aspect in massive data algorithmics. We provide lower bounds on the trade-off between the query time...

  6. Syllable structure

    Directory of Open Access Journals (Sweden)

    Jakobsen Per

    2008-01-01

    Full Text Available In traditional structuralist understanding, language is a system of signs i.e. an inseparable unity of content and expression. According to glossematic linguistic theory, the dichotomy of form and substance in the content has its parallel in the expression. The present paper shows that in one language certain consonant clusters within the syllable are allowed, in other languages they are not. The phonotactic structure, i.e. the rules of forming syllables decide the forming of new words and identify the language at the same time. This fundamental syllable structure shows that it is scientifically untenable to maintain that the Serbo-Croatian language has split up in several new languages. .

  7. Concrete structures

    CERN Document Server

    Setareh, Mehdi

    2017-01-01

    This revised, fully updated second edition covers the analysis, design, and construction of reinforced concrete structures from a real-world perspective. It examines different reinforced concrete elements such as slabs, beams, columns, foundations, basement and retaining walls and pre-stressed concrete incorporating the most up-to-date edition of the American Concrete Institute Code (ACI 318-14) requirements for the design of concrete structures. It includes a chapter on metric system in reinforced concrete design and construction. A new chapter on the design of formworks has been added which is of great value to students in the construction engineering programs along with practicing engineers and architects. This second edition also includes a new appendix with color images illustrating various concrete construction practices, and well-designed buildings. The ACI 318-14 constitutes the most extensive reorganization of the code in the past 40 years. References to the various sections of the ACI 318-14 are pro...

  8. Terminal structure

    Science.gov (United States)

    Schmidt, Frank; Allais, Arnaud; Mirebeau, Pierre; Ganhungu, Francois; Lallouet, Nicolas

    2009-10-20

    A terminal structure (2) for a superconducting cable (1) is described. It consists of a conductor (2a) and an insulator (2b) that surrounds the conductor (2a), wherein the superconducting cable (1) has a core with a superconducting conductor (5) and a layer of insulation that surrounds the conductor (5), and wherein the core is arranged in such a way that it can move longitudinally in a cryostat. The conductor (2a) of the terminal structure (2) is electrically connected with the superconducting conductor (5) or with a normal conductor (6) that is connected with the superconducting conductor (5) by means of a tubular part (7) made of an electrically conductive material, wherein the superconducting conductor (5) or the normal conductor (6) can slide in the part (7) in the direction of the superconductor.

  9. Lightweight Structures

    Science.gov (United States)

    Whittenberger, J. Daniel

    2001-01-01

    Present structural concepts for hot static structures are conventional "sheet & stringer" or truss core construction. More weight-efficient concepts such as honeycomb and lattice block are being investigated, in combination with both conventional superalloys and TiAl. Development efforts for components made from TiAl sheet are centered on lower cost methods for sheet and foil production, plus alloy development for higher temperature capability. A low-cost casting technology recently developed for aluminum and steel lattice blocks has demonstrated the required higher strength and stiffness, with weight efficiency approach- ing honeycombs. The current effort is based on extending the temperature capability by developing lattice block materials made from IN-718 and Mar-M247.

  10. STRUCTURAL GEOLOGY

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    <正>20122174 Bai Daoyuan ( Institute of Geological Survey of Hunan Province,Changsha 410011,China );Jia Baohua Neoproterozoic TectonicEvolution of the Xuefeng Orogenic Zone in Hunan Province ( Sedimentary Geology and Tethyan Geology,ISSN1009-3850,CN51-1593 / P,31 ( 3 ), 2011,p.78-87,2illus.,1 table,96refs. ) Key words:structural evolution,Neoproterozoic Era,Hunan Province This paper deals,on the basis of abundant lithogeochemical and geochronologic

  11. Structural dynamics

    CERN Document Server

    Strømmen, Einar N

    2014-01-01

    This book introduces to the theory of structural dynamics, with focus on civil engineering structures that may be described by line-like beam or beam-column type of systems, or by a system of rectangular plates. Throughout this book the mathematical presentation contains a classical analytical description as well as a description in a discrete finite element format, covering the mathematical development from basic assumptions to the final equations ready for practical dynamic response predictions. Solutions are presented in time domain as well as in frequency domain. Structural Dynamics starts off at a basic level and step by step brings the reader up to a level where the necessary safety considerations to wind or horizontal ground motion induced dynamic design problems can be performed. The special theory of the tuned mass damper has been given a comprehensive treatment, as this is a theory not fully covered elsewhere. For the same reason a chapter on the problem of moving loads on beams has been included.

  12. Microplastic Structures

    Science.gov (United States)

    Feely, Wayne E.

    1986-07-01

    Thick coatings (5-15μm) of a new dual image, aqueous developable photoresist can be exposed using a light attenuating photomask consisting of clear, opaque and grey areas and then processed to yield thermally stable 3-dimensional structures which are potentially useful as mechanical and optical components of devices. In the positive mode, relief and intaglio images are produced by processing similar to positive novolak based resists with 1- 2μm resolution and with the added feature that the images can be made thermally stable to temperatures >300° C. Negative mode processing of coated wafers imaged with the special mask produces thermally stable structures with tunnels or hollow chambers as well as cantilever beams. Because these structures are crosslinked at the time of development, processing in the negative mode shows much wider latitude than is the case in the positive mode. Images by negative mode processing are capable of submicron resolution, higher aspect ratio (>3 vs resin compositions cover a broad range of compositions so that resins can be tailored to meet specific property requirements.

  13. STRUCTURED BACKWARD ERRORS FOR STRUCTURED KKT SYSTEMS

    Institute of Scientific and Technical Information of China (English)

    Xin-xiu Li; Xin-guo Liu

    2004-01-01

    In this paper we study structured backward errors for some structured KKT systems.Normwise structured backward errors for structured KKT systems are defined, and computable formulae of the structured backward errors are obtained. Simple numerical examples show that the structured backward errors may be much larger than the unstructured ones in some cases.

  14. Stoker structure

    Energy Technology Data Exchange (ETDEWEB)

    Mros, F.

    1981-11-10

    A screw-conveyor or auger feed and associated leveling system are disclosed for underfeed stoker troughs receiving particulate, cominuted, or chunk material, such as ''green'' coal, by way of example, this for assuring a uniformly rising level of material relative to the trough. The stoker structure herein includes combustion beds which are air perforate and kept this way through periodically rising members such as tuyeres which shear or break up clinkerformation on such beds. A pneumatically-operated system may preferably be used to actuate such movable tuyeres relative to such combustion beds. Combustion air flows through the combustion beds upwardly but not over the trough; hot gasses rising rapidly from the combustion beds confine volatiles gently rising vertically from the cone within the trough for complete combustion, essentially eliminating smoke-production thereat.

  15. Structural Discrimination

    DEFF Research Database (Denmark)

    Thorsen, Mira Skadegård

    In this article, I discuss structural discrimination, an underrepresented area of study in Danish discrimination and intercultural research. It is defined here as discursive and constitutive, and presented as a central element of my analytical approach. This notion is employed in the with which...... to understand and identify aspects of power and asymmetry in communication and interactions. With this as a defining term, I address how exclusion and discrimination exist, while also being indiscernible, within widely accepted societal norms. I introduce the concepts of microdiscrimination and benevolent...... discrimination as two ways of articulating particular, opaque forms of racial discrimination that occur in everyday Danish (and other) contexts, and have therefore become normalized. I present and discuss discrimination as it surfaces in data from my empirical studies of discrimination in Danish contexts...

  16. Structural Bionic Design of Machine Tool Structures

    Institute of Scientific and Technical Information of China (English)

    ZHAO Ling; WANG Ting; GUO Hong-liang; LI Guo-meng

    2011-01-01

    A structural bionic design process is systematically presented for lightweight mechanical structures. By mimicking biological excellent structural principles, the stiffening ribs of a machining table and a moving column were redesigned for better load-bearing efficiency. Finite element method(FEM) simulation and model experiments were carried out for performance verification, which showed the increase of structural static and dynamic performance. Structural bionic offers a new solution to change conventional structures for high specific stiffness.

  17. Asteroid structure

    Science.gov (United States)

    Asphaug, E.

    2014-07-01

    Even before the first space missions to asteroids, in the mid-1990s, it was known that asteroids have weird structures. Photometry indicated complicated shapes, and the pioneering radar investigations by Ostro and colleagues followed by adaptive optics campaigns and flybys showed odd binary forms, and confirmed the common presence of satellites, and indications of highly varying surface roughness. Some asteroids turned out to be dominated by a single major cratering event, while others showed no evidence of a major crater, or perhaps for global crater erasure. The first space mission to orbit an asteroid, NEAR, found a mixture of heavily cratered terrains and geomorphically active 'ponds', and indicated evidence for global seismicity from impact. The next mission to orbit an asteroid, Hayabusa, found what most agree is a rubble pile, with no major craters and an absence of fines. There is to date no direct evidence of asteroid interior geology, other than measurements of bulk density, and inferences made for mass distribution asymmetry based on dynamics, and inferences based on surface lineaments. Interpolating from the surface to the interior is always risky and usually wrong, but of course the answer is important since we are someday destined to require this knowledge in order to divert a hazardous asteroid from impact with the Earth. Even considering the near-subsurface, here we remain as ignorant as we were about the Moon in the early 1960s, whether the surface will swallow us up in dust, or will provide secure landing and anchoring points. Laboratory experimentation in close to zero-G is still in its early stages. Adventures such as mining and colonization will surely have to wait until we better know these things. How do we get from here to there? I will focus on 3 areas of progress: (1) asteroid cratering seismology, where we use the surface craters to understand what is going on inside; (2) numerical modeling of collisions, which predicts the internal

  18. Bi{sub 1−x}Nb{sub x}O{sub 1.5+x} (x=0.0625, 0.12) fast ion conductors: Structures, stability and oxide ion migration pathways

    Energy Technology Data Exchange (ETDEWEB)

    Tate, Matthew L. [Department of Chemistry, Durham University, Science Site, South Road, Durham DH1 3LE (United Kingdom); Australian Nuclear Science and Technology Organisation, Lucas Heights 2234, NSW (Australia); Hack, Jennifer [Department of Chemistry, Durham University, Science Site, South Road, Durham DH1 3LE (United Kingdom); Institut Laue-Langevin, Grenoble (France); Kuang, Xiaojun [Department of Chemistry, Durham University, Science Site, South Road, Durham DH1 3LE (United Kingdom); McIntyre, Garry J. [Australian Nuclear Science and Technology Organisation, Lucas Heights 2234, NSW (Australia); Withers, Ray L. [Research School of Chemistry, Australian National University, Canberra, ACT (Australia); Johnson, Mark R. [Institut Laue-Langevin, Grenoble (France); Radosavljevic Evans, Ivana, E-mail: ivana.radosavljevic@durham.ac.uk [Department of Chemistry, Durham University, Science Site, South Road, Durham DH1 3LE (United Kingdom); Australian Nuclear Science and Technology Organisation, Lucas Heights 2234, NSW (Australia)

    2015-05-15

    A combined experimental and computational study of Bi{sub 1−x}Nb{sub x}O{sub 1.5+x} (x=0.0625 and 0.12) has been carried out using laboratory X-ray, neutron and electron diffraction, impedance measurements and ab-initio molecular dynamics. We demonstrate that Bi{sub 0.9375}Nb{sub 0.0625}O{sub 1.5625}, previously reported to adopt a cubic fluorite-type superstructure, can form two different polymorphs depending on the synthetic method: a metastable cubic phase is produced by quenching; while slower cooling yields a stable material with a tetragonal √2×√2×1 superstructure, which undergoes a reversible phase transition into the cubic form at ~680 °C on subsequent reheating. Neutron diffraction reveals that the tetragonal superstructure arises mainly from ordering in the oxygen sublattice, with Bi and Nb remaining disordered, although structured diffuse scattering observed in the electron diffraction patterns suggests a degree of short-range ordering. Both materials are oxide ion conductors. On thermal cycling, Bi{sub 0.88}Nb{sub 0.12}O{sub 1.62} exhibits a decrease in conductivity of approximately an order of magnitude due to partial transformation into the tetragonal phase, but still exhibits conductivity comparable to yttria-stabilised zirconia (YSZ). Ab-initio molecular dynamics simulations performed on Bi{sub 0.9375}Nb{sub 0.0625}O{sub 1.5625} show that oxide ion diffusion occurs by O{sup 2−} jumps between edge- and corner-sharing OM{sub 4} groups (M=Bi, Nb) via tetrahedral □M{sub 4} and octahedral □M{sub 6} vacancies. - Graphical abstract: Oxide ion migration in tetragonal Bi{sub 0.9375}Nb{sub 0.0625}O{sub 1.5625} occurs by O{sup 2−} jumps between edge- and corner-sharing OM{sub 4} groups (M=Bi, Nb) via tetrahedral M{sub 4} and octahedral M{sub 6} vacancies. - Highlights: • Bi{sub 0.9375}Nb{sub 0.0625}O{sub 1.5625} adopts a tetragonal √2×√2×1 fluorite superstructure. • Superstructure is due to ordering in the O-sublattice, with Bi

  19. Structural Biology Fact Sheet

    Science.gov (United States)

    ... Home > Science Education > Structural Biology Fact Sheet Structural Biology Fact Sheet Tagline (Optional) Middle/Main Content Area ​Other Fact Sheets What is structural biology? Structural biology is the study of how biological ...

  20. Collapsible Geostrut Structure

    Science.gov (United States)

    Robertson, Glen A.

    1994-01-01

    Portable truss structure collapsible into smaller volume for storage and transportation. At new site, reerected quickly, without need to reassemble parts. Structure could be tent, dome, tunnel, or platform. Key element in structure joint, called "geostrut joint," includes internal cable. Structure is network of struts attached to geostrut joints. Pulling cables taut in all joints makes structure rigid. Releasing cables relaxes structure.

  1. Magnetic multilayer structure

    Energy Technology Data Exchange (ETDEWEB)

    Herget, Philipp; O' Sullivan, Eugene J.; Romankiw, Lubomyr T.; Wang, Naigang; Webb, Bucknell C.

    2017-03-21

    A mechanism is provided for an integrated laminated magnetic device. A substrate and a multilayer stack structure form the device. The multilayer stack structure includes alternating magnetic layers and diode structures formed on the substrate. Each magnetic layer in the multilayer stack structure is separated from another magnetic layer in the multilayer stack structure by a diode structure.

  2. Magnetic multilayer structure

    Science.gov (United States)

    Herget, Philipp; O'Sullivan, Eugene J.; Romankiw, Lubomyr T.; Wang, Naigang; Webb, Bucknell C.

    2016-07-05

    A mechanism is provided for an integrated laminated magnetic device. A substrate and a multilayer stack structure form the device. The multilayer stack structure includes alternating magnetic layers and diode structures formed on the substrate. Each magnetic layer in the multilayer stack structure is separated from another magnetic layer in the multilayer stack structure by a diode structure.

  3. Structural Analysis of Plate Based Tensegrity Structures

    DEFF Research Database (Denmark)

    Hald, Frederik; Kirkegaard, Poul Henning; Damkilde, Lars

    2013-01-01

    Plate tensegrity structures combine tension cables with a cross laminated timber plate and can then form e.g. a roof structure. The topology of plate tensegrity structures is investigated through a parametric investigation. Plate tensegrity structures are investigated, and a method...... for determination of the structures pre-stresses is used. A parametric investigation is performed to determine a more optimized form of the plate based tensegrity structure. Conclusions of the use of plate based tensegrity in civil engineering and further research areas are discussed....

  4. Structural Analysis of Plate Based Tensegrity Structures

    DEFF Research Database (Denmark)

    Hald, Frederik; Kirkegaard, Poul Henning; Damkilde, Lars

    2013-01-01

    Plate tensegrity structures combine tension cables with a cross laminated timber plate and can then form e.g. a roof structure. The topology of plate tensegrity structures is investigated through a parametric investigation. Plate tensegrity structures are investigated, and a method...... for determination of the structures pre-stresses is used. A parametric investigation is performed to determine a more optimized form of the plate based tensegrity structure. Conclusions of the use of plate based tensegrity in civil engineering and further research areas are discussed....

  5. Computational structural mechanics for engine structures

    Science.gov (United States)

    Chamis, C. C.

    1989-01-01

    The computational structural mechanics (CSM) program at Lewis encompasses: (1) fundamental aspects for formulating and solving structural mechanics problems, and (2) development of integrated software systems to computationally simulate the performance/durability/life of engine structures. It is structured to mainly supplement, complement, and whenever possible replace, costly experimental efforts which are unavoidable during engineering research and development programs. Specific objectives include: investigate unique advantages of parallel and multiprocesses for: reformulating/solving structural mechanics and formulating/solving multidisciplinary mechanics and develop integrated structural system computational simulators for: predicting structural performances, evaluating newly developed methods, and for identifying and prioritizing improved/missing methods needed. Herein the CSM program is summarized with emphasis on the Engine Structures Computational Simulator (ESCS). Typical results obtained using ESCS are described to illustrate its versatility.

  6. Common structure-balance between spacetime structure and massenergy structure

    Science.gov (United States)

    Cao, Daqing; Cao, Dayong

    2017-01-01

    According to Einstein field equation, there is a balance between spacetime structure and massenergy structure. nd the paper consider it as a common structurewhich was brought forward by Daqing Cao in 2011 ecause it is general structure in the universe and everything have the same model of structure in their one system. The Jovian planets is spacetime structure of solar system because they are gas-sphere and they have more density of spacetime (spacetime/massenergy) than the density of massenergy (massenergy/spacetime). The terrestrial planets is massenergy structure of solar system because they are rock-ball and they have more density of massenergy than the density of spacetime. That can explain of that the Jovian planets of big mass is far away from sun. With the idea that the wave is spacetime and the wave effect is spacetime structure, the planets have elliptic orbits and the same direction of their revolution. Because sun is like a massenergy center of the massenergy structure and the terrestrial planets, the paper supposes there is a dark sun-a dark hole who has a spacetime center of spacetime structure and influences on the orbits of the Jovian planets. http://meetings.aps.org/Meeting/APR16/Session/M13.8

  7. Offshore Structural Control Considering Fluid Structure Interaction

    Institute of Scientific and Technical Information of China (English)

    Ju Myung KIM; Dong Hyawn KIM; Gyu Won LEE

    2006-01-01

    Tuned Mass Damper (TMD) was applied to an offshore structure to control ocean wave-induced vibration. In the analysis of the dynamic response of the offshore structure, fluid-structure interaction is considered and the errors, which occur in the linearization of the interaction, are investigated. For the investigation of the performance of TMD in controlling the vibration, both regular waves with different periods and irregular waves with different significant wave heights are used. Based on the numerical analysis it is concluded that the fluid-structure interaction should be considered in the evaluation of the capability of TMD in vibration control of offshore structures.

  8. Designing pliable structural Skins

    DEFF Research Database (Denmark)

    Tamke, Martin; Peters, Brady; Nielsen, Stig Anton;

    2013-01-01

    Structural stability can be formed through structured or seemingly unstructured approaches to fold, plead or crumble paper. This paper reports on two projects that showcase how computational design approaches can help to widen the understanding and use of structural skins....

  9. Study of Boundary Structures.

    Science.gov (United States)

    1982-09-01

    THEORY OF ABC-CBA STACKING BOUNDARY IN fcc STRUCTURE .......... 11 - 4 TRANSITIONS AND PHASE EQUILIBRIA AMONG GRAIN BOUNDARY STRUCTURES...19 B THEORY OF ABC-CBA STACKING BOUNDARY IN fcc STRUCTURE .......... 37 C TRANSITIONS AND PHASE EQUILIBRIA AMONG GRAIN BOUNDARY...layer structure. 10 SECTION 3 THEORY OF ABC-CBA STACKING BOUNDARY IN fcc STRUCTURE The (111) planes of the fcc structure is stacked as ABCABC... as

  10. Protein structure search and local structure characterization

    Directory of Open Access Journals (Sweden)

    Ku Shih-Yen

    2008-08-01

    Full Text Available Abstract Background Structural similarities among proteins can provide valuable insight into their functional mechanisms and relationships. As the number of available three-dimensional (3D protein structures increases, a greater variety of studies can be conducted with increasing efficiency, among which is the design of protein structural alphabets. Structural alphabets allow us to characterize local structures of proteins and describe the global folding structure of a protein using a one-dimensional (1D sequence. Thus, 1D sequences can be used to identify structural similarities among proteins using standard sequence alignment tools such as BLAST or FASTA. Results We used self-organizing maps in combination with a minimum spanning tree algorithm to determine the optimum size of a structural alphabet and applied the k-means algorithm to group protein fragnts into clusters. The centroids of these clusters defined the structural alphabet. We also developed a flexible matrix training system to build a substitution matrix (TRISUM-169 for our alphabet. Based on FASTA and using TRISUM-169 as the substitution matrix, we developed the SA-FAST alignment tool. We compared the performance of SA-FAST with that of various search tools in database-scale search tasks and found that SA-FAST was highly competitive in all tests conducted. Further, we evaluated the performance of our structural alphabet in recognizing specific structural domains of EGF and EGF-like proteins. Our method successfully recovered more EGF sub-domains using our structural alphabet than when using other structural alphabets. SA-FAST can be found at http://140.113.166.178/safast/. Conclusion The goal of this project was two-fold. First, we wanted to introduce a modular design pipeline to those who have been working with structural alphabets. Secondly, we wanted to open the door to researchers who have done substantial work in biological sequences but have yet to enter the field of protein

  11. Thermoelectric properties of FeAs based superconductors, with thick perovskite- and Sm-O fluorite-type blocking layers

    Science.gov (United States)

    Singh, S. J.; Shimoyama, J.; Ogino, H.; Kishio, K.

    2015-11-01

    The transport properties (electrical resistivity, Hall and Seebeck coefficient, and thermal conductivity) of iron based superconductors with thick perovskite-type oxide blocking layers and fluorine-doped SmFeAsO were studied to explore their possible potential for thermoelectric applications. The thermal conductivity of former compounds depicts the dominated role of phonon and its value decreases rapidly below the Tc, suggesting the addition of scattering of phonons. Both the Seebeck coefficient (S) and Hall coefficient (RH) of all samples were negative in the whole temperature region below 300 K, indicating that the major contribution to the normal state conductivity is by electrons. In addition, the profile of S(T) and RH(T) of all samples have similar behaviours as would be expected for a multi-band superconductors. Although the estimated thermoelectric figure of merit (ZT) of these compounds was much lower than that of practically applicable thermoelectric materials, however its improvement can be expected by optimizing microstructure of the polycrystalline materials, such as densification and grain orientation.

  12. Influence of Gold on Ce-Zr-Co Fluorite-Type Mixed Oxide Catalysts for Ethanol Steam Reforming

    Directory of Open Access Journals (Sweden)

    Véronique Pitchon

    2012-02-01

    Full Text Available The effect of gold presence on carbon monoxide oxidation and ethanol steam reforming catalytic behavior of two Ce-Zr-Co mixed oxides catalysts with a constant Co charge and different Ce/Zr ratios was investigated. The Ce-Zr-Co mixed oxides were obtained by the pseudo sol-gel like method, based on metallic propionates polymerization and thermal decomposition, whereas the gold-supported Ce-Zr-Co mixed oxides catalysts were prepared using the direct anionic exchange. The catalysts were characterized using XRD, TPR, and EDXS-TEM. The presence of Au in doped Ce-Zr-Co oxide catalyst decreases the temperature necessary to reduce the cobalt and the cerium loaded in the catalyst and favors a different reaction pathway, improving the acetaldehyde route by ethanol dehydrogenation, instead of the ethylene route by ethanol dehydration or methane re-adsorption, thus increasing the catalytic activity and selectivity into hydrogen.

  13. Thermoelectric properties of FeAs based superconductors, with thick perovskite- and Sm-O fluorite-type blocking layers

    Energy Technology Data Exchange (ETDEWEB)

    Singh, S.J., E-mail: s.j.singh@ifw-dresden.de [Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Leibniz Institute for Solid State and Materials Research (IFW), Helmhotzstrass 20, 01069 Dresden (Germany); Shimoyama, J.; Ogino, H.; Kishio, K. [Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2015-11-15

    Highlights: • Thermoelectric properties are studied for 22438 and 225411 with Sm1111. • Thermal and electrical coeff. follow almost the same behaviour for both categories. • The thermoelectric figure of merit has low value from the application point. • Major contribution to the normal state conductivity is by electron type carriers. - Abstract: The transport properties (electrical resistivity, Hall and Seebeck coefficient, and thermal conductivity) of iron based superconductors with thick perovskite-type oxide blocking layers and fluorine-doped SmFeAsO were studied to explore their possible potential for thermoelectric applications. The thermal conductivity of former compounds depicts the dominated role of phonon and its value decreases rapidly below the T{sub c}, suggesting the addition of scattering of phonons. Both the Seebeck coefficient (S) and Hall coefficient (R{sub H}) of all samples were negative in the whole temperature region below 300 K, indicating that the major contribution to the normal state conductivity is by electrons. In addition, the profile of S(T) and R{sub H}(T) of all samples have similar behaviours as would be expected for a multi-band superconductors. Although the estimated thermoelectric figure of merit (ZT) of these compounds was much lower than that of practically applicable thermoelectric materials, however its improvement can be expected by optimizing microstructure of the polycrystalline materials, such as densification and grain orientation.

  14. 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

    protons become more dominating as charge carrier at temperatures below typically 500°C under wet conditions. The hydration enthalpies were determined by simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC). The contribution from ionic conductivity increases and the hydration...... 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....

  15. Deployable Composite Structures Project

    Data.gov (United States)

    National Aeronautics and Space Administration — NASA is seeking innovative structure technologies that will advance expandable modules for orbital and surface based habitats. These secondary structures must...

  16. Composite Structures Manufacturing Facility

    Data.gov (United States)

    Federal Laboratory Consortium — The Composite Structures Manufacturing Facility specializes in the design, analysis, fabrication and testing of advanced composite structures and materials for both...

  17. Distributed Structure Searchable Toxicity

    Data.gov (United States)

    U.S. Environmental Protection Agency — The Distributed Structure Searchable Toxicity (DSSTox) online resource provides high quality chemical structures and annotations in association with toxicity data....

  18. Protein structure mining using a structural alphabet.

    Science.gov (United States)

    Tyagi, M; de Brevern, A G; Srinivasan, N; Offmann, B

    2008-05-01

    We present a comprehensive evaluation of a new structure mining method called PB-ALIGN. It is based on the encoding of protein structure as 1D sequence of a combination of 16 short structural motifs or protein blocks (PBs). PBs are short motifs capable of representing most of the local structural features of a protein backbone. Using derived PB substitution matrix and simple dynamic programming algorithm, PB sequences are aligned the same way amino acid sequences to yield structure alignment. PBs are short motifs capable of representing most of the local structural features of a protein backbone. Alignment of these local features as sequence of symbols enables fast detection of structural similarities between two proteins. Ability of the method to characterize and align regions beyond regular secondary structures, for example, N and C caps of helix and loops connecting regular structures, puts it a step ahead of existing methods, which strongly rely on secondary structure elements. PB-ALIGN achieved efficiency of 85% in extracting true fold from a large database of 7259 SCOP domains and was successful in 82% cases to identify true super-family members. On comparison to 13 existing structure comparison/mining methods, PB-ALIGN emerged as the best on general ability test dataset and was at par with methods like YAKUSA and CE on nontrivial test dataset. Furthermore, the proposed method performed well when compared to flexible structure alignment method like FATCAT and outperforms in processing speed (less than 45 s per database scan). This work also establishes a reliable cut-off value for the demarcation of similar folds. It finally shows that global alignment scores of unrelated structures using PBs follow an extreme value distribution. PB-ALIGN is freely available on web server called Protein Block Expert (PBE) at http://bioinformatics.univ-reunion.fr/PBE/.

  19. Structural behaviour of super-light structures

    DEFF Research Database (Denmark)

    Bagger, Anne; Hertz, Kristian Dahl

    2010-01-01

    with a lighter and softer material, such as lightweight concrete. The combined use of stiff and light material in SLS results in structures of high stiffness and low weight. The applied technology and the advantages of SLS are elaborated upon in [1] in these proceedings. The present paper focuses......A new structural concept, called Super-light Structures (SLS), has recently been invented and patented at the Technical University of Denmark. The basic concept of SLS is to construct a skeleton of a stiff and strong material, such as ordinary or high strength concrete, and stabilize this skeleton...... on the structural correlation between the stiff material and the light material. The shape of the skeleton can be optimized for the primary load on the structure, and it will take up the majority of the load. The lighter material forms the outer geometry of the structural component (e.g. a wall), and has several...

  20. Mechanosynthesis and structural characterization of nanocrystalline Ce{sub 1–x}Y{sub x}O{sub 2–δ} (x=0.1–0.35) solid solutions

    Energy Technology Data Exchange (ETDEWEB)

    Fabián, Martin, E-mail: fabianm@saske.sk [Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 04001 Košice (Slovakia); Antić, Bratislav [“Vinča” Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11001 Belgrade (Serbia); Girman, Vladimír [Institute of Physics, P. J. Šafárik University, Park Angelinum 9, 04154 Košice (Slovakia); Vučinić-Vasić, Milica [Faculty of Technical Sciences, University of Novi Sad, Trg D. Obradovića 6, 21000 Novi Sad (Serbia); Kremenović, Aleksandar [Laboratory of Crystallography, Faculty of Mining and Geology, University of Belgrade, Djusina 7, 11001 Belgrade (Serbia); Suzuki, Shigeru [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira 2-1-1, Aoba-ku, 980-8577 Sendai (Japan); Hahn, Horst [Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Šepelák, Vladimír [Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 04001 Košice (Slovakia)

    2015-10-15

    A series of nanostructured fluorite-type Ce{sub 1–x}Y{sub x}O{sub 2–δ} (0≤x≤0.35) solid solutions, prepared via high-energy milling of the CeO{sub 2}/Y{sub 2}O{sub 3} mixtures, are investigated by XRD, HR-TEM, EDS and Raman spectroscopy. For the first time, complementary information on both the long-range and short-range structural features of mechanosynthesized Ce{sub 1–x}Y{sub x}O{sub 2–δ}, obtained by Rietveld analysis of XRD data and Raman spectroscopy, is provided. The lattice parameters of the as-prepared solid solutions decrease with increasing yttrium content. Rietveld refinements of the XRD data reveal increase in microstrains in the host ceria lattice as a consequence of yttrium incorporation. Raman spectra are directly affected by the presence of oxygen vacancies; their existence is evidenced by the presence of vibration modes at ~560 and ~600 cm{sup –1}. The detailed spectroscopic investigations enable us to separate extrinsic and intrinsic origin of oxygen vacancies. It is demonstrated that mechanosynthesis can be successfully employed in the one-step preparation of nanocrystalline Ce{sub 1–x}Y{sub x}O{sub 2–δ} solid solutions. - Graphical abstract: Mechanosynthesis of nanocrystalline Ce{sub 1–x}Y{sub x}O{sub 2–δ} (x=0.1–0.35) solid solutions. - Highlights: • One-step mechanosynthesis of nanoscale Ce{sub 1–x}Y{sub x}O{sub 2–δ} (0≤x≤0.35) solid solutions. • Complementary information on the long-range and short-range structural features of mechanosynthesized Ce{sub 1–x}Y{sub x}O{sub 2–δ} is provided. • Structural variations as a response to the yttrium doping. • Separation of extrinsic and intrinsic origin of the induced oxygen vacancies.

  1. Electronic, elastic, acoustic and optical properties of cubic TiO{sub 2}: A DFT approach

    Energy Technology Data Exchange (ETDEWEB)

    Mahmood, Tariq, E-mail: tariq_mahmood78@hotmail.com [Research Center of Materials Science, School of Material Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); Centre for High Energy Physics, University of the Punjab, Lahore 54590 (Pakistan); Cao, Chuanbao, E-mail: cbcao@bit.edu.cn [Research Center of Materials Science, School of Material Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); Tahir, Muhammad; Idrees, Faryal [Research Center of Materials Science, School of Material Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); Ahmed, Maqsood [Centre for High Energy Physics, University of the Punjab, Lahore 54590 (Pakistan); Tanveer, M.; Aslam, Imran; Usman, Zahid; Ali, Zulfiqar; Hussain, Sajad [Research Center of Materials Science, School of Material Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China)

    2013-07-01

    The electronic, elastic, acoustic and optical properties of cubic phases TiO{sub 2} fluorite and pyrite are investigated using the first principles calculations. We have employed five different exchange–correlation functions within the local density and generalized gradient approximations using the ultrasoft plane wave pseudopotential method. The calculated band structures of cubic-TiO{sub 2} elucidate that the TiO{sub 2} fluorite and pyrite are direct and indirect semiconductors in contrast to the previous findings. From our studied properties such as bulk and shear moduli, elastic constants C{sub 44} and Debye temperature for TiO{sub 2} fluorite and pyrite, we infer that both the cubic phases are not superhard materials and the pyrite phase is harder than fluorite. The longitudinal and transversal acoustic wave speeds for both phases in the directions [100], [110] and [111] are determined using the pre-calculated elastic constants. In addition, we also calculate the optical properties such as dielectric function, absorption spectrum, refractive index and energy loss function using the pre-optimized structure. On the observation of optical properties TiO{sub 2} fluorite phase turn out to be more photocatalytic than pyrite.

  2. Chinese Conversation Structure

    Institute of Scientific and Technical Information of China (English)

    LIU Yan

    2016-01-01

    This paper aims to describe the features of Chinese conversation structure. Specifically speaking, the structure will be analyzed from the following four aspects:openings and pre-sequence, adjacency pairs, pre-closing and closing. Generally speak-ing, Chinese conversation structure is similar to English conversation structure. But still a lot of differences are found due to cul-tural factors.

  3. Crystal structure and prediction.

    Science.gov (United States)

    Thakur, Tejender S; Dubey, Ritesh; Desiraju, Gautam R

    2015-04-01

    The notion of structure is central to the subject of chemistry. This review traces the development of the idea of crystal structure since the time when a crystal structure could be determined from a three-dimensional diffraction pattern and assesses the feasibility of computationally predicting an unknown crystal structure of a given molecule. Crystal structure prediction is of considerable fundamental and applied importance, and its successful execution is by no means a solved problem. The ease of crystal structure determination today has resulted in the availability of large numbers of crystal structures of higher-energy polymorphs and pseudopolymorphs. These structural libraries lead to the concept of a crystal structure landscape. A crystal structure of a compound may accordingly be taken as a data point in such a landscape.

  4. Strategy implemented through structuring and new structures

    DEFF Research Database (Denmark)

    Nielsen, Renate

    Research objective: With the purpose of generating a new understanding of how development in organisations take place, an interpretive perspective at continuous processes in organisations will be applied: more specifically at how organisational interpretation forms an organisation's strategy...... and how the strategy is implemented through structuring, new structures and routines....

  5. Internal structure of structurally stitched NCF preform

    NARCIS (Netherlands)

    Koissin, V.; Ruopp, A.; Lomov, S.V.; Verpoest, I.; Witzel, V.; Drechsler, K.

    2006-01-01

    The paper addresses the experimental investigation of the unit cell architecture in a structurally stitched multilayer carbon-fibre preform. Each layer is a multiaxial multiply non-crimp fabric (NCF) knit with a non-structural stitching. The term “structural” presumes here that the stitching yarn do

  6. Ce4+替代Pu4+的模拟固化体(Gd1-xCex)2Zr2O7+x的合成及结构演变%Synthesis and Structural Transformations of (Gd1-xCex)2Zr2O7+x:An Analogue for Pu Immobilization

    Institute of Scientific and Technical Information of China (English)

    赵培柱; 李林艳; 徐盛明; 张覃

    2013-01-01

      Gd2Zr2O7中Gd具有很大的中子吸收截面,其烧绿石结构-缺陷萤石结构的转变能较低,使其成为理想的核废料固化基材.使用硝酸盐为原料,添加少量NaF作助熔剂,在较低温度下(和传统高温固相反应相比),合成了烧绿石型 Gd2Zr2O7.以 Ce4+模拟 Pu4+,研究了 Gd2Zr2O7对锕系核素的固化,并合成了系列模拟固化体(Gd1-xCex)2Zr2O7+x (0≤x≤0.6).采用粉末 X 射线衍射(XRD)对系列样品进行了表征.结果表明:随着 x 值的增大,样品从烧绿石结构向缺陷萤石结构转变,且晶胞大小基本保持恒定,但当x=0.6时,衍射峰明显宽化,晶格畸变比较严重,晶格稳定性降低.当x=1时,即用Ce4+完全取代Gd3+进行合成,不能得到Ce2Zr2O8,产物发生了相分离,为四方结构的(Zr0.88Ce0.12)O2和萤石结构的(Ce0.75Zr0.25)O2的混合物.模拟固化体的浸出率测试表明:当x≤0.2时,各元素浸出率均很低,但当x≥0.4时,各元素的浸出率明显升高,说明以Gd2Zr2O7作为固化Pu4+的基材, Pu4+掺入量不宜高于40%.%Gd2Zr2O7 is a wel known host for nuclear waste immobilization because of the high neutron absorption cross section of Gd and low energy transformation between ordered pyrochlore and disordered defect-fluorite structures. Pyrochlore Gd2Zr2O7 was synthesized at relatively low temperature (compared with traditional high temperature solid-state reaction) using Gd(NO3)3·nH2O, Zr(NO3)4·nH2O as a starting material and a smal amount of NaF as fluxing agent. Ce4 + was used as an analogue for Pu4 + and its immobilization behavior in Gd2Zr2O7 was studied in a series of solidified forms comprising (Gd1-xCex)2Zr2O7+x (0≤x≤0.6). Powder X-ray diffraction (XRD) data showed that the sample structure transformed from pyrochlore to defect-fluorite type with increasing x but maintained constant unit cel volumes. As x was increased to 0.6, the diffraction peaks showed broadening, suggesting considerable lattice distortion

  7. Fluoride glass fiber optics

    CERN Document Server

    Aggarwal, Ishwar D

    1991-01-01

    Fluoride Glass Fiber Optics reviews the fundamental aspects of fluoride glasses. This book is divided into nine chapters. Chapter 1 discusses the wide range of fluoride glasses with an emphasis on fluorozirconate-based compositions. The structure of simple fluoride systems, such as BaF2 binary glass is elaborated in Chapter 2. The third chapter covers the intrinsic transparency of fluoride glasses from the UV to the IR, with particular emphasis on the multiphonon edge and electronic edge. The next three chapters are devoted to ultra-low loss optical fibers, reviewing methods for purifying and

  8. Oxygen trapping and cation site-splitting in Y(2-x)PrxO3+δ (0.0≤x<2.0 and δ≤1.0)

    Science.gov (United States)

    Lussier, Joey A.; Devitt, Graham; Szkop, Kevin M.; Bieringer, Mario

    2016-10-01

    The reduction and oxidation of the solid solution Y2-xPrxO3+δ (0.0≤xtime of flight neutron diffraction data. In the bixbyite structures the 8c cation site splits into the 16c cation site and the 24d cation position migrates toward the ideal fluorite coordination upon oxidation. Reductive in-situ diffraction experiments reveal the co-existence of the fluorite and bixbyite structure only in a narrow temperature range. During oxidation of the bixbyite phase a new 16c oxide anion site is populated. The impact of the 16c oxide site population on the cation sublattice is being discussed.

  9. Building a Structural Model: Parameterization and Structurality

    Directory of Open Access Journals (Sweden)

    Michel Mouchart

    2016-04-01

    Full Text Available A specific concept of structural model is used as a background for discussing the structurality of its parameterization. Conditions for a structural model to be also causal are examined. Difficulties and pitfalls arising from the parameterization are analyzed. In particular, pitfalls when considering alternative parameterizations of a same model are shown to have lead to ungrounded conclusions in the literature. Discussions of observationally equivalent models related to different economic mechanisms are used to make clear the connection between an economically meaningful parameterization and an economically meaningful decomposition of a complex model. The design of economic policy is used for drawing some practical implications of the proposed analysis.

  10. Band structure of semiconductors

    CERN Document Server

    Tsidilkovski, I M

    2013-01-01

    Band Structure of Semiconductors provides a review of the theoretical and experimental methods of investigating band structure and an analysis of the results of the developments in this field. The book presents the problems, methods, and applications in the study of band structure. Topics on the computational methods of band structure; band structures of important semiconducting materials; behavior of an electron in a perturbed periodic field; effective masses and g-factors for the most commonly encountered band structures; and the treatment of cyclotron resonance, Shubnikov-de Haas oscillatio

  11. Structural system identification: Structural dynamics model validation

    Energy Technology Data Exchange (ETDEWEB)

    Red-Horse, J.R.

    1997-04-01

    Structural system identification is concerned with the development of systematic procedures and tools for developing predictive analytical models based on a physical structure`s dynamic response characteristics. It is a multidisciplinary process that involves the ability (1) to define high fidelity physics-based analysis models, (2) to acquire accurate test-derived information for physical specimens using diagnostic experiments, (3) to validate the numerical simulation model by reconciling differences that inevitably exist between the analysis model and the experimental data, and (4) to quantify uncertainties in the final system models and subsequent numerical simulations. The goal of this project was to develop structural system identification techniques and software suitable for both research and production applications in code and model validation.

  12. Rheology of Structured Oils

    Science.gov (United States)

    Kelbaliev, G. I.; Rasulov, S. R.; Rzaev, A. G.; Mustafaeva, G. R.

    2017-07-01

    Rheological models of structured oils are proposed and compared with available experimental data on oils from different deposits. It is shown that structured oils can possess properties of Bingham and power-law non-Newtonian fluids.

  13. Structural Measures - Hospital

    Data.gov (United States)

    U.S. Department of Health & Human Services — A list of hospitals and the availability of structural measures at that hospital. A structural measure reflects the environment in which hospitals care for patients....

  14. Structural Static Laboratory

    Data.gov (United States)

    Federal Laboratory Consortium — Structural testing is performed to verify the structural integrity of space flight and ground test hardware. Testing is also performed to verify the finite element...

  15. Growing Timber Structures

    DEFF Research Database (Denmark)

    Tamke, Martin; Evers, Henrik Leander; Stasiuk, David

    2013-01-01

    The contemporary design of timber structures has to answer questions concerning structural stability, production impact and energy implications in ever earlier stages. The interrelation of these levels creates a complexity that is difficult to resolve through contemporary linear parametric...

  16. Advanced structural inorganic chemistry

    CERN Document Server

    Li, Wai-Kee; Mak, Thomas C W

    2008-01-01

    An English edition of a textbook based on teaching at the final year undergraduate and graduate level. It presents structure and bonding, generalizations of structural trends, crystallographic data, as well as highlights from the recent literature.

  17. Antenna Structure Registrate

    Data.gov (United States)

    Department of Homeland Security — This file is an extract of the Antenna Structure Registrate (ASR). The ASR consists of antenna structures that are more than 60.96 meters (200 feet) in height or...

  18. Structural health monitoring for ship structures

    Energy Technology Data Exchange (ETDEWEB)

    Farrar, Charles [Los Alamos National Laboratory; Park, Gyuhae [Los Alamos National Laboratory; Angel, Marian [Los Alamos National Laboratory; Bement, Matthew [Los Alamos National Laboratory; Salvino, Liming [NSWC, CADEROCK

    2009-01-01

    Currently the Office of Naval Research is supporting the development of structural health monitoring (SHM) technology for U.S. Navy ship structures. This application is particularly challenging because of the physical size of these structures, the widely varying and often extreme operational and environmental conditions associated with these ships missions, lack of data from known damage conditions, limited sensing that was not designed specifically for SHM, and the management of the vast amounts of data that can be collected during a mission. This paper will first define a statistical pattern recognition paradigm for SHM by describing the four steps of (1) Operational Evaluation, (2) Data Acquisition, (3) Feature Extraction, and (4) Statistical Classification of Features as they apply to ship structures. Note that inherent in the last three steps of this process are additional tasks of data cleansing, compression, normalization and fusion. The presentation will discuss ship structure SHM challenges in the context of applying various SHM approaches to sea trials data measured on an aluminum multi-hull high-speed ship, the HSV-2 Swift. To conclude, the paper will discuss several outstanding issues that need to be addressed before SHM can make the transition from a research topic to actual field applications on ship structures and suggest approaches for addressing these issues.

  19. Fundamentals of structural dynamics

    CERN Document Server

    Craig, Roy R

    2006-01-01

    From theory and fundamentals to the latest advances in computational and experimental modal analysis, this is the definitive, updated reference on structural dynamics.This edition updates Professor Craig's classic introduction to structural dynamics, which has been an invaluable resource for practicing engineers and a textbook for undergraduate and graduate courses in vibrations and/or structural dynamics. Along with comprehensive coverage of structural dynamics fundamentals, finite-element-based computational methods, and dynamic testing methods, this Second Edition includes new and e

  20. Synchronously Deployable Truss Structures

    Science.gov (United States)

    Rhodes, M. D.; Hedgepeth, J. M.

    1986-01-01

    Structure lightweight, readily deployed, and has reliable joints. New truss concept, designated as "pac truss," developed. Features easy deployment without need for complex mechanisms. Structures of this type deployed in free flight by controlled release of stored energy in torsional springs at selected hinges located throughout structure. Double-folding technique used in beam model applicable to flat planar trusses, allowing structures of large expanse to fold into compact packages and be deployed for space-platform applications.

  1. Extended icosahedral structures

    CERN Document Server

    Jaric, Marko V

    1989-01-01

    Extended Icosahedral Structures discusses the concepts about crystal structures with extended icosahedral symmetry. This book is organized into six chapters that focus on actual modeling of extended icosahedral crystal structures. This text first presents a tiling approach to the modeling of icosahedral quasiperiodic crystals. It then describes the models for icosahedral alloys based on random connections between icosahedral units, with particular emphasis on diffraction properties. Other chapters examine the glassy structures with only icosahedral orientational order and the extent of tra

  2. HIV Structural Database

    Science.gov (United States)

    SRD 102 HIV Structural Database (Web, free access)   The HIV Protease Structural Database is an archive of experimentally determined 3-D structures of Human Immunodeficiency Virus 1 (HIV-1), Human Immunodeficiency Virus 2 (HIV-2) and Simian Immunodeficiency Virus (SIV) Proteases and their complexes with inhibitors or products of substrate cleavage.

  3. Structural Ceramics Database

    Science.gov (United States)

    SRD 30 NIST Structural Ceramics Database (Web, free access)   The NIST Structural Ceramics Database (WebSCD) provides evaluated materials property data for a wide range of advanced ceramics known variously as structural ceramics, engineering ceramics, and fine ceramics.

  4. Structural safety during construction

    NARCIS (Netherlands)

    Terwel, K.C.; Mud, M.; Frijters, A.

    2014-01-01

    Structural safety during construction is a main concern for the building industry. Collapses of temporary structures or incomplete permanent structures are a threat for the safety of persons. Based on data from Dutch Labour Inspectorate this study concluded that approximately 20% of the fatalities

  5. Programing Structural Synthesis System

    Science.gov (United States)

    Rogers, James L., Jr.

    1986-01-01

    Program aids research in analysis and optimization. Programing Structural Synthesis System (PROSSS2) developed to provide structural-synthesis capability by combining access to SPAR with CONMIN program and set of interface procedures. SPAR is large general-purpose finite-element structural-analysis program, and CONMIN is large general-purpose optimization program. PROSSS2 written in FORTRAN IV for batch execution.

  6. Structural Enhancement of Learning

    Science.gov (United States)

    Trumpower, David L.; Goldsmith, Timothy E.

    2004-01-01

    Structural learning aids, such as interactive overviews (IOs), have previously been shown to facilitate text comprehension and recall. In this study, we examined the effects of structural aids on learners' structural knowledge and their performance on a procedural transfer task. In Experiment 1, 90 college students were presented definitions of…

  7. Neutrality in bipolar structures

    DEFF Research Database (Denmark)

    Montero, Javier; Rodríguez, J. Tinguaro; Franco, Camilo

    2014-01-01

    In this paper, we want to stress that bipolar knowledge representation naturally allows a family of middle states which define as a consequence different kinds of bipolar structures. These bipolar structures are deeply related to the three types of bipolarity introduced by Dubois and Prade, but our...... approach offers a systematic explanation of how such bipolar structures appear and can be identified....

  8. Organizational Knowledge Management Structure

    Science.gov (United States)

    Walczak, Steven

    2005-01-01

    Purpose: To propose and evaluate a novel management structure that encourages knowledge sharing across an organization. Design/methodology/approach: The extant literature on the impact of organizational culture and its link to management structure is examined and used to develop a new knowledge sharing management structure. Roadblocks to…

  9. Hypermedia 1990 structured Hypertext tutorial

    Science.gov (United States)

    Johnson, J. Scott

    1990-01-01

    Hypermedia 1990 structured Hypertext tutorial is presented in the form of view-graphs. The following subject areas are covered: structured hypertext; analyzing hypertext documents for structure; designing structured hypertext documents; creating structured hypertext applications; structuring service and repair documents; maintaining structured hypertext documents; and structured hypertext conclusion.

  10. PRODUCT STRUCTURE DIGITAL MODEL

    Directory of Open Access Journals (Sweden)

    V.M. Sineglazov

    2005-02-01

    Full Text Available  Research results of representation of product structure made by means of CADDS5 computer-aided design (CAD system, Product Data Management Optegra (PDM system and Product Life Cycle Management Wind-chill system (PLM, are examined in this work. Analysis of structure component development and its storage in various systems is carried out. Algorithms of structure transformation required for correct representation of the structure are considered. Management analysis of electronic mockup presentation of the product structure is carried out for Windchill system.

  11. Shell-like structures

    CERN Document Server

    Altenbach, Holm

    2011-01-01

    In this volume, scientists and researchers from industry discuss the new trends in simulation and computing shell-like structures. The focus is put on the following problems: new theories (based on two-dimensional field equations but describing non-classical effects), new constitutive equations (for materials like sandwiches, foams, etc. and which can be combined with the two-dimensional shell equations), complex structures (folded, branching and/or self intersecting shell structures, etc.) and shell-like structures on different scales (for example: nano-tubes) or very thin structures (similar

  12. Basic structural dynamics

    CERN Document Server

    Anderson, James C

    2012-01-01

    A concise introduction to structural dynamics and earthquake engineering Basic Structural Dynamics serves as a fundamental introduction to the topic of structural dynamics. Covering single and multiple-degree-of-freedom systems while providing an introduction to earthquake engineering, the book keeps the coverage succinct and on topic at a level that is appropriate for undergraduate and graduate students. Through dozens of worked examples based on actual structures, it also introduces readers to MATLAB, a powerful software for solving both simple and complex structural d

  13. Materials and structures

    Science.gov (United States)

    Saito, Theodore T.; Langenbeck, Sharon L.; Al-Jamily, Ghanim; Arnold, Joe; Barbee, Troy; Coulter, Dan; Dolgin, Ben; Fichter, Buck; George, Patricia; Gorenstein, Paul

    1992-08-01

    Materials and structures technology covers a wide range of technical areas. Some of the most pertinent issues for the Astrotech 21 missions include dimensionally stable structural materials, advanced composites, dielectric coatings, optical metallic coatings for low scattered light applications, low scattered light surfaces, deployable and inflatable structures (including optical), support structures in 0-g and 1-g environments, cryogenic optics, optical blacks, contamination hardened surfaces, radiation hardened glasses and crystals, mono-metallic telescopes and instruments, and materials characterization. Some specific examples include low coefficients of thermal expansion (CTE) structures (0.01 ppm/K), lightweight thermally stable mirror materials, thermally stable optical assemblies, high reliability/accuracy (1 micron) deployable structures, and characterization of nanometer level behavior of materials/structures for interferometry concepts. Large filled-aperture concepts will require materials with CTE's of 10(exp 9) at 80 K, anti-contamination coatings, deployable and erectable structures, composite materials with CTE's less than 0.01 ppm/K and thermal hysteresis, 0.001 ppm/K. Gravitational detection systems such as LAGOS will require rigid/deployable structures, dimensionally stable components, lightweight materials with low conductivity, and high stability optics. The Materials and Structures panel addressed these issues and the relevance of the Astrotech 21 mission requirements by dividing materials and structures technology into five categories. These categories, the necessary development, and applicable mission/program development phasing are summarized. For each of these areas, technology assessments were made and development plans were defined.

  14. Exotic cluster structures on

    CERN Document Server

    Gekhtman, M; Vainshtein, A

    2017-01-01

    This is the second paper in the series of papers dedicated to the study of natural cluster structures in the rings of regular functions on simple complex Lie groups and Poisson-Lie structures compatible with these cluster structures. According to our main conjecture, each class in the Belavin-Drinfeld classification of Poisson-Lie structures on \\mathcal{G} corresponds to a cluster structure in \\mathcal{O}(\\mathcal{G}). The authors have shown before that this conjecture holds for any \\mathcal{G} in the case of the standard Poisson-Lie structure and for all Belavin-Drinfeld classes in SL_n, n<5. In this paper the authors establish it for the Cremmer-Gervais Poisson-Lie structure on SL_n, which is the least similar to the standard one.

  15. Structural realism beyond physics.

    Science.gov (United States)

    Tulodziecki, Dana

    2016-10-01

    The main purpose of this paper is to test structural realism against (one example from) the historical record. I begin by laying out an existing challenge to structural realism - that of providing an example of a theory exhibiting successful structures that were abandoned - and show that this challenge can be met by the miasma theory of disease. However, rather than concluding that this is an outright counterexample to structural realism, I use this case to show why it is that structural realism, in its current form, has trouble dealing with theories outside physics. I end by making some concrete suggestions for structural realists to pursue if, indeed, they are serious about extending structural realism to other domains.

  16. Reducts of Ramsey structures

    CERN Document Server

    Bodirsky, Manuel

    2011-01-01

    One way of studying a relational structure is to investigate functions which are related to that structure and which leave certain aspects of the structure invariant. Examples are the automorphism group, the self-embedding monoid, the endomorphism monoid, or the polymorphism clone of a structure. Such functions can be particularly well understood when the relational structure is countably infinite and has a first-order definition in another relational structure which has a finite language, is totally ordered and homogeneous, and has the Ramsey property. This is because in this situation, Ramsey theory provides the combinatorial tool for analyzing these functions -- in a certain sense, it allows to represent such functions by functions on finite sets. This is a survey of results in model theory and theoretical computer science obtained recently by the authors in this context. In model theory, we approach the problem of classifying the reducts of countably infinite ordered homogeneous Ramsey structures in a fin...

  17. Synthesis and sintering of ceramic nanocomposites with high mixed conductivity

    Directory of Open Access Journals (Sweden)

    Zyryanov V.V.

    2005-01-01

    Full Text Available Metastable solid solutions of complex oxides with fluorite and perovskite structures are obtained by mechanosynthesis. Dense ceramics on the base of these metastable phases was obtained by thermal sintering of nanopowders due to kinetic stabilization. Different degrees of a chemical interaction (interdiffusion are observed during sintering of "perovskite+fluorite" and "perovskite+perovskite" composites. It is shown, that optimization of the composition, mixing conditions of individual phases and their sintering, preparation of ceramic composites with mixed conductivity for use in catalytic membrane reactors is possible. Unusual behavior of complex perovskites and fluorites is discovered during sintering, enabling determination of an optimum sintering temperature and time for which a qualitative explanation is given. It is established that rearrangement of fine crystalline particles as a whole plays a key role in shrinkage.

  18. Robustness of Structures

    DEFF Research Database (Denmark)

    Faber, M.H.; Vrouwenvelder, A.C.W.M.; Sørensen, John Dalsgaard

    2011-01-01

    In 2005, the Joint Committee on Structural Safety (JCSS) together with Working Commission (WC) 1 of the International Association of Bridge and Structural Engineering (IABSE) organized a workshop on robustness of structures. Two important decisions resulted from this workshop, namely the developm......In 2005, the Joint Committee on Structural Safety (JCSS) together with Working Commission (WC) 1 of the International Association of Bridge and Structural Engineering (IABSE) organized a workshop on robustness of structures. Two important decisions resulted from this workshop, namely...... the development of a joint European project on structural robustness under the COST (European Cooperation in Science and Technology) programme and the decision to develop a more elaborate document on structural robustness in collaboration between experts from the JCSS and the IABSE. Accordingly, a project titled...... ‘COST TU0601: Robustness of Structures’ was initiated in February 2007, aiming to provide a platform for exchanging and promoting research in the area of structural robustness and to provide a basic framework, together with methods, strategies and guidelines enhancing robustness of structures...

  19. Structure - Riverine Flow Structure (Dike/Wingdam)

    Data.gov (United States)

    Army Corps of Engineers, Department of the Army, Department of Defense — A natural or man-made flow (or sediment) control structure in a water course or water body such as a dike or weir. This feature should not be used to model a levee....

  20. Exponential Dowling structures

    CERN Document Server

    Ehrenborg, Richard

    2010-01-01

    The notion of exponential Dowling structures is introduced, generalizing Stanley's original theory of exponential structures. Enumerative theory is developed to determine the M\\"obius function of exponential Dowling structures, including a restriction of these structures to elements whose types satisfy a semigroup condition. Stanley's study of permutations associated with exponential structures leads to a similar vein of study for exponential Dowling structures. In particular, for the extended r-divisible partition lattice we show the M\\"obius function is, up to a sign, the number of permutations in the symmetric group on rn+k elements having descent set {r, 2r, ..., nr}. Using Wachs' original EL-labeling of the r-divisible partition lattice, the extended r-divisible partition lattice is shown to be EL-shellable.

  1. Origami - Folded Plate Structures

    OpenAIRE

    Buri, Hans Ulrich

    2010-01-01

    This research investigates new methods of designing folded plate structures that can be built with cross-laminated timber panels. Folded plate structures are attractive to both architects and engineers for their structural, spatial, and plastic qualities. Thin surfaces can be stiffened by a series of folds, and thus not only cover space, but also act as load bearing elements. The variation of light and shadow along the folded faces emphasizes the plas...

  2. Catalytic distillation structure

    Science.gov (United States)

    Smith, L.A. Jr.

    1984-04-17

    Catalytic distillation structure is described for use in reaction distillation columns, and provides reaction sites and distillation structure consisting of a catalyst component and a resilient component intimately associated therewith. The resilient component has at least about 70 volume % open space and is present with the catalyst component in an amount such that the catalytic distillation structure consists of at least 10 volume % open space. 10 figs.

  3. Advance in structural bioinformatics

    CERN Document Server

    Wei, Dongqing; Zhao, Tangzhen; Dai, Hao

    2014-01-01

    This text examines in detail mathematical and physical modeling, computational methods and systems for obtaining and analyzing biological structures, using pioneering research cases as examples. As such, it emphasizes programming and problem-solving skills. It provides information on structure bioinformatics at various levels, with individual chapters covering introductory to advanced aspects, from fundamental methods and guidelines on acquiring and analyzing genomics and proteomics sequences, the structures of protein, DNA and RNA, to the basics of physical simulations and methods for conform

  4. Structure of Human Adenovirus

    OpenAIRE

    Nemerow, Glen R.; Phoebe L Stewart; Reddy, Vijay S.

    2012-01-01

    A detailed structural analysis of the entire human adenovirus capsid has been stymied by the complexity and size of this 150 MDa macromolecular complex. Over the past 10 years, the steady improvements in viral genome manipulation concomitant with advances in crystallographic techniques and data processing software has allowed structure determination of this virus by X-ray diffraction at 3.5 Å resolution. The virus structure revealed the location, folds, and interactions of major and minor (ce...

  5. Reforming Organizational Structures

    OpenAIRE

    Van de Walle, Steven

    2016-01-01

    textabstractPublic sectors have undergone major transformations. Public sector reform touches upon the core building blocks of the public sector: organizational structures, people and finances. These are objects of reform. This chapter presents and discusses a set of major transformations with regard to organizational structures. It provides readers a fairly comprehensive overview of the key reforms that have taken place in Western public sectors. Structural reforms in the public sector show ...

  6. Auxetic materials and structures

    CERN Document Server

    Lim, Teik-Cheng

    2015-01-01

    This book describes the fundamentals of the mechanics and design of auxetic solids and structures, which possess a negative Poisson’s ratio. It will benefit two groups of readers: (a) industry practitioners, such as product and structural designers, who need to control mechanical stress distributions using auxetic materials, and (b) academic researchers and students who intend to produce structures with unique mechanical and other physical properties using auxetic materials.

  7. Structural elements design manual

    CERN Document Server

    Draycott, Trevor

    2012-01-01

    Gives clear explanations of the logical design sequence for structural elements. The Structural Engineer says: `The book explains, in simple terms, and with many examples, Code of Practice methods for sizing structural sections in timber, concrete,masonry and steel. It is the combination into one book of section sizing methods in each of these materials that makes this text so useful....Students will find this an essential support text to the Codes of Practice in their study of element sizing'.

  8. Organisational structure of Enterprise

    OpenAIRE

    Varenytsya, Maryan

    2015-01-01

    The purpose of the bachelor final work is to identify effective organizational management structure, as well offer advice company branch of JSC "Rostelecom" for the improvement of organizational structure of management. It examines the relevance of the study, defined goals, objectives and methods of research, a review of the literature. This thesis contains information on the main causes of changes in the organizational structure of the enterprise management, the design of the organizational ...

  9. Valency and molecular structure

    CERN Document Server

    Cartmell, E

    1977-01-01

    Valency and Molecular Structure, Fourth Edition provides a comprehensive historical background and experimental foundations of theories and methods relating to valency and molecular structures. In this edition, the chapter on Bohr theory has been removed while some sections, such as structures of crystalline solids, have been expanded. Details of structures have also been revised and extended using the best available values for bond lengths and bond angles. Recent developments are mostly noted in the chapter on complex compounds, while a new chapter has been added to serve as an introduction t

  10. Linguistic Structure Prediction

    CERN Document Server

    Smith, Noah A

    2011-01-01

    A major part of natural language processing now depends on the use of text data to build linguistic analyzers. We consider statistical, computational approaches to modeling linguistic structure. We seek to unify across many approaches and many kinds of linguistic structures. Assuming a basic understanding of natural language processing and/or machine learning, we seek to bridge the gap between the two fields. Approaches to decoding (i.e., carrying out linguistic structure prediction) and supervised and unsupervised learning of models that predict discrete structures as outputs are the focus. W

  11. Structural Precast Concrete Handbook

    DEFF Research Database (Denmark)

    Kjærbye, Per Oluf H

    Structural concept for precast concrete systems. Design og precast reinforced concrete components. Design of precast concrete connections. Illustrations on design of precast concrete buildings. Precast concrete assembly....

  12. Structural Dynamics Laboratory (SDL)

    Data.gov (United States)

    Federal Laboratory Consortium — Structural dynamic testing is performed to verify the survivability of a component or assembly when exposed to vibration stress screening, or a controlled simulation...

  13. Machine tool structures

    CERN Document Server

    Koenigsberger, F

    1970-01-01

    Machine Tool Structures, Volume 1 deals with fundamental theories and calculation methods for machine tool structures. Experimental investigations into stiffness are discussed, along with the application of the results to the design of machine tool structures. Topics covered range from static and dynamic stiffness to chatter in metal cutting, stability in machine tools, and deformations of machine tool structures. This volume is divided into three sections and opens with a discussion on stiffness specifications and the effect of stiffness on the behavior of the machine under forced vibration c

  14. Flexible Volumetric Structure

    Science.gov (United States)

    Cagle, Christopher M. (Inventor); Schlecht, Robin W. (Inventor)

    2014-01-01

    A flexible volumetric structure has a first spring that defines a three-dimensional volume and includes a serpentine structure elongatable and compressible along a length thereof. A second spring is coupled to at least one outboard edge region of the first spring. The second spring is a sheet-like structure capable of elongation along an in-plane dimension thereof. The second spring is oriented such that its in-plane dimension is aligned with the length of the first spring's serpentine structure.

  15. Laboratory for Structural Acoustics

    Data.gov (United States)

    Federal Laboratory Consortium — FUNCTION: Supports experimental research where acoustic radiation, scattering, and surface vibration measurements of fluid-loaded and non-fluid-loaded structures are...

  16. Deployable Soft Composite Structures

    Science.gov (United States)

    Wang, Wei; Rodrigue, Hugo; Ahn, Sung-Hoon

    2016-02-01

    Deployable structure composed of smart materials based actuators can reconcile its inherently conflicting requirements of low mass, good shape adaptability, and high load-bearing capability. This work describes the fabrication of deployable structures using smart soft composite actuators combining a soft matrix with variable stiffness properties and hinge-like movement through a rigid skeleton. The hinge actuator has the advantage of being simple to fabricate, inexpensive, lightweight and simple to actuate. This basic actuator can then be used to form modules capable of different types of deformations, which can then be assembled into deployable structures. The design of deployable structures is based on three principles: design of basic hinge actuators, assembly of modules and assembly of modules into large-scale deployable structures. Various deployable structures such as a segmented triangular mast, a planar structure comprised of single-loop hexagonal modules and a ring structure comprised of single-loop quadrilateral modules were designed and fabricated to verify this approach. Finally, a prototype for a deployable mirror was developed by attaching a foldable reflective membrane to the designed ring structure and its functionality was tested by using it to reflect sunlight onto to a small-scale solar panel.

  17. Deployable Soft Composite Structures.

    Science.gov (United States)

    Wang, Wei; Rodrigue, Hugo; Ahn, Sung-Hoon

    2016-02-19

    Deployable structure composed of smart materials based actuators can reconcile its inherently conflicting requirements of low mass, good shape adaptability, and high load-bearing capability. This work describes the fabrication of deployable structures using smart soft composite actuators combining a soft matrix with variable stiffness properties and hinge-like movement through a rigid skeleton. The hinge actuator has the advantage of being simple to fabricate, inexpensive, lightweight and simple to actuate. This basic actuator can then be used to form modules capable of different types of deformations, which can then be assembled into deployable structures. The design of deployable structures is based on three principles: design of basic hinge actuators, assembly of modules and assembly of modules into large-scale deployable structures. Various deployable structures such as a segmented triangular mast, a planar structure comprised of single-loop hexagonal modules and a ring structure comprised of single-loop quadrilateral modules were designed and fabricated to verify this approach. Finally, a prototype for a deployable mirror was developed by attaching a foldable reflective membrane to the designed ring structure and its functionality was tested by using it to reflect sunlight onto to a small-scale solar panel.

  18. Bioinspired structural materials

    Science.gov (United States)

    Wegst, Ulrike G. K.; Bai, Hao; Saiz, Eduardo; Tomsia, Antoni P.; Ritchie, Robert O.

    2015-01-01

    Natural structural materials are built at ambient temperature from a fairly limited selection of components. They usually comprise hard and soft phases arranged in complex hierarchical architectures, with characteristic dimensions spanning from the nanoscale to the macroscale. The resulting materials are lightweight and often display unique combinations of strength and toughness, but have proven difficult to mimic synthetically. Here, we review the common design motifs of a range of natural structural materials, and discuss the difficulties associated with the design and fabrication of synthetic structures that mimic the structural and mechanical characteristics of their natural counterparts.

  19. Nuclear structure theory

    CERN Document Server

    Irvine, J M

    1972-01-01

    Nuclear Structure Theory provides a guide to nuclear structure theory. The book is comprised of 23 chapters that are organized into four parts; each part covers an aspect of nuclear structure theory. In the first part, the text discusses the experimentally observed phenomena, which nuclear structure theories need to look into and detail the information that supports those theories. The second part of the book deals with the phenomenological nucleon-nucleon potentials derived from phase shift analysis of nucleon-nucleon scattering. Part III talks about the phenomenological parameters used to de

  20. Roadmap on structured light

    Science.gov (United States)

    Rubinsztein-Dunlop, Halina; Forbes, Andrew; Berry, M. V.; Dennis, M. R.; Andrews, David L.; Mansuripur, Masud; Denz, Cornelia; Alpmann, Christina; Banzer, Peter; Bauer, Thomas; Karimi, Ebrahim; Marrucci, Lorenzo; Padgett, Miles; Ritsch-Marte, Monika; Litchinitser, Natalia M.; Bigelow, Nicholas P.; Rosales-Guzmán, C.; Belmonte, A.; Torres, J. P.; Neely, Tyler W.; Baker, Mark; Gordon, Reuven; Stilgoe, Alexander B.; Romero, Jacquiline; White, Andrew G.; Fickler, Robert; Willner, Alan E.; Xie, Guodong; McMorran, Benjamin; Weiner, Andrew M.

    2017-01-01

    Structured light refers to the generation and application of custom light fields. As the tools and technology to create and detect structured light have evolved, steadily the applications have begun to emerge. This roadmap touches on the key fields within structured light from the perspective of experts in those areas, providing insight into the current state and the challenges their respective fields face. Collectively the roadmap outlines the venerable nature of structured light research and the exciting prospects for the future that are yet to be realized.

  1. Probabilistic conditional independence structures

    CERN Document Server

    Studeny, Milan

    2005-01-01

    Probabilistic Conditional Independence Structures provides the mathematical description of probabilistic conditional independence structures; the author uses non-graphical methods of their description, and takes an algebraic approach.The monograph presents the methods of structural imsets and supermodular functions, and deals with independence implication and equivalence of structural imsets.Motivation, mathematical foundations and areas of application are included, and a rough overview of graphical methods is also given.In particular, the author has been careful to use suitable terminology, and presents the work so that it will be understood by both statisticians, and by researchers in artificial intelligence.The necessary elementary mathematical notions are recalled in an appendix.

  2. Structural patterns in nature

    DEFF Research Database (Denmark)

    Wester, Ture

    2004-01-01

    It seems that some very basic randomly produced geometric/topological patterns are commonly found in Nature and have often very distinctive structural qualities. In nature we find the same pattern in all scales from the universe to molecules, from solar systems to packing of cells, from glaciers...... to sea shells, from river systems to trees etc. Sometimes this seeming archetypical morphology involve structural action and sometimes not - but the fact that it often posses efficient structural action opens a tool for evaluation and analyses of structures in nature and at the same time might...

  3. 纳米Ce1-x(Nd0.5Fe0.5)xO2-δ固溶体的合成及结构表征%Synthesis and Structure Characterization of Nanosized Ce1-x(Nd0.5 Fe0.5)xO2-δ Solid Solutions

    Institute of Scientific and Technical Information of China (English)

    张国芳; 刘铃声; 张羊换; 葛启录; 张胤; 何长青

    2011-01-01

    Ce1-x ( Nd0.5Fe0.5 )xO2-δ solid solutions were obtained via hydrothermal metbod. The structure of the solid solutions were characterized by XRD, TEM and UV - Vis techniques. XRD results showed that the Ce1-x ( Nd0.5Fe0.5 )xO2-δsolid solutions exhibited cubic fluorite structure when the doped content below 0.20. The particle size decreased with increasing the doping content. Comparing with Ce ion, radius of Fe ion is smaller and Nd ion is larger. Therefore, the complicated variation of cell parameter was observed. TEM and EDS results showed that the samples have fine crystalline structure and the doping content was close to the experimental value. From the UV - Vis diffraction spectrum analysis results, the absorption threshold edge shift was observed, and the hand gap energy first increased and then decressed by increasing the doping content.%采用水热方法合成出Ce1-x(Nd0.5 Fe0.5)x O2-δ固溶体,通过XRD测试对固溶体晶体结构进行了表征分析及晶胞参数拟合,结果表明,当x≤0.2时,Ce1-x(Nd0.5 Fe0.5)x O2-δ固溶体保持CeO2立方萤石结构;样品粒度分布在11 nm~15 nm间,且随着掺杂量的增大,粒度逐渐减小.在CeO2中掺人小半径的Fe3+离子及大半径的Nd3+离子,半径不同的双离子掺杂引起了较为复杂的晶胞参数变化.TEM及能谱结果证明样品为结晶良好的纳米晶,固溶体中的掺杂离子含量与理论含量基本一致.紫外光谱分析表明离子的掺杂导致带隙吸收边发生变化,能隙先增大后减小.

  4. Stable umbral chromospheric structures

    Science.gov (United States)

    Henriques, V. M. J.; Scullion, E.; Mathioudakis, M.; Kiselman, D.; Gallagher, P. T.; Keenan, F. P.

    2015-02-01

    Aims: We seek to understand the morphology of the chromosphere in sunspot umbra. We investigate if the horizontal structures observed in the spectral core of the Ca II H line are ephemeral visuals caused by the shock dynamics of more stable structures, and examine their relationship with observables in the H-alpha line. Methods: Filtergrams in the core of the Ca II H and H-alpha lines as observed with the Swedish 1-m Solar Telescope are employed. We utilise a technique that creates composite images and tracks the flash propagation horizontally. Results: We find 0.̋15 wide horizontal structures, in all of the three target sunspots, for every flash where the seeing is moderate to good. Discrete dark structures are identified that are stable for at least two umbral flashes, as well as systems of structures that live for up to 24 min. We find cases of extremely extended structures with similar stability, with one such structure showing an extent of 5''. Some of these structures have a correspondence in H-alpha, but we were unable to find a one-to-one correspondence for every occurrence. If the dark streaks are formed at the same heights as umbral flashes, there are systems of structures with strong departures from the vertical for all three analysed sunspots. Conclusions: Long-lived Ca II H filamentary horizontal structures are a common and likely ever-present feature in the umbra of sunspots. If the magnetic field in the chromosphere of the umbra is indeed aligned with the structures, then the present theoretical understanding of the typical umbra needs to be revisited. Movies associated to Figs. 3 and 4 are available in electronic form at http://www.aanda.org

  5. Organisational Structure & Change

    Science.gov (United States)

    National Centre for Vocational Education Research (NCVER), 2006

    2006-01-01

    Structural change is seen as a way to meet the challenges of the future that face many organisations. While some writers agree that broad-ranging structural change may not always transform an organisation or enhance its performance, others claim that innovation will be a major source of competitive advantage to organisations, particularly when…

  6. The Structure of Reciprocity

    Science.gov (United States)

    Molm, Linda D.

    2010-01-01

    Reciprocity is one of the defining features of social exchange and social life, yet exchange theorists have tended to take it for granted. Drawing on work from a decade-long theoretical research program, I argue that reciprocity is structured and variable across different forms of exchange, that these variations in the structure of reciprocity…

  7. Tapered structure construction

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Eric D.; Takata, Rosalind K.; Slocum, Alexander H.; Nayfeh, Samir A.

    2016-04-05

    Feeding stock used to form a tapered structure into a curving device such that each point on the stock undergoes rotational motion about a peak location of the tapered structure; and the stock meets a predecessor portion of stock along one or more adjacent edges.

  8. Wave scour around structures

    DEFF Research Database (Denmark)

    Sumer, B. Mutlu; Fredsøe, Jørgen

    1999-01-01

    This review (of scour around marine structures) is organized in seven main sections: Basic concepts; Tunnel erosion; Two- and three-dimensional scour around pipelines; Scour around piles (slender bodies), including pile groups; Scour around complex structures; Scour around large, vertical cylinde......; and Scour around breakwaters (vertical-wall breakwaters and rubble-mound breakwaters)....

  9. Neutrinos and nucleon structure

    CERN Document Server

    Sehgal, L M

    1979-01-01

    The study of neutrino interactions in matter is yielding a wealth of information on the form factors and structure functions of the nucleon. These data allow tests of models of nucleon structure and of dynamical theories of quarks and gluons. The author attempts a critical appraisal of recent facts and their impact on our theoretical understanding. (35 refs).

  10. The Cambridge Structural Database.

    Science.gov (United States)

    Groom, Colin R; Bruno, Ian J; Lightfoot, Matthew P; Ward, Suzanna C

    2016-04-01

    The Cambridge Structural Database (CSD) contains a complete record of all published organic and metal-organic small-molecule crystal structures. The database has been in operation for over 50 years and continues to be the primary means of sharing structural chemistry data and knowledge across disciplines. As well as structures that are made public to support scientific articles, it includes many structures published directly as CSD Communications. All structures are processed both computationally and by expert structural chemistry editors prior to entering the database. A key component of this processing is the reliable association of the chemical identity of the structure studied with the experimental data. This important step helps ensure that data is widely discoverable and readily reusable. Content is further enriched through selective inclusion of additional experimental data. Entries are available to anyone through free CSD community web services. Linking services developed and maintained by the CCDC, combined with the use of standard identifiers, facilitate discovery from other resources. Data can also be accessed through CCDC and third party software applications and through an application programming interface.

  11. Periodic truss structures

    Science.gov (United States)

    Zok, Frank W.; Latture, Ryan M.; Begley, Matthew R.

    2016-11-01

    Despite the recognition of the enormous potential of periodic trusses for use in a broad range of technologies, there are no widely-accepted descriptors of their structure. The terminology has been based loosely either on geometry of polyhedra or of point lattices: neither of which, on its own, has an appropriate structure to fully define periodic trusses. The present article lays out a system for classification of truss structure types. The system employs concepts from crystallography and geometry to describe nodal locations and connectivity of struts. Through a series of illustrative examples of progressively increasing complexity, a rational taxonomy of truss structure is developed. Its conceptual evolution begins with elementary cubic trusses, increasing in complexity with non-cubic and compound trusses as well as supertrusses, and, finally, with complex trusses. The conventions and terminology adopted to define truss structure yield concise yet unambiguous descriptions of structure types and of specific (finite) trusses. The utility of the taxonomy is demonstrated by bringing into alignment a disparate set of ad hoc and incomplete truss designations previously employed in a broad range of science and engineering fields. Additionally, the merits of a particular compound truss (comprising two interpenetrating elementary trusses) is shown to be superior to the octet truss for applications requiring high stiffness and elastic isotropy. By systematically stepping through and analyzing the finite number of structure types identified through the present classification system, optimal structures for prescribed mechanical and functional requirements are expected to be ascertained in an expeditious manner.

  12. Structures of Mn clusters

    Indian Academy of Sciences (India)

    Tina M Briere; Marcel H F Sluiter; Vijay Kumar; Yoshiyuki Kawazoe

    2003-01-01

    The geometries of several Mn clusters in the size range Mn13–Mn23 are studied via the generalized gradient approximation to density functional theory. For the 13- and 19-atom clusters, the icosahedral structures are found to be most stable, while for the 15-atom cluster, the bcc structure is more favoured. The clusters show ferrimagnetic spin configurations.

  13. Lightweight Composite Intertank Structure

    Science.gov (United States)

    Mehle, Greg V.

    1995-01-01

    Report presents results of study for proposed lightweight composite material alternative to present semimonocoque aluminum intertank structure for advanced launch vehicles. Proposed structure integrated assembly of sandwich panels made of laminated epoxy-matrix/carbon-fiber skins, and aluminum honeycomb core.

  14. Structural Precast Concrete Handbook

    DEFF Research Database (Denmark)

    Kjærbye, Per Oluf H

    Structural concept for precast concrete systems. Design og precast reinforced concrete components. Design of precast concrete connections. Illustrations on design of precast concrete buildings. Precast concrete assembly.......Structural concept for precast concrete systems. Design og precast reinforced concrete components. Design of precast concrete connections. Illustrations on design of precast concrete buildings. Precast concrete assembly....

  15. Magnetic Nano-structures

    Institute of Scientific and Technical Information of China (English)

    姚永德

    2004-01-01

    Fabrication of magnetic nano-structures with dots array and wires has been paid attention recently due to the application of high-density magnetic recording. In this study, we fabricated the magnetic dots array and wires through several ways that ensure the arrangement of magnetic dots and wires to be the structures we designed. Their magnetic properties are studied experimentally.

  16. Hierarchical Porous Structures

    Energy Technology Data Exchange (ETDEWEB)

    Grote, Christopher John [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-06-07

    Materials Design is often at the forefront of technological innovation. While there has always been a push to generate increasingly low density materials, such as aero or hydrogels, more recently the idea of bicontinuous structures has gone more into play. This review will cover some of the methods and applications for generating both porous, and hierarchically porous structures.

  17. Fire exposed aluminium structures

    NARCIS (Netherlands)

    Maljaars, J.; Fellinger, J.H.H.; Soetens, F.

    2006-01-01

    Material properties and mechanical response models for fire design of steel structures are based on extensive research and experience. Contrarily, the behaviour of aluminium load bearing structures exposed to fire is relatively unexplored. This article gives an overview of physical and mechanical pr

  18. Solution structure of (+)-discodermolide.

    Science.gov (United States)

    Smith, A B; LaMarche, M J; Falcone-Hindley, M

    2001-03-01

    [structure: see text]. The solution structure of (+)-discodermolide (1) has been determined via 1- and 2-D NMR techniques in conjunction with Monte Carlo conformational analysis. Taken together, the results demonstrate that in solution (+)-discodermolide occupies a helical conformation remarkably similar to the solid state conformation.

  19. Hedging structured concepts

    NARCIS (Netherlands)

    Koolen, W.M.; Warmuth, M.K.; Kivinen, J.; Kalai, A.T.; Mohri, M.

    2010-01-01

    We develop an online algorithm called Component Hedge for learning structured concept classes when the loss of a structured concept sums over its components. Example classes include paths through a graph (composed of edges) and partial permutations (composed of assignments). The algorithm maintains

  20. Describing migration spatial structure

    NARCIS (Netherlands)

    Rogers, A; Willekens, F; Little, J; Raymer, J

    The age structure of a population is a fundamental concept in demography and is generally depicted in the form of an age pyramid. The spatial structure of an interregional system of origin-destination-specific migration streams is, however, a notion lacking a widely accepted definition. We offer a

  1. Structure sensitivity in adsorption

    DEFF Research Database (Denmark)

    Hammer, Bjørk; Nielsen, Ole Holm; Nørskov, Jens Kehlet

    1997-01-01

    The structure sensitivity of CO adsorption on different flat, stepped, kinked and reconstructed Pt surfaces is studied using large-scale density-functional calculations. We find an extremely strong structure sensitivity in the adsorption energy with variations up to 1 eV (or 100%) from one...

  2. Shipping Industry Structure

    NARCIS (Netherlands)

    Wijnolst, N.; Waals, F.

    1999-01-01

    Understanding Shipping Management requires a thorough understanding of the Shipping Industry Structure. This book provides this knowledge base and should be seen in conjunction with two other books: Shipping and Design Innovation in Shipping. Shipping Industry Structure was intended as the first par

  3. Wave scour around structures

    DEFF Research Database (Denmark)

    Sumer, B. Mutlu; Fredsøe, Jørgen

    1999-01-01

    This review (of scour around marine structures) is organized in seven main sections: Basic concepts; Tunnel erosion; Two- and three-dimensional scour around pipelines; Scour around piles (slender bodies), including pile groups; Scour around complex structures; Scour around large, vertical cylinders......; and Scour around breakwaters (vertical-wall breakwaters and rubble-mound breakwaters)....

  4. Piaget's Structural Developmental Psychology.

    Science.gov (United States)

    Broughton, John M.

    1981-01-01

    Piaget's theory is identified as a branch of structuralism concerned with the concept of truth, in distinction from French structuralism, which is focused on meaning. The two branches are compared and contrasted, and relations between logic and language are explored. Similarities and differences in the theories of Piaget, Levi-Strauss, and Chomsky…

  5. Robustness of structures

    DEFF Research Database (Denmark)

    Vrouwenvelder, T.; Sørensen, John Dalsgaard

    2009-01-01

    robustness is still an issue of controversy and poses difficulties in regard to interpretation as well as regulation. Typically modern structural design codes require that ‘the consequence of damages to structures should not be disproportional to the causes of the damages'. However, despite the importance...

  6. Structural Crashworthiness and Failure

    Science.gov (United States)

    1993-04-16

    structures en materiaux composite. VDI-Bericht Nr 369, 1980. 46. Kirsch, P. A. & Jahnle, H. A., Energy absorption of glass-polyester structures. SAE...materials in the automotive industry. They built two cabins, one equipped with front and rear suspension , steering assembly, rear engine, seats, outer skin

  7. Generalized holomorphic structures

    Science.gov (United States)

    Wang, Yicao

    2014-12-01

    We define the notion of generalized holomorphic principal bundles and establish that their associated vector bundles of holomorphic representations are generalized holomorphic vector bundles defined by M. Gualtieri. Motivated by our definition, several examples of generalized holomorphic structures are constructed. A reduction theorem of generalized holomorphic structures is also included.

  8. Shipping Industry Structure

    NARCIS (Netherlands)

    Wijnolst, N.; Waals, F.

    1999-01-01

    Understanding Shipping Management requires a thorough understanding of the Shipping Industry Structure. This book provides this knowledge base and should be seen in conjunction with two other books: Shipping and Design Innovation in Shipping. Shipping Industry Structure was intended as the first par

  9. Shipping Industry Structure

    NARCIS (Netherlands)

    Wijnolst, N.; Waals, F.

    1999-01-01

    Understanding Shipping Management requires a thorough understanding of the Shipping Industry Structure. This book provides this knowledge base and should be seen in conjunction with two other books: Shipping and Design Innovation in Shipping. Shipping Industry Structure was intended as the first

  10. Dynamic term structure models

    DEFF Research Database (Denmark)

    Andreasen, Martin Møller; Meldrum, Andrew

    This paper studies whether dynamic term structure models for US nominal bond yields should enforce the zero lower bound by a quadratic policy rate or a shadow rate specification. We address the question by estimating quadratic term structure models (QTSMs) and shadow rate models with at most four...

  11. Buckling of Ship Structures

    CERN Document Server

    Shama, Mohamed

    2013-01-01

    Buckling of Ship Structures presents a comprehensive analysis of the buckling problem of ship structural members. A full analysis of the various types of loadings and stresses imposed on ship plating and primary and secondary structural members is given. The main causes and consequences of the buckling mode of failure of ship structure and the methods commonly used to control buckling failure are clarified. This book contains the main equations required to determine the critical buckling stresses for both ship plating and the primary and secondary stiffening structural members. The critical buckling stresses are given for ship plating subjected to the induced various types of loadings and having the most common boundary conditions encountered in ship structures.  The text bridges the gap existing in most books covering the subject of buckling of ship structures in the classical analytical format, by putting the emphasis on the practical methods required to ensure safety against buckling of ship structur...

  12. Product Structuring, an overview

    DEFF Research Database (Denmark)

    Tichem, Marcel; Storm, Ton; Andreasen, Mogens Myrup;

    1997-01-01

    This paper presents the highlights of two WDK Workshops on Product Structuring. Product structuring plays an important role in creating products which have good functional and life-cycle related properties, in design process management, and in several other company functions like production control...

  13. Fire exposed aluminium structures

    NARCIS (Netherlands)

    Maljaars, J.; Fellinger, J.H.H.; Soetens, F.

    2006-01-01

    Material properties and mechanical response models for fire design of steel structures are based on extensive research and experience. Contrarily, the behaviour of aluminium load bearing structures exposed to fire is relatively unexplored. This article gives an overview of physical and mechanical

  14. Describing migration spatial structure

    NARCIS (Netherlands)

    Rogers, A; Willekens, F; Little, J; Raymer, J

    2002-01-01

    The age structure of a population is a fundamental concept in demography and is generally depicted in the form of an age pyramid. The spatial structure of an interregional system of origin-destination-specific migration streams is, however, a notion lacking a widely accepted definition. We offer a d

  15. Cosmic structure formation

    Science.gov (United States)

    Bertschinger, Edumund

    1994-01-01

    This article reviews the prevailing paradigm for how galaxies and larger structures formed in the universe: gravitational instability. Basic observational facts are summarized to motivate the standard cosmological framework underlying most detailed investigations of structure formation. The observed univers approaches spatial uniformity on scales larger than about 10(exp 26) cm. On these scales gravitational dynamics is almost linear and therefore relatively easy to relate to observations of large-scale structure. On smaller scales cosmic structure is complicated not only by nonlinear gravitational clustering but also by nonlinear nongravitational gas dynamical processes. The complexity of these phenomena makes galaxy formation one of the grand challenge problems of the physical sciences. No fully satisfactory theory can presently account in detail for the observed cosmic structure. However, as this article summarizes, significant progress has been made during the last few years.

  16. Iconicity as structure mapping.

    Science.gov (United States)

    Emmorey, Karen

    2014-09-19

    Linguistic and psycholinguistic evidence is presented to support the use of structure-mapping theory as a framework for understanding effects of iconicity on sign language grammar and processing. The existence of structured mappings between phonological form and semantic mental representations has been shown to explain the nature of metaphor and pronominal anaphora in sign languages. With respect to processing, it is argued that psycholinguistic effects of iconicity may only be observed when the task specifically taps into such structured mappings. In addition, language acquisition effects may only be observed when the relevant cognitive abilities are in place (e.g. the ability to make structural comparisons) and when the relevant conceptual knowledge has been acquired (i.e. information key to processing the iconic mapping). Finally, it is suggested that iconicity is better understood as a structured mapping between two mental representations than as a link between linguistic form and human experience.

  17. Nonlinear dynamics of structures

    CERN Document Server

    Oller, Sergio

    2014-01-01

    This book lays the foundation of knowledge that will allow a better understanding of nonlinear phenomena that occur in structural dynamics.   This work is intended for graduate engineering students who want to expand their knowledge on the dynamic behavior of structures, specifically in the nonlinear field, by presenting the basis of dynamic balance in non‐linear behavior structures due to the material and kinematics mechanical effects.   Particularly, this publication shows the solution of the equation of dynamic equilibrium for structure with nonlinear time‐independent materials (plasticity, damage and frequencies evolution), as well as those time dependent non‐linear behavior materials (viscoelasticity and viscoplasticity). The convergence conditions for the non‐linear dynamic structure solution  are studied, and the theoretical concepts and its programming algorithms are presented.  

  18. Regularized Structural Equation Modeling.

    Science.gov (United States)

    Jacobucci, Ross; Grimm, Kevin J; McArdle, John J

    A new method is proposed that extends the use of regularization in both lasso and ridge regression to structural equation models. The method is termed regularized structural equation modeling (RegSEM). RegSEM penalizes specific parameters in structural equation models, with the goal of creating easier to understand and simpler models. Although regularization has gained wide adoption in regression, very little has transferred to models with latent variables. By adding penalties to specific parameters in a structural equation model, researchers have a high level of flexibility in reducing model complexity, overcoming poor fitting models, and the creation of models that are more likely to generalize to new samples. The proposed method was evaluated through a simulation study, two illustrative examples involving a measurement model, and one empirical example involving the structural part of the model to demonstrate RegSEM's utility.

  19. Socio-Technical Structure

    DEFF Research Database (Denmark)

    Rose, Jeremy; Lindgren, Rikard; Henfridsson, Ole

    2004-01-01

    a reference discipline in its own right (in other words a theory exporter), this paper offers an example of integrative theory development. Instead of adapting a theory from another discipline or building a theory from empirical data, we examine the structure concept in some of its various theoretical...... adaptations in IS and try to integrate them to produce theory that focuses on IS concerns whilst resolving some of the major areas of contention. Both social and technological versions of structure are investigated through three theoretical IS perspectives drawn from different reference disciplines. The first...... perspective relates to social theories (principally structuration theory), the second to linguistic theories (principally the structural linguistics of Chomsky), and the last to science studies (principally actor-network theory). The objective is to study areas of agreement and contention around the structure...

  20. Optoelectronic Mounting Structure

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, Gene R. (Albuquerque, NM); Armendariz, Marcelino G. (Albuquerque, NM); Baca, Johnny R. F. (Albuquerque, NM); Bryan, Robert P. (Albuquerque, NM); Carson, Richard F. (Albuquerque, NM); Chu, Dahwey (Albuquerque, NM); Duckett, III, Edwin B. (Albuquerque, NM); McCormick, Frederick B. (Albuquerque, NM); Peterson, David W. (Sandia Park, NM); Peterson, Gary D. (Albuquerque, NM); Reber, Cathleen A. (Corrales, NM); Reysen, Bill H. (Lafayette, CO)

    2004-10-05

    An optoelectronic mounting structure is provided that may be used in conjunction with an optical transmitter, receiver or transceiver module. The mounting structure may be a flexible printed circuit board. Thermal vias or heat pipes in the head region may transmit heat from the mounting structure to the heat spreader. The heat spreader may provide mechanical rigidity or stiffness to the heat region. In another embodiment, an electrical contact and ground plane may pass along a surface of the head region so as to provide an electrical contact path to the optoelectronic devices and limit electromagnetic interference. In yet another embodiment, a window may be formed in the head region of the mounting structure so as to provide access to the heat spreader. Optoelectronic devices may be adapted to the heat spreader in such a manner that the devices are accessible through the window in the mounting structure.

  1. On Granular Knowledge Structures

    CERN Document Server

    Zeng, Yi

    2008-01-01

    Knowledge plays a central role in human and artificial intelligence. One of the key characteristics of knowledge is its structured organization. Knowledge can be and should be presented in multiple levels and multiple views to meet people's needs in different levels of granularities and from different perspectives. In this paper, we stand on the view point of granular computing and provide our understanding on multi-level and multi-view of knowledge through granular knowledge structures (GKS). Representation of granular knowledge structures, operations for building granular knowledge structures and how to use them are investigated. As an illustration, we provide some examples through results from an analysis of proceeding papers. Results show that granular knowledge structures could help users get better understanding of the knowledge source from set theoretical, logical and visual point of views. One may consider using them to meet specific needs or solve certain kinds of problems.

  2. DISCUSSIONS ON STRUCTURAL COUPLING

    Institute of Scientific and Technical Information of China (English)

    ZHU Wenbin; GUO Lingzhi; MA Ruishi; SUN Yan; WANG Feng

    2004-01-01

    The structural coupling is a common geological phenomenon. The structural differences between eastern and western active continental margins of modern Pacific and between paleo-Pacific and modern-Pacific continental margins are related to the characteristics and status of the subducting oceanic plate, namely, 1. subducting angle; 2. change in subducting angle; 3. subducting velocity; 4. change in subducting velocity; 5. subduction depth; 6. horizontal distance between the leading edge of the subducting plate and the trench; 7. the structural form of the subducting plate at the 670km boundary between the upper and lower mantle; 8. the displacement and the direction of displacement of subducting plate. The control and influence toward the shallow-level structures by the deep-level structural activities is a detailed representation of the structural coupling on active continental margin.The basin-maintain coupling phenomenon is an intracontinental structural coupling. The far field effect of collision between Indian plate and Eurasian plate results in the occurrence of intracontinental A-type subduction in central Asia, and the A-type subduction is the key factor that results in the atrophy of basins and the formation of mountain systems.

  3. Cell packing structures

    KAUST Repository

    Pottmann, Helmut

    2015-03-03

    This paper is an overview of architectural structures which are either composed of polyhedral cells or closely related to them. We introduce the concept of a support structure of such a polyhedral cell packing. It is formed by planar quads and obtained by connecting corresponding vertices in two combinatorially equivalent meshes whose corresponding edges are coplanar and thus determine planar quads. Since corresponding triangle meshes only yield trivial structures, we focus on support structures associated with quad meshes or hex-dominant meshes. For the quadrilateral case, we provide a short survey of recent research which reveals beautiful relations to discrete differential geometry. Those are essential for successfully initializing numerical optimization schemes for the computation of quad-based support structures. Hex-dominant structures may be designed via Voronoi tessellations, power diagrams, sphere packings and various extensions of these concepts. Apart from the obvious application as load-bearing structures, we illustrate here a new application to shading and indirect lighting. On a higher level, our work emphasizes the interplay between geometry, optimization, statics, and manufacturing, with the overall aim of combining form, function and fabrication into novel integrated design tools.

  4. Chromatin Structure and Function

    CERN Document Server

    Wolffe, Alan P

    1999-01-01

    The Third Edition of Chromatin: Structure and Function brings the reader up-to-date with the remarkable progress in chromatin research over the past three years. It has been extensively rewritten to cover new material on chromatin remodeling, histone modification, nuclear compartmentalization, DNA methylation, and transcriptional co-activators and co-repressors. The book is written in a clear and concise fashion, with 60 new illustrations. Chromatin: Structure and Function provides the reader with a concise and coherent account of the nature, structure, and assembly of chromatin and its active

  5. Deployable geodesic truss structure

    Science.gov (United States)

    Mikulas, Martin M., Jr. (Inventor); Rhodes, Marvin D. (Inventor); Simonton, J. Wayne (Inventor)

    1987-01-01

    A deployable geodesic truss structure which can be deployed from a stowed state to an erected state is described. The truss structure includes a series of bays, each bay having sets of battens connected by longitudinal cross members which give the bay its axial and torsional stiffness. The cross members are hinged at their mid point by a joint so that the cross members are foldable for deployment or collapsing. The bays are deployed and stabilized by actuator means connected between the mid point joints of the cross members. Hinged longerons may be provided to also connect the sets of battens and to collapse for stowing with the rest of the truss structure.

  6. Wind Loads on Structures

    DEFF Research Database (Denmark)

    Dyrbye, Claes; Hansen, Svend Ole

    pressure to structural response) and design criteria. Starting with an introduction of the wind load chain, the book moves on to meteorological considerations, atmospheric boundary layer, static wind load, dynamic wind load and scaling laws used in wind-tunnel tests. The dynamic wind load covers vibrations......Wind loads have to be taken into account when designing civil engineering structures. The wind load on structures can be systematised by means of the wind load chain: wind climate (global), terrain (wind at low height), aerodynamic response (wind load to pressure), mechanical response (wind...

  7. Wind Loads on Structures

    DEFF Research Database (Denmark)

    Dyrbye, Claes; Hansen, Svend Ole

    pressure to structural response) and design criteria. Starting with an introduction of the wind load chain, the book moves on to meteorological considerations, atmospheric boundary layer, static wind load, dynamic wind load and scaling laws used in wind-tunnel tests. The dynamic wind load covers vibrations......Wind loads have to be taken into account when designing civil engineering structures. The wind load on structures can be systematised by means of the wind load chain: wind climate (global), terrain (wind at low height), aerodynamic response (wind load to pressure), mechanical response (wind...

  8. Robustness of Structures

    DEFF Research Database (Denmark)

    Sørensen, John Dalsgaard

    2011-01-01

    robust design as well as strategies for maintaining the robustness of existing structures throughout their service life. This paper describes an overall theoretical framework for assessing robustness of structures developed within WG1 “Robustness of structures”. Robustness can be defined in different......An important aspect of the COST Action TU0601 “Robustness of structures” concerns the development of a theoretically sound basis for the assessment of robustness and acceptance criteria for structural robustness which can form the basis for development of practical relevant methods for ensuring...

  9. Structural Reliability Methods

    DEFF Research Database (Denmark)

    Ditlevsen, Ove Dalager; Madsen, H. O.

    of structural reliability, including the theoretical basis for these methods. Partial safety factor codes under current practice are briefly introduced and discussed. A probabilistic code format for obtaining a formal reliability evaluation system that catches the most essential features of the nature......The structural reliability methods quantitatively treat the uncertainty of predicting the behaviour and properties of a structure given the uncertain properties of its geometry, materials, and the actions it is supposed to withstand. This book addresses the probabilistic methods for evaluation...

  10. Equivariant Zariski Structures

    CERN Document Server

    Solanki, Vinesh

    2011-01-01

    A category of equivariant algebras is defined, after introducing some important examples (the first Weyl algebra, $U_{q}(sl_{2}(k))$ for generic q, quantum tori at generic parameter). To each equivariant algebra, a first order theory is assigned. Model theoretic results are established (uncountable categoricity, quantifier elimination to the level of existential formulas) and that an appropriate dimension theory exists for models, making them Zariski structures. A functor from the category of equivariant algebras to the category of Zariski structures is defined and further properties of equivariant structures are briefly discussed.

  11. Structural patterns in nature

    DEFF Research Database (Denmark)

    Wester, Ture

    2003-01-01

    It seemens that some very basic randomly produced geometric/topological patterns are commonly found in Nature and have often very distinctive structural qualities. In Nature we find the same pattern in all scales from the universe to molecules, from solar systems to packing of cells, from glaciers...... to sea shells, from river systems to trees etc. Sometimes this seeming archetypical morphology involve structrual action and sometimes not-but the fact that it often posses efficient structural action opens a tool for evaluation and analysis of structures in nature and at the same time might...

  12. Kernels for structured data

    CERN Document Server

    Gärtner, Thomas

    2009-01-01

    This book provides a unique treatment of an important area of machine learning and answers the question of how kernel methods can be applied to structured data. Kernel methods are a class of state-of-the-art learning algorithms that exhibit excellent learning results in several application domains. Originally, kernel methods were developed with data in mind that can easily be embedded in a Euclidean vector space. Much real-world data does not have this property but is inherently structured. An example of such data, often consulted in the book, is the (2D) graph structure of molecules formed by

  13. Programming language structures

    CERN Document Server

    Organick, Elliott Irving; Plummer, Robert P

    1978-01-01

    Programming Language Structures deals with the structures of programming languages and introduces the reader to five important programming languages: Algol, Fortran, Lisp, Snobol, and Pascal. The fundamental similarities and differences among these languages are discussed. A unifying framework is constructed that can be used to study the structure of other languages, such as Cobol, PL/I, and APL. Several of the tools and methodologies needed to construct large programs are also considered.Comprised of 10 chapters, this book begins with a summary of the relevant concepts and principles about al

  14. Sensemaking, structuring and strategy

    DEFF Research Database (Denmark)

    Nielsen, Renate

    With the purpose of generating a new understanding of how organisations develop, an interpretive perspective at continuous processes in organisations will be applied: more specifically at sensemaking, structuring and strategising....

  15. Robustness of Structures

    DEFF Research Database (Denmark)

    Sørensen, John Dalsgaard

    2008-01-01

    . According to Danish design rules robustness shall be documented for all structures in high consequence class. The design procedure to document sufficient robustness consists of: 1) Review of loads and possible failure modes / scenarios and determination of acceptable collapse extent; 2) Review......This paper describes the background of the robustness requirements implemented in the Danish Code of Practice for Safety of Structures and in the Danish National Annex to the Eurocode 0, see (DS-INF 146, 2003), (DS 409, 2006), (EN 1990 DK NA, 2007) and (Sørensen and Christensen, 2006). More...... frequent use of advanced types of structures with limited redundancy and serious consequences in case of failure combined with increased requirements to efficiency in design and execution followed by increased risk of human errors has made the need of requirements to robustness of new structures essential...

  16. Structural dynamic modification

    Indian Academy of Sciences (India)

    A Sestieri

    2000-06-01

    Vibration and acoustic requirements are becoming increasingly important in the design of mechanical structures, but they are not usually of primary concern in the design process. So the need to vary the structural behaviour to solve noise and vibration problems often occurs at the prototype stage, giving rise to the so-called structural modification problem. In this paper, the direct problem of determing the new response of a system, after some modifications are introduced into the sestem, is analysed using two different databases: the modal database and the frequency response function database. The limitaions of the modal database are discussed. Structural modifications that can be accounted for are lumped masses, springs, dampers and dynamic absorbers.

  17. Territorial Administrative Budgetary Structure

    Directory of Open Access Journals (Sweden)

    Lucia Risti

    2011-06-01

    Full Text Available Local budget structure is a consequence of the way the country’s venues are organized from the territorial administrative point of view, in communes, towns, municipalities and the capital, Bucharest, in districts.

  18. Extremely deformable structures

    CERN Document Server

    2015-01-01

    Recently, a new research stimulus has derived from the observation that soft structures, such as biological systems, but also rubber and gel, may work in a post critical regime, where elastic elements are subject to extreme deformations, though still exhibiting excellent mechanical performances. This is the realm of ‘extreme mechanics’, to which this book is addressed. The possibility of exploiting highly deformable structures opens new and unexpected technological possibilities. In particular, the challenge is the design of deformable and bi-stable mechanisms which can reach superior mechanical performances and can have a strong impact on several high-tech applications, including stretchable electronics, nanotube serpentines, deployable structures for aerospace engineering, cable deployment in the ocean, but also sensors and flexible actuators and vibration absorbers. Readers are introduced to a variety of interrelated topics involving the mechanics of extremely deformable structures, with emphasis on ...

  19. Shock structures of astrospheres

    CERN Document Server

    Scherer, Klaus; Kleimann, Jens; Wiengarten, Tobias; Bomans, Dominik J; Weis, Kerstin

    2015-01-01

    The interaction between a supersonic stellar wind and a (super-)sonic interstellar wind has recently been viewed with new interest. We here first give an overview of the modeling, which includes the heliosphere as an example of a special astrosphere. Then we concentrate on the shock structures of fluid models, especially of hydrodynamic (HD) models. More involved models taking into account radiation transfer and magnetic fields are briefly sketched. Even the relatively simple HD models show a rich shock structure, which might be observable in some objects. We employ a single fluid model to study these complex shock structures, and compare the results obtained including heating and cooling with results obtained without these effects. Furthermore, we show that in the hypersonic case valuable information of the shock structure can be obtained from the Rankine-Hugoniot equations. We solved the Euler equations for the single fluid case and also for a case including cooling and heating. We also discuss the analytic...

  20. Differential geometric structures

    CERN Document Server

    Poor, Walter A

    2007-01-01

    This introductory text defines geometric structure by specifying parallel transport in an appropriate fiber bundle and focusing on simplest cases of linear parallel transport in a vector bundle. 1981 edition.

  1. Structural assessment of nanocomposites.

    Science.gov (United States)

    Gan, Yong X

    2012-07-01

    This paper provides an overview on structural assessment of nanocomposite materials. First of all, a brief description of advanced structure characterization methods such as scanning electron microscopy, X-ray diffraction, transmission electron microscopy, atomic force microscopy, and scanning tunneling microscopy is presented. Secondly, applications of these methods for analysis of structures and compositions of typical nanocomposites are introduced. The nanocomposites are formed by different nanoscale processing technologies. Electrochemically polymerized polyaniline (PANi) nanocomposites, thermomechanically processed metal matrix nanocomposites, nanocast ceramic matrix composites are typical examples discussed in this paper. Case studies on several functional nanocomposites for energy storage/conversion, catalysis and sensing applications are mentioned. After that, assessment of the interface structures of nanocomposite materials using surface characterization techniques and mechanical damage models is discussed. Finally, concluding remarks are provided.

  2. Deployable Composite Structures Project

    Data.gov (United States)

    National Aeronautics and Space Administration — NASA is seeking innovative structure technologies that will advance expandable exploration space modules and surface based habitats. To address this need CTD has...

  3. Optimal Sound Absorbing Structures

    CERN Document Server

    Yang, Min; Fu, Caixing; Sheng, Ping

    2016-01-01

    Causal nature of the acoustic response, for any materials or structures, dictates an inequality that relates the absorption spectrum of the sample to its thickness. We present a general recipe for constructing sound-absorbing structures that can attain near-equality for the causal relation with very high absorption performance; such structures are denoted optimal. Our strategy involves using carefully designed acoustic metamaterials as backing to a thin layer of conventional sound absorbing material, e.g., acoustic sponge. By using this design approach, we have realized a 12 cm-thick structure that exhibits broadband, near-perfect flat absorption spectrum starting at around 400 Hz. From the causal relation, the calculated minimum sample thickness is 11.5 cm for the observed absorption spectrum. We present the theory that underlies such absorption performance, involving the evanescent waves and their interaction with a dissipative medium, and show the excellent agreement with the experiment.

  4. FEMA DFIRM Hydraulic Structures

    Data.gov (United States)

    Minnesota Department of Natural Resources — This layer and accompanying attribute table is required whenever hydraulic structures are shown in the flood profile. It is also required if levees are shown on the...

  5. Creep in structures

    Energy Technology Data Exchange (ETDEWEB)

    Zyczkowski, M. (Krakow Univ. of Technology (Poland). Inst. of Mechanics and Machine Design) (ed.)

    1991-01-01

    This volume contains 81 papers divided into three almost equal parts: Constitutive equations, combined loadings; damage, creep crack growth, creep rupture; structures, analytical and numerical methods, optimal design. (orig.).

  6. Bioinspired structured surfaces.

    Science.gov (United States)

    Bhushan, Bharat

    2012-01-24

    Nature has evolved objects with desired functionality using commonly found materials. Nature capitalizes on hierarchical structures to achieve functionality. The understanding of the functions provided by objects and processes found in nature can guide us to produce nanomaterials, nanodevices, and processes with desirable functionality. Various natural objects which provide functionality of commercial interest have been characterized to understand how a natural object provides functionality. We have modeled and fabricated structures in the lab using nature's route and developed optimum structures. Once it is understood how nature does it, optimum structures have been fabricated using smart materials and fabrication techniques. This feature article provides an overview of four topics: Lotus effect, rose petal effect, gecko feet, and shark skin.

  7. Fundamentals of Structural Engineering

    CERN Document Server

    Connor, Jerome J

    2013-01-01

    Fundamentals of Structural Engineering provides a balanced, seamless treatment of both classic, analytic methods and contemporary, computer-based techniques for conceptualizing and designing a structure. The book’s principle goal is to foster an intuitive understanding of structural behavior based on problem solving experience for students of civil engineering and architecture who have been exposed to the basic concepts of engineering mechanics and mechanics of materials. Making it distinct from many other undergraduate textbooks, the authors of this text recognize the notion that engineers reason about behavior using simple models and intuition they acquire through problem solving. The approach adopted in this text develops this type of intuition  by presenting extensive, realistic problems and case studies together with computer simulation, which allows rapid exploration of  how a structure responds to changes in geometry and physical parameters. This book also: Emphasizes problem-based understanding of...

  8. Structures and their analysis

    CERN Document Server

    Fuchs, Maurice Bernard

    2016-01-01

    Addressing structures, this book presents a classic discipline in a modern setting by combining illustrated examples with insights into the solutions. It is the fruit of the author’s many years of teaching the subject and of just as many years of research into the design of optimal structures. Although intended for an advanced level of instruction it has an undergraduate course at its core. Further, the book was written with the advantage of having massive computer power in the background, an aspect which changes the entire approach to many engineering disciplines and in particular to structures. This paradigm shift has dislodged the force (flexibility) method from its former prominence and paved the way for the displacement (stiffness) method, despite the multitude of linear equations it spawns. In this book, however, both methods are taught: the force method offers a perfect vehicle for understanding structural behavior, bearing in mind that it is the displacement method which does the heavy number crunch...

  9. Change in Business Structure

    Data.gov (United States)

    Department of Veterans Affairs — Provides information on whether a company’s change in business structure affects its Data Universal Numbering System (DUNS) Number and its Vendor Information Pages...

  10. Modern frame structure buildings

    National Research Council Canada - National Science Library

    В. М. Першаков; Т. О. Петрова; К. М. Лисницька

    2013-01-01

    The article deals with the design, construction and implementation of reinforced concrete frame structures with span 18, 21 m for agricultural production buildings, hall-premises of public buildings...

  11. Stable generalized complex structures

    CERN Document Server

    Cavalcanti, Gil R

    2015-01-01

    A stable generalized complex structure is one that is generically symplectic but degenerates along a real codimension two submanifold, where it defines a generalized Calabi-Yau structure. We introduce a Lie algebroid which allows us to view such structures as symplectic forms. This allows us to construct new examples of stable structures, and also to define period maps for their deformations in which the background three-form flux is either fixed or not, proving the unobstructedness of both deformation problems. We then use the same tools to establish local normal forms for the degeneracy locus and for Lagrangian branes. Applying our normal forms to the four-dimensional case, we prove that any compact stable generalized complex 4-manifold has a symplectic completion, in the sense that it can be modified near its degeneracy locus to produce a compact symplectic 4-manifold.

  12. Encapsulation with structured triglycerides

    Science.gov (United States)

    Lipids provide excellent materials to encapsulate bioactive compounds for food and pharmaceutical applications. Lipids are renewable, biodegradable, and easily modified to provide additional chemical functionality. The use of structured lipids that have been modified with photoactive properties are ...

  13. Structural Identification Problem

    Directory of Open Access Journals (Sweden)

    Suvorov Aleksei

    2016-01-01

    Full Text Available The identification problem of the existing structures though the Quasi-Newton and its modification, Trust region algorithms is discussed. For the structural problems, which could be represented by means of the mathematical modelling of the finite element code discussed method is extremely useful. The nonlinear minimization problem of the L2 norm for the structures with linear elastic behaviour is solved by using of the Optimization Toolbox of Matlab. The direct and inverse procedures for the composition of the desired function to minimize are illustrated for the spatial 3D truss structure as well as for the problem of plane finite elements. The truss identification problem is solved with 2 and 3 unknown parameters in order to compare the computational efforts and for the graphical purposes. The particular commands of the Matlab codes are present in this paper.

  14. Extracellular matrix structure.

    Science.gov (United States)

    Theocharis, Achilleas D; Skandalis, Spyros S; Gialeli, Chrysostomi; Karamanos, Nikos K

    2016-02-01

    Extracellular matrix (ECM) is a non-cellular three-dimensional macromolecular network composed of collagens, proteoglycans/glycosaminoglycans, elastin, fibronectin, laminins, and several other glycoproteins. Matrix components bind each other as well as cell adhesion receptors forming a complex network into which cells reside in all tissues and organs. Cell surface receptors transduce signals into cells from ECM, which regulate diverse cellular functions, such as survival, growth, migration, and differentiation, and are vital for maintaining normal homeostasis. ECM is a highly dynamic structural network that continuously undergoes remodeling mediated by several matrix-degrading enzymes during normal and pathological conditions. Deregulation of ECM composition and structure is associated with the development and progression of several pathologic conditions. This article emphasizes in the complex ECM structure as to provide a better understanding of its dynamic structural and functional multipotency. Where relevant, the implication of the various families of ECM macromolecules in health and disease is also presented.

  15. Helical surface structures

    CERN Document Server

    Brandenburg, A; Brandenburg, Axel; Blackman, Eric G.

    2002-01-01

    Over the past few years there has been growing interest in helical magnetic field structures seen at the solar surface, in coronal mass ejections, as well as in the solar wind. Although there is a great deal of randomness in the data, on average the extended structures are mostly left-handed on the northern hemisphere and right-handed on the southern. Surface field structures are also classified as dextral (= right bearing) and sinistral (= left bearing) occurring preferentially in the northern and southern hemispheres respectively. Of particular interest here is a quantitative measurement of the associated emergence rates of helical structures, which translate to magnetic helicity fluxes. In this review, we give a brief survey of what has been found so far and what is expected based on models. Particular emphasis is put on the scale dependence of the associated fields and an attempt is made to estimate the helicity flux of the mean field vs. fluctuating field.

  16. Dielectric assist accelerating structure

    Science.gov (United States)

    Satoh, D.; Yoshida, M.; Hayashizaki, N.

    2016-01-01

    A higher-order TM02 n mode accelerating structure is proposed based on a novel concept of dielectric loaded rf cavities. This accelerating structure consists of ultralow-loss dielectric cylinders and disks with irises which are periodically arranged in a metallic enclosure. Unlike conventional dielectric loaded accelerating structures, most of the rf power is stored in the vacuum space near the beam axis, leading to a significant reduction of the wall loss, much lower than that of conventional normal-conducting linac structures. This allows us to realize an extremely high quality factor and a very high shunt impedance at room temperature. A simulation of a 5 cell prototype design with an existing alumina ceramic indicates an unloaded quality factor of the accelerating mode over 120 000 and a shunt impedance exceeding 650 M Ω /m at room temperature.

  17. Adaptive structures flight experiments

    Science.gov (United States)

    Martin, Maurice

    The topics are presented in viewgraph form and include the following: adaptive structures flight experiments; enhanced resolution using active vibration suppression; Advanced Controls Technology Experiment (ACTEX); ACTEX program status; ACTEX-2; ACTEX-2 program status; modular control patch; STRV-1b Cryocooler Vibration Suppression Experiment; STRV-1b program status; Precision Optical Bench Experiment (PROBE); Clementine Spacecraft Configuration; TECHSAT all-composite spacecraft; Inexpensive Structures and Materials Flight Experiment (INFLEX); and INFLEX program status.

  18. Structure of Proton

    CERN Document Server

    Fayyazuddin, A

    2003-01-01

    Electron--proton scattering in elastic and highly inelastic region is reviewed in a unified approach. The importance of parity--violating scattering due to electro--weak interference in probing the structure of proton is emphasized. The importance of longitudnal spin--spin asymmetry as well as parity violating longitudnal asymmetry to extract the structure functions of proton in both regions are discussed. The recoil polarization of proton in the elastic scattering is also discussed.

  19. Deployable Soft Composite Structures

    OpenAIRE

    Wei Wang; Hugo Rodrigue; Sung-Hoon Ahn

    2016-01-01

    Deployable structure composed of smart materials based actuators can reconcile its inherently conflicting requirements of low mass, good shape adaptability, and high load-bearing capability. This work describes the fabrication of deployable structures using smart soft composite actuators combining a soft matrix with variable stiffness properties and hinge-like movement through a rigid skeleton. The hinge actuator has the advantage of being simple to fabricate, inexpensive, lightweight and sim...

  20. Structured luminescence conversion layer

    Science.gov (United States)

    Berben, Dirk; Antoniadis, Homer; Jermann, Frank; Krummacher, Benjamin Claus; Von Malm, Norwin; Zachau, Martin

    2012-12-11

    An apparatus device such as a light source is disclosed which has an OLED device and a structured luminescence conversion layer deposited on the substrate or transparent electrode of said OLED device and on the exterior of said OLED device. The structured luminescence conversion layer contains regions such as color-changing and non-color-changing regions with particular shapes arranged in a particular pattern.

  1. Purely Functional Structured Programming

    OpenAIRE

    Obua, Steven

    2010-01-01

    The idea of functional programming has played a big role in shaping today's landscape of mainstream programming languages. Another concept that dominates the current programming style is Dijkstra's structured programming. Both concepts have been successfully married, for example in the programming language Scala. This paper proposes how the same can be achieved for structured programming and PURELY functional programming via the notion of LINEAR SCOPE. One advantage of this proposal is that m...

  2. Renovation of Roof Structure

    DEFF Research Database (Denmark)

    Kjærbye, Per Oluf H

    1997-01-01

    A 30 year old not-watertight roof based on wooden boards with roofing felt have been changed to a pitched structure with cementos plates. At the same time more thermal insulation has been placed.......A 30 year old not-watertight roof based on wooden boards with roofing felt have been changed to a pitched structure with cementos plates. At the same time more thermal insulation has been placed....

  3. Structure function monitor

    Energy Technology Data Exchange (ETDEWEB)

    McGraw, John T [Placitas, NM; Zimmer, Peter C [Albuquerque, NM; Ackermann, Mark R [Albuquerque, NM

    2012-01-24

    Methods and apparatus for a structure function monitor provide for generation of parameters characterizing a refractive medium. In an embodiment, a structure function monitor acquires images of a pupil plane and an image plane and, from these images, retrieves the phase over an aperture, unwraps the retrieved phase, and analyzes the unwrapped retrieved phase. In an embodiment, analysis yields atmospheric parameters measured at spatial scales from zero to the diameter of a telescope used to collect light from a source.

  4. REACTOR MODERATOR STRUCTURE

    Science.gov (United States)

    Greenstreet, B.L.

    1963-12-31

    A system for maintaining the alignment of moderator block structures in reactors is presented. Integral restraining grids are placed between each layer of blocks in the moderator structure, at the top of the uppermost layer, and at the bottom of the lowermost layer. Slots are provided in the top and bottom surfaces of the moderator blocks so as to provide a keying action with the grids. The grids are maintained in alignment by vertical guiding members disposed about their peripheries. (AEC)

  5. Structural Transformation in Ecuador

    OpenAIRE

    Ricardo Hausmann; Bailey Klinger

    2010-01-01

    This paper applies new techniques and metrics to analyze Ecuador's past record of and future opportunities for structural transformation. Ecuador's export dynamics and the emergence of new export activities have been the historical drivers of the country's growth, but recently Ecuador's export basket has undergone little structural transformation. The same broad sectors continue to dominate, and the overall sophistication of the export basket has actually declined in recent years. In order to...

  6. Estonian Tax Structure

    Directory of Open Access Journals (Sweden)

    Viktor Trasberg

    2014-08-01

    Full Text Available The paper analyses Estonian tax structure changes during the last decade and critically assesses the current situation. The country’s tax mix is rather unique among EU countries – it has one of the highest proportions of consumption taxes in total taxes and the lowest level of capital and profit taxes. Such an unbalanced tax structure creates risks for public finances, limits revenue collection and distorts the business environment.

  7. Trajectory grouping structure

    Directory of Open Access Journals (Sweden)

    Maike Buchin

    2015-03-01

    Full Text Available The collective motion of a set of moving entities like people, birds, or other animals, is characterized by groups arising, merging, splitting, and ending. Given the trajectories of these entities, we define and model a structure that captures all of such changes using the Reeb graph, a concept from topology. The trajectory grouping structure has three natural parameters that allow more global views of the data in group size, group duration, and entity inter-distance. We prove complexity bounds on the maximum number of maximal groups that can be present, and give algorithms to compute the grouping structure efficiently. We also study how the trajectory grouping structure can be made robust, that is, how brief interruptions of groups can be disregarded in the global structure, adding a notion of persistence to the structure. Furthermore, we showcase the results of experiments using data generated by the NetLogo flocking model and from the Starkey project. The Starkey data describe the movement of elk, deer, and cattle. Although there is no ground truth for the grouping structure in this data, the experiments show that the trajectory grouping structure is plausible and has the desired effects when changing the essential parameters. Our research provides the first complete study of trajectory group evolvement, including combinatorial,algorithmic, and experimental results.

  8. Meteorite Seymchan structure

    Science.gov (United States)

    Hontsova, S. S.; Petrova, E. V.; Muftahetdinova, R. F.; Chulanova, V. N.; Grokhovsky, V. I.

    2016-09-01

    The meteorite Seymchan specimen was studied using optical microscopy and scanning electron microscopy. Olivine grains have roundish shapes, which was formed during matter cooling. Different features of the metal structure such as plessite structure and Neimann bands were observed. The oxide edges were observed in the boundaries between phases. The oxides were formed in the terrestrial conditions. The boundary regions between metal and olivine in the meteorite contain grains of troilite, schreibersite, and chromite.

  9. Interfacial chemical reaction and multiple gap state formation on three layer cathode in organic light-emitting diode: Ca/BaF2/Alq3

    Science.gov (United States)

    Kim, Tae Gun; Lee, Hyunbok; Yi, Yeonjin; Lee, Seung Mi; Kim, Jeong Won

    2015-07-01

    A three layer cathode is a promising stack structure for long lifetime and high efficiency in organic light-emitting diodes. The interfacial chemical reactions and their effects on electronic structures for alkaline-earth metal (Ca, Ba)/Alq3 [tris(8-hydroxyquinolinato)aluminum] and Ca/BaF2/Alq3 are investigated using in-situ X-ray and ultraviolet photoelectron spectroscopy, as well as molecular model calculation. The BaF2 interlayer initially prevents direct contact between Alq3 and the reactive Ca metal, but it is dissociated into Ba and CaF2 by the addition of Ca. As the Ca thickness increases, the Ca penetrates the interlayer to directly participate in the reaction with the underlying Alq3. This series of chemical reactions takes place irrespective of the BaF2 buffer layer thickness as long as the Ca overlayer thickness is sufficient. The interface reaction between the alkaline-earth metal and Alq3 generates two energetically separated gap states in a sequential manner. This phenomenon is explained by step-by-step charge transfer from the alkaline-earth metal to the lowest unoccupied molecular orbital states of Alq3, forming new occupied states below the Fermi level.

  10. Effect of the addition of MgF2 and NaF on the thermal, optical and magnetic properties of fluoride glasses for sensing applications

    Science.gov (United States)

    Wang, Yujie; Wang, Shuangbao; Deng, Saifu; Liu, Jianting; Zhang, Jiahui

    2017-10-01

    Optical glass was very important for the development of optical fiber sensor. In this paper, a new type fluoride glass of ZrF4-BaF2-AlF3-NaF-MgF2(ZBANM) was synthesized for sensing application which has low loss and high magneto-optical coefficient, and it was found that the glass system had at least 60% transmittance from 3.5 μm to 7 μm and smallest verdet constant of 4.628E-5/(rad A-1) at 632.8 nm. The relationship among the compositions of sample glass with its thermal property, optical absorptivity and magnetic-optical coefficients was respectively studied with Thermal Gravimetric-Differential Thermal Analyzer, Fourier Transform infrared spectroscopy and a home-made magneto optical bench. The study indicated that transmittance of fluoride glass structure had been obviously improved after moderate content of Mg2+ and Na+ was doped. Simultaneously, with the molar ratio of alkaline-earth ions Mg increased, the Verdet constant of fluoride glass was increased. And the glass structure with composition of 48%ZrF4-24%BaF2-6%AlF3-8%NaF-14%MgF2 exhibited a small molar absorptivity and the largest Verdet constant of 2.853E-4/(rad A-1).

  11. Diffuse neutron scattering from anion-excess strontium chloride

    DEFF Research Database (Denmark)

    Goff, J.P.; Clausen, K.N.; Fåk, B.

    1992-01-01

    The defect structure and diffusional processes have been studied in the anion-excess fluorite (Sr, Y)Cl2.03 by diffuse neutron scattering techniques. Static cuboctahedral clusters found at ambient temperature break up at temperatures below 1050 K, where the anion disorder is highly dynamic...

  12. Neutron diffraction and TSDC on Ba1−xUxF2+2x solid electrolytes

    DEFF Research Database (Denmark)

    Ouwerkerk, M.; Andersen, N. H.; Veldkamp, F. F.

    1986-01-01

    The defect structure of fluorite-type Ba1−xUxF2+2x solid solutions, which exhibit fast fluoride ion conductivity, has been investigated by quasi-elastic diffuse neutron scattering (QDNS) experiments, and thermally stimulated depolarisation current (TSDC) measurements. A comparison with model...

  13. Integral Textile Ceramic Structures

    Science.gov (United States)

    Marshall, David B.; Cox, Brian N.

    2008-08-01

    A new paradigm for ceramic composite structural components enables functionality in heat exchange, transpiration, detailed shape, and thermal strain management that significantly exceeds the prior art. The paradigm is based on the use of three-dimensional fiber reinforcement that is tailored to the specific shape, stress, and thermal requirements of a structural application and therefore generally requires innovative textile methods for each realization. Key features include the attainment of thin skins (less than 1 mm) that are nevertheless structurally robust, transpiration holes formed without cutting fibers, double curvature, compliant integral attachment to other structures that avoids thermal stress buildup, and microcomposite ceramic matrices that minimize spalling and allow the formation of smooth surfaces. All these features can be combined into structures of very varied gross shape and function, using a wide range of materials such as all-oxide systems and SiC and carbon fibers in SiC matrices. Illustrations are drawn from rocket nozzles, thermal protection systems, and gas turbine engines. The new design challenges that arise for such material/structure systems are being met by specialized computational modeling that departs significantly in the representation of materials behavior from that used in conventional finite element methods.

  14. Structural optimization of free-form reciprocal structures

    DEFF Research Database (Denmark)

    Parigi, Dario

    2014-01-01

    This paper presents an optimization algorithm for the design of structurally efficient free-form reciprocal structures. Because of the geometric complexity of reciprocal structures, only a few structural studies have been carried out so far, and we have a limited knowledge of the relation between...... geometry and structural behaviour in reciprocal structures. This study takes advantage of the preceding work carried by the author on the Reciprocalizer, a software tool for the generation of reciprocal geometries. The Reciprocalizer has been included into a structural optimization algorithm...... for the generation of structurally efficient free-form reciprocal structures....

  15. Structural prediction in aphasia

    Directory of Open Access Journals (Sweden)

    Tessa Warren

    2015-05-01

    Full Text Available There is considerable evidence that young healthy comprehenders predict the structure of upcoming material, and that their processing is facilitated when they encounter material matching those predictions (e.g., Staub & Clifton, 2006; Yoshida, Dickey & Sturt, 2013. However, less is known about structural prediction in aphasia. There is evidence that lexical prediction may be spared in aphasia (Dickey et al., 2014; Love & Webb, 1977; cf. Mack et al, 2013. However, predictive mechanisms supporting facilitated lexical access may not necessarily support structural facilitation. Given that many people with aphasia (PWA exhibit syntactic deficits (e.g. Goodglass, 1993, PWA with such impairments may not engage in structural prediction. However, recent evidence suggests that some PWA may indeed predict upcoming structure (Hanne, Burchert, De Bleser, & Vashishth, 2015. Hanne et al. tracked the eyes of PWA (n=8 with sentence-comprehension deficits while they listened to reversible subject-verb-object (SVO and object-verb-subject (OVS sentences in German, in a sentence-picture matching task. Hanne et al. manipulated case and number marking to disambiguate the sentences’ structure. Gazes to an OVS or SVO picture during the unfolding of a sentence were assumed to indicate prediction of the structure congruent with that picture. According to this measure, the PWA’s structural prediction was impaired compared to controls, but they did successfully predict upcoming structure when morphosyntactic cues were strong and unambiguous. Hanne et al.’s visual-world evidence is suggestive, but their forced-choice sentence-picture matching task places tight constraints on possible structural predictions. Clearer evidence of structural prediction would come from paradigms where the content of upcoming material is not as constrained. The current study used self-paced reading study to examine structural prediction among PWA in less constrained contexts. PWA (n=17 who

  16. RNA Thermodynamic Structural Entropy.

    Science.gov (United States)

    Garcia-Martin, Juan Antonio; Clote, Peter

    2015-01-01

    Conformational entropy for atomic-level, three dimensional biomolecules is known experimentally to play an important role in protein-ligand discrimination, yet reliable computation of entropy remains a difficult problem. Here we describe the first two accurate and efficient algorithms to compute the conformational entropy for RNA secondary structures, with respect to the Turner energy model, where free energy parameters are determined from UV absorption experiments. An algorithm to compute the derivational entropy for RNA secondary structures had previously been introduced, using stochastic context free grammars (SCFGs). However, the numerical value of derivational entropy depends heavily on the chosen context free grammar and on the training set used to estimate rule probabilities. Using data from the Rfam database, we determine that both of our thermodynamic methods, which agree in numerical value, are substantially faster than the SCFG method. Thermodynamic structural entropy is much smaller than derivational entropy, and the correlation between length-normalized thermodynamic entropy and derivational entropy is moderately weak to poor. In applications, we plot the structural entropy as a function of temperature for known thermoswitches, such as the repression of heat shock gene expression (ROSE) element, we determine that the correlation between hammerhead ribozyme cleavage activity and total free energy is improved by including an additional free energy term arising from conformational entropy, and we plot the structural entropy of windows of the HIV-1 genome. Our software RNAentropy can compute structural entropy for any user-specified temperature, and supports both the Turner'99 and Turner'04 energy parameters. It follows that RNAentropy is state-of-the-art software to compute RNA secondary structure conformational entropy. Source code is available at https://github.com/clotelab/RNAentropy/; a full web server is available at http

  17. RNA Thermodynamic Structural Entropy.

    Directory of Open Access Journals (Sweden)

    Juan Antonio Garcia-Martin

    Full Text Available Conformational entropy for atomic-level, three dimensional biomolecules is known experimentally to play an important role in protein-ligand discrimination, yet reliable computation of entropy remains a difficult problem. Here we describe the first two accurate and efficient algorithms to compute the conformational entropy for RNA secondary structures, with respect to the Turner energy model, where free energy parameters are determined from UV absorption experiments. An algorithm to compute the derivational entropy for RNA secondary structures had previously been introduced, using stochastic context free grammars (SCFGs. However, the numerical value of derivational entropy depends heavily on the chosen context free grammar and on the training set used to estimate rule probabilities. Using data from the Rfam database, we determine that both of our thermodynamic methods, which agree in numerical value, are substantially faster than the SCFG method. Thermodynamic structural entropy is much smaller than derivational entropy, and the correlation between length-normalized thermodynamic entropy and derivational entropy is moderately weak to poor. In applications, we plot the structural entropy as a function of temperature for known thermoswitches, such as the repression of heat shock gene expression (ROSE element, we determine that the correlation between hammerhead ribozyme cleavage activity and total free energy is improved by including an additional free energy term arising from conformational entropy, and we plot the structural entropy of windows of the HIV-1 genome. Our software RNAentropy can compute structural entropy for any user-specified temperature, and supports both the Turner'99 and Turner'04 energy parameters. It follows that RNAentropy is state-of-the-art software to compute RNA secondary structure conformational entropy. Source code is available at https://github.com/clotelab/RNAentropy/; a full web server is available at http

  18. Hierarchically Structured Electrospun Fibers

    Directory of Open Access Journals (Sweden)

    Nicole E. Zander

    2013-01-01

    Full Text Available Traditional electrospun nanofibers have a myriad of applications ranging from scaffolds for tissue engineering to components of biosensors and energy harvesting devices. The generally smooth one-dimensional structure of the fibers has stood as a limitation to several interesting novel applications. Control of fiber diameter, porosity and collector geometry will be briefly discussed, as will more traditional methods for controlling fiber morphology and fiber mat architecture. The remainder of the review will focus on new techniques to prepare hierarchically structured fibers. Fibers with hierarchical primary structures—including helical, buckled, and beads-on-a-string fibers, as well as fibers with secondary structures, such as nanopores, nanopillars, nanorods, and internally structured fibers and their applications—will be discussed. These new materials with helical/buckled morphology are expected to possess unique optical and mechanical properties with possible applications for negative refractive index materials, highly stretchable/high-tensile-strength materials, and components in microelectromechanical devices. Core-shell type fibers enable a much wider variety of materials to be electrospun and are expected to be widely applied in the sensing, drug delivery/controlled release fields, and in the encapsulation of live cells for biological applications. Materials with a hierarchical secondary structure are expected to provide new superhydrophobic and self-cleaning materials.

  19. PRSEUS Structural Concept Development

    Science.gov (United States)

    Velicki, Alex; Jegley, Dawn

    2014-01-01

    A lighter, more robust airframe is one of the key technological advancements necessary for the successful launch of any large next-generation transport aircraft. Such a premise dictates that considerable improvements beyond current state-of-the-art aluminum structures is needed, and that improvements of this magnitude will require an extensive use of composite materials that are not only lightweight, but also economical to produce. To address this challenge, researchers at NASA and The Boeing Company are developing a novel structural concept called the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) under the Environmentally Responsible Aviation (ERA) Project. It is an integrally stiffened panel concept that is stitched together and designed to maintain residual load-carrying capabilities under a variety of damage scenarios. In addition to improved structural performance, an important facet of this unique arrangement of stitched carbon fibers is its innovative manufacturing method that has the potential to lower fabrication costs by eliminating fasteners and autoclave cures. The rationale and development status for this new approach forms the basis of the work described in this paper. The test specimens described herein were fabricated, or are currently being fabricated, by The Boeing Company, while the structural analyses and testing tasks are being performed by NASA and Boeing personnel.

  20. Prosodic Structure as a Parallel to Musical Structure

    Science.gov (United States)

    Heffner, Christopher C.; Slevc, L. Robert

    2015-01-01

    What structural properties do language and music share? Although early speculation identified a wide variety of possibilities, the literature has largely focused on the parallels between musical structure and syntactic structure. Here, we argue that parallels between musical structure and prosodic structure deserve more attention. We review the evidence for a link between musical and prosodic structure and find it to be strong. In fact, certain elements of prosodic structure may provide a parsimonious comparison with musical structure without sacrificing empirical findings related to the parallels between language and music. We then develop several predictions related to such a hypothesis. PMID:26733930

  1. Structure and biophysics

    CERN Document Server

    Puglisi, Joseph D

    2007-01-01

    This volume is a collection of articles from the proceedings of the ISSBMR 7th Course: Structure and Biophysics - New Technologies for Current Challenges in Biology and Beyond. This NATO Advanced Institute (ASI) was held in Erice at the Ettore Majorana Foundation and Centre for Scientific Culture on 22 June through 3 July 2005. The ASI brought together a diverse group of experts in the fields of Structural Biology, Biophysics and Physics. Prominent lecturers, from seven different countries, and students from around the world participated in the NATO ASI organized by Professors Joseph Puglisi (Stanford University, USA) and Alexander Arseniev (Moscow, RU). Advances in nuclear magnetic resonance spectroscopy (NMR) and x-ray crystallography have allowed the three-dimensional structures of many biological macromolecules and their complexes, including the ribosome and RNA polymerase to be solved. Fundamental principles of NMR spectroscopy and dynamics, x-ray crystallography, computation and experimental dynamics we...

  2. Structural motion engineering

    CERN Document Server

    Connor, Jerome

    2014-01-01

    This innovative volume provides a systematic treatment of the basic concepts and computational procedures for structural motion design and engineering for civil installations. The authors illustrate the application of motion control to a wide spectrum of buildings through many examples. Topics covered include optimal stiffness distributions for building-type structures, the role of damping in controlling motion, tuned mass dampers, base isolation systems, linear control, and nonlinear control. The book's primary objective is the satisfaction of motion-related design requirements, such as restrictions on displacement and acceleration. The book is ideal for practicing engineers and graduate students. This book also: ·         Broadens practitioners' understanding of structural motion control, the enabling technology for motion-based design ·         Provides readers the tools to satisfy requirements of modern, ultra-high strength materials that lack corresponding stiffness, where the motion re...

  3. Freeform Honeycomb Structures

    KAUST Repository

    Jiang, Caigui

    2014-07-01

    Motivated by requirements of freeform architecture, and inspired by the geometry of hexagonal combs in beehives, this paper addresses torsion-free structures aligned with hexagonal meshes. Since repetitive geometry is a very important contribution to the reduction of production costs, we study in detail “honeycomb structures”, which are defined as torsion-free structures where the walls of cells meet at 120 degrees. Interestingly, the Gauss-Bonnet theorem is useful in deriving information on the global distribution of node axes in such honeycombs. This paper discusses the computation and modeling of honeycomb structures as well as applications, e.g. for shading systems, or for quad meshing. We consider this paper as a contribution to the wider topic of freeform patterns, polyhedral or otherwise. Such patterns require new approaches on the technical level, e.g. in the treatment of smoothness, but they also extend our view of what constitutes aesthetic freeform geometry.

  4. Graphene heat dissipating structure

    Energy Technology Data Exchange (ETDEWEB)

    Washburn, Cody M.; Lambert, Timothy N.; Wheeler, David R.; Rodenbeck, Christopher T.; Railkar, Tarak A.

    2017-08-01

    Various technologies presented herein relate to forming one or more heat dissipating structures (e.g., heat spreaders and/or heat sinks) on a substrate, wherein the substrate forms part of an electronic component. The heat dissipating structures are formed from graphene, with advantage being taken of the high thermal conductivity of graphene. The graphene (e.g., in flake form) is attached to a diazonium molecule, and further, the diazonium molecule is utilized to attach the graphene to material forming the substrate. A surface of the substrate is treated to comprise oxide-containing regions and also oxide-free regions having underlying silicon exposed. The diazonium molecule attaches to the oxide-free regions, wherein the diazonium molecule bonds (e.g., covalently) to the exposed silicon. Attachment of the diazonium plus graphene molecule is optionally repeated to enable formation of a heat dissipating structure of a required height.

  5. Implications of social structure

    DEFF Research Database (Denmark)

    Brask, Josefine Bohr

    social environment of the individual. In the last two studies, we investigate the role of social structure for cooperation in a classic natural system for behavioural research, the Trinidadian guppy (Poecilia reticulata), by means of computer simulations. Cooperation contradicts evolutionary theory......, we investigate empirically the role of the social environment of individuals for their communication patterns. Our study species is a song bird, the black-capped chickadee (Poecile atricapillus). The results suggest that individual communication in this species is influenced by features of the local...... and requires special explanations. Theory predicts that heterogeneous social structure can support and promote cooperation in populations. Our simulations suggest that social structure may not be able to explain the presence of cooperation in the guppy system. Overall the thesis provides new insights...

  6. Human Spacecraft Structures Internship

    Science.gov (United States)

    Bhakta, Kush

    2017-01-01

    DSG will be placed in halo orbit around themoon- Platform for international/commercialpartners to explore lunar surface- Testbed for technologies needed toexplore Mars• Habitat module used to house up to 4crew members aboard the DSG- Launched on EM-3- Placed inside SLS fairing Habitat Module - Task Habitat Finite Element Model Re-modeled entire structure in NX2) Used Beam and Shell elements torepresent the pressure vessel structure3) Created a point cloud of centers of massfor mass components- Can now inspect local moments andinertias for thrust ring application8/ Habitat Structure – Docking Analysis Problem: Artificial Gravity may be necessary forastronaut health in deep spaceGoal: develop concepts that show how artificialgravity might be incorporated into a spacecraft inthe near term Orion Window Radiant Heat Testing.

  7. Structure learning in action

    Science.gov (United States)

    Braun, Daniel A.; Mehring, Carsten; Wolpert, Daniel M.

    2010-01-01

    ‘Learning to learn’ phenomena have been widely investigated in cognition, perception and more recently also in action. During concept learning tasks, for example, it has been suggested that characteristic features are abstracted from a set of examples with the consequence that learning of similar tasks is facilitated—a process termed ‘learning to learn’. From a computational point of view such an extraction of invariants can be regarded as learning of an underlying structure. Here we review the evidence for structure learning as a ‘learning to learn’ mechanism, especially in sensorimotor control where the motor system has to adapt to variable environments. We review studies demonstrating that common features of variable environments are extracted during sensorimotor learning and exploited for efficient adaptation in novel tasks. We conclude that structure learning plays a fundamental role in skill learning and may underlie the unsurpassed flexibility and adaptability of the motor system. PMID:19720086

  8. Laser induced structural vibration

    Science.gov (United States)

    Koss, L. L.; Tobin, R. C.

    1983-01-01

    A technique is described for exciting structural vibration by using a focussed laser beam to vaporize material from a target attached to the structure. The rapid ejection of material results in an impulsive reaction to the target which is transmitted to the structure. The method has been studied with a Nd: glass laser, operated in the long pulse mode, in combination with a bismuth target attached in turn to a ballistic pendulum and cantilever beam. The specific mechanical energy was found to be proportional to the laser pulse energy raised to a power in the range 2.5-2.9. The highest efficiency of energy transfer achieved for the first vibrational mode of the cantilever was about 2 millipercent for the maximum laser pulse energy used, 1.5 J, the signal to noise ratio then being about 40 dB.

  9. Dynamic Data Structures

    DEFF Research Database (Denmark)

    Kejlberg-Rasmussen, Casper

    to a given key? The updates we can do are: inserting a new key or deleting a given key. Our dictionary has the working set property, which means that the running time of a query depends on the query distribution. Specifically the time to search for a key depends on when we last searched for it. Our data...... statements about our data structure, which are based on the structure of the underlying problem, that we are trying to solve. We can rely on the properties of the invariants when performing queries, and in return we need to ensure that the invariants remain true after we perform updates. When designing data......In this thesis I will address three dynamic data structure problems using the concept of invariants. The first problem is maintaining a dynamically changing set of keys – a dictionary – where the queries we can ask are: does it contain a given key? and what is the preceding (or succeeding) key...

  10. Dynamic Data Structures

    DEFF Research Database (Denmark)

    Tsakalidis, Konstantinos

    We study dynamic data structures for different variants of orthogonal range reporting query problems. In particular, we consider (1) the planar orthogonal 3-sided range reporting problem: given a set of points in the plane, report the points that lie within a given 3-sided rectangle with one....... Dynamic problems like the above arise in various applications of network optimization, VLSI layout design, computer graphics and distributed computing. For the first problem, we present dynamic data structures for internal and external memory that support planar orthogonal 3-sided range reporting queries......, and insertions and deletions of points efficiently over an average case sequence of update operations. The external memory data structures find applications in constraint and temporal databases. In particular, we assume that the coordinates of the points are drawn from different probabilistic distributions...

  11. Dynamic Data Structures

    DEFF Research Database (Denmark)

    Kejlberg-Rasmussen, Casper

    statements about our data structure, which are based on the structure of the underlying problem, that we are trying to solve. We can rely on the properties of the invariants when performing queries, and in return we need to ensure that the invariants remain true after we perform updates. When designing data......In this thesis I will address three dynamic data structure problems using the concept of invariants. The first problem is maintaining a dynamically changing set of keys – a dictionary – where the queries we can ask are: does it contain a given key? and what is the preceding (or succeeding) key...... to a given key? The updates we can do are: inserting a new key or deleting a given key. Our dictionary has the working set property, which means that the running time of a query depends on the query distribution. Specifically the time to search for a key depends on when we last searched for it. Our data...

  12. Structure of potato starch

    DEFF Research Database (Denmark)

    Bertoft, Eric; Blennow, Andreas

    2016-01-01

    are interconnected by long chains with more than 36 residues. The clusters consist of still smaller, very tightly branched building blocks. The clusters direct the semicrystalline structures found inside the starch granules. The crystals, which are ~5.2. nm thick, contain double helices formed from the external...... chains extending from the clusters. A range of enzymes is involved in the biosynthesis of the cluster structures and linear segments. These are required for sugar activation, chain elongation, branching, and trimming of the final branching pattern. As an interesting feature, potato amylopectin...... is substituted with low amounts of phosphate groups monoesterified to the C-3 and the C-6 carbons of the glucose units. They seem to align well in the granular structure and have tremendous effects on starch degradation in the potato and functionality of the refined starch. A specific dikinase catalyzes...

  13. Folksodriven Structure Network

    CERN Document Server

    Mas, Massimiliano Dal

    2011-01-01

    Nowadays folksonomy is used as a system derived from user-generated electronic tags or keywords that annotate and describe online content. But it is not a classification system as an ontology. To consider it as a classification system it would be necessary to share a representation of contexts by all the users. This paper is proposing the use of folksonomies and network theory to devise a new concept: a "Folksodriven Structure Network" to represent folksonomies. This paper proposed and analyzed the network structure of Folksodriven tags thought as folsksonomy tags suggestions for the user on a dataset built on chosen websites. It is observed that the Folksodriven Network has relative low path lengths checking it with classic networking measures (clustering coefficient). Experiment result shows it can facilitate serendipitous discovery of content among users. Neat examples and clear formulas can show how a "Folksodriven Structure Network" can be used to tackle ontology mapping challenges.

  14. Structural power flow measurement

    Energy Technology Data Exchange (ETDEWEB)

    Falter, K.J.; Keltie, R.F.

    1988-12-01

    Previous investigations of structural power flow through beam-like structures resulted in some unexplained anomalies in the calculated data. In order to develop structural power flow measurement as a viable technique for machine tool design, the causes of these anomalies needed to be found. Once found, techniques for eliminating the errors could be developed. Error sources were found in the experimental apparatus itself as well as in the instrumentation. Although flexural waves are the carriers of power in the experimental apparatus, at some frequencies longitudinal waves were excited which were picked up by the accelerometers and altered power measurements. Errors were found in the phase and gain response of the sensors and amplifiers used for measurement. A transfer function correction technique was employed to compensate for these instrumentation errors.

  15. Structural Sparse Tracking

    KAUST Repository

    Zhang, Tianzhu

    2015-06-01

    Sparse representation has been applied to visual tracking by finding the best target candidate with minimal reconstruction error by use of target templates. However, most sparse representation based trackers only consider holistic or local representations and do not make full use of the intrinsic structure among and inside target candidates, thereby making the representation less effective when similar objects appear or under occlusion. In this paper, we propose a novel Structural Sparse Tracking (SST) algorithm, which not only exploits the intrinsic relationship among target candidates and their local patches to learn their sparse representations jointly, but also preserves the spatial layout structure among the local patches inside each target candidate. We show that our SST algorithm accommodates most existing sparse trackers with the respective merits. Both qualitative and quantitative evaluations on challenging benchmark image sequences demonstrate that the proposed SST algorithm performs favorably against several state-of-the-art methods.

  16. Implications of social structure

    DEFF Research Database (Denmark)

    Brask, Josefine Bohr

    Social systems in nature are characterised by heterogeneous social structures. The pattern of social interactions or associations between individuals within populations (i.e. their social network) is typically non-random. Such structuring may have important implications for the expression......, we investigate empirically the role of the social environment of individuals for their communication patterns. Our study species is a song bird, the black-capped chickadee (Poecile atricapillus). The results suggest that individual communication in this species is influenced by features of the local...... social environment of the individual. In the last two studies, we investigate the role of social structure for cooperation in a classic natural system for behavioural research, the Trinidadian guppy (Poecilia reticulata), by means of computer simulations. Cooperation contradicts evolutionary theory...

  17. Superalloy Lattice Block Structures

    Science.gov (United States)

    Nathal, M. V.; Whittenberger, J. D.; Hebsur, M. G.; Kantzos, P. T.; Krause, D. L.

    2004-01-01

    Initial investigations of investment cast superalloy lattice block suggest that this technology will yield a low cost approach to utilize the high temperature strength and environmental resistance of superalloys in lightweight, damage tolerant structural configurations. Work to date has demonstrated that relatively large superalloy lattice block panels can be successfully investment cast from both IN-718 and Mar-M247. These castings exhibited mechanical properties consistent with the strength of the same superalloys measured from more conventional castings. The lattice block structure also accommodates significant deformation without failure, and is defect tolerant in fatigue. The potential of lattice block structures opens new opportunities for the use of superalloys in future generations of aircraft applications that demand strength and environmental resistance at elevated temperatures along with low weight.

  18. Dynamics of structures

    CERN Document Server

    Paultre, Patrick

    2013-01-01

    This book covers structural dynamics from a theoretical and algorithmic approach. It covers systems with both single and multiple degrees-of-freedom. Numerous case studies are given to provide the reader with a deeper insight into the practicalities of the area, and the solutions to these case studies are given in terms of real-time and frequency in both geometric and modal spaces. Emphasis is also given to the subject of seismic loading. The text is based on many lectures on the subject of structural dynamics given at numerous institutions and thus will be an accessible and practical aid to

  19. Cellular structural biology.

    Science.gov (United States)

    Ito, Yutaka; Selenko, Philipp

    2010-10-01

    While we appreciate the complexity of the intracellular environment as a general property of every living organism, we collectively lack the appropriate tools to analyze protein structures in a cellular context. In-cell NMR spectroscopy represents a novel biophysical tool to investigate the conformational and functional characteristics of biomolecules at the atomic level inside live cells. Here, we review recent in-cell NMR developments and provide an outlook towards future applications in prokaryotic and eukaryotic cells. We hope to thereby emphasize the usefulness of in-cell NMR techniques for cellular studies of complex biological processes and for structural analyses in native environments. Copyright © 2010 Elsevier Ltd. All rights reserved.

  20. Structured Analog CMOS Design

    CERN Document Server

    Stefanovic, Danica

    2008-01-01

    Structured Analog CMOS Design describes a structured analog design approach that makes it possible to simplify complex analog design problems and develop a design strategy that can be used for the design of large number of analog cells. It intentionally avoids treating the analog design as a mathematical problem, developing a design procedure based on the understanding of device physics and approximations that give insight into parameter interdependences. The proposed transistor-level design procedure is based on the EKV modeling approach and relies on the device inversion level as a fundament